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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 debugpat [X86] Enable PAT debugging
628 decnet.addr= [HW,NET]
629 Format: <area>[,<node>]
630 See also Documentation/networking/decnet.txt.
632 default_hugepagesz=
633 [same as hugepagesz=] The size of the default
634 HugeTLB page size. This is the size represented by
635 the legacy /proc/ hugepages APIs, used for SHM, and
636 default size when mounting hugetlbfs filesystems.
637 Defaults to the default architecture's huge page size
638 if not specified.
640 dhash_entries= [KNL]
641 Set number of hash buckets for dentry cache.
643 digi= [HW,SERIAL]
644 IO parameters + enable/disable command.
646 digiepca= [HW,SERIAL]
647 See drivers/char/README.epca and
648 Documentation/serial/digiepca.txt.
650 disable= [IPV6]
651 See Documentation/networking/ipv6.txt.
653 disable_ddw [PPC/PSERIES]
654 Disable Dynamic DMA Window support. Use this if
655 to workaround buggy firmware.
657 disable_ipv6= [IPV6]
658 See Documentation/networking/ipv6.txt.
660 disable_mtrr_cleanup [X86]
661 The kernel tries to adjust MTRR layout from continuous
662 to discrete, to make X server driver able to add WB
663 entry later. This parameter disables that.
665 disable_mtrr_trim [X86, Intel and AMD only]
666 By default the kernel will trim any uncacheable
667 memory out of your available memory pool based on
668 MTRR settings. This parameter disables that behavior,
669 possibly causing your machine to run very slowly.
671 disable_timer_pin_1 [X86]
672 Disable PIN 1 of APIC timer
673 Can be useful to work around chipset bugs.
675 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
676 this option disables the debugging code at boot.
678 dma_debug_entries=<number>
679 This option allows to tune the number of preallocated
680 entries for DMA-API debugging code. One entry is
681 required per DMA-API allocation. Use this if the
682 DMA-API debugging code disables itself because the
683 architectural default is too low.
685 dma_debug_driver=<driver_name>
686 With this option the DMA-API debugging driver
687 filter feature can be enabled at boot time. Just
688 pass the driver to filter for as the parameter.
689 The filter can be disabled or changed to another
690 driver later using sysfs.
692 dscc4.setup= [NET]
694 earlycon= [KNL] Output early console device and options.
695 uart[8250],io,<addr>[,options]
696 uart[8250],mmio,<addr>[,options]
697 uart[8250],mmio32,<addr>[,options]
698 Start an early, polled-mode console on the 8250/16550
699 UART at the specified I/O port or MMIO address.
700 MMIO inter-register address stride is either 8-bit
701 (mmio) or 32-bit (mmio32).
702 The options are the same as for ttyS, above.
704 earlyprintk= [X86,SH,BLACKFIN]
705 earlyprintk=vga
706 earlyprintk=serial[,ttySn[,baudrate]]
707 earlyprintk=ttySn[,baudrate]
708 earlyprintk=dbgp[debugController#]
710 Append ",keep" to not disable it when the real console
711 takes over.
713 Only vga or serial or usb debug port at a time.
715 Currently only ttyS0 and ttyS1 are supported.
717 Interaction with the standard serial driver is not
718 very good.
720 The VGA output is eventually overwritten by the real
721 console.
723 ekgdboc= [X86,KGDB] Allow early kernel console debugging
724 ekgdboc=kbd
726 This is designed to be used in conjunction with
727 the boot argument: earlyprintk=vga
729 edd= [EDD]
730 Format: {"off" | "on" | "skip[mbr]"}
732 eisa_irq_edge= [PARISC,HW]
733 See header of drivers/parisc/eisa.c.
735 elanfreq= [X86-32]
736 See comment before function elanfreq_setup() in
737 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
739 elevator= [IOSCHED]
740 Format: {"cfq" | "deadline" | "noop"}
741 See Documentation/block/cfq-iosched.txt and
742 Documentation/block/deadline-iosched.txt for details.
744 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
745 Specifies physical address of start of kernel core
746 image elf header and optionally the size. Generally
747 kexec loader will pass this option to capture kernel.
748 See Documentation/kdump/kdump.txt for details.
750 enable_mtrr_cleanup [X86]
751 The kernel tries to adjust MTRR layout from continuous
752 to discrete, to make X server driver able to add WB
753 entry later. This parameter enables that.
755 enable_timer_pin_1 [X86]
756 Enable PIN 1 of APIC timer
757 Can be useful to work around chipset bugs
758 (in particular on some ATI chipsets).
759 The kernel tries to set a reasonable default.
761 enforcing [SELINUX] Set initial enforcing status.
762 Format: {"0" | "1"}
763 See security/selinux/Kconfig help text.
764 0 -- permissive (log only, no denials).
765 1 -- enforcing (deny and log).
766 Default value is 0.
767 Value can be changed at runtime via /selinux/enforce.
769 erst_disable [ACPI]
770 Disable Error Record Serialization Table (ERST)
771 support.
773 ether= [HW,NET] Ethernet cards parameters
774 This option is obsoleted by the "netdev=" option, which
775 has equivalent usage. See its documentation for details.
777 evm= [EVM]
778 Format: { "fix" }
779 Permit 'security.evm' to be updated regardless of
780 current integrity status.
782 failslab=
783 fail_page_alloc=
784 fail_make_request=[KNL]
785 General fault injection mechanism.
786 Format: <interval>,<probability>,<space>,<times>
787 See also Documentation/fault-injection/.
789 floppy= [HW]
790 See Documentation/blockdev/floppy.txt.
792 force_pal_cache_flush
793 [IA-64] Avoid check_sal_cache_flush which may hang on
794 buggy SAL_CACHE_FLUSH implementations. Using this
795 parameter will force ia64_sal_cache_flush to call
796 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
798 ftrace=[tracer]
799 [FTRACE] will set and start the specified tracer
800 as early as possible in order to facilitate early
801 boot debugging.
803 ftrace_dump_on_oops[=orig_cpu]
804 [FTRACE] will dump the trace buffers on oops.
805 If no parameter is passed, ftrace will dump
806 buffers of all CPUs, but if you pass orig_cpu, it will
807 dump only the buffer of the CPU that triggered the
808 oops.
810 ftrace_filter=[function-list]
811 [FTRACE] Limit the functions traced by the function
812 tracer at boot up. function-list is a comma separated
813 list of functions. This list can be changed at run
814 time by the set_ftrace_filter file in the debugfs
815 tracing directory.
817 ftrace_notrace=[function-list]
818 [FTRACE] Do not trace the functions specified in
819 function-list. This list can be changed at run time
820 by the set_ftrace_notrace file in the debugfs
821 tracing directory.
823 ftrace_graph_filter=[function-list]
824 [FTRACE] Limit the top level callers functions traced
825 by the function graph tracer at boot up.
826 function-list is a comma separated list of functions
827 that can be changed at run time by the
828 set_graph_function file in the debugfs tracing directory.
830 gamecon.map[2|3]=
831 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
832 support via parallel port (up to 5 devices per port)
833 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
834 See also Documentation/input/joystick-parport.txt
836 gamma= [HW,DRM]
838 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
839 Format: off | on
840 default: on
842 gcov_persist= [GCOV] When non-zero (default), profiling data for
843 kernel modules is saved and remains accessible via
844 debugfs, even when the module is unloaded/reloaded.
845 When zero, profiling data is discarded and associated
846 debugfs files are removed at module unload time.
848 gpt [EFI] Forces disk with valid GPT signature but
849 invalid Protective MBR to be treated as GPT.
851 hashdist= [KNL,NUMA] Large hashes allocated during boot
852 are distributed across NUMA nodes. Defaults on
853 for 64-bit NUMA, off otherwise.
854 Format: 0 | 1 (for off | on)
856 hcl= [IA-64] SGI's Hardware Graph compatibility layer
858 hd= [EIDE] (E)IDE hard drive subsystem geometry
859 Format: <cyl>,<head>,<sect>
861 hest_disable [ACPI]
862 Disable Hardware Error Source Table (HEST) support;
863 corresponding firmware-first mode error processing
864 logic will be disabled.
866 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
867 size of <nn>. This works even on boxes that have no
868 highmem otherwise. This also works to reduce highmem
869 size on bigger boxes.
871 highres= [KNL] Enable/disable high resolution timer mode.
872 Valid parameters: "on", "off"
873 Default: "on"
875 hisax= [HW,ISDN]
876 See Documentation/isdn/README.HiSax.
878 hlt [BUGS=ARM,SH]
880 hpet= [X86-32,HPET] option to control HPET usage
881 Format: { enable (default) | disable | force |
882 verbose }
883 disable: disable HPET and use PIT instead
884 force: allow force enabled of undocumented chips (ICH4,
885 VIA, nVidia)
886 verbose: show contents of HPET registers during setup
888 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
889 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
890 On x86-64 and powerpc, this option can be specified
891 multiple times interleaved with hugepages= to reserve
892 huge pages of different sizes. Valid pages sizes on
893 x86-64 are 2M (when the CPU supports "pse") and 1G
894 (when the CPU supports the "pdpe1gb" cpuinfo flag)
895 Note that 1GB pages can only be allocated at boot time
896 using hugepages= and not freed afterwards.
898 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
899 terminal devices. Valid values: 0..8
900 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
901 If specified, z/VM IUCV HVC accepts connections
902 from listed z/VM user IDs only.
904 keep_bootcon [KNL]
905 Do not unregister boot console at start. This is only
906 useful for debugging when something happens in the window
907 between unregistering the boot console and initializing
908 the real console.
910 i2c_bus= [HW] Override the default board specific I2C bus speed
911 or register an additional I2C bus that is not
912 registered from board initialization code.
913 Format:
914 <bus_id>,<clkrate>
916 i8042.debug [HW] Toggle i8042 debug mode
917 i8042.direct [HW] Put keyboard port into non-translated mode
918 i8042.dumbkbd [HW] Pretend that controller can only read data from
919 keyboard and cannot control its state
920 (Don't attempt to blink the leds)
921 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
922 i8042.nokbd [HW] Don't check/create keyboard port
923 i8042.noloop [HW] Disable the AUX Loopback command while probing
924 for the AUX port
925 i8042.nomux [HW] Don't check presence of an active multiplexing
926 controller
927 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
928 controllers
929 i8042.notimeout [HW] Ignore timeout condition signalled by conroller
930 i8042.reset [HW] Reset the controller during init and cleanup
931 i8042.unlock [HW] Unlock (ignore) the keylock
933 i810= [HW,DRM]
935 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
936 indicates that the driver is running on unsupported
937 hardware.
938 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
939 does not match list of supported models.
940 i8k.power_status
941 [HW] Report power status in /proc/i8k
942 (disabled by default)
943 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
944 capability is set.
946 icn= [HW,ISDN]
947 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
949 ide-core.nodma= [HW] (E)IDE subsystem
950 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
951 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
952 .cdrom .chs .ignore_cable are additional options
953 See Documentation/ide/ide.txt.
955 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
956 Claim all unknown PCI IDE storage controllers.
958 idle= [X86]
959 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
960 Poll forces a polling idle loop that can slightly
961 improve the performance of waking up a idle CPU, but
962 will use a lot of power and make the system run hot.
963 Not recommended.
964 idle=mwait: On systems which support MONITOR/MWAIT but
965 the kernel chose to not use it because it doesn't save
966 as much power as a normal idle loop, use the
967 MONITOR/MWAIT idle loop anyways. Performance should be
968 the same as idle=poll.
969 idle=halt: Halt is forced to be used for CPU idle.
970 In such case C2/C3 won't be used again.
971 idle=nomwait: Disable mwait for CPU C-states
973 ignore_loglevel [KNL]
974 Ignore loglevel setting - this will print /all/
975 kernel messages to the console. Useful for debugging.
976 We also add it as printk module parameter, so users
977 could change it dynamically, usually by
978 /sys/module/printk/parameters/ignore_loglevel.
980 ihash_entries= [KNL]
981 Set number of hash buckets for inode cache.
983 ima_audit= [IMA]
984 Format: { "0" | "1" }
985 0 -- integrity auditing messages. (Default)
986 1 -- enable informational integrity auditing messages.
988 ima_hash= [IMA]
989 Format: { "sha1" | "md5" }
990 default: "sha1"
992 ima_tcb [IMA]
993 Load a policy which meets the needs of the Trusted
994 Computing Base. This means IMA will measure all
995 programs exec'd, files mmap'd for exec, and all files
996 opened for read by uid=0.
998 init= [KNL]
999 Format: <full_path>
1000 Run specified binary instead of /sbin/init as init
1001 process.
1003 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1004 for working out where the kernel is dying during
1005 startup.
1007 initrd= [BOOT] Specify the location of the initial ramdisk
1009 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1010 Format: <irq>
1012 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1013 on
1014 Enable intel iommu driver.
1015 off
1016 Disable intel iommu driver.
1017 igfx_off [Default Off]
1018 By default, gfx is mapped as normal device. If a gfx
1019 device has a dedicated DMAR unit, the DMAR unit is
1020 bypassed by not enabling DMAR with this option. In
1021 this case, gfx device will use physical address for
1022 DMA.
1023 forcedac [x86_64]
1024 With this option iommu will not optimize to look
1025 for io virtual address below 32-bit forcing dual
1026 address cycle on pci bus for cards supporting greater
1027 than 32-bit addressing. The default is to look
1028 for translation below 32-bit and if not available
1029 then look in the higher range.
1030 strict [Default Off]
1031 With this option on every unmap_single operation will
1032 result in a hardware IOTLB flush operation as opposed
1033 to batching them for performance.
1034 sp_off [Default Off]
1035 By default, super page will be supported if Intel IOMMU
1036 has the capability. With this option, super page will
1037 not be supported.
1039 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1040 0 disables intel_idle and fall back on acpi_idle.
1041 1 to 6 specify maximum depth of C-state.
1043 intremap= [X86-64, Intel-IOMMU]
1044 on enable Interrupt Remapping (default)
1045 off disable Interrupt Remapping
1046 nosid disable Source ID checking
1047 no_x2apic_optout
1048 BIOS x2APIC opt-out request will be ignored
1050 inttest= [IA-64]
1052 iomem= Disable strict checking of access to MMIO memory
1053 strict regions from userspace.
1054 relaxed
1056 iommu= [x86]
1057 off
1058 force
1059 noforce
1060 biomerge
1061 panic
1062 nopanic
1063 merge
1064 nomerge
1065 forcesac
1066 soft
1067 pt [x86, IA-64]
1069 io7= [HW] IO7 for Marvel based alpha systems
1070 See comment before marvel_specify_io7 in
1071 arch/alpha/kernel/core_marvel.c.
1073 io_delay= [X86] I/O delay method
1074 0x80
1075 Standard port 0x80 based delay
1076 0xed
1077 Alternate port 0xed based delay (needed on some systems)
1078 udelay
1079 Simple two microseconds delay
1080 none
1081 No delay
1083 ip= [IP_PNP]
1084 See Documentation/filesystems/nfs/nfsroot.txt.
1086 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1087 See comment before ip2_setup() in
1088 drivers/char/ip2/ip2base.c.
1090 irqfixup [HW]
1091 When an interrupt is not handled search all handlers
1092 for it. Intended to get systems with badly broken
1093 firmware running.
1095 irqpoll [HW]
1096 When an interrupt is not handled search all handlers
1097 for it. Also check all handlers each timer
1098 interrupt. Intended to get systems with badly broken
1099 firmware running.
1101 isapnp= [ISAPNP]
1102 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1104 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1105 Format:
1106 <cpu number>,...,<cpu number>
1107 or
1108 <cpu number>-<cpu number>
1109 (must be a positive range in ascending order)
1110 or a mixture
1111 <cpu number>,...,<cpu number>-<cpu number>
1113 This option can be used to specify one or more CPUs
1114 to isolate from the general SMP balancing and scheduling
1115 algorithms. You can move a process onto or off an
1116 "isolated" CPU via the CPU affinity syscalls or cpuset.
1117 <cpu number> begins at 0 and the maximum value is
1118 "number of CPUs in system - 1".
1120 This option is the preferred way to isolate CPUs. The
1121 alternative -- manually setting the CPU mask of all
1122 tasks in the system -- can cause problems and
1123 suboptimal load balancer performance.
1125 iucv= [HW,NET]
1127 js= [HW,JOY] Analog joystick
1128 See Documentation/input/joystick.txt.
1130 keepinitrd [HW,ARM]
1132 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1133 specifies the amount of memory usable by the kernel
1134 for non-movable allocations. The requested amount is
1135 spread evenly throughout all nodes in the system. The
1136 remaining memory in each node is used for Movable
1137 pages. In the event, a node is too small to have both
1138 kernelcore and Movable pages, kernelcore pages will
1139 take priority and other nodes will have a larger number
1140 of kernelcore pages. The Movable zone is used for the
1141 allocation of pages that may be reclaimed or moved
1142 by the page migration subsystem. This means that
1143 HugeTLB pages may not be allocated from this zone.
1144 Note that allocations like PTEs-from-HighMem still
1145 use the HighMem zone if it exists, and the Normal
1146 zone if it does not.
1148 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1149 Format: <Controller#>[,poll interval]
1150 The controller # is the number of the ehci usb debug
1151 port as it is probed via PCI. The poll interval is
1152 optional and is the number seconds in between
1153 each poll cycle to the debug port in case you need
1154 the functionality for interrupting the kernel with
1155 gdb or control-c on the dbgp connection. When
1156 not using this parameter you use sysrq-g to break into
1157 the kernel debugger.
1159 kgdboc= [KGDB,HW] kgdb over consoles.
1160 Requires a tty driver that supports console polling,
1161 or a supported polling keyboard driver (non-usb).
1162 Serial only format: <serial_device>[,baud]
1163 keyboard only format: kbd
1164 keyboard and serial format: kbd,<serial_device>[,baud]
1165 Optional Kernel mode setting:
1166 kms, kbd format: kms,kbd
1167 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1169 kgdbwait [KGDB] Stop kernel execution and enter the
1170 kernel debugger at the earliest opportunity.
1172 kmac= [MIPS] korina ethernet MAC address.
1173 Configure the RouterBoard 532 series on-chip
1174 Ethernet adapter MAC address.
1176 kmemleak= [KNL] Boot-time kmemleak enable/disable
1177 Valid arguments: on, off
1178 Default: on
1180 kstack=N [X86] Print N words from the kernel stack
1181 in oops dumps.
1183 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1184 Default is 0 (don't ignore, but inject #GP)
1186 kvm.oos_shadow= [KVM] Disable out-of-sync shadow paging.
1187 Default is 1 (enabled)
1189 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1190 KVM MMU at runtime.
1191 Default is 0 (off)
1193 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1194 Default is 1 (enabled)
1196 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1197 for all guests.
1198 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1200 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1201 (virtualized MMU) support on capable Intel chips.
1202 Default is 1 (enabled)
1204 kvm-intel.emulate_invalid_guest_state=
1205 [KVM,Intel] Enable emulation of invalid guest states
1206 Default is 0 (disabled)
1208 kvm-intel.flexpriority=
1209 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1210 Default is 1 (enabled)
1212 kvm-intel.nested=
1213 [KVM,Intel] Enable VMX nesting (nVMX).
1214 Default is 0 (disabled)
1216 kvm-intel.unrestricted_guest=
1217 [KVM,Intel] Disable unrestricted guest feature
1218 (virtualized real and unpaged mode) on capable
1219 Intel chips. Default is 1 (enabled)
1221 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1222 feature (tagged TLBs) on capable Intel chips.
1223 Default is 1 (enabled)
1225 l2cr= [PPC]
1227 l3cr= [PPC]
1229 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1230 disabled it.
1232 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1233 in C2 power state.
1235 libata.dma= [LIBATA] DMA control
1236 libata.dma=0 Disable all PATA and SATA DMA
1237 libata.dma=1 PATA and SATA Disk DMA only
1238 libata.dma=2 ATAPI (CDROM) DMA only
1239 libata.dma=4 Compact Flash DMA only
1240 Combinations also work, so libata.dma=3 enables DMA
1241 for disks and CDROMs, but not CFs.
1243 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1244 libata.ignore_hpa=0 keep BIOS limits (default)
1245 libata.ignore_hpa=1 ignore limits, using full disk
1247 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1248 when set.
1249 Format: <int>
1251 libata.force= [LIBATA] Force configurations. The format is comma
1252 separated list of "[ID:]VAL" where ID is
1253 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1254 matching port, link or device. Basically, it matches
1255 the ATA ID string printed on console by libata. If
1256 the whole ID part is omitted, the last PORT and DEVICE
1257 values are used. If ID hasn't been specified yet, the
1258 configuration applies to all ports, links and devices.
1260 If only DEVICE is omitted, the parameter applies to
1261 the port and all links and devices behind it. DEVICE
1262 number of 0 either selects the first device or the
1263 first fan-out link behind PMP device. It does not
1264 select the host link. DEVICE number of 15 selects the
1265 host link and device attached to it.
1267 The VAL specifies the configuration to force. As long
1268 as there's no ambiguity shortcut notation is allowed.
1269 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1270 The following configurations can be forced.
1272 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1273 Any ID with matching PORT is used.
1275 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1277 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1278 udma[/][16,25,33,44,66,100,133] notation is also
1279 allowed.
1281 * [no]ncq: Turn on or off NCQ.
1283 * nohrst, nosrst, norst: suppress hard, soft
1284 and both resets.
1286 * dump_id: dump IDENTIFY data.
1288 If there are multiple matching configurations changing
1289 the same attribute, the last one is used.
1291 memblock=debug [KNL] Enable memblock debug messages.
1293 load_ramdisk= [RAM] List of ramdisks to load from floppy
1294 See Documentation/blockdev/ramdisk.txt.
1296 lockd.nlm_grace_period=P [NFS] Assign grace period.
1297 Format: <integer>
1299 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1300 Format: <integer>
1302 lockd.nlm_timeout=T [NFS] Assign timeout value.
1303 Format: <integer>
1305 lockd.nlm_udpport=M [NFS] Assign UDP port.
1306 Format: <integer>
1308 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1309 Format: <irq>
1311 loglevel= All Kernel Messages with a loglevel smaller than the
1312 console loglevel will be printed to the console. It can
1313 also be changed with klogd or other programs. The
1314 loglevels are defined as follows:
1316 0 (KERN_EMERG) system is unusable
1317 1 (KERN_ALERT) action must be taken immediately
1318 2 (KERN_CRIT) critical conditions
1319 3 (KERN_ERR) error conditions
1320 4 (KERN_WARNING) warning conditions
1321 5 (KERN_NOTICE) normal but significant condition
1322 6 (KERN_INFO) informational
1323 7 (KERN_DEBUG) debug-level messages
1325 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1326 in bytes. n must be a power of two. The default
1327 size is set in the kernel config file.
1329 logo.nologo [FB] Disables display of the built-in Linux logo.
1330 This may be used to provide more screen space for
1331 kernel log messages and is useful when debugging
1332 kernel boot problems.
1334 lp=0 [LP] Specify parallel ports to use, e.g,
1335 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1336 lp=reset first parallel port). 'lp=0' disables the
1337 lp=auto printer driver. 'lp=reset' (which can be
1338 specified in addition to the ports) causes
1339 attached printers to be reset. Using
1340 lp=port1,port2,... specifies the parallel ports
1341 to associate lp devices with, starting with
1342 lp0. A port specification may be 'none' to skip
1343 that lp device, or a parport name such as
1344 'parport0'. Specifying 'lp=auto' instead of a
1345 port specification list means that device IDs
1346 from each port should be examined, to see if
1347 an IEEE 1284-compliant printer is attached; if
1348 so, the driver will manage that printer.
1349 See also header of drivers/char/lp.c.
1351 lpj=n [KNL]
1352 Sets loops_per_jiffy to given constant, thus avoiding
1353 time-consuming boot-time autodetection (up to 250 ms per
1354 CPU). 0 enables autodetection (default). To determine
1355 the correct value for your kernel, boot with normal
1356 autodetection and see what value is printed. Note that
1357 on SMP systems the preset will be applied to all CPUs,
1358 which is likely to cause problems if your CPUs need
1359 significantly divergent settings. An incorrect value
1360 will cause delays in the kernel to be wrong, leading to
1361 unpredictable I/O errors and other breakage. Although
1362 unlikely, in the extreme case this might damage your
1363 hardware.
1365 ltpc= [NET]
1366 Format: <io>,<irq>,<dma>
1368 machvec= [IA-64] Force the use of a particular machine-vector
1369 (machvec) in a generic kernel.
1370 Example: machvec=hpzx1_swiotlb
1372 machtype= [Loongson] Share the same kernel image file between different
1373 yeeloong laptop.
1374 Example: machtype=lemote-yeeloong-2f-7inch
1376 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1377 than or equal to this physical address is ignored.
1379 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1380 should make use of. maxcpus=n : n >= 0 limits the
1381 kernel to using 'n' processors. n=0 is a special case,
1382 it is equivalent to "nosmp", which also disables
1383 the IO APIC.
1385 max_loop= [LOOP] The number of loop block devices that get
1386 (loop.max_loop) unconditionally pre-created at init time. The default
1387 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1388 of statically allocating a predefined number, loop
1389 devices can be requested on-demand with the
1390 /dev/loop-control interface.
1392 mcatest= [IA-64]
1394 mce [X86-32] Machine Check Exception
1396 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1398 md= [HW] RAID subsystems devices and level
1399 See Documentation/md.txt.
1401 mdacon= [MDA]
1402 Format: <first>,<last>
1403 Specifies range of consoles to be captured by the MDA.
1405 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1406 Amount of memory to be used when the kernel is not able
1407 to see the whole system memory or for test.
1408 [X86-32] Use together with memmap= to avoid physical
1409 address space collisions. Without memmap= PCI devices
1410 could be placed at addresses belonging to unused RAM.
1412 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1413 memory.
1415 memchunk=nn[KMG]
1416 [KNL,SH] Allow user to override the default size for
1417 per-device physically contiguous DMA buffers.
1419 memmap=exactmap [KNL,X86] Enable setting of an exact
1420 E820 memory map, as specified by the user.
1421 Such memmap=exactmap lines can be constructed based on
1422 BIOS output or other requirements. See the memmap=nn@ss
1423 option description.
1425 memmap=nn[KMG]@ss[KMG]
1426 [KNL] Force usage of a specific region of memory
1427 Region of memory to be used, from ss to ss+nn.
1429 memmap=nn[KMG]#ss[KMG]
1430 [KNL,ACPI] Mark specific memory as ACPI data.
1431 Region of memory to be used, from ss to ss+nn.
1433 memmap=nn[KMG]$ss[KMG]
1434 [KNL,ACPI] Mark specific memory as reserved.
1435 Region of memory to be used, from ss to ss+nn.
1436 Example: Exclude memory from 0x18690000-0x1869ffff
1437 memmap=64K$0x18690000
1438 or
1439 memmap=0x10000$0x18690000
1441 memory_corruption_check=0/1 [X86]
1442 Some BIOSes seem to corrupt the first 64k of
1443 memory when doing things like suspend/resume.
1444 Setting this option will scan the memory
1445 looking for corruption. Enabling this will
1446 both detect corruption and prevent the kernel
1447 from using the memory being corrupted.
1448 However, its intended as a diagnostic tool; if
1449 repeatable BIOS-originated corruption always
1450 affects the same memory, you can use memmap=
1451 to prevent the kernel from using that memory.
1453 memory_corruption_check_size=size [X86]
1454 By default it checks for corruption in the low
1455 64k, making this memory unavailable for normal
1456 use. Use this parameter to scan for
1457 corruption in more or less memory.
1459 memory_corruption_check_period=seconds [X86]
1460 By default it checks for corruption every 60
1461 seconds. Use this parameter to check at some
1462 other rate. 0 disables periodic checking.
1464 memtest= [KNL,X86] Enable memtest
1465 Format: <integer>
1466 default : 0 <disable>
1467 Specifies the number of memtest passes to be
1468 performed. Each pass selects another test
1469 pattern from a given set of patterns. Memtest
1470 fills the memory with this pattern, validates
1471 memory contents and reserves bad memory
1472 regions that are detected.
1474 meye.*= [HW] Set MotionEye Camera parameters
1475 See Documentation/video4linux/meye.txt.
1477 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1478 Multi-Function General Purpose Timers on AMD Geode
1479 platforms.
1481 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1482 the BIOS has incorrectly applied a workaround. TinyBIOS
1483 version 0.98 is known to be affected, 0.99 fixes the
1484 problem by letting the user disable the workaround.
1486 mga= [HW,DRM]
1488 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1489 physical address is ignored.
1491 mini2440= [ARM,HW,KNL]
1492 Format:[0..2][b][c][t]
1493 Default: "0tb"
1494 MINI2440 configuration specification:
1495 0 - The attached screen is the 3.5" TFT
1496 1 - The attached screen is the 7" TFT
1497 2 - The VGA Shield is attached (1024x768)
1498 Leaving out the screen size parameter will not load
1499 the TFT driver, and the framebuffer will be left
1500 unconfigured.
1501 b - Enable backlight. The TFT backlight pin will be
1502 linked to the kernel VESA blanking code and a GPIO
1503 LED. This parameter is not necessary when using the
1504 VGA shield.
1505 c - Enable the s3c camera interface.
1506 t - Reserved for enabling touchscreen support. The
1507 touchscreen support is not enabled in the mainstream
1508 kernel as of 2.6.30, a preliminary port can be found
1509 in the "bleeding edge" mini2440 support kernel at
1510 http://repo.or.cz/w/linux-2.6/mini2440.git
1512 mminit_loglevel=
1513 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1514 parameter allows control of the logging verbosity for
1515 the additional memory initialisation checks. A value
1516 of 0 disables mminit logging and a level of 4 will
1517 log everything. Information is printed at KERN_DEBUG
1518 so loglevel=8 may also need to be specified.
1520 mousedev.tap_time=
1521 [MOUSE] Maximum time between finger touching and
1522 leaving touchpad surface for touch to be considered
1523 a tap and be reported as a left button click (for
1524 touchpads working in absolute mode only).
1525 Format: <msecs>
1526 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1527 reporting absolute coordinates, such as tablets
1528 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1529 reporting absolute coordinates, such as tablets
1531 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1532 is similar to kernelcore except it specifies the
1533 amount of memory used for migratable allocations.
1534 If both kernelcore and movablecore is specified,
1535 then kernelcore will be at *least* the specified
1536 value but may be more. If movablecore on its own
1537 is specified, the administrator must be careful
1538 that the amount of memory usable for all allocations
1539 is not too small.
1541 MTD_Partition= [MTD]
1542 Format: <name>,<region-number>,<size>,<offset>
1544 MTD_Region= [MTD] Format:
1545 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1547 mtdparts= [MTD]
1548 See drivers/mtd/cmdlinepart.c.
1550 multitce=off [PPC] This parameter disables the use of the pSeries
1551 firmware feature for updating multiple TCE entries
1552 at a time.
1554 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1556 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1558 boundary - index of last SLC block on Flex-OneNAND.
1559 The remaining blocks are configured as MLC blocks.
1560 lock - Configure if Flex-OneNAND boundary should be locked.
1561 Once locked, the boundary cannot be changed.
1562 1 indicates lock status, 0 indicates unlock status.
1564 mtdset= [ARM]
1565 ARM/S3C2412 JIVE boot control
1567 See arch/arm/mach-s3c2412/mach-jive.c
1569 mtouchusb.raw_coordinates=
1570 [HW] Make the MicroTouch USB driver use raw coordinates
1571 ('y', default) or cooked coordinates ('n')
1573 mtrr_chunk_size=nn[KMG] [X86]
1574 used for mtrr cleanup. It is largest continuous chunk
1575 that could hold holes aka. UC entries.
1577 mtrr_gran_size=nn[KMG] [X86]
1578 Used for mtrr cleanup. It is granularity of mtrr block.
1579 Default is 1.
1580 Large value could prevent small alignment from
1581 using up MTRRs.
1583 mtrr_spare_reg_nr=n [X86]
1584 Format: <integer>
1585 Range: 0,7 : spare reg number
1586 Default : 1
1587 Used for mtrr cleanup. It is spare mtrr entries number.
1588 Set to 2 or more if your graphical card needs more.
1590 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1592 netdev= [NET] Network devices parameters
1593 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1594 Note that mem_start is often overloaded to mean
1595 something different and driver-specific.
1596 This usage is only documented in each driver source
1597 file if at all.
1599 nf_conntrack.acct=
1600 [NETFILTER] Enable connection tracking flow accounting
1601 0 to disable accounting
1602 1 to enable accounting
1603 Default value is 0.
1605 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1606 See Documentation/filesystems/nfs/nfsroot.txt.
1608 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1609 See Documentation/filesystems/nfs/nfsroot.txt.
1611 nfsrootdebug [NFS] enable nfsroot debugging messages.
1612 See Documentation/filesystems/nfs/nfsroot.txt.
1614 nfs.callback_tcpport=
1615 [NFS] set the TCP port on which the NFSv4 callback
1616 channel should listen.
1618 nfs.cache_getent=
1619 [NFS] sets the pathname to the program which is used
1620 to update the NFS client cache entries.
1622 nfs.cache_getent_timeout=
1623 [NFS] sets the timeout after which an attempt to
1624 update a cache entry is deemed to have failed.
1626 nfs.idmap_cache_timeout=
1627 [NFS] set the maximum lifetime for idmapper cache
1628 entries.
1630 nfs.enable_ino64=
1631 [NFS] enable 64-bit inode numbers.
1632 If zero, the NFS client will fake up a 32-bit inode
1633 number for the readdir() and stat() syscalls instead
1634 of returning the full 64-bit number.
1635 The default is to return 64-bit inode numbers.
1637 nfs.nfs4_disable_idmapping=
1638 [NFSv4] When set, this option disables the NFSv4
1639 idmapper on the client, but only if the mount
1640 is using the 'sec=sys' security flavour. This may
1641 make migration from legacy NFSv2/v3 systems easier
1642 provided that the server has the appropriate support.
1643 The default is to always enable NFSv4 idmapping.
1645 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1646 when a NMI is triggered.
1647 Format: [state][,regs][,debounce][,die]
1649 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1650 Format: [panic,][nopanic,][num]
1651 Valid num: 0
1652 0 - turn nmi_watchdog off
1653 When panic is specified, panic when an NMI watchdog
1654 timeout occurs (or 'nopanic' to override the opposite
1655 default).
1656 This is useful when you use a panic=... timeout and
1657 need the box quickly up again.
1659 netpoll.carrier_timeout=
1660 [NET] Specifies amount of time (in seconds) that
1661 netpoll should wait for a carrier. By default netpoll
1662 waits 4 seconds.
1664 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1665 emulation library even if a 387 maths coprocessor
1666 is present.
1668 no_console_suspend
1669 [HW] Never suspend the console
1670 Disable suspending of consoles during suspend and
1671 hibernate operations. Once disabled, debugging
1672 messages can reach various consoles while the rest
1673 of the system is being put to sleep (ie, while
1674 debugging driver suspend/resume hooks). This may
1675 not work reliably with all consoles, but is known
1676 to work with serial and VGA consoles.
1677 To facilitate more flexible debugging, we also add
1678 console_suspend, a printk module parameter to control
1679 it. Users could use console_suspend (usually
1680 /sys/module/printk/parameters/console_suspend) to
1681 turn on/off it dynamically.
1683 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1684 caches in the slab allocator. Saves per-node memory,
1685 but will impact performance.
1687 noalign [KNL,ARM]
1689 noapic [SMP,APIC] Tells the kernel to not make use of any
1690 IOAPICs that may be present in the system.
1692 noautogroup Disable scheduler automatic task group creation.
1694 nobats [PPC] Do not use BATs for mapping kernel lowmem
1695 on "Classic" PPC cores.
1697 nocache [ARM]
1699 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1701 nodelayacct [KNL] Disable per-task delay accounting
1703 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1705 nodsp [SH] Disable hardware DSP at boot time.
1707 noefi [X86] Disable EFI runtime services support.
1709 noexec [IA-64]
1711 noexec [X86]
1712 On X86-32 available only on PAE configured kernels.
1713 noexec=on: enable non-executable mappings (default)
1714 noexec=off: disable non-executable mappings
1716 nosmep [X86]
1717 Disable SMEP (Supervisor Mode Execution Protection)
1718 even if it is supported by processor.
1720 noexec32 [X86-64]
1721 This affects only 32-bit executables.
1722 noexec32=on: enable non-executable mappings (default)
1723 read doesn't imply executable mappings
1724 noexec32=off: disable non-executable mappings
1725 read implies executable mappings
1727 nofpu [SH] Disable hardware FPU at boot time.
1729 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1730 register save and restore. The kernel will only save
1731 legacy floating-point registers on task switch.
1733 noxsave [BUGS=X86] Disables x86 extended register state save
1734 and restore using xsave. The kernel will fallback to
1735 enabling legacy floating-point and sse state.
1737 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1738 wfi(ARM) instruction doesn't work correctly and not to
1739 use it. This is also useful when using JTAG debugger.
1741 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1742 instruction doesn't work correctly and not to
1743 use it.
1745 no_file_caps Tells the kernel not to honor file capabilities. The
1746 only way then for a file to be executed with privilege
1747 is to be setuid root or executed by root.
1749 nohalt [IA-64] Tells the kernel not to use the power saving
1750 function PAL_HALT_LIGHT when idle. This increases
1751 power-consumption. On the positive side, it reduces
1752 interrupt wake-up latency, which may improve performance
1753 in certain environments such as networked servers or
1754 real-time systems.
1756 nohz= [KNL] Boottime enable/disable dynamic ticks
1757 Valid arguments: on, off
1758 Default: on
1760 noiotrap [SH] Disables trapped I/O port accesses.
1762 noirqdebug [X86-32] Disables the code which attempts to detect and
1763 disable unhandled interrupt sources.
1765 no_timer_check [X86,APIC] Disables the code which tests for
1766 broken timer IRQ sources.
1768 noisapnp [ISAPNP] Disables ISA PnP code.
1770 noinitrd [RAM] Tells the kernel not to load any configured
1771 initial RAM disk.
1773 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1774 remapping.
1775 [Deprecated - use intremap=off]
1777 nointroute [IA-64]
1779 nojitter [IA-64] Disables jitter checking for ITC timers.
1781 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1783 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1784 fault handling.
1786 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1787 steal time is computed, but won't influence scheduler
1788 behaviour
1790 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1792 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1794 noltlbs [PPC] Do not use large page/tlb entries for kernel
1795 lowmem mapping on PPC40x.
1797 nomca [IA-64] Disable machine check abort handling
1799 nomce [X86-32] Machine Check Exception
1801 nomfgpt [X86-32] Disable Multi-Function General Purpose
1802 Timer usage (for AMD Geode machines).
1804 nopat [X86] Disable PAT (page attribute table extension of
1805 pagetables) support.
1807 norandmaps Don't use address space randomization. Equivalent to
1808 echo 0 > /proc/sys/kernel/randomize_va_space
1810 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1812 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1813 with UP alternatives
1815 noresidual [PPC] Don't use residual data on PReP machines.
1817 nordrand [X86] Disable the direct use of the RDRAND
1818 instruction even if it is supported by the
1819 processor. RDRAND is still available to user
1820 space applications.
1822 noresume [SWSUSP] Disables resume and restores original swap
1823 space.
1825 no-scroll [VGA] Disables scrollback.
1826 This is required for the Braillex ib80-piezo Braille
1827 reader made by F.H. Papenmeier (Germany).
1829 nosbagart [IA-64]
1831 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1833 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1834 and disable the IO APIC. legacy for "maxcpus=0".
1836 nosoftlockup [KNL] Disable the soft-lockup detector.
1838 nosync [HW,M68K] Disables sync negotiation for all devices.
1840 notsc [BUGS=X86-32] Disable Time Stamp Counter
1842 nousb [USB] Disable the USB subsystem
1844 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1846 nowb [ARM]
1848 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1850 nptcg= [IA-64] Override max number of concurrent global TLB
1851 purges which is reported from either PAL_VM_SUMMARY or
1852 SAL PALO.
1854 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1855 could support. nr_cpus=n : n >= 1 limits the kernel to
1856 supporting 'n' processors. Later in runtime you can not
1857 use hotplug cpu feature to put more cpu back to online.
1858 just like you compile the kernel NR_CPUS=n
1860 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1862 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1863 one of ['zone', 'node', 'default'] can be specified
1864 This can be set from sysctl after boot.
1865 See Documentation/sysctl/vm.txt for details.
1867 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1868 See Documentation/debugging-via-ohci1394.txt for more
1869 info.
1871 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1872 Rather than timing out after 20 ms if an EC
1873 command is not properly ACKed, override the length
1874 of the timeout. We have interrupts disabled while
1875 waiting for the ACK, so if this is set too high
1876 interrupts *may* be lost!
1878 omap_mux= [OMAP] Override bootloader pin multiplexing.
1879 Format: <mux_mode0.mode_name=value>...
1880 For example, to override I2C bus2:
1881 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1883 oprofile.timer= [HW]
1884 Use timer interrupt instead of performance counters
1886 oprofile.cpu_type= Force an oprofile cpu type
1887 This might be useful if you have an older oprofile
1888 userland or if you want common events.
1889 Format: { arch_perfmon }
1890 arch_perfmon: [X86] Force use of architectural
1891 perfmon on Intel CPUs instead of the
1892 CPU specific event set.
1894 oops=panic Always panic on oopses. Default is to just kill the
1895 process, but there is a small probability of
1896 deadlocking the machine.
1897 This will also cause panics on machine check exceptions.
1898 Useful together with panic=30 to trigger a reboot.
1900 OSS [HW,OSS]
1901 See Documentation/sound/oss/oss-parameters.txt
1903 panic= [KNL] Kernel behaviour on panic: delay <timeout>
1904 timeout > 0: seconds before rebooting
1905 timeout = 0: wait forever
1906 timeout < 0: reboot immediately
1907 Format: <timeout>
1909 parkbd.port= [HW] Parallel port number the keyboard adapter is
1910 connected to, default is 0.
1911 Format: <parport#>
1912 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1913 0 for XT, 1 for AT (default is AT).
1914 Format: <mode>
1916 parport= [HW,PPT] Specify parallel ports. 0 disables.
1917 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1918 Use 'auto' to force the driver to use any
1919 IRQ/DMA settings detected (the default is to
1920 ignore detected IRQ/DMA settings because of
1921 possible conflicts). You can specify the base
1922 address, IRQ, and DMA settings; IRQ and DMA
1923 should be numbers, or 'auto' (for using detected
1924 settings on that particular port), or 'nofifo'
1925 (to avoid using a FIFO even if it is detected).
1926 Parallel ports are assigned in the order they
1927 are specified on the command line, starting
1928 with parport0.
1930 parport_init_mode= [HW,PPT]
1931 Configure VIA parallel port to operate in
1932 a specific mode. This is necessary on Pegasos
1933 computer where firmware has no options for setting
1934 up parallel port mode and sets it to spp.
1935 Currently this function knows 686a and 8231 chips.
1936 Format: [spp|ps2|epp|ecp|ecpepp]
1938 pause_on_oops=
1939 Halt all CPUs after the first oops has been printed for
1940 the specified number of seconds. This is to be used if
1941 your oopses keep scrolling off the screen.
1943 pcbit= [HW,ISDN]
1945 pcd. [PARIDE]
1946 See header of drivers/block/paride/pcd.c.
1947 See also Documentation/blockdev/paride.txt.
1949 pci=option[,option...] [PCI] various PCI subsystem options:
1950 earlydump [X86] dump PCI config space before the kernel
1951 changes anything
1952 off [X86] don't probe for the PCI bus
1953 bios [X86-32] force use of PCI BIOS, don't access
1954 the hardware directly. Use this if your machine
1955 has a non-standard PCI host bridge.
1956 nobios [X86-32] disallow use of PCI BIOS, only direct
1957 hardware access methods are allowed. Use this
1958 if you experience crashes upon bootup and you
1959 suspect they are caused by the BIOS.
1960 conf1 [X86] Force use of PCI Configuration
1961 Mechanism 1.
1962 conf2 [X86] Force use of PCI Configuration
1963 Mechanism 2.
1964 noaer [PCIE] If the PCIEAER kernel config parameter is
1965 enabled, this kernel boot option can be used to
1966 disable the use of PCIE advanced error reporting.
1967 nodomains [PCI] Disable support for multiple PCI
1968 root domains (aka PCI segments, in ACPI-speak).
1969 nommconf [X86] Disable use of MMCONFIG for PCI
1970 Configuration
1971 check_enable_amd_mmconf [X86] check for and enable
1972 properly configured MMIO access to PCI
1973 config space on AMD family 10h CPU
1974 nomsi [MSI] If the PCI_MSI kernel config parameter is
1975 enabled, this kernel boot option can be used to
1976 disable the use of MSI interrupts system-wide.
1977 noioapicquirk [APIC] Disable all boot interrupt quirks.
1978 Safety option to keep boot IRQs enabled. This
1979 should never be necessary.
1980 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
1981 primary IO-APIC for bridges that cannot disable
1982 boot IRQs. This fixes a source of spurious IRQs
1983 when the system masks IRQs.
1984 noioapicreroute [APIC] Disable workaround that uses the
1985 boot IRQ equivalent of an IRQ that connects to
1986 a chipset where boot IRQs cannot be disabled.
1987 The opposite of ioapicreroute.
1988 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
1989 routing table. These calls are known to be buggy
1990 on several machines and they hang the machine
1991 when used, but on other computers it's the only
1992 way to get the interrupt routing table. Try
1993 this option if the kernel is unable to allocate
1994 IRQs or discover secondary PCI buses on your
1995 motherboard.
1996 rom [X86] Assign address space to expansion ROMs.
1997 Use with caution as certain devices share
1998 address decoders between ROMs and other
1999 resources.
2000 norom [X86] Do not assign address space to
2001 expansion ROMs that do not already have
2002 BIOS assigned address ranges.
2003 nobar [X86] Do not assign address space to the
2004 BARs that weren't assigned by the BIOS.
2005 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2006 assigned automatically to PCI devices. You can
2007 make the kernel exclude IRQs of your ISA cards
2008 this way.
2009 pirqaddr=0xAAAAA [X86] Specify the physical address
2010 of the PIRQ table (normally generated
2011 by the BIOS) if it is outside the
2012 F0000h-100000h range.
2013 lastbus=N [X86] Scan all buses thru bus #N. Can be
2014 useful if the kernel is unable to find your
2015 secondary buses and you want to tell it
2016 explicitly which ones they are.
2017 assign-busses [X86] Always assign all PCI bus
2018 numbers ourselves, overriding
2019 whatever the firmware may have done.
2020 usepirqmask [X86] Honor the possible IRQ mask stored
2021 in the BIOS $PIR table. This is needed on
2022 some systems with broken BIOSes, notably
2023 some HP Pavilion N5400 and Omnibook XE3
2024 notebooks. This will have no effect if ACPI
2025 IRQ routing is enabled.
2026 noacpi [X86] Do not use ACPI for IRQ routing
2027 or for PCI scanning.
2028 use_crs [X86] Use PCI host bridge window information
2029 from ACPI. On BIOSes from 2008 or later, this
2030 is enabled by default. If you need to use this,
2031 please report a bug.
2032 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2033 If you need to use this, please report a bug.
2034 routeirq Do IRQ routing for all PCI devices.
2035 This is normally done in pci_enable_device(),
2036 so this option is a temporary workaround
2037 for broken drivers that don't call it.
2038 skip_isa_align [X86] do not align io start addr, so can
2039 handle more pci cards
2040 firmware [ARM] Do not re-enumerate the bus but instead
2041 just use the configuration from the
2042 bootloader. This is currently used on
2043 IXP2000 systems where the bus has to be
2044 configured a certain way for adjunct CPUs.
2045 noearly [X86] Don't do any early type 1 scanning.
2046 This might help on some broken boards which
2047 machine check when some devices' config space
2048 is read. But various workarounds are disabled
2049 and some IOMMU drivers will not work.
2050 bfsort Sort PCI devices into breadth-first order.
2051 This sorting is done to get a device
2052 order compatible with older (<= 2.4) kernels.
2053 nobfsort Don't sort PCI devices into breadth-first order.
2054 cbiosize=nn[KMG] The fixed amount of bus space which is
2055 reserved for the CardBus bridge's IO window.
2056 The default value is 256 bytes.
2057 cbmemsize=nn[KMG] The fixed amount of bus space which is
2058 reserved for the CardBus bridge's memory
2059 window. The default value is 64 megabytes.
2060 resource_alignment=
2061 Format:
2062 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2063 Specifies alignment and device to reassign
2064 aligned memory resources.
2065 If <order of align> is not specified,
2066 PAGE_SIZE is used as alignment.
2067 PCI-PCI bridge can be specified, if resource
2068 windows need to be expanded.
2069 ecrc= Enable/disable PCIe ECRC (transaction layer
2070 end-to-end CRC checking).
2071 bios: Use BIOS/firmware settings. This is the
2072 the default.
2073 off: Turn ECRC off
2074 on: Turn ECRC on.
2075 realloc reallocate PCI resources if allocations done by BIOS
2076 are erroneous.
2078 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2079 Management.
2080 off Disable ASPM.
2081 force Enable ASPM even on devices that claim not to support it.
2082 WARNING: Forcing ASPM on may cause system lockups.
2084 pcie_ports= [PCIE] PCIe ports handling:
2085 auto Ask the BIOS whether or not to use native PCIe services
2086 associated with PCIe ports (PME, hot-plug, AER). Use
2087 them only if that is allowed by the BIOS.
2088 native Use native PCIe services associated with PCIe ports
2089 unconditionally.
2090 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2091 ports driver.
2093 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2094 nomsi Do not use MSI for native PCIe PME signaling (this makes
2095 all PCIe root ports use INTx for all services).
2097 pcmv= [HW,PCMCIA] BadgePAD 4
2099 pd. [PARIDE]
2100 See Documentation/blockdev/paride.txt.
2102 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2103 boot time.
2104 Format: { 0 | 1 }
2105 See arch/parisc/kernel/pdc_chassis.c
2107 percpu_alloc= Select which percpu first chunk allocator to use.
2108 Currently supported values are "embed" and "page".
2109 Archs may support subset or none of the selections.
2110 See comments in mm/percpu.c for details on each
2111 allocator. This parameter is primarily for debugging
2112 and performance comparison.
2114 pf. [PARIDE]
2115 See Documentation/blockdev/paride.txt.
2117 pg. [PARIDE]
2118 See Documentation/blockdev/paride.txt.
2120 pirq= [SMP,APIC] Manual mp-table setup
2121 See Documentation/x86/i386/IO-APIC.txt.
2123 plip= [PPT,NET] Parallel port network link
2124 Format: { parport<nr> | timid | 0 }
2125 See also Documentation/parport.txt.
2127 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2128 Override pmtimer IOPort with a hex value.
2129 e.g. pmtmr=0x508
2131 pnp.debug=1 [PNP]
2132 Enable PNP debug messages (depends on the
2133 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2134 via /sys/module/pnp/parameters/debug. We always show
2135 current resource usage; turning this on also shows
2136 possible settings and some assignment information.
2138 pnpacpi= [ACPI]
2139 { off }
2141 pnpbios= [ISAPNP]
2142 { on | off | curr | res | no-curr | no-res }
2144 pnp_reserve_irq=
2145 [ISAPNP] Exclude IRQs for the autoconfiguration
2147 pnp_reserve_dma=
2148 [ISAPNP] Exclude DMAs for the autoconfiguration
2150 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2151 Ranges are in pairs (I/O port base and size).
2153 pnp_reserve_mem=
2154 [ISAPNP] Exclude memory regions for the
2155 autoconfiguration.
2156 Ranges are in pairs (memory base and size).
2158 ports= [IP_VS_FTP] IPVS ftp helper module
2159 Default is 21.
2160 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2161 may be specified.
2162 Format: <port>,<port>....
2164 print-fatal-signals=
2165 [KNL] debug: print fatal signals
2167 If enabled, warn about various signal handling
2168 related application anomalies: too many signals,
2169 too many POSIX.1 timers, fatal signals causing a
2170 coredump - etc.
2172 If you hit the warning due to signal overflow,
2173 you might want to try "ulimit -i unlimited".
2175 default: off.
2177 printk.time= Show timing data prefixed to each printk message line
2178 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2180 processor.max_cstate= [HW,ACPI]
2181 Limit processor to maximum C-state
2182 max_cstate=9 overrides any DMI blacklist limit.
2184 processor.nocst [HW,ACPI]
2185 Ignore the _CST method to determine C-states,
2186 instead using the legacy FADT method
2188 profile= [KNL] Enable kernel profiling via /proc/profile
2189 Format: [schedule,]<number>
2190 Param: "schedule" - profile schedule points.
2191 Param: <number> - step/bucket size as a power of 2 for
2192 statistical time based profiling.
2193 Param: "sleep" - profile D-state sleeping (millisecs).
2194 Requires CONFIG_SCHEDSTATS
2195 Param: "kvm" - profile VM exits.
2197 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2198 before loading.
2199 See Documentation/blockdev/ramdisk.txt.
2201 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2202 probe for; one of (bare|imps|exps|lifebook|any).
2203 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2204 per second.
2205 psmouse.resetafter= [HW,MOUSE]
2206 Try to reset the device after so many bad packets
2207 (0 = never).
2208 psmouse.resolution=
2209 [HW,MOUSE] Set desired mouse resolution, in dpi.
2210 psmouse.smartscroll=
2211 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2212 0 = disabled, 1 = enabled (default).
2214 pstore.backend= Specify the name of the pstore backend to use
2216 pt. [PARIDE]
2217 See Documentation/blockdev/paride.txt.
2219 pty.legacy_count=
2220 [KNL] Number of legacy pty's. Overwrites compiled-in
2221 default number.
2223 quiet [KNL] Disable most log messages
2225 r128= [HW,DRM]
2227 raid= [HW,RAID]
2228 See Documentation/md.txt.
2230 ramdisk_blocksize= [RAM]
2231 See Documentation/blockdev/ramdisk.txt.
2233 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2234 See Documentation/blockdev/ramdisk.txt.
2236 rcupdate.blimit= [KNL,BOOT]
2237 Set maximum number of finished RCU callbacks to process
2238 in one batch.
2240 rcupdate.qhimark= [KNL,BOOT]
2241 Set threshold of queued
2242 RCU callbacks over which batch limiting is disabled.
2244 rcupdate.qlowmark= [KNL,BOOT]
2245 Set threshold of queued RCU callbacks below which
2246 batch limiting is re-enabled.
2248 rdinit= [KNL]
2249 Format: <full_path>
2250 Run specified binary instead of /init from the ramdisk,
2251 used for early userspace startup. See initrd.
2253 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2254 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2255 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2257 relax_domain_level=
2258 [KNL, SMP] Set scheduler's default relax_domain_level.
2259 See Documentation/cgroups/cpusets.txt.
2261 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2263 reservetop= [X86-32]
2264 Format: nn[KMG]
2265 Reserves a hole at the top of the kernel virtual
2266 address space.
2268 reservelow= [X86]
2269 Format: nn[K]
2270 Set the amount of memory to reserve for BIOS at
2271 the bottom of the address space.
2273 reset_devices [KNL] Force drivers to reset the underlying device
2274 during initialization.
2276 resume= [SWSUSP]
2277 Specify the partition device for software suspend
2279 resume_offset= [SWSUSP]
2280 Specify the offset from the beginning of the partition
2281 given by "resume=" at which the swap header is located,
2282 in <PAGE_SIZE> units (needed only for swap files).
2283 See Documentation/power/swsusp-and-swap-files.txt
2285 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2286 read the resume files
2288 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2289 Useful for devices that are detected asynchronously
2290 (e.g. USB and MMC devices).
2292 hibernate= [HIBERNATION]
2293 noresume Don't check if there's a hibernation image
2294 present during boot.
2295 nocompress Don't compress/decompress hibernation images.
2297 retain_initrd [RAM] Keep initrd memory after extraction
2299 rhash_entries= [KNL,NET]
2300 Set number of hash buckets for route cache
2302 riscom8= [HW,SERIAL]
2303 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2305 ro [KNL] Mount root device read-only on boot
2307 root= [KNL] Root filesystem
2308 See name_to_dev_t comment in init/do_mounts.c.
2310 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2311 mount the root filesystem
2313 rootflags= [KNL] Set root filesystem mount option string
2315 rootfstype= [KNL] Set root filesystem type
2317 rootwait [KNL] Wait (indefinitely) for root device to show up.
2318 Useful for devices that are detected asynchronously
2319 (e.g. USB and MMC devices).
2321 rw [KNL] Mount root device read-write on boot
2323 S [KNL] Run init in single mode
2325 sa1100ir [NET]
2326 See drivers/net/irda/sa1100_ir.c.
2328 sbni= [NET] Granch SBNI12 leased line adapter
2330 sched_debug [KNL] Enables verbose scheduler debug messages.
2332 security= [SECURITY] Choose a security module to enable at boot.
2333 If this boot parameter is not specified, only the first
2334 security module asking for security registration will be
2335 loaded. An invalid security module name will be treated
2336 as if no module has been chosen.
2338 selinux= [SELINUX] Disable or enable SELinux at boot time.
2339 Format: { "0" | "1" }
2340 See security/selinux/Kconfig help text.
2341 0 -- disable.
2342 1 -- enable.
2343 Default value is set via kernel config option.
2344 If enabled at boot time, /selinux/disable can be used
2345 later to disable prior to initial policy load.
2347 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2348 Format: { "0" | "1" }
2349 See security/apparmor/Kconfig help text
2350 0 -- disable.
2351 1 -- enable.
2352 Default value is set via kernel config option.
2354 serialnumber [BUGS=X86-32]
2356 shapers= [NET]
2357 Maximal number of shapers.
2359 show_msr= [x86] show boot-time MSR settings
2360 Format: { <integer> }
2361 Show boot-time (BIOS-initialized) MSR settings.
2362 The parameter means the number of CPUs to show,
2363 for example 1 means boot CPU only.
2365 simeth= [IA-64]
2366 simscsi=
2368 slram= [HW,MTD]
2370 slub_debug[=options[,slabs]] [MM, SLUB]
2371 Enabling slub_debug allows one to determine the
2372 culprit if slab objects become corrupted. Enabling
2373 slub_debug can create guard zones around objects and
2374 may poison objects when not in use. Also tracks the
2375 last alloc / free. For more information see
2376 Documentation/vm/slub.txt.
2378 slub_max_order= [MM, SLUB]
2379 Determines the maximum allowed order for slabs.
2380 A high setting may cause OOMs due to memory
2381 fragmentation. For more information see
2382 Documentation/vm/slub.txt.
2384 slub_min_objects= [MM, SLUB]
2385 The minimum number of objects per slab. SLUB will
2386 increase the slab order up to slub_max_order to
2387 generate a sufficiently large slab able to contain
2388 the number of objects indicated. The higher the number
2389 of objects the smaller the overhead of tracking slabs
2390 and the less frequently locks need to be acquired.
2391 For more information see Documentation/vm/slub.txt.
2393 slub_min_order= [MM, SLUB]
2394 Determines the mininum page order for slabs. Must be
2395 lower than slub_max_order.
2396 For more information see Documentation/vm/slub.txt.
2398 slub_nomerge [MM, SLUB]
2399 Disable merging of slabs with similar size. May be
2400 necessary if there is some reason to distinguish
2401 allocs to different slabs. Debug options disable
2402 merging on their own.
2403 For more information see Documentation/vm/slub.txt.
2405 smart2= [HW]
2406 Format: <io1>[,<io2>[,...,<io8>]]
2408 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2409 attempt to substitute SMP alternatives once at boot.
2411 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2412 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2413 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2414 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2415 smsc-ircc2.ircc_irq= [HW] IRQ line
2416 smsc-ircc2.ircc_dma= [HW] DMA channel
2417 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2418 0: Toshiba Satellite 1800 (GP data pin select)
2419 1: Fast pin select (default)
2420 2: ATC IRMode
2422 softlockup_panic=
2423 [KNL] Should the soft-lockup detector generate panics.
2424 Format: <integer>
2426 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2427 See Documentation/laptops/sonypi.txt
2429 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2430 See Documentation/serial/specialix.txt.
2432 spia_io_base= [HW,MTD]
2433 spia_fio_base=
2434 spia_pedr=
2435 spia_peddr=
2437 stacktrace [FTRACE]
2438 Enabled the stack tracer on boot up.
2440 sti= [PARISC,HW]
2441 Format: <num>
2442 Set the STI (builtin display/keyboard on the HP-PARISC
2443 machines) console (graphic card) which should be used
2444 as the initial boot-console.
2445 See also comment in drivers/video/console/sticore.c.
2447 sti_font= [HW]
2448 See comment in drivers/video/console/sticore.c.
2450 stifb= [HW]
2451 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2453 sunrpc.min_resvport=
2454 sunrpc.max_resvport=
2455 [NFS,SUNRPC]
2456 SunRPC servers often require that client requests
2457 originate from a privileged port (i.e. a port in the
2458 range 0 < portnr < 1024).
2459 An administrator who wishes to reserve some of these
2460 ports for other uses may adjust the range that the
2461 kernel's sunrpc client considers to be privileged
2462 using these two parameters to set the minimum and
2463 maximum port values.
2465 sunrpc.pool_mode=
2466 [NFS]
2467 Control how the NFS server code allocates CPUs to
2468 service thread pools. Depending on how many NICs
2469 you have and where their interrupts are bound, this
2470 option will affect which CPUs will do NFS serving.
2471 Note: this parameter cannot be changed while the
2472 NFS server is running.
2474 auto the server chooses an appropriate mode
2475 automatically using heuristics
2476 global a single global pool contains all CPUs
2477 percpu one pool for each CPU
2478 pernode one pool for each NUMA node (equivalent
2479 to global on non-NUMA machines)
2481 sunrpc.tcp_slot_table_entries=
2482 sunrpc.udp_slot_table_entries=
2483 [NFS,SUNRPC]
2484 Sets the upper limit on the number of simultaneous
2485 RPC calls that can be sent from the client to a
2486 server. Increasing these values may allow you to
2487 improve throughput, but will also increase the
2488 amount of memory reserved for use by the client.
2490 swapaccount[=0|1]
2491 [KNL] Enable accounting of swap in memory resource
2492 controller if no parameter or 1 is given or disable
2493 it if 0 is given (See Documentation/cgroups/memory.txt)
2495 swiotlb= [IA-64] Number of I/O TLB slabs
2497 switches= [HW,M68k]
2499 sysfs.deprecated=0|1 [KNL]
2500 Enable/disable old style sysfs layout for old udev
2501 on older distributions. When this option is enabled
2502 very new udev will not work anymore. When this option
2503 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2504 in older udev will not work anymore.
2505 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2506 the kernel configuration.
2508 sysrq_always_enabled
2509 [KNL]
2510 Ignore sysrq setting - this boot parameter will
2511 neutralize any effect of /proc/sys/kernel/sysrq.
2512 Useful for debugging.
2514 tdfx= [HW,DRM]
2516 test_suspend= [SUSPEND]
2517 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2518 standby suspend) as the system sleep state to briefly
2519 enter during system startup. The system is woken from
2520 this state using a wakeup-capable RTC alarm.
2522 thash_entries= [KNL,NET]
2523 Set number of hash buckets for TCP connection
2525 thermal.act= [HW,ACPI]
2526 -1: disable all active trip points in all thermal zones
2527 <degrees C>: override all lowest active trip points
2529 thermal.crt= [HW,ACPI]
2530 -1: disable all critical trip points in all thermal zones
2531 <degrees C>: override all critical trip points
2533 thermal.nocrt= [HW,ACPI]
2534 Set to disable actions on ACPI thermal zone
2535 critical and hot trip points.
2537 thermal.off= [HW,ACPI]
2538 1: disable ACPI thermal control
2540 thermal.psv= [HW,ACPI]
2541 -1: disable all passive trip points
2542 <degrees C>: override all passive trip points to this
2543 value
2545 thermal.tzp= [HW,ACPI]
2546 Specify global default ACPI thermal zone polling rate
2547 <deci-seconds>: poll all this frequency
2548 0: no polling (default)
2550 threadirqs [KNL]
2551 Force threading of all interrupt handlers except those
2552 marked explicitely IRQF_NO_THREAD.
2554 topology= [S390]
2555 Format: {off | on}
2556 Specify if the kernel should make use of the cpu
2557 topology information if the hardware supports this.
2558 The scheduler will make use of this information and
2559 e.g. base its process migration decisions on it.
2560 Default is on.
2562 tp720= [HW,PS2]
2564 tpm_suspend_pcr=[HW,TPM]
2565 Format: integer pcr id
2566 Specify that at suspend time, the tpm driver
2567 should extend the specified pcr with zeros,
2568 as a workaround for some chips which fail to
2569 flush the last written pcr on TPM_SaveState.
2570 This will guarantee that all the other pcrs
2571 are saved.
2573 trace_buf_size=nn[KMG]
2574 [FTRACE] will set tracing buffer size.
2576 trace_event=[event-list]
2577 [FTRACE] Set and start specified trace events in order
2578 to facilitate early boot debugging.
2579 See also Documentation/trace/events.txt
2581 tsc= Disable clocksource stability checks for TSC.
2582 Format: <string>
2583 [x86] reliable: mark tsc clocksource as reliable, this
2584 disables clocksource verification at runtime, as well
2585 as the stability checks done at bootup. Used to enable
2586 high-resolution timer mode on older hardware, and in
2587 virtualized environment.
2588 [x86] noirqtime: Do not use TSC to do irq accounting.
2589 Used to run time disable IRQ_TIME_ACCOUNTING on any
2590 platforms where RDTSC is slow and this accounting
2591 can add overhead.
2593 turbografx.map[2|3]= [HW,JOY]
2594 TurboGraFX parallel port interface
2595 Format:
2596 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2597 See also Documentation/input/joystick-parport.txt
2599 udbg-immortal [PPC] When debugging early kernel crashes that
2600 happen after console_init() and before a proper
2601 console driver takes over, this boot options might
2602 help "seeing" what's going on.
2604 uhash_entries= [KNL,NET]
2605 Set number of hash buckets for UDP/UDP-Lite connections
2607 uhci-hcd.ignore_oc=
2608 [USB] Ignore overcurrent events (default N).
2609 Some badly-designed motherboards generate lots of
2610 bogus events, for ports that aren't wired to
2611 anything. Set this parameter to avoid log spamming.
2612 Note that genuine overcurrent events won't be
2613 reported either.
2615 unknown_nmi_panic
2616 [X86] Cause panic on unknown NMI.
2618 usbcore.authorized_default=
2619 [USB] Default USB device authorization:
2620 (default -1 = authorized except for wireless USB,
2621 0 = not authorized, 1 = authorized)
2623 usbcore.autosuspend=
2624 [USB] The autosuspend time delay (in seconds) used
2625 for newly-detected USB devices (default 2). This
2626 is the time required before an idle device will be
2627 autosuspended. Devices for which the delay is set
2628 to a negative value won't be autosuspended at all.
2630 usbcore.usbfs_snoop=
2631 [USB] Set to log all usbfs traffic (default 0 = off).
2633 usbcore.blinkenlights=
2634 [USB] Set to cycle leds on hubs (default 0 = off).
2636 usbcore.old_scheme_first=
2637 [USB] Start with the old device initialization
2638 scheme (default 0 = off).
2640 usbcore.use_both_schemes=
2641 [USB] Try the other device initialization scheme
2642 if the first one fails (default 1 = enabled).
2644 usbcore.initial_descriptor_timeout=
2645 [USB] Specifies timeout for the initial 64-byte
2646 USB_REQ_GET_DESCRIPTOR request in milliseconds
2647 (default 5000 = 5.0 seconds).
2649 usbhid.mousepoll=
2650 [USBHID] The interval which mice are to be polled at.
2652 usb-storage.delay_use=
2653 [UMS] The delay in seconds before a new device is
2654 scanned for Logical Units (default 5).
2656 usb-storage.quirks=
2657 [UMS] A list of quirks entries to supplement or
2658 override the built-in unusual_devs list. List
2659 entries are separated by commas. Each entry has
2660 the form VID:PID:Flags where VID and PID are Vendor
2661 and Product ID values (4-digit hex numbers) and
2662 Flags is a set of characters, each corresponding
2663 to a common usb-storage quirk flag as follows:
2664 a = SANE_SENSE (collect more than 18 bytes
2665 of sense data);
2666 b = BAD_SENSE (don't collect more than 18
2667 bytes of sense data);
2668 c = FIX_CAPACITY (decrease the reported
2669 device capacity by one sector);
2670 d = NO_READ_DISC_INFO (don't use
2671 READ_DISC_INFO command);
2672 e = NO_READ_CAPACITY_16 (don't use
2673 READ_CAPACITY_16 command);
2674 h = CAPACITY_HEURISTICS (decrease the
2675 reported device capacity by one
2676 sector if the number is odd);
2677 i = IGNORE_DEVICE (don't bind to this
2678 device);
2679 l = NOT_LOCKABLE (don't try to lock and
2680 unlock ejectable media);
2681 m = MAX_SECTORS_64 (don't transfer more
2682 than 64 sectors = 32 KB at a time);
2683 n = INITIAL_READ10 (force a retry of the
2684 initial READ(10) command);
2685 o = CAPACITY_OK (accept the capacity
2686 reported by the device);
2687 r = IGNORE_RESIDUE (the device reports
2688 bogus residue values);
2689 s = SINGLE_LUN (the device has only one
2690 Logical Unit);
2691 w = NO_WP_DETECT (don't test whether the
2692 medium is write-protected).
2693 Example: quirks=0419:aaf5:rl,0421:0433:rc
2695 user_debug= [KNL,ARM]
2696 Format: <int>
2697 See arch/arm/Kconfig.debug help text.
2698 1 - undefined instruction events
2699 2 - system calls
2700 4 - invalid data aborts
2701 8 - SIGSEGV faults
2702 16 - SIGBUS faults
2703 Example: user_debug=31
2705 userpte=
2706 [X86] Flags controlling user PTE allocations.
2708 nohigh = do not allocate PTE pages in
2709 HIGHMEM regardless of setting
2710 of CONFIG_HIGHPTE.
2712 vdso= [X86,SH]
2713 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2714 vdso=1: enable VDSO (default)
2715 vdso=0: disable VDSO mapping
2717 vdso32= [X86]
2718 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2719 vdso32=1: enable 32-bit VDSO (default)
2720 vdso32=0: disable 32-bit VDSO mapping
2722 vector= [IA-64,SMP]
2723 vector=percpu: enable percpu vector domain
2725 video= [FB] Frame buffer configuration
2726 See Documentation/fb/modedb.txt.
2728 vga= [BOOT,X86-32] Select a particular video mode
2729 See Documentation/x86/boot.txt and
2730 Documentation/svga.txt.
2731 Use vga=ask for menu.
2732 This is actually a boot loader parameter; the value is
2733 passed to the kernel using a special protocol.
2735 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2736 size of <nn>. This can be used to increase the
2737 minimum size (128MB on x86). It can also be used to
2738 decrease the size and leave more room for directly
2739 mapped kernel RAM.
2741 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2742 Format: <command>
2744 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2745 Format: <command>
2747 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2748 Format: <command>
2750 vsyscall= [X86-64]
2751 Controls the behavior of vsyscalls (i.e. calls to
2752 fixed addresses of 0xffffffffff600x00 from legacy
2753 code). Most statically-linked binaries and older
2754 versions of glibc use these calls. Because these
2755 functions are at fixed addresses, they make nice
2756 targets for exploits that can control RIP.
2758 emulate Vsyscalls turn into traps and are emulated
2759 reasonably safely.
2761 native [default] Vsyscalls are native syscall
2762 instructions.
2763 This is a little bit faster than trapping
2764 and makes a few dynamic recompilers work
2765 better than they would in emulation mode.
2766 It also makes exploits much easier to write.
2768 none Vsyscalls don't work at all. This makes
2769 them quite hard to use for exploits but
2770 might break your system.
2772 vt.cur_default= [VT] Default cursor shape.
2773 Format: 0xCCBBAA, where AA, BB, and CC are the same as
2774 the parameters of the <Esc>[?A;B;Cc escape sequence;
2775 see VGA-softcursor.txt. Default: 2 = underline.
2777 vt.default_blu= [VT]
2778 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2779 Change the default blue palette of the console.
2780 This is a 16-member array composed of values
2781 ranging from 0-255.
2783 vt.default_grn= [VT]
2784 Format: <green0>,<green1>,<green2>,...,<green15>
2785 Change the default green palette of the console.
2786 This is a 16-member array composed of values
2787 ranging from 0-255.
2789 vt.default_red= [VT]
2790 Format: <red0>,<red1>,<red2>,...,<red15>
2791 Change the default red palette of the console.
2792 This is a 16-member array composed of values
2793 ranging from 0-255.
2795 vt.default_utf8=
2796 [VT]
2797 Format=<0|1>
2798 Set system-wide default UTF-8 mode for all tty's.
2799 Default is 1, i.e. UTF-8 mode is enabled for all
2800 newly opened terminals.
2802 vt.global_cursor_default=
2803 [VT]
2804 Format=<-1|0|1>
2805 Set system-wide default for whether a cursor
2806 is shown on new VTs. Default is -1,
2807 i.e. cursors will be created by default unless
2808 overridden by individual drivers. 0 will hide
2809 cursors, 1 will display them.
2811 watchdog timers [HW,WDT] For information on watchdog timers,
2812 see Documentation/watchdog/watchdog-parameters.txt
2813 or other driver-specific files in the
2814 Documentation/watchdog/ directory.
2816 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2817 default x2apic cluster mode on platforms
2818 supporting x2apic.
2820 x86_mrst_timer= [X86-32,APBT]
2821 Choose timer option for x86 Moorestown MID platform.
2822 Two valid options are apbt timer only and lapic timer
2823 plus one apbt timer for broadcast timer.
2824 x86_mrst_timer=apbt_only | lapic_and_apbt
2826 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2827 xd_geo= See header of drivers/block/xd.c.
2829 xen_emul_unplug= [HW,X86,XEN]
2830 Unplug Xen emulated devices
2831 Format: [unplug0,][unplug1]
2832 ide-disks -- unplug primary master IDE devices
2833 aux-ide-disks -- unplug non-primary-master IDE devices
2834 nics -- unplug network devices
2835 all -- unplug all emulated devices (NICs and IDE disks)
2836 unnecessary -- unplugging emulated devices is
2837 unnecessary even if the host did not respond to
2838 the unplug protocol
2839 never -- do not unplug even if version check succeeds
2841 xirc2ps_cs= [NET,PCMCIA]
2842 Format:
2843 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2845 ______________________________________________________________________
2847 TODO:
2849 Add more DRM drivers.