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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/runtime_pm.txt, pci=noacpi
169 acpi_rsdp= [ACPI,EFI,KEXEC]
170 Pass the RSDP address to the kernel, mostly used
171 on machines running EFI runtime service to boot the
172 second kernel for kdump.
174 acpi_apic_instance= [ACPI, IOAPIC]
175 Format: <int>
176 2: use 2nd APIC table, if available
177 1,0: use 1st APIC table
178 default: 0
180 acpi_backlight= [HW,ACPI]
181 acpi_backlight=vendor
182 acpi_backlight=video
183 If set to vendor, prefer vendor specific driver
184 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
185 of the ACPI video.ko driver.
187 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
188 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
189 Format: <int>
190 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
191 debug output. Bits in debug_layer correspond to a
192 _COMPONENT in an ACPI source file, e.g.,
193 #define _COMPONENT ACPI_PCI_COMPONENT
194 Bits in debug_level correspond to a level in
195 ACPI_DEBUG_PRINT statements, e.g.,
196 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
197 The debug_level mask defaults to "info". See
198 Documentation/acpi/debug.txt for more information about
199 debug layers and levels.
201 Enable processor driver info messages:
202 acpi.debug_layer=0x20000000
203 Enable PCI/PCI interrupt routing info messages:
204 acpi.debug_layer=0x400000
205 Enable AML "Debug" output, i.e., stores to the Debug
206 object while interpreting AML:
207 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
208 Enable all messages related to ACPI hardware:
209 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
211 Some values produce so much output that the system is
212 unusable. The "log_buf_len" parameter may be useful
213 if you need to capture more output.
215 acpi_irq_balance [HW,ACPI]
216 ACPI will balance active IRQs
217 default in APIC mode
219 acpi_irq_nobalance [HW,ACPI]
220 ACPI will not move active IRQs (default)
221 default in PIC mode
223 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
224 Format: <irq>,<irq>...
226 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
227 use by PCI
228 Format: <irq>,<irq>...
230 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
232 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
233 Format: To spoof as Windows 98: ="Microsoft Windows"
235 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
236 acpi_osi="string1" # add string1 -- only one string
237 acpi_osi="!string2" # remove built-in string2
238 acpi_osi= # disable all strings
240 acpi_pm_good [X86]
241 Override the pmtimer bug detection: force the kernel
242 to assume that this machine's pmtimer latches its value
243 and always returns good values.
245 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
246 Format: { level | edge | high | low }
248 acpi_serialize [HW,ACPI] force serialization of AML methods
250 acpi_skip_timer_override [HW,ACPI]
251 Recognize and ignore IRQ0/pin2 Interrupt Override.
252 For broken nForce2 BIOS resulting in XT-PIC timer.
254 acpi_sleep= [HW,ACPI] Sleep options
255 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
256 old_ordering, nonvs, sci_force_enable }
257 See Documentation/power/video.txt for information on
258 s3_bios and s3_mode.
259 s3_beep is for debugging; it makes the PC's speaker beep
260 as soon as the kernel's real-mode entry point is called.
261 s4_nohwsig prevents ACPI hardware signature from being
262 used during resume from hibernation.
263 old_ordering causes the ACPI 1.0 ordering of the _PTS
264 control method, with respect to putting devices into
265 low power states, to be enforced (the ACPI 2.0 ordering
266 of _PTS is used by default).
267 nonvs prevents the kernel from saving/restoring the
268 ACPI NVS memory during suspend/hibernation and resume.
269 sci_force_enable causes the kernel to set SCI_EN directly
270 on resume from S1/S3 (which is against the ACPI spec,
271 but some broken systems don't work without it).
273 acpi_use_timer_override [HW,ACPI]
274 Use timer override. For some broken Nvidia NF5 boards
275 that require a timer override, but don't have HPET
277 acpi_enforce_resources= [ACPI]
278 { strict | lax | no }
279 Check for resource conflicts between native drivers
280 and ACPI OperationRegions (SystemIO and SystemMemory
281 only). IO ports and memory declared in ACPI might be
282 used by the ACPI subsystem in arbitrary AML code and
283 can interfere with legacy drivers.
284 strict (default): access to resources claimed by ACPI
285 is denied; legacy drivers trying to access reserved
286 resources will fail to bind to device using them.
287 lax: access to resources claimed by ACPI is allowed;
288 legacy drivers trying to access reserved resources
289 will bind successfully but a warning message is logged.
290 no: ACPI OperationRegions are not marked as reserved,
291 no further checks are performed.
293 add_efi_memmap [EFI; X86] Include EFI memory map in
294 kernel's map of available physical RAM.
296 agp= [AGP]
297 { off | try_unsupported }
298 off: disable AGP support
299 try_unsupported: try to drive unsupported chipsets
300 (may crash computer or cause data corruption)
302 ALSA [HW,ALSA]
303 See Documentation/sound/alsa/alsa-parameters.txt
305 alignment= [KNL,ARM]
306 Allow the default userspace alignment fault handler
307 behaviour to be specified. Bit 0 enables warnings,
308 bit 1 enables fixups, and bit 2 sends a segfault.
310 align_va_addr= [X86-64]
311 Align virtual addresses by clearing slice [14:12] when
312 allocating a VMA at process creation time. This option
313 gives you up to 3% performance improvement on AMD F15h
314 machines (where it is enabled by default) for a
315 CPU-intensive style benchmark, and it can vary highly in
316 a microbenchmark depending on workload and compiler.
318 32: only for 32-bit processes
319 64: only for 64-bit processes
320 on: enable for both 32- and 64-bit processes
321 off: disable for both 32- and 64-bit processes
323 amd_iommu= [HW,X86-64]
324 Pass parameters to the AMD IOMMU driver in the system.
325 Possible values are:
326 fullflush - enable flushing of IO/TLB entries when
327 they are unmapped. Otherwise they are
328 flushed before they will be reused, which
329 is a lot of faster
330 off - do not initialize any AMD IOMMU found in
331 the system
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/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=
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 debug_guardpage_minorder=
627 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
628 parameter allows control of the order of pages that will
629 be intentionally kept free (and hence protected) by the
630 buddy allocator. Bigger value increase the probability
631 of catching random memory corruption, but reduce the
632 amount of memory for normal system use. The maximum
633 possible value is MAX_ORDER/2. Setting this parameter
634 to 1 or 2 should be enough to identify most random
635 memory corruption problems caused by bugs in kernel or
636 driver code when a CPU writes to (or reads from) a
637 random memory location. Note that there exists a class
638 of memory corruptions problems caused by buggy H/W or
639 F/W or by drivers badly programing DMA (basically when
640 memory is written at bus level and the CPU MMU is
641 bypassed) which are not detectable by
642 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
643 tracking down these problems.
645 debugpat [X86] Enable PAT debugging
647 decnet.addr= [HW,NET]
648 Format: <area>[,<node>]
649 See also Documentation/networking/decnet.txt.
651 default_hugepagesz=
652 [same as hugepagesz=] The size of the default
653 HugeTLB page size. This is the size represented by
654 the legacy /proc/ hugepages APIs, used for SHM, and
655 default size when mounting hugetlbfs filesystems.
656 Defaults to the default architecture's huge page size
657 if not specified.
659 dhash_entries= [KNL]
660 Set number of hash buckets for dentry cache.
662 digi= [HW,SERIAL]
663 IO parameters + enable/disable command.
665 digiepca= [HW,SERIAL]
666 See drivers/char/README.epca and
667 Documentation/serial/digiepca.txt.
669 disable= [IPV6]
670 See Documentation/networking/ipv6.txt.
672 disable_ddw [PPC/PSERIES]
673 Disable Dynamic DMA Window support. Use this if
674 to workaround buggy firmware.
676 disable_ipv6= [IPV6]
677 See Documentation/networking/ipv6.txt.
679 disable_mtrr_cleanup [X86]
680 The kernel tries to adjust MTRR layout from continuous
681 to discrete, to make X server driver able to add WB
682 entry later. This parameter disables that.
684 disable_mtrr_trim [X86, Intel and AMD only]
685 By default the kernel will trim any uncacheable
686 memory out of your available memory pool based on
687 MTRR settings. This parameter disables that behavior,
688 possibly causing your machine to run very slowly.
690 disable_timer_pin_1 [X86]
691 Disable PIN 1 of APIC timer
692 Can be useful to work around chipset bugs.
694 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
695 this option disables the debugging code at boot.
697 dma_debug_entries=<number>
698 This option allows to tune the number of preallocated
699 entries for DMA-API debugging code. One entry is
700 required per DMA-API allocation. Use this if the
701 DMA-API debugging code disables itself because the
702 architectural default is too low.
704 dma_debug_driver=<driver_name>
705 With this option the DMA-API debugging driver
706 filter feature can be enabled at boot time. Just
707 pass the driver to filter for as the parameter.
708 The filter can be disabled or changed to another
709 driver later using sysfs.
711 dscc4.setup= [NET]
713 earlycon= [KNL] Output early console device and options.
714 uart[8250],io,<addr>[,options]
715 uart[8250],mmio,<addr>[,options]
716 uart[8250],mmio32,<addr>[,options]
717 Start an early, polled-mode console on the 8250/16550
718 UART at the specified I/O port or MMIO address.
719 MMIO inter-register address stride is either 8-bit
720 (mmio) or 32-bit (mmio32).
721 The options are the same as for ttyS, above.
723 earlyprintk= [X86,SH,BLACKFIN]
724 earlyprintk=vga
725 earlyprintk=serial[,ttySn[,baudrate]]
726 earlyprintk=ttySn[,baudrate]
727 earlyprintk=dbgp[debugController#]
729 Append ",keep" to not disable it when the real console
730 takes over.
732 Only vga or serial or usb debug port at a time.
734 Currently only ttyS0 and ttyS1 are supported.
736 Interaction with the standard serial driver is not
737 very good.
739 The VGA output is eventually overwritten by the real
740 console.
742 ekgdboc= [X86,KGDB] Allow early kernel console debugging
743 ekgdboc=kbd
745 This is designed to be used in conjunction with
746 the boot argument: earlyprintk=vga
748 edd= [EDD]
749 Format: {"off" | "on" | "skip[mbr]"}
751 eisa_irq_edge= [PARISC,HW]
752 See header of drivers/parisc/eisa.c.
754 elanfreq= [X86-32]
755 See comment before function elanfreq_setup() in
756 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
758 elevator= [IOSCHED]
759 Format: {"cfq" | "deadline" | "noop"}
760 See Documentation/block/cfq-iosched.txt and
761 Documentation/block/deadline-iosched.txt for details.
763 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
764 Specifies physical address of start of kernel core
765 image elf header and optionally the size. Generally
766 kexec loader will pass this option to capture kernel.
767 See Documentation/kdump/kdump.txt for details.
769 enable_mtrr_cleanup [X86]
770 The kernel tries to adjust MTRR layout from continuous
771 to discrete, to make X server driver able to add WB
772 entry later. This parameter enables that.
774 enable_timer_pin_1 [X86]
775 Enable PIN 1 of APIC timer
776 Can be useful to work around chipset bugs
777 (in particular on some ATI chipsets).
778 The kernel tries to set a reasonable default.
780 enforcing [SELINUX] Set initial enforcing status.
781 Format: {"0" | "1"}
782 See security/selinux/Kconfig help text.
783 0 -- permissive (log only, no denials).
784 1 -- enforcing (deny and log).
785 Default value is 0.
786 Value can be changed at runtime via /selinux/enforce.
788 erst_disable [ACPI]
789 Disable Error Record Serialization Table (ERST)
790 support.
792 ether= [HW,NET] Ethernet cards parameters
793 This option is obsoleted by the "netdev=" option, which
794 has equivalent usage. See its documentation for details.
796 evm= [EVM]
797 Format: { "fix" }
798 Permit 'security.evm' to be updated regardless of
799 current integrity status.
801 failslab=
802 fail_page_alloc=
803 fail_make_request=[KNL]
804 General fault injection mechanism.
805 Format: <interval>,<probability>,<space>,<times>
806 See also Documentation/fault-injection/.
808 floppy= [HW]
809 See Documentation/blockdev/floppy.txt.
811 force_pal_cache_flush
812 [IA-64] Avoid check_sal_cache_flush which may hang on
813 buggy SAL_CACHE_FLUSH implementations. Using this
814 parameter will force ia64_sal_cache_flush to call
815 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
817 ftrace=[tracer]
818 [FTRACE] will set and start the specified tracer
819 as early as possible in order to facilitate early
820 boot debugging.
822 ftrace_dump_on_oops[=orig_cpu]
823 [FTRACE] will dump the trace buffers on oops.
824 If no parameter is passed, ftrace will dump
825 buffers of all CPUs, but if you pass orig_cpu, it will
826 dump only the buffer of the CPU that triggered the
827 oops.
829 ftrace_filter=[function-list]
830 [FTRACE] Limit the functions traced by the function
831 tracer at boot up. function-list is a comma separated
832 list of functions. This list can be changed at run
833 time by the set_ftrace_filter file in the debugfs
834 tracing directory.
836 ftrace_notrace=[function-list]
837 [FTRACE] Do not trace the functions specified in
838 function-list. This list can be changed at run time
839 by the set_ftrace_notrace file in the debugfs
840 tracing directory.
842 ftrace_graph_filter=[function-list]
843 [FTRACE] Limit the top level callers functions traced
844 by the function graph tracer at boot up.
845 function-list is a comma separated list of functions
846 that can be changed at run time by the
847 set_graph_function file in the debugfs tracing directory.
849 gamecon.map[2|3]=
850 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
851 support via parallel port (up to 5 devices per port)
852 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
853 See also Documentation/input/joystick-parport.txt
855 gamma= [HW,DRM]
857 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
858 Format: off | on
859 default: on
861 gcov_persist= [GCOV] When non-zero (default), profiling data for
862 kernel modules is saved and remains accessible via
863 debugfs, even when the module is unloaded/reloaded.
864 When zero, profiling data is discarded and associated
865 debugfs files are removed at module unload time.
867 gpt [EFI] Forces disk with valid GPT signature but
868 invalid Protective MBR to be treated as GPT.
870 hashdist= [KNL,NUMA] Large hashes allocated during boot
871 are distributed across NUMA nodes. Defaults on
872 for 64-bit NUMA, off otherwise.
873 Format: 0 | 1 (for off | on)
875 hcl= [IA-64] SGI's Hardware Graph compatibility layer
877 hd= [EIDE] (E)IDE hard drive subsystem geometry
878 Format: <cyl>,<head>,<sect>
880 hest_disable [ACPI]
881 Disable Hardware Error Source Table (HEST) support;
882 corresponding firmware-first mode error processing
883 logic will be disabled.
885 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
886 size of <nn>. This works even on boxes that have no
887 highmem otherwise. This also works to reduce highmem
888 size on bigger boxes.
890 highres= [KNL] Enable/disable high resolution timer mode.
891 Valid parameters: "on", "off"
892 Default: "on"
894 hisax= [HW,ISDN]
895 See Documentation/isdn/README.HiSax.
897 hlt [BUGS=ARM,SH]
899 hpet= [X86-32,HPET] option to control HPET usage
900 Format: { enable (default) | disable | force |
901 verbose }
902 disable: disable HPET and use PIT instead
903 force: allow force enabled of undocumented chips (ICH4,
904 VIA, nVidia)
905 verbose: show contents of HPET registers during setup
907 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
908 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
909 On x86-64 and powerpc, this option can be specified
910 multiple times interleaved with hugepages= to reserve
911 huge pages of different sizes. Valid pages sizes on
912 x86-64 are 2M (when the CPU supports "pse") and 1G
913 (when the CPU supports the "pdpe1gb" cpuinfo flag)
914 Note that 1GB pages can only be allocated at boot time
915 using hugepages= and not freed afterwards.
917 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
918 terminal devices. Valid values: 0..8
919 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
920 If specified, z/VM IUCV HVC accepts connections
921 from listed z/VM user IDs only.
923 keep_bootcon [KNL]
924 Do not unregister boot console at start. This is only
925 useful for debugging when something happens in the window
926 between unregistering the boot console and initializing
927 the real console.
929 i2c_bus= [HW] Override the default board specific I2C bus speed
930 or register an additional I2C bus that is not
931 registered from board initialization code.
932 Format:
933 <bus_id>,<clkrate>
935 i8042.debug [HW] Toggle i8042 debug mode
936 i8042.direct [HW] Put keyboard port into non-translated mode
937 i8042.dumbkbd [HW] Pretend that controller can only read data from
938 keyboard and cannot control its state
939 (Don't attempt to blink the leds)
940 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
941 i8042.nokbd [HW] Don't check/create keyboard port
942 i8042.noloop [HW] Disable the AUX Loopback command while probing
943 for the AUX port
944 i8042.nomux [HW] Don't check presence of an active multiplexing
945 controller
946 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
947 controllers
948 i8042.notimeout [HW] Ignore timeout condition signalled by conroller
949 i8042.reset [HW] Reset the controller during init and cleanup
950 i8042.unlock [HW] Unlock (ignore) the keylock
952 i810= [HW,DRM]
954 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
955 indicates that the driver is running on unsupported
956 hardware.
957 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
958 does not match list of supported models.
959 i8k.power_status
960 [HW] Report power status in /proc/i8k
961 (disabled by default)
962 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
963 capability is set.
965 icn= [HW,ISDN]
966 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
968 ide-core.nodma= [HW] (E)IDE subsystem
969 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
970 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
971 .cdrom .chs .ignore_cable are additional options
972 See Documentation/ide/ide.txt.
974 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
975 Claim all unknown PCI IDE storage controllers.
977 idle= [X86]
978 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
979 Poll forces a polling idle loop that can slightly
980 improve the performance of waking up a idle CPU, but
981 will use a lot of power and make the system run hot.
982 Not recommended.
983 idle=mwait: On systems which support MONITOR/MWAIT but
984 the kernel chose to not use it because it doesn't save
985 as much power as a normal idle loop, use the
986 MONITOR/MWAIT idle loop anyways. Performance should be
987 the same as idle=poll.
988 idle=halt: Halt is forced to be used for CPU idle.
989 In such case C2/C3 won't be used again.
990 idle=nomwait: Disable mwait for CPU C-states
992 ignore_loglevel [KNL]
993 Ignore loglevel setting - this will print /all/
994 kernel messages to the console. Useful for debugging.
995 We also add it as printk module parameter, so users
996 could change it dynamically, usually by
997 /sys/module/printk/parameters/ignore_loglevel.
999 ihash_entries= [KNL]
1000 Set number of hash buckets for inode cache.
1002 ima_audit= [IMA]
1003 Format: { "0" | "1" }
1004 0 -- integrity auditing messages. (Default)
1005 1 -- enable informational integrity auditing messages.
1007 ima_hash= [IMA]
1008 Format: { "sha1" | "md5" }
1009 default: "sha1"
1011 ima_tcb [IMA]
1012 Load a policy which meets the needs of the Trusted
1013 Computing Base. This means IMA will measure all
1014 programs exec'd, files mmap'd for exec, and all files
1015 opened for read by uid=0.
1017 init= [KNL]
1018 Format: <full_path>
1019 Run specified binary instead of /sbin/init as init
1020 process.
1022 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1023 for working out where the kernel is dying during
1024 startup.
1026 initrd= [BOOT] Specify the location of the initial ramdisk
1028 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1029 Format: <irq>
1031 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1032 on
1033 Enable intel iommu driver.
1034 off
1035 Disable intel iommu driver.
1036 igfx_off [Default Off]
1037 By default, gfx is mapped as normal device. If a gfx
1038 device has a dedicated DMAR unit, the DMAR unit is
1039 bypassed by not enabling DMAR with this option. In
1040 this case, gfx device will use physical address for
1041 DMA.
1042 forcedac [x86_64]
1043 With this option iommu will not optimize to look
1044 for io virtual address below 32-bit forcing dual
1045 address cycle on pci bus for cards supporting greater
1046 than 32-bit addressing. The default is to look
1047 for translation below 32-bit and if not available
1048 then look in the higher range.
1049 strict [Default Off]
1050 With this option on every unmap_single operation will
1051 result in a hardware IOTLB flush operation as opposed
1052 to batching them for performance.
1053 sp_off [Default Off]
1054 By default, super page will be supported if Intel IOMMU
1055 has the capability. With this option, super page will
1056 not be supported.
1057 intremap= [X86-64, Intel-IOMMU]
1058 on enable Interrupt Remapping (default)
1059 off disable Interrupt Remapping
1060 nosid disable Source ID checking
1061 no_x2apic_optout
1062 BIOS x2APIC opt-out request will be ignored
1064 inttest= [IA-64]
1066 iomem= Disable strict checking of access to MMIO memory
1067 strict regions from userspace.
1068 relaxed
1070 iommu= [x86]
1071 off
1072 force
1073 noforce
1074 biomerge
1075 panic
1076 nopanic
1077 merge
1078 nomerge
1079 forcesac
1080 soft
1081 pt [x86, IA-64]
1083 io7= [HW] IO7 for Marvel based alpha systems
1084 See comment before marvel_specify_io7 in
1085 arch/alpha/kernel/core_marvel.c.
1087 io_delay= [X86] I/O delay method
1088 0x80
1089 Standard port 0x80 based delay
1090 0xed
1091 Alternate port 0xed based delay (needed on some systems)
1092 udelay
1093 Simple two microseconds delay
1094 none
1095 No delay
1097 ip= [IP_PNP]
1098 See Documentation/filesystems/nfs/nfsroot.txt.
1100 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1101 See comment before ip2_setup() in
1102 drivers/char/ip2/ip2base.c.
1104 irqfixup [HW]
1105 When an interrupt is not handled search all handlers
1106 for it. Intended to get systems with badly broken
1107 firmware running.
1109 irqpoll [HW]
1110 When an interrupt is not handled search all handlers
1111 for it. Also check all handlers each timer
1112 interrupt. Intended to get systems with badly broken
1113 firmware running.
1115 isapnp= [ISAPNP]
1116 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1118 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1119 Format:
1120 <cpu number>,...,<cpu number>
1121 or
1122 <cpu number>-<cpu number>
1123 (must be a positive range in ascending order)
1124 or a mixture
1125 <cpu number>,...,<cpu number>-<cpu number>
1127 This option can be used to specify one or more CPUs
1128 to isolate from the general SMP balancing and scheduling
1129 algorithms. You can move a process onto or off an
1130 "isolated" CPU via the CPU affinity syscalls or cpuset.
1131 <cpu number> begins at 0 and the maximum value is
1132 "number of CPUs in system - 1".
1134 This option is the preferred way to isolate CPUs. The
1135 alternative -- manually setting the CPU mask of all
1136 tasks in the system -- can cause problems and
1137 suboptimal load balancer performance.
1139 iucv= [HW,NET]
1141 js= [HW,JOY] Analog joystick
1142 See Documentation/input/joystick.txt.
1144 keepinitrd [HW,ARM]
1146 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1147 specifies the amount of memory usable by the kernel
1148 for non-movable allocations. The requested amount is
1149 spread evenly throughout all nodes in the system. The
1150 remaining memory in each node is used for Movable
1151 pages. In the event, a node is too small to have both
1152 kernelcore and Movable pages, kernelcore pages will
1153 take priority and other nodes will have a larger number
1154 of kernelcore pages. The Movable zone is used for the
1155 allocation of pages that may be reclaimed or moved
1156 by the page migration subsystem. This means that
1157 HugeTLB pages may not be allocated from this zone.
1158 Note that allocations like PTEs-from-HighMem still
1159 use the HighMem zone if it exists, and the Normal
1160 zone if it does not.
1162 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1163 Format: <Controller#>[,poll interval]
1164 The controller # is the number of the ehci usb debug
1165 port as it is probed via PCI. The poll interval is
1166 optional and is the number seconds in between
1167 each poll cycle to the debug port in case you need
1168 the functionality for interrupting the kernel with
1169 gdb or control-c on the dbgp connection. When
1170 not using this parameter you use sysrq-g to break into
1171 the kernel debugger.
1173 kgdboc= [KGDB,HW] kgdb over consoles.
1174 Requires a tty driver that supports console polling,
1175 or a supported polling keyboard driver (non-usb).
1176 Serial only format: <serial_device>[,baud]
1177 keyboard only format: kbd
1178 keyboard and serial format: kbd,<serial_device>[,baud]
1179 Optional Kernel mode setting:
1180 kms, kbd format: kms,kbd
1181 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1183 kgdbwait [KGDB] Stop kernel execution and enter the
1184 kernel debugger at the earliest opportunity.
1186 kmac= [MIPS] korina ethernet MAC address.
1187 Configure the RouterBoard 532 series on-chip
1188 Ethernet adapter MAC address.
1190 kmemleak= [KNL] Boot-time kmemleak enable/disable
1191 Valid arguments: on, off
1192 Default: on
1194 kstack=N [X86] Print N words from the kernel stack
1195 in oops dumps.
1197 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1198 Default is 0 (don't ignore, but inject #GP)
1200 kvm.oos_shadow= [KVM] Disable out-of-sync shadow paging.
1201 Default is 1 (enabled)
1203 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1204 KVM MMU at runtime.
1205 Default is 0 (off)
1207 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1208 Default is 1 (enabled)
1210 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1211 for all guests.
1212 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1214 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1215 (virtualized MMU) support on capable Intel chips.
1216 Default is 1 (enabled)
1218 kvm-intel.emulate_invalid_guest_state=
1219 [KVM,Intel] Enable emulation of invalid guest states
1220 Default is 0 (disabled)
1222 kvm-intel.flexpriority=
1223 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1224 Default is 1 (enabled)
1226 kvm-intel.nested=
1227 [KVM,Intel] Enable VMX nesting (nVMX).
1228 Default is 0 (disabled)
1230 kvm-intel.unrestricted_guest=
1231 [KVM,Intel] Disable unrestricted guest feature
1232 (virtualized real and unpaged mode) on capable
1233 Intel chips. Default is 1 (enabled)
1235 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1236 feature (tagged TLBs) on capable Intel chips.
1237 Default is 1 (enabled)
1239 l2cr= [PPC]
1241 l3cr= [PPC]
1243 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1244 disabled it.
1246 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1247 in C2 power state.
1249 libata.dma= [LIBATA] DMA control
1250 libata.dma=0 Disable all PATA and SATA DMA
1251 libata.dma=1 PATA and SATA Disk DMA only
1252 libata.dma=2 ATAPI (CDROM) DMA only
1253 libata.dma=4 Compact Flash DMA only
1254 Combinations also work, so libata.dma=3 enables DMA
1255 for disks and CDROMs, but not CFs.
1257 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1258 libata.ignore_hpa=0 keep BIOS limits (default)
1259 libata.ignore_hpa=1 ignore limits, using full disk
1261 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1262 when set.
1263 Format: <int>
1265 libata.force= [LIBATA] Force configurations. The format is comma
1266 separated list of "[ID:]VAL" where ID is
1267 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1268 matching port, link or device. Basically, it matches
1269 the ATA ID string printed on console by libata. If
1270 the whole ID part is omitted, the last PORT and DEVICE
1271 values are used. If ID hasn't been specified yet, the
1272 configuration applies to all ports, links and devices.
1274 If only DEVICE is omitted, the parameter applies to
1275 the port and all links and devices behind it. DEVICE
1276 number of 0 either selects the first device or the
1277 first fan-out link behind PMP device. It does not
1278 select the host link. DEVICE number of 15 selects the
1279 host link and device attached to it.
1281 The VAL specifies the configuration to force. As long
1282 as there's no ambiguity shortcut notation is allowed.
1283 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1284 The following configurations can be forced.
1286 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1287 Any ID with matching PORT is used.
1289 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1291 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1292 udma[/][16,25,33,44,66,100,133] notation is also
1293 allowed.
1295 * [no]ncq: Turn on or off NCQ.
1297 * nohrst, nosrst, norst: suppress hard, soft
1298 and both resets.
1300 * dump_id: dump IDENTIFY data.
1302 If there are multiple matching configurations changing
1303 the same attribute, the last one is used.
1305 memblock=debug [KNL] Enable memblock debug messages.
1307 load_ramdisk= [RAM] List of ramdisks to load from floppy
1308 See Documentation/blockdev/ramdisk.txt.
1310 lockd.nlm_grace_period=P [NFS] Assign grace period.
1311 Format: <integer>
1313 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1314 Format: <integer>
1316 lockd.nlm_timeout=T [NFS] Assign timeout value.
1317 Format: <integer>
1319 lockd.nlm_udpport=M [NFS] Assign UDP port.
1320 Format: <integer>
1322 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1323 Format: <irq>
1325 loglevel= All Kernel Messages with a loglevel smaller than the
1326 console loglevel will be printed to the console. It can
1327 also be changed with klogd or other programs. The
1328 loglevels are defined as follows:
1330 0 (KERN_EMERG) system is unusable
1331 1 (KERN_ALERT) action must be taken immediately
1332 2 (KERN_CRIT) critical conditions
1333 3 (KERN_ERR) error conditions
1334 4 (KERN_WARNING) warning conditions
1335 5 (KERN_NOTICE) normal but significant condition
1336 6 (KERN_INFO) informational
1337 7 (KERN_DEBUG) debug-level messages
1339 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1340 in bytes. n must be a power of two. The default
1341 size is set in the kernel config file.
1343 logo.nologo [FB] Disables display of the built-in Linux logo.
1344 This may be used to provide more screen space for
1345 kernel log messages and is useful when debugging
1346 kernel boot problems.
1348 lp=0 [LP] Specify parallel ports to use, e.g,
1349 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1350 lp=reset first parallel port). 'lp=0' disables the
1351 lp=auto printer driver. 'lp=reset' (which can be
1352 specified in addition to the ports) causes
1353 attached printers to be reset. Using
1354 lp=port1,port2,... specifies the parallel ports
1355 to associate lp devices with, starting with
1356 lp0. A port specification may be 'none' to skip
1357 that lp device, or a parport name such as
1358 'parport0'. Specifying 'lp=auto' instead of a
1359 port specification list means that device IDs
1360 from each port should be examined, to see if
1361 an IEEE 1284-compliant printer is attached; if
1362 so, the driver will manage that printer.
1363 See also header of drivers/char/lp.c.
1365 lpj=n [KNL]
1366 Sets loops_per_jiffy to given constant, thus avoiding
1367 time-consuming boot-time autodetection (up to 250 ms per
1368 CPU). 0 enables autodetection (default). To determine
1369 the correct value for your kernel, boot with normal
1370 autodetection and see what value is printed. Note that
1371 on SMP systems the preset will be applied to all CPUs,
1372 which is likely to cause problems if your CPUs need
1373 significantly divergent settings. An incorrect value
1374 will cause delays in the kernel to be wrong, leading to
1375 unpredictable I/O errors and other breakage. Although
1376 unlikely, in the extreme case this might damage your
1377 hardware.
1379 ltpc= [NET]
1380 Format: <io>,<irq>,<dma>
1382 machvec= [IA-64] Force the use of a particular machine-vector
1383 (machvec) in a generic kernel.
1384 Example: machvec=hpzx1_swiotlb
1386 machtype= [Loongson] Share the same kernel image file between different
1387 yeeloong laptop.
1388 Example: machtype=lemote-yeeloong-2f-7inch
1390 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1391 than or equal to this physical address is ignored.
1393 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1394 should make use of. maxcpus=n : n >= 0 limits the
1395 kernel to using 'n' processors. n=0 is a special case,
1396 it is equivalent to "nosmp", which also disables
1397 the IO APIC.
1399 max_loop= [LOOP] The number of loop block devices that get
1400 (loop.max_loop) unconditionally pre-created at init time. The default
1401 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1402 of statically allocating a predefined number, loop
1403 devices can be requested on-demand with the
1404 /dev/loop-control interface.
1406 mcatest= [IA-64]
1408 mce [X86-32] Machine Check Exception
1410 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1412 md= [HW] RAID subsystems devices and level
1413 See Documentation/md.txt.
1415 mdacon= [MDA]
1416 Format: <first>,<last>
1417 Specifies range of consoles to be captured by the MDA.
1419 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1420 Amount of memory to be used when the kernel is not able
1421 to see the whole system memory or for test.
1422 [X86-32] Use together with memmap= to avoid physical
1423 address space collisions. Without memmap= PCI devices
1424 could be placed at addresses belonging to unused RAM.
1426 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1427 memory.
1429 memchunk=nn[KMG]
1430 [KNL,SH] Allow user to override the default size for
1431 per-device physically contiguous DMA buffers.
1433 memmap=exactmap [KNL,X86] Enable setting of an exact
1434 E820 memory map, as specified by the user.
1435 Such memmap=exactmap lines can be constructed based on
1436 BIOS output or other requirements. See the memmap=nn@ss
1437 option description.
1439 memmap=nn[KMG]@ss[KMG]
1440 [KNL] Force usage of a specific region of memory
1441 Region of memory to be used, from ss to ss+nn.
1443 memmap=nn[KMG]#ss[KMG]
1444 [KNL,ACPI] Mark specific memory as ACPI data.
1445 Region of memory to be used, from ss to ss+nn.
1447 memmap=nn[KMG]$ss[KMG]
1448 [KNL,ACPI] Mark specific memory as reserved.
1449 Region of memory to be used, from ss to ss+nn.
1450 Example: Exclude memory from 0x18690000-0x1869ffff
1451 memmap=64K$0x18690000
1452 or
1453 memmap=0x10000$0x18690000
1455 memory_corruption_check=0/1 [X86]
1456 Some BIOSes seem to corrupt the first 64k of
1457 memory when doing things like suspend/resume.
1458 Setting this option will scan the memory
1459 looking for corruption. Enabling this will
1460 both detect corruption and prevent the kernel
1461 from using the memory being corrupted.
1462 However, its intended as a diagnostic tool; if
1463 repeatable BIOS-originated corruption always
1464 affects the same memory, you can use memmap=
1465 to prevent the kernel from using that memory.
1467 memory_corruption_check_size=size [X86]
1468 By default it checks for corruption in the low
1469 64k, making this memory unavailable for normal
1470 use. Use this parameter to scan for
1471 corruption in more or less memory.
1473 memory_corruption_check_period=seconds [X86]
1474 By default it checks for corruption every 60
1475 seconds. Use this parameter to check at some
1476 other rate. 0 disables periodic checking.
1478 memtest= [KNL,X86] Enable memtest
1479 Format: <integer>
1480 default : 0 <disable>
1481 Specifies the number of memtest passes to be
1482 performed. Each pass selects another test
1483 pattern from a given set of patterns. Memtest
1484 fills the memory with this pattern, validates
1485 memory contents and reserves bad memory
1486 regions that are detected.
1488 meye.*= [HW] Set MotionEye Camera parameters
1489 See Documentation/video4linux/meye.txt.
1491 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1492 Multi-Function General Purpose Timers on AMD Geode
1493 platforms.
1495 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1496 the BIOS has incorrectly applied a workaround. TinyBIOS
1497 version 0.98 is known to be affected, 0.99 fixes the
1498 problem by letting the user disable the workaround.
1500 mga= [HW,DRM]
1502 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1503 physical address is ignored.
1505 mini2440= [ARM,HW,KNL]
1506 Format:[0..2][b][c][t]
1507 Default: "0tb"
1508 MINI2440 configuration specification:
1509 0 - The attached screen is the 3.5" TFT
1510 1 - The attached screen is the 7" TFT
1511 2 - The VGA Shield is attached (1024x768)
1512 Leaving out the screen size parameter will not load
1513 the TFT driver, and the framebuffer will be left
1514 unconfigured.
1515 b - Enable backlight. The TFT backlight pin will be
1516 linked to the kernel VESA blanking code and a GPIO
1517 LED. This parameter is not necessary when using the
1518 VGA shield.
1519 c - Enable the s3c camera interface.
1520 t - Reserved for enabling touchscreen support. The
1521 touchscreen support is not enabled in the mainstream
1522 kernel as of 2.6.30, a preliminary port can be found
1523 in the "bleeding edge" mini2440 support kernel at
1524 http://repo.or.cz/w/linux-2.6/mini2440.git
1526 mminit_loglevel=
1527 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1528 parameter allows control of the logging verbosity for
1529 the additional memory initialisation checks. A value
1530 of 0 disables mminit logging and a level of 4 will
1531 log everything. Information is printed at KERN_DEBUG
1532 so loglevel=8 may also need to be specified.
1534 mousedev.tap_time=
1535 [MOUSE] Maximum time between finger touching and
1536 leaving touchpad surface for touch to be considered
1537 a tap and be reported as a left button click (for
1538 touchpads working in absolute mode only).
1539 Format: <msecs>
1540 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1541 reporting absolute coordinates, such as tablets
1542 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1543 reporting absolute coordinates, such as tablets
1545 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1546 is similar to kernelcore except it specifies the
1547 amount of memory used for migratable allocations.
1548 If both kernelcore and movablecore is specified,
1549 then kernelcore will be at *least* the specified
1550 value but may be more. If movablecore on its own
1551 is specified, the administrator must be careful
1552 that the amount of memory usable for all allocations
1553 is not too small.
1555 MTD_Partition= [MTD]
1556 Format: <name>,<region-number>,<size>,<offset>
1558 MTD_Region= [MTD] Format:
1559 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1561 mtdparts= [MTD]
1562 See drivers/mtd/cmdlinepart.c.
1564 multitce=off [PPC] This parameter disables the use of the pSeries
1565 firmware feature for updating multiple TCE entries
1566 at a time.
1568 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1570 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1572 boundary - index of last SLC block on Flex-OneNAND.
1573 The remaining blocks are configured as MLC blocks.
1574 lock - Configure if Flex-OneNAND boundary should be locked.
1575 Once locked, the boundary cannot be changed.
1576 1 indicates lock status, 0 indicates unlock status.
1578 mtdset= [ARM]
1579 ARM/S3C2412 JIVE boot control
1581 See arch/arm/mach-s3c2412/mach-jive.c
1583 mtouchusb.raw_coordinates=
1584 [HW] Make the MicroTouch USB driver use raw coordinates
1585 ('y', default) or cooked coordinates ('n')
1587 mtrr_chunk_size=nn[KMG] [X86]
1588 used for mtrr cleanup. It is largest continuous chunk
1589 that could hold holes aka. UC entries.
1591 mtrr_gran_size=nn[KMG] [X86]
1592 Used for mtrr cleanup. It is granularity of mtrr block.
1593 Default is 1.
1594 Large value could prevent small alignment from
1595 using up MTRRs.
1597 mtrr_spare_reg_nr=n [X86]
1598 Format: <integer>
1599 Range: 0,7 : spare reg number
1600 Default : 1
1601 Used for mtrr cleanup. It is spare mtrr entries number.
1602 Set to 2 or more if your graphical card needs more.
1604 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1606 netdev= [NET] Network devices parameters
1607 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1608 Note that mem_start is often overloaded to mean
1609 something different and driver-specific.
1610 This usage is only documented in each driver source
1611 file if at all.
1613 nf_conntrack.acct=
1614 [NETFILTER] Enable connection tracking flow accounting
1615 0 to disable accounting
1616 1 to enable accounting
1617 Default value is 0.
1619 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1620 See Documentation/filesystems/nfs/nfsroot.txt.
1622 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1623 See Documentation/filesystems/nfs/nfsroot.txt.
1625 nfsrootdebug [NFS] enable nfsroot debugging messages.
1626 See Documentation/filesystems/nfs/nfsroot.txt.
1628 nfs.callback_tcpport=
1629 [NFS] set the TCP port on which the NFSv4 callback
1630 channel should listen.
1632 nfs.cache_getent=
1633 [NFS] sets the pathname to the program which is used
1634 to update the NFS client cache entries.
1636 nfs.cache_getent_timeout=
1637 [NFS] sets the timeout after which an attempt to
1638 update a cache entry is deemed to have failed.
1640 nfs.idmap_cache_timeout=
1641 [NFS] set the maximum lifetime for idmapper cache
1642 entries.
1644 nfs.enable_ino64=
1645 [NFS] enable 64-bit inode numbers.
1646 If zero, the NFS client will fake up a 32-bit inode
1647 number for the readdir() and stat() syscalls instead
1648 of returning the full 64-bit number.
1649 The default is to return 64-bit inode numbers.
1651 nfs.nfs4_disable_idmapping=
1652 [NFSv4] When set, this option disables the NFSv4
1653 idmapper on the client, but only if the mount
1654 is using the 'sec=sys' security flavour. This may
1655 make migration from legacy NFSv2/v3 systems easier
1656 provided that the server has the appropriate support.
1657 The default is to always enable NFSv4 idmapping.
1659 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1660 when a NMI is triggered.
1661 Format: [state][,regs][,debounce][,die]
1663 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1664 Format: [panic,][nopanic,][num]
1665 Valid num: 0
1666 0 - turn nmi_watchdog off
1667 When panic is specified, panic when an NMI watchdog
1668 timeout occurs (or 'nopanic' to override the opposite
1669 default).
1670 This is useful when you use a panic=... timeout and
1671 need the box quickly up again.
1673 netpoll.carrier_timeout=
1674 [NET] Specifies amount of time (in seconds) that
1675 netpoll should wait for a carrier. By default netpoll
1676 waits 4 seconds.
1678 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1679 emulation library even if a 387 maths coprocessor
1680 is present.
1682 no_console_suspend
1683 [HW] Never suspend the console
1684 Disable suspending of consoles during suspend and
1685 hibernate operations. Once disabled, debugging
1686 messages can reach various consoles while the rest
1687 of the system is being put to sleep (ie, while
1688 debugging driver suspend/resume hooks). This may
1689 not work reliably with all consoles, but is known
1690 to work with serial and VGA consoles.
1691 To facilitate more flexible debugging, we also add
1692 console_suspend, a printk module parameter to control
1693 it. Users could use console_suspend (usually
1694 /sys/module/printk/parameters/console_suspend) to
1695 turn on/off it dynamically.
1697 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1698 caches in the slab allocator. Saves per-node memory,
1699 but will impact performance.
1701 noalign [KNL,ARM]
1703 noapic [SMP,APIC] Tells the kernel to not make use of any
1704 IOAPICs that may be present in the system.
1706 noautogroup Disable scheduler automatic task group creation.
1708 nobats [PPC] Do not use BATs for mapping kernel lowmem
1709 on "Classic" PPC cores.
1711 nocache [ARM]
1713 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1715 nodelayacct [KNL] Disable per-task delay accounting
1717 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1719 nodsp [SH] Disable hardware DSP at boot time.
1721 noefi [X86] Disable EFI runtime services support.
1723 noexec [IA-64]
1725 noexec [X86]
1726 On X86-32 available only on PAE configured kernels.
1727 noexec=on: enable non-executable mappings (default)
1728 noexec=off: disable non-executable mappings
1730 nosmep [X86]
1731 Disable SMEP (Supervisor Mode Execution Protection)
1732 even if it is supported by processor.
1734 noexec32 [X86-64]
1735 This affects only 32-bit executables.
1736 noexec32=on: enable non-executable mappings (default)
1737 read doesn't imply executable mappings
1738 noexec32=off: disable non-executable mappings
1739 read implies executable mappings
1741 nofpu [SH] Disable hardware FPU at boot time.
1743 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1744 register save and restore. The kernel will only save
1745 legacy floating-point registers on task switch.
1747 noxsave [BUGS=X86] Disables x86 extended register state save
1748 and restore using xsave. The kernel will fallback to
1749 enabling legacy floating-point and sse state.
1751 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1752 wfi(ARM) instruction doesn't work correctly and not to
1753 use it. This is also useful when using JTAG debugger.
1755 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1756 instruction doesn't work correctly and not to
1757 use it.
1759 no_file_caps Tells the kernel not to honor file capabilities. The
1760 only way then for a file to be executed with privilege
1761 is to be setuid root or executed by root.
1763 nohalt [IA-64] Tells the kernel not to use the power saving
1764 function PAL_HALT_LIGHT when idle. This increases
1765 power-consumption. On the positive side, it reduces
1766 interrupt wake-up latency, which may improve performance
1767 in certain environments such as networked servers or
1768 real-time systems.
1770 nohz= [KNL] Boottime enable/disable dynamic ticks
1771 Valid arguments: on, off
1772 Default: on
1774 noiotrap [SH] Disables trapped I/O port accesses.
1776 noirqdebug [X86-32] Disables the code which attempts to detect and
1777 disable unhandled interrupt sources.
1779 no_timer_check [X86,APIC] Disables the code which tests for
1780 broken timer IRQ sources.
1782 noisapnp [ISAPNP] Disables ISA PnP code.
1784 noinitrd [RAM] Tells the kernel not to load any configured
1785 initial RAM disk.
1787 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1788 remapping.
1789 [Deprecated - use intremap=off]
1791 nointroute [IA-64]
1793 nojitter [IA-64] Disables jitter checking for ITC timers.
1795 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1797 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1798 fault handling.
1800 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1801 steal time is computed, but won't influence scheduler
1802 behaviour
1804 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1806 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1808 noltlbs [PPC] Do not use large page/tlb entries for kernel
1809 lowmem mapping on PPC40x.
1811 nomca [IA-64] Disable machine check abort handling
1813 nomce [X86-32] Machine Check Exception
1815 nomfgpt [X86-32] Disable Multi-Function General Purpose
1816 Timer usage (for AMD Geode machines).
1818 nopat [X86] Disable PAT (page attribute table extension of
1819 pagetables) support.
1821 norandmaps Don't use address space randomization. Equivalent to
1822 echo 0 > /proc/sys/kernel/randomize_va_space
1824 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1826 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1827 with UP alternatives
1829 noresidual [PPC] Don't use residual data on PReP machines.
1831 nordrand [X86] Disable the direct use of the RDRAND
1832 instruction even if it is supported by the
1833 processor. RDRAND is still available to user
1834 space applications.
1836 noresume [SWSUSP] Disables resume and restores original swap
1837 space.
1839 no-scroll [VGA] Disables scrollback.
1840 This is required for the Braillex ib80-piezo Braille
1841 reader made by F.H. Papenmeier (Germany).
1843 nosbagart [IA-64]
1845 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1847 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1848 and disable the IO APIC. legacy for "maxcpus=0".
1850 nosoftlockup [KNL] Disable the soft-lockup detector.
1852 nosync [HW,M68K] Disables sync negotiation for all devices.
1854 notsc [BUGS=X86-32] Disable Time Stamp Counter
1856 nousb [USB] Disable the USB subsystem
1858 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1860 nowb [ARM]
1862 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1864 nptcg= [IA-64] Override max number of concurrent global TLB
1865 purges which is reported from either PAL_VM_SUMMARY or
1866 SAL PALO.
1868 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1869 could support. nr_cpus=n : n >= 1 limits the kernel to
1870 supporting 'n' processors. Later in runtime you can not
1871 use hotplug cpu feature to put more cpu back to online.
1872 just like you compile the kernel NR_CPUS=n
1874 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1876 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1877 one of ['zone', 'node', 'default'] can be specified
1878 This can be set from sysctl after boot.
1879 See Documentation/sysctl/vm.txt for details.
1881 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1882 See Documentation/debugging-via-ohci1394.txt for more
1883 info.
1885 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1886 Rather than timing out after 20 ms if an EC
1887 command is not properly ACKed, override the length
1888 of the timeout. We have interrupts disabled while
1889 waiting for the ACK, so if this is set too high
1890 interrupts *may* be lost!
1892 omap_mux= [OMAP] Override bootloader pin multiplexing.
1893 Format: <mux_mode0.mode_name=value>...
1894 For example, to override I2C bus2:
1895 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1897 oprofile.timer= [HW]
1898 Use timer interrupt instead of performance counters
1900 oprofile.cpu_type= Force an oprofile cpu type
1901 This might be useful if you have an older oprofile
1902 userland or if you want common events.
1903 Format: { arch_perfmon }
1904 arch_perfmon: [X86] Force use of architectural
1905 perfmon on Intel CPUs instead of the
1906 CPU specific event set.
1907 timer: [X86] Force use of architectural NMI
1908 timer mode (see also oprofile.timer
1909 for generic hr timer mode)
1910 [s390] Force legacy basic mode sampling
1911 (report cpu_type "timer")
1913 oops=panic Always panic on oopses. Default is to just kill the
1914 process, but there is a small probability of
1915 deadlocking the machine.
1916 This will also cause panics on machine check exceptions.
1917 Useful together with panic=30 to trigger a reboot.
1919 OSS [HW,OSS]
1920 See Documentation/sound/oss/oss-parameters.txt
1922 panic= [KNL] Kernel behaviour on panic: delay <timeout>
1923 timeout > 0: seconds before rebooting
1924 timeout = 0: wait forever
1925 timeout < 0: reboot immediately
1926 Format: <timeout>
1928 parkbd.port= [HW] Parallel port number the keyboard adapter is
1929 connected to, default is 0.
1930 Format: <parport#>
1931 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1932 0 for XT, 1 for AT (default is AT).
1933 Format: <mode>
1935 parport= [HW,PPT] Specify parallel ports. 0 disables.
1936 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1937 Use 'auto' to force the driver to use any
1938 IRQ/DMA settings detected (the default is to
1939 ignore detected IRQ/DMA settings because of
1940 possible conflicts). You can specify the base
1941 address, IRQ, and DMA settings; IRQ and DMA
1942 should be numbers, or 'auto' (for using detected
1943 settings on that particular port), or 'nofifo'
1944 (to avoid using a FIFO even if it is detected).
1945 Parallel ports are assigned in the order they
1946 are specified on the command line, starting
1947 with parport0.
1949 parport_init_mode= [HW,PPT]
1950 Configure VIA parallel port to operate in
1951 a specific mode. This is necessary on Pegasos
1952 computer where firmware has no options for setting
1953 up parallel port mode and sets it to spp.
1954 Currently this function knows 686a and 8231 chips.
1955 Format: [spp|ps2|epp|ecp|ecpepp]
1957 pause_on_oops=
1958 Halt all CPUs after the first oops has been printed for
1959 the specified number of seconds. This is to be used if
1960 your oopses keep scrolling off the screen.
1962 pcbit= [HW,ISDN]
1964 pcd. [PARIDE]
1965 See header of drivers/block/paride/pcd.c.
1966 See also Documentation/blockdev/paride.txt.
1968 pci=option[,option...] [PCI] various PCI subsystem options:
1969 earlydump [X86] dump PCI config space before the kernel
1970 changes anything
1971 off [X86] don't probe for the PCI bus
1972 bios [X86-32] force use of PCI BIOS, don't access
1973 the hardware directly. Use this if your machine
1974 has a non-standard PCI host bridge.
1975 nobios [X86-32] disallow use of PCI BIOS, only direct
1976 hardware access methods are allowed. Use this
1977 if you experience crashes upon bootup and you
1978 suspect they are caused by the BIOS.
1979 conf1 [X86] Force use of PCI Configuration
1980 Mechanism 1.
1981 conf2 [X86] Force use of PCI Configuration
1982 Mechanism 2.
1983 noaer [PCIE] If the PCIEAER kernel config parameter is
1984 enabled, this kernel boot option can be used to
1985 disable the use of PCIE advanced error reporting.
1986 nodomains [PCI] Disable support for multiple PCI
1987 root domains (aka PCI segments, in ACPI-speak).
1988 nommconf [X86] Disable use of MMCONFIG for PCI
1989 Configuration
1990 check_enable_amd_mmconf [X86] check for and enable
1991 properly configured MMIO access to PCI
1992 config space on AMD family 10h CPU
1993 nomsi [MSI] If the PCI_MSI kernel config parameter is
1994 enabled, this kernel boot option can be used to
1995 disable the use of MSI interrupts system-wide.
1996 noioapicquirk [APIC] Disable all boot interrupt quirks.
1997 Safety option to keep boot IRQs enabled. This
1998 should never be necessary.
1999 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2000 primary IO-APIC for bridges that cannot disable
2001 boot IRQs. This fixes a source of spurious IRQs
2002 when the system masks IRQs.
2003 noioapicreroute [APIC] Disable workaround that uses the
2004 boot IRQ equivalent of an IRQ that connects to
2005 a chipset where boot IRQs cannot be disabled.
2006 The opposite of ioapicreroute.
2007 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2008 routing table. These calls are known to be buggy
2009 on several machines and they hang the machine
2010 when used, but on other computers it's the only
2011 way to get the interrupt routing table. Try
2012 this option if the kernel is unable to allocate
2013 IRQs or discover secondary PCI buses on your
2014 motherboard.
2015 rom [X86] Assign address space to expansion ROMs.
2016 Use with caution as certain devices share
2017 address decoders between ROMs and other
2018 resources.
2019 norom [X86] Do not assign address space to
2020 expansion ROMs that do not already have
2021 BIOS assigned address ranges.
2022 nobar [X86] Do not assign address space to the
2023 BARs that weren't assigned by the BIOS.
2024 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2025 assigned automatically to PCI devices. You can
2026 make the kernel exclude IRQs of your ISA cards
2027 this way.
2028 pirqaddr=0xAAAAA [X86] Specify the physical address
2029 of the PIRQ table (normally generated
2030 by the BIOS) if it is outside the
2031 F0000h-100000h range.
2032 lastbus=N [X86] Scan all buses thru bus #N. Can be
2033 useful if the kernel is unable to find your
2034 secondary buses and you want to tell it
2035 explicitly which ones they are.
2036 assign-busses [X86] Always assign all PCI bus
2037 numbers ourselves, overriding
2038 whatever the firmware may have done.
2039 usepirqmask [X86] Honor the possible IRQ mask stored
2040 in the BIOS $PIR table. This is needed on
2041 some systems with broken BIOSes, notably
2042 some HP Pavilion N5400 and Omnibook XE3
2043 notebooks. This will have no effect if ACPI
2044 IRQ routing is enabled.
2045 noacpi [X86] Do not use ACPI for IRQ routing
2046 or for PCI scanning.
2047 use_crs [X86] Use PCI host bridge window information
2048 from ACPI. On BIOSes from 2008 or later, this
2049 is enabled by default. If you need to use this,
2050 please report a bug.
2051 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2052 If you need to use this, please report a bug.
2053 routeirq Do IRQ routing for all PCI devices.
2054 This is normally done in pci_enable_device(),
2055 so this option is a temporary workaround
2056 for broken drivers that don't call it.
2057 skip_isa_align [X86] do not align io start addr, so can
2058 handle more pci cards
2059 firmware [ARM] Do not re-enumerate the bus but instead
2060 just use the configuration from the
2061 bootloader. This is currently used on
2062 IXP2000 systems where the bus has to be
2063 configured a certain way for adjunct CPUs.
2064 noearly [X86] Don't do any early type 1 scanning.
2065 This might help on some broken boards which
2066 machine check when some devices' config space
2067 is read. But various workarounds are disabled
2068 and some IOMMU drivers will not work.
2069 bfsort Sort PCI devices into breadth-first order.
2070 This sorting is done to get a device
2071 order compatible with older (<= 2.4) kernels.
2072 nobfsort Don't sort PCI devices into breadth-first order.
2073 cbiosize=nn[KMG] The fixed amount of bus space which is
2074 reserved for the CardBus bridge's IO window.
2075 The default value is 256 bytes.
2076 cbmemsize=nn[KMG] The fixed amount of bus space which is
2077 reserved for the CardBus bridge's memory
2078 window. The default value is 64 megabytes.
2079 resource_alignment=
2080 Format:
2081 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2082 Specifies alignment and device to reassign
2083 aligned memory resources.
2084 If <order of align> is not specified,
2085 PAGE_SIZE is used as alignment.
2086 PCI-PCI bridge can be specified, if resource
2087 windows need to be expanded.
2088 ecrc= Enable/disable PCIe ECRC (transaction layer
2089 end-to-end CRC checking).
2090 bios: Use BIOS/firmware settings. This is the
2091 the default.
2092 off: Turn ECRC off
2093 on: Turn ECRC on.
2094 realloc reallocate PCI resources if allocations done by BIOS
2095 are erroneous.
2097 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2098 Management.
2099 off Disable ASPM.
2100 force Enable ASPM even on devices that claim not to support it.
2101 WARNING: Forcing ASPM on may cause system lockups.
2103 pcie_ports= [PCIE] PCIe ports handling:
2104 auto Ask the BIOS whether or not to use native PCIe services
2105 associated with PCIe ports (PME, hot-plug, AER). Use
2106 them only if that is allowed by the BIOS.
2107 native Use native PCIe services associated with PCIe ports
2108 unconditionally.
2109 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2110 ports driver.
2112 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2113 nomsi Do not use MSI for native PCIe PME signaling (this makes
2114 all PCIe root ports use INTx for all services).
2116 pcmv= [HW,PCMCIA] BadgePAD 4
2118 pd. [PARIDE]
2119 See Documentation/blockdev/paride.txt.
2121 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2122 boot time.
2123 Format: { 0 | 1 }
2124 See arch/parisc/kernel/pdc_chassis.c
2126 percpu_alloc= Select which percpu first chunk allocator to use.
2127 Currently supported values are "embed" and "page".
2128 Archs may support subset or none of the selections.
2129 See comments in mm/percpu.c for details on each
2130 allocator. This parameter is primarily for debugging
2131 and performance comparison.
2133 pf. [PARIDE]
2134 See Documentation/blockdev/paride.txt.
2136 pg. [PARIDE]
2137 See Documentation/blockdev/paride.txt.
2139 pirq= [SMP,APIC] Manual mp-table setup
2140 See Documentation/x86/i386/IO-APIC.txt.
2142 plip= [PPT,NET] Parallel port network link
2143 Format: { parport<nr> | timid | 0 }
2144 See also Documentation/parport.txt.
2146 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2147 Override pmtimer IOPort with a hex value.
2148 e.g. pmtmr=0x508
2150 pnp.debug=1 [PNP]
2151 Enable PNP debug messages (depends on the
2152 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2153 via /sys/module/pnp/parameters/debug. We always show
2154 current resource usage; turning this on also shows
2155 possible settings and some assignment information.
2157 pnpacpi= [ACPI]
2158 { off }
2160 pnpbios= [ISAPNP]
2161 { on | off | curr | res | no-curr | no-res }
2163 pnp_reserve_irq=
2164 [ISAPNP] Exclude IRQs for the autoconfiguration
2166 pnp_reserve_dma=
2167 [ISAPNP] Exclude DMAs for the autoconfiguration
2169 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2170 Ranges are in pairs (I/O port base and size).
2172 pnp_reserve_mem=
2173 [ISAPNP] Exclude memory regions for the
2174 autoconfiguration.
2175 Ranges are in pairs (memory base and size).
2177 ports= [IP_VS_FTP] IPVS ftp helper module
2178 Default is 21.
2179 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2180 may be specified.
2181 Format: <port>,<port>....
2183 print-fatal-signals=
2184 [KNL] debug: print fatal signals
2186 If enabled, warn about various signal handling
2187 related application anomalies: too many signals,
2188 too many POSIX.1 timers, fatal signals causing a
2189 coredump - etc.
2191 If you hit the warning due to signal overflow,
2192 you might want to try "ulimit -i unlimited".
2194 default: off.
2196 printk.time= Show timing data prefixed to each printk message line
2197 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2199 processor.max_cstate= [HW,ACPI]
2200 Limit processor to maximum C-state
2201 max_cstate=9 overrides any DMI blacklist limit.
2203 processor.nocst [HW,ACPI]
2204 Ignore the _CST method to determine C-states,
2205 instead using the legacy FADT method
2207 profile= [KNL] Enable kernel profiling via /proc/profile
2208 Format: [schedule,]<number>
2209 Param: "schedule" - profile schedule points.
2210 Param: <number> - step/bucket size as a power of 2 for
2211 statistical time based profiling.
2212 Param: "sleep" - profile D-state sleeping (millisecs).
2213 Requires CONFIG_SCHEDSTATS
2214 Param: "kvm" - profile VM exits.
2216 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2217 before loading.
2218 See Documentation/blockdev/ramdisk.txt.
2220 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2221 probe for; one of (bare|imps|exps|lifebook|any).
2222 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2223 per second.
2224 psmouse.resetafter= [HW,MOUSE]
2225 Try to reset the device after so many bad packets
2226 (0 = never).
2227 psmouse.resolution=
2228 [HW,MOUSE] Set desired mouse resolution, in dpi.
2229 psmouse.smartscroll=
2230 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2231 0 = disabled, 1 = enabled (default).
2233 pstore.backend= Specify the name of the pstore backend to use
2235 pt. [PARIDE]
2236 See Documentation/blockdev/paride.txt.
2238 pty.legacy_count=
2239 [KNL] Number of legacy pty's. Overwrites compiled-in
2240 default number.
2242 quiet [KNL] Disable most log messages
2244 r128= [HW,DRM]
2246 raid= [HW,RAID]
2247 See Documentation/md.txt.
2249 ramdisk_blocksize= [RAM]
2250 See Documentation/blockdev/ramdisk.txt.
2252 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2253 See Documentation/blockdev/ramdisk.txt.
2255 rcupdate.blimit= [KNL,BOOT]
2256 Set maximum number of finished RCU callbacks to process
2257 in one batch.
2259 rcupdate.qhimark= [KNL,BOOT]
2260 Set threshold of queued
2261 RCU callbacks over which batch limiting is disabled.
2263 rcupdate.qlowmark= [KNL,BOOT]
2264 Set threshold of queued RCU callbacks below which
2265 batch limiting is re-enabled.
2267 rdinit= [KNL]
2268 Format: <full_path>
2269 Run specified binary instead of /init from the ramdisk,
2270 used for early userspace startup. See initrd.
2272 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2273 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2274 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2276 relax_domain_level=
2277 [KNL, SMP] Set scheduler's default relax_domain_level.
2278 See Documentation/cgroups/cpusets.txt.
2280 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2282 reservetop= [X86-32]
2283 Format: nn[KMG]
2284 Reserves a hole at the top of the kernel virtual
2285 address space.
2287 reservelow= [X86]
2288 Format: nn[K]
2289 Set the amount of memory to reserve for BIOS at
2290 the bottom of the address space.
2292 reset_devices [KNL] Force drivers to reset the underlying device
2293 during initialization.
2295 resume= [SWSUSP]
2296 Specify the partition device for software suspend
2298 resume_offset= [SWSUSP]
2299 Specify the offset from the beginning of the partition
2300 given by "resume=" at which the swap header is located,
2301 in <PAGE_SIZE> units (needed only for swap files).
2302 See Documentation/power/swsusp-and-swap-files.txt
2304 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2305 read the resume files
2307 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2308 Useful for devices that are detected asynchronously
2309 (e.g. USB and MMC devices).
2311 hibernate= [HIBERNATION]
2312 noresume Don't check if there's a hibernation image
2313 present during boot.
2314 nocompress Don't compress/decompress hibernation images.
2316 retain_initrd [RAM] Keep initrd memory after extraction
2318 rhash_entries= [KNL,NET]
2319 Set number of hash buckets for route cache
2321 riscom8= [HW,SERIAL]
2322 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2324 ro [KNL] Mount root device read-only on boot
2326 root= [KNL] Root filesystem
2327 See name_to_dev_t comment in init/do_mounts.c.
2329 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2330 mount the root filesystem
2332 rootflags= [KNL] Set root filesystem mount option string
2334 rootfstype= [KNL] Set root filesystem type
2336 rootwait [KNL] Wait (indefinitely) for root device to show up.
2337 Useful for devices that are detected asynchronously
2338 (e.g. USB and MMC devices).
2340 rw [KNL] Mount root device read-write on boot
2342 S [KNL] Run init in single mode
2344 sa1100ir [NET]
2345 See drivers/net/irda/sa1100_ir.c.
2347 sbni= [NET] Granch SBNI12 leased line adapter
2349 sched_debug [KNL] Enables verbose scheduler debug messages.
2351 security= [SECURITY] Choose a security module to enable at boot.
2352 If this boot parameter is not specified, only the first
2353 security module asking for security registration will be
2354 loaded. An invalid security module name will be treated
2355 as if no module has been chosen.
2357 selinux= [SELINUX] Disable or enable SELinux at boot time.
2358 Format: { "0" | "1" }
2359 See security/selinux/Kconfig help text.
2360 0 -- disable.
2361 1 -- enable.
2362 Default value is set via kernel config option.
2363 If enabled at boot time, /selinux/disable can be used
2364 later to disable prior to initial policy load.
2366 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2367 Format: { "0" | "1" }
2368 See security/apparmor/Kconfig help text
2369 0 -- disable.
2370 1 -- enable.
2371 Default value is set via kernel config option.
2373 serialnumber [BUGS=X86-32]
2375 shapers= [NET]
2376 Maximal number of shapers.
2378 show_msr= [x86] show boot-time MSR settings
2379 Format: { <integer> }
2380 Show boot-time (BIOS-initialized) MSR settings.
2381 The parameter means the number of CPUs to show,
2382 for example 1 means boot CPU only.
2384 simeth= [IA-64]
2385 simscsi=
2387 slram= [HW,MTD]
2389 slub_debug[=options[,slabs]] [MM, SLUB]
2390 Enabling slub_debug allows one to determine the
2391 culprit if slab objects become corrupted. Enabling
2392 slub_debug can create guard zones around objects and
2393 may poison objects when not in use. Also tracks the
2394 last alloc / free. For more information see
2395 Documentation/vm/slub.txt.
2397 slub_max_order= [MM, SLUB]
2398 Determines the maximum allowed order for slabs.
2399 A high setting may cause OOMs due to memory
2400 fragmentation. For more information see
2401 Documentation/vm/slub.txt.
2403 slub_min_objects= [MM, SLUB]
2404 The minimum number of objects per slab. SLUB will
2405 increase the slab order up to slub_max_order to
2406 generate a sufficiently large slab able to contain
2407 the number of objects indicated. The higher the number
2408 of objects the smaller the overhead of tracking slabs
2409 and the less frequently locks need to be acquired.
2410 For more information see Documentation/vm/slub.txt.
2412 slub_min_order= [MM, SLUB]
2413 Determines the mininum page order for slabs. Must be
2414 lower than slub_max_order.
2415 For more information see Documentation/vm/slub.txt.
2417 slub_nomerge [MM, SLUB]
2418 Disable merging of slabs with similar size. May be
2419 necessary if there is some reason to distinguish
2420 allocs to different slabs. Debug options disable
2421 merging on their own.
2422 For more information see Documentation/vm/slub.txt.
2424 smart2= [HW]
2425 Format: <io1>[,<io2>[,...,<io8>]]
2427 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2428 attempt to substitute SMP alternatives once at boot.
2430 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2431 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2432 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2433 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2434 smsc-ircc2.ircc_irq= [HW] IRQ line
2435 smsc-ircc2.ircc_dma= [HW] DMA channel
2436 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2437 0: Toshiba Satellite 1800 (GP data pin select)
2438 1: Fast pin select (default)
2439 2: ATC IRMode
2441 softlockup_panic=
2442 [KNL] Should the soft-lockup detector generate panics.
2443 Format: <integer>
2445 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2446 See Documentation/laptops/sonypi.txt
2448 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2449 See Documentation/serial/specialix.txt.
2451 spia_io_base= [HW,MTD]
2452 spia_fio_base=
2453 spia_pedr=
2454 spia_peddr=
2456 stacktrace [FTRACE]
2457 Enabled the stack tracer on boot up.
2459 sti= [PARISC,HW]
2460 Format: <num>
2461 Set the STI (builtin display/keyboard on the HP-PARISC
2462 machines) console (graphic card) which should be used
2463 as the initial boot-console.
2464 See also comment in drivers/video/console/sticore.c.
2466 sti_font= [HW]
2467 See comment in drivers/video/console/sticore.c.
2469 stifb= [HW]
2470 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2472 sunrpc.min_resvport=
2473 sunrpc.max_resvport=
2474 [NFS,SUNRPC]
2475 SunRPC servers often require that client requests
2476 originate from a privileged port (i.e. a port in the
2477 range 0 < portnr < 1024).
2478 An administrator who wishes to reserve some of these
2479 ports for other uses may adjust the range that the
2480 kernel's sunrpc client considers to be privileged
2481 using these two parameters to set the minimum and
2482 maximum port values.
2484 sunrpc.pool_mode=
2485 [NFS]
2486 Control how the NFS server code allocates CPUs to
2487 service thread pools. Depending on how many NICs
2488 you have and where their interrupts are bound, this
2489 option will affect which CPUs will do NFS serving.
2490 Note: this parameter cannot be changed while the
2491 NFS server is running.
2493 auto the server chooses an appropriate mode
2494 automatically using heuristics
2495 global a single global pool contains all CPUs
2496 percpu one pool for each CPU
2497 pernode one pool for each NUMA node (equivalent
2498 to global on non-NUMA machines)
2500 sunrpc.tcp_slot_table_entries=
2501 sunrpc.udp_slot_table_entries=
2502 [NFS,SUNRPC]
2503 Sets the upper limit on the number of simultaneous
2504 RPC calls that can be sent from the client to a
2505 server. Increasing these values may allow you to
2506 improve throughput, but will also increase the
2507 amount of memory reserved for use by the client.
2509 swapaccount[=0|1]
2510 [KNL] Enable accounting of swap in memory resource
2511 controller if no parameter or 1 is given or disable
2512 it if 0 is given (See Documentation/cgroups/memory.txt)
2514 swiotlb= [IA-64] Number of I/O TLB slabs
2516 switches= [HW,M68k]
2518 sysfs.deprecated=0|1 [KNL]
2519 Enable/disable old style sysfs layout for old udev
2520 on older distributions. When this option is enabled
2521 very new udev will not work anymore. When this option
2522 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2523 in older udev will not work anymore.
2524 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2525 the kernel configuration.
2527 sysrq_always_enabled
2528 [KNL]
2529 Ignore sysrq setting - this boot parameter will
2530 neutralize any effect of /proc/sys/kernel/sysrq.
2531 Useful for debugging.
2533 tdfx= [HW,DRM]
2535 test_suspend= [SUSPEND]
2536 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2537 standby suspend) as the system sleep state to briefly
2538 enter during system startup. The system is woken from
2539 this state using a wakeup-capable RTC alarm.
2541 thash_entries= [KNL,NET]
2542 Set number of hash buckets for TCP connection
2544 thermal.act= [HW,ACPI]
2545 -1: disable all active trip points in all thermal zones
2546 <degrees C>: override all lowest active trip points
2548 thermal.crt= [HW,ACPI]
2549 -1: disable all critical trip points in all thermal zones
2550 <degrees C>: override all critical trip points
2552 thermal.nocrt= [HW,ACPI]
2553 Set to disable actions on ACPI thermal zone
2554 critical and hot trip points.
2556 thermal.off= [HW,ACPI]
2557 1: disable ACPI thermal control
2559 thermal.psv= [HW,ACPI]
2560 -1: disable all passive trip points
2561 <degrees C>: override all passive trip points to this
2562 value
2564 thermal.tzp= [HW,ACPI]
2565 Specify global default ACPI thermal zone polling rate
2566 <deci-seconds>: poll all this frequency
2567 0: no polling (default)
2569 threadirqs [KNL]
2570 Force threading of all interrupt handlers except those
2571 marked explicitely IRQF_NO_THREAD.
2573 topology= [S390]
2574 Format: {off | on}
2575 Specify if the kernel should make use of the cpu
2576 topology information if the hardware supports this.
2577 The scheduler will make use of this information and
2578 e.g. base its process migration decisions on it.
2579 Default is on.
2581 tp720= [HW,PS2]
2583 tpm_suspend_pcr=[HW,TPM]
2584 Format: integer pcr id
2585 Specify that at suspend time, the tpm driver
2586 should extend the specified pcr with zeros,
2587 as a workaround for some chips which fail to
2588 flush the last written pcr on TPM_SaveState.
2589 This will guarantee that all the other pcrs
2590 are saved.
2592 trace_buf_size=nn[KMG]
2593 [FTRACE] will set tracing buffer size.
2595 trace_event=[event-list]
2596 [FTRACE] Set and start specified trace events in order
2597 to facilitate early boot debugging.
2598 See also Documentation/trace/events.txt
2600 tsc= Disable clocksource stability checks for TSC.
2601 Format: <string>
2602 [x86] reliable: mark tsc clocksource as reliable, this
2603 disables clocksource verification at runtime, as well
2604 as the stability checks done at bootup. Used to enable
2605 high-resolution timer mode on older hardware, and in
2606 virtualized environment.
2607 [x86] noirqtime: Do not use TSC to do irq accounting.
2608 Used to run time disable IRQ_TIME_ACCOUNTING on any
2609 platforms where RDTSC is slow and this accounting
2610 can add overhead.
2612 turbografx.map[2|3]= [HW,JOY]
2613 TurboGraFX parallel port interface
2614 Format:
2615 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2616 See also Documentation/input/joystick-parport.txt
2618 udbg-immortal [PPC] When debugging early kernel crashes that
2619 happen after console_init() and before a proper
2620 console driver takes over, this boot options might
2621 help "seeing" what's going on.
2623 uhash_entries= [KNL,NET]
2624 Set number of hash buckets for UDP/UDP-Lite connections
2626 uhci-hcd.ignore_oc=
2627 [USB] Ignore overcurrent events (default N).
2628 Some badly-designed motherboards generate lots of
2629 bogus events, for ports that aren't wired to
2630 anything. Set this parameter to avoid log spamming.
2631 Note that genuine overcurrent events won't be
2632 reported either.
2634 unknown_nmi_panic
2635 [X86] Cause panic on unknown NMI.
2637 usbcore.authorized_default=
2638 [USB] Default USB device authorization:
2639 (default -1 = authorized except for wireless USB,
2640 0 = not authorized, 1 = authorized)
2642 usbcore.autosuspend=
2643 [USB] The autosuspend time delay (in seconds) used
2644 for newly-detected USB devices (default 2). This
2645 is the time required before an idle device will be
2646 autosuspended. Devices for which the delay is set
2647 to a negative value won't be autosuspended at all.
2649 usbcore.usbfs_snoop=
2650 [USB] Set to log all usbfs traffic (default 0 = off).
2652 usbcore.blinkenlights=
2653 [USB] Set to cycle leds on hubs (default 0 = off).
2655 usbcore.old_scheme_first=
2656 [USB] Start with the old device initialization
2657 scheme (default 0 = off).
2659 usbcore.usbfs_memory_mb=
2660 [USB] Memory limit (in MB) for buffers allocated by
2661 usbfs (default = 16, 0 = max = 2047).
2663 usbcore.use_both_schemes=
2664 [USB] Try the other device initialization scheme
2665 if the first one fails (default 1 = enabled).
2667 usbcore.initial_descriptor_timeout=
2668 [USB] Specifies timeout for the initial 64-byte
2669 USB_REQ_GET_DESCRIPTOR request in milliseconds
2670 (default 5000 = 5.0 seconds).
2672 usbhid.mousepoll=
2673 [USBHID] The interval which mice are to be polled at.
2675 usb-storage.delay_use=
2676 [UMS] The delay in seconds before a new device is
2677 scanned for Logical Units (default 5).
2679 usb-storage.quirks=
2680 [UMS] A list of quirks entries to supplement or
2681 override the built-in unusual_devs list. List
2682 entries are separated by commas. Each entry has
2683 the form VID:PID:Flags where VID and PID are Vendor
2684 and Product ID values (4-digit hex numbers) and
2685 Flags is a set of characters, each corresponding
2686 to a common usb-storage quirk flag as follows:
2687 a = SANE_SENSE (collect more than 18 bytes
2688 of sense data);
2689 b = BAD_SENSE (don't collect more than 18
2690 bytes of sense data);
2691 c = FIX_CAPACITY (decrease the reported
2692 device capacity by one sector);
2693 d = NO_READ_DISC_INFO (don't use
2694 READ_DISC_INFO command);
2695 e = NO_READ_CAPACITY_16 (don't use
2696 READ_CAPACITY_16 command);
2697 h = CAPACITY_HEURISTICS (decrease the
2698 reported device capacity by one
2699 sector if the number is odd);
2700 i = IGNORE_DEVICE (don't bind to this
2701 device);
2702 l = NOT_LOCKABLE (don't try to lock and
2703 unlock ejectable media);
2704 m = MAX_SECTORS_64 (don't transfer more
2705 than 64 sectors = 32 KB at a time);
2706 n = INITIAL_READ10 (force a retry of the
2707 initial READ(10) command);
2708 o = CAPACITY_OK (accept the capacity
2709 reported by the device);
2710 r = IGNORE_RESIDUE (the device reports
2711 bogus residue values);
2712 s = SINGLE_LUN (the device has only one
2713 Logical Unit);
2714 w = NO_WP_DETECT (don't test whether the
2715 medium is write-protected).
2716 Example: quirks=0419:aaf5:rl,0421:0433:rc
2718 user_debug= [KNL,ARM]
2719 Format: <int>
2720 See arch/arm/Kconfig.debug help text.
2721 1 - undefined instruction events
2722 2 - system calls
2723 4 - invalid data aborts
2724 8 - SIGSEGV faults
2725 16 - SIGBUS faults
2726 Example: user_debug=31
2728 userpte=
2729 [X86] Flags controlling user PTE allocations.
2731 nohigh = do not allocate PTE pages in
2732 HIGHMEM regardless of setting
2733 of CONFIG_HIGHPTE.
2735 vdso= [X86,SH]
2736 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2737 vdso=1: enable VDSO (default)
2738 vdso=0: disable VDSO mapping
2740 vdso32= [X86]
2741 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2742 vdso32=1: enable 32-bit VDSO (default)
2743 vdso32=0: disable 32-bit VDSO mapping
2745 vector= [IA-64,SMP]
2746 vector=percpu: enable percpu vector domain
2748 video= [FB] Frame buffer configuration
2749 See Documentation/fb/modedb.txt.
2751 vga= [BOOT,X86-32] Select a particular video mode
2752 See Documentation/x86/boot.txt and
2753 Documentation/svga.txt.
2754 Use vga=ask for menu.
2755 This is actually a boot loader parameter; the value is
2756 passed to the kernel using a special protocol.
2758 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2759 size of <nn>. This can be used to increase the
2760 minimum size (128MB on x86). It can also be used to
2761 decrease the size and leave more room for directly
2762 mapped kernel RAM.
2764 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2765 Format: <command>
2767 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2768 Format: <command>
2770 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2771 Format: <command>
2773 vsyscall= [X86-64]
2774 Controls the behavior of vsyscalls (i.e. calls to
2775 fixed addresses of 0xffffffffff600x00 from legacy
2776 code). Most statically-linked binaries and older
2777 versions of glibc use these calls. Because these
2778 functions are at fixed addresses, they make nice
2779 targets for exploits that can control RIP.
2781 emulate [default] Vsyscalls turn into traps and are
2782 emulated reasonably safely.
2784 native Vsyscalls are native syscall instructions.
2785 This is a little bit faster than trapping
2786 and makes a few dynamic recompilers work
2787 better than they would in emulation mode.
2788 It also makes exploits much easier to write.
2790 none Vsyscalls don't work at all. This makes
2791 them quite hard to use for exploits but
2792 might break your system.
2794 vt.cur_default= [VT] Default cursor shape.
2795 Format: 0xCCBBAA, where AA, BB, and CC are the same as
2796 the parameters of the <Esc>[?A;B;Cc escape sequence;
2797 see VGA-softcursor.txt. Default: 2 = underline.
2799 vt.default_blu= [VT]
2800 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2801 Change the default blue palette of the console.
2802 This is a 16-member array composed of values
2803 ranging from 0-255.
2805 vt.default_grn= [VT]
2806 Format: <green0>,<green1>,<green2>,...,<green15>
2807 Change the default green palette of the console.
2808 This is a 16-member array composed of values
2809 ranging from 0-255.
2811 vt.default_red= [VT]
2812 Format: <red0>,<red1>,<red2>,...,<red15>
2813 Change the default red palette of the console.
2814 This is a 16-member array composed of values
2815 ranging from 0-255.
2817 vt.default_utf8=
2818 [VT]
2819 Format=<0|1>
2820 Set system-wide default UTF-8 mode for all tty's.
2821 Default is 1, i.e. UTF-8 mode is enabled for all
2822 newly opened terminals.
2824 vt.global_cursor_default=
2825 [VT]
2826 Format=<-1|0|1>
2827 Set system-wide default for whether a cursor
2828 is shown on new VTs. Default is -1,
2829 i.e. cursors will be created by default unless
2830 overridden by individual drivers. 0 will hide
2831 cursors, 1 will display them.
2833 watchdog timers [HW,WDT] For information on watchdog timers,
2834 see Documentation/watchdog/watchdog-parameters.txt
2835 or other driver-specific files in the
2836 Documentation/watchdog/ directory.
2838 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2839 default x2apic cluster mode on platforms
2840 supporting x2apic.
2842 x86_mrst_timer= [X86-32,APBT]
2843 Choose timer option for x86 Moorestown MID platform.
2844 Two valid options are apbt timer only and lapic timer
2845 plus one apbt timer for broadcast timer.
2846 x86_mrst_timer=apbt_only | lapic_and_apbt
2848 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2849 xd_geo= See header of drivers/block/xd.c.
2851 xen_emul_unplug= [HW,X86,XEN]
2852 Unplug Xen emulated devices
2853 Format: [unplug0,][unplug1]
2854 ide-disks -- unplug primary master IDE devices
2855 aux-ide-disks -- unplug non-primary-master IDE devices
2856 nics -- unplug network devices
2857 all -- unplug all emulated devices (NICs and IDE disks)
2858 unnecessary -- unplugging emulated devices is
2859 unnecessary even if the host did not respond to
2860 the unplug protocol
2861 never -- do not unplug even if version check succeeds
2863 xirc2ps_cs= [NET,PCMCIA]
2864 Format:
2865 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2867 ______________________________________________________________________
2869 TODO:
2871 Add more DRM drivers.