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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
1175 i8042.kbdreset [HW] Reset device connected to KBD port
1177 i810= [HW,DRM]
1179 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1180 indicates that the driver is running on unsupported
1181 hardware.
1182 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1183 does not match list of supported models.
1184 i8k.power_status
1185 [HW] Report power status in /proc/i8k
1186 (disabled by default)
1187 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1188 capability is set.
1190 i915.invert_brightness=
1191 [DRM] Invert the sense of the variable that is used to
1192 set the brightness of the panel backlight. Normally a
1193 brightness value of 0 indicates backlight switched off,
1194 and the maximum of the brightness value sets the backlight
1195 to maximum brightness. If this parameter is set to 0
1196 (default) and the machine requires it, or this parameter
1197 is set to 1, a brightness value of 0 sets the backlight
1198 to maximum brightness, and the maximum of the brightness
1199 value switches the backlight off.
1200 -1 -- never invert brightness
1201 0 -- machine default
1202 1 -- force brightness inversion
1204 icn= [HW,ISDN]
1205 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1207 ide-core.nodma= [HW] (E)IDE subsystem
1208 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1209 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1210 .cdrom .chs .ignore_cable are additional options
1211 See Documentation/ide/ide.txt.
1213 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1214 Claim all unknown PCI IDE storage controllers.
1216 idle= [X86]
1217 Format: idle=poll, idle=halt, idle=nomwait
1218 Poll forces a polling idle loop that can slightly
1219 improve the performance of waking up a idle CPU, but
1220 will use a lot of power and make the system run hot.
1221 Not recommended.
1222 idle=halt: Halt is forced to be used for CPU idle.
1223 In such case C2/C3 won't be used again.
1224 idle=nomwait: Disable mwait for CPU C-states
1226 ignore_loglevel [KNL]
1227 Ignore loglevel setting - this will print /all/
1228 kernel messages to the console. Useful for debugging.
1229 We also add it as printk module parameter, so users
1230 could change it dynamically, usually by
1231 /sys/module/printk/parameters/ignore_loglevel.
1233 ihash_entries= [KNL]
1234 Set number of hash buckets for inode cache.
1236 ima_appraise= [IMA] appraise integrity measurements
1237 Format: { "off" | "enforce" | "fix" }
1238 default: "enforce"
1240 ima_appraise_tcb [IMA]
1241 The builtin appraise policy appraises all files
1242 owned by uid=0.
1244 ima_hash= [IMA]
1245 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1246 | sha512 | ... }
1247 default: "sha1"
1249 The list of supported hash algorithms is defined
1250 in crypto/hash_info.h.
1252 ima_tcb [IMA]
1253 Load a policy which meets the needs of the Trusted
1254 Computing Base. This means IMA will measure all
1255 programs exec'd, files mmap'd for exec, and all files
1256 opened for read by uid=0.
1258 ima_template= [IMA]
1259 Select one of defined IMA measurements template formats.
1260 Formats: { "ima" | "ima-ng" }
1261 Default: "ima-ng"
1263 init= [KNL]
1264 Format: <full_path>
1265 Run specified binary instead of /sbin/init as init
1266 process.
1268 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1269 for working out where the kernel is dying during
1270 startup.
1272 initrd= [BOOT] Specify the location of the initial ramdisk
1274 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1275 Format: <irq>
1277 int_pln_enable [x86] Enable power limit notification interrupt
1279 integrity_audit=[IMA]
1280 Format: { "0" | "1" }
1281 0 -- basic integrity auditing messages. (Default)
1282 1 -- additional integrity auditing messages.
1284 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1285 on
1286 Enable intel iommu driver.
1287 off
1288 Disable intel iommu driver.
1289 igfx_off [Default Off]
1290 By default, gfx is mapped as normal device. If a gfx
1291 device has a dedicated DMAR unit, the DMAR unit is
1292 bypassed by not enabling DMAR with this option. In
1293 this case, gfx device will use physical address for
1294 DMA.
1295 forcedac [x86_64]
1296 With this option iommu will not optimize to look
1297 for io virtual address below 32-bit forcing dual
1298 address cycle on pci bus for cards supporting greater
1299 than 32-bit addressing. The default is to look
1300 for translation below 32-bit and if not available
1301 then look in the higher range.
1302 strict [Default Off]
1303 With this option on every unmap_single operation will
1304 result in a hardware IOTLB flush operation as opposed
1305 to batching them for performance.
1306 sp_off [Default Off]
1307 By default, super page will be supported if Intel IOMMU
1308 has the capability. With this option, super page will
1309 not be supported.
1311 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1312 0 disables intel_idle and fall back on acpi_idle.
1313 1 to 6 specify maximum depth of C-state.
1315 intel_pstate= [X86]
1316 disable
1317 Do not enable intel_pstate as the default
1318 scaling driver for the supported processors
1320 intremap= [X86-64, Intel-IOMMU]
1321 on enable Interrupt Remapping (default)
1322 off disable Interrupt Remapping
1323 nosid disable Source ID checking
1324 no_x2apic_optout
1325 BIOS x2APIC opt-out request will be ignored
1327 iomem= Disable strict checking of access to MMIO memory
1328 strict regions from userspace.
1329 relaxed
1331 iommu= [x86]
1332 off
1333 force
1334 noforce
1335 biomerge
1336 panic
1337 nopanic
1338 merge
1339 nomerge
1340 forcesac
1341 soft
1342 pt [x86, IA-64]
1345 io7= [HW] IO7 for Marvel based alpha systems
1346 See comment before marvel_specify_io7 in
1347 arch/alpha/kernel/core_marvel.c.
1349 io_delay= [X86] I/O delay method
1350 0x80
1351 Standard port 0x80 based delay
1352 0xed
1353 Alternate port 0xed based delay (needed on some systems)
1354 udelay
1355 Simple two microseconds delay
1356 none
1357 No delay
1359 ip= [IP_PNP]
1360 See Documentation/filesystems/nfs/nfsroot.txt.
1362 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1363 See comment before ip2_setup() in
1364 drivers/char/ip2/ip2base.c.
1366 irqfixup [HW]
1367 When an interrupt is not handled search all handlers
1368 for it. Intended to get systems with badly broken
1369 firmware running.
1371 irqpoll [HW]
1372 When an interrupt is not handled search all handlers
1373 for it. Also check all handlers each timer
1374 interrupt. Intended to get systems with badly broken
1375 firmware running.
1377 isapnp= [ISAPNP]
1378 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1380 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1381 Format:
1382 <cpu number>,...,<cpu number>
1383 or
1384 <cpu number>-<cpu number>
1385 (must be a positive range in ascending order)
1386 or a mixture
1387 <cpu number>,...,<cpu number>-<cpu number>
1389 This option can be used to specify one or more CPUs
1390 to isolate from the general SMP balancing and scheduling
1391 algorithms. You can move a process onto or off an
1392 "isolated" CPU via the CPU affinity syscalls or cpuset.
1393 <cpu number> begins at 0 and the maximum value is
1394 "number of CPUs in system - 1".
1396 This option is the preferred way to isolate CPUs. The
1397 alternative -- manually setting the CPU mask of all
1398 tasks in the system -- can cause problems and
1399 suboptimal load balancer performance.
1401 iucv= [HW,NET]
1403 ivrs_ioapic [HW,X86_64]
1404 Provide an override to the IOAPIC-ID<->DEVICE-ID
1405 mapping provided in the IVRS ACPI table. For
1406 example, to map IOAPIC-ID decimal 10 to
1407 PCI device 00:14.0 write the parameter as:
1408 ivrs_ioapic[10]=00:14.0
1410 ivrs_hpet [HW,X86_64]
1411 Provide an override to the HPET-ID<->DEVICE-ID
1412 mapping provided in the IVRS ACPI table. For
1413 example, to map HPET-ID decimal 0 to
1414 PCI device 00:14.0 write the parameter as:
1415 ivrs_hpet[0]=00:14.0
1417 js= [HW,JOY] Analog joystick
1418 See Documentation/input/joystick.txt.
1420 keepinitrd [HW,ARM]
1422 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1423 specifies the amount of memory usable by the kernel
1424 for non-movable allocations. The requested amount is
1425 spread evenly throughout all nodes in the system. The
1426 remaining memory in each node is used for Movable
1427 pages. In the event, a node is too small to have both
1428 kernelcore and Movable pages, kernelcore pages will
1429 take priority and other nodes will have a larger number
1430 of Movable pages. The Movable zone is used for the
1431 allocation of pages that may be reclaimed or moved
1432 by the page migration subsystem. This means that
1433 HugeTLB pages may not be allocated from this zone.
1434 Note that allocations like PTEs-from-HighMem still
1435 use the HighMem zone if it exists, and the Normal
1436 zone if it does not.
1438 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1439 Format: <Controller#>[,poll interval]
1440 The controller # is the number of the ehci usb debug
1441 port as it is probed via PCI. The poll interval is
1442 optional and is the number seconds in between
1443 each poll cycle to the debug port in case you need
1444 the functionality for interrupting the kernel with
1445 gdb or control-c on the dbgp connection. When
1446 not using this parameter you use sysrq-g to break into
1447 the kernel debugger.
1449 kgdboc= [KGDB,HW] kgdb over consoles.
1450 Requires a tty driver that supports console polling,
1451 or a supported polling keyboard driver (non-usb).
1452 Serial only format: <serial_device>[,baud]
1453 keyboard only format: kbd
1454 keyboard and serial format: kbd,<serial_device>[,baud]
1455 Optional Kernel mode setting:
1456 kms, kbd format: kms,kbd
1457 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1459 kgdbwait [KGDB] Stop kernel execution and enter the
1460 kernel debugger at the earliest opportunity.
1462 kmac= [MIPS] korina ethernet MAC address.
1463 Configure the RouterBoard 532 series on-chip
1464 Ethernet adapter MAC address.
1466 kmemleak= [KNL] Boot-time kmemleak enable/disable
1467 Valid arguments: on, off
1468 Default: on
1470 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1471 Valid arguments: 0, 1, 2
1472 kmemcheck=0 (disabled)
1473 kmemcheck=1 (enabled)
1474 kmemcheck=2 (one-shot mode)
1475 Default: 2 (one-shot mode)
1477 kstack=N [X86] Print N words from the kernel stack
1478 in oops dumps.
1480 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1481 Default is 0 (don't ignore, but inject #GP)
1483 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1484 KVM MMU at runtime.
1485 Default is 0 (off)
1487 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1488 Default is 1 (enabled)
1490 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1491 for all guests.
1492 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1494 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1495 (virtualized MMU) support on capable Intel chips.
1496 Default is 1 (enabled)
1498 kvm-intel.emulate_invalid_guest_state=
1499 [KVM,Intel] Enable emulation of invalid guest states
1500 Default is 0 (disabled)
1502 kvm-intel.flexpriority=
1503 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1504 Default is 1 (enabled)
1506 kvm-intel.nested=
1507 [KVM,Intel] Enable VMX nesting (nVMX).
1508 Default is 0 (disabled)
1510 kvm-intel.unrestricted_guest=
1511 [KVM,Intel] Disable unrestricted guest feature
1512 (virtualized real and unpaged mode) on capable
1513 Intel chips. Default is 1 (enabled)
1515 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1516 feature (tagged TLBs) on capable Intel chips.
1517 Default is 1 (enabled)
1519 l2cr= [PPC]
1521 l3cr= [PPC]
1523 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1524 disabled it.
1526 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1527 value for LAPIC timer one-shot implementation. Default
1528 back to the programmable timer unit in the LAPIC.
1530 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1531 in C2 power state.
1533 libata.dma= [LIBATA] DMA control
1534 libata.dma=0 Disable all PATA and SATA DMA
1535 libata.dma=1 PATA and SATA Disk DMA only
1536 libata.dma=2 ATAPI (CDROM) DMA only
1537 libata.dma=4 Compact Flash DMA only
1538 Combinations also work, so libata.dma=3 enables DMA
1539 for disks and CDROMs, but not CFs.
1541 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1542 libata.ignore_hpa=0 keep BIOS limits (default)
1543 libata.ignore_hpa=1 ignore limits, using full disk
1545 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1546 when set.
1547 Format: <int>
1549 libata.force= [LIBATA] Force configurations. The format is comma
1550 separated list of "[ID:]VAL" where ID is
1551 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1552 matching port, link or device. Basically, it matches
1553 the ATA ID string printed on console by libata. If
1554 the whole ID part is omitted, the last PORT and DEVICE
1555 values are used. If ID hasn't been specified yet, the
1556 configuration applies to all ports, links and devices.
1558 If only DEVICE is omitted, the parameter applies to
1559 the port and all links and devices behind it. DEVICE
1560 number of 0 either selects the first device or the
1561 first fan-out link behind PMP device. It does not
1562 select the host link. DEVICE number of 15 selects the
1563 host link and device attached to it.
1565 The VAL specifies the configuration to force. As long
1566 as there's no ambiguity shortcut notation is allowed.
1567 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1568 The following configurations can be forced.
1570 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1571 Any ID with matching PORT is used.
1573 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1575 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1576 udma[/][16,25,33,44,66,100,133] notation is also
1577 allowed.
1579 * [no]ncq: Turn on or off NCQ.
1581 * nohrst, nosrst, norst: suppress hard, soft
1582 and both resets.
1584 * rstonce: only attempt one reset during
1585 hot-unplug link recovery
1587 * dump_id: dump IDENTIFY data.
1589 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1591 * disable: Disable this device.
1593 If there are multiple matching configurations changing
1594 the same attribute, the last one is used.
1596 memblock=debug [KNL] Enable memblock debug messages.
1598 load_ramdisk= [RAM] List of ramdisks to load from floppy
1599 See Documentation/blockdev/ramdisk.txt.
1601 lockd.nlm_grace_period=P [NFS] Assign grace period.
1602 Format: <integer>
1604 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1605 Format: <integer>
1607 lockd.nlm_timeout=T [NFS] Assign timeout value.
1608 Format: <integer>
1610 lockd.nlm_udpport=M [NFS] Assign UDP port.
1611 Format: <integer>
1613 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1614 Format: <irq>
1616 loglevel= All Kernel Messages with a loglevel smaller than the
1617 console loglevel will be printed to the console. It can
1618 also be changed with klogd or other programs. The
1619 loglevels are defined as follows:
1621 0 (KERN_EMERG) system is unusable
1622 1 (KERN_ALERT) action must be taken immediately
1623 2 (KERN_CRIT) critical conditions
1624 3 (KERN_ERR) error conditions
1625 4 (KERN_WARNING) warning conditions
1626 5 (KERN_NOTICE) normal but significant condition
1627 6 (KERN_INFO) informational
1628 7 (KERN_DEBUG) debug-level messages
1630 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1631 in bytes. n must be a power of two. The default
1632 size is set in the kernel config file.
1634 logo.nologo [FB] Disables display of the built-in Linux logo.
1635 This may be used to provide more screen space for
1636 kernel log messages and is useful when debugging
1637 kernel boot problems.
1639 lp=0 [LP] Specify parallel ports to use, e.g,
1640 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1641 lp=reset first parallel port). 'lp=0' disables the
1642 lp=auto printer driver. 'lp=reset' (which can be
1643 specified in addition to the ports) causes
1644 attached printers to be reset. Using
1645 lp=port1,port2,... specifies the parallel ports
1646 to associate lp devices with, starting with
1647 lp0. A port specification may be 'none' to skip
1648 that lp device, or a parport name such as
1649 'parport0'. Specifying 'lp=auto' instead of a
1650 port specification list means that device IDs
1651 from each port should be examined, to see if
1652 an IEEE 1284-compliant printer is attached; if
1653 so, the driver will manage that printer.
1654 See also header of drivers/char/lp.c.
1656 lpj=n [KNL]
1657 Sets loops_per_jiffy to given constant, thus avoiding
1658 time-consuming boot-time autodetection (up to 250 ms per
1659 CPU). 0 enables autodetection (default). To determine
1660 the correct value for your kernel, boot with normal
1661 autodetection and see what value is printed. Note that
1662 on SMP systems the preset will be applied to all CPUs,
1663 which is likely to cause problems if your CPUs need
1664 significantly divergent settings. An incorrect value
1665 will cause delays in the kernel to be wrong, leading to
1666 unpredictable I/O errors and other breakage. Although
1667 unlikely, in the extreme case this might damage your
1668 hardware.
1670 ltpc= [NET]
1671 Format: <io>,<irq>,<dma>
1673 machvec= [IA-64] Force the use of a particular machine-vector
1674 (machvec) in a generic kernel.
1675 Example: machvec=hpzx1_swiotlb
1677 machtype= [Loongson] Share the same kernel image file between different
1678 yeeloong laptop.
1679 Example: machtype=lemote-yeeloong-2f-7inch
1681 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1682 than or equal to this physical address is ignored.
1684 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1685 should make use of. maxcpus=n : n >= 0 limits the
1686 kernel to using 'n' processors. n=0 is a special case,
1687 it is equivalent to "nosmp", which also disables
1688 the IO APIC.
1690 max_loop= [LOOP] The number of loop block devices that get
1691 (loop.max_loop) unconditionally pre-created at init time. The default
1692 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1693 of statically allocating a predefined number, loop
1694 devices can be requested on-demand with the
1695 /dev/loop-control interface.
1697 mce [X86-32] Machine Check Exception
1699 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1701 md= [HW] RAID subsystems devices and level
1702 See Documentation/md.txt.
1704 mdacon= [MDA]
1705 Format: <first>,<last>
1706 Specifies range of consoles to be captured by the MDA.
1708 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1709 Amount of memory to be used when the kernel is not able
1710 to see the whole system memory or for test.
1711 [X86] Work as limiting max address. Use together
1712 with memmap= to avoid physical address space collisions.
1713 Without memmap= PCI devices could be placed at addresses
1714 belonging to unused RAM.
1716 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1717 memory.
1719 memchunk=nn[KMG]
1720 [KNL,SH] Allow user to override the default size for
1721 per-device physically contiguous DMA buffers.
1723 memmap=exactmap [KNL,X86] Enable setting of an exact
1724 E820 memory map, as specified by the user.
1725 Such memmap=exactmap lines can be constructed based on
1726 BIOS output or other requirements. See the memmap=nn@ss
1727 option description.
1729 memmap=nn[KMG]@ss[KMG]
1730 [KNL] Force usage of a specific region of memory.
1731 Region of memory to be used is from ss to ss+nn.
1733 memmap=nn[KMG]#ss[KMG]
1734 [KNL,ACPI] Mark specific memory as ACPI data.
1735 Region of memory to be marked is from ss to ss+nn.
1737 memmap=nn[KMG]$ss[KMG]
1738 [KNL,ACPI] Mark specific memory as reserved.
1739 Region of memory to be reserved is from ss to ss+nn.
1740 Example: Exclude memory from 0x18690000-0x1869ffff
1741 memmap=64K$0x18690000
1742 or
1743 memmap=0x10000$0x18690000
1745 memory_corruption_check=0/1 [X86]
1746 Some BIOSes seem to corrupt the first 64k of
1747 memory when doing things like suspend/resume.
1748 Setting this option will scan the memory
1749 looking for corruption. Enabling this will
1750 both detect corruption and prevent the kernel
1751 from using the memory being corrupted.
1752 However, its intended as a diagnostic tool; if
1753 repeatable BIOS-originated corruption always
1754 affects the same memory, you can use memmap=
1755 to prevent the kernel from using that memory.
1757 memory_corruption_check_size=size [X86]
1758 By default it checks for corruption in the low
1759 64k, making this memory unavailable for normal
1760 use. Use this parameter to scan for
1761 corruption in more or less memory.
1763 memory_corruption_check_period=seconds [X86]
1764 By default it checks for corruption every 60
1765 seconds. Use this parameter to check at some
1766 other rate. 0 disables periodic checking.
1768 memtest= [KNL,X86] Enable memtest
1769 Format: <integer>
1770 default : 0 <disable>
1771 Specifies the number of memtest passes to be
1772 performed. Each pass selects another test
1773 pattern from a given set of patterns. Memtest
1774 fills the memory with this pattern, validates
1775 memory contents and reserves bad memory
1776 regions that are detected.
1778 meye.*= [HW] Set MotionEye Camera parameters
1779 See Documentation/video4linux/meye.txt.
1781 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1782 Multi-Function General Purpose Timers on AMD Geode
1783 platforms.
1785 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1786 the BIOS has incorrectly applied a workaround. TinyBIOS
1787 version 0.98 is known to be affected, 0.99 fixes the
1788 problem by letting the user disable the workaround.
1790 mga= [HW,DRM]
1792 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1793 physical address is ignored.
1795 mini2440= [ARM,HW,KNL]
1796 Format:[0..2][b][c][t]
1797 Default: "0tb"
1798 MINI2440 configuration specification:
1799 0 - The attached screen is the 3.5" TFT
1800 1 - The attached screen is the 7" TFT
1801 2 - The VGA Shield is attached (1024x768)
1802 Leaving out the screen size parameter will not load
1803 the TFT driver, and the framebuffer will be left
1804 unconfigured.
1805 b - Enable backlight. The TFT backlight pin will be
1806 linked to the kernel VESA blanking code and a GPIO
1807 LED. This parameter is not necessary when using the
1808 VGA shield.
1809 c - Enable the s3c camera interface.
1810 t - Reserved for enabling touchscreen support. The
1811 touchscreen support is not enabled in the mainstream
1812 kernel as of 2.6.30, a preliminary port can be found
1813 in the "bleeding edge" mini2440 support kernel at
1814 http://repo.or.cz/w/linux-2.6/mini2440.git
1816 mminit_loglevel=
1817 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1818 parameter allows control of the logging verbosity for
1819 the additional memory initialisation checks. A value
1820 of 0 disables mminit logging and a level of 4 will
1821 log everything. Information is printed at KERN_DEBUG
1822 so loglevel=8 may also need to be specified.
1824 module.sig_enforce
1825 [KNL] When CONFIG_MODULE_SIG is set, this means that
1826 modules without (valid) signatures will fail to load.
1827 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1828 is always true, so this option does nothing.
1830 mousedev.tap_time=
1831 [MOUSE] Maximum time between finger touching and
1832 leaving touchpad surface for touch to be considered
1833 a tap and be reported as a left button click (for
1834 touchpads working in absolute mode only).
1835 Format: <msecs>
1836 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1837 reporting absolute coordinates, such as tablets
1838 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1839 reporting absolute coordinates, such as tablets
1841 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1842 is similar to kernelcore except it specifies the
1843 amount of memory used for migratable allocations.
1844 If both kernelcore and movablecore is specified,
1845 then kernelcore will be at *least* the specified
1846 value but may be more. If movablecore on its own
1847 is specified, the administrator must be careful
1848 that the amount of memory usable for all allocations
1849 is not too small.
1851 movable_node [KNL,X86] Boot-time switch to enable the effects
1852 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
1854 MTD_Partition= [MTD]
1855 Format: <name>,<region-number>,<size>,<offset>
1857 MTD_Region= [MTD] Format:
1858 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1860 mtdparts= [MTD]
1861 See drivers/mtd/cmdlinepart.c.
1863 multitce=off [PPC] This parameter disables the use of the pSeries
1864 firmware feature for updating multiple TCE entries
1865 at a time.
1867 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1869 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1871 boundary - index of last SLC block on Flex-OneNAND.
1872 The remaining blocks are configured as MLC blocks.
1873 lock - Configure if Flex-OneNAND boundary should be locked.
1874 Once locked, the boundary cannot be changed.
1875 1 indicates lock status, 0 indicates unlock status.
1877 mtdset= [ARM]
1878 ARM/S3C2412 JIVE boot control
1880 See arch/arm/mach-s3c2412/mach-jive.c
1882 mtouchusb.raw_coordinates=
1883 [HW] Make the MicroTouch USB driver use raw coordinates
1884 ('y', default) or cooked coordinates ('n')
1886 mtrr_chunk_size=nn[KMG] [X86]
1887 used for mtrr cleanup. It is largest continuous chunk
1888 that could hold holes aka. UC entries.
1890 mtrr_gran_size=nn[KMG] [X86]
1891 Used for mtrr cleanup. It is granularity of mtrr block.
1892 Default is 1.
1893 Large value could prevent small alignment from
1894 using up MTRRs.
1896 mtrr_spare_reg_nr=n [X86]
1897 Format: <integer>
1898 Range: 0,7 : spare reg number
1899 Default : 1
1900 Used for mtrr cleanup. It is spare mtrr entries number.
1901 Set to 2 or more if your graphical card needs more.
1903 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1905 netdev= [NET] Network devices parameters
1906 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1907 Note that mem_start is often overloaded to mean
1908 something different and driver-specific.
1909 This usage is only documented in each driver source
1910 file if at all.
1912 nf_conntrack.acct=
1913 [NETFILTER] Enable connection tracking flow accounting
1914 0 to disable accounting
1915 1 to enable accounting
1916 Default value is 0.
1918 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1919 See Documentation/filesystems/nfs/nfsroot.txt.
1921 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1922 See Documentation/filesystems/nfs/nfsroot.txt.
1924 nfsrootdebug [NFS] enable nfsroot debugging messages.
1925 See Documentation/filesystems/nfs/nfsroot.txt.
1927 nfs.callback_tcpport=
1928 [NFS] set the TCP port on which the NFSv4 callback
1929 channel should listen.
1931 nfs.cache_getent=
1932 [NFS] sets the pathname to the program which is used
1933 to update the NFS client cache entries.
1935 nfs.cache_getent_timeout=
1936 [NFS] sets the timeout after which an attempt to
1937 update a cache entry is deemed to have failed.
1939 nfs.idmap_cache_timeout=
1940 [NFS] set the maximum lifetime for idmapper cache
1941 entries.
1943 nfs.enable_ino64=
1944 [NFS] enable 64-bit inode numbers.
1945 If zero, the NFS client will fake up a 32-bit inode
1946 number for the readdir() and stat() syscalls instead
1947 of returning the full 64-bit number.
1948 The default is to return 64-bit inode numbers.
1950 nfs.max_session_slots=
1951 [NFSv4.1] Sets the maximum number of session slots
1952 the client will attempt to negotiate with the server.
1953 This limits the number of simultaneous RPC requests
1954 that the client can send to the NFSv4.1 server.
1955 Note that there is little point in setting this
1956 value higher than the max_tcp_slot_table_limit.
1958 nfs.nfs4_disable_idmapping=
1959 [NFSv4] When set to the default of '1', this option
1960 ensures that both the RPC level authentication
1961 scheme and the NFS level operations agree to use
1962 numeric uids/gids if the mount is using the
1963 'sec=sys' security flavour. In effect it is
1964 disabling idmapping, which can make migration from
1965 legacy NFSv2/v3 systems to NFSv4 easier.
1966 Servers that do not support this mode of operation
1967 will be autodetected by the client, and it will fall
1968 back to using the idmapper.
1969 To turn off this behaviour, set the value to '0'.
1970 nfs.nfs4_unique_id=
1971 [NFS4] Specify an additional fixed unique ident-
1972 ification string that NFSv4 clients can insert into
1973 their nfs_client_id4 string. This is typically a
1974 UUID that is generated at system install time.
1976 nfs.send_implementation_id =
1977 [NFSv4.1] Send client implementation identification
1978 information in exchange_id requests.
1979 If zero, no implementation identification information
1980 will be sent.
1981 The default is to send the implementation identification
1982 information.
1984 nfs.recover_lost_locks =
1985 [NFSv4] Attempt to recover locks that were lost due
1986 to a lease timeout on the server. Please note that
1987 doing this risks data corruption, since there are
1988 no guarantees that the file will remain unchanged
1989 after the locks are lost.
1990 If you want to enable the kernel legacy behaviour of
1991 attempting to recover these locks, then set this
1992 parameter to '1'.
1993 The default parameter value of '0' causes the kernel
1994 not to attempt recovery of lost locks.
1996 nfsd.nfs4_disable_idmapping=
1997 [NFSv4] When set to the default of '1', the NFSv4
1998 server will return only numeric uids and gids to
1999 clients using auth_sys, and will accept numeric uids
2000 and gids from such clients. This is intended to ease
2001 migration from NFSv2/v3.
2003 objlayoutdriver.osd_login_prog=
2004 [NFS] [OBJLAYOUT] sets the pathname to the program which
2005 is used to automatically discover and login into new
2006 osd-targets. Please see:
2007 Documentation/filesystems/pnfs.txt for more explanations
2009 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2010 when a NMI is triggered.
2011 Format: [state][,regs][,debounce][,die]
2013 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2014 Format: [panic,][nopanic,][num]
2015 Valid num: 0
2016 0 - turn nmi_watchdog off
2017 When panic is specified, panic when an NMI watchdog
2018 timeout occurs (or 'nopanic' to override the opposite
2019 default).
2020 This is useful when you use a panic=... timeout and
2021 need the box quickly up again.
2023 netpoll.carrier_timeout=
2024 [NET] Specifies amount of time (in seconds) that
2025 netpoll should wait for a carrier. By default netpoll
2026 waits 4 seconds.
2028 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2029 emulation library even if a 387 maths coprocessor
2030 is present.
2032 no_console_suspend
2033 [HW] Never suspend the console
2034 Disable suspending of consoles during suspend and
2035 hibernate operations. Once disabled, debugging
2036 messages can reach various consoles while the rest
2037 of the system is being put to sleep (ie, while
2038 debugging driver suspend/resume hooks). This may
2039 not work reliably with all consoles, but is known
2040 to work with serial and VGA consoles.
2041 To facilitate more flexible debugging, we also add
2042 console_suspend, a printk module parameter to control
2043 it. Users could use console_suspend (usually
2044 /sys/module/printk/parameters/console_suspend) to
2045 turn on/off it dynamically.
2047 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2048 caches in the slab allocator. Saves per-node memory,
2049 but will impact performance.
2051 noalign [KNL,ARM]
2053 noapic [SMP,APIC] Tells the kernel to not make use of any
2054 IOAPICs that may be present in the system.
2056 nokaslr [X86]
2057 Disable kernel base offset ASLR (Address Space
2058 Layout Randomization) if built into the kernel.
2060 noautogroup Disable scheduler automatic task group creation.
2062 nobats [PPC] Do not use BATs for mapping kernel lowmem
2063 on "Classic" PPC cores.
2065 nocache [ARM]
2067 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2069 nodelayacct [KNL] Disable per-task delay accounting
2071 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2073 nodsp [SH] Disable hardware DSP at boot time.
2075 noefi [X86] Disable EFI runtime services support.
2077 noexec [IA-64]
2079 noexec [X86]
2080 On X86-32 available only on PAE configured kernels.
2081 noexec=on: enable non-executable mappings (default)
2082 noexec=off: disable non-executable mappings
2084 nosmap [X86]
2085 Disable SMAP (Supervisor Mode Access Prevention)
2086 even if it is supported by processor.
2088 nosmep [X86]
2089 Disable SMEP (Supervisor Mode Execution Prevention)
2090 even if it is supported by processor.
2092 noexec32 [X86-64]
2093 This affects only 32-bit executables.
2094 noexec32=on: enable non-executable mappings (default)
2095 read doesn't imply executable mappings
2096 noexec32=off: disable non-executable mappings
2097 read implies executable mappings
2099 nofpu [SH] Disable hardware FPU at boot time.
2101 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2102 register save and restore. The kernel will only save
2103 legacy floating-point registers on task switch.
2105 noxsave [BUGS=X86] Disables x86 extended register state save
2106 and restore using xsave. The kernel will fallback to
2107 enabling legacy floating-point and sse state.
2109 eagerfpu= [X86]
2110 on enable eager fpu restore
2111 off disable eager fpu restore
2112 auto selects the default scheme, which automatically
2113 enables eagerfpu restore for xsaveopt.
2115 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2116 wfi(ARM) instruction doesn't work correctly and not to
2117 use it. This is also useful when using JTAG debugger.
2119 no_file_caps Tells the kernel not to honor file capabilities. The
2120 only way then for a file to be executed with privilege
2121 is to be setuid root or executed by root.
2123 nohalt [IA-64] Tells the kernel not to use the power saving
2124 function PAL_HALT_LIGHT when idle. This increases
2125 power-consumption. On the positive side, it reduces
2126 interrupt wake-up latency, which may improve performance
2127 in certain environments such as networked servers or
2128 real-time systems.
2130 nohz= [KNL] Boottime enable/disable dynamic ticks
2131 Valid arguments: on, off
2132 Default: on
2134 nohz_full= [KNL,BOOT]
2135 In kernels built with CONFIG_NO_HZ_FULL=y, set
2136 the specified list of CPUs whose tick will be stopped
2137 whenever possible. The boot CPU will be forced outside
2138 the range to maintain the timekeeping.
2139 The CPUs in this range must also be included in the
2140 rcu_nocbs= set.
2142 noiotrap [SH] Disables trapped I/O port accesses.
2144 noirqdebug [X86-32] Disables the code which attempts to detect and
2145 disable unhandled interrupt sources.
2147 no_timer_check [X86,APIC] Disables the code which tests for
2148 broken timer IRQ sources.
2150 noisapnp [ISAPNP] Disables ISA PnP code.
2152 noinitrd [RAM] Tells the kernel not to load any configured
2153 initial RAM disk.
2155 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2156 remapping.
2157 [Deprecated - use intremap=off]
2159 nointroute [IA-64]
2161 nojitter [IA-64] Disables jitter checking for ITC timers.
2163 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2165 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2166 fault handling.
2168 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2169 steal time is computed, but won't influence scheduler
2170 behaviour
2172 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2174 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2176 noltlbs [PPC] Do not use large page/tlb entries for kernel
2177 lowmem mapping on PPC40x.
2179 nomca [IA-64] Disable machine check abort handling
2181 nomce [X86-32] Machine Check Exception
2183 nomfgpt [X86-32] Disable Multi-Function General Purpose
2184 Timer usage (for AMD Geode machines).
2186 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2187 shutdown the other cpus. Instead use the REBOOT_VECTOR
2188 irq.
2190 nomodule Disable module load
2192 nopat [X86] Disable PAT (page attribute table extension of
2193 pagetables) support.
2195 norandmaps Don't use address space randomization. Equivalent to
2196 echo 0 > /proc/sys/kernel/randomize_va_space
2198 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2200 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2201 with UP alternatives
2203 nordrand [X86] Disable the direct use of the RDRAND
2204 instruction even if it is supported by the
2205 processor. RDRAND is still available to user
2206 space applications.
2208 noresume [SWSUSP] Disables resume and restores original swap
2209 space.
2211 no-scroll [VGA] Disables scrollback.
2212 This is required for the Braillex ib80-piezo Braille
2213 reader made by F.H. Papenmeier (Germany).
2215 nosbagart [IA-64]
2217 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2219 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2220 and disable the IO APIC. legacy for "maxcpus=0".
2222 nosoftlockup [KNL] Disable the soft-lockup detector.
2224 nosync [HW,M68K] Disables sync negotiation for all devices.
2226 notsc [BUGS=X86-32] Disable Time Stamp Counter
2228 nousb [USB] Disable the USB subsystem
2230 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2232 nowb [ARM]
2234 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2236 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2237 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2238 Some features depend on CPU0. Known dependencies are:
2239 1. Resume from suspend/hibernate depends on CPU0.
2240 Suspend/hibernate will fail if CPU0 is offline and you
2241 need to online CPU0 before suspend/hibernate.
2242 2. PIC interrupts also depend on CPU0. CPU0 can't be
2243 removed if a PIC interrupt is detected.
2244 It's said poweroff/reboot may depend on CPU0 on some
2245 machines although I haven't seen such issues so far
2246 after CPU0 is offline on a few tested machines.
2247 If the dependencies are under your control, you can
2248 turn on cpu0_hotplug.
2250 nptcg= [IA-64] Override max number of concurrent global TLB
2251 purges which is reported from either PAL_VM_SUMMARY or
2252 SAL PALO.
2254 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2255 could support. nr_cpus=n : n >= 1 limits the kernel to
2256 supporting 'n' processors. Later in runtime you can not
2257 use hotplug cpu feature to put more cpu back to online.
2258 just like you compile the kernel NR_CPUS=n
2260 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2262 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2263 Allowed values are enable and disable
2265 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2266 one of ['zone', 'node', 'default'] can be specified
2267 This can be set from sysctl after boot.
2268 See Documentation/sysctl/vm.txt for details.
2270 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2271 See Documentation/debugging-via-ohci1394.txt for more
2272 info.
2274 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2275 Rather than timing out after 20 ms if an EC
2276 command is not properly ACKed, override the length
2277 of the timeout. We have interrupts disabled while
2278 waiting for the ACK, so if this is set too high
2279 interrupts *may* be lost!
2281 omap_mux= [OMAP] Override bootloader pin multiplexing.
2282 Format: <mux_mode0.mode_name=value>...
2283 For example, to override I2C bus2:
2284 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2286 oprofile.timer= [HW]
2287 Use timer interrupt instead of performance counters
2289 oprofile.cpu_type= Force an oprofile cpu type
2290 This might be useful if you have an older oprofile
2291 userland or if you want common events.
2292 Format: { arch_perfmon }
2293 arch_perfmon: [X86] Force use of architectural
2294 perfmon on Intel CPUs instead of the
2295 CPU specific event set.
2296 timer: [X86] Force use of architectural NMI
2297 timer mode (see also oprofile.timer
2298 for generic hr timer mode)
2299 [s390] Force legacy basic mode sampling
2300 (report cpu_type "timer")
2302 oops=panic Always panic on oopses. Default is to just kill the
2303 process, but there is a small probability of
2304 deadlocking the machine.
2305 This will also cause panics on machine check exceptions.
2306 Useful together with panic=30 to trigger a reboot.
2308 OSS [HW,OSS]
2309 See Documentation/sound/oss/oss-parameters.txt
2311 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2312 timeout > 0: seconds before rebooting
2313 timeout = 0: wait forever
2314 timeout < 0: reboot immediately
2315 Format: <timeout>
2317 parkbd.port= [HW] Parallel port number the keyboard adapter is
2318 connected to, default is 0.
2319 Format: <parport#>
2320 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2321 0 for XT, 1 for AT (default is AT).
2322 Format: <mode>
2324 parport= [HW,PPT] Specify parallel ports. 0 disables.
2325 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2326 Use 'auto' to force the driver to use any
2327 IRQ/DMA settings detected (the default is to
2328 ignore detected IRQ/DMA settings because of
2329 possible conflicts). You can specify the base
2330 address, IRQ, and DMA settings; IRQ and DMA
2331 should be numbers, or 'auto' (for using detected
2332 settings on that particular port), or 'nofifo'
2333 (to avoid using a FIFO even if it is detected).
2334 Parallel ports are assigned in the order they
2335 are specified on the command line, starting
2336 with parport0.
2338 parport_init_mode= [HW,PPT]
2339 Configure VIA parallel port to operate in
2340 a specific mode. This is necessary on Pegasos
2341 computer where firmware has no options for setting
2342 up parallel port mode and sets it to spp.
2343 Currently this function knows 686a and 8231 chips.
2344 Format: [spp|ps2|epp|ecp|ecpepp]
2346 pause_on_oops=
2347 Halt all CPUs after the first oops has been printed for
2348 the specified number of seconds. This is to be used if
2349 your oopses keep scrolling off the screen.
2351 pcbit= [HW,ISDN]
2353 pcd. [PARIDE]
2354 See header of drivers/block/paride/pcd.c.
2355 See also Documentation/blockdev/paride.txt.
2357 pci=option[,option...] [PCI] various PCI subsystem options:
2358 earlydump [X86] dump PCI config space before the kernel
2359 changes anything
2360 off [X86] don't probe for the PCI bus
2361 bios [X86-32] force use of PCI BIOS, don't access
2362 the hardware directly. Use this if your machine
2363 has a non-standard PCI host bridge.
2364 nobios [X86-32] disallow use of PCI BIOS, only direct
2365 hardware access methods are allowed. Use this
2366 if you experience crashes upon bootup and you
2367 suspect they are caused by the BIOS.
2368 conf1 [X86] Force use of PCI Configuration
2369 Mechanism 1.
2370 conf2 [X86] Force use of PCI Configuration
2371 Mechanism 2.
2372 noaer [PCIE] If the PCIEAER kernel config parameter is
2373 enabled, this kernel boot option can be used to
2374 disable the use of PCIE advanced error reporting.
2375 nodomains [PCI] Disable support for multiple PCI
2376 root domains (aka PCI segments, in ACPI-speak).
2377 nommconf [X86] Disable use of MMCONFIG for PCI
2378 Configuration
2379 check_enable_amd_mmconf [X86] check for and enable
2380 properly configured MMIO access to PCI
2381 config space on AMD family 10h CPU
2382 nomsi [MSI] If the PCI_MSI kernel config parameter is
2383 enabled, this kernel boot option can be used to
2384 disable the use of MSI interrupts system-wide.
2385 noioapicquirk [APIC] Disable all boot interrupt quirks.
2386 Safety option to keep boot IRQs enabled. This
2387 should never be necessary.
2388 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2389 primary IO-APIC for bridges that cannot disable
2390 boot IRQs. This fixes a source of spurious IRQs
2391 when the system masks IRQs.
2392 noioapicreroute [APIC] Disable workaround that uses the
2393 boot IRQ equivalent of an IRQ that connects to
2394 a chipset where boot IRQs cannot be disabled.
2395 The opposite of ioapicreroute.
2396 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2397 routing table. These calls are known to be buggy
2398 on several machines and they hang the machine
2399 when used, but on other computers it's the only
2400 way to get the interrupt routing table. Try
2401 this option if the kernel is unable to allocate
2402 IRQs or discover secondary PCI buses on your
2403 motherboard.
2404 rom [X86] Assign address space to expansion ROMs.
2405 Use with caution as certain devices share
2406 address decoders between ROMs and other
2407 resources.
2408 norom [X86] Do not assign address space to
2409 expansion ROMs that do not already have
2410 BIOS assigned address ranges.
2411 nobar [X86] Do not assign address space to the
2412 BARs that weren't assigned by the BIOS.
2413 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2414 assigned automatically to PCI devices. You can
2415 make the kernel exclude IRQs of your ISA cards
2416 this way.
2417 pirqaddr=0xAAAAA [X86] Specify the physical address
2418 of the PIRQ table (normally generated
2419 by the BIOS) if it is outside the
2420 F0000h-100000h range.
2421 lastbus=N [X86] Scan all buses thru bus #N. Can be
2422 useful if the kernel is unable to find your
2423 secondary buses and you want to tell it
2424 explicitly which ones they are.
2425 assign-busses [X86] Always assign all PCI bus
2426 numbers ourselves, overriding
2427 whatever the firmware may have done.
2428 usepirqmask [X86] Honor the possible IRQ mask stored
2429 in the BIOS $PIR table. This is needed on
2430 some systems with broken BIOSes, notably
2431 some HP Pavilion N5400 and Omnibook XE3
2432 notebooks. This will have no effect if ACPI
2433 IRQ routing is enabled.
2434 noacpi [X86] Do not use ACPI for IRQ routing
2435 or for PCI scanning.
2436 use_crs [X86] Use PCI host bridge window information
2437 from ACPI. On BIOSes from 2008 or later, this
2438 is enabled by default. If you need to use this,
2439 please report a bug.
2440 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2441 If you need to use this, please report a bug.
2442 routeirq Do IRQ routing for all PCI devices.
2443 This is normally done in pci_enable_device(),
2444 so this option is a temporary workaround
2445 for broken drivers that don't call it.
2446 skip_isa_align [X86] do not align io start addr, so can
2447 handle more pci cards
2448 firmware [ARM] Do not re-enumerate the bus but instead
2449 just use the configuration from the
2450 bootloader. This is currently used on
2451 IXP2000 systems where the bus has to be
2452 configured a certain way for adjunct CPUs.
2453 noearly [X86] Don't do any early type 1 scanning.
2454 This might help on some broken boards which
2455 machine check when some devices' config space
2456 is read. But various workarounds are disabled
2457 and some IOMMU drivers will not work.
2458 bfsort Sort PCI devices into breadth-first order.
2459 This sorting is done to get a device
2460 order compatible with older (<= 2.4) kernels.
2461 nobfsort Don't sort PCI devices into breadth-first order.
2462 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2463 tuning and use the BIOS-configured MPS defaults.
2464 pcie_bus_safe Set every device's MPS to the largest value
2465 supported by all devices below the root complex.
2466 pcie_bus_perf Set device MPS to the largest allowable MPS
2467 based on its parent bus. Also set MRRS (Max
2468 Read Request Size) to the largest supported
2469 value (no larger than the MPS that the device
2470 or bus can support) for best performance.
2471 pcie_bus_peer2peer Set every device's MPS to 128B, which
2472 every device is guaranteed to support. This
2473 configuration allows peer-to-peer DMA between
2474 any pair of devices, possibly at the cost of
2475 reduced performance. This also guarantees
2476 that hot-added devices will work.
2477 cbiosize=nn[KMG] The fixed amount of bus space which is
2478 reserved for the CardBus bridge's IO window.
2479 The default value is 256 bytes.
2480 cbmemsize=nn[KMG] The fixed amount of bus space which is
2481 reserved for the CardBus bridge's memory
2482 window. The default value is 64 megabytes.
2483 resource_alignment=
2484 Format:
2485 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2486 Specifies alignment and device to reassign
2487 aligned memory resources.
2488 If <order of align> is not specified,
2489 PAGE_SIZE is used as alignment.
2490 PCI-PCI bridge can be specified, if resource
2491 windows need to be expanded.
2492 ecrc= Enable/disable PCIe ECRC (transaction layer
2493 end-to-end CRC checking).
2494 bios: Use BIOS/firmware settings. This is the
2495 the default.
2496 off: Turn ECRC off
2497 on: Turn ECRC on.
2498 hpiosize=nn[KMG] The fixed amount of bus space which is
2499 reserved for hotplug bridge's IO window.
2500 Default size is 256 bytes.
2501 hpmemsize=nn[KMG] The fixed amount of bus space which is
2502 reserved for hotplug bridge's memory window.
2503 Default size is 2 megabytes.
2504 realloc= Enable/disable reallocating PCI bridge resources
2505 if allocations done by BIOS are too small to
2506 accommodate resources required by all child
2507 devices.
2508 off: Turn realloc off
2509 on: Turn realloc on
2510 realloc same as realloc=on
2511 noari do not use PCIe ARI.
2512 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2513 only look for one device below a PCIe downstream
2514 port.
2516 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2517 Management.
2518 off Disable ASPM.
2519 force Enable ASPM even on devices that claim not to support it.
2520 WARNING: Forcing ASPM on may cause system lockups.
2522 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2523 nomsi Do not use MSI for PCI Express Native Hotplug (this
2524 makes all PCIe ports use INTx for hotplug services).
2526 pcie_ports= [PCIE] PCIe ports handling:
2527 auto Ask the BIOS whether or not to use native PCIe services
2528 associated with PCIe ports (PME, hot-plug, AER). Use
2529 them only if that is allowed by the BIOS.
2530 native Use native PCIe services associated with PCIe ports
2531 unconditionally.
2532 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2533 ports driver.
2535 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2536 nomsi Do not use MSI for native PCIe PME signaling (this makes
2537 all PCIe root ports use INTx for all services).
2539 pcmv= [HW,PCMCIA] BadgePAD 4
2541 pd. [PARIDE]
2542 See Documentation/blockdev/paride.txt.
2544 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2545 boot time.
2546 Format: { 0 | 1 }
2547 See arch/parisc/kernel/pdc_chassis.c
2549 percpu_alloc= Select which percpu first chunk allocator to use.
2550 Currently supported values are "embed" and "page".
2551 Archs may support subset or none of the selections.
2552 See comments in mm/percpu.c for details on each
2553 allocator. This parameter is primarily for debugging
2554 and performance comparison.
2556 pf. [PARIDE]
2557 See Documentation/blockdev/paride.txt.
2559 pg. [PARIDE]
2560 See Documentation/blockdev/paride.txt.
2562 pirq= [SMP,APIC] Manual mp-table setup
2563 See Documentation/x86/i386/IO-APIC.txt.
2565 plip= [PPT,NET] Parallel port network link
2566 Format: { parport<nr> | timid | 0 }
2567 See also Documentation/parport.txt.
2569 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2570 Override pmtimer IOPort with a hex value.
2571 e.g. pmtmr=0x508
2573 pnp.debug=1 [PNP]
2574 Enable PNP debug messages (depends on the
2575 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2576 via /sys/module/pnp/parameters/debug. We always show
2577 current resource usage; turning this on also shows
2578 possible settings and some assignment information.
2580 pnpacpi= [ACPI]
2581 { off }
2583 pnpbios= [ISAPNP]
2584 { on | off | curr | res | no-curr | no-res }
2586 pnp_reserve_irq=
2587 [ISAPNP] Exclude IRQs for the autoconfiguration
2589 pnp_reserve_dma=
2590 [ISAPNP] Exclude DMAs for the autoconfiguration
2592 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2593 Ranges are in pairs (I/O port base and size).
2595 pnp_reserve_mem=
2596 [ISAPNP] Exclude memory regions for the
2597 autoconfiguration.
2598 Ranges are in pairs (memory base and size).
2600 ports= [IP_VS_FTP] IPVS ftp helper module
2601 Default is 21.
2602 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2603 may be specified.
2604 Format: <port>,<port>....
2606 print-fatal-signals=
2607 [KNL] debug: print fatal signals
2609 If enabled, warn about various signal handling
2610 related application anomalies: too many signals,
2611 too many POSIX.1 timers, fatal signals causing a
2612 coredump - etc.
2614 If you hit the warning due to signal overflow,
2615 you might want to try "ulimit -i unlimited".
2617 default: off.
2619 printk.always_kmsg_dump=
2620 Trigger kmsg_dump for cases other than kernel oops or
2621 panics
2622 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2623 default: disabled
2625 printk.time= Show timing data prefixed to each printk message line
2626 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2628 processor.max_cstate= [HW,ACPI]
2629 Limit processor to maximum C-state
2630 max_cstate=9 overrides any DMI blacklist limit.
2632 processor.nocst [HW,ACPI]
2633 Ignore the _CST method to determine C-states,
2634 instead using the legacy FADT method
2636 profile= [KNL] Enable kernel profiling via /proc/profile
2637 Format: [schedule,]<number>
2638 Param: "schedule" - profile schedule points.
2639 Param: <number> - step/bucket size as a power of 2 for
2640 statistical time based profiling.
2641 Param: "sleep" - profile D-state sleeping (millisecs).
2642 Requires CONFIG_SCHEDSTATS
2643 Param: "kvm" - profile VM exits.
2645 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2646 before loading.
2647 See Documentation/blockdev/ramdisk.txt.
2649 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2650 probe for; one of (bare|imps|exps|lifebook|any).
2651 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2652 per second.
2653 psmouse.resetafter= [HW,MOUSE]
2654 Try to reset the device after so many bad packets
2655 (0 = never).
2656 psmouse.resolution=
2657 [HW,MOUSE] Set desired mouse resolution, in dpi.
2658 psmouse.smartscroll=
2659 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2660 0 = disabled, 1 = enabled (default).
2662 pstore.backend= Specify the name of the pstore backend to use
2664 pt. [PARIDE]
2665 See Documentation/blockdev/paride.txt.
2667 pty.legacy_count=
2668 [KNL] Number of legacy pty's. Overwrites compiled-in
2669 default number.
2671 quiet [KNL] Disable most log messages
2673 r128= [HW,DRM]
2675 raid= [HW,RAID]
2676 See Documentation/md.txt.
2678 ramdisk_blocksize= [RAM]
2679 See Documentation/blockdev/ramdisk.txt.
2681 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2682 See Documentation/blockdev/ramdisk.txt.
2684 rcu_nocbs= [KNL]
2685 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2686 the specified list of CPUs to be no-callback CPUs.
2687 Invocation of these CPUs' RCU callbacks will
2688 be offloaded to "rcuox/N" kthreads created for
2689 that purpose, where "x" is "b" for RCU-bh, "p"
2690 for RCU-preempt, and "s" for RCU-sched, and "N"
2691 is the CPU number. This reduces OS jitter on the
2692 offloaded CPUs, which can be useful for HPC and
2693 real-time workloads. It can also improve energy
2694 efficiency for asymmetric multiprocessors.
2696 rcu_nocb_poll [KNL]
2697 Rather than requiring that offloaded CPUs
2698 (specified by rcu_nocbs= above) explicitly
2699 awaken the corresponding "rcuoN" kthreads,
2700 make these kthreads poll for callbacks.
2701 This improves the real-time response for the
2702 offloaded CPUs by relieving them of the need to
2703 wake up the corresponding kthread, but degrades
2704 energy efficiency by requiring that the kthreads
2705 periodically wake up to do the polling.
2707 rcutree.blimit= [KNL]
2708 Set maximum number of finished RCU callbacks to
2709 process in one batch.
2711 rcutree.rcu_fanout_leaf= [KNL]
2712 Increase the number of CPUs assigned to each
2713 leaf rcu_node structure. Useful for very large
2714 systems.
2716 rcutree.jiffies_till_first_fqs= [KNL]
2717 Set delay from grace-period initialization to
2718 first attempt to force quiescent states.
2719 Units are jiffies, minimum value is zero,
2720 and maximum value is HZ.
2722 rcutree.jiffies_till_next_fqs= [KNL]
2723 Set delay between subsequent attempts to force
2724 quiescent states. Units are jiffies, minimum
2725 value is one, and maximum value is HZ.
2727 rcutree.qhimark= [KNL]
2728 Set threshold of queued RCU callbacks beyond which
2729 batch limiting is disabled.
2731 rcutree.qlowmark= [KNL]
2732 Set threshold of queued RCU callbacks below which
2733 batch limiting is re-enabled.
2735 rcutree.rcu_idle_gp_delay= [KNL]
2736 Set wakeup interval for idle CPUs that have
2737 RCU callbacks (RCU_FAST_NO_HZ=y).
2739 rcutree.rcu_idle_lazy_gp_delay= [KNL]
2740 Set wakeup interval for idle CPUs that have
2741 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2742 Lazy RCU callbacks are those which RCU can
2743 prove do nothing more than free memory.
2745 rcutorture.fqs_duration= [KNL]
2746 Set duration of force_quiescent_state bursts.
2748 rcutorture.fqs_holdoff= [KNL]
2749 Set holdoff time within force_quiescent_state bursts.
2751 rcutorture.fqs_stutter= [KNL]
2752 Set wait time between force_quiescent_state bursts.
2754 rcutorture.gp_exp= [KNL]
2755 Use expedited update-side primitives.
2757 rcutorture.gp_normal= [KNL]
2758 Use normal (non-expedited) update-side primitives.
2759 If both gp_exp and gp_normal are set, do both.
2760 If neither gp_exp nor gp_normal are set, still
2761 do both.
2763 rcutorture.n_barrier_cbs= [KNL]
2764 Set callbacks/threads for rcu_barrier() testing.
2766 rcutorture.nfakewriters= [KNL]
2767 Set number of concurrent RCU writers. These just
2768 stress RCU, they don't participate in the actual
2769 test, hence the "fake".
2771 rcutorture.nreaders= [KNL]
2772 Set number of RCU readers.
2774 rcutorture.object_debug= [KNL]
2775 Enable debug-object double-call_rcu() testing.
2777 rcutorture.onoff_holdoff= [KNL]
2778 Set time (s) after boot for CPU-hotplug testing.
2780 rcutorture.onoff_interval= [KNL]
2781 Set time (s) between CPU-hotplug operations, or
2782 zero to disable CPU-hotplug testing.
2784 rcutorture.rcutorture_runnable= [BOOT]
2785 Start rcutorture running at boot time.
2787 rcutorture.shuffle_interval= [KNL]
2788 Set task-shuffle interval (s). Shuffling tasks
2789 allows some CPUs to go into dyntick-idle mode
2790 during the rcutorture test.
2792 rcutorture.shutdown_secs= [KNL]
2793 Set time (s) after boot system shutdown. This
2794 is useful for hands-off automated testing.
2796 rcutorture.stall_cpu= [KNL]
2797 Duration of CPU stall (s) to test RCU CPU stall
2798 warnings, zero to disable.
2800 rcutorture.stall_cpu_holdoff= [KNL]
2801 Time to wait (s) after boot before inducing stall.
2803 rcutorture.stat_interval= [KNL]
2804 Time (s) between statistics printk()s.
2806 rcutorture.stutter= [KNL]
2807 Time (s) to stutter testing, for example, specifying
2808 five seconds causes the test to run for five seconds,
2809 wait for five seconds, and so on. This tests RCU's
2810 ability to transition abruptly to and from idle.
2812 rcutorture.test_boost= [KNL]
2813 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2814 "Maybe" means test if the RCU implementation
2815 under test support RCU priority boosting.
2817 rcutorture.test_boost_duration= [KNL]
2818 Duration (s) of each individual boost test.
2820 rcutorture.test_boost_interval= [KNL]
2821 Interval (s) between each boost test.
2823 rcutorture.test_no_idle_hz= [KNL]
2824 Test RCU's dyntick-idle handling. See also the
2825 rcutorture.shuffle_interval parameter.
2827 rcutorture.torture_type= [KNL]
2828 Specify the RCU implementation to test.
2830 rcutorture.verbose= [KNL]
2831 Enable additional printk() statements.
2833 rcupdate.rcu_expedited= [KNL]
2834 Use expedited grace-period primitives, for
2835 example, synchronize_rcu_expedited() instead
2836 of synchronize_rcu(). This reduces latency,
2837 but can increase CPU utilization, degrade
2838 real-time latency, and degrade energy efficiency.
2840 rcupdate.rcu_cpu_stall_suppress= [KNL]
2841 Suppress RCU CPU stall warning messages.
2843 rcupdate.rcu_cpu_stall_timeout= [KNL]
2844 Set timeout for RCU CPU stall warning messages.
2846 rdinit= [KNL]
2847 Format: <full_path>
2848 Run specified binary instead of /init from the ramdisk,
2849 used for early userspace startup. See initrd.
2851 reboot= [KNL]
2852 Format (x86 or x86_64):
2853 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2854 [[,]s[mp]#### \
2855 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2856 [[,]f[orce]
2857 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2858 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2859 reboot_force is either force or not specified,
2860 reboot_cpu is s[mp]#### with #### being the processor
2861 to be used for rebooting.
2863 relax_domain_level=
2864 [KNL, SMP] Set scheduler's default relax_domain_level.
2865 See Documentation/cgroups/cpusets.txt.
2867 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2869 reservetop= [X86-32]
2870 Format: nn[KMG]
2871 Reserves a hole at the top of the kernel virtual
2872 address space.
2874 reservelow= [X86]
2875 Format: nn[K]
2876 Set the amount of memory to reserve for BIOS at
2877 the bottom of the address space.
2879 reset_devices [KNL] Force drivers to reset the underlying device
2880 during initialization.
2882 resume= [SWSUSP]
2883 Specify the partition device for software suspend
2884 Format:
2885 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2887 resume_offset= [SWSUSP]
2888 Specify the offset from the beginning of the partition
2889 given by "resume=" at which the swap header is located,
2890 in <PAGE_SIZE> units (needed only for swap files).
2891 See Documentation/power/swsusp-and-swap-files.txt
2893 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2894 read the resume files
2896 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2897 Useful for devices that are detected asynchronously
2898 (e.g. USB and MMC devices).
2900 hibernate= [HIBERNATION]
2901 noresume Don't check if there's a hibernation image
2902 present during boot.
2903 nocompress Don't compress/decompress hibernation images.
2905 retain_initrd [RAM] Keep initrd memory after extraction
2907 rhash_entries= [KNL,NET]
2908 Set number of hash buckets for route cache
2910 riscom8= [HW,SERIAL]
2911 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2913 ro [KNL] Mount root device read-only on boot
2915 root= [KNL] Root filesystem
2916 See name_to_dev_t comment in init/do_mounts.c.
2918 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2919 mount the root filesystem
2921 rootflags= [KNL] Set root filesystem mount option string
2923 rootfstype= [KNL] Set root filesystem type
2925 rootwait [KNL] Wait (indefinitely) for root device to show up.
2926 Useful for devices that are detected asynchronously
2927 (e.g. USB and MMC devices).
2929 rproc_mem=nn[KMG][@address]
2930 [KNL,ARM,CMA] Remoteproc physical memory block.
2931 Memory area to be used by remote processor image,
2932 managed by CMA.
2934 rw [KNL] Mount root device read-write on boot
2936 S [KNL] Run init in single mode
2938 sa1100ir [NET]
2939 See drivers/net/irda/sa1100_ir.c.
2941 sbni= [NET] Granch SBNI12 leased line adapter
2943 sched_debug [KNL] Enables verbose scheduler debug messages.
2945 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2946 xtime_lock contention on larger systems, and/or RCU lock
2947 contention on all systems with CONFIG_MAXSMP set.
2948 Format: { "0" | "1" }
2949 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2950 1 -- enable.
2951 Note: increases power consumption, thus should only be
2952 enabled if running jitter sensitive (HPC/RT) workloads.
2954 security= [SECURITY] Choose a security module to enable at boot.
2955 If this boot parameter is not specified, only the first
2956 security module asking for security registration will be
2957 loaded. An invalid security module name will be treated
2958 as if no module has been chosen.
2960 selinux= [SELINUX] Disable or enable SELinux at boot time.
2961 Format: { "0" | "1" }
2962 See security/selinux/Kconfig help text.
2963 0 -- disable.
2964 1 -- enable.
2965 Default value is set via kernel config option.
2966 If enabled at boot time, /selinux/disable can be used
2967 later to disable prior to initial policy load.
2969 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2970 Format: { "0" | "1" }
2971 See security/apparmor/Kconfig help text
2972 0 -- disable.
2973 1 -- enable.
2974 Default value is set via kernel config option.
2976 serialnumber [BUGS=X86-32]
2978 shapers= [NET]
2979 Maximal number of shapers.
2981 show_msr= [x86] show boot-time MSR settings
2982 Format: { <integer> }
2983 Show boot-time (BIOS-initialized) MSR settings.
2984 The parameter means the number of CPUs to show,
2985 for example 1 means boot CPU only.
2987 simeth= [IA-64]
2988 simscsi=
2990 slram= [HW,MTD]
2992 slab_max_order= [MM, SLAB]
2993 Determines the maximum allowed order for slabs.
2994 A high setting may cause OOMs due to memory
2995 fragmentation. Defaults to 1 for systems with
2996 more than 32MB of RAM, 0 otherwise.
2998 slub_debug[=options[,slabs]] [MM, SLUB]
2999 Enabling slub_debug allows one to determine the
3000 culprit if slab objects become corrupted. Enabling
3001 slub_debug can create guard zones around objects and
3002 may poison objects when not in use. Also tracks the
3003 last alloc / free. For more information see
3004 Documentation/vm/slub.txt.
3006 slub_max_order= [MM, SLUB]
3007 Determines the maximum allowed order for slabs.
3008 A high setting may cause OOMs due to memory
3009 fragmentation. For more information see
3010 Documentation/vm/slub.txt.
3012 slub_min_objects= [MM, SLUB]
3013 The minimum number of objects per slab. SLUB will
3014 increase the slab order up to slub_max_order to
3015 generate a sufficiently large slab able to contain
3016 the number of objects indicated. The higher the number
3017 of objects the smaller the overhead of tracking slabs
3018 and the less frequently locks need to be acquired.
3019 For more information see Documentation/vm/slub.txt.
3021 slub_min_order= [MM, SLUB]
3022 Determines the minimum page order for slabs. Must be
3023 lower than slub_max_order.
3024 For more information see Documentation/vm/slub.txt.
3026 slub_nomerge [MM, SLUB]
3027 Disable merging of slabs with similar size. May be
3028 necessary if there is some reason to distinguish
3029 allocs to different slabs. Debug options disable
3030 merging on their own.
3031 For more information see Documentation/vm/slub.txt.
3033 smart2= [HW]
3034 Format: <io1>[,<io2>[,...,<io8>]]
3036 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3037 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3038 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3039 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3040 smsc-ircc2.ircc_irq= [HW] IRQ line
3041 smsc-ircc2.ircc_dma= [HW] DMA channel
3042 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3043 0: Toshiba Satellite 1800 (GP data pin select)
3044 1: Fast pin select (default)
3045 2: ATC IRMode
3047 softlockup_panic=
3048 [KNL] Should the soft-lockup detector generate panics.
3049 Format: <integer>
3051 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3052 See Documentation/laptops/sonypi.txt
3054 specialix= [HW,SERIAL] Specialix multi-serial port adapter
3055 See Documentation/serial/specialix.txt.
3057 spia_io_base= [HW,MTD]
3058 spia_fio_base=
3059 spia_pedr=
3060 spia_peddr=
3062 stacktrace [FTRACE]
3063 Enabled the stack tracer on boot up.
3065 stacktrace_filter=[function-list]
3066 [FTRACE] Limit the functions that the stack tracer
3067 will trace at boot up. function-list is a comma separated
3068 list of functions. This list can be changed at run
3069 time by the stack_trace_filter file in the debugfs
3070 tracing directory. Note, this enables stack tracing
3071 and the stacktrace above is not needed.
3073 sti= [PARISC,HW]
3074 Format: <num>
3075 Set the STI (builtin display/keyboard on the HP-PARISC
3076 machines) console (graphic card) which should be used
3077 as the initial boot-console.
3078 See also comment in drivers/video/console/sticore.c.
3080 sti_font= [HW]
3081 See comment in drivers/video/console/sticore.c.
3083 stifb= [HW]
3084 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3086 sunrpc.min_resvport=
3087 sunrpc.max_resvport=
3088 [NFS,SUNRPC]
3089 SunRPC servers often require that client requests
3090 originate from a privileged port (i.e. a port in the
3091 range 0 < portnr < 1024).
3092 An administrator who wishes to reserve some of these
3093 ports for other uses may adjust the range that the
3094 kernel's sunrpc client considers to be privileged
3095 using these two parameters to set the minimum and
3096 maximum port values.
3098 sunrpc.pool_mode=
3099 [NFS]
3100 Control how the NFS server code allocates CPUs to
3101 service thread pools. Depending on how many NICs
3102 you have and where their interrupts are bound, this
3103 option will affect which CPUs will do NFS serving.
3104 Note: this parameter cannot be changed while the
3105 NFS server is running.
3107 auto the server chooses an appropriate mode
3108 automatically using heuristics
3109 global a single global pool contains all CPUs
3110 percpu one pool for each CPU
3111 pernode one pool for each NUMA node (equivalent
3112 to global on non-NUMA machines)
3114 sunrpc.tcp_slot_table_entries=
3115 sunrpc.udp_slot_table_entries=
3116 [NFS,SUNRPC]
3117 Sets the upper limit on the number of simultaneous
3118 RPC calls that can be sent from the client to a
3119 server. Increasing these values may allow you to
3120 improve throughput, but will also increase the
3121 amount of memory reserved for use by the client.
3123 swapaccount=[0|1]
3124 [KNL] Enable accounting of swap in memory resource
3125 controller if no parameter or 1 is given or disable
3126 it if 0 is given (See Documentation/cgroups/memory.txt)
3128 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3129 Format: { <int> | force }
3130 <int> -- Number of I/O TLB slabs
3131 force -- force using of bounce buffers even if they
3132 wouldn't be automatically used by the kernel
3134 switches= [HW,M68k]
3136 sysfs.deprecated=0|1 [KNL]
3137 Enable/disable old style sysfs layout for old udev
3138 on older distributions. When this option is enabled
3139 very new udev will not work anymore. When this option
3140 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3141 in older udev will not work anymore.
3142 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3143 the kernel configuration.
3145 sysrq_always_enabled
3146 [KNL]
3147 Ignore sysrq setting - this boot parameter will
3148 neutralize any effect of /proc/sys/kernel/sysrq.
3149 Useful for debugging.
3151 tdfx= [HW,DRM]
3153 test_suspend= [SUSPEND]
3154 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3155 standby suspend) as the system sleep state to briefly
3156 enter during system startup. The system is woken from
3157 this state using a wakeup-capable RTC alarm.
3159 thash_entries= [KNL,NET]
3160 Set number of hash buckets for TCP connection
3162 thermal.act= [HW,ACPI]
3163 -1: disable all active trip points in all thermal zones
3164 <degrees C>: override all lowest active trip points
3166 thermal.crt= [HW,ACPI]
3167 -1: disable all critical trip points in all thermal zones
3168 <degrees C>: override all critical trip points
3170 thermal.nocrt= [HW,ACPI]
3171 Set to disable actions on ACPI thermal zone
3172 critical and hot trip points.
3174 thermal.off= [HW,ACPI]
3175 1: disable ACPI thermal control
3177 thermal.psv= [HW,ACPI]
3178 -1: disable all passive trip points
3179 <degrees C>: override all passive trip points to this
3180 value
3182 thermal.tzp= [HW,ACPI]
3183 Specify global default ACPI thermal zone polling rate
3184 <deci-seconds>: poll all this frequency
3185 0: no polling (default)
3187 threadirqs [KNL]
3188 Force threading of all interrupt handlers except those
3189 marked explicitly IRQF_NO_THREAD.
3191 tmem [KNL,XEN]
3192 Enable the Transcendent memory driver if built-in.
3194 tmem.cleancache=0|1 [KNL, XEN]
3195 Default is on (1). Disable the usage of the cleancache
3196 API to send anonymous pages to the hypervisor.
3198 tmem.frontswap=0|1 [KNL, XEN]
3199 Default is on (1). Disable the usage of the frontswap
3200 API to send swap pages to the hypervisor. If disabled
3201 the selfballooning and selfshrinking are force disabled.
3203 tmem.selfballooning=0|1 [KNL, XEN]
3204 Default is on (1). Disable the driving of swap pages
3205 to the hypervisor.
3207 tmem.selfshrinking=0|1 [KNL, XEN]
3208 Default is on (1). Partial swapoff that immediately
3209 transfers pages from Xen hypervisor back to the
3210 kernel based on different criteria.
3212 topology= [S390]
3213 Format: {off | on}
3214 Specify if the kernel should make use of the cpu
3215 topology information if the hardware supports this.
3216 The scheduler will make use of this information and
3217 e.g. base its process migration decisions on it.
3218 Default is on.
3220 tp720= [HW,PS2]
3222 tpm_suspend_pcr=[HW,TPM]
3223 Format: integer pcr id
3224 Specify that at suspend time, the tpm driver
3225 should extend the specified pcr with zeros,
3226 as a workaround for some chips which fail to
3227 flush the last written pcr on TPM_SaveState.
3228 This will guarantee that all the other pcrs
3229 are saved.
3231 trace_buf_size=nn[KMG]
3232 [FTRACE] will set tracing buffer size.
3234 trace_event=[event-list]
3235 [FTRACE] Set and start specified trace events in order
3236 to facilitate early boot debugging.
3237 See also Documentation/trace/events.txt
3239 trace_options=[option-list]
3240 [FTRACE] Enable or disable tracer options at boot.
3241 The option-list is a comma delimited list of options
3242 that can be enabled or disabled just as if you were
3243 to echo the option name into
3245 /sys/kernel/debug/tracing/trace_options
3247 For example, to enable stacktrace option (to dump the
3248 stack trace of each event), add to the command line:
3250 trace_options=stacktrace
3252 See also Documentation/trace/ftrace.txt "trace options"
3253 section.
3255 traceoff_on_warning
3256 [FTRACE] enable this option to disable tracing when a
3257 warning is hit. This turns off "tracing_on". Tracing can
3258 be enabled again by echoing '1' into the "tracing_on"
3259 file located in /sys/kernel/debug/tracing/
3261 This option is useful, as it disables the trace before
3262 the WARNING dump is called, which prevents the trace to
3263 be filled with content caused by the warning output.
3265 This option can also be set at run time via the sysctl
3266 option: kernel/traceoff_on_warning
3268 transparent_hugepage=
3269 [KNL]
3270 Format: [always|madvise|never]
3271 Can be used to control the default behavior of the system
3272 with respect to transparent hugepages.
3273 See Documentation/vm/transhuge.txt for more details.
3275 tsc= Disable clocksource stability checks for TSC.
3276 Format: <string>
3277 [x86] reliable: mark tsc clocksource as reliable, this
3278 disables clocksource verification at runtime, as well
3279 as the stability checks done at bootup. Used to enable
3280 high-resolution timer mode on older hardware, and in
3281 virtualized environment.
3282 [x86] noirqtime: Do not use TSC to do irq accounting.
3283 Used to run time disable IRQ_TIME_ACCOUNTING on any
3284 platforms where RDTSC is slow and this accounting
3285 can add overhead.
3287 turbografx.map[2|3]= [HW,JOY]
3288 TurboGraFX parallel port interface
3289 Format:
3290 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3291 See also Documentation/input/joystick-parport.txt
3293 udbg-immortal [PPC] When debugging early kernel crashes that
3294 happen after console_init() and before a proper
3295 console driver takes over, this boot options might
3296 help "seeing" what's going on.
3298 uhash_entries= [KNL,NET]
3299 Set number of hash buckets for UDP/UDP-Lite connections
3301 uhci-hcd.ignore_oc=
3302 [USB] Ignore overcurrent events (default N).
3303 Some badly-designed motherboards generate lots of
3304 bogus events, for ports that aren't wired to
3305 anything. Set this parameter to avoid log spamming.
3306 Note that genuine overcurrent events won't be
3307 reported either.
3309 unknown_nmi_panic
3310 [X86] Cause panic on unknown NMI.
3312 usbcore.authorized_default=
3313 [USB] Default USB device authorization:
3314 (default -1 = authorized except for wireless USB,
3315 0 = not authorized, 1 = authorized)
3317 usbcore.autosuspend=
3318 [USB] The autosuspend time delay (in seconds) used
3319 for newly-detected USB devices (default 2). This
3320 is the time required before an idle device will be
3321 autosuspended. Devices for which the delay is set
3322 to a negative value won't be autosuspended at all.
3324 usbcore.usbfs_snoop=
3325 [USB] Set to log all usbfs traffic (default 0 = off).
3327 usbcore.blinkenlights=
3328 [USB] Set to cycle leds on hubs (default 0 = off).
3330 usbcore.old_scheme_first=
3331 [USB] Start with the old device initialization
3332 scheme (default 0 = off).
3334 usbcore.usbfs_memory_mb=
3335 [USB] Memory limit (in MB) for buffers allocated by
3336 usbfs (default = 16, 0 = max = 2047).
3338 usbcore.use_both_schemes=
3339 [USB] Try the other device initialization scheme
3340 if the first one fails (default 1 = enabled).
3342 usbcore.initial_descriptor_timeout=
3343 [USB] Specifies timeout for the initial 64-byte
3344 USB_REQ_GET_DESCRIPTOR request in milliseconds
3345 (default 5000 = 5.0 seconds).
3347 usbhid.mousepoll=
3348 [USBHID] The interval which mice are to be polled at.
3350 usb-storage.delay_use=
3351 [UMS] The delay in seconds before a new device is
3352 scanned for Logical Units (default 5).
3354 usb-storage.quirks=
3355 [UMS] A list of quirks entries to supplement or
3356 override the built-in unusual_devs list. List
3357 entries are separated by commas. Each entry has
3358 the form VID:PID:Flags where VID and PID are Vendor
3359 and Product ID values (4-digit hex numbers) and
3360 Flags is a set of characters, each corresponding
3361 to a common usb-storage quirk flag as follows:
3362 a = SANE_SENSE (collect more than 18 bytes
3363 of sense data);
3364 b = BAD_SENSE (don't collect more than 18
3365 bytes of sense data);
3366 c = FIX_CAPACITY (decrease the reported
3367 device capacity by one sector);
3368 d = NO_READ_DISC_INFO (don't use
3369 READ_DISC_INFO command);
3370 e = NO_READ_CAPACITY_16 (don't use
3371 READ_CAPACITY_16 command);
3372 h = CAPACITY_HEURISTICS (decrease the
3373 reported device capacity by one
3374 sector if the number is odd);
3375 i = IGNORE_DEVICE (don't bind to this
3376 device);
3377 l = NOT_LOCKABLE (don't try to lock and
3378 unlock ejectable media);
3379 m = MAX_SECTORS_64 (don't transfer more
3380 than 64 sectors = 32 KB at a time);
3381 n = INITIAL_READ10 (force a retry of the
3382 initial READ(10) command);
3383 o = CAPACITY_OK (accept the capacity
3384 reported by the device);
3385 p = WRITE_CACHE (the device cache is ON
3386 by default);
3387 r = IGNORE_RESIDUE (the device reports
3388 bogus residue values);
3389 s = SINGLE_LUN (the device has only one
3390 Logical Unit);
3391 w = NO_WP_DETECT (don't test whether the
3392 medium is write-protected).
3393 Example: quirks=0419:aaf5:rl,0421:0433:rc
3395 user_debug= [KNL,ARM]
3396 Format: <int>
3397 See arch/arm/Kconfig.debug help text.
3398 1 - undefined instruction events
3399 2 - system calls
3400 4 - invalid data aborts
3401 8 - SIGSEGV faults
3402 16 - SIGBUS faults
3403 Example: user_debug=31
3405 userpte=
3406 [X86] Flags controlling user PTE allocations.
3408 nohigh = do not allocate PTE pages in
3409 HIGHMEM regardless of setting
3410 of CONFIG_HIGHPTE.
3412 vdso= [X86,SH]
3413 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3414 vdso=1: enable VDSO (default)
3415 vdso=0: disable VDSO mapping
3417 vdso32= [X86]
3418 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3419 vdso32=1: enable 32-bit VDSO (default)
3420 vdso32=0: disable 32-bit VDSO mapping
3422 vector= [IA-64,SMP]
3423 vector=percpu: enable percpu vector domain
3425 video= [FB] Frame buffer configuration
3426 See Documentation/fb/modedb.txt.
3428 video.brightness_switch_enabled= [0,1]
3429 If set to 1, on receiving an ACPI notify event
3430 generated by hotkey, video driver will adjust brightness
3431 level and then send out the event to user space through
3432 the allocated input device; If set to 0, video driver
3433 will only send out the event without touching backlight
3434 brightness level.
3435 default: 1
3437 virtio_mmio.device=
3438 [VMMIO] Memory mapped virtio (platform) device.
3440 <size>@<baseaddr>:<irq>[:<id>]
3441 where:
3442 <size> := size (can use standard suffixes
3443 like K, M and G)
3444 <baseaddr> := physical base address
3445 <irq> := interrupt number (as passed to
3446 request_irq())
3447 <id> := (optional) platform device id
3448 example:
3449 virtio_mmio.device=1K@0x100b0000:48:7
3451 Can be used multiple times for multiple devices.
3453 vga= [BOOT,X86-32] Select a particular video mode
3454 See Documentation/x86/boot.txt and
3455 Documentation/svga.txt.
3456 Use vga=ask for menu.
3457 This is actually a boot loader parameter; the value is
3458 passed to the kernel using a special protocol.
3460 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3461 size of <nn>. This can be used to increase the
3462 minimum size (128MB on x86). It can also be used to
3463 decrease the size and leave more room for directly
3464 mapped kernel RAM.
3466 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3467 Format: <command>
3469 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3470 Format: <command>
3472 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3473 Format: <command>
3475 vsyscall= [X86-64]
3476 Controls the behavior of vsyscalls (i.e. calls to
3477 fixed addresses of 0xffffffffff600x00 from legacy
3478 code). Most statically-linked binaries and older
3479 versions of glibc use these calls. Because these
3480 functions are at fixed addresses, they make nice
3481 targets for exploits that can control RIP.
3483 emulate [default] Vsyscalls turn into traps and are
3484 emulated reasonably safely.
3486 native Vsyscalls are native syscall instructions.
3487 This is a little bit faster than trapping
3488 and makes a few dynamic recompilers work
3489 better than they would in emulation mode.
3490 It also makes exploits much easier to write.
3492 none Vsyscalls don't work at all. This makes
3493 them quite hard to use for exploits but
3494 might break your system.
3496 vt.color= [VT] Default text color.
3497 Format: 0xYX, X = foreground, Y = background.
3498 Default: 0x07 = light gray on black.
3500 vt.cur_default= [VT] Default cursor shape.
3501 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3502 the parameters of the <Esc>[?A;B;Cc escape sequence;
3503 see VGA-softcursor.txt. Default: 2 = underline.
3505 vt.default_blu= [VT]
3506 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3507 Change the default blue palette of the console.
3508 This is a 16-member array composed of values
3509 ranging from 0-255.
3511 vt.default_grn= [VT]
3512 Format: <green0>,<green1>,<green2>,...,<green15>
3513 Change the default green palette of the console.
3514 This is a 16-member array composed of values
3515 ranging from 0-255.
3517 vt.default_red= [VT]
3518 Format: <red0>,<red1>,<red2>,...,<red15>
3519 Change the default red palette of the console.
3520 This is a 16-member array composed of values
3521 ranging from 0-255.
3523 vt.default_utf8=
3524 [VT]
3525 Format=<0|1>
3526 Set system-wide default UTF-8 mode for all tty's.
3527 Default is 1, i.e. UTF-8 mode is enabled for all
3528 newly opened terminals.
3530 vt.global_cursor_default=
3531 [VT]
3532 Format=<-1|0|1>
3533 Set system-wide default for whether a cursor
3534 is shown on new VTs. Default is -1,
3535 i.e. cursors will be created by default unless
3536 overridden by individual drivers. 0 will hide
3537 cursors, 1 will display them.
3539 vt.italic= [VT] Default color for italic text; 0-15.
3540 Default: 2 = green.
3542 vt.underline= [VT] Default color for underlined text; 0-15.
3543 Default: 3 = cyan.
3545 watchdog timers [HW,WDT] For information on watchdog timers,
3546 see Documentation/watchdog/watchdog-parameters.txt
3547 or other driver-specific files in the
3548 Documentation/watchdog/ directory.
3550 workqueue.disable_numa
3551 By default, all work items queued to unbound
3552 workqueues are affine to the NUMA nodes they're
3553 issued on, which results in better behavior in
3554 general. If NUMA affinity needs to be disabled for
3555 whatever reason, this option can be used. Note
3556 that this also can be controlled per-workqueue for
3557 workqueues visible under /sys/bus/workqueue/.
3559 workqueue.power_efficient
3560 Per-cpu workqueues are generally preferred because
3561 they show better performance thanks to cache
3562 locality; unfortunately, per-cpu workqueues tend to
3563 be more power hungry than unbound workqueues.
3565 Enabling this makes the per-cpu workqueues which
3566 were observed to contribute significantly to power
3567 consumption unbound, leading to measurably lower
3568 power usage at the cost of small performance
3569 overhead.
3571 The default value of this parameter is determined by
3572 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3574 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3575 default x2apic cluster mode on platforms
3576 supporting x2apic.
3578 x86_intel_mid_timer= [X86-32,APBT]
3579 Choose timer option for x86 Intel MID platform.
3580 Two valid options are apbt timer only and lapic timer
3581 plus one apbt timer for broadcast timer.
3582 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3584 xen_emul_unplug= [HW,X86,XEN]
3585 Unplug Xen emulated devices
3586 Format: [unplug0,][unplug1]
3587 ide-disks -- unplug primary master IDE devices
3588 aux-ide-disks -- unplug non-primary-master IDE devices
3589 nics -- unplug network devices
3590 all -- unplug all emulated devices (NICs and IDE disks)
3591 unnecessary -- unplugging emulated devices is
3592 unnecessary even if the host did not respond to
3593 the unplug protocol
3594 never -- do not unplug even if version check succeeds
3596 xen_nopvspin [X86,XEN]
3597 Disables the ticketlock slowpath using Xen PV
3598 optimizations.
3600 xirc2ps_cs= [NET,PCMCIA]
3601 Format:
3602 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3604 ______________________________________________________________________
3606 TODO:
3608 Add more DRM drivers.