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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
4 The following is a consolidated list of the kernel parameters as implemented
5 (mostly) by the __setup() macro and sorted into English Dictionary order
6 (defined as ignoring all punctuation and sorting digits before letters in a
7 case insensitive manner), and with descriptions where known.
9 Module parameters for loadable modules are specified only as the
10 parameter name with optional '=' and value as appropriate, such as:
12 modprobe usbcore blinkenlights=1
14 Module parameters for modules that are built into the kernel image
15 are specified on the kernel command line with the module name plus
16 '.' plus parameter name, with '=' and value if appropriate, such as:
18 usbcore.blinkenlights=1
20 Hyphens (dashes) and underscores are equivalent in parameter names, so
21 log_buf_len=1M print-fatal-signals=1
22 can also be entered as
23 log-buf-len=1M print_fatal_signals=1
26 This document may not be entirely up to date and comprehensive. The command
27 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
28 module. Loadable modules, after being loaded into the running kernel, also
29 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
30 parameters may be changed at runtime by the command
31 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
33 The parameters listed below are only valid if certain kernel build options were
34 enabled and if respective hardware is present. The text in square brackets at
35 the beginning of each description states the restrictions within which a
36 parameter is applicable:
38 ACPI ACPI support is enabled.
39 AGP AGP (Accelerated Graphics Port) is enabled.
40 ALSA ALSA sound support is enabled.
41 APIC APIC support is enabled.
42 APM Advanced Power Management support is enabled.
43 ARM ARM architecture is enabled.
44 AVR32 AVR32 architecture is enabled.
45 AX25 Appropriate AX.25 support is enabled.
46 BLACKFIN Blackfin architecture is enabled.
47 CLK Common clock infrastructure is enabled.
48 CMA Contiguous Memory Area support is enabled.
49 DRM Direct Rendering Management support is enabled.
50 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
51 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
52 EFI EFI Partitioning (GPT) is enabled
53 EIDE EIDE/ATAPI support is enabled.
54 EVM Extended Verification Module
55 FB The frame buffer device is enabled.
56 FTRACE Function tracing enabled.
57 GCOV GCOV profiling is enabled.
58 HW Appropriate hardware is enabled.
59 IA-64 IA-64 architecture is enabled.
60 IMA Integrity measurement architecture is enabled.
61 IOSCHED More than one I/O scheduler is enabled.
62 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
63 IPV6 IPv6 support is enabled.
64 ISAPNP ISA PnP code is enabled.
65 ISDN Appropriate ISDN support is enabled.
66 JOY Appropriate joystick support is enabled.
67 KGDB Kernel debugger support is enabled.
68 KVM Kernel Virtual Machine support is enabled.
69 LIBATA Libata driver is enabled
70 LP Printer support is enabled.
71 LOOP Loopback device support is enabled.
72 M68k M68k architecture is enabled.
73 These options have more detailed description inside of
74 Documentation/m68k/kernel-options.txt.
75 MDA MDA console support is enabled.
76 MIPS MIPS architecture is enabled.
77 MOUSE Appropriate mouse support is enabled.
78 MSI Message Signaled Interrupts (PCI).
79 MTD MTD (Memory Technology Device) support is enabled.
80 NET Appropriate network support is enabled.
81 NUMA NUMA support is enabled.
82 NFS Appropriate NFS support is enabled.
83 OSS OSS sound support is enabled.
84 PV_OPS A paravirtualized kernel is enabled.
85 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
86 PARISC The PA-RISC architecture is enabled.
87 PCI PCI bus support is enabled.
88 PCIE PCI Express support is enabled.
89 PCMCIA The PCMCIA subsystem is enabled.
90 PNP Plug & Play support is enabled.
91 PPC PowerPC architecture is enabled.
92 PPT Parallel port support is enabled.
93 PS2 Appropriate PS/2 support is enabled.
94 RAM RAM disk support is enabled.
95 S390 S390 architecture is enabled.
96 SCSI Appropriate SCSI support is enabled.
97 A lot of drivers have their options described inside
98 the Documentation/scsi/ sub-directory.
99 SECURITY Different security models are enabled.
100 SELINUX SELinux support is enabled.
101 APPARMOR AppArmor support is enabled.
102 SERIAL Serial support is enabled.
103 SH SuperH architecture is enabled.
104 SMP The kernel is an SMP kernel.
105 SPARC Sparc architecture is enabled.
106 SWSUSP Software suspend (hibernation) is enabled.
107 SUSPEND System suspend states are enabled.
108 TPM TPM drivers are enabled.
109 TS Appropriate touchscreen support is enabled.
110 UMS USB Mass Storage support is enabled.
111 USB USB support is enabled.
112 USBHID USB Human Interface Device support is enabled.
113 V4L Video For Linux support is enabled.
114 VMMIO Driver for memory mapped virtio devices is enabled.
115 VGA The VGA console has been enabled.
116 VT Virtual terminal support is enabled.
117 WDT Watchdog support is enabled.
118 XT IBM PC/XT MFM hard disk support is enabled.
119 X86-32 X86-32, aka i386 architecture is enabled.
120 X86-64 X86-64 architecture is enabled.
121 More X86-64 boot options can be found in
122 Documentation/x86/x86_64/boot-options.txt .
123 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
124 XEN Xen support is enabled
126 In addition, the following text indicates that the option:
128 BUGS= Relates to possible processor bugs on the said processor.
129 KNL Is a kernel start-up parameter.
130 BOOT Is a boot loader parameter.
132 Parameters denoted with BOOT are actually interpreted by the boot
133 loader, and have no meaning to the kernel directly.
134 Do not modify the syntax of boot loader parameters without extreme
135 need or coordination with <Documentation/x86/boot.txt>.
137 There are also arch-specific kernel-parameters not documented here.
138 See for example <Documentation/x86/x86_64/boot-options.txt>.
140 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
141 a trailing = on the name of any parameter states that that parameter will
142 be entered as an environment variable, whereas its absence indicates that
143 it will appear as a kernel argument readable via /proc/cmdline by programs
144 running once the system is up.
146 The number of kernel parameters is not limited, but the length of the
147 complete command line (parameters including spaces etc.) is limited to
148 a fixed number of characters. This limit depends on the architecture
149 and is between 256 and 4096 characters. It is defined in the file
150 ./include/asm/setup.h as COMMAND_LINE_SIZE.
152 Finally, the [KMG] suffix is commonly described after a number of kernel
153 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
154 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
155 bytes respectively. Such letter suffixes can also be entirely omitted.
158 acpi= [HW,ACPI,X86]
159 Advanced Configuration and Power Interface
160 Format: { force | off | strict | noirq | rsdt }
161 force -- enable ACPI if default was off
162 off -- disable ACPI if default was on
163 noirq -- do not use ACPI for IRQ routing
164 strict -- Be less tolerant of platforms that are not
165 strictly ACPI specification compliant.
166 rsdt -- prefer RSDT over (default) XSDT
167 copy_dsdt -- copy DSDT to memory
169 See also Documentation/power/runtime_pm.txt, pci=noacpi
171 acpi_rsdp= [ACPI,EFI,KEXEC]
172 Pass the RSDP address to the kernel, mostly used
173 on machines running EFI runtime service to boot the
174 second kernel for kdump.
176 acpi_apic_instance= [ACPI, IOAPIC]
177 Format: <int>
178 2: use 2nd APIC table, if available
179 1,0: use 1st APIC table
180 default: 0
182 acpi_backlight= [HW,ACPI]
183 acpi_backlight=vendor
184 acpi_backlight=video
185 If set to vendor, prefer vendor specific driver
186 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
187 of the ACPI video.ko driver.
189 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
190 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
191 Format: <int>
192 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
193 debug output. Bits in debug_layer correspond to a
194 _COMPONENT in an ACPI source file, e.g.,
195 #define _COMPONENT ACPI_PCI_COMPONENT
196 Bits in debug_level correspond to a level in
197 ACPI_DEBUG_PRINT statements, e.g.,
198 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
199 The debug_level mask defaults to "info". See
200 Documentation/acpi/debug.txt for more information about
201 debug layers and levels.
203 Enable processor driver info messages:
204 acpi.debug_layer=0x20000000
205 Enable PCI/PCI interrupt routing info messages:
206 acpi.debug_layer=0x400000
207 Enable AML "Debug" output, i.e., stores to the Debug
208 object while interpreting AML:
209 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
210 Enable all messages related to ACPI hardware:
211 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
213 Some values produce so much output that the system is
214 unusable. The "log_buf_len" parameter may be useful
215 if you need to capture more output.
217 acpi_irq_balance [HW,ACPI]
218 ACPI will balance active IRQs
219 default in APIC mode
221 acpi_irq_nobalance [HW,ACPI]
222 ACPI will not move active IRQs (default)
223 default in PIC mode
225 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
226 Format: <irq>,<irq>...
228 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
229 use by PCI
230 Format: <irq>,<irq>...
232 acpi_no_auto_serialize [HW,ACPI]
233 Disable auto-serialization of AML methods
234 AML control methods that contain the opcodes to create
235 named objects will be marked as "Serialized" by the
236 auto-serialization feature.
237 This feature is enabled by default.
238 This option allows to turn off the feature.
240 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
242 acpica_no_return_repair [HW, ACPI]
243 Disable AML predefined validation mechanism
244 This mechanism can repair the evaluation result to make
245 the return objects more ACPI specification compliant.
246 This option is useful for developers to identify the
247 root cause of an AML interpreter issue when the issue
248 has something to do with the repair mechanism.
250 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
251 Format: To spoof as Windows 98: ="Microsoft Windows"
253 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
254 acpi_osi="string1" # add string1
255 acpi_osi="!string2" # remove string2
256 acpi_osi=!* # remove all strings
257 acpi_osi=! # disable all built-in OS vendor
258 strings
259 acpi_osi= # disable all strings
261 'acpi_osi=!' can be used in combination with single or
262 multiple 'acpi_osi="string1"' to support specific OS
263 vendor string(s). Note that such command can only
264 affect the default state of the OS vendor strings, thus
265 it cannot affect the default state of the feature group
266 strings and the current state of the OS vendor strings,
267 specifying it multiple times through kernel command line
268 is meaningless. This command is useful when one do not
269 care about the state of the feature group strings which
270 should be controlled by the OSPM.
271 Examples:
272 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
273 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
274 can make '_OSI("Windows 2000")' TRUE.
276 'acpi_osi=' cannot be used in combination with other
277 'acpi_osi=' command lines, the _OSI method will not
278 exist in the ACPI namespace. NOTE that such command can
279 only affect the _OSI support state, thus specifying it
280 multiple times through kernel command line is also
281 meaningless.
282 Examples:
283 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
284 FALSE.
286 'acpi_osi=!*' can be used in combination with single or
287 multiple 'acpi_osi="string1"' to support specific
288 string(s). Note that such command can affect the
289 current state of both the OS vendor strings and the
290 feature group strings, thus specifying it multiple times
291 through kernel command line is meaningful. But it may
292 still not able to affect the final state of a string if
293 there are quirks related to this string. This command
294 is useful when one want to control the state of the
295 feature group strings to debug BIOS issues related to
296 the OSPM features.
297 Examples:
298 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
299 '_OSI("Module Device")' FALSE.
300 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
301 '_OSI("Module Device")' TRUE.
302 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
303 equivalent to
304 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
305 and
306 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
307 they all will make '_OSI("Windows 2000")' TRUE.
309 acpi_pm_good [X86]
310 Override the pmtimer bug detection: force the kernel
311 to assume that this machine's pmtimer latches its value
312 and always returns good values.
314 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
315 Format: { level | edge | high | low }
317 acpi_skip_timer_override [HW,ACPI]
318 Recognize and ignore IRQ0/pin2 Interrupt Override.
319 For broken nForce2 BIOS resulting in XT-PIC timer.
321 acpi_sleep= [HW,ACPI] Sleep options
322 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
323 old_ordering, nonvs, sci_force_enable }
324 See Documentation/power/video.txt for information on
325 s3_bios and s3_mode.
326 s3_beep is for debugging; it makes the PC's speaker beep
327 as soon as the kernel's real-mode entry point is called.
328 s4_nohwsig prevents ACPI hardware signature from being
329 used during resume from hibernation.
330 old_ordering causes the ACPI 1.0 ordering of the _PTS
331 control method, with respect to putting devices into
332 low power states, to be enforced (the ACPI 2.0 ordering
333 of _PTS is used by default).
334 nonvs prevents the kernel from saving/restoring the
335 ACPI NVS memory during suspend/hibernation and resume.
336 sci_force_enable causes the kernel to set SCI_EN directly
337 on resume from S1/S3 (which is against the ACPI spec,
338 but some broken systems don't work without it).
340 acpi_use_timer_override [HW,ACPI]
341 Use timer override. For some broken Nvidia NF5 boards
342 that require a timer override, but don't have HPET
344 acpi_enforce_resources= [ACPI]
345 { strict | lax | no }
346 Check for resource conflicts between native drivers
347 and ACPI OperationRegions (SystemIO and SystemMemory
348 only). IO ports and memory declared in ACPI might be
349 used by the ACPI subsystem in arbitrary AML code and
350 can interfere with legacy drivers.
351 strict (default): access to resources claimed by ACPI
352 is denied; legacy drivers trying to access reserved
353 resources will fail to bind to device using them.
354 lax: access to resources claimed by ACPI is allowed;
355 legacy drivers trying to access reserved resources
356 will bind successfully but a warning message is logged.
357 no: ACPI OperationRegions are not marked as reserved,
358 no further checks are performed.
360 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
361 kernels.
363 add_efi_memmap [EFI; X86] Include EFI memory map in
364 kernel's map of available physical RAM.
366 agp= [AGP]
367 { off | try_unsupported }
368 off: disable AGP support
369 try_unsupported: try to drive unsupported chipsets
370 (may crash computer or cause data corruption)
372 ALSA [HW,ALSA]
373 See Documentation/sound/alsa/alsa-parameters.txt
375 alignment= [KNL,ARM]
376 Allow the default userspace alignment fault handler
377 behaviour to be specified. Bit 0 enables warnings,
378 bit 1 enables fixups, and bit 2 sends a segfault.
380 align_va_addr= [X86-64]
381 Align virtual addresses by clearing slice [14:12] when
382 allocating a VMA at process creation time. This option
383 gives you up to 3% performance improvement on AMD F15h
384 machines (where it is enabled by default) for a
385 CPU-intensive style benchmark, and it can vary highly in
386 a microbenchmark depending on workload and compiler.
388 32: only for 32-bit processes
389 64: only for 64-bit processes
390 on: enable for both 32- and 64-bit processes
391 off: disable for both 32- and 64-bit processes
393 alloc_snapshot [FTRACE]
394 Allocate the ftrace snapshot buffer on boot up when the
395 main buffer is allocated. This is handy if debugging
396 and you need to use tracing_snapshot() on boot up, and
397 do not want to use tracing_snapshot_alloc() as it needs
398 to be done where GFP_KERNEL allocations are allowed.
400 amd_iommu= [HW,X86-64]
401 Pass parameters to the AMD IOMMU driver in the system.
402 Possible values are:
403 fullflush - enable flushing of IO/TLB entries when
404 they are unmapped. Otherwise they are
405 flushed before they will be reused, which
406 is a lot of faster
407 off - do not initialize any AMD IOMMU found in
408 the system
409 force_isolation - Force device isolation for all
410 devices. The IOMMU driver is not
411 allowed anymore to lift isolation
412 requirements as needed. This option
413 does not override iommu=pt
415 amd_iommu_dump= [HW,X86-64]
416 Enable AMD IOMMU driver option to dump the ACPI table
417 for AMD IOMMU. With this option enabled, AMD IOMMU
418 driver will print ACPI tables for AMD IOMMU during
419 IOMMU initialization.
421 amijoy.map= [HW,JOY] Amiga joystick support
422 Map of devices attached to JOY0DAT and JOY1DAT
423 Format: <a>,<b>
424 See also Documentation/input/joystick.txt
426 analog.map= [HW,JOY] Analog joystick and gamepad support
427 Specifies type or capabilities of an analog joystick
428 connected to one of 16 gameports
429 Format: <type1>,<type2>,..<type16>
431 apc= [HW,SPARC]
432 Power management functions (SPARCstation-4/5 + deriv.)
433 Format: noidle
434 Disable APC CPU standby support. SPARCstation-Fox does
435 not play well with APC CPU idle - disable it if you have
436 APC and your system crashes randomly.
438 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
439 Change the output verbosity whilst booting
440 Format: { quiet (default) | verbose | debug }
441 Change the amount of debugging information output
442 when initialising the APIC and IO-APIC components.
444 autoconf= [IPV6]
445 See Documentation/networking/ipv6.txt.
447 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
448 Limit apic dumping. The parameter defines the maximal
449 number of local apics being dumped. Also it is possible
450 to set it to "all" by meaning -- no limit here.
451 Format: { 1 (default) | 2 | ... | all }.
452 The parameter valid if only apic=debug or
453 apic=verbose is specified.
454 Example: apic=debug show_lapic=all
456 apm= [APM] Advanced Power Management
457 See header of arch/x86/kernel/apm_32.c.
459 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
460 Format: <io>,<irq>,<nodeID>
462 ataflop= [HW,M68k]
464 atarimouse= [HW,MOUSE] Atari Mouse
466 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
467 EzKey and similar keyboards
469 atkbd.reset= [HW] Reset keyboard during initialization
471 atkbd.set= [HW] Select keyboard code set
472 Format: <int> (2 = AT (default), 3 = PS/2)
474 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
475 keyboards
477 atkbd.softraw= [HW] Choose between synthetic and real raw mode
478 Format: <bool> (0 = real, 1 = synthetic (default))
480 atkbd.softrepeat= [HW]
481 Use software keyboard repeat
483 audit= [KNL] Enable the audit sub-system
484 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
485 0 - kernel audit is disabled and can not be enabled
486 until the next reboot
487 unset - kernel audit is initialized but disabled and
488 will be fully enabled by the userspace auditd.
489 1 - kernel audit is initialized and partially enabled,
490 storing at most audit_backlog_limit messages in
491 RAM until it is fully enabled by the userspace
492 auditd.
493 Default: unset
495 audit_backlog_limit= [KNL] Set the audit queue size limit.
496 Format: <int> (must be >=0)
497 Default: 64
499 baycom_epp= [HW,AX25]
500 Format: <io>,<mode>
502 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
503 Format: <io>,<mode>
504 See header of drivers/net/hamradio/baycom_par.c.
506 baycom_ser_fdx= [HW,AX25]
507 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
508 Format: <io>,<irq>,<mode>[,<baud>]
509 See header of drivers/net/hamradio/baycom_ser_fdx.c.
511 baycom_ser_hdx= [HW,AX25]
512 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
513 Format: <io>,<irq>,<mode>
514 See header of drivers/net/hamradio/baycom_ser_hdx.c.
516 blkdevparts= Manual partition parsing of block device(s) for
517 embedded devices based on command line input.
518 See Documentation/block/cmdline-partition.txt
520 boot_delay= Milliseconds to delay each printk during boot.
521 Values larger than 10 seconds (10000) are changed to
522 no delay (0).
523 Format: integer
525 bootmem_debug [KNL] Enable bootmem allocator debug messages.
527 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
528 bttv.radio= Most important insmod options are available as
529 kernel args too.
530 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
531 bttv.tuner=
533 bulk_remove=off [PPC] This parameter disables the use of the pSeries
534 firmware feature for flushing multiple hpte entries
535 at a time.
537 c101= [NET] Moxa C101 synchronous serial card
539 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
540 Sometimes CPU hardware bugs make them report the cache
541 size incorrectly. The kernel will attempt work arounds
542 to fix known problems, but for some CPUs it is not
543 possible to determine what the correct size should be.
544 This option provides an override for these situations.
546 ccw_timeout_log [S390]
547 See Documentation/s390/CommonIO for details.
549 cgroup_disable= [KNL] Disable a particular controller
550 Format: {name of the controller(s) to disable}
551 The effects of cgroup_disable=foo are:
552 - foo isn't auto-mounted if you mount all cgroups in
553 a single hierarchy
554 - foo isn't visible as an individually mountable
555 subsystem
556 {Currently only "memory" controller deal with this and
557 cut the overhead, others just disable the usage. So
558 only cgroup_disable=memory is actually worthy}
560 checkreqprot [SELINUX] Set initial checkreqprot flag value.
561 Format: { "0" | "1" }
562 See security/selinux/Kconfig help text.
563 0 -- check protection applied by kernel (includes
564 any implied execute protection).
565 1 -- check protection requested by application.
566 Default value is set via a kernel config option.
567 Value can be changed at runtime via
568 /selinux/checkreqprot.
570 cio_ignore= [S390]
571 See Documentation/s390/CommonIO for details.
572 clk_ignore_unused
573 [CLK]
574 Keep all clocks already enabled by bootloader on,
575 even if no driver has claimed them. This is useful
576 for debug and development, but should not be
577 needed on a platform with proper driver support.
578 For more information, see Documentation/clk.txt.
580 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
581 [Deprecated]
582 Forces specified clocksource (if available) to be used
583 when calculating gettimeofday(). If specified
584 clocksource is not available, it defaults to PIT.
585 Format: { pit | tsc | cyclone | pmtmr }
587 clocksource= Override the default clocksource
588 Format: <string>
589 Override the default clocksource and use the clocksource
590 with the name specified.
591 Some clocksource names to choose from, depending on
592 the platform:
593 [all] jiffies (this is the base, fallback clocksource)
594 [ACPI] acpi_pm
595 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
596 pxa_timer,timer3,32k_counter,timer0_1
597 [AVR32] avr32
598 [X86-32] pit,hpet,tsc;
599 scx200_hrt on Geode; cyclone on IBM x440
600 [MIPS] MIPS
601 [PARISC] cr16
602 [S390] tod
603 [SH] SuperH
604 [SPARC64] tick
605 [X86-64] hpet,tsc
607 clearcpuid=BITNUM [X86]
608 Disable CPUID feature X for the kernel. See
609 arch/x86/include/asm/cpufeature.h for the valid bit
610 numbers. Note the Linux specific bits are not necessarily
611 stable over kernel options, but the vendor specific
612 ones should be.
613 Also note that user programs calling CPUID directly
614 or using the feature without checking anything
615 will still see it. This just prevents it from
616 being used by the kernel or shown in /proc/cpuinfo.
617 Also note the kernel might malfunction if you disable
618 some critical bits.
620 cma=nn[MG] [ARM,KNL]
621 Sets the size of kernel global memory area for contiguous
622 memory allocations. For more information, see
623 include/linux/dma-contiguous.h
625 cmo_free_hint= [PPC] Format: { yes | no }
626 Specify whether pages are marked as being inactive
627 when they are freed. This is used in CMO environments
628 to determine OS memory pressure for page stealing by
629 a hypervisor.
630 Default: yes
632 coherent_pool=nn[KMG] [ARM,KNL]
633 Sets the size of memory pool for coherent, atomic dma
634 allocations, by default set to 256K.
636 code_bytes [X86] How many bytes of object code to print
637 in an oops report.
638 Range: 0 - 8192
639 Default: 64
641 com20020= [HW,NET] ARCnet - COM20020 chipset
642 Format:
643 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
645 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
646 Format: <io>[,<irq>]
648 com90xx= [HW,NET]
649 ARCnet - COM90xx chipset (memory-mapped buffers)
650 Format: <io>[,<irq>[,<memstart>]]
652 condev= [HW,S390] console device
653 conmode=
655 console= [KNL] Output console device and options.
657 tty<n> Use the virtual console device <n>.
659 ttyS<n>[,options]
660 ttyUSB0[,options]
661 Use the specified serial port. The options are of
662 the form "bbbbpnf", where "bbbb" is the baud rate,
663 "p" is parity ("n", "o", or "e"), "n" is number of
664 bits, and "f" is flow control ("r" for RTS or
665 omit it). Default is "9600n8".
667 See Documentation/serial-console.txt for more
668 information. See
669 Documentation/networking/netconsole.txt for an
670 alternative.
672 uart[8250],io,<addr>[,options]
673 uart[8250],mmio,<addr>[,options]
674 Start an early, polled-mode console on the 8250/16550
675 UART at the specified I/O port or MMIO address,
676 switching to the matching ttyS device later. The
677 options are the same as for ttyS, above.
678 hvc<n> Use the hypervisor console device <n>. This is for
679 both Xen and PowerPC hypervisors.
681 If the device connected to the port is not a TTY but a braille
682 device, prepend "brl," before the device type, for instance
683 console=brl,ttyS0
684 For now, only VisioBraille is supported.
686 consoleblank= [KNL] The console blank (screen saver) timeout in
687 seconds. Defaults to 10*60 = 10mins. A value of 0
688 disables the blank timer.
690 coredump_filter=
691 [KNL] Change the default value for
692 /proc/<pid>/coredump_filter.
693 See also Documentation/filesystems/proc.txt.
695 cpuidle.off=1 [CPU_IDLE]
696 disable the cpuidle sub-system
698 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
699 Format:
700 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
702 crashkernel=size[KMG][@offset[KMG]]
703 [KNL] Using kexec, Linux can switch to a 'crash kernel'
704 upon panic. This parameter reserves the physical
705 memory region [offset, offset + size] for that kernel
706 image. If '@offset' is omitted, then a suitable offset
707 is selected automatically. Check
708 Documentation/kdump/kdump.txt for further details.
710 crashkernel=range1:size1[,range2:size2,...][@offset]
711 [KNL] Same as above, but depends on the memory
712 in the running system. The syntax of range is
713 start-[end] where start and end are both
714 a memory unit (amount[KMG]). See also
715 Documentation/kdump/kdump.txt for an example.
717 crashkernel=size[KMG],high
718 [KNL, x86_64] range could be above 4G. Allow kernel
719 to allocate physical memory region from top, so could
720 be above 4G if system have more than 4G ram installed.
721 Otherwise memory region will be allocated below 4G, if
722 available.
723 It will be ignored if crashkernel=X is specified.
724 crashkernel=size[KMG],low
725 [KNL, x86_64] range under 4G. When crashkernel=X,high
726 is passed, kernel could allocate physical memory region
727 above 4G, that cause second kernel crash on system
728 that require some amount of low memory, e.g. swiotlb
729 requires at least 64M+32K low memory. Kernel would
730 try to allocate 72M below 4G automatically.
731 This one let user to specify own low range under 4G
732 for second kernel instead.
733 0: to disable low allocation.
734 It will be ignored when crashkernel=X,high is not used
735 or memory reserved is below 4G.
737 cs89x0_dma= [HW,NET]
738 Format: <dma>
740 cs89x0_media= [HW,NET]
741 Format: { rj45 | aui | bnc }
743 dasd= [HW,NET]
744 See header of drivers/s390/block/dasd_devmap.c.
746 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
747 (one device per port)
748 Format: <port#>,<type>
749 See also Documentation/input/joystick-parport.txt
751 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
752 time. See Documentation/dynamic-debug-howto.txt for
753 details. Deprecated, see dyndbg.
755 debug [KNL] Enable kernel debugging (events log level).
757 debug_locks_verbose=
758 [KNL] verbose self-tests
759 Format=<0|1>
760 Print debugging info while doing the locking API
761 self-tests.
762 We default to 0 (no extra messages), setting it to
763 1 will print _a lot_ more information - normally
764 only useful to kernel developers.
766 debug_objects [KNL] Enable object debugging
768 no_debug_objects
769 [KNL] Disable object debugging
771 debug_guardpage_minorder=
772 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
773 parameter allows control of the order of pages that will
774 be intentionally kept free (and hence protected) by the
775 buddy allocator. Bigger value increase the probability
776 of catching random memory corruption, but reduce the
777 amount of memory for normal system use. The maximum
778 possible value is MAX_ORDER/2. Setting this parameter
779 to 1 or 2 should be enough to identify most random
780 memory corruption problems caused by bugs in kernel or
781 driver code when a CPU writes to (or reads from) a
782 random memory location. Note that there exists a class
783 of memory corruptions problems caused by buggy H/W or
784 F/W or by drivers badly programing DMA (basically when
785 memory is written at bus level and the CPU MMU is
786 bypassed) which are not detectable by
787 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
788 tracking down these problems.
790 debugpat [X86] Enable PAT debugging
792 decnet.addr= [HW,NET]
793 Format: <area>[,<node>]
794 See also Documentation/networking/decnet.txt.
796 default_hugepagesz=
797 [same as hugepagesz=] The size of the default
798 HugeTLB page size. This is the size represented by
799 the legacy /proc/ hugepages APIs, used for SHM, and
800 default size when mounting hugetlbfs filesystems.
801 Defaults to the default architecture's huge page size
802 if not specified.
804 dhash_entries= [KNL]
805 Set number of hash buckets for dentry cache.
807 digi= [HW,SERIAL]
808 IO parameters + enable/disable command.
810 digiepca= [HW,SERIAL]
811 See drivers/char/README.epca and
812 Documentation/serial/digiepca.txt.
814 disable= [IPV6]
815 See Documentation/networking/ipv6.txt.
817 disable_cpu_apicid= [X86,APIC,SMP]
818 Format: <int>
819 The number of initial APIC ID for the
820 corresponding CPU to be disabled at boot,
821 mostly used for the kdump 2nd kernel to
822 disable BSP to wake up multiple CPUs without
823 causing system reset or hang due to sending
824 INIT from AP to BSP.
826 disable_ddw [PPC/PSERIES]
827 Disable Dynamic DMA Window support. Use this if
828 to workaround buggy firmware.
830 disable_ipv6= [IPV6]
831 See Documentation/networking/ipv6.txt.
833 disable_mtrr_cleanup [X86]
834 The kernel tries to adjust MTRR layout from continuous
835 to discrete, to make X server driver able to add WB
836 entry later. This parameter disables that.
838 disable_mtrr_trim [X86, Intel and AMD only]
839 By default the kernel will trim any uncacheable
840 memory out of your available memory pool based on
841 MTRR settings. This parameter disables that behavior,
842 possibly causing your machine to run very slowly.
844 disable_timer_pin_1 [X86]
845 Disable PIN 1 of APIC timer
846 Can be useful to work around chipset bugs.
848 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
849 this option disables the debugging code at boot.
851 dma_debug_entries=<number>
852 This option allows to tune the number of preallocated
853 entries for DMA-API debugging code. One entry is
854 required per DMA-API allocation. Use this if the
855 DMA-API debugging code disables itself because the
856 architectural default is too low.
858 dma_debug_driver=<driver_name>
859 With this option the DMA-API debugging driver
860 filter feature can be enabled at boot time. Just
861 pass the driver to filter for as the parameter.
862 The filter can be disabled or changed to another
863 driver later using sysfs.
865 drm_kms_helper.edid_firmware=[<connector>:]<file>
866 Broken monitors, graphic adapters and KVMs may
867 send no or incorrect EDID data sets. This parameter
868 allows to specify an EDID data set in the
869 /lib/firmware directory that is used instead.
870 Generic built-in EDID data sets are used, if one of
871 edid/1024x768.bin, edid/1280x1024.bin,
872 edid/1680x1050.bin, or edid/1920x1080.bin is given
873 and no file with the same name exists. Details and
874 instructions how to build your own EDID data are
875 available in Documentation/EDID/HOWTO.txt. An EDID
876 data set will only be used for a particular connector,
877 if its name and a colon are prepended to the EDID
878 name.
880 dscc4.setup= [NET]
882 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
883 module.dyndbg[="val"]
884 Enable debug messages at boot time. See
885 Documentation/dynamic-debug-howto.txt for details.
887 earlycon= [KNL] Output early console device and options.
888 uart[8250],io,<addr>[,options]
889 uart[8250],mmio,<addr>[,options]
890 uart[8250],mmio32,<addr>[,options]
891 Start an early, polled-mode console on the 8250/16550
892 UART at the specified I/O port or MMIO address.
893 MMIO inter-register address stride is either 8-bit
894 (mmio) or 32-bit (mmio32).
895 The options are the same as for ttyS, above.
897 earlyprintk= [X86,SH,BLACKFIN,ARM]
898 earlyprintk=vga
899 earlyprintk=efi
900 earlyprintk=xen
901 earlyprintk=serial[,ttySn[,baudrate]]
902 earlyprintk=serial[,0x...[,baudrate]]
903 earlyprintk=ttySn[,baudrate]
904 earlyprintk=dbgp[debugController#]
906 earlyprintk is useful when the kernel crashes before
907 the normal console is initialized. It is not enabled by
908 default because it has some cosmetic problems.
910 Append ",keep" to not disable it when the real console
911 takes over.
913 Only one of vga, efi, serial, or usb debug port can
914 be used at a time.
916 Currently only ttyS0 and ttyS1 may be specified by
917 name. Other I/O ports may be explicitly specified
918 on some architectures (x86 and arm at least) by
919 replacing ttySn with an I/O port address, like this:
920 earlyprintk=serial,0x1008,115200
921 You can find the port for a given device in
922 /proc/tty/driver/serial:
923 2: uart:ST16650V2 port:00001008 irq:18 ...
925 Interaction with the standard serial driver is not
926 very good.
928 The VGA and EFI output is eventually overwritten by
929 the real console.
931 The xen output can only be used by Xen PV guests.
933 edac_report= [HW,EDAC] Control how to report EDAC event
934 Format: {"on" | "off" | "force"}
935 on: enable EDAC to report H/W event. May be overridden
936 by other higher priority error reporting module.
937 off: disable H/W event reporting through EDAC.
938 force: enforce the use of EDAC to report H/W event.
939 default: on.
941 ekgdboc= [X86,KGDB] Allow early kernel console debugging
942 ekgdboc=kbd
944 This is designed to be used in conjunction with
945 the boot argument: earlyprintk=vga
947 edd= [EDD]
948 Format: {"off" | "on" | "skip[mbr]"}
950 efi= [EFI]
951 Format: { "old_map" }
952 old_map [X86-64]: switch to the old ioremap-based EFI
953 runtime services mapping. 32-bit still uses this one by
954 default.
956 efi_no_storage_paranoia [EFI; X86]
957 Using this parameter you can use more than 50% of
958 your efi variable storage. Use this parameter only if
959 you are really sure that your UEFI does sane gc and
960 fulfills the spec otherwise your board may brick.
962 eisa_irq_edge= [PARISC,HW]
963 See header of drivers/parisc/eisa.c.
965 elanfreq= [X86-32]
966 See comment before function elanfreq_setup() in
967 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
969 elevator= [IOSCHED]
970 Format: {"cfq" | "deadline" | "noop"}
971 See Documentation/block/cfq-iosched.txt and
972 Documentation/block/deadline-iosched.txt for details.
974 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
975 Specifies physical address of start of kernel core
976 image elf header and optionally the size. Generally
977 kexec loader will pass this option to capture kernel.
978 See Documentation/kdump/kdump.txt for details.
980 enable_mtrr_cleanup [X86]
981 The kernel tries to adjust MTRR layout from continuous
982 to discrete, to make X server driver able to add WB
983 entry later. This parameter enables that.
985 enable_timer_pin_1 [X86]
986 Enable PIN 1 of APIC timer
987 Can be useful to work around chipset bugs
988 (in particular on some ATI chipsets).
989 The kernel tries to set a reasonable default.
991 enforcing [SELINUX] Set initial enforcing status.
992 Format: {"0" | "1"}
993 See security/selinux/Kconfig help text.
994 0 -- permissive (log only, no denials).
995 1 -- enforcing (deny and log).
996 Default value is 0.
997 Value can be changed at runtime via /selinux/enforce.
999 erst_disable [ACPI]
1000 Disable Error Record Serialization Table (ERST)
1001 support.
1003 ether= [HW,NET] Ethernet cards parameters
1004 This option is obsoleted by the "netdev=" option, which
1005 has equivalent usage. See its documentation for details.
1007 evm= [EVM]
1008 Format: { "fix" }
1009 Permit 'security.evm' to be updated regardless of
1010 current integrity status.
1012 failslab=
1013 fail_page_alloc=
1014 fail_make_request=[KNL]
1015 General fault injection mechanism.
1016 Format: <interval>,<probability>,<space>,<times>
1017 See also Documentation/fault-injection/.
1019 floppy= [HW]
1020 See Documentation/blockdev/floppy.txt.
1022 force_pal_cache_flush
1023 [IA-64] Avoid check_sal_cache_flush which may hang on
1024 buggy SAL_CACHE_FLUSH implementations. Using this
1025 parameter will force ia64_sal_cache_flush to call
1026 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1028 forcepae [X86-32]
1029 Forcefully enable Physical Address Extension (PAE).
1030 Many Pentium M systems disable PAE but may have a
1031 functionally usable PAE implementation.
1032 Warning: use of this parameter will taint the kernel
1033 and may cause unknown problems.
1035 ftrace=[tracer]
1036 [FTRACE] will set and start the specified tracer
1037 as early as possible in order to facilitate early
1038 boot debugging.
1040 ftrace_dump_on_oops[=orig_cpu]
1041 [FTRACE] will dump the trace buffers on oops.
1042 If no parameter is passed, ftrace will dump
1043 buffers of all CPUs, but if you pass orig_cpu, it will
1044 dump only the buffer of the CPU that triggered the
1045 oops.
1047 ftrace_filter=[function-list]
1048 [FTRACE] Limit the functions traced by the function
1049 tracer at boot up. function-list is a comma separated
1050 list of functions. This list can be changed at run
1051 time by the set_ftrace_filter file in the debugfs
1052 tracing directory.
1054 ftrace_notrace=[function-list]
1055 [FTRACE] Do not trace the functions specified in
1056 function-list. This list can be changed at run time
1057 by the set_ftrace_notrace file in the debugfs
1058 tracing directory.
1060 ftrace_graph_filter=[function-list]
1061 [FTRACE] Limit the top level callers functions traced
1062 by the function graph tracer at boot up.
1063 function-list is a comma separated list of functions
1064 that can be changed at run time by the
1065 set_graph_function file in the debugfs tracing directory.
1067 gamecon.map[2|3]=
1068 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1069 support via parallel port (up to 5 devices per port)
1070 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1071 See also Documentation/input/joystick-parport.txt
1073 gamma= [HW,DRM]
1075 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1076 Format: off | on
1077 default: on
1079 gcov_persist= [GCOV] When non-zero (default), profiling data for
1080 kernel modules is saved and remains accessible via
1081 debugfs, even when the module is unloaded/reloaded.
1082 When zero, profiling data is discarded and associated
1083 debugfs files are removed at module unload time.
1085 gpt [EFI] Forces disk with valid GPT signature but
1086 invalid Protective MBR to be treated as GPT. If the
1087 primary GPT is corrupted, it enables the backup/alternate
1088 GPT to be used instead.
1090 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1091 the "Enable 0" bit of the configuration register.
1092 Format: 0 | 1
1093 Default: 0
1094 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1095 the "Enable 0" bit of the configuration register.
1096 Format: 0 | 1
1097 Default: 0
1098 grcan.select= [HW] Select which physical interface to use.
1099 Format: 0 | 1
1100 Default: 0
1101 grcan.txsize= [HW] Sets the size of the tx buffer.
1102 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1103 Default: 1024
1104 grcan.rxsize= [HW] Sets the size of the rx buffer.
1105 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1106 Default: 1024
1108 hashdist= [KNL,NUMA] Large hashes allocated during boot
1109 are distributed across NUMA nodes. Defaults on
1110 for 64-bit NUMA, off otherwise.
1111 Format: 0 | 1 (for off | on)
1113 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1115 hd= [EIDE] (E)IDE hard drive subsystem geometry
1116 Format: <cyl>,<head>,<sect>
1118 hest_disable [ACPI]
1119 Disable Hardware Error Source Table (HEST) support;
1120 corresponding firmware-first mode error processing
1121 logic will be disabled.
1123 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1124 size of <nn>. This works even on boxes that have no
1125 highmem otherwise. This also works to reduce highmem
1126 size on bigger boxes.
1128 highres= [KNL] Enable/disable high resolution timer mode.
1129 Valid parameters: "on", "off"
1130 Default: "on"
1132 hisax= [HW,ISDN]
1133 See Documentation/isdn/README.HiSax.
1135 hlt [BUGS=ARM,SH]
1137 hpet= [X86-32,HPET] option to control HPET usage
1138 Format: { enable (default) | disable | force |
1139 verbose }
1140 disable: disable HPET and use PIT instead
1141 force: allow force enabled of undocumented chips (ICH4,
1142 VIA, nVidia)
1143 verbose: show contents of HPET registers during setup
1145 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1146 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1148 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1149 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1150 On x86-64 and powerpc, this option can be specified
1151 multiple times interleaved with hugepages= to reserve
1152 huge pages of different sizes. Valid pages sizes on
1153 x86-64 are 2M (when the CPU supports "pse") and 1G
1154 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1155 Note that 1GB pages can only be allocated at boot time
1156 using hugepages= and not freed afterwards.
1158 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1159 terminal devices. Valid values: 0..8
1160 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1161 If specified, z/VM IUCV HVC accepts connections
1162 from listed z/VM user IDs only.
1164 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1165 hardware thread id mappings.
1166 Format: <cpu>:<hwthread>
1168 keep_bootcon [KNL]
1169 Do not unregister boot console at start. This is only
1170 useful for debugging when something happens in the window
1171 between unregistering the boot console and initializing
1172 the real console.
1174 i2c_bus= [HW] Override the default board specific I2C bus speed
1175 or register an additional I2C bus that is not
1176 registered from board initialization code.
1177 Format:
1178 <bus_id>,<clkrate>
1180 i8042.debug [HW] Toggle i8042 debug mode
1181 i8042.direct [HW] Put keyboard port into non-translated mode
1182 i8042.dumbkbd [HW] Pretend that controller can only read data from
1183 keyboard and cannot control its state
1184 (Don't attempt to blink the leds)
1185 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1186 i8042.nokbd [HW] Don't check/create keyboard port
1187 i8042.noloop [HW] Disable the AUX Loopback command while probing
1188 for the AUX port
1189 i8042.nomux [HW] Don't check presence of an active multiplexing
1190 controller
1191 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1192 controllers
1193 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1194 i8042.reset [HW] Reset the controller during init and cleanup
1195 i8042.unlock [HW] Unlock (ignore) the keylock
1197 i810= [HW,DRM]
1199 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1200 indicates that the driver is running on unsupported
1201 hardware.
1202 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1203 does not match list of supported models.
1204 i8k.power_status
1205 [HW] Report power status in /proc/i8k
1206 (disabled by default)
1207 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1208 capability is set.
1210 i915.invert_brightness=
1211 [DRM] Invert the sense of the variable that is used to
1212 set the brightness of the panel backlight. Normally a
1213 brightness value of 0 indicates backlight switched off,
1214 and the maximum of the brightness value sets the backlight
1215 to maximum brightness. If this parameter is set to 0
1216 (default) and the machine requires it, or this parameter
1217 is set to 1, a brightness value of 0 sets the backlight
1218 to maximum brightness, and the maximum of the brightness
1219 value switches the backlight off.
1220 -1 -- never invert brightness
1221 0 -- machine default
1222 1 -- force brightness inversion
1224 icn= [HW,ISDN]
1225 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1227 ide-core.nodma= [HW] (E)IDE subsystem
1228 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1229 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1230 .cdrom .chs .ignore_cable are additional options
1231 See Documentation/ide/ide.txt.
1233 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1234 Claim all unknown PCI IDE storage controllers.
1236 idle= [X86]
1237 Format: idle=poll, idle=halt, idle=nomwait
1238 Poll forces a polling idle loop that can slightly
1239 improve the performance of waking up a idle CPU, but
1240 will use a lot of power and make the system run hot.
1241 Not recommended.
1242 idle=halt: Halt is forced to be used for CPU idle.
1243 In such case C2/C3 won't be used again.
1244 idle=nomwait: Disable mwait for CPU C-states
1246 ignore_loglevel [KNL]
1247 Ignore loglevel setting - this will print /all/
1248 kernel messages to the console. Useful for debugging.
1249 We also add it as printk module parameter, so users
1250 could change it dynamically, usually by
1251 /sys/module/printk/parameters/ignore_loglevel.
1253 ihash_entries= [KNL]
1254 Set number of hash buckets for inode cache.
1256 ima_appraise= [IMA] appraise integrity measurements
1257 Format: { "off" | "enforce" | "fix" }
1258 default: "enforce"
1260 ima_appraise_tcb [IMA]
1261 The builtin appraise policy appraises all files
1262 owned by uid=0.
1264 ima_hash= [IMA]
1265 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1266 | sha512 | ... }
1267 default: "sha1"
1269 The list of supported hash algorithms is defined
1270 in crypto/hash_info.h.
1272 ima_tcb [IMA]
1273 Load a policy which meets the needs of the Trusted
1274 Computing Base. This means IMA will measure all
1275 programs exec'd, files mmap'd for exec, and all files
1276 opened for read by uid=0.
1278 ima_template= [IMA]
1279 Select one of defined IMA measurements template formats.
1280 Formats: { "ima" | "ima-ng" }
1281 Default: "ima-ng"
1283 init= [KNL]
1284 Format: <full_path>
1285 Run specified binary instead of /sbin/init as init
1286 process.
1288 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1289 for working out where the kernel is dying during
1290 startup.
1292 initrd= [BOOT] Specify the location of the initial ramdisk
1294 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1295 Format: <irq>
1297 int_pln_enable [x86] Enable power limit notification interrupt
1299 integrity_audit=[IMA]
1300 Format: { "0" | "1" }
1301 0 -- basic integrity auditing messages. (Default)
1302 1 -- additional integrity auditing messages.
1304 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1305 on
1306 Enable intel iommu driver.
1307 off
1308 Disable intel iommu driver.
1309 igfx_off [Default Off]
1310 By default, gfx is mapped as normal device. If a gfx
1311 device has a dedicated DMAR unit, the DMAR unit is
1312 bypassed by not enabling DMAR with this option. In
1313 this case, gfx device will use physical address for
1314 DMA.
1315 forcedac [x86_64]
1316 With this option iommu will not optimize to look
1317 for io virtual address below 32-bit forcing dual
1318 address cycle on pci bus for cards supporting greater
1319 than 32-bit addressing. The default is to look
1320 for translation below 32-bit and if not available
1321 then look in the higher range.
1322 strict [Default Off]
1323 With this option on every unmap_single operation will
1324 result in a hardware IOTLB flush operation as opposed
1325 to batching them for performance.
1326 sp_off [Default Off]
1327 By default, super page will be supported if Intel IOMMU
1328 has the capability. With this option, super page will
1329 not be supported.
1331 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1332 0 disables intel_idle and fall back on acpi_idle.
1333 1 to 6 specify maximum depth of C-state.
1335 intel_pstate= [X86]
1336 disable
1337 Do not enable intel_pstate as the default
1338 scaling driver for the supported processors
1340 intremap= [X86-64, Intel-IOMMU]
1341 on enable Interrupt Remapping (default)
1342 off disable Interrupt Remapping
1343 nosid disable Source ID checking
1344 no_x2apic_optout
1345 BIOS x2APIC opt-out request will be ignored
1347 iomem= Disable strict checking of access to MMIO memory
1348 strict regions from userspace.
1349 relaxed
1351 iommu= [x86]
1352 off
1353 force
1354 noforce
1355 biomerge
1356 panic
1357 nopanic
1358 merge
1359 nomerge
1360 forcesac
1361 soft
1362 pt [x86, IA-64]
1365 io7= [HW] IO7 for Marvel based alpha systems
1366 See comment before marvel_specify_io7 in
1367 arch/alpha/kernel/core_marvel.c.
1369 io_delay= [X86] I/O delay method
1370 0x80
1371 Standard port 0x80 based delay
1372 0xed
1373 Alternate port 0xed based delay (needed on some systems)
1374 udelay
1375 Simple two microseconds delay
1376 none
1377 No delay
1379 ip= [IP_PNP]
1380 See Documentation/filesystems/nfs/nfsroot.txt.
1382 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1383 See comment before ip2_setup() in
1384 drivers/char/ip2/ip2base.c.
1386 irqfixup [HW]
1387 When an interrupt is not handled search all handlers
1388 for it. Intended to get systems with badly broken
1389 firmware running.
1391 irqpoll [HW]
1392 When an interrupt is not handled search all handlers
1393 for it. Also check all handlers each timer
1394 interrupt. Intended to get systems with badly broken
1395 firmware running.
1397 isapnp= [ISAPNP]
1398 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1400 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1401 Format:
1402 <cpu number>,...,<cpu number>
1403 or
1404 <cpu number>-<cpu number>
1405 (must be a positive range in ascending order)
1406 or a mixture
1407 <cpu number>,...,<cpu number>-<cpu number>
1409 This option can be used to specify one or more CPUs
1410 to isolate from the general SMP balancing and scheduling
1411 algorithms. You can move a process onto or off an
1412 "isolated" CPU via the CPU affinity syscalls or cpuset.
1413 <cpu number> begins at 0 and the maximum value is
1414 "number of CPUs in system - 1".
1416 This option is the preferred way to isolate CPUs. The
1417 alternative -- manually setting the CPU mask of all
1418 tasks in the system -- can cause problems and
1419 suboptimal load balancer performance.
1421 iucv= [HW,NET]
1423 ivrs_ioapic [HW,X86_64]
1424 Provide an override to the IOAPIC-ID<->DEVICE-ID
1425 mapping provided in the IVRS ACPI table. For
1426 example, to map IOAPIC-ID decimal 10 to
1427 PCI device 00:14.0 write the parameter as:
1428 ivrs_ioapic[10]=00:14.0
1430 ivrs_hpet [HW,X86_64]
1431 Provide an override to the HPET-ID<->DEVICE-ID
1432 mapping provided in the IVRS ACPI table. For
1433 example, to map HPET-ID decimal 0 to
1434 PCI device 00:14.0 write the parameter as:
1435 ivrs_hpet[0]=00:14.0
1437 js= [HW,JOY] Analog joystick
1438 See Documentation/input/joystick.txt.
1440 keepinitrd [HW,ARM]
1442 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1443 specifies the amount of memory usable by the kernel
1444 for non-movable allocations. The requested amount is
1445 spread evenly throughout all nodes in the system. The
1446 remaining memory in each node is used for Movable
1447 pages. In the event, a node is too small to have both
1448 kernelcore and Movable pages, kernelcore pages will
1449 take priority and other nodes will have a larger number
1450 of Movable pages. The Movable zone is used for the
1451 allocation of pages that may be reclaimed or moved
1452 by the page migration subsystem. This means that
1453 HugeTLB pages may not be allocated from this zone.
1454 Note that allocations like PTEs-from-HighMem still
1455 use the HighMem zone if it exists, and the Normal
1456 zone if it does not.
1458 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1459 Format: <Controller#>[,poll interval]
1460 The controller # is the number of the ehci usb debug
1461 port as it is probed via PCI. The poll interval is
1462 optional and is the number seconds in between
1463 each poll cycle to the debug port in case you need
1464 the functionality for interrupting the kernel with
1465 gdb or control-c on the dbgp connection. When
1466 not using this parameter you use sysrq-g to break into
1467 the kernel debugger.
1469 kgdboc= [KGDB,HW] kgdb over consoles.
1470 Requires a tty driver that supports console polling,
1471 or a supported polling keyboard driver (non-usb).
1472 Serial only format: <serial_device>[,baud]
1473 keyboard only format: kbd
1474 keyboard and serial format: kbd,<serial_device>[,baud]
1475 Optional Kernel mode setting:
1476 kms, kbd format: kms,kbd
1477 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1479 kgdbwait [KGDB] Stop kernel execution and enter the
1480 kernel debugger at the earliest opportunity.
1482 kmac= [MIPS] korina ethernet MAC address.
1483 Configure the RouterBoard 532 series on-chip
1484 Ethernet adapter MAC address.
1486 kmemleak= [KNL] Boot-time kmemleak enable/disable
1487 Valid arguments: on, off
1488 Default: on
1490 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1491 Valid arguments: 0, 1, 2
1492 kmemcheck=0 (disabled)
1493 kmemcheck=1 (enabled)
1494 kmemcheck=2 (one-shot mode)
1495 Default: 2 (one-shot mode)
1497 kstack=N [X86] Print N words from the kernel stack
1498 in oops dumps.
1500 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1501 Default is 0 (don't ignore, but inject #GP)
1503 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1504 KVM MMU at runtime.
1505 Default is 0 (off)
1507 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1508 Default is 1 (enabled)
1510 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1511 for all guests.
1512 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1514 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1515 (virtualized MMU) support on capable Intel chips.
1516 Default is 1 (enabled)
1518 kvm-intel.emulate_invalid_guest_state=
1519 [KVM,Intel] Enable emulation of invalid guest states
1520 Default is 0 (disabled)
1522 kvm-intel.flexpriority=
1523 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1524 Default is 1 (enabled)
1526 kvm-intel.nested=
1527 [KVM,Intel] Enable VMX nesting (nVMX).
1528 Default is 0 (disabled)
1530 kvm-intel.unrestricted_guest=
1531 [KVM,Intel] Disable unrestricted guest feature
1532 (virtualized real and unpaged mode) on capable
1533 Intel chips. Default is 1 (enabled)
1535 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1536 feature (tagged TLBs) on capable Intel chips.
1537 Default is 1 (enabled)
1539 l2cr= [PPC]
1541 l3cr= [PPC]
1543 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1544 disabled it.
1546 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1547 value for LAPIC timer one-shot implementation. Default
1548 back to the programmable timer unit in the LAPIC.
1550 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1551 in C2 power state.
1553 libata.dma= [LIBATA] DMA control
1554 libata.dma=0 Disable all PATA and SATA DMA
1555 libata.dma=1 PATA and SATA Disk DMA only
1556 libata.dma=2 ATAPI (CDROM) DMA only
1557 libata.dma=4 Compact Flash DMA only
1558 Combinations also work, so libata.dma=3 enables DMA
1559 for disks and CDROMs, but not CFs.
1561 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1562 libata.ignore_hpa=0 keep BIOS limits (default)
1563 libata.ignore_hpa=1 ignore limits, using full disk
1565 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1566 when set.
1567 Format: <int>
1569 libata.force= [LIBATA] Force configurations. The format is comma
1570 separated list of "[ID:]VAL" where ID is
1571 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1572 matching port, link or device. Basically, it matches
1573 the ATA ID string printed on console by libata. If
1574 the whole ID part is omitted, the last PORT and DEVICE
1575 values are used. If ID hasn't been specified yet, the
1576 configuration applies to all ports, links and devices.
1578 If only DEVICE is omitted, the parameter applies to
1579 the port and all links and devices behind it. DEVICE
1580 number of 0 either selects the first device or the
1581 first fan-out link behind PMP device. It does not
1582 select the host link. DEVICE number of 15 selects the
1583 host link and device attached to it.
1585 The VAL specifies the configuration to force. As long
1586 as there's no ambiguity shortcut notation is allowed.
1587 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1588 The following configurations can be forced.
1590 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1591 Any ID with matching PORT is used.
1593 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1595 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1596 udma[/][16,25,33,44,66,100,133] notation is also
1597 allowed.
1599 * [no]ncq: Turn on or off NCQ.
1601 * nohrst, nosrst, norst: suppress hard, soft
1602 and both resets.
1604 * rstonce: only attempt one reset during
1605 hot-unplug link recovery
1607 * dump_id: dump IDENTIFY data.
1609 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1611 * disable: Disable this device.
1613 If there are multiple matching configurations changing
1614 the same attribute, the last one is used.
1616 memblock=debug [KNL] Enable memblock debug messages.
1618 load_ramdisk= [RAM] List of ramdisks to load from floppy
1619 See Documentation/blockdev/ramdisk.txt.
1621 lockd.nlm_grace_period=P [NFS] Assign grace period.
1622 Format: <integer>
1624 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1625 Format: <integer>
1627 lockd.nlm_timeout=T [NFS] Assign timeout value.
1628 Format: <integer>
1630 lockd.nlm_udpport=M [NFS] Assign UDP port.
1631 Format: <integer>
1633 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1634 Format: <irq>
1636 loglevel= All Kernel Messages with a loglevel smaller than the
1637 console loglevel will be printed to the console. It can
1638 also be changed with klogd or other programs. The
1639 loglevels are defined as follows:
1641 0 (KERN_EMERG) system is unusable
1642 1 (KERN_ALERT) action must be taken immediately
1643 2 (KERN_CRIT) critical conditions
1644 3 (KERN_ERR) error conditions
1645 4 (KERN_WARNING) warning conditions
1646 5 (KERN_NOTICE) normal but significant condition
1647 6 (KERN_INFO) informational
1648 7 (KERN_DEBUG) debug-level messages
1650 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1651 in bytes. n must be a power of two. The default
1652 size is set in the kernel config file.
1654 logo.nologo [FB] Disables display of the built-in Linux logo.
1655 This may be used to provide more screen space for
1656 kernel log messages and is useful when debugging
1657 kernel boot problems.
1659 lp=0 [LP] Specify parallel ports to use, e.g,
1660 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1661 lp=reset first parallel port). 'lp=0' disables the
1662 lp=auto printer driver. 'lp=reset' (which can be
1663 specified in addition to the ports) causes
1664 attached printers to be reset. Using
1665 lp=port1,port2,... specifies the parallel ports
1666 to associate lp devices with, starting with
1667 lp0. A port specification may be 'none' to skip
1668 that lp device, or a parport name such as
1669 'parport0'. Specifying 'lp=auto' instead of a
1670 port specification list means that device IDs
1671 from each port should be examined, to see if
1672 an IEEE 1284-compliant printer is attached; if
1673 so, the driver will manage that printer.
1674 See also header of drivers/char/lp.c.
1676 lpj=n [KNL]
1677 Sets loops_per_jiffy to given constant, thus avoiding
1678 time-consuming boot-time autodetection (up to 250 ms per
1679 CPU). 0 enables autodetection (default). To determine
1680 the correct value for your kernel, boot with normal
1681 autodetection and see what value is printed. Note that
1682 on SMP systems the preset will be applied to all CPUs,
1683 which is likely to cause problems if your CPUs need
1684 significantly divergent settings. An incorrect value
1685 will cause delays in the kernel to be wrong, leading to
1686 unpredictable I/O errors and other breakage. Although
1687 unlikely, in the extreme case this might damage your
1688 hardware.
1690 ltpc= [NET]
1691 Format: <io>,<irq>,<dma>
1693 machvec= [IA-64] Force the use of a particular machine-vector
1694 (machvec) in a generic kernel.
1695 Example: machvec=hpzx1_swiotlb
1697 machtype= [Loongson] Share the same kernel image file between different
1698 yeeloong laptop.
1699 Example: machtype=lemote-yeeloong-2f-7inch
1701 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1702 than or equal to this physical address is ignored.
1704 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1705 should make use of. maxcpus=n : n >= 0 limits the
1706 kernel to using 'n' processors. n=0 is a special case,
1707 it is equivalent to "nosmp", which also disables
1708 the IO APIC.
1710 max_loop= [LOOP] The number of loop block devices that get
1711 (loop.max_loop) unconditionally pre-created at init time. The default
1712 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1713 of statically allocating a predefined number, loop
1714 devices can be requested on-demand with the
1715 /dev/loop-control interface.
1717 mce [X86-32] Machine Check Exception
1719 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1721 md= [HW] RAID subsystems devices and level
1722 See Documentation/md.txt.
1724 mdacon= [MDA]
1725 Format: <first>,<last>
1726 Specifies range of consoles to be captured by the MDA.
1728 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1729 Amount of memory to be used when the kernel is not able
1730 to see the whole system memory or for test.
1731 [X86] Work as limiting max address. Use together
1732 with memmap= to avoid physical address space collisions.
1733 Without memmap= PCI devices could be placed at addresses
1734 belonging to unused RAM.
1736 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1737 memory.
1739 memchunk=nn[KMG]
1740 [KNL,SH] Allow user to override the default size for
1741 per-device physically contiguous DMA buffers.
1743 memmap=exactmap [KNL,X86] Enable setting of an exact
1744 E820 memory map, as specified by the user.
1745 Such memmap=exactmap lines can be constructed based on
1746 BIOS output or other requirements. See the memmap=nn@ss
1747 option description.
1749 memmap=nn[KMG]@ss[KMG]
1750 [KNL] Force usage of a specific region of memory.
1751 Region of memory to be used is from ss to ss+nn.
1753 memmap=nn[KMG]#ss[KMG]
1754 [KNL,ACPI] Mark specific memory as ACPI data.
1755 Region of memory to be marked is from ss to ss+nn.
1757 memmap=nn[KMG]$ss[KMG]
1758 [KNL,ACPI] Mark specific memory as reserved.
1759 Region of memory to be reserved is from ss to ss+nn.
1760 Example: Exclude memory from 0x18690000-0x1869ffff
1761 memmap=64K$0x18690000
1762 or
1763 memmap=0x10000$0x18690000
1765 memory_corruption_check=0/1 [X86]
1766 Some BIOSes seem to corrupt the first 64k of
1767 memory when doing things like suspend/resume.
1768 Setting this option will scan the memory
1769 looking for corruption. Enabling this will
1770 both detect corruption and prevent the kernel
1771 from using the memory being corrupted.
1772 However, its intended as a diagnostic tool; if
1773 repeatable BIOS-originated corruption always
1774 affects the same memory, you can use memmap=
1775 to prevent the kernel from using that memory.
1777 memory_corruption_check_size=size [X86]
1778 By default it checks for corruption in the low
1779 64k, making this memory unavailable for normal
1780 use. Use this parameter to scan for
1781 corruption in more or less memory.
1783 memory_corruption_check_period=seconds [X86]
1784 By default it checks for corruption every 60
1785 seconds. Use this parameter to check at some
1786 other rate. 0 disables periodic checking.
1788 memtest= [KNL,X86] Enable memtest
1789 Format: <integer>
1790 default : 0 <disable>
1791 Specifies the number of memtest passes to be
1792 performed. Each pass selects another test
1793 pattern from a given set of patterns. Memtest
1794 fills the memory with this pattern, validates
1795 memory contents and reserves bad memory
1796 regions that are detected.
1798 meye.*= [HW] Set MotionEye Camera parameters
1799 See Documentation/video4linux/meye.txt.
1801 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1802 Multi-Function General Purpose Timers on AMD Geode
1803 platforms.
1805 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1806 the BIOS has incorrectly applied a workaround. TinyBIOS
1807 version 0.98 is known to be affected, 0.99 fixes the
1808 problem by letting the user disable the workaround.
1810 mga= [HW,DRM]
1812 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1813 physical address is ignored.
1815 mini2440= [ARM,HW,KNL]
1816 Format:[0..2][b][c][t]
1817 Default: "0tb"
1818 MINI2440 configuration specification:
1819 0 - The attached screen is the 3.5" TFT
1820 1 - The attached screen is the 7" TFT
1821 2 - The VGA Shield is attached (1024x768)
1822 Leaving out the screen size parameter will not load
1823 the TFT driver, and the framebuffer will be left
1824 unconfigured.
1825 b - Enable backlight. The TFT backlight pin will be
1826 linked to the kernel VESA blanking code and a GPIO
1827 LED. This parameter is not necessary when using the
1828 VGA shield.
1829 c - Enable the s3c camera interface.
1830 t - Reserved for enabling touchscreen support. The
1831 touchscreen support is not enabled in the mainstream
1832 kernel as of 2.6.30, a preliminary port can be found
1833 in the "bleeding edge" mini2440 support kernel at
1834 http://repo.or.cz/w/linux-2.6/mini2440.git
1836 mminit_loglevel=
1837 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1838 parameter allows control of the logging verbosity for
1839 the additional memory initialisation checks. A value
1840 of 0 disables mminit logging and a level of 4 will
1841 log everything. Information is printed at KERN_DEBUG
1842 so loglevel=8 may also need to be specified.
1844 module.sig_enforce
1845 [KNL] When CONFIG_MODULE_SIG is set, this means that
1846 modules without (valid) signatures will fail to load.
1847 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1848 is always true, so this option does nothing.
1850 mousedev.tap_time=
1851 [MOUSE] Maximum time between finger touching and
1852 leaving touchpad surface for touch to be considered
1853 a tap and be reported as a left button click (for
1854 touchpads working in absolute mode only).
1855 Format: <msecs>
1856 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1857 reporting absolute coordinates, such as tablets
1858 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1859 reporting absolute coordinates, such as tablets
1861 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1862 is similar to kernelcore except it specifies the
1863 amount of memory used for migratable allocations.
1864 If both kernelcore and movablecore is specified,
1865 then kernelcore will be at *least* the specified
1866 value but may be more. If movablecore on its own
1867 is specified, the administrator must be careful
1868 that the amount of memory usable for all allocations
1869 is not too small.
1871 movable_node [KNL,X86] Boot-time switch to enable the effects
1872 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
1874 MTD_Partition= [MTD]
1875 Format: <name>,<region-number>,<size>,<offset>
1877 MTD_Region= [MTD] Format:
1878 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1880 mtdparts= [MTD]
1881 See drivers/mtd/cmdlinepart.c.
1883 multitce=off [PPC] This parameter disables the use of the pSeries
1884 firmware feature for updating multiple TCE entries
1885 at a time.
1887 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1889 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1891 boundary - index of last SLC block on Flex-OneNAND.
1892 The remaining blocks are configured as MLC blocks.
1893 lock - Configure if Flex-OneNAND boundary should be locked.
1894 Once locked, the boundary cannot be changed.
1895 1 indicates lock status, 0 indicates unlock status.
1897 mtdset= [ARM]
1898 ARM/S3C2412 JIVE boot control
1900 See arch/arm/mach-s3c2412/mach-jive.c
1902 mtouchusb.raw_coordinates=
1903 [HW] Make the MicroTouch USB driver use raw coordinates
1904 ('y', default) or cooked coordinates ('n')
1906 mtrr_chunk_size=nn[KMG] [X86]
1907 used for mtrr cleanup. It is largest continuous chunk
1908 that could hold holes aka. UC entries.
1910 mtrr_gran_size=nn[KMG] [X86]
1911 Used for mtrr cleanup. It is granularity of mtrr block.
1912 Default is 1.
1913 Large value could prevent small alignment from
1914 using up MTRRs.
1916 mtrr_spare_reg_nr=n [X86]
1917 Format: <integer>
1918 Range: 0,7 : spare reg number
1919 Default : 1
1920 Used for mtrr cleanup. It is spare mtrr entries number.
1921 Set to 2 or more if your graphical card needs more.
1923 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1925 netdev= [NET] Network devices parameters
1926 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1927 Note that mem_start is often overloaded to mean
1928 something different and driver-specific.
1929 This usage is only documented in each driver source
1930 file if at all.
1932 nf_conntrack.acct=
1933 [NETFILTER] Enable connection tracking flow accounting
1934 0 to disable accounting
1935 1 to enable accounting
1936 Default value is 0.
1938 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1939 See Documentation/filesystems/nfs/nfsroot.txt.
1941 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1942 See Documentation/filesystems/nfs/nfsroot.txt.
1944 nfsrootdebug [NFS] enable nfsroot debugging messages.
1945 See Documentation/filesystems/nfs/nfsroot.txt.
1947 nfs.callback_tcpport=
1948 [NFS] set the TCP port on which the NFSv4 callback
1949 channel should listen.
1951 nfs.cache_getent=
1952 [NFS] sets the pathname to the program which is used
1953 to update the NFS client cache entries.
1955 nfs.cache_getent_timeout=
1956 [NFS] sets the timeout after which an attempt to
1957 update a cache entry is deemed to have failed.
1959 nfs.idmap_cache_timeout=
1960 [NFS] set the maximum lifetime for idmapper cache
1961 entries.
1963 nfs.enable_ino64=
1964 [NFS] enable 64-bit inode numbers.
1965 If zero, the NFS client will fake up a 32-bit inode
1966 number for the readdir() and stat() syscalls instead
1967 of returning the full 64-bit number.
1968 The default is to return 64-bit inode numbers.
1970 nfs.max_session_slots=
1971 [NFSv4.1] Sets the maximum number of session slots
1972 the client will attempt to negotiate with the server.
1973 This limits the number of simultaneous RPC requests
1974 that the client can send to the NFSv4.1 server.
1975 Note that there is little point in setting this
1976 value higher than the max_tcp_slot_table_limit.
1978 nfs.nfs4_disable_idmapping=
1979 [NFSv4] When set to the default of '1', this option
1980 ensures that both the RPC level authentication
1981 scheme and the NFS level operations agree to use
1982 numeric uids/gids if the mount is using the
1983 'sec=sys' security flavour. In effect it is
1984 disabling idmapping, which can make migration from
1985 legacy NFSv2/v3 systems to NFSv4 easier.
1986 Servers that do not support this mode of operation
1987 will be autodetected by the client, and it will fall
1988 back to using the idmapper.
1989 To turn off this behaviour, set the value to '0'.
1990 nfs.nfs4_unique_id=
1991 [NFS4] Specify an additional fixed unique ident-
1992 ification string that NFSv4 clients can insert into
1993 their nfs_client_id4 string. This is typically a
1994 UUID that is generated at system install time.
1996 nfs.send_implementation_id =
1997 [NFSv4.1] Send client implementation identification
1998 information in exchange_id requests.
1999 If zero, no implementation identification information
2000 will be sent.
2001 The default is to send the implementation identification
2002 information.
2004 nfs.recover_lost_locks =
2005 [NFSv4] Attempt to recover locks that were lost due
2006 to a lease timeout on the server. Please note that
2007 doing this risks data corruption, since there are
2008 no guarantees that the file will remain unchanged
2009 after the locks are lost.
2010 If you want to enable the kernel legacy behaviour of
2011 attempting to recover these locks, then set this
2012 parameter to '1'.
2013 The default parameter value of '0' causes the kernel
2014 not to attempt recovery of lost locks.
2016 nfsd.nfs4_disable_idmapping=
2017 [NFSv4] When set to the default of '1', the NFSv4
2018 server will return only numeric uids and gids to
2019 clients using auth_sys, and will accept numeric uids
2020 and gids from such clients. This is intended to ease
2021 migration from NFSv2/v3.
2023 objlayoutdriver.osd_login_prog=
2024 [NFS] [OBJLAYOUT] sets the pathname to the program which
2025 is used to automatically discover and login into new
2026 osd-targets. Please see:
2027 Documentation/filesystems/pnfs.txt for more explanations
2029 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2030 when a NMI is triggered.
2031 Format: [state][,regs][,debounce][,die]
2033 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2034 Format: [panic,][nopanic,][num]
2035 Valid num: 0
2036 0 - turn nmi_watchdog off
2037 When panic is specified, panic when an NMI watchdog
2038 timeout occurs (or 'nopanic' to override the opposite
2039 default).
2040 This is useful when you use a panic=... timeout and
2041 need the box quickly up again.
2043 netpoll.carrier_timeout=
2044 [NET] Specifies amount of time (in seconds) that
2045 netpoll should wait for a carrier. By default netpoll
2046 waits 4 seconds.
2048 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2049 emulation library even if a 387 maths coprocessor
2050 is present.
2052 no_console_suspend
2053 [HW] Never suspend the console
2054 Disable suspending of consoles during suspend and
2055 hibernate operations. Once disabled, debugging
2056 messages can reach various consoles while the rest
2057 of the system is being put to sleep (ie, while
2058 debugging driver suspend/resume hooks). This may
2059 not work reliably with all consoles, but is known
2060 to work with serial and VGA consoles.
2061 To facilitate more flexible debugging, we also add
2062 console_suspend, a printk module parameter to control
2063 it. Users could use console_suspend (usually
2064 /sys/module/printk/parameters/console_suspend) to
2065 turn on/off it dynamically.
2067 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2068 caches in the slab allocator. Saves per-node memory,
2069 but will impact performance.
2071 noalign [KNL,ARM]
2073 noapic [SMP,APIC] Tells the kernel to not make use of any
2074 IOAPICs that may be present in the system.
2076 nokaslr [X86]
2077 Disable kernel and module base offset ASLR (Address
2078 Space Layout Randomization) if built into the kernel.
2080 noautogroup Disable scheduler automatic task group creation.
2082 nobats [PPC] Do not use BATs for mapping kernel lowmem
2083 on "Classic" PPC cores.
2085 nocache [ARM]
2087 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2089 nodelayacct [KNL] Disable per-task delay accounting
2091 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2093 nodsp [SH] Disable hardware DSP at boot time.
2095 noefi [X86] Disable EFI runtime services support.
2097 noexec [IA-64]
2099 noexec [X86]
2100 On X86-32 available only on PAE configured kernels.
2101 noexec=on: enable non-executable mappings (default)
2102 noexec=off: disable non-executable mappings
2104 nosmap [X86]
2105 Disable SMAP (Supervisor Mode Access Prevention)
2106 even if it is supported by processor.
2108 nosmep [X86]
2109 Disable SMEP (Supervisor Mode Execution Prevention)
2110 even if it is supported by processor.
2112 noexec32 [X86-64]
2113 This affects only 32-bit executables.
2114 noexec32=on: enable non-executable mappings (default)
2115 read doesn't imply executable mappings
2116 noexec32=off: disable non-executable mappings
2117 read implies executable mappings
2119 nofpu [SH] Disable hardware FPU at boot time.
2121 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2122 register save and restore. The kernel will only save
2123 legacy floating-point registers on task switch.
2125 noxsave [BUGS=X86] Disables x86 extended register state save
2126 and restore using xsave. The kernel will fallback to
2127 enabling legacy floating-point and sse state.
2129 eagerfpu= [X86]
2130 on enable eager fpu restore
2131 off disable eager fpu restore
2132 auto selects the default scheme, which automatically
2133 enables eagerfpu restore for xsaveopt.
2135 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2136 wfi(ARM) instruction doesn't work correctly and not to
2137 use it. This is also useful when using JTAG debugger.
2139 no_file_caps Tells the kernel not to honor file capabilities. The
2140 only way then for a file to be executed with privilege
2141 is to be setuid root or executed by root.
2143 nohalt [IA-64] Tells the kernel not to use the power saving
2144 function PAL_HALT_LIGHT when idle. This increases
2145 power-consumption. On the positive side, it reduces
2146 interrupt wake-up latency, which may improve performance
2147 in certain environments such as networked servers or
2148 real-time systems.
2150 nohz= [KNL] Boottime enable/disable dynamic ticks
2151 Valid arguments: on, off
2152 Default: on
2154 nohz_full= [KNL,BOOT]
2155 In kernels built with CONFIG_NO_HZ_FULL=y, set
2156 the specified list of CPUs whose tick will be stopped
2157 whenever possible. The boot CPU will be forced outside
2158 the range to maintain the timekeeping.
2159 The CPUs in this range must also be included in the
2160 rcu_nocbs= set.
2162 noiotrap [SH] Disables trapped I/O port accesses.
2164 noirqdebug [X86-32] Disables the code which attempts to detect and
2165 disable unhandled interrupt sources.
2167 no_timer_check [X86,APIC] Disables the code which tests for
2168 broken timer IRQ sources.
2170 noisapnp [ISAPNP] Disables ISA PnP code.
2172 noinitrd [RAM] Tells the kernel not to load any configured
2173 initial RAM disk.
2175 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2176 remapping.
2177 [Deprecated - use intremap=off]
2179 nointroute [IA-64]
2181 nojitter [IA-64] Disables jitter checking for ITC timers.
2183 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2185 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2186 fault handling.
2188 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2189 steal time is computed, but won't influence scheduler
2190 behaviour
2192 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2194 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2196 noltlbs [PPC] Do not use large page/tlb entries for kernel
2197 lowmem mapping on PPC40x.
2199 nomca [IA-64] Disable machine check abort handling
2201 nomce [X86-32] Machine Check Exception
2203 nomfgpt [X86-32] Disable Multi-Function General Purpose
2204 Timer usage (for AMD Geode machines).
2206 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2207 shutdown the other cpus. Instead use the REBOOT_VECTOR
2208 irq.
2210 nomodule Disable module load
2212 nopat [X86] Disable PAT (page attribute table extension of
2213 pagetables) support.
2215 norandmaps Don't use address space randomization. Equivalent to
2216 echo 0 > /proc/sys/kernel/randomize_va_space
2218 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2220 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2221 with UP alternatives
2223 nordrand [X86] Disable the direct use of the RDRAND
2224 instruction even if it is supported by the
2225 processor. RDRAND is still available to user
2226 space applications.
2228 noresume [SWSUSP] Disables resume and restores original swap
2229 space.
2231 no-scroll [VGA] Disables scrollback.
2232 This is required for the Braillex ib80-piezo Braille
2233 reader made by F.H. Papenmeier (Germany).
2235 nosbagart [IA-64]
2237 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2239 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2240 and disable the IO APIC. legacy for "maxcpus=0".
2242 nosoftlockup [KNL] Disable the soft-lockup detector.
2244 nosync [HW,M68K] Disables sync negotiation for all devices.
2246 notsc [BUGS=X86-32] Disable Time Stamp Counter
2248 nousb [USB] Disable the USB subsystem
2250 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2252 nowb [ARM]
2254 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2256 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2257 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2258 Some features depend on CPU0. Known dependencies are:
2259 1. Resume from suspend/hibernate depends on CPU0.
2260 Suspend/hibernate will fail if CPU0 is offline and you
2261 need to online CPU0 before suspend/hibernate.
2262 2. PIC interrupts also depend on CPU0. CPU0 can't be
2263 removed if a PIC interrupt is detected.
2264 It's said poweroff/reboot may depend on CPU0 on some
2265 machines although I haven't seen such issues so far
2266 after CPU0 is offline on a few tested machines.
2267 If the dependencies are under your control, you can
2268 turn on cpu0_hotplug.
2270 nptcg= [IA-64] Override max number of concurrent global TLB
2271 purges which is reported from either PAL_VM_SUMMARY or
2272 SAL PALO.
2274 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2275 could support. nr_cpus=n : n >= 1 limits the kernel to
2276 supporting 'n' processors. Later in runtime you can not
2277 use hotplug cpu feature to put more cpu back to online.
2278 just like you compile the kernel NR_CPUS=n
2280 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2282 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2283 Allowed values are enable and disable
2285 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2286 one of ['zone', 'node', 'default'] can be specified
2287 This can be set from sysctl after boot.
2288 See Documentation/sysctl/vm.txt for details.
2290 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2291 See Documentation/debugging-via-ohci1394.txt for more
2292 info.
2294 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2295 Rather than timing out after 20 ms if an EC
2296 command is not properly ACKed, override the length
2297 of the timeout. We have interrupts disabled while
2298 waiting for the ACK, so if this is set too high
2299 interrupts *may* be lost!
2301 omap_mux= [OMAP] Override bootloader pin multiplexing.
2302 Format: <mux_mode0.mode_name=value>...
2303 For example, to override I2C bus2:
2304 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2306 oprofile.timer= [HW]
2307 Use timer interrupt instead of performance counters
2309 oprofile.cpu_type= Force an oprofile cpu type
2310 This might be useful if you have an older oprofile
2311 userland or if you want common events.
2312 Format: { arch_perfmon }
2313 arch_perfmon: [X86] Force use of architectural
2314 perfmon on Intel CPUs instead of the
2315 CPU specific event set.
2316 timer: [X86] Force use of architectural NMI
2317 timer mode (see also oprofile.timer
2318 for generic hr timer mode)
2319 [s390] Force legacy basic mode sampling
2320 (report cpu_type "timer")
2322 oops=panic Always panic on oopses. Default is to just kill the
2323 process, but there is a small probability of
2324 deadlocking the machine.
2325 This will also cause panics on machine check exceptions.
2326 Useful together with panic=30 to trigger a reboot.
2328 OSS [HW,OSS]
2329 See Documentation/sound/oss/oss-parameters.txt
2331 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2332 timeout > 0: seconds before rebooting
2333 timeout = 0: wait forever
2334 timeout < 0: reboot immediately
2335 Format: <timeout>
2337 parkbd.port= [HW] Parallel port number the keyboard adapter is
2338 connected to, default is 0.
2339 Format: <parport#>
2340 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2341 0 for XT, 1 for AT (default is AT).
2342 Format: <mode>
2344 parport= [HW,PPT] Specify parallel ports. 0 disables.
2345 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2346 Use 'auto' to force the driver to use any
2347 IRQ/DMA settings detected (the default is to
2348 ignore detected IRQ/DMA settings because of
2349 possible conflicts). You can specify the base
2350 address, IRQ, and DMA settings; IRQ and DMA
2351 should be numbers, or 'auto' (for using detected
2352 settings on that particular port), or 'nofifo'
2353 (to avoid using a FIFO even if it is detected).
2354 Parallel ports are assigned in the order they
2355 are specified on the command line, starting
2356 with parport0.
2358 parport_init_mode= [HW,PPT]
2359 Configure VIA parallel port to operate in
2360 a specific mode. This is necessary on Pegasos
2361 computer where firmware has no options for setting
2362 up parallel port mode and sets it to spp.
2363 Currently this function knows 686a and 8231 chips.
2364 Format: [spp|ps2|epp|ecp|ecpepp]
2366 pause_on_oops=
2367 Halt all CPUs after the first oops has been printed for
2368 the specified number of seconds. This is to be used if
2369 your oopses keep scrolling off the screen.
2371 pcbit= [HW,ISDN]
2373 pcd. [PARIDE]
2374 See header of drivers/block/paride/pcd.c.
2375 See also Documentation/blockdev/paride.txt.
2377 pci=option[,option...] [PCI] various PCI subsystem options:
2378 earlydump [X86] dump PCI config space before the kernel
2379 changes anything
2380 off [X86] don't probe for the PCI bus
2381 bios [X86-32] force use of PCI BIOS, don't access
2382 the hardware directly. Use this if your machine
2383 has a non-standard PCI host bridge.
2384 nobios [X86-32] disallow use of PCI BIOS, only direct
2385 hardware access methods are allowed. Use this
2386 if you experience crashes upon bootup and you
2387 suspect they are caused by the BIOS.
2388 conf1 [X86] Force use of PCI Configuration
2389 Mechanism 1.
2390 conf2 [X86] Force use of PCI Configuration
2391 Mechanism 2.
2392 noaer [PCIE] If the PCIEAER kernel config parameter is
2393 enabled, this kernel boot option can be used to
2394 disable the use of PCIE advanced error reporting.
2395 nodomains [PCI] Disable support for multiple PCI
2396 root domains (aka PCI segments, in ACPI-speak).
2397 nommconf [X86] Disable use of MMCONFIG for PCI
2398 Configuration
2399 check_enable_amd_mmconf [X86] check for and enable
2400 properly configured MMIO access to PCI
2401 config space on AMD family 10h CPU
2402 nomsi [MSI] If the PCI_MSI kernel config parameter is
2403 enabled, this kernel boot option can be used to
2404 disable the use of MSI interrupts system-wide.
2405 noioapicquirk [APIC] Disable all boot interrupt quirks.
2406 Safety option to keep boot IRQs enabled. This
2407 should never be necessary.
2408 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2409 primary IO-APIC for bridges that cannot disable
2410 boot IRQs. This fixes a source of spurious IRQs
2411 when the system masks IRQs.
2412 noioapicreroute [APIC] Disable workaround that uses the
2413 boot IRQ equivalent of an IRQ that connects to
2414 a chipset where boot IRQs cannot be disabled.
2415 The opposite of ioapicreroute.
2416 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2417 routing table. These calls are known to be buggy
2418 on several machines and they hang the machine
2419 when used, but on other computers it's the only
2420 way to get the interrupt routing table. Try
2421 this option if the kernel is unable to allocate
2422 IRQs or discover secondary PCI buses on your
2423 motherboard.
2424 rom [X86] Assign address space to expansion ROMs.
2425 Use with caution as certain devices share
2426 address decoders between ROMs and other
2427 resources.
2428 norom [X86] Do not assign address space to
2429 expansion ROMs that do not already have
2430 BIOS assigned address ranges.
2431 nobar [X86] Do not assign address space to the
2432 BARs that weren't assigned by the BIOS.
2433 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2434 assigned automatically to PCI devices. You can
2435 make the kernel exclude IRQs of your ISA cards
2436 this way.
2437 pirqaddr=0xAAAAA [X86] Specify the physical address
2438 of the PIRQ table (normally generated
2439 by the BIOS) if it is outside the
2440 F0000h-100000h range.
2441 lastbus=N [X86] Scan all buses thru bus #N. Can be
2442 useful if the kernel is unable to find your
2443 secondary buses and you want to tell it
2444 explicitly which ones they are.
2445 assign-busses [X86] Always assign all PCI bus
2446 numbers ourselves, overriding
2447 whatever the firmware may have done.
2448 usepirqmask [X86] Honor the possible IRQ mask stored
2449 in the BIOS $PIR table. This is needed on
2450 some systems with broken BIOSes, notably
2451 some HP Pavilion N5400 and Omnibook XE3
2452 notebooks. This will have no effect if ACPI
2453 IRQ routing is enabled.
2454 noacpi [X86] Do not use ACPI for IRQ routing
2455 or for PCI scanning.
2456 use_crs [X86] Use PCI host bridge window information
2457 from ACPI. On BIOSes from 2008 or later, this
2458 is enabled by default. If you need to use this,
2459 please report a bug.
2460 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2461 If you need to use this, please report a bug.
2462 routeirq Do IRQ routing for all PCI devices.
2463 This is normally done in pci_enable_device(),
2464 so this option is a temporary workaround
2465 for broken drivers that don't call it.
2466 skip_isa_align [X86] do not align io start addr, so can
2467 handle more pci cards
2468 firmware [ARM] Do not re-enumerate the bus but instead
2469 just use the configuration from the
2470 bootloader. This is currently used on
2471 IXP2000 systems where the bus has to be
2472 configured a certain way for adjunct CPUs.
2473 noearly [X86] Don't do any early type 1 scanning.
2474 This might help on some broken boards which
2475 machine check when some devices' config space
2476 is read. But various workarounds are disabled
2477 and some IOMMU drivers will not work.
2478 bfsort Sort PCI devices into breadth-first order.
2479 This sorting is done to get a device
2480 order compatible with older (<= 2.4) kernels.
2481 nobfsort Don't sort PCI devices into breadth-first order.
2482 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2483 tuning and use the BIOS-configured MPS defaults.
2484 pcie_bus_safe Set every device's MPS to the largest value
2485 supported by all devices below the root complex.
2486 pcie_bus_perf Set device MPS to the largest allowable MPS
2487 based on its parent bus. Also set MRRS (Max
2488 Read Request Size) to the largest supported
2489 value (no larger than the MPS that the device
2490 or bus can support) for best performance.
2491 pcie_bus_peer2peer Set every device's MPS to 128B, which
2492 every device is guaranteed to support. This
2493 configuration allows peer-to-peer DMA between
2494 any pair of devices, possibly at the cost of
2495 reduced performance. This also guarantees
2496 that hot-added devices will work.
2497 cbiosize=nn[KMG] The fixed amount of bus space which is
2498 reserved for the CardBus bridge's IO window.
2499 The default value is 256 bytes.
2500 cbmemsize=nn[KMG] The fixed amount of bus space which is
2501 reserved for the CardBus bridge's memory
2502 window. The default value is 64 megabytes.
2503 resource_alignment=
2504 Format:
2505 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2506 Specifies alignment and device to reassign
2507 aligned memory resources.
2508 If <order of align> is not specified,
2509 PAGE_SIZE is used as alignment.
2510 PCI-PCI bridge can be specified, if resource
2511 windows need to be expanded.
2512 ecrc= Enable/disable PCIe ECRC (transaction layer
2513 end-to-end CRC checking).
2514 bios: Use BIOS/firmware settings. This is the
2515 the default.
2516 off: Turn ECRC off
2517 on: Turn ECRC on.
2518 hpiosize=nn[KMG] The fixed amount of bus space which is
2519 reserved for hotplug bridge's IO window.
2520 Default size is 256 bytes.
2521 hpmemsize=nn[KMG] The fixed amount of bus space which is
2522 reserved for hotplug bridge's memory window.
2523 Default size is 2 megabytes.
2524 realloc= Enable/disable reallocating PCI bridge resources
2525 if allocations done by BIOS are too small to
2526 accommodate resources required by all child
2527 devices.
2528 off: Turn realloc off
2529 on: Turn realloc on
2530 realloc same as realloc=on
2531 noari do not use PCIe ARI.
2532 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2533 only look for one device below a PCIe downstream
2534 port.
2536 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2537 Management.
2538 off Disable ASPM.
2539 force Enable ASPM even on devices that claim not to support it.
2540 WARNING: Forcing ASPM on may cause system lockups.
2542 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2543 nomsi Do not use MSI for PCI Express Native Hotplug (this
2544 makes all PCIe ports use INTx for hotplug services).
2546 pcie_ports= [PCIE] PCIe ports handling:
2547 auto Ask the BIOS whether or not to use native PCIe services
2548 associated with PCIe ports (PME, hot-plug, AER). Use
2549 them only if that is allowed by the BIOS.
2550 native Use native PCIe services associated with PCIe ports
2551 unconditionally.
2552 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2553 ports driver.
2555 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2556 nomsi Do not use MSI for native PCIe PME signaling (this makes
2557 all PCIe root ports use INTx for all services).
2559 pcmv= [HW,PCMCIA] BadgePAD 4
2561 pd. [PARIDE]
2562 See Documentation/blockdev/paride.txt.
2564 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2565 boot time.
2566 Format: { 0 | 1 }
2567 See arch/parisc/kernel/pdc_chassis.c
2569 percpu_alloc= Select which percpu first chunk allocator to use.
2570 Currently supported values are "embed" and "page".
2571 Archs may support subset or none of the selections.
2572 See comments in mm/percpu.c for details on each
2573 allocator. This parameter is primarily for debugging
2574 and performance comparison.
2576 pf. [PARIDE]
2577 See Documentation/blockdev/paride.txt.
2579 pg. [PARIDE]
2580 See Documentation/blockdev/paride.txt.
2582 pirq= [SMP,APIC] Manual mp-table setup
2583 See Documentation/x86/i386/IO-APIC.txt.
2585 plip= [PPT,NET] Parallel port network link
2586 Format: { parport<nr> | timid | 0 }
2587 See also Documentation/parport.txt.
2589 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2590 Override pmtimer IOPort with a hex value.
2591 e.g. pmtmr=0x508
2593 pnp.debug=1 [PNP]
2594 Enable PNP debug messages (depends on the
2595 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2596 via /sys/module/pnp/parameters/debug. We always show
2597 current resource usage; turning this on also shows
2598 possible settings and some assignment information.
2600 pnpacpi= [ACPI]
2601 { off }
2603 pnpbios= [ISAPNP]
2604 { on | off | curr | res | no-curr | no-res }
2606 pnp_reserve_irq=
2607 [ISAPNP] Exclude IRQs for the autoconfiguration
2609 pnp_reserve_dma=
2610 [ISAPNP] Exclude DMAs for the autoconfiguration
2612 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2613 Ranges are in pairs (I/O port base and size).
2615 pnp_reserve_mem=
2616 [ISAPNP] Exclude memory regions for the
2617 autoconfiguration.
2618 Ranges are in pairs (memory base and size).
2620 ports= [IP_VS_FTP] IPVS ftp helper module
2621 Default is 21.
2622 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2623 may be specified.
2624 Format: <port>,<port>....
2626 print-fatal-signals=
2627 [KNL] debug: print fatal signals
2629 If enabled, warn about various signal handling
2630 related application anomalies: too many signals,
2631 too many POSIX.1 timers, fatal signals causing a
2632 coredump - etc.
2634 If you hit the warning due to signal overflow,
2635 you might want to try "ulimit -i unlimited".
2637 default: off.
2639 printk.always_kmsg_dump=
2640 Trigger kmsg_dump for cases other than kernel oops or
2641 panics
2642 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2643 default: disabled
2645 printk.time= Show timing data prefixed to each printk message line
2646 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2648 processor.max_cstate= [HW,ACPI]
2649 Limit processor to maximum C-state
2650 max_cstate=9 overrides any DMI blacklist limit.
2652 processor.nocst [HW,ACPI]
2653 Ignore the _CST method to determine C-states,
2654 instead using the legacy FADT method
2656 profile= [KNL] Enable kernel profiling via /proc/profile
2657 Format: [schedule,]<number>
2658 Param: "schedule" - profile schedule points.
2659 Param: <number> - step/bucket size as a power of 2 for
2660 statistical time based profiling.
2661 Param: "sleep" - profile D-state sleeping (millisecs).
2662 Requires CONFIG_SCHEDSTATS
2663 Param: "kvm" - profile VM exits.
2665 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2666 before loading.
2667 See Documentation/blockdev/ramdisk.txt.
2669 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2670 probe for; one of (bare|imps|exps|lifebook|any).
2671 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2672 per second.
2673 psmouse.resetafter= [HW,MOUSE]
2674 Try to reset the device after so many bad packets
2675 (0 = never).
2676 psmouse.resolution=
2677 [HW,MOUSE] Set desired mouse resolution, in dpi.
2678 psmouse.smartscroll=
2679 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2680 0 = disabled, 1 = enabled (default).
2682 pstore.backend= Specify the name of the pstore backend to use
2684 pt. [PARIDE]
2685 See Documentation/blockdev/paride.txt.
2687 pty.legacy_count=
2688 [KNL] Number of legacy pty's. Overwrites compiled-in
2689 default number.
2691 quiet [KNL] Disable most log messages
2693 r128= [HW,DRM]
2695 raid= [HW,RAID]
2696 See Documentation/md.txt.
2698 ramdisk_blocksize= [RAM]
2699 See Documentation/blockdev/ramdisk.txt.
2701 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2702 See Documentation/blockdev/ramdisk.txt.
2704 rcu_nocbs= [KNL]
2705 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2706 the specified list of CPUs to be no-callback CPUs.
2707 Invocation of these CPUs' RCU callbacks will
2708 be offloaded to "rcuox/N" kthreads created for
2709 that purpose, where "x" is "b" for RCU-bh, "p"
2710 for RCU-preempt, and "s" for RCU-sched, and "N"
2711 is the CPU number. This reduces OS jitter on the
2712 offloaded CPUs, which can be useful for HPC and
2713 real-time workloads. It can also improve energy
2714 efficiency for asymmetric multiprocessors.
2716 rcu_nocb_poll [KNL]
2717 Rather than requiring that offloaded CPUs
2718 (specified by rcu_nocbs= above) explicitly
2719 awaken the corresponding "rcuoN" kthreads,
2720 make these kthreads poll for callbacks.
2721 This improves the real-time response for the
2722 offloaded CPUs by relieving them of the need to
2723 wake up the corresponding kthread, but degrades
2724 energy efficiency by requiring that the kthreads
2725 periodically wake up to do the polling.
2727 rcutree.blimit= [KNL]
2728 Set maximum number of finished RCU callbacks to
2729 process in one batch.
2731 rcutree.rcu_fanout_leaf= [KNL]
2732 Increase the number of CPUs assigned to each
2733 leaf rcu_node structure. Useful for very large
2734 systems.
2736 rcutree.jiffies_till_first_fqs= [KNL]
2737 Set delay from grace-period initialization to
2738 first attempt to force quiescent states.
2739 Units are jiffies, minimum value is zero,
2740 and maximum value is HZ.
2742 rcutree.jiffies_till_next_fqs= [KNL]
2743 Set delay between subsequent attempts to force
2744 quiescent states. Units are jiffies, minimum
2745 value is one, and maximum value is HZ.
2747 rcutree.qhimark= [KNL]
2748 Set threshold of queued RCU callbacks beyond which
2749 batch limiting is disabled.
2751 rcutree.qlowmark= [KNL]
2752 Set threshold of queued RCU callbacks below which
2753 batch limiting is re-enabled.
2755 rcutree.rcu_idle_gp_delay= [KNL]
2756 Set wakeup interval for idle CPUs that have
2757 RCU callbacks (RCU_FAST_NO_HZ=y).
2759 rcutree.rcu_idle_lazy_gp_delay= [KNL]
2760 Set wakeup interval for idle CPUs that have
2761 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2762 Lazy RCU callbacks are those which RCU can
2763 prove do nothing more than free memory.
2765 rcutorture.fqs_duration= [KNL]
2766 Set duration of force_quiescent_state bursts.
2768 rcutorture.fqs_holdoff= [KNL]
2769 Set holdoff time within force_quiescent_state bursts.
2771 rcutorture.fqs_stutter= [KNL]
2772 Set wait time between force_quiescent_state bursts.
2774 rcutorture.gp_exp= [KNL]
2775 Use expedited update-side primitives.
2777 rcutorture.gp_normal= [KNL]
2778 Use normal (non-expedited) update-side primitives.
2779 If both gp_exp and gp_normal are set, do both.
2780 If neither gp_exp nor gp_normal are set, still
2781 do both.
2783 rcutorture.n_barrier_cbs= [KNL]
2784 Set callbacks/threads for rcu_barrier() testing.
2786 rcutorture.nfakewriters= [KNL]
2787 Set number of concurrent RCU writers. These just
2788 stress RCU, they don't participate in the actual
2789 test, hence the "fake".
2791 rcutorture.nreaders= [KNL]
2792 Set number of RCU readers.
2794 rcutorture.object_debug= [KNL]
2795 Enable debug-object double-call_rcu() testing.
2797 rcutorture.onoff_holdoff= [KNL]
2798 Set time (s) after boot for CPU-hotplug testing.
2800 rcutorture.onoff_interval= [KNL]
2801 Set time (s) between CPU-hotplug operations, or
2802 zero to disable CPU-hotplug testing.
2804 rcutorture.rcutorture_runnable= [BOOT]
2805 Start rcutorture running at boot time.
2807 rcutorture.shuffle_interval= [KNL]
2808 Set task-shuffle interval (s). Shuffling tasks
2809 allows some CPUs to go into dyntick-idle mode
2810 during the rcutorture test.
2812 rcutorture.shutdown_secs= [KNL]
2813 Set time (s) after boot system shutdown. This
2814 is useful for hands-off automated testing.
2816 rcutorture.stall_cpu= [KNL]
2817 Duration of CPU stall (s) to test RCU CPU stall
2818 warnings, zero to disable.
2820 rcutorture.stall_cpu_holdoff= [KNL]
2821 Time to wait (s) after boot before inducing stall.
2823 rcutorture.stat_interval= [KNL]
2824 Time (s) between statistics printk()s.
2826 rcutorture.stutter= [KNL]
2827 Time (s) to stutter testing, for example, specifying
2828 five seconds causes the test to run for five seconds,
2829 wait for five seconds, and so on. This tests RCU's
2830 ability to transition abruptly to and from idle.
2832 rcutorture.test_boost= [KNL]
2833 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2834 "Maybe" means test if the RCU implementation
2835 under test support RCU priority boosting.
2837 rcutorture.test_boost_duration= [KNL]
2838 Duration (s) of each individual boost test.
2840 rcutorture.test_boost_interval= [KNL]
2841 Interval (s) between each boost test.
2843 rcutorture.test_no_idle_hz= [KNL]
2844 Test RCU's dyntick-idle handling. See also the
2845 rcutorture.shuffle_interval parameter.
2847 rcutorture.torture_type= [KNL]
2848 Specify the RCU implementation to test.
2850 rcutorture.verbose= [KNL]
2851 Enable additional printk() statements.
2853 rcupdate.rcu_expedited= [KNL]
2854 Use expedited grace-period primitives, for
2855 example, synchronize_rcu_expedited() instead
2856 of synchronize_rcu(). This reduces latency,
2857 but can increase CPU utilization, degrade
2858 real-time latency, and degrade energy efficiency.
2860 rcupdate.rcu_cpu_stall_suppress= [KNL]
2861 Suppress RCU CPU stall warning messages.
2863 rcupdate.rcu_cpu_stall_timeout= [KNL]
2864 Set timeout for RCU CPU stall warning messages.
2866 rdinit= [KNL]
2867 Format: <full_path>
2868 Run specified binary instead of /init from the ramdisk,
2869 used for early userspace startup. See initrd.
2871 reboot= [KNL]
2872 Format (x86 or x86_64):
2873 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2874 [[,]s[mp]#### \
2875 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2876 [[,]f[orce]
2877 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2878 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2879 reboot_force is either force or not specified,
2880 reboot_cpu is s[mp]#### with #### being the processor
2881 to be used for rebooting.
2883 relax_domain_level=
2884 [KNL, SMP] Set scheduler's default relax_domain_level.
2885 See Documentation/cgroups/cpusets.txt.
2887 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2889 reservetop= [X86-32]
2890 Format: nn[KMG]
2891 Reserves a hole at the top of the kernel virtual
2892 address space.
2894 reservelow= [X86]
2895 Format: nn[K]
2896 Set the amount of memory to reserve for BIOS at
2897 the bottom of the address space.
2899 reset_devices [KNL] Force drivers to reset the underlying device
2900 during initialization.
2902 resume= [SWSUSP]
2903 Specify the partition device for software suspend
2904 Format:
2905 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2907 resume_offset= [SWSUSP]
2908 Specify the offset from the beginning of the partition
2909 given by "resume=" at which the swap header is located,
2910 in <PAGE_SIZE> units (needed only for swap files).
2911 See Documentation/power/swsusp-and-swap-files.txt
2913 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2914 read the resume files
2916 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2917 Useful for devices that are detected asynchronously
2918 (e.g. USB and MMC devices).
2920 hibernate= [HIBERNATION]
2921 noresume Don't check if there's a hibernation image
2922 present during boot.
2923 nocompress Don't compress/decompress hibernation images.
2925 retain_initrd [RAM] Keep initrd memory after extraction
2927 rhash_entries= [KNL,NET]
2928 Set number of hash buckets for route cache
2930 riscom8= [HW,SERIAL]
2931 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2933 ro [KNL] Mount root device read-only on boot
2935 root= [KNL] Root filesystem
2936 See name_to_dev_t comment in init/do_mounts.c.
2938 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2939 mount the root filesystem
2941 rootflags= [KNL] Set root filesystem mount option string
2943 rootfstype= [KNL] Set root filesystem type
2945 rootwait [KNL] Wait (indefinitely) for root device to show up.
2946 Useful for devices that are detected asynchronously
2947 (e.g. USB and MMC devices).
2949 rproc_mem=nn[KMG][@address]
2950 [KNL,ARM,CMA] Remoteproc physical memory block.
2951 Memory area to be used by remote processor image,
2952 managed by CMA.
2954 rw [KNL] Mount root device read-write on boot
2956 S [KNL] Run init in single mode
2958 sa1100ir [NET]
2959 See drivers/net/irda/sa1100_ir.c.
2961 sbni= [NET] Granch SBNI12 leased line adapter
2963 sched_debug [KNL] Enables verbose scheduler debug messages.
2965 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2966 xtime_lock contention on larger systems, and/or RCU lock
2967 contention on all systems with CONFIG_MAXSMP set.
2968 Format: { "0" | "1" }
2969 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2970 1 -- enable.
2971 Note: increases power consumption, thus should only be
2972 enabled if running jitter sensitive (HPC/RT) workloads.
2974 security= [SECURITY] Choose a security module to enable at boot.
2975 If this boot parameter is not specified, only the first
2976 security module asking for security registration will be
2977 loaded. An invalid security module name will be treated
2978 as if no module has been chosen.
2980 selinux= [SELINUX] Disable or enable SELinux at boot time.
2981 Format: { "0" | "1" }
2982 See security/selinux/Kconfig help text.
2983 0 -- disable.
2984 1 -- enable.
2985 Default value is set via kernel config option.
2986 If enabled at boot time, /selinux/disable can be used
2987 later to disable prior to initial policy load.
2989 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2990 Format: { "0" | "1" }
2991 See security/apparmor/Kconfig help text
2992 0 -- disable.
2993 1 -- enable.
2994 Default value is set via kernel config option.
2996 serialnumber [BUGS=X86-32]
2998 shapers= [NET]
2999 Maximal number of shapers.
3001 show_msr= [x86] show boot-time MSR settings
3002 Format: { <integer> }
3003 Show boot-time (BIOS-initialized) MSR settings.
3004 The parameter means the number of CPUs to show,
3005 for example 1 means boot CPU only.
3007 simeth= [IA-64]
3008 simscsi=
3010 slram= [HW,MTD]
3012 slab_max_order= [MM, SLAB]
3013 Determines the maximum allowed order for slabs.
3014 A high setting may cause OOMs due to memory
3015 fragmentation. Defaults to 1 for systems with
3016 more than 32MB of RAM, 0 otherwise.
3018 slub_debug[=options[,slabs]] [MM, SLUB]
3019 Enabling slub_debug allows one to determine the
3020 culprit if slab objects become corrupted. Enabling
3021 slub_debug can create guard zones around objects and
3022 may poison objects when not in use. Also tracks the
3023 last alloc / free. For more information see
3024 Documentation/vm/slub.txt.
3026 slub_max_order= [MM, SLUB]
3027 Determines the maximum allowed order for slabs.
3028 A high setting may cause OOMs due to memory
3029 fragmentation. For more information see
3030 Documentation/vm/slub.txt.
3032 slub_min_objects= [MM, SLUB]
3033 The minimum number of objects per slab. SLUB will
3034 increase the slab order up to slub_max_order to
3035 generate a sufficiently large slab able to contain
3036 the number of objects indicated. The higher the number
3037 of objects the smaller the overhead of tracking slabs
3038 and the less frequently locks need to be acquired.
3039 For more information see Documentation/vm/slub.txt.
3041 slub_min_order= [MM, SLUB]
3042 Determines the minimum page order for slabs. Must be
3043 lower than slub_max_order.
3044 For more information see Documentation/vm/slub.txt.
3046 slub_nomerge [MM, SLUB]
3047 Disable merging of slabs with similar size. May be
3048 necessary if there is some reason to distinguish
3049 allocs to different slabs. Debug options disable
3050 merging on their own.
3051 For more information see Documentation/vm/slub.txt.
3053 smart2= [HW]
3054 Format: <io1>[,<io2>[,...,<io8>]]
3056 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3057 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3058 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3059 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3060 smsc-ircc2.ircc_irq= [HW] IRQ line
3061 smsc-ircc2.ircc_dma= [HW] DMA channel
3062 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3063 0: Toshiba Satellite 1800 (GP data pin select)
3064 1: Fast pin select (default)
3065 2: ATC IRMode
3067 softlockup_panic=
3068 [KNL] Should the soft-lockup detector generate panics.
3069 Format: <integer>
3071 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3072 See Documentation/laptops/sonypi.txt
3074 specialix= [HW,SERIAL] Specialix multi-serial port adapter
3075 See Documentation/serial/specialix.txt.
3077 spia_io_base= [HW,MTD]
3078 spia_fio_base=
3079 spia_pedr=
3080 spia_peddr=
3082 stacktrace [FTRACE]
3083 Enabled the stack tracer on boot up.
3085 stacktrace_filter=[function-list]
3086 [FTRACE] Limit the functions that the stack tracer
3087 will trace at boot up. function-list is a comma separated
3088 list of functions. This list can be changed at run
3089 time by the stack_trace_filter file in the debugfs
3090 tracing directory. Note, this enables stack tracing
3091 and the stacktrace above is not needed.
3093 sti= [PARISC,HW]
3094 Format: <num>
3095 Set the STI (builtin display/keyboard on the HP-PARISC
3096 machines) console (graphic card) which should be used
3097 as the initial boot-console.
3098 See also comment in drivers/video/console/sticore.c.
3100 sti_font= [HW]
3101 See comment in drivers/video/console/sticore.c.
3103 stifb= [HW]
3104 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3106 sunrpc.min_resvport=
3107 sunrpc.max_resvport=
3108 [NFS,SUNRPC]
3109 SunRPC servers often require that client requests
3110 originate from a privileged port (i.e. a port in the
3111 range 0 < portnr < 1024).
3112 An administrator who wishes to reserve some of these
3113 ports for other uses may adjust the range that the
3114 kernel's sunrpc client considers to be privileged
3115 using these two parameters to set the minimum and
3116 maximum port values.
3118 sunrpc.pool_mode=
3119 [NFS]
3120 Control how the NFS server code allocates CPUs to
3121 service thread pools. Depending on how many NICs
3122 you have and where their interrupts are bound, this
3123 option will affect which CPUs will do NFS serving.
3124 Note: this parameter cannot be changed while the
3125 NFS server is running.
3127 auto the server chooses an appropriate mode
3128 automatically using heuristics
3129 global a single global pool contains all CPUs
3130 percpu one pool for each CPU
3131 pernode one pool for each NUMA node (equivalent
3132 to global on non-NUMA machines)
3134 sunrpc.tcp_slot_table_entries=
3135 sunrpc.udp_slot_table_entries=
3136 [NFS,SUNRPC]
3137 Sets the upper limit on the number of simultaneous
3138 RPC calls that can be sent from the client to a
3139 server. Increasing these values may allow you to
3140 improve throughput, but will also increase the
3141 amount of memory reserved for use by the client.
3143 swapaccount=[0|1]
3144 [KNL] Enable accounting of swap in memory resource
3145 controller if no parameter or 1 is given or disable
3146 it if 0 is given (See Documentation/cgroups/memory.txt)
3148 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3149 Format: { <int> | force }
3150 <int> -- Number of I/O TLB slabs
3151 force -- force using of bounce buffers even if they
3152 wouldn't be automatically used by the kernel
3154 switches= [HW,M68k]
3156 sysfs.deprecated=0|1 [KNL]
3157 Enable/disable old style sysfs layout for old udev
3158 on older distributions. When this option is enabled
3159 very new udev will not work anymore. When this option
3160 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3161 in older udev will not work anymore.
3162 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3163 the kernel configuration.
3165 sysrq_always_enabled
3166 [KNL]
3167 Ignore sysrq setting - this boot parameter will
3168 neutralize any effect of /proc/sys/kernel/sysrq.
3169 Useful for debugging.
3171 tdfx= [HW,DRM]
3173 test_suspend= [SUSPEND]
3174 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3175 standby suspend) as the system sleep state to briefly
3176 enter during system startup. The system is woken from
3177 this state using a wakeup-capable RTC alarm.
3179 thash_entries= [KNL,NET]
3180 Set number of hash buckets for TCP connection
3182 thermal.act= [HW,ACPI]
3183 -1: disable all active trip points in all thermal zones
3184 <degrees C>: override all lowest active trip points
3186 thermal.crt= [HW,ACPI]
3187 -1: disable all critical trip points in all thermal zones
3188 <degrees C>: override all critical trip points
3190 thermal.nocrt= [HW,ACPI]
3191 Set to disable actions on ACPI thermal zone
3192 critical and hot trip points.
3194 thermal.off= [HW,ACPI]
3195 1: disable ACPI thermal control
3197 thermal.psv= [HW,ACPI]
3198 -1: disable all passive trip points
3199 <degrees C>: override all passive trip points to this
3200 value
3202 thermal.tzp= [HW,ACPI]
3203 Specify global default ACPI thermal zone polling rate
3204 <deci-seconds>: poll all this frequency
3205 0: no polling (default)
3207 threadirqs [KNL]
3208 Force threading of all interrupt handlers except those
3209 marked explicitly IRQF_NO_THREAD.
3211 tmem [KNL,XEN]
3212 Enable the Transcendent memory driver if built-in.
3214 tmem.cleancache=0|1 [KNL, XEN]
3215 Default is on (1). Disable the usage of the cleancache
3216 API to send anonymous pages to the hypervisor.
3218 tmem.frontswap=0|1 [KNL, XEN]
3219 Default is on (1). Disable the usage of the frontswap
3220 API to send swap pages to the hypervisor. If disabled
3221 the selfballooning and selfshrinking are force disabled.
3223 tmem.selfballooning=0|1 [KNL, XEN]
3224 Default is on (1). Disable the driving of swap pages
3225 to the hypervisor.
3227 tmem.selfshrinking=0|1 [KNL, XEN]
3228 Default is on (1). Partial swapoff that immediately
3229 transfers pages from Xen hypervisor back to the
3230 kernel based on different criteria.
3232 topology= [S390]
3233 Format: {off | on}
3234 Specify if the kernel should make use of the cpu
3235 topology information if the hardware supports this.
3236 The scheduler will make use of this information and
3237 e.g. base its process migration decisions on it.
3238 Default is on.
3240 tp720= [HW,PS2]
3242 tpm_suspend_pcr=[HW,TPM]
3243 Format: integer pcr id
3244 Specify that at suspend time, the tpm driver
3245 should extend the specified pcr with zeros,
3246 as a workaround for some chips which fail to
3247 flush the last written pcr on TPM_SaveState.
3248 This will guarantee that all the other pcrs
3249 are saved.
3251 trace_buf_size=nn[KMG]
3252 [FTRACE] will set tracing buffer size.
3254 trace_event=[event-list]
3255 [FTRACE] Set and start specified trace events in order
3256 to facilitate early boot debugging.
3257 See also Documentation/trace/events.txt
3259 trace_options=[option-list]
3260 [FTRACE] Enable or disable tracer options at boot.
3261 The option-list is a comma delimited list of options
3262 that can be enabled or disabled just as if you were
3263 to echo the option name into
3265 /sys/kernel/debug/tracing/trace_options
3267 For example, to enable stacktrace option (to dump the
3268 stack trace of each event), add to the command line:
3270 trace_options=stacktrace
3272 See also Documentation/trace/ftrace.txt "trace options"
3273 section.
3275 traceoff_on_warning
3276 [FTRACE] enable this option to disable tracing when a
3277 warning is hit. This turns off "tracing_on". Tracing can
3278 be enabled again by echoing '1' into the "tracing_on"
3279 file located in /sys/kernel/debug/tracing/
3281 This option is useful, as it disables the trace before
3282 the WARNING dump is called, which prevents the trace to
3283 be filled with content caused by the warning output.
3285 This option can also be set at run time via the sysctl
3286 option: kernel/traceoff_on_warning
3288 transparent_hugepage=
3289 [KNL]
3290 Format: [always|madvise|never]
3291 Can be used to control the default behavior of the system
3292 with respect to transparent hugepages.
3293 See Documentation/vm/transhuge.txt for more details.
3295 tsc= Disable clocksource stability checks for TSC.
3296 Format: <string>
3297 [x86] reliable: mark tsc clocksource as reliable, this
3298 disables clocksource verification at runtime, as well
3299 as the stability checks done at bootup. Used to enable
3300 high-resolution timer mode on older hardware, and in
3301 virtualized environment.
3302 [x86] noirqtime: Do not use TSC to do irq accounting.
3303 Used to run time disable IRQ_TIME_ACCOUNTING on any
3304 platforms where RDTSC is slow and this accounting
3305 can add overhead.
3307 turbografx.map[2|3]= [HW,JOY]
3308 TurboGraFX parallel port interface
3309 Format:
3310 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3311 See also Documentation/input/joystick-parport.txt
3313 udbg-immortal [PPC] When debugging early kernel crashes that
3314 happen after console_init() and before a proper
3315 console driver takes over, this boot options might
3316 help "seeing" what's going on.
3318 uhash_entries= [KNL,NET]
3319 Set number of hash buckets for UDP/UDP-Lite connections
3321 uhci-hcd.ignore_oc=
3322 [USB] Ignore overcurrent events (default N).
3323 Some badly-designed motherboards generate lots of
3324 bogus events, for ports that aren't wired to
3325 anything. Set this parameter to avoid log spamming.
3326 Note that genuine overcurrent events won't be
3327 reported either.
3329 unknown_nmi_panic
3330 [X86] Cause panic on unknown NMI.
3332 usbcore.authorized_default=
3333 [USB] Default USB device authorization:
3334 (default -1 = authorized except for wireless USB,
3335 0 = not authorized, 1 = authorized)
3337 usbcore.autosuspend=
3338 [USB] The autosuspend time delay (in seconds) used
3339 for newly-detected USB devices (default 2). This
3340 is the time required before an idle device will be
3341 autosuspended. Devices for which the delay is set
3342 to a negative value won't be autosuspended at all.
3344 usbcore.usbfs_snoop=
3345 [USB] Set to log all usbfs traffic (default 0 = off).
3347 usbcore.blinkenlights=
3348 [USB] Set to cycle leds on hubs (default 0 = off).
3350 usbcore.old_scheme_first=
3351 [USB] Start with the old device initialization
3352 scheme (default 0 = off).
3354 usbcore.usbfs_memory_mb=
3355 [USB] Memory limit (in MB) for buffers allocated by
3356 usbfs (default = 16, 0 = max = 2047).
3358 usbcore.use_both_schemes=
3359 [USB] Try the other device initialization scheme
3360 if the first one fails (default 1 = enabled).
3362 usbcore.initial_descriptor_timeout=
3363 [USB] Specifies timeout for the initial 64-byte
3364 USB_REQ_GET_DESCRIPTOR request in milliseconds
3365 (default 5000 = 5.0 seconds).
3367 usbhid.mousepoll=
3368 [USBHID] The interval which mice are to be polled at.
3370 usb-storage.delay_use=
3371 [UMS] The delay in seconds before a new device is
3372 scanned for Logical Units (default 5).
3374 usb-storage.quirks=
3375 [UMS] A list of quirks entries to supplement or
3376 override the built-in unusual_devs list. List
3377 entries are separated by commas. Each entry has
3378 the form VID:PID:Flags where VID and PID are Vendor
3379 and Product ID values (4-digit hex numbers) and
3380 Flags is a set of characters, each corresponding
3381 to a common usb-storage quirk flag as follows:
3382 a = SANE_SENSE (collect more than 18 bytes
3383 of sense data);
3384 b = BAD_SENSE (don't collect more than 18
3385 bytes of sense data);
3386 c = FIX_CAPACITY (decrease the reported
3387 device capacity by one sector);
3388 d = NO_READ_DISC_INFO (don't use
3389 READ_DISC_INFO command);
3390 e = NO_READ_CAPACITY_16 (don't use
3391 READ_CAPACITY_16 command);
3392 h = CAPACITY_HEURISTICS (decrease the
3393 reported device capacity by one
3394 sector if the number is odd);
3395 i = IGNORE_DEVICE (don't bind to this
3396 device);
3397 l = NOT_LOCKABLE (don't try to lock and
3398 unlock ejectable media);
3399 m = MAX_SECTORS_64 (don't transfer more
3400 than 64 sectors = 32 KB at a time);
3401 n = INITIAL_READ10 (force a retry of the
3402 initial READ(10) command);
3403 o = CAPACITY_OK (accept the capacity
3404 reported by the device);
3405 p = WRITE_CACHE (the device cache is ON
3406 by default);
3407 r = IGNORE_RESIDUE (the device reports
3408 bogus residue values);
3409 s = SINGLE_LUN (the device has only one
3410 Logical Unit);
3411 w = NO_WP_DETECT (don't test whether the
3412 medium is write-protected).
3413 Example: quirks=0419:aaf5:rl,0421:0433:rc
3415 user_debug= [KNL,ARM]
3416 Format: <int>
3417 See arch/arm/Kconfig.debug help text.
3418 1 - undefined instruction events
3419 2 - system calls
3420 4 - invalid data aborts
3421 8 - SIGSEGV faults
3422 16 - SIGBUS faults
3423 Example: user_debug=31
3425 userpte=
3426 [X86] Flags controlling user PTE allocations.
3428 nohigh = do not allocate PTE pages in
3429 HIGHMEM regardless of setting
3430 of CONFIG_HIGHPTE.
3432 vdso= [X86,SH]
3433 On X86_32, this is an alias for vdso32=. Otherwise:
3435 vdso=1: enable VDSO (the default)
3436 vdso=0: disable VDSO mapping
3438 vdso32= [X86] Control the 32-bit vDSO
3439 vdso32=1: enable 32-bit VDSO
3440 vdso32=0 or vdso32=2: disable 32-bit VDSO
3442 See the help text for CONFIG_COMPAT_VDSO for more
3443 details. If CONFIG_COMPAT_VDSO is set, the default is
3444 vdso32=0; otherwise, the default is vdso32=1.
3446 For compatibility with older kernels, vdso32=2 is an
3447 alias for vdso32=0.
3449 Try vdso32=0 if you encounter an error that says:
3450 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3452 vector= [IA-64,SMP]
3453 vector=percpu: enable percpu vector domain
3455 video= [FB] Frame buffer configuration
3456 See Documentation/fb/modedb.txt.
3458 video.brightness_switch_enabled= [0,1]
3459 If set to 1, on receiving an ACPI notify event
3460 generated by hotkey, video driver will adjust brightness
3461 level and then send out the event to user space through
3462 the allocated input device; If set to 0, video driver
3463 will only send out the event without touching backlight
3464 brightness level.
3465 default: 1
3467 virtio_mmio.device=
3468 [VMMIO] Memory mapped virtio (platform) device.
3470 <size>@<baseaddr>:<irq>[:<id>]
3471 where:
3472 <size> := size (can use standard suffixes
3473 like K, M and G)
3474 <baseaddr> := physical base address
3475 <irq> := interrupt number (as passed to
3476 request_irq())
3477 <id> := (optional) platform device id
3478 example:
3479 virtio_mmio.device=1K@0x100b0000:48:7
3481 Can be used multiple times for multiple devices.
3483 vga= [BOOT,X86-32] Select a particular video mode
3484 See Documentation/x86/boot.txt and
3485 Documentation/svga.txt.
3486 Use vga=ask for menu.
3487 This is actually a boot loader parameter; the value is
3488 passed to the kernel using a special protocol.
3490 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3491 size of <nn>. This can be used to increase the
3492 minimum size (128MB on x86). It can also be used to
3493 decrease the size and leave more room for directly
3494 mapped kernel RAM.
3496 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3497 Format: <command>
3499 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3500 Format: <command>
3502 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3503 Format: <command>
3505 vsyscall= [X86-64]
3506 Controls the behavior of vsyscalls (i.e. calls to
3507 fixed addresses of 0xffffffffff600x00 from legacy
3508 code). Most statically-linked binaries and older
3509 versions of glibc use these calls. Because these
3510 functions are at fixed addresses, they make nice
3511 targets for exploits that can control RIP.
3513 emulate [default] Vsyscalls turn into traps and are
3514 emulated reasonably safely.
3516 native Vsyscalls are native syscall instructions.
3517 This is a little bit faster than trapping
3518 and makes a few dynamic recompilers work
3519 better than they would in emulation mode.
3520 It also makes exploits much easier to write.
3522 none Vsyscalls don't work at all. This makes
3523 them quite hard to use for exploits but
3524 might break your system.
3526 vt.color= [VT] Default text color.
3527 Format: 0xYX, X = foreground, Y = background.
3528 Default: 0x07 = light gray on black.
3530 vt.cur_default= [VT] Default cursor shape.
3531 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3532 the parameters of the <Esc>[?A;B;Cc escape sequence;
3533 see VGA-softcursor.txt. Default: 2 = underline.
3535 vt.default_blu= [VT]
3536 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3537 Change the default blue palette of the console.
3538 This is a 16-member array composed of values
3539 ranging from 0-255.
3541 vt.default_grn= [VT]
3542 Format: <green0>,<green1>,<green2>,...,<green15>
3543 Change the default green palette of the console.
3544 This is a 16-member array composed of values
3545 ranging from 0-255.
3547 vt.default_red= [VT]
3548 Format: <red0>,<red1>,<red2>,...,<red15>
3549 Change the default red palette of the console.
3550 This is a 16-member array composed of values
3551 ranging from 0-255.
3553 vt.default_utf8=
3554 [VT]
3555 Format=<0|1>
3556 Set system-wide default UTF-8 mode for all tty's.
3557 Default is 1, i.e. UTF-8 mode is enabled for all
3558 newly opened terminals.
3560 vt.global_cursor_default=
3561 [VT]
3562 Format=<-1|0|1>
3563 Set system-wide default for whether a cursor
3564 is shown on new VTs. Default is -1,
3565 i.e. cursors will be created by default unless
3566 overridden by individual drivers. 0 will hide
3567 cursors, 1 will display them.
3569 vt.italic= [VT] Default color for italic text; 0-15.
3570 Default: 2 = green.
3572 vt.underline= [VT] Default color for underlined text; 0-15.
3573 Default: 3 = cyan.
3575 watchdog timers [HW,WDT] For information on watchdog timers,
3576 see Documentation/watchdog/watchdog-parameters.txt
3577 or other driver-specific files in the
3578 Documentation/watchdog/ directory.
3580 workqueue.disable_numa
3581 By default, all work items queued to unbound
3582 workqueues are affine to the NUMA nodes they're
3583 issued on, which results in better behavior in
3584 general. If NUMA affinity needs to be disabled for
3585 whatever reason, this option can be used. Note
3586 that this also can be controlled per-workqueue for
3587 workqueues visible under /sys/bus/workqueue/.
3589 workqueue.power_efficient
3590 Per-cpu workqueues are generally preferred because
3591 they show better performance thanks to cache
3592 locality; unfortunately, per-cpu workqueues tend to
3593 be more power hungry than unbound workqueues.
3595 Enabling this makes the per-cpu workqueues which
3596 were observed to contribute significantly to power
3597 consumption unbound, leading to measurably lower
3598 power usage at the cost of small performance
3599 overhead.
3601 The default value of this parameter is determined by
3602 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3604 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3605 default x2apic cluster mode on platforms
3606 supporting x2apic.
3608 x86_intel_mid_timer= [X86-32,APBT]
3609 Choose timer option for x86 Intel MID platform.
3610 Two valid options are apbt timer only and lapic timer
3611 plus one apbt timer for broadcast timer.
3612 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3614 xen_emul_unplug= [HW,X86,XEN]
3615 Unplug Xen emulated devices
3616 Format: [unplug0,][unplug1]
3617 ide-disks -- unplug primary master IDE devices
3618 aux-ide-disks -- unplug non-primary-master IDE devices
3619 nics -- unplug network devices
3620 all -- unplug all emulated devices (NICs and IDE disks)
3621 unnecessary -- unplugging emulated devices is
3622 unnecessary even if the host did not respond to
3623 the unplug protocol
3624 never -- do not unplug even if version check succeeds
3626 xen_nopvspin [X86,XEN]
3627 Disables the ticketlock slowpath using Xen PV
3628 optimizations.
3630 xirc2ps_cs= [NET,PCMCIA]
3631 Format:
3632 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3634 ______________________________________________________________________
3636 TODO:
3638 Add more DRM drivers.