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