| blob | a92c5ebf373e2bf4bea68072b58fbc0471ad9c13 |
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 amd_iommu_dump= [HW,X86-64]
339 Enable AMD IOMMU driver option to dump the ACPI table
340 for AMD IOMMU. With this option enabled, AMD IOMMU
341 driver will print ACPI tables for AMD IOMMU during
342 IOMMU initialization.
344 amijoy.map= [HW,JOY] Amiga joystick support
345 Map of devices attached to JOY0DAT and JOY1DAT
346 Format: <a>,<b>
347 See also Documentation/input/joystick.txt
349 analog.map= [HW,JOY] Analog joystick and gamepad support
350 Specifies type or capabilities of an analog joystick
351 connected to one of 16 gameports
352 Format: <type1>,<type2>,..<type16>
354 apc= [HW,SPARC]
355 Power management functions (SPARCstation-4/5 + deriv.)
356 Format: noidle
357 Disable APC CPU standby support. SPARCstation-Fox does
358 not play well with APC CPU idle - disable it if you have
359 APC and your system crashes randomly.
361 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
362 Change the output verbosity whilst booting
363 Format: { quiet (default) | verbose | debug }
364 Change the amount of debugging information output
365 when initialising the APIC and IO-APIC components.
367 autoconf= [IPV6]
368 See Documentation/networking/ipv6.txt.
370 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
371 Limit apic dumping. The parameter defines the maximal
372 number of local apics being dumped. Also it is possible
373 to set it to "all" by meaning -- no limit here.
374 Format: { 1 (default) | 2 | ... | all }.
375 The parameter valid if only apic=debug or
376 apic=verbose is specified.
377 Example: apic=debug show_lapic=all
379 apm= [APM] Advanced Power Management
380 See header of arch/x86/kernel/apm_32.c.
382 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
383 Format: <io>,<irq>,<nodeID>
385 ataflop= [HW,M68k]
387 atarimouse= [HW,MOUSE] Atari Mouse
389 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
390 EzKey and similar keyboards
392 atkbd.reset= [HW] Reset keyboard during initialization
394 atkbd.set= [HW] Select keyboard code set
395 Format: <int> (2 = AT (default), 3 = PS/2)
397 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
398 keyboards
400 atkbd.softraw= [HW] Choose between synthetic and real raw mode
401 Format: <bool> (0 = real, 1 = synthetic (default))
403 atkbd.softrepeat= [HW]
404 Use software keyboard repeat
406 baycom_epp= [HW,AX25]
407 Format: <io>,<mode>
409 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
410 Format: <io>,<mode>
411 See header of drivers/net/hamradio/baycom_par.c.
413 baycom_ser_fdx= [HW,AX25]
414 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
415 Format: <io>,<irq>,<mode>[,<baud>]
416 See header of drivers/net/hamradio/baycom_ser_fdx.c.
418 baycom_ser_hdx= [HW,AX25]
419 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
420 Format: <io>,<irq>,<mode>
421 See header of drivers/net/hamradio/baycom_ser_hdx.c.
423 boot_delay= Milliseconds to delay each printk during boot.
424 Values larger than 10 seconds (10000) are changed to
425 no delay (0).
426 Format: integer
428 bootmem_debug [KNL] Enable bootmem allocator debug messages.
430 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
431 bttv.radio= Most important insmod options are available as
432 kernel args too.
433 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
434 bttv.tuner=
436 bulk_remove=off [PPC] This parameter disables the use of the pSeries
437 firmware feature for flushing multiple hpte entries
438 at a time.
440 c101= [NET] Moxa C101 synchronous serial card
442 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
443 Sometimes CPU hardware bugs make them report the cache
444 size incorrectly. The kernel will attempt work arounds
445 to fix known problems, but for some CPUs it is not
446 possible to determine what the correct size should be.
447 This option provides an override for these situations.
449 capability.disable=
450 [SECURITY] Disable capabilities. This would normally
451 be used only if an alternative security model is to be
452 configured. Potentially dangerous and should only be
453 used if you are entirely sure of the consequences.
455 ccw_timeout_log [S390]
456 See Documentation/s390/CommonIO for details.
458 cgroup_disable= [KNL] Disable a particular controller
459 Format: {name of the controller(s) to disable}
460 {Currently supported controllers - "memory"}
462 checkreqprot [SELINUX] Set initial checkreqprot flag value.
463 Format: { "0" | "1" }
464 See security/selinux/Kconfig help text.
465 0 -- check protection applied by kernel (includes
466 any implied execute protection).
467 1 -- check protection requested by application.
468 Default value is set via a kernel config option.
469 Value can be changed at runtime via
470 /selinux/checkreqprot.
472 cio_ignore= [S390]
473 See Documentation/s390/CommonIO for details.
475 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
476 [Deprecated]
477 Forces specified clocksource (if available) to be used
478 when calculating gettimeofday(). If specified
479 clocksource is not available, it defaults to PIT.
480 Format: { pit | tsc | cyclone | pmtmr }
482 clocksource= Override the default clocksource
483 Format: <string>
484 Override the default clocksource and use the clocksource
485 with the name specified.
486 Some clocksource names to choose from, depending on
487 the platform:
488 [all] jiffies (this is the base, fallback clocksource)
489 [ACPI] acpi_pm
490 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
491 pxa_timer,timer3,32k_counter,timer0_1
492 [AVR32] avr32
493 [X86-32] pit,hpet,tsc;
494 scx200_hrt on Geode; cyclone on IBM x440
495 [MIPS] MIPS
496 [PARISC] cr16
497 [S390] tod
498 [SH] SuperH
499 [SPARC64] tick
500 [X86-64] hpet,tsc
502 clearcpuid=BITNUM [X86]
503 Disable CPUID feature X for the kernel. See
504 arch/x86/include/asm/cpufeature.h for the valid bit
505 numbers. Note the Linux specific bits are not necessarily
506 stable over kernel options, but the vendor specific
507 ones should be.
508 Also note that user programs calling CPUID directly
509 or using the feature without checking anything
510 will still see it. This just prevents it from
511 being used by the kernel or shown in /proc/cpuinfo.
512 Also note the kernel might malfunction if you disable
513 some critical bits.
515 cma=nn[MG] [ARM,KNL]
516 Sets the size of kernel global memory area for contiguous
517 memory allocations. For more information, see
518 include/linux/dma-contiguous.h
520 cmo_free_hint= [PPC] Format: { yes | no }
521 Specify whether pages are marked as being inactive
522 when they are freed. This is used in CMO environments
523 to determine OS memory pressure for page stealing by
524 a hypervisor.
525 Default: yes
527 coherent_pool=nn[KMG] [ARM,KNL]
528 Sets the size of memory pool for coherent, atomic dma
529 allocations if Contiguous Memory Allocator (CMA) is used.
531 code_bytes [X86] How many bytes of object code to print
532 in an oops report.
533 Range: 0 - 8192
534 Default: 64
536 com20020= [HW,NET] ARCnet - COM20020 chipset
537 Format:
538 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
540 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
541 Format: <io>[,<irq>]
543 com90xx= [HW,NET]
544 ARCnet - COM90xx chipset (memory-mapped buffers)
545 Format: <io>[,<irq>[,<memstart>]]
547 condev= [HW,S390] console device
548 conmode=
550 console= [KNL] Output console device and options.
552 tty<n> Use the virtual console device <n>.
554 ttyS<n>[,options]
555 ttyUSB0[,options]
556 Use the specified serial port. The options are of
557 the form "bbbbpnf", where "bbbb" is the baud rate,
558 "p" is parity ("n", "o", or "e"), "n" is number of
559 bits, and "f" is flow control ("r" for RTS or
560 omit it). Default is "9600n8".
562 See Documentation/serial-console.txt for more
563 information. See
564 Documentation/networking/netconsole.txt for an
565 alternative.
567 uart[8250],io,<addr>[,options]
568 uart[8250],mmio,<addr>[,options]
569 Start an early, polled-mode console on the 8250/16550
570 UART at the specified I/O port or MMIO address,
571 switching to the matching ttyS device later. The
572 options are the same as for ttyS, above.
574 If the device connected to the port is not a TTY but a braille
575 device, prepend "brl," before the device type, for instance
576 console=brl,ttyS0
577 For now, only VisioBraille is supported.
579 consoleblank= [KNL] The console blank (screen saver) timeout in
580 seconds. Defaults to 10*60 = 10mins. A value of 0
581 disables the blank timer.
583 coredump_filter=
584 [KNL] Change the default value for
585 /proc/<pid>/coredump_filter.
586 See also Documentation/filesystems/proc.txt.
588 cpuidle.off=1 [CPU_IDLE]
589 disable the cpuidle sub-system
591 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
592 Format:
593 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
595 crashkernel=size[KMG][@offset[KMG]]
596 [KNL] Using kexec, Linux can switch to a 'crash kernel'
597 upon panic. This parameter reserves the physical
598 memory region [offset, offset + size] for that kernel
599 image. If '@offset' is omitted, then a suitable offset
600 is selected automatically. Check
601 Documentation/kdump/kdump.txt for further details.
603 crashkernel=range1:size1[,range2:size2,...][@offset]
604 [KNL] Same as above, but depends on the memory
605 in the running system. The syntax of range is
606 start-[end] where start and end are both
607 a memory unit (amount[KMG]). See also
608 Documentation/kdump/kdump.txt for an example.
610 cs89x0_dma= [HW,NET]
611 Format: <dma>
613 cs89x0_media= [HW,NET]
614 Format: { rj45 | aui | bnc }
616 dasd= [HW,NET]
617 See header of drivers/s390/block/dasd_devmap.c.
619 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
620 (one device per port)
621 Format: <port#>,<type>
622 See also Documentation/input/joystick-parport.txt
624 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
625 time. See Documentation/dynamic-debug-howto.txt for
626 details. Deprecated, see dyndbg.
628 debug [KNL] Enable kernel debugging (events log level).
630 debug_locks_verbose=
631 [KNL] verbose self-tests
632 Format=<0|1>
633 Print debugging info while doing the locking API
634 self-tests.
635 We default to 0 (no extra messages), setting it to
636 1 will print _a lot_ more information - normally
637 only useful to kernel developers.
639 debug_objects [KNL] Enable object debugging
641 no_debug_objects
642 [KNL] Disable object debugging
644 debug_guardpage_minorder=
645 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
646 parameter allows control of the order of pages that will
647 be intentionally kept free (and hence protected) by the
648 buddy allocator. Bigger value increase the probability
649 of catching random memory corruption, but reduce the
650 amount of memory for normal system use. The maximum
651 possible value is MAX_ORDER/2. Setting this parameter
652 to 1 or 2 should be enough to identify most random
653 memory corruption problems caused by bugs in kernel or
654 driver code when a CPU writes to (or reads from) a
655 random memory location. Note that there exists a class
656 of memory corruptions problems caused by buggy H/W or
657 F/W or by drivers badly programing DMA (basically when
658 memory is written at bus level and the CPU MMU is
659 bypassed) which are not detectable by
660 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
661 tracking down these problems.
663 debugpat [X86] Enable PAT debugging
665 decnet.addr= [HW,NET]
666 Format: <area>[,<node>]
667 See also Documentation/networking/decnet.txt.
669 default_hugepagesz=
670 [same as hugepagesz=] The size of the default
671 HugeTLB page size. This is the size represented by
672 the legacy /proc/ hugepages APIs, used for SHM, and
673 default size when mounting hugetlbfs filesystems.
674 Defaults to the default architecture's huge page size
675 if not specified.
677 dhash_entries= [KNL]
678 Set number of hash buckets for dentry cache.
680 digi= [HW,SERIAL]
681 IO parameters + enable/disable command.
683 digiepca= [HW,SERIAL]
684 See drivers/char/README.epca and
685 Documentation/serial/digiepca.txt.
687 disable= [IPV6]
688 See Documentation/networking/ipv6.txt.
690 disable_ddw [PPC/PSERIES]
691 Disable Dynamic DMA Window support. Use this if
692 to workaround buggy firmware.
694 disable_ipv6= [IPV6]
695 See Documentation/networking/ipv6.txt.
697 disable_mtrr_cleanup [X86]
698 The kernel tries to adjust MTRR layout from continuous
699 to discrete, to make X server driver able to add WB
700 entry later. This parameter disables that.
702 disable_mtrr_trim [X86, Intel and AMD only]
703 By default the kernel will trim any uncacheable
704 memory out of your available memory pool based on
705 MTRR settings. This parameter disables that behavior,
706 possibly causing your machine to run very slowly.
708 disable_timer_pin_1 [X86]
709 Disable PIN 1 of APIC timer
710 Can be useful to work around chipset bugs.
712 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
713 this option disables the debugging code at boot.
715 dma_debug_entries=<number>
716 This option allows to tune the number of preallocated
717 entries for DMA-API debugging code. One entry is
718 required per DMA-API allocation. Use this if the
719 DMA-API debugging code disables itself because the
720 architectural default is too low.
722 dma_debug_driver=<driver_name>
723 With this option the DMA-API debugging driver
724 filter feature can be enabled at boot time. Just
725 pass the driver to filter for as the parameter.
726 The filter can be disabled or changed to another
727 driver later using sysfs.
729 drm_kms_helper.edid_firmware=[<connector>:]<file>
730 Broken monitors, graphic adapters and KVMs may
731 send no or incorrect EDID data sets. This parameter
732 allows to specify an EDID data set in the
733 /lib/firmware directory that is used instead.
734 Generic built-in EDID data sets are used, if one of
735 edid/1024x768.bin, edid/1280x1024.bin,
736 edid/1680x1050.bin, or edid/1920x1080.bin is given
737 and no file with the same name exists. Details and
738 instructions how to build your own EDID data are
739 available in Documentation/EDID/HOWTO.txt. An EDID
740 data set will only be used for a particular connector,
741 if its name and a colon are prepended to the EDID
742 name.
744 dscc4.setup= [NET]
746 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
747 module.dyndbg[="val"]
748 Enable debug messages at boot time. See
749 Documentation/dynamic-debug-howto.txt for details.
751 earlycon= [KNL] Output early console device and options.
752 uart[8250],io,<addr>[,options]
753 uart[8250],mmio,<addr>[,options]
754 uart[8250],mmio32,<addr>[,options]
755 Start an early, polled-mode console on the 8250/16550
756 UART at the specified I/O port or MMIO address.
757 MMIO inter-register address stride is either 8-bit
758 (mmio) or 32-bit (mmio32).
759 The options are the same as for ttyS, above.
761 earlyprintk= [X86,SH,BLACKFIN]
762 earlyprintk=vga
763 earlyprintk=serial[,ttySn[,baudrate]]
764 earlyprintk=ttySn[,baudrate]
765 earlyprintk=dbgp[debugController#]
767 Append ",keep" to not disable it when the real console
768 takes over.
770 Only vga or serial or usb debug port at a time.
772 Currently only ttyS0 and ttyS1 are supported.
774 Interaction with the standard serial driver is not
775 very good.
777 The VGA output is eventually overwritten by the real
778 console.
780 ekgdboc= [X86,KGDB] Allow early kernel console debugging
781 ekgdboc=kbd
783 This is designed to be used in conjunction with
784 the boot argument: earlyprintk=vga
786 edd= [EDD]
787 Format: {"off" | "on" | "skip[mbr]"}
789 eisa_irq_edge= [PARISC,HW]
790 See header of drivers/parisc/eisa.c.
792 elanfreq= [X86-32]
793 See comment before function elanfreq_setup() in
794 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
796 elevator= [IOSCHED]
797 Format: {"cfq" | "deadline" | "noop"}
798 See Documentation/block/cfq-iosched.txt and
799 Documentation/block/deadline-iosched.txt for details.
801 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
802 Specifies physical address of start of kernel core
803 image elf header and optionally the size. Generally
804 kexec loader will pass this option to capture kernel.
805 See Documentation/kdump/kdump.txt for details.
807 enable_mtrr_cleanup [X86]
808 The kernel tries to adjust MTRR layout from continuous
809 to discrete, to make X server driver able to add WB
810 entry later. This parameter enables that.
812 enable_timer_pin_1 [X86]
813 Enable PIN 1 of APIC timer
814 Can be useful to work around chipset bugs
815 (in particular on some ATI chipsets).
816 The kernel tries to set a reasonable default.
818 enforcing [SELINUX] Set initial enforcing status.
819 Format: {"0" | "1"}
820 See security/selinux/Kconfig help text.
821 0 -- permissive (log only, no denials).
822 1 -- enforcing (deny and log).
823 Default value is 0.
824 Value can be changed at runtime via /selinux/enforce.
826 erst_disable [ACPI]
827 Disable Error Record Serialization Table (ERST)
828 support.
830 ether= [HW,NET] Ethernet cards parameters
831 This option is obsoleted by the "netdev=" option, which
832 has equivalent usage. See its documentation for details.
834 evm= [EVM]
835 Format: { "fix" }
836 Permit 'security.evm' to be updated regardless of
837 current integrity status.
839 failslab=
840 fail_page_alloc=
841 fail_make_request=[KNL]
842 General fault injection mechanism.
843 Format: <interval>,<probability>,<space>,<times>
844 See also Documentation/fault-injection/.
846 floppy= [HW]
847 See Documentation/blockdev/floppy.txt.
849 force_pal_cache_flush
850 [IA-64] Avoid check_sal_cache_flush which may hang on
851 buggy SAL_CACHE_FLUSH implementations. Using this
852 parameter will force ia64_sal_cache_flush to call
853 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
855 ftrace=[tracer]
856 [FTRACE] will set and start the specified tracer
857 as early as possible in order to facilitate early
858 boot debugging.
860 ftrace_dump_on_oops[=orig_cpu]
861 [FTRACE] will dump the trace buffers on oops.
862 If no parameter is passed, ftrace will dump
863 buffers of all CPUs, but if you pass orig_cpu, it will
864 dump only the buffer of the CPU that triggered the
865 oops.
867 ftrace_filter=[function-list]
868 [FTRACE] Limit the functions traced by the function
869 tracer at boot up. function-list is a comma separated
870 list of functions. This list can be changed at run
871 time by the set_ftrace_filter file in the debugfs
872 tracing directory.
874 ftrace_notrace=[function-list]
875 [FTRACE] Do not trace the functions specified in
876 function-list. This list can be changed at run time
877 by the set_ftrace_notrace file in the debugfs
878 tracing directory.
880 ftrace_graph_filter=[function-list]
881 [FTRACE] Limit the top level callers functions traced
882 by the function graph tracer at boot up.
883 function-list is a comma separated list of functions
884 that can be changed at run time by the
885 set_graph_function file in the debugfs tracing directory.
887 gamecon.map[2|3]=
888 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
889 support via parallel port (up to 5 devices per port)
890 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
891 See also Documentation/input/joystick-parport.txt
893 gamma= [HW,DRM]
895 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
896 Format: off | on
897 default: on
899 gcov_persist= [GCOV] When non-zero (default), profiling data for
900 kernel modules is saved and remains accessible via
901 debugfs, even when the module is unloaded/reloaded.
902 When zero, profiling data is discarded and associated
903 debugfs files are removed at module unload time.
905 gpt [EFI] Forces disk with valid GPT signature but
906 invalid Protective MBR to be treated as GPT.
908 hashdist= [KNL,NUMA] Large hashes allocated during boot
909 are distributed across NUMA nodes. Defaults on
910 for 64-bit NUMA, off otherwise.
911 Format: 0 | 1 (for off | on)
913 hcl= [IA-64] SGI's Hardware Graph compatibility layer
915 hd= [EIDE] (E)IDE hard drive subsystem geometry
916 Format: <cyl>,<head>,<sect>
918 hest_disable [ACPI]
919 Disable Hardware Error Source Table (HEST) support;
920 corresponding firmware-first mode error processing
921 logic will be disabled.
923 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
924 size of <nn>. This works even on boxes that have no
925 highmem otherwise. This also works to reduce highmem
926 size on bigger boxes.
928 highres= [KNL] Enable/disable high resolution timer mode.
929 Valid parameters: "on", "off"
930 Default: "on"
932 hisax= [HW,ISDN]
933 See Documentation/isdn/README.HiSax.
935 hlt [BUGS=ARM,SH]
937 hpet= [X86-32,HPET] option to control HPET usage
938 Format: { enable (default) | disable | force |
939 verbose }
940 disable: disable HPET and use PIT instead
941 force: allow force enabled of undocumented chips (ICH4,
942 VIA, nVidia)
943 verbose: show contents of HPET registers during setup
945 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
946 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
947 On x86-64 and powerpc, this option can be specified
948 multiple times interleaved with hugepages= to reserve
949 huge pages of different sizes. Valid pages sizes on
950 x86-64 are 2M (when the CPU supports "pse") and 1G
951 (when the CPU supports the "pdpe1gb" cpuinfo flag)
952 Note that 1GB pages can only be allocated at boot time
953 using hugepages= and not freed afterwards.
955 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
956 terminal devices. Valid values: 0..8
957 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
958 If specified, z/VM IUCV HVC accepts connections
959 from listed z/VM user IDs only.
961 keep_bootcon [KNL]
962 Do not unregister boot console at start. This is only
963 useful for debugging when something happens in the window
964 between unregistering the boot console and initializing
965 the real console.
967 i2c_bus= [HW] Override the default board specific I2C bus speed
968 or register an additional I2C bus that is not
969 registered from board initialization code.
970 Format:
971 <bus_id>,<clkrate>
973 i8042.debug [HW] Toggle i8042 debug mode
974 i8042.direct [HW] Put keyboard port into non-translated mode
975 i8042.dumbkbd [HW] Pretend that controller can only read data from
976 keyboard and cannot control its state
977 (Don't attempt to blink the leds)
978 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
979 i8042.nokbd [HW] Don't check/create keyboard port
980 i8042.noloop [HW] Disable the AUX Loopback command while probing
981 for the AUX port
982 i8042.nomux [HW] Don't check presence of an active multiplexing
983 controller
984 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
985 controllers
986 i8042.notimeout [HW] Ignore timeout condition signalled by controller
987 i8042.reset [HW] Reset the controller during init and cleanup
988 i8042.unlock [HW] Unlock (ignore) the keylock
990 i810= [HW,DRM]
992 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
993 indicates that the driver is running on unsupported
994 hardware.
995 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
996 does not match list of supported models.
997 i8k.power_status
998 [HW] Report power status in /proc/i8k
999 (disabled by default)
1000 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1001 capability is set.
1003 i915.invert_brightness=
1004 [DRM] Invert the sense of the variable that is used to
1005 set the brightness of the panel backlight. Normally a
1006 brightness value of 0 indicates backlight switched off,
1007 and the maximum of the brightness value sets the backlight
1008 to maximum brightness. If this parameter is set to 0
1009 (default) and the machine requires it, or this parameter
1010 is set to 1, a brightness value of 0 sets the backlight
1011 to maximum brightness, and the maximum of the brightness
1012 value switches the backlight off.
1013 -1 -- never invert brightness
1014 0 -- machine default
1015 1 -- force brightness inversion
1017 icn= [HW,ISDN]
1018 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1020 ide-core.nodma= [HW] (E)IDE subsystem
1021 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1022 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1023 .cdrom .chs .ignore_cable are additional options
1024 See Documentation/ide/ide.txt.
1026 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1027 Claim all unknown PCI IDE storage controllers.
1029 idle= [X86]
1030 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
1031 Poll forces a polling idle loop that can slightly
1032 improve the performance of waking up a idle CPU, but
1033 will use a lot of power and make the system run hot.
1034 Not recommended.
1035 idle=mwait: On systems which support MONITOR/MWAIT but
1036 the kernel chose to not use it because it doesn't save
1037 as much power as a normal idle loop, use the
1038 MONITOR/MWAIT idle loop anyways. Performance should be
1039 the same as idle=poll.
1040 idle=halt: Halt is forced to be used for CPU idle.
1041 In such case C2/C3 won't be used again.
1042 idle=nomwait: Disable mwait for CPU C-states
1044 ignore_loglevel [KNL]
1045 Ignore loglevel setting - this will print /all/
1046 kernel messages to the console. Useful for debugging.
1047 We also add it as printk module parameter, so users
1048 could change it dynamically, usually by
1049 /sys/module/printk/parameters/ignore_loglevel.
1051 ihash_entries= [KNL]
1052 Set number of hash buckets for inode cache.
1054 ima_audit= [IMA]
1055 Format: { "0" | "1" }
1056 0 -- integrity auditing messages. (Default)
1057 1 -- enable informational integrity auditing messages.
1059 ima_hash= [IMA]
1060 Format: { "sha1" | "md5" }
1061 default: "sha1"
1063 ima_tcb [IMA]
1064 Load a policy which meets the needs of the Trusted
1065 Computing Base. This means IMA will measure all
1066 programs exec'd, files mmap'd for exec, and all files
1067 opened for read by uid=0.
1069 init= [KNL]
1070 Format: <full_path>
1071 Run specified binary instead of /sbin/init as init
1072 process.
1074 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1075 for working out where the kernel is dying during
1076 startup.
1078 initrd= [BOOT] Specify the location of the initial ramdisk
1080 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1081 Format: <irq>
1083 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1084 on
1085 Enable intel iommu driver.
1086 off
1087 Disable intel iommu driver.
1088 igfx_off [Default Off]
1089 By default, gfx is mapped as normal device. If a gfx
1090 device has a dedicated DMAR unit, the DMAR unit is
1091 bypassed by not enabling DMAR with this option. In
1092 this case, gfx device will use physical address for
1093 DMA.
1094 forcedac [x86_64]
1095 With this option iommu will not optimize to look
1096 for io virtual address below 32-bit forcing dual
1097 address cycle on pci bus for cards supporting greater
1098 than 32-bit addressing. The default is to look
1099 for translation below 32-bit and if not available
1100 then look in the higher range.
1101 strict [Default Off]
1102 With this option on every unmap_single operation will
1103 result in a hardware IOTLB flush operation as opposed
1104 to batching them for performance.
1105 sp_off [Default Off]
1106 By default, super page will be supported if Intel IOMMU
1107 has the capability. With this option, super page will
1108 not be supported.
1110 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1111 0 disables intel_idle and fall back on acpi_idle.
1112 1 to 6 specify maximum depth of C-state.
1114 intremap= [X86-64, Intel-IOMMU]
1115 on enable Interrupt Remapping (default)
1116 off disable Interrupt Remapping
1117 nosid disable Source ID checking
1118 no_x2apic_optout
1119 BIOS x2APIC opt-out request will be ignored
1121 iomem= Disable strict checking of access to MMIO memory
1122 strict regions from userspace.
1123 relaxed
1125 iommu= [x86]
1126 off
1127 force
1128 noforce
1129 biomerge
1130 panic
1131 nopanic
1132 merge
1133 nomerge
1134 forcesac
1135 soft
1136 pt [x86, IA-64]
1137 group_mf [x86, IA-64]
1140 io7= [HW] IO7 for Marvel based alpha systems
1141 See comment before marvel_specify_io7 in
1142 arch/alpha/kernel/core_marvel.c.
1144 io_delay= [X86] I/O delay method
1145 0x80
1146 Standard port 0x80 based delay
1147 0xed
1148 Alternate port 0xed based delay (needed on some systems)
1149 udelay
1150 Simple two microseconds delay
1151 none
1152 No delay
1154 ip= [IP_PNP]
1155 See Documentation/filesystems/nfs/nfsroot.txt.
1157 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1158 See comment before ip2_setup() in
1159 drivers/char/ip2/ip2base.c.
1161 irqfixup [HW]
1162 When an interrupt is not handled search all handlers
1163 for it. Intended to get systems with badly broken
1164 firmware running.
1166 irqpoll [HW]
1167 When an interrupt is not handled search all handlers
1168 for it. Also check all handlers each timer
1169 interrupt. Intended to get systems with badly broken
1170 firmware running.
1172 isapnp= [ISAPNP]
1173 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1175 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1176 Format:
1177 <cpu number>,...,<cpu number>
1178 or
1179 <cpu number>-<cpu number>
1180 (must be a positive range in ascending order)
1181 or a mixture
1182 <cpu number>,...,<cpu number>-<cpu number>
1184 This option can be used to specify one or more CPUs
1185 to isolate from the general SMP balancing and scheduling
1186 algorithms. You can move a process onto or off an
1187 "isolated" CPU via the CPU affinity syscalls or cpuset.
1188 <cpu number> begins at 0 and the maximum value is
1189 "number of CPUs in system - 1".
1191 This option is the preferred way to isolate CPUs. The
1192 alternative -- manually setting the CPU mask of all
1193 tasks in the system -- can cause problems and
1194 suboptimal load balancer performance.
1196 iucv= [HW,NET]
1198 js= [HW,JOY] Analog joystick
1199 See Documentation/input/joystick.txt.
1201 keepinitrd [HW,ARM]
1203 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1204 specifies the amount of memory usable by the kernel
1205 for non-movable allocations. The requested amount is
1206 spread evenly throughout all nodes in the system. The
1207 remaining memory in each node is used for Movable
1208 pages. In the event, a node is too small to have both
1209 kernelcore and Movable pages, kernelcore pages will
1210 take priority and other nodes will have a larger number
1211 of kernelcore pages. The Movable zone is used for the
1212 allocation of pages that may be reclaimed or moved
1213 by the page migration subsystem. This means that
1214 HugeTLB pages may not be allocated from this zone.
1215 Note that allocations like PTEs-from-HighMem still
1216 use the HighMem zone if it exists, and the Normal
1217 zone if it does not.
1219 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1220 Format: <Controller#>[,poll interval]
1221 The controller # is the number of the ehci usb debug
1222 port as it is probed via PCI. The poll interval is
1223 optional and is the number seconds in between
1224 each poll cycle to the debug port in case you need
1225 the functionality for interrupting the kernel with
1226 gdb or control-c on the dbgp connection. When
1227 not using this parameter you use sysrq-g to break into
1228 the kernel debugger.
1230 kgdboc= [KGDB,HW] kgdb over consoles.
1231 Requires a tty driver that supports console polling,
1232 or a supported polling keyboard driver (non-usb).
1233 Serial only format: <serial_device>[,baud]
1234 keyboard only format: kbd
1235 keyboard and serial format: kbd,<serial_device>[,baud]
1236 Optional Kernel mode setting:
1237 kms, kbd format: kms,kbd
1238 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1240 kgdbwait [KGDB] Stop kernel execution and enter the
1241 kernel debugger at the earliest opportunity.
1243 kmac= [MIPS] korina ethernet MAC address.
1244 Configure the RouterBoard 532 series on-chip
1245 Ethernet adapter MAC address.
1247 kmemleak= [KNL] Boot-time kmemleak enable/disable
1248 Valid arguments: on, off
1249 Default: on
1251 kstack=N [X86] Print N words from the kernel stack
1252 in oops dumps.
1254 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1255 Default is 0 (don't ignore, but inject #GP)
1257 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1258 KVM MMU at runtime.
1259 Default is 0 (off)
1261 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1262 Default is 1 (enabled)
1264 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1265 for all guests.
1266 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1268 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1269 (virtualized MMU) support on capable Intel chips.
1270 Default is 1 (enabled)
1272 kvm-intel.emulate_invalid_guest_state=
1273 [KVM,Intel] Enable emulation of invalid guest states
1274 Default is 0 (disabled)
1276 kvm-intel.flexpriority=
1277 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1278 Default is 1 (enabled)
1280 kvm-intel.nested=
1281 [KVM,Intel] Enable VMX nesting (nVMX).
1282 Default is 0 (disabled)
1284 kvm-intel.unrestricted_guest=
1285 [KVM,Intel] Disable unrestricted guest feature
1286 (virtualized real and unpaged mode) on capable
1287 Intel chips. Default is 1 (enabled)
1289 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1290 feature (tagged TLBs) on capable Intel chips.
1291 Default is 1 (enabled)
1293 l2cr= [PPC]
1295 l3cr= [PPC]
1297 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1298 disabled it.
1300 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1301 in C2 power state.
1303 libata.dma= [LIBATA] DMA control
1304 libata.dma=0 Disable all PATA and SATA DMA
1305 libata.dma=1 PATA and SATA Disk DMA only
1306 libata.dma=2 ATAPI (CDROM) DMA only
1307 libata.dma=4 Compact Flash DMA only
1308 Combinations also work, so libata.dma=3 enables DMA
1309 for disks and CDROMs, but not CFs.
1311 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1312 libata.ignore_hpa=0 keep BIOS limits (default)
1313 libata.ignore_hpa=1 ignore limits, using full disk
1315 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1316 when set.
1317 Format: <int>
1319 libata.force= [LIBATA] Force configurations. The format is comma
1320 separated list of "[ID:]VAL" where ID is
1321 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1322 matching port, link or device. Basically, it matches
1323 the ATA ID string printed on console by libata. If
1324 the whole ID part is omitted, the last PORT and DEVICE
1325 values are used. If ID hasn't been specified yet, the
1326 configuration applies to all ports, links and devices.
1328 If only DEVICE is omitted, the parameter applies to
1329 the port and all links and devices behind it. DEVICE
1330 number of 0 either selects the first device or the
1331 first fan-out link behind PMP device. It does not
1332 select the host link. DEVICE number of 15 selects the
1333 host link and device attached to it.
1335 The VAL specifies the configuration to force. As long
1336 as there's no ambiguity shortcut notation is allowed.
1337 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1338 The following configurations can be forced.
1340 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1341 Any ID with matching PORT is used.
1343 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1345 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1346 udma[/][16,25,33,44,66,100,133] notation is also
1347 allowed.
1349 * [no]ncq: Turn on or off NCQ.
1351 * nohrst, nosrst, norst: suppress hard, soft
1352 and both resets.
1354 * dump_id: dump IDENTIFY data.
1356 If there are multiple matching configurations changing
1357 the same attribute, the last one is used.
1359 memblock=debug [KNL] Enable memblock debug messages.
1361 load_ramdisk= [RAM] List of ramdisks to load from floppy
1362 See Documentation/blockdev/ramdisk.txt.
1364 lockd.nlm_grace_period=P [NFS] Assign grace period.
1365 Format: <integer>
1367 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1368 Format: <integer>
1370 lockd.nlm_timeout=T [NFS] Assign timeout value.
1371 Format: <integer>
1373 lockd.nlm_udpport=M [NFS] Assign UDP port.
1374 Format: <integer>
1376 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1377 Format: <irq>
1379 loglevel= All Kernel Messages with a loglevel smaller than the
1380 console loglevel will be printed to the console. It can
1381 also be changed with klogd or other programs. The
1382 loglevels are defined as follows:
1384 0 (KERN_EMERG) system is unusable
1385 1 (KERN_ALERT) action must be taken immediately
1386 2 (KERN_CRIT) critical conditions
1387 3 (KERN_ERR) error conditions
1388 4 (KERN_WARNING) warning conditions
1389 5 (KERN_NOTICE) normal but significant condition
1390 6 (KERN_INFO) informational
1391 7 (KERN_DEBUG) debug-level messages
1393 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1394 in bytes. n must be a power of two. The default
1395 size is set in the kernel config file.
1397 logo.nologo [FB] Disables display of the built-in Linux logo.
1398 This may be used to provide more screen space for
1399 kernel log messages and is useful when debugging
1400 kernel boot problems.
1402 lp=0 [LP] Specify parallel ports to use, e.g,
1403 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1404 lp=reset first parallel port). 'lp=0' disables the
1405 lp=auto printer driver. 'lp=reset' (which can be
1406 specified in addition to the ports) causes
1407 attached printers to be reset. Using
1408 lp=port1,port2,... specifies the parallel ports
1409 to associate lp devices with, starting with
1410 lp0. A port specification may be 'none' to skip
1411 that lp device, or a parport name such as
1412 'parport0'. Specifying 'lp=auto' instead of a
1413 port specification list means that device IDs
1414 from each port should be examined, to see if
1415 an IEEE 1284-compliant printer is attached; if
1416 so, the driver will manage that printer.
1417 See also header of drivers/char/lp.c.
1419 lpj=n [KNL]
1420 Sets loops_per_jiffy to given constant, thus avoiding
1421 time-consuming boot-time autodetection (up to 250 ms per
1422 CPU). 0 enables autodetection (default). To determine
1423 the correct value for your kernel, boot with normal
1424 autodetection and see what value is printed. Note that
1425 on SMP systems the preset will be applied to all CPUs,
1426 which is likely to cause problems if your CPUs need
1427 significantly divergent settings. An incorrect value
1428 will cause delays in the kernel to be wrong, leading to
1429 unpredictable I/O errors and other breakage. Although
1430 unlikely, in the extreme case this might damage your
1431 hardware.
1433 ltpc= [NET]
1434 Format: <io>,<irq>,<dma>
1436 machvec= [IA-64] Force the use of a particular machine-vector
1437 (machvec) in a generic kernel.
1438 Example: machvec=hpzx1_swiotlb
1440 machtype= [Loongson] Share the same kernel image file between different
1441 yeeloong laptop.
1442 Example: machtype=lemote-yeeloong-2f-7inch
1444 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1445 than or equal to this physical address is ignored.
1447 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1448 should make use of. maxcpus=n : n >= 0 limits the
1449 kernel to using 'n' processors. n=0 is a special case,
1450 it is equivalent to "nosmp", which also disables
1451 the IO APIC.
1453 max_loop= [LOOP] The number of loop block devices that get
1454 (loop.max_loop) unconditionally pre-created at init time. The default
1455 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1456 of statically allocating a predefined number, loop
1457 devices can be requested on-demand with the
1458 /dev/loop-control interface.
1460 mce [X86-32] Machine Check Exception
1462 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1464 md= [HW] RAID subsystems devices and level
1465 See Documentation/md.txt.
1467 mdacon= [MDA]
1468 Format: <first>,<last>
1469 Specifies range of consoles to be captured by the MDA.
1471 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1472 Amount of memory to be used when the kernel is not able
1473 to see the whole system memory or for test.
1474 [X86-32] Use together with memmap= to avoid physical
1475 address space collisions. Without memmap= PCI devices
1476 could be placed at addresses belonging to unused RAM.
1478 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1479 memory.
1481 memchunk=nn[KMG]
1482 [KNL,SH] Allow user to override the default size for
1483 per-device physically contiguous DMA buffers.
1485 memmap=exactmap [KNL,X86] Enable setting of an exact
1486 E820 memory map, as specified by the user.
1487 Such memmap=exactmap lines can be constructed based on
1488 BIOS output or other requirements. See the memmap=nn@ss
1489 option description.
1491 memmap=nn[KMG]@ss[KMG]
1492 [KNL] Force usage of a specific region of memory
1493 Region of memory to be used, from ss to ss+nn.
1495 memmap=nn[KMG]#ss[KMG]
1496 [KNL,ACPI] Mark specific memory as ACPI data.
1497 Region of memory to be used, from ss to ss+nn.
1499 memmap=nn[KMG]$ss[KMG]
1500 [KNL,ACPI] Mark specific memory as reserved.
1501 Region of memory to be used, from ss to ss+nn.
1502 Example: Exclude memory from 0x18690000-0x1869ffff
1503 memmap=64K$0x18690000
1504 or
1505 memmap=0x10000$0x18690000
1507 memory_corruption_check=0/1 [X86]
1508 Some BIOSes seem to corrupt the first 64k of
1509 memory when doing things like suspend/resume.
1510 Setting this option will scan the memory
1511 looking for corruption. Enabling this will
1512 both detect corruption and prevent the kernel
1513 from using the memory being corrupted.
1514 However, its intended as a diagnostic tool; if
1515 repeatable BIOS-originated corruption always
1516 affects the same memory, you can use memmap=
1517 to prevent the kernel from using that memory.
1519 memory_corruption_check_size=size [X86]
1520 By default it checks for corruption in the low
1521 64k, making this memory unavailable for normal
1522 use. Use this parameter to scan for
1523 corruption in more or less memory.
1525 memory_corruption_check_period=seconds [X86]
1526 By default it checks for corruption every 60
1527 seconds. Use this parameter to check at some
1528 other rate. 0 disables periodic checking.
1530 memtest= [KNL,X86] Enable memtest
1531 Format: <integer>
1532 default : 0 <disable>
1533 Specifies the number of memtest passes to be
1534 performed. Each pass selects another test
1535 pattern from a given set of patterns. Memtest
1536 fills the memory with this pattern, validates
1537 memory contents and reserves bad memory
1538 regions that are detected.
1540 meye.*= [HW] Set MotionEye Camera parameters
1541 See Documentation/video4linux/meye.txt.
1543 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1544 Multi-Function General Purpose Timers on AMD Geode
1545 platforms.
1547 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1548 the BIOS has incorrectly applied a workaround. TinyBIOS
1549 version 0.98 is known to be affected, 0.99 fixes the
1550 problem by letting the user disable the workaround.
1552 mga= [HW,DRM]
1554 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1555 physical address is ignored.
1557 mini2440= [ARM,HW,KNL]
1558 Format:[0..2][b][c][t]
1559 Default: "0tb"
1560 MINI2440 configuration specification:
1561 0 - The attached screen is the 3.5" TFT
1562 1 - The attached screen is the 7" TFT
1563 2 - The VGA Shield is attached (1024x768)
1564 Leaving out the screen size parameter will not load
1565 the TFT driver, and the framebuffer will be left
1566 unconfigured.
1567 b - Enable backlight. The TFT backlight pin will be
1568 linked to the kernel VESA blanking code and a GPIO
1569 LED. This parameter is not necessary when using the
1570 VGA shield.
1571 c - Enable the s3c camera interface.
1572 t - Reserved for enabling touchscreen support. The
1573 touchscreen support is not enabled in the mainstream
1574 kernel as of 2.6.30, a preliminary port can be found
1575 in the "bleeding edge" mini2440 support kernel at
1576 http://repo.or.cz/w/linux-2.6/mini2440.git
1578 mminit_loglevel=
1579 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1580 parameter allows control of the logging verbosity for
1581 the additional memory initialisation checks. A value
1582 of 0 disables mminit logging and a level of 4 will
1583 log everything. Information is printed at KERN_DEBUG
1584 so loglevel=8 may also need to be specified.
1586 mousedev.tap_time=
1587 [MOUSE] Maximum time between finger touching and
1588 leaving touchpad surface for touch to be considered
1589 a tap and be reported as a left button click (for
1590 touchpads working in absolute mode only).
1591 Format: <msecs>
1592 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1593 reporting absolute coordinates, such as tablets
1594 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1595 reporting absolute coordinates, such as tablets
1597 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1598 is similar to kernelcore except it specifies the
1599 amount of memory used for migratable allocations.
1600 If both kernelcore and movablecore is specified,
1601 then kernelcore will be at *least* the specified
1602 value but may be more. If movablecore on its own
1603 is specified, the administrator must be careful
1604 that the amount of memory usable for all allocations
1605 is not too small.
1607 MTD_Partition= [MTD]
1608 Format: <name>,<region-number>,<size>,<offset>
1610 MTD_Region= [MTD] Format:
1611 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1613 mtdparts= [MTD]
1614 See drivers/mtd/cmdlinepart.c.
1616 multitce=off [PPC] This parameter disables the use of the pSeries
1617 firmware feature for updating multiple TCE entries
1618 at a time.
1620 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1622 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1624 boundary - index of last SLC block on Flex-OneNAND.
1625 The remaining blocks are configured as MLC blocks.
1626 lock - Configure if Flex-OneNAND boundary should be locked.
1627 Once locked, the boundary cannot be changed.
1628 1 indicates lock status, 0 indicates unlock status.
1630 mtdset= [ARM]
1631 ARM/S3C2412 JIVE boot control
1633 See arch/arm/mach-s3c2412/mach-jive.c
1635 mtouchusb.raw_coordinates=
1636 [HW] Make the MicroTouch USB driver use raw coordinates
1637 ('y', default) or cooked coordinates ('n')
1639 mtrr_chunk_size=nn[KMG] [X86]
1640 used for mtrr cleanup. It is largest continuous chunk
1641 that could hold holes aka. UC entries.
1643 mtrr_gran_size=nn[KMG] [X86]
1644 Used for mtrr cleanup. It is granularity of mtrr block.
1645 Default is 1.
1646 Large value could prevent small alignment from
1647 using up MTRRs.
1649 mtrr_spare_reg_nr=n [X86]
1650 Format: <integer>
1651 Range: 0,7 : spare reg number
1652 Default : 1
1653 Used for mtrr cleanup. It is spare mtrr entries number.
1654 Set to 2 or more if your graphical card needs more.
1656 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1658 netdev= [NET] Network devices parameters
1659 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1660 Note that mem_start is often overloaded to mean
1661 something different and driver-specific.
1662 This usage is only documented in each driver source
1663 file if at all.
1665 nf_conntrack.acct=
1666 [NETFILTER] Enable connection tracking flow accounting
1667 0 to disable accounting
1668 1 to enable accounting
1669 Default value is 0.
1671 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1672 See Documentation/filesystems/nfs/nfsroot.txt.
1674 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1675 See Documentation/filesystems/nfs/nfsroot.txt.
1677 nfsrootdebug [NFS] enable nfsroot debugging messages.
1678 See Documentation/filesystems/nfs/nfsroot.txt.
1680 nfs.callback_tcpport=
1681 [NFS] set the TCP port on which the NFSv4 callback
1682 channel should listen.
1684 nfs.cache_getent=
1685 [NFS] sets the pathname to the program which is used
1686 to update the NFS client cache entries.
1688 nfs.cache_getent_timeout=
1689 [NFS] sets the timeout after which an attempt to
1690 update a cache entry is deemed to have failed.
1692 nfs.idmap_cache_timeout=
1693 [NFS] set the maximum lifetime for idmapper cache
1694 entries.
1696 nfs.enable_ino64=
1697 [NFS] enable 64-bit inode numbers.
1698 If zero, the NFS client will fake up a 32-bit inode
1699 number for the readdir() and stat() syscalls instead
1700 of returning the full 64-bit number.
1701 The default is to return 64-bit inode numbers.
1703 nfs.max_session_slots=
1704 [NFSv4.1] Sets the maximum number of session slots
1705 the client will attempt to negotiate with the server.
1706 This limits the number of simultaneous RPC requests
1707 that the client can send to the NFSv4.1 server.
1708 Note that there is little point in setting this
1709 value higher than the max_tcp_slot_table_limit.
1711 nfs.nfs4_disable_idmapping=
1712 [NFSv4] When set to the default of '1', this option
1713 ensures that both the RPC level authentication
1714 scheme and the NFS level operations agree to use
1715 numeric uids/gids if the mount is using the
1716 'sec=sys' security flavour. In effect it is
1717 disabling idmapping, which can make migration from
1718 legacy NFSv2/v3 systems to NFSv4 easier.
1719 Servers that do not support this mode of operation
1720 will be autodetected by the client, and it will fall
1721 back to using the idmapper.
1722 To turn off this behaviour, set the value to '0'.
1724 nfs.send_implementation_id =
1725 [NFSv4.1] Send client implementation identification
1726 information in exchange_id requests.
1727 If zero, no implementation identification information
1728 will be sent.
1729 The default is to send the implementation identification
1730 information.
1732 nfsd.nfs4_disable_idmapping=
1733 [NFSv4] When set to the default of '1', the NFSv4
1734 server will return only numeric uids and gids to
1735 clients using auth_sys, and will accept numeric uids
1736 and gids from such clients. This is intended to ease
1737 migration from NFSv2/v3.
1739 objlayoutdriver.osd_login_prog=
1740 [NFS] [OBJLAYOUT] sets the pathname to the program which
1741 is used to automatically discover and login into new
1742 osd-targets. Please see:
1743 Documentation/filesystems/pnfs.txt for more explanations
1745 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1746 when a NMI is triggered.
1747 Format: [state][,regs][,debounce][,die]
1749 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1750 Format: [panic,][nopanic,][num]
1751 Valid num: 0
1752 0 - turn nmi_watchdog off
1753 When panic is specified, panic when an NMI watchdog
1754 timeout occurs (or 'nopanic' to override the opposite
1755 default).
1756 This is useful when you use a panic=... timeout and
1757 need the box quickly up again.
1759 netpoll.carrier_timeout=
1760 [NET] Specifies amount of time (in seconds) that
1761 netpoll should wait for a carrier. By default netpoll
1762 waits 4 seconds.
1764 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1765 emulation library even if a 387 maths coprocessor
1766 is present.
1768 no_console_suspend
1769 [HW] Never suspend the console
1770 Disable suspending of consoles during suspend and
1771 hibernate operations. Once disabled, debugging
1772 messages can reach various consoles while the rest
1773 of the system is being put to sleep (ie, while
1774 debugging driver suspend/resume hooks). This may
1775 not work reliably with all consoles, but is known
1776 to work with serial and VGA consoles.
1777 To facilitate more flexible debugging, we also add
1778 console_suspend, a printk module parameter to control
1779 it. Users could use console_suspend (usually
1780 /sys/module/printk/parameters/console_suspend) to
1781 turn on/off it dynamically.
1783 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1784 caches in the slab allocator. Saves per-node memory,
1785 but will impact performance.
1787 noalign [KNL,ARM]
1789 noapic [SMP,APIC] Tells the kernel to not make use of any
1790 IOAPICs that may be present in the system.
1792 noautogroup Disable scheduler automatic task group creation.
1794 nobats [PPC] Do not use BATs for mapping kernel lowmem
1795 on "Classic" PPC cores.
1797 nocache [ARM]
1799 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1801 nodelayacct [KNL] Disable per-task delay accounting
1803 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1805 nodsp [SH] Disable hardware DSP at boot time.
1807 noefi [X86] Disable EFI runtime services support.
1809 noexec [IA-64]
1811 noexec [X86]
1812 On X86-32 available only on PAE configured kernels.
1813 noexec=on: enable non-executable mappings (default)
1814 noexec=off: disable non-executable mappings
1816 nosmep [X86]
1817 Disable SMEP (Supervisor Mode Execution Protection)
1818 even if it is supported by processor.
1820 noexec32 [X86-64]
1821 This affects only 32-bit executables.
1822 noexec32=on: enable non-executable mappings (default)
1823 read doesn't imply executable mappings
1824 noexec32=off: disable non-executable mappings
1825 read implies executable mappings
1827 nofpu [SH] Disable hardware FPU at boot time.
1829 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1830 register save and restore. The kernel will only save
1831 legacy floating-point registers on task switch.
1833 noxsave [BUGS=X86] Disables x86 extended register state save
1834 and restore using xsave. The kernel will fallback to
1835 enabling legacy floating-point and sse state.
1837 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1838 wfi(ARM) instruction doesn't work correctly and not to
1839 use it. This is also useful when using JTAG debugger.
1841 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1842 instruction doesn't work correctly and not to
1843 use it.
1845 no_file_caps Tells the kernel not to honor file capabilities. The
1846 only way then for a file to be executed with privilege
1847 is to be setuid root or executed by root.
1849 nohalt [IA-64] Tells the kernel not to use the power saving
1850 function PAL_HALT_LIGHT when idle. This increases
1851 power-consumption. On the positive side, it reduces
1852 interrupt wake-up latency, which may improve performance
1853 in certain environments such as networked servers or
1854 real-time systems.
1856 nohz= [KNL] Boottime enable/disable dynamic ticks
1857 Valid arguments: on, off
1858 Default: on
1860 noiotrap [SH] Disables trapped I/O port accesses.
1862 noirqdebug [X86-32] Disables the code which attempts to detect and
1863 disable unhandled interrupt sources.
1865 no_timer_check [X86,APIC] Disables the code which tests for
1866 broken timer IRQ sources.
1868 noisapnp [ISAPNP] Disables ISA PnP code.
1870 noinitrd [RAM] Tells the kernel not to load any configured
1871 initial RAM disk.
1873 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1874 remapping.
1875 [Deprecated - use intremap=off]
1877 nointroute [IA-64]
1879 nojitter [IA-64] Disables jitter checking for ITC timers.
1881 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1883 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1884 fault handling.
1886 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1887 steal time is computed, but won't influence scheduler
1888 behaviour
1890 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1892 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1894 noltlbs [PPC] Do not use large page/tlb entries for kernel
1895 lowmem mapping on PPC40x.
1897 nomca [IA-64] Disable machine check abort handling
1899 nomce [X86-32] Machine Check Exception
1901 nomfgpt [X86-32] Disable Multi-Function General Purpose
1902 Timer usage (for AMD Geode machines).
1904 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
1905 shutdown the other cpus. Instead use the REBOOT_VECTOR
1906 irq.
1908 nomodule Disable module load
1910 nopat [X86] Disable PAT (page attribute table extension of
1911 pagetables) support.
1913 norandmaps Don't use address space randomization. Equivalent to
1914 echo 0 > /proc/sys/kernel/randomize_va_space
1916 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1918 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1919 with UP alternatives
1921 noresidual [PPC] Don't use residual data on PReP machines.
1923 nordrand [X86] Disable the direct use of the RDRAND
1924 instruction even if it is supported by the
1925 processor. RDRAND is still available to user
1926 space applications.
1928 noresume [SWSUSP] Disables resume and restores original swap
1929 space.
1931 no-scroll [VGA] Disables scrollback.
1932 This is required for the Braillex ib80-piezo Braille
1933 reader made by F.H. Papenmeier (Germany).
1935 nosbagart [IA-64]
1937 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1939 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1940 and disable the IO APIC. legacy for "maxcpus=0".
1942 nosoftlockup [KNL] Disable the soft-lockup detector.
1944 nosync [HW,M68K] Disables sync negotiation for all devices.
1946 notsc [BUGS=X86-32] Disable Time Stamp Counter
1948 nousb [USB] Disable the USB subsystem
1950 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1952 nowb [ARM]
1954 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1956 nptcg= [IA-64] Override max number of concurrent global TLB
1957 purges which is reported from either PAL_VM_SUMMARY or
1958 SAL PALO.
1960 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1961 could support. nr_cpus=n : n >= 1 limits the kernel to
1962 supporting 'n' processors. Later in runtime you can not
1963 use hotplug cpu feature to put more cpu back to online.
1964 just like you compile the kernel NR_CPUS=n
1966 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1968 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1969 one of ['zone', 'node', 'default'] can be specified
1970 This can be set from sysctl after boot.
1971 See Documentation/sysctl/vm.txt for details.
1973 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1974 See Documentation/debugging-via-ohci1394.txt for more
1975 info.
1977 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1978 Rather than timing out after 20 ms if an EC
1979 command is not properly ACKed, override the length
1980 of the timeout. We have interrupts disabled while
1981 waiting for the ACK, so if this is set too high
1982 interrupts *may* be lost!
1984 omap_mux= [OMAP] Override bootloader pin multiplexing.
1985 Format: <mux_mode0.mode_name=value>...
1986 For example, to override I2C bus2:
1987 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1989 oprofile.timer= [HW]
1990 Use timer interrupt instead of performance counters
1992 oprofile.cpu_type= Force an oprofile cpu type
1993 This might be useful if you have an older oprofile
1994 userland or if you want common events.
1995 Format: { arch_perfmon }
1996 arch_perfmon: [X86] Force use of architectural
1997 perfmon on Intel CPUs instead of the
1998 CPU specific event set.
1999 timer: [X86] Force use of architectural NMI
2000 timer mode (see also oprofile.timer
2001 for generic hr timer mode)
2002 [s390] Force legacy basic mode sampling
2003 (report cpu_type "timer")
2005 oops=panic Always panic on oopses. Default is to just kill the
2006 process, but there is a small probability of
2007 deadlocking the machine.
2008 This will also cause panics on machine check exceptions.
2009 Useful together with panic=30 to trigger a reboot.
2011 OSS [HW,OSS]
2012 See Documentation/sound/oss/oss-parameters.txt
2014 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2015 timeout > 0: seconds before rebooting
2016 timeout = 0: wait forever
2017 timeout < 0: reboot immediately
2018 Format: <timeout>
2020 parkbd.port= [HW] Parallel port number the keyboard adapter is
2021 connected to, default is 0.
2022 Format: <parport#>
2023 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2024 0 for XT, 1 for AT (default is AT).
2025 Format: <mode>
2027 parport= [HW,PPT] Specify parallel ports. 0 disables.
2028 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2029 Use 'auto' to force the driver to use any
2030 IRQ/DMA settings detected (the default is to
2031 ignore detected IRQ/DMA settings because of
2032 possible conflicts). You can specify the base
2033 address, IRQ, and DMA settings; IRQ and DMA
2034 should be numbers, or 'auto' (for using detected
2035 settings on that particular port), or 'nofifo'
2036 (to avoid using a FIFO even if it is detected).
2037 Parallel ports are assigned in the order they
2038 are specified on the command line, starting
2039 with parport0.
2041 parport_init_mode= [HW,PPT]
2042 Configure VIA parallel port to operate in
2043 a specific mode. This is necessary on Pegasos
2044 computer where firmware has no options for setting
2045 up parallel port mode and sets it to spp.
2046 Currently this function knows 686a and 8231 chips.
2047 Format: [spp|ps2|epp|ecp|ecpepp]
2049 pause_on_oops=
2050 Halt all CPUs after the first oops has been printed for
2051 the specified number of seconds. This is to be used if
2052 your oopses keep scrolling off the screen.
2054 pcbit= [HW,ISDN]
2056 pcd. [PARIDE]
2057 See header of drivers/block/paride/pcd.c.
2058 See also Documentation/blockdev/paride.txt.
2060 pci=option[,option...] [PCI] various PCI subsystem options:
2061 earlydump [X86] dump PCI config space before the kernel
2062 changes anything
2063 off [X86] don't probe for the PCI bus
2064 bios [X86-32] force use of PCI BIOS, don't access
2065 the hardware directly. Use this if your machine
2066 has a non-standard PCI host bridge.
2067 nobios [X86-32] disallow use of PCI BIOS, only direct
2068 hardware access methods are allowed. Use this
2069 if you experience crashes upon bootup and you
2070 suspect they are caused by the BIOS.
2071 conf1 [X86] Force use of PCI Configuration
2072 Mechanism 1.
2073 conf2 [X86] Force use of PCI Configuration
2074 Mechanism 2.
2075 noaer [PCIE] If the PCIEAER kernel config parameter is
2076 enabled, this kernel boot option can be used to
2077 disable the use of PCIE advanced error reporting.
2078 nodomains [PCI] Disable support for multiple PCI
2079 root domains (aka PCI segments, in ACPI-speak).
2080 nommconf [X86] Disable use of MMCONFIG for PCI
2081 Configuration
2082 check_enable_amd_mmconf [X86] check for and enable
2083 properly configured MMIO access to PCI
2084 config space on AMD family 10h CPU
2085 nomsi [MSI] If the PCI_MSI kernel config parameter is
2086 enabled, this kernel boot option can be used to
2087 disable the use of MSI interrupts system-wide.
2088 noioapicquirk [APIC] Disable all boot interrupt quirks.
2089 Safety option to keep boot IRQs enabled. This
2090 should never be necessary.
2091 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2092 primary IO-APIC for bridges that cannot disable
2093 boot IRQs. This fixes a source of spurious IRQs
2094 when the system masks IRQs.
2095 noioapicreroute [APIC] Disable workaround that uses the
2096 boot IRQ equivalent of an IRQ that connects to
2097 a chipset where boot IRQs cannot be disabled.
2098 The opposite of ioapicreroute.
2099 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2100 routing table. These calls are known to be buggy
2101 on several machines and they hang the machine
2102 when used, but on other computers it's the only
2103 way to get the interrupt routing table. Try
2104 this option if the kernel is unable to allocate
2105 IRQs or discover secondary PCI buses on your
2106 motherboard.
2107 rom [X86] Assign address space to expansion ROMs.
2108 Use with caution as certain devices share
2109 address decoders between ROMs and other
2110 resources.
2111 norom [X86] Do not assign address space to
2112 expansion ROMs that do not already have
2113 BIOS assigned address ranges.
2114 nobar [X86] Do not assign address space to the
2115 BARs that weren't assigned by the BIOS.
2116 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2117 assigned automatically to PCI devices. You can
2118 make the kernel exclude IRQs of your ISA cards
2119 this way.
2120 pirqaddr=0xAAAAA [X86] Specify the physical address
2121 of the PIRQ table (normally generated
2122 by the BIOS) if it is outside the
2123 F0000h-100000h range.
2124 lastbus=N [X86] Scan all buses thru bus #N. Can be
2125 useful if the kernel is unable to find your
2126 secondary buses and you want to tell it
2127 explicitly which ones they are.
2128 assign-busses [X86] Always assign all PCI bus
2129 numbers ourselves, overriding
2130 whatever the firmware may have done.
2131 usepirqmask [X86] Honor the possible IRQ mask stored
2132 in the BIOS $PIR table. This is needed on
2133 some systems with broken BIOSes, notably
2134 some HP Pavilion N5400 and Omnibook XE3
2135 notebooks. This will have no effect if ACPI
2136 IRQ routing is enabled.
2137 noacpi [X86] Do not use ACPI for IRQ routing
2138 or for PCI scanning.
2139 use_crs [X86] Use PCI host bridge window information
2140 from ACPI. On BIOSes from 2008 or later, this
2141 is enabled by default. If you need to use this,
2142 please report a bug.
2143 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2144 If you need to use this, please report a bug.
2145 routeirq Do IRQ routing for all PCI devices.
2146 This is normally done in pci_enable_device(),
2147 so this option is a temporary workaround
2148 for broken drivers that don't call it.
2149 skip_isa_align [X86] do not align io start addr, so can
2150 handle more pci cards
2151 firmware [ARM] Do not re-enumerate the bus but instead
2152 just use the configuration from the
2153 bootloader. This is currently used on
2154 IXP2000 systems where the bus has to be
2155 configured a certain way for adjunct CPUs.
2156 noearly [X86] Don't do any early type 1 scanning.
2157 This might help on some broken boards which
2158 machine check when some devices' config space
2159 is read. But various workarounds are disabled
2160 and some IOMMU drivers will not work.
2161 bfsort Sort PCI devices into breadth-first order.
2162 This sorting is done to get a device
2163 order compatible with older (<= 2.4) kernels.
2164 nobfsort Don't sort PCI devices into breadth-first order.
2165 cbiosize=nn[KMG] The fixed amount of bus space which is
2166 reserved for the CardBus bridge's IO window.
2167 The default value is 256 bytes.
2168 cbmemsize=nn[KMG] The fixed amount of bus space which is
2169 reserved for the CardBus bridge's memory
2170 window. The default value is 64 megabytes.
2171 resource_alignment=
2172 Format:
2173 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2174 Specifies alignment and device to reassign
2175 aligned memory resources.
2176 If <order of align> is not specified,
2177 PAGE_SIZE is used as alignment.
2178 PCI-PCI bridge can be specified, if resource
2179 windows need to be expanded.
2180 ecrc= Enable/disable PCIe ECRC (transaction layer
2181 end-to-end CRC checking).
2182 bios: Use BIOS/firmware settings. This is the
2183 the default.
2184 off: Turn ECRC off
2185 on: Turn ECRC on.
2186 realloc= Enable/disable reallocating PCI bridge resources
2187 if allocations done by BIOS are too small to
2188 accommodate resources required by all child
2189 devices.
2190 off: Turn realloc off
2191 on: Turn realloc on
2192 realloc same as realloc=on
2193 noari do not use PCIe ARI.
2194 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2195 only look for one device below a PCIe downstream
2196 port.
2198 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2199 Management.
2200 off Disable ASPM.
2201 force Enable ASPM even on devices that claim not to support it.
2202 WARNING: Forcing ASPM on may cause system lockups.
2204 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2205 nomsi Do not use MSI for PCI Express Native Hotplug (this
2206 makes all PCIe ports use INTx for hotplug services).
2208 pcie_ports= [PCIE] PCIe ports handling:
2209 auto Ask the BIOS whether or not to use native PCIe services
2210 associated with PCIe ports (PME, hot-plug, AER). Use
2211 them only if that is allowed by the BIOS.
2212 native Use native PCIe services associated with PCIe ports
2213 unconditionally.
2214 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2215 ports driver.
2217 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2218 nomsi Do not use MSI for native PCIe PME signaling (this makes
2219 all PCIe root ports use INTx for all services).
2221 pcmv= [HW,PCMCIA] BadgePAD 4
2223 pd. [PARIDE]
2224 See Documentation/blockdev/paride.txt.
2226 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2227 boot time.
2228 Format: { 0 | 1 }
2229 See arch/parisc/kernel/pdc_chassis.c
2231 percpu_alloc= Select which percpu first chunk allocator to use.
2232 Currently supported values are "embed" and "page".
2233 Archs may support subset or none of the selections.
2234 See comments in mm/percpu.c for details on each
2235 allocator. This parameter is primarily for debugging
2236 and performance comparison.
2238 pf. [PARIDE]
2239 See Documentation/blockdev/paride.txt.
2241 pg. [PARIDE]
2242 See Documentation/blockdev/paride.txt.
2244 pirq= [SMP,APIC] Manual mp-table setup
2245 See Documentation/x86/i386/IO-APIC.txt.
2247 plip= [PPT,NET] Parallel port network link
2248 Format: { parport<nr> | timid | 0 }
2249 See also Documentation/parport.txt.
2251 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2252 Override pmtimer IOPort with a hex value.
2253 e.g. pmtmr=0x508
2255 pnp.debug=1 [PNP]
2256 Enable PNP debug messages (depends on the
2257 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2258 via /sys/module/pnp/parameters/debug. We always show
2259 current resource usage; turning this on also shows
2260 possible settings and some assignment information.
2262 pnpacpi= [ACPI]
2263 { off }
2265 pnpbios= [ISAPNP]
2266 { on | off | curr | res | no-curr | no-res }
2268 pnp_reserve_irq=
2269 [ISAPNP] Exclude IRQs for the autoconfiguration
2271 pnp_reserve_dma=
2272 [ISAPNP] Exclude DMAs for the autoconfiguration
2274 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2275 Ranges are in pairs (I/O port base and size).
2277 pnp_reserve_mem=
2278 [ISAPNP] Exclude memory regions for the
2279 autoconfiguration.
2280 Ranges are in pairs (memory base and size).
2282 ports= [IP_VS_FTP] IPVS ftp helper module
2283 Default is 21.
2284 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2285 may be specified.
2286 Format: <port>,<port>....
2288 print-fatal-signals=
2289 [KNL] debug: print fatal signals
2291 If enabled, warn about various signal handling
2292 related application anomalies: too many signals,
2293 too many POSIX.1 timers, fatal signals causing a
2294 coredump - etc.
2296 If you hit the warning due to signal overflow,
2297 you might want to try "ulimit -i unlimited".
2299 default: off.
2301 printk.always_kmsg_dump=
2302 Trigger kmsg_dump for cases other than kernel oops or
2303 panics
2304 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2305 default: disabled
2307 printk.time= Show timing data prefixed to each printk message line
2308 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2310 processor.max_cstate= [HW,ACPI]
2311 Limit processor to maximum C-state
2312 max_cstate=9 overrides any DMI blacklist limit.
2314 processor.nocst [HW,ACPI]
2315 Ignore the _CST method to determine C-states,
2316 instead using the legacy FADT method
2318 profile= [KNL] Enable kernel profiling via /proc/profile
2319 Format: [schedule,]<number>
2320 Param: "schedule" - profile schedule points.
2321 Param: <number> - step/bucket size as a power of 2 for
2322 statistical time based profiling.
2323 Param: "sleep" - profile D-state sleeping (millisecs).
2324 Requires CONFIG_SCHEDSTATS
2325 Param: "kvm" - profile VM exits.
2327 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2328 before loading.
2329 See Documentation/blockdev/ramdisk.txt.
2331 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2332 probe for; one of (bare|imps|exps|lifebook|any).
2333 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2334 per second.
2335 psmouse.resetafter= [HW,MOUSE]
2336 Try to reset the device after so many bad packets
2337 (0 = never).
2338 psmouse.resolution=
2339 [HW,MOUSE] Set desired mouse resolution, in dpi.
2340 psmouse.smartscroll=
2341 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2342 0 = disabled, 1 = enabled (default).
2344 pstore.backend= Specify the name of the pstore backend to use
2346 pt. [PARIDE]
2347 See Documentation/blockdev/paride.txt.
2349 pty.legacy_count=
2350 [KNL] Number of legacy pty's. Overwrites compiled-in
2351 default number.
2353 quiet [KNL] Disable most log messages
2355 r128= [HW,DRM]
2357 raid= [HW,RAID]
2358 See Documentation/md.txt.
2360 ramdisk_blocksize= [RAM]
2361 See Documentation/blockdev/ramdisk.txt.
2363 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2364 See Documentation/blockdev/ramdisk.txt.
2366 rcutree.blimit= [KNL,BOOT]
2367 Set maximum number of finished RCU callbacks to process
2368 in one batch.
2370 rcutree.qhimark= [KNL,BOOT]
2371 Set threshold of queued
2372 RCU callbacks over which batch limiting is disabled.
2374 rcutree.qlowmark= [KNL,BOOT]
2375 Set threshold of queued RCU callbacks below which
2376 batch limiting is re-enabled.
2378 rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2379 Suppress RCU CPU stall warning messages.
2381 rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2382 Set timeout for RCU CPU stall warning messages.
2384 rcutorture.fqs_duration= [KNL,BOOT]
2385 Set duration of force_quiescent_state bursts.
2387 rcutorture.fqs_holdoff= [KNL,BOOT]
2388 Set holdoff time within force_quiescent_state bursts.
2390 rcutorture.fqs_stutter= [KNL,BOOT]
2391 Set wait time between force_quiescent_state bursts.
2393 rcutorture.irqreader= [KNL,BOOT]
2394 Test RCU readers from irq handlers.
2396 rcutorture.n_barrier_cbs= [KNL,BOOT]
2397 Set callbacks/threads for rcu_barrier() testing.
2399 rcutorture.nfakewriters= [KNL,BOOT]
2400 Set number of concurrent RCU writers. These just
2401 stress RCU, they don't participate in the actual
2402 test, hence the "fake".
2404 rcutorture.nreaders= [KNL,BOOT]
2405 Set number of RCU readers.
2407 rcutorture.onoff_holdoff= [KNL,BOOT]
2408 Set time (s) after boot for CPU-hotplug testing.
2410 rcutorture.onoff_interval= [KNL,BOOT]
2411 Set time (s) between CPU-hotplug operations, or
2412 zero to disable CPU-hotplug testing.
2414 rcutorture.shuffle_interval= [KNL,BOOT]
2415 Set task-shuffle interval (s). Shuffling tasks
2416 allows some CPUs to go into dyntick-idle mode
2417 during the rcutorture test.
2419 rcutorture.shutdown_secs= [KNL,BOOT]
2420 Set time (s) after boot system shutdown. This
2421 is useful for hands-off automated testing.
2423 rcutorture.stall_cpu= [KNL,BOOT]
2424 Duration of CPU stall (s) to test RCU CPU stall
2425 warnings, zero to disable.
2427 rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2428 Time to wait (s) after boot before inducing stall.
2430 rcutorture.stat_interval= [KNL,BOOT]
2431 Time (s) between statistics printk()s.
2433 rcutorture.stutter= [KNL,BOOT]
2434 Time (s) to stutter testing, for example, specifying
2435 five seconds causes the test to run for five seconds,
2436 wait for five seconds, and so on. This tests RCU's
2437 ability to transition abruptly to and from idle.
2439 rcutorture.test_boost= [KNL,BOOT]
2440 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2441 "Maybe" means test if the RCU implementation
2442 under test support RCU priority boosting.
2444 rcutorture.test_boost_duration= [KNL,BOOT]
2445 Duration (s) of each individual boost test.
2447 rcutorture.test_boost_interval= [KNL,BOOT]
2448 Interval (s) between each boost test.
2450 rcutorture.test_no_idle_hz= [KNL,BOOT]
2451 Test RCU's dyntick-idle handling. See also the
2452 rcutorture.shuffle_interval parameter.
2454 rcutorture.torture_type= [KNL,BOOT]
2455 Specify the RCU implementation to test.
2457 rcutorture.verbose= [KNL,BOOT]
2458 Enable additional printk() statements.
2460 rdinit= [KNL]
2461 Format: <full_path>
2462 Run specified binary instead of /init from the ramdisk,
2463 used for early userspace startup. See initrd.
2465 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2466 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2467 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2469 relax_domain_level=
2470 [KNL, SMP] Set scheduler's default relax_domain_level.
2471 See Documentation/cgroups/cpusets.txt.
2473 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2475 reservetop= [X86-32]
2476 Format: nn[KMG]
2477 Reserves a hole at the top of the kernel virtual
2478 address space.
2480 reservelow= [X86]
2481 Format: nn[K]
2482 Set the amount of memory to reserve for BIOS at
2483 the bottom of the address space.
2485 reset_devices [KNL] Force drivers to reset the underlying device
2486 during initialization.
2488 resume= [SWSUSP]
2489 Specify the partition device for software suspend
2490 Format:
2491 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2493 resume_offset= [SWSUSP]
2494 Specify the offset from the beginning of the partition
2495 given by "resume=" at which the swap header is located,
2496 in <PAGE_SIZE> units (needed only for swap files).
2497 See Documentation/power/swsusp-and-swap-files.txt
2499 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2500 read the resume files
2502 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2503 Useful for devices that are detected asynchronously
2504 (e.g. USB and MMC devices).
2506 hibernate= [HIBERNATION]
2507 noresume Don't check if there's a hibernation image
2508 present during boot.
2509 nocompress Don't compress/decompress hibernation images.
2511 retain_initrd [RAM] Keep initrd memory after extraction
2513 rhash_entries= [KNL,NET]
2514 Set number of hash buckets for route cache
2516 riscom8= [HW,SERIAL]
2517 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2519 ro [KNL] Mount root device read-only on boot
2521 root= [KNL] Root filesystem
2522 See name_to_dev_t comment in init/do_mounts.c.
2524 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2525 mount the root filesystem
2527 rootflags= [KNL] Set root filesystem mount option string
2529 rootfstype= [KNL] Set root filesystem type
2531 rootwait [KNL] Wait (indefinitely) for root device to show up.
2532 Useful for devices that are detected asynchronously
2533 (e.g. USB and MMC devices).
2535 rw [KNL] Mount root device read-write on boot
2537 S [KNL] Run init in single mode
2539 sa1100ir [NET]
2540 See drivers/net/irda/sa1100_ir.c.
2542 sbni= [NET] Granch SBNI12 leased line adapter
2544 sched_debug [KNL] Enables verbose scheduler debug messages.
2546 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2547 xtime_lock contention on larger systems, and/or RCU lock
2548 contention on all systems with CONFIG_MAXSMP set.
2549 Format: { "0" | "1" }
2550 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2551 1 -- enable.
2552 Note: increases power consumption, thus should only be
2553 enabled if running jitter sensitive (HPC/RT) workloads.
2555 security= [SECURITY] Choose a security module to enable at boot.
2556 If this boot parameter is not specified, only the first
2557 security module asking for security registration will be
2558 loaded. An invalid security module name will be treated
2559 as if no module has been chosen.
2561 selinux= [SELINUX] Disable or enable SELinux at boot time.
2562 Format: { "0" | "1" }
2563 See security/selinux/Kconfig help text.
2564 0 -- disable.
2565 1 -- enable.
2566 Default value is set via kernel config option.
2567 If enabled at boot time, /selinux/disable can be used
2568 later to disable prior to initial policy load.
2570 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2571 Format: { "0" | "1" }
2572 See security/apparmor/Kconfig help text
2573 0 -- disable.
2574 1 -- enable.
2575 Default value is set via kernel config option.
2577 serialnumber [BUGS=X86-32]
2579 shapers= [NET]
2580 Maximal number of shapers.
2582 show_msr= [x86] show boot-time MSR settings
2583 Format: { <integer> }
2584 Show boot-time (BIOS-initialized) MSR settings.
2585 The parameter means the number of CPUs to show,
2586 for example 1 means boot CPU only.
2588 simeth= [IA-64]
2589 simscsi=
2591 slram= [HW,MTD]
2593 slab_max_order= [MM, SLAB]
2594 Determines the maximum allowed order for slabs.
2595 A high setting may cause OOMs due to memory
2596 fragmentation. Defaults to 1 for systems with
2597 more than 32MB of RAM, 0 otherwise.
2599 slub_debug[=options[,slabs]] [MM, SLUB]
2600 Enabling slub_debug allows one to determine the
2601 culprit if slab objects become corrupted. Enabling
2602 slub_debug can create guard zones around objects and
2603 may poison objects when not in use. Also tracks the
2604 last alloc / free. For more information see
2605 Documentation/vm/slub.txt.
2607 slub_max_order= [MM, SLUB]
2608 Determines the maximum allowed order for slabs.
2609 A high setting may cause OOMs due to memory
2610 fragmentation. For more information see
2611 Documentation/vm/slub.txt.
2613 slub_min_objects= [MM, SLUB]
2614 The minimum number of objects per slab. SLUB will
2615 increase the slab order up to slub_max_order to
2616 generate a sufficiently large slab able to contain
2617 the number of objects indicated. The higher the number
2618 of objects the smaller the overhead of tracking slabs
2619 and the less frequently locks need to be acquired.
2620 For more information see Documentation/vm/slub.txt.
2622 slub_min_order= [MM, SLUB]
2623 Determines the minimum page order for slabs. Must be
2624 lower than slub_max_order.
2625 For more information see Documentation/vm/slub.txt.
2627 slub_nomerge [MM, SLUB]
2628 Disable merging of slabs with similar size. May be
2629 necessary if there is some reason to distinguish
2630 allocs to different slabs. Debug options disable
2631 merging on their own.
2632 For more information see Documentation/vm/slub.txt.
2634 smart2= [HW]
2635 Format: <io1>[,<io2>[,...,<io8>]]
2637 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2638 attempt to substitute SMP alternatives once at boot.
2640 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2641 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2642 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2643 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2644 smsc-ircc2.ircc_irq= [HW] IRQ line
2645 smsc-ircc2.ircc_dma= [HW] DMA channel
2646 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2647 0: Toshiba Satellite 1800 (GP data pin select)
2648 1: Fast pin select (default)
2649 2: ATC IRMode
2651 softlockup_panic=
2652 [KNL] Should the soft-lockup detector generate panics.
2653 Format: <integer>
2655 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2656 See Documentation/laptops/sonypi.txt
2658 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2659 See Documentation/serial/specialix.txt.
2661 spia_io_base= [HW,MTD]
2662 spia_fio_base=
2663 spia_pedr=
2664 spia_peddr=
2666 stacktrace [FTRACE]
2667 Enabled the stack tracer on boot up.
2669 stacktrace_filter=[function-list]
2670 [FTRACE] Limit the functions that the stack tracer
2671 will trace at boot up. function-list is a comma separated
2672 list of functions. This list can be changed at run
2673 time by the stack_trace_filter file in the debugfs
2674 tracing directory. Note, this enables stack tracing
2675 and the stacktrace above is not needed.
2677 sti= [PARISC,HW]
2678 Format: <num>
2679 Set the STI (builtin display/keyboard on the HP-PARISC
2680 machines) console (graphic card) which should be used
2681 as the initial boot-console.
2682 See also comment in drivers/video/console/sticore.c.
2684 sti_font= [HW]
2685 See comment in drivers/video/console/sticore.c.
2687 stifb= [HW]
2688 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2690 sunrpc.min_resvport=
2691 sunrpc.max_resvport=
2692 [NFS,SUNRPC]
2693 SunRPC servers often require that client requests
2694 originate from a privileged port (i.e. a port in the
2695 range 0 < portnr < 1024).
2696 An administrator who wishes to reserve some of these
2697 ports for other uses may adjust the range that the
2698 kernel's sunrpc client considers to be privileged
2699 using these two parameters to set the minimum and
2700 maximum port values.
2702 sunrpc.pool_mode=
2703 [NFS]
2704 Control how the NFS server code allocates CPUs to
2705 service thread pools. Depending on how many NICs
2706 you have and where their interrupts are bound, this
2707 option will affect which CPUs will do NFS serving.
2708 Note: this parameter cannot be changed while the
2709 NFS server is running.
2711 auto the server chooses an appropriate mode
2712 automatically using heuristics
2713 global a single global pool contains all CPUs
2714 percpu one pool for each CPU
2715 pernode one pool for each NUMA node (equivalent
2716 to global on non-NUMA machines)
2718 sunrpc.tcp_slot_table_entries=
2719 sunrpc.udp_slot_table_entries=
2720 [NFS,SUNRPC]
2721 Sets the upper limit on the number of simultaneous
2722 RPC calls that can be sent from the client to a
2723 server. Increasing these values may allow you to
2724 improve throughput, but will also increase the
2725 amount of memory reserved for use by the client.
2727 swapaccount[=0|1]
2728 [KNL] Enable accounting of swap in memory resource
2729 controller if no parameter or 1 is given or disable
2730 it if 0 is given (See Documentation/cgroups/memory.txt)
2732 swiotlb= [IA-64] Number of I/O TLB slabs
2734 switches= [HW,M68k]
2736 sysfs.deprecated=0|1 [KNL]
2737 Enable/disable old style sysfs layout for old udev
2738 on older distributions. When this option is enabled
2739 very new udev will not work anymore. When this option
2740 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2741 in older udev will not work anymore.
2742 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2743 the kernel configuration.
2745 sysrq_always_enabled
2746 [KNL]
2747 Ignore sysrq setting - this boot parameter will
2748 neutralize any effect of /proc/sys/kernel/sysrq.
2749 Useful for debugging.
2751 tdfx= [HW,DRM]
2753 test_suspend= [SUSPEND]
2754 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2755 standby suspend) as the system sleep state to briefly
2756 enter during system startup. The system is woken from
2757 this state using a wakeup-capable RTC alarm.
2759 thash_entries= [KNL,NET]
2760 Set number of hash buckets for TCP connection
2762 thermal.act= [HW,ACPI]
2763 -1: disable all active trip points in all thermal zones
2764 <degrees C>: override all lowest active trip points
2766 thermal.crt= [HW,ACPI]
2767 -1: disable all critical trip points in all thermal zones
2768 <degrees C>: override all critical trip points
2770 thermal.nocrt= [HW,ACPI]
2771 Set to disable actions on ACPI thermal zone
2772 critical and hot trip points.
2774 thermal.off= [HW,ACPI]
2775 1: disable ACPI thermal control
2777 thermal.psv= [HW,ACPI]
2778 -1: disable all passive trip points
2779 <degrees C>: override all passive trip points to this
2780 value
2782 thermal.tzp= [HW,ACPI]
2783 Specify global default ACPI thermal zone polling rate
2784 <deci-seconds>: poll all this frequency
2785 0: no polling (default)
2787 threadirqs [KNL]
2788 Force threading of all interrupt handlers except those
2789 marked explicitly IRQF_NO_THREAD.
2791 topology= [S390]
2792 Format: {off | on}
2793 Specify if the kernel should make use of the cpu
2794 topology information if the hardware supports this.
2795 The scheduler will make use of this information and
2796 e.g. base its process migration decisions on it.
2797 Default is on.
2799 tp720= [HW,PS2]
2801 tpm_suspend_pcr=[HW,TPM]
2802 Format: integer pcr id
2803 Specify that at suspend time, the tpm driver
2804 should extend the specified pcr with zeros,
2805 as a workaround for some chips which fail to
2806 flush the last written pcr on TPM_SaveState.
2807 This will guarantee that all the other pcrs
2808 are saved.
2810 trace_buf_size=nn[KMG]
2811 [FTRACE] will set tracing buffer size.
2813 trace_event=[event-list]
2814 [FTRACE] Set and start specified trace events in order
2815 to facilitate early boot debugging.
2816 See also Documentation/trace/events.txt
2818 transparent_hugepage=
2819 [KNL]
2820 Format: [always|madvise|never]
2821 Can be used to control the default behavior of the system
2822 with respect to transparent hugepages.
2823 See Documentation/vm/transhuge.txt for more details.
2825 tsc= Disable clocksource stability checks for TSC.
2826 Format: <string>
2827 [x86] reliable: mark tsc clocksource as reliable, this
2828 disables clocksource verification at runtime, as well
2829 as the stability checks done at bootup. Used to enable
2830 high-resolution timer mode on older hardware, and in
2831 virtualized environment.
2832 [x86] noirqtime: Do not use TSC to do irq accounting.
2833 Used to run time disable IRQ_TIME_ACCOUNTING on any
2834 platforms where RDTSC is slow and this accounting
2835 can add overhead.
2837 turbografx.map[2|3]= [HW,JOY]
2838 TurboGraFX parallel port interface
2839 Format:
2840 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2841 See also Documentation/input/joystick-parport.txt
2843 udbg-immortal [PPC] When debugging early kernel crashes that
2844 happen after console_init() and before a proper
2845 console driver takes over, this boot options might
2846 help "seeing" what's going on.
2848 uhash_entries= [KNL,NET]
2849 Set number of hash buckets for UDP/UDP-Lite connections
2851 uhci-hcd.ignore_oc=
2852 [USB] Ignore overcurrent events (default N).
2853 Some badly-designed motherboards generate lots of
2854 bogus events, for ports that aren't wired to
2855 anything. Set this parameter to avoid log spamming.
2856 Note that genuine overcurrent events won't be
2857 reported either.
2859 unknown_nmi_panic
2860 [X86] Cause panic on unknown NMI.
2862 usbcore.authorized_default=
2863 [USB] Default USB device authorization:
2864 (default -1 = authorized except for wireless USB,
2865 0 = not authorized, 1 = authorized)
2867 usbcore.autosuspend=
2868 [USB] The autosuspend time delay (in seconds) used
2869 for newly-detected USB devices (default 2). This
2870 is the time required before an idle device will be
2871 autosuspended. Devices for which the delay is set
2872 to a negative value won't be autosuspended at all.
2874 usbcore.usbfs_snoop=
2875 [USB] Set to log all usbfs traffic (default 0 = off).
2877 usbcore.blinkenlights=
2878 [USB] Set to cycle leds on hubs (default 0 = off).
2880 usbcore.old_scheme_first=
2881 [USB] Start with the old device initialization
2882 scheme (default 0 = off).
2884 usbcore.usbfs_memory_mb=
2885 [USB] Memory limit (in MB) for buffers allocated by
2886 usbfs (default = 16, 0 = max = 2047).
2888 usbcore.use_both_schemes=
2889 [USB] Try the other device initialization scheme
2890 if the first one fails (default 1 = enabled).
2892 usbcore.initial_descriptor_timeout=
2893 [USB] Specifies timeout for the initial 64-byte
2894 USB_REQ_GET_DESCRIPTOR request in milliseconds
2895 (default 5000 = 5.0 seconds).
2897 usbhid.mousepoll=
2898 [USBHID] The interval which mice are to be polled at.
2900 usb-storage.delay_use=
2901 [UMS] The delay in seconds before a new device is
2902 scanned for Logical Units (default 5).
2904 usb-storage.quirks=
2905 [UMS] A list of quirks entries to supplement or
2906 override the built-in unusual_devs list. List
2907 entries are separated by commas. Each entry has
2908 the form VID:PID:Flags where VID and PID are Vendor
2909 and Product ID values (4-digit hex numbers) and
2910 Flags is a set of characters, each corresponding
2911 to a common usb-storage quirk flag as follows:
2912 a = SANE_SENSE (collect more than 18 bytes
2913 of sense data);
2914 b = BAD_SENSE (don't collect more than 18
2915 bytes of sense data);
2916 c = FIX_CAPACITY (decrease the reported
2917 device capacity by one sector);
2918 d = NO_READ_DISC_INFO (don't use
2919 READ_DISC_INFO command);
2920 e = NO_READ_CAPACITY_16 (don't use
2921 READ_CAPACITY_16 command);
2922 h = CAPACITY_HEURISTICS (decrease the
2923 reported device capacity by one
2924 sector if the number is odd);
2925 i = IGNORE_DEVICE (don't bind to this
2926 device);
2927 l = NOT_LOCKABLE (don't try to lock and
2928 unlock ejectable media);
2929 m = MAX_SECTORS_64 (don't transfer more
2930 than 64 sectors = 32 KB at a time);
2931 n = INITIAL_READ10 (force a retry of the
2932 initial READ(10) command);
2933 o = CAPACITY_OK (accept the capacity
2934 reported by the device);
2935 r = IGNORE_RESIDUE (the device reports
2936 bogus residue values);
2937 s = SINGLE_LUN (the device has only one
2938 Logical Unit);
2939 w = NO_WP_DETECT (don't test whether the
2940 medium is write-protected).
2941 Example: quirks=0419:aaf5:rl,0421:0433:rc
2943 user_debug= [KNL,ARM]
2944 Format: <int>
2945 See arch/arm/Kconfig.debug help text.
2946 1 - undefined instruction events
2947 2 - system calls
2948 4 - invalid data aborts
2949 8 - SIGSEGV faults
2950 16 - SIGBUS faults
2951 Example: user_debug=31
2953 userpte=
2954 [X86] Flags controlling user PTE allocations.
2956 nohigh = do not allocate PTE pages in
2957 HIGHMEM regardless of setting
2958 of CONFIG_HIGHPTE.
2960 vdso= [X86,SH]
2961 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2962 vdso=1: enable VDSO (default)
2963 vdso=0: disable VDSO mapping
2965 vdso32= [X86]
2966 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2967 vdso32=1: enable 32-bit VDSO (default)
2968 vdso32=0: disable 32-bit VDSO mapping
2970 vector= [IA-64,SMP]
2971 vector=percpu: enable percpu vector domain
2973 video= [FB] Frame buffer configuration
2974 See Documentation/fb/modedb.txt.
2976 virtio_mmio.device=
2977 [VMMIO] Memory mapped virtio (platform) device.
2979 <size>@<baseaddr>:<irq>[:<id>]
2980 where:
2981 <size> := size (can use standard suffixes
2982 like K, M and G)
2983 <baseaddr> := physical base address
2984 <irq> := interrupt number (as passed to
2985 request_irq())
2986 <id> := (optional) platform device id
2987 example:
2988 virtio_mmio.device=1K@0x100b0000:48:7
2990 Can be used multiple times for multiple devices.
2992 vga= [BOOT,X86-32] Select a particular video mode
2993 See Documentation/x86/boot.txt and
2994 Documentation/svga.txt.
2995 Use vga=ask for menu.
2996 This is actually a boot loader parameter; the value is
2997 passed to the kernel using a special protocol.
2999 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3000 size of <nn>. This can be used to increase the
3001 minimum size (128MB on x86). It can also be used to
3002 decrease the size and leave more room for directly
3003 mapped kernel RAM.
3005 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3006 Format: <command>
3008 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3009 Format: <command>
3011 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3012 Format: <command>
3014 vsyscall= [X86-64]
3015 Controls the behavior of vsyscalls (i.e. calls to
3016 fixed addresses of 0xffffffffff600x00 from legacy
3017 code). Most statically-linked binaries and older
3018 versions of glibc use these calls. Because these
3019 functions are at fixed addresses, they make nice
3020 targets for exploits that can control RIP.
3022 emulate [default] Vsyscalls turn into traps and are
3023 emulated reasonably safely.
3025 native Vsyscalls are native syscall instructions.
3026 This is a little bit faster than trapping
3027 and makes a few dynamic recompilers work
3028 better than they would in emulation mode.
3029 It also makes exploits much easier to write.
3031 none Vsyscalls don't work at all. This makes
3032 them quite hard to use for exploits but
3033 might break your system.
3035 vt.cur_default= [VT] Default cursor shape.
3036 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3037 the parameters of the <Esc>[?A;B;Cc escape sequence;
3038 see VGA-softcursor.txt. Default: 2 = underline.
3040 vt.default_blu= [VT]
3041 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3042 Change the default blue palette of the console.
3043 This is a 16-member array composed of values
3044 ranging from 0-255.
3046 vt.default_grn= [VT]
3047 Format: <green0>,<green1>,<green2>,...,<green15>
3048 Change the default green palette of the console.
3049 This is a 16-member array composed of values
3050 ranging from 0-255.
3052 vt.default_red= [VT]
3053 Format: <red0>,<red1>,<red2>,...,<red15>
3054 Change the default red palette of the console.
3055 This is a 16-member array composed of values
3056 ranging from 0-255.
3058 vt.default_utf8=
3059 [VT]
3060 Format=<0|1>
3061 Set system-wide default UTF-8 mode for all tty's.
3062 Default is 1, i.e. UTF-8 mode is enabled for all
3063 newly opened terminals.
3065 vt.global_cursor_default=
3066 [VT]
3067 Format=<-1|0|1>
3068 Set system-wide default for whether a cursor
3069 is shown on new VTs. Default is -1,
3070 i.e. cursors will be created by default unless
3071 overridden by individual drivers. 0 will hide
3072 cursors, 1 will display them.
3074 watchdog timers [HW,WDT] For information on watchdog timers,
3075 see Documentation/watchdog/watchdog-parameters.txt
3076 or other driver-specific files in the
3077 Documentation/watchdog/ directory.
3079 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3080 default x2apic cluster mode on platforms
3081 supporting x2apic.
3083 x86_mrst_timer= [X86-32,APBT]
3084 Choose timer option for x86 Moorestown MID platform.
3085 Two valid options are apbt timer only and lapic timer
3086 plus one apbt timer for broadcast timer.
3087 x86_mrst_timer=apbt_only | lapic_and_apbt
3089 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
3090 xd_geo= See header of drivers/block/xd.c.
3092 xen_emul_unplug= [HW,X86,XEN]
3093 Unplug Xen emulated devices
3094 Format: [unplug0,][unplug1]
3095 ide-disks -- unplug primary master IDE devices
3096 aux-ide-disks -- unplug non-primary-master IDE devices
3097 nics -- unplug network devices
3098 all -- unplug all emulated devices (NICs and IDE disks)
3099 unnecessary -- unplugging emulated devices is
3100 unnecessary even if the host did not respond to
3101 the unplug protocol
3102 never -- do not unplug even if version check succeeds
3104 xirc2ps_cs= [NET,PCMCIA]
3105 Format:
3106 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3108 ______________________________________________________________________
3110 TODO:
3112 Add more DRM drivers.