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.
832 debugpat [X86] Enable PAT debugging
834 decnet.addr= [HW,NET]
835 Format: <area>[,<node>]
836 See also Documentation/networking/decnet.txt.
839 [same as hugepagesz=] The size of the default
840 HugeTLB page size. This is the size represented by
841 the legacy /proc/ hugepages APIs, used for SHM, and
842 default size when mounting hugetlbfs filesystems.
843 Defaults to the default architecture's huge page size
847 Set number of hash buckets for dentry cache.
850 See Documentation/networking/ipv6.txt.
852 disable_cpu_apicid= [X86,APIC,SMP]
854 The number of initial APIC ID for the
855 corresponding CPU to be disabled at boot,
856 mostly used for the kdump 2nd kernel to
857 disable BSP to wake up multiple CPUs without
858 causing system reset or hang due to sending
861 disable_ddw [PPC/PSERIES]
862 Disable Dynamic DMA Window support. Use this if
863 to workaround buggy firmware.
866 See Documentation/networking/ipv6.txt.
868 disable_mtrr_cleanup [X86]
869 The kernel tries to adjust MTRR layout from continuous
870 to discrete, to make X server driver able to add WB
871 entry later. This parameter disables that.
873 disable_mtrr_trim [X86, Intel and AMD only]
874 By default the kernel will trim any uncacheable
875 memory out of your available memory pool based on
876 MTRR settings. This parameter disables that behavior,
877 possibly causing your machine to run very slowly.
879 disable_timer_pin_1 [X86]
880 Disable PIN 1 of APIC timer
881 Can be useful to work around chipset bugs.
883 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
884 this option disables the debugging code at boot.
886 dma_debug_entries=<number>
887 This option allows to tune the number of preallocated
888 entries for DMA-API debugging code. One entry is
889 required per DMA-API allocation. Use this if the
890 DMA-API debugging code disables itself because the
891 architectural default is too low.
893 dma_debug_driver=<driver_name>
894 With this option the DMA-API debugging driver
895 filter feature can be enabled at boot time. Just
896 pass the driver to filter for as the parameter.
897 The filter can be disabled or changed to another
898 driver later using sysfs.
900 drm_kms_helper.edid_firmware=[<connector>:]<file>
901 Broken monitors, graphic adapters and KVMs may
902 send no or incorrect EDID data sets. This parameter
903 allows to specify an EDID data set in the
904 /lib/firmware directory that is used instead.
905 Generic built-in EDID data sets are used, if one of
906 edid/1024x768.bin, edid/1280x1024.bin,
907 edid/1680x1050.bin, or edid/1920x1080.bin is given
908 and no file with the same name exists. Details and
909 instructions how to build your own EDID data are
910 available in Documentation/EDID/HOWTO.txt. An EDID
911 data set will only be used for a particular connector,
912 if its name and a colon are prepended to the EDID
917 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
918 module.dyndbg[="val"]
919 Enable debug messages at boot time. See
920 Documentation/dynamic-debug-howto.txt for details.
922 early_ioremap_debug [KNL]
923 Enable debug messages in early_ioremap support. This
924 is useful for tracking down temporary early mappings
925 which are not unmapped.
927 earlycon= [KNL] Output early console device and options.
930 Start an early, polled-mode console on a cadence serial
931 port at the specified address. The cadence serial port
932 must already be setup and configured. Options are not
935 uart[8250],io,<addr>[,options]
936 uart[8250],mmio,<addr>[,options]
937 uart[8250],mmio32,<addr>[,options]
938 Start an early, polled-mode console on the 8250/16550
939 UART at the specified I/O port or MMIO address.
940 MMIO inter-register address stride is either 8-bit
941 (mmio) or 32-bit (mmio32).
942 The options are the same as for ttyS, above.
945 Start an early, polled-mode console on a pl011 serial
946 port at the specified address. The pl011 serial port
947 must already be setup and configured. Options are not
951 Start an early, polled-mode console on an msm serial
952 port at the specified address. The serial port
953 must already be setup and configured. Options are not
957 Start an early, polled-mode console on an msm serial
958 dm port at the specified address. The serial port
959 must already be setup and configured. Options are not
962 smh Use ARM semihosting calls for early console.
964 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
968 earlyprintk=serial[,ttySn[,baudrate]]
969 earlyprintk=serial[,0x...[,baudrate]]
970 earlyprintk=ttySn[,baudrate]
971 earlyprintk=dbgp[debugController#]
973 earlyprintk is useful when the kernel crashes before
974 the normal console is initialized. It is not enabled by
975 default because it has some cosmetic problems.
977 Append ",keep" to not disable it when the real console
980 Only one of vga, efi, serial, or usb debug port can
983 Currently only ttyS0 and ttyS1 may be specified by
984 name. Other I/O ports may be explicitly specified
985 on some architectures (x86 and arm at least) by
986 replacing ttySn with an I/O port address, like this:
987 earlyprintk=serial,0x1008,115200
988 You can find the port for a given device in
989 /proc/tty/driver/serial:
990 2: uart:ST16650V2 port:00001008 irq:18 ...
992 Interaction with the standard serial driver is not
995 The VGA and EFI output is eventually overwritten by
998 The xen output can only be used by Xen PV guests.
1000 edac_report= [HW,EDAC] Control how to report EDAC event
1001 Format: {"on" | "off" | "force"}
1002 on: enable EDAC to report H/W event. May be overridden
1003 by other higher priority error reporting module.
1004 off: disable H/W event reporting through EDAC.
1005 force: enforce the use of EDAC to report H/W event.
1008 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1011 This is designed to be used in conjunction with
1012 the boot argument: earlyprintk=vga
1015 Format: {"off" | "on" | "skip[mbr]"}
1018 Format: { "old_map", "nochunk", "noruntime" }
1019 old_map [X86-64]: switch to the old ioremap-based EFI
1020 runtime services mapping. 32-bit still uses this one by
1022 nochunk: disable reading files in "chunks" in the EFI
1023 boot stub, as chunking can cause problems with some
1024 firmware implementations.
1025 noruntime : disable EFI runtime services support
1027 efi_no_storage_paranoia [EFI; X86]
1028 Using this parameter you can use more than 50% of
1029 your efi variable storage. Use this parameter only if
1030 you are really sure that your UEFI does sane gc and
1031 fulfills the spec otherwise your board may brick.
1033 eisa_irq_edge= [PARISC,HW]
1034 See header of drivers/parisc/eisa.c.
1037 See comment before function elanfreq_setup() in
1038 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1041 Format: {"cfq" | "deadline" | "noop"}
1042 See Documentation/block/cfq-iosched.txt and
1043 Documentation/block/deadline-iosched.txt for details.
1045 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1046 Specifies physical address of start of kernel core
1047 image elf header and optionally the size. Generally
1048 kexec loader will pass this option to capture kernel.
1049 See Documentation/kdump/kdump.txt for details.
1051 enable_mtrr_cleanup [X86]
1052 The kernel tries to adjust MTRR layout from continuous
1053 to discrete, to make X server driver able to add WB
1054 entry later. This parameter enables that.
1056 enable_timer_pin_1 [X86]
1057 Enable PIN 1 of APIC timer
1058 Can be useful to work around chipset bugs
1059 (in particular on some ATI chipsets).
1060 The kernel tries to set a reasonable default.
1062 enforcing [SELINUX] Set initial enforcing status.
1064 See security/selinux/Kconfig help text.
1065 0 -- permissive (log only, no denials).
1066 1 -- enforcing (deny and log).
1068 Value can be changed at runtime via /selinux/enforce.
1071 Disable Error Record Serialization Table (ERST)
1074 ether= [HW,NET] Ethernet cards parameters
1075 This option is obsoleted by the "netdev=" option, which
1076 has equivalent usage. See its documentation for details.
1080 Permit 'security.evm' to be updated regardless of
1081 current integrity status.
1085 fail_make_request=[KNL]
1086 General fault injection mechanism.
1087 Format: <interval>,<probability>,<space>,<times>
1088 See also Documentation/fault-injection/.
1091 See Documentation/blockdev/floppy.txt.
1093 force_pal_cache_flush
1094 [IA-64] Avoid check_sal_cache_flush which may hang on
1095 buggy SAL_CACHE_FLUSH implementations. Using this
1096 parameter will force ia64_sal_cache_flush to call
1097 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1100 Forcefully enable Physical Address Extension (PAE).
1101 Many Pentium M systems disable PAE but may have a
1102 functionally usable PAE implementation.
1103 Warning: use of this parameter will taint the kernel
1104 and may cause unknown problems.
1107 [FTRACE] will set and start the specified tracer
1108 as early as possible in order to facilitate early
1111 ftrace_dump_on_oops[=orig_cpu]
1112 [FTRACE] will dump the trace buffers on oops.
1113 If no parameter is passed, ftrace will dump
1114 buffers of all CPUs, but if you pass orig_cpu, it will
1115 dump only the buffer of the CPU that triggered the
1118 ftrace_filter=[function-list]
1119 [FTRACE] Limit the functions traced by the function
1120 tracer at boot up. function-list is a comma separated
1121 list of functions. This list can be changed at run
1122 time by the set_ftrace_filter file in the debugfs
1125 ftrace_notrace=[function-list]
1126 [FTRACE] Do not trace the functions specified in
1127 function-list. This list can be changed at run time
1128 by the set_ftrace_notrace file in the debugfs
1131 ftrace_graph_filter=[function-list]
1132 [FTRACE] Limit the top level callers functions traced
1133 by the function graph tracer at boot up.
1134 function-list is a comma separated list of functions
1135 that can be changed at run time by the
1136 set_graph_function file in the debugfs tracing directory.
1138 ftrace_graph_notrace=[function-list]
1139 [FTRACE] Do not trace from the functions specified in
1140 function-list. This list is a comma separated list of
1141 functions that can be changed at run time by the
1142 set_graph_notrace file in the debugfs tracing directory.
1145 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1146 support via parallel port (up to 5 devices per port)
1147 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1148 See also Documentation/input/joystick-parport.txt
1152 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1156 gcov_persist= [GCOV] When non-zero (default), profiling data for
1157 kernel modules is saved and remains accessible via
1158 debugfs, even when the module is unloaded/reloaded.
1159 When zero, profiling data is discarded and associated
1160 debugfs files are removed at module unload time.
1162 gpt [EFI] Forces disk with valid GPT signature but
1163 invalid Protective MBR to be treated as GPT. If the
1164 primary GPT is corrupted, it enables the backup/alternate
1165 GPT to be used instead.
1167 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1168 the "Enable 0" bit of the configuration register.
1171 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1172 the "Enable 0" bit of the configuration register.
1175 grcan.select= [HW] Select which physical interface to use.
1178 grcan.txsize= [HW] Sets the size of the tx buffer.
1179 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1181 grcan.rxsize= [HW] Sets the size of the rx buffer.
1182 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1185 hashdist= [KNL,NUMA] Large hashes allocated during boot
1186 are distributed across NUMA nodes. Defaults on
1187 for 64-bit NUMA, off otherwise.
1188 Format: 0 | 1 (for off | on)
1190 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1192 hd= [EIDE] (E)IDE hard drive subsystem geometry
1193 Format: <cyl>,<head>,<sect>
1196 Disable Hardware Error Source Table (HEST) support;
1197 corresponding firmware-first mode error processing
1198 logic will be disabled.
1200 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1201 size of <nn>. This works even on boxes that have no
1202 highmem otherwise. This also works to reduce highmem
1203 size on bigger boxes.
1205 highres= [KNL] Enable/disable high resolution timer mode.
1206 Valid parameters: "on", "off"
1210 See Documentation/isdn/README.HiSax.
1214 hpet= [X86-32,HPET] option to control HPET usage
1215 Format: { enable (default) | disable | force |
1217 disable: disable HPET and use PIT instead
1218 force: allow force enabled of undocumented chips (ICH4,
1220 verbose: show contents of HPET registers during setup
1222 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1223 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1225 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1226 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1227 On x86-64 and powerpc, this option can be specified
1228 multiple times interleaved with hugepages= to reserve
1229 huge pages of different sizes. Valid pages sizes on
1230 x86-64 are 2M (when the CPU supports "pse") and 1G
1231 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1232 Note that 1GB pages can only be allocated at boot time
1233 using hugepages= and not freed afterwards.
1235 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1236 terminal devices. Valid values: 0..8
1237 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1238 If specified, z/VM IUCV HVC accepts connections
1239 from listed z/VM user IDs only.
1241 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1242 hardware thread id mappings.
1243 Format: <cpu>:<hwthread>
1246 Do not unregister boot console at start. This is only
1247 useful for debugging when something happens in the window
1248 between unregistering the boot console and initializing
1251 i2c_bus= [HW] Override the default board specific I2C bus speed
1252 or register an additional I2C bus that is not
1253 registered from board initialization code.
1257 i8042.debug [HW] Toggle i8042 debug mode
1258 i8042.direct [HW] Put keyboard port into non-translated mode
1259 i8042.dumbkbd [HW] Pretend that controller can only read data from
1260 keyboard and cannot control its state
1261 (Don't attempt to blink the leds)
1262 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1263 i8042.nokbd [HW] Don't check/create keyboard port
1264 i8042.noloop [HW] Disable the AUX Loopback command while probing
1266 i8042.nomux [HW] Don't check presence of an active multiplexing
1268 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1270 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1271 i8042.reset [HW] Reset the controller during init and cleanup
1272 i8042.unlock [HW] Unlock (ignore) the keylock
1276 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1277 indicates that the driver is running on unsupported
1279 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1280 does not match list of supported models.
1282 [HW] Report power status in /proc/i8k
1283 (disabled by default)
1284 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1287 i915.invert_brightness=
1288 [DRM] Invert the sense of the variable that is used to
1289 set the brightness of the panel backlight. Normally a
1290 brightness value of 0 indicates backlight switched off,
1291 and the maximum of the brightness value sets the backlight
1292 to maximum brightness. If this parameter is set to 0
1293 (default) and the machine requires it, or this parameter
1294 is set to 1, a brightness value of 0 sets the backlight
1295 to maximum brightness, and the maximum of the brightness
1296 value switches the backlight off.
1297 -1 -- never invert brightness
1298 0 -- machine default
1299 1 -- force brightness inversion
1302 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1304 ide-core.nodma= [HW] (E)IDE subsystem
1305 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1306 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1307 .cdrom .chs .ignore_cable are additional options
1308 See Documentation/ide/ide.txt.
1310 ide-generic.probe-mask= [HW] (E)IDE subsystem
1312 Probe mask for legacy ISA IDE ports. Depending on
1313 platform up to 6 ports are supported, enabled by
1314 setting corresponding bits in the mask to 1. The
1315 default value is 0x0, which has a special meaning.
1316 On systems that have PCI, it triggers scanning the
1317 PCI bus for the first and the second port, which
1318 are then probed. On systems without PCI the value
1319 of 0x0 enables probing the two first ports as if it
1322 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1323 Claim all unknown PCI IDE storage controllers.
1326 Format: idle=poll, idle=halt, idle=nomwait
1327 Poll forces a polling idle loop that can slightly
1328 improve the performance of waking up a idle CPU, but
1329 will use a lot of power and make the system run hot.
1331 idle=halt: Halt is forced to be used for CPU idle.
1332 In such case C2/C3 won't be used again.
1333 idle=nomwait: Disable mwait for CPU C-states
1335 ignore_loglevel [KNL]
1336 Ignore loglevel setting - this will print /all/
1337 kernel messages to the console. Useful for debugging.
1338 We also add it as printk module parameter, so users
1339 could change it dynamically, usually by
1340 /sys/module/printk/parameters/ignore_loglevel.
1342 ihash_entries= [KNL]
1343 Set number of hash buckets for inode cache.
1345 ima_appraise= [IMA] appraise integrity measurements
1346 Format: { "off" | "enforce" | "fix" | "log" }
1349 ima_appraise_tcb [IMA]
1350 The builtin appraise policy appraises all files
1354 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1358 The list of supported hash algorithms is defined
1359 in crypto/hash_info.h.
1362 Load a policy which meets the needs of the Trusted
1363 Computing Base. This means IMA will measure all
1364 programs exec'd, files mmap'd for exec, and all files
1365 opened for read by uid=0.
1368 Select one of defined IMA measurements template formats.
1369 Formats: { "ima" | "ima-ng" }
1372 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1373 Format: <min_file_size>
1374 Set the minimal file size for using asynchronous hash.
1375 If left unspecified, ahash usage is disabled.
1377 ahash performance varies for different data sizes on
1378 different crypto accelerators. This option can be used
1379 to achieve the best performance for a particular HW.
1381 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1383 Set hashing buffer size. Default: 4k.
1385 ahash performance varies for different chunk sizes on
1386 different crypto accelerators. This option can be used
1387 to achieve best performance for particular HW.
1391 Run specified binary instead of /sbin/init as init
1394 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1395 for working out where the kernel is dying during
1398 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1399 initcall functions. Useful for debugging built-in
1400 modules and initcalls.
1402 initrd= [BOOT] Specify the location of the initial ramdisk
1404 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1407 int_pln_enable [x86] Enable power limit notification interrupt
1409 integrity_audit=[IMA]
1410 Format: { "0" | "1" }
1411 0 -- basic integrity auditing messages. (Default)
1412 1 -- additional integrity auditing messages.
1414 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1416 Enable intel iommu driver.
1418 Disable intel iommu driver.
1419 igfx_off [Default Off]
1420 By default, gfx is mapped as normal device. If a gfx
1421 device has a dedicated DMAR unit, the DMAR unit is
1422 bypassed by not enabling DMAR with this option. In
1423 this case, gfx device will use physical address for
1426 With this option iommu will not optimize to look
1427 for io virtual address below 32-bit forcing dual
1428 address cycle on pci bus for cards supporting greater
1429 than 32-bit addressing. The default is to look
1430 for translation below 32-bit and if not available
1431 then look in the higher range.
1432 strict [Default Off]
1433 With this option on every unmap_single operation will
1434 result in a hardware IOTLB flush operation as opposed
1435 to batching them for performance.
1436 sp_off [Default Off]
1437 By default, super page will be supported if Intel IOMMU
1438 has the capability. With this option, super page will
1441 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1442 0 disables intel_idle and fall back on acpi_idle.
1443 1 to 6 specify maximum depth of C-state.
1447 Do not enable intel_pstate as the default
1448 scaling driver for the supported processors
1450 Enable intel_pstate on systems that prohibit it by default
1451 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1452 instead of acpi-cpufreq may disable platform features, such
1453 as thermal controls and power capping, that rely on ACPI
1454 P-States information being indicated to OSPM and therefore
1455 should be used with caution. This option does not work with
1456 processors that aren't supported by the intel_pstate driver
1457 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1459 Do not enable hardware P state control (HWP)
1462 intremap= [X86-64, Intel-IOMMU]
1463 on enable Interrupt Remapping (default)
1464 off disable Interrupt Remapping
1465 nosid disable Source ID checking
1467 BIOS x2APIC opt-out request will be ignored
1469 iomem= Disable strict checking of access to MMIO memory
1470 strict regions from userspace.
1487 io7= [HW] IO7 for Marvel based alpha systems
1488 See comment before marvel_specify_io7 in
1489 arch/alpha/kernel/core_marvel.c.
1491 io_delay= [X86] I/O delay method
1493 Standard port 0x80 based delay
1495 Alternate port 0xed based delay (needed on some systems)
1497 Simple two microseconds delay
1502 See Documentation/filesystems/nfs/nfsroot.txt.
1505 When an interrupt is not handled search all handlers
1506 for it. Intended to get systems with badly broken
1510 When an interrupt is not handled search all handlers
1511 for it. Also check all handlers each timer
1512 interrupt. Intended to get systems with badly broken
1516 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1518 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1520 <cpu number>,...,<cpu number>
1522 <cpu number>-<cpu number>
1523 (must be a positive range in ascending order)
1525 <cpu number>,...,<cpu number>-<cpu number>
1527 This option can be used to specify one or more CPUs
1528 to isolate from the general SMP balancing and scheduling
1529 algorithms. You can move a process onto or off an
1530 "isolated" CPU via the CPU affinity syscalls or cpuset.
1531 <cpu number> begins at 0 and the maximum value is
1532 "number of CPUs in system - 1".
1534 This option is the preferred way to isolate CPUs. The
1535 alternative -- manually setting the CPU mask of all
1536 tasks in the system -- can cause problems and
1537 suboptimal load balancer performance.
1541 ivrs_ioapic [HW,X86_64]
1542 Provide an override to the IOAPIC-ID<->DEVICE-ID
1543 mapping provided in the IVRS ACPI table. For
1544 example, to map IOAPIC-ID decimal 10 to
1545 PCI device 00:14.0 write the parameter as:
1546 ivrs_ioapic[10]=00:14.0
1548 ivrs_hpet [HW,X86_64]
1549 Provide an override to the HPET-ID<->DEVICE-ID
1550 mapping provided in the IVRS ACPI table. For
1551 example, to map HPET-ID decimal 0 to
1552 PCI device 00:14.0 write the parameter as:
1553 ivrs_hpet[0]=00:14.0
1555 js= [HW,JOY] Analog joystick
1556 See Documentation/input/joystick.txt.
1559 Enable/disable kernel and module base offset ASLR
1560 (Address Space Layout Randomization) if built into
1561 the kernel. When CONFIG_HIBERNATION is selected,
1562 kASLR is disabled by default. When kASLR is enabled,
1563 hibernation will be disabled.
1567 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1568 specifies the amount of memory usable by the kernel
1569 for non-movable allocations. The requested amount is
1570 spread evenly throughout all nodes in the system. The
1571 remaining memory in each node is used for Movable
1572 pages. In the event, a node is too small to have both
1573 kernelcore and Movable pages, kernelcore pages will
1574 take priority and other nodes will have a larger number
1575 of Movable pages. The Movable zone is used for the
1576 allocation of pages that may be reclaimed or moved
1577 by the page migration subsystem. This means that
1578 HugeTLB pages may not be allocated from this zone.
1579 Note that allocations like PTEs-from-HighMem still
1580 use the HighMem zone if it exists, and the Normal
1581 zone if it does not.
1583 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1584 Format: <Controller#>[,poll interval]
1585 The controller # is the number of the ehci usb debug
1586 port as it is probed via PCI. The poll interval is
1587 optional and is the number seconds in between
1588 each poll cycle to the debug port in case you need
1589 the functionality for interrupting the kernel with
1590 gdb or control-c on the dbgp connection. When
1591 not using this parameter you use sysrq-g to break into
1592 the kernel debugger.
1594 kgdboc= [KGDB,HW] kgdb over consoles.
1595 Requires a tty driver that supports console polling,
1596 or a supported polling keyboard driver (non-usb).
1597 Serial only format: <serial_device>[,baud]
1598 keyboard only format: kbd
1599 keyboard and serial format: kbd,<serial_device>[,baud]
1600 Optional Kernel mode setting:
1601 kms, kbd format: kms,kbd
1602 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1604 kgdbwait [KGDB] Stop kernel execution and enter the
1605 kernel debugger at the earliest opportunity.
1607 kmac= [MIPS] korina ethernet MAC address.
1608 Configure the RouterBoard 532 series on-chip
1609 Ethernet adapter MAC address.
1611 kmemleak= [KNL] Boot-time kmemleak enable/disable
1612 Valid arguments: on, off
1614 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1617 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1618 Valid arguments: 0, 1, 2
1619 kmemcheck=0 (disabled)
1620 kmemcheck=1 (enabled)
1621 kmemcheck=2 (one-shot mode)
1622 Default: 2 (one-shot mode)
1624 kstack=N [X86] Print N words from the kernel stack
1627 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1628 Default is 0 (don't ignore, but inject #GP)
1630 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1634 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1635 Default is 1 (enabled)
1637 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1639 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1641 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1642 (virtualized MMU) support on capable Intel chips.
1643 Default is 1 (enabled)
1645 kvm-intel.emulate_invalid_guest_state=
1646 [KVM,Intel] Enable emulation of invalid guest states
1647 Default is 0 (disabled)
1649 kvm-intel.flexpriority=
1650 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1651 Default is 1 (enabled)
1654 [KVM,Intel] Enable VMX nesting (nVMX).
1655 Default is 0 (disabled)
1657 kvm-intel.unrestricted_guest=
1658 [KVM,Intel] Disable unrestricted guest feature
1659 (virtualized real and unpaged mode) on capable
1660 Intel chips. Default is 1 (enabled)
1662 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1663 feature (tagged TLBs) on capable Intel chips.
1664 Default is 1 (enabled)
1670 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1673 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1674 value for LAPIC timer one-shot implementation. Default
1675 back to the programmable timer unit in the LAPIC.
1677 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1680 libata.dma= [LIBATA] DMA control
1681 libata.dma=0 Disable all PATA and SATA DMA
1682 libata.dma=1 PATA and SATA Disk DMA only
1683 libata.dma=2 ATAPI (CDROM) DMA only
1684 libata.dma=4 Compact Flash DMA only
1685 Combinations also work, so libata.dma=3 enables DMA
1686 for disks and CDROMs, but not CFs.
1688 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1689 libata.ignore_hpa=0 keep BIOS limits (default)
1690 libata.ignore_hpa=1 ignore limits, using full disk
1692 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1696 libata.force= [LIBATA] Force configurations. The format is comma
1697 separated list of "[ID:]VAL" where ID is
1698 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1699 matching port, link or device. Basically, it matches
1700 the ATA ID string printed on console by libata. If
1701 the whole ID part is omitted, the last PORT and DEVICE
1702 values are used. If ID hasn't been specified yet, the
1703 configuration applies to all ports, links and devices.
1705 If only DEVICE is omitted, the parameter applies to
1706 the port and all links and devices behind it. DEVICE
1707 number of 0 either selects the first device or the
1708 first fan-out link behind PMP device. It does not
1709 select the host link. DEVICE number of 15 selects the
1710 host link and device attached to it.
1712 The VAL specifies the configuration to force. As long
1713 as there's no ambiguity shortcut notation is allowed.
1714 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1715 The following configurations can be forced.
1717 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1718 Any ID with matching PORT is used.
1720 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1722 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1723 udma[/][16,25,33,44,66,100,133] notation is also
1726 * [no]ncq: Turn on or off NCQ.
1728 * nohrst, nosrst, norst: suppress hard, soft
1731 * rstonce: only attempt one reset during
1732 hot-unplug link recovery
1734 * dump_id: dump IDENTIFY data.
1736 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1738 * disable: Disable this device.
1740 If there are multiple matching configurations changing
1741 the same attribute, the last one is used.
1743 memblock=debug [KNL] Enable memblock debug messages.
1745 load_ramdisk= [RAM] List of ramdisks to load from floppy
1746 See Documentation/blockdev/ramdisk.txt.
1748 lockd.nlm_grace_period=P [NFS] Assign grace period.
1751 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1754 lockd.nlm_timeout=T [NFS] Assign timeout value.
1757 lockd.nlm_udpport=M [NFS] Assign UDP port.
1760 locktorture.nreaders_stress= [KNL]
1761 Set the number of locking read-acquisition kthreads.
1762 Defaults to being automatically set based on the
1763 number of online CPUs.
1765 locktorture.nwriters_stress= [KNL]
1766 Set the number of locking write-acquisition kthreads.
1768 locktorture.onoff_holdoff= [KNL]
1769 Set time (s) after boot for CPU-hotplug testing.
1771 locktorture.onoff_interval= [KNL]
1772 Set time (s) between CPU-hotplug operations, or
1773 zero to disable CPU-hotplug testing.
1775 locktorture.shuffle_interval= [KNL]
1776 Set task-shuffle interval (jiffies). Shuffling
1777 tasks allows some CPUs to go into dyntick-idle
1778 mode during the locktorture test.
1780 locktorture.shutdown_secs= [KNL]
1781 Set time (s) after boot system shutdown. This
1782 is useful for hands-off automated testing.
1784 locktorture.stat_interval= [KNL]
1785 Time (s) between statistics printk()s.
1787 locktorture.stutter= [KNL]
1788 Time (s) to stutter testing, for example,
1789 specifying five seconds causes the test to run for
1790 five seconds, wait for five seconds, and so on.
1791 This tests the locking primitive's ability to
1792 transition abruptly to and from idle.
1794 locktorture.torture_runnable= [BOOT]
1795 Start locktorture running at boot time.
1797 locktorture.torture_type= [KNL]
1798 Specify the locking implementation to test.
1800 locktorture.verbose= [KNL]
1801 Enable additional printk() statements.
1803 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1806 loglevel= All Kernel Messages with a loglevel smaller than the
1807 console loglevel will be printed to the console. It can
1808 also be changed with klogd or other programs. The
1809 loglevels are defined as follows:
1811 0 (KERN_EMERG) system is unusable
1812 1 (KERN_ALERT) action must be taken immediately
1813 2 (KERN_CRIT) critical conditions
1814 3 (KERN_ERR) error conditions
1815 4 (KERN_WARNING) warning conditions
1816 5 (KERN_NOTICE) normal but significant condition
1817 6 (KERN_INFO) informational
1818 7 (KERN_DEBUG) debug-level messages
1820 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1821 in bytes. n must be a power of two and greater
1822 than the minimal size. The minimal size is defined
1823 by LOG_BUF_SHIFT kernel config parameter. There is
1824 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1825 that allows to increase the default size depending on
1826 the number of CPUs. See init/Kconfig for more details.
1828 logo.nologo [FB] Disables display of the built-in Linux logo.
1829 This may be used to provide more screen space for
1830 kernel log messages and is useful when debugging
1831 kernel boot problems.
1833 lp=0 [LP] Specify parallel ports to use, e.g,
1834 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1835 lp=reset first parallel port). 'lp=0' disables the
1836 lp=auto printer driver. 'lp=reset' (which can be
1837 specified in addition to the ports) causes
1838 attached printers to be reset. Using
1839 lp=port1,port2,... specifies the parallel ports
1840 to associate lp devices with, starting with
1841 lp0. A port specification may be 'none' to skip
1842 that lp device, or a parport name such as
1843 'parport0'. Specifying 'lp=auto' instead of a
1844 port specification list means that device IDs
1845 from each port should be examined, to see if
1846 an IEEE 1284-compliant printer is attached; if
1847 so, the driver will manage that printer.
1848 See also header of drivers/char/lp.c.
1851 Sets loops_per_jiffy to given constant, thus avoiding
1852 time-consuming boot-time autodetection (up to 250 ms per
1853 CPU). 0 enables autodetection (default). To determine
1854 the correct value for your kernel, boot with normal
1855 autodetection and see what value is printed. Note that
1856 on SMP systems the preset will be applied to all CPUs,
1857 which is likely to cause problems if your CPUs need
1858 significantly divergent settings. An incorrect value
1859 will cause delays in the kernel to be wrong, leading to
1860 unpredictable I/O errors and other breakage. Although
1861 unlikely, in the extreme case this might damage your
1865 Format: <io>,<irq>,<dma>
1867 machvec= [IA-64] Force the use of a particular machine-vector
1868 (machvec) in a generic kernel.
1869 Example: machvec=hpzx1_swiotlb
1871 machtype= [Loongson] Share the same kernel image file between different
1873 Example: machtype=lemote-yeeloong-2f-7inch
1875 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1876 than or equal to this physical address is ignored.
1878 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1879 should make use of. maxcpus=n : n >= 0 limits the
1880 kernel to using 'n' processors. n=0 is a special case,
1881 it is equivalent to "nosmp", which also disables
1884 max_loop= [LOOP] The number of loop block devices that get
1885 (loop.max_loop) unconditionally pre-created at init time. The default
1886 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1887 of statically allocating a predefined number, loop
1888 devices can be requested on-demand with the
1889 /dev/loop-control interface.
1891 mce [X86-32] Machine Check Exception
1893 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1895 md= [HW] RAID subsystems devices and level
1896 See Documentation/md.txt.
1899 Format: <first>,<last>
1900 Specifies range of consoles to be captured by the MDA.
1902 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1903 Amount of memory to be used when the kernel is not able
1904 to see the whole system memory or for test.
1905 [X86] Work as limiting max address. Use together
1906 with memmap= to avoid physical address space collisions.
1907 Without memmap= PCI devices could be placed at addresses
1908 belonging to unused RAM.
1910 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1914 [KNL,SH] Allow user to override the default size for
1915 per-device physically contiguous DMA buffers.
1917 memmap=exactmap [KNL,X86] Enable setting of an exact
1918 E820 memory map, as specified by the user.
1919 Such memmap=exactmap lines can be constructed based on
1920 BIOS output or other requirements. See the memmap=nn@ss
1923 memmap=nn[KMG]@ss[KMG]
1924 [KNL] Force usage of a specific region of memory.
1925 Region of memory to be used is from ss to ss+nn.
1927 memmap=nn[KMG]#ss[KMG]
1928 [KNL,ACPI] Mark specific memory as ACPI data.
1929 Region of memory to be marked is from ss to ss+nn.
1931 memmap=nn[KMG]$ss[KMG]
1932 [KNL,ACPI] Mark specific memory as reserved.
1933 Region of memory to be reserved is from ss to ss+nn.
1934 Example: Exclude memory from 0x18690000-0x1869ffff
1935 memmap=64K$0x18690000
1937 memmap=0x10000$0x18690000
1939 memory_corruption_check=0/1 [X86]
1940 Some BIOSes seem to corrupt the first 64k of
1941 memory when doing things like suspend/resume.
1942 Setting this option will scan the memory
1943 looking for corruption. Enabling this will
1944 both detect corruption and prevent the kernel
1945 from using the memory being corrupted.
1946 However, its intended as a diagnostic tool; if
1947 repeatable BIOS-originated corruption always
1948 affects the same memory, you can use memmap=
1949 to prevent the kernel from using that memory.
1951 memory_corruption_check_size=size [X86]
1952 By default it checks for corruption in the low
1953 64k, making this memory unavailable for normal
1954 use. Use this parameter to scan for
1955 corruption in more or less memory.
1957 memory_corruption_check_period=seconds [X86]
1958 By default it checks for corruption every 60
1959 seconds. Use this parameter to check at some
1960 other rate. 0 disables periodic checking.
1962 memtest= [KNL,X86] Enable memtest
1964 default : 0 <disable>
1965 Specifies the number of memtest passes to be
1966 performed. Each pass selects another test
1967 pattern from a given set of patterns. Memtest
1968 fills the memory with this pattern, validates
1969 memory contents and reserves bad memory
1970 regions that are detected.
1972 meye.*= [HW] Set MotionEye Camera parameters
1973 See Documentation/video4linux/meye.txt.
1975 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1976 Multi-Function General Purpose Timers on AMD Geode
1979 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1980 the BIOS has incorrectly applied a workaround. TinyBIOS
1981 version 0.98 is known to be affected, 0.99 fixes the
1982 problem by letting the user disable the workaround.
1986 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1987 physical address is ignored.
1989 mini2440= [ARM,HW,KNL]
1990 Format:[0..2][b][c][t]
1992 MINI2440 configuration specification:
1993 0 - The attached screen is the 3.5" TFT
1994 1 - The attached screen is the 7" TFT
1995 2 - The VGA Shield is attached (1024x768)
1996 Leaving out the screen size parameter will not load
1997 the TFT driver, and the framebuffer will be left
1999 b - Enable backlight. The TFT backlight pin will be
2000 linked to the kernel VESA blanking code and a GPIO
2001 LED. This parameter is not necessary when using the
2003 c - Enable the s3c camera interface.
2004 t - Reserved for enabling touchscreen support. The
2005 touchscreen support is not enabled in the mainstream
2006 kernel as of 2.6.30, a preliminary port can be found
2007 in the "bleeding edge" mini2440 support kernel at
2008 http://repo.or.cz/w/linux-2.6/mini2440.git
2011 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2012 parameter allows control of the logging verbosity for
2013 the additional memory initialisation checks. A value
2014 of 0 disables mminit logging and a level of 4 will
2015 log everything. Information is printed at KERN_DEBUG
2016 so loglevel=8 may also need to be specified.
2019 [KNL] When CONFIG_MODULE_SIG is set, this means that
2020 modules without (valid) signatures will fail to load.
2021 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2022 is always true, so this option does nothing.
2025 [MOUSE] Maximum time between finger touching and
2026 leaving touchpad surface for touch to be considered
2027 a tap and be reported as a left button click (for
2028 touchpads working in absolute mode only).
2030 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2031 reporting absolute coordinates, such as tablets
2032 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2033 reporting absolute coordinates, such as tablets
2035 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2036 is similar to kernelcore except it specifies the
2037 amount of memory used for migratable allocations.
2038 If both kernelcore and movablecore is specified,
2039 then kernelcore will be at *least* the specified
2040 value but may be more. If movablecore on its own
2041 is specified, the administrator must be careful
2042 that the amount of memory usable for all allocations
2045 movable_node [KNL,X86] Boot-time switch to enable the effects
2046 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2048 MTD_Partition= [MTD]
2049 Format: <name>,<region-number>,<size>,<offset>
2051 MTD_Region= [MTD] Format:
2052 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2055 See drivers/mtd/cmdlinepart.c.
2057 multitce=off [PPC] This parameter disables the use of the pSeries
2058 firmware feature for updating multiple TCE entries
2061 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2063 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2065 boundary - index of last SLC block on Flex-OneNAND.
2066 The remaining blocks are configured as MLC blocks.
2067 lock - Configure if Flex-OneNAND boundary should be locked.
2068 Once locked, the boundary cannot be changed.
2069 1 indicates lock status, 0 indicates unlock status.
2072 ARM/S3C2412 JIVE boot control
2074 See arch/arm/mach-s3c2412/mach-jive.c
2076 mtouchusb.raw_coordinates=
2077 [HW] Make the MicroTouch USB driver use raw coordinates
2078 ('y', default) or cooked coordinates ('n')
2080 mtrr_chunk_size=nn[KMG] [X86]
2081 used for mtrr cleanup. It is largest continuous chunk
2082 that could hold holes aka. UC entries.
2084 mtrr_gran_size=nn[KMG] [X86]
2085 Used for mtrr cleanup. It is granularity of mtrr block.
2087 Large value could prevent small alignment from
2090 mtrr_spare_reg_nr=n [X86]
2092 Range: 0,7 : spare reg number
2094 Used for mtrr cleanup. It is spare mtrr entries number.
2095 Set to 2 or more if your graphical card needs more.
2097 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2099 netdev= [NET] Network devices parameters
2100 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2101 Note that mem_start is often overloaded to mean
2102 something different and driver-specific.
2103 This usage is only documented in each driver source
2107 [NETFILTER] Enable connection tracking flow accounting
2108 0 to disable accounting
2109 1 to enable accounting
2112 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2113 See Documentation/filesystems/nfs/nfsroot.txt.
2115 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2116 See Documentation/filesystems/nfs/nfsroot.txt.
2118 nfsrootdebug [NFS] enable nfsroot debugging messages.
2119 See Documentation/filesystems/nfs/nfsroot.txt.
2121 nfs.callback_tcpport=
2122 [NFS] set the TCP port on which the NFSv4 callback
2123 channel should listen.
2126 [NFS] sets the pathname to the program which is used
2127 to update the NFS client cache entries.
2129 nfs.cache_getent_timeout=
2130 [NFS] sets the timeout after which an attempt to
2131 update a cache entry is deemed to have failed.
2133 nfs.idmap_cache_timeout=
2134 [NFS] set the maximum lifetime for idmapper cache
2138 [NFS] enable 64-bit inode numbers.
2139 If zero, the NFS client will fake up a 32-bit inode
2140 number for the readdir() and stat() syscalls instead
2141 of returning the full 64-bit number.
2142 The default is to return 64-bit inode numbers.
2144 nfs.max_session_slots=
2145 [NFSv4.1] Sets the maximum number of session slots
2146 the client will attempt to negotiate with the server.
2147 This limits the number of simultaneous RPC requests
2148 that the client can send to the NFSv4.1 server.
2149 Note that there is little point in setting this
2150 value higher than the max_tcp_slot_table_limit.
2152 nfs.nfs4_disable_idmapping=
2153 [NFSv4] When set to the default of '1', this option
2154 ensures that both the RPC level authentication
2155 scheme and the NFS level operations agree to use
2156 numeric uids/gids if the mount is using the
2157 'sec=sys' security flavour. In effect it is
2158 disabling idmapping, which can make migration from
2159 legacy NFSv2/v3 systems to NFSv4 easier.
2160 Servers that do not support this mode of operation
2161 will be autodetected by the client, and it will fall
2162 back to using the idmapper.
2163 To turn off this behaviour, set the value to '0'.
2165 [NFS4] Specify an additional fixed unique ident-
2166 ification string that NFSv4 clients can insert into
2167 their nfs_client_id4 string. This is typically a
2168 UUID that is generated at system install time.
2170 nfs.send_implementation_id =
2171 [NFSv4.1] Send client implementation identification
2172 information in exchange_id requests.
2173 If zero, no implementation identification information
2175 The default is to send the implementation identification
2178 nfs.recover_lost_locks =
2179 [NFSv4] Attempt to recover locks that were lost due
2180 to a lease timeout on the server. Please note that
2181 doing this risks data corruption, since there are
2182 no guarantees that the file will remain unchanged
2183 after the locks are lost.
2184 If you want to enable the kernel legacy behaviour of
2185 attempting to recover these locks, then set this
2187 The default parameter value of '0' causes the kernel
2188 not to attempt recovery of lost locks.
2190 nfsd.nfs4_disable_idmapping=
2191 [NFSv4] When set to the default of '1', the NFSv4
2192 server will return only numeric uids and gids to
2193 clients using auth_sys, and will accept numeric uids
2194 and gids from such clients. This is intended to ease
2195 migration from NFSv2/v3.
2197 objlayoutdriver.osd_login_prog=
2198 [NFS] [OBJLAYOUT] sets the pathname to the program which
2199 is used to automatically discover and login into new
2200 osd-targets. Please see:
2201 Documentation/filesystems/pnfs.txt for more explanations
2203 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2204 when a NMI is triggered.
2205 Format: [state][,regs][,debounce][,die]
2207 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2208 Format: [panic,][nopanic,][num]
2210 0 - turn nmi_watchdog off
2211 When panic is specified, panic when an NMI watchdog
2212 timeout occurs (or 'nopanic' to override the opposite
2214 This is useful when you use a panic=... timeout and
2215 need the box quickly up again.
2217 netpoll.carrier_timeout=
2218 [NET] Specifies amount of time (in seconds) that
2219 netpoll should wait for a carrier. By default netpoll
2222 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2223 emulation library even if a 387 maths coprocessor
2227 [HW] Never suspend the console
2228 Disable suspending of consoles during suspend and
2229 hibernate operations. Once disabled, debugging
2230 messages can reach various consoles while the rest
2231 of the system is being put to sleep (ie, while
2232 debugging driver suspend/resume hooks). This may
2233 not work reliably with all consoles, but is known
2234 to work with serial and VGA consoles.
2235 To facilitate more flexible debugging, we also add
2236 console_suspend, a printk module parameter to control
2237 it. Users could use console_suspend (usually
2238 /sys/module/printk/parameters/console_suspend) to
2239 turn on/off it dynamically.
2241 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2242 caches in the slab allocator. Saves per-node memory,
2243 but will impact performance.
2247 noapic [SMP,APIC] Tells the kernel to not make use of any
2248 IOAPICs that may be present in the system.
2250 noautogroup Disable scheduler automatic task group creation.
2252 nobats [PPC] Do not use BATs for mapping kernel lowmem
2253 on "Classic" PPC cores.
2257 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2259 nodelayacct [KNL] Disable per-task delay accounting
2261 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2263 nodsp [SH] Disable hardware DSP at boot time.
2265 noefi Disable EFI runtime services support.
2270 On X86-32 available only on PAE configured kernels.
2271 noexec=on: enable non-executable mappings (default)
2272 noexec=off: disable non-executable mappings
2275 Disable SMAP (Supervisor Mode Access Prevention)
2276 even if it is supported by processor.
2279 Disable SMEP (Supervisor Mode Execution Prevention)
2280 even if it is supported by processor.
2283 This affects only 32-bit executables.
2284 noexec32=on: enable non-executable mappings (default)
2285 read doesn't imply executable mappings
2286 noexec32=off: disable non-executable mappings
2287 read implies executable mappings
2289 nofpu [SH] Disable hardware FPU at boot time.
2291 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2292 register save and restore. The kernel will only save
2293 legacy floating-point registers on task switch.
2295 noxsave [BUGS=X86] Disables x86 extended register state save
2296 and restore using xsave. The kernel will fallback to
2297 enabling legacy floating-point and sse state.
2299 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2300 register states. The kernel will fall back to use
2301 xsave to save the states. By using this parameter,
2302 performance of saving the states is degraded because
2303 xsave doesn't support modified optimization while
2304 xsaveopt supports it on xsaveopt enabled systems.
2306 noxsaves [X86] Disables xsaves and xrstors used in saving and
2307 restoring x86 extended register state in compacted
2308 form of xsave area. The kernel will fall back to use
2309 xsaveopt and xrstor to save and restore the states
2310 in standard form of xsave area. By using this
2311 parameter, xsave area per process might occupy more
2312 memory on xsaves enabled systems.
2315 on enable eager fpu restore
2316 off disable eager fpu restore
2317 auto selects the default scheme, which automatically
2318 enables eagerfpu restore for xsaveopt.
2320 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2321 wfi(ARM) instruction doesn't work correctly and not to
2322 use it. This is also useful when using JTAG debugger.
2324 no_file_caps Tells the kernel not to honor file capabilities. The
2325 only way then for a file to be executed with privilege
2326 is to be setuid root or executed by root.
2328 nohalt [IA-64] Tells the kernel not to use the power saving
2329 function PAL_HALT_LIGHT when idle. This increases
2330 power-consumption. On the positive side, it reduces
2331 interrupt wake-up latency, which may improve performance
2332 in certain environments such as networked servers or
2335 nohibernate [HIBERNATION] Disable hibernation and resume.
2337 nohz= [KNL] Boottime enable/disable dynamic ticks
2338 Valid arguments: on, off
2341 nohz_full= [KNL,BOOT]
2342 In kernels built with CONFIG_NO_HZ_FULL=y, set
2343 the specified list of CPUs whose tick will be stopped
2344 whenever possible. The boot CPU will be forced outside
2345 the range to maintain the timekeeping.
2346 The CPUs in this range must also be included in the
2349 noiotrap [SH] Disables trapped I/O port accesses.
2351 noirqdebug [X86-32] Disables the code which attempts to detect and
2352 disable unhandled interrupt sources.
2354 no_timer_check [X86,APIC] Disables the code which tests for
2355 broken timer IRQ sources.
2357 noisapnp [ISAPNP] Disables ISA PnP code.
2359 noinitrd [RAM] Tells the kernel not to load any configured
2362 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2364 [Deprecated - use intremap=off]
2368 nojitter [IA-64] Disables jitter checking for ITC timers.
2370 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2372 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2375 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2376 steal time is computed, but won't influence scheduler
2379 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2381 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2383 noltlbs [PPC] Do not use large page/tlb entries for kernel
2384 lowmem mapping on PPC40x.
2386 nomca [IA-64] Disable machine check abort handling
2388 nomce [X86-32] Machine Check Exception
2390 nomfgpt [X86-32] Disable Multi-Function General Purpose
2391 Timer usage (for AMD Geode machines).
2393 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2394 shutdown the other cpus. Instead use the REBOOT_VECTOR
2397 nomodule Disable module load
2399 nopat [X86] Disable PAT (page attribute table extension of
2400 pagetables) support.
2402 norandmaps Don't use address space randomization. Equivalent to
2403 echo 0 > /proc/sys/kernel/randomize_va_space
2405 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2407 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2408 with UP alternatives
2410 nordrand [X86] Disable kernel use of the RDRAND and
2411 RDSEED instructions even if they are supported
2412 by the processor. RDRAND and RDSEED are still
2413 available to user space applications.
2415 noresume [SWSUSP] Disables resume and restores original swap
2418 no-scroll [VGA] Disables scrollback.
2419 This is required for the Braillex ib80-piezo Braille
2420 reader made by F.H. Papenmeier (Germany).
2424 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2426 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2427 and disable the IO APIC. legacy for "maxcpus=0".
2429 nosoftlockup [KNL] Disable the soft-lockup detector.
2431 nosync [HW,M68K] Disables sync negotiation for all devices.
2433 notsc [BUGS=X86-32] Disable Time Stamp Counter
2435 nousb [USB] Disable the USB subsystem
2437 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2441 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2443 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2444 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2445 Some features depend on CPU0. Known dependencies are:
2446 1. Resume from suspend/hibernate depends on CPU0.
2447 Suspend/hibernate will fail if CPU0 is offline and you
2448 need to online CPU0 before suspend/hibernate.
2449 2. PIC interrupts also depend on CPU0. CPU0 can't be
2450 removed if a PIC interrupt is detected.
2451 It's said poweroff/reboot may depend on CPU0 on some
2452 machines although I haven't seen such issues so far
2453 after CPU0 is offline on a few tested machines.
2454 If the dependencies are under your control, you can
2455 turn on cpu0_hotplug.
2457 nptcg= [IA-64] Override max number of concurrent global TLB
2458 purges which is reported from either PAL_VM_SUMMARY or
2461 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2462 could support. nr_cpus=n : n >= 1 limits the kernel to
2463 supporting 'n' processors. Later in runtime you can not
2464 use hotplug cpu feature to put more cpu back to online.
2465 just like you compile the kernel NR_CPUS=n
2467 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2469 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2470 Allowed values are enable and disable
2472 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2473 one of ['zone', 'node', 'default'] can be specified
2474 This can be set from sysctl after boot.
2475 See Documentation/sysctl/vm.txt for details.
2477 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2478 See Documentation/debugging-via-ohci1394.txt for more
2481 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2482 Rather than timing out after 20 ms if an EC
2483 command is not properly ACKed, override the length
2484 of the timeout. We have interrupts disabled while
2485 waiting for the ACK, so if this is set too high
2486 interrupts *may* be lost!
2488 omap_mux= [OMAP] Override bootloader pin multiplexing.
2489 Format: <mux_mode0.mode_name=value>...
2490 For example, to override I2C bus2:
2491 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2493 oprofile.timer= [HW]
2494 Use timer interrupt instead of performance counters
2496 oprofile.cpu_type= Force an oprofile cpu type
2497 This might be useful if you have an older oprofile
2498 userland or if you want common events.
2499 Format: { arch_perfmon }
2500 arch_perfmon: [X86] Force use of architectural
2501 perfmon on Intel CPUs instead of the
2502 CPU specific event set.
2503 timer: [X86] Force use of architectural NMI
2504 timer mode (see also oprofile.timer
2505 for generic hr timer mode)
2506 [s390] Force legacy basic mode sampling
2507 (report cpu_type "timer")
2509 oops=panic Always panic on oopses. Default is to just kill the
2510 process, but there is a small probability of
2511 deadlocking the machine.
2512 This will also cause panics on machine check exceptions.
2513 Useful together with panic=30 to trigger a reboot.
2516 See Documentation/sound/oss/oss-parameters.txt
2518 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2519 timeout > 0: seconds before rebooting
2520 timeout = 0: wait forever
2521 timeout < 0: reboot immediately
2524 crash_kexec_post_notifiers
2525 Run kdump after running panic-notifiers and dumping
2526 kmsg. This only for the users who doubt kdump always
2527 succeeds in any situation.
2528 Note that this also increases risks of kdump failure,
2529 because some panic notifiers can make the crashed
2530 kernel more unstable.
2532 parkbd.port= [HW] Parallel port number the keyboard adapter is
2533 connected to, default is 0.
2535 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2536 0 for XT, 1 for AT (default is AT).
2539 parport= [HW,PPT] Specify parallel ports. 0 disables.
2540 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2541 Use 'auto' to force the driver to use any
2542 IRQ/DMA settings detected (the default is to
2543 ignore detected IRQ/DMA settings because of
2544 possible conflicts). You can specify the base
2545 address, IRQ, and DMA settings; IRQ and DMA
2546 should be numbers, or 'auto' (for using detected
2547 settings on that particular port), or 'nofifo'
2548 (to avoid using a FIFO even if it is detected).
2549 Parallel ports are assigned in the order they
2550 are specified on the command line, starting
2553 parport_init_mode= [HW,PPT]
2554 Configure VIA parallel port to operate in
2555 a specific mode. This is necessary on Pegasos
2556 computer where firmware has no options for setting
2557 up parallel port mode and sets it to spp.
2558 Currently this function knows 686a and 8231 chips.
2559 Format: [spp|ps2|epp|ecp|ecpepp]
2562 Halt all CPUs after the first oops has been printed for
2563 the specified number of seconds. This is to be used if
2564 your oopses keep scrolling off the screen.
2569 See header of drivers/block/paride/pcd.c.
2570 See also Documentation/blockdev/paride.txt.
2572 pci=option[,option...] [PCI] various PCI subsystem options:
2573 earlydump [X86] dump PCI config space before the kernel
2575 off [X86] don't probe for the PCI bus
2576 bios [X86-32] force use of PCI BIOS, don't access
2577 the hardware directly. Use this if your machine
2578 has a non-standard PCI host bridge.
2579 nobios [X86-32] disallow use of PCI BIOS, only direct
2580 hardware access methods are allowed. Use this
2581 if you experience crashes upon bootup and you
2582 suspect they are caused by the BIOS.
2583 conf1 [X86] Force use of PCI Configuration
2585 conf2 [X86] Force use of PCI Configuration
2587 noaer [PCIE] If the PCIEAER kernel config parameter is
2588 enabled, this kernel boot option can be used to
2589 disable the use of PCIE advanced error reporting.
2590 nodomains [PCI] Disable support for multiple PCI
2591 root domains (aka PCI segments, in ACPI-speak).
2592 nommconf [X86] Disable use of MMCONFIG for PCI
2594 check_enable_amd_mmconf [X86] check for and enable
2595 properly configured MMIO access to PCI
2596 config space on AMD family 10h CPU
2597 nomsi [MSI] If the PCI_MSI kernel config parameter is
2598 enabled, this kernel boot option can be used to
2599 disable the use of MSI interrupts system-wide.
2600 noioapicquirk [APIC] Disable all boot interrupt quirks.
2601 Safety option to keep boot IRQs enabled. This
2602 should never be necessary.
2603 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2604 primary IO-APIC for bridges that cannot disable
2605 boot IRQs. This fixes a source of spurious IRQs
2606 when the system masks IRQs.
2607 noioapicreroute [APIC] Disable workaround that uses the
2608 boot IRQ equivalent of an IRQ that connects to
2609 a chipset where boot IRQs cannot be disabled.
2610 The opposite of ioapicreroute.
2611 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2612 routing table. These calls are known to be buggy
2613 on several machines and they hang the machine
2614 when used, but on other computers it's the only
2615 way to get the interrupt routing table. Try
2616 this option if the kernel is unable to allocate
2617 IRQs or discover secondary PCI buses on your
2619 rom [X86] Assign address space to expansion ROMs.
2620 Use with caution as certain devices share
2621 address decoders between ROMs and other
2623 norom [X86] Do not assign address space to
2624 expansion ROMs that do not already have
2625 BIOS assigned address ranges.
2626 nobar [X86] Do not assign address space to the
2627 BARs that weren't assigned by the BIOS.
2628 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2629 assigned automatically to PCI devices. You can
2630 make the kernel exclude IRQs of your ISA cards
2632 pirqaddr=0xAAAAA [X86] Specify the physical address
2633 of the PIRQ table (normally generated
2634 by the BIOS) if it is outside the
2635 F0000h-100000h range.
2636 lastbus=N [X86] Scan all buses thru bus #N. Can be
2637 useful if the kernel is unable to find your
2638 secondary buses and you want to tell it
2639 explicitly which ones they are.
2640 assign-busses [X86] Always assign all PCI bus
2641 numbers ourselves, overriding
2642 whatever the firmware may have done.
2643 usepirqmask [X86] Honor the possible IRQ mask stored
2644 in the BIOS $PIR table. This is needed on
2645 some systems with broken BIOSes, notably
2646 some HP Pavilion N5400 and Omnibook XE3
2647 notebooks. This will have no effect if ACPI
2648 IRQ routing is enabled.
2649 noacpi [X86] Do not use ACPI for IRQ routing
2650 or for PCI scanning.
2651 use_crs [X86] Use PCI host bridge window information
2652 from ACPI. On BIOSes from 2008 or later, this
2653 is enabled by default. If you need to use this,
2654 please report a bug.
2655 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2656 If you need to use this, please report a bug.
2657 routeirq Do IRQ routing for all PCI devices.
2658 This is normally done in pci_enable_device(),
2659 so this option is a temporary workaround
2660 for broken drivers that don't call it.
2661 skip_isa_align [X86] do not align io start addr, so can
2662 handle more pci cards
2663 firmware [ARM] Do not re-enumerate the bus but instead
2664 just use the configuration from the
2665 bootloader. This is currently used on
2666 IXP2000 systems where the bus has to be
2667 configured a certain way for adjunct CPUs.
2668 noearly [X86] Don't do any early type 1 scanning.
2669 This might help on some broken boards which
2670 machine check when some devices' config space
2671 is read. But various workarounds are disabled
2672 and some IOMMU drivers will not work.
2673 bfsort Sort PCI devices into breadth-first order.
2674 This sorting is done to get a device
2675 order compatible with older (<= 2.4) kernels.
2676 nobfsort Don't sort PCI devices into breadth-first order.
2677 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2678 tuning and use the BIOS-configured MPS defaults.
2679 pcie_bus_safe Set every device's MPS to the largest value
2680 supported by all devices below the root complex.
2681 pcie_bus_perf Set device MPS to the largest allowable MPS
2682 based on its parent bus. Also set MRRS (Max
2683 Read Request Size) to the largest supported
2684 value (no larger than the MPS that the device
2685 or bus can support) for best performance.
2686 pcie_bus_peer2peer Set every device's MPS to 128B, which
2687 every device is guaranteed to support. This
2688 configuration allows peer-to-peer DMA between
2689 any pair of devices, possibly at the cost of
2690 reduced performance. This also guarantees
2691 that hot-added devices will work.
2692 cbiosize=nn[KMG] The fixed amount of bus space which is
2693 reserved for the CardBus bridge's IO window.
2694 The default value is 256 bytes.
2695 cbmemsize=nn[KMG] The fixed amount of bus space which is
2696 reserved for the CardBus bridge's memory
2697 window. The default value is 64 megabytes.
2700 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2701 Specifies alignment and device to reassign
2702 aligned memory resources.
2703 If <order of align> is not specified,
2704 PAGE_SIZE is used as alignment.
2705 PCI-PCI bridge can be specified, if resource
2706 windows need to be expanded.
2707 ecrc= Enable/disable PCIe ECRC (transaction layer
2708 end-to-end CRC checking).
2709 bios: Use BIOS/firmware settings. This is the
2713 hpiosize=nn[KMG] The fixed amount of bus space which is
2714 reserved for hotplug bridge's IO window.
2715 Default size is 256 bytes.
2716 hpmemsize=nn[KMG] The fixed amount of bus space which is
2717 reserved for hotplug bridge's memory window.
2718 Default size is 2 megabytes.
2719 realloc= Enable/disable reallocating PCI bridge resources
2720 if allocations done by BIOS are too small to
2721 accommodate resources required by all child
2723 off: Turn realloc off
2725 realloc same as realloc=on
2726 noari do not use PCIe ARI.
2727 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2728 only look for one device below a PCIe downstream
2731 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2734 force Enable ASPM even on devices that claim not to support it.
2735 WARNING: Forcing ASPM on may cause system lockups.
2737 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2738 nomsi Do not use MSI for PCI Express Native Hotplug (this
2739 makes all PCIe ports use INTx for hotplug services).
2741 pcie_ports= [PCIE] PCIe ports handling:
2742 auto Ask the BIOS whether or not to use native PCIe services
2743 associated with PCIe ports (PME, hot-plug, AER). Use
2744 them only if that is allowed by the BIOS.
2745 native Use native PCIe services associated with PCIe ports
2747 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2750 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2751 nomsi Do not use MSI for native PCIe PME signaling (this makes
2752 all PCIe root ports use INTx for all services).
2754 pcmv= [HW,PCMCIA] BadgePAD 4
2758 Keep all power-domains already enabled by bootloader on,
2759 even if no driver has claimed them. This is useful
2760 for debug and development, but should not be
2761 needed on a platform with proper driver support.
2764 See Documentation/blockdev/paride.txt.
2766 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2769 See arch/parisc/kernel/pdc_chassis.c
2771 percpu_alloc= Select which percpu first chunk allocator to use.
2772 Currently supported values are "embed" and "page".
2773 Archs may support subset or none of the selections.
2774 See comments in mm/percpu.c for details on each
2775 allocator. This parameter is primarily for debugging
2776 and performance comparison.
2779 See Documentation/blockdev/paride.txt.
2782 See Documentation/blockdev/paride.txt.
2784 pirq= [SMP,APIC] Manual mp-table setup
2785 See Documentation/x86/i386/IO-APIC.txt.
2787 plip= [PPT,NET] Parallel port network link
2788 Format: { parport<nr> | timid | 0 }
2789 See also Documentation/parport.txt.
2791 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2792 Override pmtimer IOPort with a hex value.
2796 Enable PNP debug messages (depends on the
2797 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2798 via /sys/module/pnp/parameters/debug. We always show
2799 current resource usage; turning this on also shows
2800 possible settings and some assignment information.
2806 { on | off | curr | res | no-curr | no-res }
2809 [ISAPNP] Exclude IRQs for the autoconfiguration
2812 [ISAPNP] Exclude DMAs for the autoconfiguration
2814 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2815 Ranges are in pairs (I/O port base and size).
2818 [ISAPNP] Exclude memory regions for the
2820 Ranges are in pairs (memory base and size).
2822 ports= [IP_VS_FTP] IPVS ftp helper module
2824 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2826 Format: <port>,<port>....
2828 print-fatal-signals=
2829 [KNL] debug: print fatal signals
2831 If enabled, warn about various signal handling
2832 related application anomalies: too many signals,
2833 too many POSIX.1 timers, fatal signals causing a
2836 If you hit the warning due to signal overflow,
2837 you might want to try "ulimit -i unlimited".
2841 printk.always_kmsg_dump=
2842 Trigger kmsg_dump for cases other than kernel oops or
2844 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2847 printk.time= Show timing data prefixed to each printk message line
2848 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2850 processor.max_cstate= [HW,ACPI]
2851 Limit processor to maximum C-state
2852 max_cstate=9 overrides any DMI blacklist limit.
2854 processor.nocst [HW,ACPI]
2855 Ignore the _CST method to determine C-states,
2856 instead using the legacy FADT method
2858 profile= [KNL] Enable kernel profiling via /proc/profile
2859 Format: [schedule,]<number>
2860 Param: "schedule" - profile schedule points.
2861 Param: <number> - step/bucket size as a power of 2 for
2862 statistical time based profiling.
2863 Param: "sleep" - profile D-state sleeping (millisecs).
2864 Requires CONFIG_SCHEDSTATS
2865 Param: "kvm" - profile VM exits.
2867 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2869 See Documentation/blockdev/ramdisk.txt.
2871 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2872 probe for; one of (bare|imps|exps|lifebook|any).
2873 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2875 psmouse.resetafter= [HW,MOUSE]
2876 Try to reset the device after so many bad packets
2879 [HW,MOUSE] Set desired mouse resolution, in dpi.
2880 psmouse.smartscroll=
2881 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2882 0 = disabled, 1 = enabled (default).
2884 pstore.backend= Specify the name of the pstore backend to use
2887 See Documentation/blockdev/paride.txt.
2890 [KNL] Number of legacy pty's. Overwrites compiled-in
2893 quiet [KNL] Disable most log messages
2898 See Documentation/md.txt.
2900 ramdisk_blocksize= [RAM]
2901 See Documentation/blockdev/ramdisk.txt.
2903 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2904 See Documentation/blockdev/ramdisk.txt.
2907 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2908 the specified list of CPUs to be no-callback CPUs.
2909 Invocation of these CPUs' RCU callbacks will
2910 be offloaded to "rcuox/N" kthreads created for
2911 that purpose, where "x" is "b" for RCU-bh, "p"
2912 for RCU-preempt, and "s" for RCU-sched, and "N"
2913 is the CPU number. This reduces OS jitter on the
2914 offloaded CPUs, which can be useful for HPC and
2915 real-time workloads. It can also improve energy
2916 efficiency for asymmetric multiprocessors.
2919 Rather than requiring that offloaded CPUs
2920 (specified by rcu_nocbs= above) explicitly
2921 awaken the corresponding "rcuoN" kthreads,
2922 make these kthreads poll for callbacks.
2923 This improves the real-time response for the
2924 offloaded CPUs by relieving them of the need to
2925 wake up the corresponding kthread, but degrades
2926 energy efficiency by requiring that the kthreads
2927 periodically wake up to do the polling.
2929 rcutree.blimit= [KNL]
2930 Set maximum number of finished RCU callbacks to
2931 process in one batch.
2933 rcutree.rcu_fanout_leaf= [KNL]
2934 Increase the number of CPUs assigned to each
2935 leaf rcu_node structure. Useful for very large
2938 rcutree.jiffies_till_sched_qs= [KNL]
2939 Set required age in jiffies for a
2940 given grace period before RCU starts
2941 soliciting quiescent-state help from
2942 rcu_note_context_switch().
2944 rcutree.jiffies_till_first_fqs= [KNL]
2945 Set delay from grace-period initialization to
2946 first attempt to force quiescent states.
2947 Units are jiffies, minimum value is zero,
2948 and maximum value is HZ.
2950 rcutree.jiffies_till_next_fqs= [KNL]
2951 Set delay between subsequent attempts to force
2952 quiescent states. Units are jiffies, minimum
2953 value is one, and maximum value is HZ.
2955 rcutree.rcu_nocb_leader_stride= [KNL]
2956 Set the number of NOCB kthread groups, which
2957 defaults to the square root of the number of
2958 CPUs. Larger numbers reduces the wakeup overhead
2959 on the per-CPU grace-period kthreads, but increases
2960 that same overhead on each group's leader.
2962 rcutree.qhimark= [KNL]
2963 Set threshold of queued RCU callbacks beyond which
2964 batch limiting is disabled.
2966 rcutree.qlowmark= [KNL]
2967 Set threshold of queued RCU callbacks below which
2968 batch limiting is re-enabled.
2970 rcutree.rcu_idle_gp_delay= [KNL]
2971 Set wakeup interval for idle CPUs that have
2972 RCU callbacks (RCU_FAST_NO_HZ=y).
2974 rcutree.rcu_idle_lazy_gp_delay= [KNL]
2975 Set wakeup interval for idle CPUs that have
2976 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2977 Lazy RCU callbacks are those which RCU can
2978 prove do nothing more than free memory.
2980 rcutorture.cbflood_inter_holdoff= [KNL]
2981 Set holdoff time (jiffies) between successive
2982 callback-flood tests.
2984 rcutorture.cbflood_intra_holdoff= [KNL]
2985 Set holdoff time (jiffies) between successive
2986 bursts of callbacks within a given callback-flood
2989 rcutorture.cbflood_n_burst= [KNL]
2990 Set the number of bursts making up a given
2991 callback-flood test. Set this to zero to
2992 disable callback-flood testing.
2994 rcutorture.cbflood_n_per_burst= [KNL]
2995 Set the number of callbacks to be registered
2996 in a given burst of a callback-flood test.
2998 rcutorture.fqs_duration= [KNL]
2999 Set duration of force_quiescent_state bursts.
3001 rcutorture.fqs_holdoff= [KNL]
3002 Set holdoff time within force_quiescent_state bursts.
3004 rcutorture.fqs_stutter= [KNL]
3005 Set wait time between force_quiescent_state bursts.
3007 rcutorture.gp_exp= [KNL]
3008 Use expedited update-side primitives.
3010 rcutorture.gp_normal= [KNL]
3011 Use normal (non-expedited) update-side primitives.
3012 If both gp_exp and gp_normal are set, do both.
3013 If neither gp_exp nor gp_normal are set, still
3016 rcutorture.n_barrier_cbs= [KNL]
3017 Set callbacks/threads for rcu_barrier() testing.
3019 rcutorture.nfakewriters= [KNL]
3020 Set number of concurrent RCU writers. These just
3021 stress RCU, they don't participate in the actual
3022 test, hence the "fake".
3024 rcutorture.nreaders= [KNL]
3025 Set number of RCU readers.
3027 rcutorture.object_debug= [KNL]
3028 Enable debug-object double-call_rcu() testing.
3030 rcutorture.onoff_holdoff= [KNL]
3031 Set time (s) after boot for CPU-hotplug testing.
3033 rcutorture.onoff_interval= [KNL]
3034 Set time (s) between CPU-hotplug operations, or
3035 zero to disable CPU-hotplug testing.
3037 rcutorture.torture_runnable= [BOOT]
3038 Start rcutorture running at boot time.
3040 rcutorture.shuffle_interval= [KNL]
3041 Set task-shuffle interval (s). Shuffling tasks
3042 allows some CPUs to go into dyntick-idle mode
3043 during the rcutorture test.
3045 rcutorture.shutdown_secs= [KNL]
3046 Set time (s) after boot system shutdown. This
3047 is useful for hands-off automated testing.
3049 rcutorture.stall_cpu= [KNL]
3050 Duration of CPU stall (s) to test RCU CPU stall
3051 warnings, zero to disable.
3053 rcutorture.stall_cpu_holdoff= [KNL]
3054 Time to wait (s) after boot before inducing stall.
3056 rcutorture.stat_interval= [KNL]
3057 Time (s) between statistics printk()s.
3059 rcutorture.stutter= [KNL]
3060 Time (s) to stutter testing, for example, specifying
3061 five seconds causes the test to run for five seconds,
3062 wait for five seconds, and so on. This tests RCU's
3063 ability to transition abruptly to and from idle.
3065 rcutorture.test_boost= [KNL]
3066 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3067 "Maybe" means test if the RCU implementation
3068 under test support RCU priority boosting.
3070 rcutorture.test_boost_duration= [KNL]
3071 Duration (s) of each individual boost test.
3073 rcutorture.test_boost_interval= [KNL]
3074 Interval (s) between each boost test.
3076 rcutorture.test_no_idle_hz= [KNL]
3077 Test RCU's dyntick-idle handling. See also the
3078 rcutorture.shuffle_interval parameter.
3080 rcutorture.torture_type= [KNL]
3081 Specify the RCU implementation to test.
3083 rcutorture.verbose= [KNL]
3084 Enable additional printk() statements.
3086 rcupdate.rcu_expedited= [KNL]
3087 Use expedited grace-period primitives, for
3088 example, synchronize_rcu_expedited() instead
3089 of synchronize_rcu(). This reduces latency,
3090 but can increase CPU utilization, degrade
3091 real-time latency, and degrade energy efficiency.
3093 rcupdate.rcu_cpu_stall_suppress= [KNL]
3094 Suppress RCU CPU stall warning messages.
3096 rcupdate.rcu_cpu_stall_timeout= [KNL]
3097 Set timeout for RCU CPU stall warning messages.
3099 rcupdate.rcu_task_stall_timeout= [KNL]
3100 Set timeout in jiffies for RCU task stall warning
3101 messages. Disable with a value less than or equal
3106 Run specified binary instead of /init from the ramdisk,
3107 used for early userspace startup. See initrd.
3110 Format (x86 or x86_64):
3111 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3113 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3115 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3116 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3117 reboot_force is either force or not specified,
3118 reboot_cpu is s[mp]#### with #### being the processor
3119 to be used for rebooting.
3122 [KNL, SMP] Set scheduler's default relax_domain_level.
3123 See Documentation/cgroups/cpusets.txt.
3125 relative_sleep_states=
3126 [SUSPEND] Use sleep state labeling where the deepest
3127 state available other than hibernation is always "mem".
3128 Format: { "0" | "1" }
3129 0 -- Traditional sleep state labels.
3130 1 -- Relative sleep state labels.
3132 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3134 reservetop= [X86-32]
3136 Reserves a hole at the top of the kernel virtual
3141 Set the amount of memory to reserve for BIOS at
3142 the bottom of the address space.
3144 reset_devices [KNL] Force drivers to reset the underlying device
3145 during initialization.
3148 Specify the partition device for software suspend
3150 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3152 resume_offset= [SWSUSP]
3153 Specify the offset from the beginning of the partition
3154 given by "resume=" at which the swap header is located,
3155 in <PAGE_SIZE> units (needed only for swap files).
3156 See Documentation/power/swsusp-and-swap-files.txt
3158 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3159 read the resume files
3161 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3162 Useful for devices that are detected asynchronously
3163 (e.g. USB and MMC devices).
3165 hibernate= [HIBERNATION]
3166 noresume Don't check if there's a hibernation image
3167 present during boot.
3168 nocompress Don't compress/decompress hibernation images.
3169 no Disable hibernation and resume.
3171 retain_initrd [RAM] Keep initrd memory after extraction
3173 rhash_entries= [KNL,NET]
3174 Set number of hash buckets for route cache
3176 ro [KNL] Mount root device read-only on boot
3178 root= [KNL] Root filesystem
3179 See name_to_dev_t comment in init/do_mounts.c.
3181 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3182 mount the root filesystem
3184 rootflags= [KNL] Set root filesystem mount option string
3186 rootfstype= [KNL] Set root filesystem type
3188 rootwait [KNL] Wait (indefinitely) for root device to show up.
3189 Useful for devices that are detected asynchronously
3190 (e.g. USB and MMC devices).
3192 rproc_mem=nn[KMG][@address]
3193 [KNL,ARM,CMA] Remoteproc physical memory block.
3194 Memory area to be used by remote processor image,
3197 rw [KNL] Mount root device read-write on boot
3199 S [KNL] Run init in single mode
3201 s390_iommu= [HW,S390]
3202 Set s390 IOTLB flushing mode
3204 With strict flushing every unmap operation will result in
3205 an IOTLB flush. Default is lazy flushing before reuse,
3209 See drivers/net/irda/sa1100_ir.c.
3211 sbni= [NET] Granch SBNI12 leased line adapter
3213 sched_debug [KNL] Enables verbose scheduler debug messages.
3215 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3216 xtime_lock contention on larger systems, and/or RCU lock
3217 contention on all systems with CONFIG_MAXSMP set.
3218 Format: { "0" | "1" }
3219 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3221 Note: increases power consumption, thus should only be
3222 enabled if running jitter sensitive (HPC/RT) workloads.
3224 security= [SECURITY] Choose a security module to enable at boot.
3225 If this boot parameter is not specified, only the first
3226 security module asking for security registration will be
3227 loaded. An invalid security module name will be treated
3228 as if no module has been chosen.
3230 selinux= [SELINUX] Disable or enable SELinux at boot time.
3231 Format: { "0" | "1" }
3232 See security/selinux/Kconfig help text.
3235 Default value is set via kernel config option.
3236 If enabled at boot time, /selinux/disable can be used
3237 later to disable prior to initial policy load.
3239 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3240 Format: { "0" | "1" }
3241 See security/apparmor/Kconfig help text
3244 Default value is set via kernel config option.
3246 serialnumber [BUGS=X86-32]
3249 Maximal number of shapers.
3251 show_msr= [x86] show boot-time MSR settings
3252 Format: { <integer> }
3253 Show boot-time (BIOS-initialized) MSR settings.
3254 The parameter means the number of CPUs to show,
3255 for example 1 means boot CPU only.
3263 Disable merging of slabs with similar size. May be
3264 necessary if there is some reason to distinguish
3265 allocs to different slabs. Debug options disable
3266 merging on their own.
3267 For more information see Documentation/vm/slub.txt.
3269 slab_max_order= [MM, SLAB]
3270 Determines the maximum allowed order for slabs.
3271 A high setting may cause OOMs due to memory
3272 fragmentation. Defaults to 1 for systems with
3273 more than 32MB of RAM, 0 otherwise.
3275 slub_debug[=options[,slabs]] [MM, SLUB]
3276 Enabling slub_debug allows one to determine the
3277 culprit if slab objects become corrupted. Enabling
3278 slub_debug can create guard zones around objects and
3279 may poison objects when not in use. Also tracks the
3280 last alloc / free. For more information see
3281 Documentation/vm/slub.txt.
3283 slub_max_order= [MM, SLUB]
3284 Determines the maximum allowed order for slabs.
3285 A high setting may cause OOMs due to memory
3286 fragmentation. For more information see
3287 Documentation/vm/slub.txt.
3289 slub_min_objects= [MM, SLUB]
3290 The minimum number of objects per slab. SLUB will
3291 increase the slab order up to slub_max_order to
3292 generate a sufficiently large slab able to contain
3293 the number of objects indicated. The higher the number
3294 of objects the smaller the overhead of tracking slabs
3295 and the less frequently locks need to be acquired.
3296 For more information see Documentation/vm/slub.txt.
3298 slub_min_order= [MM, SLUB]
3299 Determines the minimum page order for slabs. Must be
3300 lower than slub_max_order.
3301 For more information see Documentation/vm/slub.txt.
3303 slub_nomerge [MM, SLUB]
3304 Same with slab_nomerge. This is supported for legacy.
3305 See slab_nomerge for more information.
3308 Format: <io1>[,<io2>[,...,<io8>]]
3310 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3311 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3312 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3313 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3314 smsc-ircc2.ircc_irq= [HW] IRQ line
3315 smsc-ircc2.ircc_dma= [HW] DMA channel
3316 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3317 0: Toshiba Satellite 1800 (GP data pin select)
3318 1: Fast pin select (default)
3322 [KNL] Should the soft-lockup detector generate panics.
3325 softlockup_all_cpu_backtrace=
3326 [KNL] Should the soft-lockup detector generate
3327 backtraces on all cpus.
3330 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3331 See Documentation/laptops/sonypi.txt
3333 spia_io_base= [HW,MTD]
3339 Enabled the stack tracer on boot up.
3341 stacktrace_filter=[function-list]
3342 [FTRACE] Limit the functions that the stack tracer
3343 will trace at boot up. function-list is a comma separated
3344 list of functions. This list can be changed at run
3345 time by the stack_trace_filter file in the debugfs
3346 tracing directory. Note, this enables stack tracing
3347 and the stacktrace above is not needed.
3351 Set the STI (builtin display/keyboard on the HP-PARISC
3352 machines) console (graphic card) which should be used
3353 as the initial boot-console.
3354 See also comment in drivers/video/console/sticore.c.
3357 See comment in drivers/video/console/sticore.c.
3360 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3362 sunrpc.min_resvport=
3363 sunrpc.max_resvport=
3365 SunRPC servers often require that client requests
3366 originate from a privileged port (i.e. a port in the
3367 range 0 < portnr < 1024).
3368 An administrator who wishes to reserve some of these
3369 ports for other uses may adjust the range that the
3370 kernel's sunrpc client considers to be privileged
3371 using these two parameters to set the minimum and
3372 maximum port values.
3376 Control how the NFS server code allocates CPUs to
3377 service thread pools. Depending on how many NICs
3378 you have and where their interrupts are bound, this
3379 option will affect which CPUs will do NFS serving.
3380 Note: this parameter cannot be changed while the
3381 NFS server is running.
3383 auto the server chooses an appropriate mode
3384 automatically using heuristics
3385 global a single global pool contains all CPUs
3386 percpu one pool for each CPU
3387 pernode one pool for each NUMA node (equivalent
3388 to global on non-NUMA machines)
3390 sunrpc.tcp_slot_table_entries=
3391 sunrpc.udp_slot_table_entries=
3393 Sets the upper limit on the number of simultaneous
3394 RPC calls that can be sent from the client to a
3395 server. Increasing these values may allow you to
3396 improve throughput, but will also increase the
3397 amount of memory reserved for use by the client.
3400 [KNL] Enable accounting of swap in memory resource
3401 controller if no parameter or 1 is given or disable
3402 it if 0 is given (See Documentation/cgroups/memory.txt)
3404 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3405 Format: { <int> | force }
3406 <int> -- Number of I/O TLB slabs
3407 force -- force using of bounce buffers even if they
3408 wouldn't be automatically used by the kernel
3412 sysfs.deprecated=0|1 [KNL]
3413 Enable/disable old style sysfs layout for old udev
3414 on older distributions. When this option is enabled
3415 very new udev will not work anymore. When this option
3416 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3417 in older udev will not work anymore.
3418 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3419 the kernel configuration.
3421 sysrq_always_enabled
3423 Ignore sysrq setting - this boot parameter will
3424 neutralize any effect of /proc/sys/kernel/sysrq.
3425 Useful for debugging.
3429 test_suspend= [SUSPEND][,N]
3430 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3431 standby suspend) or "freeze" (for suspend type freeze)
3432 as the system sleep state during system startup with
3433 the optional capability to repeat N number of times.
3434 The system is woken from this state using a
3435 wakeup-capable RTC alarm.
3437 thash_entries= [KNL,NET]
3438 Set number of hash buckets for TCP connection
3440 thermal.act= [HW,ACPI]
3441 -1: disable all active trip points in all thermal zones
3442 <degrees C>: override all lowest active trip points
3444 thermal.crt= [HW,ACPI]
3445 -1: disable all critical trip points in all thermal zones
3446 <degrees C>: override all critical trip points
3448 thermal.nocrt= [HW,ACPI]
3449 Set to disable actions on ACPI thermal zone
3450 critical and hot trip points.
3452 thermal.off= [HW,ACPI]
3453 1: disable ACPI thermal control
3455 thermal.psv= [HW,ACPI]
3456 -1: disable all passive trip points
3457 <degrees C>: override all passive trip points to this
3460 thermal.tzp= [HW,ACPI]
3461 Specify global default ACPI thermal zone polling rate
3462 <deci-seconds>: poll all this frequency
3463 0: no polling (default)
3466 Force threading of all interrupt handlers except those
3467 marked explicitly IRQF_NO_THREAD.
3470 Enable the Transcendent memory driver if built-in.
3472 tmem.cleancache=0|1 [KNL, XEN]
3473 Default is on (1). Disable the usage of the cleancache
3474 API to send anonymous pages to the hypervisor.
3476 tmem.frontswap=0|1 [KNL, XEN]
3477 Default is on (1). Disable the usage of the frontswap
3478 API to send swap pages to the hypervisor. If disabled
3479 the selfballooning and selfshrinking are force disabled.
3481 tmem.selfballooning=0|1 [KNL, XEN]
3482 Default is on (1). Disable the driving of swap pages
3485 tmem.selfshrinking=0|1 [KNL, XEN]
3486 Default is on (1). Partial swapoff that immediately
3487 transfers pages from Xen hypervisor back to the
3488 kernel based on different criteria.
3492 Specify if the kernel should make use of the cpu
3493 topology information if the hardware supports this.
3494 The scheduler will make use of this information and
3495 e.g. base its process migration decisions on it.
3498 topology_updates= [KNL, PPC, NUMA]
3500 Specify if the kernel should ignore (off)
3501 topology updates sent by the hypervisor to this
3506 tpm_suspend_pcr=[HW,TPM]
3507 Format: integer pcr id
3508 Specify that at suspend time, the tpm driver
3509 should extend the specified pcr with zeros,
3510 as a workaround for some chips which fail to
3511 flush the last written pcr on TPM_SaveState.
3512 This will guarantee that all the other pcrs
3515 trace_buf_size=nn[KMG]
3516 [FTRACE] will set tracing buffer size.
3518 trace_event=[event-list]
3519 [FTRACE] Set and start specified trace events in order
3520 to facilitate early boot debugging.
3521 See also Documentation/trace/events.txt
3523 trace_options=[option-list]
3524 [FTRACE] Enable or disable tracer options at boot.
3525 The option-list is a comma delimited list of options
3526 that can be enabled or disabled just as if you were
3527 to echo the option name into
3529 /sys/kernel/debug/tracing/trace_options
3531 For example, to enable stacktrace option (to dump the
3532 stack trace of each event), add to the command line:
3534 trace_options=stacktrace
3536 See also Documentation/trace/ftrace.txt "trace options"
3540 [FTRACE] enable this option to disable tracing when a
3541 warning is hit. This turns off "tracing_on". Tracing can
3542 be enabled again by echoing '1' into the "tracing_on"
3543 file located in /sys/kernel/debug/tracing/
3545 This option is useful, as it disables the trace before
3546 the WARNING dump is called, which prevents the trace to
3547 be filled with content caused by the warning output.
3549 This option can also be set at run time via the sysctl
3550 option: kernel/traceoff_on_warning
3552 transparent_hugepage=
3554 Format: [always|madvise|never]
3555 Can be used to control the default behavior of the system
3556 with respect to transparent hugepages.
3557 See Documentation/vm/transhuge.txt for more details.
3559 tsc= Disable clocksource stability checks for TSC.
3561 [x86] reliable: mark tsc clocksource as reliable, this
3562 disables clocksource verification at runtime, as well
3563 as the stability checks done at bootup. Used to enable
3564 high-resolution timer mode on older hardware, and in
3565 virtualized environment.
3566 [x86] noirqtime: Do not use TSC to do irq accounting.
3567 Used to run time disable IRQ_TIME_ACCOUNTING on any
3568 platforms where RDTSC is slow and this accounting
3571 turbografx.map[2|3]= [HW,JOY]
3572 TurboGraFX parallel port interface
3574 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3575 See also Documentation/input/joystick-parport.txt
3577 udbg-immortal [PPC] When debugging early kernel crashes that
3578 happen after console_init() and before a proper
3579 console driver takes over, this boot options might
3580 help "seeing" what's going on.
3582 uhash_entries= [KNL,NET]
3583 Set number of hash buckets for UDP/UDP-Lite connections
3586 [USB] Ignore overcurrent events (default N).
3587 Some badly-designed motherboards generate lots of
3588 bogus events, for ports that aren't wired to
3589 anything. Set this parameter to avoid log spamming.
3590 Note that genuine overcurrent events won't be
3594 [X86] Cause panic on unknown NMI.
3596 usbcore.authorized_default=
3597 [USB] Default USB device authorization:
3598 (default -1 = authorized except for wireless USB,
3599 0 = not authorized, 1 = authorized)
3601 usbcore.autosuspend=
3602 [USB] The autosuspend time delay (in seconds) used
3603 for newly-detected USB devices (default 2). This
3604 is the time required before an idle device will be
3605 autosuspended. Devices for which the delay is set
3606 to a negative value won't be autosuspended at all.
3608 usbcore.usbfs_snoop=
3609 [USB] Set to log all usbfs traffic (default 0 = off).
3611 usbcore.blinkenlights=
3612 [USB] Set to cycle leds on hubs (default 0 = off).
3614 usbcore.old_scheme_first=
3615 [USB] Start with the old device initialization
3616 scheme (default 0 = off).
3618 usbcore.usbfs_memory_mb=
3619 [USB] Memory limit (in MB) for buffers allocated by
3620 usbfs (default = 16, 0 = max = 2047).
3622 usbcore.use_both_schemes=
3623 [USB] Try the other device initialization scheme
3624 if the first one fails (default 1 = enabled).
3626 usbcore.initial_descriptor_timeout=
3627 [USB] Specifies timeout for the initial 64-byte
3628 USB_REQ_GET_DESCRIPTOR request in milliseconds
3629 (default 5000 = 5.0 seconds).
3632 [USBHID] The interval which mice are to be polled at.
3634 usb-storage.delay_use=
3635 [UMS] The delay in seconds before a new device is
3636 scanned for Logical Units (default 1).
3639 [UMS] A list of quirks entries to supplement or
3640 override the built-in unusual_devs list. List
3641 entries are separated by commas. Each entry has
3642 the form VID:PID:Flags where VID and PID are Vendor
3643 and Product ID values (4-digit hex numbers) and
3644 Flags is a set of characters, each corresponding
3645 to a common usb-storage quirk flag as follows:
3646 a = SANE_SENSE (collect more than 18 bytes
3648 b = BAD_SENSE (don't collect more than 18
3649 bytes of sense data);
3650 c = FIX_CAPACITY (decrease the reported
3651 device capacity by one sector);
3652 d = NO_READ_DISC_INFO (don't use
3653 READ_DISC_INFO command);
3654 e = NO_READ_CAPACITY_16 (don't use
3655 READ_CAPACITY_16 command);
3656 f = NO_REPORT_OPCODES (don't use report opcodes
3658 h = CAPACITY_HEURISTICS (decrease the
3659 reported device capacity by one
3660 sector if the number is odd);
3661 i = IGNORE_DEVICE (don't bind to this
3663 l = NOT_LOCKABLE (don't try to lock and
3664 unlock ejectable media);
3665 m = MAX_SECTORS_64 (don't transfer more
3666 than 64 sectors = 32 KB at a time);
3667 n = INITIAL_READ10 (force a retry of the
3668 initial READ(10) command);
3669 o = CAPACITY_OK (accept the capacity
3670 reported by the device);
3671 p = WRITE_CACHE (the device cache is ON
3673 r = IGNORE_RESIDUE (the device reports
3674 bogus residue values);
3675 s = SINGLE_LUN (the device has only one
3677 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3678 commands, uas only);
3679 u = IGNORE_UAS (don't bind to the uas driver);
3680 w = NO_WP_DETECT (don't test whether the
3681 medium is write-protected).
3682 Example: quirks=0419:aaf5:rl,0421:0433:rc
3684 user_debug= [KNL,ARM]
3686 See arch/arm/Kconfig.debug help text.
3687 1 - undefined instruction events
3689 4 - invalid data aborts
3692 Example: user_debug=31
3695 [X86] Flags controlling user PTE allocations.
3697 nohigh = do not allocate PTE pages in
3698 HIGHMEM regardless of setting
3702 On X86_32, this is an alias for vdso32=. Otherwise:
3704 vdso=1: enable VDSO (the default)
3705 vdso=0: disable VDSO mapping
3707 vdso32= [X86] Control the 32-bit vDSO
3708 vdso32=1: enable 32-bit VDSO
3709 vdso32=0 or vdso32=2: disable 32-bit VDSO
3711 See the help text for CONFIG_COMPAT_VDSO for more
3712 details. If CONFIG_COMPAT_VDSO is set, the default is
3713 vdso32=0; otherwise, the default is vdso32=1.
3715 For compatibility with older kernels, vdso32=2 is an
3718 Try vdso32=0 if you encounter an error that says:
3719 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3722 vector=percpu: enable percpu vector domain
3724 video= [FB] Frame buffer configuration
3725 See Documentation/fb/modedb.txt.
3727 video.brightness_switch_enabled= [0,1]
3728 If set to 1, on receiving an ACPI notify event
3729 generated by hotkey, video driver will adjust brightness
3730 level and then send out the event to user space through
3731 the allocated input device; If set to 0, video driver
3732 will only send out the event without touching backlight
3737 [VMMIO] Memory mapped virtio (platform) device.
3739 <size>@<baseaddr>:<irq>[:<id>]
3741 <size> := size (can use standard suffixes
3743 <baseaddr> := physical base address
3744 <irq> := interrupt number (as passed to
3746 <id> := (optional) platform device id
3748 virtio_mmio.device=1K@0x100b0000:48:7
3750 Can be used multiple times for multiple devices.
3752 vga= [BOOT,X86-32] Select a particular video mode
3753 See Documentation/x86/boot.txt and
3754 Documentation/svga.txt.
3755 Use vga=ask for menu.
3756 This is actually a boot loader parameter; the value is
3757 passed to the kernel using a special protocol.
3759 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3760 size of <nn>. This can be used to increase the
3761 minimum size (128MB on x86). It can also be used to
3762 decrease the size and leave more room for directly
3765 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3768 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3771 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3775 Controls the behavior of vsyscalls (i.e. calls to
3776 fixed addresses of 0xffffffffff600x00 from legacy
3777 code). Most statically-linked binaries and older
3778 versions of glibc use these calls. Because these
3779 functions are at fixed addresses, they make nice
3780 targets for exploits that can control RIP.
3782 emulate [default] Vsyscalls turn into traps and are
3783 emulated reasonably safely.
3785 native Vsyscalls are native syscall instructions.
3786 This is a little bit faster than trapping
3787 and makes a few dynamic recompilers work
3788 better than they would in emulation mode.
3789 It also makes exploits much easier to write.
3791 none Vsyscalls don't work at all. This makes
3792 them quite hard to use for exploits but
3793 might break your system.
3795 vt.color= [VT] Default text color.
3796 Format: 0xYX, X = foreground, Y = background.
3797 Default: 0x07 = light gray on black.
3799 vt.cur_default= [VT] Default cursor shape.
3800 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3801 the parameters of the <Esc>[?A;B;Cc escape sequence;
3802 see VGA-softcursor.txt. Default: 2 = underline.
3804 vt.default_blu= [VT]
3805 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3806 Change the default blue palette of the console.
3807 This is a 16-member array composed of values
3810 vt.default_grn= [VT]
3811 Format: <green0>,<green1>,<green2>,...,<green15>
3812 Change the default green palette of the console.
3813 This is a 16-member array composed of values
3816 vt.default_red= [VT]
3817 Format: <red0>,<red1>,<red2>,...,<red15>
3818 Change the default red palette of the console.
3819 This is a 16-member array composed of values
3825 Set system-wide default UTF-8 mode for all tty's.
3826 Default is 1, i.e. UTF-8 mode is enabled for all
3827 newly opened terminals.
3829 vt.global_cursor_default=
3832 Set system-wide default for whether a cursor
3833 is shown on new VTs. Default is -1,
3834 i.e. cursors will be created by default unless
3835 overridden by individual drivers. 0 will hide
3836 cursors, 1 will display them.
3838 vt.italic= [VT] Default color for italic text; 0-15.
3841 vt.underline= [VT] Default color for underlined text; 0-15.
3844 watchdog timers [HW,WDT] For information on watchdog timers,
3845 see Documentation/watchdog/watchdog-parameters.txt
3846 or other driver-specific files in the
3847 Documentation/watchdog/ directory.
3849 workqueue.disable_numa
3850 By default, all work items queued to unbound
3851 workqueues are affine to the NUMA nodes they're
3852 issued on, which results in better behavior in
3853 general. If NUMA affinity needs to be disabled for
3854 whatever reason, this option can be used. Note
3855 that this also can be controlled per-workqueue for
3856 workqueues visible under /sys/bus/workqueue/.
3858 workqueue.power_efficient
3859 Per-cpu workqueues are generally preferred because
3860 they show better performance thanks to cache
3861 locality; unfortunately, per-cpu workqueues tend to
3862 be more power hungry than unbound workqueues.
3864 Enabling this makes the per-cpu workqueues which
3865 were observed to contribute significantly to power
3866 consumption unbound, leading to measurably lower
3867 power usage at the cost of small performance
3870 The default value of this parameter is determined by
3871 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3873 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3874 default x2apic cluster mode on platforms
3877 x86_intel_mid_timer= [X86-32,APBT]
3878 Choose timer option for x86 Intel MID platform.
3879 Two valid options are apbt timer only and lapic timer
3880 plus one apbt timer for broadcast timer.
3881 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3883 xen_emul_unplug= [HW,X86,XEN]
3884 Unplug Xen emulated devices
3885 Format: [unplug0,][unplug1]
3886 ide-disks -- unplug primary master IDE devices
3887 aux-ide-disks -- unplug non-primary-master IDE devices
3888 nics -- unplug network devices
3889 all -- unplug all emulated devices (NICs and IDE disks)
3890 unnecessary -- unplugging emulated devices is
3891 unnecessary even if the host did not respond to
3893 never -- do not unplug even if version check succeeds
3895 xen_nopvspin [X86,XEN]
3896 Disables the ticketlock slowpath using Xen PV
3900 Disables the PV optimizations forcing the HVM guest to
3901 run as generic HVM guest with no PV drivers.
3903 xirc2ps_cs= [NET,PCMCIA]
3905 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3907 ______________________________________________________________________
3911 Add more DRM drivers.