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.
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
179 See also Documentation/power/runtime_pm.txt, pci=noacpi
181 acpi_rsdp= [ACPI,EFI,KEXEC]
182 Pass the RSDP address to the kernel, mostly used
183 on machines running EFI runtime service to boot the
184 second kernel for kdump.
186 acpi_apic_instance= [ACPI, IOAPIC]
188 2: use 2nd APIC table, if available
189 1,0: use 1st APIC table
192 acpi_backlight= [HW,ACPI]
193 acpi_backlight=vendor
195 If set to vendor, prefer vendor specific driver
196 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
197 of the ACPI video.ko driver.
199 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
200 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
202 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
203 debug output. Bits in debug_layer correspond to a
204 _COMPONENT in an ACPI source file, e.g.,
205 #define _COMPONENT ACPI_PCI_COMPONENT
206 Bits in debug_level correspond to a level in
207 ACPI_DEBUG_PRINT statements, e.g.,
208 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
209 The debug_level mask defaults to "info". See
210 Documentation/acpi/debug.txt for more information about
211 debug layers and levels.
213 Enable processor driver info messages:
214 acpi.debug_layer=0x20000000
215 Enable PCI/PCI interrupt routing info messages:
216 acpi.debug_layer=0x400000
217 Enable AML "Debug" output, i.e., stores to the Debug
218 object while interpreting AML:
219 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
220 Enable all messages related to ACPI hardware:
221 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
223 Some values produce so much output that the system is
224 unusable. The "log_buf_len" parameter may be useful
225 if you need to capture more output.
227 acpi_force_table_verification [HW,ACPI]
228 Enable table checksum verification during early stage.
229 By default, this is disabled due to x86 early mapping
232 acpi_irq_balance [HW,ACPI]
233 ACPI will balance active IRQs
236 acpi_irq_nobalance [HW,ACPI]
237 ACPI will not move active IRQs (default)
240 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
241 Format: <irq>,<irq>...
243 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
245 Format: <irq>,<irq>...
247 acpi_no_auto_serialize [HW,ACPI]
248 Disable auto-serialization of AML methods
249 AML control methods that contain the opcodes to create
250 named objects will be marked as "Serialized" by the
251 auto-serialization feature.
252 This feature is enabled by default.
253 This option allows to turn off the feature.
255 acpi_no_static_ssdt [HW,ACPI]
256 Disable installation of static SSDTs at early boot time
257 By default, SSDTs contained in the RSDT/XSDT will be
258 installed automatically and they will appear under
259 /sys/firmware/acpi/tables.
260 This option turns off this feature.
261 Note that specifying this option does not affect
262 dynamic table installation which will install SSDT
263 tables to /sys/firmware/acpi/tables/dynamic.
265 acpica_no_return_repair [HW, ACPI]
266 Disable AML predefined validation mechanism
267 This mechanism can repair the evaluation result to make
268 the return objects more ACPI specification compliant.
269 This option is useful for developers to identify the
270 root cause of an AML interpreter issue when the issue
271 has something to do with the repair mechanism.
273 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
274 Format: To spoof as Windows 98: ="Microsoft Windows"
276 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
277 acpi_osi="string1" # add string1
278 acpi_osi="!string2" # remove string2
279 acpi_osi=!* # remove all strings
280 acpi_osi=! # disable all built-in OS vendor
282 acpi_osi= # disable all strings
284 'acpi_osi=!' can be used in combination with single or
285 multiple 'acpi_osi="string1"' to support specific OS
286 vendor string(s). Note that such command can only
287 affect the default state of the OS vendor strings, thus
288 it cannot affect the default state of the feature group
289 strings and the current state of the OS vendor strings,
290 specifying it multiple times through kernel command line
291 is meaningless. This command is useful when one do not
292 care about the state of the feature group strings which
293 should be controlled by the OSPM.
295 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
296 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
297 can make '_OSI("Windows 2000")' TRUE.
299 'acpi_osi=' cannot be used in combination with other
300 'acpi_osi=' command lines, the _OSI method will not
301 exist in the ACPI namespace. NOTE that such command can
302 only affect the _OSI support state, thus specifying it
303 multiple times through kernel command line is also
306 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
309 'acpi_osi=!*' can be used in combination with single or
310 multiple 'acpi_osi="string1"' to support specific
311 string(s). Note that such command can affect the
312 current state of both the OS vendor strings and the
313 feature group strings, thus specifying it multiple times
314 through kernel command line is meaningful. But it may
315 still not able to affect the final state of a string if
316 there are quirks related to this string. This command
317 is useful when one want to control the state of the
318 feature group strings to debug BIOS issues related to
321 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
322 '_OSI("Module Device")' FALSE.
323 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
324 '_OSI("Module Device")' TRUE.
325 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
327 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
329 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
330 they all will make '_OSI("Windows 2000")' TRUE.
333 Override the pmtimer bug detection: force the kernel
334 to assume that this machine's pmtimer latches its value
335 and always returns good values.
337 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
338 Format: { level | edge | high | low }
340 acpi_skip_timer_override [HW,ACPI]
341 Recognize and ignore IRQ0/pin2 Interrupt Override.
342 For broken nForce2 BIOS resulting in XT-PIC timer.
344 acpi_sleep= [HW,ACPI] Sleep options
345 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
346 old_ordering, nonvs, sci_force_enable }
347 See Documentation/power/video.txt for information on
349 s3_beep is for debugging; it makes the PC's speaker beep
350 as soon as the kernel's real-mode entry point is called.
351 s4_nohwsig prevents ACPI hardware signature from being
352 used during resume from hibernation.
353 old_ordering causes the ACPI 1.0 ordering of the _PTS
354 control method, with respect to putting devices into
355 low power states, to be enforced (the ACPI 2.0 ordering
356 of _PTS is used by default).
357 nonvs prevents the kernel from saving/restoring the
358 ACPI NVS memory during suspend/hibernation and resume.
359 sci_force_enable causes the kernel to set SCI_EN directly
360 on resume from S1/S3 (which is against the ACPI spec,
361 but some broken systems don't work without it).
363 acpi_use_timer_override [HW,ACPI]
364 Use timer override. For some broken Nvidia NF5 boards
365 that require a timer override, but don't have HPET
367 acpi_enforce_resources= [ACPI]
368 { strict | lax | no }
369 Check for resource conflicts between native drivers
370 and ACPI OperationRegions (SystemIO and SystemMemory
371 only). IO ports and memory declared in ACPI might be
372 used by the ACPI subsystem in arbitrary AML code and
373 can interfere with legacy drivers.
374 strict (default): access to resources claimed by ACPI
375 is denied; legacy drivers trying to access reserved
376 resources will fail to bind to device using them.
377 lax: access to resources claimed by ACPI is allowed;
378 legacy drivers trying to access reserved resources
379 will bind successfully but a warning message is logged.
380 no: ACPI OperationRegions are not marked as reserved,
381 no further checks are performed.
383 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
386 add_efi_memmap [EFI; X86] Include EFI memory map in
387 kernel's map of available physical RAM.
390 { off | try_unsupported }
391 off: disable AGP support
392 try_unsupported: try to drive unsupported chipsets
393 (may crash computer or cause data corruption)
396 See Documentation/sound/alsa/alsa-parameters.txt
399 Allow the default userspace alignment fault handler
400 behaviour to be specified. Bit 0 enables warnings,
401 bit 1 enables fixups, and bit 2 sends a segfault.
403 align_va_addr= [X86-64]
404 Align virtual addresses by clearing slice [14:12] when
405 allocating a VMA at process creation time. This option
406 gives you up to 3% performance improvement on AMD F15h
407 machines (where it is enabled by default) for a
408 CPU-intensive style benchmark, and it can vary highly in
409 a microbenchmark depending on workload and compiler.
411 32: only for 32-bit processes
412 64: only for 64-bit processes
413 on: enable for both 32- and 64-bit processes
414 off: disable for both 32- and 64-bit processes
416 alloc_snapshot [FTRACE]
417 Allocate the ftrace snapshot buffer on boot up when the
418 main buffer is allocated. This is handy if debugging
419 and you need to use tracing_snapshot() on boot up, and
420 do not want to use tracing_snapshot_alloc() as it needs
421 to be done where GFP_KERNEL allocations are allowed.
423 amd_iommu= [HW,X86-64]
424 Pass parameters to the AMD IOMMU driver in the system.
426 fullflush - enable flushing of IO/TLB entries when
427 they are unmapped. Otherwise they are
428 flushed before they will be reused, which
430 off - do not initialize any AMD IOMMU found in
432 force_isolation - Force device isolation for all
433 devices. The IOMMU driver is not
434 allowed anymore to lift isolation
435 requirements as needed. This option
436 does not override iommu=pt
438 amd_iommu_dump= [HW,X86-64]
439 Enable AMD IOMMU driver option to dump the ACPI table
440 for AMD IOMMU. With this option enabled, AMD IOMMU
441 driver will print ACPI tables for AMD IOMMU during
442 IOMMU initialization.
444 amijoy.map= [HW,JOY] Amiga joystick support
445 Map of devices attached to JOY0DAT and JOY1DAT
447 See also Documentation/input/joystick.txt
449 analog.map= [HW,JOY] Analog joystick and gamepad support
450 Specifies type or capabilities of an analog joystick
451 connected to one of 16 gameports
452 Format: <type1>,<type2>,..<type16>
455 Power management functions (SPARCstation-4/5 + deriv.)
457 Disable APC CPU standby support. SPARCstation-Fox does
458 not play well with APC CPU idle - disable it if you have
459 APC and your system crashes randomly.
461 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
462 Change the output verbosity whilst booting
463 Format: { quiet (default) | verbose | debug }
464 Change the amount of debugging information output
465 when initialising the APIC and IO-APIC components.
468 See Documentation/networking/ipv6.txt.
470 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
471 Limit apic dumping. The parameter defines the maximal
472 number of local apics being dumped. Also it is possible
473 to set it to "all" by meaning -- no limit here.
474 Format: { 1 (default) | 2 | ... | all }.
475 The parameter valid if only apic=debug or
476 apic=verbose is specified.
477 Example: apic=debug show_lapic=all
479 apm= [APM] Advanced Power Management
480 See header of arch/x86/kernel/apm_32.c.
482 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
483 Format: <io>,<irq>,<nodeID>
487 atarimouse= [HW,MOUSE] Atari Mouse
489 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
490 EzKey and similar keyboards
492 atkbd.reset= [HW] Reset keyboard during initialization
494 atkbd.set= [HW] Select keyboard code set
495 Format: <int> (2 = AT (default), 3 = PS/2)
497 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
500 atkbd.softraw= [HW] Choose between synthetic and real raw mode
501 Format: <bool> (0 = real, 1 = synthetic (default))
503 atkbd.softrepeat= [HW]
504 Use software keyboard repeat
506 audit= [KNL] Enable the audit sub-system
507 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
508 0 - kernel audit is disabled and can not be enabled
509 until the next reboot
510 unset - kernel audit is initialized but disabled and
511 will be fully enabled by the userspace auditd.
512 1 - kernel audit is initialized and partially enabled,
513 storing at most audit_backlog_limit messages in
514 RAM until it is fully enabled by the userspace
518 audit_backlog_limit= [KNL] Set the audit queue size limit.
519 Format: <int> (must be >=0)
522 baycom_epp= [HW,AX25]
525 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
527 See header of drivers/net/hamradio/baycom_par.c.
529 baycom_ser_fdx= [HW,AX25]
530 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
531 Format: <io>,<irq>,<mode>[,<baud>]
532 See header of drivers/net/hamradio/baycom_ser_fdx.c.
534 baycom_ser_hdx= [HW,AX25]
535 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
536 Format: <io>,<irq>,<mode>
537 See header of drivers/net/hamradio/baycom_ser_hdx.c.
539 blkdevparts= Manual partition parsing of block device(s) for
540 embedded devices based on command line input.
541 See Documentation/block/cmdline-partition.txt
543 boot_delay= Milliseconds to delay each printk during boot.
544 Values larger than 10 seconds (10000) are changed to
548 bootmem_debug [KNL] Enable bootmem allocator debug messages.
550 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
551 bttv.radio= Most important insmod options are available as
553 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
556 bulk_remove=off [PPC] This parameter disables the use of the pSeries
557 firmware feature for flushing multiple hpte entries
560 c101= [NET] Moxa C101 synchronous serial card
562 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
563 Sometimes CPU hardware bugs make them report the cache
564 size incorrectly. The kernel will attempt work arounds
565 to fix known problems, but for some CPUs it is not
566 possible to determine what the correct size should be.
567 This option provides an override for these situations.
569 ca_keys= [KEYS] This parameter identifies a specific key(s) on
570 the system trusted keyring to be used for certificate
572 format: { id:<keyid> | builtin }
574 cca= [MIPS] Override the kernel pages' cache coherency
575 algorithm. Accepted values range from 0 to 7
576 inclusive. See arch/mips/include/asm/pgtable-bits.h
577 for platform specific values (SB1, Loongson3 and
580 ccw_timeout_log [S390]
581 See Documentation/s390/CommonIO for details.
583 cgroup_disable= [KNL] Disable a particular controller
584 Format: {name of the controller(s) to disable}
585 The effects of cgroup_disable=foo are:
586 - foo isn't auto-mounted if you mount all cgroups in
588 - foo isn't visible as an individually mountable
590 {Currently only "memory" controller deal with this and
591 cut the overhead, others just disable the usage. So
592 only cgroup_disable=memory is actually worthy}
594 checkreqprot [SELINUX] Set initial checkreqprot flag value.
595 Format: { "0" | "1" }
596 See security/selinux/Kconfig help text.
597 0 -- check protection applied by kernel (includes
598 any implied execute protection).
599 1 -- check protection requested by application.
600 Default value is set via a kernel config option.
601 Value can be changed at runtime via
602 /selinux/checkreqprot.
605 See Documentation/s390/CommonIO for details.
608 Prevents the clock framework from automatically gating
609 clocks that have not been explicitly enabled by a Linux
610 device driver but are enabled in hardware at reset or
611 by the bootloader/firmware. Note that this does not
612 force such clocks to be always-on nor does it reserve
613 those clocks in any way. This parameter is useful for
614 debug and development, but should not be needed on a
615 platform with proper driver support. For more
616 information, see Documentation/clk.txt.
618 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
620 Forces specified clocksource (if available) to be used
621 when calculating gettimeofday(). If specified
622 clocksource is not available, it defaults to PIT.
623 Format: { pit | tsc | cyclone | pmtmr }
625 clocksource= Override the default clocksource
627 Override the default clocksource and use the clocksource
628 with the name specified.
629 Some clocksource names to choose from, depending on
631 [all] jiffies (this is the base, fallback clocksource)
633 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
634 pxa_timer,timer3,32k_counter,timer0_1
636 [X86-32] pit,hpet,tsc;
637 scx200_hrt on Geode; cyclone on IBM x440
645 clearcpuid=BITNUM [X86]
646 Disable CPUID feature X for the kernel. See
647 arch/x86/include/asm/cpufeature.h for the valid bit
648 numbers. Note the Linux specific bits are not necessarily
649 stable over kernel options, but the vendor specific
651 Also note that user programs calling CPUID directly
652 or using the feature without checking anything
653 will still see it. This just prevents it from
654 being used by the kernel or shown in /proc/cpuinfo.
655 Also note the kernel might malfunction if you disable
658 cma=nn[MG]@[start[MG][-end[MG]]]
660 Sets the size of kernel global memory area for
661 contiguous memory allocations and optionally the
662 placement constraint by the physical address range of
663 memory allocations. A value of 0 disables CMA
664 altogether. For more information, see
665 include/linux/dma-contiguous.h
667 cmo_free_hint= [PPC] Format: { yes | no }
668 Specify whether pages are marked as being inactive
669 when they are freed. This is used in CMO environments
670 to determine OS memory pressure for page stealing by
674 coherent_pool=nn[KMG] [ARM,KNL]
675 Sets the size of memory pool for coherent, atomic dma
676 allocations, by default set to 256K.
678 code_bytes [X86] How many bytes of object code to print
683 com20020= [HW,NET] ARCnet - COM20020 chipset
685 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
687 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
691 ARCnet - COM90xx chipset (memory-mapped buffers)
692 Format: <io>[,<irq>[,<memstart>]]
694 condev= [HW,S390] console device
697 console= [KNL] Output console device and options.
699 tty<n> Use the virtual console device <n>.
703 Use the specified serial port. The options are of
704 the form "bbbbpnf", where "bbbb" is the baud rate,
705 "p" is parity ("n", "o", or "e"), "n" is number of
706 bits, and "f" is flow control ("r" for RTS or
707 omit it). Default is "9600n8".
709 See Documentation/serial-console.txt for more
711 Documentation/networking/netconsole.txt for an
714 uart[8250],io,<addr>[,options]
715 uart[8250],mmio,<addr>[,options]
716 Start an early, polled-mode console on the 8250/16550
717 UART at the specified I/O port or MMIO address,
718 switching to the matching ttyS device later. The
719 options are the same as for ttyS, above.
720 hvc<n> Use the hypervisor console device <n>. This is for
721 both Xen and PowerPC hypervisors.
723 If the device connected to the port is not a TTY but a braille
724 device, prepend "brl," before the device type, for instance
726 For now, only VisioBraille is supported.
728 consoleblank= [KNL] The console blank (screen saver) timeout in
729 seconds. Defaults to 10*60 = 10mins. A value of 0
730 disables the blank timer.
733 [KNL] Change the default value for
734 /proc/<pid>/coredump_filter.
735 See also Documentation/filesystems/proc.txt.
737 cpuidle.off=1 [CPU_IDLE]
738 disable the cpuidle sub-system
740 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
742 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
744 crashkernel=size[KMG][@offset[KMG]]
745 [KNL] Using kexec, Linux can switch to a 'crash kernel'
746 upon panic. This parameter reserves the physical
747 memory region [offset, offset + size] for that kernel
748 image. If '@offset' is omitted, then a suitable offset
749 is selected automatically. Check
750 Documentation/kdump/kdump.txt for further details.
752 crashkernel=range1:size1[,range2:size2,...][@offset]
753 [KNL] Same as above, but depends on the memory
754 in the running system. The syntax of range is
755 start-[end] where start and end are both
756 a memory unit (amount[KMG]). See also
757 Documentation/kdump/kdump.txt for an example.
759 crashkernel=size[KMG],high
760 [KNL, x86_64] range could be above 4G. Allow kernel
761 to allocate physical memory region from top, so could
762 be above 4G if system have more than 4G ram installed.
763 Otherwise memory region will be allocated below 4G, if
765 It will be ignored if crashkernel=X is specified.
766 crashkernel=size[KMG],low
767 [KNL, x86_64] range under 4G. When crashkernel=X,high
768 is passed, kernel could allocate physical memory region
769 above 4G, that cause second kernel crash on system
770 that require some amount of low memory, e.g. swiotlb
771 requires at least 64M+32K low memory. Kernel would
772 try to allocate 72M below 4G automatically.
773 This one let user to specify own low range under 4G
774 for second kernel instead.
775 0: to disable low allocation.
776 It will be ignored when crashkernel=X,high is not used
777 or memory reserved is below 4G.
782 cs89x0_media= [HW,NET]
783 Format: { rj45 | aui | bnc }
786 See header of drivers/s390/block/dasd_devmap.c.
788 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
789 (one device per port)
790 Format: <port#>,<type>
791 See also Documentation/input/joystick-parport.txt
793 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
794 time. See Documentation/dynamic-debug-howto.txt for
795 details. Deprecated, see dyndbg.
797 debug [KNL] Enable kernel debugging (events log level).
800 [KNL] verbose self-tests
802 Print debugging info while doing the locking API
804 We default to 0 (no extra messages), setting it to
805 1 will print _a lot_ more information - normally
806 only useful to kernel developers.
808 debug_objects [KNL] Enable object debugging
811 [KNL] Disable object debugging
813 debug_guardpage_minorder=
814 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
815 parameter allows control of the order of pages that will
816 be intentionally kept free (and hence protected) by the
817 buddy allocator. Bigger value increase the probability
818 of catching random memory corruption, but reduce the
819 amount of memory for normal system use. The maximum
820 possible value is MAX_ORDER/2. Setting this parameter
821 to 1 or 2 should be enough to identify most random
822 memory corruption problems caused by bugs in kernel or
823 driver code when a CPU writes to (or reads from) a
824 random memory location. Note that there exists a class
825 of memory corruptions problems caused by buggy H/W or
826 F/W or by drivers badly programing DMA (basically when
827 memory is written at bus level and the CPU MMU is
828 bypassed) which are not detectable by
829 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
830 tracking down these problems.
833 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
834 parameter enables the feature at boot time. In
835 default, it is disabled. We can avoid allocating huge
836 chunk of memory for debug pagealloc if we don't enable
837 it at boot time and the system will work mostly same
838 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
839 on: enable the feature
841 debugpat [X86] Enable PAT debugging
843 decnet.addr= [HW,NET]
844 Format: <area>[,<node>]
845 See also Documentation/networking/decnet.txt.
848 [same as hugepagesz=] The size of the default
849 HugeTLB page size. This is the size represented by
850 the legacy /proc/ hugepages APIs, used for SHM, and
851 default size when mounting hugetlbfs filesystems.
852 Defaults to the default architecture's huge page size
856 Set number of hash buckets for dentry cache.
859 See Documentation/networking/ipv6.txt.
861 disable_cpu_apicid= [X86,APIC,SMP]
863 The number of initial APIC ID for the
864 corresponding CPU to be disabled at boot,
865 mostly used for the kdump 2nd kernel to
866 disable BSP to wake up multiple CPUs without
867 causing system reset or hang due to sending
870 disable_ddw [PPC/PSERIES]
871 Disable Dynamic DMA Window support. Use this if
872 to workaround buggy firmware.
875 See Documentation/networking/ipv6.txt.
877 disable_mtrr_cleanup [X86]
878 The kernel tries to adjust MTRR layout from continuous
879 to discrete, to make X server driver able to add WB
880 entry later. This parameter disables that.
882 disable_mtrr_trim [X86, Intel and AMD only]
883 By default the kernel will trim any uncacheable
884 memory out of your available memory pool based on
885 MTRR settings. This parameter disables that behavior,
886 possibly causing your machine to run very slowly.
888 disable_timer_pin_1 [X86]
889 Disable PIN 1 of APIC timer
890 Can be useful to work around chipset bugs.
892 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
893 this option disables the debugging code at boot.
895 dma_debug_entries=<number>
896 This option allows to tune the number of preallocated
897 entries for DMA-API debugging code. One entry is
898 required per DMA-API allocation. Use this if the
899 DMA-API debugging code disables itself because the
900 architectural default is too low.
902 dma_debug_driver=<driver_name>
903 With this option the DMA-API debugging driver
904 filter feature can be enabled at boot time. Just
905 pass the driver to filter for as the parameter.
906 The filter can be disabled or changed to another
907 driver later using sysfs.
909 drm_kms_helper.edid_firmware=[<connector>:]<file>
910 Broken monitors, graphic adapters and KVMs may
911 send no or incorrect EDID data sets. This parameter
912 allows to specify an EDID data set in the
913 /lib/firmware directory that is used instead.
914 Generic built-in EDID data sets are used, if one of
915 edid/1024x768.bin, edid/1280x1024.bin,
916 edid/1680x1050.bin, or edid/1920x1080.bin is given
917 and no file with the same name exists. Details and
918 instructions how to build your own EDID data are
919 available in Documentation/EDID/HOWTO.txt. An EDID
920 data set will only be used for a particular connector,
921 if its name and a colon are prepended to the EDID
926 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
927 module.dyndbg[="val"]
928 Enable debug messages at boot time. See
929 Documentation/dynamic-debug-howto.txt for details.
931 early_ioremap_debug [KNL]
932 Enable debug messages in early_ioremap support. This
933 is useful for tracking down temporary early mappings
934 which are not unmapped.
936 earlycon= [KNL] Output early console device and options.
939 Start an early, polled-mode console on a cadence serial
940 port at the specified address. The cadence serial port
941 must already be setup and configured. Options are not
944 uart[8250],io,<addr>[,options]
945 uart[8250],mmio,<addr>[,options]
946 uart[8250],mmio32,<addr>[,options]
947 Start an early, polled-mode console on the 8250/16550
948 UART at the specified I/O port or MMIO address.
949 MMIO inter-register address stride is either 8-bit
950 (mmio) or 32-bit (mmio32).
951 The options are the same as for ttyS, above.
954 Start an early, polled-mode console on a pl011 serial
955 port at the specified address. The pl011 serial port
956 must already be setup and configured. Options are not
960 Start an early, polled-mode console on an msm serial
961 port at the specified address. The serial port
962 must already be setup and configured. Options are not
966 Start an early, polled-mode console on an msm serial
967 dm port at the specified address. The serial port
968 must already be setup and configured. Options are not
971 smh Use ARM semihosting calls for early console.
973 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
977 earlyprintk=serial[,ttySn[,baudrate]]
978 earlyprintk=serial[,0x...[,baudrate]]
979 earlyprintk=ttySn[,baudrate]
980 earlyprintk=dbgp[debugController#]
982 earlyprintk is useful when the kernel crashes before
983 the normal console is initialized. It is not enabled by
984 default because it has some cosmetic problems.
986 Append ",keep" to not disable it when the real console
989 Only one of vga, efi, serial, or usb debug port can
992 Currently only ttyS0 and ttyS1 may be specified by
993 name. Other I/O ports may be explicitly specified
994 on some architectures (x86 and arm at least) by
995 replacing ttySn with an I/O port address, like this:
996 earlyprintk=serial,0x1008,115200
997 You can find the port for a given device in
998 /proc/tty/driver/serial:
999 2: uart:ST16650V2 port:00001008 irq:18 ...
1001 Interaction with the standard serial driver is not
1004 The VGA and EFI output is eventually overwritten by
1007 The xen output can only be used by Xen PV guests.
1009 edac_report= [HW,EDAC] Control how to report EDAC event
1010 Format: {"on" | "off" | "force"}
1011 on: enable EDAC to report H/W event. May be overridden
1012 by other higher priority error reporting module.
1013 off: disable H/W event reporting through EDAC.
1014 force: enforce the use of EDAC to report H/W event.
1017 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1020 This is designed to be used in conjunction with
1021 the boot argument: earlyprintk=vga
1024 Format: {"off" | "on" | "skip[mbr]"}
1027 Format: { "old_map", "nochunk", "noruntime" }
1028 old_map [X86-64]: switch to the old ioremap-based EFI
1029 runtime services mapping. 32-bit still uses this one by
1031 nochunk: disable reading files in "chunks" in the EFI
1032 boot stub, as chunking can cause problems with some
1033 firmware implementations.
1034 noruntime : disable EFI runtime services support
1036 efi_no_storage_paranoia [EFI; X86]
1037 Using this parameter you can use more than 50% of
1038 your efi variable storage. Use this parameter only if
1039 you are really sure that your UEFI does sane gc and
1040 fulfills the spec otherwise your board may brick.
1042 eisa_irq_edge= [PARISC,HW]
1043 See header of drivers/parisc/eisa.c.
1046 See comment before function elanfreq_setup() in
1047 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1050 Format: {"cfq" | "deadline" | "noop"}
1051 See Documentation/block/cfq-iosched.txt and
1052 Documentation/block/deadline-iosched.txt for details.
1054 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1055 Specifies physical address of start of kernel core
1056 image elf header and optionally the size. Generally
1057 kexec loader will pass this option to capture kernel.
1058 See Documentation/kdump/kdump.txt for details.
1060 enable_mtrr_cleanup [X86]
1061 The kernel tries to adjust MTRR layout from continuous
1062 to discrete, to make X server driver able to add WB
1063 entry later. This parameter enables that.
1065 enable_timer_pin_1 [X86]
1066 Enable PIN 1 of APIC timer
1067 Can be useful to work around chipset bugs
1068 (in particular on some ATI chipsets).
1069 The kernel tries to set a reasonable default.
1071 enforcing [SELINUX] Set initial enforcing status.
1073 See security/selinux/Kconfig help text.
1074 0 -- permissive (log only, no denials).
1075 1 -- enforcing (deny and log).
1077 Value can be changed at runtime via /selinux/enforce.
1080 Disable Error Record Serialization Table (ERST)
1083 ether= [HW,NET] Ethernet cards parameters
1084 This option is obsoleted by the "netdev=" option, which
1085 has equivalent usage. See its documentation for details.
1089 Permit 'security.evm' to be updated regardless of
1090 current integrity status.
1094 fail_make_request=[KNL]
1095 General fault injection mechanism.
1096 Format: <interval>,<probability>,<space>,<times>
1097 See also Documentation/fault-injection/.
1100 See Documentation/blockdev/floppy.txt.
1102 force_pal_cache_flush
1103 [IA-64] Avoid check_sal_cache_flush which may hang on
1104 buggy SAL_CACHE_FLUSH implementations. Using this
1105 parameter will force ia64_sal_cache_flush to call
1106 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1109 Forcefully enable Physical Address Extension (PAE).
1110 Many Pentium M systems disable PAE but may have a
1111 functionally usable PAE implementation.
1112 Warning: use of this parameter will taint the kernel
1113 and may cause unknown problems.
1116 [FTRACE] will set and start the specified tracer
1117 as early as possible in order to facilitate early
1120 ftrace_dump_on_oops[=orig_cpu]
1121 [FTRACE] will dump the trace buffers on oops.
1122 If no parameter is passed, ftrace will dump
1123 buffers of all CPUs, but if you pass orig_cpu, it will
1124 dump only the buffer of the CPU that triggered the
1127 ftrace_filter=[function-list]
1128 [FTRACE] Limit the functions traced by the function
1129 tracer at boot up. function-list is a comma separated
1130 list of functions. This list can be changed at run
1131 time by the set_ftrace_filter file in the debugfs
1134 ftrace_notrace=[function-list]
1135 [FTRACE] Do not trace the functions specified in
1136 function-list. This list can be changed at run time
1137 by the set_ftrace_notrace file in the debugfs
1140 ftrace_graph_filter=[function-list]
1141 [FTRACE] Limit the top level callers functions traced
1142 by the function graph tracer at boot up.
1143 function-list is a comma separated list of functions
1144 that can be changed at run time by the
1145 set_graph_function file in the debugfs tracing directory.
1147 ftrace_graph_notrace=[function-list]
1148 [FTRACE] Do not trace from the functions specified in
1149 function-list. This list is a comma separated list of
1150 functions that can be changed at run time by the
1151 set_graph_notrace file in the debugfs tracing directory.
1154 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1155 support via parallel port (up to 5 devices per port)
1156 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1157 See also Documentation/input/joystick-parport.txt
1161 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1165 gcov_persist= [GCOV] When non-zero (default), profiling data for
1166 kernel modules is saved and remains accessible via
1167 debugfs, even when the module is unloaded/reloaded.
1168 When zero, profiling data is discarded and associated
1169 debugfs files are removed at module unload time.
1171 gpt [EFI] Forces disk with valid GPT signature but
1172 invalid Protective MBR to be treated as GPT. If the
1173 primary GPT is corrupted, it enables the backup/alternate
1174 GPT to be used instead.
1176 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1177 the "Enable 0" bit of the configuration register.
1180 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1181 the "Enable 0" bit of the configuration register.
1184 grcan.select= [HW] Select which physical interface to use.
1187 grcan.txsize= [HW] Sets the size of the tx buffer.
1188 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1190 grcan.rxsize= [HW] Sets the size of the rx buffer.
1191 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1194 hashdist= [KNL,NUMA] Large hashes allocated during boot
1195 are distributed across NUMA nodes. Defaults on
1196 for 64-bit NUMA, off otherwise.
1197 Format: 0 | 1 (for off | on)
1199 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1201 hd= [EIDE] (E)IDE hard drive subsystem geometry
1202 Format: <cyl>,<head>,<sect>
1205 Disable Hardware Error Source Table (HEST) support;
1206 corresponding firmware-first mode error processing
1207 logic will be disabled.
1209 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1210 size of <nn>. This works even on boxes that have no
1211 highmem otherwise. This also works to reduce highmem
1212 size on bigger boxes.
1214 highres= [KNL] Enable/disable high resolution timer mode.
1215 Valid parameters: "on", "off"
1219 See Documentation/isdn/README.HiSax.
1223 hpet= [X86-32,HPET] option to control HPET usage
1224 Format: { enable (default) | disable | force |
1226 disable: disable HPET and use PIT instead
1227 force: allow force enabled of undocumented chips (ICH4,
1229 verbose: show contents of HPET registers during setup
1231 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1232 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1234 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1235 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1236 On x86-64 and powerpc, this option can be specified
1237 multiple times interleaved with hugepages= to reserve
1238 huge pages of different sizes. Valid pages sizes on
1239 x86-64 are 2M (when the CPU supports "pse") and 1G
1240 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1242 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1243 terminal devices. Valid values: 0..8
1244 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1245 If specified, z/VM IUCV HVC accepts connections
1246 from listed z/VM user IDs only.
1248 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1249 hardware thread id mappings.
1250 Format: <cpu>:<hwthread>
1253 Do not unregister boot console at start. This is only
1254 useful for debugging when something happens in the window
1255 between unregistering the boot console and initializing
1258 i2c_bus= [HW] Override the default board specific I2C bus speed
1259 or register an additional I2C bus that is not
1260 registered from board initialization code.
1264 i8042.debug [HW] Toggle i8042 debug mode
1265 i8042.direct [HW] Put keyboard port into non-translated mode
1266 i8042.dumbkbd [HW] Pretend that controller can only read data from
1267 keyboard and cannot control its state
1268 (Don't attempt to blink the leds)
1269 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1270 i8042.nokbd [HW] Don't check/create keyboard port
1271 i8042.noloop [HW] Disable the AUX Loopback command while probing
1273 i8042.nomux [HW] Don't check presence of an active multiplexing
1275 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1277 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1278 i8042.reset [HW] Reset the controller during init and cleanup
1279 i8042.unlock [HW] Unlock (ignore) the keylock
1283 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1284 indicates that the driver is running on unsupported
1286 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1287 does not match list of supported models.
1289 [HW] Report power status in /proc/i8k
1290 (disabled by default)
1291 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1294 i915.invert_brightness=
1295 [DRM] Invert the sense of the variable that is used to
1296 set the brightness of the panel backlight. Normally a
1297 brightness value of 0 indicates backlight switched off,
1298 and the maximum of the brightness value sets the backlight
1299 to maximum brightness. If this parameter is set to 0
1300 (default) and the machine requires it, or this parameter
1301 is set to 1, a brightness value of 0 sets the backlight
1302 to maximum brightness, and the maximum of the brightness
1303 value switches the backlight off.
1304 -1 -- never invert brightness
1305 0 -- machine default
1306 1 -- force brightness inversion
1309 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1311 ide-core.nodma= [HW] (E)IDE subsystem
1312 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1313 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1314 .cdrom .chs .ignore_cable are additional options
1315 See Documentation/ide/ide.txt.
1317 ide-generic.probe-mask= [HW] (E)IDE subsystem
1319 Probe mask for legacy ISA IDE ports. Depending on
1320 platform up to 6 ports are supported, enabled by
1321 setting corresponding bits in the mask to 1. The
1322 default value is 0x0, which has a special meaning.
1323 On systems that have PCI, it triggers scanning the
1324 PCI bus for the first and the second port, which
1325 are then probed. On systems without PCI the value
1326 of 0x0 enables probing the two first ports as if it
1329 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1330 Claim all unknown PCI IDE storage controllers.
1333 Format: idle=poll, idle=halt, idle=nomwait
1334 Poll forces a polling idle loop that can slightly
1335 improve the performance of waking up a idle CPU, but
1336 will use a lot of power and make the system run hot.
1338 idle=halt: Halt is forced to be used for CPU idle.
1339 In such case C2/C3 won't be used again.
1340 idle=nomwait: Disable mwait for CPU C-states
1342 ignore_loglevel [KNL]
1343 Ignore loglevel setting - this will print /all/
1344 kernel messages to the console. Useful for debugging.
1345 We also add it as printk module parameter, so users
1346 could change it dynamically, usually by
1347 /sys/module/printk/parameters/ignore_loglevel.
1349 ihash_entries= [KNL]
1350 Set number of hash buckets for inode cache.
1352 ima_appraise= [IMA] appraise integrity measurements
1353 Format: { "off" | "enforce" | "fix" | "log" }
1356 ima_appraise_tcb [IMA]
1357 The builtin appraise policy appraises all files
1361 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1365 The list of supported hash algorithms is defined
1366 in crypto/hash_info.h.
1369 Load a policy which meets the needs of the Trusted
1370 Computing Base. This means IMA will measure all
1371 programs exec'd, files mmap'd for exec, and all files
1372 opened for read by uid=0.
1375 Select one of defined IMA measurements template formats.
1376 Formats: { "ima" | "ima-ng" }
1379 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1380 Format: <min_file_size>
1381 Set the minimal file size for using asynchronous hash.
1382 If left unspecified, ahash usage is disabled.
1384 ahash performance varies for different data sizes on
1385 different crypto accelerators. This option can be used
1386 to achieve the best performance for a particular HW.
1388 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1390 Set hashing buffer size. Default: 4k.
1392 ahash performance varies for different chunk sizes on
1393 different crypto accelerators. This option can be used
1394 to achieve best performance for particular HW.
1398 Run specified binary instead of /sbin/init as init
1401 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1402 for working out where the kernel is dying during
1405 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1406 initcall functions. Useful for debugging built-in
1407 modules and initcalls.
1409 initrd= [BOOT] Specify the location of the initial ramdisk
1411 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1414 int_pln_enable [x86] Enable power limit notification interrupt
1416 integrity_audit=[IMA]
1417 Format: { "0" | "1" }
1418 0 -- basic integrity auditing messages. (Default)
1419 1 -- additional integrity auditing messages.
1421 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1423 Enable intel iommu driver.
1425 Disable intel iommu driver.
1426 igfx_off [Default Off]
1427 By default, gfx is mapped as normal device. If a gfx
1428 device has a dedicated DMAR unit, the DMAR unit is
1429 bypassed by not enabling DMAR with this option. In
1430 this case, gfx device will use physical address for
1433 With this option iommu will not optimize to look
1434 for io virtual address below 32-bit forcing dual
1435 address cycle on pci bus for cards supporting greater
1436 than 32-bit addressing. The default is to look
1437 for translation below 32-bit and if not available
1438 then look in the higher range.
1439 strict [Default Off]
1440 With this option on every unmap_single operation will
1441 result in a hardware IOTLB flush operation as opposed
1442 to batching them for performance.
1443 sp_off [Default Off]
1444 By default, super page will be supported if Intel IOMMU
1445 has the capability. With this option, super page will
1448 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1449 0 disables intel_idle and fall back on acpi_idle.
1450 1 to 6 specify maximum depth of C-state.
1454 Do not enable intel_pstate as the default
1455 scaling driver for the supported processors
1457 Do not enable hardware P state control (HWP)
1460 intremap= [X86-64, Intel-IOMMU]
1461 on enable Interrupt Remapping (default)
1462 off disable Interrupt Remapping
1463 nosid disable Source ID checking
1465 BIOS x2APIC opt-out request will be ignored
1467 iomem= Disable strict checking of access to MMIO memory
1468 strict regions from userspace.
1485 io7= [HW] IO7 for Marvel based alpha systems
1486 See comment before marvel_specify_io7 in
1487 arch/alpha/kernel/core_marvel.c.
1489 io_delay= [X86] I/O delay method
1491 Standard port 0x80 based delay
1493 Alternate port 0xed based delay (needed on some systems)
1495 Simple two microseconds delay
1500 See Documentation/filesystems/nfs/nfsroot.txt.
1503 When an interrupt is not handled search all handlers
1504 for it. Intended to get systems with badly broken
1508 When an interrupt is not handled search all handlers
1509 for it. Also check all handlers each timer
1510 interrupt. Intended to get systems with badly broken
1514 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1516 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1518 <cpu number>,...,<cpu number>
1520 <cpu number>-<cpu number>
1521 (must be a positive range in ascending order)
1523 <cpu number>,...,<cpu number>-<cpu number>
1525 This option can be used to specify one or more CPUs
1526 to isolate from the general SMP balancing and scheduling
1527 algorithms. You can move a process onto or off an
1528 "isolated" CPU via the CPU affinity syscalls or cpuset.
1529 <cpu number> begins at 0 and the maximum value is
1530 "number of CPUs in system - 1".
1532 This option is the preferred way to isolate CPUs. The
1533 alternative -- manually setting the CPU mask of all
1534 tasks in the system -- can cause problems and
1535 suboptimal load balancer performance.
1539 ivrs_ioapic [HW,X86_64]
1540 Provide an override to the IOAPIC-ID<->DEVICE-ID
1541 mapping provided in the IVRS ACPI table. For
1542 example, to map IOAPIC-ID decimal 10 to
1543 PCI device 00:14.0 write the parameter as:
1544 ivrs_ioapic[10]=00:14.0
1546 ivrs_hpet [HW,X86_64]
1547 Provide an override to the HPET-ID<->DEVICE-ID
1548 mapping provided in the IVRS ACPI table. For
1549 example, to map HPET-ID decimal 0 to
1550 PCI device 00:14.0 write the parameter as:
1551 ivrs_hpet[0]=00:14.0
1553 js= [HW,JOY] Analog joystick
1554 See Documentation/input/joystick.txt.
1557 Enable/disable kernel and module base offset ASLR
1558 (Address Space Layout Randomization) if built into
1559 the kernel. When CONFIG_HIBERNATION is selected,
1560 kASLR is disabled by default. When kASLR is enabled,
1561 hibernation will be disabled.
1565 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1566 specifies the amount of memory usable by the kernel
1567 for non-movable allocations. The requested amount is
1568 spread evenly throughout all nodes in the system. The
1569 remaining memory in each node is used for Movable
1570 pages. In the event, a node is too small to have both
1571 kernelcore and Movable pages, kernelcore pages will
1572 take priority and other nodes will have a larger number
1573 of Movable pages. The Movable zone is used for the
1574 allocation of pages that may be reclaimed or moved
1575 by the page migration subsystem. This means that
1576 HugeTLB pages may not be allocated from this zone.
1577 Note that allocations like PTEs-from-HighMem still
1578 use the HighMem zone if it exists, and the Normal
1579 zone if it does not.
1581 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1582 Format: <Controller#>[,poll interval]
1583 The controller # is the number of the ehci usb debug
1584 port as it is probed via PCI. The poll interval is
1585 optional and is the number seconds in between
1586 each poll cycle to the debug port in case you need
1587 the functionality for interrupting the kernel with
1588 gdb or control-c on the dbgp connection. When
1589 not using this parameter you use sysrq-g to break into
1590 the kernel debugger.
1592 kgdboc= [KGDB,HW] kgdb over consoles.
1593 Requires a tty driver that supports console polling,
1594 or a supported polling keyboard driver (non-usb).
1595 Serial only format: <serial_device>[,baud]
1596 keyboard only format: kbd
1597 keyboard and serial format: kbd,<serial_device>[,baud]
1598 Optional Kernel mode setting:
1599 kms, kbd format: kms,kbd
1600 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1602 kgdbwait [KGDB] Stop kernel execution and enter the
1603 kernel debugger at the earliest opportunity.
1605 kmac= [MIPS] korina ethernet MAC address.
1606 Configure the RouterBoard 532 series on-chip
1607 Ethernet adapter MAC address.
1609 kmemleak= [KNL] Boot-time kmemleak enable/disable
1610 Valid arguments: on, off
1612 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1615 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1616 Valid arguments: 0, 1, 2
1617 kmemcheck=0 (disabled)
1618 kmemcheck=1 (enabled)
1619 kmemcheck=2 (one-shot mode)
1620 Default: 2 (one-shot mode)
1622 kstack=N [X86] Print N words from the kernel stack
1625 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1626 Default is 0 (don't ignore, but inject #GP)
1628 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1632 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1633 Default is 1 (enabled)
1635 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1637 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1639 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1640 (virtualized MMU) support on capable Intel chips.
1641 Default is 1 (enabled)
1643 kvm-intel.emulate_invalid_guest_state=
1644 [KVM,Intel] Enable emulation of invalid guest states
1645 Default is 0 (disabled)
1647 kvm-intel.flexpriority=
1648 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1649 Default is 1 (enabled)
1652 [KVM,Intel] Enable VMX nesting (nVMX).
1653 Default is 0 (disabled)
1655 kvm-intel.unrestricted_guest=
1656 [KVM,Intel] Disable unrestricted guest feature
1657 (virtualized real and unpaged mode) on capable
1658 Intel chips. Default is 1 (enabled)
1660 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1661 feature (tagged TLBs) on capable Intel chips.
1662 Default is 1 (enabled)
1668 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1671 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1672 value for LAPIC timer one-shot implementation. Default
1673 back to the programmable timer unit in the LAPIC.
1675 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1678 libata.dma= [LIBATA] DMA control
1679 libata.dma=0 Disable all PATA and SATA DMA
1680 libata.dma=1 PATA and SATA Disk DMA only
1681 libata.dma=2 ATAPI (CDROM) DMA only
1682 libata.dma=4 Compact Flash DMA only
1683 Combinations also work, so libata.dma=3 enables DMA
1684 for disks and CDROMs, but not CFs.
1686 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1687 libata.ignore_hpa=0 keep BIOS limits (default)
1688 libata.ignore_hpa=1 ignore limits, using full disk
1690 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1694 libata.force= [LIBATA] Force configurations. The format is comma
1695 separated list of "[ID:]VAL" where ID is
1696 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1697 matching port, link or device. Basically, it matches
1698 the ATA ID string printed on console by libata. If
1699 the whole ID part is omitted, the last PORT and DEVICE
1700 values are used. If ID hasn't been specified yet, the
1701 configuration applies to all ports, links and devices.
1703 If only DEVICE is omitted, the parameter applies to
1704 the port and all links and devices behind it. DEVICE
1705 number of 0 either selects the first device or the
1706 first fan-out link behind PMP device. It does not
1707 select the host link. DEVICE number of 15 selects the
1708 host link and device attached to it.
1710 The VAL specifies the configuration to force. As long
1711 as there's no ambiguity shortcut notation is allowed.
1712 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1713 The following configurations can be forced.
1715 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1716 Any ID with matching PORT is used.
1718 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1720 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1721 udma[/][16,25,33,44,66,100,133] notation is also
1724 * [no]ncq: Turn on or off NCQ.
1726 * nohrst, nosrst, norst: suppress hard, soft
1729 * rstonce: only attempt one reset during
1730 hot-unplug link recovery
1732 * dump_id: dump IDENTIFY data.
1734 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1736 * disable: Disable this device.
1738 If there are multiple matching configurations changing
1739 the same attribute, the last one is used.
1741 memblock=debug [KNL] Enable memblock debug messages.
1743 load_ramdisk= [RAM] List of ramdisks to load from floppy
1744 See Documentation/blockdev/ramdisk.txt.
1746 lockd.nlm_grace_period=P [NFS] Assign grace period.
1749 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1752 lockd.nlm_timeout=T [NFS] Assign timeout value.
1755 lockd.nlm_udpport=M [NFS] Assign UDP port.
1758 locktorture.nreaders_stress= [KNL]
1759 Set the number of locking read-acquisition kthreads.
1760 Defaults to being automatically set based on the
1761 number of online CPUs.
1763 locktorture.nwriters_stress= [KNL]
1764 Set the number of locking write-acquisition kthreads.
1766 locktorture.onoff_holdoff= [KNL]
1767 Set time (s) after boot for CPU-hotplug testing.
1769 locktorture.onoff_interval= [KNL]
1770 Set time (s) between CPU-hotplug operations, or
1771 zero to disable CPU-hotplug testing.
1773 locktorture.shuffle_interval= [KNL]
1774 Set task-shuffle interval (jiffies). Shuffling
1775 tasks allows some CPUs to go into dyntick-idle
1776 mode during the locktorture test.
1778 locktorture.shutdown_secs= [KNL]
1779 Set time (s) after boot system shutdown. This
1780 is useful for hands-off automated testing.
1782 locktorture.stat_interval= [KNL]
1783 Time (s) between statistics printk()s.
1785 locktorture.stutter= [KNL]
1786 Time (s) to stutter testing, for example,
1787 specifying five seconds causes the test to run for
1788 five seconds, wait for five seconds, and so on.
1789 This tests the locking primitive's ability to
1790 transition abruptly to and from idle.
1792 locktorture.torture_runnable= [BOOT]
1793 Start locktorture running at boot time.
1795 locktorture.torture_type= [KNL]
1796 Specify the locking implementation to test.
1798 locktorture.verbose= [KNL]
1799 Enable additional printk() statements.
1801 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1804 loglevel= All Kernel Messages with a loglevel smaller than the
1805 console loglevel will be printed to the console. It can
1806 also be changed with klogd or other programs. The
1807 loglevels are defined as follows:
1809 0 (KERN_EMERG) system is unusable
1810 1 (KERN_ALERT) action must be taken immediately
1811 2 (KERN_CRIT) critical conditions
1812 3 (KERN_ERR) error conditions
1813 4 (KERN_WARNING) warning conditions
1814 5 (KERN_NOTICE) normal but significant condition
1815 6 (KERN_INFO) informational
1816 7 (KERN_DEBUG) debug-level messages
1818 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1819 in bytes. n must be a power of two and greater
1820 than the minimal size. The minimal size is defined
1821 by LOG_BUF_SHIFT kernel config parameter. There is
1822 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1823 that allows to increase the default size depending on
1824 the number of CPUs. See init/Kconfig for more details.
1826 logo.nologo [FB] Disables display of the built-in Linux logo.
1827 This may be used to provide more screen space for
1828 kernel log messages and is useful when debugging
1829 kernel boot problems.
1831 lp=0 [LP] Specify parallel ports to use, e.g,
1832 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1833 lp=reset first parallel port). 'lp=0' disables the
1834 lp=auto printer driver. 'lp=reset' (which can be
1835 specified in addition to the ports) causes
1836 attached printers to be reset. Using
1837 lp=port1,port2,... specifies the parallel ports
1838 to associate lp devices with, starting with
1839 lp0. A port specification may be 'none' to skip
1840 that lp device, or a parport name such as
1841 'parport0'. Specifying 'lp=auto' instead of a
1842 port specification list means that device IDs
1843 from each port should be examined, to see if
1844 an IEEE 1284-compliant printer is attached; if
1845 so, the driver will manage that printer.
1846 See also header of drivers/char/lp.c.
1849 Sets loops_per_jiffy to given constant, thus avoiding
1850 time-consuming boot-time autodetection (up to 250 ms per
1851 CPU). 0 enables autodetection (default). To determine
1852 the correct value for your kernel, boot with normal
1853 autodetection and see what value is printed. Note that
1854 on SMP systems the preset will be applied to all CPUs,
1855 which is likely to cause problems if your CPUs need
1856 significantly divergent settings. An incorrect value
1857 will cause delays in the kernel to be wrong, leading to
1858 unpredictable I/O errors and other breakage. Although
1859 unlikely, in the extreme case this might damage your
1863 Format: <io>,<irq>,<dma>
1865 machvec= [IA-64] Force the use of a particular machine-vector
1866 (machvec) in a generic kernel.
1867 Example: machvec=hpzx1_swiotlb
1869 machtype= [Loongson] Share the same kernel image file between different
1871 Example: machtype=lemote-yeeloong-2f-7inch
1873 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1874 than or equal to this physical address is ignored.
1876 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1877 should make use of. maxcpus=n : n >= 0 limits the
1878 kernel to using 'n' processors. n=0 is a special case,
1879 it is equivalent to "nosmp", which also disables
1882 max_loop= [LOOP] The number of loop block devices that get
1883 (loop.max_loop) unconditionally pre-created at init time. The default
1884 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1885 of statically allocating a predefined number, loop
1886 devices can be requested on-demand with the
1887 /dev/loop-control interface.
1889 mce [X86-32] Machine Check Exception
1891 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1893 md= [HW] RAID subsystems devices and level
1894 See Documentation/md.txt.
1897 Format: <first>,<last>
1898 Specifies range of consoles to be captured by the MDA.
1900 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1901 Amount of memory to be used when the kernel is not able
1902 to see the whole system memory or for test.
1903 [X86] Work as limiting max address. Use together
1904 with memmap= to avoid physical address space collisions.
1905 Without memmap= PCI devices could be placed at addresses
1906 belonging to unused RAM.
1908 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1912 [KNL,SH] Allow user to override the default size for
1913 per-device physically contiguous DMA buffers.
1915 memmap=exactmap [KNL,X86] Enable setting of an exact
1916 E820 memory map, as specified by the user.
1917 Such memmap=exactmap lines can be constructed based on
1918 BIOS output or other requirements. See the memmap=nn@ss
1921 memmap=nn[KMG]@ss[KMG]
1922 [KNL] Force usage of a specific region of memory.
1923 Region of memory to be used is from ss to ss+nn.
1925 memmap=nn[KMG]#ss[KMG]
1926 [KNL,ACPI] Mark specific memory as ACPI data.
1927 Region of memory to be marked is from ss to ss+nn.
1929 memmap=nn[KMG]$ss[KMG]
1930 [KNL,ACPI] Mark specific memory as reserved.
1931 Region of memory to be reserved is from ss to ss+nn.
1932 Example: Exclude memory from 0x18690000-0x1869ffff
1933 memmap=64K$0x18690000
1935 memmap=0x10000$0x18690000
1937 memory_corruption_check=0/1 [X86]
1938 Some BIOSes seem to corrupt the first 64k of
1939 memory when doing things like suspend/resume.
1940 Setting this option will scan the memory
1941 looking for corruption. Enabling this will
1942 both detect corruption and prevent the kernel
1943 from using the memory being corrupted.
1944 However, its intended as a diagnostic tool; if
1945 repeatable BIOS-originated corruption always
1946 affects the same memory, you can use memmap=
1947 to prevent the kernel from using that memory.
1949 memory_corruption_check_size=size [X86]
1950 By default it checks for corruption in the low
1951 64k, making this memory unavailable for normal
1952 use. Use this parameter to scan for
1953 corruption in more or less memory.
1955 memory_corruption_check_period=seconds [X86]
1956 By default it checks for corruption every 60
1957 seconds. Use this parameter to check at some
1958 other rate. 0 disables periodic checking.
1960 memtest= [KNL,X86] Enable memtest
1962 default : 0 <disable>
1963 Specifies the number of memtest passes to be
1964 performed. Each pass selects another test
1965 pattern from a given set of patterns. Memtest
1966 fills the memory with this pattern, validates
1967 memory contents and reserves bad memory
1968 regions that are detected.
1970 meye.*= [HW] Set MotionEye Camera parameters
1971 See Documentation/video4linux/meye.txt.
1973 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1974 Multi-Function General Purpose Timers on AMD Geode
1977 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1978 the BIOS has incorrectly applied a workaround. TinyBIOS
1979 version 0.98 is known to be affected, 0.99 fixes the
1980 problem by letting the user disable the workaround.
1984 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1985 physical address is ignored.
1987 mini2440= [ARM,HW,KNL]
1988 Format:[0..2][b][c][t]
1990 MINI2440 configuration specification:
1991 0 - The attached screen is the 3.5" TFT
1992 1 - The attached screen is the 7" TFT
1993 2 - The VGA Shield is attached (1024x768)
1994 Leaving out the screen size parameter will not load
1995 the TFT driver, and the framebuffer will be left
1997 b - Enable backlight. The TFT backlight pin will be
1998 linked to the kernel VESA blanking code and a GPIO
1999 LED. This parameter is not necessary when using the
2001 c - Enable the s3c camera interface.
2002 t - Reserved for enabling touchscreen support. The
2003 touchscreen support is not enabled in the mainstream
2004 kernel as of 2.6.30, a preliminary port can be found
2005 in the "bleeding edge" mini2440 support kernel at
2006 http://repo.or.cz/w/linux-2.6/mini2440.git
2009 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2010 parameter allows control of the logging verbosity for
2011 the additional memory initialisation checks. A value
2012 of 0 disables mminit logging and a level of 4 will
2013 log everything. Information is printed at KERN_DEBUG
2014 so loglevel=8 may also need to be specified.
2017 [KNL] When CONFIG_MODULE_SIG is set, this means that
2018 modules without (valid) signatures will fail to load.
2019 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2020 is always true, so this option does nothing.
2023 [MOUSE] Maximum time between finger touching and
2024 leaving touchpad surface for touch to be considered
2025 a tap and be reported as a left button click (for
2026 touchpads working in absolute mode only).
2028 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2029 reporting absolute coordinates, such as tablets
2030 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2031 reporting absolute coordinates, such as tablets
2033 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2034 is similar to kernelcore except it specifies the
2035 amount of memory used for migratable allocations.
2036 If both kernelcore and movablecore is specified,
2037 then kernelcore will be at *least* the specified
2038 value but may be more. If movablecore on its own
2039 is specified, the administrator must be careful
2040 that the amount of memory usable for all allocations
2043 movable_node [KNL,X86] Boot-time switch to enable the effects
2044 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2046 MTD_Partition= [MTD]
2047 Format: <name>,<region-number>,<size>,<offset>
2049 MTD_Region= [MTD] Format:
2050 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2053 See drivers/mtd/cmdlinepart.c.
2055 multitce=off [PPC] This parameter disables the use of the pSeries
2056 firmware feature for updating multiple TCE entries
2059 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2061 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2063 boundary - index of last SLC block on Flex-OneNAND.
2064 The remaining blocks are configured as MLC blocks.
2065 lock - Configure if Flex-OneNAND boundary should be locked.
2066 Once locked, the boundary cannot be changed.
2067 1 indicates lock status, 0 indicates unlock status.
2070 ARM/S3C2412 JIVE boot control
2072 See arch/arm/mach-s3c2412/mach-jive.c
2074 mtouchusb.raw_coordinates=
2075 [HW] Make the MicroTouch USB driver use raw coordinates
2076 ('y', default) or cooked coordinates ('n')
2078 mtrr_chunk_size=nn[KMG] [X86]
2079 used for mtrr cleanup. It is largest continuous chunk
2080 that could hold holes aka. UC entries.
2082 mtrr_gran_size=nn[KMG] [X86]
2083 Used for mtrr cleanup. It is granularity of mtrr block.
2085 Large value could prevent small alignment from
2088 mtrr_spare_reg_nr=n [X86]
2090 Range: 0,7 : spare reg number
2092 Used for mtrr cleanup. It is spare mtrr entries number.
2093 Set to 2 or more if your graphical card needs more.
2095 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2097 netdev= [NET] Network devices parameters
2098 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2099 Note that mem_start is often overloaded to mean
2100 something different and driver-specific.
2101 This usage is only documented in each driver source
2105 [NETFILTER] Enable connection tracking flow accounting
2106 0 to disable accounting
2107 1 to enable accounting
2110 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2111 See Documentation/filesystems/nfs/nfsroot.txt.
2113 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2114 See Documentation/filesystems/nfs/nfsroot.txt.
2116 nfsrootdebug [NFS] enable nfsroot debugging messages.
2117 See Documentation/filesystems/nfs/nfsroot.txt.
2119 nfs.callback_tcpport=
2120 [NFS] set the TCP port on which the NFSv4 callback
2121 channel should listen.
2124 [NFS] sets the pathname to the program which is used
2125 to update the NFS client cache entries.
2127 nfs.cache_getent_timeout=
2128 [NFS] sets the timeout after which an attempt to
2129 update a cache entry is deemed to have failed.
2131 nfs.idmap_cache_timeout=
2132 [NFS] set the maximum lifetime for idmapper cache
2136 [NFS] enable 64-bit inode numbers.
2137 If zero, the NFS client will fake up a 32-bit inode
2138 number for the readdir() and stat() syscalls instead
2139 of returning the full 64-bit number.
2140 The default is to return 64-bit inode numbers.
2142 nfs.max_session_slots=
2143 [NFSv4.1] Sets the maximum number of session slots
2144 the client will attempt to negotiate with the server.
2145 This limits the number of simultaneous RPC requests
2146 that the client can send to the NFSv4.1 server.
2147 Note that there is little point in setting this
2148 value higher than the max_tcp_slot_table_limit.
2150 nfs.nfs4_disable_idmapping=
2151 [NFSv4] When set to the default of '1', this option
2152 ensures that both the RPC level authentication
2153 scheme and the NFS level operations agree to use
2154 numeric uids/gids if the mount is using the
2155 'sec=sys' security flavour. In effect it is
2156 disabling idmapping, which can make migration from
2157 legacy NFSv2/v3 systems to NFSv4 easier.
2158 Servers that do not support this mode of operation
2159 will be autodetected by the client, and it will fall
2160 back to using the idmapper.
2161 To turn off this behaviour, set the value to '0'.
2163 [NFS4] Specify an additional fixed unique ident-
2164 ification string that NFSv4 clients can insert into
2165 their nfs_client_id4 string. This is typically a
2166 UUID that is generated at system install time.
2168 nfs.send_implementation_id =
2169 [NFSv4.1] Send client implementation identification
2170 information in exchange_id requests.
2171 If zero, no implementation identification information
2173 The default is to send the implementation identification
2176 nfs.recover_lost_locks =
2177 [NFSv4] Attempt to recover locks that were lost due
2178 to a lease timeout on the server. Please note that
2179 doing this risks data corruption, since there are
2180 no guarantees that the file will remain unchanged
2181 after the locks are lost.
2182 If you want to enable the kernel legacy behaviour of
2183 attempting to recover these locks, then set this
2185 The default parameter value of '0' causes the kernel
2186 not to attempt recovery of lost locks.
2188 nfsd.nfs4_disable_idmapping=
2189 [NFSv4] When set to the default of '1', the NFSv4
2190 server will return only numeric uids and gids to
2191 clients using auth_sys, and will accept numeric uids
2192 and gids from such clients. This is intended to ease
2193 migration from NFSv2/v3.
2195 objlayoutdriver.osd_login_prog=
2196 [NFS] [OBJLAYOUT] sets the pathname to the program which
2197 is used to automatically discover and login into new
2198 osd-targets. Please see:
2199 Documentation/filesystems/pnfs.txt for more explanations
2201 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2202 when a NMI is triggered.
2203 Format: [state][,regs][,debounce][,die]
2205 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2206 Format: [panic,][nopanic,][num]
2208 0 - turn nmi_watchdog off
2209 When panic is specified, panic when an NMI watchdog
2210 timeout occurs (or 'nopanic' to override the opposite
2212 This is useful when you use a panic=... timeout and
2213 need the box quickly up again.
2215 netpoll.carrier_timeout=
2216 [NET] Specifies amount of time (in seconds) that
2217 netpoll should wait for a carrier. By default netpoll
2220 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2221 emulation library even if a 387 maths coprocessor
2225 [HW] Never suspend the console
2226 Disable suspending of consoles during suspend and
2227 hibernate operations. Once disabled, debugging
2228 messages can reach various consoles while the rest
2229 of the system is being put to sleep (ie, while
2230 debugging driver suspend/resume hooks). This may
2231 not work reliably with all consoles, but is known
2232 to work with serial and VGA consoles.
2233 To facilitate more flexible debugging, we also add
2234 console_suspend, a printk module parameter to control
2235 it. Users could use console_suspend (usually
2236 /sys/module/printk/parameters/console_suspend) to
2237 turn on/off it dynamically.
2239 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2240 caches in the slab allocator. Saves per-node memory,
2241 but will impact performance.
2245 noapic [SMP,APIC] Tells the kernel to not make use of any
2246 IOAPICs that may be present in the system.
2248 noautogroup Disable scheduler automatic task group creation.
2250 nobats [PPC] Do not use BATs for mapping kernel lowmem
2251 on "Classic" PPC cores.
2255 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2257 nodelayacct [KNL] Disable per-task delay accounting
2259 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2261 nodsp [SH] Disable hardware DSP at boot time.
2263 noefi Disable EFI runtime services support.
2268 On X86-32 available only on PAE configured kernels.
2269 noexec=on: enable non-executable mappings (default)
2270 noexec=off: disable non-executable mappings
2273 Disable SMAP (Supervisor Mode Access Prevention)
2274 even if it is supported by processor.
2277 Disable SMEP (Supervisor Mode Execution Prevention)
2278 even if it is supported by processor.
2281 This affects only 32-bit executables.
2282 noexec32=on: enable non-executable mappings (default)
2283 read doesn't imply executable mappings
2284 noexec32=off: disable non-executable mappings
2285 read implies executable mappings
2287 nofpu [SH] Disable hardware FPU at boot time.
2289 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2290 register save and restore. The kernel will only save
2291 legacy floating-point registers on task switch.
2293 noxsave [BUGS=X86] Disables x86 extended register state save
2294 and restore using xsave. The kernel will fallback to
2295 enabling legacy floating-point and sse state.
2297 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2298 register states. The kernel will fall back to use
2299 xsave to save the states. By using this parameter,
2300 performance of saving the states is degraded because
2301 xsave doesn't support modified optimization while
2302 xsaveopt supports it on xsaveopt enabled systems.
2304 noxsaves [X86] Disables xsaves and xrstors used in saving and
2305 restoring x86 extended register state in compacted
2306 form of xsave area. The kernel will fall back to use
2307 xsaveopt and xrstor to save and restore the states
2308 in standard form of xsave area. By using this
2309 parameter, xsave area per process might occupy more
2310 memory on xsaves enabled systems.
2313 on enable eager fpu restore
2314 off disable eager fpu restore
2315 auto selects the default scheme, which automatically
2316 enables eagerfpu restore for xsaveopt.
2318 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2319 wfi(ARM) instruction doesn't work correctly and not to
2320 use it. This is also useful when using JTAG debugger.
2322 no_file_caps Tells the kernel not to honor file capabilities. The
2323 only way then for a file to be executed with privilege
2324 is to be setuid root or executed by root.
2326 nohalt [IA-64] Tells the kernel not to use the power saving
2327 function PAL_HALT_LIGHT when idle. This increases
2328 power-consumption. On the positive side, it reduces
2329 interrupt wake-up latency, which may improve performance
2330 in certain environments such as networked servers or
2333 nohibernate [HIBERNATION] Disable hibernation and resume.
2335 nohz= [KNL] Boottime enable/disable dynamic ticks
2336 Valid arguments: on, off
2339 nohz_full= [KNL,BOOT]
2340 In kernels built with CONFIG_NO_HZ_FULL=y, set
2341 the specified list of CPUs whose tick will be stopped
2342 whenever possible. The boot CPU will be forced outside
2343 the range to maintain the timekeeping.
2344 The CPUs in this range must also be included in the
2347 noiotrap [SH] Disables trapped I/O port accesses.
2349 noirqdebug [X86-32] Disables the code which attempts to detect and
2350 disable unhandled interrupt sources.
2352 no_timer_check [X86,APIC] Disables the code which tests for
2353 broken timer IRQ sources.
2355 noisapnp [ISAPNP] Disables ISA PnP code.
2357 noinitrd [RAM] Tells the kernel not to load any configured
2360 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2362 [Deprecated - use intremap=off]
2366 nojitter [IA-64] Disables jitter checking for ITC timers.
2368 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2370 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2373 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2374 steal time is computed, but won't influence scheduler
2377 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2379 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2381 noltlbs [PPC] Do not use large page/tlb entries for kernel
2382 lowmem mapping on PPC40x.
2384 nomca [IA-64] Disable machine check abort handling
2386 nomce [X86-32] Machine Check Exception
2388 nomfgpt [X86-32] Disable Multi-Function General Purpose
2389 Timer usage (for AMD Geode machines).
2391 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2392 shutdown the other cpus. Instead use the REBOOT_VECTOR
2395 nomodule Disable module load
2397 nopat [X86] Disable PAT (page attribute table extension of
2398 pagetables) support.
2400 norandmaps Don't use address space randomization. Equivalent to
2401 echo 0 > /proc/sys/kernel/randomize_va_space
2403 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2405 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2406 with UP alternatives
2408 nordrand [X86] Disable kernel use of the RDRAND and
2409 RDSEED instructions even if they are supported
2410 by the processor. RDRAND and RDSEED are still
2411 available to user space applications.
2413 noresume [SWSUSP] Disables resume and restores original swap
2416 no-scroll [VGA] Disables scrollback.
2417 This is required for the Braillex ib80-piezo Braille
2418 reader made by F.H. Papenmeier (Germany).
2422 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2424 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2425 and disable the IO APIC. legacy for "maxcpus=0".
2427 nosoftlockup [KNL] Disable the soft-lockup detector.
2429 nosync [HW,M68K] Disables sync negotiation for all devices.
2431 notsc [BUGS=X86-32] Disable Time Stamp Counter
2433 nousb [USB] Disable the USB subsystem
2435 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2439 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2441 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2442 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2443 Some features depend on CPU0. Known dependencies are:
2444 1. Resume from suspend/hibernate depends on CPU0.
2445 Suspend/hibernate will fail if CPU0 is offline and you
2446 need to online CPU0 before suspend/hibernate.
2447 2. PIC interrupts also depend on CPU0. CPU0 can't be
2448 removed if a PIC interrupt is detected.
2449 It's said poweroff/reboot may depend on CPU0 on some
2450 machines although I haven't seen such issues so far
2451 after CPU0 is offline on a few tested machines.
2452 If the dependencies are under your control, you can
2453 turn on cpu0_hotplug.
2455 nptcg= [IA-64] Override max number of concurrent global TLB
2456 purges which is reported from either PAL_VM_SUMMARY or
2459 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2460 could support. nr_cpus=n : n >= 1 limits the kernel to
2461 supporting 'n' processors. Later in runtime you can not
2462 use hotplug cpu feature to put more cpu back to online.
2463 just like you compile the kernel NR_CPUS=n
2465 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2467 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2468 Allowed values are enable and disable
2470 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2471 one of ['zone', 'node', 'default'] can be specified
2472 This can be set from sysctl after boot.
2473 See Documentation/sysctl/vm.txt for details.
2475 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2476 See Documentation/debugging-via-ohci1394.txt for more
2479 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2480 Rather than timing out after 20 ms if an EC
2481 command is not properly ACKed, override the length
2482 of the timeout. We have interrupts disabled while
2483 waiting for the ACK, so if this is set too high
2484 interrupts *may* be lost!
2486 omap_mux= [OMAP] Override bootloader pin multiplexing.
2487 Format: <mux_mode0.mode_name=value>...
2488 For example, to override I2C bus2:
2489 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2491 oprofile.timer= [HW]
2492 Use timer interrupt instead of performance counters
2494 oprofile.cpu_type= Force an oprofile cpu type
2495 This might be useful if you have an older oprofile
2496 userland or if you want common events.
2497 Format: { arch_perfmon }
2498 arch_perfmon: [X86] Force use of architectural
2499 perfmon on Intel CPUs instead of the
2500 CPU specific event set.
2501 timer: [X86] Force use of architectural NMI
2502 timer mode (see also oprofile.timer
2503 for generic hr timer mode)
2504 [s390] Force legacy basic mode sampling
2505 (report cpu_type "timer")
2507 oops=panic Always panic on oopses. Default is to just kill the
2508 process, but there is a small probability of
2509 deadlocking the machine.
2510 This will also cause panics on machine check exceptions.
2511 Useful together with panic=30 to trigger a reboot.
2514 See Documentation/sound/oss/oss-parameters.txt
2516 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2517 timeout > 0: seconds before rebooting
2518 timeout = 0: wait forever
2519 timeout < 0: reboot immediately
2522 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2525 crash_kexec_post_notifiers
2526 Run kdump after running panic-notifiers and dumping
2527 kmsg. This only for the users who doubt kdump always
2528 succeeds in any situation.
2529 Note that this also increases risks of kdump failure,
2530 because some panic notifiers can make the crashed
2531 kernel more unstable.
2533 parkbd.port= [HW] Parallel port number the keyboard adapter is
2534 connected to, default is 0.
2536 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2537 0 for XT, 1 for AT (default is AT).
2540 parport= [HW,PPT] Specify parallel ports. 0 disables.
2541 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2542 Use 'auto' to force the driver to use any
2543 IRQ/DMA settings detected (the default is to
2544 ignore detected IRQ/DMA settings because of
2545 possible conflicts). You can specify the base
2546 address, IRQ, and DMA settings; IRQ and DMA
2547 should be numbers, or 'auto' (for using detected
2548 settings on that particular port), or 'nofifo'
2549 (to avoid using a FIFO even if it is detected).
2550 Parallel ports are assigned in the order they
2551 are specified on the command line, starting
2554 parport_init_mode= [HW,PPT]
2555 Configure VIA parallel port to operate in
2556 a specific mode. This is necessary on Pegasos
2557 computer where firmware has no options for setting
2558 up parallel port mode and sets it to spp.
2559 Currently this function knows 686a and 8231 chips.
2560 Format: [spp|ps2|epp|ecp|ecpepp]
2563 Halt all CPUs after the first oops has been printed for
2564 the specified number of seconds. This is to be used if
2565 your oopses keep scrolling off the screen.
2570 See header of drivers/block/paride/pcd.c.
2571 See also Documentation/blockdev/paride.txt.
2573 pci=option[,option...] [PCI] various PCI subsystem options:
2574 earlydump [X86] dump PCI config space before the kernel
2576 off [X86] don't probe for the PCI bus
2577 bios [X86-32] force use of PCI BIOS, don't access
2578 the hardware directly. Use this if your machine
2579 has a non-standard PCI host bridge.
2580 nobios [X86-32] disallow use of PCI BIOS, only direct
2581 hardware access methods are allowed. Use this
2582 if you experience crashes upon bootup and you
2583 suspect they are caused by the BIOS.
2584 conf1 [X86] Force use of PCI Configuration
2586 conf2 [X86] Force use of PCI Configuration
2588 noaer [PCIE] If the PCIEAER kernel config parameter is
2589 enabled, this kernel boot option can be used to
2590 disable the use of PCIE advanced error reporting.
2591 nodomains [PCI] Disable support for multiple PCI
2592 root domains (aka PCI segments, in ACPI-speak).
2593 nommconf [X86] Disable use of MMCONFIG for PCI
2595 check_enable_amd_mmconf [X86] check for and enable
2596 properly configured MMIO access to PCI
2597 config space on AMD family 10h CPU
2598 nomsi [MSI] If the PCI_MSI kernel config parameter is
2599 enabled, this kernel boot option can be used to
2600 disable the use of MSI interrupts system-wide.
2601 noioapicquirk [APIC] Disable all boot interrupt quirks.
2602 Safety option to keep boot IRQs enabled. This
2603 should never be necessary.
2604 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2605 primary IO-APIC for bridges that cannot disable
2606 boot IRQs. This fixes a source of spurious IRQs
2607 when the system masks IRQs.
2608 noioapicreroute [APIC] Disable workaround that uses the
2609 boot IRQ equivalent of an IRQ that connects to
2610 a chipset where boot IRQs cannot be disabled.
2611 The opposite of ioapicreroute.
2612 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2613 routing table. These calls are known to be buggy
2614 on several machines and they hang the machine
2615 when used, but on other computers it's the only
2616 way to get the interrupt routing table. Try
2617 this option if the kernel is unable to allocate
2618 IRQs or discover secondary PCI buses on your
2620 rom [X86] Assign address space to expansion ROMs.
2621 Use with caution as certain devices share
2622 address decoders between ROMs and other
2624 norom [X86] Do not assign address space to
2625 expansion ROMs that do not already have
2626 BIOS assigned address ranges.
2627 nobar [X86] Do not assign address space to the
2628 BARs that weren't assigned by the BIOS.
2629 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2630 assigned automatically to PCI devices. You can
2631 make the kernel exclude IRQs of your ISA cards
2633 pirqaddr=0xAAAAA [X86] Specify the physical address
2634 of the PIRQ table (normally generated
2635 by the BIOS) if it is outside the
2636 F0000h-100000h range.
2637 lastbus=N [X86] Scan all buses thru bus #N. Can be
2638 useful if the kernel is unable to find your
2639 secondary buses and you want to tell it
2640 explicitly which ones they are.
2641 assign-busses [X86] Always assign all PCI bus
2642 numbers ourselves, overriding
2643 whatever the firmware may have done.
2644 usepirqmask [X86] Honor the possible IRQ mask stored
2645 in the BIOS $PIR table. This is needed on
2646 some systems with broken BIOSes, notably
2647 some HP Pavilion N5400 and Omnibook XE3
2648 notebooks. This will have no effect if ACPI
2649 IRQ routing is enabled.
2650 noacpi [X86] Do not use ACPI for IRQ routing
2651 or for PCI scanning.
2652 use_crs [X86] Use PCI host bridge window information
2653 from ACPI. On BIOSes from 2008 or later, this
2654 is enabled by default. If you need to use this,
2655 please report a bug.
2656 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2657 If you need to use this, please report a bug.
2658 routeirq Do IRQ routing for all PCI devices.
2659 This is normally done in pci_enable_device(),
2660 so this option is a temporary workaround
2661 for broken drivers that don't call it.
2662 skip_isa_align [X86] do not align io start addr, so can
2663 handle more pci cards
2664 firmware [ARM] Do not re-enumerate the bus but instead
2665 just use the configuration from the
2666 bootloader. This is currently used on
2667 IXP2000 systems where the bus has to be
2668 configured a certain way for adjunct CPUs.
2669 noearly [X86] Don't do any early type 1 scanning.
2670 This might help on some broken boards which
2671 machine check when some devices' config space
2672 is read. But various workarounds are disabled
2673 and some IOMMU drivers will not work.
2674 bfsort Sort PCI devices into breadth-first order.
2675 This sorting is done to get a device
2676 order compatible with older (<= 2.4) kernels.
2677 nobfsort Don't sort PCI devices into breadth-first order.
2678 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2679 tuning and use the BIOS-configured MPS defaults.
2680 pcie_bus_safe Set every device's MPS to the largest value
2681 supported by all devices below the root complex.
2682 pcie_bus_perf Set device MPS to the largest allowable MPS
2683 based on its parent bus. Also set MRRS (Max
2684 Read Request Size) to the largest supported
2685 value (no larger than the MPS that the device
2686 or bus can support) for best performance.
2687 pcie_bus_peer2peer Set every device's MPS to 128B, which
2688 every device is guaranteed to support. This
2689 configuration allows peer-to-peer DMA between
2690 any pair of devices, possibly at the cost of
2691 reduced performance. This also guarantees
2692 that hot-added devices will work.
2693 cbiosize=nn[KMG] The fixed amount of bus space which is
2694 reserved for the CardBus bridge's IO window.
2695 The default value is 256 bytes.
2696 cbmemsize=nn[KMG] The fixed amount of bus space which is
2697 reserved for the CardBus bridge's memory
2698 window. The default value is 64 megabytes.
2701 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2702 Specifies alignment and device to reassign
2703 aligned memory resources.
2704 If <order of align> is not specified,
2705 PAGE_SIZE is used as alignment.
2706 PCI-PCI bridge can be specified, if resource
2707 windows need to be expanded.
2708 ecrc= Enable/disable PCIe ECRC (transaction layer
2709 end-to-end CRC checking).
2710 bios: Use BIOS/firmware settings. This is the
2714 hpiosize=nn[KMG] The fixed amount of bus space which is
2715 reserved for hotplug bridge's IO window.
2716 Default size is 256 bytes.
2717 hpmemsize=nn[KMG] The fixed amount of bus space which is
2718 reserved for hotplug bridge's memory window.
2719 Default size is 2 megabytes.
2720 realloc= Enable/disable reallocating PCI bridge resources
2721 if allocations done by BIOS are too small to
2722 accommodate resources required by all child
2724 off: Turn realloc off
2726 realloc same as realloc=on
2727 noari do not use PCIe ARI.
2728 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2729 only look for one device below a PCIe downstream
2732 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2735 force Enable ASPM even on devices that claim not to support it.
2736 WARNING: Forcing ASPM on may cause system lockups.
2738 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2739 nomsi Do not use MSI for PCI Express Native Hotplug (this
2740 makes all PCIe ports use INTx for hotplug services).
2742 pcie_ports= [PCIE] PCIe ports handling:
2743 auto Ask the BIOS whether or not to use native PCIe services
2744 associated with PCIe ports (PME, hot-plug, AER). Use
2745 them only if that is allowed by the BIOS.
2746 native Use native PCIe services associated with PCIe ports
2748 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2751 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2752 nomsi Do not use MSI for native PCIe PME signaling (this makes
2753 all PCIe root ports use INTx for all services).
2755 pcmv= [HW,PCMCIA] BadgePAD 4
2759 Keep all power-domains already enabled by bootloader on,
2760 even if no driver has claimed them. This is useful
2761 for debug and development, but should not be
2762 needed on a platform with proper driver support.
2765 See Documentation/blockdev/paride.txt.
2767 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2770 See arch/parisc/kernel/pdc_chassis.c
2772 percpu_alloc= Select which percpu first chunk allocator to use.
2773 Currently supported values are "embed" and "page".
2774 Archs may support subset or none of the selections.
2775 See comments in mm/percpu.c for details on each
2776 allocator. This parameter is primarily for debugging
2777 and performance comparison.
2780 See Documentation/blockdev/paride.txt.
2783 See Documentation/blockdev/paride.txt.
2785 pirq= [SMP,APIC] Manual mp-table setup
2786 See Documentation/x86/i386/IO-APIC.txt.
2788 plip= [PPT,NET] Parallel port network link
2789 Format: { parport<nr> | timid | 0 }
2790 See also Documentation/parport.txt.
2792 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2793 Override pmtimer IOPort with a hex value.
2797 Enable PNP debug messages (depends on the
2798 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2799 via /sys/module/pnp/parameters/debug. We always show
2800 current resource usage; turning this on also shows
2801 possible settings and some assignment information.
2807 { on | off | curr | res | no-curr | no-res }
2810 [ISAPNP] Exclude IRQs for the autoconfiguration
2813 [ISAPNP] Exclude DMAs for the autoconfiguration
2815 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2816 Ranges are in pairs (I/O port base and size).
2819 [ISAPNP] Exclude memory regions for the
2821 Ranges are in pairs (memory base and size).
2823 ports= [IP_VS_FTP] IPVS ftp helper module
2825 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2827 Format: <port>,<port>....
2829 print-fatal-signals=
2830 [KNL] debug: print fatal signals
2832 If enabled, warn about various signal handling
2833 related application anomalies: too many signals,
2834 too many POSIX.1 timers, fatal signals causing a
2837 If you hit the warning due to signal overflow,
2838 you might want to try "ulimit -i unlimited".
2842 printk.always_kmsg_dump=
2843 Trigger kmsg_dump for cases other than kernel oops or
2845 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2848 printk.time= Show timing data prefixed to each printk message line
2849 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2851 processor.max_cstate= [HW,ACPI]
2852 Limit processor to maximum C-state
2853 max_cstate=9 overrides any DMI blacklist limit.
2855 processor.nocst [HW,ACPI]
2856 Ignore the _CST method to determine C-states,
2857 instead using the legacy FADT method
2859 profile= [KNL] Enable kernel profiling via /proc/profile
2860 Format: [schedule,]<number>
2861 Param: "schedule" - profile schedule points.
2862 Param: <number> - step/bucket size as a power of 2 for
2863 statistical time based profiling.
2864 Param: "sleep" - profile D-state sleeping (millisecs).
2865 Requires CONFIG_SCHEDSTATS
2866 Param: "kvm" - profile VM exits.
2868 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2870 See Documentation/blockdev/ramdisk.txt.
2872 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2873 probe for; one of (bare|imps|exps|lifebook|any).
2874 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2876 psmouse.resetafter= [HW,MOUSE]
2877 Try to reset the device after so many bad packets
2880 [HW,MOUSE] Set desired mouse resolution, in dpi.
2881 psmouse.smartscroll=
2882 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2883 0 = disabled, 1 = enabled (default).
2885 pstore.backend= Specify the name of the pstore backend to use
2888 See Documentation/blockdev/paride.txt.
2891 [KNL] Number of legacy pty's. Overwrites compiled-in
2894 quiet [KNL] Disable most log messages
2899 See Documentation/md.txt.
2901 ramdisk_blocksize= [RAM]
2902 See Documentation/blockdev/ramdisk.txt.
2904 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2905 See Documentation/blockdev/ramdisk.txt.
2908 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2909 the specified list of CPUs to be no-callback CPUs.
2910 Invocation of these CPUs' RCU callbacks will
2911 be offloaded to "rcuox/N" kthreads created for
2912 that purpose, where "x" is "b" for RCU-bh, "p"
2913 for RCU-preempt, and "s" for RCU-sched, and "N"
2914 is the CPU number. This reduces OS jitter on the
2915 offloaded CPUs, which can be useful for HPC and
2916 real-time workloads. It can also improve energy
2917 efficiency for asymmetric multiprocessors.
2920 Rather than requiring that offloaded CPUs
2921 (specified by rcu_nocbs= above) explicitly
2922 awaken the corresponding "rcuoN" kthreads,
2923 make these kthreads poll for callbacks.
2924 This improves the real-time response for the
2925 offloaded CPUs by relieving them of the need to
2926 wake up the corresponding kthread, but degrades
2927 energy efficiency by requiring that the kthreads
2928 periodically wake up to do the polling.
2930 rcutree.blimit= [KNL]
2931 Set maximum number of finished RCU callbacks to
2932 process in one batch.
2934 rcutree.rcu_fanout_leaf= [KNL]
2935 Increase the number of CPUs assigned to each
2936 leaf rcu_node structure. Useful for very large
2939 rcutree.jiffies_till_sched_qs= [KNL]
2940 Set required age in jiffies for a
2941 given grace period before RCU starts
2942 soliciting quiescent-state help from
2943 rcu_note_context_switch().
2945 rcutree.jiffies_till_first_fqs= [KNL]
2946 Set delay from grace-period initialization to
2947 first attempt to force quiescent states.
2948 Units are jiffies, minimum value is zero,
2949 and maximum value is HZ.
2951 rcutree.jiffies_till_next_fqs= [KNL]
2952 Set delay between subsequent attempts to force
2953 quiescent states. Units are jiffies, minimum
2954 value is one, and maximum value is HZ.
2956 rcutree.kthread_prio= [KNL,BOOT]
2957 Set the SCHED_FIFO priority of the RCU
2958 per-CPU kthreads (rcuc/N). This value is also
2959 used for the priority of the RCU boost threads
2960 (rcub/N). Valid values are 1-99 and the default
2961 is 1 (the least-favored priority).
2963 rcutree.rcu_nocb_leader_stride= [KNL]
2964 Set the number of NOCB kthread groups, which
2965 defaults to the square root of the number of
2966 CPUs. Larger numbers reduces the wakeup overhead
2967 on the per-CPU grace-period kthreads, but increases
2968 that same overhead on each group's leader.
2970 rcutree.qhimark= [KNL]
2971 Set threshold of queued RCU callbacks beyond which
2972 batch limiting is disabled.
2974 rcutree.qlowmark= [KNL]
2975 Set threshold of queued RCU callbacks below which
2976 batch limiting is re-enabled.
2978 rcutree.rcu_idle_gp_delay= [KNL]
2979 Set wakeup interval for idle CPUs that have
2980 RCU callbacks (RCU_FAST_NO_HZ=y).
2982 rcutree.rcu_idle_lazy_gp_delay= [KNL]
2983 Set wakeup interval for idle CPUs that have
2984 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2985 Lazy RCU callbacks are those which RCU can
2986 prove do nothing more than free memory.
2988 rcutorture.cbflood_inter_holdoff= [KNL]
2989 Set holdoff time (jiffies) between successive
2990 callback-flood tests.
2992 rcutorture.cbflood_intra_holdoff= [KNL]
2993 Set holdoff time (jiffies) between successive
2994 bursts of callbacks within a given callback-flood
2997 rcutorture.cbflood_n_burst= [KNL]
2998 Set the number of bursts making up a given
2999 callback-flood test. Set this to zero to
3000 disable callback-flood testing.
3002 rcutorture.cbflood_n_per_burst= [KNL]
3003 Set the number of callbacks to be registered
3004 in a given burst of a callback-flood test.
3006 rcutorture.fqs_duration= [KNL]
3007 Set duration of force_quiescent_state bursts.
3009 rcutorture.fqs_holdoff= [KNL]
3010 Set holdoff time within force_quiescent_state bursts.
3012 rcutorture.fqs_stutter= [KNL]
3013 Set wait time between force_quiescent_state bursts.
3015 rcutorture.gp_exp= [KNL]
3016 Use expedited update-side primitives.
3018 rcutorture.gp_normal= [KNL]
3019 Use normal (non-expedited) update-side primitives.
3020 If both gp_exp and gp_normal are set, do both.
3021 If neither gp_exp nor gp_normal are set, still
3024 rcutorture.n_barrier_cbs= [KNL]
3025 Set callbacks/threads for rcu_barrier() testing.
3027 rcutorture.nfakewriters= [KNL]
3028 Set number of concurrent RCU writers. These just
3029 stress RCU, they don't participate in the actual
3030 test, hence the "fake".
3032 rcutorture.nreaders= [KNL]
3033 Set number of RCU readers.
3035 rcutorture.object_debug= [KNL]
3036 Enable debug-object double-call_rcu() testing.
3038 rcutorture.onoff_holdoff= [KNL]
3039 Set time (s) after boot for CPU-hotplug testing.
3041 rcutorture.onoff_interval= [KNL]
3042 Set time (s) between CPU-hotplug operations, or
3043 zero to disable CPU-hotplug testing.
3045 rcutorture.torture_runnable= [BOOT]
3046 Start rcutorture running at boot time.
3048 rcutorture.shuffle_interval= [KNL]
3049 Set task-shuffle interval (s). Shuffling tasks
3050 allows some CPUs to go into dyntick-idle mode
3051 during the rcutorture test.
3053 rcutorture.shutdown_secs= [KNL]
3054 Set time (s) after boot system shutdown. This
3055 is useful for hands-off automated testing.
3057 rcutorture.stall_cpu= [KNL]
3058 Duration of CPU stall (s) to test RCU CPU stall
3059 warnings, zero to disable.
3061 rcutorture.stall_cpu_holdoff= [KNL]
3062 Time to wait (s) after boot before inducing stall.
3064 rcutorture.stat_interval= [KNL]
3065 Time (s) between statistics printk()s.
3067 rcutorture.stutter= [KNL]
3068 Time (s) to stutter testing, for example, specifying
3069 five seconds causes the test to run for five seconds,
3070 wait for five seconds, and so on. This tests RCU's
3071 ability to transition abruptly to and from idle.
3073 rcutorture.test_boost= [KNL]
3074 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3075 "Maybe" means test if the RCU implementation
3076 under test support RCU priority boosting.
3078 rcutorture.test_boost_duration= [KNL]
3079 Duration (s) of each individual boost test.
3081 rcutorture.test_boost_interval= [KNL]
3082 Interval (s) between each boost test.
3084 rcutorture.test_no_idle_hz= [KNL]
3085 Test RCU's dyntick-idle handling. See also the
3086 rcutorture.shuffle_interval parameter.
3088 rcutorture.torture_type= [KNL]
3089 Specify the RCU implementation to test.
3091 rcutorture.verbose= [KNL]
3092 Enable additional printk() statements.
3094 rcupdate.rcu_expedited= [KNL]
3095 Use expedited grace-period primitives, for
3096 example, synchronize_rcu_expedited() instead
3097 of synchronize_rcu(). This reduces latency,
3098 but can increase CPU utilization, degrade
3099 real-time latency, and degrade energy efficiency.
3101 rcupdate.rcu_cpu_stall_suppress= [KNL]
3102 Suppress RCU CPU stall warning messages.
3104 rcupdate.rcu_cpu_stall_timeout= [KNL]
3105 Set timeout for RCU CPU stall warning messages.
3107 rcupdate.rcu_task_stall_timeout= [KNL]
3108 Set timeout in jiffies for RCU task stall warning
3109 messages. Disable with a value less than or equal
3112 rcupdate.rcu_self_test= [KNL]
3113 Run the RCU early boot self tests
3115 rcupdate.rcu_self_test_bh= [KNL]
3116 Run the RCU bh early boot self tests
3118 rcupdate.rcu_self_test_sched= [KNL]
3119 Run the RCU sched early boot self tests
3123 Run specified binary instead of /init from the ramdisk,
3124 used for early userspace startup. See initrd.
3127 Format (x86 or x86_64):
3128 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3130 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3132 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3133 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3134 reboot_force is either force or not specified,
3135 reboot_cpu is s[mp]#### with #### being the processor
3136 to be used for rebooting.
3139 [KNL, SMP] Set scheduler's default relax_domain_level.
3140 See Documentation/cgroups/cpusets.txt.
3142 relative_sleep_states=
3143 [SUSPEND] Use sleep state labeling where the deepest
3144 state available other than hibernation is always "mem".
3145 Format: { "0" | "1" }
3146 0 -- Traditional sleep state labels.
3147 1 -- Relative sleep state labels.
3149 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3151 reservetop= [X86-32]
3153 Reserves a hole at the top of the kernel virtual
3158 Set the amount of memory to reserve for BIOS at
3159 the bottom of the address space.
3161 reset_devices [KNL] Force drivers to reset the underlying device
3162 during initialization.
3165 Specify the partition device for software suspend
3167 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3169 resume_offset= [SWSUSP]
3170 Specify the offset from the beginning of the partition
3171 given by "resume=" at which the swap header is located,
3172 in <PAGE_SIZE> units (needed only for swap files).
3173 See Documentation/power/swsusp-and-swap-files.txt
3175 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3176 read the resume files
3178 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3179 Useful for devices that are detected asynchronously
3180 (e.g. USB and MMC devices).
3182 hibernate= [HIBERNATION]
3183 noresume Don't check if there's a hibernation image
3184 present during boot.
3185 nocompress Don't compress/decompress hibernation images.
3186 no Disable hibernation and resume.
3188 retain_initrd [RAM] Keep initrd memory after extraction
3190 rhash_entries= [KNL,NET]
3191 Set number of hash buckets for route cache
3193 ro [KNL] Mount root device read-only on boot
3195 root= [KNL] Root filesystem
3196 See name_to_dev_t comment in init/do_mounts.c.
3198 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3199 mount the root filesystem
3201 rootflags= [KNL] Set root filesystem mount option string
3203 rootfstype= [KNL] Set root filesystem type
3205 rootwait [KNL] Wait (indefinitely) for root device to show up.
3206 Useful for devices that are detected asynchronously
3207 (e.g. USB and MMC devices).
3209 rproc_mem=nn[KMG][@address]
3210 [KNL,ARM,CMA] Remoteproc physical memory block.
3211 Memory area to be used by remote processor image,
3214 rw [KNL] Mount root device read-write on boot
3216 S [KNL] Run init in single mode
3218 s390_iommu= [HW,S390]
3219 Set s390 IOTLB flushing mode
3221 With strict flushing every unmap operation will result in
3222 an IOTLB flush. Default is lazy flushing before reuse,
3226 See drivers/net/irda/sa1100_ir.c.
3228 sbni= [NET] Granch SBNI12 leased line adapter
3230 sched_debug [KNL] Enables verbose scheduler debug messages.
3232 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3233 xtime_lock contention on larger systems, and/or RCU lock
3234 contention on all systems with CONFIG_MAXSMP set.
3235 Format: { "0" | "1" }
3236 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3238 Note: increases power consumption, thus should only be
3239 enabled if running jitter sensitive (HPC/RT) workloads.
3241 security= [SECURITY] Choose a security module to enable at boot.
3242 If this boot parameter is not specified, only the first
3243 security module asking for security registration will be
3244 loaded. An invalid security module name will be treated
3245 as if no module has been chosen.
3247 selinux= [SELINUX] Disable or enable SELinux at boot time.
3248 Format: { "0" | "1" }
3249 See security/selinux/Kconfig help text.
3252 Default value is set via kernel config option.
3253 If enabled at boot time, /selinux/disable can be used
3254 later to disable prior to initial policy load.
3256 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3257 Format: { "0" | "1" }
3258 See security/apparmor/Kconfig help text
3261 Default value is set via kernel config option.
3263 serialnumber [BUGS=X86-32]
3266 Maximal number of shapers.
3268 show_msr= [x86] show boot-time MSR settings
3269 Format: { <integer> }
3270 Show boot-time (BIOS-initialized) MSR settings.
3271 The parameter means the number of CPUs to show,
3272 for example 1 means boot CPU only.
3280 Disable merging of slabs with similar size. May be
3281 necessary if there is some reason to distinguish
3282 allocs to different slabs. Debug options disable
3283 merging on their own.
3284 For more information see Documentation/vm/slub.txt.
3286 slab_max_order= [MM, SLAB]
3287 Determines the maximum allowed order for slabs.
3288 A high setting may cause OOMs due to memory
3289 fragmentation. Defaults to 1 for systems with
3290 more than 32MB of RAM, 0 otherwise.
3292 slub_debug[=options[,slabs]] [MM, SLUB]
3293 Enabling slub_debug allows one to determine the
3294 culprit if slab objects become corrupted. Enabling
3295 slub_debug can create guard zones around objects and
3296 may poison objects when not in use. Also tracks the
3297 last alloc / free. For more information see
3298 Documentation/vm/slub.txt.
3300 slub_max_order= [MM, SLUB]
3301 Determines the maximum allowed order for slabs.
3302 A high setting may cause OOMs due to memory
3303 fragmentation. For more information see
3304 Documentation/vm/slub.txt.
3306 slub_min_objects= [MM, SLUB]
3307 The minimum number of objects per slab. SLUB will
3308 increase the slab order up to slub_max_order to
3309 generate a sufficiently large slab able to contain
3310 the number of objects indicated. The higher the number
3311 of objects the smaller the overhead of tracking slabs
3312 and the less frequently locks need to be acquired.
3313 For more information see Documentation/vm/slub.txt.
3315 slub_min_order= [MM, SLUB]
3316 Determines the minimum page order for slabs. Must be
3317 lower than slub_max_order.
3318 For more information see Documentation/vm/slub.txt.
3320 slub_nomerge [MM, SLUB]
3321 Same with slab_nomerge. This is supported for legacy.
3322 See slab_nomerge for more information.
3325 Format: <io1>[,<io2>[,...,<io8>]]
3327 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3328 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3329 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3330 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3331 smsc-ircc2.ircc_irq= [HW] IRQ line
3332 smsc-ircc2.ircc_dma= [HW] DMA channel
3333 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3334 0: Toshiba Satellite 1800 (GP data pin select)
3335 1: Fast pin select (default)
3339 [KNL] Should the soft-lockup detector generate panics.
3342 softlockup_all_cpu_backtrace=
3343 [KNL] Should the soft-lockup detector generate
3344 backtraces on all cpus.
3347 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3348 See Documentation/laptops/sonypi.txt
3350 spia_io_base= [HW,MTD]
3356 Enabled the stack tracer on boot up.
3358 stacktrace_filter=[function-list]
3359 [FTRACE] Limit the functions that the stack tracer
3360 will trace at boot up. function-list is a comma separated
3361 list of functions. This list can be changed at run
3362 time by the stack_trace_filter file in the debugfs
3363 tracing directory. Note, this enables stack tracing
3364 and the stacktrace above is not needed.
3368 Set the STI (builtin display/keyboard on the HP-PARISC
3369 machines) console (graphic card) which should be used
3370 as the initial boot-console.
3371 See also comment in drivers/video/console/sticore.c.
3374 See comment in drivers/video/console/sticore.c.
3377 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3379 sunrpc.min_resvport=
3380 sunrpc.max_resvport=
3382 SunRPC servers often require that client requests
3383 originate from a privileged port (i.e. a port in the
3384 range 0 < portnr < 1024).
3385 An administrator who wishes to reserve some of these
3386 ports for other uses may adjust the range that the
3387 kernel's sunrpc client considers to be privileged
3388 using these two parameters to set the minimum and
3389 maximum port values.
3393 Control how the NFS server code allocates CPUs to
3394 service thread pools. Depending on how many NICs
3395 you have and where their interrupts are bound, this
3396 option will affect which CPUs will do NFS serving.
3397 Note: this parameter cannot be changed while the
3398 NFS server is running.
3400 auto the server chooses an appropriate mode
3401 automatically using heuristics
3402 global a single global pool contains all CPUs
3403 percpu one pool for each CPU
3404 pernode one pool for each NUMA node (equivalent
3405 to global on non-NUMA machines)
3407 sunrpc.tcp_slot_table_entries=
3408 sunrpc.udp_slot_table_entries=
3410 Sets the upper limit on the number of simultaneous
3411 RPC calls that can be sent from the client to a
3412 server. Increasing these values may allow you to
3413 improve throughput, but will also increase the
3414 amount of memory reserved for use by the client.
3417 [KNL] Enable accounting of swap in memory resource
3418 controller if no parameter or 1 is given or disable
3419 it if 0 is given (See Documentation/cgroups/memory.txt)
3421 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3422 Format: { <int> | force }
3423 <int> -- Number of I/O TLB slabs
3424 force -- force using of bounce buffers even if they
3425 wouldn't be automatically used by the kernel
3429 sysfs.deprecated=0|1 [KNL]
3430 Enable/disable old style sysfs layout for old udev
3431 on older distributions. When this option is enabled
3432 very new udev will not work anymore. When this option
3433 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3434 in older udev will not work anymore.
3435 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3436 the kernel configuration.
3438 sysrq_always_enabled
3440 Ignore sysrq setting - this boot parameter will
3441 neutralize any effect of /proc/sys/kernel/sysrq.
3442 Useful for debugging.
3446 test_suspend= [SUSPEND][,N]
3447 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3448 standby suspend) or "freeze" (for suspend type freeze)
3449 as the system sleep state during system startup with
3450 the optional capability to repeat N number of times.
3451 The system is woken from this state using a
3452 wakeup-capable RTC alarm.
3454 thash_entries= [KNL,NET]
3455 Set number of hash buckets for TCP connection
3457 thermal.act= [HW,ACPI]
3458 -1: disable all active trip points in all thermal zones
3459 <degrees C>: override all lowest active trip points
3461 thermal.crt= [HW,ACPI]
3462 -1: disable all critical trip points in all thermal zones
3463 <degrees C>: override all critical trip points
3465 thermal.nocrt= [HW,ACPI]
3466 Set to disable actions on ACPI thermal zone
3467 critical and hot trip points.
3469 thermal.off= [HW,ACPI]
3470 1: disable ACPI thermal control
3472 thermal.psv= [HW,ACPI]
3473 -1: disable all passive trip points
3474 <degrees C>: override all passive trip points to this
3477 thermal.tzp= [HW,ACPI]
3478 Specify global default ACPI thermal zone polling rate
3479 <deci-seconds>: poll all this frequency
3480 0: no polling (default)
3483 Force threading of all interrupt handlers except those
3484 marked explicitly IRQF_NO_THREAD.
3487 Enable the Transcendent memory driver if built-in.
3489 tmem.cleancache=0|1 [KNL, XEN]
3490 Default is on (1). Disable the usage of the cleancache
3491 API to send anonymous pages to the hypervisor.
3493 tmem.frontswap=0|1 [KNL, XEN]
3494 Default is on (1). Disable the usage of the frontswap
3495 API to send swap pages to the hypervisor. If disabled
3496 the selfballooning and selfshrinking are force disabled.
3498 tmem.selfballooning=0|1 [KNL, XEN]
3499 Default is on (1). Disable the driving of swap pages
3502 tmem.selfshrinking=0|1 [KNL, XEN]
3503 Default is on (1). Partial swapoff that immediately
3504 transfers pages from Xen hypervisor back to the
3505 kernel based on different criteria.
3509 Specify if the kernel should make use of the cpu
3510 topology information if the hardware supports this.
3511 The scheduler will make use of this information and
3512 e.g. base its process migration decisions on it.
3515 topology_updates= [KNL, PPC, NUMA]
3517 Specify if the kernel should ignore (off)
3518 topology updates sent by the hypervisor to this
3523 tpm_suspend_pcr=[HW,TPM]
3524 Format: integer pcr id
3525 Specify that at suspend time, the tpm driver
3526 should extend the specified pcr with zeros,
3527 as a workaround for some chips which fail to
3528 flush the last written pcr on TPM_SaveState.
3529 This will guarantee that all the other pcrs
3532 trace_buf_size=nn[KMG]
3533 [FTRACE] will set tracing buffer size on each cpu.
3535 trace_event=[event-list]
3536 [FTRACE] Set and start specified trace events in order
3537 to facilitate early boot debugging.
3538 See also Documentation/trace/events.txt
3540 trace_options=[option-list]
3541 [FTRACE] Enable or disable tracer options at boot.
3542 The option-list is a comma delimited list of options
3543 that can be enabled or disabled just as if you were
3544 to echo the option name into
3546 /sys/kernel/debug/tracing/trace_options
3548 For example, to enable stacktrace option (to dump the
3549 stack trace of each event), add to the command line:
3551 trace_options=stacktrace
3553 See also Documentation/trace/ftrace.txt "trace options"
3557 [FTRACE] enable this option to disable tracing when a
3558 warning is hit. This turns off "tracing_on". Tracing can
3559 be enabled again by echoing '1' into the "tracing_on"
3560 file located in /sys/kernel/debug/tracing/
3562 This option is useful, as it disables the trace before
3563 the WARNING dump is called, which prevents the trace to
3564 be filled with content caused by the warning output.
3566 This option can also be set at run time via the sysctl
3567 option: kernel/traceoff_on_warning
3569 transparent_hugepage=
3571 Format: [always|madvise|never]
3572 Can be used to control the default behavior of the system
3573 with respect to transparent hugepages.
3574 See Documentation/vm/transhuge.txt for more details.
3576 tsc= Disable clocksource stability checks for TSC.
3578 [x86] reliable: mark tsc clocksource as reliable, this
3579 disables clocksource verification at runtime, as well
3580 as the stability checks done at bootup. Used to enable
3581 high-resolution timer mode on older hardware, and in
3582 virtualized environment.
3583 [x86] noirqtime: Do not use TSC to do irq accounting.
3584 Used to run time disable IRQ_TIME_ACCOUNTING on any
3585 platforms where RDTSC is slow and this accounting
3588 turbografx.map[2|3]= [HW,JOY]
3589 TurboGraFX parallel port interface
3591 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3592 See also Documentation/input/joystick-parport.txt
3594 udbg-immortal [PPC] When debugging early kernel crashes that
3595 happen after console_init() and before a proper
3596 console driver takes over, this boot options might
3597 help "seeing" what's going on.
3599 uhash_entries= [KNL,NET]
3600 Set number of hash buckets for UDP/UDP-Lite connections
3603 [USB] Ignore overcurrent events (default N).
3604 Some badly-designed motherboards generate lots of
3605 bogus events, for ports that aren't wired to
3606 anything. Set this parameter to avoid log spamming.
3607 Note that genuine overcurrent events won't be
3611 [X86] Cause panic on unknown NMI.
3613 usbcore.authorized_default=
3614 [USB] Default USB device authorization:
3615 (default -1 = authorized except for wireless USB,
3616 0 = not authorized, 1 = authorized)
3618 usbcore.autosuspend=
3619 [USB] The autosuspend time delay (in seconds) used
3620 for newly-detected USB devices (default 2). This
3621 is the time required before an idle device will be
3622 autosuspended. Devices for which the delay is set
3623 to a negative value won't be autosuspended at all.
3625 usbcore.usbfs_snoop=
3626 [USB] Set to log all usbfs traffic (default 0 = off).
3628 usbcore.blinkenlights=
3629 [USB] Set to cycle leds on hubs (default 0 = off).
3631 usbcore.old_scheme_first=
3632 [USB] Start with the old device initialization
3633 scheme (default 0 = off).
3635 usbcore.usbfs_memory_mb=
3636 [USB] Memory limit (in MB) for buffers allocated by
3637 usbfs (default = 16, 0 = max = 2047).
3639 usbcore.use_both_schemes=
3640 [USB] Try the other device initialization scheme
3641 if the first one fails (default 1 = enabled).
3643 usbcore.initial_descriptor_timeout=
3644 [USB] Specifies timeout for the initial 64-byte
3645 USB_REQ_GET_DESCRIPTOR request in milliseconds
3646 (default 5000 = 5.0 seconds).
3649 [USBHID] The interval which mice are to be polled at.
3651 usb-storage.delay_use=
3652 [UMS] The delay in seconds before a new device is
3653 scanned for Logical Units (default 1).
3656 [UMS] A list of quirks entries to supplement or
3657 override the built-in unusual_devs list. List
3658 entries are separated by commas. Each entry has
3659 the form VID:PID:Flags where VID and PID are Vendor
3660 and Product ID values (4-digit hex numbers) and
3661 Flags is a set of characters, each corresponding
3662 to a common usb-storage quirk flag as follows:
3663 a = SANE_SENSE (collect more than 18 bytes
3665 b = BAD_SENSE (don't collect more than 18
3666 bytes of sense data);
3667 c = FIX_CAPACITY (decrease the reported
3668 device capacity by one sector);
3669 d = NO_READ_DISC_INFO (don't use
3670 READ_DISC_INFO command);
3671 e = NO_READ_CAPACITY_16 (don't use
3672 READ_CAPACITY_16 command);
3673 f = NO_REPORT_OPCODES (don't use report opcodes
3675 h = CAPACITY_HEURISTICS (decrease the
3676 reported device capacity by one
3677 sector if the number is odd);
3678 i = IGNORE_DEVICE (don't bind to this
3680 l = NOT_LOCKABLE (don't try to lock and
3681 unlock ejectable media);
3682 m = MAX_SECTORS_64 (don't transfer more
3683 than 64 sectors = 32 KB at a time);
3684 n = INITIAL_READ10 (force a retry of the
3685 initial READ(10) command);
3686 o = CAPACITY_OK (accept the capacity
3687 reported by the device);
3688 p = WRITE_CACHE (the device cache is ON
3690 r = IGNORE_RESIDUE (the device reports
3691 bogus residue values);
3692 s = SINGLE_LUN (the device has only one
3694 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3695 commands, uas only);
3696 u = IGNORE_UAS (don't bind to the uas driver);
3697 w = NO_WP_DETECT (don't test whether the
3698 medium is write-protected).
3699 Example: quirks=0419:aaf5:rl,0421:0433:rc
3701 user_debug= [KNL,ARM]
3703 See arch/arm/Kconfig.debug help text.
3704 1 - undefined instruction events
3706 4 - invalid data aborts
3709 Example: user_debug=31
3712 [X86] Flags controlling user PTE allocations.
3714 nohigh = do not allocate PTE pages in
3715 HIGHMEM regardless of setting
3719 On X86_32, this is an alias for vdso32=. Otherwise:
3721 vdso=1: enable VDSO (the default)
3722 vdso=0: disable VDSO mapping
3724 vdso32= [X86] Control the 32-bit vDSO
3725 vdso32=1: enable 32-bit VDSO
3726 vdso32=0 or vdso32=2: disable 32-bit VDSO
3728 See the help text for CONFIG_COMPAT_VDSO for more
3729 details. If CONFIG_COMPAT_VDSO is set, the default is
3730 vdso32=0; otherwise, the default is vdso32=1.
3732 For compatibility with older kernels, vdso32=2 is an
3735 Try vdso32=0 if you encounter an error that says:
3736 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3739 vector=percpu: enable percpu vector domain
3741 video= [FB] Frame buffer configuration
3742 See Documentation/fb/modedb.txt.
3744 video.brightness_switch_enabled= [0,1]
3745 If set to 1, on receiving an ACPI notify event
3746 generated by hotkey, video driver will adjust brightness
3747 level and then send out the event to user space through
3748 the allocated input device; If set to 0, video driver
3749 will only send out the event without touching backlight
3754 [VMMIO] Memory mapped virtio (platform) device.
3756 <size>@<baseaddr>:<irq>[:<id>]
3758 <size> := size (can use standard suffixes
3760 <baseaddr> := physical base address
3761 <irq> := interrupt number (as passed to
3763 <id> := (optional) platform device id
3765 virtio_mmio.device=1K@0x100b0000:48:7
3767 Can be used multiple times for multiple devices.
3769 vga= [BOOT,X86-32] Select a particular video mode
3770 See Documentation/x86/boot.txt and
3771 Documentation/svga.txt.
3772 Use vga=ask for menu.
3773 This is actually a boot loader parameter; the value is
3774 passed to the kernel using a special protocol.
3776 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3777 size of <nn>. This can be used to increase the
3778 minimum size (128MB on x86). It can also be used to
3779 decrease the size and leave more room for directly
3782 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3785 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3788 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3792 Controls the behavior of vsyscalls (i.e. calls to
3793 fixed addresses of 0xffffffffff600x00 from legacy
3794 code). Most statically-linked binaries and older
3795 versions of glibc use these calls. Because these
3796 functions are at fixed addresses, they make nice
3797 targets for exploits that can control RIP.
3799 emulate [default] Vsyscalls turn into traps and are
3800 emulated reasonably safely.
3802 native Vsyscalls are native syscall instructions.
3803 This is a little bit faster than trapping
3804 and makes a few dynamic recompilers work
3805 better than they would in emulation mode.
3806 It also makes exploits much easier to write.
3808 none Vsyscalls don't work at all. This makes
3809 them quite hard to use for exploits but
3810 might break your system.
3812 vt.color= [VT] Default text color.
3813 Format: 0xYX, X = foreground, Y = background.
3814 Default: 0x07 = light gray on black.
3816 vt.cur_default= [VT] Default cursor shape.
3817 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3818 the parameters of the <Esc>[?A;B;Cc escape sequence;
3819 see VGA-softcursor.txt. Default: 2 = underline.
3821 vt.default_blu= [VT]
3822 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3823 Change the default blue palette of the console.
3824 This is a 16-member array composed of values
3827 vt.default_grn= [VT]
3828 Format: <green0>,<green1>,<green2>,...,<green15>
3829 Change the default green palette of the console.
3830 This is a 16-member array composed of values
3833 vt.default_red= [VT]
3834 Format: <red0>,<red1>,<red2>,...,<red15>
3835 Change the default red palette of the console.
3836 This is a 16-member array composed of values
3842 Set system-wide default UTF-8 mode for all tty's.
3843 Default is 1, i.e. UTF-8 mode is enabled for all
3844 newly opened terminals.
3846 vt.global_cursor_default=
3849 Set system-wide default for whether a cursor
3850 is shown on new VTs. Default is -1,
3851 i.e. cursors will be created by default unless
3852 overridden by individual drivers. 0 will hide
3853 cursors, 1 will display them.
3855 vt.italic= [VT] Default color for italic text; 0-15.
3858 vt.underline= [VT] Default color for underlined text; 0-15.
3861 watchdog timers [HW,WDT] For information on watchdog timers,
3862 see Documentation/watchdog/watchdog-parameters.txt
3863 or other driver-specific files in the
3864 Documentation/watchdog/ directory.
3866 workqueue.disable_numa
3867 By default, all work items queued to unbound
3868 workqueues are affine to the NUMA nodes they're
3869 issued on, which results in better behavior in
3870 general. If NUMA affinity needs to be disabled for
3871 whatever reason, this option can be used. Note
3872 that this also can be controlled per-workqueue for
3873 workqueues visible under /sys/bus/workqueue/.
3875 workqueue.power_efficient
3876 Per-cpu workqueues are generally preferred because
3877 they show better performance thanks to cache
3878 locality; unfortunately, per-cpu workqueues tend to
3879 be more power hungry than unbound workqueues.
3881 Enabling this makes the per-cpu workqueues which
3882 were observed to contribute significantly to power
3883 consumption unbound, leading to measurably lower
3884 power usage at the cost of small performance
3887 The default value of this parameter is determined by
3888 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3890 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3891 default x2apic cluster mode on platforms
3894 x86_intel_mid_timer= [X86-32,APBT]
3895 Choose timer option for x86 Intel MID platform.
3896 Two valid options are apbt timer only and lapic timer
3897 plus one apbt timer for broadcast timer.
3898 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3900 xen_emul_unplug= [HW,X86,XEN]
3901 Unplug Xen emulated devices
3902 Format: [unplug0,][unplug1]
3903 ide-disks -- unplug primary master IDE devices
3904 aux-ide-disks -- unplug non-primary-master IDE devices
3905 nics -- unplug network devices
3906 all -- unplug all emulated devices (NICs and IDE disks)
3907 unnecessary -- unplugging emulated devices is
3908 unnecessary even if the host did not respond to
3910 never -- do not unplug even if version check succeeds
3912 xen_nopvspin [X86,XEN]
3913 Disables the ticketlock slowpath using Xen PV
3917 Disables the PV optimizations forcing the HVM guest to
3918 run as generic HVM guest with no PV drivers.
3920 xirc2ps_cs= [NET,PCMCIA]
3922 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3924 ______________________________________________________________________
3928 Add more DRM drivers.
projects / linux.git / blob