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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 dscc4.setup= [NET]
718 earlycon= [KNL] Output early console device and options.
719 uart[8250],io,<addr>[,options]
720 uart[8250],mmio,<addr>[,options]
721 uart[8250],mmio32,<addr>[,options]
722 Start an early, polled-mode console on the 8250/16550
723 UART at the specified I/O port or MMIO address.
724 MMIO inter-register address stride is either 8-bit
725 (mmio) or 32-bit (mmio32).
726 The options are the same as for ttyS, above.
728 earlyprintk= [X86,SH,BLACKFIN]
729 earlyprintk=vga
730 earlyprintk=serial[,ttySn[,baudrate]]
731 earlyprintk=ttySn[,baudrate]
732 earlyprintk=dbgp[debugController#]
734 Append ",keep" to not disable it when the real console
735 takes over.
737 Only vga or serial or usb debug port at a time.
739 Currently only ttyS0 and ttyS1 are supported.
741 Interaction with the standard serial driver is not
742 very good.
744 The VGA output is eventually overwritten by the real
745 console.
747 ekgdboc= [X86,KGDB] Allow early kernel console debugging
748 ekgdboc=kbd
750 This is designed to be used in conjunction with
751 the boot argument: earlyprintk=vga
753 edd= [EDD]
754 Format: {"off" | "on" | "skip[mbr]"}
756 eisa_irq_edge= [PARISC,HW]
757 See header of drivers/parisc/eisa.c.
759 elanfreq= [X86-32]
760 See comment before function elanfreq_setup() in
761 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
763 elevator= [IOSCHED]
764 Format: {"cfq" | "deadline" | "noop"}
765 See Documentation/block/cfq-iosched.txt and
766 Documentation/block/deadline-iosched.txt for details.
768 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
769 Specifies physical address of start of kernel core
770 image elf header and optionally the size. Generally
771 kexec loader will pass this option to capture kernel.
772 See Documentation/kdump/kdump.txt for details.
774 enable_mtrr_cleanup [X86]
775 The kernel tries to adjust MTRR layout from continuous
776 to discrete, to make X server driver able to add WB
777 entry later. This parameter enables that.
779 enable_timer_pin_1 [X86]
780 Enable PIN 1 of APIC timer
781 Can be useful to work around chipset bugs
782 (in particular on some ATI chipsets).
783 The kernel tries to set a reasonable default.
785 enforcing [SELINUX] Set initial enforcing status.
786 Format: {"0" | "1"}
787 See security/selinux/Kconfig help text.
788 0 -- permissive (log only, no denials).
789 1 -- enforcing (deny and log).
790 Default value is 0.
791 Value can be changed at runtime via /selinux/enforce.
793 erst_disable [ACPI]
794 Disable Error Record Serialization Table (ERST)
795 support.
797 ether= [HW,NET] Ethernet cards parameters
798 This option is obsoleted by the "netdev=" option, which
799 has equivalent usage. See its documentation for details.
801 evm= [EVM]
802 Format: { "fix" }
803 Permit 'security.evm' to be updated regardless of
804 current integrity status.
806 failslab=
807 fail_page_alloc=
808 fail_make_request=[KNL]
809 General fault injection mechanism.
810 Format: <interval>,<probability>,<space>,<times>
811 See also Documentation/fault-injection/.
813 floppy= [HW]
814 See Documentation/blockdev/floppy.txt.
816 force_pal_cache_flush
817 [IA-64] Avoid check_sal_cache_flush which may hang on
818 buggy SAL_CACHE_FLUSH implementations. Using this
819 parameter will force ia64_sal_cache_flush to call
820 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
822 ftrace=[tracer]
823 [FTRACE] will set and start the specified tracer
824 as early as possible in order to facilitate early
825 boot debugging.
827 ftrace_dump_on_oops[=orig_cpu]
828 [FTRACE] will dump the trace buffers on oops.
829 If no parameter is passed, ftrace will dump
830 buffers of all CPUs, but if you pass orig_cpu, it will
831 dump only the buffer of the CPU that triggered the
832 oops.
834 ftrace_filter=[function-list]
835 [FTRACE] Limit the functions traced by the function
836 tracer at boot up. function-list is a comma separated
837 list of functions. This list can be changed at run
838 time by the set_ftrace_filter file in the debugfs
839 tracing directory.
841 ftrace_notrace=[function-list]
842 [FTRACE] Do not trace the functions specified in
843 function-list. This list can be changed at run time
844 by the set_ftrace_notrace file in the debugfs
845 tracing directory.
847 ftrace_graph_filter=[function-list]
848 [FTRACE] Limit the top level callers functions traced
849 by the function graph tracer at boot up.
850 function-list is a comma separated list of functions
851 that can be changed at run time by the
852 set_graph_function file in the debugfs tracing directory.
854 gamecon.map[2|3]=
855 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
856 support via parallel port (up to 5 devices per port)
857 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
858 See also Documentation/input/joystick-parport.txt
860 gamma= [HW,DRM]
862 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
863 Format: off | on
864 default: on
866 gcov_persist= [GCOV] When non-zero (default), profiling data for
867 kernel modules is saved and remains accessible via
868 debugfs, even when the module is unloaded/reloaded.
869 When zero, profiling data is discarded and associated
870 debugfs files are removed at module unload time.
872 gpt [EFI] Forces disk with valid GPT signature but
873 invalid Protective MBR to be treated as GPT.
875 hashdist= [KNL,NUMA] Large hashes allocated during boot
876 are distributed across NUMA nodes. Defaults on
877 for 64-bit NUMA, off otherwise.
878 Format: 0 | 1 (for off | on)
880 hcl= [IA-64] SGI's Hardware Graph compatibility layer
882 hd= [EIDE] (E)IDE hard drive subsystem geometry
883 Format: <cyl>,<head>,<sect>
885 hest_disable [ACPI]
886 Disable Hardware Error Source Table (HEST) support;
887 corresponding firmware-first mode error processing
888 logic will be disabled.
890 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
891 size of <nn>. This works even on boxes that have no
892 highmem otherwise. This also works to reduce highmem
893 size on bigger boxes.
895 highres= [KNL] Enable/disable high resolution timer mode.
896 Valid parameters: "on", "off"
897 Default: "on"
899 hisax= [HW,ISDN]
900 See Documentation/isdn/README.HiSax.
902 hlt [BUGS=ARM,SH]
904 hpet= [X86-32,HPET] option to control HPET usage
905 Format: { enable (default) | disable | force |
906 verbose }
907 disable: disable HPET and use PIT instead
908 force: allow force enabled of undocumented chips (ICH4,
909 VIA, nVidia)
910 verbose: show contents of HPET registers during setup
912 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
913 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
914 On x86-64 and powerpc, this option can be specified
915 multiple times interleaved with hugepages= to reserve
916 huge pages of different sizes. Valid pages sizes on
917 x86-64 are 2M (when the CPU supports "pse") and 1G
918 (when the CPU supports the "pdpe1gb" cpuinfo flag)
919 Note that 1GB pages can only be allocated at boot time
920 using hugepages= and not freed afterwards.
922 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
923 terminal devices. Valid values: 0..8
924 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
925 If specified, z/VM IUCV HVC accepts connections
926 from listed z/VM user IDs only.
928 keep_bootcon [KNL]
929 Do not unregister boot console at start. This is only
930 useful for debugging when something happens in the window
931 between unregistering the boot console and initializing
932 the real console.
934 i2c_bus= [HW] Override the default board specific I2C bus speed
935 or register an additional I2C bus that is not
936 registered from board initialization code.
937 Format:
938 <bus_id>,<clkrate>
940 i8042.debug [HW] Toggle i8042 debug mode
941 i8042.direct [HW] Put keyboard port into non-translated mode
942 i8042.dumbkbd [HW] Pretend that controller can only read data from
943 keyboard and cannot control its state
944 (Don't attempt to blink the leds)
945 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
946 i8042.nokbd [HW] Don't check/create keyboard port
947 i8042.noloop [HW] Disable the AUX Loopback command while probing
948 for the AUX port
949 i8042.nomux [HW] Don't check presence of an active multiplexing
950 controller
951 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
952 controllers
953 i8042.notimeout [HW] Ignore timeout condition signalled by conroller
954 i8042.reset [HW] Reset the controller during init and cleanup
955 i8042.unlock [HW] Unlock (ignore) the keylock
957 i810= [HW,DRM]
959 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
960 indicates that the driver is running on unsupported
961 hardware.
962 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
963 does not match list of supported models.
964 i8k.power_status
965 [HW] Report power status in /proc/i8k
966 (disabled by default)
967 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
968 capability is set.
970 icn= [HW,ISDN]
971 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
973 ide-core.nodma= [HW] (E)IDE subsystem
974 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
975 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
976 .cdrom .chs .ignore_cable are additional options
977 See Documentation/ide/ide.txt.
979 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
980 Claim all unknown PCI IDE storage controllers.
982 idle= [X86]
983 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
984 Poll forces a polling idle loop that can slightly
985 improve the performance of waking up a idle CPU, but
986 will use a lot of power and make the system run hot.
987 Not recommended.
988 idle=mwait: On systems which support MONITOR/MWAIT but
989 the kernel chose to not use it because it doesn't save
990 as much power as a normal idle loop, use the
991 MONITOR/MWAIT idle loop anyways. Performance should be
992 the same as idle=poll.
993 idle=halt: Halt is forced to be used for CPU idle.
994 In such case C2/C3 won't be used again.
995 idle=nomwait: Disable mwait for CPU C-states
997 ignore_loglevel [KNL]
998 Ignore loglevel setting - this will print /all/
999 kernel messages to the console. Useful for debugging.
1000 We also add it as printk module parameter, so users
1001 could change it dynamically, usually by
1002 /sys/module/printk/parameters/ignore_loglevel.
1004 ihash_entries= [KNL]
1005 Set number of hash buckets for inode cache.
1007 ima_audit= [IMA]
1008 Format: { "0" | "1" }
1009 0 -- integrity auditing messages. (Default)
1010 1 -- enable informational integrity auditing messages.
1012 ima_hash= [IMA]
1013 Format: { "sha1" | "md5" }
1014 default: "sha1"
1016 ima_tcb [IMA]
1017 Load a policy which meets the needs of the Trusted
1018 Computing Base. This means IMA will measure all
1019 programs exec'd, files mmap'd for exec, and all files
1020 opened for read by uid=0.
1022 init= [KNL]
1023 Format: <full_path>
1024 Run specified binary instead of /sbin/init as init
1025 process.
1027 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1028 for working out where the kernel is dying during
1029 startup.
1031 initrd= [BOOT] Specify the location of the initial ramdisk
1033 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1034 Format: <irq>
1036 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1037 on
1038 Enable intel iommu driver.
1039 off
1040 Disable intel iommu driver.
1041 igfx_off [Default Off]
1042 By default, gfx is mapped as normal device. If a gfx
1043 device has a dedicated DMAR unit, the DMAR unit is
1044 bypassed by not enabling DMAR with this option. In
1045 this case, gfx device will use physical address for
1046 DMA.
1047 forcedac [x86_64]
1048 With this option iommu will not optimize to look
1049 for io virtual address below 32-bit forcing dual
1050 address cycle on pci bus for cards supporting greater
1051 than 32-bit addressing. The default is to look
1052 for translation below 32-bit and if not available
1053 then look in the higher range.
1054 strict [Default Off]
1055 With this option on every unmap_single operation will
1056 result in a hardware IOTLB flush operation as opposed
1057 to batching them for performance.
1058 sp_off [Default Off]
1059 By default, super page will be supported if Intel IOMMU
1060 has the capability. With this option, super page will
1061 not be supported.
1063 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1064 0 disables intel_idle and fall back on acpi_idle.
1065 1 to 6 specify maximum depth of C-state.
1067 intremap= [X86-64, Intel-IOMMU]
1068 on enable Interrupt Remapping (default)
1069 off disable Interrupt Remapping
1070 nosid disable Source ID checking
1071 no_x2apic_optout
1072 BIOS x2APIC opt-out request will be ignored
1074 inttest= [IA-64]
1076 iomem= Disable strict checking of access to MMIO memory
1077 strict regions from userspace.
1078 relaxed
1080 iommu= [x86]
1081 off
1082 force
1083 noforce
1084 biomerge
1085 panic
1086 nopanic
1087 merge
1088 nomerge
1089 forcesac
1090 soft
1091 pt [x86, IA-64]
1092 group_mf [x86, IA-64]
1095 io7= [HW] IO7 for Marvel based alpha systems
1096 See comment before marvel_specify_io7 in
1097 arch/alpha/kernel/core_marvel.c.
1099 io_delay= [X86] I/O delay method
1100 0x80
1101 Standard port 0x80 based delay
1102 0xed
1103 Alternate port 0xed based delay (needed on some systems)
1104 udelay
1105 Simple two microseconds delay
1106 none
1107 No delay
1109 ip= [IP_PNP]
1110 See Documentation/filesystems/nfs/nfsroot.txt.
1112 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1113 See comment before ip2_setup() in
1114 drivers/char/ip2/ip2base.c.
1116 irqfixup [HW]
1117 When an interrupt is not handled search all handlers
1118 for it. Intended to get systems with badly broken
1119 firmware running.
1121 irqpoll [HW]
1122 When an interrupt is not handled search all handlers
1123 for it. Also check all handlers each timer
1124 interrupt. Intended to get systems with badly broken
1125 firmware running.
1127 isapnp= [ISAPNP]
1128 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1130 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1131 Format:
1132 <cpu number>,...,<cpu number>
1133 or
1134 <cpu number>-<cpu number>
1135 (must be a positive range in ascending order)
1136 or a mixture
1137 <cpu number>,...,<cpu number>-<cpu number>
1139 This option can be used to specify one or more CPUs
1140 to isolate from the general SMP balancing and scheduling
1141 algorithms. You can move a process onto or off an
1142 "isolated" CPU via the CPU affinity syscalls or cpuset.
1143 <cpu number> begins at 0 and the maximum value is
1144 "number of CPUs in system - 1".
1146 This option is the preferred way to isolate CPUs. The
1147 alternative -- manually setting the CPU mask of all
1148 tasks in the system -- can cause problems and
1149 suboptimal load balancer performance.
1151 iucv= [HW,NET]
1153 js= [HW,JOY] Analog joystick
1154 See Documentation/input/joystick.txt.
1156 keepinitrd [HW,ARM]
1158 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1159 specifies the amount of memory usable by the kernel
1160 for non-movable allocations. The requested amount is
1161 spread evenly throughout all nodes in the system. The
1162 remaining memory in each node is used for Movable
1163 pages. In the event, a node is too small to have both
1164 kernelcore and Movable pages, kernelcore pages will
1165 take priority and other nodes will have a larger number
1166 of kernelcore pages. The Movable zone is used for the
1167 allocation of pages that may be reclaimed or moved
1168 by the page migration subsystem. This means that
1169 HugeTLB pages may not be allocated from this zone.
1170 Note that allocations like PTEs-from-HighMem still
1171 use the HighMem zone if it exists, and the Normal
1172 zone if it does not.
1174 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1175 Format: <Controller#>[,poll interval]
1176 The controller # is the number of the ehci usb debug
1177 port as it is probed via PCI. The poll interval is
1178 optional and is the number seconds in between
1179 each poll cycle to the debug port in case you need
1180 the functionality for interrupting the kernel with
1181 gdb or control-c on the dbgp connection. When
1182 not using this parameter you use sysrq-g to break into
1183 the kernel debugger.
1185 kgdboc= [KGDB,HW] kgdb over consoles.
1186 Requires a tty driver that supports console polling,
1187 or a supported polling keyboard driver (non-usb).
1188 Serial only format: <serial_device>[,baud]
1189 keyboard only format: kbd
1190 keyboard and serial format: kbd,<serial_device>[,baud]
1191 Optional Kernel mode setting:
1192 kms, kbd format: kms,kbd
1193 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1195 kgdbwait [KGDB] Stop kernel execution and enter the
1196 kernel debugger at the earliest opportunity.
1198 kmac= [MIPS] korina ethernet MAC address.
1199 Configure the RouterBoard 532 series on-chip
1200 Ethernet adapter MAC address.
1202 kmemleak= [KNL] Boot-time kmemleak enable/disable
1203 Valid arguments: on, off
1204 Default: on
1206 kstack=N [X86] Print N words from the kernel stack
1207 in oops dumps.
1209 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1210 Default is 0 (don't ignore, but inject #GP)
1212 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1213 KVM MMU at runtime.
1214 Default is 0 (off)
1216 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1217 Default is 1 (enabled)
1219 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1220 for all guests.
1221 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1223 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1224 (virtualized MMU) support on capable Intel chips.
1225 Default is 1 (enabled)
1227 kvm-intel.emulate_invalid_guest_state=
1228 [KVM,Intel] Enable emulation of invalid guest states
1229 Default is 0 (disabled)
1231 kvm-intel.flexpriority=
1232 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1233 Default is 1 (enabled)
1235 kvm-intel.nested=
1236 [KVM,Intel] Enable VMX nesting (nVMX).
1237 Default is 0 (disabled)
1239 kvm-intel.unrestricted_guest=
1240 [KVM,Intel] Disable unrestricted guest feature
1241 (virtualized real and unpaged mode) on capable
1242 Intel chips. Default is 1 (enabled)
1244 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1245 feature (tagged TLBs) on capable Intel chips.
1246 Default is 1 (enabled)
1248 l2cr= [PPC]
1250 l3cr= [PPC]
1252 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1253 disabled it.
1255 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1256 in C2 power state.
1258 libata.dma= [LIBATA] DMA control
1259 libata.dma=0 Disable all PATA and SATA DMA
1260 libata.dma=1 PATA and SATA Disk DMA only
1261 libata.dma=2 ATAPI (CDROM) DMA only
1262 libata.dma=4 Compact Flash DMA only
1263 Combinations also work, so libata.dma=3 enables DMA
1264 for disks and CDROMs, but not CFs.
1266 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1267 libata.ignore_hpa=0 keep BIOS limits (default)
1268 libata.ignore_hpa=1 ignore limits, using full disk
1270 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1271 when set.
1272 Format: <int>
1274 libata.force= [LIBATA] Force configurations. The format is comma
1275 separated list of "[ID:]VAL" where ID is
1276 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1277 matching port, link or device. Basically, it matches
1278 the ATA ID string printed on console by libata. If
1279 the whole ID part is omitted, the last PORT and DEVICE
1280 values are used. If ID hasn't been specified yet, the
1281 configuration applies to all ports, links and devices.
1283 If only DEVICE is omitted, the parameter applies to
1284 the port and all links and devices behind it. DEVICE
1285 number of 0 either selects the first device or the
1286 first fan-out link behind PMP device. It does not
1287 select the host link. DEVICE number of 15 selects the
1288 host link and device attached to it.
1290 The VAL specifies the configuration to force. As long
1291 as there's no ambiguity shortcut notation is allowed.
1292 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1293 The following configurations can be forced.
1295 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1296 Any ID with matching PORT is used.
1298 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1300 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1301 udma[/][16,25,33,44,66,100,133] notation is also
1302 allowed.
1304 * [no]ncq: Turn on or off NCQ.
1306 * nohrst, nosrst, norst: suppress hard, soft
1307 and both resets.
1309 * dump_id: dump IDENTIFY data.
1311 If there are multiple matching configurations changing
1312 the same attribute, the last one is used.
1314 memblock=debug [KNL] Enable memblock debug messages.
1316 load_ramdisk= [RAM] List of ramdisks to load from floppy
1317 See Documentation/blockdev/ramdisk.txt.
1319 lockd.nlm_grace_period=P [NFS] Assign grace period.
1320 Format: <integer>
1322 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1323 Format: <integer>
1325 lockd.nlm_timeout=T [NFS] Assign timeout value.
1326 Format: <integer>
1328 lockd.nlm_udpport=M [NFS] Assign UDP port.
1329 Format: <integer>
1331 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1332 Format: <irq>
1334 loglevel= All Kernel Messages with a loglevel smaller than the
1335 console loglevel will be printed to the console. It can
1336 also be changed with klogd or other programs. The
1337 loglevels are defined as follows:
1339 0 (KERN_EMERG) system is unusable
1340 1 (KERN_ALERT) action must be taken immediately
1341 2 (KERN_CRIT) critical conditions
1342 3 (KERN_ERR) error conditions
1343 4 (KERN_WARNING) warning conditions
1344 5 (KERN_NOTICE) normal but significant condition
1345 6 (KERN_INFO) informational
1346 7 (KERN_DEBUG) debug-level messages
1348 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1349 in bytes. n must be a power of two. The default
1350 size is set in the kernel config file.
1352 logo.nologo [FB] Disables display of the built-in Linux logo.
1353 This may be used to provide more screen space for
1354 kernel log messages and is useful when debugging
1355 kernel boot problems.
1357 lp=0 [LP] Specify parallel ports to use, e.g,
1358 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1359 lp=reset first parallel port). 'lp=0' disables the
1360 lp=auto printer driver. 'lp=reset' (which can be
1361 specified in addition to the ports) causes
1362 attached printers to be reset. Using
1363 lp=port1,port2,... specifies the parallel ports
1364 to associate lp devices with, starting with
1365 lp0. A port specification may be 'none' to skip
1366 that lp device, or a parport name such as
1367 'parport0'. Specifying 'lp=auto' instead of a
1368 port specification list means that device IDs
1369 from each port should be examined, to see if
1370 an IEEE 1284-compliant printer is attached; if
1371 so, the driver will manage that printer.
1372 See also header of drivers/char/lp.c.
1374 lpj=n [KNL]
1375 Sets loops_per_jiffy to given constant, thus avoiding
1376 time-consuming boot-time autodetection (up to 250 ms per
1377 CPU). 0 enables autodetection (default). To determine
1378 the correct value for your kernel, boot with normal
1379 autodetection and see what value is printed. Note that
1380 on SMP systems the preset will be applied to all CPUs,
1381 which is likely to cause problems if your CPUs need
1382 significantly divergent settings. An incorrect value
1383 will cause delays in the kernel to be wrong, leading to
1384 unpredictable I/O errors and other breakage. Although
1385 unlikely, in the extreme case this might damage your
1386 hardware.
1388 ltpc= [NET]
1389 Format: <io>,<irq>,<dma>
1391 machvec= [IA-64] Force the use of a particular machine-vector
1392 (machvec) in a generic kernel.
1393 Example: machvec=hpzx1_swiotlb
1395 machtype= [Loongson] Share the same kernel image file between different
1396 yeeloong laptop.
1397 Example: machtype=lemote-yeeloong-2f-7inch
1399 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1400 than or equal to this physical address is ignored.
1402 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1403 should make use of. maxcpus=n : n >= 0 limits the
1404 kernel to using 'n' processors. n=0 is a special case,
1405 it is equivalent to "nosmp", which also disables
1406 the IO APIC.
1408 max_loop= [LOOP] The number of loop block devices that get
1409 (loop.max_loop) unconditionally pre-created at init time. The default
1410 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1411 of statically allocating a predefined number, loop
1412 devices can be requested on-demand with the
1413 /dev/loop-control interface.
1415 mcatest= [IA-64]
1417 mce [X86-32] Machine Check Exception
1419 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1421 md= [HW] RAID subsystems devices and level
1422 See Documentation/md.txt.
1424 mdacon= [MDA]
1425 Format: <first>,<last>
1426 Specifies range of consoles to be captured by the MDA.
1428 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1429 Amount of memory to be used when the kernel is not able
1430 to see the whole system memory or for test.
1431 [X86-32] Use together with memmap= to avoid physical
1432 address space collisions. Without memmap= PCI devices
1433 could be placed at addresses belonging to unused RAM.
1435 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1436 memory.
1438 memchunk=nn[KMG]
1439 [KNL,SH] Allow user to override the default size for
1440 per-device physically contiguous DMA buffers.
1442 memmap=exactmap [KNL,X86] Enable setting of an exact
1443 E820 memory map, as specified by the user.
1444 Such memmap=exactmap lines can be constructed based on
1445 BIOS output or other requirements. See the memmap=nn@ss
1446 option description.
1448 memmap=nn[KMG]@ss[KMG]
1449 [KNL] Force usage of a specific region of memory
1450 Region of memory to be used, from ss to ss+nn.
1452 memmap=nn[KMG]#ss[KMG]
1453 [KNL,ACPI] Mark specific memory as ACPI data.
1454 Region of memory to be used, from ss to ss+nn.
1456 memmap=nn[KMG]$ss[KMG]
1457 [KNL,ACPI] Mark specific memory as reserved.
1458 Region of memory to be used, from ss to ss+nn.
1459 Example: Exclude memory from 0x18690000-0x1869ffff
1460 memmap=64K$0x18690000
1461 or
1462 memmap=0x10000$0x18690000
1464 memory_corruption_check=0/1 [X86]
1465 Some BIOSes seem to corrupt the first 64k of
1466 memory when doing things like suspend/resume.
1467 Setting this option will scan the memory
1468 looking for corruption. Enabling this will
1469 both detect corruption and prevent the kernel
1470 from using the memory being corrupted.
1471 However, its intended as a diagnostic tool; if
1472 repeatable BIOS-originated corruption always
1473 affects the same memory, you can use memmap=
1474 to prevent the kernel from using that memory.
1476 memory_corruption_check_size=size [X86]
1477 By default it checks for corruption in the low
1478 64k, making this memory unavailable for normal
1479 use. Use this parameter to scan for
1480 corruption in more or less memory.
1482 memory_corruption_check_period=seconds [X86]
1483 By default it checks for corruption every 60
1484 seconds. Use this parameter to check at some
1485 other rate. 0 disables periodic checking.
1487 memtest= [KNL,X86] Enable memtest
1488 Format: <integer>
1489 default : 0 <disable>
1490 Specifies the number of memtest passes to be
1491 performed. Each pass selects another test
1492 pattern from a given set of patterns. Memtest
1493 fills the memory with this pattern, validates
1494 memory contents and reserves bad memory
1495 regions that are detected.
1497 meye.*= [HW] Set MotionEye Camera parameters
1498 See Documentation/video4linux/meye.txt.
1500 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1501 Multi-Function General Purpose Timers on AMD Geode
1502 platforms.
1504 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1505 the BIOS has incorrectly applied a workaround. TinyBIOS
1506 version 0.98 is known to be affected, 0.99 fixes the
1507 problem by letting the user disable the workaround.
1509 mga= [HW,DRM]
1511 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1512 physical address is ignored.
1514 mini2440= [ARM,HW,KNL]
1515 Format:[0..2][b][c][t]
1516 Default: "0tb"
1517 MINI2440 configuration specification:
1518 0 - The attached screen is the 3.5" TFT
1519 1 - The attached screen is the 7" TFT
1520 2 - The VGA Shield is attached (1024x768)
1521 Leaving out the screen size parameter will not load
1522 the TFT driver, and the framebuffer will be left
1523 unconfigured.
1524 b - Enable backlight. The TFT backlight pin will be
1525 linked to the kernel VESA blanking code and a GPIO
1526 LED. This parameter is not necessary when using the
1527 VGA shield.
1528 c - Enable the s3c camera interface.
1529 t - Reserved for enabling touchscreen support. The
1530 touchscreen support is not enabled in the mainstream
1531 kernel as of 2.6.30, a preliminary port can be found
1532 in the "bleeding edge" mini2440 support kernel at
1533 http://repo.or.cz/w/linux-2.6/mini2440.git
1535 mminit_loglevel=
1536 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1537 parameter allows control of the logging verbosity for
1538 the additional memory initialisation checks. A value
1539 of 0 disables mminit logging and a level of 4 will
1540 log everything. Information is printed at KERN_DEBUG
1541 so loglevel=8 may also need to be specified.
1543 mousedev.tap_time=
1544 [MOUSE] Maximum time between finger touching and
1545 leaving touchpad surface for touch to be considered
1546 a tap and be reported as a left button click (for
1547 touchpads working in absolute mode only).
1548 Format: <msecs>
1549 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1550 reporting absolute coordinates, such as tablets
1551 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1552 reporting absolute coordinates, such as tablets
1554 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1555 is similar to kernelcore except it specifies the
1556 amount of memory used for migratable allocations.
1557 If both kernelcore and movablecore is specified,
1558 then kernelcore will be at *least* the specified
1559 value but may be more. If movablecore on its own
1560 is specified, the administrator must be careful
1561 that the amount of memory usable for all allocations
1562 is not too small.
1564 MTD_Partition= [MTD]
1565 Format: <name>,<region-number>,<size>,<offset>
1567 MTD_Region= [MTD] Format:
1568 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1570 mtdparts= [MTD]
1571 See drivers/mtd/cmdlinepart.c.
1573 multitce=off [PPC] This parameter disables the use of the pSeries
1574 firmware feature for updating multiple TCE entries
1575 at a time.
1577 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1579 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1581 boundary - index of last SLC block on Flex-OneNAND.
1582 The remaining blocks are configured as MLC blocks.
1583 lock - Configure if Flex-OneNAND boundary should be locked.
1584 Once locked, the boundary cannot be changed.
1585 1 indicates lock status, 0 indicates unlock status.
1587 mtdset= [ARM]
1588 ARM/S3C2412 JIVE boot control
1590 See arch/arm/mach-s3c2412/mach-jive.c
1592 mtouchusb.raw_coordinates=
1593 [HW] Make the MicroTouch USB driver use raw coordinates
1594 ('y', default) or cooked coordinates ('n')
1596 mtrr_chunk_size=nn[KMG] [X86]
1597 used for mtrr cleanup. It is largest continuous chunk
1598 that could hold holes aka. UC entries.
1600 mtrr_gran_size=nn[KMG] [X86]
1601 Used for mtrr cleanup. It is granularity of mtrr block.
1602 Default is 1.
1603 Large value could prevent small alignment from
1604 using up MTRRs.
1606 mtrr_spare_reg_nr=n [X86]
1607 Format: <integer>
1608 Range: 0,7 : spare reg number
1609 Default : 1
1610 Used for mtrr cleanup. It is spare mtrr entries number.
1611 Set to 2 or more if your graphical card needs more.
1613 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1615 netdev= [NET] Network devices parameters
1616 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1617 Note that mem_start is often overloaded to mean
1618 something different and driver-specific.
1619 This usage is only documented in each driver source
1620 file if at all.
1622 nf_conntrack.acct=
1623 [NETFILTER] Enable connection tracking flow accounting
1624 0 to disable accounting
1625 1 to enable accounting
1626 Default value is 0.
1628 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1629 See Documentation/filesystems/nfs/nfsroot.txt.
1631 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1632 See Documentation/filesystems/nfs/nfsroot.txt.
1634 nfsrootdebug [NFS] enable nfsroot debugging messages.
1635 See Documentation/filesystems/nfs/nfsroot.txt.
1637 nfs.callback_tcpport=
1638 [NFS] set the TCP port on which the NFSv4 callback
1639 channel should listen.
1641 nfs.cache_getent=
1642 [NFS] sets the pathname to the program which is used
1643 to update the NFS client cache entries.
1645 nfs.cache_getent_timeout=
1646 [NFS] sets the timeout after which an attempt to
1647 update a cache entry is deemed to have failed.
1649 nfs.idmap_cache_timeout=
1650 [NFS] set the maximum lifetime for idmapper cache
1651 entries.
1653 nfs.enable_ino64=
1654 [NFS] enable 64-bit inode numbers.
1655 If zero, the NFS client will fake up a 32-bit inode
1656 number for the readdir() and stat() syscalls instead
1657 of returning the full 64-bit number.
1658 The default is to return 64-bit inode numbers.
1660 nfs.nfs4_disable_idmapping=
1661 [NFSv4] When set to the default of '1', this option
1662 ensures that both the RPC level authentication
1663 scheme and the NFS level operations agree to use
1664 numeric uids/gids if the mount is using the
1665 'sec=sys' security flavour. In effect it is
1666 disabling idmapping, which can make migration from
1667 legacy NFSv2/v3 systems to NFSv4 easier.
1668 Servers that do not support this mode of operation
1669 will be autodetected by the client, and it will fall
1670 back to using the idmapper.
1671 To turn off this behaviour, set the value to '0'.
1673 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1674 when a NMI is triggered.
1675 Format: [state][,regs][,debounce][,die]
1677 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1678 Format: [panic,][nopanic,][num]
1679 Valid num: 0
1680 0 - turn nmi_watchdog off
1681 When panic is specified, panic when an NMI watchdog
1682 timeout occurs (or 'nopanic' to override the opposite
1683 default).
1684 This is useful when you use a panic=... timeout and
1685 need the box quickly up again.
1687 netpoll.carrier_timeout=
1688 [NET] Specifies amount of time (in seconds) that
1689 netpoll should wait for a carrier. By default netpoll
1690 waits 4 seconds.
1692 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1693 emulation library even if a 387 maths coprocessor
1694 is present.
1696 no_console_suspend
1697 [HW] Never suspend the console
1698 Disable suspending of consoles during suspend and
1699 hibernate operations. Once disabled, debugging
1700 messages can reach various consoles while the rest
1701 of the system is being put to sleep (ie, while
1702 debugging driver suspend/resume hooks). This may
1703 not work reliably with all consoles, but is known
1704 to work with serial and VGA consoles.
1705 To facilitate more flexible debugging, we also add
1706 console_suspend, a printk module parameter to control
1707 it. Users could use console_suspend (usually
1708 /sys/module/printk/parameters/console_suspend) to
1709 turn on/off it dynamically.
1711 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1712 caches in the slab allocator. Saves per-node memory,
1713 but will impact performance.
1715 noalign [KNL,ARM]
1717 noapic [SMP,APIC] Tells the kernel to not make use of any
1718 IOAPICs that may be present in the system.
1720 noautogroup Disable scheduler automatic task group creation.
1722 nobats [PPC] Do not use BATs for mapping kernel lowmem
1723 on "Classic" PPC cores.
1725 nocache [ARM]
1727 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1729 nodelayacct [KNL] Disable per-task delay accounting
1731 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1733 nodsp [SH] Disable hardware DSP at boot time.
1735 noefi [X86] Disable EFI runtime services support.
1737 noexec [IA-64]
1739 noexec [X86]
1740 On X86-32 available only on PAE configured kernels.
1741 noexec=on: enable non-executable mappings (default)
1742 noexec=off: disable non-executable mappings
1744 nosmep [X86]
1745 Disable SMEP (Supervisor Mode Execution Protection)
1746 even if it is supported by processor.
1748 noexec32 [X86-64]
1749 This affects only 32-bit executables.
1750 noexec32=on: enable non-executable mappings (default)
1751 read doesn't imply executable mappings
1752 noexec32=off: disable non-executable mappings
1753 read implies executable mappings
1755 nofpu [SH] Disable hardware FPU at boot time.
1757 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1758 register save and restore. The kernel will only save
1759 legacy floating-point registers on task switch.
1761 noxsave [BUGS=X86] Disables x86 extended register state save
1762 and restore using xsave. The kernel will fallback to
1763 enabling legacy floating-point and sse state.
1765 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1766 wfi(ARM) instruction doesn't work correctly and not to
1767 use it. This is also useful when using JTAG debugger.
1769 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1770 instruction doesn't work correctly and not to
1771 use it.
1773 no_file_caps Tells the kernel not to honor file capabilities. The
1774 only way then for a file to be executed with privilege
1775 is to be setuid root or executed by root.
1777 nohalt [IA-64] Tells the kernel not to use the power saving
1778 function PAL_HALT_LIGHT when idle. This increases
1779 power-consumption. On the positive side, it reduces
1780 interrupt wake-up latency, which may improve performance
1781 in certain environments such as networked servers or
1782 real-time systems.
1784 nohz= [KNL] Boottime enable/disable dynamic ticks
1785 Valid arguments: on, off
1786 Default: on
1788 noiotrap [SH] Disables trapped I/O port accesses.
1790 noirqdebug [X86-32] Disables the code which attempts to detect and
1791 disable unhandled interrupt sources.
1793 no_timer_check [X86,APIC] Disables the code which tests for
1794 broken timer IRQ sources.
1796 noisapnp [ISAPNP] Disables ISA PnP code.
1798 noinitrd [RAM] Tells the kernel not to load any configured
1799 initial RAM disk.
1801 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1802 remapping.
1803 [Deprecated - use intremap=off]
1805 nointroute [IA-64]
1807 nojitter [IA-64] Disables jitter checking for ITC timers.
1809 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1811 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1812 fault handling.
1814 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1815 steal time is computed, but won't influence scheduler
1816 behaviour
1818 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1820 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1822 noltlbs [PPC] Do not use large page/tlb entries for kernel
1823 lowmem mapping on PPC40x.
1825 nomca [IA-64] Disable machine check abort handling
1827 nomce [X86-32] Machine Check Exception
1829 nomfgpt [X86-32] Disable Multi-Function General Purpose
1830 Timer usage (for AMD Geode machines).
1832 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
1833 shutdown the other cpus. Instead use the REBOOT_VECTOR
1834 irq.
1836 nopat [X86] Disable PAT (page attribute table extension of
1837 pagetables) support.
1839 norandmaps Don't use address space randomization. Equivalent to
1840 echo 0 > /proc/sys/kernel/randomize_va_space
1842 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1844 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1845 with UP alternatives
1847 noresidual [PPC] Don't use residual data on PReP machines.
1849 nordrand [X86] Disable the direct use of the RDRAND
1850 instruction even if it is supported by the
1851 processor. RDRAND is still available to user
1852 space applications.
1854 noresume [SWSUSP] Disables resume and restores original swap
1855 space.
1857 no-scroll [VGA] Disables scrollback.
1858 This is required for the Braillex ib80-piezo Braille
1859 reader made by F.H. Papenmeier (Germany).
1861 nosbagart [IA-64]
1863 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1865 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1866 and disable the IO APIC. legacy for "maxcpus=0".
1868 nosoftlockup [KNL] Disable the soft-lockup detector.
1870 nosync [HW,M68K] Disables sync negotiation for all devices.
1872 notsc [BUGS=X86-32] Disable Time Stamp Counter
1874 nousb [USB] Disable the USB subsystem
1876 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1878 nowb [ARM]
1880 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1882 nptcg= [IA-64] Override max number of concurrent global TLB
1883 purges which is reported from either PAL_VM_SUMMARY or
1884 SAL PALO.
1886 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1887 could support. nr_cpus=n : n >= 1 limits the kernel to
1888 supporting 'n' processors. Later in runtime you can not
1889 use hotplug cpu feature to put more cpu back to online.
1890 just like you compile the kernel NR_CPUS=n
1892 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1894 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1895 one of ['zone', 'node', 'default'] can be specified
1896 This can be set from sysctl after boot.
1897 See Documentation/sysctl/vm.txt for details.
1899 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1900 See Documentation/debugging-via-ohci1394.txt for more
1901 info.
1903 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1904 Rather than timing out after 20 ms if an EC
1905 command is not properly ACKed, override the length
1906 of the timeout. We have interrupts disabled while
1907 waiting for the ACK, so if this is set too high
1908 interrupts *may* be lost!
1910 omap_mux= [OMAP] Override bootloader pin multiplexing.
1911 Format: <mux_mode0.mode_name=value>...
1912 For example, to override I2C bus2:
1913 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1915 oprofile.timer= [HW]
1916 Use timer interrupt instead of performance counters
1918 oprofile.cpu_type= Force an oprofile cpu type
1919 This might be useful if you have an older oprofile
1920 userland or if you want common events.
1921 Format: { arch_perfmon }
1922 arch_perfmon: [X86] Force use of architectural
1923 perfmon on Intel CPUs instead of the
1924 CPU specific event set.
1925 timer: [X86] Force use of architectural NMI
1926 timer mode (see also oprofile.timer
1927 for generic hr timer mode)
1928 [s390] Force legacy basic mode sampling
1929 (report cpu_type "timer")
1931 oops=panic Always panic on oopses. Default is to just kill the
1932 process, but there is a small probability of
1933 deadlocking the machine.
1934 This will also cause panics on machine check exceptions.
1935 Useful together with panic=30 to trigger a reboot.
1937 OSS [HW,OSS]
1938 See Documentation/sound/oss/oss-parameters.txt
1940 panic= [KNL] Kernel behaviour on panic: delay <timeout>
1941 timeout > 0: seconds before rebooting
1942 timeout = 0: wait forever
1943 timeout < 0: reboot immediately
1944 Format: <timeout>
1946 parkbd.port= [HW] Parallel port number the keyboard adapter is
1947 connected to, default is 0.
1948 Format: <parport#>
1949 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1950 0 for XT, 1 for AT (default is AT).
1951 Format: <mode>
1953 parport= [HW,PPT] Specify parallel ports. 0 disables.
1954 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1955 Use 'auto' to force the driver to use any
1956 IRQ/DMA settings detected (the default is to
1957 ignore detected IRQ/DMA settings because of
1958 possible conflicts). You can specify the base
1959 address, IRQ, and DMA settings; IRQ and DMA
1960 should be numbers, or 'auto' (for using detected
1961 settings on that particular port), or 'nofifo'
1962 (to avoid using a FIFO even if it is detected).
1963 Parallel ports are assigned in the order they
1964 are specified on the command line, starting
1965 with parport0.
1967 parport_init_mode= [HW,PPT]
1968 Configure VIA parallel port to operate in
1969 a specific mode. This is necessary on Pegasos
1970 computer where firmware has no options for setting
1971 up parallel port mode and sets it to spp.
1972 Currently this function knows 686a and 8231 chips.
1973 Format: [spp|ps2|epp|ecp|ecpepp]
1975 pause_on_oops=
1976 Halt all CPUs after the first oops has been printed for
1977 the specified number of seconds. This is to be used if
1978 your oopses keep scrolling off the screen.
1980 pcbit= [HW,ISDN]
1982 pcd. [PARIDE]
1983 See header of drivers/block/paride/pcd.c.
1984 See also Documentation/blockdev/paride.txt.
1986 pci=option[,option...] [PCI] various PCI subsystem options:
1987 earlydump [X86] dump PCI config space before the kernel
1988 changes anything
1989 off [X86] don't probe for the PCI bus
1990 bios [X86-32] force use of PCI BIOS, don't access
1991 the hardware directly. Use this if your machine
1992 has a non-standard PCI host bridge.
1993 nobios [X86-32] disallow use of PCI BIOS, only direct
1994 hardware access methods are allowed. Use this
1995 if you experience crashes upon bootup and you
1996 suspect they are caused by the BIOS.
1997 conf1 [X86] Force use of PCI Configuration
1998 Mechanism 1.
1999 conf2 [X86] Force use of PCI Configuration
2000 Mechanism 2.
2001 noaer [PCIE] If the PCIEAER kernel config parameter is
2002 enabled, this kernel boot option can be used to
2003 disable the use of PCIE advanced error reporting.
2004 nodomains [PCI] Disable support for multiple PCI
2005 root domains (aka PCI segments, in ACPI-speak).
2006 nommconf [X86] Disable use of MMCONFIG for PCI
2007 Configuration
2008 check_enable_amd_mmconf [X86] check for and enable
2009 properly configured MMIO access to PCI
2010 config space on AMD family 10h CPU
2011 nomsi [MSI] If the PCI_MSI kernel config parameter is
2012 enabled, this kernel boot option can be used to
2013 disable the use of MSI interrupts system-wide.
2014 noioapicquirk [APIC] Disable all boot interrupt quirks.
2015 Safety option to keep boot IRQs enabled. This
2016 should never be necessary.
2017 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2018 primary IO-APIC for bridges that cannot disable
2019 boot IRQs. This fixes a source of spurious IRQs
2020 when the system masks IRQs.
2021 noioapicreroute [APIC] Disable workaround that uses the
2022 boot IRQ equivalent of an IRQ that connects to
2023 a chipset where boot IRQs cannot be disabled.
2024 The opposite of ioapicreroute.
2025 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2026 routing table. These calls are known to be buggy
2027 on several machines and they hang the machine
2028 when used, but on other computers it's the only
2029 way to get the interrupt routing table. Try
2030 this option if the kernel is unable to allocate
2031 IRQs or discover secondary PCI buses on your
2032 motherboard.
2033 rom [X86] Assign address space to expansion ROMs.
2034 Use with caution as certain devices share
2035 address decoders between ROMs and other
2036 resources.
2037 norom [X86] Do not assign address space to
2038 expansion ROMs that do not already have
2039 BIOS assigned address ranges.
2040 nobar [X86] Do not assign address space to the
2041 BARs that weren't assigned by the BIOS.
2042 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2043 assigned automatically to PCI devices. You can
2044 make the kernel exclude IRQs of your ISA cards
2045 this way.
2046 pirqaddr=0xAAAAA [X86] Specify the physical address
2047 of the PIRQ table (normally generated
2048 by the BIOS) if it is outside the
2049 F0000h-100000h range.
2050 lastbus=N [X86] Scan all buses thru bus #N. Can be
2051 useful if the kernel is unable to find your
2052 secondary buses and you want to tell it
2053 explicitly which ones they are.
2054 assign-busses [X86] Always assign all PCI bus
2055 numbers ourselves, overriding
2056 whatever the firmware may have done.
2057 usepirqmask [X86] Honor the possible IRQ mask stored
2058 in the BIOS $PIR table. This is needed on
2059 some systems with broken BIOSes, notably
2060 some HP Pavilion N5400 and Omnibook XE3
2061 notebooks. This will have no effect if ACPI
2062 IRQ routing is enabled.
2063 noacpi [X86] Do not use ACPI for IRQ routing
2064 or for PCI scanning.
2065 use_crs [X86] Use PCI host bridge window information
2066 from ACPI. On BIOSes from 2008 or later, this
2067 is enabled by default. If you need to use this,
2068 please report a bug.
2069 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2070 If you need to use this, please report a bug.
2071 routeirq Do IRQ routing for all PCI devices.
2072 This is normally done in pci_enable_device(),
2073 so this option is a temporary workaround
2074 for broken drivers that don't call it.
2075 skip_isa_align [X86] do not align io start addr, so can
2076 handle more pci cards
2077 firmware [ARM] Do not re-enumerate the bus but instead
2078 just use the configuration from the
2079 bootloader. This is currently used on
2080 IXP2000 systems where the bus has to be
2081 configured a certain way for adjunct CPUs.
2082 noearly [X86] Don't do any early type 1 scanning.
2083 This might help on some broken boards which
2084 machine check when some devices' config space
2085 is read. But various workarounds are disabled
2086 and some IOMMU drivers will not work.
2087 bfsort Sort PCI devices into breadth-first order.
2088 This sorting is done to get a device
2089 order compatible with older (<= 2.4) kernels.
2090 nobfsort Don't sort PCI devices into breadth-first order.
2091 cbiosize=nn[KMG] The fixed amount of bus space which is
2092 reserved for the CardBus bridge's IO window.
2093 The default value is 256 bytes.
2094 cbmemsize=nn[KMG] The fixed amount of bus space which is
2095 reserved for the CardBus bridge's memory
2096 window. The default value is 64 megabytes.
2097 resource_alignment=
2098 Format:
2099 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2100 Specifies alignment and device to reassign
2101 aligned memory resources.
2102 If <order of align> is not specified,
2103 PAGE_SIZE is used as alignment.
2104 PCI-PCI bridge can be specified, if resource
2105 windows need to be expanded.
2106 ecrc= Enable/disable PCIe ECRC (transaction layer
2107 end-to-end CRC checking).
2108 bios: Use BIOS/firmware settings. This is the
2109 the default.
2110 off: Turn ECRC off
2111 on: Turn ECRC on.
2112 realloc reallocate PCI resources if allocations done by BIOS
2113 are erroneous.
2115 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2116 Management.
2117 off Disable ASPM.
2118 force Enable ASPM even on devices that claim not to support it.
2119 WARNING: Forcing ASPM on may cause system lockups.
2121 pcie_ports= [PCIE] PCIe ports handling:
2122 auto Ask the BIOS whether or not to use native PCIe services
2123 associated with PCIe ports (PME, hot-plug, AER). Use
2124 them only if that is allowed by the BIOS.
2125 native Use native PCIe services associated with PCIe ports
2126 unconditionally.
2127 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2128 ports driver.
2130 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2131 nomsi Do not use MSI for native PCIe PME signaling (this makes
2132 all PCIe root ports use INTx for all services).
2134 pcmv= [HW,PCMCIA] BadgePAD 4
2136 pd. [PARIDE]
2137 See Documentation/blockdev/paride.txt.
2139 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2140 boot time.
2141 Format: { 0 | 1 }
2142 See arch/parisc/kernel/pdc_chassis.c
2144 percpu_alloc= Select which percpu first chunk allocator to use.
2145 Currently supported values are "embed" and "page".
2146 Archs may support subset or none of the selections.
2147 See comments in mm/percpu.c for details on each
2148 allocator. This parameter is primarily for debugging
2149 and performance comparison.
2151 pf. [PARIDE]
2152 See Documentation/blockdev/paride.txt.
2154 pg. [PARIDE]
2155 See Documentation/blockdev/paride.txt.
2157 pirq= [SMP,APIC] Manual mp-table setup
2158 See Documentation/x86/i386/IO-APIC.txt.
2160 plip= [PPT,NET] Parallel port network link
2161 Format: { parport<nr> | timid | 0 }
2162 See also Documentation/parport.txt.
2164 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2165 Override pmtimer IOPort with a hex value.
2166 e.g. pmtmr=0x508
2168 pnp.debug=1 [PNP]
2169 Enable PNP debug messages (depends on the
2170 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2171 via /sys/module/pnp/parameters/debug. We always show
2172 current resource usage; turning this on also shows
2173 possible settings and some assignment information.
2175 pnpacpi= [ACPI]
2176 { off }
2178 pnpbios= [ISAPNP]
2179 { on | off | curr | res | no-curr | no-res }
2181 pnp_reserve_irq=
2182 [ISAPNP] Exclude IRQs for the autoconfiguration
2184 pnp_reserve_dma=
2185 [ISAPNP] Exclude DMAs for the autoconfiguration
2187 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2188 Ranges are in pairs (I/O port base and size).
2190 pnp_reserve_mem=
2191 [ISAPNP] Exclude memory regions for the
2192 autoconfiguration.
2193 Ranges are in pairs (memory base and size).
2195 ports= [IP_VS_FTP] IPVS ftp helper module
2196 Default is 21.
2197 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2198 may be specified.
2199 Format: <port>,<port>....
2201 print-fatal-signals=
2202 [KNL] debug: print fatal signals
2204 If enabled, warn about various signal handling
2205 related application anomalies: too many signals,
2206 too many POSIX.1 timers, fatal signals causing a
2207 coredump - etc.
2209 If you hit the warning due to signal overflow,
2210 you might want to try "ulimit -i unlimited".
2212 default: off.
2214 printk.time= Show timing data prefixed to each printk message line
2215 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2217 processor.max_cstate= [HW,ACPI]
2218 Limit processor to maximum C-state
2219 max_cstate=9 overrides any DMI blacklist limit.
2221 processor.nocst [HW,ACPI]
2222 Ignore the _CST method to determine C-states,
2223 instead using the legacy FADT method
2225 profile= [KNL] Enable kernel profiling via /proc/profile
2226 Format: [schedule,]<number>
2227 Param: "schedule" - profile schedule points.
2228 Param: <number> - step/bucket size as a power of 2 for
2229 statistical time based profiling.
2230 Param: "sleep" - profile D-state sleeping (millisecs).
2231 Requires CONFIG_SCHEDSTATS
2232 Param: "kvm" - profile VM exits.
2234 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2235 before loading.
2236 See Documentation/blockdev/ramdisk.txt.
2238 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2239 probe for; one of (bare|imps|exps|lifebook|any).
2240 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2241 per second.
2242 psmouse.resetafter= [HW,MOUSE]
2243 Try to reset the device after so many bad packets
2244 (0 = never).
2245 psmouse.resolution=
2246 [HW,MOUSE] Set desired mouse resolution, in dpi.
2247 psmouse.smartscroll=
2248 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2249 0 = disabled, 1 = enabled (default).
2251 pstore.backend= Specify the name of the pstore backend to use
2253 pt. [PARIDE]
2254 See Documentation/blockdev/paride.txt.
2256 pty.legacy_count=
2257 [KNL] Number of legacy pty's. Overwrites compiled-in
2258 default number.
2260 quiet [KNL] Disable most log messages
2262 r128= [HW,DRM]
2264 raid= [HW,RAID]
2265 See Documentation/md.txt.
2267 ramdisk_blocksize= [RAM]
2268 See Documentation/blockdev/ramdisk.txt.
2270 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2271 See Documentation/blockdev/ramdisk.txt.
2273 rcupdate.blimit= [KNL,BOOT]
2274 Set maximum number of finished RCU callbacks to process
2275 in one batch.
2277 rcupdate.qhimark= [KNL,BOOT]
2278 Set threshold of queued
2279 RCU callbacks over which batch limiting is disabled.
2281 rcupdate.qlowmark= [KNL,BOOT]
2282 Set threshold of queued RCU callbacks below which
2283 batch limiting is re-enabled.
2285 rdinit= [KNL]
2286 Format: <full_path>
2287 Run specified binary instead of /init from the ramdisk,
2288 used for early userspace startup. See initrd.
2290 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2291 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2292 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2294 relax_domain_level=
2295 [KNL, SMP] Set scheduler's default relax_domain_level.
2296 See Documentation/cgroups/cpusets.txt.
2298 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2300 reservetop= [X86-32]
2301 Format: nn[KMG]
2302 Reserves a hole at the top of the kernel virtual
2303 address space.
2305 reservelow= [X86]
2306 Format: nn[K]
2307 Set the amount of memory to reserve for BIOS at
2308 the bottom of the address space.
2310 reset_devices [KNL] Force drivers to reset the underlying device
2311 during initialization.
2313 resume= [SWSUSP]
2314 Specify the partition device for software suspend
2316 resume_offset= [SWSUSP]
2317 Specify the offset from the beginning of the partition
2318 given by "resume=" at which the swap header is located,
2319 in <PAGE_SIZE> units (needed only for swap files).
2320 See Documentation/power/swsusp-and-swap-files.txt
2322 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2323 read the resume files
2325 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2326 Useful for devices that are detected asynchronously
2327 (e.g. USB and MMC devices).
2329 hibernate= [HIBERNATION]
2330 noresume Don't check if there's a hibernation image
2331 present during boot.
2332 nocompress Don't compress/decompress hibernation images.
2334 retain_initrd [RAM] Keep initrd memory after extraction
2336 rhash_entries= [KNL,NET]
2337 Set number of hash buckets for route cache
2339 riscom8= [HW,SERIAL]
2340 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2342 ro [KNL] Mount root device read-only on boot
2344 root= [KNL] Root filesystem
2345 See name_to_dev_t comment in init/do_mounts.c.
2347 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2348 mount the root filesystem
2350 rootflags= [KNL] Set root filesystem mount option string
2352 rootfstype= [KNL] Set root filesystem type
2354 rootwait [KNL] Wait (indefinitely) for root device to show up.
2355 Useful for devices that are detected asynchronously
2356 (e.g. USB and MMC devices).
2358 rw [KNL] Mount root device read-write on boot
2360 S [KNL] Run init in single mode
2362 sa1100ir [NET]
2363 See drivers/net/irda/sa1100_ir.c.
2365 sbni= [NET] Granch SBNI12 leased line adapter
2367 sched_debug [KNL] Enables verbose scheduler debug messages.
2369 security= [SECURITY] Choose a security module to enable at boot.
2370 If this boot parameter is not specified, only the first
2371 security module asking for security registration will be
2372 loaded. An invalid security module name will be treated
2373 as if no module has been chosen.
2375 selinux= [SELINUX] Disable or enable SELinux at boot time.
2376 Format: { "0" | "1" }
2377 See security/selinux/Kconfig help text.
2378 0 -- disable.
2379 1 -- enable.
2380 Default value is set via kernel config option.
2381 If enabled at boot time, /selinux/disable can be used
2382 later to disable prior to initial policy load.
2384 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2385 Format: { "0" | "1" }
2386 See security/apparmor/Kconfig help text
2387 0 -- disable.
2388 1 -- enable.
2389 Default value is set via kernel config option.
2391 serialnumber [BUGS=X86-32]
2393 shapers= [NET]
2394 Maximal number of shapers.
2396 show_msr= [x86] show boot-time MSR settings
2397 Format: { <integer> }
2398 Show boot-time (BIOS-initialized) MSR settings.
2399 The parameter means the number of CPUs to show,
2400 for example 1 means boot CPU only.
2402 simeth= [IA-64]
2403 simscsi=
2405 slram= [HW,MTD]
2407 slab_max_order= [MM, SLAB]
2408 Determines the maximum allowed order for slabs.
2409 A high setting may cause OOMs due to memory
2410 fragmentation. Defaults to 1 for systems with
2411 more than 32MB of RAM, 0 otherwise.
2413 slub_debug[=options[,slabs]] [MM, SLUB]
2414 Enabling slub_debug allows one to determine the
2415 culprit if slab objects become corrupted. Enabling
2416 slub_debug can create guard zones around objects and
2417 may poison objects when not in use. Also tracks the
2418 last alloc / free. For more information see
2419 Documentation/vm/slub.txt.
2421 slub_max_order= [MM, SLUB]
2422 Determines the maximum allowed order for slabs.
2423 A high setting may cause OOMs due to memory
2424 fragmentation. For more information see
2425 Documentation/vm/slub.txt.
2427 slub_min_objects= [MM, SLUB]
2428 The minimum number of objects per slab. SLUB will
2429 increase the slab order up to slub_max_order to
2430 generate a sufficiently large slab able to contain
2431 the number of objects indicated. The higher the number
2432 of objects the smaller the overhead of tracking slabs
2433 and the less frequently locks need to be acquired.
2434 For more information see Documentation/vm/slub.txt.
2436 slub_min_order= [MM, SLUB]
2437 Determines the mininum page order for slabs. Must be
2438 lower than slub_max_order.
2439 For more information see Documentation/vm/slub.txt.
2441 slub_nomerge [MM, SLUB]
2442 Disable merging of slabs with similar size. May be
2443 necessary if there is some reason to distinguish
2444 allocs to different slabs. Debug options disable
2445 merging on their own.
2446 For more information see Documentation/vm/slub.txt.
2448 smart2= [HW]
2449 Format: <io1>[,<io2>[,...,<io8>]]
2451 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2452 attempt to substitute SMP alternatives once at boot.
2454 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2455 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2456 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2457 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2458 smsc-ircc2.ircc_irq= [HW] IRQ line
2459 smsc-ircc2.ircc_dma= [HW] DMA channel
2460 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2461 0: Toshiba Satellite 1800 (GP data pin select)
2462 1: Fast pin select (default)
2463 2: ATC IRMode
2465 softlockup_panic=
2466 [KNL] Should the soft-lockup detector generate panics.
2467 Format: <integer>
2469 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2470 See Documentation/laptops/sonypi.txt
2472 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2473 See Documentation/serial/specialix.txt.
2475 spia_io_base= [HW,MTD]
2476 spia_fio_base=
2477 spia_pedr=
2478 spia_peddr=
2480 stacktrace [FTRACE]
2481 Enabled the stack tracer on boot up.
2483 stacktrace_filter=[function-list]
2484 [FTRACE] Limit the functions that the stack tracer
2485 will trace at boot up. function-list is a comma separated
2486 list of functions. This list can be changed at run
2487 time by the stack_trace_filter file in the debugfs
2488 tracing directory. Note, this enables stack tracing
2489 and the stacktrace above is not needed.
2491 sti= [PARISC,HW]
2492 Format: <num>
2493 Set the STI (builtin display/keyboard on the HP-PARISC
2494 machines) console (graphic card) which should be used
2495 as the initial boot-console.
2496 See also comment in drivers/video/console/sticore.c.
2498 sti_font= [HW]
2499 See comment in drivers/video/console/sticore.c.
2501 stifb= [HW]
2502 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2504 sunrpc.min_resvport=
2505 sunrpc.max_resvport=
2506 [NFS,SUNRPC]
2507 SunRPC servers often require that client requests
2508 originate from a privileged port (i.e. a port in the
2509 range 0 < portnr < 1024).
2510 An administrator who wishes to reserve some of these
2511 ports for other uses may adjust the range that the
2512 kernel's sunrpc client considers to be privileged
2513 using these two parameters to set the minimum and
2514 maximum port values.
2516 sunrpc.pool_mode=
2517 [NFS]
2518 Control how the NFS server code allocates CPUs to
2519 service thread pools. Depending on how many NICs
2520 you have and where their interrupts are bound, this
2521 option will affect which CPUs will do NFS serving.
2522 Note: this parameter cannot be changed while the
2523 NFS server is running.
2525 auto the server chooses an appropriate mode
2526 automatically using heuristics
2527 global a single global pool contains all CPUs
2528 percpu one pool for each CPU
2529 pernode one pool for each NUMA node (equivalent
2530 to global on non-NUMA machines)
2532 sunrpc.tcp_slot_table_entries=
2533 sunrpc.udp_slot_table_entries=
2534 [NFS,SUNRPC]
2535 Sets the upper limit on the number of simultaneous
2536 RPC calls that can be sent from the client to a
2537 server. Increasing these values may allow you to
2538 improve throughput, but will also increase the
2539 amount of memory reserved for use by the client.
2541 swapaccount[=0|1]
2542 [KNL] Enable accounting of swap in memory resource
2543 controller if no parameter or 1 is given or disable
2544 it if 0 is given (See Documentation/cgroups/memory.txt)
2546 swiotlb= [IA-64] Number of I/O TLB slabs
2548 switches= [HW,M68k]
2550 sysfs.deprecated=0|1 [KNL]
2551 Enable/disable old style sysfs layout for old udev
2552 on older distributions. When this option is enabled
2553 very new udev will not work anymore. When this option
2554 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2555 in older udev will not work anymore.
2556 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2557 the kernel configuration.
2559 sysrq_always_enabled
2560 [KNL]
2561 Ignore sysrq setting - this boot parameter will
2562 neutralize any effect of /proc/sys/kernel/sysrq.
2563 Useful for debugging.
2565 tdfx= [HW,DRM]
2567 test_suspend= [SUSPEND]
2568 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2569 standby suspend) as the system sleep state to briefly
2570 enter during system startup. The system is woken from
2571 this state using a wakeup-capable RTC alarm.
2573 thash_entries= [KNL,NET]
2574 Set number of hash buckets for TCP connection
2576 thermal.act= [HW,ACPI]
2577 -1: disable all active trip points in all thermal zones
2578 <degrees C>: override all lowest active trip points
2580 thermal.crt= [HW,ACPI]
2581 -1: disable all critical trip points in all thermal zones
2582 <degrees C>: override all critical trip points
2584 thermal.nocrt= [HW,ACPI]
2585 Set to disable actions on ACPI thermal zone
2586 critical and hot trip points.
2588 thermal.off= [HW,ACPI]
2589 1: disable ACPI thermal control
2591 thermal.psv= [HW,ACPI]
2592 -1: disable all passive trip points
2593 <degrees C>: override all passive trip points to this
2594 value
2596 thermal.tzp= [HW,ACPI]
2597 Specify global default ACPI thermal zone polling rate
2598 <deci-seconds>: poll all this frequency
2599 0: no polling (default)
2601 threadirqs [KNL]
2602 Force threading of all interrupt handlers except those
2603 marked explicitely IRQF_NO_THREAD.
2605 topology= [S390]
2606 Format: {off | on}
2607 Specify if the kernel should make use of the cpu
2608 topology information if the hardware supports this.
2609 The scheduler will make use of this information and
2610 e.g. base its process migration decisions on it.
2611 Default is on.
2613 tp720= [HW,PS2]
2615 tpm_suspend_pcr=[HW,TPM]
2616 Format: integer pcr id
2617 Specify that at suspend time, the tpm driver
2618 should extend the specified pcr with zeros,
2619 as a workaround for some chips which fail to
2620 flush the last written pcr on TPM_SaveState.
2621 This will guarantee that all the other pcrs
2622 are saved.
2624 trace_buf_size=nn[KMG]
2625 [FTRACE] will set tracing buffer size.
2627 trace_event=[event-list]
2628 [FTRACE] Set and start specified trace events in order
2629 to facilitate early boot debugging.
2630 See also Documentation/trace/events.txt
2632 tsc= Disable clocksource stability checks for TSC.
2633 Format: <string>
2634 [x86] reliable: mark tsc clocksource as reliable, this
2635 disables clocksource verification at runtime, as well
2636 as the stability checks done at bootup. Used to enable
2637 high-resolution timer mode on older hardware, and in
2638 virtualized environment.
2639 [x86] noirqtime: Do not use TSC to do irq accounting.
2640 Used to run time disable IRQ_TIME_ACCOUNTING on any
2641 platforms where RDTSC is slow and this accounting
2642 can add overhead.
2644 turbografx.map[2|3]= [HW,JOY]
2645 TurboGraFX parallel port interface
2646 Format:
2647 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2648 See also Documentation/input/joystick-parport.txt
2650 udbg-immortal [PPC] When debugging early kernel crashes that
2651 happen after console_init() and before a proper
2652 console driver takes over, this boot options might
2653 help "seeing" what's going on.
2655 uhash_entries= [KNL,NET]
2656 Set number of hash buckets for UDP/UDP-Lite connections
2658 uhci-hcd.ignore_oc=
2659 [USB] Ignore overcurrent events (default N).
2660 Some badly-designed motherboards generate lots of
2661 bogus events, for ports that aren't wired to
2662 anything. Set this parameter to avoid log spamming.
2663 Note that genuine overcurrent events won't be
2664 reported either.
2666 unknown_nmi_panic
2667 [X86] Cause panic on unknown NMI.
2669 usbcore.authorized_default=
2670 [USB] Default USB device authorization:
2671 (default -1 = authorized except for wireless USB,
2672 0 = not authorized, 1 = authorized)
2674 usbcore.autosuspend=
2675 [USB] The autosuspend time delay (in seconds) used
2676 for newly-detected USB devices (default 2). This
2677 is the time required before an idle device will be
2678 autosuspended. Devices for which the delay is set
2679 to a negative value won't be autosuspended at all.
2681 usbcore.usbfs_snoop=
2682 [USB] Set to log all usbfs traffic (default 0 = off).
2684 usbcore.blinkenlights=
2685 [USB] Set to cycle leds on hubs (default 0 = off).
2687 usbcore.old_scheme_first=
2688 [USB] Start with the old device initialization
2689 scheme (default 0 = off).
2691 usbcore.usbfs_memory_mb=
2692 [USB] Memory limit (in MB) for buffers allocated by
2693 usbfs (default = 16, 0 = max = 2047).
2695 usbcore.use_both_schemes=
2696 [USB] Try the other device initialization scheme
2697 if the first one fails (default 1 = enabled).
2699 usbcore.initial_descriptor_timeout=
2700 [USB] Specifies timeout for the initial 64-byte
2701 USB_REQ_GET_DESCRIPTOR request in milliseconds
2702 (default 5000 = 5.0 seconds).
2704 usbhid.mousepoll=
2705 [USBHID] The interval which mice are to be polled at.
2707 usb-storage.delay_use=
2708 [UMS] The delay in seconds before a new device is
2709 scanned for Logical Units (default 5).
2711 usb-storage.quirks=
2712 [UMS] A list of quirks entries to supplement or
2713 override the built-in unusual_devs list. List
2714 entries are separated by commas. Each entry has
2715 the form VID:PID:Flags where VID and PID are Vendor
2716 and Product ID values (4-digit hex numbers) and
2717 Flags is a set of characters, each corresponding
2718 to a common usb-storage quirk flag as follows:
2719 a = SANE_SENSE (collect more than 18 bytes
2720 of sense data);
2721 b = BAD_SENSE (don't collect more than 18
2722 bytes of sense data);
2723 c = FIX_CAPACITY (decrease the reported
2724 device capacity by one sector);
2725 d = NO_READ_DISC_INFO (don't use
2726 READ_DISC_INFO command);
2727 e = NO_READ_CAPACITY_16 (don't use
2728 READ_CAPACITY_16 command);
2729 h = CAPACITY_HEURISTICS (decrease the
2730 reported device capacity by one
2731 sector if the number is odd);
2732 i = IGNORE_DEVICE (don't bind to this
2733 device);
2734 l = NOT_LOCKABLE (don't try to lock and
2735 unlock ejectable media);
2736 m = MAX_SECTORS_64 (don't transfer more
2737 than 64 sectors = 32 KB at a time);
2738 n = INITIAL_READ10 (force a retry of the
2739 initial READ(10) command);
2740 o = CAPACITY_OK (accept the capacity
2741 reported by the device);
2742 r = IGNORE_RESIDUE (the device reports
2743 bogus residue values);
2744 s = SINGLE_LUN (the device has only one
2745 Logical Unit);
2746 w = NO_WP_DETECT (don't test whether the
2747 medium is write-protected).
2748 Example: quirks=0419:aaf5:rl,0421:0433:rc
2750 user_debug= [KNL,ARM]
2751 Format: <int>
2752 See arch/arm/Kconfig.debug help text.
2753 1 - undefined instruction events
2754 2 - system calls
2755 4 - invalid data aborts
2756 8 - SIGSEGV faults
2757 16 - SIGBUS faults
2758 Example: user_debug=31
2760 userpte=
2761 [X86] Flags controlling user PTE allocations.
2763 nohigh = do not allocate PTE pages in
2764 HIGHMEM regardless of setting
2765 of CONFIG_HIGHPTE.
2767 vdso= [X86,SH]
2768 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2769 vdso=1: enable VDSO (default)
2770 vdso=0: disable VDSO mapping
2772 vdso32= [X86]
2773 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2774 vdso32=1: enable 32-bit VDSO (default)
2775 vdso32=0: disable 32-bit VDSO mapping
2777 vector= [IA-64,SMP]
2778 vector=percpu: enable percpu vector domain
2780 video= [FB] Frame buffer configuration
2781 See Documentation/fb/modedb.txt.
2783 vga= [BOOT,X86-32] Select a particular video mode
2784 See Documentation/x86/boot.txt and
2785 Documentation/svga.txt.
2786 Use vga=ask for menu.
2787 This is actually a boot loader parameter; the value is
2788 passed to the kernel using a special protocol.
2790 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2791 size of <nn>. This can be used to increase the
2792 minimum size (128MB on x86). It can also be used to
2793 decrease the size and leave more room for directly
2794 mapped kernel RAM.
2796 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2797 Format: <command>
2799 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2800 Format: <command>
2802 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2803 Format: <command>
2805 vsyscall= [X86-64]
2806 Controls the behavior of vsyscalls (i.e. calls to
2807 fixed addresses of 0xffffffffff600x00 from legacy
2808 code). Most statically-linked binaries and older
2809 versions of glibc use these calls. Because these
2810 functions are at fixed addresses, they make nice
2811 targets for exploits that can control RIP.
2813 emulate [default] Vsyscalls turn into traps and are
2814 emulated reasonably safely.
2816 native Vsyscalls are native syscall instructions.
2817 This is a little bit faster than trapping
2818 and makes a few dynamic recompilers work
2819 better than they would in emulation mode.
2820 It also makes exploits much easier to write.
2822 none Vsyscalls don't work at all. This makes
2823 them quite hard to use for exploits but
2824 might break your system.
2826 vt.cur_default= [VT] Default cursor shape.
2827 Format: 0xCCBBAA, where AA, BB, and CC are the same as
2828 the parameters of the <Esc>[?A;B;Cc escape sequence;
2829 see VGA-softcursor.txt. Default: 2 = underline.
2831 vt.default_blu= [VT]
2832 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2833 Change the default blue palette of the console.
2834 This is a 16-member array composed of values
2835 ranging from 0-255.
2837 vt.default_grn= [VT]
2838 Format: <green0>,<green1>,<green2>,...,<green15>
2839 Change the default green palette of the console.
2840 This is a 16-member array composed of values
2841 ranging from 0-255.
2843 vt.default_red= [VT]
2844 Format: <red0>,<red1>,<red2>,...,<red15>
2845 Change the default red palette of the console.
2846 This is a 16-member array composed of values
2847 ranging from 0-255.
2849 vt.default_utf8=
2850 [VT]
2851 Format=<0|1>
2852 Set system-wide default UTF-8 mode for all tty's.
2853 Default is 1, i.e. UTF-8 mode is enabled for all
2854 newly opened terminals.
2856 vt.global_cursor_default=
2857 [VT]
2858 Format=<-1|0|1>
2859 Set system-wide default for whether a cursor
2860 is shown on new VTs. Default is -1,
2861 i.e. cursors will be created by default unless
2862 overridden by individual drivers. 0 will hide
2863 cursors, 1 will display them.
2865 watchdog timers [HW,WDT] For information on watchdog timers,
2866 see Documentation/watchdog/watchdog-parameters.txt
2867 or other driver-specific files in the
2868 Documentation/watchdog/ directory.
2870 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2871 default x2apic cluster mode on platforms
2872 supporting x2apic.
2874 x86_mrst_timer= [X86-32,APBT]
2875 Choose timer option for x86 Moorestown MID platform.
2876 Two valid options are apbt timer only and lapic timer
2877 plus one apbt timer for broadcast timer.
2878 x86_mrst_timer=apbt_only | lapic_and_apbt
2880 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2881 xd_geo= See header of drivers/block/xd.c.
2883 xen_emul_unplug= [HW,X86,XEN]
2884 Unplug Xen emulated devices
2885 Format: [unplug0,][unplug1]
2886 ide-disks -- unplug primary master IDE devices
2887 aux-ide-disks -- unplug non-primary-master IDE devices
2888 nics -- unplug network devices
2889 all -- unplug all emulated devices (NICs and IDE disks)
2890 unnecessary -- unplugging emulated devices is
2891 unnecessary even if the host did not respond to
2892 the unplug protocol
2893 never -- do not unplug even if version check succeeds
2895 xirc2ps_cs= [NET,PCMCIA]
2896 Format:
2897 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2899 ______________________________________________________________________
2901 TODO:
2903 Add more DRM drivers.