| blob | 176d4fe4f076be0c785de56ade5cbca399e591e2 |
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]
169 Advanced Configuration and Power Interface
170 Format: { force | off | strict | noirq | rsdt }
171 force -- enable ACPI if default was off
172 off -- disable ACPI if default was on
173 noirq -- do not use ACPI for IRQ routing
174 strict -- Be less tolerant of platforms that are not
175 strictly ACPI specification compliant.
176 rsdt -- prefer RSDT over (default) XSDT
177 copy_dsdt -- copy DSDT to memory
179 See also Documentation/power/runtime_pm.txt, pci=noacpi
181 acpi_rsdp= [ACPI,EFI,KEXEC]
182 Pass the RSDP address to the kernel, mostly used
183 on machines running EFI runtime service to boot the
184 second kernel for kdump.
186 acpi_apic_instance= [ACPI, IOAPIC]
187 Format: <int>
188 2: use 2nd APIC table, if available
189 1,0: use 1st APIC table
190 default: 0
192 acpi_backlight= [HW,ACPI]
193 acpi_backlight=vendor
194 acpi_backlight=video
195 If set to vendor, prefer vendor specific driver
196 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
197 of the ACPI video.ko driver.
199 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
200 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
201 Format: <int>
202 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
203 debug output. Bits in debug_layer correspond to a
204 _COMPONENT in an ACPI source file, e.g.,
205 #define _COMPONENT ACPI_PCI_COMPONENT
206 Bits in debug_level correspond to a level in
207 ACPI_DEBUG_PRINT statements, e.g.,
208 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
209 The debug_level mask defaults to "info". See
210 Documentation/acpi/debug.txt for more information about
211 debug layers and levels.
213 Enable processor driver info messages:
214 acpi.debug_layer=0x20000000
215 Enable PCI/PCI interrupt routing info messages:
216 acpi.debug_layer=0x400000
217 Enable AML "Debug" output, i.e., stores to the Debug
218 object while interpreting AML:
219 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
220 Enable all messages related to ACPI hardware:
221 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
223 Some values produce so much output that the system is
224 unusable. The "log_buf_len" parameter may be useful
225 if you need to capture more output.
227 acpi_force_table_verification [HW,ACPI]
228 Enable table checksum verification during early stage.
229 By default, this is disabled due to x86 early mapping
230 size limitation.
232 acpi_irq_balance [HW,ACPI]
233 ACPI will balance active IRQs
234 default in APIC mode
236 acpi_irq_nobalance [HW,ACPI]
237 ACPI will not move active IRQs (default)
238 default in PIC mode
240 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
241 Format: <irq>,<irq>...
243 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
244 use by PCI
245 Format: <irq>,<irq>...
247 acpi_no_auto_serialize [HW,ACPI]
248 Disable auto-serialization of AML methods
249 AML control methods that contain the opcodes to create
250 named objects will be marked as "Serialized" by the
251 auto-serialization feature.
252 This feature is enabled by default.
253 This option allows to turn off the feature.
255 acpi_no_static_ssdt [HW,ACPI]
256 Disable installation of static SSDTs at early boot time
257 By default, SSDTs contained in the RSDT/XSDT will be
258 installed automatically and they will appear under
259 /sys/firmware/acpi/tables.
260 This option turns off this feature.
261 Note that specifying this option does not affect
262 dynamic table installation which will install SSDT
263 tables to /sys/firmware/acpi/tables/dynamic.
265 acpica_no_return_repair [HW, ACPI]
266 Disable AML predefined validation mechanism
267 This mechanism can repair the evaluation result to make
268 the return objects more ACPI specification compliant.
269 This option is useful for developers to identify the
270 root cause of an AML interpreter issue when the issue
271 has something to do with the repair mechanism.
273 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
274 Format: To spoof as Windows 98: ="Microsoft Windows"
276 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
277 acpi_osi="string1" # add string1
278 acpi_osi="!string2" # remove string2
279 acpi_osi=!* # remove all strings
280 acpi_osi=! # disable all built-in OS vendor
281 strings
282 acpi_osi= # disable all strings
284 'acpi_osi=!' can be used in combination with single or
285 multiple 'acpi_osi="string1"' to support specific OS
286 vendor string(s). Note that such command can only
287 affect the default state of the OS vendor strings, thus
288 it cannot affect the default state of the feature group
289 strings and the current state of the OS vendor strings,
290 specifying it multiple times through kernel command line
291 is meaningless. This command is useful when one do not
292 care about the state of the feature group strings which
293 should be controlled by the OSPM.
294 Examples:
295 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
296 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
297 can make '_OSI("Windows 2000")' TRUE.
299 'acpi_osi=' cannot be used in combination with other
300 'acpi_osi=' command lines, the _OSI method will not
301 exist in the ACPI namespace. NOTE that such command can
302 only affect the _OSI support state, thus specifying it
303 multiple times through kernel command line is also
304 meaningless.
305 Examples:
306 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
307 FALSE.
309 'acpi_osi=!*' can be used in combination with single or
310 multiple 'acpi_osi="string1"' to support specific
311 string(s). Note that such command can affect the
312 current state of both the OS vendor strings and the
313 feature group strings, thus specifying it multiple times
314 through kernel command line is meaningful. But it may
315 still not able to affect the final state of a string if
316 there are quirks related to this string. This command
317 is useful when one want to control the state of the
318 feature group strings to debug BIOS issues related to
319 the OSPM features.
320 Examples:
321 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
322 '_OSI("Module Device")' FALSE.
323 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
324 '_OSI("Module Device")' TRUE.
325 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
326 equivalent to
327 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
328 and
329 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
330 they all will make '_OSI("Windows 2000")' TRUE.
332 acpi_pm_good [X86]
333 Override the pmtimer bug detection: force the kernel
334 to assume that this machine's pmtimer latches its value
335 and always returns good values.
337 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
338 Format: { level | edge | high | low }
340 acpi_skip_timer_override [HW,ACPI]
341 Recognize and ignore IRQ0/pin2 Interrupt Override.
342 For broken nForce2 BIOS resulting in XT-PIC timer.
344 acpi_sleep= [HW,ACPI] Sleep options
345 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
346 old_ordering, nonvs, sci_force_enable }
347 See Documentation/power/video.txt for information on
348 s3_bios and s3_mode.
349 s3_beep is for debugging; it makes the PC's speaker beep
350 as soon as the kernel's real-mode entry point is called.
351 s4_nohwsig prevents ACPI hardware signature from being
352 used during resume from hibernation.
353 old_ordering causes the ACPI 1.0 ordering of the _PTS
354 control method, with respect to putting devices into
355 low power states, to be enforced (the ACPI 2.0 ordering
356 of _PTS is used by default).
357 nonvs prevents the kernel from saving/restoring the
358 ACPI NVS memory during suspend/hibernation and resume.
359 sci_force_enable causes the kernel to set SCI_EN directly
360 on resume from S1/S3 (which is against the ACPI spec,
361 but some broken systems don't work without it).
363 acpi_use_timer_override [HW,ACPI]
364 Use timer override. For some broken Nvidia NF5 boards
365 that require a timer override, but don't have HPET
367 acpi_enforce_resources= [ACPI]
368 { strict | lax | no }
369 Check for resource conflicts between native drivers
370 and ACPI OperationRegions (SystemIO and SystemMemory
371 only). IO ports and memory declared in ACPI might be
372 used by the ACPI subsystem in arbitrary AML code and
373 can interfere with legacy drivers.
374 strict (default): access to resources claimed by ACPI
375 is denied; legacy drivers trying to access reserved
376 resources will fail to bind to device using them.
377 lax: access to resources claimed by ACPI is allowed;
378 legacy drivers trying to access reserved resources
379 will bind successfully but a warning message is logged.
380 no: ACPI OperationRegions are not marked as reserved,
381 no further checks are performed.
383 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
384 kernels.
386 add_efi_memmap [EFI; X86] Include EFI memory map in
387 kernel's map of available physical RAM.
389 agp= [AGP]
390 { off | try_unsupported }
391 off: disable AGP support
392 try_unsupported: try to drive unsupported chipsets
393 (may crash computer or cause data corruption)
395 ALSA [HW,ALSA]
396 See Documentation/sound/alsa/alsa-parameters.txt
398 alignment= [KNL,ARM]
399 Allow the default userspace alignment fault handler
400 behaviour to be specified. Bit 0 enables warnings,
401 bit 1 enables fixups, and bit 2 sends a segfault.
403 align_va_addr= [X86-64]
404 Align virtual addresses by clearing slice [14:12] when
405 allocating a VMA at process creation time. This option
406 gives you up to 3% performance improvement on AMD F15h
407 machines (where it is enabled by default) for a
408 CPU-intensive style benchmark, and it can vary highly in
409 a microbenchmark depending on workload and compiler.
411 32: only for 32-bit processes
412 64: only for 64-bit processes
413 on: enable for both 32- and 64-bit processes
414 off: disable for both 32- and 64-bit processes
416 alloc_snapshot [FTRACE]
417 Allocate the ftrace snapshot buffer on boot up when the
418 main buffer is allocated. This is handy if debugging
419 and you need to use tracing_snapshot() on boot up, and
420 do not want to use tracing_snapshot_alloc() as it needs
421 to be done where GFP_KERNEL allocations are allowed.
423 amd_iommu= [HW,X86-64]
424 Pass parameters to the AMD IOMMU driver in the system.
425 Possible values are:
426 fullflush - enable flushing of IO/TLB entries when
427 they are unmapped. Otherwise they are
428 flushed before they will be reused, which
429 is a lot of faster
430 off - do not initialize any AMD IOMMU found in
431 the system
432 force_isolation - Force device isolation for all
433 devices. The IOMMU driver is not
434 allowed anymore to lift isolation
435 requirements as needed. This option
436 does not override iommu=pt
438 amd_iommu_dump= [HW,X86-64]
439 Enable AMD IOMMU driver option to dump the ACPI table
440 for AMD IOMMU. With this option enabled, AMD IOMMU
441 driver will print ACPI tables for AMD IOMMU during
442 IOMMU initialization.
444 amijoy.map= [HW,JOY] Amiga joystick support
445 Map of devices attached to JOY0DAT and JOY1DAT
446 Format: <a>,<b>
447 See also Documentation/input/joystick.txt
449 analog.map= [HW,JOY] Analog joystick and gamepad support
450 Specifies type or capabilities of an analog joystick
451 connected to one of 16 gameports
452 Format: <type1>,<type2>,..<type16>
454 apc= [HW,SPARC]
455 Power management functions (SPARCstation-4/5 + deriv.)
456 Format: noidle
457 Disable APC CPU standby support. SPARCstation-Fox does
458 not play well with APC CPU idle - disable it if you have
459 APC and your system crashes randomly.
461 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
462 Change the output verbosity whilst booting
463 Format: { quiet (default) | verbose | debug }
464 Change the amount of debugging information output
465 when initialising the APIC and IO-APIC components.
467 autoconf= [IPV6]
468 See Documentation/networking/ipv6.txt.
470 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
471 Limit apic dumping. The parameter defines the maximal
472 number of local apics being dumped. Also it is possible
473 to set it to "all" by meaning -- no limit here.
474 Format: { 1 (default) | 2 | ... | all }.
475 The parameter valid if only apic=debug or
476 apic=verbose is specified.
477 Example: apic=debug show_lapic=all
479 apm= [APM] Advanced Power Management
480 See header of arch/x86/kernel/apm_32.c.
482 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
483 Format: <io>,<irq>,<nodeID>
485 ataflop= [HW,M68k]
487 atarimouse= [HW,MOUSE] Atari Mouse
489 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
490 EzKey and similar keyboards
492 atkbd.reset= [HW] Reset keyboard during initialization
494 atkbd.set= [HW] Select keyboard code set
495 Format: <int> (2 = AT (default), 3 = PS/2)
497 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
498 keyboards
500 atkbd.softraw= [HW] Choose between synthetic and real raw mode
501 Format: <bool> (0 = real, 1 = synthetic (default))
503 atkbd.softrepeat= [HW]
504 Use software keyboard repeat
506 audit= [KNL] Enable the audit sub-system
507 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
508 0 - kernel audit is disabled and can not be enabled
509 until the next reboot
510 unset - kernel audit is initialized but disabled and
511 will be fully enabled by the userspace auditd.
512 1 - kernel audit is initialized and partially enabled,
513 storing at most audit_backlog_limit messages in
514 RAM until it is fully enabled by the userspace
515 auditd.
516 Default: unset
518 audit_backlog_limit= [KNL] Set the audit queue size limit.
519 Format: <int> (must be >=0)
520 Default: 64
522 baycom_epp= [HW,AX25]
523 Format: <io>,<mode>
525 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
526 Format: <io>,<mode>
527 See header of drivers/net/hamradio/baycom_par.c.
529 baycom_ser_fdx= [HW,AX25]
530 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
531 Format: <io>,<irq>,<mode>[,<baud>]
532 See header of drivers/net/hamradio/baycom_ser_fdx.c.
534 baycom_ser_hdx= [HW,AX25]
535 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
536 Format: <io>,<irq>,<mode>
537 See header of drivers/net/hamradio/baycom_ser_hdx.c.
539 blkdevparts= Manual partition parsing of block device(s) for
540 embedded devices based on command line input.
541 See Documentation/block/cmdline-partition.txt
543 boot_delay= Milliseconds to delay each printk during boot.
544 Values larger than 10 seconds (10000) are changed to
545 no delay (0).
546 Format: integer
548 bootmem_debug [KNL] Enable bootmem allocator debug messages.
550 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
551 bttv.radio= Most important insmod options are available as
552 kernel args too.
553 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
554 bttv.tuner=
556 bulk_remove=off [PPC] This parameter disables the use of the pSeries
557 firmware feature for flushing multiple hpte entries
558 at a time.
560 c101= [NET] Moxa C101 synchronous serial card
562 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
563 Sometimes CPU hardware bugs make them report the cache
564 size incorrectly. The kernel will attempt work arounds
565 to fix known problems, but for some CPUs it is not
566 possible to determine what the correct size should be.
567 This option provides an override for these situations.
569 ca_keys= [KEYS] This parameter identifies a specific key(s) on
570 the system trusted keyring to be used for certificate
571 trust validation.
572 format: { id:<keyid> | builtin }
574 cca= [MIPS] Override the kernel pages' cache coherency
575 algorithm. Accepted values range from 0 to 7
576 inclusive. See arch/mips/include/asm/pgtable-bits.h
577 for platform specific values (SB1, Loongson3 and
578 others).
580 ccw_timeout_log [S390]
581 See Documentation/s390/CommonIO for details.
583 cgroup_disable= [KNL] Disable a particular controller
584 Format: {name of the controller(s) to disable}
585 The effects of cgroup_disable=foo are:
586 - foo isn't auto-mounted if you mount all cgroups in
587 a single hierarchy
588 - foo isn't visible as an individually mountable
589 subsystem
590 {Currently only "memory" controller deal with this and
591 cut the overhead, others just disable the usage. So
592 only cgroup_disable=memory is actually worthy}
594 checkreqprot [SELINUX] Set initial checkreqprot flag value.
595 Format: { "0" | "1" }
596 See security/selinux/Kconfig help text.
597 0 -- check protection applied by kernel (includes
598 any implied execute protection).
599 1 -- check protection requested by application.
600 Default value is set via a kernel config option.
601 Value can be changed at runtime via
602 /selinux/checkreqprot.
604 cio_ignore= [S390]
605 See Documentation/s390/CommonIO for details.
606 clk_ignore_unused
607 [CLK]
608 Prevents the clock framework from automatically gating
609 clocks that have not been explicitly enabled by a Linux
610 device driver but are enabled in hardware at reset or
611 by the bootloader/firmware. Note that this does not
612 force such clocks to be always-on nor does it reserve
613 those clocks in any way. This parameter is useful for
614 debug and development, but should not be needed on a
615 platform with proper driver support. For more
616 information, see Documentation/clk.txt.
618 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
619 [Deprecated]
620 Forces specified clocksource (if available) to be used
621 when calculating gettimeofday(). If specified
622 clocksource is not available, it defaults to PIT.
623 Format: { pit | tsc | cyclone | pmtmr }
625 clocksource= Override the default clocksource
626 Format: <string>
627 Override the default clocksource and use the clocksource
628 with the name specified.
629 Some clocksource names to choose from, depending on
630 the platform:
631 [all] jiffies (this is the base, fallback clocksource)
632 [ACPI] acpi_pm
633 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
634 pxa_timer,timer3,32k_counter,timer0_1
635 [AVR32] avr32
636 [X86-32] pit,hpet,tsc;
637 scx200_hrt on Geode; cyclone on IBM x440
638 [MIPS] MIPS
639 [PARISC] cr16
640 [S390] tod
641 [SH] SuperH
642 [SPARC64] tick
643 [X86-64] hpet,tsc
645 clearcpuid=BITNUM [X86]
646 Disable CPUID feature X for the kernel. See
647 arch/x86/include/asm/cpufeature.h for the valid bit
648 numbers. Note the Linux specific bits are not necessarily
649 stable over kernel options, but the vendor specific
650 ones should be.
651 Also note that user programs calling CPUID directly
652 or using the feature without checking anything
653 will still see it. This just prevents it from
654 being used by the kernel or shown in /proc/cpuinfo.
655 Also note the kernel might malfunction if you disable
656 some critical bits.
658 cma=nn[MG]@[start[MG][-end[MG]]]
659 [ARM,X86,KNL]
660 Sets the size of kernel global memory area for
661 contiguous memory allocations and optionally the
662 placement constraint by the physical address range of
663 memory allocations. A value of 0 disables CMA
664 altogether. For more information, see
665 include/linux/dma-contiguous.h
667 cmo_free_hint= [PPC] Format: { yes | no }
668 Specify whether pages are marked as being inactive
669 when they are freed. This is used in CMO environments
670 to determine OS memory pressure for page stealing by
671 a hypervisor.
672 Default: yes
674 coherent_pool=nn[KMG] [ARM,KNL]
675 Sets the size of memory pool for coherent, atomic dma
676 allocations, by default set to 256K.
678 code_bytes [X86] How many bytes of object code to print
679 in an oops report.
680 Range: 0 - 8192
681 Default: 64
683 com20020= [HW,NET] ARCnet - COM20020 chipset
684 Format:
685 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
687 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
688 Format: <io>[,<irq>]
690 com90xx= [HW,NET]
691 ARCnet - COM90xx chipset (memory-mapped buffers)
692 Format: <io>[,<irq>[,<memstart>]]
694 condev= [HW,S390] console device
695 conmode=
697 console= [KNL] Output console device and options.
699 tty<n> Use the virtual console device <n>.
701 ttyS<n>[,options]
702 ttyUSB0[,options]
703 Use the specified serial port. The options are of
704 the form "bbbbpnf", where "bbbb" is the baud rate,
705 "p" is parity ("n", "o", or "e"), "n" is number of
706 bits, and "f" is flow control ("r" for RTS or
707 omit it). Default is "9600n8".
709 See Documentation/serial-console.txt for more
710 information. See
711 Documentation/networking/netconsole.txt for an
712 alternative.
714 uart[8250],io,<addr>[,options]
715 uart[8250],mmio,<addr>[,options]
716 Start an early, polled-mode console on the 8250/16550
717 UART at the specified I/O port or MMIO address,
718 switching to the matching ttyS device later. The
719 options are the same as for ttyS, above.
720 hvc<n> Use the hypervisor console device <n>. This is for
721 both Xen and PowerPC hypervisors.
723 If the device connected to the port is not a TTY but a braille
724 device, prepend "brl," before the device type, for instance
725 console=brl,ttyS0
726 For now, only VisioBraille is supported.
728 consoleblank= [KNL] The console blank (screen saver) timeout in
729 seconds. Defaults to 10*60 = 10mins. A value of 0
730 disables the blank timer.
732 coredump_filter=
733 [KNL] Change the default value for
734 /proc/<pid>/coredump_filter.
735 See also Documentation/filesystems/proc.txt.
737 cpuidle.off=1 [CPU_IDLE]
738 disable the cpuidle sub-system
740 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
741 Format:
742 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
744 crashkernel=size[KMG][@offset[KMG]]
745 [KNL] Using kexec, Linux can switch to a 'crash kernel'
746 upon panic. This parameter reserves the physical
747 memory region [offset, offset + size] for that kernel
748 image. If '@offset' is omitted, then a suitable offset
749 is selected automatically. Check
750 Documentation/kdump/kdump.txt for further details.
752 crashkernel=range1:size1[,range2:size2,...][@offset]
753 [KNL] Same as above, but depends on the memory
754 in the running system. The syntax of range is
755 start-[end] where start and end are both
756 a memory unit (amount[KMG]). See also
757 Documentation/kdump/kdump.txt for an example.
759 crashkernel=size[KMG],high
760 [KNL, x86_64] range could be above 4G. Allow kernel
761 to allocate physical memory region from top, so could
762 be above 4G if system have more than 4G ram installed.
763 Otherwise memory region will be allocated below 4G, if
764 available.
765 It will be ignored if crashkernel=X is specified.
766 crashkernel=size[KMG],low
767 [KNL, x86_64] range under 4G. When crashkernel=X,high
768 is passed, kernel could allocate physical memory region
769 above 4G, that cause second kernel crash on system
770 that require some amount of low memory, e.g. swiotlb
771 requires at least 64M+32K low memory. Kernel would
772 try to allocate 72M below 4G automatically.
773 This one let user to specify own low range under 4G
774 for second kernel instead.
775 0: to disable low allocation.
776 It will be ignored when crashkernel=X,high is not used
777 or memory reserved is below 4G.
779 cs89x0_dma= [HW,NET]
780 Format: <dma>
782 cs89x0_media= [HW,NET]
783 Format: { rj45 | aui | bnc }
785 dasd= [HW,NET]
786 See header of drivers/s390/block/dasd_devmap.c.
788 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
789 (one device per port)
790 Format: <port#>,<type>
791 See also Documentation/input/joystick-parport.txt
793 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
794 time. See Documentation/dynamic-debug-howto.txt for
795 details. Deprecated, see dyndbg.
797 debug [KNL] Enable kernel debugging (events log level).
799 debug_locks_verbose=
800 [KNL] verbose self-tests
801 Format=<0|1>
802 Print debugging info while doing the locking API
803 self-tests.
804 We default to 0 (no extra messages), setting it to
805 1 will print _a lot_ more information - normally
806 only useful to kernel developers.
808 debug_objects [KNL] Enable object debugging
810 no_debug_objects
811 [KNL] Disable object debugging
813 debug_guardpage_minorder=
814 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
815 parameter allows control of the order of pages that will
816 be intentionally kept free (and hence protected) by the
817 buddy allocator. Bigger value increase the probability
818 of catching random memory corruption, but reduce the
819 amount of memory for normal system use. The maximum
820 possible value is MAX_ORDER/2. Setting this parameter
821 to 1 or 2 should be enough to identify most random
822 memory corruption problems caused by bugs in kernel or
823 driver code when a CPU writes to (or reads from) a
824 random memory location. Note that there exists a class
825 of memory corruptions problems caused by buggy H/W or
826 F/W or by drivers badly programing DMA (basically when
827 memory is written at bus level and the CPU MMU is
828 bypassed) which are not detectable by
829 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
830 tracking down these problems.
832 debug_pagealloc=
833 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
834 parameter enables the feature at boot time. In
835 default, it is disabled. We can avoid allocating huge
836 chunk of memory for debug pagealloc if we don't enable
837 it at boot time and the system will work mostly same
838 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
839 on: enable the feature
841 debugpat [X86] Enable PAT debugging
843 decnet.addr= [HW,NET]
844 Format: <area>[,<node>]
845 See also Documentation/networking/decnet.txt.
847 default_hugepagesz=
848 [same as hugepagesz=] The size of the default
849 HugeTLB page size. This is the size represented by
850 the legacy /proc/ hugepages APIs, used for SHM, and
851 default size when mounting hugetlbfs filesystems.
852 Defaults to the default architecture's huge page size
853 if not specified.
855 dhash_entries= [KNL]
856 Set number of hash buckets for dentry cache.
858 disable= [IPV6]
859 See Documentation/networking/ipv6.txt.
861 disable_cpu_apicid= [X86,APIC,SMP]
862 Format: <int>
863 The number of initial APIC ID for the
864 corresponding CPU to be disabled at boot,
865 mostly used for the kdump 2nd kernel to
866 disable BSP to wake up multiple CPUs without
867 causing system reset or hang due to sending
868 INIT from AP to BSP.
870 disable_ddw [PPC/PSERIES]
871 Disable Dynamic DMA Window support. Use this if
872 to workaround buggy firmware.
874 disable_ipv6= [IPV6]
875 See Documentation/networking/ipv6.txt.
877 disable_mtrr_cleanup [X86]
878 The kernel tries to adjust MTRR layout from continuous
879 to discrete, to make X server driver able to add WB
880 entry later. This parameter disables that.
882 disable_mtrr_trim [X86, Intel and AMD only]
883 By default the kernel will trim any uncacheable
884 memory out of your available memory pool based on
885 MTRR settings. This parameter disables that behavior,
886 possibly causing your machine to run very slowly.
888 disable_timer_pin_1 [X86]
889 Disable PIN 1 of APIC timer
890 Can be useful to work around chipset bugs.
892 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
893 this option disables the debugging code at boot.
895 dma_debug_entries=<number>
896 This option allows to tune the number of preallocated
897 entries for DMA-API debugging code. One entry is
898 required per DMA-API allocation. Use this if the
899 DMA-API debugging code disables itself because the
900 architectural default is too low.
902 dma_debug_driver=<driver_name>
903 With this option the DMA-API debugging driver
904 filter feature can be enabled at boot time. Just
905 pass the driver to filter for as the parameter.
906 The filter can be disabled or changed to another
907 driver later using sysfs.
909 drm_kms_helper.edid_firmware=[<connector>:]<file>
910 Broken monitors, graphic adapters and KVMs may
911 send no or incorrect EDID data sets. This parameter
912 allows to specify an EDID data set in the
913 /lib/firmware directory that is used instead.
914 Generic built-in EDID data sets are used, if one of
915 edid/1024x768.bin, edid/1280x1024.bin,
916 edid/1680x1050.bin, or edid/1920x1080.bin is given
917 and no file with the same name exists. Details and
918 instructions how to build your own EDID data are
919 available in Documentation/EDID/HOWTO.txt. An EDID
920 data set will only be used for a particular connector,
921 if its name and a colon are prepended to the EDID
922 name.
924 dscc4.setup= [NET]
926 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
927 module.dyndbg[="val"]
928 Enable debug messages at boot time. See
929 Documentation/dynamic-debug-howto.txt for details.
931 early_ioremap_debug [KNL]
932 Enable debug messages in early_ioremap support. This
933 is useful for tracking down temporary early mappings
934 which are not unmapped.
936 earlycon= [KNL] Output early console device and options.
938 cdns,<addr>
939 Start an early, polled-mode console on a cadence serial
940 port at the specified address. The cadence serial port
941 must already be setup and configured. Options are not
942 yet supported.
944 uart[8250],io,<addr>[,options]
945 uart[8250],mmio,<addr>[,options]
946 uart[8250],mmio32,<addr>[,options]
947 Start an early, polled-mode console on the 8250/16550
948 UART at the specified I/O port or MMIO address.
949 MMIO inter-register address stride is either 8-bit
950 (mmio) or 32-bit (mmio32).
951 The options are the same as for ttyS, above.
953 pl011,<addr>
954 Start an early, polled-mode console on a pl011 serial
955 port at the specified address. The pl011 serial port
956 must already be setup and configured. Options are not
957 yet supported.
959 msm_serial,<addr>
960 Start an early, polled-mode console on an msm serial
961 port at the specified address. The serial port
962 must already be setup and configured. Options are not
963 yet supported.
965 msm_serial_dm,<addr>
966 Start an early, polled-mode console on an msm serial
967 dm port at the specified address. The serial port
968 must already be setup and configured. Options are not
969 yet supported.
971 smh Use ARM semihosting calls for early console.
973 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
974 earlyprintk=vga
975 earlyprintk=efi
976 earlyprintk=xen
977 earlyprintk=serial[,ttySn[,baudrate]]
978 earlyprintk=serial[,0x...[,baudrate]]
979 earlyprintk=ttySn[,baudrate]
980 earlyprintk=dbgp[debugController#]
982 earlyprintk is useful when the kernel crashes before
983 the normal console is initialized. It is not enabled by
984 default because it has some cosmetic problems.
986 Append ",keep" to not disable it when the real console
987 takes over.
989 Only one of vga, efi, serial, or usb debug port can
990 be used at a time.
992 Currently only ttyS0 and ttyS1 may be specified by
993 name. Other I/O ports may be explicitly specified
994 on some architectures (x86 and arm at least) by
995 replacing ttySn with an I/O port address, like this:
996 earlyprintk=serial,0x1008,115200
997 You can find the port for a given device in
998 /proc/tty/driver/serial:
999 2: uart:ST16650V2 port:00001008 irq:18 ...
1001 Interaction with the standard serial driver is not
1002 very good.
1004 The VGA and EFI output is eventually overwritten by
1005 the real console.
1007 The xen output can only be used by Xen PV guests.
1009 edac_report= [HW,EDAC] Control how to report EDAC event
1010 Format: {"on" | "off" | "force"}
1011 on: enable EDAC to report H/W event. May be overridden
1012 by other higher priority error reporting module.
1013 off: disable H/W event reporting through EDAC.
1014 force: enforce the use of EDAC to report H/W event.
1015 default: on.
1017 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1018 ekgdboc=kbd
1020 This is designed to be used in conjunction with
1021 the boot argument: earlyprintk=vga
1023 edd= [EDD]
1024 Format: {"off" | "on" | "skip[mbr]"}
1026 efi= [EFI]
1027 Format: { "old_map", "nochunk", "noruntime" }
1028 old_map [X86-64]: switch to the old ioremap-based EFI
1029 runtime services mapping. 32-bit still uses this one by
1030 default.
1031 nochunk: disable reading files in "chunks" in the EFI
1032 boot stub, as chunking can cause problems with some
1033 firmware implementations.
1034 noruntime : disable EFI runtime services support
1036 efi_no_storage_paranoia [EFI; X86]
1037 Using this parameter you can use more than 50% of
1038 your efi variable storage. Use this parameter only if
1039 you are really sure that your UEFI does sane gc and
1040 fulfills the spec otherwise your board may brick.
1042 eisa_irq_edge= [PARISC,HW]
1043 See header of drivers/parisc/eisa.c.
1045 elanfreq= [X86-32]
1046 See comment before function elanfreq_setup() in
1047 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1049 elevator= [IOSCHED]
1050 Format: {"cfq" | "deadline" | "noop"}
1051 See Documentation/block/cfq-iosched.txt and
1052 Documentation/block/deadline-iosched.txt for details.
1054 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1055 Specifies physical address of start of kernel core
1056 image elf header and optionally the size. Generally
1057 kexec loader will pass this option to capture kernel.
1058 See Documentation/kdump/kdump.txt for details.
1060 enable_mtrr_cleanup [X86]
1061 The kernel tries to adjust MTRR layout from continuous
1062 to discrete, to make X server driver able to add WB
1063 entry later. This parameter enables that.
1065 enable_timer_pin_1 [X86]
1066 Enable PIN 1 of APIC timer
1067 Can be useful to work around chipset bugs
1068 (in particular on some ATI chipsets).
1069 The kernel tries to set a reasonable default.
1071 enforcing [SELINUX] Set initial enforcing status.
1072 Format: {"0" | "1"}
1073 See security/selinux/Kconfig help text.
1074 0 -- permissive (log only, no denials).
1075 1 -- enforcing (deny and log).
1076 Default value is 0.
1077 Value can be changed at runtime via /selinux/enforce.
1079 erst_disable [ACPI]
1080 Disable Error Record Serialization Table (ERST)
1081 support.
1083 ether= [HW,NET] Ethernet cards parameters
1084 This option is obsoleted by the "netdev=" option, which
1085 has equivalent usage. See its documentation for details.
1087 evm= [EVM]
1088 Format: { "fix" }
1089 Permit 'security.evm' to be updated regardless of
1090 current integrity status.
1092 failslab=
1093 fail_page_alloc=
1094 fail_make_request=[KNL]
1095 General fault injection mechanism.
1096 Format: <interval>,<probability>,<space>,<times>
1097 See also Documentation/fault-injection/.
1099 floppy= [HW]
1100 See Documentation/blockdev/floppy.txt.
1102 force_pal_cache_flush
1103 [IA-64] Avoid check_sal_cache_flush which may hang on
1104 buggy SAL_CACHE_FLUSH implementations. Using this
1105 parameter will force ia64_sal_cache_flush to call
1106 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1108 forcepae [X86-32]
1109 Forcefully enable Physical Address Extension (PAE).
1110 Many Pentium M systems disable PAE but may have a
1111 functionally usable PAE implementation.
1112 Warning: use of this parameter will taint the kernel
1113 and may cause unknown problems.
1115 ftrace=[tracer]
1116 [FTRACE] will set and start the specified tracer
1117 as early as possible in order to facilitate early
1118 boot debugging.
1120 ftrace_dump_on_oops[=orig_cpu]
1121 [FTRACE] will dump the trace buffers on oops.
1122 If no parameter is passed, ftrace will dump
1123 buffers of all CPUs, but if you pass orig_cpu, it will
1124 dump only the buffer of the CPU that triggered the
1125 oops.
1127 ftrace_filter=[function-list]
1128 [FTRACE] Limit the functions traced by the function
1129 tracer at boot up. function-list is a comma separated
1130 list of functions. This list can be changed at run
1131 time by the set_ftrace_filter file in the debugfs
1132 tracing directory.
1134 ftrace_notrace=[function-list]
1135 [FTRACE] Do not trace the functions specified in
1136 function-list. This list can be changed at run time
1137 by the set_ftrace_notrace file in the debugfs
1138 tracing directory.
1140 ftrace_graph_filter=[function-list]
1141 [FTRACE] Limit the top level callers functions traced
1142 by the function graph tracer at boot up.
1143 function-list is a comma separated list of functions
1144 that can be changed at run time by the
1145 set_graph_function file in the debugfs tracing directory.
1147 ftrace_graph_notrace=[function-list]
1148 [FTRACE] Do not trace from the functions specified in
1149 function-list. This list is a comma separated list of
1150 functions that can be changed at run time by the
1151 set_graph_notrace file in the debugfs tracing directory.
1153 gamecon.map[2|3]=
1154 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1155 support via parallel port (up to 5 devices per port)
1156 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1157 See also Documentation/input/joystick-parport.txt
1159 gamma= [HW,DRM]
1161 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1162 Format: off | on
1163 default: on
1165 gcov_persist= [GCOV] When non-zero (default), profiling data for
1166 kernel modules is saved and remains accessible via
1167 debugfs, even when the module is unloaded/reloaded.
1168 When zero, profiling data is discarded and associated
1169 debugfs files are removed at module unload time.
1171 gpt [EFI] Forces disk with valid GPT signature but
1172 invalid Protective MBR to be treated as GPT. If the
1173 primary GPT is corrupted, it enables the backup/alternate
1174 GPT to be used instead.
1176 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1177 the "Enable 0" bit of the configuration register.
1178 Format: 0 | 1
1179 Default: 0
1180 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1181 the "Enable 0" bit of the configuration register.
1182 Format: 0 | 1
1183 Default: 0
1184 grcan.select= [HW] Select which physical interface to use.
1185 Format: 0 | 1
1186 Default: 0
1187 grcan.txsize= [HW] Sets the size of the tx buffer.
1188 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1189 Default: 1024
1190 grcan.rxsize= [HW] Sets the size of the rx buffer.
1191 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1192 Default: 1024
1194 hashdist= [KNL,NUMA] Large hashes allocated during boot
1195 are distributed across NUMA nodes. Defaults on
1196 for 64-bit NUMA, off otherwise.
1197 Format: 0 | 1 (for off | on)
1199 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1201 hd= [EIDE] (E)IDE hard drive subsystem geometry
1202 Format: <cyl>,<head>,<sect>
1204 hest_disable [ACPI]
1205 Disable Hardware Error Source Table (HEST) support;
1206 corresponding firmware-first mode error processing
1207 logic will be disabled.
1209 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1210 size of <nn>. This works even on boxes that have no
1211 highmem otherwise. This also works to reduce highmem
1212 size on bigger boxes.
1214 highres= [KNL] Enable/disable high resolution timer mode.
1215 Valid parameters: "on", "off"
1216 Default: "on"
1218 hisax= [HW,ISDN]
1219 See Documentation/isdn/README.HiSax.
1221 hlt [BUGS=ARM,SH]
1223 hpet= [X86-32,HPET] option to control HPET usage
1224 Format: { enable (default) | disable | force |
1225 verbose }
1226 disable: disable HPET and use PIT instead
1227 force: allow force enabled of undocumented chips (ICH4,
1228 VIA, nVidia)
1229 verbose: show contents of HPET registers during setup
1231 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1232 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1234 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1235 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1236 On x86-64 and powerpc, this option can be specified
1237 multiple times interleaved with hugepages= to reserve
1238 huge pages of different sizes. Valid pages sizes on
1239 x86-64 are 2M (when the CPU supports "pse") and 1G
1240 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1242 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1243 terminal devices. Valid values: 0..8
1244 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1245 If specified, z/VM IUCV HVC accepts connections
1246 from listed z/VM user IDs only.
1248 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1249 hardware thread id mappings.
1250 Format: <cpu>:<hwthread>
1252 keep_bootcon [KNL]
1253 Do not unregister boot console at start. This is only
1254 useful for debugging when something happens in the window
1255 between unregistering the boot console and initializing
1256 the real console.
1258 i2c_bus= [HW] Override the default board specific I2C bus speed
1259 or register an additional I2C bus that is not
1260 registered from board initialization code.
1261 Format:
1262 <bus_id>,<clkrate>
1264 i8042.debug [HW] Toggle i8042 debug mode
1265 i8042.direct [HW] Put keyboard port into non-translated mode
1266 i8042.dumbkbd [HW] Pretend that controller can only read data from
1267 keyboard and cannot control its state
1268 (Don't attempt to blink the leds)
1269 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1270 i8042.nokbd [HW] Don't check/create keyboard port
1271 i8042.noloop [HW] Disable the AUX Loopback command while probing
1272 for the AUX port
1273 i8042.nomux [HW] Don't check presence of an active multiplexing
1274 controller
1275 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1276 controllers
1277 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1278 i8042.reset [HW] Reset the controller during init and cleanup
1279 i8042.unlock [HW] Unlock (ignore) the keylock
1280 i8042.kbdreset [HW] Reset device connected to KBD port
1282 i810= [HW,DRM]
1284 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1285 indicates that the driver is running on unsupported
1286 hardware.
1287 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1288 does not match list of supported models.
1289 i8k.power_status
1290 [HW] Report power status in /proc/i8k
1291 (disabled by default)
1292 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1293 capability is set.
1295 i915.invert_brightness=
1296 [DRM] Invert the sense of the variable that is used to
1297 set the brightness of the panel backlight. Normally a
1298 brightness value of 0 indicates backlight switched off,
1299 and the maximum of the brightness value sets the backlight
1300 to maximum brightness. If this parameter is set to 0
1301 (default) and the machine requires it, or this parameter
1302 is set to 1, a brightness value of 0 sets the backlight
1303 to maximum brightness, and the maximum of the brightness
1304 value switches the backlight off.
1305 -1 -- never invert brightness
1306 0 -- machine default
1307 1 -- force brightness inversion
1309 icn= [HW,ISDN]
1310 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1312 ide-core.nodma= [HW] (E)IDE subsystem
1313 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1314 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1315 .cdrom .chs .ignore_cable are additional options
1316 See Documentation/ide/ide.txt.
1318 ide-generic.probe-mask= [HW] (E)IDE subsystem
1319 Format: <int>
1320 Probe mask for legacy ISA IDE ports. Depending on
1321 platform up to 6 ports are supported, enabled by
1322 setting corresponding bits in the mask to 1. The
1323 default value is 0x0, which has a special meaning.
1324 On systems that have PCI, it triggers scanning the
1325 PCI bus for the first and the second port, which
1326 are then probed. On systems without PCI the value
1327 of 0x0 enables probing the two first ports as if it
1328 was 0x3.
1330 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1331 Claim all unknown PCI IDE storage controllers.
1333 idle= [X86]
1334 Format: idle=poll, idle=halt, idle=nomwait
1335 Poll forces a polling idle loop that can slightly
1336 improve the performance of waking up a idle CPU, but
1337 will use a lot of power and make the system run hot.
1338 Not recommended.
1339 idle=halt: Halt is forced to be used for CPU idle.
1340 In such case C2/C3 won't be used again.
1341 idle=nomwait: Disable mwait for CPU C-states
1343 ignore_loglevel [KNL]
1344 Ignore loglevel setting - this will print /all/
1345 kernel messages to the console. Useful for debugging.
1346 We also add it as printk module parameter, so users
1347 could change it dynamically, usually by
1348 /sys/module/printk/parameters/ignore_loglevel.
1350 ihash_entries= [KNL]
1351 Set number of hash buckets for inode cache.
1353 ima_appraise= [IMA] appraise integrity measurements
1354 Format: { "off" | "enforce" | "fix" | "log" }
1355 default: "enforce"
1357 ima_appraise_tcb [IMA]
1358 The builtin appraise policy appraises all files
1359 owned by uid=0.
1361 ima_hash= [IMA]
1362 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1363 | sha512 | ... }
1364 default: "sha1"
1366 The list of supported hash algorithms is defined
1367 in crypto/hash_info.h.
1369 ima_tcb [IMA]
1370 Load a policy which meets the needs of the Trusted
1371 Computing Base. This means IMA will measure all
1372 programs exec'd, files mmap'd for exec, and all files
1373 opened for read by uid=0.
1375 ima_template= [IMA]
1376 Select one of defined IMA measurements template formats.
1377 Formats: { "ima" | "ima-ng" }
1378 Default: "ima-ng"
1380 ima_template_fmt=
1381 [IMA] Define a custom template format.
1382 Format: { "field1|...|fieldN" }
1384 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1385 Format: <min_file_size>
1386 Set the minimal file size for using asynchronous hash.
1387 If left unspecified, ahash usage is disabled.
1389 ahash performance varies for different data sizes on
1390 different crypto accelerators. This option can be used
1391 to achieve the best performance for a particular HW.
1393 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1394 Format: <bufsize>
1395 Set hashing buffer size. Default: 4k.
1397 ahash performance varies for different chunk sizes on
1398 different crypto accelerators. This option can be used
1399 to achieve best performance for particular HW.
1401 init= [KNL]
1402 Format: <full_path>
1403 Run specified binary instead of /sbin/init as init
1404 process.
1406 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1407 for working out where the kernel is dying during
1408 startup.
1410 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1411 initcall functions. Useful for debugging built-in
1412 modules and initcalls.
1414 initrd= [BOOT] Specify the location of the initial ramdisk
1416 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1417 Format: <irq>
1419 int_pln_enable [x86] Enable power limit notification interrupt
1421 integrity_audit=[IMA]
1422 Format: { "0" | "1" }
1423 0 -- basic integrity auditing messages. (Default)
1424 1 -- additional integrity auditing messages.
1426 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1427 on
1428 Enable intel iommu driver.
1429 off
1430 Disable intel iommu driver.
1431 igfx_off [Default Off]
1432 By default, gfx is mapped as normal device. If a gfx
1433 device has a dedicated DMAR unit, the DMAR unit is
1434 bypassed by not enabling DMAR with this option. In
1435 this case, gfx device will use physical address for
1436 DMA.
1437 forcedac [x86_64]
1438 With this option iommu will not optimize to look
1439 for io virtual address below 32-bit forcing dual
1440 address cycle on pci bus for cards supporting greater
1441 than 32-bit addressing. The default is to look
1442 for translation below 32-bit and if not available
1443 then look in the higher range.
1444 strict [Default Off]
1445 With this option on every unmap_single operation will
1446 result in a hardware IOTLB flush operation as opposed
1447 to batching them for performance.
1448 sp_off [Default Off]
1449 By default, super page will be supported if Intel IOMMU
1450 has the capability. With this option, super page will
1451 not be supported.
1453 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1454 0 disables intel_idle and fall back on acpi_idle.
1455 1 to 6 specify maximum depth of C-state.
1457 intel_pstate= [X86]
1458 disable
1459 Do not enable intel_pstate as the default
1460 scaling driver for the supported processors
1461 force
1462 Enable intel_pstate on systems that prohibit it by default
1463 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1464 instead of acpi-cpufreq may disable platform features, such
1465 as thermal controls and power capping, that rely on ACPI
1466 P-States information being indicated to OSPM and therefore
1467 should be used with caution. This option does not work with
1468 processors that aren't supported by the intel_pstate driver
1469 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1470 no_hwp
1471 Do not enable hardware P state control (HWP)
1472 if available.
1474 intremap= [X86-64, Intel-IOMMU]
1475 on enable Interrupt Remapping (default)
1476 off disable Interrupt Remapping
1477 nosid disable Source ID checking
1478 no_x2apic_optout
1479 BIOS x2APIC opt-out request will be ignored
1481 iomem= Disable strict checking of access to MMIO memory
1482 strict regions from userspace.
1483 relaxed
1485 iommu= [x86]
1486 off
1487 force
1488 noforce
1489 biomerge
1490 panic
1491 nopanic
1492 merge
1493 nomerge
1494 forcesac
1495 soft
1496 pt [x86, IA-64]
1499 io7= [HW] IO7 for Marvel based alpha systems
1500 See comment before marvel_specify_io7 in
1501 arch/alpha/kernel/core_marvel.c.
1503 io_delay= [X86] I/O delay method
1504 0x80
1505 Standard port 0x80 based delay
1506 0xed
1507 Alternate port 0xed based delay (needed on some systems)
1508 udelay
1509 Simple two microseconds delay
1510 none
1511 No delay
1513 ip= [IP_PNP]
1514 See Documentation/filesystems/nfs/nfsroot.txt.
1516 irqfixup [HW]
1517 When an interrupt is not handled search all handlers
1518 for it. Intended to get systems with badly broken
1519 firmware running.
1521 irqpoll [HW]
1522 When an interrupt is not handled search all handlers
1523 for it. Also check all handlers each timer
1524 interrupt. Intended to get systems with badly broken
1525 firmware running.
1527 isapnp= [ISAPNP]
1528 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1530 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1531 Format:
1532 <cpu number>,...,<cpu number>
1533 or
1534 <cpu number>-<cpu number>
1535 (must be a positive range in ascending order)
1536 or a mixture
1537 <cpu number>,...,<cpu number>-<cpu number>
1539 This option can be used to specify one or more CPUs
1540 to isolate from the general SMP balancing and scheduling
1541 algorithms. You can move a process onto or off an
1542 "isolated" CPU via the CPU affinity syscalls or cpuset.
1543 <cpu number> begins at 0 and the maximum value is
1544 "number of CPUs in system - 1".
1546 This option is the preferred way to isolate CPUs. The
1547 alternative -- manually setting the CPU mask of all
1548 tasks in the system -- can cause problems and
1549 suboptimal load balancer performance.
1551 iucv= [HW,NET]
1553 ivrs_ioapic [HW,X86_64]
1554 Provide an override to the IOAPIC-ID<->DEVICE-ID
1555 mapping provided in the IVRS ACPI table. For
1556 example, to map IOAPIC-ID decimal 10 to
1557 PCI device 00:14.0 write the parameter as:
1558 ivrs_ioapic[10]=00:14.0
1560 ivrs_hpet [HW,X86_64]
1561 Provide an override to the HPET-ID<->DEVICE-ID
1562 mapping provided in the IVRS ACPI table. For
1563 example, to map HPET-ID decimal 0 to
1564 PCI device 00:14.0 write the parameter as:
1565 ivrs_hpet[0]=00:14.0
1567 js= [HW,JOY] Analog joystick
1568 See Documentation/input/joystick.txt.
1570 kaslr/nokaslr [X86]
1571 Enable/disable kernel and module base offset ASLR
1572 (Address Space Layout Randomization) if built into
1573 the kernel. When CONFIG_HIBERNATION is selected,
1574 kASLR is disabled by default. When kASLR is enabled,
1575 hibernation will be disabled.
1577 keepinitrd [HW,ARM]
1579 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1580 specifies the amount of memory usable by the kernel
1581 for non-movable allocations. The requested amount is
1582 spread evenly throughout all nodes in the system. The
1583 remaining memory in each node is used for Movable
1584 pages. In the event, a node is too small to have both
1585 kernelcore and Movable pages, kernelcore pages will
1586 take priority and other nodes will have a larger number
1587 of Movable pages. The Movable zone is used for the
1588 allocation of pages that may be reclaimed or moved
1589 by the page migration subsystem. This means that
1590 HugeTLB pages may not be allocated from this zone.
1591 Note that allocations like PTEs-from-HighMem still
1592 use the HighMem zone if it exists, and the Normal
1593 zone if it does not.
1595 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1596 Format: <Controller#>[,poll interval]
1597 The controller # is the number of the ehci usb debug
1598 port as it is probed via PCI. The poll interval is
1599 optional and is the number seconds in between
1600 each poll cycle to the debug port in case you need
1601 the functionality for interrupting the kernel with
1602 gdb or control-c on the dbgp connection. When
1603 not using this parameter you use sysrq-g to break into
1604 the kernel debugger.
1606 kgdboc= [KGDB,HW] kgdb over consoles.
1607 Requires a tty driver that supports console polling,
1608 or a supported polling keyboard driver (non-usb).
1609 Serial only format: <serial_device>[,baud]
1610 keyboard only format: kbd
1611 keyboard and serial format: kbd,<serial_device>[,baud]
1612 Optional Kernel mode setting:
1613 kms, kbd format: kms,kbd
1614 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1616 kgdbwait [KGDB] Stop kernel execution and enter the
1617 kernel debugger at the earliest opportunity.
1619 kmac= [MIPS] korina ethernet MAC address.
1620 Configure the RouterBoard 532 series on-chip
1621 Ethernet adapter MAC address.
1623 kmemleak= [KNL] Boot-time kmemleak enable/disable
1624 Valid arguments: on, off
1625 Default: on
1626 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1627 the default is off.
1629 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1630 Valid arguments: 0, 1, 2
1631 kmemcheck=0 (disabled)
1632 kmemcheck=1 (enabled)
1633 kmemcheck=2 (one-shot mode)
1634 Default: 2 (one-shot mode)
1636 kstack=N [X86] Print N words from the kernel stack
1637 in oops dumps.
1639 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1640 Default is 0 (don't ignore, but inject #GP)
1642 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1643 KVM MMU at runtime.
1644 Default is 0 (off)
1646 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1647 Default is 1 (enabled)
1649 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1650 for all guests.
1651 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1653 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1654 (virtualized MMU) support on capable Intel chips.
1655 Default is 1 (enabled)
1657 kvm-intel.emulate_invalid_guest_state=
1658 [KVM,Intel] Enable emulation of invalid guest states
1659 Default is 0 (disabled)
1661 kvm-intel.flexpriority=
1662 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1663 Default is 1 (enabled)
1665 kvm-intel.nested=
1666 [KVM,Intel] Enable VMX nesting (nVMX).
1667 Default is 0 (disabled)
1669 kvm-intel.unrestricted_guest=
1670 [KVM,Intel] Disable unrestricted guest feature
1671 (virtualized real and unpaged mode) on capable
1672 Intel chips. Default is 1 (enabled)
1674 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1675 feature (tagged TLBs) on capable Intel chips.
1676 Default is 1 (enabled)
1678 l2cr= [PPC]
1680 l3cr= [PPC]
1682 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1683 disabled it.
1685 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1686 value for LAPIC timer one-shot implementation. Default
1687 back to the programmable timer unit in the LAPIC.
1689 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1690 in C2 power state.
1692 libata.dma= [LIBATA] DMA control
1693 libata.dma=0 Disable all PATA and SATA DMA
1694 libata.dma=1 PATA and SATA Disk DMA only
1695 libata.dma=2 ATAPI (CDROM) DMA only
1696 libata.dma=4 Compact Flash DMA only
1697 Combinations also work, so libata.dma=3 enables DMA
1698 for disks and CDROMs, but not CFs.
1700 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1701 libata.ignore_hpa=0 keep BIOS limits (default)
1702 libata.ignore_hpa=1 ignore limits, using full disk
1704 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1705 when set.
1706 Format: <int>
1708 libata.force= [LIBATA] Force configurations. The format is comma
1709 separated list of "[ID:]VAL" where ID is
1710 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1711 matching port, link or device. Basically, it matches
1712 the ATA ID string printed on console by libata. If
1713 the whole ID part is omitted, the last PORT and DEVICE
1714 values are used. If ID hasn't been specified yet, the
1715 configuration applies to all ports, links and devices.
1717 If only DEVICE is omitted, the parameter applies to
1718 the port and all links and devices behind it. DEVICE
1719 number of 0 either selects the first device or the
1720 first fan-out link behind PMP device. It does not
1721 select the host link. DEVICE number of 15 selects the
1722 host link and device attached to it.
1724 The VAL specifies the configuration to force. As long
1725 as there's no ambiguity shortcut notation is allowed.
1726 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1727 The following configurations can be forced.
1729 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1730 Any ID with matching PORT is used.
1732 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1734 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1735 udma[/][16,25,33,44,66,100,133] notation is also
1736 allowed.
1738 * [no]ncq: Turn on or off NCQ.
1740 * nohrst, nosrst, norst: suppress hard, soft
1741 and both resets.
1743 * rstonce: only attempt one reset during
1744 hot-unplug link recovery
1746 * dump_id: dump IDENTIFY data.
1748 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1750 * disable: Disable this device.
1752 If there are multiple matching configurations changing
1753 the same attribute, the last one is used.
1755 memblock=debug [KNL] Enable memblock debug messages.
1757 load_ramdisk= [RAM] List of ramdisks to load from floppy
1758 See Documentation/blockdev/ramdisk.txt.
1760 lockd.nlm_grace_period=P [NFS] Assign grace period.
1761 Format: <integer>
1763 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1764 Format: <integer>
1766 lockd.nlm_timeout=T [NFS] Assign timeout value.
1767 Format: <integer>
1769 lockd.nlm_udpport=M [NFS] Assign UDP port.
1770 Format: <integer>
1772 locktorture.nreaders_stress= [KNL]
1773 Set the number of locking read-acquisition kthreads.
1774 Defaults to being automatically set based on the
1775 number of online CPUs.
1777 locktorture.nwriters_stress= [KNL]
1778 Set the number of locking write-acquisition kthreads.
1780 locktorture.onoff_holdoff= [KNL]
1781 Set time (s) after boot for CPU-hotplug testing.
1783 locktorture.onoff_interval= [KNL]
1784 Set time (s) between CPU-hotplug operations, or
1785 zero to disable CPU-hotplug testing.
1787 locktorture.shuffle_interval= [KNL]
1788 Set task-shuffle interval (jiffies). Shuffling
1789 tasks allows some CPUs to go into dyntick-idle
1790 mode during the locktorture test.
1792 locktorture.shutdown_secs= [KNL]
1793 Set time (s) after boot system shutdown. This
1794 is useful for hands-off automated testing.
1796 locktorture.stat_interval= [KNL]
1797 Time (s) between statistics printk()s.
1799 locktorture.stutter= [KNL]
1800 Time (s) to stutter testing, for example,
1801 specifying five seconds causes the test to run for
1802 five seconds, wait for five seconds, and so on.
1803 This tests the locking primitive's ability to
1804 transition abruptly to and from idle.
1806 locktorture.torture_runnable= [BOOT]
1807 Start locktorture running at boot time.
1809 locktorture.torture_type= [KNL]
1810 Specify the locking implementation to test.
1812 locktorture.verbose= [KNL]
1813 Enable additional printk() statements.
1815 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1816 Format: <irq>
1818 loglevel= All Kernel Messages with a loglevel smaller than the
1819 console loglevel will be printed to the console. It can
1820 also be changed with klogd or other programs. The
1821 loglevels are defined as follows:
1823 0 (KERN_EMERG) system is unusable
1824 1 (KERN_ALERT) action must be taken immediately
1825 2 (KERN_CRIT) critical conditions
1826 3 (KERN_ERR) error conditions
1827 4 (KERN_WARNING) warning conditions
1828 5 (KERN_NOTICE) normal but significant condition
1829 6 (KERN_INFO) informational
1830 7 (KERN_DEBUG) debug-level messages
1832 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1833 in bytes. n must be a power of two and greater
1834 than the minimal size. The minimal size is defined
1835 by LOG_BUF_SHIFT kernel config parameter. There is
1836 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1837 that allows to increase the default size depending on
1838 the number of CPUs. See init/Kconfig for more details.
1840 logo.nologo [FB] Disables display of the built-in Linux logo.
1841 This may be used to provide more screen space for
1842 kernel log messages and is useful when debugging
1843 kernel boot problems.
1845 lp=0 [LP] Specify parallel ports to use, e.g,
1846 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1847 lp=reset first parallel port). 'lp=0' disables the
1848 lp=auto printer driver. 'lp=reset' (which can be
1849 specified in addition to the ports) causes
1850 attached printers to be reset. Using
1851 lp=port1,port2,... specifies the parallel ports
1852 to associate lp devices with, starting with
1853 lp0. A port specification may be 'none' to skip
1854 that lp device, or a parport name such as
1855 'parport0'. Specifying 'lp=auto' instead of a
1856 port specification list means that device IDs
1857 from each port should be examined, to see if
1858 an IEEE 1284-compliant printer is attached; if
1859 so, the driver will manage that printer.
1860 See also header of drivers/char/lp.c.
1862 lpj=n [KNL]
1863 Sets loops_per_jiffy to given constant, thus avoiding
1864 time-consuming boot-time autodetection (up to 250 ms per
1865 CPU). 0 enables autodetection (default). To determine
1866 the correct value for your kernel, boot with normal
1867 autodetection and see what value is printed. Note that
1868 on SMP systems the preset will be applied to all CPUs,
1869 which is likely to cause problems if your CPUs need
1870 significantly divergent settings. An incorrect value
1871 will cause delays in the kernel to be wrong, leading to
1872 unpredictable I/O errors and other breakage. Although
1873 unlikely, in the extreme case this might damage your
1874 hardware.
1876 ltpc= [NET]
1877 Format: <io>,<irq>,<dma>
1879 machvec= [IA-64] Force the use of a particular machine-vector
1880 (machvec) in a generic kernel.
1881 Example: machvec=hpzx1_swiotlb
1883 machtype= [Loongson] Share the same kernel image file between different
1884 yeeloong laptop.
1885 Example: machtype=lemote-yeeloong-2f-7inch
1887 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1888 than or equal to this physical address is ignored.
1890 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1891 should make use of. maxcpus=n : n >= 0 limits the
1892 kernel to using 'n' processors. n=0 is a special case,
1893 it is equivalent to "nosmp", which also disables
1894 the IO APIC.
1896 max_loop= [LOOP] The number of loop block devices that get
1897 (loop.max_loop) unconditionally pre-created at init time. The default
1898 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1899 of statically allocating a predefined number, loop
1900 devices can be requested on-demand with the
1901 /dev/loop-control interface.
1903 mce [X86-32] Machine Check Exception
1905 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1907 md= [HW] RAID subsystems devices and level
1908 See Documentation/md.txt.
1910 mdacon= [MDA]
1911 Format: <first>,<last>
1912 Specifies range of consoles to be captured by the MDA.
1914 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1915 Amount of memory to be used when the kernel is not able
1916 to see the whole system memory or for test.
1917 [X86] Work as limiting max address. Use together
1918 with memmap= to avoid physical address space collisions.
1919 Without memmap= PCI devices could be placed at addresses
1920 belonging to unused RAM.
1922 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1923 memory.
1925 memchunk=nn[KMG]
1926 [KNL,SH] Allow user to override the default size for
1927 per-device physically contiguous DMA buffers.
1929 memmap=exactmap [KNL,X86] Enable setting of an exact
1930 E820 memory map, as specified by the user.
1931 Such memmap=exactmap lines can be constructed based on
1932 BIOS output or other requirements. See the memmap=nn@ss
1933 option description.
1935 memmap=nn[KMG]@ss[KMG]
1936 [KNL] Force usage of a specific region of memory.
1937 Region of memory to be used is from ss to ss+nn.
1939 memmap=nn[KMG]#ss[KMG]
1940 [KNL,ACPI] Mark specific memory as ACPI data.
1941 Region of memory to be marked is from ss to ss+nn.
1943 memmap=nn[KMG]$ss[KMG]
1944 [KNL,ACPI] Mark specific memory as reserved.
1945 Region of memory to be reserved is from ss to ss+nn.
1946 Example: Exclude memory from 0x18690000-0x1869ffff
1947 memmap=64K$0x18690000
1948 or
1949 memmap=0x10000$0x18690000
1951 memory_corruption_check=0/1 [X86]
1952 Some BIOSes seem to corrupt the first 64k of
1953 memory when doing things like suspend/resume.
1954 Setting this option will scan the memory
1955 looking for corruption. Enabling this will
1956 both detect corruption and prevent the kernel
1957 from using the memory being corrupted.
1958 However, its intended as a diagnostic tool; if
1959 repeatable BIOS-originated corruption always
1960 affects the same memory, you can use memmap=
1961 to prevent the kernel from using that memory.
1963 memory_corruption_check_size=size [X86]
1964 By default it checks for corruption in the low
1965 64k, making this memory unavailable for normal
1966 use. Use this parameter to scan for
1967 corruption in more or less memory.
1969 memory_corruption_check_period=seconds [X86]
1970 By default it checks for corruption every 60
1971 seconds. Use this parameter to check at some
1972 other rate. 0 disables periodic checking.
1974 memtest= [KNL,X86] Enable memtest
1975 Format: <integer>
1976 default : 0 <disable>
1977 Specifies the number of memtest passes to be
1978 performed. Each pass selects another test
1979 pattern from a given set of patterns. Memtest
1980 fills the memory with this pattern, validates
1981 memory contents and reserves bad memory
1982 regions that are detected.
1984 meye.*= [HW] Set MotionEye Camera parameters
1985 See Documentation/video4linux/meye.txt.
1987 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1988 Multi-Function General Purpose Timers on AMD Geode
1989 platforms.
1991 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1992 the BIOS has incorrectly applied a workaround. TinyBIOS
1993 version 0.98 is known to be affected, 0.99 fixes the
1994 problem by letting the user disable the workaround.
1996 mga= [HW,DRM]
1998 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1999 physical address is ignored.
2001 mini2440= [ARM,HW,KNL]
2002 Format:[0..2][b][c][t]
2003 Default: "0tb"
2004 MINI2440 configuration specification:
2005 0 - The attached screen is the 3.5" TFT
2006 1 - The attached screen is the 7" TFT
2007 2 - The VGA Shield is attached (1024x768)
2008 Leaving out the screen size parameter will not load
2009 the TFT driver, and the framebuffer will be left
2010 unconfigured.
2011 b - Enable backlight. The TFT backlight pin will be
2012 linked to the kernel VESA blanking code and a GPIO
2013 LED. This parameter is not necessary when using the
2014 VGA shield.
2015 c - Enable the s3c camera interface.
2016 t - Reserved for enabling touchscreen support. The
2017 touchscreen support is not enabled in the mainstream
2018 kernel as of 2.6.30, a preliminary port can be found
2019 in the "bleeding edge" mini2440 support kernel at
2020 http://repo.or.cz/w/linux-2.6/mini2440.git
2022 mminit_loglevel=
2023 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2024 parameter allows control of the logging verbosity for
2025 the additional memory initialisation checks. A value
2026 of 0 disables mminit logging and a level of 4 will
2027 log everything. Information is printed at KERN_DEBUG
2028 so loglevel=8 may also need to be specified.
2030 module.sig_enforce
2031 [KNL] When CONFIG_MODULE_SIG is set, this means that
2032 modules without (valid) signatures will fail to load.
2033 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2034 is always true, so this option does nothing.
2036 mousedev.tap_time=
2037 [MOUSE] Maximum time between finger touching and
2038 leaving touchpad surface for touch to be considered
2039 a tap and be reported as a left button click (for
2040 touchpads working in absolute mode only).
2041 Format: <msecs>
2042 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2043 reporting absolute coordinates, such as tablets
2044 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2045 reporting absolute coordinates, such as tablets
2047 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2048 is similar to kernelcore except it specifies the
2049 amount of memory used for migratable allocations.
2050 If both kernelcore and movablecore is specified,
2051 then kernelcore will be at *least* the specified
2052 value but may be more. If movablecore on its own
2053 is specified, the administrator must be careful
2054 that the amount of memory usable for all allocations
2055 is not too small.
2057 movable_node [KNL,X86] Boot-time switch to enable the effects
2058 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2060 MTD_Partition= [MTD]
2061 Format: <name>,<region-number>,<size>,<offset>
2063 MTD_Region= [MTD] Format:
2064 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2066 mtdparts= [MTD]
2067 See drivers/mtd/cmdlinepart.c.
2069 multitce=off [PPC] This parameter disables the use of the pSeries
2070 firmware feature for updating multiple TCE entries
2071 at a time.
2073 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2075 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2077 boundary - index of last SLC block on Flex-OneNAND.
2078 The remaining blocks are configured as MLC blocks.
2079 lock - Configure if Flex-OneNAND boundary should be locked.
2080 Once locked, the boundary cannot be changed.
2081 1 indicates lock status, 0 indicates unlock status.
2083 mtdset= [ARM]
2084 ARM/S3C2412 JIVE boot control
2086 See arch/arm/mach-s3c2412/mach-jive.c
2088 mtouchusb.raw_coordinates=
2089 [HW] Make the MicroTouch USB driver use raw coordinates
2090 ('y', default) or cooked coordinates ('n')
2092 mtrr_chunk_size=nn[KMG] [X86]
2093 used for mtrr cleanup. It is largest continuous chunk
2094 that could hold holes aka. UC entries.
2096 mtrr_gran_size=nn[KMG] [X86]
2097 Used for mtrr cleanup. It is granularity of mtrr block.
2098 Default is 1.
2099 Large value could prevent small alignment from
2100 using up MTRRs.
2102 mtrr_spare_reg_nr=n [X86]
2103 Format: <integer>
2104 Range: 0,7 : spare reg number
2105 Default : 1
2106 Used for mtrr cleanup. It is spare mtrr entries number.
2107 Set to 2 or more if your graphical card needs more.
2109 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2111 netdev= [NET] Network devices parameters
2112 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2113 Note that mem_start is often overloaded to mean
2114 something different and driver-specific.
2115 This usage is only documented in each driver source
2116 file if at all.
2118 nf_conntrack.acct=
2119 [NETFILTER] Enable connection tracking flow accounting
2120 0 to disable accounting
2121 1 to enable accounting
2122 Default value is 0.
2124 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2125 See Documentation/filesystems/nfs/nfsroot.txt.
2127 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2128 See Documentation/filesystems/nfs/nfsroot.txt.
2130 nfsrootdebug [NFS] enable nfsroot debugging messages.
2131 See Documentation/filesystems/nfs/nfsroot.txt.
2133 nfs.callback_tcpport=
2134 [NFS] set the TCP port on which the NFSv4 callback
2135 channel should listen.
2137 nfs.cache_getent=
2138 [NFS] sets the pathname to the program which is used
2139 to update the NFS client cache entries.
2141 nfs.cache_getent_timeout=
2142 [NFS] sets the timeout after which an attempt to
2143 update a cache entry is deemed to have failed.
2145 nfs.idmap_cache_timeout=
2146 [NFS] set the maximum lifetime for idmapper cache
2147 entries.
2149 nfs.enable_ino64=
2150 [NFS] enable 64-bit inode numbers.
2151 If zero, the NFS client will fake up a 32-bit inode
2152 number for the readdir() and stat() syscalls instead
2153 of returning the full 64-bit number.
2154 The default is to return 64-bit inode numbers.
2156 nfs.max_session_slots=
2157 [NFSv4.1] Sets the maximum number of session slots
2158 the client will attempt to negotiate with the server.
2159 This limits the number of simultaneous RPC requests
2160 that the client can send to the NFSv4.1 server.
2161 Note that there is little point in setting this
2162 value higher than the max_tcp_slot_table_limit.
2164 nfs.nfs4_disable_idmapping=
2165 [NFSv4] When set to the default of '1', this option
2166 ensures that both the RPC level authentication
2167 scheme and the NFS level operations agree to use
2168 numeric uids/gids if the mount is using the
2169 'sec=sys' security flavour. In effect it is
2170 disabling idmapping, which can make migration from
2171 legacy NFSv2/v3 systems to NFSv4 easier.
2172 Servers that do not support this mode of operation
2173 will be autodetected by the client, and it will fall
2174 back to using the idmapper.
2175 To turn off this behaviour, set the value to '0'.
2176 nfs.nfs4_unique_id=
2177 [NFS4] Specify an additional fixed unique ident-
2178 ification string that NFSv4 clients can insert into
2179 their nfs_client_id4 string. This is typically a
2180 UUID that is generated at system install time.
2182 nfs.send_implementation_id =
2183 [NFSv4.1] Send client implementation identification
2184 information in exchange_id requests.
2185 If zero, no implementation identification information
2186 will be sent.
2187 The default is to send the implementation identification
2188 information.
2190 nfs.recover_lost_locks =
2191 [NFSv4] Attempt to recover locks that were lost due
2192 to a lease timeout on the server. Please note that
2193 doing this risks data corruption, since there are
2194 no guarantees that the file will remain unchanged
2195 after the locks are lost.
2196 If you want to enable the kernel legacy behaviour of
2197 attempting to recover these locks, then set this
2198 parameter to '1'.
2199 The default parameter value of '0' causes the kernel
2200 not to attempt recovery of lost locks.
2202 nfsd.nfs4_disable_idmapping=
2203 [NFSv4] When set to the default of '1', the NFSv4
2204 server will return only numeric uids and gids to
2205 clients using auth_sys, and will accept numeric uids
2206 and gids from such clients. This is intended to ease
2207 migration from NFSv2/v3.
2209 objlayoutdriver.osd_login_prog=
2210 [NFS] [OBJLAYOUT] sets the pathname to the program which
2211 is used to automatically discover and login into new
2212 osd-targets. Please see:
2213 Documentation/filesystems/pnfs.txt for more explanations
2215 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2216 when a NMI is triggered.
2217 Format: [state][,regs][,debounce][,die]
2219 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2220 Format: [panic,][nopanic,][num]
2221 Valid num: 0
2222 0 - turn nmi_watchdog off
2223 When panic is specified, panic when an NMI watchdog
2224 timeout occurs (or 'nopanic' to override the opposite
2225 default).
2226 This is useful when you use a panic=... timeout and
2227 need the box quickly up again.
2229 netpoll.carrier_timeout=
2230 [NET] Specifies amount of time (in seconds) that
2231 netpoll should wait for a carrier. By default netpoll
2232 waits 4 seconds.
2234 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2235 emulation library even if a 387 maths coprocessor
2236 is present.
2238 no_console_suspend
2239 [HW] Never suspend the console
2240 Disable suspending of consoles during suspend and
2241 hibernate operations. Once disabled, debugging
2242 messages can reach various consoles while the rest
2243 of the system is being put to sleep (ie, while
2244 debugging driver suspend/resume hooks). This may
2245 not work reliably with all consoles, but is known
2246 to work with serial and VGA consoles.
2247 To facilitate more flexible debugging, we also add
2248 console_suspend, a printk module parameter to control
2249 it. Users could use console_suspend (usually
2250 /sys/module/printk/parameters/console_suspend) to
2251 turn on/off it dynamically.
2253 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2254 caches in the slab allocator. Saves per-node memory,
2255 but will impact performance.
2257 noalign [KNL,ARM]
2259 noapic [SMP,APIC] Tells the kernel to not make use of any
2260 IOAPICs that may be present in the system.
2262 noautogroup Disable scheduler automatic task group creation.
2264 nobats [PPC] Do not use BATs for mapping kernel lowmem
2265 on "Classic" PPC cores.
2267 nocache [ARM]
2269 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2271 nodelayacct [KNL] Disable per-task delay accounting
2273 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2275 nodsp [SH] Disable hardware DSP at boot time.
2277 noefi Disable EFI runtime services support.
2279 noexec [IA-64]
2281 noexec [X86]
2282 On X86-32 available only on PAE configured kernels.
2283 noexec=on: enable non-executable mappings (default)
2284 noexec=off: disable non-executable mappings
2286 nosmap [X86]
2287 Disable SMAP (Supervisor Mode Access Prevention)
2288 even if it is supported by processor.
2290 nosmep [X86]
2291 Disable SMEP (Supervisor Mode Execution Prevention)
2292 even if it is supported by processor.
2294 noexec32 [X86-64]
2295 This affects only 32-bit executables.
2296 noexec32=on: enable non-executable mappings (default)
2297 read doesn't imply executable mappings
2298 noexec32=off: disable non-executable mappings
2299 read implies executable mappings
2301 nofpu [SH] Disable hardware FPU at boot time.
2303 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2304 register save and restore. The kernel will only save
2305 legacy floating-point registers on task switch.
2307 noxsave [BUGS=X86] Disables x86 extended register state save
2308 and restore using xsave. The kernel will fallback to
2309 enabling legacy floating-point and sse state.
2311 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2312 register states. The kernel will fall back to use
2313 xsave to save the states. By using this parameter,
2314 performance of saving the states is degraded because
2315 xsave doesn't support modified optimization while
2316 xsaveopt supports it on xsaveopt enabled systems.
2318 noxsaves [X86] Disables xsaves and xrstors used in saving and
2319 restoring x86 extended register state in compacted
2320 form of xsave area. The kernel will fall back to use
2321 xsaveopt and xrstor to save and restore the states
2322 in standard form of xsave area. By using this
2323 parameter, xsave area per process might occupy more
2324 memory on xsaves enabled systems.
2326 eagerfpu= [X86]
2327 on enable eager fpu restore
2328 off disable eager fpu restore
2329 auto selects the default scheme, which automatically
2330 enables eagerfpu restore for xsaveopt.
2332 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2333 wfi(ARM) instruction doesn't work correctly and not to
2334 use it. This is also useful when using JTAG debugger.
2336 no_file_caps Tells the kernel not to honor file capabilities. The
2337 only way then for a file to be executed with privilege
2338 is to be setuid root or executed by root.
2340 nohalt [IA-64] Tells the kernel not to use the power saving
2341 function PAL_HALT_LIGHT when idle. This increases
2342 power-consumption. On the positive side, it reduces
2343 interrupt wake-up latency, which may improve performance
2344 in certain environments such as networked servers or
2345 real-time systems.
2347 nohibernate [HIBERNATION] Disable hibernation and resume.
2349 nohz= [KNL] Boottime enable/disable dynamic ticks
2350 Valid arguments: on, off
2351 Default: on
2353 nohz_full= [KNL,BOOT]
2354 In kernels built with CONFIG_NO_HZ_FULL=y, set
2355 the specified list of CPUs whose tick will be stopped
2356 whenever possible. The boot CPU will be forced outside
2357 the range to maintain the timekeeping.
2358 The CPUs in this range must also be included in the
2359 rcu_nocbs= set.
2361 noiotrap [SH] Disables trapped I/O port accesses.
2363 noirqdebug [X86-32] Disables the code which attempts to detect and
2364 disable unhandled interrupt sources.
2366 no_timer_check [X86,APIC] Disables the code which tests for
2367 broken timer IRQ sources.
2369 noisapnp [ISAPNP] Disables ISA PnP code.
2371 noinitrd [RAM] Tells the kernel not to load any configured
2372 initial RAM disk.
2374 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2375 remapping.
2376 [Deprecated - use intremap=off]
2378 nointroute [IA-64]
2380 nojitter [IA-64] Disables jitter checking for ITC timers.
2382 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2384 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2385 fault handling.
2387 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2388 steal time is computed, but won't influence scheduler
2389 behaviour
2391 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2393 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2395 noltlbs [PPC] Do not use large page/tlb entries for kernel
2396 lowmem mapping on PPC40x.
2398 nomca [IA-64] Disable machine check abort handling
2400 nomce [X86-32] Machine Check Exception
2402 nomfgpt [X86-32] Disable Multi-Function General Purpose
2403 Timer usage (for AMD Geode machines).
2405 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2406 shutdown the other cpus. Instead use the REBOOT_VECTOR
2407 irq.
2409 nomodule Disable module load
2411 nopat [X86] Disable PAT (page attribute table extension of
2412 pagetables) support.
2414 norandmaps Don't use address space randomization. Equivalent to
2415 echo 0 > /proc/sys/kernel/randomize_va_space
2417 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2419 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2420 with UP alternatives
2422 nordrand [X86] Disable kernel use of the RDRAND and
2423 RDSEED instructions even if they are supported
2424 by the processor. RDRAND and RDSEED are still
2425 available to user space applications.
2427 noresume [SWSUSP] Disables resume and restores original swap
2428 space.
2430 no-scroll [VGA] Disables scrollback.
2431 This is required for the Braillex ib80-piezo Braille
2432 reader made by F.H. Papenmeier (Germany).
2434 nosbagart [IA-64]
2436 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2438 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2439 and disable the IO APIC. legacy for "maxcpus=0".
2441 nosoftlockup [KNL] Disable the soft-lockup detector.
2443 nosync [HW,M68K] Disables sync negotiation for all devices.
2445 notsc [BUGS=X86-32] Disable Time Stamp Counter
2447 nousb [USB] Disable the USB subsystem
2449 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2451 nowb [ARM]
2453 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2455 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2456 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2457 Some features depend on CPU0. Known dependencies are:
2458 1. Resume from suspend/hibernate depends on CPU0.
2459 Suspend/hibernate will fail if CPU0 is offline and you
2460 need to online CPU0 before suspend/hibernate.
2461 2. PIC interrupts also depend on CPU0. CPU0 can't be
2462 removed if a PIC interrupt is detected.
2463 It's said poweroff/reboot may depend on CPU0 on some
2464 machines although I haven't seen such issues so far
2465 after CPU0 is offline on a few tested machines.
2466 If the dependencies are under your control, you can
2467 turn on cpu0_hotplug.
2469 nptcg= [IA-64] Override max number of concurrent global TLB
2470 purges which is reported from either PAL_VM_SUMMARY or
2471 SAL PALO.
2473 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2474 could support. nr_cpus=n : n >= 1 limits the kernel to
2475 supporting 'n' processors. Later in runtime you can not
2476 use hotplug cpu feature to put more cpu back to online.
2477 just like you compile the kernel NR_CPUS=n
2479 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2481 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2482 Allowed values are enable and disable
2484 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2485 one of ['zone', 'node', 'default'] can be specified
2486 This can be set from sysctl after boot.
2487 See Documentation/sysctl/vm.txt for details.
2489 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2490 See Documentation/debugging-via-ohci1394.txt for more
2491 info.
2493 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2494 Rather than timing out after 20 ms if an EC
2495 command is not properly ACKed, override the length
2496 of the timeout. We have interrupts disabled while
2497 waiting for the ACK, so if this is set too high
2498 interrupts *may* be lost!
2500 omap_mux= [OMAP] Override bootloader pin multiplexing.
2501 Format: <mux_mode0.mode_name=value>...
2502 For example, to override I2C bus2:
2503 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2505 oprofile.timer= [HW]
2506 Use timer interrupt instead of performance counters
2508 oprofile.cpu_type= Force an oprofile cpu type
2509 This might be useful if you have an older oprofile
2510 userland or if you want common events.
2511 Format: { arch_perfmon }
2512 arch_perfmon: [X86] Force use of architectural
2513 perfmon on Intel CPUs instead of the
2514 CPU specific event set.
2515 timer: [X86] Force use of architectural NMI
2516 timer mode (see also oprofile.timer
2517 for generic hr timer mode)
2518 [s390] Force legacy basic mode sampling
2519 (report cpu_type "timer")
2521 oops=panic Always panic on oopses. Default is to just kill the
2522 process, but there is a small probability of
2523 deadlocking the machine.
2524 This will also cause panics on machine check exceptions.
2525 Useful together with panic=30 to trigger a reboot.
2527 OSS [HW,OSS]
2528 See Documentation/sound/oss/oss-parameters.txt
2530 page_owner= [KNL] Boot-time page_owner enabling option.
2531 Storage of the information about who allocated
2532 each page is disabled in default. With this switch,
2533 we can turn it on.
2534 on: enable the feature
2536 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2537 timeout > 0: seconds before rebooting
2538 timeout = 0: wait forever
2539 timeout < 0: reboot immediately
2540 Format: <timeout>
2542 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2543 on a WARN().
2545 crash_kexec_post_notifiers
2546 Run kdump after running panic-notifiers and dumping
2547 kmsg. This only for the users who doubt kdump always
2548 succeeds in any situation.
2549 Note that this also increases risks of kdump failure,
2550 because some panic notifiers can make the crashed
2551 kernel more unstable.
2553 parkbd.port= [HW] Parallel port number the keyboard adapter is
2554 connected to, default is 0.
2555 Format: <parport#>
2556 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2557 0 for XT, 1 for AT (default is AT).
2558 Format: <mode>
2560 parport= [HW,PPT] Specify parallel ports. 0 disables.
2561 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2562 Use 'auto' to force the driver to use any
2563 IRQ/DMA settings detected (the default is to
2564 ignore detected IRQ/DMA settings because of
2565 possible conflicts). You can specify the base
2566 address, IRQ, and DMA settings; IRQ and DMA
2567 should be numbers, or 'auto' (for using detected
2568 settings on that particular port), or 'nofifo'
2569 (to avoid using a FIFO even if it is detected).
2570 Parallel ports are assigned in the order they
2571 are specified on the command line, starting
2572 with parport0.
2574 parport_init_mode= [HW,PPT]
2575 Configure VIA parallel port to operate in
2576 a specific mode. This is necessary on Pegasos
2577 computer where firmware has no options for setting
2578 up parallel port mode and sets it to spp.
2579 Currently this function knows 686a and 8231 chips.
2580 Format: [spp|ps2|epp|ecp|ecpepp]
2582 pause_on_oops=
2583 Halt all CPUs after the first oops has been printed for
2584 the specified number of seconds. This is to be used if
2585 your oopses keep scrolling off the screen.
2587 pcbit= [HW,ISDN]
2589 pcd. [PARIDE]
2590 See header of drivers/block/paride/pcd.c.
2591 See also Documentation/blockdev/paride.txt.
2593 pci=option[,option...] [PCI] various PCI subsystem options:
2594 earlydump [X86] dump PCI config space before the kernel
2595 changes anything
2596 off [X86] don't probe for the PCI bus
2597 bios [X86-32] force use of PCI BIOS, don't access
2598 the hardware directly. Use this if your machine
2599 has a non-standard PCI host bridge.
2600 nobios [X86-32] disallow use of PCI BIOS, only direct
2601 hardware access methods are allowed. Use this
2602 if you experience crashes upon bootup and you
2603 suspect they are caused by the BIOS.
2604 conf1 [X86] Force use of PCI Configuration
2605 Mechanism 1.
2606 conf2 [X86] Force use of PCI Configuration
2607 Mechanism 2.
2608 noaer [PCIE] If the PCIEAER kernel config parameter is
2609 enabled, this kernel boot option can be used to
2610 disable the use of PCIE advanced error reporting.
2611 nodomains [PCI] Disable support for multiple PCI
2612 root domains (aka PCI segments, in ACPI-speak).
2613 nommconf [X86] Disable use of MMCONFIG for PCI
2614 Configuration
2615 check_enable_amd_mmconf [X86] check for and enable
2616 properly configured MMIO access to PCI
2617 config space on AMD family 10h CPU
2618 nomsi [MSI] If the PCI_MSI kernel config parameter is
2619 enabled, this kernel boot option can be used to
2620 disable the use of MSI interrupts system-wide.
2621 noioapicquirk [APIC] Disable all boot interrupt quirks.
2622 Safety option to keep boot IRQs enabled. This
2623 should never be necessary.
2624 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2625 primary IO-APIC for bridges that cannot disable
2626 boot IRQs. This fixes a source of spurious IRQs
2627 when the system masks IRQs.
2628 noioapicreroute [APIC] Disable workaround that uses the
2629 boot IRQ equivalent of an IRQ that connects to
2630 a chipset where boot IRQs cannot be disabled.
2631 The opposite of ioapicreroute.
2632 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2633 routing table. These calls are known to be buggy
2634 on several machines and they hang the machine
2635 when used, but on other computers it's the only
2636 way to get the interrupt routing table. Try
2637 this option if the kernel is unable to allocate
2638 IRQs or discover secondary PCI buses on your
2639 motherboard.
2640 rom [X86] Assign address space to expansion ROMs.
2641 Use with caution as certain devices share
2642 address decoders between ROMs and other
2643 resources.
2644 norom [X86] Do not assign address space to
2645 expansion ROMs that do not already have
2646 BIOS assigned address ranges.
2647 nobar [X86] Do not assign address space to the
2648 BARs that weren't assigned by the BIOS.
2649 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2650 assigned automatically to PCI devices. You can
2651 make the kernel exclude IRQs of your ISA cards
2652 this way.
2653 pirqaddr=0xAAAAA [X86] Specify the physical address
2654 of the PIRQ table (normally generated
2655 by the BIOS) if it is outside the
2656 F0000h-100000h range.
2657 lastbus=N [X86] Scan all buses thru bus #N. Can be
2658 useful if the kernel is unable to find your
2659 secondary buses and you want to tell it
2660 explicitly which ones they are.
2661 assign-busses [X86] Always assign all PCI bus
2662 numbers ourselves, overriding
2663 whatever the firmware may have done.
2664 usepirqmask [X86] Honor the possible IRQ mask stored
2665 in the BIOS $PIR table. This is needed on
2666 some systems with broken BIOSes, notably
2667 some HP Pavilion N5400 and Omnibook XE3
2668 notebooks. This will have no effect if ACPI
2669 IRQ routing is enabled.
2670 noacpi [X86] Do not use ACPI for IRQ routing
2671 or for PCI scanning.
2672 use_crs [X86] Use PCI host bridge window information
2673 from ACPI. On BIOSes from 2008 or later, this
2674 is enabled by default. If you need to use this,
2675 please report a bug.
2676 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2677 If you need to use this, please report a bug.
2678 routeirq Do IRQ routing for all PCI devices.
2679 This is normally done in pci_enable_device(),
2680 so this option is a temporary workaround
2681 for broken drivers that don't call it.
2682 skip_isa_align [X86] do not align io start addr, so can
2683 handle more pci cards
2684 firmware [ARM] Do not re-enumerate the bus but instead
2685 just use the configuration from the
2686 bootloader. This is currently used on
2687 IXP2000 systems where the bus has to be
2688 configured a certain way for adjunct CPUs.
2689 noearly [X86] Don't do any early type 1 scanning.
2690 This might help on some broken boards which
2691 machine check when some devices' config space
2692 is read. But various workarounds are disabled
2693 and some IOMMU drivers will not work.
2694 bfsort Sort PCI devices into breadth-first order.
2695 This sorting is done to get a device
2696 order compatible with older (<= 2.4) kernels.
2697 nobfsort Don't sort PCI devices into breadth-first order.
2698 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2699 tuning and use the BIOS-configured MPS defaults.
2700 pcie_bus_safe Set every device's MPS to the largest value
2701 supported by all devices below the root complex.
2702 pcie_bus_perf Set device MPS to the largest allowable MPS
2703 based on its parent bus. Also set MRRS (Max
2704 Read Request Size) to the largest supported
2705 value (no larger than the MPS that the device
2706 or bus can support) for best performance.
2707 pcie_bus_peer2peer Set every device's MPS to 128B, which
2708 every device is guaranteed to support. This
2709 configuration allows peer-to-peer DMA between
2710 any pair of devices, possibly at the cost of
2711 reduced performance. This also guarantees
2712 that hot-added devices will work.
2713 cbiosize=nn[KMG] The fixed amount of bus space which is
2714 reserved for the CardBus bridge's IO window.
2715 The default value is 256 bytes.
2716 cbmemsize=nn[KMG] The fixed amount of bus space which is
2717 reserved for the CardBus bridge's memory
2718 window. The default value is 64 megabytes.
2719 resource_alignment=
2720 Format:
2721 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2722 Specifies alignment and device to reassign
2723 aligned memory resources.
2724 If <order of align> is not specified,
2725 PAGE_SIZE is used as alignment.
2726 PCI-PCI bridge can be specified, if resource
2727 windows need to be expanded.
2728 ecrc= Enable/disable PCIe ECRC (transaction layer
2729 end-to-end CRC checking).
2730 bios: Use BIOS/firmware settings. This is the
2731 the default.
2732 off: Turn ECRC off
2733 on: Turn ECRC on.
2734 hpiosize=nn[KMG] The fixed amount of bus space which is
2735 reserved for hotplug bridge's IO window.
2736 Default size is 256 bytes.
2737 hpmemsize=nn[KMG] The fixed amount of bus space which is
2738 reserved for hotplug bridge's memory window.
2739 Default size is 2 megabytes.
2740 realloc= Enable/disable reallocating PCI bridge resources
2741 if allocations done by BIOS are too small to
2742 accommodate resources required by all child
2743 devices.
2744 off: Turn realloc off
2745 on: Turn realloc on
2746 realloc same as realloc=on
2747 noari do not use PCIe ARI.
2748 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2749 only look for one device below a PCIe downstream
2750 port.
2752 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2753 Management.
2754 off Disable ASPM.
2755 force Enable ASPM even on devices that claim not to support it.
2756 WARNING: Forcing ASPM on may cause system lockups.
2758 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2759 nomsi Do not use MSI for PCI Express Native Hotplug (this
2760 makes all PCIe ports use INTx for hotplug services).
2762 pcie_ports= [PCIE] PCIe ports handling:
2763 auto Ask the BIOS whether or not to use native PCIe services
2764 associated with PCIe ports (PME, hot-plug, AER). Use
2765 them only if that is allowed by the BIOS.
2766 native Use native PCIe services associated with PCIe ports
2767 unconditionally.
2768 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2769 ports driver.
2771 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2772 nomsi Do not use MSI for native PCIe PME signaling (this makes
2773 all PCIe root ports use INTx for all services).
2775 pcmv= [HW,PCMCIA] BadgePAD 4
2777 pd_ignore_unused
2778 [PM]
2779 Keep all power-domains already enabled by bootloader on,
2780 even if no driver has claimed them. This is useful
2781 for debug and development, but should not be
2782 needed on a platform with proper driver support.
2784 pd. [PARIDE]
2785 See Documentation/blockdev/paride.txt.
2787 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2788 boot time.
2789 Format: { 0 | 1 }
2790 See arch/parisc/kernel/pdc_chassis.c
2792 percpu_alloc= Select which percpu first chunk allocator to use.
2793 Currently supported values are "embed" and "page".
2794 Archs may support subset or none of the selections.
2795 See comments in mm/percpu.c for details on each
2796 allocator. This parameter is primarily for debugging
2797 and performance comparison.
2799 pf. [PARIDE]
2800 See Documentation/blockdev/paride.txt.
2802 pg. [PARIDE]
2803 See Documentation/blockdev/paride.txt.
2805 pirq= [SMP,APIC] Manual mp-table setup
2806 See Documentation/x86/i386/IO-APIC.txt.
2808 plip= [PPT,NET] Parallel port network link
2809 Format: { parport<nr> | timid | 0 }
2810 See also Documentation/parport.txt.
2812 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2813 Override pmtimer IOPort with a hex value.
2814 e.g. pmtmr=0x508
2816 pnp.debug=1 [PNP]
2817 Enable PNP debug messages (depends on the
2818 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2819 via /sys/module/pnp/parameters/debug. We always show
2820 current resource usage; turning this on also shows
2821 possible settings and some assignment information.
2823 pnpacpi= [ACPI]
2824 { off }
2826 pnpbios= [ISAPNP]
2827 { on | off | curr | res | no-curr | no-res }
2829 pnp_reserve_irq=
2830 [ISAPNP] Exclude IRQs for the autoconfiguration
2832 pnp_reserve_dma=
2833 [ISAPNP] Exclude DMAs for the autoconfiguration
2835 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2836 Ranges are in pairs (I/O port base and size).
2838 pnp_reserve_mem=
2839 [ISAPNP] Exclude memory regions for the
2840 autoconfiguration.
2841 Ranges are in pairs (memory base and size).
2843 ports= [IP_VS_FTP] IPVS ftp helper module
2844 Default is 21.
2845 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2846 may be specified.
2847 Format: <port>,<port>....
2849 print-fatal-signals=
2850 [KNL] debug: print fatal signals
2852 If enabled, warn about various signal handling
2853 related application anomalies: too many signals,
2854 too many POSIX.1 timers, fatal signals causing a
2855 coredump - etc.
2857 If you hit the warning due to signal overflow,
2858 you might want to try "ulimit -i unlimited".
2860 default: off.
2862 printk.always_kmsg_dump=
2863 Trigger kmsg_dump for cases other than kernel oops or
2864 panics
2865 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2866 default: disabled
2868 printk.time= Show timing data prefixed to each printk message line
2869 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2871 processor.max_cstate= [HW,ACPI]
2872 Limit processor to maximum C-state
2873 max_cstate=9 overrides any DMI blacklist limit.
2875 processor.nocst [HW,ACPI]
2876 Ignore the _CST method to determine C-states,
2877 instead using the legacy FADT method
2879 profile= [KNL] Enable kernel profiling via /proc/profile
2880 Format: [schedule,]<number>
2881 Param: "schedule" - profile schedule points.
2882 Param: <number> - step/bucket size as a power of 2 for
2883 statistical time based profiling.
2884 Param: "sleep" - profile D-state sleeping (millisecs).
2885 Requires CONFIG_SCHEDSTATS
2886 Param: "kvm" - profile VM exits.
2888 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2889 before loading.
2890 See Documentation/blockdev/ramdisk.txt.
2892 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2893 probe for; one of (bare|imps|exps|lifebook|any).
2894 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2895 per second.
2896 psmouse.resetafter= [HW,MOUSE]
2897 Try to reset the device after so many bad packets
2898 (0 = never).
2899 psmouse.resolution=
2900 [HW,MOUSE] Set desired mouse resolution, in dpi.
2901 psmouse.smartscroll=
2902 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2903 0 = disabled, 1 = enabled (default).
2905 pstore.backend= Specify the name of the pstore backend to use
2907 pt. [PARIDE]
2908 See Documentation/blockdev/paride.txt.
2910 pty.legacy_count=
2911 [KNL] Number of legacy pty's. Overwrites compiled-in
2912 default number.
2914 quiet [KNL] Disable most log messages
2916 r128= [HW,DRM]
2918 raid= [HW,RAID]
2919 See Documentation/md.txt.
2921 ramdisk_blocksize= [RAM]
2922 See Documentation/blockdev/ramdisk.txt.
2924 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2925 See Documentation/blockdev/ramdisk.txt.
2927 rcu_nocbs= [KNL]
2928 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2929 the specified list of CPUs to be no-callback CPUs.
2930 Invocation of these CPUs' RCU callbacks will
2931 be offloaded to "rcuox/N" kthreads created for
2932 that purpose, where "x" is "b" for RCU-bh, "p"
2933 for RCU-preempt, and "s" for RCU-sched, and "N"
2934 is the CPU number. This reduces OS jitter on the
2935 offloaded CPUs, which can be useful for HPC and
2936 real-time workloads. It can also improve energy
2937 efficiency for asymmetric multiprocessors.
2939 rcu_nocb_poll [KNL]
2940 Rather than requiring that offloaded CPUs
2941 (specified by rcu_nocbs= above) explicitly
2942 awaken the corresponding "rcuoN" kthreads,
2943 make these kthreads poll for callbacks.
2944 This improves the real-time response for the
2945 offloaded CPUs by relieving them of the need to
2946 wake up the corresponding kthread, but degrades
2947 energy efficiency by requiring that the kthreads
2948 periodically wake up to do the polling.
2950 rcutree.blimit= [KNL]
2951 Set maximum number of finished RCU callbacks to
2952 process in one batch.
2954 rcutree.rcu_fanout_leaf= [KNL]
2955 Increase the number of CPUs assigned to each
2956 leaf rcu_node structure. Useful for very large
2957 systems.
2959 rcutree.jiffies_till_sched_qs= [KNL]
2960 Set required age in jiffies for a
2961 given grace period before RCU starts
2962 soliciting quiescent-state help from
2963 rcu_note_context_switch().
2965 rcutree.jiffies_till_first_fqs= [KNL]
2966 Set delay from grace-period initialization to
2967 first attempt to force quiescent states.
2968 Units are jiffies, minimum value is zero,
2969 and maximum value is HZ.
2971 rcutree.jiffies_till_next_fqs= [KNL]
2972 Set delay between subsequent attempts to force
2973 quiescent states. Units are jiffies, minimum
2974 value is one, and maximum value is HZ.
2976 rcutree.kthread_prio= [KNL,BOOT]
2977 Set the SCHED_FIFO priority of the RCU
2978 per-CPU kthreads (rcuc/N). This value is also
2979 used for the priority of the RCU boost threads
2980 (rcub/N). Valid values are 1-99 and the default
2981 is 1 (the least-favored priority).
2983 rcutree.rcu_nocb_leader_stride= [KNL]
2984 Set the number of NOCB kthread groups, which
2985 defaults to the square root of the number of
2986 CPUs. Larger numbers reduces the wakeup overhead
2987 on the per-CPU grace-period kthreads, but increases
2988 that same overhead on each group's leader.
2990 rcutree.qhimark= [KNL]
2991 Set threshold of queued RCU callbacks beyond which
2992 batch limiting is disabled.
2994 rcutree.qlowmark= [KNL]
2995 Set threshold of queued RCU callbacks below which
2996 batch limiting is re-enabled.
2998 rcutree.rcu_idle_gp_delay= [KNL]
2999 Set wakeup interval for idle CPUs that have
3000 RCU callbacks (RCU_FAST_NO_HZ=y).
3002 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3003 Set wakeup interval for idle CPUs that have
3004 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3005 Lazy RCU callbacks are those which RCU can
3006 prove do nothing more than free memory.
3008 rcutorture.cbflood_inter_holdoff= [KNL]
3009 Set holdoff time (jiffies) between successive
3010 callback-flood tests.
3012 rcutorture.cbflood_intra_holdoff= [KNL]
3013 Set holdoff time (jiffies) between successive
3014 bursts of callbacks within a given callback-flood
3015 test.
3017 rcutorture.cbflood_n_burst= [KNL]
3018 Set the number of bursts making up a given
3019 callback-flood test. Set this to zero to
3020 disable callback-flood testing.
3022 rcutorture.cbflood_n_per_burst= [KNL]
3023 Set the number of callbacks to be registered
3024 in a given burst of a callback-flood test.
3026 rcutorture.fqs_duration= [KNL]
3027 Set duration of force_quiescent_state bursts.
3029 rcutorture.fqs_holdoff= [KNL]
3030 Set holdoff time within force_quiescent_state bursts.
3032 rcutorture.fqs_stutter= [KNL]
3033 Set wait time between force_quiescent_state bursts.
3035 rcutorture.gp_exp= [KNL]
3036 Use expedited update-side primitives.
3038 rcutorture.gp_normal= [KNL]
3039 Use normal (non-expedited) update-side primitives.
3040 If both gp_exp and gp_normal are set, do both.
3041 If neither gp_exp nor gp_normal are set, still
3042 do both.
3044 rcutorture.n_barrier_cbs= [KNL]
3045 Set callbacks/threads for rcu_barrier() testing.
3047 rcutorture.nfakewriters= [KNL]
3048 Set number of concurrent RCU writers. These just
3049 stress RCU, they don't participate in the actual
3050 test, hence the "fake".
3052 rcutorture.nreaders= [KNL]
3053 Set number of RCU readers.
3055 rcutorture.object_debug= [KNL]
3056 Enable debug-object double-call_rcu() testing.
3058 rcutorture.onoff_holdoff= [KNL]
3059 Set time (s) after boot for CPU-hotplug testing.
3061 rcutorture.onoff_interval= [KNL]
3062 Set time (s) between CPU-hotplug operations, or
3063 zero to disable CPU-hotplug testing.
3065 rcutorture.torture_runnable= [BOOT]
3066 Start rcutorture running at boot time.
3068 rcutorture.shuffle_interval= [KNL]
3069 Set task-shuffle interval (s). Shuffling tasks
3070 allows some CPUs to go into dyntick-idle mode
3071 during the rcutorture test.
3073 rcutorture.shutdown_secs= [KNL]
3074 Set time (s) after boot system shutdown. This
3075 is useful for hands-off automated testing.
3077 rcutorture.stall_cpu= [KNL]
3078 Duration of CPU stall (s) to test RCU CPU stall
3079 warnings, zero to disable.
3081 rcutorture.stall_cpu_holdoff= [KNL]
3082 Time to wait (s) after boot before inducing stall.
3084 rcutorture.stat_interval= [KNL]
3085 Time (s) between statistics printk()s.
3087 rcutorture.stutter= [KNL]
3088 Time (s) to stutter testing, for example, specifying
3089 five seconds causes the test to run for five seconds,
3090 wait for five seconds, and so on. This tests RCU's
3091 ability to transition abruptly to and from idle.
3093 rcutorture.test_boost= [KNL]
3094 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3095 "Maybe" means test if the RCU implementation
3096 under test support RCU priority boosting.
3098 rcutorture.test_boost_duration= [KNL]
3099 Duration (s) of each individual boost test.
3101 rcutorture.test_boost_interval= [KNL]
3102 Interval (s) between each boost test.
3104 rcutorture.test_no_idle_hz= [KNL]
3105 Test RCU's dyntick-idle handling. See also the
3106 rcutorture.shuffle_interval parameter.
3108 rcutorture.torture_type= [KNL]
3109 Specify the RCU implementation to test.
3111 rcutorture.verbose= [KNL]
3112 Enable additional printk() statements.
3114 rcupdate.rcu_expedited= [KNL]
3115 Use expedited grace-period primitives, for
3116 example, synchronize_rcu_expedited() instead
3117 of synchronize_rcu(). This reduces latency,
3118 but can increase CPU utilization, degrade
3119 real-time latency, and degrade energy efficiency.
3121 rcupdate.rcu_cpu_stall_suppress= [KNL]
3122 Suppress RCU CPU stall warning messages.
3124 rcupdate.rcu_cpu_stall_timeout= [KNL]
3125 Set timeout for RCU CPU stall warning messages.
3127 rcupdate.rcu_task_stall_timeout= [KNL]
3128 Set timeout in jiffies for RCU task stall warning
3129 messages. Disable with a value less than or equal
3130 to zero.
3132 rcupdate.rcu_self_test= [KNL]
3133 Run the RCU early boot self tests
3135 rcupdate.rcu_self_test_bh= [KNL]
3136 Run the RCU bh early boot self tests
3138 rcupdate.rcu_self_test_sched= [KNL]
3139 Run the RCU sched early boot self tests
3141 rdinit= [KNL]
3142 Format: <full_path>
3143 Run specified binary instead of /init from the ramdisk,
3144 used for early userspace startup. See initrd.
3146 reboot= [KNL]
3147 Format (x86 or x86_64):
3148 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3149 [[,]s[mp]#### \
3150 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3151 [[,]f[orce]
3152 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3153 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3154 reboot_force is either force or not specified,
3155 reboot_cpu is s[mp]#### with #### being the processor
3156 to be used for rebooting.
3158 relax_domain_level=
3159 [KNL, SMP] Set scheduler's default relax_domain_level.
3160 See Documentation/cgroups/cpusets.txt.
3162 relative_sleep_states=
3163 [SUSPEND] Use sleep state labeling where the deepest
3164 state available other than hibernation is always "mem".
3165 Format: { "0" | "1" }
3166 0 -- Traditional sleep state labels.
3167 1 -- Relative sleep state labels.
3169 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3171 reservetop= [X86-32]
3172 Format: nn[KMG]
3173 Reserves a hole at the top of the kernel virtual
3174 address space.
3176 reservelow= [X86]
3177 Format: nn[K]
3178 Set the amount of memory to reserve for BIOS at
3179 the bottom of the address space.
3181 reset_devices [KNL] Force drivers to reset the underlying device
3182 during initialization.
3184 resume= [SWSUSP]
3185 Specify the partition device for software suspend
3186 Format:
3187 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3189 resume_offset= [SWSUSP]
3190 Specify the offset from the beginning of the partition
3191 given by "resume=" at which the swap header is located,
3192 in <PAGE_SIZE> units (needed only for swap files).
3193 See Documentation/power/swsusp-and-swap-files.txt
3195 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3196 read the resume files
3198 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3199 Useful for devices that are detected asynchronously
3200 (e.g. USB and MMC devices).
3202 hibernate= [HIBERNATION]
3203 noresume Don't check if there's a hibernation image
3204 present during boot.
3205 nocompress Don't compress/decompress hibernation images.
3206 no Disable hibernation and resume.
3208 retain_initrd [RAM] Keep initrd memory after extraction
3210 rhash_entries= [KNL,NET]
3211 Set number of hash buckets for route cache
3213 ro [KNL] Mount root device read-only on boot
3215 root= [KNL] Root filesystem
3216 See name_to_dev_t comment in init/do_mounts.c.
3218 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3219 mount the root filesystem
3221 rootflags= [KNL] Set root filesystem mount option string
3223 rootfstype= [KNL] Set root filesystem type
3225 rootwait [KNL] Wait (indefinitely) for root device to show up.
3226 Useful for devices that are detected asynchronously
3227 (e.g. USB and MMC devices).
3229 rproc_mem=nn[KMG][@address]
3230 [KNL,ARM,CMA] Remoteproc physical memory block.
3231 Memory area to be used by remote processor image,
3232 managed by CMA.
3234 rw [KNL] Mount root device read-write on boot
3236 S [KNL] Run init in single mode
3238 s390_iommu= [HW,S390]
3239 Set s390 IOTLB flushing mode
3240 strict
3241 With strict flushing every unmap operation will result in
3242 an IOTLB flush. Default is lazy flushing before reuse,
3243 which is faster.
3245 sa1100ir [NET]
3246 See drivers/net/irda/sa1100_ir.c.
3248 sbni= [NET] Granch SBNI12 leased line adapter
3250 sched_debug [KNL] Enables verbose scheduler debug messages.
3252 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3253 xtime_lock contention on larger systems, and/or RCU lock
3254 contention on all systems with CONFIG_MAXSMP set.
3255 Format: { "0" | "1" }
3256 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3257 1 -- enable.
3258 Note: increases power consumption, thus should only be
3259 enabled if running jitter sensitive (HPC/RT) workloads.
3261 security= [SECURITY] Choose a security module to enable at boot.
3262 If this boot parameter is not specified, only the first
3263 security module asking for security registration will be
3264 loaded. An invalid security module name will be treated
3265 as if no module has been chosen.
3267 selinux= [SELINUX] Disable or enable SELinux at boot time.
3268 Format: { "0" | "1" }
3269 See security/selinux/Kconfig help text.
3270 0 -- disable.
3271 1 -- enable.
3272 Default value is set via kernel config option.
3273 If enabled at boot time, /selinux/disable can be used
3274 later to disable prior to initial policy load.
3276 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3277 Format: { "0" | "1" }
3278 See security/apparmor/Kconfig help text
3279 0 -- disable.
3280 1 -- enable.
3281 Default value is set via kernel config option.
3283 serialnumber [BUGS=X86-32]
3285 shapers= [NET]
3286 Maximal number of shapers.
3288 show_msr= [x86] show boot-time MSR settings
3289 Format: { <integer> }
3290 Show boot-time (BIOS-initialized) MSR settings.
3291 The parameter means the number of CPUs to show,
3292 for example 1 means boot CPU only.
3294 simeth= [IA-64]
3295 simscsi=
3297 slram= [HW,MTD]
3299 slab_nomerge [MM]
3300 Disable merging of slabs with similar size. May be
3301 necessary if there is some reason to distinguish
3302 allocs to different slabs. Debug options disable
3303 merging on their own.
3304 For more information see Documentation/vm/slub.txt.
3306 slab_max_order= [MM, SLAB]
3307 Determines the maximum allowed order for slabs.
3308 A high setting may cause OOMs due to memory
3309 fragmentation. Defaults to 1 for systems with
3310 more than 32MB of RAM, 0 otherwise.
3312 slub_debug[=options[,slabs]] [MM, SLUB]
3313 Enabling slub_debug allows one to determine the
3314 culprit if slab objects become corrupted. Enabling
3315 slub_debug can create guard zones around objects and
3316 may poison objects when not in use. Also tracks the
3317 last alloc / free. For more information see
3318 Documentation/vm/slub.txt.
3320 slub_max_order= [MM, SLUB]
3321 Determines the maximum allowed order for slabs.
3322 A high setting may cause OOMs due to memory
3323 fragmentation. For more information see
3324 Documentation/vm/slub.txt.
3326 slub_min_objects= [MM, SLUB]
3327 The minimum number of objects per slab. SLUB will
3328 increase the slab order up to slub_max_order to
3329 generate a sufficiently large slab able to contain
3330 the number of objects indicated. The higher the number
3331 of objects the smaller the overhead of tracking slabs
3332 and the less frequently locks need to be acquired.
3333 For more information see Documentation/vm/slub.txt.
3335 slub_min_order= [MM, SLUB]
3336 Determines the minimum page order for slabs. Must be
3337 lower than slub_max_order.
3338 For more information see Documentation/vm/slub.txt.
3340 slub_nomerge [MM, SLUB]
3341 Same with slab_nomerge. This is supported for legacy.
3342 See slab_nomerge for more information.
3344 smart2= [HW]
3345 Format: <io1>[,<io2>[,...,<io8>]]
3347 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3348 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3349 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3350 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3351 smsc-ircc2.ircc_irq= [HW] IRQ line
3352 smsc-ircc2.ircc_dma= [HW] DMA channel
3353 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3354 0: Toshiba Satellite 1800 (GP data pin select)
3355 1: Fast pin select (default)
3356 2: ATC IRMode
3358 softlockup_panic=
3359 [KNL] Should the soft-lockup detector generate panics.
3360 Format: <integer>
3362 softlockup_all_cpu_backtrace=
3363 [KNL] Should the soft-lockup detector generate
3364 backtraces on all cpus.
3365 Format: <integer>
3367 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3368 See Documentation/laptops/sonypi.txt
3370 spia_io_base= [HW,MTD]
3371 spia_fio_base=
3372 spia_pedr=
3373 spia_peddr=
3375 stacktrace [FTRACE]
3376 Enabled the stack tracer on boot up.
3378 stacktrace_filter=[function-list]
3379 [FTRACE] Limit the functions that the stack tracer
3380 will trace at boot up. function-list is a comma separated
3381 list of functions. This list can be changed at run
3382 time by the stack_trace_filter file in the debugfs
3383 tracing directory. Note, this enables stack tracing
3384 and the stacktrace above is not needed.
3386 sti= [PARISC,HW]
3387 Format: <num>
3388 Set the STI (builtin display/keyboard on the HP-PARISC
3389 machines) console (graphic card) which should be used
3390 as the initial boot-console.
3391 See also comment in drivers/video/console/sticore.c.
3393 sti_font= [HW]
3394 See comment in drivers/video/console/sticore.c.
3396 stifb= [HW]
3397 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3399 sunrpc.min_resvport=
3400 sunrpc.max_resvport=
3401 [NFS,SUNRPC]
3402 SunRPC servers often require that client requests
3403 originate from a privileged port (i.e. a port in the
3404 range 0 < portnr < 1024).
3405 An administrator who wishes to reserve some of these
3406 ports for other uses may adjust the range that the
3407 kernel's sunrpc client considers to be privileged
3408 using these two parameters to set the minimum and
3409 maximum port values.
3411 sunrpc.pool_mode=
3412 [NFS]
3413 Control how the NFS server code allocates CPUs to
3414 service thread pools. Depending on how many NICs
3415 you have and where their interrupts are bound, this
3416 option will affect which CPUs will do NFS serving.
3417 Note: this parameter cannot be changed while the
3418 NFS server is running.
3420 auto the server chooses an appropriate mode
3421 automatically using heuristics
3422 global a single global pool contains all CPUs
3423 percpu one pool for each CPU
3424 pernode one pool for each NUMA node (equivalent
3425 to global on non-NUMA machines)
3427 sunrpc.tcp_slot_table_entries=
3428 sunrpc.udp_slot_table_entries=
3429 [NFS,SUNRPC]
3430 Sets the upper limit on the number of simultaneous
3431 RPC calls that can be sent from the client to a
3432 server. Increasing these values may allow you to
3433 improve throughput, but will also increase the
3434 amount of memory reserved for use by the client.
3436 swapaccount=[0|1]
3437 [KNL] Enable accounting of swap in memory resource
3438 controller if no parameter or 1 is given or disable
3439 it if 0 is given (See Documentation/cgroups/memory.txt)
3441 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3442 Format: { <int> | force }
3443 <int> -- Number of I/O TLB slabs
3444 force -- force using of bounce buffers even if they
3445 wouldn't be automatically used by the kernel
3447 switches= [HW,M68k]
3449 sysfs.deprecated=0|1 [KNL]
3450 Enable/disable old style sysfs layout for old udev
3451 on older distributions. When this option is enabled
3452 very new udev will not work anymore. When this option
3453 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3454 in older udev will not work anymore.
3455 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3456 the kernel configuration.
3458 sysrq_always_enabled
3459 [KNL]
3460 Ignore sysrq setting - this boot parameter will
3461 neutralize any effect of /proc/sys/kernel/sysrq.
3462 Useful for debugging.
3464 tcpmhash_entries= [KNL,NET]
3465 Set the number of tcp_metrics_hash slots.
3466 Default value is 8192 or 16384 depending on total
3467 ram pages. This is used to specify the TCP metrics
3468 cache size. See Documentation/networking/ip-sysctl.txt
3469 "tcp_no_metrics_save" section for more details.
3471 tdfx= [HW,DRM]
3473 test_suspend= [SUSPEND][,N]
3474 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3475 standby suspend) or "freeze" (for suspend type freeze)
3476 as the system sleep state during system startup with
3477 the optional capability to repeat N number of times.
3478 The system is woken from this state using a
3479 wakeup-capable RTC alarm.
3481 thash_entries= [KNL,NET]
3482 Set number of hash buckets for TCP connection
3484 thermal.act= [HW,ACPI]
3485 -1: disable all active trip points in all thermal zones
3486 <degrees C>: override all lowest active trip points
3488 thermal.crt= [HW,ACPI]
3489 -1: disable all critical trip points in all thermal zones
3490 <degrees C>: override all critical trip points
3492 thermal.nocrt= [HW,ACPI]
3493 Set to disable actions on ACPI thermal zone
3494 critical and hot trip points.
3496 thermal.off= [HW,ACPI]
3497 1: disable ACPI thermal control
3499 thermal.psv= [HW,ACPI]
3500 -1: disable all passive trip points
3501 <degrees C>: override all passive trip points to this
3502 value
3504 thermal.tzp= [HW,ACPI]
3505 Specify global default ACPI thermal zone polling rate
3506 <deci-seconds>: poll all this frequency
3507 0: no polling (default)
3509 threadirqs [KNL]
3510 Force threading of all interrupt handlers except those
3511 marked explicitly IRQF_NO_THREAD.
3513 tmem [KNL,XEN]
3514 Enable the Transcendent memory driver if built-in.
3516 tmem.cleancache=0|1 [KNL, XEN]
3517 Default is on (1). Disable the usage of the cleancache
3518 API to send anonymous pages to the hypervisor.
3520 tmem.frontswap=0|1 [KNL, XEN]
3521 Default is on (1). Disable the usage of the frontswap
3522 API to send swap pages to the hypervisor. If disabled
3523 the selfballooning and selfshrinking are force disabled.
3525 tmem.selfballooning=0|1 [KNL, XEN]
3526 Default is on (1). Disable the driving of swap pages
3527 to the hypervisor.
3529 tmem.selfshrinking=0|1 [KNL, XEN]
3530 Default is on (1). Partial swapoff that immediately
3531 transfers pages from Xen hypervisor back to the
3532 kernel based on different criteria.
3534 topology= [S390]
3535 Format: {off | on}
3536 Specify if the kernel should make use of the cpu
3537 topology information if the hardware supports this.
3538 The scheduler will make use of this information and
3539 e.g. base its process migration decisions on it.
3540 Default is on.
3542 topology_updates= [KNL, PPC, NUMA]
3543 Format: {off}
3544 Specify if the kernel should ignore (off)
3545 topology updates sent by the hypervisor to this
3546 LPAR.
3548 tp720= [HW,PS2]
3550 tpm_suspend_pcr=[HW,TPM]
3551 Format: integer pcr id
3552 Specify that at suspend time, the tpm driver
3553 should extend the specified pcr with zeros,
3554 as a workaround for some chips which fail to
3555 flush the last written pcr on TPM_SaveState.
3556 This will guarantee that all the other pcrs
3557 are saved.
3559 trace_buf_size=nn[KMG]
3560 [FTRACE] will set tracing buffer size on each cpu.
3562 trace_event=[event-list]
3563 [FTRACE] Set and start specified trace events in order
3564 to facilitate early boot debugging.
3565 See also Documentation/trace/events.txt
3567 trace_options=[option-list]
3568 [FTRACE] Enable or disable tracer options at boot.
3569 The option-list is a comma delimited list of options
3570 that can be enabled or disabled just as if you were
3571 to echo the option name into
3573 /sys/kernel/debug/tracing/trace_options
3575 For example, to enable stacktrace option (to dump the
3576 stack trace of each event), add to the command line:
3578 trace_options=stacktrace
3580 See also Documentation/trace/ftrace.txt "trace options"
3581 section.
3583 tp_printk[FTRACE]
3584 Have the tracepoints sent to printk as well as the
3585 tracing ring buffer. This is useful for early boot up
3586 where the system hangs or reboots and does not give the
3587 option for reading the tracing buffer or performing a
3588 ftrace_dump_on_oops.
3590 To turn off having tracepoints sent to printk,
3591 echo 0 > /proc/sys/kernel/tracepoint_printk
3592 Note, echoing 1 into this file without the
3593 tracepoint_printk kernel cmdline option has no effect.
3595 ** CAUTION **
3597 Having tracepoints sent to printk() and activating high
3598 frequency tracepoints such as irq or sched, can cause
3599 the system to live lock.
3601 traceoff_on_warning
3602 [FTRACE] enable this option to disable tracing when a
3603 warning is hit. This turns off "tracing_on". Tracing can
3604 be enabled again by echoing '1' into the "tracing_on"
3605 file located in /sys/kernel/debug/tracing/
3607 This option is useful, as it disables the trace before
3608 the WARNING dump is called, which prevents the trace to
3609 be filled with content caused by the warning output.
3611 This option can also be set at run time via the sysctl
3612 option: kernel/traceoff_on_warning
3614 transparent_hugepage=
3615 [KNL]
3616 Format: [always|madvise|never]
3617 Can be used to control the default behavior of the system
3618 with respect to transparent hugepages.
3619 See Documentation/vm/transhuge.txt for more details.
3621 tsc= Disable clocksource stability checks for TSC.
3622 Format: <string>
3623 [x86] reliable: mark tsc clocksource as reliable, this
3624 disables clocksource verification at runtime, as well
3625 as the stability checks done at bootup. Used to enable
3626 high-resolution timer mode on older hardware, and in
3627 virtualized environment.
3628 [x86] noirqtime: Do not use TSC to do irq accounting.
3629 Used to run time disable IRQ_TIME_ACCOUNTING on any
3630 platforms where RDTSC is slow and this accounting
3631 can add overhead.
3633 turbografx.map[2|3]= [HW,JOY]
3634 TurboGraFX parallel port interface
3635 Format:
3636 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3637 See also Documentation/input/joystick-parport.txt
3639 udbg-immortal [PPC] When debugging early kernel crashes that
3640 happen after console_init() and before a proper
3641 console driver takes over, this boot options might
3642 help "seeing" what's going on.
3644 uhash_entries= [KNL,NET]
3645 Set number of hash buckets for UDP/UDP-Lite connections
3647 uhci-hcd.ignore_oc=
3648 [USB] Ignore overcurrent events (default N).
3649 Some badly-designed motherboards generate lots of
3650 bogus events, for ports that aren't wired to
3651 anything. Set this parameter to avoid log spamming.
3652 Note that genuine overcurrent events won't be
3653 reported either.
3655 unknown_nmi_panic
3656 [X86] Cause panic on unknown NMI.
3658 usbcore.authorized_default=
3659 [USB] Default USB device authorization:
3660 (default -1 = authorized except for wireless USB,
3661 0 = not authorized, 1 = authorized)
3663 usbcore.autosuspend=
3664 [USB] The autosuspend time delay (in seconds) used
3665 for newly-detected USB devices (default 2). This
3666 is the time required before an idle device will be
3667 autosuspended. Devices for which the delay is set
3668 to a negative value won't be autosuspended at all.
3670 usbcore.usbfs_snoop=
3671 [USB] Set to log all usbfs traffic (default 0 = off).
3673 usbcore.blinkenlights=
3674 [USB] Set to cycle leds on hubs (default 0 = off).
3676 usbcore.old_scheme_first=
3677 [USB] Start with the old device initialization
3678 scheme (default 0 = off).
3680 usbcore.usbfs_memory_mb=
3681 [USB] Memory limit (in MB) for buffers allocated by
3682 usbfs (default = 16, 0 = max = 2047).
3684 usbcore.use_both_schemes=
3685 [USB] Try the other device initialization scheme
3686 if the first one fails (default 1 = enabled).
3688 usbcore.initial_descriptor_timeout=
3689 [USB] Specifies timeout for the initial 64-byte
3690 USB_REQ_GET_DESCRIPTOR request in milliseconds
3691 (default 5000 = 5.0 seconds).
3693 usbhid.mousepoll=
3694 [USBHID] The interval which mice are to be polled at.
3696 usb-storage.delay_use=
3697 [UMS] The delay in seconds before a new device is
3698 scanned for Logical Units (default 1).
3700 usb-storage.quirks=
3701 [UMS] A list of quirks entries to supplement or
3702 override the built-in unusual_devs list. List
3703 entries are separated by commas. Each entry has
3704 the form VID:PID:Flags where VID and PID are Vendor
3705 and Product ID values (4-digit hex numbers) and
3706 Flags is a set of characters, each corresponding
3707 to a common usb-storage quirk flag as follows:
3708 a = SANE_SENSE (collect more than 18 bytes
3709 of sense data);
3710 b = BAD_SENSE (don't collect more than 18
3711 bytes of sense data);
3712 c = FIX_CAPACITY (decrease the reported
3713 device capacity by one sector);
3714 d = NO_READ_DISC_INFO (don't use
3715 READ_DISC_INFO command);
3716 e = NO_READ_CAPACITY_16 (don't use
3717 READ_CAPACITY_16 command);
3718 f = NO_REPORT_OPCODES (don't use report opcodes
3719 command, uas only);
3720 h = CAPACITY_HEURISTICS (decrease the
3721 reported device capacity by one
3722 sector if the number is odd);
3723 i = IGNORE_DEVICE (don't bind to this
3724 device);
3725 l = NOT_LOCKABLE (don't try to lock and
3726 unlock ejectable media);
3727 m = MAX_SECTORS_64 (don't transfer more
3728 than 64 sectors = 32 KB at a time);
3729 n = INITIAL_READ10 (force a retry of the
3730 initial READ(10) command);
3731 o = CAPACITY_OK (accept the capacity
3732 reported by the device);
3733 p = WRITE_CACHE (the device cache is ON
3734 by default);
3735 r = IGNORE_RESIDUE (the device reports
3736 bogus residue values);
3737 s = SINGLE_LUN (the device has only one
3738 Logical Unit);
3739 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3740 commands, uas only);
3741 u = IGNORE_UAS (don't bind to the uas driver);
3742 w = NO_WP_DETECT (don't test whether the
3743 medium is write-protected).
3744 Example: quirks=0419:aaf5:rl,0421:0433:rc
3746 user_debug= [KNL,ARM]
3747 Format: <int>
3748 See arch/arm/Kconfig.debug help text.
3749 1 - undefined instruction events
3750 2 - system calls
3751 4 - invalid data aborts
3752 8 - SIGSEGV faults
3753 16 - SIGBUS faults
3754 Example: user_debug=31
3756 userpte=
3757 [X86] Flags controlling user PTE allocations.
3759 nohigh = do not allocate PTE pages in
3760 HIGHMEM regardless of setting
3761 of CONFIG_HIGHPTE.
3763 vdso= [X86,SH]
3764 On X86_32, this is an alias for vdso32=. Otherwise:
3766 vdso=1: enable VDSO (the default)
3767 vdso=0: disable VDSO mapping
3769 vdso32= [X86] Control the 32-bit vDSO
3770 vdso32=1: enable 32-bit VDSO
3771 vdso32=0 or vdso32=2: disable 32-bit VDSO
3773 See the help text for CONFIG_COMPAT_VDSO for more
3774 details. If CONFIG_COMPAT_VDSO is set, the default is
3775 vdso32=0; otherwise, the default is vdso32=1.
3777 For compatibility with older kernels, vdso32=2 is an
3778 alias for vdso32=0.
3780 Try vdso32=0 if you encounter an error that says:
3781 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3783 vector= [IA-64,SMP]
3784 vector=percpu: enable percpu vector domain
3786 video= [FB] Frame buffer configuration
3787 See Documentation/fb/modedb.txt.
3789 video.brightness_switch_enabled= [0,1]
3790 If set to 1, on receiving an ACPI notify event
3791 generated by hotkey, video driver will adjust brightness
3792 level and then send out the event to user space through
3793 the allocated input device; If set to 0, video driver
3794 will only send out the event without touching backlight
3795 brightness level.
3796 default: 1
3798 virtio_mmio.device=
3799 [VMMIO] Memory mapped virtio (platform) device.
3801 <size>@<baseaddr>:<irq>[:<id>]
3802 where:
3803 <size> := size (can use standard suffixes
3804 like K, M and G)
3805 <baseaddr> := physical base address
3806 <irq> := interrupt number (as passed to
3807 request_irq())
3808 <id> := (optional) platform device id
3809 example:
3810 virtio_mmio.device=1K@0x100b0000:48:7
3812 Can be used multiple times for multiple devices.
3814 vga= [BOOT,X86-32] Select a particular video mode
3815 See Documentation/x86/boot.txt and
3816 Documentation/svga.txt.
3817 Use vga=ask for menu.
3818 This is actually a boot loader parameter; the value is
3819 passed to the kernel using a special protocol.
3821 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3822 size of <nn>. This can be used to increase the
3823 minimum size (128MB on x86). It can also be used to
3824 decrease the size and leave more room for directly
3825 mapped kernel RAM.
3827 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3828 Format: <command>
3830 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3831 Format: <command>
3833 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3834 Format: <command>
3836 vsyscall= [X86-64]
3837 Controls the behavior of vsyscalls (i.e. calls to
3838 fixed addresses of 0xffffffffff600x00 from legacy
3839 code). Most statically-linked binaries and older
3840 versions of glibc use these calls. Because these
3841 functions are at fixed addresses, they make nice
3842 targets for exploits that can control RIP.
3844 emulate [default] Vsyscalls turn into traps and are
3845 emulated reasonably safely.
3847 native Vsyscalls are native syscall instructions.
3848 This is a little bit faster than trapping
3849 and makes a few dynamic recompilers work
3850 better than they would in emulation mode.
3851 It also makes exploits much easier to write.
3853 none Vsyscalls don't work at all. This makes
3854 them quite hard to use for exploits but
3855 might break your system.
3857 vt.color= [VT] Default text color.
3858 Format: 0xYX, X = foreground, Y = background.
3859 Default: 0x07 = light gray on black.
3861 vt.cur_default= [VT] Default cursor shape.
3862 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3863 the parameters of the <Esc>[?A;B;Cc escape sequence;
3864 see VGA-softcursor.txt. Default: 2 = underline.
3866 vt.default_blu= [VT]
3867 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3868 Change the default blue palette of the console.
3869 This is a 16-member array composed of values
3870 ranging from 0-255.
3872 vt.default_grn= [VT]
3873 Format: <green0>,<green1>,<green2>,...,<green15>
3874 Change the default green palette of the console.
3875 This is a 16-member array composed of values
3876 ranging from 0-255.
3878 vt.default_red= [VT]
3879 Format: <red0>,<red1>,<red2>,...,<red15>
3880 Change the default red palette of the console.
3881 This is a 16-member array composed of values
3882 ranging from 0-255.
3884 vt.default_utf8=
3885 [VT]
3886 Format=<0|1>
3887 Set system-wide default UTF-8 mode for all tty's.
3888 Default is 1, i.e. UTF-8 mode is enabled for all
3889 newly opened terminals.
3891 vt.global_cursor_default=
3892 [VT]
3893 Format=<-1|0|1>
3894 Set system-wide default for whether a cursor
3895 is shown on new VTs. Default is -1,
3896 i.e. cursors will be created by default unless
3897 overridden by individual drivers. 0 will hide
3898 cursors, 1 will display them.
3900 vt.italic= [VT] Default color for italic text; 0-15.
3901 Default: 2 = green.
3903 vt.underline= [VT] Default color for underlined text; 0-15.
3904 Default: 3 = cyan.
3906 watchdog timers [HW,WDT] For information on watchdog timers,
3907 see Documentation/watchdog/watchdog-parameters.txt
3908 or other driver-specific files in the
3909 Documentation/watchdog/ directory.
3911 workqueue.disable_numa
3912 By default, all work items queued to unbound
3913 workqueues are affine to the NUMA nodes they're
3914 issued on, which results in better behavior in
3915 general. If NUMA affinity needs to be disabled for
3916 whatever reason, this option can be used. Note
3917 that this also can be controlled per-workqueue for
3918 workqueues visible under /sys/bus/workqueue/.
3920 workqueue.power_efficient
3921 Per-cpu workqueues are generally preferred because
3922 they show better performance thanks to cache
3923 locality; unfortunately, per-cpu workqueues tend to
3924 be more power hungry than unbound workqueues.
3926 Enabling this makes the per-cpu workqueues which
3927 were observed to contribute significantly to power
3928 consumption unbound, leading to measurably lower
3929 power usage at the cost of small performance
3930 overhead.
3932 The default value of this parameter is determined by
3933 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3935 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3936 default x2apic cluster mode on platforms
3937 supporting x2apic.
3939 x86_intel_mid_timer= [X86-32,APBT]
3940 Choose timer option for x86 Intel MID platform.
3941 Two valid options are apbt timer only and lapic timer
3942 plus one apbt timer for broadcast timer.
3943 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3945 xen_emul_unplug= [HW,X86,XEN]
3946 Unplug Xen emulated devices
3947 Format: [unplug0,][unplug1]
3948 ide-disks -- unplug primary master IDE devices
3949 aux-ide-disks -- unplug non-primary-master IDE devices
3950 nics -- unplug network devices
3951 all -- unplug all emulated devices (NICs and IDE disks)
3952 unnecessary -- unplugging emulated devices is
3953 unnecessary even if the host did not respond to
3954 the unplug protocol
3955 never -- do not unplug even if version check succeeds
3957 xen_nopvspin [X86,XEN]
3958 Disables the ticketlock slowpath using Xen PV
3959 optimizations.
3961 xen_nopv [X86]
3962 Disables the PV optimizations forcing the HVM guest to
3963 run as generic HVM guest with no PV drivers.
3965 xirc2ps_cs= [NET,PCMCIA]
3966 Format:
3967 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3969 ______________________________________________________________________
3971 TODO:
3973 Add more DRM drivers.