| blob | 2ba8272a4b82a2b6dbf5a69101e7afce94cc8ebb |
1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
4 The following is a consolidated list of the kernel parameters as implemented
5 (mostly) by the __setup() macro and sorted into English Dictionary order
6 (defined as ignoring all punctuation and sorting digits before letters in a
7 case insensitive manner), and with descriptions where known.
9 Module parameters for loadable modules are specified only as the
10 parameter name with optional '=' and value as appropriate, such as:
12 modprobe usbcore blinkenlights=1
14 Module parameters for modules that are built into the kernel image
15 are specified on the kernel command line with the module name plus
16 '.' plus parameter name, with '=' and value if appropriate, such as:
18 usbcore.blinkenlights=1
20 Hyphens (dashes) and underscores are equivalent in parameter names, so
21 log_buf_len=1M print-fatal-signals=1
22 can also be entered as
23 log-buf-len=1M print_fatal_signals=1
26 This document may not be entirely up to date and comprehensive. The command
27 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
28 module. Loadable modules, after being loaded into the running kernel, also
29 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
30 parameters may be changed at runtime by the command
31 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
33 The parameters listed below are only valid if certain kernel build options were
34 enabled and if respective hardware is present. The text in square brackets at
35 the beginning of each description states the restrictions within which a
36 parameter is applicable:
38 ACPI ACPI support is enabled.
39 AGP AGP (Accelerated Graphics Port) is enabled.
40 ALSA ALSA sound support is enabled.
41 APIC APIC support is enabled.
42 APM Advanced Power Management support is enabled.
43 ARM ARM architecture is enabled.
44 AVR32 AVR32 architecture is enabled.
45 AX25 Appropriate AX.25 support is enabled.
46 BLACKFIN Blackfin architecture is enabled.
47 DRM Direct Rendering Management support is enabled.
48 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
49 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
50 EFI EFI Partitioning (GPT) is enabled
51 EIDE EIDE/ATAPI support is enabled.
52 EVM Extended Verification Module
53 FB The frame buffer device is enabled.
54 FTRACE Function tracing enabled.
55 GCOV GCOV profiling is enabled.
56 HW Appropriate hardware is enabled.
57 IA-64 IA-64 architecture is enabled.
58 IMA Integrity measurement architecture is enabled.
59 IOSCHED More than one I/O scheduler is enabled.
60 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
61 IPV6 IPv6 support is enabled.
62 ISAPNP ISA PnP code is enabled.
63 ISDN Appropriate ISDN support is enabled.
64 JOY Appropriate joystick support is enabled.
65 KGDB Kernel debugger support is enabled.
66 KVM Kernel Virtual Machine support is enabled.
67 LIBATA Libata driver is enabled
68 LP Printer support is enabled.
69 LOOP Loopback device support is enabled.
70 M68k M68k architecture is enabled.
71 These options have more detailed description inside of
72 Documentation/m68k/kernel-options.txt.
73 MCA MCA bus support is enabled.
74 MDA MDA console support is enabled.
75 MIPS MIPS architecture is enabled.
76 MOUSE Appropriate mouse support is enabled.
77 MSI Message Signaled Interrupts (PCI).
78 MTD MTD (Memory Technology Device) support is enabled.
79 NET Appropriate network support is enabled.
80 NUMA NUMA support is enabled.
81 NFS Appropriate NFS support is enabled.
82 OSS OSS sound support is enabled.
83 PV_OPS A paravirtualized kernel is enabled.
84 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
85 PARISC The PA-RISC architecture is enabled.
86 PCI PCI bus support is enabled.
87 PCIE PCI Express support is enabled.
88 PCMCIA The PCMCIA subsystem is enabled.
89 PNP Plug & Play support is enabled.
90 PPC PowerPC architecture is enabled.
91 PPT Parallel port support is enabled.
92 PS2 Appropriate PS/2 support is enabled.
93 RAM RAM disk support is enabled.
94 S390 S390 architecture is enabled.
95 SCSI Appropriate SCSI support is enabled.
96 A lot of drivers have their options described inside
97 the Documentation/scsi/ sub-directory.
98 SECURITY Different security models are enabled.
99 SELINUX SELinux support is enabled.
100 APPARMOR AppArmor support is enabled.
101 SERIAL Serial support is enabled.
102 SH SuperH architecture is enabled.
103 SMP The kernel is an SMP kernel.
104 SPARC Sparc architecture is enabled.
105 SWSUSP Software suspend (hibernation) is enabled.
106 SUSPEND System suspend states are enabled.
107 TPM TPM drivers are enabled.
108 TS Appropriate touchscreen support is enabled.
109 UMS USB Mass Storage support is enabled.
110 USB USB support is enabled.
111 USBHID USB Human Interface Device support is enabled.
112 V4L Video For Linux support is enabled.
113 VGA The VGA console has been enabled.
114 VT Virtual terminal support is enabled.
115 WDT Watchdog support is enabled.
116 XT IBM PC/XT MFM hard disk support is enabled.
117 X86-32 X86-32, aka i386 architecture is enabled.
118 X86-64 X86-64 architecture is enabled.
119 More X86-64 boot options can be found in
120 Documentation/x86/x86_64/boot-options.txt .
121 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
122 XEN Xen support is enabled
124 In addition, the following text indicates that the option:
126 BUGS= Relates to possible processor bugs on the said processor.
127 KNL Is a kernel start-up parameter.
128 BOOT Is a boot loader parameter.
130 Parameters denoted with BOOT are actually interpreted by the boot
131 loader, and have no meaning to the kernel directly.
132 Do not modify the syntax of boot loader parameters without extreme
133 need or coordination with <Documentation/x86/boot.txt>.
135 There are also arch-specific kernel-parameters not documented here.
136 See for example <Documentation/x86/x86_64/boot-options.txt>.
138 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
139 a trailing = on the name of any parameter states that that parameter will
140 be entered as an environment variable, whereas its absence indicates that
141 it will appear as a kernel argument readable via /proc/cmdline by programs
142 running once the system is up.
144 The number of kernel parameters is not limited, but the length of the
145 complete command line (parameters including spaces etc.) is limited to
146 a fixed number of characters. This limit depends on the architecture
147 and is between 256 and 4096 characters. It is defined in the file
148 ./include/asm/setup.h as COMMAND_LINE_SIZE.
150 Finally, the [KMG] suffix is commonly described after a number of kernel
151 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
152 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
153 bytes respectively. Such letter suffixes can also be entirely omitted.
156 acpi= [HW,ACPI,X86]
157 Advanced Configuration and Power Interface
158 Format: { force | off | strict | noirq | rsdt }
159 force -- enable ACPI if default was off
160 off -- disable ACPI if default was on
161 noirq -- do not use ACPI for IRQ routing
162 strict -- Be less tolerant of platforms that are not
163 strictly ACPI specification compliant.
164 rsdt -- prefer RSDT over (default) XSDT
165 copy_dsdt -- copy DSDT to memory
167 See also Documentation/power/runtime_pm.txt, pci=noacpi
169 acpi_rsdp= [ACPI,EFI,KEXEC]
170 Pass the RSDP address to the kernel, mostly used
171 on machines running EFI runtime service to boot the
172 second kernel for kdump.
174 acpi_apic_instance= [ACPI, IOAPIC]
175 Format: <int>
176 2: use 2nd APIC table, if available
177 1,0: use 1st APIC table
178 default: 0
180 acpi_backlight= [HW,ACPI]
181 acpi_backlight=vendor
182 acpi_backlight=video
183 If set to vendor, prefer vendor specific driver
184 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
185 of the ACPI video.ko driver.
187 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
188 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
189 Format: <int>
190 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
191 debug output. Bits in debug_layer correspond to a
192 _COMPONENT in an ACPI source file, e.g.,
193 #define _COMPONENT ACPI_PCI_COMPONENT
194 Bits in debug_level correspond to a level in
195 ACPI_DEBUG_PRINT statements, e.g.,
196 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
197 The debug_level mask defaults to "info". See
198 Documentation/acpi/debug.txt for more information about
199 debug layers and levels.
201 Enable processor driver info messages:
202 acpi.debug_layer=0x20000000
203 Enable PCI/PCI interrupt routing info messages:
204 acpi.debug_layer=0x400000
205 Enable AML "Debug" output, i.e., stores to the Debug
206 object while interpreting AML:
207 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
208 Enable all messages related to ACPI hardware:
209 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
211 Some values produce so much output that the system is
212 unusable. The "log_buf_len" parameter may be useful
213 if you need to capture more output.
215 acpi_irq_balance [HW,ACPI]
216 ACPI will balance active IRQs
217 default in APIC mode
219 acpi_irq_nobalance [HW,ACPI]
220 ACPI will not move active IRQs (default)
221 default in PIC mode
223 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
224 Format: <irq>,<irq>...
226 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
227 use by PCI
228 Format: <irq>,<irq>...
230 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
232 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
233 Format: To spoof as Windows 98: ="Microsoft Windows"
235 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
236 acpi_osi="string1" # add string1 -- only one string
237 acpi_osi="!string2" # remove built-in string2
238 acpi_osi= # disable all strings
240 acpi_pm_good [X86]
241 Override the pmtimer bug detection: force the kernel
242 to assume that this machine's pmtimer latches its value
243 and always returns good values.
245 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
246 Format: { level | edge | high | low }
248 acpi_serialize [HW,ACPI] force serialization of AML methods
250 acpi_skip_timer_override [HW,ACPI]
251 Recognize and ignore IRQ0/pin2 Interrupt Override.
252 For broken nForce2 BIOS resulting in XT-PIC timer.
254 acpi_sleep= [HW,ACPI] Sleep options
255 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
256 old_ordering, nonvs, sci_force_enable }
257 See Documentation/power/video.txt for information on
258 s3_bios and s3_mode.
259 s3_beep is for debugging; it makes the PC's speaker beep
260 as soon as the kernel's real-mode entry point is called.
261 s4_nohwsig prevents ACPI hardware signature from being
262 used during resume from hibernation.
263 old_ordering causes the ACPI 1.0 ordering of the _PTS
264 control method, with respect to putting devices into
265 low power states, to be enforced (the ACPI 2.0 ordering
266 of _PTS is used by default).
267 nonvs prevents the kernel from saving/restoring the
268 ACPI NVS memory during suspend/hibernation and resume.
269 sci_force_enable causes the kernel to set SCI_EN directly
270 on resume from S1/S3 (which is against the ACPI spec,
271 but some broken systems don't work without it).
273 acpi_use_timer_override [HW,ACPI]
274 Use timer override. For some broken Nvidia NF5 boards
275 that require a timer override, but don't have HPET
277 acpi_enforce_resources= [ACPI]
278 { strict | lax | no }
279 Check for resource conflicts between native drivers
280 and ACPI OperationRegions (SystemIO and SystemMemory
281 only). IO ports and memory declared in ACPI might be
282 used by the ACPI subsystem in arbitrary AML code and
283 can interfere with legacy drivers.
284 strict (default): access to resources claimed by ACPI
285 is denied; legacy drivers trying to access reserved
286 resources will fail to bind to device using them.
287 lax: access to resources claimed by ACPI is allowed;
288 legacy drivers trying to access reserved resources
289 will bind successfully but a warning message is logged.
290 no: ACPI OperationRegions are not marked as reserved,
291 no further checks are performed.
293 add_efi_memmap [EFI; X86] Include EFI memory map in
294 kernel's map of available physical RAM.
296 agp= [AGP]
297 { off | try_unsupported }
298 off: disable AGP support
299 try_unsupported: try to drive unsupported chipsets
300 (may crash computer or cause data corruption)
302 ALSA [HW,ALSA]
303 See Documentation/sound/alsa/alsa-parameters.txt
305 alignment= [KNL,ARM]
306 Allow the default userspace alignment fault handler
307 behaviour to be specified. Bit 0 enables warnings,
308 bit 1 enables fixups, and bit 2 sends a segfault.
310 align_va_addr= [X86-64]
311 Align virtual addresses by clearing slice [14:12] when
312 allocating a VMA at process creation time. This option
313 gives you up to 3% performance improvement on AMD F15h
314 machines (where it is enabled by default) for a
315 CPU-intensive style benchmark, and it can vary highly in
316 a microbenchmark depending on workload and compiler.
318 32: only for 32-bit processes
319 64: only for 64-bit processes
320 on: enable for both 32- and 64-bit processes
321 off: disable for both 32- and 64-bit processes
323 amd_iommu= [HW,X86-64]
324 Pass parameters to the AMD IOMMU driver in the system.
325 Possible values are:
326 fullflush - enable flushing of IO/TLB entries when
327 they are unmapped. Otherwise they are
328 flushed before they will be reused, which
329 is a lot of faster
330 off - do not initialize any AMD IOMMU found in
331 the system
333 amijoy.map= [HW,JOY] Amiga joystick support
334 Map of devices attached to JOY0DAT and JOY1DAT
335 Format: <a>,<b>
336 See also Documentation/input/joystick.txt
338 analog.map= [HW,JOY] Analog joystick and gamepad support
339 Specifies type or capabilities of an analog joystick
340 connected to one of 16 gameports
341 Format: <type1>,<type2>,..<type16>
343 apc= [HW,SPARC]
344 Power management functions (SPARCstation-4/5 + deriv.)
345 Format: noidle
346 Disable APC CPU standby support. SPARCstation-Fox does
347 not play well with APC CPU idle - disable it if you have
348 APC and your system crashes randomly.
350 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
351 Change the output verbosity whilst booting
352 Format: { quiet (default) | verbose | debug }
353 Change the amount of debugging information output
354 when initialising the APIC and IO-APIC components.
356 autoconf= [IPV6]
357 See Documentation/networking/ipv6.txt.
359 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
360 Limit apic dumping. The parameter defines the maximal
361 number of local apics being dumped. Also it is possible
362 to set it to "all" by meaning -- no limit here.
363 Format: { 1 (default) | 2 | ... | all }.
364 The parameter valid if only apic=debug or
365 apic=verbose is specified.
366 Example: apic=debug show_lapic=all
368 apm= [APM] Advanced Power Management
369 See header of arch/x86/kernel/apm_32.c.
371 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
372 Format: <io>,<irq>,<nodeID>
374 ataflop= [HW,M68k]
376 atarimouse= [HW,MOUSE] Atari Mouse
378 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
379 EzKey and similar keyboards
381 atkbd.reset= [HW] Reset keyboard during initialization
383 atkbd.set= [HW] Select keyboard code set
384 Format: <int> (2 = AT (default), 3 = PS/2)
386 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
387 keyboards
389 atkbd.softraw= [HW] Choose between synthetic and real raw mode
390 Format: <bool> (0 = real, 1 = synthetic (default))
392 atkbd.softrepeat= [HW]
393 Use software keyboard repeat
395 autotest [IA-64]
397 baycom_epp= [HW,AX25]
398 Format: <io>,<mode>
400 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
401 Format: <io>,<mode>
402 See header of drivers/net/hamradio/baycom_par.c.
404 baycom_ser_fdx= [HW,AX25]
405 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
406 Format: <io>,<irq>,<mode>[,<baud>]
407 See header of drivers/net/hamradio/baycom_ser_fdx.c.
409 baycom_ser_hdx= [HW,AX25]
410 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
411 Format: <io>,<irq>,<mode>
412 See header of drivers/net/hamradio/baycom_ser_hdx.c.
414 boot_delay= Milliseconds to delay each printk during boot.
415 Values larger than 10 seconds (10000) are changed to
416 no delay (0).
417 Format: integer
419 bootmem_debug [KNL] Enable bootmem allocator debug messages.
421 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
422 bttv.radio= Most important insmod options are available as
423 kernel args too.
424 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
425 bttv.tuner=
427 bulk_remove=off [PPC] This parameter disables the use of the pSeries
428 firmware feature for flushing multiple hpte entries
429 at a time.
431 c101= [NET] Moxa C101 synchronous serial card
433 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
434 Sometimes CPU hardware bugs make them report the cache
435 size incorrectly. The kernel will attempt work arounds
436 to fix known problems, but for some CPUs it is not
437 possible to determine what the correct size should be.
438 This option provides an override for these situations.
440 capability.disable=
441 [SECURITY] Disable capabilities. This would normally
442 be used only if an alternative security model is to be
443 configured. Potentially dangerous and should only be
444 used if you are entirely sure of the consequences.
446 ccw_timeout_log [S390]
447 See Documentation/s390/CommonIO for details.
449 cgroup_disable= [KNL] Disable a particular controller
450 Format: {name of the controller(s) to disable}
451 {Currently supported controllers - "memory"}
453 checkreqprot [SELINUX] Set initial checkreqprot flag value.
454 Format: { "0" | "1" }
455 See security/selinux/Kconfig help text.
456 0 -- check protection applied by kernel (includes
457 any implied execute protection).
458 1 -- check protection requested by application.
459 Default value is set via a kernel config option.
460 Value can be changed at runtime via
461 /selinux/checkreqprot.
463 cio_ignore= [S390]
464 See Documentation/s390/CommonIO for details.
466 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
467 [Deprecated]
468 Forces specified clocksource (if available) to be used
469 when calculating gettimeofday(). If specified
470 clocksource is not available, it defaults to PIT.
471 Format: { pit | tsc | cyclone | pmtmr }
473 clocksource= Override the default clocksource
474 Format: <string>
475 Override the default clocksource and use the clocksource
476 with the name specified.
477 Some clocksource names to choose from, depending on
478 the platform:
479 [all] jiffies (this is the base, fallback clocksource)
480 [ACPI] acpi_pm
481 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
482 pxa_timer,timer3,32k_counter,timer0_1
483 [AVR32] avr32
484 [X86-32] pit,hpet,tsc;
485 scx200_hrt on Geode; cyclone on IBM x440
486 [MIPS] MIPS
487 [PARISC] cr16
488 [S390] tod
489 [SH] SuperH
490 [SPARC64] tick
491 [X86-64] hpet,tsc
493 clearcpuid=BITNUM [X86]
494 Disable CPUID feature X for the kernel. See
495 arch/x86/include/asm/cpufeature.h for the valid bit
496 numbers. Note the Linux specific bits are not necessarily
497 stable over kernel options, but the vendor specific
498 ones should be.
499 Also note that user programs calling CPUID directly
500 or using the feature without checking anything
501 will still see it. This just prevents it from
502 being used by the kernel or shown in /proc/cpuinfo.
503 Also note the kernel might malfunction if you disable
504 some critical bits.
506 cmo_free_hint= [PPC] Format: { yes | no }
507 Specify whether pages are marked as being inactive
508 when they are freed. This is used in CMO environments
509 to determine OS memory pressure for page stealing by
510 a hypervisor.
511 Default: yes
513 code_bytes [X86] How many bytes of object code to print
514 in an oops report.
515 Range: 0 - 8192
516 Default: 64
518 com20020= [HW,NET] ARCnet - COM20020 chipset
519 Format:
520 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
522 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
523 Format: <io>[,<irq>]
525 com90xx= [HW,NET]
526 ARCnet - COM90xx chipset (memory-mapped buffers)
527 Format: <io>[,<irq>[,<memstart>]]
529 condev= [HW,S390] console device
530 conmode=
532 console= [KNL] Output console device and options.
534 tty<n> Use the virtual console device <n>.
536 ttyS<n>[,options]
537 ttyUSB0[,options]
538 Use the specified serial port. The options are of
539 the form "bbbbpnf", where "bbbb" is the baud rate,
540 "p" is parity ("n", "o", or "e"), "n" is number of
541 bits, and "f" is flow control ("r" for RTS or
542 omit it). Default is "9600n8".
544 See Documentation/serial-console.txt for more
545 information. See
546 Documentation/networking/netconsole.txt for an
547 alternative.
549 uart[8250],io,<addr>[,options]
550 uart[8250],mmio,<addr>[,options]
551 Start an early, polled-mode console on the 8250/16550
552 UART at the specified I/O port or MMIO address,
553 switching to the matching ttyS device later. The
554 options are the same as for ttyS, above.
555 hvc<n> Use the hypervisor console device <n>. This is for
556 both Xen and PowerPC hypervisors.
558 If the device connected to the port is not a TTY but a braille
559 device, prepend "brl," before the device type, for instance
560 console=brl,ttyS0
561 For now, only VisioBraille is supported.
563 consoleblank= [KNL] The console blank (screen saver) timeout in
564 seconds. Defaults to 10*60 = 10mins. A value of 0
565 disables the blank timer.
567 coredump_filter=
568 [KNL] Change the default value for
569 /proc/<pid>/coredump_filter.
570 See also Documentation/filesystems/proc.txt.
572 cpuidle.off=1 [CPU_IDLE]
573 disable the cpuidle sub-system
575 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
576 Format:
577 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
579 crashkernel=size[KMG][@offset[KMG]]
580 [KNL] Using kexec, Linux can switch to a 'crash kernel'
581 upon panic. This parameter reserves the physical
582 memory region [offset, offset + size] for that kernel
583 image. If '@offset' is omitted, then a suitable offset
584 is selected automatically. Check
585 Documentation/kdump/kdump.txt for further details.
587 crashkernel=range1:size1[,range2:size2,...][@offset]
588 [KNL] Same as above, but depends on the memory
589 in the running system. The syntax of range is
590 start-[end] where start and end are both
591 a memory unit (amount[KMG]). See also
592 Documentation/kdump/kdump.txt for an example.
594 cs89x0_dma= [HW,NET]
595 Format: <dma>
597 cs89x0_media= [HW,NET]
598 Format: { rj45 | aui | bnc }
600 dasd= [HW,NET]
601 See header of drivers/s390/block/dasd_devmap.c.
603 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
604 (one device per port)
605 Format: <port#>,<type>
606 See also Documentation/input/joystick-parport.txt
608 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
609 time. See Documentation/dynamic-debug-howto.txt for
610 details.
612 debug [KNL] Enable kernel debugging (events log level).
614 debug_locks_verbose=
615 [KNL] verbose self-tests
616 Format=<0|1>
617 Print debugging info while doing the locking API
618 self-tests.
619 We default to 0 (no extra messages), setting it to
620 1 will print _a lot_ more information - normally
621 only useful to kernel developers.
623 debug_objects [KNL] Enable object debugging
625 no_debug_objects
626 [KNL] Disable object debugging
628 debugpat [X86] Enable PAT debugging
630 decnet.addr= [HW,NET]
631 Format: <area>[,<node>]
632 See also Documentation/networking/decnet.txt.
634 default_hugepagesz=
635 [same as hugepagesz=] The size of the default
636 HugeTLB page size. This is the size represented by
637 the legacy /proc/ hugepages APIs, used for SHM, and
638 default size when mounting hugetlbfs filesystems.
639 Defaults to the default architecture's huge page size
640 if not specified.
642 dhash_entries= [KNL]
643 Set number of hash buckets for dentry cache.
645 digi= [HW,SERIAL]
646 IO parameters + enable/disable command.
648 digiepca= [HW,SERIAL]
649 See drivers/char/README.epca and
650 Documentation/serial/digiepca.txt.
652 disable= [IPV6]
653 See Documentation/networking/ipv6.txt.
655 disable_ddw [PPC/PSERIES]
656 Disable Dynamic DMA Window support. Use this if
657 to workaround buggy firmware.
659 disable_ipv6= [IPV6]
660 See Documentation/networking/ipv6.txt.
662 disable_mtrr_cleanup [X86]
663 The kernel tries to adjust MTRR layout from continuous
664 to discrete, to make X server driver able to add WB
665 entry later. This parameter disables that.
667 disable_mtrr_trim [X86, Intel and AMD only]
668 By default the kernel will trim any uncacheable
669 memory out of your available memory pool based on
670 MTRR settings. This parameter disables that behavior,
671 possibly causing your machine to run very slowly.
673 disable_timer_pin_1 [X86]
674 Disable PIN 1 of APIC timer
675 Can be useful to work around chipset bugs.
677 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
678 this option disables the debugging code at boot.
680 dma_debug_entries=<number>
681 This option allows to tune the number of preallocated
682 entries for DMA-API debugging code. One entry is
683 required per DMA-API allocation. Use this if the
684 DMA-API debugging code disables itself because the
685 architectural default is too low.
687 dma_debug_driver=<driver_name>
688 With this option the DMA-API debugging driver
689 filter feature can be enabled at boot time. Just
690 pass the driver to filter for as the parameter.
691 The filter can be disabled or changed to another
692 driver later using sysfs.
694 dscc4.setup= [NET]
696 earlycon= [KNL] Output early console device and options.
697 uart[8250],io,<addr>[,options]
698 uart[8250],mmio,<addr>[,options]
699 uart[8250],mmio32,<addr>[,options]
700 Start an early, polled-mode console on the 8250/16550
701 UART at the specified I/O port or MMIO address.
702 MMIO inter-register address stride is either 8-bit
703 (mmio) or 32-bit (mmio32).
704 The options are the same as for ttyS, above.
706 earlyprintk= [X86,SH,BLACKFIN]
707 earlyprintk=vga
708 earlyprintk=xen
709 earlyprintk=serial[,ttySn[,baudrate]]
710 earlyprintk=ttySn[,baudrate]
711 earlyprintk=dbgp[debugController#]
713 Append ",keep" to not disable it when the real console
714 takes over.
716 Only vga or serial or usb debug port at a time.
718 Currently only ttyS0 and ttyS1 are supported.
720 Interaction with the standard serial driver is not
721 very good.
723 The VGA output is eventually overwritten by the real
724 console.
726 The xen output can only be used by Xen PV guests.
728 ekgdboc= [X86,KGDB] Allow early kernel console debugging
729 ekgdboc=kbd
731 This is designed to be used in conjunction with
732 the boot argument: earlyprintk=vga
734 edd= [EDD]
735 Format: {"off" | "on" | "skip[mbr]"}
737 efi_no_storage_paranoia [EFI; X86]
738 Using this parameter you can use more than 50% of
739 your efi variable storage. Use this parameter only if
740 you are really sure that your UEFI does sane gc and
741 fulfills the spec otherwise your board may brick.
743 eisa_irq_edge= [PARISC,HW]
744 See header of drivers/parisc/eisa.c.
746 elanfreq= [X86-32]
747 See comment before function elanfreq_setup() in
748 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
750 elevator= [IOSCHED]
751 Format: {"cfq" | "deadline" | "noop"}
752 See Documentation/block/cfq-iosched.txt and
753 Documentation/block/deadline-iosched.txt for details.
755 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
756 Specifies physical address of start of kernel core
757 image elf header and optionally the size. Generally
758 kexec loader will pass this option to capture kernel.
759 See Documentation/kdump/kdump.txt for details.
761 enable_mtrr_cleanup [X86]
762 The kernel tries to adjust MTRR layout from continuous
763 to discrete, to make X server driver able to add WB
764 entry later. This parameter enables that.
766 enable_timer_pin_1 [X86]
767 Enable PIN 1 of APIC timer
768 Can be useful to work around chipset bugs
769 (in particular on some ATI chipsets).
770 The kernel tries to set a reasonable default.
772 enforcing [SELINUX] Set initial enforcing status.
773 Format: {"0" | "1"}
774 See security/selinux/Kconfig help text.
775 0 -- permissive (log only, no denials).
776 1 -- enforcing (deny and log).
777 Default value is 0.
778 Value can be changed at runtime via /selinux/enforce.
780 erst_disable [ACPI]
781 Disable Error Record Serialization Table (ERST)
782 support.
784 ether= [HW,NET] Ethernet cards parameters
785 This option is obsoleted by the "netdev=" option, which
786 has equivalent usage. See its documentation for details.
788 evm= [EVM]
789 Format: { "fix" }
790 Permit 'security.evm' to be updated regardless of
791 current integrity status.
793 failslab=
794 fail_page_alloc=
795 fail_make_request=[KNL]
796 General fault injection mechanism.
797 Format: <interval>,<probability>,<space>,<times>
798 See also Documentation/fault-injection/.
800 floppy= [HW]
801 See Documentation/blockdev/floppy.txt.
803 force_pal_cache_flush
804 [IA-64] Avoid check_sal_cache_flush which may hang on
805 buggy SAL_CACHE_FLUSH implementations. Using this
806 parameter will force ia64_sal_cache_flush to call
807 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
809 ftrace=[tracer]
810 [FTRACE] will set and start the specified tracer
811 as early as possible in order to facilitate early
812 boot debugging.
814 ftrace_dump_on_oops[=orig_cpu]
815 [FTRACE] will dump the trace buffers on oops.
816 If no parameter is passed, ftrace will dump
817 buffers of all CPUs, but if you pass orig_cpu, it will
818 dump only the buffer of the CPU that triggered the
819 oops.
821 ftrace_filter=[function-list]
822 [FTRACE] Limit the functions traced by the function
823 tracer at boot up. function-list is a comma separated
824 list of functions. This list can be changed at run
825 time by the set_ftrace_filter file in the debugfs
826 tracing directory.
828 ftrace_notrace=[function-list]
829 [FTRACE] Do not trace the functions specified in
830 function-list. This list can be changed at run time
831 by the set_ftrace_notrace file in the debugfs
832 tracing directory.
834 ftrace_graph_filter=[function-list]
835 [FTRACE] Limit the top level callers functions traced
836 by the function graph tracer at boot up.
837 function-list is a comma separated list of functions
838 that can be changed at run time by the
839 set_graph_function file in the debugfs tracing directory.
841 gamecon.map[2|3]=
842 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
843 support via parallel port (up to 5 devices per port)
844 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
845 See also Documentation/input/joystick-parport.txt
847 gamma= [HW,DRM]
849 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
850 Format: off | on
851 default: on
853 gcov_persist= [GCOV] When non-zero (default), profiling data for
854 kernel modules is saved and remains accessible via
855 debugfs, even when the module is unloaded/reloaded.
856 When zero, profiling data is discarded and associated
857 debugfs files are removed at module unload time.
859 gpt [EFI] Forces disk with valid GPT signature but
860 invalid Protective MBR to be treated as GPT.
862 hashdist= [KNL,NUMA] Large hashes allocated during boot
863 are distributed across NUMA nodes. Defaults on
864 for 64-bit NUMA, off otherwise.
865 Format: 0 | 1 (for off | on)
867 hcl= [IA-64] SGI's Hardware Graph compatibility layer
869 hd= [EIDE] (E)IDE hard drive subsystem geometry
870 Format: <cyl>,<head>,<sect>
872 hest_disable [ACPI]
873 Disable Hardware Error Source Table (HEST) support;
874 corresponding firmware-first mode error processing
875 logic will be disabled.
877 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
878 size of <nn>. This works even on boxes that have no
879 highmem otherwise. This also works to reduce highmem
880 size on bigger boxes.
882 highres= [KNL] Enable/disable high resolution timer mode.
883 Valid parameters: "on", "off"
884 Default: "on"
886 hisax= [HW,ISDN]
887 See Documentation/isdn/README.HiSax.
889 hlt [BUGS=ARM,SH]
891 hpet= [X86-32,HPET] option to control HPET usage
892 Format: { enable (default) | disable | force |
893 verbose }
894 disable: disable HPET and use PIT instead
895 force: allow force enabled of undocumented chips (ICH4,
896 VIA, nVidia)
897 verbose: show contents of HPET registers during setup
899 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
900 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
901 On x86-64 and powerpc, this option can be specified
902 multiple times interleaved with hugepages= to reserve
903 huge pages of different sizes. Valid pages sizes on
904 x86-64 are 2M (when the CPU supports "pse") and 1G
905 (when the CPU supports the "pdpe1gb" cpuinfo flag)
906 Note that 1GB pages can only be allocated at boot time
907 using hugepages= and not freed afterwards.
909 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
910 terminal devices. Valid values: 0..8
911 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
912 If specified, z/VM IUCV HVC accepts connections
913 from listed z/VM user IDs only.
915 keep_bootcon [KNL]
916 Do not unregister boot console at start. This is only
917 useful for debugging when something happens in the window
918 between unregistering the boot console and initializing
919 the real console.
921 i2c_bus= [HW] Override the default board specific I2C bus speed
922 or register an additional I2C bus that is not
923 registered from board initialization code.
924 Format:
925 <bus_id>,<clkrate>
927 i8042.debug [HW] Toggle i8042 debug mode
928 i8042.direct [HW] Put keyboard port into non-translated mode
929 i8042.dumbkbd [HW] Pretend that controller can only read data from
930 keyboard and cannot control its state
931 (Don't attempt to blink the leds)
932 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
933 i8042.nokbd [HW] Don't check/create keyboard port
934 i8042.noloop [HW] Disable the AUX Loopback command while probing
935 for the AUX port
936 i8042.nomux [HW] Don't check presence of an active multiplexing
937 controller
938 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
939 controllers
940 i8042.notimeout [HW] Ignore timeout condition signalled by conroller
941 i8042.reset [HW] Reset the controller during init and cleanup
942 i8042.unlock [HW] Unlock (ignore) the keylock
944 i810= [HW,DRM]
946 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
947 indicates that the driver is running on unsupported
948 hardware.
949 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
950 does not match list of supported models.
951 i8k.power_status
952 [HW] Report power status in /proc/i8k
953 (disabled by default)
954 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
955 capability is set.
957 i915.invert_brightness=
958 [DRM] Invert the sense of the variable that is used to
959 set the brightness of the panel backlight. Normally a
960 brightness value of 0 indicates backlight switched off,
961 and the maximum of the brightness value sets the backlight
962 to maximum brightness. If this parameter is set to 0
963 (default) and the machine requires it, or this parameter
964 is set to 1, a brightness value of 0 sets the backlight
965 to maximum brightness, and the maximum of the brightness
966 value switches the backlight off.
967 -1 -- never invert brightness
968 0 -- machine default
969 1 -- force brightness inversion
971 icn= [HW,ISDN]
972 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
974 ide-core.nodma= [HW] (E)IDE subsystem
975 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
976 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
977 .cdrom .chs .ignore_cable are additional options
978 See Documentation/ide/ide.txt.
980 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
981 Claim all unknown PCI IDE storage controllers.
983 idle= [X86]
984 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
985 Poll forces a polling idle loop that can slightly
986 improve the performance of waking up a idle CPU, but
987 will use a lot of power and make the system run hot.
988 Not recommended.
989 idle=mwait: On systems which support MONITOR/MWAIT but
990 the kernel chose to not use it because it doesn't save
991 as much power as a normal idle loop, use the
992 MONITOR/MWAIT idle loop anyways. Performance should be
993 the same as idle=poll.
994 idle=halt: Halt is forced to be used for CPU idle.
995 In such case C2/C3 won't be used again.
996 idle=nomwait: Disable mwait for CPU C-states
998 ignore_loglevel [KNL]
999 Ignore loglevel setting - this will print /all/
1000 kernel messages to the console. Useful for debugging.
1001 We also add it as printk module parameter, so users
1002 could change it dynamically, usually by
1003 /sys/module/printk/parameters/ignore_loglevel.
1005 ihash_entries= [KNL]
1006 Set number of hash buckets for inode cache.
1008 ima_audit= [IMA]
1009 Format: { "0" | "1" }
1010 0 -- integrity auditing messages. (Default)
1011 1 -- enable informational integrity auditing messages.
1013 ima_hash= [IMA]
1014 Format: { "sha1" | "md5" }
1015 default: "sha1"
1017 ima_tcb [IMA]
1018 Load a policy which meets the needs of the Trusted
1019 Computing Base. This means IMA will measure all
1020 programs exec'd, files mmap'd for exec, and all files
1021 opened for read by uid=0.
1023 init= [KNL]
1024 Format: <full_path>
1025 Run specified binary instead of /sbin/init as init
1026 process.
1028 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1029 for working out where the kernel is dying during
1030 startup.
1032 initrd= [BOOT] Specify the location of the initial ramdisk
1034 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1035 Format: <irq>
1037 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1038 on
1039 Enable intel iommu driver.
1040 off
1041 Disable intel iommu driver.
1042 igfx_off [Default Off]
1043 By default, gfx is mapped as normal device. If a gfx
1044 device has a dedicated DMAR unit, the DMAR unit is
1045 bypassed by not enabling DMAR with this option. In
1046 this case, gfx device will use physical address for
1047 DMA.
1048 forcedac [x86_64]
1049 With this option iommu will not optimize to look
1050 for io virtual address below 32-bit forcing dual
1051 address cycle on pci bus for cards supporting greater
1052 than 32-bit addressing. The default is to look
1053 for translation below 32-bit and if not available
1054 then look in the higher range.
1055 strict [Default Off]
1056 With this option on every unmap_single operation will
1057 result in a hardware IOTLB flush operation as opposed
1058 to batching them for performance.
1059 sp_off [Default Off]
1060 By default, super page will be supported if Intel IOMMU
1061 has the capability. With this option, super page will
1062 not be supported.
1063 intremap= [X86-64, Intel-IOMMU]
1064 on enable Interrupt Remapping (default)
1065 off disable Interrupt Remapping
1066 nosid disable Source ID checking
1067 no_x2apic_optout
1068 BIOS x2APIC opt-out request will be ignored
1070 inttest= [IA-64]
1072 iomem= Disable strict checking of access to MMIO memory
1073 strict regions from userspace.
1074 relaxed
1076 iommu= [x86]
1077 off
1078 force
1079 noforce
1080 biomerge
1081 panic
1082 nopanic
1083 merge
1084 nomerge
1085 forcesac
1086 soft
1087 pt [x86, IA-64]
1089 io7= [HW] IO7 for Marvel based alpha systems
1090 See comment before marvel_specify_io7 in
1091 arch/alpha/kernel/core_marvel.c.
1093 io_delay= [X86] I/O delay method
1094 0x80
1095 Standard port 0x80 based delay
1096 0xed
1097 Alternate port 0xed based delay (needed on some systems)
1098 udelay
1099 Simple two microseconds delay
1100 none
1101 No delay
1103 ip= [IP_PNP]
1104 See Documentation/filesystems/nfs/nfsroot.txt.
1106 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1107 See comment before ip2_setup() in
1108 drivers/char/ip2/ip2base.c.
1110 irqfixup [HW]
1111 When an interrupt is not handled search all handlers
1112 for it. Intended to get systems with badly broken
1113 firmware running.
1115 irqpoll [HW]
1116 When an interrupt is not handled search all handlers
1117 for it. Also check all handlers each timer
1118 interrupt. Intended to get systems with badly broken
1119 firmware running.
1121 isapnp= [ISAPNP]
1122 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1124 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1125 Format:
1126 <cpu number>,...,<cpu number>
1127 or
1128 <cpu number>-<cpu number>
1129 (must be a positive range in ascending order)
1130 or a mixture
1131 <cpu number>,...,<cpu number>-<cpu number>
1133 This option can be used to specify one or more CPUs
1134 to isolate from the general SMP balancing and scheduling
1135 algorithms. You can move a process onto or off an
1136 "isolated" CPU via the CPU affinity syscalls or cpuset.
1137 <cpu number> begins at 0 and the maximum value is
1138 "number of CPUs in system - 1".
1140 This option is the preferred way to isolate CPUs. The
1141 alternative -- manually setting the CPU mask of all
1142 tasks in the system -- can cause problems and
1143 suboptimal load balancer performance.
1145 iucv= [HW,NET]
1147 js= [HW,JOY] Analog joystick
1148 See Documentation/input/joystick.txt.
1150 keepinitrd [HW,ARM]
1152 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1153 specifies the amount of memory usable by the kernel
1154 for non-movable allocations. The requested amount is
1155 spread evenly throughout all nodes in the system. The
1156 remaining memory in each node is used for Movable
1157 pages. In the event, a node is too small to have both
1158 kernelcore and Movable pages, kernelcore pages will
1159 take priority and other nodes will have a larger number
1160 of kernelcore pages. The Movable zone is used for the
1161 allocation of pages that may be reclaimed or moved
1162 by the page migration subsystem. This means that
1163 HugeTLB pages may not be allocated from this zone.
1164 Note that allocations like PTEs-from-HighMem still
1165 use the HighMem zone if it exists, and the Normal
1166 zone if it does not.
1168 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1169 Format: <Controller#>[,poll interval]
1170 The controller # is the number of the ehci usb debug
1171 port as it is probed via PCI. The poll interval is
1172 optional and is the number seconds in between
1173 each poll cycle to the debug port in case you need
1174 the functionality for interrupting the kernel with
1175 gdb or control-c on the dbgp connection. When
1176 not using this parameter you use sysrq-g to break into
1177 the kernel debugger.
1179 kgdboc= [KGDB,HW] kgdb over consoles.
1180 Requires a tty driver that supports console polling,
1181 or a supported polling keyboard driver (non-usb).
1182 Serial only format: <serial_device>[,baud]
1183 keyboard only format: kbd
1184 keyboard and serial format: kbd,<serial_device>[,baud]
1185 Optional Kernel mode setting:
1186 kms, kbd format: kms,kbd
1187 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1189 kgdbwait [KGDB] Stop kernel execution and enter the
1190 kernel debugger at the earliest opportunity.
1192 kmac= [MIPS] korina ethernet MAC address.
1193 Configure the RouterBoard 532 series on-chip
1194 Ethernet adapter MAC address.
1196 kmemleak= [KNL] Boot-time kmemleak enable/disable
1197 Valid arguments: on, off
1198 Default: on
1200 kstack=N [X86] Print N words from the kernel stack
1201 in oops dumps.
1203 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1204 Default is 0 (don't ignore, but inject #GP)
1206 kvm.oos_shadow= [KVM] Disable out-of-sync shadow paging.
1207 Default is 1 (enabled)
1209 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1210 KVM MMU at runtime.
1211 Default is 0 (off)
1213 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1214 Default is 1 (enabled)
1216 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1217 for all guests.
1218 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1220 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1221 (virtualized MMU) support on capable Intel chips.
1222 Default is 1 (enabled)
1224 kvm-intel.emulate_invalid_guest_state=
1225 [KVM,Intel] Enable emulation of invalid guest states
1226 Default is 0 (disabled)
1228 kvm-intel.flexpriority=
1229 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1230 Default is 1 (enabled)
1232 kvm-intel.nested=
1233 [KVM,Intel] Enable VMX nesting (nVMX).
1234 Default is 0 (disabled)
1236 kvm-intel.unrestricted_guest=
1237 [KVM,Intel] Disable unrestricted guest feature
1238 (virtualized real and unpaged mode) on capable
1239 Intel chips. Default is 1 (enabled)
1241 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1242 feature (tagged TLBs) on capable Intel chips.
1243 Default is 1 (enabled)
1245 l2cr= [PPC]
1247 l3cr= [PPC]
1249 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1250 disabled it.
1252 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1253 in C2 power state.
1255 libata.dma= [LIBATA] DMA control
1256 libata.dma=0 Disable all PATA and SATA DMA
1257 libata.dma=1 PATA and SATA Disk DMA only
1258 libata.dma=2 ATAPI (CDROM) DMA only
1259 libata.dma=4 Compact Flash DMA only
1260 Combinations also work, so libata.dma=3 enables DMA
1261 for disks and CDROMs, but not CFs.
1263 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1264 libata.ignore_hpa=0 keep BIOS limits (default)
1265 libata.ignore_hpa=1 ignore limits, using full disk
1267 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1268 when set.
1269 Format: <int>
1271 libata.force= [LIBATA] Force configurations. The format is comma
1272 separated list of "[ID:]VAL" where ID is
1273 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1274 matching port, link or device. Basically, it matches
1275 the ATA ID string printed on console by libata. If
1276 the whole ID part is omitted, the last PORT and DEVICE
1277 values are used. If ID hasn't been specified yet, the
1278 configuration applies to all ports, links and devices.
1280 If only DEVICE is omitted, the parameter applies to
1281 the port and all links and devices behind it. DEVICE
1282 number of 0 either selects the first device or the
1283 first fan-out link behind PMP device. It does not
1284 select the host link. DEVICE number of 15 selects the
1285 host link and device attached to it.
1287 The VAL specifies the configuration to force. As long
1288 as there's no ambiguity shortcut notation is allowed.
1289 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1290 The following configurations can be forced.
1292 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1293 Any ID with matching PORT is used.
1295 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1297 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1298 udma[/][16,25,33,44,66,100,133] notation is also
1299 allowed.
1301 * [no]ncq: Turn on or off NCQ.
1303 * nohrst, nosrst, norst: suppress hard, soft
1304 and both resets.
1306 * dump_id: dump IDENTIFY data.
1308 If there are multiple matching configurations changing
1309 the same attribute, the last one is used.
1311 memblock=debug [KNL] Enable memblock debug messages.
1313 load_ramdisk= [RAM] List of ramdisks to load from floppy
1314 See Documentation/blockdev/ramdisk.txt.
1316 lockd.nlm_grace_period=P [NFS] Assign grace period.
1317 Format: <integer>
1319 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1320 Format: <integer>
1322 lockd.nlm_timeout=T [NFS] Assign timeout value.
1323 Format: <integer>
1325 lockd.nlm_udpport=M [NFS] Assign UDP port.
1326 Format: <integer>
1328 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1329 Format: <irq>
1331 loglevel= All Kernel Messages with a loglevel smaller than the
1332 console loglevel will be printed to the console. It can
1333 also be changed with klogd or other programs. The
1334 loglevels are defined as follows:
1336 0 (KERN_EMERG) system is unusable
1337 1 (KERN_ALERT) action must be taken immediately
1338 2 (KERN_CRIT) critical conditions
1339 3 (KERN_ERR) error conditions
1340 4 (KERN_WARNING) warning conditions
1341 5 (KERN_NOTICE) normal but significant condition
1342 6 (KERN_INFO) informational
1343 7 (KERN_DEBUG) debug-level messages
1345 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1346 in bytes. n must be a power of two. The default
1347 size is set in the kernel config file.
1349 logo.nologo [FB] Disables display of the built-in Linux logo.
1350 This may be used to provide more screen space for
1351 kernel log messages and is useful when debugging
1352 kernel boot problems.
1354 lp=0 [LP] Specify parallel ports to use, e.g,
1355 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1356 lp=reset first parallel port). 'lp=0' disables the
1357 lp=auto printer driver. 'lp=reset' (which can be
1358 specified in addition to the ports) causes
1359 attached printers to be reset. Using
1360 lp=port1,port2,... specifies the parallel ports
1361 to associate lp devices with, starting with
1362 lp0. A port specification may be 'none' to skip
1363 that lp device, or a parport name such as
1364 'parport0'. Specifying 'lp=auto' instead of a
1365 port specification list means that device IDs
1366 from each port should be examined, to see if
1367 an IEEE 1284-compliant printer is attached; if
1368 so, the driver will manage that printer.
1369 See also header of drivers/char/lp.c.
1371 lpj=n [KNL]
1372 Sets loops_per_jiffy to given constant, thus avoiding
1373 time-consuming boot-time autodetection (up to 250 ms per
1374 CPU). 0 enables autodetection (default). To determine
1375 the correct value for your kernel, boot with normal
1376 autodetection and see what value is printed. Note that
1377 on SMP systems the preset will be applied to all CPUs,
1378 which is likely to cause problems if your CPUs need
1379 significantly divergent settings. An incorrect value
1380 will cause delays in the kernel to be wrong, leading to
1381 unpredictable I/O errors and other breakage. Although
1382 unlikely, in the extreme case this might damage your
1383 hardware.
1385 ltpc= [NET]
1386 Format: <io>,<irq>,<dma>
1388 machvec= [IA-64] Force the use of a particular machine-vector
1389 (machvec) in a generic kernel.
1390 Example: machvec=hpzx1_swiotlb
1392 machtype= [Loongson] Share the same kernel image file between different
1393 yeeloong laptop.
1394 Example: machtype=lemote-yeeloong-2f-7inch
1396 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1397 than or equal to this physical address is ignored.
1399 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1400 should make use of. maxcpus=n : n >= 0 limits the
1401 kernel to using 'n' processors. n=0 is a special case,
1402 it is equivalent to "nosmp", which also disables
1403 the IO APIC.
1405 max_loop= [LOOP] The number of loop block devices that get
1406 (loop.max_loop) unconditionally pre-created at init time. The default
1407 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1408 of statically allocating a predefined number, loop
1409 devices can be requested on-demand with the
1410 /dev/loop-control interface.
1412 mcatest= [IA-64]
1414 mce [X86-32] Machine Check Exception
1416 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1418 md= [HW] RAID subsystems devices and level
1419 See Documentation/md.txt.
1421 mdacon= [MDA]
1422 Format: <first>,<last>
1423 Specifies range of consoles to be captured by the MDA.
1425 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1426 Amount of memory to be used when the kernel is not able
1427 to see the whole system memory or for test.
1428 [X86-32] Use together with memmap= to avoid physical
1429 address space collisions. Without memmap= PCI devices
1430 could be placed at addresses belonging to unused RAM.
1432 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1433 memory.
1435 memchunk=nn[KMG]
1436 [KNL,SH] Allow user to override the default size for
1437 per-device physically contiguous DMA buffers.
1439 memmap=exactmap [KNL,X86] Enable setting of an exact
1440 E820 memory map, as specified by the user.
1441 Such memmap=exactmap lines can be constructed based on
1442 BIOS output or other requirements. See the memmap=nn@ss
1443 option description.
1445 memmap=nn[KMG]@ss[KMG]
1446 [KNL] Force usage of a specific region of memory
1447 Region of memory to be used, from ss to ss+nn.
1449 memmap=nn[KMG]#ss[KMG]
1450 [KNL,ACPI] Mark specific memory as ACPI data.
1451 Region of memory to be used, from ss to ss+nn.
1453 memmap=nn[KMG]$ss[KMG]
1454 [KNL,ACPI] Mark specific memory as reserved.
1455 Region of memory to be used, from ss to ss+nn.
1456 Example: Exclude memory from 0x18690000-0x1869ffff
1457 memmap=64K$0x18690000
1458 or
1459 memmap=0x10000$0x18690000
1461 memory_corruption_check=0/1 [X86]
1462 Some BIOSes seem to corrupt the first 64k of
1463 memory when doing things like suspend/resume.
1464 Setting this option will scan the memory
1465 looking for corruption. Enabling this will
1466 both detect corruption and prevent the kernel
1467 from using the memory being corrupted.
1468 However, its intended as a diagnostic tool; if
1469 repeatable BIOS-originated corruption always
1470 affects the same memory, you can use memmap=
1471 to prevent the kernel from using that memory.
1473 memory_corruption_check_size=size [X86]
1474 By default it checks for corruption in the low
1475 64k, making this memory unavailable for normal
1476 use. Use this parameter to scan for
1477 corruption in more or less memory.
1479 memory_corruption_check_period=seconds [X86]
1480 By default it checks for corruption every 60
1481 seconds. Use this parameter to check at some
1482 other rate. 0 disables periodic checking.
1484 memtest= [KNL,X86] Enable memtest
1485 Format: <integer>
1486 default : 0 <disable>
1487 Specifies the number of memtest passes to be
1488 performed. Each pass selects another test
1489 pattern from a given set of patterns. Memtest
1490 fills the memory with this pattern, validates
1491 memory contents and reserves bad memory
1492 regions that are detected.
1494 meye.*= [HW] Set MotionEye Camera parameters
1495 See Documentation/video4linux/meye.txt.
1497 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1498 Multi-Function General Purpose Timers on AMD Geode
1499 platforms.
1501 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1502 the BIOS has incorrectly applied a workaround. TinyBIOS
1503 version 0.98 is known to be affected, 0.99 fixes the
1504 problem by letting the user disable the workaround.
1506 mga= [HW,DRM]
1508 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1509 physical address is ignored.
1511 mini2440= [ARM,HW,KNL]
1512 Format:[0..2][b][c][t]
1513 Default: "0tb"
1514 MINI2440 configuration specification:
1515 0 - The attached screen is the 3.5" TFT
1516 1 - The attached screen is the 7" TFT
1517 2 - The VGA Shield is attached (1024x768)
1518 Leaving out the screen size parameter will not load
1519 the TFT driver, and the framebuffer will be left
1520 unconfigured.
1521 b - Enable backlight. The TFT backlight pin will be
1522 linked to the kernel VESA blanking code and a GPIO
1523 LED. This parameter is not necessary when using the
1524 VGA shield.
1525 c - Enable the s3c camera interface.
1526 t - Reserved for enabling touchscreen support. The
1527 touchscreen support is not enabled in the mainstream
1528 kernel as of 2.6.30, a preliminary port can be found
1529 in the "bleeding edge" mini2440 support kernel at
1530 http://repo.or.cz/w/linux-2.6/mini2440.git
1532 mminit_loglevel=
1533 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1534 parameter allows control of the logging verbosity for
1535 the additional memory initialisation checks. A value
1536 of 0 disables mminit logging and a level of 4 will
1537 log everything. Information is printed at KERN_DEBUG
1538 so loglevel=8 may also need to be specified.
1540 mousedev.tap_time=
1541 [MOUSE] Maximum time between finger touching and
1542 leaving touchpad surface for touch to be considered
1543 a tap and be reported as a left button click (for
1544 touchpads working in absolute mode only).
1545 Format: <msecs>
1546 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1547 reporting absolute coordinates, such as tablets
1548 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1549 reporting absolute coordinates, such as tablets
1551 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1552 is similar to kernelcore except it specifies the
1553 amount of memory used for migratable allocations.
1554 If both kernelcore and movablecore is specified,
1555 then kernelcore will be at *least* the specified
1556 value but may be more. If movablecore on its own
1557 is specified, the administrator must be careful
1558 that the amount of memory usable for all allocations
1559 is not too small.
1561 MTD_Partition= [MTD]
1562 Format: <name>,<region-number>,<size>,<offset>
1564 MTD_Region= [MTD] Format:
1565 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1567 mtdparts= [MTD]
1568 See drivers/mtd/cmdlinepart.c.
1570 multitce=off [PPC] This parameter disables the use of the pSeries
1571 firmware feature for updating multiple TCE entries
1572 at a time.
1574 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1576 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1578 boundary - index of last SLC block on Flex-OneNAND.
1579 The remaining blocks are configured as MLC blocks.
1580 lock - Configure if Flex-OneNAND boundary should be locked.
1581 Once locked, the boundary cannot be changed.
1582 1 indicates lock status, 0 indicates unlock status.
1584 mtdset= [ARM]
1585 ARM/S3C2412 JIVE boot control
1587 See arch/arm/mach-s3c2412/mach-jive.c
1589 mtouchusb.raw_coordinates=
1590 [HW] Make the MicroTouch USB driver use raw coordinates
1591 ('y', default) or cooked coordinates ('n')
1593 mtrr_chunk_size=nn[KMG] [X86]
1594 used for mtrr cleanup. It is largest continuous chunk
1595 that could hold holes aka. UC entries.
1597 mtrr_gran_size=nn[KMG] [X86]
1598 Used for mtrr cleanup. It is granularity of mtrr block.
1599 Default is 1.
1600 Large value could prevent small alignment from
1601 using up MTRRs.
1603 mtrr_spare_reg_nr=n [X86]
1604 Format: <integer>
1605 Range: 0,7 : spare reg number
1606 Default : 1
1607 Used for mtrr cleanup. It is spare mtrr entries number.
1608 Set to 2 or more if your graphical card needs more.
1610 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1612 netdev= [NET] Network devices parameters
1613 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1614 Note that mem_start is often overloaded to mean
1615 something different and driver-specific.
1616 This usage is only documented in each driver source
1617 file if at all.
1619 nf_conntrack.acct=
1620 [NETFILTER] Enable connection tracking flow accounting
1621 0 to disable accounting
1622 1 to enable accounting
1623 Default value is 0.
1625 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1626 See Documentation/filesystems/nfs/nfsroot.txt.
1628 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1629 See Documentation/filesystems/nfs/nfsroot.txt.
1631 nfsrootdebug [NFS] enable nfsroot debugging messages.
1632 See Documentation/filesystems/nfs/nfsroot.txt.
1634 nfs.callback_tcpport=
1635 [NFS] set the TCP port on which the NFSv4 callback
1636 channel should listen.
1638 nfs.cache_getent=
1639 [NFS] sets the pathname to the program which is used
1640 to update the NFS client cache entries.
1642 nfs.cache_getent_timeout=
1643 [NFS] sets the timeout after which an attempt to
1644 update a cache entry is deemed to have failed.
1646 nfs.idmap_cache_timeout=
1647 [NFS] set the maximum lifetime for idmapper cache
1648 entries.
1650 nfs.enable_ino64=
1651 [NFS] enable 64-bit inode numbers.
1652 If zero, the NFS client will fake up a 32-bit inode
1653 number for the readdir() and stat() syscalls instead
1654 of returning the full 64-bit number.
1655 The default is to return 64-bit inode numbers.
1657 nfs.nfs4_disable_idmapping=
1658 [NFSv4] When set, this option disables the NFSv4
1659 idmapper on the client, but only if the mount
1660 is using the 'sec=sys' security flavour. This may
1661 make migration from legacy NFSv2/v3 systems easier
1662 provided that the server has the appropriate support.
1663 The default is to always enable NFSv4 idmapping.
1665 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1666 when a NMI is triggered.
1667 Format: [state][,regs][,debounce][,die]
1669 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1670 Format: [panic,][nopanic,][num]
1671 Valid num: 0
1672 0 - turn nmi_watchdog off
1673 When panic is specified, panic when an NMI watchdog
1674 timeout occurs (or 'nopanic' to override the opposite
1675 default).
1676 This is useful when you use a panic=... timeout and
1677 need the box quickly up again.
1679 netpoll.carrier_timeout=
1680 [NET] Specifies amount of time (in seconds) that
1681 netpoll should wait for a carrier. By default netpoll
1682 waits 4 seconds.
1684 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1685 emulation library even if a 387 maths coprocessor
1686 is present.
1688 no_console_suspend
1689 [HW] Never suspend the console
1690 Disable suspending of consoles during suspend and
1691 hibernate operations. Once disabled, debugging
1692 messages can reach various consoles while the rest
1693 of the system is being put to sleep (ie, while
1694 debugging driver suspend/resume hooks). This may
1695 not work reliably with all consoles, but is known
1696 to work with serial and VGA consoles.
1697 To facilitate more flexible debugging, we also add
1698 console_suspend, a printk module parameter to control
1699 it. Users could use console_suspend (usually
1700 /sys/module/printk/parameters/console_suspend) to
1701 turn on/off it dynamically.
1703 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1704 caches in the slab allocator. Saves per-node memory,
1705 but will impact performance.
1707 noalign [KNL,ARM]
1709 noapic [SMP,APIC] Tells the kernel to not make use of any
1710 IOAPICs that may be present in the system.
1712 noautogroup Disable scheduler automatic task group creation.
1714 nobats [PPC] Do not use BATs for mapping kernel lowmem
1715 on "Classic" PPC cores.
1717 nocache [ARM]
1719 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1721 nodelayacct [KNL] Disable per-task delay accounting
1723 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1725 nodsp [SH] Disable hardware DSP at boot time.
1727 noefi [X86] Disable EFI runtime services support.
1729 noexec [IA-64]
1731 noexec [X86]
1732 On X86-32 available only on PAE configured kernels.
1733 noexec=on: enable non-executable mappings (default)
1734 noexec=off: disable non-executable mappings
1736 nosmep [X86]
1737 Disable SMEP (Supervisor Mode Execution Protection)
1738 even if it is supported by processor.
1740 noexec32 [X86-64]
1741 This affects only 32-bit executables.
1742 noexec32=on: enable non-executable mappings (default)
1743 read doesn't imply executable mappings
1744 noexec32=off: disable non-executable mappings
1745 read implies executable mappings
1747 nofpu [SH] Disable hardware FPU at boot time.
1749 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1750 register save and restore. The kernel will only save
1751 legacy floating-point registers on task switch.
1753 noxsave [BUGS=X86] Disables x86 extended register state save
1754 and restore using xsave. The kernel will fallback to
1755 enabling legacy floating-point and sse state.
1757 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1758 wfi(ARM) instruction doesn't work correctly and not to
1759 use it. This is also useful when using JTAG debugger.
1761 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1762 instruction doesn't work correctly and not to
1763 use it.
1765 no_file_caps Tells the kernel not to honor file capabilities. The
1766 only way then for a file to be executed with privilege
1767 is to be setuid root or executed by root.
1769 nohalt [IA-64] Tells the kernel not to use the power saving
1770 function PAL_HALT_LIGHT when idle. This increases
1771 power-consumption. On the positive side, it reduces
1772 interrupt wake-up latency, which may improve performance
1773 in certain environments such as networked servers or
1774 real-time systems.
1776 nohz= [KNL] Boottime enable/disable dynamic ticks
1777 Valid arguments: on, off
1778 Default: on
1780 noiotrap [SH] Disables trapped I/O port accesses.
1782 noirqdebug [X86-32] Disables the code which attempts to detect and
1783 disable unhandled interrupt sources.
1785 no_timer_check [X86,APIC] Disables the code which tests for
1786 broken timer IRQ sources.
1788 noisapnp [ISAPNP] Disables ISA PnP code.
1790 noinitrd [RAM] Tells the kernel not to load any configured
1791 initial RAM disk.
1793 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1794 remapping.
1795 [Deprecated - use intremap=off]
1797 nointroute [IA-64]
1799 nojitter [IA-64] Disables jitter checking for ITC timers.
1801 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1803 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1804 fault handling.
1806 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1807 steal time is computed, but won't influence scheduler
1808 behaviour
1810 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1812 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1814 noltlbs [PPC] Do not use large page/tlb entries for kernel
1815 lowmem mapping on PPC40x.
1817 nomca [IA-64] Disable machine check abort handling
1819 nomce [X86-32] Machine Check Exception
1821 nomfgpt [X86-32] Disable Multi-Function General Purpose
1822 Timer usage (for AMD Geode machines).
1824 nopat [X86] Disable PAT (page attribute table extension of
1825 pagetables) support.
1827 norandmaps Don't use address space randomization. Equivalent to
1828 echo 0 > /proc/sys/kernel/randomize_va_space
1830 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1832 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1833 with UP alternatives
1835 noresidual [PPC] Don't use residual data on PReP machines.
1837 nordrand [X86] Disable the direct use of the RDRAND
1838 instruction even if it is supported by the
1839 processor. RDRAND is still available to user
1840 space applications.
1842 noresume [SWSUSP] Disables resume and restores original swap
1843 space.
1845 no-scroll [VGA] Disables scrollback.
1846 This is required for the Braillex ib80-piezo Braille
1847 reader made by F.H. Papenmeier (Germany).
1849 nosbagart [IA-64]
1851 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1853 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1854 and disable the IO APIC. legacy for "maxcpus=0".
1856 nosoftlockup [KNL] Disable the soft-lockup detector.
1858 nosync [HW,M68K] Disables sync negotiation for all devices.
1860 notsc [BUGS=X86-32] Disable Time Stamp Counter
1862 nousb [USB] Disable the USB subsystem
1864 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1866 nowb [ARM]
1868 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1870 nptcg= [IA-64] Override max number of concurrent global TLB
1871 purges which is reported from either PAL_VM_SUMMARY or
1872 SAL PALO.
1874 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1875 could support. nr_cpus=n : n >= 1 limits the kernel to
1876 supporting 'n' processors. Later in runtime you can not
1877 use hotplug cpu feature to put more cpu back to online.
1878 just like you compile the kernel NR_CPUS=n
1880 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1882 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1883 one of ['zone', 'node', 'default'] can be specified
1884 This can be set from sysctl after boot.
1885 See Documentation/sysctl/vm.txt for details.
1887 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1888 See Documentation/debugging-via-ohci1394.txt for more
1889 info.
1891 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1892 Rather than timing out after 20 ms if an EC
1893 command is not properly ACKed, override the length
1894 of the timeout. We have interrupts disabled while
1895 waiting for the ACK, so if this is set too high
1896 interrupts *may* be lost!
1898 omap_mux= [OMAP] Override bootloader pin multiplexing.
1899 Format: <mux_mode0.mode_name=value>...
1900 For example, to override I2C bus2:
1901 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1903 oprofile.timer= [HW]
1904 Use timer interrupt instead of performance counters
1906 oprofile.cpu_type= Force an oprofile cpu type
1907 This might be useful if you have an older oprofile
1908 userland or if you want common events.
1909 Format: { arch_perfmon }
1910 arch_perfmon: [X86] Force use of architectural
1911 perfmon on Intel CPUs instead of the
1912 CPU specific event set.
1914 oops=panic Always panic on oopses. Default is to just kill the
1915 process, but there is a small probability of
1916 deadlocking the machine.
1917 This will also cause panics on machine check exceptions.
1918 Useful together with panic=30 to trigger a reboot.
1920 OSS [HW,OSS]
1921 See Documentation/sound/oss/oss-parameters.txt
1923 panic= [KNL] Kernel behaviour on panic: delay <timeout>
1924 timeout > 0: seconds before rebooting
1925 timeout = 0: wait forever
1926 timeout < 0: reboot immediately
1927 Format: <timeout>
1929 parkbd.port= [HW] Parallel port number the keyboard adapter is
1930 connected to, default is 0.
1931 Format: <parport#>
1932 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1933 0 for XT, 1 for AT (default is AT).
1934 Format: <mode>
1936 parport= [HW,PPT] Specify parallel ports. 0 disables.
1937 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1938 Use 'auto' to force the driver to use any
1939 IRQ/DMA settings detected (the default is to
1940 ignore detected IRQ/DMA settings because of
1941 possible conflicts). You can specify the base
1942 address, IRQ, and DMA settings; IRQ and DMA
1943 should be numbers, or 'auto' (for using detected
1944 settings on that particular port), or 'nofifo'
1945 (to avoid using a FIFO even if it is detected).
1946 Parallel ports are assigned in the order they
1947 are specified on the command line, starting
1948 with parport0.
1950 parport_init_mode= [HW,PPT]
1951 Configure VIA parallel port to operate in
1952 a specific mode. This is necessary on Pegasos
1953 computer where firmware has no options for setting
1954 up parallel port mode and sets it to spp.
1955 Currently this function knows 686a and 8231 chips.
1956 Format: [spp|ps2|epp|ecp|ecpepp]
1958 pause_on_oops=
1959 Halt all CPUs after the first oops has been printed for
1960 the specified number of seconds. This is to be used if
1961 your oopses keep scrolling off the screen.
1963 pcbit= [HW,ISDN]
1965 pcd. [PARIDE]
1966 See header of drivers/block/paride/pcd.c.
1967 See also Documentation/blockdev/paride.txt.
1969 pci=option[,option...] [PCI] various PCI subsystem options:
1970 earlydump [X86] dump PCI config space before the kernel
1971 changes anything
1972 off [X86] don't probe for the PCI bus
1973 bios [X86-32] force use of PCI BIOS, don't access
1974 the hardware directly. Use this if your machine
1975 has a non-standard PCI host bridge.
1976 nobios [X86-32] disallow use of PCI BIOS, only direct
1977 hardware access methods are allowed. Use this
1978 if you experience crashes upon bootup and you
1979 suspect they are caused by the BIOS.
1980 conf1 [X86] Force use of PCI Configuration
1981 Mechanism 1.
1982 conf2 [X86] Force use of PCI Configuration
1983 Mechanism 2.
1984 noaer [PCIE] If the PCIEAER kernel config parameter is
1985 enabled, this kernel boot option can be used to
1986 disable the use of PCIE advanced error reporting.
1987 nodomains [PCI] Disable support for multiple PCI
1988 root domains (aka PCI segments, in ACPI-speak).
1989 nommconf [X86] Disable use of MMCONFIG for PCI
1990 Configuration
1991 check_enable_amd_mmconf [X86] check for and enable
1992 properly configured MMIO access to PCI
1993 config space on AMD family 10h CPU
1994 nomsi [MSI] If the PCI_MSI kernel config parameter is
1995 enabled, this kernel boot option can be used to
1996 disable the use of MSI interrupts system-wide.
1997 noioapicquirk [APIC] Disable all boot interrupt quirks.
1998 Safety option to keep boot IRQs enabled. This
1999 should never be necessary.
2000 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2001 primary IO-APIC for bridges that cannot disable
2002 boot IRQs. This fixes a source of spurious IRQs
2003 when the system masks IRQs.
2004 noioapicreroute [APIC] Disable workaround that uses the
2005 boot IRQ equivalent of an IRQ that connects to
2006 a chipset where boot IRQs cannot be disabled.
2007 The opposite of ioapicreroute.
2008 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2009 routing table. These calls are known to be buggy
2010 on several machines and they hang the machine
2011 when used, but on other computers it's the only
2012 way to get the interrupt routing table. Try
2013 this option if the kernel is unable to allocate
2014 IRQs or discover secondary PCI buses on your
2015 motherboard.
2016 rom [X86] Assign address space to expansion ROMs.
2017 Use with caution as certain devices share
2018 address decoders between ROMs and other
2019 resources.
2020 norom [X86] Do not assign address space to
2021 expansion ROMs that do not already have
2022 BIOS assigned address ranges.
2023 nobar [X86] Do not assign address space to the
2024 BARs that weren't assigned by the BIOS.
2025 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2026 assigned automatically to PCI devices. You can
2027 make the kernel exclude IRQs of your ISA cards
2028 this way.
2029 pirqaddr=0xAAAAA [X86] Specify the physical address
2030 of the PIRQ table (normally generated
2031 by the BIOS) if it is outside the
2032 F0000h-100000h range.
2033 lastbus=N [X86] Scan all buses thru bus #N. Can be
2034 useful if the kernel is unable to find your
2035 secondary buses and you want to tell it
2036 explicitly which ones they are.
2037 assign-busses [X86] Always assign all PCI bus
2038 numbers ourselves, overriding
2039 whatever the firmware may have done.
2040 usepirqmask [X86] Honor the possible IRQ mask stored
2041 in the BIOS $PIR table. This is needed on
2042 some systems with broken BIOSes, notably
2043 some HP Pavilion N5400 and Omnibook XE3
2044 notebooks. This will have no effect if ACPI
2045 IRQ routing is enabled.
2046 noacpi [X86] Do not use ACPI for IRQ routing
2047 or for PCI scanning.
2048 use_crs [X86] Use PCI host bridge window information
2049 from ACPI. On BIOSes from 2008 or later, this
2050 is enabled by default. If you need to use this,
2051 please report a bug.
2052 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2053 If you need to use this, please report a bug.
2054 routeirq Do IRQ routing for all PCI devices.
2055 This is normally done in pci_enable_device(),
2056 so this option is a temporary workaround
2057 for broken drivers that don't call it.
2058 skip_isa_align [X86] do not align io start addr, so can
2059 handle more pci cards
2060 firmware [ARM] Do not re-enumerate the bus but instead
2061 just use the configuration from the
2062 bootloader. This is currently used on
2063 IXP2000 systems where the bus has to be
2064 configured a certain way for adjunct CPUs.
2065 noearly [X86] Don't do any early type 1 scanning.
2066 This might help on some broken boards which
2067 machine check when some devices' config space
2068 is read. But various workarounds are disabled
2069 and some IOMMU drivers will not work.
2070 bfsort Sort PCI devices into breadth-first order.
2071 This sorting is done to get a device
2072 order compatible with older (<= 2.4) kernels.
2073 nobfsort Don't sort PCI devices into breadth-first order.
2074 cbiosize=nn[KMG] The fixed amount of bus space which is
2075 reserved for the CardBus bridge's IO window.
2076 The default value is 256 bytes.
2077 cbmemsize=nn[KMG] The fixed amount of bus space which is
2078 reserved for the CardBus bridge's memory
2079 window. The default value is 64 megabytes.
2080 resource_alignment=
2081 Format:
2082 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2083 Specifies alignment and device to reassign
2084 aligned memory resources.
2085 If <order of align> is not specified,
2086 PAGE_SIZE is used as alignment.
2087 PCI-PCI bridge can be specified, if resource
2088 windows need to be expanded.
2089 ecrc= Enable/disable PCIe ECRC (transaction layer
2090 end-to-end CRC checking).
2091 bios: Use BIOS/firmware settings. This is the
2092 the default.
2093 off: Turn ECRC off
2094 on: Turn ECRC on.
2095 realloc reallocate PCI resources if allocations done by BIOS
2096 are erroneous.
2098 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2099 Management.
2100 off Disable ASPM.
2101 force Enable ASPM even on devices that claim not to support it.
2102 WARNING: Forcing ASPM on may cause system lockups.
2104 pcie_ports= [PCIE] PCIe ports handling:
2105 auto Ask the BIOS whether or not to use native PCIe services
2106 associated with PCIe ports (PME, hot-plug, AER). Use
2107 them only if that is allowed by the BIOS.
2108 native Use native PCIe services associated with PCIe ports
2109 unconditionally.
2110 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2111 ports driver.
2113 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2114 nomsi Do not use MSI for native PCIe PME signaling (this makes
2115 all PCIe root ports use INTx for all services).
2117 pcmv= [HW,PCMCIA] BadgePAD 4
2119 pd. [PARIDE]
2120 See Documentation/blockdev/paride.txt.
2122 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2123 boot time.
2124 Format: { 0 | 1 }
2125 See arch/parisc/kernel/pdc_chassis.c
2127 percpu_alloc= Select which percpu first chunk allocator to use.
2128 Currently supported values are "embed" and "page".
2129 Archs may support subset or none of the selections.
2130 See comments in mm/percpu.c for details on each
2131 allocator. This parameter is primarily for debugging
2132 and performance comparison.
2134 pf. [PARIDE]
2135 See Documentation/blockdev/paride.txt.
2137 pg. [PARIDE]
2138 See Documentation/blockdev/paride.txt.
2140 pirq= [SMP,APIC] Manual mp-table setup
2141 See Documentation/x86/i386/IO-APIC.txt.
2143 plip= [PPT,NET] Parallel port network link
2144 Format: { parport<nr> | timid | 0 }
2145 See also Documentation/parport.txt.
2147 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2148 Override pmtimer IOPort with a hex value.
2149 e.g. pmtmr=0x508
2151 pnp.debug=1 [PNP]
2152 Enable PNP debug messages (depends on the
2153 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2154 via /sys/module/pnp/parameters/debug. We always show
2155 current resource usage; turning this on also shows
2156 possible settings and some assignment information.
2158 pnpacpi= [ACPI]
2159 { off }
2161 pnpbios= [ISAPNP]
2162 { on | off | curr | res | no-curr | no-res }
2164 pnp_reserve_irq=
2165 [ISAPNP] Exclude IRQs for the autoconfiguration
2167 pnp_reserve_dma=
2168 [ISAPNP] Exclude DMAs for the autoconfiguration
2170 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2171 Ranges are in pairs (I/O port base and size).
2173 pnp_reserve_mem=
2174 [ISAPNP] Exclude memory regions for the
2175 autoconfiguration.
2176 Ranges are in pairs (memory base and size).
2178 ports= [IP_VS_FTP] IPVS ftp helper module
2179 Default is 21.
2180 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2181 may be specified.
2182 Format: <port>,<port>....
2184 print-fatal-signals=
2185 [KNL] debug: print fatal signals
2187 If enabled, warn about various signal handling
2188 related application anomalies: too many signals,
2189 too many POSIX.1 timers, fatal signals causing a
2190 coredump - etc.
2192 If you hit the warning due to signal overflow,
2193 you might want to try "ulimit -i unlimited".
2195 default: off.
2197 printk.time= Show timing data prefixed to each printk message line
2198 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2200 processor.max_cstate= [HW,ACPI]
2201 Limit processor to maximum C-state
2202 max_cstate=9 overrides any DMI blacklist limit.
2204 processor.nocst [HW,ACPI]
2205 Ignore the _CST method to determine C-states,
2206 instead using the legacy FADT method
2208 profile= [KNL] Enable kernel profiling via /proc/profile
2209 Format: [schedule,]<number>
2210 Param: "schedule" - profile schedule points.
2211 Param: <number> - step/bucket size as a power of 2 for
2212 statistical time based profiling.
2213 Param: "sleep" - profile D-state sleeping (millisecs).
2214 Requires CONFIG_SCHEDSTATS
2215 Param: "kvm" - profile VM exits.
2217 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2218 before loading.
2219 See Documentation/blockdev/ramdisk.txt.
2221 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2222 probe for; one of (bare|imps|exps|lifebook|any).
2223 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2224 per second.
2225 psmouse.resetafter= [HW,MOUSE]
2226 Try to reset the device after so many bad packets
2227 (0 = never).
2228 psmouse.resolution=
2229 [HW,MOUSE] Set desired mouse resolution, in dpi.
2230 psmouse.smartscroll=
2231 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2232 0 = disabled, 1 = enabled (default).
2234 pstore.backend= Specify the name of the pstore backend to use
2236 pt. [PARIDE]
2237 See Documentation/blockdev/paride.txt.
2239 pty.legacy_count=
2240 [KNL] Number of legacy pty's. Overwrites compiled-in
2241 default number.
2243 quiet [KNL] Disable most log messages
2245 r128= [HW,DRM]
2247 raid= [HW,RAID]
2248 See Documentation/md.txt.
2250 ramdisk_blocksize= [RAM]
2251 See Documentation/blockdev/ramdisk.txt.
2253 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2254 See Documentation/blockdev/ramdisk.txt.
2256 rcupdate.blimit= [KNL,BOOT]
2257 Set maximum number of finished RCU callbacks to process
2258 in one batch.
2260 rcupdate.qhimark= [KNL,BOOT]
2261 Set threshold of queued
2262 RCU callbacks over which batch limiting is disabled.
2264 rcupdate.qlowmark= [KNL,BOOT]
2265 Set threshold of queued RCU callbacks below which
2266 batch limiting is re-enabled.
2268 rdinit= [KNL]
2269 Format: <full_path>
2270 Run specified binary instead of /init from the ramdisk,
2271 used for early userspace startup. See initrd.
2273 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2274 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2275 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2277 relax_domain_level=
2278 [KNL, SMP] Set scheduler's default relax_domain_level.
2279 See Documentation/cgroups/cpusets.txt.
2281 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2283 reservetop= [X86-32]
2284 Format: nn[KMG]
2285 Reserves a hole at the top of the kernel virtual
2286 address space.
2288 reservelow= [X86]
2289 Format: nn[K]
2290 Set the amount of memory to reserve for BIOS at
2291 the bottom of the address space.
2293 reset_devices [KNL] Force drivers to reset the underlying device
2294 during initialization.
2296 resume= [SWSUSP]
2297 Specify the partition device for software suspend
2299 resume_offset= [SWSUSP]
2300 Specify the offset from the beginning of the partition
2301 given by "resume=" at which the swap header is located,
2302 in <PAGE_SIZE> units (needed only for swap files).
2303 See Documentation/power/swsusp-and-swap-files.txt
2305 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2306 read the resume files
2308 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2309 Useful for devices that are detected asynchronously
2310 (e.g. USB and MMC devices).
2312 hibernate= [HIBERNATION]
2313 noresume Don't check if there's a hibernation image
2314 present during boot.
2315 nocompress Don't compress/decompress hibernation images.
2317 retain_initrd [RAM] Keep initrd memory after extraction
2319 rhash_entries= [KNL,NET]
2320 Set number of hash buckets for route cache
2322 riscom8= [HW,SERIAL]
2323 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2325 ro [KNL] Mount root device read-only on boot
2327 root= [KNL] Root filesystem
2328 See name_to_dev_t comment in init/do_mounts.c.
2330 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2331 mount the root filesystem
2333 rootflags= [KNL] Set root filesystem mount option string
2335 rootfstype= [KNL] Set root filesystem type
2337 rootwait [KNL] Wait (indefinitely) for root device to show up.
2338 Useful for devices that are detected asynchronously
2339 (e.g. USB and MMC devices).
2341 rw [KNL] Mount root device read-write on boot
2343 S [KNL] Run init in single mode
2345 sa1100ir [NET]
2346 See drivers/net/irda/sa1100_ir.c.
2348 sbni= [NET] Granch SBNI12 leased line adapter
2350 sched_debug [KNL] Enables verbose scheduler debug messages.
2352 security= [SECURITY] Choose a security module to enable at boot.
2353 If this boot parameter is not specified, only the first
2354 security module asking for security registration will be
2355 loaded. An invalid security module name will be treated
2356 as if no module has been chosen.
2358 selinux= [SELINUX] Disable or enable SELinux at boot time.
2359 Format: { "0" | "1" }
2360 See security/selinux/Kconfig help text.
2361 0 -- disable.
2362 1 -- enable.
2363 Default value is set via kernel config option.
2364 If enabled at boot time, /selinux/disable can be used
2365 later to disable prior to initial policy load.
2367 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2368 Format: { "0" | "1" }
2369 See security/apparmor/Kconfig help text
2370 0 -- disable.
2371 1 -- enable.
2372 Default value is set via kernel config option.
2374 serialnumber [BUGS=X86-32]
2376 shapers= [NET]
2377 Maximal number of shapers.
2379 show_msr= [x86] show boot-time MSR settings
2380 Format: { <integer> }
2381 Show boot-time (BIOS-initialized) MSR settings.
2382 The parameter means the number of CPUs to show,
2383 for example 1 means boot CPU only.
2385 simeth= [IA-64]
2386 simscsi=
2388 slram= [HW,MTD]
2390 slub_debug[=options[,slabs]] [MM, SLUB]
2391 Enabling slub_debug allows one to determine the
2392 culprit if slab objects become corrupted. Enabling
2393 slub_debug can create guard zones around objects and
2394 may poison objects when not in use. Also tracks the
2395 last alloc / free. For more information see
2396 Documentation/vm/slub.txt.
2398 slub_max_order= [MM, SLUB]
2399 Determines the maximum allowed order for slabs.
2400 A high setting may cause OOMs due to memory
2401 fragmentation. For more information see
2402 Documentation/vm/slub.txt.
2404 slub_min_objects= [MM, SLUB]
2405 The minimum number of objects per slab. SLUB will
2406 increase the slab order up to slub_max_order to
2407 generate a sufficiently large slab able to contain
2408 the number of objects indicated. The higher the number
2409 of objects the smaller the overhead of tracking slabs
2410 and the less frequently locks need to be acquired.
2411 For more information see Documentation/vm/slub.txt.
2413 slub_min_order= [MM, SLUB]
2414 Determines the mininum page order for slabs. Must be
2415 lower than slub_max_order.
2416 For more information see Documentation/vm/slub.txt.
2418 slub_nomerge [MM, SLUB]
2419 Disable merging of slabs with similar size. May be
2420 necessary if there is some reason to distinguish
2421 allocs to different slabs. Debug options disable
2422 merging on their own.
2423 For more information see Documentation/vm/slub.txt.
2425 smart2= [HW]
2426 Format: <io1>[,<io2>[,...,<io8>]]
2428 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2429 attempt to substitute SMP alternatives once at boot.
2431 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2432 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2433 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2434 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2435 smsc-ircc2.ircc_irq= [HW] IRQ line
2436 smsc-ircc2.ircc_dma= [HW] DMA channel
2437 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2438 0: Toshiba Satellite 1800 (GP data pin select)
2439 1: Fast pin select (default)
2440 2: ATC IRMode
2442 softlockup_panic=
2443 [KNL] Should the soft-lockup detector generate panics.
2444 Format: <integer>
2446 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2447 See Documentation/laptops/sonypi.txt
2449 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2450 See Documentation/serial/specialix.txt.
2452 spia_io_base= [HW,MTD]
2453 spia_fio_base=
2454 spia_pedr=
2455 spia_peddr=
2457 stacktrace [FTRACE]
2458 Enabled the stack tracer on boot up.
2460 sti= [PARISC,HW]
2461 Format: <num>
2462 Set the STI (builtin display/keyboard on the HP-PARISC
2463 machines) console (graphic card) which should be used
2464 as the initial boot-console.
2465 See also comment in drivers/video/console/sticore.c.
2467 sti_font= [HW]
2468 See comment in drivers/video/console/sticore.c.
2470 stifb= [HW]
2471 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2473 sunrpc.min_resvport=
2474 sunrpc.max_resvport=
2475 [NFS,SUNRPC]
2476 SunRPC servers often require that client requests
2477 originate from a privileged port (i.e. a port in the
2478 range 0 < portnr < 1024).
2479 An administrator who wishes to reserve some of these
2480 ports for other uses may adjust the range that the
2481 kernel's sunrpc client considers to be privileged
2482 using these two parameters to set the minimum and
2483 maximum port values.
2485 sunrpc.pool_mode=
2486 [NFS]
2487 Control how the NFS server code allocates CPUs to
2488 service thread pools. Depending on how many NICs
2489 you have and where their interrupts are bound, this
2490 option will affect which CPUs will do NFS serving.
2491 Note: this parameter cannot be changed while the
2492 NFS server is running.
2494 auto the server chooses an appropriate mode
2495 automatically using heuristics
2496 global a single global pool contains all CPUs
2497 percpu one pool for each CPU
2498 pernode one pool for each NUMA node (equivalent
2499 to global on non-NUMA machines)
2501 sunrpc.tcp_slot_table_entries=
2502 sunrpc.udp_slot_table_entries=
2503 [NFS,SUNRPC]
2504 Sets the upper limit on the number of simultaneous
2505 RPC calls that can be sent from the client to a
2506 server. Increasing these values may allow you to
2507 improve throughput, but will also increase the
2508 amount of memory reserved for use by the client.
2510 swapaccount[=0|1]
2511 [KNL] Enable accounting of swap in memory resource
2512 controller if no parameter or 1 is given or disable
2513 it if 0 is given (See Documentation/cgroups/memory.txt)
2515 swiotlb= [IA-64] Number of I/O TLB slabs
2517 switches= [HW,M68k]
2519 sysfs.deprecated=0|1 [KNL]
2520 Enable/disable old style sysfs layout for old udev
2521 on older distributions. When this option is enabled
2522 very new udev will not work anymore. When this option
2523 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2524 in older udev will not work anymore.
2525 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2526 the kernel configuration.
2528 sysrq_always_enabled
2529 [KNL]
2530 Ignore sysrq setting - this boot parameter will
2531 neutralize any effect of /proc/sys/kernel/sysrq.
2532 Useful for debugging.
2534 tdfx= [HW,DRM]
2536 test_suspend= [SUSPEND]
2537 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2538 standby suspend) as the system sleep state to briefly
2539 enter during system startup. The system is woken from
2540 this state using a wakeup-capable RTC alarm.
2542 thash_entries= [KNL,NET]
2543 Set number of hash buckets for TCP connection
2545 thermal.act= [HW,ACPI]
2546 -1: disable all active trip points in all thermal zones
2547 <degrees C>: override all lowest active trip points
2549 thermal.crt= [HW,ACPI]
2550 -1: disable all critical trip points in all thermal zones
2551 <degrees C>: override all critical trip points
2553 thermal.nocrt= [HW,ACPI]
2554 Set to disable actions on ACPI thermal zone
2555 critical and hot trip points.
2557 thermal.off= [HW,ACPI]
2558 1: disable ACPI thermal control
2560 thermal.psv= [HW,ACPI]
2561 -1: disable all passive trip points
2562 <degrees C>: override all passive trip points to this
2563 value
2565 thermal.tzp= [HW,ACPI]
2566 Specify global default ACPI thermal zone polling rate
2567 <deci-seconds>: poll all this frequency
2568 0: no polling (default)
2570 threadirqs [KNL]
2571 Force threading of all interrupt handlers except those
2572 marked explicitely IRQF_NO_THREAD.
2574 topology= [S390]
2575 Format: {off | on}
2576 Specify if the kernel should make use of the cpu
2577 topology information if the hardware supports this.
2578 The scheduler will make use of this information and
2579 e.g. base its process migration decisions on it.
2580 Default is on.
2582 tp720= [HW,PS2]
2584 tpm_suspend_pcr=[HW,TPM]
2585 Format: integer pcr id
2586 Specify that at suspend time, the tpm driver
2587 should extend the specified pcr with zeros,
2588 as a workaround for some chips which fail to
2589 flush the last written pcr on TPM_SaveState.
2590 This will guarantee that all the other pcrs
2591 are saved.
2593 trace_buf_size=nn[KMG]
2594 [FTRACE] will set tracing buffer size.
2596 trace_event=[event-list]
2597 [FTRACE] Set and start specified trace events in order
2598 to facilitate early boot debugging.
2599 See also Documentation/trace/events.txt
2601 tsc= Disable clocksource stability checks for TSC.
2602 Format: <string>
2603 [x86] reliable: mark tsc clocksource as reliable, this
2604 disables clocksource verification at runtime, as well
2605 as the stability checks done at bootup. Used to enable
2606 high-resolution timer mode on older hardware, and in
2607 virtualized environment.
2608 [x86] noirqtime: Do not use TSC to do irq accounting.
2609 Used to run time disable IRQ_TIME_ACCOUNTING on any
2610 platforms where RDTSC is slow and this accounting
2611 can add overhead.
2613 turbografx.map[2|3]= [HW,JOY]
2614 TurboGraFX parallel port interface
2615 Format:
2616 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2617 See also Documentation/input/joystick-parport.txt
2619 udbg-immortal [PPC] When debugging early kernel crashes that
2620 happen after console_init() and before a proper
2621 console driver takes over, this boot options might
2622 help "seeing" what's going on.
2624 uhash_entries= [KNL,NET]
2625 Set number of hash buckets for UDP/UDP-Lite connections
2627 uhci-hcd.ignore_oc=
2628 [USB] Ignore overcurrent events (default N).
2629 Some badly-designed motherboards generate lots of
2630 bogus events, for ports that aren't wired to
2631 anything. Set this parameter to avoid log spamming.
2632 Note that genuine overcurrent events won't be
2633 reported either.
2635 unknown_nmi_panic
2636 [X86] Cause panic on unknown NMI.
2638 usbcore.authorized_default=
2639 [USB] Default USB device authorization:
2640 (default -1 = authorized except for wireless USB,
2641 0 = not authorized, 1 = authorized)
2643 usbcore.autosuspend=
2644 [USB] The autosuspend time delay (in seconds) used
2645 for newly-detected USB devices (default 2). This
2646 is the time required before an idle device will be
2647 autosuspended. Devices for which the delay is set
2648 to a negative value won't be autosuspended at all.
2650 usbcore.usbfs_snoop=
2651 [USB] Set to log all usbfs traffic (default 0 = off).
2653 usbcore.blinkenlights=
2654 [USB] Set to cycle leds on hubs (default 0 = off).
2656 usbcore.old_scheme_first=
2657 [USB] Start with the old device initialization
2658 scheme (default 0 = off).
2660 usbcore.use_both_schemes=
2661 [USB] Try the other device initialization scheme
2662 if the first one fails (default 1 = enabled).
2664 usbcore.initial_descriptor_timeout=
2665 [USB] Specifies timeout for the initial 64-byte
2666 USB_REQ_GET_DESCRIPTOR request in milliseconds
2667 (default 5000 = 5.0 seconds).
2669 usbhid.mousepoll=
2670 [USBHID] The interval which mice are to be polled at.
2672 usb-storage.delay_use=
2673 [UMS] The delay in seconds before a new device is
2674 scanned for Logical Units (default 5).
2676 usb-storage.quirks=
2677 [UMS] A list of quirks entries to supplement or
2678 override the built-in unusual_devs list. List
2679 entries are separated by commas. Each entry has
2680 the form VID:PID:Flags where VID and PID are Vendor
2681 and Product ID values (4-digit hex numbers) and
2682 Flags is a set of characters, each corresponding
2683 to a common usb-storage quirk flag as follows:
2684 a = SANE_SENSE (collect more than 18 bytes
2685 of sense data);
2686 b = BAD_SENSE (don't collect more than 18
2687 bytes of sense data);
2688 c = FIX_CAPACITY (decrease the reported
2689 device capacity by one sector);
2690 d = NO_READ_DISC_INFO (don't use
2691 READ_DISC_INFO command);
2692 e = NO_READ_CAPACITY_16 (don't use
2693 READ_CAPACITY_16 command);
2694 h = CAPACITY_HEURISTICS (decrease the
2695 reported device capacity by one
2696 sector if the number is odd);
2697 i = IGNORE_DEVICE (don't bind to this
2698 device);
2699 l = NOT_LOCKABLE (don't try to lock and
2700 unlock ejectable media);
2701 m = MAX_SECTORS_64 (don't transfer more
2702 than 64 sectors = 32 KB at a time);
2703 n = INITIAL_READ10 (force a retry of the
2704 initial READ(10) command);
2705 o = CAPACITY_OK (accept the capacity
2706 reported by the device);
2707 r = IGNORE_RESIDUE (the device reports
2708 bogus residue values);
2709 s = SINGLE_LUN (the device has only one
2710 Logical Unit);
2711 w = NO_WP_DETECT (don't test whether the
2712 medium is write-protected).
2713 Example: quirks=0419:aaf5:rl,0421:0433:rc
2715 user_debug= [KNL,ARM]
2716 Format: <int>
2717 See arch/arm/Kconfig.debug help text.
2718 1 - undefined instruction events
2719 2 - system calls
2720 4 - invalid data aborts
2721 8 - SIGSEGV faults
2722 16 - SIGBUS faults
2723 Example: user_debug=31
2725 userpte=
2726 [X86] Flags controlling user PTE allocations.
2728 nohigh = do not allocate PTE pages in
2729 HIGHMEM regardless of setting
2730 of CONFIG_HIGHPTE.
2732 vdso= [X86,SH]
2733 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2734 vdso=1: enable VDSO (default)
2735 vdso=0: disable VDSO mapping
2737 vdso32= [X86]
2738 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2739 vdso32=1: enable 32-bit VDSO (default)
2740 vdso32=0: disable 32-bit VDSO mapping
2742 vector= [IA-64,SMP]
2743 vector=percpu: enable percpu vector domain
2745 video= [FB] Frame buffer configuration
2746 See Documentation/fb/modedb.txt.
2748 vga= [BOOT,X86-32] Select a particular video mode
2749 See Documentation/x86/boot.txt and
2750 Documentation/svga.txt.
2751 Use vga=ask for menu.
2752 This is actually a boot loader parameter; the value is
2753 passed to the kernel using a special protocol.
2755 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2756 size of <nn>. This can be used to increase the
2757 minimum size (128MB on x86). It can also be used to
2758 decrease the size and leave more room for directly
2759 mapped kernel RAM.
2761 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2762 Format: <command>
2764 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2765 Format: <command>
2767 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2768 Format: <command>
2770 vsyscall= [X86-64]
2771 Controls the behavior of vsyscalls (i.e. calls to
2772 fixed addresses of 0xffffffffff600x00 from legacy
2773 code). Most statically-linked binaries and older
2774 versions of glibc use these calls. Because these
2775 functions are at fixed addresses, they make nice
2776 targets for exploits that can control RIP.
2778 emulate Vsyscalls turn into traps and are emulated
2779 reasonably safely.
2781 native [default] Vsyscalls are native syscall
2782 instructions.
2783 This is a little bit faster than trapping
2784 and makes a few dynamic recompilers work
2785 better than they would in emulation mode.
2786 It also makes exploits much easier to write.
2788 none Vsyscalls don't work at all. This makes
2789 them quite hard to use for exploits but
2790 might break your system.
2792 vt.cur_default= [VT] Default cursor shape.
2793 Format: 0xCCBBAA, where AA, BB, and CC are the same as
2794 the parameters of the <Esc>[?A;B;Cc escape sequence;
2795 see VGA-softcursor.txt. Default: 2 = underline.
2797 vt.default_blu= [VT]
2798 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2799 Change the default blue palette of the console.
2800 This is a 16-member array composed of values
2801 ranging from 0-255.
2803 vt.default_grn= [VT]
2804 Format: <green0>,<green1>,<green2>,...,<green15>
2805 Change the default green palette of the console.
2806 This is a 16-member array composed of values
2807 ranging from 0-255.
2809 vt.default_red= [VT]
2810 Format: <red0>,<red1>,<red2>,...,<red15>
2811 Change the default red palette of the console.
2812 This is a 16-member array composed of values
2813 ranging from 0-255.
2815 vt.default_utf8=
2816 [VT]
2817 Format=<0|1>
2818 Set system-wide default UTF-8 mode for all tty's.
2819 Default is 1, i.e. UTF-8 mode is enabled for all
2820 newly opened terminals.
2822 vt.global_cursor_default=
2823 [VT]
2824 Format=<-1|0|1>
2825 Set system-wide default for whether a cursor
2826 is shown on new VTs. Default is -1,
2827 i.e. cursors will be created by default unless
2828 overridden by individual drivers. 0 will hide
2829 cursors, 1 will display them.
2831 watchdog timers [HW,WDT] For information on watchdog timers,
2832 see Documentation/watchdog/watchdog-parameters.txt
2833 or other driver-specific files in the
2834 Documentation/watchdog/ directory.
2836 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2837 default x2apic cluster mode on platforms
2838 supporting x2apic.
2840 x86_mrst_timer= [X86-32,APBT]
2841 Choose timer option for x86 Moorestown MID platform.
2842 Two valid options are apbt timer only and lapic timer
2843 plus one apbt timer for broadcast timer.
2844 x86_mrst_timer=apbt_only | lapic_and_apbt
2846 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2847 xd_geo= See header of drivers/block/xd.c.
2849 xen_emul_unplug= [HW,X86,XEN]
2850 Unplug Xen emulated devices
2851 Format: [unplug0,][unplug1]
2852 ide-disks -- unplug primary master IDE devices
2853 aux-ide-disks -- unplug non-primary-master IDE devices
2854 nics -- unplug network devices
2855 all -- unplug all emulated devices (NICs and IDE disks)
2856 unnecessary -- unplugging emulated devices is
2857 unnecessary even if the host did not respond to
2858 the unplug protocol
2859 never -- do not unplug even if version check succeeds
2861 xirc2ps_cs= [NET,PCMCIA]
2862 Format:
2863 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2865 ______________________________________________________________________
2867 TODO:
2869 Add more DRM drivers.