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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
4 The following is a consolidated list of the kernel parameters as implemented
5 (mostly) by the __setup() macro and sorted into English Dictionary order
6 (defined as ignoring all punctuation and sorting digits before letters in a
7 case insensitive manner), and with descriptions where known.
9 Module parameters for loadable modules are specified only as the
10 parameter name with optional '=' and value as appropriate, such as:
12 modprobe usbcore blinkenlights=1
14 Module parameters for modules that are built into the kernel image
15 are specified on the kernel command line with the module name plus
16 '.' plus parameter name, with '=' and value if appropriate, such as:
18 usbcore.blinkenlights=1
20 Hyphens (dashes) and underscores are equivalent in parameter names, so
21 log_buf_len=1M print-fatal-signals=1
22 can also be entered as
23 log-buf-len=1M print_fatal_signals=1
26 This document may not be entirely up to date and comprehensive. The command
27 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
28 module. Loadable modules, after being loaded into the running kernel, also
29 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
30 parameters may be changed at runtime by the command
31 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
33 The parameters listed below are only valid if certain kernel build options were
34 enabled and if respective hardware is present. The text in square brackets at
35 the beginning of each description states the restrictions within which a
36 parameter is applicable:
38 ACPI ACPI support is enabled.
39 AGP AGP (Accelerated Graphics Port) is enabled.
40 ALSA ALSA sound support is enabled.
41 APIC APIC support is enabled.
42 APM Advanced Power Management support is enabled.
43 ARM ARM architecture is enabled.
44 AVR32 AVR32 architecture is enabled.
45 AX25 Appropriate AX.25 support is enabled.
46 BLACKFIN Blackfin architecture is enabled.
47 DRM Direct Rendering Management support is enabled.
48 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
49 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
50 EFI EFI Partitioning (GPT) is enabled
51 EIDE EIDE/ATAPI support is enabled.
52 EVM Extended Verification Module
53 FB The frame buffer device is enabled.
54 FTRACE Function tracing enabled.
55 GCOV GCOV profiling is enabled.
56 HW Appropriate hardware is enabled.
57 IA-64 IA-64 architecture is enabled.
58 IMA Integrity measurement architecture is enabled.
59 IOSCHED More than one I/O scheduler is enabled.
60 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
61 IPV6 IPv6 support is enabled.
62 ISAPNP ISA PnP code is enabled.
63 ISDN Appropriate ISDN support is enabled.
64 JOY Appropriate joystick support is enabled.
65 KGDB Kernel debugger support is enabled.
66 KVM Kernel Virtual Machine support is enabled.
67 LIBATA Libata driver is enabled
68 LP Printer support is enabled.
69 LOOP Loopback device support is enabled.
70 M68k M68k architecture is enabled.
71 These options have more detailed description inside of
72 Documentation/m68k/kernel-options.txt.
73 MCA MCA bus support is enabled.
74 MDA MDA console support is enabled.
75 MIPS MIPS architecture is enabled.
76 MOUSE Appropriate mouse support is enabled.
77 MSI Message Signaled Interrupts (PCI).
78 MTD MTD (Memory Technology Device) support is enabled.
79 NET Appropriate network support is enabled.
80 NUMA NUMA support is enabled.
81 NFS Appropriate NFS support is enabled.
82 OSS OSS sound support is enabled.
83 PV_OPS A paravirtualized kernel is enabled.
84 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
85 PARISC The PA-RISC architecture is enabled.
86 PCI PCI bus support is enabled.
87 PCIE PCI Express support is enabled.
88 PCMCIA The PCMCIA subsystem is enabled.
89 PNP Plug & Play support is enabled.
90 PPC PowerPC architecture is enabled.
91 PPT Parallel port support is enabled.
92 PS2 Appropriate PS/2 support is enabled.
93 RAM RAM disk support is enabled.
94 S390 S390 architecture is enabled.
95 SCSI Appropriate SCSI support is enabled.
96 A lot of drivers have their options described inside
97 the Documentation/scsi/ sub-directory.
98 SECURITY Different security models are enabled.
99 SELINUX SELinux support is enabled.
100 APPARMOR AppArmor support is enabled.
101 SERIAL Serial support is enabled.
102 SH SuperH architecture is enabled.
103 SMP The kernel is an SMP kernel.
104 SPARC Sparc architecture is enabled.
105 SWSUSP Software suspend (hibernation) is enabled.
106 SUSPEND System suspend states are enabled.
107 TPM TPM drivers are enabled.
108 TS Appropriate touchscreen support is enabled.
109 UMS USB Mass Storage support is enabled.
110 USB USB support is enabled.
111 USBHID USB Human Interface Device support is enabled.
112 V4L Video For Linux support is enabled.
113 VGA The VGA console has been enabled.
114 VT Virtual terminal support is enabled.
115 WDT Watchdog support is enabled.
116 XT IBM PC/XT MFM hard disk support is enabled.
117 X86-32 X86-32, aka i386 architecture is enabled.
118 X86-64 X86-64 architecture is enabled.
119 More X86-64 boot options can be found in
120 Documentation/x86/x86_64/boot-options.txt .
121 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
122 XEN Xen support is enabled
124 In addition, the following text indicates that the option:
126 BUGS= Relates to possible processor bugs on the said processor.
127 KNL Is a kernel start-up parameter.
128 BOOT Is a boot loader parameter.
130 Parameters denoted with BOOT are actually interpreted by the boot
131 loader, and have no meaning to the kernel directly.
132 Do not modify the syntax of boot loader parameters without extreme
133 need or coordination with <Documentation/x86/boot.txt>.
135 There are also arch-specific kernel-parameters not documented here.
136 See for example <Documentation/x86/x86_64/boot-options.txt>.
138 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
139 a trailing = on the name of any parameter states that that parameter will
140 be entered as an environment variable, whereas its absence indicates that
141 it will appear as a kernel argument readable via /proc/cmdline by programs
142 running once the system is up.
144 The number of kernel parameters is not limited, but the length of the
145 complete command line (parameters including spaces etc.) is limited to
146 a fixed number of characters. This limit depends on the architecture
147 and is between 256 and 4096 characters. It is defined in the file
148 ./include/asm/setup.h as COMMAND_LINE_SIZE.
150 Finally, the [KMG] suffix is commonly described after a number of kernel
151 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
152 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
153 bytes respectively. Such letter suffixes can also be entirely omitted.
156 acpi= [HW,ACPI,X86]
157 Advanced Configuration and Power Interface
158 Format: { force | off | strict | noirq | rsdt }
159 force -- enable ACPI if default was off
160 off -- disable ACPI if default was on
161 noirq -- do not use ACPI for IRQ routing
162 strict -- Be less tolerant of platforms that are not
163 strictly ACPI specification compliant.
164 rsdt -- prefer RSDT over (default) XSDT
165 copy_dsdt -- copy DSDT to memory
167 See also Documentation/power/runtime_pm.txt, pci=noacpi
169 acpi_rsdp= [ACPI,EFI,KEXEC]
170 Pass the RSDP address to the kernel, mostly used
171 on machines running EFI runtime service to boot the
172 second kernel for kdump.
174 acpi_apic_instance= [ACPI, IOAPIC]
175 Format: <int>
176 2: use 2nd APIC table, if available
177 1,0: use 1st APIC table
178 default: 0
180 acpi_backlight= [HW,ACPI]
181 acpi_backlight=vendor
182 acpi_backlight=video
183 If set to vendor, prefer vendor specific driver
184 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
185 of the ACPI video.ko driver.
187 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
188 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
189 Format: <int>
190 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
191 debug output. Bits in debug_layer correspond to a
192 _COMPONENT in an ACPI source file, e.g.,
193 #define _COMPONENT ACPI_PCI_COMPONENT
194 Bits in debug_level correspond to a level in
195 ACPI_DEBUG_PRINT statements, e.g.,
196 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
197 The debug_level mask defaults to "info". See
198 Documentation/acpi/debug.txt for more information about
199 debug layers and levels.
201 Enable processor driver info messages:
202 acpi.debug_layer=0x20000000
203 Enable PCI/PCI interrupt routing info messages:
204 acpi.debug_layer=0x400000
205 Enable AML "Debug" output, i.e., stores to the Debug
206 object while interpreting AML:
207 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
208 Enable all messages related to ACPI hardware:
209 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
211 Some values produce so much output that the system is
212 unusable. The "log_buf_len" parameter may be useful
213 if you need to capture more output.
215 acpi_irq_balance [HW,ACPI]
216 ACPI will balance active IRQs
217 default in APIC mode
219 acpi_irq_nobalance [HW,ACPI]
220 ACPI will not move active IRQs (default)
221 default in PIC mode
223 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
224 Format: <irq>,<irq>...
226 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
227 use by PCI
228 Format: <irq>,<irq>...
230 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
232 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
233 Format: To spoof as Windows 98: ="Microsoft Windows"
235 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
236 acpi_osi="string1" # add string1 -- only one string
237 acpi_osi="!string2" # remove built-in string2
238 acpi_osi= # disable all strings
240 acpi_pm_good [X86]
241 Override the pmtimer bug detection: force the kernel
242 to assume that this machine's pmtimer latches its value
243 and always returns good values.
245 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
246 Format: { level | edge | high | low }
248 acpi_serialize [HW,ACPI] force serialization of AML methods
250 acpi_skip_timer_override [HW,ACPI]
251 Recognize and ignore IRQ0/pin2 Interrupt Override.
252 For broken nForce2 BIOS resulting in XT-PIC timer.
254 acpi_sleep= [HW,ACPI] Sleep options
255 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
256 old_ordering, nonvs, sci_force_enable }
257 See Documentation/power/video.txt for information on
258 s3_bios and s3_mode.
259 s3_beep is for debugging; it makes the PC's speaker beep
260 as soon as the kernel's real-mode entry point is called.
261 s4_nohwsig prevents ACPI hardware signature from being
262 used during resume from hibernation.
263 old_ordering causes the ACPI 1.0 ordering of the _PTS
264 control method, with respect to putting devices into
265 low power states, to be enforced (the ACPI 2.0 ordering
266 of _PTS is used by default).
267 nonvs prevents the kernel from saving/restoring the
268 ACPI NVS memory during suspend/hibernation and resume.
269 sci_force_enable causes the kernel to set SCI_EN directly
270 on resume from S1/S3 (which is against the ACPI spec,
271 but some broken systems don't work without it).
273 acpi_use_timer_override [HW,ACPI]
274 Use timer override. For some broken Nvidia NF5 boards
275 that require a timer override, but don't have HPET
277 acpi_enforce_resources= [ACPI]
278 { strict | lax | no }
279 Check for resource conflicts between native drivers
280 and ACPI OperationRegions (SystemIO and SystemMemory
281 only). IO ports and memory declared in ACPI might be
282 used by the ACPI subsystem in arbitrary AML code and
283 can interfere with legacy drivers.
284 strict (default): access to resources claimed by ACPI
285 is denied; legacy drivers trying to access reserved
286 resources will fail to bind to device using them.
287 lax: access to resources claimed by ACPI is allowed;
288 legacy drivers trying to access reserved resources
289 will bind successfully but a warning message is logged.
290 no: ACPI OperationRegions are not marked as reserved,
291 no further checks are performed.
293 add_efi_memmap [EFI; X86] Include EFI memory map in
294 kernel's map of available physical RAM.
296 agp= [AGP]
297 { off | try_unsupported }
298 off: disable AGP support
299 try_unsupported: try to drive unsupported chipsets
300 (may crash computer or cause data corruption)
302 ALSA [HW,ALSA]
303 See Documentation/sound/alsa/alsa-parameters.txt
305 alignment= [KNL,ARM]
306 Allow the default userspace alignment fault handler
307 behaviour to be specified. Bit 0 enables warnings,
308 bit 1 enables fixups, and bit 2 sends a segfault.
310 align_va_addr= [X86-64]
311 Align virtual addresses by clearing slice [14:12] when
312 allocating a VMA at process creation time. This option
313 gives you up to 3% performance improvement on AMD F15h
314 machines (where it is enabled by default) for a
315 CPU-intensive style benchmark, and it can vary highly in
316 a microbenchmark depending on workload and compiler.
318 32: only for 32-bit processes
319 64: only for 64-bit processes
320 on: enable for both 32- and 64-bit processes
321 off: disable for both 32- and 64-bit processes
323 amd_iommu= [HW,X86-64]
324 Pass parameters to the AMD IOMMU driver in the system.
325 Possible values are:
326 fullflush - enable flushing of IO/TLB entries when
327 they are unmapped. Otherwise they are
328 flushed before they will be reused, which
329 is a lot of faster
330 off - do not initialize any AMD IOMMU found in
331 the system
332 force_isolation - Force device isolation for all
333 devices. The IOMMU driver is not
334 allowed anymore to lift isolation
335 requirements as needed. This option
336 does not override iommu=pt
338 amijoy.map= [HW,JOY] Amiga joystick support
339 Map of devices attached to JOY0DAT and JOY1DAT
340 Format: <a>,<b>
341 See also Documentation/input/joystick.txt
343 analog.map= [HW,JOY] Analog joystick and gamepad support
344 Specifies type or capabilities of an analog joystick
345 connected to one of 16 gameports
346 Format: <type1>,<type2>,..<type16>
348 apc= [HW,SPARC]
349 Power management functions (SPARCstation-4/5 + deriv.)
350 Format: noidle
351 Disable APC CPU standby support. SPARCstation-Fox does
352 not play well with APC CPU idle - disable it if you have
353 APC and your system crashes randomly.
355 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
356 Change the output verbosity whilst booting
357 Format: { quiet (default) | verbose | debug }
358 Change the amount of debugging information output
359 when initialising the APIC and IO-APIC components.
361 autoconf= [IPV6]
362 See Documentation/networking/ipv6.txt.
364 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
365 Limit apic dumping. The parameter defines the maximal
366 number of local apics being dumped. Also it is possible
367 to set it to "all" by meaning -- no limit here.
368 Format: { 1 (default) | 2 | ... | all }.
369 The parameter valid if only apic=debug or
370 apic=verbose is specified.
371 Example: apic=debug show_lapic=all
373 apm= [APM] Advanced Power Management
374 See header of arch/x86/kernel/apm_32.c.
376 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
377 Format: <io>,<irq>,<nodeID>
379 ataflop= [HW,M68k]
381 atarimouse= [HW,MOUSE] Atari Mouse
383 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
384 EzKey and similar keyboards
386 atkbd.reset= [HW] Reset keyboard during initialization
388 atkbd.set= [HW] Select keyboard code set
389 Format: <int> (2 = AT (default), 3 = PS/2)
391 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
392 keyboards
394 atkbd.softraw= [HW] Choose between synthetic and real raw mode
395 Format: <bool> (0 = real, 1 = synthetic (default))
397 atkbd.softrepeat= [HW]
398 Use software keyboard repeat
400 autotest [IA-64]
402 baycom_epp= [HW,AX25]
403 Format: <io>,<mode>
405 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
406 Format: <io>,<mode>
407 See header of drivers/net/hamradio/baycom_par.c.
409 baycom_ser_fdx= [HW,AX25]
410 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
411 Format: <io>,<irq>,<mode>[,<baud>]
412 See header of drivers/net/hamradio/baycom_ser_fdx.c.
414 baycom_ser_hdx= [HW,AX25]
415 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
416 Format: <io>,<irq>,<mode>
417 See header of drivers/net/hamradio/baycom_ser_hdx.c.
419 boot_delay= Milliseconds to delay each printk during boot.
420 Values larger than 10 seconds (10000) are changed to
421 no delay (0).
422 Format: integer
424 bootmem_debug [KNL] Enable bootmem allocator debug messages.
426 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
427 bttv.radio= Most important insmod options are available as
428 kernel args too.
429 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
430 bttv.tuner=
432 bulk_remove=off [PPC] This parameter disables the use of the pSeries
433 firmware feature for flushing multiple hpte entries
434 at a time.
436 c101= [NET] Moxa C101 synchronous serial card
438 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
439 Sometimes CPU hardware bugs make them report the cache
440 size incorrectly. The kernel will attempt work arounds
441 to fix known problems, but for some CPUs it is not
442 possible to determine what the correct size should be.
443 This option provides an override for these situations.
445 capability.disable=
446 [SECURITY] Disable capabilities. This would normally
447 be used only if an alternative security model is to be
448 configured. Potentially dangerous and should only be
449 used if you are entirely sure of the consequences.
451 ccw_timeout_log [S390]
452 See Documentation/s390/CommonIO for details.
454 cgroup_disable= [KNL] Disable a particular controller
455 Format: {name of the controller(s) to disable}
456 {Currently supported controllers - "memory"}
458 checkreqprot [SELINUX] Set initial checkreqprot flag value.
459 Format: { "0" | "1" }
460 See security/selinux/Kconfig help text.
461 0 -- check protection applied by kernel (includes
462 any implied execute protection).
463 1 -- check protection requested by application.
464 Default value is set via a kernel config option.
465 Value can be changed at runtime via
466 /selinux/checkreqprot.
468 cio_ignore= [S390]
469 See Documentation/s390/CommonIO for details.
471 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
472 [Deprecated]
473 Forces specified clocksource (if available) to be used
474 when calculating gettimeofday(). If specified
475 clocksource is not available, it defaults to PIT.
476 Format: { pit | tsc | cyclone | pmtmr }
478 clocksource= Override the default clocksource
479 Format: <string>
480 Override the default clocksource and use the clocksource
481 with the name specified.
482 Some clocksource names to choose from, depending on
483 the platform:
484 [all] jiffies (this is the base, fallback clocksource)
485 [ACPI] acpi_pm
486 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
487 pxa_timer,timer3,32k_counter,timer0_1
488 [AVR32] avr32
489 [X86-32] pit,hpet,tsc;
490 scx200_hrt on Geode; cyclone on IBM x440
491 [MIPS] MIPS
492 [PARISC] cr16
493 [S390] tod
494 [SH] SuperH
495 [SPARC64] tick
496 [X86-64] hpet,tsc
498 clearcpuid=BITNUM [X86]
499 Disable CPUID feature X for the kernel. See
500 arch/x86/include/asm/cpufeature.h for the valid bit
501 numbers. Note the Linux specific bits are not necessarily
502 stable over kernel options, but the vendor specific
503 ones should be.
504 Also note that user programs calling CPUID directly
505 or using the feature without checking anything
506 will still see it. This just prevents it from
507 being used by the kernel or shown in /proc/cpuinfo.
508 Also note the kernel might malfunction if you disable
509 some critical bits.
511 cmo_free_hint= [PPC] Format: { yes | no }
512 Specify whether pages are marked as being inactive
513 when they are freed. This is used in CMO environments
514 to determine OS memory pressure for page stealing by
515 a hypervisor.
516 Default: yes
518 code_bytes [X86] How many bytes of object code to print
519 in an oops report.
520 Range: 0 - 8192
521 Default: 64
523 com20020= [HW,NET] ARCnet - COM20020 chipset
524 Format:
525 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
527 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
528 Format: <io>[,<irq>]
530 com90xx= [HW,NET]
531 ARCnet - COM90xx chipset (memory-mapped buffers)
532 Format: <io>[,<irq>[,<memstart>]]
534 condev= [HW,S390] console device
535 conmode=
537 console= [KNL] Output console device and options.
539 tty<n> Use the virtual console device <n>.
541 ttyS<n>[,options]
542 ttyUSB0[,options]
543 Use the specified serial port. The options are of
544 the form "bbbbpnf", where "bbbb" is the baud rate,
545 "p" is parity ("n", "o", or "e"), "n" is number of
546 bits, and "f" is flow control ("r" for RTS or
547 omit it). Default is "9600n8".
549 See Documentation/serial-console.txt for more
550 information. See
551 Documentation/networking/netconsole.txt for an
552 alternative.
554 uart[8250],io,<addr>[,options]
555 uart[8250],mmio,<addr>[,options]
556 Start an early, polled-mode console on the 8250/16550
557 UART at the specified I/O port or MMIO address,
558 switching to the matching ttyS device later. The
559 options are the same as for ttyS, above.
561 If the device connected to the port is not a TTY but a braille
562 device, prepend "brl," before the device type, for instance
563 console=brl,ttyS0
564 For now, only VisioBraille is supported.
566 consoleblank= [KNL] The console blank (screen saver) timeout in
567 seconds. Defaults to 10*60 = 10mins. A value of 0
568 disables the blank timer.
570 coredump_filter=
571 [KNL] Change the default value for
572 /proc/<pid>/coredump_filter.
573 See also Documentation/filesystems/proc.txt.
575 cpuidle.off=1 [CPU_IDLE]
576 disable the cpuidle sub-system
578 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
579 Format:
580 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
582 crashkernel=size[KMG][@offset[KMG]]
583 [KNL] Using kexec, Linux can switch to a 'crash kernel'
584 upon panic. This parameter reserves the physical
585 memory region [offset, offset + size] for that kernel
586 image. If '@offset' is omitted, then a suitable offset
587 is selected automatically. Check
588 Documentation/kdump/kdump.txt for further details.
590 crashkernel=range1:size1[,range2:size2,...][@offset]
591 [KNL] Same as above, but depends on the memory
592 in the running system. The syntax of range is
593 start-[end] where start and end are both
594 a memory unit (amount[KMG]). See also
595 Documentation/kdump/kdump.txt for an example.
597 cs89x0_dma= [HW,NET]
598 Format: <dma>
600 cs89x0_media= [HW,NET]
601 Format: { rj45 | aui | bnc }
603 dasd= [HW,NET]
604 See header of drivers/s390/block/dasd_devmap.c.
606 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
607 (one device per port)
608 Format: <port#>,<type>
609 See also Documentation/input/joystick-parport.txt
611 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
612 time. See Documentation/dynamic-debug-howto.txt for
613 details.
615 debug [KNL] Enable kernel debugging (events log level).
617 debug_locks_verbose=
618 [KNL] verbose self-tests
619 Format=<0|1>
620 Print debugging info while doing the locking API
621 self-tests.
622 We default to 0 (no extra messages), setting it to
623 1 will print _a lot_ more information - normally
624 only useful to kernel developers.
626 debug_objects [KNL] Enable object debugging
628 no_debug_objects
629 [KNL] Disable object debugging
631 debug_guardpage_minorder=
632 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
633 parameter allows control of the order of pages that will
634 be intentionally kept free (and hence protected) by the
635 buddy allocator. Bigger value increase the probability
636 of catching random memory corruption, but reduce the
637 amount of memory for normal system use. The maximum
638 possible value is MAX_ORDER/2. Setting this parameter
639 to 1 or 2 should be enough to identify most random
640 memory corruption problems caused by bugs in kernel or
641 driver code when a CPU writes to (or reads from) a
642 random memory location. Note that there exists a class
643 of memory corruptions problems caused by buggy H/W or
644 F/W or by drivers badly programing DMA (basically when
645 memory is written at bus level and the CPU MMU is
646 bypassed) which are not detectable by
647 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
648 tracking down these problems.
650 debugpat [X86] Enable PAT debugging
652 decnet.addr= [HW,NET]
653 Format: <area>[,<node>]
654 See also Documentation/networking/decnet.txt.
656 default_hugepagesz=
657 [same as hugepagesz=] The size of the default
658 HugeTLB page size. This is the size represented by
659 the legacy /proc/ hugepages APIs, used for SHM, and
660 default size when mounting hugetlbfs filesystems.
661 Defaults to the default architecture's huge page size
662 if not specified.
664 dhash_entries= [KNL]
665 Set number of hash buckets for dentry cache.
667 digi= [HW,SERIAL]
668 IO parameters + enable/disable command.
670 digiepca= [HW,SERIAL]
671 See drivers/char/README.epca and
672 Documentation/serial/digiepca.txt.
674 disable= [IPV6]
675 See Documentation/networking/ipv6.txt.
677 disable_ddw [PPC/PSERIES]
678 Disable Dynamic DMA Window support. Use this if
679 to workaround buggy firmware.
681 disable_ipv6= [IPV6]
682 See Documentation/networking/ipv6.txt.
684 disable_mtrr_cleanup [X86]
685 The kernel tries to adjust MTRR layout from continuous
686 to discrete, to make X server driver able to add WB
687 entry later. This parameter disables that.
689 disable_mtrr_trim [X86, Intel and AMD only]
690 By default the kernel will trim any uncacheable
691 memory out of your available memory pool based on
692 MTRR settings. This parameter disables that behavior,
693 possibly causing your machine to run very slowly.
695 disable_timer_pin_1 [X86]
696 Disable PIN 1 of APIC timer
697 Can be useful to work around chipset bugs.
699 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
700 this option disables the debugging code at boot.
702 dma_debug_entries=<number>
703 This option allows to tune the number of preallocated
704 entries for DMA-API debugging code. One entry is
705 required per DMA-API allocation. Use this if the
706 DMA-API debugging code disables itself because the
707 architectural default is too low.
709 dma_debug_driver=<driver_name>
710 With this option the DMA-API debugging driver
711 filter feature can be enabled at boot time. Just
712 pass the driver to filter for as the parameter.
713 The filter can be disabled or changed to another
714 driver later using sysfs.
716 drm_kms_helper.edid_firmware=[<connector>:]<file>
717 Broken monitors, graphic adapters and KVMs may
718 send no or incorrect EDID data sets. This parameter
719 allows to specify an EDID data set in the
720 /lib/firmware directory that is used instead.
721 Generic built-in EDID data sets are used, if one of
722 edid/1024x768.bin, edid/1280x1024.bin,
723 edid/1680x1050.bin, or edid/1920x1080.bin is given
724 and no file with the same name exists. Details and
725 instructions how to build your own EDID data are
726 available in Documentation/EDID/HOWTO.txt. An EDID
727 data set will only be used for a particular connector,
728 if its name and a colon are prepended to the EDID
729 name.
731 dscc4.setup= [NET]
733 earlycon= [KNL] Output early console device and options.
734 uart[8250],io,<addr>[,options]
735 uart[8250],mmio,<addr>[,options]
736 uart[8250],mmio32,<addr>[,options]
737 Start an early, polled-mode console on the 8250/16550
738 UART at the specified I/O port or MMIO address.
739 MMIO inter-register address stride is either 8-bit
740 (mmio) or 32-bit (mmio32).
741 The options are the same as for ttyS, above.
743 earlyprintk= [X86,SH,BLACKFIN]
744 earlyprintk=vga
745 earlyprintk=serial[,ttySn[,baudrate]]
746 earlyprintk=ttySn[,baudrate]
747 earlyprintk=dbgp[debugController#]
749 Append ",keep" to not disable it when the real console
750 takes over.
752 Only vga or serial or usb debug port at a time.
754 Currently only ttyS0 and ttyS1 are supported.
756 Interaction with the standard serial driver is not
757 very good.
759 The VGA output is eventually overwritten by the real
760 console.
762 ekgdboc= [X86,KGDB] Allow early kernel console debugging
763 ekgdboc=kbd
765 This is designed to be used in conjunction with
766 the boot argument: earlyprintk=vga
768 edd= [EDD]
769 Format: {"off" | "on" | "skip[mbr]"}
771 eisa_irq_edge= [PARISC,HW]
772 See header of drivers/parisc/eisa.c.
774 elanfreq= [X86-32]
775 See comment before function elanfreq_setup() in
776 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
778 elevator= [IOSCHED]
779 Format: {"cfq" | "deadline" | "noop"}
780 See Documentation/block/cfq-iosched.txt and
781 Documentation/block/deadline-iosched.txt for details.
783 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
784 Specifies physical address of start of kernel core
785 image elf header and optionally the size. Generally
786 kexec loader will pass this option to capture kernel.
787 See Documentation/kdump/kdump.txt for details.
789 enable_mtrr_cleanup [X86]
790 The kernel tries to adjust MTRR layout from continuous
791 to discrete, to make X server driver able to add WB
792 entry later. This parameter enables that.
794 enable_timer_pin_1 [X86]
795 Enable PIN 1 of APIC timer
796 Can be useful to work around chipset bugs
797 (in particular on some ATI chipsets).
798 The kernel tries to set a reasonable default.
800 enforcing [SELINUX] Set initial enforcing status.
801 Format: {"0" | "1"}
802 See security/selinux/Kconfig help text.
803 0 -- permissive (log only, no denials).
804 1 -- enforcing (deny and log).
805 Default value is 0.
806 Value can be changed at runtime via /selinux/enforce.
808 erst_disable [ACPI]
809 Disable Error Record Serialization Table (ERST)
810 support.
812 ether= [HW,NET] Ethernet cards parameters
813 This option is obsoleted by the "netdev=" option, which
814 has equivalent usage. See its documentation for details.
816 evm= [EVM]
817 Format: { "fix" }
818 Permit 'security.evm' to be updated regardless of
819 current integrity status.
821 failslab=
822 fail_page_alloc=
823 fail_make_request=[KNL]
824 General fault injection mechanism.
825 Format: <interval>,<probability>,<space>,<times>
826 See also Documentation/fault-injection/.
828 floppy= [HW]
829 See Documentation/blockdev/floppy.txt.
831 force_pal_cache_flush
832 [IA-64] Avoid check_sal_cache_flush which may hang on
833 buggy SAL_CACHE_FLUSH implementations. Using this
834 parameter will force ia64_sal_cache_flush to call
835 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
837 ftrace=[tracer]
838 [FTRACE] will set and start the specified tracer
839 as early as possible in order to facilitate early
840 boot debugging.
842 ftrace_dump_on_oops[=orig_cpu]
843 [FTRACE] will dump the trace buffers on oops.
844 If no parameter is passed, ftrace will dump
845 buffers of all CPUs, but if you pass orig_cpu, it will
846 dump only the buffer of the CPU that triggered the
847 oops.
849 ftrace_filter=[function-list]
850 [FTRACE] Limit the functions traced by the function
851 tracer at boot up. function-list is a comma separated
852 list of functions. This list can be changed at run
853 time by the set_ftrace_filter file in the debugfs
854 tracing directory.
856 ftrace_notrace=[function-list]
857 [FTRACE] Do not trace the functions specified in
858 function-list. This list can be changed at run time
859 by the set_ftrace_notrace file in the debugfs
860 tracing directory.
862 ftrace_graph_filter=[function-list]
863 [FTRACE] Limit the top level callers functions traced
864 by the function graph tracer at boot up.
865 function-list is a comma separated list of functions
866 that can be changed at run time by the
867 set_graph_function file in the debugfs tracing directory.
869 gamecon.map[2|3]=
870 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
871 support via parallel port (up to 5 devices per port)
872 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
873 See also Documentation/input/joystick-parport.txt
875 gamma= [HW,DRM]
877 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
878 Format: off | on
879 default: on
881 gcov_persist= [GCOV] When non-zero (default), profiling data for
882 kernel modules is saved and remains accessible via
883 debugfs, even when the module is unloaded/reloaded.
884 When zero, profiling data is discarded and associated
885 debugfs files are removed at module unload time.
887 gpt [EFI] Forces disk with valid GPT signature but
888 invalid Protective MBR to be treated as GPT.
890 hashdist= [KNL,NUMA] Large hashes allocated during boot
891 are distributed across NUMA nodes. Defaults on
892 for 64-bit NUMA, off otherwise.
893 Format: 0 | 1 (for off | on)
895 hcl= [IA-64] SGI's Hardware Graph compatibility layer
897 hd= [EIDE] (E)IDE hard drive subsystem geometry
898 Format: <cyl>,<head>,<sect>
900 hest_disable [ACPI]
901 Disable Hardware Error Source Table (HEST) support;
902 corresponding firmware-first mode error processing
903 logic will be disabled.
905 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
906 size of <nn>. This works even on boxes that have no
907 highmem otherwise. This also works to reduce highmem
908 size on bigger boxes.
910 highres= [KNL] Enable/disable high resolution timer mode.
911 Valid parameters: "on", "off"
912 Default: "on"
914 hisax= [HW,ISDN]
915 See Documentation/isdn/README.HiSax.
917 hlt [BUGS=ARM,SH]
919 hpet= [X86-32,HPET] option to control HPET usage
920 Format: { enable (default) | disable | force |
921 verbose }
922 disable: disable HPET and use PIT instead
923 force: allow force enabled of undocumented chips (ICH4,
924 VIA, nVidia)
925 verbose: show contents of HPET registers during setup
927 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
928 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
929 On x86-64 and powerpc, this option can be specified
930 multiple times interleaved with hugepages= to reserve
931 huge pages of different sizes. Valid pages sizes on
932 x86-64 are 2M (when the CPU supports "pse") and 1G
933 (when the CPU supports the "pdpe1gb" cpuinfo flag)
934 Note that 1GB pages can only be allocated at boot time
935 using hugepages= and not freed afterwards.
937 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
938 terminal devices. Valid values: 0..8
939 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
940 If specified, z/VM IUCV HVC accepts connections
941 from listed z/VM user IDs only.
943 keep_bootcon [KNL]
944 Do not unregister boot console at start. This is only
945 useful for debugging when something happens in the window
946 between unregistering the boot console and initializing
947 the real console.
949 i2c_bus= [HW] Override the default board specific I2C bus speed
950 or register an additional I2C bus that is not
951 registered from board initialization code.
952 Format:
953 <bus_id>,<clkrate>
955 i8042.debug [HW] Toggle i8042 debug mode
956 i8042.direct [HW] Put keyboard port into non-translated mode
957 i8042.dumbkbd [HW] Pretend that controller can only read data from
958 keyboard and cannot control its state
959 (Don't attempt to blink the leds)
960 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
961 i8042.nokbd [HW] Don't check/create keyboard port
962 i8042.noloop [HW] Disable the AUX Loopback command while probing
963 for the AUX port
964 i8042.nomux [HW] Don't check presence of an active multiplexing
965 controller
966 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
967 controllers
968 i8042.notimeout [HW] Ignore timeout condition signalled by controller
969 i8042.reset [HW] Reset the controller during init and cleanup
970 i8042.unlock [HW] Unlock (ignore) the keylock
972 i810= [HW,DRM]
974 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
975 indicates that the driver is running on unsupported
976 hardware.
977 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
978 does not match list of supported models.
979 i8k.power_status
980 [HW] Report power status in /proc/i8k
981 (disabled by default)
982 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
983 capability is set.
985 i915.invert_brightness=
986 [DRM] Invert the sense of the variable that is used to
987 set the brightness of the panel backlight. Normally a
988 brightness value of 0 indicates backlight switched off,
989 and the maximum of the brightness value sets the backlight
990 to maximum brightness. If this parameter is set to 0
991 (default) and the machine requires it, or this parameter
992 is set to 1, a brightness value of 0 sets the backlight
993 to maximum brightness, and the maximum of the brightness
994 value switches the backlight off.
995 -1 -- never invert brightness
996 0 -- machine default
997 1 -- force brightness inversion
999 icn= [HW,ISDN]
1000 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1002 ide-core.nodma= [HW] (E)IDE subsystem
1003 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1004 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1005 .cdrom .chs .ignore_cable are additional options
1006 See Documentation/ide/ide.txt.
1008 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1009 Claim all unknown PCI IDE storage controllers.
1011 idle= [X86]
1012 Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
1013 Poll forces a polling idle loop that can slightly
1014 improve the performance of waking up a idle CPU, but
1015 will use a lot of power and make the system run hot.
1016 Not recommended.
1017 idle=mwait: On systems which support MONITOR/MWAIT but
1018 the kernel chose to not use it because it doesn't save
1019 as much power as a normal idle loop, use the
1020 MONITOR/MWAIT idle loop anyways. Performance should be
1021 the same as idle=poll.
1022 idle=halt: Halt is forced to be used for CPU idle.
1023 In such case C2/C3 won't be used again.
1024 idle=nomwait: Disable mwait for CPU C-states
1026 ignore_loglevel [KNL]
1027 Ignore loglevel setting - this will print /all/
1028 kernel messages to the console. Useful for debugging.
1029 We also add it as printk module parameter, so users
1030 could change it dynamically, usually by
1031 /sys/module/printk/parameters/ignore_loglevel.
1033 ihash_entries= [KNL]
1034 Set number of hash buckets for inode cache.
1036 ima_audit= [IMA]
1037 Format: { "0" | "1" }
1038 0 -- integrity auditing messages. (Default)
1039 1 -- enable informational integrity auditing messages.
1041 ima_hash= [IMA]
1042 Format: { "sha1" | "md5" }
1043 default: "sha1"
1045 ima_tcb [IMA]
1046 Load a policy which meets the needs of the Trusted
1047 Computing Base. This means IMA will measure all
1048 programs exec'd, files mmap'd for exec, and all files
1049 opened for read by uid=0.
1051 init= [KNL]
1052 Format: <full_path>
1053 Run specified binary instead of /sbin/init as init
1054 process.
1056 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1057 for working out where the kernel is dying during
1058 startup.
1060 initrd= [BOOT] Specify the location of the initial ramdisk
1062 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1063 Format: <irq>
1065 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1066 on
1067 Enable intel iommu driver.
1068 off
1069 Disable intel iommu driver.
1070 igfx_off [Default Off]
1071 By default, gfx is mapped as normal device. If a gfx
1072 device has a dedicated DMAR unit, the DMAR unit is
1073 bypassed by not enabling DMAR with this option. In
1074 this case, gfx device will use physical address for
1075 DMA.
1076 forcedac [x86_64]
1077 With this option iommu will not optimize to look
1078 for io virtual address below 32-bit forcing dual
1079 address cycle on pci bus for cards supporting greater
1080 than 32-bit addressing. The default is to look
1081 for translation below 32-bit and if not available
1082 then look in the higher range.
1083 strict [Default Off]
1084 With this option on every unmap_single operation will
1085 result in a hardware IOTLB flush operation as opposed
1086 to batching them for performance.
1087 sp_off [Default Off]
1088 By default, super page will be supported if Intel IOMMU
1089 has the capability. With this option, super page will
1090 not be supported.
1092 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1093 0 disables intel_idle and fall back on acpi_idle.
1094 1 to 6 specify maximum depth of C-state.
1096 intremap= [X86-64, Intel-IOMMU]
1097 on enable Interrupt Remapping (default)
1098 off disable Interrupt Remapping
1099 nosid disable Source ID checking
1100 no_x2apic_optout
1101 BIOS x2APIC opt-out request will be ignored
1103 iomem= Disable strict checking of access to MMIO memory
1104 strict regions from userspace.
1105 relaxed
1107 iommu= [x86]
1108 off
1109 force
1110 noforce
1111 biomerge
1112 panic
1113 nopanic
1114 merge
1115 nomerge
1116 forcesac
1117 soft
1118 pt [x86, IA-64]
1119 group_mf [x86, IA-64]
1122 io7= [HW] IO7 for Marvel based alpha systems
1123 See comment before marvel_specify_io7 in
1124 arch/alpha/kernel/core_marvel.c.
1126 io_delay= [X86] I/O delay method
1127 0x80
1128 Standard port 0x80 based delay
1129 0xed
1130 Alternate port 0xed based delay (needed on some systems)
1131 udelay
1132 Simple two microseconds delay
1133 none
1134 No delay
1136 ip= [IP_PNP]
1137 See Documentation/filesystems/nfs/nfsroot.txt.
1139 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1140 See comment before ip2_setup() in
1141 drivers/char/ip2/ip2base.c.
1143 irqfixup [HW]
1144 When an interrupt is not handled search all handlers
1145 for it. Intended to get systems with badly broken
1146 firmware running.
1148 irqpoll [HW]
1149 When an interrupt is not handled search all handlers
1150 for it. Also check all handlers each timer
1151 interrupt. Intended to get systems with badly broken
1152 firmware running.
1154 isapnp= [ISAPNP]
1155 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1157 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1158 Format:
1159 <cpu number>,...,<cpu number>
1160 or
1161 <cpu number>-<cpu number>
1162 (must be a positive range in ascending order)
1163 or a mixture
1164 <cpu number>,...,<cpu number>-<cpu number>
1166 This option can be used to specify one or more CPUs
1167 to isolate from the general SMP balancing and scheduling
1168 algorithms. You can move a process onto or off an
1169 "isolated" CPU via the CPU affinity syscalls or cpuset.
1170 <cpu number> begins at 0 and the maximum value is
1171 "number of CPUs in system - 1".
1173 This option is the preferred way to isolate CPUs. The
1174 alternative -- manually setting the CPU mask of all
1175 tasks in the system -- can cause problems and
1176 suboptimal load balancer performance.
1178 iucv= [HW,NET]
1180 js= [HW,JOY] Analog joystick
1181 See Documentation/input/joystick.txt.
1183 keepinitrd [HW,ARM]
1185 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1186 specifies the amount of memory usable by the kernel
1187 for non-movable allocations. The requested amount is
1188 spread evenly throughout all nodes in the system. The
1189 remaining memory in each node is used for Movable
1190 pages. In the event, a node is too small to have both
1191 kernelcore and Movable pages, kernelcore pages will
1192 take priority and other nodes will have a larger number
1193 of kernelcore pages. The Movable zone is used for the
1194 allocation of pages that may be reclaimed or moved
1195 by the page migration subsystem. This means that
1196 HugeTLB pages may not be allocated from this zone.
1197 Note that allocations like PTEs-from-HighMem still
1198 use the HighMem zone if it exists, and the Normal
1199 zone if it does not.
1201 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1202 Format: <Controller#>[,poll interval]
1203 The controller # is the number of the ehci usb debug
1204 port as it is probed via PCI. The poll interval is
1205 optional and is the number seconds in between
1206 each poll cycle to the debug port in case you need
1207 the functionality for interrupting the kernel with
1208 gdb or control-c on the dbgp connection. When
1209 not using this parameter you use sysrq-g to break into
1210 the kernel debugger.
1212 kgdboc= [KGDB,HW] kgdb over consoles.
1213 Requires a tty driver that supports console polling,
1214 or a supported polling keyboard driver (non-usb).
1215 Serial only format: <serial_device>[,baud]
1216 keyboard only format: kbd
1217 keyboard and serial format: kbd,<serial_device>[,baud]
1218 Optional Kernel mode setting:
1219 kms, kbd format: kms,kbd
1220 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1222 kgdbwait [KGDB] Stop kernel execution and enter the
1223 kernel debugger at the earliest opportunity.
1225 kmac= [MIPS] korina ethernet MAC address.
1226 Configure the RouterBoard 532 series on-chip
1227 Ethernet adapter MAC address.
1229 kmemleak= [KNL] Boot-time kmemleak enable/disable
1230 Valid arguments: on, off
1231 Default: on
1233 kstack=N [X86] Print N words from the kernel stack
1234 in oops dumps.
1236 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1237 Default is 0 (don't ignore, but inject #GP)
1239 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1240 KVM MMU at runtime.
1241 Default is 0 (off)
1243 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1244 Default is 1 (enabled)
1246 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1247 for all guests.
1248 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1250 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1251 (virtualized MMU) support on capable Intel chips.
1252 Default is 1 (enabled)
1254 kvm-intel.emulate_invalid_guest_state=
1255 [KVM,Intel] Enable emulation of invalid guest states
1256 Default is 0 (disabled)
1258 kvm-intel.flexpriority=
1259 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1260 Default is 1 (enabled)
1262 kvm-intel.nested=
1263 [KVM,Intel] Enable VMX nesting (nVMX).
1264 Default is 0 (disabled)
1266 kvm-intel.unrestricted_guest=
1267 [KVM,Intel] Disable unrestricted guest feature
1268 (virtualized real and unpaged mode) on capable
1269 Intel chips. Default is 1 (enabled)
1271 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1272 feature (tagged TLBs) on capable Intel chips.
1273 Default is 1 (enabled)
1275 l2cr= [PPC]
1277 l3cr= [PPC]
1279 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1280 disabled it.
1282 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1283 in C2 power state.
1285 libata.dma= [LIBATA] DMA control
1286 libata.dma=0 Disable all PATA and SATA DMA
1287 libata.dma=1 PATA and SATA Disk DMA only
1288 libata.dma=2 ATAPI (CDROM) DMA only
1289 libata.dma=4 Compact Flash DMA only
1290 Combinations also work, so libata.dma=3 enables DMA
1291 for disks and CDROMs, but not CFs.
1293 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1294 libata.ignore_hpa=0 keep BIOS limits (default)
1295 libata.ignore_hpa=1 ignore limits, using full disk
1297 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1298 when set.
1299 Format: <int>
1301 libata.force= [LIBATA] Force configurations. The format is comma
1302 separated list of "[ID:]VAL" where ID is
1303 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1304 matching port, link or device. Basically, it matches
1305 the ATA ID string printed on console by libata. If
1306 the whole ID part is omitted, the last PORT and DEVICE
1307 values are used. If ID hasn't been specified yet, the
1308 configuration applies to all ports, links and devices.
1310 If only DEVICE is omitted, the parameter applies to
1311 the port and all links and devices behind it. DEVICE
1312 number of 0 either selects the first device or the
1313 first fan-out link behind PMP device. It does not
1314 select the host link. DEVICE number of 15 selects the
1315 host link and device attached to it.
1317 The VAL specifies the configuration to force. As long
1318 as there's no ambiguity shortcut notation is allowed.
1319 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1320 The following configurations can be forced.
1322 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1323 Any ID with matching PORT is used.
1325 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1327 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1328 udma[/][16,25,33,44,66,100,133] notation is also
1329 allowed.
1331 * [no]ncq: Turn on or off NCQ.
1333 * nohrst, nosrst, norst: suppress hard, soft
1334 and both resets.
1336 * dump_id: dump IDENTIFY data.
1338 If there are multiple matching configurations changing
1339 the same attribute, the last one is used.
1341 memblock=debug [KNL] Enable memblock debug messages.
1343 load_ramdisk= [RAM] List of ramdisks to load from floppy
1344 See Documentation/blockdev/ramdisk.txt.
1346 lockd.nlm_grace_period=P [NFS] Assign grace period.
1347 Format: <integer>
1349 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1350 Format: <integer>
1352 lockd.nlm_timeout=T [NFS] Assign timeout value.
1353 Format: <integer>
1355 lockd.nlm_udpport=M [NFS] Assign UDP port.
1356 Format: <integer>
1358 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1359 Format: <irq>
1361 loglevel= All Kernel Messages with a loglevel smaller than the
1362 console loglevel will be printed to the console. It can
1363 also be changed with klogd or other programs. The
1364 loglevels are defined as follows:
1366 0 (KERN_EMERG) system is unusable
1367 1 (KERN_ALERT) action must be taken immediately
1368 2 (KERN_CRIT) critical conditions
1369 3 (KERN_ERR) error conditions
1370 4 (KERN_WARNING) warning conditions
1371 5 (KERN_NOTICE) normal but significant condition
1372 6 (KERN_INFO) informational
1373 7 (KERN_DEBUG) debug-level messages
1375 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1376 in bytes. n must be a power of two. The default
1377 size is set in the kernel config file.
1379 logo.nologo [FB] Disables display of the built-in Linux logo.
1380 This may be used to provide more screen space for
1381 kernel log messages and is useful when debugging
1382 kernel boot problems.
1384 lp=0 [LP] Specify parallel ports to use, e.g,
1385 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1386 lp=reset first parallel port). 'lp=0' disables the
1387 lp=auto printer driver. 'lp=reset' (which can be
1388 specified in addition to the ports) causes
1389 attached printers to be reset. Using
1390 lp=port1,port2,... specifies the parallel ports
1391 to associate lp devices with, starting with
1392 lp0. A port specification may be 'none' to skip
1393 that lp device, or a parport name such as
1394 'parport0'. Specifying 'lp=auto' instead of a
1395 port specification list means that device IDs
1396 from each port should be examined, to see if
1397 an IEEE 1284-compliant printer is attached; if
1398 so, the driver will manage that printer.
1399 See also header of drivers/char/lp.c.
1401 lpj=n [KNL]
1402 Sets loops_per_jiffy to given constant, thus avoiding
1403 time-consuming boot-time autodetection (up to 250 ms per
1404 CPU). 0 enables autodetection (default). To determine
1405 the correct value for your kernel, boot with normal
1406 autodetection and see what value is printed. Note that
1407 on SMP systems the preset will be applied to all CPUs,
1408 which is likely to cause problems if your CPUs need
1409 significantly divergent settings. An incorrect value
1410 will cause delays in the kernel to be wrong, leading to
1411 unpredictable I/O errors and other breakage. Although
1412 unlikely, in the extreme case this might damage your
1413 hardware.
1415 ltpc= [NET]
1416 Format: <io>,<irq>,<dma>
1418 machvec= [IA-64] Force the use of a particular machine-vector
1419 (machvec) in a generic kernel.
1420 Example: machvec=hpzx1_swiotlb
1422 machtype= [Loongson] Share the same kernel image file between different
1423 yeeloong laptop.
1424 Example: machtype=lemote-yeeloong-2f-7inch
1426 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1427 than or equal to this physical address is ignored.
1429 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1430 should make use of. maxcpus=n : n >= 0 limits the
1431 kernel to using 'n' processors. n=0 is a special case,
1432 it is equivalent to "nosmp", which also disables
1433 the IO APIC.
1435 max_loop= [LOOP] The number of loop block devices that get
1436 (loop.max_loop) unconditionally pre-created at init time. The default
1437 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1438 of statically allocating a predefined number, loop
1439 devices can be requested on-demand with the
1440 /dev/loop-control interface.
1442 mcatest= [IA-64]
1444 mce [X86-32] Machine Check Exception
1446 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1448 md= [HW] RAID subsystems devices and level
1449 See Documentation/md.txt.
1451 mdacon= [MDA]
1452 Format: <first>,<last>
1453 Specifies range of consoles to be captured by the MDA.
1455 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1456 Amount of memory to be used when the kernel is not able
1457 to see the whole system memory or for test.
1458 [X86-32] Use together with memmap= to avoid physical
1459 address space collisions. Without memmap= PCI devices
1460 could be placed at addresses belonging to unused RAM.
1462 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1463 memory.
1465 memchunk=nn[KMG]
1466 [KNL,SH] Allow user to override the default size for
1467 per-device physically contiguous DMA buffers.
1469 memmap=exactmap [KNL,X86] Enable setting of an exact
1470 E820 memory map, as specified by the user.
1471 Such memmap=exactmap lines can be constructed based on
1472 BIOS output or other requirements. See the memmap=nn@ss
1473 option description.
1475 memmap=nn[KMG]@ss[KMG]
1476 [KNL] Force usage of a specific region of memory
1477 Region of memory to be used, from ss to ss+nn.
1479 memmap=nn[KMG]#ss[KMG]
1480 [KNL,ACPI] Mark specific memory as ACPI data.
1481 Region of memory to be used, from ss to ss+nn.
1483 memmap=nn[KMG]$ss[KMG]
1484 [KNL,ACPI] Mark specific memory as reserved.
1485 Region of memory to be used, from ss to ss+nn.
1486 Example: Exclude memory from 0x18690000-0x1869ffff
1487 memmap=64K$0x18690000
1488 or
1489 memmap=0x10000$0x18690000
1491 memory_corruption_check=0/1 [X86]
1492 Some BIOSes seem to corrupt the first 64k of
1493 memory when doing things like suspend/resume.
1494 Setting this option will scan the memory
1495 looking for corruption. Enabling this will
1496 both detect corruption and prevent the kernel
1497 from using the memory being corrupted.
1498 However, its intended as a diagnostic tool; if
1499 repeatable BIOS-originated corruption always
1500 affects the same memory, you can use memmap=
1501 to prevent the kernel from using that memory.
1503 memory_corruption_check_size=size [X86]
1504 By default it checks for corruption in the low
1505 64k, making this memory unavailable for normal
1506 use. Use this parameter to scan for
1507 corruption in more or less memory.
1509 memory_corruption_check_period=seconds [X86]
1510 By default it checks for corruption every 60
1511 seconds. Use this parameter to check at some
1512 other rate. 0 disables periodic checking.
1514 memtest= [KNL,X86] Enable memtest
1515 Format: <integer>
1516 default : 0 <disable>
1517 Specifies the number of memtest passes to be
1518 performed. Each pass selects another test
1519 pattern from a given set of patterns. Memtest
1520 fills the memory with this pattern, validates
1521 memory contents and reserves bad memory
1522 regions that are detected.
1524 meye.*= [HW] Set MotionEye Camera parameters
1525 See Documentation/video4linux/meye.txt.
1527 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1528 Multi-Function General Purpose Timers on AMD Geode
1529 platforms.
1531 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1532 the BIOS has incorrectly applied a workaround. TinyBIOS
1533 version 0.98 is known to be affected, 0.99 fixes the
1534 problem by letting the user disable the workaround.
1536 mga= [HW,DRM]
1538 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1539 physical address is ignored.
1541 mini2440= [ARM,HW,KNL]
1542 Format:[0..2][b][c][t]
1543 Default: "0tb"
1544 MINI2440 configuration specification:
1545 0 - The attached screen is the 3.5" TFT
1546 1 - The attached screen is the 7" TFT
1547 2 - The VGA Shield is attached (1024x768)
1548 Leaving out the screen size parameter will not load
1549 the TFT driver, and the framebuffer will be left
1550 unconfigured.
1551 b - Enable backlight. The TFT backlight pin will be
1552 linked to the kernel VESA blanking code and a GPIO
1553 LED. This parameter is not necessary when using the
1554 VGA shield.
1555 c - Enable the s3c camera interface.
1556 t - Reserved for enabling touchscreen support. The
1557 touchscreen support is not enabled in the mainstream
1558 kernel as of 2.6.30, a preliminary port can be found
1559 in the "bleeding edge" mini2440 support kernel at
1560 http://repo.or.cz/w/linux-2.6/mini2440.git
1562 mminit_loglevel=
1563 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1564 parameter allows control of the logging verbosity for
1565 the additional memory initialisation checks. A value
1566 of 0 disables mminit logging and a level of 4 will
1567 log everything. Information is printed at KERN_DEBUG
1568 so loglevel=8 may also need to be specified.
1570 mousedev.tap_time=
1571 [MOUSE] Maximum time between finger touching and
1572 leaving touchpad surface for touch to be considered
1573 a tap and be reported as a left button click (for
1574 touchpads working in absolute mode only).
1575 Format: <msecs>
1576 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1577 reporting absolute coordinates, such as tablets
1578 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1579 reporting absolute coordinates, such as tablets
1581 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1582 is similar to kernelcore except it specifies the
1583 amount of memory used for migratable allocations.
1584 If both kernelcore and movablecore is specified,
1585 then kernelcore will be at *least* the specified
1586 value but may be more. If movablecore on its own
1587 is specified, the administrator must be careful
1588 that the amount of memory usable for all allocations
1589 is not too small.
1591 MTD_Partition= [MTD]
1592 Format: <name>,<region-number>,<size>,<offset>
1594 MTD_Region= [MTD] Format:
1595 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1597 mtdparts= [MTD]
1598 See drivers/mtd/cmdlinepart.c.
1600 multitce=off [PPC] This parameter disables the use of the pSeries
1601 firmware feature for updating multiple TCE entries
1602 at a time.
1604 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1606 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1608 boundary - index of last SLC block on Flex-OneNAND.
1609 The remaining blocks are configured as MLC blocks.
1610 lock - Configure if Flex-OneNAND boundary should be locked.
1611 Once locked, the boundary cannot be changed.
1612 1 indicates lock status, 0 indicates unlock status.
1614 mtdset= [ARM]
1615 ARM/S3C2412 JIVE boot control
1617 See arch/arm/mach-s3c2412/mach-jive.c
1619 mtouchusb.raw_coordinates=
1620 [HW] Make the MicroTouch USB driver use raw coordinates
1621 ('y', default) or cooked coordinates ('n')
1623 mtrr_chunk_size=nn[KMG] [X86]
1624 used for mtrr cleanup. It is largest continuous chunk
1625 that could hold holes aka. UC entries.
1627 mtrr_gran_size=nn[KMG] [X86]
1628 Used for mtrr cleanup. It is granularity of mtrr block.
1629 Default is 1.
1630 Large value could prevent small alignment from
1631 using up MTRRs.
1633 mtrr_spare_reg_nr=n [X86]
1634 Format: <integer>
1635 Range: 0,7 : spare reg number
1636 Default : 1
1637 Used for mtrr cleanup. It is spare mtrr entries number.
1638 Set to 2 or more if your graphical card needs more.
1640 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1642 netdev= [NET] Network devices parameters
1643 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1644 Note that mem_start is often overloaded to mean
1645 something different and driver-specific.
1646 This usage is only documented in each driver source
1647 file if at all.
1649 nf_conntrack.acct=
1650 [NETFILTER] Enable connection tracking flow accounting
1651 0 to disable accounting
1652 1 to enable accounting
1653 Default value is 0.
1655 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1656 See Documentation/filesystems/nfs/nfsroot.txt.
1658 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1659 See Documentation/filesystems/nfs/nfsroot.txt.
1661 nfsrootdebug [NFS] enable nfsroot debugging messages.
1662 See Documentation/filesystems/nfs/nfsroot.txt.
1664 nfs.callback_tcpport=
1665 [NFS] set the TCP port on which the NFSv4 callback
1666 channel should listen.
1668 nfs.cache_getent=
1669 [NFS] sets the pathname to the program which is used
1670 to update the NFS client cache entries.
1672 nfs.cache_getent_timeout=
1673 [NFS] sets the timeout after which an attempt to
1674 update a cache entry is deemed to have failed.
1676 nfs.idmap_cache_timeout=
1677 [NFS] set the maximum lifetime for idmapper cache
1678 entries.
1680 nfs.enable_ino64=
1681 [NFS] enable 64-bit inode numbers.
1682 If zero, the NFS client will fake up a 32-bit inode
1683 number for the readdir() and stat() syscalls instead
1684 of returning the full 64-bit number.
1685 The default is to return 64-bit inode numbers.
1687 nfs.max_session_slots=
1688 [NFSv4.1] Sets the maximum number of session slots
1689 the client will attempt to negotiate with the server.
1690 This limits the number of simultaneous RPC requests
1691 that the client can send to the NFSv4.1 server.
1692 Note that there is little point in setting this
1693 value higher than the max_tcp_slot_table_limit.
1695 nfs.nfs4_disable_idmapping=
1696 [NFSv4] When set to the default of '1', this option
1697 ensures that both the RPC level authentication
1698 scheme and the NFS level operations agree to use
1699 numeric uids/gids if the mount is using the
1700 'sec=sys' security flavour. In effect it is
1701 disabling idmapping, which can make migration from
1702 legacy NFSv2/v3 systems to NFSv4 easier.
1703 Servers that do not support this mode of operation
1704 will be autodetected by the client, and it will fall
1705 back to using the idmapper.
1706 To turn off this behaviour, set the value to '0'.
1708 nfs.send_implementation_id =
1709 [NFSv4.1] Send client implementation identification
1710 information in exchange_id requests.
1711 If zero, no implementation identification information
1712 will be sent.
1713 The default is to send the implementation identification
1714 information.
1716 nfsd.nfs4_disable_idmapping=
1717 [NFSv4] When set to the default of '1', the NFSv4
1718 server will return only numeric uids and gids to
1719 clients using auth_sys, and will accept numeric uids
1720 and gids from such clients. This is intended to ease
1721 migration from NFSv2/v3.
1723 objlayoutdriver.osd_login_prog=
1724 [NFS] [OBJLAYOUT] sets the pathname to the program which
1725 is used to automatically discover and login into new
1726 osd-targets. Please see:
1727 Documentation/filesystems/pnfs.txt for more explanations
1729 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1730 when a NMI is triggered.
1731 Format: [state][,regs][,debounce][,die]
1733 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1734 Format: [panic,][nopanic,][num]
1735 Valid num: 0
1736 0 - turn nmi_watchdog off
1737 When panic is specified, panic when an NMI watchdog
1738 timeout occurs (or 'nopanic' to override the opposite
1739 default).
1740 This is useful when you use a panic=... timeout and
1741 need the box quickly up again.
1743 netpoll.carrier_timeout=
1744 [NET] Specifies amount of time (in seconds) that
1745 netpoll should wait for a carrier. By default netpoll
1746 waits 4 seconds.
1748 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1749 emulation library even if a 387 maths coprocessor
1750 is present.
1752 no_console_suspend
1753 [HW] Never suspend the console
1754 Disable suspending of consoles during suspend and
1755 hibernate operations. Once disabled, debugging
1756 messages can reach various consoles while the rest
1757 of the system is being put to sleep (ie, while
1758 debugging driver suspend/resume hooks). This may
1759 not work reliably with all consoles, but is known
1760 to work with serial and VGA consoles.
1761 To facilitate more flexible debugging, we also add
1762 console_suspend, a printk module parameter to control
1763 it. Users could use console_suspend (usually
1764 /sys/module/printk/parameters/console_suspend) to
1765 turn on/off it dynamically.
1767 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1768 caches in the slab allocator. Saves per-node memory,
1769 but will impact performance.
1771 noalign [KNL,ARM]
1773 noapic [SMP,APIC] Tells the kernel to not make use of any
1774 IOAPICs that may be present in the system.
1776 noautogroup Disable scheduler automatic task group creation.
1778 nobats [PPC] Do not use BATs for mapping kernel lowmem
1779 on "Classic" PPC cores.
1781 nocache [ARM]
1783 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1785 nodelayacct [KNL] Disable per-task delay accounting
1787 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1789 nodsp [SH] Disable hardware DSP at boot time.
1791 noefi [X86] Disable EFI runtime services support.
1793 noexec [IA-64]
1795 noexec [X86]
1796 On X86-32 available only on PAE configured kernels.
1797 noexec=on: enable non-executable mappings (default)
1798 noexec=off: disable non-executable mappings
1800 nosmep [X86]
1801 Disable SMEP (Supervisor Mode Execution Protection)
1802 even if it is supported by processor.
1804 noexec32 [X86-64]
1805 This affects only 32-bit executables.
1806 noexec32=on: enable non-executable mappings (default)
1807 read doesn't imply executable mappings
1808 noexec32=off: disable non-executable mappings
1809 read implies executable mappings
1811 nofpu [SH] Disable hardware FPU at boot time.
1813 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1814 register save and restore. The kernel will only save
1815 legacy floating-point registers on task switch.
1817 noxsave [BUGS=X86] Disables x86 extended register state save
1818 and restore using xsave. The kernel will fallback to
1819 enabling legacy floating-point and sse state.
1821 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1822 wfi(ARM) instruction doesn't work correctly and not to
1823 use it. This is also useful when using JTAG debugger.
1825 no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1826 instruction doesn't work correctly and not to
1827 use it.
1829 no_file_caps Tells the kernel not to honor file capabilities. The
1830 only way then for a file to be executed with privilege
1831 is to be setuid root or executed by root.
1833 nohalt [IA-64] Tells the kernel not to use the power saving
1834 function PAL_HALT_LIGHT when idle. This increases
1835 power-consumption. On the positive side, it reduces
1836 interrupt wake-up latency, which may improve performance
1837 in certain environments such as networked servers or
1838 real-time systems.
1840 nohz= [KNL] Boottime enable/disable dynamic ticks
1841 Valid arguments: on, off
1842 Default: on
1844 noiotrap [SH] Disables trapped I/O port accesses.
1846 noirqdebug [X86-32] Disables the code which attempts to detect and
1847 disable unhandled interrupt sources.
1849 no_timer_check [X86,APIC] Disables the code which tests for
1850 broken timer IRQ sources.
1852 noisapnp [ISAPNP] Disables ISA PnP code.
1854 noinitrd [RAM] Tells the kernel not to load any configured
1855 initial RAM disk.
1857 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1858 remapping.
1859 [Deprecated - use intremap=off]
1861 nointroute [IA-64]
1863 nojitter [IA-64] Disables jitter checking for ITC timers.
1865 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1867 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1868 fault handling.
1870 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1871 steal time is computed, but won't influence scheduler
1872 behaviour
1874 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1876 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1878 noltlbs [PPC] Do not use large page/tlb entries for kernel
1879 lowmem mapping on PPC40x.
1881 nomca [IA-64] Disable machine check abort handling
1883 nomce [X86-32] Machine Check Exception
1885 nomfgpt [X86-32] Disable Multi-Function General Purpose
1886 Timer usage (for AMD Geode machines).
1888 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
1889 shutdown the other cpus. Instead use the REBOOT_VECTOR
1890 irq.
1892 nomodule Disable module load
1894 nopat [X86] Disable PAT (page attribute table extension of
1895 pagetables) support.
1897 norandmaps Don't use address space randomization. Equivalent to
1898 echo 0 > /proc/sys/kernel/randomize_va_space
1900 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1902 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1903 with UP alternatives
1905 noresidual [PPC] Don't use residual data on PReP machines.
1907 nordrand [X86] Disable the direct use of the RDRAND
1908 instruction even if it is supported by the
1909 processor. RDRAND is still available to user
1910 space applications.
1912 noresume [SWSUSP] Disables resume and restores original swap
1913 space.
1915 no-scroll [VGA] Disables scrollback.
1916 This is required for the Braillex ib80-piezo Braille
1917 reader made by F.H. Papenmeier (Germany).
1919 nosbagart [IA-64]
1921 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1923 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1924 and disable the IO APIC. legacy for "maxcpus=0".
1926 nosoftlockup [KNL] Disable the soft-lockup detector.
1928 nosync [HW,M68K] Disables sync negotiation for all devices.
1930 notsc [BUGS=X86-32] Disable Time Stamp Counter
1932 nousb [USB] Disable the USB subsystem
1934 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1936 nowb [ARM]
1938 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1940 nptcg= [IA-64] Override max number of concurrent global TLB
1941 purges which is reported from either PAL_VM_SUMMARY or
1942 SAL PALO.
1944 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1945 could support. nr_cpus=n : n >= 1 limits the kernel to
1946 supporting 'n' processors. Later in runtime you can not
1947 use hotplug cpu feature to put more cpu back to online.
1948 just like you compile the kernel NR_CPUS=n
1950 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1952 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1953 one of ['zone', 'node', 'default'] can be specified
1954 This can be set from sysctl after boot.
1955 See Documentation/sysctl/vm.txt for details.
1957 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1958 See Documentation/debugging-via-ohci1394.txt for more
1959 info.
1961 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1962 Rather than timing out after 20 ms if an EC
1963 command is not properly ACKed, override the length
1964 of the timeout. We have interrupts disabled while
1965 waiting for the ACK, so if this is set too high
1966 interrupts *may* be lost!
1968 omap_mux= [OMAP] Override bootloader pin multiplexing.
1969 Format: <mux_mode0.mode_name=value>...
1970 For example, to override I2C bus2:
1971 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1973 oprofile.timer= [HW]
1974 Use timer interrupt instead of performance counters
1976 oprofile.cpu_type= Force an oprofile cpu type
1977 This might be useful if you have an older oprofile
1978 userland or if you want common events.
1979 Format: { arch_perfmon }
1980 arch_perfmon: [X86] Force use of architectural
1981 perfmon on Intel CPUs instead of the
1982 CPU specific event set.
1983 timer: [X86] Force use of architectural NMI
1984 timer mode (see also oprofile.timer
1985 for generic hr timer mode)
1986 [s390] Force legacy basic mode sampling
1987 (report cpu_type "timer")
1989 oops=panic Always panic on oopses. Default is to just kill the
1990 process, but there is a small probability of
1991 deadlocking the machine.
1992 This will also cause panics on machine check exceptions.
1993 Useful together with panic=30 to trigger a reboot.
1995 OSS [HW,OSS]
1996 See Documentation/sound/oss/oss-parameters.txt
1998 panic= [KNL] Kernel behaviour on panic: delay <timeout>
1999 timeout > 0: seconds before rebooting
2000 timeout = 0: wait forever
2001 timeout < 0: reboot immediately
2002 Format: <timeout>
2004 parkbd.port= [HW] Parallel port number the keyboard adapter is
2005 connected to, default is 0.
2006 Format: <parport#>
2007 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2008 0 for XT, 1 for AT (default is AT).
2009 Format: <mode>
2011 parport= [HW,PPT] Specify parallel ports. 0 disables.
2012 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2013 Use 'auto' to force the driver to use any
2014 IRQ/DMA settings detected (the default is to
2015 ignore detected IRQ/DMA settings because of
2016 possible conflicts). You can specify the base
2017 address, IRQ, and DMA settings; IRQ and DMA
2018 should be numbers, or 'auto' (for using detected
2019 settings on that particular port), or 'nofifo'
2020 (to avoid using a FIFO even if it is detected).
2021 Parallel ports are assigned in the order they
2022 are specified on the command line, starting
2023 with parport0.
2025 parport_init_mode= [HW,PPT]
2026 Configure VIA parallel port to operate in
2027 a specific mode. This is necessary on Pegasos
2028 computer where firmware has no options for setting
2029 up parallel port mode and sets it to spp.
2030 Currently this function knows 686a and 8231 chips.
2031 Format: [spp|ps2|epp|ecp|ecpepp]
2033 pause_on_oops=
2034 Halt all CPUs after the first oops has been printed for
2035 the specified number of seconds. This is to be used if
2036 your oopses keep scrolling off the screen.
2038 pcbit= [HW,ISDN]
2040 pcd. [PARIDE]
2041 See header of drivers/block/paride/pcd.c.
2042 See also Documentation/blockdev/paride.txt.
2044 pci=option[,option...] [PCI] various PCI subsystem options:
2045 earlydump [X86] dump PCI config space before the kernel
2046 changes anything
2047 off [X86] don't probe for the PCI bus
2048 bios [X86-32] force use of PCI BIOS, don't access
2049 the hardware directly. Use this if your machine
2050 has a non-standard PCI host bridge.
2051 nobios [X86-32] disallow use of PCI BIOS, only direct
2052 hardware access methods are allowed. Use this
2053 if you experience crashes upon bootup and you
2054 suspect they are caused by the BIOS.
2055 conf1 [X86] Force use of PCI Configuration
2056 Mechanism 1.
2057 conf2 [X86] Force use of PCI Configuration
2058 Mechanism 2.
2059 noaer [PCIE] If the PCIEAER kernel config parameter is
2060 enabled, this kernel boot option can be used to
2061 disable the use of PCIE advanced error reporting.
2062 nodomains [PCI] Disable support for multiple PCI
2063 root domains (aka PCI segments, in ACPI-speak).
2064 nommconf [X86] Disable use of MMCONFIG for PCI
2065 Configuration
2066 check_enable_amd_mmconf [X86] check for and enable
2067 properly configured MMIO access to PCI
2068 config space on AMD family 10h CPU
2069 nomsi [MSI] If the PCI_MSI kernel config parameter is
2070 enabled, this kernel boot option can be used to
2071 disable the use of MSI interrupts system-wide.
2072 noioapicquirk [APIC] Disable all boot interrupt quirks.
2073 Safety option to keep boot IRQs enabled. This
2074 should never be necessary.
2075 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2076 primary IO-APIC for bridges that cannot disable
2077 boot IRQs. This fixes a source of spurious IRQs
2078 when the system masks IRQs.
2079 noioapicreroute [APIC] Disable workaround that uses the
2080 boot IRQ equivalent of an IRQ that connects to
2081 a chipset where boot IRQs cannot be disabled.
2082 The opposite of ioapicreroute.
2083 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2084 routing table. These calls are known to be buggy
2085 on several machines and they hang the machine
2086 when used, but on other computers it's the only
2087 way to get the interrupt routing table. Try
2088 this option if the kernel is unable to allocate
2089 IRQs or discover secondary PCI buses on your
2090 motherboard.
2091 rom [X86] Assign address space to expansion ROMs.
2092 Use with caution as certain devices share
2093 address decoders between ROMs and other
2094 resources.
2095 norom [X86] Do not assign address space to
2096 expansion ROMs that do not already have
2097 BIOS assigned address ranges.
2098 nobar [X86] Do not assign address space to the
2099 BARs that weren't assigned by the BIOS.
2100 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2101 assigned automatically to PCI devices. You can
2102 make the kernel exclude IRQs of your ISA cards
2103 this way.
2104 pirqaddr=0xAAAAA [X86] Specify the physical address
2105 of the PIRQ table (normally generated
2106 by the BIOS) if it is outside the
2107 F0000h-100000h range.
2108 lastbus=N [X86] Scan all buses thru bus #N. Can be
2109 useful if the kernel is unable to find your
2110 secondary buses and you want to tell it
2111 explicitly which ones they are.
2112 assign-busses [X86] Always assign all PCI bus
2113 numbers ourselves, overriding
2114 whatever the firmware may have done.
2115 usepirqmask [X86] Honor the possible IRQ mask stored
2116 in the BIOS $PIR table. This is needed on
2117 some systems with broken BIOSes, notably
2118 some HP Pavilion N5400 and Omnibook XE3
2119 notebooks. This will have no effect if ACPI
2120 IRQ routing is enabled.
2121 noacpi [X86] Do not use ACPI for IRQ routing
2122 or for PCI scanning.
2123 use_crs [X86] Use PCI host bridge window information
2124 from ACPI. On BIOSes from 2008 or later, this
2125 is enabled by default. If you need to use this,
2126 please report a bug.
2127 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2128 If you need to use this, please report a bug.
2129 routeirq Do IRQ routing for all PCI devices.
2130 This is normally done in pci_enable_device(),
2131 so this option is a temporary workaround
2132 for broken drivers that don't call it.
2133 skip_isa_align [X86] do not align io start addr, so can
2134 handle more pci cards
2135 firmware [ARM] Do not re-enumerate the bus but instead
2136 just use the configuration from the
2137 bootloader. This is currently used on
2138 IXP2000 systems where the bus has to be
2139 configured a certain way for adjunct CPUs.
2140 noearly [X86] Don't do any early type 1 scanning.
2141 This might help on some broken boards which
2142 machine check when some devices' config space
2143 is read. But various workarounds are disabled
2144 and some IOMMU drivers will not work.
2145 bfsort Sort PCI devices into breadth-first order.
2146 This sorting is done to get a device
2147 order compatible with older (<= 2.4) kernels.
2148 nobfsort Don't sort PCI devices into breadth-first order.
2149 cbiosize=nn[KMG] The fixed amount of bus space which is
2150 reserved for the CardBus bridge's IO window.
2151 The default value is 256 bytes.
2152 cbmemsize=nn[KMG] The fixed amount of bus space which is
2153 reserved for the CardBus bridge's memory
2154 window. The default value is 64 megabytes.
2155 resource_alignment=
2156 Format:
2157 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2158 Specifies alignment and device to reassign
2159 aligned memory resources.
2160 If <order of align> is not specified,
2161 PAGE_SIZE is used as alignment.
2162 PCI-PCI bridge can be specified, if resource
2163 windows need to be expanded.
2164 ecrc= Enable/disable PCIe ECRC (transaction layer
2165 end-to-end CRC checking).
2166 bios: Use BIOS/firmware settings. This is the
2167 the default.
2168 off: Turn ECRC off
2169 on: Turn ECRC on.
2170 realloc= Enable/disable reallocating PCI bridge resources
2171 if allocations done by BIOS are too small to
2172 accommodate resources required by all child
2173 devices.
2174 off: Turn realloc off
2175 on: Turn realloc on
2176 realloc same as realloc=on
2177 noari do not use PCIe ARI.
2179 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2180 Management.
2181 off Disable ASPM.
2182 force Enable ASPM even on devices that claim not to support it.
2183 WARNING: Forcing ASPM on may cause system lockups.
2185 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2186 nomsi Do not use MSI for PCI Express Native Hotplug (this
2187 makes all PCIe ports use INTx for hotplug services).
2189 pcie_ports= [PCIE] PCIe ports handling:
2190 auto Ask the BIOS whether or not to use native PCIe services
2191 associated with PCIe ports (PME, hot-plug, AER). Use
2192 them only if that is allowed by the BIOS.
2193 native Use native PCIe services associated with PCIe ports
2194 unconditionally.
2195 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2196 ports driver.
2198 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2199 nomsi Do not use MSI for native PCIe PME signaling (this makes
2200 all PCIe root ports use INTx for all services).
2202 pcmv= [HW,PCMCIA] BadgePAD 4
2204 pd. [PARIDE]
2205 See Documentation/blockdev/paride.txt.
2207 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2208 boot time.
2209 Format: { 0 | 1 }
2210 See arch/parisc/kernel/pdc_chassis.c
2212 percpu_alloc= Select which percpu first chunk allocator to use.
2213 Currently supported values are "embed" and "page".
2214 Archs may support subset or none of the selections.
2215 See comments in mm/percpu.c for details on each
2216 allocator. This parameter is primarily for debugging
2217 and performance comparison.
2219 pf. [PARIDE]
2220 See Documentation/blockdev/paride.txt.
2222 pg. [PARIDE]
2223 See Documentation/blockdev/paride.txt.
2225 pirq= [SMP,APIC] Manual mp-table setup
2226 See Documentation/x86/i386/IO-APIC.txt.
2228 plip= [PPT,NET] Parallel port network link
2229 Format: { parport<nr> | timid | 0 }
2230 See also Documentation/parport.txt.
2232 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2233 Override pmtimer IOPort with a hex value.
2234 e.g. pmtmr=0x508
2236 pnp.debug=1 [PNP]
2237 Enable PNP debug messages (depends on the
2238 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2239 via /sys/module/pnp/parameters/debug. We always show
2240 current resource usage; turning this on also shows
2241 possible settings and some assignment information.
2243 pnpacpi= [ACPI]
2244 { off }
2246 pnpbios= [ISAPNP]
2247 { on | off | curr | res | no-curr | no-res }
2249 pnp_reserve_irq=
2250 [ISAPNP] Exclude IRQs for the autoconfiguration
2252 pnp_reserve_dma=
2253 [ISAPNP] Exclude DMAs for the autoconfiguration
2255 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2256 Ranges are in pairs (I/O port base and size).
2258 pnp_reserve_mem=
2259 [ISAPNP] Exclude memory regions for the
2260 autoconfiguration.
2261 Ranges are in pairs (memory base and size).
2263 ports= [IP_VS_FTP] IPVS ftp helper module
2264 Default is 21.
2265 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2266 may be specified.
2267 Format: <port>,<port>....
2269 print-fatal-signals=
2270 [KNL] debug: print fatal signals
2272 If enabled, warn about various signal handling
2273 related application anomalies: too many signals,
2274 too many POSIX.1 timers, fatal signals causing a
2275 coredump - etc.
2277 If you hit the warning due to signal overflow,
2278 you might want to try "ulimit -i unlimited".
2280 default: off.
2282 printk.always_kmsg_dump=
2283 Trigger kmsg_dump for cases other than kernel oops or
2284 panics
2285 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2286 default: disabled
2288 printk.time= Show timing data prefixed to each printk message line
2289 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2291 processor.max_cstate= [HW,ACPI]
2292 Limit processor to maximum C-state
2293 max_cstate=9 overrides any DMI blacklist limit.
2295 processor.nocst [HW,ACPI]
2296 Ignore the _CST method to determine C-states,
2297 instead using the legacy FADT method
2299 profile= [KNL] Enable kernel profiling via /proc/profile
2300 Format: [schedule,]<number>
2301 Param: "schedule" - profile schedule points.
2302 Param: <number> - step/bucket size as a power of 2 for
2303 statistical time based profiling.
2304 Param: "sleep" - profile D-state sleeping (millisecs).
2305 Requires CONFIG_SCHEDSTATS
2306 Param: "kvm" - profile VM exits.
2308 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2309 before loading.
2310 See Documentation/blockdev/ramdisk.txt.
2312 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2313 probe for; one of (bare|imps|exps|lifebook|any).
2314 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2315 per second.
2316 psmouse.resetafter= [HW,MOUSE]
2317 Try to reset the device after so many bad packets
2318 (0 = never).
2319 psmouse.resolution=
2320 [HW,MOUSE] Set desired mouse resolution, in dpi.
2321 psmouse.smartscroll=
2322 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2323 0 = disabled, 1 = enabled (default).
2325 pstore.backend= Specify the name of the pstore backend to use
2327 pt. [PARIDE]
2328 See Documentation/blockdev/paride.txt.
2330 pty.legacy_count=
2331 [KNL] Number of legacy pty's. Overwrites compiled-in
2332 default number.
2334 quiet [KNL] Disable most log messages
2336 r128= [HW,DRM]
2338 raid= [HW,RAID]
2339 See Documentation/md.txt.
2341 ramdisk_blocksize= [RAM]
2342 See Documentation/blockdev/ramdisk.txt.
2344 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2345 See Documentation/blockdev/ramdisk.txt.
2347 rcupdate.blimit= [KNL,BOOT]
2348 Set maximum number of finished RCU callbacks to process
2349 in one batch.
2351 rcupdate.qhimark= [KNL,BOOT]
2352 Set threshold of queued
2353 RCU callbacks over which batch limiting is disabled.
2355 rcupdate.qlowmark= [KNL,BOOT]
2356 Set threshold of queued RCU callbacks below which
2357 batch limiting is re-enabled.
2359 rdinit= [KNL]
2360 Format: <full_path>
2361 Run specified binary instead of /init from the ramdisk,
2362 used for early userspace startup. See initrd.
2364 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2365 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2366 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2368 relax_domain_level=
2369 [KNL, SMP] Set scheduler's default relax_domain_level.
2370 See Documentation/cgroups/cpusets.txt.
2372 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2374 reservetop= [X86-32]
2375 Format: nn[KMG]
2376 Reserves a hole at the top of the kernel virtual
2377 address space.
2379 reservelow= [X86]
2380 Format: nn[K]
2381 Set the amount of memory to reserve for BIOS at
2382 the bottom of the address space.
2384 reset_devices [KNL] Force drivers to reset the underlying device
2385 during initialization.
2387 resume= [SWSUSP]
2388 Specify the partition device for software suspend
2390 resume_offset= [SWSUSP]
2391 Specify the offset from the beginning of the partition
2392 given by "resume=" at which the swap header is located,
2393 in <PAGE_SIZE> units (needed only for swap files).
2394 See Documentation/power/swsusp-and-swap-files.txt
2396 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2397 read the resume files
2399 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2400 Useful for devices that are detected asynchronously
2401 (e.g. USB and MMC devices).
2403 hibernate= [HIBERNATION]
2404 noresume Don't check if there's a hibernation image
2405 present during boot.
2406 nocompress Don't compress/decompress hibernation images.
2408 retain_initrd [RAM] Keep initrd memory after extraction
2410 rhash_entries= [KNL,NET]
2411 Set number of hash buckets for route cache
2413 riscom8= [HW,SERIAL]
2414 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2416 ro [KNL] Mount root device read-only on boot
2418 root= [KNL] Root filesystem
2419 See name_to_dev_t comment in init/do_mounts.c.
2421 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2422 mount the root filesystem
2424 rootflags= [KNL] Set root filesystem mount option string
2426 rootfstype= [KNL] Set root filesystem type
2428 rootwait [KNL] Wait (indefinitely) for root device to show up.
2429 Useful for devices that are detected asynchronously
2430 (e.g. USB and MMC devices).
2432 rw [KNL] Mount root device read-write on boot
2434 S [KNL] Run init in single mode
2436 sa1100ir [NET]
2437 See drivers/net/irda/sa1100_ir.c.
2439 sbni= [NET] Granch SBNI12 leased line adapter
2441 sched_debug [KNL] Enables verbose scheduler debug messages.
2443 security= [SECURITY] Choose a security module to enable at boot.
2444 If this boot parameter is not specified, only the first
2445 security module asking for security registration will be
2446 loaded. An invalid security module name will be treated
2447 as if no module has been chosen.
2449 selinux= [SELINUX] Disable or enable SELinux at boot time.
2450 Format: { "0" | "1" }
2451 See security/selinux/Kconfig help text.
2452 0 -- disable.
2453 1 -- enable.
2454 Default value is set via kernel config option.
2455 If enabled at boot time, /selinux/disable can be used
2456 later to disable prior to initial policy load.
2458 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2459 Format: { "0" | "1" }
2460 See security/apparmor/Kconfig help text
2461 0 -- disable.
2462 1 -- enable.
2463 Default value is set via kernel config option.
2465 serialnumber [BUGS=X86-32]
2467 shapers= [NET]
2468 Maximal number of shapers.
2470 show_msr= [x86] show boot-time MSR settings
2471 Format: { <integer> }
2472 Show boot-time (BIOS-initialized) MSR settings.
2473 The parameter means the number of CPUs to show,
2474 for example 1 means boot CPU only.
2476 simeth= [IA-64]
2477 simscsi=
2479 slram= [HW,MTD]
2481 slab_max_order= [MM, SLAB]
2482 Determines the maximum allowed order for slabs.
2483 A high setting may cause OOMs due to memory
2484 fragmentation. Defaults to 1 for systems with
2485 more than 32MB of RAM, 0 otherwise.
2487 slub_debug[=options[,slabs]] [MM, SLUB]
2488 Enabling slub_debug allows one to determine the
2489 culprit if slab objects become corrupted. Enabling
2490 slub_debug can create guard zones around objects and
2491 may poison objects when not in use. Also tracks the
2492 last alloc / free. For more information see
2493 Documentation/vm/slub.txt.
2495 slub_max_order= [MM, SLUB]
2496 Determines the maximum allowed order for slabs.
2497 A high setting may cause OOMs due to memory
2498 fragmentation. For more information see
2499 Documentation/vm/slub.txt.
2501 slub_min_objects= [MM, SLUB]
2502 The minimum number of objects per slab. SLUB will
2503 increase the slab order up to slub_max_order to
2504 generate a sufficiently large slab able to contain
2505 the number of objects indicated. The higher the number
2506 of objects the smaller the overhead of tracking slabs
2507 and the less frequently locks need to be acquired.
2508 For more information see Documentation/vm/slub.txt.
2510 slub_min_order= [MM, SLUB]
2511 Determines the minimum page order for slabs. Must be
2512 lower than slub_max_order.
2513 For more information see Documentation/vm/slub.txt.
2515 slub_nomerge [MM, SLUB]
2516 Disable merging of slabs with similar size. May be
2517 necessary if there is some reason to distinguish
2518 allocs to different slabs. Debug options disable
2519 merging on their own.
2520 For more information see Documentation/vm/slub.txt.
2522 smart2= [HW]
2523 Format: <io1>[,<io2>[,...,<io8>]]
2525 smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2526 attempt to substitute SMP alternatives once at boot.
2528 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2529 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2530 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2531 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2532 smsc-ircc2.ircc_irq= [HW] IRQ line
2533 smsc-ircc2.ircc_dma= [HW] DMA channel
2534 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2535 0: Toshiba Satellite 1800 (GP data pin select)
2536 1: Fast pin select (default)
2537 2: ATC IRMode
2539 softlockup_panic=
2540 [KNL] Should the soft-lockup detector generate panics.
2541 Format: <integer>
2543 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2544 See Documentation/laptops/sonypi.txt
2546 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2547 See Documentation/serial/specialix.txt.
2549 spia_io_base= [HW,MTD]
2550 spia_fio_base=
2551 spia_pedr=
2552 spia_peddr=
2554 stacktrace [FTRACE]
2555 Enabled the stack tracer on boot up.
2557 stacktrace_filter=[function-list]
2558 [FTRACE] Limit the functions that the stack tracer
2559 will trace at boot up. function-list is a comma separated
2560 list of functions. This list can be changed at run
2561 time by the stack_trace_filter file in the debugfs
2562 tracing directory. Note, this enables stack tracing
2563 and the stacktrace above is not needed.
2565 sti= [PARISC,HW]
2566 Format: <num>
2567 Set the STI (builtin display/keyboard on the HP-PARISC
2568 machines) console (graphic card) which should be used
2569 as the initial boot-console.
2570 See also comment in drivers/video/console/sticore.c.
2572 sti_font= [HW]
2573 See comment in drivers/video/console/sticore.c.
2575 stifb= [HW]
2576 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2578 sunrpc.min_resvport=
2579 sunrpc.max_resvport=
2580 [NFS,SUNRPC]
2581 SunRPC servers often require that client requests
2582 originate from a privileged port (i.e. a port in the
2583 range 0 < portnr < 1024).
2584 An administrator who wishes to reserve some of these
2585 ports for other uses may adjust the range that the
2586 kernel's sunrpc client considers to be privileged
2587 using these two parameters to set the minimum and
2588 maximum port values.
2590 sunrpc.pool_mode=
2591 [NFS]
2592 Control how the NFS server code allocates CPUs to
2593 service thread pools. Depending on how many NICs
2594 you have and where their interrupts are bound, this
2595 option will affect which CPUs will do NFS serving.
2596 Note: this parameter cannot be changed while the
2597 NFS server is running.
2599 auto the server chooses an appropriate mode
2600 automatically using heuristics
2601 global a single global pool contains all CPUs
2602 percpu one pool for each CPU
2603 pernode one pool for each NUMA node (equivalent
2604 to global on non-NUMA machines)
2606 sunrpc.tcp_slot_table_entries=
2607 sunrpc.udp_slot_table_entries=
2608 [NFS,SUNRPC]
2609 Sets the upper limit on the number of simultaneous
2610 RPC calls that can be sent from the client to a
2611 server. Increasing these values may allow you to
2612 improve throughput, but will also increase the
2613 amount of memory reserved for use by the client.
2615 swapaccount[=0|1]
2616 [KNL] Enable accounting of swap in memory resource
2617 controller if no parameter or 1 is given or disable
2618 it if 0 is given (See Documentation/cgroups/memory.txt)
2620 swiotlb= [IA-64] Number of I/O TLB slabs
2622 switches= [HW,M68k]
2624 sysfs.deprecated=0|1 [KNL]
2625 Enable/disable old style sysfs layout for old udev
2626 on older distributions. When this option is enabled
2627 very new udev will not work anymore. When this option
2628 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2629 in older udev will not work anymore.
2630 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2631 the kernel configuration.
2633 sysrq_always_enabled
2634 [KNL]
2635 Ignore sysrq setting - this boot parameter will
2636 neutralize any effect of /proc/sys/kernel/sysrq.
2637 Useful for debugging.
2639 tdfx= [HW,DRM]
2641 test_suspend= [SUSPEND]
2642 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2643 standby suspend) as the system sleep state to briefly
2644 enter during system startup. The system is woken from
2645 this state using a wakeup-capable RTC alarm.
2647 thash_entries= [KNL,NET]
2648 Set number of hash buckets for TCP connection
2650 thermal.act= [HW,ACPI]
2651 -1: disable all active trip points in all thermal zones
2652 <degrees C>: override all lowest active trip points
2654 thermal.crt= [HW,ACPI]
2655 -1: disable all critical trip points in all thermal zones
2656 <degrees C>: override all critical trip points
2658 thermal.nocrt= [HW,ACPI]
2659 Set to disable actions on ACPI thermal zone
2660 critical and hot trip points.
2662 thermal.off= [HW,ACPI]
2663 1: disable ACPI thermal control
2665 thermal.psv= [HW,ACPI]
2666 -1: disable all passive trip points
2667 <degrees C>: override all passive trip points to this
2668 value
2670 thermal.tzp= [HW,ACPI]
2671 Specify global default ACPI thermal zone polling rate
2672 <deci-seconds>: poll all this frequency
2673 0: no polling (default)
2675 threadirqs [KNL]
2676 Force threading of all interrupt handlers except those
2677 marked explicitly IRQF_NO_THREAD.
2679 topology= [S390]
2680 Format: {off | on}
2681 Specify if the kernel should make use of the cpu
2682 topology information if the hardware supports this.
2683 The scheduler will make use of this information and
2684 e.g. base its process migration decisions on it.
2685 Default is on.
2687 tp720= [HW,PS2]
2689 tpm_suspend_pcr=[HW,TPM]
2690 Format: integer pcr id
2691 Specify that at suspend time, the tpm driver
2692 should extend the specified pcr with zeros,
2693 as a workaround for some chips which fail to
2694 flush the last written pcr on TPM_SaveState.
2695 This will guarantee that all the other pcrs
2696 are saved.
2698 trace_buf_size=nn[KMG]
2699 [FTRACE] will set tracing buffer size.
2701 trace_event=[event-list]
2702 [FTRACE] Set and start specified trace events in order
2703 to facilitate early boot debugging.
2704 See also Documentation/trace/events.txt
2706 transparent_hugepage=
2707 [KNL]
2708 Format: [always|madvise|never]
2709 Can be used to control the default behavior of the system
2710 with respect to transparent hugepages.
2711 See Documentation/vm/transhuge.txt for more details.
2713 tsc= Disable clocksource stability checks for TSC.
2714 Format: <string>
2715 [x86] reliable: mark tsc clocksource as reliable, this
2716 disables clocksource verification at runtime, as well
2717 as the stability checks done at bootup. Used to enable
2718 high-resolution timer mode on older hardware, and in
2719 virtualized environment.
2720 [x86] noirqtime: Do not use TSC to do irq accounting.
2721 Used to run time disable IRQ_TIME_ACCOUNTING on any
2722 platforms where RDTSC is slow and this accounting
2723 can add overhead.
2725 turbografx.map[2|3]= [HW,JOY]
2726 TurboGraFX parallel port interface
2727 Format:
2728 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2729 See also Documentation/input/joystick-parport.txt
2731 udbg-immortal [PPC] When debugging early kernel crashes that
2732 happen after console_init() and before a proper
2733 console driver takes over, this boot options might
2734 help "seeing" what's going on.
2736 uhash_entries= [KNL,NET]
2737 Set number of hash buckets for UDP/UDP-Lite connections
2739 uhci-hcd.ignore_oc=
2740 [USB] Ignore overcurrent events (default N).
2741 Some badly-designed motherboards generate lots of
2742 bogus events, for ports that aren't wired to
2743 anything. Set this parameter to avoid log spamming.
2744 Note that genuine overcurrent events won't be
2745 reported either.
2747 unknown_nmi_panic
2748 [X86] Cause panic on unknown NMI.
2750 usbcore.authorized_default=
2751 [USB] Default USB device authorization:
2752 (default -1 = authorized except for wireless USB,
2753 0 = not authorized, 1 = authorized)
2755 usbcore.autosuspend=
2756 [USB] The autosuspend time delay (in seconds) used
2757 for newly-detected USB devices (default 2). This
2758 is the time required before an idle device will be
2759 autosuspended. Devices for which the delay is set
2760 to a negative value won't be autosuspended at all.
2762 usbcore.usbfs_snoop=
2763 [USB] Set to log all usbfs traffic (default 0 = off).
2765 usbcore.blinkenlights=
2766 [USB] Set to cycle leds on hubs (default 0 = off).
2768 usbcore.old_scheme_first=
2769 [USB] Start with the old device initialization
2770 scheme (default 0 = off).
2772 usbcore.usbfs_memory_mb=
2773 [USB] Memory limit (in MB) for buffers allocated by
2774 usbfs (default = 16, 0 = max = 2047).
2776 usbcore.use_both_schemes=
2777 [USB] Try the other device initialization scheme
2778 if the first one fails (default 1 = enabled).
2780 usbcore.initial_descriptor_timeout=
2781 [USB] Specifies timeout for the initial 64-byte
2782 USB_REQ_GET_DESCRIPTOR request in milliseconds
2783 (default 5000 = 5.0 seconds).
2785 usbhid.mousepoll=
2786 [USBHID] The interval which mice are to be polled at.
2788 usb-storage.delay_use=
2789 [UMS] The delay in seconds before a new device is
2790 scanned for Logical Units (default 5).
2792 usb-storage.quirks=
2793 [UMS] A list of quirks entries to supplement or
2794 override the built-in unusual_devs list. List
2795 entries are separated by commas. Each entry has
2796 the form VID:PID:Flags where VID and PID are Vendor
2797 and Product ID values (4-digit hex numbers) and
2798 Flags is a set of characters, each corresponding
2799 to a common usb-storage quirk flag as follows:
2800 a = SANE_SENSE (collect more than 18 bytes
2801 of sense data);
2802 b = BAD_SENSE (don't collect more than 18
2803 bytes of sense data);
2804 c = FIX_CAPACITY (decrease the reported
2805 device capacity by one sector);
2806 d = NO_READ_DISC_INFO (don't use
2807 READ_DISC_INFO command);
2808 e = NO_READ_CAPACITY_16 (don't use
2809 READ_CAPACITY_16 command);
2810 h = CAPACITY_HEURISTICS (decrease the
2811 reported device capacity by one
2812 sector if the number is odd);
2813 i = IGNORE_DEVICE (don't bind to this
2814 device);
2815 l = NOT_LOCKABLE (don't try to lock and
2816 unlock ejectable media);
2817 m = MAX_SECTORS_64 (don't transfer more
2818 than 64 sectors = 32 KB at a time);
2819 n = INITIAL_READ10 (force a retry of the
2820 initial READ(10) command);
2821 o = CAPACITY_OK (accept the capacity
2822 reported by the device);
2823 r = IGNORE_RESIDUE (the device reports
2824 bogus residue values);
2825 s = SINGLE_LUN (the device has only one
2826 Logical Unit);
2827 w = NO_WP_DETECT (don't test whether the
2828 medium is write-protected).
2829 Example: quirks=0419:aaf5:rl,0421:0433:rc
2831 user_debug= [KNL,ARM]
2832 Format: <int>
2833 See arch/arm/Kconfig.debug help text.
2834 1 - undefined instruction events
2835 2 - system calls
2836 4 - invalid data aborts
2837 8 - SIGSEGV faults
2838 16 - SIGBUS faults
2839 Example: user_debug=31
2841 userpte=
2842 [X86] Flags controlling user PTE allocations.
2844 nohigh = do not allocate PTE pages in
2845 HIGHMEM regardless of setting
2846 of CONFIG_HIGHPTE.
2848 vdso= [X86,SH]
2849 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2850 vdso=1: enable VDSO (default)
2851 vdso=0: disable VDSO mapping
2853 vdso32= [X86]
2854 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2855 vdso32=1: enable 32-bit VDSO (default)
2856 vdso32=0: disable 32-bit VDSO mapping
2858 vector= [IA-64,SMP]
2859 vector=percpu: enable percpu vector domain
2861 video= [FB] Frame buffer configuration
2862 See Documentation/fb/modedb.txt.
2864 vga= [BOOT,X86-32] Select a particular video mode
2865 See Documentation/x86/boot.txt and
2866 Documentation/svga.txt.
2867 Use vga=ask for menu.
2868 This is actually a boot loader parameter; the value is
2869 passed to the kernel using a special protocol.
2871 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2872 size of <nn>. This can be used to increase the
2873 minimum size (128MB on x86). It can also be used to
2874 decrease the size and leave more room for directly
2875 mapped kernel RAM.
2877 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2878 Format: <command>
2880 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2881 Format: <command>
2883 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2884 Format: <command>
2886 vsyscall= [X86-64]
2887 Controls the behavior of vsyscalls (i.e. calls to
2888 fixed addresses of 0xffffffffff600x00 from legacy
2889 code). Most statically-linked binaries and older
2890 versions of glibc use these calls. Because these
2891 functions are at fixed addresses, they make nice
2892 targets for exploits that can control RIP.
2894 emulate [default] Vsyscalls turn into traps and are
2895 emulated reasonably safely.
2897 native Vsyscalls are native syscall instructions.
2898 This is a little bit faster than trapping
2899 and makes a few dynamic recompilers work
2900 better than they would in emulation mode.
2901 It also makes exploits much easier to write.
2903 none Vsyscalls don't work at all. This makes
2904 them quite hard to use for exploits but
2905 might break your system.
2907 vt.cur_default= [VT] Default cursor shape.
2908 Format: 0xCCBBAA, where AA, BB, and CC are the same as
2909 the parameters of the <Esc>[?A;B;Cc escape sequence;
2910 see VGA-softcursor.txt. Default: 2 = underline.
2912 vt.default_blu= [VT]
2913 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2914 Change the default blue palette of the console.
2915 This is a 16-member array composed of values
2916 ranging from 0-255.
2918 vt.default_grn= [VT]
2919 Format: <green0>,<green1>,<green2>,...,<green15>
2920 Change the default green palette of the console.
2921 This is a 16-member array composed of values
2922 ranging from 0-255.
2924 vt.default_red= [VT]
2925 Format: <red0>,<red1>,<red2>,...,<red15>
2926 Change the default red palette of the console.
2927 This is a 16-member array composed of values
2928 ranging from 0-255.
2930 vt.default_utf8=
2931 [VT]
2932 Format=<0|1>
2933 Set system-wide default UTF-8 mode for all tty's.
2934 Default is 1, i.e. UTF-8 mode is enabled for all
2935 newly opened terminals.
2937 vt.global_cursor_default=
2938 [VT]
2939 Format=<-1|0|1>
2940 Set system-wide default for whether a cursor
2941 is shown on new VTs. Default is -1,
2942 i.e. cursors will be created by default unless
2943 overridden by individual drivers. 0 will hide
2944 cursors, 1 will display them.
2946 watchdog timers [HW,WDT] For information on watchdog timers,
2947 see Documentation/watchdog/watchdog-parameters.txt
2948 or other driver-specific files in the
2949 Documentation/watchdog/ directory.
2951 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2952 default x2apic cluster mode on platforms
2953 supporting x2apic.
2955 x86_mrst_timer= [X86-32,APBT]
2956 Choose timer option for x86 Moorestown MID platform.
2957 Two valid options are apbt timer only and lapic timer
2958 plus one apbt timer for broadcast timer.
2959 x86_mrst_timer=apbt_only | lapic_and_apbt
2961 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2962 xd_geo= See header of drivers/block/xd.c.
2964 xen_emul_unplug= [HW,X86,XEN]
2965 Unplug Xen emulated devices
2966 Format: [unplug0,][unplug1]
2967 ide-disks -- unplug primary master IDE devices
2968 aux-ide-disks -- unplug non-primary-master IDE devices
2969 nics -- unplug network devices
2970 all -- unplug all emulated devices (NICs and IDE disks)
2971 unnecessary -- unplugging emulated devices is
2972 unnecessary even if the host did not respond to
2973 the unplug protocol
2974 never -- do not unplug even if version check succeeds
2976 xirc2ps_cs= [NET,PCMCIA]
2977 Format:
2978 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2980 ______________________________________________________________________
2982 TODO:
2984 Add more DRM drivers.