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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
4 The following is a consolidated list of the kernel parameters as implemented
5 (mostly) by the __setup() macro and sorted into English Dictionary order
6 (defined as ignoring all punctuation and sorting digits before letters in a
7 case insensitive manner), and with descriptions where known.
9 Module parameters for loadable modules are specified only as the
10 parameter name with optional '=' and value as appropriate, such as:
12 modprobe usbcore blinkenlights=1
14 Module parameters for modules that are built into the kernel image
15 are specified on the kernel command line with the module name plus
16 '.' plus parameter name, with '=' and value if appropriate, such as:
18 usbcore.blinkenlights=1
20 Hyphens (dashes) and underscores are equivalent in parameter names, so
21 log_buf_len=1M print-fatal-signals=1
22 can also be entered as
23 log-buf-len=1M print_fatal_signals=1
26 This document may not be entirely up to date and comprehensive. The command
27 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
28 module. Loadable modules, after being loaded into the running kernel, also
29 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
30 parameters may be changed at runtime by the command
31 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
33 The parameters listed below are only valid if certain kernel build options were
34 enabled and if respective hardware is present. The text in square brackets at
35 the beginning of each description states the restrictions within which a
36 parameter is applicable:
38 ACPI ACPI support is enabled.
39 AGP AGP (Accelerated Graphics Port) is enabled.
40 ALSA ALSA sound support is enabled.
41 APIC APIC support is enabled.
42 APM Advanced Power Management support is enabled.
43 ARM ARM architecture is enabled.
44 AVR32 AVR32 architecture is enabled.
45 AX25 Appropriate AX.25 support is enabled.
46 BLACKFIN Blackfin architecture is enabled.
47 DRM Direct Rendering Management support is enabled.
48 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
49 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
50 EFI EFI Partitioning (GPT) is enabled
51 EIDE EIDE/ATAPI support is enabled.
52 EVM Extended Verification Module
53 FB The frame buffer device is enabled.
54 FTRACE Function tracing enabled.
55 GCOV GCOV profiling is enabled.
56 HW Appropriate hardware is enabled.
57 IA-64 IA-64 architecture is enabled.
58 IMA Integrity measurement architecture is enabled.
59 IOSCHED More than one I/O scheduler is enabled.
60 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
61 IPV6 IPv6 support is enabled.
62 ISAPNP ISA PnP code is enabled.
63 ISDN Appropriate ISDN support is enabled.
64 JOY Appropriate joystick support is enabled.
65 KGDB Kernel debugger support is enabled.
66 KVM Kernel Virtual Machine support is enabled.
67 LIBATA Libata driver is enabled
68 LP Printer support is enabled.
69 LOOP Loopback device support is enabled.
70 M68k M68k architecture is enabled.
71 These options have more detailed description inside of
72 Documentation/m68k/kernel-options.txt.
73 MDA MDA console support is enabled.
74 MIPS MIPS architecture is enabled.
75 MOUSE Appropriate mouse support is enabled.
76 MSI Message Signaled Interrupts (PCI).
77 MTD MTD (Memory Technology Device) support is enabled.
78 NET Appropriate network support is enabled.
79 NUMA NUMA support is enabled.
80 NFS Appropriate NFS support is enabled.
81 OSS OSS sound support is enabled.
82 PV_OPS A paravirtualized kernel is enabled.
83 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
84 PARISC The PA-RISC architecture is enabled.
85 PCI PCI bus support is enabled.
86 PCIE PCI Express support is enabled.
87 PCMCIA The PCMCIA subsystem is enabled.
88 PNP Plug & Play support is enabled.
89 PPC PowerPC architecture is enabled.
90 PPT Parallel port support is enabled.
91 PS2 Appropriate PS/2 support is enabled.
92 RAM RAM disk support is enabled.
93 S390 S390 architecture is enabled.
94 SCSI Appropriate SCSI support is enabled.
95 A lot of drivers have their options described inside
96 the Documentation/scsi/ sub-directory.
97 SECURITY Different security models are enabled.
98 SELINUX SELinux support is enabled.
99 APPARMOR AppArmor support is enabled.
100 SERIAL Serial support is enabled.
101 SH SuperH architecture is enabled.
102 SMP The kernel is an SMP kernel.
103 SPARC Sparc architecture is enabled.
104 SWSUSP Software suspend (hibernation) is enabled.
105 SUSPEND System suspend states are enabled.
106 TPM TPM drivers are enabled.
107 TS Appropriate touchscreen support is enabled.
108 UMS USB Mass Storage support is enabled.
109 USB USB support is enabled.
110 USBHID USB Human Interface Device support is enabled.
111 V4L Video For Linux support is enabled.
112 VMMIO Driver for memory mapped virtio devices is enabled.
113 VGA The VGA console has been enabled.
114 VT Virtual terminal support is enabled.
115 WDT Watchdog support is enabled.
116 XT IBM PC/XT MFM hard disk support is enabled.
117 X86-32 X86-32, aka i386 architecture is enabled.
118 X86-64 X86-64 architecture is enabled.
119 More X86-64 boot options can be found in
120 Documentation/x86/x86_64/boot-options.txt .
121 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
122 XEN Xen support is enabled
124 In addition, the following text indicates that the option:
126 BUGS= Relates to possible processor bugs on the said processor.
127 KNL Is a kernel start-up parameter.
128 BOOT Is a boot loader parameter.
130 Parameters denoted with BOOT are actually interpreted by the boot
131 loader, and have no meaning to the kernel directly.
132 Do not modify the syntax of boot loader parameters without extreme
133 need or coordination with <Documentation/x86/boot.txt>.
135 There are also arch-specific kernel-parameters not documented here.
136 See for example <Documentation/x86/x86_64/boot-options.txt>.
138 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
139 a trailing = on the name of any parameter states that that parameter will
140 be entered as an environment variable, whereas its absence indicates that
141 it will appear as a kernel argument readable via /proc/cmdline by programs
142 running once the system is up.
144 The number of kernel parameters is not limited, but the length of the
145 complete command line (parameters including spaces etc.) is limited to
146 a fixed number of characters. This limit depends on the architecture
147 and is between 256 and 4096 characters. It is defined in the file
148 ./include/asm/setup.h as COMMAND_LINE_SIZE.
150 Finally, the [KMG] suffix is commonly described after a number of kernel
151 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
152 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
153 bytes respectively. Such letter suffixes can also be entirely omitted.
156 acpi= [HW,ACPI,X86]
157 Advanced Configuration and Power Interface
158 Format: { force | off | strict | noirq | rsdt }
159 force -- enable ACPI if default was off
160 off -- disable ACPI if default was on
161 noirq -- do not use ACPI for IRQ routing
162 strict -- Be less tolerant of platforms that are not
163 strictly ACPI specification compliant.
164 rsdt -- prefer RSDT over (default) XSDT
165 copy_dsdt -- copy DSDT to memory
167 See also Documentation/power/runtime_pm.txt, pci=noacpi
169 acpi_rsdp= [ACPI,EFI,KEXEC]
170 Pass the RSDP address to the kernel, mostly used
171 on machines running EFI runtime service to boot the
172 second kernel for kdump.
174 acpi_apic_instance= [ACPI, IOAPIC]
175 Format: <int>
176 2: use 2nd APIC table, if available
177 1,0: use 1st APIC table
178 default: 0
180 acpi_backlight= [HW,ACPI]
181 acpi_backlight=vendor
182 acpi_backlight=video
183 If set to vendor, prefer vendor specific driver
184 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
185 of the ACPI video.ko driver.
187 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
188 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
189 Format: <int>
190 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
191 debug output. Bits in debug_layer correspond to a
192 _COMPONENT in an ACPI source file, e.g.,
193 #define _COMPONENT ACPI_PCI_COMPONENT
194 Bits in debug_level correspond to a level in
195 ACPI_DEBUG_PRINT statements, e.g.,
196 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
197 The debug_level mask defaults to "info". See
198 Documentation/acpi/debug.txt for more information about
199 debug layers and levels.
201 Enable processor driver info messages:
202 acpi.debug_layer=0x20000000
203 Enable PCI/PCI interrupt routing info messages:
204 acpi.debug_layer=0x400000
205 Enable AML "Debug" output, i.e., stores to the Debug
206 object while interpreting AML:
207 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
208 Enable all messages related to ACPI hardware:
209 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
211 Some values produce so much output that the system is
212 unusable. The "log_buf_len" parameter may be useful
213 if you need to capture more output.
215 acpi_irq_balance [HW,ACPI]
216 ACPI will balance active IRQs
217 default in APIC mode
219 acpi_irq_nobalance [HW,ACPI]
220 ACPI will not move active IRQs (default)
221 default in PIC mode
223 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
224 Format: <irq>,<irq>...
226 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
227 use by PCI
228 Format: <irq>,<irq>...
230 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
232 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
233 Format: To spoof as Windows 98: ="Microsoft Windows"
235 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
236 acpi_osi="string1" # add string1 -- only one string
237 acpi_osi="!string2" # remove built-in string2
238 acpi_osi= # disable all strings
240 acpi_pm_good [X86]
241 Override the pmtimer bug detection: force the kernel
242 to assume that this machine's pmtimer latches its value
243 and always returns good values.
245 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
246 Format: { level | edge | high | low }
248 acpi_serialize [HW,ACPI] force serialization of AML methods
250 acpi_skip_timer_override [HW,ACPI]
251 Recognize and ignore IRQ0/pin2 Interrupt Override.
252 For broken nForce2 BIOS resulting in XT-PIC timer.
254 acpi_sleep= [HW,ACPI] Sleep options
255 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
256 old_ordering, nonvs, sci_force_enable }
257 See Documentation/power/video.txt for information on
258 s3_bios and s3_mode.
259 s3_beep is for debugging; it makes the PC's speaker beep
260 as soon as the kernel's real-mode entry point is called.
261 s4_nohwsig prevents ACPI hardware signature from being
262 used during resume from hibernation.
263 old_ordering causes the ACPI 1.0 ordering of the _PTS
264 control method, with respect to putting devices into
265 low power states, to be enforced (the ACPI 2.0 ordering
266 of _PTS is used by default).
267 nonvs prevents the kernel from saving/restoring the
268 ACPI NVS memory during suspend/hibernation and resume.
269 sci_force_enable causes the kernel to set SCI_EN directly
270 on resume from S1/S3 (which is against the ACPI spec,
271 but some broken systems don't work without it).
273 acpi_use_timer_override [HW,ACPI]
274 Use timer override. For some broken Nvidia NF5 boards
275 that require a timer override, but don't have HPET
277 acpi_enforce_resources= [ACPI]
278 { strict | lax | no }
279 Check for resource conflicts between native drivers
280 and ACPI OperationRegions (SystemIO and SystemMemory
281 only). IO ports and memory declared in ACPI might be
282 used by the ACPI subsystem in arbitrary AML code and
283 can interfere with legacy drivers.
284 strict (default): access to resources claimed by ACPI
285 is denied; legacy drivers trying to access reserved
286 resources will fail to bind to device using them.
287 lax: access to resources claimed by ACPI is allowed;
288 legacy drivers trying to access reserved resources
289 will bind successfully but a warning message is logged.
290 no: ACPI OperationRegions are not marked as reserved,
291 no further checks are performed.
293 add_efi_memmap [EFI; X86] Include EFI memory map in
294 kernel's map of available physical RAM.
296 agp= [AGP]
297 { off | try_unsupported }
298 off: disable AGP support
299 try_unsupported: try to drive unsupported chipsets
300 (may crash computer or cause data corruption)
302 ALSA [HW,ALSA]
303 See Documentation/sound/alsa/alsa-parameters.txt
305 alignment= [KNL,ARM]
306 Allow the default userspace alignment fault handler
307 behaviour to be specified. Bit 0 enables warnings,
308 bit 1 enables fixups, and bit 2 sends a segfault.
310 align_va_addr= [X86-64]
311 Align virtual addresses by clearing slice [14:12] when
312 allocating a VMA at process creation time. This option
313 gives you up to 3% performance improvement on AMD F15h
314 machines (where it is enabled by default) for a
315 CPU-intensive style benchmark, and it can vary highly in
316 a microbenchmark depending on workload and compiler.
318 32: only for 32-bit processes
319 64: only for 64-bit processes
320 on: enable for both 32- and 64-bit processes
321 off: disable for both 32- and 64-bit processes
323 amd_iommu= [HW,X86-64]
324 Pass parameters to the AMD IOMMU driver in the system.
325 Possible values are:
326 fullflush - enable flushing of IO/TLB entries when
327 they are unmapped. Otherwise they are
328 flushed before they will be reused, which
329 is a lot of faster
330 off - do not initialize any AMD IOMMU found in
331 the system
332 force_isolation - Force device isolation for all
333 devices. The IOMMU driver is not
334 allowed anymore to lift isolation
335 requirements as needed. This option
336 does not override iommu=pt
338 amd_iommu_dump= [HW,X86-64]
339 Enable AMD IOMMU driver option to dump the ACPI table
340 for AMD IOMMU. With this option enabled, AMD IOMMU
341 driver will print ACPI tables for AMD IOMMU during
342 IOMMU initialization.
344 amijoy.map= [HW,JOY] Amiga joystick support
345 Map of devices attached to JOY0DAT and JOY1DAT
346 Format: <a>,<b>
347 See also Documentation/input/joystick.txt
349 analog.map= [HW,JOY] Analog joystick and gamepad support
350 Specifies type or capabilities of an analog joystick
351 connected to one of 16 gameports
352 Format: <type1>,<type2>,..<type16>
354 apc= [HW,SPARC]
355 Power management functions (SPARCstation-4/5 + deriv.)
356 Format: noidle
357 Disable APC CPU standby support. SPARCstation-Fox does
358 not play well with APC CPU idle - disable it if you have
359 APC and your system crashes randomly.
361 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
362 Change the output verbosity whilst booting
363 Format: { quiet (default) | verbose | debug }
364 Change the amount of debugging information output
365 when initialising the APIC and IO-APIC components.
367 autoconf= [IPV6]
368 See Documentation/networking/ipv6.txt.
370 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
371 Limit apic dumping. The parameter defines the maximal
372 number of local apics being dumped. Also it is possible
373 to set it to "all" by meaning -- no limit here.
374 Format: { 1 (default) | 2 | ... | all }.
375 The parameter valid if only apic=debug or
376 apic=verbose is specified.
377 Example: apic=debug show_lapic=all
379 apm= [APM] Advanced Power Management
380 See header of arch/x86/kernel/apm_32.c.
382 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
383 Format: <io>,<irq>,<nodeID>
385 ataflop= [HW,M68k]
387 atarimouse= [HW,MOUSE] Atari Mouse
389 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
390 EzKey and similar keyboards
392 atkbd.reset= [HW] Reset keyboard during initialization
394 atkbd.set= [HW] Select keyboard code set
395 Format: <int> (2 = AT (default), 3 = PS/2)
397 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
398 keyboards
400 atkbd.softraw= [HW] Choose between synthetic and real raw mode
401 Format: <bool> (0 = real, 1 = synthetic (default))
403 atkbd.softrepeat= [HW]
404 Use software keyboard repeat
406 baycom_epp= [HW,AX25]
407 Format: <io>,<mode>
409 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
410 Format: <io>,<mode>
411 See header of drivers/net/hamradio/baycom_par.c.
413 baycom_ser_fdx= [HW,AX25]
414 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
415 Format: <io>,<irq>,<mode>[,<baud>]
416 See header of drivers/net/hamradio/baycom_ser_fdx.c.
418 baycom_ser_hdx= [HW,AX25]
419 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
420 Format: <io>,<irq>,<mode>
421 See header of drivers/net/hamradio/baycom_ser_hdx.c.
423 boot_delay= Milliseconds to delay each printk during boot.
424 Values larger than 10 seconds (10000) are changed to
425 no delay (0).
426 Format: integer
428 bootmem_debug [KNL] Enable bootmem allocator debug messages.
430 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
431 bttv.radio= Most important insmod options are available as
432 kernel args too.
433 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
434 bttv.tuner=
436 bulk_remove=off [PPC] This parameter disables the use of the pSeries
437 firmware feature for flushing multiple hpte entries
438 at a time.
440 c101= [NET] Moxa C101 synchronous serial card
442 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
443 Sometimes CPU hardware bugs make them report the cache
444 size incorrectly. The kernel will attempt work arounds
445 to fix known problems, but for some CPUs it is not
446 possible to determine what the correct size should be.
447 This option provides an override for these situations.
449 ccw_timeout_log [S390]
450 See Documentation/s390/CommonIO for details.
452 cgroup_disable= [KNL] Disable a particular controller
453 Format: {name of the controller(s) to disable}
454 {Currently supported controllers - "memory"}
456 checkreqprot [SELINUX] Set initial checkreqprot flag value.
457 Format: { "0" | "1" }
458 See security/selinux/Kconfig help text.
459 0 -- check protection applied by kernel (includes
460 any implied execute protection).
461 1 -- check protection requested by application.
462 Default value is set via a kernel config option.
463 Value can be changed at runtime via
464 /selinux/checkreqprot.
466 cio_ignore= [S390]
467 See Documentation/s390/CommonIO for details.
469 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
470 [Deprecated]
471 Forces specified clocksource (if available) to be used
472 when calculating gettimeofday(). If specified
473 clocksource is not available, it defaults to PIT.
474 Format: { pit | tsc | cyclone | pmtmr }
476 clocksource= Override the default clocksource
477 Format: <string>
478 Override the default clocksource and use the clocksource
479 with the name specified.
480 Some clocksource names to choose from, depending on
481 the platform:
482 [all] jiffies (this is the base, fallback clocksource)
483 [ACPI] acpi_pm
484 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
485 pxa_timer,timer3,32k_counter,timer0_1
486 [AVR32] avr32
487 [X86-32] pit,hpet,tsc;
488 scx200_hrt on Geode; cyclone on IBM x440
489 [MIPS] MIPS
490 [PARISC] cr16
491 [S390] tod
492 [SH] SuperH
493 [SPARC64] tick
494 [X86-64] hpet,tsc
496 clearcpuid=BITNUM [X86]
497 Disable CPUID feature X for the kernel. See
498 arch/x86/include/asm/cpufeature.h for the valid bit
499 numbers. Note the Linux specific bits are not necessarily
500 stable over kernel options, but the vendor specific
501 ones should be.
502 Also note that user programs calling CPUID directly
503 or using the feature without checking anything
504 will still see it. This just prevents it from
505 being used by the kernel or shown in /proc/cpuinfo.
506 Also note the kernel might malfunction if you disable
507 some critical bits.
509 cma=nn[MG] [ARM,KNL]
510 Sets the size of kernel global memory area for contiguous
511 memory allocations. For more information, see
512 include/linux/dma-contiguous.h
514 cmo_free_hint= [PPC] Format: { yes | no }
515 Specify whether pages are marked as being inactive
516 when they are freed. This is used in CMO environments
517 to determine OS memory pressure for page stealing by
518 a hypervisor.
519 Default: yes
521 coherent_pool=nn[KMG] [ARM,KNL]
522 Sets the size of memory pool for coherent, atomic dma
523 allocations, by default set to 256K.
525 code_bytes [X86] How many bytes of object code to print
526 in an oops report.
527 Range: 0 - 8192
528 Default: 64
530 com20020= [HW,NET] ARCnet - COM20020 chipset
531 Format:
532 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
534 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
535 Format: <io>[,<irq>]
537 com90xx= [HW,NET]
538 ARCnet - COM90xx chipset (memory-mapped buffers)
539 Format: <io>[,<irq>[,<memstart>]]
541 condev= [HW,S390] console device
542 conmode=
544 console= [KNL] Output console device and options.
546 tty<n> Use the virtual console device <n>.
548 ttyS<n>[,options]
549 ttyUSB0[,options]
550 Use the specified serial port. The options are of
551 the form "bbbbpnf", where "bbbb" is the baud rate,
552 "p" is parity ("n", "o", or "e"), "n" is number of
553 bits, and "f" is flow control ("r" for RTS or
554 omit it). Default is "9600n8".
556 See Documentation/serial-console.txt for more
557 information. See
558 Documentation/networking/netconsole.txt for an
559 alternative.
561 uart[8250],io,<addr>[,options]
562 uart[8250],mmio,<addr>[,options]
563 Start an early, polled-mode console on the 8250/16550
564 UART at the specified I/O port or MMIO address,
565 switching to the matching ttyS device later. The
566 options are the same as for ttyS, above.
567 hvc<n> Use the hypervisor console device <n>. This is for
568 both Xen and PowerPC hypervisors.
570 If the device connected to the port is not a TTY but a braille
571 device, prepend "brl," before the device type, for instance
572 console=brl,ttyS0
573 For now, only VisioBraille is supported.
575 consoleblank= [KNL] The console blank (screen saver) timeout in
576 seconds. Defaults to 10*60 = 10mins. A value of 0
577 disables the blank timer.
579 coredump_filter=
580 [KNL] Change the default value for
581 /proc/<pid>/coredump_filter.
582 See also Documentation/filesystems/proc.txt.
584 cpuidle.off=1 [CPU_IDLE]
585 disable the cpuidle sub-system
587 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
588 Format:
589 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
591 crashkernel=size[KMG][@offset[KMG]]
592 [KNL] Using kexec, Linux can switch to a 'crash kernel'
593 upon panic. This parameter reserves the physical
594 memory region [offset, offset + size] for that kernel
595 image. If '@offset' is omitted, then a suitable offset
596 is selected automatically. Check
597 Documentation/kdump/kdump.txt for further details.
599 crashkernel_low=size[KMG]
600 [KNL, x86] parts under 4G.
602 crashkernel=range1:size1[,range2:size2,...][@offset]
603 [KNL] Same as above, but depends on the memory
604 in the running system. The syntax of range is
605 start-[end] where start and end are both
606 a memory unit (amount[KMG]). See also
607 Documentation/kdump/kdump.txt for an example.
609 cs89x0_dma= [HW,NET]
610 Format: <dma>
612 cs89x0_media= [HW,NET]
613 Format: { rj45 | aui | bnc }
615 dasd= [HW,NET]
616 See header of drivers/s390/block/dasd_devmap.c.
618 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
619 (one device per port)
620 Format: <port#>,<type>
621 See also Documentation/input/joystick-parport.txt
623 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
624 time. See Documentation/dynamic-debug-howto.txt for
625 details. Deprecated, see dyndbg.
627 debug [KNL] Enable kernel debugging (events log level).
629 debug_locks_verbose=
630 [KNL] verbose self-tests
631 Format=<0|1>
632 Print debugging info while doing the locking API
633 self-tests.
634 We default to 0 (no extra messages), setting it to
635 1 will print _a lot_ more information - normally
636 only useful to kernel developers.
638 debug_objects [KNL] Enable object debugging
640 no_debug_objects
641 [KNL] Disable object debugging
643 debug_guardpage_minorder=
644 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
645 parameter allows control of the order of pages that will
646 be intentionally kept free (and hence protected) by the
647 buddy allocator. Bigger value increase the probability
648 of catching random memory corruption, but reduce the
649 amount of memory for normal system use. The maximum
650 possible value is MAX_ORDER/2. Setting this parameter
651 to 1 or 2 should be enough to identify most random
652 memory corruption problems caused by bugs in kernel or
653 driver code when a CPU writes to (or reads from) a
654 random memory location. Note that there exists a class
655 of memory corruptions problems caused by buggy H/W or
656 F/W or by drivers badly programing DMA (basically when
657 memory is written at bus level and the CPU MMU is
658 bypassed) which are not detectable by
659 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
660 tracking down these problems.
662 debugpat [X86] Enable PAT debugging
664 decnet.addr= [HW,NET]
665 Format: <area>[,<node>]
666 See also Documentation/networking/decnet.txt.
668 default_hugepagesz=
669 [same as hugepagesz=] The size of the default
670 HugeTLB page size. This is the size represented by
671 the legacy /proc/ hugepages APIs, used for SHM, and
672 default size when mounting hugetlbfs filesystems.
673 Defaults to the default architecture's huge page size
674 if not specified.
676 dhash_entries= [KNL]
677 Set number of hash buckets for dentry cache.
679 digi= [HW,SERIAL]
680 IO parameters + enable/disable command.
682 digiepca= [HW,SERIAL]
683 See drivers/char/README.epca and
684 Documentation/serial/digiepca.txt.
686 disable= [IPV6]
687 See Documentation/networking/ipv6.txt.
689 disable_ddw [PPC/PSERIES]
690 Disable Dynamic DMA Window support. Use this if
691 to workaround buggy firmware.
693 disable_ipv6= [IPV6]
694 See Documentation/networking/ipv6.txt.
696 disable_mtrr_cleanup [X86]
697 The kernel tries to adjust MTRR layout from continuous
698 to discrete, to make X server driver able to add WB
699 entry later. This parameter disables that.
701 disable_mtrr_trim [X86, Intel and AMD only]
702 By default the kernel will trim any uncacheable
703 memory out of your available memory pool based on
704 MTRR settings. This parameter disables that behavior,
705 possibly causing your machine to run very slowly.
707 disable_timer_pin_1 [X86]
708 Disable PIN 1 of APIC timer
709 Can be useful to work around chipset bugs.
711 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
712 this option disables the debugging code at boot.
714 dma_debug_entries=<number>
715 This option allows to tune the number of preallocated
716 entries for DMA-API debugging code. One entry is
717 required per DMA-API allocation. Use this if the
718 DMA-API debugging code disables itself because the
719 architectural default is too low.
721 dma_debug_driver=<driver_name>
722 With this option the DMA-API debugging driver
723 filter feature can be enabled at boot time. Just
724 pass the driver to filter for as the parameter.
725 The filter can be disabled or changed to another
726 driver later using sysfs.
728 drm_kms_helper.edid_firmware=[<connector>:]<file>
729 Broken monitors, graphic adapters and KVMs may
730 send no or incorrect EDID data sets. This parameter
731 allows to specify an EDID data set in the
732 /lib/firmware directory that is used instead.
733 Generic built-in EDID data sets are used, if one of
734 edid/1024x768.bin, edid/1280x1024.bin,
735 edid/1680x1050.bin, or edid/1920x1080.bin is given
736 and no file with the same name exists. Details and
737 instructions how to build your own EDID data are
738 available in Documentation/EDID/HOWTO.txt. An EDID
739 data set will only be used for a particular connector,
740 if its name and a colon are prepended to the EDID
741 name.
743 dscc4.setup= [NET]
745 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
746 module.dyndbg[="val"]
747 Enable debug messages at boot time. See
748 Documentation/dynamic-debug-howto.txt for details.
750 earlycon= [KNL] Output early console device and options.
751 uart[8250],io,<addr>[,options]
752 uart[8250],mmio,<addr>[,options]
753 uart[8250],mmio32,<addr>[,options]
754 Start an early, polled-mode console on the 8250/16550
755 UART at the specified I/O port or MMIO address.
756 MMIO inter-register address stride is either 8-bit
757 (mmio) or 32-bit (mmio32).
758 The options are the same as for ttyS, above.
760 earlyprintk= [X86,SH,BLACKFIN]
761 earlyprintk=vga
762 earlyprintk=xen
763 earlyprintk=serial[,ttySn[,baudrate]]
764 earlyprintk=ttySn[,baudrate]
765 earlyprintk=dbgp[debugController#]
767 Append ",keep" to not disable it when the real console
768 takes over.
770 Only vga or serial or usb debug port at a time.
772 Currently only ttyS0 and ttyS1 are supported.
774 Interaction with the standard serial driver is not
775 very good.
777 The VGA output is eventually overwritten by the real
778 console.
780 The xen output can only be used by Xen PV guests.
782 ekgdboc= [X86,KGDB] Allow early kernel console debugging
783 ekgdboc=kbd
785 This is designed to be used in conjunction with
786 the boot argument: earlyprintk=vga
788 edd= [EDD]
789 Format: {"off" | "on" | "skip[mbr]"}
791 eisa_irq_edge= [PARISC,HW]
792 See header of drivers/parisc/eisa.c.
794 elanfreq= [X86-32]
795 See comment before function elanfreq_setup() in
796 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
798 elevator= [IOSCHED]
799 Format: {"cfq" | "deadline" | "noop"}
800 See Documentation/block/cfq-iosched.txt and
801 Documentation/block/deadline-iosched.txt for details.
803 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
804 Specifies physical address of start of kernel core
805 image elf header and optionally the size. Generally
806 kexec loader will pass this option to capture kernel.
807 See Documentation/kdump/kdump.txt for details.
809 enable_mtrr_cleanup [X86]
810 The kernel tries to adjust MTRR layout from continuous
811 to discrete, to make X server driver able to add WB
812 entry later. This parameter enables that.
814 enable_timer_pin_1 [X86]
815 Enable PIN 1 of APIC timer
816 Can be useful to work around chipset bugs
817 (in particular on some ATI chipsets).
818 The kernel tries to set a reasonable default.
820 enforcing [SELINUX] Set initial enforcing status.
821 Format: {"0" | "1"}
822 See security/selinux/Kconfig help text.
823 0 -- permissive (log only, no denials).
824 1 -- enforcing (deny and log).
825 Default value is 0.
826 Value can be changed at runtime via /selinux/enforce.
828 erst_disable [ACPI]
829 Disable Error Record Serialization Table (ERST)
830 support.
832 ether= [HW,NET] Ethernet cards parameters
833 This option is obsoleted by the "netdev=" option, which
834 has equivalent usage. See its documentation for details.
836 evm= [EVM]
837 Format: { "fix" }
838 Permit 'security.evm' to be updated regardless of
839 current integrity status.
841 failslab=
842 fail_page_alloc=
843 fail_make_request=[KNL]
844 General fault injection mechanism.
845 Format: <interval>,<probability>,<space>,<times>
846 See also Documentation/fault-injection/.
848 floppy= [HW]
849 See Documentation/blockdev/floppy.txt.
851 force_pal_cache_flush
852 [IA-64] Avoid check_sal_cache_flush which may hang on
853 buggy SAL_CACHE_FLUSH implementations. Using this
854 parameter will force ia64_sal_cache_flush to call
855 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
857 ftrace=[tracer]
858 [FTRACE] will set and start the specified tracer
859 as early as possible in order to facilitate early
860 boot debugging.
862 ftrace_dump_on_oops[=orig_cpu]
863 [FTRACE] will dump the trace buffers on oops.
864 If no parameter is passed, ftrace will dump
865 buffers of all CPUs, but if you pass orig_cpu, it will
866 dump only the buffer of the CPU that triggered the
867 oops.
869 ftrace_filter=[function-list]
870 [FTRACE] Limit the functions traced by the function
871 tracer at boot up. function-list is a comma separated
872 list of functions. This list can be changed at run
873 time by the set_ftrace_filter file in the debugfs
874 tracing directory.
876 ftrace_notrace=[function-list]
877 [FTRACE] Do not trace the functions specified in
878 function-list. This list can be changed at run time
879 by the set_ftrace_notrace file in the debugfs
880 tracing directory.
882 ftrace_graph_filter=[function-list]
883 [FTRACE] Limit the top level callers functions traced
884 by the function graph tracer at boot up.
885 function-list is a comma separated list of functions
886 that can be changed at run time by the
887 set_graph_function file in the debugfs tracing directory.
889 gamecon.map[2|3]=
890 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
891 support via parallel port (up to 5 devices per port)
892 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
893 See also Documentation/input/joystick-parport.txt
895 gamma= [HW,DRM]
897 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
898 Format: off | on
899 default: on
901 gcov_persist= [GCOV] When non-zero (default), profiling data for
902 kernel modules is saved and remains accessible via
903 debugfs, even when the module is unloaded/reloaded.
904 When zero, profiling data is discarded and associated
905 debugfs files are removed at module unload time.
907 gpt [EFI] Forces disk with valid GPT signature but
908 invalid Protective MBR to be treated as GPT.
910 grcan.enable0= [HW] Configuration of physical interface 0. Determines
911 the "Enable 0" bit of the configuration register.
912 Format: 0 | 1
913 Default: 0
914 grcan.enable1= [HW] Configuration of physical interface 1. Determines
915 the "Enable 0" bit of the configuration register.
916 Format: 0 | 1
917 Default: 0
918 grcan.select= [HW] Select which physical interface to use.
919 Format: 0 | 1
920 Default: 0
921 grcan.txsize= [HW] Sets the size of the tx buffer.
922 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
923 Default: 1024
924 grcan.rxsize= [HW] Sets the size of the rx buffer.
925 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
926 Default: 1024
928 hashdist= [KNL,NUMA] Large hashes allocated during boot
929 are distributed across NUMA nodes. Defaults on
930 for 64-bit NUMA, off otherwise.
931 Format: 0 | 1 (for off | on)
933 hcl= [IA-64] SGI's Hardware Graph compatibility layer
935 hd= [EIDE] (E)IDE hard drive subsystem geometry
936 Format: <cyl>,<head>,<sect>
938 hest_disable [ACPI]
939 Disable Hardware Error Source Table (HEST) support;
940 corresponding firmware-first mode error processing
941 logic will be disabled.
943 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
944 size of <nn>. This works even on boxes that have no
945 highmem otherwise. This also works to reduce highmem
946 size on bigger boxes.
948 highres= [KNL] Enable/disable high resolution timer mode.
949 Valid parameters: "on", "off"
950 Default: "on"
952 hisax= [HW,ISDN]
953 See Documentation/isdn/README.HiSax.
955 hlt [BUGS=ARM,SH]
957 hpet= [X86-32,HPET] option to control HPET usage
958 Format: { enable (default) | disable | force |
959 verbose }
960 disable: disable HPET and use PIT instead
961 force: allow force enabled of undocumented chips (ICH4,
962 VIA, nVidia)
963 verbose: show contents of HPET registers during setup
965 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
966 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
967 On x86-64 and powerpc, this option can be specified
968 multiple times interleaved with hugepages= to reserve
969 huge pages of different sizes. Valid pages sizes on
970 x86-64 are 2M (when the CPU supports "pse") and 1G
971 (when the CPU supports the "pdpe1gb" cpuinfo flag)
972 Note that 1GB pages can only be allocated at boot time
973 using hugepages= and not freed afterwards.
975 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
976 terminal devices. Valid values: 0..8
977 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
978 If specified, z/VM IUCV HVC accepts connections
979 from listed z/VM user IDs only.
981 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
982 hardware thread id mappings.
983 Format: <cpu>:<hwthread>
985 keep_bootcon [KNL]
986 Do not unregister boot console at start. This is only
987 useful for debugging when something happens in the window
988 between unregistering the boot console and initializing
989 the real console.
991 i2c_bus= [HW] Override the default board specific I2C bus speed
992 or register an additional I2C bus that is not
993 registered from board initialization code.
994 Format:
995 <bus_id>,<clkrate>
997 i8042.debug [HW] Toggle i8042 debug mode
998 i8042.direct [HW] Put keyboard port into non-translated mode
999 i8042.dumbkbd [HW] Pretend that controller can only read data from
1000 keyboard and cannot control its state
1001 (Don't attempt to blink the leds)
1002 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1003 i8042.nokbd [HW] Don't check/create keyboard port
1004 i8042.noloop [HW] Disable the AUX Loopback command while probing
1005 for the AUX port
1006 i8042.nomux [HW] Don't check presence of an active multiplexing
1007 controller
1008 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1009 controllers
1010 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1011 i8042.reset [HW] Reset the controller during init and cleanup
1012 i8042.unlock [HW] Unlock (ignore) the keylock
1014 i810= [HW,DRM]
1016 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1017 indicates that the driver is running on unsupported
1018 hardware.
1019 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1020 does not match list of supported models.
1021 i8k.power_status
1022 [HW] Report power status in /proc/i8k
1023 (disabled by default)
1024 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1025 capability is set.
1027 i915.invert_brightness=
1028 [DRM] Invert the sense of the variable that is used to
1029 set the brightness of the panel backlight. Normally a
1030 brightness value of 0 indicates backlight switched off,
1031 and the maximum of the brightness value sets the backlight
1032 to maximum brightness. If this parameter is set to 0
1033 (default) and the machine requires it, or this parameter
1034 is set to 1, a brightness value of 0 sets the backlight
1035 to maximum brightness, and the maximum of the brightness
1036 value switches the backlight off.
1037 -1 -- never invert brightness
1038 0 -- machine default
1039 1 -- force brightness inversion
1041 icn= [HW,ISDN]
1042 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1044 ide-core.nodma= [HW] (E)IDE subsystem
1045 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1046 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1047 .cdrom .chs .ignore_cable are additional options
1048 See Documentation/ide/ide.txt.
1050 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1051 Claim all unknown PCI IDE storage controllers.
1053 idle= [X86]
1054 Format: idle=poll, idle=halt, idle=nomwait
1055 Poll forces a polling idle loop that can slightly
1056 improve the performance of waking up a idle CPU, but
1057 will use a lot of power and make the system run hot.
1058 Not recommended.
1059 idle=halt: Halt is forced to be used for CPU idle.
1060 In such case C2/C3 won't be used again.
1061 idle=nomwait: Disable mwait for CPU C-states
1063 ignore_loglevel [KNL]
1064 Ignore loglevel setting - this will print /all/
1065 kernel messages to the console. Useful for debugging.
1066 We also add it as printk module parameter, so users
1067 could change it dynamically, usually by
1068 /sys/module/printk/parameters/ignore_loglevel.
1070 ihash_entries= [KNL]
1071 Set number of hash buckets for inode cache.
1073 ima_appraise= [IMA] appraise integrity measurements
1074 Format: { "off" | "enforce" | "fix" }
1075 default: "enforce"
1077 ima_appraise_tcb [IMA]
1078 The builtin appraise policy appraises all files
1079 owned by uid=0.
1081 ima_audit= [IMA]
1082 Format: { "0" | "1" }
1083 0 -- integrity auditing messages. (Default)
1084 1 -- enable informational integrity auditing messages.
1086 ima_hash= [IMA]
1087 Format: { "sha1" | "md5" }
1088 default: "sha1"
1090 ima_tcb [IMA]
1091 Load a policy which meets the needs of the Trusted
1092 Computing Base. This means IMA will measure all
1093 programs exec'd, files mmap'd for exec, and all files
1094 opened for read by uid=0.
1096 init= [KNL]
1097 Format: <full_path>
1098 Run specified binary instead of /sbin/init as init
1099 process.
1101 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1102 for working out where the kernel is dying during
1103 startup.
1105 initrd= [BOOT] Specify the location of the initial ramdisk
1107 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1108 Format: <irq>
1110 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1111 on
1112 Enable intel iommu driver.
1113 off
1114 Disable intel iommu driver.
1115 igfx_off [Default Off]
1116 By default, gfx is mapped as normal device. If a gfx
1117 device has a dedicated DMAR unit, the DMAR unit is
1118 bypassed by not enabling DMAR with this option. In
1119 this case, gfx device will use physical address for
1120 DMA.
1121 forcedac [x86_64]
1122 With this option iommu will not optimize to look
1123 for io virtual address below 32-bit forcing dual
1124 address cycle on pci bus for cards supporting greater
1125 than 32-bit addressing. The default is to look
1126 for translation below 32-bit and if not available
1127 then look in the higher range.
1128 strict [Default Off]
1129 With this option on every unmap_single operation will
1130 result in a hardware IOTLB flush operation as opposed
1131 to batching them for performance.
1132 sp_off [Default Off]
1133 By default, super page will be supported if Intel IOMMU
1134 has the capability. With this option, super page will
1135 not be supported.
1137 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1138 0 disables intel_idle and fall back on acpi_idle.
1139 1 to 6 specify maximum depth of C-state.
1141 intel_pstate= [X86]
1142 disable
1143 Do not enable intel_pstate as the default
1144 scaling driver for the supported processors
1146 intremap= [X86-64, Intel-IOMMU]
1147 on enable Interrupt Remapping (default)
1148 off disable Interrupt Remapping
1149 nosid disable Source ID checking
1150 no_x2apic_optout
1151 BIOS x2APIC opt-out request will be ignored
1153 iomem= Disable strict checking of access to MMIO memory
1154 strict regions from userspace.
1155 relaxed
1157 iommu= [x86]
1158 off
1159 force
1160 noforce
1161 biomerge
1162 panic
1163 nopanic
1164 merge
1165 nomerge
1166 forcesac
1167 soft
1168 pt [x86, IA-64]
1171 io7= [HW] IO7 for Marvel based alpha systems
1172 See comment before marvel_specify_io7 in
1173 arch/alpha/kernel/core_marvel.c.
1175 io_delay= [X86] I/O delay method
1176 0x80
1177 Standard port 0x80 based delay
1178 0xed
1179 Alternate port 0xed based delay (needed on some systems)
1180 udelay
1181 Simple two microseconds delay
1182 none
1183 No delay
1185 ip= [IP_PNP]
1186 See Documentation/filesystems/nfs/nfsroot.txt.
1188 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1189 See comment before ip2_setup() in
1190 drivers/char/ip2/ip2base.c.
1192 irqfixup [HW]
1193 When an interrupt is not handled search all handlers
1194 for it. Intended to get systems with badly broken
1195 firmware running.
1197 irqpoll [HW]
1198 When an interrupt is not handled search all handlers
1199 for it. Also check all handlers each timer
1200 interrupt. Intended to get systems with badly broken
1201 firmware running.
1203 isapnp= [ISAPNP]
1204 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1206 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1207 Format:
1208 <cpu number>,...,<cpu number>
1209 or
1210 <cpu number>-<cpu number>
1211 (must be a positive range in ascending order)
1212 or a mixture
1213 <cpu number>,...,<cpu number>-<cpu number>
1215 This option can be used to specify one or more CPUs
1216 to isolate from the general SMP balancing and scheduling
1217 algorithms. You can move a process onto or off an
1218 "isolated" CPU via the CPU affinity syscalls or cpuset.
1219 <cpu number> begins at 0 and the maximum value is
1220 "number of CPUs in system - 1".
1222 This option is the preferred way to isolate CPUs. The
1223 alternative -- manually setting the CPU mask of all
1224 tasks in the system -- can cause problems and
1225 suboptimal load balancer performance.
1227 iucv= [HW,NET]
1229 js= [HW,JOY] Analog joystick
1230 See Documentation/input/joystick.txt.
1232 keepinitrd [HW,ARM]
1234 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1235 specifies the amount of memory usable by the kernel
1236 for non-movable allocations. The requested amount is
1237 spread evenly throughout all nodes in the system. The
1238 remaining memory in each node is used for Movable
1239 pages. In the event, a node is too small to have both
1240 kernelcore and Movable pages, kernelcore pages will
1241 take priority and other nodes will have a larger number
1242 of kernelcore pages. The Movable zone is used for the
1243 allocation of pages that may be reclaimed or moved
1244 by the page migration subsystem. This means that
1245 HugeTLB pages may not be allocated from this zone.
1246 Note that allocations like PTEs-from-HighMem still
1247 use the HighMem zone if it exists, and the Normal
1248 zone if it does not.
1250 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1251 Format: <Controller#>[,poll interval]
1252 The controller # is the number of the ehci usb debug
1253 port as it is probed via PCI. The poll interval is
1254 optional and is the number seconds in between
1255 each poll cycle to the debug port in case you need
1256 the functionality for interrupting the kernel with
1257 gdb or control-c on the dbgp connection. When
1258 not using this parameter you use sysrq-g to break into
1259 the kernel debugger.
1261 kgdboc= [KGDB,HW] kgdb over consoles.
1262 Requires a tty driver that supports console polling,
1263 or a supported polling keyboard driver (non-usb).
1264 Serial only format: <serial_device>[,baud]
1265 keyboard only format: kbd
1266 keyboard and serial format: kbd,<serial_device>[,baud]
1267 Optional Kernel mode setting:
1268 kms, kbd format: kms,kbd
1269 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1271 kgdbwait [KGDB] Stop kernel execution and enter the
1272 kernel debugger at the earliest opportunity.
1274 kmac= [MIPS] korina ethernet MAC address.
1275 Configure the RouterBoard 532 series on-chip
1276 Ethernet adapter MAC address.
1278 kmemleak= [KNL] Boot-time kmemleak enable/disable
1279 Valid arguments: on, off
1280 Default: on
1282 kstack=N [X86] Print N words from the kernel stack
1283 in oops dumps.
1285 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1286 Default is 0 (don't ignore, but inject #GP)
1288 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1289 KVM MMU at runtime.
1290 Default is 0 (off)
1292 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1293 Default is 1 (enabled)
1295 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1296 for all guests.
1297 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1299 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1300 (virtualized MMU) support on capable Intel chips.
1301 Default is 1 (enabled)
1303 kvm-intel.emulate_invalid_guest_state=
1304 [KVM,Intel] Enable emulation of invalid guest states
1305 Default is 0 (disabled)
1307 kvm-intel.flexpriority=
1308 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1309 Default is 1 (enabled)
1311 kvm-intel.nested=
1312 [KVM,Intel] Enable VMX nesting (nVMX).
1313 Default is 0 (disabled)
1315 kvm-intel.unrestricted_guest=
1316 [KVM,Intel] Disable unrestricted guest feature
1317 (virtualized real and unpaged mode) on capable
1318 Intel chips. Default is 1 (enabled)
1320 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1321 feature (tagged TLBs) on capable Intel chips.
1322 Default is 1 (enabled)
1324 l2cr= [PPC]
1326 l3cr= [PPC]
1328 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1329 disabled it.
1331 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1332 value for LAPIC timer one-shot implementation. Default
1333 back to the programmable timer unit in the LAPIC.
1335 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1336 in C2 power state.
1338 libata.dma= [LIBATA] DMA control
1339 libata.dma=0 Disable all PATA and SATA DMA
1340 libata.dma=1 PATA and SATA Disk DMA only
1341 libata.dma=2 ATAPI (CDROM) DMA only
1342 libata.dma=4 Compact Flash DMA only
1343 Combinations also work, so libata.dma=3 enables DMA
1344 for disks and CDROMs, but not CFs.
1346 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1347 libata.ignore_hpa=0 keep BIOS limits (default)
1348 libata.ignore_hpa=1 ignore limits, using full disk
1350 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1351 when set.
1352 Format: <int>
1354 libata.force= [LIBATA] Force configurations. The format is comma
1355 separated list of "[ID:]VAL" where ID is
1356 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1357 matching port, link or device. Basically, it matches
1358 the ATA ID string printed on console by libata. If
1359 the whole ID part is omitted, the last PORT and DEVICE
1360 values are used. If ID hasn't been specified yet, the
1361 configuration applies to all ports, links and devices.
1363 If only DEVICE is omitted, the parameter applies to
1364 the port and all links and devices behind it. DEVICE
1365 number of 0 either selects the first device or the
1366 first fan-out link behind PMP device. It does not
1367 select the host link. DEVICE number of 15 selects the
1368 host link and device attached to it.
1370 The VAL specifies the configuration to force. As long
1371 as there's no ambiguity shortcut notation is allowed.
1372 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1373 The following configurations can be forced.
1375 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1376 Any ID with matching PORT is used.
1378 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1380 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1381 udma[/][16,25,33,44,66,100,133] notation is also
1382 allowed.
1384 * [no]ncq: Turn on or off NCQ.
1386 * nohrst, nosrst, norst: suppress hard, soft
1387 and both resets.
1389 * rstonce: only attempt one reset during
1390 hot-unplug link recovery
1392 * dump_id: dump IDENTIFY data.
1394 If there are multiple matching configurations changing
1395 the same attribute, the last one is used.
1397 memblock=debug [KNL] Enable memblock debug messages.
1399 load_ramdisk= [RAM] List of ramdisks to load from floppy
1400 See Documentation/blockdev/ramdisk.txt.
1402 lockd.nlm_grace_period=P [NFS] Assign grace period.
1403 Format: <integer>
1405 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1406 Format: <integer>
1408 lockd.nlm_timeout=T [NFS] Assign timeout value.
1409 Format: <integer>
1411 lockd.nlm_udpport=M [NFS] Assign UDP port.
1412 Format: <integer>
1414 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1415 Format: <irq>
1417 loglevel= All Kernel Messages with a loglevel smaller than the
1418 console loglevel will be printed to the console. It can
1419 also be changed with klogd or other programs. The
1420 loglevels are defined as follows:
1422 0 (KERN_EMERG) system is unusable
1423 1 (KERN_ALERT) action must be taken immediately
1424 2 (KERN_CRIT) critical conditions
1425 3 (KERN_ERR) error conditions
1426 4 (KERN_WARNING) warning conditions
1427 5 (KERN_NOTICE) normal but significant condition
1428 6 (KERN_INFO) informational
1429 7 (KERN_DEBUG) debug-level messages
1431 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1432 in bytes. n must be a power of two. The default
1433 size is set in the kernel config file.
1435 logo.nologo [FB] Disables display of the built-in Linux logo.
1436 This may be used to provide more screen space for
1437 kernel log messages and is useful when debugging
1438 kernel boot problems.
1440 lp=0 [LP] Specify parallel ports to use, e.g,
1441 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1442 lp=reset first parallel port). 'lp=0' disables the
1443 lp=auto printer driver. 'lp=reset' (which can be
1444 specified in addition to the ports) causes
1445 attached printers to be reset. Using
1446 lp=port1,port2,... specifies the parallel ports
1447 to associate lp devices with, starting with
1448 lp0. A port specification may be 'none' to skip
1449 that lp device, or a parport name such as
1450 'parport0'. Specifying 'lp=auto' instead of a
1451 port specification list means that device IDs
1452 from each port should be examined, to see if
1453 an IEEE 1284-compliant printer is attached; if
1454 so, the driver will manage that printer.
1455 See also header of drivers/char/lp.c.
1457 lpj=n [KNL]
1458 Sets loops_per_jiffy to given constant, thus avoiding
1459 time-consuming boot-time autodetection (up to 250 ms per
1460 CPU). 0 enables autodetection (default). To determine
1461 the correct value for your kernel, boot with normal
1462 autodetection and see what value is printed. Note that
1463 on SMP systems the preset will be applied to all CPUs,
1464 which is likely to cause problems if your CPUs need
1465 significantly divergent settings. An incorrect value
1466 will cause delays in the kernel to be wrong, leading to
1467 unpredictable I/O errors and other breakage. Although
1468 unlikely, in the extreme case this might damage your
1469 hardware.
1471 ltpc= [NET]
1472 Format: <io>,<irq>,<dma>
1474 machvec= [IA-64] Force the use of a particular machine-vector
1475 (machvec) in a generic kernel.
1476 Example: machvec=hpzx1_swiotlb
1478 machtype= [Loongson] Share the same kernel image file between different
1479 yeeloong laptop.
1480 Example: machtype=lemote-yeeloong-2f-7inch
1482 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1483 than or equal to this physical address is ignored.
1485 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1486 should make use of. maxcpus=n : n >= 0 limits the
1487 kernel to using 'n' processors. n=0 is a special case,
1488 it is equivalent to "nosmp", which also disables
1489 the IO APIC.
1491 max_loop= [LOOP] The number of loop block devices that get
1492 (loop.max_loop) unconditionally pre-created at init time. The default
1493 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1494 of statically allocating a predefined number, loop
1495 devices can be requested on-demand with the
1496 /dev/loop-control interface.
1498 mce [X86-32] Machine Check Exception
1500 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1502 md= [HW] RAID subsystems devices and level
1503 See Documentation/md.txt.
1505 mdacon= [MDA]
1506 Format: <first>,<last>
1507 Specifies range of consoles to be captured by the MDA.
1509 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1510 Amount of memory to be used when the kernel is not able
1511 to see the whole system memory or for test.
1512 [X86] Work as limiting max address. Use together
1513 with memmap= to avoid physical address space collisions.
1514 Without memmap= PCI devices could be placed at addresses
1515 belonging to unused RAM.
1517 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1518 memory.
1520 memchunk=nn[KMG]
1521 [KNL,SH] Allow user to override the default size for
1522 per-device physically contiguous DMA buffers.
1524 memmap=exactmap [KNL,X86] Enable setting of an exact
1525 E820 memory map, as specified by the user.
1526 Such memmap=exactmap lines can be constructed based on
1527 BIOS output or other requirements. See the memmap=nn@ss
1528 option description.
1530 memmap=nn[KMG]@ss[KMG]
1531 [KNL] Force usage of a specific region of memory
1532 Region of memory to be used, from ss to ss+nn.
1534 memmap=nn[KMG]#ss[KMG]
1535 [KNL,ACPI] Mark specific memory as ACPI data.
1536 Region of memory to be used, from ss to ss+nn.
1538 memmap=nn[KMG]$ss[KMG]
1539 [KNL,ACPI] Mark specific memory as reserved.
1540 Region of memory to be used, from ss to ss+nn.
1541 Example: Exclude memory from 0x18690000-0x1869ffff
1542 memmap=64K$0x18690000
1543 or
1544 memmap=0x10000$0x18690000
1546 memory_corruption_check=0/1 [X86]
1547 Some BIOSes seem to corrupt the first 64k of
1548 memory when doing things like suspend/resume.
1549 Setting this option will scan the memory
1550 looking for corruption. Enabling this will
1551 both detect corruption and prevent the kernel
1552 from using the memory being corrupted.
1553 However, its intended as a diagnostic tool; if
1554 repeatable BIOS-originated corruption always
1555 affects the same memory, you can use memmap=
1556 to prevent the kernel from using that memory.
1558 memory_corruption_check_size=size [X86]
1559 By default it checks for corruption in the low
1560 64k, making this memory unavailable for normal
1561 use. Use this parameter to scan for
1562 corruption in more or less memory.
1564 memory_corruption_check_period=seconds [X86]
1565 By default it checks for corruption every 60
1566 seconds. Use this parameter to check at some
1567 other rate. 0 disables periodic checking.
1569 memtest= [KNL,X86] Enable memtest
1570 Format: <integer>
1571 default : 0 <disable>
1572 Specifies the number of memtest passes to be
1573 performed. Each pass selects another test
1574 pattern from a given set of patterns. Memtest
1575 fills the memory with this pattern, validates
1576 memory contents and reserves bad memory
1577 regions that are detected.
1579 meye.*= [HW] Set MotionEye Camera parameters
1580 See Documentation/video4linux/meye.txt.
1582 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1583 Multi-Function General Purpose Timers on AMD Geode
1584 platforms.
1586 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1587 the BIOS has incorrectly applied a workaround. TinyBIOS
1588 version 0.98 is known to be affected, 0.99 fixes the
1589 problem by letting the user disable the workaround.
1591 mga= [HW,DRM]
1593 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1594 physical address is ignored.
1596 mini2440= [ARM,HW,KNL]
1597 Format:[0..2][b][c][t]
1598 Default: "0tb"
1599 MINI2440 configuration specification:
1600 0 - The attached screen is the 3.5" TFT
1601 1 - The attached screen is the 7" TFT
1602 2 - The VGA Shield is attached (1024x768)
1603 Leaving out the screen size parameter will not load
1604 the TFT driver, and the framebuffer will be left
1605 unconfigured.
1606 b - Enable backlight. The TFT backlight pin will be
1607 linked to the kernel VESA blanking code and a GPIO
1608 LED. This parameter is not necessary when using the
1609 VGA shield.
1610 c - Enable the s3c camera interface.
1611 t - Reserved for enabling touchscreen support. The
1612 touchscreen support is not enabled in the mainstream
1613 kernel as of 2.6.30, a preliminary port can be found
1614 in the "bleeding edge" mini2440 support kernel at
1615 http://repo.or.cz/w/linux-2.6/mini2440.git
1617 mminit_loglevel=
1618 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1619 parameter allows control of the logging verbosity for
1620 the additional memory initialisation checks. A value
1621 of 0 disables mminit logging and a level of 4 will
1622 log everything. Information is printed at KERN_DEBUG
1623 so loglevel=8 may also need to be specified.
1625 module.sig_enforce
1626 [KNL] When CONFIG_MODULE_SIG is set, this means that
1627 modules without (valid) signatures will fail to load.
1628 Note that if CONFIG_MODULE_SIG_ENFORCE is set, that
1629 is always true, so this option does nothing.
1631 mousedev.tap_time=
1632 [MOUSE] Maximum time between finger touching and
1633 leaving touchpad surface for touch to be considered
1634 a tap and be reported as a left button click (for
1635 touchpads working in absolute mode only).
1636 Format: <msecs>
1637 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1638 reporting absolute coordinates, such as tablets
1639 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1640 reporting absolute coordinates, such as tablets
1642 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1643 is similar to kernelcore except it specifies the
1644 amount of memory used for migratable allocations.
1645 If both kernelcore and movablecore is specified,
1646 then kernelcore will be at *least* the specified
1647 value but may be more. If movablecore on its own
1648 is specified, the administrator must be careful
1649 that the amount of memory usable for all allocations
1650 is not too small.
1652 MTD_Partition= [MTD]
1653 Format: <name>,<region-number>,<size>,<offset>
1655 MTD_Region= [MTD] Format:
1656 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1658 mtdparts= [MTD]
1659 See drivers/mtd/cmdlinepart.c.
1661 multitce=off [PPC] This parameter disables the use of the pSeries
1662 firmware feature for updating multiple TCE entries
1663 at a time.
1665 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1667 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1669 boundary - index of last SLC block on Flex-OneNAND.
1670 The remaining blocks are configured as MLC blocks.
1671 lock - Configure if Flex-OneNAND boundary should be locked.
1672 Once locked, the boundary cannot be changed.
1673 1 indicates lock status, 0 indicates unlock status.
1675 mtdset= [ARM]
1676 ARM/S3C2412 JIVE boot control
1678 See arch/arm/mach-s3c2412/mach-jive.c
1680 mtouchusb.raw_coordinates=
1681 [HW] Make the MicroTouch USB driver use raw coordinates
1682 ('y', default) or cooked coordinates ('n')
1684 mtrr_chunk_size=nn[KMG] [X86]
1685 used for mtrr cleanup. It is largest continuous chunk
1686 that could hold holes aka. UC entries.
1688 mtrr_gran_size=nn[KMG] [X86]
1689 Used for mtrr cleanup. It is granularity of mtrr block.
1690 Default is 1.
1691 Large value could prevent small alignment from
1692 using up MTRRs.
1694 mtrr_spare_reg_nr=n [X86]
1695 Format: <integer>
1696 Range: 0,7 : spare reg number
1697 Default : 1
1698 Used for mtrr cleanup. It is spare mtrr entries number.
1699 Set to 2 or more if your graphical card needs more.
1701 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1703 netdev= [NET] Network devices parameters
1704 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1705 Note that mem_start is often overloaded to mean
1706 something different and driver-specific.
1707 This usage is only documented in each driver source
1708 file if at all.
1710 nf_conntrack.acct=
1711 [NETFILTER] Enable connection tracking flow accounting
1712 0 to disable accounting
1713 1 to enable accounting
1714 Default value is 0.
1716 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1717 See Documentation/filesystems/nfs/nfsroot.txt.
1719 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1720 See Documentation/filesystems/nfs/nfsroot.txt.
1722 nfsrootdebug [NFS] enable nfsroot debugging messages.
1723 See Documentation/filesystems/nfs/nfsroot.txt.
1725 nfs.callback_tcpport=
1726 [NFS] set the TCP port on which the NFSv4 callback
1727 channel should listen.
1729 nfs.cache_getent=
1730 [NFS] sets the pathname to the program which is used
1731 to update the NFS client cache entries.
1733 nfs.cache_getent_timeout=
1734 [NFS] sets the timeout after which an attempt to
1735 update a cache entry is deemed to have failed.
1737 nfs.idmap_cache_timeout=
1738 [NFS] set the maximum lifetime for idmapper cache
1739 entries.
1741 nfs.enable_ino64=
1742 [NFS] enable 64-bit inode numbers.
1743 If zero, the NFS client will fake up a 32-bit inode
1744 number for the readdir() and stat() syscalls instead
1745 of returning the full 64-bit number.
1746 The default is to return 64-bit inode numbers.
1748 nfs.max_session_slots=
1749 [NFSv4.1] Sets the maximum number of session slots
1750 the client will attempt to negotiate with the server.
1751 This limits the number of simultaneous RPC requests
1752 that the client can send to the NFSv4.1 server.
1753 Note that there is little point in setting this
1754 value higher than the max_tcp_slot_table_limit.
1756 nfs.nfs4_disable_idmapping=
1757 [NFSv4] When set to the default of '1', this option
1758 ensures that both the RPC level authentication
1759 scheme and the NFS level operations agree to use
1760 numeric uids/gids if the mount is using the
1761 'sec=sys' security flavour. In effect it is
1762 disabling idmapping, which can make migration from
1763 legacy NFSv2/v3 systems to NFSv4 easier.
1764 Servers that do not support this mode of operation
1765 will be autodetected by the client, and it will fall
1766 back to using the idmapper.
1767 To turn off this behaviour, set the value to '0'.
1768 nfs.nfs4_unique_id=
1769 [NFS4] Specify an additional fixed unique ident-
1770 ification string that NFSv4 clients can insert into
1771 their nfs_client_id4 string. This is typically a
1772 UUID that is generated at system install time.
1774 nfs.send_implementation_id =
1775 [NFSv4.1] Send client implementation identification
1776 information in exchange_id requests.
1777 If zero, no implementation identification information
1778 will be sent.
1779 The default is to send the implementation identification
1780 information.
1782 nfsd.nfs4_disable_idmapping=
1783 [NFSv4] When set to the default of '1', the NFSv4
1784 server will return only numeric uids and gids to
1785 clients using auth_sys, and will accept numeric uids
1786 and gids from such clients. This is intended to ease
1787 migration from NFSv2/v3.
1789 objlayoutdriver.osd_login_prog=
1790 [NFS] [OBJLAYOUT] sets the pathname to the program which
1791 is used to automatically discover and login into new
1792 osd-targets. Please see:
1793 Documentation/filesystems/pnfs.txt for more explanations
1795 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1796 when a NMI is triggered.
1797 Format: [state][,regs][,debounce][,die]
1799 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1800 Format: [panic,][nopanic,][num]
1801 Valid num: 0
1802 0 - turn nmi_watchdog off
1803 When panic is specified, panic when an NMI watchdog
1804 timeout occurs (or 'nopanic' to override the opposite
1805 default).
1806 This is useful when you use a panic=... timeout and
1807 need the box quickly up again.
1809 netpoll.carrier_timeout=
1810 [NET] Specifies amount of time (in seconds) that
1811 netpoll should wait for a carrier. By default netpoll
1812 waits 4 seconds.
1814 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1815 emulation library even if a 387 maths coprocessor
1816 is present.
1818 no_console_suspend
1819 [HW] Never suspend the console
1820 Disable suspending of consoles during suspend and
1821 hibernate operations. Once disabled, debugging
1822 messages can reach various consoles while the rest
1823 of the system is being put to sleep (ie, while
1824 debugging driver suspend/resume hooks). This may
1825 not work reliably with all consoles, but is known
1826 to work with serial and VGA consoles.
1827 To facilitate more flexible debugging, we also add
1828 console_suspend, a printk module parameter to control
1829 it. Users could use console_suspend (usually
1830 /sys/module/printk/parameters/console_suspend) to
1831 turn on/off it dynamically.
1833 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1834 caches in the slab allocator. Saves per-node memory,
1835 but will impact performance.
1837 noalign [KNL,ARM]
1839 noapic [SMP,APIC] Tells the kernel to not make use of any
1840 IOAPICs that may be present in the system.
1842 noautogroup Disable scheduler automatic task group creation.
1844 nobats [PPC] Do not use BATs for mapping kernel lowmem
1845 on "Classic" PPC cores.
1847 nocache [ARM]
1849 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1851 nodelayacct [KNL] Disable per-task delay accounting
1853 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1855 nodsp [SH] Disable hardware DSP at boot time.
1857 noefi [X86] Disable EFI runtime services support.
1859 noexec [IA-64]
1861 noexec [X86]
1862 On X86-32 available only on PAE configured kernels.
1863 noexec=on: enable non-executable mappings (default)
1864 noexec=off: disable non-executable mappings
1866 nosmap [X86]
1867 Disable SMAP (Supervisor Mode Access Prevention)
1868 even if it is supported by processor.
1870 nosmep [X86]
1871 Disable SMEP (Supervisor Mode Execution Prevention)
1872 even if it is supported by processor.
1874 noexec32 [X86-64]
1875 This affects only 32-bit executables.
1876 noexec32=on: enable non-executable mappings (default)
1877 read doesn't imply executable mappings
1878 noexec32=off: disable non-executable mappings
1879 read implies executable mappings
1881 nofpu [SH] Disable hardware FPU at boot time.
1883 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1884 register save and restore. The kernel will only save
1885 legacy floating-point registers on task switch.
1887 noxsave [BUGS=X86] Disables x86 extended register state save
1888 and restore using xsave. The kernel will fallback to
1889 enabling legacy floating-point and sse state.
1891 eagerfpu= [X86]
1892 on enable eager fpu restore
1893 off disable eager fpu restore
1894 auto selects the default scheme, which automatically
1895 enables eagerfpu restore for xsaveopt.
1897 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1898 wfi(ARM) instruction doesn't work correctly and not to
1899 use it. This is also useful when using JTAG debugger.
1901 no_file_caps Tells the kernel not to honor file capabilities. The
1902 only way then for a file to be executed with privilege
1903 is to be setuid root or executed by root.
1905 nohalt [IA-64] Tells the kernel not to use the power saving
1906 function PAL_HALT_LIGHT when idle. This increases
1907 power-consumption. On the positive side, it reduces
1908 interrupt wake-up latency, which may improve performance
1909 in certain environments such as networked servers or
1910 real-time systems.
1912 nohz= [KNL] Boottime enable/disable dynamic ticks
1913 Valid arguments: on, off
1914 Default: on
1916 noiotrap [SH] Disables trapped I/O port accesses.
1918 noirqdebug [X86-32] Disables the code which attempts to detect and
1919 disable unhandled interrupt sources.
1921 no_timer_check [X86,APIC] Disables the code which tests for
1922 broken timer IRQ sources.
1924 noisapnp [ISAPNP] Disables ISA PnP code.
1926 noinitrd [RAM] Tells the kernel not to load any configured
1927 initial RAM disk.
1929 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1930 remapping.
1931 [Deprecated - use intremap=off]
1933 nointroute [IA-64]
1935 nojitter [IA-64] Disables jitter checking for ITC timers.
1937 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1939 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1940 fault handling.
1942 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1943 steal time is computed, but won't influence scheduler
1944 behaviour
1946 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1948 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1950 noltlbs [PPC] Do not use large page/tlb entries for kernel
1951 lowmem mapping on PPC40x.
1953 nomca [IA-64] Disable machine check abort handling
1955 nomce [X86-32] Machine Check Exception
1957 nomfgpt [X86-32] Disable Multi-Function General Purpose
1958 Timer usage (for AMD Geode machines).
1960 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
1961 shutdown the other cpus. Instead use the REBOOT_VECTOR
1962 irq.
1964 nomodule Disable module load
1966 nopat [X86] Disable PAT (page attribute table extension of
1967 pagetables) support.
1969 norandmaps Don't use address space randomization. Equivalent to
1970 echo 0 > /proc/sys/kernel/randomize_va_space
1972 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1974 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1975 with UP alternatives
1977 noresidual [PPC] Don't use residual data on PReP machines.
1979 nordrand [X86] Disable the direct use of the RDRAND
1980 instruction even if it is supported by the
1981 processor. RDRAND is still available to user
1982 space applications.
1984 noresume [SWSUSP] Disables resume and restores original swap
1985 space.
1987 no-scroll [VGA] Disables scrollback.
1988 This is required for the Braillex ib80-piezo Braille
1989 reader made by F.H. Papenmeier (Germany).
1991 nosbagart [IA-64]
1993 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1995 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1996 and disable the IO APIC. legacy for "maxcpus=0".
1998 nosoftlockup [KNL] Disable the soft-lockup detector.
2000 nosync [HW,M68K] Disables sync negotiation for all devices.
2002 notsc [BUGS=X86-32] Disable Time Stamp Counter
2004 nousb [USB] Disable the USB subsystem
2006 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2008 nowb [ARM]
2010 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2012 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2013 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2014 Some features depend on CPU0. Known dependencies are:
2015 1. Resume from suspend/hibernate depends on CPU0.
2016 Suspend/hibernate will fail if CPU0 is offline and you
2017 need to online CPU0 before suspend/hibernate.
2018 2. PIC interrupts also depend on CPU0. CPU0 can't be
2019 removed if a PIC interrupt is detected.
2020 It's said poweroff/reboot may depend on CPU0 on some
2021 machines although I haven't seen such issues so far
2022 after CPU0 is offline on a few tested machines.
2023 If the dependencies are under your control, you can
2024 turn on cpu0_hotplug.
2026 nptcg= [IA-64] Override max number of concurrent global TLB
2027 purges which is reported from either PAL_VM_SUMMARY or
2028 SAL PALO.
2030 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2031 could support. nr_cpus=n : n >= 1 limits the kernel to
2032 supporting 'n' processors. Later in runtime you can not
2033 use hotplug cpu feature to put more cpu back to online.
2034 just like you compile the kernel NR_CPUS=n
2036 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2038 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2039 Allowed values are enable and disable
2041 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2042 one of ['zone', 'node', 'default'] can be specified
2043 This can be set from sysctl after boot.
2044 See Documentation/sysctl/vm.txt for details.
2046 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2047 See Documentation/debugging-via-ohci1394.txt for more
2048 info.
2050 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2051 Rather than timing out after 20 ms if an EC
2052 command is not properly ACKed, override the length
2053 of the timeout. We have interrupts disabled while
2054 waiting for the ACK, so if this is set too high
2055 interrupts *may* be lost!
2057 omap_mux= [OMAP] Override bootloader pin multiplexing.
2058 Format: <mux_mode0.mode_name=value>...
2059 For example, to override I2C bus2:
2060 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2062 oprofile.timer= [HW]
2063 Use timer interrupt instead of performance counters
2065 oprofile.cpu_type= Force an oprofile cpu type
2066 This might be useful if you have an older oprofile
2067 userland or if you want common events.
2068 Format: { arch_perfmon }
2069 arch_perfmon: [X86] Force use of architectural
2070 perfmon on Intel CPUs instead of the
2071 CPU specific event set.
2072 timer: [X86] Force use of architectural NMI
2073 timer mode (see also oprofile.timer
2074 for generic hr timer mode)
2075 [s390] Force legacy basic mode sampling
2076 (report cpu_type "timer")
2078 oops=panic Always panic on oopses. Default is to just kill the
2079 process, but there is a small probability of
2080 deadlocking the machine.
2081 This will also cause panics on machine check exceptions.
2082 Useful together with panic=30 to trigger a reboot.
2084 OSS [HW,OSS]
2085 See Documentation/sound/oss/oss-parameters.txt
2087 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2088 timeout > 0: seconds before rebooting
2089 timeout = 0: wait forever
2090 timeout < 0: reboot immediately
2091 Format: <timeout>
2093 parkbd.port= [HW] Parallel port number the keyboard adapter is
2094 connected to, default is 0.
2095 Format: <parport#>
2096 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2097 0 for XT, 1 for AT (default is AT).
2098 Format: <mode>
2100 parport= [HW,PPT] Specify parallel ports. 0 disables.
2101 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2102 Use 'auto' to force the driver to use any
2103 IRQ/DMA settings detected (the default is to
2104 ignore detected IRQ/DMA settings because of
2105 possible conflicts). You can specify the base
2106 address, IRQ, and DMA settings; IRQ and DMA
2107 should be numbers, or 'auto' (for using detected
2108 settings on that particular port), or 'nofifo'
2109 (to avoid using a FIFO even if it is detected).
2110 Parallel ports are assigned in the order they
2111 are specified on the command line, starting
2112 with parport0.
2114 parport_init_mode= [HW,PPT]
2115 Configure VIA parallel port to operate in
2116 a specific mode. This is necessary on Pegasos
2117 computer where firmware has no options for setting
2118 up parallel port mode and sets it to spp.
2119 Currently this function knows 686a and 8231 chips.
2120 Format: [spp|ps2|epp|ecp|ecpepp]
2122 pause_on_oops=
2123 Halt all CPUs after the first oops has been printed for
2124 the specified number of seconds. This is to be used if
2125 your oopses keep scrolling off the screen.
2127 pcbit= [HW,ISDN]
2129 pcd. [PARIDE]
2130 See header of drivers/block/paride/pcd.c.
2131 See also Documentation/blockdev/paride.txt.
2133 pci=option[,option...] [PCI] various PCI subsystem options:
2134 earlydump [X86] dump PCI config space before the kernel
2135 changes anything
2136 off [X86] don't probe for the PCI bus
2137 bios [X86-32] force use of PCI BIOS, don't access
2138 the hardware directly. Use this if your machine
2139 has a non-standard PCI host bridge.
2140 nobios [X86-32] disallow use of PCI BIOS, only direct
2141 hardware access methods are allowed. Use this
2142 if you experience crashes upon bootup and you
2143 suspect they are caused by the BIOS.
2144 conf1 [X86] Force use of PCI Configuration
2145 Mechanism 1.
2146 conf2 [X86] Force use of PCI Configuration
2147 Mechanism 2.
2148 noaer [PCIE] If the PCIEAER kernel config parameter is
2149 enabled, this kernel boot option can be used to
2150 disable the use of PCIE advanced error reporting.
2151 nodomains [PCI] Disable support for multiple PCI
2152 root domains (aka PCI segments, in ACPI-speak).
2153 nommconf [X86] Disable use of MMCONFIG for PCI
2154 Configuration
2155 check_enable_amd_mmconf [X86] check for and enable
2156 properly configured MMIO access to PCI
2157 config space on AMD family 10h CPU
2158 nomsi [MSI] If the PCI_MSI kernel config parameter is
2159 enabled, this kernel boot option can be used to
2160 disable the use of MSI interrupts system-wide.
2161 noioapicquirk [APIC] Disable all boot interrupt quirks.
2162 Safety option to keep boot IRQs enabled. This
2163 should never be necessary.
2164 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2165 primary IO-APIC for bridges that cannot disable
2166 boot IRQs. This fixes a source of spurious IRQs
2167 when the system masks IRQs.
2168 noioapicreroute [APIC] Disable workaround that uses the
2169 boot IRQ equivalent of an IRQ that connects to
2170 a chipset where boot IRQs cannot be disabled.
2171 The opposite of ioapicreroute.
2172 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2173 routing table. These calls are known to be buggy
2174 on several machines and they hang the machine
2175 when used, but on other computers it's the only
2176 way to get the interrupt routing table. Try
2177 this option if the kernel is unable to allocate
2178 IRQs or discover secondary PCI buses on your
2179 motherboard.
2180 rom [X86] Assign address space to expansion ROMs.
2181 Use with caution as certain devices share
2182 address decoders between ROMs and other
2183 resources.
2184 norom [X86] Do not assign address space to
2185 expansion ROMs that do not already have
2186 BIOS assigned address ranges.
2187 nobar [X86] Do not assign address space to the
2188 BARs that weren't assigned by the BIOS.
2189 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2190 assigned automatically to PCI devices. You can
2191 make the kernel exclude IRQs of your ISA cards
2192 this way.
2193 pirqaddr=0xAAAAA [X86] Specify the physical address
2194 of the PIRQ table (normally generated
2195 by the BIOS) if it is outside the
2196 F0000h-100000h range.
2197 lastbus=N [X86] Scan all buses thru bus #N. Can be
2198 useful if the kernel is unable to find your
2199 secondary buses and you want to tell it
2200 explicitly which ones they are.
2201 assign-busses [X86] Always assign all PCI bus
2202 numbers ourselves, overriding
2203 whatever the firmware may have done.
2204 usepirqmask [X86] Honor the possible IRQ mask stored
2205 in the BIOS $PIR table. This is needed on
2206 some systems with broken BIOSes, notably
2207 some HP Pavilion N5400 and Omnibook XE3
2208 notebooks. This will have no effect if ACPI
2209 IRQ routing is enabled.
2210 noacpi [X86] Do not use ACPI for IRQ routing
2211 or for PCI scanning.
2212 use_crs [X86] Use PCI host bridge window information
2213 from ACPI. On BIOSes from 2008 or later, this
2214 is enabled by default. If you need to use this,
2215 please report a bug.
2216 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2217 If you need to use this, please report a bug.
2218 routeirq Do IRQ routing for all PCI devices.
2219 This is normally done in pci_enable_device(),
2220 so this option is a temporary workaround
2221 for broken drivers that don't call it.
2222 skip_isa_align [X86] do not align io start addr, so can
2223 handle more pci cards
2224 firmware [ARM] Do not re-enumerate the bus but instead
2225 just use the configuration from the
2226 bootloader. This is currently used on
2227 IXP2000 systems where the bus has to be
2228 configured a certain way for adjunct CPUs.
2229 noearly [X86] Don't do any early type 1 scanning.
2230 This might help on some broken boards which
2231 machine check when some devices' config space
2232 is read. But various workarounds are disabled
2233 and some IOMMU drivers will not work.
2234 bfsort Sort PCI devices into breadth-first order.
2235 This sorting is done to get a device
2236 order compatible with older (<= 2.4) kernels.
2237 nobfsort Don't sort PCI devices into breadth-first order.
2238 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2239 tuning and use the BIOS-configured MPS defaults.
2240 pcie_bus_safe Set every device's MPS to the largest value
2241 supported by all devices below the root complex.
2242 pcie_bus_perf Set device MPS to the largest allowable MPS
2243 based on its parent bus. Also set MRRS (Max
2244 Read Request Size) to the largest supported
2245 value (no larger than the MPS that the device
2246 or bus can support) for best performance.
2247 pcie_bus_peer2peer Set every device's MPS to 128B, which
2248 every device is guaranteed to support. This
2249 configuration allows peer-to-peer DMA between
2250 any pair of devices, possibly at the cost of
2251 reduced performance. This also guarantees
2252 that hot-added devices will work.
2253 cbiosize=nn[KMG] The fixed amount of bus space which is
2254 reserved for the CardBus bridge's IO window.
2255 The default value is 256 bytes.
2256 cbmemsize=nn[KMG] The fixed amount of bus space which is
2257 reserved for the CardBus bridge's memory
2258 window. The default value is 64 megabytes.
2259 resource_alignment=
2260 Format:
2261 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2262 Specifies alignment and device to reassign
2263 aligned memory resources.
2264 If <order of align> is not specified,
2265 PAGE_SIZE is used as alignment.
2266 PCI-PCI bridge can be specified, if resource
2267 windows need to be expanded.
2268 ecrc= Enable/disable PCIe ECRC (transaction layer
2269 end-to-end CRC checking).
2270 bios: Use BIOS/firmware settings. This is the
2271 the default.
2272 off: Turn ECRC off
2273 on: Turn ECRC on.
2274 hpiosize=nn[KMG] The fixed amount of bus space which is
2275 reserved for hotplug bridge's IO window.
2276 Default size is 256 bytes.
2277 hpmemsize=nn[KMG] The fixed amount of bus space which is
2278 reserved for hotplug bridge's memory window.
2279 Default size is 2 megabytes.
2280 realloc= Enable/disable reallocating PCI bridge resources
2281 if allocations done by BIOS are too small to
2282 accommodate resources required by all child
2283 devices.
2284 off: Turn realloc off
2285 on: Turn realloc on
2286 realloc same as realloc=on
2287 noari do not use PCIe ARI.
2288 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2289 only look for one device below a PCIe downstream
2290 port.
2292 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2293 Management.
2294 off Disable ASPM.
2295 force Enable ASPM even on devices that claim not to support it.
2296 WARNING: Forcing ASPM on may cause system lockups.
2298 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2299 nomsi Do not use MSI for PCI Express Native Hotplug (this
2300 makes all PCIe ports use INTx for hotplug services).
2302 pcie_ports= [PCIE] PCIe ports handling:
2303 auto Ask the BIOS whether or not to use native PCIe services
2304 associated with PCIe ports (PME, hot-plug, AER). Use
2305 them only if that is allowed by the BIOS.
2306 native Use native PCIe services associated with PCIe ports
2307 unconditionally.
2308 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2309 ports driver.
2311 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2312 nomsi Do not use MSI for native PCIe PME signaling (this makes
2313 all PCIe root ports use INTx for all services).
2315 pcmv= [HW,PCMCIA] BadgePAD 4
2317 pd. [PARIDE]
2318 See Documentation/blockdev/paride.txt.
2320 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2321 boot time.
2322 Format: { 0 | 1 }
2323 See arch/parisc/kernel/pdc_chassis.c
2325 percpu_alloc= Select which percpu first chunk allocator to use.
2326 Currently supported values are "embed" and "page".
2327 Archs may support subset or none of the selections.
2328 See comments in mm/percpu.c for details on each
2329 allocator. This parameter is primarily for debugging
2330 and performance comparison.
2332 pf. [PARIDE]
2333 See Documentation/blockdev/paride.txt.
2335 pg. [PARIDE]
2336 See Documentation/blockdev/paride.txt.
2338 pirq= [SMP,APIC] Manual mp-table setup
2339 See Documentation/x86/i386/IO-APIC.txt.
2341 plip= [PPT,NET] Parallel port network link
2342 Format: { parport<nr> | timid | 0 }
2343 See also Documentation/parport.txt.
2345 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2346 Override pmtimer IOPort with a hex value.
2347 e.g. pmtmr=0x508
2349 pnp.debug=1 [PNP]
2350 Enable PNP debug messages (depends on the
2351 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2352 via /sys/module/pnp/parameters/debug. We always show
2353 current resource usage; turning this on also shows
2354 possible settings and some assignment information.
2356 pnpacpi= [ACPI]
2357 { off }
2359 pnpbios= [ISAPNP]
2360 { on | off | curr | res | no-curr | no-res }
2362 pnp_reserve_irq=
2363 [ISAPNP] Exclude IRQs for the autoconfiguration
2365 pnp_reserve_dma=
2366 [ISAPNP] Exclude DMAs for the autoconfiguration
2368 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2369 Ranges are in pairs (I/O port base and size).
2371 pnp_reserve_mem=
2372 [ISAPNP] Exclude memory regions for the
2373 autoconfiguration.
2374 Ranges are in pairs (memory base and size).
2376 ports= [IP_VS_FTP] IPVS ftp helper module
2377 Default is 21.
2378 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2379 may be specified.
2380 Format: <port>,<port>....
2382 print-fatal-signals=
2383 [KNL] debug: print fatal signals
2385 If enabled, warn about various signal handling
2386 related application anomalies: too many signals,
2387 too many POSIX.1 timers, fatal signals causing a
2388 coredump - etc.
2390 If you hit the warning due to signal overflow,
2391 you might want to try "ulimit -i unlimited".
2393 default: off.
2395 printk.always_kmsg_dump=
2396 Trigger kmsg_dump for cases other than kernel oops or
2397 panics
2398 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2399 default: disabled
2401 printk.time= Show timing data prefixed to each printk message line
2402 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2404 processor.max_cstate= [HW,ACPI]
2405 Limit processor to maximum C-state
2406 max_cstate=9 overrides any DMI blacklist limit.
2408 processor.nocst [HW,ACPI]
2409 Ignore the _CST method to determine C-states,
2410 instead using the legacy FADT method
2412 profile= [KNL] Enable kernel profiling via /proc/profile
2413 Format: [schedule,]<number>
2414 Param: "schedule" - profile schedule points.
2415 Param: <number> - step/bucket size as a power of 2 for
2416 statistical time based profiling.
2417 Param: "sleep" - profile D-state sleeping (millisecs).
2418 Requires CONFIG_SCHEDSTATS
2419 Param: "kvm" - profile VM exits.
2421 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2422 before loading.
2423 See Documentation/blockdev/ramdisk.txt.
2425 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2426 probe for; one of (bare|imps|exps|lifebook|any).
2427 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2428 per second.
2429 psmouse.resetafter= [HW,MOUSE]
2430 Try to reset the device after so many bad packets
2431 (0 = never).
2432 psmouse.resolution=
2433 [HW,MOUSE] Set desired mouse resolution, in dpi.
2434 psmouse.smartscroll=
2435 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2436 0 = disabled, 1 = enabled (default).
2438 pstore.backend= Specify the name of the pstore backend to use
2440 pt. [PARIDE]
2441 See Documentation/blockdev/paride.txt.
2443 pty.legacy_count=
2444 [KNL] Number of legacy pty's. Overwrites compiled-in
2445 default number.
2447 quiet [KNL] Disable most log messages
2449 r128= [HW,DRM]
2451 raid= [HW,RAID]
2452 See Documentation/md.txt.
2454 ramdisk_blocksize= [RAM]
2455 See Documentation/blockdev/ramdisk.txt.
2457 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2458 See Documentation/blockdev/ramdisk.txt.
2460 rcu_nocbs= [KNL,BOOT]
2461 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2462 the specified list of CPUs to be no-callback CPUs.
2463 Invocation of these CPUs' RCU callbacks will
2464 be offloaded to "rcuoN" kthreads created for
2465 that purpose. This reduces OS jitter on the
2466 offloaded CPUs, which can be useful for HPC and
2467 real-time workloads. It can also improve energy
2468 efficiency for asymmetric multiprocessors.
2470 rcu_nocb_poll [KNL,BOOT]
2471 Rather than requiring that offloaded CPUs
2472 (specified by rcu_nocbs= above) explicitly
2473 awaken the corresponding "rcuoN" kthreads,
2474 make these kthreads poll for callbacks.
2475 This improves the real-time response for the
2476 offloaded CPUs by relieving them of the need to
2477 wake up the corresponding kthread, but degrades
2478 energy efficiency by requiring that the kthreads
2479 periodically wake up to do the polling.
2481 rcutree.blimit= [KNL,BOOT]
2482 Set maximum number of finished RCU callbacks to process
2483 in one batch.
2485 rcutree.fanout_leaf= [KNL,BOOT]
2486 Increase the number of CPUs assigned to each
2487 leaf rcu_node structure. Useful for very large
2488 systems.
2490 rcutree.qhimark= [KNL,BOOT]
2491 Set threshold of queued
2492 RCU callbacks over which batch limiting is disabled.
2494 rcutree.qlowmark= [KNL,BOOT]
2495 Set threshold of queued RCU callbacks below which
2496 batch limiting is re-enabled.
2498 rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2499 Suppress RCU CPU stall warning messages.
2501 rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2502 Set timeout for RCU CPU stall warning messages.
2504 rcutree.jiffies_till_first_fqs= [KNL,BOOT]
2505 Set delay from grace-period initialization to
2506 first attempt to force quiescent states.
2507 Units are jiffies, minimum value is zero,
2508 and maximum value is HZ.
2510 rcutree.jiffies_till_next_fqs= [KNL,BOOT]
2511 Set delay between subsequent attempts to force
2512 quiescent states. Units are jiffies, minimum
2513 value is one, and maximum value is HZ.
2515 rcutorture.fqs_duration= [KNL,BOOT]
2516 Set duration of force_quiescent_state bursts.
2518 rcutorture.fqs_holdoff= [KNL,BOOT]
2519 Set holdoff time within force_quiescent_state bursts.
2521 rcutorture.fqs_stutter= [KNL,BOOT]
2522 Set wait time between force_quiescent_state bursts.
2524 rcutorture.irqreader= [KNL,BOOT]
2525 Test RCU readers from irq handlers.
2527 rcutorture.n_barrier_cbs= [KNL,BOOT]
2528 Set callbacks/threads for rcu_barrier() testing.
2530 rcutorture.nfakewriters= [KNL,BOOT]
2531 Set number of concurrent RCU writers. These just
2532 stress RCU, they don't participate in the actual
2533 test, hence the "fake".
2535 rcutorture.nreaders= [KNL,BOOT]
2536 Set number of RCU readers.
2538 rcutorture.onoff_holdoff= [KNL,BOOT]
2539 Set time (s) after boot for CPU-hotplug testing.
2541 rcutorture.onoff_interval= [KNL,BOOT]
2542 Set time (s) between CPU-hotplug operations, or
2543 zero to disable CPU-hotplug testing.
2545 rcutorture.shuffle_interval= [KNL,BOOT]
2546 Set task-shuffle interval (s). Shuffling tasks
2547 allows some CPUs to go into dyntick-idle mode
2548 during the rcutorture test.
2550 rcutorture.shutdown_secs= [KNL,BOOT]
2551 Set time (s) after boot system shutdown. This
2552 is useful for hands-off automated testing.
2554 rcutorture.stall_cpu= [KNL,BOOT]
2555 Duration of CPU stall (s) to test RCU CPU stall
2556 warnings, zero to disable.
2558 rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2559 Time to wait (s) after boot before inducing stall.
2561 rcutorture.stat_interval= [KNL,BOOT]
2562 Time (s) between statistics printk()s.
2564 rcutorture.stutter= [KNL,BOOT]
2565 Time (s) to stutter testing, for example, specifying
2566 five seconds causes the test to run for five seconds,
2567 wait for five seconds, and so on. This tests RCU's
2568 ability to transition abruptly to and from idle.
2570 rcutorture.test_boost= [KNL,BOOT]
2571 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2572 "Maybe" means test if the RCU implementation
2573 under test support RCU priority boosting.
2575 rcutorture.test_boost_duration= [KNL,BOOT]
2576 Duration (s) of each individual boost test.
2578 rcutorture.test_boost_interval= [KNL,BOOT]
2579 Interval (s) between each boost test.
2581 rcutorture.test_no_idle_hz= [KNL,BOOT]
2582 Test RCU's dyntick-idle handling. See also the
2583 rcutorture.shuffle_interval parameter.
2585 rcutorture.torture_type= [KNL,BOOT]
2586 Specify the RCU implementation to test.
2588 rcutorture.verbose= [KNL,BOOT]
2589 Enable additional printk() statements.
2591 rdinit= [KNL]
2592 Format: <full_path>
2593 Run specified binary instead of /init from the ramdisk,
2594 used for early userspace startup. See initrd.
2596 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2597 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2598 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2600 relax_domain_level=
2601 [KNL, SMP] Set scheduler's default relax_domain_level.
2602 See Documentation/cgroups/cpusets.txt.
2604 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2606 reservetop= [X86-32]
2607 Format: nn[KMG]
2608 Reserves a hole at the top of the kernel virtual
2609 address space.
2611 reservelow= [X86]
2612 Format: nn[K]
2613 Set the amount of memory to reserve for BIOS at
2614 the bottom of the address space.
2616 reset_devices [KNL] Force drivers to reset the underlying device
2617 during initialization.
2619 resume= [SWSUSP]
2620 Specify the partition device for software suspend
2621 Format:
2622 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2624 resume_offset= [SWSUSP]
2625 Specify the offset from the beginning of the partition
2626 given by "resume=" at which the swap header is located,
2627 in <PAGE_SIZE> units (needed only for swap files).
2628 See Documentation/power/swsusp-and-swap-files.txt
2630 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2631 read the resume files
2633 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2634 Useful for devices that are detected asynchronously
2635 (e.g. USB and MMC devices).
2637 hibernate= [HIBERNATION]
2638 noresume Don't check if there's a hibernation image
2639 present during boot.
2640 nocompress Don't compress/decompress hibernation images.
2642 retain_initrd [RAM] Keep initrd memory after extraction
2644 rhash_entries= [KNL,NET]
2645 Set number of hash buckets for route cache
2647 riscom8= [HW,SERIAL]
2648 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2650 ro [KNL] Mount root device read-only on boot
2652 root= [KNL] Root filesystem
2653 See name_to_dev_t comment in init/do_mounts.c.
2655 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2656 mount the root filesystem
2658 rootflags= [KNL] Set root filesystem mount option string
2660 rootfstype= [KNL] Set root filesystem type
2662 rootwait [KNL] Wait (indefinitely) for root device to show up.
2663 Useful for devices that are detected asynchronously
2664 (e.g. USB and MMC devices).
2666 rw [KNL] Mount root device read-write on boot
2668 S [KNL] Run init in single mode
2670 sa1100ir [NET]
2671 See drivers/net/irda/sa1100_ir.c.
2673 sbni= [NET] Granch SBNI12 leased line adapter
2675 sched_debug [KNL] Enables verbose scheduler debug messages.
2677 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2678 xtime_lock contention on larger systems, and/or RCU lock
2679 contention on all systems with CONFIG_MAXSMP set.
2680 Format: { "0" | "1" }
2681 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2682 1 -- enable.
2683 Note: increases power consumption, thus should only be
2684 enabled if running jitter sensitive (HPC/RT) workloads.
2686 security= [SECURITY] Choose a security module to enable at boot.
2687 If this boot parameter is not specified, only the first
2688 security module asking for security registration will be
2689 loaded. An invalid security module name will be treated
2690 as if no module has been chosen.
2692 selinux= [SELINUX] Disable or enable SELinux at boot time.
2693 Format: { "0" | "1" }
2694 See security/selinux/Kconfig help text.
2695 0 -- disable.
2696 1 -- enable.
2697 Default value is set via kernel config option.
2698 If enabled at boot time, /selinux/disable can be used
2699 later to disable prior to initial policy load.
2701 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2702 Format: { "0" | "1" }
2703 See security/apparmor/Kconfig help text
2704 0 -- disable.
2705 1 -- enable.
2706 Default value is set via kernel config option.
2708 serialnumber [BUGS=X86-32]
2710 shapers= [NET]
2711 Maximal number of shapers.
2713 show_msr= [x86] show boot-time MSR settings
2714 Format: { <integer> }
2715 Show boot-time (BIOS-initialized) MSR settings.
2716 The parameter means the number of CPUs to show,
2717 for example 1 means boot CPU only.
2719 simeth= [IA-64]
2720 simscsi=
2722 slram= [HW,MTD]
2724 slab_max_order= [MM, SLAB]
2725 Determines the maximum allowed order for slabs.
2726 A high setting may cause OOMs due to memory
2727 fragmentation. Defaults to 1 for systems with
2728 more than 32MB of RAM, 0 otherwise.
2730 slub_debug[=options[,slabs]] [MM, SLUB]
2731 Enabling slub_debug allows one to determine the
2732 culprit if slab objects become corrupted. Enabling
2733 slub_debug can create guard zones around objects and
2734 may poison objects when not in use. Also tracks the
2735 last alloc / free. For more information see
2736 Documentation/vm/slub.txt.
2738 slub_max_order= [MM, SLUB]
2739 Determines the maximum allowed order for slabs.
2740 A high setting may cause OOMs due to memory
2741 fragmentation. For more information see
2742 Documentation/vm/slub.txt.
2744 slub_min_objects= [MM, SLUB]
2745 The minimum number of objects per slab. SLUB will
2746 increase the slab order up to slub_max_order to
2747 generate a sufficiently large slab able to contain
2748 the number of objects indicated. The higher the number
2749 of objects the smaller the overhead of tracking slabs
2750 and the less frequently locks need to be acquired.
2751 For more information see Documentation/vm/slub.txt.
2753 slub_min_order= [MM, SLUB]
2754 Determines the minimum page order for slabs. Must be
2755 lower than slub_max_order.
2756 For more information see Documentation/vm/slub.txt.
2758 slub_nomerge [MM, SLUB]
2759 Disable merging of slabs with similar size. May be
2760 necessary if there is some reason to distinguish
2761 allocs to different slabs. Debug options disable
2762 merging on their own.
2763 For more information see Documentation/vm/slub.txt.
2765 smart2= [HW]
2766 Format: <io1>[,<io2>[,...,<io8>]]
2768 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2769 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2770 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2771 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2772 smsc-ircc2.ircc_irq= [HW] IRQ line
2773 smsc-ircc2.ircc_dma= [HW] DMA channel
2774 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2775 0: Toshiba Satellite 1800 (GP data pin select)
2776 1: Fast pin select (default)
2777 2: ATC IRMode
2779 softlockup_panic=
2780 [KNL] Should the soft-lockup detector generate panics.
2781 Format: <integer>
2783 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2784 See Documentation/laptops/sonypi.txt
2786 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2787 See Documentation/serial/specialix.txt.
2789 spia_io_base= [HW,MTD]
2790 spia_fio_base=
2791 spia_pedr=
2792 spia_peddr=
2794 stacktrace [FTRACE]
2795 Enabled the stack tracer on boot up.
2797 stacktrace_filter=[function-list]
2798 [FTRACE] Limit the functions that the stack tracer
2799 will trace at boot up. function-list is a comma separated
2800 list of functions. This list can be changed at run
2801 time by the stack_trace_filter file in the debugfs
2802 tracing directory. Note, this enables stack tracing
2803 and the stacktrace above is not needed.
2805 sti= [PARISC,HW]
2806 Format: <num>
2807 Set the STI (builtin display/keyboard on the HP-PARISC
2808 machines) console (graphic card) which should be used
2809 as the initial boot-console.
2810 See also comment in drivers/video/console/sticore.c.
2812 sti_font= [HW]
2813 See comment in drivers/video/console/sticore.c.
2815 stifb= [HW]
2816 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2818 sunrpc.min_resvport=
2819 sunrpc.max_resvport=
2820 [NFS,SUNRPC]
2821 SunRPC servers often require that client requests
2822 originate from a privileged port (i.e. a port in the
2823 range 0 < portnr < 1024).
2824 An administrator who wishes to reserve some of these
2825 ports for other uses may adjust the range that the
2826 kernel's sunrpc client considers to be privileged
2827 using these two parameters to set the minimum and
2828 maximum port values.
2830 sunrpc.pool_mode=
2831 [NFS]
2832 Control how the NFS server code allocates CPUs to
2833 service thread pools. Depending on how many NICs
2834 you have and where their interrupts are bound, this
2835 option will affect which CPUs will do NFS serving.
2836 Note: this parameter cannot be changed while the
2837 NFS server is running.
2839 auto the server chooses an appropriate mode
2840 automatically using heuristics
2841 global a single global pool contains all CPUs
2842 percpu one pool for each CPU
2843 pernode one pool for each NUMA node (equivalent
2844 to global on non-NUMA machines)
2846 sunrpc.tcp_slot_table_entries=
2847 sunrpc.udp_slot_table_entries=
2848 [NFS,SUNRPC]
2849 Sets the upper limit on the number of simultaneous
2850 RPC calls that can be sent from the client to a
2851 server. Increasing these values may allow you to
2852 improve throughput, but will also increase the
2853 amount of memory reserved for use by the client.
2855 swapaccount[=0|1]
2856 [KNL] Enable accounting of swap in memory resource
2857 controller if no parameter or 1 is given or disable
2858 it if 0 is given (See Documentation/cgroups/memory.txt)
2860 swiotlb= [IA-64] Number of I/O TLB slabs
2862 switches= [HW,M68k]
2864 sysfs.deprecated=0|1 [KNL]
2865 Enable/disable old style sysfs layout for old udev
2866 on older distributions. When this option is enabled
2867 very new udev will not work anymore. When this option
2868 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2869 in older udev will not work anymore.
2870 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2871 the kernel configuration.
2873 sysrq_always_enabled
2874 [KNL]
2875 Ignore sysrq setting - this boot parameter will
2876 neutralize any effect of /proc/sys/kernel/sysrq.
2877 Useful for debugging.
2879 tdfx= [HW,DRM]
2881 test_suspend= [SUSPEND]
2882 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2883 standby suspend) as the system sleep state to briefly
2884 enter during system startup. The system is woken from
2885 this state using a wakeup-capable RTC alarm.
2887 thash_entries= [KNL,NET]
2888 Set number of hash buckets for TCP connection
2890 thermal.act= [HW,ACPI]
2891 -1: disable all active trip points in all thermal zones
2892 <degrees C>: override all lowest active trip points
2894 thermal.crt= [HW,ACPI]
2895 -1: disable all critical trip points in all thermal zones
2896 <degrees C>: override all critical trip points
2898 thermal.nocrt= [HW,ACPI]
2899 Set to disable actions on ACPI thermal zone
2900 critical and hot trip points.
2902 thermal.off= [HW,ACPI]
2903 1: disable ACPI thermal control
2905 thermal.psv= [HW,ACPI]
2906 -1: disable all passive trip points
2907 <degrees C>: override all passive trip points to this
2908 value
2910 thermal.tzp= [HW,ACPI]
2911 Specify global default ACPI thermal zone polling rate
2912 <deci-seconds>: poll all this frequency
2913 0: no polling (default)
2915 threadirqs [KNL]
2916 Force threading of all interrupt handlers except those
2917 marked explicitly IRQF_NO_THREAD.
2919 topology= [S390]
2920 Format: {off | on}
2921 Specify if the kernel should make use of the cpu
2922 topology information if the hardware supports this.
2923 The scheduler will make use of this information and
2924 e.g. base its process migration decisions on it.
2925 Default is on.
2927 tp720= [HW,PS2]
2929 tpm_suspend_pcr=[HW,TPM]
2930 Format: integer pcr id
2931 Specify that at suspend time, the tpm driver
2932 should extend the specified pcr with zeros,
2933 as a workaround for some chips which fail to
2934 flush the last written pcr on TPM_SaveState.
2935 This will guarantee that all the other pcrs
2936 are saved.
2938 trace_buf_size=nn[KMG]
2939 [FTRACE] will set tracing buffer size.
2941 trace_event=[event-list]
2942 [FTRACE] Set and start specified trace events in order
2943 to facilitate early boot debugging.
2944 See also Documentation/trace/events.txt
2946 trace_options=[option-list]
2947 [FTRACE] Enable or disable tracer options at boot.
2948 The option-list is a comma delimited list of options
2949 that can be enabled or disabled just as if you were
2950 to echo the option name into
2952 /sys/kernel/debug/tracing/trace_options
2954 For example, to enable stacktrace option (to dump the
2955 stack trace of each event), add to the command line:
2957 trace_options=stacktrace
2959 See also Documentation/trace/ftrace.txt "trace options"
2960 section.
2962 transparent_hugepage=
2963 [KNL]
2964 Format: [always|madvise|never]
2965 Can be used to control the default behavior of the system
2966 with respect to transparent hugepages.
2967 See Documentation/vm/transhuge.txt for more details.
2969 tsc= Disable clocksource stability checks for TSC.
2970 Format: <string>
2971 [x86] reliable: mark tsc clocksource as reliable, this
2972 disables clocksource verification at runtime, as well
2973 as the stability checks done at bootup. Used to enable
2974 high-resolution timer mode on older hardware, and in
2975 virtualized environment.
2976 [x86] noirqtime: Do not use TSC to do irq accounting.
2977 Used to run time disable IRQ_TIME_ACCOUNTING on any
2978 platforms where RDTSC is slow and this accounting
2979 can add overhead.
2981 turbografx.map[2|3]= [HW,JOY]
2982 TurboGraFX parallel port interface
2983 Format:
2984 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2985 See also Documentation/input/joystick-parport.txt
2987 udbg-immortal [PPC] When debugging early kernel crashes that
2988 happen after console_init() and before a proper
2989 console driver takes over, this boot options might
2990 help "seeing" what's going on.
2992 uhash_entries= [KNL,NET]
2993 Set number of hash buckets for UDP/UDP-Lite connections
2995 uhci-hcd.ignore_oc=
2996 [USB] Ignore overcurrent events (default N).
2997 Some badly-designed motherboards generate lots of
2998 bogus events, for ports that aren't wired to
2999 anything. Set this parameter to avoid log spamming.
3000 Note that genuine overcurrent events won't be
3001 reported either.
3003 unknown_nmi_panic
3004 [X86] Cause panic on unknown NMI.
3006 usbcore.authorized_default=
3007 [USB] Default USB device authorization:
3008 (default -1 = authorized except for wireless USB,
3009 0 = not authorized, 1 = authorized)
3011 usbcore.autosuspend=
3012 [USB] The autosuspend time delay (in seconds) used
3013 for newly-detected USB devices (default 2). This
3014 is the time required before an idle device will be
3015 autosuspended. Devices for which the delay is set
3016 to a negative value won't be autosuspended at all.
3018 usbcore.usbfs_snoop=
3019 [USB] Set to log all usbfs traffic (default 0 = off).
3021 usbcore.blinkenlights=
3022 [USB] Set to cycle leds on hubs (default 0 = off).
3024 usbcore.old_scheme_first=
3025 [USB] Start with the old device initialization
3026 scheme (default 0 = off).
3028 usbcore.usbfs_memory_mb=
3029 [USB] Memory limit (in MB) for buffers allocated by
3030 usbfs (default = 16, 0 = max = 2047).
3032 usbcore.use_both_schemes=
3033 [USB] Try the other device initialization scheme
3034 if the first one fails (default 1 = enabled).
3036 usbcore.initial_descriptor_timeout=
3037 [USB] Specifies timeout for the initial 64-byte
3038 USB_REQ_GET_DESCRIPTOR request in milliseconds
3039 (default 5000 = 5.0 seconds).
3041 usbhid.mousepoll=
3042 [USBHID] The interval which mice are to be polled at.
3044 usb-storage.delay_use=
3045 [UMS] The delay in seconds before a new device is
3046 scanned for Logical Units (default 5).
3048 usb-storage.quirks=
3049 [UMS] A list of quirks entries to supplement or
3050 override the built-in unusual_devs list. List
3051 entries are separated by commas. Each entry has
3052 the form VID:PID:Flags where VID and PID are Vendor
3053 and Product ID values (4-digit hex numbers) and
3054 Flags is a set of characters, each corresponding
3055 to a common usb-storage quirk flag as follows:
3056 a = SANE_SENSE (collect more than 18 bytes
3057 of sense data);
3058 b = BAD_SENSE (don't collect more than 18
3059 bytes of sense data);
3060 c = FIX_CAPACITY (decrease the reported
3061 device capacity by one sector);
3062 d = NO_READ_DISC_INFO (don't use
3063 READ_DISC_INFO command);
3064 e = NO_READ_CAPACITY_16 (don't use
3065 READ_CAPACITY_16 command);
3066 h = CAPACITY_HEURISTICS (decrease the
3067 reported device capacity by one
3068 sector if the number is odd);
3069 i = IGNORE_DEVICE (don't bind to this
3070 device);
3071 l = NOT_LOCKABLE (don't try to lock and
3072 unlock ejectable media);
3073 m = MAX_SECTORS_64 (don't transfer more
3074 than 64 sectors = 32 KB at a time);
3075 n = INITIAL_READ10 (force a retry of the
3076 initial READ(10) command);
3077 o = CAPACITY_OK (accept the capacity
3078 reported by the device);
3079 p = WRITE_CACHE (the device cache is ON
3080 by default);
3081 r = IGNORE_RESIDUE (the device reports
3082 bogus residue values);
3083 s = SINGLE_LUN (the device has only one
3084 Logical Unit);
3085 w = NO_WP_DETECT (don't test whether the
3086 medium is write-protected).
3087 Example: quirks=0419:aaf5:rl,0421:0433:rc
3089 user_debug= [KNL,ARM]
3090 Format: <int>
3091 See arch/arm/Kconfig.debug help text.
3092 1 - undefined instruction events
3093 2 - system calls
3094 4 - invalid data aborts
3095 8 - SIGSEGV faults
3096 16 - SIGBUS faults
3097 Example: user_debug=31
3099 userpte=
3100 [X86] Flags controlling user PTE allocations.
3102 nohigh = do not allocate PTE pages in
3103 HIGHMEM regardless of setting
3104 of CONFIG_HIGHPTE.
3106 vdso= [X86,SH]
3107 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3108 vdso=1: enable VDSO (default)
3109 vdso=0: disable VDSO mapping
3111 vdso32= [X86]
3112 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3113 vdso32=1: enable 32-bit VDSO (default)
3114 vdso32=0: disable 32-bit VDSO mapping
3116 vector= [IA-64,SMP]
3117 vector=percpu: enable percpu vector domain
3119 video= [FB] Frame buffer configuration
3120 See Documentation/fb/modedb.txt.
3122 virtio_mmio.device=
3123 [VMMIO] Memory mapped virtio (platform) device.
3125 <size>@<baseaddr>:<irq>[:<id>]
3126 where:
3127 <size> := size (can use standard suffixes
3128 like K, M and G)
3129 <baseaddr> := physical base address
3130 <irq> := interrupt number (as passed to
3131 request_irq())
3132 <id> := (optional) platform device id
3133 example:
3134 virtio_mmio.device=1K@0x100b0000:48:7
3136 Can be used multiple times for multiple devices.
3138 vga= [BOOT,X86-32] Select a particular video mode
3139 See Documentation/x86/boot.txt and
3140 Documentation/svga.txt.
3141 Use vga=ask for menu.
3142 This is actually a boot loader parameter; the value is
3143 passed to the kernel using a special protocol.
3145 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3146 size of <nn>. This can be used to increase the
3147 minimum size (128MB on x86). It can also be used to
3148 decrease the size and leave more room for directly
3149 mapped kernel RAM.
3151 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3152 Format: <command>
3154 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3155 Format: <command>
3157 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3158 Format: <command>
3160 vsyscall= [X86-64]
3161 Controls the behavior of vsyscalls (i.e. calls to
3162 fixed addresses of 0xffffffffff600x00 from legacy
3163 code). Most statically-linked binaries and older
3164 versions of glibc use these calls. Because these
3165 functions are at fixed addresses, they make nice
3166 targets for exploits that can control RIP.
3168 emulate [default] Vsyscalls turn into traps and are
3169 emulated reasonably safely.
3171 native Vsyscalls are native syscall instructions.
3172 This is a little bit faster than trapping
3173 and makes a few dynamic recompilers work
3174 better than they would in emulation mode.
3175 It also makes exploits much easier to write.
3177 none Vsyscalls don't work at all. This makes
3178 them quite hard to use for exploits but
3179 might break your system.
3181 vt.cur_default= [VT] Default cursor shape.
3182 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3183 the parameters of the <Esc>[?A;B;Cc escape sequence;
3184 see VGA-softcursor.txt. Default: 2 = underline.
3186 vt.default_blu= [VT]
3187 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3188 Change the default blue palette of the console.
3189 This is a 16-member array composed of values
3190 ranging from 0-255.
3192 vt.default_grn= [VT]
3193 Format: <green0>,<green1>,<green2>,...,<green15>
3194 Change the default green palette of the console.
3195 This is a 16-member array composed of values
3196 ranging from 0-255.
3198 vt.default_red= [VT]
3199 Format: <red0>,<red1>,<red2>,...,<red15>
3200 Change the default red palette of the console.
3201 This is a 16-member array composed of values
3202 ranging from 0-255.
3204 vt.default_utf8=
3205 [VT]
3206 Format=<0|1>
3207 Set system-wide default UTF-8 mode for all tty's.
3208 Default is 1, i.e. UTF-8 mode is enabled for all
3209 newly opened terminals.
3211 vt.global_cursor_default=
3212 [VT]
3213 Format=<-1|0|1>
3214 Set system-wide default for whether a cursor
3215 is shown on new VTs. Default is -1,
3216 i.e. cursors will be created by default unless
3217 overridden by individual drivers. 0 will hide
3218 cursors, 1 will display them.
3220 watchdog timers [HW,WDT] For information on watchdog timers,
3221 see Documentation/watchdog/watchdog-parameters.txt
3222 or other driver-specific files in the
3223 Documentation/watchdog/ directory.
3225 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3226 default x2apic cluster mode on platforms
3227 supporting x2apic.
3229 x86_mrst_timer= [X86-32,APBT]
3230 Choose timer option for x86 Moorestown MID platform.
3231 Two valid options are apbt timer only and lapic timer
3232 plus one apbt timer for broadcast timer.
3233 x86_mrst_timer=apbt_only | lapic_and_apbt
3235 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
3236 xd_geo= See header of drivers/block/xd.c.
3238 xen_emul_unplug= [HW,X86,XEN]
3239 Unplug Xen emulated devices
3240 Format: [unplug0,][unplug1]
3241 ide-disks -- unplug primary master IDE devices
3242 aux-ide-disks -- unplug non-primary-master IDE devices
3243 nics -- unplug network devices
3244 all -- unplug all emulated devices (NICs and IDE disks)
3245 unnecessary -- unplugging emulated devices is
3246 unnecessary even if the host did not respond to
3247 the unplug protocol
3248 never -- do not unplug even if version check succeeds
3250 xirc2ps_cs= [NET,PCMCIA]
3251 Format:
3252 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3254 ______________________________________________________________________
3256 TODO:
3258 Add more DRM drivers.