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" }
1380 [IMA] Define a custom template format.
1381 Format: { "field1|...|fieldN" }
1383 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1384 Format: <min_file_size>
1385 Set the minimal file size for using asynchronous hash.
1386 If left unspecified, ahash usage is disabled.
1388 ahash performance varies for different data sizes on
1389 different crypto accelerators. This option can be used
1390 to achieve the best performance for a particular HW.
1392 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1394 Set hashing buffer size. Default: 4k.
1396 ahash performance varies for different chunk sizes on
1397 different crypto accelerators. This option can be used
1398 to achieve best performance for particular HW.
1402 Run specified binary instead of /sbin/init as init
1405 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1406 for working out where the kernel is dying during
1409 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1410 initcall functions. Useful for debugging built-in
1411 modules and initcalls.
1413 initrd= [BOOT] Specify the location of the initial ramdisk
1415 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1418 int_pln_enable [x86] Enable power limit notification interrupt
1420 integrity_audit=[IMA]
1421 Format: { "0" | "1" }
1422 0 -- basic integrity auditing messages. (Default)
1423 1 -- additional integrity auditing messages.
1425 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1427 Enable intel iommu driver.
1429 Disable intel iommu driver.
1430 igfx_off [Default Off]
1431 By default, gfx is mapped as normal device. If a gfx
1432 device has a dedicated DMAR unit, the DMAR unit is
1433 bypassed by not enabling DMAR with this option. In
1434 this case, gfx device will use physical address for
1437 With this option iommu will not optimize to look
1438 for io virtual address below 32-bit forcing dual
1439 address cycle on pci bus for cards supporting greater
1440 than 32-bit addressing. The default is to look
1441 for translation below 32-bit and if not available
1442 then look in the higher range.
1443 strict [Default Off]
1444 With this option on every unmap_single operation will
1445 result in a hardware IOTLB flush operation as opposed
1446 to batching them for performance.
1447 sp_off [Default Off]
1448 By default, super page will be supported if Intel IOMMU
1449 has the capability. With this option, super page will
1452 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1453 0 disables intel_idle and fall back on acpi_idle.
1454 1 to 6 specify maximum depth of C-state.
1458 Do not enable intel_pstate as the default
1459 scaling driver for the supported processors
1461 Enable intel_pstate on systems that prohibit it by default
1462 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1463 instead of acpi-cpufreq may disable platform features, such
1464 as thermal controls and power capping, that rely on ACPI
1465 P-States information being indicated to OSPM and therefore
1466 should be used with caution. This option does not work with
1467 processors that aren't supported by the intel_pstate driver
1468 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1470 Do not enable hardware P state control (HWP)
1473 Only load intel_pstate on systems which support
1474 hardware P state control (HWP) if available.
1476 intremap= [X86-64, Intel-IOMMU]
1477 on enable Interrupt Remapping (default)
1478 off disable Interrupt Remapping
1479 nosid disable Source ID checking
1481 BIOS x2APIC opt-out request will be ignored
1483 iomem= Disable strict checking of access to MMIO memory
1484 strict regions from userspace.
1501 io7= [HW] IO7 for Marvel based alpha systems
1502 See comment before marvel_specify_io7 in
1503 arch/alpha/kernel/core_marvel.c.
1505 io_delay= [X86] I/O delay method
1507 Standard port 0x80 based delay
1509 Alternate port 0xed based delay (needed on some systems)
1511 Simple two microseconds delay
1516 See Documentation/filesystems/nfs/nfsroot.txt.
1519 When an interrupt is not handled search all handlers
1520 for it. Intended to get systems with badly broken
1524 When an interrupt is not handled search all handlers
1525 for it. Also check all handlers each timer
1526 interrupt. Intended to get systems with badly broken
1530 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1532 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1534 <cpu number>,...,<cpu number>
1536 <cpu number>-<cpu number>
1537 (must be a positive range in ascending order)
1539 <cpu number>,...,<cpu number>-<cpu number>
1541 This option can be used to specify one or more CPUs
1542 to isolate from the general SMP balancing and scheduling
1543 algorithms. You can move a process onto or off an
1544 "isolated" CPU via the CPU affinity syscalls or cpuset.
1545 <cpu number> begins at 0 and the maximum value is
1546 "number of CPUs in system - 1".
1548 This option is the preferred way to isolate CPUs. The
1549 alternative -- manually setting the CPU mask of all
1550 tasks in the system -- can cause problems and
1551 suboptimal load balancer performance.
1555 ivrs_ioapic [HW,X86_64]
1556 Provide an override to the IOAPIC-ID<->DEVICE-ID
1557 mapping provided in the IVRS ACPI table. For
1558 example, to map IOAPIC-ID decimal 10 to
1559 PCI device 00:14.0 write the parameter as:
1560 ivrs_ioapic[10]=00:14.0
1562 ivrs_hpet [HW,X86_64]
1563 Provide an override to the HPET-ID<->DEVICE-ID
1564 mapping provided in the IVRS ACPI table. For
1565 example, to map HPET-ID decimal 0 to
1566 PCI device 00:14.0 write the parameter as:
1567 ivrs_hpet[0]=00:14.0
1569 js= [HW,JOY] Analog joystick
1570 See Documentation/input/joystick.txt.
1573 Enable/disable kernel and module base offset ASLR
1574 (Address Space Layout Randomization) if built into
1575 the kernel. When CONFIG_HIBERNATION is selected,
1576 kASLR is disabled by default. When kASLR is enabled,
1577 hibernation will be disabled.
1581 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1582 specifies the amount of memory usable by the kernel
1583 for non-movable allocations. The requested amount is
1584 spread evenly throughout all nodes in the system. The
1585 remaining memory in each node is used for Movable
1586 pages. In the event, a node is too small to have both
1587 kernelcore and Movable pages, kernelcore pages will
1588 take priority and other nodes will have a larger number
1589 of Movable pages. The Movable zone is used for the
1590 allocation of pages that may be reclaimed or moved
1591 by the page migration subsystem. This means that
1592 HugeTLB pages may not be allocated from this zone.
1593 Note that allocations like PTEs-from-HighMem still
1594 use the HighMem zone if it exists, and the Normal
1595 zone if it does not.
1597 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1598 Format: <Controller#>[,poll interval]
1599 The controller # is the number of the ehci usb debug
1600 port as it is probed via PCI. The poll interval is
1601 optional and is the number seconds in between
1602 each poll cycle to the debug port in case you need
1603 the functionality for interrupting the kernel with
1604 gdb or control-c on the dbgp connection. When
1605 not using this parameter you use sysrq-g to break into
1606 the kernel debugger.
1608 kgdboc= [KGDB,HW] kgdb over consoles.
1609 Requires a tty driver that supports console polling,
1610 or a supported polling keyboard driver (non-usb).
1611 Serial only format: <serial_device>[,baud]
1612 keyboard only format: kbd
1613 keyboard and serial format: kbd,<serial_device>[,baud]
1614 Optional Kernel mode setting:
1615 kms, kbd format: kms,kbd
1616 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1618 kgdbwait [KGDB] Stop kernel execution and enter the
1619 kernel debugger at the earliest opportunity.
1621 kmac= [MIPS] korina ethernet MAC address.
1622 Configure the RouterBoard 532 series on-chip
1623 Ethernet adapter MAC address.
1625 kmemleak= [KNL] Boot-time kmemleak enable/disable
1626 Valid arguments: on, off
1628 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1631 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1632 Valid arguments: 0, 1, 2
1633 kmemcheck=0 (disabled)
1634 kmemcheck=1 (enabled)
1635 kmemcheck=2 (one-shot mode)
1636 Default: 2 (one-shot mode)
1638 kstack=N [X86] Print N words from the kernel stack
1641 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1642 Default is 0 (don't ignore, but inject #GP)
1644 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1648 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1649 Default is 1 (enabled)
1651 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1653 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1655 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1656 (virtualized MMU) support on capable Intel chips.
1657 Default is 1 (enabled)
1659 kvm-intel.emulate_invalid_guest_state=
1660 [KVM,Intel] Enable emulation of invalid guest states
1661 Default is 0 (disabled)
1663 kvm-intel.flexpriority=
1664 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1665 Default is 1 (enabled)
1668 [KVM,Intel] Enable VMX nesting (nVMX).
1669 Default is 0 (disabled)
1671 kvm-intel.unrestricted_guest=
1672 [KVM,Intel] Disable unrestricted guest feature
1673 (virtualized real and unpaged mode) on capable
1674 Intel chips. Default is 1 (enabled)
1676 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1677 feature (tagged TLBs) on capable Intel chips.
1678 Default is 1 (enabled)
1684 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1687 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1688 value for LAPIC timer one-shot implementation. Default
1689 back to the programmable timer unit in the LAPIC.
1691 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1694 libata.dma= [LIBATA] DMA control
1695 libata.dma=0 Disable all PATA and SATA DMA
1696 libata.dma=1 PATA and SATA Disk DMA only
1697 libata.dma=2 ATAPI (CDROM) DMA only
1698 libata.dma=4 Compact Flash DMA only
1699 Combinations also work, so libata.dma=3 enables DMA
1700 for disks and CDROMs, but not CFs.
1702 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1703 libata.ignore_hpa=0 keep BIOS limits (default)
1704 libata.ignore_hpa=1 ignore limits, using full disk
1706 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1710 libata.force= [LIBATA] Force configurations. The format is comma
1711 separated list of "[ID:]VAL" where ID is
1712 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1713 matching port, link or device. Basically, it matches
1714 the ATA ID string printed on console by libata. If
1715 the whole ID part is omitted, the last PORT and DEVICE
1716 values are used. If ID hasn't been specified yet, the
1717 configuration applies to all ports, links and devices.
1719 If only DEVICE is omitted, the parameter applies to
1720 the port and all links and devices behind it. DEVICE
1721 number of 0 either selects the first device or the
1722 first fan-out link behind PMP device. It does not
1723 select the host link. DEVICE number of 15 selects the
1724 host link and device attached to it.
1726 The VAL specifies the configuration to force. As long
1727 as there's no ambiguity shortcut notation is allowed.
1728 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1729 The following configurations can be forced.
1731 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1732 Any ID with matching PORT is used.
1734 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1736 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1737 udma[/][16,25,33,44,66,100,133] notation is also
1740 * [no]ncq: Turn on or off NCQ.
1742 * nohrst, nosrst, norst: suppress hard, soft
1745 * rstonce: only attempt one reset during
1746 hot-unplug link recovery
1748 * dump_id: dump IDENTIFY data.
1750 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1752 * disable: Disable this device.
1754 If there are multiple matching configurations changing
1755 the same attribute, the last one is used.
1757 memblock=debug [KNL] Enable memblock debug messages.
1759 load_ramdisk= [RAM] List of ramdisks to load from floppy
1760 See Documentation/blockdev/ramdisk.txt.
1762 lockd.nlm_grace_period=P [NFS] Assign grace period.
1765 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1768 lockd.nlm_timeout=T [NFS] Assign timeout value.
1771 lockd.nlm_udpport=M [NFS] Assign UDP port.
1774 locktorture.nreaders_stress= [KNL]
1775 Set the number of locking read-acquisition kthreads.
1776 Defaults to being automatically set based on the
1777 number of online CPUs.
1779 locktorture.nwriters_stress= [KNL]
1780 Set the number of locking write-acquisition kthreads.
1782 locktorture.onoff_holdoff= [KNL]
1783 Set time (s) after boot for CPU-hotplug testing.
1785 locktorture.onoff_interval= [KNL]
1786 Set time (s) between CPU-hotplug operations, or
1787 zero to disable CPU-hotplug testing.
1789 locktorture.shuffle_interval= [KNL]
1790 Set task-shuffle interval (jiffies). Shuffling
1791 tasks allows some CPUs to go into dyntick-idle
1792 mode during the locktorture test.
1794 locktorture.shutdown_secs= [KNL]
1795 Set time (s) after boot system shutdown. This
1796 is useful for hands-off automated testing.
1798 locktorture.stat_interval= [KNL]
1799 Time (s) between statistics printk()s.
1801 locktorture.stutter= [KNL]
1802 Time (s) to stutter testing, for example,
1803 specifying five seconds causes the test to run for
1804 five seconds, wait for five seconds, and so on.
1805 This tests the locking primitive's ability to
1806 transition abruptly to and from idle.
1808 locktorture.torture_runnable= [BOOT]
1809 Start locktorture running at boot time.
1811 locktorture.torture_type= [KNL]
1812 Specify the locking implementation to test.
1814 locktorture.verbose= [KNL]
1815 Enable additional printk() statements.
1817 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1820 loglevel= All Kernel Messages with a loglevel smaller than the
1821 console loglevel will be printed to the console. It can
1822 also be changed with klogd or other programs. The
1823 loglevels are defined as follows:
1825 0 (KERN_EMERG) system is unusable
1826 1 (KERN_ALERT) action must be taken immediately
1827 2 (KERN_CRIT) critical conditions
1828 3 (KERN_ERR) error conditions
1829 4 (KERN_WARNING) warning conditions
1830 5 (KERN_NOTICE) normal but significant condition
1831 6 (KERN_INFO) informational
1832 7 (KERN_DEBUG) debug-level messages
1834 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1835 in bytes. n must be a power of two and greater
1836 than the minimal size. The minimal size is defined
1837 by LOG_BUF_SHIFT kernel config parameter. There is
1838 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1839 that allows to increase the default size depending on
1840 the number of CPUs. See init/Kconfig for more details.
1842 logo.nologo [FB] Disables display of the built-in Linux logo.
1843 This may be used to provide more screen space for
1844 kernel log messages and is useful when debugging
1845 kernel boot problems.
1847 lp=0 [LP] Specify parallel ports to use, e.g,
1848 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1849 lp=reset first parallel port). 'lp=0' disables the
1850 lp=auto printer driver. 'lp=reset' (which can be
1851 specified in addition to the ports) causes
1852 attached printers to be reset. Using
1853 lp=port1,port2,... specifies the parallel ports
1854 to associate lp devices with, starting with
1855 lp0. A port specification may be 'none' to skip
1856 that lp device, or a parport name such as
1857 'parport0'. Specifying 'lp=auto' instead of a
1858 port specification list means that device IDs
1859 from each port should be examined, to see if
1860 an IEEE 1284-compliant printer is attached; if
1861 so, the driver will manage that printer.
1862 See also header of drivers/char/lp.c.
1865 Sets loops_per_jiffy to given constant, thus avoiding
1866 time-consuming boot-time autodetection (up to 250 ms per
1867 CPU). 0 enables autodetection (default). To determine
1868 the correct value for your kernel, boot with normal
1869 autodetection and see what value is printed. Note that
1870 on SMP systems the preset will be applied to all CPUs,
1871 which is likely to cause problems if your CPUs need
1872 significantly divergent settings. An incorrect value
1873 will cause delays in the kernel to be wrong, leading to
1874 unpredictable I/O errors and other breakage. Although
1875 unlikely, in the extreme case this might damage your
1879 Format: <io>,<irq>,<dma>
1881 machvec= [IA-64] Force the use of a particular machine-vector
1882 (machvec) in a generic kernel.
1883 Example: machvec=hpzx1_swiotlb
1885 machtype= [Loongson] Share the same kernel image file between different
1887 Example: machtype=lemote-yeeloong-2f-7inch
1889 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1890 than or equal to this physical address is ignored.
1892 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1893 should make use of. maxcpus=n : n >= 0 limits the
1894 kernel to using 'n' processors. n=0 is a special case,
1895 it is equivalent to "nosmp", which also disables
1898 max_loop= [LOOP] The number of loop block devices that get
1899 (loop.max_loop) unconditionally pre-created at init time. The default
1900 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1901 of statically allocating a predefined number, loop
1902 devices can be requested on-demand with the
1903 /dev/loop-control interface.
1905 mce [X86-32] Machine Check Exception
1907 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1909 md= [HW] RAID subsystems devices and level
1910 See Documentation/md.txt.
1913 Format: <first>,<last>
1914 Specifies range of consoles to be captured by the MDA.
1916 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1917 Amount of memory to be used when the kernel is not able
1918 to see the whole system memory or for test.
1919 [X86] Work as limiting max address. Use together
1920 with memmap= to avoid physical address space collisions.
1921 Without memmap= PCI devices could be placed at addresses
1922 belonging to unused RAM.
1924 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1928 [KNL,SH] Allow user to override the default size for
1929 per-device physically contiguous DMA buffers.
1931 memmap=exactmap [KNL,X86] Enable setting of an exact
1932 E820 memory map, as specified by the user.
1933 Such memmap=exactmap lines can be constructed based on
1934 BIOS output or other requirements. See the memmap=nn@ss
1937 memmap=nn[KMG]@ss[KMG]
1938 [KNL] Force usage of a specific region of memory.
1939 Region of memory to be used is from ss to ss+nn.
1941 memmap=nn[KMG]#ss[KMG]
1942 [KNL,ACPI] Mark specific memory as ACPI data.
1943 Region of memory to be marked is from ss to ss+nn.
1945 memmap=nn[KMG]$ss[KMG]
1946 [KNL,ACPI] Mark specific memory as reserved.
1947 Region of memory to be reserved is from ss to ss+nn.
1948 Example: Exclude memory from 0x18690000-0x1869ffff
1949 memmap=64K$0x18690000
1951 memmap=0x10000$0x18690000
1953 memory_corruption_check=0/1 [X86]
1954 Some BIOSes seem to corrupt the first 64k of
1955 memory when doing things like suspend/resume.
1956 Setting this option will scan the memory
1957 looking for corruption. Enabling this will
1958 both detect corruption and prevent the kernel
1959 from using the memory being corrupted.
1960 However, its intended as a diagnostic tool; if
1961 repeatable BIOS-originated corruption always
1962 affects the same memory, you can use memmap=
1963 to prevent the kernel from using that memory.
1965 memory_corruption_check_size=size [X86]
1966 By default it checks for corruption in the low
1967 64k, making this memory unavailable for normal
1968 use. Use this parameter to scan for
1969 corruption in more or less memory.
1971 memory_corruption_check_period=seconds [X86]
1972 By default it checks for corruption every 60
1973 seconds. Use this parameter to check at some
1974 other rate. 0 disables periodic checking.
1976 memtest= [KNL,X86] Enable memtest
1978 default : 0 <disable>
1979 Specifies the number of memtest passes to be
1980 performed. Each pass selects another test
1981 pattern from a given set of patterns. Memtest
1982 fills the memory with this pattern, validates
1983 memory contents and reserves bad memory
1984 regions that are detected.
1986 meye.*= [HW] Set MotionEye Camera parameters
1987 See Documentation/video4linux/meye.txt.
1989 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1990 Multi-Function General Purpose Timers on AMD Geode
1993 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1994 the BIOS has incorrectly applied a workaround. TinyBIOS
1995 version 0.98 is known to be affected, 0.99 fixes the
1996 problem by letting the user disable the workaround.
2000 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2001 physical address is ignored.
2003 mini2440= [ARM,HW,KNL]
2004 Format:[0..2][b][c][t]
2006 MINI2440 configuration specification:
2007 0 - The attached screen is the 3.5" TFT
2008 1 - The attached screen is the 7" TFT
2009 2 - The VGA Shield is attached (1024x768)
2010 Leaving out the screen size parameter will not load
2011 the TFT driver, and the framebuffer will be left
2013 b - Enable backlight. The TFT backlight pin will be
2014 linked to the kernel VESA blanking code and a GPIO
2015 LED. This parameter is not necessary when using the
2017 c - Enable the s3c camera interface.
2018 t - Reserved for enabling touchscreen support. The
2019 touchscreen support is not enabled in the mainstream
2020 kernel as of 2.6.30, a preliminary port can be found
2021 in the "bleeding edge" mini2440 support kernel at
2022 http://repo.or.cz/w/linux-2.6/mini2440.git
2025 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2026 parameter allows control of the logging verbosity for
2027 the additional memory initialisation checks. A value
2028 of 0 disables mminit logging and a level of 4 will
2029 log everything. Information is printed at KERN_DEBUG
2030 so loglevel=8 may also need to be specified.
2033 [KNL] When CONFIG_MODULE_SIG is set, this means that
2034 modules without (valid) signatures will fail to load.
2035 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2036 is always true, so this option does nothing.
2039 [MOUSE] Maximum time between finger touching and
2040 leaving touchpad surface for touch to be considered
2041 a tap and be reported as a left button click (for
2042 touchpads working in absolute mode only).
2044 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2045 reporting absolute coordinates, such as tablets
2046 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2047 reporting absolute coordinates, such as tablets
2049 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2050 is similar to kernelcore except it specifies the
2051 amount of memory used for migratable allocations.
2052 If both kernelcore and movablecore is specified,
2053 then kernelcore will be at *least* the specified
2054 value but may be more. If movablecore on its own
2055 is specified, the administrator must be careful
2056 that the amount of memory usable for all allocations
2059 movable_node [KNL,X86] Boot-time switch to enable the effects
2060 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2062 MTD_Partition= [MTD]
2063 Format: <name>,<region-number>,<size>,<offset>
2065 MTD_Region= [MTD] Format:
2066 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2069 See drivers/mtd/cmdlinepart.c.
2071 multitce=off [PPC] This parameter disables the use of the pSeries
2072 firmware feature for updating multiple TCE entries
2075 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2077 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2079 boundary - index of last SLC block on Flex-OneNAND.
2080 The remaining blocks are configured as MLC blocks.
2081 lock - Configure if Flex-OneNAND boundary should be locked.
2082 Once locked, the boundary cannot be changed.
2083 1 indicates lock status, 0 indicates unlock status.
2086 ARM/S3C2412 JIVE boot control
2088 See arch/arm/mach-s3c2412/mach-jive.c
2090 mtouchusb.raw_coordinates=
2091 [HW] Make the MicroTouch USB driver use raw coordinates
2092 ('y', default) or cooked coordinates ('n')
2094 mtrr_chunk_size=nn[KMG] [X86]
2095 used for mtrr cleanup. It is largest continuous chunk
2096 that could hold holes aka. UC entries.
2098 mtrr_gran_size=nn[KMG] [X86]
2099 Used for mtrr cleanup. It is granularity of mtrr block.
2101 Large value could prevent small alignment from
2104 mtrr_spare_reg_nr=n [X86]
2106 Range: 0,7 : spare reg number
2108 Used for mtrr cleanup. It is spare mtrr entries number.
2109 Set to 2 or more if your graphical card needs more.
2111 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2113 netdev= [NET] Network devices parameters
2114 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2115 Note that mem_start is often overloaded to mean
2116 something different and driver-specific.
2117 This usage is only documented in each driver source
2121 [NETFILTER] Enable connection tracking flow accounting
2122 0 to disable accounting
2123 1 to enable accounting
2126 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2127 See Documentation/filesystems/nfs/nfsroot.txt.
2129 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2130 See Documentation/filesystems/nfs/nfsroot.txt.
2132 nfsrootdebug [NFS] enable nfsroot debugging messages.
2133 See Documentation/filesystems/nfs/nfsroot.txt.
2135 nfs.callback_tcpport=
2136 [NFS] set the TCP port on which the NFSv4 callback
2137 channel should listen.
2140 [NFS] sets the pathname to the program which is used
2141 to update the NFS client cache entries.
2143 nfs.cache_getent_timeout=
2144 [NFS] sets the timeout after which an attempt to
2145 update a cache entry is deemed to have failed.
2147 nfs.idmap_cache_timeout=
2148 [NFS] set the maximum lifetime for idmapper cache
2152 [NFS] enable 64-bit inode numbers.
2153 If zero, the NFS client will fake up a 32-bit inode
2154 number for the readdir() and stat() syscalls instead
2155 of returning the full 64-bit number.
2156 The default is to return 64-bit inode numbers.
2158 nfs.max_session_slots=
2159 [NFSv4.1] Sets the maximum number of session slots
2160 the client will attempt to negotiate with the server.
2161 This limits the number of simultaneous RPC requests
2162 that the client can send to the NFSv4.1 server.
2163 Note that there is little point in setting this
2164 value higher than the max_tcp_slot_table_limit.
2166 nfs.nfs4_disable_idmapping=
2167 [NFSv4] When set to the default of '1', this option
2168 ensures that both the RPC level authentication
2169 scheme and the NFS level operations agree to use
2170 numeric uids/gids if the mount is using the
2171 'sec=sys' security flavour. In effect it is
2172 disabling idmapping, which can make migration from
2173 legacy NFSv2/v3 systems to NFSv4 easier.
2174 Servers that do not support this mode of operation
2175 will be autodetected by the client, and it will fall
2176 back to using the idmapper.
2177 To turn off this behaviour, set the value to '0'.
2179 [NFS4] Specify an additional fixed unique ident-
2180 ification string that NFSv4 clients can insert into
2181 their nfs_client_id4 string. This is typically a
2182 UUID that is generated at system install time.
2184 nfs.send_implementation_id =
2185 [NFSv4.1] Send client implementation identification
2186 information in exchange_id requests.
2187 If zero, no implementation identification information
2189 The default is to send the implementation identification
2192 nfs.recover_lost_locks =
2193 [NFSv4] Attempt to recover locks that were lost due
2194 to a lease timeout on the server. Please note that
2195 doing this risks data corruption, since there are
2196 no guarantees that the file will remain unchanged
2197 after the locks are lost.
2198 If you want to enable the kernel legacy behaviour of
2199 attempting to recover these locks, then set this
2201 The default parameter value of '0' causes the kernel
2202 not to attempt recovery of lost locks.
2204 nfsd.nfs4_disable_idmapping=
2205 [NFSv4] When set to the default of '1', the NFSv4
2206 server will return only numeric uids and gids to
2207 clients using auth_sys, and will accept numeric uids
2208 and gids from such clients. This is intended to ease
2209 migration from NFSv2/v3.
2211 objlayoutdriver.osd_login_prog=
2212 [NFS] [OBJLAYOUT] sets the pathname to the program which
2213 is used to automatically discover and login into new
2214 osd-targets. Please see:
2215 Documentation/filesystems/pnfs.txt for more explanations
2217 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2218 when a NMI is triggered.
2219 Format: [state][,regs][,debounce][,die]
2221 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2222 Format: [panic,][nopanic,][num]
2224 0 - turn nmi_watchdog off
2225 When panic is specified, panic when an NMI watchdog
2226 timeout occurs (or 'nopanic' to override the opposite
2228 This is useful when you use a panic=... timeout and
2229 need the box quickly up again.
2231 netpoll.carrier_timeout=
2232 [NET] Specifies amount of time (in seconds) that
2233 netpoll should wait for a carrier. By default netpoll
2236 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2237 emulation library even if a 387 maths coprocessor
2241 [HW] Never suspend the console
2242 Disable suspending of consoles during suspend and
2243 hibernate operations. Once disabled, debugging
2244 messages can reach various consoles while the rest
2245 of the system is being put to sleep (ie, while
2246 debugging driver suspend/resume hooks). This may
2247 not work reliably with all consoles, but is known
2248 to work with serial and VGA consoles.
2249 To facilitate more flexible debugging, we also add
2250 console_suspend, a printk module parameter to control
2251 it. Users could use console_suspend (usually
2252 /sys/module/printk/parameters/console_suspend) to
2253 turn on/off it dynamically.
2255 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2256 caches in the slab allocator. Saves per-node memory,
2257 but will impact performance.
2261 noapic [SMP,APIC] Tells the kernel to not make use of any
2262 IOAPICs that may be present in the system.
2264 noautogroup Disable scheduler automatic task group creation.
2266 nobats [PPC] Do not use BATs for mapping kernel lowmem
2267 on "Classic" PPC cores.
2271 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2273 nodelayacct [KNL] Disable per-task delay accounting
2275 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2277 nodsp [SH] Disable hardware DSP at boot time.
2279 noefi Disable EFI runtime services support.
2284 On X86-32 available only on PAE configured kernels.
2285 noexec=on: enable non-executable mappings (default)
2286 noexec=off: disable non-executable mappings
2289 Disable SMAP (Supervisor Mode Access Prevention)
2290 even if it is supported by processor.
2293 Disable SMEP (Supervisor Mode Execution Prevention)
2294 even if it is supported by processor.
2297 This affects only 32-bit executables.
2298 noexec32=on: enable non-executable mappings (default)
2299 read doesn't imply executable mappings
2300 noexec32=off: disable non-executable mappings
2301 read implies executable mappings
2303 nofpu [SH] Disable hardware FPU at boot time.
2305 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2306 register save and restore. The kernel will only save
2307 legacy floating-point registers on task switch.
2309 noxsave [BUGS=X86] Disables x86 extended register state save
2310 and restore using xsave. The kernel will fallback to
2311 enabling legacy floating-point and sse state.
2313 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2314 register states. The kernel will fall back to use
2315 xsave to save the states. By using this parameter,
2316 performance of saving the states is degraded because
2317 xsave doesn't support modified optimization while
2318 xsaveopt supports it on xsaveopt enabled systems.
2320 noxsaves [X86] Disables xsaves and xrstors used in saving and
2321 restoring x86 extended register state in compacted
2322 form of xsave area. The kernel will fall back to use
2323 xsaveopt and xrstor to save and restore the states
2324 in standard form of xsave area. By using this
2325 parameter, xsave area per process might occupy more
2326 memory on xsaves enabled systems.
2329 on enable eager fpu restore
2330 off disable eager fpu restore
2331 auto selects the default scheme, which automatically
2332 enables eagerfpu restore for xsaveopt.
2334 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2335 wfi(ARM) instruction doesn't work correctly and not to
2336 use it. This is also useful when using JTAG debugger.
2338 no_file_caps Tells the kernel not to honor file capabilities. The
2339 only way then for a file to be executed with privilege
2340 is to be setuid root or executed by root.
2342 nohalt [IA-64] Tells the kernel not to use the power saving
2343 function PAL_HALT_LIGHT when idle. This increases
2344 power-consumption. On the positive side, it reduces
2345 interrupt wake-up latency, which may improve performance
2346 in certain environments such as networked servers or
2349 nohibernate [HIBERNATION] Disable hibernation and resume.
2351 nohz= [KNL] Boottime enable/disable dynamic ticks
2352 Valid arguments: on, off
2355 nohz_full= [KNL,BOOT]
2356 In kernels built with CONFIG_NO_HZ_FULL=y, set
2357 the specified list of CPUs whose tick will be stopped
2358 whenever possible. The boot CPU will be forced outside
2359 the range to maintain the timekeeping.
2360 The CPUs in this range must also be included in the
2363 noiotrap [SH] Disables trapped I/O port accesses.
2365 noirqdebug [X86-32] Disables the code which attempts to detect and
2366 disable unhandled interrupt sources.
2368 no_timer_check [X86,APIC] Disables the code which tests for
2369 broken timer IRQ sources.
2371 noisapnp [ISAPNP] Disables ISA PnP code.
2373 noinitrd [RAM] Tells the kernel not to load any configured
2376 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2378 [Deprecated - use intremap=off]
2382 nojitter [IA-64] Disables jitter checking for ITC timers.
2384 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2386 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2389 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2390 steal time is computed, but won't influence scheduler
2393 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2395 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2397 noltlbs [PPC] Do not use large page/tlb entries for kernel
2398 lowmem mapping on PPC40x.
2400 nomca [IA-64] Disable machine check abort handling
2402 nomce [X86-32] Machine Check Exception
2404 nomfgpt [X86-32] Disable Multi-Function General Purpose
2405 Timer usage (for AMD Geode machines).
2407 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2408 shutdown the other cpus. Instead use the REBOOT_VECTOR
2411 nomodule Disable module load
2413 nopat [X86] Disable PAT (page attribute table extension of
2414 pagetables) support.
2416 norandmaps Don't use address space randomization. Equivalent to
2417 echo 0 > /proc/sys/kernel/randomize_va_space
2419 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2421 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2422 with UP alternatives
2424 nordrand [X86] Disable kernel use of the RDRAND and
2425 RDSEED instructions even if they are supported
2426 by the processor. RDRAND and RDSEED are still
2427 available to user space applications.
2429 noresume [SWSUSP] Disables resume and restores original swap
2432 no-scroll [VGA] Disables scrollback.
2433 This is required for the Braillex ib80-piezo Braille
2434 reader made by F.H. Papenmeier (Germany).
2438 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2440 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2441 and disable the IO APIC. legacy for "maxcpus=0".
2443 nosoftlockup [KNL] Disable the soft-lockup detector.
2445 nosync [HW,M68K] Disables sync negotiation for all devices.
2447 notsc [BUGS=X86-32] Disable Time Stamp Counter
2449 nousb [USB] Disable the USB subsystem
2451 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2455 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2457 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2458 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2459 Some features depend on CPU0. Known dependencies are:
2460 1. Resume from suspend/hibernate depends on CPU0.
2461 Suspend/hibernate will fail if CPU0 is offline and you
2462 need to online CPU0 before suspend/hibernate.
2463 2. PIC interrupts also depend on CPU0. CPU0 can't be
2464 removed if a PIC interrupt is detected.
2465 It's said poweroff/reboot may depend on CPU0 on some
2466 machines although I haven't seen such issues so far
2467 after CPU0 is offline on a few tested machines.
2468 If the dependencies are under your control, you can
2469 turn on cpu0_hotplug.
2471 nptcg= [IA-64] Override max number of concurrent global TLB
2472 purges which is reported from either PAL_VM_SUMMARY or
2475 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2476 could support. nr_cpus=n : n >= 1 limits the kernel to
2477 supporting 'n' processors. Later in runtime you can not
2478 use hotplug cpu feature to put more cpu back to online.
2479 just like you compile the kernel NR_CPUS=n
2481 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2483 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2484 Allowed values are enable and disable
2486 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2487 one of ['zone', 'node', 'default'] can be specified
2488 This can be set from sysctl after boot.
2489 See Documentation/sysctl/vm.txt for details.
2491 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2492 See Documentation/debugging-via-ohci1394.txt for more
2495 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2496 Rather than timing out after 20 ms if an EC
2497 command is not properly ACKed, override the length
2498 of the timeout. We have interrupts disabled while
2499 waiting for the ACK, so if this is set too high
2500 interrupts *may* be lost!
2502 omap_mux= [OMAP] Override bootloader pin multiplexing.
2503 Format: <mux_mode0.mode_name=value>...
2504 For example, to override I2C bus2:
2505 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2507 oprofile.timer= [HW]
2508 Use timer interrupt instead of performance counters
2510 oprofile.cpu_type= Force an oprofile cpu type
2511 This might be useful if you have an older oprofile
2512 userland or if you want common events.
2513 Format: { arch_perfmon }
2514 arch_perfmon: [X86] Force use of architectural
2515 perfmon on Intel CPUs instead of the
2516 CPU specific event set.
2517 timer: [X86] Force use of architectural NMI
2518 timer mode (see also oprofile.timer
2519 for generic hr timer mode)
2520 [s390] Force legacy basic mode sampling
2521 (report cpu_type "timer")
2523 oops=panic Always panic on oopses. Default is to just kill the
2524 process, but there is a small probability of
2525 deadlocking the machine.
2526 This will also cause panics on machine check exceptions.
2527 Useful together with panic=30 to trigger a reboot.
2530 See Documentation/sound/oss/oss-parameters.txt
2532 page_owner= [KNL] Boot-time page_owner enabling option.
2533 Storage of the information about who allocated
2534 each page is disabled in default. With this switch,
2536 on: enable the feature
2538 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2539 timeout > 0: seconds before rebooting
2540 timeout = 0: wait forever
2541 timeout < 0: reboot immediately
2544 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2547 crash_kexec_post_notifiers
2548 Run kdump after running panic-notifiers and dumping
2549 kmsg. This only for the users who doubt kdump always
2550 succeeds in any situation.
2551 Note that this also increases risks of kdump failure,
2552 because some panic notifiers can make the crashed
2553 kernel more unstable.
2555 parkbd.port= [HW] Parallel port number the keyboard adapter is
2556 connected to, default is 0.
2558 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2559 0 for XT, 1 for AT (default is AT).
2562 parport= [HW,PPT] Specify parallel ports. 0 disables.
2563 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2564 Use 'auto' to force the driver to use any
2565 IRQ/DMA settings detected (the default is to
2566 ignore detected IRQ/DMA settings because of
2567 possible conflicts). You can specify the base
2568 address, IRQ, and DMA settings; IRQ and DMA
2569 should be numbers, or 'auto' (for using detected
2570 settings on that particular port), or 'nofifo'
2571 (to avoid using a FIFO even if it is detected).
2572 Parallel ports are assigned in the order they
2573 are specified on the command line, starting
2576 parport_init_mode= [HW,PPT]
2577 Configure VIA parallel port to operate in
2578 a specific mode. This is necessary on Pegasos
2579 computer where firmware has no options for setting
2580 up parallel port mode and sets it to spp.
2581 Currently this function knows 686a and 8231 chips.
2582 Format: [spp|ps2|epp|ecp|ecpepp]
2585 Halt all CPUs after the first oops has been printed for
2586 the specified number of seconds. This is to be used if
2587 your oopses keep scrolling off the screen.
2592 See header of drivers/block/paride/pcd.c.
2593 See also Documentation/blockdev/paride.txt.
2595 pci=option[,option...] [PCI] various PCI subsystem options:
2596 earlydump [X86] dump PCI config space before the kernel
2598 off [X86] don't probe for the PCI bus
2599 bios [X86-32] force use of PCI BIOS, don't access
2600 the hardware directly. Use this if your machine
2601 has a non-standard PCI host bridge.
2602 nobios [X86-32] disallow use of PCI BIOS, only direct
2603 hardware access methods are allowed. Use this
2604 if you experience crashes upon bootup and you
2605 suspect they are caused by the BIOS.
2606 conf1 [X86] Force use of PCI Configuration
2608 conf2 [X86] Force use of PCI Configuration
2610 noaer [PCIE] If the PCIEAER kernel config parameter is
2611 enabled, this kernel boot option can be used to
2612 disable the use of PCIE advanced error reporting.
2613 nodomains [PCI] Disable support for multiple PCI
2614 root domains (aka PCI segments, in ACPI-speak).
2615 nommconf [X86] Disable use of MMCONFIG for PCI
2617 check_enable_amd_mmconf [X86] check for and enable
2618 properly configured MMIO access to PCI
2619 config space on AMD family 10h CPU
2620 nomsi [MSI] If the PCI_MSI kernel config parameter is
2621 enabled, this kernel boot option can be used to
2622 disable the use of MSI interrupts system-wide.
2623 noioapicquirk [APIC] Disable all boot interrupt quirks.
2624 Safety option to keep boot IRQs enabled. This
2625 should never be necessary.
2626 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2627 primary IO-APIC for bridges that cannot disable
2628 boot IRQs. This fixes a source of spurious IRQs
2629 when the system masks IRQs.
2630 noioapicreroute [APIC] Disable workaround that uses the
2631 boot IRQ equivalent of an IRQ that connects to
2632 a chipset where boot IRQs cannot be disabled.
2633 The opposite of ioapicreroute.
2634 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2635 routing table. These calls are known to be buggy
2636 on several machines and they hang the machine
2637 when used, but on other computers it's the only
2638 way to get the interrupt routing table. Try
2639 this option if the kernel is unable to allocate
2640 IRQs or discover secondary PCI buses on your
2642 rom [X86] Assign address space to expansion ROMs.
2643 Use with caution as certain devices share
2644 address decoders between ROMs and other
2646 norom [X86] Do not assign address space to
2647 expansion ROMs that do not already have
2648 BIOS assigned address ranges.
2649 nobar [X86] Do not assign address space to the
2650 BARs that weren't assigned by the BIOS.
2651 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2652 assigned automatically to PCI devices. You can
2653 make the kernel exclude IRQs of your ISA cards
2655 pirqaddr=0xAAAAA [X86] Specify the physical address
2656 of the PIRQ table (normally generated
2657 by the BIOS) if it is outside the
2658 F0000h-100000h range.
2659 lastbus=N [X86] Scan all buses thru bus #N. Can be
2660 useful if the kernel is unable to find your
2661 secondary buses and you want to tell it
2662 explicitly which ones they are.
2663 assign-busses [X86] Always assign all PCI bus
2664 numbers ourselves, overriding
2665 whatever the firmware may have done.
2666 usepirqmask [X86] Honor the possible IRQ mask stored
2667 in the BIOS $PIR table. This is needed on
2668 some systems with broken BIOSes, notably
2669 some HP Pavilion N5400 and Omnibook XE3
2670 notebooks. This will have no effect if ACPI
2671 IRQ routing is enabled.
2672 noacpi [X86] Do not use ACPI for IRQ routing
2673 or for PCI scanning.
2674 use_crs [X86] Use PCI host bridge window information
2675 from ACPI. On BIOSes from 2008 or later, this
2676 is enabled by default. If you need to use this,
2677 please report a bug.
2678 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2679 If you need to use this, please report a bug.
2680 routeirq Do IRQ routing for all PCI devices.
2681 This is normally done in pci_enable_device(),
2682 so this option is a temporary workaround
2683 for broken drivers that don't call it.
2684 skip_isa_align [X86] do not align io start addr, so can
2685 handle more pci cards
2686 firmware [ARM] Do not re-enumerate the bus but instead
2687 just use the configuration from the
2688 bootloader. This is currently used on
2689 IXP2000 systems where the bus has to be
2690 configured a certain way for adjunct CPUs.
2691 noearly [X86] Don't do any early type 1 scanning.
2692 This might help on some broken boards which
2693 machine check when some devices' config space
2694 is read. But various workarounds are disabled
2695 and some IOMMU drivers will not work.
2696 bfsort Sort PCI devices into breadth-first order.
2697 This sorting is done to get a device
2698 order compatible with older (<= 2.4) kernels.
2699 nobfsort Don't sort PCI devices into breadth-first order.
2700 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2701 tuning and use the BIOS-configured MPS defaults.
2702 pcie_bus_safe Set every device's MPS to the largest value
2703 supported by all devices below the root complex.
2704 pcie_bus_perf Set device MPS to the largest allowable MPS
2705 based on its parent bus. Also set MRRS (Max
2706 Read Request Size) to the largest supported
2707 value (no larger than the MPS that the device
2708 or bus can support) for best performance.
2709 pcie_bus_peer2peer Set every device's MPS to 128B, which
2710 every device is guaranteed to support. This
2711 configuration allows peer-to-peer DMA between
2712 any pair of devices, possibly at the cost of
2713 reduced performance. This also guarantees
2714 that hot-added devices will work.
2715 cbiosize=nn[KMG] The fixed amount of bus space which is
2716 reserved for the CardBus bridge's IO window.
2717 The default value is 256 bytes.
2718 cbmemsize=nn[KMG] The fixed amount of bus space which is
2719 reserved for the CardBus bridge's memory
2720 window. The default value is 64 megabytes.
2723 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2724 Specifies alignment and device to reassign
2725 aligned memory resources.
2726 If <order of align> is not specified,
2727 PAGE_SIZE is used as alignment.
2728 PCI-PCI bridge can be specified, if resource
2729 windows need to be expanded.
2730 ecrc= Enable/disable PCIe ECRC (transaction layer
2731 end-to-end CRC checking).
2732 bios: Use BIOS/firmware settings. This is the
2736 hpiosize=nn[KMG] The fixed amount of bus space which is
2737 reserved for hotplug bridge's IO window.
2738 Default size is 256 bytes.
2739 hpmemsize=nn[KMG] The fixed amount of bus space which is
2740 reserved for hotplug bridge's memory window.
2741 Default size is 2 megabytes.
2742 realloc= Enable/disable reallocating PCI bridge resources
2743 if allocations done by BIOS are too small to
2744 accommodate resources required by all child
2746 off: Turn realloc off
2748 realloc same as realloc=on
2749 noari do not use PCIe ARI.
2750 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2751 only look for one device below a PCIe downstream
2754 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2757 force Enable ASPM even on devices that claim not to support it.
2758 WARNING: Forcing ASPM on may cause system lockups.
2760 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2761 nomsi Do not use MSI for PCI Express Native Hotplug (this
2762 makes all PCIe ports use INTx for hotplug services).
2764 pcie_ports= [PCIE] PCIe ports handling:
2765 auto Ask the BIOS whether or not to use native PCIe services
2766 associated with PCIe ports (PME, hot-plug, AER). Use
2767 them only if that is allowed by the BIOS.
2768 native Use native PCIe services associated with PCIe ports
2770 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2773 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2774 nomsi Do not use MSI for native PCIe PME signaling (this makes
2775 all PCIe root ports use INTx for all services).
2777 pcmv= [HW,PCMCIA] BadgePAD 4
2781 Keep all power-domains already enabled by bootloader on,
2782 even if no driver has claimed them. This is useful
2783 for debug and development, but should not be
2784 needed on a platform with proper driver support.
2787 See Documentation/blockdev/paride.txt.
2789 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2792 See arch/parisc/kernel/pdc_chassis.c
2794 percpu_alloc= Select which percpu first chunk allocator to use.
2795 Currently supported values are "embed" and "page".
2796 Archs may support subset or none of the selections.
2797 See comments in mm/percpu.c for details on each
2798 allocator. This parameter is primarily for debugging
2799 and performance comparison.
2802 See Documentation/blockdev/paride.txt.
2805 See Documentation/blockdev/paride.txt.
2807 pirq= [SMP,APIC] Manual mp-table setup
2808 See Documentation/x86/i386/IO-APIC.txt.
2810 plip= [PPT,NET] Parallel port network link
2811 Format: { parport<nr> | timid | 0 }
2812 See also Documentation/parport.txt.
2814 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2815 Override pmtimer IOPort with a hex value.
2819 Enable PNP debug messages (depends on the
2820 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2821 via /sys/module/pnp/parameters/debug. We always show
2822 current resource usage; turning this on also shows
2823 possible settings and some assignment information.
2829 { on | off | curr | res | no-curr | no-res }
2832 [ISAPNP] Exclude IRQs for the autoconfiguration
2835 [ISAPNP] Exclude DMAs for the autoconfiguration
2837 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2838 Ranges are in pairs (I/O port base and size).
2841 [ISAPNP] Exclude memory regions for the
2843 Ranges are in pairs (memory base and size).
2845 ports= [IP_VS_FTP] IPVS ftp helper module
2847 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2849 Format: <port>,<port>....
2851 print-fatal-signals=
2852 [KNL] debug: print fatal signals
2854 If enabled, warn about various signal handling
2855 related application anomalies: too many signals,
2856 too many POSIX.1 timers, fatal signals causing a
2859 If you hit the warning due to signal overflow,
2860 you might want to try "ulimit -i unlimited".
2864 printk.always_kmsg_dump=
2865 Trigger kmsg_dump for cases other than kernel oops or
2867 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2870 printk.time= Show timing data prefixed to each printk message line
2871 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2873 processor.max_cstate= [HW,ACPI]
2874 Limit processor to maximum C-state
2875 max_cstate=9 overrides any DMI blacklist limit.
2877 processor.nocst [HW,ACPI]
2878 Ignore the _CST method to determine C-states,
2879 instead using the legacy FADT method
2881 profile= [KNL] Enable kernel profiling via /proc/profile
2882 Format: [schedule,]<number>
2883 Param: "schedule" - profile schedule points.
2884 Param: <number> - step/bucket size as a power of 2 for
2885 statistical time based profiling.
2886 Param: "sleep" - profile D-state sleeping (millisecs).
2887 Requires CONFIG_SCHEDSTATS
2888 Param: "kvm" - profile VM exits.
2890 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2892 See Documentation/blockdev/ramdisk.txt.
2894 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2895 probe for; one of (bare|imps|exps|lifebook|any).
2896 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2898 psmouse.resetafter= [HW,MOUSE]
2899 Try to reset the device after so many bad packets
2902 [HW,MOUSE] Set desired mouse resolution, in dpi.
2903 psmouse.smartscroll=
2904 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2905 0 = disabled, 1 = enabled (default).
2907 pstore.backend= Specify the name of the pstore backend to use
2910 See Documentation/blockdev/paride.txt.
2913 [KNL] Number of legacy pty's. Overwrites compiled-in
2916 quiet [KNL] Disable most log messages
2921 See Documentation/md.txt.
2923 ramdisk_blocksize= [RAM]
2924 See Documentation/blockdev/ramdisk.txt.
2926 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2927 See Documentation/blockdev/ramdisk.txt.
2930 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2931 the specified list of CPUs to be no-callback CPUs.
2932 Invocation of these CPUs' RCU callbacks will
2933 be offloaded to "rcuox/N" kthreads created for
2934 that purpose, where "x" is "b" for RCU-bh, "p"
2935 for RCU-preempt, and "s" for RCU-sched, and "N"
2936 is the CPU number. This reduces OS jitter on the
2937 offloaded CPUs, which can be useful for HPC and
2938 real-time workloads. It can also improve energy
2939 efficiency for asymmetric multiprocessors.
2942 Rather than requiring that offloaded CPUs
2943 (specified by rcu_nocbs= above) explicitly
2944 awaken the corresponding "rcuoN" kthreads,
2945 make these kthreads poll for callbacks.
2946 This improves the real-time response for the
2947 offloaded CPUs by relieving them of the need to
2948 wake up the corresponding kthread, but degrades
2949 energy efficiency by requiring that the kthreads
2950 periodically wake up to do the polling.
2952 rcutree.blimit= [KNL]
2953 Set maximum number of finished RCU callbacks to
2954 process in one batch.
2956 rcutree.rcu_fanout_leaf= [KNL]
2957 Increase the number of CPUs assigned to each
2958 leaf rcu_node structure. Useful for very large
2961 rcutree.jiffies_till_sched_qs= [KNL]
2962 Set required age in jiffies for a
2963 given grace period before RCU starts
2964 soliciting quiescent-state help from
2965 rcu_note_context_switch().
2967 rcutree.jiffies_till_first_fqs= [KNL]
2968 Set delay from grace-period initialization to
2969 first attempt to force quiescent states.
2970 Units are jiffies, minimum value is zero,
2971 and maximum value is HZ.
2973 rcutree.jiffies_till_next_fqs= [KNL]
2974 Set delay between subsequent attempts to force
2975 quiescent states. Units are jiffies, minimum
2976 value is one, and maximum value is HZ.
2978 rcutree.kthread_prio= [KNL,BOOT]
2979 Set the SCHED_FIFO priority of the RCU
2980 per-CPU kthreads (rcuc/N). This value is also
2981 used for the priority of the RCU boost threads
2982 (rcub/N). Valid values are 1-99 and the default
2983 is 1 (the least-favored priority).
2985 rcutree.rcu_nocb_leader_stride= [KNL]
2986 Set the number of NOCB kthread groups, which
2987 defaults to the square root of the number of
2988 CPUs. Larger numbers reduces the wakeup overhead
2989 on the per-CPU grace-period kthreads, but increases
2990 that same overhead on each group's leader.
2992 rcutree.qhimark= [KNL]
2993 Set threshold of queued RCU callbacks beyond which
2994 batch limiting is disabled.
2996 rcutree.qlowmark= [KNL]
2997 Set threshold of queued RCU callbacks below which
2998 batch limiting is re-enabled.
3000 rcutree.rcu_idle_gp_delay= [KNL]
3001 Set wakeup interval for idle CPUs that have
3002 RCU callbacks (RCU_FAST_NO_HZ=y).
3004 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3005 Set wakeup interval for idle CPUs that have
3006 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3007 Lazy RCU callbacks are those which RCU can
3008 prove do nothing more than free memory.
3010 rcutorture.cbflood_inter_holdoff= [KNL]
3011 Set holdoff time (jiffies) between successive
3012 callback-flood tests.
3014 rcutorture.cbflood_intra_holdoff= [KNL]
3015 Set holdoff time (jiffies) between successive
3016 bursts of callbacks within a given callback-flood
3019 rcutorture.cbflood_n_burst= [KNL]
3020 Set the number of bursts making up a given
3021 callback-flood test. Set this to zero to
3022 disable callback-flood testing.
3024 rcutorture.cbflood_n_per_burst= [KNL]
3025 Set the number of callbacks to be registered
3026 in a given burst of a callback-flood test.
3028 rcutorture.fqs_duration= [KNL]
3029 Set duration of force_quiescent_state bursts.
3031 rcutorture.fqs_holdoff= [KNL]
3032 Set holdoff time within force_quiescent_state bursts.
3034 rcutorture.fqs_stutter= [KNL]
3035 Set wait time between force_quiescent_state bursts.
3037 rcutorture.gp_exp= [KNL]
3038 Use expedited update-side primitives.
3040 rcutorture.gp_normal= [KNL]
3041 Use normal (non-expedited) update-side primitives.
3042 If both gp_exp and gp_normal are set, do both.
3043 If neither gp_exp nor gp_normal are set, still
3046 rcutorture.n_barrier_cbs= [KNL]
3047 Set callbacks/threads for rcu_barrier() testing.
3049 rcutorture.nfakewriters= [KNL]
3050 Set number of concurrent RCU writers. These just
3051 stress RCU, they don't participate in the actual
3052 test, hence the "fake".
3054 rcutorture.nreaders= [KNL]
3055 Set number of RCU readers.
3057 rcutorture.object_debug= [KNL]
3058 Enable debug-object double-call_rcu() testing.
3060 rcutorture.onoff_holdoff= [KNL]
3061 Set time (s) after boot for CPU-hotplug testing.
3063 rcutorture.onoff_interval= [KNL]
3064 Set time (s) between CPU-hotplug operations, or
3065 zero to disable CPU-hotplug testing.
3067 rcutorture.torture_runnable= [BOOT]
3068 Start rcutorture running at boot time.
3070 rcutorture.shuffle_interval= [KNL]
3071 Set task-shuffle interval (s). Shuffling tasks
3072 allows some CPUs to go into dyntick-idle mode
3073 during the rcutorture test.
3075 rcutorture.shutdown_secs= [KNL]
3076 Set time (s) after boot system shutdown. This
3077 is useful for hands-off automated testing.
3079 rcutorture.stall_cpu= [KNL]
3080 Duration of CPU stall (s) to test RCU CPU stall
3081 warnings, zero to disable.
3083 rcutorture.stall_cpu_holdoff= [KNL]
3084 Time to wait (s) after boot before inducing stall.
3086 rcutorture.stat_interval= [KNL]
3087 Time (s) between statistics printk()s.
3089 rcutorture.stutter= [KNL]
3090 Time (s) to stutter testing, for example, specifying
3091 five seconds causes the test to run for five seconds,
3092 wait for five seconds, and so on. This tests RCU's
3093 ability to transition abruptly to and from idle.
3095 rcutorture.test_boost= [KNL]
3096 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3097 "Maybe" means test if the RCU implementation
3098 under test support RCU priority boosting.
3100 rcutorture.test_boost_duration= [KNL]
3101 Duration (s) of each individual boost test.
3103 rcutorture.test_boost_interval= [KNL]
3104 Interval (s) between each boost test.
3106 rcutorture.test_no_idle_hz= [KNL]
3107 Test RCU's dyntick-idle handling. See also the
3108 rcutorture.shuffle_interval parameter.
3110 rcutorture.torture_type= [KNL]
3111 Specify the RCU implementation to test.
3113 rcutorture.verbose= [KNL]
3114 Enable additional printk() statements.
3116 rcupdate.rcu_expedited= [KNL]
3117 Use expedited grace-period primitives, for
3118 example, synchronize_rcu_expedited() instead
3119 of synchronize_rcu(). This reduces latency,
3120 but can increase CPU utilization, degrade
3121 real-time latency, and degrade energy efficiency.
3123 rcupdate.rcu_cpu_stall_suppress= [KNL]
3124 Suppress RCU CPU stall warning messages.
3126 rcupdate.rcu_cpu_stall_timeout= [KNL]
3127 Set timeout for RCU CPU stall warning messages.
3129 rcupdate.rcu_task_stall_timeout= [KNL]
3130 Set timeout in jiffies for RCU task stall warning
3131 messages. Disable with a value less than or equal
3134 rcupdate.rcu_self_test= [KNL]
3135 Run the RCU early boot self tests
3137 rcupdate.rcu_self_test_bh= [KNL]
3138 Run the RCU bh early boot self tests
3140 rcupdate.rcu_self_test_sched= [KNL]
3141 Run the RCU sched early boot self tests
3145 Run specified binary instead of /init from the ramdisk,
3146 used for early userspace startup. See initrd.
3149 Format (x86 or x86_64):
3150 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3152 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3154 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3155 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3156 reboot_force is either force or not specified,
3157 reboot_cpu is s[mp]#### with #### being the processor
3158 to be used for rebooting.
3161 [KNL, SMP] Set scheduler's default relax_domain_level.
3162 See Documentation/cgroups/cpusets.txt.
3164 relative_sleep_states=
3165 [SUSPEND] Use sleep state labeling where the deepest
3166 state available other than hibernation is always "mem".
3167 Format: { "0" | "1" }
3168 0 -- Traditional sleep state labels.
3169 1 -- Relative sleep state labels.
3171 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3173 reservetop= [X86-32]
3175 Reserves a hole at the top of the kernel virtual
3180 Set the amount of memory to reserve for BIOS at
3181 the bottom of the address space.
3183 reset_devices [KNL] Force drivers to reset the underlying device
3184 during initialization.
3187 Specify the partition device for software suspend
3189 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3191 resume_offset= [SWSUSP]
3192 Specify the offset from the beginning of the partition
3193 given by "resume=" at which the swap header is located,
3194 in <PAGE_SIZE> units (needed only for swap files).
3195 See Documentation/power/swsusp-and-swap-files.txt
3197 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3198 read the resume files
3200 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3201 Useful for devices that are detected asynchronously
3202 (e.g. USB and MMC devices).
3204 hibernate= [HIBERNATION]
3205 noresume Don't check if there's a hibernation image
3206 present during boot.
3207 nocompress Don't compress/decompress hibernation images.
3208 no Disable hibernation and resume.
3210 retain_initrd [RAM] Keep initrd memory after extraction
3212 rhash_entries= [KNL,NET]
3213 Set number of hash buckets for route cache
3215 ro [KNL] Mount root device read-only on boot
3217 root= [KNL] Root filesystem
3218 See name_to_dev_t comment in init/do_mounts.c.
3220 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3221 mount the root filesystem
3223 rootflags= [KNL] Set root filesystem mount option string
3225 rootfstype= [KNL] Set root filesystem type
3227 rootwait [KNL] Wait (indefinitely) for root device to show up.
3228 Useful for devices that are detected asynchronously
3229 (e.g. USB and MMC devices).
3231 rproc_mem=nn[KMG][@address]
3232 [KNL,ARM,CMA] Remoteproc physical memory block.
3233 Memory area to be used by remote processor image,
3236 rw [KNL] Mount root device read-write on boot
3238 S [KNL] Run init in single mode
3240 s390_iommu= [HW,S390]
3241 Set s390 IOTLB flushing mode
3243 With strict flushing every unmap operation will result in
3244 an IOTLB flush. Default is lazy flushing before reuse,
3248 See drivers/net/irda/sa1100_ir.c.
3250 sbni= [NET] Granch SBNI12 leased line adapter
3252 sched_debug [KNL] Enables verbose scheduler debug messages.
3254 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3255 xtime_lock contention on larger systems, and/or RCU lock
3256 contention on all systems with CONFIG_MAXSMP set.
3257 Format: { "0" | "1" }
3258 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3260 Note: increases power consumption, thus should only be
3261 enabled if running jitter sensitive (HPC/RT) workloads.
3263 security= [SECURITY] Choose a security module to enable at boot.
3264 If this boot parameter is not specified, only the first
3265 security module asking for security registration will be
3266 loaded. An invalid security module name will be treated
3267 as if no module has been chosen.
3269 selinux= [SELINUX] Disable or enable SELinux at boot time.
3270 Format: { "0" | "1" }
3271 See security/selinux/Kconfig help text.
3274 Default value is set via kernel config option.
3275 If enabled at boot time, /selinux/disable can be used
3276 later to disable prior to initial policy load.
3278 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3279 Format: { "0" | "1" }
3280 See security/apparmor/Kconfig help text
3283 Default value is set via kernel config option.
3285 serialnumber [BUGS=X86-32]
3288 Maximal number of shapers.
3290 show_msr= [x86] show boot-time MSR settings
3291 Format: { <integer> }
3292 Show boot-time (BIOS-initialized) MSR settings.
3293 The parameter means the number of CPUs to show,
3294 for example 1 means boot CPU only.
3302 Disable merging of slabs with similar size. May be
3303 necessary if there is some reason to distinguish
3304 allocs to different slabs. Debug options disable
3305 merging on their own.
3306 For more information see Documentation/vm/slub.txt.
3308 slab_max_order= [MM, SLAB]
3309 Determines the maximum allowed order for slabs.
3310 A high setting may cause OOMs due to memory
3311 fragmentation. Defaults to 1 for systems with
3312 more than 32MB of RAM, 0 otherwise.
3314 slub_debug[=options[,slabs]] [MM, SLUB]
3315 Enabling slub_debug allows one to determine the
3316 culprit if slab objects become corrupted. Enabling
3317 slub_debug can create guard zones around objects and
3318 may poison objects when not in use. Also tracks the
3319 last alloc / free. For more information see
3320 Documentation/vm/slub.txt.
3322 slub_max_order= [MM, SLUB]
3323 Determines the maximum allowed order for slabs.
3324 A high setting may cause OOMs due to memory
3325 fragmentation. For more information see
3326 Documentation/vm/slub.txt.
3328 slub_min_objects= [MM, SLUB]
3329 The minimum number of objects per slab. SLUB will
3330 increase the slab order up to slub_max_order to
3331 generate a sufficiently large slab able to contain
3332 the number of objects indicated. The higher the number
3333 of objects the smaller the overhead of tracking slabs
3334 and the less frequently locks need to be acquired.
3335 For more information see Documentation/vm/slub.txt.
3337 slub_min_order= [MM, SLUB]
3338 Determines the minimum page order for slabs. Must be
3339 lower than slub_max_order.
3340 For more information see Documentation/vm/slub.txt.
3342 slub_nomerge [MM, SLUB]
3343 Same with slab_nomerge. This is supported for legacy.
3344 See slab_nomerge for more information.
3347 Format: <io1>[,<io2>[,...,<io8>]]
3349 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3350 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3351 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3352 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3353 smsc-ircc2.ircc_irq= [HW] IRQ line
3354 smsc-ircc2.ircc_dma= [HW] DMA channel
3355 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3356 0: Toshiba Satellite 1800 (GP data pin select)
3357 1: Fast pin select (default)
3361 [KNL] Should the soft-lockup detector generate panics.
3364 softlockup_all_cpu_backtrace=
3365 [KNL] Should the soft-lockup detector generate
3366 backtraces on all cpus.
3369 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3370 See Documentation/laptops/sonypi.txt
3372 spia_io_base= [HW,MTD]
3378 Enabled the stack tracer on boot up.
3380 stacktrace_filter=[function-list]
3381 [FTRACE] Limit the functions that the stack tracer
3382 will trace at boot up. function-list is a comma separated
3383 list of functions. This list can be changed at run
3384 time by the stack_trace_filter file in the debugfs
3385 tracing directory. Note, this enables stack tracing
3386 and the stacktrace above is not needed.
3390 Set the STI (builtin display/keyboard on the HP-PARISC
3391 machines) console (graphic card) which should be used
3392 as the initial boot-console.
3393 See also comment in drivers/video/console/sticore.c.
3396 See comment in drivers/video/console/sticore.c.
3399 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3401 sunrpc.min_resvport=
3402 sunrpc.max_resvport=
3404 SunRPC servers often require that client requests
3405 originate from a privileged port (i.e. a port in the
3406 range 0 < portnr < 1024).
3407 An administrator who wishes to reserve some of these
3408 ports for other uses may adjust the range that the
3409 kernel's sunrpc client considers to be privileged
3410 using these two parameters to set the minimum and
3411 maximum port values.
3415 Control how the NFS server code allocates CPUs to
3416 service thread pools. Depending on how many NICs
3417 you have and where their interrupts are bound, this
3418 option will affect which CPUs will do NFS serving.
3419 Note: this parameter cannot be changed while the
3420 NFS server is running.
3422 auto the server chooses an appropriate mode
3423 automatically using heuristics
3424 global a single global pool contains all CPUs
3425 percpu one pool for each CPU
3426 pernode one pool for each NUMA node (equivalent
3427 to global on non-NUMA machines)
3429 sunrpc.tcp_slot_table_entries=
3430 sunrpc.udp_slot_table_entries=
3432 Sets the upper limit on the number of simultaneous
3433 RPC calls that can be sent from the client to a
3434 server. Increasing these values may allow you to
3435 improve throughput, but will also increase the
3436 amount of memory reserved for use by the client.
3439 [KNL] Enable accounting of swap in memory resource
3440 controller if no parameter or 1 is given or disable
3441 it if 0 is given (See Documentation/cgroups/memory.txt)
3443 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3444 Format: { <int> | force }
3445 <int> -- Number of I/O TLB slabs
3446 force -- force using of bounce buffers even if they
3447 wouldn't be automatically used by the kernel
3451 sysfs.deprecated=0|1 [KNL]
3452 Enable/disable old style sysfs layout for old udev
3453 on older distributions. When this option is enabled
3454 very new udev will not work anymore. When this option
3455 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3456 in older udev will not work anymore.
3457 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3458 the kernel configuration.
3460 sysrq_always_enabled
3462 Ignore sysrq setting - this boot parameter will
3463 neutralize any effect of /proc/sys/kernel/sysrq.
3464 Useful for debugging.
3466 tcpmhash_entries= [KNL,NET]
3467 Set the number of tcp_metrics_hash slots.
3468 Default value is 8192 or 16384 depending on total
3469 ram pages. This is used to specify the TCP metrics
3470 cache size. See Documentation/networking/ip-sysctl.txt
3471 "tcp_no_metrics_save" section for more details.
3475 test_suspend= [SUSPEND][,N]
3476 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3477 standby suspend) or "freeze" (for suspend type freeze)
3478 as the system sleep state during system startup with
3479 the optional capability to repeat N number of times.
3480 The system is woken from this state using a
3481 wakeup-capable RTC alarm.
3483 thash_entries= [KNL,NET]
3484 Set number of hash buckets for TCP connection
3486 thermal.act= [HW,ACPI]
3487 -1: disable all active trip points in all thermal zones
3488 <degrees C>: override all lowest active trip points
3490 thermal.crt= [HW,ACPI]
3491 -1: disable all critical trip points in all thermal zones
3492 <degrees C>: override all critical trip points
3494 thermal.nocrt= [HW,ACPI]
3495 Set to disable actions on ACPI thermal zone
3496 critical and hot trip points.
3498 thermal.off= [HW,ACPI]
3499 1: disable ACPI thermal control
3501 thermal.psv= [HW,ACPI]
3502 -1: disable all passive trip points
3503 <degrees C>: override all passive trip points to this
3506 thermal.tzp= [HW,ACPI]
3507 Specify global default ACPI thermal zone polling rate
3508 <deci-seconds>: poll all this frequency
3509 0: no polling (default)
3512 Force threading of all interrupt handlers except those
3513 marked explicitly IRQF_NO_THREAD.
3516 Enable the Transcendent memory driver if built-in.
3518 tmem.cleancache=0|1 [KNL, XEN]
3519 Default is on (1). Disable the usage of the cleancache
3520 API to send anonymous pages to the hypervisor.
3522 tmem.frontswap=0|1 [KNL, XEN]
3523 Default is on (1). Disable the usage of the frontswap
3524 API to send swap pages to the hypervisor. If disabled
3525 the selfballooning and selfshrinking are force disabled.
3527 tmem.selfballooning=0|1 [KNL, XEN]
3528 Default is on (1). Disable the driving of swap pages
3531 tmem.selfshrinking=0|1 [KNL, XEN]
3532 Default is on (1). Partial swapoff that immediately
3533 transfers pages from Xen hypervisor back to the
3534 kernel based on different criteria.
3538 Specify if the kernel should make use of the cpu
3539 topology information if the hardware supports this.
3540 The scheduler will make use of this information and
3541 e.g. base its process migration decisions on it.
3544 topology_updates= [KNL, PPC, NUMA]
3546 Specify if the kernel should ignore (off)
3547 topology updates sent by the hypervisor to this
3552 tpm_suspend_pcr=[HW,TPM]
3553 Format: integer pcr id
3554 Specify that at suspend time, the tpm driver
3555 should extend the specified pcr with zeros,
3556 as a workaround for some chips which fail to
3557 flush the last written pcr on TPM_SaveState.
3558 This will guarantee that all the other pcrs
3561 trace_buf_size=nn[KMG]
3562 [FTRACE] will set tracing buffer size on each cpu.
3564 trace_event=[event-list]
3565 [FTRACE] Set and start specified trace events in order
3566 to facilitate early boot debugging.
3567 See also Documentation/trace/events.txt
3569 trace_options=[option-list]
3570 [FTRACE] Enable or disable tracer options at boot.
3571 The option-list is a comma delimited list of options
3572 that can be enabled or disabled just as if you were
3573 to echo the option name into
3575 /sys/kernel/debug/tracing/trace_options
3577 For example, to enable stacktrace option (to dump the
3578 stack trace of each event), add to the command line:
3580 trace_options=stacktrace
3582 See also Documentation/trace/ftrace.txt "trace options"
3586 Have the tracepoints sent to printk as well as the
3587 tracing ring buffer. This is useful for early boot up
3588 where the system hangs or reboots and does not give the
3589 option for reading the tracing buffer or performing a
3590 ftrace_dump_on_oops.
3592 To turn off having tracepoints sent to printk,
3593 echo 0 > /proc/sys/kernel/tracepoint_printk
3594 Note, echoing 1 into this file without the
3595 tracepoint_printk kernel cmdline option has no effect.
3599 Having tracepoints sent to printk() and activating high
3600 frequency tracepoints such as irq or sched, can cause
3601 the system to live lock.
3604 [FTRACE] enable this option to disable tracing when a
3605 warning is hit. This turns off "tracing_on". Tracing can
3606 be enabled again by echoing '1' into the "tracing_on"
3607 file located in /sys/kernel/debug/tracing/
3609 This option is useful, as it disables the trace before
3610 the WARNING dump is called, which prevents the trace to
3611 be filled with content caused by the warning output.
3613 This option can also be set at run time via the sysctl
3614 option: kernel/traceoff_on_warning
3616 transparent_hugepage=
3618 Format: [always|madvise|never]
3619 Can be used to control the default behavior of the system
3620 with respect to transparent hugepages.
3621 See Documentation/vm/transhuge.txt for more details.
3623 tsc= Disable clocksource stability checks for TSC.
3625 [x86] reliable: mark tsc clocksource as reliable, this
3626 disables clocksource verification at runtime, as well
3627 as the stability checks done at bootup. Used to enable
3628 high-resolution timer mode on older hardware, and in
3629 virtualized environment.
3630 [x86] noirqtime: Do not use TSC to do irq accounting.
3631 Used to run time disable IRQ_TIME_ACCOUNTING on any
3632 platforms where RDTSC is slow and this accounting
3635 turbografx.map[2|3]= [HW,JOY]
3636 TurboGraFX parallel port interface
3638 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3639 See also Documentation/input/joystick-parport.txt
3641 udbg-immortal [PPC] When debugging early kernel crashes that
3642 happen after console_init() and before a proper
3643 console driver takes over, this boot options might
3644 help "seeing" what's going on.
3646 uhash_entries= [KNL,NET]
3647 Set number of hash buckets for UDP/UDP-Lite connections
3650 [USB] Ignore overcurrent events (default N).
3651 Some badly-designed motherboards generate lots of
3652 bogus events, for ports that aren't wired to
3653 anything. Set this parameter to avoid log spamming.
3654 Note that genuine overcurrent events won't be
3658 [X86] Cause panic on unknown NMI.
3660 usbcore.authorized_default=
3661 [USB] Default USB device authorization:
3662 (default -1 = authorized except for wireless USB,
3663 0 = not authorized, 1 = authorized)
3665 usbcore.autosuspend=
3666 [USB] The autosuspend time delay (in seconds) used
3667 for newly-detected USB devices (default 2). This
3668 is the time required before an idle device will be
3669 autosuspended. Devices for which the delay is set
3670 to a negative value won't be autosuspended at all.
3672 usbcore.usbfs_snoop=
3673 [USB] Set to log all usbfs traffic (default 0 = off).
3675 usbcore.blinkenlights=
3676 [USB] Set to cycle leds on hubs (default 0 = off).
3678 usbcore.old_scheme_first=
3679 [USB] Start with the old device initialization
3680 scheme (default 0 = off).
3682 usbcore.usbfs_memory_mb=
3683 [USB] Memory limit (in MB) for buffers allocated by
3684 usbfs (default = 16, 0 = max = 2047).
3686 usbcore.use_both_schemes=
3687 [USB] Try the other device initialization scheme
3688 if the first one fails (default 1 = enabled).
3690 usbcore.initial_descriptor_timeout=
3691 [USB] Specifies timeout for the initial 64-byte
3692 USB_REQ_GET_DESCRIPTOR request in milliseconds
3693 (default 5000 = 5.0 seconds).
3696 [USBHID] The interval which mice are to be polled at.
3698 usb-storage.delay_use=
3699 [UMS] The delay in seconds before a new device is
3700 scanned for Logical Units (default 1).
3703 [UMS] A list of quirks entries to supplement or
3704 override the built-in unusual_devs list. List
3705 entries are separated by commas. Each entry has
3706 the form VID:PID:Flags where VID and PID are Vendor
3707 and Product ID values (4-digit hex numbers) and
3708 Flags is a set of characters, each corresponding
3709 to a common usb-storage quirk flag as follows:
3710 a = SANE_SENSE (collect more than 18 bytes
3712 b = BAD_SENSE (don't collect more than 18
3713 bytes of sense data);
3714 c = FIX_CAPACITY (decrease the reported
3715 device capacity by one sector);
3716 d = NO_READ_DISC_INFO (don't use
3717 READ_DISC_INFO command);
3718 e = NO_READ_CAPACITY_16 (don't use
3719 READ_CAPACITY_16 command);
3720 f = NO_REPORT_OPCODES (don't use report opcodes
3722 h = CAPACITY_HEURISTICS (decrease the
3723 reported device capacity by one
3724 sector if the number is odd);
3725 i = IGNORE_DEVICE (don't bind to this
3727 l = NOT_LOCKABLE (don't try to lock and
3728 unlock ejectable media);
3729 m = MAX_SECTORS_64 (don't transfer more
3730 than 64 sectors = 32 KB at a time);
3731 n = INITIAL_READ10 (force a retry of the
3732 initial READ(10) command);
3733 o = CAPACITY_OK (accept the capacity
3734 reported by the device);
3735 p = WRITE_CACHE (the device cache is ON
3737 r = IGNORE_RESIDUE (the device reports
3738 bogus residue values);
3739 s = SINGLE_LUN (the device has only one
3741 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3742 commands, uas only);
3743 u = IGNORE_UAS (don't bind to the uas driver);
3744 w = NO_WP_DETECT (don't test whether the
3745 medium is write-protected).
3746 Example: quirks=0419:aaf5:rl,0421:0433:rc
3748 user_debug= [KNL,ARM]
3750 See arch/arm/Kconfig.debug help text.
3751 1 - undefined instruction events
3753 4 - invalid data aborts
3756 Example: user_debug=31
3759 [X86] Flags controlling user PTE allocations.
3761 nohigh = do not allocate PTE pages in
3762 HIGHMEM regardless of setting
3766 On X86_32, this is an alias for vdso32=. Otherwise:
3768 vdso=1: enable VDSO (the default)
3769 vdso=0: disable VDSO mapping
3771 vdso32= [X86] Control the 32-bit vDSO
3772 vdso32=1: enable 32-bit VDSO
3773 vdso32=0 or vdso32=2: disable 32-bit VDSO
3775 See the help text for CONFIG_COMPAT_VDSO for more
3776 details. If CONFIG_COMPAT_VDSO is set, the default is
3777 vdso32=0; otherwise, the default is vdso32=1.
3779 For compatibility with older kernels, vdso32=2 is an
3782 Try vdso32=0 if you encounter an error that says:
3783 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3786 vector=percpu: enable percpu vector domain
3788 video= [FB] Frame buffer configuration
3789 See Documentation/fb/modedb.txt.
3791 video.brightness_switch_enabled= [0,1]
3792 If set to 1, on receiving an ACPI notify event
3793 generated by hotkey, video driver will adjust brightness
3794 level and then send out the event to user space through
3795 the allocated input device; If set to 0, video driver
3796 will only send out the event without touching backlight
3801 [VMMIO] Memory mapped virtio (platform) device.
3803 <size>@<baseaddr>:<irq>[:<id>]
3805 <size> := size (can use standard suffixes
3807 <baseaddr> := physical base address
3808 <irq> := interrupt number (as passed to
3810 <id> := (optional) platform device id
3812 virtio_mmio.device=1K@0x100b0000:48:7
3814 Can be used multiple times for multiple devices.
3816 vga= [BOOT,X86-32] Select a particular video mode
3817 See Documentation/x86/boot.txt and
3818 Documentation/svga.txt.
3819 Use vga=ask for menu.
3820 This is actually a boot loader parameter; the value is
3821 passed to the kernel using a special protocol.
3823 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3824 size of <nn>. This can be used to increase the
3825 minimum size (128MB on x86). It can also be used to
3826 decrease the size and leave more room for directly
3829 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3832 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3835 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3839 Controls the behavior of vsyscalls (i.e. calls to
3840 fixed addresses of 0xffffffffff600x00 from legacy
3841 code). Most statically-linked binaries and older
3842 versions of glibc use these calls. Because these
3843 functions are at fixed addresses, they make nice
3844 targets for exploits that can control RIP.
3846 emulate [default] Vsyscalls turn into traps and are
3847 emulated reasonably safely.
3849 native Vsyscalls are native syscall instructions.
3850 This is a little bit faster than trapping
3851 and makes a few dynamic recompilers work
3852 better than they would in emulation mode.
3853 It also makes exploits much easier to write.
3855 none Vsyscalls don't work at all. This makes
3856 them quite hard to use for exploits but
3857 might break your system.
3859 vt.color= [VT] Default text color.
3860 Format: 0xYX, X = foreground, Y = background.
3861 Default: 0x07 = light gray on black.
3863 vt.cur_default= [VT] Default cursor shape.
3864 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3865 the parameters of the <Esc>[?A;B;Cc escape sequence;
3866 see VGA-softcursor.txt. Default: 2 = underline.
3868 vt.default_blu= [VT]
3869 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3870 Change the default blue palette of the console.
3871 This is a 16-member array composed of values
3874 vt.default_grn= [VT]
3875 Format: <green0>,<green1>,<green2>,...,<green15>
3876 Change the default green palette of the console.
3877 This is a 16-member array composed of values
3880 vt.default_red= [VT]
3881 Format: <red0>,<red1>,<red2>,...,<red15>
3882 Change the default red palette of the console.
3883 This is a 16-member array composed of values
3889 Set system-wide default UTF-8 mode for all tty's.
3890 Default is 1, i.e. UTF-8 mode is enabled for all
3891 newly opened terminals.
3893 vt.global_cursor_default=
3896 Set system-wide default for whether a cursor
3897 is shown on new VTs. Default is -1,
3898 i.e. cursors will be created by default unless
3899 overridden by individual drivers. 0 will hide
3900 cursors, 1 will display them.
3902 vt.italic= [VT] Default color for italic text; 0-15.
3905 vt.underline= [VT] Default color for underlined text; 0-15.
3908 watchdog timers [HW,WDT] For information on watchdog timers,
3909 see Documentation/watchdog/watchdog-parameters.txt
3910 or other driver-specific files in the
3911 Documentation/watchdog/ directory.
3913 workqueue.disable_numa
3914 By default, all work items queued to unbound
3915 workqueues are affine to the NUMA nodes they're
3916 issued on, which results in better behavior in
3917 general. If NUMA affinity needs to be disabled for
3918 whatever reason, this option can be used. Note
3919 that this also can be controlled per-workqueue for
3920 workqueues visible under /sys/bus/workqueue/.
3922 workqueue.power_efficient
3923 Per-cpu workqueues are generally preferred because
3924 they show better performance thanks to cache
3925 locality; unfortunately, per-cpu workqueues tend to
3926 be more power hungry than unbound workqueues.
3928 Enabling this makes the per-cpu workqueues which
3929 were observed to contribute significantly to power
3930 consumption unbound, leading to measurably lower
3931 power usage at the cost of small performance
3934 The default value of this parameter is determined by
3935 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3937 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3938 default x2apic cluster mode on platforms
3941 x86_intel_mid_timer= [X86-32,APBT]
3942 Choose timer option for x86 Intel MID platform.
3943 Two valid options are apbt timer only and lapic timer
3944 plus one apbt timer for broadcast timer.
3945 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3947 xen_emul_unplug= [HW,X86,XEN]
3948 Unplug Xen emulated devices
3949 Format: [unplug0,][unplug1]
3950 ide-disks -- unplug primary master IDE devices
3951 aux-ide-disks -- unplug non-primary-master IDE devices
3952 nics -- unplug network devices
3953 all -- unplug all emulated devices (NICs and IDE disks)
3954 unnecessary -- unplugging emulated devices is
3955 unnecessary even if the host did not respond to
3957 never -- do not unplug even if version check succeeds
3959 xen_nopvspin [X86,XEN]
3960 Disables the ticketlock slowpath using Xen PV
3964 Disables the PV optimizations forcing the HVM guest to
3965 run as generic HVM guest with no PV drivers.
3967 xirc2ps_cs= [NET,PCMCIA]
3969 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3971 ______________________________________________________________________
3975 Add more DRM drivers.