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authorMauro Carvalho Chehab <mchehab@s-opensource.com>2016-09-21 08:51:11 -0400
committerMauro Carvalho Chehab <mchehab@s-opensource.com>2016-10-24 06:12:35 -0400
commit9d85025b0418163fae079c9ba8f8445212de8568 (patch)
tree4629e2dedf4a9ed45a6855c129101f9b52138372 /Documentation/admin-guide/kernel-parameters.rst
parent186128f75392f8478ad1b32a675627d738881ca4 (diff)
docs-rst: create an user's manual book
Place README, REPORTING-BUGS, SecurityBugs and kernel-parameters on an user's manual book. As we'll be numbering the user's manual, remove the manual numbering from SecurityBugs. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
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1Kernel 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
30 log_buf_len=1M print-fatal-signals=1
31
32can also be entered as::
33
34 log-buf-len=1M print_fatal_signals=1
35
36Double-quotes can be used to protect spaces in values, e.g.::
37
38 param="spaces in here"
39
40cpu lists:
41----------
42
43Some kernel parameters take a list of CPUs as a value, e.g. isolcpus,
44nohz_full, irqaffinity, rcu_nocbs. The format of this list is:
45
46 <cpu number>,...,<cpu number>
47
48or
49
50 <cpu number>-<cpu number>
51 (must be a positive range in ascending order)
52
53or a mixture
54
55<cpu number>,...,<cpu number>-<cpu number>
56
57Note that for the special case of a range one can split the range into equal
58sized groups and for each group use some amount from the beginning of that
59group:
60
61 <cpu number>-cpu number>:<used size>/<group size>
62
63For example one can add to the command line following parameter:
64
65 isolcpus=1,2,10-20,100-2000:2/25
66
67where the final item represents CPUs 100,101,125,126,150,151,...
68
69
70
71This document may not be entirely up to date and comprehensive. The command
72"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
73module. Loadable modules, after being loaded into the running kernel, also
74reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
75parameters may be changed at runtime by the command
76``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.
77
78The parameters listed below are only valid if certain kernel build options were
79enabled and if respective hardware is present. The text in square brackets at
80the beginning of each description states the restrictions within which a
81parameter is applicable::
82
83 ACPI ACPI support is enabled.
84 AGP AGP (Accelerated Graphics Port) is enabled.
85 ALSA ALSA sound support is enabled.
86 APIC APIC support is enabled.
87 APM Advanced Power Management support is enabled.
88 ARM ARM architecture is enabled.
89 AVR32 AVR32 architecture is enabled.
90 AX25 Appropriate AX.25 support is enabled.
91 BLACKFIN Blackfin architecture is enabled.
92 CLK Common clock infrastructure is enabled.
93 CMA Contiguous Memory Area support is enabled.
94 DRM Direct Rendering Management support is enabled.
95 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
96 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
97 EFI EFI Partitioning (GPT) is enabled
98 EIDE EIDE/ATAPI support is enabled.
99 EVM Extended Verification Module
100 FB The frame buffer device is enabled.
101 FTRACE Function tracing enabled.
102 GCOV GCOV profiling is enabled.
103 HW Appropriate hardware is enabled.
104 IA-64 IA-64 architecture is enabled.
105 IMA Integrity measurement architecture is enabled.
106 IOSCHED More than one I/O scheduler is enabled.
107 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
108 IPV6 IPv6 support is enabled.
109 ISAPNP ISA PnP code is enabled.
110 ISDN Appropriate ISDN support is enabled.
111 JOY Appropriate joystick support is enabled.
112 KGDB Kernel debugger support is enabled.
113 KVM Kernel Virtual Machine support is enabled.
114 LIBATA Libata driver is enabled
115 LP Printer support is enabled.
116 LOOP Loopback device support is enabled.
117 M68k M68k architecture is enabled.
118 These options have more detailed description inside of
119 Documentation/m68k/kernel-options.txt.
120 MDA MDA console support is enabled.
121 MIPS MIPS architecture is enabled.
122 MOUSE Appropriate mouse support is enabled.
123 MSI Message Signaled Interrupts (PCI).
124 MTD MTD (Memory Technology Device) support is enabled.
125 NET Appropriate network support is enabled.
126 NUMA NUMA support is enabled.
127 NFS Appropriate NFS support is enabled.
128 OSS OSS sound support is enabled.
129 PV_OPS A paravirtualized kernel is enabled.
130 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
131 PARISC The PA-RISC architecture is enabled.
132 PCI PCI bus support is enabled.
133 PCIE PCI Express support is enabled.
134 PCMCIA The PCMCIA subsystem is enabled.
135 PNP Plug & Play support is enabled.
136 PPC PowerPC architecture is enabled.
137 PPT Parallel port support is enabled.
138 PS2 Appropriate PS/2 support is enabled.
139 RAM RAM disk support is enabled.
140 S390 S390 architecture is enabled.
141 SCSI Appropriate SCSI support is enabled.
142 A lot of drivers have their options described inside
143 the Documentation/scsi/ sub-directory.
144 SECURITY Different security models are enabled.
145 SELINUX SELinux support is enabled.
146 APPARMOR AppArmor support is enabled.
147 SERIAL Serial support is enabled.
148 SH SuperH architecture is enabled.
149 SMP The kernel is an SMP kernel.
150 SPARC Sparc architecture is enabled.
151 SWSUSP Software suspend (hibernation) is enabled.
152 SUSPEND System suspend states are enabled.
153 TPM TPM drivers are enabled.
154 TS Appropriate touchscreen support is enabled.
155 UMS USB Mass Storage support is enabled.
156 USB USB support is enabled.
157 USBHID USB Human Interface Device support is enabled.
158 V4L Video For Linux support is enabled.
159 VMMIO Driver for memory mapped virtio devices is enabled.
160 VGA The VGA console has been enabled.
161 VT Virtual terminal support is enabled.
162 WDT Watchdog support is enabled.
163 XT IBM PC/XT MFM hard disk support is enabled.
164 X86-32 X86-32, aka i386 architecture is enabled.
165 X86-64 X86-64 architecture is enabled.
166 More X86-64 boot options can be found in
167 Documentation/x86/x86_64/boot-options.txt .
168 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
169 X86_UV SGI UV support is enabled.
170 XEN Xen support is enabled
171
172In addition, the following text indicates that the option::
173
174 BUGS= Relates to possible processor bugs on the said processor.
175 KNL Is a kernel start-up parameter.
176 BOOT Is a boot loader parameter.
177
178Parameters denoted with BOOT are actually interpreted by the boot
179loader, and have no meaning to the kernel directly.
180Do not modify the syntax of boot loader parameters without extreme
181need or coordination with <Documentation/x86/boot.txt>.
182
183There are also arch-specific kernel-parameters not documented here.
184See for example <Documentation/x86/x86_64/boot-options.txt>.
185
186Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
187a trailing = on the name of any parameter states that that parameter will
188be entered as an environment variable, whereas its absence indicates that
189it will appear as a kernel argument readable via /proc/cmdline by programs
190running once the system is up.
191
192The number of kernel parameters is not limited, but the length of the
193complete command line (parameters including spaces etc.) is limited to
194a fixed number of characters. This limit depends on the architecture
195and is between 256 and 4096 characters. It is defined in the file
196./include/asm/setup.h as COMMAND_LINE_SIZE.
197
198Finally, the [KMG] suffix is commonly described after a number of kernel
199parameter values. These 'K', 'M', and 'G' letters represent the _binary_
200multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
201bytes respectively. Such letter suffixes can also be entirely omitted::
202
203
204 acpi= [HW,ACPI,X86,ARM64]
205 Advanced Configuration and Power Interface
206 Format: { force | on | off | strict | noirq | rsdt |
207 copy_dsdt }
208 force -- enable ACPI if default was off
209 on -- enable ACPI but allow fallback to DT [arm64]
210 off -- disable ACPI if default was on
211 noirq -- do not use ACPI for IRQ routing
212 strict -- Be less tolerant of platforms that are not
213 strictly ACPI specification compliant.
214 rsdt -- prefer RSDT over (default) XSDT
215 copy_dsdt -- copy DSDT to memory
216 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
217 are available
218
219 See also Documentation/power/runtime_pm.txt, pci=noacpi
220
221 acpi_apic_instance= [ACPI, IOAPIC]
222 Format: <int>
223 2: use 2nd APIC table, if available
224 1,0: use 1st APIC table
225 default: 0
226
227 acpi_backlight= [HW,ACPI]
228 acpi_backlight=vendor
229 acpi_backlight=video
230 If set to vendor, prefer vendor specific driver
231 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
232 of the ACPI video.ko driver.
233
234 acpi_force_32bit_fadt_addr
235 force FADT to use 32 bit addresses rather than the
236 64 bit X_* addresses. Some firmware have broken 64
237 bit addresses for force ACPI ignore these and use
238 the older legacy 32 bit addresses.
239
240 acpica_no_return_repair [HW, ACPI]
241 Disable AML predefined validation mechanism
242 This mechanism can repair the evaluation result to make
243 the return objects more ACPI specification compliant.
244 This option is useful for developers to identify the
245 root cause of an AML interpreter issue when the issue
246 has something to do with the repair mechanism.
247
248 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
249 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
250 Format: <int>
251 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
252 debug output. Bits in debug_layer correspond to a
253 _COMPONENT in an ACPI source file, e.g.,
254 #define _COMPONENT ACPI_PCI_COMPONENT
255 Bits in debug_level correspond to a level in
256 ACPI_DEBUG_PRINT statements, e.g.,
257 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
258 The debug_level mask defaults to "info". See
259 Documentation/acpi/debug.txt for more information about
260 debug layers and levels.
261
262 Enable processor driver info messages:
263 acpi.debug_layer=0x20000000
264 Enable PCI/PCI interrupt routing info messages:
265 acpi.debug_layer=0x400000
266 Enable AML "Debug" output, i.e., stores to the Debug
267 object while interpreting AML:
268 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
269 Enable all messages related to ACPI hardware:
270 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
271
272 Some values produce so much output that the system is
273 unusable. The "log_buf_len" parameter may be useful
274 if you need to capture more output.
275
276 acpi_enforce_resources= [ACPI]
277 { strict | lax | no }
278 Check for resource conflicts between native drivers
279 and ACPI OperationRegions (SystemIO and SystemMemory
280 only). IO ports and memory declared in ACPI might be
281 used by the ACPI subsystem in arbitrary AML code and
282 can interfere with legacy drivers.
283 strict (default): access to resources claimed by ACPI
284 is denied; legacy drivers trying to access reserved
285 resources will fail to bind to device using them.
286 lax: access to resources claimed by ACPI is allowed;
287 legacy drivers trying to access reserved resources
288 will bind successfully but a warning message is logged.
289 no: ACPI OperationRegions are not marked as reserved,
290 no further checks are performed.
291
292 acpi_force_table_verification [HW,ACPI]
293 Enable table checksum verification during early stage.
294 By default, this is disabled due to x86 early mapping
295 size limitation.
296
297 acpi_irq_balance [HW,ACPI]
298 ACPI will balance active IRQs
299 default in APIC mode
300
301 acpi_irq_nobalance [HW,ACPI]
302 ACPI will not move active IRQs (default)
303 default in PIC mode
304
305 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
306 Format: <irq>,<irq>...
307
308 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
309 use by PCI
310 Format: <irq>,<irq>...
311
312 acpi_no_auto_serialize [HW,ACPI]
313 Disable auto-serialization of AML methods
314 AML control methods that contain the opcodes to create
315 named objects will be marked as "Serialized" by the
316 auto-serialization feature.
317 This feature is enabled by default.
318 This option allows to turn off the feature.
319
320 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
321 kernels.
322
323 acpi_no_static_ssdt [HW,ACPI]
324 Disable installation of static SSDTs at early boot time
325 By default, SSDTs contained in the RSDT/XSDT will be
326 installed automatically and they will appear under
327 /sys/firmware/acpi/tables.
328 This option turns off this feature.
329 Note that specifying this option does not affect
330 dynamic table installation which will install SSDT
331 tables to /sys/firmware/acpi/tables/dynamic.
332
333 acpi_rsdp= [ACPI,EFI,KEXEC]
334 Pass the RSDP address to the kernel, mostly used
335 on machines running EFI runtime service to boot the
336 second kernel for kdump.
337
338 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
339 Format: To spoof as Windows 98: ="Microsoft Windows"
340
341 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
342 of 2 which is mandated by ACPI 6) as the supported ACPI
343 specification revision (when using this switch, it may
344 be necessary to carry out a cold reboot _twice_ in a
345 row to make it take effect on the platform firmware).
346
347 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
348 acpi_osi="string1" # add string1
349 acpi_osi="!string2" # remove string2
350 acpi_osi=!* # remove all strings
351 acpi_osi=! # disable all built-in OS vendor
352 strings
353 acpi_osi=!! # enable all built-in OS vendor
354 strings
355 acpi_osi= # disable all strings
356
357 'acpi_osi=!' can be used in combination with single or
358 multiple 'acpi_osi="string1"' to support specific OS
359 vendor string(s). Note that such command can only
360 affect the default state of the OS vendor strings, thus
361 it cannot affect the default state of the feature group
362 strings and the current state of the OS vendor strings,
363 specifying it multiple times through kernel command line
364 is meaningless. This command is useful when one do not
365 care about the state of the feature group strings which
366 should be controlled by the OSPM.
367 Examples:
368 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
369 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
370 can make '_OSI("Windows 2000")' TRUE.
371
372 'acpi_osi=' cannot be used in combination with other
373 'acpi_osi=' command lines, the _OSI method will not
374 exist in the ACPI namespace. NOTE that such command can
375 only affect the _OSI support state, thus specifying it
376 multiple times through kernel command line is also
377 meaningless.
378 Examples:
379 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
380 FALSE.
381
382 'acpi_osi=!*' can be used in combination with single or
383 multiple 'acpi_osi="string1"' to support specific
384 string(s). Note that such command can affect the
385 current state of both the OS vendor strings and the
386 feature group strings, thus specifying it multiple times
387 through kernel command line is meaningful. But it may
388 still not able to affect the final state of a string if
389 there are quirks related to this string. This command
390 is useful when one want to control the state of the
391 feature group strings to debug BIOS issues related to
392 the OSPM features.
393 Examples:
394 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
395 '_OSI("Module Device")' FALSE.
396 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
397 '_OSI("Module Device")' TRUE.
398 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
399 equivalent to
400 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
401 and
402 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
403 they all will make '_OSI("Windows 2000")' TRUE.
404
405 acpi_pm_good [X86]
406 Override the pmtimer bug detection: force the kernel
407 to assume that this machine's pmtimer latches its value
408 and always returns good values.
409
410 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
411 Format: { level | edge | high | low }
412
413 acpi_skip_timer_override [HW,ACPI]
414 Recognize and ignore IRQ0/pin2 Interrupt Override.
415 For broken nForce2 BIOS resulting in XT-PIC timer.
416
417 acpi_sleep= [HW,ACPI] Sleep options
418 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
419 old_ordering, nonvs, sci_force_enable }
420 See Documentation/power/video.txt for information on
421 s3_bios and s3_mode.
422 s3_beep is for debugging; it makes the PC's speaker beep
423 as soon as the kernel's real-mode entry point is called.
424 s4_nohwsig prevents ACPI hardware signature from being
425 used during resume from hibernation.
426 old_ordering causes the ACPI 1.0 ordering of the _PTS
427 control method, with respect to putting devices into
428 low power states, to be enforced (the ACPI 2.0 ordering
429 of _PTS is used by default).
430 nonvs prevents the kernel from saving/restoring the
431 ACPI NVS memory during suspend/hibernation and resume.
432 sci_force_enable causes the kernel to set SCI_EN directly
433 on resume from S1/S3 (which is against the ACPI spec,
434 but some broken systems don't work without it).
435
436 acpi_use_timer_override [HW,ACPI]
437 Use timer override. For some broken Nvidia NF5 boards
438 that require a timer override, but don't have HPET
439
440 add_efi_memmap [EFI; X86] Include EFI memory map in
441 kernel's map of available physical RAM.
442
443 agp= [AGP]
444 { off | try_unsupported }
445 off: disable AGP support
446 try_unsupported: try to drive unsupported chipsets
447 (may crash computer or cause data corruption)
448
449 ALSA [HW,ALSA]
450 See Documentation/sound/alsa/alsa-parameters.txt
451
452 alignment= [KNL,ARM]
453 Allow the default userspace alignment fault handler
454 behaviour to be specified. Bit 0 enables warnings,
455 bit 1 enables fixups, and bit 2 sends a segfault.
456
457 align_va_addr= [X86-64]
458 Align virtual addresses by clearing slice [14:12] when
459 allocating a VMA at process creation time. This option
460 gives you up to 3% performance improvement on AMD F15h
461 machines (where it is enabled by default) for a
462 CPU-intensive style benchmark, and it can vary highly in
463 a microbenchmark depending on workload and compiler.
464
465 32: only for 32-bit processes
466 64: only for 64-bit processes
467 on: enable for both 32- and 64-bit processes
468 off: disable for both 32- and 64-bit processes
469
470 alloc_snapshot [FTRACE]
471 Allocate the ftrace snapshot buffer on boot up when the
472 main buffer is allocated. This is handy if debugging
473 and you need to use tracing_snapshot() on boot up, and
474 do not want to use tracing_snapshot_alloc() as it needs
475 to be done where GFP_KERNEL allocations are allowed.
476
477 amd_iommu= [HW,X86-64]
478 Pass parameters to the AMD IOMMU driver in the system.
479 Possible values are:
480 fullflush - enable flushing of IO/TLB entries when
481 they are unmapped. Otherwise they are
482 flushed before they will be reused, which
483 is a lot of faster
484 off - do not initialize any AMD IOMMU found in
485 the system
486 force_isolation - Force device isolation for all
487 devices. The IOMMU driver is not
488 allowed anymore to lift isolation
489 requirements as needed. This option
490 does not override iommu=pt
491
492 amd_iommu_dump= [HW,X86-64]
493 Enable AMD IOMMU driver option to dump the ACPI table
494 for AMD IOMMU. With this option enabled, AMD IOMMU
495 driver will print ACPI tables for AMD IOMMU during
496 IOMMU initialization.
497
498 amd_iommu_intr= [HW,X86-64]
499 Specifies one of the following AMD IOMMU interrupt
500 remapping modes:
501 legacy - Use legacy interrupt remapping mode.
502 vapic - Use virtual APIC mode, which allows IOMMU
503 to inject interrupts directly into guest.
504 This mode requires kvm-amd.avic=1.
505 (Default when IOMMU HW support is present.)
506
507 amijoy.map= [HW,JOY] Amiga joystick support
508 Map of devices attached to JOY0DAT and JOY1DAT
509 Format: <a>,<b>
510 See also Documentation/input/joystick.txt
511
512 analog.map= [HW,JOY] Analog joystick and gamepad support
513 Specifies type or capabilities of an analog joystick
514 connected to one of 16 gameports
515 Format: <type1>,<type2>,..<type16>
516
517 apc= [HW,SPARC]
518 Power management functions (SPARCstation-4/5 + deriv.)
519 Format: noidle
520 Disable APC CPU standby support. SPARCstation-Fox does
521 not play well with APC CPU idle - disable it if you have
522 APC and your system crashes randomly.
523
524 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
525 Change the output verbosity whilst booting
526 Format: { quiet (default) | verbose | debug }
527 Change the amount of debugging information output
528 when initialising the APIC and IO-APIC components.
529
530 apic_extnmi= [APIC,X86] External NMI delivery setting
531 Format: { bsp (default) | all | none }
532 bsp: External NMI is delivered only to CPU 0
533 all: External NMIs are broadcast to all CPUs as a
534 backup of CPU 0
535 none: External NMI is masked for all CPUs. This is
536 useful so that a dump capture kernel won't be
537 shot down by NMI
538
539 autoconf= [IPV6]
540 See Documentation/networking/ipv6.txt.
541
542 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
543 Limit apic dumping. The parameter defines the maximal
544 number of local apics being dumped. Also it is possible
545 to set it to "all" by meaning -- no limit here.
546 Format: { 1 (default) | 2 | ... | all }.
547 The parameter valid if only apic=debug or
548 apic=verbose is specified.
549 Example: apic=debug show_lapic=all
550
551 apm= [APM] Advanced Power Management
552 See header of arch/x86/kernel/apm_32.c.
553
554 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
555 Format: <io>,<irq>,<nodeID>
556
557 ataflop= [HW,M68k]
558
559 atarimouse= [HW,MOUSE] Atari Mouse
560
561 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
562 EzKey and similar keyboards
563
564 atkbd.reset= [HW] Reset keyboard during initialization
565
566 atkbd.set= [HW] Select keyboard code set
567 Format: <int> (2 = AT (default), 3 = PS/2)
568
569 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
570 keyboards
571
572 atkbd.softraw= [HW] Choose between synthetic and real raw mode
573 Format: <bool> (0 = real, 1 = synthetic (default))
574
575 atkbd.softrepeat= [HW]
576 Use software keyboard repeat
577
578 audit= [KNL] Enable the audit sub-system
579 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
580 0 - kernel audit is disabled and can not be enabled
581 until the next reboot
582 unset - kernel audit is initialized but disabled and
583 will be fully enabled by the userspace auditd.
584 1 - kernel audit is initialized and partially enabled,
585 storing at most audit_backlog_limit messages in
586 RAM until it is fully enabled by the userspace
587 auditd.
588 Default: unset
589
590 audit_backlog_limit= [KNL] Set the audit queue size limit.
591 Format: <int> (must be >=0)
592 Default: 64
593
594 bau= [X86_UV] Enable the BAU on SGI UV. The default
595 behavior is to disable the BAU (i.e. bau=0).
596 Format: { "0" | "1" }
597 0 - Disable the BAU.
598 1 - Enable the BAU.
599 unset - Disable the BAU.
600
601 baycom_epp= [HW,AX25]
602 Format: <io>,<mode>
603
604 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
605 Format: <io>,<mode>
606 See header of drivers/net/hamradio/baycom_par.c.
607
608 baycom_ser_fdx= [HW,AX25]
609 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
610 Format: <io>,<irq>,<mode>[,<baud>]
611 See header of drivers/net/hamradio/baycom_ser_fdx.c.
612
613 baycom_ser_hdx= [HW,AX25]
614 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
615 Format: <io>,<irq>,<mode>
616 See header of drivers/net/hamradio/baycom_ser_hdx.c.
617
618 blkdevparts= Manual partition parsing of block device(s) for
619 embedded devices based on command line input.
620 See Documentation/block/cmdline-partition.txt
621
622 boot_delay= Milliseconds to delay each printk during boot.
623 Values larger than 10 seconds (10000) are changed to
624 no delay (0).
625 Format: integer
626
627 bootmem_debug [KNL] Enable bootmem allocator debug messages.
628
629 bert_disable [ACPI]
630 Disable BERT OS support on buggy BIOSes.
631
632 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
633 bttv.radio= Most important insmod options are available as
634 kernel args too.
635 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
636 bttv.tuner=
637
638 bulk_remove=off [PPC] This parameter disables the use of the pSeries
639 firmware feature for flushing multiple hpte entries
640 at a time.
641
642 c101= [NET] Moxa C101 synchronous serial card
643
644 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
645 Sometimes CPU hardware bugs make them report the cache
646 size incorrectly. The kernel will attempt work arounds
647 to fix known problems, but for some CPUs it is not
648 possible to determine what the correct size should be.
649 This option provides an override for these situations.
650
651 ca_keys= [KEYS] This parameter identifies a specific key(s) on
652 the system trusted keyring to be used for certificate
653 trust validation.
654 format: { id:<keyid> | builtin }
655
656 cca= [MIPS] Override the kernel pages' cache coherency
657 algorithm. Accepted values range from 0 to 7
658 inclusive. See arch/mips/include/asm/pgtable-bits.h
659 for platform specific values (SB1, Loongson3 and
660 others).
661
662 ccw_timeout_log [S390]
663 See Documentation/s390/CommonIO for details.
664
665 cgroup_disable= [KNL] Disable a particular controller
666 Format: {name of the controller(s) to disable}
667 The effects of cgroup_disable=foo are:
668 - foo isn't auto-mounted if you mount all cgroups in
669 a single hierarchy
670 - foo isn't visible as an individually mountable
671 subsystem
672 {Currently only "memory" controller deal with this and
673 cut the overhead, others just disable the usage. So
674 only cgroup_disable=memory is actually worthy}
675
676 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
677 Format: { controller[,controller...] | "all" }
678 Like cgroup_disable, but only applies to cgroup v1;
679 the blacklisted controllers remain available in cgroup2.
680
681 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
682 Format: <string>
683 nosocket -- Disable socket memory accounting.
684 nokmem -- Disable kernel memory accounting.
685
686 checkreqprot [SELINUX] Set initial checkreqprot flag value.
687 Format: { "0" | "1" }
688 See security/selinux/Kconfig help text.
689 0 -- check protection applied by kernel (includes
690 any implied execute protection).
691 1 -- check protection requested by application.
692 Default value is set via a kernel config option.
693 Value can be changed at runtime via
694 /selinux/checkreqprot.
695
696 cio_ignore= [S390]
697 See Documentation/s390/CommonIO for details.
698 clk_ignore_unused
699 [CLK]
700 Prevents the clock framework from automatically gating
701 clocks that have not been explicitly enabled by a Linux
702 device driver but are enabled in hardware at reset or
703 by the bootloader/firmware. Note that this does not
704 force such clocks to be always-on nor does it reserve
705 those clocks in any way. This parameter is useful for
706 debug and development, but should not be needed on a
707 platform with proper driver support. For more
708 information, see Documentation/clk.txt.
709
710 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
711 [Deprecated]
712 Forces specified clocksource (if available) to be used
713 when calculating gettimeofday(). If specified
714 clocksource is not available, it defaults to PIT.
715 Format: { pit | tsc | cyclone | pmtmr }
716
717 clocksource= Override the default clocksource
718 Format: <string>
719 Override the default clocksource and use the clocksource
720 with the name specified.
721 Some clocksource names to choose from, depending on
722 the platform:
723 [all] jiffies (this is the base, fallback clocksource)
724 [ACPI] acpi_pm
725 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
726 pxa_timer,timer3,32k_counter,timer0_1
727 [AVR32] avr32
728 [X86-32] pit,hpet,tsc;
729 scx200_hrt on Geode; cyclone on IBM x440
730 [MIPS] MIPS
731 [PARISC] cr16
732 [S390] tod
733 [SH] SuperH
734 [SPARC64] tick
735 [X86-64] hpet,tsc
736
737 clocksource.arm_arch_timer.evtstrm=
738 [ARM,ARM64]
739 Format: <bool>
740 Enable/disable the eventstream feature of the ARM
741 architected timer so that code using WFE-based polling
742 loops can be debugged more effectively on production
743 systems.
744
745 clocksource.arm_arch_timer.fsl-a008585=
746 [ARM64]
747 Format: <bool>
748 Enable/disable the workaround of Freescale/NXP
749 erratum A-008585. This can be useful for KVM
750 guests, if the guest device tree doesn't show the
751 erratum. If unspecified, the workaround is
752 enabled based on the device tree.
753
754 clearcpuid=BITNUM [X86]
755 Disable CPUID feature X for the kernel. See
756 arch/x86/include/asm/cpufeatures.h for the valid bit
757 numbers. Note the Linux specific bits are not necessarily
758 stable over kernel options, but the vendor specific
759 ones should be.
760 Also note that user programs calling CPUID directly
761 or using the feature without checking anything
762 will still see it. This just prevents it from
763 being used by the kernel or shown in /proc/cpuinfo.
764 Also note the kernel might malfunction if you disable
765 some critical bits.
766
767 cma=nn[MG]@[start[MG][-end[MG]]]
768 [ARM,X86,KNL]
769 Sets the size of kernel global memory area for
770 contiguous memory allocations and optionally the
771 placement constraint by the physical address range of
772 memory allocations. A value of 0 disables CMA
773 altogether. For more information, see
774 include/linux/dma-contiguous.h
775
776 cmo_free_hint= [PPC] Format: { yes | no }
777 Specify whether pages are marked as being inactive
778 when they are freed. This is used in CMO environments
779 to determine OS memory pressure for page stealing by
780 a hypervisor.
781 Default: yes
782
783 coherent_pool=nn[KMG] [ARM,KNL]
784 Sets the size of memory pool for coherent, atomic dma
785 allocations, by default set to 256K.
786
787 code_bytes [X86] How many bytes of object code to print
788 in an oops report.
789 Range: 0 - 8192
790 Default: 64
791
792 com20020= [HW,NET] ARCnet - COM20020 chipset
793 Format:
794 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
795
796 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
797 Format: <io>[,<irq>]
798
799 com90xx= [HW,NET]
800 ARCnet - COM90xx chipset (memory-mapped buffers)
801 Format: <io>[,<irq>[,<memstart>]]
802
803 condev= [HW,S390] console device
804 conmode=
805
806 console= [KNL] Output console device and options.
807
808 tty<n> Use the virtual console device <n>.
809
810 ttyS<n>[,options]
811 ttyUSB0[,options]
812 Use the specified serial port. The options are of
813 the form "bbbbpnf", where "bbbb" is the baud rate,
814 "p" is parity ("n", "o", or "e"), "n" is number of
815 bits, and "f" is flow control ("r" for RTS or
816 omit it). Default is "9600n8".
817
818 See Documentation/serial-console.txt for more
819 information. See
820 Documentation/networking/netconsole.txt for an
821 alternative.
822
823 uart[8250],io,<addr>[,options]
824 uart[8250],mmio,<addr>[,options]
825 uart[8250],mmio16,<addr>[,options]
826 uart[8250],mmio32,<addr>[,options]
827 uart[8250],0x<addr>[,options]
828 Start an early, polled-mode console on the 8250/16550
829 UART at the specified I/O port or MMIO address,
830 switching to the matching ttyS device later.
831 MMIO inter-register address stride is either 8-bit
832 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
833 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
834 to be equivalent to 'mmio'. 'options' are specified in
835 the same format described for ttyS above; if unspecified,
836 the h/w is not re-initialized.
837
838 hvc<n> Use the hypervisor console device <n>. This is for
839 both Xen and PowerPC hypervisors.
840
841 If the device connected to the port is not a TTY but a braille
842 device, prepend "brl," before the device type, for instance
843 console=brl,ttyS0
844 For now, only VisioBraille is supported.
845
846 consoleblank= [KNL] The console blank (screen saver) timeout in
847 seconds. Defaults to 10*60 = 10mins. A value of 0
848 disables the blank timer.
849
850 coredump_filter=
851 [KNL] Change the default value for
852 /proc/<pid>/coredump_filter.
853 See also Documentation/filesystems/proc.txt.
854
855 cpuidle.off=1 [CPU_IDLE]
856 disable the cpuidle sub-system
857
858 cpu_init_udelay=N
859 [X86] Delay for N microsec between assert and de-assert
860 of APIC INIT to start processors. This delay occurs
861 on every CPU online, such as boot, and resume from suspend.
862 Default: 10000
863
864 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
865 Format:
866 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
867
868 crashkernel=size[KMG][@offset[KMG]]
869 [KNL] Using kexec, Linux can switch to a 'crash kernel'
870 upon panic. This parameter reserves the physical
871 memory region [offset, offset + size] for that kernel
872 image. If '@offset' is omitted, then a suitable offset
873 is selected automatically. Check
874 Documentation/kdump/kdump.txt for further details.
875
876 crashkernel=range1:size1[,range2:size2,...][@offset]
877 [KNL] Same as above, but depends on the memory
878 in the running system. The syntax of range is
879 start-[end] where start and end are both
880 a memory unit (amount[KMG]). See also
881 Documentation/kdump/kdump.txt for an example.
882
883 crashkernel=size[KMG],high
884 [KNL, x86_64] range could be above 4G. Allow kernel
885 to allocate physical memory region from top, so could
886 be above 4G if system have more than 4G ram installed.
887 Otherwise memory region will be allocated below 4G, if
888 available.
889 It will be ignored if crashkernel=X is specified.
890 crashkernel=size[KMG],low
891 [KNL, x86_64] range under 4G. When crashkernel=X,high
892 is passed, kernel could allocate physical memory region
893 above 4G, that cause second kernel crash on system
894 that require some amount of low memory, e.g. swiotlb
895 requires at least 64M+32K low memory, also enough extra
896 low memory is needed to make sure DMA buffers for 32-bit
897 devices won't run out. Kernel would try to allocate at
898 at least 256M below 4G automatically.
899 This one let user to specify own low range under 4G
900 for second kernel instead.
901 0: to disable low allocation.
902 It will be ignored when crashkernel=X,high is not used
903 or memory reserved is below 4G.
904
905 cryptomgr.notests
906 [KNL] Disable crypto self-tests
907
908 cs89x0_dma= [HW,NET]
909 Format: <dma>
910
911 cs89x0_media= [HW,NET]
912 Format: { rj45 | aui | bnc }
913
914 dasd= [HW,NET]
915 See header of drivers/s390/block/dasd_devmap.c.
916
917 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
918 (one device per port)
919 Format: <port#>,<type>
920 See also Documentation/input/joystick-parport.txt
921
922 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
923 time. See Documentation/dynamic-debug-howto.txt for
924 details. Deprecated, see dyndbg.
925
926 debug [KNL] Enable kernel debugging (events log level).
927
928 debug_locks_verbose=
929 [KNL] verbose self-tests
930 Format=<0|1>
931 Print debugging info while doing the locking API
932 self-tests.
933 We default to 0 (no extra messages), setting it to
934 1 will print _a lot_ more information - normally
935 only useful to kernel developers.
936
937 debug_objects [KNL] Enable object debugging
938
939 no_debug_objects
940 [KNL] Disable object debugging
941
942 debug_guardpage_minorder=
943 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
944 parameter allows control of the order of pages that will
945 be intentionally kept free (and hence protected) by the
946 buddy allocator. Bigger value increase the probability
947 of catching random memory corruption, but reduce the
948 amount of memory for normal system use. The maximum
949 possible value is MAX_ORDER/2. Setting this parameter
950 to 1 or 2 should be enough to identify most random
951 memory corruption problems caused by bugs in kernel or
952 driver code when a CPU writes to (or reads from) a
953 random memory location. Note that there exists a class
954 of memory corruptions problems caused by buggy H/W or
955 F/W or by drivers badly programing DMA (basically when
956 memory is written at bus level and the CPU MMU is
957 bypassed) which are not detectable by
958 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
959 tracking down these problems.
960
961 debug_pagealloc=
962 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
963 parameter enables the feature at boot time. In
964 default, it is disabled. We can avoid allocating huge
965 chunk of memory for debug pagealloc if we don't enable
966 it at boot time and the system will work mostly same
967 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
968 on: enable the feature
969
970 debugpat [X86] Enable PAT debugging
971
972 decnet.addr= [HW,NET]
973 Format: <area>[,<node>]
974 See also Documentation/networking/decnet.txt.
975
976 default_hugepagesz=
977 [same as hugepagesz=] The size of the default
978 HugeTLB page size. This is the size represented by
979 the legacy /proc/ hugepages APIs, used for SHM, and
980 default size when mounting hugetlbfs filesystems.
981 Defaults to the default architecture's huge page size
982 if not specified.
983
984 dhash_entries= [KNL]
985 Set number of hash buckets for dentry cache.
986
987 disable_1tb_segments [PPC]
988 Disables the use of 1TB hash page table segments. This
989 causes the kernel to fall back to 256MB segments which
990 can be useful when debugging issues that require an SLB
991 miss to occur.
992
993 disable= [IPV6]
994 See Documentation/networking/ipv6.txt.
995
996 disable_radix [PPC]
997 Disable RADIX MMU mode on POWER9
998
999 disable_cpu_apicid= [X86,APIC,SMP]
1000 Format: <int>
1001 The number of initial APIC ID for the
1002 corresponding CPU to be disabled at boot,
1003 mostly used for the kdump 2nd kernel to
1004 disable BSP to wake up multiple CPUs without
1005 causing system reset or hang due to sending
1006 INIT from AP to BSP.
1007
1008 disable_ddw [PPC/PSERIES]
1009 Disable Dynamic DMA Window support. Use this if
1010 to workaround buggy firmware.
1011
1012 disable_ipv6= [IPV6]
1013 See Documentation/networking/ipv6.txt.
1014
1015 disable_mtrr_cleanup [X86]
1016 The kernel tries to adjust MTRR layout from continuous
1017 to discrete, to make X server driver able to add WB
1018 entry later. This parameter disables that.
1019
1020 disable_mtrr_trim [X86, Intel and AMD only]
1021 By default the kernel will trim any uncacheable
1022 memory out of your available memory pool based on
1023 MTRR settings. This parameter disables that behavior,
1024 possibly causing your machine to run very slowly.
1025
1026 disable_timer_pin_1 [X86]
1027 Disable PIN 1 of APIC timer
1028 Can be useful to work around chipset bugs.
1029
1030 dis_ucode_ldr [X86] Disable the microcode loader.
1031
1032 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1033 this option disables the debugging code at boot.
1034
1035 dma_debug_entries=<number>
1036 This option allows to tune the number of preallocated
1037 entries for DMA-API debugging code. One entry is
1038 required per DMA-API allocation. Use this if the
1039 DMA-API debugging code disables itself because the
1040 architectural default is too low.
1041
1042 dma_debug_driver=<driver_name>
1043 With this option the DMA-API debugging driver
1044 filter feature can be enabled at boot time. Just
1045 pass the driver to filter for as the parameter.
1046 The filter can be disabled or changed to another
1047 driver later using sysfs.
1048
1049 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1050 Broken monitors, graphic adapters, KVMs and EDIDless
1051 panels may send no or incorrect EDID data sets.
1052 This parameter allows to specify an EDID data sets
1053 in the /lib/firmware directory that are used instead.
1054 Generic built-in EDID data sets are used, if one of
1055 edid/1024x768.bin, edid/1280x1024.bin,
1056 edid/1680x1050.bin, or edid/1920x1080.bin is given
1057 and no file with the same name exists. Details and
1058 instructions how to build your own EDID data are
1059 available in Documentation/EDID/HOWTO.txt. An EDID
1060 data set will only be used for a particular connector,
1061 if its name and a colon are prepended to the EDID
1062 name. Each connector may use a unique EDID data
1063 set by separating the files with a comma. An EDID
1064 data set with no connector name will be used for
1065 any connectors not explicitly specified.
1066
1067 dscc4.setup= [NET]
1068
1069 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1070 module.dyndbg[="val"]
1071 Enable debug messages at boot time. See
1072 Documentation/dynamic-debug-howto.txt for details.
1073
1074 nompx [X86] Disables Intel Memory Protection Extensions.
1075 See Documentation/x86/intel_mpx.txt for more
1076 information about the feature.
1077
1078 nopku [X86] Disable Memory Protection Keys CPU feature found
1079 in some Intel CPUs.
1080
1081 eagerfpu= [X86]
1082 on enable eager fpu restore
1083 off disable eager fpu restore
1084 auto selects the default scheme, which automatically
1085 enables eagerfpu restore for xsaveopt.
1086
1087 module.async_probe [KNL]
1088 Enable asynchronous probe on this module.
1089
1090 early_ioremap_debug [KNL]
1091 Enable debug messages in early_ioremap support. This
1092 is useful for tracking down temporary early mappings
1093 which are not unmapped.
1094
1095 earlycon= [KNL] Output early console device and options.
1096
1097 When used with no options, the early console is
1098 determined by the stdout-path property in device
1099 tree's chosen node.
1100
1101 cdns,<addr>[,options]
1102 Start an early, polled-mode console on a Cadence
1103 (xuartps) serial port at the specified address. Only
1104 supported option is baud rate. If baud rate is not
1105 specified, the serial port must already be setup and
1106 configured.
1107
1108 uart[8250],io,<addr>[,options]
1109 uart[8250],mmio,<addr>[,options]
1110 uart[8250],mmio32,<addr>[,options]
1111 uart[8250],mmio32be,<addr>[,options]
1112 uart[8250],0x<addr>[,options]
1113 Start an early, polled-mode console on the 8250/16550
1114 UART at the specified I/O port or MMIO address.
1115 MMIO inter-register address stride is either 8-bit
1116 (mmio) or 32-bit (mmio32 or mmio32be).
1117 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1118 to be equivalent to 'mmio'. 'options' are specified
1119 in the same format described for "console=ttyS<n>"; if
1120 unspecified, the h/w is not initialized.
1121
1122 pl011,<addr>
1123 pl011,mmio32,<addr>
1124 Start an early, polled-mode console on a pl011 serial
1125 port at the specified address. The pl011 serial port
1126 must already be setup and configured. Options are not
1127 yet supported. If 'mmio32' is specified, then only
1128 the driver will use only 32-bit accessors to read/write
1129 the device registers.
1130
1131 meson,<addr>
1132 Start an early, polled-mode console on a meson serial
1133 port at the specified address. The serial port must
1134 already be setup and configured. Options are not yet
1135 supported.
1136
1137 msm_serial,<addr>
1138 Start an early, polled-mode console on an msm serial
1139 port at the specified address. The serial port
1140 must already be setup and configured. Options are not
1141 yet supported.
1142
1143 msm_serial_dm,<addr>
1144 Start an early, polled-mode console on an msm serial
1145 dm port at the specified address. The serial port
1146 must already be setup and configured. Options are not
1147 yet supported.
1148
1149 smh Use ARM semihosting calls for early console.
1150
1151 s3c2410,<addr>
1152 s3c2412,<addr>
1153 s3c2440,<addr>
1154 s3c6400,<addr>
1155 s5pv210,<addr>
1156 exynos4210,<addr>
1157 Use early console provided by serial driver available
1158 on Samsung SoCs, requires selecting proper type and
1159 a correct base address of the selected UART port. The
1160 serial port must already be setup and configured.
1161 Options are not yet supported.
1162
1163 lpuart,<addr>
1164 lpuart32,<addr>
1165 Use early console provided by Freescale LP UART driver
1166 found on Freescale Vybrid and QorIQ LS1021A processors.
1167 A valid base address must be provided, and the serial
1168 port must already be setup and configured.
1169
1170 armada3700_uart,<addr>
1171 Start an early, polled-mode console on the
1172 Armada 3700 serial port at the specified
1173 address. The serial port must already be setup
1174 and configured. Options are not yet supported.
1175
1176 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1177 earlyprintk=vga
1178 earlyprintk=efi
1179 earlyprintk=xen
1180 earlyprintk=serial[,ttySn[,baudrate]]
1181 earlyprintk=serial[,0x...[,baudrate]]
1182 earlyprintk=ttySn[,baudrate]
1183 earlyprintk=dbgp[debugController#]
1184 earlyprintk=pciserial,bus:device.function[,baudrate]
1185
1186 earlyprintk is useful when the kernel crashes before
1187 the normal console is initialized. It is not enabled by
1188 default because it has some cosmetic problems.
1189
1190 Append ",keep" to not disable it when the real console
1191 takes over.
1192
1193 Only one of vga, efi, serial, or usb debug port can
1194 be used at a time.
1195
1196 Currently only ttyS0 and ttyS1 may be specified by
1197 name. Other I/O ports may be explicitly specified
1198 on some architectures (x86 and arm at least) by
1199 replacing ttySn with an I/O port address, like this:
1200 earlyprintk=serial,0x1008,115200
1201 You can find the port for a given device in
1202 /proc/tty/driver/serial:
1203 2: uart:ST16650V2 port:00001008 irq:18 ...
1204
1205 Interaction with the standard serial driver is not
1206 very good.
1207
1208 The VGA and EFI output is eventually overwritten by
1209 the real console.
1210
1211 The xen output can only be used by Xen PV guests.
1212
1213 edac_report= [HW,EDAC] Control how to report EDAC event
1214 Format: {"on" | "off" | "force"}
1215 on: enable EDAC to report H/W event. May be overridden
1216 by other higher priority error reporting module.
1217 off: disable H/W event reporting through EDAC.
1218 force: enforce the use of EDAC to report H/W event.
1219 default: on.
1220
1221 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1222 ekgdboc=kbd
1223
1224 This is designed to be used in conjunction with
1225 the boot argument: earlyprintk=vga
1226
1227 edd= [EDD]
1228 Format: {"off" | "on" | "skip[mbr]"}
1229
1230 efi= [EFI]
1231 Format: { "old_map", "nochunk", "noruntime", "debug" }
1232 old_map [X86-64]: switch to the old ioremap-based EFI
1233 runtime services mapping. 32-bit still uses this one by
1234 default.
1235 nochunk: disable reading files in "chunks" in the EFI
1236 boot stub, as chunking can cause problems with some
1237 firmware implementations.
1238 noruntime : disable EFI runtime services support
1239 debug: enable misc debug output
1240
1241 efi_no_storage_paranoia [EFI; X86]
1242 Using this parameter you can use more than 50% of
1243 your efi variable storage. Use this parameter only if
1244 you are really sure that your UEFI does sane gc and
1245 fulfills the spec otherwise your board may brick.
1246
1247 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1248 Add arbitrary attribute to specific memory range by
1249 updating original EFI memory map.
1250 Region of memory which aa attribute is added to is
1251 from ss to ss+nn.
1252 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1253 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1254 attribute is added to range 0x100000000-0x180000000 and
1255 0x10a0000000-0x1120000000.
1256
1257 Using this parameter you can do debugging of EFI memmap
1258 related feature. For example, you can do debugging of
1259 Address Range Mirroring feature even if your box
1260 doesn't support it.
1261
1262 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1263 that is to be dynamically loaded by Linux. If there are
1264 multiple variables with the same name but with different
1265 vendor GUIDs, all of them will be loaded. See
1266 Documentation/acpi/ssdt-overlays.txt for details.
1267
1268
1269 eisa_irq_edge= [PARISC,HW]
1270 See header of drivers/parisc/eisa.c.
1271
1272 elanfreq= [X86-32]
1273 See comment before function elanfreq_setup() in
1274 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1275
1276 elevator= [IOSCHED]
1277 Format: {"cfq" | "deadline" | "noop"}
1278 See Documentation/block/cfq-iosched.txt and
1279 Documentation/block/deadline-iosched.txt for details.
1280
1281 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1282 Specifies physical address of start of kernel core
1283 image elf header and optionally the size. Generally
1284 kexec loader will pass this option to capture kernel.
1285 See Documentation/kdump/kdump.txt for details.
1286
1287 enable_mtrr_cleanup [X86]
1288 The kernel tries to adjust MTRR layout from continuous
1289 to discrete, to make X server driver able to add WB
1290 entry later. This parameter enables that.
1291
1292 enable_timer_pin_1 [X86]
1293 Enable PIN 1 of APIC timer
1294 Can be useful to work around chipset bugs
1295 (in particular on some ATI chipsets).
1296 The kernel tries to set a reasonable default.
1297
1298 enforcing [SELINUX] Set initial enforcing status.
1299 Format: {"0" | "1"}
1300 See security/selinux/Kconfig help text.
1301 0 -- permissive (log only, no denials).
1302 1 -- enforcing (deny and log).
1303 Default value is 0.
1304 Value can be changed at runtime via /selinux/enforce.
1305
1306 erst_disable [ACPI]
1307 Disable Error Record Serialization Table (ERST)
1308 support.
1309
1310 ether= [HW,NET] Ethernet cards parameters
1311 This option is obsoleted by the "netdev=" option, which
1312 has equivalent usage. See its documentation for details.
1313
1314 evm= [EVM]
1315 Format: { "fix" }
1316 Permit 'security.evm' to be updated regardless of
1317 current integrity status.
1318
1319 failslab=
1320 fail_page_alloc=
1321 fail_make_request=[KNL]
1322 General fault injection mechanism.
1323 Format: <interval>,<probability>,<space>,<times>
1324 See also Documentation/fault-injection/.
1325
1326 floppy= [HW]
1327 See Documentation/blockdev/floppy.txt.
1328
1329 force_pal_cache_flush
1330 [IA-64] Avoid check_sal_cache_flush which may hang on
1331 buggy SAL_CACHE_FLUSH implementations. Using this
1332 parameter will force ia64_sal_cache_flush to call
1333 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1334
1335 forcepae [X86-32]
1336 Forcefully enable Physical Address Extension (PAE).
1337 Many Pentium M systems disable PAE but may have a
1338 functionally usable PAE implementation.
1339 Warning: use of this parameter will taint the kernel
1340 and may cause unknown problems.
1341
1342 ftrace=[tracer]
1343 [FTRACE] will set and start the specified tracer
1344 as early as possible in order to facilitate early
1345 boot debugging.
1346
1347 ftrace_dump_on_oops[=orig_cpu]
1348 [FTRACE] will dump the trace buffers on oops.
1349 If no parameter is passed, ftrace will dump
1350 buffers of all CPUs, but if you pass orig_cpu, it will
1351 dump only the buffer of the CPU that triggered the
1352 oops.
1353
1354 ftrace_filter=[function-list]
1355 [FTRACE] Limit the functions traced by the function
1356 tracer at boot up. function-list is a comma separated
1357 list of functions. This list can be changed at run
1358 time by the set_ftrace_filter file in the debugfs
1359 tracing directory.
1360
1361 ftrace_notrace=[function-list]
1362 [FTRACE] Do not trace the functions specified in
1363 function-list. This list can be changed at run time
1364 by the set_ftrace_notrace file in the debugfs
1365 tracing directory.
1366
1367 ftrace_graph_filter=[function-list]
1368 [FTRACE] Limit the top level callers functions traced
1369 by the function graph tracer at boot up.
1370 function-list is a comma separated list of functions
1371 that can be changed at run time by the
1372 set_graph_function file in the debugfs tracing directory.
1373
1374 ftrace_graph_notrace=[function-list]
1375 [FTRACE] Do not trace from the functions specified in
1376 function-list. This list is a comma separated list of
1377 functions that can be changed at run time by the
1378 set_graph_notrace file in the debugfs tracing directory.
1379
1380 gamecon.map[2|3]=
1381 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1382 support via parallel port (up to 5 devices per port)
1383 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1384 See also Documentation/input/joystick-parport.txt
1385
1386 gamma= [HW,DRM]
1387
1388 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1389 Format: off | on
1390 default: on
1391
1392 gcov_persist= [GCOV] When non-zero (default), profiling data for
1393 kernel modules is saved and remains accessible via
1394 debugfs, even when the module is unloaded/reloaded.
1395 When zero, profiling data is discarded and associated
1396 debugfs files are removed at module unload time.
1397
1398 gpt [EFI] Forces disk with valid GPT signature but
1399 invalid Protective MBR to be treated as GPT. If the
1400 primary GPT is corrupted, it enables the backup/alternate
1401 GPT to be used instead.
1402
1403 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1404 the "Enable 0" bit of the configuration register.
1405 Format: 0 | 1
1406 Default: 0
1407 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1408 the "Enable 0" bit of the configuration register.
1409 Format: 0 | 1
1410 Default: 0
1411 grcan.select= [HW] Select which physical interface to use.
1412 Format: 0 | 1
1413 Default: 0
1414 grcan.txsize= [HW] Sets the size of the tx buffer.
1415 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1416 Default: 1024
1417 grcan.rxsize= [HW] Sets the size of the rx buffer.
1418 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1419 Default: 1024
1420
1421 gpio-mockup.gpio_mockup_ranges
1422 [HW] Sets the ranges of gpiochip of for this device.
1423 Format: <start1>,<end1>,<start2>,<end2>...
1424
1425 hardlockup_all_cpu_backtrace=
1426 [KNL] Should the hard-lockup detector generate
1427 backtraces on all cpus.
1428 Format: <integer>
1429
1430 hashdist= [KNL,NUMA] Large hashes allocated during boot
1431 are distributed across NUMA nodes. Defaults on
1432 for 64-bit NUMA, off otherwise.
1433 Format: 0 | 1 (for off | on)
1434
1435 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1436
1437 hd= [EIDE] (E)IDE hard drive subsystem geometry
1438 Format: <cyl>,<head>,<sect>
1439
1440 hest_disable [ACPI]
1441 Disable Hardware Error Source Table (HEST) support;
1442 corresponding firmware-first mode error processing
1443 logic will be disabled.
1444
1445 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1446 size of <nn>. This works even on boxes that have no
1447 highmem otherwise. This also works to reduce highmem
1448 size on bigger boxes.
1449
1450 highres= [KNL] Enable/disable high resolution timer mode.
1451 Valid parameters: "on", "off"
1452 Default: "on"
1453
1454 hisax= [HW,ISDN]
1455 See Documentation/isdn/README.HiSax.
1456
1457 hlt [BUGS=ARM,SH]
1458
1459 hpet= [X86-32,HPET] option to control HPET usage
1460 Format: { enable (default) | disable | force |
1461 verbose }
1462 disable: disable HPET and use PIT instead
1463 force: allow force enabled of undocumented chips (ICH4,
1464 VIA, nVidia)
1465 verbose: show contents of HPET registers during setup
1466
1467 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1468 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1469
1470 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1471 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1472 On x86-64 and powerpc, this option can be specified
1473 multiple times interleaved with hugepages= to reserve
1474 huge pages of different sizes. Valid pages sizes on
1475 x86-64 are 2M (when the CPU supports "pse") and 1G
1476 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1477
1478 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1479 terminal devices. Valid values: 0..8
1480 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1481 If specified, z/VM IUCV HVC accepts connections
1482 from listed z/VM user IDs only.
1483
1484 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1485 hardware thread id mappings.
1486 Format: <cpu>:<hwthread>
1487
1488 keep_bootcon [KNL]
1489 Do not unregister boot console at start. This is only
1490 useful for debugging when something happens in the window
1491 between unregistering the boot console and initializing
1492 the real console.
1493
1494 i2c_bus= [HW] Override the default board specific I2C bus speed
1495 or register an additional I2C bus that is not
1496 registered from board initialization code.
1497 Format:
1498 <bus_id>,<clkrate>
1499
1500 i8042.debug [HW] Toggle i8042 debug mode
1501 i8042.unmask_kbd_data
1502 [HW] Enable printing of interrupt data from the KBD port
1503 (disabled by default, and as a pre-condition
1504 requires that i8042.debug=1 be enabled)
1505 i8042.direct [HW] Put keyboard port into non-translated mode
1506 i8042.dumbkbd [HW] Pretend that controller can only read data from
1507 keyboard and cannot control its state
1508 (Don't attempt to blink the leds)
1509 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1510 i8042.nokbd [HW] Don't check/create keyboard port
1511 i8042.noloop [HW] Disable the AUX Loopback command while probing
1512 for the AUX port
1513 i8042.nomux [HW] Don't check presence of an active multiplexing
1514 controller
1515 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1516 controllers
1517 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1518 i8042.reset [HW] Reset the controller during init, cleanup and
1519 suspend-to-ram transitions, only during s2r
1520 transitions, or never reset
1521 Format: { 1 | Y | y | 0 | N | n }
1522 1, Y, y: always reset controller
1523 0, N, n: don't ever reset controller
1524 Default: only on s2r transitions on x86; most other
1525 architectures force reset to be always executed
1526 i8042.unlock [HW] Unlock (ignore) the keylock
1527 i8042.kbdreset [HW] Reset device connected to KBD port
1528
1529 i810= [HW,DRM]
1530
1531 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1532 indicates that the driver is running on unsupported
1533 hardware.
1534 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1535 does not match list of supported models.
1536 i8k.power_status
1537 [HW] Report power status in /proc/i8k
1538 (disabled by default)
1539 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1540 capability is set.
1541
1542 i915.invert_brightness=
1543 [DRM] Invert the sense of the variable that is used to
1544 set the brightness of the panel backlight. Normally a
1545 brightness value of 0 indicates backlight switched off,
1546 and the maximum of the brightness value sets the backlight
1547 to maximum brightness. If this parameter is set to 0
1548 (default) and the machine requires it, or this parameter
1549 is set to 1, a brightness value of 0 sets the backlight
1550 to maximum brightness, and the maximum of the brightness
1551 value switches the backlight off.
1552 -1 -- never invert brightness
1553 0 -- machine default
1554 1 -- force brightness inversion
1555
1556 icn= [HW,ISDN]
1557 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1558
1559 ide-core.nodma= [HW] (E)IDE subsystem
1560 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1561 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1562 .cdrom .chs .ignore_cable are additional options
1563 See Documentation/ide/ide.txt.
1564
1565 ide-generic.probe-mask= [HW] (E)IDE subsystem
1566 Format: <int>
1567 Probe mask for legacy ISA IDE ports. Depending on
1568 platform up to 6 ports are supported, enabled by
1569 setting corresponding bits in the mask to 1. The
1570 default value is 0x0, which has a special meaning.
1571 On systems that have PCI, it triggers scanning the
1572 PCI bus for the first and the second port, which
1573 are then probed. On systems without PCI the value
1574 of 0x0 enables probing the two first ports as if it
1575 was 0x3.
1576
1577 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1578 Claim all unknown PCI IDE storage controllers.
1579
1580 idle= [X86]
1581 Format: idle=poll, idle=halt, idle=nomwait
1582 Poll forces a polling idle loop that can slightly
1583 improve the performance of waking up a idle CPU, but
1584 will use a lot of power and make the system run hot.
1585 Not recommended.
1586 idle=halt: Halt is forced to be used for CPU idle.
1587 In such case C2/C3 won't be used again.
1588 idle=nomwait: Disable mwait for CPU C-states
1589
1590 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1591 Format: { strict | legacy | 2008 | relaxed }
1592 Default: strict
1593
1594 Choose which programs will be accepted for execution
1595 based on the IEEE 754 NaN encoding(s) supported by
1596 the FPU and the NaN encoding requested with the value
1597 of an ELF file header flag individually set by each
1598 binary. Hardware implementations are permitted to
1599 support either or both of the legacy and the 2008 NaN
1600 encoding mode.
1601
1602 Available settings are as follows:
1603 strict accept binaries that request a NaN encoding
1604 supported by the FPU
1605 legacy only accept legacy-NaN binaries, if supported
1606 by the FPU
1607 2008 only accept 2008-NaN binaries, if supported
1608 by the FPU
1609 relaxed accept any binaries regardless of whether
1610 supported by the FPU
1611
1612 The FPU emulator is always able to support both NaN
1613 encodings, so if no FPU hardware is present or it has
1614 been disabled with 'nofpu', then the settings of
1615 'legacy' and '2008' strap the emulator accordingly,
1616 'relaxed' straps the emulator for both legacy-NaN and
1617 2008-NaN, whereas 'strict' enables legacy-NaN only on
1618 legacy processors and both NaN encodings on MIPS32 or
1619 MIPS64 CPUs.
1620
1621 The setting for ABS.fmt/NEG.fmt instruction execution
1622 mode generally follows that for the NaN encoding,
1623 except where unsupported by hardware.
1624
1625 ignore_loglevel [KNL]
1626 Ignore loglevel setting - this will print /all/
1627 kernel messages to the console. Useful for debugging.
1628 We also add it as printk module parameter, so users
1629 could change it dynamically, usually by
1630 /sys/module/printk/parameters/ignore_loglevel.
1631
1632 ignore_rlimit_data
1633 Ignore RLIMIT_DATA setting for data mappings,
1634 print warning at first misuse. Can be changed via
1635 /sys/module/kernel/parameters/ignore_rlimit_data.
1636
1637 ihash_entries= [KNL]
1638 Set number of hash buckets for inode cache.
1639
1640 ima_appraise= [IMA] appraise integrity measurements
1641 Format: { "off" | "enforce" | "fix" | "log" }
1642 default: "enforce"
1643
1644 ima_appraise_tcb [IMA]
1645 The builtin appraise policy appraises all files
1646 owned by uid=0.
1647
1648 ima_hash= [IMA]
1649 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1650 | sha512 | ... }
1651 default: "sha1"
1652
1653 The list of supported hash algorithms is defined
1654 in crypto/hash_info.h.
1655
1656 ima_policy= [IMA]
1657 The builtin measurement policy to load during IMA
1658 setup. Specyfing "tcb" as the value, measures all
1659 programs exec'd, files mmap'd for exec, and all files
1660 opened with the read mode bit set by either the
1661 effective uid (euid=0) or uid=0.
1662 Format: "tcb"
1663
1664 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1665 Load a policy which meets the needs of the Trusted
1666 Computing Base. This means IMA will measure all
1667 programs exec'd, files mmap'd for exec, and all files
1668 opened for read by uid=0.
1669
1670 ima_template= [IMA]
1671 Select one of defined IMA measurements template formats.
1672 Formats: { "ima" | "ima-ng" | "ima-sig" }
1673 Default: "ima-ng"
1674
1675 ima_template_fmt=
1676 [IMA] Define a custom template format.
1677 Format: { "field1|...|fieldN" }
1678
1679 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1680 Format: <min_file_size>
1681 Set the minimal file size for using asynchronous hash.
1682 If left unspecified, ahash usage is disabled.
1683
1684 ahash performance varies for different data sizes on
1685 different crypto accelerators. This option can be used
1686 to achieve the best performance for a particular HW.
1687
1688 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1689 Format: <bufsize>
1690 Set hashing buffer size. Default: 4k.
1691
1692 ahash performance varies for different chunk sizes on
1693 different crypto accelerators. This option can be used
1694 to achieve best performance for particular HW.
1695
1696 init= [KNL]
1697 Format: <full_path>
1698 Run specified binary instead of /sbin/init as init
1699 process.
1700
1701 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1702 for working out where the kernel is dying during
1703 startup.
1704
1705 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1706 initcall functions. Useful for debugging built-in
1707 modules and initcalls.
1708
1709 initrd= [BOOT] Specify the location of the initial ramdisk
1710
1711 init_pkru= [x86] Specify the default memory protection keys rights
1712 register contents for all processes. 0x55555554 by
1713 default (disallow access to all but pkey 0). Can
1714 override in debugfs after boot.
1715
1716 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1717 Format: <irq>
1718
1719 int_pln_enable [x86] Enable power limit notification interrupt
1720
1721 integrity_audit=[IMA]
1722 Format: { "0" | "1" }
1723 0 -- basic integrity auditing messages. (Default)
1724 1 -- additional integrity auditing messages.
1725
1726 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1727 on
1728 Enable intel iommu driver.
1729 off
1730 Disable intel iommu driver.
1731 igfx_off [Default Off]
1732 By default, gfx is mapped as normal device. If a gfx
1733 device has a dedicated DMAR unit, the DMAR unit is
1734 bypassed by not enabling DMAR with this option. In
1735 this case, gfx device will use physical address for
1736 DMA.
1737 forcedac [x86_64]
1738 With this option iommu will not optimize to look
1739 for io virtual address below 32-bit forcing dual
1740 address cycle on pci bus for cards supporting greater
1741 than 32-bit addressing. The default is to look
1742 for translation below 32-bit and if not available
1743 then look in the higher range.
1744 strict [Default Off]
1745 With this option on every unmap_single operation will
1746 result in a hardware IOTLB flush operation as opposed
1747 to batching them for performance.
1748 sp_off [Default Off]
1749 By default, super page will be supported if Intel IOMMU
1750 has the capability. With this option, super page will
1751 not be supported.
1752 ecs_off [Default Off]
1753 By default, extended context tables will be supported if
1754 the hardware advertises that it has support both for the
1755 extended tables themselves, and also PASID support. With
1756 this option set, extended tables will not be used even
1757 on hardware which claims to support them.
1758
1759 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1760 0 disables intel_idle and fall back on acpi_idle.
1761 1 to 9 specify maximum depth of C-state.
1762
1763 intel_pstate= [X86]
1764 disable
1765 Do not enable intel_pstate as the default
1766 scaling driver for the supported processors
1767 force
1768 Enable intel_pstate on systems that prohibit it by default
1769 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1770 instead of acpi-cpufreq may disable platform features, such
1771 as thermal controls and power capping, that rely on ACPI
1772 P-States information being indicated to OSPM and therefore
1773 should be used with caution. This option does not work with
1774 processors that aren't supported by the intel_pstate driver
1775 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1776 no_hwp
1777 Do not enable hardware P state control (HWP)
1778 if available.
1779 hwp_only
1780 Only load intel_pstate on systems which support
1781 hardware P state control (HWP) if available.
1782 support_acpi_ppc
1783 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1784 Description Table, specifies preferred power management
1785 profile as "Enterprise Server" or "Performance Server",
1786 then this feature is turned on by default.
1787
1788 intremap= [X86-64, Intel-IOMMU]
1789 on enable Interrupt Remapping (default)
1790 off disable Interrupt Remapping
1791 nosid disable Source ID checking
1792 no_x2apic_optout
1793 BIOS x2APIC opt-out request will be ignored
1794 nopost disable Interrupt Posting
1795
1796 iomem= Disable strict checking of access to MMIO memory
1797 strict regions from userspace.
1798 relaxed
1799
1800 iommu= [x86]
1801 off
1802 force
1803 noforce
1804 biomerge
1805 panic
1806 nopanic
1807 merge
1808 nomerge
1809 forcesac
1810 soft
1811 pt [x86, IA-64]
1812 nobypass [PPC/POWERNV]
1813 Disable IOMMU bypass, using IOMMU for PCI devices.
1814
1815
1816 io7= [HW] IO7 for Marvel based alpha systems
1817 See comment before marvel_specify_io7 in
1818 arch/alpha/kernel/core_marvel.c.
1819
1820 io_delay= [X86] I/O delay method
1821 0x80
1822 Standard port 0x80 based delay
1823 0xed
1824 Alternate port 0xed based delay (needed on some systems)
1825 udelay
1826 Simple two microseconds delay
1827 none
1828 No delay
1829
1830 ip= [IP_PNP]
1831 See Documentation/filesystems/nfs/nfsroot.txt.
1832
1833 irqaffinity= [SMP] Set the default irq affinity mask
1834 The argument is a cpu list, as described above.
1835
1836 irqfixup [HW]
1837 When an interrupt is not handled search all handlers
1838 for it. Intended to get systems with badly broken
1839 firmware running.
1840
1841 irqpoll [HW]
1842 When an interrupt is not handled search all handlers
1843 for it. Also check all handlers each timer
1844 interrupt. Intended to get systems with badly broken
1845 firmware running.
1846
1847 isapnp= [ISAPNP]
1848 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1849
1850 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1851 The argument is a cpu list, as described above.
1852
1853 This option can be used to specify one or more CPUs
1854 to isolate from the general SMP balancing and scheduling
1855 algorithms. You can move a process onto or off an
1856 "isolated" CPU via the CPU affinity syscalls or cpuset.
1857 <cpu number> begins at 0 and the maximum value is
1858 "number of CPUs in system - 1".
1859
1860 This option is the preferred way to isolate CPUs. The
1861 alternative -- manually setting the CPU mask of all
1862 tasks in the system -- can cause problems and
1863 suboptimal load balancer performance.
1864
1865 iucv= [HW,NET]
1866
1867 ivrs_ioapic [HW,X86_64]
1868 Provide an override to the IOAPIC-ID<->DEVICE-ID
1869 mapping provided in the IVRS ACPI table. For
1870 example, to map IOAPIC-ID decimal 10 to
1871 PCI device 00:14.0 write the parameter as:
1872 ivrs_ioapic[10]=00:14.0
1873
1874 ivrs_hpet [HW,X86_64]
1875 Provide an override to the HPET-ID<->DEVICE-ID
1876 mapping provided in the IVRS ACPI table. For
1877 example, to map HPET-ID decimal 0 to
1878 PCI device 00:14.0 write the parameter as:
1879 ivrs_hpet[0]=00:14.0
1880
1881 ivrs_acpihid [HW,X86_64]
1882 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1883 mapping provided in the IVRS ACPI table. For
1884 example, to map UART-HID:UID AMD0020:0 to
1885 PCI device 00:14.5 write the parameter as:
1886 ivrs_acpihid[00:14.5]=AMD0020:0
1887
1888 js= [HW,JOY] Analog joystick
1889 See Documentation/input/joystick.txt.
1890
1891 nokaslr [KNL]
1892 When CONFIG_RANDOMIZE_BASE is set, this disables
1893 kernel and module base offset ASLR (Address Space
1894 Layout Randomization).
1895
1896 keepinitrd [HW,ARM]
1897
1898 kernelcore= [KNL,X86,IA-64,PPC]
1899 Format: nn[KMGTPE] | "mirror"
1900 This parameter
1901 specifies the amount of memory usable by the kernel
1902 for non-movable allocations. The requested amount is
1903 spread evenly throughout all nodes in the system. The
1904 remaining memory in each node is used for Movable
1905 pages. In the event, a node is too small to have both
1906 kernelcore and Movable pages, kernelcore pages will
1907 take priority and other nodes will have a larger number
1908 of Movable pages. The Movable zone is used for the
1909 allocation of pages that may be reclaimed or moved
1910 by the page migration subsystem. This means that
1911 HugeTLB pages may not be allocated from this zone.
1912 Note that allocations like PTEs-from-HighMem still
1913 use the HighMem zone if it exists, and the Normal
1914 zone if it does not.
1915
1916 Instead of specifying the amount of memory (nn[KMGTPE]),
1917 you can specify "mirror" option. In case "mirror"
1918 option is specified, mirrored (reliable) memory is used
1919 for non-movable allocations and remaining memory is used
1920 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1921 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1922 time.
1923
1924 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1925 Format: <Controller#>[,poll interval]
1926 The controller # is the number of the ehci usb debug
1927 port as it is probed via PCI. The poll interval is
1928 optional and is the number seconds in between
1929 each poll cycle to the debug port in case you need
1930 the functionality for interrupting the kernel with
1931 gdb or control-c on the dbgp connection. When
1932 not using this parameter you use sysrq-g to break into
1933 the kernel debugger.
1934
1935 kgdboc= [KGDB,HW] kgdb over consoles.
1936 Requires a tty driver that supports console polling,
1937 or a supported polling keyboard driver (non-usb).
1938 Serial only format: <serial_device>[,baud]
1939 keyboard only format: kbd
1940 keyboard and serial format: kbd,<serial_device>[,baud]
1941 Optional Kernel mode setting:
1942 kms, kbd format: kms,kbd
1943 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1944
1945 kgdbwait [KGDB] Stop kernel execution and enter the
1946 kernel debugger at the earliest opportunity.
1947
1948 kmac= [MIPS] korina ethernet MAC address.
1949 Configure the RouterBoard 532 series on-chip
1950 Ethernet adapter MAC address.
1951
1952 kmemleak= [KNL] Boot-time kmemleak enable/disable
1953 Valid arguments: on, off
1954 Default: on
1955 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1956 the default is off.
1957
1958 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1959 Valid arguments: 0, 1, 2
1960 kmemcheck=0 (disabled)
1961 kmemcheck=1 (enabled)
1962 kmemcheck=2 (one-shot mode)
1963 Default: 2 (one-shot mode)
1964
1965 kstack=N [X86] Print N words from the kernel stack
1966 in oops dumps.
1967
1968 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1969 Default is 0 (don't ignore, but inject #GP)
1970
1971 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1972 KVM MMU at runtime.
1973 Default is 0 (off)
1974
1975 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1976 Default is 1 (enabled)
1977
1978 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1979 for all guests.
1980 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1981
1982 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1983 (virtualized MMU) support on capable Intel chips.
1984 Default is 1 (enabled)
1985
1986 kvm-intel.emulate_invalid_guest_state=
1987 [KVM,Intel] Enable emulation of invalid guest states
1988 Default is 0 (disabled)
1989
1990 kvm-intel.flexpriority=
1991 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1992 Default is 1 (enabled)
1993
1994 kvm-intel.nested=
1995 [KVM,Intel] Enable VMX nesting (nVMX).
1996 Default is 0 (disabled)
1997
1998 kvm-intel.unrestricted_guest=
1999 [KVM,Intel] Disable unrestricted guest feature
2000 (virtualized real and unpaged mode) on capable
2001 Intel chips. Default is 1 (enabled)
2002
2003 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2004 feature (tagged TLBs) on capable Intel chips.
2005 Default is 1 (enabled)
2006
2007 l2cr= [PPC]
2008
2009 l3cr= [PPC]
2010
2011 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2012 disabled it.
2013
2014 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2015 value for LAPIC timer one-shot implementation. Default
2016 back to the programmable timer unit in the LAPIC.
2017
2018 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2019 in C2 power state.
2020
2021 libata.dma= [LIBATA] DMA control
2022 libata.dma=0 Disable all PATA and SATA DMA
2023 libata.dma=1 PATA and SATA Disk DMA only
2024 libata.dma=2 ATAPI (CDROM) DMA only
2025 libata.dma=4 Compact Flash DMA only
2026 Combinations also work, so libata.dma=3 enables DMA
2027 for disks and CDROMs, but not CFs.
2028
2029 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2030 libata.ignore_hpa=0 keep BIOS limits (default)
2031 libata.ignore_hpa=1 ignore limits, using full disk
2032
2033 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2034 when set.
2035 Format: <int>
2036
2037 libata.force= [LIBATA] Force configurations. The format is comma
2038 separated list of "[ID:]VAL" where ID is
2039 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2040 matching port, link or device. Basically, it matches
2041 the ATA ID string printed on console by libata. If
2042 the whole ID part is omitted, the last PORT and DEVICE
2043 values are used. If ID hasn't been specified yet, the
2044 configuration applies to all ports, links and devices.
2045
2046 If only DEVICE is omitted, the parameter applies to
2047 the port and all links and devices behind it. DEVICE
2048 number of 0 either selects the first device or the
2049 first fan-out link behind PMP device. It does not
2050 select the host link. DEVICE number of 15 selects the
2051 host link and device attached to it.
2052
2053 The VAL specifies the configuration to force. As long
2054 as there's no ambiguity shortcut notation is allowed.
2055 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2056 The following configurations can be forced.
2057
2058 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2059 Any ID with matching PORT is used.
2060
2061 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2062
2063 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2064 udma[/][16,25,33,44,66,100,133] notation is also
2065 allowed.
2066
2067 * [no]ncq: Turn on or off NCQ.
2068
2069 * [no]ncqtrim: Turn off queued DSM TRIM.
2070
2071 * nohrst, nosrst, norst: suppress hard, soft
2072 and both resets.
2073
2074 * rstonce: only attempt one reset during
2075 hot-unplug link recovery
2076
2077 * dump_id: dump IDENTIFY data.
2078
2079 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2080
2081 * disable: Disable this device.
2082
2083 If there are multiple matching configurations changing
2084 the same attribute, the last one is used.
2085
2086 memblock=debug [KNL] Enable memblock debug messages.
2087
2088 load_ramdisk= [RAM] List of ramdisks to load from floppy
2089 See Documentation/blockdev/ramdisk.txt.
2090
2091 lockd.nlm_grace_period=P [NFS] Assign grace period.
2092 Format: <integer>
2093
2094 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2095 Format: <integer>
2096
2097 lockd.nlm_timeout=T [NFS] Assign timeout value.
2098 Format: <integer>
2099
2100 lockd.nlm_udpport=M [NFS] Assign UDP port.
2101 Format: <integer>
2102
2103 locktorture.nreaders_stress= [KNL]
2104 Set the number of locking read-acquisition kthreads.
2105 Defaults to being automatically set based on the
2106 number of online CPUs.
2107
2108 locktorture.nwriters_stress= [KNL]
2109 Set the number of locking write-acquisition kthreads.
2110
2111 locktorture.onoff_holdoff= [KNL]
2112 Set time (s) after boot for CPU-hotplug testing.
2113
2114 locktorture.onoff_interval= [KNL]
2115 Set time (s) between CPU-hotplug operations, or
2116 zero to disable CPU-hotplug testing.
2117
2118 locktorture.shuffle_interval= [KNL]
2119 Set task-shuffle interval (jiffies). Shuffling
2120 tasks allows some CPUs to go into dyntick-idle
2121 mode during the locktorture test.
2122
2123 locktorture.shutdown_secs= [KNL]
2124 Set time (s) after boot system shutdown. This
2125 is useful for hands-off automated testing.
2126
2127 locktorture.stat_interval= [KNL]
2128 Time (s) between statistics printk()s.
2129
2130 locktorture.stutter= [KNL]
2131 Time (s) to stutter testing, for example,
2132 specifying five seconds causes the test to run for
2133 five seconds, wait for five seconds, and so on.
2134 This tests the locking primitive's ability to
2135 transition abruptly to and from idle.
2136
2137 locktorture.torture_runnable= [BOOT]
2138 Start locktorture running at boot time.
2139
2140 locktorture.torture_type= [KNL]
2141 Specify the locking implementation to test.
2142
2143 locktorture.verbose= [KNL]
2144 Enable additional printk() statements.
2145
2146 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2147 Format: <irq>
2148
2149 loglevel= All Kernel Messages with a loglevel smaller than the
2150 console loglevel will be printed to the console. It can
2151 also be changed with klogd or other programs. The
2152 loglevels are defined as follows:
2153
2154 0 (KERN_EMERG) system is unusable
2155 1 (KERN_ALERT) action must be taken immediately
2156 2 (KERN_CRIT) critical conditions
2157 3 (KERN_ERR) error conditions
2158 4 (KERN_WARNING) warning conditions
2159 5 (KERN_NOTICE) normal but significant condition
2160 6 (KERN_INFO) informational
2161 7 (KERN_DEBUG) debug-level messages
2162
2163 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2164 in bytes. n must be a power of two and greater
2165 than the minimal size. The minimal size is defined
2166 by LOG_BUF_SHIFT kernel config parameter. There is
2167 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2168 that allows to increase the default size depending on
2169 the number of CPUs. See init/Kconfig for more details.
2170
2171 logo.nologo [FB] Disables display of the built-in Linux logo.
2172 This may be used to provide more screen space for
2173 kernel log messages and is useful when debugging
2174 kernel boot problems.
2175
2176 lp=0 [LP] Specify parallel ports to use, e.g,
2177 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2178 lp=reset first parallel port). 'lp=0' disables the
2179 lp=auto printer driver. 'lp=reset' (which can be
2180 specified in addition to the ports) causes
2181 attached printers to be reset. Using
2182 lp=port1,port2,... specifies the parallel ports
2183 to associate lp devices with, starting with
2184 lp0. A port specification may be 'none' to skip
2185 that lp device, or a parport name such as
2186 'parport0'. Specifying 'lp=auto' instead of a
2187 port specification list means that device IDs
2188 from each port should be examined, to see if
2189 an IEEE 1284-compliant printer is attached; if
2190 so, the driver will manage that printer.
2191 See also header of drivers/char/lp.c.
2192
2193 lpj=n [KNL]
2194 Sets loops_per_jiffy to given constant, thus avoiding
2195 time-consuming boot-time autodetection (up to 250 ms per
2196 CPU). 0 enables autodetection (default). To determine
2197 the correct value for your kernel, boot with normal
2198 autodetection and see what value is printed. Note that
2199 on SMP systems the preset will be applied to all CPUs,
2200 which is likely to cause problems if your CPUs need
2201 significantly divergent settings. An incorrect value
2202 will cause delays in the kernel to be wrong, leading to
2203 unpredictable I/O errors and other breakage. Although
2204 unlikely, in the extreme case this might damage your
2205 hardware.
2206
2207 ltpc= [NET]
2208 Format: <io>,<irq>,<dma>
2209
2210 machvec= [IA-64] Force the use of a particular machine-vector
2211 (machvec) in a generic kernel.
2212 Example: machvec=hpzx1_swiotlb
2213
2214 machtype= [Loongson] Share the same kernel image file between different
2215 yeeloong laptop.
2216 Example: machtype=lemote-yeeloong-2f-7inch
2217
2218 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2219 than or equal to this physical address is ignored.
2220
2221 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2222 will bring up during bootup. maxcpus=n : n >= 0 limits
2223 the kernel to bring up 'n' processors. Surely after
2224 bootup you can bring up the other plugged cpu by executing
2225 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2226 only takes effect during system bootup.
2227 While n=0 is a special case, it is equivalent to "nosmp",
2228 which also disables the IO APIC.
2229
2230 max_loop= [LOOP] The number of loop block devices that get
2231 (loop.max_loop) unconditionally pre-created at init time. The default
2232 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2233 of statically allocating a predefined number, loop
2234 devices can be requested on-demand with the
2235 /dev/loop-control interface.
2236
2237 mce [X86-32] Machine Check Exception
2238
2239 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2240
2241 md= [HW] RAID subsystems devices and level
2242 See Documentation/md.txt.
2243
2244 mdacon= [MDA]
2245 Format: <first>,<last>
2246 Specifies range of consoles to be captured by the MDA.
2247
2248 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2249 Amount of memory to be used when the kernel is not able
2250 to see the whole system memory or for test.
2251 [X86] Work as limiting max address. Use together
2252 with memmap= to avoid physical address space collisions.
2253 Without memmap= PCI devices could be placed at addresses
2254 belonging to unused RAM.
2255
2256 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2257 memory.
2258
2259 memchunk=nn[KMG]
2260 [KNL,SH] Allow user to override the default size for
2261 per-device physically contiguous DMA buffers.
2262
2263 memhp_default_state=online/offline
2264 [KNL] Set the initial state for the memory hotplug
2265 onlining policy. If not specified, the default value is
2266 set according to the
2267 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2268 option.
2269 See Documentation/memory-hotplug.txt.
2270
2271 memmap=exactmap [KNL,X86] Enable setting of an exact
2272 E820 memory map, as specified by the user.
2273 Such memmap=exactmap lines can be constructed based on
2274 BIOS output or other requirements. See the memmap=nn@ss
2275 option description.
2276
2277 memmap=nn[KMG]@ss[KMG]
2278 [KNL] Force usage of a specific region of memory.
2279 Region of memory to be used is from ss to ss+nn.
2280
2281 memmap=nn[KMG]#ss[KMG]
2282 [KNL,ACPI] Mark specific memory as ACPI data.
2283 Region of memory to be marked is from ss to ss+nn.
2284
2285 memmap=nn[KMG]$ss[KMG]
2286 [KNL,ACPI] Mark specific memory as reserved.
2287 Region of memory to be reserved is from ss to ss+nn.
2288 Example: Exclude memory from 0x18690000-0x1869ffff
2289 memmap=64K$0x18690000
2290 or
2291 memmap=0x10000$0x18690000
2292
2293 memmap=nn[KMG]!ss[KMG]
2294 [KNL,X86] Mark specific memory as protected.
2295 Region of memory to be used, from ss to ss+nn.
2296 The memory region may be marked as e820 type 12 (0xc)
2297 and is NVDIMM or ADR memory.
2298
2299 memory_corruption_check=0/1 [X86]
2300 Some BIOSes seem to corrupt the first 64k of
2301 memory when doing things like suspend/resume.
2302 Setting this option will scan the memory
2303 looking for corruption. Enabling this will
2304 both detect corruption and prevent the kernel
2305 from using the memory being corrupted.
2306 However, its intended as a diagnostic tool; if
2307 repeatable BIOS-originated corruption always
2308 affects the same memory, you can use memmap=
2309 to prevent the kernel from using that memory.
2310
2311 memory_corruption_check_size=size [X86]
2312 By default it checks for corruption in the low
2313 64k, making this memory unavailable for normal
2314 use. Use this parameter to scan for
2315 corruption in more or less memory.
2316
2317 memory_corruption_check_period=seconds [X86]
2318 By default it checks for corruption every 60
2319 seconds. Use this parameter to check at some
2320 other rate. 0 disables periodic checking.
2321
2322 memtest= [KNL,X86,ARM] Enable memtest
2323 Format: <integer>
2324 default : 0 <disable>
2325 Specifies the number of memtest passes to be
2326 performed. Each pass selects another test
2327 pattern from a given set of patterns. Memtest
2328 fills the memory with this pattern, validates
2329 memory contents and reserves bad memory
2330 regions that are detected.
2331
2332 meye.*= [HW] Set MotionEye Camera parameters
2333 See Documentation/video4linux/meye.txt.
2334
2335 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2336 Multi-Function General Purpose Timers on AMD Geode
2337 platforms.
2338
2339 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2340 the BIOS has incorrectly applied a workaround. TinyBIOS
2341 version 0.98 is known to be affected, 0.99 fixes the
2342 problem by letting the user disable the workaround.
2343
2344 mga= [HW,DRM]
2345
2346 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2347 physical address is ignored.
2348
2349 mini2440= [ARM,HW,KNL]
2350 Format:[0..2][b][c][t]
2351 Default: "0tb"
2352 MINI2440 configuration specification:
2353 0 - The attached screen is the 3.5" TFT
2354 1 - The attached screen is the 7" TFT
2355 2 - The VGA Shield is attached (1024x768)
2356 Leaving out the screen size parameter will not load
2357 the TFT driver, and the framebuffer will be left
2358 unconfigured.
2359 b - Enable backlight. The TFT backlight pin will be
2360 linked to the kernel VESA blanking code and a GPIO
2361 LED. This parameter is not necessary when using the
2362 VGA shield.
2363 c - Enable the s3c camera interface.
2364 t - Reserved for enabling touchscreen support. The
2365 touchscreen support is not enabled in the mainstream
2366 kernel as of 2.6.30, a preliminary port can be found
2367 in the "bleeding edge" mini2440 support kernel at
2368 http://repo.or.cz/w/linux-2.6/mini2440.git
2369
2370 mminit_loglevel=
2371 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2372 parameter allows control of the logging verbosity for
2373 the additional memory initialisation checks. A value
2374 of 0 disables mminit logging and a level of 4 will
2375 log everything. Information is printed at KERN_DEBUG
2376 so loglevel=8 may also need to be specified.
2377
2378 module.sig_enforce
2379 [KNL] When CONFIG_MODULE_SIG is set, this means that
2380 modules without (valid) signatures will fail to load.
2381 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2382 is always true, so this option does nothing.
2383
2384 module_blacklist= [KNL] Do not load a comma-separated list of
2385 modules. Useful for debugging problem modules.
2386
2387 mousedev.tap_time=
2388 [MOUSE] Maximum time between finger touching and
2389 leaving touchpad surface for touch to be considered
2390 a tap and be reported as a left button click (for
2391 touchpads working in absolute mode only).
2392 Format: <msecs>
2393 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2394 reporting absolute coordinates, such as tablets
2395 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2396 reporting absolute coordinates, such as tablets
2397
2398 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2399 is similar to kernelcore except it specifies the
2400 amount of memory used for migratable allocations.
2401 If both kernelcore and movablecore is specified,
2402 then kernelcore will be at *least* the specified
2403 value but may be more. If movablecore on its own
2404 is specified, the administrator must be careful
2405 that the amount of memory usable for all allocations
2406 is not too small.
2407
2408 movable_node [KNL,X86] Boot-time switch to enable the effects
2409 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2410
2411 MTD_Partition= [MTD]
2412 Format: <name>,<region-number>,<size>,<offset>
2413
2414 MTD_Region= [MTD] Format:
2415 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2416
2417 mtdparts= [MTD]
2418 See drivers/mtd/cmdlinepart.c.
2419
2420 multitce=off [PPC] This parameter disables the use of the pSeries
2421 firmware feature for updating multiple TCE entries
2422 at a time.
2423
2424 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2425
2426 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2427
2428 boundary - index of last SLC block on Flex-OneNAND.
2429 The remaining blocks are configured as MLC blocks.
2430 lock - Configure if Flex-OneNAND boundary should be locked.
2431 Once locked, the boundary cannot be changed.
2432 1 indicates lock status, 0 indicates unlock status.
2433
2434 mtdset= [ARM]
2435 ARM/S3C2412 JIVE boot control
2436
2437 See arch/arm/mach-s3c2412/mach-jive.c
2438
2439 mtouchusb.raw_coordinates=
2440 [HW] Make the MicroTouch USB driver use raw coordinates
2441 ('y', default) or cooked coordinates ('n')
2442
2443 mtrr_chunk_size=nn[KMG] [X86]
2444 used for mtrr cleanup. It is largest continuous chunk
2445 that could hold holes aka. UC entries.
2446
2447 mtrr_gran_size=nn[KMG] [X86]
2448 Used for mtrr cleanup. It is granularity of mtrr block.
2449 Default is 1.
2450 Large value could prevent small alignment from
2451 using up MTRRs.
2452
2453 mtrr_spare_reg_nr=n [X86]
2454 Format: <integer>
2455 Range: 0,7 : spare reg number
2456 Default : 1
2457 Used for mtrr cleanup. It is spare mtrr entries number.
2458 Set to 2 or more if your graphical card needs more.
2459
2460 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2461
2462 netdev= [NET] Network devices parameters
2463 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2464 Note that mem_start is often overloaded to mean
2465 something different and driver-specific.
2466 This usage is only documented in each driver source
2467 file if at all.
2468
2469 nf_conntrack.acct=
2470 [NETFILTER] Enable connection tracking flow accounting
2471 0 to disable accounting
2472 1 to enable accounting
2473 Default value is 0.
2474
2475 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2476 See Documentation/filesystems/nfs/nfsroot.txt.
2477
2478 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2479 See Documentation/filesystems/nfs/nfsroot.txt.
2480
2481 nfsrootdebug [NFS] enable nfsroot debugging messages.
2482 See Documentation/filesystems/nfs/nfsroot.txt.
2483
2484 nfs.callback_nr_threads=
2485 [NFSv4] set the total number of threads that the
2486 NFS client will assign to service NFSv4 callback
2487 requests.
2488
2489 nfs.callback_tcpport=
2490 [NFS] set the TCP port on which the NFSv4 callback
2491 channel should listen.
2492
2493 nfs.cache_getent=
2494 [NFS] sets the pathname to the program which is used
2495 to update the NFS client cache entries.
2496
2497 nfs.cache_getent_timeout=
2498 [NFS] sets the timeout after which an attempt to
2499 update a cache entry is deemed to have failed.
2500
2501 nfs.idmap_cache_timeout=
2502 [NFS] set the maximum lifetime for idmapper cache
2503 entries.
2504
2505 nfs.enable_ino64=
2506 [NFS] enable 64-bit inode numbers.
2507 If zero, the NFS client will fake up a 32-bit inode
2508 number for the readdir() and stat() syscalls instead
2509 of returning the full 64-bit number.
2510 The default is to return 64-bit inode numbers.
2511
2512 nfs.max_session_cb_slots=
2513 [NFSv4.1] Sets the maximum number of session
2514 slots the client will assign to the callback
2515 channel. This determines the maximum number of
2516 callbacks the client will process in parallel for
2517 a particular server.
2518
2519 nfs.max_session_slots=
2520 [NFSv4.1] Sets the maximum number of session slots
2521 the client will attempt to negotiate with the server.
2522 This limits the number of simultaneous RPC requests
2523 that the client can send to the NFSv4.1 server.
2524 Note that there is little point in setting this
2525 value higher than the max_tcp_slot_table_limit.
2526
2527 nfs.nfs4_disable_idmapping=
2528 [NFSv4] When set to the default of '1', this option
2529 ensures that both the RPC level authentication
2530 scheme and the NFS level operations agree to use
2531 numeric uids/gids if the mount is using the
2532 'sec=sys' security flavour. In effect it is
2533 disabling idmapping, which can make migration from
2534 legacy NFSv2/v3 systems to NFSv4 easier.
2535 Servers that do not support this mode of operation
2536 will be autodetected by the client, and it will fall
2537 back to using the idmapper.
2538 To turn off this behaviour, set the value to '0'.
2539 nfs.nfs4_unique_id=
2540 [NFS4] Specify an additional fixed unique ident-
2541 ification string that NFSv4 clients can insert into
2542 their nfs_client_id4 string. This is typically a
2543 UUID that is generated at system install time.
2544
2545 nfs.send_implementation_id =
2546 [NFSv4.1] Send client implementation identification
2547 information in exchange_id requests.
2548 If zero, no implementation identification information
2549 will be sent.
2550 The default is to send the implementation identification
2551 information.
2552
2553 nfs.recover_lost_locks =
2554 [NFSv4] Attempt to recover locks that were lost due
2555 to a lease timeout on the server. Please note that
2556 doing this risks data corruption, since there are
2557 no guarantees that the file will remain unchanged
2558 after the locks are lost.
2559 If you want to enable the kernel legacy behaviour of
2560 attempting to recover these locks, then set this
2561 parameter to '1'.
2562 The default parameter value of '0' causes the kernel
2563 not to attempt recovery of lost locks.
2564
2565 nfs4.layoutstats_timer =
2566 [NFSv4.2] Change the rate at which the kernel sends
2567 layoutstats to the pNFS metadata server.
2568
2569 Setting this to value to 0 causes the kernel to use
2570 whatever value is the default set by the layout
2571 driver. A non-zero value sets the minimum interval
2572 in seconds between layoutstats transmissions.
2573
2574 nfsd.nfs4_disable_idmapping=
2575 [NFSv4] When set to the default of '1', the NFSv4
2576 server will return only numeric uids and gids to
2577 clients using auth_sys, and will accept numeric uids
2578 and gids from such clients. This is intended to ease
2579 migration from NFSv2/v3.
2580
2581 objlayoutdriver.osd_login_prog=
2582 [NFS] [OBJLAYOUT] sets the pathname to the program which
2583 is used to automatically discover and login into new
2584 osd-targets. Please see:
2585 Documentation/filesystems/pnfs.txt for more explanations
2586
2587 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2588 when a NMI is triggered.
2589 Format: [state][,regs][,debounce][,die]
2590
2591 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2592 Format: [panic,][nopanic,][num]
2593 Valid num: 0 or 1
2594 0 - turn hardlockup detector in nmi_watchdog off
2595 1 - turn hardlockup detector in nmi_watchdog on
2596 When panic is specified, panic when an NMI watchdog
2597 timeout occurs (or 'nopanic' to override the opposite
2598 default). To disable both hard and soft lockup detectors,
2599 please see 'nowatchdog'.
2600 This is useful when you use a panic=... timeout and
2601 need the box quickly up again.
2602
2603 netpoll.carrier_timeout=
2604 [NET] Specifies amount of time (in seconds) that
2605 netpoll should wait for a carrier. By default netpoll
2606 waits 4 seconds.
2607
2608 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2609 emulation library even if a 387 maths coprocessor
2610 is present.
2611
2612 no_console_suspend
2613 [HW] Never suspend the console
2614 Disable suspending of consoles during suspend and
2615 hibernate operations. Once disabled, debugging
2616 messages can reach various consoles while the rest
2617 of the system is being put to sleep (ie, while
2618 debugging driver suspend/resume hooks). This may
2619 not work reliably with all consoles, but is known
2620 to work with serial and VGA consoles.
2621 To facilitate more flexible debugging, we also add
2622 console_suspend, a printk module parameter to control
2623 it. Users could use console_suspend (usually
2624 /sys/module/printk/parameters/console_suspend) to
2625 turn on/off it dynamically.
2626
2627 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2628 caches in the slab allocator. Saves per-node memory,
2629 but will impact performance.
2630
2631 noalign [KNL,ARM]
2632
2633 noapic [SMP,APIC] Tells the kernel to not make use of any
2634 IOAPICs that may be present in the system.
2635
2636 noautogroup Disable scheduler automatic task group creation.
2637
2638 nobats [PPC] Do not use BATs for mapping kernel lowmem
2639 on "Classic" PPC cores.
2640
2641 nocache [ARM]
2642
2643 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2644
2645 nodelayacct [KNL] Disable per-task delay accounting
2646
2647 nodsp [SH] Disable hardware DSP at boot time.
2648
2649 noefi Disable EFI runtime services support.
2650
2651 noexec [IA-64]
2652
2653 noexec [X86]
2654 On X86-32 available only on PAE configured kernels.
2655 noexec=on: enable non-executable mappings (default)
2656 noexec=off: disable non-executable mappings
2657
2658 nosmap [X86]
2659 Disable SMAP (Supervisor Mode Access Prevention)
2660 even if it is supported by processor.
2661
2662 nosmep [X86]
2663 Disable SMEP (Supervisor Mode Execution Prevention)
2664 even if it is supported by processor.
2665
2666 noexec32 [X86-64]
2667 This affects only 32-bit executables.
2668 noexec32=on: enable non-executable mappings (default)
2669 read doesn't imply executable mappings
2670 noexec32=off: disable non-executable mappings
2671 read implies executable mappings
2672
2673 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2674
2675 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2676 register save and restore. The kernel will only save
2677 legacy floating-point registers on task switch.
2678
2679 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2680
2681 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2682 Equivalent to smt=1.
2683
2684 noxsave [BUGS=X86] Disables x86 extended register state save
2685 and restore using xsave. The kernel will fallback to
2686 enabling legacy floating-point and sse state.
2687
2688 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2689 register states. The kernel will fall back to use
2690 xsave to save the states. By using this parameter,
2691 performance of saving the states is degraded because
2692 xsave doesn't support modified optimization while
2693 xsaveopt supports it on xsaveopt enabled systems.
2694
2695 noxsaves [X86] Disables xsaves and xrstors used in saving and
2696 restoring x86 extended register state in compacted
2697 form of xsave area. The kernel will fall back to use
2698 xsaveopt and xrstor to save and restore the states
2699 in standard form of xsave area. By using this
2700 parameter, xsave area per process might occupy more
2701 memory on xsaves enabled systems.
2702
2703 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2704 wfi(ARM) instruction doesn't work correctly and not to
2705 use it. This is also useful when using JTAG debugger.
2706
2707 no_file_caps Tells the kernel not to honor file capabilities. The
2708 only way then for a file to be executed with privilege
2709 is to be setuid root or executed by root.
2710
2711 nohalt [IA-64] Tells the kernel not to use the power saving
2712 function PAL_HALT_LIGHT when idle. This increases
2713 power-consumption. On the positive side, it reduces
2714 interrupt wake-up latency, which may improve performance
2715 in certain environments such as networked servers or
2716 real-time systems.
2717
2718 nohibernate [HIBERNATION] Disable hibernation and resume.
2719
2720 nohz= [KNL] Boottime enable/disable dynamic ticks
2721 Valid arguments: on, off
2722 Default: on
2723
2724 nohz_full= [KNL,BOOT]
2725 The argument is a cpu list, as described above.
2726 In kernels built with CONFIG_NO_HZ_FULL=y, set
2727 the specified list of CPUs whose tick will be stopped
2728 whenever possible. The boot CPU will be forced outside
2729 the range to maintain the timekeeping.
2730 The CPUs in this range must also be included in the
2731 rcu_nocbs= set.
2732
2733 noiotrap [SH] Disables trapped I/O port accesses.
2734
2735 noirqdebug [X86-32] Disables the code which attempts to detect and
2736 disable unhandled interrupt sources.
2737
2738 no_timer_check [X86,APIC] Disables the code which tests for
2739 broken timer IRQ sources.
2740
2741 noisapnp [ISAPNP] Disables ISA PnP code.
2742
2743 noinitrd [RAM] Tells the kernel not to load any configured
2744 initial RAM disk.
2745
2746 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2747 remapping.
2748 [Deprecated - use intremap=off]
2749
2750 nointroute [IA-64]
2751
2752 noinvpcid [X86] Disable the INVPCID cpu feature.
2753
2754 nojitter [IA-64] Disables jitter checking for ITC timers.
2755
2756 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2757
2758 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2759 fault handling.
2760
2761 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2762 steal time is computed, but won't influence scheduler
2763 behaviour
2764
2765 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2766
2767 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2768
2769 noltlbs [PPC] Do not use large page/tlb entries for kernel
2770 lowmem mapping on PPC40x and PPC8xx
2771
2772 nomca [IA-64] Disable machine check abort handling
2773
2774 nomce [X86-32] Disable Machine Check Exception
2775
2776 nomfgpt [X86-32] Disable Multi-Function General Purpose
2777 Timer usage (for AMD Geode machines).
2778
2779 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2780 shutdown the other cpus. Instead use the REBOOT_VECTOR
2781 irq.
2782
2783 nomodule Disable module load
2784
2785 nopat [X86] Disable PAT (page attribute table extension of
2786 pagetables) support.
2787
2788 norandmaps Don't use address space randomization. Equivalent to
2789 echo 0 > /proc/sys/kernel/randomize_va_space
2790
2791 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2792
2793 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2794 with UP alternatives
2795
2796 nordrand [X86] Disable kernel use of the RDRAND and
2797 RDSEED instructions even if they are supported
2798 by the processor. RDRAND and RDSEED are still
2799 available to user space applications.
2800
2801 noresume [SWSUSP] Disables resume and restores original swap
2802 space.
2803
2804 no-scroll [VGA] Disables scrollback.
2805 This is required for the Braillex ib80-piezo Braille
2806 reader made by F.H. Papenmeier (Germany).
2807
2808 nosbagart [IA-64]
2809
2810 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2811
2812 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2813 and disable the IO APIC. legacy for "maxcpus=0".
2814
2815 nosoftlockup [KNL] Disable the soft-lockup detector.
2816
2817 nosync [HW,M68K] Disables sync negotiation for all devices.
2818
2819 notsc [BUGS=X86-32] Disable Time Stamp Counter
2820
2821 nowatchdog [KNL] Disable both lockup detectors, i.e.
2822 soft-lockup and NMI watchdog (hard-lockup).
2823
2824 nowb [ARM]
2825
2826 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2827
2828 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2829 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2830 Some features depend on CPU0. Known dependencies are:
2831 1. Resume from suspend/hibernate depends on CPU0.
2832 Suspend/hibernate will fail if CPU0 is offline and you
2833 need to online CPU0 before suspend/hibernate.
2834 2. PIC interrupts also depend on CPU0. CPU0 can't be
2835 removed if a PIC interrupt is detected.
2836 It's said poweroff/reboot may depend on CPU0 on some
2837 machines although I haven't seen such issues so far
2838 after CPU0 is offline on a few tested machines.
2839 If the dependencies are under your control, you can
2840 turn on cpu0_hotplug.
2841
2842 nptcg= [IA-64] Override max number of concurrent global TLB
2843 purges which is reported from either PAL_VM_SUMMARY or
2844 SAL PALO.
2845
2846 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2847 could support. nr_cpus=n : n >= 1 limits the kernel to
2848 support 'n' processors. It could be larger than the
2849 number of already plugged CPU during bootup, later in
2850 runtime you can physically add extra cpu until it reaches
2851 n. So during boot up some boot time memory for per-cpu
2852 variables need be pre-allocated for later physical cpu
2853 hot plugging.
2854
2855 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2856
2857 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2858 Allowed values are enable and disable
2859
2860 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2861 one of ['zone', 'node', 'default'] can be specified
2862 This can be set from sysctl after boot.
2863 See Documentation/sysctl/vm.txt for details.
2864
2865 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2866 See Documentation/debugging-via-ohci1394.txt for more
2867 info.
2868
2869 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2870 Rather than timing out after 20 ms if an EC
2871 command is not properly ACKed, override the length
2872 of the timeout. We have interrupts disabled while
2873 waiting for the ACK, so if this is set too high
2874 interrupts *may* be lost!
2875
2876 omap_mux= [OMAP] Override bootloader pin multiplexing.
2877 Format: <mux_mode0.mode_name=value>...
2878 For example, to override I2C bus2:
2879 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2880
2881 oprofile.timer= [HW]
2882 Use timer interrupt instead of performance counters
2883
2884 oprofile.cpu_type= Force an oprofile cpu type
2885 This might be useful if you have an older oprofile
2886 userland or if you want common events.
2887 Format: { arch_perfmon }
2888 arch_perfmon: [X86] Force use of architectural
2889 perfmon on Intel CPUs instead of the
2890 CPU specific event set.
2891 timer: [X86] Force use of architectural NMI
2892 timer mode (see also oprofile.timer
2893 for generic hr timer mode)
2894
2895 oops=panic Always panic on oopses. Default is to just kill the
2896 process, but there is a small probability of
2897 deadlocking the machine.
2898 This will also cause panics on machine check exceptions.
2899 Useful together with panic=30 to trigger a reboot.
2900
2901 OSS [HW,OSS]
2902 See Documentation/sound/oss/oss-parameters.txt
2903
2904 page_owner= [KNL] Boot-time page_owner enabling option.
2905 Storage of the information about who allocated
2906 each page is disabled in default. With this switch,
2907 we can turn it on.
2908 on: enable the feature
2909
2910 page_poison= [KNL] Boot-time parameter changing the state of
2911 poisoning on the buddy allocator.
2912 off: turn off poisoning
2913 on: turn on poisoning
2914
2915 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2916 timeout > 0: seconds before rebooting
2917 timeout = 0: wait forever
2918 timeout < 0: reboot immediately
2919 Format: <timeout>
2920
2921 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2922 on a WARN().
2923
2924 crash_kexec_post_notifiers
2925 Run kdump after running panic-notifiers and dumping
2926 kmsg. This only for the users who doubt kdump always
2927 succeeds in any situation.
2928 Note that this also increases risks of kdump failure,
2929 because some panic notifiers can make the crashed
2930 kernel more unstable.
2931
2932 parkbd.port= [HW] Parallel port number the keyboard adapter is
2933 connected to, default is 0.
2934 Format: <parport#>
2935 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2936 0 for XT, 1 for AT (default is AT).
2937 Format: <mode>
2938
2939 parport= [HW,PPT] Specify parallel ports. 0 disables.
2940 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2941 Use 'auto' to force the driver to use any
2942 IRQ/DMA settings detected (the default is to
2943 ignore detected IRQ/DMA settings because of
2944 possible conflicts). You can specify the base
2945 address, IRQ, and DMA settings; IRQ and DMA
2946 should be numbers, or 'auto' (for using detected
2947 settings on that particular port), or 'nofifo'
2948 (to avoid using a FIFO even if it is detected).
2949 Parallel ports are assigned in the order they
2950 are specified on the command line, starting
2951 with parport0.
2952
2953 parport_init_mode= [HW,PPT]
2954 Configure VIA parallel port to operate in
2955 a specific mode. This is necessary on Pegasos
2956 computer where firmware has no options for setting
2957 up parallel port mode and sets it to spp.
2958 Currently this function knows 686a and 8231 chips.
2959 Format: [spp|ps2|epp|ecp|ecpepp]
2960
2961 pause_on_oops=
2962 Halt all CPUs after the first oops has been printed for
2963 the specified number of seconds. This is to be used if
2964 your oopses keep scrolling off the screen.
2965
2966 pcbit= [HW,ISDN]
2967
2968 pcd. [PARIDE]
2969 See header of drivers/block/paride/pcd.c.
2970 See also Documentation/blockdev/paride.txt.
2971
2972 pci=option[,option...] [PCI] various PCI subsystem options:
2973 earlydump [X86] dump PCI config space before the kernel
2974 changes anything
2975 off [X86] don't probe for the PCI bus
2976 bios [X86-32] force use of PCI BIOS, don't access
2977 the hardware directly. Use this if your machine
2978 has a non-standard PCI host bridge.
2979 nobios [X86-32] disallow use of PCI BIOS, only direct
2980 hardware access methods are allowed. Use this
2981 if you experience crashes upon bootup and you
2982 suspect they are caused by the BIOS.
2983 conf1 [X86] Force use of PCI Configuration Access
2984 Mechanism 1 (config address in IO port 0xCF8,
2985 data in IO port 0xCFC, both 32-bit).
2986 conf2 [X86] Force use of PCI Configuration Access
2987 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2988 the function, IO port 0xCFA, also 8-bit, sets
2989 bus number. The config space is then accessed
2990 through ports 0xC000-0xCFFF).
2991 See http://wiki.osdev.org/PCI for more info
2992 on the configuration access mechanisms.
2993 noaer [PCIE] If the PCIEAER kernel config parameter is
2994 enabled, this kernel boot option can be used to
2995 disable the use of PCIE advanced error reporting.
2996 nodomains [PCI] Disable support for multiple PCI
2997 root domains (aka PCI segments, in ACPI-speak).
2998 nommconf [X86] Disable use of MMCONFIG for PCI
2999 Configuration
3000 check_enable_amd_mmconf [X86] check for and enable
3001 properly configured MMIO access to PCI
3002 config space on AMD family 10h CPU
3003 nomsi [MSI] If the PCI_MSI kernel config parameter is
3004 enabled, this kernel boot option can be used to
3005 disable the use of MSI interrupts system-wide.
3006 noioapicquirk [APIC] Disable all boot interrupt quirks.
3007 Safety option to keep boot IRQs enabled. This
3008 should never be necessary.
3009 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3010 primary IO-APIC for bridges that cannot disable
3011 boot IRQs. This fixes a source of spurious IRQs
3012 when the system masks IRQs.
3013 noioapicreroute [APIC] Disable workaround that uses the
3014 boot IRQ equivalent of an IRQ that connects to
3015 a chipset where boot IRQs cannot be disabled.
3016 The opposite of ioapicreroute.
3017 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3018 routing table. These calls are known to be buggy
3019 on several machines and they hang the machine
3020 when used, but on other computers it's the only
3021 way to get the interrupt routing table. Try
3022 this option if the kernel is unable to allocate
3023 IRQs or discover secondary PCI buses on your
3024 motherboard.
3025 rom [X86] Assign address space to expansion ROMs.
3026 Use with caution as certain devices share
3027 address decoders between ROMs and other
3028 resources.
3029 norom [X86] Do not assign address space to
3030 expansion ROMs that do not already have
3031 BIOS assigned address ranges.
3032 nobar [X86] Do not assign address space to the
3033 BARs that weren't assigned by the BIOS.
3034 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3035 assigned automatically to PCI devices. You can
3036 make the kernel exclude IRQs of your ISA cards
3037 this way.
3038 pirqaddr=0xAAAAA [X86] Specify the physical address
3039 of the PIRQ table (normally generated
3040 by the BIOS) if it is outside the
3041 F0000h-100000h range.
3042 lastbus=N [X86] Scan all buses thru bus #N. Can be
3043 useful if the kernel is unable to find your
3044 secondary buses and you want to tell it
3045 explicitly which ones they are.
3046 assign-busses [X86] Always assign all PCI bus
3047 numbers ourselves, overriding
3048 whatever the firmware may have done.
3049 usepirqmask [X86] Honor the possible IRQ mask stored
3050 in the BIOS $PIR table. This is needed on
3051 some systems with broken BIOSes, notably
3052 some HP Pavilion N5400 and Omnibook XE3
3053 notebooks. This will have no effect if ACPI
3054 IRQ routing is enabled.
3055 noacpi [X86] Do not use ACPI for IRQ routing
3056 or for PCI scanning.
3057 use_crs [X86] Use PCI host bridge window information
3058 from ACPI. On BIOSes from 2008 or later, this
3059 is enabled by default. If you need to use this,
3060 please report a bug.
3061 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3062 If you need to use this, please report a bug.
3063 routeirq Do IRQ routing for all PCI devices.
3064 This is normally done in pci_enable_device(),
3065 so this option is a temporary workaround
3066 for broken drivers that don't call it.
3067 skip_isa_align [X86] do not align io start addr, so can
3068 handle more pci cards
3069 noearly [X86] Don't do any early type 1 scanning.
3070 This might help on some broken boards which
3071 machine check when some devices' config space
3072 is read. But various workarounds are disabled
3073 and some IOMMU drivers will not work.
3074 bfsort Sort PCI devices into breadth-first order.
3075 This sorting is done to get a device
3076 order compatible with older (<= 2.4) kernels.
3077 nobfsort Don't sort PCI devices into breadth-first order.
3078 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3079 tuning and use the BIOS-configured MPS defaults.
3080 pcie_bus_safe Set every device's MPS to the largest value
3081 supported by all devices below the root complex.
3082 pcie_bus_perf Set device MPS to the largest allowable MPS
3083 based on its parent bus. Also set MRRS (Max
3084 Read Request Size) to the largest supported
3085 value (no larger than the MPS that the device
3086 or bus can support) for best performance.
3087 pcie_bus_peer2peer Set every device's MPS to 128B, which
3088 every device is guaranteed to support. This
3089 configuration allows peer-to-peer DMA between
3090 any pair of devices, possibly at the cost of
3091 reduced performance. This also guarantees
3092 that hot-added devices will work.
3093 cbiosize=nn[KMG] The fixed amount of bus space which is
3094 reserved for the CardBus bridge's IO window.
3095 The default value is 256 bytes.
3096 cbmemsize=nn[KMG] The fixed amount of bus space which is
3097 reserved for the CardBus bridge's memory
3098 window. The default value is 64 megabytes.
3099 resource_alignment=
3100 Format:
3101 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3102 [<order of align>@]pci:<vendor>:<device>\
3103 [:<subvendor>:<subdevice>][; ...]
3104 Specifies alignment and device to reassign
3105 aligned memory resources.
3106 If <order of align> is not specified,
3107 PAGE_SIZE is used as alignment.
3108 PCI-PCI bridge can be specified, if resource
3109 windows need to be expanded.
3110 To specify the alignment for several
3111 instances of a device, the PCI vendor,
3112 device, subvendor, and subdevice may be
3113 specified, e.g., 4096@pci:8086:9c22:103c:198f
3114 ecrc= Enable/disable PCIe ECRC (transaction layer
3115 end-to-end CRC checking).
3116 bios: Use BIOS/firmware settings. This is the
3117 the default.
3118 off: Turn ECRC off
3119 on: Turn ECRC on.
3120 hpiosize=nn[KMG] The fixed amount of bus space which is
3121 reserved for hotplug bridge's IO window.
3122 Default size is 256 bytes.
3123 hpmemsize=nn[KMG] The fixed amount of bus space which is
3124 reserved for hotplug bridge's memory window.
3125 Default size is 2 megabytes.
3126 hpbussize=nn The minimum amount of additional bus numbers
3127 reserved for buses below a hotplug bridge.
3128 Default is 1.
3129 realloc= Enable/disable reallocating PCI bridge resources
3130 if allocations done by BIOS are too small to
3131 accommodate resources required by all child
3132 devices.
3133 off: Turn realloc off
3134 on: Turn realloc on
3135 realloc same as realloc=on
3136 noari do not use PCIe ARI.
3137 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3138 only look for one device below a PCIe downstream
3139 port.
3140
3141 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3142 Management.
3143 off Disable ASPM.
3144 force Enable ASPM even on devices that claim not to support it.
3145 WARNING: Forcing ASPM on may cause system lockups.
3146
3147 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3148 nomsi Do not use MSI for PCI Express Native Hotplug (this
3149 makes all PCIe ports use INTx for hotplug services).
3150
3151 pcie_ports= [PCIE] PCIe ports handling:
3152 auto Ask the BIOS whether or not to use native PCIe services
3153 associated with PCIe ports (PME, hot-plug, AER). Use
3154 them only if that is allowed by the BIOS.
3155 native Use native PCIe services associated with PCIe ports
3156 unconditionally.
3157 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3158 ports driver.
3159
3160 pcie_port_pm= [PCIE] PCIe port power management handling:
3161 off Disable power management of all PCIe ports
3162 force Forcibly enable power management of all PCIe ports
3163
3164 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3165 nomsi Do not use MSI for native PCIe PME signaling (this makes
3166 all PCIe root ports use INTx for all services).
3167
3168 pcmv= [HW,PCMCIA] BadgePAD 4
3169
3170 pd_ignore_unused
3171 [PM]
3172 Keep all power-domains already enabled by bootloader on,
3173 even if no driver has claimed them. This is useful
3174 for debug and development, but should not be
3175 needed on a platform with proper driver support.
3176
3177 pd. [PARIDE]
3178 See Documentation/blockdev/paride.txt.
3179
3180 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3181 boot time.
3182 Format: { 0 | 1 }
3183 See arch/parisc/kernel/pdc_chassis.c
3184
3185 percpu_alloc= Select which percpu first chunk allocator to use.
3186 Currently supported values are "embed" and "page".
3187 Archs may support subset or none of the selections.
3188 See comments in mm/percpu.c for details on each
3189 allocator. This parameter is primarily for debugging
3190 and performance comparison.
3191
3192 pf. [PARIDE]
3193 See Documentation/blockdev/paride.txt.
3194
3195 pg. [PARIDE]
3196 See Documentation/blockdev/paride.txt.
3197
3198 pirq= [SMP,APIC] Manual mp-table setup
3199 See Documentation/x86/i386/IO-APIC.txt.
3200
3201 plip= [PPT,NET] Parallel port network link
3202 Format: { parport<nr> | timid | 0 }
3203 See also Documentation/parport.txt.
3204
3205 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3206 Override pmtimer IOPort with a hex value.
3207 e.g. pmtmr=0x508
3208
3209 pnp.debug=1 [PNP]
3210 Enable PNP debug messages (depends on the
3211 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3212 via /sys/module/pnp/parameters/debug. We always show
3213 current resource usage; turning this on also shows
3214 possible settings and some assignment information.
3215
3216 pnpacpi= [ACPI]
3217 { off }
3218
3219 pnpbios= [ISAPNP]
3220 { on | off | curr | res | no-curr | no-res }
3221
3222 pnp_reserve_irq=
3223 [ISAPNP] Exclude IRQs for the autoconfiguration
3224
3225 pnp_reserve_dma=
3226 [ISAPNP] Exclude DMAs for the autoconfiguration
3227
3228 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3229 Ranges are in pairs (I/O port base and size).
3230
3231 pnp_reserve_mem=
3232 [ISAPNP] Exclude memory regions for the
3233 autoconfiguration.
3234 Ranges are in pairs (memory base and size).
3235
3236 ports= [IP_VS_FTP] IPVS ftp helper module
3237 Default is 21.
3238 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3239 may be specified.
3240 Format: <port>,<port>....
3241
3242 ppc_strict_facility_enable
3243 [PPC] This option catches any kernel floating point,
3244 Altivec, VSX and SPE outside of regions specifically
3245 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3246 There is some performance impact when enabling this.
3247
3248 print-fatal-signals=
3249 [KNL] debug: print fatal signals
3250
3251 If enabled, warn about various signal handling
3252 related application anomalies: too many signals,
3253 too many POSIX.1 timers, fatal signals causing a
3254 coredump - etc.
3255
3256 If you hit the warning due to signal overflow,
3257 you might want to try "ulimit -i unlimited".
3258
3259 default: off.
3260
3261 printk.always_kmsg_dump=
3262 Trigger kmsg_dump for cases other than kernel oops or
3263 panics
3264 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3265 default: disabled
3266
3267 printk.devkmsg={on,off,ratelimit}
3268 Control writing to /dev/kmsg.
3269 on - unlimited logging to /dev/kmsg from userspace
3270 off - logging to /dev/kmsg disabled
3271 ratelimit - ratelimit the logging
3272 Default: ratelimit
3273
3274 printk.time= Show timing data prefixed to each printk message line
3275 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3276
3277 processor.max_cstate= [HW,ACPI]
3278 Limit processor to maximum C-state
3279 max_cstate=9 overrides any DMI blacklist limit.
3280
3281 processor.nocst [HW,ACPI]
3282 Ignore the _CST method to determine C-states,
3283 instead using the legacy FADT method
3284
3285 profile= [KNL] Enable kernel profiling via /proc/profile
3286 Format: [schedule,]<number>
3287 Param: "schedule" - profile schedule points.
3288 Param: <number> - step/bucket size as a power of 2 for
3289 statistical time based profiling.
3290 Param: "sleep" - profile D-state sleeping (millisecs).
3291 Requires CONFIG_SCHEDSTATS
3292 Param: "kvm" - profile VM exits.
3293
3294 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3295 before loading.
3296 See Documentation/blockdev/ramdisk.txt.
3297
3298 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3299 probe for; one of (bare|imps|exps|lifebook|any).
3300 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3301 per second.
3302 psmouse.resetafter= [HW,MOUSE]
3303 Try to reset the device after so many bad packets
3304 (0 = never).
3305 psmouse.resolution=
3306 [HW,MOUSE] Set desired mouse resolution, in dpi.
3307 psmouse.smartscroll=
3308 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3309 0 = disabled, 1 = enabled (default).
3310
3311 pstore.backend= Specify the name of the pstore backend to use
3312
3313 pt. [PARIDE]
3314 See Documentation/blockdev/paride.txt.
3315
3316 pty.legacy_count=
3317 [KNL] Number of legacy pty's. Overwrites compiled-in
3318 default number.
3319
3320 quiet [KNL] Disable most log messages
3321
3322 r128= [HW,DRM]
3323
3324 raid= [HW,RAID]
3325 See Documentation/md.txt.
3326
3327 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3328 See Documentation/blockdev/ramdisk.txt.
3329
3330 rcu_nocbs= [KNL]
3331 The argument is a cpu list, as described above.
3332
3333 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3334 the specified list of CPUs to be no-callback CPUs.
3335 Invocation of these CPUs' RCU callbacks will
3336 be offloaded to "rcuox/N" kthreads created for
3337 that purpose, where "x" is "b" for RCU-bh, "p"
3338 for RCU-preempt, and "s" for RCU-sched, and "N"
3339 is the CPU number. This reduces OS jitter on the
3340 offloaded CPUs, which can be useful for HPC and
3341 real-time workloads. It can also improve energy
3342 efficiency for asymmetric multiprocessors.
3343
3344 rcu_nocb_poll [KNL]
3345 Rather than requiring that offloaded CPUs
3346 (specified by rcu_nocbs= above) explicitly
3347 awaken the corresponding "rcuoN" kthreads,
3348 make these kthreads poll for callbacks.
3349 This improves the real-time response for the
3350 offloaded CPUs by relieving them of the need to
3351 wake up the corresponding kthread, but degrades
3352 energy efficiency by requiring that the kthreads
3353 periodically wake up to do the polling.
3354
3355 rcutree.blimit= [KNL]
3356 Set maximum number of finished RCU callbacks to
3357 process in one batch.
3358
3359 rcutree.dump_tree= [KNL]
3360 Dump the structure of the rcu_node combining tree
3361 out at early boot. This is used for diagnostic
3362 purposes, to verify correct tree setup.
3363
3364 rcutree.gp_cleanup_delay= [KNL]
3365 Set the number of jiffies to delay each step of
3366 RCU grace-period cleanup. This only has effect
3367 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3368
3369 rcutree.gp_init_delay= [KNL]
3370 Set the number of jiffies to delay each step of
3371 RCU grace-period initialization. This only has
3372 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3373 is set.
3374
3375 rcutree.gp_preinit_delay= [KNL]
3376 Set the number of jiffies to delay each step of
3377 RCU grace-period pre-initialization, that is,
3378 the propagation of recent CPU-hotplug changes up
3379 the rcu_node combining tree. This only has effect
3380 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3381
3382 rcutree.rcu_fanout_exact= [KNL]
3383 Disable autobalancing of the rcu_node combining
3384 tree. This is used by rcutorture, and might
3385 possibly be useful for architectures having high
3386 cache-to-cache transfer latencies.
3387
3388 rcutree.rcu_fanout_leaf= [KNL]
3389 Change the number of CPUs assigned to each
3390 leaf rcu_node structure. Useful for very
3391 large systems, which will choose the value 64,
3392 and for NUMA systems with large remote-access
3393 latencies, which will choose a value aligned
3394 with the appropriate hardware boundaries.
3395
3396 rcutree.jiffies_till_sched_qs= [KNL]
3397 Set required age in jiffies for a
3398 given grace period before RCU starts
3399 soliciting quiescent-state help from
3400 rcu_note_context_switch().
3401
3402 rcutree.jiffies_till_first_fqs= [KNL]
3403 Set delay from grace-period initialization to
3404 first attempt to force quiescent states.
3405 Units are jiffies, minimum value is zero,
3406 and maximum value is HZ.
3407
3408 rcutree.jiffies_till_next_fqs= [KNL]
3409 Set delay between subsequent attempts to force
3410 quiescent states. Units are jiffies, minimum
3411 value is one, and maximum value is HZ.
3412
3413 rcutree.kthread_prio= [KNL,BOOT]
3414 Set the SCHED_FIFO priority of the RCU per-CPU
3415 kthreads (rcuc/N). This value is also used for
3416 the priority of the RCU boost threads (rcub/N)
3417 and for the RCU grace-period kthreads (rcu_bh,
3418 rcu_preempt, and rcu_sched). If RCU_BOOST is
3419 set, valid values are 1-99 and the default is 1
3420 (the least-favored priority). Otherwise, when
3421 RCU_BOOST is not set, valid values are 0-99 and
3422 the default is zero (non-realtime operation).
3423
3424 rcutree.rcu_nocb_leader_stride= [KNL]
3425 Set the number of NOCB kthread groups, which
3426 defaults to the square root of the number of
3427 CPUs. Larger numbers reduces the wakeup overhead
3428 on the per-CPU grace-period kthreads, but increases
3429 that same overhead on each group's leader.
3430
3431 rcutree.qhimark= [KNL]
3432 Set threshold of queued RCU callbacks beyond which
3433 batch limiting is disabled.
3434
3435 rcutree.qlowmark= [KNL]
3436 Set threshold of queued RCU callbacks below which
3437 batch limiting is re-enabled.
3438
3439 rcutree.rcu_idle_gp_delay= [KNL]
3440 Set wakeup interval for idle CPUs that have
3441 RCU callbacks (RCU_FAST_NO_HZ=y).
3442
3443 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3444 Set wakeup interval for idle CPUs that have
3445 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3446 Lazy RCU callbacks are those which RCU can
3447 prove do nothing more than free memory.
3448
3449 rcuperf.gp_exp= [KNL]
3450 Measure performance of expedited synchronous
3451 grace-period primitives.
3452
3453 rcuperf.holdoff= [KNL]
3454 Set test-start holdoff period. The purpose of
3455 this parameter is to delay the start of the
3456 test until boot completes in order to avoid
3457 interference.
3458
3459 rcuperf.nreaders= [KNL]
3460 Set number of RCU readers. The value -1 selects
3461 N, where N is the number of CPUs. A value
3462 "n" less than -1 selects N-n+1, where N is again
3463 the number of CPUs. For example, -2 selects N
3464 (the number of CPUs), -3 selects N+1, and so on.
3465 A value of "n" less than or equal to -N selects
3466 a single reader.
3467
3468 rcuperf.nwriters= [KNL]
3469 Set number of RCU writers. The values operate
3470 the same as for rcuperf.nreaders.
3471 N, where N is the number of CPUs
3472
3473 rcuperf.perf_runnable= [BOOT]
3474 Start rcuperf running at boot time.
3475
3476 rcuperf.shutdown= [KNL]
3477 Shut the system down after performance tests
3478 complete. This is useful for hands-off automated
3479 testing.
3480
3481 rcuperf.perf_type= [KNL]
3482 Specify the RCU implementation to test.
3483
3484 rcuperf.verbose= [KNL]
3485 Enable additional printk() statements.
3486
3487 rcutorture.cbflood_inter_holdoff= [KNL]
3488 Set holdoff time (jiffies) between successive
3489 callback-flood tests.
3490
3491 rcutorture.cbflood_intra_holdoff= [KNL]
3492 Set holdoff time (jiffies) between successive
3493 bursts of callbacks within a given callback-flood
3494 test.
3495
3496 rcutorture.cbflood_n_burst= [KNL]
3497 Set the number of bursts making up a given
3498 callback-flood test. Set this to zero to
3499 disable callback-flood testing.
3500
3501 rcutorture.cbflood_n_per_burst= [KNL]
3502 Set the number of callbacks to be registered
3503 in a given burst of a callback-flood test.
3504
3505 rcutorture.fqs_duration= [KNL]
3506 Set duration of force_quiescent_state bursts
3507 in microseconds.
3508
3509 rcutorture.fqs_holdoff= [KNL]
3510 Set holdoff time within force_quiescent_state bursts
3511 in microseconds.
3512
3513 rcutorture.fqs_stutter= [KNL]
3514 Set wait time between force_quiescent_state bursts
3515 in seconds.
3516
3517 rcutorture.gp_cond= [KNL]
3518 Use conditional/asynchronous update-side
3519 primitives, if available.
3520
3521 rcutorture.gp_exp= [KNL]
3522 Use expedited update-side primitives, if available.
3523
3524 rcutorture.gp_normal= [KNL]
3525 Use normal (non-expedited) asynchronous
3526 update-side primitives, if available.
3527
3528 rcutorture.gp_sync= [KNL]
3529 Use normal (non-expedited) synchronous
3530 update-side primitives, if available. If all
3531 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3532 rcutorture.gp_normal=, and rcutorture.gp_sync=
3533 are zero, rcutorture acts as if is interpreted
3534 they are all non-zero.
3535
3536 rcutorture.n_barrier_cbs= [KNL]
3537 Set callbacks/threads for rcu_barrier() testing.
3538
3539 rcutorture.nfakewriters= [KNL]
3540 Set number of concurrent RCU writers. These just
3541 stress RCU, they don't participate in the actual
3542 test, hence the "fake".
3543
3544 rcutorture.nreaders= [KNL]
3545 Set number of RCU readers. The value -1 selects
3546 N-1, where N is the number of CPUs. A value
3547 "n" less than -1 selects N-n-2, where N is again
3548 the number of CPUs. For example, -2 selects N
3549 (the number of CPUs), -3 selects N+1, and so on.
3550
3551 rcutorture.object_debug= [KNL]
3552 Enable debug-object double-call_rcu() testing.
3553
3554 rcutorture.onoff_holdoff= [KNL]
3555 Set time (s) after boot for CPU-hotplug testing.
3556
3557 rcutorture.onoff_interval= [KNL]
3558 Set time (s) between CPU-hotplug operations, or
3559 zero to disable CPU-hotplug testing.
3560
3561 rcutorture.shuffle_interval= [KNL]
3562 Set task-shuffle interval (s). Shuffling tasks
3563 allows some CPUs to go into dyntick-idle mode
3564 during the rcutorture test.
3565
3566 rcutorture.shutdown_secs= [KNL]
3567 Set time (s) after boot system shutdown. This
3568 is useful for hands-off automated testing.
3569
3570 rcutorture.stall_cpu= [KNL]
3571 Duration of CPU stall (s) to test RCU CPU stall
3572 warnings, zero to disable.
3573
3574 rcutorture.stall_cpu_holdoff= [KNL]
3575 Time to wait (s) after boot before inducing stall.
3576
3577 rcutorture.stat_interval= [KNL]
3578 Time (s) between statistics printk()s.
3579
3580 rcutorture.stutter= [KNL]
3581 Time (s) to stutter testing, for example, specifying
3582 five seconds causes the test to run for five seconds,
3583 wait for five seconds, and so on. This tests RCU's
3584 ability to transition abruptly to and from idle.
3585
3586 rcutorture.test_boost= [KNL]
3587 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3588 "Maybe" means test if the RCU implementation
3589 under test support RCU priority boosting.
3590
3591 rcutorture.test_boost_duration= [KNL]
3592 Duration (s) of each individual boost test.
3593
3594 rcutorture.test_boost_interval= [KNL]
3595 Interval (s) between each boost test.
3596
3597 rcutorture.test_no_idle_hz= [KNL]
3598 Test RCU's dyntick-idle handling. See also the
3599 rcutorture.shuffle_interval parameter.
3600
3601 rcutorture.torture_runnable= [BOOT]
3602 Start rcutorture running at boot time.
3603
3604 rcutorture.torture_type= [KNL]
3605 Specify the RCU implementation to test.
3606
3607 rcutorture.verbose= [KNL]
3608 Enable additional printk() statements.
3609
3610 rcupdate.rcu_cpu_stall_suppress= [KNL]
3611 Suppress RCU CPU stall warning messages.
3612
3613 rcupdate.rcu_cpu_stall_timeout= [KNL]
3614 Set timeout for RCU CPU stall warning messages.
3615
3616 rcupdate.rcu_expedited= [KNL]
3617 Use expedited grace-period primitives, for
3618 example, synchronize_rcu_expedited() instead
3619 of synchronize_rcu(). This reduces latency,
3620 but can increase CPU utilization, degrade
3621 real-time latency, and degrade energy efficiency.
3622 No effect on CONFIG_TINY_RCU kernels.
3623
3624 rcupdate.rcu_normal= [KNL]
3625 Use only normal grace-period primitives,
3626 for example, synchronize_rcu() instead of
3627 synchronize_rcu_expedited(). This improves
3628 real-time latency, CPU utilization, and
3629 energy efficiency, but can expose users to
3630 increased grace-period latency. This parameter
3631 overrides rcupdate.rcu_expedited. No effect on
3632 CONFIG_TINY_RCU kernels.
3633
3634 rcupdate.rcu_normal_after_boot= [KNL]
3635 Once boot has completed (that is, after
3636 rcu_end_inkernel_boot() has been invoked), use
3637 only normal grace-period primitives. No effect
3638 on CONFIG_TINY_RCU kernels.
3639
3640 rcupdate.rcu_task_stall_timeout= [KNL]
3641 Set timeout in jiffies for RCU task stall warning
3642 messages. Disable with a value less than or equal
3643 to zero.
3644
3645 rcupdate.rcu_self_test= [KNL]
3646 Run the RCU early boot self tests
3647
3648 rcupdate.rcu_self_test_bh= [KNL]
3649 Run the RCU bh early boot self tests
3650
3651 rcupdate.rcu_self_test_sched= [KNL]
3652 Run the RCU sched early boot self tests
3653
3654 rdinit= [KNL]
3655 Format: <full_path>
3656 Run specified binary instead of /init from the ramdisk,
3657 used for early userspace startup. See initrd.
3658
3659 reboot= [KNL]
3660 Format (x86 or x86_64):
3661 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3662 [[,]s[mp]#### \
3663 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3664 [[,]f[orce]
3665 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3666 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3667 reboot_force is either force or not specified,
3668 reboot_cpu is s[mp]#### with #### being the processor
3669 to be used for rebooting.
3670
3671 relax_domain_level=
3672 [KNL, SMP] Set scheduler's default relax_domain_level.
3673 See Documentation/cgroup-v1/cpusets.txt.
3674
3675 relative_sleep_states=
3676 [SUSPEND] Use sleep state labeling where the deepest
3677 state available other than hibernation is always "mem".
3678 Format: { "0" | "1" }
3679 0 -- Traditional sleep state labels.
3680 1 -- Relative sleep state labels.
3681
3682 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3683
3684 reservetop= [X86-32]
3685 Format: nn[KMG]
3686 Reserves a hole at the top of the kernel virtual
3687 address space.
3688
3689 reservelow= [X86]
3690 Format: nn[K]
3691 Set the amount of memory to reserve for BIOS at
3692 the bottom of the address space.
3693
3694 reset_devices [KNL] Force drivers to reset the underlying device
3695 during initialization.
3696
3697 resume= [SWSUSP]
3698 Specify the partition device for software suspend
3699 Format:
3700 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3701
3702 resume_offset= [SWSUSP]
3703 Specify the offset from the beginning of the partition
3704 given by "resume=" at which the swap header is located,
3705 in <PAGE_SIZE> units (needed only for swap files).
3706 See Documentation/power/swsusp-and-swap-files.txt
3707
3708 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3709 read the resume files
3710
3711 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3712 Useful for devices that are detected asynchronously
3713 (e.g. USB and MMC devices).
3714
3715 hibernate= [HIBERNATION]
3716 noresume Don't check if there's a hibernation image
3717 present during boot.
3718 nocompress Don't compress/decompress hibernation images.
3719 no Disable hibernation and resume.
3720 protect_image Turn on image protection during restoration
3721 (that will set all pages holding image data
3722 during restoration read-only).
3723
3724 retain_initrd [RAM] Keep initrd memory after extraction
3725
3726 rfkill.default_state=
3727 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3728 etc. communication is blocked by default.
3729 1 Unblocked.
3730
3731 rfkill.master_switch_mode=
3732 0 The "airplane mode" button does nothing.
3733 1 The "airplane mode" button toggles between everything
3734 blocked and the previous configuration.
3735 2 The "airplane mode" button toggles between everything
3736 blocked and everything unblocked.
3737
3738 rhash_entries= [KNL,NET]
3739 Set number of hash buckets for route cache
3740
3741 ro [KNL] Mount root device read-only on boot
3742
3743 rodata= [KNL]
3744 on Mark read-only kernel memory as read-only (default).
3745 off Leave read-only kernel memory writable for debugging.
3746
3747 rockchip.usb_uart
3748 Enable the uart passthrough on the designated usb port
3749 on Rockchip SoCs. When active, the signals of the
3750 debug-uart get routed to the D+ and D- pins of the usb
3751 port and the regular usb controller gets disabled.
3752
3753 root= [KNL] Root filesystem
3754 See name_to_dev_t comment in init/do_mounts.c.
3755
3756 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3757 mount the root filesystem
3758
3759 rootflags= [KNL] Set root filesystem mount option string
3760
3761 rootfstype= [KNL] Set root filesystem type
3762
3763 rootwait [KNL] Wait (indefinitely) for root device to show up.
3764 Useful for devices that are detected asynchronously
3765 (e.g. USB and MMC devices).
3766
3767 rproc_mem=nn[KMG][@address]
3768 [KNL,ARM,CMA] Remoteproc physical memory block.
3769 Memory area to be used by remote processor image,
3770 managed by CMA.
3771
3772 rw [KNL] Mount root device read-write on boot
3773
3774 S [KNL] Run init in single mode
3775
3776 s390_iommu= [HW,S390]
3777 Set s390 IOTLB flushing mode
3778 strict
3779 With strict flushing every unmap operation will result in
3780 an IOTLB flush. Default is lazy flushing before reuse,
3781 which is faster.
3782
3783 sa1100ir [NET]
3784 See drivers/net/irda/sa1100_ir.c.
3785
3786 sbni= [NET] Granch SBNI12 leased line adapter
3787
3788 sched_debug [KNL] Enables verbose scheduler debug messages.
3789
3790 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3791 Allowed values are enable and disable. This feature
3792 incurs a small amount of overhead in the scheduler
3793 but is useful for debugging and performance tuning.
3794
3795 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3796 xtime_lock contention on larger systems, and/or RCU lock
3797 contention on all systems with CONFIG_MAXSMP set.
3798 Format: { "0" | "1" }
3799 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3800 1 -- enable.
3801 Note: increases power consumption, thus should only be
3802 enabled if running jitter sensitive (HPC/RT) workloads.
3803
3804 security= [SECURITY] Choose a security module to enable at boot.
3805 If this boot parameter is not specified, only the first
3806 security module asking for security registration will be
3807 loaded. An invalid security module name will be treated
3808 as if no module has been chosen.
3809
3810 selinux= [SELINUX] Disable or enable SELinux at boot time.
3811 Format: { "0" | "1" }
3812 See security/selinux/Kconfig help text.
3813 0 -- disable.
3814 1 -- enable.
3815 Default value is set via kernel config option.
3816 If enabled at boot time, /selinux/disable can be used
3817 later to disable prior to initial policy load.
3818
3819 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3820 Format: { "0" | "1" }
3821 See security/apparmor/Kconfig help text
3822 0 -- disable.
3823 1 -- enable.
3824 Default value is set via kernel config option.
3825
3826 serialnumber [BUGS=X86-32]
3827
3828 shapers= [NET]
3829 Maximal number of shapers.
3830
3831 show_msr= [x86] show boot-time MSR settings
3832 Format: { <integer> }
3833 Show boot-time (BIOS-initialized) MSR settings.
3834 The parameter means the number of CPUs to show,
3835 for example 1 means boot CPU only.
3836
3837 simeth= [IA-64]
3838 simscsi=
3839
3840 slram= [HW,MTD]
3841
3842 slab_nomerge [MM]
3843 Disable merging of slabs with similar size. May be
3844 necessary if there is some reason to distinguish
3845 allocs to different slabs. Debug options disable
3846 merging on their own.
3847 For more information see Documentation/vm/slub.txt.
3848
3849 slab_max_order= [MM, SLAB]
3850 Determines the maximum allowed order for slabs.
3851 A high setting may cause OOMs due to memory
3852 fragmentation. Defaults to 1 for systems with
3853 more than 32MB of RAM, 0 otherwise.
3854
3855 slub_debug[=options[,slabs]] [MM, SLUB]
3856 Enabling slub_debug allows one to determine the
3857 culprit if slab objects become corrupted. Enabling
3858 slub_debug can create guard zones around objects and
3859 may poison objects when not in use. Also tracks the
3860 last alloc / free. For more information see
3861 Documentation/vm/slub.txt.
3862
3863 slub_max_order= [MM, SLUB]
3864 Determines the maximum allowed order for slabs.
3865 A high setting may cause OOMs due to memory
3866 fragmentation. For more information see
3867 Documentation/vm/slub.txt.
3868
3869 slub_min_objects= [MM, SLUB]
3870 The minimum number of objects per slab. SLUB will
3871 increase the slab order up to slub_max_order to
3872 generate a sufficiently large slab able to contain
3873 the number of objects indicated. The higher the number
3874 of objects the smaller the overhead of tracking slabs
3875 and the less frequently locks need to be acquired.
3876 For more information see Documentation/vm/slub.txt.
3877
3878 slub_min_order= [MM, SLUB]
3879 Determines the minimum page order for slabs. Must be
3880 lower than slub_max_order.
3881 For more information see Documentation/vm/slub.txt.
3882
3883 slub_nomerge [MM, SLUB]
3884 Same with slab_nomerge. This is supported for legacy.
3885 See slab_nomerge for more information.
3886
3887 smart2= [HW]
3888 Format: <io1>[,<io2>[,...,<io8>]]
3889
3890 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3891 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3892 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3893 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3894 smsc-ircc2.ircc_irq= [HW] IRQ line
3895 smsc-ircc2.ircc_dma= [HW] DMA channel
3896 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3897 0: Toshiba Satellite 1800 (GP data pin select)
3898 1: Fast pin select (default)
3899 2: ATC IRMode
3900
3901 smt [KNL,S390] Set the maximum number of threads (logical
3902 CPUs) to use per physical CPU on systems capable of
3903 symmetric multithreading (SMT). Will be capped to the
3904 actual hardware limit.
3905 Format: <integer>
3906 Default: -1 (no limit)
3907
3908 softlockup_panic=
3909 [KNL] Should the soft-lockup detector generate panics.
3910 Format: <integer>
3911
3912 softlockup_all_cpu_backtrace=
3913 [KNL] Should the soft-lockup detector generate
3914 backtraces on all cpus.
3915 Format: <integer>
3916
3917 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3918 See Documentation/laptops/sonypi.txt
3919
3920 spia_io_base= [HW,MTD]
3921 spia_fio_base=
3922 spia_pedr=
3923 spia_peddr=
3924
3925 stacktrace [FTRACE]
3926 Enabled the stack tracer on boot up.
3927
3928 stacktrace_filter=[function-list]
3929 [FTRACE] Limit the functions that the stack tracer
3930 will trace at boot up. function-list is a comma separated
3931 list of functions. This list can be changed at run
3932 time by the stack_trace_filter file in the debugfs
3933 tracing directory. Note, this enables stack tracing
3934 and the stacktrace above is not needed.
3935
3936 sti= [PARISC,HW]
3937 Format: <num>
3938 Set the STI (builtin display/keyboard on the HP-PARISC
3939 machines) console (graphic card) which should be used
3940 as the initial boot-console.
3941 See also comment in drivers/video/console/sticore.c.
3942
3943 sti_font= [HW]
3944 See comment in drivers/video/console/sticore.c.
3945
3946 stifb= [HW]
3947 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3948
3949 sunrpc.min_resvport=
3950 sunrpc.max_resvport=
3951 [NFS,SUNRPC]
3952 SunRPC servers often require that client requests
3953 originate from a privileged port (i.e. a port in the
3954 range 0 < portnr < 1024).
3955 An administrator who wishes to reserve some of these
3956 ports for other uses may adjust the range that the
3957 kernel's sunrpc client considers to be privileged
3958 using these two parameters to set the minimum and
3959 maximum port values.
3960
3961 sunrpc.svc_rpc_per_connection_limit=
3962 [NFS,SUNRPC]
3963 Limit the number of requests that the server will
3964 process in parallel from a single connection.
3965 The default value is 0 (no limit).
3966
3967 sunrpc.pool_mode=
3968 [NFS]
3969 Control how the NFS server code allocates CPUs to
3970 service thread pools. Depending on how many NICs
3971 you have and where their interrupts are bound, this
3972 option will affect which CPUs will do NFS serving.
3973 Note: this parameter cannot be changed while the
3974 NFS server is running.
3975
3976 auto the server chooses an appropriate mode
3977 automatically using heuristics
3978 global a single global pool contains all CPUs
3979 percpu one pool for each CPU
3980 pernode one pool for each NUMA node (equivalent
3981 to global on non-NUMA machines)
3982
3983 sunrpc.tcp_slot_table_entries=
3984 sunrpc.udp_slot_table_entries=
3985 [NFS,SUNRPC]
3986 Sets the upper limit on the number of simultaneous
3987 RPC calls that can be sent from the client to a
3988 server. Increasing these values may allow you to
3989 improve throughput, but will also increase the
3990 amount of memory reserved for use by the client.
3991
3992 suspend.pm_test_delay=
3993 [SUSPEND]
3994 Sets the number of seconds to remain in a suspend test
3995 mode before resuming the system (see
3996 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3997 is set. Default value is 5.
3998
3999 swapaccount=[0|1]
4000 [KNL] Enable accounting of swap in memory resource
4001 controller if no parameter or 1 is given or disable
4002 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4003
4004 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4005 Format: { <int> | force }
4006 <int> -- Number of I/O TLB slabs
4007 force -- force using of bounce buffers even if they
4008 wouldn't be automatically used by the kernel
4009
4010 switches= [HW,M68k]
4011
4012 sysfs.deprecated=0|1 [KNL]
4013 Enable/disable old style sysfs layout for old udev
4014 on older distributions. When this option is enabled
4015 very new udev will not work anymore. When this option
4016 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4017 in older udev will not work anymore.
4018 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4019 the kernel configuration.
4020
4021 sysrq_always_enabled
4022 [KNL]
4023 Ignore sysrq setting - this boot parameter will
4024 neutralize any effect of /proc/sys/kernel/sysrq.
4025 Useful for debugging.
4026
4027 tcpmhash_entries= [KNL,NET]
4028 Set the number of tcp_metrics_hash slots.
4029 Default value is 8192 or 16384 depending on total
4030 ram pages. This is used to specify the TCP metrics
4031 cache size. See Documentation/networking/ip-sysctl.txt
4032 "tcp_no_metrics_save" section for more details.
4033
4034 tdfx= [HW,DRM]
4035
4036 test_suspend= [SUSPEND][,N]
4037 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4038 standby suspend) or "freeze" (for suspend type freeze)
4039 as the system sleep state during system startup with
4040 the optional capability to repeat N number of times.
4041 The system is woken from this state using a
4042 wakeup-capable RTC alarm.
4043
4044 thash_entries= [KNL,NET]
4045 Set number of hash buckets for TCP connection
4046
4047 thermal.act= [HW,ACPI]
4048 -1: disable all active trip points in all thermal zones
4049 <degrees C>: override all lowest active trip points
4050
4051 thermal.crt= [HW,ACPI]
4052 -1: disable all critical trip points in all thermal zones
4053 <degrees C>: override all critical trip points
4054
4055 thermal.nocrt= [HW,ACPI]
4056 Set to disable actions on ACPI thermal zone
4057 critical and hot trip points.
4058
4059 thermal.off= [HW,ACPI]
4060 1: disable ACPI thermal control
4061
4062 thermal.psv= [HW,ACPI]
4063 -1: disable all passive trip points
4064 <degrees C>: override all passive trip points to this
4065 value
4066
4067 thermal.tzp= [HW,ACPI]
4068 Specify global default ACPI thermal zone polling rate
4069 <deci-seconds>: poll all this frequency
4070 0: no polling (default)
4071
4072 threadirqs [KNL]
4073 Force threading of all interrupt handlers except those
4074 marked explicitly IRQF_NO_THREAD.
4075
4076 tmem [KNL,XEN]
4077 Enable the Transcendent memory driver if built-in.
4078
4079 tmem.cleancache=0|1 [KNL, XEN]
4080 Default is on (1). Disable the usage of the cleancache
4081 API to send anonymous pages to the hypervisor.
4082
4083 tmem.frontswap=0|1 [KNL, XEN]
4084 Default is on (1). Disable the usage of the frontswap
4085 API to send swap pages to the hypervisor. If disabled
4086 the selfballooning and selfshrinking are force disabled.
4087
4088 tmem.selfballooning=0|1 [KNL, XEN]
4089 Default is on (1). Disable the driving of swap pages
4090 to the hypervisor.
4091
4092 tmem.selfshrinking=0|1 [KNL, XEN]
4093 Default is on (1). Partial swapoff that immediately
4094 transfers pages from Xen hypervisor back to the
4095 kernel based on different criteria.
4096
4097 topology= [S390]
4098 Format: {off | on}
4099 Specify if the kernel should make use of the cpu
4100 topology information if the hardware supports this.
4101 The scheduler will make use of this information and
4102 e.g. base its process migration decisions on it.
4103 Default is on.
4104
4105 topology_updates= [KNL, PPC, NUMA]
4106 Format: {off}
4107 Specify if the kernel should ignore (off)
4108 topology updates sent by the hypervisor to this
4109 LPAR.
4110
4111 tp720= [HW,PS2]
4112
4113 tpm_suspend_pcr=[HW,TPM]
4114 Format: integer pcr id
4115 Specify that at suspend time, the tpm driver
4116 should extend the specified pcr with zeros,
4117 as a workaround for some chips which fail to
4118 flush the last written pcr on TPM_SaveState.
4119 This will guarantee that all the other pcrs
4120 are saved.
4121
4122 trace_buf_size=nn[KMG]
4123 [FTRACE] will set tracing buffer size on each cpu.
4124
4125 trace_event=[event-list]
4126 [FTRACE] Set and start specified trace events in order
4127 to facilitate early boot debugging. The event-list is a
4128 comma separated list of trace events to enable. See
4129 also Documentation/trace/events.txt
4130
4131 trace_options=[option-list]
4132 [FTRACE] Enable or disable tracer options at boot.
4133 The option-list is a comma delimited list of options
4134 that can be enabled or disabled just as if you were
4135 to echo the option name into
4136
4137 /sys/kernel/debug/tracing/trace_options
4138
4139 For example, to enable stacktrace option (to dump the
4140 stack trace of each event), add to the command line:
4141
4142 trace_options=stacktrace
4143
4144 See also Documentation/trace/ftrace.txt "trace options"
4145 section.
4146
4147 tp_printk[FTRACE]
4148 Have the tracepoints sent to printk as well as the
4149 tracing ring buffer. This is useful for early boot up
4150 where the system hangs or reboots and does not give the
4151 option for reading the tracing buffer or performing a
4152 ftrace_dump_on_oops.
4153
4154 To turn off having tracepoints sent to printk,
4155 echo 0 > /proc/sys/kernel/tracepoint_printk
4156 Note, echoing 1 into this file without the
4157 tracepoint_printk kernel cmdline option has no effect.
4158
4159 ** CAUTION **
4160
4161 Having tracepoints sent to printk() and activating high
4162 frequency tracepoints such as irq or sched, can cause
4163 the system to live lock.
4164
4165 traceoff_on_warning
4166 [FTRACE] enable this option to disable tracing when a
4167 warning is hit. This turns off "tracing_on". Tracing can
4168 be enabled again by echoing '1' into the "tracing_on"
4169 file located in /sys/kernel/debug/tracing/
4170
4171 This option is useful, as it disables the trace before
4172 the WARNING dump is called, which prevents the trace to
4173 be filled with content caused by the warning output.
4174
4175 This option can also be set at run time via the sysctl
4176 option: kernel/traceoff_on_warning
4177
4178 transparent_hugepage=
4179 [KNL]
4180 Format: [always|madvise|never]
4181 Can be used to control the default behavior of the system
4182 with respect to transparent hugepages.
4183 See Documentation/vm/transhuge.txt for more details.
4184
4185 tsc= Disable clocksource stability checks for TSC.
4186 Format: <string>
4187 [x86] reliable: mark tsc clocksource as reliable, this
4188 disables clocksource verification at runtime, as well
4189 as the stability checks done at bootup. Used to enable
4190 high-resolution timer mode on older hardware, and in
4191 virtualized environment.
4192 [x86] noirqtime: Do not use TSC to do irq accounting.
4193 Used to run time disable IRQ_TIME_ACCOUNTING on any
4194 platforms where RDTSC is slow and this accounting
4195 can add overhead.
4196
4197 turbografx.map[2|3]= [HW,JOY]
4198 TurboGraFX parallel port interface
4199 Format:
4200 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4201 See also Documentation/input/joystick-parport.txt
4202
4203 udbg-immortal [PPC] When debugging early kernel crashes that
4204 happen after console_init() and before a proper
4205 console driver takes over, this boot options might
4206 help "seeing" what's going on.
4207
4208 uhash_entries= [KNL,NET]
4209 Set number of hash buckets for UDP/UDP-Lite connections
4210
4211 uhci-hcd.ignore_oc=
4212 [USB] Ignore overcurrent events (default N).
4213 Some badly-designed motherboards generate lots of
4214 bogus events, for ports that aren't wired to
4215 anything. Set this parameter to avoid log spamming.
4216 Note that genuine overcurrent events won't be
4217 reported either.
4218
4219 unknown_nmi_panic
4220 [X86] Cause panic on unknown NMI.
4221
4222 usbcore.authorized_default=
4223 [USB] Default USB device authorization:
4224 (default -1 = authorized except for wireless USB,
4225 0 = not authorized, 1 = authorized)
4226
4227 usbcore.autosuspend=
4228 [USB] The autosuspend time delay (in seconds) used
4229 for newly-detected USB devices (default 2). This
4230 is the time required before an idle device will be
4231 autosuspended. Devices for which the delay is set
4232 to a negative value won't be autosuspended at all.
4233
4234 usbcore.usbfs_snoop=
4235 [USB] Set to log all usbfs traffic (default 0 = off).
4236
4237 usbcore.usbfs_snoop_max=
4238 [USB] Maximum number of bytes to snoop in each URB
4239 (default = 65536).
4240
4241 usbcore.blinkenlights=
4242 [USB] Set to cycle leds on hubs (default 0 = off).
4243
4244 usbcore.old_scheme_first=
4245 [USB] Start with the old device initialization
4246 scheme (default 0 = off).
4247
4248 usbcore.usbfs_memory_mb=
4249 [USB] Memory limit (in MB) for buffers allocated by
4250 usbfs (default = 16, 0 = max = 2047).
4251
4252 usbcore.use_both_schemes=
4253 [USB] Try the other device initialization scheme
4254 if the first one fails (default 1 = enabled).
4255
4256 usbcore.initial_descriptor_timeout=
4257 [USB] Specifies timeout for the initial 64-byte
4258 USB_REQ_GET_DESCRIPTOR request in milliseconds
4259 (default 5000 = 5.0 seconds).
4260
4261 usbcore.nousb [USB] Disable the USB subsystem
4262
4263 usbhid.mousepoll=
4264 [USBHID] The interval which mice are to be polled at.
4265
4266 usb-storage.delay_use=
4267 [UMS] The delay in seconds before a new device is
4268 scanned for Logical Units (default 1).
4269
4270 usb-storage.quirks=
4271 [UMS] A list of quirks entries to supplement or
4272 override the built-in unusual_devs list. List
4273 entries are separated by commas. Each entry has
4274 the form VID:PID:Flags where VID and PID are Vendor
4275 and Product ID values (4-digit hex numbers) and
4276 Flags is a set of characters, each corresponding
4277 to a common usb-storage quirk flag as follows:
4278 a = SANE_SENSE (collect more than 18 bytes
4279 of sense data);
4280 b = BAD_SENSE (don't collect more than 18
4281 bytes of sense data);
4282 c = FIX_CAPACITY (decrease the reported
4283 device capacity by one sector);
4284 d = NO_READ_DISC_INFO (don't use
4285 READ_DISC_INFO command);
4286 e = NO_READ_CAPACITY_16 (don't use
4287 READ_CAPACITY_16 command);
4288 f = NO_REPORT_OPCODES (don't use report opcodes
4289 command, uas only);
4290 g = MAX_SECTORS_240 (don't transfer more than
4291 240 sectors at a time, uas only);
4292 h = CAPACITY_HEURISTICS (decrease the
4293 reported device capacity by one
4294 sector if the number is odd);
4295 i = IGNORE_DEVICE (don't bind to this
4296 device);
4297 j = NO_REPORT_LUNS (don't use report luns
4298 command, uas only);
4299 l = NOT_LOCKABLE (don't try to lock and
4300 unlock ejectable media);
4301 m = MAX_SECTORS_64 (don't transfer more
4302 than 64 sectors = 32 KB at a time);
4303 n = INITIAL_READ10 (force a retry of the
4304 initial READ(10) command);
4305 o = CAPACITY_OK (accept the capacity
4306 reported by the device);
4307 p = WRITE_CACHE (the device cache is ON
4308 by default);
4309 r = IGNORE_RESIDUE (the device reports
4310 bogus residue values);
4311 s = SINGLE_LUN (the device has only one
4312 Logical Unit);
4313 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4314 commands, uas only);
4315 u = IGNORE_UAS (don't bind to the uas driver);
4316 w = NO_WP_DETECT (don't test whether the
4317 medium is write-protected).
4318 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4319 even if the device claims no cache)
4320 Example: quirks=0419:aaf5:rl,0421:0433:rc
4321
4322 user_debug= [KNL,ARM]
4323 Format: <int>
4324 See arch/arm/Kconfig.debug help text.
4325 1 - undefined instruction events
4326 2 - system calls
4327 4 - invalid data aborts
4328 8 - SIGSEGV faults
4329 16 - SIGBUS faults
4330 Example: user_debug=31
4331
4332 userpte=
4333 [X86] Flags controlling user PTE allocations.
4334
4335 nohigh = do not allocate PTE pages in
4336 HIGHMEM regardless of setting
4337 of CONFIG_HIGHPTE.
4338
4339 vdso= [X86,SH]
4340 On X86_32, this is an alias for vdso32=. Otherwise:
4341
4342 vdso=1: enable VDSO (the default)
4343 vdso=0: disable VDSO mapping
4344
4345 vdso32= [X86] Control the 32-bit vDSO
4346 vdso32=1: enable 32-bit VDSO
4347 vdso32=0 or vdso32=2: disable 32-bit VDSO
4348
4349 See the help text for CONFIG_COMPAT_VDSO for more
4350 details. If CONFIG_COMPAT_VDSO is set, the default is
4351 vdso32=0; otherwise, the default is vdso32=1.
4352
4353 For compatibility with older kernels, vdso32=2 is an
4354 alias for vdso32=0.
4355
4356 Try vdso32=0 if you encounter an error that says:
4357 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4358
4359 vector= [IA-64,SMP]
4360 vector=percpu: enable percpu vector domain
4361
4362 video= [FB] Frame buffer configuration
4363 See Documentation/fb/modedb.txt.
4364
4365 video.brightness_switch_enabled= [0,1]
4366 If set to 1, on receiving an ACPI notify event
4367 generated by hotkey, video driver will adjust brightness
4368 level and then send out the event to user space through
4369 the allocated input device; If set to 0, video driver
4370 will only send out the event without touching backlight
4371 brightness level.
4372 default: 1
4373
4374 virtio_mmio.device=
4375 [VMMIO] Memory mapped virtio (platform) device.
4376
4377 <size>@<baseaddr>:<irq>[:<id>]
4378 where:
4379 <size> := size (can use standard suffixes
4380 like K, M and G)
4381 <baseaddr> := physical base address
4382 <irq> := interrupt number (as passed to
4383 request_irq())
4384 <id> := (optional) platform device id
4385 example:
4386 virtio_mmio.device=1K@0x100b0000:48:7
4387
4388 Can be used multiple times for multiple devices.
4389
4390 vga= [BOOT,X86-32] Select a particular video mode
4391 See Documentation/x86/boot.txt and
4392 Documentation/svga.txt.
4393 Use vga=ask for menu.
4394 This is actually a boot loader parameter; the value is
4395 passed to the kernel using a special protocol.
4396
4397 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4398 size of <nn>. This can be used to increase the
4399 minimum size (128MB on x86). It can also be used to
4400 decrease the size and leave more room for directly
4401 mapped kernel RAM.
4402
4403 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4404 Format: <command>
4405
4406 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4407 Format: <command>
4408
4409 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4410 Format: <command>
4411
4412 vsyscall= [X86-64]
4413 Controls the behavior of vsyscalls (i.e. calls to
4414 fixed addresses of 0xffffffffff600x00 from legacy
4415 code). Most statically-linked binaries and older
4416 versions of glibc use these calls. Because these
4417 functions are at fixed addresses, they make nice
4418 targets for exploits that can control RIP.
4419
4420 emulate [default] Vsyscalls turn into traps and are
4421 emulated reasonably safely.
4422
4423 native Vsyscalls are native syscall instructions.
4424 This is a little bit faster than trapping
4425 and makes a few dynamic recompilers work
4426 better than they would in emulation mode.
4427 It also makes exploits much easier to write.
4428
4429 none Vsyscalls don't work at all. This makes
4430 them quite hard to use for exploits but
4431 might break your system.
4432
4433 vt.color= [VT] Default text color.
4434 Format: 0xYX, X = foreground, Y = background.
4435 Default: 0x07 = light gray on black.
4436
4437 vt.cur_default= [VT] Default cursor shape.
4438 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4439 the parameters of the <Esc>[?A;B;Cc escape sequence;
4440 see VGA-softcursor.txt. Default: 2 = underline.
4441
4442 vt.default_blu= [VT]
4443 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4444 Change the default blue palette of the console.
4445 This is a 16-member array composed of values
4446 ranging from 0-255.
4447
4448 vt.default_grn= [VT]
4449 Format: <green0>,<green1>,<green2>,...,<green15>
4450 Change the default green palette of the console.
4451 This is a 16-member array composed of values
4452 ranging from 0-255.
4453
4454 vt.default_red= [VT]
4455 Format: <red0>,<red1>,<red2>,...,<red15>
4456 Change the default red palette of the console.
4457 This is a 16-member array composed of values
4458 ranging from 0-255.
4459
4460 vt.default_utf8=
4461 [VT]
4462 Format=<0|1>
4463 Set system-wide default UTF-8 mode for all tty's.
4464 Default is 1, i.e. UTF-8 mode is enabled for all
4465 newly opened terminals.
4466
4467 vt.global_cursor_default=
4468 [VT]
4469 Format=<-1|0|1>
4470 Set system-wide default for whether a cursor
4471 is shown on new VTs. Default is -1,
4472 i.e. cursors will be created by default unless
4473 overridden by individual drivers. 0 will hide
4474 cursors, 1 will display them.
4475
4476 vt.italic= [VT] Default color for italic text; 0-15.
4477 Default: 2 = green.
4478
4479 vt.underline= [VT] Default color for underlined text; 0-15.
4480 Default: 3 = cyan.
4481
4482 watchdog timers [HW,WDT] For information on watchdog timers,
4483 see Documentation/watchdog/watchdog-parameters.txt
4484 or other driver-specific files in the
4485 Documentation/watchdog/ directory.
4486
4487 workqueue.watchdog_thresh=
4488 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4489 warn stall conditions and dump internal state to
4490 help debugging. 0 disables workqueue stall
4491 detection; otherwise, it's the stall threshold
4492 duration in seconds. The default value is 30 and
4493 it can be updated at runtime by writing to the
4494 corresponding sysfs file.
4495
4496 workqueue.disable_numa
4497 By default, all work items queued to unbound
4498 workqueues are affine to the NUMA nodes they're
4499 issued on, which results in better behavior in
4500 general. If NUMA affinity needs to be disabled for
4501 whatever reason, this option can be used. Note
4502 that this also can be controlled per-workqueue for
4503 workqueues visible under /sys/bus/workqueue/.
4504
4505 workqueue.power_efficient
4506 Per-cpu workqueues are generally preferred because
4507 they show better performance thanks to cache
4508 locality; unfortunately, per-cpu workqueues tend to
4509 be more power hungry than unbound workqueues.
4510
4511 Enabling this makes the per-cpu workqueues which
4512 were observed to contribute significantly to power
4513 consumption unbound, leading to measurably lower
4514 power usage at the cost of small performance
4515 overhead.
4516
4517 The default value of this parameter is determined by
4518 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4519
4520 workqueue.debug_force_rr_cpu
4521 Workqueue used to implicitly guarantee that work
4522 items queued without explicit CPU specified are put
4523 on the local CPU. This guarantee is no longer true
4524 and while local CPU is still preferred work items
4525 may be put on foreign CPUs. This debug option
4526 forces round-robin CPU selection to flush out
4527 usages which depend on the now broken guarantee.
4528 When enabled, memory and cache locality will be
4529 impacted.
4530
4531 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4532 default x2apic cluster mode on platforms
4533 supporting x2apic.
4534
4535 x86_intel_mid_timer= [X86-32,APBT]
4536 Choose timer option for x86 Intel MID platform.
4537 Two valid options are apbt timer only and lapic timer
4538 plus one apbt timer for broadcast timer.
4539 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4540
4541 xen_512gb_limit [KNL,X86-64,XEN]
4542 Restricts the kernel running paravirtualized under Xen
4543 to use only up to 512 GB of RAM. The reason to do so is
4544 crash analysis tools and Xen tools for doing domain
4545 save/restore/migration must be enabled to handle larger
4546 domains.
4547
4548 xen_emul_unplug= [HW,X86,XEN]
4549 Unplug Xen emulated devices
4550 Format: [unplug0,][unplug1]
4551 ide-disks -- unplug primary master IDE devices
4552 aux-ide-disks -- unplug non-primary-master IDE devices
4553 nics -- unplug network devices
4554 all -- unplug all emulated devices (NICs and IDE disks)
4555 unnecessary -- unplugging emulated devices is
4556 unnecessary even if the host did not respond to
4557 the unplug protocol
4558 never -- do not unplug even if version check succeeds
4559
4560 xen_nopvspin [X86,XEN]
4561 Disables the ticketlock slowpath using Xen PV
4562 optimizations.
4563
4564 xen_nopv [X86]
4565 Disables the PV optimizations forcing the HVM guest to
4566 run as generic HVM guest with no PV drivers.
4567
4568 xirc2ps_cs= [NET,PCMCIA]
4569 Format:
4570 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4571
4572------------------------
4573
4574Todo
4575----
4576
4577 Add more DRM drivers.
generated by cgit v1.2.2 (git 2.25.0) at 2025-09-17 21:30:56 -0400