4 The following is a consolidated list of the kernel parameters as
5 implemented by the __setup(), core_param() and module_param() macros
6 and sorted into English Dictionary order (defined as ignoring all
7 punctuation and sorting digits before letters in a case insensitive
8 manner), and with descriptions where known.
10 The kernel parses parameters from the kernel command line up to "--";
11 if it doesn't recognize a parameter and it doesn't contain a '.', the
12 parameter gets passed to init: parameters with '=' go into init's
13 environment, others are passed as command line arguments to init.
14 Everything after "--" is passed as an argument to init.
16 Module parameters can be specified in two ways: via the kernel command
17 line with a module name prefix, or via modprobe, e.g.:
19 (kernel command line) usbcore.blinkenlights=1
20 (modprobe command line) modprobe usbcore blinkenlights=1
22 Parameters for modules which are built into the kernel need to be
23 specified on the kernel command line. modprobe looks through the
24 kernel command line (/proc/cmdline) and collects module parameters
25 when it loads a module, so the kernel command line can be used for
28 Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30 can also be entered as
31 log-buf-len=1M print_fatal_signals=1
33 Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
36 This document may not be entirely up to date and comprehensive. The command
37 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
38 module. Loadable modules, after being loaded into the running kernel, also
39 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
40 parameters may be changed at runtime by the command
41 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
43 The parameters listed below are only valid if certain kernel build options were
44 enabled and if respective hardware is present. The text in square brackets at
45 the beginning of each description states the restrictions within which a
46 parameter is applicable:
48 ACPI ACPI support is enabled.
49 AGP AGP (Accelerated Graphics Port) is enabled.
50 ALSA ALSA sound support is enabled.
51 APIC APIC support is enabled.
52 APM Advanced Power Management support is enabled.
53 ARM ARM architecture is enabled.
54 AVR32 AVR32 architecture is enabled.
55 AX25 Appropriate AX.25 support is enabled.
56 BLACKFIN Blackfin architecture is enabled.
57 CLK Common clock infrastructure is enabled.
58 CMA Contiguous Memory Area support is enabled.
59 DRM Direct Rendering Management support is enabled.
60 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
61 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
62 EFI EFI Partitioning (GPT) is enabled
63 EIDE EIDE/ATAPI support is enabled.
64 EVM Extended Verification Module
65 FB The frame buffer device is enabled.
66 FTRACE Function tracing enabled.
67 GCOV GCOV profiling is enabled.
68 HW Appropriate hardware is enabled.
69 IA-64 IA-64 architecture is enabled.
70 IMA Integrity measurement architecture is enabled.
71 IOSCHED More than one I/O scheduler is enabled.
72 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
73 IPV6 IPv6 support is enabled.
74 ISAPNP ISA PnP code is enabled.
75 ISDN Appropriate ISDN support is enabled.
76 JOY Appropriate joystick support is enabled.
77 KGDB Kernel debugger support is enabled.
78 KVM Kernel Virtual Machine support is enabled.
79 LIBATA Libata driver is enabled
80 LP Printer support is enabled.
81 LOOP Loopback device support is enabled.
82 M68k M68k architecture is enabled.
83 These options have more detailed description inside of
84 Documentation/m68k/kernel-options.txt.
85 MDA MDA console support is enabled.
86 MIPS MIPS architecture is enabled.
87 MOUSE Appropriate mouse support is enabled.
88 MSI Message Signaled Interrupts (PCI).
89 MTD MTD (Memory Technology Device) support is enabled.
90 NET Appropriate network support is enabled.
91 NUMA NUMA support is enabled.
92 NFS Appropriate NFS support is enabled.
93 OSS OSS sound support is enabled.
94 PV_OPS A paravirtualized kernel is enabled.
95 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
96 PARISC The PA-RISC architecture is enabled.
97 PCI PCI bus support is enabled.
98 PCIE PCI Express support is enabled.
99 PCMCIA The PCMCIA subsystem is enabled.
100 PNP Plug & Play support is enabled.
101 PPC PowerPC architecture is enabled.
102 PPT Parallel port support is enabled.
103 PS2 Appropriate PS/2 support is enabled.
104 RAM RAM disk support is enabled.
105 S390 S390 architecture is enabled.
106 SCSI Appropriate SCSI support is enabled.
107 A lot of drivers have their options described inside
108 the Documentation/scsi/ sub-directory.
109 SECURITY Different security models are enabled.
110 SELINUX SELinux support is enabled.
111 APPARMOR AppArmor support is enabled.
112 SERIAL Serial support is enabled.
113 SH SuperH architecture is enabled.
114 SMP The kernel is an SMP kernel.
115 SPARC Sparc architecture is enabled.
116 SWSUSP Software suspend (hibernation) is enabled.
117 SUSPEND System suspend states are enabled.
118 TPM TPM drivers are enabled.
119 TS Appropriate touchscreen support is enabled.
120 UMS USB Mass Storage support is enabled.
121 USB USB support is enabled.
122 USBHID USB Human Interface Device support is enabled.
123 V4L Video For Linux support is enabled.
124 VMMIO Driver for memory mapped virtio devices is enabled.
125 VGA The VGA console has been enabled.
126 VT Virtual terminal support is enabled.
127 WDT Watchdog support is enabled.
128 XT IBM PC/XT MFM hard disk support is enabled.
129 X86-32 X86-32, aka i386 architecture is enabled.
130 X86-64 X86-64 architecture is enabled.
131 More X86-64 boot options can be found in
132 Documentation/x86/x86_64/boot-options.txt .
133 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
134 XEN Xen support is enabled
136 In addition, the following text indicates that the option:
138 BUGS= Relates to possible processor bugs on the said processor.
139 KNL Is a kernel start-up parameter.
140 BOOT Is a boot loader parameter.
142 Parameters denoted with BOOT are actually interpreted by the boot
143 loader, and have no meaning to the kernel directly.
144 Do not modify the syntax of boot loader parameters without extreme
145 need or coordination with <Documentation/x86/boot.txt>.
147 There are also arch-specific kernel-parameters not documented here.
148 See for example <Documentation/x86/x86_64/boot-options.txt>.
150 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
151 a trailing = on the name of any parameter states that that parameter will
152 be entered as an environment variable, whereas its absence indicates that
153 it will appear as a kernel argument readable via /proc/cmdline by programs
154 running once the system is up.
156 The number of kernel parameters is not limited, but the length of the
157 complete command line (parameters including spaces etc.) is limited to
158 a fixed number of characters. This limit depends on the architecture
159 and is between 256 and 4096 characters. It is defined in the file
160 ./include/asm/setup.h as COMMAND_LINE_SIZE.
162 Finally, the [KMG] suffix is commonly described after a number of kernel
163 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
164 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
165 bytes respectively. Such letter suffixes can also be entirely omitted.
168 acpi= [HW,ACPI,X86,ARM64]
169 Advanced Configuration and Power Interface
170 Format: { force | off | strict | noirq | rsdt }
171 force -- enable ACPI if default was off
172 off -- disable ACPI if default was on
173 noirq -- do not use ACPI for IRQ routing
174 strict -- Be less tolerant of platforms that are not
175 strictly ACPI specification compliant.
176 rsdt -- prefer RSDT over (default) XSDT
177 copy_dsdt -- copy DSDT to memory
178 For ARM64, ONLY "acpi=off" or "acpi=force" are available
180 See also Documentation/power/runtime_pm.txt, pci=noacpi
182 acpi_apic_instance= [ACPI, IOAPIC]
184 2: use 2nd APIC table, if available
185 1,0: use 1st APIC table
188 acpi_backlight= [HW,ACPI]
189 acpi_backlight=vendor
191 If set to vendor, prefer vendor specific driver
192 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
193 of the ACPI video.ko driver.
195 acpica_no_return_repair [HW, ACPI]
196 Disable AML predefined validation mechanism
197 This mechanism can repair the evaluation result to make
198 the return objects more ACPI specification compliant.
199 This option is useful for developers to identify the
200 root cause of an AML interpreter issue when the issue
201 has something to do with the repair mechanism.
203 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
204 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
206 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
207 debug output. Bits in debug_layer correspond to a
208 _COMPONENT in an ACPI source file, e.g.,
209 #define _COMPONENT ACPI_PCI_COMPONENT
210 Bits in debug_level correspond to a level in
211 ACPI_DEBUG_PRINT statements, e.g.,
212 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
213 The debug_level mask defaults to "info". See
214 Documentation/acpi/debug.txt for more information about
215 debug layers and levels.
217 Enable processor driver info messages:
218 acpi.debug_layer=0x20000000
219 Enable PCI/PCI interrupt routing info messages:
220 acpi.debug_layer=0x400000
221 Enable AML "Debug" output, i.e., stores to the Debug
222 object while interpreting AML:
223 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
224 Enable all messages related to ACPI hardware:
225 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
227 Some values produce so much output that the system is
228 unusable. The "log_buf_len" parameter may be useful
229 if you need to capture more output.
231 acpi_enforce_resources= [ACPI]
232 { strict | lax | no }
233 Check for resource conflicts between native drivers
234 and ACPI OperationRegions (SystemIO and SystemMemory
235 only). IO ports and memory declared in ACPI might be
236 used by the ACPI subsystem in arbitrary AML code and
237 can interfere with legacy drivers.
238 strict (default): access to resources claimed by ACPI
239 is denied; legacy drivers trying to access reserved
240 resources will fail to bind to device using them.
241 lax: access to resources claimed by ACPI is allowed;
242 legacy drivers trying to access reserved resources
243 will bind successfully but a warning message is logged.
244 no: ACPI OperationRegions are not marked as reserved,
245 no further checks are performed.
247 acpi_force_table_verification [HW,ACPI]
248 Enable table checksum verification during early stage.
249 By default, this is disabled due to x86 early mapping
252 acpi_irq_balance [HW,ACPI]
253 ACPI will balance active IRQs
256 acpi_irq_nobalance [HW,ACPI]
257 ACPI will not move active IRQs (default)
260 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
261 Format: <irq>,<irq>...
263 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
265 Format: <irq>,<irq>...
267 acpi_no_auto_serialize [HW,ACPI]
268 Disable auto-serialization of AML methods
269 AML control methods that contain the opcodes to create
270 named objects will be marked as "Serialized" by the
271 auto-serialization feature.
272 This feature is enabled by default.
273 This option allows to turn off the feature.
275 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
278 acpi_no_static_ssdt [HW,ACPI]
279 Disable installation of static SSDTs at early boot time
280 By default, SSDTs contained in the RSDT/XSDT will be
281 installed automatically and they will appear under
282 /sys/firmware/acpi/tables.
283 This option turns off this feature.
284 Note that specifying this option does not affect
285 dynamic table installation which will install SSDT
286 tables to /sys/firmware/acpi/tables/dynamic.
288 acpi_rsdp= [ACPI,EFI,KEXEC]
289 Pass the RSDP address to the kernel, mostly used
290 on machines running EFI runtime service to boot the
291 second kernel for kdump.
293 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
294 Format: To spoof as Windows 98: ="Microsoft Windows"
296 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
297 acpi_osi="string1" # add string1
298 acpi_osi="!string2" # remove string2
299 acpi_osi=!* # remove all strings
300 acpi_osi=! # disable all built-in OS vendor
302 acpi_osi= # disable all strings
304 'acpi_osi=!' can be used in combination with single or
305 multiple 'acpi_osi="string1"' to support specific OS
306 vendor string(s). Note that such command can only
307 affect the default state of the OS vendor strings, thus
308 it cannot affect the default state of the feature group
309 strings and the current state of the OS vendor strings,
310 specifying it multiple times through kernel command line
311 is meaningless. This command is useful when one do not
312 care about the state of the feature group strings which
313 should be controlled by the OSPM.
315 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
316 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
317 can make '_OSI("Windows 2000")' TRUE.
319 'acpi_osi=' cannot be used in combination with other
320 'acpi_osi=' command lines, the _OSI method will not
321 exist in the ACPI namespace. NOTE that such command can
322 only affect the _OSI support state, thus specifying it
323 multiple times through kernel command line is also
326 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
329 'acpi_osi=!*' can be used in combination with single or
330 multiple 'acpi_osi="string1"' to support specific
331 string(s). Note that such command can affect the
332 current state of both the OS vendor strings and the
333 feature group strings, thus specifying it multiple times
334 through kernel command line is meaningful. But it may
335 still not able to affect the final state of a string if
336 there are quirks related to this string. This command
337 is useful when one want to control the state of the
338 feature group strings to debug BIOS issues related to
341 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
342 '_OSI("Module Device")' FALSE.
343 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
344 '_OSI("Module Device")' TRUE.
345 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
347 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
349 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
350 they all will make '_OSI("Windows 2000")' TRUE.
353 Override the pmtimer bug detection: force the kernel
354 to assume that this machine's pmtimer latches its value
355 and always returns good values.
357 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
358 Format: { level | edge | high | low }
360 acpi_skip_timer_override [HW,ACPI]
361 Recognize and ignore IRQ0/pin2 Interrupt Override.
362 For broken nForce2 BIOS resulting in XT-PIC timer.
364 acpi_sleep= [HW,ACPI] Sleep options
365 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
366 old_ordering, nonvs, sci_force_enable }
367 See Documentation/power/video.txt for information on
369 s3_beep is for debugging; it makes the PC's speaker beep
370 as soon as the kernel's real-mode entry point is called.
371 s4_nohwsig prevents ACPI hardware signature from being
372 used during resume from hibernation.
373 old_ordering causes the ACPI 1.0 ordering of the _PTS
374 control method, with respect to putting devices into
375 low power states, to be enforced (the ACPI 2.0 ordering
376 of _PTS is used by default).
377 nonvs prevents the kernel from saving/restoring the
378 ACPI NVS memory during suspend/hibernation and resume.
379 sci_force_enable causes the kernel to set SCI_EN directly
380 on resume from S1/S3 (which is against the ACPI spec,
381 but some broken systems don't work without it).
383 acpi_use_timer_override [HW,ACPI]
384 Use timer override. For some broken Nvidia NF5 boards
385 that require a timer override, but don't have HPET
387 add_efi_memmap [EFI; X86] Include EFI memory map in
388 kernel's map of available physical RAM.
391 { off | try_unsupported }
392 off: disable AGP support
393 try_unsupported: try to drive unsupported chipsets
394 (may crash computer or cause data corruption)
397 See Documentation/sound/alsa/alsa-parameters.txt
400 Allow the default userspace alignment fault handler
401 behaviour to be specified. Bit 0 enables warnings,
402 bit 1 enables fixups, and bit 2 sends a segfault.
404 align_va_addr= [X86-64]
405 Align virtual addresses by clearing slice [14:12] when
406 allocating a VMA at process creation time. This option
407 gives you up to 3% performance improvement on AMD F15h
408 machines (where it is enabled by default) for a
409 CPU-intensive style benchmark, and it can vary highly in
410 a microbenchmark depending on workload and compiler.
412 32: only for 32-bit processes
413 64: only for 64-bit processes
414 on: enable for both 32- and 64-bit processes
415 off: disable for both 32- and 64-bit processes
417 alloc_snapshot [FTRACE]
418 Allocate the ftrace snapshot buffer on boot up when the
419 main buffer is allocated. This is handy if debugging
420 and you need to use tracing_snapshot() on boot up, and
421 do not want to use tracing_snapshot_alloc() as it needs
422 to be done where GFP_KERNEL allocations are allowed.
424 amd_iommu= [HW,X86-64]
425 Pass parameters to the AMD IOMMU driver in the system.
427 fullflush - enable flushing of IO/TLB entries when
428 they are unmapped. Otherwise they are
429 flushed before they will be reused, which
431 off - do not initialize any AMD IOMMU found in
433 force_isolation - Force device isolation for all
434 devices. The IOMMU driver is not
435 allowed anymore to lift isolation
436 requirements as needed. This option
437 does not override iommu=pt
439 amd_iommu_dump= [HW,X86-64]
440 Enable AMD IOMMU driver option to dump the ACPI table
441 for AMD IOMMU. With this option enabled, AMD IOMMU
442 driver will print ACPI tables for AMD IOMMU during
443 IOMMU initialization.
445 amijoy.map= [HW,JOY] Amiga joystick support
446 Map of devices attached to JOY0DAT and JOY1DAT
448 See also Documentation/input/joystick.txt
450 analog.map= [HW,JOY] Analog joystick and gamepad support
451 Specifies type or capabilities of an analog joystick
452 connected to one of 16 gameports
453 Format: <type1>,<type2>,..<type16>
456 Power management functions (SPARCstation-4/5 + deriv.)
458 Disable APC CPU standby support. SPARCstation-Fox does
459 not play well with APC CPU idle - disable it if you have
460 APC and your system crashes randomly.
462 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
463 Change the output verbosity whilst booting
464 Format: { quiet (default) | verbose | debug }
465 Change the amount of debugging information output
466 when initialising the APIC and IO-APIC components.
469 See Documentation/networking/ipv6.txt.
471 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
472 Limit apic dumping. The parameter defines the maximal
473 number of local apics being dumped. Also it is possible
474 to set it to "all" by meaning -- no limit here.
475 Format: { 1 (default) | 2 | ... | all }.
476 The parameter valid if only apic=debug or
477 apic=verbose is specified.
478 Example: apic=debug show_lapic=all
480 apm= [APM] Advanced Power Management
481 See header of arch/x86/kernel/apm_32.c.
483 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
484 Format: <io>,<irq>,<nodeID>
488 atarimouse= [HW,MOUSE] Atari Mouse
490 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
491 EzKey and similar keyboards
493 atkbd.reset= [HW] Reset keyboard during initialization
495 atkbd.set= [HW] Select keyboard code set
496 Format: <int> (2 = AT (default), 3 = PS/2)
498 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
501 atkbd.softraw= [HW] Choose between synthetic and real raw mode
502 Format: <bool> (0 = real, 1 = synthetic (default))
504 atkbd.softrepeat= [HW]
505 Use software keyboard repeat
507 audit= [KNL] Enable the audit sub-system
508 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
509 0 - kernel audit is disabled and can not be enabled
510 until the next reboot
511 unset - kernel audit is initialized but disabled and
512 will be fully enabled by the userspace auditd.
513 1 - kernel audit is initialized and partially enabled,
514 storing at most audit_backlog_limit messages in
515 RAM until it is fully enabled by the userspace
519 audit_backlog_limit= [KNL] Set the audit queue size limit.
520 Format: <int> (must be >=0)
523 baycom_epp= [HW,AX25]
526 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
528 See header of drivers/net/hamradio/baycom_par.c.
530 baycom_ser_fdx= [HW,AX25]
531 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
532 Format: <io>,<irq>,<mode>[,<baud>]
533 See header of drivers/net/hamradio/baycom_ser_fdx.c.
535 baycom_ser_hdx= [HW,AX25]
536 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
537 Format: <io>,<irq>,<mode>
538 See header of drivers/net/hamradio/baycom_ser_hdx.c.
540 blkdevparts= Manual partition parsing of block device(s) for
541 embedded devices based on command line input.
542 See Documentation/block/cmdline-partition.txt
544 boot_delay= Milliseconds to delay each printk during boot.
545 Values larger than 10 seconds (10000) are changed to
549 bootmem_debug [KNL] Enable bootmem allocator debug messages.
551 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
552 bttv.radio= Most important insmod options are available as
554 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
557 bulk_remove=off [PPC] This parameter disables the use of the pSeries
558 firmware feature for flushing multiple hpte entries
561 c101= [NET] Moxa C101 synchronous serial card
563 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
564 Sometimes CPU hardware bugs make them report the cache
565 size incorrectly. The kernel will attempt work arounds
566 to fix known problems, but for some CPUs it is not
567 possible to determine what the correct size should be.
568 This option provides an override for these situations.
570 ca_keys= [KEYS] This parameter identifies a specific key(s) on
571 the system trusted keyring to be used for certificate
573 format: { id:<keyid> | builtin }
575 cca= [MIPS] Override the kernel pages' cache coherency
576 algorithm. Accepted values range from 0 to 7
577 inclusive. See arch/mips/include/asm/pgtable-bits.h
578 for platform specific values (SB1, Loongson3 and
581 ccw_timeout_log [S390]
582 See Documentation/s390/CommonIO for details.
584 cgroup_disable= [KNL] Disable a particular controller
585 Format: {name of the controller(s) to disable}
586 The effects of cgroup_disable=foo are:
587 - foo isn't auto-mounted if you mount all cgroups in
589 - foo isn't visible as an individually mountable
591 {Currently only "memory" controller deal with this and
592 cut the overhead, others just disable the usage. So
593 only cgroup_disable=memory is actually worthy}
595 checkreqprot [SELINUX] Set initial checkreqprot flag value.
596 Format: { "0" | "1" }
597 See security/selinux/Kconfig help text.
598 0 -- check protection applied by kernel (includes
599 any implied execute protection).
600 1 -- check protection requested by application.
601 Default value is set via a kernel config option.
602 Value can be changed at runtime via
603 /selinux/checkreqprot.
606 See Documentation/s390/CommonIO for details.
609 Prevents the clock framework from automatically gating
610 clocks that have not been explicitly enabled by a Linux
611 device driver but are enabled in hardware at reset or
612 by the bootloader/firmware. Note that this does not
613 force such clocks to be always-on nor does it reserve
614 those clocks in any way. This parameter is useful for
615 debug and development, but should not be needed on a
616 platform with proper driver support. For more
617 information, see Documentation/clk.txt.
619 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
621 Forces specified clocksource (if available) to be used
622 when calculating gettimeofday(). If specified
623 clocksource is not available, it defaults to PIT.
624 Format: { pit | tsc | cyclone | pmtmr }
626 clocksource= Override the default clocksource
628 Override the default clocksource and use the clocksource
629 with the name specified.
630 Some clocksource names to choose from, depending on
632 [all] jiffies (this is the base, fallback clocksource)
634 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
635 pxa_timer,timer3,32k_counter,timer0_1
637 [X86-32] pit,hpet,tsc;
638 scx200_hrt on Geode; cyclone on IBM x440
646 clearcpuid=BITNUM [X86]
647 Disable CPUID feature X for the kernel. See
648 arch/x86/include/asm/cpufeature.h for the valid bit
649 numbers. Note the Linux specific bits are not necessarily
650 stable over kernel options, but the vendor specific
652 Also note that user programs calling CPUID directly
653 or using the feature without checking anything
654 will still see it. This just prevents it from
655 being used by the kernel or shown in /proc/cpuinfo.
656 Also note the kernel might malfunction if you disable
659 cma=nn[MG]@[start[MG][-end[MG]]]
661 Sets the size of kernel global memory area for
662 contiguous memory allocations and optionally the
663 placement constraint by the physical address range of
664 memory allocations. A value of 0 disables CMA
665 altogether. For more information, see
666 include/linux/dma-contiguous.h
668 cmo_free_hint= [PPC] Format: { yes | no }
669 Specify whether pages are marked as being inactive
670 when they are freed. This is used in CMO environments
671 to determine OS memory pressure for page stealing by
675 coherent_pool=nn[KMG] [ARM,KNL]
676 Sets the size of memory pool for coherent, atomic dma
677 allocations, by default set to 256K.
679 code_bytes [X86] How many bytes of object code to print
684 com20020= [HW,NET] ARCnet - COM20020 chipset
686 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
688 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
692 ARCnet - COM90xx chipset (memory-mapped buffers)
693 Format: <io>[,<irq>[,<memstart>]]
695 condev= [HW,S390] console device
698 console= [KNL] Output console device and options.
700 tty<n> Use the virtual console device <n>.
704 Use the specified serial port. The options are of
705 the form "bbbbpnf", where "bbbb" is the baud rate,
706 "p" is parity ("n", "o", or "e"), "n" is number of
707 bits, and "f" is flow control ("r" for RTS or
708 omit it). Default is "9600n8".
710 See Documentation/serial-console.txt for more
712 Documentation/networking/netconsole.txt for an
715 uart[8250],io,<addr>[,options]
716 uart[8250],mmio,<addr>[,options]
717 uart[8250],mmio32,<addr>[,options]
718 uart[8250],0x<addr>[,options]
719 Start an early, polled-mode console on the 8250/16550
720 UART at the specified I/O port or MMIO address,
721 switching to the matching ttyS device later.
722 MMIO inter-register address stride is either 8-bit
723 (mmio) or 32-bit (mmio32).
724 If none of [io|mmio|mmio32], <addr> is assumed to be
725 equivalent to 'mmio'. 'options' are specified in the
726 same format described for ttyS above; if unspecified,
727 the h/w is not re-initialized.
729 hvc<n> Use the hypervisor console device <n>. This is for
730 both Xen and PowerPC hypervisors.
732 If the device connected to the port is not a TTY but a braille
733 device, prepend "brl," before the device type, for instance
735 For now, only VisioBraille is supported.
737 consoleblank= [KNL] The console blank (screen saver) timeout in
738 seconds. Defaults to 10*60 = 10mins. A value of 0
739 disables the blank timer.
742 [KNL] Change the default value for
743 /proc/<pid>/coredump_filter.
744 See also Documentation/filesystems/proc.txt.
746 cpuidle.off=1 [CPU_IDLE]
747 disable the cpuidle sub-system
750 [X86] Delay for N microsec between assert and de-assert
751 of APIC INIT to start processors. This delay occurs
752 on every CPU online, such as boot, and resume from suspend.
755 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
757 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
759 crashkernel=size[KMG][@offset[KMG]]
760 [KNL] Using kexec, Linux can switch to a 'crash kernel'
761 upon panic. This parameter reserves the physical
762 memory region [offset, offset + size] for that kernel
763 image. If '@offset' is omitted, then a suitable offset
764 is selected automatically. Check
765 Documentation/kdump/kdump.txt for further details.
767 crashkernel=range1:size1[,range2:size2,...][@offset]
768 [KNL] Same as above, but depends on the memory
769 in the running system. The syntax of range is
770 start-[end] where start and end are both
771 a memory unit (amount[KMG]). See also
772 Documentation/kdump/kdump.txt for an example.
774 crashkernel=size[KMG],high
775 [KNL, x86_64] range could be above 4G. Allow kernel
776 to allocate physical memory region from top, so could
777 be above 4G if system have more than 4G ram installed.
778 Otherwise memory region will be allocated below 4G, if
780 It will be ignored if crashkernel=X is specified.
781 crashkernel=size[KMG],low
782 [KNL, x86_64] range under 4G. When crashkernel=X,high
783 is passed, kernel could allocate physical memory region
784 above 4G, that cause second kernel crash on system
785 that require some amount of low memory, e.g. swiotlb
786 requires at least 64M+32K low memory. Kernel would
787 try to allocate 72M below 4G automatically.
788 This one let user to specify own low range under 4G
789 for second kernel instead.
790 0: to disable low allocation.
791 It will be ignored when crashkernel=X,high is not used
792 or memory reserved is below 4G.
797 cs89x0_media= [HW,NET]
798 Format: { rj45 | aui | bnc }
801 See header of drivers/s390/block/dasd_devmap.c.
803 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
804 (one device per port)
805 Format: <port#>,<type>
806 See also Documentation/input/joystick-parport.txt
808 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
809 time. See Documentation/dynamic-debug-howto.txt for
810 details. Deprecated, see dyndbg.
812 debug [KNL] Enable kernel debugging (events log level).
815 [KNL] verbose self-tests
817 Print debugging info while doing the locking API
819 We default to 0 (no extra messages), setting it to
820 1 will print _a lot_ more information - normally
821 only useful to kernel developers.
823 debug_objects [KNL] Enable object debugging
826 [KNL] Disable object debugging
828 debug_guardpage_minorder=
829 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
830 parameter allows control of the order of pages that will
831 be intentionally kept free (and hence protected) by the
832 buddy allocator. Bigger value increase the probability
833 of catching random memory corruption, but reduce the
834 amount of memory for normal system use. The maximum
835 possible value is MAX_ORDER/2. Setting this parameter
836 to 1 or 2 should be enough to identify most random
837 memory corruption problems caused by bugs in kernel or
838 driver code when a CPU writes to (or reads from) a
839 random memory location. Note that there exists a class
840 of memory corruptions problems caused by buggy H/W or
841 F/W or by drivers badly programing DMA (basically when
842 memory is written at bus level and the CPU MMU is
843 bypassed) which are not detectable by
844 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
845 tracking down these problems.
848 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
849 parameter enables the feature at boot time. In
850 default, it is disabled. We can avoid allocating huge
851 chunk of memory for debug pagealloc if we don't enable
852 it at boot time and the system will work mostly same
853 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
854 on: enable the feature
856 debugpat [X86] Enable PAT debugging
858 decnet.addr= [HW,NET]
859 Format: <area>[,<node>]
860 See also Documentation/networking/decnet.txt.
863 [same as hugepagesz=] The size of the default
864 HugeTLB page size. This is the size represented by
865 the legacy /proc/ hugepages APIs, used for SHM, and
866 default size when mounting hugetlbfs filesystems.
867 Defaults to the default architecture's huge page size
871 Set number of hash buckets for dentry cache.
874 See Documentation/networking/ipv6.txt.
876 disable_cpu_apicid= [X86,APIC,SMP]
878 The number of initial APIC ID for the
879 corresponding CPU to be disabled at boot,
880 mostly used for the kdump 2nd kernel to
881 disable BSP to wake up multiple CPUs without
882 causing system reset or hang due to sending
885 disable_ddw [PPC/PSERIES]
886 Disable Dynamic DMA Window support. Use this if
887 to workaround buggy firmware.
890 See Documentation/networking/ipv6.txt.
892 disable_mtrr_cleanup [X86]
893 The kernel tries to adjust MTRR layout from continuous
894 to discrete, to make X server driver able to add WB
895 entry later. This parameter disables that.
897 disable_mtrr_trim [X86, Intel and AMD only]
898 By default the kernel will trim any uncacheable
899 memory out of your available memory pool based on
900 MTRR settings. This parameter disables that behavior,
901 possibly causing your machine to run very slowly.
903 disable_timer_pin_1 [X86]
904 Disable PIN 1 of APIC timer
905 Can be useful to work around chipset bugs.
907 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
908 this option disables the debugging code at boot.
910 dma_debug_entries=<number>
911 This option allows to tune the number of preallocated
912 entries for DMA-API debugging code. One entry is
913 required per DMA-API allocation. Use this if the
914 DMA-API debugging code disables itself because the
915 architectural default is too low.
917 dma_debug_driver=<driver_name>
918 With this option the DMA-API debugging driver
919 filter feature can be enabled at boot time. Just
920 pass the driver to filter for as the parameter.
921 The filter can be disabled or changed to another
922 driver later using sysfs.
924 drm_kms_helper.edid_firmware=[<connector>:]<file>
925 Broken monitors, graphic adapters and KVMs may
926 send no or incorrect EDID data sets. This parameter
927 allows to specify an EDID data set in the
928 /lib/firmware directory that is used instead.
929 Generic built-in EDID data sets are used, if one of
930 edid/1024x768.bin, edid/1280x1024.bin,
931 edid/1680x1050.bin, or edid/1920x1080.bin is given
932 and no file with the same name exists. Details and
933 instructions how to build your own EDID data are
934 available in Documentation/EDID/HOWTO.txt. An EDID
935 data set will only be used for a particular connector,
936 if its name and a colon are prepended to the EDID
941 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
942 module.dyndbg[="val"]
943 Enable debug messages at boot time. See
944 Documentation/dynamic-debug-howto.txt for details.
946 nompx [X86] Disables Intel Memory Protection Extensions.
947 See Documentation/x86/intel_mpx.txt for more
948 information about the feature.
951 on enable eager fpu restore
952 off disable eager fpu restore
953 auto selects the default scheme, which automatically
954 enables eagerfpu restore for xsaveopt.
956 module.async_probe [KNL]
957 Enable asynchronous probe on this module.
959 early_ioremap_debug [KNL]
960 Enable debug messages in early_ioremap support. This
961 is useful for tracking down temporary early mappings
962 which are not unmapped.
964 earlycon= [KNL] Output early console device and options.
967 Start an early, polled-mode console on a cadence serial
968 port at the specified address. The cadence serial port
969 must already be setup and configured. Options are not
972 uart[8250],io,<addr>[,options]
973 uart[8250],mmio,<addr>[,options]
974 uart[8250],mmio32,<addr>[,options]
975 uart[8250],mmio32be,<addr>[,options]
976 uart[8250],0x<addr>[,options]
977 Start an early, polled-mode console on the 8250/16550
978 UART at the specified I/O port or MMIO address.
979 MMIO inter-register address stride is either 8-bit
980 (mmio) or 32-bit (mmio32 or mmio32be).
981 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
982 to be equivalent to 'mmio'. 'options' are specified
983 in the same format described for "console=ttyS<n>"; if
984 unspecified, the h/w is not initialized.
987 Start an early, polled-mode console on a pl011 serial
988 port at the specified address. The pl011 serial port
989 must already be setup and configured. Options are not
993 Start an early, polled-mode console on an msm serial
994 port at the specified address. The serial port
995 must already be setup and configured. Options are not
999 Start an early, polled-mode console on an msm serial
1000 dm port at the specified address. The serial port
1001 must already be setup and configured. Options are not
1004 smh Use ARM semihosting calls for early console.
1012 Use early console provided by serial driver available
1013 on Samsung SoCs, requires selecting proper type and
1014 a correct base address of the selected UART port. The
1015 serial port must already be setup and configured.
1016 Options are not yet supported.
1018 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1022 earlyprintk=serial[,ttySn[,baudrate]]
1023 earlyprintk=serial[,0x...[,baudrate]]
1024 earlyprintk=ttySn[,baudrate]
1025 earlyprintk=dbgp[debugController#]
1026 earlyprintk=pciserial,bus:device.function[,baudrate]
1028 earlyprintk is useful when the kernel crashes before
1029 the normal console is initialized. It is not enabled by
1030 default because it has some cosmetic problems.
1032 Append ",keep" to not disable it when the real console
1035 Only one of vga, efi, serial, or usb debug port can
1038 Currently only ttyS0 and ttyS1 may be specified by
1039 name. Other I/O ports may be explicitly specified
1040 on some architectures (x86 and arm at least) by
1041 replacing ttySn with an I/O port address, like this:
1042 earlyprintk=serial,0x1008,115200
1043 You can find the port for a given device in
1044 /proc/tty/driver/serial:
1045 2: uart:ST16650V2 port:00001008 irq:18 ...
1047 Interaction with the standard serial driver is not
1050 The VGA and EFI output is eventually overwritten by
1053 The xen output can only be used by Xen PV guests.
1055 edac_report= [HW,EDAC] Control how to report EDAC event
1056 Format: {"on" | "off" | "force"}
1057 on: enable EDAC to report H/W event. May be overridden
1058 by other higher priority error reporting module.
1059 off: disable H/W event reporting through EDAC.
1060 force: enforce the use of EDAC to report H/W event.
1063 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1066 This is designed to be used in conjunction with
1067 the boot argument: earlyprintk=vga
1070 Format: {"off" | "on" | "skip[mbr]"}
1073 Format: { "old_map", "nochunk", "noruntime", "debug" }
1074 old_map [X86-64]: switch to the old ioremap-based EFI
1075 runtime services mapping. 32-bit still uses this one by
1077 nochunk: disable reading files in "chunks" in the EFI
1078 boot stub, as chunking can cause problems with some
1079 firmware implementations.
1080 noruntime : disable EFI runtime services support
1081 debug: enable misc debug output
1083 efi_no_storage_paranoia [EFI; X86]
1084 Using this parameter you can use more than 50% of
1085 your efi variable storage. Use this parameter only if
1086 you are really sure that your UEFI does sane gc and
1087 fulfills the spec otherwise your board may brick.
1089 eisa_irq_edge= [PARISC,HW]
1090 See header of drivers/parisc/eisa.c.
1093 See comment before function elanfreq_setup() in
1094 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1097 Format: {"cfq" | "deadline" | "noop"}
1098 See Documentation/block/cfq-iosched.txt and
1099 Documentation/block/deadline-iosched.txt for details.
1101 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1102 Specifies physical address of start of kernel core
1103 image elf header and optionally the size. Generally
1104 kexec loader will pass this option to capture kernel.
1105 See Documentation/kdump/kdump.txt for details.
1107 enable_mtrr_cleanup [X86]
1108 The kernel tries to adjust MTRR layout from continuous
1109 to discrete, to make X server driver able to add WB
1110 entry later. This parameter enables that.
1112 enable_timer_pin_1 [X86]
1113 Enable PIN 1 of APIC timer
1114 Can be useful to work around chipset bugs
1115 (in particular on some ATI chipsets).
1116 The kernel tries to set a reasonable default.
1118 enforcing [SELINUX] Set initial enforcing status.
1120 See security/selinux/Kconfig help text.
1121 0 -- permissive (log only, no denials).
1122 1 -- enforcing (deny and log).
1124 Value can be changed at runtime via /selinux/enforce.
1127 Disable Error Record Serialization Table (ERST)
1130 ether= [HW,NET] Ethernet cards parameters
1131 This option is obsoleted by the "netdev=" option, which
1132 has equivalent usage. See its documentation for details.
1136 Permit 'security.evm' to be updated regardless of
1137 current integrity status.
1141 fail_make_request=[KNL]
1142 General fault injection mechanism.
1143 Format: <interval>,<probability>,<space>,<times>
1144 See also Documentation/fault-injection/.
1147 See Documentation/blockdev/floppy.txt.
1149 force_pal_cache_flush
1150 [IA-64] Avoid check_sal_cache_flush which may hang on
1151 buggy SAL_CACHE_FLUSH implementations. Using this
1152 parameter will force ia64_sal_cache_flush to call
1153 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1156 Forcefully enable Physical Address Extension (PAE).
1157 Many Pentium M systems disable PAE but may have a
1158 functionally usable PAE implementation.
1159 Warning: use of this parameter will taint the kernel
1160 and may cause unknown problems.
1163 [FTRACE] will set and start the specified tracer
1164 as early as possible in order to facilitate early
1167 ftrace_dump_on_oops[=orig_cpu]
1168 [FTRACE] will dump the trace buffers on oops.
1169 If no parameter is passed, ftrace will dump
1170 buffers of all CPUs, but if you pass orig_cpu, it will
1171 dump only the buffer of the CPU that triggered the
1174 ftrace_filter=[function-list]
1175 [FTRACE] Limit the functions traced by the function
1176 tracer at boot up. function-list is a comma separated
1177 list of functions. This list can be changed at run
1178 time by the set_ftrace_filter file in the debugfs
1181 ftrace_notrace=[function-list]
1182 [FTRACE] Do not trace the functions specified in
1183 function-list. This list can be changed at run time
1184 by the set_ftrace_notrace file in the debugfs
1187 ftrace_graph_filter=[function-list]
1188 [FTRACE] Limit the top level callers functions traced
1189 by the function graph tracer at boot up.
1190 function-list is a comma separated list of functions
1191 that can be changed at run time by the
1192 set_graph_function file in the debugfs tracing directory.
1194 ftrace_graph_notrace=[function-list]
1195 [FTRACE] Do not trace from the functions specified in
1196 function-list. This list is a comma separated list of
1197 functions that can be changed at run time by the
1198 set_graph_notrace file in the debugfs tracing directory.
1201 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1202 support via parallel port (up to 5 devices per port)
1203 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1204 See also Documentation/input/joystick-parport.txt
1208 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1212 gcov_persist= [GCOV] When non-zero (default), profiling data for
1213 kernel modules is saved and remains accessible via
1214 debugfs, even when the module is unloaded/reloaded.
1215 When zero, profiling data is discarded and associated
1216 debugfs files are removed at module unload time.
1218 gpt [EFI] Forces disk with valid GPT signature but
1219 invalid Protective MBR to be treated as GPT. If the
1220 primary GPT is corrupted, it enables the backup/alternate
1221 GPT to be used instead.
1223 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1224 the "Enable 0" bit of the configuration register.
1227 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1228 the "Enable 0" bit of the configuration register.
1231 grcan.select= [HW] Select which physical interface to use.
1234 grcan.txsize= [HW] Sets the size of the tx buffer.
1235 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1237 grcan.rxsize= [HW] Sets the size of the rx buffer.
1238 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1241 hashdist= [KNL,NUMA] Large hashes allocated during boot
1242 are distributed across NUMA nodes. Defaults on
1243 for 64-bit NUMA, off otherwise.
1244 Format: 0 | 1 (for off | on)
1246 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1248 hd= [EIDE] (E)IDE hard drive subsystem geometry
1249 Format: <cyl>,<head>,<sect>
1252 Disable Hardware Error Source Table (HEST) support;
1253 corresponding firmware-first mode error processing
1254 logic will be disabled.
1256 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1257 size of <nn>. This works even on boxes that have no
1258 highmem otherwise. This also works to reduce highmem
1259 size on bigger boxes.
1261 highres= [KNL] Enable/disable high resolution timer mode.
1262 Valid parameters: "on", "off"
1266 See Documentation/isdn/README.HiSax.
1270 hpet= [X86-32,HPET] option to control HPET usage
1271 Format: { enable (default) | disable | force |
1273 disable: disable HPET and use PIT instead
1274 force: allow force enabled of undocumented chips (ICH4,
1276 verbose: show contents of HPET registers during setup
1278 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1279 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1281 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1282 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1283 On x86-64 and powerpc, this option can be specified
1284 multiple times interleaved with hugepages= to reserve
1285 huge pages of different sizes. Valid pages sizes on
1286 x86-64 are 2M (when the CPU supports "pse") and 1G
1287 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1289 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1290 terminal devices. Valid values: 0..8
1291 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1292 If specified, z/VM IUCV HVC accepts connections
1293 from listed z/VM user IDs only.
1295 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1296 hardware thread id mappings.
1297 Format: <cpu>:<hwthread>
1300 Do not unregister boot console at start. This is only
1301 useful for debugging when something happens in the window
1302 between unregistering the boot console and initializing
1305 i2c_bus= [HW] Override the default board specific I2C bus speed
1306 or register an additional I2C bus that is not
1307 registered from board initialization code.
1311 i8042.debug [HW] Toggle i8042 debug mode
1312 i8042.direct [HW] Put keyboard port into non-translated mode
1313 i8042.dumbkbd [HW] Pretend that controller can only read data from
1314 keyboard and cannot control its state
1315 (Don't attempt to blink the leds)
1316 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1317 i8042.nokbd [HW] Don't check/create keyboard port
1318 i8042.noloop [HW] Disable the AUX Loopback command while probing
1320 i8042.nomux [HW] Don't check presence of an active multiplexing
1322 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1324 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1325 i8042.reset [HW] Reset the controller during init and cleanup
1326 i8042.unlock [HW] Unlock (ignore) the keylock
1327 i8042.kbdreset [HW] Reset device connected to KBD port
1331 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1332 indicates that the driver is running on unsupported
1334 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1335 does not match list of supported models.
1337 [HW] Report power status in /proc/i8k
1338 (disabled by default)
1339 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1342 i915.invert_brightness=
1343 [DRM] Invert the sense of the variable that is used to
1344 set the brightness of the panel backlight. Normally a
1345 brightness value of 0 indicates backlight switched off,
1346 and the maximum of the brightness value sets the backlight
1347 to maximum brightness. If this parameter is set to 0
1348 (default) and the machine requires it, or this parameter
1349 is set to 1, a brightness value of 0 sets the backlight
1350 to maximum brightness, and the maximum of the brightness
1351 value switches the backlight off.
1352 -1 -- never invert brightness
1353 0 -- machine default
1354 1 -- force brightness inversion
1357 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1359 ide-core.nodma= [HW] (E)IDE subsystem
1360 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1361 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1362 .cdrom .chs .ignore_cable are additional options
1363 See Documentation/ide/ide.txt.
1365 ide-generic.probe-mask= [HW] (E)IDE subsystem
1367 Probe mask for legacy ISA IDE ports. Depending on
1368 platform up to 6 ports are supported, enabled by
1369 setting corresponding bits in the mask to 1. The
1370 default value is 0x0, which has a special meaning.
1371 On systems that have PCI, it triggers scanning the
1372 PCI bus for the first and the second port, which
1373 are then probed. On systems without PCI the value
1374 of 0x0 enables probing the two first ports as if it
1377 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1378 Claim all unknown PCI IDE storage controllers.
1381 Format: idle=poll, idle=halt, idle=nomwait
1382 Poll forces a polling idle loop that can slightly
1383 improve the performance of waking up a idle CPU, but
1384 will use a lot of power and make the system run hot.
1386 idle=halt: Halt is forced to be used for CPU idle.
1387 In such case C2/C3 won't be used again.
1388 idle=nomwait: Disable mwait for CPU C-states
1390 ignore_loglevel [KNL]
1391 Ignore loglevel setting - this will print /all/
1392 kernel messages to the console. Useful for debugging.
1393 We also add it as printk module parameter, so users
1394 could change it dynamically, usually by
1395 /sys/module/printk/parameters/ignore_loglevel.
1397 ihash_entries= [KNL]
1398 Set number of hash buckets for inode cache.
1400 ima_appraise= [IMA] appraise integrity measurements
1401 Format: { "off" | "enforce" | "fix" | "log" }
1404 ima_appraise_tcb [IMA]
1405 The builtin appraise policy appraises all files
1409 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1413 The list of supported hash algorithms is defined
1414 in crypto/hash_info.h.
1417 The builtin measurement policy to load during IMA
1418 setup. Specyfing "tcb" as the value, measures all
1419 programs exec'd, files mmap'd for exec, and all files
1420 opened with the read mode bit set by either the
1421 effective uid (euid=0) or uid=0.
1424 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1425 Load a policy which meets the needs of the Trusted
1426 Computing Base. This means IMA will measure all
1427 programs exec'd, files mmap'd for exec, and all files
1428 opened for read by uid=0.
1431 Select one of defined IMA measurements template formats.
1432 Formats: { "ima" | "ima-ng" | "ima-sig" }
1436 [IMA] Define a custom template format.
1437 Format: { "field1|...|fieldN" }
1439 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1440 Format: <min_file_size>
1441 Set the minimal file size for using asynchronous hash.
1442 If left unspecified, ahash usage is disabled.
1444 ahash performance varies for different data sizes on
1445 different crypto accelerators. This option can be used
1446 to achieve the best performance for a particular HW.
1448 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1450 Set hashing buffer size. Default: 4k.
1452 ahash performance varies for different chunk sizes on
1453 different crypto accelerators. This option can be used
1454 to achieve best performance for particular HW.
1458 Run specified binary instead of /sbin/init as init
1461 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1462 for working out where the kernel is dying during
1465 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1466 initcall functions. Useful for debugging built-in
1467 modules and initcalls.
1469 initrd= [BOOT] Specify the location of the initial ramdisk
1471 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1474 int_pln_enable [x86] Enable power limit notification interrupt
1476 integrity_audit=[IMA]
1477 Format: { "0" | "1" }
1478 0 -- basic integrity auditing messages. (Default)
1479 1 -- additional integrity auditing messages.
1481 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1483 Enable intel iommu driver.
1485 Disable intel iommu driver.
1486 igfx_off [Default Off]
1487 By default, gfx is mapped as normal device. If a gfx
1488 device has a dedicated DMAR unit, the DMAR unit is
1489 bypassed by not enabling DMAR with this option. In
1490 this case, gfx device will use physical address for
1493 With this option iommu will not optimize to look
1494 for io virtual address below 32-bit forcing dual
1495 address cycle on pci bus for cards supporting greater
1496 than 32-bit addressing. The default is to look
1497 for translation below 32-bit and if not available
1498 then look in the higher range.
1499 strict [Default Off]
1500 With this option on every unmap_single operation will
1501 result in a hardware IOTLB flush operation as opposed
1502 to batching them for performance.
1503 sp_off [Default Off]
1504 By default, super page will be supported if Intel IOMMU
1505 has the capability. With this option, super page will
1507 ecs_off [Default Off]
1508 By default, extended context tables will be supported if
1509 the hardware advertises that it has support both for the
1510 extended tables themselves, and also PASID support. With
1511 this option set, extended tables will not be used even
1512 on hardware which claims to support them.
1514 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1515 0 disables intel_idle and fall back on acpi_idle.
1516 1 to 6 specify maximum depth of C-state.
1520 Do not enable intel_pstate as the default
1521 scaling driver for the supported processors
1523 Enable intel_pstate on systems that prohibit it by default
1524 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1525 instead of acpi-cpufreq may disable platform features, such
1526 as thermal controls and power capping, that rely on ACPI
1527 P-States information being indicated to OSPM and therefore
1528 should be used with caution. This option does not work with
1529 processors that aren't supported by the intel_pstate driver
1530 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1532 Do not enable hardware P state control (HWP)
1535 Only load intel_pstate on systems which support
1536 hardware P state control (HWP) if available.
1538 intremap= [X86-64, Intel-IOMMU]
1539 on enable Interrupt Remapping (default)
1540 off disable Interrupt Remapping
1541 nosid disable Source ID checking
1543 BIOS x2APIC opt-out request will be ignored
1545 iomem= Disable strict checking of access to MMIO memory
1546 strict regions from userspace.
1561 nobypass [PPC/POWERNV]
1562 Disable IOMMU bypass, using IOMMU for PCI devices.
1565 io7= [HW] IO7 for Marvel based alpha systems
1566 See comment before marvel_specify_io7 in
1567 arch/alpha/kernel/core_marvel.c.
1569 io_delay= [X86] I/O delay method
1571 Standard port 0x80 based delay
1573 Alternate port 0xed based delay (needed on some systems)
1575 Simple two microseconds delay
1580 See Documentation/filesystems/nfs/nfsroot.txt.
1583 When an interrupt is not handled search all handlers
1584 for it. Intended to get systems with badly broken
1588 When an interrupt is not handled search all handlers
1589 for it. Also check all handlers each timer
1590 interrupt. Intended to get systems with badly broken
1594 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1596 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1598 <cpu number>,...,<cpu number>
1600 <cpu number>-<cpu number>
1601 (must be a positive range in ascending order)
1603 <cpu number>,...,<cpu number>-<cpu number>
1605 This option can be used to specify one or more CPUs
1606 to isolate from the general SMP balancing and scheduling
1607 algorithms. You can move a process onto or off an
1608 "isolated" CPU via the CPU affinity syscalls or cpuset.
1609 <cpu number> begins at 0 and the maximum value is
1610 "number of CPUs in system - 1".
1612 This option is the preferred way to isolate CPUs. The
1613 alternative -- manually setting the CPU mask of all
1614 tasks in the system -- can cause problems and
1615 suboptimal load balancer performance.
1619 ivrs_ioapic [HW,X86_64]
1620 Provide an override to the IOAPIC-ID<->DEVICE-ID
1621 mapping provided in the IVRS ACPI table. For
1622 example, to map IOAPIC-ID decimal 10 to
1623 PCI device 00:14.0 write the parameter as:
1624 ivrs_ioapic[10]=00:14.0
1626 ivrs_hpet [HW,X86_64]
1627 Provide an override to the HPET-ID<->DEVICE-ID
1628 mapping provided in the IVRS ACPI table. For
1629 example, to map HPET-ID decimal 0 to
1630 PCI device 00:14.0 write the parameter as:
1631 ivrs_hpet[0]=00:14.0
1633 js= [HW,JOY] Analog joystick
1634 See Documentation/input/joystick.txt.
1637 Enable/disable kernel and module base offset ASLR
1638 (Address Space Layout Randomization) if built into
1639 the kernel. When CONFIG_HIBERNATION is selected,
1640 kASLR is disabled by default. When kASLR is enabled,
1641 hibernation will be disabled.
1645 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1646 specifies the amount of memory usable by the kernel
1647 for non-movable allocations. The requested amount is
1648 spread evenly throughout all nodes in the system. The
1649 remaining memory in each node is used for Movable
1650 pages. In the event, a node is too small to have both
1651 kernelcore and Movable pages, kernelcore pages will
1652 take priority and other nodes will have a larger number
1653 of Movable pages. The Movable zone is used for the
1654 allocation of pages that may be reclaimed or moved
1655 by the page migration subsystem. This means that
1656 HugeTLB pages may not be allocated from this zone.
1657 Note that allocations like PTEs-from-HighMem still
1658 use the HighMem zone if it exists, and the Normal
1659 zone if it does not.
1661 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1662 Format: <Controller#>[,poll interval]
1663 The controller # is the number of the ehci usb debug
1664 port as it is probed via PCI. The poll interval is
1665 optional and is the number seconds in between
1666 each poll cycle to the debug port in case you need
1667 the functionality for interrupting the kernel with
1668 gdb or control-c on the dbgp connection. When
1669 not using this parameter you use sysrq-g to break into
1670 the kernel debugger.
1672 kgdboc= [KGDB,HW] kgdb over consoles.
1673 Requires a tty driver that supports console polling,
1674 or a supported polling keyboard driver (non-usb).
1675 Serial only format: <serial_device>[,baud]
1676 keyboard only format: kbd
1677 keyboard and serial format: kbd,<serial_device>[,baud]
1678 Optional Kernel mode setting:
1679 kms, kbd format: kms,kbd
1680 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1682 kgdbwait [KGDB] Stop kernel execution and enter the
1683 kernel debugger at the earliest opportunity.
1685 kmac= [MIPS] korina ethernet MAC address.
1686 Configure the RouterBoard 532 series on-chip
1687 Ethernet adapter MAC address.
1689 kmemleak= [KNL] Boot-time kmemleak enable/disable
1690 Valid arguments: on, off
1692 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1695 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1696 Valid arguments: 0, 1, 2
1697 kmemcheck=0 (disabled)
1698 kmemcheck=1 (enabled)
1699 kmemcheck=2 (one-shot mode)
1700 Default: 2 (one-shot mode)
1702 kstack=N [X86] Print N words from the kernel stack
1705 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1706 Default is 0 (don't ignore, but inject #GP)
1708 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1712 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1713 Default is 1 (enabled)
1715 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1717 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1719 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1720 (virtualized MMU) support on capable Intel chips.
1721 Default is 1 (enabled)
1723 kvm-intel.emulate_invalid_guest_state=
1724 [KVM,Intel] Enable emulation of invalid guest states
1725 Default is 0 (disabled)
1727 kvm-intel.flexpriority=
1728 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1729 Default is 1 (enabled)
1732 [KVM,Intel] Enable VMX nesting (nVMX).
1733 Default is 0 (disabled)
1735 kvm-intel.unrestricted_guest=
1736 [KVM,Intel] Disable unrestricted guest feature
1737 (virtualized real and unpaged mode) on capable
1738 Intel chips. Default is 1 (enabled)
1740 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1741 feature (tagged TLBs) on capable Intel chips.
1742 Default is 1 (enabled)
1748 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1751 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1752 value for LAPIC timer one-shot implementation. Default
1753 back to the programmable timer unit in the LAPIC.
1755 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1758 libata.dma= [LIBATA] DMA control
1759 libata.dma=0 Disable all PATA and SATA DMA
1760 libata.dma=1 PATA and SATA Disk DMA only
1761 libata.dma=2 ATAPI (CDROM) DMA only
1762 libata.dma=4 Compact Flash DMA only
1763 Combinations also work, so libata.dma=3 enables DMA
1764 for disks and CDROMs, but not CFs.
1766 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1767 libata.ignore_hpa=0 keep BIOS limits (default)
1768 libata.ignore_hpa=1 ignore limits, using full disk
1770 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1774 libata.force= [LIBATA] Force configurations. The format is comma
1775 separated list of "[ID:]VAL" where ID is
1776 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1777 matching port, link or device. Basically, it matches
1778 the ATA ID string printed on console by libata. If
1779 the whole ID part is omitted, the last PORT and DEVICE
1780 values are used. If ID hasn't been specified yet, the
1781 configuration applies to all ports, links and devices.
1783 If only DEVICE is omitted, the parameter applies to
1784 the port and all links and devices behind it. DEVICE
1785 number of 0 either selects the first device or the
1786 first fan-out link behind PMP device. It does not
1787 select the host link. DEVICE number of 15 selects the
1788 host link and device attached to it.
1790 The VAL specifies the configuration to force. As long
1791 as there's no ambiguity shortcut notation is allowed.
1792 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1793 The following configurations can be forced.
1795 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1796 Any ID with matching PORT is used.
1798 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1800 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1801 udma[/][16,25,33,44,66,100,133] notation is also
1804 * [no]ncq: Turn on or off NCQ.
1806 * [no]ncqtrim: Turn off queued DSM TRIM.
1808 * nohrst, nosrst, norst: suppress hard, soft
1811 * rstonce: only attempt one reset during
1812 hot-unplug link recovery
1814 * dump_id: dump IDENTIFY data.
1816 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1818 * disable: Disable this device.
1820 If there are multiple matching configurations changing
1821 the same attribute, the last one is used.
1823 memblock=debug [KNL] Enable memblock debug messages.
1825 load_ramdisk= [RAM] List of ramdisks to load from floppy
1826 See Documentation/blockdev/ramdisk.txt.
1828 lockd.nlm_grace_period=P [NFS] Assign grace period.
1831 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1834 lockd.nlm_timeout=T [NFS] Assign timeout value.
1837 lockd.nlm_udpport=M [NFS] Assign UDP port.
1840 locktorture.nreaders_stress= [KNL]
1841 Set the number of locking read-acquisition kthreads.
1842 Defaults to being automatically set based on the
1843 number of online CPUs.
1845 locktorture.nwriters_stress= [KNL]
1846 Set the number of locking write-acquisition kthreads.
1848 locktorture.onoff_holdoff= [KNL]
1849 Set time (s) after boot for CPU-hotplug testing.
1851 locktorture.onoff_interval= [KNL]
1852 Set time (s) between CPU-hotplug operations, or
1853 zero to disable CPU-hotplug testing.
1855 locktorture.shuffle_interval= [KNL]
1856 Set task-shuffle interval (jiffies). Shuffling
1857 tasks allows some CPUs to go into dyntick-idle
1858 mode during the locktorture test.
1860 locktorture.shutdown_secs= [KNL]
1861 Set time (s) after boot system shutdown. This
1862 is useful for hands-off automated testing.
1864 locktorture.stat_interval= [KNL]
1865 Time (s) between statistics printk()s.
1867 locktorture.stutter= [KNL]
1868 Time (s) to stutter testing, for example,
1869 specifying five seconds causes the test to run for
1870 five seconds, wait for five seconds, and so on.
1871 This tests the locking primitive's ability to
1872 transition abruptly to and from idle.
1874 locktorture.torture_runnable= [BOOT]
1875 Start locktorture running at boot time.
1877 locktorture.torture_type= [KNL]
1878 Specify the locking implementation to test.
1880 locktorture.verbose= [KNL]
1881 Enable additional printk() statements.
1883 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1886 loglevel= All Kernel Messages with a loglevel smaller than the
1887 console loglevel will be printed to the console. It can
1888 also be changed with klogd or other programs. The
1889 loglevels are defined as follows:
1891 0 (KERN_EMERG) system is unusable
1892 1 (KERN_ALERT) action must be taken immediately
1893 2 (KERN_CRIT) critical conditions
1894 3 (KERN_ERR) error conditions
1895 4 (KERN_WARNING) warning conditions
1896 5 (KERN_NOTICE) normal but significant condition
1897 6 (KERN_INFO) informational
1898 7 (KERN_DEBUG) debug-level messages
1900 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1901 in bytes. n must be a power of two and greater
1902 than the minimal size. The minimal size is defined
1903 by LOG_BUF_SHIFT kernel config parameter. There is
1904 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1905 that allows to increase the default size depending on
1906 the number of CPUs. See init/Kconfig for more details.
1908 logo.nologo [FB] Disables display of the built-in Linux logo.
1909 This may be used to provide more screen space for
1910 kernel log messages and is useful when debugging
1911 kernel boot problems.
1913 lp=0 [LP] Specify parallel ports to use, e.g,
1914 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1915 lp=reset first parallel port). 'lp=0' disables the
1916 lp=auto printer driver. 'lp=reset' (which can be
1917 specified in addition to the ports) causes
1918 attached printers to be reset. Using
1919 lp=port1,port2,... specifies the parallel ports
1920 to associate lp devices with, starting with
1921 lp0. A port specification may be 'none' to skip
1922 that lp device, or a parport name such as
1923 'parport0'. Specifying 'lp=auto' instead of a
1924 port specification list means that device IDs
1925 from each port should be examined, to see if
1926 an IEEE 1284-compliant printer is attached; if
1927 so, the driver will manage that printer.
1928 See also header of drivers/char/lp.c.
1931 Sets loops_per_jiffy to given constant, thus avoiding
1932 time-consuming boot-time autodetection (up to 250 ms per
1933 CPU). 0 enables autodetection (default). To determine
1934 the correct value for your kernel, boot with normal
1935 autodetection and see what value is printed. Note that
1936 on SMP systems the preset will be applied to all CPUs,
1937 which is likely to cause problems if your CPUs need
1938 significantly divergent settings. An incorrect value
1939 will cause delays in the kernel to be wrong, leading to
1940 unpredictable I/O errors and other breakage. Although
1941 unlikely, in the extreme case this might damage your
1945 Format: <io>,<irq>,<dma>
1947 machvec= [IA-64] Force the use of a particular machine-vector
1948 (machvec) in a generic kernel.
1949 Example: machvec=hpzx1_swiotlb
1951 machtype= [Loongson] Share the same kernel image file between different
1953 Example: machtype=lemote-yeeloong-2f-7inch
1955 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1956 than or equal to this physical address is ignored.
1958 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1959 should make use of. maxcpus=n : n >= 0 limits the
1960 kernel to using 'n' processors. n=0 is a special case,
1961 it is equivalent to "nosmp", which also disables
1964 max_loop= [LOOP] The number of loop block devices that get
1965 (loop.max_loop) unconditionally pre-created at init time. The default
1966 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1967 of statically allocating a predefined number, loop
1968 devices can be requested on-demand with the
1969 /dev/loop-control interface.
1971 mce [X86-32] Machine Check Exception
1973 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1975 md= [HW] RAID subsystems devices and level
1976 See Documentation/md.txt.
1979 Format: <first>,<last>
1980 Specifies range of consoles to be captured by the MDA.
1982 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1983 Amount of memory to be used when the kernel is not able
1984 to see the whole system memory or for test.
1985 [X86] Work as limiting max address. Use together
1986 with memmap= to avoid physical address space collisions.
1987 Without memmap= PCI devices could be placed at addresses
1988 belonging to unused RAM.
1990 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1994 [KNL,SH] Allow user to override the default size for
1995 per-device physically contiguous DMA buffers.
1997 memmap=exactmap [KNL,X86] Enable setting of an exact
1998 E820 memory map, as specified by the user.
1999 Such memmap=exactmap lines can be constructed based on
2000 BIOS output or other requirements. See the memmap=nn@ss
2003 memmap=nn[KMG]@ss[KMG]
2004 [KNL] Force usage of a specific region of memory.
2005 Region of memory to be used is from ss to ss+nn.
2007 memmap=nn[KMG]#ss[KMG]
2008 [KNL,ACPI] Mark specific memory as ACPI data.
2009 Region of memory to be marked is from ss to ss+nn.
2011 memmap=nn[KMG]$ss[KMG]
2012 [KNL,ACPI] Mark specific memory as reserved.
2013 Region of memory to be reserved is from ss to ss+nn.
2014 Example: Exclude memory from 0x18690000-0x1869ffff
2015 memmap=64K$0x18690000
2017 memmap=0x10000$0x18690000
2019 memmap=nn[KMG]!ss[KMG]
2020 [KNL,X86] Mark specific memory as protected.
2021 Region of memory to be used, from ss to ss+nn.
2022 The memory region may be marked as e820 type 12 (0xc)
2023 and is NVDIMM or ADR memory.
2025 memory_corruption_check=0/1 [X86]
2026 Some BIOSes seem to corrupt the first 64k of
2027 memory when doing things like suspend/resume.
2028 Setting this option will scan the memory
2029 looking for corruption. Enabling this will
2030 both detect corruption and prevent the kernel
2031 from using the memory being corrupted.
2032 However, its intended as a diagnostic tool; if
2033 repeatable BIOS-originated corruption always
2034 affects the same memory, you can use memmap=
2035 to prevent the kernel from using that memory.
2037 memory_corruption_check_size=size [X86]
2038 By default it checks for corruption in the low
2039 64k, making this memory unavailable for normal
2040 use. Use this parameter to scan for
2041 corruption in more or less memory.
2043 memory_corruption_check_period=seconds [X86]
2044 By default it checks for corruption every 60
2045 seconds. Use this parameter to check at some
2046 other rate. 0 disables periodic checking.
2048 memtest= [KNL,X86,ARM] Enable memtest
2050 default : 0 <disable>
2051 Specifies the number of memtest passes to be
2052 performed. Each pass selects another test
2053 pattern from a given set of patterns. Memtest
2054 fills the memory with this pattern, validates
2055 memory contents and reserves bad memory
2056 regions that are detected.
2058 meye.*= [HW] Set MotionEye Camera parameters
2059 See Documentation/video4linux/meye.txt.
2061 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2062 Multi-Function General Purpose Timers on AMD Geode
2065 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2066 the BIOS has incorrectly applied a workaround. TinyBIOS
2067 version 0.98 is known to be affected, 0.99 fixes the
2068 problem by letting the user disable the workaround.
2072 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2073 physical address is ignored.
2075 mini2440= [ARM,HW,KNL]
2076 Format:[0..2][b][c][t]
2078 MINI2440 configuration specification:
2079 0 - The attached screen is the 3.5" TFT
2080 1 - The attached screen is the 7" TFT
2081 2 - The VGA Shield is attached (1024x768)
2082 Leaving out the screen size parameter will not load
2083 the TFT driver, and the framebuffer will be left
2085 b - Enable backlight. The TFT backlight pin will be
2086 linked to the kernel VESA blanking code and a GPIO
2087 LED. This parameter is not necessary when using the
2089 c - Enable the s3c camera interface.
2090 t - Reserved for enabling touchscreen support. The
2091 touchscreen support is not enabled in the mainstream
2092 kernel as of 2.6.30, a preliminary port can be found
2093 in the "bleeding edge" mini2440 support kernel at
2094 http://repo.or.cz/w/linux-2.6/mini2440.git
2097 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2098 parameter allows control of the logging verbosity for
2099 the additional memory initialisation checks. A value
2100 of 0 disables mminit logging and a level of 4 will
2101 log everything. Information is printed at KERN_DEBUG
2102 so loglevel=8 may also need to be specified.
2105 [KNL] When CONFIG_MODULE_SIG is set, this means that
2106 modules without (valid) signatures will fail to load.
2107 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2108 is always true, so this option does nothing.
2111 [MOUSE] Maximum time between finger touching and
2112 leaving touchpad surface for touch to be considered
2113 a tap and be reported as a left button click (for
2114 touchpads working in absolute mode only).
2116 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2117 reporting absolute coordinates, such as tablets
2118 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2119 reporting absolute coordinates, such as tablets
2121 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2122 is similar to kernelcore except it specifies the
2123 amount of memory used for migratable allocations.
2124 If both kernelcore and movablecore is specified,
2125 then kernelcore will be at *least* the specified
2126 value but may be more. If movablecore on its own
2127 is specified, the administrator must be careful
2128 that the amount of memory usable for all allocations
2131 movable_node [KNL,X86] Boot-time switch to enable the effects
2132 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2134 MTD_Partition= [MTD]
2135 Format: <name>,<region-number>,<size>,<offset>
2137 MTD_Region= [MTD] Format:
2138 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2141 See drivers/mtd/cmdlinepart.c.
2143 multitce=off [PPC] This parameter disables the use of the pSeries
2144 firmware feature for updating multiple TCE entries
2147 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2149 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2151 boundary - index of last SLC block on Flex-OneNAND.
2152 The remaining blocks are configured as MLC blocks.
2153 lock - Configure if Flex-OneNAND boundary should be locked.
2154 Once locked, the boundary cannot be changed.
2155 1 indicates lock status, 0 indicates unlock status.
2158 ARM/S3C2412 JIVE boot control
2160 See arch/arm/mach-s3c2412/mach-jive.c
2162 mtouchusb.raw_coordinates=
2163 [HW] Make the MicroTouch USB driver use raw coordinates
2164 ('y', default) or cooked coordinates ('n')
2166 mtrr_chunk_size=nn[KMG] [X86]
2167 used for mtrr cleanup. It is largest continuous chunk
2168 that could hold holes aka. UC entries.
2170 mtrr_gran_size=nn[KMG] [X86]
2171 Used for mtrr cleanup. It is granularity of mtrr block.
2173 Large value could prevent small alignment from
2176 mtrr_spare_reg_nr=n [X86]
2178 Range: 0,7 : spare reg number
2180 Used for mtrr cleanup. It is spare mtrr entries number.
2181 Set to 2 or more if your graphical card needs more.
2183 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2185 netdev= [NET] Network devices parameters
2186 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2187 Note that mem_start is often overloaded to mean
2188 something different and driver-specific.
2189 This usage is only documented in each driver source
2193 [NETFILTER] Enable connection tracking flow accounting
2194 0 to disable accounting
2195 1 to enable accounting
2198 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2199 See Documentation/filesystems/nfs/nfsroot.txt.
2201 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2202 See Documentation/filesystems/nfs/nfsroot.txt.
2204 nfsrootdebug [NFS] enable nfsroot debugging messages.
2205 See Documentation/filesystems/nfs/nfsroot.txt.
2207 nfs.callback_tcpport=
2208 [NFS] set the TCP port on which the NFSv4 callback
2209 channel should listen.
2212 [NFS] sets the pathname to the program which is used
2213 to update the NFS client cache entries.
2215 nfs.cache_getent_timeout=
2216 [NFS] sets the timeout after which an attempt to
2217 update a cache entry is deemed to have failed.
2219 nfs.idmap_cache_timeout=
2220 [NFS] set the maximum lifetime for idmapper cache
2224 [NFS] enable 64-bit inode numbers.
2225 If zero, the NFS client will fake up a 32-bit inode
2226 number for the readdir() and stat() syscalls instead
2227 of returning the full 64-bit number.
2228 The default is to return 64-bit inode numbers.
2230 nfs.max_session_slots=
2231 [NFSv4.1] Sets the maximum number of session slots
2232 the client will attempt to negotiate with the server.
2233 This limits the number of simultaneous RPC requests
2234 that the client can send to the NFSv4.1 server.
2235 Note that there is little point in setting this
2236 value higher than the max_tcp_slot_table_limit.
2238 nfs.nfs4_disable_idmapping=
2239 [NFSv4] When set to the default of '1', this option
2240 ensures that both the RPC level authentication
2241 scheme and the NFS level operations agree to use
2242 numeric uids/gids if the mount is using the
2243 'sec=sys' security flavour. In effect it is
2244 disabling idmapping, which can make migration from
2245 legacy NFSv2/v3 systems to NFSv4 easier.
2246 Servers that do not support this mode of operation
2247 will be autodetected by the client, and it will fall
2248 back to using the idmapper.
2249 To turn off this behaviour, set the value to '0'.
2251 [NFS4] Specify an additional fixed unique ident-
2252 ification string that NFSv4 clients can insert into
2253 their nfs_client_id4 string. This is typically a
2254 UUID that is generated at system install time.
2256 nfs.send_implementation_id =
2257 [NFSv4.1] Send client implementation identification
2258 information in exchange_id requests.
2259 If zero, no implementation identification information
2261 The default is to send the implementation identification
2264 nfs.recover_lost_locks =
2265 [NFSv4] Attempt to recover locks that were lost due
2266 to a lease timeout on the server. Please note that
2267 doing this risks data corruption, since there are
2268 no guarantees that the file will remain unchanged
2269 after the locks are lost.
2270 If you want to enable the kernel legacy behaviour of
2271 attempting to recover these locks, then set this
2273 The default parameter value of '0' causes the kernel
2274 not to attempt recovery of lost locks.
2276 nfsd.nfs4_disable_idmapping=
2277 [NFSv4] When set to the default of '1', the NFSv4
2278 server will return only numeric uids and gids to
2279 clients using auth_sys, and will accept numeric uids
2280 and gids from such clients. This is intended to ease
2281 migration from NFSv2/v3.
2283 objlayoutdriver.osd_login_prog=
2284 [NFS] [OBJLAYOUT] sets the pathname to the program which
2285 is used to automatically discover and login into new
2286 osd-targets. Please see:
2287 Documentation/filesystems/pnfs.txt for more explanations
2289 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2290 when a NMI is triggered.
2291 Format: [state][,regs][,debounce][,die]
2293 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2294 Format: [panic,][nopanic,][num]
2296 0 - turn nmi_watchdog off
2297 1 - turn nmi_watchdog on
2298 When panic is specified, panic when an NMI watchdog
2299 timeout occurs (or 'nopanic' to override the opposite
2301 This is useful when you use a panic=... timeout and
2302 need the box quickly up again.
2304 netpoll.carrier_timeout=
2305 [NET] Specifies amount of time (in seconds) that
2306 netpoll should wait for a carrier. By default netpoll
2309 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2310 emulation library even if a 387 maths coprocessor
2314 [HW] Never suspend the console
2315 Disable suspending of consoles during suspend and
2316 hibernate operations. Once disabled, debugging
2317 messages can reach various consoles while the rest
2318 of the system is being put to sleep (ie, while
2319 debugging driver suspend/resume hooks). This may
2320 not work reliably with all consoles, but is known
2321 to work with serial and VGA consoles.
2322 To facilitate more flexible debugging, we also add
2323 console_suspend, a printk module parameter to control
2324 it. Users could use console_suspend (usually
2325 /sys/module/printk/parameters/console_suspend) to
2326 turn on/off it dynamically.
2328 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2329 caches in the slab allocator. Saves per-node memory,
2330 but will impact performance.
2334 noapic [SMP,APIC] Tells the kernel to not make use of any
2335 IOAPICs that may be present in the system.
2337 noautogroup Disable scheduler automatic task group creation.
2339 nobats [PPC] Do not use BATs for mapping kernel lowmem
2340 on "Classic" PPC cores.
2344 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2346 nodelayacct [KNL] Disable per-task delay accounting
2348 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2350 nodsp [SH] Disable hardware DSP at boot time.
2352 noefi Disable EFI runtime services support.
2357 On X86-32 available only on PAE configured kernels.
2358 noexec=on: enable non-executable mappings (default)
2359 noexec=off: disable non-executable mappings
2362 Disable SMAP (Supervisor Mode Access Prevention)
2363 even if it is supported by processor.
2366 Disable SMEP (Supervisor Mode Execution Prevention)
2367 even if it is supported by processor.
2370 This affects only 32-bit executables.
2371 noexec32=on: enable non-executable mappings (default)
2372 read doesn't imply executable mappings
2373 noexec32=off: disable non-executable mappings
2374 read implies executable mappings
2376 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2378 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2379 register save and restore. The kernel will only save
2380 legacy floating-point registers on task switch.
2382 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2384 noxsave [BUGS=X86] Disables x86 extended register state save
2385 and restore using xsave. The kernel will fallback to
2386 enabling legacy floating-point and sse state.
2388 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2389 register states. The kernel will fall back to use
2390 xsave to save the states. By using this parameter,
2391 performance of saving the states is degraded because
2392 xsave doesn't support modified optimization while
2393 xsaveopt supports it on xsaveopt enabled systems.
2395 noxsaves [X86] Disables xsaves and xrstors used in saving and
2396 restoring x86 extended register state in compacted
2397 form of xsave area. The kernel will fall back to use
2398 xsaveopt and xrstor to save and restore the states
2399 in standard form of xsave area. By using this
2400 parameter, xsave area per process might occupy more
2401 memory on xsaves enabled systems.
2403 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2404 wfi(ARM) instruction doesn't work correctly and not to
2405 use it. This is also useful when using JTAG debugger.
2407 no_file_caps Tells the kernel not to honor file capabilities. The
2408 only way then for a file to be executed with privilege
2409 is to be setuid root or executed by root.
2411 nohalt [IA-64] Tells the kernel not to use the power saving
2412 function PAL_HALT_LIGHT when idle. This increases
2413 power-consumption. On the positive side, it reduces
2414 interrupt wake-up latency, which may improve performance
2415 in certain environments such as networked servers or
2418 nohibernate [HIBERNATION] Disable hibernation and resume.
2420 nohz= [KNL] Boottime enable/disable dynamic ticks
2421 Valid arguments: on, off
2424 nohz_full= [KNL,BOOT]
2425 In kernels built with CONFIG_NO_HZ_FULL=y, set
2426 the specified list of CPUs whose tick will be stopped
2427 whenever possible. The boot CPU will be forced outside
2428 the range to maintain the timekeeping.
2429 The CPUs in this range must also be included in the
2432 noiotrap [SH] Disables trapped I/O port accesses.
2434 noirqdebug [X86-32] Disables the code which attempts to detect and
2435 disable unhandled interrupt sources.
2437 no_timer_check [X86,APIC] Disables the code which tests for
2438 broken timer IRQ sources.
2440 noisapnp [ISAPNP] Disables ISA PnP code.
2442 noinitrd [RAM] Tells the kernel not to load any configured
2445 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2447 [Deprecated - use intremap=off]
2451 nojitter [IA-64] Disables jitter checking for ITC timers.
2453 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2455 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2458 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2459 steal time is computed, but won't influence scheduler
2462 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2464 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2466 noltlbs [PPC] Do not use large page/tlb entries for kernel
2467 lowmem mapping on PPC40x.
2469 nomca [IA-64] Disable machine check abort handling
2471 nomce [X86-32] Disable Machine Check Exception
2473 nomfgpt [X86-32] Disable Multi-Function General Purpose
2474 Timer usage (for AMD Geode machines).
2476 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2477 shutdown the other cpus. Instead use the REBOOT_VECTOR
2480 nomodule Disable module load
2482 nopat [X86] Disable PAT (page attribute table extension of
2483 pagetables) support.
2485 norandmaps Don't use address space randomization. Equivalent to
2486 echo 0 > /proc/sys/kernel/randomize_va_space
2488 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2490 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2491 with UP alternatives
2493 nordrand [X86] Disable kernel use of the RDRAND and
2494 RDSEED instructions even if they are supported
2495 by the processor. RDRAND and RDSEED are still
2496 available to user space applications.
2498 noresume [SWSUSP] Disables resume and restores original swap
2501 no-scroll [VGA] Disables scrollback.
2502 This is required for the Braillex ib80-piezo Braille
2503 reader made by F.H. Papenmeier (Germany).
2507 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2509 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2510 and disable the IO APIC. legacy for "maxcpus=0".
2512 nosoftlockup [KNL] Disable the soft-lockup detector.
2514 nosync [HW,M68K] Disables sync negotiation for all devices.
2516 notsc [BUGS=X86-32] Disable Time Stamp Counter
2518 nousb [USB] Disable the USB subsystem
2520 nowatchdog [KNL] Disable both lockup detectors, i.e.
2521 soft-lockup and NMI watchdog (hard-lockup).
2525 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2527 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2528 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2529 Some features depend on CPU0. Known dependencies are:
2530 1. Resume from suspend/hibernate depends on CPU0.
2531 Suspend/hibernate will fail if CPU0 is offline and you
2532 need to online CPU0 before suspend/hibernate.
2533 2. PIC interrupts also depend on CPU0. CPU0 can't be
2534 removed if a PIC interrupt is detected.
2535 It's said poweroff/reboot may depend on CPU0 on some
2536 machines although I haven't seen such issues so far
2537 after CPU0 is offline on a few tested machines.
2538 If the dependencies are under your control, you can
2539 turn on cpu0_hotplug.
2541 nptcg= [IA-64] Override max number of concurrent global TLB
2542 purges which is reported from either PAL_VM_SUMMARY or
2545 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2546 could support. nr_cpus=n : n >= 1 limits the kernel to
2547 supporting 'n' processors. Later in runtime you can not
2548 use hotplug cpu feature to put more cpu back to online.
2549 just like you compile the kernel NR_CPUS=n
2551 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2553 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2554 Allowed values are enable and disable
2556 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2557 one of ['zone', 'node', 'default'] can be specified
2558 This can be set from sysctl after boot.
2559 See Documentation/sysctl/vm.txt for details.
2561 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2562 See Documentation/debugging-via-ohci1394.txt for more
2565 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2566 Rather than timing out after 20 ms if an EC
2567 command is not properly ACKed, override the length
2568 of the timeout. We have interrupts disabled while
2569 waiting for the ACK, so if this is set too high
2570 interrupts *may* be lost!
2572 omap_mux= [OMAP] Override bootloader pin multiplexing.
2573 Format: <mux_mode0.mode_name=value>...
2574 For example, to override I2C bus2:
2575 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2577 oprofile.timer= [HW]
2578 Use timer interrupt instead of performance counters
2580 oprofile.cpu_type= Force an oprofile cpu type
2581 This might be useful if you have an older oprofile
2582 userland or if you want common events.
2583 Format: { arch_perfmon }
2584 arch_perfmon: [X86] Force use of architectural
2585 perfmon on Intel CPUs instead of the
2586 CPU specific event set.
2587 timer: [X86] Force use of architectural NMI
2588 timer mode (see also oprofile.timer
2589 for generic hr timer mode)
2590 [s390] Force legacy basic mode sampling
2591 (report cpu_type "timer")
2593 oops=panic Always panic on oopses. Default is to just kill the
2594 process, but there is a small probability of
2595 deadlocking the machine.
2596 This will also cause panics on machine check exceptions.
2597 Useful together with panic=30 to trigger a reboot.
2600 See Documentation/sound/oss/oss-parameters.txt
2602 page_owner= [KNL] Boot-time page_owner enabling option.
2603 Storage of the information about who allocated
2604 each page is disabled in default. With this switch,
2606 on: enable the feature
2608 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2609 timeout > 0: seconds before rebooting
2610 timeout = 0: wait forever
2611 timeout < 0: reboot immediately
2614 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2617 crash_kexec_post_notifiers
2618 Run kdump after running panic-notifiers and dumping
2619 kmsg. This only for the users who doubt kdump always
2620 succeeds in any situation.
2621 Note that this also increases risks of kdump failure,
2622 because some panic notifiers can make the crashed
2623 kernel more unstable.
2625 parkbd.port= [HW] Parallel port number the keyboard adapter is
2626 connected to, default is 0.
2628 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2629 0 for XT, 1 for AT (default is AT).
2632 parport= [HW,PPT] Specify parallel ports. 0 disables.
2633 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2634 Use 'auto' to force the driver to use any
2635 IRQ/DMA settings detected (the default is to
2636 ignore detected IRQ/DMA settings because of
2637 possible conflicts). You can specify the base
2638 address, IRQ, and DMA settings; IRQ and DMA
2639 should be numbers, or 'auto' (for using detected
2640 settings on that particular port), or 'nofifo'
2641 (to avoid using a FIFO even if it is detected).
2642 Parallel ports are assigned in the order they
2643 are specified on the command line, starting
2646 parport_init_mode= [HW,PPT]
2647 Configure VIA parallel port to operate in
2648 a specific mode. This is necessary on Pegasos
2649 computer where firmware has no options for setting
2650 up parallel port mode and sets it to spp.
2651 Currently this function knows 686a and 8231 chips.
2652 Format: [spp|ps2|epp|ecp|ecpepp]
2655 Halt all CPUs after the first oops has been printed for
2656 the specified number of seconds. This is to be used if
2657 your oopses keep scrolling off the screen.
2662 See header of drivers/block/paride/pcd.c.
2663 See also Documentation/blockdev/paride.txt.
2665 pci=option[,option...] [PCI] various PCI subsystem options:
2666 earlydump [X86] dump PCI config space before the kernel
2668 off [X86] don't probe for the PCI bus
2669 bios [X86-32] force use of PCI BIOS, don't access
2670 the hardware directly. Use this if your machine
2671 has a non-standard PCI host bridge.
2672 nobios [X86-32] disallow use of PCI BIOS, only direct
2673 hardware access methods are allowed. Use this
2674 if you experience crashes upon bootup and you
2675 suspect they are caused by the BIOS.
2676 conf1 [X86] Force use of PCI Configuration
2678 conf2 [X86] Force use of PCI Configuration
2680 noaer [PCIE] If the PCIEAER kernel config parameter is
2681 enabled, this kernel boot option can be used to
2682 disable the use of PCIE advanced error reporting.
2683 nodomains [PCI] Disable support for multiple PCI
2684 root domains (aka PCI segments, in ACPI-speak).
2685 nommconf [X86] Disable use of MMCONFIG for PCI
2687 check_enable_amd_mmconf [X86] check for and enable
2688 properly configured MMIO access to PCI
2689 config space on AMD family 10h CPU
2690 nomsi [MSI] If the PCI_MSI kernel config parameter is
2691 enabled, this kernel boot option can be used to
2692 disable the use of MSI interrupts system-wide.
2693 noioapicquirk [APIC] Disable all boot interrupt quirks.
2694 Safety option to keep boot IRQs enabled. This
2695 should never be necessary.
2696 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2697 primary IO-APIC for bridges that cannot disable
2698 boot IRQs. This fixes a source of spurious IRQs
2699 when the system masks IRQs.
2700 noioapicreroute [APIC] Disable workaround that uses the
2701 boot IRQ equivalent of an IRQ that connects to
2702 a chipset where boot IRQs cannot be disabled.
2703 The opposite of ioapicreroute.
2704 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2705 routing table. These calls are known to be buggy
2706 on several machines and they hang the machine
2707 when used, but on other computers it's the only
2708 way to get the interrupt routing table. Try
2709 this option if the kernel is unable to allocate
2710 IRQs or discover secondary PCI buses on your
2712 rom [X86] Assign address space to expansion ROMs.
2713 Use with caution as certain devices share
2714 address decoders between ROMs and other
2716 norom [X86] Do not assign address space to
2717 expansion ROMs that do not already have
2718 BIOS assigned address ranges.
2719 nobar [X86] Do not assign address space to the
2720 BARs that weren't assigned by the BIOS.
2721 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2722 assigned automatically to PCI devices. You can
2723 make the kernel exclude IRQs of your ISA cards
2725 pirqaddr=0xAAAAA [X86] Specify the physical address
2726 of the PIRQ table (normally generated
2727 by the BIOS) if it is outside the
2728 F0000h-100000h range.
2729 lastbus=N [X86] Scan all buses thru bus #N. Can be
2730 useful if the kernel is unable to find your
2731 secondary buses and you want to tell it
2732 explicitly which ones they are.
2733 assign-busses [X86] Always assign all PCI bus
2734 numbers ourselves, overriding
2735 whatever the firmware may have done.
2736 usepirqmask [X86] Honor the possible IRQ mask stored
2737 in the BIOS $PIR table. This is needed on
2738 some systems with broken BIOSes, notably
2739 some HP Pavilion N5400 and Omnibook XE3
2740 notebooks. This will have no effect if ACPI
2741 IRQ routing is enabled.
2742 noacpi [X86] Do not use ACPI for IRQ routing
2743 or for PCI scanning.
2744 use_crs [X86] Use PCI host bridge window information
2745 from ACPI. On BIOSes from 2008 or later, this
2746 is enabled by default. If you need to use this,
2747 please report a bug.
2748 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2749 If you need to use this, please report a bug.
2750 routeirq Do IRQ routing for all PCI devices.
2751 This is normally done in pci_enable_device(),
2752 so this option is a temporary workaround
2753 for broken drivers that don't call it.
2754 skip_isa_align [X86] do not align io start addr, so can
2755 handle more pci cards
2756 firmware [ARM] Do not re-enumerate the bus but instead
2757 just use the configuration from the
2758 bootloader. This is currently used on
2759 IXP2000 systems where the bus has to be
2760 configured a certain way for adjunct CPUs.
2761 noearly [X86] Don't do any early type 1 scanning.
2762 This might help on some broken boards which
2763 machine check when some devices' config space
2764 is read. But various workarounds are disabled
2765 and some IOMMU drivers will not work.
2766 bfsort Sort PCI devices into breadth-first order.
2767 This sorting is done to get a device
2768 order compatible with older (<= 2.4) kernels.
2769 nobfsort Don't sort PCI devices into breadth-first order.
2770 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2771 tuning and use the BIOS-configured MPS defaults.
2772 pcie_bus_safe Set every device's MPS to the largest value
2773 supported by all devices below the root complex.
2774 pcie_bus_perf Set device MPS to the largest allowable MPS
2775 based on its parent bus. Also set MRRS (Max
2776 Read Request Size) to the largest supported
2777 value (no larger than the MPS that the device
2778 or bus can support) for best performance.
2779 pcie_bus_peer2peer Set every device's MPS to 128B, which
2780 every device is guaranteed to support. This
2781 configuration allows peer-to-peer DMA between
2782 any pair of devices, possibly at the cost of
2783 reduced performance. This also guarantees
2784 that hot-added devices will work.
2785 cbiosize=nn[KMG] The fixed amount of bus space which is
2786 reserved for the CardBus bridge's IO window.
2787 The default value is 256 bytes.
2788 cbmemsize=nn[KMG] The fixed amount of bus space which is
2789 reserved for the CardBus bridge's memory
2790 window. The default value is 64 megabytes.
2793 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2794 Specifies alignment and device to reassign
2795 aligned memory resources.
2796 If <order of align> is not specified,
2797 PAGE_SIZE is used as alignment.
2798 PCI-PCI bridge can be specified, if resource
2799 windows need to be expanded.
2800 ecrc= Enable/disable PCIe ECRC (transaction layer
2801 end-to-end CRC checking).
2802 bios: Use BIOS/firmware settings. This is the
2806 hpiosize=nn[KMG] The fixed amount of bus space which is
2807 reserved for hotplug bridge's IO window.
2808 Default size is 256 bytes.
2809 hpmemsize=nn[KMG] The fixed amount of bus space which is
2810 reserved for hotplug bridge's memory window.
2811 Default size is 2 megabytes.
2812 realloc= Enable/disable reallocating PCI bridge resources
2813 if allocations done by BIOS are too small to
2814 accommodate resources required by all child
2816 off: Turn realloc off
2818 realloc same as realloc=on
2819 noari do not use PCIe ARI.
2820 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2821 only look for one device below a PCIe downstream
2824 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2827 force Enable ASPM even on devices that claim not to support it.
2828 WARNING: Forcing ASPM on may cause system lockups.
2830 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2831 nomsi Do not use MSI for PCI Express Native Hotplug (this
2832 makes all PCIe ports use INTx for hotplug services).
2834 pcie_ports= [PCIE] PCIe ports handling:
2835 auto Ask the BIOS whether or not to use native PCIe services
2836 associated with PCIe ports (PME, hot-plug, AER). Use
2837 them only if that is allowed by the BIOS.
2838 native Use native PCIe services associated with PCIe ports
2840 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2843 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2844 nomsi Do not use MSI for native PCIe PME signaling (this makes
2845 all PCIe root ports use INTx for all services).
2847 pcmv= [HW,PCMCIA] BadgePAD 4
2851 Keep all power-domains already enabled by bootloader on,
2852 even if no driver has claimed them. This is useful
2853 for debug and development, but should not be
2854 needed on a platform with proper driver support.
2857 See Documentation/blockdev/paride.txt.
2859 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2862 See arch/parisc/kernel/pdc_chassis.c
2864 percpu_alloc= Select which percpu first chunk allocator to use.
2865 Currently supported values are "embed" and "page".
2866 Archs may support subset or none of the selections.
2867 See comments in mm/percpu.c for details on each
2868 allocator. This parameter is primarily for debugging
2869 and performance comparison.
2872 See Documentation/blockdev/paride.txt.
2875 See Documentation/blockdev/paride.txt.
2877 pirq= [SMP,APIC] Manual mp-table setup
2878 See Documentation/x86/i386/IO-APIC.txt.
2880 plip= [PPT,NET] Parallel port network link
2881 Format: { parport<nr> | timid | 0 }
2882 See also Documentation/parport.txt.
2884 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2885 Override pmtimer IOPort with a hex value.
2889 Enable PNP debug messages (depends on the
2890 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2891 via /sys/module/pnp/parameters/debug. We always show
2892 current resource usage; turning this on also shows
2893 possible settings and some assignment information.
2899 { on | off | curr | res | no-curr | no-res }
2902 [ISAPNP] Exclude IRQs for the autoconfiguration
2905 [ISAPNP] Exclude DMAs for the autoconfiguration
2907 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2908 Ranges are in pairs (I/O port base and size).
2911 [ISAPNP] Exclude memory regions for the
2913 Ranges are in pairs (memory base and size).
2915 ports= [IP_VS_FTP] IPVS ftp helper module
2917 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2919 Format: <port>,<port>....
2921 print-fatal-signals=
2922 [KNL] debug: print fatal signals
2924 If enabled, warn about various signal handling
2925 related application anomalies: too many signals,
2926 too many POSIX.1 timers, fatal signals causing a
2929 If you hit the warning due to signal overflow,
2930 you might want to try "ulimit -i unlimited".
2934 printk.always_kmsg_dump=
2935 Trigger kmsg_dump for cases other than kernel oops or
2937 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2940 printk.time= Show timing data prefixed to each printk message line
2941 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2943 processor.max_cstate= [HW,ACPI]
2944 Limit processor to maximum C-state
2945 max_cstate=9 overrides any DMI blacklist limit.
2947 processor.nocst [HW,ACPI]
2948 Ignore the _CST method to determine C-states,
2949 instead using the legacy FADT method
2951 profile= [KNL] Enable kernel profiling via /proc/profile
2952 Format: [schedule,]<number>
2953 Param: "schedule" - profile schedule points.
2954 Param: <number> - step/bucket size as a power of 2 for
2955 statistical time based profiling.
2956 Param: "sleep" - profile D-state sleeping (millisecs).
2957 Requires CONFIG_SCHEDSTATS
2958 Param: "kvm" - profile VM exits.
2960 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2962 See Documentation/blockdev/ramdisk.txt.
2964 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2965 probe for; one of (bare|imps|exps|lifebook|any).
2966 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2968 psmouse.resetafter= [HW,MOUSE]
2969 Try to reset the device after so many bad packets
2972 [HW,MOUSE] Set desired mouse resolution, in dpi.
2973 psmouse.smartscroll=
2974 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2975 0 = disabled, 1 = enabled (default).
2977 pstore.backend= Specify the name of the pstore backend to use
2980 See Documentation/blockdev/paride.txt.
2983 [KNL] Number of legacy pty's. Overwrites compiled-in
2986 quiet [KNL] Disable most log messages
2991 See Documentation/md.txt.
2993 ramdisk_blocksize= [RAM]
2994 See Documentation/blockdev/ramdisk.txt.
2996 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2997 See Documentation/blockdev/ramdisk.txt.
3000 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3001 the specified list of CPUs to be no-callback CPUs.
3002 Invocation of these CPUs' RCU callbacks will
3003 be offloaded to "rcuox/N" kthreads created for
3004 that purpose, where "x" is "b" for RCU-bh, "p"
3005 for RCU-preempt, and "s" for RCU-sched, and "N"
3006 is the CPU number. This reduces OS jitter on the
3007 offloaded CPUs, which can be useful for HPC and
3008 real-time workloads. It can also improve energy
3009 efficiency for asymmetric multiprocessors.
3012 Rather than requiring that offloaded CPUs
3013 (specified by rcu_nocbs= above) explicitly
3014 awaken the corresponding "rcuoN" kthreads,
3015 make these kthreads poll for callbacks.
3016 This improves the real-time response for the
3017 offloaded CPUs by relieving them of the need to
3018 wake up the corresponding kthread, but degrades
3019 energy efficiency by requiring that the kthreads
3020 periodically wake up to do the polling.
3022 rcutree.blimit= [KNL]
3023 Set maximum number of finished RCU callbacks to
3024 process in one batch.
3026 rcutree.dump_tree= [KNL]
3027 Dump the structure of the rcu_node combining tree
3028 out at early boot. This is used for diagnostic
3029 purposes, to verify correct tree setup.
3031 rcutree.gp_cleanup_delay= [KNL]
3032 Set the number of jiffies to delay each step of
3033 RCU grace-period cleanup. This only has effect
3034 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3036 rcutree.gp_init_delay= [KNL]
3037 Set the number of jiffies to delay each step of
3038 RCU grace-period initialization. This only has
3039 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3042 rcutree.gp_preinit_delay= [KNL]
3043 Set the number of jiffies to delay each step of
3044 RCU grace-period pre-initialization, that is,
3045 the propagation of recent CPU-hotplug changes up
3046 the rcu_node combining tree. This only has effect
3047 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3049 rcutree.rcu_fanout_exact= [KNL]
3050 Disable autobalancing of the rcu_node combining
3051 tree. This is used by rcutorture, and might
3052 possibly be useful for architectures having high
3053 cache-to-cache transfer latencies.
3055 rcutree.rcu_fanout_leaf= [KNL]
3056 Increase the number of CPUs assigned to each
3057 leaf rcu_node structure. Useful for very large
3060 rcutree.jiffies_till_sched_qs= [KNL]
3061 Set required age in jiffies for a
3062 given grace period before RCU starts
3063 soliciting quiescent-state help from
3064 rcu_note_context_switch().
3066 rcutree.jiffies_till_first_fqs= [KNL]
3067 Set delay from grace-period initialization to
3068 first attempt to force quiescent states.
3069 Units are jiffies, minimum value is zero,
3070 and maximum value is HZ.
3072 rcutree.jiffies_till_next_fqs= [KNL]
3073 Set delay between subsequent attempts to force
3074 quiescent states. Units are jiffies, minimum
3075 value is one, and maximum value is HZ.
3077 rcutree.kthread_prio= [KNL,BOOT]
3078 Set the SCHED_FIFO priority of the RCU per-CPU
3079 kthreads (rcuc/N). This value is also used for
3080 the priority of the RCU boost threads (rcub/N)
3081 and for the RCU grace-period kthreads (rcu_bh,
3082 rcu_preempt, and rcu_sched). If RCU_BOOST is
3083 set, valid values are 1-99 and the default is 1
3084 (the least-favored priority). Otherwise, when
3085 RCU_BOOST is not set, valid values are 0-99 and
3086 the default is zero (non-realtime operation).
3088 rcutree.rcu_nocb_leader_stride= [KNL]
3089 Set the number of NOCB kthread groups, which
3090 defaults to the square root of the number of
3091 CPUs. Larger numbers reduces the wakeup overhead
3092 on the per-CPU grace-period kthreads, but increases
3093 that same overhead on each group's leader.
3095 rcutree.qhimark= [KNL]
3096 Set threshold of queued RCU callbacks beyond which
3097 batch limiting is disabled.
3099 rcutree.qlowmark= [KNL]
3100 Set threshold of queued RCU callbacks below which
3101 batch limiting is re-enabled.
3103 rcutree.rcu_idle_gp_delay= [KNL]
3104 Set wakeup interval for idle CPUs that have
3105 RCU callbacks (RCU_FAST_NO_HZ=y).
3107 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3108 Set wakeup interval for idle CPUs that have
3109 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3110 Lazy RCU callbacks are those which RCU can
3111 prove do nothing more than free memory.
3113 rcutorture.cbflood_inter_holdoff= [KNL]
3114 Set holdoff time (jiffies) between successive
3115 callback-flood tests.
3117 rcutorture.cbflood_intra_holdoff= [KNL]
3118 Set holdoff time (jiffies) between successive
3119 bursts of callbacks within a given callback-flood
3122 rcutorture.cbflood_n_burst= [KNL]
3123 Set the number of bursts making up a given
3124 callback-flood test. Set this to zero to
3125 disable callback-flood testing.
3127 rcutorture.cbflood_n_per_burst= [KNL]
3128 Set the number of callbacks to be registered
3129 in a given burst of a callback-flood test.
3131 rcutorture.fqs_duration= [KNL]
3132 Set duration of force_quiescent_state bursts.
3134 rcutorture.fqs_holdoff= [KNL]
3135 Set holdoff time within force_quiescent_state bursts.
3137 rcutorture.fqs_stutter= [KNL]
3138 Set wait time between force_quiescent_state bursts.
3140 rcutorture.gp_exp= [KNL]
3141 Use expedited update-side primitives.
3143 rcutorture.gp_normal= [KNL]
3144 Use normal (non-expedited) update-side primitives.
3145 If both gp_exp and gp_normal are set, do both.
3146 If neither gp_exp nor gp_normal are set, still
3149 rcutorture.n_barrier_cbs= [KNL]
3150 Set callbacks/threads for rcu_barrier() testing.
3152 rcutorture.nfakewriters= [KNL]
3153 Set number of concurrent RCU writers. These just
3154 stress RCU, they don't participate in the actual
3155 test, hence the "fake".
3157 rcutorture.nreaders= [KNL]
3158 Set number of RCU readers. The value -1 selects
3159 N-1, where N is the number of CPUs. A value
3160 "n" less than -1 selects N-n-2, where N is again
3161 the number of CPUs. For example, -2 selects N
3162 (the number of CPUs), -3 selects N+1, and so on.
3164 rcutorture.object_debug= [KNL]
3165 Enable debug-object double-call_rcu() testing.
3167 rcutorture.onoff_holdoff= [KNL]
3168 Set time (s) after boot for CPU-hotplug testing.
3170 rcutorture.onoff_interval= [KNL]
3171 Set time (s) between CPU-hotplug operations, or
3172 zero to disable CPU-hotplug testing.
3174 rcutorture.torture_runnable= [BOOT]
3175 Start rcutorture running at boot time.
3177 rcutorture.shuffle_interval= [KNL]
3178 Set task-shuffle interval (s). Shuffling tasks
3179 allows some CPUs to go into dyntick-idle mode
3180 during the rcutorture test.
3182 rcutorture.shutdown_secs= [KNL]
3183 Set time (s) after boot system shutdown. This
3184 is useful for hands-off automated testing.
3186 rcutorture.stall_cpu= [KNL]
3187 Duration of CPU stall (s) to test RCU CPU stall
3188 warnings, zero to disable.
3190 rcutorture.stall_cpu_holdoff= [KNL]
3191 Time to wait (s) after boot before inducing stall.
3193 rcutorture.stat_interval= [KNL]
3194 Time (s) between statistics printk()s.
3196 rcutorture.stutter= [KNL]
3197 Time (s) to stutter testing, for example, specifying
3198 five seconds causes the test to run for five seconds,
3199 wait for five seconds, and so on. This tests RCU's
3200 ability to transition abruptly to and from idle.
3202 rcutorture.test_boost= [KNL]
3203 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3204 "Maybe" means test if the RCU implementation
3205 under test support RCU priority boosting.
3207 rcutorture.test_boost_duration= [KNL]
3208 Duration (s) of each individual boost test.
3210 rcutorture.test_boost_interval= [KNL]
3211 Interval (s) between each boost test.
3213 rcutorture.test_no_idle_hz= [KNL]
3214 Test RCU's dyntick-idle handling. See also the
3215 rcutorture.shuffle_interval parameter.
3217 rcutorture.torture_type= [KNL]
3218 Specify the RCU implementation to test.
3220 rcutorture.verbose= [KNL]
3221 Enable additional printk() statements.
3223 rcupdate.rcu_expedited= [KNL]
3224 Use expedited grace-period primitives, for
3225 example, synchronize_rcu_expedited() instead
3226 of synchronize_rcu(). This reduces latency,
3227 but can increase CPU utilization, degrade
3228 real-time latency, and degrade energy efficiency.
3230 rcupdate.rcu_cpu_stall_suppress= [KNL]
3231 Suppress RCU CPU stall warning messages.
3233 rcupdate.rcu_cpu_stall_timeout= [KNL]
3234 Set timeout for RCU CPU stall warning messages.
3236 rcupdate.rcu_task_stall_timeout= [KNL]
3237 Set timeout in jiffies for RCU task stall warning
3238 messages. Disable with a value less than or equal
3241 rcupdate.rcu_self_test= [KNL]
3242 Run the RCU early boot self tests
3244 rcupdate.rcu_self_test_bh= [KNL]
3245 Run the RCU bh early boot self tests
3247 rcupdate.rcu_self_test_sched= [KNL]
3248 Run the RCU sched early boot self tests
3252 Run specified binary instead of /init from the ramdisk,
3253 used for early userspace startup. See initrd.
3256 Format (x86 or x86_64):
3257 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3259 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3261 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3262 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3263 reboot_force is either force or not specified,
3264 reboot_cpu is s[mp]#### with #### being the processor
3265 to be used for rebooting.
3268 [KNL, SMP] Set scheduler's default relax_domain_level.
3269 See Documentation/cgroups/cpusets.txt.
3271 relative_sleep_states=
3272 [SUSPEND] Use sleep state labeling where the deepest
3273 state available other than hibernation is always "mem".
3274 Format: { "0" | "1" }
3275 0 -- Traditional sleep state labels.
3276 1 -- Relative sleep state labels.
3278 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3280 reservetop= [X86-32]
3282 Reserves a hole at the top of the kernel virtual
3287 Set the amount of memory to reserve for BIOS at
3288 the bottom of the address space.
3290 reset_devices [KNL] Force drivers to reset the underlying device
3291 during initialization.
3294 Specify the partition device for software suspend
3296 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3298 resume_offset= [SWSUSP]
3299 Specify the offset from the beginning of the partition
3300 given by "resume=" at which the swap header is located,
3301 in <PAGE_SIZE> units (needed only for swap files).
3302 See Documentation/power/swsusp-and-swap-files.txt
3304 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3305 read the resume files
3307 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3308 Useful for devices that are detected asynchronously
3309 (e.g. USB and MMC devices).
3311 hibernate= [HIBERNATION]
3312 noresume Don't check if there's a hibernation image
3313 present during boot.
3314 nocompress Don't compress/decompress hibernation images.
3315 no Disable hibernation and resume.
3317 retain_initrd [RAM] Keep initrd memory after extraction
3319 rfkill.default_state=
3320 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3321 etc. communication is blocked by default.
3324 rfkill.master_switch_mode=
3325 0 The "airplane mode" button does nothing.
3326 1 The "airplane mode" button toggles between everything
3327 blocked and the previous configuration.
3328 2 The "airplane mode" button toggles between everything
3329 blocked and everything unblocked.
3331 rhash_entries= [KNL,NET]
3332 Set number of hash buckets for route cache
3334 ro [KNL] Mount root device read-only on boot
3336 root= [KNL] Root filesystem
3337 See name_to_dev_t comment in init/do_mounts.c.
3339 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3340 mount the root filesystem
3342 rootflags= [KNL] Set root filesystem mount option string
3344 rootfstype= [KNL] Set root filesystem type
3346 rootwait [KNL] Wait (indefinitely) for root device to show up.
3347 Useful for devices that are detected asynchronously
3348 (e.g. USB and MMC devices).
3350 rproc_mem=nn[KMG][@address]
3351 [KNL,ARM,CMA] Remoteproc physical memory block.
3352 Memory area to be used by remote processor image,
3355 rw [KNL] Mount root device read-write on boot
3357 S [KNL] Run init in single mode
3359 s390_iommu= [HW,S390]
3360 Set s390 IOTLB flushing mode
3362 With strict flushing every unmap operation will result in
3363 an IOTLB flush. Default is lazy flushing before reuse,
3367 See drivers/net/irda/sa1100_ir.c.
3369 sbni= [NET] Granch SBNI12 leased line adapter
3371 sched_debug [KNL] Enables verbose scheduler debug messages.
3373 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3374 xtime_lock contention on larger systems, and/or RCU lock
3375 contention on all systems with CONFIG_MAXSMP set.
3376 Format: { "0" | "1" }
3377 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3379 Note: increases power consumption, thus should only be
3380 enabled if running jitter sensitive (HPC/RT) workloads.
3382 security= [SECURITY] Choose a security module to enable at boot.
3383 If this boot parameter is not specified, only the first
3384 security module asking for security registration will be
3385 loaded. An invalid security module name will be treated
3386 as if no module has been chosen.
3388 selinux= [SELINUX] Disable or enable SELinux at boot time.
3389 Format: { "0" | "1" }
3390 See security/selinux/Kconfig help text.
3393 Default value is set via kernel config option.
3394 If enabled at boot time, /selinux/disable can be used
3395 later to disable prior to initial policy load.
3397 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3398 Format: { "0" | "1" }
3399 See security/apparmor/Kconfig help text
3402 Default value is set via kernel config option.
3404 serialnumber [BUGS=X86-32]
3407 Maximal number of shapers.
3409 show_msr= [x86] show boot-time MSR settings
3410 Format: { <integer> }
3411 Show boot-time (BIOS-initialized) MSR settings.
3412 The parameter means the number of CPUs to show,
3413 for example 1 means boot CPU only.
3421 Disable merging of slabs with similar size. May be
3422 necessary if there is some reason to distinguish
3423 allocs to different slabs. Debug options disable
3424 merging on their own.
3425 For more information see Documentation/vm/slub.txt.
3427 slab_max_order= [MM, SLAB]
3428 Determines the maximum allowed order for slabs.
3429 A high setting may cause OOMs due to memory
3430 fragmentation. Defaults to 1 for systems with
3431 more than 32MB of RAM, 0 otherwise.
3433 slub_debug[=options[,slabs]] [MM, SLUB]
3434 Enabling slub_debug allows one to determine the
3435 culprit if slab objects become corrupted. Enabling
3436 slub_debug can create guard zones around objects and
3437 may poison objects when not in use. Also tracks the
3438 last alloc / free. For more information see
3439 Documentation/vm/slub.txt.
3441 slub_max_order= [MM, SLUB]
3442 Determines the maximum allowed order for slabs.
3443 A high setting may cause OOMs due to memory
3444 fragmentation. For more information see
3445 Documentation/vm/slub.txt.
3447 slub_min_objects= [MM, SLUB]
3448 The minimum number of objects per slab. SLUB will
3449 increase the slab order up to slub_max_order to
3450 generate a sufficiently large slab able to contain
3451 the number of objects indicated. The higher the number
3452 of objects the smaller the overhead of tracking slabs
3453 and the less frequently locks need to be acquired.
3454 For more information see Documentation/vm/slub.txt.
3456 slub_min_order= [MM, SLUB]
3457 Determines the minimum page order for slabs. Must be
3458 lower than slub_max_order.
3459 For more information see Documentation/vm/slub.txt.
3461 slub_nomerge [MM, SLUB]
3462 Same with slab_nomerge. This is supported for legacy.
3463 See slab_nomerge for more information.
3466 Format: <io1>[,<io2>[,...,<io8>]]
3468 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3469 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3470 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3471 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3472 smsc-ircc2.ircc_irq= [HW] IRQ line
3473 smsc-ircc2.ircc_dma= [HW] DMA channel
3474 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3475 0: Toshiba Satellite 1800 (GP data pin select)
3476 1: Fast pin select (default)
3480 [KNL] Should the soft-lockup detector generate panics.
3483 softlockup_all_cpu_backtrace=
3484 [KNL] Should the soft-lockup detector generate
3485 backtraces on all cpus.
3488 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3489 See Documentation/laptops/sonypi.txt
3491 spia_io_base= [HW,MTD]
3497 Enabled the stack tracer on boot up.
3499 stacktrace_filter=[function-list]
3500 [FTRACE] Limit the functions that the stack tracer
3501 will trace at boot up. function-list is a comma separated
3502 list of functions. This list can be changed at run
3503 time by the stack_trace_filter file in the debugfs
3504 tracing directory. Note, this enables stack tracing
3505 and the stacktrace above is not needed.
3509 Set the STI (builtin display/keyboard on the HP-PARISC
3510 machines) console (graphic card) which should be used
3511 as the initial boot-console.
3512 See also comment in drivers/video/console/sticore.c.
3515 See comment in drivers/video/console/sticore.c.
3518 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3520 sunrpc.min_resvport=
3521 sunrpc.max_resvport=
3523 SunRPC servers often require that client requests
3524 originate from a privileged port (i.e. a port in the
3525 range 0 < portnr < 1024).
3526 An administrator who wishes to reserve some of these
3527 ports for other uses may adjust the range that the
3528 kernel's sunrpc client considers to be privileged
3529 using these two parameters to set the minimum and
3530 maximum port values.
3534 Control how the NFS server code allocates CPUs to
3535 service thread pools. Depending on how many NICs
3536 you have and where their interrupts are bound, this
3537 option will affect which CPUs will do NFS serving.
3538 Note: this parameter cannot be changed while the
3539 NFS server is running.
3541 auto the server chooses an appropriate mode
3542 automatically using heuristics
3543 global a single global pool contains all CPUs
3544 percpu one pool for each CPU
3545 pernode one pool for each NUMA node (equivalent
3546 to global on non-NUMA machines)
3548 sunrpc.tcp_slot_table_entries=
3549 sunrpc.udp_slot_table_entries=
3551 Sets the upper limit on the number of simultaneous
3552 RPC calls that can be sent from the client to a
3553 server. Increasing these values may allow you to
3554 improve throughput, but will also increase the
3555 amount of memory reserved for use by the client.
3557 suspend.pm_test_delay=
3559 Sets the number of seconds to remain in a suspend test
3560 mode before resuming the system (see
3561 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3562 is set. Default value is 5.
3565 [KNL] Enable accounting of swap in memory resource
3566 controller if no parameter or 1 is given or disable
3567 it if 0 is given (See Documentation/cgroups/memory.txt)
3569 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3570 Format: { <int> | force }
3571 <int> -- Number of I/O TLB slabs
3572 force -- force using of bounce buffers even if they
3573 wouldn't be automatically used by the kernel
3577 sysfs.deprecated=0|1 [KNL]
3578 Enable/disable old style sysfs layout for old udev
3579 on older distributions. When this option is enabled
3580 very new udev will not work anymore. When this option
3581 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3582 in older udev will not work anymore.
3583 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3584 the kernel configuration.
3586 sysrq_always_enabled
3588 Ignore sysrq setting - this boot parameter will
3589 neutralize any effect of /proc/sys/kernel/sysrq.
3590 Useful for debugging.
3592 tcpmhash_entries= [KNL,NET]
3593 Set the number of tcp_metrics_hash slots.
3594 Default value is 8192 or 16384 depending on total
3595 ram pages. This is used to specify the TCP metrics
3596 cache size. See Documentation/networking/ip-sysctl.txt
3597 "tcp_no_metrics_save" section for more details.
3601 test_suspend= [SUSPEND][,N]
3602 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3603 standby suspend) or "freeze" (for suspend type freeze)
3604 as the system sleep state during system startup with
3605 the optional capability to repeat N number of times.
3606 The system is woken from this state using a
3607 wakeup-capable RTC alarm.
3609 thash_entries= [KNL,NET]
3610 Set number of hash buckets for TCP connection
3612 thermal.act= [HW,ACPI]
3613 -1: disable all active trip points in all thermal zones
3614 <degrees C>: override all lowest active trip points
3616 thermal.crt= [HW,ACPI]
3617 -1: disable all critical trip points in all thermal zones
3618 <degrees C>: override all critical trip points
3620 thermal.nocrt= [HW,ACPI]
3621 Set to disable actions on ACPI thermal zone
3622 critical and hot trip points.
3624 thermal.off= [HW,ACPI]
3625 1: disable ACPI thermal control
3627 thermal.psv= [HW,ACPI]
3628 -1: disable all passive trip points
3629 <degrees C>: override all passive trip points to this
3632 thermal.tzp= [HW,ACPI]
3633 Specify global default ACPI thermal zone polling rate
3634 <deci-seconds>: poll all this frequency
3635 0: no polling (default)
3638 Force threading of all interrupt handlers except those
3639 marked explicitly IRQF_NO_THREAD.
3642 Enable the Transcendent memory driver if built-in.
3644 tmem.cleancache=0|1 [KNL, XEN]
3645 Default is on (1). Disable the usage of the cleancache
3646 API to send anonymous pages to the hypervisor.
3648 tmem.frontswap=0|1 [KNL, XEN]
3649 Default is on (1). Disable the usage of the frontswap
3650 API to send swap pages to the hypervisor. If disabled
3651 the selfballooning and selfshrinking are force disabled.
3653 tmem.selfballooning=0|1 [KNL, XEN]
3654 Default is on (1). Disable the driving of swap pages
3657 tmem.selfshrinking=0|1 [KNL, XEN]
3658 Default is on (1). Partial swapoff that immediately
3659 transfers pages from Xen hypervisor back to the
3660 kernel based on different criteria.
3664 Specify if the kernel should make use of the cpu
3665 topology information if the hardware supports this.
3666 The scheduler will make use of this information and
3667 e.g. base its process migration decisions on it.
3670 topology_updates= [KNL, PPC, NUMA]
3672 Specify if the kernel should ignore (off)
3673 topology updates sent by the hypervisor to this
3678 tpm_suspend_pcr=[HW,TPM]
3679 Format: integer pcr id
3680 Specify that at suspend time, the tpm driver
3681 should extend the specified pcr with zeros,
3682 as a workaround for some chips which fail to
3683 flush the last written pcr on TPM_SaveState.
3684 This will guarantee that all the other pcrs
3687 trace_buf_size=nn[KMG]
3688 [FTRACE] will set tracing buffer size on each cpu.
3690 trace_event=[event-list]
3691 [FTRACE] Set and start specified trace events in order
3692 to facilitate early boot debugging.
3693 See also Documentation/trace/events.txt
3695 trace_options=[option-list]
3696 [FTRACE] Enable or disable tracer options at boot.
3697 The option-list is a comma delimited list of options
3698 that can be enabled or disabled just as if you were
3699 to echo the option name into
3701 /sys/kernel/debug/tracing/trace_options
3703 For example, to enable stacktrace option (to dump the
3704 stack trace of each event), add to the command line:
3706 trace_options=stacktrace
3708 See also Documentation/trace/ftrace.txt "trace options"
3712 Have the tracepoints sent to printk as well as the
3713 tracing ring buffer. This is useful for early boot up
3714 where the system hangs or reboots and does not give the
3715 option for reading the tracing buffer or performing a
3716 ftrace_dump_on_oops.
3718 To turn off having tracepoints sent to printk,
3719 echo 0 > /proc/sys/kernel/tracepoint_printk
3720 Note, echoing 1 into this file without the
3721 tracepoint_printk kernel cmdline option has no effect.
3725 Having tracepoints sent to printk() and activating high
3726 frequency tracepoints such as irq or sched, can cause
3727 the system to live lock.
3730 [FTRACE] enable this option to disable tracing when a
3731 warning is hit. This turns off "tracing_on". Tracing can
3732 be enabled again by echoing '1' into the "tracing_on"
3733 file located in /sys/kernel/debug/tracing/
3735 This option is useful, as it disables the trace before
3736 the WARNING dump is called, which prevents the trace to
3737 be filled with content caused by the warning output.
3739 This option can also be set at run time via the sysctl
3740 option: kernel/traceoff_on_warning
3742 transparent_hugepage=
3744 Format: [always|madvise|never]
3745 Can be used to control the default behavior of the system
3746 with respect to transparent hugepages.
3747 See Documentation/vm/transhuge.txt for more details.
3749 tsc= Disable clocksource stability checks for TSC.
3751 [x86] reliable: mark tsc clocksource as reliable, this
3752 disables clocksource verification at runtime, as well
3753 as the stability checks done at bootup. Used to enable
3754 high-resolution timer mode on older hardware, and in
3755 virtualized environment.
3756 [x86] noirqtime: Do not use TSC to do irq accounting.
3757 Used to run time disable IRQ_TIME_ACCOUNTING on any
3758 platforms where RDTSC is slow and this accounting
3761 turbografx.map[2|3]= [HW,JOY]
3762 TurboGraFX parallel port interface
3764 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3765 See also Documentation/input/joystick-parport.txt
3767 udbg-immortal [PPC] When debugging early kernel crashes that
3768 happen after console_init() and before a proper
3769 console driver takes over, this boot options might
3770 help "seeing" what's going on.
3772 uhash_entries= [KNL,NET]
3773 Set number of hash buckets for UDP/UDP-Lite connections
3776 [USB] Ignore overcurrent events (default N).
3777 Some badly-designed motherboards generate lots of
3778 bogus events, for ports that aren't wired to
3779 anything. Set this parameter to avoid log spamming.
3780 Note that genuine overcurrent events won't be
3784 [X86] Cause panic on unknown NMI.
3786 usbcore.authorized_default=
3787 [USB] Default USB device authorization:
3788 (default -1 = authorized except for wireless USB,
3789 0 = not authorized, 1 = authorized)
3791 usbcore.autosuspend=
3792 [USB] The autosuspend time delay (in seconds) used
3793 for newly-detected USB devices (default 2). This
3794 is the time required before an idle device will be
3795 autosuspended. Devices for which the delay is set
3796 to a negative value won't be autosuspended at all.
3798 usbcore.usbfs_snoop=
3799 [USB] Set to log all usbfs traffic (default 0 = off).
3801 usbcore.blinkenlights=
3802 [USB] Set to cycle leds on hubs (default 0 = off).
3804 usbcore.old_scheme_first=
3805 [USB] Start with the old device initialization
3806 scheme (default 0 = off).
3808 usbcore.usbfs_memory_mb=
3809 [USB] Memory limit (in MB) for buffers allocated by
3810 usbfs (default = 16, 0 = max = 2047).
3812 usbcore.use_both_schemes=
3813 [USB] Try the other device initialization scheme
3814 if the first one fails (default 1 = enabled).
3816 usbcore.initial_descriptor_timeout=
3817 [USB] Specifies timeout for the initial 64-byte
3818 USB_REQ_GET_DESCRIPTOR request in milliseconds
3819 (default 5000 = 5.0 seconds).
3822 [USBHID] The interval which mice are to be polled at.
3824 usb-storage.delay_use=
3825 [UMS] The delay in seconds before a new device is
3826 scanned for Logical Units (default 1).
3829 [UMS] A list of quirks entries to supplement or
3830 override the built-in unusual_devs list. List
3831 entries are separated by commas. Each entry has
3832 the form VID:PID:Flags where VID and PID are Vendor
3833 and Product ID values (4-digit hex numbers) and
3834 Flags is a set of characters, each corresponding
3835 to a common usb-storage quirk flag as follows:
3836 a = SANE_SENSE (collect more than 18 bytes
3838 b = BAD_SENSE (don't collect more than 18
3839 bytes of sense data);
3840 c = FIX_CAPACITY (decrease the reported
3841 device capacity by one sector);
3842 d = NO_READ_DISC_INFO (don't use
3843 READ_DISC_INFO command);
3844 e = NO_READ_CAPACITY_16 (don't use
3845 READ_CAPACITY_16 command);
3846 f = NO_REPORT_OPCODES (don't use report opcodes
3848 g = MAX_SECTORS_240 (don't transfer more than
3849 240 sectors at a time, uas only);
3850 h = CAPACITY_HEURISTICS (decrease the
3851 reported device capacity by one
3852 sector if the number is odd);
3853 i = IGNORE_DEVICE (don't bind to this
3855 l = NOT_LOCKABLE (don't try to lock and
3856 unlock ejectable media);
3857 m = MAX_SECTORS_64 (don't transfer more
3858 than 64 sectors = 32 KB at a time);
3859 n = INITIAL_READ10 (force a retry of the
3860 initial READ(10) command);
3861 o = CAPACITY_OK (accept the capacity
3862 reported by the device);
3863 p = WRITE_CACHE (the device cache is ON
3865 r = IGNORE_RESIDUE (the device reports
3866 bogus residue values);
3867 s = SINGLE_LUN (the device has only one
3869 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3870 commands, uas only);
3871 u = IGNORE_UAS (don't bind to the uas driver);
3872 w = NO_WP_DETECT (don't test whether the
3873 medium is write-protected).
3874 Example: quirks=0419:aaf5:rl,0421:0433:rc
3876 user_debug= [KNL,ARM]
3878 See arch/arm/Kconfig.debug help text.
3879 1 - undefined instruction events
3881 4 - invalid data aborts
3884 Example: user_debug=31
3887 [X86] Flags controlling user PTE allocations.
3889 nohigh = do not allocate PTE pages in
3890 HIGHMEM regardless of setting
3894 On X86_32, this is an alias for vdso32=. Otherwise:
3896 vdso=1: enable VDSO (the default)
3897 vdso=0: disable VDSO mapping
3899 vdso32= [X86] Control the 32-bit vDSO
3900 vdso32=1: enable 32-bit VDSO
3901 vdso32=0 or vdso32=2: disable 32-bit VDSO
3903 See the help text for CONFIG_COMPAT_VDSO for more
3904 details. If CONFIG_COMPAT_VDSO is set, the default is
3905 vdso32=0; otherwise, the default is vdso32=1.
3907 For compatibility with older kernels, vdso32=2 is an
3910 Try vdso32=0 if you encounter an error that says:
3911 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3914 vector=percpu: enable percpu vector domain
3916 video= [FB] Frame buffer configuration
3917 See Documentation/fb/modedb.txt.
3919 video.brightness_switch_enabled= [0,1]
3920 If set to 1, on receiving an ACPI notify event
3921 generated by hotkey, video driver will adjust brightness
3922 level and then send out the event to user space through
3923 the allocated input device; If set to 0, video driver
3924 will only send out the event without touching backlight
3929 [VMMIO] Memory mapped virtio (platform) device.
3931 <size>@<baseaddr>:<irq>[:<id>]
3933 <size> := size (can use standard suffixes
3935 <baseaddr> := physical base address
3936 <irq> := interrupt number (as passed to
3938 <id> := (optional) platform device id
3940 virtio_mmio.device=1K@0x100b0000:48:7
3942 Can be used multiple times for multiple devices.
3944 vga= [BOOT,X86-32] Select a particular video mode
3945 See Documentation/x86/boot.txt and
3946 Documentation/svga.txt.
3947 Use vga=ask for menu.
3948 This is actually a boot loader parameter; the value is
3949 passed to the kernel using a special protocol.
3951 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3952 size of <nn>. This can be used to increase the
3953 minimum size (128MB on x86). It can also be used to
3954 decrease the size and leave more room for directly
3957 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3960 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3963 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3967 Controls the behavior of vsyscalls (i.e. calls to
3968 fixed addresses of 0xffffffffff600x00 from legacy
3969 code). Most statically-linked binaries and older
3970 versions of glibc use these calls. Because these
3971 functions are at fixed addresses, they make nice
3972 targets for exploits that can control RIP.
3974 emulate [default] Vsyscalls turn into traps and are
3975 emulated reasonably safely.
3977 native Vsyscalls are native syscall instructions.
3978 This is a little bit faster than trapping
3979 and makes a few dynamic recompilers work
3980 better than they would in emulation mode.
3981 It also makes exploits much easier to write.
3983 none Vsyscalls don't work at all. This makes
3984 them quite hard to use for exploits but
3985 might break your system.
3987 vt.color= [VT] Default text color.
3988 Format: 0xYX, X = foreground, Y = background.
3989 Default: 0x07 = light gray on black.
3991 vt.cur_default= [VT] Default cursor shape.
3992 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3993 the parameters of the <Esc>[?A;B;Cc escape sequence;
3994 see VGA-softcursor.txt. Default: 2 = underline.
3996 vt.default_blu= [VT]
3997 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3998 Change the default blue palette of the console.
3999 This is a 16-member array composed of values
4002 vt.default_grn= [VT]
4003 Format: <green0>,<green1>,<green2>,...,<green15>
4004 Change the default green palette of the console.
4005 This is a 16-member array composed of values
4008 vt.default_red= [VT]
4009 Format: <red0>,<red1>,<red2>,...,<red15>
4010 Change the default red palette of the console.
4011 This is a 16-member array composed of values
4017 Set system-wide default UTF-8 mode for all tty's.
4018 Default is 1, i.e. UTF-8 mode is enabled for all
4019 newly opened terminals.
4021 vt.global_cursor_default=
4024 Set system-wide default for whether a cursor
4025 is shown on new VTs. Default is -1,
4026 i.e. cursors will be created by default unless
4027 overridden by individual drivers. 0 will hide
4028 cursors, 1 will display them.
4030 vt.italic= [VT] Default color for italic text; 0-15.
4033 vt.underline= [VT] Default color for underlined text; 0-15.
4036 watchdog timers [HW,WDT] For information on watchdog timers,
4037 see Documentation/watchdog/watchdog-parameters.txt
4038 or other driver-specific files in the
4039 Documentation/watchdog/ directory.
4041 workqueue.disable_numa
4042 By default, all work items queued to unbound
4043 workqueues are affine to the NUMA nodes they're
4044 issued on, which results in better behavior in
4045 general. If NUMA affinity needs to be disabled for
4046 whatever reason, this option can be used. Note
4047 that this also can be controlled per-workqueue for
4048 workqueues visible under /sys/bus/workqueue/.
4050 workqueue.power_efficient
4051 Per-cpu workqueues are generally preferred because
4052 they show better performance thanks to cache
4053 locality; unfortunately, per-cpu workqueues tend to
4054 be more power hungry than unbound workqueues.
4056 Enabling this makes the per-cpu workqueues which
4057 were observed to contribute significantly to power
4058 consumption unbound, leading to measurably lower
4059 power usage at the cost of small performance
4062 The default value of this parameter is determined by
4063 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4065 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4066 default x2apic cluster mode on platforms
4069 x86_intel_mid_timer= [X86-32,APBT]
4070 Choose timer option for x86 Intel MID platform.
4071 Two valid options are apbt timer only and lapic timer
4072 plus one apbt timer for broadcast timer.
4073 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4075 xen_emul_unplug= [HW,X86,XEN]
4076 Unplug Xen emulated devices
4077 Format: [unplug0,][unplug1]
4078 ide-disks -- unplug primary master IDE devices
4079 aux-ide-disks -- unplug non-primary-master IDE devices
4080 nics -- unplug network devices
4081 all -- unplug all emulated devices (NICs and IDE disks)
4082 unnecessary -- unplugging emulated devices is
4083 unnecessary even if the host did not respond to
4085 never -- do not unplug even if version check succeeds
4087 xen_nopvspin [X86,XEN]
4088 Disables the ticketlock slowpath using Xen PV
4092 Disables the PV optimizations forcing the HVM guest to
4093 run as generic HVM guest with no PV drivers.
4095 xirc2ps_cs= [NET,PCMCIA]
4097 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4099 ______________________________________________________________________
4103 Add more DRM drivers.
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