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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_ssdt [HW,ACPI] Disable automatic loading of SSDT
234 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
235 Format: To spoof as Windows 98: ="Microsoft Windows"
237 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
238 acpi_osi="string1" # add string1
239 acpi_osi="!string2" # remove string2
240 acpi_osi=!* # remove all strings
241 acpi_osi=! # disable all built-in OS vendor
242 strings
243 acpi_osi= # disable all strings
245 'acpi_osi=!' can be used in combination with single or
246 multiple 'acpi_osi="string1"' to support specific OS
247 vendor string(s). Note that such command can only
248 affect the default state of the OS vendor strings, thus
249 it cannot affect the default state of the feature group
250 strings and the current state of the OS vendor strings,
251 specifying it multiple times through kernel command line
252 is meaningless. This command is useful when one do not
253 care about the state of the feature group strings which
254 should be controlled by the OSPM.
255 Examples:
256 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
257 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
258 can make '_OSI("Windows 2000")' TRUE.
260 'acpi_osi=' cannot be used in combination with other
261 'acpi_osi=' command lines, the _OSI method will not
262 exist in the ACPI namespace. NOTE that such command can
263 only affect the _OSI support state, thus specifying it
264 multiple times through kernel command line is also
265 meaningless.
266 Examples:
267 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
268 FALSE.
270 'acpi_osi=!*' can be used in combination with single or
271 multiple 'acpi_osi="string1"' to support specific
272 string(s). Note that such command can affect the
273 current state of both the OS vendor strings and the
274 feature group strings, thus specifying it multiple times
275 through kernel command line is meaningful. But it may
276 still not able to affect the final state of a string if
277 there are quirks related to this string. This command
278 is useful when one want to control the state of the
279 feature group strings to debug BIOS issues related to
280 the OSPM features.
281 Examples:
282 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
283 '_OSI("Module Device")' FALSE.
284 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
285 '_OSI("Module Device")' TRUE.
286 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
287 equivalent to
288 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
289 and
290 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
291 they all will make '_OSI("Windows 2000")' TRUE.
293 acpi_pm_good [X86]
294 Override the pmtimer bug detection: force the kernel
295 to assume that this machine's pmtimer latches its value
296 and always returns good values.
298 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
299 Format: { level | edge | high | low }
301 acpi_serialize [HW,ACPI] force serialization of AML methods
303 acpi_skip_timer_override [HW,ACPI]
304 Recognize and ignore IRQ0/pin2 Interrupt Override.
305 For broken nForce2 BIOS resulting in XT-PIC timer.
307 acpi_sleep= [HW,ACPI] Sleep options
308 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
309 old_ordering, nonvs, sci_force_enable }
310 See Documentation/power/video.txt for information on
311 s3_bios and s3_mode.
312 s3_beep is for debugging; it makes the PC's speaker beep
313 as soon as the kernel's real-mode entry point is called.
314 s4_nohwsig prevents ACPI hardware signature from being
315 used during resume from hibernation.
316 old_ordering causes the ACPI 1.0 ordering of the _PTS
317 control method, with respect to putting devices into
318 low power states, to be enforced (the ACPI 2.0 ordering
319 of _PTS is used by default).
320 nonvs prevents the kernel from saving/restoring the
321 ACPI NVS memory during suspend/hibernation and resume.
322 sci_force_enable causes the kernel to set SCI_EN directly
323 on resume from S1/S3 (which is against the ACPI spec,
324 but some broken systems don't work without it).
326 acpi_use_timer_override [HW,ACPI]
327 Use timer override. For some broken Nvidia NF5 boards
328 that require a timer override, but don't have HPET
330 acpi_enforce_resources= [ACPI]
331 { strict | lax | no }
332 Check for resource conflicts between native drivers
333 and ACPI OperationRegions (SystemIO and SystemMemory
334 only). IO ports and memory declared in ACPI might be
335 used by the ACPI subsystem in arbitrary AML code and
336 can interfere with legacy drivers.
337 strict (default): access to resources claimed by ACPI
338 is denied; legacy drivers trying to access reserved
339 resources will fail to bind to device using them.
340 lax: access to resources claimed by ACPI is allowed;
341 legacy drivers trying to access reserved resources
342 will bind successfully but a warning message is logged.
343 no: ACPI OperationRegions are not marked as reserved,
344 no further checks are performed.
346 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
347 kernels.
349 add_efi_memmap [EFI; X86] Include EFI memory map in
350 kernel's map of available physical RAM.
352 agp= [AGP]
353 { off | try_unsupported }
354 off: disable AGP support
355 try_unsupported: try to drive unsupported chipsets
356 (may crash computer or cause data corruption)
358 ALSA [HW,ALSA]
359 See Documentation/sound/alsa/alsa-parameters.txt
361 alignment= [KNL,ARM]
362 Allow the default userspace alignment fault handler
363 behaviour to be specified. Bit 0 enables warnings,
364 bit 1 enables fixups, and bit 2 sends a segfault.
366 align_va_addr= [X86-64]
367 Align virtual addresses by clearing slice [14:12] when
368 allocating a VMA at process creation time. This option
369 gives you up to 3% performance improvement on AMD F15h
370 machines (where it is enabled by default) for a
371 CPU-intensive style benchmark, and it can vary highly in
372 a microbenchmark depending on workload and compiler.
374 32: only for 32-bit processes
375 64: only for 64-bit processes
376 on: enable for both 32- and 64-bit processes
377 off: disable for both 32- and 64-bit processes
379 alloc_snapshot [FTRACE]
380 Allocate the ftrace snapshot buffer on boot up when the
381 main buffer is allocated. This is handy if debugging
382 and you need to use tracing_snapshot() on boot up, and
383 do not want to use tracing_snapshot_alloc() as it needs
384 to be done where GFP_KERNEL allocations are allowed.
386 amd_iommu= [HW,X86-64]
387 Pass parameters to the AMD IOMMU driver in the system.
388 Possible values are:
389 fullflush - enable flushing of IO/TLB entries when
390 they are unmapped. Otherwise they are
391 flushed before they will be reused, which
392 is a lot of faster
393 off - do not initialize any AMD IOMMU found in
394 the system
395 force_isolation - Force device isolation for all
396 devices. The IOMMU driver is not
397 allowed anymore to lift isolation
398 requirements as needed. This option
399 does not override iommu=pt
401 amd_iommu_dump= [HW,X86-64]
402 Enable AMD IOMMU driver option to dump the ACPI table
403 for AMD IOMMU. With this option enabled, AMD IOMMU
404 driver will print ACPI tables for AMD IOMMU during
405 IOMMU initialization.
407 amijoy.map= [HW,JOY] Amiga joystick support
408 Map of devices attached to JOY0DAT and JOY1DAT
409 Format: <a>,<b>
410 See also Documentation/input/joystick.txt
412 analog.map= [HW,JOY] Analog joystick and gamepad support
413 Specifies type or capabilities of an analog joystick
414 connected to one of 16 gameports
415 Format: <type1>,<type2>,..<type16>
417 apc= [HW,SPARC]
418 Power management functions (SPARCstation-4/5 + deriv.)
419 Format: noidle
420 Disable APC CPU standby support. SPARCstation-Fox does
421 not play well with APC CPU idle - disable it if you have
422 APC and your system crashes randomly.
424 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
425 Change the output verbosity whilst booting
426 Format: { quiet (default) | verbose | debug }
427 Change the amount of debugging information output
428 when initialising the APIC and IO-APIC components.
430 autoconf= [IPV6]
431 See Documentation/networking/ipv6.txt.
433 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
434 Limit apic dumping. The parameter defines the maximal
435 number of local apics being dumped. Also it is possible
436 to set it to "all" by meaning -- no limit here.
437 Format: { 1 (default) | 2 | ... | all }.
438 The parameter valid if only apic=debug or
439 apic=verbose is specified.
440 Example: apic=debug show_lapic=all
442 apm= [APM] Advanced Power Management
443 See header of arch/x86/kernel/apm_32.c.
445 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
446 Format: <io>,<irq>,<nodeID>
448 ataflop= [HW,M68k]
450 atarimouse= [HW,MOUSE] Atari Mouse
452 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
453 EzKey and similar keyboards
455 atkbd.reset= [HW] Reset keyboard during initialization
457 atkbd.set= [HW] Select keyboard code set
458 Format: <int> (2 = AT (default), 3 = PS/2)
460 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
461 keyboards
463 atkbd.softraw= [HW] Choose between synthetic and real raw mode
464 Format: <bool> (0 = real, 1 = synthetic (default))
466 atkbd.softrepeat= [HW]
467 Use software keyboard repeat
469 audit= [KNL] Enable the audit sub-system
470 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
471 0 - kernel audit is disabled and can not be enabled
472 until the next reboot
473 unset - kernel audit is initialized but disabled and
474 will be fully enabled by the userspace auditd.
475 1 - kernel audit is initialized and partially enabled,
476 storing at most audit_backlog_limit messages in
477 RAM until it is fully enabled by the userspace
478 auditd.
479 Default: unset
481 audit_backlog_limit= [KNL] Set the audit queue size limit.
482 Format: <int> (must be >=0)
483 Default: 64
485 baycom_epp= [HW,AX25]
486 Format: <io>,<mode>
488 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
489 Format: <io>,<mode>
490 See header of drivers/net/hamradio/baycom_par.c.
492 baycom_ser_fdx= [HW,AX25]
493 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
494 Format: <io>,<irq>,<mode>[,<baud>]
495 See header of drivers/net/hamradio/baycom_ser_fdx.c.
497 baycom_ser_hdx= [HW,AX25]
498 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
499 Format: <io>,<irq>,<mode>
500 See header of drivers/net/hamradio/baycom_ser_hdx.c.
502 blkdevparts= Manual partition parsing of block device(s) for
503 embedded devices based on command line input.
504 See Documentation/block/cmdline-partition.txt
506 boot_delay= Milliseconds to delay each printk during boot.
507 Values larger than 10 seconds (10000) are changed to
508 no delay (0).
509 Format: integer
511 bootmem_debug [KNL] Enable bootmem allocator debug messages.
513 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
514 bttv.radio= Most important insmod options are available as
515 kernel args too.
516 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
517 bttv.tuner=
519 bulk_remove=off [PPC] This parameter disables the use of the pSeries
520 firmware feature for flushing multiple hpte entries
521 at a time.
523 c101= [NET] Moxa C101 synchronous serial card
525 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
526 Sometimes CPU hardware bugs make them report the cache
527 size incorrectly. The kernel will attempt work arounds
528 to fix known problems, but for some CPUs it is not
529 possible to determine what the correct size should be.
530 This option provides an override for these situations.
532 ccw_timeout_log [S390]
533 See Documentation/s390/CommonIO for details.
535 cgroup_disable= [KNL] Disable a particular controller
536 Format: {name of the controller(s) to disable}
537 The effects of cgroup_disable=foo are:
538 - foo isn't auto-mounted if you mount all cgroups in
539 a single hierarchy
540 - foo isn't visible as an individually mountable
541 subsystem
542 {Currently only "memory" controller deal with this and
543 cut the overhead, others just disable the usage. So
544 only cgroup_disable=memory is actually worthy}
546 checkreqprot [SELINUX] Set initial checkreqprot flag value.
547 Format: { "0" | "1" }
548 See security/selinux/Kconfig help text.
549 0 -- check protection applied by kernel (includes
550 any implied execute protection).
551 1 -- check protection requested by application.
552 Default value is set via a kernel config option.
553 Value can be changed at runtime via
554 /selinux/checkreqprot.
556 cio_ignore= [S390]
557 See Documentation/s390/CommonIO for details.
558 clk_ignore_unused
559 [CLK]
560 Keep all clocks already enabled by bootloader on,
561 even if no driver has claimed them. This is useful
562 for debug and development, but should not be
563 needed on a platform with proper driver support.
564 For more information, see Documentation/clk.txt.
566 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
567 [Deprecated]
568 Forces specified clocksource (if available) to be used
569 when calculating gettimeofday(). If specified
570 clocksource is not available, it defaults to PIT.
571 Format: { pit | tsc | cyclone | pmtmr }
573 clocksource= Override the default clocksource
574 Format: <string>
575 Override the default clocksource and use the clocksource
576 with the name specified.
577 Some clocksource names to choose from, depending on
578 the platform:
579 [all] jiffies (this is the base, fallback clocksource)
580 [ACPI] acpi_pm
581 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
582 pxa_timer,timer3,32k_counter,timer0_1
583 [AVR32] avr32
584 [X86-32] pit,hpet,tsc;
585 scx200_hrt on Geode; cyclone on IBM x440
586 [MIPS] MIPS
587 [PARISC] cr16
588 [S390] tod
589 [SH] SuperH
590 [SPARC64] tick
591 [X86-64] hpet,tsc
593 clearcpuid=BITNUM [X86]
594 Disable CPUID feature X for the kernel. See
595 arch/x86/include/asm/cpufeature.h for the valid bit
596 numbers. Note the Linux specific bits are not necessarily
597 stable over kernel options, but the vendor specific
598 ones should be.
599 Also note that user programs calling CPUID directly
600 or using the feature without checking anything
601 will still see it. This just prevents it from
602 being used by the kernel or shown in /proc/cpuinfo.
603 Also note the kernel might malfunction if you disable
604 some critical bits.
606 cma=nn[MG] [ARM,KNL]
607 Sets the size of kernel global memory area for contiguous
608 memory allocations. For more information, see
609 include/linux/dma-contiguous.h
611 cmo_free_hint= [PPC] Format: { yes | no }
612 Specify whether pages are marked as being inactive
613 when they are freed. This is used in CMO environments
614 to determine OS memory pressure for page stealing by
615 a hypervisor.
616 Default: yes
618 coherent_pool=nn[KMG] [ARM,KNL]
619 Sets the size of memory pool for coherent, atomic dma
620 allocations, by default set to 256K.
622 code_bytes [X86] How many bytes of object code to print
623 in an oops report.
624 Range: 0 - 8192
625 Default: 64
627 com20020= [HW,NET] ARCnet - COM20020 chipset
628 Format:
629 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
631 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
632 Format: <io>[,<irq>]
634 com90xx= [HW,NET]
635 ARCnet - COM90xx chipset (memory-mapped buffers)
636 Format: <io>[,<irq>[,<memstart>]]
638 condev= [HW,S390] console device
639 conmode=
641 console= [KNL] Output console device and options.
643 tty<n> Use the virtual console device <n>.
645 ttyS<n>[,options]
646 ttyUSB0[,options]
647 Use the specified serial port. The options are of
648 the form "bbbbpnf", where "bbbb" is the baud rate,
649 "p" is parity ("n", "o", or "e"), "n" is number of
650 bits, and "f" is flow control ("r" for RTS or
651 omit it). Default is "9600n8".
653 See Documentation/serial-console.txt for more
654 information. See
655 Documentation/networking/netconsole.txt for an
656 alternative.
658 uart[8250],io,<addr>[,options]
659 uart[8250],mmio,<addr>[,options]
660 Start an early, polled-mode console on the 8250/16550
661 UART at the specified I/O port or MMIO address,
662 switching to the matching ttyS device later. The
663 options are the same as for ttyS, above.
664 hvc<n> Use the hypervisor console device <n>. This is for
665 both Xen and PowerPC hypervisors.
667 If the device connected to the port is not a TTY but a braille
668 device, prepend "brl," before the device type, for instance
669 console=brl,ttyS0
670 For now, only VisioBraille is supported.
672 consoleblank= [KNL] The console blank (screen saver) timeout in
673 seconds. Defaults to 10*60 = 10mins. A value of 0
674 disables the blank timer.
676 coredump_filter=
677 [KNL] Change the default value for
678 /proc/<pid>/coredump_filter.
679 See also Documentation/filesystems/proc.txt.
681 cpuidle.off=1 [CPU_IDLE]
682 disable the cpuidle sub-system
684 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
685 Format:
686 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
688 crashkernel=size[KMG][@offset[KMG]]
689 [KNL] Using kexec, Linux can switch to a 'crash kernel'
690 upon panic. This parameter reserves the physical
691 memory region [offset, offset + size] for that kernel
692 image. If '@offset' is omitted, then a suitable offset
693 is selected automatically. Check
694 Documentation/kdump/kdump.txt for further details.
696 crashkernel=range1:size1[,range2:size2,...][@offset]
697 [KNL] Same as above, but depends on the memory
698 in the running system. The syntax of range is
699 start-[end] where start and end are both
700 a memory unit (amount[KMG]). See also
701 Documentation/kdump/kdump.txt for an example.
703 crashkernel=size[KMG],high
704 [KNL, x86_64] range could be above 4G. Allow kernel
705 to allocate physical memory region from top, so could
706 be above 4G if system have more than 4G ram installed.
707 Otherwise memory region will be allocated below 4G, if
708 available.
709 It will be ignored if crashkernel=X is specified.
710 crashkernel=size[KMG],low
711 [KNL, x86_64] range under 4G. When crashkernel=X,high
712 is passed, kernel could allocate physical memory region
713 above 4G, that cause second kernel crash on system
714 that require some amount of low memory, e.g. swiotlb
715 requires at least 64M+32K low memory. Kernel would
716 try to allocate 72M below 4G automatically.
717 This one let user to specify own low range under 4G
718 for second kernel instead.
719 0: to disable low allocation.
720 It will be ignored when crashkernel=X,high is not used
721 or memory reserved is below 4G.
723 cs89x0_dma= [HW,NET]
724 Format: <dma>
726 cs89x0_media= [HW,NET]
727 Format: { rj45 | aui | bnc }
729 dasd= [HW,NET]
730 See header of drivers/s390/block/dasd_devmap.c.
732 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
733 (one device per port)
734 Format: <port#>,<type>
735 See also Documentation/input/joystick-parport.txt
737 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
738 time. See Documentation/dynamic-debug-howto.txt for
739 details. Deprecated, see dyndbg.
741 debug [KNL] Enable kernel debugging (events log level).
743 debug_locks_verbose=
744 [KNL] verbose self-tests
745 Format=<0|1>
746 Print debugging info while doing the locking API
747 self-tests.
748 We default to 0 (no extra messages), setting it to
749 1 will print _a lot_ more information - normally
750 only useful to kernel developers.
752 debug_objects [KNL] Enable object debugging
754 no_debug_objects
755 [KNL] Disable object debugging
757 debug_guardpage_minorder=
758 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
759 parameter allows control of the order of pages that will
760 be intentionally kept free (and hence protected) by the
761 buddy allocator. Bigger value increase the probability
762 of catching random memory corruption, but reduce the
763 amount of memory for normal system use. The maximum
764 possible value is MAX_ORDER/2. Setting this parameter
765 to 1 or 2 should be enough to identify most random
766 memory corruption problems caused by bugs in kernel or
767 driver code when a CPU writes to (or reads from) a
768 random memory location. Note that there exists a class
769 of memory corruptions problems caused by buggy H/W or
770 F/W or by drivers badly programing DMA (basically when
771 memory is written at bus level and the CPU MMU is
772 bypassed) which are not detectable by
773 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
774 tracking down these problems.
776 debugpat [X86] Enable PAT debugging
778 decnet.addr= [HW,NET]
779 Format: <area>[,<node>]
780 See also Documentation/networking/decnet.txt.
782 default_hugepagesz=
783 [same as hugepagesz=] The size of the default
784 HugeTLB page size. This is the size represented by
785 the legacy /proc/ hugepages APIs, used for SHM, and
786 default size when mounting hugetlbfs filesystems.
787 Defaults to the default architecture's huge page size
788 if not specified.
790 dhash_entries= [KNL]
791 Set number of hash buckets for dentry cache.
793 digi= [HW,SERIAL]
794 IO parameters + enable/disable command.
796 digiepca= [HW,SERIAL]
797 See drivers/char/README.epca and
798 Documentation/serial/digiepca.txt.
800 disable= [IPV6]
801 See Documentation/networking/ipv6.txt.
803 disable_cpu_apicid= [X86,APIC,SMP]
804 Format: <int>
805 The number of initial APIC ID for the
806 corresponding CPU to be disabled at boot,
807 mostly used for the kdump 2nd kernel to
808 disable BSP to wake up multiple CPUs without
809 causing system reset or hang due to sending
810 INIT from AP to BSP.
812 disable_ddw [PPC/PSERIES]
813 Disable Dynamic DMA Window support. Use this if
814 to workaround buggy firmware.
816 disable_ipv6= [IPV6]
817 See Documentation/networking/ipv6.txt.
819 disable_mtrr_cleanup [X86]
820 The kernel tries to adjust MTRR layout from continuous
821 to discrete, to make X server driver able to add WB
822 entry later. This parameter disables that.
824 disable_mtrr_trim [X86, Intel and AMD only]
825 By default the kernel will trim any uncacheable
826 memory out of your available memory pool based on
827 MTRR settings. This parameter disables that behavior,
828 possibly causing your machine to run very slowly.
830 disable_timer_pin_1 [X86]
831 Disable PIN 1 of APIC timer
832 Can be useful to work around chipset bugs.
834 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
835 this option disables the debugging code at boot.
837 dma_debug_entries=<number>
838 This option allows to tune the number of preallocated
839 entries for DMA-API debugging code. One entry is
840 required per DMA-API allocation. Use this if the
841 DMA-API debugging code disables itself because the
842 architectural default is too low.
844 dma_debug_driver=<driver_name>
845 With this option the DMA-API debugging driver
846 filter feature can be enabled at boot time. Just
847 pass the driver to filter for as the parameter.
848 The filter can be disabled or changed to another
849 driver later using sysfs.
851 drm_kms_helper.edid_firmware=[<connector>:]<file>
852 Broken monitors, graphic adapters and KVMs may
853 send no or incorrect EDID data sets. This parameter
854 allows to specify an EDID data set in the
855 /lib/firmware directory that is used instead.
856 Generic built-in EDID data sets are used, if one of
857 edid/1024x768.bin, edid/1280x1024.bin,
858 edid/1680x1050.bin, or edid/1920x1080.bin is given
859 and no file with the same name exists. Details and
860 instructions how to build your own EDID data are
861 available in Documentation/EDID/HOWTO.txt. An EDID
862 data set will only be used for a particular connector,
863 if its name and a colon are prepended to the EDID
864 name.
866 dscc4.setup= [NET]
868 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
869 module.dyndbg[="val"]
870 Enable debug messages at boot time. See
871 Documentation/dynamic-debug-howto.txt for details.
873 earlycon= [KNL] Output early console device and options.
874 uart[8250],io,<addr>[,options]
875 uart[8250],mmio,<addr>[,options]
876 uart[8250],mmio32,<addr>[,options]
877 Start an early, polled-mode console on the 8250/16550
878 UART at the specified I/O port or MMIO address.
879 MMIO inter-register address stride is either 8-bit
880 (mmio) or 32-bit (mmio32).
881 The options are the same as for ttyS, above.
883 earlyprintk= [X86,SH,BLACKFIN,ARM]
884 earlyprintk=vga
885 earlyprintk=efi
886 earlyprintk=xen
887 earlyprintk=serial[,ttySn[,baudrate]]
888 earlyprintk=serial[,0x...[,baudrate]]
889 earlyprintk=ttySn[,baudrate]
890 earlyprintk=dbgp[debugController#]
892 earlyprintk is useful when the kernel crashes before
893 the normal console is initialized. It is not enabled by
894 default because it has some cosmetic problems.
896 Append ",keep" to not disable it when the real console
897 takes over.
899 Only one of vga, efi, serial, or usb debug port can
900 be used at a time.
902 Currently only ttyS0 and ttyS1 may be specified by
903 name. Other I/O ports may be explicitly specified
904 on some architectures (x86 and arm at least) by
905 replacing ttySn with an I/O port address, like this:
906 earlyprintk=serial,0x1008,115200
907 You can find the port for a given device in
908 /proc/tty/driver/serial:
909 2: uart:ST16650V2 port:00001008 irq:18 ...
911 Interaction with the standard serial driver is not
912 very good.
914 The VGA and EFI output is eventually overwritten by
915 the real console.
917 The xen output can only be used by Xen PV guests.
919 edac_report= [HW,EDAC] Control how to report EDAC event
920 Format: {"on" | "off" | "force"}
921 on: enable EDAC to report H/W event. May be overridden
922 by other higher priority error reporting module.
923 off: disable H/W event reporting through EDAC.
924 force: enforce the use of EDAC to report H/W event.
925 default: on.
927 ekgdboc= [X86,KGDB] Allow early kernel console debugging
928 ekgdboc=kbd
930 This is designed to be used in conjunction with
931 the boot argument: earlyprintk=vga
933 edd= [EDD]
934 Format: {"off" | "on" | "skip[mbr]"}
936 efi= [EFI]
937 Format: { "old_map" }
938 old_map [X86-64]: switch to the old ioremap-based EFI
939 runtime services mapping. 32-bit still uses this one by
940 default.
942 efi_no_storage_paranoia [EFI; X86]
943 Using this parameter you can use more than 50% of
944 your efi variable storage. Use this parameter only if
945 you are really sure that your UEFI does sane gc and
946 fulfills the spec otherwise your board may brick.
948 eisa_irq_edge= [PARISC,HW]
949 See header of drivers/parisc/eisa.c.
951 elanfreq= [X86-32]
952 See comment before function elanfreq_setup() in
953 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
955 elevator= [IOSCHED]
956 Format: {"cfq" | "deadline" | "noop"}
957 See Documentation/block/cfq-iosched.txt and
958 Documentation/block/deadline-iosched.txt for details.
960 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
961 Specifies physical address of start of kernel core
962 image elf header and optionally the size. Generally
963 kexec loader will pass this option to capture kernel.
964 See Documentation/kdump/kdump.txt for details.
966 enable_mtrr_cleanup [X86]
967 The kernel tries to adjust MTRR layout from continuous
968 to discrete, to make X server driver able to add WB
969 entry later. This parameter enables that.
971 enable_timer_pin_1 [X86]
972 Enable PIN 1 of APIC timer
973 Can be useful to work around chipset bugs
974 (in particular on some ATI chipsets).
975 The kernel tries to set a reasonable default.
977 enforcing [SELINUX] Set initial enforcing status.
978 Format: {"0" | "1"}
979 See security/selinux/Kconfig help text.
980 0 -- permissive (log only, no denials).
981 1 -- enforcing (deny and log).
982 Default value is 0.
983 Value can be changed at runtime via /selinux/enforce.
985 erst_disable [ACPI]
986 Disable Error Record Serialization Table (ERST)
987 support.
989 ether= [HW,NET] Ethernet cards parameters
990 This option is obsoleted by the "netdev=" option, which
991 has equivalent usage. See its documentation for details.
993 evm= [EVM]
994 Format: { "fix" }
995 Permit 'security.evm' to be updated regardless of
996 current integrity status.
998 failslab=
999 fail_page_alloc=
1000 fail_make_request=[KNL]
1001 General fault injection mechanism.
1002 Format: <interval>,<probability>,<space>,<times>
1003 See also Documentation/fault-injection/.
1005 floppy= [HW]
1006 See Documentation/blockdev/floppy.txt.
1008 force_pal_cache_flush
1009 [IA-64] Avoid check_sal_cache_flush which may hang on
1010 buggy SAL_CACHE_FLUSH implementations. Using this
1011 parameter will force ia64_sal_cache_flush to call
1012 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1014 ftrace=[tracer]
1015 [FTRACE] will set and start the specified tracer
1016 as early as possible in order to facilitate early
1017 boot debugging.
1019 ftrace_dump_on_oops[=orig_cpu]
1020 [FTRACE] will dump the trace buffers on oops.
1021 If no parameter is passed, ftrace will dump
1022 buffers of all CPUs, but if you pass orig_cpu, it will
1023 dump only the buffer of the CPU that triggered the
1024 oops.
1026 ftrace_filter=[function-list]
1027 [FTRACE] Limit the functions traced by the function
1028 tracer at boot up. function-list is a comma separated
1029 list of functions. This list can be changed at run
1030 time by the set_ftrace_filter file in the debugfs
1031 tracing directory.
1033 ftrace_notrace=[function-list]
1034 [FTRACE] Do not trace the functions specified in
1035 function-list. This list can be changed at run time
1036 by the set_ftrace_notrace file in the debugfs
1037 tracing directory.
1039 ftrace_graph_filter=[function-list]
1040 [FTRACE] Limit the top level callers functions traced
1041 by the function graph tracer at boot up.
1042 function-list is a comma separated list of functions
1043 that can be changed at run time by the
1044 set_graph_function file in the debugfs tracing directory.
1046 gamecon.map[2|3]=
1047 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1048 support via parallel port (up to 5 devices per port)
1049 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1050 See also Documentation/input/joystick-parport.txt
1052 gamma= [HW,DRM]
1054 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1055 Format: off | on
1056 default: on
1058 gcov_persist= [GCOV] When non-zero (default), profiling data for
1059 kernel modules is saved and remains accessible via
1060 debugfs, even when the module is unloaded/reloaded.
1061 When zero, profiling data is discarded and associated
1062 debugfs files are removed at module unload time.
1064 gpt [EFI] Forces disk with valid GPT signature but
1065 invalid Protective MBR to be treated as GPT. If the
1066 primary GPT is corrupted, it enables the backup/alternate
1067 GPT to be used instead.
1069 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1070 the "Enable 0" bit of the configuration register.
1071 Format: 0 | 1
1072 Default: 0
1073 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1074 the "Enable 0" bit of the configuration register.
1075 Format: 0 | 1
1076 Default: 0
1077 grcan.select= [HW] Select which physical interface to use.
1078 Format: 0 | 1
1079 Default: 0
1080 grcan.txsize= [HW] Sets the size of the tx buffer.
1081 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1082 Default: 1024
1083 grcan.rxsize= [HW] Sets the size of the rx buffer.
1084 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1085 Default: 1024
1087 hashdist= [KNL,NUMA] Large hashes allocated during boot
1088 are distributed across NUMA nodes. Defaults on
1089 for 64-bit NUMA, off otherwise.
1090 Format: 0 | 1 (for off | on)
1092 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1094 hd= [EIDE] (E)IDE hard drive subsystem geometry
1095 Format: <cyl>,<head>,<sect>
1097 hest_disable [ACPI]
1098 Disable Hardware Error Source Table (HEST) support;
1099 corresponding firmware-first mode error processing
1100 logic will be disabled.
1102 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1103 size of <nn>. This works even on boxes that have no
1104 highmem otherwise. This also works to reduce highmem
1105 size on bigger boxes.
1107 highres= [KNL] Enable/disable high resolution timer mode.
1108 Valid parameters: "on", "off"
1109 Default: "on"
1111 hisax= [HW,ISDN]
1112 See Documentation/isdn/README.HiSax.
1114 hlt [BUGS=ARM,SH]
1116 hpet= [X86-32,HPET] option to control HPET usage
1117 Format: { enable (default) | disable | force |
1118 verbose }
1119 disable: disable HPET and use PIT instead
1120 force: allow force enabled of undocumented chips (ICH4,
1121 VIA, nVidia)
1122 verbose: show contents of HPET registers during setup
1124 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1125 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1127 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1128 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1129 On x86-64 and powerpc, this option can be specified
1130 multiple times interleaved with hugepages= to reserve
1131 huge pages of different sizes. Valid pages sizes on
1132 x86-64 are 2M (when the CPU supports "pse") and 1G
1133 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1134 Note that 1GB pages can only be allocated at boot time
1135 using hugepages= and not freed afterwards.
1137 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1138 terminal devices. Valid values: 0..8
1139 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1140 If specified, z/VM IUCV HVC accepts connections
1141 from listed z/VM user IDs only.
1143 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1144 hardware thread id mappings.
1145 Format: <cpu>:<hwthread>
1147 keep_bootcon [KNL]
1148 Do not unregister boot console at start. This is only
1149 useful for debugging when something happens in the window
1150 between unregistering the boot console and initializing
1151 the real console.
1153 i2c_bus= [HW] Override the default board specific I2C bus speed
1154 or register an additional I2C bus that is not
1155 registered from board initialization code.
1156 Format:
1157 <bus_id>,<clkrate>
1159 i8042.debug [HW] Toggle i8042 debug mode
1160 i8042.direct [HW] Put keyboard port into non-translated mode
1161 i8042.dumbkbd [HW] Pretend that controller can only read data from
1162 keyboard and cannot control its state
1163 (Don't attempt to blink the leds)
1164 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1165 i8042.nokbd [HW] Don't check/create keyboard port
1166 i8042.noloop [HW] Disable the AUX Loopback command while probing
1167 for the AUX port
1168 i8042.nomux [HW] Don't check presence of an active multiplexing
1169 controller
1170 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1171 controllers
1172 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1173 i8042.reset [HW] Reset the controller during init and cleanup
1174 i8042.unlock [HW] Unlock (ignore) the keylock
1176 i810= [HW,DRM]
1178 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1179 indicates that the driver is running on unsupported
1180 hardware.
1181 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1182 does not match list of supported models.
1183 i8k.power_status
1184 [HW] Report power status in /proc/i8k
1185 (disabled by default)
1186 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1187 capability is set.
1189 i915.invert_brightness=
1190 [DRM] Invert the sense of the variable that is used to
1191 set the brightness of the panel backlight. Normally a
1192 brightness value of 0 indicates backlight switched off,
1193 and the maximum of the brightness value sets the backlight
1194 to maximum brightness. If this parameter is set to 0
1195 (default) and the machine requires it, or this parameter
1196 is set to 1, a brightness value of 0 sets the backlight
1197 to maximum brightness, and the maximum of the brightness
1198 value switches the backlight off.
1199 -1 -- never invert brightness
1200 0 -- machine default
1201 1 -- force brightness inversion
1203 icn= [HW,ISDN]
1204 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1206 ide-core.nodma= [HW] (E)IDE subsystem
1207 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1208 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1209 .cdrom .chs .ignore_cable are additional options
1210 See Documentation/ide/ide.txt.
1212 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1213 Claim all unknown PCI IDE storage controllers.
1215 idle= [X86]
1216 Format: idle=poll, idle=halt, idle=nomwait
1217 Poll forces a polling idle loop that can slightly
1218 improve the performance of waking up a idle CPU, but
1219 will use a lot of power and make the system run hot.
1220 Not recommended.
1221 idle=halt: Halt is forced to be used for CPU idle.
1222 In such case C2/C3 won't be used again.
1223 idle=nomwait: Disable mwait for CPU C-states
1225 ignore_loglevel [KNL]
1226 Ignore loglevel setting - this will print /all/
1227 kernel messages to the console. Useful for debugging.
1228 We also add it as printk module parameter, so users
1229 could change it dynamically, usually by
1230 /sys/module/printk/parameters/ignore_loglevel.
1232 ihash_entries= [KNL]
1233 Set number of hash buckets for inode cache.
1235 ima_appraise= [IMA] appraise integrity measurements
1236 Format: { "off" | "enforce" | "fix" }
1237 default: "enforce"
1239 ima_appraise_tcb [IMA]
1240 The builtin appraise policy appraises all files
1241 owned by uid=0.
1243 ima_hash= [IMA]
1244 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1245 | sha512 | ... }
1246 default: "sha1"
1248 The list of supported hash algorithms is defined
1249 in crypto/hash_info.h.
1251 ima_tcb [IMA]
1252 Load a policy which meets the needs of the Trusted
1253 Computing Base. This means IMA will measure all
1254 programs exec'd, files mmap'd for exec, and all files
1255 opened for read by uid=0.
1257 ima_template= [IMA]
1258 Select one of defined IMA measurements template formats.
1259 Formats: { "ima" | "ima-ng" }
1260 Default: "ima-ng"
1262 init= [KNL]
1263 Format: <full_path>
1264 Run specified binary instead of /sbin/init as init
1265 process.
1267 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1268 for working out where the kernel is dying during
1269 startup.
1271 initrd= [BOOT] Specify the location of the initial ramdisk
1273 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1274 Format: <irq>
1276 int_pln_enable [x86] Enable power limit notification interrupt
1278 integrity_audit=[IMA]
1279 Format: { "0" | "1" }
1280 0 -- basic integrity auditing messages. (Default)
1281 1 -- additional integrity auditing messages.
1283 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1284 on
1285 Enable intel iommu driver.
1286 off
1287 Disable intel iommu driver.
1288 igfx_off [Default Off]
1289 By default, gfx is mapped as normal device. If a gfx
1290 device has a dedicated DMAR unit, the DMAR unit is
1291 bypassed by not enabling DMAR with this option. In
1292 this case, gfx device will use physical address for
1293 DMA.
1294 forcedac [x86_64]
1295 With this option iommu will not optimize to look
1296 for io virtual address below 32-bit forcing dual
1297 address cycle on pci bus for cards supporting greater
1298 than 32-bit addressing. The default is to look
1299 for translation below 32-bit and if not available
1300 then look in the higher range.
1301 strict [Default Off]
1302 With this option on every unmap_single operation will
1303 result in a hardware IOTLB flush operation as opposed
1304 to batching them for performance.
1305 sp_off [Default Off]
1306 By default, super page will be supported if Intel IOMMU
1307 has the capability. With this option, super page will
1308 not be supported.
1310 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1311 0 disables intel_idle and fall back on acpi_idle.
1312 1 to 6 specify maximum depth of C-state.
1314 intel_pstate= [X86]
1315 disable
1316 Do not enable intel_pstate as the default
1317 scaling driver for the supported processors
1319 intremap= [X86-64, Intel-IOMMU]
1320 on enable Interrupt Remapping (default)
1321 off disable Interrupt Remapping
1322 nosid disable Source ID checking
1323 no_x2apic_optout
1324 BIOS x2APIC opt-out request will be ignored
1326 iomem= Disable strict checking of access to MMIO memory
1327 strict regions from userspace.
1328 relaxed
1330 iommu= [x86]
1331 off
1332 force
1333 noforce
1334 biomerge
1335 panic
1336 nopanic
1337 merge
1338 nomerge
1339 forcesac
1340 soft
1341 pt [x86, IA-64]
1344 io7= [HW] IO7 for Marvel based alpha systems
1345 See comment before marvel_specify_io7 in
1346 arch/alpha/kernel/core_marvel.c.
1348 io_delay= [X86] I/O delay method
1349 0x80
1350 Standard port 0x80 based delay
1351 0xed
1352 Alternate port 0xed based delay (needed on some systems)
1353 udelay
1354 Simple two microseconds delay
1355 none
1356 No delay
1358 ip= [IP_PNP]
1359 See Documentation/filesystems/nfs/nfsroot.txt.
1361 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1362 See comment before ip2_setup() in
1363 drivers/char/ip2/ip2base.c.
1365 irqfixup [HW]
1366 When an interrupt is not handled search all handlers
1367 for it. Intended to get systems with badly broken
1368 firmware running.
1370 irqpoll [HW]
1371 When an interrupt is not handled search all handlers
1372 for it. Also check all handlers each timer
1373 interrupt. Intended to get systems with badly broken
1374 firmware running.
1376 isapnp= [ISAPNP]
1377 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1379 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1380 Format:
1381 <cpu number>,...,<cpu number>
1382 or
1383 <cpu number>-<cpu number>
1384 (must be a positive range in ascending order)
1385 or a mixture
1386 <cpu number>,...,<cpu number>-<cpu number>
1388 This option can be used to specify one or more CPUs
1389 to isolate from the general SMP balancing and scheduling
1390 algorithms. You can move a process onto or off an
1391 "isolated" CPU via the CPU affinity syscalls or cpuset.
1392 <cpu number> begins at 0 and the maximum value is
1393 "number of CPUs in system - 1".
1395 This option is the preferred way to isolate CPUs. The
1396 alternative -- manually setting the CPU mask of all
1397 tasks in the system -- can cause problems and
1398 suboptimal load balancer performance.
1400 iucv= [HW,NET]
1402 ivrs_ioapic [HW,X86_64]
1403 Provide an override to the IOAPIC-ID<->DEVICE-ID
1404 mapping provided in the IVRS ACPI table. For
1405 example, to map IOAPIC-ID decimal 10 to
1406 PCI device 00:14.0 write the parameter as:
1407 ivrs_ioapic[10]=00:14.0
1409 ivrs_hpet [HW,X86_64]
1410 Provide an override to the HPET-ID<->DEVICE-ID
1411 mapping provided in the IVRS ACPI table. For
1412 example, to map HPET-ID decimal 0 to
1413 PCI device 00:14.0 write the parameter as:
1414 ivrs_hpet[0]=00:14.0
1416 js= [HW,JOY] Analog joystick
1417 See Documentation/input/joystick.txt.
1419 keepinitrd [HW,ARM]
1421 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1422 specifies the amount of memory usable by the kernel
1423 for non-movable allocations. The requested amount is
1424 spread evenly throughout all nodes in the system. The
1425 remaining memory in each node is used for Movable
1426 pages. In the event, a node is too small to have both
1427 kernelcore and Movable pages, kernelcore pages will
1428 take priority and other nodes will have a larger number
1429 of Movable pages. The Movable zone is used for the
1430 allocation of pages that may be reclaimed or moved
1431 by the page migration subsystem. This means that
1432 HugeTLB pages may not be allocated from this zone.
1433 Note that allocations like PTEs-from-HighMem still
1434 use the HighMem zone if it exists, and the Normal
1435 zone if it does not.
1437 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1438 Format: <Controller#>[,poll interval]
1439 The controller # is the number of the ehci usb debug
1440 port as it is probed via PCI. The poll interval is
1441 optional and is the number seconds in between
1442 each poll cycle to the debug port in case you need
1443 the functionality for interrupting the kernel with
1444 gdb or control-c on the dbgp connection. When
1445 not using this parameter you use sysrq-g to break into
1446 the kernel debugger.
1448 kgdboc= [KGDB,HW] kgdb over consoles.
1449 Requires a tty driver that supports console polling,
1450 or a supported polling keyboard driver (non-usb).
1451 Serial only format: <serial_device>[,baud]
1452 keyboard only format: kbd
1453 keyboard and serial format: kbd,<serial_device>[,baud]
1454 Optional Kernel mode setting:
1455 kms, kbd format: kms,kbd
1456 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1458 kgdbwait [KGDB] Stop kernel execution and enter the
1459 kernel debugger at the earliest opportunity.
1461 kmac= [MIPS] korina ethernet MAC address.
1462 Configure the RouterBoard 532 series on-chip
1463 Ethernet adapter MAC address.
1465 kmemleak= [KNL] Boot-time kmemleak enable/disable
1466 Valid arguments: on, off
1467 Default: on
1469 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1470 Valid arguments: 0, 1, 2
1471 kmemcheck=0 (disabled)
1472 kmemcheck=1 (enabled)
1473 kmemcheck=2 (one-shot mode)
1474 Default: 2 (one-shot mode)
1476 kstack=N [X86] Print N words from the kernel stack
1477 in oops dumps.
1479 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1480 Default is 0 (don't ignore, but inject #GP)
1482 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1483 KVM MMU at runtime.
1484 Default is 0 (off)
1486 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1487 Default is 1 (enabled)
1489 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1490 for all guests.
1491 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1493 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1494 (virtualized MMU) support on capable Intel chips.
1495 Default is 1 (enabled)
1497 kvm-intel.emulate_invalid_guest_state=
1498 [KVM,Intel] Enable emulation of invalid guest states
1499 Default is 0 (disabled)
1501 kvm-intel.flexpriority=
1502 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1503 Default is 1 (enabled)
1505 kvm-intel.nested=
1506 [KVM,Intel] Enable VMX nesting (nVMX).
1507 Default is 0 (disabled)
1509 kvm-intel.unrestricted_guest=
1510 [KVM,Intel] Disable unrestricted guest feature
1511 (virtualized real and unpaged mode) on capable
1512 Intel chips. Default is 1 (enabled)
1514 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1515 feature (tagged TLBs) on capable Intel chips.
1516 Default is 1 (enabled)
1518 l2cr= [PPC]
1520 l3cr= [PPC]
1522 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1523 disabled it.
1525 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1526 value for LAPIC timer one-shot implementation. Default
1527 back to the programmable timer unit in the LAPIC.
1529 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1530 in C2 power state.
1532 libata.dma= [LIBATA] DMA control
1533 libata.dma=0 Disable all PATA and SATA DMA
1534 libata.dma=1 PATA and SATA Disk DMA only
1535 libata.dma=2 ATAPI (CDROM) DMA only
1536 libata.dma=4 Compact Flash DMA only
1537 Combinations also work, so libata.dma=3 enables DMA
1538 for disks and CDROMs, but not CFs.
1540 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1541 libata.ignore_hpa=0 keep BIOS limits (default)
1542 libata.ignore_hpa=1 ignore limits, using full disk
1544 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1545 when set.
1546 Format: <int>
1548 libata.force= [LIBATA] Force configurations. The format is comma
1549 separated list of "[ID:]VAL" where ID is
1550 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1551 matching port, link or device. Basically, it matches
1552 the ATA ID string printed on console by libata. If
1553 the whole ID part is omitted, the last PORT and DEVICE
1554 values are used. If ID hasn't been specified yet, the
1555 configuration applies to all ports, links and devices.
1557 If only DEVICE is omitted, the parameter applies to
1558 the port and all links and devices behind it. DEVICE
1559 number of 0 either selects the first device or the
1560 first fan-out link behind PMP device. It does not
1561 select the host link. DEVICE number of 15 selects the
1562 host link and device attached to it.
1564 The VAL specifies the configuration to force. As long
1565 as there's no ambiguity shortcut notation is allowed.
1566 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1567 The following configurations can be forced.
1569 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1570 Any ID with matching PORT is used.
1572 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1574 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1575 udma[/][16,25,33,44,66,100,133] notation is also
1576 allowed.
1578 * [no]ncq: Turn on or off NCQ.
1580 * nohrst, nosrst, norst: suppress hard, soft
1581 and both resets.
1583 * rstonce: only attempt one reset during
1584 hot-unplug link recovery
1586 * dump_id: dump IDENTIFY data.
1588 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1590 * disable: Disable this device.
1592 If there are multiple matching configurations changing
1593 the same attribute, the last one is used.
1595 memblock=debug [KNL] Enable memblock debug messages.
1597 load_ramdisk= [RAM] List of ramdisks to load from floppy
1598 See Documentation/blockdev/ramdisk.txt.
1600 lockd.nlm_grace_period=P [NFS] Assign grace period.
1601 Format: <integer>
1603 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1604 Format: <integer>
1606 lockd.nlm_timeout=T [NFS] Assign timeout value.
1607 Format: <integer>
1609 lockd.nlm_udpport=M [NFS] Assign UDP port.
1610 Format: <integer>
1612 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1613 Format: <irq>
1615 loglevel= All Kernel Messages with a loglevel smaller than the
1616 console loglevel will be printed to the console. It can
1617 also be changed with klogd or other programs. The
1618 loglevels are defined as follows:
1620 0 (KERN_EMERG) system is unusable
1621 1 (KERN_ALERT) action must be taken immediately
1622 2 (KERN_CRIT) critical conditions
1623 3 (KERN_ERR) error conditions
1624 4 (KERN_WARNING) warning conditions
1625 5 (KERN_NOTICE) normal but significant condition
1626 6 (KERN_INFO) informational
1627 7 (KERN_DEBUG) debug-level messages
1629 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1630 in bytes. n must be a power of two. The default
1631 size is set in the kernel config file.
1633 logo.nologo [FB] Disables display of the built-in Linux logo.
1634 This may be used to provide more screen space for
1635 kernel log messages and is useful when debugging
1636 kernel boot problems.
1638 lp=0 [LP] Specify parallel ports to use, e.g,
1639 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1640 lp=reset first parallel port). 'lp=0' disables the
1641 lp=auto printer driver. 'lp=reset' (which can be
1642 specified in addition to the ports) causes
1643 attached printers to be reset. Using
1644 lp=port1,port2,... specifies the parallel ports
1645 to associate lp devices with, starting with
1646 lp0. A port specification may be 'none' to skip
1647 that lp device, or a parport name such as
1648 'parport0'. Specifying 'lp=auto' instead of a
1649 port specification list means that device IDs
1650 from each port should be examined, to see if
1651 an IEEE 1284-compliant printer is attached; if
1652 so, the driver will manage that printer.
1653 See also header of drivers/char/lp.c.
1655 lpj=n [KNL]
1656 Sets loops_per_jiffy to given constant, thus avoiding
1657 time-consuming boot-time autodetection (up to 250 ms per
1658 CPU). 0 enables autodetection (default). To determine
1659 the correct value for your kernel, boot with normal
1660 autodetection and see what value is printed. Note that
1661 on SMP systems the preset will be applied to all CPUs,
1662 which is likely to cause problems if your CPUs need
1663 significantly divergent settings. An incorrect value
1664 will cause delays in the kernel to be wrong, leading to
1665 unpredictable I/O errors and other breakage. Although
1666 unlikely, in the extreme case this might damage your
1667 hardware.
1669 ltpc= [NET]
1670 Format: <io>,<irq>,<dma>
1672 machvec= [IA-64] Force the use of a particular machine-vector
1673 (machvec) in a generic kernel.
1674 Example: machvec=hpzx1_swiotlb
1676 machtype= [Loongson] Share the same kernel image file between different
1677 yeeloong laptop.
1678 Example: machtype=lemote-yeeloong-2f-7inch
1680 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1681 than or equal to this physical address is ignored.
1683 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1684 should make use of. maxcpus=n : n >= 0 limits the
1685 kernel to using 'n' processors. n=0 is a special case,
1686 it is equivalent to "nosmp", which also disables
1687 the IO APIC.
1689 max_loop= [LOOP] The number of loop block devices that get
1690 (loop.max_loop) unconditionally pre-created at init time. The default
1691 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1692 of statically allocating a predefined number, loop
1693 devices can be requested on-demand with the
1694 /dev/loop-control interface.
1696 mce [X86-32] Machine Check Exception
1698 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1700 md= [HW] RAID subsystems devices and level
1701 See Documentation/md.txt.
1703 mdacon= [MDA]
1704 Format: <first>,<last>
1705 Specifies range of consoles to be captured by the MDA.
1707 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1708 Amount of memory to be used when the kernel is not able
1709 to see the whole system memory or for test.
1710 [X86] Work as limiting max address. Use together
1711 with memmap= to avoid physical address space collisions.
1712 Without memmap= PCI devices could be placed at addresses
1713 belonging to unused RAM.
1715 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1716 memory.
1718 memchunk=nn[KMG]
1719 [KNL,SH] Allow user to override the default size for
1720 per-device physically contiguous DMA buffers.
1722 memmap=exactmap [KNL,X86] Enable setting of an exact
1723 E820 memory map, as specified by the user.
1724 Such memmap=exactmap lines can be constructed based on
1725 BIOS output or other requirements. See the memmap=nn@ss
1726 option description.
1728 memmap=nn[KMG]@ss[KMG]
1729 [KNL] Force usage of a specific region of memory.
1730 Region of memory to be used is from ss to ss+nn.
1732 memmap=nn[KMG]#ss[KMG]
1733 [KNL,ACPI] Mark specific memory as ACPI data.
1734 Region of memory to be marked is from ss to ss+nn.
1736 memmap=nn[KMG]$ss[KMG]
1737 [KNL,ACPI] Mark specific memory as reserved.
1738 Region of memory to be reserved is from ss to ss+nn.
1739 Example: Exclude memory from 0x18690000-0x1869ffff
1740 memmap=64K$0x18690000
1741 or
1742 memmap=0x10000$0x18690000
1744 memory_corruption_check=0/1 [X86]
1745 Some BIOSes seem to corrupt the first 64k of
1746 memory when doing things like suspend/resume.
1747 Setting this option will scan the memory
1748 looking for corruption. Enabling this will
1749 both detect corruption and prevent the kernel
1750 from using the memory being corrupted.
1751 However, its intended as a diagnostic tool; if
1752 repeatable BIOS-originated corruption always
1753 affects the same memory, you can use memmap=
1754 to prevent the kernel from using that memory.
1756 memory_corruption_check_size=size [X86]
1757 By default it checks for corruption in the low
1758 64k, making this memory unavailable for normal
1759 use. Use this parameter to scan for
1760 corruption in more or less memory.
1762 memory_corruption_check_period=seconds [X86]
1763 By default it checks for corruption every 60
1764 seconds. Use this parameter to check at some
1765 other rate. 0 disables periodic checking.
1767 memtest= [KNL,X86] Enable memtest
1768 Format: <integer>
1769 default : 0 <disable>
1770 Specifies the number of memtest passes to be
1771 performed. Each pass selects another test
1772 pattern from a given set of patterns. Memtest
1773 fills the memory with this pattern, validates
1774 memory contents and reserves bad memory
1775 regions that are detected.
1777 meye.*= [HW] Set MotionEye Camera parameters
1778 See Documentation/video4linux/meye.txt.
1780 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1781 Multi-Function General Purpose Timers on AMD Geode
1782 platforms.
1784 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1785 the BIOS has incorrectly applied a workaround. TinyBIOS
1786 version 0.98 is known to be affected, 0.99 fixes the
1787 problem by letting the user disable the workaround.
1789 mga= [HW,DRM]
1791 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1792 physical address is ignored.
1794 mini2440= [ARM,HW,KNL]
1795 Format:[0..2][b][c][t]
1796 Default: "0tb"
1797 MINI2440 configuration specification:
1798 0 - The attached screen is the 3.5" TFT
1799 1 - The attached screen is the 7" TFT
1800 2 - The VGA Shield is attached (1024x768)
1801 Leaving out the screen size parameter will not load
1802 the TFT driver, and the framebuffer will be left
1803 unconfigured.
1804 b - Enable backlight. The TFT backlight pin will be
1805 linked to the kernel VESA blanking code and a GPIO
1806 LED. This parameter is not necessary when using the
1807 VGA shield.
1808 c - Enable the s3c camera interface.
1809 t - Reserved for enabling touchscreen support. The
1810 touchscreen support is not enabled in the mainstream
1811 kernel as of 2.6.30, a preliminary port can be found
1812 in the "bleeding edge" mini2440 support kernel at
1813 http://repo.or.cz/w/linux-2.6/mini2440.git
1815 mminit_loglevel=
1816 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1817 parameter allows control of the logging verbosity for
1818 the additional memory initialisation checks. A value
1819 of 0 disables mminit logging and a level of 4 will
1820 log everything. Information is printed at KERN_DEBUG
1821 so loglevel=8 may also need to be specified.
1823 module.sig_enforce
1824 [KNL] When CONFIG_MODULE_SIG is set, this means that
1825 modules without (valid) signatures will fail to load.
1826 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1827 is always true, so this option does nothing.
1829 mousedev.tap_time=
1830 [MOUSE] Maximum time between finger touching and
1831 leaving touchpad surface for touch to be considered
1832 a tap and be reported as a left button click (for
1833 touchpads working in absolute mode only).
1834 Format: <msecs>
1835 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1836 reporting absolute coordinates, such as tablets
1837 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1838 reporting absolute coordinates, such as tablets
1840 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1841 is similar to kernelcore except it specifies the
1842 amount of memory used for migratable allocations.
1843 If both kernelcore and movablecore is specified,
1844 then kernelcore will be at *least* the specified
1845 value but may be more. If movablecore on its own
1846 is specified, the administrator must be careful
1847 that the amount of memory usable for all allocations
1848 is not too small.
1850 movable_node [KNL,X86] Boot-time switch to enable the effects
1851 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
1853 MTD_Partition= [MTD]
1854 Format: <name>,<region-number>,<size>,<offset>
1856 MTD_Region= [MTD] Format:
1857 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1859 mtdparts= [MTD]
1860 See drivers/mtd/cmdlinepart.c.
1862 multitce=off [PPC] This parameter disables the use of the pSeries
1863 firmware feature for updating multiple TCE entries
1864 at a time.
1866 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1868 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1870 boundary - index of last SLC block on Flex-OneNAND.
1871 The remaining blocks are configured as MLC blocks.
1872 lock - Configure if Flex-OneNAND boundary should be locked.
1873 Once locked, the boundary cannot be changed.
1874 1 indicates lock status, 0 indicates unlock status.
1876 mtdset= [ARM]
1877 ARM/S3C2412 JIVE boot control
1879 See arch/arm/mach-s3c2412/mach-jive.c
1881 mtouchusb.raw_coordinates=
1882 [HW] Make the MicroTouch USB driver use raw coordinates
1883 ('y', default) or cooked coordinates ('n')
1885 mtrr_chunk_size=nn[KMG] [X86]
1886 used for mtrr cleanup. It is largest continuous chunk
1887 that could hold holes aka. UC entries.
1889 mtrr_gran_size=nn[KMG] [X86]
1890 Used for mtrr cleanup. It is granularity of mtrr block.
1891 Default is 1.
1892 Large value could prevent small alignment from
1893 using up MTRRs.
1895 mtrr_spare_reg_nr=n [X86]
1896 Format: <integer>
1897 Range: 0,7 : spare reg number
1898 Default : 1
1899 Used for mtrr cleanup. It is spare mtrr entries number.
1900 Set to 2 or more if your graphical card needs more.
1902 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1904 netdev= [NET] Network devices parameters
1905 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1906 Note that mem_start is often overloaded to mean
1907 something different and driver-specific.
1908 This usage is only documented in each driver source
1909 file if at all.
1911 nf_conntrack.acct=
1912 [NETFILTER] Enable connection tracking flow accounting
1913 0 to disable accounting
1914 1 to enable accounting
1915 Default value is 0.
1917 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1918 See Documentation/filesystems/nfs/nfsroot.txt.
1920 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1921 See Documentation/filesystems/nfs/nfsroot.txt.
1923 nfsrootdebug [NFS] enable nfsroot debugging messages.
1924 See Documentation/filesystems/nfs/nfsroot.txt.
1926 nfs.callback_tcpport=
1927 [NFS] set the TCP port on which the NFSv4 callback
1928 channel should listen.
1930 nfs.cache_getent=
1931 [NFS] sets the pathname to the program which is used
1932 to update the NFS client cache entries.
1934 nfs.cache_getent_timeout=
1935 [NFS] sets the timeout after which an attempt to
1936 update a cache entry is deemed to have failed.
1938 nfs.idmap_cache_timeout=
1939 [NFS] set the maximum lifetime for idmapper cache
1940 entries.
1942 nfs.enable_ino64=
1943 [NFS] enable 64-bit inode numbers.
1944 If zero, the NFS client will fake up a 32-bit inode
1945 number for the readdir() and stat() syscalls instead
1946 of returning the full 64-bit number.
1947 The default is to return 64-bit inode numbers.
1949 nfs.max_session_slots=
1950 [NFSv4.1] Sets the maximum number of session slots
1951 the client will attempt to negotiate with the server.
1952 This limits the number of simultaneous RPC requests
1953 that the client can send to the NFSv4.1 server.
1954 Note that there is little point in setting this
1955 value higher than the max_tcp_slot_table_limit.
1957 nfs.nfs4_disable_idmapping=
1958 [NFSv4] When set to the default of '1', this option
1959 ensures that both the RPC level authentication
1960 scheme and the NFS level operations agree to use
1961 numeric uids/gids if the mount is using the
1962 'sec=sys' security flavour. In effect it is
1963 disabling idmapping, which can make migration from
1964 legacy NFSv2/v3 systems to NFSv4 easier.
1965 Servers that do not support this mode of operation
1966 will be autodetected by the client, and it will fall
1967 back to using the idmapper.
1968 To turn off this behaviour, set the value to '0'.
1969 nfs.nfs4_unique_id=
1970 [NFS4] Specify an additional fixed unique ident-
1971 ification string that NFSv4 clients can insert into
1972 their nfs_client_id4 string. This is typically a
1973 UUID that is generated at system install time.
1975 nfs.send_implementation_id =
1976 [NFSv4.1] Send client implementation identification
1977 information in exchange_id requests.
1978 If zero, no implementation identification information
1979 will be sent.
1980 The default is to send the implementation identification
1981 information.
1983 nfs.recover_lost_locks =
1984 [NFSv4] Attempt to recover locks that were lost due
1985 to a lease timeout on the server. Please note that
1986 doing this risks data corruption, since there are
1987 no guarantees that the file will remain unchanged
1988 after the locks are lost.
1989 If you want to enable the kernel legacy behaviour of
1990 attempting to recover these locks, then set this
1991 parameter to '1'.
1992 The default parameter value of '0' causes the kernel
1993 not to attempt recovery of lost locks.
1995 nfsd.nfs4_disable_idmapping=
1996 [NFSv4] When set to the default of '1', the NFSv4
1997 server will return only numeric uids and gids to
1998 clients using auth_sys, and will accept numeric uids
1999 and gids from such clients. This is intended to ease
2000 migration from NFSv2/v3.
2002 objlayoutdriver.osd_login_prog=
2003 [NFS] [OBJLAYOUT] sets the pathname to the program which
2004 is used to automatically discover and login into new
2005 osd-targets. Please see:
2006 Documentation/filesystems/pnfs.txt for more explanations
2008 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2009 when a NMI is triggered.
2010 Format: [state][,regs][,debounce][,die]
2012 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2013 Format: [panic,][nopanic,][num]
2014 Valid num: 0
2015 0 - turn nmi_watchdog off
2016 When panic is specified, panic when an NMI watchdog
2017 timeout occurs (or 'nopanic' to override the opposite
2018 default).
2019 This is useful when you use a panic=... timeout and
2020 need the box quickly up again.
2022 netpoll.carrier_timeout=
2023 [NET] Specifies amount of time (in seconds) that
2024 netpoll should wait for a carrier. By default netpoll
2025 waits 4 seconds.
2027 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2028 emulation library even if a 387 maths coprocessor
2029 is present.
2031 no_console_suspend
2032 [HW] Never suspend the console
2033 Disable suspending of consoles during suspend and
2034 hibernate operations. Once disabled, debugging
2035 messages can reach various consoles while the rest
2036 of the system is being put to sleep (ie, while
2037 debugging driver suspend/resume hooks). This may
2038 not work reliably with all consoles, but is known
2039 to work with serial and VGA consoles.
2040 To facilitate more flexible debugging, we also add
2041 console_suspend, a printk module parameter to control
2042 it. Users could use console_suspend (usually
2043 /sys/module/printk/parameters/console_suspend) to
2044 turn on/off it dynamically.
2046 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2047 caches in the slab allocator. Saves per-node memory,
2048 but will impact performance.
2050 noalign [KNL,ARM]
2052 noapic [SMP,APIC] Tells the kernel to not make use of any
2053 IOAPICs that may be present in the system.
2055 nokaslr [X86]
2056 Disable kernel base offset ASLR (Address Space
2057 Layout Randomization) if built into the kernel.
2059 noautogroup Disable scheduler automatic task group creation.
2061 nobats [PPC] Do not use BATs for mapping kernel lowmem
2062 on "Classic" PPC cores.
2064 nocache [ARM]
2066 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2068 nodelayacct [KNL] Disable per-task delay accounting
2070 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2072 nodsp [SH] Disable hardware DSP at boot time.
2074 noefi [X86] Disable EFI runtime services support.
2076 noexec [IA-64]
2078 noexec [X86]
2079 On X86-32 available only on PAE configured kernels.
2080 noexec=on: enable non-executable mappings (default)
2081 noexec=off: disable non-executable mappings
2083 nosmap [X86]
2084 Disable SMAP (Supervisor Mode Access Prevention)
2085 even if it is supported by processor.
2087 nosmep [X86]
2088 Disable SMEP (Supervisor Mode Execution Prevention)
2089 even if it is supported by processor.
2091 noexec32 [X86-64]
2092 This affects only 32-bit executables.
2093 noexec32=on: enable non-executable mappings (default)
2094 read doesn't imply executable mappings
2095 noexec32=off: disable non-executable mappings
2096 read implies executable mappings
2098 nofpu [SH] Disable hardware FPU at boot time.
2100 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2101 register save and restore. The kernel will only save
2102 legacy floating-point registers on task switch.
2104 noxsave [BUGS=X86] Disables x86 extended register state save
2105 and restore using xsave. The kernel will fallback to
2106 enabling legacy floating-point and sse state.
2108 eagerfpu= [X86]
2109 on enable eager fpu restore
2110 off disable eager fpu restore
2111 auto selects the default scheme, which automatically
2112 enables eagerfpu restore for xsaveopt.
2114 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2115 wfi(ARM) instruction doesn't work correctly and not to
2116 use it. This is also useful when using JTAG debugger.
2118 no_file_caps Tells the kernel not to honor file capabilities. The
2119 only way then for a file to be executed with privilege
2120 is to be setuid root or executed by root.
2122 nohalt [IA-64] Tells the kernel not to use the power saving
2123 function PAL_HALT_LIGHT when idle. This increases
2124 power-consumption. On the positive side, it reduces
2125 interrupt wake-up latency, which may improve performance
2126 in certain environments such as networked servers or
2127 real-time systems.
2129 nohz= [KNL] Boottime enable/disable dynamic ticks
2130 Valid arguments: on, off
2131 Default: on
2133 nohz_full= [KNL,BOOT]
2134 In kernels built with CONFIG_NO_HZ_FULL=y, set
2135 the specified list of CPUs whose tick will be stopped
2136 whenever possible. The boot CPU will be forced outside
2137 the range to maintain the timekeeping.
2138 The CPUs in this range must also be included in the
2139 rcu_nocbs= set.
2141 noiotrap [SH] Disables trapped I/O port accesses.
2143 noirqdebug [X86-32] Disables the code which attempts to detect and
2144 disable unhandled interrupt sources.
2146 no_timer_check [X86,APIC] Disables the code which tests for
2147 broken timer IRQ sources.
2149 noisapnp [ISAPNP] Disables ISA PnP code.
2151 noinitrd [RAM] Tells the kernel not to load any configured
2152 initial RAM disk.
2154 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2155 remapping.
2156 [Deprecated - use intremap=off]
2158 nointroute [IA-64]
2160 nojitter [IA-64] Disables jitter checking for ITC timers.
2162 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2164 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2165 fault handling.
2167 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2168 steal time is computed, but won't influence scheduler
2169 behaviour
2171 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2173 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2175 noltlbs [PPC] Do not use large page/tlb entries for kernel
2176 lowmem mapping on PPC40x.
2178 nomca [IA-64] Disable machine check abort handling
2180 nomce [X86-32] Machine Check Exception
2182 nomfgpt [X86-32] Disable Multi-Function General Purpose
2183 Timer usage (for AMD Geode machines).
2185 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2186 shutdown the other cpus. Instead use the REBOOT_VECTOR
2187 irq.
2189 nomodule Disable module load
2191 nopat [X86] Disable PAT (page attribute table extension of
2192 pagetables) support.
2194 norandmaps Don't use address space randomization. Equivalent to
2195 echo 0 > /proc/sys/kernel/randomize_va_space
2197 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2199 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2200 with UP alternatives
2202 nordrand [X86] Disable the direct use of the RDRAND
2203 instruction even if it is supported by the
2204 processor. RDRAND is still available to user
2205 space applications.
2207 noresume [SWSUSP] Disables resume and restores original swap
2208 space.
2210 no-scroll [VGA] Disables scrollback.
2211 This is required for the Braillex ib80-piezo Braille
2212 reader made by F.H. Papenmeier (Germany).
2214 nosbagart [IA-64]
2216 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2218 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2219 and disable the IO APIC. legacy for "maxcpus=0".
2221 nosoftlockup [KNL] Disable the soft-lockup detector.
2223 nosync [HW,M68K] Disables sync negotiation for all devices.
2225 notsc [BUGS=X86-32] Disable Time Stamp Counter
2227 nousb [USB] Disable the USB subsystem
2229 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2231 nowb [ARM]
2233 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2235 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2236 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2237 Some features depend on CPU0. Known dependencies are:
2238 1. Resume from suspend/hibernate depends on CPU0.
2239 Suspend/hibernate will fail if CPU0 is offline and you
2240 need to online CPU0 before suspend/hibernate.
2241 2. PIC interrupts also depend on CPU0. CPU0 can't be
2242 removed if a PIC interrupt is detected.
2243 It's said poweroff/reboot may depend on CPU0 on some
2244 machines although I haven't seen such issues so far
2245 after CPU0 is offline on a few tested machines.
2246 If the dependencies are under your control, you can
2247 turn on cpu0_hotplug.
2249 nptcg= [IA-64] Override max number of concurrent global TLB
2250 purges which is reported from either PAL_VM_SUMMARY or
2251 SAL PALO.
2253 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2254 could support. nr_cpus=n : n >= 1 limits the kernel to
2255 supporting 'n' processors. Later in runtime you can not
2256 use hotplug cpu feature to put more cpu back to online.
2257 just like you compile the kernel NR_CPUS=n
2259 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2261 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2262 Allowed values are enable and disable
2264 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2265 one of ['zone', 'node', 'default'] can be specified
2266 This can be set from sysctl after boot.
2267 See Documentation/sysctl/vm.txt for details.
2269 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2270 See Documentation/debugging-via-ohci1394.txt for more
2271 info.
2273 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2274 Rather than timing out after 20 ms if an EC
2275 command is not properly ACKed, override the length
2276 of the timeout. We have interrupts disabled while
2277 waiting for the ACK, so if this is set too high
2278 interrupts *may* be lost!
2280 omap_mux= [OMAP] Override bootloader pin multiplexing.
2281 Format: <mux_mode0.mode_name=value>...
2282 For example, to override I2C bus2:
2283 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2285 oprofile.timer= [HW]
2286 Use timer interrupt instead of performance counters
2288 oprofile.cpu_type= Force an oprofile cpu type
2289 This might be useful if you have an older oprofile
2290 userland or if you want common events.
2291 Format: { arch_perfmon }
2292 arch_perfmon: [X86] Force use of architectural
2293 perfmon on Intel CPUs instead of the
2294 CPU specific event set.
2295 timer: [X86] Force use of architectural NMI
2296 timer mode (see also oprofile.timer
2297 for generic hr timer mode)
2298 [s390] Force legacy basic mode sampling
2299 (report cpu_type "timer")
2301 oops=panic Always panic on oopses. Default is to just kill the
2302 process, but there is a small probability of
2303 deadlocking the machine.
2304 This will also cause panics on machine check exceptions.
2305 Useful together with panic=30 to trigger a reboot.
2307 OSS [HW,OSS]
2308 See Documentation/sound/oss/oss-parameters.txt
2310 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2311 timeout > 0: seconds before rebooting
2312 timeout = 0: wait forever
2313 timeout < 0: reboot immediately
2314 Format: <timeout>
2316 parkbd.port= [HW] Parallel port number the keyboard adapter is
2317 connected to, default is 0.
2318 Format: <parport#>
2319 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2320 0 for XT, 1 for AT (default is AT).
2321 Format: <mode>
2323 parport= [HW,PPT] Specify parallel ports. 0 disables.
2324 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2325 Use 'auto' to force the driver to use any
2326 IRQ/DMA settings detected (the default is to
2327 ignore detected IRQ/DMA settings because of
2328 possible conflicts). You can specify the base
2329 address, IRQ, and DMA settings; IRQ and DMA
2330 should be numbers, or 'auto' (for using detected
2331 settings on that particular port), or 'nofifo'
2332 (to avoid using a FIFO even if it is detected).
2333 Parallel ports are assigned in the order they
2334 are specified on the command line, starting
2335 with parport0.
2337 parport_init_mode= [HW,PPT]
2338 Configure VIA parallel port to operate in
2339 a specific mode. This is necessary on Pegasos
2340 computer where firmware has no options for setting
2341 up parallel port mode and sets it to spp.
2342 Currently this function knows 686a and 8231 chips.
2343 Format: [spp|ps2|epp|ecp|ecpepp]
2345 pause_on_oops=
2346 Halt all CPUs after the first oops has been printed for
2347 the specified number of seconds. This is to be used if
2348 your oopses keep scrolling off the screen.
2350 pcbit= [HW,ISDN]
2352 pcd. [PARIDE]
2353 See header of drivers/block/paride/pcd.c.
2354 See also Documentation/blockdev/paride.txt.
2356 pci=option[,option...] [PCI] various PCI subsystem options:
2357 earlydump [X86] dump PCI config space before the kernel
2358 changes anything
2359 off [X86] don't probe for the PCI bus
2360 bios [X86-32] force use of PCI BIOS, don't access
2361 the hardware directly. Use this if your machine
2362 has a non-standard PCI host bridge.
2363 nobios [X86-32] disallow use of PCI BIOS, only direct
2364 hardware access methods are allowed. Use this
2365 if you experience crashes upon bootup and you
2366 suspect they are caused by the BIOS.
2367 conf1 [X86] Force use of PCI Configuration
2368 Mechanism 1.
2369 conf2 [X86] Force use of PCI Configuration
2370 Mechanism 2.
2371 noaer [PCIE] If the PCIEAER kernel config parameter is
2372 enabled, this kernel boot option can be used to
2373 disable the use of PCIE advanced error reporting.
2374 nodomains [PCI] Disable support for multiple PCI
2375 root domains (aka PCI segments, in ACPI-speak).
2376 nommconf [X86] Disable use of MMCONFIG for PCI
2377 Configuration
2378 check_enable_amd_mmconf [X86] check for and enable
2379 properly configured MMIO access to PCI
2380 config space on AMD family 10h CPU
2381 nomsi [MSI] If the PCI_MSI kernel config parameter is
2382 enabled, this kernel boot option can be used to
2383 disable the use of MSI interrupts system-wide.
2384 noioapicquirk [APIC] Disable all boot interrupt quirks.
2385 Safety option to keep boot IRQs enabled. This
2386 should never be necessary.
2387 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2388 primary IO-APIC for bridges that cannot disable
2389 boot IRQs. This fixes a source of spurious IRQs
2390 when the system masks IRQs.
2391 noioapicreroute [APIC] Disable workaround that uses the
2392 boot IRQ equivalent of an IRQ that connects to
2393 a chipset where boot IRQs cannot be disabled.
2394 The opposite of ioapicreroute.
2395 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2396 routing table. These calls are known to be buggy
2397 on several machines and they hang the machine
2398 when used, but on other computers it's the only
2399 way to get the interrupt routing table. Try
2400 this option if the kernel is unable to allocate
2401 IRQs or discover secondary PCI buses on your
2402 motherboard.
2403 rom [X86] Assign address space to expansion ROMs.
2404 Use with caution as certain devices share
2405 address decoders between ROMs and other
2406 resources.
2407 norom [X86] Do not assign address space to
2408 expansion ROMs that do not already have
2409 BIOS assigned address ranges.
2410 nobar [X86] Do not assign address space to the
2411 BARs that weren't assigned by the BIOS.
2412 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2413 assigned automatically to PCI devices. You can
2414 make the kernel exclude IRQs of your ISA cards
2415 this way.
2416 pirqaddr=0xAAAAA [X86] Specify the physical address
2417 of the PIRQ table (normally generated
2418 by the BIOS) if it is outside the
2419 F0000h-100000h range.
2420 lastbus=N [X86] Scan all buses thru bus #N. Can be
2421 useful if the kernel is unable to find your
2422 secondary buses and you want to tell it
2423 explicitly which ones they are.
2424 assign-busses [X86] Always assign all PCI bus
2425 numbers ourselves, overriding
2426 whatever the firmware may have done.
2427 usepirqmask [X86] Honor the possible IRQ mask stored
2428 in the BIOS $PIR table. This is needed on
2429 some systems with broken BIOSes, notably
2430 some HP Pavilion N5400 and Omnibook XE3
2431 notebooks. This will have no effect if ACPI
2432 IRQ routing is enabled.
2433 noacpi [X86] Do not use ACPI for IRQ routing
2434 or for PCI scanning.
2435 use_crs [X86] Use PCI host bridge window information
2436 from ACPI. On BIOSes from 2008 or later, this
2437 is enabled by default. If you need to use this,
2438 please report a bug.
2439 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2440 If you need to use this, please report a bug.
2441 routeirq Do IRQ routing for all PCI devices.
2442 This is normally done in pci_enable_device(),
2443 so this option is a temporary workaround
2444 for broken drivers that don't call it.
2445 skip_isa_align [X86] do not align io start addr, so can
2446 handle more pci cards
2447 firmware [ARM] Do not re-enumerate the bus but instead
2448 just use the configuration from the
2449 bootloader. This is currently used on
2450 IXP2000 systems where the bus has to be
2451 configured a certain way for adjunct CPUs.
2452 noearly [X86] Don't do any early type 1 scanning.
2453 This might help on some broken boards which
2454 machine check when some devices' config space
2455 is read. But various workarounds are disabled
2456 and some IOMMU drivers will not work.
2457 bfsort Sort PCI devices into breadth-first order.
2458 This sorting is done to get a device
2459 order compatible with older (<= 2.4) kernels.
2460 nobfsort Don't sort PCI devices into breadth-first order.
2461 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2462 tuning and use the BIOS-configured MPS defaults.
2463 pcie_bus_safe Set every device's MPS to the largest value
2464 supported by all devices below the root complex.
2465 pcie_bus_perf Set device MPS to the largest allowable MPS
2466 based on its parent bus. Also set MRRS (Max
2467 Read Request Size) to the largest supported
2468 value (no larger than the MPS that the device
2469 or bus can support) for best performance.
2470 pcie_bus_peer2peer Set every device's MPS to 128B, which
2471 every device is guaranteed to support. This
2472 configuration allows peer-to-peer DMA between
2473 any pair of devices, possibly at the cost of
2474 reduced performance. This also guarantees
2475 that hot-added devices will work.
2476 cbiosize=nn[KMG] The fixed amount of bus space which is
2477 reserved for the CardBus bridge's IO window.
2478 The default value is 256 bytes.
2479 cbmemsize=nn[KMG] The fixed amount of bus space which is
2480 reserved for the CardBus bridge's memory
2481 window. The default value is 64 megabytes.
2482 resource_alignment=
2483 Format:
2484 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2485 Specifies alignment and device to reassign
2486 aligned memory resources.
2487 If <order of align> is not specified,
2488 PAGE_SIZE is used as alignment.
2489 PCI-PCI bridge can be specified, if resource
2490 windows need to be expanded.
2491 ecrc= Enable/disable PCIe ECRC (transaction layer
2492 end-to-end CRC checking).
2493 bios: Use BIOS/firmware settings. This is the
2494 the default.
2495 off: Turn ECRC off
2496 on: Turn ECRC on.
2497 hpiosize=nn[KMG] The fixed amount of bus space which is
2498 reserved for hotplug bridge's IO window.
2499 Default size is 256 bytes.
2500 hpmemsize=nn[KMG] The fixed amount of bus space which is
2501 reserved for hotplug bridge's memory window.
2502 Default size is 2 megabytes.
2503 realloc= Enable/disable reallocating PCI bridge resources
2504 if allocations done by BIOS are too small to
2505 accommodate resources required by all child
2506 devices.
2507 off: Turn realloc off
2508 on: Turn realloc on
2509 realloc same as realloc=on
2510 noari do not use PCIe ARI.
2511 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2512 only look for one device below a PCIe downstream
2513 port.
2515 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2516 Management.
2517 off Disable ASPM.
2518 force Enable ASPM even on devices that claim not to support it.
2519 WARNING: Forcing ASPM on may cause system lockups.
2521 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2522 nomsi Do not use MSI for PCI Express Native Hotplug (this
2523 makes all PCIe ports use INTx for hotplug services).
2525 pcie_ports= [PCIE] PCIe ports handling:
2526 auto Ask the BIOS whether or not to use native PCIe services
2527 associated with PCIe ports (PME, hot-plug, AER). Use
2528 them only if that is allowed by the BIOS.
2529 native Use native PCIe services associated with PCIe ports
2530 unconditionally.
2531 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2532 ports driver.
2534 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2535 nomsi Do not use MSI for native PCIe PME signaling (this makes
2536 all PCIe root ports use INTx for all services).
2538 pcmv= [HW,PCMCIA] BadgePAD 4
2540 pd. [PARIDE]
2541 See Documentation/blockdev/paride.txt.
2543 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2544 boot time.
2545 Format: { 0 | 1 }
2546 See arch/parisc/kernel/pdc_chassis.c
2548 percpu_alloc= Select which percpu first chunk allocator to use.
2549 Currently supported values are "embed" and "page".
2550 Archs may support subset or none of the selections.
2551 See comments in mm/percpu.c for details on each
2552 allocator. This parameter is primarily for debugging
2553 and performance comparison.
2555 pf. [PARIDE]
2556 See Documentation/blockdev/paride.txt.
2558 pg. [PARIDE]
2559 See Documentation/blockdev/paride.txt.
2561 pirq= [SMP,APIC] Manual mp-table setup
2562 See Documentation/x86/i386/IO-APIC.txt.
2564 plip= [PPT,NET] Parallel port network link
2565 Format: { parport<nr> | timid | 0 }
2566 See also Documentation/parport.txt.
2568 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2569 Override pmtimer IOPort with a hex value.
2570 e.g. pmtmr=0x508
2572 pnp.debug=1 [PNP]
2573 Enable PNP debug messages (depends on the
2574 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2575 via /sys/module/pnp/parameters/debug. We always show
2576 current resource usage; turning this on also shows
2577 possible settings and some assignment information.
2579 pnpacpi= [ACPI]
2580 { off }
2582 pnpbios= [ISAPNP]
2583 { on | off | curr | res | no-curr | no-res }
2585 pnp_reserve_irq=
2586 [ISAPNP] Exclude IRQs for the autoconfiguration
2588 pnp_reserve_dma=
2589 [ISAPNP] Exclude DMAs for the autoconfiguration
2591 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2592 Ranges are in pairs (I/O port base and size).
2594 pnp_reserve_mem=
2595 [ISAPNP] Exclude memory regions for the
2596 autoconfiguration.
2597 Ranges are in pairs (memory base and size).
2599 ports= [IP_VS_FTP] IPVS ftp helper module
2600 Default is 21.
2601 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2602 may be specified.
2603 Format: <port>,<port>....
2605 print-fatal-signals=
2606 [KNL] debug: print fatal signals
2608 If enabled, warn about various signal handling
2609 related application anomalies: too many signals,
2610 too many POSIX.1 timers, fatal signals causing a
2611 coredump - etc.
2613 If you hit the warning due to signal overflow,
2614 you might want to try "ulimit -i unlimited".
2616 default: off.
2618 printk.always_kmsg_dump=
2619 Trigger kmsg_dump for cases other than kernel oops or
2620 panics
2621 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2622 default: disabled
2624 printk.time= Show timing data prefixed to each printk message line
2625 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2627 processor.max_cstate= [HW,ACPI]
2628 Limit processor to maximum C-state
2629 max_cstate=9 overrides any DMI blacklist limit.
2631 processor.nocst [HW,ACPI]
2632 Ignore the _CST method to determine C-states,
2633 instead using the legacy FADT method
2635 profile= [KNL] Enable kernel profiling via /proc/profile
2636 Format: [schedule,]<number>
2637 Param: "schedule" - profile schedule points.
2638 Param: <number> - step/bucket size as a power of 2 for
2639 statistical time based profiling.
2640 Param: "sleep" - profile D-state sleeping (millisecs).
2641 Requires CONFIG_SCHEDSTATS
2642 Param: "kvm" - profile VM exits.
2644 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2645 before loading.
2646 See Documentation/blockdev/ramdisk.txt.
2648 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2649 probe for; one of (bare|imps|exps|lifebook|any).
2650 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2651 per second.
2652 psmouse.resetafter= [HW,MOUSE]
2653 Try to reset the device after so many bad packets
2654 (0 = never).
2655 psmouse.resolution=
2656 [HW,MOUSE] Set desired mouse resolution, in dpi.
2657 psmouse.smartscroll=
2658 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2659 0 = disabled, 1 = enabled (default).
2661 pstore.backend= Specify the name of the pstore backend to use
2663 pt. [PARIDE]
2664 See Documentation/blockdev/paride.txt.
2666 pty.legacy_count=
2667 [KNL] Number of legacy pty's. Overwrites compiled-in
2668 default number.
2670 quiet [KNL] Disable most log messages
2672 r128= [HW,DRM]
2674 raid= [HW,RAID]
2675 See Documentation/md.txt.
2677 ramdisk_blocksize= [RAM]
2678 See Documentation/blockdev/ramdisk.txt.
2680 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2681 See Documentation/blockdev/ramdisk.txt.
2683 rcu_nocbs= [KNL]
2684 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2685 the specified list of CPUs to be no-callback CPUs.
2686 Invocation of these CPUs' RCU callbacks will
2687 be offloaded to "rcuox/N" kthreads created for
2688 that purpose, where "x" is "b" for RCU-bh, "p"
2689 for RCU-preempt, and "s" for RCU-sched, and "N"
2690 is the CPU number. This reduces OS jitter on the
2691 offloaded CPUs, which can be useful for HPC and
2692 real-time workloads. It can also improve energy
2693 efficiency for asymmetric multiprocessors.
2695 rcu_nocb_poll [KNL]
2696 Rather than requiring that offloaded CPUs
2697 (specified by rcu_nocbs= above) explicitly
2698 awaken the corresponding "rcuoN" kthreads,
2699 make these kthreads poll for callbacks.
2700 This improves the real-time response for the
2701 offloaded CPUs by relieving them of the need to
2702 wake up the corresponding kthread, but degrades
2703 energy efficiency by requiring that the kthreads
2704 periodically wake up to do the polling.
2706 rcutree.blimit= [KNL]
2707 Set maximum number of finished RCU callbacks to
2708 process in one batch.
2710 rcutree.rcu_fanout_leaf= [KNL]
2711 Increase the number of CPUs assigned to each
2712 leaf rcu_node structure. Useful for very large
2713 systems.
2715 rcutree.jiffies_till_first_fqs= [KNL]
2716 Set delay from grace-period initialization to
2717 first attempt to force quiescent states.
2718 Units are jiffies, minimum value is zero,
2719 and maximum value is HZ.
2721 rcutree.jiffies_till_next_fqs= [KNL]
2722 Set delay between subsequent attempts to force
2723 quiescent states. Units are jiffies, minimum
2724 value is one, and maximum value is HZ.
2726 rcutree.qhimark= [KNL]
2727 Set threshold of queued RCU callbacks beyond which
2728 batch limiting is disabled.
2730 rcutree.qlowmark= [KNL]
2731 Set threshold of queued RCU callbacks below which
2732 batch limiting is re-enabled.
2734 rcutree.rcu_idle_gp_delay= [KNL]
2735 Set wakeup interval for idle CPUs that have
2736 RCU callbacks (RCU_FAST_NO_HZ=y).
2738 rcutree.rcu_idle_lazy_gp_delay= [KNL]
2739 Set wakeup interval for idle CPUs that have
2740 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2741 Lazy RCU callbacks are those which RCU can
2742 prove do nothing more than free memory.
2744 rcutorture.fqs_duration= [KNL]
2745 Set duration of force_quiescent_state bursts.
2747 rcutorture.fqs_holdoff= [KNL]
2748 Set holdoff time within force_quiescent_state bursts.
2750 rcutorture.fqs_stutter= [KNL]
2751 Set wait time between force_quiescent_state bursts.
2753 rcutorture.gp_exp= [KNL]
2754 Use expedited update-side primitives.
2756 rcutorture.gp_normal= [KNL]
2757 Use normal (non-expedited) update-side primitives.
2758 If both gp_exp and gp_normal are set, do both.
2759 If neither gp_exp nor gp_normal are set, still
2760 do both.
2762 rcutorture.n_barrier_cbs= [KNL]
2763 Set callbacks/threads for rcu_barrier() testing.
2765 rcutorture.nfakewriters= [KNL]
2766 Set number of concurrent RCU writers. These just
2767 stress RCU, they don't participate in the actual
2768 test, hence the "fake".
2770 rcutorture.nreaders= [KNL]
2771 Set number of RCU readers.
2773 rcutorture.object_debug= [KNL]
2774 Enable debug-object double-call_rcu() testing.
2776 rcutorture.onoff_holdoff= [KNL]
2777 Set time (s) after boot for CPU-hotplug testing.
2779 rcutorture.onoff_interval= [KNL]
2780 Set time (s) between CPU-hotplug operations, or
2781 zero to disable CPU-hotplug testing.
2783 rcutorture.rcutorture_runnable= [BOOT]
2784 Start rcutorture running at boot time.
2786 rcutorture.shuffle_interval= [KNL]
2787 Set task-shuffle interval (s). Shuffling tasks
2788 allows some CPUs to go into dyntick-idle mode
2789 during the rcutorture test.
2791 rcutorture.shutdown_secs= [KNL]
2792 Set time (s) after boot system shutdown. This
2793 is useful for hands-off automated testing.
2795 rcutorture.stall_cpu= [KNL]
2796 Duration of CPU stall (s) to test RCU CPU stall
2797 warnings, zero to disable.
2799 rcutorture.stall_cpu_holdoff= [KNL]
2800 Time to wait (s) after boot before inducing stall.
2802 rcutorture.stat_interval= [KNL]
2803 Time (s) between statistics printk()s.
2805 rcutorture.stutter= [KNL]
2806 Time (s) to stutter testing, for example, specifying
2807 five seconds causes the test to run for five seconds,
2808 wait for five seconds, and so on. This tests RCU's
2809 ability to transition abruptly to and from idle.
2811 rcutorture.test_boost= [KNL]
2812 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2813 "Maybe" means test if the RCU implementation
2814 under test support RCU priority boosting.
2816 rcutorture.test_boost_duration= [KNL]
2817 Duration (s) of each individual boost test.
2819 rcutorture.test_boost_interval= [KNL]
2820 Interval (s) between each boost test.
2822 rcutorture.test_no_idle_hz= [KNL]
2823 Test RCU's dyntick-idle handling. See also the
2824 rcutorture.shuffle_interval parameter.
2826 rcutorture.torture_type= [KNL]
2827 Specify the RCU implementation to test.
2829 rcutorture.verbose= [KNL]
2830 Enable additional printk() statements.
2832 rcupdate.rcu_expedited= [KNL]
2833 Use expedited grace-period primitives, for
2834 example, synchronize_rcu_expedited() instead
2835 of synchronize_rcu(). This reduces latency,
2836 but can increase CPU utilization, degrade
2837 real-time latency, and degrade energy efficiency.
2839 rcupdate.rcu_cpu_stall_suppress= [KNL]
2840 Suppress RCU CPU stall warning messages.
2842 rcupdate.rcu_cpu_stall_timeout= [KNL]
2843 Set timeout for RCU CPU stall warning messages.
2845 rdinit= [KNL]
2846 Format: <full_path>
2847 Run specified binary instead of /init from the ramdisk,
2848 used for early userspace startup. See initrd.
2850 reboot= [KNL]
2851 Format (x86 or x86_64):
2852 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2853 [[,]s[mp]#### \
2854 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2855 [[,]f[orce]
2856 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2857 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2858 reboot_force is either force or not specified,
2859 reboot_cpu is s[mp]#### with #### being the processor
2860 to be used for rebooting.
2862 relax_domain_level=
2863 [KNL, SMP] Set scheduler's default relax_domain_level.
2864 See Documentation/cgroups/cpusets.txt.
2866 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2868 reservetop= [X86-32]
2869 Format: nn[KMG]
2870 Reserves a hole at the top of the kernel virtual
2871 address space.
2873 reservelow= [X86]
2874 Format: nn[K]
2875 Set the amount of memory to reserve for BIOS at
2876 the bottom of the address space.
2878 reset_devices [KNL] Force drivers to reset the underlying device
2879 during initialization.
2881 resume= [SWSUSP]
2882 Specify the partition device for software suspend
2883 Format:
2884 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2886 resume_offset= [SWSUSP]
2887 Specify the offset from the beginning of the partition
2888 given by "resume=" at which the swap header is located,
2889 in <PAGE_SIZE> units (needed only for swap files).
2890 See Documentation/power/swsusp-and-swap-files.txt
2892 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2893 read the resume files
2895 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2896 Useful for devices that are detected asynchronously
2897 (e.g. USB and MMC devices).
2899 hibernate= [HIBERNATION]
2900 noresume Don't check if there's a hibernation image
2901 present during boot.
2902 nocompress Don't compress/decompress hibernation images.
2904 retain_initrd [RAM] Keep initrd memory after extraction
2906 rhash_entries= [KNL,NET]
2907 Set number of hash buckets for route cache
2909 riscom8= [HW,SERIAL]
2910 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2912 ro [KNL] Mount root device read-only on boot
2914 root= [KNL] Root filesystem
2915 See name_to_dev_t comment in init/do_mounts.c.
2917 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2918 mount the root filesystem
2920 rootflags= [KNL] Set root filesystem mount option string
2922 rootfstype= [KNL] Set root filesystem type
2924 rootwait [KNL] Wait (indefinitely) for root device to show up.
2925 Useful for devices that are detected asynchronously
2926 (e.g. USB and MMC devices).
2928 rproc_mem=nn[KMG][@address]
2929 [KNL,ARM,CMA] Remoteproc physical memory block.
2930 Memory area to be used by remote processor image,
2931 managed by CMA.
2933 rw [KNL] Mount root device read-write on boot
2935 S [KNL] Run init in single mode
2937 sa1100ir [NET]
2938 See drivers/net/irda/sa1100_ir.c.
2940 sbni= [NET] Granch SBNI12 leased line adapter
2942 sched_debug [KNL] Enables verbose scheduler debug messages.
2944 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2945 xtime_lock contention on larger systems, and/or RCU lock
2946 contention on all systems with CONFIG_MAXSMP set.
2947 Format: { "0" | "1" }
2948 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2949 1 -- enable.
2950 Note: increases power consumption, thus should only be
2951 enabled if running jitter sensitive (HPC/RT) workloads.
2953 security= [SECURITY] Choose a security module to enable at boot.
2954 If this boot parameter is not specified, only the first
2955 security module asking for security registration will be
2956 loaded. An invalid security module name will be treated
2957 as if no module has been chosen.
2959 selinux= [SELINUX] Disable or enable SELinux at boot time.
2960 Format: { "0" | "1" }
2961 See security/selinux/Kconfig help text.
2962 0 -- disable.
2963 1 -- enable.
2964 Default value is set via kernel config option.
2965 If enabled at boot time, /selinux/disable can be used
2966 later to disable prior to initial policy load.
2968 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2969 Format: { "0" | "1" }
2970 See security/apparmor/Kconfig help text
2971 0 -- disable.
2972 1 -- enable.
2973 Default value is set via kernel config option.
2975 serialnumber [BUGS=X86-32]
2977 shapers= [NET]
2978 Maximal number of shapers.
2980 show_msr= [x86] show boot-time MSR settings
2981 Format: { <integer> }
2982 Show boot-time (BIOS-initialized) MSR settings.
2983 The parameter means the number of CPUs to show,
2984 for example 1 means boot CPU only.
2986 simeth= [IA-64]
2987 simscsi=
2989 slram= [HW,MTD]
2991 slab_max_order= [MM, SLAB]
2992 Determines the maximum allowed order for slabs.
2993 A high setting may cause OOMs due to memory
2994 fragmentation. Defaults to 1 for systems with
2995 more than 32MB of RAM, 0 otherwise.
2997 slub_debug[=options[,slabs]] [MM, SLUB]
2998 Enabling slub_debug allows one to determine the
2999 culprit if slab objects become corrupted. Enabling
3000 slub_debug can create guard zones around objects and
3001 may poison objects when not in use. Also tracks the
3002 last alloc / free. For more information see
3003 Documentation/vm/slub.txt.
3005 slub_max_order= [MM, SLUB]
3006 Determines the maximum allowed order for slabs.
3007 A high setting may cause OOMs due to memory
3008 fragmentation. For more information see
3009 Documentation/vm/slub.txt.
3011 slub_min_objects= [MM, SLUB]
3012 The minimum number of objects per slab. SLUB will
3013 increase the slab order up to slub_max_order to
3014 generate a sufficiently large slab able to contain
3015 the number of objects indicated. The higher the number
3016 of objects the smaller the overhead of tracking slabs
3017 and the less frequently locks need to be acquired.
3018 For more information see Documentation/vm/slub.txt.
3020 slub_min_order= [MM, SLUB]
3021 Determines the minimum page order for slabs. Must be
3022 lower than slub_max_order.
3023 For more information see Documentation/vm/slub.txt.
3025 slub_nomerge [MM, SLUB]
3026 Disable merging of slabs with similar size. May be
3027 necessary if there is some reason to distinguish
3028 allocs to different slabs. Debug options disable
3029 merging on their own.
3030 For more information see Documentation/vm/slub.txt.
3032 smart2= [HW]
3033 Format: <io1>[,<io2>[,...,<io8>]]
3035 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3036 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3037 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3038 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3039 smsc-ircc2.ircc_irq= [HW] IRQ line
3040 smsc-ircc2.ircc_dma= [HW] DMA channel
3041 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3042 0: Toshiba Satellite 1800 (GP data pin select)
3043 1: Fast pin select (default)
3044 2: ATC IRMode
3046 softlockup_panic=
3047 [KNL] Should the soft-lockup detector generate panics.
3048 Format: <integer>
3050 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3051 See Documentation/laptops/sonypi.txt
3053 specialix= [HW,SERIAL] Specialix multi-serial port adapter
3054 See Documentation/serial/specialix.txt.
3056 spia_io_base= [HW,MTD]
3057 spia_fio_base=
3058 spia_pedr=
3059 spia_peddr=
3061 stacktrace [FTRACE]
3062 Enabled the stack tracer on boot up.
3064 stacktrace_filter=[function-list]
3065 [FTRACE] Limit the functions that the stack tracer
3066 will trace at boot up. function-list is a comma separated
3067 list of functions. This list can be changed at run
3068 time by the stack_trace_filter file in the debugfs
3069 tracing directory. Note, this enables stack tracing
3070 and the stacktrace above is not needed.
3072 sti= [PARISC,HW]
3073 Format: <num>
3074 Set the STI (builtin display/keyboard on the HP-PARISC
3075 machines) console (graphic card) which should be used
3076 as the initial boot-console.
3077 See also comment in drivers/video/console/sticore.c.
3079 sti_font= [HW]
3080 See comment in drivers/video/console/sticore.c.
3082 stifb= [HW]
3083 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3085 sunrpc.min_resvport=
3086 sunrpc.max_resvport=
3087 [NFS,SUNRPC]
3088 SunRPC servers often require that client requests
3089 originate from a privileged port (i.e. a port in the
3090 range 0 < portnr < 1024).
3091 An administrator who wishes to reserve some of these
3092 ports for other uses may adjust the range that the
3093 kernel's sunrpc client considers to be privileged
3094 using these two parameters to set the minimum and
3095 maximum port values.
3097 sunrpc.pool_mode=
3098 [NFS]
3099 Control how the NFS server code allocates CPUs to
3100 service thread pools. Depending on how many NICs
3101 you have and where their interrupts are bound, this
3102 option will affect which CPUs will do NFS serving.
3103 Note: this parameter cannot be changed while the
3104 NFS server is running.
3106 auto the server chooses an appropriate mode
3107 automatically using heuristics
3108 global a single global pool contains all CPUs
3109 percpu one pool for each CPU
3110 pernode one pool for each NUMA node (equivalent
3111 to global on non-NUMA machines)
3113 sunrpc.tcp_slot_table_entries=
3114 sunrpc.udp_slot_table_entries=
3115 [NFS,SUNRPC]
3116 Sets the upper limit on the number of simultaneous
3117 RPC calls that can be sent from the client to a
3118 server. Increasing these values may allow you to
3119 improve throughput, but will also increase the
3120 amount of memory reserved for use by the client.
3122 swapaccount=[0|1]
3123 [KNL] Enable accounting of swap in memory resource
3124 controller if no parameter or 1 is given or disable
3125 it if 0 is given (See Documentation/cgroups/memory.txt)
3127 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3128 Format: { <int> | force }
3129 <int> -- Number of I/O TLB slabs
3130 force -- force using of bounce buffers even if they
3131 wouldn't be automatically used by the kernel
3133 switches= [HW,M68k]
3135 sysfs.deprecated=0|1 [KNL]
3136 Enable/disable old style sysfs layout for old udev
3137 on older distributions. When this option is enabled
3138 very new udev will not work anymore. When this option
3139 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3140 in older udev will not work anymore.
3141 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3142 the kernel configuration.
3144 sysrq_always_enabled
3145 [KNL]
3146 Ignore sysrq setting - this boot parameter will
3147 neutralize any effect of /proc/sys/kernel/sysrq.
3148 Useful for debugging.
3150 tdfx= [HW,DRM]
3152 test_suspend= [SUSPEND]
3153 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3154 standby suspend) as the system sleep state to briefly
3155 enter during system startup. The system is woken from
3156 this state using a wakeup-capable RTC alarm.
3158 thash_entries= [KNL,NET]
3159 Set number of hash buckets for TCP connection
3161 thermal.act= [HW,ACPI]
3162 -1: disable all active trip points in all thermal zones
3163 <degrees C>: override all lowest active trip points
3165 thermal.crt= [HW,ACPI]
3166 -1: disable all critical trip points in all thermal zones
3167 <degrees C>: override all critical trip points
3169 thermal.nocrt= [HW,ACPI]
3170 Set to disable actions on ACPI thermal zone
3171 critical and hot trip points.
3173 thermal.off= [HW,ACPI]
3174 1: disable ACPI thermal control
3176 thermal.psv= [HW,ACPI]
3177 -1: disable all passive trip points
3178 <degrees C>: override all passive trip points to this
3179 value
3181 thermal.tzp= [HW,ACPI]
3182 Specify global default ACPI thermal zone polling rate
3183 <deci-seconds>: poll all this frequency
3184 0: no polling (default)
3186 threadirqs [KNL]
3187 Force threading of all interrupt handlers except those
3188 marked explicitly IRQF_NO_THREAD.
3190 tmem [KNL,XEN]
3191 Enable the Transcendent memory driver if built-in.
3193 tmem.cleancache=0|1 [KNL, XEN]
3194 Default is on (1). Disable the usage of the cleancache
3195 API to send anonymous pages to the hypervisor.
3197 tmem.frontswap=0|1 [KNL, XEN]
3198 Default is on (1). Disable the usage of the frontswap
3199 API to send swap pages to the hypervisor. If disabled
3200 the selfballooning and selfshrinking are force disabled.
3202 tmem.selfballooning=0|1 [KNL, XEN]
3203 Default is on (1). Disable the driving of swap pages
3204 to the hypervisor.
3206 tmem.selfshrinking=0|1 [KNL, XEN]
3207 Default is on (1). Partial swapoff that immediately
3208 transfers pages from Xen hypervisor back to the
3209 kernel based on different criteria.
3211 topology= [S390]
3212 Format: {off | on}
3213 Specify if the kernel should make use of the cpu
3214 topology information if the hardware supports this.
3215 The scheduler will make use of this information and
3216 e.g. base its process migration decisions on it.
3217 Default is on.
3219 tp720= [HW,PS2]
3221 tpm_suspend_pcr=[HW,TPM]
3222 Format: integer pcr id
3223 Specify that at suspend time, the tpm driver
3224 should extend the specified pcr with zeros,
3225 as a workaround for some chips which fail to
3226 flush the last written pcr on TPM_SaveState.
3227 This will guarantee that all the other pcrs
3228 are saved.
3230 trace_buf_size=nn[KMG]
3231 [FTRACE] will set tracing buffer size.
3233 trace_event=[event-list]
3234 [FTRACE] Set and start specified trace events in order
3235 to facilitate early boot debugging.
3236 See also Documentation/trace/events.txt
3238 trace_options=[option-list]
3239 [FTRACE] Enable or disable tracer options at boot.
3240 The option-list is a comma delimited list of options
3241 that can be enabled or disabled just as if you were
3242 to echo the option name into
3244 /sys/kernel/debug/tracing/trace_options
3246 For example, to enable stacktrace option (to dump the
3247 stack trace of each event), add to the command line:
3249 trace_options=stacktrace
3251 See also Documentation/trace/ftrace.txt "trace options"
3252 section.
3254 traceoff_on_warning
3255 [FTRACE] enable this option to disable tracing when a
3256 warning is hit. This turns off "tracing_on". Tracing can
3257 be enabled again by echoing '1' into the "tracing_on"
3258 file located in /sys/kernel/debug/tracing/
3260 This option is useful, as it disables the trace before
3261 the WARNING dump is called, which prevents the trace to
3262 be filled with content caused by the warning output.
3264 This option can also be set at run time via the sysctl
3265 option: kernel/traceoff_on_warning
3267 transparent_hugepage=
3268 [KNL]
3269 Format: [always|madvise|never]
3270 Can be used to control the default behavior of the system
3271 with respect to transparent hugepages.
3272 See Documentation/vm/transhuge.txt for more details.
3274 tsc= Disable clocksource stability checks for TSC.
3275 Format: <string>
3276 [x86] reliable: mark tsc clocksource as reliable, this
3277 disables clocksource verification at runtime, as well
3278 as the stability checks done at bootup. Used to enable
3279 high-resolution timer mode on older hardware, and in
3280 virtualized environment.
3281 [x86] noirqtime: Do not use TSC to do irq accounting.
3282 Used to run time disable IRQ_TIME_ACCOUNTING on any
3283 platforms where RDTSC is slow and this accounting
3284 can add overhead.
3286 turbografx.map[2|3]= [HW,JOY]
3287 TurboGraFX parallel port interface
3288 Format:
3289 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3290 See also Documentation/input/joystick-parport.txt
3292 udbg-immortal [PPC] When debugging early kernel crashes that
3293 happen after console_init() and before a proper
3294 console driver takes over, this boot options might
3295 help "seeing" what's going on.
3297 uhash_entries= [KNL,NET]
3298 Set number of hash buckets for UDP/UDP-Lite connections
3300 uhci-hcd.ignore_oc=
3301 [USB] Ignore overcurrent events (default N).
3302 Some badly-designed motherboards generate lots of
3303 bogus events, for ports that aren't wired to
3304 anything. Set this parameter to avoid log spamming.
3305 Note that genuine overcurrent events won't be
3306 reported either.
3308 unknown_nmi_panic
3309 [X86] Cause panic on unknown NMI.
3311 usbcore.authorized_default=
3312 [USB] Default USB device authorization:
3313 (default -1 = authorized except for wireless USB,
3314 0 = not authorized, 1 = authorized)
3316 usbcore.autosuspend=
3317 [USB] The autosuspend time delay (in seconds) used
3318 for newly-detected USB devices (default 2). This
3319 is the time required before an idle device will be
3320 autosuspended. Devices for which the delay is set
3321 to a negative value won't be autosuspended at all.
3323 usbcore.usbfs_snoop=
3324 [USB] Set to log all usbfs traffic (default 0 = off).
3326 usbcore.blinkenlights=
3327 [USB] Set to cycle leds on hubs (default 0 = off).
3329 usbcore.old_scheme_first=
3330 [USB] Start with the old device initialization
3331 scheme (default 0 = off).
3333 usbcore.usbfs_memory_mb=
3334 [USB] Memory limit (in MB) for buffers allocated by
3335 usbfs (default = 16, 0 = max = 2047).
3337 usbcore.use_both_schemes=
3338 [USB] Try the other device initialization scheme
3339 if the first one fails (default 1 = enabled).
3341 usbcore.initial_descriptor_timeout=
3342 [USB] Specifies timeout for the initial 64-byte
3343 USB_REQ_GET_DESCRIPTOR request in milliseconds
3344 (default 5000 = 5.0 seconds).
3346 usbhid.mousepoll=
3347 [USBHID] The interval which mice are to be polled at.
3349 usb-storage.delay_use=
3350 [UMS] The delay in seconds before a new device is
3351 scanned for Logical Units (default 5).
3353 usb-storage.quirks=
3354 [UMS] A list of quirks entries to supplement or
3355 override the built-in unusual_devs list. List
3356 entries are separated by commas. Each entry has
3357 the form VID:PID:Flags where VID and PID are Vendor
3358 and Product ID values (4-digit hex numbers) and
3359 Flags is a set of characters, each corresponding
3360 to a common usb-storage quirk flag as follows:
3361 a = SANE_SENSE (collect more than 18 bytes
3362 of sense data);
3363 b = BAD_SENSE (don't collect more than 18
3364 bytes of sense data);
3365 c = FIX_CAPACITY (decrease the reported
3366 device capacity by one sector);
3367 d = NO_READ_DISC_INFO (don't use
3368 READ_DISC_INFO command);
3369 e = NO_READ_CAPACITY_16 (don't use
3370 READ_CAPACITY_16 command);
3371 h = CAPACITY_HEURISTICS (decrease the
3372 reported device capacity by one
3373 sector if the number is odd);
3374 i = IGNORE_DEVICE (don't bind to this
3375 device);
3376 l = NOT_LOCKABLE (don't try to lock and
3377 unlock ejectable media);
3378 m = MAX_SECTORS_64 (don't transfer more
3379 than 64 sectors = 32 KB at a time);
3380 n = INITIAL_READ10 (force a retry of the
3381 initial READ(10) command);
3382 o = CAPACITY_OK (accept the capacity
3383 reported by the device);
3384 p = WRITE_CACHE (the device cache is ON
3385 by default);
3386 r = IGNORE_RESIDUE (the device reports
3387 bogus residue values);
3388 s = SINGLE_LUN (the device has only one
3389 Logical Unit);
3390 w = NO_WP_DETECT (don't test whether the
3391 medium is write-protected).
3392 Example: quirks=0419:aaf5:rl,0421:0433:rc
3394 user_debug= [KNL,ARM]
3395 Format: <int>
3396 See arch/arm/Kconfig.debug help text.
3397 1 - undefined instruction events
3398 2 - system calls
3399 4 - invalid data aborts
3400 8 - SIGSEGV faults
3401 16 - SIGBUS faults
3402 Example: user_debug=31
3404 userpte=
3405 [X86] Flags controlling user PTE allocations.
3407 nohigh = do not allocate PTE pages in
3408 HIGHMEM regardless of setting
3409 of CONFIG_HIGHPTE.
3411 vdso= [X86,SH]
3412 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3413 vdso=1: enable VDSO (default)
3414 vdso=0: disable VDSO mapping
3416 vdso32= [X86]
3417 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3418 vdso32=1: enable 32-bit VDSO (default)
3419 vdso32=0: disable 32-bit VDSO mapping
3421 vector= [IA-64,SMP]
3422 vector=percpu: enable percpu vector domain
3424 video= [FB] Frame buffer configuration
3425 See Documentation/fb/modedb.txt.
3427 video.brightness_switch_enabled= [0,1]
3428 If set to 1, on receiving an ACPI notify event
3429 generated by hotkey, video driver will adjust brightness
3430 level and then send out the event to user space through
3431 the allocated input device; If set to 0, video driver
3432 will only send out the event without touching backlight
3433 brightness level.
3434 default: 1
3436 virtio_mmio.device=
3437 [VMMIO] Memory mapped virtio (platform) device.
3439 <size>@<baseaddr>:<irq>[:<id>]
3440 where:
3441 <size> := size (can use standard suffixes
3442 like K, M and G)
3443 <baseaddr> := physical base address
3444 <irq> := interrupt number (as passed to
3445 request_irq())
3446 <id> := (optional) platform device id
3447 example:
3448 virtio_mmio.device=1K@0x100b0000:48:7
3450 Can be used multiple times for multiple devices.
3452 vga= [BOOT,X86-32] Select a particular video mode
3453 See Documentation/x86/boot.txt and
3454 Documentation/svga.txt.
3455 Use vga=ask for menu.
3456 This is actually a boot loader parameter; the value is
3457 passed to the kernel using a special protocol.
3459 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3460 size of <nn>. This can be used to increase the
3461 minimum size (128MB on x86). It can also be used to
3462 decrease the size and leave more room for directly
3463 mapped kernel RAM.
3465 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3466 Format: <command>
3468 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3469 Format: <command>
3471 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3472 Format: <command>
3474 vsyscall= [X86-64]
3475 Controls the behavior of vsyscalls (i.e. calls to
3476 fixed addresses of 0xffffffffff600x00 from legacy
3477 code). Most statically-linked binaries and older
3478 versions of glibc use these calls. Because these
3479 functions are at fixed addresses, they make nice
3480 targets for exploits that can control RIP.
3482 emulate [default] Vsyscalls turn into traps and are
3483 emulated reasonably safely.
3485 native Vsyscalls are native syscall instructions.
3486 This is a little bit faster than trapping
3487 and makes a few dynamic recompilers work
3488 better than they would in emulation mode.
3489 It also makes exploits much easier to write.
3491 none Vsyscalls don't work at all. This makes
3492 them quite hard to use for exploits but
3493 might break your system.
3495 vt.color= [VT] Default text color.
3496 Format: 0xYX, X = foreground, Y = background.
3497 Default: 0x07 = light gray on black.
3499 vt.cur_default= [VT] Default cursor shape.
3500 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3501 the parameters of the <Esc>[?A;B;Cc escape sequence;
3502 see VGA-softcursor.txt. Default: 2 = underline.
3504 vt.default_blu= [VT]
3505 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3506 Change the default blue palette of the console.
3507 This is a 16-member array composed of values
3508 ranging from 0-255.
3510 vt.default_grn= [VT]
3511 Format: <green0>,<green1>,<green2>,...,<green15>
3512 Change the default green palette of the console.
3513 This is a 16-member array composed of values
3514 ranging from 0-255.
3516 vt.default_red= [VT]
3517 Format: <red0>,<red1>,<red2>,...,<red15>
3518 Change the default red palette of the console.
3519 This is a 16-member array composed of values
3520 ranging from 0-255.
3522 vt.default_utf8=
3523 [VT]
3524 Format=<0|1>
3525 Set system-wide default UTF-8 mode for all tty's.
3526 Default is 1, i.e. UTF-8 mode is enabled for all
3527 newly opened terminals.
3529 vt.global_cursor_default=
3530 [VT]
3531 Format=<-1|0|1>
3532 Set system-wide default for whether a cursor
3533 is shown on new VTs. Default is -1,
3534 i.e. cursors will be created by default unless
3535 overridden by individual drivers. 0 will hide
3536 cursors, 1 will display them.
3538 vt.italic= [VT] Default color for italic text; 0-15.
3539 Default: 2 = green.
3541 vt.underline= [VT] Default color for underlined text; 0-15.
3542 Default: 3 = cyan.
3544 watchdog timers [HW,WDT] For information on watchdog timers,
3545 see Documentation/watchdog/watchdog-parameters.txt
3546 or other driver-specific files in the
3547 Documentation/watchdog/ directory.
3549 workqueue.disable_numa
3550 By default, all work items queued to unbound
3551 workqueues are affine to the NUMA nodes they're
3552 issued on, which results in better behavior in
3553 general. If NUMA affinity needs to be disabled for
3554 whatever reason, this option can be used. Note
3555 that this also can be controlled per-workqueue for
3556 workqueues visible under /sys/bus/workqueue/.
3558 workqueue.power_efficient
3559 Per-cpu workqueues are generally preferred because
3560 they show better performance thanks to cache
3561 locality; unfortunately, per-cpu workqueues tend to
3562 be more power hungry than unbound workqueues.
3564 Enabling this makes the per-cpu workqueues which
3565 were observed to contribute significantly to power
3566 consumption unbound, leading to measurably lower
3567 power usage at the cost of small performance
3568 overhead.
3570 The default value of this parameter is determined by
3571 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3573 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3574 default x2apic cluster mode on platforms
3575 supporting x2apic.
3577 x86_intel_mid_timer= [X86-32,APBT]
3578 Choose timer option for x86 Intel MID platform.
3579 Two valid options are apbt timer only and lapic timer
3580 plus one apbt timer for broadcast timer.
3581 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3583 xen_emul_unplug= [HW,X86,XEN]
3584 Unplug Xen emulated devices
3585 Format: [unplug0,][unplug1]
3586 ide-disks -- unplug primary master IDE devices
3587 aux-ide-disks -- unplug non-primary-master IDE devices
3588 nics -- unplug network devices
3589 all -- unplug all emulated devices (NICs and IDE disks)
3590 unnecessary -- unplugging emulated devices is
3591 unnecessary even if the host did not respond to
3592 the unplug protocol
3593 never -- do not unplug even if version check succeeds
3595 xen_nopvspin [X86,XEN]
3596 Disables the ticketlock slowpath using Xen PV
3597 optimizations.
3599 xirc2ps_cs= [NET,PCMCIA]
3600 Format:
3601 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3603 ______________________________________________________________________
3605 TODO:
3607 Add more DRM drivers.