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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
4 The following is a consolidated list of the kernel parameters as implemented
5 (mostly) by the __setup() macro and sorted into English Dictionary order
6 (defined as ignoring all punctuation and sorting digits before letters in a
7 case insensitive manner), and with descriptions where known.
9 Module parameters for loadable modules are specified only as the
10 parameter name with optional '=' and value as appropriate, such as:
12 modprobe usbcore blinkenlights=1
14 Module parameters for modules that are built into the kernel image
15 are specified on the kernel command line with the module name plus
16 '.' plus parameter name, with '=' and value if appropriate, such as:
18 usbcore.blinkenlights=1
20 Hyphens (dashes) and underscores are equivalent in parameter names, so
21 log_buf_len=1M print-fatal-signals=1
22 can also be entered as
23 log-buf-len=1M print_fatal_signals=1
26 This document may not be entirely up to date and comprehensive. The command
27 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
28 module. Loadable modules, after being loaded into the running kernel, also
29 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
30 parameters may be changed at runtime by the command
31 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
33 The parameters listed below are only valid if certain kernel build options were
34 enabled and if respective hardware is present. The text in square brackets at
35 the beginning of each description states the restrictions within which a
36 parameter is applicable:
38 ACPI ACPI support is enabled.
39 AGP AGP (Accelerated Graphics Port) is enabled.
40 ALSA ALSA sound support is enabled.
41 APIC APIC support is enabled.
42 APM Advanced Power Management support is enabled.
43 ARM ARM architecture is enabled.
44 AVR32 AVR32 architecture is enabled.
45 AX25 Appropriate AX.25 support is enabled.
46 BLACKFIN Blackfin architecture is enabled.
47 DRM Direct Rendering Management support is enabled.
48 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
49 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
50 EFI EFI Partitioning (GPT) is enabled
51 EIDE EIDE/ATAPI support is enabled.
52 EVM Extended Verification Module
53 FB The frame buffer device is enabled.
54 FTRACE Function tracing enabled.
55 GCOV GCOV profiling is enabled.
56 HW Appropriate hardware is enabled.
57 IA-64 IA-64 architecture is enabled.
58 IMA Integrity measurement architecture is enabled.
59 IOSCHED More than one I/O scheduler is enabled.
60 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
61 IPV6 IPv6 support is enabled.
62 ISAPNP ISA PnP code is enabled.
63 ISDN Appropriate ISDN support is enabled.
64 JOY Appropriate joystick support is enabled.
65 KGDB Kernel debugger support is enabled.
66 KVM Kernel Virtual Machine support is enabled.
67 LIBATA Libata driver is enabled
68 LP Printer support is enabled.
69 LOOP Loopback device support is enabled.
70 M68k M68k architecture is enabled.
71 These options have more detailed description inside of
72 Documentation/m68k/kernel-options.txt.
73 MDA MDA console support is enabled.
74 MIPS MIPS architecture is enabled.
75 MOUSE Appropriate mouse support is enabled.
76 MSI Message Signaled Interrupts (PCI).
77 MTD MTD (Memory Technology Device) support is enabled.
78 NET Appropriate network support is enabled.
79 NUMA NUMA support is enabled.
80 NFS Appropriate NFS support is enabled.
81 OSS OSS sound support is enabled.
82 PV_OPS A paravirtualized kernel is enabled.
83 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
84 PARISC The PA-RISC architecture is enabled.
85 PCI PCI bus support is enabled.
86 PCIE PCI Express support is enabled.
87 PCMCIA The PCMCIA subsystem is enabled.
88 PNP Plug & Play support is enabled.
89 PPC PowerPC architecture is enabled.
90 PPT Parallel port support is enabled.
91 PS2 Appropriate PS/2 support is enabled.
92 RAM RAM disk support is enabled.
93 S390 S390 architecture is enabled.
94 SCSI Appropriate SCSI support is enabled.
95 A lot of drivers have their options described inside
96 the Documentation/scsi/ sub-directory.
97 SECURITY Different security models are enabled.
98 SELINUX SELinux support is enabled.
99 APPARMOR AppArmor support is enabled.
100 SERIAL Serial support is enabled.
101 SH SuperH architecture is enabled.
102 SMP The kernel is an SMP kernel.
103 SPARC Sparc architecture is enabled.
104 SWSUSP Software suspend (hibernation) is enabled.
105 SUSPEND System suspend states are enabled.
106 TPM TPM drivers are enabled.
107 TS Appropriate touchscreen support is enabled.
108 UMS USB Mass Storage support is enabled.
109 USB USB support is enabled.
110 USBHID USB Human Interface Device support is enabled.
111 V4L Video For Linux support is enabled.
112 VMMIO Driver for memory mapped virtio devices is enabled.
113 VGA The VGA console has been enabled.
114 VT Virtual terminal support is enabled.
115 WDT Watchdog support is enabled.
116 XT IBM PC/XT MFM hard disk support is enabled.
117 X86-32 X86-32, aka i386 architecture is enabled.
118 X86-64 X86-64 architecture is enabled.
119 More X86-64 boot options can be found in
120 Documentation/x86/x86_64/boot-options.txt .
121 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
122 XEN Xen support is enabled
124 In addition, the following text indicates that the option:
126 BUGS= Relates to possible processor bugs on the said processor.
127 KNL Is a kernel start-up parameter.
128 BOOT Is a boot loader parameter.
130 Parameters denoted with BOOT are actually interpreted by the boot
131 loader, and have no meaning to the kernel directly.
132 Do not modify the syntax of boot loader parameters without extreme
133 need or coordination with <Documentation/x86/boot.txt>.
135 There are also arch-specific kernel-parameters not documented here.
136 See for example <Documentation/x86/x86_64/boot-options.txt>.
138 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
139 a trailing = on the name of any parameter states that that parameter will
140 be entered as an environment variable, whereas its absence indicates that
141 it will appear as a kernel argument readable via /proc/cmdline by programs
142 running once the system is up.
144 The number of kernel parameters is not limited, but the length of the
145 complete command line (parameters including spaces etc.) is limited to
146 a fixed number of characters. This limit depends on the architecture
147 and is between 256 and 4096 characters. It is defined in the file
148 ./include/asm/setup.h as COMMAND_LINE_SIZE.
150 Finally, the [KMG] suffix is commonly described after a number of kernel
151 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
152 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
153 bytes respectively. Such letter suffixes can also be entirely omitted.
156 acpi= [HW,ACPI,X86]
157 Advanced Configuration and Power Interface
158 Format: { force | off | strict | noirq | rsdt }
159 force -- enable ACPI if default was off
160 off -- disable ACPI if default was on
161 noirq -- do not use ACPI for IRQ routing
162 strict -- Be less tolerant of platforms that are not
163 strictly ACPI specification compliant.
164 rsdt -- prefer RSDT over (default) XSDT
165 copy_dsdt -- copy DSDT to memory
167 See also Documentation/power/runtime_pm.txt, pci=noacpi
169 acpi_rsdp= [ACPI,EFI,KEXEC]
170 Pass the RSDP address to the kernel, mostly used
171 on machines running EFI runtime service to boot the
172 second kernel for kdump.
174 acpi_apic_instance= [ACPI, IOAPIC]
175 Format: <int>
176 2: use 2nd APIC table, if available
177 1,0: use 1st APIC table
178 default: 0
180 acpi_backlight= [HW,ACPI]
181 acpi_backlight=vendor
182 acpi_backlight=video
183 If set to vendor, prefer vendor specific driver
184 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
185 of the ACPI video.ko driver.
187 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
188 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
189 Format: <int>
190 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
191 debug output. Bits in debug_layer correspond to a
192 _COMPONENT in an ACPI source file, e.g.,
193 #define _COMPONENT ACPI_PCI_COMPONENT
194 Bits in debug_level correspond to a level in
195 ACPI_DEBUG_PRINT statements, e.g.,
196 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
197 The debug_level mask defaults to "info". See
198 Documentation/acpi/debug.txt for more information about
199 debug layers and levels.
201 Enable processor driver info messages:
202 acpi.debug_layer=0x20000000
203 Enable PCI/PCI interrupt routing info messages:
204 acpi.debug_layer=0x400000
205 Enable AML "Debug" output, i.e., stores to the Debug
206 object while interpreting AML:
207 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
208 Enable all messages related to ACPI hardware:
209 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
211 Some values produce so much output that the system is
212 unusable. The "log_buf_len" parameter may be useful
213 if you need to capture more output.
215 acpi_irq_balance [HW,ACPI]
216 ACPI will balance active IRQs
217 default in APIC mode
219 acpi_irq_nobalance [HW,ACPI]
220 ACPI will not move active IRQs (default)
221 default in PIC mode
223 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
224 Format: <irq>,<irq>...
226 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
227 use by PCI
228 Format: <irq>,<irq>...
230 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
232 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
233 Format: To spoof as Windows 98: ="Microsoft Windows"
235 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
236 acpi_osi="string1" # add string1 -- only one string
237 acpi_osi="!string2" # remove built-in string2
238 acpi_osi= # disable all strings
240 acpi_pm_good [X86]
241 Override the pmtimer bug detection: force the kernel
242 to assume that this machine's pmtimer latches its value
243 and always returns good values.
245 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
246 Format: { level | edge | high | low }
248 acpi_serialize [HW,ACPI] force serialization of AML methods
250 acpi_skip_timer_override [HW,ACPI]
251 Recognize and ignore IRQ0/pin2 Interrupt Override.
252 For broken nForce2 BIOS resulting in XT-PIC timer.
254 acpi_sleep= [HW,ACPI] Sleep options
255 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
256 old_ordering, nonvs, sci_force_enable }
257 See Documentation/power/video.txt for information on
258 s3_bios and s3_mode.
259 s3_beep is for debugging; it makes the PC's speaker beep
260 as soon as the kernel's real-mode entry point is called.
261 s4_nohwsig prevents ACPI hardware signature from being
262 used during resume from hibernation.
263 old_ordering causes the ACPI 1.0 ordering of the _PTS
264 control method, with respect to putting devices into
265 low power states, to be enforced (the ACPI 2.0 ordering
266 of _PTS is used by default).
267 nonvs prevents the kernel from saving/restoring the
268 ACPI NVS memory during suspend/hibernation and resume.
269 sci_force_enable causes the kernel to set SCI_EN directly
270 on resume from S1/S3 (which is against the ACPI spec,
271 but some broken systems don't work without it).
273 acpi_use_timer_override [HW,ACPI]
274 Use timer override. For some broken Nvidia NF5 boards
275 that require a timer override, but don't have HPET
277 acpi_enforce_resources= [ACPI]
278 { strict | lax | no }
279 Check for resource conflicts between native drivers
280 and ACPI OperationRegions (SystemIO and SystemMemory
281 only). IO ports and memory declared in ACPI might be
282 used by the ACPI subsystem in arbitrary AML code and
283 can interfere with legacy drivers.
284 strict (default): access to resources claimed by ACPI
285 is denied; legacy drivers trying to access reserved
286 resources will fail to bind to device using them.
287 lax: access to resources claimed by ACPI is allowed;
288 legacy drivers trying to access reserved resources
289 will bind successfully but a warning message is logged.
290 no: ACPI OperationRegions are not marked as reserved,
291 no further checks are performed.
293 add_efi_memmap [EFI; X86] Include EFI memory map in
294 kernel's map of available physical RAM.
296 agp= [AGP]
297 { off | try_unsupported }
298 off: disable AGP support
299 try_unsupported: try to drive unsupported chipsets
300 (may crash computer or cause data corruption)
302 ALSA [HW,ALSA]
303 See Documentation/sound/alsa/alsa-parameters.txt
305 alignment= [KNL,ARM]
306 Allow the default userspace alignment fault handler
307 behaviour to be specified. Bit 0 enables warnings,
308 bit 1 enables fixups, and bit 2 sends a segfault.
310 align_va_addr= [X86-64]
311 Align virtual addresses by clearing slice [14:12] when
312 allocating a VMA at process creation time. This option
313 gives you up to 3% performance improvement on AMD F15h
314 machines (where it is enabled by default) for a
315 CPU-intensive style benchmark, and it can vary highly in
316 a microbenchmark depending on workload and compiler.
318 32: only for 32-bit processes
319 64: only for 64-bit processes
320 on: enable for both 32- and 64-bit processes
321 off: disable for both 32- and 64-bit processes
323 amd_iommu= [HW,X86-64]
324 Pass parameters to the AMD IOMMU driver in the system.
325 Possible values are:
326 fullflush - enable flushing of IO/TLB entries when
327 they are unmapped. Otherwise they are
328 flushed before they will be reused, which
329 is a lot of faster
330 off - do not initialize any AMD IOMMU found in
331 the system
332 force_isolation - Force device isolation for all
333 devices. The IOMMU driver is not
334 allowed anymore to lift isolation
335 requirements as needed. This option
336 does not override iommu=pt
338 amijoy.map= [HW,JOY] Amiga joystick support
339 Map of devices attached to JOY0DAT and JOY1DAT
340 Format: <a>,<b>
341 See also Documentation/input/joystick.txt
343 analog.map= [HW,JOY] Analog joystick and gamepad support
344 Specifies type or capabilities of an analog joystick
345 connected to one of 16 gameports
346 Format: <type1>,<type2>,..<type16>
348 apc= [HW,SPARC]
349 Power management functions (SPARCstation-4/5 + deriv.)
350 Format: noidle
351 Disable APC CPU standby support. SPARCstation-Fox does
352 not play well with APC CPU idle - disable it if you have
353 APC and your system crashes randomly.
355 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
356 Change the output verbosity whilst booting
357 Format: { quiet (default) | verbose | debug }
358 Change the amount of debugging information output
359 when initialising the APIC and IO-APIC components.
361 autoconf= [IPV6]
362 See Documentation/networking/ipv6.txt.
364 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
365 Limit apic dumping. The parameter defines the maximal
366 number of local apics being dumped. Also it is possible
367 to set it to "all" by meaning -- no limit here.
368 Format: { 1 (default) | 2 | ... | all }.
369 The parameter valid if only apic=debug or
370 apic=verbose is specified.
371 Example: apic=debug show_lapic=all
373 apm= [APM] Advanced Power Management
374 See header of arch/x86/kernel/apm_32.c.
376 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
377 Format: <io>,<irq>,<nodeID>
379 ataflop= [HW,M68k]
381 atarimouse= [HW,MOUSE] Atari Mouse
383 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
384 EzKey and similar keyboards
386 atkbd.reset= [HW] Reset keyboard during initialization
388 atkbd.set= [HW] Select keyboard code set
389 Format: <int> (2 = AT (default), 3 = PS/2)
391 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
392 keyboards
394 atkbd.softraw= [HW] Choose between synthetic and real raw mode
395 Format: <bool> (0 = real, 1 = synthetic (default))
397 atkbd.softrepeat= [HW]
398 Use software keyboard repeat
400 autotest [IA-64]
402 baycom_epp= [HW,AX25]
403 Format: <io>,<mode>
405 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
406 Format: <io>,<mode>
407 See header of drivers/net/hamradio/baycom_par.c.
409 baycom_ser_fdx= [HW,AX25]
410 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
411 Format: <io>,<irq>,<mode>[,<baud>]
412 See header of drivers/net/hamradio/baycom_ser_fdx.c.
414 baycom_ser_hdx= [HW,AX25]
415 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
416 Format: <io>,<irq>,<mode>
417 See header of drivers/net/hamradio/baycom_ser_hdx.c.
419 boot_delay= Milliseconds to delay each printk during boot.
420 Values larger than 10 seconds (10000) are changed to
421 no delay (0).
422 Format: integer
424 bootmem_debug [KNL] Enable bootmem allocator debug messages.
426 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
427 bttv.radio= Most important insmod options are available as
428 kernel args too.
429 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
430 bttv.tuner=
432 bulk_remove=off [PPC] This parameter disables the use of the pSeries
433 firmware feature for flushing multiple hpte entries
434 at a time.
436 c101= [NET] Moxa C101 synchronous serial card
438 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
439 Sometimes CPU hardware bugs make them report the cache
440 size incorrectly. The kernel will attempt work arounds
441 to fix known problems, but for some CPUs it is not
442 possible to determine what the correct size should be.
443 This option provides an override for these situations.
445 capability.disable=
446 [SECURITY] Disable capabilities. This would normally
447 be used only if an alternative security model is to be
448 configured. Potentially dangerous and should only be
449 used if you are entirely sure of the consequences.
451 ccw_timeout_log [S390]
452 See Documentation/s390/CommonIO for details.
454 cgroup_disable= [KNL] Disable a particular controller
455 Format: {name of the controller(s) to disable}
456 {Currently supported controllers - "memory"}
458 checkreqprot [SELINUX] Set initial checkreqprot flag value.
459 Format: { "0" | "1" }
460 See security/selinux/Kconfig help text.
461 0 -- check protection applied by kernel (includes
462 any implied execute protection).
463 1 -- check protection requested by application.
464 Default value is set via a kernel config option.
465 Value can be changed at runtime via
466 /selinux/checkreqprot.
468 cio_ignore= [S390]
469 See Documentation/s390/CommonIO for details.
471 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
472 [Deprecated]
473 Forces specified clocksource (if available) to be used
474 when calculating gettimeofday(). If specified
475 clocksource is not available, it defaults to PIT.
476 Format: { pit | tsc | cyclone | pmtmr }
478 clocksource= Override the default clocksource
479 Format: <string>
480 Override the default clocksource and use the clocksource
481 with the name specified.
482 Some clocksource names to choose from, depending on
483 the platform:
484 [all] jiffies (this is the base, fallback clocksource)
485 [ACPI] acpi_pm
486 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
487 pxa_timer,timer3,32k_counter,timer0_1
488 [AVR32] avr32
489 [X86-32] pit,hpet,tsc;
490 scx200_hrt on Geode; cyclone on IBM x440
491 [MIPS] MIPS
492 [PARISC] cr16
493 [S390] tod
494 [SH] SuperH
495 [SPARC64] tick
496 [X86-64] hpet,tsc
498 clearcpuid=BITNUM [X86]
499 Disable CPUID feature X for the kernel. See
500 arch/x86/include/asm/cpufeature.h for the valid bit
501 numbers. Note the Linux specific bits are not necessarily
502 stable over kernel options, but the vendor specific
503 ones should be.
504 Also note that user programs calling CPUID directly
505 or using the feature without checking anything
506 will still see it. This just prevents it from
507 being used by the kernel or shown in /proc/cpuinfo.
508 Also note the kernel might malfunction if you disable
509 some critical bits.
511 cmo_free_hint= [PPC] Format: { yes | no }
512 Specify whether pages are marked as being inactive
513 when they are freed. This is used in CMO environments
514 to determine OS memory pressure for page stealing by
515 a hypervisor.
516 Default: yes
518 code_bytes [X86] How many bytes of object code to print
519 in an oops report.
520 Range: 0 - 8192
521 Default: 64
523 com20020= [HW,NET] ARCnet - COM20020 chipset
524 Format:
525 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
527 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
528 Format: <io>[,<irq>]
530 com90xx= [HW,NET]
531 ARCnet - COM90xx chipset (memory-mapped buffers)
532 Format: <io>[,<irq>[,<memstart>]]
534 condev= [HW,S390] console device
535 conmode=
537 console= [KNL] Output console device and options.
539 tty<n> Use the virtual console device <n>.
541 ttyS<n>[,options]
542 ttyUSB0[,options]
543 Use the specified serial port. The options are of
544 the form "bbbbpnf", where "bbbb" is the baud rate,
545 "p" is parity ("n", "o", or "e"), "n" is number of
546 bits, and "f" is flow control ("r" for RTS or
547 omit it). Default is "9600n8".
549 See Documentation/serial-console.txt for more
550 information. See
551 Documentation/networking/netconsole.txt for an
552 alternative.
554 uart[8250],io,<addr>[,options]
555 uart[8250],mmio,<addr>[,options]
556 Start an early, polled-mode console on the 8250/16550
557 UART at the specified I/O port or MMIO address,
558 switching to the matching ttyS device later. The
559 options are the same as for ttyS, above.
561 If the device connected to the port is not a TTY but a braille
562 device, prepend "brl," before the device type, for instance
563 console=brl,ttyS0
564 For now, only VisioBraille is supported.
566 consoleblank= [KNL] The console blank (screen saver) timeout in
567 seconds. Defaults to 10*60 = 10mins. A value of 0
568 disables the blank timer.
570 coredump_filter=
571 [KNL] Change the default value for
572 /proc/<pid>/coredump_filter.
573 See also Documentation/filesystems/proc.txt.
575 cpuidle.off=1 [CPU_IDLE]
576 disable the cpuidle sub-system
578 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
579 Format:
580 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
582 crashkernel=size[KMG][@offset[KMG]]
583 [KNL] Using kexec, Linux can switch to a 'crash kernel'
584 upon panic. This parameter reserves the physical
585 memory region [offset, offset + size] for that kernel
586 image. If '@offset' is omitted, then a suitable offset
587 is selected automatically. Check
588 Documentation/kdump/kdump.txt for further details.
590 crashkernel=range1:size1[,range2:size2,...][@offset]
591 [KNL] Same as above, but depends on the memory
592 in the running system. The syntax of range is
593 start-[end] where start and end are both
594 a memory unit (amount[KMG]). See also
595 Documentation/kdump/kdump.txt for an example.
597 cs89x0_dma= [HW,NET]
598 Format: <dma>
600 cs89x0_media= [HW,NET]
601 Format: { rj45 | aui | bnc }
603 dasd= [HW,NET]
604 See header of drivers/s390/block/dasd_devmap.c.
606 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
607 (one device per port)
608 Format: <port#>,<type>
609 See also Documentation/input/joystick-parport.txt
611 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
612 time. See Documentation/dynamic-debug-howto.txt for
613 details. Deprecated, see dyndbg.
615 debug [KNL] Enable kernel debugging (events log level).
617 debug_locks_verbose=
618 [KNL] verbose self-tests
619 Format=<0|1>
620 Print debugging info while doing the locking API
621 self-tests.
622 We default to 0 (no extra messages), setting it to
623 1 will print _a lot_ more information - normally
624 only useful to kernel developers.
626 debug_objects [KNL] Enable object debugging
628 no_debug_objects
629 [KNL] Disable object debugging
631 debug_guardpage_minorder=
632 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
633 parameter allows control of the order of pages that will
634 be intentionally kept free (and hence protected) by the
635 buddy allocator. Bigger value increase the probability
636 of catching random memory corruption, but reduce the
637 amount of memory for normal system use. The maximum
638 possible value is MAX_ORDER/2. Setting this parameter
639 to 1 or 2 should be enough to identify most random
640 memory corruption problems caused by bugs in kernel or
641 driver code when a CPU writes to (or reads from) a
642 random memory location. Note that there exists a class
643 of memory corruptions problems caused by buggy H/W or
644 F/W or by drivers badly programing DMA (basically when
645 memory is written at bus level and the CPU MMU is
646 bypassed) which are not detectable by
647 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
648 tracking down these problems.
650 debugpat [X86] Enable PAT debugging
652 decnet.addr= [HW,NET]
653 Format: <area>[,<node>]
654 See also Documentation/networking/decnet.txt.
656 default_hugepagesz=
657 [same as hugepagesz=] The size of the default
658 HugeTLB page size. This is the size represented by
659 the legacy /proc/ hugepages APIs, used for SHM, and
660 default size when mounting hugetlbfs filesystems.
661 Defaults to the default architecture's huge page size
662 if not specified.
664 dhash_entries= [KNL]
665 Set number of hash buckets for dentry cache.
667 digi= [HW,SERIAL]
668 IO parameters + enable/disable command.
670 digiepca= [HW,SERIAL]
671 See drivers/char/README.epca and
672 Documentation/serial/digiepca.txt.
674 disable= [IPV6]
675 See Documentation/networking/ipv6.txt.
677 disable_ddw [PPC/PSERIES]
678 Disable Dynamic DMA Window support. Use this if
679 to workaround buggy firmware.
681 disable_ipv6= [IPV6]
682 See Documentation/networking/ipv6.txt.
684 disable_mtrr_cleanup [X86]
685 The kernel tries to adjust MTRR layout from continuous
686 to discrete, to make X server driver able to add WB
687 entry later. This parameter disables that.
689 disable_mtrr_trim [X86, Intel and AMD only]
690 By default the kernel will trim any uncacheable
691 memory out of your available memory pool based on
692 MTRR settings. This parameter disables that behavior,
693 possibly causing your machine to run very slowly.
695 disable_timer_pin_1 [X86]
696 Disable PIN 1 of APIC timer
697 Can be useful to work around chipset bugs.
699 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
700 this option disables the debugging code at boot.
702 dma_debug_entries=<number>
703 This option allows to tune the number of preallocated
704 entries for DMA-API debugging code. One entry is
705 required per DMA-API allocation. Use this if the
706 DMA-API debugging code disables itself because the
707 architectural default is too low.
709 dma_debug_driver=<driver_name>
710 With this option the DMA-API debugging driver
711 filter feature can be enabled at boot time. Just
712 pass the driver to filter for as the parameter.
713 The filter can be disabled or changed to another
714 driver later using sysfs.
716 drm_kms_helper.edid_firmware=[<connector>:]<file>
717 Broken monitors, graphic adapters and KVMs may
718 send no or incorrect EDID data sets. This parameter
719 allows to specify an EDID data set in the
720 /lib/firmware directory that is used instead.
721 Generic built-in EDID data sets are used, if one of
722 edid/1024x768.bin, edid/1280x1024.bin,
723 edid/1680x1050.bin, or edid/1920x1080.bin is given
724 and no file with the same name exists. Details and
725 instructions how to build your own EDID data are
726 available in Documentation/EDID/HOWTO.txt. An EDID
727 data set will only be used for a particular connector,
728 if its name and a colon are prepended to the EDID
729 name.
731 dscc4.setup= [NET]
733 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
734 module.dyndbg[="val"]
735 Enable debug messages at boot time. See
736 Documentation/dynamic-debug-howto.txt for details.
738 earlycon= [KNL] Output early console device and options.
739 uart[8250],io,<addr>[,options]
740 uart[8250],mmio,<addr>[,options]
741 uart[8250],mmio32,<addr>[,options]
742 Start an early, polled-mode console on the 8250/16550
743 UART at the specified I/O port or MMIO address.
744 MMIO inter-register address stride is either 8-bit
745 (mmio) or 32-bit (mmio32).
746 The options are the same as for ttyS, above.
748 earlyprintk= [X86,SH,BLACKFIN]
749 earlyprintk=vga
750 earlyprintk=serial[,ttySn[,baudrate]]
751 earlyprintk=ttySn[,baudrate]
752 earlyprintk=dbgp[debugController#]
754 Append ",keep" to not disable it when the real console
755 takes over.
757 Only vga or serial or usb debug port at a time.
759 Currently only ttyS0 and ttyS1 are supported.
761 Interaction with the standard serial driver is not
762 very good.
764 The VGA output is eventually overwritten by the real
765 console.
767 ekgdboc= [X86,KGDB] Allow early kernel console debugging
768 ekgdboc=kbd
770 This is designed to be used in conjunction with
771 the boot argument: earlyprintk=vga
773 edd= [EDD]
774 Format: {"off" | "on" | "skip[mbr]"}
776 eisa_irq_edge= [PARISC,HW]
777 See header of drivers/parisc/eisa.c.
779 elanfreq= [X86-32]
780 See comment before function elanfreq_setup() in
781 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
783 elevator= [IOSCHED]
784 Format: {"cfq" | "deadline" | "noop"}
785 See Documentation/block/cfq-iosched.txt and
786 Documentation/block/deadline-iosched.txt for details.
788 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
789 Specifies physical address of start of kernel core
790 image elf header and optionally the size. Generally
791 kexec loader will pass this option to capture kernel.
792 See Documentation/kdump/kdump.txt for details.
794 enable_mtrr_cleanup [X86]
795 The kernel tries to adjust MTRR layout from continuous
796 to discrete, to make X server driver able to add WB
797 entry later. This parameter enables that.
799 enable_timer_pin_1 [X86]
800 Enable PIN 1 of APIC timer
801 Can be useful to work around chipset bugs
802 (in particular on some ATI chipsets).
803 The kernel tries to set a reasonable default.
805 enforcing [SELINUX] Set initial enforcing status.
806 Format: {"0" | "1"}
807 See security/selinux/Kconfig help text.
808 0 -- permissive (log only, no denials).
809 1 -- enforcing (deny and log).
810 Default value is 0.
811 Value can be changed at runtime via /selinux/enforce.
813 erst_disable [ACPI]
814 Disable Error Record Serialization Table (ERST)
815 support.
817 ether= [HW,NET] Ethernet cards parameters
818 This option is obsoleted by the "netdev=" option, which
819 has equivalent usage. See its documentation for details.
821 evm= [EVM]
822 Format: { "fix" }
823 Permit 'security.evm' to be updated regardless of
824 current integrity status.
826 failslab=
827 fail_page_alloc=
828 fail_make_request=[KNL]
829 General fault injection mechanism.
830 Format: <interval>,<probability>,<space>,<times>
831 See also Documentation/fault-injection/.
833 floppy= [HW]
834 See Documentation/blockdev/floppy.txt.
836 force_pal_cache_flush
837 [IA-64] Avoid check_sal_cache_flush which may hang on
838 buggy SAL_CACHE_FLUSH implementations. Using this
839 parameter will force ia64_sal_cache_flush to call
840 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
842 ftrace=[tracer]
843 [FTRACE] will set and start the specified tracer
844 as early as possible in order to facilitate early
845 boot debugging.
847 ftrace_dump_on_oops[=orig_cpu]
848 [FTRACE] will dump the trace buffers on oops.
849 If no parameter is passed, ftrace will dump
850 buffers of all CPUs, but if you pass orig_cpu, it will
851 dump only the buffer of the CPU that triggered the
852 oops.
854 ftrace_filter=[function-list]
855 [FTRACE] Limit the functions traced by the function
856 tracer at boot up. function-list is a comma separated
857 list of functions. This list can be changed at run
858 time by the set_ftrace_filter file in the debugfs
859 tracing directory.
861 ftrace_notrace=[function-list]
862 [FTRACE] Do not trace the functions specified in
863 function-list. This list can be changed at run time
864 by the set_ftrace_notrace file in the debugfs
865 tracing directory.
867 ftrace_graph_filter=[function-list]
868 [FTRACE] Limit the top level callers functions traced
869 by the function graph tracer at boot up.
870 function-list is a comma separated list of functions
871 that can be changed at run time by the
872 set_graph_function file in the debugfs tracing directory.
874 gamecon.map[2|3]=
875 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
876 support via parallel port (up to 5 devices per port)
877 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
878 See also Documentation/input/joystick-parport.txt
880 gamma= [HW,DRM]
882 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
883 Format: off | on
884 default: on
886 gcov_persist= [GCOV] When non-zero (default), profiling data for
887 kernel modules is saved and remains accessible via
888 debugfs, even when the module is unloaded/reloaded.
889 When zero, profiling data is discarded and associated
890 debugfs files are removed at module unload time.
892 gpt [EFI] Forces disk with valid GPT signature but
893 invalid Protective MBR to be treated as GPT.
895 hashdist= [KNL,NUMA] Large hashes allocated during boot
896 are distributed across NUMA nodes. Defaults on
897 for 64-bit NUMA, off otherwise.
898 Format: 0 | 1 (for off | on)
900 hcl= [IA-64] SGI's Hardware Graph compatibility layer
902 hd= [EIDE] (E)IDE hard drive subsystem geometry
903 Format: <cyl>,<head>,<sect>
905 hest_disable [ACPI]
906 Disable Hardware Error Source Table (HEST) support;
907 corresponding firmware-first mode error processing
908 logic will be disabled.
910 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
911 size of <nn>. This works even on boxes that have no
912 highmem otherwise. This also works to reduce highmem
913 size on bigger boxes.
915 highres= [KNL] Enable/disable high resolution timer mode.
916 Valid parameters: "on", "off"
917 Default: "on"
919 hisax= [HW,ISDN]
920 See Documentation/isdn/README.HiSax.
922 hlt [BUGS=ARM,SH]
924 hpet= [X86-32,HPET] option to control HPET usage
925 Format: { enable (default) | disable | force |
926 verbose }
927 disable: disable HPET and use PIT instead
928 force: allow force enabled of undocumented chips (ICH4,
929 VIA, nVidia)
930 verbose: show contents of HPET registers during setup
932 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
933 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
934 On x86-64 and powerpc, this option can be specified
935 multiple times interleaved with hugepages= to reserve
936 huge pages of different sizes. Valid pages sizes on
937 x86-64 are 2M (when the CPU supports "pse") and 1G
938 (when the CPU supports the "pdpe1gb" cpuinfo flag)
939 Note that 1GB pages can only be allocated at boot time
940 using hugepages= and not freed afterwards.
942 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
943 terminal devices. Valid values: 0..8
944 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
945 If specified, z/VM IUCV HVC accepts connections
946 from listed z/VM user IDs only.
948 keep_bootcon [KNL]
949 Do not unregister boot console at start. This is only
950 useful for debugging when something happens in the window
951 between unregistering the boot console and initializing
952 the real console.
954 i2c_bus= [HW] Override the default board specific I2C bus speed
955 or register an additional I2C bus that is not
956 registered from board initialization code.
957 Format:
958 <bus_id>,<clkrate>
960 i8042.debug [HW] Toggle i8042 debug mode
961 i8042.direct [HW] Put keyboard port into non-translated mode
962 i8042.dumbkbd [HW] Pretend that controller can only read data from
963 keyboard and cannot control its state
964 (Don't attempt to blink the leds)
965 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
966 i8042.nokbd [HW] Don't check/create keyboard port
967 i8042.noloop [HW] Disable the AUX Loopback command while probing
968 for the AUX port
969 i8042.nomux [HW] Don't check presence of an active multiplexing
970 controller
971 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
972 controllers
973 i8042.notimeout [HW] Ignore timeout condition signalled by controller
974 i8042.reset [HW] Reset the controller during init and cleanup
975 i8042.unlock [HW] Unlock (ignore) the keylock
977 i810= [HW,DRM]
979 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
980 indicates that the driver is running on unsupported
981 hardware.
982 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
983 does not match list of supported models.
984 i8k.power_status
985 [HW] Report power status in /proc/i8k
986 (disabled by default)
987 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
988 capability is set.
990 i915.invert_brightness=
991 [DRM] Invert the sense of the variable that is used to
992 set the brightness of the panel backlight. Normally a
993 brightness value of 0 indicates backlight switched off,
994 and the maximum of the brightness value sets the backlight
995 to maximum brightness. If this parameter is set to 0
996 (default) and the machine requires it, or this parameter
997 is set to 1, a brightness value of 0 sets the backlight
998 to maximum brightness, and the maximum of the brightness
999 value switches the backlight off.
1000 -1 -- never invert brightness
1001 0 -- machine default
1002 1 -- force brightness inversion
1004 icn= [HW,ISDN]
1005 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1007 ide-core.nodma= [HW] (E)IDE subsystem
1008 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1009 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1010 .cdrom .chs .ignore_cable are additional options
1011 See Documentation/ide/ide.txt.
1013 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1014 Claim all unknown PCI IDE storage controllers.
1016 idle= [X86]
1017 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
1018 Poll forces a polling idle loop that can slightly
1019 improve the performance of waking up a idle CPU, but
1020 will use a lot of power and make the system run hot.
1021 Not recommended.
1022 idle=mwait: On systems which support MONITOR/MWAIT but
1023 the kernel chose to not use it because it doesn't save
1024 as much power as a normal idle loop, use the
1025 MONITOR/MWAIT idle loop anyways. Performance should be
1026 the same as idle=poll.
1027 idle=halt: Halt is forced to be used for CPU idle.
1028 In such case C2/C3 won't be used again.
1029 idle=nomwait: Disable mwait for CPU C-states
1031 ignore_loglevel [KNL]
1032 Ignore loglevel setting - this will print /all/
1033 kernel messages to the console. Useful for debugging.
1034 We also add it as printk module parameter, so users
1035 could change it dynamically, usually by
1036 /sys/module/printk/parameters/ignore_loglevel.
1038 ihash_entries= [KNL]
1039 Set number of hash buckets for inode cache.
1041 ima_audit= [IMA]
1042 Format: { "0" | "1" }
1043 0 -- integrity auditing messages. (Default)
1044 1 -- enable informational integrity auditing messages.
1046 ima_hash= [IMA]
1047 Format: { "sha1" | "md5" }
1048 default: "sha1"
1050 ima_tcb [IMA]
1051 Load a policy which meets the needs of the Trusted
1052 Computing Base. This means IMA will measure all
1053 programs exec'd, files mmap'd for exec, and all files
1054 opened for read by uid=0.
1056 init= [KNL]
1057 Format: <full_path>
1058 Run specified binary instead of /sbin/init as init
1059 process.
1061 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1062 for working out where the kernel is dying during
1063 startup.
1065 initrd= [BOOT] Specify the location of the initial ramdisk
1067 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1068 Format: <irq>
1070 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1071 on
1072 Enable intel iommu driver.
1073 off
1074 Disable intel iommu driver.
1075 igfx_off [Default Off]
1076 By default, gfx is mapped as normal device. If a gfx
1077 device has a dedicated DMAR unit, the DMAR unit is
1078 bypassed by not enabling DMAR with this option. In
1079 this case, gfx device will use physical address for
1080 DMA.
1081 forcedac [x86_64]
1082 With this option iommu will not optimize to look
1083 for io virtual address below 32-bit forcing dual
1084 address cycle on pci bus for cards supporting greater
1085 than 32-bit addressing. The default is to look
1086 for translation below 32-bit and if not available
1087 then look in the higher range.
1088 strict [Default Off]
1089 With this option on every unmap_single operation will
1090 result in a hardware IOTLB flush operation as opposed
1091 to batching them for performance.
1092 sp_off [Default Off]
1093 By default, super page will be supported if Intel IOMMU
1094 has the capability. With this option, super page will
1095 not be supported.
1097 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1098 0 disables intel_idle and fall back on acpi_idle.
1099 1 to 6 specify maximum depth of C-state.
1101 intremap= [X86-64, Intel-IOMMU]
1102 on enable Interrupt Remapping (default)
1103 off disable Interrupt Remapping
1104 nosid disable Source ID checking
1105 no_x2apic_optout
1106 BIOS x2APIC opt-out request will be ignored
1108 iomem= Disable strict checking of access to MMIO memory
1109 strict regions from userspace.
1110 relaxed
1112 iommu= [x86]
1113 off
1114 force
1115 noforce
1116 biomerge
1117 panic
1118 nopanic
1119 merge
1120 nomerge
1121 forcesac
1122 soft
1123 pt [x86, IA-64]
1124 group_mf [x86, IA-64]
1127 io7= [HW] IO7 for Marvel based alpha systems
1128 See comment before marvel_specify_io7 in
1129 arch/alpha/kernel/core_marvel.c.
1131 io_delay= [X86] I/O delay method
1132 0x80
1133 Standard port 0x80 based delay
1134 0xed
1135 Alternate port 0xed based delay (needed on some systems)
1136 udelay
1137 Simple two microseconds delay
1138 none
1139 No delay
1141 ip= [IP_PNP]
1142 See Documentation/filesystems/nfs/nfsroot.txt.
1144 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1145 See comment before ip2_setup() in
1146 drivers/char/ip2/ip2base.c.
1148 irqfixup [HW]
1149 When an interrupt is not handled search all handlers
1150 for it. Intended to get systems with badly broken
1151 firmware running.
1153 irqpoll [HW]
1154 When an interrupt is not handled search all handlers
1155 for it. Also check all handlers each timer
1156 interrupt. Intended to get systems with badly broken
1157 firmware running.
1159 isapnp= [ISAPNP]
1160 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1162 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1163 Format:
1164 <cpu number>,...,<cpu number>
1165 or
1166 <cpu number>-<cpu number>
1167 (must be a positive range in ascending order)
1168 or a mixture
1169 <cpu number>,...,<cpu number>-<cpu number>
1171 This option can be used to specify one or more CPUs
1172 to isolate from the general SMP balancing and scheduling
1173 algorithms. You can move a process onto or off an
1174 "isolated" CPU via the CPU affinity syscalls or cpuset.
1175 <cpu number> begins at 0 and the maximum value is
1176 "number of CPUs in system - 1".
1178 This option is the preferred way to isolate CPUs. The
1179 alternative -- manually setting the CPU mask of all
1180 tasks in the system -- can cause problems and
1181 suboptimal load balancer performance.
1183 iucv= [HW,NET]
1185 js= [HW,JOY] Analog joystick
1186 See Documentation/input/joystick.txt.
1188 keepinitrd [HW,ARM]
1190 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1191 specifies the amount of memory usable by the kernel
1192 for non-movable allocations. The requested amount is
1193 spread evenly throughout all nodes in the system. The
1194 remaining memory in each node is used for Movable
1195 pages. In the event, a node is too small to have both
1196 kernelcore and Movable pages, kernelcore pages will
1197 take priority and other nodes will have a larger number
1198 of kernelcore pages. The Movable zone is used for the
1199 allocation of pages that may be reclaimed or moved
1200 by the page migration subsystem. This means that
1201 HugeTLB pages may not be allocated from this zone.
1202 Note that allocations like PTEs-from-HighMem still
1203 use the HighMem zone if it exists, and the Normal
1204 zone if it does not.
1206 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1207 Format: <Controller#>[,poll interval]
1208 The controller # is the number of the ehci usb debug
1209 port as it is probed via PCI. The poll interval is
1210 optional and is the number seconds in between
1211 each poll cycle to the debug port in case you need
1212 the functionality for interrupting the kernel with
1213 gdb or control-c on the dbgp connection. When
1214 not using this parameter you use sysrq-g to break into
1215 the kernel debugger.
1217 kgdboc= [KGDB,HW] kgdb over consoles.
1218 Requires a tty driver that supports console polling,
1219 or a supported polling keyboard driver (non-usb).
1220 Serial only format: <serial_device>[,baud]
1221 keyboard only format: kbd
1222 keyboard and serial format: kbd,<serial_device>[,baud]
1223 Optional Kernel mode setting:
1224 kms, kbd format: kms,kbd
1225 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1227 kgdbwait [KGDB] Stop kernel execution and enter the
1228 kernel debugger at the earliest opportunity.
1230 kmac= [MIPS] korina ethernet MAC address.
1231 Configure the RouterBoard 532 series on-chip
1232 Ethernet adapter MAC address.
1234 kmemleak= [KNL] Boot-time kmemleak enable/disable
1235 Valid arguments: on, off
1236 Default: on
1238 kstack=N [X86] Print N words from the kernel stack
1239 in oops dumps.
1241 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1242 Default is 0 (don't ignore, but inject #GP)
1244 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1245 KVM MMU at runtime.
1246 Default is 0 (off)
1248 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1249 Default is 1 (enabled)
1251 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1252 for all guests.
1253 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1255 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1256 (virtualized MMU) support on capable Intel chips.
1257 Default is 1 (enabled)
1259 kvm-intel.emulate_invalid_guest_state=
1260 [KVM,Intel] Enable emulation of invalid guest states
1261 Default is 0 (disabled)
1263 kvm-intel.flexpriority=
1264 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1265 Default is 1 (enabled)
1267 kvm-intel.nested=
1268 [KVM,Intel] Enable VMX nesting (nVMX).
1269 Default is 0 (disabled)
1271 kvm-intel.unrestricted_guest=
1272 [KVM,Intel] Disable unrestricted guest feature
1273 (virtualized real and unpaged mode) on capable
1274 Intel chips. Default is 1 (enabled)
1276 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1277 feature (tagged TLBs) on capable Intel chips.
1278 Default is 1 (enabled)
1280 l2cr= [PPC]
1282 l3cr= [PPC]
1284 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1285 disabled it.
1287 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1288 in C2 power state.
1290 libata.dma= [LIBATA] DMA control
1291 libata.dma=0 Disable all PATA and SATA DMA
1292 libata.dma=1 PATA and SATA Disk DMA only
1293 libata.dma=2 ATAPI (CDROM) DMA only
1294 libata.dma=4 Compact Flash DMA only
1295 Combinations also work, so libata.dma=3 enables DMA
1296 for disks and CDROMs, but not CFs.
1298 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1299 libata.ignore_hpa=0 keep BIOS limits (default)
1300 libata.ignore_hpa=1 ignore limits, using full disk
1302 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1303 when set.
1304 Format: <int>
1306 libata.force= [LIBATA] Force configurations. The format is comma
1307 separated list of "[ID:]VAL" where ID is
1308 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1309 matching port, link or device. Basically, it matches
1310 the ATA ID string printed on console by libata. If
1311 the whole ID part is omitted, the last PORT and DEVICE
1312 values are used. If ID hasn't been specified yet, the
1313 configuration applies to all ports, links and devices.
1315 If only DEVICE is omitted, the parameter applies to
1316 the port and all links and devices behind it. DEVICE
1317 number of 0 either selects the first device or the
1318 first fan-out link behind PMP device. It does not
1319 select the host link. DEVICE number of 15 selects the
1320 host link and device attached to it.
1322 The VAL specifies the configuration to force. As long
1323 as there's no ambiguity shortcut notation is allowed.
1324 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1325 The following configurations can be forced.
1327 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1328 Any ID with matching PORT is used.
1330 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1332 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1333 udma[/][16,25,33,44,66,100,133] notation is also
1334 allowed.
1336 * [no]ncq: Turn on or off NCQ.
1338 * nohrst, nosrst, norst: suppress hard, soft
1339 and both resets.
1341 * dump_id: dump IDENTIFY data.
1343 If there are multiple matching configurations changing
1344 the same attribute, the last one is used.
1346 memblock=debug [KNL] Enable memblock debug messages.
1348 load_ramdisk= [RAM] List of ramdisks to load from floppy
1349 See Documentation/blockdev/ramdisk.txt.
1351 lockd.nlm_grace_period=P [NFS] Assign grace period.
1352 Format: <integer>
1354 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1355 Format: <integer>
1357 lockd.nlm_timeout=T [NFS] Assign timeout value.
1358 Format: <integer>
1360 lockd.nlm_udpport=M [NFS] Assign UDP port.
1361 Format: <integer>
1363 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1364 Format: <irq>
1366 loglevel= All Kernel Messages with a loglevel smaller than the
1367 console loglevel will be printed to the console. It can
1368 also be changed with klogd or other programs. The
1369 loglevels are defined as follows:
1371 0 (KERN_EMERG) system is unusable
1372 1 (KERN_ALERT) action must be taken immediately
1373 2 (KERN_CRIT) critical conditions
1374 3 (KERN_ERR) error conditions
1375 4 (KERN_WARNING) warning conditions
1376 5 (KERN_NOTICE) normal but significant condition
1377 6 (KERN_INFO) informational
1378 7 (KERN_DEBUG) debug-level messages
1380 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1381 in bytes. n must be a power of two. The default
1382 size is set in the kernel config file.
1384 logo.nologo [FB] Disables display of the built-in Linux logo.
1385 This may be used to provide more screen space for
1386 kernel log messages and is useful when debugging
1387 kernel boot problems.
1389 lp=0 [LP] Specify parallel ports to use, e.g,
1390 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1391 lp=reset first parallel port). 'lp=0' disables the
1392 lp=auto printer driver. 'lp=reset' (which can be
1393 specified in addition to the ports) causes
1394 attached printers to be reset. Using
1395 lp=port1,port2,... specifies the parallel ports
1396 to associate lp devices with, starting with
1397 lp0. A port specification may be 'none' to skip
1398 that lp device, or a parport name such as
1399 'parport0'. Specifying 'lp=auto' instead of a
1400 port specification list means that device IDs
1401 from each port should be examined, to see if
1402 an IEEE 1284-compliant printer is attached; if
1403 so, the driver will manage that printer.
1404 See also header of drivers/char/lp.c.
1406 lpj=n [KNL]
1407 Sets loops_per_jiffy to given constant, thus avoiding
1408 time-consuming boot-time autodetection (up to 250 ms per
1409 CPU). 0 enables autodetection (default). To determine
1410 the correct value for your kernel, boot with normal
1411 autodetection and see what value is printed. Note that
1412 on SMP systems the preset will be applied to all CPUs,
1413 which is likely to cause problems if your CPUs need
1414 significantly divergent settings. An incorrect value
1415 will cause delays in the kernel to be wrong, leading to
1416 unpredictable I/O errors and other breakage. Although
1417 unlikely, in the extreme case this might damage your
1418 hardware.
1420 ltpc= [NET]
1421 Format: <io>,<irq>,<dma>
1423 machvec= [IA-64] Force the use of a particular machine-vector
1424 (machvec) in a generic kernel.
1425 Example: machvec=hpzx1_swiotlb
1427 machtype= [Loongson] Share the same kernel image file between different
1428 yeeloong laptop.
1429 Example: machtype=lemote-yeeloong-2f-7inch
1431 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1432 than or equal to this physical address is ignored.
1434 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1435 should make use of. maxcpus=n : n >= 0 limits the
1436 kernel to using 'n' processors. n=0 is a special case,
1437 it is equivalent to "nosmp", which also disables
1438 the IO APIC.
1440 max_loop= [LOOP] The number of loop block devices that get
1441 (loop.max_loop) unconditionally pre-created at init time. The default
1442 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1443 of statically allocating a predefined number, loop
1444 devices can be requested on-demand with the
1445 /dev/loop-control interface.
1447 mcatest= [IA-64]
1449 mce [X86-32] Machine Check Exception
1451 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1453 md= [HW] RAID subsystems devices and level
1454 See Documentation/md.txt.
1456 mdacon= [MDA]
1457 Format: <first>,<last>
1458 Specifies range of consoles to be captured by the MDA.
1460 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1461 Amount of memory to be used when the kernel is not able
1462 to see the whole system memory or for test.
1463 [X86-32] Use together with memmap= to avoid physical
1464 address space collisions. Without memmap= PCI devices
1465 could be placed at addresses belonging to unused RAM.
1467 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1468 memory.
1470 memchunk=nn[KMG]
1471 [KNL,SH] Allow user to override the default size for
1472 per-device physically contiguous DMA buffers.
1474 memmap=exactmap [KNL,X86] Enable setting of an exact
1475 E820 memory map, as specified by the user.
1476 Such memmap=exactmap lines can be constructed based on
1477 BIOS output or other requirements. See the memmap=nn@ss
1478 option description.
1480 memmap=nn[KMG]@ss[KMG]
1481 [KNL] Force usage of a specific region of memory
1482 Region of memory to be used, from ss to ss+nn.
1484 memmap=nn[KMG]#ss[KMG]
1485 [KNL,ACPI] Mark specific memory as ACPI data.
1486 Region of memory to be used, from ss to ss+nn.
1488 memmap=nn[KMG]$ss[KMG]
1489 [KNL,ACPI] Mark specific memory as reserved.
1490 Region of memory to be used, from ss to ss+nn.
1491 Example: Exclude memory from 0x18690000-0x1869ffff
1492 memmap=64K$0x18690000
1493 or
1494 memmap=0x10000$0x18690000
1496 memory_corruption_check=0/1 [X86]
1497 Some BIOSes seem to corrupt the first 64k of
1498 memory when doing things like suspend/resume.
1499 Setting this option will scan the memory
1500 looking for corruption. Enabling this will
1501 both detect corruption and prevent the kernel
1502 from using the memory being corrupted.
1503 However, its intended as a diagnostic tool; if
1504 repeatable BIOS-originated corruption always
1505 affects the same memory, you can use memmap=
1506 to prevent the kernel from using that memory.
1508 memory_corruption_check_size=size [X86]
1509 By default it checks for corruption in the low
1510 64k, making this memory unavailable for normal
1511 use. Use this parameter to scan for
1512 corruption in more or less memory.
1514 memory_corruption_check_period=seconds [X86]
1515 By default it checks for corruption every 60
1516 seconds. Use this parameter to check at some
1517 other rate. 0 disables periodic checking.
1519 memtest= [KNL,X86] Enable memtest
1520 Format: <integer>
1521 default : 0 <disable>
1522 Specifies the number of memtest passes to be
1523 performed. Each pass selects another test
1524 pattern from a given set of patterns. Memtest
1525 fills the memory with this pattern, validates
1526 memory contents and reserves bad memory
1527 regions that are detected.
1529 meye.*= [HW] Set MotionEye Camera parameters
1530 See Documentation/video4linux/meye.txt.
1532 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1533 Multi-Function General Purpose Timers on AMD Geode
1534 platforms.
1536 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1537 the BIOS has incorrectly applied a workaround. TinyBIOS
1538 version 0.98 is known to be affected, 0.99 fixes the
1539 problem by letting the user disable the workaround.
1541 mga= [HW,DRM]
1543 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1544 physical address is ignored.
1546 mini2440= [ARM,HW,KNL]
1547 Format:[0..2][b][c][t]
1548 Default: "0tb"
1549 MINI2440 configuration specification:
1550 0 - The attached screen is the 3.5" TFT
1551 1 - The attached screen is the 7" TFT
1552 2 - The VGA Shield is attached (1024x768)
1553 Leaving out the screen size parameter will not load
1554 the TFT driver, and the framebuffer will be left
1555 unconfigured.
1556 b - Enable backlight. The TFT backlight pin will be
1557 linked to the kernel VESA blanking code and a GPIO
1558 LED. This parameter is not necessary when using the
1559 VGA shield.
1560 c - Enable the s3c camera interface.
1561 t - Reserved for enabling touchscreen support. The
1562 touchscreen support is not enabled in the mainstream
1563 kernel as of 2.6.30, a preliminary port can be found
1564 in the "bleeding edge" mini2440 support kernel at
1565 http://repo.or.cz/w/linux-2.6/mini2440.git
1567 mminit_loglevel=
1568 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1569 parameter allows control of the logging verbosity for
1570 the additional memory initialisation checks. A value
1571 of 0 disables mminit logging and a level of 4 will
1572 log everything. Information is printed at KERN_DEBUG
1573 so loglevel=8 may also need to be specified.
1575 mousedev.tap_time=
1576 [MOUSE] Maximum time between finger touching and
1577 leaving touchpad surface for touch to be considered
1578 a tap and be reported as a left button click (for
1579 touchpads working in absolute mode only).
1580 Format: <msecs>
1581 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1582 reporting absolute coordinates, such as tablets
1583 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1584 reporting absolute coordinates, such as tablets
1586 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1587 is similar to kernelcore except it specifies the
1588 amount of memory used for migratable allocations.
1589 If both kernelcore and movablecore is specified,
1590 then kernelcore will be at *least* the specified
1591 value but may be more. If movablecore on its own
1592 is specified, the administrator must be careful
1593 that the amount of memory usable for all allocations
1594 is not too small.
1596 MTD_Partition= [MTD]
1597 Format: <name>,<region-number>,<size>,<offset>
1599 MTD_Region= [MTD] Format:
1600 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1602 mtdparts= [MTD]
1603 See drivers/mtd/cmdlinepart.c.
1605 multitce=off [PPC] This parameter disables the use of the pSeries
1606 firmware feature for updating multiple TCE entries
1607 at a time.
1609 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1611 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1613 boundary - index of last SLC block on Flex-OneNAND.
1614 The remaining blocks are configured as MLC blocks.
1615 lock - Configure if Flex-OneNAND boundary should be locked.
1616 Once locked, the boundary cannot be changed.
1617 1 indicates lock status, 0 indicates unlock status.
1619 mtdset= [ARM]
1620 ARM/S3C2412 JIVE boot control
1622 See arch/arm/mach-s3c2412/mach-jive.c
1624 mtouchusb.raw_coordinates=
1625 [HW] Make the MicroTouch USB driver use raw coordinates
1626 ('y', default) or cooked coordinates ('n')
1628 mtrr_chunk_size=nn[KMG] [X86]
1629 used for mtrr cleanup. It is largest continuous chunk
1630 that could hold holes aka. UC entries.
1632 mtrr_gran_size=nn[KMG] [X86]
1633 Used for mtrr cleanup. It is granularity of mtrr block.
1634 Default is 1.
1635 Large value could prevent small alignment from
1636 using up MTRRs.
1638 mtrr_spare_reg_nr=n [X86]
1639 Format: <integer>
1640 Range: 0,7 : spare reg number
1641 Default : 1
1642 Used for mtrr cleanup. It is spare mtrr entries number.
1643 Set to 2 or more if your graphical card needs more.
1645 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1647 netdev= [NET] Network devices parameters
1648 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1649 Note that mem_start is often overloaded to mean
1650 something different and driver-specific.
1651 This usage is only documented in each driver source
1652 file if at all.
1654 nf_conntrack.acct=
1655 [NETFILTER] Enable connection tracking flow accounting
1656 0 to disable accounting
1657 1 to enable accounting
1658 Default value is 0.
1660 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1661 See Documentation/filesystems/nfs/nfsroot.txt.
1663 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1664 See Documentation/filesystems/nfs/nfsroot.txt.
1666 nfsrootdebug [NFS] enable nfsroot debugging messages.
1667 See Documentation/filesystems/nfs/nfsroot.txt.
1669 nfs.callback_tcpport=
1670 [NFS] set the TCP port on which the NFSv4 callback
1671 channel should listen.
1673 nfs.cache_getent=
1674 [NFS] sets the pathname to the program which is used
1675 to update the NFS client cache entries.
1677 nfs.cache_getent_timeout=
1678 [NFS] sets the timeout after which an attempt to
1679 update a cache entry is deemed to have failed.
1681 nfs.idmap_cache_timeout=
1682 [NFS] set the maximum lifetime for idmapper cache
1683 entries.
1685 nfs.enable_ino64=
1686 [NFS] enable 64-bit inode numbers.
1687 If zero, the NFS client will fake up a 32-bit inode
1688 number for the readdir() and stat() syscalls instead
1689 of returning the full 64-bit number.
1690 The default is to return 64-bit inode numbers.
1692 nfs.max_session_slots=
1693 [NFSv4.1] Sets the maximum number of session slots
1694 the client will attempt to negotiate with the server.
1695 This limits the number of simultaneous RPC requests
1696 that the client can send to the NFSv4.1 server.
1697 Note that there is little point in setting this
1698 value higher than the max_tcp_slot_table_limit.
1700 nfs.nfs4_disable_idmapping=
1701 [NFSv4] When set to the default of '1', this option
1702 ensures that both the RPC level authentication
1703 scheme and the NFS level operations agree to use
1704 numeric uids/gids if the mount is using the
1705 'sec=sys' security flavour. In effect it is
1706 disabling idmapping, which can make migration from
1707 legacy NFSv2/v3 systems to NFSv4 easier.
1708 Servers that do not support this mode of operation
1709 will be autodetected by the client, and it will fall
1710 back to using the idmapper.
1711 To turn off this behaviour, set the value to '0'.
1713 nfs.send_implementation_id =
1714 [NFSv4.1] Send client implementation identification
1715 information in exchange_id requests.
1716 If zero, no implementation identification information
1717 will be sent.
1718 The default is to send the implementation identification
1719 information.
1721 nfsd.nfs4_disable_idmapping=
1722 [NFSv4] When set to the default of '1', the NFSv4
1723 server will return only numeric uids and gids to
1724 clients using auth_sys, and will accept numeric uids
1725 and gids from such clients. This is intended to ease
1726 migration from NFSv2/v3.
1728 objlayoutdriver.osd_login_prog=
1729 [NFS] [OBJLAYOUT] sets the pathname to the program which
1730 is used to automatically discover and login into new
1731 osd-targets. Please see:
1732 Documentation/filesystems/pnfs.txt for more explanations
1734 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1735 when a NMI is triggered.
1736 Format: [state][,regs][,debounce][,die]
1738 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1739 Format: [panic,][nopanic,][num]
1740 Valid num: 0
1741 0 - turn nmi_watchdog off
1742 When panic is specified, panic when an NMI watchdog
1743 timeout occurs (or 'nopanic' to override the opposite
1744 default).
1745 This is useful when you use a panic=... timeout and
1746 need the box quickly up again.
1748 netpoll.carrier_timeout=
1749 [NET] Specifies amount of time (in seconds) that
1750 netpoll should wait for a carrier. By default netpoll
1751 waits 4 seconds.
1753 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1754 emulation library even if a 387 maths coprocessor
1755 is present.
1757 no_console_suspend
1758 [HW] Never suspend the console
1759 Disable suspending of consoles during suspend and
1760 hibernate operations. Once disabled, debugging
1761 messages can reach various consoles while the rest
1762 of the system is being put to sleep (ie, while
1763 debugging driver suspend/resume hooks). This may
1764 not work reliably with all consoles, but is known
1765 to work with serial and VGA consoles.
1766 To facilitate more flexible debugging, we also add
1767 console_suspend, a printk module parameter to control
1768 it. Users could use console_suspend (usually
1769 /sys/module/printk/parameters/console_suspend) to
1770 turn on/off it dynamically.
1772 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1773 caches in the slab allocator. Saves per-node memory,
1774 but will impact performance.
1776 noalign [KNL,ARM]
1778 noapic [SMP,APIC] Tells the kernel to not make use of any
1779 IOAPICs that may be present in the system.
1781 noautogroup Disable scheduler automatic task group creation.
1783 nobats [PPC] Do not use BATs for mapping kernel lowmem
1784 on "Classic" PPC cores.
1786 nocache [ARM]
1788 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1790 nodelayacct [KNL] Disable per-task delay accounting
1792 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1794 nodsp [SH] Disable hardware DSP at boot time.
1796 noefi [X86] Disable EFI runtime services support.
1798 noexec [IA-64]
1800 noexec [X86]
1801 On X86-32 available only on PAE configured kernels.
1802 noexec=on: enable non-executable mappings (default)
1803 noexec=off: disable non-executable mappings
1805 nosmep [X86]
1806 Disable SMEP (Supervisor Mode Execution Protection)
1807 even if it is supported by processor.
1809 noexec32 [X86-64]
1810 This affects only 32-bit executables.
1811 noexec32=on: enable non-executable mappings (default)
1812 read doesn't imply executable mappings
1813 noexec32=off: disable non-executable mappings
1814 read implies executable mappings
1816 nofpu [SH] Disable hardware FPU at boot time.
1818 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1819 register save and restore. The kernel will only save
1820 legacy floating-point registers on task switch.
1822 noxsave [BUGS=X86] Disables x86 extended register state save
1823 and restore using xsave. The kernel will fallback to
1824 enabling legacy floating-point and sse state.
1826 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1827 wfi(ARM) instruction doesn't work correctly and not to
1828 use it. This is also useful when using JTAG debugger.
1830 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1831 instruction doesn't work correctly and not to
1832 use it.
1834 no_file_caps Tells the kernel not to honor file capabilities. The
1835 only way then for a file to be executed with privilege
1836 is to be setuid root or executed by root.
1838 nohalt [IA-64] Tells the kernel not to use the power saving
1839 function PAL_HALT_LIGHT when idle. This increases
1840 power-consumption. On the positive side, it reduces
1841 interrupt wake-up latency, which may improve performance
1842 in certain environments such as networked servers or
1843 real-time systems.
1845 nohz= [KNL] Boottime enable/disable dynamic ticks
1846 Valid arguments: on, off
1847 Default: on
1849 noiotrap [SH] Disables trapped I/O port accesses.
1851 noirqdebug [X86-32] Disables the code which attempts to detect and
1852 disable unhandled interrupt sources.
1854 no_timer_check [X86,APIC] Disables the code which tests for
1855 broken timer IRQ sources.
1857 noisapnp [ISAPNP] Disables ISA PnP code.
1859 noinitrd [RAM] Tells the kernel not to load any configured
1860 initial RAM disk.
1862 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1863 remapping.
1864 [Deprecated - use intremap=off]
1866 nointroute [IA-64]
1868 nojitter [IA-64] Disables jitter checking for ITC timers.
1870 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1872 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1873 fault handling.
1875 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1876 steal time is computed, but won't influence scheduler
1877 behaviour
1879 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1881 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1883 noltlbs [PPC] Do not use large page/tlb entries for kernel
1884 lowmem mapping on PPC40x.
1886 nomca [IA-64] Disable machine check abort handling
1888 nomce [X86-32] Machine Check Exception
1890 nomfgpt [X86-32] Disable Multi-Function General Purpose
1891 Timer usage (for AMD Geode machines).
1893 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
1894 shutdown the other cpus. Instead use the REBOOT_VECTOR
1895 irq.
1897 nomodule Disable module load
1899 nopat [X86] Disable PAT (page attribute table extension of
1900 pagetables) support.
1902 norandmaps Don't use address space randomization. Equivalent to
1903 echo 0 > /proc/sys/kernel/randomize_va_space
1905 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1907 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1908 with UP alternatives
1910 noresidual [PPC] Don't use residual data on PReP machines.
1912 nordrand [X86] Disable the direct use of the RDRAND
1913 instruction even if it is supported by the
1914 processor. RDRAND is still available to user
1915 space applications.
1917 noresume [SWSUSP] Disables resume and restores original swap
1918 space.
1920 no-scroll [VGA] Disables scrollback.
1921 This is required for the Braillex ib80-piezo Braille
1922 reader made by F.H. Papenmeier (Germany).
1924 nosbagart [IA-64]
1926 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1928 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1929 and disable the IO APIC. legacy for "maxcpus=0".
1931 nosoftlockup [KNL] Disable the soft-lockup detector.
1933 nosync [HW,M68K] Disables sync negotiation for all devices.
1935 notsc [BUGS=X86-32] Disable Time Stamp Counter
1937 nousb [USB] Disable the USB subsystem
1939 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1941 nowb [ARM]
1943 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1945 nptcg= [IA-64] Override max number of concurrent global TLB
1946 purges which is reported from either PAL_VM_SUMMARY or
1947 SAL PALO.
1949 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1950 could support. nr_cpus=n : n >= 1 limits the kernel to
1951 supporting 'n' processors. Later in runtime you can not
1952 use hotplug cpu feature to put more cpu back to online.
1953 just like you compile the kernel NR_CPUS=n
1955 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1957 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1958 one of ['zone', 'node', 'default'] can be specified
1959 This can be set from sysctl after boot.
1960 See Documentation/sysctl/vm.txt for details.
1962 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1963 See Documentation/debugging-via-ohci1394.txt for more
1964 info.
1966 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1967 Rather than timing out after 20 ms if an EC
1968 command is not properly ACKed, override the length
1969 of the timeout. We have interrupts disabled while
1970 waiting for the ACK, so if this is set too high
1971 interrupts *may* be lost!
1973 omap_mux= [OMAP] Override bootloader pin multiplexing.
1974 Format: <mux_mode0.mode_name=value>...
1975 For example, to override I2C bus2:
1976 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1978 oprofile.timer= [HW]
1979 Use timer interrupt instead of performance counters
1981 oprofile.cpu_type= Force an oprofile cpu type
1982 This might be useful if you have an older oprofile
1983 userland or if you want common events.
1984 Format: { arch_perfmon }
1985 arch_perfmon: [X86] Force use of architectural
1986 perfmon on Intel CPUs instead of the
1987 CPU specific event set.
1988 timer: [X86] Force use of architectural NMI
1989 timer mode (see also oprofile.timer
1990 for generic hr timer mode)
1991 [s390] Force legacy basic mode sampling
1992 (report cpu_type "timer")
1994 oops=panic Always panic on oopses. Default is to just kill the
1995 process, but there is a small probability of
1996 deadlocking the machine.
1997 This will also cause panics on machine check exceptions.
1998 Useful together with panic=30 to trigger a reboot.
2000 OSS [HW,OSS]
2001 See Documentation/sound/oss/oss-parameters.txt
2003 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2004 timeout > 0: seconds before rebooting
2005 timeout = 0: wait forever
2006 timeout < 0: reboot immediately
2007 Format: <timeout>
2009 parkbd.port= [HW] Parallel port number the keyboard adapter is
2010 connected to, default is 0.
2011 Format: <parport#>
2012 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2013 0 for XT, 1 for AT (default is AT).
2014 Format: <mode>
2016 parport= [HW,PPT] Specify parallel ports. 0 disables.
2017 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2018 Use 'auto' to force the driver to use any
2019 IRQ/DMA settings detected (the default is to
2020 ignore detected IRQ/DMA settings because of
2021 possible conflicts). You can specify the base
2022 address, IRQ, and DMA settings; IRQ and DMA
2023 should be numbers, or 'auto' (for using detected
2024 settings on that particular port), or 'nofifo'
2025 (to avoid using a FIFO even if it is detected).
2026 Parallel ports are assigned in the order they
2027 are specified on the command line, starting
2028 with parport0.
2030 parport_init_mode= [HW,PPT]
2031 Configure VIA parallel port to operate in
2032 a specific mode. This is necessary on Pegasos
2033 computer where firmware has no options for setting
2034 up parallel port mode and sets it to spp.
2035 Currently this function knows 686a and 8231 chips.
2036 Format: [spp|ps2|epp|ecp|ecpepp]
2038 pause_on_oops=
2039 Halt all CPUs after the first oops has been printed for
2040 the specified number of seconds. This is to be used if
2041 your oopses keep scrolling off the screen.
2043 pcbit= [HW,ISDN]
2045 pcd. [PARIDE]
2046 See header of drivers/block/paride/pcd.c.
2047 See also Documentation/blockdev/paride.txt.
2049 pci=option[,option...] [PCI] various PCI subsystem options:
2050 earlydump [X86] dump PCI config space before the kernel
2051 changes anything
2052 off [X86] don't probe for the PCI bus
2053 bios [X86-32] force use of PCI BIOS, don't access
2054 the hardware directly. Use this if your machine
2055 has a non-standard PCI host bridge.
2056 nobios [X86-32] disallow use of PCI BIOS, only direct
2057 hardware access methods are allowed. Use this
2058 if you experience crashes upon bootup and you
2059 suspect they are caused by the BIOS.
2060 conf1 [X86] Force use of PCI Configuration
2061 Mechanism 1.
2062 conf2 [X86] Force use of PCI Configuration
2063 Mechanism 2.
2064 noaer [PCIE] If the PCIEAER kernel config parameter is
2065 enabled, this kernel boot option can be used to
2066 disable the use of PCIE advanced error reporting.
2067 nodomains [PCI] Disable support for multiple PCI
2068 root domains (aka PCI segments, in ACPI-speak).
2069 nommconf [X86] Disable use of MMCONFIG for PCI
2070 Configuration
2071 check_enable_amd_mmconf [X86] check for and enable
2072 properly configured MMIO access to PCI
2073 config space on AMD family 10h CPU
2074 nomsi [MSI] If the PCI_MSI kernel config parameter is
2075 enabled, this kernel boot option can be used to
2076 disable the use of MSI interrupts system-wide.
2077 noioapicquirk [APIC] Disable all boot interrupt quirks.
2078 Safety option to keep boot IRQs enabled. This
2079 should never be necessary.
2080 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2081 primary IO-APIC for bridges that cannot disable
2082 boot IRQs. This fixes a source of spurious IRQs
2083 when the system masks IRQs.
2084 noioapicreroute [APIC] Disable workaround that uses the
2085 boot IRQ equivalent of an IRQ that connects to
2086 a chipset where boot IRQs cannot be disabled.
2087 The opposite of ioapicreroute.
2088 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2089 routing table. These calls are known to be buggy
2090 on several machines and they hang the machine
2091 when used, but on other computers it's the only
2092 way to get the interrupt routing table. Try
2093 this option if the kernel is unable to allocate
2094 IRQs or discover secondary PCI buses on your
2095 motherboard.
2096 rom [X86] Assign address space to expansion ROMs.
2097 Use with caution as certain devices share
2098 address decoders between ROMs and other
2099 resources.
2100 norom [X86] Do not assign address space to
2101 expansion ROMs that do not already have
2102 BIOS assigned address ranges.
2103 nobar [X86] Do not assign address space to the
2104 BARs that weren't assigned by the BIOS.
2105 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2106 assigned automatically to PCI devices. You can
2107 make the kernel exclude IRQs of your ISA cards
2108 this way.
2109 pirqaddr=0xAAAAA [X86] Specify the physical address
2110 of the PIRQ table (normally generated
2111 by the BIOS) if it is outside the
2112 F0000h-100000h range.
2113 lastbus=N [X86] Scan all buses thru bus #N. Can be
2114 useful if the kernel is unable to find your
2115 secondary buses and you want to tell it
2116 explicitly which ones they are.
2117 assign-busses [X86] Always assign all PCI bus
2118 numbers ourselves, overriding
2119 whatever the firmware may have done.
2120 usepirqmask [X86] Honor the possible IRQ mask stored
2121 in the BIOS $PIR table. This is needed on
2122 some systems with broken BIOSes, notably
2123 some HP Pavilion N5400 and Omnibook XE3
2124 notebooks. This will have no effect if ACPI
2125 IRQ routing is enabled.
2126 noacpi [X86] Do not use ACPI for IRQ routing
2127 or for PCI scanning.
2128 use_crs [X86] Use PCI host bridge window information
2129 from ACPI. On BIOSes from 2008 or later, this
2130 is enabled by default. If you need to use this,
2131 please report a bug.
2132 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2133 If you need to use this, please report a bug.
2134 routeirq Do IRQ routing for all PCI devices.
2135 This is normally done in pci_enable_device(),
2136 so this option is a temporary workaround
2137 for broken drivers that don't call it.
2138 skip_isa_align [X86] do not align io start addr, so can
2139 handle more pci cards
2140 firmware [ARM] Do not re-enumerate the bus but instead
2141 just use the configuration from the
2142 bootloader. This is currently used on
2143 IXP2000 systems where the bus has to be
2144 configured a certain way for adjunct CPUs.
2145 noearly [X86] Don't do any early type 1 scanning.
2146 This might help on some broken boards which
2147 machine check when some devices' config space
2148 is read. But various workarounds are disabled
2149 and some IOMMU drivers will not work.
2150 bfsort Sort PCI devices into breadth-first order.
2151 This sorting is done to get a device
2152 order compatible with older (<= 2.4) kernels.
2153 nobfsort Don't sort PCI devices into breadth-first order.
2154 cbiosize=nn[KMG] The fixed amount of bus space which is
2155 reserved for the CardBus bridge's IO window.
2156 The default value is 256 bytes.
2157 cbmemsize=nn[KMG] The fixed amount of bus space which is
2158 reserved for the CardBus bridge's memory
2159 window. The default value is 64 megabytes.
2160 resource_alignment=
2161 Format:
2162 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2163 Specifies alignment and device to reassign
2164 aligned memory resources.
2165 If <order of align> is not specified,
2166 PAGE_SIZE is used as alignment.
2167 PCI-PCI bridge can be specified, if resource
2168 windows need to be expanded.
2169 ecrc= Enable/disable PCIe ECRC (transaction layer
2170 end-to-end CRC checking).
2171 bios: Use BIOS/firmware settings. This is the
2172 the default.
2173 off: Turn ECRC off
2174 on: Turn ECRC on.
2175 realloc= Enable/disable reallocating PCI bridge resources
2176 if allocations done by BIOS are too small to
2177 accommodate resources required by all child
2178 devices.
2179 off: Turn realloc off
2180 on: Turn realloc on
2181 realloc same as realloc=on
2182 noari do not use PCIe ARI.
2183 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2184 only look for one device below a PCIe downstream
2185 port.
2187 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2188 Management.
2189 off Disable ASPM.
2190 force Enable ASPM even on devices that claim not to support it.
2191 WARNING: Forcing ASPM on may cause system lockups.
2193 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2194 nomsi Do not use MSI for PCI Express Native Hotplug (this
2195 makes all PCIe ports use INTx for hotplug services).
2197 pcie_ports= [PCIE] PCIe ports handling:
2198 auto Ask the BIOS whether or not to use native PCIe services
2199 associated with PCIe ports (PME, hot-plug, AER). Use
2200 them only if that is allowed by the BIOS.
2201 native Use native PCIe services associated with PCIe ports
2202 unconditionally.
2203 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2204 ports driver.
2206 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2207 nomsi Do not use MSI for native PCIe PME signaling (this makes
2208 all PCIe root ports use INTx for all services).
2210 pcmv= [HW,PCMCIA] BadgePAD 4
2212 pd. [PARIDE]
2213 See Documentation/blockdev/paride.txt.
2215 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2216 boot time.
2217 Format: { 0 | 1 }
2218 See arch/parisc/kernel/pdc_chassis.c
2220 percpu_alloc= Select which percpu first chunk allocator to use.
2221 Currently supported values are "embed" and "page".
2222 Archs may support subset or none of the selections.
2223 See comments in mm/percpu.c for details on each
2224 allocator. This parameter is primarily for debugging
2225 and performance comparison.
2227 pf. [PARIDE]
2228 See Documentation/blockdev/paride.txt.
2230 pg. [PARIDE]
2231 See Documentation/blockdev/paride.txt.
2233 pirq= [SMP,APIC] Manual mp-table setup
2234 See Documentation/x86/i386/IO-APIC.txt.
2236 plip= [PPT,NET] Parallel port network link
2237 Format: { parport<nr> | timid | 0 }
2238 See also Documentation/parport.txt.
2240 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2241 Override pmtimer IOPort with a hex value.
2242 e.g. pmtmr=0x508
2244 pnp.debug=1 [PNP]
2245 Enable PNP debug messages (depends on the
2246 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2247 via /sys/module/pnp/parameters/debug. We always show
2248 current resource usage; turning this on also shows
2249 possible settings and some assignment information.
2251 pnpacpi= [ACPI]
2252 { off }
2254 pnpbios= [ISAPNP]
2255 { on | off | curr | res | no-curr | no-res }
2257 pnp_reserve_irq=
2258 [ISAPNP] Exclude IRQs for the autoconfiguration
2260 pnp_reserve_dma=
2261 [ISAPNP] Exclude DMAs for the autoconfiguration
2263 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2264 Ranges are in pairs (I/O port base and size).
2266 pnp_reserve_mem=
2267 [ISAPNP] Exclude memory regions for the
2268 autoconfiguration.
2269 Ranges are in pairs (memory base and size).
2271 ports= [IP_VS_FTP] IPVS ftp helper module
2272 Default is 21.
2273 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2274 may be specified.
2275 Format: <port>,<port>....
2277 print-fatal-signals=
2278 [KNL] debug: print fatal signals
2280 If enabled, warn about various signal handling
2281 related application anomalies: too many signals,
2282 too many POSIX.1 timers, fatal signals causing a
2283 coredump - etc.
2285 If you hit the warning due to signal overflow,
2286 you might want to try "ulimit -i unlimited".
2288 default: off.
2290 printk.always_kmsg_dump=
2291 Trigger kmsg_dump for cases other than kernel oops or
2292 panics
2293 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2294 default: disabled
2296 printk.time= Show timing data prefixed to each printk message line
2297 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2299 processor.max_cstate= [HW,ACPI]
2300 Limit processor to maximum C-state
2301 max_cstate=9 overrides any DMI blacklist limit.
2303 processor.nocst [HW,ACPI]
2304 Ignore the _CST method to determine C-states,
2305 instead using the legacy FADT method
2307 profile= [KNL] Enable kernel profiling via /proc/profile
2308 Format: [schedule,]<number>
2309 Param: "schedule" - profile schedule points.
2310 Param: <number> - step/bucket size as a power of 2 for
2311 statistical time based profiling.
2312 Param: "sleep" - profile D-state sleeping (millisecs).
2313 Requires CONFIG_SCHEDSTATS
2314 Param: "kvm" - profile VM exits.
2316 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2317 before loading.
2318 See Documentation/blockdev/ramdisk.txt.
2320 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2321 probe for; one of (bare|imps|exps|lifebook|any).
2322 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2323 per second.
2324 psmouse.resetafter= [HW,MOUSE]
2325 Try to reset the device after so many bad packets
2326 (0 = never).
2327 psmouse.resolution=
2328 [HW,MOUSE] Set desired mouse resolution, in dpi.
2329 psmouse.smartscroll=
2330 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2331 0 = disabled, 1 = enabled (default).
2333 pstore.backend= Specify the name of the pstore backend to use
2335 pt. [PARIDE]
2336 See Documentation/blockdev/paride.txt.
2338 pty.legacy_count=
2339 [KNL] Number of legacy pty's. Overwrites compiled-in
2340 default number.
2342 quiet [KNL] Disable most log messages
2344 r128= [HW,DRM]
2346 raid= [HW,RAID]
2347 See Documentation/md.txt.
2349 ramdisk_blocksize= [RAM]
2350 See Documentation/blockdev/ramdisk.txt.
2352 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2353 See Documentation/blockdev/ramdisk.txt.
2355 rcutree.blimit= [KNL,BOOT]
2356 Set maximum number of finished RCU callbacks to process
2357 in one batch.
2359 rcutree.qhimark= [KNL,BOOT]
2360 Set threshold of queued
2361 RCU callbacks over which batch limiting is disabled.
2363 rcutree.qlowmark= [KNL,BOOT]
2364 Set threshold of queued RCU callbacks below which
2365 batch limiting is re-enabled.
2367 rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2368 Suppress RCU CPU stall warning messages.
2370 rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2371 Set timeout for RCU CPU stall warning messages.
2373 rcutorture.fqs_duration= [KNL,BOOT]
2374 Set duration of force_quiescent_state bursts.
2376 rcutorture.fqs_holdoff= [KNL,BOOT]
2377 Set holdoff time within force_quiescent_state bursts.
2379 rcutorture.fqs_stutter= [KNL,BOOT]
2380 Set wait time between force_quiescent_state bursts.
2382 rcutorture.irqreader= [KNL,BOOT]
2383 Test RCU readers from irq handlers.
2385 rcutorture.n_barrier_cbs= [KNL,BOOT]
2386 Set callbacks/threads for rcu_barrier() testing.
2388 rcutorture.nfakewriters= [KNL,BOOT]
2389 Set number of concurrent RCU writers. These just
2390 stress RCU, they don't participate in the actual
2391 test, hence the "fake".
2393 rcutorture.nreaders= [KNL,BOOT]
2394 Set number of RCU readers.
2396 rcutorture.onoff_holdoff= [KNL,BOOT]
2397 Set time (s) after boot for CPU-hotplug testing.
2399 rcutorture.onoff_interval= [KNL,BOOT]
2400 Set time (s) between CPU-hotplug operations, or
2401 zero to disable CPU-hotplug testing.
2403 rcutorture.shuffle_interval= [KNL,BOOT]
2404 Set task-shuffle interval (s). Shuffling tasks
2405 allows some CPUs to go into dyntick-idle mode
2406 during the rcutorture test.
2408 rcutorture.shutdown_secs= [KNL,BOOT]
2409 Set time (s) after boot system shutdown. This
2410 is useful for hands-off automated testing.
2412 rcutorture.stall_cpu= [KNL,BOOT]
2413 Duration of CPU stall (s) to test RCU CPU stall
2414 warnings, zero to disable.
2416 rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2417 Time to wait (s) after boot before inducing stall.
2419 rcutorture.stat_interval= [KNL,BOOT]
2420 Time (s) between statistics printk()s.
2422 rcutorture.stutter= [KNL,BOOT]
2423 Time (s) to stutter testing, for example, specifying
2424 five seconds causes the test to run for five seconds,
2425 wait for five seconds, and so on. This tests RCU's
2426 ability to transition abruptly to and from idle.
2428 rcutorture.test_boost= [KNL,BOOT]
2429 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2430 "Maybe" means test if the RCU implementation
2431 under test support RCU priority boosting.
2433 rcutorture.test_boost_duration= [KNL,BOOT]
2434 Duration (s) of each individual boost test.
2436 rcutorture.test_boost_interval= [KNL,BOOT]
2437 Interval (s) between each boost test.
2439 rcutorture.test_no_idle_hz= [KNL,BOOT]
2440 Test RCU's dyntick-idle handling. See also the
2441 rcutorture.shuffle_interval parameter.
2443 rcutorture.torture_type= [KNL,BOOT]
2444 Specify the RCU implementation to test.
2446 rcutorture.verbose= [KNL,BOOT]
2447 Enable additional printk() statements.
2449 rdinit= [KNL]
2450 Format: <full_path>
2451 Run specified binary instead of /init from the ramdisk,
2452 used for early userspace startup. See initrd.
2454 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2455 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2456 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2458 relax_domain_level=
2459 [KNL, SMP] Set scheduler's default relax_domain_level.
2460 See Documentation/cgroups/cpusets.txt.
2462 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2464 reservetop= [X86-32]
2465 Format: nn[KMG]
2466 Reserves a hole at the top of the kernel virtual
2467 address space.
2469 reservelow= [X86]
2470 Format: nn[K]
2471 Set the amount of memory to reserve for BIOS at
2472 the bottom of the address space.
2474 reset_devices [KNL] Force drivers to reset the underlying device
2475 during initialization.
2477 resume= [SWSUSP]
2478 Specify the partition device for software suspend
2479 Format:
2480 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2482 resume_offset= [SWSUSP]
2483 Specify the offset from the beginning of the partition
2484 given by "resume=" at which the swap header is located,
2485 in <PAGE_SIZE> units (needed only for swap files).
2486 See Documentation/power/swsusp-and-swap-files.txt
2488 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2489 read the resume files
2491 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2492 Useful for devices that are detected asynchronously
2493 (e.g. USB and MMC devices).
2495 hibernate= [HIBERNATION]
2496 noresume Don't check if there's a hibernation image
2497 present during boot.
2498 nocompress Don't compress/decompress hibernation images.
2500 retain_initrd [RAM] Keep initrd memory after extraction
2502 rhash_entries= [KNL,NET]
2503 Set number of hash buckets for route cache
2505 riscom8= [HW,SERIAL]
2506 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2508 ro [KNL] Mount root device read-only on boot
2510 root= [KNL] Root filesystem
2511 See name_to_dev_t comment in init/do_mounts.c.
2513 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2514 mount the root filesystem
2516 rootflags= [KNL] Set root filesystem mount option string
2518 rootfstype= [KNL] Set root filesystem type
2520 rootwait [KNL] Wait (indefinitely) for root device to show up.
2521 Useful for devices that are detected asynchronously
2522 (e.g. USB and MMC devices).
2524 rw [KNL] Mount root device read-write on boot
2526 S [KNL] Run init in single mode
2528 sa1100ir [NET]
2529 See drivers/net/irda/sa1100_ir.c.
2531 sbni= [NET] Granch SBNI12 leased line adapter
2533 sched_debug [KNL] Enables verbose scheduler debug messages.
2535 security= [SECURITY] Choose a security module to enable at boot.
2536 If this boot parameter is not specified, only the first
2537 security module asking for security registration will be
2538 loaded. An invalid security module name will be treated
2539 as if no module has been chosen.
2541 selinux= [SELINUX] Disable or enable SELinux at boot time.
2542 Format: { "0" | "1" }
2543 See security/selinux/Kconfig help text.
2544 0 -- disable.
2545 1 -- enable.
2546 Default value is set via kernel config option.
2547 If enabled at boot time, /selinux/disable can be used
2548 later to disable prior to initial policy load.
2550 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2551 Format: { "0" | "1" }
2552 See security/apparmor/Kconfig help text
2553 0 -- disable.
2554 1 -- enable.
2555 Default value is set via kernel config option.
2557 serialnumber [BUGS=X86-32]
2559 shapers= [NET]
2560 Maximal number of shapers.
2562 show_msr= [x86] show boot-time MSR settings
2563 Format: { <integer> }
2564 Show boot-time (BIOS-initialized) MSR settings.
2565 The parameter means the number of CPUs to show,
2566 for example 1 means boot CPU only.
2568 simeth= [IA-64]
2569 simscsi=
2571 slram= [HW,MTD]
2573 slab_max_order= [MM, SLAB]
2574 Determines the maximum allowed order for slabs.
2575 A high setting may cause OOMs due to memory
2576 fragmentation. Defaults to 1 for systems with
2577 more than 32MB of RAM, 0 otherwise.
2579 slub_debug[=options[,slabs]] [MM, SLUB]
2580 Enabling slub_debug allows one to determine the
2581 culprit if slab objects become corrupted. Enabling
2582 slub_debug can create guard zones around objects and
2583 may poison objects when not in use. Also tracks the
2584 last alloc / free. For more information see
2585 Documentation/vm/slub.txt.
2587 slub_max_order= [MM, SLUB]
2588 Determines the maximum allowed order for slabs.
2589 A high setting may cause OOMs due to memory
2590 fragmentation. For more information see
2591 Documentation/vm/slub.txt.
2593 slub_min_objects= [MM, SLUB]
2594 The minimum number of objects per slab. SLUB will
2595 increase the slab order up to slub_max_order to
2596 generate a sufficiently large slab able to contain
2597 the number of objects indicated. The higher the number
2598 of objects the smaller the overhead of tracking slabs
2599 and the less frequently locks need to be acquired.
2600 For more information see Documentation/vm/slub.txt.
2602 slub_min_order= [MM, SLUB]
2603 Determines the minimum page order for slabs. Must be
2604 lower than slub_max_order.
2605 For more information see Documentation/vm/slub.txt.
2607 slub_nomerge [MM, SLUB]
2608 Disable merging of slabs with similar size. May be
2609 necessary if there is some reason to distinguish
2610 allocs to different slabs. Debug options disable
2611 merging on their own.
2612 For more information see Documentation/vm/slub.txt.
2614 smart2= [HW]
2615 Format: <io1>[,<io2>[,...,<io8>]]
2617 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2618 attempt to substitute SMP alternatives once at boot.
2620 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2621 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2622 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2623 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2624 smsc-ircc2.ircc_irq= [HW] IRQ line
2625 smsc-ircc2.ircc_dma= [HW] DMA channel
2626 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2627 0: Toshiba Satellite 1800 (GP data pin select)
2628 1: Fast pin select (default)
2629 2: ATC IRMode
2631 softlockup_panic=
2632 [KNL] Should the soft-lockup detector generate panics.
2633 Format: <integer>
2635 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2636 See Documentation/laptops/sonypi.txt
2638 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2639 See Documentation/serial/specialix.txt.
2641 spia_io_base= [HW,MTD]
2642 spia_fio_base=
2643 spia_pedr=
2644 spia_peddr=
2646 stacktrace [FTRACE]
2647 Enabled the stack tracer on boot up.
2649 stacktrace_filter=[function-list]
2650 [FTRACE] Limit the functions that the stack tracer
2651 will trace at boot up. function-list is a comma separated
2652 list of functions. This list can be changed at run
2653 time by the stack_trace_filter file in the debugfs
2654 tracing directory. Note, this enables stack tracing
2655 and the stacktrace above is not needed.
2657 sti= [PARISC,HW]
2658 Format: <num>
2659 Set the STI (builtin display/keyboard on the HP-PARISC
2660 machines) console (graphic card) which should be used
2661 as the initial boot-console.
2662 See also comment in drivers/video/console/sticore.c.
2664 sti_font= [HW]
2665 See comment in drivers/video/console/sticore.c.
2667 stifb= [HW]
2668 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2670 sunrpc.min_resvport=
2671 sunrpc.max_resvport=
2672 [NFS,SUNRPC]
2673 SunRPC servers often require that client requests
2674 originate from a privileged port (i.e. a port in the
2675 range 0 < portnr < 1024).
2676 An administrator who wishes to reserve some of these
2677 ports for other uses may adjust the range that the
2678 kernel's sunrpc client considers to be privileged
2679 using these two parameters to set the minimum and
2680 maximum port values.
2682 sunrpc.pool_mode=
2683 [NFS]
2684 Control how the NFS server code allocates CPUs to
2685 service thread pools. Depending on how many NICs
2686 you have and where their interrupts are bound, this
2687 option will affect which CPUs will do NFS serving.
2688 Note: this parameter cannot be changed while the
2689 NFS server is running.
2691 auto the server chooses an appropriate mode
2692 automatically using heuristics
2693 global a single global pool contains all CPUs
2694 percpu one pool for each CPU
2695 pernode one pool for each NUMA node (equivalent
2696 to global on non-NUMA machines)
2698 sunrpc.tcp_slot_table_entries=
2699 sunrpc.udp_slot_table_entries=
2700 [NFS,SUNRPC]
2701 Sets the upper limit on the number of simultaneous
2702 RPC calls that can be sent from the client to a
2703 server. Increasing these values may allow you to
2704 improve throughput, but will also increase the
2705 amount of memory reserved for use by the client.
2707 swapaccount[=0|1]
2708 [KNL] Enable accounting of swap in memory resource
2709 controller if no parameter or 1 is given or disable
2710 it if 0 is given (See Documentation/cgroups/memory.txt)
2712 swiotlb= [IA-64] Number of I/O TLB slabs
2714 switches= [HW,M68k]
2716 sysfs.deprecated=0|1 [KNL]
2717 Enable/disable old style sysfs layout for old udev
2718 on older distributions. When this option is enabled
2719 very new udev will not work anymore. When this option
2720 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2721 in older udev will not work anymore.
2722 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2723 the kernel configuration.
2725 sysrq_always_enabled
2726 [KNL]
2727 Ignore sysrq setting - this boot parameter will
2728 neutralize any effect of /proc/sys/kernel/sysrq.
2729 Useful for debugging.
2731 tdfx= [HW,DRM]
2733 test_suspend= [SUSPEND]
2734 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2735 standby suspend) as the system sleep state to briefly
2736 enter during system startup. The system is woken from
2737 this state using a wakeup-capable RTC alarm.
2739 thash_entries= [KNL,NET]
2740 Set number of hash buckets for TCP connection
2742 thermal.act= [HW,ACPI]
2743 -1: disable all active trip points in all thermal zones
2744 <degrees C>: override all lowest active trip points
2746 thermal.crt= [HW,ACPI]
2747 -1: disable all critical trip points in all thermal zones
2748 <degrees C>: override all critical trip points
2750 thermal.nocrt= [HW,ACPI]
2751 Set to disable actions on ACPI thermal zone
2752 critical and hot trip points.
2754 thermal.off= [HW,ACPI]
2755 1: disable ACPI thermal control
2757 thermal.psv= [HW,ACPI]
2758 -1: disable all passive trip points
2759 <degrees C>: override all passive trip points to this
2760 value
2762 thermal.tzp= [HW,ACPI]
2763 Specify global default ACPI thermal zone polling rate
2764 <deci-seconds>: poll all this frequency
2765 0: no polling (default)
2767 threadirqs [KNL]
2768 Force threading of all interrupt handlers except those
2769 marked explicitly IRQF_NO_THREAD.
2771 topology= [S390]
2772 Format: {off | on}
2773 Specify if the kernel should make use of the cpu
2774 topology information if the hardware supports this.
2775 The scheduler will make use of this information and
2776 e.g. base its process migration decisions on it.
2777 Default is on.
2779 tp720= [HW,PS2]
2781 tpm_suspend_pcr=[HW,TPM]
2782 Format: integer pcr id
2783 Specify that at suspend time, the tpm driver
2784 should extend the specified pcr with zeros,
2785 as a workaround for some chips which fail to
2786 flush the last written pcr on TPM_SaveState.
2787 This will guarantee that all the other pcrs
2788 are saved.
2790 trace_buf_size=nn[KMG]
2791 [FTRACE] will set tracing buffer size.
2793 trace_event=[event-list]
2794 [FTRACE] Set and start specified trace events in order
2795 to facilitate early boot debugging.
2796 See also Documentation/trace/events.txt
2798 transparent_hugepage=
2799 [KNL]
2800 Format: [always|madvise|never]
2801 Can be used to control the default behavior of the system
2802 with respect to transparent hugepages.
2803 See Documentation/vm/transhuge.txt for more details.
2805 tsc= Disable clocksource stability checks for TSC.
2806 Format: <string>
2807 [x86] reliable: mark tsc clocksource as reliable, this
2808 disables clocksource verification at runtime, as well
2809 as the stability checks done at bootup. Used to enable
2810 high-resolution timer mode on older hardware, and in
2811 virtualized environment.
2812 [x86] noirqtime: Do not use TSC to do irq accounting.
2813 Used to run time disable IRQ_TIME_ACCOUNTING on any
2814 platforms where RDTSC is slow and this accounting
2815 can add overhead.
2817 turbografx.map[2|3]= [HW,JOY]
2818 TurboGraFX parallel port interface
2819 Format:
2820 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2821 See also Documentation/input/joystick-parport.txt
2823 udbg-immortal [PPC] When debugging early kernel crashes that
2824 happen after console_init() and before a proper
2825 console driver takes over, this boot options might
2826 help "seeing" what's going on.
2828 uhash_entries= [KNL,NET]
2829 Set number of hash buckets for UDP/UDP-Lite connections
2831 uhci-hcd.ignore_oc=
2832 [USB] Ignore overcurrent events (default N).
2833 Some badly-designed motherboards generate lots of
2834 bogus events, for ports that aren't wired to
2835 anything. Set this parameter to avoid log spamming.
2836 Note that genuine overcurrent events won't be
2837 reported either.
2839 unknown_nmi_panic
2840 [X86] Cause panic on unknown NMI.
2842 usbcore.authorized_default=
2843 [USB] Default USB device authorization:
2844 (default -1 = authorized except for wireless USB,
2845 0 = not authorized, 1 = authorized)
2847 usbcore.autosuspend=
2848 [USB] The autosuspend time delay (in seconds) used
2849 for newly-detected USB devices (default 2). This
2850 is the time required before an idle device will be
2851 autosuspended. Devices for which the delay is set
2852 to a negative value won't be autosuspended at all.
2854 usbcore.usbfs_snoop=
2855 [USB] Set to log all usbfs traffic (default 0 = off).
2857 usbcore.blinkenlights=
2858 [USB] Set to cycle leds on hubs (default 0 = off).
2860 usbcore.old_scheme_first=
2861 [USB] Start with the old device initialization
2862 scheme (default 0 = off).
2864 usbcore.usbfs_memory_mb=
2865 [USB] Memory limit (in MB) for buffers allocated by
2866 usbfs (default = 16, 0 = max = 2047).
2868 usbcore.use_both_schemes=
2869 [USB] Try the other device initialization scheme
2870 if the first one fails (default 1 = enabled).
2872 usbcore.initial_descriptor_timeout=
2873 [USB] Specifies timeout for the initial 64-byte
2874 USB_REQ_GET_DESCRIPTOR request in milliseconds
2875 (default 5000 = 5.0 seconds).
2877 usbhid.mousepoll=
2878 [USBHID] The interval which mice are to be polled at.
2880 usb-storage.delay_use=
2881 [UMS] The delay in seconds before a new device is
2882 scanned for Logical Units (default 5).
2884 usb-storage.quirks=
2885 [UMS] A list of quirks entries to supplement or
2886 override the built-in unusual_devs list. List
2887 entries are separated by commas. Each entry has
2888 the form VID:PID:Flags where VID and PID are Vendor
2889 and Product ID values (4-digit hex numbers) and
2890 Flags is a set of characters, each corresponding
2891 to a common usb-storage quirk flag as follows:
2892 a = SANE_SENSE (collect more than 18 bytes
2893 of sense data);
2894 b = BAD_SENSE (don't collect more than 18
2895 bytes of sense data);
2896 c = FIX_CAPACITY (decrease the reported
2897 device capacity by one sector);
2898 d = NO_READ_DISC_INFO (don't use
2899 READ_DISC_INFO command);
2900 e = NO_READ_CAPACITY_16 (don't use
2901 READ_CAPACITY_16 command);
2902 h = CAPACITY_HEURISTICS (decrease the
2903 reported device capacity by one
2904 sector if the number is odd);
2905 i = IGNORE_DEVICE (don't bind to this
2906 device);
2907 l = NOT_LOCKABLE (don't try to lock and
2908 unlock ejectable media);
2909 m = MAX_SECTORS_64 (don't transfer more
2910 than 64 sectors = 32 KB at a time);
2911 n = INITIAL_READ10 (force a retry of the
2912 initial READ(10) command);
2913 o = CAPACITY_OK (accept the capacity
2914 reported by the device);
2915 r = IGNORE_RESIDUE (the device reports
2916 bogus residue values);
2917 s = SINGLE_LUN (the device has only one
2918 Logical Unit);
2919 w = NO_WP_DETECT (don't test whether the
2920 medium is write-protected).
2921 Example: quirks=0419:aaf5:rl,0421:0433:rc
2923 user_debug= [KNL,ARM]
2924 Format: <int>
2925 See arch/arm/Kconfig.debug help text.
2926 1 - undefined instruction events
2927 2 - system calls
2928 4 - invalid data aborts
2929 8 - SIGSEGV faults
2930 16 - SIGBUS faults
2931 Example: user_debug=31
2933 userpte=
2934 [X86] Flags controlling user PTE allocations.
2936 nohigh = do not allocate PTE pages in
2937 HIGHMEM regardless of setting
2938 of CONFIG_HIGHPTE.
2940 vdso= [X86,SH]
2941 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2942 vdso=1: enable VDSO (default)
2943 vdso=0: disable VDSO mapping
2945 vdso32= [X86]
2946 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2947 vdso32=1: enable 32-bit VDSO (default)
2948 vdso32=0: disable 32-bit VDSO mapping
2950 vector= [IA-64,SMP]
2951 vector=percpu: enable percpu vector domain
2953 video= [FB] Frame buffer configuration
2954 See Documentation/fb/modedb.txt.
2956 virtio_mmio.device=
2957 [VMMIO] Memory mapped virtio (platform) device.
2959 <size>@<baseaddr>:<irq>[:<id>]
2960 where:
2961 <size> := size (can use standard suffixes
2962 like K, M and G)
2963 <baseaddr> := physical base address
2964 <irq> := interrupt number (as passed to
2965 request_irq())
2966 <id> := (optional) platform device id
2967 example:
2968 virtio_mmio.device=1K@0x100b0000:48:7
2970 Can be used multiple times for multiple devices.
2972 vga= [BOOT,X86-32] Select a particular video mode
2973 See Documentation/x86/boot.txt and
2974 Documentation/svga.txt.
2975 Use vga=ask for menu.
2976 This is actually a boot loader parameter; the value is
2977 passed to the kernel using a special protocol.
2979 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2980 size of <nn>. This can be used to increase the
2981 minimum size (128MB on x86). It can also be used to
2982 decrease the size and leave more room for directly
2983 mapped kernel RAM.
2985 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2986 Format: <command>
2988 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2989 Format: <command>
2991 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2992 Format: <command>
2994 vsyscall= [X86-64]
2995 Controls the behavior of vsyscalls (i.e. calls to
2996 fixed addresses of 0xffffffffff600x00 from legacy
2997 code). Most statically-linked binaries and older
2998 versions of glibc use these calls. Because these
2999 functions are at fixed addresses, they make nice
3000 targets for exploits that can control RIP.
3002 emulate [default] Vsyscalls turn into traps and are
3003 emulated reasonably safely.
3005 native Vsyscalls are native syscall instructions.
3006 This is a little bit faster than trapping
3007 and makes a few dynamic recompilers work
3008 better than they would in emulation mode.
3009 It also makes exploits much easier to write.
3011 none Vsyscalls don't work at all. This makes
3012 them quite hard to use for exploits but
3013 might break your system.
3015 vt.cur_default= [VT] Default cursor shape.
3016 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3017 the parameters of the <Esc>[?A;B;Cc escape sequence;
3018 see VGA-softcursor.txt. Default: 2 = underline.
3020 vt.default_blu= [VT]
3021 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3022 Change the default blue palette of the console.
3023 This is a 16-member array composed of values
3024 ranging from 0-255.
3026 vt.default_grn= [VT]
3027 Format: <green0>,<green1>,<green2>,...,<green15>
3028 Change the default green palette of the console.
3029 This is a 16-member array composed of values
3030 ranging from 0-255.
3032 vt.default_red= [VT]
3033 Format: <red0>,<red1>,<red2>,...,<red15>
3034 Change the default red palette of the console.
3035 This is a 16-member array composed of values
3036 ranging from 0-255.
3038 vt.default_utf8=
3039 [VT]
3040 Format=<0|1>
3041 Set system-wide default UTF-8 mode for all tty's.
3042 Default is 1, i.e. UTF-8 mode is enabled for all
3043 newly opened terminals.
3045 vt.global_cursor_default=
3046 [VT]
3047 Format=<-1|0|1>
3048 Set system-wide default for whether a cursor
3049 is shown on new VTs. Default is -1,
3050 i.e. cursors will be created by default unless
3051 overridden by individual drivers. 0 will hide
3052 cursors, 1 will display them.
3054 watchdog timers [HW,WDT] For information on watchdog timers,
3055 see Documentation/watchdog/watchdog-parameters.txt
3056 or other driver-specific files in the
3057 Documentation/watchdog/ directory.
3059 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3060 default x2apic cluster mode on platforms
3061 supporting x2apic.
3063 x86_mrst_timer= [X86-32,APBT]
3064 Choose timer option for x86 Moorestown MID platform.
3065 Two valid options are apbt timer only and lapic timer
3066 plus one apbt timer for broadcast timer.
3067 x86_mrst_timer=apbt_only | lapic_and_apbt
3069 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
3070 xd_geo= See header of drivers/block/xd.c.
3072 xen_emul_unplug= [HW,X86,XEN]
3073 Unplug Xen emulated devices
3074 Format: [unplug0,][unplug1]
3075 ide-disks -- unplug primary master IDE devices
3076 aux-ide-disks -- unplug non-primary-master IDE devices
3077 nics -- unplug network devices
3078 all -- unplug all emulated devices (NICs and IDE disks)
3079 unnecessary -- unplugging emulated devices is
3080 unnecessary even if the host did not respond to
3081 the unplug protocol
3082 never -- do not unplug even if version check succeeds
3084 xirc2ps_cs= [NET,PCMCIA]
3085 Format:
3086 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3088 ______________________________________________________________________
3090 TODO:
3092 Add more DRM drivers.