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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
4 The following is a consolidated list of the kernel parameters as implemented
5 (mostly) by the __setup() macro and sorted into English Dictionary order
6 (defined as ignoring all punctuation and sorting digits before letters in a
7 case insensitive manner), and with descriptions where known.
9 Module parameters for loadable modules are specified only as the
10 parameter name with optional '=' and value as appropriate, such as:
12 modprobe usbcore blinkenlights=1
14 Module parameters for modules that are built into the kernel image
15 are specified on the kernel command line with the module name plus
16 '.' plus parameter name, with '=' and value if appropriate, such as:
18 usbcore.blinkenlights=1
20 Hyphens (dashes) and underscores are equivalent in parameter names, so
21 log_buf_len=1M print-fatal-signals=1
22 can also be entered as
23 log-buf-len=1M print_fatal_signals=1
26 This document may not be entirely up to date and comprehensive. The command
27 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
28 module. Loadable modules, after being loaded into the running kernel, also
29 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
30 parameters may be changed at runtime by the command
31 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
33 The parameters listed below are only valid if certain kernel build options were
34 enabled and if respective hardware is present. The text in square brackets at
35 the beginning of each description states the restrictions within which a
36 parameter is applicable:
38 ACPI ACPI support is enabled.
39 AGP AGP (Accelerated Graphics Port) is enabled.
40 ALSA ALSA sound support is enabled.
41 APIC APIC support is enabled.
42 APM Advanced Power Management support is enabled.
43 ARM ARM architecture is enabled.
44 AVR32 AVR32 architecture is enabled.
45 AX25 Appropriate AX.25 support is enabled.
46 BLACKFIN Blackfin architecture is enabled.
47 DRM Direct Rendering Management support is enabled.
48 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
49 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
50 EFI EFI Partitioning (GPT) is enabled
51 EIDE EIDE/ATAPI support is enabled.
52 EVM Extended Verification Module
53 FB The frame buffer device is enabled.
54 FTRACE Function tracing enabled.
55 GCOV GCOV profiling is enabled.
56 HW Appropriate hardware is enabled.
57 IA-64 IA-64 architecture is enabled.
58 IMA Integrity measurement architecture is enabled.
59 IOSCHED More than one I/O scheduler is enabled.
60 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
61 IPV6 IPv6 support is enabled.
62 ISAPNP ISA PnP code is enabled.
63 ISDN Appropriate ISDN support is enabled.
64 JOY Appropriate joystick support is enabled.
65 KGDB Kernel debugger support is enabled.
66 KVM Kernel Virtual Machine support is enabled.
67 LIBATA Libata driver is enabled
68 LP Printer support is enabled.
69 LOOP Loopback device support is enabled.
70 M68k M68k architecture is enabled.
71 These options have more detailed description inside of
72 Documentation/m68k/kernel-options.txt.
73 MCA MCA bus support is enabled.
74 MDA MDA console support is enabled.
75 MIPS MIPS architecture is enabled.
76 MOUSE Appropriate mouse support is enabled.
77 MSI Message Signaled Interrupts (PCI).
78 MTD MTD (Memory Technology Device) support is enabled.
79 NET Appropriate network support is enabled.
80 NUMA NUMA support is enabled.
81 NFS Appropriate NFS support is enabled.
82 OSS OSS sound support is enabled.
83 PV_OPS A paravirtualized kernel is enabled.
84 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
85 PARISC The PA-RISC architecture is enabled.
86 PCI PCI bus support is enabled.
87 PCIE PCI Express support is enabled.
88 PCMCIA The PCMCIA subsystem is enabled.
89 PNP Plug & Play support is enabled.
90 PPC PowerPC architecture is enabled.
91 PPT Parallel port support is enabled.
92 PS2 Appropriate PS/2 support is enabled.
93 RAM RAM disk support is enabled.
94 S390 S390 architecture is enabled.
95 SCSI Appropriate SCSI support is enabled.
96 A lot of drivers have their options described inside
97 the Documentation/scsi/ sub-directory.
98 SECURITY Different security models are enabled.
99 SELINUX SELinux support is enabled.
100 APPARMOR AppArmor support is enabled.
101 SERIAL Serial support is enabled.
102 SH SuperH architecture is enabled.
103 SMP The kernel is an SMP kernel.
104 SPARC Sparc architecture is enabled.
105 SWSUSP Software suspend (hibernation) is enabled.
106 SUSPEND System suspend states are enabled.
107 TPM TPM drivers are enabled.
108 TS Appropriate touchscreen support is enabled.
109 UMS USB Mass Storage support is enabled.
110 USB USB support is enabled.
111 USBHID USB Human Interface Device support is enabled.
112 V4L Video For Linux support is enabled.
113 VGA The VGA console has been enabled.
114 VT Virtual terminal support is enabled.
115 WDT Watchdog support is enabled.
116 XT IBM PC/XT MFM hard disk support is enabled.
117 X86-32 X86-32, aka i386 architecture is enabled.
118 X86-64 X86-64 architecture is enabled.
119 More X86-64 boot options can be found in
120 Documentation/x86/x86_64/boot-options.txt .
121 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
122 XEN Xen support is enabled
124 In addition, the following text indicates that the option:
126 BUGS= Relates to possible processor bugs on the said processor.
127 KNL Is a kernel start-up parameter.
128 BOOT Is a boot loader parameter.
130 Parameters denoted with BOOT are actually interpreted by the boot
131 loader, and have no meaning to the kernel directly.
132 Do not modify the syntax of boot loader parameters without extreme
133 need or coordination with <Documentation/x86/boot.txt>.
135 There are also arch-specific kernel-parameters not documented here.
136 See for example <Documentation/x86/x86_64/boot-options.txt>.
138 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
139 a trailing = on the name of any parameter states that that parameter will
140 be entered as an environment variable, whereas its absence indicates that
141 it will appear as a kernel argument readable via /proc/cmdline by programs
142 running once the system is up.
144 The number of kernel parameters is not limited, but the length of the
145 complete command line (parameters including spaces etc.) is limited to
146 a fixed number of characters. This limit depends on the architecture
147 and is between 256 and 4096 characters. It is defined in the file
148 ./include/asm/setup.h as COMMAND_LINE_SIZE.
150 Finally, the [KMG] suffix is commonly described after a number of kernel
151 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
152 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
153 bytes respectively. Such letter suffixes can also be entirely omitted.
156 acpi= [HW,ACPI,X86]
157 Advanced Configuration and Power Interface
158 Format: { force | off | strict | noirq | rsdt }
159 force -- enable ACPI if default was off
160 off -- disable ACPI if default was on
161 noirq -- do not use ACPI for IRQ routing
162 strict -- Be less tolerant of platforms that are not
163 strictly ACPI specification compliant.
164 rsdt -- prefer RSDT over (default) XSDT
165 copy_dsdt -- copy DSDT to memory
167 See also Documentation/power/runtime_pm.txt, pci=noacpi
169 acpi_rsdp= [ACPI,EFI,KEXEC]
170 Pass the RSDP address to the kernel, mostly used
171 on machines running EFI runtime service to boot the
172 second kernel for kdump.
174 acpi_apic_instance= [ACPI, IOAPIC]
175 Format: <int>
176 2: use 2nd APIC table, if available
177 1,0: use 1st APIC table
178 default: 0
180 acpi_backlight= [HW,ACPI]
181 acpi_backlight=vendor
182 acpi_backlight=video
183 If set to vendor, prefer vendor specific driver
184 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
185 of the ACPI video.ko driver.
187 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
188 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
189 Format: <int>
190 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
191 debug output. Bits in debug_layer correspond to a
192 _COMPONENT in an ACPI source file, e.g.,
193 #define _COMPONENT ACPI_PCI_COMPONENT
194 Bits in debug_level correspond to a level in
195 ACPI_DEBUG_PRINT statements, e.g.,
196 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
197 The debug_level mask defaults to "info". See
198 Documentation/acpi/debug.txt for more information about
199 debug layers and levels.
201 Enable processor driver info messages:
202 acpi.debug_layer=0x20000000
203 Enable PCI/PCI interrupt routing info messages:
204 acpi.debug_layer=0x400000
205 Enable AML "Debug" output, i.e., stores to the Debug
206 object while interpreting AML:
207 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
208 Enable all messages related to ACPI hardware:
209 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
211 Some values produce so much output that the system is
212 unusable. The "log_buf_len" parameter may be useful
213 if you need to capture more output.
215 acpi_irq_balance [HW,ACPI]
216 ACPI will balance active IRQs
217 default in APIC mode
219 acpi_irq_nobalance [HW,ACPI]
220 ACPI will not move active IRQs (default)
221 default in PIC mode
223 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
224 Format: <irq>,<irq>...
226 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
227 use by PCI
228 Format: <irq>,<irq>...
230 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
232 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
233 Format: To spoof as Windows 98: ="Microsoft Windows"
235 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
236 acpi_osi="string1" # add string1 -- only one string
237 acpi_osi="!string2" # remove built-in string2
238 acpi_osi= # disable all strings
240 acpi_pm_good [X86]
241 Override the pmtimer bug detection: force the kernel
242 to assume that this machine's pmtimer latches its value
243 and always returns good values.
245 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
246 Format: { level | edge | high | low }
248 acpi_serialize [HW,ACPI] force serialization of AML methods
250 acpi_skip_timer_override [HW,ACPI]
251 Recognize and ignore IRQ0/pin2 Interrupt Override.
252 For broken nForce2 BIOS resulting in XT-PIC timer.
254 acpi_sleep= [HW,ACPI] Sleep options
255 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
256 old_ordering, nonvs, sci_force_enable }
257 See Documentation/power/video.txt for information on
258 s3_bios and s3_mode.
259 s3_beep is for debugging; it makes the PC's speaker beep
260 as soon as the kernel's real-mode entry point is called.
261 s4_nohwsig prevents ACPI hardware signature from being
262 used during resume from hibernation.
263 old_ordering causes the ACPI 1.0 ordering of the _PTS
264 control method, with respect to putting devices into
265 low power states, to be enforced (the ACPI 2.0 ordering
266 of _PTS is used by default).
267 nonvs prevents the kernel from saving/restoring the
268 ACPI NVS memory during suspend/hibernation and resume.
269 sci_force_enable causes the kernel to set SCI_EN directly
270 on resume from S1/S3 (which is against the ACPI spec,
271 but some broken systems don't work without it).
273 acpi_use_timer_override [HW,ACPI]
274 Use timer override. For some broken Nvidia NF5 boards
275 that require a timer override, but don't have HPET
277 acpi_enforce_resources= [ACPI]
278 { strict | lax | no }
279 Check for resource conflicts between native drivers
280 and ACPI OperationRegions (SystemIO and SystemMemory
281 only). IO ports and memory declared in ACPI might be
282 used by the ACPI subsystem in arbitrary AML code and
283 can interfere with legacy drivers.
284 strict (default): access to resources claimed by ACPI
285 is denied; legacy drivers trying to access reserved
286 resources will fail to bind to device using them.
287 lax: access to resources claimed by ACPI is allowed;
288 legacy drivers trying to access reserved resources
289 will bind successfully but a warning message is logged.
290 no: ACPI OperationRegions are not marked as reserved,
291 no further checks are performed.
293 add_efi_memmap [EFI; X86] Include EFI memory map in
294 kernel's map of available physical RAM.
296 agp= [AGP]
297 { off | try_unsupported }
298 off: disable AGP support
299 try_unsupported: try to drive unsupported chipsets
300 (may crash computer or cause data corruption)
302 ALSA [HW,ALSA]
303 See Documentation/sound/alsa/alsa-parameters.txt
305 alignment= [KNL,ARM]
306 Allow the default userspace alignment fault handler
307 behaviour to be specified. Bit 0 enables warnings,
308 bit 1 enables fixups, and bit 2 sends a segfault.
310 align_va_addr= [X86-64]
311 Align virtual addresses by clearing slice [14:12] when
312 allocating a VMA at process creation time. This option
313 gives you up to 3% performance improvement on AMD F15h
314 machines (where it is enabled by default) for a
315 CPU-intensive style benchmark, and it can vary highly in
316 a microbenchmark depending on workload and compiler.
318 32: only for 32-bit processes
319 64: only for 64-bit processes
320 on: enable for both 32- and 64-bit processes
321 off: disable for both 32- and 64-bit processes
323 amd_iommu= [HW,X86-64]
324 Pass parameters to the AMD IOMMU driver in the system.
325 Possible values are:
326 fullflush - enable flushing of IO/TLB entries when
327 they are unmapped. Otherwise they are
328 flushed before they will be reused, which
329 is a lot of faster
330 off - do not initialize any AMD IOMMU found in
331 the system
332 force_isolation - Force device isolation for all
333 devices. The IOMMU driver is not
334 allowed anymore to lift isolation
335 requirements as needed. This option
336 does not override iommu=pt
338 amijoy.map= [HW,JOY] Amiga joystick support
339 Map of devices attached to JOY0DAT and JOY1DAT
340 Format: <a>,<b>
341 See also Documentation/input/joystick.txt
343 analog.map= [HW,JOY] Analog joystick and gamepad support
344 Specifies type or capabilities of an analog joystick
345 connected to one of 16 gameports
346 Format: <type1>,<type2>,..<type16>
348 apc= [HW,SPARC]
349 Power management functions (SPARCstation-4/5 + deriv.)
350 Format: noidle
351 Disable APC CPU standby support. SPARCstation-Fox does
352 not play well with APC CPU idle - disable it if you have
353 APC and your system crashes randomly.
355 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
356 Change the output verbosity whilst booting
357 Format: { quiet (default) | verbose | debug }
358 Change the amount of debugging information output
359 when initialising the APIC and IO-APIC components.
361 autoconf= [IPV6]
362 See Documentation/networking/ipv6.txt.
364 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
365 Limit apic dumping. The parameter defines the maximal
366 number of local apics being dumped. Also it is possible
367 to set it to "all" by meaning -- no limit here.
368 Format: { 1 (default) | 2 | ... | all }.
369 The parameter valid if only apic=debug or
370 apic=verbose is specified.
371 Example: apic=debug show_lapic=all
373 apm= [APM] Advanced Power Management
374 See header of arch/x86/kernel/apm_32.c.
376 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
377 Format: <io>,<irq>,<nodeID>
379 ataflop= [HW,M68k]
381 atarimouse= [HW,MOUSE] Atari Mouse
383 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
384 EzKey and similar keyboards
386 atkbd.reset= [HW] Reset keyboard during initialization
388 atkbd.set= [HW] Select keyboard code set
389 Format: <int> (2 = AT (default), 3 = PS/2)
391 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
392 keyboards
394 atkbd.softraw= [HW] Choose between synthetic and real raw mode
395 Format: <bool> (0 = real, 1 = synthetic (default))
397 atkbd.softrepeat= [HW]
398 Use software keyboard repeat
400 autotest [IA-64]
402 baycom_epp= [HW,AX25]
403 Format: <io>,<mode>
405 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
406 Format: <io>,<mode>
407 See header of drivers/net/hamradio/baycom_par.c.
409 baycom_ser_fdx= [HW,AX25]
410 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
411 Format: <io>,<irq>,<mode>[,<baud>]
412 See header of drivers/net/hamradio/baycom_ser_fdx.c.
414 baycom_ser_hdx= [HW,AX25]
415 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
416 Format: <io>,<irq>,<mode>
417 See header of drivers/net/hamradio/baycom_ser_hdx.c.
419 boot_delay= Milliseconds to delay each printk during boot.
420 Values larger than 10 seconds (10000) are changed to
421 no delay (0).
422 Format: integer
424 bootmem_debug [KNL] Enable bootmem allocator debug messages.
426 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
427 bttv.radio= Most important insmod options are available as
428 kernel args too.
429 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
430 bttv.tuner=
432 bulk_remove=off [PPC] This parameter disables the use of the pSeries
433 firmware feature for flushing multiple hpte entries
434 at a time.
436 c101= [NET] Moxa C101 synchronous serial card
438 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
439 Sometimes CPU hardware bugs make them report the cache
440 size incorrectly. The kernel will attempt work arounds
441 to fix known problems, but for some CPUs it is not
442 possible to determine what the correct size should be.
443 This option provides an override for these situations.
445 capability.disable=
446 [SECURITY] Disable capabilities. This would normally
447 be used only if an alternative security model is to be
448 configured. Potentially dangerous and should only be
449 used if you are entirely sure of the consequences.
451 ccw_timeout_log [S390]
452 See Documentation/s390/CommonIO for details.
454 cgroup_disable= [KNL] Disable a particular controller
455 Format: {name of the controller(s) to disable}
456 {Currently supported controllers - "memory"}
458 checkreqprot [SELINUX] Set initial checkreqprot flag value.
459 Format: { "0" | "1" }
460 See security/selinux/Kconfig help text.
461 0 -- check protection applied by kernel (includes
462 any implied execute protection).
463 1 -- check protection requested by application.
464 Default value is set via a kernel config option.
465 Value can be changed at runtime via
466 /selinux/checkreqprot.
468 cio_ignore= [S390]
469 See Documentation/s390/CommonIO for details.
471 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
472 [Deprecated]
473 Forces specified clocksource (if available) to be used
474 when calculating gettimeofday(). If specified
475 clocksource is not available, it defaults to PIT.
476 Format: { pit | tsc | cyclone | pmtmr }
478 clocksource= Override the default clocksource
479 Format: <string>
480 Override the default clocksource and use the clocksource
481 with the name specified.
482 Some clocksource names to choose from, depending on
483 the platform:
484 [all] jiffies (this is the base, fallback clocksource)
485 [ACPI] acpi_pm
486 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
487 pxa_timer,timer3,32k_counter,timer0_1
488 [AVR32] avr32
489 [X86-32] pit,hpet,tsc;
490 scx200_hrt on Geode; cyclone on IBM x440
491 [MIPS] MIPS
492 [PARISC] cr16
493 [S390] tod
494 [SH] SuperH
495 [SPARC64] tick
496 [X86-64] hpet,tsc
498 clearcpuid=BITNUM [X86]
499 Disable CPUID feature X for the kernel. See
500 arch/x86/include/asm/cpufeature.h for the valid bit
501 numbers. Note the Linux specific bits are not necessarily
502 stable over kernel options, but the vendor specific
503 ones should be.
504 Also note that user programs calling CPUID directly
505 or using the feature without checking anything
506 will still see it. This just prevents it from
507 being used by the kernel or shown in /proc/cpuinfo.
508 Also note the kernel might malfunction if you disable
509 some critical bits.
511 cmo_free_hint= [PPC] Format: { yes | no }
512 Specify whether pages are marked as being inactive
513 when they are freed. This is used in CMO environments
514 to determine OS memory pressure for page stealing by
515 a hypervisor.
516 Default: yes
518 code_bytes [X86] How many bytes of object code to print
519 in an oops report.
520 Range: 0 - 8192
521 Default: 64
523 com20020= [HW,NET] ARCnet - COM20020 chipset
524 Format:
525 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
527 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
528 Format: <io>[,<irq>]
530 com90xx= [HW,NET]
531 ARCnet - COM90xx chipset (memory-mapped buffers)
532 Format: <io>[,<irq>[,<memstart>]]
534 condev= [HW,S390] console device
535 conmode=
537 console= [KNL] Output console device and options.
539 tty<n> Use the virtual console device <n>.
541 ttyS<n>[,options]
542 ttyUSB0[,options]
543 Use the specified serial port. The options are of
544 the form "bbbbpnf", where "bbbb" is the baud rate,
545 "p" is parity ("n", "o", or "e"), "n" is number of
546 bits, and "f" is flow control ("r" for RTS or
547 omit it). Default is "9600n8".
549 See Documentation/serial-console.txt for more
550 information. See
551 Documentation/networking/netconsole.txt for an
552 alternative.
554 uart[8250],io,<addr>[,options]
555 uart[8250],mmio,<addr>[,options]
556 Start an early, polled-mode console on the 8250/16550
557 UART at the specified I/O port or MMIO address,
558 switching to the matching ttyS device later. The
559 options are the same as for ttyS, above.
561 If the device connected to the port is not a TTY but a braille
562 device, prepend "brl," before the device type, for instance
563 console=brl,ttyS0
564 For now, only VisioBraille is supported.
566 consoleblank= [KNL] The console blank (screen saver) timeout in
567 seconds. Defaults to 10*60 = 10mins. A value of 0
568 disables the blank timer.
570 coredump_filter=
571 [KNL] Change the default value for
572 /proc/<pid>/coredump_filter.
573 See also Documentation/filesystems/proc.txt.
575 cpuidle.off=1 [CPU_IDLE]
576 disable the cpuidle sub-system
578 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
579 Format:
580 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
582 crashkernel=size[KMG][@offset[KMG]]
583 [KNL] Using kexec, Linux can switch to a 'crash kernel'
584 upon panic. This parameter reserves the physical
585 memory region [offset, offset + size] for that kernel
586 image. If '@offset' is omitted, then a suitable offset
587 is selected automatically. Check
588 Documentation/kdump/kdump.txt for further details.
590 crashkernel=range1:size1[,range2:size2,...][@offset]
591 [KNL] Same as above, but depends on the memory
592 in the running system. The syntax of range is
593 start-[end] where start and end are both
594 a memory unit (amount[KMG]). See also
595 Documentation/kdump/kdump.txt for an example.
597 cs89x0_dma= [HW,NET]
598 Format: <dma>
600 cs89x0_media= [HW,NET]
601 Format: { rj45 | aui | bnc }
603 dasd= [HW,NET]
604 See header of drivers/s390/block/dasd_devmap.c.
606 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
607 (one device per port)
608 Format: <port#>,<type>
609 See also Documentation/input/joystick-parport.txt
611 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
612 time. See Documentation/dynamic-debug-howto.txt for
613 details.
615 debug [KNL] Enable kernel debugging (events log level).
617 debug_locks_verbose=
618 [KNL] verbose self-tests
619 Format=<0|1>
620 Print debugging info while doing the locking API
621 self-tests.
622 We default to 0 (no extra messages), setting it to
623 1 will print _a lot_ more information - normally
624 only useful to kernel developers.
626 debug_objects [KNL] Enable object debugging
628 no_debug_objects
629 [KNL] Disable object debugging
631 debug_guardpage_minorder=
632 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
633 parameter allows control of the order of pages that will
634 be intentionally kept free (and hence protected) by the
635 buddy allocator. Bigger value increase the probability
636 of catching random memory corruption, but reduce the
637 amount of memory for normal system use. The maximum
638 possible value is MAX_ORDER/2. Setting this parameter
639 to 1 or 2 should be enough to identify most random
640 memory corruption problems caused by bugs in kernel or
641 driver code when a CPU writes to (or reads from) a
642 random memory location. Note that there exists a class
643 of memory corruptions problems caused by buggy H/W or
644 F/W or by drivers badly programing DMA (basically when
645 memory is written at bus level and the CPU MMU is
646 bypassed) which are not detectable by
647 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
648 tracking down these problems.
650 debugpat [X86] Enable PAT debugging
652 decnet.addr= [HW,NET]
653 Format: <area>[,<node>]
654 See also Documentation/networking/decnet.txt.
656 default_hugepagesz=
657 [same as hugepagesz=] The size of the default
658 HugeTLB page size. This is the size represented by
659 the legacy /proc/ hugepages APIs, used for SHM, and
660 default size when mounting hugetlbfs filesystems.
661 Defaults to the default architecture's huge page size
662 if not specified.
664 dhash_entries= [KNL]
665 Set number of hash buckets for dentry cache.
667 digi= [HW,SERIAL]
668 IO parameters + enable/disable command.
670 digiepca= [HW,SERIAL]
671 See drivers/char/README.epca and
672 Documentation/serial/digiepca.txt.
674 disable= [IPV6]
675 See Documentation/networking/ipv6.txt.
677 disable_ddw [PPC/PSERIES]
678 Disable Dynamic DMA Window support. Use this if
679 to workaround buggy firmware.
681 disable_ipv6= [IPV6]
682 See Documentation/networking/ipv6.txt.
684 disable_mtrr_cleanup [X86]
685 The kernel tries to adjust MTRR layout from continuous
686 to discrete, to make X server driver able to add WB
687 entry later. This parameter disables that.
689 disable_mtrr_trim [X86, Intel and AMD only]
690 By default the kernel will trim any uncacheable
691 memory out of your available memory pool based on
692 MTRR settings. This parameter disables that behavior,
693 possibly causing your machine to run very slowly.
695 disable_timer_pin_1 [X86]
696 Disable PIN 1 of APIC timer
697 Can be useful to work around chipset bugs.
699 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
700 this option disables the debugging code at boot.
702 dma_debug_entries=<number>
703 This option allows to tune the number of preallocated
704 entries for DMA-API debugging code. One entry is
705 required per DMA-API allocation. Use this if the
706 DMA-API debugging code disables itself because the
707 architectural default is too low.
709 dma_debug_driver=<driver_name>
710 With this option the DMA-API debugging driver
711 filter feature can be enabled at boot time. Just
712 pass the driver to filter for as the parameter.
713 The filter can be disabled or changed to another
714 driver later using sysfs.
716 drm_kms_helper.edid_firmware=[<connector>:]<file>
717 Broken monitors, graphic adapters and KVMs may
718 send no or incorrect EDID data sets. This parameter
719 allows to specify an EDID data set in the
720 /lib/firmware directory that is used instead.
721 Generic built-in EDID data sets are used, if one of
722 edid/1024x768.bin, edid/1280x1024.bin,
723 edid/1680x1050.bin, or edid/1920x1080.bin is given
724 and no file with the same name exists. Details and
725 instructions how to build your own EDID data are
726 available in Documentation/EDID/HOWTO.txt. An EDID
727 data set will only be used for a particular connector,
728 if its name and a colon are prepended to the EDID
729 name.
731 dscc4.setup= [NET]
733 earlycon= [KNL] Output early console device and options.
734 uart[8250],io,<addr>[,options]
735 uart[8250],mmio,<addr>[,options]
736 uart[8250],mmio32,<addr>[,options]
737 Start an early, polled-mode console on the 8250/16550
738 UART at the specified I/O port or MMIO address.
739 MMIO inter-register address stride is either 8-bit
740 (mmio) or 32-bit (mmio32).
741 The options are the same as for ttyS, above.
743 earlyprintk= [X86,SH,BLACKFIN]
744 earlyprintk=vga
745 earlyprintk=serial[,ttySn[,baudrate]]
746 earlyprintk=ttySn[,baudrate]
747 earlyprintk=dbgp[debugController#]
749 Append ",keep" to not disable it when the real console
750 takes over.
752 Only vga or serial or usb debug port at a time.
754 Currently only ttyS0 and ttyS1 are supported.
756 Interaction with the standard serial driver is not
757 very good.
759 The VGA output is eventually overwritten by the real
760 console.
762 ekgdboc= [X86,KGDB] Allow early kernel console debugging
763 ekgdboc=kbd
765 This is designed to be used in conjunction with
766 the boot argument: earlyprintk=vga
768 edd= [EDD]
769 Format: {"off" | "on" | "skip[mbr]"}
771 eisa_irq_edge= [PARISC,HW]
772 See header of drivers/parisc/eisa.c.
774 elanfreq= [X86-32]
775 See comment before function elanfreq_setup() in
776 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
778 elevator= [IOSCHED]
779 Format: {"cfq" | "deadline" | "noop"}
780 See Documentation/block/cfq-iosched.txt and
781 Documentation/block/deadline-iosched.txt for details.
783 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
784 Specifies physical address of start of kernel core
785 image elf header and optionally the size. Generally
786 kexec loader will pass this option to capture kernel.
787 See Documentation/kdump/kdump.txt for details.
789 enable_mtrr_cleanup [X86]
790 The kernel tries to adjust MTRR layout from continuous
791 to discrete, to make X server driver able to add WB
792 entry later. This parameter enables that.
794 enable_timer_pin_1 [X86]
795 Enable PIN 1 of APIC timer
796 Can be useful to work around chipset bugs
797 (in particular on some ATI chipsets).
798 The kernel tries to set a reasonable default.
800 enforcing [SELINUX] Set initial enforcing status.
801 Format: {"0" | "1"}
802 See security/selinux/Kconfig help text.
803 0 -- permissive (log only, no denials).
804 1 -- enforcing (deny and log).
805 Default value is 0.
806 Value can be changed at runtime via /selinux/enforce.
808 erst_disable [ACPI]
809 Disable Error Record Serialization Table (ERST)
810 support.
812 ether= [HW,NET] Ethernet cards parameters
813 This option is obsoleted by the "netdev=" option, which
814 has equivalent usage. See its documentation for details.
816 evm= [EVM]
817 Format: { "fix" }
818 Permit 'security.evm' to be updated regardless of
819 current integrity status.
821 failslab=
822 fail_page_alloc=
823 fail_make_request=[KNL]
824 General fault injection mechanism.
825 Format: <interval>,<probability>,<space>,<times>
826 See also Documentation/fault-injection/.
828 floppy= [HW]
829 See Documentation/blockdev/floppy.txt.
831 force_pal_cache_flush
832 [IA-64] Avoid check_sal_cache_flush which may hang on
833 buggy SAL_CACHE_FLUSH implementations. Using this
834 parameter will force ia64_sal_cache_flush to call
835 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
837 ftrace=[tracer]
838 [FTRACE] will set and start the specified tracer
839 as early as possible in order to facilitate early
840 boot debugging.
842 ftrace_dump_on_oops[=orig_cpu]
843 [FTRACE] will dump the trace buffers on oops.
844 If no parameter is passed, ftrace will dump
845 buffers of all CPUs, but if you pass orig_cpu, it will
846 dump only the buffer of the CPU that triggered the
847 oops.
849 ftrace_filter=[function-list]
850 [FTRACE] Limit the functions traced by the function
851 tracer at boot up. function-list is a comma separated
852 list of functions. This list can be changed at run
853 time by the set_ftrace_filter file in the debugfs
854 tracing directory.
856 ftrace_notrace=[function-list]
857 [FTRACE] Do not trace the functions specified in
858 function-list. This list can be changed at run time
859 by the set_ftrace_notrace file in the debugfs
860 tracing directory.
862 ftrace_graph_filter=[function-list]
863 [FTRACE] Limit the top level callers functions traced
864 by the function graph tracer at boot up.
865 function-list is a comma separated list of functions
866 that can be changed at run time by the
867 set_graph_function file in the debugfs tracing directory.
869 gamecon.map[2|3]=
870 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
871 support via parallel port (up to 5 devices per port)
872 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
873 See also Documentation/input/joystick-parport.txt
875 gamma= [HW,DRM]
877 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
878 Format: off | on
879 default: on
881 gcov_persist= [GCOV] When non-zero (default), profiling data for
882 kernel modules is saved and remains accessible via
883 debugfs, even when the module is unloaded/reloaded.
884 When zero, profiling data is discarded and associated
885 debugfs files are removed at module unload time.
887 gpt [EFI] Forces disk with valid GPT signature but
888 invalid Protective MBR to be treated as GPT.
890 hashdist= [KNL,NUMA] Large hashes allocated during boot
891 are distributed across NUMA nodes. Defaults on
892 for 64-bit NUMA, off otherwise.
893 Format: 0 | 1 (for off | on)
895 hcl= [IA-64] SGI's Hardware Graph compatibility layer
897 hd= [EIDE] (E)IDE hard drive subsystem geometry
898 Format: <cyl>,<head>,<sect>
900 hest_disable [ACPI]
901 Disable Hardware Error Source Table (HEST) support;
902 corresponding firmware-first mode error processing
903 logic will be disabled.
905 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
906 size of <nn>. This works even on boxes that have no
907 highmem otherwise. This also works to reduce highmem
908 size on bigger boxes.
910 highres= [KNL] Enable/disable high resolution timer mode.
911 Valid parameters: "on", "off"
912 Default: "on"
914 hisax= [HW,ISDN]
915 See Documentation/isdn/README.HiSax.
917 hlt [BUGS=ARM,SH]
919 hpet= [X86-32,HPET] option to control HPET usage
920 Format: { enable (default) | disable | force |
921 verbose }
922 disable: disable HPET and use PIT instead
923 force: allow force enabled of undocumented chips (ICH4,
924 VIA, nVidia)
925 verbose: show contents of HPET registers during setup
927 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
928 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
929 On x86-64 and powerpc, this option can be specified
930 multiple times interleaved with hugepages= to reserve
931 huge pages of different sizes. Valid pages sizes on
932 x86-64 are 2M (when the CPU supports "pse") and 1G
933 (when the CPU supports the "pdpe1gb" cpuinfo flag)
934 Note that 1GB pages can only be allocated at boot time
935 using hugepages= and not freed afterwards.
937 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
938 terminal devices. Valid values: 0..8
939 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
940 If specified, z/VM IUCV HVC accepts connections
941 from listed z/VM user IDs only.
943 keep_bootcon [KNL]
944 Do not unregister boot console at start. This is only
945 useful for debugging when something happens in the window
946 between unregistering the boot console and initializing
947 the real console.
949 i2c_bus= [HW] Override the default board specific I2C bus speed
950 or register an additional I2C bus that is not
951 registered from board initialization code.
952 Format:
953 <bus_id>,<clkrate>
955 i8042.debug [HW] Toggle i8042 debug mode
956 i8042.direct [HW] Put keyboard port into non-translated mode
957 i8042.dumbkbd [HW] Pretend that controller can only read data from
958 keyboard and cannot control its state
959 (Don't attempt to blink the leds)
960 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
961 i8042.nokbd [HW] Don't check/create keyboard port
962 i8042.noloop [HW] Disable the AUX Loopback command while probing
963 for the AUX port
964 i8042.nomux [HW] Don't check presence of an active multiplexing
965 controller
966 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
967 controllers
968 i8042.notimeout [HW] Ignore timeout condition signalled by controller
969 i8042.reset [HW] Reset the controller during init and cleanup
970 i8042.unlock [HW] Unlock (ignore) the keylock
972 i810= [HW,DRM]
974 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
975 indicates that the driver is running on unsupported
976 hardware.
977 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
978 does not match list of supported models.
979 i8k.power_status
980 [HW] Report power status in /proc/i8k
981 (disabled by default)
982 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
983 capability is set.
985 icn= [HW,ISDN]
986 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
988 ide-core.nodma= [HW] (E)IDE subsystem
989 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
990 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
991 .cdrom .chs .ignore_cable are additional options
992 See Documentation/ide/ide.txt.
994 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
995 Claim all unknown PCI IDE storage controllers.
997 idle= [X86]
998 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
999 Poll forces a polling idle loop that can slightly
1000 improve the performance of waking up a idle CPU, but
1001 will use a lot of power and make the system run hot.
1002 Not recommended.
1003 idle=mwait: On systems which support MONITOR/MWAIT but
1004 the kernel chose to not use it because it doesn't save
1005 as much power as a normal idle loop, use the
1006 MONITOR/MWAIT idle loop anyways. Performance should be
1007 the same as idle=poll.
1008 idle=halt: Halt is forced to be used for CPU idle.
1009 In such case C2/C3 won't be used again.
1010 idle=nomwait: Disable mwait for CPU C-states
1012 ignore_loglevel [KNL]
1013 Ignore loglevel setting - this will print /all/
1014 kernel messages to the console. Useful for debugging.
1015 We also add it as printk module parameter, so users
1016 could change it dynamically, usually by
1017 /sys/module/printk/parameters/ignore_loglevel.
1019 ihash_entries= [KNL]
1020 Set number of hash buckets for inode cache.
1022 ima_audit= [IMA]
1023 Format: { "0" | "1" }
1024 0 -- integrity auditing messages. (Default)
1025 1 -- enable informational integrity auditing messages.
1027 ima_hash= [IMA]
1028 Format: { "sha1" | "md5" }
1029 default: "sha1"
1031 ima_tcb [IMA]
1032 Load a policy which meets the needs of the Trusted
1033 Computing Base. This means IMA will measure all
1034 programs exec'd, files mmap'd for exec, and all files
1035 opened for read by uid=0.
1037 init= [KNL]
1038 Format: <full_path>
1039 Run specified binary instead of /sbin/init as init
1040 process.
1042 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1043 for working out where the kernel is dying during
1044 startup.
1046 initrd= [BOOT] Specify the location of the initial ramdisk
1048 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1049 Format: <irq>
1051 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1052 on
1053 Enable intel iommu driver.
1054 off
1055 Disable intel iommu driver.
1056 igfx_off [Default Off]
1057 By default, gfx is mapped as normal device. If a gfx
1058 device has a dedicated DMAR unit, the DMAR unit is
1059 bypassed by not enabling DMAR with this option. In
1060 this case, gfx device will use physical address for
1061 DMA.
1062 forcedac [x86_64]
1063 With this option iommu will not optimize to look
1064 for io virtual address below 32-bit forcing dual
1065 address cycle on pci bus for cards supporting greater
1066 than 32-bit addressing. The default is to look
1067 for translation below 32-bit and if not available
1068 then look in the higher range.
1069 strict [Default Off]
1070 With this option on every unmap_single operation will
1071 result in a hardware IOTLB flush operation as opposed
1072 to batching them for performance.
1073 sp_off [Default Off]
1074 By default, super page will be supported if Intel IOMMU
1075 has the capability. With this option, super page will
1076 not be supported.
1078 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1079 0 disables intel_idle and fall back on acpi_idle.
1080 1 to 6 specify maximum depth of C-state.
1082 intremap= [X86-64, Intel-IOMMU]
1083 on enable Interrupt Remapping (default)
1084 off disable Interrupt Remapping
1085 nosid disable Source ID checking
1086 no_x2apic_optout
1087 BIOS x2APIC opt-out request will be ignored
1089 iomem= Disable strict checking of access to MMIO memory
1090 strict regions from userspace.
1091 relaxed
1093 iommu= [x86]
1094 off
1095 force
1096 noforce
1097 biomerge
1098 panic
1099 nopanic
1100 merge
1101 nomerge
1102 forcesac
1103 soft
1104 pt [x86, IA-64]
1105 group_mf [x86, IA-64]
1108 io7= [HW] IO7 for Marvel based alpha systems
1109 See comment before marvel_specify_io7 in
1110 arch/alpha/kernel/core_marvel.c.
1112 io_delay= [X86] I/O delay method
1113 0x80
1114 Standard port 0x80 based delay
1115 0xed
1116 Alternate port 0xed based delay (needed on some systems)
1117 udelay
1118 Simple two microseconds delay
1119 none
1120 No delay
1122 ip= [IP_PNP]
1123 See Documentation/filesystems/nfs/nfsroot.txt.
1125 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1126 See comment before ip2_setup() in
1127 drivers/char/ip2/ip2base.c.
1129 irqfixup [HW]
1130 When an interrupt is not handled search all handlers
1131 for it. Intended to get systems with badly broken
1132 firmware running.
1134 irqpoll [HW]
1135 When an interrupt is not handled search all handlers
1136 for it. Also check all handlers each timer
1137 interrupt. Intended to get systems with badly broken
1138 firmware running.
1140 isapnp= [ISAPNP]
1141 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1143 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1144 Format:
1145 <cpu number>,...,<cpu number>
1146 or
1147 <cpu number>-<cpu number>
1148 (must be a positive range in ascending order)
1149 or a mixture
1150 <cpu number>,...,<cpu number>-<cpu number>
1152 This option can be used to specify one or more CPUs
1153 to isolate from the general SMP balancing and scheduling
1154 algorithms. You can move a process onto or off an
1155 "isolated" CPU via the CPU affinity syscalls or cpuset.
1156 <cpu number> begins at 0 and the maximum value is
1157 "number of CPUs in system - 1".
1159 This option is the preferred way to isolate CPUs. The
1160 alternative -- manually setting the CPU mask of all
1161 tasks in the system -- can cause problems and
1162 suboptimal load balancer performance.
1164 iucv= [HW,NET]
1166 js= [HW,JOY] Analog joystick
1167 See Documentation/input/joystick.txt.
1169 keepinitrd [HW,ARM]
1171 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1172 specifies the amount of memory usable by the kernel
1173 for non-movable allocations. The requested amount is
1174 spread evenly throughout all nodes in the system. The
1175 remaining memory in each node is used for Movable
1176 pages. In the event, a node is too small to have both
1177 kernelcore and Movable pages, kernelcore pages will
1178 take priority and other nodes will have a larger number
1179 of kernelcore pages. The Movable zone is used for the
1180 allocation of pages that may be reclaimed or moved
1181 by the page migration subsystem. This means that
1182 HugeTLB pages may not be allocated from this zone.
1183 Note that allocations like PTEs-from-HighMem still
1184 use the HighMem zone if it exists, and the Normal
1185 zone if it does not.
1187 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1188 Format: <Controller#>[,poll interval]
1189 The controller # is the number of the ehci usb debug
1190 port as it is probed via PCI. The poll interval is
1191 optional and is the number seconds in between
1192 each poll cycle to the debug port in case you need
1193 the functionality for interrupting the kernel with
1194 gdb or control-c on the dbgp connection. When
1195 not using this parameter you use sysrq-g to break into
1196 the kernel debugger.
1198 kgdboc= [KGDB,HW] kgdb over consoles.
1199 Requires a tty driver that supports console polling,
1200 or a supported polling keyboard driver (non-usb).
1201 Serial only format: <serial_device>[,baud]
1202 keyboard only format: kbd
1203 keyboard and serial format: kbd,<serial_device>[,baud]
1204 Optional Kernel mode setting:
1205 kms, kbd format: kms,kbd
1206 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1208 kgdbwait [KGDB] Stop kernel execution and enter the
1209 kernel debugger at the earliest opportunity.
1211 kmac= [MIPS] korina ethernet MAC address.
1212 Configure the RouterBoard 532 series on-chip
1213 Ethernet adapter MAC address.
1215 kmemleak= [KNL] Boot-time kmemleak enable/disable
1216 Valid arguments: on, off
1217 Default: on
1219 kstack=N [X86] Print N words from the kernel stack
1220 in oops dumps.
1222 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1223 Default is 0 (don't ignore, but inject #GP)
1225 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1226 KVM MMU at runtime.
1227 Default is 0 (off)
1229 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1230 Default is 1 (enabled)
1232 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1233 for all guests.
1234 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1236 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1237 (virtualized MMU) support on capable Intel chips.
1238 Default is 1 (enabled)
1240 kvm-intel.emulate_invalid_guest_state=
1241 [KVM,Intel] Enable emulation of invalid guest states
1242 Default is 0 (disabled)
1244 kvm-intel.flexpriority=
1245 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1246 Default is 1 (enabled)
1248 kvm-intel.nested=
1249 [KVM,Intel] Enable VMX nesting (nVMX).
1250 Default is 0 (disabled)
1252 kvm-intel.unrestricted_guest=
1253 [KVM,Intel] Disable unrestricted guest feature
1254 (virtualized real and unpaged mode) on capable
1255 Intel chips. Default is 1 (enabled)
1257 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1258 feature (tagged TLBs) on capable Intel chips.
1259 Default is 1 (enabled)
1261 l2cr= [PPC]
1263 l3cr= [PPC]
1265 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1266 disabled it.
1268 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1269 in C2 power state.
1271 libata.dma= [LIBATA] DMA control
1272 libata.dma=0 Disable all PATA and SATA DMA
1273 libata.dma=1 PATA and SATA Disk DMA only
1274 libata.dma=2 ATAPI (CDROM) DMA only
1275 libata.dma=4 Compact Flash DMA only
1276 Combinations also work, so libata.dma=3 enables DMA
1277 for disks and CDROMs, but not CFs.
1279 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1280 libata.ignore_hpa=0 keep BIOS limits (default)
1281 libata.ignore_hpa=1 ignore limits, using full disk
1283 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1284 when set.
1285 Format: <int>
1287 libata.force= [LIBATA] Force configurations. The format is comma
1288 separated list of "[ID:]VAL" where ID is
1289 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1290 matching port, link or device. Basically, it matches
1291 the ATA ID string printed on console by libata. If
1292 the whole ID part is omitted, the last PORT and DEVICE
1293 values are used. If ID hasn't been specified yet, the
1294 configuration applies to all ports, links and devices.
1296 If only DEVICE is omitted, the parameter applies to
1297 the port and all links and devices behind it. DEVICE
1298 number of 0 either selects the first device or the
1299 first fan-out link behind PMP device. It does not
1300 select the host link. DEVICE number of 15 selects the
1301 host link and device attached to it.
1303 The VAL specifies the configuration to force. As long
1304 as there's no ambiguity shortcut notation is allowed.
1305 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1306 The following configurations can be forced.
1308 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1309 Any ID with matching PORT is used.
1311 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1313 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1314 udma[/][16,25,33,44,66,100,133] notation is also
1315 allowed.
1317 * [no]ncq: Turn on or off NCQ.
1319 * nohrst, nosrst, norst: suppress hard, soft
1320 and both resets.
1322 * dump_id: dump IDENTIFY data.
1324 If there are multiple matching configurations changing
1325 the same attribute, the last one is used.
1327 memblock=debug [KNL] Enable memblock debug messages.
1329 load_ramdisk= [RAM] List of ramdisks to load from floppy
1330 See Documentation/blockdev/ramdisk.txt.
1332 lockd.nlm_grace_period=P [NFS] Assign grace period.
1333 Format: <integer>
1335 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1336 Format: <integer>
1338 lockd.nlm_timeout=T [NFS] Assign timeout value.
1339 Format: <integer>
1341 lockd.nlm_udpport=M [NFS] Assign UDP port.
1342 Format: <integer>
1344 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1345 Format: <irq>
1347 loglevel= All Kernel Messages with a loglevel smaller than the
1348 console loglevel will be printed to the console. It can
1349 also be changed with klogd or other programs. The
1350 loglevels are defined as follows:
1352 0 (KERN_EMERG) system is unusable
1353 1 (KERN_ALERT) action must be taken immediately
1354 2 (KERN_CRIT) critical conditions
1355 3 (KERN_ERR) error conditions
1356 4 (KERN_WARNING) warning conditions
1357 5 (KERN_NOTICE) normal but significant condition
1358 6 (KERN_INFO) informational
1359 7 (KERN_DEBUG) debug-level messages
1361 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1362 in bytes. n must be a power of two. The default
1363 size is set in the kernel config file.
1365 logo.nologo [FB] Disables display of the built-in Linux logo.
1366 This may be used to provide more screen space for
1367 kernel log messages and is useful when debugging
1368 kernel boot problems.
1370 lp=0 [LP] Specify parallel ports to use, e.g,
1371 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1372 lp=reset first parallel port). 'lp=0' disables the
1373 lp=auto printer driver. 'lp=reset' (which can be
1374 specified in addition to the ports) causes
1375 attached printers to be reset. Using
1376 lp=port1,port2,... specifies the parallel ports
1377 to associate lp devices with, starting with
1378 lp0. A port specification may be 'none' to skip
1379 that lp device, or a parport name such as
1380 'parport0'. Specifying 'lp=auto' instead of a
1381 port specification list means that device IDs
1382 from each port should be examined, to see if
1383 an IEEE 1284-compliant printer is attached; if
1384 so, the driver will manage that printer.
1385 See also header of drivers/char/lp.c.
1387 lpj=n [KNL]
1388 Sets loops_per_jiffy to given constant, thus avoiding
1389 time-consuming boot-time autodetection (up to 250 ms per
1390 CPU). 0 enables autodetection (default). To determine
1391 the correct value for your kernel, boot with normal
1392 autodetection and see what value is printed. Note that
1393 on SMP systems the preset will be applied to all CPUs,
1394 which is likely to cause problems if your CPUs need
1395 significantly divergent settings. An incorrect value
1396 will cause delays in the kernel to be wrong, leading to
1397 unpredictable I/O errors and other breakage. Although
1398 unlikely, in the extreme case this might damage your
1399 hardware.
1401 ltpc= [NET]
1402 Format: <io>,<irq>,<dma>
1404 machvec= [IA-64] Force the use of a particular machine-vector
1405 (machvec) in a generic kernel.
1406 Example: machvec=hpzx1_swiotlb
1408 machtype= [Loongson] Share the same kernel image file between different
1409 yeeloong laptop.
1410 Example: machtype=lemote-yeeloong-2f-7inch
1412 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1413 than or equal to this physical address is ignored.
1415 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1416 should make use of. maxcpus=n : n >= 0 limits the
1417 kernel to using 'n' processors. n=0 is a special case,
1418 it is equivalent to "nosmp", which also disables
1419 the IO APIC.
1421 max_loop= [LOOP] The number of loop block devices that get
1422 (loop.max_loop) unconditionally pre-created at init time. The default
1423 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1424 of statically allocating a predefined number, loop
1425 devices can be requested on-demand with the
1426 /dev/loop-control interface.
1428 mcatest= [IA-64]
1430 mce [X86-32] Machine Check Exception
1432 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1434 md= [HW] RAID subsystems devices and level
1435 See Documentation/md.txt.
1437 mdacon= [MDA]
1438 Format: <first>,<last>
1439 Specifies range of consoles to be captured by the MDA.
1441 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1442 Amount of memory to be used when the kernel is not able
1443 to see the whole system memory or for test.
1444 [X86-32] Use together with memmap= to avoid physical
1445 address space collisions. Without memmap= PCI devices
1446 could be placed at addresses belonging to unused RAM.
1448 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1449 memory.
1451 memchunk=nn[KMG]
1452 [KNL,SH] Allow user to override the default size for
1453 per-device physically contiguous DMA buffers.
1455 memmap=exactmap [KNL,X86] Enable setting of an exact
1456 E820 memory map, as specified by the user.
1457 Such memmap=exactmap lines can be constructed based on
1458 BIOS output or other requirements. See the memmap=nn@ss
1459 option description.
1461 memmap=nn[KMG]@ss[KMG]
1462 [KNL] Force usage of a specific region of memory
1463 Region of memory to be used, from ss to ss+nn.
1465 memmap=nn[KMG]#ss[KMG]
1466 [KNL,ACPI] Mark specific memory as ACPI data.
1467 Region of memory to be used, from ss to ss+nn.
1469 memmap=nn[KMG]$ss[KMG]
1470 [KNL,ACPI] Mark specific memory as reserved.
1471 Region of memory to be used, from ss to ss+nn.
1472 Example: Exclude memory from 0x18690000-0x1869ffff
1473 memmap=64K$0x18690000
1474 or
1475 memmap=0x10000$0x18690000
1477 memory_corruption_check=0/1 [X86]
1478 Some BIOSes seem to corrupt the first 64k of
1479 memory when doing things like suspend/resume.
1480 Setting this option will scan the memory
1481 looking for corruption. Enabling this will
1482 both detect corruption and prevent the kernel
1483 from using the memory being corrupted.
1484 However, its intended as a diagnostic tool; if
1485 repeatable BIOS-originated corruption always
1486 affects the same memory, you can use memmap=
1487 to prevent the kernel from using that memory.
1489 memory_corruption_check_size=size [X86]
1490 By default it checks for corruption in the low
1491 64k, making this memory unavailable for normal
1492 use. Use this parameter to scan for
1493 corruption in more or less memory.
1495 memory_corruption_check_period=seconds [X86]
1496 By default it checks for corruption every 60
1497 seconds. Use this parameter to check at some
1498 other rate. 0 disables periodic checking.
1500 memtest= [KNL,X86] Enable memtest
1501 Format: <integer>
1502 default : 0 <disable>
1503 Specifies the number of memtest passes to be
1504 performed. Each pass selects another test
1505 pattern from a given set of patterns. Memtest
1506 fills the memory with this pattern, validates
1507 memory contents and reserves bad memory
1508 regions that are detected.
1510 meye.*= [HW] Set MotionEye Camera parameters
1511 See Documentation/video4linux/meye.txt.
1513 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1514 Multi-Function General Purpose Timers on AMD Geode
1515 platforms.
1517 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1518 the BIOS has incorrectly applied a workaround. TinyBIOS
1519 version 0.98 is known to be affected, 0.99 fixes the
1520 problem by letting the user disable the workaround.
1522 mga= [HW,DRM]
1524 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1525 physical address is ignored.
1527 mini2440= [ARM,HW,KNL]
1528 Format:[0..2][b][c][t]
1529 Default: "0tb"
1530 MINI2440 configuration specification:
1531 0 - The attached screen is the 3.5" TFT
1532 1 - The attached screen is the 7" TFT
1533 2 - The VGA Shield is attached (1024x768)
1534 Leaving out the screen size parameter will not load
1535 the TFT driver, and the framebuffer will be left
1536 unconfigured.
1537 b - Enable backlight. The TFT backlight pin will be
1538 linked to the kernel VESA blanking code and a GPIO
1539 LED. This parameter is not necessary when using the
1540 VGA shield.
1541 c - Enable the s3c camera interface.
1542 t - Reserved for enabling touchscreen support. The
1543 touchscreen support is not enabled in the mainstream
1544 kernel as of 2.6.30, a preliminary port can be found
1545 in the "bleeding edge" mini2440 support kernel at
1546 http://repo.or.cz/w/linux-2.6/mini2440.git
1548 mminit_loglevel=
1549 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1550 parameter allows control of the logging verbosity for
1551 the additional memory initialisation checks. A value
1552 of 0 disables mminit logging and a level of 4 will
1553 log everything. Information is printed at KERN_DEBUG
1554 so loglevel=8 may also need to be specified.
1556 mousedev.tap_time=
1557 [MOUSE] Maximum time between finger touching and
1558 leaving touchpad surface for touch to be considered
1559 a tap and be reported as a left button click (for
1560 touchpads working in absolute mode only).
1561 Format: <msecs>
1562 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1563 reporting absolute coordinates, such as tablets
1564 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1565 reporting absolute coordinates, such as tablets
1567 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1568 is similar to kernelcore except it specifies the
1569 amount of memory used for migratable allocations.
1570 If both kernelcore and movablecore is specified,
1571 then kernelcore will be at *least* the specified
1572 value but may be more. If movablecore on its own
1573 is specified, the administrator must be careful
1574 that the amount of memory usable for all allocations
1575 is not too small.
1577 MTD_Partition= [MTD]
1578 Format: <name>,<region-number>,<size>,<offset>
1580 MTD_Region= [MTD] Format:
1581 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1583 mtdparts= [MTD]
1584 See drivers/mtd/cmdlinepart.c.
1586 multitce=off [PPC] This parameter disables the use of the pSeries
1587 firmware feature for updating multiple TCE entries
1588 at a time.
1590 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1592 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1594 boundary - index of last SLC block on Flex-OneNAND.
1595 The remaining blocks are configured as MLC blocks.
1596 lock - Configure if Flex-OneNAND boundary should be locked.
1597 Once locked, the boundary cannot be changed.
1598 1 indicates lock status, 0 indicates unlock status.
1600 mtdset= [ARM]
1601 ARM/S3C2412 JIVE boot control
1603 See arch/arm/mach-s3c2412/mach-jive.c
1605 mtouchusb.raw_coordinates=
1606 [HW] Make the MicroTouch USB driver use raw coordinates
1607 ('y', default) or cooked coordinates ('n')
1609 mtrr_chunk_size=nn[KMG] [X86]
1610 used for mtrr cleanup. It is largest continuous chunk
1611 that could hold holes aka. UC entries.
1613 mtrr_gran_size=nn[KMG] [X86]
1614 Used for mtrr cleanup. It is granularity of mtrr block.
1615 Default is 1.
1616 Large value could prevent small alignment from
1617 using up MTRRs.
1619 mtrr_spare_reg_nr=n [X86]
1620 Format: <integer>
1621 Range: 0,7 : spare reg number
1622 Default : 1
1623 Used for mtrr cleanup. It is spare mtrr entries number.
1624 Set to 2 or more if your graphical card needs more.
1626 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1628 netdev= [NET] Network devices parameters
1629 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1630 Note that mem_start is often overloaded to mean
1631 something different and driver-specific.
1632 This usage is only documented in each driver source
1633 file if at all.
1635 nf_conntrack.acct=
1636 [NETFILTER] Enable connection tracking flow accounting
1637 0 to disable accounting
1638 1 to enable accounting
1639 Default value is 0.
1641 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1642 See Documentation/filesystems/nfs/nfsroot.txt.
1644 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1645 See Documentation/filesystems/nfs/nfsroot.txt.
1647 nfsrootdebug [NFS] enable nfsroot debugging messages.
1648 See Documentation/filesystems/nfs/nfsroot.txt.
1650 nfs.callback_tcpport=
1651 [NFS] set the TCP port on which the NFSv4 callback
1652 channel should listen.
1654 nfs.cache_getent=
1655 [NFS] sets the pathname to the program which is used
1656 to update the NFS client cache entries.
1658 nfs.cache_getent_timeout=
1659 [NFS] sets the timeout after which an attempt to
1660 update a cache entry is deemed to have failed.
1662 nfs.idmap_cache_timeout=
1663 [NFS] set the maximum lifetime for idmapper cache
1664 entries.
1666 nfs.enable_ino64=
1667 [NFS] enable 64-bit inode numbers.
1668 If zero, the NFS client will fake up a 32-bit inode
1669 number for the readdir() and stat() syscalls instead
1670 of returning the full 64-bit number.
1671 The default is to return 64-bit inode numbers.
1673 nfs.max_session_slots=
1674 [NFSv4.1] Sets the maximum number of session slots
1675 the client will attempt to negotiate with the server.
1676 This limits the number of simultaneous RPC requests
1677 that the client can send to the NFSv4.1 server.
1678 Note that there is little point in setting this
1679 value higher than the max_tcp_slot_table_limit.
1681 nfs.nfs4_disable_idmapping=
1682 [NFSv4] When set to the default of '1', this option
1683 ensures that both the RPC level authentication
1684 scheme and the NFS level operations agree to use
1685 numeric uids/gids if the mount is using the
1686 'sec=sys' security flavour. In effect it is
1687 disabling idmapping, which can make migration from
1688 legacy NFSv2/v3 systems to NFSv4 easier.
1689 Servers that do not support this mode of operation
1690 will be autodetected by the client, and it will fall
1691 back to using the idmapper.
1692 To turn off this behaviour, set the value to '0'.
1694 nfs.send_implementation_id =
1695 [NFSv4.1] Send client implementation identification
1696 information in exchange_id requests.
1697 If zero, no implementation identification information
1698 will be sent.
1699 The default is to send the implementation identification
1700 information.
1702 nfsd.nfs4_disable_idmapping=
1703 [NFSv4] When set to the default of '1', the NFSv4
1704 server will return only numeric uids and gids to
1705 clients using auth_sys, and will accept numeric uids
1706 and gids from such clients. This is intended to ease
1707 migration from NFSv2/v3.
1709 objlayoutdriver.osd_login_prog=
1710 [NFS] [OBJLAYOUT] sets the pathname to the program which
1711 is used to automatically discover and login into new
1712 osd-targets. Please see:
1713 Documentation/filesystems/pnfs.txt for more explanations
1715 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1716 when a NMI is triggered.
1717 Format: [state][,regs][,debounce][,die]
1719 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1720 Format: [panic,][nopanic,][num]
1721 Valid num: 0
1722 0 - turn nmi_watchdog off
1723 When panic is specified, panic when an NMI watchdog
1724 timeout occurs (or 'nopanic' to override the opposite
1725 default).
1726 This is useful when you use a panic=... timeout and
1727 need the box quickly up again.
1729 netpoll.carrier_timeout=
1730 [NET] Specifies amount of time (in seconds) that
1731 netpoll should wait for a carrier. By default netpoll
1732 waits 4 seconds.
1734 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1735 emulation library even if a 387 maths coprocessor
1736 is present.
1738 no_console_suspend
1739 [HW] Never suspend the console
1740 Disable suspending of consoles during suspend and
1741 hibernate operations. Once disabled, debugging
1742 messages can reach various consoles while the rest
1743 of the system is being put to sleep (ie, while
1744 debugging driver suspend/resume hooks). This may
1745 not work reliably with all consoles, but is known
1746 to work with serial and VGA consoles.
1747 To facilitate more flexible debugging, we also add
1748 console_suspend, a printk module parameter to control
1749 it. Users could use console_suspend (usually
1750 /sys/module/printk/parameters/console_suspend) to
1751 turn on/off it dynamically.
1753 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1754 caches in the slab allocator. Saves per-node memory,
1755 but will impact performance.
1757 noalign [KNL,ARM]
1759 noapic [SMP,APIC] Tells the kernel to not make use of any
1760 IOAPICs that may be present in the system.
1762 noautogroup Disable scheduler automatic task group creation.
1764 nobats [PPC] Do not use BATs for mapping kernel lowmem
1765 on "Classic" PPC cores.
1767 nocache [ARM]
1769 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1771 nodelayacct [KNL] Disable per-task delay accounting
1773 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1775 nodsp [SH] Disable hardware DSP at boot time.
1777 noefi [X86] Disable EFI runtime services support.
1779 noexec [IA-64]
1781 noexec [X86]
1782 On X86-32 available only on PAE configured kernels.
1783 noexec=on: enable non-executable mappings (default)
1784 noexec=off: disable non-executable mappings
1786 nosmep [X86]
1787 Disable SMEP (Supervisor Mode Execution Protection)
1788 even if it is supported by processor.
1790 noexec32 [X86-64]
1791 This affects only 32-bit executables.
1792 noexec32=on: enable non-executable mappings (default)
1793 read doesn't imply executable mappings
1794 noexec32=off: disable non-executable mappings
1795 read implies executable mappings
1797 nofpu [SH] Disable hardware FPU at boot time.
1799 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1800 register save and restore. The kernel will only save
1801 legacy floating-point registers on task switch.
1803 noxsave [BUGS=X86] Disables x86 extended register state save
1804 and restore using xsave. The kernel will fallback to
1805 enabling legacy floating-point and sse state.
1807 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1808 wfi(ARM) instruction doesn't work correctly and not to
1809 use it. This is also useful when using JTAG debugger.
1811 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1812 instruction doesn't work correctly and not to
1813 use it.
1815 no_file_caps Tells the kernel not to honor file capabilities. The
1816 only way then for a file to be executed with privilege
1817 is to be setuid root or executed by root.
1819 nohalt [IA-64] Tells the kernel not to use the power saving
1820 function PAL_HALT_LIGHT when idle. This increases
1821 power-consumption. On the positive side, it reduces
1822 interrupt wake-up latency, which may improve performance
1823 in certain environments such as networked servers or
1824 real-time systems.
1826 nohz= [KNL] Boottime enable/disable dynamic ticks
1827 Valid arguments: on, off
1828 Default: on
1830 noiotrap [SH] Disables trapped I/O port accesses.
1832 noirqdebug [X86-32] Disables the code which attempts to detect and
1833 disable unhandled interrupt sources.
1835 no_timer_check [X86,APIC] Disables the code which tests for
1836 broken timer IRQ sources.
1838 noisapnp [ISAPNP] Disables ISA PnP code.
1840 noinitrd [RAM] Tells the kernel not to load any configured
1841 initial RAM disk.
1843 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1844 remapping.
1845 [Deprecated - use intremap=off]
1847 nointroute [IA-64]
1849 nojitter [IA-64] Disables jitter checking for ITC timers.
1851 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1853 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1854 fault handling.
1856 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1857 steal time is computed, but won't influence scheduler
1858 behaviour
1860 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1862 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1864 noltlbs [PPC] Do not use large page/tlb entries for kernel
1865 lowmem mapping on PPC40x.
1867 nomca [IA-64] Disable machine check abort handling
1869 nomce [X86-32] Machine Check Exception
1871 nomfgpt [X86-32] Disable Multi-Function General Purpose
1872 Timer usage (for AMD Geode machines).
1874 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
1875 shutdown the other cpus. Instead use the REBOOT_VECTOR
1876 irq.
1878 nomodule Disable module load
1880 nopat [X86] Disable PAT (page attribute table extension of
1881 pagetables) support.
1883 norandmaps Don't use address space randomization. Equivalent to
1884 echo 0 > /proc/sys/kernel/randomize_va_space
1886 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1888 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1889 with UP alternatives
1891 noresidual [PPC] Don't use residual data on PReP machines.
1893 nordrand [X86] Disable the direct use of the RDRAND
1894 instruction even if it is supported by the
1895 processor. RDRAND is still available to user
1896 space applications.
1898 noresume [SWSUSP] Disables resume and restores original swap
1899 space.
1901 no-scroll [VGA] Disables scrollback.
1902 This is required for the Braillex ib80-piezo Braille
1903 reader made by F.H. Papenmeier (Germany).
1905 nosbagart [IA-64]
1907 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1909 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1910 and disable the IO APIC. legacy for "maxcpus=0".
1912 nosoftlockup [KNL] Disable the soft-lockup detector.
1914 nosync [HW,M68K] Disables sync negotiation for all devices.
1916 notsc [BUGS=X86-32] Disable Time Stamp Counter
1918 nousb [USB] Disable the USB subsystem
1920 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1922 nowb [ARM]
1924 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1926 nptcg= [IA-64] Override max number of concurrent global TLB
1927 purges which is reported from either PAL_VM_SUMMARY or
1928 SAL PALO.
1930 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1931 could support. nr_cpus=n : n >= 1 limits the kernel to
1932 supporting 'n' processors. Later in runtime you can not
1933 use hotplug cpu feature to put more cpu back to online.
1934 just like you compile the kernel NR_CPUS=n
1936 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1938 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1939 one of ['zone', 'node', 'default'] can be specified
1940 This can be set from sysctl after boot.
1941 See Documentation/sysctl/vm.txt for details.
1943 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1944 See Documentation/debugging-via-ohci1394.txt for more
1945 info.
1947 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1948 Rather than timing out after 20 ms if an EC
1949 command is not properly ACKed, override the length
1950 of the timeout. We have interrupts disabled while
1951 waiting for the ACK, so if this is set too high
1952 interrupts *may* be lost!
1954 omap_mux= [OMAP] Override bootloader pin multiplexing.
1955 Format: <mux_mode0.mode_name=value>...
1956 For example, to override I2C bus2:
1957 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1959 oprofile.timer= [HW]
1960 Use timer interrupt instead of performance counters
1962 oprofile.cpu_type= Force an oprofile cpu type
1963 This might be useful if you have an older oprofile
1964 userland or if you want common events.
1965 Format: { arch_perfmon }
1966 arch_perfmon: [X86] Force use of architectural
1967 perfmon on Intel CPUs instead of the
1968 CPU specific event set.
1969 timer: [X86] Force use of architectural NMI
1970 timer mode (see also oprofile.timer
1971 for generic hr timer mode)
1972 [s390] Force legacy basic mode sampling
1973 (report cpu_type "timer")
1975 oops=panic Always panic on oopses. Default is to just kill the
1976 process, but there is a small probability of
1977 deadlocking the machine.
1978 This will also cause panics on machine check exceptions.
1979 Useful together with panic=30 to trigger a reboot.
1981 OSS [HW,OSS]
1982 See Documentation/sound/oss/oss-parameters.txt
1984 panic= [KNL] Kernel behaviour on panic: delay <timeout>
1985 timeout > 0: seconds before rebooting
1986 timeout = 0: wait forever
1987 timeout < 0: reboot immediately
1988 Format: <timeout>
1990 parkbd.port= [HW] Parallel port number the keyboard adapter is
1991 connected to, default is 0.
1992 Format: <parport#>
1993 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1994 0 for XT, 1 for AT (default is AT).
1995 Format: <mode>
1997 parport= [HW,PPT] Specify parallel ports. 0 disables.
1998 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1999 Use 'auto' to force the driver to use any
2000 IRQ/DMA settings detected (the default is to
2001 ignore detected IRQ/DMA settings because of
2002 possible conflicts). You can specify the base
2003 address, IRQ, and DMA settings; IRQ and DMA
2004 should be numbers, or 'auto' (for using detected
2005 settings on that particular port), or 'nofifo'
2006 (to avoid using a FIFO even if it is detected).
2007 Parallel ports are assigned in the order they
2008 are specified on the command line, starting
2009 with parport0.
2011 parport_init_mode= [HW,PPT]
2012 Configure VIA parallel port to operate in
2013 a specific mode. This is necessary on Pegasos
2014 computer where firmware has no options for setting
2015 up parallel port mode and sets it to spp.
2016 Currently this function knows 686a and 8231 chips.
2017 Format: [spp|ps2|epp|ecp|ecpepp]
2019 pause_on_oops=
2020 Halt all CPUs after the first oops has been printed for
2021 the specified number of seconds. This is to be used if
2022 your oopses keep scrolling off the screen.
2024 pcbit= [HW,ISDN]
2026 pcd. [PARIDE]
2027 See header of drivers/block/paride/pcd.c.
2028 See also Documentation/blockdev/paride.txt.
2030 pci=option[,option...] [PCI] various PCI subsystem options:
2031 earlydump [X86] dump PCI config space before the kernel
2032 changes anything
2033 off [X86] don't probe for the PCI bus
2034 bios [X86-32] force use of PCI BIOS, don't access
2035 the hardware directly. Use this if your machine
2036 has a non-standard PCI host bridge.
2037 nobios [X86-32] disallow use of PCI BIOS, only direct
2038 hardware access methods are allowed. Use this
2039 if you experience crashes upon bootup and you
2040 suspect they are caused by the BIOS.
2041 conf1 [X86] Force use of PCI Configuration
2042 Mechanism 1.
2043 conf2 [X86] Force use of PCI Configuration
2044 Mechanism 2.
2045 noaer [PCIE] If the PCIEAER kernel config parameter is
2046 enabled, this kernel boot option can be used to
2047 disable the use of PCIE advanced error reporting.
2048 nodomains [PCI] Disable support for multiple PCI
2049 root domains (aka PCI segments, in ACPI-speak).
2050 nommconf [X86] Disable use of MMCONFIG for PCI
2051 Configuration
2052 check_enable_amd_mmconf [X86] check for and enable
2053 properly configured MMIO access to PCI
2054 config space on AMD family 10h CPU
2055 nomsi [MSI] If the PCI_MSI kernel config parameter is
2056 enabled, this kernel boot option can be used to
2057 disable the use of MSI interrupts system-wide.
2058 noioapicquirk [APIC] Disable all boot interrupt quirks.
2059 Safety option to keep boot IRQs enabled. This
2060 should never be necessary.
2061 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2062 primary IO-APIC for bridges that cannot disable
2063 boot IRQs. This fixes a source of spurious IRQs
2064 when the system masks IRQs.
2065 noioapicreroute [APIC] Disable workaround that uses the
2066 boot IRQ equivalent of an IRQ that connects to
2067 a chipset where boot IRQs cannot be disabled.
2068 The opposite of ioapicreroute.
2069 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2070 routing table. These calls are known to be buggy
2071 on several machines and they hang the machine
2072 when used, but on other computers it's the only
2073 way to get the interrupt routing table. Try
2074 this option if the kernel is unable to allocate
2075 IRQs or discover secondary PCI buses on your
2076 motherboard.
2077 rom [X86] Assign address space to expansion ROMs.
2078 Use with caution as certain devices share
2079 address decoders between ROMs and other
2080 resources.
2081 norom [X86] Do not assign address space to
2082 expansion ROMs that do not already have
2083 BIOS assigned address ranges.
2084 nobar [X86] Do not assign address space to the
2085 BARs that weren't assigned by the BIOS.
2086 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2087 assigned automatically to PCI devices. You can
2088 make the kernel exclude IRQs of your ISA cards
2089 this way.
2090 pirqaddr=0xAAAAA [X86] Specify the physical address
2091 of the PIRQ table (normally generated
2092 by the BIOS) if it is outside the
2093 F0000h-100000h range.
2094 lastbus=N [X86] Scan all buses thru bus #N. Can be
2095 useful if the kernel is unable to find your
2096 secondary buses and you want to tell it
2097 explicitly which ones they are.
2098 assign-busses [X86] Always assign all PCI bus
2099 numbers ourselves, overriding
2100 whatever the firmware may have done.
2101 usepirqmask [X86] Honor the possible IRQ mask stored
2102 in the BIOS $PIR table. This is needed on
2103 some systems with broken BIOSes, notably
2104 some HP Pavilion N5400 and Omnibook XE3
2105 notebooks. This will have no effect if ACPI
2106 IRQ routing is enabled.
2107 noacpi [X86] Do not use ACPI for IRQ routing
2108 or for PCI scanning.
2109 use_crs [X86] Use PCI host bridge window information
2110 from ACPI. On BIOSes from 2008 or later, this
2111 is enabled by default. If you need to use this,
2112 please report a bug.
2113 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2114 If you need to use this, please report a bug.
2115 routeirq Do IRQ routing for all PCI devices.
2116 This is normally done in pci_enable_device(),
2117 so this option is a temporary workaround
2118 for broken drivers that don't call it.
2119 skip_isa_align [X86] do not align io start addr, so can
2120 handle more pci cards
2121 firmware [ARM] Do not re-enumerate the bus but instead
2122 just use the configuration from the
2123 bootloader. This is currently used on
2124 IXP2000 systems where the bus has to be
2125 configured a certain way for adjunct CPUs.
2126 noearly [X86] Don't do any early type 1 scanning.
2127 This might help on some broken boards which
2128 machine check when some devices' config space
2129 is read. But various workarounds are disabled
2130 and some IOMMU drivers will not work.
2131 bfsort Sort PCI devices into breadth-first order.
2132 This sorting is done to get a device
2133 order compatible with older (<= 2.4) kernels.
2134 nobfsort Don't sort PCI devices into breadth-first order.
2135 cbiosize=nn[KMG] The fixed amount of bus space which is
2136 reserved for the CardBus bridge's IO window.
2137 The default value is 256 bytes.
2138 cbmemsize=nn[KMG] The fixed amount of bus space which is
2139 reserved for the CardBus bridge's memory
2140 window. The default value is 64 megabytes.
2141 resource_alignment=
2142 Format:
2143 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2144 Specifies alignment and device to reassign
2145 aligned memory resources.
2146 If <order of align> is not specified,
2147 PAGE_SIZE is used as alignment.
2148 PCI-PCI bridge can be specified, if resource
2149 windows need to be expanded.
2150 ecrc= Enable/disable PCIe ECRC (transaction layer
2151 end-to-end CRC checking).
2152 bios: Use BIOS/firmware settings. This is the
2153 the default.
2154 off: Turn ECRC off
2155 on: Turn ECRC on.
2156 realloc= Enable/disable reallocating PCI bridge resources
2157 if allocations done by BIOS are too small to
2158 accommodate resources required by all child
2159 devices.
2160 off: Turn realloc off
2161 on: Turn realloc on
2162 realloc same as realloc=on
2163 noari do not use PCIe ARI.
2165 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2166 Management.
2167 off Disable ASPM.
2168 force Enable ASPM even on devices that claim not to support it.
2169 WARNING: Forcing ASPM on may cause system lockups.
2171 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2172 nomsi Do not use MSI for PCI Express Native Hotplug (this
2173 makes all PCIe ports use INTx for hotplug services).
2175 pcie_ports= [PCIE] PCIe ports handling:
2176 auto Ask the BIOS whether or not to use native PCIe services
2177 associated with PCIe ports (PME, hot-plug, AER). Use
2178 them only if that is allowed by the BIOS.
2179 native Use native PCIe services associated with PCIe ports
2180 unconditionally.
2181 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2182 ports driver.
2184 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2185 nomsi Do not use MSI for native PCIe PME signaling (this makes
2186 all PCIe root ports use INTx for all services).
2188 pcmv= [HW,PCMCIA] BadgePAD 4
2190 pd. [PARIDE]
2191 See Documentation/blockdev/paride.txt.
2193 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2194 boot time.
2195 Format: { 0 | 1 }
2196 See arch/parisc/kernel/pdc_chassis.c
2198 percpu_alloc= Select which percpu first chunk allocator to use.
2199 Currently supported values are "embed" and "page".
2200 Archs may support subset or none of the selections.
2201 See comments in mm/percpu.c for details on each
2202 allocator. This parameter is primarily for debugging
2203 and performance comparison.
2205 pf. [PARIDE]
2206 See Documentation/blockdev/paride.txt.
2208 pg. [PARIDE]
2209 See Documentation/blockdev/paride.txt.
2211 pirq= [SMP,APIC] Manual mp-table setup
2212 See Documentation/x86/i386/IO-APIC.txt.
2214 plip= [PPT,NET] Parallel port network link
2215 Format: { parport<nr> | timid | 0 }
2216 See also Documentation/parport.txt.
2218 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2219 Override pmtimer IOPort with a hex value.
2220 e.g. pmtmr=0x508
2222 pnp.debug=1 [PNP]
2223 Enable PNP debug messages (depends on the
2224 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2225 via /sys/module/pnp/parameters/debug. We always show
2226 current resource usage; turning this on also shows
2227 possible settings and some assignment information.
2229 pnpacpi= [ACPI]
2230 { off }
2232 pnpbios= [ISAPNP]
2233 { on | off | curr | res | no-curr | no-res }
2235 pnp_reserve_irq=
2236 [ISAPNP] Exclude IRQs for the autoconfiguration
2238 pnp_reserve_dma=
2239 [ISAPNP] Exclude DMAs for the autoconfiguration
2241 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2242 Ranges are in pairs (I/O port base and size).
2244 pnp_reserve_mem=
2245 [ISAPNP] Exclude memory regions for the
2246 autoconfiguration.
2247 Ranges are in pairs (memory base and size).
2249 ports= [IP_VS_FTP] IPVS ftp helper module
2250 Default is 21.
2251 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2252 may be specified.
2253 Format: <port>,<port>....
2255 print-fatal-signals=
2256 [KNL] debug: print fatal signals
2258 If enabled, warn about various signal handling
2259 related application anomalies: too many signals,
2260 too many POSIX.1 timers, fatal signals causing a
2261 coredump - etc.
2263 If you hit the warning due to signal overflow,
2264 you might want to try "ulimit -i unlimited".
2266 default: off.
2268 printk.always_kmsg_dump=
2269 Trigger kmsg_dump for cases other than kernel oops or
2270 panics
2271 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2272 default: disabled
2274 printk.time= Show timing data prefixed to each printk message line
2275 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2277 processor.max_cstate= [HW,ACPI]
2278 Limit processor to maximum C-state
2279 max_cstate=9 overrides any DMI blacklist limit.
2281 processor.nocst [HW,ACPI]
2282 Ignore the _CST method to determine C-states,
2283 instead using the legacy FADT method
2285 profile= [KNL] Enable kernel profiling via /proc/profile
2286 Format: [schedule,]<number>
2287 Param: "schedule" - profile schedule points.
2288 Param: <number> - step/bucket size as a power of 2 for
2289 statistical time based profiling.
2290 Param: "sleep" - profile D-state sleeping (millisecs).
2291 Requires CONFIG_SCHEDSTATS
2292 Param: "kvm" - profile VM exits.
2294 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2295 before loading.
2296 See Documentation/blockdev/ramdisk.txt.
2298 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2299 probe for; one of (bare|imps|exps|lifebook|any).
2300 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2301 per second.
2302 psmouse.resetafter= [HW,MOUSE]
2303 Try to reset the device after so many bad packets
2304 (0 = never).
2305 psmouse.resolution=
2306 [HW,MOUSE] Set desired mouse resolution, in dpi.
2307 psmouse.smartscroll=
2308 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2309 0 = disabled, 1 = enabled (default).
2311 pstore.backend= Specify the name of the pstore backend to use
2313 pt. [PARIDE]
2314 See Documentation/blockdev/paride.txt.
2316 pty.legacy_count=
2317 [KNL] Number of legacy pty's. Overwrites compiled-in
2318 default number.
2320 quiet [KNL] Disable most log messages
2322 r128= [HW,DRM]
2324 raid= [HW,RAID]
2325 See Documentation/md.txt.
2327 ramdisk_blocksize= [RAM]
2328 See Documentation/blockdev/ramdisk.txt.
2330 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2331 See Documentation/blockdev/ramdisk.txt.
2333 rcupdate.blimit= [KNL,BOOT]
2334 Set maximum number of finished RCU callbacks to process
2335 in one batch.
2337 rcupdate.qhimark= [KNL,BOOT]
2338 Set threshold of queued
2339 RCU callbacks over which batch limiting is disabled.
2341 rcupdate.qlowmark= [KNL,BOOT]
2342 Set threshold of queued RCU callbacks below which
2343 batch limiting is re-enabled.
2345 rdinit= [KNL]
2346 Format: <full_path>
2347 Run specified binary instead of /init from the ramdisk,
2348 used for early userspace startup. See initrd.
2350 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2351 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2352 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2354 relax_domain_level=
2355 [KNL, SMP] Set scheduler's default relax_domain_level.
2356 See Documentation/cgroups/cpusets.txt.
2358 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2360 reservetop= [X86-32]
2361 Format: nn[KMG]
2362 Reserves a hole at the top of the kernel virtual
2363 address space.
2365 reservelow= [X86]
2366 Format: nn[K]
2367 Set the amount of memory to reserve for BIOS at
2368 the bottom of the address space.
2370 reset_devices [KNL] Force drivers to reset the underlying device
2371 during initialization.
2373 resume= [SWSUSP]
2374 Specify the partition device for software suspend
2376 resume_offset= [SWSUSP]
2377 Specify the offset from the beginning of the partition
2378 given by "resume=" at which the swap header is located,
2379 in <PAGE_SIZE> units (needed only for swap files).
2380 See Documentation/power/swsusp-and-swap-files.txt
2382 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2383 read the resume files
2385 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2386 Useful for devices that are detected asynchronously
2387 (e.g. USB and MMC devices).
2389 hibernate= [HIBERNATION]
2390 noresume Don't check if there's a hibernation image
2391 present during boot.
2392 nocompress Don't compress/decompress hibernation images.
2394 retain_initrd [RAM] Keep initrd memory after extraction
2396 rhash_entries= [KNL,NET]
2397 Set number of hash buckets for route cache
2399 riscom8= [HW,SERIAL]
2400 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2402 ro [KNL] Mount root device read-only on boot
2404 root= [KNL] Root filesystem
2405 See name_to_dev_t comment in init/do_mounts.c.
2407 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2408 mount the root filesystem
2410 rootflags= [KNL] Set root filesystem mount option string
2412 rootfstype= [KNL] Set root filesystem type
2414 rootwait [KNL] Wait (indefinitely) for root device to show up.
2415 Useful for devices that are detected asynchronously
2416 (e.g. USB and MMC devices).
2418 rw [KNL] Mount root device read-write on boot
2420 S [KNL] Run init in single mode
2422 sa1100ir [NET]
2423 See drivers/net/irda/sa1100_ir.c.
2425 sbni= [NET] Granch SBNI12 leased line adapter
2427 sched_debug [KNL] Enables verbose scheduler debug messages.
2429 security= [SECURITY] Choose a security module to enable at boot.
2430 If this boot parameter is not specified, only the first
2431 security module asking for security registration will be
2432 loaded. An invalid security module name will be treated
2433 as if no module has been chosen.
2435 selinux= [SELINUX] Disable or enable SELinux at boot time.
2436 Format: { "0" | "1" }
2437 See security/selinux/Kconfig help text.
2438 0 -- disable.
2439 1 -- enable.
2440 Default value is set via kernel config option.
2441 If enabled at boot time, /selinux/disable can be used
2442 later to disable prior to initial policy load.
2444 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2445 Format: { "0" | "1" }
2446 See security/apparmor/Kconfig help text
2447 0 -- disable.
2448 1 -- enable.
2449 Default value is set via kernel config option.
2451 serialnumber [BUGS=X86-32]
2453 shapers= [NET]
2454 Maximal number of shapers.
2456 show_msr= [x86] show boot-time MSR settings
2457 Format: { <integer> }
2458 Show boot-time (BIOS-initialized) MSR settings.
2459 The parameter means the number of CPUs to show,
2460 for example 1 means boot CPU only.
2462 simeth= [IA-64]
2463 simscsi=
2465 slram= [HW,MTD]
2467 slab_max_order= [MM, SLAB]
2468 Determines the maximum allowed order for slabs.
2469 A high setting may cause OOMs due to memory
2470 fragmentation. Defaults to 1 for systems with
2471 more than 32MB of RAM, 0 otherwise.
2473 slub_debug[=options[,slabs]] [MM, SLUB]
2474 Enabling slub_debug allows one to determine the
2475 culprit if slab objects become corrupted. Enabling
2476 slub_debug can create guard zones around objects and
2477 may poison objects when not in use. Also tracks the
2478 last alloc / free. For more information see
2479 Documentation/vm/slub.txt.
2481 slub_max_order= [MM, SLUB]
2482 Determines the maximum allowed order for slabs.
2483 A high setting may cause OOMs due to memory
2484 fragmentation. For more information see
2485 Documentation/vm/slub.txt.
2487 slub_min_objects= [MM, SLUB]
2488 The minimum number of objects per slab. SLUB will
2489 increase the slab order up to slub_max_order to
2490 generate a sufficiently large slab able to contain
2491 the number of objects indicated. The higher the number
2492 of objects the smaller the overhead of tracking slabs
2493 and the less frequently locks need to be acquired.
2494 For more information see Documentation/vm/slub.txt.
2496 slub_min_order= [MM, SLUB]
2497 Determines the minimum page order for slabs. Must be
2498 lower than slub_max_order.
2499 For more information see Documentation/vm/slub.txt.
2501 slub_nomerge [MM, SLUB]
2502 Disable merging of slabs with similar size. May be
2503 necessary if there is some reason to distinguish
2504 allocs to different slabs. Debug options disable
2505 merging on their own.
2506 For more information see Documentation/vm/slub.txt.
2508 smart2= [HW]
2509 Format: <io1>[,<io2>[,...,<io8>]]
2511 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2512 attempt to substitute SMP alternatives once at boot.
2514 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2515 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2516 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2517 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2518 smsc-ircc2.ircc_irq= [HW] IRQ line
2519 smsc-ircc2.ircc_dma= [HW] DMA channel
2520 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2521 0: Toshiba Satellite 1800 (GP data pin select)
2522 1: Fast pin select (default)
2523 2: ATC IRMode
2525 softlockup_panic=
2526 [KNL] Should the soft-lockup detector generate panics.
2527 Format: <integer>
2529 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2530 See Documentation/laptops/sonypi.txt
2532 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2533 See Documentation/serial/specialix.txt.
2535 spia_io_base= [HW,MTD]
2536 spia_fio_base=
2537 spia_pedr=
2538 spia_peddr=
2540 stacktrace [FTRACE]
2541 Enabled the stack tracer on boot up.
2543 stacktrace_filter=[function-list]
2544 [FTRACE] Limit the functions that the stack tracer
2545 will trace at boot up. function-list is a comma separated
2546 list of functions. This list can be changed at run
2547 time by the stack_trace_filter file in the debugfs
2548 tracing directory. Note, this enables stack tracing
2549 and the stacktrace above is not needed.
2551 sti= [PARISC,HW]
2552 Format: <num>
2553 Set the STI (builtin display/keyboard on the HP-PARISC
2554 machines) console (graphic card) which should be used
2555 as the initial boot-console.
2556 See also comment in drivers/video/console/sticore.c.
2558 sti_font= [HW]
2559 See comment in drivers/video/console/sticore.c.
2561 stifb= [HW]
2562 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2564 sunrpc.min_resvport=
2565 sunrpc.max_resvport=
2566 [NFS,SUNRPC]
2567 SunRPC servers often require that client requests
2568 originate from a privileged port (i.e. a port in the
2569 range 0 < portnr < 1024).
2570 An administrator who wishes to reserve some of these
2571 ports for other uses may adjust the range that the
2572 kernel's sunrpc client considers to be privileged
2573 using these two parameters to set the minimum and
2574 maximum port values.
2576 sunrpc.pool_mode=
2577 [NFS]
2578 Control how the NFS server code allocates CPUs to
2579 service thread pools. Depending on how many NICs
2580 you have and where their interrupts are bound, this
2581 option will affect which CPUs will do NFS serving.
2582 Note: this parameter cannot be changed while the
2583 NFS server is running.
2585 auto the server chooses an appropriate mode
2586 automatically using heuristics
2587 global a single global pool contains all CPUs
2588 percpu one pool for each CPU
2589 pernode one pool for each NUMA node (equivalent
2590 to global on non-NUMA machines)
2592 sunrpc.tcp_slot_table_entries=
2593 sunrpc.udp_slot_table_entries=
2594 [NFS,SUNRPC]
2595 Sets the upper limit on the number of simultaneous
2596 RPC calls that can be sent from the client to a
2597 server. Increasing these values may allow you to
2598 improve throughput, but will also increase the
2599 amount of memory reserved for use by the client.
2601 swapaccount[=0|1]
2602 [KNL] Enable accounting of swap in memory resource
2603 controller if no parameter or 1 is given or disable
2604 it if 0 is given (See Documentation/cgroups/memory.txt)
2606 swiotlb= [IA-64] Number of I/O TLB slabs
2608 switches= [HW,M68k]
2610 sysfs.deprecated=0|1 [KNL]
2611 Enable/disable old style sysfs layout for old udev
2612 on older distributions. When this option is enabled
2613 very new udev will not work anymore. When this option
2614 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2615 in older udev will not work anymore.
2616 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2617 the kernel configuration.
2619 sysrq_always_enabled
2620 [KNL]
2621 Ignore sysrq setting - this boot parameter will
2622 neutralize any effect of /proc/sys/kernel/sysrq.
2623 Useful for debugging.
2625 tdfx= [HW,DRM]
2627 test_suspend= [SUSPEND]
2628 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2629 standby suspend) as the system sleep state to briefly
2630 enter during system startup. The system is woken from
2631 this state using a wakeup-capable RTC alarm.
2633 thash_entries= [KNL,NET]
2634 Set number of hash buckets for TCP connection
2636 thermal.act= [HW,ACPI]
2637 -1: disable all active trip points in all thermal zones
2638 <degrees C>: override all lowest active trip points
2640 thermal.crt= [HW,ACPI]
2641 -1: disable all critical trip points in all thermal zones
2642 <degrees C>: override all critical trip points
2644 thermal.nocrt= [HW,ACPI]
2645 Set to disable actions on ACPI thermal zone
2646 critical and hot trip points.
2648 thermal.off= [HW,ACPI]
2649 1: disable ACPI thermal control
2651 thermal.psv= [HW,ACPI]
2652 -1: disable all passive trip points
2653 <degrees C>: override all passive trip points to this
2654 value
2656 thermal.tzp= [HW,ACPI]
2657 Specify global default ACPI thermal zone polling rate
2658 <deci-seconds>: poll all this frequency
2659 0: no polling (default)
2661 threadirqs [KNL]
2662 Force threading of all interrupt handlers except those
2663 marked explicitly IRQF_NO_THREAD.
2665 topology= [S390]
2666 Format: {off | on}
2667 Specify if the kernel should make use of the cpu
2668 topology information if the hardware supports this.
2669 The scheduler will make use of this information and
2670 e.g. base its process migration decisions on it.
2671 Default is on.
2673 tp720= [HW,PS2]
2675 tpm_suspend_pcr=[HW,TPM]
2676 Format: integer pcr id
2677 Specify that at suspend time, the tpm driver
2678 should extend the specified pcr with zeros,
2679 as a workaround for some chips which fail to
2680 flush the last written pcr on TPM_SaveState.
2681 This will guarantee that all the other pcrs
2682 are saved.
2684 trace_buf_size=nn[KMG]
2685 [FTRACE] will set tracing buffer size.
2687 trace_event=[event-list]
2688 [FTRACE] Set and start specified trace events in order
2689 to facilitate early boot debugging.
2690 See also Documentation/trace/events.txt
2692 transparent_hugepage=
2693 [KNL]
2694 Format: [always|madvise|never]
2695 Can be used to control the default behavior of the system
2696 with respect to transparent hugepages.
2697 See Documentation/vm/transhuge.txt for more details.
2699 tsc= Disable clocksource stability checks for TSC.
2700 Format: <string>
2701 [x86] reliable: mark tsc clocksource as reliable, this
2702 disables clocksource verification at runtime, as well
2703 as the stability checks done at bootup. Used to enable
2704 high-resolution timer mode on older hardware, and in
2705 virtualized environment.
2706 [x86] noirqtime: Do not use TSC to do irq accounting.
2707 Used to run time disable IRQ_TIME_ACCOUNTING on any
2708 platforms where RDTSC is slow and this accounting
2709 can add overhead.
2711 turbografx.map[2|3]= [HW,JOY]
2712 TurboGraFX parallel port interface
2713 Format:
2714 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2715 See also Documentation/input/joystick-parport.txt
2717 udbg-immortal [PPC] When debugging early kernel crashes that
2718 happen after console_init() and before a proper
2719 console driver takes over, this boot options might
2720 help "seeing" what's going on.
2722 uhash_entries= [KNL,NET]
2723 Set number of hash buckets for UDP/UDP-Lite connections
2725 uhci-hcd.ignore_oc=
2726 [USB] Ignore overcurrent events (default N).
2727 Some badly-designed motherboards generate lots of
2728 bogus events, for ports that aren't wired to
2729 anything. Set this parameter to avoid log spamming.
2730 Note that genuine overcurrent events won't be
2731 reported either.
2733 unknown_nmi_panic
2734 [X86] Cause panic on unknown NMI.
2736 usbcore.authorized_default=
2737 [USB] Default USB device authorization:
2738 (default -1 = authorized except for wireless USB,
2739 0 = not authorized, 1 = authorized)
2741 usbcore.autosuspend=
2742 [USB] The autosuspend time delay (in seconds) used
2743 for newly-detected USB devices (default 2). This
2744 is the time required before an idle device will be
2745 autosuspended. Devices for which the delay is set
2746 to a negative value won't be autosuspended at all.
2748 usbcore.usbfs_snoop=
2749 [USB] Set to log all usbfs traffic (default 0 = off).
2751 usbcore.blinkenlights=
2752 [USB] Set to cycle leds on hubs (default 0 = off).
2754 usbcore.old_scheme_first=
2755 [USB] Start with the old device initialization
2756 scheme (default 0 = off).
2758 usbcore.usbfs_memory_mb=
2759 [USB] Memory limit (in MB) for buffers allocated by
2760 usbfs (default = 16, 0 = max = 2047).
2762 usbcore.use_both_schemes=
2763 [USB] Try the other device initialization scheme
2764 if the first one fails (default 1 = enabled).
2766 usbcore.initial_descriptor_timeout=
2767 [USB] Specifies timeout for the initial 64-byte
2768 USB_REQ_GET_DESCRIPTOR request in milliseconds
2769 (default 5000 = 5.0 seconds).
2771 usbhid.mousepoll=
2772 [USBHID] The interval which mice are to be polled at.
2774 usb-storage.delay_use=
2775 [UMS] The delay in seconds before a new device is
2776 scanned for Logical Units (default 5).
2778 usb-storage.quirks=
2779 [UMS] A list of quirks entries to supplement or
2780 override the built-in unusual_devs list. List
2781 entries are separated by commas. Each entry has
2782 the form VID:PID:Flags where VID and PID are Vendor
2783 and Product ID values (4-digit hex numbers) and
2784 Flags is a set of characters, each corresponding
2785 to a common usb-storage quirk flag as follows:
2786 a = SANE_SENSE (collect more than 18 bytes
2787 of sense data);
2788 b = BAD_SENSE (don't collect more than 18
2789 bytes of sense data);
2790 c = FIX_CAPACITY (decrease the reported
2791 device capacity by one sector);
2792 d = NO_READ_DISC_INFO (don't use
2793 READ_DISC_INFO command);
2794 e = NO_READ_CAPACITY_16 (don't use
2795 READ_CAPACITY_16 command);
2796 h = CAPACITY_HEURISTICS (decrease the
2797 reported device capacity by one
2798 sector if the number is odd);
2799 i = IGNORE_DEVICE (don't bind to this
2800 device);
2801 l = NOT_LOCKABLE (don't try to lock and
2802 unlock ejectable media);
2803 m = MAX_SECTORS_64 (don't transfer more
2804 than 64 sectors = 32 KB at a time);
2805 n = INITIAL_READ10 (force a retry of the
2806 initial READ(10) command);
2807 o = CAPACITY_OK (accept the capacity
2808 reported by the device);
2809 r = IGNORE_RESIDUE (the device reports
2810 bogus residue values);
2811 s = SINGLE_LUN (the device has only one
2812 Logical Unit);
2813 w = NO_WP_DETECT (don't test whether the
2814 medium is write-protected).
2815 Example: quirks=0419:aaf5:rl,0421:0433:rc
2817 user_debug= [KNL,ARM]
2818 Format: <int>
2819 See arch/arm/Kconfig.debug help text.
2820 1 - undefined instruction events
2821 2 - system calls
2822 4 - invalid data aborts
2823 8 - SIGSEGV faults
2824 16 - SIGBUS faults
2825 Example: user_debug=31
2827 userpte=
2828 [X86] Flags controlling user PTE allocations.
2830 nohigh = do not allocate PTE pages in
2831 HIGHMEM regardless of setting
2832 of CONFIG_HIGHPTE.
2834 vdso= [X86,SH]
2835 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2836 vdso=1: enable VDSO (default)
2837 vdso=0: disable VDSO mapping
2839 vdso32= [X86]
2840 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2841 vdso32=1: enable 32-bit VDSO (default)
2842 vdso32=0: disable 32-bit VDSO mapping
2844 vector= [IA-64,SMP]
2845 vector=percpu: enable percpu vector domain
2847 video= [FB] Frame buffer configuration
2848 See Documentation/fb/modedb.txt.
2850 vga= [BOOT,X86-32] Select a particular video mode
2851 See Documentation/x86/boot.txt and
2852 Documentation/svga.txt.
2853 Use vga=ask for menu.
2854 This is actually a boot loader parameter; the value is
2855 passed to the kernel using a special protocol.
2857 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2858 size of <nn>. This can be used to increase the
2859 minimum size (128MB on x86). It can also be used to
2860 decrease the size and leave more room for directly
2861 mapped kernel RAM.
2863 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2864 Format: <command>
2866 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2867 Format: <command>
2869 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2870 Format: <command>
2872 vsyscall= [X86-64]
2873 Controls the behavior of vsyscalls (i.e. calls to
2874 fixed addresses of 0xffffffffff600x00 from legacy
2875 code). Most statically-linked binaries and older
2876 versions of glibc use these calls. Because these
2877 functions are at fixed addresses, they make nice
2878 targets for exploits that can control RIP.
2880 emulate [default] Vsyscalls turn into traps and are
2881 emulated reasonably safely.
2883 native Vsyscalls are native syscall instructions.
2884 This is a little bit faster than trapping
2885 and makes a few dynamic recompilers work
2886 better than they would in emulation mode.
2887 It also makes exploits much easier to write.
2889 none Vsyscalls don't work at all. This makes
2890 them quite hard to use for exploits but
2891 might break your system.
2893 vt.cur_default= [VT] Default cursor shape.
2894 Format: 0xCCBBAA, where AA, BB, and CC are the same as
2895 the parameters of the <Esc>[?A;B;Cc escape sequence;
2896 see VGA-softcursor.txt. Default: 2 = underline.
2898 vt.default_blu= [VT]
2899 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2900 Change the default blue palette of the console.
2901 This is a 16-member array composed of values
2902 ranging from 0-255.
2904 vt.default_grn= [VT]
2905 Format: <green0>,<green1>,<green2>,...,<green15>
2906 Change the default green palette of the console.
2907 This is a 16-member array composed of values
2908 ranging from 0-255.
2910 vt.default_red= [VT]
2911 Format: <red0>,<red1>,<red2>,...,<red15>
2912 Change the default red palette of the console.
2913 This is a 16-member array composed of values
2914 ranging from 0-255.
2916 vt.default_utf8=
2917 [VT]
2918 Format=<0|1>
2919 Set system-wide default UTF-8 mode for all tty's.
2920 Default is 1, i.e. UTF-8 mode is enabled for all
2921 newly opened terminals.
2923 vt.global_cursor_default=
2924 [VT]
2925 Format=<-1|0|1>
2926 Set system-wide default for whether a cursor
2927 is shown on new VTs. Default is -1,
2928 i.e. cursors will be created by default unless
2929 overridden by individual drivers. 0 will hide
2930 cursors, 1 will display them.
2932 watchdog timers [HW,WDT] For information on watchdog timers,
2933 see Documentation/watchdog/watchdog-parameters.txt
2934 or other driver-specific files in the
2935 Documentation/watchdog/ directory.
2937 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2938 default x2apic cluster mode on platforms
2939 supporting x2apic.
2941 x86_mrst_timer= [X86-32,APBT]
2942 Choose timer option for x86 Moorestown MID platform.
2943 Two valid options are apbt timer only and lapic timer
2944 plus one apbt timer for broadcast timer.
2945 x86_mrst_timer=apbt_only | lapic_and_apbt
2947 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2948 xd_geo= See header of drivers/block/xd.c.
2950 xen_emul_unplug= [HW,X86,XEN]
2951 Unplug Xen emulated devices
2952 Format: [unplug0,][unplug1]
2953 ide-disks -- unplug primary master IDE devices
2954 aux-ide-disks -- unplug non-primary-master IDE devices
2955 nics -- unplug network devices
2956 all -- unplug all emulated devices (NICs and IDE disks)
2957 unnecessary -- unplugging emulated devices is
2958 unnecessary even if the host did not respond to
2959 the unplug protocol
2960 never -- do not unplug even if version check succeeds
2962 xirc2ps_cs= [NET,PCMCIA]
2963 Format:
2964 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2966 ______________________________________________________________________
2968 TODO:
2970 Add more DRM drivers.