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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
3
4The following is a consolidated list of the kernel parameters as
5implemented by the __setup(), core_param() and module_param() macros
6and sorted into English Dictionary order (defined as ignoring all
7punctuation and sorting digits before letters in a case insensitive
8manner), and with descriptions where known.
9
10The kernel parses parameters from the kernel command line up to "--";
11if it doesn't recognize a parameter and it doesn't contain a '.', the
12parameter gets passed to init: parameters with '=' go into init's
13environment, others are passed as command line arguments to init.
14Everything after "--" is passed as an argument to init.
15
16Module parameters can be specified in two ways: via the kernel command
17line with a module name prefix, or via modprobe, e.g.:
18
19 (kernel command line) usbcore.blinkenlights=1
20 (modprobe command line) modprobe usbcore blinkenlights=1
21
22Parameters for modules which are built into the kernel need to be
23specified on the kernel command line. modprobe looks through the
24kernel command line (/proc/cmdline) and collects module parameters
25when it loads a module, so the kernel command line can be used for
26loadable modules too.
27
28Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30can also be entered as
31 log-buf-len=1M print_fatal_signals=1
32
33Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
35
36This document may not be entirely up to date and comprehensive. The command
37"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
38module. Loadable modules, after being loaded into the running kernel, also
39reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
40parameters may be changed at runtime by the command
41"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
42
43The parameters listed below are only valid if certain kernel build options were
44enabled and if respective hardware is present. The text in square brackets at
45the beginning of each description states the restrictions within which a
46parameter is applicable:
47
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
135
136In addition, the following text indicates that the option:
137
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.
141
142Parameters denoted with BOOT are actually interpreted by the boot
143loader, and have no meaning to the kernel directly.
144Do not modify the syntax of boot loader parameters without extreme
145need or coordination with <Documentation/x86/boot.txt>.
146
147There are also arch-specific kernel-parameters not documented here.
148See for example <Documentation/x86/x86_64/boot-options.txt>.
149
150Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
151a trailing = on the name of any parameter states that that parameter will
152be entered as an environment variable, whereas its absence indicates that
153it will appear as a kernel argument readable via /proc/cmdline by programs
154running once the system is up.
155
156The number of kernel parameters is not limited, but the length of the
157complete command line (parameters including spaces etc.) is limited to
158a fixed number of characters. This limit depends on the architecture
159and is between 256 and 4096 characters. It is defined in the file
160./include/asm/setup.h as COMMAND_LINE_SIZE.
161
162Finally, the [KMG] suffix is commonly described after a number of kernel
163parameter values. These 'K', 'M', and 'G' letters represent the _binary_
164multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
165bytes respectively. Such letter suffixes can also be entirely omitted.
166
167
168 acpi= [HW,ACPI,X86,ARM64]
169 Advanced Configuration and Power Interface
170 Format: { force | off | strict | noirq | rsdt |
171 copy_dsdt }
172 force -- enable ACPI if default was off
173 off -- disable ACPI if default was on
174 noirq -- do not use ACPI for IRQ routing
175 strict -- Be less tolerant of platforms that are not
176 strictly ACPI specification compliant.
177 rsdt -- prefer RSDT over (default) XSDT
178 copy_dsdt -- copy DSDT to memory
179 For ARM64, ONLY "acpi=off" or "acpi=force" are available
180
181 See also Documentation/power/runtime_pm.txt, pci=noacpi
182
183 acpi_apic_instance= [ACPI, IOAPIC]
184 Format: <int>
185 2: use 2nd APIC table, if available
186 1,0: use 1st APIC table
187 default: 0
188
189 acpi_backlight= [HW,ACPI]
190 acpi_backlight=vendor
191 acpi_backlight=video
192 If set to vendor, prefer vendor specific driver
193 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
194 of the ACPI video.ko driver.
195
196 acpi_force_32bit_fadt_addr
197 force FADT to use 32 bit addresses rather than the
198 64 bit X_* addresses. Some firmware have broken 64
199 bit addresses for force ACPI ignore these and use
200 the older legacy 32 bit addresses.
201
202 acpica_no_return_repair [HW, ACPI]
203 Disable AML predefined validation mechanism
204 This mechanism can repair the evaluation result to make
205 the return objects more ACPI specification compliant.
206 This option is useful for developers to identify the
207 root cause of an AML interpreter issue when the issue
208 has something to do with the repair mechanism.
209
210 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
211 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
212 Format: <int>
213 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
214 debug output. Bits in debug_layer correspond to a
215 _COMPONENT in an ACPI source file, e.g.,
216 #define _COMPONENT ACPI_PCI_COMPONENT
217 Bits in debug_level correspond to a level in
218 ACPI_DEBUG_PRINT statements, e.g.,
219 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
220 The debug_level mask defaults to "info". See
221 Documentation/acpi/debug.txt for more information about
222 debug layers and levels.
223
224 Enable processor driver info messages:
225 acpi.debug_layer=0x20000000
226 Enable PCI/PCI interrupt routing info messages:
227 acpi.debug_layer=0x400000
228 Enable AML "Debug" output, i.e., stores to the Debug
229 object while interpreting AML:
230 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
231 Enable all messages related to ACPI hardware:
232 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
233
234 Some values produce so much output that the system is
235 unusable. The "log_buf_len" parameter may be useful
236 if you need to capture more output.
237
238 acpi_enforce_resources= [ACPI]
239 { strict | lax | no }
240 Check for resource conflicts between native drivers
241 and ACPI OperationRegions (SystemIO and SystemMemory
242 only). IO ports and memory declared in ACPI might be
243 used by the ACPI subsystem in arbitrary AML code and
244 can interfere with legacy drivers.
245 strict (default): access to resources claimed by ACPI
246 is denied; legacy drivers trying to access reserved
247 resources will fail to bind to device using them.
248 lax: access to resources claimed by ACPI is allowed;
249 legacy drivers trying to access reserved resources
250 will bind successfully but a warning message is logged.
251 no: ACPI OperationRegions are not marked as reserved,
252 no further checks are performed.
253
254 acpi_force_table_verification [HW,ACPI]
255 Enable table checksum verification during early stage.
256 By default, this is disabled due to x86 early mapping
257 size limitation.
258
259 acpi_irq_balance [HW,ACPI]
260 ACPI will balance active IRQs
261 default in APIC mode
262
263 acpi_irq_nobalance [HW,ACPI]
264 ACPI will not move active IRQs (default)
265 default in PIC mode
266
267 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
268 Format: <irq>,<irq>...
269
270 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
271 use by PCI
272 Format: <irq>,<irq>...
273
274 acpi_no_auto_serialize [HW,ACPI]
275 Disable auto-serialization of AML methods
276 AML control methods that contain the opcodes to create
277 named objects will be marked as "Serialized" by the
278 auto-serialization feature.
279 This feature is enabled by default.
280 This option allows to turn off the feature.
281
282 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
283 kernels.
284
285 acpi_no_static_ssdt [HW,ACPI]
286 Disable installation of static SSDTs at early boot time
287 By default, SSDTs contained in the RSDT/XSDT will be
288 installed automatically and they will appear under
289 /sys/firmware/acpi/tables.
290 This option turns off this feature.
291 Note that specifying this option does not affect
292 dynamic table installation which will install SSDT
293 tables to /sys/firmware/acpi/tables/dynamic.
294
295 acpi_rsdp= [ACPI,EFI,KEXEC]
296 Pass the RSDP address to the kernel, mostly used
297 on machines running EFI runtime service to boot the
298 second kernel for kdump.
299
300 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
301 Format: To spoof as Windows 98: ="Microsoft Windows"
302
303 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
304 of 2 which is mandated by ACPI 6) as the supported ACPI
305 specification revision (when using this switch, it may
306 be necessary to carry out a cold reboot _twice_ in a
307 row to make it take effect on the platform firmware).
308
309 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
310 acpi_osi="string1" # add string1
311 acpi_osi="!string2" # remove string2
312 acpi_osi=!* # remove all strings
313 acpi_osi=! # disable all built-in OS vendor
314 strings
315 acpi_osi= # disable all strings
316
317 'acpi_osi=!' can be used in combination with single or
318 multiple 'acpi_osi="string1"' to support specific OS
319 vendor string(s). Note that such command can only
320 affect the default state of the OS vendor strings, thus
321 it cannot affect the default state of the feature group
322 strings and the current state of the OS vendor strings,
323 specifying it multiple times through kernel command line
324 is meaningless. This command is useful when one do not
325 care about the state of the feature group strings which
326 should be controlled by the OSPM.
327 Examples:
328 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
329 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
330 can make '_OSI("Windows 2000")' TRUE.
331
332 'acpi_osi=' cannot be used in combination with other
333 'acpi_osi=' command lines, the _OSI method will not
334 exist in the ACPI namespace. NOTE that such command can
335 only affect the _OSI support state, thus specifying it
336 multiple times through kernel command line is also
337 meaningless.
338 Examples:
339 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
340 FALSE.
341
342 'acpi_osi=!*' can be used in combination with single or
343 multiple 'acpi_osi="string1"' to support specific
344 string(s). Note that such command can affect the
345 current state of both the OS vendor strings and the
346 feature group strings, thus specifying it multiple times
347 through kernel command line is meaningful. But it may
348 still not able to affect the final state of a string if
349 there are quirks related to this string. This command
350 is useful when one want to control the state of the
351 feature group strings to debug BIOS issues related to
352 the OSPM features.
353 Examples:
354 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
355 '_OSI("Module Device")' FALSE.
356 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
357 '_OSI("Module Device")' TRUE.
358 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
359 equivalent to
360 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
361 and
362 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
363 they all will make '_OSI("Windows 2000")' TRUE.
364
365 acpi_pm_good [X86]
366 Override the pmtimer bug detection: force the kernel
367 to assume that this machine's pmtimer latches its value
368 and always returns good values.
369
370 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
371 Format: { level | edge | high | low }
372
373 acpi_skip_timer_override [HW,ACPI]
374 Recognize and ignore IRQ0/pin2 Interrupt Override.
375 For broken nForce2 BIOS resulting in XT-PIC timer.
376
377 acpi_sleep= [HW,ACPI] Sleep options
378 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
379 old_ordering, nonvs, sci_force_enable }
380 See Documentation/power/video.txt for information on
381 s3_bios and s3_mode.
382 s3_beep is for debugging; it makes the PC's speaker beep
383 as soon as the kernel's real-mode entry point is called.
384 s4_nohwsig prevents ACPI hardware signature from being
385 used during resume from hibernation.
386 old_ordering causes the ACPI 1.0 ordering of the _PTS
387 control method, with respect to putting devices into
388 low power states, to be enforced (the ACPI 2.0 ordering
389 of _PTS is used by default).
390 nonvs prevents the kernel from saving/restoring the
391 ACPI NVS memory during suspend/hibernation and resume.
392 sci_force_enable causes the kernel to set SCI_EN directly
393 on resume from S1/S3 (which is against the ACPI spec,
394 but some broken systems don't work without it).
395
396 acpi_use_timer_override [HW,ACPI]
397 Use timer override. For some broken Nvidia NF5 boards
398 that require a timer override, but don't have HPET
399
400 add_efi_memmap [EFI; X86] Include EFI memory map in
401 kernel's map of available physical RAM.
402
403 agp= [AGP]
404 { off | try_unsupported }
405 off: disable AGP support
406 try_unsupported: try to drive unsupported chipsets
407 (may crash computer or cause data corruption)
408
409 ALSA [HW,ALSA]
410 See Documentation/sound/alsa/alsa-parameters.txt
411
412 alignment= [KNL,ARM]
413 Allow the default userspace alignment fault handler
414 behaviour to be specified. Bit 0 enables warnings,
415 bit 1 enables fixups, and bit 2 sends a segfault.
416
417 align_va_addr= [X86-64]
418 Align virtual addresses by clearing slice [14:12] when
419 allocating a VMA at process creation time. This option
420 gives you up to 3% performance improvement on AMD F15h
421 machines (where it is enabled by default) for a
422 CPU-intensive style benchmark, and it can vary highly in
423 a microbenchmark depending on workload and compiler.
424
425 32: only for 32-bit processes
426 64: only for 64-bit processes
427 on: enable for both 32- and 64-bit processes
428 off: disable for both 32- and 64-bit processes
429
430 alloc_snapshot [FTRACE]
431 Allocate the ftrace snapshot buffer on boot up when the
432 main buffer is allocated. This is handy if debugging
433 and you need to use tracing_snapshot() on boot up, and
434 do not want to use tracing_snapshot_alloc() as it needs
435 to be done where GFP_KERNEL allocations are allowed.
436
437 amd_iommu= [HW,X86-64]
438 Pass parameters to the AMD IOMMU driver in the system.
439 Possible values are:
440 fullflush - enable flushing of IO/TLB entries when
441 they are unmapped. Otherwise they are
442 flushed before they will be reused, which
443 is a lot of faster
444 off - do not initialize any AMD IOMMU found in
445 the system
446 force_isolation - Force device isolation for all
447 devices. The IOMMU driver is not
448 allowed anymore to lift isolation
449 requirements as needed. This option
450 does not override iommu=pt
451
452 amd_iommu_dump= [HW,X86-64]
453 Enable AMD IOMMU driver option to dump the ACPI table
454 for AMD IOMMU. With this option enabled, AMD IOMMU
455 driver will print ACPI tables for AMD IOMMU during
456 IOMMU initialization.
457
458 amijoy.map= [HW,JOY] Amiga joystick support
459 Map of devices attached to JOY0DAT and JOY1DAT
460 Format: <a>,<b>
461 See also Documentation/input/joystick.txt
462
463 analog.map= [HW,JOY] Analog joystick and gamepad support
464 Specifies type or capabilities of an analog joystick
465 connected to one of 16 gameports
466 Format: <type1>,<type2>,..<type16>
467
468 apc= [HW,SPARC]
469 Power management functions (SPARCstation-4/5 + deriv.)
470 Format: noidle
471 Disable APC CPU standby support. SPARCstation-Fox does
472 not play well with APC CPU idle - disable it if you have
473 APC and your system crashes randomly.
474
475 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
476 Change the output verbosity whilst booting
477 Format: { quiet (default) | verbose | debug }
478 Change the amount of debugging information output
479 when initialising the APIC and IO-APIC components.
480
481 apic_extnmi= [APIC,X86] External NMI delivery setting
482 Format: { bsp (default) | all | none }
483 bsp: External NMI is delivered only to CPU 0
484 all: External NMIs are broadcast to all CPUs as a
485 backup of CPU 0
486 none: External NMI is masked for all CPUs. This is
487 useful so that a dump capture kernel won't be
488 shot down by NMI
489
490 autoconf= [IPV6]
491 See Documentation/networking/ipv6.txt.
492
493 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
494 Limit apic dumping. The parameter defines the maximal
495 number of local apics being dumped. Also it is possible
496 to set it to "all" by meaning -- no limit here.
497 Format: { 1 (default) | 2 | ... | all }.
498 The parameter valid if only apic=debug or
499 apic=verbose is specified.
500 Example: apic=debug show_lapic=all
501
502 apm= [APM] Advanced Power Management
503 See header of arch/x86/kernel/apm_32.c.
504
505 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
506 Format: <io>,<irq>,<nodeID>
507
508 ataflop= [HW,M68k]
509
510 atarimouse= [HW,MOUSE] Atari Mouse
511
512 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
513 EzKey and similar keyboards
514
515 atkbd.reset= [HW] Reset keyboard during initialization
516
517 atkbd.set= [HW] Select keyboard code set
518 Format: <int> (2 = AT (default), 3 = PS/2)
519
520 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
521 keyboards
522
523 atkbd.softraw= [HW] Choose between synthetic and real raw mode
524 Format: <bool> (0 = real, 1 = synthetic (default))
525
526 atkbd.softrepeat= [HW]
527 Use software keyboard repeat
528
529 audit= [KNL] Enable the audit sub-system
530 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
531 0 - kernel audit is disabled and can not be enabled
532 until the next reboot
533 unset - kernel audit is initialized but disabled and
534 will be fully enabled by the userspace auditd.
535 1 - kernel audit is initialized and partially enabled,
536 storing at most audit_backlog_limit messages in
537 RAM until it is fully enabled by the userspace
538 auditd.
539 Default: unset
540
541 audit_backlog_limit= [KNL] Set the audit queue size limit.
542 Format: <int> (must be >=0)
543 Default: 64
544
545 baycom_epp= [HW,AX25]
546 Format: <io>,<mode>
547
548 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
549 Format: <io>,<mode>
550 See header of drivers/net/hamradio/baycom_par.c.
551
552 baycom_ser_fdx= [HW,AX25]
553 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
554 Format: <io>,<irq>,<mode>[,<baud>]
555 See header of drivers/net/hamradio/baycom_ser_fdx.c.
556
557 baycom_ser_hdx= [HW,AX25]
558 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
559 Format: <io>,<irq>,<mode>
560 See header of drivers/net/hamradio/baycom_ser_hdx.c.
561
562 blkdevparts= Manual partition parsing of block device(s) for
563 embedded devices based on command line input.
564 See Documentation/block/cmdline-partition.txt
565
566 boot_delay= Milliseconds to delay each printk during boot.
567 Values larger than 10 seconds (10000) are changed to
568 no delay (0).
569 Format: integer
570
571 bootmem_debug [KNL] Enable bootmem allocator debug messages.
572
573 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
574 bttv.radio= Most important insmod options are available as
575 kernel args too.
576 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
577 bttv.tuner=
578
579 bulk_remove=off [PPC] This parameter disables the use of the pSeries
580 firmware feature for flushing multiple hpte entries
581 at a time.
582
583 c101= [NET] Moxa C101 synchronous serial card
584
585 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
586 Sometimes CPU hardware bugs make them report the cache
587 size incorrectly. The kernel will attempt work arounds
588 to fix known problems, but for some CPUs it is not
589 possible to determine what the correct size should be.
590 This option provides an override for these situations.
591
592 ca_keys= [KEYS] This parameter identifies a specific key(s) on
593 the system trusted keyring to be used for certificate
594 trust validation.
595 format: { id:<keyid> | builtin }
596
597 cca= [MIPS] Override the kernel pages' cache coherency
598 algorithm. Accepted values range from 0 to 7
599 inclusive. See arch/mips/include/asm/pgtable-bits.h
600 for platform specific values (SB1, Loongson3 and
601 others).
602
603 ccw_timeout_log [S390]
604 See Documentation/s390/CommonIO for details.
605
606 cgroup_disable= [KNL] Disable a particular controller
607 Format: {name of the controller(s) to disable}
608 The effects of cgroup_disable=foo are:
609 - foo isn't auto-mounted if you mount all cgroups in
610 a single hierarchy
611 - foo isn't visible as an individually mountable
612 subsystem
613 {Currently only "memory" controller deal with this and
614 cut the overhead, others just disable the usage. So
615 only cgroup_disable=memory is actually worthy}
616
617 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
618 Format: { controller[,controller...] | "all" }
619 Like cgroup_disable, but only applies to cgroup v1;
620 the blacklisted controllers remain available in cgroup2.
621
622 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
623 Format: <string>
624 nosocket -- Disable socket memory accounting.
625 nokmem -- Disable kernel memory accounting.
626
627 checkreqprot [SELINUX] Set initial checkreqprot flag value.
628 Format: { "0" | "1" }
629 See security/selinux/Kconfig help text.
630 0 -- check protection applied by kernel (includes
631 any implied execute protection).
632 1 -- check protection requested by application.
633 Default value is set via a kernel config option.
634 Value can be changed at runtime via
635 /selinux/checkreqprot.
636
637 cio_ignore= [S390]
638 See Documentation/s390/CommonIO for details.
639 clk_ignore_unused
640 [CLK]
641 Prevents the clock framework from automatically gating
642 clocks that have not been explicitly enabled by a Linux
643 device driver but are enabled in hardware at reset or
644 by the bootloader/firmware. Note that this does not
645 force such clocks to be always-on nor does it reserve
646 those clocks in any way. This parameter is useful for
647 debug and development, but should not be needed on a
648 platform with proper driver support. For more
649 information, see Documentation/clk.txt.
650
651 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
652 [Deprecated]
653 Forces specified clocksource (if available) to be used
654 when calculating gettimeofday(). If specified
655 clocksource is not available, it defaults to PIT.
656 Format: { pit | tsc | cyclone | pmtmr }
657
658 clocksource= Override the default clocksource
659 Format: <string>
660 Override the default clocksource and use the clocksource
661 with the name specified.
662 Some clocksource names to choose from, depending on
663 the platform:
664 [all] jiffies (this is the base, fallback clocksource)
665 [ACPI] acpi_pm
666 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
667 pxa_timer,timer3,32k_counter,timer0_1
668 [AVR32] avr32
669 [X86-32] pit,hpet,tsc;
670 scx200_hrt on Geode; cyclone on IBM x440
671 [MIPS] MIPS
672 [PARISC] cr16
673 [S390] tod
674 [SH] SuperH
675 [SPARC64] tick
676 [X86-64] hpet,tsc
677
678 clearcpuid=BITNUM [X86]
679 Disable CPUID feature X for the kernel. See
680 arch/x86/include/asm/cpufeatures.h for the valid bit
681 numbers. Note the Linux specific bits are not necessarily
682 stable over kernel options, but the vendor specific
683 ones should be.
684 Also note that user programs calling CPUID directly
685 or using the feature without checking anything
686 will still see it. This just prevents it from
687 being used by the kernel or shown in /proc/cpuinfo.
688 Also note the kernel might malfunction if you disable
689 some critical bits.
690
691 cma=nn[MG]@[start[MG][-end[MG]]]
692 [ARM,X86,KNL]
693 Sets the size of kernel global memory area for
694 contiguous memory allocations and optionally the
695 placement constraint by the physical address range of
696 memory allocations. A value of 0 disables CMA
697 altogether. For more information, see
698 include/linux/dma-contiguous.h
699
700 cmo_free_hint= [PPC] Format: { yes | no }
701 Specify whether pages are marked as being inactive
702 when they are freed. This is used in CMO environments
703 to determine OS memory pressure for page stealing by
704 a hypervisor.
705 Default: yes
706
707 coherent_pool=nn[KMG] [ARM,KNL]
708 Sets the size of memory pool for coherent, atomic dma
709 allocations, by default set to 256K.
710
711 code_bytes [X86] How many bytes of object code to print
712 in an oops report.
713 Range: 0 - 8192
714 Default: 64
715
716 com20020= [HW,NET] ARCnet - COM20020 chipset
717 Format:
718 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
719
720 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
721 Format: <io>[,<irq>]
722
723 com90xx= [HW,NET]
724 ARCnet - COM90xx chipset (memory-mapped buffers)
725 Format: <io>[,<irq>[,<memstart>]]
726
727 condev= [HW,S390] console device
728 conmode=
729
730 console= [KNL] Output console device and options.
731
732 tty<n> Use the virtual console device <n>.
733
734 ttyS<n>[,options]
735 ttyUSB0[,options]
736 Use the specified serial port. The options are of
737 the form "bbbbpnf", where "bbbb" is the baud rate,
738 "p" is parity ("n", "o", or "e"), "n" is number of
739 bits, and "f" is flow control ("r" for RTS or
740 omit it). Default is "9600n8".
741
742 See Documentation/serial-console.txt for more
743 information. See
744 Documentation/networking/netconsole.txt for an
745 alternative.
746
747 uart[8250],io,<addr>[,options]
748 uart[8250],mmio,<addr>[,options]
749 uart[8250],mmio16,<addr>[,options]
750 uart[8250],mmio32,<addr>[,options]
751 uart[8250],0x<addr>[,options]
752 Start an early, polled-mode console on the 8250/16550
753 UART at the specified I/O port or MMIO address,
754 switching to the matching ttyS device later.
755 MMIO inter-register address stride is either 8-bit
756 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
757 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
758 to be equivalent to 'mmio'. 'options' are specified in
759 the same format described for ttyS above; if unspecified,
760 the h/w is not re-initialized.
761
762 hvc<n> Use the hypervisor console device <n>. This is for
763 both Xen and PowerPC hypervisors.
764
765 If the device connected to the port is not a TTY but a braille
766 device, prepend "brl," before the device type, for instance
767 console=brl,ttyS0
768 For now, only VisioBraille is supported.
769
770 consoleblank= [KNL] The console blank (screen saver) timeout in
771 seconds. Defaults to 10*60 = 10mins. A value of 0
772 disables the blank timer.
773
774 coredump_filter=
775 [KNL] Change the default value for
776 /proc/<pid>/coredump_filter.
777 See also Documentation/filesystems/proc.txt.
778
779 cpuidle.off=1 [CPU_IDLE]
780 disable the cpuidle sub-system
781
782 cpu_init_udelay=N
783 [X86] Delay for N microsec between assert and de-assert
784 of APIC INIT to start processors. This delay occurs
785 on every CPU online, such as boot, and resume from suspend.
786 Default: 10000
787
788 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
789 Format:
790 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
791
792 crashkernel=size[KMG][@offset[KMG]]
793 [KNL] Using kexec, Linux can switch to a 'crash kernel'
794 upon panic. This parameter reserves the physical
795 memory region [offset, offset + size] for that kernel
796 image. If '@offset' is omitted, then a suitable offset
797 is selected automatically. Check
798 Documentation/kdump/kdump.txt for further details.
799
800 crashkernel=range1:size1[,range2:size2,...][@offset]
801 [KNL] Same as above, but depends on the memory
802 in the running system. The syntax of range is
803 start-[end] where start and end are both
804 a memory unit (amount[KMG]). See also
805 Documentation/kdump/kdump.txt for an example.
806
807 crashkernel=size[KMG],high
808 [KNL, x86_64] range could be above 4G. Allow kernel
809 to allocate physical memory region from top, so could
810 be above 4G if system have more than 4G ram installed.
811 Otherwise memory region will be allocated below 4G, if
812 available.
813 It will be ignored if crashkernel=X is specified.
814 crashkernel=size[KMG],low
815 [KNL, x86_64] range under 4G. When crashkernel=X,high
816 is passed, kernel could allocate physical memory region
817 above 4G, that cause second kernel crash on system
818 that require some amount of low memory, e.g. swiotlb
819 requires at least 64M+32K low memory, also enough extra
820 low memory is needed to make sure DMA buffers for 32-bit
821 devices won't run out. Kernel would try to allocate at
822 at least 256M below 4G automatically.
823 This one let user to specify own low range under 4G
824 for second kernel instead.
825 0: to disable low allocation.
826 It will be ignored when crashkernel=X,high is not used
827 or memory reserved is below 4G.
828
829 cs89x0_dma= [HW,NET]
830 Format: <dma>
831
832 cs89x0_media= [HW,NET]
833 Format: { rj45 | aui | bnc }
834
835 dasd= [HW,NET]
836 See header of drivers/s390/block/dasd_devmap.c.
837
838 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
839 (one device per port)
840 Format: <port#>,<type>
841 See also Documentation/input/joystick-parport.txt
842
843 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
844 time. See Documentation/dynamic-debug-howto.txt for
845 details. Deprecated, see dyndbg.
846
847 debug [KNL] Enable kernel debugging (events log level).
848
849 debug_locks_verbose=
850 [KNL] verbose self-tests
851 Format=<0|1>
852 Print debugging info while doing the locking API
853 self-tests.
854 We default to 0 (no extra messages), setting it to
855 1 will print _a lot_ more information - normally
856 only useful to kernel developers.
857
858 debug_objects [KNL] Enable object debugging
859
860 no_debug_objects
861 [KNL] Disable object debugging
862
863 debug_guardpage_minorder=
864 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
865 parameter allows control of the order of pages that will
866 be intentionally kept free (and hence protected) by the
867 buddy allocator. Bigger value increase the probability
868 of catching random memory corruption, but reduce the
869 amount of memory for normal system use. The maximum
870 possible value is MAX_ORDER/2. Setting this parameter
871 to 1 or 2 should be enough to identify most random
872 memory corruption problems caused by bugs in kernel or
873 driver code when a CPU writes to (or reads from) a
874 random memory location. Note that there exists a class
875 of memory corruptions problems caused by buggy H/W or
876 F/W or by drivers badly programing DMA (basically when
877 memory is written at bus level and the CPU MMU is
878 bypassed) which are not detectable by
879 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
880 tracking down these problems.
881
882 debug_pagealloc=
883 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
884 parameter enables the feature at boot time. In
885 default, it is disabled. We can avoid allocating huge
886 chunk of memory for debug pagealloc if we don't enable
887 it at boot time and the system will work mostly same
888 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
889 on: enable the feature
890
891 debugpat [X86] Enable PAT debugging
892
893 decnet.addr= [HW,NET]
894 Format: <area>[,<node>]
895 See also Documentation/networking/decnet.txt.
896
897 default_hugepagesz=
898 [same as hugepagesz=] The size of the default
899 HugeTLB page size. This is the size represented by
900 the legacy /proc/ hugepages APIs, used for SHM, and
901 default size when mounting hugetlbfs filesystems.
902 Defaults to the default architecture's huge page size
903 if not specified.
904
905 dhash_entries= [KNL]
906 Set number of hash buckets for dentry cache.
907
908 disable= [IPV6]
909 See Documentation/networking/ipv6.txt.
910
911 disable_cpu_apicid= [X86,APIC,SMP]
912 Format: <int>
913 The number of initial APIC ID for the
914 corresponding CPU to be disabled at boot,
915 mostly used for the kdump 2nd kernel to
916 disable BSP to wake up multiple CPUs without
917 causing system reset or hang due to sending
918 INIT from AP to BSP.
919
920 disable_ddw [PPC/PSERIES]
921 Disable Dynamic DMA Window support. Use this if
922 to workaround buggy firmware.
923
924 disable_ipv6= [IPV6]
925 See Documentation/networking/ipv6.txt.
926
927 disable_mtrr_cleanup [X86]
928 The kernel tries to adjust MTRR layout from continuous
929 to discrete, to make X server driver able to add WB
930 entry later. This parameter disables that.
931
932 disable_mtrr_trim [X86, Intel and AMD only]
933 By default the kernel will trim any uncacheable
934 memory out of your available memory pool based on
935 MTRR settings. This parameter disables that behavior,
936 possibly causing your machine to run very slowly.
937
938 disable_timer_pin_1 [X86]
939 Disable PIN 1 of APIC timer
940 Can be useful to work around chipset bugs.
941
942 dis_ucode_ldr [X86] Disable the microcode loader.
943
944 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
945 this option disables the debugging code at boot.
946
947 dma_debug_entries=<number>
948 This option allows to tune the number of preallocated
949 entries for DMA-API debugging code. One entry is
950 required per DMA-API allocation. Use this if the
951 DMA-API debugging code disables itself because the
952 architectural default is too low.
953
954 dma_debug_driver=<driver_name>
955 With this option the DMA-API debugging driver
956 filter feature can be enabled at boot time. Just
957 pass the driver to filter for as the parameter.
958 The filter can be disabled or changed to another
959 driver later using sysfs.
960
961 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
962 Broken monitors, graphic adapters, KVMs and EDIDless
963 panels may send no or incorrect EDID data sets.
964 This parameter allows to specify an EDID data sets
965 in the /lib/firmware directory that are used instead.
966 Generic built-in EDID data sets are used, if one of
967 edid/1024x768.bin, edid/1280x1024.bin,
968 edid/1680x1050.bin, or edid/1920x1080.bin is given
969 and no file with the same name exists. Details and
970 instructions how to build your own EDID data are
971 available in Documentation/EDID/HOWTO.txt. An EDID
972 data set will only be used for a particular connector,
973 if its name and a colon are prepended to the EDID
974 name. Each connector may use a unique EDID data
975 set by separating the files with a comma. An EDID
976 data set with no connector name will be used for
977 any connectors not explicitly specified.
978
979 dscc4.setup= [NET]
980
981 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
982 module.dyndbg[="val"]
983 Enable debug messages at boot time. See
984 Documentation/dynamic-debug-howto.txt for details.
985
986 nompx [X86] Disables Intel Memory Protection Extensions.
987 See Documentation/x86/intel_mpx.txt for more
988 information about the feature.
989
990 nopku [X86] Disable Memory Protection Keys CPU feature found
991 in some Intel CPUs.
992
993 eagerfpu= [X86]
994 on enable eager fpu restore
995 off disable eager fpu restore
996 auto selects the default scheme, which automatically
997 enables eagerfpu restore for xsaveopt.
998
999 module.async_probe [KNL]
1000 Enable asynchronous probe on this module.
1001
1002 early_ioremap_debug [KNL]
1003 Enable debug messages in early_ioremap support. This
1004 is useful for tracking down temporary early mappings
1005 which are not unmapped.
1006
1007 earlycon= [KNL] Output early console device and options.
1008
1009 When used with no options, the early console is
1010 determined by the stdout-path property in device
1011 tree's chosen node.
1012
1013 cdns,<addr>
1014 Start an early, polled-mode console on a cadence serial
1015 port at the specified address. The cadence serial port
1016 must already be setup and configured. Options are not
1017 yet supported.
1018
1019 uart[8250],io,<addr>[,options]
1020 uart[8250],mmio,<addr>[,options]
1021 uart[8250],mmio32,<addr>[,options]
1022 uart[8250],mmio32be,<addr>[,options]
1023 uart[8250],0x<addr>[,options]
1024 Start an early, polled-mode console on the 8250/16550
1025 UART at the specified I/O port or MMIO address.
1026 MMIO inter-register address stride is either 8-bit
1027 (mmio) or 32-bit (mmio32 or mmio32be).
1028 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1029 to be equivalent to 'mmio'. 'options' are specified
1030 in the same format described for "console=ttyS<n>"; if
1031 unspecified, the h/w is not initialized.
1032
1033 pl011,<addr>
1034 pl011,mmio32,<addr>
1035 Start an early, polled-mode console on a pl011 serial
1036 port at the specified address. The pl011 serial port
1037 must already be setup and configured. Options are not
1038 yet supported. If 'mmio32' is specified, then only
1039 the driver will use only 32-bit accessors to read/write
1040 the device registers.
1041
1042 msm_serial,<addr>
1043 Start an early, polled-mode console on an msm serial
1044 port at the specified address. The serial port
1045 must already be setup and configured. Options are not
1046 yet supported.
1047
1048 msm_serial_dm,<addr>
1049 Start an early, polled-mode console on an msm serial
1050 dm port at the specified address. The serial port
1051 must already be setup and configured. Options are not
1052 yet supported.
1053
1054 smh Use ARM semihosting calls for early console.
1055
1056 s3c2410,<addr>
1057 s3c2412,<addr>
1058 s3c2440,<addr>
1059 s3c6400,<addr>
1060 s5pv210,<addr>
1061 exynos4210,<addr>
1062 Use early console provided by serial driver available
1063 on Samsung SoCs, requires selecting proper type and
1064 a correct base address of the selected UART port. The
1065 serial port must already be setup and configured.
1066 Options are not yet supported.
1067
1068 lpuart,<addr>
1069 lpuart32,<addr>
1070 Use early console provided by Freescale LP UART driver
1071 found on Freescale Vybrid and QorIQ LS1021A processors.
1072 A valid base address must be provided, and the serial
1073 port must already be setup and configured.
1074
1075 armada3700_uart,<addr>
1076 Start an early, polled-mode console on the
1077 Armada 3700 serial port at the specified
1078 address. The serial port must already be setup
1079 and configured. Options are not yet supported.
1080
1081 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1082 earlyprintk=vga
1083 earlyprintk=efi
1084 earlyprintk=xen
1085 earlyprintk=serial[,ttySn[,baudrate]]
1086 earlyprintk=serial[,0x...[,baudrate]]
1087 earlyprintk=ttySn[,baudrate]
1088 earlyprintk=dbgp[debugController#]
1089 earlyprintk=pciserial,bus:device.function[,baudrate]
1090
1091 earlyprintk is useful when the kernel crashes before
1092 the normal console is initialized. It is not enabled by
1093 default because it has some cosmetic problems.
1094
1095 Append ",keep" to not disable it when the real console
1096 takes over.
1097
1098 Only one of vga, efi, serial, or usb debug port can
1099 be used at a time.
1100
1101 Currently only ttyS0 and ttyS1 may be specified by
1102 name. Other I/O ports may be explicitly specified
1103 on some architectures (x86 and arm at least) by
1104 replacing ttySn with an I/O port address, like this:
1105 earlyprintk=serial,0x1008,115200
1106 You can find the port for a given device in
1107 /proc/tty/driver/serial:
1108 2: uart:ST16650V2 port:00001008 irq:18 ...
1109
1110 Interaction with the standard serial driver is not
1111 very good.
1112
1113 The VGA and EFI output is eventually overwritten by
1114 the real console.
1115
1116 The xen output can only be used by Xen PV guests.
1117
1118 edac_report= [HW,EDAC] Control how to report EDAC event
1119 Format: {"on" | "off" | "force"}
1120 on: enable EDAC to report H/W event. May be overridden
1121 by other higher priority error reporting module.
1122 off: disable H/W event reporting through EDAC.
1123 force: enforce the use of EDAC to report H/W event.
1124 default: on.
1125
1126 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1127 ekgdboc=kbd
1128
1129 This is designed to be used in conjunction with
1130 the boot argument: earlyprintk=vga
1131
1132 edd= [EDD]
1133 Format: {"off" | "on" | "skip[mbr]"}
1134
1135 efi= [EFI]
1136 Format: { "old_map", "nochunk", "noruntime", "debug" }
1137 old_map [X86-64]: switch to the old ioremap-based EFI
1138 runtime services mapping. 32-bit still uses this one by
1139 default.
1140 nochunk: disable reading files in "chunks" in the EFI
1141 boot stub, as chunking can cause problems with some
1142 firmware implementations.
1143 noruntime : disable EFI runtime services support
1144 debug: enable misc debug output
1145
1146 efi_no_storage_paranoia [EFI; X86]
1147 Using this parameter you can use more than 50% of
1148 your efi variable storage. Use this parameter only if
1149 you are really sure that your UEFI does sane gc and
1150 fulfills the spec otherwise your board may brick.
1151
1152 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1153 Add arbitrary attribute to specific memory range by
1154 updating original EFI memory map.
1155 Region of memory which aa attribute is added to is
1156 from ss to ss+nn.
1157 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1158 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1159 attribute is added to range 0x100000000-0x180000000 and
1160 0x10a0000000-0x1120000000.
1161
1162 Using this parameter you can do debugging of EFI memmap
1163 related feature. For example, you can do debugging of
1164 Address Range Mirroring feature even if your box
1165 doesn't support it.
1166
1167 eisa_irq_edge= [PARISC,HW]
1168 See header of drivers/parisc/eisa.c.
1169
1170 elanfreq= [X86-32]
1171 See comment before function elanfreq_setup() in
1172 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1173
1174 elevator= [IOSCHED]
1175 Format: {"cfq" | "deadline" | "noop"}
1176 See Documentation/block/cfq-iosched.txt and
1177 Documentation/block/deadline-iosched.txt for details.
1178
1179 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1180 Specifies physical address of start of kernel core
1181 image elf header and optionally the size. Generally
1182 kexec loader will pass this option to capture kernel.
1183 See Documentation/kdump/kdump.txt for details.
1184
1185 enable_mtrr_cleanup [X86]
1186 The kernel tries to adjust MTRR layout from continuous
1187 to discrete, to make X server driver able to add WB
1188 entry later. This parameter enables that.
1189
1190 enable_timer_pin_1 [X86]
1191 Enable PIN 1 of APIC timer
1192 Can be useful to work around chipset bugs
1193 (in particular on some ATI chipsets).
1194 The kernel tries to set a reasonable default.
1195
1196 enforcing [SELINUX] Set initial enforcing status.
1197 Format: {"0" | "1"}
1198 See security/selinux/Kconfig help text.
1199 0 -- permissive (log only, no denials).
1200 1 -- enforcing (deny and log).
1201 Default value is 0.
1202 Value can be changed at runtime via /selinux/enforce.
1203
1204 erst_disable [ACPI]
1205 Disable Error Record Serialization Table (ERST)
1206 support.
1207
1208 ether= [HW,NET] Ethernet cards parameters
1209 This option is obsoleted by the "netdev=" option, which
1210 has equivalent usage. See its documentation for details.
1211
1212 evm= [EVM]
1213 Format: { "fix" }
1214 Permit 'security.evm' to be updated regardless of
1215 current integrity status.
1216
1217 failslab=
1218 fail_page_alloc=
1219 fail_make_request=[KNL]
1220 General fault injection mechanism.
1221 Format: <interval>,<probability>,<space>,<times>
1222 See also Documentation/fault-injection/.
1223
1224 floppy= [HW]
1225 See Documentation/blockdev/floppy.txt.
1226
1227 force_pal_cache_flush
1228 [IA-64] Avoid check_sal_cache_flush which may hang on
1229 buggy SAL_CACHE_FLUSH implementations. Using this
1230 parameter will force ia64_sal_cache_flush to call
1231 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1232
1233 forcepae [X86-32]
1234 Forcefully enable Physical Address Extension (PAE).
1235 Many Pentium M systems disable PAE but may have a
1236 functionally usable PAE implementation.
1237 Warning: use of this parameter will taint the kernel
1238 and may cause unknown problems.
1239
1240 ftrace=[tracer]
1241 [FTRACE] will set and start the specified tracer
1242 as early as possible in order to facilitate early
1243 boot debugging.
1244
1245 ftrace_dump_on_oops[=orig_cpu]
1246 [FTRACE] will dump the trace buffers on oops.
1247 If no parameter is passed, ftrace will dump
1248 buffers of all CPUs, but if you pass orig_cpu, it will
1249 dump only the buffer of the CPU that triggered the
1250 oops.
1251
1252 ftrace_filter=[function-list]
1253 [FTRACE] Limit the functions traced by the function
1254 tracer at boot up. function-list is a comma separated
1255 list of functions. This list can be changed at run
1256 time by the set_ftrace_filter file in the debugfs
1257 tracing directory.
1258
1259 ftrace_notrace=[function-list]
1260 [FTRACE] Do not trace the functions specified in
1261 function-list. This list can be changed at run time
1262 by the set_ftrace_notrace file in the debugfs
1263 tracing directory.
1264
1265 ftrace_graph_filter=[function-list]
1266 [FTRACE] Limit the top level callers functions traced
1267 by the function graph tracer at boot up.
1268 function-list is a comma separated list of functions
1269 that can be changed at run time by the
1270 set_graph_function file in the debugfs tracing directory.
1271
1272 ftrace_graph_notrace=[function-list]
1273 [FTRACE] Do not trace from the functions specified in
1274 function-list. This list is a comma separated list of
1275 functions that can be changed at run time by the
1276 set_graph_notrace file in the debugfs tracing directory.
1277
1278 gamecon.map[2|3]=
1279 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1280 support via parallel port (up to 5 devices per port)
1281 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1282 See also Documentation/input/joystick-parport.txt
1283
1284 gamma= [HW,DRM]
1285
1286 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1287 Format: off | on
1288 default: on
1289
1290 gcov_persist= [GCOV] When non-zero (default), profiling data for
1291 kernel modules is saved and remains accessible via
1292 debugfs, even when the module is unloaded/reloaded.
1293 When zero, profiling data is discarded and associated
1294 debugfs files are removed at module unload time.
1295
1296 gpt [EFI] Forces disk with valid GPT signature but
1297 invalid Protective MBR to be treated as GPT. If the
1298 primary GPT is corrupted, it enables the backup/alternate
1299 GPT to be used instead.
1300
1301 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1302 the "Enable 0" bit of the configuration register.
1303 Format: 0 | 1
1304 Default: 0
1305 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1306 the "Enable 0" bit of the configuration register.
1307 Format: 0 | 1
1308 Default: 0
1309 grcan.select= [HW] Select which physical interface to use.
1310 Format: 0 | 1
1311 Default: 0
1312 grcan.txsize= [HW] Sets the size of the tx buffer.
1313 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1314 Default: 1024
1315 grcan.rxsize= [HW] Sets the size of the rx buffer.
1316 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1317 Default: 1024
1318
1319 hardlockup_all_cpu_backtrace=
1320 [KNL] Should the hard-lockup detector generate
1321 backtraces on all cpus.
1322 Format: <integer>
1323
1324 hashdist= [KNL,NUMA] Large hashes allocated during boot
1325 are distributed across NUMA nodes. Defaults on
1326 for 64-bit NUMA, off otherwise.
1327 Format: 0 | 1 (for off | on)
1328
1329 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1330
1331 hd= [EIDE] (E)IDE hard drive subsystem geometry
1332 Format: <cyl>,<head>,<sect>
1333
1334 hest_disable [ACPI]
1335 Disable Hardware Error Source Table (HEST) support;
1336 corresponding firmware-first mode error processing
1337 logic will be disabled.
1338
1339 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1340 size of <nn>. This works even on boxes that have no
1341 highmem otherwise. This also works to reduce highmem
1342 size on bigger boxes.
1343
1344 highres= [KNL] Enable/disable high resolution timer mode.
1345 Valid parameters: "on", "off"
1346 Default: "on"
1347
1348 hisax= [HW,ISDN]
1349 See Documentation/isdn/README.HiSax.
1350
1351 hlt [BUGS=ARM,SH]
1352
1353 hpet= [X86-32,HPET] option to control HPET usage
1354 Format: { enable (default) | disable | force |
1355 verbose }
1356 disable: disable HPET and use PIT instead
1357 force: allow force enabled of undocumented chips (ICH4,
1358 VIA, nVidia)
1359 verbose: show contents of HPET registers during setup
1360
1361 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1362 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1363
1364 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1365 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1366 On x86-64 and powerpc, this option can be specified
1367 multiple times interleaved with hugepages= to reserve
1368 huge pages of different sizes. Valid pages sizes on
1369 x86-64 are 2M (when the CPU supports "pse") and 1G
1370 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1371
1372 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1373 terminal devices. Valid values: 0..8
1374 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1375 If specified, z/VM IUCV HVC accepts connections
1376 from listed z/VM user IDs only.
1377
1378 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1379 hardware thread id mappings.
1380 Format: <cpu>:<hwthread>
1381
1382 keep_bootcon [KNL]
1383 Do not unregister boot console at start. This is only
1384 useful for debugging when something happens in the window
1385 between unregistering the boot console and initializing
1386 the real console.
1387
1388 i2c_bus= [HW] Override the default board specific I2C bus speed
1389 or register an additional I2C bus that is not
1390 registered from board initialization code.
1391 Format:
1392 <bus_id>,<clkrate>
1393
1394 i8042.debug [HW] Toggle i8042 debug mode
1395 i8042.unmask_kbd_data
1396 [HW] Enable printing of interrupt data from the KBD port
1397 (disabled by default, and as a pre-condition
1398 requires that i8042.debug=1 be enabled)
1399 i8042.direct [HW] Put keyboard port into non-translated mode
1400 i8042.dumbkbd [HW] Pretend that controller can only read data from
1401 keyboard and cannot control its state
1402 (Don't attempt to blink the leds)
1403 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1404 i8042.nokbd [HW] Don't check/create keyboard port
1405 i8042.noloop [HW] Disable the AUX Loopback command while probing
1406 for the AUX port
1407 i8042.nomux [HW] Don't check presence of an active multiplexing
1408 controller
1409 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1410 controllers
1411 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1412 i8042.reset [HW] Reset the controller during init and cleanup
1413 i8042.unlock [HW] Unlock (ignore) the keylock
1414 i8042.kbdreset [HW] Reset device connected to KBD port
1415
1416 i810= [HW,DRM]
1417
1418 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1419 indicates that the driver is running on unsupported
1420 hardware.
1421 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1422 does not match list of supported models.
1423 i8k.power_status
1424 [HW] Report power status in /proc/i8k
1425 (disabled by default)
1426 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1427 capability is set.
1428
1429 i915.invert_brightness=
1430 [DRM] Invert the sense of the variable that is used to
1431 set the brightness of the panel backlight. Normally a
1432 brightness value of 0 indicates backlight switched off,
1433 and the maximum of the brightness value sets the backlight
1434 to maximum brightness. If this parameter is set to 0
1435 (default) and the machine requires it, or this parameter
1436 is set to 1, a brightness value of 0 sets the backlight
1437 to maximum brightness, and the maximum of the brightness
1438 value switches the backlight off.
1439 -1 -- never invert brightness
1440 0 -- machine default
1441 1 -- force brightness inversion
1442
1443 icn= [HW,ISDN]
1444 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1445
1446 ide-core.nodma= [HW] (E)IDE subsystem
1447 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1448 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1449 .cdrom .chs .ignore_cable are additional options
1450 See Documentation/ide/ide.txt.
1451
1452 ide-generic.probe-mask= [HW] (E)IDE subsystem
1453 Format: <int>
1454 Probe mask for legacy ISA IDE ports. Depending on
1455 platform up to 6 ports are supported, enabled by
1456 setting corresponding bits in the mask to 1. The
1457 default value is 0x0, which has a special meaning.
1458 On systems that have PCI, it triggers scanning the
1459 PCI bus for the first and the second port, which
1460 are then probed. On systems without PCI the value
1461 of 0x0 enables probing the two first ports as if it
1462 was 0x3.
1463
1464 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1465 Claim all unknown PCI IDE storage controllers.
1466
1467 idle= [X86]
1468 Format: idle=poll, idle=halt, idle=nomwait
1469 Poll forces a polling idle loop that can slightly
1470 improve the performance of waking up a idle CPU, but
1471 will use a lot of power and make the system run hot.
1472 Not recommended.
1473 idle=halt: Halt is forced to be used for CPU idle.
1474 In such case C2/C3 won't be used again.
1475 idle=nomwait: Disable mwait for CPU C-states
1476
1477 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1478 Format: { strict | legacy | 2008 | relaxed }
1479 Default: strict
1480
1481 Choose which programs will be accepted for execution
1482 based on the IEEE 754 NaN encoding(s) supported by
1483 the FPU and the NaN encoding requested with the value
1484 of an ELF file header flag individually set by each
1485 binary. Hardware implementations are permitted to
1486 support either or both of the legacy and the 2008 NaN
1487 encoding mode.
1488
1489 Available settings are as follows:
1490 strict accept binaries that request a NaN encoding
1491 supported by the FPU
1492 legacy only accept legacy-NaN binaries, if supported
1493 by the FPU
1494 2008 only accept 2008-NaN binaries, if supported
1495 by the FPU
1496 relaxed accept any binaries regardless of whether
1497 supported by the FPU
1498
1499 The FPU emulator is always able to support both NaN
1500 encodings, so if no FPU hardware is present or it has
1501 been disabled with 'nofpu', then the settings of
1502 'legacy' and '2008' strap the emulator accordingly,
1503 'relaxed' straps the emulator for both legacy-NaN and
1504 2008-NaN, whereas 'strict' enables legacy-NaN only on
1505 legacy processors and both NaN encodings on MIPS32 or
1506 MIPS64 CPUs.
1507
1508 The setting for ABS.fmt/NEG.fmt instruction execution
1509 mode generally follows that for the NaN encoding,
1510 except where unsupported by hardware.
1511
1512 ignore_loglevel [KNL]
1513 Ignore loglevel setting - this will print /all/
1514 kernel messages to the console. Useful for debugging.
1515 We also add it as printk module parameter, so users
1516 could change it dynamically, usually by
1517 /sys/module/printk/parameters/ignore_loglevel.
1518
1519 ignore_rlimit_data
1520 Ignore RLIMIT_DATA setting for data mappings,
1521 print warning at first misuse. Can be changed via
1522 /sys/module/kernel/parameters/ignore_rlimit_data.
1523
1524 ihash_entries= [KNL]
1525 Set number of hash buckets for inode cache.
1526
1527 ima_appraise= [IMA] appraise integrity measurements
1528 Format: { "off" | "enforce" | "fix" | "log" }
1529 default: "enforce"
1530
1531 ima_appraise_tcb [IMA]
1532 The builtin appraise policy appraises all files
1533 owned by uid=0.
1534
1535 ima_hash= [IMA]
1536 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1537 | sha512 | ... }
1538 default: "sha1"
1539
1540 The list of supported hash algorithms is defined
1541 in crypto/hash_info.h.
1542
1543 ima_policy= [IMA]
1544 The builtin measurement policy to load during IMA
1545 setup. Specyfing "tcb" as the value, measures all
1546 programs exec'd, files mmap'd for exec, and all files
1547 opened with the read mode bit set by either the
1548 effective uid (euid=0) or uid=0.
1549 Format: "tcb"
1550
1551 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1552 Load a policy which meets the needs of the Trusted
1553 Computing Base. This means IMA will measure all
1554 programs exec'd, files mmap'd for exec, and all files
1555 opened for read by uid=0.
1556
1557 ima_template= [IMA]
1558 Select one of defined IMA measurements template formats.
1559 Formats: { "ima" | "ima-ng" | "ima-sig" }
1560 Default: "ima-ng"
1561
1562 ima_template_fmt=
1563 [IMA] Define a custom template format.
1564 Format: { "field1|...|fieldN" }
1565
1566 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1567 Format: <min_file_size>
1568 Set the minimal file size for using asynchronous hash.
1569 If left unspecified, ahash usage is disabled.
1570
1571 ahash performance varies for different data sizes on
1572 different crypto accelerators. This option can be used
1573 to achieve the best performance for a particular HW.
1574
1575 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1576 Format: <bufsize>
1577 Set hashing buffer size. Default: 4k.
1578
1579 ahash performance varies for different chunk sizes on
1580 different crypto accelerators. This option can be used
1581 to achieve best performance for particular HW.
1582
1583 init= [KNL]
1584 Format: <full_path>
1585 Run specified binary instead of /sbin/init as init
1586 process.
1587
1588 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1589 for working out where the kernel is dying during
1590 startup.
1591
1592 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1593 initcall functions. Useful for debugging built-in
1594 modules and initcalls.
1595
1596 initrd= [BOOT] Specify the location of the initial ramdisk
1597
1598 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1599 Format: <irq>
1600
1601 int_pln_enable [x86] Enable power limit notification interrupt
1602
1603 integrity_audit=[IMA]
1604 Format: { "0" | "1" }
1605 0 -- basic integrity auditing messages. (Default)
1606 1 -- additional integrity auditing messages.
1607
1608 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1609 on
1610 Enable intel iommu driver.
1611 off
1612 Disable intel iommu driver.
1613 igfx_off [Default Off]
1614 By default, gfx is mapped as normal device. If a gfx
1615 device has a dedicated DMAR unit, the DMAR unit is
1616 bypassed by not enabling DMAR with this option. In
1617 this case, gfx device will use physical address for
1618 DMA.
1619 forcedac [x86_64]
1620 With this option iommu will not optimize to look
1621 for io virtual address below 32-bit forcing dual
1622 address cycle on pci bus for cards supporting greater
1623 than 32-bit addressing. The default is to look
1624 for translation below 32-bit and if not available
1625 then look in the higher range.
1626 strict [Default Off]
1627 With this option on every unmap_single operation will
1628 result in a hardware IOTLB flush operation as opposed
1629 to batching them for performance.
1630 sp_off [Default Off]
1631 By default, super page will be supported if Intel IOMMU
1632 has the capability. With this option, super page will
1633 not be supported.
1634 ecs_off [Default Off]
1635 By default, extended context tables will be supported if
1636 the hardware advertises that it has support both for the
1637 extended tables themselves, and also PASID support. With
1638 this option set, extended tables will not be used even
1639 on hardware which claims to support them.
1640
1641 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1642 0 disables intel_idle and fall back on acpi_idle.
1643 1 to 6 specify maximum depth of C-state.
1644
1645 intel_pstate= [X86]
1646 disable
1647 Do not enable intel_pstate as the default
1648 scaling driver for the supported processors
1649 force
1650 Enable intel_pstate on systems that prohibit it by default
1651 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1652 instead of acpi-cpufreq may disable platform features, such
1653 as thermal controls and power capping, that rely on ACPI
1654 P-States information being indicated to OSPM and therefore
1655 should be used with caution. This option does not work with
1656 processors that aren't supported by the intel_pstate driver
1657 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1658 no_hwp
1659 Do not enable hardware P state control (HWP)
1660 if available.
1661 hwp_only
1662 Only load intel_pstate on systems which support
1663 hardware P state control (HWP) if available.
1664
1665 intremap= [X86-64, Intel-IOMMU]
1666 on enable Interrupt Remapping (default)
1667 off disable Interrupt Remapping
1668 nosid disable Source ID checking
1669 no_x2apic_optout
1670 BIOS x2APIC opt-out request will be ignored
1671 nopost disable Interrupt Posting
1672
1673 iomem= Disable strict checking of access to MMIO memory
1674 strict regions from userspace.
1675 relaxed
1676
1677 iommu= [x86]
1678 off
1679 force
1680 noforce
1681 biomerge
1682 panic
1683 nopanic
1684 merge
1685 nomerge
1686 forcesac
1687 soft
1688 pt [x86, IA-64]
1689 nobypass [PPC/POWERNV]
1690 Disable IOMMU bypass, using IOMMU for PCI devices.
1691
1692
1693 io7= [HW] IO7 for Marvel based alpha systems
1694 See comment before marvel_specify_io7 in
1695 arch/alpha/kernel/core_marvel.c.
1696
1697 io_delay= [X86] I/O delay method
1698 0x80
1699 Standard port 0x80 based delay
1700 0xed
1701 Alternate port 0xed based delay (needed on some systems)
1702 udelay
1703 Simple two microseconds delay
1704 none
1705 No delay
1706
1707 ip= [IP_PNP]
1708 See Documentation/filesystems/nfs/nfsroot.txt.
1709
1710 irqaffinity= [SMP] Set the default irq affinity mask
1711 Format:
1712 <cpu number>,...,<cpu number>
1713 or
1714 <cpu number>-<cpu number>
1715 (must be a positive range in ascending order)
1716 or a mixture
1717 <cpu number>,...,<cpu number>-<cpu number>
1718
1719 irqfixup [HW]
1720 When an interrupt is not handled search all handlers
1721 for it. Intended to get systems with badly broken
1722 firmware running.
1723
1724 irqpoll [HW]
1725 When an interrupt is not handled search all handlers
1726 for it. Also check all handlers each timer
1727 interrupt. Intended to get systems with badly broken
1728 firmware running.
1729
1730 isapnp= [ISAPNP]
1731 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1732
1733 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1734 Format:
1735 <cpu number>,...,<cpu number>
1736 or
1737 <cpu number>-<cpu number>
1738 (must be a positive range in ascending order)
1739 or a mixture
1740 <cpu number>,...,<cpu number>-<cpu number>
1741
1742 This option can be used to specify one or more CPUs
1743 to isolate from the general SMP balancing and scheduling
1744 algorithms. You can move a process onto or off an
1745 "isolated" CPU via the CPU affinity syscalls or cpuset.
1746 <cpu number> begins at 0 and the maximum value is
1747 "number of CPUs in system - 1".
1748
1749 This option is the preferred way to isolate CPUs. The
1750 alternative -- manually setting the CPU mask of all
1751 tasks in the system -- can cause problems and
1752 suboptimal load balancer performance.
1753
1754 iucv= [HW,NET]
1755
1756 ivrs_ioapic [HW,X86_64]
1757 Provide an override to the IOAPIC-ID<->DEVICE-ID
1758 mapping provided in the IVRS ACPI table. For
1759 example, to map IOAPIC-ID decimal 10 to
1760 PCI device 00:14.0 write the parameter as:
1761 ivrs_ioapic[10]=00:14.0
1762
1763 ivrs_hpet [HW,X86_64]
1764 Provide an override to the HPET-ID<->DEVICE-ID
1765 mapping provided in the IVRS ACPI table. For
1766 example, to map HPET-ID decimal 0 to
1767 PCI device 00:14.0 write the parameter as:
1768 ivrs_hpet[0]=00:14.0
1769
1770 js= [HW,JOY] Analog joystick
1771 See Documentation/input/joystick.txt.
1772
1773 kaslr/nokaslr [X86]
1774 Enable/disable kernel and module base offset ASLR
1775 (Address Space Layout Randomization) if built into
1776 the kernel. When CONFIG_HIBERNATION is selected,
1777 kASLR is disabled by default. When kASLR is enabled,
1778 hibernation will be disabled.
1779
1780 keepinitrd [HW,ARM]
1781
1782 kernelcore= [KNL,X86,IA-64,PPC]
1783 Format: nn[KMGTPE] | "mirror"
1784 This parameter
1785 specifies the amount of memory usable by the kernel
1786 for non-movable allocations. The requested amount is
1787 spread evenly throughout all nodes in the system. The
1788 remaining memory in each node is used for Movable
1789 pages. In the event, a node is too small to have both
1790 kernelcore and Movable pages, kernelcore pages will
1791 take priority and other nodes will have a larger number
1792 of Movable pages. The Movable zone is used for the
1793 allocation of pages that may be reclaimed or moved
1794 by the page migration subsystem. This means that
1795 HugeTLB pages may not be allocated from this zone.
1796 Note that allocations like PTEs-from-HighMem still
1797 use the HighMem zone if it exists, and the Normal
1798 zone if it does not.
1799
1800 Instead of specifying the amount of memory (nn[KMGTPE]),
1801 you can specify "mirror" option. In case "mirror"
1802 option is specified, mirrored (reliable) memory is used
1803 for non-movable allocations and remaining memory is used
1804 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1805 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1806 time.
1807
1808 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1809 Format: <Controller#>[,poll interval]
1810 The controller # is the number of the ehci usb debug
1811 port as it is probed via PCI. The poll interval is
1812 optional and is the number seconds in between
1813 each poll cycle to the debug port in case you need
1814 the functionality for interrupting the kernel with
1815 gdb or control-c on the dbgp connection. When
1816 not using this parameter you use sysrq-g to break into
1817 the kernel debugger.
1818
1819 kgdboc= [KGDB,HW] kgdb over consoles.
1820 Requires a tty driver that supports console polling,
1821 or a supported polling keyboard driver (non-usb).
1822 Serial only format: <serial_device>[,baud]
1823 keyboard only format: kbd
1824 keyboard and serial format: kbd,<serial_device>[,baud]
1825 Optional Kernel mode setting:
1826 kms, kbd format: kms,kbd
1827 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1828
1829 kgdbwait [KGDB] Stop kernel execution and enter the
1830 kernel debugger at the earliest opportunity.
1831
1832 kmac= [MIPS] korina ethernet MAC address.
1833 Configure the RouterBoard 532 series on-chip
1834 Ethernet adapter MAC address.
1835
1836 kmemleak= [KNL] Boot-time kmemleak enable/disable
1837 Valid arguments: on, off
1838 Default: on
1839 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1840 the default is off.
1841
1842 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1843 Valid arguments: 0, 1, 2
1844 kmemcheck=0 (disabled)
1845 kmemcheck=1 (enabled)
1846 kmemcheck=2 (one-shot mode)
1847 Default: 2 (one-shot mode)
1848
1849 kstack=N [X86] Print N words from the kernel stack
1850 in oops dumps.
1851
1852 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1853 Default is 0 (don't ignore, but inject #GP)
1854
1855 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1856 KVM MMU at runtime.
1857 Default is 0 (off)
1858
1859 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1860 Default is 1 (enabled)
1861
1862 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1863 for all guests.
1864 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1865
1866 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1867 (virtualized MMU) support on capable Intel chips.
1868 Default is 1 (enabled)
1869
1870 kvm-intel.emulate_invalid_guest_state=
1871 [KVM,Intel] Enable emulation of invalid guest states
1872 Default is 0 (disabled)
1873
1874 kvm-intel.flexpriority=
1875 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1876 Default is 1 (enabled)
1877
1878 kvm-intel.nested=
1879 [KVM,Intel] Enable VMX nesting (nVMX).
1880 Default is 0 (disabled)
1881
1882 kvm-intel.unrestricted_guest=
1883 [KVM,Intel] Disable unrestricted guest feature
1884 (virtualized real and unpaged mode) on capable
1885 Intel chips. Default is 1 (enabled)
1886
1887 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1888 feature (tagged TLBs) on capable Intel chips.
1889 Default is 1 (enabled)
1890
1891 l2cr= [PPC]
1892
1893 l3cr= [PPC]
1894
1895 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1896 disabled it.
1897
1898 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1899 value for LAPIC timer one-shot implementation. Default
1900 back to the programmable timer unit in the LAPIC.
1901
1902 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1903 in C2 power state.
1904
1905 libata.dma= [LIBATA] DMA control
1906 libata.dma=0 Disable all PATA and SATA DMA
1907 libata.dma=1 PATA and SATA Disk DMA only
1908 libata.dma=2 ATAPI (CDROM) DMA only
1909 libata.dma=4 Compact Flash DMA only
1910 Combinations also work, so libata.dma=3 enables DMA
1911 for disks and CDROMs, but not CFs.
1912
1913 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1914 libata.ignore_hpa=0 keep BIOS limits (default)
1915 libata.ignore_hpa=1 ignore limits, using full disk
1916
1917 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1918 when set.
1919 Format: <int>
1920
1921 libata.force= [LIBATA] Force configurations. The format is comma
1922 separated list of "[ID:]VAL" where ID is
1923 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1924 matching port, link or device. Basically, it matches
1925 the ATA ID string printed on console by libata. If
1926 the whole ID part is omitted, the last PORT and DEVICE
1927 values are used. If ID hasn't been specified yet, the
1928 configuration applies to all ports, links and devices.
1929
1930 If only DEVICE is omitted, the parameter applies to
1931 the port and all links and devices behind it. DEVICE
1932 number of 0 either selects the first device or the
1933 first fan-out link behind PMP device. It does not
1934 select the host link. DEVICE number of 15 selects the
1935 host link and device attached to it.
1936
1937 The VAL specifies the configuration to force. As long
1938 as there's no ambiguity shortcut notation is allowed.
1939 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1940 The following configurations can be forced.
1941
1942 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1943 Any ID with matching PORT is used.
1944
1945 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1946
1947 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1948 udma[/][16,25,33,44,66,100,133] notation is also
1949 allowed.
1950
1951 * [no]ncq: Turn on or off NCQ.
1952
1953 * [no]ncqtrim: Turn off queued DSM TRIM.
1954
1955 * nohrst, nosrst, norst: suppress hard, soft
1956 and both resets.
1957
1958 * rstonce: only attempt one reset during
1959 hot-unplug link recovery
1960
1961 * dump_id: dump IDENTIFY data.
1962
1963 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1964
1965 * disable: Disable this device.
1966
1967 If there are multiple matching configurations changing
1968 the same attribute, the last one is used.
1969
1970 memblock=debug [KNL] Enable memblock debug messages.
1971
1972 load_ramdisk= [RAM] List of ramdisks to load from floppy
1973 See Documentation/blockdev/ramdisk.txt.
1974
1975 lockd.nlm_grace_period=P [NFS] Assign grace period.
1976 Format: <integer>
1977
1978 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1979 Format: <integer>
1980
1981 lockd.nlm_timeout=T [NFS] Assign timeout value.
1982 Format: <integer>
1983
1984 lockd.nlm_udpport=M [NFS] Assign UDP port.
1985 Format: <integer>
1986
1987 locktorture.nreaders_stress= [KNL]
1988 Set the number of locking read-acquisition kthreads.
1989 Defaults to being automatically set based on the
1990 number of online CPUs.
1991
1992 locktorture.nwriters_stress= [KNL]
1993 Set the number of locking write-acquisition kthreads.
1994
1995 locktorture.onoff_holdoff= [KNL]
1996 Set time (s) after boot for CPU-hotplug testing.
1997
1998 locktorture.onoff_interval= [KNL]
1999 Set time (s) between CPU-hotplug operations, or
2000 zero to disable CPU-hotplug testing.
2001
2002 locktorture.shuffle_interval= [KNL]
2003 Set task-shuffle interval (jiffies). Shuffling
2004 tasks allows some CPUs to go into dyntick-idle
2005 mode during the locktorture test.
2006
2007 locktorture.shutdown_secs= [KNL]
2008 Set time (s) after boot system shutdown. This
2009 is useful for hands-off automated testing.
2010
2011 locktorture.stat_interval= [KNL]
2012 Time (s) between statistics printk()s.
2013
2014 locktorture.stutter= [KNL]
2015 Time (s) to stutter testing, for example,
2016 specifying five seconds causes the test to run for
2017 five seconds, wait for five seconds, and so on.
2018 This tests the locking primitive's ability to
2019 transition abruptly to and from idle.
2020
2021 locktorture.torture_runnable= [BOOT]
2022 Start locktorture running at boot time.
2023
2024 locktorture.torture_type= [KNL]
2025 Specify the locking implementation to test.
2026
2027 locktorture.verbose= [KNL]
2028 Enable additional printk() statements.
2029
2030 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2031 Format: <irq>
2032
2033 loglevel= All Kernel Messages with a loglevel smaller than the
2034 console loglevel will be printed to the console. It can
2035 also be changed with klogd or other programs. The
2036 loglevels are defined as follows:
2037
2038 0 (KERN_EMERG) system is unusable
2039 1 (KERN_ALERT) action must be taken immediately
2040 2 (KERN_CRIT) critical conditions
2041 3 (KERN_ERR) error conditions
2042 4 (KERN_WARNING) warning conditions
2043 5 (KERN_NOTICE) normal but significant condition
2044 6 (KERN_INFO) informational
2045 7 (KERN_DEBUG) debug-level messages
2046
2047 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2048 in bytes. n must be a power of two and greater
2049 than the minimal size. The minimal size is defined
2050 by LOG_BUF_SHIFT kernel config parameter. There is
2051 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2052 that allows to increase the default size depending on
2053 the number of CPUs. See init/Kconfig for more details.
2054
2055 logo.nologo [FB] Disables display of the built-in Linux logo.
2056 This may be used to provide more screen space for
2057 kernel log messages and is useful when debugging
2058 kernel boot problems.
2059
2060 lp=0 [LP] Specify parallel ports to use, e.g,
2061 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2062 lp=reset first parallel port). 'lp=0' disables the
2063 lp=auto printer driver. 'lp=reset' (which can be
2064 specified in addition to the ports) causes
2065 attached printers to be reset. Using
2066 lp=port1,port2,... specifies the parallel ports
2067 to associate lp devices with, starting with
2068 lp0. A port specification may be 'none' to skip
2069 that lp device, or a parport name such as
2070 'parport0'. Specifying 'lp=auto' instead of a
2071 port specification list means that device IDs
2072 from each port should be examined, to see if
2073 an IEEE 1284-compliant printer is attached; if
2074 so, the driver will manage that printer.
2075 See also header of drivers/char/lp.c.
2076
2077 lpj=n [KNL]
2078 Sets loops_per_jiffy to given constant, thus avoiding
2079 time-consuming boot-time autodetection (up to 250 ms per
2080 CPU). 0 enables autodetection (default). To determine
2081 the correct value for your kernel, boot with normal
2082 autodetection and see what value is printed. Note that
2083 on SMP systems the preset will be applied to all CPUs,
2084 which is likely to cause problems if your CPUs need
2085 significantly divergent settings. An incorrect value
2086 will cause delays in the kernel to be wrong, leading to
2087 unpredictable I/O errors and other breakage. Although
2088 unlikely, in the extreme case this might damage your
2089 hardware.
2090
2091 ltpc= [NET]
2092 Format: <io>,<irq>,<dma>
2093
2094 machvec= [IA-64] Force the use of a particular machine-vector
2095 (machvec) in a generic kernel.
2096 Example: machvec=hpzx1_swiotlb
2097
2098 machtype= [Loongson] Share the same kernel image file between different
2099 yeeloong laptop.
2100 Example: machtype=lemote-yeeloong-2f-7inch
2101
2102 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2103 than or equal to this physical address is ignored.
2104
2105 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2106 should make use of. maxcpus=n : n >= 0 limits the
2107 kernel to using 'n' processors. n=0 is a special case,
2108 it is equivalent to "nosmp", which also disables
2109 the IO APIC.
2110
2111 max_loop= [LOOP] The number of loop block devices that get
2112 (loop.max_loop) unconditionally pre-created at init time. The default
2113 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2114 of statically allocating a predefined number, loop
2115 devices can be requested on-demand with the
2116 /dev/loop-control interface.
2117
2118 mce [X86-32] Machine Check Exception
2119
2120 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2121
2122 md= [HW] RAID subsystems devices and level
2123 See Documentation/md.txt.
2124
2125 mdacon= [MDA]
2126 Format: <first>,<last>
2127 Specifies range of consoles to be captured by the MDA.
2128
2129 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2130 Amount of memory to be used when the kernel is not able
2131 to see the whole system memory or for test.
2132 [X86] Work as limiting max address. Use together
2133 with memmap= to avoid physical address space collisions.
2134 Without memmap= PCI devices could be placed at addresses
2135 belonging to unused RAM.
2136
2137 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2138 memory.
2139
2140 memchunk=nn[KMG]
2141 [KNL,SH] Allow user to override the default size for
2142 per-device physically contiguous DMA buffers.
2143
2144 memmap=exactmap [KNL,X86] Enable setting of an exact
2145 E820 memory map, as specified by the user.
2146 Such memmap=exactmap lines can be constructed based on
2147 BIOS output or other requirements. See the memmap=nn@ss
2148 option description.
2149
2150 memmap=nn[KMG]@ss[KMG]
2151 [KNL] Force usage of a specific region of memory.
2152 Region of memory to be used is from ss to ss+nn.
2153
2154 memmap=nn[KMG]#ss[KMG]
2155 [KNL,ACPI] Mark specific memory as ACPI data.
2156 Region of memory to be marked is from ss to ss+nn.
2157
2158 memmap=nn[KMG]$ss[KMG]
2159 [KNL,ACPI] Mark specific memory as reserved.
2160 Region of memory to be reserved is from ss to ss+nn.
2161 Example: Exclude memory from 0x18690000-0x1869ffff
2162 memmap=64K$0x18690000
2163 or
2164 memmap=0x10000$0x18690000
2165
2166 memmap=nn[KMG]!ss[KMG]
2167 [KNL,X86] Mark specific memory as protected.
2168 Region of memory to be used, from ss to ss+nn.
2169 The memory region may be marked as e820 type 12 (0xc)
2170 and is NVDIMM or ADR memory.
2171
2172 memory_corruption_check=0/1 [X86]
2173 Some BIOSes seem to corrupt the first 64k of
2174 memory when doing things like suspend/resume.
2175 Setting this option will scan the memory
2176 looking for corruption. Enabling this will
2177 both detect corruption and prevent the kernel
2178 from using the memory being corrupted.
2179 However, its intended as a diagnostic tool; if
2180 repeatable BIOS-originated corruption always
2181 affects the same memory, you can use memmap=
2182 to prevent the kernel from using that memory.
2183
2184 memory_corruption_check_size=size [X86]
2185 By default it checks for corruption in the low
2186 64k, making this memory unavailable for normal
2187 use. Use this parameter to scan for
2188 corruption in more or less memory.
2189
2190 memory_corruption_check_period=seconds [X86]
2191 By default it checks for corruption every 60
2192 seconds. Use this parameter to check at some
2193 other rate. 0 disables periodic checking.
2194
2195 memtest= [KNL,X86,ARM] Enable memtest
2196 Format: <integer>
2197 default : 0 <disable>
2198 Specifies the number of memtest passes to be
2199 performed. Each pass selects another test
2200 pattern from a given set of patterns. Memtest
2201 fills the memory with this pattern, validates
2202 memory contents and reserves bad memory
2203 regions that are detected.
2204
2205 meye.*= [HW] Set MotionEye Camera parameters
2206 See Documentation/video4linux/meye.txt.
2207
2208 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2209 Multi-Function General Purpose Timers on AMD Geode
2210 platforms.
2211
2212 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2213 the BIOS has incorrectly applied a workaround. TinyBIOS
2214 version 0.98 is known to be affected, 0.99 fixes the
2215 problem by letting the user disable the workaround.
2216
2217 mga= [HW,DRM]
2218
2219 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2220 physical address is ignored.
2221
2222 mini2440= [ARM,HW,KNL]
2223 Format:[0..2][b][c][t]
2224 Default: "0tb"
2225 MINI2440 configuration specification:
2226 0 - The attached screen is the 3.5" TFT
2227 1 - The attached screen is the 7" TFT
2228 2 - The VGA Shield is attached (1024x768)
2229 Leaving out the screen size parameter will not load
2230 the TFT driver, and the framebuffer will be left
2231 unconfigured.
2232 b - Enable backlight. The TFT backlight pin will be
2233 linked to the kernel VESA blanking code and a GPIO
2234 LED. This parameter is not necessary when using the
2235 VGA shield.
2236 c - Enable the s3c camera interface.
2237 t - Reserved for enabling touchscreen support. The
2238 touchscreen support is not enabled in the mainstream
2239 kernel as of 2.6.30, a preliminary port can be found
2240 in the "bleeding edge" mini2440 support kernel at
2241 http://repo.or.cz/w/linux-2.6/mini2440.git
2242
2243 mminit_loglevel=
2244 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2245 parameter allows control of the logging verbosity for
2246 the additional memory initialisation checks. A value
2247 of 0 disables mminit logging and a level of 4 will
2248 log everything. Information is printed at KERN_DEBUG
2249 so loglevel=8 may also need to be specified.
2250
2251 module.sig_enforce
2252 [KNL] When CONFIG_MODULE_SIG is set, this means that
2253 modules without (valid) signatures will fail to load.
2254 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2255 is always true, so this option does nothing.
2256
2257 mousedev.tap_time=
2258 [MOUSE] Maximum time between finger touching and
2259 leaving touchpad surface for touch to be considered
2260 a tap and be reported as a left button click (for
2261 touchpads working in absolute mode only).
2262 Format: <msecs>
2263 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2264 reporting absolute coordinates, such as tablets
2265 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2266 reporting absolute coordinates, such as tablets
2267
2268 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2269 is similar to kernelcore except it specifies the
2270 amount of memory used for migratable allocations.
2271 If both kernelcore and movablecore is specified,
2272 then kernelcore will be at *least* the specified
2273 value but may be more. If movablecore on its own
2274 is specified, the administrator must be careful
2275 that the amount of memory usable for all allocations
2276 is not too small.
2277
2278 movable_node [KNL,X86] Boot-time switch to enable the effects
2279 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2280
2281 MTD_Partition= [MTD]
2282 Format: <name>,<region-number>,<size>,<offset>
2283
2284 MTD_Region= [MTD] Format:
2285 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2286
2287 mtdparts= [MTD]
2288 See drivers/mtd/cmdlinepart.c.
2289
2290 multitce=off [PPC] This parameter disables the use of the pSeries
2291 firmware feature for updating multiple TCE entries
2292 at a time.
2293
2294 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2295
2296 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2297
2298 boundary - index of last SLC block on Flex-OneNAND.
2299 The remaining blocks are configured as MLC blocks.
2300 lock - Configure if Flex-OneNAND boundary should be locked.
2301 Once locked, the boundary cannot be changed.
2302 1 indicates lock status, 0 indicates unlock status.
2303
2304 mtdset= [ARM]
2305 ARM/S3C2412 JIVE boot control
2306
2307 See arch/arm/mach-s3c2412/mach-jive.c
2308
2309 mtouchusb.raw_coordinates=
2310 [HW] Make the MicroTouch USB driver use raw coordinates
2311 ('y', default) or cooked coordinates ('n')
2312
2313 mtrr_chunk_size=nn[KMG] [X86]
2314 used for mtrr cleanup. It is largest continuous chunk
2315 that could hold holes aka. UC entries.
2316
2317 mtrr_gran_size=nn[KMG] [X86]
2318 Used for mtrr cleanup. It is granularity of mtrr block.
2319 Default is 1.
2320 Large value could prevent small alignment from
2321 using up MTRRs.
2322
2323 mtrr_spare_reg_nr=n [X86]
2324 Format: <integer>
2325 Range: 0,7 : spare reg number
2326 Default : 1
2327 Used for mtrr cleanup. It is spare mtrr entries number.
2328 Set to 2 or more if your graphical card needs more.
2329
2330 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2331
2332 netdev= [NET] Network devices parameters
2333 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2334 Note that mem_start is often overloaded to mean
2335 something different and driver-specific.
2336 This usage is only documented in each driver source
2337 file if at all.
2338
2339 nf_conntrack.acct=
2340 [NETFILTER] Enable connection tracking flow accounting
2341 0 to disable accounting
2342 1 to enable accounting
2343 Default value is 0.
2344
2345 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2346 See Documentation/filesystems/nfs/nfsroot.txt.
2347
2348 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2349 See Documentation/filesystems/nfs/nfsroot.txt.
2350
2351 nfsrootdebug [NFS] enable nfsroot debugging messages.
2352 See Documentation/filesystems/nfs/nfsroot.txt.
2353
2354 nfs.callback_tcpport=
2355 [NFS] set the TCP port on which the NFSv4 callback
2356 channel should listen.
2357
2358 nfs.cache_getent=
2359 [NFS] sets the pathname to the program which is used
2360 to update the NFS client cache entries.
2361
2362 nfs.cache_getent_timeout=
2363 [NFS] sets the timeout after which an attempt to
2364 update a cache entry is deemed to have failed.
2365
2366 nfs.idmap_cache_timeout=
2367 [NFS] set the maximum lifetime for idmapper cache
2368 entries.
2369
2370 nfs.enable_ino64=
2371 [NFS] enable 64-bit inode numbers.
2372 If zero, the NFS client will fake up a 32-bit inode
2373 number for the readdir() and stat() syscalls instead
2374 of returning the full 64-bit number.
2375 The default is to return 64-bit inode numbers.
2376
2377 nfs.max_session_slots=
2378 [NFSv4.1] Sets the maximum number of session slots
2379 the client will attempt to negotiate with the server.
2380 This limits the number of simultaneous RPC requests
2381 that the client can send to the NFSv4.1 server.
2382 Note that there is little point in setting this
2383 value higher than the max_tcp_slot_table_limit.
2384
2385 nfs.nfs4_disable_idmapping=
2386 [NFSv4] When set to the default of '1', this option
2387 ensures that both the RPC level authentication
2388 scheme and the NFS level operations agree to use
2389 numeric uids/gids if the mount is using the
2390 'sec=sys' security flavour. In effect it is
2391 disabling idmapping, which can make migration from
2392 legacy NFSv2/v3 systems to NFSv4 easier.
2393 Servers that do not support this mode of operation
2394 will be autodetected by the client, and it will fall
2395 back to using the idmapper.
2396 To turn off this behaviour, set the value to '0'.
2397 nfs.nfs4_unique_id=
2398 [NFS4] Specify an additional fixed unique ident-
2399 ification string that NFSv4 clients can insert into
2400 their nfs_client_id4 string. This is typically a
2401 UUID that is generated at system install time.
2402
2403 nfs.send_implementation_id =
2404 [NFSv4.1] Send client implementation identification
2405 information in exchange_id requests.
2406 If zero, no implementation identification information
2407 will be sent.
2408 The default is to send the implementation identification
2409 information.
2410
2411 nfs.recover_lost_locks =
2412 [NFSv4] Attempt to recover locks that were lost due
2413 to a lease timeout on the server. Please note that
2414 doing this risks data corruption, since there are
2415 no guarantees that the file will remain unchanged
2416 after the locks are lost.
2417 If you want to enable the kernel legacy behaviour of
2418 attempting to recover these locks, then set this
2419 parameter to '1'.
2420 The default parameter value of '0' causes the kernel
2421 not to attempt recovery of lost locks.
2422
2423 nfs4.layoutstats_timer =
2424 [NFSv4.2] Change the rate at which the kernel sends
2425 layoutstats to the pNFS metadata server.
2426
2427 Setting this to value to 0 causes the kernel to use
2428 whatever value is the default set by the layout
2429 driver. A non-zero value sets the minimum interval
2430 in seconds between layoutstats transmissions.
2431
2432 nfsd.nfs4_disable_idmapping=
2433 [NFSv4] When set to the default of '1', the NFSv4
2434 server will return only numeric uids and gids to
2435 clients using auth_sys, and will accept numeric uids
2436 and gids from such clients. This is intended to ease
2437 migration from NFSv2/v3.
2438
2439 objlayoutdriver.osd_login_prog=
2440 [NFS] [OBJLAYOUT] sets the pathname to the program which
2441 is used to automatically discover and login into new
2442 osd-targets. Please see:
2443 Documentation/filesystems/pnfs.txt for more explanations
2444
2445 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2446 when a NMI is triggered.
2447 Format: [state][,regs][,debounce][,die]
2448
2449 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2450 Format: [panic,][nopanic,][num]
2451 Valid num: 0 or 1
2452 0 - turn hardlockup detector in nmi_watchdog off
2453 1 - turn hardlockup detector in nmi_watchdog on
2454 When panic is specified, panic when an NMI watchdog
2455 timeout occurs (or 'nopanic' to override the opposite
2456 default). To disable both hard and soft lockup detectors,
2457 please see 'nowatchdog'.
2458 This is useful when you use a panic=... timeout and
2459 need the box quickly up again.
2460
2461 netpoll.carrier_timeout=
2462 [NET] Specifies amount of time (in seconds) that
2463 netpoll should wait for a carrier. By default netpoll
2464 waits 4 seconds.
2465
2466 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2467 emulation library even if a 387 maths coprocessor
2468 is present.
2469
2470 no_console_suspend
2471 [HW] Never suspend the console
2472 Disable suspending of consoles during suspend and
2473 hibernate operations. Once disabled, debugging
2474 messages can reach various consoles while the rest
2475 of the system is being put to sleep (ie, while
2476 debugging driver suspend/resume hooks). This may
2477 not work reliably with all consoles, but is known
2478 to work with serial and VGA consoles.
2479 To facilitate more flexible debugging, we also add
2480 console_suspend, a printk module parameter to control
2481 it. Users could use console_suspend (usually
2482 /sys/module/printk/parameters/console_suspend) to
2483 turn on/off it dynamically.
2484
2485 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2486 caches in the slab allocator. Saves per-node memory,
2487 but will impact performance.
2488
2489 noalign [KNL,ARM]
2490
2491 noapic [SMP,APIC] Tells the kernel to not make use of any
2492 IOAPICs that may be present in the system.
2493
2494 noautogroup Disable scheduler automatic task group creation.
2495
2496 nobats [PPC] Do not use BATs for mapping kernel lowmem
2497 on "Classic" PPC cores.
2498
2499 nocache [ARM]
2500
2501 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2502
2503 nodelayacct [KNL] Disable per-task delay accounting
2504
2505 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2506
2507 nodsp [SH] Disable hardware DSP at boot time.
2508
2509 noefi Disable EFI runtime services support.
2510
2511 noexec [IA-64]
2512
2513 noexec [X86]
2514 On X86-32 available only on PAE configured kernels.
2515 noexec=on: enable non-executable mappings (default)
2516 noexec=off: disable non-executable mappings
2517
2518 nosmap [X86]
2519 Disable SMAP (Supervisor Mode Access Prevention)
2520 even if it is supported by processor.
2521
2522 nosmep [X86]
2523 Disable SMEP (Supervisor Mode Execution Prevention)
2524 even if it is supported by processor.
2525
2526 noexec32 [X86-64]
2527 This affects only 32-bit executables.
2528 noexec32=on: enable non-executable mappings (default)
2529 read doesn't imply executable mappings
2530 noexec32=off: disable non-executable mappings
2531 read implies executable mappings
2532
2533 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2534
2535 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2536 register save and restore. The kernel will only save
2537 legacy floating-point registers on task switch.
2538
2539 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2540
2541 noxsave [BUGS=X86] Disables x86 extended register state save
2542 and restore using xsave. The kernel will fallback to
2543 enabling legacy floating-point and sse state.
2544
2545 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2546 register states. The kernel will fall back to use
2547 xsave to save the states. By using this parameter,
2548 performance of saving the states is degraded because
2549 xsave doesn't support modified optimization while
2550 xsaveopt supports it on xsaveopt enabled systems.
2551
2552 noxsaves [X86] Disables xsaves and xrstors used in saving and
2553 restoring x86 extended register state in compacted
2554 form of xsave area. The kernel will fall back to use
2555 xsaveopt and xrstor to save and restore the states
2556 in standard form of xsave area. By using this
2557 parameter, xsave area per process might occupy more
2558 memory on xsaves enabled systems.
2559
2560 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2561 wfi(ARM) instruction doesn't work correctly and not to
2562 use it. This is also useful when using JTAG debugger.
2563
2564 no_file_caps Tells the kernel not to honor file capabilities. The
2565 only way then for a file to be executed with privilege
2566 is to be setuid root or executed by root.
2567
2568 nohalt [IA-64] Tells the kernel not to use the power saving
2569 function PAL_HALT_LIGHT when idle. This increases
2570 power-consumption. On the positive side, it reduces
2571 interrupt wake-up latency, which may improve performance
2572 in certain environments such as networked servers or
2573 real-time systems.
2574
2575 nohibernate [HIBERNATION] Disable hibernation and resume.
2576
2577 nohz= [KNL] Boottime enable/disable dynamic ticks
2578 Valid arguments: on, off
2579 Default: on
2580
2581 nohz_full= [KNL,BOOT]
2582 In kernels built with CONFIG_NO_HZ_FULL=y, set
2583 the specified list of CPUs whose tick will be stopped
2584 whenever possible. The boot CPU will be forced outside
2585 the range to maintain the timekeeping.
2586 The CPUs in this range must also be included in the
2587 rcu_nocbs= set.
2588
2589 noiotrap [SH] Disables trapped I/O port accesses.
2590
2591 noirqdebug [X86-32] Disables the code which attempts to detect and
2592 disable unhandled interrupt sources.
2593
2594 no_timer_check [X86,APIC] Disables the code which tests for
2595 broken timer IRQ sources.
2596
2597 noisapnp [ISAPNP] Disables ISA PnP code.
2598
2599 noinitrd [RAM] Tells the kernel not to load any configured
2600 initial RAM disk.
2601
2602 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2603 remapping.
2604 [Deprecated - use intremap=off]
2605
2606 nointroute [IA-64]
2607
2608 noinvpcid [X86] Disable the INVPCID cpu feature.
2609
2610 nojitter [IA-64] Disables jitter checking for ITC timers.
2611
2612 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2613
2614 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2615 fault handling.
2616
2617 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2618 steal time is computed, but won't influence scheduler
2619 behaviour
2620
2621 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2622
2623 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2624
2625 noltlbs [PPC] Do not use large page/tlb entries for kernel
2626 lowmem mapping on PPC40x and PPC8xx
2627
2628 nomca [IA-64] Disable machine check abort handling
2629
2630 nomce [X86-32] Disable Machine Check Exception
2631
2632 nomfgpt [X86-32] Disable Multi-Function General Purpose
2633 Timer usage (for AMD Geode machines).
2634
2635 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2636 shutdown the other cpus. Instead use the REBOOT_VECTOR
2637 irq.
2638
2639 nomodule Disable module load
2640
2641 nopat [X86] Disable PAT (page attribute table extension of
2642 pagetables) support.
2643
2644 norandmaps Don't use address space randomization. Equivalent to
2645 echo 0 > /proc/sys/kernel/randomize_va_space
2646
2647 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2648
2649 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2650 with UP alternatives
2651
2652 nordrand [X86] Disable kernel use of the RDRAND and
2653 RDSEED instructions even if they are supported
2654 by the processor. RDRAND and RDSEED are still
2655 available to user space applications.
2656
2657 noresume [SWSUSP] Disables resume and restores original swap
2658 space.
2659
2660 no-scroll [VGA] Disables scrollback.
2661 This is required for the Braillex ib80-piezo Braille
2662 reader made by F.H. Papenmeier (Germany).
2663
2664 nosbagart [IA-64]
2665
2666 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2667
2668 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2669 and disable the IO APIC. legacy for "maxcpus=0".
2670
2671 nosoftlockup [KNL] Disable the soft-lockup detector.
2672
2673 nosync [HW,M68K] Disables sync negotiation for all devices.
2674
2675 notsc [BUGS=X86-32] Disable Time Stamp Counter
2676
2677 nowatchdog [KNL] Disable both lockup detectors, i.e.
2678 soft-lockup and NMI watchdog (hard-lockup).
2679
2680 nowb [ARM]
2681
2682 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2683
2684 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2685 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2686 Some features depend on CPU0. Known dependencies are:
2687 1. Resume from suspend/hibernate depends on CPU0.
2688 Suspend/hibernate will fail if CPU0 is offline and you
2689 need to online CPU0 before suspend/hibernate.
2690 2. PIC interrupts also depend on CPU0. CPU0 can't be
2691 removed if a PIC interrupt is detected.
2692 It's said poweroff/reboot may depend on CPU0 on some
2693 machines although I haven't seen such issues so far
2694 after CPU0 is offline on a few tested machines.
2695 If the dependencies are under your control, you can
2696 turn on cpu0_hotplug.
2697
2698 nptcg= [IA-64] Override max number of concurrent global TLB
2699 purges which is reported from either PAL_VM_SUMMARY or
2700 SAL PALO.
2701
2702 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2703 could support. nr_cpus=n : n >= 1 limits the kernel to
2704 supporting 'n' processors. Later in runtime you can not
2705 use hotplug cpu feature to put more cpu back to online.
2706 just like you compile the kernel NR_CPUS=n
2707
2708 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2709
2710 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2711 Allowed values are enable and disable
2712
2713 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2714 one of ['zone', 'node', 'default'] can be specified
2715 This can be set from sysctl after boot.
2716 See Documentation/sysctl/vm.txt for details.
2717
2718 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2719 See Documentation/debugging-via-ohci1394.txt for more
2720 info.
2721
2722 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2723 Rather than timing out after 20 ms if an EC
2724 command is not properly ACKed, override the length
2725 of the timeout. We have interrupts disabled while
2726 waiting for the ACK, so if this is set too high
2727 interrupts *may* be lost!
2728
2729 omap_mux= [OMAP] Override bootloader pin multiplexing.
2730 Format: <mux_mode0.mode_name=value>...
2731 For example, to override I2C bus2:
2732 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2733
2734 oprofile.timer= [HW]
2735 Use timer interrupt instead of performance counters
2736
2737 oprofile.cpu_type= Force an oprofile cpu type
2738 This might be useful if you have an older oprofile
2739 userland or if you want common events.
2740 Format: { arch_perfmon }
2741 arch_perfmon: [X86] Force use of architectural
2742 perfmon on Intel CPUs instead of the
2743 CPU specific event set.
2744 timer: [X86] Force use of architectural NMI
2745 timer mode (see also oprofile.timer
2746 for generic hr timer mode)
2747 [s390] Force legacy basic mode sampling
2748 (report cpu_type "timer")
2749
2750 oops=panic Always panic on oopses. Default is to just kill the
2751 process, but there is a small probability of
2752 deadlocking the machine.
2753 This will also cause panics on machine check exceptions.
2754 Useful together with panic=30 to trigger a reboot.
2755
2756 OSS [HW,OSS]
2757 See Documentation/sound/oss/oss-parameters.txt
2758
2759 page_owner= [KNL] Boot-time page_owner enabling option.
2760 Storage of the information about who allocated
2761 each page is disabled in default. With this switch,
2762 we can turn it on.
2763 on: enable the feature
2764
2765 page_poison= [KNL] Boot-time parameter changing the state of
2766 poisoning on the buddy allocator.
2767 off: turn off poisoning
2768 on: turn on poisoning
2769
2770 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2771 timeout > 0: seconds before rebooting
2772 timeout = 0: wait forever
2773 timeout < 0: reboot immediately
2774 Format: <timeout>
2775
2776 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2777 on a WARN().
2778
2779 crash_kexec_post_notifiers
2780 Run kdump after running panic-notifiers and dumping
2781 kmsg. This only for the users who doubt kdump always
2782 succeeds in any situation.
2783 Note that this also increases risks of kdump failure,
2784 because some panic notifiers can make the crashed
2785 kernel more unstable.
2786
2787 parkbd.port= [HW] Parallel port number the keyboard adapter is
2788 connected to, default is 0.
2789 Format: <parport#>
2790 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2791 0 for XT, 1 for AT (default is AT).
2792 Format: <mode>
2793
2794 parport= [HW,PPT] Specify parallel ports. 0 disables.
2795 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2796 Use 'auto' to force the driver to use any
2797 IRQ/DMA settings detected (the default is to
2798 ignore detected IRQ/DMA settings because of
2799 possible conflicts). You can specify the base
2800 address, IRQ, and DMA settings; IRQ and DMA
2801 should be numbers, or 'auto' (for using detected
2802 settings on that particular port), or 'nofifo'
2803 (to avoid using a FIFO even if it is detected).
2804 Parallel ports are assigned in the order they
2805 are specified on the command line, starting
2806 with parport0.
2807
2808 parport_init_mode= [HW,PPT]
2809 Configure VIA parallel port to operate in
2810 a specific mode. This is necessary on Pegasos
2811 computer where firmware has no options for setting
2812 up parallel port mode and sets it to spp.
2813 Currently this function knows 686a and 8231 chips.
2814 Format: [spp|ps2|epp|ecp|ecpepp]
2815
2816 pause_on_oops=
2817 Halt all CPUs after the first oops has been printed for
2818 the specified number of seconds. This is to be used if
2819 your oopses keep scrolling off the screen.
2820
2821 pcbit= [HW,ISDN]
2822
2823 pcd. [PARIDE]
2824 See header of drivers/block/paride/pcd.c.
2825 See also Documentation/blockdev/paride.txt.
2826
2827 pci=option[,option...] [PCI] various PCI subsystem options:
2828 earlydump [X86] dump PCI config space before the kernel
2829 changes anything
2830 off [X86] don't probe for the PCI bus
2831 bios [X86-32] force use of PCI BIOS, don't access
2832 the hardware directly. Use this if your machine
2833 has a non-standard PCI host bridge.
2834 nobios [X86-32] disallow use of PCI BIOS, only direct
2835 hardware access methods are allowed. Use this
2836 if you experience crashes upon bootup and you
2837 suspect they are caused by the BIOS.
2838 conf1 [X86] Force use of PCI Configuration Access
2839 Mechanism 1 (config address in IO port 0xCF8,
2840 data in IO port 0xCFC, both 32-bit).
2841 conf2 [X86] Force use of PCI Configuration Access
2842 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2843 the function, IO port 0xCFA, also 8-bit, sets
2844 bus number. The config space is then accessed
2845 through ports 0xC000-0xCFFF).
2846 See http://wiki.osdev.org/PCI for more info
2847 on the configuration access mechanisms.
2848 noaer [PCIE] If the PCIEAER kernel config parameter is
2849 enabled, this kernel boot option can be used to
2850 disable the use of PCIE advanced error reporting.
2851 nodomains [PCI] Disable support for multiple PCI
2852 root domains (aka PCI segments, in ACPI-speak).
2853 nommconf [X86] Disable use of MMCONFIG for PCI
2854 Configuration
2855 check_enable_amd_mmconf [X86] check for and enable
2856 properly configured MMIO access to PCI
2857 config space on AMD family 10h CPU
2858 nomsi [MSI] If the PCI_MSI kernel config parameter is
2859 enabled, this kernel boot option can be used to
2860 disable the use of MSI interrupts system-wide.
2861 noioapicquirk [APIC] Disable all boot interrupt quirks.
2862 Safety option to keep boot IRQs enabled. This
2863 should never be necessary.
2864 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2865 primary IO-APIC for bridges that cannot disable
2866 boot IRQs. This fixes a source of spurious IRQs
2867 when the system masks IRQs.
2868 noioapicreroute [APIC] Disable workaround that uses the
2869 boot IRQ equivalent of an IRQ that connects to
2870 a chipset where boot IRQs cannot be disabled.
2871 The opposite of ioapicreroute.
2872 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2873 routing table. These calls are known to be buggy
2874 on several machines and they hang the machine
2875 when used, but on other computers it's the only
2876 way to get the interrupt routing table. Try
2877 this option if the kernel is unable to allocate
2878 IRQs or discover secondary PCI buses on your
2879 motherboard.
2880 rom [X86] Assign address space to expansion ROMs.
2881 Use with caution as certain devices share
2882 address decoders between ROMs and other
2883 resources.
2884 norom [X86] Do not assign address space to
2885 expansion ROMs that do not already have
2886 BIOS assigned address ranges.
2887 nobar [X86] Do not assign address space to the
2888 BARs that weren't assigned by the BIOS.
2889 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2890 assigned automatically to PCI devices. You can
2891 make the kernel exclude IRQs of your ISA cards
2892 this way.
2893 pirqaddr=0xAAAAA [X86] Specify the physical address
2894 of the PIRQ table (normally generated
2895 by the BIOS) if it is outside the
2896 F0000h-100000h range.
2897 lastbus=N [X86] Scan all buses thru bus #N. Can be
2898 useful if the kernel is unable to find your
2899 secondary buses and you want to tell it
2900 explicitly which ones they are.
2901 assign-busses [X86] Always assign all PCI bus
2902 numbers ourselves, overriding
2903 whatever the firmware may have done.
2904 usepirqmask [X86] Honor the possible IRQ mask stored
2905 in the BIOS $PIR table. This is needed on
2906 some systems with broken BIOSes, notably
2907 some HP Pavilion N5400 and Omnibook XE3
2908 notebooks. This will have no effect if ACPI
2909 IRQ routing is enabled.
2910 noacpi [X86] Do not use ACPI for IRQ routing
2911 or for PCI scanning.
2912 use_crs [X86] Use PCI host bridge window information
2913 from ACPI. On BIOSes from 2008 or later, this
2914 is enabled by default. If you need to use this,
2915 please report a bug.
2916 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2917 If you need to use this, please report a bug.
2918 routeirq Do IRQ routing for all PCI devices.
2919 This is normally done in pci_enable_device(),
2920 so this option is a temporary workaround
2921 for broken drivers that don't call it.
2922 skip_isa_align [X86] do not align io start addr, so can
2923 handle more pci cards
2924 firmware [ARM] Do not re-enumerate the bus but instead
2925 just use the configuration from the
2926 bootloader. This is currently used on
2927 IXP2000 systems where the bus has to be
2928 configured a certain way for adjunct CPUs.
2929 noearly [X86] Don't do any early type 1 scanning.
2930 This might help on some broken boards which
2931 machine check when some devices' config space
2932 is read. But various workarounds are disabled
2933 and some IOMMU drivers will not work.
2934 bfsort Sort PCI devices into breadth-first order.
2935 This sorting is done to get a device
2936 order compatible with older (<= 2.4) kernels.
2937 nobfsort Don't sort PCI devices into breadth-first order.
2938 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2939 tuning and use the BIOS-configured MPS defaults.
2940 pcie_bus_safe Set every device's MPS to the largest value
2941 supported by all devices below the root complex.
2942 pcie_bus_perf Set device MPS to the largest allowable MPS
2943 based on its parent bus. Also set MRRS (Max
2944 Read Request Size) to the largest supported
2945 value (no larger than the MPS that the device
2946 or bus can support) for best performance.
2947 pcie_bus_peer2peer Set every device's MPS to 128B, which
2948 every device is guaranteed to support. This
2949 configuration allows peer-to-peer DMA between
2950 any pair of devices, possibly at the cost of
2951 reduced performance. This also guarantees
2952 that hot-added devices will work.
2953 cbiosize=nn[KMG] The fixed amount of bus space which is
2954 reserved for the CardBus bridge's IO window.
2955 The default value is 256 bytes.
2956 cbmemsize=nn[KMG] The fixed amount of bus space which is
2957 reserved for the CardBus bridge's memory
2958 window. The default value is 64 megabytes.
2959 resource_alignment=
2960 Format:
2961 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2962 Specifies alignment and device to reassign
2963 aligned memory resources.
2964 If <order of align> is not specified,
2965 PAGE_SIZE is used as alignment.
2966 PCI-PCI bridge can be specified, if resource
2967 windows need to be expanded.
2968 ecrc= Enable/disable PCIe ECRC (transaction layer
2969 end-to-end CRC checking).
2970 bios: Use BIOS/firmware settings. This is the
2971 the default.
2972 off: Turn ECRC off
2973 on: Turn ECRC on.
2974 hpiosize=nn[KMG] The fixed amount of bus space which is
2975 reserved for hotplug bridge's IO window.
2976 Default size is 256 bytes.
2977 hpmemsize=nn[KMG] The fixed amount of bus space which is
2978 reserved for hotplug bridge's memory window.
2979 Default size is 2 megabytes.
2980 realloc= Enable/disable reallocating PCI bridge resources
2981 if allocations done by BIOS are too small to
2982 accommodate resources required by all child
2983 devices.
2984 off: Turn realloc off
2985 on: Turn realloc on
2986 realloc same as realloc=on
2987 noari do not use PCIe ARI.
2988 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2989 only look for one device below a PCIe downstream
2990 port.
2991
2992 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2993 Management.
2994 off Disable ASPM.
2995 force Enable ASPM even on devices that claim not to support it.
2996 WARNING: Forcing ASPM on may cause system lockups.
2997
2998 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2999 nomsi Do not use MSI for PCI Express Native Hotplug (this
3000 makes all PCIe ports use INTx for hotplug services).
3001
3002 pcie_ports= [PCIE] PCIe ports handling:
3003 auto Ask the BIOS whether or not to use native PCIe services
3004 associated with PCIe ports (PME, hot-plug, AER). Use
3005 them only if that is allowed by the BIOS.
3006 native Use native PCIe services associated with PCIe ports
3007 unconditionally.
3008 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3009 ports driver.
3010
3011 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3012 nomsi Do not use MSI for native PCIe PME signaling (this makes
3013 all PCIe root ports use INTx for all services).
3014
3015 pcmv= [HW,PCMCIA] BadgePAD 4
3016
3017 pd_ignore_unused
3018 [PM]
3019 Keep all power-domains already enabled by bootloader on,
3020 even if no driver has claimed them. This is useful
3021 for debug and development, but should not be
3022 needed on a platform with proper driver support.
3023
3024 pd. [PARIDE]
3025 See Documentation/blockdev/paride.txt.
3026
3027 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3028 boot time.
3029 Format: { 0 | 1 }
3030 See arch/parisc/kernel/pdc_chassis.c
3031
3032 percpu_alloc= Select which percpu first chunk allocator to use.
3033 Currently supported values are "embed" and "page".
3034 Archs may support subset or none of the selections.
3035 See comments in mm/percpu.c for details on each
3036 allocator. This parameter is primarily for debugging
3037 and performance comparison.
3038
3039 pf. [PARIDE]
3040 See Documentation/blockdev/paride.txt.
3041
3042 pg. [PARIDE]
3043 See Documentation/blockdev/paride.txt.
3044
3045 pirq= [SMP,APIC] Manual mp-table setup
3046 See Documentation/x86/i386/IO-APIC.txt.
3047
3048 plip= [PPT,NET] Parallel port network link
3049 Format: { parport<nr> | timid | 0 }
3050 See also Documentation/parport.txt.
3051
3052 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3053 Override pmtimer IOPort with a hex value.
3054 e.g. pmtmr=0x508
3055
3056 pnp.debug=1 [PNP]
3057 Enable PNP debug messages (depends on the
3058 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3059 via /sys/module/pnp/parameters/debug. We always show
3060 current resource usage; turning this on also shows
3061 possible settings and some assignment information.
3062
3063 pnpacpi= [ACPI]
3064 { off }
3065
3066 pnpbios= [ISAPNP]
3067 { on | off | curr | res | no-curr | no-res }
3068
3069 pnp_reserve_irq=
3070 [ISAPNP] Exclude IRQs for the autoconfiguration
3071
3072 pnp_reserve_dma=
3073 [ISAPNP] Exclude DMAs for the autoconfiguration
3074
3075 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3076 Ranges are in pairs (I/O port base and size).
3077
3078 pnp_reserve_mem=
3079 [ISAPNP] Exclude memory regions for the
3080 autoconfiguration.
3081 Ranges are in pairs (memory base and size).
3082
3083 ports= [IP_VS_FTP] IPVS ftp helper module
3084 Default is 21.
3085 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3086 may be specified.
3087 Format: <port>,<port>....
3088
3089 ppc_strict_facility_enable
3090 [PPC] This option catches any kernel floating point,
3091 Altivec, VSX and SPE outside of regions specifically
3092 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3093 There is some performance impact when enabling this.
3094
3095 print-fatal-signals=
3096 [KNL] debug: print fatal signals
3097
3098 If enabled, warn about various signal handling
3099 related application anomalies: too many signals,
3100 too many POSIX.1 timers, fatal signals causing a
3101 coredump - etc.
3102
3103 If you hit the warning due to signal overflow,
3104 you might want to try "ulimit -i unlimited".
3105
3106 default: off.
3107
3108 printk.always_kmsg_dump=
3109 Trigger kmsg_dump for cases other than kernel oops or
3110 panics
3111 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3112 default: disabled
3113
3114 printk.time= Show timing data prefixed to each printk message line
3115 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3116
3117 processor.max_cstate= [HW,ACPI]
3118 Limit processor to maximum C-state
3119 max_cstate=9 overrides any DMI blacklist limit.
3120
3121 processor.nocst [HW,ACPI]
3122 Ignore the _CST method to determine C-states,
3123 instead using the legacy FADT method
3124
3125 profile= [KNL] Enable kernel profiling via /proc/profile
3126 Format: [schedule,]<number>
3127 Param: "schedule" - profile schedule points.
3128 Param: <number> - step/bucket size as a power of 2 for
3129 statistical time based profiling.
3130 Param: "sleep" - profile D-state sleeping (millisecs).
3131 Requires CONFIG_SCHEDSTATS
3132 Param: "kvm" - profile VM exits.
3133
3134 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3135 before loading.
3136 See Documentation/blockdev/ramdisk.txt.
3137
3138 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3139 probe for; one of (bare|imps|exps|lifebook|any).
3140 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3141 per second.
3142 psmouse.resetafter= [HW,MOUSE]
3143 Try to reset the device after so many bad packets
3144 (0 = never).
3145 psmouse.resolution=
3146 [HW,MOUSE] Set desired mouse resolution, in dpi.
3147 psmouse.smartscroll=
3148 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3149 0 = disabled, 1 = enabled (default).
3150
3151 pstore.backend= Specify the name of the pstore backend to use
3152
3153 pt. [PARIDE]
3154 See Documentation/blockdev/paride.txt.
3155
3156 pty.legacy_count=
3157 [KNL] Number of legacy pty's. Overwrites compiled-in
3158 default number.
3159
3160 quiet [KNL] Disable most log messages
3161
3162 r128= [HW,DRM]
3163
3164 raid= [HW,RAID]
3165 See Documentation/md.txt.
3166
3167 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3168 See Documentation/blockdev/ramdisk.txt.
3169
3170 rcu_nocbs= [KNL]
3171 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3172 the specified list of CPUs to be no-callback CPUs.
3173 Invocation of these CPUs' RCU callbacks will
3174 be offloaded to "rcuox/N" kthreads created for
3175 that purpose, where "x" is "b" for RCU-bh, "p"
3176 for RCU-preempt, and "s" for RCU-sched, and "N"
3177 is the CPU number. This reduces OS jitter on the
3178 offloaded CPUs, which can be useful for HPC and
3179 real-time workloads. It can also improve energy
3180 efficiency for asymmetric multiprocessors.
3181
3182 rcu_nocb_poll [KNL]
3183 Rather than requiring that offloaded CPUs
3184 (specified by rcu_nocbs= above) explicitly
3185 awaken the corresponding "rcuoN" kthreads,
3186 make these kthreads poll for callbacks.
3187 This improves the real-time response for the
3188 offloaded CPUs by relieving them of the need to
3189 wake up the corresponding kthread, but degrades
3190 energy efficiency by requiring that the kthreads
3191 periodically wake up to do the polling.
3192
3193 rcutree.blimit= [KNL]
3194 Set maximum number of finished RCU callbacks to
3195 process in one batch.
3196
3197 rcutree.dump_tree= [KNL]
3198 Dump the structure of the rcu_node combining tree
3199 out at early boot. This is used for diagnostic
3200 purposes, to verify correct tree setup.
3201
3202 rcutree.gp_cleanup_delay= [KNL]
3203 Set the number of jiffies to delay each step of
3204 RCU grace-period cleanup. This only has effect
3205 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3206
3207 rcutree.gp_init_delay= [KNL]
3208 Set the number of jiffies to delay each step of
3209 RCU grace-period initialization. This only has
3210 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3211 is set.
3212
3213 rcutree.gp_preinit_delay= [KNL]
3214 Set the number of jiffies to delay each step of
3215 RCU grace-period pre-initialization, that is,
3216 the propagation of recent CPU-hotplug changes up
3217 the rcu_node combining tree. This only has effect
3218 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3219
3220 rcutree.rcu_fanout_exact= [KNL]
3221 Disable autobalancing of the rcu_node combining
3222 tree. This is used by rcutorture, and might
3223 possibly be useful for architectures having high
3224 cache-to-cache transfer latencies.
3225
3226 rcutree.rcu_fanout_leaf= [KNL]
3227 Change the number of CPUs assigned to each
3228 leaf rcu_node structure. Useful for very
3229 large systems, which will choose the value 64,
3230 and for NUMA systems with large remote-access
3231 latencies, which will choose a value aligned
3232 with the appropriate hardware boundaries.
3233
3234 rcutree.jiffies_till_sched_qs= [KNL]
3235 Set required age in jiffies for a
3236 given grace period before RCU starts
3237 soliciting quiescent-state help from
3238 rcu_note_context_switch().
3239
3240 rcutree.jiffies_till_first_fqs= [KNL]
3241 Set delay from grace-period initialization to
3242 first attempt to force quiescent states.
3243 Units are jiffies, minimum value is zero,
3244 and maximum value is HZ.
3245
3246 rcutree.jiffies_till_next_fqs= [KNL]
3247 Set delay between subsequent attempts to force
3248 quiescent states. Units are jiffies, minimum
3249 value is one, and maximum value is HZ.
3250
3251 rcutree.kthread_prio= [KNL,BOOT]
3252 Set the SCHED_FIFO priority of the RCU per-CPU
3253 kthreads (rcuc/N). This value is also used for
3254 the priority of the RCU boost threads (rcub/N)
3255 and for the RCU grace-period kthreads (rcu_bh,
3256 rcu_preempt, and rcu_sched). If RCU_BOOST is
3257 set, valid values are 1-99 and the default is 1
3258 (the least-favored priority). Otherwise, when
3259 RCU_BOOST is not set, valid values are 0-99 and
3260 the default is zero (non-realtime operation).
3261
3262 rcutree.rcu_nocb_leader_stride= [KNL]
3263 Set the number of NOCB kthread groups, which
3264 defaults to the square root of the number of
3265 CPUs. Larger numbers reduces the wakeup overhead
3266 on the per-CPU grace-period kthreads, but increases
3267 that same overhead on each group's leader.
3268
3269 rcutree.qhimark= [KNL]
3270 Set threshold of queued RCU callbacks beyond which
3271 batch limiting is disabled.
3272
3273 rcutree.qlowmark= [KNL]
3274 Set threshold of queued RCU callbacks below which
3275 batch limiting is re-enabled.
3276
3277 rcutree.rcu_idle_gp_delay= [KNL]
3278 Set wakeup interval for idle CPUs that have
3279 RCU callbacks (RCU_FAST_NO_HZ=y).
3280
3281 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3282 Set wakeup interval for idle CPUs that have
3283 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3284 Lazy RCU callbacks are those which RCU can
3285 prove do nothing more than free memory.
3286
3287 rcutorture.cbflood_inter_holdoff= [KNL]
3288 Set holdoff time (jiffies) between successive
3289 callback-flood tests.
3290
3291 rcutorture.cbflood_intra_holdoff= [KNL]
3292 Set holdoff time (jiffies) between successive
3293 bursts of callbacks within a given callback-flood
3294 test.
3295
3296 rcutorture.cbflood_n_burst= [KNL]
3297 Set the number of bursts making up a given
3298 callback-flood test. Set this to zero to
3299 disable callback-flood testing.
3300
3301 rcutorture.cbflood_n_per_burst= [KNL]
3302 Set the number of callbacks to be registered
3303 in a given burst of a callback-flood test.
3304
3305 rcutorture.fqs_duration= [KNL]
3306 Set duration of force_quiescent_state bursts
3307 in microseconds.
3308
3309 rcutorture.fqs_holdoff= [KNL]
3310 Set holdoff time within force_quiescent_state bursts
3311 in microseconds.
3312
3313 rcutorture.fqs_stutter= [KNL]
3314 Set wait time between force_quiescent_state bursts
3315 in seconds.
3316
3317 rcutorture.gp_cond= [KNL]
3318 Use conditional/asynchronous update-side
3319 primitives, if available.
3320
3321 rcutorture.gp_exp= [KNL]
3322 Use expedited update-side primitives, if available.
3323
3324 rcutorture.gp_normal= [KNL]
3325 Use normal (non-expedited) asynchronous
3326 update-side primitives, if available.
3327
3328 rcutorture.gp_sync= [KNL]
3329 Use normal (non-expedited) synchronous
3330 update-side primitives, if available. If all
3331 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3332 rcutorture.gp_normal=, and rcutorture.gp_sync=
3333 are zero, rcutorture acts as if is interpreted
3334 they are all non-zero.
3335
3336 rcutorture.n_barrier_cbs= [KNL]
3337 Set callbacks/threads for rcu_barrier() testing.
3338
3339 rcutorture.nfakewriters= [KNL]
3340 Set number of concurrent RCU writers. These just
3341 stress RCU, they don't participate in the actual
3342 test, hence the "fake".
3343
3344 rcutorture.nreaders= [KNL]
3345 Set number of RCU readers. The value -1 selects
3346 N-1, where N is the number of CPUs. A value
3347 "n" less than -1 selects N-n-2, where N is again
3348 the number of CPUs. For example, -2 selects N
3349 (the number of CPUs), -3 selects N+1, and so on.
3350
3351 rcutorture.object_debug= [KNL]
3352 Enable debug-object double-call_rcu() testing.
3353
3354 rcutorture.onoff_holdoff= [KNL]
3355 Set time (s) after boot for CPU-hotplug testing.
3356
3357 rcutorture.onoff_interval= [KNL]
3358 Set time (s) between CPU-hotplug operations, or
3359 zero to disable CPU-hotplug testing.
3360
3361 rcutorture.shuffle_interval= [KNL]
3362 Set task-shuffle interval (s). Shuffling tasks
3363 allows some CPUs to go into dyntick-idle mode
3364 during the rcutorture test.
3365
3366 rcutorture.shutdown_secs= [KNL]
3367 Set time (s) after boot system shutdown. This
3368 is useful for hands-off automated testing.
3369
3370 rcutorture.stall_cpu= [KNL]
3371 Duration of CPU stall (s) to test RCU CPU stall
3372 warnings, zero to disable.
3373
3374 rcutorture.stall_cpu_holdoff= [KNL]
3375 Time to wait (s) after boot before inducing stall.
3376
3377 rcutorture.stat_interval= [KNL]
3378 Time (s) between statistics printk()s.
3379
3380 rcutorture.stutter= [KNL]
3381 Time (s) to stutter testing, for example, specifying
3382 five seconds causes the test to run for five seconds,
3383 wait for five seconds, and so on. This tests RCU's
3384 ability to transition abruptly to and from idle.
3385
3386 rcutorture.test_boost= [KNL]
3387 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3388 "Maybe" means test if the RCU implementation
3389 under test support RCU priority boosting.
3390
3391 rcutorture.test_boost_duration= [KNL]
3392 Duration (s) of each individual boost test.
3393
3394 rcutorture.test_boost_interval= [KNL]
3395 Interval (s) between each boost test.
3396
3397 rcutorture.test_no_idle_hz= [KNL]
3398 Test RCU's dyntick-idle handling. See also the
3399 rcutorture.shuffle_interval parameter.
3400
3401 rcutorture.torture_runnable= [BOOT]
3402 Start rcutorture running at boot time.
3403
3404 rcutorture.torture_type= [KNL]
3405 Specify the RCU implementation to test.
3406
3407 rcutorture.verbose= [KNL]
3408 Enable additional printk() statements.
3409
3410 rcupdate.rcu_cpu_stall_suppress= [KNL]
3411 Suppress RCU CPU stall warning messages.
3412
3413 rcupdate.rcu_cpu_stall_timeout= [KNL]
3414 Set timeout for RCU CPU stall warning messages.
3415
3416 rcupdate.rcu_expedited= [KNL]
3417 Use expedited grace-period primitives, for
3418 example, synchronize_rcu_expedited() instead
3419 of synchronize_rcu(). This reduces latency,
3420 but can increase CPU utilization, degrade
3421 real-time latency, and degrade energy efficiency.
3422 No effect on CONFIG_TINY_RCU kernels.
3423
3424 rcupdate.rcu_normal= [KNL]
3425 Use only normal grace-period primitives,
3426 for example, synchronize_rcu() instead of
3427 synchronize_rcu_expedited(). This improves
3428 real-time latency, CPU utilization, and
3429 energy efficiency, but can expose users to
3430 increased grace-period latency. This parameter
3431 overrides rcupdate.rcu_expedited. No effect on
3432 CONFIG_TINY_RCU kernels.
3433
3434 rcupdate.rcu_normal_after_boot= [KNL]
3435 Once boot has completed (that is, after
3436 rcu_end_inkernel_boot() has been invoked), use
3437 only normal grace-period primitives. No effect
3438 on CONFIG_TINY_RCU kernels.
3439
3440 rcupdate.rcu_task_stall_timeout= [KNL]
3441 Set timeout in jiffies for RCU task stall warning
3442 messages. Disable with a value less than or equal
3443 to zero.
3444
3445 rcupdate.rcu_self_test= [KNL]
3446 Run the RCU early boot self tests
3447
3448 rcupdate.rcu_self_test_bh= [KNL]
3449 Run the RCU bh early boot self tests
3450
3451 rcupdate.rcu_self_test_sched= [KNL]
3452 Run the RCU sched early boot self tests
3453
3454 rdinit= [KNL]
3455 Format: <full_path>
3456 Run specified binary instead of /init from the ramdisk,
3457 used for early userspace startup. See initrd.
3458
3459 reboot= [KNL]
3460 Format (x86 or x86_64):
3461 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3462 [[,]s[mp]#### \
3463 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3464 [[,]f[orce]
3465 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3466 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3467 reboot_force is either force or not specified,
3468 reboot_cpu is s[mp]#### with #### being the processor
3469 to be used for rebooting.
3470
3471 relax_domain_level=
3472 [KNL, SMP] Set scheduler's default relax_domain_level.
3473 See Documentation/cgroups/cpusets.txt.
3474
3475 relative_sleep_states=
3476 [SUSPEND] Use sleep state labeling where the deepest
3477 state available other than hibernation is always "mem".
3478 Format: { "0" | "1" }
3479 0 -- Traditional sleep state labels.
3480 1 -- Relative sleep state labels.
3481
3482 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3483
3484 reservetop= [X86-32]
3485 Format: nn[KMG]
3486 Reserves a hole at the top of the kernel virtual
3487 address space.
3488
3489 reservelow= [X86]
3490 Format: nn[K]
3491 Set the amount of memory to reserve for BIOS at
3492 the bottom of the address space.
3493
3494 reset_devices [KNL] Force drivers to reset the underlying device
3495 during initialization.
3496
3497 resume= [SWSUSP]
3498 Specify the partition device for software suspend
3499 Format:
3500 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3501
3502 resume_offset= [SWSUSP]
3503 Specify the offset from the beginning of the partition
3504 given by "resume=" at which the swap header is located,
3505 in <PAGE_SIZE> units (needed only for swap files).
3506 See Documentation/power/swsusp-and-swap-files.txt
3507
3508 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3509 read the resume files
3510
3511 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3512 Useful for devices that are detected asynchronously
3513 (e.g. USB and MMC devices).
3514
3515 hibernate= [HIBERNATION]
3516 noresume Don't check if there's a hibernation image
3517 present during boot.
3518 nocompress Don't compress/decompress hibernation images.
3519 no Disable hibernation and resume.
3520
3521 retain_initrd [RAM] Keep initrd memory after extraction
3522
3523 rfkill.default_state=
3524 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3525 etc. communication is blocked by default.
3526 1 Unblocked.
3527
3528 rfkill.master_switch_mode=
3529 0 The "airplane mode" button does nothing.
3530 1 The "airplane mode" button toggles between everything
3531 blocked and the previous configuration.
3532 2 The "airplane mode" button toggles between everything
3533 blocked and everything unblocked.
3534
3535 rhash_entries= [KNL,NET]
3536 Set number of hash buckets for route cache
3537
3538 ro [KNL] Mount root device read-only on boot
3539
3540 rodata= [KNL]
3541 on Mark read-only kernel memory as read-only (default).
3542 off Leave read-only kernel memory writable for debugging.
3543
3544 rockchip.usb_uart
3545 Enable the uart passthrough on the designated usb port
3546 on Rockchip SoCs. When active, the signals of the
3547 debug-uart get routed to the D+ and D- pins of the usb
3548 port and the regular usb controller gets disabled.
3549
3550 root= [KNL] Root filesystem
3551 See name_to_dev_t comment in init/do_mounts.c.
3552
3553 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3554 mount the root filesystem
3555
3556 rootflags= [KNL] Set root filesystem mount option string
3557
3558 rootfstype= [KNL] Set root filesystem type
3559
3560 rootwait [KNL] Wait (indefinitely) for root device to show up.
3561 Useful for devices that are detected asynchronously
3562 (e.g. USB and MMC devices).
3563
3564 rproc_mem=nn[KMG][@address]
3565 [KNL,ARM,CMA] Remoteproc physical memory block.
3566 Memory area to be used by remote processor image,
3567 managed by CMA.
3568
3569 rw [KNL] Mount root device read-write on boot
3570
3571 S [KNL] Run init in single mode
3572
3573 s390_iommu= [HW,S390]
3574 Set s390 IOTLB flushing mode
3575 strict
3576 With strict flushing every unmap operation will result in
3577 an IOTLB flush. Default is lazy flushing before reuse,
3578 which is faster.
3579
3580 sa1100ir [NET]
3581 See drivers/net/irda/sa1100_ir.c.
3582
3583 sbni= [NET] Granch SBNI12 leased line adapter
3584
3585 sched_debug [KNL] Enables verbose scheduler debug messages.
3586
3587 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3588 Allowed values are enable and disable. This feature
3589 incurs a small amount of overhead in the scheduler
3590 but is useful for debugging and performance tuning.
3591
3592 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3593 xtime_lock contention on larger systems, and/or RCU lock
3594 contention on all systems with CONFIG_MAXSMP set.
3595 Format: { "0" | "1" }
3596 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3597 1 -- enable.
3598 Note: increases power consumption, thus should only be
3599 enabled if running jitter sensitive (HPC/RT) workloads.
3600
3601 security= [SECURITY] Choose a security module to enable at boot.
3602 If this boot parameter is not specified, only the first
3603 security module asking for security registration will be
3604 loaded. An invalid security module name will be treated
3605 as if no module has been chosen.
3606
3607 selinux= [SELINUX] Disable or enable SELinux at boot time.
3608 Format: { "0" | "1" }
3609 See security/selinux/Kconfig help text.
3610 0 -- disable.
3611 1 -- enable.
3612 Default value is set via kernel config option.
3613 If enabled at boot time, /selinux/disable can be used
3614 later to disable prior to initial policy load.
3615
3616 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3617 Format: { "0" | "1" }
3618 See security/apparmor/Kconfig help text
3619 0 -- disable.
3620 1 -- enable.
3621 Default value is set via kernel config option.
3622
3623 serialnumber [BUGS=X86-32]
3624
3625 shapers= [NET]
3626 Maximal number of shapers.
3627
3628 show_msr= [x86] show boot-time MSR settings
3629 Format: { <integer> }
3630 Show boot-time (BIOS-initialized) MSR settings.
3631 The parameter means the number of CPUs to show,
3632 for example 1 means boot CPU only.
3633
3634 simeth= [IA-64]
3635 simscsi=
3636
3637 slram= [HW,MTD]
3638
3639 slab_nomerge [MM]
3640 Disable merging of slabs with similar size. May be
3641 necessary if there is some reason to distinguish
3642 allocs to different slabs. Debug options disable
3643 merging on their own.
3644 For more information see Documentation/vm/slub.txt.
3645
3646 slab_max_order= [MM, SLAB]
3647 Determines the maximum allowed order for slabs.
3648 A high setting may cause OOMs due to memory
3649 fragmentation. Defaults to 1 for systems with
3650 more than 32MB of RAM, 0 otherwise.
3651
3652 slub_debug[=options[,slabs]] [MM, SLUB]
3653 Enabling slub_debug allows one to determine the
3654 culprit if slab objects become corrupted. Enabling
3655 slub_debug can create guard zones around objects and
3656 may poison objects when not in use. Also tracks the
3657 last alloc / free. For more information see
3658 Documentation/vm/slub.txt.
3659
3660 slub_max_order= [MM, SLUB]
3661 Determines the maximum allowed order for slabs.
3662 A high setting may cause OOMs due to memory
3663 fragmentation. For more information see
3664 Documentation/vm/slub.txt.
3665
3666 slub_min_objects= [MM, SLUB]
3667 The minimum number of objects per slab. SLUB will
3668 increase the slab order up to slub_max_order to
3669 generate a sufficiently large slab able to contain
3670 the number of objects indicated. The higher the number
3671 of objects the smaller the overhead of tracking slabs
3672 and the less frequently locks need to be acquired.
3673 For more information see Documentation/vm/slub.txt.
3674
3675 slub_min_order= [MM, SLUB]
3676 Determines the minimum page order for slabs. Must be
3677 lower than slub_max_order.
3678 For more information see Documentation/vm/slub.txt.
3679
3680 slub_nomerge [MM, SLUB]
3681 Same with slab_nomerge. This is supported for legacy.
3682 See slab_nomerge for more information.
3683
3684 smart2= [HW]
3685 Format: <io1>[,<io2>[,...,<io8>]]
3686
3687 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3688 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3689 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3690 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3691 smsc-ircc2.ircc_irq= [HW] IRQ line
3692 smsc-ircc2.ircc_dma= [HW] DMA channel
3693 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3694 0: Toshiba Satellite 1800 (GP data pin select)
3695 1: Fast pin select (default)
3696 2: ATC IRMode
3697
3698 softlockup_panic=
3699 [KNL] Should the soft-lockup detector generate panics.
3700 Format: <integer>
3701
3702 softlockup_all_cpu_backtrace=
3703 [KNL] Should the soft-lockup detector generate
3704 backtraces on all cpus.
3705 Format: <integer>
3706
3707 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3708 See Documentation/laptops/sonypi.txt
3709
3710 spia_io_base= [HW,MTD]
3711 spia_fio_base=
3712 spia_pedr=
3713 spia_peddr=
3714
3715 stacktrace [FTRACE]
3716 Enabled the stack tracer on boot up.
3717
3718 stacktrace_filter=[function-list]
3719 [FTRACE] Limit the functions that the stack tracer
3720 will trace at boot up. function-list is a comma separated
3721 list of functions. This list can be changed at run
3722 time by the stack_trace_filter file in the debugfs
3723 tracing directory. Note, this enables stack tracing
3724 and the stacktrace above is not needed.
3725
3726 sti= [PARISC,HW]
3727 Format: <num>
3728 Set the STI (builtin display/keyboard on the HP-PARISC
3729 machines) console (graphic card) which should be used
3730 as the initial boot-console.
3731 See also comment in drivers/video/console/sticore.c.
3732
3733 sti_font= [HW]
3734 See comment in drivers/video/console/sticore.c.
3735
3736 stifb= [HW]
3737 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3738
3739 sunrpc.min_resvport=
3740 sunrpc.max_resvport=
3741 [NFS,SUNRPC]
3742 SunRPC servers often require that client requests
3743 originate from a privileged port (i.e. a port in the
3744 range 0 < portnr < 1024).
3745 An administrator who wishes to reserve some of these
3746 ports for other uses may adjust the range that the
3747 kernel's sunrpc client considers to be privileged
3748 using these two parameters to set the minimum and
3749 maximum port values.
3750
3751 sunrpc.pool_mode=
3752 [NFS]
3753 Control how the NFS server code allocates CPUs to
3754 service thread pools. Depending on how many NICs
3755 you have and where their interrupts are bound, this
3756 option will affect which CPUs will do NFS serving.
3757 Note: this parameter cannot be changed while the
3758 NFS server is running.
3759
3760 auto the server chooses an appropriate mode
3761 automatically using heuristics
3762 global a single global pool contains all CPUs
3763 percpu one pool for each CPU
3764 pernode one pool for each NUMA node (equivalent
3765 to global on non-NUMA machines)
3766
3767 sunrpc.tcp_slot_table_entries=
3768 sunrpc.udp_slot_table_entries=
3769 [NFS,SUNRPC]
3770 Sets the upper limit on the number of simultaneous
3771 RPC calls that can be sent from the client to a
3772 server. Increasing these values may allow you to
3773 improve throughput, but will also increase the
3774 amount of memory reserved for use by the client.
3775
3776 suspend.pm_test_delay=
3777 [SUSPEND]
3778 Sets the number of seconds to remain in a suspend test
3779 mode before resuming the system (see
3780 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3781 is set. Default value is 5.
3782
3783 swapaccount=[0|1]
3784 [KNL] Enable accounting of swap in memory resource
3785 controller if no parameter or 1 is given or disable
3786 it if 0 is given (See Documentation/cgroups/memory.txt)
3787
3788 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3789 Format: { <int> | force }
3790 <int> -- Number of I/O TLB slabs
3791 force -- force using of bounce buffers even if they
3792 wouldn't be automatically used by the kernel
3793
3794 switches= [HW,M68k]
3795
3796 sysfs.deprecated=0|1 [KNL]
3797 Enable/disable old style sysfs layout for old udev
3798 on older distributions. When this option is enabled
3799 very new udev will not work anymore. When this option
3800 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3801 in older udev will not work anymore.
3802 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3803 the kernel configuration.
3804
3805 sysrq_always_enabled
3806 [KNL]
3807 Ignore sysrq setting - this boot parameter will
3808 neutralize any effect of /proc/sys/kernel/sysrq.
3809 Useful for debugging.
3810
3811 tcpmhash_entries= [KNL,NET]
3812 Set the number of tcp_metrics_hash slots.
3813 Default value is 8192 or 16384 depending on total
3814 ram pages. This is used to specify the TCP metrics
3815 cache size. See Documentation/networking/ip-sysctl.txt
3816 "tcp_no_metrics_save" section for more details.
3817
3818 tdfx= [HW,DRM]
3819
3820 test_suspend= [SUSPEND][,N]
3821 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3822 standby suspend) or "freeze" (for suspend type freeze)
3823 as the system sleep state during system startup with
3824 the optional capability to repeat N number of times.
3825 The system is woken from this state using a
3826 wakeup-capable RTC alarm.
3827
3828 thash_entries= [KNL,NET]
3829 Set number of hash buckets for TCP connection
3830
3831 thermal.act= [HW,ACPI]
3832 -1: disable all active trip points in all thermal zones
3833 <degrees C>: override all lowest active trip points
3834
3835 thermal.crt= [HW,ACPI]
3836 -1: disable all critical trip points in all thermal zones
3837 <degrees C>: override all critical trip points
3838
3839 thermal.nocrt= [HW,ACPI]
3840 Set to disable actions on ACPI thermal zone
3841 critical and hot trip points.
3842
3843 thermal.off= [HW,ACPI]
3844 1: disable ACPI thermal control
3845
3846 thermal.psv= [HW,ACPI]
3847 -1: disable all passive trip points
3848 <degrees C>: override all passive trip points to this
3849 value
3850
3851 thermal.tzp= [HW,ACPI]
3852 Specify global default ACPI thermal zone polling rate
3853 <deci-seconds>: poll all this frequency
3854 0: no polling (default)
3855
3856 threadirqs [KNL]
3857 Force threading of all interrupt handlers except those
3858 marked explicitly IRQF_NO_THREAD.
3859
3860 tmem [KNL,XEN]
3861 Enable the Transcendent memory driver if built-in.
3862
3863 tmem.cleancache=0|1 [KNL, XEN]
3864 Default is on (1). Disable the usage of the cleancache
3865 API to send anonymous pages to the hypervisor.
3866
3867 tmem.frontswap=0|1 [KNL, XEN]
3868 Default is on (1). Disable the usage of the frontswap
3869 API to send swap pages to the hypervisor. If disabled
3870 the selfballooning and selfshrinking are force disabled.
3871
3872 tmem.selfballooning=0|1 [KNL, XEN]
3873 Default is on (1). Disable the driving of swap pages
3874 to the hypervisor.
3875
3876 tmem.selfshrinking=0|1 [KNL, XEN]
3877 Default is on (1). Partial swapoff that immediately
3878 transfers pages from Xen hypervisor back to the
3879 kernel based on different criteria.
3880
3881 topology= [S390]
3882 Format: {off | on}
3883 Specify if the kernel should make use of the cpu
3884 topology information if the hardware supports this.
3885 The scheduler will make use of this information and
3886 e.g. base its process migration decisions on it.
3887 Default is on.
3888
3889 topology_updates= [KNL, PPC, NUMA]
3890 Format: {off}
3891 Specify if the kernel should ignore (off)
3892 topology updates sent by the hypervisor to this
3893 LPAR.
3894
3895 tp720= [HW,PS2]
3896
3897 tpm_suspend_pcr=[HW,TPM]
3898 Format: integer pcr id
3899 Specify that at suspend time, the tpm driver
3900 should extend the specified pcr with zeros,
3901 as a workaround for some chips which fail to
3902 flush the last written pcr on TPM_SaveState.
3903 This will guarantee that all the other pcrs
3904 are saved.
3905
3906 trace_buf_size=nn[KMG]
3907 [FTRACE] will set tracing buffer size on each cpu.
3908
3909 trace_event=[event-list]
3910 [FTRACE] Set and start specified trace events in order
3911 to facilitate early boot debugging.
3912 See also Documentation/trace/events.txt
3913
3914 trace_options=[option-list]
3915 [FTRACE] Enable or disable tracer options at boot.
3916 The option-list is a comma delimited list of options
3917 that can be enabled or disabled just as if you were
3918 to echo the option name into
3919
3920 /sys/kernel/debug/tracing/trace_options
3921
3922 For example, to enable stacktrace option (to dump the
3923 stack trace of each event), add to the command line:
3924
3925 trace_options=stacktrace
3926
3927 See also Documentation/trace/ftrace.txt "trace options"
3928 section.
3929
3930 tp_printk[FTRACE]
3931 Have the tracepoints sent to printk as well as the
3932 tracing ring buffer. This is useful for early boot up
3933 where the system hangs or reboots and does not give the
3934 option for reading the tracing buffer or performing a
3935 ftrace_dump_on_oops.
3936
3937 To turn off having tracepoints sent to printk,
3938 echo 0 > /proc/sys/kernel/tracepoint_printk
3939 Note, echoing 1 into this file without the
3940 tracepoint_printk kernel cmdline option has no effect.
3941
3942 ** CAUTION **
3943
3944 Having tracepoints sent to printk() and activating high
3945 frequency tracepoints such as irq or sched, can cause
3946 the system to live lock.
3947
3948 traceoff_on_warning
3949 [FTRACE] enable this option to disable tracing when a
3950 warning is hit. This turns off "tracing_on". Tracing can
3951 be enabled again by echoing '1' into the "tracing_on"
3952 file located in /sys/kernel/debug/tracing/
3953
3954 This option is useful, as it disables the trace before
3955 the WARNING dump is called, which prevents the trace to
3956 be filled with content caused by the warning output.
3957
3958 This option can also be set at run time via the sysctl
3959 option: kernel/traceoff_on_warning
3960
3961 transparent_hugepage=
3962 [KNL]
3963 Format: [always|madvise|never]
3964 Can be used to control the default behavior of the system
3965 with respect to transparent hugepages.
3966 See Documentation/vm/transhuge.txt for more details.
3967
3968 tsc= Disable clocksource stability checks for TSC.
3969 Format: <string>
3970 [x86] reliable: mark tsc clocksource as reliable, this
3971 disables clocksource verification at runtime, as well
3972 as the stability checks done at bootup. Used to enable
3973 high-resolution timer mode on older hardware, and in
3974 virtualized environment.
3975 [x86] noirqtime: Do not use TSC to do irq accounting.
3976 Used to run time disable IRQ_TIME_ACCOUNTING on any
3977 platforms where RDTSC is slow and this accounting
3978 can add overhead.
3979
3980 turbografx.map[2|3]= [HW,JOY]
3981 TurboGraFX parallel port interface
3982 Format:
3983 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3984 See also Documentation/input/joystick-parport.txt
3985
3986 udbg-immortal [PPC] When debugging early kernel crashes that
3987 happen after console_init() and before a proper
3988 console driver takes over, this boot options might
3989 help "seeing" what's going on.
3990
3991 uhash_entries= [KNL,NET]
3992 Set number of hash buckets for UDP/UDP-Lite connections
3993
3994 uhci-hcd.ignore_oc=
3995 [USB] Ignore overcurrent events (default N).
3996 Some badly-designed motherboards generate lots of
3997 bogus events, for ports that aren't wired to
3998 anything. Set this parameter to avoid log spamming.
3999 Note that genuine overcurrent events won't be
4000 reported either.
4001
4002 unknown_nmi_panic
4003 [X86] Cause panic on unknown NMI.
4004
4005 usbcore.authorized_default=
4006 [USB] Default USB device authorization:
4007 (default -1 = authorized except for wireless USB,
4008 0 = not authorized, 1 = authorized)
4009
4010 usbcore.autosuspend=
4011 [USB] The autosuspend time delay (in seconds) used
4012 for newly-detected USB devices (default 2). This
4013 is the time required before an idle device will be
4014 autosuspended. Devices for which the delay is set
4015 to a negative value won't be autosuspended at all.
4016
4017 usbcore.usbfs_snoop=
4018 [USB] Set to log all usbfs traffic (default 0 = off).
4019
4020 usbcore.usbfs_snoop_max=
4021 [USB] Maximum number of bytes to snoop in each URB
4022 (default = 65536).
4023
4024 usbcore.blinkenlights=
4025 [USB] Set to cycle leds on hubs (default 0 = off).
4026
4027 usbcore.old_scheme_first=
4028 [USB] Start with the old device initialization
4029 scheme (default 0 = off).
4030
4031 usbcore.usbfs_memory_mb=
4032 [USB] Memory limit (in MB) for buffers allocated by
4033 usbfs (default = 16, 0 = max = 2047).
4034
4035 usbcore.use_both_schemes=
4036 [USB] Try the other device initialization scheme
4037 if the first one fails (default 1 = enabled).
4038
4039 usbcore.initial_descriptor_timeout=
4040 [USB] Specifies timeout for the initial 64-byte
4041 USB_REQ_GET_DESCRIPTOR request in milliseconds
4042 (default 5000 = 5.0 seconds).
4043
4044 usbcore.nousb [USB] Disable the USB subsystem
4045
4046 usbhid.mousepoll=
4047 [USBHID] The interval which mice are to be polled at.
4048
4049 usb-storage.delay_use=
4050 [UMS] The delay in seconds before a new device is
4051 scanned for Logical Units (default 1).
4052
4053 usb-storage.quirks=
4054 [UMS] A list of quirks entries to supplement or
4055 override the built-in unusual_devs list. List
4056 entries are separated by commas. Each entry has
4057 the form VID:PID:Flags where VID and PID are Vendor
4058 and Product ID values (4-digit hex numbers) and
4059 Flags is a set of characters, each corresponding
4060 to a common usb-storage quirk flag as follows:
4061 a = SANE_SENSE (collect more than 18 bytes
4062 of sense data);
4063 b = BAD_SENSE (don't collect more than 18
4064 bytes of sense data);
4065 c = FIX_CAPACITY (decrease the reported
4066 device capacity by one sector);
4067 d = NO_READ_DISC_INFO (don't use
4068 READ_DISC_INFO command);
4069 e = NO_READ_CAPACITY_16 (don't use
4070 READ_CAPACITY_16 command);
4071 f = NO_REPORT_OPCODES (don't use report opcodes
4072 command, uas only);
4073 g = MAX_SECTORS_240 (don't transfer more than
4074 240 sectors at a time, uas only);
4075 h = CAPACITY_HEURISTICS (decrease the
4076 reported device capacity by one
4077 sector if the number is odd);
4078 i = IGNORE_DEVICE (don't bind to this
4079 device);
4080 j = NO_REPORT_LUNS (don't use report luns
4081 command, uas only);
4082 l = NOT_LOCKABLE (don't try to lock and
4083 unlock ejectable media);
4084 m = MAX_SECTORS_64 (don't transfer more
4085 than 64 sectors = 32 KB at a time);
4086 n = INITIAL_READ10 (force a retry of the
4087 initial READ(10) command);
4088 o = CAPACITY_OK (accept the capacity
4089 reported by the device);
4090 p = WRITE_CACHE (the device cache is ON
4091 by default);
4092 r = IGNORE_RESIDUE (the device reports
4093 bogus residue values);
4094 s = SINGLE_LUN (the device has only one
4095 Logical Unit);
4096 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4097 commands, uas only);
4098 u = IGNORE_UAS (don't bind to the uas driver);
4099 w = NO_WP_DETECT (don't test whether the
4100 medium is write-protected).
4101 Example: quirks=0419:aaf5:rl,0421:0433:rc
4102
4103 user_debug= [KNL,ARM]
4104 Format: <int>
4105 See arch/arm/Kconfig.debug help text.
4106 1 - undefined instruction events
4107 2 - system calls
4108 4 - invalid data aborts
4109 8 - SIGSEGV faults
4110 16 - SIGBUS faults
4111 Example: user_debug=31
4112
4113 userpte=
4114 [X86] Flags controlling user PTE allocations.
4115
4116 nohigh = do not allocate PTE pages in
4117 HIGHMEM regardless of setting
4118 of CONFIG_HIGHPTE.
4119
4120 vdso= [X86,SH]
4121 On X86_32, this is an alias for vdso32=. Otherwise:
4122
4123 vdso=1: enable VDSO (the default)
4124 vdso=0: disable VDSO mapping
4125
4126 vdso32= [X86] Control the 32-bit vDSO
4127 vdso32=1: enable 32-bit VDSO
4128 vdso32=0 or vdso32=2: disable 32-bit VDSO
4129
4130 See the help text for CONFIG_COMPAT_VDSO for more
4131 details. If CONFIG_COMPAT_VDSO is set, the default is
4132 vdso32=0; otherwise, the default is vdso32=1.
4133
4134 For compatibility with older kernels, vdso32=2 is an
4135 alias for vdso32=0.
4136
4137 Try vdso32=0 if you encounter an error that says:
4138 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4139
4140 vector= [IA-64,SMP]
4141 vector=percpu: enable percpu vector domain
4142
4143 video= [FB] Frame buffer configuration
4144 See Documentation/fb/modedb.txt.
4145
4146 video.brightness_switch_enabled= [0,1]
4147 If set to 1, on receiving an ACPI notify event
4148 generated by hotkey, video driver will adjust brightness
4149 level and then send out the event to user space through
4150 the allocated input device; If set to 0, video driver
4151 will only send out the event without touching backlight
4152 brightness level.
4153 default: 1
4154
4155 virtio_mmio.device=
4156 [VMMIO] Memory mapped virtio (platform) device.
4157
4158 <size>@<baseaddr>:<irq>[:<id>]
4159 where:
4160 <size> := size (can use standard suffixes
4161 like K, M and G)
4162 <baseaddr> := physical base address
4163 <irq> := interrupt number (as passed to
4164 request_irq())
4165 <id> := (optional) platform device id
4166 example:
4167 virtio_mmio.device=1K@0x100b0000:48:7
4168
4169 Can be used multiple times for multiple devices.
4170
4171 vga= [BOOT,X86-32] Select a particular video mode
4172 See Documentation/x86/boot.txt and
4173 Documentation/svga.txt.
4174 Use vga=ask for menu.
4175 This is actually a boot loader parameter; the value is
4176 passed to the kernel using a special protocol.
4177
4178 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4179 size of <nn>. This can be used to increase the
4180 minimum size (128MB on x86). It can also be used to
4181 decrease the size and leave more room for directly
4182 mapped kernel RAM.
4183
4184 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4185 Format: <command>
4186
4187 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4188 Format: <command>
4189
4190 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4191 Format: <command>
4192
4193 vsyscall= [X86-64]
4194 Controls the behavior of vsyscalls (i.e. calls to
4195 fixed addresses of 0xffffffffff600x00 from legacy
4196 code). Most statically-linked binaries and older
4197 versions of glibc use these calls. Because these
4198 functions are at fixed addresses, they make nice
4199 targets for exploits that can control RIP.
4200
4201 emulate [default] Vsyscalls turn into traps and are
4202 emulated reasonably safely.
4203
4204 native Vsyscalls are native syscall instructions.
4205 This is a little bit faster than trapping
4206 and makes a few dynamic recompilers work
4207 better than they would in emulation mode.
4208 It also makes exploits much easier to write.
4209
4210 none Vsyscalls don't work at all. This makes
4211 them quite hard to use for exploits but
4212 might break your system.
4213
4214 vt.color= [VT] Default text color.
4215 Format: 0xYX, X = foreground, Y = background.
4216 Default: 0x07 = light gray on black.
4217
4218 vt.cur_default= [VT] Default cursor shape.
4219 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4220 the parameters of the <Esc>[?A;B;Cc escape sequence;
4221 see VGA-softcursor.txt. Default: 2 = underline.
4222
4223 vt.default_blu= [VT]
4224 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4225 Change the default blue palette of the console.
4226 This is a 16-member array composed of values
4227 ranging from 0-255.
4228
4229 vt.default_grn= [VT]
4230 Format: <green0>,<green1>,<green2>,...,<green15>
4231 Change the default green palette of the console.
4232 This is a 16-member array composed of values
4233 ranging from 0-255.
4234
4235 vt.default_red= [VT]
4236 Format: <red0>,<red1>,<red2>,...,<red15>
4237 Change the default red palette of the console.
4238 This is a 16-member array composed of values
4239 ranging from 0-255.
4240
4241 vt.default_utf8=
4242 [VT]
4243 Format=<0|1>
4244 Set system-wide default UTF-8 mode for all tty's.
4245 Default is 1, i.e. UTF-8 mode is enabled for all
4246 newly opened terminals.
4247
4248 vt.global_cursor_default=
4249 [VT]
4250 Format=<-1|0|1>
4251 Set system-wide default for whether a cursor
4252 is shown on new VTs. Default is -1,
4253 i.e. cursors will be created by default unless
4254 overridden by individual drivers. 0 will hide
4255 cursors, 1 will display them.
4256
4257 vt.italic= [VT] Default color for italic text; 0-15.
4258 Default: 2 = green.
4259
4260 vt.underline= [VT] Default color for underlined text; 0-15.
4261 Default: 3 = cyan.
4262
4263 watchdog timers [HW,WDT] For information on watchdog timers,
4264 see Documentation/watchdog/watchdog-parameters.txt
4265 or other driver-specific files in the
4266 Documentation/watchdog/ directory.
4267
4268 workqueue.watchdog_thresh=
4269 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4270 warn stall conditions and dump internal state to
4271 help debugging. 0 disables workqueue stall
4272 detection; otherwise, it's the stall threshold
4273 duration in seconds. The default value is 30 and
4274 it can be updated at runtime by writing to the
4275 corresponding sysfs file.
4276
4277 workqueue.disable_numa
4278 By default, all work items queued to unbound
4279 workqueues are affine to the NUMA nodes they're
4280 issued on, which results in better behavior in
4281 general. If NUMA affinity needs to be disabled for
4282 whatever reason, this option can be used. Note
4283 that this also can be controlled per-workqueue for
4284 workqueues visible under /sys/bus/workqueue/.
4285
4286 workqueue.power_efficient
4287 Per-cpu workqueues are generally preferred because
4288 they show better performance thanks to cache
4289 locality; unfortunately, per-cpu workqueues tend to
4290 be more power hungry than unbound workqueues.
4291
4292 Enabling this makes the per-cpu workqueues which
4293 were observed to contribute significantly to power
4294 consumption unbound, leading to measurably lower
4295 power usage at the cost of small performance
4296 overhead.
4297
4298 The default value of this parameter is determined by
4299 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4300
4301 workqueue.debug_force_rr_cpu
4302 Workqueue used to implicitly guarantee that work
4303 items queued without explicit CPU specified are put
4304 on the local CPU. This guarantee is no longer true
4305 and while local CPU is still preferred work items
4306 may be put on foreign CPUs. This debug option
4307 forces round-robin CPU selection to flush out
4308 usages which depend on the now broken guarantee.
4309 When enabled, memory and cache locality will be
4310 impacted.
4311
4312 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4313 default x2apic cluster mode on platforms
4314 supporting x2apic.
4315
4316 x86_intel_mid_timer= [X86-32,APBT]
4317 Choose timer option for x86 Intel MID platform.
4318 Two valid options are apbt timer only and lapic timer
4319 plus one apbt timer for broadcast timer.
4320 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4321
4322 xen_512gb_limit [KNL,X86-64,XEN]
4323 Restricts the kernel running paravirtualized under Xen
4324 to use only up to 512 GB of RAM. The reason to do so is
4325 crash analysis tools and Xen tools for doing domain
4326 save/restore/migration must be enabled to handle larger
4327 domains.
4328
4329 xen_emul_unplug= [HW,X86,XEN]
4330 Unplug Xen emulated devices
4331 Format: [unplug0,][unplug1]
4332 ide-disks -- unplug primary master IDE devices
4333 aux-ide-disks -- unplug non-primary-master IDE devices
4334 nics -- unplug network devices
4335 all -- unplug all emulated devices (NICs and IDE disks)
4336 unnecessary -- unplugging emulated devices is
4337 unnecessary even if the host did not respond to
4338 the unplug protocol
4339 never -- do not unplug even if version check succeeds
4340
4341 xen_nopvspin [X86,XEN]
4342 Disables the ticketlock slowpath using Xen PV
4343 optimizations.
4344
4345 xen_nopv [X86]
4346 Disables the PV optimizations forcing the HVM guest to
4347 run as generic HVM guest with no PV drivers.
4348
4349 xirc2ps_cs= [NET,PCMCIA]
4350 Format:
4351 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4352
4353______________________________________________________________________
4354
4355TODO:
4356
4357 Add more DRM drivers.