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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
4 The following is a consolidated list of the kernel parameters as implemented
5 (mostly) by the __setup() macro and sorted into English Dictionary order
6 (defined as ignoring all punctuation and sorting digits before letters in a
7 case insensitive manner), and with descriptions where known.
9 Module parameters for loadable modules are specified only as the
10 parameter name with optional '=' and value as appropriate, such as:
12 modprobe usbcore blinkenlights=1
14 Module parameters for modules that are built into the kernel image
15 are specified on the kernel command line with the module name plus
16 '.' plus parameter name, with '=' and value if appropriate, such as:
18 usbcore.blinkenlights=1
20 Hyphens (dashes) and underscores are equivalent in parameter names, so
21 log_buf_len=1M print-fatal-signals=1
22 can also be entered as
23 log-buf-len=1M print_fatal_signals=1
26 This document may not be entirely up to date and comprehensive. The command
27 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
28 module. Loadable modules, after being loaded into the running kernel, also
29 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
30 parameters may be changed at runtime by the command
31 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
33 The parameters listed below are only valid if certain kernel build options were
34 enabled and if respective hardware is present. The text in square brackets at
35 the beginning of each description states the restrictions within which a
36 parameter is applicable:
38 ACPI ACPI support is enabled.
39 AGP AGP (Accelerated Graphics Port) is enabled.
40 ALSA ALSA sound support is enabled.
41 APIC APIC support is enabled.
42 APM Advanced Power Management support is enabled.
43 ARM ARM architecture is enabled.
44 AVR32 AVR32 architecture is enabled.
45 AX25 Appropriate AX.25 support is enabled.
46 BLACKFIN Blackfin architecture is enabled.
47 DRM Direct Rendering Management support is enabled.
48 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
49 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
50 EFI EFI Partitioning (GPT) is enabled
51 EIDE EIDE/ATAPI support is enabled.
52 EVM Extended Verification Module
53 FB The frame buffer device is enabled.
54 FTRACE Function tracing enabled.
55 GCOV GCOV profiling is enabled.
56 HW Appropriate hardware is enabled.
57 IA-64 IA-64 architecture is enabled.
58 IMA Integrity measurement architecture is enabled.
59 IOSCHED More than one I/O scheduler is enabled.
60 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
61 IPV6 IPv6 support is enabled.
62 ISAPNP ISA PnP code is enabled.
63 ISDN Appropriate ISDN support is enabled.
64 JOY Appropriate joystick support is enabled.
65 KGDB Kernel debugger support is enabled.
66 KVM Kernel Virtual Machine support is enabled.
67 LIBATA Libata driver is enabled
68 LP Printer support is enabled.
69 LOOP Loopback device support is enabled.
70 M68k M68k architecture is enabled.
71 These options have more detailed description inside of
72 Documentation/m68k/kernel-options.txt.
73 MCA MCA bus support is enabled.
74 MDA MDA console support is enabled.
75 MIPS MIPS architecture is enabled.
76 MOUSE Appropriate mouse support is enabled.
77 MSI Message Signaled Interrupts (PCI).
78 MTD MTD (Memory Technology Device) support is enabled.
79 NET Appropriate network support is enabled.
80 NUMA NUMA support is enabled.
81 NFS Appropriate NFS support is enabled.
82 OSS OSS sound support is enabled.
83 PV_OPS A paravirtualized kernel is enabled.
84 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
85 PARISC The PA-RISC architecture is enabled.
86 PCI PCI bus support is enabled.
87 PCIE PCI Express support is enabled.
88 PCMCIA The PCMCIA subsystem is enabled.
89 PNP Plug & Play support is enabled.
90 PPC PowerPC architecture is enabled.
91 PPT Parallel port support is enabled.
92 PS2 Appropriate PS/2 support is enabled.
93 RAM RAM disk support is enabled.
94 S390 S390 architecture is enabled.
95 SCSI Appropriate SCSI support is enabled.
96 A lot of drivers have their options described inside
97 the Documentation/scsi/ sub-directory.
98 SECURITY Different security models are enabled.
99 SELINUX SELinux support is enabled.
100 APPARMOR AppArmor support is enabled.
101 SERIAL Serial support is enabled.
102 SH SuperH architecture is enabled.
103 SMP The kernel is an SMP kernel.
104 SPARC Sparc architecture is enabled.
105 SWSUSP Software suspend (hibernation) is enabled.
106 SUSPEND System suspend states are enabled.
107 TPM TPM drivers are enabled.
108 TS Appropriate touchscreen support is enabled.
109 UMS USB Mass Storage support is enabled.
110 USB USB support is enabled.
111 USBHID USB Human Interface Device support is enabled.
112 V4L Video For Linux support 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/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 1: only for 32-bit processes
319 2: 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,X86-84]
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
333 amijoy.map= [HW,JOY] Amiga joystick support
334 Map of devices attached to JOY0DAT and JOY1DAT
335 Format: <a>,<b>
336 See also Documentation/kernel/input/joystick.txt
338 analog.map= [HW,JOY] Analog joystick and gamepad support
339 Specifies type or capabilities of an analog joystick
340 connected to one of 16 gameports
341 Format: <type1>,<type2>,..<type16>
343 apc= [HW,SPARC]
344 Power management functions (SPARCstation-4/5 + deriv.)
345 Format: noidle
346 Disable APC CPU standby support. SPARCstation-Fox does
347 not play well with APC CPU idle - disable it if you have
348 APC and your system crashes randomly.
350 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
351 Change the output verbosity whilst booting
352 Format: { quiet (default) | verbose | debug }
353 Change the amount of debugging information output
354 when initialising the APIC and IO-APIC components.
356 autoconf= [IPV6]
357 See Documentation/networking/ipv6.txt.
359 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
360 Limit apic dumping. The parameter defines the maximal
361 number of local apics being dumped. Also it is possible
362 to set it to "all" by meaning -- no limit here.
363 Format: { 1 (default) | 2 | ... | all }.
364 The parameter valid if only apic=debug or
365 apic=verbose is specified.
366 Example: apic=debug show_lapic=all
368 apm= [APM] Advanced Power Management
369 See header of arch/x86/kernel/apm_32.c.
371 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
372 Format: <io>,<irq>,<nodeID>
374 ataflop= [HW,M68k]
376 atarimouse= [HW,MOUSE] Atari Mouse
378 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
379 EzKey and similar keyboards
381 atkbd.reset= [HW] Reset keyboard during initialization
383 atkbd.set= [HW] Select keyboard code set
384 Format: <int> (2 = AT (default), 3 = PS/2)
386 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
387 keyboards
389 atkbd.softraw= [HW] Choose between synthetic and real raw mode
390 Format: <bool> (0 = real, 1 = synthetic (default))
392 atkbd.softrepeat= [HW]
393 Use software keyboard repeat
395 autotest [IA-64]
397 baycom_epp= [HW,AX25]
398 Format: <io>,<mode>
400 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
401 Format: <io>,<mode>
402 See header of drivers/net/hamradio/baycom_par.c.
404 baycom_ser_fdx= [HW,AX25]
405 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
406 Format: <io>,<irq>,<mode>[,<baud>]
407 See header of drivers/net/hamradio/baycom_ser_fdx.c.
409 baycom_ser_hdx= [HW,AX25]
410 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
411 Format: <io>,<irq>,<mode>
412 See header of drivers/net/hamradio/baycom_ser_hdx.c.
414 boot_delay= Milliseconds to delay each printk during boot.
415 Values larger than 10 seconds (10000) are changed to
416 no delay (0).
417 Format: integer
419 bootmem_debug [KNL] Enable bootmem allocator debug messages.
421 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
422 bttv.radio= Most important insmod options are available as
423 kernel args too.
424 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
425 bttv.tuner= and Documentation/video4linux/bttv/CARDLIST
427 bulk_remove=off [PPC] This parameter disables the use of the pSeries
428 firmware feature for flushing multiple hpte entries
429 at a time.
431 c101= [NET] Moxa C101 synchronous serial card
433 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
434 Sometimes CPU hardware bugs make them report the cache
435 size incorrectly. The kernel will attempt work arounds
436 to fix known problems, but for some CPUs it is not
437 possible to determine what the correct size should be.
438 This option provides an override for these situations.
440 capability.disable=
441 [SECURITY] Disable capabilities. This would normally
442 be used only if an alternative security model is to be
443 configured. Potentially dangerous and should only be
444 used if you are entirely sure of the consequences.
446 ccw_timeout_log [S390]
447 See Documentation/s390/CommonIO for details.
449 cgroup_disable= [KNL] Disable a particular controller
450 Format: {name of the controller(s) to disable}
451 {Currently supported controllers - "memory"}
453 checkreqprot [SELINUX] Set initial checkreqprot flag value.
454 Format: { "0" | "1" }
455 See security/selinux/Kconfig help text.
456 0 -- check protection applied by kernel (includes
457 any implied execute protection).
458 1 -- check protection requested by application.
459 Default value is set via a kernel config option.
460 Value can be changed at runtime via
461 /selinux/checkreqprot.
463 cio_ignore= [S390]
464 See Documentation/s390/CommonIO for details.
466 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
467 [Deprecated]
468 Forces specified clocksource (if available) to be used
469 when calculating gettimeofday(). If specified
470 clocksource is not available, it defaults to PIT.
471 Format: { pit | tsc | cyclone | pmtmr }
473 clocksource= Override the default clocksource
474 Format: <string>
475 Override the default clocksource and use the clocksource
476 with the name specified.
477 Some clocksource names to choose from, depending on
478 the platform:
479 [all] jiffies (this is the base, fallback clocksource)
480 [ACPI] acpi_pm
481 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
482 pxa_timer,timer3,32k_counter,timer0_1
483 [AVR32] avr32
484 [X86-32] pit,hpet,tsc;
485 scx200_hrt on Geode; cyclone on IBM x440
486 [MIPS] MIPS
487 [PARISC] cr16
488 [S390] tod
489 [SH] SuperH
490 [SPARC64] tick
491 [X86-64] hpet,tsc
493 clearcpuid=BITNUM [X86]
494 Disable CPUID feature X for the kernel. See
495 arch/x86/include/asm/cpufeature.h for the valid bit
496 numbers. Note the Linux specific bits are not necessarily
497 stable over kernel options, but the vendor specific
498 ones should be.
499 Also note that user programs calling CPUID directly
500 or using the feature without checking anything
501 will still see it. This just prevents it from
502 being used by the kernel or shown in /proc/cpuinfo.
503 Also note the kernel might malfunction if you disable
504 some critical bits.
506 cmo_free_hint= [PPC] Format: { yes | no }
507 Specify whether pages are marked as being inactive
508 when they are freed. This is used in CMO environments
509 to determine OS memory pressure for page stealing by
510 a hypervisor.
511 Default: yes
513 code_bytes [X86] How many bytes of object code to print
514 in an oops report.
515 Range: 0 - 8192
516 Default: 64
518 com20020= [HW,NET] ARCnet - COM20020 chipset
519 Format:
520 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
522 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
523 Format: <io>[,<irq>]
525 com90xx= [HW,NET]
526 ARCnet - COM90xx chipset (memory-mapped buffers)
527 Format: <io>[,<irq>[,<memstart>]]
529 condev= [HW,S390] console device
530 conmode=
532 console= [KNL] Output console device and options.
534 tty<n> Use the virtual console device <n>.
536 ttyS<n>[,options]
537 ttyUSB0[,options]
538 Use the specified serial port. The options are of
539 the form "bbbbpnf", where "bbbb" is the baud rate,
540 "p" is parity ("n", "o", or "e"), "n" is number of
541 bits, and "f" is flow control ("r" for RTS or
542 omit it). Default is "9600n8".
544 See Documentation/serial-console.txt for more
545 information. See
546 Documentation/networking/netconsole.txt for an
547 alternative.
549 uart[8250],io,<addr>[,options]
550 uart[8250],mmio,<addr>[,options]
551 Start an early, polled-mode console on the 8250/16550
552 UART at the specified I/O port or MMIO address,
553 switching to the matching ttyS device later. The
554 options are the same as for ttyS, above.
556 If the device connected to the port is not a TTY but a braille
557 device, prepend "brl," before the device type, for instance
558 console=brl,ttyS0
559 For now, only VisioBraille is supported.
561 consoleblank= [KNL] The console blank (screen saver) timeout in
562 seconds. Defaults to 10*60 = 10mins. A value of 0
563 disables the blank timer.
565 coredump_filter=
566 [KNL] Change the default value for
567 /proc/<pid>/coredump_filter.
568 See also Documentation/filesystems/proc.txt.
570 cpuidle.off=1 [CPU_IDLE]
571 disable the cpuidle sub-system
573 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
574 Format:
575 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
577 crashkernel=size[KMG][@offset[KMG]]
578 [KNL] Using kexec, Linux can switch to a 'crash kernel'
579 upon panic. This parameter reserves the physical
580 memory region [offset, offset + size] for that kernel
581 image. If '@offset' is omitted, then a suitable offset
582 is selected automatically. Check
583 Documentation/kdump/kdump.txt for further details.
585 crashkernel=range1:size1[,range2:size2,...][@offset]
586 [KNL] Same as above, but depends on the memory
587 in the running system. The syntax of range is
588 start-[end] where start and end are both
589 a memory unit (amount[KMG]). See also
590 Documentation/kdump/kdump.txt for an example.
592 cs89x0_dma= [HW,NET]
593 Format: <dma>
595 cs89x0_media= [HW,NET]
596 Format: { rj45 | aui | bnc }
598 dasd= [HW,NET]
599 See header of drivers/s390/block/dasd_devmap.c.
601 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
602 (one device per port)
603 Format: <port#>,<type>
604 See also Documentation/input/joystick-parport.txt
606 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
607 time. See Documentation/dynamic-debug-howto.txt for
608 details.
610 debug [KNL] Enable kernel debugging (events log level).
612 debug_locks_verbose=
613 [KNL] verbose self-tests
614 Format=<0|1>
615 Print debugging info while doing the locking API
616 self-tests.
617 We default to 0 (no extra messages), setting it to
618 1 will print _a lot_ more information - normally
619 only useful to kernel developers.
621 debug_objects [KNL] Enable object debugging
623 no_debug_objects
624 [KNL] Disable object debugging
626 debugpat [X86] Enable PAT debugging
628 decnet.addr= [HW,NET]
629 Format: <area>[,<node>]
630 See also Documentation/networking/decnet.txt.
632 default_hugepagesz=
633 [same as hugepagesz=] The size of the default
634 HugeTLB page size. This is the size represented by
635 the legacy /proc/ hugepages APIs, used for SHM, and
636 default size when mounting hugetlbfs filesystems.
637 Defaults to the default architecture's huge page size
638 if not specified.
640 dhash_entries= [KNL]
641 Set number of hash buckets for dentry cache.
643 digi= [HW,SERIAL]
644 IO parameters + enable/disable command.
646 digiepca= [HW,SERIAL]
647 See drivers/char/README.epca and
648 Documentation/serial/digiepca.txt.
650 disable= [IPV6]
651 See Documentation/networking/ipv6.txt.
653 disable_ddw [PPC/PSERIES]
654 Disable Dynamic DMA Window support. Use this if
655 to workaround buggy firmware.
657 disable_ipv6= [IPV6]
658 See Documentation/networking/ipv6.txt.
660 disable_mtrr_cleanup [X86]
661 The kernel tries to adjust MTRR layout from continuous
662 to discrete, to make X server driver able to add WB
663 entry later. This parameter disables that.
665 disable_mtrr_trim [X86, Intel and AMD only]
666 By default the kernel will trim any uncacheable
667 memory out of your available memory pool based on
668 MTRR settings. This parameter disables that behavior,
669 possibly causing your machine to run very slowly.
671 disable_timer_pin_1 [X86]
672 Disable PIN 1 of APIC timer
673 Can be useful to work around chipset bugs.
675 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
676 this option disables the debugging code at boot.
678 dma_debug_entries=<number>
679 This option allows to tune the number of preallocated
680 entries for DMA-API debugging code. One entry is
681 required per DMA-API allocation. Use this if the
682 DMA-API debugging code disables itself because the
683 architectural default is too low.
685 dma_debug_driver=<driver_name>
686 With this option the DMA-API debugging driver
687 filter feature can be enabled at boot time. Just
688 pass the driver to filter for as the parameter.
689 The filter can be disabled or changed to another
690 driver later using sysfs.
692 dscc4.setup= [NET]
694 earlycon= [KNL] Output early console device and options.
695 uart[8250],io,<addr>[,options]
696 uart[8250],mmio,<addr>[,options]
697 uart[8250],mmio32,<addr>[,options]
698 Start an early, polled-mode console on the 8250/16550
699 UART at the specified I/O port or MMIO address.
700 MMIO inter-register address stride is either 8-bit
701 (mmio) or 32-bit (mmio32).
702 The options are the same as for ttyS, above.
704 earlyprintk= [X86,SH,BLACKFIN]
705 earlyprintk=vga
706 earlyprintk=serial[,ttySn[,baudrate]]
707 earlyprintk=ttySn[,baudrate]
708 earlyprintk=dbgp[debugController#]
710 Append ",keep" to not disable it when the real console
711 takes over.
713 Only vga or serial or usb debug port at a time.
715 Currently only ttyS0 and ttyS1 are supported.
717 Interaction with the standard serial driver is not
718 very good.
720 The VGA output is eventually overwritten by the real
721 console.
723 ekgdboc= [X86,KGDB] Allow early kernel console debugging
724 ekgdboc=kbd
726 This is designed to be used in conjunction with
727 the boot argument: earlyprintk=vga
729 edd= [EDD]
730 Format: {"off" | "on" | "skip[mbr]"}
732 eisa_irq_edge= [PARISC,HW]
733 See header of drivers/parisc/eisa.c.
735 elanfreq= [X86-32]
736 See comment before function elanfreq_setup() in
737 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
739 elevator= [IOSCHED]
740 Format: {"cfq" | "deadline" | "noop"}
741 See Documentation/block/as-iosched.txt and
742 Documentation/block/deadline-iosched.txt for details.
744 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
745 Specifies physical address of start of kernel core
746 image elf header and optionally the size. Generally
747 kexec loader will pass this option to capture kernel.
748 See Documentation/kdump/kdump.txt for details.
750 enable_mtrr_cleanup [X86]
751 The kernel tries to adjust MTRR layout from continuous
752 to discrete, to make X server driver able to add WB
753 entry later. This parameter enables that.
755 enable_timer_pin_1 [X86]
756 Enable PIN 1 of APIC timer
757 Can be useful to work around chipset bugs
758 (in particular on some ATI chipsets).
759 The kernel tries to set a reasonable default.
761 enforcing [SELINUX] Set initial enforcing status.
762 Format: {"0" | "1"}
763 See security/selinux/Kconfig help text.
764 0 -- permissive (log only, no denials).
765 1 -- enforcing (deny and log).
766 Default value is 0.
767 Value can be changed at runtime via /selinux/enforce.
769 erst_disable [ACPI]
770 Disable Error Record Serialization Table (ERST)
771 support.
773 ether= [HW,NET] Ethernet cards parameters
774 This option is obsoleted by the "netdev=" option, which
775 has equivalent usage. See its documentation for details.
777 evm= [EVM]
778 Format: { "fix" }
779 Permit 'security.evm' to be updated regardless of
780 current integrity status.
782 failslab=
783 fail_page_alloc=
784 fail_make_request=[KNL]
785 General fault injection mechanism.
786 Format: <interval>,<probability>,<space>,<times>
787 See also /Documentation/fault-injection/.
789 floppy= [HW]
790 See Documentation/blockdev/floppy.txt.
792 force_pal_cache_flush
793 [IA-64] Avoid check_sal_cache_flush which may hang on
794 buggy SAL_CACHE_FLUSH implementations. Using this
795 parameter will force ia64_sal_cache_flush to call
796 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
798 ftrace=[tracer]
799 [FTRACE] will set and start the specified tracer
800 as early as possible in order to facilitate early
801 boot debugging.
803 ftrace_dump_on_oops[=orig_cpu]
804 [FTRACE] will dump the trace buffers on oops.
805 If no parameter is passed, ftrace will dump
806 buffers of all CPUs, but if you pass orig_cpu, it will
807 dump only the buffer of the CPU that triggered the
808 oops.
810 ftrace_filter=[function-list]
811 [FTRACE] Limit the functions traced by the function
812 tracer at boot up. function-list is a comma separated
813 list of functions. This list can be changed at run
814 time by the set_ftrace_filter file in the debugfs
815 tracing directory.
817 ftrace_notrace=[function-list]
818 [FTRACE] Do not trace the functions specified in
819 function-list. This list can be changed at run time
820 by the set_ftrace_notrace file in the debugfs
821 tracing directory.
823 ftrace_graph_filter=[function-list]
824 [FTRACE] Limit the top level callers functions traced
825 by the function graph tracer at boot up.
826 function-list is a comma separated list of functions
827 that can be changed at run time by the
828 set_graph_function file in the debugfs tracing directory.
830 gamecon.map[2|3]=
831 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
832 support via parallel port (up to 5 devices per port)
833 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
834 See also Documentation/input/joystick-parport.txt
836 gamma= [HW,DRM]
838 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
839 Format: off | on
840 default: on
842 gcov_persist= [GCOV] When non-zero (default), profiling data for
843 kernel modules is saved and remains accessible via
844 debugfs, even when the module is unloaded/reloaded.
845 When zero, profiling data is discarded and associated
846 debugfs files are removed at module unload time.
848 gpt [EFI] Forces disk with valid GPT signature but
849 invalid Protective MBR to be treated as GPT.
851 hashdist= [KNL,NUMA] Large hashes allocated during boot
852 are distributed across NUMA nodes. Defaults on
853 for 64-bit NUMA, off otherwise.
854 Format: 0 | 1 (for off | on)
856 hcl= [IA-64] SGI's Hardware Graph compatibility layer
858 hd= [EIDE] (E)IDE hard drive subsystem geometry
859 Format: <cyl>,<head>,<sect>
861 hest_disable [ACPI]
862 Disable Hardware Error Source Table (HEST) support;
863 corresponding firmware-first mode error processing
864 logic will be disabled.
866 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
867 size of <nn>. This works even on boxes that have no
868 highmem otherwise. This also works to reduce highmem
869 size on bigger boxes.
871 highres= [KNL] Enable/disable high resolution timer mode.
872 Valid parameters: "on", "off"
873 Default: "on"
875 hisax= [HW,ISDN]
876 See Documentation/isdn/README.HiSax.
878 hlt [BUGS=ARM,SH]
880 hpet= [X86-32,HPET] option to control HPET usage
881 Format: { enable (default) | disable | force |
882 verbose }
883 disable: disable HPET and use PIT instead
884 force: allow force enabled of undocumented chips (ICH4,
885 VIA, nVidia)
886 verbose: show contents of HPET registers during setup
888 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
889 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
890 On x86-64 and powerpc, this option can be specified
891 multiple times interleaved with hugepages= to reserve
892 huge pages of different sizes. Valid pages sizes on
893 x86-64 are 2M (when the CPU supports "pse") and 1G
894 (when the CPU supports the "pdpe1gb" cpuinfo flag)
895 Note that 1GB pages can only be allocated at boot time
896 using hugepages= and not freed afterwards.
898 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
899 terminal devices. Valid values: 0..8
900 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
901 If specified, z/VM IUCV HVC accepts connections
902 from listed z/VM user IDs only.
904 keep_bootcon [KNL]
905 Do not unregister boot console at start. This is only
906 useful for debugging when something happens in the window
907 between unregistering the boot console and initializing
908 the real console.
910 i2c_bus= [HW] Override the default board specific I2C bus speed
911 or register an additional I2C bus that is not
912 registered from board initialization code.
913 Format:
914 <bus_id>,<clkrate>
916 i8042.debug [HW] Toggle i8042 debug mode
917 i8042.direct [HW] Put keyboard port into non-translated mode
918 i8042.dumbkbd [HW] Pretend that controller can only read data from
919 keyboard and cannot control its state
920 (Don't attempt to blink the leds)
921 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
922 i8042.nokbd [HW] Don't check/create keyboard port
923 i8042.noloop [HW] Disable the AUX Loopback command while probing
924 for the AUX port
925 i8042.nomux [HW] Don't check presence of an active multiplexing
926 controller
927 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
928 controllers
929 i8042.notimeout [HW] Ignore timeout condition signalled by conroller
930 i8042.reset [HW] Reset the controller during init and cleanup
931 i8042.unlock [HW] Unlock (ignore) the keylock
933 i810= [HW,DRM]
935 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
936 indicates that the driver is running on unsupported
937 hardware.
938 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
939 does not match list of supported models.
940 i8k.power_status
941 [HW] Report power status in /proc/i8k
942 (disabled by default)
943 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
944 capability is set.
946 icn= [HW,ISDN]
947 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
949 ide-core.nodma= [HW] (E)IDE subsystem
950 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
951 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
952 .cdrom .chs .ignore_cable are additional options
953 See Documentation/ide/ide.txt.
955 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
956 Claim all unknown PCI IDE storage controllers.
958 idle= [X86]
959 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
960 Poll forces a polling idle loop that can slightly
961 improve the performance of waking up a idle CPU, but
962 will use a lot of power and make the system run hot.
963 Not recommended.
964 idle=mwait: On systems which support MONITOR/MWAIT but
965 the kernel chose to not use it because it doesn't save
966 as much power as a normal idle loop, use the
967 MONITOR/MWAIT idle loop anyways. Performance should be
968 the same as idle=poll.
969 idle=halt: Halt is forced to be used for CPU idle.
970 In such case C2/C3 won't be used again.
971 idle=nomwait: Disable mwait for CPU C-states
973 ignore_loglevel [KNL]
974 Ignore loglevel setting - this will print /all/
975 kernel messages to the console. Useful for debugging.
976 We also add it as printk module parameter, so users
977 could change it dynamically, usually by
978 /sys/module/printk/parameters/ignore_loglevel.
980 ihash_entries= [KNL]
981 Set number of hash buckets for inode cache.
983 ima_audit= [IMA]
984 Format: { "0" | "1" }
985 0 -- integrity auditing messages. (Default)
986 1 -- enable informational integrity auditing messages.
988 ima_hash= [IMA]
989 Format: { "sha1" | "md5" }
990 default: "sha1"
992 ima_tcb [IMA]
993 Load a policy which meets the needs of the Trusted
994 Computing Base. This means IMA will measure all
995 programs exec'd, files mmap'd for exec, and all files
996 opened for read by uid=0.
998 init= [KNL]
999 Format: <full_path>
1000 Run specified binary instead of /sbin/init as init
1001 process.
1003 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1004 for working out where the kernel is dying during
1005 startup.
1007 initrd= [BOOT] Specify the location of the initial ramdisk
1009 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1010 Format: <irq>
1012 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1013 on
1014 Enable intel iommu driver.
1015 off
1016 Disable intel iommu driver.
1017 igfx_off [Default Off]
1018 By default, gfx is mapped as normal device. If a gfx
1019 device has a dedicated DMAR unit, the DMAR unit is
1020 bypassed by not enabling DMAR with this option. In
1021 this case, gfx device will use physical address for
1022 DMA.
1023 forcedac [x86_64]
1024 With this option iommu will not optimize to look
1025 for io virtual address below 32-bit forcing dual
1026 address cycle on pci bus for cards supporting greater
1027 than 32-bit addressing. The default is to look
1028 for translation below 32-bit and if not available
1029 then look in the higher range.
1030 strict [Default Off]
1031 With this option on every unmap_single operation will
1032 result in a hardware IOTLB flush operation as opposed
1033 to batching them for performance.
1034 sp_off [Default Off]
1035 By default, super page will be supported if Intel IOMMU
1036 has the capability. With this option, super page will
1037 not be supported.
1038 intremap= [X86-64, Intel-IOMMU]
1039 Format: { on (default) | off | nosid }
1040 on enable Interrupt Remapping (default)
1041 off disable Interrupt Remapping
1042 nosid disable Source ID checking
1044 inttest= [IA-64]
1046 iomem= Disable strict checking of access to MMIO memory
1047 strict regions from userspace.
1048 relaxed
1050 iommu= [x86]
1051 off
1052 force
1053 noforce
1054 biomerge
1055 panic
1056 nopanic
1057 merge
1058 nomerge
1059 forcesac
1060 soft
1061 pt [x86, IA-64]
1063 io7= [HW] IO7 for Marvel based alpha systems
1064 See comment before marvel_specify_io7 in
1065 arch/alpha/kernel/core_marvel.c.
1067 io_delay= [X86] I/O delay method
1068 0x80
1069 Standard port 0x80 based delay
1070 0xed
1071 Alternate port 0xed based delay (needed on some systems)
1072 udelay
1073 Simple two microseconds delay
1074 none
1075 No delay
1077 ip= [IP_PNP]
1078 See Documentation/filesystems/nfs/nfsroot.txt.
1080 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1081 See comment before ip2_setup() in
1082 drivers/char/ip2/ip2base.c.
1084 irqfixup [HW]
1085 When an interrupt is not handled search all handlers
1086 for it. Intended to get systems with badly broken
1087 firmware running.
1089 irqpoll [HW]
1090 When an interrupt is not handled search all handlers
1091 for it. Also check all handlers each timer
1092 interrupt. Intended to get systems with badly broken
1093 firmware running.
1095 isapnp= [ISAPNP]
1096 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1098 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1099 Format:
1100 <cpu number>,...,<cpu number>
1101 or
1102 <cpu number>-<cpu number>
1103 (must be a positive range in ascending order)
1104 or a mixture
1105 <cpu number>,...,<cpu number>-<cpu number>
1107 This option can be used to specify one or more CPUs
1108 to isolate from the general SMP balancing and scheduling
1109 algorithms. You can move a process onto or off an
1110 "isolated" CPU via the CPU affinity syscalls or cpuset.
1111 <cpu number> begins at 0 and the maximum value is
1112 "number of CPUs in system - 1".
1114 This option is the preferred way to isolate CPUs. The
1115 alternative -- manually setting the CPU mask of all
1116 tasks in the system -- can cause problems and
1117 suboptimal load balancer performance.
1119 iucv= [HW,NET]
1121 js= [HW,JOY] Analog joystick
1122 See Documentation/input/joystick.txt.
1124 keepinitrd [HW,ARM]
1126 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1127 specifies the amount of memory usable by the kernel
1128 for non-movable allocations. The requested amount is
1129 spread evenly throughout all nodes in the system. The
1130 remaining memory in each node is used for Movable
1131 pages. In the event, a node is too small to have both
1132 kernelcore and Movable pages, kernelcore pages will
1133 take priority and other nodes will have a larger number
1134 of kernelcore pages. The Movable zone is used for the
1135 allocation of pages that may be reclaimed or moved
1136 by the page migration subsystem. This means that
1137 HugeTLB pages may not be allocated from this zone.
1138 Note that allocations like PTEs-from-HighMem still
1139 use the HighMem zone if it exists, and the Normal
1140 zone if it does not.
1142 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1143 Format: <Controller#>[,poll interval]
1144 The controller # is the number of the ehci usb debug
1145 port as it is probed via PCI. The poll interval is
1146 optional and is the number seconds in between
1147 each poll cycle to the debug port in case you need
1148 the functionality for interrupting the kernel with
1149 gdb or control-c on the dbgp connection. When
1150 not using this parameter you use sysrq-g to break into
1151 the kernel debugger.
1153 kgdboc= [KGDB,HW] kgdb over consoles.
1154 Requires a tty driver that supports console polling,
1155 or a supported polling keyboard driver (non-usb).
1156 Serial only format: <serial_device>[,baud]
1157 keyboard only format: kbd
1158 keyboard and serial format: kbd,<serial_device>[,baud]
1159 Optional Kernel mode setting:
1160 kms, kbd format: kms,kbd
1161 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1163 kgdbwait [KGDB] Stop kernel execution and enter the
1164 kernel debugger at the earliest opportunity.
1166 kmac= [MIPS] korina ethernet MAC address.
1167 Configure the RouterBoard 532 series on-chip
1168 Ethernet adapter MAC address.
1170 kmemleak= [KNL] Boot-time kmemleak enable/disable
1171 Valid arguments: on, off
1172 Default: on
1174 kstack=N [X86] Print N words from the kernel stack
1175 in oops dumps.
1177 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1178 Default is 0 (don't ignore, but inject #GP)
1180 kvm.oos_shadow= [KVM] Disable out-of-sync shadow paging.
1181 Default is 1 (enabled)
1183 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1184 KVM MMU at runtime.
1185 Default is 0 (off)
1187 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1188 Default is 1 (enabled)
1190 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1191 for all guests.
1192 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1194 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1195 (virtualized MMU) support on capable Intel chips.
1196 Default is 1 (enabled)
1198 kvm-intel.emulate_invalid_guest_state=
1199 [KVM,Intel] Enable emulation of invalid guest states
1200 Default is 0 (disabled)
1202 kvm-intel.flexpriority=
1203 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1204 Default is 1 (enabled)
1206 kvm-intel.nested=
1207 [KVM,Intel] Enable VMX nesting (nVMX).
1208 Default is 0 (disabled)
1210 kvm-intel.unrestricted_guest=
1211 [KVM,Intel] Disable unrestricted guest feature
1212 (virtualized real and unpaged mode) on capable
1213 Intel chips. Default is 1 (enabled)
1215 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1216 feature (tagged TLBs) on capable Intel chips.
1217 Default is 1 (enabled)
1219 l2cr= [PPC]
1221 l3cr= [PPC]
1223 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1224 disabled it.
1226 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1227 in C2 power state.
1229 libata.dma= [LIBATA] DMA control
1230 libata.dma=0 Disable all PATA and SATA DMA
1231 libata.dma=1 PATA and SATA Disk DMA only
1232 libata.dma=2 ATAPI (CDROM) DMA only
1233 libata.dma=4 Compact Flash DMA only
1234 Combinations also work, so libata.dma=3 enables DMA
1235 for disks and CDROMs, but not CFs.
1237 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1238 libata.ignore_hpa=0 keep BIOS limits (default)
1239 libata.ignore_hpa=1 ignore limits, using full disk
1241 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1242 when set.
1243 Format: <int>
1245 libata.force= [LIBATA] Force configurations. The format is comma
1246 separated list of "[ID:]VAL" where ID is
1247 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1248 matching port, link or device. Basically, it matches
1249 the ATA ID string printed on console by libata. If
1250 the whole ID part is omitted, the last PORT and DEVICE
1251 values are used. If ID hasn't been specified yet, the
1252 configuration applies to all ports, links and devices.
1254 If only DEVICE is omitted, the parameter applies to
1255 the port and all links and devices behind it. DEVICE
1256 number of 0 either selects the first device or the
1257 first fan-out link behind PMP device. It does not
1258 select the host link. DEVICE number of 15 selects the
1259 host link and device attached to it.
1261 The VAL specifies the configuration to force. As long
1262 as there's no ambiguity shortcut notation is allowed.
1263 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1264 The following configurations can be forced.
1266 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1267 Any ID with matching PORT is used.
1269 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1271 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1272 udma[/][16,25,33,44,66,100,133] notation is also
1273 allowed.
1275 * [no]ncq: Turn on or off NCQ.
1277 * nohrst, nosrst, norst: suppress hard, soft
1278 and both resets.
1280 * dump_id: dump IDENTIFY data.
1282 If there are multiple matching configurations changing
1283 the same attribute, the last one is used.
1285 memblock=debug [KNL] Enable memblock debug messages.
1287 load_ramdisk= [RAM] List of ramdisks to load from floppy
1288 See Documentation/blockdev/ramdisk.txt.
1290 lockd.nlm_grace_period=P [NFS] Assign grace period.
1291 Format: <integer>
1293 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1294 Format: <integer>
1296 lockd.nlm_timeout=T [NFS] Assign timeout value.
1297 Format: <integer>
1299 lockd.nlm_udpport=M [NFS] Assign UDP port.
1300 Format: <integer>
1302 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1303 Format: <irq>
1305 loglevel= All Kernel Messages with a loglevel smaller than the
1306 console loglevel will be printed to the console. It can
1307 also be changed with klogd or other programs. The
1308 loglevels are defined as follows:
1310 0 (KERN_EMERG) system is unusable
1311 1 (KERN_ALERT) action must be taken immediately
1312 2 (KERN_CRIT) critical conditions
1313 3 (KERN_ERR) error conditions
1314 4 (KERN_WARNING) warning conditions
1315 5 (KERN_NOTICE) normal but significant condition
1316 6 (KERN_INFO) informational
1317 7 (KERN_DEBUG) debug-level messages
1319 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1320 in bytes. n must be a power of two. The default
1321 size is set in the kernel config file.
1323 logo.nologo [FB] Disables display of the built-in Linux logo.
1324 This may be used to provide more screen space for
1325 kernel log messages and is useful when debugging
1326 kernel boot problems.
1328 lp=0 [LP] Specify parallel ports to use, e.g,
1329 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1330 lp=reset first parallel port). 'lp=0' disables the
1331 lp=auto printer driver. 'lp=reset' (which can be
1332 specified in addition to the ports) causes
1333 attached printers to be reset. Using
1334 lp=port1,port2,... specifies the parallel ports
1335 to associate lp devices with, starting with
1336 lp0. A port specification may be 'none' to skip
1337 that lp device, or a parport name such as
1338 'parport0'. Specifying 'lp=auto' instead of a
1339 port specification list means that device IDs
1340 from each port should be examined, to see if
1341 an IEEE 1284-compliant printer is attached; if
1342 so, the driver will manage that printer.
1343 See also header of drivers/char/lp.c.
1345 lpj=n [KNL]
1346 Sets loops_per_jiffy to given constant, thus avoiding
1347 time-consuming boot-time autodetection (up to 250 ms per
1348 CPU). 0 enables autodetection (default). To determine
1349 the correct value for your kernel, boot with normal
1350 autodetection and see what value is printed. Note that
1351 on SMP systems the preset will be applied to all CPUs,
1352 which is likely to cause problems if your CPUs need
1353 significantly divergent settings. An incorrect value
1354 will cause delays in the kernel to be wrong, leading to
1355 unpredictable I/O errors and other breakage. Although
1356 unlikely, in the extreme case this might damage your
1357 hardware.
1359 ltpc= [NET]
1360 Format: <io>,<irq>,<dma>
1362 machvec= [IA-64] Force the use of a particular machine-vector
1363 (machvec) in a generic kernel.
1364 Example: machvec=hpzx1_swiotlb
1366 machtype= [Loongson] Share the same kernel image file between different
1367 yeeloong laptop.
1368 Example: machtype=lemote-yeeloong-2f-7inch
1370 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1371 than or equal to this physical address is ignored.
1373 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1374 should make use of. maxcpus=n : n >= 0 limits the
1375 kernel to using 'n' processors. n=0 is a special case,
1376 it is equivalent to "nosmp", which also disables
1377 the IO APIC.
1379 max_loop= [LOOP] The number of loop block devices that get
1380 (loop.max_loop) unconditionally pre-created at init time. The default
1381 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1382 of statically allocating a predefined number, loop
1383 devices can be requested on-demand with the
1384 /dev/loop-control interface.
1386 mcatest= [IA-64]
1388 mce [X86-32] Machine Check Exception
1390 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1392 md= [HW] RAID subsystems devices and level
1393 See Documentation/md.txt.
1395 mdacon= [MDA]
1396 Format: <first>,<last>
1397 Specifies range of consoles to be captured by the MDA.
1399 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1400 Amount of memory to be used when the kernel is not able
1401 to see the whole system memory or for test.
1402 [X86-32] Use together with memmap= to avoid physical
1403 address space collisions. Without memmap= PCI devices
1404 could be placed at addresses belonging to unused RAM.
1406 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1407 memory.
1409 memchunk=nn[KMG]
1410 [KNL,SH] Allow user to override the default size for
1411 per-device physically contiguous DMA buffers.
1413 memmap=exactmap [KNL,X86] Enable setting of an exact
1414 E820 memory map, as specified by the user.
1415 Such memmap=exactmap lines can be constructed based on
1416 BIOS output or other requirements. See the memmap=nn@ss
1417 option description.
1419 memmap=nn[KMG]@ss[KMG]
1420 [KNL] Force usage of a specific region of memory
1421 Region of memory to be used, from ss to ss+nn.
1423 memmap=nn[KMG]#ss[KMG]
1424 [KNL,ACPI] Mark specific memory as ACPI data.
1425 Region of memory to be used, from ss to ss+nn.
1427 memmap=nn[KMG]$ss[KMG]
1428 [KNL,ACPI] Mark specific memory as reserved.
1429 Region of memory to be used, from ss to ss+nn.
1430 Example: Exclude memory from 0x18690000-0x1869ffff
1431 memmap=64K$0x18690000
1432 or
1433 memmap=0x10000$0x18690000
1435 memory_corruption_check=0/1 [X86]
1436 Some BIOSes seem to corrupt the first 64k of
1437 memory when doing things like suspend/resume.
1438 Setting this option will scan the memory
1439 looking for corruption. Enabling this will
1440 both detect corruption and prevent the kernel
1441 from using the memory being corrupted.
1442 However, its intended as a diagnostic tool; if
1443 repeatable BIOS-originated corruption always
1444 affects the same memory, you can use memmap=
1445 to prevent the kernel from using that memory.
1447 memory_corruption_check_size=size [X86]
1448 By default it checks for corruption in the low
1449 64k, making this memory unavailable for normal
1450 use. Use this parameter to scan for
1451 corruption in more or less memory.
1453 memory_corruption_check_period=seconds [X86]
1454 By default it checks for corruption every 60
1455 seconds. Use this parameter to check at some
1456 other rate. 0 disables periodic checking.
1458 memtest= [KNL,X86] Enable memtest
1459 Format: <integer>
1460 default : 0 <disable>
1461 Specifies the number of memtest passes to be
1462 performed. Each pass selects another test
1463 pattern from a given set of patterns. Memtest
1464 fills the memory with this pattern, validates
1465 memory contents and reserves bad memory
1466 regions that are detected.
1468 meye.*= [HW] Set MotionEye Camera parameters
1469 See Documentation/video4linux/meye.txt.
1471 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1472 Multi-Function General Purpose Timers on AMD Geode
1473 platforms.
1475 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1476 the BIOS has incorrectly applied a workaround. TinyBIOS
1477 version 0.98 is known to be affected, 0.99 fixes the
1478 problem by letting the user disable the workaround.
1480 mga= [HW,DRM]
1482 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1483 physical address is ignored.
1485 mini2440= [ARM,HW,KNL]
1486 Format:[0..2][b][c][t]
1487 Default: "0tb"
1488 MINI2440 configuration specification:
1489 0 - The attached screen is the 3.5" TFT
1490 1 - The attached screen is the 7" TFT
1491 2 - The VGA Shield is attached (1024x768)
1492 Leaving out the screen size parameter will not load
1493 the TFT driver, and the framebuffer will be left
1494 unconfigured.
1495 b - Enable backlight. The TFT backlight pin will be
1496 linked to the kernel VESA blanking code and a GPIO
1497 LED. This parameter is not necessary when using the
1498 VGA shield.
1499 c - Enable the s3c camera interface.
1500 t - Reserved for enabling touchscreen support. The
1501 touchscreen support is not enabled in the mainstream
1502 kernel as of 2.6.30, a preliminary port can be found
1503 in the "bleeding edge" mini2440 support kernel at
1504 http://repo.or.cz/w/linux-2.6/mini2440.git
1506 mminit_loglevel=
1507 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1508 parameter allows control of the logging verbosity for
1509 the additional memory initialisation checks. A value
1510 of 0 disables mminit logging and a level of 4 will
1511 log everything. Information is printed at KERN_DEBUG
1512 so loglevel=8 may also need to be specified.
1514 mousedev.tap_time=
1515 [MOUSE] Maximum time between finger touching and
1516 leaving touchpad surface for touch to be considered
1517 a tap and be reported as a left button click (for
1518 touchpads working in absolute mode only).
1519 Format: <msecs>
1520 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1521 reporting absolute coordinates, such as tablets
1522 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1523 reporting absolute coordinates, such as tablets
1525 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1526 is similar to kernelcore except it specifies the
1527 amount of memory used for migratable allocations.
1528 If both kernelcore and movablecore is specified,
1529 then kernelcore will be at *least* the specified
1530 value but may be more. If movablecore on its own
1531 is specified, the administrator must be careful
1532 that the amount of memory usable for all allocations
1533 is not too small.
1535 MTD_Partition= [MTD]
1536 Format: <name>,<region-number>,<size>,<offset>
1538 MTD_Region= [MTD] Format:
1539 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1541 mtdparts= [MTD]
1542 See drivers/mtd/cmdlinepart.c.
1544 multitce=off [PPC] This parameter disables the use of the pSeries
1545 firmware feature for updating multiple TCE entries
1546 at a time.
1548 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1550 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1552 boundary - index of last SLC block on Flex-OneNAND.
1553 The remaining blocks are configured as MLC blocks.
1554 lock - Configure if Flex-OneNAND boundary should be locked.
1555 Once locked, the boundary cannot be changed.
1556 1 indicates lock status, 0 indicates unlock status.
1558 mtdset= [ARM]
1559 ARM/S3C2412 JIVE boot control
1561 See arch/arm/mach-s3c2412/mach-jive.c
1563 mtouchusb.raw_coordinates=
1564 [HW] Make the MicroTouch USB driver use raw coordinates
1565 ('y', default) or cooked coordinates ('n')
1567 mtrr_chunk_size=nn[KMG] [X86]
1568 used for mtrr cleanup. It is largest continuous chunk
1569 that could hold holes aka. UC entries.
1571 mtrr_gran_size=nn[KMG] [X86]
1572 Used for mtrr cleanup. It is granularity of mtrr block.
1573 Default is 1.
1574 Large value could prevent small alignment from
1575 using up MTRRs.
1577 mtrr_spare_reg_nr=n [X86]
1578 Format: <integer>
1579 Range: 0,7 : spare reg number
1580 Default : 1
1581 Used for mtrr cleanup. It is spare mtrr entries number.
1582 Set to 2 or more if your graphical card needs more.
1584 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1586 netdev= [NET] Network devices parameters
1587 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1588 Note that mem_start is often overloaded to mean
1589 something different and driver-specific.
1590 This usage is only documented in each driver source
1591 file if at all.
1593 nf_conntrack.acct=
1594 [NETFILTER] Enable connection tracking flow accounting
1595 0 to disable accounting
1596 1 to enable accounting
1597 Default value is 0.
1599 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1600 See Documentation/filesystems/nfs/nfsroot.txt.
1602 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1603 See Documentation/filesystems/nfs/nfsroot.txt.
1605 nfsrootdebug [NFS] enable nfsroot debugging messages.
1606 See Documentation/filesystems/nfs/nfsroot.txt.
1608 nfs.callback_tcpport=
1609 [NFS] set the TCP port on which the NFSv4 callback
1610 channel should listen.
1612 nfs.cache_getent=
1613 [NFS] sets the pathname to the program which is used
1614 to update the NFS client cache entries.
1616 nfs.cache_getent_timeout=
1617 [NFS] sets the timeout after which an attempt to
1618 update a cache entry is deemed to have failed.
1620 nfs.idmap_cache_timeout=
1621 [NFS] set the maximum lifetime for idmapper cache
1622 entries.
1624 nfs.enable_ino64=
1625 [NFS] enable 64-bit inode numbers.
1626 If zero, the NFS client will fake up a 32-bit inode
1627 number for the readdir() and stat() syscalls instead
1628 of returning the full 64-bit number.
1629 The default is to return 64-bit inode numbers.
1631 nfs.nfs4_disable_idmapping=
1632 [NFSv4] When set, this option disables the NFSv4
1633 idmapper on the client, but only if the mount
1634 is using the 'sec=sys' security flavour. This may
1635 make migration from legacy NFSv2/v3 systems easier
1636 provided that the server has the appropriate support.
1637 The default is to always enable NFSv4 idmapping.
1639 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1640 when a NMI is triggered.
1641 Format: [state][,regs][,debounce][,die]
1643 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1644 Format: [panic,][nopanic,][num]
1645 Valid num: 0
1646 0 - turn nmi_watchdog off
1647 When panic is specified, panic when an NMI watchdog
1648 timeout occurs (or 'nopanic' to override the opposite
1649 default).
1650 This is useful when you use a panic=... timeout and
1651 need the box quickly up again.
1653 netpoll.carrier_timeout=
1654 [NET] Specifies amount of time (in seconds) that
1655 netpoll should wait for a carrier. By default netpoll
1656 waits 4 seconds.
1658 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1659 emulation library even if a 387 maths coprocessor
1660 is present.
1662 no_console_suspend
1663 [HW] Never suspend the console
1664 Disable suspending of consoles during suspend and
1665 hibernate operations. Once disabled, debugging
1666 messages can reach various consoles while the rest
1667 of the system is being put to sleep (ie, while
1668 debugging driver suspend/resume hooks). This may
1669 not work reliably with all consoles, but is known
1670 to work with serial and VGA consoles.
1671 To facilitate more flexible debugging, we also add
1672 console_suspend, a printk module parameter to control
1673 it. Users could use console_suspend (usually
1674 /sys/module/printk/parameters/console_suspend) to
1675 turn on/off it dynamically.
1677 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1678 caches in the slab allocator. Saves per-node memory,
1679 but will impact performance.
1681 noalign [KNL,ARM]
1683 noapic [SMP,APIC] Tells the kernel to not make use of any
1684 IOAPICs that may be present in the system.
1686 noautogroup Disable scheduler automatic task group creation.
1688 nobats [PPC] Do not use BATs for mapping kernel lowmem
1689 on "Classic" PPC cores.
1691 nocache [ARM]
1693 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1695 nodelayacct [KNL] Disable per-task delay accounting
1697 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1699 nodsp [SH] Disable hardware DSP at boot time.
1701 noefi [X86] Disable EFI runtime services support.
1703 noexec [IA-64]
1705 noexec [X86]
1706 On X86-32 available only on PAE configured kernels.
1707 noexec=on: enable non-executable mappings (default)
1708 noexec=off: disable non-executable mappings
1710 nosmep [X86]
1711 Disable SMEP (Supervisor Mode Execution Protection)
1712 even if it is supported by processor.
1714 noexec32 [X86-64]
1715 This affects only 32-bit executables.
1716 noexec32=on: enable non-executable mappings (default)
1717 read doesn't imply executable mappings
1718 noexec32=off: disable non-executable mappings
1719 read implies executable mappings
1721 nofpu [SH] Disable hardware FPU at boot time.
1723 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1724 register save and restore. The kernel will only save
1725 legacy floating-point registers on task switch.
1727 noxsave [BUGS=X86] Disables x86 extended register state save
1728 and restore using xsave. The kernel will fallback to
1729 enabling legacy floating-point and sse state.
1731 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1732 wfi(ARM) instruction doesn't work correctly and not to
1733 use it. This is also useful when using JTAG debugger.
1735 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1736 instruction doesn't work correctly and not to
1737 use it.
1739 no_file_caps Tells the kernel not to honor file capabilities. The
1740 only way then for a file to be executed with privilege
1741 is to be setuid root or executed by root.
1743 nohalt [IA-64] Tells the kernel not to use the power saving
1744 function PAL_HALT_LIGHT when idle. This increases
1745 power-consumption. On the positive side, it reduces
1746 interrupt wake-up latency, which may improve performance
1747 in certain environments such as networked servers or
1748 real-time systems.
1750 nohz= [KNL] Boottime enable/disable dynamic ticks
1751 Valid arguments: on, off
1752 Default: on
1754 noiotrap [SH] Disables trapped I/O port accesses.
1756 noirqdebug [X86-32] Disables the code which attempts to detect and
1757 disable unhandled interrupt sources.
1759 no_timer_check [X86,APIC] Disables the code which tests for
1760 broken timer IRQ sources.
1762 noisapnp [ISAPNP] Disables ISA PnP code.
1764 noinitrd [RAM] Tells the kernel not to load any configured
1765 initial RAM disk.
1767 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1768 remapping.
1769 [Deprecated - use intremap=off]
1771 nointroute [IA-64]
1773 nojitter [IA-64] Disables jitter checking for ITC timers.
1775 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1777 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1778 fault handling.
1780 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1781 steal time is computed, but won't influence scheduler
1782 behaviour
1784 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1786 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1788 noltlbs [PPC] Do not use large page/tlb entries for kernel
1789 lowmem mapping on PPC40x.
1791 nomca [IA-64] Disable machine check abort handling
1793 nomce [X86-32] Machine Check Exception
1795 nomfgpt [X86-32] Disable Multi-Function General Purpose
1796 Timer usage (for AMD Geode machines).
1798 nopat [X86] Disable PAT (page attribute table extension of
1799 pagetables) support.
1801 norandmaps Don't use address space randomization. Equivalent to
1802 echo 0 > /proc/sys/kernel/randomize_va_space
1804 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1806 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1807 with UP alternatives
1809 noresidual [PPC] Don't use residual data on PReP machines.
1811 nordrand [X86] Disable the direct use of the RDRAND
1812 instruction even if it is supported by the
1813 processor. RDRAND is still available to user
1814 space applications.
1816 noresume [SWSUSP] Disables resume and restores original swap
1817 space.
1819 no-scroll [VGA] Disables scrollback.
1820 This is required for the Braillex ib80-piezo Braille
1821 reader made by F.H. Papenmeier (Germany).
1823 nosbagart [IA-64]
1825 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1827 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1828 and disable the IO APIC. legacy for "maxcpus=0".
1830 nosoftlockup [KNL] Disable the soft-lockup detector.
1832 nosync [HW,M68K] Disables sync negotiation for all devices.
1834 notsc [BUGS=X86-32] Disable Time Stamp Counter
1836 nousb [USB] Disable the USB subsystem
1838 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1840 nowb [ARM]
1842 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1844 nptcg= [IA-64] Override max number of concurrent global TLB
1845 purges which is reported from either PAL_VM_SUMMARY or
1846 SAL PALO.
1848 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1849 could support. nr_cpus=n : n >= 1 limits the kernel to
1850 supporting 'n' processors. Later in runtime you can not
1851 use hotplug cpu feature to put more cpu back to online.
1852 just like you compile the kernel NR_CPUS=n
1854 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1856 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1857 one of ['zone', 'node', 'default'] can be specified
1858 This can be set from sysctl after boot.
1859 See Documentation/sysctl/vm.txt for details.
1861 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1862 See Documentation/debugging-via-ohci1394.txt for more
1863 info.
1865 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1866 Rather than timing out after 20 ms if an EC
1867 command is not properly ACKed, override the length
1868 of the timeout. We have interrupts disabled while
1869 waiting for the ACK, so if this is set too high
1870 interrupts *may* be lost!
1872 omap_mux= [OMAP] Override bootloader pin multiplexing.
1873 Format: <mux_mode0.mode_name=value>...
1874 For example, to override I2C bus2:
1875 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1877 oprofile.timer= [HW]
1878 Use timer interrupt instead of performance counters
1880 oprofile.cpu_type= Force an oprofile cpu type
1881 This might be useful if you have an older oprofile
1882 userland or if you want common events.
1883 Format: { arch_perfmon }
1884 arch_perfmon: [X86] Force use of architectural
1885 perfmon on Intel CPUs instead of the
1886 CPU specific event set.
1888 oops=panic Always panic on oopses. Default is to just kill the
1889 process, but there is a small probability of
1890 deadlocking the machine.
1891 This will also cause panics on machine check exceptions.
1892 Useful together with panic=30 to trigger a reboot.
1894 OSS [HW,OSS]
1895 See Documentation/sound/oss/oss-parameters.txt
1897 panic= [KNL] Kernel behaviour on panic: delay <timeout>
1898 timeout > 0: seconds before rebooting
1899 timeout = 0: wait forever
1900 timeout < 0: reboot immediately
1901 Format: <timeout>
1903 parkbd.port= [HW] Parallel port number the keyboard adapter is
1904 connected to, default is 0.
1905 Format: <parport#>
1906 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1907 0 for XT, 1 for AT (default is AT).
1908 Format: <mode>
1910 parport= [HW,PPT] Specify parallel ports. 0 disables.
1911 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1912 Use 'auto' to force the driver to use any
1913 IRQ/DMA settings detected (the default is to
1914 ignore detected IRQ/DMA settings because of
1915 possible conflicts). You can specify the base
1916 address, IRQ, and DMA settings; IRQ and DMA
1917 should be numbers, or 'auto' (for using detected
1918 settings on that particular port), or 'nofifo'
1919 (to avoid using a FIFO even if it is detected).
1920 Parallel ports are assigned in the order they
1921 are specified on the command line, starting
1922 with parport0.
1924 parport_init_mode= [HW,PPT]
1925 Configure VIA parallel port to operate in
1926 a specific mode. This is necessary on Pegasos
1927 computer where firmware has no options for setting
1928 up parallel port mode and sets it to spp.
1929 Currently this function knows 686a and 8231 chips.
1930 Format: [spp|ps2|epp|ecp|ecpepp]
1932 pause_on_oops=
1933 Halt all CPUs after the first oops has been printed for
1934 the specified number of seconds. This is to be used if
1935 your oopses keep scrolling off the screen.
1937 pcbit= [HW,ISDN]
1939 pcd. [PARIDE]
1940 See header of drivers/block/paride/pcd.c.
1941 See also Documentation/blockdev/paride.txt.
1943 pci=option[,option...] [PCI] various PCI subsystem options:
1944 earlydump [X86] dump PCI config space before the kernel
1945 changes anything
1946 off [X86] don't probe for the PCI bus
1947 bios [X86-32] force use of PCI BIOS, don't access
1948 the hardware directly. Use this if your machine
1949 has a non-standard PCI host bridge.
1950 nobios [X86-32] disallow use of PCI BIOS, only direct
1951 hardware access methods are allowed. Use this
1952 if you experience crashes upon bootup and you
1953 suspect they are caused by the BIOS.
1954 conf1 [X86] Force use of PCI Configuration
1955 Mechanism 1.
1956 conf2 [X86] Force use of PCI Configuration
1957 Mechanism 2.
1958 noaer [PCIE] If the PCIEAER kernel config parameter is
1959 enabled, this kernel boot option can be used to
1960 disable the use of PCIE advanced error reporting.
1961 nodomains [PCI] Disable support for multiple PCI
1962 root domains (aka PCI segments, in ACPI-speak).
1963 nommconf [X86] Disable use of MMCONFIG for PCI
1964 Configuration
1965 check_enable_amd_mmconf [X86] check for and enable
1966 properly configured MMIO access to PCI
1967 config space on AMD family 10h CPU
1968 nomsi [MSI] If the PCI_MSI kernel config parameter is
1969 enabled, this kernel boot option can be used to
1970 disable the use of MSI interrupts system-wide.
1971 noioapicquirk [APIC] Disable all boot interrupt quirks.
1972 Safety option to keep boot IRQs enabled. This
1973 should never be necessary.
1974 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
1975 primary IO-APIC for bridges that cannot disable
1976 boot IRQs. This fixes a source of spurious IRQs
1977 when the system masks IRQs.
1978 noioapicreroute [APIC] Disable workaround that uses the
1979 boot IRQ equivalent of an IRQ that connects to
1980 a chipset where boot IRQs cannot be disabled.
1981 The opposite of ioapicreroute.
1982 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
1983 routing table. These calls are known to be buggy
1984 on several machines and they hang the machine
1985 when used, but on other computers it's the only
1986 way to get the interrupt routing table. Try
1987 this option if the kernel is unable to allocate
1988 IRQs or discover secondary PCI buses on your
1989 motherboard.
1990 rom [X86] Assign address space to expansion ROMs.
1991 Use with caution as certain devices share
1992 address decoders between ROMs and other
1993 resources.
1994 norom [X86] Do not assign address space to
1995 expansion ROMs that do not already have
1996 BIOS assigned address ranges.
1997 nobar [X86] Do not assign address space to the
1998 BARs that weren't assigned by the BIOS.
1999 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2000 assigned automatically to PCI devices. You can
2001 make the kernel exclude IRQs of your ISA cards
2002 this way.
2003 pirqaddr=0xAAAAA [X86] Specify the physical address
2004 of the PIRQ table (normally generated
2005 by the BIOS) if it is outside the
2006 F0000h-100000h range.
2007 lastbus=N [X86] Scan all buses thru bus #N. Can be
2008 useful if the kernel is unable to find your
2009 secondary buses and you want to tell it
2010 explicitly which ones they are.
2011 assign-busses [X86] Always assign all PCI bus
2012 numbers ourselves, overriding
2013 whatever the firmware may have done.
2014 usepirqmask [X86] Honor the possible IRQ mask stored
2015 in the BIOS $PIR table. This is needed on
2016 some systems with broken BIOSes, notably
2017 some HP Pavilion N5400 and Omnibook XE3
2018 notebooks. This will have no effect if ACPI
2019 IRQ routing is enabled.
2020 noacpi [X86] Do not use ACPI for IRQ routing
2021 or for PCI scanning.
2022 use_crs [X86] Use PCI host bridge window information
2023 from ACPI. On BIOSes from 2008 or later, this
2024 is enabled by default. If you need to use this,
2025 please report a bug.
2026 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2027 If you need to use this, please report a bug.
2028 routeirq Do IRQ routing for all PCI devices.
2029 This is normally done in pci_enable_device(),
2030 so this option is a temporary workaround
2031 for broken drivers that don't call it.
2032 skip_isa_align [X86] do not align io start addr, so can
2033 handle more pci cards
2034 firmware [ARM] Do not re-enumerate the bus but instead
2035 just use the configuration from the
2036 bootloader. This is currently used on
2037 IXP2000 systems where the bus has to be
2038 configured a certain way for adjunct CPUs.
2039 noearly [X86] Don't do any early type 1 scanning.
2040 This might help on some broken boards which
2041 machine check when some devices' config space
2042 is read. But various workarounds are disabled
2043 and some IOMMU drivers will not work.
2044 bfsort Sort PCI devices into breadth-first order.
2045 This sorting is done to get a device
2046 order compatible with older (<= 2.4) kernels.
2047 nobfsort Don't sort PCI devices into breadth-first order.
2048 cbiosize=nn[KMG] The fixed amount of bus space which is
2049 reserved for the CardBus bridge's IO window.
2050 The default value is 256 bytes.
2051 cbmemsize=nn[KMG] The fixed amount of bus space which is
2052 reserved for the CardBus bridge's memory
2053 window. The default value is 64 megabytes.
2054 resource_alignment=
2055 Format:
2056 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2057 Specifies alignment and device to reassign
2058 aligned memory resources.
2059 If <order of align> is not specified,
2060 PAGE_SIZE is used as alignment.
2061 PCI-PCI bridge can be specified, if resource
2062 windows need to be expanded.
2063 ecrc= Enable/disable PCIe ECRC (transaction layer
2064 end-to-end CRC checking).
2065 bios: Use BIOS/firmware settings. This is the
2066 the default.
2067 off: Turn ECRC off
2068 on: Turn ECRC on.
2069 realloc reallocate PCI resources if allocations done by BIOS
2070 are erroneous.
2072 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2073 Management.
2074 off Disable ASPM.
2075 force Enable ASPM even on devices that claim not to support it.
2076 WARNING: Forcing ASPM on may cause system lockups.
2078 pcie_ports= [PCIE] PCIe ports handling:
2079 auto Ask the BIOS whether or not to use native PCIe services
2080 associated with PCIe ports (PME, hot-plug, AER). Use
2081 them only if that is allowed by the BIOS.
2082 native Use native PCIe services associated with PCIe ports
2083 unconditionally.
2084 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2085 ports driver.
2087 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2088 nomsi Do not use MSI for native PCIe PME signaling (this makes
2089 all PCIe root ports use INTx for all services).
2091 pcmv= [HW,PCMCIA] BadgePAD 4
2093 pd. [PARIDE]
2094 See Documentation/blockdev/paride.txt.
2096 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2097 boot time.
2098 Format: { 0 | 1 }
2099 See arch/parisc/kernel/pdc_chassis.c
2101 percpu_alloc= Select which percpu first chunk allocator to use.
2102 Currently supported values are "embed" and "page".
2103 Archs may support subset or none of the selections.
2104 See comments in mm/percpu.c for details on each
2105 allocator. This parameter is primarily for debugging
2106 and performance comparison.
2108 pf. [PARIDE]
2109 See Documentation/blockdev/paride.txt.
2111 pg. [PARIDE]
2112 See Documentation/blockdev/paride.txt.
2114 pirq= [SMP,APIC] Manual mp-table setup
2115 See Documentation/x86/i386/IO-APIC.txt.
2117 plip= [PPT,NET] Parallel port network link
2118 Format: { parport<nr> | timid | 0 }
2119 See also Documentation/parport.txt.
2121 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2122 Override pmtimer IOPort with a hex value.
2123 e.g. pmtmr=0x508
2125 pnp.debug=1 [PNP]
2126 Enable PNP debug messages (depends on the
2127 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2128 via /sys/module/pnp/parameters/debug. We always show
2129 current resource usage; turning this on also shows
2130 possible settings and some assignment information.
2132 pnpacpi= [ACPI]
2133 { off }
2135 pnpbios= [ISAPNP]
2136 { on | off | curr | res | no-curr | no-res }
2138 pnp_reserve_irq=
2139 [ISAPNP] Exclude IRQs for the autoconfiguration
2141 pnp_reserve_dma=
2142 [ISAPNP] Exclude DMAs for the autoconfiguration
2144 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2145 Ranges are in pairs (I/O port base and size).
2147 pnp_reserve_mem=
2148 [ISAPNP] Exclude memory regions for the
2149 autoconfiguration.
2150 Ranges are in pairs (memory base and size).
2152 ports= [IP_VS_FTP] IPVS ftp helper module
2153 Default is 21.
2154 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2155 may be specified.
2156 Format: <port>,<port>....
2158 print-fatal-signals=
2159 [KNL] debug: print fatal signals
2161 If enabled, warn about various signal handling
2162 related application anomalies: too many signals,
2163 too many POSIX.1 timers, fatal signals causing a
2164 coredump - etc.
2166 If you hit the warning due to signal overflow,
2167 you might want to try "ulimit -i unlimited".
2169 default: off.
2171 printk.time= Show timing data prefixed to each printk message line
2172 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2174 processor.max_cstate= [HW,ACPI]
2175 Limit processor to maximum C-state
2176 max_cstate=9 overrides any DMI blacklist limit.
2178 processor.nocst [HW,ACPI]
2179 Ignore the _CST method to determine C-states,
2180 instead using the legacy FADT method
2182 profile= [KNL] Enable kernel profiling via /proc/profile
2183 Format: [schedule,]<number>
2184 Param: "schedule" - profile schedule points.
2185 Param: <number> - step/bucket size as a power of 2 for
2186 statistical time based profiling.
2187 Param: "sleep" - profile D-state sleeping (millisecs).
2188 Requires CONFIG_SCHEDSTATS
2189 Param: "kvm" - profile VM exits.
2191 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2192 before loading.
2193 See Documentation/blockdev/ramdisk.txt.
2195 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2196 probe for; one of (bare|imps|exps|lifebook|any).
2197 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2198 per second.
2199 psmouse.resetafter= [HW,MOUSE]
2200 Try to reset the device after so many bad packets
2201 (0 = never).
2202 psmouse.resolution=
2203 [HW,MOUSE] Set desired mouse resolution, in dpi.
2204 psmouse.smartscroll=
2205 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2206 0 = disabled, 1 = enabled (default).
2208 pstore.backend= Specify the name of the pstore backend to use
2210 pt. [PARIDE]
2211 See Documentation/blockdev/paride.txt.
2213 pty.legacy_count=
2214 [KNL] Number of legacy pty's. Overwrites compiled-in
2215 default number.
2217 quiet [KNL] Disable most log messages
2219 r128= [HW,DRM]
2221 raid= [HW,RAID]
2222 See Documentation/md.txt.
2224 ramdisk_blocksize= [RAM]
2225 See Documentation/blockdev/ramdisk.txt.
2227 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2228 See Documentation/blockdev/ramdisk.txt.
2230 rcupdate.blimit= [KNL,BOOT]
2231 Set maximum number of finished RCU callbacks to process
2232 in one batch.
2234 rcupdate.qhimark= [KNL,BOOT]
2235 Set threshold of queued
2236 RCU callbacks over which batch limiting is disabled.
2238 rcupdate.qlowmark= [KNL,BOOT]
2239 Set threshold of queued RCU callbacks below which
2240 batch limiting is re-enabled.
2242 rdinit= [KNL]
2243 Format: <full_path>
2244 Run specified binary instead of /init from the ramdisk,
2245 used for early userspace startup. See initrd.
2247 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2248 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2249 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2251 relax_domain_level=
2252 [KNL, SMP] Set scheduler's default relax_domain_level.
2253 See Documentation/cgroups/cpusets.txt.
2255 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2257 reservetop= [X86-32]
2258 Format: nn[KMG]
2259 Reserves a hole at the top of the kernel virtual
2260 address space.
2262 reservelow= [X86]
2263 Format: nn[K]
2264 Set the amount of memory to reserve for BIOS at
2265 the bottom of the address space.
2267 reset_devices [KNL] Force drivers to reset the underlying device
2268 during initialization.
2270 resume= [SWSUSP]
2271 Specify the partition device for software suspend
2273 resume_offset= [SWSUSP]
2274 Specify the offset from the beginning of the partition
2275 given by "resume=" at which the swap header is located,
2276 in <PAGE_SIZE> units (needed only for swap files).
2277 See Documentation/power/swsusp-and-swap-files.txt
2279 hibernate= [HIBERNATION]
2280 noresume Don't check if there's a hibernation image
2281 present during boot.
2282 nocompress Don't compress/decompress hibernation images.
2284 retain_initrd [RAM] Keep initrd memory after extraction
2286 rhash_entries= [KNL,NET]
2287 Set number of hash buckets for route cache
2289 riscom8= [HW,SERIAL]
2290 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2292 ro [KNL] Mount root device read-only on boot
2294 root= [KNL] Root filesystem
2295 See name_to_dev_t comment in init/do_mounts.c.
2297 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2298 mount the root filesystem
2300 rootflags= [KNL] Set root filesystem mount option string
2302 rootfstype= [KNL] Set root filesystem type
2304 rootwait [KNL] Wait (indefinitely) for root device to show up.
2305 Useful for devices that are detected asynchronously
2306 (e.g. USB and MMC devices).
2308 rw [KNL] Mount root device read-write on boot
2310 S [KNL] Run init in single mode
2312 sa1100ir [NET]
2313 See drivers/net/irda/sa1100_ir.c.
2315 sbni= [NET] Granch SBNI12 leased line adapter
2317 sched_debug [KNL] Enables verbose scheduler debug messages.
2319 security= [SECURITY] Choose a security module to enable at boot.
2320 If this boot parameter is not specified, only the first
2321 security module asking for security registration will be
2322 loaded. An invalid security module name will be treated
2323 as if no module has been chosen.
2325 selinux= [SELINUX] Disable or enable SELinux at boot time.
2326 Format: { "0" | "1" }
2327 See security/selinux/Kconfig help text.
2328 0 -- disable.
2329 1 -- enable.
2330 Default value is set via kernel config option.
2331 If enabled at boot time, /selinux/disable can be used
2332 later to disable prior to initial policy load.
2334 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2335 Format: { "0" | "1" }
2336 See security/apparmor/Kconfig help text
2337 0 -- disable.
2338 1 -- enable.
2339 Default value is set via kernel config option.
2341 serialnumber [BUGS=X86-32]
2343 shapers= [NET]
2344 Maximal number of shapers.
2346 show_msr= [x86] show boot-time MSR settings
2347 Format: { <integer> }
2348 Show boot-time (BIOS-initialized) MSR settings.
2349 The parameter means the number of CPUs to show,
2350 for example 1 means boot CPU only.
2352 simeth= [IA-64]
2353 simscsi=
2355 slram= [HW,MTD]
2357 slub_debug[=options[,slabs]] [MM, SLUB]
2358 Enabling slub_debug allows one to determine the
2359 culprit if slab objects become corrupted. Enabling
2360 slub_debug can create guard zones around objects and
2361 may poison objects when not in use. Also tracks the
2362 last alloc / free. For more information see
2363 Documentation/vm/slub.txt.
2365 slub_max_order= [MM, SLUB]
2366 Determines the maximum allowed order for slabs.
2367 A high setting may cause OOMs due to memory
2368 fragmentation. For more information see
2369 Documentation/vm/slub.txt.
2371 slub_min_objects= [MM, SLUB]
2372 The minimum number of objects per slab. SLUB will
2373 increase the slab order up to slub_max_order to
2374 generate a sufficiently large slab able to contain
2375 the number of objects indicated. The higher the number
2376 of objects the smaller the overhead of tracking slabs
2377 and the less frequently locks need to be acquired.
2378 For more information see Documentation/vm/slub.txt.
2380 slub_min_order= [MM, SLUB]
2381 Determines the mininum page order for slabs. Must be
2382 lower than slub_max_order.
2383 For more information see Documentation/vm/slub.txt.
2385 slub_nomerge [MM, SLUB]
2386 Disable merging of slabs with similar size. May be
2387 necessary if there is some reason to distinguish
2388 allocs to different slabs. Debug options disable
2389 merging on their own.
2390 For more information see Documentation/vm/slub.txt.
2392 smart2= [HW]
2393 Format: <io1>[,<io2>[,...,<io8>]]
2395 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2396 attempt to substitute SMP alternatives once at boot.
2398 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2399 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2400 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2401 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2402 smsc-ircc2.ircc_irq= [HW] IRQ line
2403 smsc-ircc2.ircc_dma= [HW] DMA channel
2404 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2405 0: Toshiba Satellite 1800 (GP data pin select)
2406 1: Fast pin select (default)
2407 2: ATC IRMode
2409 softlockup_panic=
2410 [KNL] Should the soft-lockup detector generate panics.
2411 Format: <integer>
2413 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2414 See Documentation/sonypi.txt
2416 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2417 See Documentation/serial/specialix.txt.
2419 spia_io_base= [HW,MTD]
2420 spia_fio_base=
2421 spia_pedr=
2422 spia_peddr=
2424 stacktrace [FTRACE]
2425 Enabled the stack tracer on boot up.
2427 sti= [PARISC,HW]
2428 Format: <num>
2429 Set the STI (builtin display/keyboard on the HP-PARISC
2430 machines) console (graphic card) which should be used
2431 as the initial boot-console.
2432 See also comment in drivers/video/console/sticore.c.
2434 sti_font= [HW]
2435 See comment in drivers/video/console/sticore.c.
2437 stifb= [HW]
2438 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2440 sunrpc.min_resvport=
2441 sunrpc.max_resvport=
2442 [NFS,SUNRPC]
2443 SunRPC servers often require that client requests
2444 originate from a privileged port (i.e. a port in the
2445 range 0 < portnr < 1024).
2446 An administrator who wishes to reserve some of these
2447 ports for other uses may adjust the range that the
2448 kernel's sunrpc client considers to be privileged
2449 using these two parameters to set the minimum and
2450 maximum port values.
2452 sunrpc.pool_mode=
2453 [NFS]
2454 Control how the NFS server code allocates CPUs to
2455 service thread pools. Depending on how many NICs
2456 you have and where their interrupts are bound, this
2457 option will affect which CPUs will do NFS serving.
2458 Note: this parameter cannot be changed while the
2459 NFS server is running.
2461 auto the server chooses an appropriate mode
2462 automatically using heuristics
2463 global a single global pool contains all CPUs
2464 percpu one pool for each CPU
2465 pernode one pool for each NUMA node (equivalent
2466 to global on non-NUMA machines)
2468 sunrpc.tcp_slot_table_entries=
2469 sunrpc.udp_slot_table_entries=
2470 [NFS,SUNRPC]
2471 Sets the upper limit on the number of simultaneous
2472 RPC calls that can be sent from the client to a
2473 server. Increasing these values may allow you to
2474 improve throughput, but will also increase the
2475 amount of memory reserved for use by the client.
2477 swapaccount[=0|1]
2478 [KNL] Enable accounting of swap in memory resource
2479 controller if no parameter or 1 is given or disable
2480 it if 0 is given (See Documentation/cgroups/memory.txt)
2482 swiotlb= [IA-64] Number of I/O TLB slabs
2484 switches= [HW,M68k]
2486 sysfs.deprecated=0|1 [KNL]
2487 Enable/disable old style sysfs layout for old udev
2488 on older distributions. When this option is enabled
2489 very new udev will not work anymore. When this option
2490 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2491 in older udev will not work anymore.
2492 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2493 the kernel configuration.
2495 sysrq_always_enabled
2496 [KNL]
2497 Ignore sysrq setting - this boot parameter will
2498 neutralize any effect of /proc/sys/kernel/sysrq.
2499 Useful for debugging.
2501 tdfx= [HW,DRM]
2503 test_suspend= [SUSPEND]
2504 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2505 standby suspend) as the system sleep state to briefly
2506 enter during system startup. The system is woken from
2507 this state using a wakeup-capable RTC alarm.
2509 thash_entries= [KNL,NET]
2510 Set number of hash buckets for TCP connection
2512 thermal.act= [HW,ACPI]
2513 -1: disable all active trip points in all thermal zones
2514 <degrees C>: override all lowest active trip points
2516 thermal.crt= [HW,ACPI]
2517 -1: disable all critical trip points in all thermal zones
2518 <degrees C>: override all critical trip points
2520 thermal.nocrt= [HW,ACPI]
2521 Set to disable actions on ACPI thermal zone
2522 critical and hot trip points.
2524 thermal.off= [HW,ACPI]
2525 1: disable ACPI thermal control
2527 thermal.psv= [HW,ACPI]
2528 -1: disable all passive trip points
2529 <degrees C>: override all passive trip points to this
2530 value
2532 thermal.tzp= [HW,ACPI]
2533 Specify global default ACPI thermal zone polling rate
2534 <deci-seconds>: poll all this frequency
2535 0: no polling (default)
2537 threadirqs [KNL]
2538 Force threading of all interrupt handlers except those
2539 marked explicitely IRQF_NO_THREAD.
2541 topology= [S390]
2542 Format: {off | on}
2543 Specify if the kernel should make use of the cpu
2544 topology information if the hardware supports this.
2545 The scheduler will make use of this information and
2546 e.g. base its process migration decisions on it.
2547 Default is on.
2549 tp720= [HW,PS2]
2551 tpm_suspend_pcr=[HW,TPM]
2552 Format: integer pcr id
2553 Specify that at suspend time, the tpm driver
2554 should extend the specified pcr with zeros,
2555 as a workaround for some chips which fail to
2556 flush the last written pcr on TPM_SaveState.
2557 This will guarantee that all the other pcrs
2558 are saved.
2560 trace_buf_size=nn[KMG]
2561 [FTRACE] will set tracing buffer size.
2563 trace_event=[event-list]
2564 [FTRACE] Set and start specified trace events in order
2565 to facilitate early boot debugging.
2566 See also Documentation/trace/events.txt
2568 tsc= Disable clocksource stability checks for TSC.
2569 Format: <string>
2570 [x86] reliable: mark tsc clocksource as reliable, this
2571 disables clocksource verification at runtime, as well
2572 as the stability checks done at bootup. Used to enable
2573 high-resolution timer mode on older hardware, and in
2574 virtualized environment.
2575 [x86] noirqtime: Do not use TSC to do irq accounting.
2576 Used to run time disable IRQ_TIME_ACCOUNTING on any
2577 platforms where RDTSC is slow and this accounting
2578 can add overhead.
2580 turbografx.map[2|3]= [HW,JOY]
2581 TurboGraFX parallel port interface
2582 Format:
2583 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2584 See also Documentation/input/joystick-parport.txt
2586 udbg-immortal [PPC] When debugging early kernel crashes that
2587 happen after console_init() and before a proper
2588 console driver takes over, this boot options might
2589 help "seeing" what's going on.
2591 uhash_entries= [KNL,NET]
2592 Set number of hash buckets for UDP/UDP-Lite connections
2594 uhci-hcd.ignore_oc=
2595 [USB] Ignore overcurrent events (default N).
2596 Some badly-designed motherboards generate lots of
2597 bogus events, for ports that aren't wired to
2598 anything. Set this parameter to avoid log spamming.
2599 Note that genuine overcurrent events won't be
2600 reported either.
2602 unknown_nmi_panic
2603 [X86] Cause panic on unknown NMI.
2605 usbcore.authorized_default=
2606 [USB] Default USB device authorization:
2607 (default -1 = authorized except for wireless USB,
2608 0 = not authorized, 1 = authorized)
2610 usbcore.autosuspend=
2611 [USB] The autosuspend time delay (in seconds) used
2612 for newly-detected USB devices (default 2). This
2613 is the time required before an idle device will be
2614 autosuspended. Devices for which the delay is set
2615 to a negative value won't be autosuspended at all.
2617 usbcore.usbfs_snoop=
2618 [USB] Set to log all usbfs traffic (default 0 = off).
2620 usbcore.blinkenlights=
2621 [USB] Set to cycle leds on hubs (default 0 = off).
2623 usbcore.old_scheme_first=
2624 [USB] Start with the old device initialization
2625 scheme (default 0 = off).
2627 usbcore.use_both_schemes=
2628 [USB] Try the other device initialization scheme
2629 if the first one fails (default 1 = enabled).
2631 usbcore.initial_descriptor_timeout=
2632 [USB] Specifies timeout for the initial 64-byte
2633 USB_REQ_GET_DESCRIPTOR request in milliseconds
2634 (default 5000 = 5.0 seconds).
2636 usbhid.mousepoll=
2637 [USBHID] The interval which mice are to be polled at.
2639 usb-storage.delay_use=
2640 [UMS] The delay in seconds before a new device is
2641 scanned for Logical Units (default 5).
2643 usb-storage.quirks=
2644 [UMS] A list of quirks entries to supplement or
2645 override the built-in unusual_devs list. List
2646 entries are separated by commas. Each entry has
2647 the form VID:PID:Flags where VID and PID are Vendor
2648 and Product ID values (4-digit hex numbers) and
2649 Flags is a set of characters, each corresponding
2650 to a common usb-storage quirk flag as follows:
2651 a = SANE_SENSE (collect more than 18 bytes
2652 of sense data);
2653 b = BAD_SENSE (don't collect more than 18
2654 bytes of sense data);
2655 c = FIX_CAPACITY (decrease the reported
2656 device capacity by one sector);
2657 d = NO_READ_DISC_INFO (don't use
2658 READ_DISC_INFO command);
2659 e = NO_READ_CAPACITY_16 (don't use
2660 READ_CAPACITY_16 command);
2661 h = CAPACITY_HEURISTICS (decrease the
2662 reported device capacity by one
2663 sector if the number is odd);
2664 i = IGNORE_DEVICE (don't bind to this
2665 device);
2666 l = NOT_LOCKABLE (don't try to lock and
2667 unlock ejectable media);
2668 m = MAX_SECTORS_64 (don't transfer more
2669 than 64 sectors = 32 KB at a time);
2670 n = INITIAL_READ10 (force a retry of the
2671 initial READ(10) command);
2672 o = CAPACITY_OK (accept the capacity
2673 reported by the device);
2674 r = IGNORE_RESIDUE (the device reports
2675 bogus residue values);
2676 s = SINGLE_LUN (the device has only one
2677 Logical Unit);
2678 w = NO_WP_DETECT (don't test whether the
2679 medium is write-protected).
2680 Example: quirks=0419:aaf5:rl,0421:0433:rc
2682 user_debug= [KNL,ARM]
2683 Format: <int>
2684 See arch/arm/Kconfig.debug help text.
2685 1 - undefined instruction events
2686 2 - system calls
2687 4 - invalid data aborts
2688 8 - SIGSEGV faults
2689 16 - SIGBUS faults
2690 Example: user_debug=31
2692 userpte=
2693 [X86] Flags controlling user PTE allocations.
2695 nohigh = do not allocate PTE pages in
2696 HIGHMEM regardless of setting
2697 of CONFIG_HIGHPTE.
2699 vdso= [X86,SH]
2700 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2701 vdso=1: enable VDSO (default)
2702 vdso=0: disable VDSO mapping
2704 vdso32= [X86]
2705 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2706 vdso32=1: enable 32-bit VDSO (default)
2707 vdso32=0: disable 32-bit VDSO mapping
2709 vector= [IA-64,SMP]
2710 vector=percpu: enable percpu vector domain
2712 video= [FB] Frame buffer configuration
2713 See Documentation/fb/modedb.txt.
2715 vga= [BOOT,X86-32] Select a particular video mode
2716 See Documentation/x86/boot.txt and
2717 Documentation/svga.txt.
2718 Use vga=ask for menu.
2719 This is actually a boot loader parameter; the value is
2720 passed to the kernel using a special protocol.
2722 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2723 size of <nn>. This can be used to increase the
2724 minimum size (128MB on x86). It can also be used to
2725 decrease the size and leave more room for directly
2726 mapped kernel RAM.
2728 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2729 Format: <command>
2731 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2732 Format: <command>
2734 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2735 Format: <command>
2737 vsyscall= [X86-64]
2738 Controls the behavior of vsyscalls (i.e. calls to
2739 fixed addresses of 0xffffffffff600x00 from legacy
2740 code). Most statically-linked binaries and older
2741 versions of glibc use these calls. Because these
2742 functions are at fixed addresses, they make nice
2743 targets for exploits that can control RIP.
2745 emulate [default] Vsyscalls turn into traps and are
2746 emulated reasonably safely.
2748 native Vsyscalls are native syscall instructions.
2749 This is a little bit faster than trapping
2750 and makes a few dynamic recompilers work
2751 better than they would in emulation mode.
2752 It also makes exploits much easier to write.
2754 none Vsyscalls don't work at all. This makes
2755 them quite hard to use for exploits but
2756 might break your system.
2758 vt.cur_default= [VT] Default cursor shape.
2759 Format: 0xCCBBAA, where AA, BB, and CC are the same as
2760 the parameters of the <Esc>[?A;B;Cc escape sequence;
2761 see VGA-softcursor.txt. Default: 2 = underline.
2763 vt.default_blu= [VT]
2764 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2765 Change the default blue palette of the console.
2766 This is a 16-member array composed of values
2767 ranging from 0-255.
2769 vt.default_grn= [VT]
2770 Format: <green0>,<green1>,<green2>,...,<green15>
2771 Change the default green palette of the console.
2772 This is a 16-member array composed of values
2773 ranging from 0-255.
2775 vt.default_red= [VT]
2776 Format: <red0>,<red1>,<red2>,...,<red15>
2777 Change the default red palette of the console.
2778 This is a 16-member array composed of values
2779 ranging from 0-255.
2781 vt.default_utf8=
2782 [VT]
2783 Format=<0|1>
2784 Set system-wide default UTF-8 mode for all tty's.
2785 Default is 1, i.e. UTF-8 mode is enabled for all
2786 newly opened terminals.
2788 vt.global_cursor_default=
2789 [VT]
2790 Format=<-1|0|1>
2791 Set system-wide default for whether a cursor
2792 is shown on new VTs. Default is -1,
2793 i.e. cursors will be created by default unless
2794 overridden by individual drivers. 0 will hide
2795 cursors, 1 will display them.
2797 watchdog timers [HW,WDT] For information on watchdog timers,
2798 see Documentation/watchdog/watchdog-parameters.txt
2799 or other driver-specific files in the
2800 Documentation/watchdog/ directory.
2802 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2803 default x2apic cluster mode on platforms
2804 supporting x2apic.
2806 x86_mrst_timer= [X86-32,APBT]
2807 Choose timer option for x86 Moorestown MID platform.
2808 Two valid options are apbt timer only and lapic timer
2809 plus one apbt timer for broadcast timer.
2810 x86_mrst_timer=apbt_only | lapic_and_apbt
2812 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2813 xd_geo= See header of drivers/block/xd.c.
2815 xen_emul_unplug= [HW,X86,XEN]
2816 Unplug Xen emulated devices
2817 Format: [unplug0,][unplug1]
2818 ide-disks -- unplug primary master IDE devices
2819 aux-ide-disks -- unplug non-primary-master IDE devices
2820 nics -- unplug network devices
2821 all -- unplug all emulated devices (NICs and IDE disks)
2822 unnecessary -- unplugging emulated devices is
2823 unnecessary even if the host did not respond to
2824 the unplug protocol
2825 never -- do not unplug even if version check succeeds
2827 xirc2ps_cs= [NET,PCMCIA]
2828 Format:
2829 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2831 ______________________________________________________________________
2833 TODO:
2835 Add more DRM drivers.