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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.direct [HW] Put keyboard port into non-translated mode
1321 i8042.dumbkbd [HW] Pretend that controller can only read data from
1322 keyboard and cannot control its state
1323 (Don't attempt to blink the leds)
1324 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1325 i8042.nokbd [HW] Don't check/create keyboard port
1326 i8042.noloop [HW] Disable the AUX Loopback command while probing
1327 for the AUX port
1328 i8042.nomux [HW] Don't check presence of an active multiplexing
1329 controller
1330 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1331 controllers
1332 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1333 i8042.reset [HW] Reset the controller during init and cleanup
1334 i8042.unlock [HW] Unlock (ignore) the keylock
1335 i8042.kbdreset [HW] Reset device connected to KBD port
1337 i810= [HW,DRM]
1339 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1340 indicates that the driver is running on unsupported
1341 hardware.
1342 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1343 does not match list of supported models.
1344 i8k.power_status
1345 [HW] Report power status in /proc/i8k
1346 (disabled by default)
1347 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1348 capability is set.
1350 i915.invert_brightness=
1351 [DRM] Invert the sense of the variable that is used to
1352 set the brightness of the panel backlight. Normally a
1353 brightness value of 0 indicates backlight switched off,
1354 and the maximum of the brightness value sets the backlight
1355 to maximum brightness. If this parameter is set to 0
1356 (default) and the machine requires it, or this parameter
1357 is set to 1, a brightness value of 0 sets the backlight
1358 to maximum brightness, and the maximum of the brightness
1359 value switches the backlight off.
1360 -1 -- never invert brightness
1361 0 -- machine default
1362 1 -- force brightness inversion
1364 icn= [HW,ISDN]
1365 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1367 ide-core.nodma= [HW] (E)IDE subsystem
1368 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1369 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1370 .cdrom .chs .ignore_cable are additional options
1371 See Documentation/ide/ide.txt.
1373 ide-generic.probe-mask= [HW] (E)IDE subsystem
1374 Format: <int>
1375 Probe mask for legacy ISA IDE ports. Depending on
1376 platform up to 6 ports are supported, enabled by
1377 setting corresponding bits in the mask to 1. The
1378 default value is 0x0, which has a special meaning.
1379 On systems that have PCI, it triggers scanning the
1380 PCI bus for the first and the second port, which
1381 are then probed. On systems without PCI the value
1382 of 0x0 enables probing the two first ports as if it
1383 was 0x3.
1385 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1386 Claim all unknown PCI IDE storage controllers.
1388 idle= [X86]
1389 Format: idle=poll, idle=halt, idle=nomwait
1390 Poll forces a polling idle loop that can slightly
1391 improve the performance of waking up a idle CPU, but
1392 will use a lot of power and make the system run hot.
1393 Not recommended.
1394 idle=halt: Halt is forced to be used for CPU idle.
1395 In such case C2/C3 won't be used again.
1396 idle=nomwait: Disable mwait for CPU C-states
1398 ignore_loglevel [KNL]
1399 Ignore loglevel setting - this will print /all/
1400 kernel messages to the console. Useful for debugging.
1401 We also add it as printk module parameter, so users
1402 could change it dynamically, usually by
1403 /sys/module/printk/parameters/ignore_loglevel.
1405 ihash_entries= [KNL]
1406 Set number of hash buckets for inode cache.
1408 ima_appraise= [IMA] appraise integrity measurements
1409 Format: { "off" | "enforce" | "fix" | "log" }
1410 default: "enforce"
1412 ima_appraise_tcb [IMA]
1413 The builtin appraise policy appraises all files
1414 owned by uid=0.
1416 ima_hash= [IMA]
1417 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1418 | sha512 | ... }
1419 default: "sha1"
1421 The list of supported hash algorithms is defined
1422 in crypto/hash_info.h.
1424 ima_policy= [IMA]
1425 The builtin measurement policy to load during IMA
1426 setup. Specyfing "tcb" as the value, measures all
1427 programs exec'd, files mmap'd for exec, and all files
1428 opened with the read mode bit set by either the
1429 effective uid (euid=0) or uid=0.
1430 Format: "tcb"
1432 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1433 Load a policy which meets the needs of the Trusted
1434 Computing Base. This means IMA will measure all
1435 programs exec'd, files mmap'd for exec, and all files
1436 opened for read by uid=0.
1438 ima_template= [IMA]
1439 Select one of defined IMA measurements template formats.
1440 Formats: { "ima" | "ima-ng" | "ima-sig" }
1441 Default: "ima-ng"
1443 ima_template_fmt=
1444 [IMA] Define a custom template format.
1445 Format: { "field1|...|fieldN" }
1447 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1448 Format: <min_file_size>
1449 Set the minimal file size for using asynchronous hash.
1450 If left unspecified, ahash usage is disabled.
1452 ahash performance varies for different data sizes on
1453 different crypto accelerators. This option can be used
1454 to achieve the best performance for a particular HW.
1456 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1457 Format: <bufsize>
1458 Set hashing buffer size. Default: 4k.
1460 ahash performance varies for different chunk sizes on
1461 different crypto accelerators. This option can be used
1462 to achieve best performance for particular HW.
1464 init= [KNL]
1465 Format: <full_path>
1466 Run specified binary instead of /sbin/init as init
1467 process.
1469 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1470 for working out where the kernel is dying during
1471 startup.
1473 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1474 initcall functions. Useful for debugging built-in
1475 modules and initcalls.
1477 initrd= [BOOT] Specify the location of the initial ramdisk
1479 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1480 Format: <irq>
1482 int_pln_enable [x86] Enable power limit notification interrupt
1484 integrity_audit=[IMA]
1485 Format: { "0" | "1" }
1486 0 -- basic integrity auditing messages. (Default)
1487 1 -- additional integrity auditing messages.
1489 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1490 on
1491 Enable intel iommu driver.
1492 off
1493 Disable intel iommu driver.
1494 igfx_off [Default Off]
1495 By default, gfx is mapped as normal device. If a gfx
1496 device has a dedicated DMAR unit, the DMAR unit is
1497 bypassed by not enabling DMAR with this option. In
1498 this case, gfx device will use physical address for
1499 DMA.
1500 forcedac [x86_64]
1501 With this option iommu will not optimize to look
1502 for io virtual address below 32-bit forcing dual
1503 address cycle on pci bus for cards supporting greater
1504 than 32-bit addressing. The default is to look
1505 for translation below 32-bit and if not available
1506 then look in the higher range.
1507 strict [Default Off]
1508 With this option on every unmap_single operation will
1509 result in a hardware IOTLB flush operation as opposed
1510 to batching them for performance.
1511 sp_off [Default Off]
1512 By default, super page will be supported if Intel IOMMU
1513 has the capability. With this option, super page will
1514 not be supported.
1515 ecs_off [Default Off]
1516 By default, extended context tables will be supported if
1517 the hardware advertises that it has support both for the
1518 extended tables themselves, and also PASID support. With
1519 this option set, extended tables will not be used even
1520 on hardware which claims to support them.
1522 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1523 0 disables intel_idle and fall back on acpi_idle.
1524 1 to 6 specify maximum depth of C-state.
1526 intel_pstate= [X86]
1527 disable
1528 Do not enable intel_pstate as the default
1529 scaling driver for the supported processors
1530 force
1531 Enable intel_pstate on systems that prohibit it by default
1532 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1533 instead of acpi-cpufreq may disable platform features, such
1534 as thermal controls and power capping, that rely on ACPI
1535 P-States information being indicated to OSPM and therefore
1536 should be used with caution. This option does not work with
1537 processors that aren't supported by the intel_pstate driver
1538 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1539 no_hwp
1540 Do not enable hardware P state control (HWP)
1541 if available.
1542 hwp_only
1543 Only load intel_pstate on systems which support
1544 hardware P state control (HWP) if available.
1546 intremap= [X86-64, Intel-IOMMU]
1547 on enable Interrupt Remapping (default)
1548 off disable Interrupt Remapping
1549 nosid disable Source ID checking
1550 no_x2apic_optout
1551 BIOS x2APIC opt-out request will be ignored
1553 iomem= Disable strict checking of access to MMIO memory
1554 strict regions from userspace.
1555 relaxed
1557 iommu= [x86]
1558 off
1559 force
1560 noforce
1561 biomerge
1562 panic
1563 nopanic
1564 merge
1565 nomerge
1566 forcesac
1567 soft
1568 pt [x86, IA-64]
1569 nobypass [PPC/POWERNV]
1570 Disable IOMMU bypass, using IOMMU for PCI devices.
1573 io7= [HW] IO7 for Marvel based alpha systems
1574 See comment before marvel_specify_io7 in
1575 arch/alpha/kernel/core_marvel.c.
1577 io_delay= [X86] I/O delay method
1578 0x80
1579 Standard port 0x80 based delay
1580 0xed
1581 Alternate port 0xed based delay (needed on some systems)
1582 udelay
1583 Simple two microseconds delay
1584 none
1585 No delay
1587 ip= [IP_PNP]
1588 See Documentation/filesystems/nfs/nfsroot.txt.
1590 irqfixup [HW]
1591 When an interrupt is not handled search all handlers
1592 for it. Intended to get systems with badly broken
1593 firmware running.
1595 irqpoll [HW]
1596 When an interrupt is not handled search all handlers
1597 for it. Also check all handlers each timer
1598 interrupt. Intended to get systems with badly broken
1599 firmware running.
1601 isapnp= [ISAPNP]
1602 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1604 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1605 Format:
1606 <cpu number>,...,<cpu number>
1607 or
1608 <cpu number>-<cpu number>
1609 (must be a positive range in ascending order)
1610 or a mixture
1611 <cpu number>,...,<cpu number>-<cpu number>
1613 This option can be used to specify one or more CPUs
1614 to isolate from the general SMP balancing and scheduling
1615 algorithms. You can move a process onto or off an
1616 "isolated" CPU via the CPU affinity syscalls or cpuset.
1617 <cpu number> begins at 0 and the maximum value is
1618 "number of CPUs in system - 1".
1620 This option is the preferred way to isolate CPUs. The
1621 alternative -- manually setting the CPU mask of all
1622 tasks in the system -- can cause problems and
1623 suboptimal load balancer performance.
1625 iucv= [HW,NET]
1627 ivrs_ioapic [HW,X86_64]
1628 Provide an override to the IOAPIC-ID<->DEVICE-ID
1629 mapping provided in the IVRS ACPI table. For
1630 example, to map IOAPIC-ID decimal 10 to
1631 PCI device 00:14.0 write the parameter as:
1632 ivrs_ioapic[10]=00:14.0
1634 ivrs_hpet [HW,X86_64]
1635 Provide an override to the HPET-ID<->DEVICE-ID
1636 mapping provided in the IVRS ACPI table. For
1637 example, to map HPET-ID decimal 0 to
1638 PCI device 00:14.0 write the parameter as:
1639 ivrs_hpet[0]=00:14.0
1641 js= [HW,JOY] Analog joystick
1642 See Documentation/input/joystick.txt.
1644 kaslr/nokaslr [X86]
1645 Enable/disable kernel and module base offset ASLR
1646 (Address Space Layout Randomization) if built into
1647 the kernel. When CONFIG_HIBERNATION is selected,
1648 kASLR is disabled by default. When kASLR is enabled,
1649 hibernation will be disabled.
1651 keepinitrd [HW,ARM]
1653 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1654 specifies the amount of memory usable by the kernel
1655 for non-movable allocations. The requested amount is
1656 spread evenly throughout all nodes in the system. The
1657 remaining memory in each node is used for Movable
1658 pages. In the event, a node is too small to have both
1659 kernelcore and Movable pages, kernelcore pages will
1660 take priority and other nodes will have a larger number
1661 of Movable pages. The Movable zone is used for the
1662 allocation of pages that may be reclaimed or moved
1663 by the page migration subsystem. This means that
1664 HugeTLB pages may not be allocated from this zone.
1665 Note that allocations like PTEs-from-HighMem still
1666 use the HighMem zone if it exists, and the Normal
1667 zone if it does not.
1669 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1670 Format: <Controller#>[,poll interval]
1671 The controller # is the number of the ehci usb debug
1672 port as it is probed via PCI. The poll interval is
1673 optional and is the number seconds in between
1674 each poll cycle to the debug port in case you need
1675 the functionality for interrupting the kernel with
1676 gdb or control-c on the dbgp connection. When
1677 not using this parameter you use sysrq-g to break into
1678 the kernel debugger.
1680 kgdboc= [KGDB,HW] kgdb over consoles.
1681 Requires a tty driver that supports console polling,
1682 or a supported polling keyboard driver (non-usb).
1683 Serial only format: <serial_device>[,baud]
1684 keyboard only format: kbd
1685 keyboard and serial format: kbd,<serial_device>[,baud]
1686 Optional Kernel mode setting:
1687 kms, kbd format: kms,kbd
1688 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1690 kgdbwait [KGDB] Stop kernel execution and enter the
1691 kernel debugger at the earliest opportunity.
1693 kmac= [MIPS] korina ethernet MAC address.
1694 Configure the RouterBoard 532 series on-chip
1695 Ethernet adapter MAC address.
1697 kmemleak= [KNL] Boot-time kmemleak enable/disable
1698 Valid arguments: on, off
1699 Default: on
1700 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1701 the default is off.
1703 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1704 Valid arguments: 0, 1, 2
1705 kmemcheck=0 (disabled)
1706 kmemcheck=1 (enabled)
1707 kmemcheck=2 (one-shot mode)
1708 Default: 2 (one-shot mode)
1710 kstack=N [X86] Print N words from the kernel stack
1711 in oops dumps.
1713 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1714 Default is 0 (don't ignore, but inject #GP)
1716 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1717 KVM MMU at runtime.
1718 Default is 0 (off)
1720 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1721 Default is 1 (enabled)
1723 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1724 for all guests.
1725 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1727 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1728 (virtualized MMU) support on capable Intel chips.
1729 Default is 1 (enabled)
1731 kvm-intel.emulate_invalid_guest_state=
1732 [KVM,Intel] Enable emulation of invalid guest states
1733 Default is 0 (disabled)
1735 kvm-intel.flexpriority=
1736 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1737 Default is 1 (enabled)
1739 kvm-intel.nested=
1740 [KVM,Intel] Enable VMX nesting (nVMX).
1741 Default is 0 (disabled)
1743 kvm-intel.unrestricted_guest=
1744 [KVM,Intel] Disable unrestricted guest feature
1745 (virtualized real and unpaged mode) on capable
1746 Intel chips. Default is 1 (enabled)
1748 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1749 feature (tagged TLBs) on capable Intel chips.
1750 Default is 1 (enabled)
1752 l2cr= [PPC]
1754 l3cr= [PPC]
1756 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1757 disabled it.
1759 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1760 value for LAPIC timer one-shot implementation. Default
1761 back to the programmable timer unit in the LAPIC.
1763 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1764 in C2 power state.
1766 libata.dma= [LIBATA] DMA control
1767 libata.dma=0 Disable all PATA and SATA DMA
1768 libata.dma=1 PATA and SATA Disk DMA only
1769 libata.dma=2 ATAPI (CDROM) DMA only
1770 libata.dma=4 Compact Flash DMA only
1771 Combinations also work, so libata.dma=3 enables DMA
1772 for disks and CDROMs, but not CFs.
1774 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1775 libata.ignore_hpa=0 keep BIOS limits (default)
1776 libata.ignore_hpa=1 ignore limits, using full disk
1778 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1779 when set.
1780 Format: <int>
1782 libata.force= [LIBATA] Force configurations. The format is comma
1783 separated list of "[ID:]VAL" where ID is
1784 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1785 matching port, link or device. Basically, it matches
1786 the ATA ID string printed on console by libata. If
1787 the whole ID part is omitted, the last PORT and DEVICE
1788 values are used. If ID hasn't been specified yet, the
1789 configuration applies to all ports, links and devices.
1791 If only DEVICE is omitted, the parameter applies to
1792 the port and all links and devices behind it. DEVICE
1793 number of 0 either selects the first device or the
1794 first fan-out link behind PMP device. It does not
1795 select the host link. DEVICE number of 15 selects the
1796 host link and device attached to it.
1798 The VAL specifies the configuration to force. As long
1799 as there's no ambiguity shortcut notation is allowed.
1800 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1801 The following configurations can be forced.
1803 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1804 Any ID with matching PORT is used.
1806 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1808 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1809 udma[/][16,25,33,44,66,100,133] notation is also
1810 allowed.
1812 * [no]ncq: Turn on or off NCQ.
1814 * [no]ncqtrim: Turn off queued DSM TRIM.
1816 * nohrst, nosrst, norst: suppress hard, soft
1817 and both resets.
1819 * rstonce: only attempt one reset during
1820 hot-unplug link recovery
1822 * dump_id: dump IDENTIFY data.
1824 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1826 * disable: Disable this device.
1828 If there are multiple matching configurations changing
1829 the same attribute, the last one is used.
1831 memblock=debug [KNL] Enable memblock debug messages.
1833 load_ramdisk= [RAM] List of ramdisks to load from floppy
1834 See Documentation/blockdev/ramdisk.txt.
1836 lockd.nlm_grace_period=P [NFS] Assign grace period.
1837 Format: <integer>
1839 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1840 Format: <integer>
1842 lockd.nlm_timeout=T [NFS] Assign timeout value.
1843 Format: <integer>
1845 lockd.nlm_udpport=M [NFS] Assign UDP port.
1846 Format: <integer>
1848 locktorture.nreaders_stress= [KNL]
1849 Set the number of locking read-acquisition kthreads.
1850 Defaults to being automatically set based on the
1851 number of online CPUs.
1853 locktorture.nwriters_stress= [KNL]
1854 Set the number of locking write-acquisition kthreads.
1856 locktorture.onoff_holdoff= [KNL]
1857 Set time (s) after boot for CPU-hotplug testing.
1859 locktorture.onoff_interval= [KNL]
1860 Set time (s) between CPU-hotplug operations, or
1861 zero to disable CPU-hotplug testing.
1863 locktorture.shuffle_interval= [KNL]
1864 Set task-shuffle interval (jiffies). Shuffling
1865 tasks allows some CPUs to go into dyntick-idle
1866 mode during the locktorture test.
1868 locktorture.shutdown_secs= [KNL]
1869 Set time (s) after boot system shutdown. This
1870 is useful for hands-off automated testing.
1872 locktorture.stat_interval= [KNL]
1873 Time (s) between statistics printk()s.
1875 locktorture.stutter= [KNL]
1876 Time (s) to stutter testing, for example,
1877 specifying five seconds causes the test to run for
1878 five seconds, wait for five seconds, and so on.
1879 This tests the locking primitive's ability to
1880 transition abruptly to and from idle.
1882 locktorture.torture_runnable= [BOOT]
1883 Start locktorture running at boot time.
1885 locktorture.torture_type= [KNL]
1886 Specify the locking implementation to test.
1888 locktorture.verbose= [KNL]
1889 Enable additional printk() statements.
1891 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1892 Format: <irq>
1894 loglevel= All Kernel Messages with a loglevel smaller than the
1895 console loglevel will be printed to the console. It can
1896 also be changed with klogd or other programs. The
1897 loglevels are defined as follows:
1899 0 (KERN_EMERG) system is unusable
1900 1 (KERN_ALERT) action must be taken immediately
1901 2 (KERN_CRIT) critical conditions
1902 3 (KERN_ERR) error conditions
1903 4 (KERN_WARNING) warning conditions
1904 5 (KERN_NOTICE) normal but significant condition
1905 6 (KERN_INFO) informational
1906 7 (KERN_DEBUG) debug-level messages
1908 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1909 in bytes. n must be a power of two and greater
1910 than the minimal size. The minimal size is defined
1911 by LOG_BUF_SHIFT kernel config parameter. There is
1912 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1913 that allows to increase the default size depending on
1914 the number of CPUs. See init/Kconfig for more details.
1916 logo.nologo [FB] Disables display of the built-in Linux logo.
1917 This may be used to provide more screen space for
1918 kernel log messages and is useful when debugging
1919 kernel boot problems.
1921 lp=0 [LP] Specify parallel ports to use, e.g,
1922 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1923 lp=reset first parallel port). 'lp=0' disables the
1924 lp=auto printer driver. 'lp=reset' (which can be
1925 specified in addition to the ports) causes
1926 attached printers to be reset. Using
1927 lp=port1,port2,... specifies the parallel ports
1928 to associate lp devices with, starting with
1929 lp0. A port specification may be 'none' to skip
1930 that lp device, or a parport name such as
1931 'parport0'. Specifying 'lp=auto' instead of a
1932 port specification list means that device IDs
1933 from each port should be examined, to see if
1934 an IEEE 1284-compliant printer is attached; if
1935 so, the driver will manage that printer.
1936 See also header of drivers/char/lp.c.
1938 lpj=n [KNL]
1939 Sets loops_per_jiffy to given constant, thus avoiding
1940 time-consuming boot-time autodetection (up to 250 ms per
1941 CPU). 0 enables autodetection (default). To determine
1942 the correct value for your kernel, boot with normal
1943 autodetection and see what value is printed. Note that
1944 on SMP systems the preset will be applied to all CPUs,
1945 which is likely to cause problems if your CPUs need
1946 significantly divergent settings. An incorrect value
1947 will cause delays in the kernel to be wrong, leading to
1948 unpredictable I/O errors and other breakage. Although
1949 unlikely, in the extreme case this might damage your
1950 hardware.
1952 ltpc= [NET]
1953 Format: <io>,<irq>,<dma>
1955 machvec= [IA-64] Force the use of a particular machine-vector
1956 (machvec) in a generic kernel.
1957 Example: machvec=hpzx1_swiotlb
1959 machtype= [Loongson] Share the same kernel image file between different
1960 yeeloong laptop.
1961 Example: machtype=lemote-yeeloong-2f-7inch
1963 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1964 than or equal to this physical address is ignored.
1966 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1967 should make use of. maxcpus=n : n >= 0 limits the
1968 kernel to using 'n' processors. n=0 is a special case,
1969 it is equivalent to "nosmp", which also disables
1970 the IO APIC.
1972 max_loop= [LOOP] The number of loop block devices that get
1973 (loop.max_loop) unconditionally pre-created at init time. The default
1974 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1975 of statically allocating a predefined number, loop
1976 devices can be requested on-demand with the
1977 /dev/loop-control interface.
1979 mce [X86-32] Machine Check Exception
1981 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1983 md= [HW] RAID subsystems devices and level
1984 See Documentation/md.txt.
1986 mdacon= [MDA]
1987 Format: <first>,<last>
1988 Specifies range of consoles to be captured by the MDA.
1990 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1991 Amount of memory to be used when the kernel is not able
1992 to see the whole system memory or for test.
1993 [X86] Work as limiting max address. Use together
1994 with memmap= to avoid physical address space collisions.
1995 Without memmap= PCI devices could be placed at addresses
1996 belonging to unused RAM.
1998 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1999 memory.
2001 memchunk=nn[KMG]
2002 [KNL,SH] Allow user to override the default size for
2003 per-device physically contiguous DMA buffers.
2005 memmap=exactmap [KNL,X86] Enable setting of an exact
2006 E820 memory map, as specified by the user.
2007 Such memmap=exactmap lines can be constructed based on
2008 BIOS output or other requirements. See the memmap=nn@ss
2009 option description.
2011 memmap=nn[KMG]@ss[KMG]
2012 [KNL] Force usage of a specific region of memory.
2013 Region of memory to be used is from ss to ss+nn.
2015 memmap=nn[KMG]#ss[KMG]
2016 [KNL,ACPI] Mark specific memory as ACPI data.
2017 Region of memory to be marked is from ss to ss+nn.
2019 memmap=nn[KMG]$ss[KMG]
2020 [KNL,ACPI] Mark specific memory as reserved.
2021 Region of memory to be reserved is from ss to ss+nn.
2022 Example: Exclude memory from 0x18690000-0x1869ffff
2023 memmap=64K$0x18690000
2024 or
2025 memmap=0x10000$0x18690000
2027 memmap=nn[KMG]!ss[KMG]
2028 [KNL,X86] Mark specific memory as protected.
2029 Region of memory to be used, from ss to ss+nn.
2030 The memory region may be marked as e820 type 12 (0xc)
2031 and is NVDIMM or ADR memory.
2033 memory_corruption_check=0/1 [X86]
2034 Some BIOSes seem to corrupt the first 64k of
2035 memory when doing things like suspend/resume.
2036 Setting this option will scan the memory
2037 looking for corruption. Enabling this will
2038 both detect corruption and prevent the kernel
2039 from using the memory being corrupted.
2040 However, its intended as a diagnostic tool; if
2041 repeatable BIOS-originated corruption always
2042 affects the same memory, you can use memmap=
2043 to prevent the kernel from using that memory.
2045 memory_corruption_check_size=size [X86]
2046 By default it checks for corruption in the low
2047 64k, making this memory unavailable for normal
2048 use. Use this parameter to scan for
2049 corruption in more or less memory.
2051 memory_corruption_check_period=seconds [X86]
2052 By default it checks for corruption every 60
2053 seconds. Use this parameter to check at some
2054 other rate. 0 disables periodic checking.
2056 memtest= [KNL,X86,ARM] Enable memtest
2057 Format: <integer>
2058 default : 0 <disable>
2059 Specifies the number of memtest passes to be
2060 performed. Each pass selects another test
2061 pattern from a given set of patterns. Memtest
2062 fills the memory with this pattern, validates
2063 memory contents and reserves bad memory
2064 regions that are detected.
2066 meye.*= [HW] Set MotionEye Camera parameters
2067 See Documentation/video4linux/meye.txt.
2069 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2070 Multi-Function General Purpose Timers on AMD Geode
2071 platforms.
2073 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2074 the BIOS has incorrectly applied a workaround. TinyBIOS
2075 version 0.98 is known to be affected, 0.99 fixes the
2076 problem by letting the user disable the workaround.
2078 mga= [HW,DRM]
2080 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2081 physical address is ignored.
2083 mini2440= [ARM,HW,KNL]
2084 Format:[0..2][b][c][t]
2085 Default: "0tb"
2086 MINI2440 configuration specification:
2087 0 - The attached screen is the 3.5" TFT
2088 1 - The attached screen is the 7" TFT
2089 2 - The VGA Shield is attached (1024x768)
2090 Leaving out the screen size parameter will not load
2091 the TFT driver, and the framebuffer will be left
2092 unconfigured.
2093 b - Enable backlight. The TFT backlight pin will be
2094 linked to the kernel VESA blanking code and a GPIO
2095 LED. This parameter is not necessary when using the
2096 VGA shield.
2097 c - Enable the s3c camera interface.
2098 t - Reserved for enabling touchscreen support. The
2099 touchscreen support is not enabled in the mainstream
2100 kernel as of 2.6.30, a preliminary port can be found
2101 in the "bleeding edge" mini2440 support kernel at
2102 http://repo.or.cz/w/linux-2.6/mini2440.git
2104 mminit_loglevel=
2105 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2106 parameter allows control of the logging verbosity for
2107 the additional memory initialisation checks. A value
2108 of 0 disables mminit logging and a level of 4 will
2109 log everything. Information is printed at KERN_DEBUG
2110 so loglevel=8 may also need to be specified.
2112 module.sig_enforce
2113 [KNL] When CONFIG_MODULE_SIG is set, this means that
2114 modules without (valid) signatures will fail to load.
2115 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2116 is always true, so this option does nothing.
2118 mousedev.tap_time=
2119 [MOUSE] Maximum time between finger touching and
2120 leaving touchpad surface for touch to be considered
2121 a tap and be reported as a left button click (for
2122 touchpads working in absolute mode only).
2123 Format: <msecs>
2124 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2125 reporting absolute coordinates, such as tablets
2126 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2127 reporting absolute coordinates, such as tablets
2129 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2130 is similar to kernelcore except it specifies the
2131 amount of memory used for migratable allocations.
2132 If both kernelcore and movablecore is specified,
2133 then kernelcore will be at *least* the specified
2134 value but may be more. If movablecore on its own
2135 is specified, the administrator must be careful
2136 that the amount of memory usable for all allocations
2137 is not too small.
2139 movable_node [KNL,X86] Boot-time switch to enable the effects
2140 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2142 MTD_Partition= [MTD]
2143 Format: <name>,<region-number>,<size>,<offset>
2145 MTD_Region= [MTD] Format:
2146 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2148 mtdparts= [MTD]
2149 See drivers/mtd/cmdlinepart.c.
2151 multitce=off [PPC] This parameter disables the use of the pSeries
2152 firmware feature for updating multiple TCE entries
2153 at a time.
2155 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2157 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2159 boundary - index of last SLC block on Flex-OneNAND.
2160 The remaining blocks are configured as MLC blocks.
2161 lock - Configure if Flex-OneNAND boundary should be locked.
2162 Once locked, the boundary cannot be changed.
2163 1 indicates lock status, 0 indicates unlock status.
2165 mtdset= [ARM]
2166 ARM/S3C2412 JIVE boot control
2168 See arch/arm/mach-s3c2412/mach-jive.c
2170 mtouchusb.raw_coordinates=
2171 [HW] Make the MicroTouch USB driver use raw coordinates
2172 ('y', default) or cooked coordinates ('n')
2174 mtrr_chunk_size=nn[KMG] [X86]
2175 used for mtrr cleanup. It is largest continuous chunk
2176 that could hold holes aka. UC entries.
2178 mtrr_gran_size=nn[KMG] [X86]
2179 Used for mtrr cleanup. It is granularity of mtrr block.
2180 Default is 1.
2181 Large value could prevent small alignment from
2182 using up MTRRs.
2184 mtrr_spare_reg_nr=n [X86]
2185 Format: <integer>
2186 Range: 0,7 : spare reg number
2187 Default : 1
2188 Used for mtrr cleanup. It is spare mtrr entries number.
2189 Set to 2 or more if your graphical card needs more.
2191 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2193 netdev= [NET] Network devices parameters
2194 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2195 Note that mem_start is often overloaded to mean
2196 something different and driver-specific.
2197 This usage is only documented in each driver source
2198 file if at all.
2200 nf_conntrack.acct=
2201 [NETFILTER] Enable connection tracking flow accounting
2202 0 to disable accounting
2203 1 to enable accounting
2204 Default value is 0.
2206 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2207 See Documentation/filesystems/nfs/nfsroot.txt.
2209 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2210 See Documentation/filesystems/nfs/nfsroot.txt.
2212 nfsrootdebug [NFS] enable nfsroot debugging messages.
2213 See Documentation/filesystems/nfs/nfsroot.txt.
2215 nfs.callback_tcpport=
2216 [NFS] set the TCP port on which the NFSv4 callback
2217 channel should listen.
2219 nfs.cache_getent=
2220 [NFS] sets the pathname to the program which is used
2221 to update the NFS client cache entries.
2223 nfs.cache_getent_timeout=
2224 [NFS] sets the timeout after which an attempt to
2225 update a cache entry is deemed to have failed.
2227 nfs.idmap_cache_timeout=
2228 [NFS] set the maximum lifetime for idmapper cache
2229 entries.
2231 nfs.enable_ino64=
2232 [NFS] enable 64-bit inode numbers.
2233 If zero, the NFS client will fake up a 32-bit inode
2234 number for the readdir() and stat() syscalls instead
2235 of returning the full 64-bit number.
2236 The default is to return 64-bit inode numbers.
2238 nfs.max_session_slots=
2239 [NFSv4.1] Sets the maximum number of session slots
2240 the client will attempt to negotiate with the server.
2241 This limits the number of simultaneous RPC requests
2242 that the client can send to the NFSv4.1 server.
2243 Note that there is little point in setting this
2244 value higher than the max_tcp_slot_table_limit.
2246 nfs.nfs4_disable_idmapping=
2247 [NFSv4] When set to the default of '1', this option
2248 ensures that both the RPC level authentication
2249 scheme and the NFS level operations agree to use
2250 numeric uids/gids if the mount is using the
2251 'sec=sys' security flavour. In effect it is
2252 disabling idmapping, which can make migration from
2253 legacy NFSv2/v3 systems to NFSv4 easier.
2254 Servers that do not support this mode of operation
2255 will be autodetected by the client, and it will fall
2256 back to using the idmapper.
2257 To turn off this behaviour, set the value to '0'.
2258 nfs.nfs4_unique_id=
2259 [NFS4] Specify an additional fixed unique ident-
2260 ification string that NFSv4 clients can insert into
2261 their nfs_client_id4 string. This is typically a
2262 UUID that is generated at system install time.
2264 nfs.send_implementation_id =
2265 [NFSv4.1] Send client implementation identification
2266 information in exchange_id requests.
2267 If zero, no implementation identification information
2268 will be sent.
2269 The default is to send the implementation identification
2270 information.
2272 nfs.recover_lost_locks =
2273 [NFSv4] Attempt to recover locks that were lost due
2274 to a lease timeout on the server. Please note that
2275 doing this risks data corruption, since there are
2276 no guarantees that the file will remain unchanged
2277 after the locks are lost.
2278 If you want to enable the kernel legacy behaviour of
2279 attempting to recover these locks, then set this
2280 parameter to '1'.
2281 The default parameter value of '0' causes the kernel
2282 not to attempt recovery of lost locks.
2284 nfsd.nfs4_disable_idmapping=
2285 [NFSv4] When set to the default of '1', the NFSv4
2286 server will return only numeric uids and gids to
2287 clients using auth_sys, and will accept numeric uids
2288 and gids from such clients. This is intended to ease
2289 migration from NFSv2/v3.
2291 objlayoutdriver.osd_login_prog=
2292 [NFS] [OBJLAYOUT] sets the pathname to the program which
2293 is used to automatically discover and login into new
2294 osd-targets. Please see:
2295 Documentation/filesystems/pnfs.txt for more explanations
2297 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2298 when a NMI is triggered.
2299 Format: [state][,regs][,debounce][,die]
2301 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2302 Format: [panic,][nopanic,][num]
2303 Valid num: 0 or 1
2304 0 - turn nmi_watchdog off
2305 1 - turn nmi_watchdog on
2306 When panic is specified, panic when an NMI watchdog
2307 timeout occurs (or 'nopanic' to override the opposite
2308 default).
2309 This is useful when you use a panic=... timeout and
2310 need the box quickly up again.
2312 netpoll.carrier_timeout=
2313 [NET] Specifies amount of time (in seconds) that
2314 netpoll should wait for a carrier. By default netpoll
2315 waits 4 seconds.
2317 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2318 emulation library even if a 387 maths coprocessor
2319 is present.
2321 no_console_suspend
2322 [HW] Never suspend the console
2323 Disable suspending of consoles during suspend and
2324 hibernate operations. Once disabled, debugging
2325 messages can reach various consoles while the rest
2326 of the system is being put to sleep (ie, while
2327 debugging driver suspend/resume hooks). This may
2328 not work reliably with all consoles, but is known
2329 to work with serial and VGA consoles.
2330 To facilitate more flexible debugging, we also add
2331 console_suspend, a printk module parameter to control
2332 it. Users could use console_suspend (usually
2333 /sys/module/printk/parameters/console_suspend) to
2334 turn on/off it dynamically.
2336 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2337 caches in the slab allocator. Saves per-node memory,
2338 but will impact performance.
2340 noalign [KNL,ARM]
2342 noapic [SMP,APIC] Tells the kernel to not make use of any
2343 IOAPICs that may be present in the system.
2345 noautogroup Disable scheduler automatic task group creation.
2347 nobats [PPC] Do not use BATs for mapping kernel lowmem
2348 on "Classic" PPC cores.
2350 nocache [ARM]
2352 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2354 nodelayacct [KNL] Disable per-task delay accounting
2356 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2358 nodsp [SH] Disable hardware DSP at boot time.
2360 noefi Disable EFI runtime services support.
2362 noexec [IA-64]
2364 noexec [X86]
2365 On X86-32 available only on PAE configured kernels.
2366 noexec=on: enable non-executable mappings (default)
2367 noexec=off: disable non-executable mappings
2369 nosmap [X86]
2370 Disable SMAP (Supervisor Mode Access Prevention)
2371 even if it is supported by processor.
2373 nosmep [X86]
2374 Disable SMEP (Supervisor Mode Execution Prevention)
2375 even if it is supported by processor.
2377 noexec32 [X86-64]
2378 This affects only 32-bit executables.
2379 noexec32=on: enable non-executable mappings (default)
2380 read doesn't imply executable mappings
2381 noexec32=off: disable non-executable mappings
2382 read implies executable mappings
2384 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2386 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2387 register save and restore. The kernel will only save
2388 legacy floating-point registers on task switch.
2390 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2392 noxsave [BUGS=X86] Disables x86 extended register state save
2393 and restore using xsave. The kernel will fallback to
2394 enabling legacy floating-point and sse state.
2396 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2397 register states. The kernel will fall back to use
2398 xsave to save the states. By using this parameter,
2399 performance of saving the states is degraded because
2400 xsave doesn't support modified optimization while
2401 xsaveopt supports it on xsaveopt enabled systems.
2403 noxsaves [X86] Disables xsaves and xrstors used in saving and
2404 restoring x86 extended register state in compacted
2405 form of xsave area. The kernel will fall back to use
2406 xsaveopt and xrstor to save and restore the states
2407 in standard form of xsave area. By using this
2408 parameter, xsave area per process might occupy more
2409 memory on xsaves enabled systems.
2411 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2412 wfi(ARM) instruction doesn't work correctly and not to
2413 use it. This is also useful when using JTAG debugger.
2415 no_file_caps Tells the kernel not to honor file capabilities. The
2416 only way then for a file to be executed with privilege
2417 is to be setuid root or executed by root.
2419 nohalt [IA-64] Tells the kernel not to use the power saving
2420 function PAL_HALT_LIGHT when idle. This increases
2421 power-consumption. On the positive side, it reduces
2422 interrupt wake-up latency, which may improve performance
2423 in certain environments such as networked servers or
2424 real-time systems.
2426 nohibernate [HIBERNATION] Disable hibernation and resume.
2428 nohz= [KNL] Boottime enable/disable dynamic ticks
2429 Valid arguments: on, off
2430 Default: on
2432 nohz_full= [KNL,BOOT]
2433 In kernels built with CONFIG_NO_HZ_FULL=y, set
2434 the specified list of CPUs whose tick will be stopped
2435 whenever possible. The boot CPU will be forced outside
2436 the range to maintain the timekeeping.
2437 The CPUs in this range must also be included in the
2438 rcu_nocbs= set.
2440 noiotrap [SH] Disables trapped I/O port accesses.
2442 noirqdebug [X86-32] Disables the code which attempts to detect and
2443 disable unhandled interrupt sources.
2445 no_timer_check [X86,APIC] Disables the code which tests for
2446 broken timer IRQ sources.
2448 noisapnp [ISAPNP] Disables ISA PnP code.
2450 noinitrd [RAM] Tells the kernel not to load any configured
2451 initial RAM disk.
2453 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2454 remapping.
2455 [Deprecated - use intremap=off]
2457 nointroute [IA-64]
2459 nojitter [IA-64] Disables jitter checking for ITC timers.
2461 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2463 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2464 fault handling.
2466 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2467 steal time is computed, but won't influence scheduler
2468 behaviour
2470 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2472 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2474 noltlbs [PPC] Do not use large page/tlb entries for kernel
2475 lowmem mapping on PPC40x.
2477 nomca [IA-64] Disable machine check abort handling
2479 nomce [X86-32] Disable Machine Check Exception
2481 nomfgpt [X86-32] Disable Multi-Function General Purpose
2482 Timer usage (for AMD Geode machines).
2484 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2485 shutdown the other cpus. Instead use the REBOOT_VECTOR
2486 irq.
2488 nomodule Disable module load
2490 nopat [X86] Disable PAT (page attribute table extension of
2491 pagetables) support.
2493 norandmaps Don't use address space randomization. Equivalent to
2494 echo 0 > /proc/sys/kernel/randomize_va_space
2496 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2498 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2499 with UP alternatives
2501 nordrand [X86] Disable kernel use of the RDRAND and
2502 RDSEED instructions even if they are supported
2503 by the processor. RDRAND and RDSEED are still
2504 available to user space applications.
2506 noresume [SWSUSP] Disables resume and restores original swap
2507 space.
2509 no-scroll [VGA] Disables scrollback.
2510 This is required for the Braillex ib80-piezo Braille
2511 reader made by F.H. Papenmeier (Germany).
2513 nosbagart [IA-64]
2515 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2517 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2518 and disable the IO APIC. legacy for "maxcpus=0".
2520 nosoftlockup [KNL] Disable the soft-lockup detector.
2522 nosync [HW,M68K] Disables sync negotiation for all devices.
2524 notsc [BUGS=X86-32] Disable Time Stamp Counter
2526 nousb [USB] Disable the USB subsystem
2528 nowatchdog [KNL] Disable both lockup detectors, i.e.
2529 soft-lockup and NMI watchdog (hard-lockup).
2531 nowb [ARM]
2533 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2535 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2536 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2537 Some features depend on CPU0. Known dependencies are:
2538 1. Resume from suspend/hibernate depends on CPU0.
2539 Suspend/hibernate will fail if CPU0 is offline and you
2540 need to online CPU0 before suspend/hibernate.
2541 2. PIC interrupts also depend on CPU0. CPU0 can't be
2542 removed if a PIC interrupt is detected.
2543 It's said poweroff/reboot may depend on CPU0 on some
2544 machines although I haven't seen such issues so far
2545 after CPU0 is offline on a few tested machines.
2546 If the dependencies are under your control, you can
2547 turn on cpu0_hotplug.
2549 nptcg= [IA-64] Override max number of concurrent global TLB
2550 purges which is reported from either PAL_VM_SUMMARY or
2551 SAL PALO.
2553 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2554 could support. nr_cpus=n : n >= 1 limits the kernel to
2555 supporting 'n' processors. Later in runtime you can not
2556 use hotplug cpu feature to put more cpu back to online.
2557 just like you compile the kernel NR_CPUS=n
2559 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2561 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2562 Allowed values are enable and disable
2564 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2565 one of ['zone', 'node', 'default'] can be specified
2566 This can be set from sysctl after boot.
2567 See Documentation/sysctl/vm.txt for details.
2569 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2570 See Documentation/debugging-via-ohci1394.txt for more
2571 info.
2573 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2574 Rather than timing out after 20 ms if an EC
2575 command is not properly ACKed, override the length
2576 of the timeout. We have interrupts disabled while
2577 waiting for the ACK, so if this is set too high
2578 interrupts *may* be lost!
2580 omap_mux= [OMAP] Override bootloader pin multiplexing.
2581 Format: <mux_mode0.mode_name=value>...
2582 For example, to override I2C bus2:
2583 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2585 oprofile.timer= [HW]
2586 Use timer interrupt instead of performance counters
2588 oprofile.cpu_type= Force an oprofile cpu type
2589 This might be useful if you have an older oprofile
2590 userland or if you want common events.
2591 Format: { arch_perfmon }
2592 arch_perfmon: [X86] Force use of architectural
2593 perfmon on Intel CPUs instead of the
2594 CPU specific event set.
2595 timer: [X86] Force use of architectural NMI
2596 timer mode (see also oprofile.timer
2597 for generic hr timer mode)
2598 [s390] Force legacy basic mode sampling
2599 (report cpu_type "timer")
2601 oops=panic Always panic on oopses. Default is to just kill the
2602 process, but there is a small probability of
2603 deadlocking the machine.
2604 This will also cause panics on machine check exceptions.
2605 Useful together with panic=30 to trigger a reboot.
2607 OSS [HW,OSS]
2608 See Documentation/sound/oss/oss-parameters.txt
2610 page_owner= [KNL] Boot-time page_owner enabling option.
2611 Storage of the information about who allocated
2612 each page is disabled in default. With this switch,
2613 we can turn it on.
2614 on: enable the feature
2616 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2617 timeout > 0: seconds before rebooting
2618 timeout = 0: wait forever
2619 timeout < 0: reboot immediately
2620 Format: <timeout>
2622 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2623 on a WARN().
2625 crash_kexec_post_notifiers
2626 Run kdump after running panic-notifiers and dumping
2627 kmsg. This only for the users who doubt kdump always
2628 succeeds in any situation.
2629 Note that this also increases risks of kdump failure,
2630 because some panic notifiers can make the crashed
2631 kernel more unstable.
2633 parkbd.port= [HW] Parallel port number the keyboard adapter is
2634 connected to, default is 0.
2635 Format: <parport#>
2636 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2637 0 for XT, 1 for AT (default is AT).
2638 Format: <mode>
2640 parport= [HW,PPT] Specify parallel ports. 0 disables.
2641 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2642 Use 'auto' to force the driver to use any
2643 IRQ/DMA settings detected (the default is to
2644 ignore detected IRQ/DMA settings because of
2645 possible conflicts). You can specify the base
2646 address, IRQ, and DMA settings; IRQ and DMA
2647 should be numbers, or 'auto' (for using detected
2648 settings on that particular port), or 'nofifo'
2649 (to avoid using a FIFO even if it is detected).
2650 Parallel ports are assigned in the order they
2651 are specified on the command line, starting
2652 with parport0.
2654 parport_init_mode= [HW,PPT]
2655 Configure VIA parallel port to operate in
2656 a specific mode. This is necessary on Pegasos
2657 computer where firmware has no options for setting
2658 up parallel port mode and sets it to spp.
2659 Currently this function knows 686a and 8231 chips.
2660 Format: [spp|ps2|epp|ecp|ecpepp]
2662 pause_on_oops=
2663 Halt all CPUs after the first oops has been printed for
2664 the specified number of seconds. This is to be used if
2665 your oopses keep scrolling off the screen.
2667 pcbit= [HW,ISDN]
2669 pcd. [PARIDE]
2670 See header of drivers/block/paride/pcd.c.
2671 See also Documentation/blockdev/paride.txt.
2673 pci=option[,option...] [PCI] various PCI subsystem options:
2674 earlydump [X86] dump PCI config space before the kernel
2675 changes anything
2676 off [X86] don't probe for the PCI bus
2677 bios [X86-32] force use of PCI BIOS, don't access
2678 the hardware directly. Use this if your machine
2679 has a non-standard PCI host bridge.
2680 nobios [X86-32] disallow use of PCI BIOS, only direct
2681 hardware access methods are allowed. Use this
2682 if you experience crashes upon bootup and you
2683 suspect they are caused by the BIOS.
2684 conf1 [X86] Force use of PCI Configuration
2685 Mechanism 1.
2686 conf2 [X86] Force use of PCI Configuration
2687 Mechanism 2.
2688 noaer [PCIE] If the PCIEAER kernel config parameter is
2689 enabled, this kernel boot option can be used to
2690 disable the use of PCIE advanced error reporting.
2691 nodomains [PCI] Disable support for multiple PCI
2692 root domains (aka PCI segments, in ACPI-speak).
2693 nommconf [X86] Disable use of MMCONFIG for PCI
2694 Configuration
2695 check_enable_amd_mmconf [X86] check for and enable
2696 properly configured MMIO access to PCI
2697 config space on AMD family 10h CPU
2698 nomsi [MSI] If the PCI_MSI kernel config parameter is
2699 enabled, this kernel boot option can be used to
2700 disable the use of MSI interrupts system-wide.
2701 noioapicquirk [APIC] Disable all boot interrupt quirks.
2702 Safety option to keep boot IRQs enabled. This
2703 should never be necessary.
2704 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2705 primary IO-APIC for bridges that cannot disable
2706 boot IRQs. This fixes a source of spurious IRQs
2707 when the system masks IRQs.
2708 noioapicreroute [APIC] Disable workaround that uses the
2709 boot IRQ equivalent of an IRQ that connects to
2710 a chipset where boot IRQs cannot be disabled.
2711 The opposite of ioapicreroute.
2712 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2713 routing table. These calls are known to be buggy
2714 on several machines and they hang the machine
2715 when used, but on other computers it's the only
2716 way to get the interrupt routing table. Try
2717 this option if the kernel is unable to allocate
2718 IRQs or discover secondary PCI buses on your
2719 motherboard.
2720 rom [X86] Assign address space to expansion ROMs.
2721 Use with caution as certain devices share
2722 address decoders between ROMs and other
2723 resources.
2724 norom [X86] Do not assign address space to
2725 expansion ROMs that do not already have
2726 BIOS assigned address ranges.
2727 nobar [X86] Do not assign address space to the
2728 BARs that weren't assigned by the BIOS.
2729 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2730 assigned automatically to PCI devices. You can
2731 make the kernel exclude IRQs of your ISA cards
2732 this way.
2733 pirqaddr=0xAAAAA [X86] Specify the physical address
2734 of the PIRQ table (normally generated
2735 by the BIOS) if it is outside the
2736 F0000h-100000h range.
2737 lastbus=N [X86] Scan all buses thru bus #N. Can be
2738 useful if the kernel is unable to find your
2739 secondary buses and you want to tell it
2740 explicitly which ones they are.
2741 assign-busses [X86] Always assign all PCI bus
2742 numbers ourselves, overriding
2743 whatever the firmware may have done.
2744 usepirqmask [X86] Honor the possible IRQ mask stored
2745 in the BIOS $PIR table. This is needed on
2746 some systems with broken BIOSes, notably
2747 some HP Pavilion N5400 and Omnibook XE3
2748 notebooks. This will have no effect if ACPI
2749 IRQ routing is enabled.
2750 noacpi [X86] Do not use ACPI for IRQ routing
2751 or for PCI scanning.
2752 use_crs [X86] Use PCI host bridge window information
2753 from ACPI. On BIOSes from 2008 or later, this
2754 is enabled by default. If you need to use this,
2755 please report a bug.
2756 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2757 If you need to use this, please report a bug.
2758 routeirq Do IRQ routing for all PCI devices.
2759 This is normally done in pci_enable_device(),
2760 so this option is a temporary workaround
2761 for broken drivers that don't call it.
2762 skip_isa_align [X86] do not align io start addr, so can
2763 handle more pci cards
2764 firmware [ARM] Do not re-enumerate the bus but instead
2765 just use the configuration from the
2766 bootloader. This is currently used on
2767 IXP2000 systems where the bus has to be
2768 configured a certain way for adjunct CPUs.
2769 noearly [X86] Don't do any early type 1 scanning.
2770 This might help on some broken boards which
2771 machine check when some devices' config space
2772 is read. But various workarounds are disabled
2773 and some IOMMU drivers will not work.
2774 bfsort Sort PCI devices into breadth-first order.
2775 This sorting is done to get a device
2776 order compatible with older (<= 2.4) kernels.
2777 nobfsort Don't sort PCI devices into breadth-first order.
2778 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2779 tuning and use the BIOS-configured MPS defaults.
2780 pcie_bus_safe Set every device's MPS to the largest value
2781 supported by all devices below the root complex.
2782 pcie_bus_perf Set device MPS to the largest allowable MPS
2783 based on its parent bus. Also set MRRS (Max
2784 Read Request Size) to the largest supported
2785 value (no larger than the MPS that the device
2786 or bus can support) for best performance.
2787 pcie_bus_peer2peer Set every device's MPS to 128B, which
2788 every device is guaranteed to support. This
2789 configuration allows peer-to-peer DMA between
2790 any pair of devices, possibly at the cost of
2791 reduced performance. This also guarantees
2792 that hot-added devices will work.
2793 cbiosize=nn[KMG] The fixed amount of bus space which is
2794 reserved for the CardBus bridge's IO window.
2795 The default value is 256 bytes.
2796 cbmemsize=nn[KMG] The fixed amount of bus space which is
2797 reserved for the CardBus bridge's memory
2798 window. The default value is 64 megabytes.
2799 resource_alignment=
2800 Format:
2801 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2802 Specifies alignment and device to reassign
2803 aligned memory resources.
2804 If <order of align> is not specified,
2805 PAGE_SIZE is used as alignment.
2806 PCI-PCI bridge can be specified, if resource
2807 windows need to be expanded.
2808 ecrc= Enable/disable PCIe ECRC (transaction layer
2809 end-to-end CRC checking).
2810 bios: Use BIOS/firmware settings. This is the
2811 the default.
2812 off: Turn ECRC off
2813 on: Turn ECRC on.
2814 hpiosize=nn[KMG] The fixed amount of bus space which is
2815 reserved for hotplug bridge's IO window.
2816 Default size is 256 bytes.
2817 hpmemsize=nn[KMG] The fixed amount of bus space which is
2818 reserved for hotplug bridge's memory window.
2819 Default size is 2 megabytes.
2820 realloc= Enable/disable reallocating PCI bridge resources
2821 if allocations done by BIOS are too small to
2822 accommodate resources required by all child
2823 devices.
2824 off: Turn realloc off
2825 on: Turn realloc on
2826 realloc same as realloc=on
2827 noari do not use PCIe ARI.
2828 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2829 only look for one device below a PCIe downstream
2830 port.
2832 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2833 Management.
2834 off Disable ASPM.
2835 force Enable ASPM even on devices that claim not to support it.
2836 WARNING: Forcing ASPM on may cause system lockups.
2838 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2839 nomsi Do not use MSI for PCI Express Native Hotplug (this
2840 makes all PCIe ports use INTx for hotplug services).
2842 pcie_ports= [PCIE] PCIe ports handling:
2843 auto Ask the BIOS whether or not to use native PCIe services
2844 associated with PCIe ports (PME, hot-plug, AER). Use
2845 them only if that is allowed by the BIOS.
2846 native Use native PCIe services associated with PCIe ports
2847 unconditionally.
2848 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2849 ports driver.
2851 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2852 nomsi Do not use MSI for native PCIe PME signaling (this makes
2853 all PCIe root ports use INTx for all services).
2855 pcmv= [HW,PCMCIA] BadgePAD 4
2857 pd_ignore_unused
2858 [PM]
2859 Keep all power-domains already enabled by bootloader on,
2860 even if no driver has claimed them. This is useful
2861 for debug and development, but should not be
2862 needed on a platform with proper driver support.
2864 pd. [PARIDE]
2865 See Documentation/blockdev/paride.txt.
2867 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2868 boot time.
2869 Format: { 0 | 1 }
2870 See arch/parisc/kernel/pdc_chassis.c
2872 percpu_alloc= Select which percpu first chunk allocator to use.
2873 Currently supported values are "embed" and "page".
2874 Archs may support subset or none of the selections.
2875 See comments in mm/percpu.c for details on each
2876 allocator. This parameter is primarily for debugging
2877 and performance comparison.
2879 pf. [PARIDE]
2880 See Documentation/blockdev/paride.txt.
2882 pg. [PARIDE]
2883 See Documentation/blockdev/paride.txt.
2885 pirq= [SMP,APIC] Manual mp-table setup
2886 See Documentation/x86/i386/IO-APIC.txt.
2888 plip= [PPT,NET] Parallel port network link
2889 Format: { parport<nr> | timid | 0 }
2890 See also Documentation/parport.txt.
2892 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2893 Override pmtimer IOPort with a hex value.
2894 e.g. pmtmr=0x508
2896 pnp.debug=1 [PNP]
2897 Enable PNP debug messages (depends on the
2898 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2899 via /sys/module/pnp/parameters/debug. We always show
2900 current resource usage; turning this on also shows
2901 possible settings and some assignment information.
2903 pnpacpi= [ACPI]
2904 { off }
2906 pnpbios= [ISAPNP]
2907 { on | off | curr | res | no-curr | no-res }
2909 pnp_reserve_irq=
2910 [ISAPNP] Exclude IRQs for the autoconfiguration
2912 pnp_reserve_dma=
2913 [ISAPNP] Exclude DMAs for the autoconfiguration
2915 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2916 Ranges are in pairs (I/O port base and size).
2918 pnp_reserve_mem=
2919 [ISAPNP] Exclude memory regions for the
2920 autoconfiguration.
2921 Ranges are in pairs (memory base and size).
2923 ports= [IP_VS_FTP] IPVS ftp helper module
2924 Default is 21.
2925 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2926 may be specified.
2927 Format: <port>,<port>....
2929 print-fatal-signals=
2930 [KNL] debug: print fatal signals
2932 If enabled, warn about various signal handling
2933 related application anomalies: too many signals,
2934 too many POSIX.1 timers, fatal signals causing a
2935 coredump - etc.
2937 If you hit the warning due to signal overflow,
2938 you might want to try "ulimit -i unlimited".
2940 default: off.
2942 printk.always_kmsg_dump=
2943 Trigger kmsg_dump for cases other than kernel oops or
2944 panics
2945 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2946 default: disabled
2948 printk.time= Show timing data prefixed to each printk message line
2949 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2951 processor.max_cstate= [HW,ACPI]
2952 Limit processor to maximum C-state
2953 max_cstate=9 overrides any DMI blacklist limit.
2955 processor.nocst [HW,ACPI]
2956 Ignore the _CST method to determine C-states,
2957 instead using the legacy FADT method
2959 profile= [KNL] Enable kernel profiling via /proc/profile
2960 Format: [schedule,]<number>
2961 Param: "schedule" - profile schedule points.
2962 Param: <number> - step/bucket size as a power of 2 for
2963 statistical time based profiling.
2964 Param: "sleep" - profile D-state sleeping (millisecs).
2965 Requires CONFIG_SCHEDSTATS
2966 Param: "kvm" - profile VM exits.
2968 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2969 before loading.
2970 See Documentation/blockdev/ramdisk.txt.
2972 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2973 probe for; one of (bare|imps|exps|lifebook|any).
2974 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2975 per second.
2976 psmouse.resetafter= [HW,MOUSE]
2977 Try to reset the device after so many bad packets
2978 (0 = never).
2979 psmouse.resolution=
2980 [HW,MOUSE] Set desired mouse resolution, in dpi.
2981 psmouse.smartscroll=
2982 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2983 0 = disabled, 1 = enabled (default).
2985 pstore.backend= Specify the name of the pstore backend to use
2987 pt. [PARIDE]
2988 See Documentation/blockdev/paride.txt.
2990 pty.legacy_count=
2991 [KNL] Number of legacy pty's. Overwrites compiled-in
2992 default number.
2994 quiet [KNL] Disable most log messages
2996 r128= [HW,DRM]
2998 raid= [HW,RAID]
2999 See Documentation/md.txt.
3001 ramdisk_blocksize= [RAM]
3002 See Documentation/blockdev/ramdisk.txt.
3004 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3005 See Documentation/blockdev/ramdisk.txt.
3007 rcu_nocbs= [KNL]
3008 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3009 the specified list of CPUs to be no-callback CPUs.
3010 Invocation of these CPUs' RCU callbacks will
3011 be offloaded to "rcuox/N" kthreads created for
3012 that purpose, where "x" is "b" for RCU-bh, "p"
3013 for RCU-preempt, and "s" for RCU-sched, and "N"
3014 is the CPU number. This reduces OS jitter on the
3015 offloaded CPUs, which can be useful for HPC and
3016 real-time workloads. It can also improve energy
3017 efficiency for asymmetric multiprocessors.
3019 rcu_nocb_poll [KNL]
3020 Rather than requiring that offloaded CPUs
3021 (specified by rcu_nocbs= above) explicitly
3022 awaken the corresponding "rcuoN" kthreads,
3023 make these kthreads poll for callbacks.
3024 This improves the real-time response for the
3025 offloaded CPUs by relieving them of the need to
3026 wake up the corresponding kthread, but degrades
3027 energy efficiency by requiring that the kthreads
3028 periodically wake up to do the polling.
3030 rcutree.blimit= [KNL]
3031 Set maximum number of finished RCU callbacks to
3032 process in one batch.
3034 rcutree.dump_tree= [KNL]
3035 Dump the structure of the rcu_node combining tree
3036 out at early boot. This is used for diagnostic
3037 purposes, to verify correct tree setup.
3039 rcutree.gp_cleanup_delay= [KNL]
3040 Set the number of jiffies to delay each step of
3041 RCU grace-period cleanup. This only has effect
3042 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3044 rcutree.gp_init_delay= [KNL]
3045 Set the number of jiffies to delay each step of
3046 RCU grace-period initialization. This only has
3047 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3048 is set.
3050 rcutree.gp_preinit_delay= [KNL]
3051 Set the number of jiffies to delay each step of
3052 RCU grace-period pre-initialization, that is,
3053 the propagation of recent CPU-hotplug changes up
3054 the rcu_node combining tree. This only has effect
3055 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3057 rcutree.rcu_fanout_exact= [KNL]
3058 Disable autobalancing of the rcu_node combining
3059 tree. This is used by rcutorture, and might
3060 possibly be useful for architectures having high
3061 cache-to-cache transfer latencies.
3063 rcutree.rcu_fanout_leaf= [KNL]
3064 Increase the number of CPUs assigned to each
3065 leaf rcu_node structure. Useful for very large
3066 systems.
3068 rcutree.jiffies_till_sched_qs= [KNL]
3069 Set required age in jiffies for a
3070 given grace period before RCU starts
3071 soliciting quiescent-state help from
3072 rcu_note_context_switch().
3074 rcutree.jiffies_till_first_fqs= [KNL]
3075 Set delay from grace-period initialization to
3076 first attempt to force quiescent states.
3077 Units are jiffies, minimum value is zero,
3078 and maximum value is HZ.
3080 rcutree.jiffies_till_next_fqs= [KNL]
3081 Set delay between subsequent attempts to force
3082 quiescent states. Units are jiffies, minimum
3083 value is one, and maximum value is HZ.
3085 rcutree.kthread_prio= [KNL,BOOT]
3086 Set the SCHED_FIFO priority of the RCU per-CPU
3087 kthreads (rcuc/N). This value is also used for
3088 the priority of the RCU boost threads (rcub/N)
3089 and for the RCU grace-period kthreads (rcu_bh,
3090 rcu_preempt, and rcu_sched). If RCU_BOOST is
3091 set, valid values are 1-99 and the default is 1
3092 (the least-favored priority). Otherwise, when
3093 RCU_BOOST is not set, valid values are 0-99 and
3094 the default is zero (non-realtime operation).
3096 rcutree.rcu_nocb_leader_stride= [KNL]
3097 Set the number of NOCB kthread groups, which
3098 defaults to the square root of the number of
3099 CPUs. Larger numbers reduces the wakeup overhead
3100 on the per-CPU grace-period kthreads, but increases
3101 that same overhead on each group's leader.
3103 rcutree.qhimark= [KNL]
3104 Set threshold of queued RCU callbacks beyond which
3105 batch limiting is disabled.
3107 rcutree.qlowmark= [KNL]
3108 Set threshold of queued RCU callbacks below which
3109 batch limiting is re-enabled.
3111 rcutree.rcu_idle_gp_delay= [KNL]
3112 Set wakeup interval for idle CPUs that have
3113 RCU callbacks (RCU_FAST_NO_HZ=y).
3115 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3116 Set wakeup interval for idle CPUs that have
3117 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3118 Lazy RCU callbacks are those which RCU can
3119 prove do nothing more than free memory.
3121 rcutorture.cbflood_inter_holdoff= [KNL]
3122 Set holdoff time (jiffies) between successive
3123 callback-flood tests.
3125 rcutorture.cbflood_intra_holdoff= [KNL]
3126 Set holdoff time (jiffies) between successive
3127 bursts of callbacks within a given callback-flood
3128 test.
3130 rcutorture.cbflood_n_burst= [KNL]
3131 Set the number of bursts making up a given
3132 callback-flood test. Set this to zero to
3133 disable callback-flood testing.
3135 rcutorture.cbflood_n_per_burst= [KNL]
3136 Set the number of callbacks to be registered
3137 in a given burst of a callback-flood test.
3139 rcutorture.fqs_duration= [KNL]
3140 Set duration of force_quiescent_state bursts
3141 in microseconds.
3143 rcutorture.fqs_holdoff= [KNL]
3144 Set holdoff time within force_quiescent_state bursts
3145 in microseconds.
3147 rcutorture.fqs_stutter= [KNL]
3148 Set wait time between force_quiescent_state bursts
3149 in seconds.
3151 rcutorture.gp_cond= [KNL]
3152 Use conditional/asynchronous update-side
3153 primitives, if available.
3155 rcutorture.gp_exp= [KNL]
3156 Use expedited update-side primitives, if available.
3158 rcutorture.gp_normal= [KNL]
3159 Use normal (non-expedited) asynchronous
3160 update-side primitives, if available.
3162 rcutorture.gp_sync= [KNL]
3163 Use normal (non-expedited) synchronous
3164 update-side primitives, if available. If all
3165 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3166 rcutorture.gp_normal=, and rcutorture.gp_sync=
3167 are zero, rcutorture acts as if is interpreted
3168 they are all non-zero.
3170 rcutorture.n_barrier_cbs= [KNL]
3171 Set callbacks/threads for rcu_barrier() testing.
3173 rcutorture.nfakewriters= [KNL]
3174 Set number of concurrent RCU writers. These just
3175 stress RCU, they don't participate in the actual
3176 test, hence the "fake".
3178 rcutorture.nreaders= [KNL]
3179 Set number of RCU readers. The value -1 selects
3180 N-1, where N is the number of CPUs. A value
3181 "n" less than -1 selects N-n-2, where N is again
3182 the number of CPUs. For example, -2 selects N
3183 (the number of CPUs), -3 selects N+1, and so on.
3185 rcutorture.object_debug= [KNL]
3186 Enable debug-object double-call_rcu() testing.
3188 rcutorture.onoff_holdoff= [KNL]
3189 Set time (s) after boot for CPU-hotplug testing.
3191 rcutorture.onoff_interval= [KNL]
3192 Set time (s) between CPU-hotplug operations, or
3193 zero to disable CPU-hotplug testing.
3195 rcutorture.shuffle_interval= [KNL]
3196 Set task-shuffle interval (s). Shuffling tasks
3197 allows some CPUs to go into dyntick-idle mode
3198 during the rcutorture test.
3200 rcutorture.shutdown_secs= [KNL]
3201 Set time (s) after boot system shutdown. This
3202 is useful for hands-off automated testing.
3204 rcutorture.stall_cpu= [KNL]
3205 Duration of CPU stall (s) to test RCU CPU stall
3206 warnings, zero to disable.
3208 rcutorture.stall_cpu_holdoff= [KNL]
3209 Time to wait (s) after boot before inducing stall.
3211 rcutorture.stat_interval= [KNL]
3212 Time (s) between statistics printk()s.
3214 rcutorture.stutter= [KNL]
3215 Time (s) to stutter testing, for example, specifying
3216 five seconds causes the test to run for five seconds,
3217 wait for five seconds, and so on. This tests RCU's
3218 ability to transition abruptly to and from idle.
3220 rcutorture.test_boost= [KNL]
3221 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3222 "Maybe" means test if the RCU implementation
3223 under test support RCU priority boosting.
3225 rcutorture.test_boost_duration= [KNL]
3226 Duration (s) of each individual boost test.
3228 rcutorture.test_boost_interval= [KNL]
3229 Interval (s) between each boost test.
3231 rcutorture.test_no_idle_hz= [KNL]
3232 Test RCU's dyntick-idle handling. See also the
3233 rcutorture.shuffle_interval parameter.
3235 rcutorture.torture_runnable= [BOOT]
3236 Start rcutorture running at boot time.
3238 rcutorture.torture_type= [KNL]
3239 Specify the RCU implementation to test.
3241 rcutorture.verbose= [KNL]
3242 Enable additional printk() statements.
3244 rcupdate.rcu_expedited= [KNL]
3245 Use expedited grace-period primitives, for
3246 example, synchronize_rcu_expedited() instead
3247 of synchronize_rcu(). This reduces latency,
3248 but can increase CPU utilization, degrade
3249 real-time latency, and degrade energy efficiency.
3251 rcupdate.rcu_cpu_stall_suppress= [KNL]
3252 Suppress RCU CPU stall warning messages.
3254 rcupdate.rcu_cpu_stall_timeout= [KNL]
3255 Set timeout for RCU CPU stall warning messages.
3257 rcupdate.rcu_task_stall_timeout= [KNL]
3258 Set timeout in jiffies for RCU task stall warning
3259 messages. Disable with a value less than or equal
3260 to zero.
3262 rcupdate.rcu_self_test= [KNL]
3263 Run the RCU early boot self tests
3265 rcupdate.rcu_self_test_bh= [KNL]
3266 Run the RCU bh early boot self tests
3268 rcupdate.rcu_self_test_sched= [KNL]
3269 Run the RCU sched early boot self tests
3271 rdinit= [KNL]
3272 Format: <full_path>
3273 Run specified binary instead of /init from the ramdisk,
3274 used for early userspace startup. See initrd.
3276 reboot= [KNL]
3277 Format (x86 or x86_64):
3278 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3279 [[,]s[mp]#### \
3280 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3281 [[,]f[orce]
3282 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3283 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3284 reboot_force is either force or not specified,
3285 reboot_cpu is s[mp]#### with #### being the processor
3286 to be used for rebooting.
3288 relax_domain_level=
3289 [KNL, SMP] Set scheduler's default relax_domain_level.
3290 See Documentation/cgroups/cpusets.txt.
3292 relative_sleep_states=
3293 [SUSPEND] Use sleep state labeling where the deepest
3294 state available other than hibernation is always "mem".
3295 Format: { "0" | "1" }
3296 0 -- Traditional sleep state labels.
3297 1 -- Relative sleep state labels.
3299 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3301 reservetop= [X86-32]
3302 Format: nn[KMG]
3303 Reserves a hole at the top of the kernel virtual
3304 address space.
3306 reservelow= [X86]
3307 Format: nn[K]
3308 Set the amount of memory to reserve for BIOS at
3309 the bottom of the address space.
3311 reset_devices [KNL] Force drivers to reset the underlying device
3312 during initialization.
3314 resume= [SWSUSP]
3315 Specify the partition device for software suspend
3316 Format:
3317 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3319 resume_offset= [SWSUSP]
3320 Specify the offset from the beginning of the partition
3321 given by "resume=" at which the swap header is located,
3322 in <PAGE_SIZE> units (needed only for swap files).
3323 See Documentation/power/swsusp-and-swap-files.txt
3325 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3326 read the resume files
3328 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3329 Useful for devices that are detected asynchronously
3330 (e.g. USB and MMC devices).
3332 hibernate= [HIBERNATION]
3333 noresume Don't check if there's a hibernation image
3334 present during boot.
3335 nocompress Don't compress/decompress hibernation images.
3336 no Disable hibernation and resume.
3338 retain_initrd [RAM] Keep initrd memory after extraction
3340 rfkill.default_state=
3341 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3342 etc. communication is blocked by default.
3343 1 Unblocked.
3345 rfkill.master_switch_mode=
3346 0 The "airplane mode" button does nothing.
3347 1 The "airplane mode" button toggles between everything
3348 blocked and the previous configuration.
3349 2 The "airplane mode" button toggles between everything
3350 blocked and everything unblocked.
3352 rhash_entries= [KNL,NET]
3353 Set number of hash buckets for route cache
3355 ro [KNL] Mount root device read-only on boot
3357 root= [KNL] Root filesystem
3358 See name_to_dev_t comment in init/do_mounts.c.
3360 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3361 mount the root filesystem
3363 rootflags= [KNL] Set root filesystem mount option string
3365 rootfstype= [KNL] Set root filesystem type
3367 rootwait [KNL] Wait (indefinitely) for root device to show up.
3368 Useful for devices that are detected asynchronously
3369 (e.g. USB and MMC devices).
3371 rproc_mem=nn[KMG][@address]
3372 [KNL,ARM,CMA] Remoteproc physical memory block.
3373 Memory area to be used by remote processor image,
3374 managed by CMA.
3376 rw [KNL] Mount root device read-write on boot
3378 S [KNL] Run init in single mode
3380 s390_iommu= [HW,S390]
3381 Set s390 IOTLB flushing mode
3382 strict
3383 With strict flushing every unmap operation will result in
3384 an IOTLB flush. Default is lazy flushing before reuse,
3385 which is faster.
3387 sa1100ir [NET]
3388 See drivers/net/irda/sa1100_ir.c.
3390 sbni= [NET] Granch SBNI12 leased line adapter
3392 sched_debug [KNL] Enables verbose scheduler debug messages.
3394 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3395 xtime_lock contention on larger systems, and/or RCU lock
3396 contention on all systems with CONFIG_MAXSMP set.
3397 Format: { "0" | "1" }
3398 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3399 1 -- enable.
3400 Note: increases power consumption, thus should only be
3401 enabled if running jitter sensitive (HPC/RT) workloads.
3403 security= [SECURITY] Choose a security module to enable at boot.
3404 If this boot parameter is not specified, only the first
3405 security module asking for security registration will be
3406 loaded. An invalid security module name will be treated
3407 as if no module has been chosen.
3409 selinux= [SELINUX] Disable or enable SELinux at boot time.
3410 Format: { "0" | "1" }
3411 See security/selinux/Kconfig help text.
3412 0 -- disable.
3413 1 -- enable.
3414 Default value is set via kernel config option.
3415 If enabled at boot time, /selinux/disable can be used
3416 later to disable prior to initial policy load.
3418 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3419 Format: { "0" | "1" }
3420 See security/apparmor/Kconfig help text
3421 0 -- disable.
3422 1 -- enable.
3423 Default value is set via kernel config option.
3425 serialnumber [BUGS=X86-32]
3427 shapers= [NET]
3428 Maximal number of shapers.
3430 show_msr= [x86] show boot-time MSR settings
3431 Format: { <integer> }
3432 Show boot-time (BIOS-initialized) MSR settings.
3433 The parameter means the number of CPUs to show,
3434 for example 1 means boot CPU only.
3436 simeth= [IA-64]
3437 simscsi=
3439 slram= [HW,MTD]
3441 slab_nomerge [MM]
3442 Disable merging of slabs with similar size. May be
3443 necessary if there is some reason to distinguish
3444 allocs to different slabs. Debug options disable
3445 merging on their own.
3446 For more information see Documentation/vm/slub.txt.
3448 slab_max_order= [MM, SLAB]
3449 Determines the maximum allowed order for slabs.
3450 A high setting may cause OOMs due to memory
3451 fragmentation. Defaults to 1 for systems with
3452 more than 32MB of RAM, 0 otherwise.
3454 slub_debug[=options[,slabs]] [MM, SLUB]
3455 Enabling slub_debug allows one to determine the
3456 culprit if slab objects become corrupted. Enabling
3457 slub_debug can create guard zones around objects and
3458 may poison objects when not in use. Also tracks the
3459 last alloc / free. For more information see
3460 Documentation/vm/slub.txt.
3462 slub_max_order= [MM, SLUB]
3463 Determines the maximum allowed order for slabs.
3464 A high setting may cause OOMs due to memory
3465 fragmentation. For more information see
3466 Documentation/vm/slub.txt.
3468 slub_min_objects= [MM, SLUB]
3469 The minimum number of objects per slab. SLUB will
3470 increase the slab order up to slub_max_order to
3471 generate a sufficiently large slab able to contain
3472 the number of objects indicated. The higher the number
3473 of objects the smaller the overhead of tracking slabs
3474 and the less frequently locks need to be acquired.
3475 For more information see Documentation/vm/slub.txt.
3477 slub_min_order= [MM, SLUB]
3478 Determines the minimum page order for slabs. Must be
3479 lower than slub_max_order.
3480 For more information see Documentation/vm/slub.txt.
3482 slub_nomerge [MM, SLUB]
3483 Same with slab_nomerge. This is supported for legacy.
3484 See slab_nomerge for more information.
3486 smart2= [HW]
3487 Format: <io1>[,<io2>[,...,<io8>]]
3489 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3490 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3491 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3492 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3493 smsc-ircc2.ircc_irq= [HW] IRQ line
3494 smsc-ircc2.ircc_dma= [HW] DMA channel
3495 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3496 0: Toshiba Satellite 1800 (GP data pin select)
3497 1: Fast pin select (default)
3498 2: ATC IRMode
3500 softlockup_panic=
3501 [KNL] Should the soft-lockup detector generate panics.
3502 Format: <integer>
3504 softlockup_all_cpu_backtrace=
3505 [KNL] Should the soft-lockup detector generate
3506 backtraces on all cpus.
3507 Format: <integer>
3509 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3510 See Documentation/laptops/sonypi.txt
3512 spia_io_base= [HW,MTD]
3513 spia_fio_base=
3514 spia_pedr=
3515 spia_peddr=
3517 stacktrace [FTRACE]
3518 Enabled the stack tracer on boot up.
3520 stacktrace_filter=[function-list]
3521 [FTRACE] Limit the functions that the stack tracer
3522 will trace at boot up. function-list is a comma separated
3523 list of functions. This list can be changed at run
3524 time by the stack_trace_filter file in the debugfs
3525 tracing directory. Note, this enables stack tracing
3526 and the stacktrace above is not needed.
3528 sti= [PARISC,HW]
3529 Format: <num>
3530 Set the STI (builtin display/keyboard on the HP-PARISC
3531 machines) console (graphic card) which should be used
3532 as the initial boot-console.
3533 See also comment in drivers/video/console/sticore.c.
3535 sti_font= [HW]
3536 See comment in drivers/video/console/sticore.c.
3538 stifb= [HW]
3539 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3541 sunrpc.min_resvport=
3542 sunrpc.max_resvport=
3543 [NFS,SUNRPC]
3544 SunRPC servers often require that client requests
3545 originate from a privileged port (i.e. a port in the
3546 range 0 < portnr < 1024).
3547 An administrator who wishes to reserve some of these
3548 ports for other uses may adjust the range that the
3549 kernel's sunrpc client considers to be privileged
3550 using these two parameters to set the minimum and
3551 maximum port values.
3553 sunrpc.pool_mode=
3554 [NFS]
3555 Control how the NFS server code allocates CPUs to
3556 service thread pools. Depending on how many NICs
3557 you have and where their interrupts are bound, this
3558 option will affect which CPUs will do NFS serving.
3559 Note: this parameter cannot be changed while the
3560 NFS server is running.
3562 auto the server chooses an appropriate mode
3563 automatically using heuristics
3564 global a single global pool contains all CPUs
3565 percpu one pool for each CPU
3566 pernode one pool for each NUMA node (equivalent
3567 to global on non-NUMA machines)
3569 sunrpc.tcp_slot_table_entries=
3570 sunrpc.udp_slot_table_entries=
3571 [NFS,SUNRPC]
3572 Sets the upper limit on the number of simultaneous
3573 RPC calls that can be sent from the client to a
3574 server. Increasing these values may allow you to
3575 improve throughput, but will also increase the
3576 amount of memory reserved for use by the client.
3578 suspend.pm_test_delay=
3579 [SUSPEND]
3580 Sets the number of seconds to remain in a suspend test
3581 mode before resuming the system (see
3582 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3583 is set. Default value is 5.
3585 swapaccount=[0|1]
3586 [KNL] Enable accounting of swap in memory resource
3587 controller if no parameter or 1 is given or disable
3588 it if 0 is given (See Documentation/cgroups/memory.txt)
3590 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3591 Format: { <int> | force }
3592 <int> -- Number of I/O TLB slabs
3593 force -- force using of bounce buffers even if they
3594 wouldn't be automatically used by the kernel
3596 switches= [HW,M68k]
3598 sysfs.deprecated=0|1 [KNL]
3599 Enable/disable old style sysfs layout for old udev
3600 on older distributions. When this option is enabled
3601 very new udev will not work anymore. When this option
3602 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3603 in older udev will not work anymore.
3604 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3605 the kernel configuration.
3607 sysrq_always_enabled
3608 [KNL]
3609 Ignore sysrq setting - this boot parameter will
3610 neutralize any effect of /proc/sys/kernel/sysrq.
3611 Useful for debugging.
3613 tcpmhash_entries= [KNL,NET]
3614 Set the number of tcp_metrics_hash slots.
3615 Default value is 8192 or 16384 depending on total
3616 ram pages. This is used to specify the TCP metrics
3617 cache size. See Documentation/networking/ip-sysctl.txt
3618 "tcp_no_metrics_save" section for more details.
3620 tdfx= [HW,DRM]
3622 test_suspend= [SUSPEND][,N]
3623 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3624 standby suspend) or "freeze" (for suspend type freeze)
3625 as the system sleep state during system startup with
3626 the optional capability to repeat N number of times.
3627 The system is woken from this state using a
3628 wakeup-capable RTC alarm.
3630 thash_entries= [KNL,NET]
3631 Set number of hash buckets for TCP connection
3633 thermal.act= [HW,ACPI]
3634 -1: disable all active trip points in all thermal zones
3635 <degrees C>: override all lowest active trip points
3637 thermal.crt= [HW,ACPI]
3638 -1: disable all critical trip points in all thermal zones
3639 <degrees C>: override all critical trip points
3641 thermal.nocrt= [HW,ACPI]
3642 Set to disable actions on ACPI thermal zone
3643 critical and hot trip points.
3645 thermal.off= [HW,ACPI]
3646 1: disable ACPI thermal control
3648 thermal.psv= [HW,ACPI]
3649 -1: disable all passive trip points
3650 <degrees C>: override all passive trip points to this
3651 value
3653 thermal.tzp= [HW,ACPI]
3654 Specify global default ACPI thermal zone polling rate
3655 <deci-seconds>: poll all this frequency
3656 0: no polling (default)
3658 threadirqs [KNL]
3659 Force threading of all interrupt handlers except those
3660 marked explicitly IRQF_NO_THREAD.
3662 tmem [KNL,XEN]
3663 Enable the Transcendent memory driver if built-in.
3665 tmem.cleancache=0|1 [KNL, XEN]
3666 Default is on (1). Disable the usage of the cleancache
3667 API to send anonymous pages to the hypervisor.
3669 tmem.frontswap=0|1 [KNL, XEN]
3670 Default is on (1). Disable the usage of the frontswap
3671 API to send swap pages to the hypervisor. If disabled
3672 the selfballooning and selfshrinking are force disabled.
3674 tmem.selfballooning=0|1 [KNL, XEN]
3675 Default is on (1). Disable the driving of swap pages
3676 to the hypervisor.
3678 tmem.selfshrinking=0|1 [KNL, XEN]
3679 Default is on (1). Partial swapoff that immediately
3680 transfers pages from Xen hypervisor back to the
3681 kernel based on different criteria.
3683 topology= [S390]
3684 Format: {off | on}
3685 Specify if the kernel should make use of the cpu
3686 topology information if the hardware supports this.
3687 The scheduler will make use of this information and
3688 e.g. base its process migration decisions on it.
3689 Default is on.
3691 topology_updates= [KNL, PPC, NUMA]
3692 Format: {off}
3693 Specify if the kernel should ignore (off)
3694 topology updates sent by the hypervisor to this
3695 LPAR.
3697 tp720= [HW,PS2]
3699 tpm_suspend_pcr=[HW,TPM]
3700 Format: integer pcr id
3701 Specify that at suspend time, the tpm driver
3702 should extend the specified pcr with zeros,
3703 as a workaround for some chips which fail to
3704 flush the last written pcr on TPM_SaveState.
3705 This will guarantee that all the other pcrs
3706 are saved.
3708 trace_buf_size=nn[KMG]
3709 [FTRACE] will set tracing buffer size on each cpu.
3711 trace_event=[event-list]
3712 [FTRACE] Set and start specified trace events in order
3713 to facilitate early boot debugging.
3714 See also Documentation/trace/events.txt
3716 trace_options=[option-list]
3717 [FTRACE] Enable or disable tracer options at boot.
3718 The option-list is a comma delimited list of options
3719 that can be enabled or disabled just as if you were
3720 to echo the option name into
3722 /sys/kernel/debug/tracing/trace_options
3724 For example, to enable stacktrace option (to dump the
3725 stack trace of each event), add to the command line:
3727 trace_options=stacktrace
3729 See also Documentation/trace/ftrace.txt "trace options"
3730 section.
3732 tp_printk[FTRACE]
3733 Have the tracepoints sent to printk as well as the
3734 tracing ring buffer. This is useful for early boot up
3735 where the system hangs or reboots and does not give the
3736 option for reading the tracing buffer or performing a
3737 ftrace_dump_on_oops.
3739 To turn off having tracepoints sent to printk,
3740 echo 0 > /proc/sys/kernel/tracepoint_printk
3741 Note, echoing 1 into this file without the
3742 tracepoint_printk kernel cmdline option has no effect.
3744 ** CAUTION **
3746 Having tracepoints sent to printk() and activating high
3747 frequency tracepoints such as irq or sched, can cause
3748 the system to live lock.
3750 traceoff_on_warning
3751 [FTRACE] enable this option to disable tracing when a
3752 warning is hit. This turns off "tracing_on". Tracing can
3753 be enabled again by echoing '1' into the "tracing_on"
3754 file located in /sys/kernel/debug/tracing/
3756 This option is useful, as it disables the trace before
3757 the WARNING dump is called, which prevents the trace to
3758 be filled with content caused by the warning output.
3760 This option can also be set at run time via the sysctl
3761 option: kernel/traceoff_on_warning
3763 transparent_hugepage=
3764 [KNL]
3765 Format: [always|madvise|never]
3766 Can be used to control the default behavior of the system
3767 with respect to transparent hugepages.
3768 See Documentation/vm/transhuge.txt for more details.
3770 tsc= Disable clocksource stability checks for TSC.
3771 Format: <string>
3772 [x86] reliable: mark tsc clocksource as reliable, this
3773 disables clocksource verification at runtime, as well
3774 as the stability checks done at bootup. Used to enable
3775 high-resolution timer mode on older hardware, and in
3776 virtualized environment.
3777 [x86] noirqtime: Do not use TSC to do irq accounting.
3778 Used to run time disable IRQ_TIME_ACCOUNTING on any
3779 platforms where RDTSC is slow and this accounting
3780 can add overhead.
3782 turbografx.map[2|3]= [HW,JOY]
3783 TurboGraFX parallel port interface
3784 Format:
3785 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3786 See also Documentation/input/joystick-parport.txt
3788 udbg-immortal [PPC] When debugging early kernel crashes that
3789 happen after console_init() and before a proper
3790 console driver takes over, this boot options might
3791 help "seeing" what's going on.
3793 uhash_entries= [KNL,NET]
3794 Set number of hash buckets for UDP/UDP-Lite connections
3796 uhci-hcd.ignore_oc=
3797 [USB] Ignore overcurrent events (default N).
3798 Some badly-designed motherboards generate lots of
3799 bogus events, for ports that aren't wired to
3800 anything. Set this parameter to avoid log spamming.
3801 Note that genuine overcurrent events won't be
3802 reported either.
3804 unknown_nmi_panic
3805 [X86] Cause panic on unknown NMI.
3807 usbcore.authorized_default=
3808 [USB] Default USB device authorization:
3809 (default -1 = authorized except for wireless USB,
3810 0 = not authorized, 1 = authorized)
3812 usbcore.autosuspend=
3813 [USB] The autosuspend time delay (in seconds) used
3814 for newly-detected USB devices (default 2). This
3815 is the time required before an idle device will be
3816 autosuspended. Devices for which the delay is set
3817 to a negative value won't be autosuspended at all.
3819 usbcore.usbfs_snoop=
3820 [USB] Set to log all usbfs traffic (default 0 = off).
3822 usbcore.blinkenlights=
3823 [USB] Set to cycle leds on hubs (default 0 = off).
3825 usbcore.old_scheme_first=
3826 [USB] Start with the old device initialization
3827 scheme (default 0 = off).
3829 usbcore.usbfs_memory_mb=
3830 [USB] Memory limit (in MB) for buffers allocated by
3831 usbfs (default = 16, 0 = max = 2047).
3833 usbcore.use_both_schemes=
3834 [USB] Try the other device initialization scheme
3835 if the first one fails (default 1 = enabled).
3837 usbcore.initial_descriptor_timeout=
3838 [USB] Specifies timeout for the initial 64-byte
3839 USB_REQ_GET_DESCRIPTOR request in milliseconds
3840 (default 5000 = 5.0 seconds).
3842 usbhid.mousepoll=
3843 [USBHID] The interval which mice are to be polled at.
3845 usb-storage.delay_use=
3846 [UMS] The delay in seconds before a new device is
3847 scanned for Logical Units (default 1).
3849 usb-storage.quirks=
3850 [UMS] A list of quirks entries to supplement or
3851 override the built-in unusual_devs list. List
3852 entries are separated by commas. Each entry has
3853 the form VID:PID:Flags where VID and PID are Vendor
3854 and Product ID values (4-digit hex numbers) and
3855 Flags is a set of characters, each corresponding
3856 to a common usb-storage quirk flag as follows:
3857 a = SANE_SENSE (collect more than 18 bytes
3858 of sense data);
3859 b = BAD_SENSE (don't collect more than 18
3860 bytes of sense data);
3861 c = FIX_CAPACITY (decrease the reported
3862 device capacity by one sector);
3863 d = NO_READ_DISC_INFO (don't use
3864 READ_DISC_INFO command);
3865 e = NO_READ_CAPACITY_16 (don't use
3866 READ_CAPACITY_16 command);
3867 f = NO_REPORT_OPCODES (don't use report opcodes
3868 command, uas only);
3869 g = MAX_SECTORS_240 (don't transfer more than
3870 240 sectors at a time, uas only);
3871 h = CAPACITY_HEURISTICS (decrease the
3872 reported device capacity by one
3873 sector if the number is odd);
3874 i = IGNORE_DEVICE (don't bind to this
3875 device);
3876 l = NOT_LOCKABLE (don't try to lock and
3877 unlock ejectable media);
3878 m = MAX_SECTORS_64 (don't transfer more
3879 than 64 sectors = 32 KB at a time);
3880 n = INITIAL_READ10 (force a retry of the
3881 initial READ(10) command);
3882 o = CAPACITY_OK (accept the capacity
3883 reported by the device);
3884 p = WRITE_CACHE (the device cache is ON
3885 by default);
3886 r = IGNORE_RESIDUE (the device reports
3887 bogus residue values);
3888 s = SINGLE_LUN (the device has only one
3889 Logical Unit);
3890 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3891 commands, uas only);
3892 u = IGNORE_UAS (don't bind to the uas driver);
3893 w = NO_WP_DETECT (don't test whether the
3894 medium is write-protected).
3895 Example: quirks=0419:aaf5:rl,0421:0433:rc
3897 user_debug= [KNL,ARM]
3898 Format: <int>
3899 See arch/arm/Kconfig.debug help text.
3900 1 - undefined instruction events
3901 2 - system calls
3902 4 - invalid data aborts
3903 8 - SIGSEGV faults
3904 16 - SIGBUS faults
3905 Example: user_debug=31
3907 userpte=
3908 [X86] Flags controlling user PTE allocations.
3910 nohigh = do not allocate PTE pages in
3911 HIGHMEM regardless of setting
3912 of CONFIG_HIGHPTE.
3914 vdso= [X86,SH]
3915 On X86_32, this is an alias for vdso32=. Otherwise:
3917 vdso=1: enable VDSO (the default)
3918 vdso=0: disable VDSO mapping
3920 vdso32= [X86] Control the 32-bit vDSO
3921 vdso32=1: enable 32-bit VDSO
3922 vdso32=0 or vdso32=2: disable 32-bit VDSO
3924 See the help text for CONFIG_COMPAT_VDSO for more
3925 details. If CONFIG_COMPAT_VDSO is set, the default is
3926 vdso32=0; otherwise, the default is vdso32=1.
3928 For compatibility with older kernels, vdso32=2 is an
3929 alias for vdso32=0.
3931 Try vdso32=0 if you encounter an error that says:
3932 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3934 vector= [IA-64,SMP]
3935 vector=percpu: enable percpu vector domain
3937 video= [FB] Frame buffer configuration
3938 See Documentation/fb/modedb.txt.
3940 video.brightness_switch_enabled= [0,1]
3941 If set to 1, on receiving an ACPI notify event
3942 generated by hotkey, video driver will adjust brightness
3943 level and then send out the event to user space through
3944 the allocated input device; If set to 0, video driver
3945 will only send out the event without touching backlight
3946 brightness level.
3947 default: 1
3949 virtio_mmio.device=
3950 [VMMIO] Memory mapped virtio (platform) device.
3952 <size>@<baseaddr>:<irq>[:<id>]
3953 where:
3954 <size> := size (can use standard suffixes
3955 like K, M and G)
3956 <baseaddr> := physical base address
3957 <irq> := interrupt number (as passed to
3958 request_irq())
3959 <id> := (optional) platform device id
3960 example:
3961 virtio_mmio.device=1K@0x100b0000:48:7
3963 Can be used multiple times for multiple devices.
3965 vga= [BOOT,X86-32] Select a particular video mode
3966 See Documentation/x86/boot.txt and
3967 Documentation/svga.txt.
3968 Use vga=ask for menu.
3969 This is actually a boot loader parameter; the value is
3970 passed to the kernel using a special protocol.
3972 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3973 size of <nn>. This can be used to increase the
3974 minimum size (128MB on x86). It can also be used to
3975 decrease the size and leave more room for directly
3976 mapped kernel RAM.
3978 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3979 Format: <command>
3981 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3982 Format: <command>
3984 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3985 Format: <command>
3987 vsyscall= [X86-64]
3988 Controls the behavior of vsyscalls (i.e. calls to
3989 fixed addresses of 0xffffffffff600x00 from legacy
3990 code). Most statically-linked binaries and older
3991 versions of glibc use these calls. Because these
3992 functions are at fixed addresses, they make nice
3993 targets for exploits that can control RIP.
3995 emulate [default] Vsyscalls turn into traps and are
3996 emulated reasonably safely.
3998 native Vsyscalls are native syscall instructions.
3999 This is a little bit faster than trapping
4000 and makes a few dynamic recompilers work
4001 better than they would in emulation mode.
4002 It also makes exploits much easier to write.
4004 none Vsyscalls don't work at all. This makes
4005 them quite hard to use for exploits but
4006 might break your system.
4008 vt.color= [VT] Default text color.
4009 Format: 0xYX, X = foreground, Y = background.
4010 Default: 0x07 = light gray on black.
4012 vt.cur_default= [VT] Default cursor shape.
4013 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4014 the parameters of the <Esc>[?A;B;Cc escape sequence;
4015 see VGA-softcursor.txt. Default: 2 = underline.
4017 vt.default_blu= [VT]
4018 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4019 Change the default blue palette of the console.
4020 This is a 16-member array composed of values
4021 ranging from 0-255.
4023 vt.default_grn= [VT]
4024 Format: <green0>,<green1>,<green2>,...,<green15>
4025 Change the default green palette of the console.
4026 This is a 16-member array composed of values
4027 ranging from 0-255.
4029 vt.default_red= [VT]
4030 Format: <red0>,<red1>,<red2>,...,<red15>
4031 Change the default red palette of the console.
4032 This is a 16-member array composed of values
4033 ranging from 0-255.
4035 vt.default_utf8=
4036 [VT]
4037 Format=<0|1>
4038 Set system-wide default UTF-8 mode for all tty's.
4039 Default is 1, i.e. UTF-8 mode is enabled for all
4040 newly opened terminals.
4042 vt.global_cursor_default=
4043 [VT]
4044 Format=<-1|0|1>
4045 Set system-wide default for whether a cursor
4046 is shown on new VTs. Default is -1,
4047 i.e. cursors will be created by default unless
4048 overridden by individual drivers. 0 will hide
4049 cursors, 1 will display them.
4051 vt.italic= [VT] Default color for italic text; 0-15.
4052 Default: 2 = green.
4054 vt.underline= [VT] Default color for underlined text; 0-15.
4055 Default: 3 = cyan.
4057 watchdog timers [HW,WDT] For information on watchdog timers,
4058 see Documentation/watchdog/watchdog-parameters.txt
4059 or other driver-specific files in the
4060 Documentation/watchdog/ directory.
4062 workqueue.disable_numa
4063 By default, all work items queued to unbound
4064 workqueues are affine to the NUMA nodes they're
4065 issued on, which results in better behavior in
4066 general. If NUMA affinity needs to be disabled for
4067 whatever reason, this option can be used. Note
4068 that this also can be controlled per-workqueue for
4069 workqueues visible under /sys/bus/workqueue/.
4071 workqueue.power_efficient
4072 Per-cpu workqueues are generally preferred because
4073 they show better performance thanks to cache
4074 locality; unfortunately, per-cpu workqueues tend to
4075 be more power hungry than unbound workqueues.
4077 Enabling this makes the per-cpu workqueues which
4078 were observed to contribute significantly to power
4079 consumption unbound, leading to measurably lower
4080 power usage at the cost of small performance
4081 overhead.
4083 The default value of this parameter is determined by
4084 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4086 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4087 default x2apic cluster mode on platforms
4088 supporting x2apic.
4090 x86_intel_mid_timer= [X86-32,APBT]
4091 Choose timer option for x86 Intel MID platform.
4092 Two valid options are apbt timer only and lapic timer
4093 plus one apbt timer for broadcast timer.
4094 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4096 xen_emul_unplug= [HW,X86,XEN]
4097 Unplug Xen emulated devices
4098 Format: [unplug0,][unplug1]
4099 ide-disks -- unplug primary master IDE devices
4100 aux-ide-disks -- unplug non-primary-master IDE devices
4101 nics -- unplug network devices
4102 all -- unplug all emulated devices (NICs and IDE disks)
4103 unnecessary -- unplugging emulated devices is
4104 unnecessary even if the host did not respond to
4105 the unplug protocol
4106 never -- do not unplug even if version check succeeds
4108 xen_nopvspin [X86,XEN]
4109 Disables the ticketlock slowpath using Xen PV
4110 optimizations.
4112 xen_nopv [X86]
4113 Disables the PV optimizations forcing the HVM guest to
4114 run as generic HVM guest with no PV drivers.
4116 xirc2ps_cs= [NET,PCMCIA]
4117 Format:
4118 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4120 ______________________________________________________________________
4122 TODO:
4124 Add more DRM drivers.