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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 FB The frame buffer device is enabled.
53 FTRACE Function tracing enabled.
54 GCOV GCOV profiling is enabled.
55 HW Appropriate hardware is enabled.
56 IA-64 IA-64 architecture is enabled.
57 IMA Integrity measurement architecture is enabled.
58 IOSCHED More than one I/O scheduler is enabled.
59 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
60 IPV6 IPv6 support is enabled.
61 ISAPNP ISA PnP code is enabled.
62 ISDN Appropriate ISDN support is enabled.
63 JOY Appropriate joystick support is enabled.
64 KGDB Kernel debugger support is enabled.
65 KVM Kernel Virtual Machine support is enabled.
66 LIBATA Libata driver is enabled
67 LP Printer support is enabled.
68 LOOP Loopback device support is enabled.
69 M68k M68k architecture is enabled.
70 These options have more detailed description inside of
71 Documentation/m68k/kernel-options.txt.
72 MCA MCA bus support is enabled.
73 MDA MDA console support is enabled.
74 MIPS MIPS architecture is enabled.
75 MOUSE Appropriate mouse support is enabled.
76 MSI Message Signaled Interrupts (PCI).
77 MTD MTD (Memory Technology Device) support is enabled.
78 NET Appropriate network support is enabled.
79 NUMA NUMA support is enabled.
80 NFS Appropriate NFS support is enabled.
81 OSS OSS sound support is enabled.
82 PV_OPS A paravirtualized kernel is enabled.
83 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
84 PARISC The PA-RISC architecture is enabled.
85 PCI PCI bus support is enabled.
86 PCIE PCI Express support is enabled.
87 PCMCIA The PCMCIA subsystem is enabled.
88 PNP Plug & Play support is enabled.
89 PPC PowerPC architecture is enabled.
90 PPT Parallel port support is enabled.
91 PS2 Appropriate PS/2 support is enabled.
92 RAM RAM disk support is enabled.
93 S390 S390 architecture is enabled.
94 SCSI Appropriate SCSI support is enabled.
95 A lot of drivers have their options described inside
96 the Documentation/scsi/ sub-directory.
97 SECURITY Different security models are enabled.
98 SELINUX SELinux support is enabled.
99 APPARMOR AppArmor support is enabled.
100 SERIAL Serial support is enabled.
101 SH SuperH architecture is enabled.
102 SMP The kernel is an SMP kernel.
103 SPARC Sparc architecture is enabled.
104 SWSUSP Software suspend (hibernation) is enabled.
105 SUSPEND System suspend states are enabled.
106 TPM TPM drivers are enabled.
107 TS Appropriate touchscreen support is enabled.
108 UMS USB Mass Storage support is enabled.
109 USB USB support is enabled.
110 USBHID USB Human Interface Device support is enabled.
111 V4L Video For Linux support is enabled.
112 VGA The VGA console has been enabled.
113 VT Virtual terminal support is enabled.
114 WDT Watchdog support is enabled.
115 XT IBM PC/XT MFM hard disk support is enabled.
116 X86-32 X86-32, aka i386 architecture is enabled.
117 X86-64 X86-64 architecture is enabled.
118 More X86-64 boot options can be found in
119 Documentation/x86/x86_64/boot-options.txt .
120 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
121 XEN Xen support is enabled
123 In addition, the following text indicates that the option:
125 BUGS= Relates to possible processor bugs on the said processor.
126 KNL Is a kernel start-up parameter.
127 BOOT Is a boot loader parameter.
129 Parameters denoted with BOOT are actually interpreted by the boot
130 loader, and have no meaning to the kernel directly.
131 Do not modify the syntax of boot loader parameters without extreme
132 need or coordination with <Documentation/x86/boot.txt>.
134 There are also arch-specific kernel-parameters not documented here.
135 See for example <Documentation/x86/x86_64/boot-options.txt>.
137 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
138 a trailing = on the name of any parameter states that that parameter will
139 be entered as an environment variable, whereas its absence indicates that
140 it will appear as a kernel argument readable via /proc/cmdline by programs
141 running once the system is up.
143 The number of kernel parameters is not limited, but the length of the
144 complete command line (parameters including spaces etc.) is limited to
145 a fixed number of characters. This limit depends on the architecture
146 and is between 256 and 4096 characters. It is defined in the file
147 ./include/asm/setup.h as COMMAND_LINE_SIZE.
149 Finally, the [KMG] suffix is commonly described after a number of kernel
150 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
151 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
152 bytes respectively. Such letter suffixes can also be entirely omitted.
155 acpi= [HW,ACPI,X86]
156 Advanced Configuration and Power Interface
157 Format: { force | off | strict | noirq | rsdt }
158 force -- enable ACPI if default was off
159 off -- disable ACPI if default was on
160 noirq -- do not use ACPI for IRQ routing
161 strict -- Be less tolerant of platforms that are not
162 strictly ACPI specification compliant.
163 rsdt -- prefer RSDT over (default) XSDT
164 copy_dsdt -- copy DSDT to memory
166 See also Documentation/power/pm.txt, pci=noacpi
168 acpi_rsdp= [ACPI,EFI,KEXEC]
169 Pass the RSDP address to the kernel, mostly used
170 on machines running EFI runtime service to boot the
171 second kernel for kdump.
173 acpi_apic_instance= [ACPI, IOAPIC]
174 Format: <int>
175 2: use 2nd APIC table, if available
176 1,0: use 1st APIC table
177 default: 0
179 acpi_backlight= [HW,ACPI]
180 acpi_backlight=vendor
181 acpi_backlight=video
182 If set to vendor, prefer vendor specific driver
183 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
184 of the ACPI video.ko driver.
186 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
187 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
188 Format: <int>
189 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
190 debug output. Bits in debug_layer correspond to a
191 _COMPONENT in an ACPI source file, e.g.,
192 #define _COMPONENT ACPI_PCI_COMPONENT
193 Bits in debug_level correspond to a level in
194 ACPI_DEBUG_PRINT statements, e.g.,
195 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
196 The debug_level mask defaults to "info". See
197 Documentation/acpi/debug.txt for more information about
198 debug layers and levels.
200 Enable processor driver info messages:
201 acpi.debug_layer=0x20000000
202 Enable PCI/PCI interrupt routing info messages:
203 acpi.debug_layer=0x400000
204 Enable AML "Debug" output, i.e., stores to the Debug
205 object while interpreting AML:
206 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
207 Enable all messages related to ACPI hardware:
208 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
210 Some values produce so much output that the system is
211 unusable. The "log_buf_len" parameter may be useful
212 if you need to capture more output.
214 acpi_irq_balance [HW,ACPI]
215 ACPI will balance active IRQs
216 default in APIC mode
218 acpi_irq_nobalance [HW,ACPI]
219 ACPI will not move active IRQs (default)
220 default in PIC mode
222 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
223 Format: <irq>,<irq>...
225 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
226 use by PCI
227 Format: <irq>,<irq>...
229 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
231 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
232 Format: To spoof as Windows 98: ="Microsoft Windows"
234 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
235 acpi_osi="string1" # add string1 -- only one string
236 acpi_osi="!string2" # remove built-in string2
237 acpi_osi= # disable all strings
239 acpi_pm_good [X86]
240 Override the pmtimer bug detection: force the kernel
241 to assume that this machine's pmtimer latches its value
242 and always returns good values.
244 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
245 Format: { level | edge | high | low }
247 acpi_serialize [HW,ACPI] force serialization of AML methods
249 acpi_skip_timer_override [HW,ACPI]
250 Recognize and ignore IRQ0/pin2 Interrupt Override.
251 For broken nForce2 BIOS resulting in XT-PIC timer.
253 acpi_sleep= [HW,ACPI] Sleep options
254 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
255 old_ordering, nonvs, sci_force_enable }
256 See Documentation/power/video.txt for information on
257 s3_bios and s3_mode.
258 s3_beep is for debugging; it makes the PC's speaker beep
259 as soon as the kernel's real-mode entry point is called.
260 s4_nohwsig prevents ACPI hardware signature from being
261 used during resume from hibernation.
262 old_ordering causes the ACPI 1.0 ordering of the _PTS
263 control method, with respect to putting devices into
264 low power states, to be enforced (the ACPI 2.0 ordering
265 of _PTS is used by default).
266 nonvs prevents the kernel from saving/restoring the
267 ACPI NVS memory during suspend/hibernation and resume.
268 sci_force_enable causes the kernel to set SCI_EN directly
269 on resume from S1/S3 (which is against the ACPI spec,
270 but some broken systems don't work without it).
272 acpi_use_timer_override [HW,ACPI]
273 Use timer override. For some broken Nvidia NF5 boards
274 that require a timer override, but don't have HPET
276 acpi_enforce_resources= [ACPI]
277 { strict | lax | no }
278 Check for resource conflicts between native drivers
279 and ACPI OperationRegions (SystemIO and SystemMemory
280 only). IO ports and memory declared in ACPI might be
281 used by the ACPI subsystem in arbitrary AML code and
282 can interfere with legacy drivers.
283 strict (default): access to resources claimed by ACPI
284 is denied; legacy drivers trying to access reserved
285 resources will fail to bind to device using them.
286 lax: access to resources claimed by ACPI is allowed;
287 legacy drivers trying to access reserved resources
288 will bind successfully but a warning message is logged.
289 no: ACPI OperationRegions are not marked as reserved,
290 no further checks are performed.
292 add_efi_memmap [EFI; X86] Include EFI memory map in
293 kernel's map of available physical RAM.
295 agp= [AGP]
296 { off | try_unsupported }
297 off: disable AGP support
298 try_unsupported: try to drive unsupported chipsets
299 (may crash computer or cause data corruption)
301 ALSA [HW,ALSA]
302 See Documentation/sound/alsa/alsa-parameters.txt
304 alignment= [KNL,ARM]
305 Allow the default userspace alignment fault handler
306 behaviour to be specified. Bit 0 enables warnings,
307 bit 1 enables fixups, and bit 2 sends a segfault.
309 amd_iommu= [HW,X86-84]
310 Pass parameters to the AMD IOMMU driver in the system.
311 Possible values are:
312 fullflush - enable flushing of IO/TLB entries when
313 they are unmapped. Otherwise they are
314 flushed before they will be reused, which
315 is a lot of faster
316 off - do not initialize any AMD IOMMU found in
317 the system
319 amijoy.map= [HW,JOY] Amiga joystick support
320 Map of devices attached to JOY0DAT and JOY1DAT
321 Format: <a>,<b>
322 See also Documentation/kernel/input/joystick.txt
324 analog.map= [HW,JOY] Analog joystick and gamepad support
325 Specifies type or capabilities of an analog joystick
326 connected to one of 16 gameports
327 Format: <type1>,<type2>,..<type16>
329 apc= [HW,SPARC]
330 Power management functions (SPARCstation-4/5 + deriv.)
331 Format: noidle
332 Disable APC CPU standby support. SPARCstation-Fox does
333 not play well with APC CPU idle - disable it if you have
334 APC and your system crashes randomly.
336 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
337 Change the output verbosity whilst booting
338 Format: { quiet (default) | verbose | debug }
339 Change the amount of debugging information output
340 when initialising the APIC and IO-APIC components.
342 autoconf= [IPV6]
343 See Documentation/networking/ipv6.txt.
345 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
346 Limit apic dumping. The parameter defines the maximal
347 number of local apics being dumped. Also it is possible
348 to set it to "all" by meaning -- no limit here.
349 Format: { 1 (default) | 2 | ... | all }.
350 The parameter valid if only apic=debug or
351 apic=verbose is specified.
352 Example: apic=debug show_lapic=all
354 apm= [APM] Advanced Power Management
355 See header of arch/x86/kernel/apm_32.c.
357 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
358 Format: <io>,<irq>,<nodeID>
360 ataflop= [HW,M68k]
362 atarimouse= [HW,MOUSE] Atari Mouse
364 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
365 EzKey and similar keyboards
367 atkbd.reset= [HW] Reset keyboard during initialization
369 atkbd.set= [HW] Select keyboard code set
370 Format: <int> (2 = AT (default), 3 = PS/2)
372 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
373 keyboards
375 atkbd.softraw= [HW] Choose between synthetic and real raw mode
376 Format: <bool> (0 = real, 1 = synthetic (default))
378 atkbd.softrepeat= [HW]
379 Use software keyboard repeat
381 autotest [IA-64]
383 baycom_epp= [HW,AX25]
384 Format: <io>,<mode>
386 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
387 Format: <io>,<mode>
388 See header of drivers/net/hamradio/baycom_par.c.
390 baycom_ser_fdx= [HW,AX25]
391 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
392 Format: <io>,<irq>,<mode>[,<baud>]
393 See header of drivers/net/hamradio/baycom_ser_fdx.c.
395 baycom_ser_hdx= [HW,AX25]
396 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
397 Format: <io>,<irq>,<mode>
398 See header of drivers/net/hamradio/baycom_ser_hdx.c.
400 boot_delay= Milliseconds to delay each printk during boot.
401 Values larger than 10 seconds (10000) are changed to
402 no delay (0).
403 Format: integer
405 bootmem_debug [KNL] Enable bootmem allocator debug messages.
407 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
408 bttv.radio= Most important insmod options are available as
409 kernel args too.
410 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
411 bttv.tuner= and Documentation/video4linux/bttv/CARDLIST
413 bulk_remove=off [PPC] This parameter disables the use of the pSeries
414 firmware feature for flushing multiple hpte entries
415 at a time.
417 c101= [NET] Moxa C101 synchronous serial card
419 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
420 Sometimes CPU hardware bugs make them report the cache
421 size incorrectly. The kernel will attempt work arounds
422 to fix known problems, but for some CPUs it is not
423 possible to determine what the correct size should be.
424 This option provides an override for these situations.
426 capability.disable=
427 [SECURITY] Disable capabilities. This would normally
428 be used only if an alternative security model is to be
429 configured. Potentially dangerous and should only be
430 used if you are entirely sure of the consequences.
432 ccw_timeout_log [S390]
433 See Documentation/s390/CommonIO for details.
435 cgroup_disable= [KNL] Disable a particular controller
436 Format: {name of the controller(s) to disable}
437 {Currently supported controllers - "memory"}
439 checkreqprot [SELINUX] Set initial checkreqprot flag value.
440 Format: { "0" | "1" }
441 See security/selinux/Kconfig help text.
442 0 -- check protection applied by kernel (includes
443 any implied execute protection).
444 1 -- check protection requested by application.
445 Default value is set via a kernel config option.
446 Value can be changed at runtime via
447 /selinux/checkreqprot.
449 cio_ignore= [S390]
450 See Documentation/s390/CommonIO for details.
452 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
453 [Deprecated]
454 Forces specified clocksource (if available) to be used
455 when calculating gettimeofday(). If specified
456 clocksource is not available, it defaults to PIT.
457 Format: { pit | tsc | cyclone | pmtmr }
459 clocksource= Override the default clocksource
460 Format: <string>
461 Override the default clocksource and use the clocksource
462 with the name specified.
463 Some clocksource names to choose from, depending on
464 the platform:
465 [all] jiffies (this is the base, fallback clocksource)
466 [ACPI] acpi_pm
467 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
468 pxa_timer,timer3,32k_counter,timer0_1
469 [AVR32] avr32
470 [X86-32] pit,hpet,tsc;
471 scx200_hrt on Geode; cyclone on IBM x440
472 [MIPS] MIPS
473 [PARISC] cr16
474 [S390] tod
475 [SH] SuperH
476 [SPARC64] tick
477 [X86-64] hpet,tsc
479 clearcpuid=BITNUM [X86]
480 Disable CPUID feature X for the kernel. See
481 arch/x86/include/asm/cpufeature.h for the valid bit
482 numbers. Note the Linux specific bits are not necessarily
483 stable over kernel options, but the vendor specific
484 ones should be.
485 Also note that user programs calling CPUID directly
486 or using the feature without checking anything
487 will still see it. This just prevents it from
488 being used by the kernel or shown in /proc/cpuinfo.
489 Also note the kernel might malfunction if you disable
490 some critical bits.
492 cmo_free_hint= [PPC] Format: { yes | no }
493 Specify whether pages are marked as being inactive
494 when they are freed. This is used in CMO environments
495 to determine OS memory pressure for page stealing by
496 a hypervisor.
497 Default: yes
499 code_bytes [X86] How many bytes of object code to print
500 in an oops report.
501 Range: 0 - 8192
502 Default: 64
504 com20020= [HW,NET] ARCnet - COM20020 chipset
505 Format:
506 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
508 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
509 Format: <io>[,<irq>]
511 com90xx= [HW,NET]
512 ARCnet - COM90xx chipset (memory-mapped buffers)
513 Format: <io>[,<irq>[,<memstart>]]
515 condev= [HW,S390] console device
516 conmode=
518 console= [KNL] Output console device and options.
520 tty<n> Use the virtual console device <n>.
522 ttyS<n>[,options]
523 ttyUSB0[,options]
524 Use the specified serial port. The options are of
525 the form "bbbbpnf", where "bbbb" is the baud rate,
526 "p" is parity ("n", "o", or "e"), "n" is number of
527 bits, and "f" is flow control ("r" for RTS or
528 omit it). Default is "9600n8".
530 See Documentation/serial-console.txt for more
531 information. See
532 Documentation/networking/netconsole.txt for an
533 alternative.
535 uart[8250],io,<addr>[,options]
536 uart[8250],mmio,<addr>[,options]
537 Start an early, polled-mode console on the 8250/16550
538 UART at the specified I/O port or MMIO address,
539 switching to the matching ttyS device later. The
540 options are the same as for ttyS, above.
542 If the device connected to the port is not a TTY but a braille
543 device, prepend "brl," before the device type, for instance
544 console=brl,ttyS0
545 For now, only VisioBraille is supported.
547 consoleblank= [KNL] The console blank (screen saver) timeout in
548 seconds. Defaults to 10*60 = 10mins. A value of 0
549 disables the blank timer.
551 coredump_filter=
552 [KNL] Change the default value for
553 /proc/<pid>/coredump_filter.
554 See also Documentation/filesystems/proc.txt.
556 cpuidle.off=1 [CPU_IDLE]
557 disable the cpuidle sub-system
559 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
560 Format:
561 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
563 crashkernel=size[KMG][@offset[KMG]]
564 [KNL] Using kexec, Linux can switch to a 'crash kernel'
565 upon panic. This parameter reserves the physical
566 memory region [offset, offset + size] for that kernel
567 image. If '@offset' is omitted, then a suitable offset
568 is selected automatically. Check
569 Documentation/kdump/kdump.txt for further details.
571 crashkernel=range1:size1[,range2:size2,...][@offset]
572 [KNL] Same as above, but depends on the memory
573 in the running system. The syntax of range is
574 start-[end] where start and end are both
575 a memory unit (amount[KMG]). See also
576 Documentation/kdump/kdump.txt for an example.
578 cs89x0_dma= [HW,NET]
579 Format: <dma>
581 cs89x0_media= [HW,NET]
582 Format: { rj45 | aui | bnc }
584 dasd= [HW,NET]
585 See header of drivers/s390/block/dasd_devmap.c.
587 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
588 (one device per port)
589 Format: <port#>,<type>
590 See also Documentation/input/joystick-parport.txt
592 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
593 time. See Documentation/dynamic-debug-howto.txt for
594 details.
596 debug [KNL] Enable kernel debugging (events log level).
598 debug_locks_verbose=
599 [KNL] verbose self-tests
600 Format=<0|1>
601 Print debugging info while doing the locking API
602 self-tests.
603 We default to 0 (no extra messages), setting it to
604 1 will print _a lot_ more information - normally
605 only useful to kernel developers.
607 debug_objects [KNL] Enable object debugging
609 no_debug_objects
610 [KNL] Disable object debugging
612 debugpat [X86] Enable PAT debugging
614 decnet.addr= [HW,NET]
615 Format: <area>[,<node>]
616 See also Documentation/networking/decnet.txt.
618 default_hugepagesz=
619 [same as hugepagesz=] The size of the default
620 HugeTLB page size. This is the size represented by
621 the legacy /proc/ hugepages APIs, used for SHM, and
622 default size when mounting hugetlbfs filesystems.
623 Defaults to the default architecture's huge page size
624 if not specified.
626 dhash_entries= [KNL]
627 Set number of hash buckets for dentry cache.
629 digi= [HW,SERIAL]
630 IO parameters + enable/disable command.
632 digiepca= [HW,SERIAL]
633 See drivers/char/README.epca and
634 Documentation/serial/digiepca.txt.
636 disable= [IPV6]
637 See Documentation/networking/ipv6.txt.
639 disable_ddw [PPC/PSERIES]
640 Disable Dynamic DMA Window support. Use this if
641 to workaround buggy firmware.
643 disable_ipv6= [IPV6]
644 See Documentation/networking/ipv6.txt.
646 disable_mtrr_cleanup [X86]
647 The kernel tries to adjust MTRR layout from continuous
648 to discrete, to make X server driver able to add WB
649 entry later. This parameter disables that.
651 disable_mtrr_trim [X86, Intel and AMD only]
652 By default the kernel will trim any uncacheable
653 memory out of your available memory pool based on
654 MTRR settings. This parameter disables that behavior,
655 possibly causing your machine to run very slowly.
657 disable_timer_pin_1 [X86]
658 Disable PIN 1 of APIC timer
659 Can be useful to work around chipset bugs.
661 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
662 this option disables the debugging code at boot.
664 dma_debug_entries=<number>
665 This option allows to tune the number of preallocated
666 entries for DMA-API debugging code. One entry is
667 required per DMA-API allocation. Use this if the
668 DMA-API debugging code disables itself because the
669 architectural default is too low.
671 dma_debug_driver=<driver_name>
672 With this option the DMA-API debugging driver
673 filter feature can be enabled at boot time. Just
674 pass the driver to filter for as the parameter.
675 The filter can be disabled or changed to another
676 driver later using sysfs.
678 dscc4.setup= [NET]
680 earlycon= [KNL] Output early console device and options.
681 uart[8250],io,<addr>[,options]
682 uart[8250],mmio,<addr>[,options]
683 uart[8250],mmio32,<addr>[,options]
684 Start an early, polled-mode console on the 8250/16550
685 UART at the specified I/O port or MMIO address.
686 MMIO inter-register address stride is either 8-bit
687 (mmio) or 32-bit (mmio32).
688 The options are the same as for ttyS, above.
690 earlyprintk= [X86,SH,BLACKFIN]
691 earlyprintk=vga
692 earlyprintk=serial[,ttySn[,baudrate]]
693 earlyprintk=ttySn[,baudrate]
694 earlyprintk=dbgp[debugController#]
696 Append ",keep" to not disable it when the real console
697 takes over.
699 Only vga or serial or usb debug port at a time.
701 Currently only ttyS0 and ttyS1 are supported.
703 Interaction with the standard serial driver is not
704 very good.
706 The VGA output is eventually overwritten by the real
707 console.
709 ekgdboc= [X86,KGDB] Allow early kernel console debugging
710 ekgdboc=kbd
712 This is designed to be used in conjunction with
713 the boot argument: earlyprintk=vga
715 edd= [EDD]
716 Format: {"off" | "on" | "skip[mbr]"}
718 eisa_irq_edge= [PARISC,HW]
719 See header of drivers/parisc/eisa.c.
721 elanfreq= [X86-32]
722 See comment before function elanfreq_setup() in
723 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
725 elevator= [IOSCHED]
726 Format: {"cfq" | "deadline" | "noop"}
727 See Documentation/block/as-iosched.txt and
728 Documentation/block/deadline-iosched.txt for details.
730 elfcorehdr= [IA-64,PPC,SH,X86]
731 Specifies physical address of start of kernel core
732 image elf header. Generally kexec loader will
733 pass this option to capture kernel.
734 See Documentation/kdump/kdump.txt for details.
736 enable_mtrr_cleanup [X86]
737 The kernel tries to adjust MTRR layout from continuous
738 to discrete, to make X server driver able to add WB
739 entry later. This parameter enables that.
741 enable_timer_pin_1 [X86]
742 Enable PIN 1 of APIC timer
743 Can be useful to work around chipset bugs
744 (in particular on some ATI chipsets).
745 The kernel tries to set a reasonable default.
747 enforcing [SELINUX] Set initial enforcing status.
748 Format: {"0" | "1"}
749 See security/selinux/Kconfig help text.
750 0 -- permissive (log only, no denials).
751 1 -- enforcing (deny and log).
752 Default value is 0.
753 Value can be changed at runtime via /selinux/enforce.
755 erst_disable [ACPI]
756 Disable Error Record Serialization Table (ERST)
757 support.
759 ether= [HW,NET] Ethernet cards parameters
760 This option is obsoleted by the "netdev=" option, which
761 has equivalent usage. See its documentation for details.
763 failslab=
764 fail_page_alloc=
765 fail_make_request=[KNL]
766 General fault injection mechanism.
767 Format: <interval>,<probability>,<space>,<times>
768 See also /Documentation/fault-injection/.
770 floppy= [HW]
771 See Documentation/blockdev/floppy.txt.
773 force_pal_cache_flush
774 [IA-64] Avoid check_sal_cache_flush which may hang on
775 buggy SAL_CACHE_FLUSH implementations. Using this
776 parameter will force ia64_sal_cache_flush to call
777 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
779 ftrace=[tracer]
780 [FTRACE] will set and start the specified tracer
781 as early as possible in order to facilitate early
782 boot debugging.
784 ftrace_dump_on_oops[=orig_cpu]
785 [FTRACE] will dump the trace buffers on oops.
786 If no parameter is passed, ftrace will dump
787 buffers of all CPUs, but if you pass orig_cpu, it will
788 dump only the buffer of the CPU that triggered the
789 oops.
791 ftrace_filter=[function-list]
792 [FTRACE] Limit the functions traced by the function
793 tracer at boot up. function-list is a comma separated
794 list of functions. This list can be changed at run
795 time by the set_ftrace_filter file in the debugfs
796 tracing directory.
798 ftrace_notrace=[function-list]
799 [FTRACE] Do not trace the functions specified in
800 function-list. This list can be changed at run time
801 by the set_ftrace_notrace file in the debugfs
802 tracing directory.
804 ftrace_graph_filter=[function-list]
805 [FTRACE] Limit the top level callers functions traced
806 by the function graph tracer at boot up.
807 function-list is a comma separated list of functions
808 that can be changed at run time by the
809 set_graph_function file in the debugfs tracing directory.
811 gamecon.map[2|3]=
812 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
813 support via parallel port (up to 5 devices per port)
814 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
815 See also Documentation/input/joystick-parport.txt
817 gamma= [HW,DRM]
819 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
820 Format: off | on
821 default: on
823 gcov_persist= [GCOV] When non-zero (default), profiling data for
824 kernel modules is saved and remains accessible via
825 debugfs, even when the module is unloaded/reloaded.
826 When zero, profiling data is discarded and associated
827 debugfs files are removed at module unload time.
829 gpt [EFI] Forces disk with valid GPT signature but
830 invalid Protective MBR to be treated as GPT.
832 hashdist= [KNL,NUMA] Large hashes allocated during boot
833 are distributed across NUMA nodes. Defaults on
834 for 64-bit NUMA, off otherwise.
835 Format: 0 | 1 (for off | on)
837 hcl= [IA-64] SGI's Hardware Graph compatibility layer
839 hd= [EIDE] (E)IDE hard drive subsystem geometry
840 Format: <cyl>,<head>,<sect>
842 hest_disable [ACPI]
843 Disable Hardware Error Source Table (HEST) support;
844 corresponding firmware-first mode error processing
845 logic will be disabled.
847 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
848 size of <nn>. This works even on boxes that have no
849 highmem otherwise. This also works to reduce highmem
850 size on bigger boxes.
852 highres= [KNL] Enable/disable high resolution timer mode.
853 Valid parameters: "on", "off"
854 Default: "on"
856 hisax= [HW,ISDN]
857 See Documentation/isdn/README.HiSax.
859 hlt [BUGS=ARM,SH]
861 hpet= [X86-32,HPET] option to control HPET usage
862 Format: { enable (default) | disable | force |
863 verbose }
864 disable: disable HPET and use PIT instead
865 force: allow force enabled of undocumented chips (ICH4,
866 VIA, nVidia)
867 verbose: show contents of HPET registers during setup
869 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
870 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
871 On x86-64 and powerpc, this option can be specified
872 multiple times interleaved with hugepages= to reserve
873 huge pages of different sizes. Valid pages sizes on
874 x86-64 are 2M (when the CPU supports "pse") and 1G
875 (when the CPU supports the "pdpe1gb" cpuinfo flag)
876 Note that 1GB pages can only be allocated at boot time
877 using hugepages= and not freed afterwards.
879 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
880 terminal devices. Valid values: 0..8
881 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
882 If specified, z/VM IUCV HVC accepts connections
883 from listed z/VM user IDs only.
885 keep_bootcon [KNL]
886 Do not unregister boot console at start. This is only
887 useful for debugging when something happens in the window
888 between unregistering the boot console and initializing
889 the real console.
891 i2c_bus= [HW] Override the default board specific I2C bus speed
892 or register an additional I2C bus that is not
893 registered from board initialization code.
894 Format:
895 <bus_id>,<clkrate>
897 i8042.debug [HW] Toggle i8042 debug mode
898 i8042.direct [HW] Put keyboard port into non-translated mode
899 i8042.dumbkbd [HW] Pretend that controller can only read data from
900 keyboard and cannot control its state
901 (Don't attempt to blink the leds)
902 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
903 i8042.nokbd [HW] Don't check/create keyboard port
904 i8042.noloop [HW] Disable the AUX Loopback command while probing
905 for the AUX port
906 i8042.nomux [HW] Don't check presence of an active multiplexing
907 controller
908 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
909 controllers
910 i8042.notimeout [HW] Ignore timeout condition signalled by conroller
911 i8042.reset [HW] Reset the controller during init and cleanup
912 i8042.unlock [HW] Unlock (ignore) the keylock
914 i810= [HW,DRM]
916 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
917 indicates that the driver is running on unsupported
918 hardware.
919 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
920 does not match list of supported models.
921 i8k.power_status
922 [HW] Report power status in /proc/i8k
923 (disabled by default)
924 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
925 capability is set.
927 icn= [HW,ISDN]
928 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
930 ide-core.nodma= [HW] (E)IDE subsystem
931 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
932 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
933 .cdrom .chs .ignore_cable are additional options
934 See Documentation/ide/ide.txt.
936 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
937 Claim all unknown PCI IDE storage controllers.
939 idle= [X86]
940 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
941 Poll forces a polling idle loop that can slightly
942 improve the performance of waking up a idle CPU, but
943 will use a lot of power and make the system run hot.
944 Not recommended.
945 idle=mwait: On systems which support MONITOR/MWAIT but
946 the kernel chose to not use it because it doesn't save
947 as much power as a normal idle loop, use the
948 MONITOR/MWAIT idle loop anyways. Performance should be
949 the same as idle=poll.
950 idle=halt: Halt is forced to be used for CPU idle.
951 In such case C2/C3 won't be used again.
952 idle=nomwait: Disable mwait for CPU C-states
954 ignore_loglevel [KNL]
955 Ignore loglevel setting - this will print /all/
956 kernel messages to the console. Useful for debugging.
958 ihash_entries= [KNL]
959 Set number of hash buckets for inode cache.
961 ima_audit= [IMA]
962 Format: { "0" | "1" }
963 0 -- integrity auditing messages. (Default)
964 1 -- enable informational integrity auditing messages.
966 ima_hash= [IMA]
967 Format: { "sha1" | "md5" }
968 default: "sha1"
970 ima_tcb [IMA]
971 Load a policy which meets the needs of the Trusted
972 Computing Base. This means IMA will measure all
973 programs exec'd, files mmap'd for exec, and all files
974 opened for read by uid=0.
976 init= [KNL]
977 Format: <full_path>
978 Run specified binary instead of /sbin/init as init
979 process.
981 initcall_debug [KNL] Trace initcalls as they are executed. Useful
982 for working out where the kernel is dying during
983 startup.
985 initrd= [BOOT] Specify the location of the initial ramdisk
987 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
988 Format: <irq>
990 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
991 on
992 Enable intel iommu driver.
993 off
994 Disable intel iommu driver.
995 igfx_off [Default Off]
996 By default, gfx is mapped as normal device. If a gfx
997 device has a dedicated DMAR unit, the DMAR unit is
998 bypassed by not enabling DMAR with this option. In
999 this case, gfx device will use physical address for
1000 DMA.
1001 forcedac [x86_64]
1002 With this option iommu will not optimize to look
1003 for io virtual address below 32-bit forcing dual
1004 address cycle on pci bus for cards supporting greater
1005 than 32-bit addressing. The default is to look
1006 for translation below 32-bit and if not available
1007 then look in the higher range.
1008 strict [Default Off]
1009 With this option on every unmap_single operation will
1010 result in a hardware IOTLB flush operation as opposed
1011 to batching them for performance.
1012 sp_off [Default Off]
1013 By default, super page will be supported if Intel IOMMU
1014 has the capability. With this option, super page will
1015 not be supported.
1016 intremap= [X86-64, Intel-IOMMU]
1017 Format: { on (default) | off | nosid }
1018 on enable Interrupt Remapping (default)
1019 off disable Interrupt Remapping
1020 nosid disable Source ID checking
1022 inttest= [IA-64]
1024 iomem= Disable strict checking of access to MMIO memory
1025 strict regions from userspace.
1026 relaxed
1028 iommu= [x86]
1029 off
1030 force
1031 noforce
1032 biomerge
1033 panic
1034 nopanic
1035 merge
1036 nomerge
1037 forcesac
1038 soft
1039 pt [x86, IA-64]
1041 io7= [HW] IO7 for Marvel based alpha systems
1042 See comment before marvel_specify_io7 in
1043 arch/alpha/kernel/core_marvel.c.
1045 io_delay= [X86] I/O delay method
1046 0x80
1047 Standard port 0x80 based delay
1048 0xed
1049 Alternate port 0xed based delay (needed on some systems)
1050 udelay
1051 Simple two microseconds delay
1052 none
1053 No delay
1055 ip= [IP_PNP]
1056 See Documentation/filesystems/nfs/nfsroot.txt.
1058 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1059 See comment before ip2_setup() in
1060 drivers/char/ip2/ip2base.c.
1062 irqfixup [HW]
1063 When an interrupt is not handled search all handlers
1064 for it. Intended to get systems with badly broken
1065 firmware running.
1067 irqpoll [HW]
1068 When an interrupt is not handled search all handlers
1069 for it. Also check all handlers each timer
1070 interrupt. Intended to get systems with badly broken
1071 firmware running.
1073 isapnp= [ISAPNP]
1074 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1076 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1077 Format:
1078 <cpu number>,...,<cpu number>
1079 or
1080 <cpu number>-<cpu number>
1081 (must be a positive range in ascending order)
1082 or a mixture
1083 <cpu number>,...,<cpu number>-<cpu number>
1085 This option can be used to specify one or more CPUs
1086 to isolate from the general SMP balancing and scheduling
1087 algorithms. You can move a process onto or off an
1088 "isolated" CPU via the CPU affinity syscalls or cpuset.
1089 <cpu number> begins at 0 and the maximum value is
1090 "number of CPUs in system - 1".
1092 This option is the preferred way to isolate CPUs. The
1093 alternative -- manually setting the CPU mask of all
1094 tasks in the system -- can cause problems and
1095 suboptimal load balancer performance.
1097 iucv= [HW,NET]
1099 js= [HW,JOY] Analog joystick
1100 See Documentation/input/joystick.txt.
1102 keepinitrd [HW,ARM]
1104 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1105 specifies the amount of memory usable by the kernel
1106 for non-movable allocations. The requested amount is
1107 spread evenly throughout all nodes in the system. The
1108 remaining memory in each node is used for Movable
1109 pages. In the event, a node is too small to have both
1110 kernelcore and Movable pages, kernelcore pages will
1111 take priority and other nodes will have a larger number
1112 of kernelcore pages. The Movable zone is used for the
1113 allocation of pages that may be reclaimed or moved
1114 by the page migration subsystem. This means that
1115 HugeTLB pages may not be allocated from this zone.
1116 Note that allocations like PTEs-from-HighMem still
1117 use the HighMem zone if it exists, and the Normal
1118 zone if it does not.
1120 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1121 Format: <Controller#>[,poll interval]
1122 The controller # is the number of the ehci usb debug
1123 port as it is probed via PCI. The poll interval is
1124 optional and is the number seconds in between
1125 each poll cycle to the debug port in case you need
1126 the functionality for interrupting the kernel with
1127 gdb or control-c on the dbgp connection. When
1128 not using this parameter you use sysrq-g to break into
1129 the kernel debugger.
1131 kgdboc= [KGDB,HW] kgdb over consoles.
1132 Requires a tty driver that supports console polling,
1133 or a supported polling keyboard driver (non-usb).
1134 Serial only format: <serial_device>[,baud]
1135 keyboard only format: kbd
1136 keyboard and serial format: kbd,<serial_device>[,baud]
1137 Optional Kernel mode setting:
1138 kms, kbd format: kms,kbd
1139 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1141 kgdbwait [KGDB] Stop kernel execution and enter the
1142 kernel debugger at the earliest opportunity.
1144 kmac= [MIPS] korina ethernet MAC address.
1145 Configure the RouterBoard 532 series on-chip
1146 Ethernet adapter MAC address.
1148 kmemleak= [KNL] Boot-time kmemleak enable/disable
1149 Valid arguments: on, off
1150 Default: on
1152 kstack=N [X86] Print N words from the kernel stack
1153 in oops dumps.
1155 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1156 Default is 0 (don't ignore, but inject #GP)
1158 kvm.oos_shadow= [KVM] Disable out-of-sync shadow paging.
1159 Default is 1 (enabled)
1161 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1162 KVM MMU at runtime.
1163 Default is 0 (off)
1165 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1166 Default is 1 (enabled)
1168 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1169 for all guests.
1170 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1172 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1173 (virtualized MMU) support on capable Intel chips.
1174 Default is 1 (enabled)
1176 kvm-intel.emulate_invalid_guest_state=
1177 [KVM,Intel] Enable emulation of invalid guest states
1178 Default is 0 (disabled)
1180 kvm-intel.flexpriority=
1181 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1182 Default is 1 (enabled)
1184 kvm-intel.unrestricted_guest=
1185 [KVM,Intel] Disable unrestricted guest feature
1186 (virtualized real and unpaged mode) on capable
1187 Intel chips. Default is 1 (enabled)
1189 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1190 feature (tagged TLBs) on capable Intel chips.
1191 Default is 1 (enabled)
1193 l2cr= [PPC]
1195 l3cr= [PPC]
1197 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1198 disabled it.
1200 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1201 in C2 power state.
1203 libata.dma= [LIBATA] DMA control
1204 libata.dma=0 Disable all PATA and SATA DMA
1205 libata.dma=1 PATA and SATA Disk DMA only
1206 libata.dma=2 ATAPI (CDROM) DMA only
1207 libata.dma=4 Compact Flash DMA only
1208 Combinations also work, so libata.dma=3 enables DMA
1209 for disks and CDROMs, but not CFs.
1211 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1212 libata.ignore_hpa=0 keep BIOS limits (default)
1213 libata.ignore_hpa=1 ignore limits, using full disk
1215 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1216 when set.
1217 Format: <int>
1219 libata.force= [LIBATA] Force configurations. The format is comma
1220 separated list of "[ID:]VAL" where ID is
1221 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1222 matching port, link or device. Basically, it matches
1223 the ATA ID string printed on console by libata. If
1224 the whole ID part is omitted, the last PORT and DEVICE
1225 values are used. If ID hasn't been specified yet, the
1226 configuration applies to all ports, links and devices.
1228 If only DEVICE is omitted, the parameter applies to
1229 the port and all links and devices behind it. DEVICE
1230 number of 0 either selects the first device or the
1231 first fan-out link behind PMP device. It does not
1232 select the host link. DEVICE number of 15 selects the
1233 host link and device attached to it.
1235 The VAL specifies the configuration to force. As long
1236 as there's no ambiguity shortcut notation is allowed.
1237 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1238 The following configurations can be forced.
1240 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1241 Any ID with matching PORT is used.
1243 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1245 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1246 udma[/][16,25,33,44,66,100,133] notation is also
1247 allowed.
1249 * [no]ncq: Turn on or off NCQ.
1251 * nohrst, nosrst, norst: suppress hard, soft
1252 and both resets.
1254 * dump_id: dump IDENTIFY data.
1256 If there are multiple matching configurations changing
1257 the same attribute, the last one is used.
1259 memblock=debug [KNL] Enable memblock debug messages.
1261 load_ramdisk= [RAM] List of ramdisks to load from floppy
1262 See Documentation/blockdev/ramdisk.txt.
1264 lockd.nlm_grace_period=P [NFS] Assign grace period.
1265 Format: <integer>
1267 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1268 Format: <integer>
1270 lockd.nlm_timeout=T [NFS] Assign timeout value.
1271 Format: <integer>
1273 lockd.nlm_udpport=M [NFS] Assign UDP port.
1274 Format: <integer>
1276 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1277 Format: <irq>
1279 loglevel= All Kernel Messages with a loglevel smaller than the
1280 console loglevel will be printed to the console. It can
1281 also be changed with klogd or other programs. The
1282 loglevels are defined as follows:
1284 0 (KERN_EMERG) system is unusable
1285 1 (KERN_ALERT) action must be taken immediately
1286 2 (KERN_CRIT) critical conditions
1287 3 (KERN_ERR) error conditions
1288 4 (KERN_WARNING) warning conditions
1289 5 (KERN_NOTICE) normal but significant condition
1290 6 (KERN_INFO) informational
1291 7 (KERN_DEBUG) debug-level messages
1293 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1294 in bytes. n must be a power of two. The default
1295 size is set in the kernel config file.
1297 logo.nologo [FB] Disables display of the built-in Linux logo.
1298 This may be used to provide more screen space for
1299 kernel log messages and is useful when debugging
1300 kernel boot problems.
1302 lp=0 [LP] Specify parallel ports to use, e.g,
1303 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1304 lp=reset first parallel port). 'lp=0' disables the
1305 lp=auto printer driver. 'lp=reset' (which can be
1306 specified in addition to the ports) causes
1307 attached printers to be reset. Using
1308 lp=port1,port2,... specifies the parallel ports
1309 to associate lp devices with, starting with
1310 lp0. A port specification may be 'none' to skip
1311 that lp device, or a parport name such as
1312 'parport0'. Specifying 'lp=auto' instead of a
1313 port specification list means that device IDs
1314 from each port should be examined, to see if
1315 an IEEE 1284-compliant printer is attached; if
1316 so, the driver will manage that printer.
1317 See also header of drivers/char/lp.c.
1319 lpj=n [KNL]
1320 Sets loops_per_jiffy to given constant, thus avoiding
1321 time-consuming boot-time autodetection (up to 250 ms per
1322 CPU). 0 enables autodetection (default). To determine
1323 the correct value for your kernel, boot with normal
1324 autodetection and see what value is printed. Note that
1325 on SMP systems the preset will be applied to all CPUs,
1326 which is likely to cause problems if your CPUs need
1327 significantly divergent settings. An incorrect value
1328 will cause delays in the kernel to be wrong, leading to
1329 unpredictable I/O errors and other breakage. Although
1330 unlikely, in the extreme case this might damage your
1331 hardware.
1333 ltpc= [NET]
1334 Format: <io>,<irq>,<dma>
1336 machvec= [IA-64] Force the use of a particular machine-vector
1337 (machvec) in a generic kernel.
1338 Example: machvec=hpzx1_swiotlb
1340 machtype= [Loongson] Share the same kernel image file between different
1341 yeeloong laptop.
1342 Example: machtype=lemote-yeeloong-2f-7inch
1344 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1345 than or equal to this physical address is ignored.
1347 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1348 should make use of. maxcpus=n : n >= 0 limits the
1349 kernel to using 'n' processors. n=0 is a special case,
1350 it is equivalent to "nosmp", which also disables
1351 the IO APIC.
1353 max_loop= [LOOP] The number of loop block devices that get
1354 (loop.max_loop) unconditionally pre-created at init time. The default
1355 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1356 of statically allocating a predefined number, loop
1357 devices can be requested on-demand with the
1358 /dev/loop-control interface.
1360 mcatest= [IA-64]
1362 mce [X86-32] Machine Check Exception
1364 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1366 md= [HW] RAID subsystems devices and level
1367 See Documentation/md.txt.
1369 mdacon= [MDA]
1370 Format: <first>,<last>
1371 Specifies range of consoles to be captured by the MDA.
1373 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1374 Amount of memory to be used when the kernel is not able
1375 to see the whole system memory or for test.
1376 [X86-32] Use together with memmap= to avoid physical
1377 address space collisions. Without memmap= PCI devices
1378 could be placed at addresses belonging to unused RAM.
1380 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1381 memory.
1383 memchunk=nn[KMG]
1384 [KNL,SH] Allow user to override the default size for
1385 per-device physically contiguous DMA buffers.
1387 memmap=exactmap [KNL,X86] Enable setting of an exact
1388 E820 memory map, as specified by the user.
1389 Such memmap=exactmap lines can be constructed based on
1390 BIOS output or other requirements. See the memmap=nn@ss
1391 option description.
1393 memmap=nn[KMG]@ss[KMG]
1394 [KNL] Force usage of a specific region of memory
1395 Region of memory to be used, from ss to ss+nn.
1397 memmap=nn[KMG]#ss[KMG]
1398 [KNL,ACPI] Mark specific memory as ACPI data.
1399 Region of memory to be used, from ss to ss+nn.
1401 memmap=nn[KMG]$ss[KMG]
1402 [KNL,ACPI] Mark specific memory as reserved.
1403 Region of memory to be used, from ss to ss+nn.
1404 Example: Exclude memory from 0x18690000-0x1869ffff
1405 memmap=64K$0x18690000
1406 or
1407 memmap=0x10000$0x18690000
1409 memory_corruption_check=0/1 [X86]
1410 Some BIOSes seem to corrupt the first 64k of
1411 memory when doing things like suspend/resume.
1412 Setting this option will scan the memory
1413 looking for corruption. Enabling this will
1414 both detect corruption and prevent the kernel
1415 from using the memory being corrupted.
1416 However, its intended as a diagnostic tool; if
1417 repeatable BIOS-originated corruption always
1418 affects the same memory, you can use memmap=
1419 to prevent the kernel from using that memory.
1421 memory_corruption_check_size=size [X86]
1422 By default it checks for corruption in the low
1423 64k, making this memory unavailable for normal
1424 use. Use this parameter to scan for
1425 corruption in more or less memory.
1427 memory_corruption_check_period=seconds [X86]
1428 By default it checks for corruption every 60
1429 seconds. Use this parameter to check at some
1430 other rate. 0 disables periodic checking.
1432 memtest= [KNL,X86] Enable memtest
1433 Format: <integer>
1434 default : 0 <disable>
1435 Specifies the number of memtest passes to be
1436 performed. Each pass selects another test
1437 pattern from a given set of patterns. Memtest
1438 fills the memory with this pattern, validates
1439 memory contents and reserves bad memory
1440 regions that are detected.
1442 meye.*= [HW] Set MotionEye Camera parameters
1443 See Documentation/video4linux/meye.txt.
1445 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1446 Multi-Function General Purpose Timers on AMD Geode
1447 platforms.
1449 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1450 the BIOS has incorrectly applied a workaround. TinyBIOS
1451 version 0.98 is known to be affected, 0.99 fixes the
1452 problem by letting the user disable the workaround.
1454 mga= [HW,DRM]
1456 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1457 physical address is ignored.
1459 mini2440= [ARM,HW,KNL]
1460 Format:[0..2][b][c][t]
1461 Default: "0tb"
1462 MINI2440 configuration specification:
1463 0 - The attached screen is the 3.5" TFT
1464 1 - The attached screen is the 7" TFT
1465 2 - The VGA Shield is attached (1024x768)
1466 Leaving out the screen size parameter will not load
1467 the TFT driver, and the framebuffer will be left
1468 unconfigured.
1469 b - Enable backlight. The TFT backlight pin will be
1470 linked to the kernel VESA blanking code and a GPIO
1471 LED. This parameter is not necessary when using the
1472 VGA shield.
1473 c - Enable the s3c camera interface.
1474 t - Reserved for enabling touchscreen support. The
1475 touchscreen support is not enabled in the mainstream
1476 kernel as of 2.6.30, a preliminary port can be found
1477 in the "bleeding edge" mini2440 support kernel at
1478 http://repo.or.cz/w/linux-2.6/mini2440.git
1480 mminit_loglevel=
1481 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1482 parameter allows control of the logging verbosity for
1483 the additional memory initialisation checks. A value
1484 of 0 disables mminit logging and a level of 4 will
1485 log everything. Information is printed at KERN_DEBUG
1486 so loglevel=8 may also need to be specified.
1488 mousedev.tap_time=
1489 [MOUSE] Maximum time between finger touching and
1490 leaving touchpad surface for touch to be considered
1491 a tap and be reported as a left button click (for
1492 touchpads working in absolute mode only).
1493 Format: <msecs>
1494 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1495 reporting absolute coordinates, such as tablets
1496 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1497 reporting absolute coordinates, such as tablets
1499 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1500 is similar to kernelcore except it specifies the
1501 amount of memory used for migratable allocations.
1502 If both kernelcore and movablecore is specified,
1503 then kernelcore will be at *least* the specified
1504 value but may be more. If movablecore on its own
1505 is specified, the administrator must be careful
1506 that the amount of memory usable for all allocations
1507 is not too small.
1509 MTD_Partition= [MTD]
1510 Format: <name>,<region-number>,<size>,<offset>
1512 MTD_Region= [MTD] Format:
1513 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1515 mtdparts= [MTD]
1516 See drivers/mtd/cmdlinepart.c.
1518 multitce=off [PPC] This parameter disables the use of the pSeries
1519 firmware feature for updating multiple TCE entries
1520 at a time.
1522 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1524 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1526 boundary - index of last SLC block on Flex-OneNAND.
1527 The remaining blocks are configured as MLC blocks.
1528 lock - Configure if Flex-OneNAND boundary should be locked.
1529 Once locked, the boundary cannot be changed.
1530 1 indicates lock status, 0 indicates unlock status.
1532 mtdset= [ARM]
1533 ARM/S3C2412 JIVE boot control
1535 See arch/arm/mach-s3c2412/mach-jive.c
1537 mtouchusb.raw_coordinates=
1538 [HW] Make the MicroTouch USB driver use raw coordinates
1539 ('y', default) or cooked coordinates ('n')
1541 mtrr_chunk_size=nn[KMG] [X86]
1542 used for mtrr cleanup. It is largest continuous chunk
1543 that could hold holes aka. UC entries.
1545 mtrr_gran_size=nn[KMG] [X86]
1546 Used for mtrr cleanup. It is granularity of mtrr block.
1547 Default is 1.
1548 Large value could prevent small alignment from
1549 using up MTRRs.
1551 mtrr_spare_reg_nr=n [X86]
1552 Format: <integer>
1553 Range: 0,7 : spare reg number
1554 Default : 1
1555 Used for mtrr cleanup. It is spare mtrr entries number.
1556 Set to 2 or more if your graphical card needs more.
1558 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1560 netdev= [NET] Network devices parameters
1561 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1562 Note that mem_start is often overloaded to mean
1563 something different and driver-specific.
1564 This usage is only documented in each driver source
1565 file if at all.
1567 nf_conntrack.acct=
1568 [NETFILTER] Enable connection tracking flow accounting
1569 0 to disable accounting
1570 1 to enable accounting
1571 Default value is 0.
1573 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1574 See Documentation/filesystems/nfs/nfsroot.txt.
1576 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1577 See Documentation/filesystems/nfs/nfsroot.txt.
1579 nfsrootdebug [NFS] enable nfsroot debugging messages.
1580 See Documentation/filesystems/nfs/nfsroot.txt.
1582 nfs.callback_tcpport=
1583 [NFS] set the TCP port on which the NFSv4 callback
1584 channel should listen.
1586 nfs.cache_getent=
1587 [NFS] sets the pathname to the program which is used
1588 to update the NFS client cache entries.
1590 nfs.cache_getent_timeout=
1591 [NFS] sets the timeout after which an attempt to
1592 update a cache entry is deemed to have failed.
1594 nfs.idmap_cache_timeout=
1595 [NFS] set the maximum lifetime for idmapper cache
1596 entries.
1598 nfs.enable_ino64=
1599 [NFS] enable 64-bit inode numbers.
1600 If zero, the NFS client will fake up a 32-bit inode
1601 number for the readdir() and stat() syscalls instead
1602 of returning the full 64-bit number.
1603 The default is to return 64-bit inode numbers.
1605 nfs.nfs4_disable_idmapping=
1606 [NFSv4] When set, this option disables the NFSv4
1607 idmapper on the client, but only if the mount
1608 is using the 'sec=sys' security flavour. This may
1609 make migration from legacy NFSv2/v3 systems easier
1610 provided that the server has the appropriate support.
1611 The default is to always enable NFSv4 idmapping.
1613 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1614 when a NMI is triggered.
1615 Format: [state][,regs][,debounce][,die]
1617 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1618 Format: [panic,][nopanic,][num]
1619 Valid num: 0
1620 0 - turn nmi_watchdog off
1621 When panic is specified, panic when an NMI watchdog
1622 timeout occurs (or 'nopanic' to override the opposite
1623 default).
1624 This is useful when you use a panic=... timeout and
1625 need the box quickly up again.
1627 netpoll.carrier_timeout=
1628 [NET] Specifies amount of time (in seconds) that
1629 netpoll should wait for a carrier. By default netpoll
1630 waits 4 seconds.
1632 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1633 emulation library even if a 387 maths coprocessor
1634 is present.
1636 no_console_suspend
1637 [HW] Never suspend the console
1638 Disable suspending of consoles during suspend and
1639 hibernate operations. Once disabled, debugging
1640 messages can reach various consoles while the rest
1641 of the system is being put to sleep (ie, while
1642 debugging driver suspend/resume hooks). This may
1643 not work reliably with all consoles, but is known
1644 to work with serial and VGA consoles.
1646 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1647 caches in the slab allocator. Saves per-node memory,
1648 but will impact performance.
1650 noalign [KNL,ARM]
1652 noapic [SMP,APIC] Tells the kernel to not make use of any
1653 IOAPICs that may be present in the system.
1655 noautogroup Disable scheduler automatic task group creation.
1657 nobats [PPC] Do not use BATs for mapping kernel lowmem
1658 on "Classic" PPC cores.
1660 nocache [ARM]
1662 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1664 nodelayacct [KNL] Disable per-task delay accounting
1666 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1668 nodsp [SH] Disable hardware DSP at boot time.
1670 noefi [X86] Disable EFI runtime services support.
1672 noexec [IA-64]
1674 noexec [X86]
1675 On X86-32 available only on PAE configured kernels.
1676 noexec=on: enable non-executable mappings (default)
1677 noexec=off: disable non-executable mappings
1679 nosmep [X86]
1680 Disable SMEP (Supervisor Mode Execution Protection)
1681 even if it is supported by processor.
1683 noexec32 [X86-64]
1684 This affects only 32-bit executables.
1685 noexec32=on: enable non-executable mappings (default)
1686 read doesn't imply executable mappings
1687 noexec32=off: disable non-executable mappings
1688 read implies executable mappings
1690 nofpu [SH] Disable hardware FPU at boot time.
1692 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1693 register save and restore. The kernel will only save
1694 legacy floating-point registers on task switch.
1696 noxsave [BUGS=X86] Disables x86 extended register state save
1697 and restore using xsave. The kernel will fallback to
1698 enabling legacy floating-point and sse state.
1700 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1701 wfi(ARM) instruction doesn't work correctly and not to
1702 use it. This is also useful when using JTAG debugger.
1704 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1705 instruction doesn't work correctly and not to
1706 use it.
1708 no_file_caps Tells the kernel not to honor file capabilities. The
1709 only way then for a file to be executed with privilege
1710 is to be setuid root or executed by root.
1712 nohalt [IA-64] Tells the kernel not to use the power saving
1713 function PAL_HALT_LIGHT when idle. This increases
1714 power-consumption. On the positive side, it reduces
1715 interrupt wake-up latency, which may improve performance
1716 in certain environments such as networked servers or
1717 real-time systems.
1719 nohz= [KNL] Boottime enable/disable dynamic ticks
1720 Valid arguments: on, off
1721 Default: on
1723 noiotrap [SH] Disables trapped I/O port accesses.
1725 noirqdebug [X86-32] Disables the code which attempts to detect and
1726 disable unhandled interrupt sources.
1728 no_timer_check [X86,APIC] Disables the code which tests for
1729 broken timer IRQ sources.
1731 noisapnp [ISAPNP] Disables ISA PnP code.
1733 noinitrd [RAM] Tells the kernel not to load any configured
1734 initial RAM disk.
1736 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1737 remapping.
1738 [Deprecated - use intremap=off]
1740 nointroute [IA-64]
1742 nojitter [IA-64] Disables jitter checking for ITC timers.
1744 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1746 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1747 fault handling.
1749 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1750 steal time is computed, but won't influence scheduler
1751 behaviour
1753 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1755 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1757 noltlbs [PPC] Do not use large page/tlb entries for kernel
1758 lowmem mapping on PPC40x.
1760 nomca [IA-64] Disable machine check abort handling
1762 nomce [X86-32] Machine Check Exception
1764 nomfgpt [X86-32] Disable Multi-Function General Purpose
1765 Timer usage (for AMD Geode machines).
1767 nopat [X86] Disable PAT (page attribute table extension of
1768 pagetables) support.
1770 norandmaps Don't use address space randomization. Equivalent to
1771 echo 0 > /proc/sys/kernel/randomize_va_space
1773 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1775 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1776 with UP alternatives
1778 noresidual [PPC] Don't use residual data on PReP machines.
1780 noresume [SWSUSP] Disables resume and restores original swap
1781 space.
1783 no-scroll [VGA] Disables scrollback.
1784 This is required for the Braillex ib80-piezo Braille
1785 reader made by F.H. Papenmeier (Germany).
1787 nosbagart [IA-64]
1789 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1791 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1792 and disable the IO APIC. legacy for "maxcpus=0".
1794 nosoftlockup [KNL] Disable the soft-lockup detector.
1796 nosync [HW,M68K] Disables sync negotiation for all devices.
1798 notsc [BUGS=X86-32] Disable Time Stamp Counter
1800 nousb [USB] Disable the USB subsystem
1802 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1804 nowb [ARM]
1806 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1808 nptcg= [IA-64] Override max number of concurrent global TLB
1809 purges which is reported from either PAL_VM_SUMMARY or
1810 SAL PALO.
1812 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1813 could support. nr_cpus=n : n >= 1 limits the kernel to
1814 supporting 'n' processors. Later in runtime you can not
1815 use hotplug cpu feature to put more cpu back to online.
1816 just like you compile the kernel NR_CPUS=n
1818 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1820 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1821 one of ['zone', 'node', 'default'] can be specified
1822 This can be set from sysctl after boot.
1823 See Documentation/sysctl/vm.txt for details.
1825 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1826 See Documentation/debugging-via-ohci1394.txt for more
1827 info.
1829 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1830 Rather than timing out after 20 ms if an EC
1831 command is not properly ACKed, override the length
1832 of the timeout. We have interrupts disabled while
1833 waiting for the ACK, so if this is set too high
1834 interrupts *may* be lost!
1836 omap_mux= [OMAP] Override bootloader pin multiplexing.
1837 Format: <mux_mode0.mode_name=value>...
1838 For example, to override I2C bus2:
1839 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1841 oprofile.timer= [HW]
1842 Use timer interrupt instead of performance counters
1844 oprofile.cpu_type= Force an oprofile cpu type
1845 This might be useful if you have an older oprofile
1846 userland or if you want common events.
1847 Format: { arch_perfmon }
1848 arch_perfmon: [X86] Force use of architectural
1849 perfmon on Intel CPUs instead of the
1850 CPU specific event set.
1852 oops=panic Always panic on oopses. Default is to just kill the
1853 process, but there is a small probability of
1854 deadlocking the machine.
1855 This will also cause panics on machine check exceptions.
1856 Useful together with panic=30 to trigger a reboot.
1858 OSS [HW,OSS]
1859 See Documentation/sound/oss/oss-parameters.txt
1861 panic= [KNL] Kernel behaviour on panic: delay <timeout>
1862 timeout > 0: seconds before rebooting
1863 timeout = 0: wait forever
1864 timeout < 0: reboot immediately
1865 Format: <timeout>
1867 parkbd.port= [HW] Parallel port number the keyboard adapter is
1868 connected to, default is 0.
1869 Format: <parport#>
1870 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1871 0 for XT, 1 for AT (default is AT).
1872 Format: <mode>
1874 parport= [HW,PPT] Specify parallel ports. 0 disables.
1875 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1876 Use 'auto' to force the driver to use any
1877 IRQ/DMA settings detected (the default is to
1878 ignore detected IRQ/DMA settings because of
1879 possible conflicts). You can specify the base
1880 address, IRQ, and DMA settings; IRQ and DMA
1881 should be numbers, or 'auto' (for using detected
1882 settings on that particular port), or 'nofifo'
1883 (to avoid using a FIFO even if it is detected).
1884 Parallel ports are assigned in the order they
1885 are specified on the command line, starting
1886 with parport0.
1888 parport_init_mode= [HW,PPT]
1889 Configure VIA parallel port to operate in
1890 a specific mode. This is necessary on Pegasos
1891 computer where firmware has no options for setting
1892 up parallel port mode and sets it to spp.
1893 Currently this function knows 686a and 8231 chips.
1894 Format: [spp|ps2|epp|ecp|ecpepp]
1896 pause_on_oops=
1897 Halt all CPUs after the first oops has been printed for
1898 the specified number of seconds. This is to be used if
1899 your oopses keep scrolling off the screen.
1901 pcbit= [HW,ISDN]
1903 pcd. [PARIDE]
1904 See header of drivers/block/paride/pcd.c.
1905 See also Documentation/blockdev/paride.txt.
1907 pci=option[,option...] [PCI] various PCI subsystem options:
1908 earlydump [X86] dump PCI config space before the kernel
1909 changes anything
1910 off [X86] don't probe for the PCI bus
1911 bios [X86-32] force use of PCI BIOS, don't access
1912 the hardware directly. Use this if your machine
1913 has a non-standard PCI host bridge.
1914 nobios [X86-32] disallow use of PCI BIOS, only direct
1915 hardware access methods are allowed. Use this
1916 if you experience crashes upon bootup and you
1917 suspect they are caused by the BIOS.
1918 conf1 [X86] Force use of PCI Configuration
1919 Mechanism 1.
1920 conf2 [X86] Force use of PCI Configuration
1921 Mechanism 2.
1922 noaer [PCIE] If the PCIEAER kernel config parameter is
1923 enabled, this kernel boot option can be used to
1924 disable the use of PCIE advanced error reporting.
1925 nodomains [PCI] Disable support for multiple PCI
1926 root domains (aka PCI segments, in ACPI-speak).
1927 nommconf [X86] Disable use of MMCONFIG for PCI
1928 Configuration
1929 check_enable_amd_mmconf [X86] check for and enable
1930 properly configured MMIO access to PCI
1931 config space on AMD family 10h CPU
1932 nomsi [MSI] If the PCI_MSI kernel config parameter is
1933 enabled, this kernel boot option can be used to
1934 disable the use of MSI interrupts system-wide.
1935 noioapicquirk [APIC] Disable all boot interrupt quirks.
1936 Safety option to keep boot IRQs enabled. This
1937 should never be necessary.
1938 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
1939 primary IO-APIC for bridges that cannot disable
1940 boot IRQs. This fixes a source of spurious IRQs
1941 when the system masks IRQs.
1942 noioapicreroute [APIC] Disable workaround that uses the
1943 boot IRQ equivalent of an IRQ that connects to
1944 a chipset where boot IRQs cannot be disabled.
1945 The opposite of ioapicreroute.
1946 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
1947 routing table. These calls are known to be buggy
1948 on several machines and they hang the machine
1949 when used, but on other computers it's the only
1950 way to get the interrupt routing table. Try
1951 this option if the kernel is unable to allocate
1952 IRQs or discover secondary PCI buses on your
1953 motherboard.
1954 rom [X86] Assign address space to expansion ROMs.
1955 Use with caution as certain devices share
1956 address decoders between ROMs and other
1957 resources.
1958 norom [X86] Do not assign address space to
1959 expansion ROMs that do not already have
1960 BIOS assigned address ranges.
1961 nobar [X86] Do not assign address space to the
1962 BARs that weren't assigned by the BIOS.
1963 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
1964 assigned automatically to PCI devices. You can
1965 make the kernel exclude IRQs of your ISA cards
1966 this way.
1967 pirqaddr=0xAAAAA [X86] Specify the physical address
1968 of the PIRQ table (normally generated
1969 by the BIOS) if it is outside the
1970 F0000h-100000h range.
1971 lastbus=N [X86] Scan all buses thru bus #N. Can be
1972 useful if the kernel is unable to find your
1973 secondary buses and you want to tell it
1974 explicitly which ones they are.
1975 assign-busses [X86] Always assign all PCI bus
1976 numbers ourselves, overriding
1977 whatever the firmware may have done.
1978 usepirqmask [X86] Honor the possible IRQ mask stored
1979 in the BIOS $PIR table. This is needed on
1980 some systems with broken BIOSes, notably
1981 some HP Pavilion N5400 and Omnibook XE3
1982 notebooks. This will have no effect if ACPI
1983 IRQ routing is enabled.
1984 noacpi [X86] Do not use ACPI for IRQ routing
1985 or for PCI scanning.
1986 use_crs [X86] Use PCI host bridge window information
1987 from ACPI. On BIOSes from 2008 or later, this
1988 is enabled by default. If you need to use this,
1989 please report a bug.
1990 nocrs [X86] Ignore PCI host bridge windows from ACPI.
1991 If you need to use this, please report a bug.
1992 routeirq Do IRQ routing for all PCI devices.
1993 This is normally done in pci_enable_device(),
1994 so this option is a temporary workaround
1995 for broken drivers that don't call it.
1996 skip_isa_align [X86] do not align io start addr, so can
1997 handle more pci cards
1998 firmware [ARM] Do not re-enumerate the bus but instead
1999 just use the configuration from the
2000 bootloader. This is currently used on
2001 IXP2000 systems where the bus has to be
2002 configured a certain way for adjunct CPUs.
2003 noearly [X86] Don't do any early type 1 scanning.
2004 This might help on some broken boards which
2005 machine check when some devices' config space
2006 is read. But various workarounds are disabled
2007 and some IOMMU drivers will not work.
2008 bfsort Sort PCI devices into breadth-first order.
2009 This sorting is done to get a device
2010 order compatible with older (<= 2.4) kernels.
2011 nobfsort Don't sort PCI devices into breadth-first order.
2012 cbiosize=nn[KMG] The fixed amount of bus space which is
2013 reserved for the CardBus bridge's IO window.
2014 The default value is 256 bytes.
2015 cbmemsize=nn[KMG] The fixed amount of bus space which is
2016 reserved for the CardBus bridge's memory
2017 window. The default value is 64 megabytes.
2018 resource_alignment=
2019 Format:
2020 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2021 Specifies alignment and device to reassign
2022 aligned memory resources.
2023 If <order of align> is not specified,
2024 PAGE_SIZE is used as alignment.
2025 PCI-PCI bridge can be specified, if resource
2026 windows need to be expanded.
2027 ecrc= Enable/disable PCIe ECRC (transaction layer
2028 end-to-end CRC checking).
2029 bios: Use BIOS/firmware settings. This is the
2030 the default.
2031 off: Turn ECRC off
2032 on: Turn ECRC on.
2033 realloc reallocate PCI resources if allocations done by BIOS
2034 are erroneous.
2036 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2037 Management.
2038 off Disable ASPM.
2039 force Enable ASPM even on devices that claim not to support it.
2040 WARNING: Forcing ASPM on may cause system lockups.
2042 pcie_ports= [PCIE] PCIe ports handling:
2043 auto Ask the BIOS whether or not to use native PCIe services
2044 associated with PCIe ports (PME, hot-plug, AER). Use
2045 them only if that is allowed by the BIOS.
2046 native Use native PCIe services associated with PCIe ports
2047 unconditionally.
2048 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2049 ports driver.
2051 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2052 nomsi Do not use MSI for native PCIe PME signaling (this makes
2053 all PCIe root ports use INTx for all services).
2055 pcmv= [HW,PCMCIA] BadgePAD 4
2057 pd. [PARIDE]
2058 See Documentation/blockdev/paride.txt.
2060 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2061 boot time.
2062 Format: { 0 | 1 }
2063 See arch/parisc/kernel/pdc_chassis.c
2065 percpu_alloc= Select which percpu first chunk allocator to use.
2066 Currently supported values are "embed" and "page".
2067 Archs may support subset or none of the selections.
2068 See comments in mm/percpu.c for details on each
2069 allocator. This parameter is primarily for debugging
2070 and performance comparison.
2072 pf. [PARIDE]
2073 See Documentation/blockdev/paride.txt.
2075 pg. [PARIDE]
2076 See Documentation/blockdev/paride.txt.
2078 pirq= [SMP,APIC] Manual mp-table setup
2079 See Documentation/x86/i386/IO-APIC.txt.
2081 plip= [PPT,NET] Parallel port network link
2082 Format: { parport<nr> | timid | 0 }
2083 See also Documentation/parport.txt.
2085 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2086 Override pmtimer IOPort with a hex value.
2087 e.g. pmtmr=0x508
2089 pnp.debug [PNP]
2090 Enable PNP debug messages. This depends on the
2091 CONFIG_PNP_DEBUG_MESSAGES option.
2093 pnpacpi= [ACPI]
2094 { off }
2096 pnpbios= [ISAPNP]
2097 { on | off | curr | res | no-curr | no-res }
2099 pnp_reserve_irq=
2100 [ISAPNP] Exclude IRQs for the autoconfiguration
2102 pnp_reserve_dma=
2103 [ISAPNP] Exclude DMAs for the autoconfiguration
2105 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2106 Ranges are in pairs (I/O port base and size).
2108 pnp_reserve_mem=
2109 [ISAPNP] Exclude memory regions for the
2110 autoconfiguration.
2111 Ranges are in pairs (memory base and size).
2113 ports= [IP_VS_FTP] IPVS ftp helper module
2114 Default is 21.
2115 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2116 may be specified.
2117 Format: <port>,<port>....
2119 print-fatal-signals=
2120 [KNL] debug: print fatal signals
2122 If enabled, warn about various signal handling
2123 related application anomalies: too many signals,
2124 too many POSIX.1 timers, fatal signals causing a
2125 coredump - etc.
2127 If you hit the warning due to signal overflow,
2128 you might want to try "ulimit -i unlimited".
2130 default: off.
2132 printk.time= Show timing data prefixed to each printk message line
2133 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2135 processor.max_cstate= [HW,ACPI]
2136 Limit processor to maximum C-state
2137 max_cstate=9 overrides any DMI blacklist limit.
2139 processor.nocst [HW,ACPI]
2140 Ignore the _CST method to determine C-states,
2141 instead using the legacy FADT method
2143 profile= [KNL] Enable kernel profiling via /proc/profile
2144 Format: [schedule,]<number>
2145 Param: "schedule" - profile schedule points.
2146 Param: <number> - step/bucket size as a power of 2 for
2147 statistical time based profiling.
2148 Param: "sleep" - profile D-state sleeping (millisecs).
2149 Requires CONFIG_SCHEDSTATS
2150 Param: "kvm" - profile VM exits.
2152 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2153 before loading.
2154 See Documentation/blockdev/ramdisk.txt.
2156 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2157 probe for; one of (bare|imps|exps|lifebook|any).
2158 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2159 per second.
2160 psmouse.resetafter= [HW,MOUSE]
2161 Try to reset the device after so many bad packets
2162 (0 = never).
2163 psmouse.resolution=
2164 [HW,MOUSE] Set desired mouse resolution, in dpi.
2165 psmouse.smartscroll=
2166 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2167 0 = disabled, 1 = enabled (default).
2169 pstore.backend= Specify the name of the pstore backend to use
2171 pt. [PARIDE]
2172 See Documentation/blockdev/paride.txt.
2174 pty.legacy_count=
2175 [KNL] Number of legacy pty's. Overwrites compiled-in
2176 default number.
2178 quiet [KNL] Disable most log messages
2180 r128= [HW,DRM]
2182 raid= [HW,RAID]
2183 See Documentation/md.txt.
2185 ramdisk_blocksize= [RAM]
2186 See Documentation/blockdev/ramdisk.txt.
2188 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2189 See Documentation/blockdev/ramdisk.txt.
2191 rcupdate.blimit= [KNL,BOOT]
2192 Set maximum number of finished RCU callbacks to process
2193 in one batch.
2195 rcupdate.qhimark= [KNL,BOOT]
2196 Set threshold of queued
2197 RCU callbacks over which batch limiting is disabled.
2199 rcupdate.qlowmark= [KNL,BOOT]
2200 Set threshold of queued RCU callbacks below which
2201 batch limiting is re-enabled.
2203 rdinit= [KNL]
2204 Format: <full_path>
2205 Run specified binary instead of /init from the ramdisk,
2206 used for early userspace startup. See initrd.
2208 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2209 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2210 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2212 relax_domain_level=
2213 [KNL, SMP] Set scheduler's default relax_domain_level.
2214 See Documentation/cgroups/cpusets.txt.
2216 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2218 reservetop= [X86-32]
2219 Format: nn[KMG]
2220 Reserves a hole at the top of the kernel virtual
2221 address space.
2223 reservelow= [X86]
2224 Format: nn[K]
2225 Set the amount of memory to reserve for BIOS at
2226 the bottom of the address space.
2228 reset_devices [KNL] Force drivers to reset the underlying device
2229 during initialization.
2231 resume= [SWSUSP]
2232 Specify the partition device for software suspend
2234 resume_offset= [SWSUSP]
2235 Specify the offset from the beginning of the partition
2236 given by "resume=" at which the swap header is located,
2237 in <PAGE_SIZE> units (needed only for swap files).
2238 See Documentation/power/swsusp-and-swap-files.txt
2240 hibernate= [HIBERNATION]
2241 noresume Don't check if there's a hibernation image
2242 present during boot.
2243 nocompress Don't compress/decompress hibernation images.
2245 retain_initrd [RAM] Keep initrd memory after extraction
2247 rhash_entries= [KNL,NET]
2248 Set number of hash buckets for route cache
2250 riscom8= [HW,SERIAL]
2251 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2253 ro [KNL] Mount root device read-only on boot
2255 root= [KNL] Root filesystem
2256 See name_to_dev_t comment in init/do_mounts.c.
2258 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2259 mount the root filesystem
2261 rootflags= [KNL] Set root filesystem mount option string
2263 rootfstype= [KNL] Set root filesystem type
2265 rootwait [KNL] Wait (indefinitely) for root device to show up.
2266 Useful for devices that are detected asynchronously
2267 (e.g. USB and MMC devices).
2269 rw [KNL] Mount root device read-write on boot
2271 S [KNL] Run init in single mode
2273 sa1100ir [NET]
2274 See drivers/net/irda/sa1100_ir.c.
2276 sbni= [NET] Granch SBNI12 leased line adapter
2278 sched_debug [KNL] Enables verbose scheduler debug messages.
2280 security= [SECURITY] Choose a security module to enable at boot.
2281 If this boot parameter is not specified, only the first
2282 security module asking for security registration will be
2283 loaded. An invalid security module name will be treated
2284 as if no module has been chosen.
2286 selinux= [SELINUX] Disable or enable SELinux at boot time.
2287 Format: { "0" | "1" }
2288 See security/selinux/Kconfig help text.
2289 0 -- disable.
2290 1 -- enable.
2291 Default value is set via kernel config option.
2292 If enabled at boot time, /selinux/disable can be used
2293 later to disable prior to initial policy load.
2295 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2296 Format: { "0" | "1" }
2297 See security/apparmor/Kconfig help text
2298 0 -- disable.
2299 1 -- enable.
2300 Default value is set via kernel config option.
2302 serialnumber [BUGS=X86-32]
2304 shapers= [NET]
2305 Maximal number of shapers.
2307 show_msr= [x86] show boot-time MSR settings
2308 Format: { <integer> }
2309 Show boot-time (BIOS-initialized) MSR settings.
2310 The parameter means the number of CPUs to show,
2311 for example 1 means boot CPU only.
2313 simeth= [IA-64]
2314 simscsi=
2316 slram= [HW,MTD]
2318 slub_debug[=options[,slabs]] [MM, SLUB]
2319 Enabling slub_debug allows one to determine the
2320 culprit if slab objects become corrupted. Enabling
2321 slub_debug can create guard zones around objects and
2322 may poison objects when not in use. Also tracks the
2323 last alloc / free. For more information see
2324 Documentation/vm/slub.txt.
2326 slub_max_order= [MM, SLUB]
2327 Determines the maximum allowed order for slabs.
2328 A high setting may cause OOMs due to memory
2329 fragmentation. For more information see
2330 Documentation/vm/slub.txt.
2332 slub_min_objects= [MM, SLUB]
2333 The minimum number of objects per slab. SLUB will
2334 increase the slab order up to slub_max_order to
2335 generate a sufficiently large slab able to contain
2336 the number of objects indicated. The higher the number
2337 of objects the smaller the overhead of tracking slabs
2338 and the less frequently locks need to be acquired.
2339 For more information see Documentation/vm/slub.txt.
2341 slub_min_order= [MM, SLUB]
2342 Determines the mininum page order for slabs. Must be
2343 lower than slub_max_order.
2344 For more information see Documentation/vm/slub.txt.
2346 slub_nomerge [MM, SLUB]
2347 Disable merging of slabs with similar size. May be
2348 necessary if there is some reason to distinguish
2349 allocs to different slabs. Debug options disable
2350 merging on their own.
2351 For more information see Documentation/vm/slub.txt.
2353 smart2= [HW]
2354 Format: <io1>[,<io2>[,...,<io8>]]
2356 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2357 attempt to substitute SMP alternatives once at boot.
2359 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2360 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2361 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2362 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2363 smsc-ircc2.ircc_irq= [HW] IRQ line
2364 smsc-ircc2.ircc_dma= [HW] DMA channel
2365 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2366 0: Toshiba Satellite 1800 (GP data pin select)
2367 1: Fast pin select (default)
2368 2: ATC IRMode
2370 softlockup_panic=
2371 [KNL] Should the soft-lockup detector generate panics.
2372 Format: <integer>
2374 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2375 See Documentation/sonypi.txt
2377 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2378 See Documentation/serial/specialix.txt.
2380 spia_io_base= [HW,MTD]
2381 spia_fio_base=
2382 spia_pedr=
2383 spia_peddr=
2385 stacktrace [FTRACE]
2386 Enabled the stack tracer on boot up.
2388 sti= [PARISC,HW]
2389 Format: <num>
2390 Set the STI (builtin display/keyboard on the HP-PARISC
2391 machines) console (graphic card) which should be used
2392 as the initial boot-console.
2393 See also comment in drivers/video/console/sticore.c.
2395 sti_font= [HW]
2396 See comment in drivers/video/console/sticore.c.
2398 stifb= [HW]
2399 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2401 sunrpc.min_resvport=
2402 sunrpc.max_resvport=
2403 [NFS,SUNRPC]
2404 SunRPC servers often require that client requests
2405 originate from a privileged port (i.e. a port in the
2406 range 0 < portnr < 1024).
2407 An administrator who wishes to reserve some of these
2408 ports for other uses may adjust the range that the
2409 kernel's sunrpc client considers to be privileged
2410 using these two parameters to set the minimum and
2411 maximum port values.
2413 sunrpc.pool_mode=
2414 [NFS]
2415 Control how the NFS server code allocates CPUs to
2416 service thread pools. Depending on how many NICs
2417 you have and where their interrupts are bound, this
2418 option will affect which CPUs will do NFS serving.
2419 Note: this parameter cannot be changed while the
2420 NFS server is running.
2422 auto the server chooses an appropriate mode
2423 automatically using heuristics
2424 global a single global pool contains all CPUs
2425 percpu one pool for each CPU
2426 pernode one pool for each NUMA node (equivalent
2427 to global on non-NUMA machines)
2429 sunrpc.tcp_slot_table_entries=
2430 sunrpc.udp_slot_table_entries=
2431 [NFS,SUNRPC]
2432 Sets the upper limit on the number of simultaneous
2433 RPC calls that can be sent from the client to a
2434 server. Increasing these values may allow you to
2435 improve throughput, but will also increase the
2436 amount of memory reserved for use by the client.
2438 swapaccount[=0|1]
2439 [KNL] Enable accounting of swap in memory resource
2440 controller if no parameter or 1 is given or disable
2441 it if 0 is given (See Documentation/cgroups/memory.txt)
2443 swiotlb= [IA-64] Number of I/O TLB slabs
2445 switches= [HW,M68k]
2447 sysfs.deprecated=0|1 [KNL]
2448 Enable/disable old style sysfs layout for old udev
2449 on older distributions. When this option is enabled
2450 very new udev will not work anymore. When this option
2451 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2452 in older udev will not work anymore.
2453 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2454 the kernel configuration.
2456 sysrq_always_enabled
2457 [KNL]
2458 Ignore sysrq setting - this boot parameter will
2459 neutralize any effect of /proc/sys/kernel/sysrq.
2460 Useful for debugging.
2462 tdfx= [HW,DRM]
2464 test_suspend= [SUSPEND]
2465 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2466 standby suspend) as the system sleep state to briefly
2467 enter during system startup. The system is woken from
2468 this state using a wakeup-capable RTC alarm.
2470 thash_entries= [KNL,NET]
2471 Set number of hash buckets for TCP connection
2473 thermal.act= [HW,ACPI]
2474 -1: disable all active trip points in all thermal zones
2475 <degrees C>: override all lowest active trip points
2477 thermal.crt= [HW,ACPI]
2478 -1: disable all critical trip points in all thermal zones
2479 <degrees C>: override all critical trip points
2481 thermal.nocrt= [HW,ACPI]
2482 Set to disable actions on ACPI thermal zone
2483 critical and hot trip points.
2485 thermal.off= [HW,ACPI]
2486 1: disable ACPI thermal control
2488 thermal.psv= [HW,ACPI]
2489 -1: disable all passive trip points
2490 <degrees C>: override all passive trip points to this
2491 value
2493 thermal.tzp= [HW,ACPI]
2494 Specify global default ACPI thermal zone polling rate
2495 <deci-seconds>: poll all this frequency
2496 0: no polling (default)
2498 threadirqs [KNL]
2499 Force threading of all interrupt handlers except those
2500 marked explicitely IRQF_NO_THREAD.
2502 topology= [S390]
2503 Format: {off | on}
2504 Specify if the kernel should make use of the cpu
2505 topology information if the hardware supports this.
2506 The scheduler will make use of this information and
2507 e.g. base its process migration decisions on it.
2508 Default is on.
2510 tp720= [HW,PS2]
2512 tpm_suspend_pcr=[HW,TPM]
2513 Format: integer pcr id
2514 Specify that at suspend time, the tpm driver
2515 should extend the specified pcr with zeros,
2516 as a workaround for some chips which fail to
2517 flush the last written pcr on TPM_SaveState.
2518 This will guarantee that all the other pcrs
2519 are saved.
2521 trace_buf_size=nn[KMG]
2522 [FTRACE] will set tracing buffer size.
2524 trace_event=[event-list]
2525 [FTRACE] Set and start specified trace events in order
2526 to facilitate early boot debugging.
2527 See also Documentation/trace/events.txt
2529 tsc= Disable clocksource stability checks for TSC.
2530 Format: <string>
2531 [x86] reliable: mark tsc clocksource as reliable, this
2532 disables clocksource verification at runtime, as well
2533 as the stability checks done at bootup. Used to enable
2534 high-resolution timer mode on older hardware, and in
2535 virtualized environment.
2536 [x86] noirqtime: Do not use TSC to do irq accounting.
2537 Used to run time disable IRQ_TIME_ACCOUNTING on any
2538 platforms where RDTSC is slow and this accounting
2539 can add overhead.
2541 turbografx.map[2|3]= [HW,JOY]
2542 TurboGraFX parallel port interface
2543 Format:
2544 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2545 See also Documentation/input/joystick-parport.txt
2547 udbg-immortal [PPC] When debugging early kernel crashes that
2548 happen after console_init() and before a proper
2549 console driver takes over, this boot options might
2550 help "seeing" what's going on.
2552 uhash_entries= [KNL,NET]
2553 Set number of hash buckets for UDP/UDP-Lite connections
2555 uhci-hcd.ignore_oc=
2556 [USB] Ignore overcurrent events (default N).
2557 Some badly-designed motherboards generate lots of
2558 bogus events, for ports that aren't wired to
2559 anything. Set this parameter to avoid log spamming.
2560 Note that genuine overcurrent events won't be
2561 reported either.
2563 unknown_nmi_panic
2564 [X86] Cause panic on unknown NMI.
2566 usbcore.authorized_default=
2567 [USB] Default USB device authorization:
2568 (default -1 = authorized except for wireless USB,
2569 0 = not authorized, 1 = authorized)
2571 usbcore.autosuspend=
2572 [USB] The autosuspend time delay (in seconds) used
2573 for newly-detected USB devices (default 2). This
2574 is the time required before an idle device will be
2575 autosuspended. Devices for which the delay is set
2576 to a negative value won't be autosuspended at all.
2578 usbcore.usbfs_snoop=
2579 [USB] Set to log all usbfs traffic (default 0 = off).
2581 usbcore.blinkenlights=
2582 [USB] Set to cycle leds on hubs (default 0 = off).
2584 usbcore.old_scheme_first=
2585 [USB] Start with the old device initialization
2586 scheme (default 0 = off).
2588 usbcore.use_both_schemes=
2589 [USB] Try the other device initialization scheme
2590 if the first one fails (default 1 = enabled).
2592 usbcore.initial_descriptor_timeout=
2593 [USB] Specifies timeout for the initial 64-byte
2594 USB_REQ_GET_DESCRIPTOR request in milliseconds
2595 (default 5000 = 5.0 seconds).
2597 usbhid.mousepoll=
2598 [USBHID] The interval which mice are to be polled at.
2600 usb-storage.delay_use=
2601 [UMS] The delay in seconds before a new device is
2602 scanned for Logical Units (default 5).
2604 usb-storage.quirks=
2605 [UMS] A list of quirks entries to supplement or
2606 override the built-in unusual_devs list. List
2607 entries are separated by commas. Each entry has
2608 the form VID:PID:Flags where VID and PID are Vendor
2609 and Product ID values (4-digit hex numbers) and
2610 Flags is a set of characters, each corresponding
2611 to a common usb-storage quirk flag as follows:
2612 a = SANE_SENSE (collect more than 18 bytes
2613 of sense data);
2614 b = BAD_SENSE (don't collect more than 18
2615 bytes of sense data);
2616 c = FIX_CAPACITY (decrease the reported
2617 device capacity by one sector);
2618 d = NO_READ_DISC_INFO (don't use
2619 READ_DISC_INFO command);
2620 e = NO_READ_CAPACITY_16 (don't use
2621 READ_CAPACITY_16 command);
2622 h = CAPACITY_HEURISTICS (decrease the
2623 reported device capacity by one
2624 sector if the number is odd);
2625 i = IGNORE_DEVICE (don't bind to this
2626 device);
2627 l = NOT_LOCKABLE (don't try to lock and
2628 unlock ejectable media);
2629 m = MAX_SECTORS_64 (don't transfer more
2630 than 64 sectors = 32 KB at a time);
2631 n = INITIAL_READ10 (force a retry of the
2632 initial READ(10) command);
2633 o = CAPACITY_OK (accept the capacity
2634 reported by the device);
2635 r = IGNORE_RESIDUE (the device reports
2636 bogus residue values);
2637 s = SINGLE_LUN (the device has only one
2638 Logical Unit);
2639 w = NO_WP_DETECT (don't test whether the
2640 medium is write-protected).
2641 Example: quirks=0419:aaf5:rl,0421:0433:rc
2643 user_debug= [KNL,ARM]
2644 Format: <int>
2645 See arch/arm/Kconfig.debug help text.
2646 1 - undefined instruction events
2647 2 - system calls
2648 4 - invalid data aborts
2649 8 - SIGSEGV faults
2650 16 - SIGBUS faults
2651 Example: user_debug=31
2653 userpte=
2654 [X86] Flags controlling user PTE allocations.
2656 nohigh = do not allocate PTE pages in
2657 HIGHMEM regardless of setting
2658 of CONFIG_HIGHPTE.
2660 vdso= [X86,SH]
2661 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2662 vdso=1: enable VDSO (default)
2663 vdso=0: disable VDSO mapping
2665 vdso32= [X86]
2666 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2667 vdso32=1: enable 32-bit VDSO (default)
2668 vdso32=0: disable 32-bit VDSO mapping
2670 vector= [IA-64,SMP]
2671 vector=percpu: enable percpu vector domain
2673 video= [FB] Frame buffer configuration
2674 See Documentation/fb/modedb.txt.
2676 vga= [BOOT,X86-32] Select a particular video mode
2677 See Documentation/x86/boot.txt and
2678 Documentation/svga.txt.
2679 Use vga=ask for menu.
2680 This is actually a boot loader parameter; the value is
2681 passed to the kernel using a special protocol.
2683 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2684 size of <nn>. This can be used to increase the
2685 minimum size (128MB on x86). It can also be used to
2686 decrease the size and leave more room for directly
2687 mapped kernel RAM.
2689 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2690 Format: <command>
2692 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2693 Format: <command>
2695 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2696 Format: <command>
2698 vsyscall= [X86-64]
2699 Controls the behavior of vsyscalls (i.e. calls to
2700 fixed addresses of 0xffffffffff600x00 from legacy
2701 code). Most statically-linked binaries and older
2702 versions of glibc use these calls. Because these
2703 functions are at fixed addresses, they make nice
2704 targets for exploits that can control RIP.
2706 emulate [default] Vsyscalls turn into traps and are
2707 emulated reasonably safely.
2709 native Vsyscalls are native syscall instructions.
2710 This is a little bit faster than trapping
2711 and makes a few dynamic recompilers work
2712 better than they would in emulation mode.
2713 It also makes exploits much easier to write.
2715 none Vsyscalls don't work at all. This makes
2716 them quite hard to use for exploits but
2717 might break your system.
2719 vt.cur_default= [VT] Default cursor shape.
2720 Format: 0xCCBBAA, where AA, BB, and CC are the same as
2721 the parameters of the <Esc>[?A;B;Cc escape sequence;
2722 see VGA-softcursor.txt. Default: 2 = underline.
2724 vt.default_blu= [VT]
2725 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2726 Change the default blue palette of the console.
2727 This is a 16-member array composed of values
2728 ranging from 0-255.
2730 vt.default_grn= [VT]
2731 Format: <green0>,<green1>,<green2>,...,<green15>
2732 Change the default green palette of the console.
2733 This is a 16-member array composed of values
2734 ranging from 0-255.
2736 vt.default_red= [VT]
2737 Format: <red0>,<red1>,<red2>,...,<red15>
2738 Change the default red palette of the console.
2739 This is a 16-member array composed of values
2740 ranging from 0-255.
2742 vt.default_utf8=
2743 [VT]
2744 Format=<0|1>
2745 Set system-wide default UTF-8 mode for all tty's.
2746 Default is 1, i.e. UTF-8 mode is enabled for all
2747 newly opened terminals.
2749 vt.global_cursor_default=
2750 [VT]
2751 Format=<-1|0|1>
2752 Set system-wide default for whether a cursor
2753 is shown on new VTs. Default is -1,
2754 i.e. cursors will be created by default unless
2755 overridden by individual drivers. 0 will hide
2756 cursors, 1 will display them.
2758 watchdog timers [HW,WDT] For information on watchdog timers,
2759 see Documentation/watchdog/watchdog-parameters.txt
2760 or other driver-specific files in the
2761 Documentation/watchdog/ directory.
2763 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2764 default x2apic cluster mode on platforms
2765 supporting x2apic.
2767 x86_mrst_timer= [X86-32,APBT]
2768 Choose timer option for x86 Moorestown MID platform.
2769 Two valid options are apbt timer only and lapic timer
2770 plus one apbt timer for broadcast timer.
2771 x86_mrst_timer=apbt_only | lapic_and_apbt
2773 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2774 xd_geo= See header of drivers/block/xd.c.
2776 xen_emul_unplug= [HW,X86,XEN]
2777 Unplug Xen emulated devices
2778 Format: [unplug0,][unplug1]
2779 ide-disks -- unplug primary master IDE devices
2780 aux-ide-disks -- unplug non-primary-master IDE devices
2781 nics -- unplug network devices
2782 all -- unplug all emulated devices (NICs and IDE disks)
2783 unnecessary -- unplugging emulated devices is
2784 unnecessary even if the host did not respond to
2785 the unplug protocol
2786 never -- do not unplug even if version check succeeds
2788 xirc2ps_cs= [NET,PCMCIA]
2789 Format:
2790 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2792 ______________________________________________________________________
2794 TODO:
2796 Add more DRM drivers.