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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
4 The following is a consolidated list of the kernel parameters as
5 implemented by the __setup(), core_param() and module_param() macros
6 and sorted into English Dictionary order (defined as ignoring all
7 punctuation and sorting digits before letters in a case insensitive
8 manner), and with descriptions where known.
10 The kernel parses parameters from the kernel command line up to "--";
11 if it doesn't recognize a parameter and it doesn't contain a '.', the
12 parameter gets passed to init: parameters with '=' go into init's
13 environment, others are passed as command line arguments to init.
14 Everything after "--" is passed as an argument to init.
16 Module parameters can be specified in two ways: via the kernel command
17 line with a module name prefix, or via modprobe, e.g.:
19 (kernel command line) usbcore.blinkenlights=1
20 (modprobe command line) modprobe usbcore blinkenlights=1
22 Parameters for modules which are built into the kernel need to be
23 specified on the kernel command line. modprobe looks through the
24 kernel command line (/proc/cmdline) and collects module parameters
25 when it loads a module, so the kernel command line can be used for
26 loadable modules too.
28 Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30 can also be entered as
31 log-buf-len=1M print_fatal_signals=1
33 Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
36 This document may not be entirely up to date and comprehensive. The command
37 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
38 module. Loadable modules, after being loaded into the running kernel, also
39 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
40 parameters may be changed at runtime by the command
41 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
43 The parameters listed below are only valid if certain kernel build options were
44 enabled and if respective hardware is present. The text in square brackets at
45 the beginning of each description states the restrictions within which a
46 parameter is applicable:
48 ACPI ACPI support is enabled.
49 AGP AGP (Accelerated Graphics Port) is enabled.
50 ALSA ALSA sound support is enabled.
51 APIC APIC support is enabled.
52 APM Advanced Power Management support is enabled.
53 ARM ARM architecture is enabled.
54 AVR32 AVR32 architecture is enabled.
55 AX25 Appropriate AX.25 support is enabled.
56 BLACKFIN Blackfin architecture is enabled.
57 CLK Common clock infrastructure is enabled.
58 CMA Contiguous Memory Area support is enabled.
59 DRM Direct Rendering Management support is enabled.
60 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
61 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
62 EFI EFI Partitioning (GPT) is enabled
63 EIDE EIDE/ATAPI support is enabled.
64 EVM Extended Verification Module
65 FB The frame buffer device is enabled.
66 FTRACE Function tracing enabled.
67 GCOV GCOV profiling is enabled.
68 HW Appropriate hardware is enabled.
69 IA-64 IA-64 architecture is enabled.
70 IMA Integrity measurement architecture is enabled.
71 IOSCHED More than one I/O scheduler is enabled.
72 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
73 IPV6 IPv6 support is enabled.
74 ISAPNP ISA PnP code is enabled.
75 ISDN Appropriate ISDN support is enabled.
76 JOY Appropriate joystick support is enabled.
77 KGDB Kernel debugger support is enabled.
78 KVM Kernel Virtual Machine support is enabled.
79 LIBATA Libata driver is enabled
80 LP Printer support is enabled.
81 LOOP Loopback device support is enabled.
82 M68k M68k architecture is enabled.
83 These options have more detailed description inside of
84 Documentation/m68k/kernel-options.txt.
85 MDA MDA console support is enabled.
86 MIPS MIPS architecture is enabled.
87 MOUSE Appropriate mouse support is enabled.
88 MSI Message Signaled Interrupts (PCI).
89 MTD MTD (Memory Technology Device) support is enabled.
90 NET Appropriate network support is enabled.
91 NUMA NUMA support is enabled.
92 NFS Appropriate NFS support is enabled.
93 OSS OSS sound support is enabled.
94 PV_OPS A paravirtualized kernel is enabled.
95 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
96 PARISC The PA-RISC architecture is enabled.
97 PCI PCI bus support is enabled.
98 PCIE PCI Express support is enabled.
99 PCMCIA The PCMCIA subsystem is enabled.
100 PNP Plug & Play support is enabled.
101 PPC PowerPC architecture is enabled.
102 PPT Parallel port support is enabled.
103 PS2 Appropriate PS/2 support is enabled.
104 RAM RAM disk support is enabled.
105 S390 S390 architecture is enabled.
106 SCSI Appropriate SCSI support is enabled.
107 A lot of drivers have their options described inside
108 the Documentation/scsi/ sub-directory.
109 SECURITY Different security models are enabled.
110 SELINUX SELinux support is enabled.
111 APPARMOR AppArmor support is enabled.
112 SERIAL Serial support is enabled.
113 SH SuperH architecture is enabled.
114 SMP The kernel is an SMP kernel.
115 SPARC Sparc architecture is enabled.
116 SWSUSP Software suspend (hibernation) is enabled.
117 SUSPEND System suspend states are enabled.
118 TPM TPM drivers are enabled.
119 TS Appropriate touchscreen support is enabled.
120 UMS USB Mass Storage support is enabled.
121 USB USB support is enabled.
122 USBHID USB Human Interface Device support is enabled.
123 V4L Video For Linux support is enabled.
124 VMMIO Driver for memory mapped virtio devices is enabled.
125 VGA The VGA console has been enabled.
126 VT Virtual terminal support is enabled.
127 WDT Watchdog support is enabled.
128 XT IBM PC/XT MFM hard disk support is enabled.
129 X86-32 X86-32, aka i386 architecture is enabled.
130 X86-64 X86-64 architecture is enabled.
131 More X86-64 boot options can be found in
132 Documentation/x86/x86_64/boot-options.txt .
133 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
134 XEN Xen support is enabled
136 In addition, the following text indicates that the option:
138 BUGS= Relates to possible processor bugs on the said processor.
139 KNL Is a kernel start-up parameter.
140 BOOT Is a boot loader parameter.
142 Parameters denoted with BOOT are actually interpreted by the boot
143 loader, and have no meaning to the kernel directly.
144 Do not modify the syntax of boot loader parameters without extreme
145 need or coordination with <Documentation/x86/boot.txt>.
147 There are also arch-specific kernel-parameters not documented here.
148 See for example <Documentation/x86/x86_64/boot-options.txt>.
150 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
151 a trailing = on the name of any parameter states that that parameter will
152 be entered as an environment variable, whereas its absence indicates that
153 it will appear as a kernel argument readable via /proc/cmdline by programs
154 running once the system is up.
156 The number of kernel parameters is not limited, but the length of the
157 complete command line (parameters including spaces etc.) is limited to
158 a fixed number of characters. This limit depends on the architecture
159 and is between 256 and 4096 characters. It is defined in the file
160 ./include/asm/setup.h as COMMAND_LINE_SIZE.
162 Finally, the [KMG] suffix is commonly described after a number of kernel
163 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
164 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
165 bytes respectively. Such letter suffixes can also be entirely omitted.
168 acpi= [HW,ACPI,X86]
169 Advanced Configuration and Power Interface
170 Format: { force | off | strict | noirq | rsdt }
171 force -- enable ACPI if default was off
172 off -- disable ACPI if default was on
173 noirq -- do not use ACPI for IRQ routing
174 strict -- Be less tolerant of platforms that are not
175 strictly ACPI specification compliant.
176 rsdt -- prefer RSDT over (default) XSDT
177 copy_dsdt -- copy DSDT to memory
179 See also Documentation/power/runtime_pm.txt, pci=noacpi
181 acpi_rsdp= [ACPI,EFI,KEXEC]
182 Pass the RSDP address to the kernel, mostly used
183 on machines running EFI runtime service to boot the
184 second kernel for kdump.
186 acpi_apic_instance= [ACPI, IOAPIC]
187 Format: <int>
188 2: use 2nd APIC table, if available
189 1,0: use 1st APIC table
190 default: 0
192 acpi_backlight= [HW,ACPI]
193 acpi_backlight=vendor
194 acpi_backlight=video
195 If set to vendor, prefer vendor specific driver
196 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
197 of the ACPI video.ko driver.
199 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
200 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
201 Format: <int>
202 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
203 debug output. Bits in debug_layer correspond to a
204 _COMPONENT in an ACPI source file, e.g.,
205 #define _COMPONENT ACPI_PCI_COMPONENT
206 Bits in debug_level correspond to a level in
207 ACPI_DEBUG_PRINT statements, e.g.,
208 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
209 The debug_level mask defaults to "info". See
210 Documentation/acpi/debug.txt for more information about
211 debug layers and levels.
213 Enable processor driver info messages:
214 acpi.debug_layer=0x20000000
215 Enable PCI/PCI interrupt routing info messages:
216 acpi.debug_layer=0x400000
217 Enable AML "Debug" output, i.e., stores to the Debug
218 object while interpreting AML:
219 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
220 Enable all messages related to ACPI hardware:
221 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
223 Some values produce so much output that the system is
224 unusable. The "log_buf_len" parameter may be useful
225 if you need to capture more output.
227 acpi_force_table_verification [HW,ACPI]
228 Enable table checksum verification during early stage.
229 By default, this is disabled due to x86 early mapping
230 size limitation.
232 acpi_irq_balance [HW,ACPI]
233 ACPI will balance active IRQs
234 default in APIC mode
236 acpi_irq_nobalance [HW,ACPI]
237 ACPI will not move active IRQs (default)
238 default in PIC mode
240 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
241 Format: <irq>,<irq>...
243 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
244 use by PCI
245 Format: <irq>,<irq>...
247 acpi_no_auto_serialize [HW,ACPI]
248 Disable auto-serialization of AML methods
249 AML control methods that contain the opcodes to create
250 named objects will be marked as "Serialized" by the
251 auto-serialization feature.
252 This feature is enabled by default.
253 This option allows to turn off the feature.
255 acpi_no_static_ssdt [HW,ACPI]
256 Disable installation of static SSDTs at early boot time
257 By default, SSDTs contained in the RSDT/XSDT will be
258 installed automatically and they will appear under
259 /sys/firmware/acpi/tables.
260 This option turns off this feature.
261 Note that specifying this option does not affect
262 dynamic table installation which will install SSDT
263 tables to /sys/firmware/acpi/tables/dynamic.
265 acpica_no_return_repair [HW, ACPI]
266 Disable AML predefined validation mechanism
267 This mechanism can repair the evaluation result to make
268 the return objects more ACPI specification compliant.
269 This option is useful for developers to identify the
270 root cause of an AML interpreter issue when the issue
271 has something to do with the repair mechanism.
273 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
274 Format: To spoof as Windows 98: ="Microsoft Windows"
276 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
277 acpi_osi="string1" # add string1
278 acpi_osi="!string2" # remove string2
279 acpi_osi=!* # remove all strings
280 acpi_osi=! # disable all built-in OS vendor
281 strings
282 acpi_osi= # disable all strings
284 'acpi_osi=!' can be used in combination with single or
285 multiple 'acpi_osi="string1"' to support specific OS
286 vendor string(s). Note that such command can only
287 affect the default state of the OS vendor strings, thus
288 it cannot affect the default state of the feature group
289 strings and the current state of the OS vendor strings,
290 specifying it multiple times through kernel command line
291 is meaningless. This command is useful when one do not
292 care about the state of the feature group strings which
293 should be controlled by the OSPM.
294 Examples:
295 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
296 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
297 can make '_OSI("Windows 2000")' TRUE.
299 'acpi_osi=' cannot be used in combination with other
300 'acpi_osi=' command lines, the _OSI method will not
301 exist in the ACPI namespace. NOTE that such command can
302 only affect the _OSI support state, thus specifying it
303 multiple times through kernel command line is also
304 meaningless.
305 Examples:
306 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
307 FALSE.
309 'acpi_osi=!*' can be used in combination with single or
310 multiple 'acpi_osi="string1"' to support specific
311 string(s). Note that such command can affect the
312 current state of both the OS vendor strings and the
313 feature group strings, thus specifying it multiple times
314 through kernel command line is meaningful. But it may
315 still not able to affect the final state of a string if
316 there are quirks related to this string. This command
317 is useful when one want to control the state of the
318 feature group strings to debug BIOS issues related to
319 the OSPM features.
320 Examples:
321 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
322 '_OSI("Module Device")' FALSE.
323 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
324 '_OSI("Module Device")' TRUE.
325 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
326 equivalent to
327 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
328 and
329 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
330 they all will make '_OSI("Windows 2000")' TRUE.
332 acpi_pm_good [X86]
333 Override the pmtimer bug detection: force the kernel
334 to assume that this machine's pmtimer latches its value
335 and always returns good values.
337 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
338 Format: { level | edge | high | low }
340 acpi_skip_timer_override [HW,ACPI]
341 Recognize and ignore IRQ0/pin2 Interrupt Override.
342 For broken nForce2 BIOS resulting in XT-PIC timer.
344 acpi_sleep= [HW,ACPI] Sleep options
345 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
346 old_ordering, nonvs, sci_force_enable }
347 See Documentation/power/video.txt for information on
348 s3_bios and s3_mode.
349 s3_beep is for debugging; it makes the PC's speaker beep
350 as soon as the kernel's real-mode entry point is called.
351 s4_nohwsig prevents ACPI hardware signature from being
352 used during resume from hibernation.
353 old_ordering causes the ACPI 1.0 ordering of the _PTS
354 control method, with respect to putting devices into
355 low power states, to be enforced (the ACPI 2.0 ordering
356 of _PTS is used by default).
357 nonvs prevents the kernel from saving/restoring the
358 ACPI NVS memory during suspend/hibernation and resume.
359 sci_force_enable causes the kernel to set SCI_EN directly
360 on resume from S1/S3 (which is against the ACPI spec,
361 but some broken systems don't work without it).
363 acpi_use_timer_override [HW,ACPI]
364 Use timer override. For some broken Nvidia NF5 boards
365 that require a timer override, but don't have HPET
367 acpi_enforce_resources= [ACPI]
368 { strict | lax | no }
369 Check for resource conflicts between native drivers
370 and ACPI OperationRegions (SystemIO and SystemMemory
371 only). IO ports and memory declared in ACPI might be
372 used by the ACPI subsystem in arbitrary AML code and
373 can interfere with legacy drivers.
374 strict (default): access to resources claimed by ACPI
375 is denied; legacy drivers trying to access reserved
376 resources will fail to bind to device using them.
377 lax: access to resources claimed by ACPI is allowed;
378 legacy drivers trying to access reserved resources
379 will bind successfully but a warning message is logged.
380 no: ACPI OperationRegions are not marked as reserved,
381 no further checks are performed.
383 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
384 kernels.
386 add_efi_memmap [EFI; X86] Include EFI memory map in
387 kernel's map of available physical RAM.
389 agp= [AGP]
390 { off | try_unsupported }
391 off: disable AGP support
392 try_unsupported: try to drive unsupported chipsets
393 (may crash computer or cause data corruption)
395 ALSA [HW,ALSA]
396 See Documentation/sound/alsa/alsa-parameters.txt
398 alignment= [KNL,ARM]
399 Allow the default userspace alignment fault handler
400 behaviour to be specified. Bit 0 enables warnings,
401 bit 1 enables fixups, and bit 2 sends a segfault.
403 align_va_addr= [X86-64]
404 Align virtual addresses by clearing slice [14:12] when
405 allocating a VMA at process creation time. This option
406 gives you up to 3% performance improvement on AMD F15h
407 machines (where it is enabled by default) for a
408 CPU-intensive style benchmark, and it can vary highly in
409 a microbenchmark depending on workload and compiler.
411 32: only for 32-bit processes
412 64: only for 64-bit processes
413 on: enable for both 32- and 64-bit processes
414 off: disable for both 32- and 64-bit processes
416 alloc_snapshot [FTRACE]
417 Allocate the ftrace snapshot buffer on boot up when the
418 main buffer is allocated. This is handy if debugging
419 and you need to use tracing_snapshot() on boot up, and
420 do not want to use tracing_snapshot_alloc() as it needs
421 to be done where GFP_KERNEL allocations are allowed.
423 amd_iommu= [HW,X86-64]
424 Pass parameters to the AMD IOMMU driver in the system.
425 Possible values are:
426 fullflush - enable flushing of IO/TLB entries when
427 they are unmapped. Otherwise they are
428 flushed before they will be reused, which
429 is a lot of faster
430 off - do not initialize any AMD IOMMU found in
431 the system
432 force_isolation - Force device isolation for all
433 devices. The IOMMU driver is not
434 allowed anymore to lift isolation
435 requirements as needed. This option
436 does not override iommu=pt
438 amd_iommu_dump= [HW,X86-64]
439 Enable AMD IOMMU driver option to dump the ACPI table
440 for AMD IOMMU. With this option enabled, AMD IOMMU
441 driver will print ACPI tables for AMD IOMMU during
442 IOMMU initialization.
444 amijoy.map= [HW,JOY] Amiga joystick support
445 Map of devices attached to JOY0DAT and JOY1DAT
446 Format: <a>,<b>
447 See also Documentation/input/joystick.txt
449 analog.map= [HW,JOY] Analog joystick and gamepad support
450 Specifies type or capabilities of an analog joystick
451 connected to one of 16 gameports
452 Format: <type1>,<type2>,..<type16>
454 apc= [HW,SPARC]
455 Power management functions (SPARCstation-4/5 + deriv.)
456 Format: noidle
457 Disable APC CPU standby support. SPARCstation-Fox does
458 not play well with APC CPU idle - disable it if you have
459 APC and your system crashes randomly.
461 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
462 Change the output verbosity whilst booting
463 Format: { quiet (default) | verbose | debug }
464 Change the amount of debugging information output
465 when initialising the APIC and IO-APIC components.
467 autoconf= [IPV6]
468 See Documentation/networking/ipv6.txt.
470 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
471 Limit apic dumping. The parameter defines the maximal
472 number of local apics being dumped. Also it is possible
473 to set it to "all" by meaning -- no limit here.
474 Format: { 1 (default) | 2 | ... | all }.
475 The parameter valid if only apic=debug or
476 apic=verbose is specified.
477 Example: apic=debug show_lapic=all
479 apm= [APM] Advanced Power Management
480 See header of arch/x86/kernel/apm_32.c.
482 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
483 Format: <io>,<irq>,<nodeID>
485 ataflop= [HW,M68k]
487 atarimouse= [HW,MOUSE] Atari Mouse
489 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
490 EzKey and similar keyboards
492 atkbd.reset= [HW] Reset keyboard during initialization
494 atkbd.set= [HW] Select keyboard code set
495 Format: <int> (2 = AT (default), 3 = PS/2)
497 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
498 keyboards
500 atkbd.softraw= [HW] Choose between synthetic and real raw mode
501 Format: <bool> (0 = real, 1 = synthetic (default))
503 atkbd.softrepeat= [HW]
504 Use software keyboard repeat
506 audit= [KNL] Enable the audit sub-system
507 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
508 0 - kernel audit is disabled and can not be enabled
509 until the next reboot
510 unset - kernel audit is initialized but disabled and
511 will be fully enabled by the userspace auditd.
512 1 - kernel audit is initialized and partially enabled,
513 storing at most audit_backlog_limit messages in
514 RAM until it is fully enabled by the userspace
515 auditd.
516 Default: unset
518 audit_backlog_limit= [KNL] Set the audit queue size limit.
519 Format: <int> (must be >=0)
520 Default: 64
522 baycom_epp= [HW,AX25]
523 Format: <io>,<mode>
525 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
526 Format: <io>,<mode>
527 See header of drivers/net/hamradio/baycom_par.c.
529 baycom_ser_fdx= [HW,AX25]
530 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
531 Format: <io>,<irq>,<mode>[,<baud>]
532 See header of drivers/net/hamradio/baycom_ser_fdx.c.
534 baycom_ser_hdx= [HW,AX25]
535 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
536 Format: <io>,<irq>,<mode>
537 See header of drivers/net/hamradio/baycom_ser_hdx.c.
539 blkdevparts= Manual partition parsing of block device(s) for
540 embedded devices based on command line input.
541 See Documentation/block/cmdline-partition.txt
543 boot_delay= Milliseconds to delay each printk during boot.
544 Values larger than 10 seconds (10000) are changed to
545 no delay (0).
546 Format: integer
548 bootmem_debug [KNL] Enable bootmem allocator debug messages.
550 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
551 bttv.radio= Most important insmod options are available as
552 kernel args too.
553 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
554 bttv.tuner=
556 bulk_remove=off [PPC] This parameter disables the use of the pSeries
557 firmware feature for flushing multiple hpte entries
558 at a time.
560 c101= [NET] Moxa C101 synchronous serial card
562 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
563 Sometimes CPU hardware bugs make them report the cache
564 size incorrectly. The kernel will attempt work arounds
565 to fix known problems, but for some CPUs it is not
566 possible to determine what the correct size should be.
567 This option provides an override for these situations.
569 ccw_timeout_log [S390]
570 See Documentation/s390/CommonIO for details.
572 cgroup_disable= [KNL] Disable a particular controller
573 Format: {name of the controller(s) to disable}
574 The effects of cgroup_disable=foo are:
575 - foo isn't auto-mounted if you mount all cgroups in
576 a single hierarchy
577 - foo isn't visible as an individually mountable
578 subsystem
579 {Currently only "memory" controller deal with this and
580 cut the overhead, others just disable the usage. So
581 only cgroup_disable=memory is actually worthy}
583 checkreqprot [SELINUX] Set initial checkreqprot flag value.
584 Format: { "0" | "1" }
585 See security/selinux/Kconfig help text.
586 0 -- check protection applied by kernel (includes
587 any implied execute protection).
588 1 -- check protection requested by application.
589 Default value is set via a kernel config option.
590 Value can be changed at runtime via
591 /selinux/checkreqprot.
593 cio_ignore= [S390]
594 See Documentation/s390/CommonIO for details.
595 clk_ignore_unused
596 [CLK]
597 Keep all clocks already enabled by bootloader on,
598 even if no driver has claimed them. This is useful
599 for debug and development, but should not be
600 needed on a platform with proper driver support.
601 For more information, see Documentation/clk.txt.
603 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
604 [Deprecated]
605 Forces specified clocksource (if available) to be used
606 when calculating gettimeofday(). If specified
607 clocksource is not available, it defaults to PIT.
608 Format: { pit | tsc | cyclone | pmtmr }
610 clocksource= Override the default clocksource
611 Format: <string>
612 Override the default clocksource and use the clocksource
613 with the name specified.
614 Some clocksource names to choose from, depending on
615 the platform:
616 [all] jiffies (this is the base, fallback clocksource)
617 [ACPI] acpi_pm
618 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
619 pxa_timer,timer3,32k_counter,timer0_1
620 [AVR32] avr32
621 [X86-32] pit,hpet,tsc;
622 scx200_hrt on Geode; cyclone on IBM x440
623 [MIPS] MIPS
624 [PARISC] cr16
625 [S390] tod
626 [SH] SuperH
627 [SPARC64] tick
628 [X86-64] hpet,tsc
630 clearcpuid=BITNUM [X86]
631 Disable CPUID feature X for the kernel. See
632 arch/x86/include/asm/cpufeature.h for the valid bit
633 numbers. Note the Linux specific bits are not necessarily
634 stable over kernel options, but the vendor specific
635 ones should be.
636 Also note that user programs calling CPUID directly
637 or using the feature without checking anything
638 will still see it. This just prevents it from
639 being used by the kernel or shown in /proc/cpuinfo.
640 Also note the kernel might malfunction if you disable
641 some critical bits.
643 cma=nn[MG]@[start[MG][-end[MG]]]
644 [ARM,X86,KNL]
645 Sets the size of kernel global memory area for
646 contiguous memory allocations and optionally the
647 placement constraint by the physical address range of
648 memory allocations. For more information, see
649 include/linux/dma-contiguous.h
651 cmo_free_hint= [PPC] Format: { yes | no }
652 Specify whether pages are marked as being inactive
653 when they are freed. This is used in CMO environments
654 to determine OS memory pressure for page stealing by
655 a hypervisor.
656 Default: yes
658 coherent_pool=nn[KMG] [ARM,KNL]
659 Sets the size of memory pool for coherent, atomic dma
660 allocations, by default set to 256K.
662 code_bytes [X86] How many bytes of object code to print
663 in an oops report.
664 Range: 0 - 8192
665 Default: 64
667 com20020= [HW,NET] ARCnet - COM20020 chipset
668 Format:
669 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
671 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
672 Format: <io>[,<irq>]
674 com90xx= [HW,NET]
675 ARCnet - COM90xx chipset (memory-mapped buffers)
676 Format: <io>[,<irq>[,<memstart>]]
678 condev= [HW,S390] console device
679 conmode=
681 console= [KNL] Output console device and options.
683 tty<n> Use the virtual console device <n>.
685 ttyS<n>[,options]
686 ttyUSB0[,options]
687 Use the specified serial port. The options are of
688 the form "bbbbpnf", where "bbbb" is the baud rate,
689 "p" is parity ("n", "o", or "e"), "n" is number of
690 bits, and "f" is flow control ("r" for RTS or
691 omit it). Default is "9600n8".
693 See Documentation/serial-console.txt for more
694 information. See
695 Documentation/networking/netconsole.txt for an
696 alternative.
698 uart[8250],io,<addr>[,options]
699 uart[8250],mmio,<addr>[,options]
700 Start an early, polled-mode console on the 8250/16550
701 UART at the specified I/O port or MMIO address,
702 switching to the matching ttyS device later. The
703 options are the same as for ttyS, above.
704 hvc<n> Use the hypervisor console device <n>. This is for
705 both Xen and PowerPC hypervisors.
707 If the device connected to the port is not a TTY but a braille
708 device, prepend "brl," before the device type, for instance
709 console=brl,ttyS0
710 For now, only VisioBraille is supported.
712 consoleblank= [KNL] The console blank (screen saver) timeout in
713 seconds. Defaults to 10*60 = 10mins. A value of 0
714 disables the blank timer.
716 coredump_filter=
717 [KNL] Change the default value for
718 /proc/<pid>/coredump_filter.
719 See also Documentation/filesystems/proc.txt.
721 cpuidle.off=1 [CPU_IDLE]
722 disable the cpuidle sub-system
724 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
725 Format:
726 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
728 crashkernel=size[KMG][@offset[KMG]]
729 [KNL] Using kexec, Linux can switch to a 'crash kernel'
730 upon panic. This parameter reserves the physical
731 memory region [offset, offset + size] for that kernel
732 image. If '@offset' is omitted, then a suitable offset
733 is selected automatically. Check
734 Documentation/kdump/kdump.txt for further details.
736 crashkernel=range1:size1[,range2:size2,...][@offset]
737 [KNL] Same as above, but depends on the memory
738 in the running system. The syntax of range is
739 start-[end] where start and end are both
740 a memory unit (amount[KMG]). See also
741 Documentation/kdump/kdump.txt for an example.
743 crashkernel=size[KMG],high
744 [KNL, x86_64] range could be above 4G. Allow kernel
745 to allocate physical memory region from top, so could
746 be above 4G if system have more than 4G ram installed.
747 Otherwise memory region will be allocated below 4G, if
748 available.
749 It will be ignored if crashkernel=X is specified.
750 crashkernel=size[KMG],low
751 [KNL, x86_64] range under 4G. When crashkernel=X,high
752 is passed, kernel could allocate physical memory region
753 above 4G, that cause second kernel crash on system
754 that require some amount of low memory, e.g. swiotlb
755 requires at least 64M+32K low memory. Kernel would
756 try to allocate 72M below 4G automatically.
757 This one let user to specify own low range under 4G
758 for second kernel instead.
759 0: to disable low allocation.
760 It will be ignored when crashkernel=X,high is not used
761 or memory reserved is below 4G.
763 cs89x0_dma= [HW,NET]
764 Format: <dma>
766 cs89x0_media= [HW,NET]
767 Format: { rj45 | aui | bnc }
769 dasd= [HW,NET]
770 See header of drivers/s390/block/dasd_devmap.c.
772 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
773 (one device per port)
774 Format: <port#>,<type>
775 See also Documentation/input/joystick-parport.txt
777 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
778 time. See Documentation/dynamic-debug-howto.txt for
779 details. Deprecated, see dyndbg.
781 debug [KNL] Enable kernel debugging (events log level).
783 debug_locks_verbose=
784 [KNL] verbose self-tests
785 Format=<0|1>
786 Print debugging info while doing the locking API
787 self-tests.
788 We default to 0 (no extra messages), setting it to
789 1 will print _a lot_ more information - normally
790 only useful to kernel developers.
792 debug_objects [KNL] Enable object debugging
794 no_debug_objects
795 [KNL] Disable object debugging
797 debug_guardpage_minorder=
798 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
799 parameter allows control of the order of pages that will
800 be intentionally kept free (and hence protected) by the
801 buddy allocator. Bigger value increase the probability
802 of catching random memory corruption, but reduce the
803 amount of memory for normal system use. The maximum
804 possible value is MAX_ORDER/2. Setting this parameter
805 to 1 or 2 should be enough to identify most random
806 memory corruption problems caused by bugs in kernel or
807 driver code when a CPU writes to (or reads from) a
808 random memory location. Note that there exists a class
809 of memory corruptions problems caused by buggy H/W or
810 F/W or by drivers badly programing DMA (basically when
811 memory is written at bus level and the CPU MMU is
812 bypassed) which are not detectable by
813 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
814 tracking down these problems.
816 debugpat [X86] Enable PAT debugging
818 decnet.addr= [HW,NET]
819 Format: <area>[,<node>]
820 See also Documentation/networking/decnet.txt.
822 default_hugepagesz=
823 [same as hugepagesz=] The size of the default
824 HugeTLB page size. This is the size represented by
825 the legacy /proc/ hugepages APIs, used for SHM, and
826 default size when mounting hugetlbfs filesystems.
827 Defaults to the default architecture's huge page size
828 if not specified.
830 dhash_entries= [KNL]
831 Set number of hash buckets for dentry cache.
833 disable= [IPV6]
834 See Documentation/networking/ipv6.txt.
836 disable_cpu_apicid= [X86,APIC,SMP]
837 Format: <int>
838 The number of initial APIC ID for the
839 corresponding CPU to be disabled at boot,
840 mostly used for the kdump 2nd kernel to
841 disable BSP to wake up multiple CPUs without
842 causing system reset or hang due to sending
843 INIT from AP to BSP.
845 disable_ddw [PPC/PSERIES]
846 Disable Dynamic DMA Window support. Use this if
847 to workaround buggy firmware.
849 disable_ipv6= [IPV6]
850 See Documentation/networking/ipv6.txt.
852 disable_mtrr_cleanup [X86]
853 The kernel tries to adjust MTRR layout from continuous
854 to discrete, to make X server driver able to add WB
855 entry later. This parameter disables that.
857 disable_mtrr_trim [X86, Intel and AMD only]
858 By default the kernel will trim any uncacheable
859 memory out of your available memory pool based on
860 MTRR settings. This parameter disables that behavior,
861 possibly causing your machine to run very slowly.
863 disable_timer_pin_1 [X86]
864 Disable PIN 1 of APIC timer
865 Can be useful to work around chipset bugs.
867 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
868 this option disables the debugging code at boot.
870 dma_debug_entries=<number>
871 This option allows to tune the number of preallocated
872 entries for DMA-API debugging code. One entry is
873 required per DMA-API allocation. Use this if the
874 DMA-API debugging code disables itself because the
875 architectural default is too low.
877 dma_debug_driver=<driver_name>
878 With this option the DMA-API debugging driver
879 filter feature can be enabled at boot time. Just
880 pass the driver to filter for as the parameter.
881 The filter can be disabled or changed to another
882 driver later using sysfs.
884 drm_kms_helper.edid_firmware=[<connector>:]<file>
885 Broken monitors, graphic adapters and KVMs may
886 send no or incorrect EDID data sets. This parameter
887 allows to specify an EDID data set in the
888 /lib/firmware directory that is used instead.
889 Generic built-in EDID data sets are used, if one of
890 edid/1024x768.bin, edid/1280x1024.bin,
891 edid/1680x1050.bin, or edid/1920x1080.bin is given
892 and no file with the same name exists. Details and
893 instructions how to build your own EDID data are
894 available in Documentation/EDID/HOWTO.txt. An EDID
895 data set will only be used for a particular connector,
896 if its name and a colon are prepended to the EDID
897 name.
899 dscc4.setup= [NET]
901 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
902 module.dyndbg[="val"]
903 Enable debug messages at boot time. See
904 Documentation/dynamic-debug-howto.txt for details.
906 early_ioremap_debug [KNL]
907 Enable debug messages in early_ioremap support. This
908 is useful for tracking down temporary early mappings
909 which are not unmapped.
911 earlycon= [KNL] Output early console device and options.
913 uart[8250],io,<addr>[,options]
914 uart[8250],mmio,<addr>[,options]
915 uart[8250],mmio32,<addr>[,options]
916 Start an early, polled-mode console on the 8250/16550
917 UART at the specified I/O port or MMIO address.
918 MMIO inter-register address stride is either 8-bit
919 (mmio) or 32-bit (mmio32).
920 The options are the same as for ttyS, above.
922 pl011,<addr>
923 Start an early, polled-mode console on a pl011 serial
924 port at the specified address. The pl011 serial port
925 must already be setup and configured. Options are not
926 yet supported.
928 smh Use ARM semihosting calls for early console.
930 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
931 earlyprintk=vga
932 earlyprintk=efi
933 earlyprintk=xen
934 earlyprintk=serial[,ttySn[,baudrate]]
935 earlyprintk=serial[,0x...[,baudrate]]
936 earlyprintk=ttySn[,baudrate]
937 earlyprintk=dbgp[debugController#]
939 earlyprintk is useful when the kernel crashes before
940 the normal console is initialized. It is not enabled by
941 default because it has some cosmetic problems.
943 Append ",keep" to not disable it when the real console
944 takes over.
946 Only one of vga, efi, serial, or usb debug port can
947 be used at a time.
949 Currently only ttyS0 and ttyS1 may be specified by
950 name. Other I/O ports may be explicitly specified
951 on some architectures (x86 and arm at least) by
952 replacing ttySn with an I/O port address, like this:
953 earlyprintk=serial,0x1008,115200
954 You can find the port for a given device in
955 /proc/tty/driver/serial:
956 2: uart:ST16650V2 port:00001008 irq:18 ...
958 Interaction with the standard serial driver is not
959 very good.
961 The VGA and EFI output is eventually overwritten by
962 the real console.
964 The xen output can only be used by Xen PV guests.
966 edac_report= [HW,EDAC] Control how to report EDAC event
967 Format: {"on" | "off" | "force"}
968 on: enable EDAC to report H/W event. May be overridden
969 by other higher priority error reporting module.
970 off: disable H/W event reporting through EDAC.
971 force: enforce the use of EDAC to report H/W event.
972 default: on.
974 ekgdboc= [X86,KGDB] Allow early kernel console debugging
975 ekgdboc=kbd
977 This is designed to be used in conjunction with
978 the boot argument: earlyprintk=vga
980 edd= [EDD]
981 Format: {"off" | "on" | "skip[mbr]"}
983 efi= [EFI]
984 Format: { "old_map" }
985 old_map [X86-64]: switch to the old ioremap-based EFI
986 runtime services mapping. 32-bit still uses this one by
987 default.
989 efi_no_storage_paranoia [EFI; X86]
990 Using this parameter you can use more than 50% of
991 your efi variable storage. Use this parameter only if
992 you are really sure that your UEFI does sane gc and
993 fulfills the spec otherwise your board may brick.
995 eisa_irq_edge= [PARISC,HW]
996 See header of drivers/parisc/eisa.c.
998 elanfreq= [X86-32]
999 See comment before function elanfreq_setup() in
1000 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1002 elevator= [IOSCHED]
1003 Format: {"cfq" | "deadline" | "noop"}
1004 See Documentation/block/cfq-iosched.txt and
1005 Documentation/block/deadline-iosched.txt for details.
1007 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1008 Specifies physical address of start of kernel core
1009 image elf header and optionally the size. Generally
1010 kexec loader will pass this option to capture kernel.
1011 See Documentation/kdump/kdump.txt for details.
1013 enable_mtrr_cleanup [X86]
1014 The kernel tries to adjust MTRR layout from continuous
1015 to discrete, to make X server driver able to add WB
1016 entry later. This parameter enables that.
1018 enable_timer_pin_1 [X86]
1019 Enable PIN 1 of APIC timer
1020 Can be useful to work around chipset bugs
1021 (in particular on some ATI chipsets).
1022 The kernel tries to set a reasonable default.
1024 enforcing [SELINUX] Set initial enforcing status.
1025 Format: {"0" | "1"}
1026 See security/selinux/Kconfig help text.
1027 0 -- permissive (log only, no denials).
1028 1 -- enforcing (deny and log).
1029 Default value is 0.
1030 Value can be changed at runtime via /selinux/enforce.
1032 erst_disable [ACPI]
1033 Disable Error Record Serialization Table (ERST)
1034 support.
1036 ether= [HW,NET] Ethernet cards parameters
1037 This option is obsoleted by the "netdev=" option, which
1038 has equivalent usage. See its documentation for details.
1040 evm= [EVM]
1041 Format: { "fix" }
1042 Permit 'security.evm' to be updated regardless of
1043 current integrity status.
1045 failslab=
1046 fail_page_alloc=
1047 fail_make_request=[KNL]
1048 General fault injection mechanism.
1049 Format: <interval>,<probability>,<space>,<times>
1050 See also Documentation/fault-injection/.
1052 floppy= [HW]
1053 See Documentation/blockdev/floppy.txt.
1055 force_pal_cache_flush
1056 [IA-64] Avoid check_sal_cache_flush which may hang on
1057 buggy SAL_CACHE_FLUSH implementations. Using this
1058 parameter will force ia64_sal_cache_flush to call
1059 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1061 forcepae [X86-32]
1062 Forcefully enable Physical Address Extension (PAE).
1063 Many Pentium M systems disable PAE but may have a
1064 functionally usable PAE implementation.
1065 Warning: use of this parameter will taint the kernel
1066 and may cause unknown problems.
1068 ftrace=[tracer]
1069 [FTRACE] will set and start the specified tracer
1070 as early as possible in order to facilitate early
1071 boot debugging.
1073 ftrace_dump_on_oops[=orig_cpu]
1074 [FTRACE] will dump the trace buffers on oops.
1075 If no parameter is passed, ftrace will dump
1076 buffers of all CPUs, but if you pass orig_cpu, it will
1077 dump only the buffer of the CPU that triggered the
1078 oops.
1080 ftrace_filter=[function-list]
1081 [FTRACE] Limit the functions traced by the function
1082 tracer at boot up. function-list is a comma separated
1083 list of functions. This list can be changed at run
1084 time by the set_ftrace_filter file in the debugfs
1085 tracing directory.
1087 ftrace_notrace=[function-list]
1088 [FTRACE] Do not trace the functions specified in
1089 function-list. This list can be changed at run time
1090 by the set_ftrace_notrace file in the debugfs
1091 tracing directory.
1093 ftrace_graph_filter=[function-list]
1094 [FTRACE] Limit the top level callers functions traced
1095 by the function graph tracer at boot up.
1096 function-list is a comma separated list of functions
1097 that can be changed at run time by the
1098 set_graph_function file in the debugfs tracing directory.
1100 gamecon.map[2|3]=
1101 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1102 support via parallel port (up to 5 devices per port)
1103 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1104 See also Documentation/input/joystick-parport.txt
1106 gamma= [HW,DRM]
1108 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1109 Format: off | on
1110 default: on
1112 gcov_persist= [GCOV] When non-zero (default), profiling data for
1113 kernel modules is saved and remains accessible via
1114 debugfs, even when the module is unloaded/reloaded.
1115 When zero, profiling data is discarded and associated
1116 debugfs files are removed at module unload time.
1118 gpt [EFI] Forces disk with valid GPT signature but
1119 invalid Protective MBR to be treated as GPT. If the
1120 primary GPT is corrupted, it enables the backup/alternate
1121 GPT to be used instead.
1123 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1124 the "Enable 0" bit of the configuration register.
1125 Format: 0 | 1
1126 Default: 0
1127 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1128 the "Enable 0" bit of the configuration register.
1129 Format: 0 | 1
1130 Default: 0
1131 grcan.select= [HW] Select which physical interface to use.
1132 Format: 0 | 1
1133 Default: 0
1134 grcan.txsize= [HW] Sets the size of the tx buffer.
1135 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1136 Default: 1024
1137 grcan.rxsize= [HW] Sets the size of the rx buffer.
1138 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1139 Default: 1024
1141 hashdist= [KNL,NUMA] Large hashes allocated during boot
1142 are distributed across NUMA nodes. Defaults on
1143 for 64-bit NUMA, off otherwise.
1144 Format: 0 | 1 (for off | on)
1146 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1148 hd= [EIDE] (E)IDE hard drive subsystem geometry
1149 Format: <cyl>,<head>,<sect>
1151 hest_disable [ACPI]
1152 Disable Hardware Error Source Table (HEST) support;
1153 corresponding firmware-first mode error processing
1154 logic will be disabled.
1156 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1157 size of <nn>. This works even on boxes that have no
1158 highmem otherwise. This also works to reduce highmem
1159 size on bigger boxes.
1161 highres= [KNL] Enable/disable high resolution timer mode.
1162 Valid parameters: "on", "off"
1163 Default: "on"
1165 hisax= [HW,ISDN]
1166 See Documentation/isdn/README.HiSax.
1168 hlt [BUGS=ARM,SH]
1170 hpet= [X86-32,HPET] option to control HPET usage
1171 Format: { enable (default) | disable | force |
1172 verbose }
1173 disable: disable HPET and use PIT instead
1174 force: allow force enabled of undocumented chips (ICH4,
1175 VIA, nVidia)
1176 verbose: show contents of HPET registers during setup
1178 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1179 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1181 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1182 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1183 On x86-64 and powerpc, this option can be specified
1184 multiple times interleaved with hugepages= to reserve
1185 huge pages of different sizes. Valid pages sizes on
1186 x86-64 are 2M (when the CPU supports "pse") and 1G
1187 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1188 Note that 1GB pages can only be allocated at boot time
1189 using hugepages= and not freed afterwards.
1191 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1192 terminal devices. Valid values: 0..8
1193 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1194 If specified, z/VM IUCV HVC accepts connections
1195 from listed z/VM user IDs only.
1197 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1198 hardware thread id mappings.
1199 Format: <cpu>:<hwthread>
1201 keep_bootcon [KNL]
1202 Do not unregister boot console at start. This is only
1203 useful for debugging when something happens in the window
1204 between unregistering the boot console and initializing
1205 the real console.
1207 i2c_bus= [HW] Override the default board specific I2C bus speed
1208 or register an additional I2C bus that is not
1209 registered from board initialization code.
1210 Format:
1211 <bus_id>,<clkrate>
1213 i8042.debug [HW] Toggle i8042 debug mode
1214 i8042.direct [HW] Put keyboard port into non-translated mode
1215 i8042.dumbkbd [HW] Pretend that controller can only read data from
1216 keyboard and cannot control its state
1217 (Don't attempt to blink the leds)
1218 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1219 i8042.nokbd [HW] Don't check/create keyboard port
1220 i8042.noloop [HW] Disable the AUX Loopback command while probing
1221 for the AUX port
1222 i8042.nomux [HW] Don't check presence of an active multiplexing
1223 controller
1224 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1225 controllers
1226 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1227 i8042.reset [HW] Reset the controller during init and cleanup
1228 i8042.unlock [HW] Unlock (ignore) the keylock
1230 i810= [HW,DRM]
1232 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1233 indicates that the driver is running on unsupported
1234 hardware.
1235 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1236 does not match list of supported models.
1237 i8k.power_status
1238 [HW] Report power status in /proc/i8k
1239 (disabled by default)
1240 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1241 capability is set.
1243 i915.invert_brightness=
1244 [DRM] Invert the sense of the variable that is used to
1245 set the brightness of the panel backlight. Normally a
1246 brightness value of 0 indicates backlight switched off,
1247 and the maximum of the brightness value sets the backlight
1248 to maximum brightness. If this parameter is set to 0
1249 (default) and the machine requires it, or this parameter
1250 is set to 1, a brightness value of 0 sets the backlight
1251 to maximum brightness, and the maximum of the brightness
1252 value switches the backlight off.
1253 -1 -- never invert brightness
1254 0 -- machine default
1255 1 -- force brightness inversion
1257 icn= [HW,ISDN]
1258 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1260 ide-core.nodma= [HW] (E)IDE subsystem
1261 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1262 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1263 .cdrom .chs .ignore_cable are additional options
1264 See Documentation/ide/ide.txt.
1266 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1267 Claim all unknown PCI IDE storage controllers.
1269 idle= [X86]
1270 Format: idle=poll, idle=halt, idle=nomwait
1271 Poll forces a polling idle loop that can slightly
1272 improve the performance of waking up a idle CPU, but
1273 will use a lot of power and make the system run hot.
1274 Not recommended.
1275 idle=halt: Halt is forced to be used for CPU idle.
1276 In such case C2/C3 won't be used again.
1277 idle=nomwait: Disable mwait for CPU C-states
1279 ignore_loglevel [KNL]
1280 Ignore loglevel setting - this will print /all/
1281 kernel messages to the console. Useful for debugging.
1282 We also add it as printk module parameter, so users
1283 could change it dynamically, usually by
1284 /sys/module/printk/parameters/ignore_loglevel.
1286 ihash_entries= [KNL]
1287 Set number of hash buckets for inode cache.
1289 ima_appraise= [IMA] appraise integrity measurements
1290 Format: { "off" | "enforce" | "fix" }
1291 default: "enforce"
1293 ima_appraise_tcb [IMA]
1294 The builtin appraise policy appraises all files
1295 owned by uid=0.
1297 ima_hash= [IMA]
1298 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1299 | sha512 | ... }
1300 default: "sha1"
1302 The list of supported hash algorithms is defined
1303 in crypto/hash_info.h.
1305 ima_tcb [IMA]
1306 Load a policy which meets the needs of the Trusted
1307 Computing Base. This means IMA will measure all
1308 programs exec'd, files mmap'd for exec, and all files
1309 opened for read by uid=0.
1311 ima_template= [IMA]
1312 Select one of defined IMA measurements template formats.
1313 Formats: { "ima" | "ima-ng" }
1314 Default: "ima-ng"
1316 init= [KNL]
1317 Format: <full_path>
1318 Run specified binary instead of /sbin/init as init
1319 process.
1321 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1322 for working out where the kernel is dying during
1323 startup.
1325 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1326 initcall functions. Useful for debugging built-in
1327 modules and initcalls.
1329 initrd= [BOOT] Specify the location of the initial ramdisk
1331 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1332 Format: <irq>
1334 int_pln_enable [x86] Enable power limit notification interrupt
1336 integrity_audit=[IMA]
1337 Format: { "0" | "1" }
1338 0 -- basic integrity auditing messages. (Default)
1339 1 -- additional integrity auditing messages.
1341 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1342 on
1343 Enable intel iommu driver.
1344 off
1345 Disable intel iommu driver.
1346 igfx_off [Default Off]
1347 By default, gfx is mapped as normal device. If a gfx
1348 device has a dedicated DMAR unit, the DMAR unit is
1349 bypassed by not enabling DMAR with this option. In
1350 this case, gfx device will use physical address for
1351 DMA.
1352 forcedac [x86_64]
1353 With this option iommu will not optimize to look
1354 for io virtual address below 32-bit forcing dual
1355 address cycle on pci bus for cards supporting greater
1356 than 32-bit addressing. The default is to look
1357 for translation below 32-bit and if not available
1358 then look in the higher range.
1359 strict [Default Off]
1360 With this option on every unmap_single operation will
1361 result in a hardware IOTLB flush operation as opposed
1362 to batching them for performance.
1363 sp_off [Default Off]
1364 By default, super page will be supported if Intel IOMMU
1365 has the capability. With this option, super page will
1366 not be supported.
1368 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1369 0 disables intel_idle and fall back on acpi_idle.
1370 1 to 6 specify maximum depth of C-state.
1372 intel_pstate= [X86]
1373 disable
1374 Do not enable intel_pstate as the default
1375 scaling driver for the supported processors
1377 intremap= [X86-64, Intel-IOMMU]
1378 on enable Interrupt Remapping (default)
1379 off disable Interrupt Remapping
1380 nosid disable Source ID checking
1381 no_x2apic_optout
1382 BIOS x2APIC opt-out request will be ignored
1384 iomem= Disable strict checking of access to MMIO memory
1385 strict regions from userspace.
1386 relaxed
1388 iommu= [x86]
1389 off
1390 force
1391 noforce
1392 biomerge
1393 panic
1394 nopanic
1395 merge
1396 nomerge
1397 forcesac
1398 soft
1399 pt [x86, IA-64]
1402 io7= [HW] IO7 for Marvel based alpha systems
1403 See comment before marvel_specify_io7 in
1404 arch/alpha/kernel/core_marvel.c.
1406 io_delay= [X86] I/O delay method
1407 0x80
1408 Standard port 0x80 based delay
1409 0xed
1410 Alternate port 0xed based delay (needed on some systems)
1411 udelay
1412 Simple two microseconds delay
1413 none
1414 No delay
1416 ip= [IP_PNP]
1417 See Documentation/filesystems/nfs/nfsroot.txt.
1419 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1420 See comment before ip2_setup() in
1421 drivers/char/ip2/ip2base.c.
1423 irqfixup [HW]
1424 When an interrupt is not handled search all handlers
1425 for it. Intended to get systems with badly broken
1426 firmware running.
1428 irqpoll [HW]
1429 When an interrupt is not handled search all handlers
1430 for it. Also check all handlers each timer
1431 interrupt. Intended to get systems with badly broken
1432 firmware running.
1434 isapnp= [ISAPNP]
1435 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1437 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1438 Format:
1439 <cpu number>,...,<cpu number>
1440 or
1441 <cpu number>-<cpu number>
1442 (must be a positive range in ascending order)
1443 or a mixture
1444 <cpu number>,...,<cpu number>-<cpu number>
1446 This option can be used to specify one or more CPUs
1447 to isolate from the general SMP balancing and scheduling
1448 algorithms. You can move a process onto or off an
1449 "isolated" CPU via the CPU affinity syscalls or cpuset.
1450 <cpu number> begins at 0 and the maximum value is
1451 "number of CPUs in system - 1".
1453 This option is the preferred way to isolate CPUs. The
1454 alternative -- manually setting the CPU mask of all
1455 tasks in the system -- can cause problems and
1456 suboptimal load balancer performance.
1458 iucv= [HW,NET]
1460 ivrs_ioapic [HW,X86_64]
1461 Provide an override to the IOAPIC-ID<->DEVICE-ID
1462 mapping provided in the IVRS ACPI table. For
1463 example, to map IOAPIC-ID decimal 10 to
1464 PCI device 00:14.0 write the parameter as:
1465 ivrs_ioapic[10]=00:14.0
1467 ivrs_hpet [HW,X86_64]
1468 Provide an override to the HPET-ID<->DEVICE-ID
1469 mapping provided in the IVRS ACPI table. For
1470 example, to map HPET-ID decimal 0 to
1471 PCI device 00:14.0 write the parameter as:
1472 ivrs_hpet[0]=00:14.0
1474 js= [HW,JOY] Analog joystick
1475 See Documentation/input/joystick.txt.
1477 kaslr/nokaslr [X86]
1478 Enable/disable kernel and module base offset ASLR
1479 (Address Space Layout Randomization) if built into
1480 the kernel. When CONFIG_HIBERNATION is selected,
1481 kASLR is disabled by default. When kASLR is enabled,
1482 hibernation will be disabled.
1484 keepinitrd [HW,ARM]
1486 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1487 specifies the amount of memory usable by the kernel
1488 for non-movable allocations. The requested amount is
1489 spread evenly throughout all nodes in the system. The
1490 remaining memory in each node is used for Movable
1491 pages. In the event, a node is too small to have both
1492 kernelcore and Movable pages, kernelcore pages will
1493 take priority and other nodes will have a larger number
1494 of Movable pages. The Movable zone is used for the
1495 allocation of pages that may be reclaimed or moved
1496 by the page migration subsystem. This means that
1497 HugeTLB pages may not be allocated from this zone.
1498 Note that allocations like PTEs-from-HighMem still
1499 use the HighMem zone if it exists, and the Normal
1500 zone if it does not.
1502 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1503 Format: <Controller#>[,poll interval]
1504 The controller # is the number of the ehci usb debug
1505 port as it is probed via PCI. The poll interval is
1506 optional and is the number seconds in between
1507 each poll cycle to the debug port in case you need
1508 the functionality for interrupting the kernel with
1509 gdb or control-c on the dbgp connection. When
1510 not using this parameter you use sysrq-g to break into
1511 the kernel debugger.
1513 kgdboc= [KGDB,HW] kgdb over consoles.
1514 Requires a tty driver that supports console polling,
1515 or a supported polling keyboard driver (non-usb).
1516 Serial only format: <serial_device>[,baud]
1517 keyboard only format: kbd
1518 keyboard and serial format: kbd,<serial_device>[,baud]
1519 Optional Kernel mode setting:
1520 kms, kbd format: kms,kbd
1521 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1523 kgdbwait [KGDB] Stop kernel execution and enter the
1524 kernel debugger at the earliest opportunity.
1526 kmac= [MIPS] korina ethernet MAC address.
1527 Configure the RouterBoard 532 series on-chip
1528 Ethernet adapter MAC address.
1530 kmemleak= [KNL] Boot-time kmemleak enable/disable
1531 Valid arguments: on, off
1532 Default: on
1534 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1535 Valid arguments: 0, 1, 2
1536 kmemcheck=0 (disabled)
1537 kmemcheck=1 (enabled)
1538 kmemcheck=2 (one-shot mode)
1539 Default: 2 (one-shot mode)
1541 kstack=N [X86] Print N words from the kernel stack
1542 in oops dumps.
1544 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1545 Default is 0 (don't ignore, but inject #GP)
1547 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1548 KVM MMU at runtime.
1549 Default is 0 (off)
1551 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1552 Default is 1 (enabled)
1554 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1555 for all guests.
1556 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1558 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1559 (virtualized MMU) support on capable Intel chips.
1560 Default is 1 (enabled)
1562 kvm-intel.emulate_invalid_guest_state=
1563 [KVM,Intel] Enable emulation of invalid guest states
1564 Default is 0 (disabled)
1566 kvm-intel.flexpriority=
1567 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1568 Default is 1 (enabled)
1570 kvm-intel.nested=
1571 [KVM,Intel] Enable VMX nesting (nVMX).
1572 Default is 0 (disabled)
1574 kvm-intel.unrestricted_guest=
1575 [KVM,Intel] Disable unrestricted guest feature
1576 (virtualized real and unpaged mode) on capable
1577 Intel chips. Default is 1 (enabled)
1579 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1580 feature (tagged TLBs) on capable Intel chips.
1581 Default is 1 (enabled)
1583 l2cr= [PPC]
1585 l3cr= [PPC]
1587 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1588 disabled it.
1590 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1591 value for LAPIC timer one-shot implementation. Default
1592 back to the programmable timer unit in the LAPIC.
1594 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1595 in C2 power state.
1597 libata.dma= [LIBATA] DMA control
1598 libata.dma=0 Disable all PATA and SATA DMA
1599 libata.dma=1 PATA and SATA Disk DMA only
1600 libata.dma=2 ATAPI (CDROM) DMA only
1601 libata.dma=4 Compact Flash DMA only
1602 Combinations also work, so libata.dma=3 enables DMA
1603 for disks and CDROMs, but not CFs.
1605 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1606 libata.ignore_hpa=0 keep BIOS limits (default)
1607 libata.ignore_hpa=1 ignore limits, using full disk
1609 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1610 when set.
1611 Format: <int>
1613 libata.force= [LIBATA] Force configurations. The format is comma
1614 separated list of "[ID:]VAL" where ID is
1615 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1616 matching port, link or device. Basically, it matches
1617 the ATA ID string printed on console by libata. If
1618 the whole ID part is omitted, the last PORT and DEVICE
1619 values are used. If ID hasn't been specified yet, the
1620 configuration applies to all ports, links and devices.
1622 If only DEVICE is omitted, the parameter applies to
1623 the port and all links and devices behind it. DEVICE
1624 number of 0 either selects the first device or the
1625 first fan-out link behind PMP device. It does not
1626 select the host link. DEVICE number of 15 selects the
1627 host link and device attached to it.
1629 The VAL specifies the configuration to force. As long
1630 as there's no ambiguity shortcut notation is allowed.
1631 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1632 The following configurations can be forced.
1634 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1635 Any ID with matching PORT is used.
1637 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1639 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1640 udma[/][16,25,33,44,66,100,133] notation is also
1641 allowed.
1643 * [no]ncq: Turn on or off NCQ.
1645 * nohrst, nosrst, norst: suppress hard, soft
1646 and both resets.
1648 * rstonce: only attempt one reset during
1649 hot-unplug link recovery
1651 * dump_id: dump IDENTIFY data.
1653 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1655 * disable: Disable this device.
1657 If there are multiple matching configurations changing
1658 the same attribute, the last one is used.
1660 memblock=debug [KNL] Enable memblock debug messages.
1662 load_ramdisk= [RAM] List of ramdisks to load from floppy
1663 See Documentation/blockdev/ramdisk.txt.
1665 lockd.nlm_grace_period=P [NFS] Assign grace period.
1666 Format: <integer>
1668 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1669 Format: <integer>
1671 lockd.nlm_timeout=T [NFS] Assign timeout value.
1672 Format: <integer>
1674 lockd.nlm_udpport=M [NFS] Assign UDP port.
1675 Format: <integer>
1677 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1678 Format: <irq>
1680 loglevel= All Kernel Messages with a loglevel smaller than the
1681 console loglevel will be printed to the console. It can
1682 also be changed with klogd or other programs. The
1683 loglevels are defined as follows:
1685 0 (KERN_EMERG) system is unusable
1686 1 (KERN_ALERT) action must be taken immediately
1687 2 (KERN_CRIT) critical conditions
1688 3 (KERN_ERR) error conditions
1689 4 (KERN_WARNING) warning conditions
1690 5 (KERN_NOTICE) normal but significant condition
1691 6 (KERN_INFO) informational
1692 7 (KERN_DEBUG) debug-level messages
1694 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1695 in bytes. n must be a power of two. The default
1696 size is set in the kernel config file.
1698 logo.nologo [FB] Disables display of the built-in Linux logo.
1699 This may be used to provide more screen space for
1700 kernel log messages and is useful when debugging
1701 kernel boot problems.
1703 lp=0 [LP] Specify parallel ports to use, e.g,
1704 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1705 lp=reset first parallel port). 'lp=0' disables the
1706 lp=auto printer driver. 'lp=reset' (which can be
1707 specified in addition to the ports) causes
1708 attached printers to be reset. Using
1709 lp=port1,port2,... specifies the parallel ports
1710 to associate lp devices with, starting with
1711 lp0. A port specification may be 'none' to skip
1712 that lp device, or a parport name such as
1713 'parport0'. Specifying 'lp=auto' instead of a
1714 port specification list means that device IDs
1715 from each port should be examined, to see if
1716 an IEEE 1284-compliant printer is attached; if
1717 so, the driver will manage that printer.
1718 See also header of drivers/char/lp.c.
1720 lpj=n [KNL]
1721 Sets loops_per_jiffy to given constant, thus avoiding
1722 time-consuming boot-time autodetection (up to 250 ms per
1723 CPU). 0 enables autodetection (default). To determine
1724 the correct value for your kernel, boot with normal
1725 autodetection and see what value is printed. Note that
1726 on SMP systems the preset will be applied to all CPUs,
1727 which is likely to cause problems if your CPUs need
1728 significantly divergent settings. An incorrect value
1729 will cause delays in the kernel to be wrong, leading to
1730 unpredictable I/O errors and other breakage. Although
1731 unlikely, in the extreme case this might damage your
1732 hardware.
1734 ltpc= [NET]
1735 Format: <io>,<irq>,<dma>
1737 machvec= [IA-64] Force the use of a particular machine-vector
1738 (machvec) in a generic kernel.
1739 Example: machvec=hpzx1_swiotlb
1741 machtype= [Loongson] Share the same kernel image file between different
1742 yeeloong laptop.
1743 Example: machtype=lemote-yeeloong-2f-7inch
1745 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1746 than or equal to this physical address is ignored.
1748 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1749 should make use of. maxcpus=n : n >= 0 limits the
1750 kernel to using 'n' processors. n=0 is a special case,
1751 it is equivalent to "nosmp", which also disables
1752 the IO APIC.
1754 max_loop= [LOOP] The number of loop block devices that get
1755 (loop.max_loop) unconditionally pre-created at init time. The default
1756 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1757 of statically allocating a predefined number, loop
1758 devices can be requested on-demand with the
1759 /dev/loop-control interface.
1761 mce [X86-32] Machine Check Exception
1763 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1765 md= [HW] RAID subsystems devices and level
1766 See Documentation/md.txt.
1768 mdacon= [MDA]
1769 Format: <first>,<last>
1770 Specifies range of consoles to be captured by the MDA.
1772 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1773 Amount of memory to be used when the kernel is not able
1774 to see the whole system memory or for test.
1775 [X86] Work as limiting max address. Use together
1776 with memmap= to avoid physical address space collisions.
1777 Without memmap= PCI devices could be placed at addresses
1778 belonging to unused RAM.
1780 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1781 memory.
1783 memchunk=nn[KMG]
1784 [KNL,SH] Allow user to override the default size for
1785 per-device physically contiguous DMA buffers.
1787 memmap=exactmap [KNL,X86] Enable setting of an exact
1788 E820 memory map, as specified by the user.
1789 Such memmap=exactmap lines can be constructed based on
1790 BIOS output or other requirements. See the memmap=nn@ss
1791 option description.
1793 memmap=nn[KMG]@ss[KMG]
1794 [KNL] Force usage of a specific region of memory.
1795 Region of memory to be used is from ss to ss+nn.
1797 memmap=nn[KMG]#ss[KMG]
1798 [KNL,ACPI] Mark specific memory as ACPI data.
1799 Region of memory to be marked is from ss to ss+nn.
1801 memmap=nn[KMG]$ss[KMG]
1802 [KNL,ACPI] Mark specific memory as reserved.
1803 Region of memory to be reserved is from ss to ss+nn.
1804 Example: Exclude memory from 0x18690000-0x1869ffff
1805 memmap=64K$0x18690000
1806 or
1807 memmap=0x10000$0x18690000
1809 memory_corruption_check=0/1 [X86]
1810 Some BIOSes seem to corrupt the first 64k of
1811 memory when doing things like suspend/resume.
1812 Setting this option will scan the memory
1813 looking for corruption. Enabling this will
1814 both detect corruption and prevent the kernel
1815 from using the memory being corrupted.
1816 However, its intended as a diagnostic tool; if
1817 repeatable BIOS-originated corruption always
1818 affects the same memory, you can use memmap=
1819 to prevent the kernel from using that memory.
1821 memory_corruption_check_size=size [X86]
1822 By default it checks for corruption in the low
1823 64k, making this memory unavailable for normal
1824 use. Use this parameter to scan for
1825 corruption in more or less memory.
1827 memory_corruption_check_period=seconds [X86]
1828 By default it checks for corruption every 60
1829 seconds. Use this parameter to check at some
1830 other rate. 0 disables periodic checking.
1832 memtest= [KNL,X86] Enable memtest
1833 Format: <integer>
1834 default : 0 <disable>
1835 Specifies the number of memtest passes to be
1836 performed. Each pass selects another test
1837 pattern from a given set of patterns. Memtest
1838 fills the memory with this pattern, validates
1839 memory contents and reserves bad memory
1840 regions that are detected.
1842 meye.*= [HW] Set MotionEye Camera parameters
1843 See Documentation/video4linux/meye.txt.
1845 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1846 Multi-Function General Purpose Timers on AMD Geode
1847 platforms.
1849 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1850 the BIOS has incorrectly applied a workaround. TinyBIOS
1851 version 0.98 is known to be affected, 0.99 fixes the
1852 problem by letting the user disable the workaround.
1854 mga= [HW,DRM]
1856 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1857 physical address is ignored.
1859 mini2440= [ARM,HW,KNL]
1860 Format:[0..2][b][c][t]
1861 Default: "0tb"
1862 MINI2440 configuration specification:
1863 0 - The attached screen is the 3.5" TFT
1864 1 - The attached screen is the 7" TFT
1865 2 - The VGA Shield is attached (1024x768)
1866 Leaving out the screen size parameter will not load
1867 the TFT driver, and the framebuffer will be left
1868 unconfigured.
1869 b - Enable backlight. The TFT backlight pin will be
1870 linked to the kernel VESA blanking code and a GPIO
1871 LED. This parameter is not necessary when using the
1872 VGA shield.
1873 c - Enable the s3c camera interface.
1874 t - Reserved for enabling touchscreen support. The
1875 touchscreen support is not enabled in the mainstream
1876 kernel as of 2.6.30, a preliminary port can be found
1877 in the "bleeding edge" mini2440 support kernel at
1878 http://repo.or.cz/w/linux-2.6/mini2440.git
1880 mminit_loglevel=
1881 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1882 parameter allows control of the logging verbosity for
1883 the additional memory initialisation checks. A value
1884 of 0 disables mminit logging and a level of 4 will
1885 log everything. Information is printed at KERN_DEBUG
1886 so loglevel=8 may also need to be specified.
1888 module.sig_enforce
1889 [KNL] When CONFIG_MODULE_SIG is set, this means that
1890 modules without (valid) signatures will fail to load.
1891 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1892 is always true, so this option does nothing.
1894 mousedev.tap_time=
1895 [MOUSE] Maximum time between finger touching and
1896 leaving touchpad surface for touch to be considered
1897 a tap and be reported as a left button click (for
1898 touchpads working in absolute mode only).
1899 Format: <msecs>
1900 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1901 reporting absolute coordinates, such as tablets
1902 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1903 reporting absolute coordinates, such as tablets
1905 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1906 is similar to kernelcore except it specifies the
1907 amount of memory used for migratable allocations.
1908 If both kernelcore and movablecore is specified,
1909 then kernelcore will be at *least* the specified
1910 value but may be more. If movablecore on its own
1911 is specified, the administrator must be careful
1912 that the amount of memory usable for all allocations
1913 is not too small.
1915 movable_node [KNL,X86] Boot-time switch to enable the effects
1916 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
1918 MTD_Partition= [MTD]
1919 Format: <name>,<region-number>,<size>,<offset>
1921 MTD_Region= [MTD] Format:
1922 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1924 mtdparts= [MTD]
1925 See drivers/mtd/cmdlinepart.c.
1927 multitce=off [PPC] This parameter disables the use of the pSeries
1928 firmware feature for updating multiple TCE entries
1929 at a time.
1931 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1933 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1935 boundary - index of last SLC block on Flex-OneNAND.
1936 The remaining blocks are configured as MLC blocks.
1937 lock - Configure if Flex-OneNAND boundary should be locked.
1938 Once locked, the boundary cannot be changed.
1939 1 indicates lock status, 0 indicates unlock status.
1941 mtdset= [ARM]
1942 ARM/S3C2412 JIVE boot control
1944 See arch/arm/mach-s3c2412/mach-jive.c
1946 mtouchusb.raw_coordinates=
1947 [HW] Make the MicroTouch USB driver use raw coordinates
1948 ('y', default) or cooked coordinates ('n')
1950 mtrr_chunk_size=nn[KMG] [X86]
1951 used for mtrr cleanup. It is largest continuous chunk
1952 that could hold holes aka. UC entries.
1954 mtrr_gran_size=nn[KMG] [X86]
1955 Used for mtrr cleanup. It is granularity of mtrr block.
1956 Default is 1.
1957 Large value could prevent small alignment from
1958 using up MTRRs.
1960 mtrr_spare_reg_nr=n [X86]
1961 Format: <integer>
1962 Range: 0,7 : spare reg number
1963 Default : 1
1964 Used for mtrr cleanup. It is spare mtrr entries number.
1965 Set to 2 or more if your graphical card needs more.
1967 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1969 netdev= [NET] Network devices parameters
1970 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1971 Note that mem_start is often overloaded to mean
1972 something different and driver-specific.
1973 This usage is only documented in each driver source
1974 file if at all.
1976 nf_conntrack.acct=
1977 [NETFILTER] Enable connection tracking flow accounting
1978 0 to disable accounting
1979 1 to enable accounting
1980 Default value is 0.
1982 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1983 See Documentation/filesystems/nfs/nfsroot.txt.
1985 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1986 See Documentation/filesystems/nfs/nfsroot.txt.
1988 nfsrootdebug [NFS] enable nfsroot debugging messages.
1989 See Documentation/filesystems/nfs/nfsroot.txt.
1991 nfs.callback_tcpport=
1992 [NFS] set the TCP port on which the NFSv4 callback
1993 channel should listen.
1995 nfs.cache_getent=
1996 [NFS] sets the pathname to the program which is used
1997 to update the NFS client cache entries.
1999 nfs.cache_getent_timeout=
2000 [NFS] sets the timeout after which an attempt to
2001 update a cache entry is deemed to have failed.
2003 nfs.idmap_cache_timeout=
2004 [NFS] set the maximum lifetime for idmapper cache
2005 entries.
2007 nfs.enable_ino64=
2008 [NFS] enable 64-bit inode numbers.
2009 If zero, the NFS client will fake up a 32-bit inode
2010 number for the readdir() and stat() syscalls instead
2011 of returning the full 64-bit number.
2012 The default is to return 64-bit inode numbers.
2014 nfs.max_session_slots=
2015 [NFSv4.1] Sets the maximum number of session slots
2016 the client will attempt to negotiate with the server.
2017 This limits the number of simultaneous RPC requests
2018 that the client can send to the NFSv4.1 server.
2019 Note that there is little point in setting this
2020 value higher than the max_tcp_slot_table_limit.
2022 nfs.nfs4_disable_idmapping=
2023 [NFSv4] When set to the default of '1', this option
2024 ensures that both the RPC level authentication
2025 scheme and the NFS level operations agree to use
2026 numeric uids/gids if the mount is using the
2027 'sec=sys' security flavour. In effect it is
2028 disabling idmapping, which can make migration from
2029 legacy NFSv2/v3 systems to NFSv4 easier.
2030 Servers that do not support this mode of operation
2031 will be autodetected by the client, and it will fall
2032 back to using the idmapper.
2033 To turn off this behaviour, set the value to '0'.
2034 nfs.nfs4_unique_id=
2035 [NFS4] Specify an additional fixed unique ident-
2036 ification string that NFSv4 clients can insert into
2037 their nfs_client_id4 string. This is typically a
2038 UUID that is generated at system install time.
2040 nfs.send_implementation_id =
2041 [NFSv4.1] Send client implementation identification
2042 information in exchange_id requests.
2043 If zero, no implementation identification information
2044 will be sent.
2045 The default is to send the implementation identification
2046 information.
2048 nfs.recover_lost_locks =
2049 [NFSv4] Attempt to recover locks that were lost due
2050 to a lease timeout on the server. Please note that
2051 doing this risks data corruption, since there are
2052 no guarantees that the file will remain unchanged
2053 after the locks are lost.
2054 If you want to enable the kernel legacy behaviour of
2055 attempting to recover these locks, then set this
2056 parameter to '1'.
2057 The default parameter value of '0' causes the kernel
2058 not to attempt recovery of lost locks.
2060 nfsd.nfs4_disable_idmapping=
2061 [NFSv4] When set to the default of '1', the NFSv4
2062 server will return only numeric uids and gids to
2063 clients using auth_sys, and will accept numeric uids
2064 and gids from such clients. This is intended to ease
2065 migration from NFSv2/v3.
2067 objlayoutdriver.osd_login_prog=
2068 [NFS] [OBJLAYOUT] sets the pathname to the program which
2069 is used to automatically discover and login into new
2070 osd-targets. Please see:
2071 Documentation/filesystems/pnfs.txt for more explanations
2073 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2074 when a NMI is triggered.
2075 Format: [state][,regs][,debounce][,die]
2077 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2078 Format: [panic,][nopanic,][num]
2079 Valid num: 0
2080 0 - turn nmi_watchdog off
2081 When panic is specified, panic when an NMI watchdog
2082 timeout occurs (or 'nopanic' to override the opposite
2083 default).
2084 This is useful when you use a panic=... timeout and
2085 need the box quickly up again.
2087 netpoll.carrier_timeout=
2088 [NET] Specifies amount of time (in seconds) that
2089 netpoll should wait for a carrier. By default netpoll
2090 waits 4 seconds.
2092 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2093 emulation library even if a 387 maths coprocessor
2094 is present.
2096 no_console_suspend
2097 [HW] Never suspend the console
2098 Disable suspending of consoles during suspend and
2099 hibernate operations. Once disabled, debugging
2100 messages can reach various consoles while the rest
2101 of the system is being put to sleep (ie, while
2102 debugging driver suspend/resume hooks). This may
2103 not work reliably with all consoles, but is known
2104 to work with serial and VGA consoles.
2105 To facilitate more flexible debugging, we also add
2106 console_suspend, a printk module parameter to control
2107 it. Users could use console_suspend (usually
2108 /sys/module/printk/parameters/console_suspend) to
2109 turn on/off it dynamically.
2111 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2112 caches in the slab allocator. Saves per-node memory,
2113 but will impact performance.
2115 noalign [KNL,ARM]
2117 noapic [SMP,APIC] Tells the kernel to not make use of any
2118 IOAPICs that may be present in the system.
2120 noautogroup Disable scheduler automatic task group creation.
2122 nobats [PPC] Do not use BATs for mapping kernel lowmem
2123 on "Classic" PPC cores.
2125 nocache [ARM]
2127 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2129 nodelayacct [KNL] Disable per-task delay accounting
2131 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2133 nodsp [SH] Disable hardware DSP at boot time.
2135 noefi [X86] Disable EFI runtime services support.
2137 noexec [IA-64]
2139 noexec [X86]
2140 On X86-32 available only on PAE configured kernels.
2141 noexec=on: enable non-executable mappings (default)
2142 noexec=off: disable non-executable mappings
2144 nosmap [X86]
2145 Disable SMAP (Supervisor Mode Access Prevention)
2146 even if it is supported by processor.
2148 nosmep [X86]
2149 Disable SMEP (Supervisor Mode Execution Prevention)
2150 even if it is supported by processor.
2152 noexec32 [X86-64]
2153 This affects only 32-bit executables.
2154 noexec32=on: enable non-executable mappings (default)
2155 read doesn't imply executable mappings
2156 noexec32=off: disable non-executable mappings
2157 read implies executable mappings
2159 nofpu [SH] Disable hardware FPU at boot time.
2161 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2162 register save and restore. The kernel will only save
2163 legacy floating-point registers on task switch.
2165 noxsave [BUGS=X86] Disables x86 extended register state save
2166 and restore using xsave. The kernel will fallback to
2167 enabling legacy floating-point and sse state.
2169 eagerfpu= [X86]
2170 on enable eager fpu restore
2171 off disable eager fpu restore
2172 auto selects the default scheme, which automatically
2173 enables eagerfpu restore for xsaveopt.
2175 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2176 wfi(ARM) instruction doesn't work correctly and not to
2177 use it. This is also useful when using JTAG debugger.
2179 no_file_caps Tells the kernel not to honor file capabilities. The
2180 only way then for a file to be executed with privilege
2181 is to be setuid root or executed by root.
2183 nohalt [IA-64] Tells the kernel not to use the power saving
2184 function PAL_HALT_LIGHT when idle. This increases
2185 power-consumption. On the positive side, it reduces
2186 interrupt wake-up latency, which may improve performance
2187 in certain environments such as networked servers or
2188 real-time systems.
2190 nohibernate [HIBERNATION] Disable hibernation and resume.
2192 nohz= [KNL] Boottime enable/disable dynamic ticks
2193 Valid arguments: on, off
2194 Default: on
2196 nohz_full= [KNL,BOOT]
2197 In kernels built with CONFIG_NO_HZ_FULL=y, set
2198 the specified list of CPUs whose tick will be stopped
2199 whenever possible. The boot CPU will be forced outside
2200 the range to maintain the timekeeping.
2201 The CPUs in this range must also be included in the
2202 rcu_nocbs= set.
2204 noiotrap [SH] Disables trapped I/O port accesses.
2206 noirqdebug [X86-32] Disables the code which attempts to detect and
2207 disable unhandled interrupt sources.
2209 no_timer_check [X86,APIC] Disables the code which tests for
2210 broken timer IRQ sources.
2212 noisapnp [ISAPNP] Disables ISA PnP code.
2214 noinitrd [RAM] Tells the kernel not to load any configured
2215 initial RAM disk.
2217 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2218 remapping.
2219 [Deprecated - use intremap=off]
2221 nointroute [IA-64]
2223 nojitter [IA-64] Disables jitter checking for ITC timers.
2225 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2227 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2228 fault handling.
2230 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2231 steal time is computed, but won't influence scheduler
2232 behaviour
2234 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2236 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2238 noltlbs [PPC] Do not use large page/tlb entries for kernel
2239 lowmem mapping on PPC40x.
2241 nomca [IA-64] Disable machine check abort handling
2243 nomce [X86-32] Machine Check Exception
2245 nomfgpt [X86-32] Disable Multi-Function General Purpose
2246 Timer usage (for AMD Geode machines).
2248 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2249 shutdown the other cpus. Instead use the REBOOT_VECTOR
2250 irq.
2252 nomodule Disable module load
2254 nopat [X86] Disable PAT (page attribute table extension of
2255 pagetables) support.
2257 norandmaps Don't use address space randomization. Equivalent to
2258 echo 0 > /proc/sys/kernel/randomize_va_space
2260 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2262 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2263 with UP alternatives
2265 nordrand [X86] Disable kernel use of the RDRAND and
2266 RDSEED instructions even if they are supported
2267 by the processor. RDRAND and RDSEED are still
2268 available to user space applications.
2270 noresume [SWSUSP] Disables resume and restores original swap
2271 space.
2273 no-scroll [VGA] Disables scrollback.
2274 This is required for the Braillex ib80-piezo Braille
2275 reader made by F.H. Papenmeier (Germany).
2277 nosbagart [IA-64]
2279 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2281 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2282 and disable the IO APIC. legacy for "maxcpus=0".
2284 nosoftlockup [KNL] Disable the soft-lockup detector.
2286 nosync [HW,M68K] Disables sync negotiation for all devices.
2288 notsc [BUGS=X86-32] Disable Time Stamp Counter
2290 nousb [USB] Disable the USB subsystem
2292 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2294 nowb [ARM]
2296 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2298 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2299 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2300 Some features depend on CPU0. Known dependencies are:
2301 1. Resume from suspend/hibernate depends on CPU0.
2302 Suspend/hibernate will fail if CPU0 is offline and you
2303 need to online CPU0 before suspend/hibernate.
2304 2. PIC interrupts also depend on CPU0. CPU0 can't be
2305 removed if a PIC interrupt is detected.
2306 It's said poweroff/reboot may depend on CPU0 on some
2307 machines although I haven't seen such issues so far
2308 after CPU0 is offline on a few tested machines.
2309 If the dependencies are under your control, you can
2310 turn on cpu0_hotplug.
2312 nptcg= [IA-64] Override max number of concurrent global TLB
2313 purges which is reported from either PAL_VM_SUMMARY or
2314 SAL PALO.
2316 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2317 could support. nr_cpus=n : n >= 1 limits the kernel to
2318 supporting 'n' processors. Later in runtime you can not
2319 use hotplug cpu feature to put more cpu back to online.
2320 just like you compile the kernel NR_CPUS=n
2322 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2324 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2325 Allowed values are enable and disable
2327 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2328 one of ['zone', 'node', 'default'] can be specified
2329 This can be set from sysctl after boot.
2330 See Documentation/sysctl/vm.txt for details.
2332 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2333 See Documentation/debugging-via-ohci1394.txt for more
2334 info.
2336 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2337 Rather than timing out after 20 ms if an EC
2338 command is not properly ACKed, override the length
2339 of the timeout. We have interrupts disabled while
2340 waiting for the ACK, so if this is set too high
2341 interrupts *may* be lost!
2343 omap_mux= [OMAP] Override bootloader pin multiplexing.
2344 Format: <mux_mode0.mode_name=value>...
2345 For example, to override I2C bus2:
2346 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2348 oprofile.timer= [HW]
2349 Use timer interrupt instead of performance counters
2351 oprofile.cpu_type= Force an oprofile cpu type
2352 This might be useful if you have an older oprofile
2353 userland or if you want common events.
2354 Format: { arch_perfmon }
2355 arch_perfmon: [X86] Force use of architectural
2356 perfmon on Intel CPUs instead of the
2357 CPU specific event set.
2358 timer: [X86] Force use of architectural NMI
2359 timer mode (see also oprofile.timer
2360 for generic hr timer mode)
2361 [s390] Force legacy basic mode sampling
2362 (report cpu_type "timer")
2364 oops=panic Always panic on oopses. Default is to just kill the
2365 process, but there is a small probability of
2366 deadlocking the machine.
2367 This will also cause panics on machine check exceptions.
2368 Useful together with panic=30 to trigger a reboot.
2370 OSS [HW,OSS]
2371 See Documentation/sound/oss/oss-parameters.txt
2373 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2374 timeout > 0: seconds before rebooting
2375 timeout = 0: wait forever
2376 timeout < 0: reboot immediately
2377 Format: <timeout>
2379 crash_kexec_post_notifiers
2380 Run kdump after running panic-notifiers and dumping
2381 kmsg. This only for the users who doubt kdump always
2382 succeeds in any situation.
2383 Note that this also increases risks of kdump failure,
2384 because some panic notifiers can make the crashed
2385 kernel more unstable.
2387 parkbd.port= [HW] Parallel port number the keyboard adapter is
2388 connected to, default is 0.
2389 Format: <parport#>
2390 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2391 0 for XT, 1 for AT (default is AT).
2392 Format: <mode>
2394 parport= [HW,PPT] Specify parallel ports. 0 disables.
2395 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2396 Use 'auto' to force the driver to use any
2397 IRQ/DMA settings detected (the default is to
2398 ignore detected IRQ/DMA settings because of
2399 possible conflicts). You can specify the base
2400 address, IRQ, and DMA settings; IRQ and DMA
2401 should be numbers, or 'auto' (for using detected
2402 settings on that particular port), or 'nofifo'
2403 (to avoid using a FIFO even if it is detected).
2404 Parallel ports are assigned in the order they
2405 are specified on the command line, starting
2406 with parport0.
2408 parport_init_mode= [HW,PPT]
2409 Configure VIA parallel port to operate in
2410 a specific mode. This is necessary on Pegasos
2411 computer where firmware has no options for setting
2412 up parallel port mode and sets it to spp.
2413 Currently this function knows 686a and 8231 chips.
2414 Format: [spp|ps2|epp|ecp|ecpepp]
2416 pause_on_oops=
2417 Halt all CPUs after the first oops has been printed for
2418 the specified number of seconds. This is to be used if
2419 your oopses keep scrolling off the screen.
2421 pcbit= [HW,ISDN]
2423 pcd. [PARIDE]
2424 See header of drivers/block/paride/pcd.c.
2425 See also Documentation/blockdev/paride.txt.
2427 pci=option[,option...] [PCI] various PCI subsystem options:
2428 earlydump [X86] dump PCI config space before the kernel
2429 changes anything
2430 off [X86] don't probe for the PCI bus
2431 bios [X86-32] force use of PCI BIOS, don't access
2432 the hardware directly. Use this if your machine
2433 has a non-standard PCI host bridge.
2434 nobios [X86-32] disallow use of PCI BIOS, only direct
2435 hardware access methods are allowed. Use this
2436 if you experience crashes upon bootup and you
2437 suspect they are caused by the BIOS.
2438 conf1 [X86] Force use of PCI Configuration
2439 Mechanism 1.
2440 conf2 [X86] Force use of PCI Configuration
2441 Mechanism 2.
2442 noaer [PCIE] If the PCIEAER kernel config parameter is
2443 enabled, this kernel boot option can be used to
2444 disable the use of PCIE advanced error reporting.
2445 nodomains [PCI] Disable support for multiple PCI
2446 root domains (aka PCI segments, in ACPI-speak).
2447 nommconf [X86] Disable use of MMCONFIG for PCI
2448 Configuration
2449 check_enable_amd_mmconf [X86] check for and enable
2450 properly configured MMIO access to PCI
2451 config space on AMD family 10h CPU
2452 nomsi [MSI] If the PCI_MSI kernel config parameter is
2453 enabled, this kernel boot option can be used to
2454 disable the use of MSI interrupts system-wide.
2455 noioapicquirk [APIC] Disable all boot interrupt quirks.
2456 Safety option to keep boot IRQs enabled. This
2457 should never be necessary.
2458 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2459 primary IO-APIC for bridges that cannot disable
2460 boot IRQs. This fixes a source of spurious IRQs
2461 when the system masks IRQs.
2462 noioapicreroute [APIC] Disable workaround that uses the
2463 boot IRQ equivalent of an IRQ that connects to
2464 a chipset where boot IRQs cannot be disabled.
2465 The opposite of ioapicreroute.
2466 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2467 routing table. These calls are known to be buggy
2468 on several machines and they hang the machine
2469 when used, but on other computers it's the only
2470 way to get the interrupt routing table. Try
2471 this option if the kernel is unable to allocate
2472 IRQs or discover secondary PCI buses on your
2473 motherboard.
2474 rom [X86] Assign address space to expansion ROMs.
2475 Use with caution as certain devices share
2476 address decoders between ROMs and other
2477 resources.
2478 norom [X86] Do not assign address space to
2479 expansion ROMs that do not already have
2480 BIOS assigned address ranges.
2481 nobar [X86] Do not assign address space to the
2482 BARs that weren't assigned by the BIOS.
2483 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2484 assigned automatically to PCI devices. You can
2485 make the kernel exclude IRQs of your ISA cards
2486 this way.
2487 pirqaddr=0xAAAAA [X86] Specify the physical address
2488 of the PIRQ table (normally generated
2489 by the BIOS) if it is outside the
2490 F0000h-100000h range.
2491 lastbus=N [X86] Scan all buses thru bus #N. Can be
2492 useful if the kernel is unable to find your
2493 secondary buses and you want to tell it
2494 explicitly which ones they are.
2495 assign-busses [X86] Always assign all PCI bus
2496 numbers ourselves, overriding
2497 whatever the firmware may have done.
2498 usepirqmask [X86] Honor the possible IRQ mask stored
2499 in the BIOS $PIR table. This is needed on
2500 some systems with broken BIOSes, notably
2501 some HP Pavilion N5400 and Omnibook XE3
2502 notebooks. This will have no effect if ACPI
2503 IRQ routing is enabled.
2504 noacpi [X86] Do not use ACPI for IRQ routing
2505 or for PCI scanning.
2506 use_crs [X86] Use PCI host bridge window information
2507 from ACPI. On BIOSes from 2008 or later, this
2508 is enabled by default. If you need to use this,
2509 please report a bug.
2510 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2511 If you need to use this, please report a bug.
2512 routeirq Do IRQ routing for all PCI devices.
2513 This is normally done in pci_enable_device(),
2514 so this option is a temporary workaround
2515 for broken drivers that don't call it.
2516 skip_isa_align [X86] do not align io start addr, so can
2517 handle more pci cards
2518 firmware [ARM] Do not re-enumerate the bus but instead
2519 just use the configuration from the
2520 bootloader. This is currently used on
2521 IXP2000 systems where the bus has to be
2522 configured a certain way for adjunct CPUs.
2523 noearly [X86] Don't do any early type 1 scanning.
2524 This might help on some broken boards which
2525 machine check when some devices' config space
2526 is read. But various workarounds are disabled
2527 and some IOMMU drivers will not work.
2528 bfsort Sort PCI devices into breadth-first order.
2529 This sorting is done to get a device
2530 order compatible with older (<= 2.4) kernels.
2531 nobfsort Don't sort PCI devices into breadth-first order.
2532 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2533 tuning and use the BIOS-configured MPS defaults.
2534 pcie_bus_safe Set every device's MPS to the largest value
2535 supported by all devices below the root complex.
2536 pcie_bus_perf Set device MPS to the largest allowable MPS
2537 based on its parent bus. Also set MRRS (Max
2538 Read Request Size) to the largest supported
2539 value (no larger than the MPS that the device
2540 or bus can support) for best performance.
2541 pcie_bus_peer2peer Set every device's MPS to 128B, which
2542 every device is guaranteed to support. This
2543 configuration allows peer-to-peer DMA between
2544 any pair of devices, possibly at the cost of
2545 reduced performance. This also guarantees
2546 that hot-added devices will work.
2547 cbiosize=nn[KMG] The fixed amount of bus space which is
2548 reserved for the CardBus bridge's IO window.
2549 The default value is 256 bytes.
2550 cbmemsize=nn[KMG] The fixed amount of bus space which is
2551 reserved for the CardBus bridge's memory
2552 window. The default value is 64 megabytes.
2553 resource_alignment=
2554 Format:
2555 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2556 Specifies alignment and device to reassign
2557 aligned memory resources.
2558 If <order of align> is not specified,
2559 PAGE_SIZE is used as alignment.
2560 PCI-PCI bridge can be specified, if resource
2561 windows need to be expanded.
2562 ecrc= Enable/disable PCIe ECRC (transaction layer
2563 end-to-end CRC checking).
2564 bios: Use BIOS/firmware settings. This is the
2565 the default.
2566 off: Turn ECRC off
2567 on: Turn ECRC on.
2568 hpiosize=nn[KMG] The fixed amount of bus space which is
2569 reserved for hotplug bridge's IO window.
2570 Default size is 256 bytes.
2571 hpmemsize=nn[KMG] The fixed amount of bus space which is
2572 reserved for hotplug bridge's memory window.
2573 Default size is 2 megabytes.
2574 realloc= Enable/disable reallocating PCI bridge resources
2575 if allocations done by BIOS are too small to
2576 accommodate resources required by all child
2577 devices.
2578 off: Turn realloc off
2579 on: Turn realloc on
2580 realloc same as realloc=on
2581 noari do not use PCIe ARI.
2582 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2583 only look for one device below a PCIe downstream
2584 port.
2586 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2587 Management.
2588 off Disable ASPM.
2589 force Enable ASPM even on devices that claim not to support it.
2590 WARNING: Forcing ASPM on may cause system lockups.
2592 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2593 nomsi Do not use MSI for PCI Express Native Hotplug (this
2594 makes all PCIe ports use INTx for hotplug services).
2596 pcie_ports= [PCIE] PCIe ports handling:
2597 auto Ask the BIOS whether or not to use native PCIe services
2598 associated with PCIe ports (PME, hot-plug, AER). Use
2599 them only if that is allowed by the BIOS.
2600 native Use native PCIe services associated with PCIe ports
2601 unconditionally.
2602 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2603 ports driver.
2605 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2606 nomsi Do not use MSI for native PCIe PME signaling (this makes
2607 all PCIe root ports use INTx for all services).
2609 pcmv= [HW,PCMCIA] BadgePAD 4
2611 pd_ignore_unused
2612 [PM]
2613 Keep all power-domains already enabled by bootloader on,
2614 even if no driver has claimed them. This is useful
2615 for debug and development, but should not be
2616 needed on a platform with proper driver support.
2618 pd. [PARIDE]
2619 See Documentation/blockdev/paride.txt.
2621 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2622 boot time.
2623 Format: { 0 | 1 }
2624 See arch/parisc/kernel/pdc_chassis.c
2626 percpu_alloc= Select which percpu first chunk allocator to use.
2627 Currently supported values are "embed" and "page".
2628 Archs may support subset or none of the selections.
2629 See comments in mm/percpu.c for details on each
2630 allocator. This parameter is primarily for debugging
2631 and performance comparison.
2633 pf. [PARIDE]
2634 See Documentation/blockdev/paride.txt.
2636 pg. [PARIDE]
2637 See Documentation/blockdev/paride.txt.
2639 pirq= [SMP,APIC] Manual mp-table setup
2640 See Documentation/x86/i386/IO-APIC.txt.
2642 plip= [PPT,NET] Parallel port network link
2643 Format: { parport<nr> | timid | 0 }
2644 See also Documentation/parport.txt.
2646 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2647 Override pmtimer IOPort with a hex value.
2648 e.g. pmtmr=0x508
2650 pnp.debug=1 [PNP]
2651 Enable PNP debug messages (depends on the
2652 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2653 via /sys/module/pnp/parameters/debug. We always show
2654 current resource usage; turning this on also shows
2655 possible settings and some assignment information.
2657 pnpacpi= [ACPI]
2658 { off }
2660 pnpbios= [ISAPNP]
2661 { on | off | curr | res | no-curr | no-res }
2663 pnp_reserve_irq=
2664 [ISAPNP] Exclude IRQs for the autoconfiguration
2666 pnp_reserve_dma=
2667 [ISAPNP] Exclude DMAs for the autoconfiguration
2669 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2670 Ranges are in pairs (I/O port base and size).
2672 pnp_reserve_mem=
2673 [ISAPNP] Exclude memory regions for the
2674 autoconfiguration.
2675 Ranges are in pairs (memory base and size).
2677 ports= [IP_VS_FTP] IPVS ftp helper module
2678 Default is 21.
2679 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2680 may be specified.
2681 Format: <port>,<port>....
2683 print-fatal-signals=
2684 [KNL] debug: print fatal signals
2686 If enabled, warn about various signal handling
2687 related application anomalies: too many signals,
2688 too many POSIX.1 timers, fatal signals causing a
2689 coredump - etc.
2691 If you hit the warning due to signal overflow,
2692 you might want to try "ulimit -i unlimited".
2694 default: off.
2696 printk.always_kmsg_dump=
2697 Trigger kmsg_dump for cases other than kernel oops or
2698 panics
2699 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2700 default: disabled
2702 printk.time= Show timing data prefixed to each printk message line
2703 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2705 processor.max_cstate= [HW,ACPI]
2706 Limit processor to maximum C-state
2707 max_cstate=9 overrides any DMI blacklist limit.
2709 processor.nocst [HW,ACPI]
2710 Ignore the _CST method to determine C-states,
2711 instead using the legacy FADT method
2713 profile= [KNL] Enable kernel profiling via /proc/profile
2714 Format: [schedule,]<number>
2715 Param: "schedule" - profile schedule points.
2716 Param: <number> - step/bucket size as a power of 2 for
2717 statistical time based profiling.
2718 Param: "sleep" - profile D-state sleeping (millisecs).
2719 Requires CONFIG_SCHEDSTATS
2720 Param: "kvm" - profile VM exits.
2722 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2723 before loading.
2724 See Documentation/blockdev/ramdisk.txt.
2726 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2727 probe for; one of (bare|imps|exps|lifebook|any).
2728 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2729 per second.
2730 psmouse.resetafter= [HW,MOUSE]
2731 Try to reset the device after so many bad packets
2732 (0 = never).
2733 psmouse.resolution=
2734 [HW,MOUSE] Set desired mouse resolution, in dpi.
2735 psmouse.smartscroll=
2736 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2737 0 = disabled, 1 = enabled (default).
2739 pstore.backend= Specify the name of the pstore backend to use
2741 pt. [PARIDE]
2742 See Documentation/blockdev/paride.txt.
2744 pty.legacy_count=
2745 [KNL] Number of legacy pty's. Overwrites compiled-in
2746 default number.
2748 quiet [KNL] Disable most log messages
2750 r128= [HW,DRM]
2752 raid= [HW,RAID]
2753 See Documentation/md.txt.
2755 ramdisk_blocksize= [RAM]
2756 See Documentation/blockdev/ramdisk.txt.
2758 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2759 See Documentation/blockdev/ramdisk.txt.
2761 rcu_nocbs= [KNL]
2762 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2763 the specified list of CPUs to be no-callback CPUs.
2764 Invocation of these CPUs' RCU callbacks will
2765 be offloaded to "rcuox/N" kthreads created for
2766 that purpose, where "x" is "b" for RCU-bh, "p"
2767 for RCU-preempt, and "s" for RCU-sched, and "N"
2768 is the CPU number. This reduces OS jitter on the
2769 offloaded CPUs, which can be useful for HPC and
2770 real-time workloads. It can also improve energy
2771 efficiency for asymmetric multiprocessors.
2773 rcu_nocb_poll [KNL]
2774 Rather than requiring that offloaded CPUs
2775 (specified by rcu_nocbs= above) explicitly
2776 awaken the corresponding "rcuoN" kthreads,
2777 make these kthreads poll for callbacks.
2778 This improves the real-time response for the
2779 offloaded CPUs by relieving them of the need to
2780 wake up the corresponding kthread, but degrades
2781 energy efficiency by requiring that the kthreads
2782 periodically wake up to do the polling.
2784 rcutree.blimit= [KNL]
2785 Set maximum number of finished RCU callbacks to
2786 process in one batch.
2788 rcutree.rcu_fanout_leaf= [KNL]
2789 Increase the number of CPUs assigned to each
2790 leaf rcu_node structure. Useful for very large
2791 systems.
2793 rcutree.jiffies_till_sched_qs= [KNL]
2794 Set required age in jiffies for a
2795 given grace period before RCU starts
2796 soliciting quiescent-state help from
2797 rcu_note_context_switch().
2799 rcutree.jiffies_till_first_fqs= [KNL]
2800 Set delay from grace-period initialization to
2801 first attempt to force quiescent states.
2802 Units are jiffies, minimum value is zero,
2803 and maximum value is HZ.
2805 rcutree.jiffies_till_next_fqs= [KNL]
2806 Set delay between subsequent attempts to force
2807 quiescent states. Units are jiffies, minimum
2808 value is one, and maximum value is HZ.
2810 rcutree.qhimark= [KNL]
2811 Set threshold of queued RCU callbacks beyond which
2812 batch limiting is disabled.
2814 rcutree.qlowmark= [KNL]
2815 Set threshold of queued RCU callbacks below which
2816 batch limiting is re-enabled.
2818 rcutree.rcu_idle_gp_delay= [KNL]
2819 Set wakeup interval for idle CPUs that have
2820 RCU callbacks (RCU_FAST_NO_HZ=y).
2822 rcutree.rcu_idle_lazy_gp_delay= [KNL]
2823 Set wakeup interval for idle CPUs that have
2824 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2825 Lazy RCU callbacks are those which RCU can
2826 prove do nothing more than free memory.
2828 rcutorture.fqs_duration= [KNL]
2829 Set duration of force_quiescent_state bursts.
2831 rcutorture.fqs_holdoff= [KNL]
2832 Set holdoff time within force_quiescent_state bursts.
2834 rcutorture.fqs_stutter= [KNL]
2835 Set wait time between force_quiescent_state bursts.
2837 rcutorture.gp_exp= [KNL]
2838 Use expedited update-side primitives.
2840 rcutorture.gp_normal= [KNL]
2841 Use normal (non-expedited) update-side primitives.
2842 If both gp_exp and gp_normal are set, do both.
2843 If neither gp_exp nor gp_normal are set, still
2844 do both.
2846 rcutorture.n_barrier_cbs= [KNL]
2847 Set callbacks/threads for rcu_barrier() testing.
2849 rcutorture.nfakewriters= [KNL]
2850 Set number of concurrent RCU writers. These just
2851 stress RCU, they don't participate in the actual
2852 test, hence the "fake".
2854 rcutorture.nreaders= [KNL]
2855 Set number of RCU readers.
2857 rcutorture.object_debug= [KNL]
2858 Enable debug-object double-call_rcu() testing.
2860 rcutorture.onoff_holdoff= [KNL]
2861 Set time (s) after boot for CPU-hotplug testing.
2863 rcutorture.onoff_interval= [KNL]
2864 Set time (s) between CPU-hotplug operations, or
2865 zero to disable CPU-hotplug testing.
2867 rcutorture.rcutorture_runnable= [BOOT]
2868 Start rcutorture running at boot time.
2870 rcutorture.shuffle_interval= [KNL]
2871 Set task-shuffle interval (s). Shuffling tasks
2872 allows some CPUs to go into dyntick-idle mode
2873 during the rcutorture test.
2875 rcutorture.shutdown_secs= [KNL]
2876 Set time (s) after boot system shutdown. This
2877 is useful for hands-off automated testing.
2879 rcutorture.stall_cpu= [KNL]
2880 Duration of CPU stall (s) to test RCU CPU stall
2881 warnings, zero to disable.
2883 rcutorture.stall_cpu_holdoff= [KNL]
2884 Time to wait (s) after boot before inducing stall.
2886 rcutorture.stat_interval= [KNL]
2887 Time (s) between statistics printk()s.
2889 rcutorture.stutter= [KNL]
2890 Time (s) to stutter testing, for example, specifying
2891 five seconds causes the test to run for five seconds,
2892 wait for five seconds, and so on. This tests RCU's
2893 ability to transition abruptly to and from idle.
2895 rcutorture.test_boost= [KNL]
2896 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2897 "Maybe" means test if the RCU implementation
2898 under test support RCU priority boosting.
2900 rcutorture.test_boost_duration= [KNL]
2901 Duration (s) of each individual boost test.
2903 rcutorture.test_boost_interval= [KNL]
2904 Interval (s) between each boost test.
2906 rcutorture.test_no_idle_hz= [KNL]
2907 Test RCU's dyntick-idle handling. See also the
2908 rcutorture.shuffle_interval parameter.
2910 rcutorture.torture_type= [KNL]
2911 Specify the RCU implementation to test.
2913 rcutorture.verbose= [KNL]
2914 Enable additional printk() statements.
2916 rcupdate.rcu_expedited= [KNL]
2917 Use expedited grace-period primitives, for
2918 example, synchronize_rcu_expedited() instead
2919 of synchronize_rcu(). This reduces latency,
2920 but can increase CPU utilization, degrade
2921 real-time latency, and degrade energy efficiency.
2923 rcupdate.rcu_cpu_stall_suppress= [KNL]
2924 Suppress RCU CPU stall warning messages.
2926 rcupdate.rcu_cpu_stall_timeout= [KNL]
2927 Set timeout for RCU CPU stall warning messages.
2929 rdinit= [KNL]
2930 Format: <full_path>
2931 Run specified binary instead of /init from the ramdisk,
2932 used for early userspace startup. See initrd.
2934 reboot= [KNL]
2935 Format (x86 or x86_64):
2936 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2937 [[,]s[mp]#### \
2938 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2939 [[,]f[orce]
2940 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2941 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2942 reboot_force is either force or not specified,
2943 reboot_cpu is s[mp]#### with #### being the processor
2944 to be used for rebooting.
2946 relax_domain_level=
2947 [KNL, SMP] Set scheduler's default relax_domain_level.
2948 See Documentation/cgroups/cpusets.txt.
2950 relative_sleep_states=
2951 [SUSPEND] Use sleep state labeling where the deepest
2952 state available other than hibernation is always "mem".
2953 Format: { "0" | "1" }
2954 0 -- Traditional sleep state labels.
2955 1 -- Relative sleep state labels.
2957 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2959 reservetop= [X86-32]
2960 Format: nn[KMG]
2961 Reserves a hole at the top of the kernel virtual
2962 address space.
2964 reservelow= [X86]
2965 Format: nn[K]
2966 Set the amount of memory to reserve for BIOS at
2967 the bottom of the address space.
2969 reset_devices [KNL] Force drivers to reset the underlying device
2970 during initialization.
2972 resume= [SWSUSP]
2973 Specify the partition device for software suspend
2974 Format:
2975 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2977 resume_offset= [SWSUSP]
2978 Specify the offset from the beginning of the partition
2979 given by "resume=" at which the swap header is located,
2980 in <PAGE_SIZE> units (needed only for swap files).
2981 See Documentation/power/swsusp-and-swap-files.txt
2983 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2984 read the resume files
2986 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2987 Useful for devices that are detected asynchronously
2988 (e.g. USB and MMC devices).
2990 hibernate= [HIBERNATION]
2991 noresume Don't check if there's a hibernation image
2992 present during boot.
2993 nocompress Don't compress/decompress hibernation images.
2994 no Disable hibernation and resume.
2996 retain_initrd [RAM] Keep initrd memory after extraction
2998 rhash_entries= [KNL,NET]
2999 Set number of hash buckets for route cache
3001 ro [KNL] Mount root device read-only on boot
3003 root= [KNL] Root filesystem
3004 See name_to_dev_t comment in init/do_mounts.c.
3006 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3007 mount the root filesystem
3009 rootflags= [KNL] Set root filesystem mount option string
3011 rootfstype= [KNL] Set root filesystem type
3013 rootwait [KNL] Wait (indefinitely) for root device to show up.
3014 Useful for devices that are detected asynchronously
3015 (e.g. USB and MMC devices).
3017 rproc_mem=nn[KMG][@address]
3018 [KNL,ARM,CMA] Remoteproc physical memory block.
3019 Memory area to be used by remote processor image,
3020 managed by CMA.
3022 rw [KNL] Mount root device read-write on boot
3024 S [KNL] Run init in single mode
3026 sa1100ir [NET]
3027 See drivers/net/irda/sa1100_ir.c.
3029 sbni= [NET] Granch SBNI12 leased line adapter
3031 sched_debug [KNL] Enables verbose scheduler debug messages.
3033 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3034 xtime_lock contention on larger systems, and/or RCU lock
3035 contention on all systems with CONFIG_MAXSMP set.
3036 Format: { "0" | "1" }
3037 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3038 1 -- enable.
3039 Note: increases power consumption, thus should only be
3040 enabled if running jitter sensitive (HPC/RT) workloads.
3042 security= [SECURITY] Choose a security module to enable at boot.
3043 If this boot parameter is not specified, only the first
3044 security module asking for security registration will be
3045 loaded. An invalid security module name will be treated
3046 as if no module has been chosen.
3048 selinux= [SELINUX] Disable or enable SELinux at boot time.
3049 Format: { "0" | "1" }
3050 See security/selinux/Kconfig help text.
3051 0 -- disable.
3052 1 -- enable.
3053 Default value is set via kernel config option.
3054 If enabled at boot time, /selinux/disable can be used
3055 later to disable prior to initial policy load.
3057 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3058 Format: { "0" | "1" }
3059 See security/apparmor/Kconfig help text
3060 0 -- disable.
3061 1 -- enable.
3062 Default value is set via kernel config option.
3064 serialnumber [BUGS=X86-32]
3066 shapers= [NET]
3067 Maximal number of shapers.
3069 show_msr= [x86] show boot-time MSR settings
3070 Format: { <integer> }
3071 Show boot-time (BIOS-initialized) MSR settings.
3072 The parameter means the number of CPUs to show,
3073 for example 1 means boot CPU only.
3075 simeth= [IA-64]
3076 simscsi=
3078 slram= [HW,MTD]
3080 slab_max_order= [MM, SLAB]
3081 Determines the maximum allowed order for slabs.
3082 A high setting may cause OOMs due to memory
3083 fragmentation. Defaults to 1 for systems with
3084 more than 32MB of RAM, 0 otherwise.
3086 slub_debug[=options[,slabs]] [MM, SLUB]
3087 Enabling slub_debug allows one to determine the
3088 culprit if slab objects become corrupted. Enabling
3089 slub_debug can create guard zones around objects and
3090 may poison objects when not in use. Also tracks the
3091 last alloc / free. For more information see
3092 Documentation/vm/slub.txt.
3094 slub_max_order= [MM, SLUB]
3095 Determines the maximum allowed order for slabs.
3096 A high setting may cause OOMs due to memory
3097 fragmentation. For more information see
3098 Documentation/vm/slub.txt.
3100 slub_min_objects= [MM, SLUB]
3101 The minimum number of objects per slab. SLUB will
3102 increase the slab order up to slub_max_order to
3103 generate a sufficiently large slab able to contain
3104 the number of objects indicated. The higher the number
3105 of objects the smaller the overhead of tracking slabs
3106 and the less frequently locks need to be acquired.
3107 For more information see Documentation/vm/slub.txt.
3109 slub_min_order= [MM, SLUB]
3110 Determines the minimum page order for slabs. Must be
3111 lower than slub_max_order.
3112 For more information see Documentation/vm/slub.txt.
3114 slub_nomerge [MM, SLUB]
3115 Disable merging of slabs with similar size. May be
3116 necessary if there is some reason to distinguish
3117 allocs to different slabs. Debug options disable
3118 merging on their own.
3119 For more information see Documentation/vm/slub.txt.
3121 smart2= [HW]
3122 Format: <io1>[,<io2>[,...,<io8>]]
3124 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3125 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3126 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3127 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3128 smsc-ircc2.ircc_irq= [HW] IRQ line
3129 smsc-ircc2.ircc_dma= [HW] DMA channel
3130 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3131 0: Toshiba Satellite 1800 (GP data pin select)
3132 1: Fast pin select (default)
3133 2: ATC IRMode
3135 softlockup_panic=
3136 [KNL] Should the soft-lockup detector generate panics.
3137 Format: <integer>
3139 softlockup_all_cpu_backtrace=
3140 [KNL] Should the soft-lockup detector generate
3141 backtraces on all cpus.
3142 Format: <integer>
3144 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3145 See Documentation/laptops/sonypi.txt
3147 spia_io_base= [HW,MTD]
3148 spia_fio_base=
3149 spia_pedr=
3150 spia_peddr=
3152 stacktrace [FTRACE]
3153 Enabled the stack tracer on boot up.
3155 stacktrace_filter=[function-list]
3156 [FTRACE] Limit the functions that the stack tracer
3157 will trace at boot up. function-list is a comma separated
3158 list of functions. This list can be changed at run
3159 time by the stack_trace_filter file in the debugfs
3160 tracing directory. Note, this enables stack tracing
3161 and the stacktrace above is not needed.
3163 sti= [PARISC,HW]
3164 Format: <num>
3165 Set the STI (builtin display/keyboard on the HP-PARISC
3166 machines) console (graphic card) which should be used
3167 as the initial boot-console.
3168 See also comment in drivers/video/console/sticore.c.
3170 sti_font= [HW]
3171 See comment in drivers/video/console/sticore.c.
3173 stifb= [HW]
3174 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3176 sunrpc.min_resvport=
3177 sunrpc.max_resvport=
3178 [NFS,SUNRPC]
3179 SunRPC servers often require that client requests
3180 originate from a privileged port (i.e. a port in the
3181 range 0 < portnr < 1024).
3182 An administrator who wishes to reserve some of these
3183 ports for other uses may adjust the range that the
3184 kernel's sunrpc client considers to be privileged
3185 using these two parameters to set the minimum and
3186 maximum port values.
3188 sunrpc.pool_mode=
3189 [NFS]
3190 Control how the NFS server code allocates CPUs to
3191 service thread pools. Depending on how many NICs
3192 you have and where their interrupts are bound, this
3193 option will affect which CPUs will do NFS serving.
3194 Note: this parameter cannot be changed while the
3195 NFS server is running.
3197 auto the server chooses an appropriate mode
3198 automatically using heuristics
3199 global a single global pool contains all CPUs
3200 percpu one pool for each CPU
3201 pernode one pool for each NUMA node (equivalent
3202 to global on non-NUMA machines)
3204 sunrpc.tcp_slot_table_entries=
3205 sunrpc.udp_slot_table_entries=
3206 [NFS,SUNRPC]
3207 Sets the upper limit on the number of simultaneous
3208 RPC calls that can be sent from the client to a
3209 server. Increasing these values may allow you to
3210 improve throughput, but will also increase the
3211 amount of memory reserved for use by the client.
3213 swapaccount=[0|1]
3214 [KNL] Enable accounting of swap in memory resource
3215 controller if no parameter or 1 is given or disable
3216 it if 0 is given (See Documentation/cgroups/memory.txt)
3218 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3219 Format: { <int> | force }
3220 <int> -- Number of I/O TLB slabs
3221 force -- force using of bounce buffers even if they
3222 wouldn't be automatically used by the kernel
3224 switches= [HW,M68k]
3226 sysfs.deprecated=0|1 [KNL]
3227 Enable/disable old style sysfs layout for old udev
3228 on older distributions. When this option is enabled
3229 very new udev will not work anymore. When this option
3230 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3231 in older udev will not work anymore.
3232 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3233 the kernel configuration.
3235 sysrq_always_enabled
3236 [KNL]
3237 Ignore sysrq setting - this boot parameter will
3238 neutralize any effect of /proc/sys/kernel/sysrq.
3239 Useful for debugging.
3241 tdfx= [HW,DRM]
3243 test_suspend= [SUSPEND]
3244 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3245 standby suspend) as the system sleep state to briefly
3246 enter during system startup. The system is woken from
3247 this state using a wakeup-capable RTC alarm.
3249 thash_entries= [KNL,NET]
3250 Set number of hash buckets for TCP connection
3252 thermal.act= [HW,ACPI]
3253 -1: disable all active trip points in all thermal zones
3254 <degrees C>: override all lowest active trip points
3256 thermal.crt= [HW,ACPI]
3257 -1: disable all critical trip points in all thermal zones
3258 <degrees C>: override all critical trip points
3260 thermal.nocrt= [HW,ACPI]
3261 Set to disable actions on ACPI thermal zone
3262 critical and hot trip points.
3264 thermal.off= [HW,ACPI]
3265 1: disable ACPI thermal control
3267 thermal.psv= [HW,ACPI]
3268 -1: disable all passive trip points
3269 <degrees C>: override all passive trip points to this
3270 value
3272 thermal.tzp= [HW,ACPI]
3273 Specify global default ACPI thermal zone polling rate
3274 <deci-seconds>: poll all this frequency
3275 0: no polling (default)
3277 threadirqs [KNL]
3278 Force threading of all interrupt handlers except those
3279 marked explicitly IRQF_NO_THREAD.
3281 tmem [KNL,XEN]
3282 Enable the Transcendent memory driver if built-in.
3284 tmem.cleancache=0|1 [KNL, XEN]
3285 Default is on (1). Disable the usage of the cleancache
3286 API to send anonymous pages to the hypervisor.
3288 tmem.frontswap=0|1 [KNL, XEN]
3289 Default is on (1). Disable the usage of the frontswap
3290 API to send swap pages to the hypervisor. If disabled
3291 the selfballooning and selfshrinking are force disabled.
3293 tmem.selfballooning=0|1 [KNL, XEN]
3294 Default is on (1). Disable the driving of swap pages
3295 to the hypervisor.
3297 tmem.selfshrinking=0|1 [KNL, XEN]
3298 Default is on (1). Partial swapoff that immediately
3299 transfers pages from Xen hypervisor back to the
3300 kernel based on different criteria.
3302 topology= [S390]
3303 Format: {off | on}
3304 Specify if the kernel should make use of the cpu
3305 topology information if the hardware supports this.
3306 The scheduler will make use of this information and
3307 e.g. base its process migration decisions on it.
3308 Default is on.
3310 tp720= [HW,PS2]
3312 tpm_suspend_pcr=[HW,TPM]
3313 Format: integer pcr id
3314 Specify that at suspend time, the tpm driver
3315 should extend the specified pcr with zeros,
3316 as a workaround for some chips which fail to
3317 flush the last written pcr on TPM_SaveState.
3318 This will guarantee that all the other pcrs
3319 are saved.
3321 trace_buf_size=nn[KMG]
3322 [FTRACE] will set tracing buffer size.
3324 trace_event=[event-list]
3325 [FTRACE] Set and start specified trace events in order
3326 to facilitate early boot debugging.
3327 See also Documentation/trace/events.txt
3329 trace_options=[option-list]
3330 [FTRACE] Enable or disable tracer options at boot.
3331 The option-list is a comma delimited list of options
3332 that can be enabled or disabled just as if you were
3333 to echo the option name into
3335 /sys/kernel/debug/tracing/trace_options
3337 For example, to enable stacktrace option (to dump the
3338 stack trace of each event), add to the command line:
3340 trace_options=stacktrace
3342 See also Documentation/trace/ftrace.txt "trace options"
3343 section.
3345 traceoff_on_warning
3346 [FTRACE] enable this option to disable tracing when a
3347 warning is hit. This turns off "tracing_on". Tracing can
3348 be enabled again by echoing '1' into the "tracing_on"
3349 file located in /sys/kernel/debug/tracing/
3351 This option is useful, as it disables the trace before
3352 the WARNING dump is called, which prevents the trace to
3353 be filled with content caused by the warning output.
3355 This option can also be set at run time via the sysctl
3356 option: kernel/traceoff_on_warning
3358 transparent_hugepage=
3359 [KNL]
3360 Format: [always|madvise|never]
3361 Can be used to control the default behavior of the system
3362 with respect to transparent hugepages.
3363 See Documentation/vm/transhuge.txt for more details.
3365 tsc= Disable clocksource stability checks for TSC.
3366 Format: <string>
3367 [x86] reliable: mark tsc clocksource as reliable, this
3368 disables clocksource verification at runtime, as well
3369 as the stability checks done at bootup. Used to enable
3370 high-resolution timer mode on older hardware, and in
3371 virtualized environment.
3372 [x86] noirqtime: Do not use TSC to do irq accounting.
3373 Used to run time disable IRQ_TIME_ACCOUNTING on any
3374 platforms where RDTSC is slow and this accounting
3375 can add overhead.
3377 turbografx.map[2|3]= [HW,JOY]
3378 TurboGraFX parallel port interface
3379 Format:
3380 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3381 See also Documentation/input/joystick-parport.txt
3383 udbg-immortal [PPC] When debugging early kernel crashes that
3384 happen after console_init() and before a proper
3385 console driver takes over, this boot options might
3386 help "seeing" what's going on.
3388 uhash_entries= [KNL,NET]
3389 Set number of hash buckets for UDP/UDP-Lite connections
3391 uhci-hcd.ignore_oc=
3392 [USB] Ignore overcurrent events (default N).
3393 Some badly-designed motherboards generate lots of
3394 bogus events, for ports that aren't wired to
3395 anything. Set this parameter to avoid log spamming.
3396 Note that genuine overcurrent events won't be
3397 reported either.
3399 unknown_nmi_panic
3400 [X86] Cause panic on unknown NMI.
3402 usbcore.authorized_default=
3403 [USB] Default USB device authorization:
3404 (default -1 = authorized except for wireless USB,
3405 0 = not authorized, 1 = authorized)
3407 usbcore.autosuspend=
3408 [USB] The autosuspend time delay (in seconds) used
3409 for newly-detected USB devices (default 2). This
3410 is the time required before an idle device will be
3411 autosuspended. Devices for which the delay is set
3412 to a negative value won't be autosuspended at all.
3414 usbcore.usbfs_snoop=
3415 [USB] Set to log all usbfs traffic (default 0 = off).
3417 usbcore.blinkenlights=
3418 [USB] Set to cycle leds on hubs (default 0 = off).
3420 usbcore.old_scheme_first=
3421 [USB] Start with the old device initialization
3422 scheme (default 0 = off).
3424 usbcore.usbfs_memory_mb=
3425 [USB] Memory limit (in MB) for buffers allocated by
3426 usbfs (default = 16, 0 = max = 2047).
3428 usbcore.use_both_schemes=
3429 [USB] Try the other device initialization scheme
3430 if the first one fails (default 1 = enabled).
3432 usbcore.initial_descriptor_timeout=
3433 [USB] Specifies timeout for the initial 64-byte
3434 USB_REQ_GET_DESCRIPTOR request in milliseconds
3435 (default 5000 = 5.0 seconds).
3437 usbhid.mousepoll=
3438 [USBHID] The interval which mice are to be polled at.
3440 usb-storage.delay_use=
3441 [UMS] The delay in seconds before a new device is
3442 scanned for Logical Units (default 5).
3444 usb-storage.quirks=
3445 [UMS] A list of quirks entries to supplement or
3446 override the built-in unusual_devs list. List
3447 entries are separated by commas. Each entry has
3448 the form VID:PID:Flags where VID and PID are Vendor
3449 and Product ID values (4-digit hex numbers) and
3450 Flags is a set of characters, each corresponding
3451 to a common usb-storage quirk flag as follows:
3452 a = SANE_SENSE (collect more than 18 bytes
3453 of sense data);
3454 b = BAD_SENSE (don't collect more than 18
3455 bytes of sense data);
3456 c = FIX_CAPACITY (decrease the reported
3457 device capacity by one sector);
3458 d = NO_READ_DISC_INFO (don't use
3459 READ_DISC_INFO command);
3460 e = NO_READ_CAPACITY_16 (don't use
3461 READ_CAPACITY_16 command);
3462 h = CAPACITY_HEURISTICS (decrease the
3463 reported device capacity by one
3464 sector if the number is odd);
3465 i = IGNORE_DEVICE (don't bind to this
3466 device);
3467 l = NOT_LOCKABLE (don't try to lock and
3468 unlock ejectable media);
3469 m = MAX_SECTORS_64 (don't transfer more
3470 than 64 sectors = 32 KB at a time);
3471 n = INITIAL_READ10 (force a retry of the
3472 initial READ(10) command);
3473 o = CAPACITY_OK (accept the capacity
3474 reported by the device);
3475 p = WRITE_CACHE (the device cache is ON
3476 by default);
3477 r = IGNORE_RESIDUE (the device reports
3478 bogus residue values);
3479 s = SINGLE_LUN (the device has only one
3480 Logical Unit);
3481 u = IGNORE_UAS (don't bind to the uas driver);
3482 w = NO_WP_DETECT (don't test whether the
3483 medium is write-protected).
3484 Example: quirks=0419:aaf5:rl,0421:0433:rc
3486 user_debug= [KNL,ARM]
3487 Format: <int>
3488 See arch/arm/Kconfig.debug help text.
3489 1 - undefined instruction events
3490 2 - system calls
3491 4 - invalid data aborts
3492 8 - SIGSEGV faults
3493 16 - SIGBUS faults
3494 Example: user_debug=31
3496 userpte=
3497 [X86] Flags controlling user PTE allocations.
3499 nohigh = do not allocate PTE pages in
3500 HIGHMEM regardless of setting
3501 of CONFIG_HIGHPTE.
3503 vdso= [X86,SH]
3504 On X86_32, this is an alias for vdso32=. Otherwise:
3506 vdso=1: enable VDSO (the default)
3507 vdso=0: disable VDSO mapping
3509 vdso32= [X86] Control the 32-bit vDSO
3510 vdso32=1: enable 32-bit VDSO
3511 vdso32=0 or vdso32=2: disable 32-bit VDSO
3513 See the help text for CONFIG_COMPAT_VDSO for more
3514 details. If CONFIG_COMPAT_VDSO is set, the default is
3515 vdso32=0; otherwise, the default is vdso32=1.
3517 For compatibility with older kernels, vdso32=2 is an
3518 alias for vdso32=0.
3520 Try vdso32=0 if you encounter an error that says:
3521 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3523 vector= [IA-64,SMP]
3524 vector=percpu: enable percpu vector domain
3526 video= [FB] Frame buffer configuration
3527 See Documentation/fb/modedb.txt.
3529 video.brightness_switch_enabled= [0,1]
3530 If set to 1, on receiving an ACPI notify event
3531 generated by hotkey, video driver will adjust brightness
3532 level and then send out the event to user space through
3533 the allocated input device; If set to 0, video driver
3534 will only send out the event without touching backlight
3535 brightness level.
3536 default: 1
3538 virtio_mmio.device=
3539 [VMMIO] Memory mapped virtio (platform) device.
3541 <size>@<baseaddr>:<irq>[:<id>]
3542 where:
3543 <size> := size (can use standard suffixes
3544 like K, M and G)
3545 <baseaddr> := physical base address
3546 <irq> := interrupt number (as passed to
3547 request_irq())
3548 <id> := (optional) platform device id
3549 example:
3550 virtio_mmio.device=1K@0x100b0000:48:7
3552 Can be used multiple times for multiple devices.
3554 vga= [BOOT,X86-32] Select a particular video mode
3555 See Documentation/x86/boot.txt and
3556 Documentation/svga.txt.
3557 Use vga=ask for menu.
3558 This is actually a boot loader parameter; the value is
3559 passed to the kernel using a special protocol.
3561 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3562 size of <nn>. This can be used to increase the
3563 minimum size (128MB on x86). It can also be used to
3564 decrease the size and leave more room for directly
3565 mapped kernel RAM.
3567 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3568 Format: <command>
3570 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3571 Format: <command>
3573 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3574 Format: <command>
3576 vsyscall= [X86-64]
3577 Controls the behavior of vsyscalls (i.e. calls to
3578 fixed addresses of 0xffffffffff600x00 from legacy
3579 code). Most statically-linked binaries and older
3580 versions of glibc use these calls. Because these
3581 functions are at fixed addresses, they make nice
3582 targets for exploits that can control RIP.
3584 emulate [default] Vsyscalls turn into traps and are
3585 emulated reasonably safely.
3587 native Vsyscalls are native syscall instructions.
3588 This is a little bit faster than trapping
3589 and makes a few dynamic recompilers work
3590 better than they would in emulation mode.
3591 It also makes exploits much easier to write.
3593 none Vsyscalls don't work at all. This makes
3594 them quite hard to use for exploits but
3595 might break your system.
3597 vt.color= [VT] Default text color.
3598 Format: 0xYX, X = foreground, Y = background.
3599 Default: 0x07 = light gray on black.
3601 vt.cur_default= [VT] Default cursor shape.
3602 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3603 the parameters of the <Esc>[?A;B;Cc escape sequence;
3604 see VGA-softcursor.txt. Default: 2 = underline.
3606 vt.default_blu= [VT]
3607 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3608 Change the default blue palette of the console.
3609 This is a 16-member array composed of values
3610 ranging from 0-255.
3612 vt.default_grn= [VT]
3613 Format: <green0>,<green1>,<green2>,...,<green15>
3614 Change the default green palette of the console.
3615 This is a 16-member array composed of values
3616 ranging from 0-255.
3618 vt.default_red= [VT]
3619 Format: <red0>,<red1>,<red2>,...,<red15>
3620 Change the default red palette of the console.
3621 This is a 16-member array composed of values
3622 ranging from 0-255.
3624 vt.default_utf8=
3625 [VT]
3626 Format=<0|1>
3627 Set system-wide default UTF-8 mode for all tty's.
3628 Default is 1, i.e. UTF-8 mode is enabled for all
3629 newly opened terminals.
3631 vt.global_cursor_default=
3632 [VT]
3633 Format=<-1|0|1>
3634 Set system-wide default for whether a cursor
3635 is shown on new VTs. Default is -1,
3636 i.e. cursors will be created by default unless
3637 overridden by individual drivers. 0 will hide
3638 cursors, 1 will display them.
3640 vt.italic= [VT] Default color for italic text; 0-15.
3641 Default: 2 = green.
3643 vt.underline= [VT] Default color for underlined text; 0-15.
3644 Default: 3 = cyan.
3646 watchdog timers [HW,WDT] For information on watchdog timers,
3647 see Documentation/watchdog/watchdog-parameters.txt
3648 or other driver-specific files in the
3649 Documentation/watchdog/ directory.
3651 workqueue.disable_numa
3652 By default, all work items queued to unbound
3653 workqueues are affine to the NUMA nodes they're
3654 issued on, which results in better behavior in
3655 general. If NUMA affinity needs to be disabled for
3656 whatever reason, this option can be used. Note
3657 that this also can be controlled per-workqueue for
3658 workqueues visible under /sys/bus/workqueue/.
3660 workqueue.power_efficient
3661 Per-cpu workqueues are generally preferred because
3662 they show better performance thanks to cache
3663 locality; unfortunately, per-cpu workqueues tend to
3664 be more power hungry than unbound workqueues.
3666 Enabling this makes the per-cpu workqueues which
3667 were observed to contribute significantly to power
3668 consumption unbound, leading to measurably lower
3669 power usage at the cost of small performance
3670 overhead.
3672 The default value of this parameter is determined by
3673 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3675 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3676 default x2apic cluster mode on platforms
3677 supporting x2apic.
3679 x86_intel_mid_timer= [X86-32,APBT]
3680 Choose timer option for x86 Intel MID platform.
3681 Two valid options are apbt timer only and lapic timer
3682 plus one apbt timer for broadcast timer.
3683 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3685 xen_emul_unplug= [HW,X86,XEN]
3686 Unplug Xen emulated devices
3687 Format: [unplug0,][unplug1]
3688 ide-disks -- unplug primary master IDE devices
3689 aux-ide-disks -- unplug non-primary-master IDE devices
3690 nics -- unplug network devices
3691 all -- unplug all emulated devices (NICs and IDE disks)
3692 unnecessary -- unplugging emulated devices is
3693 unnecessary even if the host did not respond to
3694 the unplug protocol
3695 never -- do not unplug even if version check succeeds
3697 xen_nopvspin [X86,XEN]
3698 Disables the ticketlock slowpath using Xen PV
3699 optimizations.
3701 xirc2ps_cs= [NET,PCMCIA]
3702 Format:
3703 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3705 ______________________________________________________________________
3707 TODO:
3709 Add more DRM drivers.