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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 CLK Common clock infrastructure is enabled.
48 CMA Contiguous Memory Area support is enabled.
49 DRM Direct Rendering Management support is enabled.
50 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
51 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
52 EFI EFI Partitioning (GPT) is enabled
53 EIDE EIDE/ATAPI support is enabled.
54 EVM Extended Verification Module
55 FB The frame buffer device is enabled.
56 FTRACE Function tracing enabled.
57 GCOV GCOV profiling is enabled.
58 HW Appropriate hardware is enabled.
59 IA-64 IA-64 architecture is enabled.
60 IMA Integrity measurement architecture is enabled.
61 IOSCHED More than one I/O scheduler is enabled.
62 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
63 IPV6 IPv6 support is enabled.
64 ISAPNP ISA PnP code is enabled.
65 ISDN Appropriate ISDN support is enabled.
66 JOY Appropriate joystick support is enabled.
67 KGDB Kernel debugger support is enabled.
68 KVM Kernel Virtual Machine support is enabled.
69 LIBATA Libata driver is enabled
70 LP Printer support is enabled.
71 LOOP Loopback device support is enabled.
72 M68k M68k architecture is enabled.
73 These options have more detailed description inside of
74 Documentation/m68k/kernel-options.txt.
75 MDA MDA console support is enabled.
76 MIPS MIPS architecture is enabled.
77 MOUSE Appropriate mouse support is enabled.
78 MSI Message Signaled Interrupts (PCI).
79 MTD MTD (Memory Technology Device) support is enabled.
80 NET Appropriate network support is enabled.
81 NUMA NUMA support is enabled.
82 NFS Appropriate NFS support is enabled.
83 OSS OSS sound support is enabled.
84 PV_OPS A paravirtualized kernel is enabled.
85 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
86 PARISC The PA-RISC architecture is enabled.
87 PCI PCI bus support is enabled.
88 PCIE PCI Express support is enabled.
89 PCMCIA The PCMCIA subsystem is enabled.
90 PNP Plug & Play support is enabled.
91 PPC PowerPC architecture is enabled.
92 PPT Parallel port support is enabled.
93 PS2 Appropriate PS/2 support is enabled.
94 RAM RAM disk support is enabled.
95 S390 S390 architecture is enabled.
96 SCSI Appropriate SCSI support is enabled.
97 A lot of drivers have their options described inside
98 the Documentation/scsi/ sub-directory.
99 SECURITY Different security models are enabled.
100 SELINUX SELinux support is enabled.
101 APPARMOR AppArmor support is enabled.
102 SERIAL Serial support is enabled.
103 SH SuperH architecture is enabled.
104 SMP The kernel is an SMP kernel.
105 SPARC Sparc architecture is enabled.
106 SWSUSP Software suspend (hibernation) is enabled.
107 SUSPEND System suspend states are enabled.
108 TPM TPM drivers are enabled.
109 TS Appropriate touchscreen support is enabled.
110 UMS USB Mass Storage support is enabled.
111 USB USB support is enabled.
112 USBHID USB Human Interface Device support is enabled.
113 V4L Video For Linux support is enabled.
114 VMMIO Driver for memory mapped virtio devices is enabled.
115 VGA The VGA console has been enabled.
116 VT Virtual terminal support is enabled.
117 WDT Watchdog support is enabled.
118 XT IBM PC/XT MFM hard disk support is enabled.
119 X86-32 X86-32, aka i386 architecture is enabled.
120 X86-64 X86-64 architecture is enabled.
121 More X86-64 boot options can be found in
122 Documentation/x86/x86_64/boot-options.txt .
123 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
124 XEN Xen support is enabled
126 In addition, the following text indicates that the option:
128 BUGS= Relates to possible processor bugs on the said processor.
129 KNL Is a kernel start-up parameter.
130 BOOT Is a boot loader parameter.
132 Parameters denoted with BOOT are actually interpreted by the boot
133 loader, and have no meaning to the kernel directly.
134 Do not modify the syntax of boot loader parameters without extreme
135 need or coordination with <Documentation/x86/boot.txt>.
137 There are also arch-specific kernel-parameters not documented here.
138 See for example <Documentation/x86/x86_64/boot-options.txt>.
140 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
141 a trailing = on the name of any parameter states that that parameter will
142 be entered as an environment variable, whereas its absence indicates that
143 it will appear as a kernel argument readable via /proc/cmdline by programs
144 running once the system is up.
146 The number of kernel parameters is not limited, but the length of the
147 complete command line (parameters including spaces etc.) is limited to
148 a fixed number of characters. This limit depends on the architecture
149 and is between 256 and 4096 characters. It is defined in the file
150 ./include/asm/setup.h as COMMAND_LINE_SIZE.
152 Finally, the [KMG] suffix is commonly described after a number of kernel
153 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
154 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
155 bytes respectively. Such letter suffixes can also be entirely omitted.
158 acpi= [HW,ACPI,X86]
159 Advanced Configuration and Power Interface
160 Format: { force | off | strict | noirq | rsdt }
161 force -- enable ACPI if default was off
162 off -- disable ACPI if default was on
163 noirq -- do not use ACPI for IRQ routing
164 strict -- Be less tolerant of platforms that are not
165 strictly ACPI specification compliant.
166 rsdt -- prefer RSDT over (default) XSDT
167 copy_dsdt -- copy DSDT to memory
169 See also Documentation/power/runtime_pm.txt, pci=noacpi
171 acpi_rsdp= [ACPI,EFI,KEXEC]
172 Pass the RSDP address to the kernel, mostly used
173 on machines running EFI runtime service to boot the
174 second kernel for kdump.
176 acpi_apic_instance= [ACPI, IOAPIC]
177 Format: <int>
178 2: use 2nd APIC table, if available
179 1,0: use 1st APIC table
180 default: 0
182 acpi_backlight= [HW,ACPI]
183 acpi_backlight=vendor
184 acpi_backlight=video
185 If set to vendor, prefer vendor specific driver
186 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
187 of the ACPI video.ko driver.
189 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
190 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
191 Format: <int>
192 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
193 debug output. Bits in debug_layer correspond to a
194 _COMPONENT in an ACPI source file, e.g.,
195 #define _COMPONENT ACPI_PCI_COMPONENT
196 Bits in debug_level correspond to a level in
197 ACPI_DEBUG_PRINT statements, e.g.,
198 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
199 The debug_level mask defaults to "info". See
200 Documentation/acpi/debug.txt for more information about
201 debug layers and levels.
203 Enable processor driver info messages:
204 acpi.debug_layer=0x20000000
205 Enable PCI/PCI interrupt routing info messages:
206 acpi.debug_layer=0x400000
207 Enable AML "Debug" output, i.e., stores to the Debug
208 object while interpreting AML:
209 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
210 Enable all messages related to ACPI hardware:
211 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
213 Some values produce so much output that the system is
214 unusable. The "log_buf_len" parameter may be useful
215 if you need to capture more output.
217 acpi_irq_balance [HW,ACPI]
218 ACPI will balance active IRQs
219 default in APIC mode
221 acpi_irq_nobalance [HW,ACPI]
222 ACPI will not move active IRQs (default)
223 default in PIC mode
225 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
226 Format: <irq>,<irq>...
228 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
229 use by PCI
230 Format: <irq>,<irq>...
232 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
234 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
235 Format: To spoof as Windows 98: ="Microsoft Windows"
237 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
238 acpi_osi="string1" # add string1 -- only one string
239 acpi_osi="!string2" # remove built-in string2
240 acpi_osi= # disable all strings
242 acpi_pm_good [X86]
243 Override the pmtimer bug detection: force the kernel
244 to assume that this machine's pmtimer latches its value
245 and always returns good values.
247 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
248 Format: { level | edge | high | low }
250 acpi_serialize [HW,ACPI] force serialization of AML methods
252 acpi_skip_timer_override [HW,ACPI]
253 Recognize and ignore IRQ0/pin2 Interrupt Override.
254 For broken nForce2 BIOS resulting in XT-PIC timer.
256 acpi_sleep= [HW,ACPI] Sleep options
257 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
258 old_ordering, nonvs, sci_force_enable }
259 See Documentation/power/video.txt for information on
260 s3_bios and s3_mode.
261 s3_beep is for debugging; it makes the PC's speaker beep
262 as soon as the kernel's real-mode entry point is called.
263 s4_nohwsig prevents ACPI hardware signature from being
264 used during resume from hibernation.
265 old_ordering causes the ACPI 1.0 ordering of the _PTS
266 control method, with respect to putting devices into
267 low power states, to be enforced (the ACPI 2.0 ordering
268 of _PTS is used by default).
269 nonvs prevents the kernel from saving/restoring the
270 ACPI NVS memory during suspend/hibernation and resume.
271 sci_force_enable causes the kernel to set SCI_EN directly
272 on resume from S1/S3 (which is against the ACPI spec,
273 but some broken systems don't work without it).
275 acpi_use_timer_override [HW,ACPI]
276 Use timer override. For some broken Nvidia NF5 boards
277 that require a timer override, but don't have HPET
279 acpi_enforce_resources= [ACPI]
280 { strict | lax | no }
281 Check for resource conflicts between native drivers
282 and ACPI OperationRegions (SystemIO and SystemMemory
283 only). IO ports and memory declared in ACPI might be
284 used by the ACPI subsystem in arbitrary AML code and
285 can interfere with legacy drivers.
286 strict (default): access to resources claimed by ACPI
287 is denied; legacy drivers trying to access reserved
288 resources will fail to bind to device using them.
289 lax: access to resources claimed by ACPI is allowed;
290 legacy drivers trying to access reserved resources
291 will bind successfully but a warning message is logged.
292 no: ACPI OperationRegions are not marked as reserved,
293 no further checks are performed.
295 add_efi_memmap [EFI; X86] Include EFI memory map in
296 kernel's map of available physical RAM.
298 agp= [AGP]
299 { off | try_unsupported }
300 off: disable AGP support
301 try_unsupported: try to drive unsupported chipsets
302 (may crash computer or cause data corruption)
304 ALSA [HW,ALSA]
305 See Documentation/sound/alsa/alsa-parameters.txt
307 alignment= [KNL,ARM]
308 Allow the default userspace alignment fault handler
309 behaviour to be specified. Bit 0 enables warnings,
310 bit 1 enables fixups, and bit 2 sends a segfault.
312 align_va_addr= [X86-64]
313 Align virtual addresses by clearing slice [14:12] when
314 allocating a VMA at process creation time. This option
315 gives you up to 3% performance improvement on AMD F15h
316 machines (where it is enabled by default) for a
317 CPU-intensive style benchmark, and it can vary highly in
318 a microbenchmark depending on workload and compiler.
320 32: only for 32-bit processes
321 64: only for 64-bit processes
322 on: enable for both 32- and 64-bit processes
323 off: disable for both 32- and 64-bit processes
325 alloc_snapshot [FTRACE]
326 Allocate the ftrace snapshot buffer on boot up when the
327 main buffer is allocated. This is handy if debugging
328 and you need to use tracing_snapshot() on boot up, and
329 do not want to use tracing_snapshot_alloc() as it needs
330 to be done where GFP_KERNEL allocations are allowed.
332 amd_iommu= [HW,X86-64]
333 Pass parameters to the AMD IOMMU driver in the system.
334 Possible values are:
335 fullflush - enable flushing of IO/TLB entries when
336 they are unmapped. Otherwise they are
337 flushed before they will be reused, which
338 is a lot of faster
339 off - do not initialize any AMD IOMMU found in
340 the system
341 force_isolation - Force device isolation for all
342 devices. The IOMMU driver is not
343 allowed anymore to lift isolation
344 requirements as needed. This option
345 does not override iommu=pt
347 amd_iommu_dump= [HW,X86-64]
348 Enable AMD IOMMU driver option to dump the ACPI table
349 for AMD IOMMU. With this option enabled, AMD IOMMU
350 driver will print ACPI tables for AMD IOMMU during
351 IOMMU initialization.
353 amijoy.map= [HW,JOY] Amiga joystick support
354 Map of devices attached to JOY0DAT and JOY1DAT
355 Format: <a>,<b>
356 See also Documentation/input/joystick.txt
358 analog.map= [HW,JOY] Analog joystick and gamepad support
359 Specifies type or capabilities of an analog joystick
360 connected to one of 16 gameports
361 Format: <type1>,<type2>,..<type16>
363 apc= [HW,SPARC]
364 Power management functions (SPARCstation-4/5 + deriv.)
365 Format: noidle
366 Disable APC CPU standby support. SPARCstation-Fox does
367 not play well with APC CPU idle - disable it if you have
368 APC and your system crashes randomly.
370 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
371 Change the output verbosity whilst booting
372 Format: { quiet (default) | verbose | debug }
373 Change the amount of debugging information output
374 when initialising the APIC and IO-APIC components.
376 autoconf= [IPV6]
377 See Documentation/networking/ipv6.txt.
379 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
380 Limit apic dumping. The parameter defines the maximal
381 number of local apics being dumped. Also it is possible
382 to set it to "all" by meaning -- no limit here.
383 Format: { 1 (default) | 2 | ... | all }.
384 The parameter valid if only apic=debug or
385 apic=verbose is specified.
386 Example: apic=debug show_lapic=all
388 apm= [APM] Advanced Power Management
389 See header of arch/x86/kernel/apm_32.c.
391 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
392 Format: <io>,<irq>,<nodeID>
394 ataflop= [HW,M68k]
396 atarimouse= [HW,MOUSE] Atari Mouse
398 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
399 EzKey and similar keyboards
401 atkbd.reset= [HW] Reset keyboard during initialization
403 atkbd.set= [HW] Select keyboard code set
404 Format: <int> (2 = AT (default), 3 = PS/2)
406 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
407 keyboards
409 atkbd.softraw= [HW] Choose between synthetic and real raw mode
410 Format: <bool> (0 = real, 1 = synthetic (default))
412 atkbd.softrepeat= [HW]
413 Use software keyboard repeat
415 baycom_epp= [HW,AX25]
416 Format: <io>,<mode>
418 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
419 Format: <io>,<mode>
420 See header of drivers/net/hamradio/baycom_par.c.
422 baycom_ser_fdx= [HW,AX25]
423 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
424 Format: <io>,<irq>,<mode>[,<baud>]
425 See header of drivers/net/hamradio/baycom_ser_fdx.c.
427 baycom_ser_hdx= [HW,AX25]
428 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
429 Format: <io>,<irq>,<mode>
430 See header of drivers/net/hamradio/baycom_ser_hdx.c.
432 boot_delay= Milliseconds to delay each printk during boot.
433 Values larger than 10 seconds (10000) are changed to
434 no delay (0).
435 Format: integer
437 bootmem_debug [KNL] Enable bootmem allocator debug messages.
439 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
440 bttv.radio= Most important insmod options are available as
441 kernel args too.
442 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
443 bttv.tuner=
445 bulk_remove=off [PPC] This parameter disables the use of the pSeries
446 firmware feature for flushing multiple hpte entries
447 at a time.
449 c101= [NET] Moxa C101 synchronous serial card
451 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
452 Sometimes CPU hardware bugs make them report the cache
453 size incorrectly. The kernel will attempt work arounds
454 to fix known problems, but for some CPUs it is not
455 possible to determine what the correct size should be.
456 This option provides an override for these situations.
458 ccw_timeout_log [S390]
459 See Documentation/s390/CommonIO for details.
461 cgroup_disable= [KNL] Disable a particular controller
462 Format: {name of the controller(s) to disable}
463 {Currently supported controllers - "memory"}
465 checkreqprot [SELINUX] Set initial checkreqprot flag value.
466 Format: { "0" | "1" }
467 See security/selinux/Kconfig help text.
468 0 -- check protection applied by kernel (includes
469 any implied execute protection).
470 1 -- check protection requested by application.
471 Default value is set via a kernel config option.
472 Value can be changed at runtime via
473 /selinux/checkreqprot.
475 cio_ignore= [S390]
476 See Documentation/s390/CommonIO for details.
477 clk_ignore_unused
478 [CLK]
479 Keep all clocks already enabled by bootloader on,
480 even if no driver has claimed them. This is useful
481 for debug and development, but should not be
482 needed on a platform with proper driver support.
483 For more information, see Documentation/clk.txt.
485 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
486 [Deprecated]
487 Forces specified clocksource (if available) to be used
488 when calculating gettimeofday(). If specified
489 clocksource is not available, it defaults to PIT.
490 Format: { pit | tsc | cyclone | pmtmr }
492 clocksource= Override the default clocksource
493 Format: <string>
494 Override the default clocksource and use the clocksource
495 with the name specified.
496 Some clocksource names to choose from, depending on
497 the platform:
498 [all] jiffies (this is the base, fallback clocksource)
499 [ACPI] acpi_pm
500 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
501 pxa_timer,timer3,32k_counter,timer0_1
502 [AVR32] avr32
503 [X86-32] pit,hpet,tsc;
504 scx200_hrt on Geode; cyclone on IBM x440
505 [MIPS] MIPS
506 [PARISC] cr16
507 [S390] tod
508 [SH] SuperH
509 [SPARC64] tick
510 [X86-64] hpet,tsc
512 clearcpuid=BITNUM [X86]
513 Disable CPUID feature X for the kernel. See
514 arch/x86/include/asm/cpufeature.h for the valid bit
515 numbers. Note the Linux specific bits are not necessarily
516 stable over kernel options, but the vendor specific
517 ones should be.
518 Also note that user programs calling CPUID directly
519 or using the feature without checking anything
520 will still see it. This just prevents it from
521 being used by the kernel or shown in /proc/cpuinfo.
522 Also note the kernel might malfunction if you disable
523 some critical bits.
525 cma=nn[MG] [ARM,KNL]
526 Sets the size of kernel global memory area for contiguous
527 memory allocations. For more information, see
528 include/linux/dma-contiguous.h
530 cmo_free_hint= [PPC] Format: { yes | no }
531 Specify whether pages are marked as being inactive
532 when they are freed. This is used in CMO environments
533 to determine OS memory pressure for page stealing by
534 a hypervisor.
535 Default: yes
537 coherent_pool=nn[KMG] [ARM,KNL]
538 Sets the size of memory pool for coherent, atomic dma
539 allocations, by default set to 256K.
541 code_bytes [X86] How many bytes of object code to print
542 in an oops report.
543 Range: 0 - 8192
544 Default: 64
546 com20020= [HW,NET] ARCnet - COM20020 chipset
547 Format:
548 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
550 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
551 Format: <io>[,<irq>]
553 com90xx= [HW,NET]
554 ARCnet - COM90xx chipset (memory-mapped buffers)
555 Format: <io>[,<irq>[,<memstart>]]
557 condev= [HW,S390] console device
558 conmode=
560 console= [KNL] Output console device and options.
562 tty<n> Use the virtual console device <n>.
564 ttyS<n>[,options]
565 ttyUSB0[,options]
566 Use the specified serial port. The options are of
567 the form "bbbbpnf", where "bbbb" is the baud rate,
568 "p" is parity ("n", "o", or "e"), "n" is number of
569 bits, and "f" is flow control ("r" for RTS or
570 omit it). Default is "9600n8".
572 See Documentation/serial-console.txt for more
573 information. See
574 Documentation/networking/netconsole.txt for an
575 alternative.
577 uart[8250],io,<addr>[,options]
578 uart[8250],mmio,<addr>[,options]
579 Start an early, polled-mode console on the 8250/16550
580 UART at the specified I/O port or MMIO address,
581 switching to the matching ttyS device later. The
582 options are the same as for ttyS, above.
583 hvc<n> Use the hypervisor console device <n>. This is for
584 both Xen and PowerPC hypervisors.
586 If the device connected to the port is not a TTY but a braille
587 device, prepend "brl," before the device type, for instance
588 console=brl,ttyS0
589 For now, only VisioBraille is supported.
591 consoleblank= [KNL] The console blank (screen saver) timeout in
592 seconds. Defaults to 10*60 = 10mins. A value of 0
593 disables the blank timer.
595 coredump_filter=
596 [KNL] Change the default value for
597 /proc/<pid>/coredump_filter.
598 See also Documentation/filesystems/proc.txt.
600 cpuidle.off=1 [CPU_IDLE]
601 disable the cpuidle sub-system
603 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
604 Format:
605 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
607 crashkernel=size[KMG][@offset[KMG]]
608 [KNL] Using kexec, Linux can switch to a 'crash kernel'
609 upon panic. This parameter reserves the physical
610 memory region [offset, offset + size] for that kernel
611 image. If '@offset' is omitted, then a suitable offset
612 is selected automatically. Check
613 Documentation/kdump/kdump.txt for further details.
615 crashkernel=range1:size1[,range2:size2,...][@offset]
616 [KNL] Same as above, but depends on the memory
617 in the running system. The syntax of range is
618 start-[end] where start and end are both
619 a memory unit (amount[KMG]). See also
620 Documentation/kdump/kdump.txt for an example.
622 crashkernel=size[KMG],high
623 [KNL, x86_64] range could be above 4G. Allow kernel
624 to allocate physical memory region from top, so could
625 be above 4G if system have more than 4G ram installed.
626 Otherwise memory region will be allocated below 4G, if
627 available.
628 It will be ignored if crashkernel=X is specified.
629 crashkernel=size[KMG],low
630 [KNL, x86_64] range under 4G. When crashkernel=X,high
631 is passed, kernel could allocate physical memory region
632 above 4G, that cause second kernel crash on system
633 that require some amount of low memory, e.g. swiotlb
634 requires at least 64M+32K low memory. Kernel would
635 try to allocate 72M below 4G automatically.
636 This one let user to specify own low range under 4G
637 for second kernel instead.
638 0: to disable low allocation.
639 It will be ignored when crashkernel=X,high is not used
640 or memory reserved is below 4G.
642 cs89x0_dma= [HW,NET]
643 Format: <dma>
645 cs89x0_media= [HW,NET]
646 Format: { rj45 | aui | bnc }
648 dasd= [HW,NET]
649 See header of drivers/s390/block/dasd_devmap.c.
651 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
652 (one device per port)
653 Format: <port#>,<type>
654 See also Documentation/input/joystick-parport.txt
656 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
657 time. See Documentation/dynamic-debug-howto.txt for
658 details. Deprecated, see dyndbg.
660 debug [KNL] Enable kernel debugging (events log level).
662 debug_locks_verbose=
663 [KNL] verbose self-tests
664 Format=<0|1>
665 Print debugging info while doing the locking API
666 self-tests.
667 We default to 0 (no extra messages), setting it to
668 1 will print _a lot_ more information - normally
669 only useful to kernel developers.
671 debug_objects [KNL] Enable object debugging
673 no_debug_objects
674 [KNL] Disable object debugging
676 debug_guardpage_minorder=
677 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
678 parameter allows control of the order of pages that will
679 be intentionally kept free (and hence protected) by the
680 buddy allocator. Bigger value increase the probability
681 of catching random memory corruption, but reduce the
682 amount of memory for normal system use. The maximum
683 possible value is MAX_ORDER/2. Setting this parameter
684 to 1 or 2 should be enough to identify most random
685 memory corruption problems caused by bugs in kernel or
686 driver code when a CPU writes to (or reads from) a
687 random memory location. Note that there exists a class
688 of memory corruptions problems caused by buggy H/W or
689 F/W or by drivers badly programing DMA (basically when
690 memory is written at bus level and the CPU MMU is
691 bypassed) which are not detectable by
692 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
693 tracking down these problems.
695 debugpat [X86] Enable PAT debugging
697 decnet.addr= [HW,NET]
698 Format: <area>[,<node>]
699 See also Documentation/networking/decnet.txt.
701 default_hugepagesz=
702 [same as hugepagesz=] The size of the default
703 HugeTLB page size. This is the size represented by
704 the legacy /proc/ hugepages APIs, used for SHM, and
705 default size when mounting hugetlbfs filesystems.
706 Defaults to the default architecture's huge page size
707 if not specified.
709 dhash_entries= [KNL]
710 Set number of hash buckets for dentry cache.
712 digi= [HW,SERIAL]
713 IO parameters + enable/disable command.
715 digiepca= [HW,SERIAL]
716 See drivers/char/README.epca and
717 Documentation/serial/digiepca.txt.
719 disable= [IPV6]
720 See Documentation/networking/ipv6.txt.
722 disable_ddw [PPC/PSERIES]
723 Disable Dynamic DMA Window support. Use this if
724 to workaround buggy firmware.
726 disable_ipv6= [IPV6]
727 See Documentation/networking/ipv6.txt.
729 disable_mtrr_cleanup [X86]
730 The kernel tries to adjust MTRR layout from continuous
731 to discrete, to make X server driver able to add WB
732 entry later. This parameter disables that.
734 disable_mtrr_trim [X86, Intel and AMD only]
735 By default the kernel will trim any uncacheable
736 memory out of your available memory pool based on
737 MTRR settings. This parameter disables that behavior,
738 possibly causing your machine to run very slowly.
740 disable_timer_pin_1 [X86]
741 Disable PIN 1 of APIC timer
742 Can be useful to work around chipset bugs.
744 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
745 this option disables the debugging code at boot.
747 dma_debug_entries=<number>
748 This option allows to tune the number of preallocated
749 entries for DMA-API debugging code. One entry is
750 required per DMA-API allocation. Use this if the
751 DMA-API debugging code disables itself because the
752 architectural default is too low.
754 dma_debug_driver=<driver_name>
755 With this option the DMA-API debugging driver
756 filter feature can be enabled at boot time. Just
757 pass the driver to filter for as the parameter.
758 The filter can be disabled or changed to another
759 driver later using sysfs.
761 drm_kms_helper.edid_firmware=[<connector>:]<file>
762 Broken monitors, graphic adapters and KVMs may
763 send no or incorrect EDID data sets. This parameter
764 allows to specify an EDID data set in the
765 /lib/firmware directory that is used instead.
766 Generic built-in EDID data sets are used, if one of
767 edid/1024x768.bin, edid/1280x1024.bin,
768 edid/1680x1050.bin, or edid/1920x1080.bin is given
769 and no file with the same name exists. Details and
770 instructions how to build your own EDID data are
771 available in Documentation/EDID/HOWTO.txt. An EDID
772 data set will only be used for a particular connector,
773 if its name and a colon are prepended to the EDID
774 name.
776 dscc4.setup= [NET]
778 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
779 module.dyndbg[="val"]
780 Enable debug messages at boot time. See
781 Documentation/dynamic-debug-howto.txt for details.
783 earlycon= [KNL] Output early console device and options.
784 uart[8250],io,<addr>[,options]
785 uart[8250],mmio,<addr>[,options]
786 uart[8250],mmio32,<addr>[,options]
787 Start an early, polled-mode console on the 8250/16550
788 UART at the specified I/O port or MMIO address.
789 MMIO inter-register address stride is either 8-bit
790 (mmio) or 32-bit (mmio32).
791 The options are the same as for ttyS, above.
793 earlyprintk= [X86,SH,BLACKFIN,ARM]
794 earlyprintk=vga
795 earlyprintk=xen
796 earlyprintk=serial[,ttySn[,baudrate]]
797 earlyprintk=serial[,0x...[,baudrate]]
798 earlyprintk=ttySn[,baudrate]
799 earlyprintk=dbgp[debugController#]
801 earlyprintk is useful when the kernel crashes before
802 the normal console is initialized. It is not enabled by
803 default because it has some cosmetic problems.
805 Append ",keep" to not disable it when the real console
806 takes over.
808 Only vga or serial or usb debug port at a time.
810 Currently only ttyS0 and ttyS1 may be specified by
811 name. Other I/O ports may be explicitly specified
812 on some architectures (x86 and arm at least) by
813 replacing ttySn with an I/O port address, like this:
814 earlyprintk=serial,0x1008,115200
815 You can find the port for a given device in
816 /proc/tty/driver/serial:
817 2: uart:ST16650V2 port:00001008 irq:18 ...
819 Interaction with the standard serial driver is not
820 very good.
822 The VGA output is eventually overwritten by the real
823 console.
825 The xen output can only be used by Xen PV guests.
827 ekgdboc= [X86,KGDB] Allow early kernel console debugging
828 ekgdboc=kbd
830 This is designed to be used in conjunction with
831 the boot argument: earlyprintk=vga
833 edd= [EDD]
834 Format: {"off" | "on" | "skip[mbr]"}
836 efi_no_storage_paranoia [EFI; X86]
837 Using this parameter you can use more than 50% of
838 your efi variable storage. Use this parameter only if
839 you are really sure that your UEFI does sane gc and
840 fulfills the spec otherwise your board may brick.
842 eisa_irq_edge= [PARISC,HW]
843 See header of drivers/parisc/eisa.c.
845 elanfreq= [X86-32]
846 See comment before function elanfreq_setup() in
847 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
849 elevator= [IOSCHED]
850 Format: {"cfq" | "deadline" | "noop"}
851 See Documentation/block/cfq-iosched.txt and
852 Documentation/block/deadline-iosched.txt for details.
854 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
855 Specifies physical address of start of kernel core
856 image elf header and optionally the size. Generally
857 kexec loader will pass this option to capture kernel.
858 See Documentation/kdump/kdump.txt for details.
860 enable_mtrr_cleanup [X86]
861 The kernel tries to adjust MTRR layout from continuous
862 to discrete, to make X server driver able to add WB
863 entry later. This parameter enables that.
865 enable_timer_pin_1 [X86]
866 Enable PIN 1 of APIC timer
867 Can be useful to work around chipset bugs
868 (in particular on some ATI chipsets).
869 The kernel tries to set a reasonable default.
871 enforcing [SELINUX] Set initial enforcing status.
872 Format: {"0" | "1"}
873 See security/selinux/Kconfig help text.
874 0 -- permissive (log only, no denials).
875 1 -- enforcing (deny and log).
876 Default value is 0.
877 Value can be changed at runtime via /selinux/enforce.
879 erst_disable [ACPI]
880 Disable Error Record Serialization Table (ERST)
881 support.
883 ether= [HW,NET] Ethernet cards parameters
884 This option is obsoleted by the "netdev=" option, which
885 has equivalent usage. See its documentation for details.
887 evm= [EVM]
888 Format: { "fix" }
889 Permit 'security.evm' to be updated regardless of
890 current integrity status.
892 failslab=
893 fail_page_alloc=
894 fail_make_request=[KNL]
895 General fault injection mechanism.
896 Format: <interval>,<probability>,<space>,<times>
897 See also Documentation/fault-injection/.
899 floppy= [HW]
900 See Documentation/blockdev/floppy.txt.
902 force_pal_cache_flush
903 [IA-64] Avoid check_sal_cache_flush which may hang on
904 buggy SAL_CACHE_FLUSH implementations. Using this
905 parameter will force ia64_sal_cache_flush to call
906 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
908 ftrace=[tracer]
909 [FTRACE] will set and start the specified tracer
910 as early as possible in order to facilitate early
911 boot debugging.
913 ftrace_dump_on_oops[=orig_cpu]
914 [FTRACE] will dump the trace buffers on oops.
915 If no parameter is passed, ftrace will dump
916 buffers of all CPUs, but if you pass orig_cpu, it will
917 dump only the buffer of the CPU that triggered the
918 oops.
920 ftrace_filter=[function-list]
921 [FTRACE] Limit the functions traced by the function
922 tracer at boot up. function-list is a comma separated
923 list of functions. This list can be changed at run
924 time by the set_ftrace_filter file in the debugfs
925 tracing directory.
927 ftrace_notrace=[function-list]
928 [FTRACE] Do not trace the functions specified in
929 function-list. This list can be changed at run time
930 by the set_ftrace_notrace file in the debugfs
931 tracing directory.
933 ftrace_graph_filter=[function-list]
934 [FTRACE] Limit the top level callers functions traced
935 by the function graph tracer at boot up.
936 function-list is a comma separated list of functions
937 that can be changed at run time by the
938 set_graph_function file in the debugfs tracing directory.
940 gamecon.map[2|3]=
941 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
942 support via parallel port (up to 5 devices per port)
943 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
944 See also Documentation/input/joystick-parport.txt
946 gamma= [HW,DRM]
948 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
949 Format: off | on
950 default: on
952 gcov_persist= [GCOV] When non-zero (default), profiling data for
953 kernel modules is saved and remains accessible via
954 debugfs, even when the module is unloaded/reloaded.
955 When zero, profiling data is discarded and associated
956 debugfs files are removed at module unload time.
958 gpt [EFI] Forces disk with valid GPT signature but
959 invalid Protective MBR to be treated as GPT.
961 grcan.enable0= [HW] Configuration of physical interface 0. Determines
962 the "Enable 0" bit of the configuration register.
963 Format: 0 | 1
964 Default: 0
965 grcan.enable1= [HW] Configuration of physical interface 1. Determines
966 the "Enable 0" bit of the configuration register.
967 Format: 0 | 1
968 Default: 0
969 grcan.select= [HW] Select which physical interface to use.
970 Format: 0 | 1
971 Default: 0
972 grcan.txsize= [HW] Sets the size of the tx buffer.
973 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
974 Default: 1024
975 grcan.rxsize= [HW] Sets the size of the rx buffer.
976 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
977 Default: 1024
979 hashdist= [KNL,NUMA] Large hashes allocated during boot
980 are distributed across NUMA nodes. Defaults on
981 for 64-bit NUMA, off otherwise.
982 Format: 0 | 1 (for off | on)
984 hcl= [IA-64] SGI's Hardware Graph compatibility layer
986 hd= [EIDE] (E)IDE hard drive subsystem geometry
987 Format: <cyl>,<head>,<sect>
989 hest_disable [ACPI]
990 Disable Hardware Error Source Table (HEST) support;
991 corresponding firmware-first mode error processing
992 logic will be disabled.
994 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
995 size of <nn>. This works even on boxes that have no
996 highmem otherwise. This also works to reduce highmem
997 size on bigger boxes.
999 highres= [KNL] Enable/disable high resolution timer mode.
1000 Valid parameters: "on", "off"
1001 Default: "on"
1003 hisax= [HW,ISDN]
1004 See Documentation/isdn/README.HiSax.
1006 hlt [BUGS=ARM,SH]
1008 hpet= [X86-32,HPET] option to control HPET usage
1009 Format: { enable (default) | disable | force |
1010 verbose }
1011 disable: disable HPET and use PIT instead
1012 force: allow force enabled of undocumented chips (ICH4,
1013 VIA, nVidia)
1014 verbose: show contents of HPET registers during setup
1016 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1017 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1018 On x86-64 and powerpc, this option can be specified
1019 multiple times interleaved with hugepages= to reserve
1020 huge pages of different sizes. Valid pages sizes on
1021 x86-64 are 2M (when the CPU supports "pse") and 1G
1022 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1023 Note that 1GB pages can only be allocated at boot time
1024 using hugepages= and not freed afterwards.
1026 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1027 terminal devices. Valid values: 0..8
1028 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1029 If specified, z/VM IUCV HVC accepts connections
1030 from listed z/VM user IDs only.
1032 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1033 hardware thread id mappings.
1034 Format: <cpu>:<hwthread>
1036 keep_bootcon [KNL]
1037 Do not unregister boot console at start. This is only
1038 useful for debugging when something happens in the window
1039 between unregistering the boot console and initializing
1040 the real console.
1042 i2c_bus= [HW] Override the default board specific I2C bus speed
1043 or register an additional I2C bus that is not
1044 registered from board initialization code.
1045 Format:
1046 <bus_id>,<clkrate>
1048 i8042.debug [HW] Toggle i8042 debug mode
1049 i8042.direct [HW] Put keyboard port into non-translated mode
1050 i8042.dumbkbd [HW] Pretend that controller can only read data from
1051 keyboard and cannot control its state
1052 (Don't attempt to blink the leds)
1053 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1054 i8042.nokbd [HW] Don't check/create keyboard port
1055 i8042.noloop [HW] Disable the AUX Loopback command while probing
1056 for the AUX port
1057 i8042.nomux [HW] Don't check presence of an active multiplexing
1058 controller
1059 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1060 controllers
1061 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1062 i8042.reset [HW] Reset the controller during init and cleanup
1063 i8042.unlock [HW] Unlock (ignore) the keylock
1065 i810= [HW,DRM]
1067 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1068 indicates that the driver is running on unsupported
1069 hardware.
1070 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1071 does not match list of supported models.
1072 i8k.power_status
1073 [HW] Report power status in /proc/i8k
1074 (disabled by default)
1075 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1076 capability is set.
1078 i915.invert_brightness=
1079 [DRM] Invert the sense of the variable that is used to
1080 set the brightness of the panel backlight. Normally a
1081 brightness value of 0 indicates backlight switched off,
1082 and the maximum of the brightness value sets the backlight
1083 to maximum brightness. If this parameter is set to 0
1084 (default) and the machine requires it, or this parameter
1085 is set to 1, a brightness value of 0 sets the backlight
1086 to maximum brightness, and the maximum of the brightness
1087 value switches the backlight off.
1088 -1 -- never invert brightness
1089 0 -- machine default
1090 1 -- force brightness inversion
1092 icn= [HW,ISDN]
1093 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1095 ide-core.nodma= [HW] (E)IDE subsystem
1096 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1097 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1098 .cdrom .chs .ignore_cable are additional options
1099 See Documentation/ide/ide.txt.
1101 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1102 Claim all unknown PCI IDE storage controllers.
1104 idle= [X86]
1105 Format: idle=poll, idle=halt, idle=nomwait
1106 Poll forces a polling idle loop that can slightly
1107 improve the performance of waking up a idle CPU, but
1108 will use a lot of power and make the system run hot.
1109 Not recommended.
1110 idle=halt: Halt is forced to be used for CPU idle.
1111 In such case C2/C3 won't be used again.
1112 idle=nomwait: Disable mwait for CPU C-states
1114 ignore_loglevel [KNL]
1115 Ignore loglevel setting - this will print /all/
1116 kernel messages to the console. Useful for debugging.
1117 We also add it as printk module parameter, so users
1118 could change it dynamically, usually by
1119 /sys/module/printk/parameters/ignore_loglevel.
1121 ihash_entries= [KNL]
1122 Set number of hash buckets for inode cache.
1124 ima_appraise= [IMA] appraise integrity measurements
1125 Format: { "off" | "enforce" | "fix" }
1126 default: "enforce"
1128 ima_appraise_tcb [IMA]
1129 The builtin appraise policy appraises all files
1130 owned by uid=0.
1132 ima_audit= [IMA]
1133 Format: { "0" | "1" }
1134 0 -- integrity auditing messages. (Default)
1135 1 -- enable informational integrity auditing messages.
1137 ima_hash= [IMA]
1138 Format: { "sha1" | "md5" }
1139 default: "sha1"
1141 ima_tcb [IMA]
1142 Load a policy which meets the needs of the Trusted
1143 Computing Base. This means IMA will measure all
1144 programs exec'd, files mmap'd for exec, and all files
1145 opened for read by uid=0.
1147 init= [KNL]
1148 Format: <full_path>
1149 Run specified binary instead of /sbin/init as init
1150 process.
1152 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1153 for working out where the kernel is dying during
1154 startup.
1156 initrd= [BOOT] Specify the location of the initial ramdisk
1158 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1159 Format: <irq>
1161 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1162 on
1163 Enable intel iommu driver.
1164 off
1165 Disable intel iommu driver.
1166 igfx_off [Default Off]
1167 By default, gfx is mapped as normal device. If a gfx
1168 device has a dedicated DMAR unit, the DMAR unit is
1169 bypassed by not enabling DMAR with this option. In
1170 this case, gfx device will use physical address for
1171 DMA.
1172 forcedac [x86_64]
1173 With this option iommu will not optimize to look
1174 for io virtual address below 32-bit forcing dual
1175 address cycle on pci bus for cards supporting greater
1176 than 32-bit addressing. The default is to look
1177 for translation below 32-bit and if not available
1178 then look in the higher range.
1179 strict [Default Off]
1180 With this option on every unmap_single operation will
1181 result in a hardware IOTLB flush operation as opposed
1182 to batching them for performance.
1183 sp_off [Default Off]
1184 By default, super page will be supported if Intel IOMMU
1185 has the capability. With this option, super page will
1186 not be supported.
1188 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1189 0 disables intel_idle and fall back on acpi_idle.
1190 1 to 6 specify maximum depth of C-state.
1192 intel_pstate= [X86]
1193 disable
1194 Do not enable intel_pstate as the default
1195 scaling driver for the supported processors
1197 intremap= [X86-64, Intel-IOMMU]
1198 on enable Interrupt Remapping (default)
1199 off disable Interrupt Remapping
1200 nosid disable Source ID checking
1201 no_x2apic_optout
1202 BIOS x2APIC opt-out request will be ignored
1204 iomem= Disable strict checking of access to MMIO memory
1205 strict regions from userspace.
1206 relaxed
1208 iommu= [x86]
1209 off
1210 force
1211 noforce
1212 biomerge
1213 panic
1214 nopanic
1215 merge
1216 nomerge
1217 forcesac
1218 soft
1219 pt [x86, IA-64]
1222 io7= [HW] IO7 for Marvel based alpha systems
1223 See comment before marvel_specify_io7 in
1224 arch/alpha/kernel/core_marvel.c.
1226 io_delay= [X86] I/O delay method
1227 0x80
1228 Standard port 0x80 based delay
1229 0xed
1230 Alternate port 0xed based delay (needed on some systems)
1231 udelay
1232 Simple two microseconds delay
1233 none
1234 No delay
1236 ip= [IP_PNP]
1237 See Documentation/filesystems/nfs/nfsroot.txt.
1239 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1240 See comment before ip2_setup() in
1241 drivers/char/ip2/ip2base.c.
1243 irqfixup [HW]
1244 When an interrupt is not handled search all handlers
1245 for it. Intended to get systems with badly broken
1246 firmware running.
1248 irqpoll [HW]
1249 When an interrupt is not handled search all handlers
1250 for it. Also check all handlers each timer
1251 interrupt. Intended to get systems with badly broken
1252 firmware running.
1254 isapnp= [ISAPNP]
1255 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1257 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1258 Format:
1259 <cpu number>,...,<cpu number>
1260 or
1261 <cpu number>-<cpu number>
1262 (must be a positive range in ascending order)
1263 or a mixture
1264 <cpu number>,...,<cpu number>-<cpu number>
1266 This option can be used to specify one or more CPUs
1267 to isolate from the general SMP balancing and scheduling
1268 algorithms. You can move a process onto or off an
1269 "isolated" CPU via the CPU affinity syscalls or cpuset.
1270 <cpu number> begins at 0 and the maximum value is
1271 "number of CPUs in system - 1".
1273 This option is the preferred way to isolate CPUs. The
1274 alternative -- manually setting the CPU mask of all
1275 tasks in the system -- can cause problems and
1276 suboptimal load balancer performance.
1278 iucv= [HW,NET]
1280 ivrs_ioapic [HW,X86_64]
1281 Provide an override to the IOAPIC-ID<->DEVICE-ID
1282 mapping provided in the IVRS ACPI table. For
1283 example, to map IOAPIC-ID decimal 10 to
1284 PCI device 00:14.0 write the parameter as:
1285 ivrs_ioapic[10]=00:14.0
1287 ivrs_hpet [HW,X86_64]
1288 Provide an override to the HPET-ID<->DEVICE-ID
1289 mapping provided in the IVRS ACPI table. For
1290 example, to map HPET-ID decimal 0 to
1291 PCI device 00:14.0 write the parameter as:
1292 ivrs_hpet[0]=00:14.0
1294 js= [HW,JOY] Analog joystick
1295 See Documentation/input/joystick.txt.
1297 keepinitrd [HW,ARM]
1299 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1300 specifies the amount of memory usable by the kernel
1301 for non-movable allocations. The requested amount is
1302 spread evenly throughout all nodes in the system. The
1303 remaining memory in each node is used for Movable
1304 pages. In the event, a node is too small to have both
1305 kernelcore and Movable pages, kernelcore pages will
1306 take priority and other nodes will have a larger number
1307 of kernelcore pages. The Movable zone is used for the
1308 allocation of pages that may be reclaimed or moved
1309 by the page migration subsystem. This means that
1310 HugeTLB pages may not be allocated from this zone.
1311 Note that allocations like PTEs-from-HighMem still
1312 use the HighMem zone if it exists, and the Normal
1313 zone if it does not.
1315 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1316 Format: <Controller#>[,poll interval]
1317 The controller # is the number of the ehci usb debug
1318 port as it is probed via PCI. The poll interval is
1319 optional and is the number seconds in between
1320 each poll cycle to the debug port in case you need
1321 the functionality for interrupting the kernel with
1322 gdb or control-c on the dbgp connection. When
1323 not using this parameter you use sysrq-g to break into
1324 the kernel debugger.
1326 kgdboc= [KGDB,HW] kgdb over consoles.
1327 Requires a tty driver that supports console polling,
1328 or a supported polling keyboard driver (non-usb).
1329 Serial only format: <serial_device>[,baud]
1330 keyboard only format: kbd
1331 keyboard and serial format: kbd,<serial_device>[,baud]
1332 Optional Kernel mode setting:
1333 kms, kbd format: kms,kbd
1334 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1336 kgdbwait [KGDB] Stop kernel execution and enter the
1337 kernel debugger at the earliest opportunity.
1339 kmac= [MIPS] korina ethernet MAC address.
1340 Configure the RouterBoard 532 series on-chip
1341 Ethernet adapter MAC address.
1343 kmemleak= [KNL] Boot-time kmemleak enable/disable
1344 Valid arguments: on, off
1345 Default: on
1347 kstack=N [X86] Print N words from the kernel stack
1348 in oops dumps.
1350 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1351 Default is 0 (don't ignore, but inject #GP)
1353 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1354 KVM MMU at runtime.
1355 Default is 0 (off)
1357 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1358 Default is 1 (enabled)
1360 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1361 for all guests.
1362 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1364 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1365 (virtualized MMU) support on capable Intel chips.
1366 Default is 1 (enabled)
1368 kvm-intel.emulate_invalid_guest_state=
1369 [KVM,Intel] Enable emulation of invalid guest states
1370 Default is 0 (disabled)
1372 kvm-intel.flexpriority=
1373 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1374 Default is 1 (enabled)
1376 kvm-intel.nested=
1377 [KVM,Intel] Enable VMX nesting (nVMX).
1378 Default is 0 (disabled)
1380 kvm-intel.unrestricted_guest=
1381 [KVM,Intel] Disable unrestricted guest feature
1382 (virtualized real and unpaged mode) on capable
1383 Intel chips. Default is 1 (enabled)
1385 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1386 feature (tagged TLBs) on capable Intel chips.
1387 Default is 1 (enabled)
1389 l2cr= [PPC]
1391 l3cr= [PPC]
1393 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1394 disabled it.
1396 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1397 value for LAPIC timer one-shot implementation. Default
1398 back to the programmable timer unit in the LAPIC.
1400 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1401 in C2 power state.
1403 libata.dma= [LIBATA] DMA control
1404 libata.dma=0 Disable all PATA and SATA DMA
1405 libata.dma=1 PATA and SATA Disk DMA only
1406 libata.dma=2 ATAPI (CDROM) DMA only
1407 libata.dma=4 Compact Flash DMA only
1408 Combinations also work, so libata.dma=3 enables DMA
1409 for disks and CDROMs, but not CFs.
1411 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1412 libata.ignore_hpa=0 keep BIOS limits (default)
1413 libata.ignore_hpa=1 ignore limits, using full disk
1415 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1416 when set.
1417 Format: <int>
1419 libata.force= [LIBATA] Force configurations. The format is comma
1420 separated list of "[ID:]VAL" where ID is
1421 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1422 matching port, link or device. Basically, it matches
1423 the ATA ID string printed on console by libata. If
1424 the whole ID part is omitted, the last PORT and DEVICE
1425 values are used. If ID hasn't been specified yet, the
1426 configuration applies to all ports, links and devices.
1428 If only DEVICE is omitted, the parameter applies to
1429 the port and all links and devices behind it. DEVICE
1430 number of 0 either selects the first device or the
1431 first fan-out link behind PMP device. It does not
1432 select the host link. DEVICE number of 15 selects the
1433 host link and device attached to it.
1435 The VAL specifies the configuration to force. As long
1436 as there's no ambiguity shortcut notation is allowed.
1437 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1438 The following configurations can be forced.
1440 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1441 Any ID with matching PORT is used.
1443 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1445 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1446 udma[/][16,25,33,44,66,100,133] notation is also
1447 allowed.
1449 * [no]ncq: Turn on or off NCQ.
1451 * nohrst, nosrst, norst: suppress hard, soft
1452 and both resets.
1454 * rstonce: only attempt one reset during
1455 hot-unplug link recovery
1457 * dump_id: dump IDENTIFY data.
1459 If there are multiple matching configurations changing
1460 the same attribute, the last one is used.
1462 memblock=debug [KNL] Enable memblock debug messages.
1464 load_ramdisk= [RAM] List of ramdisks to load from floppy
1465 See Documentation/blockdev/ramdisk.txt.
1467 lockd.nlm_grace_period=P [NFS] Assign grace period.
1468 Format: <integer>
1470 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1471 Format: <integer>
1473 lockd.nlm_timeout=T [NFS] Assign timeout value.
1474 Format: <integer>
1476 lockd.nlm_udpport=M [NFS] Assign UDP port.
1477 Format: <integer>
1479 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1480 Format: <irq>
1482 loglevel= All Kernel Messages with a loglevel smaller than the
1483 console loglevel will be printed to the console. It can
1484 also be changed with klogd or other programs. The
1485 loglevels are defined as follows:
1487 0 (KERN_EMERG) system is unusable
1488 1 (KERN_ALERT) action must be taken immediately
1489 2 (KERN_CRIT) critical conditions
1490 3 (KERN_ERR) error conditions
1491 4 (KERN_WARNING) warning conditions
1492 5 (KERN_NOTICE) normal but significant condition
1493 6 (KERN_INFO) informational
1494 7 (KERN_DEBUG) debug-level messages
1496 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1497 in bytes. n must be a power of two. The default
1498 size is set in the kernel config file.
1500 logo.nologo [FB] Disables display of the built-in Linux logo.
1501 This may be used to provide more screen space for
1502 kernel log messages and is useful when debugging
1503 kernel boot problems.
1505 lp=0 [LP] Specify parallel ports to use, e.g,
1506 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1507 lp=reset first parallel port). 'lp=0' disables the
1508 lp=auto printer driver. 'lp=reset' (which can be
1509 specified in addition to the ports) causes
1510 attached printers to be reset. Using
1511 lp=port1,port2,... specifies the parallel ports
1512 to associate lp devices with, starting with
1513 lp0. A port specification may be 'none' to skip
1514 that lp device, or a parport name such as
1515 'parport0'. Specifying 'lp=auto' instead of a
1516 port specification list means that device IDs
1517 from each port should be examined, to see if
1518 an IEEE 1284-compliant printer is attached; if
1519 so, the driver will manage that printer.
1520 See also header of drivers/char/lp.c.
1522 lpj=n [KNL]
1523 Sets loops_per_jiffy to given constant, thus avoiding
1524 time-consuming boot-time autodetection (up to 250 ms per
1525 CPU). 0 enables autodetection (default). To determine
1526 the correct value for your kernel, boot with normal
1527 autodetection and see what value is printed. Note that
1528 on SMP systems the preset will be applied to all CPUs,
1529 which is likely to cause problems if your CPUs need
1530 significantly divergent settings. An incorrect value
1531 will cause delays in the kernel to be wrong, leading to
1532 unpredictable I/O errors and other breakage. Although
1533 unlikely, in the extreme case this might damage your
1534 hardware.
1536 ltpc= [NET]
1537 Format: <io>,<irq>,<dma>
1539 machvec= [IA-64] Force the use of a particular machine-vector
1540 (machvec) in a generic kernel.
1541 Example: machvec=hpzx1_swiotlb
1543 machtype= [Loongson] Share the same kernel image file between different
1544 yeeloong laptop.
1545 Example: machtype=lemote-yeeloong-2f-7inch
1547 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1548 than or equal to this physical address is ignored.
1550 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1551 should make use of. maxcpus=n : n >= 0 limits the
1552 kernel to using 'n' processors. n=0 is a special case,
1553 it is equivalent to "nosmp", which also disables
1554 the IO APIC.
1556 max_loop= [LOOP] The number of loop block devices that get
1557 (loop.max_loop) unconditionally pre-created at init time. The default
1558 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1559 of statically allocating a predefined number, loop
1560 devices can be requested on-demand with the
1561 /dev/loop-control interface.
1563 mce [X86-32] Machine Check Exception
1565 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1567 md= [HW] RAID subsystems devices and level
1568 See Documentation/md.txt.
1570 mdacon= [MDA]
1571 Format: <first>,<last>
1572 Specifies range of consoles to be captured by the MDA.
1574 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1575 Amount of memory to be used when the kernel is not able
1576 to see the whole system memory or for test.
1577 [X86] Work as limiting max address. Use together
1578 with memmap= to avoid physical address space collisions.
1579 Without memmap= PCI devices could be placed at addresses
1580 belonging to unused RAM.
1582 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1583 memory.
1585 memchunk=nn[KMG]
1586 [KNL,SH] Allow user to override the default size for
1587 per-device physically contiguous DMA buffers.
1589 memmap=exactmap [KNL,X86] Enable setting of an exact
1590 E820 memory map, as specified by the user.
1591 Such memmap=exactmap lines can be constructed based on
1592 BIOS output or other requirements. See the memmap=nn@ss
1593 option description.
1595 memmap=nn[KMG]@ss[KMG]
1596 [KNL] Force usage of a specific region of memory
1597 Region of memory to be used, from ss to ss+nn.
1599 memmap=nn[KMG]#ss[KMG]
1600 [KNL,ACPI] Mark specific memory as ACPI data.
1601 Region of memory to be used, from ss to ss+nn.
1603 memmap=nn[KMG]$ss[KMG]
1604 [KNL,ACPI] Mark specific memory as reserved.
1605 Region of memory to be used, from ss to ss+nn.
1606 Example: Exclude memory from 0x18690000-0x1869ffff
1607 memmap=64K$0x18690000
1608 or
1609 memmap=0x10000$0x18690000
1611 memory_corruption_check=0/1 [X86]
1612 Some BIOSes seem to corrupt the first 64k of
1613 memory when doing things like suspend/resume.
1614 Setting this option will scan the memory
1615 looking for corruption. Enabling this will
1616 both detect corruption and prevent the kernel
1617 from using the memory being corrupted.
1618 However, its intended as a diagnostic tool; if
1619 repeatable BIOS-originated corruption always
1620 affects the same memory, you can use memmap=
1621 to prevent the kernel from using that memory.
1623 memory_corruption_check_size=size [X86]
1624 By default it checks for corruption in the low
1625 64k, making this memory unavailable for normal
1626 use. Use this parameter to scan for
1627 corruption in more or less memory.
1629 memory_corruption_check_period=seconds [X86]
1630 By default it checks for corruption every 60
1631 seconds. Use this parameter to check at some
1632 other rate. 0 disables periodic checking.
1634 memtest= [KNL,X86] Enable memtest
1635 Format: <integer>
1636 default : 0 <disable>
1637 Specifies the number of memtest passes to be
1638 performed. Each pass selects another test
1639 pattern from a given set of patterns. Memtest
1640 fills the memory with this pattern, validates
1641 memory contents and reserves bad memory
1642 regions that are detected.
1644 meye.*= [HW] Set MotionEye Camera parameters
1645 See Documentation/video4linux/meye.txt.
1647 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1648 Multi-Function General Purpose Timers on AMD Geode
1649 platforms.
1651 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1652 the BIOS has incorrectly applied a workaround. TinyBIOS
1653 version 0.98 is known to be affected, 0.99 fixes the
1654 problem by letting the user disable the workaround.
1656 mga= [HW,DRM]
1658 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1659 physical address is ignored.
1661 mini2440= [ARM,HW,KNL]
1662 Format:[0..2][b][c][t]
1663 Default: "0tb"
1664 MINI2440 configuration specification:
1665 0 - The attached screen is the 3.5" TFT
1666 1 - The attached screen is the 7" TFT
1667 2 - The VGA Shield is attached (1024x768)
1668 Leaving out the screen size parameter will not load
1669 the TFT driver, and the framebuffer will be left
1670 unconfigured.
1671 b - Enable backlight. The TFT backlight pin will be
1672 linked to the kernel VESA blanking code and a GPIO
1673 LED. This parameter is not necessary when using the
1674 VGA shield.
1675 c - Enable the s3c camera interface.
1676 t - Reserved for enabling touchscreen support. The
1677 touchscreen support is not enabled in the mainstream
1678 kernel as of 2.6.30, a preliminary port can be found
1679 in the "bleeding edge" mini2440 support kernel at
1680 http://repo.or.cz/w/linux-2.6/mini2440.git
1682 mminit_loglevel=
1683 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1684 parameter allows control of the logging verbosity for
1685 the additional memory initialisation checks. A value
1686 of 0 disables mminit logging and a level of 4 will
1687 log everything. Information is printed at KERN_DEBUG
1688 so loglevel=8 may also need to be specified.
1690 module.sig_enforce
1691 [KNL] When CONFIG_MODULE_SIG is set, this means that
1692 modules without (valid) signatures will fail to load.
1693 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1694 is always true, so this option does nothing.
1696 mousedev.tap_time=
1697 [MOUSE] Maximum time between finger touching and
1698 leaving touchpad surface for touch to be considered
1699 a tap and be reported as a left button click (for
1700 touchpads working in absolute mode only).
1701 Format: <msecs>
1702 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1703 reporting absolute coordinates, such as tablets
1704 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1705 reporting absolute coordinates, such as tablets
1707 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1708 is similar to kernelcore except it specifies the
1709 amount of memory used for migratable allocations.
1710 If both kernelcore and movablecore is specified,
1711 then kernelcore will be at *least* the specified
1712 value but may be more. If movablecore on its own
1713 is specified, the administrator must be careful
1714 that the amount of memory usable for all allocations
1715 is not too small.
1717 MTD_Partition= [MTD]
1718 Format: <name>,<region-number>,<size>,<offset>
1720 MTD_Region= [MTD] Format:
1721 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1723 mtdparts= [MTD]
1724 See drivers/mtd/cmdlinepart.c.
1726 multitce=off [PPC] This parameter disables the use of the pSeries
1727 firmware feature for updating multiple TCE entries
1728 at a time.
1730 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1732 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1734 boundary - index of last SLC block on Flex-OneNAND.
1735 The remaining blocks are configured as MLC blocks.
1736 lock - Configure if Flex-OneNAND boundary should be locked.
1737 Once locked, the boundary cannot be changed.
1738 1 indicates lock status, 0 indicates unlock status.
1740 mtdset= [ARM]
1741 ARM/S3C2412 JIVE boot control
1743 See arch/arm/mach-s3c2412/mach-jive.c
1745 mtouchusb.raw_coordinates=
1746 [HW] Make the MicroTouch USB driver use raw coordinates
1747 ('y', default) or cooked coordinates ('n')
1749 mtrr_chunk_size=nn[KMG] [X86]
1750 used for mtrr cleanup. It is largest continuous chunk
1751 that could hold holes aka. UC entries.
1753 mtrr_gran_size=nn[KMG] [X86]
1754 Used for mtrr cleanup. It is granularity of mtrr block.
1755 Default is 1.
1756 Large value could prevent small alignment from
1757 using up MTRRs.
1759 mtrr_spare_reg_nr=n [X86]
1760 Format: <integer>
1761 Range: 0,7 : spare reg number
1762 Default : 1
1763 Used for mtrr cleanup. It is spare mtrr entries number.
1764 Set to 2 or more if your graphical card needs more.
1766 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1768 netdev= [NET] Network devices parameters
1769 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1770 Note that mem_start is often overloaded to mean
1771 something different and driver-specific.
1772 This usage is only documented in each driver source
1773 file if at all.
1775 nf_conntrack.acct=
1776 [NETFILTER] Enable connection tracking flow accounting
1777 0 to disable accounting
1778 1 to enable accounting
1779 Default value is 0.
1781 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1782 See Documentation/filesystems/nfs/nfsroot.txt.
1784 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1785 See Documentation/filesystems/nfs/nfsroot.txt.
1787 nfsrootdebug [NFS] enable nfsroot debugging messages.
1788 See Documentation/filesystems/nfs/nfsroot.txt.
1790 nfs.callback_tcpport=
1791 [NFS] set the TCP port on which the NFSv4 callback
1792 channel should listen.
1794 nfs.cache_getent=
1795 [NFS] sets the pathname to the program which is used
1796 to update the NFS client cache entries.
1798 nfs.cache_getent_timeout=
1799 [NFS] sets the timeout after which an attempt to
1800 update a cache entry is deemed to have failed.
1802 nfs.idmap_cache_timeout=
1803 [NFS] set the maximum lifetime for idmapper cache
1804 entries.
1806 nfs.enable_ino64=
1807 [NFS] enable 64-bit inode numbers.
1808 If zero, the NFS client will fake up a 32-bit inode
1809 number for the readdir() and stat() syscalls instead
1810 of returning the full 64-bit number.
1811 The default is to return 64-bit inode numbers.
1813 nfs.max_session_slots=
1814 [NFSv4.1] Sets the maximum number of session slots
1815 the client will attempt to negotiate with the server.
1816 This limits the number of simultaneous RPC requests
1817 that the client can send to the NFSv4.1 server.
1818 Note that there is little point in setting this
1819 value higher than the max_tcp_slot_table_limit.
1821 nfs.nfs4_disable_idmapping=
1822 [NFSv4] When set to the default of '1', this option
1823 ensures that both the RPC level authentication
1824 scheme and the NFS level operations agree to use
1825 numeric uids/gids if the mount is using the
1826 'sec=sys' security flavour. In effect it is
1827 disabling idmapping, which can make migration from
1828 legacy NFSv2/v3 systems to NFSv4 easier.
1829 Servers that do not support this mode of operation
1830 will be autodetected by the client, and it will fall
1831 back to using the idmapper.
1832 To turn off this behaviour, set the value to '0'.
1833 nfs.nfs4_unique_id=
1834 [NFS4] Specify an additional fixed unique ident-
1835 ification string that NFSv4 clients can insert into
1836 their nfs_client_id4 string. This is typically a
1837 UUID that is generated at system install time.
1839 nfs.send_implementation_id =
1840 [NFSv4.1] Send client implementation identification
1841 information in exchange_id requests.
1842 If zero, no implementation identification information
1843 will be sent.
1844 The default is to send the implementation identification
1845 information.
1847 nfsd.nfs4_disable_idmapping=
1848 [NFSv4] When set to the default of '1', the NFSv4
1849 server will return only numeric uids and gids to
1850 clients using auth_sys, and will accept numeric uids
1851 and gids from such clients. This is intended to ease
1852 migration from NFSv2/v3.
1854 objlayoutdriver.osd_login_prog=
1855 [NFS] [OBJLAYOUT] sets the pathname to the program which
1856 is used to automatically discover and login into new
1857 osd-targets. Please see:
1858 Documentation/filesystems/pnfs.txt for more explanations
1860 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1861 when a NMI is triggered.
1862 Format: [state][,regs][,debounce][,die]
1864 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1865 Format: [panic,][nopanic,][num]
1866 Valid num: 0
1867 0 - turn nmi_watchdog off
1868 When panic is specified, panic when an NMI watchdog
1869 timeout occurs (or 'nopanic' to override the opposite
1870 default).
1871 This is useful when you use a panic=... timeout and
1872 need the box quickly up again.
1874 netpoll.carrier_timeout=
1875 [NET] Specifies amount of time (in seconds) that
1876 netpoll should wait for a carrier. By default netpoll
1877 waits 4 seconds.
1879 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1880 emulation library even if a 387 maths coprocessor
1881 is present.
1883 no_console_suspend
1884 [HW] Never suspend the console
1885 Disable suspending of consoles during suspend and
1886 hibernate operations. Once disabled, debugging
1887 messages can reach various consoles while the rest
1888 of the system is being put to sleep (ie, while
1889 debugging driver suspend/resume hooks). This may
1890 not work reliably with all consoles, but is known
1891 to work with serial and VGA consoles.
1892 To facilitate more flexible debugging, we also add
1893 console_suspend, a printk module parameter to control
1894 it. Users could use console_suspend (usually
1895 /sys/module/printk/parameters/console_suspend) to
1896 turn on/off it dynamically.
1898 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1899 caches in the slab allocator. Saves per-node memory,
1900 but will impact performance.
1902 noalign [KNL,ARM]
1904 noapic [SMP,APIC] Tells the kernel to not make use of any
1905 IOAPICs that may be present in the system.
1907 noautogroup Disable scheduler automatic task group creation.
1909 nobats [PPC] Do not use BATs for mapping kernel lowmem
1910 on "Classic" PPC cores.
1912 nocache [ARM]
1914 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1916 nodelayacct [KNL] Disable per-task delay accounting
1918 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1920 nodsp [SH] Disable hardware DSP at boot time.
1922 noefi [X86] Disable EFI runtime services support.
1924 noexec [IA-64]
1926 noexec [X86]
1927 On X86-32 available only on PAE configured kernels.
1928 noexec=on: enable non-executable mappings (default)
1929 noexec=off: disable non-executable mappings
1931 nosmap [X86]
1932 Disable SMAP (Supervisor Mode Access Prevention)
1933 even if it is supported by processor.
1935 nosmep [X86]
1936 Disable SMEP (Supervisor Mode Execution Prevention)
1937 even if it is supported by processor.
1939 noexec32 [X86-64]
1940 This affects only 32-bit executables.
1941 noexec32=on: enable non-executable mappings (default)
1942 read doesn't imply executable mappings
1943 noexec32=off: disable non-executable mappings
1944 read implies executable mappings
1946 nofpu [SH] Disable hardware FPU at boot time.
1948 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1949 register save and restore. The kernel will only save
1950 legacy floating-point registers on task switch.
1952 noxsave [BUGS=X86] Disables x86 extended register state save
1953 and restore using xsave. The kernel will fallback to
1954 enabling legacy floating-point and sse state.
1956 eagerfpu= [X86]
1957 on enable eager fpu restore
1958 off disable eager fpu restore
1959 auto selects the default scheme, which automatically
1960 enables eagerfpu restore for xsaveopt.
1962 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1963 wfi(ARM) instruction doesn't work correctly and not to
1964 use it. This is also useful when using JTAG debugger.
1966 no_file_caps Tells the kernel not to honor file capabilities. The
1967 only way then for a file to be executed with privilege
1968 is to be setuid root or executed by root.
1970 nohalt [IA-64] Tells the kernel not to use the power saving
1971 function PAL_HALT_LIGHT when idle. This increases
1972 power-consumption. On the positive side, it reduces
1973 interrupt wake-up latency, which may improve performance
1974 in certain environments such as networked servers or
1975 real-time systems.
1977 nohz= [KNL] Boottime enable/disable dynamic ticks
1978 Valid arguments: on, off
1979 Default: on
1981 nohz_full= [KNL,BOOT]
1982 In kernels built with CONFIG_NO_HZ_FULL=y, set
1983 the specified list of CPUs whose tick will be stopped
1984 whenever possible. The boot CPU will be forced outside
1985 the range to maintain the timekeeping.
1986 The CPUs in this range must also be included in the
1987 rcu_nocbs= set.
1989 noiotrap [SH] Disables trapped I/O port accesses.
1991 noirqdebug [X86-32] Disables the code which attempts to detect and
1992 disable unhandled interrupt sources.
1994 no_timer_check [X86,APIC] Disables the code which tests for
1995 broken timer IRQ sources.
1997 noisapnp [ISAPNP] Disables ISA PnP code.
1999 noinitrd [RAM] Tells the kernel not to load any configured
2000 initial RAM disk.
2002 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2003 remapping.
2004 [Deprecated - use intremap=off]
2006 nointroute [IA-64]
2008 nojitter [IA-64] Disables jitter checking for ITC timers.
2010 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2012 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2013 fault handling.
2015 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2016 steal time is computed, but won't influence scheduler
2017 behaviour
2019 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2021 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2023 noltlbs [PPC] Do not use large page/tlb entries for kernel
2024 lowmem mapping on PPC40x.
2026 nomca [IA-64] Disable machine check abort handling
2028 nomce [X86-32] Machine Check Exception
2030 nomfgpt [X86-32] Disable Multi-Function General Purpose
2031 Timer usage (for AMD Geode machines).
2033 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2034 shutdown the other cpus. Instead use the REBOOT_VECTOR
2035 irq.
2037 nomodule Disable module load
2039 nopat [X86] Disable PAT (page attribute table extension of
2040 pagetables) support.
2042 norandmaps Don't use address space randomization. Equivalent to
2043 echo 0 > /proc/sys/kernel/randomize_va_space
2045 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2047 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2048 with UP alternatives
2050 nordrand [X86] Disable the direct use of the RDRAND
2051 instruction even if it is supported by the
2052 processor. RDRAND is still available to user
2053 space applications.
2055 noresume [SWSUSP] Disables resume and restores original swap
2056 space.
2058 no-scroll [VGA] Disables scrollback.
2059 This is required for the Braillex ib80-piezo Braille
2060 reader made by F.H. Papenmeier (Germany).
2062 nosbagart [IA-64]
2064 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2066 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2067 and disable the IO APIC. legacy for "maxcpus=0".
2069 nosoftlockup [KNL] Disable the soft-lockup detector.
2071 nosync [HW,M68K] Disables sync negotiation for all devices.
2073 notsc [BUGS=X86-32] Disable Time Stamp Counter
2075 nousb [USB] Disable the USB subsystem
2077 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2079 nowb [ARM]
2081 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2083 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2084 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2085 Some features depend on CPU0. Known dependencies are:
2086 1. Resume from suspend/hibernate depends on CPU0.
2087 Suspend/hibernate will fail if CPU0 is offline and you
2088 need to online CPU0 before suspend/hibernate.
2089 2. PIC interrupts also depend on CPU0. CPU0 can't be
2090 removed if a PIC interrupt is detected.
2091 It's said poweroff/reboot may depend on CPU0 on some
2092 machines although I haven't seen such issues so far
2093 after CPU0 is offline on a few tested machines.
2094 If the dependencies are under your control, you can
2095 turn on cpu0_hotplug.
2097 nptcg= [IA-64] Override max number of concurrent global TLB
2098 purges which is reported from either PAL_VM_SUMMARY or
2099 SAL PALO.
2101 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2102 could support. nr_cpus=n : n >= 1 limits the kernel to
2103 supporting 'n' processors. Later in runtime you can not
2104 use hotplug cpu feature to put more cpu back to online.
2105 just like you compile the kernel NR_CPUS=n
2107 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2109 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2110 Allowed values are enable and disable
2112 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2113 one of ['zone', 'node', 'default'] can be specified
2114 This can be set from sysctl after boot.
2115 See Documentation/sysctl/vm.txt for details.
2117 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2118 See Documentation/debugging-via-ohci1394.txt for more
2119 info.
2121 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2122 Rather than timing out after 20 ms if an EC
2123 command is not properly ACKed, override the length
2124 of the timeout. We have interrupts disabled while
2125 waiting for the ACK, so if this is set too high
2126 interrupts *may* be lost!
2128 omap_mux= [OMAP] Override bootloader pin multiplexing.
2129 Format: <mux_mode0.mode_name=value>...
2130 For example, to override I2C bus2:
2131 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2133 oprofile.timer= [HW]
2134 Use timer interrupt instead of performance counters
2136 oprofile.cpu_type= Force an oprofile cpu type
2137 This might be useful if you have an older oprofile
2138 userland or if you want common events.
2139 Format: { arch_perfmon }
2140 arch_perfmon: [X86] Force use of architectural
2141 perfmon on Intel CPUs instead of the
2142 CPU specific event set.
2143 timer: [X86] Force use of architectural NMI
2144 timer mode (see also oprofile.timer
2145 for generic hr timer mode)
2146 [s390] Force legacy basic mode sampling
2147 (report cpu_type "timer")
2149 oops=panic Always panic on oopses. Default is to just kill the
2150 process, but there is a small probability of
2151 deadlocking the machine.
2152 This will also cause panics on machine check exceptions.
2153 Useful together with panic=30 to trigger a reboot.
2155 OSS [HW,OSS]
2156 See Documentation/sound/oss/oss-parameters.txt
2158 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2159 timeout > 0: seconds before rebooting
2160 timeout = 0: wait forever
2161 timeout < 0: reboot immediately
2162 Format: <timeout>
2164 parkbd.port= [HW] Parallel port number the keyboard adapter is
2165 connected to, default is 0.
2166 Format: <parport#>
2167 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2168 0 for XT, 1 for AT (default is AT).
2169 Format: <mode>
2171 parport= [HW,PPT] Specify parallel ports. 0 disables.
2172 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2173 Use 'auto' to force the driver to use any
2174 IRQ/DMA settings detected (the default is to
2175 ignore detected IRQ/DMA settings because of
2176 possible conflicts). You can specify the base
2177 address, IRQ, and DMA settings; IRQ and DMA
2178 should be numbers, or 'auto' (for using detected
2179 settings on that particular port), or 'nofifo'
2180 (to avoid using a FIFO even if it is detected).
2181 Parallel ports are assigned in the order they
2182 are specified on the command line, starting
2183 with parport0.
2185 parport_init_mode= [HW,PPT]
2186 Configure VIA parallel port to operate in
2187 a specific mode. This is necessary on Pegasos
2188 computer where firmware has no options for setting
2189 up parallel port mode and sets it to spp.
2190 Currently this function knows 686a and 8231 chips.
2191 Format: [spp|ps2|epp|ecp|ecpepp]
2193 pause_on_oops=
2194 Halt all CPUs after the first oops has been printed for
2195 the specified number of seconds. This is to be used if
2196 your oopses keep scrolling off the screen.
2198 pcbit= [HW,ISDN]
2200 pcd. [PARIDE]
2201 See header of drivers/block/paride/pcd.c.
2202 See also Documentation/blockdev/paride.txt.
2204 pci=option[,option...] [PCI] various PCI subsystem options:
2205 earlydump [X86] dump PCI config space before the kernel
2206 changes anything
2207 off [X86] don't probe for the PCI bus
2208 bios [X86-32] force use of PCI BIOS, don't access
2209 the hardware directly. Use this if your machine
2210 has a non-standard PCI host bridge.
2211 nobios [X86-32] disallow use of PCI BIOS, only direct
2212 hardware access methods are allowed. Use this
2213 if you experience crashes upon bootup and you
2214 suspect they are caused by the BIOS.
2215 conf1 [X86] Force use of PCI Configuration
2216 Mechanism 1.
2217 conf2 [X86] Force use of PCI Configuration
2218 Mechanism 2.
2219 noaer [PCIE] If the PCIEAER kernel config parameter is
2220 enabled, this kernel boot option can be used to
2221 disable the use of PCIE advanced error reporting.
2222 nodomains [PCI] Disable support for multiple PCI
2223 root domains (aka PCI segments, in ACPI-speak).
2224 nommconf [X86] Disable use of MMCONFIG for PCI
2225 Configuration
2226 check_enable_amd_mmconf [X86] check for and enable
2227 properly configured MMIO access to PCI
2228 config space on AMD family 10h CPU
2229 nomsi [MSI] If the PCI_MSI kernel config parameter is
2230 enabled, this kernel boot option can be used to
2231 disable the use of MSI interrupts system-wide.
2232 noioapicquirk [APIC] Disable all boot interrupt quirks.
2233 Safety option to keep boot IRQs enabled. This
2234 should never be necessary.
2235 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2236 primary IO-APIC for bridges that cannot disable
2237 boot IRQs. This fixes a source of spurious IRQs
2238 when the system masks IRQs.
2239 noioapicreroute [APIC] Disable workaround that uses the
2240 boot IRQ equivalent of an IRQ that connects to
2241 a chipset where boot IRQs cannot be disabled.
2242 The opposite of ioapicreroute.
2243 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2244 routing table. These calls are known to be buggy
2245 on several machines and they hang the machine
2246 when used, but on other computers it's the only
2247 way to get the interrupt routing table. Try
2248 this option if the kernel is unable to allocate
2249 IRQs or discover secondary PCI buses on your
2250 motherboard.
2251 rom [X86] Assign address space to expansion ROMs.
2252 Use with caution as certain devices share
2253 address decoders between ROMs and other
2254 resources.
2255 norom [X86] Do not assign address space to
2256 expansion ROMs that do not already have
2257 BIOS assigned address ranges.
2258 nobar [X86] Do not assign address space to the
2259 BARs that weren't assigned by the BIOS.
2260 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2261 assigned automatically to PCI devices. You can
2262 make the kernel exclude IRQs of your ISA cards
2263 this way.
2264 pirqaddr=0xAAAAA [X86] Specify the physical address
2265 of the PIRQ table (normally generated
2266 by the BIOS) if it is outside the
2267 F0000h-100000h range.
2268 lastbus=N [X86] Scan all buses thru bus #N. Can be
2269 useful if the kernel is unable to find your
2270 secondary buses and you want to tell it
2271 explicitly which ones they are.
2272 assign-busses [X86] Always assign all PCI bus
2273 numbers ourselves, overriding
2274 whatever the firmware may have done.
2275 usepirqmask [X86] Honor the possible IRQ mask stored
2276 in the BIOS $PIR table. This is needed on
2277 some systems with broken BIOSes, notably
2278 some HP Pavilion N5400 and Omnibook XE3
2279 notebooks. This will have no effect if ACPI
2280 IRQ routing is enabled.
2281 noacpi [X86] Do not use ACPI for IRQ routing
2282 or for PCI scanning.
2283 use_crs [X86] Use PCI host bridge window information
2284 from ACPI. On BIOSes from 2008 or later, this
2285 is enabled by default. If you need to use this,
2286 please report a bug.
2287 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2288 If you need to use this, please report a bug.
2289 routeirq Do IRQ routing for all PCI devices.
2290 This is normally done in pci_enable_device(),
2291 so this option is a temporary workaround
2292 for broken drivers that don't call it.
2293 skip_isa_align [X86] do not align io start addr, so can
2294 handle more pci cards
2295 firmware [ARM] Do not re-enumerate the bus but instead
2296 just use the configuration from the
2297 bootloader. This is currently used on
2298 IXP2000 systems where the bus has to be
2299 configured a certain way for adjunct CPUs.
2300 noearly [X86] Don't do any early type 1 scanning.
2301 This might help on some broken boards which
2302 machine check when some devices' config space
2303 is read. But various workarounds are disabled
2304 and some IOMMU drivers will not work.
2305 bfsort Sort PCI devices into breadth-first order.
2306 This sorting is done to get a device
2307 order compatible with older (<= 2.4) kernels.
2308 nobfsort Don't sort PCI devices into breadth-first order.
2309 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2310 tuning and use the BIOS-configured MPS defaults.
2311 pcie_bus_safe Set every device's MPS to the largest value
2312 supported by all devices below the root complex.
2313 pcie_bus_perf Set device MPS to the largest allowable MPS
2314 based on its parent bus. Also set MRRS (Max
2315 Read Request Size) to the largest supported
2316 value (no larger than the MPS that the device
2317 or bus can support) for best performance.
2318 pcie_bus_peer2peer Set every device's MPS to 128B, which
2319 every device is guaranteed to support. This
2320 configuration allows peer-to-peer DMA between
2321 any pair of devices, possibly at the cost of
2322 reduced performance. This also guarantees
2323 that hot-added devices will work.
2324 cbiosize=nn[KMG] The fixed amount of bus space which is
2325 reserved for the CardBus bridge's IO window.
2326 The default value is 256 bytes.
2327 cbmemsize=nn[KMG] The fixed amount of bus space which is
2328 reserved for the CardBus bridge's memory
2329 window. The default value is 64 megabytes.
2330 resource_alignment=
2331 Format:
2332 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2333 Specifies alignment and device to reassign
2334 aligned memory resources.
2335 If <order of align> is not specified,
2336 PAGE_SIZE is used as alignment.
2337 PCI-PCI bridge can be specified, if resource
2338 windows need to be expanded.
2339 ecrc= Enable/disable PCIe ECRC (transaction layer
2340 end-to-end CRC checking).
2341 bios: Use BIOS/firmware settings. This is the
2342 the default.
2343 off: Turn ECRC off
2344 on: Turn ECRC on.
2345 hpiosize=nn[KMG] The fixed amount of bus space which is
2346 reserved for hotplug bridge's IO window.
2347 Default size is 256 bytes.
2348 hpmemsize=nn[KMG] The fixed amount of bus space which is
2349 reserved for hotplug bridge's memory window.
2350 Default size is 2 megabytes.
2351 realloc= Enable/disable reallocating PCI bridge resources
2352 if allocations done by BIOS are too small to
2353 accommodate resources required by all child
2354 devices.
2355 off: Turn realloc off
2356 on: Turn realloc on
2357 realloc same as realloc=on
2358 noari do not use PCIe ARI.
2359 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2360 only look for one device below a PCIe downstream
2361 port.
2363 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2364 Management.
2365 off Disable ASPM.
2366 force Enable ASPM even on devices that claim not to support it.
2367 WARNING: Forcing ASPM on may cause system lockups.
2369 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2370 nomsi Do not use MSI for PCI Express Native Hotplug (this
2371 makes all PCIe ports use INTx for hotplug services).
2373 pcie_ports= [PCIE] PCIe ports handling:
2374 auto Ask the BIOS whether or not to use native PCIe services
2375 associated with PCIe ports (PME, hot-plug, AER). Use
2376 them only if that is allowed by the BIOS.
2377 native Use native PCIe services associated with PCIe ports
2378 unconditionally.
2379 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2380 ports driver.
2382 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2383 nomsi Do not use MSI for native PCIe PME signaling (this makes
2384 all PCIe root ports use INTx for all services).
2386 pcmv= [HW,PCMCIA] BadgePAD 4
2388 pd. [PARIDE]
2389 See Documentation/blockdev/paride.txt.
2391 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2392 boot time.
2393 Format: { 0 | 1 }
2394 See arch/parisc/kernel/pdc_chassis.c
2396 percpu_alloc= Select which percpu first chunk allocator to use.
2397 Currently supported values are "embed" and "page".
2398 Archs may support subset or none of the selections.
2399 See comments in mm/percpu.c for details on each
2400 allocator. This parameter is primarily for debugging
2401 and performance comparison.
2403 pf. [PARIDE]
2404 See Documentation/blockdev/paride.txt.
2406 pg. [PARIDE]
2407 See Documentation/blockdev/paride.txt.
2409 pirq= [SMP,APIC] Manual mp-table setup
2410 See Documentation/x86/i386/IO-APIC.txt.
2412 plip= [PPT,NET] Parallel port network link
2413 Format: { parport<nr> | timid | 0 }
2414 See also Documentation/parport.txt.
2416 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2417 Override pmtimer IOPort with a hex value.
2418 e.g. pmtmr=0x508
2420 pnp.debug=1 [PNP]
2421 Enable PNP debug messages (depends on the
2422 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2423 via /sys/module/pnp/parameters/debug. We always show
2424 current resource usage; turning this on also shows
2425 possible settings and some assignment information.
2427 pnpacpi= [ACPI]
2428 { off }
2430 pnpbios= [ISAPNP]
2431 { on | off | curr | res | no-curr | no-res }
2433 pnp_reserve_irq=
2434 [ISAPNP] Exclude IRQs for the autoconfiguration
2436 pnp_reserve_dma=
2437 [ISAPNP] Exclude DMAs for the autoconfiguration
2439 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2440 Ranges are in pairs (I/O port base and size).
2442 pnp_reserve_mem=
2443 [ISAPNP] Exclude memory regions for the
2444 autoconfiguration.
2445 Ranges are in pairs (memory base and size).
2447 ports= [IP_VS_FTP] IPVS ftp helper module
2448 Default is 21.
2449 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2450 may be specified.
2451 Format: <port>,<port>....
2453 print-fatal-signals=
2454 [KNL] debug: print fatal signals
2456 If enabled, warn about various signal handling
2457 related application anomalies: too many signals,
2458 too many POSIX.1 timers, fatal signals causing a
2459 coredump - etc.
2461 If you hit the warning due to signal overflow,
2462 you might want to try "ulimit -i unlimited".
2464 default: off.
2466 printk.always_kmsg_dump=
2467 Trigger kmsg_dump for cases other than kernel oops or
2468 panics
2469 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2470 default: disabled
2472 printk.time= Show timing data prefixed to each printk message line
2473 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2475 processor.max_cstate= [HW,ACPI]
2476 Limit processor to maximum C-state
2477 max_cstate=9 overrides any DMI blacklist limit.
2479 processor.nocst [HW,ACPI]
2480 Ignore the _CST method to determine C-states,
2481 instead using the legacy FADT method
2483 profile= [KNL] Enable kernel profiling via /proc/profile
2484 Format: [schedule,]<number>
2485 Param: "schedule" - profile schedule points.
2486 Param: <number> - step/bucket size as a power of 2 for
2487 statistical time based profiling.
2488 Param: "sleep" - profile D-state sleeping (millisecs).
2489 Requires CONFIG_SCHEDSTATS
2490 Param: "kvm" - profile VM exits.
2492 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2493 before loading.
2494 See Documentation/blockdev/ramdisk.txt.
2496 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2497 probe for; one of (bare|imps|exps|lifebook|any).
2498 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2499 per second.
2500 psmouse.resetafter= [HW,MOUSE]
2501 Try to reset the device after so many bad packets
2502 (0 = never).
2503 psmouse.resolution=
2504 [HW,MOUSE] Set desired mouse resolution, in dpi.
2505 psmouse.smartscroll=
2506 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2507 0 = disabled, 1 = enabled (default).
2509 pstore.backend= Specify the name of the pstore backend to use
2511 pt. [PARIDE]
2512 See Documentation/blockdev/paride.txt.
2514 pty.legacy_count=
2515 [KNL] Number of legacy pty's. Overwrites compiled-in
2516 default number.
2518 quiet [KNL] Disable most log messages
2520 r128= [HW,DRM]
2522 raid= [HW,RAID]
2523 See Documentation/md.txt.
2525 ramdisk_blocksize= [RAM]
2526 See Documentation/blockdev/ramdisk.txt.
2528 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2529 See Documentation/blockdev/ramdisk.txt.
2531 rcu_nocbs= [KNL,BOOT]
2532 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2533 the specified list of CPUs to be no-callback CPUs.
2534 Invocation of these CPUs' RCU callbacks will
2535 be offloaded to "rcuox/N" kthreads created for
2536 that purpose, where "x" is "b" for RCU-bh, "p"
2537 for RCU-preempt, and "s" for RCU-sched, and "N"
2538 is the CPU number. This reduces OS jitter on the
2539 offloaded CPUs, which can be useful for HPC and
2541 real-time workloads. It can also improve energy
2542 efficiency for asymmetric multiprocessors.
2544 rcu_nocb_poll [KNL,BOOT]
2545 Rather than requiring that offloaded CPUs
2546 (specified by rcu_nocbs= above) explicitly
2547 awaken the corresponding "rcuoN" kthreads,
2548 make these kthreads poll for callbacks.
2549 This improves the real-time response for the
2550 offloaded CPUs by relieving them of the need to
2551 wake up the corresponding kthread, but degrades
2552 energy efficiency by requiring that the kthreads
2553 periodically wake up to do the polling.
2555 rcutree.blimit= [KNL,BOOT]
2556 Set maximum number of finished RCU callbacks to process
2557 in one batch.
2559 rcutree.fanout_leaf= [KNL,BOOT]
2560 Increase the number of CPUs assigned to each
2561 leaf rcu_node structure. Useful for very large
2562 systems.
2564 rcutree.jiffies_till_first_fqs= [KNL,BOOT]
2565 Set delay from grace-period initialization to
2566 first attempt to force quiescent states.
2567 Units are jiffies, minimum value is zero,
2568 and maximum value is HZ.
2570 rcutree.jiffies_till_next_fqs= [KNL,BOOT]
2571 Set delay between subsequent attempts to force
2572 quiescent states. Units are jiffies, minimum
2573 value is one, and maximum value is HZ.
2575 rcutree.qhimark= [KNL,BOOT]
2576 Set threshold of queued
2577 RCU callbacks over which batch limiting is disabled.
2579 rcutree.qlowmark= [KNL,BOOT]
2580 Set threshold of queued RCU callbacks below which
2581 batch limiting is re-enabled.
2583 rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2584 Suppress RCU CPU stall warning messages.
2586 rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2587 Set timeout for RCU CPU stall warning messages.
2589 rcutree.rcu_idle_gp_delay= [KNL,BOOT]
2590 Set wakeup interval for idle CPUs that have
2591 RCU callbacks (RCU_FAST_NO_HZ=y).
2593 rcutree.rcu_idle_lazy_gp_delay= [KNL,BOOT]
2594 Set wakeup interval for idle CPUs that have
2595 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2596 Lazy RCU callbacks are those which RCU can
2597 prove do nothing more than free memory.
2599 rcutorture.fqs_duration= [KNL,BOOT]
2600 Set duration of force_quiescent_state bursts.
2602 rcutorture.fqs_holdoff= [KNL,BOOT]
2603 Set holdoff time within force_quiescent_state bursts.
2605 rcutorture.fqs_stutter= [KNL,BOOT]
2606 Set wait time between force_quiescent_state bursts.
2608 rcutorture.irqreader= [KNL,BOOT]
2609 Test RCU readers from irq handlers.
2611 rcutorture.n_barrier_cbs= [KNL,BOOT]
2612 Set callbacks/threads for rcu_barrier() testing.
2614 rcutorture.nfakewriters= [KNL,BOOT]
2615 Set number of concurrent RCU writers. These just
2616 stress RCU, they don't participate in the actual
2617 test, hence the "fake".
2619 rcutorture.nreaders= [KNL,BOOT]
2620 Set number of RCU readers.
2622 rcutorture.onoff_holdoff= [KNL,BOOT]
2623 Set time (s) after boot for CPU-hotplug testing.
2625 rcutorture.onoff_interval= [KNL,BOOT]
2626 Set time (s) between CPU-hotplug operations, or
2627 zero to disable CPU-hotplug testing.
2629 rcutorture.shuffle_interval= [KNL,BOOT]
2630 Set task-shuffle interval (s). Shuffling tasks
2631 allows some CPUs to go into dyntick-idle mode
2632 during the rcutorture test.
2634 rcutorture.shutdown_secs= [KNL,BOOT]
2635 Set time (s) after boot system shutdown. This
2636 is useful for hands-off automated testing.
2638 rcutorture.stall_cpu= [KNL,BOOT]
2639 Duration of CPU stall (s) to test RCU CPU stall
2640 warnings, zero to disable.
2642 rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2643 Time to wait (s) after boot before inducing stall.
2645 rcutorture.stat_interval= [KNL,BOOT]
2646 Time (s) between statistics printk()s.
2648 rcutorture.stutter= [KNL,BOOT]
2649 Time (s) to stutter testing, for example, specifying
2650 five seconds causes the test to run for five seconds,
2651 wait for five seconds, and so on. This tests RCU's
2652 ability to transition abruptly to and from idle.
2654 rcutorture.test_boost= [KNL,BOOT]
2655 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2656 "Maybe" means test if the RCU implementation
2657 under test support RCU priority boosting.
2659 rcutorture.test_boost_duration= [KNL,BOOT]
2660 Duration (s) of each individual boost test.
2662 rcutorture.test_boost_interval= [KNL,BOOT]
2663 Interval (s) between each boost test.
2665 rcutorture.test_no_idle_hz= [KNL,BOOT]
2666 Test RCU's dyntick-idle handling. See also the
2667 rcutorture.shuffle_interval parameter.
2669 rcutorture.torture_type= [KNL,BOOT]
2670 Specify the RCU implementation to test.
2672 rcutorture.verbose= [KNL,BOOT]
2673 Enable additional printk() statements.
2675 rdinit= [KNL]
2676 Format: <full_path>
2677 Run specified binary instead of /init from the ramdisk,
2678 used for early userspace startup. See initrd.
2680 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2681 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2682 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2684 relax_domain_level=
2685 [KNL, SMP] Set scheduler's default relax_domain_level.
2686 See Documentation/cgroups/cpusets.txt.
2688 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2690 reservetop= [X86-32]
2691 Format: nn[KMG]
2692 Reserves a hole at the top of the kernel virtual
2693 address space.
2695 reservelow= [X86]
2696 Format: nn[K]
2697 Set the amount of memory to reserve for BIOS at
2698 the bottom of the address space.
2700 reset_devices [KNL] Force drivers to reset the underlying device
2701 during initialization.
2703 resume= [SWSUSP]
2704 Specify the partition device for software suspend
2705 Format:
2706 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2708 resume_offset= [SWSUSP]
2709 Specify the offset from the beginning of the partition
2710 given by "resume=" at which the swap header is located,
2711 in <PAGE_SIZE> units (needed only for swap files).
2712 See Documentation/power/swsusp-and-swap-files.txt
2714 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2715 read the resume files
2717 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2718 Useful for devices that are detected asynchronously
2719 (e.g. USB and MMC devices).
2721 hibernate= [HIBERNATION]
2722 noresume Don't check if there's a hibernation image
2723 present during boot.
2724 nocompress Don't compress/decompress hibernation images.
2726 retain_initrd [RAM] Keep initrd memory after extraction
2728 rhash_entries= [KNL,NET]
2729 Set number of hash buckets for route cache
2731 riscom8= [HW,SERIAL]
2732 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2734 ro [KNL] Mount root device read-only on boot
2736 root= [KNL] Root filesystem
2737 See name_to_dev_t comment in init/do_mounts.c.
2739 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2740 mount the root filesystem
2742 rootflags= [KNL] Set root filesystem mount option string
2744 rootfstype= [KNL] Set root filesystem type
2746 rootwait [KNL] Wait (indefinitely) for root device to show up.
2747 Useful for devices that are detected asynchronously
2748 (e.g. USB and MMC devices).
2750 rproc_mem=nn[KMG][@address]
2751 [KNL,ARM,CMA] Remoteproc physical memory block.
2752 Memory area to be used by remote processor image,
2753 managed by CMA.
2755 rw [KNL] Mount root device read-write on boot
2757 S [KNL] Run init in single mode
2759 sa1100ir [NET]
2760 See drivers/net/irda/sa1100_ir.c.
2762 sbni= [NET] Granch SBNI12 leased line adapter
2764 sched_debug [KNL] Enables verbose scheduler debug messages.
2766 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2767 xtime_lock contention on larger systems, and/or RCU lock
2768 contention on all systems with CONFIG_MAXSMP set.
2769 Format: { "0" | "1" }
2770 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2771 1 -- enable.
2772 Note: increases power consumption, thus should only be
2773 enabled if running jitter sensitive (HPC/RT) workloads.
2775 security= [SECURITY] Choose a security module to enable at boot.
2776 If this boot parameter is not specified, only the first
2777 security module asking for security registration will be
2778 loaded. An invalid security module name will be treated
2779 as if no module has been chosen.
2781 selinux= [SELINUX] Disable or enable SELinux at boot time.
2782 Format: { "0" | "1" }
2783 See security/selinux/Kconfig help text.
2784 0 -- disable.
2785 1 -- enable.
2786 Default value is set via kernel config option.
2787 If enabled at boot time, /selinux/disable can be used
2788 later to disable prior to initial policy load.
2790 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2791 Format: { "0" | "1" }
2792 See security/apparmor/Kconfig help text
2793 0 -- disable.
2794 1 -- enable.
2795 Default value is set via kernel config option.
2797 serialnumber [BUGS=X86-32]
2799 shapers= [NET]
2800 Maximal number of shapers.
2802 show_msr= [x86] show boot-time MSR settings
2803 Format: { <integer> }
2804 Show boot-time (BIOS-initialized) MSR settings.
2805 The parameter means the number of CPUs to show,
2806 for example 1 means boot CPU only.
2808 simeth= [IA-64]
2809 simscsi=
2811 slram= [HW,MTD]
2813 slab_max_order= [MM, SLAB]
2814 Determines the maximum allowed order for slabs.
2815 A high setting may cause OOMs due to memory
2816 fragmentation. Defaults to 1 for systems with
2817 more than 32MB of RAM, 0 otherwise.
2819 slub_debug[=options[,slabs]] [MM, SLUB]
2820 Enabling slub_debug allows one to determine the
2821 culprit if slab objects become corrupted. Enabling
2822 slub_debug can create guard zones around objects and
2823 may poison objects when not in use. Also tracks the
2824 last alloc / free. For more information see
2825 Documentation/vm/slub.txt.
2827 slub_max_order= [MM, SLUB]
2828 Determines the maximum allowed order for slabs.
2829 A high setting may cause OOMs due to memory
2830 fragmentation. For more information see
2831 Documentation/vm/slub.txt.
2833 slub_min_objects= [MM, SLUB]
2834 The minimum number of objects per slab. SLUB will
2835 increase the slab order up to slub_max_order to
2836 generate a sufficiently large slab able to contain
2837 the number of objects indicated. The higher the number
2838 of objects the smaller the overhead of tracking slabs
2839 and the less frequently locks need to be acquired.
2840 For more information see Documentation/vm/slub.txt.
2842 slub_min_order= [MM, SLUB]
2843 Determines the minimum page order for slabs. Must be
2844 lower than slub_max_order.
2845 For more information see Documentation/vm/slub.txt.
2847 slub_nomerge [MM, SLUB]
2848 Disable merging of slabs with similar size. May be
2849 necessary if there is some reason to distinguish
2850 allocs to different slabs. Debug options disable
2851 merging on their own.
2852 For more information see Documentation/vm/slub.txt.
2854 smart2= [HW]
2855 Format: <io1>[,<io2>[,...,<io8>]]
2857 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2858 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2859 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2860 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2861 smsc-ircc2.ircc_irq= [HW] IRQ line
2862 smsc-ircc2.ircc_dma= [HW] DMA channel
2863 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2864 0: Toshiba Satellite 1800 (GP data pin select)
2865 1: Fast pin select (default)
2866 2: ATC IRMode
2868 softlockup_panic=
2869 [KNL] Should the soft-lockup detector generate panics.
2870 Format: <integer>
2872 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2873 See Documentation/laptops/sonypi.txt
2875 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2876 See Documentation/serial/specialix.txt.
2878 spia_io_base= [HW,MTD]
2879 spia_fio_base=
2880 spia_pedr=
2881 spia_peddr=
2883 stacktrace [FTRACE]
2884 Enabled the stack tracer on boot up.
2886 stacktrace_filter=[function-list]
2887 [FTRACE] Limit the functions that the stack tracer
2888 will trace at boot up. function-list is a comma separated
2889 list of functions. This list can be changed at run
2890 time by the stack_trace_filter file in the debugfs
2891 tracing directory. Note, this enables stack tracing
2892 and the stacktrace above is not needed.
2894 sti= [PARISC,HW]
2895 Format: <num>
2896 Set the STI (builtin display/keyboard on the HP-PARISC
2897 machines) console (graphic card) which should be used
2898 as the initial boot-console.
2899 See also comment in drivers/video/console/sticore.c.
2901 sti_font= [HW]
2902 See comment in drivers/video/console/sticore.c.
2904 stifb= [HW]
2905 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2907 sunrpc.min_resvport=
2908 sunrpc.max_resvport=
2909 [NFS,SUNRPC]
2910 SunRPC servers often require that client requests
2911 originate from a privileged port (i.e. a port in the
2912 range 0 < portnr < 1024).
2913 An administrator who wishes to reserve some of these
2914 ports for other uses may adjust the range that the
2915 kernel's sunrpc client considers to be privileged
2916 using these two parameters to set the minimum and
2917 maximum port values.
2919 sunrpc.pool_mode=
2920 [NFS]
2921 Control how the NFS server code allocates CPUs to
2922 service thread pools. Depending on how many NICs
2923 you have and where their interrupts are bound, this
2924 option will affect which CPUs will do NFS serving.
2925 Note: this parameter cannot be changed while the
2926 NFS server is running.
2928 auto the server chooses an appropriate mode
2929 automatically using heuristics
2930 global a single global pool contains all CPUs
2931 percpu one pool for each CPU
2932 pernode one pool for each NUMA node (equivalent
2933 to global on non-NUMA machines)
2935 sunrpc.tcp_slot_table_entries=
2936 sunrpc.udp_slot_table_entries=
2937 [NFS,SUNRPC]
2938 Sets the upper limit on the number of simultaneous
2939 RPC calls that can be sent from the client to a
2940 server. Increasing these values may allow you to
2941 improve throughput, but will also increase the
2942 amount of memory reserved for use by the client.
2944 swapaccount[=0|1]
2945 [KNL] Enable accounting of swap in memory resource
2946 controller if no parameter or 1 is given or disable
2947 it if 0 is given (See Documentation/cgroups/memory.txt)
2949 swiotlb= [IA-64] Number of I/O TLB slabs
2951 switches= [HW,M68k]
2953 sysfs.deprecated=0|1 [KNL]
2954 Enable/disable old style sysfs layout for old udev
2955 on older distributions. When this option is enabled
2956 very new udev will not work anymore. When this option
2957 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2958 in older udev will not work anymore.
2959 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2960 the kernel configuration.
2962 sysrq_always_enabled
2963 [KNL]
2964 Ignore sysrq setting - this boot parameter will
2965 neutralize any effect of /proc/sys/kernel/sysrq.
2966 Useful for debugging.
2968 tdfx= [HW,DRM]
2970 test_suspend= [SUSPEND]
2971 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2972 standby suspend) as the system sleep state to briefly
2973 enter during system startup. The system is woken from
2974 this state using a wakeup-capable RTC alarm.
2976 thash_entries= [KNL,NET]
2977 Set number of hash buckets for TCP connection
2979 thermal.act= [HW,ACPI]
2980 -1: disable all active trip points in all thermal zones
2981 <degrees C>: override all lowest active trip points
2983 thermal.crt= [HW,ACPI]
2984 -1: disable all critical trip points in all thermal zones
2985 <degrees C>: override all critical trip points
2987 thermal.nocrt= [HW,ACPI]
2988 Set to disable actions on ACPI thermal zone
2989 critical and hot trip points.
2991 thermal.off= [HW,ACPI]
2992 1: disable ACPI thermal control
2994 thermal.psv= [HW,ACPI]
2995 -1: disable all passive trip points
2996 <degrees C>: override all passive trip points to this
2997 value
2999 thermal.tzp= [HW,ACPI]
3000 Specify global default ACPI thermal zone polling rate
3001 <deci-seconds>: poll all this frequency
3002 0: no polling (default)
3004 threadirqs [KNL]
3005 Force threading of all interrupt handlers except those
3006 marked explicitly IRQF_NO_THREAD.
3008 tmem [KNL,XEN]
3009 Enable the Transcendent memory driver if built-in.
3011 tmem.cleancache=0|1 [KNL, XEN]
3012 Default is on (1). Disable the usage of the cleancache
3013 API to send anonymous pages to the hypervisor.
3015 tmem.frontswap=0|1 [KNL, XEN]
3016 Default is on (1). Disable the usage of the frontswap
3017 API to send swap pages to the hypervisor. If disabled
3018 the selfballooning and selfshrinking are force disabled.
3020 tmem.selfballooning=0|1 [KNL, XEN]
3021 Default is on (1). Disable the driving of swap pages
3022 to the hypervisor.
3024 tmem.selfshrinking=0|1 [KNL, XEN]
3025 Default is on (1). Partial swapoff that immediately
3026 transfers pages from Xen hypervisor back to the
3027 kernel based on different criteria.
3029 topology= [S390]
3030 Format: {off | on}
3031 Specify if the kernel should make use of the cpu
3032 topology information if the hardware supports this.
3033 The scheduler will make use of this information and
3034 e.g. base its process migration decisions on it.
3035 Default is on.
3037 tp720= [HW,PS2]
3039 tpm_suspend_pcr=[HW,TPM]
3040 Format: integer pcr id
3041 Specify that at suspend time, the tpm driver
3042 should extend the specified pcr with zeros,
3043 as a workaround for some chips which fail to
3044 flush the last written pcr on TPM_SaveState.
3045 This will guarantee that all the other pcrs
3046 are saved.
3048 trace_buf_size=nn[KMG]
3049 [FTRACE] will set tracing buffer size.
3051 trace_event=[event-list]
3052 [FTRACE] Set and start specified trace events in order
3053 to facilitate early boot debugging.
3054 See also Documentation/trace/events.txt
3056 trace_options=[option-list]
3057 [FTRACE] Enable or disable tracer options at boot.
3058 The option-list is a comma delimited list of options
3059 that can be enabled or disabled just as if you were
3060 to echo the option name into
3062 /sys/kernel/debug/tracing/trace_options
3064 For example, to enable stacktrace option (to dump the
3065 stack trace of each event), add to the command line:
3067 trace_options=stacktrace
3069 See also Documentation/trace/ftrace.txt "trace options"
3070 section.
3072 transparent_hugepage=
3073 [KNL]
3074 Format: [always|madvise|never]
3075 Can be used to control the default behavior of the system
3076 with respect to transparent hugepages.
3077 See Documentation/vm/transhuge.txt for more details.
3079 tsc= Disable clocksource stability checks for TSC.
3080 Format: <string>
3081 [x86] reliable: mark tsc clocksource as reliable, this
3082 disables clocksource verification at runtime, as well
3083 as the stability checks done at bootup. Used to enable
3084 high-resolution timer mode on older hardware, and in
3085 virtualized environment.
3086 [x86] noirqtime: Do not use TSC to do irq accounting.
3087 Used to run time disable IRQ_TIME_ACCOUNTING on any
3088 platforms where RDTSC is slow and this accounting
3089 can add overhead.
3091 turbografx.map[2|3]= [HW,JOY]
3092 TurboGraFX parallel port interface
3093 Format:
3094 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3095 See also Documentation/input/joystick-parport.txt
3097 udbg-immortal [PPC] When debugging early kernel crashes that
3098 happen after console_init() and before a proper
3099 console driver takes over, this boot options might
3100 help "seeing" what's going on.
3102 uhash_entries= [KNL,NET]
3103 Set number of hash buckets for UDP/UDP-Lite connections
3105 uhci-hcd.ignore_oc=
3106 [USB] Ignore overcurrent events (default N).
3107 Some badly-designed motherboards generate lots of
3108 bogus events, for ports that aren't wired to
3109 anything. Set this parameter to avoid log spamming.
3110 Note that genuine overcurrent events won't be
3111 reported either.
3113 unknown_nmi_panic
3114 [X86] Cause panic on unknown NMI.
3116 usbcore.authorized_default=
3117 [USB] Default USB device authorization:
3118 (default -1 = authorized except for wireless USB,
3119 0 = not authorized, 1 = authorized)
3121 usbcore.autosuspend=
3122 [USB] The autosuspend time delay (in seconds) used
3123 for newly-detected USB devices (default 2). This
3124 is the time required before an idle device will be
3125 autosuspended. Devices for which the delay is set
3126 to a negative value won't be autosuspended at all.
3128 usbcore.usbfs_snoop=
3129 [USB] Set to log all usbfs traffic (default 0 = off).
3131 usbcore.blinkenlights=
3132 [USB] Set to cycle leds on hubs (default 0 = off).
3134 usbcore.old_scheme_first=
3135 [USB] Start with the old device initialization
3136 scheme (default 0 = off).
3138 usbcore.usbfs_memory_mb=
3139 [USB] Memory limit (in MB) for buffers allocated by
3140 usbfs (default = 16, 0 = max = 2047).
3142 usbcore.use_both_schemes=
3143 [USB] Try the other device initialization scheme
3144 if the first one fails (default 1 = enabled).
3146 usbcore.initial_descriptor_timeout=
3147 [USB] Specifies timeout for the initial 64-byte
3148 USB_REQ_GET_DESCRIPTOR request in milliseconds
3149 (default 5000 = 5.0 seconds).
3151 usbhid.mousepoll=
3152 [USBHID] The interval which mice are to be polled at.
3154 usb-storage.delay_use=
3155 [UMS] The delay in seconds before a new device is
3156 scanned for Logical Units (default 5).
3158 usb-storage.quirks=
3159 [UMS] A list of quirks entries to supplement or
3160 override the built-in unusual_devs list. List
3161 entries are separated by commas. Each entry has
3162 the form VID:PID:Flags where VID and PID are Vendor
3163 and Product ID values (4-digit hex numbers) and
3164 Flags is a set of characters, each corresponding
3165 to a common usb-storage quirk flag as follows:
3166 a = SANE_SENSE (collect more than 18 bytes
3167 of sense data);
3168 b = BAD_SENSE (don't collect more than 18
3169 bytes of sense data);
3170 c = FIX_CAPACITY (decrease the reported
3171 device capacity by one sector);
3172 d = NO_READ_DISC_INFO (don't use
3173 READ_DISC_INFO command);
3174 e = NO_READ_CAPACITY_16 (don't use
3175 READ_CAPACITY_16 command);
3176 h = CAPACITY_HEURISTICS (decrease the
3177 reported device capacity by one
3178 sector if the number is odd);
3179 i = IGNORE_DEVICE (don't bind to this
3180 device);
3181 l = NOT_LOCKABLE (don't try to lock and
3182 unlock ejectable media);
3183 m = MAX_SECTORS_64 (don't transfer more
3184 than 64 sectors = 32 KB at a time);
3185 n = INITIAL_READ10 (force a retry of the
3186 initial READ(10) command);
3187 o = CAPACITY_OK (accept the capacity
3188 reported by the device);
3189 p = WRITE_CACHE (the device cache is ON
3190 by default);
3191 r = IGNORE_RESIDUE (the device reports
3192 bogus residue values);
3193 s = SINGLE_LUN (the device has only one
3194 Logical Unit);
3195 w = NO_WP_DETECT (don't test whether the
3196 medium is write-protected).
3197 Example: quirks=0419:aaf5:rl,0421:0433:rc
3199 user_debug= [KNL,ARM]
3200 Format: <int>
3201 See arch/arm/Kconfig.debug help text.
3202 1 - undefined instruction events
3203 2 - system calls
3204 4 - invalid data aborts
3205 8 - SIGSEGV faults
3206 16 - SIGBUS faults
3207 Example: user_debug=31
3209 userpte=
3210 [X86] Flags controlling user PTE allocations.
3212 nohigh = do not allocate PTE pages in
3213 HIGHMEM regardless of setting
3214 of CONFIG_HIGHPTE.
3216 vdso= [X86,SH]
3217 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3218 vdso=1: enable VDSO (default)
3219 vdso=0: disable VDSO mapping
3221 vdso32= [X86]
3222 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3223 vdso32=1: enable 32-bit VDSO (default)
3224 vdso32=0: disable 32-bit VDSO mapping
3226 vector= [IA-64,SMP]
3227 vector=percpu: enable percpu vector domain
3229 video= [FB] Frame buffer configuration
3230 See Documentation/fb/modedb.txt.
3232 virtio_mmio.device=
3233 [VMMIO] Memory mapped virtio (platform) device.
3235 <size>@<baseaddr>:<irq>[:<id>]
3236 where:
3237 <size> := size (can use standard suffixes
3238 like K, M and G)
3239 <baseaddr> := physical base address
3240 <irq> := interrupt number (as passed to
3241 request_irq())
3242 <id> := (optional) platform device id
3243 example:
3244 virtio_mmio.device=1K@0x100b0000:48:7
3246 Can be used multiple times for multiple devices.
3248 vga= [BOOT,X86-32] Select a particular video mode
3249 See Documentation/x86/boot.txt and
3250 Documentation/svga.txt.
3251 Use vga=ask for menu.
3252 This is actually a boot loader parameter; the value is
3253 passed to the kernel using a special protocol.
3255 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3256 size of <nn>. This can be used to increase the
3257 minimum size (128MB on x86). It can also be used to
3258 decrease the size and leave more room for directly
3259 mapped kernel RAM.
3261 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3262 Format: <command>
3264 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3265 Format: <command>
3267 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3268 Format: <command>
3270 vsyscall= [X86-64]
3271 Controls the behavior of vsyscalls (i.e. calls to
3272 fixed addresses of 0xffffffffff600x00 from legacy
3273 code). Most statically-linked binaries and older
3274 versions of glibc use these calls. Because these
3275 functions are at fixed addresses, they make nice
3276 targets for exploits that can control RIP.
3278 emulate [default] Vsyscalls turn into traps and are
3279 emulated reasonably safely.
3281 native Vsyscalls are native syscall instructions.
3282 This is a little bit faster than trapping
3283 and makes a few dynamic recompilers work
3284 better than they would in emulation mode.
3285 It also makes exploits much easier to write.
3287 none Vsyscalls don't work at all. This makes
3288 them quite hard to use for exploits but
3289 might break your system.
3291 vt.cur_default= [VT] Default cursor shape.
3292 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3293 the parameters of the <Esc>[?A;B;Cc escape sequence;
3294 see VGA-softcursor.txt. Default: 2 = underline.
3296 vt.default_blu= [VT]
3297 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3298 Change the default blue palette of the console.
3299 This is a 16-member array composed of values
3300 ranging from 0-255.
3302 vt.default_grn= [VT]
3303 Format: <green0>,<green1>,<green2>,...,<green15>
3304 Change the default green palette of the console.
3305 This is a 16-member array composed of values
3306 ranging from 0-255.
3308 vt.default_red= [VT]
3309 Format: <red0>,<red1>,<red2>,...,<red15>
3310 Change the default red palette of the console.
3311 This is a 16-member array composed of values
3312 ranging from 0-255.
3314 vt.default_utf8=
3315 [VT]
3316 Format=<0|1>
3317 Set system-wide default UTF-8 mode for all tty's.
3318 Default is 1, i.e. UTF-8 mode is enabled for all
3319 newly opened terminals.
3321 vt.global_cursor_default=
3322 [VT]
3323 Format=<-1|0|1>
3324 Set system-wide default for whether a cursor
3325 is shown on new VTs. Default is -1,
3326 i.e. cursors will be created by default unless
3327 overridden by individual drivers. 0 will hide
3328 cursors, 1 will display them.
3330 watchdog timers [HW,WDT] For information on watchdog timers,
3331 see Documentation/watchdog/watchdog-parameters.txt
3332 or other driver-specific files in the
3333 Documentation/watchdog/ directory.
3335 workqueue.disable_numa
3336 By default, all work items queued to unbound
3337 workqueues are affine to the NUMA nodes they're
3338 issued on, which results in better behavior in
3339 general. If NUMA affinity needs to be disabled for
3340 whatever reason, this option can be used. Note
3341 that this also can be controlled per-workqueue for
3342 workqueues visible under /sys/bus/workqueue/.
3344 workqueue.power_efficient
3345 Per-cpu workqueues are generally preferred because
3346 they show better performance thanks to cache
3347 locality; unfortunately, per-cpu workqueues tend to
3348 be more power hungry than unbound workqueues.
3350 Enabling this makes the per-cpu workqueues which
3351 were observed to contribute significantly to power
3352 consumption unbound, leading to measurably lower
3353 power usage at the cost of small performance
3354 overhead.
3356 The default value of this parameter is determined by
3357 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3359 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3360 default x2apic cluster mode on platforms
3361 supporting x2apic.
3363 x86_mrst_timer= [X86-32,APBT]
3364 Choose timer option for x86 Moorestown MID platform.
3365 Two valid options are apbt timer only and lapic timer
3366 plus one apbt timer for broadcast timer.
3367 x86_mrst_timer=apbt_only | lapic_and_apbt
3369 xen_emul_unplug= [HW,X86,XEN]
3370 Unplug Xen emulated devices
3371 Format: [unplug0,][unplug1]
3372 ide-disks -- unplug primary master IDE devices
3373 aux-ide-disks -- unplug non-primary-master IDE devices
3374 nics -- unplug network devices
3375 all -- unplug all emulated devices (NICs and IDE disks)
3376 unnecessary -- unplugging emulated devices is
3377 unnecessary even if the host did not respond to
3378 the unplug protocol
3379 never -- do not unplug even if version check succeeds
3381 xirc2ps_cs= [NET,PCMCIA]
3382 Format:
3383 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3385 ______________________________________________________________________
3387 TODO:
3389 Add more DRM drivers.