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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
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
26 loadable modules too.
28 Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30 can also be entered as
31 log-buf-len=1M print_fatal_signals=1
33 Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
36 This document may not be entirely up to date and comprehensive. The command
37 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
38 module. Loadable modules, after being loaded into the running kernel, also
39 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
40 parameters may be changed at runtime by the command
41 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
43 The parameters listed below are only valid if certain kernel build options were
44 enabled and if respective hardware is present. The text in square brackets at
45 the beginning of each description states the restrictions within which a
46 parameter is applicable:
48 ACPI ACPI support is enabled.
49 AGP AGP (Accelerated Graphics Port) is enabled.
50 ALSA ALSA sound support is enabled.
51 APIC APIC support is enabled.
52 APM Advanced Power Management support is enabled.
53 ARM ARM architecture is enabled.
54 AVR32 AVR32 architecture is enabled.
55 AX25 Appropriate AX.25 support is enabled.
56 BLACKFIN Blackfin architecture is enabled.
57 CLK Common clock infrastructure is enabled.
58 CMA Contiguous Memory Area support is enabled.
59 DRM Direct Rendering Management support is enabled.
60 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
61 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
62 EFI EFI Partitioning (GPT) is enabled
63 EIDE EIDE/ATAPI support is enabled.
64 EVM Extended Verification Module
65 FB The frame buffer device is enabled.
66 FTRACE Function tracing enabled.
67 GCOV GCOV profiling is enabled.
68 HW Appropriate hardware is enabled.
69 IA-64 IA-64 architecture is enabled.
70 IMA Integrity measurement architecture is enabled.
71 IOSCHED More than one I/O scheduler is enabled.
72 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
73 IPV6 IPv6 support is enabled.
74 ISAPNP ISA PnP code is enabled.
75 ISDN Appropriate ISDN support is enabled.
76 JOY Appropriate joystick support is enabled.
77 KGDB Kernel debugger support is enabled.
78 KVM Kernel Virtual Machine support is enabled.
79 LIBATA Libata driver is enabled
80 LP Printer support is enabled.
81 LOOP Loopback device support is enabled.
82 M68k M68k architecture is enabled.
83 These options have more detailed description inside of
84 Documentation/m68k/kernel-options.txt.
85 MDA MDA console support is enabled.
86 MIPS MIPS architecture is enabled.
87 MOUSE Appropriate mouse support is enabled.
88 MSI Message Signaled Interrupts (PCI).
89 MTD MTD (Memory Technology Device) support is enabled.
90 NET Appropriate network support is enabled.
91 NUMA NUMA support is enabled.
92 NFS Appropriate NFS support is enabled.
93 OSS OSS sound support is enabled.
94 PV_OPS A paravirtualized kernel is enabled.
95 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
96 PARISC The PA-RISC architecture is enabled.
97 PCI PCI bus support is enabled.
98 PCIE PCI Express support is enabled.
99 PCMCIA The PCMCIA subsystem is enabled.
100 PNP Plug & Play support is enabled.
101 PPC PowerPC architecture is enabled.
102 PPT Parallel port support is enabled.
103 PS2 Appropriate PS/2 support is enabled.
104 RAM RAM disk support is enabled.
105 S390 S390 architecture is enabled.
106 SCSI Appropriate SCSI support is enabled.
107 A lot of drivers have their options described inside
108 the Documentation/scsi/ sub-directory.
109 SECURITY Different security models are enabled.
110 SELINUX SELinux support is enabled.
111 APPARMOR AppArmor support is enabled.
112 SERIAL Serial support is enabled.
113 SH SuperH architecture is enabled.
114 SMP The kernel is an SMP kernel.
115 SPARC Sparc architecture is enabled.
116 SWSUSP Software suspend (hibernation) is enabled.
117 SUSPEND System suspend states are enabled.
118 TPM TPM drivers are enabled.
119 TS Appropriate touchscreen support is enabled.
120 UMS USB Mass Storage support is enabled.
121 USB USB support is enabled.
122 USBHID USB Human Interface Device support is enabled.
123 V4L Video For Linux support is enabled.
124 VMMIO Driver for memory mapped virtio devices is enabled.
125 VGA The VGA console has been enabled.
126 VT Virtual terminal support is enabled.
127 WDT Watchdog support is enabled.
128 XT IBM PC/XT MFM hard disk support is enabled.
129 X86-32 X86-32, aka i386 architecture is enabled.
130 X86-64 X86-64 architecture is enabled.
131 More X86-64 boot options can be found in
132 Documentation/x86/x86_64/boot-options.txt .
133 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
134 XEN Xen support is enabled
136 In addition, the following text indicates that the option:
138 BUGS= Relates to possible processor bugs on the said processor.
139 KNL Is a kernel start-up parameter.
140 BOOT Is a boot loader parameter.
142 Parameters denoted with BOOT are actually interpreted by the boot
143 loader, and have no meaning to the kernel directly.
144 Do not modify the syntax of boot loader parameters without extreme
145 need or coordination with <Documentation/x86/boot.txt>.
147 There are also arch-specific kernel-parameters not documented here.
148 See for example <Documentation/x86/x86_64/boot-options.txt>.
150 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
151 a trailing = on the name of any parameter states that that parameter will
152 be entered as an environment variable, whereas its absence indicates that
153 it will appear as a kernel argument readable via /proc/cmdline by programs
154 running once the system is up.
156 The number of kernel parameters is not limited, but the length of the
157 complete command line (parameters including spaces etc.) is limited to
158 a fixed number of characters. This limit depends on the architecture
159 and is between 256 and 4096 characters. It is defined in the file
160 ./include/asm/setup.h as COMMAND_LINE_SIZE.
162 Finally, the [KMG] suffix is commonly described after a number of kernel
163 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
164 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
165 bytes respectively. Such letter suffixes can also be entirely omitted.
168 acpi= [HW,ACPI,X86,ARM64]
169 Advanced Configuration and Power Interface
170 Format: { force | off | strict | noirq | rsdt }
171 force -- enable ACPI if default was off
172 off -- disable ACPI if default was on
173 noirq -- do not use ACPI for IRQ routing
174 strict -- Be less tolerant of platforms that are not
175 strictly ACPI specification compliant.
176 rsdt -- prefer RSDT over (default) XSDT
177 copy_dsdt -- copy DSDT to memory
178 For ARM64, ONLY "acpi=off" or "acpi=force" are available
180 See also Documentation/power/runtime_pm.txt, pci=noacpi
182 acpi_apic_instance= [ACPI, IOAPIC]
183 Format: <int>
184 2: use 2nd APIC table, if available
185 1,0: use 1st APIC table
186 default: 0
188 acpi_backlight= [HW,ACPI]
189 acpi_backlight=vendor
190 acpi_backlight=video
191 If set to vendor, prefer vendor specific driver
192 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
193 of the ACPI video.ko driver.
195 acpica_no_return_repair [HW, ACPI]
196 Disable AML predefined validation mechanism
197 This mechanism can repair the evaluation result to make
198 the return objects more ACPI specification compliant.
199 This option is useful for developers to identify the
200 root cause of an AML interpreter issue when the issue
201 has something to do with the repair mechanism.
203 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
204 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
205 Format: <int>
206 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
207 debug output. Bits in debug_layer correspond to a
208 _COMPONENT in an ACPI source file, e.g.,
209 #define _COMPONENT ACPI_PCI_COMPONENT
210 Bits in debug_level correspond to a level in
211 ACPI_DEBUG_PRINT statements, e.g.,
212 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
213 The debug_level mask defaults to "info". See
214 Documentation/acpi/debug.txt for more information about
215 debug layers and levels.
217 Enable processor driver info messages:
218 acpi.debug_layer=0x20000000
219 Enable PCI/PCI interrupt routing info messages:
220 acpi.debug_layer=0x400000
221 Enable AML "Debug" output, i.e., stores to the Debug
222 object while interpreting AML:
223 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
224 Enable all messages related to ACPI hardware:
225 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
227 Some values produce so much output that the system is
228 unusable. The "log_buf_len" parameter may be useful
229 if you need to capture more output.
231 acpi_enforce_resources= [ACPI]
232 { strict | lax | no }
233 Check for resource conflicts between native drivers
234 and ACPI OperationRegions (SystemIO and SystemMemory
235 only). IO ports and memory declared in ACPI might be
236 used by the ACPI subsystem in arbitrary AML code and
237 can interfere with legacy drivers.
238 strict (default): access to resources claimed by ACPI
239 is denied; legacy drivers trying to access reserved
240 resources will fail to bind to device using them.
241 lax: access to resources claimed by ACPI is allowed;
242 legacy drivers trying to access reserved resources
243 will bind successfully but a warning message is logged.
244 no: ACPI OperationRegions are not marked as reserved,
245 no further checks are performed.
247 acpi_force_table_verification [HW,ACPI]
248 Enable table checksum verification during early stage.
249 By default, this is disabled due to x86 early mapping
250 size limitation.
252 acpi_irq_balance [HW,ACPI]
253 ACPI will balance active IRQs
254 default in APIC mode
256 acpi_irq_nobalance [HW,ACPI]
257 ACPI will not move active IRQs (default)
258 default in PIC mode
260 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
261 Format: <irq>,<irq>...
263 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
264 use by PCI
265 Format: <irq>,<irq>...
267 acpi_no_auto_serialize [HW,ACPI]
268 Disable auto-serialization of AML methods
269 AML control methods that contain the opcodes to create
270 named objects will be marked as "Serialized" by the
271 auto-serialization feature.
272 This feature is enabled by default.
273 This option allows to turn off the feature.
275 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
276 kernels.
278 acpi_no_static_ssdt [HW,ACPI]
279 Disable installation of static SSDTs at early boot time
280 By default, SSDTs contained in the RSDT/XSDT will be
281 installed automatically and they will appear under
282 /sys/firmware/acpi/tables.
283 This option turns off this feature.
284 Note that specifying this option does not affect
285 dynamic table installation which will install SSDT
286 tables to /sys/firmware/acpi/tables/dynamic.
288 acpi_rsdp= [ACPI,EFI,KEXEC]
289 Pass the RSDP address to the kernel, mostly used
290 on machines running EFI runtime service to boot the
291 second kernel for kdump.
293 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
294 Format: To spoof as Windows 98: ="Microsoft Windows"
296 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
297 of 2 which is mandated by ACPI 6) as the supported ACPI
298 specification revision (when using this switch, it may
299 be necessary to carry out a cold reboot _twice_ in a
300 row to make it take effect on the platform firmware).
302 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
303 acpi_osi="string1" # add string1
304 acpi_osi="!string2" # remove string2
305 acpi_osi=!* # remove all strings
306 acpi_osi=! # disable all built-in OS vendor
307 strings
308 acpi_osi= # disable all strings
310 'acpi_osi=!' can be used in combination with single or
311 multiple 'acpi_osi="string1"' to support specific OS
312 vendor string(s). Note that such command can only
313 affect the default state of the OS vendor strings, thus
314 it cannot affect the default state of the feature group
315 strings and the current state of the OS vendor strings,
316 specifying it multiple times through kernel command line
317 is meaningless. This command is useful when one do not
318 care about the state of the feature group strings which
319 should be controlled by the OSPM.
320 Examples:
321 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
322 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
323 can make '_OSI("Windows 2000")' TRUE.
325 'acpi_osi=' cannot be used in combination with other
326 'acpi_osi=' command lines, the _OSI method will not
327 exist in the ACPI namespace. NOTE that such command can
328 only affect the _OSI support state, thus specifying it
329 multiple times through kernel command line is also
330 meaningless.
331 Examples:
332 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
333 FALSE.
335 'acpi_osi=!*' can be used in combination with single or
336 multiple 'acpi_osi="string1"' to support specific
337 string(s). Note that such command can affect the
338 current state of both the OS vendor strings and the
339 feature group strings, thus specifying it multiple times
340 through kernel command line is meaningful. But it may
341 still not able to affect the final state of a string if
342 there are quirks related to this string. This command
343 is useful when one want to control the state of the
344 feature group strings to debug BIOS issues related to
345 the OSPM features.
346 Examples:
347 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
348 '_OSI("Module Device")' FALSE.
349 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
350 '_OSI("Module Device")' TRUE.
351 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
352 equivalent to
353 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
354 and
355 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
356 they all will make '_OSI("Windows 2000")' TRUE.
358 acpi_pm_good [X86]
359 Override the pmtimer bug detection: force the kernel
360 to assume that this machine's pmtimer latches its value
361 and always returns good values.
363 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
364 Format: { level | edge | high | low }
366 acpi_skip_timer_override [HW,ACPI]
367 Recognize and ignore IRQ0/pin2 Interrupt Override.
368 For broken nForce2 BIOS resulting in XT-PIC timer.
370 acpi_sleep= [HW,ACPI] Sleep options
371 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
372 old_ordering, nonvs, sci_force_enable }
373 See Documentation/power/video.txt for information on
374 s3_bios and s3_mode.
375 s3_beep is for debugging; it makes the PC's speaker beep
376 as soon as the kernel's real-mode entry point is called.
377 s4_nohwsig prevents ACPI hardware signature from being
378 used during resume from hibernation.
379 old_ordering causes the ACPI 1.0 ordering of the _PTS
380 control method, with respect to putting devices into
381 low power states, to be enforced (the ACPI 2.0 ordering
382 of _PTS is used by default).
383 nonvs prevents the kernel from saving/restoring the
384 ACPI NVS memory during suspend/hibernation and resume.
385 sci_force_enable causes the kernel to set SCI_EN directly
386 on resume from S1/S3 (which is against the ACPI spec,
387 but some broken systems don't work without it).
389 acpi_use_timer_override [HW,ACPI]
390 Use timer override. For some broken Nvidia NF5 boards
391 that require a timer override, but don't have HPET
393 add_efi_memmap [EFI; X86] Include EFI memory map in
394 kernel's map of available physical RAM.
396 agp= [AGP]
397 { off | try_unsupported }
398 off: disable AGP support
399 try_unsupported: try to drive unsupported chipsets
400 (may crash computer or cause data corruption)
402 ALSA [HW,ALSA]
403 See Documentation/sound/alsa/alsa-parameters.txt
405 alignment= [KNL,ARM]
406 Allow the default userspace alignment fault handler
407 behaviour to be specified. Bit 0 enables warnings,
408 bit 1 enables fixups, and bit 2 sends a segfault.
410 align_va_addr= [X86-64]
411 Align virtual addresses by clearing slice [14:12] when
412 allocating a VMA at process creation time. This option
413 gives you up to 3% performance improvement on AMD F15h
414 machines (where it is enabled by default) for a
415 CPU-intensive style benchmark, and it can vary highly in
416 a microbenchmark depending on workload and compiler.
418 32: only for 32-bit processes
419 64: only for 64-bit processes
420 on: enable for both 32- and 64-bit processes
421 off: disable for both 32- and 64-bit processes
423 alloc_snapshot [FTRACE]
424 Allocate the ftrace snapshot buffer on boot up when the
425 main buffer is allocated. This is handy if debugging
426 and you need to use tracing_snapshot() on boot up, and
427 do not want to use tracing_snapshot_alloc() as it needs
428 to be done where GFP_KERNEL allocations are allowed.
430 amd_iommu= [HW,X86-64]
431 Pass parameters to the AMD IOMMU driver in the system.
432 Possible values are:
433 fullflush - enable flushing of IO/TLB entries when
434 they are unmapped. Otherwise they are
435 flushed before they will be reused, which
436 is a lot of faster
437 off - do not initialize any AMD IOMMU found in
438 the system
439 force_isolation - Force device isolation for all
440 devices. The IOMMU driver is not
441 allowed anymore to lift isolation
442 requirements as needed. This option
443 does not override iommu=pt
445 amd_iommu_dump= [HW,X86-64]
446 Enable AMD IOMMU driver option to dump the ACPI table
447 for AMD IOMMU. With this option enabled, AMD IOMMU
448 driver will print ACPI tables for AMD IOMMU during
449 IOMMU initialization.
451 amijoy.map= [HW,JOY] Amiga joystick support
452 Map of devices attached to JOY0DAT and JOY1DAT
453 Format: <a>,<b>
454 See also Documentation/input/joystick.txt
456 analog.map= [HW,JOY] Analog joystick and gamepad support
457 Specifies type or capabilities of an analog joystick
458 connected to one of 16 gameports
459 Format: <type1>,<type2>,..<type16>
461 apc= [HW,SPARC]
462 Power management functions (SPARCstation-4/5 + deriv.)
463 Format: noidle
464 Disable APC CPU standby support. SPARCstation-Fox does
465 not play well with APC CPU idle - disable it if you have
466 APC and your system crashes randomly.
468 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
469 Change the output verbosity whilst booting
470 Format: { quiet (default) | verbose | debug }
471 Change the amount of debugging information output
472 when initialising the APIC and IO-APIC components.
474 autoconf= [IPV6]
475 See Documentation/networking/ipv6.txt.
477 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
478 Limit apic dumping. The parameter defines the maximal
479 number of local apics being dumped. Also it is possible
480 to set it to "all" by meaning -- no limit here.
481 Format: { 1 (default) | 2 | ... | all }.
482 The parameter valid if only apic=debug or
483 apic=verbose is specified.
484 Example: apic=debug show_lapic=all
486 apm= [APM] Advanced Power Management
487 See header of arch/x86/kernel/apm_32.c.
489 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
490 Format: <io>,<irq>,<nodeID>
492 ataflop= [HW,M68k]
494 atarimouse= [HW,MOUSE] Atari Mouse
496 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
497 EzKey and similar keyboards
499 atkbd.reset= [HW] Reset keyboard during initialization
501 atkbd.set= [HW] Select keyboard code set
502 Format: <int> (2 = AT (default), 3 = PS/2)
504 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
505 keyboards
507 atkbd.softraw= [HW] Choose between synthetic and real raw mode
508 Format: <bool> (0 = real, 1 = synthetic (default))
510 atkbd.softrepeat= [HW]
511 Use software keyboard repeat
513 audit= [KNL] Enable the audit sub-system
514 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
515 0 - kernel audit is disabled and can not be enabled
516 until the next reboot
517 unset - kernel audit is initialized but disabled and
518 will be fully enabled by the userspace auditd.
519 1 - kernel audit is initialized and partially enabled,
520 storing at most audit_backlog_limit messages in
521 RAM until it is fully enabled by the userspace
522 auditd.
523 Default: unset
525 audit_backlog_limit= [KNL] Set the audit queue size limit.
526 Format: <int> (must be >=0)
527 Default: 64
529 baycom_epp= [HW,AX25]
530 Format: <io>,<mode>
532 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
533 Format: <io>,<mode>
534 See header of drivers/net/hamradio/baycom_par.c.
536 baycom_ser_fdx= [HW,AX25]
537 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
538 Format: <io>,<irq>,<mode>[,<baud>]
539 See header of drivers/net/hamradio/baycom_ser_fdx.c.
541 baycom_ser_hdx= [HW,AX25]
542 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
543 Format: <io>,<irq>,<mode>
544 See header of drivers/net/hamradio/baycom_ser_hdx.c.
546 blkdevparts= Manual partition parsing of block device(s) for
547 embedded devices based on command line input.
548 See Documentation/block/cmdline-partition.txt
550 boot_delay= Milliseconds to delay each printk during boot.
551 Values larger than 10 seconds (10000) are changed to
552 no delay (0).
553 Format: integer
555 bootmem_debug [KNL] Enable bootmem allocator debug messages.
557 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
558 bttv.radio= Most important insmod options are available as
559 kernel args too.
560 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
561 bttv.tuner=
563 bulk_remove=off [PPC] This parameter disables the use of the pSeries
564 firmware feature for flushing multiple hpte entries
565 at a time.
567 c101= [NET] Moxa C101 synchronous serial card
569 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
570 Sometimes CPU hardware bugs make them report the cache
571 size incorrectly. The kernel will attempt work arounds
572 to fix known problems, but for some CPUs it is not
573 possible to determine what the correct size should be.
574 This option provides an override for these situations.
576 ca_keys= [KEYS] This parameter identifies a specific key(s) on
577 the system trusted keyring to be used for certificate
578 trust validation.
579 format: { id:<keyid> | builtin }
581 cca= [MIPS] Override the kernel pages' cache coherency
582 algorithm. Accepted values range from 0 to 7
583 inclusive. See arch/mips/include/asm/pgtable-bits.h
584 for platform specific values (SB1, Loongson3 and
585 others).
587 ccw_timeout_log [S390]
588 See Documentation/s390/CommonIO for details.
590 cgroup_disable= [KNL] Disable a particular controller
591 Format: {name of the controller(s) to disable}
592 The effects of cgroup_disable=foo are:
593 - foo isn't auto-mounted if you mount all cgroups in
594 a single hierarchy
595 - foo isn't visible as an individually mountable
596 subsystem
597 {Currently only "memory" controller deal with this and
598 cut the overhead, others just disable the usage. So
599 only cgroup_disable=memory is actually worthy}
601 checkreqprot [SELINUX] Set initial checkreqprot flag value.
602 Format: { "0" | "1" }
603 See security/selinux/Kconfig help text.
604 0 -- check protection applied by kernel (includes
605 any implied execute protection).
606 1 -- check protection requested by application.
607 Default value is set via a kernel config option.
608 Value can be changed at runtime via
609 /selinux/checkreqprot.
611 cio_ignore= [S390]
612 See Documentation/s390/CommonIO for details.
613 clk_ignore_unused
614 [CLK]
615 Prevents the clock framework from automatically gating
616 clocks that have not been explicitly enabled by a Linux
617 device driver but are enabled in hardware at reset or
618 by the bootloader/firmware. Note that this does not
619 force such clocks to be always-on nor does it reserve
620 those clocks in any way. This parameter is useful for
621 debug and development, but should not be needed on a
622 platform with proper driver support. For more
623 information, see Documentation/clk.txt.
625 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
626 [Deprecated]
627 Forces specified clocksource (if available) to be used
628 when calculating gettimeofday(). If specified
629 clocksource is not available, it defaults to PIT.
630 Format: { pit | tsc | cyclone | pmtmr }
632 clocksource= Override the default clocksource
633 Format: <string>
634 Override the default clocksource and use the clocksource
635 with the name specified.
636 Some clocksource names to choose from, depending on
637 the platform:
638 [all] jiffies (this is the base, fallback clocksource)
639 [ACPI] acpi_pm
640 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
641 pxa_timer,timer3,32k_counter,timer0_1
642 [AVR32] avr32
643 [X86-32] pit,hpet,tsc;
644 scx200_hrt on Geode; cyclone on IBM x440
645 [MIPS] MIPS
646 [PARISC] cr16
647 [S390] tod
648 [SH] SuperH
649 [SPARC64] tick
650 [X86-64] hpet,tsc
652 clearcpuid=BITNUM [X86]
653 Disable CPUID feature X for the kernel. See
654 arch/x86/include/asm/cpufeature.h for the valid bit
655 numbers. Note the Linux specific bits are not necessarily
656 stable over kernel options, but the vendor specific
657 ones should be.
658 Also note that user programs calling CPUID directly
659 or using the feature without checking anything
660 will still see it. This just prevents it from
661 being used by the kernel or shown in /proc/cpuinfo.
662 Also note the kernel might malfunction if you disable
663 some critical bits.
665 cma=nn[MG]@[start[MG][-end[MG]]]
666 [ARM,X86,KNL]
667 Sets the size of kernel global memory area for
668 contiguous memory allocations and optionally the
669 placement constraint by the physical address range of
670 memory allocations. A value of 0 disables CMA
671 altogether. For more information, see
672 include/linux/dma-contiguous.h
674 cmo_free_hint= [PPC] Format: { yes | no }
675 Specify whether pages are marked as being inactive
676 when they are freed. This is used in CMO environments
677 to determine OS memory pressure for page stealing by
678 a hypervisor.
679 Default: yes
681 coherent_pool=nn[KMG] [ARM,KNL]
682 Sets the size of memory pool for coherent, atomic dma
683 allocations, by default set to 256K.
685 code_bytes [X86] How many bytes of object code to print
686 in an oops report.
687 Range: 0 - 8192
688 Default: 64
690 com20020= [HW,NET] ARCnet - COM20020 chipset
691 Format:
692 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
694 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
695 Format: <io>[,<irq>]
697 com90xx= [HW,NET]
698 ARCnet - COM90xx chipset (memory-mapped buffers)
699 Format: <io>[,<irq>[,<memstart>]]
701 condev= [HW,S390] console device
702 conmode=
704 console= [KNL] Output console device and options.
706 tty<n> Use the virtual console device <n>.
708 ttyS<n>[,options]
709 ttyUSB0[,options]
710 Use the specified serial port. The options are of
711 the form "bbbbpnf", where "bbbb" is the baud rate,
712 "p" is parity ("n", "o", or "e"), "n" is number of
713 bits, and "f" is flow control ("r" for RTS or
714 omit it). Default is "9600n8".
716 See Documentation/serial-console.txt for more
717 information. See
718 Documentation/networking/netconsole.txt for an
719 alternative.
721 uart[8250],io,<addr>[,options]
722 uart[8250],mmio,<addr>[,options]
723 uart[8250],mmio32,<addr>[,options]
724 uart[8250],0x<addr>[,options]
725 Start an early, polled-mode console on the 8250/16550
726 UART at the specified I/O port or MMIO address,
727 switching to the matching ttyS device later.
728 MMIO inter-register address stride is either 8-bit
729 (mmio) or 32-bit (mmio32).
730 If none of [io|mmio|mmio32], <addr> is assumed to be
731 equivalent to 'mmio'. 'options' are specified in the
732 same format described for ttyS above; if unspecified,
733 the h/w is not re-initialized.
735 hvc<n> Use the hypervisor console device <n>. This is for
736 both Xen and PowerPC hypervisors.
738 If the device connected to the port is not a TTY but a braille
739 device, prepend "brl," before the device type, for instance
740 console=brl,ttyS0
741 For now, only VisioBraille is supported.
743 consoleblank= [KNL] The console blank (screen saver) timeout in
744 seconds. Defaults to 10*60 = 10mins. A value of 0
745 disables the blank timer.
747 coredump_filter=
748 [KNL] Change the default value for
749 /proc/<pid>/coredump_filter.
750 See also Documentation/filesystems/proc.txt.
752 cpuidle.off=1 [CPU_IDLE]
753 disable the cpuidle sub-system
755 cpu_init_udelay=N
756 [X86] Delay for N microsec between assert and de-assert
757 of APIC INIT to start processors. This delay occurs
758 on every CPU online, such as boot, and resume from suspend.
759 Default: 10000
761 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
762 Format:
763 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
765 crashkernel=size[KMG][@offset[KMG]]
766 [KNL] Using kexec, Linux can switch to a 'crash kernel'
767 upon panic. This parameter reserves the physical
768 memory region [offset, offset + size] for that kernel
769 image. If '@offset' is omitted, then a suitable offset
770 is selected automatically. Check
771 Documentation/kdump/kdump.txt for further details.
773 crashkernel=range1:size1[,range2:size2,...][@offset]
774 [KNL] Same as above, but depends on the memory
775 in the running system. The syntax of range is
776 start-[end] where start and end are both
777 a memory unit (amount[KMG]). See also
778 Documentation/kdump/kdump.txt for an example.
780 crashkernel=size[KMG],high
781 [KNL, x86_64] range could be above 4G. Allow kernel
782 to allocate physical memory region from top, so could
783 be above 4G if system have more than 4G ram installed.
784 Otherwise memory region will be allocated below 4G, if
785 available.
786 It will be ignored if crashkernel=X is specified.
787 crashkernel=size[KMG],low
788 [KNL, x86_64] range under 4G. When crashkernel=X,high
789 is passed, kernel could allocate physical memory region
790 above 4G, that cause second kernel crash on system
791 that require some amount of low memory, e.g. swiotlb
792 requires at least 64M+32K low memory. Kernel would
793 try to allocate 72M below 4G automatically.
794 This one let user to specify own low range under 4G
795 for second kernel instead.
796 0: to disable low allocation.
797 It will be ignored when crashkernel=X,high is not used
798 or memory reserved is below 4G.
800 cs89x0_dma= [HW,NET]
801 Format: <dma>
803 cs89x0_media= [HW,NET]
804 Format: { rj45 | aui | bnc }
806 dasd= [HW,NET]
807 See header of drivers/s390/block/dasd_devmap.c.
809 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
810 (one device per port)
811 Format: <port#>,<type>
812 See also Documentation/input/joystick-parport.txt
814 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
815 time. See Documentation/dynamic-debug-howto.txt for
816 details. Deprecated, see dyndbg.
818 debug [KNL] Enable kernel debugging (events log level).
820 debug_locks_verbose=
821 [KNL] verbose self-tests
822 Format=<0|1>
823 Print debugging info while doing the locking API
824 self-tests.
825 We default to 0 (no extra messages), setting it to
826 1 will print _a lot_ more information - normally
827 only useful to kernel developers.
829 debug_objects [KNL] Enable object debugging
831 no_debug_objects
832 [KNL] Disable object debugging
834 debug_guardpage_minorder=
835 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
836 parameter allows control of the order of pages that will
837 be intentionally kept free (and hence protected) by the
838 buddy allocator. Bigger value increase the probability
839 of catching random memory corruption, but reduce the
840 amount of memory for normal system use. The maximum
841 possible value is MAX_ORDER/2. Setting this parameter
842 to 1 or 2 should be enough to identify most random
843 memory corruption problems caused by bugs in kernel or
844 driver code when a CPU writes to (or reads from) a
845 random memory location. Note that there exists a class
846 of memory corruptions problems caused by buggy H/W or
847 F/W or by drivers badly programing DMA (basically when
848 memory is written at bus level and the CPU MMU is
849 bypassed) which are not detectable by
850 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
851 tracking down these problems.
853 debug_pagealloc=
854 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
855 parameter enables the feature at boot time. In
856 default, it is disabled. We can avoid allocating huge
857 chunk of memory for debug pagealloc if we don't enable
858 it at boot time and the system will work mostly same
859 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
860 on: enable the feature
862 debugpat [X86] Enable PAT debugging
864 decnet.addr= [HW,NET]
865 Format: <area>[,<node>]
866 See also Documentation/networking/decnet.txt.
868 default_hugepagesz=
869 [same as hugepagesz=] The size of the default
870 HugeTLB page size. This is the size represented by
871 the legacy /proc/ hugepages APIs, used for SHM, and
872 default size when mounting hugetlbfs filesystems.
873 Defaults to the default architecture's huge page size
874 if not specified.
876 dhash_entries= [KNL]
877 Set number of hash buckets for dentry cache.
879 disable= [IPV6]
880 See Documentation/networking/ipv6.txt.
882 disable_cpu_apicid= [X86,APIC,SMP]
883 Format: <int>
884 The number of initial APIC ID for the
885 corresponding CPU to be disabled at boot,
886 mostly used for the kdump 2nd kernel to
887 disable BSP to wake up multiple CPUs without
888 causing system reset or hang due to sending
889 INIT from AP to BSP.
891 disable_ddw [PPC/PSERIES]
892 Disable Dynamic DMA Window support. Use this if
893 to workaround buggy firmware.
895 disable_ipv6= [IPV6]
896 See Documentation/networking/ipv6.txt.
898 disable_mtrr_cleanup [X86]
899 The kernel tries to adjust MTRR layout from continuous
900 to discrete, to make X server driver able to add WB
901 entry later. This parameter disables that.
903 disable_mtrr_trim [X86, Intel and AMD only]
904 By default the kernel will trim any uncacheable
905 memory out of your available memory pool based on
906 MTRR settings. This parameter disables that behavior,
907 possibly causing your machine to run very slowly.
909 disable_timer_pin_1 [X86]
910 Disable PIN 1 of APIC timer
911 Can be useful to work around chipset bugs.
913 dis_ucode_ldr [X86] Disable the microcode loader.
915 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
916 this option disables the debugging code at boot.
918 dma_debug_entries=<number>
919 This option allows to tune the number of preallocated
920 entries for DMA-API debugging code. One entry is
921 required per DMA-API allocation. Use this if the
922 DMA-API debugging code disables itself because the
923 architectural default is too low.
925 dma_debug_driver=<driver_name>
926 With this option the DMA-API debugging driver
927 filter feature can be enabled at boot time. Just
928 pass the driver to filter for as the parameter.
929 The filter can be disabled or changed to another
930 driver later using sysfs.
932 drm_kms_helper.edid_firmware=[<connector>:]<file>
933 Broken monitors, graphic adapters and KVMs may
934 send no or incorrect EDID data sets. This parameter
935 allows to specify an EDID data set in the
936 /lib/firmware directory that is used instead.
937 Generic built-in EDID data sets are used, if one of
938 edid/1024x768.bin, edid/1280x1024.bin,
939 edid/1680x1050.bin, or edid/1920x1080.bin is given
940 and no file with the same name exists. Details and
941 instructions how to build your own EDID data are
942 available in Documentation/EDID/HOWTO.txt. An EDID
943 data set will only be used for a particular connector,
944 if its name and a colon are prepended to the EDID
945 name.
947 dscc4.setup= [NET]
949 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
950 module.dyndbg[="val"]
951 Enable debug messages at boot time. See
952 Documentation/dynamic-debug-howto.txt for details.
954 nompx [X86] Disables Intel Memory Protection Extensions.
955 See Documentation/x86/intel_mpx.txt for more
956 information about the feature.
958 eagerfpu= [X86]
959 on enable eager fpu restore
960 off disable eager fpu restore
961 auto selects the default scheme, which automatically
962 enables eagerfpu restore for xsaveopt.
964 module.async_probe [KNL]
965 Enable asynchronous probe on this module.
967 early_ioremap_debug [KNL]
968 Enable debug messages in early_ioremap support. This
969 is useful for tracking down temporary early mappings
970 which are not unmapped.
972 earlycon= [KNL] Output early console device and options.
974 cdns,<addr>
975 Start an early, polled-mode console on a cadence serial
976 port at the specified address. The cadence serial port
977 must already be setup and configured. Options are not
978 yet supported.
980 uart[8250],io,<addr>[,options]
981 uart[8250],mmio,<addr>[,options]
982 uart[8250],mmio32,<addr>[,options]
983 uart[8250],mmio32be,<addr>[,options]
984 uart[8250],0x<addr>[,options]
985 Start an early, polled-mode console on the 8250/16550
986 UART at the specified I/O port or MMIO address.
987 MMIO inter-register address stride is either 8-bit
988 (mmio) or 32-bit (mmio32 or mmio32be).
989 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
990 to be equivalent to 'mmio'. 'options' are specified
991 in the same format described for "console=ttyS<n>"; if
992 unspecified, the h/w is not initialized.
994 pl011,<addr>
995 Start an early, polled-mode console on a pl011 serial
996 port at the specified address. The pl011 serial port
997 must already be setup and configured. Options are not
998 yet supported.
1000 msm_serial,<addr>
1001 Start an early, polled-mode console on an msm serial
1002 port at the specified address. The serial port
1003 must already be setup and configured. Options are not
1004 yet supported.
1006 msm_serial_dm,<addr>
1007 Start an early, polled-mode console on an msm serial
1008 dm port at the specified address. The serial port
1009 must already be setup and configured. Options are not
1010 yet supported.
1012 smh Use ARM semihosting calls for early console.
1014 s3c2410,<addr>
1015 s3c2412,<addr>
1016 s3c2440,<addr>
1017 s3c6400,<addr>
1018 s5pv210,<addr>
1019 exynos4210,<addr>
1020 Use early console provided by serial driver available
1021 on Samsung SoCs, requires selecting proper type and
1022 a correct base address of the selected UART port. The
1023 serial port must already be setup and configured.
1024 Options are not yet supported.
1026 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1027 earlyprintk=vga
1028 earlyprintk=efi
1029 earlyprintk=xen
1030 earlyprintk=serial[,ttySn[,baudrate]]
1031 earlyprintk=serial[,0x...[,baudrate]]
1032 earlyprintk=ttySn[,baudrate]
1033 earlyprintk=dbgp[debugController#]
1034 earlyprintk=pciserial,bus:device.function[,baudrate]
1036 earlyprintk is useful when the kernel crashes before
1037 the normal console is initialized. It is not enabled by
1038 default because it has some cosmetic problems.
1040 Append ",keep" to not disable it when the real console
1041 takes over.
1043 Only one of vga, efi, serial, or usb debug port can
1044 be used at a time.
1046 Currently only ttyS0 and ttyS1 may be specified by
1047 name. Other I/O ports may be explicitly specified
1048 on some architectures (x86 and arm at least) by
1049 replacing ttySn with an I/O port address, like this:
1050 earlyprintk=serial,0x1008,115200
1051 You can find the port for a given device in
1052 /proc/tty/driver/serial:
1053 2: uart:ST16650V2 port:00001008 irq:18 ...
1055 Interaction with the standard serial driver is not
1056 very good.
1058 The VGA and EFI output is eventually overwritten by
1059 the real console.
1061 The xen output can only be used by Xen PV guests.
1063 edac_report= [HW,EDAC] Control how to report EDAC event
1064 Format: {"on" | "off" | "force"}
1065 on: enable EDAC to report H/W event. May be overridden
1066 by other higher priority error reporting module.
1067 off: disable H/W event reporting through EDAC.
1068 force: enforce the use of EDAC to report H/W event.
1069 default: on.
1071 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1072 ekgdboc=kbd
1074 This is designed to be used in conjunction with
1075 the boot argument: earlyprintk=vga
1077 edd= [EDD]
1078 Format: {"off" | "on" | "skip[mbr]"}
1080 efi= [EFI]
1081 Format: { "old_map", "nochunk", "noruntime", "debug" }
1082 old_map [X86-64]: switch to the old ioremap-based EFI
1083 runtime services mapping. 32-bit still uses this one by
1084 default.
1085 nochunk: disable reading files in "chunks" in the EFI
1086 boot stub, as chunking can cause problems with some
1087 firmware implementations.
1088 noruntime : disable EFI runtime services support
1089 debug: enable misc debug output
1091 efi_no_storage_paranoia [EFI; X86]
1092 Using this parameter you can use more than 50% of
1093 your efi variable storage. Use this parameter only if
1094 you are really sure that your UEFI does sane gc and
1095 fulfills the spec otherwise your board may brick.
1097 eisa_irq_edge= [PARISC,HW]
1098 See header of drivers/parisc/eisa.c.
1100 elanfreq= [X86-32]
1101 See comment before function elanfreq_setup() in
1102 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1104 elevator= [IOSCHED]
1105 Format: {"cfq" | "deadline" | "noop"}
1106 See Documentation/block/cfq-iosched.txt and
1107 Documentation/block/deadline-iosched.txt for details.
1109 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1110 Specifies physical address of start of kernel core
1111 image elf header and optionally the size. Generally
1112 kexec loader will pass this option to capture kernel.
1113 See Documentation/kdump/kdump.txt for details.
1115 enable_mtrr_cleanup [X86]
1116 The kernel tries to adjust MTRR layout from continuous
1117 to discrete, to make X server driver able to add WB
1118 entry later. This parameter enables that.
1120 enable_timer_pin_1 [X86]
1121 Enable PIN 1 of APIC timer
1122 Can be useful to work around chipset bugs
1123 (in particular on some ATI chipsets).
1124 The kernel tries to set a reasonable default.
1126 enforcing [SELINUX] Set initial enforcing status.
1127 Format: {"0" | "1"}
1128 See security/selinux/Kconfig help text.
1129 0 -- permissive (log only, no denials).
1130 1 -- enforcing (deny and log).
1131 Default value is 0.
1132 Value can be changed at runtime via /selinux/enforce.
1134 erst_disable [ACPI]
1135 Disable Error Record Serialization Table (ERST)
1136 support.
1138 ether= [HW,NET] Ethernet cards parameters
1139 This option is obsoleted by the "netdev=" option, which
1140 has equivalent usage. See its documentation for details.
1142 evm= [EVM]
1143 Format: { "fix" }
1144 Permit 'security.evm' to be updated regardless of
1145 current integrity status.
1147 failslab=
1148 fail_page_alloc=
1149 fail_make_request=[KNL]
1150 General fault injection mechanism.
1151 Format: <interval>,<probability>,<space>,<times>
1152 See also Documentation/fault-injection/.
1154 floppy= [HW]
1155 See Documentation/blockdev/floppy.txt.
1157 force_pal_cache_flush
1158 [IA-64] Avoid check_sal_cache_flush which may hang on
1159 buggy SAL_CACHE_FLUSH implementations. Using this
1160 parameter will force ia64_sal_cache_flush to call
1161 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1163 forcepae [X86-32]
1164 Forcefully enable Physical Address Extension (PAE).
1165 Many Pentium M systems disable PAE but may have a
1166 functionally usable PAE implementation.
1167 Warning: use of this parameter will taint the kernel
1168 and may cause unknown problems.
1170 ftrace=[tracer]
1171 [FTRACE] will set and start the specified tracer
1172 as early as possible in order to facilitate early
1173 boot debugging.
1175 ftrace_dump_on_oops[=orig_cpu]
1176 [FTRACE] will dump the trace buffers on oops.
1177 If no parameter is passed, ftrace will dump
1178 buffers of all CPUs, but if you pass orig_cpu, it will
1179 dump only the buffer of the CPU that triggered the
1180 oops.
1182 ftrace_filter=[function-list]
1183 [FTRACE] Limit the functions traced by the function
1184 tracer at boot up. function-list is a comma separated
1185 list of functions. This list can be changed at run
1186 time by the set_ftrace_filter file in the debugfs
1187 tracing directory.
1189 ftrace_notrace=[function-list]
1190 [FTRACE] Do not trace the functions specified in
1191 function-list. This list can be changed at run time
1192 by the set_ftrace_notrace file in the debugfs
1193 tracing directory.
1195 ftrace_graph_filter=[function-list]
1196 [FTRACE] Limit the top level callers functions traced
1197 by the function graph tracer at boot up.
1198 function-list is a comma separated list of functions
1199 that can be changed at run time by the
1200 set_graph_function file in the debugfs tracing directory.
1202 ftrace_graph_notrace=[function-list]
1203 [FTRACE] Do not trace from the functions specified in
1204 function-list. This list is a comma separated list of
1205 functions that can be changed at run time by the
1206 set_graph_notrace file in the debugfs tracing directory.
1208 gamecon.map[2|3]=
1209 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1210 support via parallel port (up to 5 devices per port)
1211 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1212 See also Documentation/input/joystick-parport.txt
1214 gamma= [HW,DRM]
1216 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1217 Format: off | on
1218 default: on
1220 gcov_persist= [GCOV] When non-zero (default), profiling data for
1221 kernel modules is saved and remains accessible via
1222 debugfs, even when the module is unloaded/reloaded.
1223 When zero, profiling data is discarded and associated
1224 debugfs files are removed at module unload time.
1226 gpt [EFI] Forces disk with valid GPT signature but
1227 invalid Protective MBR to be treated as GPT. If the
1228 primary GPT is corrupted, it enables the backup/alternate
1229 GPT to be used instead.
1231 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1232 the "Enable 0" bit of the configuration register.
1233 Format: 0 | 1
1234 Default: 0
1235 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1236 the "Enable 0" bit of the configuration register.
1237 Format: 0 | 1
1238 Default: 0
1239 grcan.select= [HW] Select which physical interface to use.
1240 Format: 0 | 1
1241 Default: 0
1242 grcan.txsize= [HW] Sets the size of the tx buffer.
1243 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1244 Default: 1024
1245 grcan.rxsize= [HW] Sets the size of the rx buffer.
1246 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1247 Default: 1024
1249 hashdist= [KNL,NUMA] Large hashes allocated during boot
1250 are distributed across NUMA nodes. Defaults on
1251 for 64-bit NUMA, off otherwise.
1252 Format: 0 | 1 (for off | on)
1254 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1256 hd= [EIDE] (E)IDE hard drive subsystem geometry
1257 Format: <cyl>,<head>,<sect>
1259 hest_disable [ACPI]
1260 Disable Hardware Error Source Table (HEST) support;
1261 corresponding firmware-first mode error processing
1262 logic will be disabled.
1264 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1265 size of <nn>. This works even on boxes that have no
1266 highmem otherwise. This also works to reduce highmem
1267 size on bigger boxes.
1269 highres= [KNL] Enable/disable high resolution timer mode.
1270 Valid parameters: "on", "off"
1271 Default: "on"
1273 hisax= [HW,ISDN]
1274 See Documentation/isdn/README.HiSax.
1276 hlt [BUGS=ARM,SH]
1278 hpet= [X86-32,HPET] option to control HPET usage
1279 Format: { enable (default) | disable | force |
1280 verbose }
1281 disable: disable HPET and use PIT instead
1282 force: allow force enabled of undocumented chips (ICH4,
1283 VIA, nVidia)
1284 verbose: show contents of HPET registers during setup
1286 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1287 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1289 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1290 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1291 On x86-64 and powerpc, this option can be specified
1292 multiple times interleaved with hugepages= to reserve
1293 huge pages of different sizes. Valid pages sizes on
1294 x86-64 are 2M (when the CPU supports "pse") and 1G
1295 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1297 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1298 terminal devices. Valid values: 0..8
1299 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1300 If specified, z/VM IUCV HVC accepts connections
1301 from listed z/VM user IDs only.
1303 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1304 hardware thread id mappings.
1305 Format: <cpu>:<hwthread>
1307 keep_bootcon [KNL]
1308 Do not unregister boot console at start. This is only
1309 useful for debugging when something happens in the window
1310 between unregistering the boot console and initializing
1311 the real console.
1313 i2c_bus= [HW] Override the default board specific I2C bus speed
1314 or register an additional I2C bus that is not
1315 registered from board initialization code.
1316 Format:
1317 <bus_id>,<clkrate>
1319 i8042.debug [HW] Toggle i8042 debug mode
1320 i8042.unmask_kbd_data
1321 [HW] Enable printing of interrupt data from the KBD port
1322 (disabled by default, and as a pre-condition
1323 requires that i8042.debug=1 be enabled)
1324 i8042.direct [HW] Put keyboard port into non-translated mode
1325 i8042.dumbkbd [HW] Pretend that controller can only read data from
1326 keyboard and cannot control its state
1327 (Don't attempt to blink the leds)
1328 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1329 i8042.nokbd [HW] Don't check/create keyboard port
1330 i8042.noloop [HW] Disable the AUX Loopback command while probing
1331 for the AUX port
1332 i8042.nomux [HW] Don't check presence of an active multiplexing
1333 controller
1334 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1335 controllers
1336 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1337 i8042.reset [HW] Reset the controller during init and cleanup
1338 i8042.unlock [HW] Unlock (ignore) the keylock
1339 i8042.kbdreset [HW] Reset device connected to KBD port
1341 i810= [HW,DRM]
1343 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1344 indicates that the driver is running on unsupported
1345 hardware.
1346 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1347 does not match list of supported models.
1348 i8k.power_status
1349 [HW] Report power status in /proc/i8k
1350 (disabled by default)
1351 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1352 capability is set.
1354 i915.invert_brightness=
1355 [DRM] Invert the sense of the variable that is used to
1356 set the brightness of the panel backlight. Normally a
1357 brightness value of 0 indicates backlight switched off,
1358 and the maximum of the brightness value sets the backlight
1359 to maximum brightness. If this parameter is set to 0
1360 (default) and the machine requires it, or this parameter
1361 is set to 1, a brightness value of 0 sets the backlight
1362 to maximum brightness, and the maximum of the brightness
1363 value switches the backlight off.
1364 -1 -- never invert brightness
1365 0 -- machine default
1366 1 -- force brightness inversion
1368 icn= [HW,ISDN]
1369 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1371 ide-core.nodma= [HW] (E)IDE subsystem
1372 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1373 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1374 .cdrom .chs .ignore_cable are additional options
1375 See Documentation/ide/ide.txt.
1377 ide-generic.probe-mask= [HW] (E)IDE subsystem
1378 Format: <int>
1379 Probe mask for legacy ISA IDE ports. Depending on
1380 platform up to 6 ports are supported, enabled by
1381 setting corresponding bits in the mask to 1. The
1382 default value is 0x0, which has a special meaning.
1383 On systems that have PCI, it triggers scanning the
1384 PCI bus for the first and the second port, which
1385 are then probed. On systems without PCI the value
1386 of 0x0 enables probing the two first ports as if it
1387 was 0x3.
1389 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1390 Claim all unknown PCI IDE storage controllers.
1392 idle= [X86]
1393 Format: idle=poll, idle=halt, idle=nomwait
1394 Poll forces a polling idle loop that can slightly
1395 improve the performance of waking up a idle CPU, but
1396 will use a lot of power and make the system run hot.
1397 Not recommended.
1398 idle=halt: Halt is forced to be used for CPU idle.
1399 In such case C2/C3 won't be used again.
1400 idle=nomwait: Disable mwait for CPU C-states
1402 ignore_loglevel [KNL]
1403 Ignore loglevel setting - this will print /all/
1404 kernel messages to the console. Useful for debugging.
1405 We also add it as printk module parameter, so users
1406 could change it dynamically, usually by
1407 /sys/module/printk/parameters/ignore_loglevel.
1409 ihash_entries= [KNL]
1410 Set number of hash buckets for inode cache.
1412 ima_appraise= [IMA] appraise integrity measurements
1413 Format: { "off" | "enforce" | "fix" | "log" }
1414 default: "enforce"
1416 ima_appraise_tcb [IMA]
1417 The builtin appraise policy appraises all files
1418 owned by uid=0.
1420 ima_hash= [IMA]
1421 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1422 | sha512 | ... }
1423 default: "sha1"
1425 The list of supported hash algorithms is defined
1426 in crypto/hash_info.h.
1428 ima_policy= [IMA]
1429 The builtin measurement policy to load during IMA
1430 setup. Specyfing "tcb" as the value, measures all
1431 programs exec'd, files mmap'd for exec, and all files
1432 opened with the read mode bit set by either the
1433 effective uid (euid=0) or uid=0.
1434 Format: "tcb"
1436 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1437 Load a policy which meets the needs of the Trusted
1438 Computing Base. This means IMA will measure all
1439 programs exec'd, files mmap'd for exec, and all files
1440 opened for read by uid=0.
1442 ima_template= [IMA]
1443 Select one of defined IMA measurements template formats.
1444 Formats: { "ima" | "ima-ng" | "ima-sig" }
1445 Default: "ima-ng"
1447 ima_template_fmt=
1448 [IMA] Define a custom template format.
1449 Format: { "field1|...|fieldN" }
1451 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1452 Format: <min_file_size>
1453 Set the minimal file size for using asynchronous hash.
1454 If left unspecified, ahash usage is disabled.
1456 ahash performance varies for different data sizes on
1457 different crypto accelerators. This option can be used
1458 to achieve the best performance for a particular HW.
1460 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1461 Format: <bufsize>
1462 Set hashing buffer size. Default: 4k.
1464 ahash performance varies for different chunk sizes on
1465 different crypto accelerators. This option can be used
1466 to achieve best performance for particular HW.
1468 init= [KNL]
1469 Format: <full_path>
1470 Run specified binary instead of /sbin/init as init
1471 process.
1473 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1474 for working out where the kernel is dying during
1475 startup.
1477 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1478 initcall functions. Useful for debugging built-in
1479 modules and initcalls.
1481 initrd= [BOOT] Specify the location of the initial ramdisk
1483 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1484 Format: <irq>
1486 int_pln_enable [x86] Enable power limit notification interrupt
1488 integrity_audit=[IMA]
1489 Format: { "0" | "1" }
1490 0 -- basic integrity auditing messages. (Default)
1491 1 -- additional integrity auditing messages.
1493 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1494 on
1495 Enable intel iommu driver.
1496 off
1497 Disable intel iommu driver.
1498 igfx_off [Default Off]
1499 By default, gfx is mapped as normal device. If a gfx
1500 device has a dedicated DMAR unit, the DMAR unit is
1501 bypassed by not enabling DMAR with this option. In
1502 this case, gfx device will use physical address for
1503 DMA.
1504 forcedac [x86_64]
1505 With this option iommu will not optimize to look
1506 for io virtual address below 32-bit forcing dual
1507 address cycle on pci bus for cards supporting greater
1508 than 32-bit addressing. The default is to look
1509 for translation below 32-bit and if not available
1510 then look in the higher range.
1511 strict [Default Off]
1512 With this option on every unmap_single operation will
1513 result in a hardware IOTLB flush operation as opposed
1514 to batching them for performance.
1515 sp_off [Default Off]
1516 By default, super page will be supported if Intel IOMMU
1517 has the capability. With this option, super page will
1518 not be supported.
1519 ecs_off [Default Off]
1520 By default, extended context tables will be supported if
1521 the hardware advertises that it has support both for the
1522 extended tables themselves, and also PASID support. With
1523 this option set, extended tables will not be used even
1524 on hardware which claims to support them.
1526 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1527 0 disables intel_idle and fall back on acpi_idle.
1528 1 to 6 specify maximum depth of C-state.
1530 intel_pstate= [X86]
1531 disable
1532 Do not enable intel_pstate as the default
1533 scaling driver for the supported processors
1534 force
1535 Enable intel_pstate on systems that prohibit it by default
1536 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1537 instead of acpi-cpufreq may disable platform features, such
1538 as thermal controls and power capping, that rely on ACPI
1539 P-States information being indicated to OSPM and therefore
1540 should be used with caution. This option does not work with
1541 processors that aren't supported by the intel_pstate driver
1542 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1543 no_hwp
1544 Do not enable hardware P state control (HWP)
1545 if available.
1546 hwp_only
1547 Only load intel_pstate on systems which support
1548 hardware P state control (HWP) if available.
1550 intremap= [X86-64, Intel-IOMMU]
1551 on enable Interrupt Remapping (default)
1552 off disable Interrupt Remapping
1553 nosid disable Source ID checking
1554 no_x2apic_optout
1555 BIOS x2APIC opt-out request will be ignored
1557 iomem= Disable strict checking of access to MMIO memory
1558 strict regions from userspace.
1559 relaxed
1561 iommu= [x86]
1562 off
1563 force
1564 noforce
1565 biomerge
1566 panic
1567 nopanic
1568 merge
1569 nomerge
1570 forcesac
1571 soft
1572 pt [x86, IA-64]
1573 nobypass [PPC/POWERNV]
1574 Disable IOMMU bypass, using IOMMU for PCI devices.
1577 io7= [HW] IO7 for Marvel based alpha systems
1578 See comment before marvel_specify_io7 in
1579 arch/alpha/kernel/core_marvel.c.
1581 io_delay= [X86] I/O delay method
1582 0x80
1583 Standard port 0x80 based delay
1584 0xed
1585 Alternate port 0xed based delay (needed on some systems)
1586 udelay
1587 Simple two microseconds delay
1588 none
1589 No delay
1591 ip= [IP_PNP]
1592 See Documentation/filesystems/nfs/nfsroot.txt.
1594 irqfixup [HW]
1595 When an interrupt is not handled search all handlers
1596 for it. Intended to get systems with badly broken
1597 firmware running.
1599 irqpoll [HW]
1600 When an interrupt is not handled search all handlers
1601 for it. Also check all handlers each timer
1602 interrupt. Intended to get systems with badly broken
1603 firmware running.
1605 isapnp= [ISAPNP]
1606 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1608 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1609 Format:
1610 <cpu number>,...,<cpu number>
1611 or
1612 <cpu number>-<cpu number>
1613 (must be a positive range in ascending order)
1614 or a mixture
1615 <cpu number>,...,<cpu number>-<cpu number>
1617 This option can be used to specify one or more CPUs
1618 to isolate from the general SMP balancing and scheduling
1619 algorithms. You can move a process onto or off an
1620 "isolated" CPU via the CPU affinity syscalls or cpuset.
1621 <cpu number> begins at 0 and the maximum value is
1622 "number of CPUs in system - 1".
1624 This option is the preferred way to isolate CPUs. The
1625 alternative -- manually setting the CPU mask of all
1626 tasks in the system -- can cause problems and
1627 suboptimal load balancer performance.
1629 iucv= [HW,NET]
1631 ivrs_ioapic [HW,X86_64]
1632 Provide an override to the IOAPIC-ID<->DEVICE-ID
1633 mapping provided in the IVRS ACPI table. For
1634 example, to map IOAPIC-ID decimal 10 to
1635 PCI device 00:14.0 write the parameter as:
1636 ivrs_ioapic[10]=00:14.0
1638 ivrs_hpet [HW,X86_64]
1639 Provide an override to the HPET-ID<->DEVICE-ID
1640 mapping provided in the IVRS ACPI table. For
1641 example, to map HPET-ID decimal 0 to
1642 PCI device 00:14.0 write the parameter as:
1643 ivrs_hpet[0]=00:14.0
1645 js= [HW,JOY] Analog joystick
1646 See Documentation/input/joystick.txt.
1648 kaslr/nokaslr [X86]
1649 Enable/disable kernel and module base offset ASLR
1650 (Address Space Layout Randomization) if built into
1651 the kernel. When CONFIG_HIBERNATION is selected,
1652 kASLR is disabled by default. When kASLR is enabled,
1653 hibernation will be disabled.
1655 keepinitrd [HW,ARM]
1657 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1658 specifies the amount of memory usable by the kernel
1659 for non-movable allocations. The requested amount is
1660 spread evenly throughout all nodes in the system. The
1661 remaining memory in each node is used for Movable
1662 pages. In the event, a node is too small to have both
1663 kernelcore and Movable pages, kernelcore pages will
1664 take priority and other nodes will have a larger number
1665 of Movable pages. The Movable zone is used for the
1666 allocation of pages that may be reclaimed or moved
1667 by the page migration subsystem. This means that
1668 HugeTLB pages may not be allocated from this zone.
1669 Note that allocations like PTEs-from-HighMem still
1670 use the HighMem zone if it exists, and the Normal
1671 zone if it does not.
1673 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1674 Format: <Controller#>[,poll interval]
1675 The controller # is the number of the ehci usb debug
1676 port as it is probed via PCI. The poll interval is
1677 optional and is the number seconds in between
1678 each poll cycle to the debug port in case you need
1679 the functionality for interrupting the kernel with
1680 gdb or control-c on the dbgp connection. When
1681 not using this parameter you use sysrq-g to break into
1682 the kernel debugger.
1684 kgdboc= [KGDB,HW] kgdb over consoles.
1685 Requires a tty driver that supports console polling,
1686 or a supported polling keyboard driver (non-usb).
1687 Serial only format: <serial_device>[,baud]
1688 keyboard only format: kbd
1689 keyboard and serial format: kbd,<serial_device>[,baud]
1690 Optional Kernel mode setting:
1691 kms, kbd format: kms,kbd
1692 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1694 kgdbwait [KGDB] Stop kernel execution and enter the
1695 kernel debugger at the earliest opportunity.
1697 kmac= [MIPS] korina ethernet MAC address.
1698 Configure the RouterBoard 532 series on-chip
1699 Ethernet adapter MAC address.
1701 kmemleak= [KNL] Boot-time kmemleak enable/disable
1702 Valid arguments: on, off
1703 Default: on
1704 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1705 the default is off.
1707 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1708 Valid arguments: 0, 1, 2
1709 kmemcheck=0 (disabled)
1710 kmemcheck=1 (enabled)
1711 kmemcheck=2 (one-shot mode)
1712 Default: 2 (one-shot mode)
1714 kstack=N [X86] Print N words from the kernel stack
1715 in oops dumps.
1717 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1718 Default is 0 (don't ignore, but inject #GP)
1720 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1721 KVM MMU at runtime.
1722 Default is 0 (off)
1724 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1725 Default is 1 (enabled)
1727 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1728 for all guests.
1729 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1731 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1732 (virtualized MMU) support on capable Intel chips.
1733 Default is 1 (enabled)
1735 kvm-intel.emulate_invalid_guest_state=
1736 [KVM,Intel] Enable emulation of invalid guest states
1737 Default is 0 (disabled)
1739 kvm-intel.flexpriority=
1740 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1741 Default is 1 (enabled)
1743 kvm-intel.nested=
1744 [KVM,Intel] Enable VMX nesting (nVMX).
1745 Default is 0 (disabled)
1747 kvm-intel.unrestricted_guest=
1748 [KVM,Intel] Disable unrestricted guest feature
1749 (virtualized real and unpaged mode) on capable
1750 Intel chips. Default is 1 (enabled)
1752 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1753 feature (tagged TLBs) on capable Intel chips.
1754 Default is 1 (enabled)
1756 l2cr= [PPC]
1758 l3cr= [PPC]
1760 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1761 disabled it.
1763 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1764 value for LAPIC timer one-shot implementation. Default
1765 back to the programmable timer unit in the LAPIC.
1767 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1768 in C2 power state.
1770 libata.dma= [LIBATA] DMA control
1771 libata.dma=0 Disable all PATA and SATA DMA
1772 libata.dma=1 PATA and SATA Disk DMA only
1773 libata.dma=2 ATAPI (CDROM) DMA only
1774 libata.dma=4 Compact Flash DMA only
1775 Combinations also work, so libata.dma=3 enables DMA
1776 for disks and CDROMs, but not CFs.
1778 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1779 libata.ignore_hpa=0 keep BIOS limits (default)
1780 libata.ignore_hpa=1 ignore limits, using full disk
1782 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1783 when set.
1784 Format: <int>
1786 libata.force= [LIBATA] Force configurations. The format is comma
1787 separated list of "[ID:]VAL" where ID is
1788 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1789 matching port, link or device. Basically, it matches
1790 the ATA ID string printed on console by libata. If
1791 the whole ID part is omitted, the last PORT and DEVICE
1792 values are used. If ID hasn't been specified yet, the
1793 configuration applies to all ports, links and devices.
1795 If only DEVICE is omitted, the parameter applies to
1796 the port and all links and devices behind it. DEVICE
1797 number of 0 either selects the first device or the
1798 first fan-out link behind PMP device. It does not
1799 select the host link. DEVICE number of 15 selects the
1800 host link and device attached to it.
1802 The VAL specifies the configuration to force. As long
1803 as there's no ambiguity shortcut notation is allowed.
1804 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1805 The following configurations can be forced.
1807 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1808 Any ID with matching PORT is used.
1810 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1812 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1813 udma[/][16,25,33,44,66,100,133] notation is also
1814 allowed.
1816 * [no]ncq: Turn on or off NCQ.
1818 * [no]ncqtrim: Turn off queued DSM TRIM.
1820 * nohrst, nosrst, norst: suppress hard, soft
1821 and both resets.
1823 * rstonce: only attempt one reset during
1824 hot-unplug link recovery
1826 * dump_id: dump IDENTIFY data.
1828 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1830 * disable: Disable this device.
1832 If there are multiple matching configurations changing
1833 the same attribute, the last one is used.
1835 memblock=debug [KNL] Enable memblock debug messages.
1837 load_ramdisk= [RAM] List of ramdisks to load from floppy
1838 See Documentation/blockdev/ramdisk.txt.
1840 lockd.nlm_grace_period=P [NFS] Assign grace period.
1841 Format: <integer>
1843 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1844 Format: <integer>
1846 lockd.nlm_timeout=T [NFS] Assign timeout value.
1847 Format: <integer>
1849 lockd.nlm_udpport=M [NFS] Assign UDP port.
1850 Format: <integer>
1852 locktorture.nreaders_stress= [KNL]
1853 Set the number of locking read-acquisition kthreads.
1854 Defaults to being automatically set based on the
1855 number of online CPUs.
1857 locktorture.nwriters_stress= [KNL]
1858 Set the number of locking write-acquisition kthreads.
1860 locktorture.onoff_holdoff= [KNL]
1861 Set time (s) after boot for CPU-hotplug testing.
1863 locktorture.onoff_interval= [KNL]
1864 Set time (s) between CPU-hotplug operations, or
1865 zero to disable CPU-hotplug testing.
1867 locktorture.shuffle_interval= [KNL]
1868 Set task-shuffle interval (jiffies). Shuffling
1869 tasks allows some CPUs to go into dyntick-idle
1870 mode during the locktorture test.
1872 locktorture.shutdown_secs= [KNL]
1873 Set time (s) after boot system shutdown. This
1874 is useful for hands-off automated testing.
1876 locktorture.stat_interval= [KNL]
1877 Time (s) between statistics printk()s.
1879 locktorture.stutter= [KNL]
1880 Time (s) to stutter testing, for example,
1881 specifying five seconds causes the test to run for
1882 five seconds, wait for five seconds, and so on.
1883 This tests the locking primitive's ability to
1884 transition abruptly to and from idle.
1886 locktorture.torture_runnable= [BOOT]
1887 Start locktorture running at boot time.
1889 locktorture.torture_type= [KNL]
1890 Specify the locking implementation to test.
1892 locktorture.verbose= [KNL]
1893 Enable additional printk() statements.
1895 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1896 Format: <irq>
1898 loglevel= All Kernel Messages with a loglevel smaller than the
1899 console loglevel will be printed to the console. It can
1900 also be changed with klogd or other programs. The
1901 loglevels are defined as follows:
1903 0 (KERN_EMERG) system is unusable
1904 1 (KERN_ALERT) action must be taken immediately
1905 2 (KERN_CRIT) critical conditions
1906 3 (KERN_ERR) error conditions
1907 4 (KERN_WARNING) warning conditions
1908 5 (KERN_NOTICE) normal but significant condition
1909 6 (KERN_INFO) informational
1910 7 (KERN_DEBUG) debug-level messages
1912 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1913 in bytes. n must be a power of two and greater
1914 than the minimal size. The minimal size is defined
1915 by LOG_BUF_SHIFT kernel config parameter. There is
1916 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1917 that allows to increase the default size depending on
1918 the number of CPUs. See init/Kconfig for more details.
1920 logo.nologo [FB] Disables display of the built-in Linux logo.
1921 This may be used to provide more screen space for
1922 kernel log messages and is useful when debugging
1923 kernel boot problems.
1925 lp=0 [LP] Specify parallel ports to use, e.g,
1926 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1927 lp=reset first parallel port). 'lp=0' disables the
1928 lp=auto printer driver. 'lp=reset' (which can be
1929 specified in addition to the ports) causes
1930 attached printers to be reset. Using
1931 lp=port1,port2,... specifies the parallel ports
1932 to associate lp devices with, starting with
1933 lp0. A port specification may be 'none' to skip
1934 that lp device, or a parport name such as
1935 'parport0'. Specifying 'lp=auto' instead of a
1936 port specification list means that device IDs
1937 from each port should be examined, to see if
1938 an IEEE 1284-compliant printer is attached; if
1939 so, the driver will manage that printer.
1940 See also header of drivers/char/lp.c.
1942 lpj=n [KNL]
1943 Sets loops_per_jiffy to given constant, thus avoiding
1944 time-consuming boot-time autodetection (up to 250 ms per
1945 CPU). 0 enables autodetection (default). To determine
1946 the correct value for your kernel, boot with normal
1947 autodetection and see what value is printed. Note that
1948 on SMP systems the preset will be applied to all CPUs,
1949 which is likely to cause problems if your CPUs need
1950 significantly divergent settings. An incorrect value
1951 will cause delays in the kernel to be wrong, leading to
1952 unpredictable I/O errors and other breakage. Although
1953 unlikely, in the extreme case this might damage your
1954 hardware.
1956 ltpc= [NET]
1957 Format: <io>,<irq>,<dma>
1959 machvec= [IA-64] Force the use of a particular machine-vector
1960 (machvec) in a generic kernel.
1961 Example: machvec=hpzx1_swiotlb
1963 machtype= [Loongson] Share the same kernel image file between different
1964 yeeloong laptop.
1965 Example: machtype=lemote-yeeloong-2f-7inch
1967 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1968 than or equal to this physical address is ignored.
1970 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1971 should make use of. maxcpus=n : n >= 0 limits the
1972 kernel to using 'n' processors. n=0 is a special case,
1973 it is equivalent to "nosmp", which also disables
1974 the IO APIC.
1976 max_loop= [LOOP] The number of loop block devices that get
1977 (loop.max_loop) unconditionally pre-created at init time. The default
1978 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1979 of statically allocating a predefined number, loop
1980 devices can be requested on-demand with the
1981 /dev/loop-control interface.
1983 mce [X86-32] Machine Check Exception
1985 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1987 md= [HW] RAID subsystems devices and level
1988 See Documentation/md.txt.
1990 mdacon= [MDA]
1991 Format: <first>,<last>
1992 Specifies range of consoles to be captured by the MDA.
1994 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1995 Amount of memory to be used when the kernel is not able
1996 to see the whole system memory or for test.
1997 [X86] Work as limiting max address. Use together
1998 with memmap= to avoid physical address space collisions.
1999 Without memmap= PCI devices could be placed at addresses
2000 belonging to unused RAM.
2002 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2003 memory.
2005 memchunk=nn[KMG]
2006 [KNL,SH] Allow user to override the default size for
2007 per-device physically contiguous DMA buffers.
2009 memmap=exactmap [KNL,X86] Enable setting of an exact
2010 E820 memory map, as specified by the user.
2011 Such memmap=exactmap lines can be constructed based on
2012 BIOS output or other requirements. See the memmap=nn@ss
2013 option description.
2015 memmap=nn[KMG]@ss[KMG]
2016 [KNL] Force usage of a specific region of memory.
2017 Region of memory to be used is from ss to ss+nn.
2019 memmap=nn[KMG]#ss[KMG]
2020 [KNL,ACPI] Mark specific memory as ACPI data.
2021 Region of memory to be marked is from ss to ss+nn.
2023 memmap=nn[KMG]$ss[KMG]
2024 [KNL,ACPI] Mark specific memory as reserved.
2025 Region of memory to be reserved is from ss to ss+nn.
2026 Example: Exclude memory from 0x18690000-0x1869ffff
2027 memmap=64K$0x18690000
2028 or
2029 memmap=0x10000$0x18690000
2031 memmap=nn[KMG]!ss[KMG]
2032 [KNL,X86] Mark specific memory as protected.
2033 Region of memory to be used, from ss to ss+nn.
2034 The memory region may be marked as e820 type 12 (0xc)
2035 and is NVDIMM or ADR memory.
2037 memory_corruption_check=0/1 [X86]
2038 Some BIOSes seem to corrupt the first 64k of
2039 memory when doing things like suspend/resume.
2040 Setting this option will scan the memory
2041 looking for corruption. Enabling this will
2042 both detect corruption and prevent the kernel
2043 from using the memory being corrupted.
2044 However, its intended as a diagnostic tool; if
2045 repeatable BIOS-originated corruption always
2046 affects the same memory, you can use memmap=
2047 to prevent the kernel from using that memory.
2049 memory_corruption_check_size=size [X86]
2050 By default it checks for corruption in the low
2051 64k, making this memory unavailable for normal
2052 use. Use this parameter to scan for
2053 corruption in more or less memory.
2055 memory_corruption_check_period=seconds [X86]
2056 By default it checks for corruption every 60
2057 seconds. Use this parameter to check at some
2058 other rate. 0 disables periodic checking.
2060 memtest= [KNL,X86,ARM] Enable memtest
2061 Format: <integer>
2062 default : 0 <disable>
2063 Specifies the number of memtest passes to be
2064 performed. Each pass selects another test
2065 pattern from a given set of patterns. Memtest
2066 fills the memory with this pattern, validates
2067 memory contents and reserves bad memory
2068 regions that are detected.
2070 meye.*= [HW] Set MotionEye Camera parameters
2071 See Documentation/video4linux/meye.txt.
2073 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2074 Multi-Function General Purpose Timers on AMD Geode
2075 platforms.
2077 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2078 the BIOS has incorrectly applied a workaround. TinyBIOS
2079 version 0.98 is known to be affected, 0.99 fixes the
2080 problem by letting the user disable the workaround.
2082 mga= [HW,DRM]
2084 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2085 physical address is ignored.
2087 mini2440= [ARM,HW,KNL]
2088 Format:[0..2][b][c][t]
2089 Default: "0tb"
2090 MINI2440 configuration specification:
2091 0 - The attached screen is the 3.5" TFT
2092 1 - The attached screen is the 7" TFT
2093 2 - The VGA Shield is attached (1024x768)
2094 Leaving out the screen size parameter will not load
2095 the TFT driver, and the framebuffer will be left
2096 unconfigured.
2097 b - Enable backlight. The TFT backlight pin will be
2098 linked to the kernel VESA blanking code and a GPIO
2099 LED. This parameter is not necessary when using the
2100 VGA shield.
2101 c - Enable the s3c camera interface.
2102 t - Reserved for enabling touchscreen support. The
2103 touchscreen support is not enabled in the mainstream
2104 kernel as of 2.6.30, a preliminary port can be found
2105 in the "bleeding edge" mini2440 support kernel at
2106 http://repo.or.cz/w/linux-2.6/mini2440.git
2108 mminit_loglevel=
2109 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2110 parameter allows control of the logging verbosity for
2111 the additional memory initialisation checks. A value
2112 of 0 disables mminit logging and a level of 4 will
2113 log everything. Information is printed at KERN_DEBUG
2114 so loglevel=8 may also need to be specified.
2116 module.sig_enforce
2117 [KNL] When CONFIG_MODULE_SIG is set, this means that
2118 modules without (valid) signatures will fail to load.
2119 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2120 is always true, so this option does nothing.
2122 mousedev.tap_time=
2123 [MOUSE] Maximum time between finger touching and
2124 leaving touchpad surface for touch to be considered
2125 a tap and be reported as a left button click (for
2126 touchpads working in absolute mode only).
2127 Format: <msecs>
2128 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2129 reporting absolute coordinates, such as tablets
2130 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2131 reporting absolute coordinates, such as tablets
2133 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2134 is similar to kernelcore except it specifies the
2135 amount of memory used for migratable allocations.
2136 If both kernelcore and movablecore is specified,
2137 then kernelcore will be at *least* the specified
2138 value but may be more. If movablecore on its own
2139 is specified, the administrator must be careful
2140 that the amount of memory usable for all allocations
2141 is not too small.
2143 movable_node [KNL,X86] Boot-time switch to enable the effects
2144 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2146 MTD_Partition= [MTD]
2147 Format: <name>,<region-number>,<size>,<offset>
2149 MTD_Region= [MTD] Format:
2150 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2152 mtdparts= [MTD]
2153 See drivers/mtd/cmdlinepart.c.
2155 multitce=off [PPC] This parameter disables the use of the pSeries
2156 firmware feature for updating multiple TCE entries
2157 at a time.
2159 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2161 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2163 boundary - index of last SLC block on Flex-OneNAND.
2164 The remaining blocks are configured as MLC blocks.
2165 lock - Configure if Flex-OneNAND boundary should be locked.
2166 Once locked, the boundary cannot be changed.
2167 1 indicates lock status, 0 indicates unlock status.
2169 mtdset= [ARM]
2170 ARM/S3C2412 JIVE boot control
2172 See arch/arm/mach-s3c2412/mach-jive.c
2174 mtouchusb.raw_coordinates=
2175 [HW] Make the MicroTouch USB driver use raw coordinates
2176 ('y', default) or cooked coordinates ('n')
2178 mtrr_chunk_size=nn[KMG] [X86]
2179 used for mtrr cleanup. It is largest continuous chunk
2180 that could hold holes aka. UC entries.
2182 mtrr_gran_size=nn[KMG] [X86]
2183 Used for mtrr cleanup. It is granularity of mtrr block.
2184 Default is 1.
2185 Large value could prevent small alignment from
2186 using up MTRRs.
2188 mtrr_spare_reg_nr=n [X86]
2189 Format: <integer>
2190 Range: 0,7 : spare reg number
2191 Default : 1
2192 Used for mtrr cleanup. It is spare mtrr entries number.
2193 Set to 2 or more if your graphical card needs more.
2195 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2197 netdev= [NET] Network devices parameters
2198 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2199 Note that mem_start is often overloaded to mean
2200 something different and driver-specific.
2201 This usage is only documented in each driver source
2202 file if at all.
2204 nf_conntrack.acct=
2205 [NETFILTER] Enable connection tracking flow accounting
2206 0 to disable accounting
2207 1 to enable accounting
2208 Default value is 0.
2210 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2211 See Documentation/filesystems/nfs/nfsroot.txt.
2213 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2214 See Documentation/filesystems/nfs/nfsroot.txt.
2216 nfsrootdebug [NFS] enable nfsroot debugging messages.
2217 See Documentation/filesystems/nfs/nfsroot.txt.
2219 nfs.callback_tcpport=
2220 [NFS] set the TCP port on which the NFSv4 callback
2221 channel should listen.
2223 nfs.cache_getent=
2224 [NFS] sets the pathname to the program which is used
2225 to update the NFS client cache entries.
2227 nfs.cache_getent_timeout=
2228 [NFS] sets the timeout after which an attempt to
2229 update a cache entry is deemed to have failed.
2231 nfs.idmap_cache_timeout=
2232 [NFS] set the maximum lifetime for idmapper cache
2233 entries.
2235 nfs.enable_ino64=
2236 [NFS] enable 64-bit inode numbers.
2237 If zero, the NFS client will fake up a 32-bit inode
2238 number for the readdir() and stat() syscalls instead
2239 of returning the full 64-bit number.
2240 The default is to return 64-bit inode numbers.
2242 nfs.max_session_slots=
2243 [NFSv4.1] Sets the maximum number of session slots
2244 the client will attempt to negotiate with the server.
2245 This limits the number of simultaneous RPC requests
2246 that the client can send to the NFSv4.1 server.
2247 Note that there is little point in setting this
2248 value higher than the max_tcp_slot_table_limit.
2250 nfs.nfs4_disable_idmapping=
2251 [NFSv4] When set to the default of '1', this option
2252 ensures that both the RPC level authentication
2253 scheme and the NFS level operations agree to use
2254 numeric uids/gids if the mount is using the
2255 'sec=sys' security flavour. In effect it is
2256 disabling idmapping, which can make migration from
2257 legacy NFSv2/v3 systems to NFSv4 easier.
2258 Servers that do not support this mode of operation
2259 will be autodetected by the client, and it will fall
2260 back to using the idmapper.
2261 To turn off this behaviour, set the value to '0'.
2262 nfs.nfs4_unique_id=
2263 [NFS4] Specify an additional fixed unique ident-
2264 ification string that NFSv4 clients can insert into
2265 their nfs_client_id4 string. This is typically a
2266 UUID that is generated at system install time.
2268 nfs.send_implementation_id =
2269 [NFSv4.1] Send client implementation identification
2270 information in exchange_id requests.
2271 If zero, no implementation identification information
2272 will be sent.
2273 The default is to send the implementation identification
2274 information.
2276 nfs.recover_lost_locks =
2277 [NFSv4] Attempt to recover locks that were lost due
2278 to a lease timeout on the server. Please note that
2279 doing this risks data corruption, since there are
2280 no guarantees that the file will remain unchanged
2281 after the locks are lost.
2282 If you want to enable the kernel legacy behaviour of
2283 attempting to recover these locks, then set this
2284 parameter to '1'.
2285 The default parameter value of '0' causes the kernel
2286 not to attempt recovery of lost locks.
2288 nfs4.layoutstats_timer =
2289 [NFSv4.2] Change the rate at which the kernel sends
2290 layoutstats to the pNFS metadata server.
2292 Setting this to value to 0 causes the kernel to use
2293 whatever value is the default set by the layout
2294 driver. A non-zero value sets the minimum interval
2295 in seconds between layoutstats transmissions.
2297 nfsd.nfs4_disable_idmapping=
2298 [NFSv4] When set to the default of '1', the NFSv4
2299 server will return only numeric uids and gids to
2300 clients using auth_sys, and will accept numeric uids
2301 and gids from such clients. This is intended to ease
2302 migration from NFSv2/v3.
2304 objlayoutdriver.osd_login_prog=
2305 [NFS] [OBJLAYOUT] sets the pathname to the program which
2306 is used to automatically discover and login into new
2307 osd-targets. Please see:
2308 Documentation/filesystems/pnfs.txt for more explanations
2310 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2311 when a NMI is triggered.
2312 Format: [state][,regs][,debounce][,die]
2314 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2315 Format: [panic,][nopanic,][num]
2316 Valid num: 0 or 1
2317 0 - turn nmi_watchdog off
2318 1 - turn nmi_watchdog on
2319 When panic is specified, panic when an NMI watchdog
2320 timeout occurs (or 'nopanic' to override the opposite
2321 default).
2322 This is useful when you use a panic=... timeout and
2323 need the box quickly up again.
2325 netpoll.carrier_timeout=
2326 [NET] Specifies amount of time (in seconds) that
2327 netpoll should wait for a carrier. By default netpoll
2328 waits 4 seconds.
2330 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2331 emulation library even if a 387 maths coprocessor
2332 is present.
2334 no_console_suspend
2335 [HW] Never suspend the console
2336 Disable suspending of consoles during suspend and
2337 hibernate operations. Once disabled, debugging
2338 messages can reach various consoles while the rest
2339 of the system is being put to sleep (ie, while
2340 debugging driver suspend/resume hooks). This may
2341 not work reliably with all consoles, but is known
2342 to work with serial and VGA consoles.
2343 To facilitate more flexible debugging, we also add
2344 console_suspend, a printk module parameter to control
2345 it. Users could use console_suspend (usually
2346 /sys/module/printk/parameters/console_suspend) to
2347 turn on/off it dynamically.
2349 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2350 caches in the slab allocator. Saves per-node memory,
2351 but will impact performance.
2353 noalign [KNL,ARM]
2355 noapic [SMP,APIC] Tells the kernel to not make use of any
2356 IOAPICs that may be present in the system.
2358 noautogroup Disable scheduler automatic task group creation.
2360 nobats [PPC] Do not use BATs for mapping kernel lowmem
2361 on "Classic" PPC cores.
2363 nocache [ARM]
2365 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2367 nodelayacct [KNL] Disable per-task delay accounting
2369 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2371 nodsp [SH] Disable hardware DSP at boot time.
2373 noefi Disable EFI runtime services support.
2375 noexec [IA-64]
2377 noexec [X86]
2378 On X86-32 available only on PAE configured kernels.
2379 noexec=on: enable non-executable mappings (default)
2380 noexec=off: disable non-executable mappings
2382 nosmap [X86]
2383 Disable SMAP (Supervisor Mode Access Prevention)
2384 even if it is supported by processor.
2386 nosmep [X86]
2387 Disable SMEP (Supervisor Mode Execution Prevention)
2388 even if it is supported by processor.
2390 noexec32 [X86-64]
2391 This affects only 32-bit executables.
2392 noexec32=on: enable non-executable mappings (default)
2393 read doesn't imply executable mappings
2394 noexec32=off: disable non-executable mappings
2395 read implies executable mappings
2397 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2399 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2400 register save and restore. The kernel will only save
2401 legacy floating-point registers on task switch.
2403 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2405 noxsave [BUGS=X86] Disables x86 extended register state save
2406 and restore using xsave. The kernel will fallback to
2407 enabling legacy floating-point and sse state.
2409 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2410 register states. The kernel will fall back to use
2411 xsave to save the states. By using this parameter,
2412 performance of saving the states is degraded because
2413 xsave doesn't support modified optimization while
2414 xsaveopt supports it on xsaveopt enabled systems.
2416 noxsaves [X86] Disables xsaves and xrstors used in saving and
2417 restoring x86 extended register state in compacted
2418 form of xsave area. The kernel will fall back to use
2419 xsaveopt and xrstor to save and restore the states
2420 in standard form of xsave area. By using this
2421 parameter, xsave area per process might occupy more
2422 memory on xsaves enabled systems.
2424 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2425 wfi(ARM) instruction doesn't work correctly and not to
2426 use it. This is also useful when using JTAG debugger.
2428 no_file_caps Tells the kernel not to honor file capabilities. The
2429 only way then for a file to be executed with privilege
2430 is to be setuid root or executed by root.
2432 nohalt [IA-64] Tells the kernel not to use the power saving
2433 function PAL_HALT_LIGHT when idle. This increases
2434 power-consumption. On the positive side, it reduces
2435 interrupt wake-up latency, which may improve performance
2436 in certain environments such as networked servers or
2437 real-time systems.
2439 nohibernate [HIBERNATION] Disable hibernation and resume.
2441 nohz= [KNL] Boottime enable/disable dynamic ticks
2442 Valid arguments: on, off
2443 Default: on
2445 nohz_full= [KNL,BOOT]
2446 In kernels built with CONFIG_NO_HZ_FULL=y, set
2447 the specified list of CPUs whose tick will be stopped
2448 whenever possible. The boot CPU will be forced outside
2449 the range to maintain the timekeeping.
2450 The CPUs in this range must also be included in the
2451 rcu_nocbs= set.
2453 noiotrap [SH] Disables trapped I/O port accesses.
2455 noirqdebug [X86-32] Disables the code which attempts to detect and
2456 disable unhandled interrupt sources.
2458 no_timer_check [X86,APIC] Disables the code which tests for
2459 broken timer IRQ sources.
2461 noisapnp [ISAPNP] Disables ISA PnP code.
2463 noinitrd [RAM] Tells the kernel not to load any configured
2464 initial RAM disk.
2466 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2467 remapping.
2468 [Deprecated - use intremap=off]
2470 nointroute [IA-64]
2472 nojitter [IA-64] Disables jitter checking for ITC timers.
2474 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2476 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2477 fault handling.
2479 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2480 steal time is computed, but won't influence scheduler
2481 behaviour
2483 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2485 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2487 noltlbs [PPC] Do not use large page/tlb entries for kernel
2488 lowmem mapping on PPC40x.
2490 nomca [IA-64] Disable machine check abort handling
2492 nomce [X86-32] Disable Machine Check Exception
2494 nomfgpt [X86-32] Disable Multi-Function General Purpose
2495 Timer usage (for AMD Geode machines).
2497 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2498 shutdown the other cpus. Instead use the REBOOT_VECTOR
2499 irq.
2501 nomodule Disable module load
2503 nopat [X86] Disable PAT (page attribute table extension of
2504 pagetables) support.
2506 norandmaps Don't use address space randomization. Equivalent to
2507 echo 0 > /proc/sys/kernel/randomize_va_space
2509 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2511 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2512 with UP alternatives
2514 nordrand [X86] Disable kernel use of the RDRAND and
2515 RDSEED instructions even if they are supported
2516 by the processor. RDRAND and RDSEED are still
2517 available to user space applications.
2519 noresume [SWSUSP] Disables resume and restores original swap
2520 space.
2522 no-scroll [VGA] Disables scrollback.
2523 This is required for the Braillex ib80-piezo Braille
2524 reader made by F.H. Papenmeier (Germany).
2526 nosbagart [IA-64]
2528 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2530 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2531 and disable the IO APIC. legacy for "maxcpus=0".
2533 nosoftlockup [KNL] Disable the soft-lockup detector.
2535 nosync [HW,M68K] Disables sync negotiation for all devices.
2537 notsc [BUGS=X86-32] Disable Time Stamp Counter
2539 nousb [USB] Disable the USB subsystem
2541 nowatchdog [KNL] Disable both lockup detectors, i.e.
2542 soft-lockup and NMI watchdog (hard-lockup).
2544 nowb [ARM]
2546 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2548 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2549 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2550 Some features depend on CPU0. Known dependencies are:
2551 1. Resume from suspend/hibernate depends on CPU0.
2552 Suspend/hibernate will fail if CPU0 is offline and you
2553 need to online CPU0 before suspend/hibernate.
2554 2. PIC interrupts also depend on CPU0. CPU0 can't be
2555 removed if a PIC interrupt is detected.
2556 It's said poweroff/reboot may depend on CPU0 on some
2557 machines although I haven't seen such issues so far
2558 after CPU0 is offline on a few tested machines.
2559 If the dependencies are under your control, you can
2560 turn on cpu0_hotplug.
2562 nptcg= [IA-64] Override max number of concurrent global TLB
2563 purges which is reported from either PAL_VM_SUMMARY or
2564 SAL PALO.
2566 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2567 could support. nr_cpus=n : n >= 1 limits the kernel to
2568 supporting 'n' processors. Later in runtime you can not
2569 use hotplug cpu feature to put more cpu back to online.
2570 just like you compile the kernel NR_CPUS=n
2572 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2574 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2575 Allowed values are enable and disable
2577 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2578 one of ['zone', 'node', 'default'] can be specified
2579 This can be set from sysctl after boot.
2580 See Documentation/sysctl/vm.txt for details.
2582 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2583 See Documentation/debugging-via-ohci1394.txt for more
2584 info.
2586 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2587 Rather than timing out after 20 ms if an EC
2588 command is not properly ACKed, override the length
2589 of the timeout. We have interrupts disabled while
2590 waiting for the ACK, so if this is set too high
2591 interrupts *may* be lost!
2593 omap_mux= [OMAP] Override bootloader pin multiplexing.
2594 Format: <mux_mode0.mode_name=value>...
2595 For example, to override I2C bus2:
2596 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2598 oprofile.timer= [HW]
2599 Use timer interrupt instead of performance counters
2601 oprofile.cpu_type= Force an oprofile cpu type
2602 This might be useful if you have an older oprofile
2603 userland or if you want common events.
2604 Format: { arch_perfmon }
2605 arch_perfmon: [X86] Force use of architectural
2606 perfmon on Intel CPUs instead of the
2607 CPU specific event set.
2608 timer: [X86] Force use of architectural NMI
2609 timer mode (see also oprofile.timer
2610 for generic hr timer mode)
2611 [s390] Force legacy basic mode sampling
2612 (report cpu_type "timer")
2614 oops=panic Always panic on oopses. Default is to just kill the
2615 process, but there is a small probability of
2616 deadlocking the machine.
2617 This will also cause panics on machine check exceptions.
2618 Useful together with panic=30 to trigger a reboot.
2620 OSS [HW,OSS]
2621 See Documentation/sound/oss/oss-parameters.txt
2623 page_owner= [KNL] Boot-time page_owner enabling option.
2624 Storage of the information about who allocated
2625 each page is disabled in default. With this switch,
2626 we can turn it on.
2627 on: enable the feature
2629 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2630 timeout > 0: seconds before rebooting
2631 timeout = 0: wait forever
2632 timeout < 0: reboot immediately
2633 Format: <timeout>
2635 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2636 on a WARN().
2638 crash_kexec_post_notifiers
2639 Run kdump after running panic-notifiers and dumping
2640 kmsg. This only for the users who doubt kdump always
2641 succeeds in any situation.
2642 Note that this also increases risks of kdump failure,
2643 because some panic notifiers can make the crashed
2644 kernel more unstable.
2646 parkbd.port= [HW] Parallel port number the keyboard adapter is
2647 connected to, default is 0.
2648 Format: <parport#>
2649 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2650 0 for XT, 1 for AT (default is AT).
2651 Format: <mode>
2653 parport= [HW,PPT] Specify parallel ports. 0 disables.
2654 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2655 Use 'auto' to force the driver to use any
2656 IRQ/DMA settings detected (the default is to
2657 ignore detected IRQ/DMA settings because of
2658 possible conflicts). You can specify the base
2659 address, IRQ, and DMA settings; IRQ and DMA
2660 should be numbers, or 'auto' (for using detected
2661 settings on that particular port), or 'nofifo'
2662 (to avoid using a FIFO even if it is detected).
2663 Parallel ports are assigned in the order they
2664 are specified on the command line, starting
2665 with parport0.
2667 parport_init_mode= [HW,PPT]
2668 Configure VIA parallel port to operate in
2669 a specific mode. This is necessary on Pegasos
2670 computer where firmware has no options for setting
2671 up parallel port mode and sets it to spp.
2672 Currently this function knows 686a and 8231 chips.
2673 Format: [spp|ps2|epp|ecp|ecpepp]
2675 pause_on_oops=
2676 Halt all CPUs after the first oops has been printed for
2677 the specified number of seconds. This is to be used if
2678 your oopses keep scrolling off the screen.
2680 pcbit= [HW,ISDN]
2682 pcd. [PARIDE]
2683 See header of drivers/block/paride/pcd.c.
2684 See also Documentation/blockdev/paride.txt.
2686 pci=option[,option...] [PCI] various PCI subsystem options:
2687 earlydump [X86] dump PCI config space before the kernel
2688 changes anything
2689 off [X86] don't probe for the PCI bus
2690 bios [X86-32] force use of PCI BIOS, don't access
2691 the hardware directly. Use this if your machine
2692 has a non-standard PCI host bridge.
2693 nobios [X86-32] disallow use of PCI BIOS, only direct
2694 hardware access methods are allowed. Use this
2695 if you experience crashes upon bootup and you
2696 suspect they are caused by the BIOS.
2697 conf1 [X86] Force use of PCI Configuration
2698 Mechanism 1.
2699 conf2 [X86] Force use of PCI Configuration
2700 Mechanism 2.
2701 noaer [PCIE] If the PCIEAER kernel config parameter is
2702 enabled, this kernel boot option can be used to
2703 disable the use of PCIE advanced error reporting.
2704 nodomains [PCI] Disable support for multiple PCI
2705 root domains (aka PCI segments, in ACPI-speak).
2706 nommconf [X86] Disable use of MMCONFIG for PCI
2707 Configuration
2708 check_enable_amd_mmconf [X86] check for and enable
2709 properly configured MMIO access to PCI
2710 config space on AMD family 10h CPU
2711 nomsi [MSI] If the PCI_MSI kernel config parameter is
2712 enabled, this kernel boot option can be used to
2713 disable the use of MSI interrupts system-wide.
2714 noioapicquirk [APIC] Disable all boot interrupt quirks.
2715 Safety option to keep boot IRQs enabled. This
2716 should never be necessary.
2717 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2718 primary IO-APIC for bridges that cannot disable
2719 boot IRQs. This fixes a source of spurious IRQs
2720 when the system masks IRQs.
2721 noioapicreroute [APIC] Disable workaround that uses the
2722 boot IRQ equivalent of an IRQ that connects to
2723 a chipset where boot IRQs cannot be disabled.
2724 The opposite of ioapicreroute.
2725 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2726 routing table. These calls are known to be buggy
2727 on several machines and they hang the machine
2728 when used, but on other computers it's the only
2729 way to get the interrupt routing table. Try
2730 this option if the kernel is unable to allocate
2731 IRQs or discover secondary PCI buses on your
2732 motherboard.
2733 rom [X86] Assign address space to expansion ROMs.
2734 Use with caution as certain devices share
2735 address decoders between ROMs and other
2736 resources.
2737 norom [X86] Do not assign address space to
2738 expansion ROMs that do not already have
2739 BIOS assigned address ranges.
2740 nobar [X86] Do not assign address space to the
2741 BARs that weren't assigned by the BIOS.
2742 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2743 assigned automatically to PCI devices. You can
2744 make the kernel exclude IRQs of your ISA cards
2745 this way.
2746 pirqaddr=0xAAAAA [X86] Specify the physical address
2747 of the PIRQ table (normally generated
2748 by the BIOS) if it is outside the
2749 F0000h-100000h range.
2750 lastbus=N [X86] Scan all buses thru bus #N. Can be
2751 useful if the kernel is unable to find your
2752 secondary buses and you want to tell it
2753 explicitly which ones they are.
2754 assign-busses [X86] Always assign all PCI bus
2755 numbers ourselves, overriding
2756 whatever the firmware may have done.
2757 usepirqmask [X86] Honor the possible IRQ mask stored
2758 in the BIOS $PIR table. This is needed on
2759 some systems with broken BIOSes, notably
2760 some HP Pavilion N5400 and Omnibook XE3
2761 notebooks. This will have no effect if ACPI
2762 IRQ routing is enabled.
2763 noacpi [X86] Do not use ACPI for IRQ routing
2764 or for PCI scanning.
2765 use_crs [X86] Use PCI host bridge window information
2766 from ACPI. On BIOSes from 2008 or later, this
2767 is enabled by default. If you need to use this,
2768 please report a bug.
2769 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2770 If you need to use this, please report a bug.
2771 routeirq Do IRQ routing for all PCI devices.
2772 This is normally done in pci_enable_device(),
2773 so this option is a temporary workaround
2774 for broken drivers that don't call it.
2775 skip_isa_align [X86] do not align io start addr, so can
2776 handle more pci cards
2777 firmware [ARM] Do not re-enumerate the bus but instead
2778 just use the configuration from the
2779 bootloader. This is currently used on
2780 IXP2000 systems where the bus has to be
2781 configured a certain way for adjunct CPUs.
2782 noearly [X86] Don't do any early type 1 scanning.
2783 This might help on some broken boards which
2784 machine check when some devices' config space
2785 is read. But various workarounds are disabled
2786 and some IOMMU drivers will not work.
2787 bfsort Sort PCI devices into breadth-first order.
2788 This sorting is done to get a device
2789 order compatible with older (<= 2.4) kernels.
2790 nobfsort Don't sort PCI devices into breadth-first order.
2791 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2792 tuning and use the BIOS-configured MPS defaults.
2793 pcie_bus_safe Set every device's MPS to the largest value
2794 supported by all devices below the root complex.
2795 pcie_bus_perf Set device MPS to the largest allowable MPS
2796 based on its parent bus. Also set MRRS (Max
2797 Read Request Size) to the largest supported
2798 value (no larger than the MPS that the device
2799 or bus can support) for best performance.
2800 pcie_bus_peer2peer Set every device's MPS to 128B, which
2801 every device is guaranteed to support. This
2802 configuration allows peer-to-peer DMA between
2803 any pair of devices, possibly at the cost of
2804 reduced performance. This also guarantees
2805 that hot-added devices will work.
2806 cbiosize=nn[KMG] The fixed amount of bus space which is
2807 reserved for the CardBus bridge's IO window.
2808 The default value is 256 bytes.
2809 cbmemsize=nn[KMG] The fixed amount of bus space which is
2810 reserved for the CardBus bridge's memory
2811 window. The default value is 64 megabytes.
2812 resource_alignment=
2813 Format:
2814 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2815 Specifies alignment and device to reassign
2816 aligned memory resources.
2817 If <order of align> is not specified,
2818 PAGE_SIZE is used as alignment.
2819 PCI-PCI bridge can be specified, if resource
2820 windows need to be expanded.
2821 ecrc= Enable/disable PCIe ECRC (transaction layer
2822 end-to-end CRC checking).
2823 bios: Use BIOS/firmware settings. This is the
2824 the default.
2825 off: Turn ECRC off
2826 on: Turn ECRC on.
2827 hpiosize=nn[KMG] The fixed amount of bus space which is
2828 reserved for hotplug bridge's IO window.
2829 Default size is 256 bytes.
2830 hpmemsize=nn[KMG] The fixed amount of bus space which is
2831 reserved for hotplug bridge's memory window.
2832 Default size is 2 megabytes.
2833 realloc= Enable/disable reallocating PCI bridge resources
2834 if allocations done by BIOS are too small to
2835 accommodate resources required by all child
2836 devices.
2837 off: Turn realloc off
2838 on: Turn realloc on
2839 realloc same as realloc=on
2840 noari do not use PCIe ARI.
2841 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2842 only look for one device below a PCIe downstream
2843 port.
2845 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2846 Management.
2847 off Disable ASPM.
2848 force Enable ASPM even on devices that claim not to support it.
2849 WARNING: Forcing ASPM on may cause system lockups.
2851 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2852 nomsi Do not use MSI for PCI Express Native Hotplug (this
2853 makes all PCIe ports use INTx for hotplug services).
2855 pcie_ports= [PCIE] PCIe ports handling:
2856 auto Ask the BIOS whether or not to use native PCIe services
2857 associated with PCIe ports (PME, hot-plug, AER). Use
2858 them only if that is allowed by the BIOS.
2859 native Use native PCIe services associated with PCIe ports
2860 unconditionally.
2861 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2862 ports driver.
2864 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2865 nomsi Do not use MSI for native PCIe PME signaling (this makes
2866 all PCIe root ports use INTx for all services).
2868 pcmv= [HW,PCMCIA] BadgePAD 4
2870 pd_ignore_unused
2871 [PM]
2872 Keep all power-domains already enabled by bootloader on,
2873 even if no driver has claimed them. This is useful
2874 for debug and development, but should not be
2875 needed on a platform with proper driver support.
2877 pd. [PARIDE]
2878 See Documentation/blockdev/paride.txt.
2880 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2881 boot time.
2882 Format: { 0 | 1 }
2883 See arch/parisc/kernel/pdc_chassis.c
2885 percpu_alloc= Select which percpu first chunk allocator to use.
2886 Currently supported values are "embed" and "page".
2887 Archs may support subset or none of the selections.
2888 See comments in mm/percpu.c for details on each
2889 allocator. This parameter is primarily for debugging
2890 and performance comparison.
2892 pf. [PARIDE]
2893 See Documentation/blockdev/paride.txt.
2895 pg. [PARIDE]
2896 See Documentation/blockdev/paride.txt.
2898 pirq= [SMP,APIC] Manual mp-table setup
2899 See Documentation/x86/i386/IO-APIC.txt.
2901 plip= [PPT,NET] Parallel port network link
2902 Format: { parport<nr> | timid | 0 }
2903 See also Documentation/parport.txt.
2905 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2906 Override pmtimer IOPort with a hex value.
2907 e.g. pmtmr=0x508
2909 pnp.debug=1 [PNP]
2910 Enable PNP debug messages (depends on the
2911 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2912 via /sys/module/pnp/parameters/debug. We always show
2913 current resource usage; turning this on also shows
2914 possible settings and some assignment information.
2916 pnpacpi= [ACPI]
2917 { off }
2919 pnpbios= [ISAPNP]
2920 { on | off | curr | res | no-curr | no-res }
2922 pnp_reserve_irq=
2923 [ISAPNP] Exclude IRQs for the autoconfiguration
2925 pnp_reserve_dma=
2926 [ISAPNP] Exclude DMAs for the autoconfiguration
2928 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2929 Ranges are in pairs (I/O port base and size).
2931 pnp_reserve_mem=
2932 [ISAPNP] Exclude memory regions for the
2933 autoconfiguration.
2934 Ranges are in pairs (memory base and size).
2936 ports= [IP_VS_FTP] IPVS ftp helper module
2937 Default is 21.
2938 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2939 may be specified.
2940 Format: <port>,<port>....
2942 print-fatal-signals=
2943 [KNL] debug: print fatal signals
2945 If enabled, warn about various signal handling
2946 related application anomalies: too many signals,
2947 too many POSIX.1 timers, fatal signals causing a
2948 coredump - etc.
2950 If you hit the warning due to signal overflow,
2951 you might want to try "ulimit -i unlimited".
2953 default: off.
2955 printk.always_kmsg_dump=
2956 Trigger kmsg_dump for cases other than kernel oops or
2957 panics
2958 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2959 default: disabled
2961 printk.time= Show timing data prefixed to each printk message line
2962 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2964 processor.max_cstate= [HW,ACPI]
2965 Limit processor to maximum C-state
2966 max_cstate=9 overrides any DMI blacklist limit.
2968 processor.nocst [HW,ACPI]
2969 Ignore the _CST method to determine C-states,
2970 instead using the legacy FADT method
2972 profile= [KNL] Enable kernel profiling via /proc/profile
2973 Format: [schedule,]<number>
2974 Param: "schedule" - profile schedule points.
2975 Param: <number> - step/bucket size as a power of 2 for
2976 statistical time based profiling.
2977 Param: "sleep" - profile D-state sleeping (millisecs).
2978 Requires CONFIG_SCHEDSTATS
2979 Param: "kvm" - profile VM exits.
2981 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2982 before loading.
2983 See Documentation/blockdev/ramdisk.txt.
2985 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2986 probe for; one of (bare|imps|exps|lifebook|any).
2987 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2988 per second.
2989 psmouse.resetafter= [HW,MOUSE]
2990 Try to reset the device after so many bad packets
2991 (0 = never).
2992 psmouse.resolution=
2993 [HW,MOUSE] Set desired mouse resolution, in dpi.
2994 psmouse.smartscroll=
2995 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2996 0 = disabled, 1 = enabled (default).
2998 pstore.backend= Specify the name of the pstore backend to use
3000 pt. [PARIDE]
3001 See Documentation/blockdev/paride.txt.
3003 pty.legacy_count=
3004 [KNL] Number of legacy pty's. Overwrites compiled-in
3005 default number.
3007 quiet [KNL] Disable most log messages
3009 r128= [HW,DRM]
3011 raid= [HW,RAID]
3012 See Documentation/md.txt.
3014 ramdisk_blocksize= [RAM]
3015 See Documentation/blockdev/ramdisk.txt.
3017 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3018 See Documentation/blockdev/ramdisk.txt.
3020 rcu_nocbs= [KNL]
3021 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3022 the specified list of CPUs to be no-callback CPUs.
3023 Invocation of these CPUs' RCU callbacks will
3024 be offloaded to "rcuox/N" kthreads created for
3025 that purpose, where "x" is "b" for RCU-bh, "p"
3026 for RCU-preempt, and "s" for RCU-sched, and "N"
3027 is the CPU number. This reduces OS jitter on the
3028 offloaded CPUs, which can be useful for HPC and
3029 real-time workloads. It can also improve energy
3030 efficiency for asymmetric multiprocessors.
3032 rcu_nocb_poll [KNL]
3033 Rather than requiring that offloaded CPUs
3034 (specified by rcu_nocbs= above) explicitly
3035 awaken the corresponding "rcuoN" kthreads,
3036 make these kthreads poll for callbacks.
3037 This improves the real-time response for the
3038 offloaded CPUs by relieving them of the need to
3039 wake up the corresponding kthread, but degrades
3040 energy efficiency by requiring that the kthreads
3041 periodically wake up to do the polling.
3043 rcutree.blimit= [KNL]
3044 Set maximum number of finished RCU callbacks to
3045 process in one batch.
3047 rcutree.dump_tree= [KNL]
3048 Dump the structure of the rcu_node combining tree
3049 out at early boot. This is used for diagnostic
3050 purposes, to verify correct tree setup.
3052 rcutree.gp_cleanup_delay= [KNL]
3053 Set the number of jiffies to delay each step of
3054 RCU grace-period cleanup. This only has effect
3055 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3057 rcutree.gp_init_delay= [KNL]
3058 Set the number of jiffies to delay each step of
3059 RCU grace-period initialization. This only has
3060 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3061 is set.
3063 rcutree.gp_preinit_delay= [KNL]
3064 Set the number of jiffies to delay each step of
3065 RCU grace-period pre-initialization, that is,
3066 the propagation of recent CPU-hotplug changes up
3067 the rcu_node combining tree. This only has effect
3068 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3070 rcutree.rcu_fanout_exact= [KNL]
3071 Disable autobalancing of the rcu_node combining
3072 tree. This is used by rcutorture, and might
3073 possibly be useful for architectures having high
3074 cache-to-cache transfer latencies.
3076 rcutree.rcu_fanout_leaf= [KNL]
3077 Increase the number of CPUs assigned to each
3078 leaf rcu_node structure. Useful for very large
3079 systems.
3081 rcutree.jiffies_till_sched_qs= [KNL]
3082 Set required age in jiffies for a
3083 given grace period before RCU starts
3084 soliciting quiescent-state help from
3085 rcu_note_context_switch().
3087 rcutree.jiffies_till_first_fqs= [KNL]
3088 Set delay from grace-period initialization to
3089 first attempt to force quiescent states.
3090 Units are jiffies, minimum value is zero,
3091 and maximum value is HZ.
3093 rcutree.jiffies_till_next_fqs= [KNL]
3094 Set delay between subsequent attempts to force
3095 quiescent states. Units are jiffies, minimum
3096 value is one, and maximum value is HZ.
3098 rcutree.kthread_prio= [KNL,BOOT]
3099 Set the SCHED_FIFO priority of the RCU per-CPU
3100 kthreads (rcuc/N). This value is also used for
3101 the priority of the RCU boost threads (rcub/N)
3102 and for the RCU grace-period kthreads (rcu_bh,
3103 rcu_preempt, and rcu_sched). If RCU_BOOST is
3104 set, valid values are 1-99 and the default is 1
3105 (the least-favored priority). Otherwise, when
3106 RCU_BOOST is not set, valid values are 0-99 and
3107 the default is zero (non-realtime operation).
3109 rcutree.rcu_nocb_leader_stride= [KNL]
3110 Set the number of NOCB kthread groups, which
3111 defaults to the square root of the number of
3112 CPUs. Larger numbers reduces the wakeup overhead
3113 on the per-CPU grace-period kthreads, but increases
3114 that same overhead on each group's leader.
3116 rcutree.qhimark= [KNL]
3117 Set threshold of queued RCU callbacks beyond which
3118 batch limiting is disabled.
3120 rcutree.qlowmark= [KNL]
3121 Set threshold of queued RCU callbacks below which
3122 batch limiting is re-enabled.
3124 rcutree.rcu_idle_gp_delay= [KNL]
3125 Set wakeup interval for idle CPUs that have
3126 RCU callbacks (RCU_FAST_NO_HZ=y).
3128 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3129 Set wakeup interval for idle CPUs that have
3130 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3131 Lazy RCU callbacks are those which RCU can
3132 prove do nothing more than free memory.
3134 rcutorture.cbflood_inter_holdoff= [KNL]
3135 Set holdoff time (jiffies) between successive
3136 callback-flood tests.
3138 rcutorture.cbflood_intra_holdoff= [KNL]
3139 Set holdoff time (jiffies) between successive
3140 bursts of callbacks within a given callback-flood
3141 test.
3143 rcutorture.cbflood_n_burst= [KNL]
3144 Set the number of bursts making up a given
3145 callback-flood test. Set this to zero to
3146 disable callback-flood testing.
3148 rcutorture.cbflood_n_per_burst= [KNL]
3149 Set the number of callbacks to be registered
3150 in a given burst of a callback-flood test.
3152 rcutorture.fqs_duration= [KNL]
3153 Set duration of force_quiescent_state bursts
3154 in microseconds.
3156 rcutorture.fqs_holdoff= [KNL]
3157 Set holdoff time within force_quiescent_state bursts
3158 in microseconds.
3160 rcutorture.fqs_stutter= [KNL]
3161 Set wait time between force_quiescent_state bursts
3162 in seconds.
3164 rcutorture.gp_cond= [KNL]
3165 Use conditional/asynchronous update-side
3166 primitives, if available.
3168 rcutorture.gp_exp= [KNL]
3169 Use expedited update-side primitives, if available.
3171 rcutorture.gp_normal= [KNL]
3172 Use normal (non-expedited) asynchronous
3173 update-side primitives, if available.
3175 rcutorture.gp_sync= [KNL]
3176 Use normal (non-expedited) synchronous
3177 update-side primitives, if available. If all
3178 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3179 rcutorture.gp_normal=, and rcutorture.gp_sync=
3180 are zero, rcutorture acts as if is interpreted
3181 they are all non-zero.
3183 rcutorture.n_barrier_cbs= [KNL]
3184 Set callbacks/threads for rcu_barrier() testing.
3186 rcutorture.nfakewriters= [KNL]
3187 Set number of concurrent RCU writers. These just
3188 stress RCU, they don't participate in the actual
3189 test, hence the "fake".
3191 rcutorture.nreaders= [KNL]
3192 Set number of RCU readers. The value -1 selects
3193 N-1, where N is the number of CPUs. A value
3194 "n" less than -1 selects N-n-2, where N is again
3195 the number of CPUs. For example, -2 selects N
3196 (the number of CPUs), -3 selects N+1, and so on.
3198 rcutorture.object_debug= [KNL]
3199 Enable debug-object double-call_rcu() testing.
3201 rcutorture.onoff_holdoff= [KNL]
3202 Set time (s) after boot for CPU-hotplug testing.
3204 rcutorture.onoff_interval= [KNL]
3205 Set time (s) between CPU-hotplug operations, or
3206 zero to disable CPU-hotplug testing.
3208 rcutorture.shuffle_interval= [KNL]
3209 Set task-shuffle interval (s). Shuffling tasks
3210 allows some CPUs to go into dyntick-idle mode
3211 during the rcutorture test.
3213 rcutorture.shutdown_secs= [KNL]
3214 Set time (s) after boot system shutdown. This
3215 is useful for hands-off automated testing.
3217 rcutorture.stall_cpu= [KNL]
3218 Duration of CPU stall (s) to test RCU CPU stall
3219 warnings, zero to disable.
3221 rcutorture.stall_cpu_holdoff= [KNL]
3222 Time to wait (s) after boot before inducing stall.
3224 rcutorture.stat_interval= [KNL]
3225 Time (s) between statistics printk()s.
3227 rcutorture.stutter= [KNL]
3228 Time (s) to stutter testing, for example, specifying
3229 five seconds causes the test to run for five seconds,
3230 wait for five seconds, and so on. This tests RCU's
3231 ability to transition abruptly to and from idle.
3233 rcutorture.test_boost= [KNL]
3234 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3235 "Maybe" means test if the RCU implementation
3236 under test support RCU priority boosting.
3238 rcutorture.test_boost_duration= [KNL]
3239 Duration (s) of each individual boost test.
3241 rcutorture.test_boost_interval= [KNL]
3242 Interval (s) between each boost test.
3244 rcutorture.test_no_idle_hz= [KNL]
3245 Test RCU's dyntick-idle handling. See also the
3246 rcutorture.shuffle_interval parameter.
3248 rcutorture.torture_runnable= [BOOT]
3249 Start rcutorture running at boot time.
3251 rcutorture.torture_type= [KNL]
3252 Specify the RCU implementation to test.
3254 rcutorture.verbose= [KNL]
3255 Enable additional printk() statements.
3257 rcupdate.rcu_expedited= [KNL]
3258 Use expedited grace-period primitives, for
3259 example, synchronize_rcu_expedited() instead
3260 of synchronize_rcu(). This reduces latency,
3261 but can increase CPU utilization, degrade
3262 real-time latency, and degrade energy efficiency.
3264 rcupdate.rcu_cpu_stall_suppress= [KNL]
3265 Suppress RCU CPU stall warning messages.
3267 rcupdate.rcu_cpu_stall_timeout= [KNL]
3268 Set timeout for RCU CPU stall warning messages.
3270 rcupdate.rcu_task_stall_timeout= [KNL]
3271 Set timeout in jiffies for RCU task stall warning
3272 messages. Disable with a value less than or equal
3273 to zero.
3275 rcupdate.rcu_self_test= [KNL]
3276 Run the RCU early boot self tests
3278 rcupdate.rcu_self_test_bh= [KNL]
3279 Run the RCU bh early boot self tests
3281 rcupdate.rcu_self_test_sched= [KNL]
3282 Run the RCU sched early boot self tests
3284 rdinit= [KNL]
3285 Format: <full_path>
3286 Run specified binary instead of /init from the ramdisk,
3287 used for early userspace startup. See initrd.
3289 reboot= [KNL]
3290 Format (x86 or x86_64):
3291 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3292 [[,]s[mp]#### \
3293 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3294 [[,]f[orce]
3295 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3296 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3297 reboot_force is either force or not specified,
3298 reboot_cpu is s[mp]#### with #### being the processor
3299 to be used for rebooting.
3301 relax_domain_level=
3302 [KNL, SMP] Set scheduler's default relax_domain_level.
3303 See Documentation/cgroups/cpusets.txt.
3305 relative_sleep_states=
3306 [SUSPEND] Use sleep state labeling where the deepest
3307 state available other than hibernation is always "mem".
3308 Format: { "0" | "1" }
3309 0 -- Traditional sleep state labels.
3310 1 -- Relative sleep state labels.
3312 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3314 reservetop= [X86-32]
3315 Format: nn[KMG]
3316 Reserves a hole at the top of the kernel virtual
3317 address space.
3319 reservelow= [X86]
3320 Format: nn[K]
3321 Set the amount of memory to reserve for BIOS at
3322 the bottom of the address space.
3324 reset_devices [KNL] Force drivers to reset the underlying device
3325 during initialization.
3327 resume= [SWSUSP]
3328 Specify the partition device for software suspend
3329 Format:
3330 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3332 resume_offset= [SWSUSP]
3333 Specify the offset from the beginning of the partition
3334 given by "resume=" at which the swap header is located,
3335 in <PAGE_SIZE> units (needed only for swap files).
3336 See Documentation/power/swsusp-and-swap-files.txt
3338 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3339 read the resume files
3341 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3342 Useful for devices that are detected asynchronously
3343 (e.g. USB and MMC devices).
3345 hibernate= [HIBERNATION]
3346 noresume Don't check if there's a hibernation image
3347 present during boot.
3348 nocompress Don't compress/decompress hibernation images.
3349 no Disable hibernation and resume.
3351 retain_initrd [RAM] Keep initrd memory after extraction
3353 rfkill.default_state=
3354 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3355 etc. communication is blocked by default.
3356 1 Unblocked.
3358 rfkill.master_switch_mode=
3359 0 The "airplane mode" button does nothing.
3360 1 The "airplane mode" button toggles between everything
3361 blocked and the previous configuration.
3362 2 The "airplane mode" button toggles between everything
3363 blocked and everything unblocked.
3365 rhash_entries= [KNL,NET]
3366 Set number of hash buckets for route cache
3368 ro [KNL] Mount root device read-only on boot
3370 root= [KNL] Root filesystem
3371 See name_to_dev_t comment in init/do_mounts.c.
3373 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3374 mount the root filesystem
3376 rootflags= [KNL] Set root filesystem mount option string
3378 rootfstype= [KNL] Set root filesystem type
3380 rootwait [KNL] Wait (indefinitely) for root device to show up.
3381 Useful for devices that are detected asynchronously
3382 (e.g. USB and MMC devices).
3384 rproc_mem=nn[KMG][@address]
3385 [KNL,ARM,CMA] Remoteproc physical memory block.
3386 Memory area to be used by remote processor image,
3387 managed by CMA.
3389 rw [KNL] Mount root device read-write on boot
3391 S [KNL] Run init in single mode
3393 s390_iommu= [HW,S390]
3394 Set s390 IOTLB flushing mode
3395 strict
3396 With strict flushing every unmap operation will result in
3397 an IOTLB flush. Default is lazy flushing before reuse,
3398 which is faster.
3400 sa1100ir [NET]
3401 See drivers/net/irda/sa1100_ir.c.
3403 sbni= [NET] Granch SBNI12 leased line adapter
3405 sched_debug [KNL] Enables verbose scheduler debug messages.
3407 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3408 xtime_lock contention on larger systems, and/or RCU lock
3409 contention on all systems with CONFIG_MAXSMP set.
3410 Format: { "0" | "1" }
3411 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3412 1 -- enable.
3413 Note: increases power consumption, thus should only be
3414 enabled if running jitter sensitive (HPC/RT) workloads.
3416 security= [SECURITY] Choose a security module to enable at boot.
3417 If this boot parameter is not specified, only the first
3418 security module asking for security registration will be
3419 loaded. An invalid security module name will be treated
3420 as if no module has been chosen.
3422 selinux= [SELINUX] Disable or enable SELinux at boot time.
3423 Format: { "0" | "1" }
3424 See security/selinux/Kconfig help text.
3425 0 -- disable.
3426 1 -- enable.
3427 Default value is set via kernel config option.
3428 If enabled at boot time, /selinux/disable can be used
3429 later to disable prior to initial policy load.
3431 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3432 Format: { "0" | "1" }
3433 See security/apparmor/Kconfig help text
3434 0 -- disable.
3435 1 -- enable.
3436 Default value is set via kernel config option.
3438 serialnumber [BUGS=X86-32]
3440 shapers= [NET]
3441 Maximal number of shapers.
3443 show_msr= [x86] show boot-time MSR settings
3444 Format: { <integer> }
3445 Show boot-time (BIOS-initialized) MSR settings.
3446 The parameter means the number of CPUs to show,
3447 for example 1 means boot CPU only.
3449 simeth= [IA-64]
3450 simscsi=
3452 slram= [HW,MTD]
3454 slab_nomerge [MM]
3455 Disable merging of slabs with similar size. May be
3456 necessary if there is some reason to distinguish
3457 allocs to different slabs. Debug options disable
3458 merging on their own.
3459 For more information see Documentation/vm/slub.txt.
3461 slab_max_order= [MM, SLAB]
3462 Determines the maximum allowed order for slabs.
3463 A high setting may cause OOMs due to memory
3464 fragmentation. Defaults to 1 for systems with
3465 more than 32MB of RAM, 0 otherwise.
3467 slub_debug[=options[,slabs]] [MM, SLUB]
3468 Enabling slub_debug allows one to determine the
3469 culprit if slab objects become corrupted. Enabling
3470 slub_debug can create guard zones around objects and
3471 may poison objects when not in use. Also tracks the
3472 last alloc / free. For more information see
3473 Documentation/vm/slub.txt.
3475 slub_max_order= [MM, SLUB]
3476 Determines the maximum allowed order for slabs.
3477 A high setting may cause OOMs due to memory
3478 fragmentation. For more information see
3479 Documentation/vm/slub.txt.
3481 slub_min_objects= [MM, SLUB]
3482 The minimum number of objects per slab. SLUB will
3483 increase the slab order up to slub_max_order to
3484 generate a sufficiently large slab able to contain
3485 the number of objects indicated. The higher the number
3486 of objects the smaller the overhead of tracking slabs
3487 and the less frequently locks need to be acquired.
3488 For more information see Documentation/vm/slub.txt.
3490 slub_min_order= [MM, SLUB]
3491 Determines the minimum page order for slabs. Must be
3492 lower than slub_max_order.
3493 For more information see Documentation/vm/slub.txt.
3495 slub_nomerge [MM, SLUB]
3496 Same with slab_nomerge. This is supported for legacy.
3497 See slab_nomerge for more information.
3499 smart2= [HW]
3500 Format: <io1>[,<io2>[,...,<io8>]]
3502 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3503 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3504 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3505 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3506 smsc-ircc2.ircc_irq= [HW] IRQ line
3507 smsc-ircc2.ircc_dma= [HW] DMA channel
3508 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3509 0: Toshiba Satellite 1800 (GP data pin select)
3510 1: Fast pin select (default)
3511 2: ATC IRMode
3513 softlockup_panic=
3514 [KNL] Should the soft-lockup detector generate panics.
3515 Format: <integer>
3517 softlockup_all_cpu_backtrace=
3518 [KNL] Should the soft-lockup detector generate
3519 backtraces on all cpus.
3520 Format: <integer>
3522 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3523 See Documentation/laptops/sonypi.txt
3525 spia_io_base= [HW,MTD]
3526 spia_fio_base=
3527 spia_pedr=
3528 spia_peddr=
3530 stacktrace [FTRACE]
3531 Enabled the stack tracer on boot up.
3533 stacktrace_filter=[function-list]
3534 [FTRACE] Limit the functions that the stack tracer
3535 will trace at boot up. function-list is a comma separated
3536 list of functions. This list can be changed at run
3537 time by the stack_trace_filter file in the debugfs
3538 tracing directory. Note, this enables stack tracing
3539 and the stacktrace above is not needed.
3541 sti= [PARISC,HW]
3542 Format: <num>
3543 Set the STI (builtin display/keyboard on the HP-PARISC
3544 machines) console (graphic card) which should be used
3545 as the initial boot-console.
3546 See also comment in drivers/video/console/sticore.c.
3548 sti_font= [HW]
3549 See comment in drivers/video/console/sticore.c.
3551 stifb= [HW]
3552 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3554 sunrpc.min_resvport=
3555 sunrpc.max_resvport=
3556 [NFS,SUNRPC]
3557 SunRPC servers often require that client requests
3558 originate from a privileged port (i.e. a port in the
3559 range 0 < portnr < 1024).
3560 An administrator who wishes to reserve some of these
3561 ports for other uses may adjust the range that the
3562 kernel's sunrpc client considers to be privileged
3563 using these two parameters to set the minimum and
3564 maximum port values.
3566 sunrpc.pool_mode=
3567 [NFS]
3568 Control how the NFS server code allocates CPUs to
3569 service thread pools. Depending on how many NICs
3570 you have and where their interrupts are bound, this
3571 option will affect which CPUs will do NFS serving.
3572 Note: this parameter cannot be changed while the
3573 NFS server is running.
3575 auto the server chooses an appropriate mode
3576 automatically using heuristics
3577 global a single global pool contains all CPUs
3578 percpu one pool for each CPU
3579 pernode one pool for each NUMA node (equivalent
3580 to global on non-NUMA machines)
3582 sunrpc.tcp_slot_table_entries=
3583 sunrpc.udp_slot_table_entries=
3584 [NFS,SUNRPC]
3585 Sets the upper limit on the number of simultaneous
3586 RPC calls that can be sent from the client to a
3587 server. Increasing these values may allow you to
3588 improve throughput, but will also increase the
3589 amount of memory reserved for use by the client.
3591 suspend.pm_test_delay=
3592 [SUSPEND]
3593 Sets the number of seconds to remain in a suspend test
3594 mode before resuming the system (see
3595 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3596 is set. Default value is 5.
3598 swapaccount=[0|1]
3599 [KNL] Enable accounting of swap in memory resource
3600 controller if no parameter or 1 is given or disable
3601 it if 0 is given (See Documentation/cgroups/memory.txt)
3603 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3604 Format: { <int> | force }
3605 <int> -- Number of I/O TLB slabs
3606 force -- force using of bounce buffers even if they
3607 wouldn't be automatically used by the kernel
3609 switches= [HW,M68k]
3611 sysfs.deprecated=0|1 [KNL]
3612 Enable/disable old style sysfs layout for old udev
3613 on older distributions. When this option is enabled
3614 very new udev will not work anymore. When this option
3615 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3616 in older udev will not work anymore.
3617 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3618 the kernel configuration.
3620 sysrq_always_enabled
3621 [KNL]
3622 Ignore sysrq setting - this boot parameter will
3623 neutralize any effect of /proc/sys/kernel/sysrq.
3624 Useful for debugging.
3626 tcpmhash_entries= [KNL,NET]
3627 Set the number of tcp_metrics_hash slots.
3628 Default value is 8192 or 16384 depending on total
3629 ram pages. This is used to specify the TCP metrics
3630 cache size. See Documentation/networking/ip-sysctl.txt
3631 "tcp_no_metrics_save" section for more details.
3633 tdfx= [HW,DRM]
3635 test_suspend= [SUSPEND][,N]
3636 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3637 standby suspend) or "freeze" (for suspend type freeze)
3638 as the system sleep state during system startup with
3639 the optional capability to repeat N number of times.
3640 The system is woken from this state using a
3641 wakeup-capable RTC alarm.
3643 thash_entries= [KNL,NET]
3644 Set number of hash buckets for TCP connection
3646 thermal.act= [HW,ACPI]
3647 -1: disable all active trip points in all thermal zones
3648 <degrees C>: override all lowest active trip points
3650 thermal.crt= [HW,ACPI]
3651 -1: disable all critical trip points in all thermal zones
3652 <degrees C>: override all critical trip points
3654 thermal.nocrt= [HW,ACPI]
3655 Set to disable actions on ACPI thermal zone
3656 critical and hot trip points.
3658 thermal.off= [HW,ACPI]
3659 1: disable ACPI thermal control
3661 thermal.psv= [HW,ACPI]
3662 -1: disable all passive trip points
3663 <degrees C>: override all passive trip points to this
3664 value
3666 thermal.tzp= [HW,ACPI]
3667 Specify global default ACPI thermal zone polling rate
3668 <deci-seconds>: poll all this frequency
3669 0: no polling (default)
3671 threadirqs [KNL]
3672 Force threading of all interrupt handlers except those
3673 marked explicitly IRQF_NO_THREAD.
3675 tmem [KNL,XEN]
3676 Enable the Transcendent memory driver if built-in.
3678 tmem.cleancache=0|1 [KNL, XEN]
3679 Default is on (1). Disable the usage of the cleancache
3680 API to send anonymous pages to the hypervisor.
3682 tmem.frontswap=0|1 [KNL, XEN]
3683 Default is on (1). Disable the usage of the frontswap
3684 API to send swap pages to the hypervisor. If disabled
3685 the selfballooning and selfshrinking are force disabled.
3687 tmem.selfballooning=0|1 [KNL, XEN]
3688 Default is on (1). Disable the driving of swap pages
3689 to the hypervisor.
3691 tmem.selfshrinking=0|1 [KNL, XEN]
3692 Default is on (1). Partial swapoff that immediately
3693 transfers pages from Xen hypervisor back to the
3694 kernel based on different criteria.
3696 topology= [S390]
3697 Format: {off | on}
3698 Specify if the kernel should make use of the cpu
3699 topology information if the hardware supports this.
3700 The scheduler will make use of this information and
3701 e.g. base its process migration decisions on it.
3702 Default is on.
3704 topology_updates= [KNL, PPC, NUMA]
3705 Format: {off}
3706 Specify if the kernel should ignore (off)
3707 topology updates sent by the hypervisor to this
3708 LPAR.
3710 tp720= [HW,PS2]
3712 tpm_suspend_pcr=[HW,TPM]
3713 Format: integer pcr id
3714 Specify that at suspend time, the tpm driver
3715 should extend the specified pcr with zeros,
3716 as a workaround for some chips which fail to
3717 flush the last written pcr on TPM_SaveState.
3718 This will guarantee that all the other pcrs
3719 are saved.
3721 trace_buf_size=nn[KMG]
3722 [FTRACE] will set tracing buffer size on each cpu.
3724 trace_event=[event-list]
3725 [FTRACE] Set and start specified trace events in order
3726 to facilitate early boot debugging.
3727 See also Documentation/trace/events.txt
3729 trace_options=[option-list]
3730 [FTRACE] Enable or disable tracer options at boot.
3731 The option-list is a comma delimited list of options
3732 that can be enabled or disabled just as if you were
3733 to echo the option name into
3735 /sys/kernel/debug/tracing/trace_options
3737 For example, to enable stacktrace option (to dump the
3738 stack trace of each event), add to the command line:
3740 trace_options=stacktrace
3742 See also Documentation/trace/ftrace.txt "trace options"
3743 section.
3745 tp_printk[FTRACE]
3746 Have the tracepoints sent to printk as well as the
3747 tracing ring buffer. This is useful for early boot up
3748 where the system hangs or reboots and does not give the
3749 option for reading the tracing buffer or performing a
3750 ftrace_dump_on_oops.
3752 To turn off having tracepoints sent to printk,
3753 echo 0 > /proc/sys/kernel/tracepoint_printk
3754 Note, echoing 1 into this file without the
3755 tracepoint_printk kernel cmdline option has no effect.
3757 ** CAUTION **
3759 Having tracepoints sent to printk() and activating high
3760 frequency tracepoints such as irq or sched, can cause
3761 the system to live lock.
3763 traceoff_on_warning
3764 [FTRACE] enable this option to disable tracing when a
3765 warning is hit. This turns off "tracing_on". Tracing can
3766 be enabled again by echoing '1' into the "tracing_on"
3767 file located in /sys/kernel/debug/tracing/
3769 This option is useful, as it disables the trace before
3770 the WARNING dump is called, which prevents the trace to
3771 be filled with content caused by the warning output.
3773 This option can also be set at run time via the sysctl
3774 option: kernel/traceoff_on_warning
3776 transparent_hugepage=
3777 [KNL]
3778 Format: [always|madvise|never]
3779 Can be used to control the default behavior of the system
3780 with respect to transparent hugepages.
3781 See Documentation/vm/transhuge.txt for more details.
3783 tsc= Disable clocksource stability checks for TSC.
3784 Format: <string>
3785 [x86] reliable: mark tsc clocksource as reliable, this
3786 disables clocksource verification at runtime, as well
3787 as the stability checks done at bootup. Used to enable
3788 high-resolution timer mode on older hardware, and in
3789 virtualized environment.
3790 [x86] noirqtime: Do not use TSC to do irq accounting.
3791 Used to run time disable IRQ_TIME_ACCOUNTING on any
3792 platforms where RDTSC is slow and this accounting
3793 can add overhead.
3795 turbografx.map[2|3]= [HW,JOY]
3796 TurboGraFX parallel port interface
3797 Format:
3798 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3799 See also Documentation/input/joystick-parport.txt
3801 udbg-immortal [PPC] When debugging early kernel crashes that
3802 happen after console_init() and before a proper
3803 console driver takes over, this boot options might
3804 help "seeing" what's going on.
3806 uhash_entries= [KNL,NET]
3807 Set number of hash buckets for UDP/UDP-Lite connections
3809 uhci-hcd.ignore_oc=
3810 [USB] Ignore overcurrent events (default N).
3811 Some badly-designed motherboards generate lots of
3812 bogus events, for ports that aren't wired to
3813 anything. Set this parameter to avoid log spamming.
3814 Note that genuine overcurrent events won't be
3815 reported either.
3817 unknown_nmi_panic
3818 [X86] Cause panic on unknown NMI.
3820 usbcore.authorized_default=
3821 [USB] Default USB device authorization:
3822 (default -1 = authorized except for wireless USB,
3823 0 = not authorized, 1 = authorized)
3825 usbcore.autosuspend=
3826 [USB] The autosuspend time delay (in seconds) used
3827 for newly-detected USB devices (default 2). This
3828 is the time required before an idle device will be
3829 autosuspended. Devices for which the delay is set
3830 to a negative value won't be autosuspended at all.
3832 usbcore.usbfs_snoop=
3833 [USB] Set to log all usbfs traffic (default 0 = off).
3835 usbcore.blinkenlights=
3836 [USB] Set to cycle leds on hubs (default 0 = off).
3838 usbcore.old_scheme_first=
3839 [USB] Start with the old device initialization
3840 scheme (default 0 = off).
3842 usbcore.usbfs_memory_mb=
3843 [USB] Memory limit (in MB) for buffers allocated by
3844 usbfs (default = 16, 0 = max = 2047).
3846 usbcore.use_both_schemes=
3847 [USB] Try the other device initialization scheme
3848 if the first one fails (default 1 = enabled).
3850 usbcore.initial_descriptor_timeout=
3851 [USB] Specifies timeout for the initial 64-byte
3852 USB_REQ_GET_DESCRIPTOR request in milliseconds
3853 (default 5000 = 5.0 seconds).
3855 usbhid.mousepoll=
3856 [USBHID] The interval which mice are to be polled at.
3858 usb-storage.delay_use=
3859 [UMS] The delay in seconds before a new device is
3860 scanned for Logical Units (default 1).
3862 usb-storage.quirks=
3863 [UMS] A list of quirks entries to supplement or
3864 override the built-in unusual_devs list. List
3865 entries are separated by commas. Each entry has
3866 the form VID:PID:Flags where VID and PID are Vendor
3867 and Product ID values (4-digit hex numbers) and
3868 Flags is a set of characters, each corresponding
3869 to a common usb-storage quirk flag as follows:
3870 a = SANE_SENSE (collect more than 18 bytes
3871 of sense data);
3872 b = BAD_SENSE (don't collect more than 18
3873 bytes of sense data);
3874 c = FIX_CAPACITY (decrease the reported
3875 device capacity by one sector);
3876 d = NO_READ_DISC_INFO (don't use
3877 READ_DISC_INFO command);
3878 e = NO_READ_CAPACITY_16 (don't use
3879 READ_CAPACITY_16 command);
3880 f = NO_REPORT_OPCODES (don't use report opcodes
3881 command, uas only);
3882 g = MAX_SECTORS_240 (don't transfer more than
3883 240 sectors at a time, uas only);
3884 h = CAPACITY_HEURISTICS (decrease the
3885 reported device capacity by one
3886 sector if the number is odd);
3887 i = IGNORE_DEVICE (don't bind to this
3888 device);
3889 l = NOT_LOCKABLE (don't try to lock and
3890 unlock ejectable media);
3891 m = MAX_SECTORS_64 (don't transfer more
3892 than 64 sectors = 32 KB at a time);
3893 n = INITIAL_READ10 (force a retry of the
3894 initial READ(10) command);
3895 o = CAPACITY_OK (accept the capacity
3896 reported by the device);
3897 p = WRITE_CACHE (the device cache is ON
3898 by default);
3899 r = IGNORE_RESIDUE (the device reports
3900 bogus residue values);
3901 s = SINGLE_LUN (the device has only one
3902 Logical Unit);
3903 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3904 commands, uas only);
3905 u = IGNORE_UAS (don't bind to the uas driver);
3906 w = NO_WP_DETECT (don't test whether the
3907 medium is write-protected).
3908 Example: quirks=0419:aaf5:rl,0421:0433:rc
3910 user_debug= [KNL,ARM]
3911 Format: <int>
3912 See arch/arm/Kconfig.debug help text.
3913 1 - undefined instruction events
3914 2 - system calls
3915 4 - invalid data aborts
3916 8 - SIGSEGV faults
3917 16 - SIGBUS faults
3918 Example: user_debug=31
3920 userpte=
3921 [X86] Flags controlling user PTE allocations.
3923 nohigh = do not allocate PTE pages in
3924 HIGHMEM regardless of setting
3925 of CONFIG_HIGHPTE.
3927 vdso= [X86,SH]
3928 On X86_32, this is an alias for vdso32=. Otherwise:
3930 vdso=1: enable VDSO (the default)
3931 vdso=0: disable VDSO mapping
3933 vdso32= [X86] Control the 32-bit vDSO
3934 vdso32=1: enable 32-bit VDSO
3935 vdso32=0 or vdso32=2: disable 32-bit VDSO
3937 See the help text for CONFIG_COMPAT_VDSO for more
3938 details. If CONFIG_COMPAT_VDSO is set, the default is
3939 vdso32=0; otherwise, the default is vdso32=1.
3941 For compatibility with older kernels, vdso32=2 is an
3942 alias for vdso32=0.
3944 Try vdso32=0 if you encounter an error that says:
3945 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3947 vector= [IA-64,SMP]
3948 vector=percpu: enable percpu vector domain
3950 video= [FB] Frame buffer configuration
3951 See Documentation/fb/modedb.txt.
3953 video.brightness_switch_enabled= [0,1]
3954 If set to 1, on receiving an ACPI notify event
3955 generated by hotkey, video driver will adjust brightness
3956 level and then send out the event to user space through
3957 the allocated input device; If set to 0, video driver
3958 will only send out the event without touching backlight
3959 brightness level.
3960 default: 1
3962 virtio_mmio.device=
3963 [VMMIO] Memory mapped virtio (platform) device.
3965 <size>@<baseaddr>:<irq>[:<id>]
3966 where:
3967 <size> := size (can use standard suffixes
3968 like K, M and G)
3969 <baseaddr> := physical base address
3970 <irq> := interrupt number (as passed to
3971 request_irq())
3972 <id> := (optional) platform device id
3973 example:
3974 virtio_mmio.device=1K@0x100b0000:48:7
3976 Can be used multiple times for multiple devices.
3978 vga= [BOOT,X86-32] Select a particular video mode
3979 See Documentation/x86/boot.txt and
3980 Documentation/svga.txt.
3981 Use vga=ask for menu.
3982 This is actually a boot loader parameter; the value is
3983 passed to the kernel using a special protocol.
3985 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3986 size of <nn>. This can be used to increase the
3987 minimum size (128MB on x86). It can also be used to
3988 decrease the size and leave more room for directly
3989 mapped kernel RAM.
3991 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3992 Format: <command>
3994 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3995 Format: <command>
3997 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3998 Format: <command>
4000 vsyscall= [X86-64]
4001 Controls the behavior of vsyscalls (i.e. calls to
4002 fixed addresses of 0xffffffffff600x00 from legacy
4003 code). Most statically-linked binaries and older
4004 versions of glibc use these calls. Because these
4005 functions are at fixed addresses, they make nice
4006 targets for exploits that can control RIP.
4008 emulate [default] Vsyscalls turn into traps and are
4009 emulated reasonably safely.
4011 native Vsyscalls are native syscall instructions.
4012 This is a little bit faster than trapping
4013 and makes a few dynamic recompilers work
4014 better than they would in emulation mode.
4015 It also makes exploits much easier to write.
4017 none Vsyscalls don't work at all. This makes
4018 them quite hard to use for exploits but
4019 might break your system.
4021 vt.color= [VT] Default text color.
4022 Format: 0xYX, X = foreground, Y = background.
4023 Default: 0x07 = light gray on black.
4025 vt.cur_default= [VT] Default cursor shape.
4026 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4027 the parameters of the <Esc>[?A;B;Cc escape sequence;
4028 see VGA-softcursor.txt. Default: 2 = underline.
4030 vt.default_blu= [VT]
4031 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4032 Change the default blue palette of the console.
4033 This is a 16-member array composed of values
4034 ranging from 0-255.
4036 vt.default_grn= [VT]
4037 Format: <green0>,<green1>,<green2>,...,<green15>
4038 Change the default green palette of the console.
4039 This is a 16-member array composed of values
4040 ranging from 0-255.
4042 vt.default_red= [VT]
4043 Format: <red0>,<red1>,<red2>,...,<red15>
4044 Change the default red palette of the console.
4045 This is a 16-member array composed of values
4046 ranging from 0-255.
4048 vt.default_utf8=
4049 [VT]
4050 Format=<0|1>
4051 Set system-wide default UTF-8 mode for all tty's.
4052 Default is 1, i.e. UTF-8 mode is enabled for all
4053 newly opened terminals.
4055 vt.global_cursor_default=
4056 [VT]
4057 Format=<-1|0|1>
4058 Set system-wide default for whether a cursor
4059 is shown on new VTs. Default is -1,
4060 i.e. cursors will be created by default unless
4061 overridden by individual drivers. 0 will hide
4062 cursors, 1 will display them.
4064 vt.italic= [VT] Default color for italic text; 0-15.
4065 Default: 2 = green.
4067 vt.underline= [VT] Default color for underlined text; 0-15.
4068 Default: 3 = cyan.
4070 watchdog timers [HW,WDT] For information on watchdog timers,
4071 see Documentation/watchdog/watchdog-parameters.txt
4072 or other driver-specific files in the
4073 Documentation/watchdog/ directory.
4075 workqueue.disable_numa
4076 By default, all work items queued to unbound
4077 workqueues are affine to the NUMA nodes they're
4078 issued on, which results in better behavior in
4079 general. If NUMA affinity needs to be disabled for
4080 whatever reason, this option can be used. Note
4081 that this also can be controlled per-workqueue for
4082 workqueues visible under /sys/bus/workqueue/.
4084 workqueue.power_efficient
4085 Per-cpu workqueues are generally preferred because
4086 they show better performance thanks to cache
4087 locality; unfortunately, per-cpu workqueues tend to
4088 be more power hungry than unbound workqueues.
4090 Enabling this makes the per-cpu workqueues which
4091 were observed to contribute significantly to power
4092 consumption unbound, leading to measurably lower
4093 power usage at the cost of small performance
4094 overhead.
4096 The default value of this parameter is determined by
4097 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4099 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4100 default x2apic cluster mode on platforms
4101 supporting x2apic.
4103 x86_intel_mid_timer= [X86-32,APBT]
4104 Choose timer option for x86 Intel MID platform.
4105 Two valid options are apbt timer only and lapic timer
4106 plus one apbt timer for broadcast timer.
4107 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4109 xen_512gb_limit [KNL,X86-64,XEN]
4110 Restricts the kernel running paravirtualized under Xen
4111 to use only up to 512 GB of RAM. The reason to do so is
4112 crash analysis tools and Xen tools for doing domain
4113 save/restore/migration must be enabled to handle larger
4114 domains.
4116 xen_emul_unplug= [HW,X86,XEN]
4117 Unplug Xen emulated devices
4118 Format: [unplug0,][unplug1]
4119 ide-disks -- unplug primary master IDE devices
4120 aux-ide-disks -- unplug non-primary-master IDE devices
4121 nics -- unplug network devices
4122 all -- unplug all emulated devices (NICs and IDE disks)
4123 unnecessary -- unplugging emulated devices is
4124 unnecessary even if the host did not respond to
4125 the unplug protocol
4126 never -- do not unplug even if version check succeeds
4128 xen_nopvspin [X86,XEN]
4129 Disables the ticketlock slowpath using Xen PV
4130 optimizations.
4132 xen_nopv [X86]
4133 Disables the PV optimizations forcing the HVM guest to
4134 run as generic HVM guest with no PV drivers.
4136 xirc2ps_cs= [NET,PCMCIA]
4137 Format:
4138 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4140 ______________________________________________________________________
4142 TODO:
4144 Add more DRM drivers.