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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
4 The following is a consolidated list of the kernel parameters as implemented
5 (mostly) by the __setup() macro and sorted into English Dictionary order
6 (defined as ignoring all punctuation and sorting digits before letters in a
7 case insensitive manner), and with descriptions where known.
9 Module parameters for loadable modules are specified only as the
10 parameter name with optional '=' and value as appropriate, such as:
12 modprobe usbcore blinkenlights=1
14 Module parameters for modules that are built into the kernel image
15 are specified on the kernel command line with the module name plus
16 '.' plus parameter name, with '=' and value if appropriate, such as:
18 usbcore.blinkenlights=1
20 Hyphens (dashes) and underscores are equivalent in parameter names, so
21 log_buf_len=1M print-fatal-signals=1
22 can also be entered as
23 log-buf-len=1M print_fatal_signals=1
26 This document may not be entirely up to date and comprehensive. The command
27 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
28 module. Loadable modules, after being loaded into the running kernel, also
29 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
30 parameters may be changed at runtime by the command
31 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
33 The parameters listed below are only valid if certain kernel build options were
34 enabled and if respective hardware is present. The text in square brackets at
35 the beginning of each description states the restrictions within which a
36 parameter is applicable:
38 ACPI ACPI support is enabled.
39 AGP AGP (Accelerated Graphics Port) is enabled.
40 ALSA ALSA sound support is enabled.
41 APIC APIC support is enabled.
42 APM Advanced Power Management support is enabled.
43 ARM ARM architecture is enabled.
44 AVR32 AVR32 architecture is enabled.
45 AX25 Appropriate AX.25 support is enabled.
46 BLACKFIN Blackfin architecture is enabled.
47 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
126 In addition, the following text indicates that the option:
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.
132 Parameters denoted with BOOT are actually interpreted by the boot
133 loader, and have no meaning to the kernel directly.
134 Do not modify the syntax of boot loader parameters without extreme
135 need or coordination with <Documentation/x86/boot.txt>.
137 There are also arch-specific kernel-parameters not documented here.
138 See for example <Documentation/x86/x86_64/boot-options.txt>.
140 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
141 a trailing = on the name of any parameter states that that parameter will
142 be entered as an environment variable, whereas its absence indicates that
143 it will appear as a kernel argument readable via /proc/cmdline by programs
144 running once the system is up.
146 The number of kernel parameters is not limited, but the length of the
147 complete command line (parameters including spaces etc.) is limited to
148 a fixed number of characters. This limit depends on the architecture
149 and is between 256 and 4096 characters. It is defined in the file
150 ./include/asm/setup.h as COMMAND_LINE_SIZE.
152 Finally, the [KMG] suffix is commonly described after a number of kernel
153 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
154 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
155 bytes respectively. Such letter suffixes can also be entirely omitted.
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
169 See also Documentation/power/runtime_pm.txt, pci=noacpi
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.
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
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.
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.
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
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.
217 acpi_irq_balance [HW,ACPI]
218 ACPI will balance active IRQs
219 default in APIC mode
221 acpi_irq_nobalance [HW,ACPI]
222 ACPI will not move active IRQs (default)
223 default in PIC mode
225 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
226 Format: <irq>,<irq>...
228 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
229 use by PCI
230 Format: <irq>,<irq>...
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.
240 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
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.
250 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
251 Format: To spoof as Windows 98: ="Microsoft Windows"
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
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.
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.
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.
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.
314 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
315 Format: { level | edge | high | low }
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.
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).
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
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.
360 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
361 kernels.
363 add_efi_memmap [EFI; X86] Include EFI memory map in
364 kernel's map of available physical RAM.
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)
372 ALSA [HW,ALSA]
373 See Documentation/sound/alsa/alsa-parameters.txt
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.
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.
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
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.
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
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.
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
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>
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.
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.
444 autoconf= [IPV6]
445 See Documentation/networking/ipv6.txt.
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
456 apm= [APM] Advanced Power Management
457 See header of arch/x86/kernel/apm_32.c.
459 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
460 Format: <io>,<irq>,<nodeID>
462 ataflop= [HW,M68k]
464 atarimouse= [HW,MOUSE] Atari Mouse
466 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
467 EzKey and similar keyboards
469 atkbd.reset= [HW] Reset keyboard during initialization
471 atkbd.set= [HW] Select keyboard code set
472 Format: <int> (2 = AT (default), 3 = PS/2)
474 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
475 keyboards
477 atkbd.softraw= [HW] Choose between synthetic and real raw mode
478 Format: <bool> (0 = real, 1 = synthetic (default))
480 atkbd.softrepeat= [HW]
481 Use software keyboard repeat
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
495 audit_backlog_limit= [KNL] Set the audit queue size limit.
496 Format: <int> (must be >=0)
497 Default: 64
499 baycom_epp= [HW,AX25]
500 Format: <io>,<mode>
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.
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.
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.
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
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
525 bootmem_debug [KNL] Enable bootmem allocator debug messages.
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=
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.
537 c101= [NET] Moxa C101 synchronous serial card
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.
546 ccw_timeout_log [S390]
547 See Documentation/s390/CommonIO for details.
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}
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.
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.
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 }
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
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.
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
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
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.
636 code_bytes [X86] How many bytes of object code to print
637 in an oops report.
638 Range: 0 - 8192
639 Default: 64
641 com20020= [HW,NET] ARCnet - COM20020 chipset
642 Format:
643 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
645 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
646 Format: <io>[,<irq>]
648 com90xx= [HW,NET]
649 ARCnet - COM90xx chipset (memory-mapped buffers)
650 Format: <io>[,<irq>[,<memstart>]]
652 condev= [HW,S390] console device
653 conmode=
655 console= [KNL] Output console device and options.
657 tty<n> Use the virtual console device <n>.
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".
667 See Documentation/serial-console.txt for more
668 information. See
669 Documentation/networking/netconsole.txt for an
670 alternative.
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.
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.
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.
690 coredump_filter=
691 [KNL] Change the default value for
692 /proc/<pid>/coredump_filter.
693 See also Documentation/filesystems/proc.txt.
695 cpuidle.off=1 [CPU_IDLE]
696 disable the cpuidle sub-system
698 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
699 Format:
700 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
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.
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.
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.
737 cs89x0_dma= [HW,NET]
738 Format: <dma>
740 cs89x0_media= [HW,NET]
741 Format: { rj45 | aui | bnc }
743 dasd= [HW,NET]
744 See header of drivers/s390/block/dasd_devmap.c.
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
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.
755 debug [KNL] Enable kernel debugging (events log level).
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.
766 debug_objects [KNL] Enable object debugging
768 no_debug_objects
769 [KNL] Disable object debugging
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.
790 debugpat [X86] Enable PAT debugging
792 decnet.addr= [HW,NET]
793 Format: <area>[,<node>]
794 See also Documentation/networking/decnet.txt.
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.
804 dhash_entries= [KNL]
805 Set number of hash buckets for dentry cache.
807 digi= [HW,SERIAL]
808 IO parameters + enable/disable command.
810 digiepca= [HW,SERIAL]
811 See drivers/char/README.epca and
812 Documentation/serial/digiepca.txt.
814 disable= [IPV6]
815 See Documentation/networking/ipv6.txt.
817 disable_cpu_apicid= [X86,APIC,SMP]
818 Format: <int>
819 The number of initial APIC ID for the
820 corresponding CPU to be disabled at boot,
821 mostly used for the kdump 2nd kernel to
822 disable BSP to wake up multiple CPUs without
823 causing system reset or hang due to sending
824 INIT from AP to BSP.
826 disable_ddw [PPC/PSERIES]
827 Disable Dynamic DMA Window support. Use this if
828 to workaround buggy firmware.
830 disable_ipv6= [IPV6]
831 See Documentation/networking/ipv6.txt.
833 disable_mtrr_cleanup [X86]
834 The kernel tries to adjust MTRR layout from continuous
835 to discrete, to make X server driver able to add WB
836 entry later. This parameter disables that.
838 disable_mtrr_trim [X86, Intel and AMD only]
839 By default the kernel will trim any uncacheable
840 memory out of your available memory pool based on
841 MTRR settings. This parameter disables that behavior,
842 possibly causing your machine to run very slowly.
844 disable_timer_pin_1 [X86]
845 Disable PIN 1 of APIC timer
846 Can be useful to work around chipset bugs.
848 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
849 this option disables the debugging code at boot.
851 dma_debug_entries=<number>
852 This option allows to tune the number of preallocated
853 entries for DMA-API debugging code. One entry is
854 required per DMA-API allocation. Use this if the
855 DMA-API debugging code disables itself because the
856 architectural default is too low.
858 dma_debug_driver=<driver_name>
859 With this option the DMA-API debugging driver
860 filter feature can be enabled at boot time. Just
861 pass the driver to filter for as the parameter.
862 The filter can be disabled or changed to another
863 driver later using sysfs.
865 drm_kms_helper.edid_firmware=[<connector>:]<file>
866 Broken monitors, graphic adapters and KVMs may
867 send no or incorrect EDID data sets. This parameter
868 allows to specify an EDID data set in the
869 /lib/firmware directory that is used instead.
870 Generic built-in EDID data sets are used, if one of
871 edid/1024x768.bin, edid/1280x1024.bin,
872 edid/1680x1050.bin, or edid/1920x1080.bin is given
873 and no file with the same name exists. Details and
874 instructions how to build your own EDID data are
875 available in Documentation/EDID/HOWTO.txt. An EDID
876 data set will only be used for a particular connector,
877 if its name and a colon are prepended to the EDID
878 name.
880 dscc4.setup= [NET]
882 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
883 module.dyndbg[="val"]
884 Enable debug messages at boot time. See
885 Documentation/dynamic-debug-howto.txt for details.
887 early_ioremap_debug [KNL]
888 Enable debug messages in early_ioremap support. This
889 is useful for tracking down temporary early mappings
890 which are not unmapped.
892 earlycon= [KNL] Output early console device and options.
893 uart[8250],io,<addr>[,options]
894 uart[8250],mmio,<addr>[,options]
895 uart[8250],mmio32,<addr>[,options]
896 Start an early, polled-mode console on the 8250/16550
897 UART at the specified I/O port or MMIO address.
898 MMIO inter-register address stride is either 8-bit
899 (mmio) or 32-bit (mmio32).
900 The options are the same as for ttyS, above.
902 earlyprintk= [X86,SH,BLACKFIN,ARM]
903 earlyprintk=vga
904 earlyprintk=efi
905 earlyprintk=xen
906 earlyprintk=serial[,ttySn[,baudrate]]
907 earlyprintk=serial[,0x...[,baudrate]]
908 earlyprintk=ttySn[,baudrate]
909 earlyprintk=dbgp[debugController#]
911 earlyprintk is useful when the kernel crashes before
912 the normal console is initialized. It is not enabled by
913 default because it has some cosmetic problems.
915 Append ",keep" to not disable it when the real console
916 takes over.
918 Only one of vga, efi, serial, or usb debug port can
919 be used at a time.
921 Currently only ttyS0 and ttyS1 may be specified by
922 name. Other I/O ports may be explicitly specified
923 on some architectures (x86 and arm at least) by
924 replacing ttySn with an I/O port address, like this:
925 earlyprintk=serial,0x1008,115200
926 You can find the port for a given device in
927 /proc/tty/driver/serial:
928 2: uart:ST16650V2 port:00001008 irq:18 ...
930 Interaction with the standard serial driver is not
931 very good.
933 The VGA and EFI output is eventually overwritten by
934 the real console.
936 The xen output can only be used by Xen PV guests.
938 edac_report= [HW,EDAC] Control how to report EDAC event
939 Format: {"on" | "off" | "force"}
940 on: enable EDAC to report H/W event. May be overridden
941 by other higher priority error reporting module.
942 off: disable H/W event reporting through EDAC.
943 force: enforce the use of EDAC to report H/W event.
944 default: on.
946 ekgdboc= [X86,KGDB] Allow early kernel console debugging
947 ekgdboc=kbd
949 This is designed to be used in conjunction with
950 the boot argument: earlyprintk=vga
952 edd= [EDD]
953 Format: {"off" | "on" | "skip[mbr]"}
955 efi= [EFI]
956 Format: { "old_map" }
957 old_map [X86-64]: switch to the old ioremap-based EFI
958 runtime services mapping. 32-bit still uses this one by
959 default.
961 efi_no_storage_paranoia [EFI; X86]
962 Using this parameter you can use more than 50% of
963 your efi variable storage. Use this parameter only if
964 you are really sure that your UEFI does sane gc and
965 fulfills the spec otherwise your board may brick.
967 eisa_irq_edge= [PARISC,HW]
968 See header of drivers/parisc/eisa.c.
970 elanfreq= [X86-32]
971 See comment before function elanfreq_setup() in
972 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
974 elevator= [IOSCHED]
975 Format: {"cfq" | "deadline" | "noop"}
976 See Documentation/block/cfq-iosched.txt and
977 Documentation/block/deadline-iosched.txt for details.
979 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
980 Specifies physical address of start of kernel core
981 image elf header and optionally the size. Generally
982 kexec loader will pass this option to capture kernel.
983 See Documentation/kdump/kdump.txt for details.
985 enable_mtrr_cleanup [X86]
986 The kernel tries to adjust MTRR layout from continuous
987 to discrete, to make X server driver able to add WB
988 entry later. This parameter enables that.
990 enable_timer_pin_1 [X86]
991 Enable PIN 1 of APIC timer
992 Can be useful to work around chipset bugs
993 (in particular on some ATI chipsets).
994 The kernel tries to set a reasonable default.
996 enforcing [SELINUX] Set initial enforcing status.
997 Format: {"0" | "1"}
998 See security/selinux/Kconfig help text.
999 0 -- permissive (log only, no denials).
1000 1 -- enforcing (deny and log).
1001 Default value is 0.
1002 Value can be changed at runtime via /selinux/enforce.
1004 erst_disable [ACPI]
1005 Disable Error Record Serialization Table (ERST)
1006 support.
1008 ether= [HW,NET] Ethernet cards parameters
1009 This option is obsoleted by the "netdev=" option, which
1010 has equivalent usage. See its documentation for details.
1012 evm= [EVM]
1013 Format: { "fix" }
1014 Permit 'security.evm' to be updated regardless of
1015 current integrity status.
1017 failslab=
1018 fail_page_alloc=
1019 fail_make_request=[KNL]
1020 General fault injection mechanism.
1021 Format: <interval>,<probability>,<space>,<times>
1022 See also Documentation/fault-injection/.
1024 floppy= [HW]
1025 See Documentation/blockdev/floppy.txt.
1027 force_pal_cache_flush
1028 [IA-64] Avoid check_sal_cache_flush which may hang on
1029 buggy SAL_CACHE_FLUSH implementations. Using this
1030 parameter will force ia64_sal_cache_flush to call
1031 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1033 forcepae [X86-32]
1034 Forcefully enable Physical Address Extension (PAE).
1035 Many Pentium M systems disable PAE but may have a
1036 functionally usable PAE implementation.
1037 Warning: use of this parameter will taint the kernel
1038 and may cause unknown problems.
1040 ftrace=[tracer]
1041 [FTRACE] will set and start the specified tracer
1042 as early as possible in order to facilitate early
1043 boot debugging.
1045 ftrace_dump_on_oops[=orig_cpu]
1046 [FTRACE] will dump the trace buffers on oops.
1047 If no parameter is passed, ftrace will dump
1048 buffers of all CPUs, but if you pass orig_cpu, it will
1049 dump only the buffer of the CPU that triggered the
1050 oops.
1052 ftrace_filter=[function-list]
1053 [FTRACE] Limit the functions traced by the function
1054 tracer at boot up. function-list is a comma separated
1055 list of functions. This list can be changed at run
1056 time by the set_ftrace_filter file in the debugfs
1057 tracing directory.
1059 ftrace_notrace=[function-list]
1060 [FTRACE] Do not trace the functions specified in
1061 function-list. This list can be changed at run time
1062 by the set_ftrace_notrace file in the debugfs
1063 tracing directory.
1065 ftrace_graph_filter=[function-list]
1066 [FTRACE] Limit the top level callers functions traced
1067 by the function graph tracer at boot up.
1068 function-list is a comma separated list of functions
1069 that can be changed at run time by the
1070 set_graph_function file in the debugfs tracing directory.
1072 gamecon.map[2|3]=
1073 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1074 support via parallel port (up to 5 devices per port)
1075 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1076 See also Documentation/input/joystick-parport.txt
1078 gamma= [HW,DRM]
1080 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1081 Format: off | on
1082 default: on
1084 gcov_persist= [GCOV] When non-zero (default), profiling data for
1085 kernel modules is saved and remains accessible via
1086 debugfs, even when the module is unloaded/reloaded.
1087 When zero, profiling data is discarded and associated
1088 debugfs files are removed at module unload time.
1090 gpt [EFI] Forces disk with valid GPT signature but
1091 invalid Protective MBR to be treated as GPT. If the
1092 primary GPT is corrupted, it enables the backup/alternate
1093 GPT to be used instead.
1095 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1096 the "Enable 0" bit of the configuration register.
1097 Format: 0 | 1
1098 Default: 0
1099 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1100 the "Enable 0" bit of the configuration register.
1101 Format: 0 | 1
1102 Default: 0
1103 grcan.select= [HW] Select which physical interface to use.
1104 Format: 0 | 1
1105 Default: 0
1106 grcan.txsize= [HW] Sets the size of the tx buffer.
1107 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1108 Default: 1024
1109 grcan.rxsize= [HW] Sets the size of the rx buffer.
1110 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1111 Default: 1024
1113 hashdist= [KNL,NUMA] Large hashes allocated during boot
1114 are distributed across NUMA nodes. Defaults on
1115 for 64-bit NUMA, off otherwise.
1116 Format: 0 | 1 (for off | on)
1118 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1120 hd= [EIDE] (E)IDE hard drive subsystem geometry
1121 Format: <cyl>,<head>,<sect>
1123 hest_disable [ACPI]
1124 Disable Hardware Error Source Table (HEST) support;
1125 corresponding firmware-first mode error processing
1126 logic will be disabled.
1128 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1129 size of <nn>. This works even on boxes that have no
1130 highmem otherwise. This also works to reduce highmem
1131 size on bigger boxes.
1133 highres= [KNL] Enable/disable high resolution timer mode.
1134 Valid parameters: "on", "off"
1135 Default: "on"
1137 hisax= [HW,ISDN]
1138 See Documentation/isdn/README.HiSax.
1140 hlt [BUGS=ARM,SH]
1142 hpet= [X86-32,HPET] option to control HPET usage
1143 Format: { enable (default) | disable | force |
1144 verbose }
1145 disable: disable HPET and use PIT instead
1146 force: allow force enabled of undocumented chips (ICH4,
1147 VIA, nVidia)
1148 verbose: show contents of HPET registers during setup
1150 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1151 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1153 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1154 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1155 On x86-64 and powerpc, this option can be specified
1156 multiple times interleaved with hugepages= to reserve
1157 huge pages of different sizes. Valid pages sizes on
1158 x86-64 are 2M (when the CPU supports "pse") and 1G
1159 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1160 Note that 1GB pages can only be allocated at boot time
1161 using hugepages= and not freed afterwards.
1163 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1164 terminal devices. Valid values: 0..8
1165 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1166 If specified, z/VM IUCV HVC accepts connections
1167 from listed z/VM user IDs only.
1169 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1170 hardware thread id mappings.
1171 Format: <cpu>:<hwthread>
1173 keep_bootcon [KNL]
1174 Do not unregister boot console at start. This is only
1175 useful for debugging when something happens in the window
1176 between unregistering the boot console and initializing
1177 the real console.
1179 i2c_bus= [HW] Override the default board specific I2C bus speed
1180 or register an additional I2C bus that is not
1181 registered from board initialization code.
1182 Format:
1183 <bus_id>,<clkrate>
1185 i8042.debug [HW] Toggle i8042 debug mode
1186 i8042.direct [HW] Put keyboard port into non-translated mode
1187 i8042.dumbkbd [HW] Pretend that controller can only read data from
1188 keyboard and cannot control its state
1189 (Don't attempt to blink the leds)
1190 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1191 i8042.nokbd [HW] Don't check/create keyboard port
1192 i8042.noloop [HW] Disable the AUX Loopback command while probing
1193 for the AUX port
1194 i8042.nomux [HW] Don't check presence of an active multiplexing
1195 controller
1196 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1197 controllers
1198 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1199 i8042.reset [HW] Reset the controller during init and cleanup
1200 i8042.unlock [HW] Unlock (ignore) the keylock
1202 i810= [HW,DRM]
1204 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1205 indicates that the driver is running on unsupported
1206 hardware.
1207 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1208 does not match list of supported models.
1209 i8k.power_status
1210 [HW] Report power status in /proc/i8k
1211 (disabled by default)
1212 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1213 capability is set.
1215 i915.invert_brightness=
1216 [DRM] Invert the sense of the variable that is used to
1217 set the brightness of the panel backlight. Normally a
1218 brightness value of 0 indicates backlight switched off,
1219 and the maximum of the brightness value sets the backlight
1220 to maximum brightness. If this parameter is set to 0
1221 (default) and the machine requires it, or this parameter
1222 is set to 1, a brightness value of 0 sets the backlight
1223 to maximum brightness, and the maximum of the brightness
1224 value switches the backlight off.
1225 -1 -- never invert brightness
1226 0 -- machine default
1227 1 -- force brightness inversion
1229 icn= [HW,ISDN]
1230 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1232 ide-core.nodma= [HW] (E)IDE subsystem
1233 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1234 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1235 .cdrom .chs .ignore_cable are additional options
1236 See Documentation/ide/ide.txt.
1238 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1239 Claim all unknown PCI IDE storage controllers.
1241 idle= [X86]
1242 Format: idle=poll, idle=halt, idle=nomwait
1243 Poll forces a polling idle loop that can slightly
1244 improve the performance of waking up a idle CPU, but
1245 will use a lot of power and make the system run hot.
1246 Not recommended.
1247 idle=halt: Halt is forced to be used for CPU idle.
1248 In such case C2/C3 won't be used again.
1249 idle=nomwait: Disable mwait for CPU C-states
1251 ignore_loglevel [KNL]
1252 Ignore loglevel setting - this will print /all/
1253 kernel messages to the console. Useful for debugging.
1254 We also add it as printk module parameter, so users
1255 could change it dynamically, usually by
1256 /sys/module/printk/parameters/ignore_loglevel.
1258 ihash_entries= [KNL]
1259 Set number of hash buckets for inode cache.
1261 ima_appraise= [IMA] appraise integrity measurements
1262 Format: { "off" | "enforce" | "fix" }
1263 default: "enforce"
1265 ima_appraise_tcb [IMA]
1266 The builtin appraise policy appraises all files
1267 owned by uid=0.
1269 ima_hash= [IMA]
1270 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1271 | sha512 | ... }
1272 default: "sha1"
1274 The list of supported hash algorithms is defined
1275 in crypto/hash_info.h.
1277 ima_tcb [IMA]
1278 Load a policy which meets the needs of the Trusted
1279 Computing Base. This means IMA will measure all
1280 programs exec'd, files mmap'd for exec, and all files
1281 opened for read by uid=0.
1283 ima_template= [IMA]
1284 Select one of defined IMA measurements template formats.
1285 Formats: { "ima" | "ima-ng" }
1286 Default: "ima-ng"
1288 init= [KNL]
1289 Format: <full_path>
1290 Run specified binary instead of /sbin/init as init
1291 process.
1293 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1294 for working out where the kernel is dying during
1295 startup.
1297 initrd= [BOOT] Specify the location of the initial ramdisk
1299 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1300 Format: <irq>
1302 int_pln_enable [x86] Enable power limit notification interrupt
1304 integrity_audit=[IMA]
1305 Format: { "0" | "1" }
1306 0 -- basic integrity auditing messages. (Default)
1307 1 -- additional integrity auditing messages.
1309 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1310 on
1311 Enable intel iommu driver.
1312 off
1313 Disable intel iommu driver.
1314 igfx_off [Default Off]
1315 By default, gfx is mapped as normal device. If a gfx
1316 device has a dedicated DMAR unit, the DMAR unit is
1317 bypassed by not enabling DMAR with this option. In
1318 this case, gfx device will use physical address for
1319 DMA.
1320 forcedac [x86_64]
1321 With this option iommu will not optimize to look
1322 for io virtual address below 32-bit forcing dual
1323 address cycle on pci bus for cards supporting greater
1324 than 32-bit addressing. The default is to look
1325 for translation below 32-bit and if not available
1326 then look in the higher range.
1327 strict [Default Off]
1328 With this option on every unmap_single operation will
1329 result in a hardware IOTLB flush operation as opposed
1330 to batching them for performance.
1331 sp_off [Default Off]
1332 By default, super page will be supported if Intel IOMMU
1333 has the capability. With this option, super page will
1334 not be supported.
1336 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1337 0 disables intel_idle and fall back on acpi_idle.
1338 1 to 6 specify maximum depth of C-state.
1340 intel_pstate= [X86]
1341 disable
1342 Do not enable intel_pstate as the default
1343 scaling driver for the supported processors
1345 intremap= [X86-64, Intel-IOMMU]
1346 on enable Interrupt Remapping (default)
1347 off disable Interrupt Remapping
1348 nosid disable Source ID checking
1349 no_x2apic_optout
1350 BIOS x2APIC opt-out request will be ignored
1352 iomem= Disable strict checking of access to MMIO memory
1353 strict regions from userspace.
1354 relaxed
1356 iommu= [x86]
1357 off
1358 force
1359 noforce
1360 biomerge
1361 panic
1362 nopanic
1363 merge
1364 nomerge
1365 forcesac
1366 soft
1367 pt [x86, IA-64]
1370 io7= [HW] IO7 for Marvel based alpha systems
1371 See comment before marvel_specify_io7 in
1372 arch/alpha/kernel/core_marvel.c.
1374 io_delay= [X86] I/O delay method
1375 0x80
1376 Standard port 0x80 based delay
1377 0xed
1378 Alternate port 0xed based delay (needed on some systems)
1379 udelay
1380 Simple two microseconds delay
1381 none
1382 No delay
1384 ip= [IP_PNP]
1385 See Documentation/filesystems/nfs/nfsroot.txt.
1387 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1388 See comment before ip2_setup() in
1389 drivers/char/ip2/ip2base.c.
1391 irqfixup [HW]
1392 When an interrupt is not handled search all handlers
1393 for it. Intended to get systems with badly broken
1394 firmware running.
1396 irqpoll [HW]
1397 When an interrupt is not handled search all handlers
1398 for it. Also check all handlers each timer
1399 interrupt. Intended to get systems with badly broken
1400 firmware running.
1402 isapnp= [ISAPNP]
1403 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1405 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1406 Format:
1407 <cpu number>,...,<cpu number>
1408 or
1409 <cpu number>-<cpu number>
1410 (must be a positive range in ascending order)
1411 or a mixture
1412 <cpu number>,...,<cpu number>-<cpu number>
1414 This option can be used to specify one or more CPUs
1415 to isolate from the general SMP balancing and scheduling
1416 algorithms. You can move a process onto or off an
1417 "isolated" CPU via the CPU affinity syscalls or cpuset.
1418 <cpu number> begins at 0 and the maximum value is
1419 "number of CPUs in system - 1".
1421 This option is the preferred way to isolate CPUs. The
1422 alternative -- manually setting the CPU mask of all
1423 tasks in the system -- can cause problems and
1424 suboptimal load balancer performance.
1426 iucv= [HW,NET]
1428 ivrs_ioapic [HW,X86_64]
1429 Provide an override to the IOAPIC-ID<->DEVICE-ID
1430 mapping provided in the IVRS ACPI table. For
1431 example, to map IOAPIC-ID decimal 10 to
1432 PCI device 00:14.0 write the parameter as:
1433 ivrs_ioapic[10]=00:14.0
1435 ivrs_hpet [HW,X86_64]
1436 Provide an override to the HPET-ID<->DEVICE-ID
1437 mapping provided in the IVRS ACPI table. For
1438 example, to map HPET-ID decimal 0 to
1439 PCI device 00:14.0 write the parameter as:
1440 ivrs_hpet[0]=00:14.0
1442 js= [HW,JOY] Analog joystick
1443 See Documentation/input/joystick.txt.
1445 keepinitrd [HW,ARM]
1447 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1448 specifies the amount of memory usable by the kernel
1449 for non-movable allocations. The requested amount is
1450 spread evenly throughout all nodes in the system. The
1451 remaining memory in each node is used for Movable
1452 pages. In the event, a node is too small to have both
1453 kernelcore and Movable pages, kernelcore pages will
1454 take priority and other nodes will have a larger number
1455 of Movable pages. The Movable zone is used for the
1456 allocation of pages that may be reclaimed or moved
1457 by the page migration subsystem. This means that
1458 HugeTLB pages may not be allocated from this zone.
1459 Note that allocations like PTEs-from-HighMem still
1460 use the HighMem zone if it exists, and the Normal
1461 zone if it does not.
1463 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1464 Format: <Controller#>[,poll interval]
1465 The controller # is the number of the ehci usb debug
1466 port as it is probed via PCI. The poll interval is
1467 optional and is the number seconds in between
1468 each poll cycle to the debug port in case you need
1469 the functionality for interrupting the kernel with
1470 gdb or control-c on the dbgp connection. When
1471 not using this parameter you use sysrq-g to break into
1472 the kernel debugger.
1474 kgdboc= [KGDB,HW] kgdb over consoles.
1475 Requires a tty driver that supports console polling,
1476 or a supported polling keyboard driver (non-usb).
1477 Serial only format: <serial_device>[,baud]
1478 keyboard only format: kbd
1479 keyboard and serial format: kbd,<serial_device>[,baud]
1480 Optional Kernel mode setting:
1481 kms, kbd format: kms,kbd
1482 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1484 kgdbwait [KGDB] Stop kernel execution and enter the
1485 kernel debugger at the earliest opportunity.
1487 kmac= [MIPS] korina ethernet MAC address.
1488 Configure the RouterBoard 532 series on-chip
1489 Ethernet adapter MAC address.
1491 kmemleak= [KNL] Boot-time kmemleak enable/disable
1492 Valid arguments: on, off
1493 Default: on
1495 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1496 Valid arguments: 0, 1, 2
1497 kmemcheck=0 (disabled)
1498 kmemcheck=1 (enabled)
1499 kmemcheck=2 (one-shot mode)
1500 Default: 2 (one-shot mode)
1502 kstack=N [X86] Print N words from the kernel stack
1503 in oops dumps.
1505 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1506 Default is 0 (don't ignore, but inject #GP)
1508 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1509 KVM MMU at runtime.
1510 Default is 0 (off)
1512 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1513 Default is 1 (enabled)
1515 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1516 for all guests.
1517 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1519 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1520 (virtualized MMU) support on capable Intel chips.
1521 Default is 1 (enabled)
1523 kvm-intel.emulate_invalid_guest_state=
1524 [KVM,Intel] Enable emulation of invalid guest states
1525 Default is 0 (disabled)
1527 kvm-intel.flexpriority=
1528 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1529 Default is 1 (enabled)
1531 kvm-intel.nested=
1532 [KVM,Intel] Enable VMX nesting (nVMX).
1533 Default is 0 (disabled)
1535 kvm-intel.unrestricted_guest=
1536 [KVM,Intel] Disable unrestricted guest feature
1537 (virtualized real and unpaged mode) on capable
1538 Intel chips. Default is 1 (enabled)
1540 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1541 feature (tagged TLBs) on capable Intel chips.
1542 Default is 1 (enabled)
1544 l2cr= [PPC]
1546 l3cr= [PPC]
1548 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1549 disabled it.
1551 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1552 value for LAPIC timer one-shot implementation. Default
1553 back to the programmable timer unit in the LAPIC.
1555 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1556 in C2 power state.
1558 libata.dma= [LIBATA] DMA control
1559 libata.dma=0 Disable all PATA and SATA DMA
1560 libata.dma=1 PATA and SATA Disk DMA only
1561 libata.dma=2 ATAPI (CDROM) DMA only
1562 libata.dma=4 Compact Flash DMA only
1563 Combinations also work, so libata.dma=3 enables DMA
1564 for disks and CDROMs, but not CFs.
1566 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1567 libata.ignore_hpa=0 keep BIOS limits (default)
1568 libata.ignore_hpa=1 ignore limits, using full disk
1570 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1571 when set.
1572 Format: <int>
1574 libata.force= [LIBATA] Force configurations. The format is comma
1575 separated list of "[ID:]VAL" where ID is
1576 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1577 matching port, link or device. Basically, it matches
1578 the ATA ID string printed on console by libata. If
1579 the whole ID part is omitted, the last PORT and DEVICE
1580 values are used. If ID hasn't been specified yet, the
1581 configuration applies to all ports, links and devices.
1583 If only DEVICE is omitted, the parameter applies to
1584 the port and all links and devices behind it. DEVICE
1585 number of 0 either selects the first device or the
1586 first fan-out link behind PMP device. It does not
1587 select the host link. DEVICE number of 15 selects the
1588 host link and device attached to it.
1590 The VAL specifies the configuration to force. As long
1591 as there's no ambiguity shortcut notation is allowed.
1592 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1593 The following configurations can be forced.
1595 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1596 Any ID with matching PORT is used.
1598 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1600 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1601 udma[/][16,25,33,44,66,100,133] notation is also
1602 allowed.
1604 * [no]ncq: Turn on or off NCQ.
1606 * nohrst, nosrst, norst: suppress hard, soft
1607 and both resets.
1609 * rstonce: only attempt one reset during
1610 hot-unplug link recovery
1612 * dump_id: dump IDENTIFY data.
1614 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1616 * disable: Disable this device.
1618 If there are multiple matching configurations changing
1619 the same attribute, the last one is used.
1621 memblock=debug [KNL] Enable memblock debug messages.
1623 load_ramdisk= [RAM] List of ramdisks to load from floppy
1624 See Documentation/blockdev/ramdisk.txt.
1626 lockd.nlm_grace_period=P [NFS] Assign grace period.
1627 Format: <integer>
1629 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1630 Format: <integer>
1632 lockd.nlm_timeout=T [NFS] Assign timeout value.
1633 Format: <integer>
1635 lockd.nlm_udpport=M [NFS] Assign UDP port.
1636 Format: <integer>
1638 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1639 Format: <irq>
1641 loglevel= All Kernel Messages with a loglevel smaller than the
1642 console loglevel will be printed to the console. It can
1643 also be changed with klogd or other programs. The
1644 loglevels are defined as follows:
1646 0 (KERN_EMERG) system is unusable
1647 1 (KERN_ALERT) action must be taken immediately
1648 2 (KERN_CRIT) critical conditions
1649 3 (KERN_ERR) error conditions
1650 4 (KERN_WARNING) warning conditions
1651 5 (KERN_NOTICE) normal but significant condition
1652 6 (KERN_INFO) informational
1653 7 (KERN_DEBUG) debug-level messages
1655 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1656 in bytes. n must be a power of two. The default
1657 size is set in the kernel config file.
1659 logo.nologo [FB] Disables display of the built-in Linux logo.
1660 This may be used to provide more screen space for
1661 kernel log messages and is useful when debugging
1662 kernel boot problems.
1664 lp=0 [LP] Specify parallel ports to use, e.g,
1665 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1666 lp=reset first parallel port). 'lp=0' disables the
1667 lp=auto printer driver. 'lp=reset' (which can be
1668 specified in addition to the ports) causes
1669 attached printers to be reset. Using
1670 lp=port1,port2,... specifies the parallel ports
1671 to associate lp devices with, starting with
1672 lp0. A port specification may be 'none' to skip
1673 that lp device, or a parport name such as
1674 'parport0'. Specifying 'lp=auto' instead of a
1675 port specification list means that device IDs
1676 from each port should be examined, to see if
1677 an IEEE 1284-compliant printer is attached; if
1678 so, the driver will manage that printer.
1679 See also header of drivers/char/lp.c.
1681 lpj=n [KNL]
1682 Sets loops_per_jiffy to given constant, thus avoiding
1683 time-consuming boot-time autodetection (up to 250 ms per
1684 CPU). 0 enables autodetection (default). To determine
1685 the correct value for your kernel, boot with normal
1686 autodetection and see what value is printed. Note that
1687 on SMP systems the preset will be applied to all CPUs,
1688 which is likely to cause problems if your CPUs need
1689 significantly divergent settings. An incorrect value
1690 will cause delays in the kernel to be wrong, leading to
1691 unpredictable I/O errors and other breakage. Although
1692 unlikely, in the extreme case this might damage your
1693 hardware.
1695 ltpc= [NET]
1696 Format: <io>,<irq>,<dma>
1698 machvec= [IA-64] Force the use of a particular machine-vector
1699 (machvec) in a generic kernel.
1700 Example: machvec=hpzx1_swiotlb
1702 machtype= [Loongson] Share the same kernel image file between different
1703 yeeloong laptop.
1704 Example: machtype=lemote-yeeloong-2f-7inch
1706 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1707 than or equal to this physical address is ignored.
1709 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1710 should make use of. maxcpus=n : n >= 0 limits the
1711 kernel to using 'n' processors. n=0 is a special case,
1712 it is equivalent to "nosmp", which also disables
1713 the IO APIC.
1715 max_loop= [LOOP] The number of loop block devices that get
1716 (loop.max_loop) unconditionally pre-created at init time. The default
1717 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1718 of statically allocating a predefined number, loop
1719 devices can be requested on-demand with the
1720 /dev/loop-control interface.
1722 mce [X86-32] Machine Check Exception
1724 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1726 md= [HW] RAID subsystems devices and level
1727 See Documentation/md.txt.
1729 mdacon= [MDA]
1730 Format: <first>,<last>
1731 Specifies range of consoles to be captured by the MDA.
1733 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1734 Amount of memory to be used when the kernel is not able
1735 to see the whole system memory or for test.
1736 [X86] Work as limiting max address. Use together
1737 with memmap= to avoid physical address space collisions.
1738 Without memmap= PCI devices could be placed at addresses
1739 belonging to unused RAM.
1741 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1742 memory.
1744 memchunk=nn[KMG]
1745 [KNL,SH] Allow user to override the default size for
1746 per-device physically contiguous DMA buffers.
1748 memmap=exactmap [KNL,X86] Enable setting of an exact
1749 E820 memory map, as specified by the user.
1750 Such memmap=exactmap lines can be constructed based on
1751 BIOS output or other requirements. See the memmap=nn@ss
1752 option description.
1754 memmap=nn[KMG]@ss[KMG]
1755 [KNL] Force usage of a specific region of memory.
1756 Region of memory to be used is from ss to ss+nn.
1758 memmap=nn[KMG]#ss[KMG]
1759 [KNL,ACPI] Mark specific memory as ACPI data.
1760 Region of memory to be marked is from ss to ss+nn.
1762 memmap=nn[KMG]$ss[KMG]
1763 [KNL,ACPI] Mark specific memory as reserved.
1764 Region of memory to be reserved is from ss to ss+nn.
1765 Example: Exclude memory from 0x18690000-0x1869ffff
1766 memmap=64K$0x18690000
1767 or
1768 memmap=0x10000$0x18690000
1770 memory_corruption_check=0/1 [X86]
1771 Some BIOSes seem to corrupt the first 64k of
1772 memory when doing things like suspend/resume.
1773 Setting this option will scan the memory
1774 looking for corruption. Enabling this will
1775 both detect corruption and prevent the kernel
1776 from using the memory being corrupted.
1777 However, its intended as a diagnostic tool; if
1778 repeatable BIOS-originated corruption always
1779 affects the same memory, you can use memmap=
1780 to prevent the kernel from using that memory.
1782 memory_corruption_check_size=size [X86]
1783 By default it checks for corruption in the low
1784 64k, making this memory unavailable for normal
1785 use. Use this parameter to scan for
1786 corruption in more or less memory.
1788 memory_corruption_check_period=seconds [X86]
1789 By default it checks for corruption every 60
1790 seconds. Use this parameter to check at some
1791 other rate. 0 disables periodic checking.
1793 memtest= [KNL,X86] Enable memtest
1794 Format: <integer>
1795 default : 0 <disable>
1796 Specifies the number of memtest passes to be
1797 performed. Each pass selects another test
1798 pattern from a given set of patterns. Memtest
1799 fills the memory with this pattern, validates
1800 memory contents and reserves bad memory
1801 regions that are detected.
1803 meye.*= [HW] Set MotionEye Camera parameters
1804 See Documentation/video4linux/meye.txt.
1806 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1807 Multi-Function General Purpose Timers on AMD Geode
1808 platforms.
1810 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1811 the BIOS has incorrectly applied a workaround. TinyBIOS
1812 version 0.98 is known to be affected, 0.99 fixes the
1813 problem by letting the user disable the workaround.
1815 mga= [HW,DRM]
1817 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1818 physical address is ignored.
1820 mini2440= [ARM,HW,KNL]
1821 Format:[0..2][b][c][t]
1822 Default: "0tb"
1823 MINI2440 configuration specification:
1824 0 - The attached screen is the 3.5" TFT
1825 1 - The attached screen is the 7" TFT
1826 2 - The VGA Shield is attached (1024x768)
1827 Leaving out the screen size parameter will not load
1828 the TFT driver, and the framebuffer will be left
1829 unconfigured.
1830 b - Enable backlight. The TFT backlight pin will be
1831 linked to the kernel VESA blanking code and a GPIO
1832 LED. This parameter is not necessary when using the
1833 VGA shield.
1834 c - Enable the s3c camera interface.
1835 t - Reserved for enabling touchscreen support. The
1836 touchscreen support is not enabled in the mainstream
1837 kernel as of 2.6.30, a preliminary port can be found
1838 in the "bleeding edge" mini2440 support kernel at
1839 http://repo.or.cz/w/linux-2.6/mini2440.git
1841 mminit_loglevel=
1842 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1843 parameter allows control of the logging verbosity for
1844 the additional memory initialisation checks. A value
1845 of 0 disables mminit logging and a level of 4 will
1846 log everything. Information is printed at KERN_DEBUG
1847 so loglevel=8 may also need to be specified.
1849 module.sig_enforce
1850 [KNL] When CONFIG_MODULE_SIG is set, this means that
1851 modules without (valid) signatures will fail to load.
1852 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1853 is always true, so this option does nothing.
1855 mousedev.tap_time=
1856 [MOUSE] Maximum time between finger touching and
1857 leaving touchpad surface for touch to be considered
1858 a tap and be reported as a left button click (for
1859 touchpads working in absolute mode only).
1860 Format: <msecs>
1861 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1862 reporting absolute coordinates, such as tablets
1863 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1864 reporting absolute coordinates, such as tablets
1866 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1867 is similar to kernelcore except it specifies the
1868 amount of memory used for migratable allocations.
1869 If both kernelcore and movablecore is specified,
1870 then kernelcore will be at *least* the specified
1871 value but may be more. If movablecore on its own
1872 is specified, the administrator must be careful
1873 that the amount of memory usable for all allocations
1874 is not too small.
1876 movable_node [KNL,X86] Boot-time switch to enable the effects
1877 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
1879 MTD_Partition= [MTD]
1880 Format: <name>,<region-number>,<size>,<offset>
1882 MTD_Region= [MTD] Format:
1883 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1885 mtdparts= [MTD]
1886 See drivers/mtd/cmdlinepart.c.
1888 multitce=off [PPC] This parameter disables the use of the pSeries
1889 firmware feature for updating multiple TCE entries
1890 at a time.
1892 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1894 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1896 boundary - index of last SLC block on Flex-OneNAND.
1897 The remaining blocks are configured as MLC blocks.
1898 lock - Configure if Flex-OneNAND boundary should be locked.
1899 Once locked, the boundary cannot be changed.
1900 1 indicates lock status, 0 indicates unlock status.
1902 mtdset= [ARM]
1903 ARM/S3C2412 JIVE boot control
1905 See arch/arm/mach-s3c2412/mach-jive.c
1907 mtouchusb.raw_coordinates=
1908 [HW] Make the MicroTouch USB driver use raw coordinates
1909 ('y', default) or cooked coordinates ('n')
1911 mtrr_chunk_size=nn[KMG] [X86]
1912 used for mtrr cleanup. It is largest continuous chunk
1913 that could hold holes aka. UC entries.
1915 mtrr_gran_size=nn[KMG] [X86]
1916 Used for mtrr cleanup. It is granularity of mtrr block.
1917 Default is 1.
1918 Large value could prevent small alignment from
1919 using up MTRRs.
1921 mtrr_spare_reg_nr=n [X86]
1922 Format: <integer>
1923 Range: 0,7 : spare reg number
1924 Default : 1
1925 Used for mtrr cleanup. It is spare mtrr entries number.
1926 Set to 2 or more if your graphical card needs more.
1928 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1930 netdev= [NET] Network devices parameters
1931 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1932 Note that mem_start is often overloaded to mean
1933 something different and driver-specific.
1934 This usage is only documented in each driver source
1935 file if at all.
1937 nf_conntrack.acct=
1938 [NETFILTER] Enable connection tracking flow accounting
1939 0 to disable accounting
1940 1 to enable accounting
1941 Default value is 0.
1943 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1944 See Documentation/filesystems/nfs/nfsroot.txt.
1946 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1947 See Documentation/filesystems/nfs/nfsroot.txt.
1949 nfsrootdebug [NFS] enable nfsroot debugging messages.
1950 See Documentation/filesystems/nfs/nfsroot.txt.
1952 nfs.callback_tcpport=
1953 [NFS] set the TCP port on which the NFSv4 callback
1954 channel should listen.
1956 nfs.cache_getent=
1957 [NFS] sets the pathname to the program which is used
1958 to update the NFS client cache entries.
1960 nfs.cache_getent_timeout=
1961 [NFS] sets the timeout after which an attempt to
1962 update a cache entry is deemed to have failed.
1964 nfs.idmap_cache_timeout=
1965 [NFS] set the maximum lifetime for idmapper cache
1966 entries.
1968 nfs.enable_ino64=
1969 [NFS] enable 64-bit inode numbers.
1970 If zero, the NFS client will fake up a 32-bit inode
1971 number for the readdir() and stat() syscalls instead
1972 of returning the full 64-bit number.
1973 The default is to return 64-bit inode numbers.
1975 nfs.max_session_slots=
1976 [NFSv4.1] Sets the maximum number of session slots
1977 the client will attempt to negotiate with the server.
1978 This limits the number of simultaneous RPC requests
1979 that the client can send to the NFSv4.1 server.
1980 Note that there is little point in setting this
1981 value higher than the max_tcp_slot_table_limit.
1983 nfs.nfs4_disable_idmapping=
1984 [NFSv4] When set to the default of '1', this option
1985 ensures that both the RPC level authentication
1986 scheme and the NFS level operations agree to use
1987 numeric uids/gids if the mount is using the
1988 'sec=sys' security flavour. In effect it is
1989 disabling idmapping, which can make migration from
1990 legacy NFSv2/v3 systems to NFSv4 easier.
1991 Servers that do not support this mode of operation
1992 will be autodetected by the client, and it will fall
1993 back to using the idmapper.
1994 To turn off this behaviour, set the value to '0'.
1995 nfs.nfs4_unique_id=
1996 [NFS4] Specify an additional fixed unique ident-
1997 ification string that NFSv4 clients can insert into
1998 their nfs_client_id4 string. This is typically a
1999 UUID that is generated at system install time.
2001 nfs.send_implementation_id =
2002 [NFSv4.1] Send client implementation identification
2003 information in exchange_id requests.
2004 If zero, no implementation identification information
2005 will be sent.
2006 The default is to send the implementation identification
2007 information.
2009 nfs.recover_lost_locks =
2010 [NFSv4] Attempt to recover locks that were lost due
2011 to a lease timeout on the server. Please note that
2012 doing this risks data corruption, since there are
2013 no guarantees that the file will remain unchanged
2014 after the locks are lost.
2015 If you want to enable the kernel legacy behaviour of
2016 attempting to recover these locks, then set this
2017 parameter to '1'.
2018 The default parameter value of '0' causes the kernel
2019 not to attempt recovery of lost locks.
2021 nfsd.nfs4_disable_idmapping=
2022 [NFSv4] When set to the default of '1', the NFSv4
2023 server will return only numeric uids and gids to
2024 clients using auth_sys, and will accept numeric uids
2025 and gids from such clients. This is intended to ease
2026 migration from NFSv2/v3.
2028 objlayoutdriver.osd_login_prog=
2029 [NFS] [OBJLAYOUT] sets the pathname to the program which
2030 is used to automatically discover and login into new
2031 osd-targets. Please see:
2032 Documentation/filesystems/pnfs.txt for more explanations
2034 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2035 when a NMI is triggered.
2036 Format: [state][,regs][,debounce][,die]
2038 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2039 Format: [panic,][nopanic,][num]
2040 Valid num: 0
2041 0 - turn nmi_watchdog off
2042 When panic is specified, panic when an NMI watchdog
2043 timeout occurs (or 'nopanic' to override the opposite
2044 default).
2045 This is useful when you use a panic=... timeout and
2046 need the box quickly up again.
2048 netpoll.carrier_timeout=
2049 [NET] Specifies amount of time (in seconds) that
2050 netpoll should wait for a carrier. By default netpoll
2051 waits 4 seconds.
2053 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2054 emulation library even if a 387 maths coprocessor
2055 is present.
2057 no_console_suspend
2058 [HW] Never suspend the console
2059 Disable suspending of consoles during suspend and
2060 hibernate operations. Once disabled, debugging
2061 messages can reach various consoles while the rest
2062 of the system is being put to sleep (ie, while
2063 debugging driver suspend/resume hooks). This may
2064 not work reliably with all consoles, but is known
2065 to work with serial and VGA consoles.
2066 To facilitate more flexible debugging, we also add
2067 console_suspend, a printk module parameter to control
2068 it. Users could use console_suspend (usually
2069 /sys/module/printk/parameters/console_suspend) to
2070 turn on/off it dynamically.
2072 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2073 caches in the slab allocator. Saves per-node memory,
2074 but will impact performance.
2076 noalign [KNL,ARM]
2078 noapic [SMP,APIC] Tells the kernel to not make use of any
2079 IOAPICs that may be present in the system.
2081 nokaslr [X86]
2082 Disable kernel and module base offset ASLR (Address
2083 Space Layout Randomization) if built into the kernel.
2085 noautogroup Disable scheduler automatic task group creation.
2087 nobats [PPC] Do not use BATs for mapping kernel lowmem
2088 on "Classic" PPC cores.
2090 nocache [ARM]
2092 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2094 nodelayacct [KNL] Disable per-task delay accounting
2096 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2098 nodsp [SH] Disable hardware DSP at boot time.
2100 noefi [X86] Disable EFI runtime services support.
2102 noexec [IA-64]
2104 noexec [X86]
2105 On X86-32 available only on PAE configured kernels.
2106 noexec=on: enable non-executable mappings (default)
2107 noexec=off: disable non-executable mappings
2109 nosmap [X86]
2110 Disable SMAP (Supervisor Mode Access Prevention)
2111 even if it is supported by processor.
2113 nosmep [X86]
2114 Disable SMEP (Supervisor Mode Execution Prevention)
2115 even if it is supported by processor.
2117 noexec32 [X86-64]
2118 This affects only 32-bit executables.
2119 noexec32=on: enable non-executable mappings (default)
2120 read doesn't imply executable mappings
2121 noexec32=off: disable non-executable mappings
2122 read implies executable mappings
2124 nofpu [SH] Disable hardware FPU at boot time.
2126 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2127 register save and restore. The kernel will only save
2128 legacy floating-point registers on task switch.
2130 noxsave [BUGS=X86] Disables x86 extended register state save
2131 and restore using xsave. The kernel will fallback to
2132 enabling legacy floating-point and sse state.
2134 eagerfpu= [X86]
2135 on enable eager fpu restore
2136 off disable eager fpu restore
2137 auto selects the default scheme, which automatically
2138 enables eagerfpu restore for xsaveopt.
2140 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2141 wfi(ARM) instruction doesn't work correctly and not to
2142 use it. This is also useful when using JTAG debugger.
2144 no_file_caps Tells the kernel not to honor file capabilities. The
2145 only way then for a file to be executed with privilege
2146 is to be setuid root or executed by root.
2148 nohalt [IA-64] Tells the kernel not to use the power saving
2149 function PAL_HALT_LIGHT when idle. This increases
2150 power-consumption. On the positive side, it reduces
2151 interrupt wake-up latency, which may improve performance
2152 in certain environments such as networked servers or
2153 real-time systems.
2155 nohz= [KNL] Boottime enable/disable dynamic ticks
2156 Valid arguments: on, off
2157 Default: on
2159 nohz_full= [KNL,BOOT]
2160 In kernels built with CONFIG_NO_HZ_FULL=y, set
2161 the specified list of CPUs whose tick will be stopped
2162 whenever possible. The boot CPU will be forced outside
2163 the range to maintain the timekeeping.
2164 The CPUs in this range must also be included in the
2165 rcu_nocbs= set.
2167 noiotrap [SH] Disables trapped I/O port accesses.
2169 noirqdebug [X86-32] Disables the code which attempts to detect and
2170 disable unhandled interrupt sources.
2172 no_timer_check [X86,APIC] Disables the code which tests for
2173 broken timer IRQ sources.
2175 noisapnp [ISAPNP] Disables ISA PnP code.
2177 noinitrd [RAM] Tells the kernel not to load any configured
2178 initial RAM disk.
2180 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2181 remapping.
2182 [Deprecated - use intremap=off]
2184 nointroute [IA-64]
2186 nojitter [IA-64] Disables jitter checking for ITC timers.
2188 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2190 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2191 fault handling.
2193 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2194 steal time is computed, but won't influence scheduler
2195 behaviour
2197 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2199 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2201 noltlbs [PPC] Do not use large page/tlb entries for kernel
2202 lowmem mapping on PPC40x.
2204 nomca [IA-64] Disable machine check abort handling
2206 nomce [X86-32] Machine Check Exception
2208 nomfgpt [X86-32] Disable Multi-Function General Purpose
2209 Timer usage (for AMD Geode machines).
2211 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2212 shutdown the other cpus. Instead use the REBOOT_VECTOR
2213 irq.
2215 nomodule Disable module load
2217 nopat [X86] Disable PAT (page attribute table extension of
2218 pagetables) support.
2220 norandmaps Don't use address space randomization. Equivalent to
2221 echo 0 > /proc/sys/kernel/randomize_va_space
2223 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2225 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2226 with UP alternatives
2228 nordrand [X86] Disable the direct use of the RDRAND
2229 instruction even if it is supported by the
2230 processor. RDRAND is still available to user
2231 space applications.
2233 noresume [SWSUSP] Disables resume and restores original swap
2234 space.
2236 no-scroll [VGA] Disables scrollback.
2237 This is required for the Braillex ib80-piezo Braille
2238 reader made by F.H. Papenmeier (Germany).
2240 nosbagart [IA-64]
2242 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2244 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2245 and disable the IO APIC. legacy for "maxcpus=0".
2247 nosoftlockup [KNL] Disable the soft-lockup detector.
2249 nosync [HW,M68K] Disables sync negotiation for all devices.
2251 notsc [BUGS=X86-32] Disable Time Stamp Counter
2253 nousb [USB] Disable the USB subsystem
2255 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2257 nowb [ARM]
2259 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2261 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2262 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2263 Some features depend on CPU0. Known dependencies are:
2264 1. Resume from suspend/hibernate depends on CPU0.
2265 Suspend/hibernate will fail if CPU0 is offline and you
2266 need to online CPU0 before suspend/hibernate.
2267 2. PIC interrupts also depend on CPU0. CPU0 can't be
2268 removed if a PIC interrupt is detected.
2269 It's said poweroff/reboot may depend on CPU0 on some
2270 machines although I haven't seen such issues so far
2271 after CPU0 is offline on a few tested machines.
2272 If the dependencies are under your control, you can
2273 turn on cpu0_hotplug.
2275 nptcg= [IA-64] Override max number of concurrent global TLB
2276 purges which is reported from either PAL_VM_SUMMARY or
2277 SAL PALO.
2279 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2280 could support. nr_cpus=n : n >= 1 limits the kernel to
2281 supporting 'n' processors. Later in runtime you can not
2282 use hotplug cpu feature to put more cpu back to online.
2283 just like you compile the kernel NR_CPUS=n
2285 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2287 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2288 Allowed values are enable and disable
2290 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2291 one of ['zone', 'node', 'default'] can be specified
2292 This can be set from sysctl after boot.
2293 See Documentation/sysctl/vm.txt for details.
2295 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2296 See Documentation/debugging-via-ohci1394.txt for more
2297 info.
2299 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2300 Rather than timing out after 20 ms if an EC
2301 command is not properly ACKed, override the length
2302 of the timeout. We have interrupts disabled while
2303 waiting for the ACK, so if this is set too high
2304 interrupts *may* be lost!
2306 omap_mux= [OMAP] Override bootloader pin multiplexing.
2307 Format: <mux_mode0.mode_name=value>...
2308 For example, to override I2C bus2:
2309 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2311 oprofile.timer= [HW]
2312 Use timer interrupt instead of performance counters
2314 oprofile.cpu_type= Force an oprofile cpu type
2315 This might be useful if you have an older oprofile
2316 userland or if you want common events.
2317 Format: { arch_perfmon }
2318 arch_perfmon: [X86] Force use of architectural
2319 perfmon on Intel CPUs instead of the
2320 CPU specific event set.
2321 timer: [X86] Force use of architectural NMI
2322 timer mode (see also oprofile.timer
2323 for generic hr timer mode)
2324 [s390] Force legacy basic mode sampling
2325 (report cpu_type "timer")
2327 oops=panic Always panic on oopses. Default is to just kill the
2328 process, but there is a small probability of
2329 deadlocking the machine.
2330 This will also cause panics on machine check exceptions.
2331 Useful together with panic=30 to trigger a reboot.
2333 OSS [HW,OSS]
2334 See Documentation/sound/oss/oss-parameters.txt
2336 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2337 timeout > 0: seconds before rebooting
2338 timeout = 0: wait forever
2339 timeout < 0: reboot immediately
2340 Format: <timeout>
2342 parkbd.port= [HW] Parallel port number the keyboard adapter is
2343 connected to, default is 0.
2344 Format: <parport#>
2345 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2346 0 for XT, 1 for AT (default is AT).
2347 Format: <mode>
2349 parport= [HW,PPT] Specify parallel ports. 0 disables.
2350 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2351 Use 'auto' to force the driver to use any
2352 IRQ/DMA settings detected (the default is to
2353 ignore detected IRQ/DMA settings because of
2354 possible conflicts). You can specify the base
2355 address, IRQ, and DMA settings; IRQ and DMA
2356 should be numbers, or 'auto' (for using detected
2357 settings on that particular port), or 'nofifo'
2358 (to avoid using a FIFO even if it is detected).
2359 Parallel ports are assigned in the order they
2360 are specified on the command line, starting
2361 with parport0.
2363 parport_init_mode= [HW,PPT]
2364 Configure VIA parallel port to operate in
2365 a specific mode. This is necessary on Pegasos
2366 computer where firmware has no options for setting
2367 up parallel port mode and sets it to spp.
2368 Currently this function knows 686a and 8231 chips.
2369 Format: [spp|ps2|epp|ecp|ecpepp]
2371 pause_on_oops=
2372 Halt all CPUs after the first oops has been printed for
2373 the specified number of seconds. This is to be used if
2374 your oopses keep scrolling off the screen.
2376 pcbit= [HW,ISDN]
2378 pcd. [PARIDE]
2379 See header of drivers/block/paride/pcd.c.
2380 See also Documentation/blockdev/paride.txt.
2382 pci=option[,option...] [PCI] various PCI subsystem options:
2383 earlydump [X86] dump PCI config space before the kernel
2384 changes anything
2385 off [X86] don't probe for the PCI bus
2386 bios [X86-32] force use of PCI BIOS, don't access
2387 the hardware directly. Use this if your machine
2388 has a non-standard PCI host bridge.
2389 nobios [X86-32] disallow use of PCI BIOS, only direct
2390 hardware access methods are allowed. Use this
2391 if you experience crashes upon bootup and you
2392 suspect they are caused by the BIOS.
2393 conf1 [X86] Force use of PCI Configuration
2394 Mechanism 1.
2395 conf2 [X86] Force use of PCI Configuration
2396 Mechanism 2.
2397 noaer [PCIE] If the PCIEAER kernel config parameter is
2398 enabled, this kernel boot option can be used to
2399 disable the use of PCIE advanced error reporting.
2400 nodomains [PCI] Disable support for multiple PCI
2401 root domains (aka PCI segments, in ACPI-speak).
2402 nommconf [X86] Disable use of MMCONFIG for PCI
2403 Configuration
2404 check_enable_amd_mmconf [X86] check for and enable
2405 properly configured MMIO access to PCI
2406 config space on AMD family 10h CPU
2407 nomsi [MSI] If the PCI_MSI kernel config parameter is
2408 enabled, this kernel boot option can be used to
2409 disable the use of MSI interrupts system-wide.
2410 noioapicquirk [APIC] Disable all boot interrupt quirks.
2411 Safety option to keep boot IRQs enabled. This
2412 should never be necessary.
2413 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2414 primary IO-APIC for bridges that cannot disable
2415 boot IRQs. This fixes a source of spurious IRQs
2416 when the system masks IRQs.
2417 noioapicreroute [APIC] Disable workaround that uses the
2418 boot IRQ equivalent of an IRQ that connects to
2419 a chipset where boot IRQs cannot be disabled.
2420 The opposite of ioapicreroute.
2421 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2422 routing table. These calls are known to be buggy
2423 on several machines and they hang the machine
2424 when used, but on other computers it's the only
2425 way to get the interrupt routing table. Try
2426 this option if the kernel is unable to allocate
2427 IRQs or discover secondary PCI buses on your
2428 motherboard.
2429 rom [X86] Assign address space to expansion ROMs.
2430 Use with caution as certain devices share
2431 address decoders between ROMs and other
2432 resources.
2433 norom [X86] Do not assign address space to
2434 expansion ROMs that do not already have
2435 BIOS assigned address ranges.
2436 nobar [X86] Do not assign address space to the
2437 BARs that weren't assigned by the BIOS.
2438 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2439 assigned automatically to PCI devices. You can
2440 make the kernel exclude IRQs of your ISA cards
2441 this way.
2442 pirqaddr=0xAAAAA [X86] Specify the physical address
2443 of the PIRQ table (normally generated
2444 by the BIOS) if it is outside the
2445 F0000h-100000h range.
2446 lastbus=N [X86] Scan all buses thru bus #N. Can be
2447 useful if the kernel is unable to find your
2448 secondary buses and you want to tell it
2449 explicitly which ones they are.
2450 assign-busses [X86] Always assign all PCI bus
2451 numbers ourselves, overriding
2452 whatever the firmware may have done.
2453 usepirqmask [X86] Honor the possible IRQ mask stored
2454 in the BIOS $PIR table. This is needed on
2455 some systems with broken BIOSes, notably
2456 some HP Pavilion N5400 and Omnibook XE3
2457 notebooks. This will have no effect if ACPI
2458 IRQ routing is enabled.
2459 noacpi [X86] Do not use ACPI for IRQ routing
2460 or for PCI scanning.
2461 use_crs [X86] Use PCI host bridge window information
2462 from ACPI. On BIOSes from 2008 or later, this
2463 is enabled by default. If you need to use this,
2464 please report a bug.
2465 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2466 If you need to use this, please report a bug.
2467 routeirq Do IRQ routing for all PCI devices.
2468 This is normally done in pci_enable_device(),
2469 so this option is a temporary workaround
2470 for broken drivers that don't call it.
2471 skip_isa_align [X86] do not align io start addr, so can
2472 handle more pci cards
2473 firmware [ARM] Do not re-enumerate the bus but instead
2474 just use the configuration from the
2475 bootloader. This is currently used on
2476 IXP2000 systems where the bus has to be
2477 configured a certain way for adjunct CPUs.
2478 noearly [X86] Don't do any early type 1 scanning.
2479 This might help on some broken boards which
2480 machine check when some devices' config space
2481 is read. But various workarounds are disabled
2482 and some IOMMU drivers will not work.
2483 bfsort Sort PCI devices into breadth-first order.
2484 This sorting is done to get a device
2485 order compatible with older (<= 2.4) kernels.
2486 nobfsort Don't sort PCI devices into breadth-first order.
2487 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2488 tuning and use the BIOS-configured MPS defaults.
2489 pcie_bus_safe Set every device's MPS to the largest value
2490 supported by all devices below the root complex.
2491 pcie_bus_perf Set device MPS to the largest allowable MPS
2492 based on its parent bus. Also set MRRS (Max
2493 Read Request Size) to the largest supported
2494 value (no larger than the MPS that the device
2495 or bus can support) for best performance.
2496 pcie_bus_peer2peer Set every device's MPS to 128B, which
2497 every device is guaranteed to support. This
2498 configuration allows peer-to-peer DMA between
2499 any pair of devices, possibly at the cost of
2500 reduced performance. This also guarantees
2501 that hot-added devices will work.
2502 cbiosize=nn[KMG] The fixed amount of bus space which is
2503 reserved for the CardBus bridge's IO window.
2504 The default value is 256 bytes.
2505 cbmemsize=nn[KMG] The fixed amount of bus space which is
2506 reserved for the CardBus bridge's memory
2507 window. The default value is 64 megabytes.
2508 resource_alignment=
2509 Format:
2510 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2511 Specifies alignment and device to reassign
2512 aligned memory resources.
2513 If <order of align> is not specified,
2514 PAGE_SIZE is used as alignment.
2515 PCI-PCI bridge can be specified, if resource
2516 windows need to be expanded.
2517 ecrc= Enable/disable PCIe ECRC (transaction layer
2518 end-to-end CRC checking).
2519 bios: Use BIOS/firmware settings. This is the
2520 the default.
2521 off: Turn ECRC off
2522 on: Turn ECRC on.
2523 hpiosize=nn[KMG] The fixed amount of bus space which is
2524 reserved for hotplug bridge's IO window.
2525 Default size is 256 bytes.
2526 hpmemsize=nn[KMG] The fixed amount of bus space which is
2527 reserved for hotplug bridge's memory window.
2528 Default size is 2 megabytes.
2529 realloc= Enable/disable reallocating PCI bridge resources
2530 if allocations done by BIOS are too small to
2531 accommodate resources required by all child
2532 devices.
2533 off: Turn realloc off
2534 on: Turn realloc on
2535 realloc same as realloc=on
2536 noari do not use PCIe ARI.
2537 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2538 only look for one device below a PCIe downstream
2539 port.
2541 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2542 Management.
2543 off Disable ASPM.
2544 force Enable ASPM even on devices that claim not to support it.
2545 WARNING: Forcing ASPM on may cause system lockups.
2547 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2548 nomsi Do not use MSI for PCI Express Native Hotplug (this
2549 makes all PCIe ports use INTx for hotplug services).
2551 pcie_ports= [PCIE] PCIe ports handling:
2552 auto Ask the BIOS whether or not to use native PCIe services
2553 associated with PCIe ports (PME, hot-plug, AER). Use
2554 them only if that is allowed by the BIOS.
2555 native Use native PCIe services associated with PCIe ports
2556 unconditionally.
2557 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2558 ports driver.
2560 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2561 nomsi Do not use MSI for native PCIe PME signaling (this makes
2562 all PCIe root ports use INTx for all services).
2564 pcmv= [HW,PCMCIA] BadgePAD 4
2566 pd_ignore_unused
2567 [PM]
2568 Keep all power-domains already enabled by bootloader on,
2569 even if no driver has claimed them. This is useful
2570 for debug and development, but should not be
2571 needed on a platform with proper driver support.
2573 pd. [PARIDE]
2574 See Documentation/blockdev/paride.txt.
2576 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2577 boot time.
2578 Format: { 0 | 1 }
2579 See arch/parisc/kernel/pdc_chassis.c
2581 percpu_alloc= Select which percpu first chunk allocator to use.
2582 Currently supported values are "embed" and "page".
2583 Archs may support subset or none of the selections.
2584 See comments in mm/percpu.c for details on each
2585 allocator. This parameter is primarily for debugging
2586 and performance comparison.
2588 pf. [PARIDE]
2589 See Documentation/blockdev/paride.txt.
2591 pg. [PARIDE]
2592 See Documentation/blockdev/paride.txt.
2594 pirq= [SMP,APIC] Manual mp-table setup
2595 See Documentation/x86/i386/IO-APIC.txt.
2597 plip= [PPT,NET] Parallel port network link
2598 Format: { parport<nr> | timid | 0 }
2599 See also Documentation/parport.txt.
2601 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2602 Override pmtimer IOPort with a hex value.
2603 e.g. pmtmr=0x508
2605 pnp.debug=1 [PNP]
2606 Enable PNP debug messages (depends on the
2607 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2608 via /sys/module/pnp/parameters/debug. We always show
2609 current resource usage; turning this on also shows
2610 possible settings and some assignment information.
2612 pnpacpi= [ACPI]
2613 { off }
2615 pnpbios= [ISAPNP]
2616 { on | off | curr | res | no-curr | no-res }
2618 pnp_reserve_irq=
2619 [ISAPNP] Exclude IRQs for the autoconfiguration
2621 pnp_reserve_dma=
2622 [ISAPNP] Exclude DMAs for the autoconfiguration
2624 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2625 Ranges are in pairs (I/O port base and size).
2627 pnp_reserve_mem=
2628 [ISAPNP] Exclude memory regions for the
2629 autoconfiguration.
2630 Ranges are in pairs (memory base and size).
2632 ports= [IP_VS_FTP] IPVS ftp helper module
2633 Default is 21.
2634 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2635 may be specified.
2636 Format: <port>,<port>....
2638 print-fatal-signals=
2639 [KNL] debug: print fatal signals
2641 If enabled, warn about various signal handling
2642 related application anomalies: too many signals,
2643 too many POSIX.1 timers, fatal signals causing a
2644 coredump - etc.
2646 If you hit the warning due to signal overflow,
2647 you might want to try "ulimit -i unlimited".
2649 default: off.
2651 printk.always_kmsg_dump=
2652 Trigger kmsg_dump for cases other than kernel oops or
2653 panics
2654 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2655 default: disabled
2657 printk.time= Show timing data prefixed to each printk message line
2658 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2660 processor.max_cstate= [HW,ACPI]
2661 Limit processor to maximum C-state
2662 max_cstate=9 overrides any DMI blacklist limit.
2664 processor.nocst [HW,ACPI]
2665 Ignore the _CST method to determine C-states,
2666 instead using the legacy FADT method
2668 profile= [KNL] Enable kernel profiling via /proc/profile
2669 Format: [schedule,]<number>
2670 Param: "schedule" - profile schedule points.
2671 Param: <number> - step/bucket size as a power of 2 for
2672 statistical time based profiling.
2673 Param: "sleep" - profile D-state sleeping (millisecs).
2674 Requires CONFIG_SCHEDSTATS
2675 Param: "kvm" - profile VM exits.
2677 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2678 before loading.
2679 See Documentation/blockdev/ramdisk.txt.
2681 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2682 probe for; one of (bare|imps|exps|lifebook|any).
2683 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2684 per second.
2685 psmouse.resetafter= [HW,MOUSE]
2686 Try to reset the device after so many bad packets
2687 (0 = never).
2688 psmouse.resolution=
2689 [HW,MOUSE] Set desired mouse resolution, in dpi.
2690 psmouse.smartscroll=
2691 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2692 0 = disabled, 1 = enabled (default).
2694 pstore.backend= Specify the name of the pstore backend to use
2696 pt. [PARIDE]
2697 See Documentation/blockdev/paride.txt.
2699 pty.legacy_count=
2700 [KNL] Number of legacy pty's. Overwrites compiled-in
2701 default number.
2703 quiet [KNL] Disable most log messages
2705 r128= [HW,DRM]
2707 raid= [HW,RAID]
2708 See Documentation/md.txt.
2710 ramdisk_blocksize= [RAM]
2711 See Documentation/blockdev/ramdisk.txt.
2713 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2714 See Documentation/blockdev/ramdisk.txt.
2716 rcu_nocbs= [KNL]
2717 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2718 the specified list of CPUs to be no-callback CPUs.
2719 Invocation of these CPUs' RCU callbacks will
2720 be offloaded to "rcuox/N" kthreads created for
2721 that purpose, where "x" is "b" for RCU-bh, "p"
2722 for RCU-preempt, and "s" for RCU-sched, and "N"
2723 is the CPU number. This reduces OS jitter on the
2724 offloaded CPUs, which can be useful for HPC and
2725 real-time workloads. It can also improve energy
2726 efficiency for asymmetric multiprocessors.
2728 rcu_nocb_poll [KNL]
2729 Rather than requiring that offloaded CPUs
2730 (specified by rcu_nocbs= above) explicitly
2731 awaken the corresponding "rcuoN" kthreads,
2732 make these kthreads poll for callbacks.
2733 This improves the real-time response for the
2734 offloaded CPUs by relieving them of the need to
2735 wake up the corresponding kthread, but degrades
2736 energy efficiency by requiring that the kthreads
2737 periodically wake up to do the polling.
2739 rcutree.blimit= [KNL]
2740 Set maximum number of finished RCU callbacks to
2741 process in one batch.
2743 rcutree.rcu_fanout_leaf= [KNL]
2744 Increase the number of CPUs assigned to each
2745 leaf rcu_node structure. Useful for very large
2746 systems.
2748 rcutree.jiffies_till_first_fqs= [KNL]
2749 Set delay from grace-period initialization to
2750 first attempt to force quiescent states.
2751 Units are jiffies, minimum value is zero,
2752 and maximum value is HZ.
2754 rcutree.jiffies_till_next_fqs= [KNL]
2755 Set delay between subsequent attempts to force
2756 quiescent states. Units are jiffies, minimum
2757 value is one, and maximum value is HZ.
2759 rcutree.qhimark= [KNL]
2760 Set threshold of queued RCU callbacks beyond which
2761 batch limiting is disabled.
2763 rcutree.qlowmark= [KNL]
2764 Set threshold of queued RCU callbacks below which
2765 batch limiting is re-enabled.
2767 rcutree.rcu_idle_gp_delay= [KNL]
2768 Set wakeup interval for idle CPUs that have
2769 RCU callbacks (RCU_FAST_NO_HZ=y).
2771 rcutree.rcu_idle_lazy_gp_delay= [KNL]
2772 Set wakeup interval for idle CPUs that have
2773 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2774 Lazy RCU callbacks are those which RCU can
2775 prove do nothing more than free memory.
2777 rcutorture.fqs_duration= [KNL]
2778 Set duration of force_quiescent_state bursts.
2780 rcutorture.fqs_holdoff= [KNL]
2781 Set holdoff time within force_quiescent_state bursts.
2783 rcutorture.fqs_stutter= [KNL]
2784 Set wait time between force_quiescent_state bursts.
2786 rcutorture.gp_exp= [KNL]
2787 Use expedited update-side primitives.
2789 rcutorture.gp_normal= [KNL]
2790 Use normal (non-expedited) update-side primitives.
2791 If both gp_exp and gp_normal are set, do both.
2792 If neither gp_exp nor gp_normal are set, still
2793 do both.
2795 rcutorture.n_barrier_cbs= [KNL]
2796 Set callbacks/threads for rcu_barrier() testing.
2798 rcutorture.nfakewriters= [KNL]
2799 Set number of concurrent RCU writers. These just
2800 stress RCU, they don't participate in the actual
2801 test, hence the "fake".
2803 rcutorture.nreaders= [KNL]
2804 Set number of RCU readers.
2806 rcutorture.object_debug= [KNL]
2807 Enable debug-object double-call_rcu() testing.
2809 rcutorture.onoff_holdoff= [KNL]
2810 Set time (s) after boot for CPU-hotplug testing.
2812 rcutorture.onoff_interval= [KNL]
2813 Set time (s) between CPU-hotplug operations, or
2814 zero to disable CPU-hotplug testing.
2816 rcutorture.rcutorture_runnable= [BOOT]
2817 Start rcutorture running at boot time.
2819 rcutorture.shuffle_interval= [KNL]
2820 Set task-shuffle interval (s). Shuffling tasks
2821 allows some CPUs to go into dyntick-idle mode
2822 during the rcutorture test.
2824 rcutorture.shutdown_secs= [KNL]
2825 Set time (s) after boot system shutdown. This
2826 is useful for hands-off automated testing.
2828 rcutorture.stall_cpu= [KNL]
2829 Duration of CPU stall (s) to test RCU CPU stall
2830 warnings, zero to disable.
2832 rcutorture.stall_cpu_holdoff= [KNL]
2833 Time to wait (s) after boot before inducing stall.
2835 rcutorture.stat_interval= [KNL]
2836 Time (s) between statistics printk()s.
2838 rcutorture.stutter= [KNL]
2839 Time (s) to stutter testing, for example, specifying
2840 five seconds causes the test to run for five seconds,
2841 wait for five seconds, and so on. This tests RCU's
2842 ability to transition abruptly to and from idle.
2844 rcutorture.test_boost= [KNL]
2845 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2846 "Maybe" means test if the RCU implementation
2847 under test support RCU priority boosting.
2849 rcutorture.test_boost_duration= [KNL]
2850 Duration (s) of each individual boost test.
2852 rcutorture.test_boost_interval= [KNL]
2853 Interval (s) between each boost test.
2855 rcutorture.test_no_idle_hz= [KNL]
2856 Test RCU's dyntick-idle handling. See also the
2857 rcutorture.shuffle_interval parameter.
2859 rcutorture.torture_type= [KNL]
2860 Specify the RCU implementation to test.
2862 rcutorture.verbose= [KNL]
2863 Enable additional printk() statements.
2865 rcupdate.rcu_expedited= [KNL]
2866 Use expedited grace-period primitives, for
2867 example, synchronize_rcu_expedited() instead
2868 of synchronize_rcu(). This reduces latency,
2869 but can increase CPU utilization, degrade
2870 real-time latency, and degrade energy efficiency.
2872 rcupdate.rcu_cpu_stall_suppress= [KNL]
2873 Suppress RCU CPU stall warning messages.
2875 rcupdate.rcu_cpu_stall_timeout= [KNL]
2876 Set timeout for RCU CPU stall warning messages.
2878 rdinit= [KNL]
2879 Format: <full_path>
2880 Run specified binary instead of /init from the ramdisk,
2881 used for early userspace startup. See initrd.
2883 reboot= [KNL]
2884 Format (x86 or x86_64):
2885 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2886 [[,]s[mp]#### \
2887 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2888 [[,]f[orce]
2889 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2890 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2891 reboot_force is either force or not specified,
2892 reboot_cpu is s[mp]#### with #### being the processor
2893 to be used for rebooting.
2895 relax_domain_level=
2896 [KNL, SMP] Set scheduler's default relax_domain_level.
2897 See Documentation/cgroups/cpusets.txt.
2899 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2901 reservetop= [X86-32]
2902 Format: nn[KMG]
2903 Reserves a hole at the top of the kernel virtual
2904 address space.
2906 reservelow= [X86]
2907 Format: nn[K]
2908 Set the amount of memory to reserve for BIOS at
2909 the bottom of the address space.
2911 reset_devices [KNL] Force drivers to reset the underlying device
2912 during initialization.
2914 resume= [SWSUSP]
2915 Specify the partition device for software suspend
2916 Format:
2917 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2919 resume_offset= [SWSUSP]
2920 Specify the offset from the beginning of the partition
2921 given by "resume=" at which the swap header is located,
2922 in <PAGE_SIZE> units (needed only for swap files).
2923 See Documentation/power/swsusp-and-swap-files.txt
2925 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2926 read the resume files
2928 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2929 Useful for devices that are detected asynchronously
2930 (e.g. USB and MMC devices).
2932 hibernate= [HIBERNATION]
2933 noresume Don't check if there's a hibernation image
2934 present during boot.
2935 nocompress Don't compress/decompress hibernation images.
2937 retain_initrd [RAM] Keep initrd memory after extraction
2939 rhash_entries= [KNL,NET]
2940 Set number of hash buckets for route cache
2942 riscom8= [HW,SERIAL]
2943 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2945 ro [KNL] Mount root device read-only on boot
2947 root= [KNL] Root filesystem
2948 See name_to_dev_t comment in init/do_mounts.c.
2950 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2951 mount the root filesystem
2953 rootflags= [KNL] Set root filesystem mount option string
2955 rootfstype= [KNL] Set root filesystem type
2957 rootwait [KNL] Wait (indefinitely) for root device to show up.
2958 Useful for devices that are detected asynchronously
2959 (e.g. USB and MMC devices).
2961 rproc_mem=nn[KMG][@address]
2962 [KNL,ARM,CMA] Remoteproc physical memory block.
2963 Memory area to be used by remote processor image,
2964 managed by CMA.
2966 rw [KNL] Mount root device read-write on boot
2968 S [KNL] Run init in single mode
2970 sa1100ir [NET]
2971 See drivers/net/irda/sa1100_ir.c.
2973 sbni= [NET] Granch SBNI12 leased line adapter
2975 sched_debug [KNL] Enables verbose scheduler debug messages.
2977 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2978 xtime_lock contention on larger systems, and/or RCU lock
2979 contention on all systems with CONFIG_MAXSMP set.
2980 Format: { "0" | "1" }
2981 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2982 1 -- enable.
2983 Note: increases power consumption, thus should only be
2984 enabled if running jitter sensitive (HPC/RT) workloads.
2986 security= [SECURITY] Choose a security module to enable at boot.
2987 If this boot parameter is not specified, only the first
2988 security module asking for security registration will be
2989 loaded. An invalid security module name will be treated
2990 as if no module has been chosen.
2992 selinux= [SELINUX] Disable or enable SELinux at boot time.
2993 Format: { "0" | "1" }
2994 See security/selinux/Kconfig help text.
2995 0 -- disable.
2996 1 -- enable.
2997 Default value is set via kernel config option.
2998 If enabled at boot time, /selinux/disable can be used
2999 later to disable prior to initial policy load.
3001 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3002 Format: { "0" | "1" }
3003 See security/apparmor/Kconfig help text
3004 0 -- disable.
3005 1 -- enable.
3006 Default value is set via kernel config option.
3008 serialnumber [BUGS=X86-32]
3010 shapers= [NET]
3011 Maximal number of shapers.
3013 show_msr= [x86] show boot-time MSR settings
3014 Format: { <integer> }
3015 Show boot-time (BIOS-initialized) MSR settings.
3016 The parameter means the number of CPUs to show,
3017 for example 1 means boot CPU only.
3019 simeth= [IA-64]
3020 simscsi=
3022 slram= [HW,MTD]
3024 slab_max_order= [MM, SLAB]
3025 Determines the maximum allowed order for slabs.
3026 A high setting may cause OOMs due to memory
3027 fragmentation. Defaults to 1 for systems with
3028 more than 32MB of RAM, 0 otherwise.
3030 slub_debug[=options[,slabs]] [MM, SLUB]
3031 Enabling slub_debug allows one to determine the
3032 culprit if slab objects become corrupted. Enabling
3033 slub_debug can create guard zones around objects and
3034 may poison objects when not in use. Also tracks the
3035 last alloc / free. For more information see
3036 Documentation/vm/slub.txt.
3038 slub_max_order= [MM, SLUB]
3039 Determines the maximum allowed order for slabs.
3040 A high setting may cause OOMs due to memory
3041 fragmentation. For more information see
3042 Documentation/vm/slub.txt.
3044 slub_min_objects= [MM, SLUB]
3045 The minimum number of objects per slab. SLUB will
3046 increase the slab order up to slub_max_order to
3047 generate a sufficiently large slab able to contain
3048 the number of objects indicated. The higher the number
3049 of objects the smaller the overhead of tracking slabs
3050 and the less frequently locks need to be acquired.
3051 For more information see Documentation/vm/slub.txt.
3053 slub_min_order= [MM, SLUB]
3054 Determines the minimum page order for slabs. Must be
3055 lower than slub_max_order.
3056 For more information see Documentation/vm/slub.txt.
3058 slub_nomerge [MM, SLUB]
3059 Disable merging of slabs with similar size. May be
3060 necessary if there is some reason to distinguish
3061 allocs to different slabs. Debug options disable
3062 merging on their own.
3063 For more information see Documentation/vm/slub.txt.
3065 smart2= [HW]
3066 Format: <io1>[,<io2>[,...,<io8>]]
3068 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3069 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3070 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3071 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3072 smsc-ircc2.ircc_irq= [HW] IRQ line
3073 smsc-ircc2.ircc_dma= [HW] DMA channel
3074 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3075 0: Toshiba Satellite 1800 (GP data pin select)
3076 1: Fast pin select (default)
3077 2: ATC IRMode
3079 softlockup_panic=
3080 [KNL] Should the soft-lockup detector generate panics.
3081 Format: <integer>
3083 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3084 See Documentation/laptops/sonypi.txt
3086 specialix= [HW,SERIAL] Specialix multi-serial port adapter
3087 See Documentation/serial/specialix.txt.
3089 spia_io_base= [HW,MTD]
3090 spia_fio_base=
3091 spia_pedr=
3092 spia_peddr=
3094 stacktrace [FTRACE]
3095 Enabled the stack tracer on boot up.
3097 stacktrace_filter=[function-list]
3098 [FTRACE] Limit the functions that the stack tracer
3099 will trace at boot up. function-list is a comma separated
3100 list of functions. This list can be changed at run
3101 time by the stack_trace_filter file in the debugfs
3102 tracing directory. Note, this enables stack tracing
3103 and the stacktrace above is not needed.
3105 sti= [PARISC,HW]
3106 Format: <num>
3107 Set the STI (builtin display/keyboard on the HP-PARISC
3108 machines) console (graphic card) which should be used
3109 as the initial boot-console.
3110 See also comment in drivers/video/console/sticore.c.
3112 sti_font= [HW]
3113 See comment in drivers/video/console/sticore.c.
3115 stifb= [HW]
3116 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3118 sunrpc.min_resvport=
3119 sunrpc.max_resvport=
3120 [NFS,SUNRPC]
3121 SunRPC servers often require that client requests
3122 originate from a privileged port (i.e. a port in the
3123 range 0 < portnr < 1024).
3124 An administrator who wishes to reserve some of these
3125 ports for other uses may adjust the range that the
3126 kernel's sunrpc client considers to be privileged
3127 using these two parameters to set the minimum and
3128 maximum port values.
3130 sunrpc.pool_mode=
3131 [NFS]
3132 Control how the NFS server code allocates CPUs to
3133 service thread pools. Depending on how many NICs
3134 you have and where their interrupts are bound, this
3135 option will affect which CPUs will do NFS serving.
3136 Note: this parameter cannot be changed while the
3137 NFS server is running.
3139 auto the server chooses an appropriate mode
3140 automatically using heuristics
3141 global a single global pool contains all CPUs
3142 percpu one pool for each CPU
3143 pernode one pool for each NUMA node (equivalent
3144 to global on non-NUMA machines)
3146 sunrpc.tcp_slot_table_entries=
3147 sunrpc.udp_slot_table_entries=
3148 [NFS,SUNRPC]
3149 Sets the upper limit on the number of simultaneous
3150 RPC calls that can be sent from the client to a
3151 server. Increasing these values may allow you to
3152 improve throughput, but will also increase the
3153 amount of memory reserved for use by the client.
3155 swapaccount=[0|1]
3156 [KNL] Enable accounting of swap in memory resource
3157 controller if no parameter or 1 is given or disable
3158 it if 0 is given (See Documentation/cgroups/memory.txt)
3160 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3161 Format: { <int> | force }
3162 <int> -- Number of I/O TLB slabs
3163 force -- force using of bounce buffers even if they
3164 wouldn't be automatically used by the kernel
3166 switches= [HW,M68k]
3168 sysfs.deprecated=0|1 [KNL]
3169 Enable/disable old style sysfs layout for old udev
3170 on older distributions. When this option is enabled
3171 very new udev will not work anymore. When this option
3172 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3173 in older udev will not work anymore.
3174 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3175 the kernel configuration.
3177 sysrq_always_enabled
3178 [KNL]
3179 Ignore sysrq setting - this boot parameter will
3180 neutralize any effect of /proc/sys/kernel/sysrq.
3181 Useful for debugging.
3183 tdfx= [HW,DRM]
3185 test_suspend= [SUSPEND]
3186 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3187 standby suspend) as the system sleep state to briefly
3188 enter during system startup. The system is woken from
3189 this state using a wakeup-capable RTC alarm.
3191 thash_entries= [KNL,NET]
3192 Set number of hash buckets for TCP connection
3194 thermal.act= [HW,ACPI]
3195 -1: disable all active trip points in all thermal zones
3196 <degrees C>: override all lowest active trip points
3198 thermal.crt= [HW,ACPI]
3199 -1: disable all critical trip points in all thermal zones
3200 <degrees C>: override all critical trip points
3202 thermal.nocrt= [HW,ACPI]
3203 Set to disable actions on ACPI thermal zone
3204 critical and hot trip points.
3206 thermal.off= [HW,ACPI]
3207 1: disable ACPI thermal control
3209 thermal.psv= [HW,ACPI]
3210 -1: disable all passive trip points
3211 <degrees C>: override all passive trip points to this
3212 value
3214 thermal.tzp= [HW,ACPI]
3215 Specify global default ACPI thermal zone polling rate
3216 <deci-seconds>: poll all this frequency
3217 0: no polling (default)
3219 threadirqs [KNL]
3220 Force threading of all interrupt handlers except those
3221 marked explicitly IRQF_NO_THREAD.
3223 tmem [KNL,XEN]
3224 Enable the Transcendent memory driver if built-in.
3226 tmem.cleancache=0|1 [KNL, XEN]
3227 Default is on (1). Disable the usage of the cleancache
3228 API to send anonymous pages to the hypervisor.
3230 tmem.frontswap=0|1 [KNL, XEN]
3231 Default is on (1). Disable the usage of the frontswap
3232 API to send swap pages to the hypervisor. If disabled
3233 the selfballooning and selfshrinking are force disabled.
3235 tmem.selfballooning=0|1 [KNL, XEN]
3236 Default is on (1). Disable the driving of swap pages
3237 to the hypervisor.
3239 tmem.selfshrinking=0|1 [KNL, XEN]
3240 Default is on (1). Partial swapoff that immediately
3241 transfers pages from Xen hypervisor back to the
3242 kernel based on different criteria.
3244 topology= [S390]
3245 Format: {off | on}
3246 Specify if the kernel should make use of the cpu
3247 topology information if the hardware supports this.
3248 The scheduler will make use of this information and
3249 e.g. base its process migration decisions on it.
3250 Default is on.
3252 tp720= [HW,PS2]
3254 tpm_suspend_pcr=[HW,TPM]
3255 Format: integer pcr id
3256 Specify that at suspend time, the tpm driver
3257 should extend the specified pcr with zeros,
3258 as a workaround for some chips which fail to
3259 flush the last written pcr on TPM_SaveState.
3260 This will guarantee that all the other pcrs
3261 are saved.
3263 trace_buf_size=nn[KMG]
3264 [FTRACE] will set tracing buffer size.
3266 trace_event=[event-list]
3267 [FTRACE] Set and start specified trace events in order
3268 to facilitate early boot debugging.
3269 See also Documentation/trace/events.txt
3271 trace_options=[option-list]
3272 [FTRACE] Enable or disable tracer options at boot.
3273 The option-list is a comma delimited list of options
3274 that can be enabled or disabled just as if you were
3275 to echo the option name into
3277 /sys/kernel/debug/tracing/trace_options
3279 For example, to enable stacktrace option (to dump the
3280 stack trace of each event), add to the command line:
3282 trace_options=stacktrace
3284 See also Documentation/trace/ftrace.txt "trace options"
3285 section.
3287 traceoff_on_warning
3288 [FTRACE] enable this option to disable tracing when a
3289 warning is hit. This turns off "tracing_on". Tracing can
3290 be enabled again by echoing '1' into the "tracing_on"
3291 file located in /sys/kernel/debug/tracing/
3293 This option is useful, as it disables the trace before
3294 the WARNING dump is called, which prevents the trace to
3295 be filled with content caused by the warning output.
3297 This option can also be set at run time via the sysctl
3298 option: kernel/traceoff_on_warning
3300 transparent_hugepage=
3301 [KNL]
3302 Format: [always|madvise|never]
3303 Can be used to control the default behavior of the system
3304 with respect to transparent hugepages.
3305 See Documentation/vm/transhuge.txt for more details.
3307 tsc= Disable clocksource stability checks for TSC.
3308 Format: <string>
3309 [x86] reliable: mark tsc clocksource as reliable, this
3310 disables clocksource verification at runtime, as well
3311 as the stability checks done at bootup. Used to enable
3312 high-resolution timer mode on older hardware, and in
3313 virtualized environment.
3314 [x86] noirqtime: Do not use TSC to do irq accounting.
3315 Used to run time disable IRQ_TIME_ACCOUNTING on any
3316 platforms where RDTSC is slow and this accounting
3317 can add overhead.
3319 turbografx.map[2|3]= [HW,JOY]
3320 TurboGraFX parallel port interface
3321 Format:
3322 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3323 See also Documentation/input/joystick-parport.txt
3325 udbg-immortal [PPC] When debugging early kernel crashes that
3326 happen after console_init() and before a proper
3327 console driver takes over, this boot options might
3328 help "seeing" what's going on.
3330 uhash_entries= [KNL,NET]
3331 Set number of hash buckets for UDP/UDP-Lite connections
3333 uhci-hcd.ignore_oc=
3334 [USB] Ignore overcurrent events (default N).
3335 Some badly-designed motherboards generate lots of
3336 bogus events, for ports that aren't wired to
3337 anything. Set this parameter to avoid log spamming.
3338 Note that genuine overcurrent events won't be
3339 reported either.
3341 unknown_nmi_panic
3342 [X86] Cause panic on unknown NMI.
3344 usbcore.authorized_default=
3345 [USB] Default USB device authorization:
3346 (default -1 = authorized except for wireless USB,
3347 0 = not authorized, 1 = authorized)
3349 usbcore.autosuspend=
3350 [USB] The autosuspend time delay (in seconds) used
3351 for newly-detected USB devices (default 2). This
3352 is the time required before an idle device will be
3353 autosuspended. Devices for which the delay is set
3354 to a negative value won't be autosuspended at all.
3356 usbcore.usbfs_snoop=
3357 [USB] Set to log all usbfs traffic (default 0 = off).
3359 usbcore.blinkenlights=
3360 [USB] Set to cycle leds on hubs (default 0 = off).
3362 usbcore.old_scheme_first=
3363 [USB] Start with the old device initialization
3364 scheme (default 0 = off).
3366 usbcore.usbfs_memory_mb=
3367 [USB] Memory limit (in MB) for buffers allocated by
3368 usbfs (default = 16, 0 = max = 2047).
3370 usbcore.use_both_schemes=
3371 [USB] Try the other device initialization scheme
3372 if the first one fails (default 1 = enabled).
3374 usbcore.initial_descriptor_timeout=
3375 [USB] Specifies timeout for the initial 64-byte
3376 USB_REQ_GET_DESCRIPTOR request in milliseconds
3377 (default 5000 = 5.0 seconds).
3379 usbhid.mousepoll=
3380 [USBHID] The interval which mice are to be polled at.
3382 usb-storage.delay_use=
3383 [UMS] The delay in seconds before a new device is
3384 scanned for Logical Units (default 5).
3386 usb-storage.quirks=
3387 [UMS] A list of quirks entries to supplement or
3388 override the built-in unusual_devs list. List
3389 entries are separated by commas. Each entry has
3390 the form VID:PID:Flags where VID and PID are Vendor
3391 and Product ID values (4-digit hex numbers) and
3392 Flags is a set of characters, each corresponding
3393 to a common usb-storage quirk flag as follows:
3394 a = SANE_SENSE (collect more than 18 bytes
3395 of sense data);
3396 b = BAD_SENSE (don't collect more than 18
3397 bytes of sense data);
3398 c = FIX_CAPACITY (decrease the reported
3399 device capacity by one sector);
3400 d = NO_READ_DISC_INFO (don't use
3401 READ_DISC_INFO command);
3402 e = NO_READ_CAPACITY_16 (don't use
3403 READ_CAPACITY_16 command);
3404 h = CAPACITY_HEURISTICS (decrease the
3405 reported device capacity by one
3406 sector if the number is odd);
3407 i = IGNORE_DEVICE (don't bind to this
3408 device);
3409 l = NOT_LOCKABLE (don't try to lock and
3410 unlock ejectable media);
3411 m = MAX_SECTORS_64 (don't transfer more
3412 than 64 sectors = 32 KB at a time);
3413 n = INITIAL_READ10 (force a retry of the
3414 initial READ(10) command);
3415 o = CAPACITY_OK (accept the capacity
3416 reported by the device);
3417 p = WRITE_CACHE (the device cache is ON
3418 by default);
3419 r = IGNORE_RESIDUE (the device reports
3420 bogus residue values);
3421 s = SINGLE_LUN (the device has only one
3422 Logical Unit);
3423 w = NO_WP_DETECT (don't test whether the
3424 medium is write-protected).
3425 Example: quirks=0419:aaf5:rl,0421:0433:rc
3427 user_debug= [KNL,ARM]
3428 Format: <int>
3429 See arch/arm/Kconfig.debug help text.
3430 1 - undefined instruction events
3431 2 - system calls
3432 4 - invalid data aborts
3433 8 - SIGSEGV faults
3434 16 - SIGBUS faults
3435 Example: user_debug=31
3437 userpte=
3438 [X86] Flags controlling user PTE allocations.
3440 nohigh = do not allocate PTE pages in
3441 HIGHMEM regardless of setting
3442 of CONFIG_HIGHPTE.
3444 vdso= [X86,SH]
3445 On X86_32, this is an alias for vdso32=. Otherwise:
3447 vdso=1: enable VDSO (the default)
3448 vdso=0: disable VDSO mapping
3450 vdso32= [X86] Control the 32-bit vDSO
3451 vdso32=1: enable 32-bit VDSO
3452 vdso32=0 or vdso32=2: disable 32-bit VDSO
3454 See the help text for CONFIG_COMPAT_VDSO for more
3455 details. If CONFIG_COMPAT_VDSO is set, the default is
3456 vdso32=0; otherwise, the default is vdso32=1.
3458 For compatibility with older kernels, vdso32=2 is an
3459 alias for vdso32=0.
3461 Try vdso32=0 if you encounter an error that says:
3462 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3464 vector= [IA-64,SMP]
3465 vector=percpu: enable percpu vector domain
3467 video= [FB] Frame buffer configuration
3468 See Documentation/fb/modedb.txt.
3470 video.brightness_switch_enabled= [0,1]
3471 If set to 1, on receiving an ACPI notify event
3472 generated by hotkey, video driver will adjust brightness
3473 level and then send out the event to user space through
3474 the allocated input device; If set to 0, video driver
3475 will only send out the event without touching backlight
3476 brightness level.
3477 default: 1
3479 virtio_mmio.device=
3480 [VMMIO] Memory mapped virtio (platform) device.
3482 <size>@<baseaddr>:<irq>[:<id>]
3483 where:
3484 <size> := size (can use standard suffixes
3485 like K, M and G)
3486 <baseaddr> := physical base address
3487 <irq> := interrupt number (as passed to
3488 request_irq())
3489 <id> := (optional) platform device id
3490 example:
3491 virtio_mmio.device=1K@0x100b0000:48:7
3493 Can be used multiple times for multiple devices.
3495 vga= [BOOT,X86-32] Select a particular video mode
3496 See Documentation/x86/boot.txt and
3497 Documentation/svga.txt.
3498 Use vga=ask for menu.
3499 This is actually a boot loader parameter; the value is
3500 passed to the kernel using a special protocol.
3502 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3503 size of <nn>. This can be used to increase the
3504 minimum size (128MB on x86). It can also be used to
3505 decrease the size and leave more room for directly
3506 mapped kernel RAM.
3508 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3509 Format: <command>
3511 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3512 Format: <command>
3514 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3515 Format: <command>
3517 vsyscall= [X86-64]
3518 Controls the behavior of vsyscalls (i.e. calls to
3519 fixed addresses of 0xffffffffff600x00 from legacy
3520 code). Most statically-linked binaries and older
3521 versions of glibc use these calls. Because these
3522 functions are at fixed addresses, they make nice
3523 targets for exploits that can control RIP.
3525 emulate [default] Vsyscalls turn into traps and are
3526 emulated reasonably safely.
3528 native Vsyscalls are native syscall instructions.
3529 This is a little bit faster than trapping
3530 and makes a few dynamic recompilers work
3531 better than they would in emulation mode.
3532 It also makes exploits much easier to write.
3534 none Vsyscalls don't work at all. This makes
3535 them quite hard to use for exploits but
3536 might break your system.
3538 vt.color= [VT] Default text color.
3539 Format: 0xYX, X = foreground, Y = background.
3540 Default: 0x07 = light gray on black.
3542 vt.cur_default= [VT] Default cursor shape.
3543 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3544 the parameters of the <Esc>[?A;B;Cc escape sequence;
3545 see VGA-softcursor.txt. Default: 2 = underline.
3547 vt.default_blu= [VT]
3548 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3549 Change the default blue palette of the console.
3550 This is a 16-member array composed of values
3551 ranging from 0-255.
3553 vt.default_grn= [VT]
3554 Format: <green0>,<green1>,<green2>,...,<green15>
3555 Change the default green palette of the console.
3556 This is a 16-member array composed of values
3557 ranging from 0-255.
3559 vt.default_red= [VT]
3560 Format: <red0>,<red1>,<red2>,...,<red15>
3561 Change the default red palette of the console.
3562 This is a 16-member array composed of values
3563 ranging from 0-255.
3565 vt.default_utf8=
3566 [VT]
3567 Format=<0|1>
3568 Set system-wide default UTF-8 mode for all tty's.
3569 Default is 1, i.e. UTF-8 mode is enabled for all
3570 newly opened terminals.
3572 vt.global_cursor_default=
3573 [VT]
3574 Format=<-1|0|1>
3575 Set system-wide default for whether a cursor
3576 is shown on new VTs. Default is -1,
3577 i.e. cursors will be created by default unless
3578 overridden by individual drivers. 0 will hide
3579 cursors, 1 will display them.
3581 vt.italic= [VT] Default color for italic text; 0-15.
3582 Default: 2 = green.
3584 vt.underline= [VT] Default color for underlined text; 0-15.
3585 Default: 3 = cyan.
3587 watchdog timers [HW,WDT] For information on watchdog timers,
3588 see Documentation/watchdog/watchdog-parameters.txt
3589 or other driver-specific files in the
3590 Documentation/watchdog/ directory.
3592 workqueue.disable_numa
3593 By default, all work items queued to unbound
3594 workqueues are affine to the NUMA nodes they're
3595 issued on, which results in better behavior in
3596 general. If NUMA affinity needs to be disabled for
3597 whatever reason, this option can be used. Note
3598 that this also can be controlled per-workqueue for
3599 workqueues visible under /sys/bus/workqueue/.
3601 workqueue.power_efficient
3602 Per-cpu workqueues are generally preferred because
3603 they show better performance thanks to cache
3604 locality; unfortunately, per-cpu workqueues tend to
3605 be more power hungry than unbound workqueues.
3607 Enabling this makes the per-cpu workqueues which
3608 were observed to contribute significantly to power
3609 consumption unbound, leading to measurably lower
3610 power usage at the cost of small performance
3611 overhead.
3613 The default value of this parameter is determined by
3614 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3616 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3617 default x2apic cluster mode on platforms
3618 supporting x2apic.
3620 x86_intel_mid_timer= [X86-32,APBT]
3621 Choose timer option for x86 Intel MID platform.
3622 Two valid options are apbt timer only and lapic timer
3623 plus one apbt timer for broadcast timer.
3624 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3626 xen_emul_unplug= [HW,X86,XEN]
3627 Unplug Xen emulated devices
3628 Format: [unplug0,][unplug1]
3629 ide-disks -- unplug primary master IDE devices
3630 aux-ide-disks -- unplug non-primary-master IDE devices
3631 nics -- unplug network devices
3632 all -- unplug all emulated devices (NICs and IDE disks)
3633 unnecessary -- unplugging emulated devices is
3634 unnecessary even if the host did not respond to
3635 the unplug protocol
3636 never -- do not unplug even if version check succeeds
3638 xen_nopvspin [X86,XEN]
3639 Disables the ticketlock slowpath using Xen PV
3640 optimizations.
3642 xirc2ps_cs= [NET,PCMCIA]
3643 Format:
3644 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3646 ______________________________________________________________________
3648 TODO:
3650 Add more DRM drivers.