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
28 Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30 can also be entered as
31 log-buf-len=1M print_fatal_signals=1
33 Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
36 This document may not be entirely up to date and comprehensive. The command
37 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
38 module. Loadable modules, after being loaded into the running kernel, also
39 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
40 parameters may be changed at runtime by the command
41 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
43 The parameters listed below are only valid if certain kernel build options were
44 enabled and if respective hardware is present. The text in square brackets at
45 the beginning of each description states the restrictions within which a
46 parameter is applicable:
48 ACPI ACPI support is enabled.
49 AGP AGP (Accelerated Graphics Port) is enabled.
50 ALSA ALSA sound support is enabled.
51 APIC APIC support is enabled.
52 APM Advanced Power Management support is enabled.
53 ARM ARM architecture is enabled.
54 AVR32 AVR32 architecture is enabled.
55 AX25 Appropriate AX.25 support is enabled.
56 BLACKFIN Blackfin architecture is enabled.
57 CLK Common clock infrastructure is enabled.
58 CMA Contiguous Memory Area support is enabled.
59 DRM Direct Rendering Management support is enabled.
60 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
61 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
62 EFI EFI Partitioning (GPT) is enabled
63 EIDE EIDE/ATAPI support is enabled.
64 EVM Extended Verification Module
65 FB The frame buffer device is enabled.
66 FTRACE Function tracing enabled.
67 GCOV GCOV profiling is enabled.
68 HW Appropriate hardware is enabled.
69 IA-64 IA-64 architecture is enabled.
70 IMA Integrity measurement architecture is enabled.
71 IOSCHED More than one I/O scheduler is enabled.
72 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
73 IPV6 IPv6 support is enabled.
74 ISAPNP ISA PnP code is enabled.
75 ISDN Appropriate ISDN support is enabled.
76 JOY Appropriate joystick support is enabled.
77 KGDB Kernel debugger support is enabled.
78 KVM Kernel Virtual Machine support is enabled.
79 LIBATA Libata driver is enabled
80 LP Printer support is enabled.
81 LOOP Loopback device support is enabled.
82 M68k M68k architecture is enabled.
83 These options have more detailed description inside of
84 Documentation/m68k/kernel-options.txt.
85 MDA MDA console support is enabled.
86 MIPS MIPS architecture is enabled.
87 MOUSE Appropriate mouse support is enabled.
88 MSI Message Signaled Interrupts (PCI).
89 MTD MTD (Memory Technology Device) support is enabled.
90 NET Appropriate network support is enabled.
91 NUMA NUMA support is enabled.
92 NFS Appropriate NFS support is enabled.
93 OSS OSS sound support is enabled.
94 PV_OPS A paravirtualized kernel is enabled.
95 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
96 PARISC The PA-RISC architecture is enabled.
97 PCI PCI bus support is enabled.
98 PCIE PCI Express support is enabled.
99 PCMCIA The PCMCIA subsystem is enabled.
100 PNP Plug & Play support is enabled.
101 PPC PowerPC architecture is enabled.
102 PPT Parallel port support is enabled.
103 PS2 Appropriate PS/2 support is enabled.
104 RAM RAM disk support is enabled.
105 S390 S390 architecture is enabled.
106 SCSI Appropriate SCSI support is enabled.
107 A lot of drivers have their options described inside
108 the Documentation/scsi/ sub-directory.
109 SECURITY Different security models are enabled.
110 SELINUX SELinux support is enabled.
111 APPARMOR AppArmor support is enabled.
112 SERIAL Serial support is enabled.
113 SH SuperH architecture is enabled.
114 SMP The kernel is an SMP kernel.
115 SPARC Sparc architecture is enabled.
116 SWSUSP Software suspend (hibernation) is enabled.
117 SUSPEND System suspend states are enabled.
118 TPM TPM drivers are enabled.
119 TS Appropriate touchscreen support is enabled.
120 UMS USB Mass Storage support is enabled.
121 USB USB support is enabled.
122 USBHID USB Human Interface Device support is enabled.
123 V4L Video For Linux support is enabled.
124 VMMIO Driver for memory mapped virtio devices is enabled.
125 VGA The VGA console has been enabled.
126 VT Virtual terminal support is enabled.
127 WDT Watchdog support is enabled.
128 XT IBM PC/XT MFM hard disk support is enabled.
129 X86-32 X86-32, aka i386 architecture is enabled.
130 X86-64 X86-64 architecture is enabled.
131 More X86-64 boot options can be found in
132 Documentation/x86/x86_64/boot-options.txt .
133 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
134 XEN Xen support is enabled
136 In addition, the following text indicates that the option:
138 BUGS= Relates to possible processor bugs on the said processor.
139 KNL Is a kernel start-up parameter.
140 BOOT Is a boot loader parameter.
142 Parameters denoted with BOOT are actually interpreted by the boot
143 loader, and have no meaning to the kernel directly.
144 Do not modify the syntax of boot loader parameters without extreme
145 need or coordination with <Documentation/x86/boot.txt>.
147 There are also arch-specific kernel-parameters not documented here.
148 See for example <Documentation/x86/x86_64/boot-options.txt>.
150 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
151 a trailing = on the name of any parameter states that that parameter will
152 be entered as an environment variable, whereas its absence indicates that
153 it will appear as a kernel argument readable via /proc/cmdline by programs
154 running once the system is up.
156 The number of kernel parameters is not limited, but the length of the
157 complete command line (parameters including spaces etc.) is limited to
158 a fixed number of characters. This limit depends on the architecture
159 and is between 256 and 4096 characters. It is defined in the file
160 ./include/asm/setup.h as COMMAND_LINE_SIZE.
162 Finally, the [KMG] suffix is commonly described after a number of kernel
163 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
164 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
165 bytes respectively. Such letter suffixes can also be entirely omitted.
169 Advanced Configuration and Power Interface
170 Format: { force | off | strict | noirq | rsdt }
171 force -- enable ACPI if default was off
172 off -- disable ACPI if default was on
173 noirq -- do not use ACPI for IRQ routing
174 strict -- Be less tolerant of platforms that are not
175 strictly ACPI specification compliant.
176 rsdt -- prefer RSDT over (default) XSDT
177 copy_dsdt -- copy DSDT to memory
179 See also Documentation/power/runtime_pm.txt, pci=noacpi
181 acpi_rsdp= [ACPI,EFI,KEXEC]
182 Pass the RSDP address to the kernel, mostly used
183 on machines running EFI runtime service to boot the
184 second kernel for kdump.
186 acpi_apic_instance= [ACPI, IOAPIC]
188 2: use 2nd APIC table, if available
189 1,0: use 1st APIC table
192 acpi_backlight= [HW,ACPI]
193 acpi_backlight=vendor
195 If set to vendor, prefer vendor specific driver
196 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
197 of the ACPI video.ko driver.
199 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
200 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
202 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
203 debug output. Bits in debug_layer correspond to a
204 _COMPONENT in an ACPI source file, e.g.,
205 #define _COMPONENT ACPI_PCI_COMPONENT
206 Bits in debug_level correspond to a level in
207 ACPI_DEBUG_PRINT statements, e.g.,
208 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
209 The debug_level mask defaults to "info". See
210 Documentation/acpi/debug.txt for more information about
211 debug layers and levels.
213 Enable processor driver info messages:
214 acpi.debug_layer=0x20000000
215 Enable PCI/PCI interrupt routing info messages:
216 acpi.debug_layer=0x400000
217 Enable AML "Debug" output, i.e., stores to the Debug
218 object while interpreting AML:
219 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
220 Enable all messages related to ACPI hardware:
221 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
223 Some values produce so much output that the system is
224 unusable. The "log_buf_len" parameter may be useful
225 if you need to capture more output.
227 acpi_force_table_verification [HW,ACPI]
228 Enable table checksum verification during early stage.
229 By default, this is disabled due to x86 early mapping
232 acpi_irq_balance [HW,ACPI]
233 ACPI will balance active IRQs
236 acpi_irq_nobalance [HW,ACPI]
237 ACPI will not move active IRQs (default)
240 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
241 Format: <irq>,<irq>...
243 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
245 Format: <irq>,<irq>...
247 acpi_no_auto_serialize [HW,ACPI]
248 Disable auto-serialization of AML methods
249 AML control methods that contain the opcodes to create
250 named objects will be marked as "Serialized" by the
251 auto-serialization feature.
252 This feature is enabled by default.
253 This option allows to turn off the feature.
255 acpi_no_static_ssdt [HW,ACPI]
256 Disable installation of static SSDTs at early boot time
257 By default, SSDTs contained in the RSDT/XSDT will be
258 installed automatically and they will appear under
259 /sys/firmware/acpi/tables.
260 This option turns off this feature.
261 Note that specifying this option does not affect
262 dynamic table installation which will install SSDT
263 tables to /sys/firmware/acpi/tables/dynamic.
265 acpica_no_return_repair [HW, ACPI]
266 Disable AML predefined validation mechanism
267 This mechanism can repair the evaluation result to make
268 the return objects more ACPI specification compliant.
269 This option is useful for developers to identify the
270 root cause of an AML interpreter issue when the issue
271 has something to do with the repair mechanism.
273 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
274 Format: To spoof as Windows 98: ="Microsoft Windows"
276 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
277 acpi_osi="string1" # add string1
278 acpi_osi="!string2" # remove string2
279 acpi_osi=!* # remove all strings
280 acpi_osi=! # disable all built-in OS vendor
282 acpi_osi= # disable all strings
284 'acpi_osi=!' can be used in combination with single or
285 multiple 'acpi_osi="string1"' to support specific OS
286 vendor string(s). Note that such command can only
287 affect the default state of the OS vendor strings, thus
288 it cannot affect the default state of the feature group
289 strings and the current state of the OS vendor strings,
290 specifying it multiple times through kernel command line
291 is meaningless. This command is useful when one do not
292 care about the state of the feature group strings which
293 should be controlled by the OSPM.
295 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
296 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
297 can make '_OSI("Windows 2000")' TRUE.
299 'acpi_osi=' cannot be used in combination with other
300 'acpi_osi=' command lines, the _OSI method will not
301 exist in the ACPI namespace. NOTE that such command can
302 only affect the _OSI support state, thus specifying it
303 multiple times through kernel command line is also
306 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
309 'acpi_osi=!*' can be used in combination with single or
310 multiple 'acpi_osi="string1"' to support specific
311 string(s). Note that such command can affect the
312 current state of both the OS vendor strings and the
313 feature group strings, thus specifying it multiple times
314 through kernel command line is meaningful. But it may
315 still not able to affect the final state of a string if
316 there are quirks related to this string. This command
317 is useful when one want to control the state of the
318 feature group strings to debug BIOS issues related to
321 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
322 '_OSI("Module Device")' FALSE.
323 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
324 '_OSI("Module Device")' TRUE.
325 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
327 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
329 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
330 they all will make '_OSI("Windows 2000")' TRUE.
333 Override the pmtimer bug detection: force the kernel
334 to assume that this machine's pmtimer latches its value
335 and always returns good values.
337 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
338 Format: { level | edge | high | low }
340 acpi_skip_timer_override [HW,ACPI]
341 Recognize and ignore IRQ0/pin2 Interrupt Override.
342 For broken nForce2 BIOS resulting in XT-PIC timer.
344 acpi_sleep= [HW,ACPI] Sleep options
345 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
346 old_ordering, nonvs, sci_force_enable }
347 See Documentation/power/video.txt for information on
349 s3_beep is for debugging; it makes the PC's speaker beep
350 as soon as the kernel's real-mode entry point is called.
351 s4_nohwsig prevents ACPI hardware signature from being
352 used during resume from hibernation.
353 old_ordering causes the ACPI 1.0 ordering of the _PTS
354 control method, with respect to putting devices into
355 low power states, to be enforced (the ACPI 2.0 ordering
356 of _PTS is used by default).
357 nonvs prevents the kernel from saving/restoring the
358 ACPI NVS memory during suspend/hibernation and resume.
359 sci_force_enable causes the kernel to set SCI_EN directly
360 on resume from S1/S3 (which is against the ACPI spec,
361 but some broken systems don't work without it).
363 acpi_use_timer_override [HW,ACPI]
364 Use timer override. For some broken Nvidia NF5 boards
365 that require a timer override, but don't have HPET
367 acpi_enforce_resources= [ACPI]
368 { strict | lax | no }
369 Check for resource conflicts between native drivers
370 and ACPI OperationRegions (SystemIO and SystemMemory
371 only). IO ports and memory declared in ACPI might be
372 used by the ACPI subsystem in arbitrary AML code and
373 can interfere with legacy drivers.
374 strict (default): access to resources claimed by ACPI
375 is denied; legacy drivers trying to access reserved
376 resources will fail to bind to device using them.
377 lax: access to resources claimed by ACPI is allowed;
378 legacy drivers trying to access reserved resources
379 will bind successfully but a warning message is logged.
380 no: ACPI OperationRegions are not marked as reserved,
381 no further checks are performed.
383 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
386 add_efi_memmap [EFI; X86] Include EFI memory map in
387 kernel's map of available physical RAM.
390 { off | try_unsupported }
391 off: disable AGP support
392 try_unsupported: try to drive unsupported chipsets
393 (may crash computer or cause data corruption)
396 See Documentation/sound/alsa/alsa-parameters.txt
399 Allow the default userspace alignment fault handler
400 behaviour to be specified. Bit 0 enables warnings,
401 bit 1 enables fixups, and bit 2 sends a segfault.
403 align_va_addr= [X86-64]
404 Align virtual addresses by clearing slice [14:12] when
405 allocating a VMA at process creation time. This option
406 gives you up to 3% performance improvement on AMD F15h
407 machines (where it is enabled by default) for a
408 CPU-intensive style benchmark, and it can vary highly in
409 a microbenchmark depending on workload and compiler.
411 32: only for 32-bit processes
412 64: only for 64-bit processes
413 on: enable for both 32- and 64-bit processes
414 off: disable for both 32- and 64-bit processes
416 alloc_snapshot [FTRACE]
417 Allocate the ftrace snapshot buffer on boot up when the
418 main buffer is allocated. This is handy if debugging
419 and you need to use tracing_snapshot() on boot up, and
420 do not want to use tracing_snapshot_alloc() as it needs
421 to be done where GFP_KERNEL allocations are allowed.
423 amd_iommu= [HW,X86-64]
424 Pass parameters to the AMD IOMMU driver in the system.
426 fullflush - enable flushing of IO/TLB entries when
427 they are unmapped. Otherwise they are
428 flushed before they will be reused, which
430 off - do not initialize any AMD IOMMU found in
432 force_isolation - Force device isolation for all
433 devices. The IOMMU driver is not
434 allowed anymore to lift isolation
435 requirements as needed. This option
436 does not override iommu=pt
438 amd_iommu_dump= [HW,X86-64]
439 Enable AMD IOMMU driver option to dump the ACPI table
440 for AMD IOMMU. With this option enabled, AMD IOMMU
441 driver will print ACPI tables for AMD IOMMU during
442 IOMMU initialization.
444 amijoy.map= [HW,JOY] Amiga joystick support
445 Map of devices attached to JOY0DAT and JOY1DAT
447 See also Documentation/input/joystick.txt
449 analog.map= [HW,JOY] Analog joystick and gamepad support
450 Specifies type or capabilities of an analog joystick
451 connected to one of 16 gameports
452 Format: <type1>,<type2>,..<type16>
455 Power management functions (SPARCstation-4/5 + deriv.)
457 Disable APC CPU standby support. SPARCstation-Fox does
458 not play well with APC CPU idle - disable it if you have
459 APC and your system crashes randomly.
461 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
462 Change the output verbosity whilst booting
463 Format: { quiet (default) | verbose | debug }
464 Change the amount of debugging information output
465 when initialising the APIC and IO-APIC components.
468 See Documentation/networking/ipv6.txt.
470 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
471 Limit apic dumping. The parameter defines the maximal
472 number of local apics being dumped. Also it is possible
473 to set it to "all" by meaning -- no limit here.
474 Format: { 1 (default) | 2 | ... | all }.
475 The parameter valid if only apic=debug or
476 apic=verbose is specified.
477 Example: apic=debug show_lapic=all
479 apm= [APM] Advanced Power Management
480 See header of arch/x86/kernel/apm_32.c.
482 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
483 Format: <io>,<irq>,<nodeID>
487 atarimouse= [HW,MOUSE] Atari Mouse
489 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
490 EzKey and similar keyboards
492 atkbd.reset= [HW] Reset keyboard during initialization
494 atkbd.set= [HW] Select keyboard code set
495 Format: <int> (2 = AT (default), 3 = PS/2)
497 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
500 atkbd.softraw= [HW] Choose between synthetic and real raw mode
501 Format: <bool> (0 = real, 1 = synthetic (default))
503 atkbd.softrepeat= [HW]
504 Use software keyboard repeat
506 audit= [KNL] Enable the audit sub-system
507 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
508 0 - kernel audit is disabled and can not be enabled
509 until the next reboot
510 unset - kernel audit is initialized but disabled and
511 will be fully enabled by the userspace auditd.
512 1 - kernel audit is initialized and partially enabled,
513 storing at most audit_backlog_limit messages in
514 RAM until it is fully enabled by the userspace
518 audit_backlog_limit= [KNL] Set the audit queue size limit.
519 Format: <int> (must be >=0)
522 baycom_epp= [HW,AX25]
525 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
527 See header of drivers/net/hamradio/baycom_par.c.
529 baycom_ser_fdx= [HW,AX25]
530 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
531 Format: <io>,<irq>,<mode>[,<baud>]
532 See header of drivers/net/hamradio/baycom_ser_fdx.c.
534 baycom_ser_hdx= [HW,AX25]
535 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
536 Format: <io>,<irq>,<mode>
537 See header of drivers/net/hamradio/baycom_ser_hdx.c.
539 blkdevparts= Manual partition parsing of block device(s) for
540 embedded devices based on command line input.
541 See Documentation/block/cmdline-partition.txt
543 boot_delay= Milliseconds to delay each printk during boot.
544 Values larger than 10 seconds (10000) are changed to
548 bootmem_debug [KNL] Enable bootmem allocator debug messages.
550 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
551 bttv.radio= Most important insmod options are available as
553 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
556 bulk_remove=off [PPC] This parameter disables the use of the pSeries
557 firmware feature for flushing multiple hpte entries
560 c101= [NET] Moxa C101 synchronous serial card
562 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
563 Sometimes CPU hardware bugs make them report the cache
564 size incorrectly. The kernel will attempt work arounds
565 to fix known problems, but for some CPUs it is not
566 possible to determine what the correct size should be.
567 This option provides an override for these situations.
569 ca_keys= [KEYS] This parameter identifies a specific key(s) on
570 the system trusted keyring to be used for certificate
572 format: { id:<keyid> | builtin }
574 cca= [MIPS] Override the kernel pages' cache coherency
575 algorithm. Accepted values range from 0 to 7
576 inclusive. See arch/mips/include/asm/pgtable-bits.h
577 for platform specific values (SB1, Loongson3 and
580 ccw_timeout_log [S390]
581 See Documentation/s390/CommonIO for details.
583 cgroup_disable= [KNL] Disable a particular controller
584 Format: {name of the controller(s) to disable}
585 The effects of cgroup_disable=foo are:
586 - foo isn't auto-mounted if you mount all cgroups in
588 - foo isn't visible as an individually mountable
590 {Currently only "memory" controller deal with this and
591 cut the overhead, others just disable the usage. So
592 only cgroup_disable=memory is actually worthy}
594 checkreqprot [SELINUX] Set initial checkreqprot flag value.
595 Format: { "0" | "1" }
596 See security/selinux/Kconfig help text.
597 0 -- check protection applied by kernel (includes
598 any implied execute protection).
599 1 -- check protection requested by application.
600 Default value is set via a kernel config option.
601 Value can be changed at runtime via
602 /selinux/checkreqprot.
605 See Documentation/s390/CommonIO for details.
608 Keep all clocks already enabled by bootloader on,
609 even if no driver has claimed them. This is useful
610 for debug and development, but should not be
611 needed on a platform with proper driver support.
612 For more information, see Documentation/clk.txt.
614 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
616 Forces specified clocksource (if available) to be used
617 when calculating gettimeofday(). If specified
618 clocksource is not available, it defaults to PIT.
619 Format: { pit | tsc | cyclone | pmtmr }
621 clocksource= Override the default clocksource
623 Override the default clocksource and use the clocksource
624 with the name specified.
625 Some clocksource names to choose from, depending on
627 [all] jiffies (this is the base, fallback clocksource)
629 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
630 pxa_timer,timer3,32k_counter,timer0_1
632 [X86-32] pit,hpet,tsc;
633 scx200_hrt on Geode; cyclone on IBM x440
641 clearcpuid=BITNUM [X86]
642 Disable CPUID feature X for the kernel. See
643 arch/x86/include/asm/cpufeature.h for the valid bit
644 numbers. Note the Linux specific bits are not necessarily
645 stable over kernel options, but the vendor specific
647 Also note that user programs calling CPUID directly
648 or using the feature without checking anything
649 will still see it. This just prevents it from
650 being used by the kernel or shown in /proc/cpuinfo.
651 Also note the kernel might malfunction if you disable
654 cma=nn[MG]@[start[MG][-end[MG]]]
656 Sets the size of kernel global memory area for
657 contiguous memory allocations and optionally the
658 placement constraint by the physical address range of
659 memory allocations. For more information, see
660 include/linux/dma-contiguous.h
662 cmo_free_hint= [PPC] Format: { yes | no }
663 Specify whether pages are marked as being inactive
664 when they are freed. This is used in CMO environments
665 to determine OS memory pressure for page stealing by
669 coherent_pool=nn[KMG] [ARM,KNL]
670 Sets the size of memory pool for coherent, atomic dma
671 allocations, by default set to 256K.
673 code_bytes [X86] How many bytes of object code to print
678 com20020= [HW,NET] ARCnet - COM20020 chipset
680 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
682 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
686 ARCnet - COM90xx chipset (memory-mapped buffers)
687 Format: <io>[,<irq>[,<memstart>]]
689 condev= [HW,S390] console device
692 console= [KNL] Output console device and options.
694 tty<n> Use the virtual console device <n>.
698 Use the specified serial port. The options are of
699 the form "bbbbpnf", where "bbbb" is the baud rate,
700 "p" is parity ("n", "o", or "e"), "n" is number of
701 bits, and "f" is flow control ("r" for RTS or
702 omit it). Default is "9600n8".
704 See Documentation/serial-console.txt for more
706 Documentation/networking/netconsole.txt for an
709 uart[8250],io,<addr>[,options]
710 uart[8250],mmio,<addr>[,options]
711 Start an early, polled-mode console on the 8250/16550
712 UART at the specified I/O port or MMIO address,
713 switching to the matching ttyS device later. The
714 options are the same as for ttyS, above.
715 hvc<n> Use the hypervisor console device <n>. This is for
716 both Xen and PowerPC hypervisors.
718 If the device connected to the port is not a TTY but a braille
719 device, prepend "brl," before the device type, for instance
721 For now, only VisioBraille is supported.
723 consoleblank= [KNL] The console blank (screen saver) timeout in
724 seconds. Defaults to 10*60 = 10mins. A value of 0
725 disables the blank timer.
728 [KNL] Change the default value for
729 /proc/<pid>/coredump_filter.
730 See also Documentation/filesystems/proc.txt.
732 cpuidle.off=1 [CPU_IDLE]
733 disable the cpuidle sub-system
735 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
737 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
739 crashkernel=size[KMG][@offset[KMG]]
740 [KNL] Using kexec, Linux can switch to a 'crash kernel'
741 upon panic. This parameter reserves the physical
742 memory region [offset, offset + size] for that kernel
743 image. If '@offset' is omitted, then a suitable offset
744 is selected automatically. Check
745 Documentation/kdump/kdump.txt for further details.
747 crashkernel=range1:size1[,range2:size2,...][@offset]
748 [KNL] Same as above, but depends on the memory
749 in the running system. The syntax of range is
750 start-[end] where start and end are both
751 a memory unit (amount[KMG]). See also
752 Documentation/kdump/kdump.txt for an example.
754 crashkernel=size[KMG],high
755 [KNL, x86_64] range could be above 4G. Allow kernel
756 to allocate physical memory region from top, so could
757 be above 4G if system have more than 4G ram installed.
758 Otherwise memory region will be allocated below 4G, if
760 It will be ignored if crashkernel=X is specified.
761 crashkernel=size[KMG],low
762 [KNL, x86_64] range under 4G. When crashkernel=X,high
763 is passed, kernel could allocate physical memory region
764 above 4G, that cause second kernel crash on system
765 that require some amount of low memory, e.g. swiotlb
766 requires at least 64M+32K low memory. Kernel would
767 try to allocate 72M below 4G automatically.
768 This one let user to specify own low range under 4G
769 for second kernel instead.
770 0: to disable low allocation.
771 It will be ignored when crashkernel=X,high is not used
772 or memory reserved is below 4G.
777 cs89x0_media= [HW,NET]
778 Format: { rj45 | aui | bnc }
781 See header of drivers/s390/block/dasd_devmap.c.
783 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
784 (one device per port)
785 Format: <port#>,<type>
786 See also Documentation/input/joystick-parport.txt
788 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
789 time. See Documentation/dynamic-debug-howto.txt for
790 details. Deprecated, see dyndbg.
792 debug [KNL] Enable kernel debugging (events log level).
795 [KNL] verbose self-tests
797 Print debugging info while doing the locking API
799 We default to 0 (no extra messages), setting it to
800 1 will print _a lot_ more information - normally
801 only useful to kernel developers.
803 debug_objects [KNL] Enable object debugging
806 [KNL] Disable object debugging
808 debug_guardpage_minorder=
809 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
810 parameter allows control of the order of pages that will
811 be intentionally kept free (and hence protected) by the
812 buddy allocator. Bigger value increase the probability
813 of catching random memory corruption, but reduce the
814 amount of memory for normal system use. The maximum
815 possible value is MAX_ORDER/2. Setting this parameter
816 to 1 or 2 should be enough to identify most random
817 memory corruption problems caused by bugs in kernel or
818 driver code when a CPU writes to (or reads from) a
819 random memory location. Note that there exists a class
820 of memory corruptions problems caused by buggy H/W or
821 F/W or by drivers badly programing DMA (basically when
822 memory is written at bus level and the CPU MMU is
823 bypassed) which are not detectable by
824 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
825 tracking down these problems.
827 debugpat [X86] Enable PAT debugging
829 decnet.addr= [HW,NET]
830 Format: <area>[,<node>]
831 See also Documentation/networking/decnet.txt.
834 [same as hugepagesz=] The size of the default
835 HugeTLB page size. This is the size represented by
836 the legacy /proc/ hugepages APIs, used for SHM, and
837 default size when mounting hugetlbfs filesystems.
838 Defaults to the default architecture's huge page size
842 Set number of hash buckets for dentry cache.
845 See Documentation/networking/ipv6.txt.
847 disable_cpu_apicid= [X86,APIC,SMP]
849 The number of initial APIC ID for the
850 corresponding CPU to be disabled at boot,
851 mostly used for the kdump 2nd kernel to
852 disable BSP to wake up multiple CPUs without
853 causing system reset or hang due to sending
856 disable_ddw [PPC/PSERIES]
857 Disable Dynamic DMA Window support. Use this if
858 to workaround buggy firmware.
861 See Documentation/networking/ipv6.txt.
863 disable_mtrr_cleanup [X86]
864 The kernel tries to adjust MTRR layout from continuous
865 to discrete, to make X server driver able to add WB
866 entry later. This parameter disables that.
868 disable_mtrr_trim [X86, Intel and AMD only]
869 By default the kernel will trim any uncacheable
870 memory out of your available memory pool based on
871 MTRR settings. This parameter disables that behavior,
872 possibly causing your machine to run very slowly.
874 disable_timer_pin_1 [X86]
875 Disable PIN 1 of APIC timer
876 Can be useful to work around chipset bugs.
878 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
879 this option disables the debugging code at boot.
881 dma_debug_entries=<number>
882 This option allows to tune the number of preallocated
883 entries for DMA-API debugging code. One entry is
884 required per DMA-API allocation. Use this if the
885 DMA-API debugging code disables itself because the
886 architectural default is too low.
888 dma_debug_driver=<driver_name>
889 With this option the DMA-API debugging driver
890 filter feature can be enabled at boot time. Just
891 pass the driver to filter for as the parameter.
892 The filter can be disabled or changed to another
893 driver later using sysfs.
895 drm_kms_helper.edid_firmware=[<connector>:]<file>
896 Broken monitors, graphic adapters and KVMs may
897 send no or incorrect EDID data sets. This parameter
898 allows to specify an EDID data set in the
899 /lib/firmware directory that is used instead.
900 Generic built-in EDID data sets are used, if one of
901 edid/1024x768.bin, edid/1280x1024.bin,
902 edid/1680x1050.bin, or edid/1920x1080.bin is given
903 and no file with the same name exists. Details and
904 instructions how to build your own EDID data are
905 available in Documentation/EDID/HOWTO.txt. An EDID
906 data set will only be used for a particular connector,
907 if its name and a colon are prepended to the EDID
912 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
913 module.dyndbg[="val"]
914 Enable debug messages at boot time. See
915 Documentation/dynamic-debug-howto.txt for details.
917 early_ioremap_debug [KNL]
918 Enable debug messages in early_ioremap support. This
919 is useful for tracking down temporary early mappings
920 which are not unmapped.
922 earlycon= [KNL] Output early console device and options.
924 uart[8250],io,<addr>[,options]
925 uart[8250],mmio,<addr>[,options]
926 uart[8250],mmio32,<addr>[,options]
927 Start an early, polled-mode console on the 8250/16550
928 UART at the specified I/O port or MMIO address.
929 MMIO inter-register address stride is either 8-bit
930 (mmio) or 32-bit (mmio32).
931 The options are the same as for ttyS, above.
934 Start an early, polled-mode console on a pl011 serial
935 port at the specified address. The pl011 serial port
936 must already be setup and configured. Options are not
939 smh Use ARM semihosting calls for early console.
941 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
945 earlyprintk=serial[,ttySn[,baudrate]]
946 earlyprintk=serial[,0x...[,baudrate]]
947 earlyprintk=ttySn[,baudrate]
948 earlyprintk=dbgp[debugController#]
950 earlyprintk is useful when the kernel crashes before
951 the normal console is initialized. It is not enabled by
952 default because it has some cosmetic problems.
954 Append ",keep" to not disable it when the real console
957 Only one of vga, efi, serial, or usb debug port can
960 Currently only ttyS0 and ttyS1 may be specified by
961 name. Other I/O ports may be explicitly specified
962 on some architectures (x86 and arm at least) by
963 replacing ttySn with an I/O port address, like this:
964 earlyprintk=serial,0x1008,115200
965 You can find the port for a given device in
966 /proc/tty/driver/serial:
967 2: uart:ST16650V2 port:00001008 irq:18 ...
969 Interaction with the standard serial driver is not
972 The VGA and EFI output is eventually overwritten by
975 The xen output can only be used by Xen PV guests.
977 edac_report= [HW,EDAC] Control how to report EDAC event
978 Format: {"on" | "off" | "force"}
979 on: enable EDAC to report H/W event. May be overridden
980 by other higher priority error reporting module.
981 off: disable H/W event reporting through EDAC.
982 force: enforce the use of EDAC to report H/W event.
985 ekgdboc= [X86,KGDB] Allow early kernel console debugging
988 This is designed to be used in conjunction with
989 the boot argument: earlyprintk=vga
992 Format: {"off" | "on" | "skip[mbr]"}
995 Format: { "old_map" }
996 old_map [X86-64]: switch to the old ioremap-based EFI
997 runtime services mapping. 32-bit still uses this one by
1000 efi_no_storage_paranoia [EFI; X86]
1001 Using this parameter you can use more than 50% of
1002 your efi variable storage. Use this parameter only if
1003 you are really sure that your UEFI does sane gc and
1004 fulfills the spec otherwise your board may brick.
1006 eisa_irq_edge= [PARISC,HW]
1007 See header of drivers/parisc/eisa.c.
1010 See comment before function elanfreq_setup() in
1011 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1014 Format: {"cfq" | "deadline" | "noop"}
1015 See Documentation/block/cfq-iosched.txt and
1016 Documentation/block/deadline-iosched.txt for details.
1018 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1019 Specifies physical address of start of kernel core
1020 image elf header and optionally the size. Generally
1021 kexec loader will pass this option to capture kernel.
1022 See Documentation/kdump/kdump.txt for details.
1024 enable_mtrr_cleanup [X86]
1025 The kernel tries to adjust MTRR layout from continuous
1026 to discrete, to make X server driver able to add WB
1027 entry later. This parameter enables that.
1029 enable_timer_pin_1 [X86]
1030 Enable PIN 1 of APIC timer
1031 Can be useful to work around chipset bugs
1032 (in particular on some ATI chipsets).
1033 The kernel tries to set a reasonable default.
1035 enforcing [SELINUX] Set initial enforcing status.
1037 See security/selinux/Kconfig help text.
1038 0 -- permissive (log only, no denials).
1039 1 -- enforcing (deny and log).
1041 Value can be changed at runtime via /selinux/enforce.
1044 Disable Error Record Serialization Table (ERST)
1047 ether= [HW,NET] Ethernet cards parameters
1048 This option is obsoleted by the "netdev=" option, which
1049 has equivalent usage. See its documentation for details.
1053 Permit 'security.evm' to be updated regardless of
1054 current integrity status.
1058 fail_make_request=[KNL]
1059 General fault injection mechanism.
1060 Format: <interval>,<probability>,<space>,<times>
1061 See also Documentation/fault-injection/.
1064 See Documentation/blockdev/floppy.txt.
1066 force_pal_cache_flush
1067 [IA-64] Avoid check_sal_cache_flush which may hang on
1068 buggy SAL_CACHE_FLUSH implementations. Using this
1069 parameter will force ia64_sal_cache_flush to call
1070 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1073 Forcefully enable Physical Address Extension (PAE).
1074 Many Pentium M systems disable PAE but may have a
1075 functionally usable PAE implementation.
1076 Warning: use of this parameter will taint the kernel
1077 and may cause unknown problems.
1080 [FTRACE] will set and start the specified tracer
1081 as early as possible in order to facilitate early
1084 ftrace_dump_on_oops[=orig_cpu]
1085 [FTRACE] will dump the trace buffers on oops.
1086 If no parameter is passed, ftrace will dump
1087 buffers of all CPUs, but if you pass orig_cpu, it will
1088 dump only the buffer of the CPU that triggered the
1091 ftrace_filter=[function-list]
1092 [FTRACE] Limit the functions traced by the function
1093 tracer at boot up. function-list is a comma separated
1094 list of functions. This list can be changed at run
1095 time by the set_ftrace_filter file in the debugfs
1098 ftrace_notrace=[function-list]
1099 [FTRACE] Do not trace the functions specified in
1100 function-list. This list can be changed at run time
1101 by the set_ftrace_notrace file in the debugfs
1104 ftrace_graph_filter=[function-list]
1105 [FTRACE] Limit the top level callers functions traced
1106 by the function graph tracer at boot up.
1107 function-list is a comma separated list of functions
1108 that can be changed at run time by the
1109 set_graph_function file in the debugfs tracing directory.
1111 ftrace_graph_notrace=[function-list]
1112 [FTRACE] Do not trace from the functions specified in
1113 function-list. This list is a comma separated list of
1114 functions that can be changed at run time by the
1115 set_graph_notrace file in the debugfs tracing directory.
1118 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1119 support via parallel port (up to 5 devices per port)
1120 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1121 See also Documentation/input/joystick-parport.txt
1125 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1129 gcov_persist= [GCOV] When non-zero (default), profiling data for
1130 kernel modules is saved and remains accessible via
1131 debugfs, even when the module is unloaded/reloaded.
1132 When zero, profiling data is discarded and associated
1133 debugfs files are removed at module unload time.
1135 gpt [EFI] Forces disk with valid GPT signature but
1136 invalid Protective MBR to be treated as GPT. If the
1137 primary GPT is corrupted, it enables the backup/alternate
1138 GPT to be used instead.
1140 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1141 the "Enable 0" bit of the configuration register.
1144 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1145 the "Enable 0" bit of the configuration register.
1148 grcan.select= [HW] Select which physical interface to use.
1151 grcan.txsize= [HW] Sets the size of the tx buffer.
1152 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1154 grcan.rxsize= [HW] Sets the size of the rx buffer.
1155 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1158 hashdist= [KNL,NUMA] Large hashes allocated during boot
1159 are distributed across NUMA nodes. Defaults on
1160 for 64-bit NUMA, off otherwise.
1161 Format: 0 | 1 (for off | on)
1163 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1165 hd= [EIDE] (E)IDE hard drive subsystem geometry
1166 Format: <cyl>,<head>,<sect>
1169 Disable Hardware Error Source Table (HEST) support;
1170 corresponding firmware-first mode error processing
1171 logic will be disabled.
1173 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1174 size of <nn>. This works even on boxes that have no
1175 highmem otherwise. This also works to reduce highmem
1176 size on bigger boxes.
1178 highres= [KNL] Enable/disable high resolution timer mode.
1179 Valid parameters: "on", "off"
1183 See Documentation/isdn/README.HiSax.
1187 hpet= [X86-32,HPET] option to control HPET usage
1188 Format: { enable (default) | disable | force |
1190 disable: disable HPET and use PIT instead
1191 force: allow force enabled of undocumented chips (ICH4,
1193 verbose: show contents of HPET registers during setup
1195 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1196 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1198 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1199 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1200 On x86-64 and powerpc, this option can be specified
1201 multiple times interleaved with hugepages= to reserve
1202 huge pages of different sizes. Valid pages sizes on
1203 x86-64 are 2M (when the CPU supports "pse") and 1G
1204 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1205 Note that 1GB pages can only be allocated at boot time
1206 using hugepages= and not freed afterwards.
1208 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1209 terminal devices. Valid values: 0..8
1210 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1211 If specified, z/VM IUCV HVC accepts connections
1212 from listed z/VM user IDs only.
1214 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1215 hardware thread id mappings.
1216 Format: <cpu>:<hwthread>
1219 Do not unregister boot console at start. This is only
1220 useful for debugging when something happens in the window
1221 between unregistering the boot console and initializing
1224 i2c_bus= [HW] Override the default board specific I2C bus speed
1225 or register an additional I2C bus that is not
1226 registered from board initialization code.
1230 i8042.debug [HW] Toggle i8042 debug mode
1231 i8042.direct [HW] Put keyboard port into non-translated mode
1232 i8042.dumbkbd [HW] Pretend that controller can only read data from
1233 keyboard and cannot control its state
1234 (Don't attempt to blink the leds)
1235 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1236 i8042.nokbd [HW] Don't check/create keyboard port
1237 i8042.noloop [HW] Disable the AUX Loopback command while probing
1239 i8042.nomux [HW] Don't check presence of an active multiplexing
1241 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1243 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1244 i8042.reset [HW] Reset the controller during init and cleanup
1245 i8042.unlock [HW] Unlock (ignore) the keylock
1249 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1250 indicates that the driver is running on unsupported
1252 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1253 does not match list of supported models.
1255 [HW] Report power status in /proc/i8k
1256 (disabled by default)
1257 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1260 i915.invert_brightness=
1261 [DRM] Invert the sense of the variable that is used to
1262 set the brightness of the panel backlight. Normally a
1263 brightness value of 0 indicates backlight switched off,
1264 and the maximum of the brightness value sets the backlight
1265 to maximum brightness. If this parameter is set to 0
1266 (default) and the machine requires it, or this parameter
1267 is set to 1, a brightness value of 0 sets the backlight
1268 to maximum brightness, and the maximum of the brightness
1269 value switches the backlight off.
1270 -1 -- never invert brightness
1271 0 -- machine default
1272 1 -- force brightness inversion
1275 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1277 ide-core.nodma= [HW] (E)IDE subsystem
1278 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1279 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1280 .cdrom .chs .ignore_cable are additional options
1281 See Documentation/ide/ide.txt.
1283 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1284 Claim all unknown PCI IDE storage controllers.
1287 Format: idle=poll, idle=halt, idle=nomwait
1288 Poll forces a polling idle loop that can slightly
1289 improve the performance of waking up a idle CPU, but
1290 will use a lot of power and make the system run hot.
1292 idle=halt: Halt is forced to be used for CPU idle.
1293 In such case C2/C3 won't be used again.
1294 idle=nomwait: Disable mwait for CPU C-states
1296 ignore_loglevel [KNL]
1297 Ignore loglevel setting - this will print /all/
1298 kernel messages to the console. Useful for debugging.
1299 We also add it as printk module parameter, so users
1300 could change it dynamically, usually by
1301 /sys/module/printk/parameters/ignore_loglevel.
1303 ihash_entries= [KNL]
1304 Set number of hash buckets for inode cache.
1306 ima_appraise= [IMA] appraise integrity measurements
1307 Format: { "off" | "enforce" | "fix" | "log" }
1310 ima_appraise_tcb [IMA]
1311 The builtin appraise policy appraises all files
1315 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1319 The list of supported hash algorithms is defined
1320 in crypto/hash_info.h.
1323 Load a policy which meets the needs of the Trusted
1324 Computing Base. This means IMA will measure all
1325 programs exec'd, files mmap'd for exec, and all files
1326 opened for read by uid=0.
1329 Select one of defined IMA measurements template formats.
1330 Formats: { "ima" | "ima-ng" }
1334 [IMA] Define a custom template format.
1335 Format: { "field1|...|fieldN" }
1337 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1338 Format: <min_file_size>
1339 Set the minimal file size for using asynchronous hash.
1340 If left unspecified, ahash usage is disabled.
1342 ahash performance varies for different data sizes on
1343 different crypto accelerators. This option can be used
1344 to achieve the best performance for a particular HW.
1346 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1348 Set hashing buffer size. Default: 4k.
1350 ahash performance varies for different chunk sizes on
1351 different crypto accelerators. This option can be used
1352 to achieve best performance for particular HW.
1356 Run specified binary instead of /sbin/init as init
1359 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1360 for working out where the kernel is dying during
1363 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1364 initcall functions. Useful for debugging built-in
1365 modules and initcalls.
1367 initrd= [BOOT] Specify the location of the initial ramdisk
1369 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1372 int_pln_enable [x86] Enable power limit notification interrupt
1374 integrity_audit=[IMA]
1375 Format: { "0" | "1" }
1376 0 -- basic integrity auditing messages. (Default)
1377 1 -- additional integrity auditing messages.
1379 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1381 Enable intel iommu driver.
1383 Disable intel iommu driver.
1384 igfx_off [Default Off]
1385 By default, gfx is mapped as normal device. If a gfx
1386 device has a dedicated DMAR unit, the DMAR unit is
1387 bypassed by not enabling DMAR with this option. In
1388 this case, gfx device will use physical address for
1391 With this option iommu will not optimize to look
1392 for io virtual address below 32-bit forcing dual
1393 address cycle on pci bus for cards supporting greater
1394 than 32-bit addressing. The default is to look
1395 for translation below 32-bit and if not available
1396 then look in the higher range.
1397 strict [Default Off]
1398 With this option on every unmap_single operation will
1399 result in a hardware IOTLB flush operation as opposed
1400 to batching them for performance.
1401 sp_off [Default Off]
1402 By default, super page will be supported if Intel IOMMU
1403 has the capability. With this option, super page will
1406 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1407 0 disables intel_idle and fall back on acpi_idle.
1408 1 to 6 specify maximum depth of C-state.
1412 Do not enable intel_pstate as the default
1413 scaling driver for the supported processors
1415 intremap= [X86-64, Intel-IOMMU]
1416 on enable Interrupt Remapping (default)
1417 off disable Interrupt Remapping
1418 nosid disable Source ID checking
1420 BIOS x2APIC opt-out request will be ignored
1422 iomem= Disable strict checking of access to MMIO memory
1423 strict regions from userspace.
1440 io7= [HW] IO7 for Marvel based alpha systems
1441 See comment before marvel_specify_io7 in
1442 arch/alpha/kernel/core_marvel.c.
1444 io_delay= [X86] I/O delay method
1446 Standard port 0x80 based delay
1448 Alternate port 0xed based delay (needed on some systems)
1450 Simple two microseconds delay
1455 See Documentation/filesystems/nfs/nfsroot.txt.
1458 When an interrupt is not handled search all handlers
1459 for it. Intended to get systems with badly broken
1463 When an interrupt is not handled search all handlers
1464 for it. Also check all handlers each timer
1465 interrupt. Intended to get systems with badly broken
1469 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1471 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1473 <cpu number>,...,<cpu number>
1475 <cpu number>-<cpu number>
1476 (must be a positive range in ascending order)
1478 <cpu number>,...,<cpu number>-<cpu number>
1480 This option can be used to specify one or more CPUs
1481 to isolate from the general SMP balancing and scheduling
1482 algorithms. You can move a process onto or off an
1483 "isolated" CPU via the CPU affinity syscalls or cpuset.
1484 <cpu number> begins at 0 and the maximum value is
1485 "number of CPUs in system - 1".
1487 This option is the preferred way to isolate CPUs. The
1488 alternative -- manually setting the CPU mask of all
1489 tasks in the system -- can cause problems and
1490 suboptimal load balancer performance.
1494 ivrs_ioapic [HW,X86_64]
1495 Provide an override to the IOAPIC-ID<->DEVICE-ID
1496 mapping provided in the IVRS ACPI table. For
1497 example, to map IOAPIC-ID decimal 10 to
1498 PCI device 00:14.0 write the parameter as:
1499 ivrs_ioapic[10]=00:14.0
1501 ivrs_hpet [HW,X86_64]
1502 Provide an override to the HPET-ID<->DEVICE-ID
1503 mapping provided in the IVRS ACPI table. For
1504 example, to map HPET-ID decimal 0 to
1505 PCI device 00:14.0 write the parameter as:
1506 ivrs_hpet[0]=00:14.0
1508 js= [HW,JOY] Analog joystick
1509 See Documentation/input/joystick.txt.
1512 Enable/disable kernel and module base offset ASLR
1513 (Address Space Layout Randomization) if built into
1514 the kernel. When CONFIG_HIBERNATION is selected,
1515 kASLR is disabled by default. When kASLR is enabled,
1516 hibernation will be disabled.
1520 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1521 specifies the amount of memory usable by the kernel
1522 for non-movable allocations. The requested amount is
1523 spread evenly throughout all nodes in the system. The
1524 remaining memory in each node is used for Movable
1525 pages. In the event, a node is too small to have both
1526 kernelcore and Movable pages, kernelcore pages will
1527 take priority and other nodes will have a larger number
1528 of Movable pages. The Movable zone is used for the
1529 allocation of pages that may be reclaimed or moved
1530 by the page migration subsystem. This means that
1531 HugeTLB pages may not be allocated from this zone.
1532 Note that allocations like PTEs-from-HighMem still
1533 use the HighMem zone if it exists, and the Normal
1534 zone if it does not.
1536 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1537 Format: <Controller#>[,poll interval]
1538 The controller # is the number of the ehci usb debug
1539 port as it is probed via PCI. The poll interval is
1540 optional and is the number seconds in between
1541 each poll cycle to the debug port in case you need
1542 the functionality for interrupting the kernel with
1543 gdb or control-c on the dbgp connection. When
1544 not using this parameter you use sysrq-g to break into
1545 the kernel debugger.
1547 kgdboc= [KGDB,HW] kgdb over consoles.
1548 Requires a tty driver that supports console polling,
1549 or a supported polling keyboard driver (non-usb).
1550 Serial only format: <serial_device>[,baud]
1551 keyboard only format: kbd
1552 keyboard and serial format: kbd,<serial_device>[,baud]
1553 Optional Kernel mode setting:
1554 kms, kbd format: kms,kbd
1555 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1557 kgdbwait [KGDB] Stop kernel execution and enter the
1558 kernel debugger at the earliest opportunity.
1560 kmac= [MIPS] korina ethernet MAC address.
1561 Configure the RouterBoard 532 series on-chip
1562 Ethernet adapter MAC address.
1564 kmemleak= [KNL] Boot-time kmemleak enable/disable
1565 Valid arguments: on, off
1568 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1569 Valid arguments: 0, 1, 2
1570 kmemcheck=0 (disabled)
1571 kmemcheck=1 (enabled)
1572 kmemcheck=2 (one-shot mode)
1573 Default: 2 (one-shot mode)
1575 kstack=N [X86] Print N words from the kernel stack
1578 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1579 Default is 0 (don't ignore, but inject #GP)
1581 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1585 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1586 Default is 1 (enabled)
1588 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1590 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1592 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1593 (virtualized MMU) support on capable Intel chips.
1594 Default is 1 (enabled)
1596 kvm-intel.emulate_invalid_guest_state=
1597 [KVM,Intel] Enable emulation of invalid guest states
1598 Default is 0 (disabled)
1600 kvm-intel.flexpriority=
1601 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1602 Default is 1 (enabled)
1605 [KVM,Intel] Enable VMX nesting (nVMX).
1606 Default is 0 (disabled)
1608 kvm-intel.unrestricted_guest=
1609 [KVM,Intel] Disable unrestricted guest feature
1610 (virtualized real and unpaged mode) on capable
1611 Intel chips. Default is 1 (enabled)
1613 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1614 feature (tagged TLBs) on capable Intel chips.
1615 Default is 1 (enabled)
1621 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1624 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1625 value for LAPIC timer one-shot implementation. Default
1626 back to the programmable timer unit in the LAPIC.
1628 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1631 libata.dma= [LIBATA] DMA control
1632 libata.dma=0 Disable all PATA and SATA DMA
1633 libata.dma=1 PATA and SATA Disk DMA only
1634 libata.dma=2 ATAPI (CDROM) DMA only
1635 libata.dma=4 Compact Flash DMA only
1636 Combinations also work, so libata.dma=3 enables DMA
1637 for disks and CDROMs, but not CFs.
1639 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1640 libata.ignore_hpa=0 keep BIOS limits (default)
1641 libata.ignore_hpa=1 ignore limits, using full disk
1643 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1647 libata.force= [LIBATA] Force configurations. The format is comma
1648 separated list of "[ID:]VAL" where ID is
1649 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1650 matching port, link or device. Basically, it matches
1651 the ATA ID string printed on console by libata. If
1652 the whole ID part is omitted, the last PORT and DEVICE
1653 values are used. If ID hasn't been specified yet, the
1654 configuration applies to all ports, links and devices.
1656 If only DEVICE is omitted, the parameter applies to
1657 the port and all links and devices behind it. DEVICE
1658 number of 0 either selects the first device or the
1659 first fan-out link behind PMP device. It does not
1660 select the host link. DEVICE number of 15 selects the
1661 host link and device attached to it.
1663 The VAL specifies the configuration to force. As long
1664 as there's no ambiguity shortcut notation is allowed.
1665 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1666 The following configurations can be forced.
1668 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1669 Any ID with matching PORT is used.
1671 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1673 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1674 udma[/][16,25,33,44,66,100,133] notation is also
1677 * [no]ncq: Turn on or off NCQ.
1679 * nohrst, nosrst, norst: suppress hard, soft
1682 * rstonce: only attempt one reset during
1683 hot-unplug link recovery
1685 * dump_id: dump IDENTIFY data.
1687 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1689 * disable: Disable this device.
1691 If there are multiple matching configurations changing
1692 the same attribute, the last one is used.
1694 memblock=debug [KNL] Enable memblock debug messages.
1696 load_ramdisk= [RAM] List of ramdisks to load from floppy
1697 See Documentation/blockdev/ramdisk.txt.
1699 lockd.nlm_grace_period=P [NFS] Assign grace period.
1702 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1705 lockd.nlm_timeout=T [NFS] Assign timeout value.
1708 lockd.nlm_udpport=M [NFS] Assign UDP port.
1711 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1714 loglevel= All Kernel Messages with a loglevel smaller than the
1715 console loglevel will be printed to the console. It can
1716 also be changed with klogd or other programs. The
1717 loglevels are defined as follows:
1719 0 (KERN_EMERG) system is unusable
1720 1 (KERN_ALERT) action must be taken immediately
1721 2 (KERN_CRIT) critical conditions
1722 3 (KERN_ERR) error conditions
1723 4 (KERN_WARNING) warning conditions
1724 5 (KERN_NOTICE) normal but significant condition
1725 6 (KERN_INFO) informational
1726 7 (KERN_DEBUG) debug-level messages
1728 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1729 in bytes. n must be a power of two and greater
1730 than the minimal size. The minimal size is defined
1731 by LOG_BUF_SHIFT kernel config parameter. There is
1732 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1733 that allows to increase the default size depending on
1734 the number of CPUs. See init/Kconfig for more details.
1736 logo.nologo [FB] Disables display of the built-in Linux logo.
1737 This may be used to provide more screen space for
1738 kernel log messages and is useful when debugging
1739 kernel boot problems.
1741 lp=0 [LP] Specify parallel ports to use, e.g,
1742 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1743 lp=reset first parallel port). 'lp=0' disables the
1744 lp=auto printer driver. 'lp=reset' (which can be
1745 specified in addition to the ports) causes
1746 attached printers to be reset. Using
1747 lp=port1,port2,... specifies the parallel ports
1748 to associate lp devices with, starting with
1749 lp0. A port specification may be 'none' to skip
1750 that lp device, or a parport name such as
1751 'parport0'. Specifying 'lp=auto' instead of a
1752 port specification list means that device IDs
1753 from each port should be examined, to see if
1754 an IEEE 1284-compliant printer is attached; if
1755 so, the driver will manage that printer.
1756 See also header of drivers/char/lp.c.
1759 Sets loops_per_jiffy to given constant, thus avoiding
1760 time-consuming boot-time autodetection (up to 250 ms per
1761 CPU). 0 enables autodetection (default). To determine
1762 the correct value for your kernel, boot with normal
1763 autodetection and see what value is printed. Note that
1764 on SMP systems the preset will be applied to all CPUs,
1765 which is likely to cause problems if your CPUs need
1766 significantly divergent settings. An incorrect value
1767 will cause delays in the kernel to be wrong, leading to
1768 unpredictable I/O errors and other breakage. Although
1769 unlikely, in the extreme case this might damage your
1773 Format: <io>,<irq>,<dma>
1775 machvec= [IA-64] Force the use of a particular machine-vector
1776 (machvec) in a generic kernel.
1777 Example: machvec=hpzx1_swiotlb
1779 machtype= [Loongson] Share the same kernel image file between different
1781 Example: machtype=lemote-yeeloong-2f-7inch
1783 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1784 than or equal to this physical address is ignored.
1786 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1787 should make use of. maxcpus=n : n >= 0 limits the
1788 kernel to using 'n' processors. n=0 is a special case,
1789 it is equivalent to "nosmp", which also disables
1792 max_loop= [LOOP] The number of loop block devices that get
1793 (loop.max_loop) unconditionally pre-created at init time. The default
1794 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1795 of statically allocating a predefined number, loop
1796 devices can be requested on-demand with the
1797 /dev/loop-control interface.
1799 mce [X86-32] Machine Check Exception
1801 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1803 md= [HW] RAID subsystems devices and level
1804 See Documentation/md.txt.
1807 Format: <first>,<last>
1808 Specifies range of consoles to be captured by the MDA.
1810 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1811 Amount of memory to be used when the kernel is not able
1812 to see the whole system memory or for test.
1813 [X86] Work as limiting max address. Use together
1814 with memmap= to avoid physical address space collisions.
1815 Without memmap= PCI devices could be placed at addresses
1816 belonging to unused RAM.
1818 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1822 [KNL,SH] Allow user to override the default size for
1823 per-device physically contiguous DMA buffers.
1825 memmap=exactmap [KNL,X86] Enable setting of an exact
1826 E820 memory map, as specified by the user.
1827 Such memmap=exactmap lines can be constructed based on
1828 BIOS output or other requirements. See the memmap=nn@ss
1831 memmap=nn[KMG]@ss[KMG]
1832 [KNL] Force usage of a specific region of memory.
1833 Region of memory to be used is from ss to ss+nn.
1835 memmap=nn[KMG]#ss[KMG]
1836 [KNL,ACPI] Mark specific memory as ACPI data.
1837 Region of memory to be marked is from ss to ss+nn.
1839 memmap=nn[KMG]$ss[KMG]
1840 [KNL,ACPI] Mark specific memory as reserved.
1841 Region of memory to be reserved is from ss to ss+nn.
1842 Example: Exclude memory from 0x18690000-0x1869ffff
1843 memmap=64K$0x18690000
1845 memmap=0x10000$0x18690000
1847 memory_corruption_check=0/1 [X86]
1848 Some BIOSes seem to corrupt the first 64k of
1849 memory when doing things like suspend/resume.
1850 Setting this option will scan the memory
1851 looking for corruption. Enabling this will
1852 both detect corruption and prevent the kernel
1853 from using the memory being corrupted.
1854 However, its intended as a diagnostic tool; if
1855 repeatable BIOS-originated corruption always
1856 affects the same memory, you can use memmap=
1857 to prevent the kernel from using that memory.
1859 memory_corruption_check_size=size [X86]
1860 By default it checks for corruption in the low
1861 64k, making this memory unavailable for normal
1862 use. Use this parameter to scan for
1863 corruption in more or less memory.
1865 memory_corruption_check_period=seconds [X86]
1866 By default it checks for corruption every 60
1867 seconds. Use this parameter to check at some
1868 other rate. 0 disables periodic checking.
1870 memtest= [KNL,X86] Enable memtest
1872 default : 0 <disable>
1873 Specifies the number of memtest passes to be
1874 performed. Each pass selects another test
1875 pattern from a given set of patterns. Memtest
1876 fills the memory with this pattern, validates
1877 memory contents and reserves bad memory
1878 regions that are detected.
1880 meye.*= [HW] Set MotionEye Camera parameters
1881 See Documentation/video4linux/meye.txt.
1883 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1884 Multi-Function General Purpose Timers on AMD Geode
1887 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1888 the BIOS has incorrectly applied a workaround. TinyBIOS
1889 version 0.98 is known to be affected, 0.99 fixes the
1890 problem by letting the user disable the workaround.
1894 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1895 physical address is ignored.
1897 mini2440= [ARM,HW,KNL]
1898 Format:[0..2][b][c][t]
1900 MINI2440 configuration specification:
1901 0 - The attached screen is the 3.5" TFT
1902 1 - The attached screen is the 7" TFT
1903 2 - The VGA Shield is attached (1024x768)
1904 Leaving out the screen size parameter will not load
1905 the TFT driver, and the framebuffer will be left
1907 b - Enable backlight. The TFT backlight pin will be
1908 linked to the kernel VESA blanking code and a GPIO
1909 LED. This parameter is not necessary when using the
1911 c - Enable the s3c camera interface.
1912 t - Reserved for enabling touchscreen support. The
1913 touchscreen support is not enabled in the mainstream
1914 kernel as of 2.6.30, a preliminary port can be found
1915 in the "bleeding edge" mini2440 support kernel at
1916 http://repo.or.cz/w/linux-2.6/mini2440.git
1919 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1920 parameter allows control of the logging verbosity for
1921 the additional memory initialisation checks. A value
1922 of 0 disables mminit logging and a level of 4 will
1923 log everything. Information is printed at KERN_DEBUG
1924 so loglevel=8 may also need to be specified.
1927 [KNL] When CONFIG_MODULE_SIG is set, this means that
1928 modules without (valid) signatures will fail to load.
1929 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1930 is always true, so this option does nothing.
1933 [MOUSE] Maximum time between finger touching and
1934 leaving touchpad surface for touch to be considered
1935 a tap and be reported as a left button click (for
1936 touchpads working in absolute mode only).
1938 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1939 reporting absolute coordinates, such as tablets
1940 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1941 reporting absolute coordinates, such as tablets
1943 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1944 is similar to kernelcore except it specifies the
1945 amount of memory used for migratable allocations.
1946 If both kernelcore and movablecore is specified,
1947 then kernelcore will be at *least* the specified
1948 value but may be more. If movablecore on its own
1949 is specified, the administrator must be careful
1950 that the amount of memory usable for all allocations
1953 movable_node [KNL,X86] Boot-time switch to enable the effects
1954 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
1956 MTD_Partition= [MTD]
1957 Format: <name>,<region-number>,<size>,<offset>
1959 MTD_Region= [MTD] Format:
1960 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1963 See drivers/mtd/cmdlinepart.c.
1965 multitce=off [PPC] This parameter disables the use of the pSeries
1966 firmware feature for updating multiple TCE entries
1969 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1971 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1973 boundary - index of last SLC block on Flex-OneNAND.
1974 The remaining blocks are configured as MLC blocks.
1975 lock - Configure if Flex-OneNAND boundary should be locked.
1976 Once locked, the boundary cannot be changed.
1977 1 indicates lock status, 0 indicates unlock status.
1980 ARM/S3C2412 JIVE boot control
1982 See arch/arm/mach-s3c2412/mach-jive.c
1984 mtouchusb.raw_coordinates=
1985 [HW] Make the MicroTouch USB driver use raw coordinates
1986 ('y', default) or cooked coordinates ('n')
1988 mtrr_chunk_size=nn[KMG] [X86]
1989 used for mtrr cleanup. It is largest continuous chunk
1990 that could hold holes aka. UC entries.
1992 mtrr_gran_size=nn[KMG] [X86]
1993 Used for mtrr cleanup. It is granularity of mtrr block.
1995 Large value could prevent small alignment from
1998 mtrr_spare_reg_nr=n [X86]
2000 Range: 0,7 : spare reg number
2002 Used for mtrr cleanup. It is spare mtrr entries number.
2003 Set to 2 or more if your graphical card needs more.
2005 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2007 netdev= [NET] Network devices parameters
2008 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2009 Note that mem_start is often overloaded to mean
2010 something different and driver-specific.
2011 This usage is only documented in each driver source
2015 [NETFILTER] Enable connection tracking flow accounting
2016 0 to disable accounting
2017 1 to enable accounting
2020 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2021 See Documentation/filesystems/nfs/nfsroot.txt.
2023 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2024 See Documentation/filesystems/nfs/nfsroot.txt.
2026 nfsrootdebug [NFS] enable nfsroot debugging messages.
2027 See Documentation/filesystems/nfs/nfsroot.txt.
2029 nfs.callback_tcpport=
2030 [NFS] set the TCP port on which the NFSv4 callback
2031 channel should listen.
2034 [NFS] sets the pathname to the program which is used
2035 to update the NFS client cache entries.
2037 nfs.cache_getent_timeout=
2038 [NFS] sets the timeout after which an attempt to
2039 update a cache entry is deemed to have failed.
2041 nfs.idmap_cache_timeout=
2042 [NFS] set the maximum lifetime for idmapper cache
2046 [NFS] enable 64-bit inode numbers.
2047 If zero, the NFS client will fake up a 32-bit inode
2048 number for the readdir() and stat() syscalls instead
2049 of returning the full 64-bit number.
2050 The default is to return 64-bit inode numbers.
2052 nfs.max_session_slots=
2053 [NFSv4.1] Sets the maximum number of session slots
2054 the client will attempt to negotiate with the server.
2055 This limits the number of simultaneous RPC requests
2056 that the client can send to the NFSv4.1 server.
2057 Note that there is little point in setting this
2058 value higher than the max_tcp_slot_table_limit.
2060 nfs.nfs4_disable_idmapping=
2061 [NFSv4] When set to the default of '1', this option
2062 ensures that both the RPC level authentication
2063 scheme and the NFS level operations agree to use
2064 numeric uids/gids if the mount is using the
2065 'sec=sys' security flavour. In effect it is
2066 disabling idmapping, which can make migration from
2067 legacy NFSv2/v3 systems to NFSv4 easier.
2068 Servers that do not support this mode of operation
2069 will be autodetected by the client, and it will fall
2070 back to using the idmapper.
2071 To turn off this behaviour, set the value to '0'.
2073 [NFS4] Specify an additional fixed unique ident-
2074 ification string that NFSv4 clients can insert into
2075 their nfs_client_id4 string. This is typically a
2076 UUID that is generated at system install time.
2078 nfs.send_implementation_id =
2079 [NFSv4.1] Send client implementation identification
2080 information in exchange_id requests.
2081 If zero, no implementation identification information
2083 The default is to send the implementation identification
2086 nfs.recover_lost_locks =
2087 [NFSv4] Attempt to recover locks that were lost due
2088 to a lease timeout on the server. Please note that
2089 doing this risks data corruption, since there are
2090 no guarantees that the file will remain unchanged
2091 after the locks are lost.
2092 If you want to enable the kernel legacy behaviour of
2093 attempting to recover these locks, then set this
2095 The default parameter value of '0' causes the kernel
2096 not to attempt recovery of lost locks.
2098 nfsd.nfs4_disable_idmapping=
2099 [NFSv4] When set to the default of '1', the NFSv4
2100 server will return only numeric uids and gids to
2101 clients using auth_sys, and will accept numeric uids
2102 and gids from such clients. This is intended to ease
2103 migration from NFSv2/v3.
2105 objlayoutdriver.osd_login_prog=
2106 [NFS] [OBJLAYOUT] sets the pathname to the program which
2107 is used to automatically discover and login into new
2108 osd-targets. Please see:
2109 Documentation/filesystems/pnfs.txt for more explanations
2111 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2112 when a NMI is triggered.
2113 Format: [state][,regs][,debounce][,die]
2115 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2116 Format: [panic,][nopanic,][num]
2118 0 - turn nmi_watchdog off
2119 When panic is specified, panic when an NMI watchdog
2120 timeout occurs (or 'nopanic' to override the opposite
2122 This is useful when you use a panic=... timeout and
2123 need the box quickly up again.
2125 netpoll.carrier_timeout=
2126 [NET] Specifies amount of time (in seconds) that
2127 netpoll should wait for a carrier. By default netpoll
2130 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2131 emulation library even if a 387 maths coprocessor
2135 [HW] Never suspend the console
2136 Disable suspending of consoles during suspend and
2137 hibernate operations. Once disabled, debugging
2138 messages can reach various consoles while the rest
2139 of the system is being put to sleep (ie, while
2140 debugging driver suspend/resume hooks). This may
2141 not work reliably with all consoles, but is known
2142 to work with serial and VGA consoles.
2143 To facilitate more flexible debugging, we also add
2144 console_suspend, a printk module parameter to control
2145 it. Users could use console_suspend (usually
2146 /sys/module/printk/parameters/console_suspend) to
2147 turn on/off it dynamically.
2149 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2150 caches in the slab allocator. Saves per-node memory,
2151 but will impact performance.
2155 noapic [SMP,APIC] Tells the kernel to not make use of any
2156 IOAPICs that may be present in the system.
2158 noautogroup Disable scheduler automatic task group creation.
2160 nobats [PPC] Do not use BATs for mapping kernel lowmem
2161 on "Classic" PPC cores.
2165 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2167 nodelayacct [KNL] Disable per-task delay accounting
2169 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2171 nodsp [SH] Disable hardware DSP at boot time.
2173 noefi [X86] Disable EFI runtime services support.
2178 On X86-32 available only on PAE configured kernels.
2179 noexec=on: enable non-executable mappings (default)
2180 noexec=off: disable non-executable mappings
2183 Disable SMAP (Supervisor Mode Access Prevention)
2184 even if it is supported by processor.
2187 Disable SMEP (Supervisor Mode Execution Prevention)
2188 even if it is supported by processor.
2191 This affects only 32-bit executables.
2192 noexec32=on: enable non-executable mappings (default)
2193 read doesn't imply executable mappings
2194 noexec32=off: disable non-executable mappings
2195 read implies executable mappings
2197 nofpu [SH] Disable hardware FPU at boot time.
2199 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2200 register save and restore. The kernel will only save
2201 legacy floating-point registers on task switch.
2203 noxsave [BUGS=X86] Disables x86 extended register state save
2204 and restore using xsave. The kernel will fallback to
2205 enabling legacy floating-point and sse state.
2207 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2208 register states. The kernel will fall back to use
2209 xsave to save the states. By using this parameter,
2210 performance of saving the states is degraded because
2211 xsave doesn't support modified optimization while
2212 xsaveopt supports it on xsaveopt enabled systems.
2214 noxsaves [X86] Disables xsaves and xrstors used in saving and
2215 restoring x86 extended register state in compacted
2216 form of xsave area. The kernel will fall back to use
2217 xsaveopt and xrstor to save and restore the states
2218 in standard form of xsave area. By using this
2219 parameter, xsave area per process might occupy more
2220 memory on xsaves enabled systems.
2223 on enable eager fpu restore
2224 off disable eager fpu restore
2225 auto selects the default scheme, which automatically
2226 enables eagerfpu restore for xsaveopt.
2228 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2229 wfi(ARM) instruction doesn't work correctly and not to
2230 use it. This is also useful when using JTAG debugger.
2232 no_file_caps Tells the kernel not to honor file capabilities. The
2233 only way then for a file to be executed with privilege
2234 is to be setuid root or executed by root.
2236 nohalt [IA-64] Tells the kernel not to use the power saving
2237 function PAL_HALT_LIGHT when idle. This increases
2238 power-consumption. On the positive side, it reduces
2239 interrupt wake-up latency, which may improve performance
2240 in certain environments such as networked servers or
2243 nohibernate [HIBERNATION] Disable hibernation and resume.
2245 nohz= [KNL] Boottime enable/disable dynamic ticks
2246 Valid arguments: on, off
2249 nohz_full= [KNL,BOOT]
2250 In kernels built with CONFIG_NO_HZ_FULL=y, set
2251 the specified list of CPUs whose tick will be stopped
2252 whenever possible. The boot CPU will be forced outside
2253 the range to maintain the timekeeping.
2254 The CPUs in this range must also be included in the
2257 noiotrap [SH] Disables trapped I/O port accesses.
2259 noirqdebug [X86-32] Disables the code which attempts to detect and
2260 disable unhandled interrupt sources.
2262 no_timer_check [X86,APIC] Disables the code which tests for
2263 broken timer IRQ sources.
2265 noisapnp [ISAPNP] Disables ISA PnP code.
2267 noinitrd [RAM] Tells the kernel not to load any configured
2270 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2272 [Deprecated - use intremap=off]
2276 nojitter [IA-64] Disables jitter checking for ITC timers.
2278 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2280 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2283 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2284 steal time is computed, but won't influence scheduler
2287 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2289 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2291 noltlbs [PPC] Do not use large page/tlb entries for kernel
2292 lowmem mapping on PPC40x.
2294 nomca [IA-64] Disable machine check abort handling
2296 nomce [X86-32] Machine Check Exception
2298 nomfgpt [X86-32] Disable Multi-Function General Purpose
2299 Timer usage (for AMD Geode machines).
2301 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2302 shutdown the other cpus. Instead use the REBOOT_VECTOR
2305 nomodule Disable module load
2307 nopat [X86] Disable PAT (page attribute table extension of
2308 pagetables) support.
2310 norandmaps Don't use address space randomization. Equivalent to
2311 echo 0 > /proc/sys/kernel/randomize_va_space
2313 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2315 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2316 with UP alternatives
2318 nordrand [X86] Disable kernel use of the RDRAND and
2319 RDSEED instructions even if they are supported
2320 by the processor. RDRAND and RDSEED are still
2321 available to user space applications.
2323 noresume [SWSUSP] Disables resume and restores original swap
2326 no-scroll [VGA] Disables scrollback.
2327 This is required for the Braillex ib80-piezo Braille
2328 reader made by F.H. Papenmeier (Germany).
2332 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2334 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2335 and disable the IO APIC. legacy for "maxcpus=0".
2337 nosoftlockup [KNL] Disable the soft-lockup detector.
2339 nosync [HW,M68K] Disables sync negotiation for all devices.
2341 notsc [BUGS=X86-32] Disable Time Stamp Counter
2343 nousb [USB] Disable the USB subsystem
2345 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2349 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2351 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2352 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2353 Some features depend on CPU0. Known dependencies are:
2354 1. Resume from suspend/hibernate depends on CPU0.
2355 Suspend/hibernate will fail if CPU0 is offline and you
2356 need to online CPU0 before suspend/hibernate.
2357 2. PIC interrupts also depend on CPU0. CPU0 can't be
2358 removed if a PIC interrupt is detected.
2359 It's said poweroff/reboot may depend on CPU0 on some
2360 machines although I haven't seen such issues so far
2361 after CPU0 is offline on a few tested machines.
2362 If the dependencies are under your control, you can
2363 turn on cpu0_hotplug.
2365 nptcg= [IA-64] Override max number of concurrent global TLB
2366 purges which is reported from either PAL_VM_SUMMARY or
2369 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2370 could support. nr_cpus=n : n >= 1 limits the kernel to
2371 supporting 'n' processors. Later in runtime you can not
2372 use hotplug cpu feature to put more cpu back to online.
2373 just like you compile the kernel NR_CPUS=n
2375 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2377 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2378 Allowed values are enable and disable
2380 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2381 one of ['zone', 'node', 'default'] can be specified
2382 This can be set from sysctl after boot.
2383 See Documentation/sysctl/vm.txt for details.
2385 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2386 See Documentation/debugging-via-ohci1394.txt for more
2389 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2390 Rather than timing out after 20 ms if an EC
2391 command is not properly ACKed, override the length
2392 of the timeout. We have interrupts disabled while
2393 waiting for the ACK, so if this is set too high
2394 interrupts *may* be lost!
2396 omap_mux= [OMAP] Override bootloader pin multiplexing.
2397 Format: <mux_mode0.mode_name=value>...
2398 For example, to override I2C bus2:
2399 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2401 oprofile.timer= [HW]
2402 Use timer interrupt instead of performance counters
2404 oprofile.cpu_type= Force an oprofile cpu type
2405 This might be useful if you have an older oprofile
2406 userland or if you want common events.
2407 Format: { arch_perfmon }
2408 arch_perfmon: [X86] Force use of architectural
2409 perfmon on Intel CPUs instead of the
2410 CPU specific event set.
2411 timer: [X86] Force use of architectural NMI
2412 timer mode (see also oprofile.timer
2413 for generic hr timer mode)
2414 [s390] Force legacy basic mode sampling
2415 (report cpu_type "timer")
2417 oops=panic Always panic on oopses. Default is to just kill the
2418 process, but there is a small probability of
2419 deadlocking the machine.
2420 This will also cause panics on machine check exceptions.
2421 Useful together with panic=30 to trigger a reboot.
2424 See Documentation/sound/oss/oss-parameters.txt
2426 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2427 timeout > 0: seconds before rebooting
2428 timeout = 0: wait forever
2429 timeout < 0: reboot immediately
2432 crash_kexec_post_notifiers
2433 Run kdump after running panic-notifiers and dumping
2434 kmsg. This only for the users who doubt kdump always
2435 succeeds in any situation.
2436 Note that this also increases risks of kdump failure,
2437 because some panic notifiers can make the crashed
2438 kernel more unstable.
2440 parkbd.port= [HW] Parallel port number the keyboard adapter is
2441 connected to, default is 0.
2443 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2444 0 for XT, 1 for AT (default is AT).
2447 parport= [HW,PPT] Specify parallel ports. 0 disables.
2448 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2449 Use 'auto' to force the driver to use any
2450 IRQ/DMA settings detected (the default is to
2451 ignore detected IRQ/DMA settings because of
2452 possible conflicts). You can specify the base
2453 address, IRQ, and DMA settings; IRQ and DMA
2454 should be numbers, or 'auto' (for using detected
2455 settings on that particular port), or 'nofifo'
2456 (to avoid using a FIFO even if it is detected).
2457 Parallel ports are assigned in the order they
2458 are specified on the command line, starting
2461 parport_init_mode= [HW,PPT]
2462 Configure VIA parallel port to operate in
2463 a specific mode. This is necessary on Pegasos
2464 computer where firmware has no options for setting
2465 up parallel port mode and sets it to spp.
2466 Currently this function knows 686a and 8231 chips.
2467 Format: [spp|ps2|epp|ecp|ecpepp]
2470 Halt all CPUs after the first oops has been printed for
2471 the specified number of seconds. This is to be used if
2472 your oopses keep scrolling off the screen.
2477 See header of drivers/block/paride/pcd.c.
2478 See also Documentation/blockdev/paride.txt.
2480 pci=option[,option...] [PCI] various PCI subsystem options:
2481 earlydump [X86] dump PCI config space before the kernel
2483 off [X86] don't probe for the PCI bus
2484 bios [X86-32] force use of PCI BIOS, don't access
2485 the hardware directly. Use this if your machine
2486 has a non-standard PCI host bridge.
2487 nobios [X86-32] disallow use of PCI BIOS, only direct
2488 hardware access methods are allowed. Use this
2489 if you experience crashes upon bootup and you
2490 suspect they are caused by the BIOS.
2491 conf1 [X86] Force use of PCI Configuration
2493 conf2 [X86] Force use of PCI Configuration
2495 noaer [PCIE] If the PCIEAER kernel config parameter is
2496 enabled, this kernel boot option can be used to
2497 disable the use of PCIE advanced error reporting.
2498 nodomains [PCI] Disable support for multiple PCI
2499 root domains (aka PCI segments, in ACPI-speak).
2500 nommconf [X86] Disable use of MMCONFIG for PCI
2502 check_enable_amd_mmconf [X86] check for and enable
2503 properly configured MMIO access to PCI
2504 config space on AMD family 10h CPU
2505 nomsi [MSI] If the PCI_MSI kernel config parameter is
2506 enabled, this kernel boot option can be used to
2507 disable the use of MSI interrupts system-wide.
2508 noioapicquirk [APIC] Disable all boot interrupt quirks.
2509 Safety option to keep boot IRQs enabled. This
2510 should never be necessary.
2511 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2512 primary IO-APIC for bridges that cannot disable
2513 boot IRQs. This fixes a source of spurious IRQs
2514 when the system masks IRQs.
2515 noioapicreroute [APIC] Disable workaround that uses the
2516 boot IRQ equivalent of an IRQ that connects to
2517 a chipset where boot IRQs cannot be disabled.
2518 The opposite of ioapicreroute.
2519 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2520 routing table. These calls are known to be buggy
2521 on several machines and they hang the machine
2522 when used, but on other computers it's the only
2523 way to get the interrupt routing table. Try
2524 this option if the kernel is unable to allocate
2525 IRQs or discover secondary PCI buses on your
2527 rom [X86] Assign address space to expansion ROMs.
2528 Use with caution as certain devices share
2529 address decoders between ROMs and other
2531 norom [X86] Do not assign address space to
2532 expansion ROMs that do not already have
2533 BIOS assigned address ranges.
2534 nobar [X86] Do not assign address space to the
2535 BARs that weren't assigned by the BIOS.
2536 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2537 assigned automatically to PCI devices. You can
2538 make the kernel exclude IRQs of your ISA cards
2540 pirqaddr=0xAAAAA [X86] Specify the physical address
2541 of the PIRQ table (normally generated
2542 by the BIOS) if it is outside the
2543 F0000h-100000h range.
2544 lastbus=N [X86] Scan all buses thru bus #N. Can be
2545 useful if the kernel is unable to find your
2546 secondary buses and you want to tell it
2547 explicitly which ones they are.
2548 assign-busses [X86] Always assign all PCI bus
2549 numbers ourselves, overriding
2550 whatever the firmware may have done.
2551 usepirqmask [X86] Honor the possible IRQ mask stored
2552 in the BIOS $PIR table. This is needed on
2553 some systems with broken BIOSes, notably
2554 some HP Pavilion N5400 and Omnibook XE3
2555 notebooks. This will have no effect if ACPI
2556 IRQ routing is enabled.
2557 noacpi [X86] Do not use ACPI for IRQ routing
2558 or for PCI scanning.
2559 use_crs [X86] Use PCI host bridge window information
2560 from ACPI. On BIOSes from 2008 or later, this
2561 is enabled by default. If you need to use this,
2562 please report a bug.
2563 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2564 If you need to use this, please report a bug.
2565 routeirq Do IRQ routing for all PCI devices.
2566 This is normally done in pci_enable_device(),
2567 so this option is a temporary workaround
2568 for broken drivers that don't call it.
2569 skip_isa_align [X86] do not align io start addr, so can
2570 handle more pci cards
2571 firmware [ARM] Do not re-enumerate the bus but instead
2572 just use the configuration from the
2573 bootloader. This is currently used on
2574 IXP2000 systems where the bus has to be
2575 configured a certain way for adjunct CPUs.
2576 noearly [X86] Don't do any early type 1 scanning.
2577 This might help on some broken boards which
2578 machine check when some devices' config space
2579 is read. But various workarounds are disabled
2580 and some IOMMU drivers will not work.
2581 bfsort Sort PCI devices into breadth-first order.
2582 This sorting is done to get a device
2583 order compatible with older (<= 2.4) kernels.
2584 nobfsort Don't sort PCI devices into breadth-first order.
2585 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2586 tuning and use the BIOS-configured MPS defaults.
2587 pcie_bus_safe Set every device's MPS to the largest value
2588 supported by all devices below the root complex.
2589 pcie_bus_perf Set device MPS to the largest allowable MPS
2590 based on its parent bus. Also set MRRS (Max
2591 Read Request Size) to the largest supported
2592 value (no larger than the MPS that the device
2593 or bus can support) for best performance.
2594 pcie_bus_peer2peer Set every device's MPS to 128B, which
2595 every device is guaranteed to support. This
2596 configuration allows peer-to-peer DMA between
2597 any pair of devices, possibly at the cost of
2598 reduced performance. This also guarantees
2599 that hot-added devices will work.
2600 cbiosize=nn[KMG] The fixed amount of bus space which is
2601 reserved for the CardBus bridge's IO window.
2602 The default value is 256 bytes.
2603 cbmemsize=nn[KMG] The fixed amount of bus space which is
2604 reserved for the CardBus bridge's memory
2605 window. The default value is 64 megabytes.
2608 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2609 Specifies alignment and device to reassign
2610 aligned memory resources.
2611 If <order of align> is not specified,
2612 PAGE_SIZE is used as alignment.
2613 PCI-PCI bridge can be specified, if resource
2614 windows need to be expanded.
2615 ecrc= Enable/disable PCIe ECRC (transaction layer
2616 end-to-end CRC checking).
2617 bios: Use BIOS/firmware settings. This is the
2621 hpiosize=nn[KMG] The fixed amount of bus space which is
2622 reserved for hotplug bridge's IO window.
2623 Default size is 256 bytes.
2624 hpmemsize=nn[KMG] The fixed amount of bus space which is
2625 reserved for hotplug bridge's memory window.
2626 Default size is 2 megabytes.
2627 realloc= Enable/disable reallocating PCI bridge resources
2628 if allocations done by BIOS are too small to
2629 accommodate resources required by all child
2631 off: Turn realloc off
2633 realloc same as realloc=on
2634 noari do not use PCIe ARI.
2635 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2636 only look for one device below a PCIe downstream
2639 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2642 force Enable ASPM even on devices that claim not to support it.
2643 WARNING: Forcing ASPM on may cause system lockups.
2645 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2646 nomsi Do not use MSI for PCI Express Native Hotplug (this
2647 makes all PCIe ports use INTx for hotplug services).
2649 pcie_ports= [PCIE] PCIe ports handling:
2650 auto Ask the BIOS whether or not to use native PCIe services
2651 associated with PCIe ports (PME, hot-plug, AER). Use
2652 them only if that is allowed by the BIOS.
2653 native Use native PCIe services associated with PCIe ports
2655 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2658 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2659 nomsi Do not use MSI for native PCIe PME signaling (this makes
2660 all PCIe root ports use INTx for all services).
2662 pcmv= [HW,PCMCIA] BadgePAD 4
2666 Keep all power-domains already enabled by bootloader on,
2667 even if no driver has claimed them. This is useful
2668 for debug and development, but should not be
2669 needed on a platform with proper driver support.
2672 See Documentation/blockdev/paride.txt.
2674 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2677 See arch/parisc/kernel/pdc_chassis.c
2679 percpu_alloc= Select which percpu first chunk allocator to use.
2680 Currently supported values are "embed" and "page".
2681 Archs may support subset or none of the selections.
2682 See comments in mm/percpu.c for details on each
2683 allocator. This parameter is primarily for debugging
2684 and performance comparison.
2687 See Documentation/blockdev/paride.txt.
2690 See Documentation/blockdev/paride.txt.
2692 pirq= [SMP,APIC] Manual mp-table setup
2693 See Documentation/x86/i386/IO-APIC.txt.
2695 plip= [PPT,NET] Parallel port network link
2696 Format: { parport<nr> | timid | 0 }
2697 See also Documentation/parport.txt.
2699 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2700 Override pmtimer IOPort with a hex value.
2704 Enable PNP debug messages (depends on the
2705 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2706 via /sys/module/pnp/parameters/debug. We always show
2707 current resource usage; turning this on also shows
2708 possible settings and some assignment information.
2714 { on | off | curr | res | no-curr | no-res }
2717 [ISAPNP] Exclude IRQs for the autoconfiguration
2720 [ISAPNP] Exclude DMAs for the autoconfiguration
2722 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2723 Ranges are in pairs (I/O port base and size).
2726 [ISAPNP] Exclude memory regions for the
2728 Ranges are in pairs (memory base and size).
2730 ports= [IP_VS_FTP] IPVS ftp helper module
2732 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2734 Format: <port>,<port>....
2736 print-fatal-signals=
2737 [KNL] debug: print fatal signals
2739 If enabled, warn about various signal handling
2740 related application anomalies: too many signals,
2741 too many POSIX.1 timers, fatal signals causing a
2744 If you hit the warning due to signal overflow,
2745 you might want to try "ulimit -i unlimited".
2749 printk.always_kmsg_dump=
2750 Trigger kmsg_dump for cases other than kernel oops or
2752 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2755 printk.time= Show timing data prefixed to each printk message line
2756 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2758 processor.max_cstate= [HW,ACPI]
2759 Limit processor to maximum C-state
2760 max_cstate=9 overrides any DMI blacklist limit.
2762 processor.nocst [HW,ACPI]
2763 Ignore the _CST method to determine C-states,
2764 instead using the legacy FADT method
2766 profile= [KNL] Enable kernel profiling via /proc/profile
2767 Format: [schedule,]<number>
2768 Param: "schedule" - profile schedule points.
2769 Param: <number> - step/bucket size as a power of 2 for
2770 statistical time based profiling.
2771 Param: "sleep" - profile D-state sleeping (millisecs).
2772 Requires CONFIG_SCHEDSTATS
2773 Param: "kvm" - profile VM exits.
2775 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2777 See Documentation/blockdev/ramdisk.txt.
2779 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2780 probe for; one of (bare|imps|exps|lifebook|any).
2781 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2783 psmouse.resetafter= [HW,MOUSE]
2784 Try to reset the device after so many bad packets
2787 [HW,MOUSE] Set desired mouse resolution, in dpi.
2788 psmouse.smartscroll=
2789 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2790 0 = disabled, 1 = enabled (default).
2792 pstore.backend= Specify the name of the pstore backend to use
2795 See Documentation/blockdev/paride.txt.
2798 [KNL] Number of legacy pty's. Overwrites compiled-in
2801 quiet [KNL] Disable most log messages
2806 See Documentation/md.txt.
2808 ramdisk_blocksize= [RAM]
2809 See Documentation/blockdev/ramdisk.txt.
2811 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2812 See Documentation/blockdev/ramdisk.txt.
2815 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2816 the specified list of CPUs to be no-callback CPUs.
2817 Invocation of these CPUs' RCU callbacks will
2818 be offloaded to "rcuox/N" kthreads created for
2819 that purpose, where "x" is "b" for RCU-bh, "p"
2820 for RCU-preempt, and "s" for RCU-sched, and "N"
2821 is the CPU number. This reduces OS jitter on the
2822 offloaded CPUs, which can be useful for HPC and
2823 real-time workloads. It can also improve energy
2824 efficiency for asymmetric multiprocessors.
2827 Rather than requiring that offloaded CPUs
2828 (specified by rcu_nocbs= above) explicitly
2829 awaken the corresponding "rcuoN" kthreads,
2830 make these kthreads poll for callbacks.
2831 This improves the real-time response for the
2832 offloaded CPUs by relieving them of the need to
2833 wake up the corresponding kthread, but degrades
2834 energy efficiency by requiring that the kthreads
2835 periodically wake up to do the polling.
2837 rcutree.blimit= [KNL]
2838 Set maximum number of finished RCU callbacks to
2839 process in one batch.
2841 rcutree.rcu_fanout_leaf= [KNL]
2842 Increase the number of CPUs assigned to each
2843 leaf rcu_node structure. Useful for very large
2846 rcutree.jiffies_till_sched_qs= [KNL]
2847 Set required age in jiffies for a
2848 given grace period before RCU starts
2849 soliciting quiescent-state help from
2850 rcu_note_context_switch().
2852 rcutree.jiffies_till_first_fqs= [KNL]
2853 Set delay from grace-period initialization to
2854 first attempt to force quiescent states.
2855 Units are jiffies, minimum value is zero,
2856 and maximum value is HZ.
2858 rcutree.jiffies_till_next_fqs= [KNL]
2859 Set delay between subsequent attempts to force
2860 quiescent states. Units are jiffies, minimum
2861 value is one, and maximum value is HZ.
2863 rcutree.rcu_nocb_leader_stride= [KNL]
2864 Set the number of NOCB kthread groups, which
2865 defaults to the square root of the number of
2866 CPUs. Larger numbers reduces the wakeup overhead
2867 on the per-CPU grace-period kthreads, but increases
2868 that same overhead on each group's leader.
2870 rcutree.qhimark= [KNL]
2871 Set threshold of queued RCU callbacks beyond which
2872 batch limiting is disabled.
2874 rcutree.qlowmark= [KNL]
2875 Set threshold of queued RCU callbacks below which
2876 batch limiting is re-enabled.
2878 rcutree.rcu_idle_gp_delay= [KNL]
2879 Set wakeup interval for idle CPUs that have
2880 RCU callbacks (RCU_FAST_NO_HZ=y).
2882 rcutree.rcu_idle_lazy_gp_delay= [KNL]
2883 Set wakeup interval for idle CPUs that have
2884 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2885 Lazy RCU callbacks are those which RCU can
2886 prove do nothing more than free memory.
2888 rcutorture.fqs_duration= [KNL]
2889 Set duration of force_quiescent_state bursts.
2891 rcutorture.fqs_holdoff= [KNL]
2892 Set holdoff time within force_quiescent_state bursts.
2894 rcutorture.fqs_stutter= [KNL]
2895 Set wait time between force_quiescent_state bursts.
2897 rcutorture.gp_exp= [KNL]
2898 Use expedited update-side primitives.
2900 rcutorture.gp_normal= [KNL]
2901 Use normal (non-expedited) update-side primitives.
2902 If both gp_exp and gp_normal are set, do both.
2903 If neither gp_exp nor gp_normal are set, still
2906 rcutorture.n_barrier_cbs= [KNL]
2907 Set callbacks/threads for rcu_barrier() testing.
2909 rcutorture.nfakewriters= [KNL]
2910 Set number of concurrent RCU writers. These just
2911 stress RCU, they don't participate in the actual
2912 test, hence the "fake".
2914 rcutorture.nreaders= [KNL]
2915 Set number of RCU readers.
2917 rcutorture.object_debug= [KNL]
2918 Enable debug-object double-call_rcu() testing.
2920 rcutorture.onoff_holdoff= [KNL]
2921 Set time (s) after boot for CPU-hotplug testing.
2923 rcutorture.onoff_interval= [KNL]
2924 Set time (s) between CPU-hotplug operations, or
2925 zero to disable CPU-hotplug testing.
2927 rcutorture.rcutorture_runnable= [BOOT]
2928 Start rcutorture running at boot time.
2930 rcutorture.shuffle_interval= [KNL]
2931 Set task-shuffle interval (s). Shuffling tasks
2932 allows some CPUs to go into dyntick-idle mode
2933 during the rcutorture test.
2935 rcutorture.shutdown_secs= [KNL]
2936 Set time (s) after boot system shutdown. This
2937 is useful for hands-off automated testing.
2939 rcutorture.stall_cpu= [KNL]
2940 Duration of CPU stall (s) to test RCU CPU stall
2941 warnings, zero to disable.
2943 rcutorture.stall_cpu_holdoff= [KNL]
2944 Time to wait (s) after boot before inducing stall.
2946 rcutorture.stat_interval= [KNL]
2947 Time (s) between statistics printk()s.
2949 rcutorture.stutter= [KNL]
2950 Time (s) to stutter testing, for example, specifying
2951 five seconds causes the test to run for five seconds,
2952 wait for five seconds, and so on. This tests RCU's
2953 ability to transition abruptly to and from idle.
2955 rcutorture.test_boost= [KNL]
2956 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2957 "Maybe" means test if the RCU implementation
2958 under test support RCU priority boosting.
2960 rcutorture.test_boost_duration= [KNL]
2961 Duration (s) of each individual boost test.
2963 rcutorture.test_boost_interval= [KNL]
2964 Interval (s) between each boost test.
2966 rcutorture.test_no_idle_hz= [KNL]
2967 Test RCU's dyntick-idle handling. See also the
2968 rcutorture.shuffle_interval parameter.
2970 rcutorture.torture_type= [KNL]
2971 Specify the RCU implementation to test.
2973 rcutorture.verbose= [KNL]
2974 Enable additional printk() statements.
2976 rcupdate.rcu_expedited= [KNL]
2977 Use expedited grace-period primitives, for
2978 example, synchronize_rcu_expedited() instead
2979 of synchronize_rcu(). This reduces latency,
2980 but can increase CPU utilization, degrade
2981 real-time latency, and degrade energy efficiency.
2983 rcupdate.rcu_cpu_stall_suppress= [KNL]
2984 Suppress RCU CPU stall warning messages.
2986 rcupdate.rcu_cpu_stall_timeout= [KNL]
2987 Set timeout for RCU CPU stall warning messages.
2991 Run specified binary instead of /init from the ramdisk,
2992 used for early userspace startup. See initrd.
2995 Format (x86 or x86_64):
2996 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2998 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3000 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3001 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3002 reboot_force is either force or not specified,
3003 reboot_cpu is s[mp]#### with #### being the processor
3004 to be used for rebooting.
3007 [KNL, SMP] Set scheduler's default relax_domain_level.
3008 See Documentation/cgroups/cpusets.txt.
3010 relative_sleep_states=
3011 [SUSPEND] Use sleep state labeling where the deepest
3012 state available other than hibernation is always "mem".
3013 Format: { "0" | "1" }
3014 0 -- Traditional sleep state labels.
3015 1 -- Relative sleep state labels.
3017 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3019 reservetop= [X86-32]
3021 Reserves a hole at the top of the kernel virtual
3026 Set the amount of memory to reserve for BIOS at
3027 the bottom of the address space.
3029 reset_devices [KNL] Force drivers to reset the underlying device
3030 during initialization.
3033 Specify the partition device for software suspend
3035 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3037 resume_offset= [SWSUSP]
3038 Specify the offset from the beginning of the partition
3039 given by "resume=" at which the swap header is located,
3040 in <PAGE_SIZE> units (needed only for swap files).
3041 See Documentation/power/swsusp-and-swap-files.txt
3043 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3044 read the resume files
3046 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3047 Useful for devices that are detected asynchronously
3048 (e.g. USB and MMC devices).
3050 hibernate= [HIBERNATION]
3051 noresume Don't check if there's a hibernation image
3052 present during boot.
3053 nocompress Don't compress/decompress hibernation images.
3054 no Disable hibernation and resume.
3056 retain_initrd [RAM] Keep initrd memory after extraction
3058 rhash_entries= [KNL,NET]
3059 Set number of hash buckets for route cache
3061 ro [KNL] Mount root device read-only on boot
3063 root= [KNL] Root filesystem
3064 See name_to_dev_t comment in init/do_mounts.c.
3066 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3067 mount the root filesystem
3069 rootflags= [KNL] Set root filesystem mount option string
3071 rootfstype= [KNL] Set root filesystem type
3073 rootwait [KNL] Wait (indefinitely) for root device to show up.
3074 Useful for devices that are detected asynchronously
3075 (e.g. USB and MMC devices).
3077 rproc_mem=nn[KMG][@address]
3078 [KNL,ARM,CMA] Remoteproc physical memory block.
3079 Memory area to be used by remote processor image,
3082 rw [KNL] Mount root device read-write on boot
3084 S [KNL] Run init in single mode
3086 s390_iommu= [HW,S390]
3087 Set s390 IOTLB flushing mode
3089 With strict flushing every unmap operation will result in
3090 an IOTLB flush. Default is lazy flushing before reuse,
3094 See drivers/net/irda/sa1100_ir.c.
3096 sbni= [NET] Granch SBNI12 leased line adapter
3098 sched_debug [KNL] Enables verbose scheduler debug messages.
3100 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3101 xtime_lock contention on larger systems, and/or RCU lock
3102 contention on all systems with CONFIG_MAXSMP set.
3103 Format: { "0" | "1" }
3104 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3106 Note: increases power consumption, thus should only be
3107 enabled if running jitter sensitive (HPC/RT) workloads.
3109 security= [SECURITY] Choose a security module to enable at boot.
3110 If this boot parameter is not specified, only the first
3111 security module asking for security registration will be
3112 loaded. An invalid security module name will be treated
3113 as if no module has been chosen.
3115 selinux= [SELINUX] Disable or enable SELinux at boot time.
3116 Format: { "0" | "1" }
3117 See security/selinux/Kconfig help text.
3120 Default value is set via kernel config option.
3121 If enabled at boot time, /selinux/disable can be used
3122 later to disable prior to initial policy load.
3124 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3125 Format: { "0" | "1" }
3126 See security/apparmor/Kconfig help text
3129 Default value is set via kernel config option.
3131 serialnumber [BUGS=X86-32]
3134 Maximal number of shapers.
3136 show_msr= [x86] show boot-time MSR settings
3137 Format: { <integer> }
3138 Show boot-time (BIOS-initialized) MSR settings.
3139 The parameter means the number of CPUs to show,
3140 for example 1 means boot CPU only.
3147 slab_max_order= [MM, SLAB]
3148 Determines the maximum allowed order for slabs.
3149 A high setting may cause OOMs due to memory
3150 fragmentation. Defaults to 1 for systems with
3151 more than 32MB of RAM, 0 otherwise.
3153 slub_debug[=options[,slabs]] [MM, SLUB]
3154 Enabling slub_debug allows one to determine the
3155 culprit if slab objects become corrupted. Enabling
3156 slub_debug can create guard zones around objects and
3157 may poison objects when not in use. Also tracks the
3158 last alloc / free. For more information see
3159 Documentation/vm/slub.txt.
3161 slub_max_order= [MM, SLUB]
3162 Determines the maximum allowed order for slabs.
3163 A high setting may cause OOMs due to memory
3164 fragmentation. For more information see
3165 Documentation/vm/slub.txt.
3167 slub_min_objects= [MM, SLUB]
3168 The minimum number of objects per slab. SLUB will
3169 increase the slab order up to slub_max_order to
3170 generate a sufficiently large slab able to contain
3171 the number of objects indicated. The higher the number
3172 of objects the smaller the overhead of tracking slabs
3173 and the less frequently locks need to be acquired.
3174 For more information see Documentation/vm/slub.txt.
3176 slub_min_order= [MM, SLUB]
3177 Determines the minimum page order for slabs. Must be
3178 lower than slub_max_order.
3179 For more information see Documentation/vm/slub.txt.
3181 slub_nomerge [MM, SLUB]
3182 Disable merging of slabs with similar size. May be
3183 necessary if there is some reason to distinguish
3184 allocs to different slabs. Debug options disable
3185 merging on their own.
3186 For more information see Documentation/vm/slub.txt.
3189 Format: <io1>[,<io2>[,...,<io8>]]
3191 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3192 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3193 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3194 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3195 smsc-ircc2.ircc_irq= [HW] IRQ line
3196 smsc-ircc2.ircc_dma= [HW] DMA channel
3197 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3198 0: Toshiba Satellite 1800 (GP data pin select)
3199 1: Fast pin select (default)
3203 [KNL] Should the soft-lockup detector generate panics.
3206 softlockup_all_cpu_backtrace=
3207 [KNL] Should the soft-lockup detector generate
3208 backtraces on all cpus.
3211 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3212 See Documentation/laptops/sonypi.txt
3214 spia_io_base= [HW,MTD]
3220 Enabled the stack tracer on boot up.
3222 stacktrace_filter=[function-list]
3223 [FTRACE] Limit the functions that the stack tracer
3224 will trace at boot up. function-list is a comma separated
3225 list of functions. This list can be changed at run
3226 time by the stack_trace_filter file in the debugfs
3227 tracing directory. Note, this enables stack tracing
3228 and the stacktrace above is not needed.
3232 Set the STI (builtin display/keyboard on the HP-PARISC
3233 machines) console (graphic card) which should be used
3234 as the initial boot-console.
3235 See also comment in drivers/video/console/sticore.c.
3238 See comment in drivers/video/console/sticore.c.
3241 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3243 sunrpc.min_resvport=
3244 sunrpc.max_resvport=
3246 SunRPC servers often require that client requests
3247 originate from a privileged port (i.e. a port in the
3248 range 0 < portnr < 1024).
3249 An administrator who wishes to reserve some of these
3250 ports for other uses may adjust the range that the
3251 kernel's sunrpc client considers to be privileged
3252 using these two parameters to set the minimum and
3253 maximum port values.
3257 Control how the NFS server code allocates CPUs to
3258 service thread pools. Depending on how many NICs
3259 you have and where their interrupts are bound, this
3260 option will affect which CPUs will do NFS serving.
3261 Note: this parameter cannot be changed while the
3262 NFS server is running.
3264 auto the server chooses an appropriate mode
3265 automatically using heuristics
3266 global a single global pool contains all CPUs
3267 percpu one pool for each CPU
3268 pernode one pool for each NUMA node (equivalent
3269 to global on non-NUMA machines)
3271 sunrpc.tcp_slot_table_entries=
3272 sunrpc.udp_slot_table_entries=
3274 Sets the upper limit on the number of simultaneous
3275 RPC calls that can be sent from the client to a
3276 server. Increasing these values may allow you to
3277 improve throughput, but will also increase the
3278 amount of memory reserved for use by the client.
3281 [KNL] Enable accounting of swap in memory resource
3282 controller if no parameter or 1 is given or disable
3283 it if 0 is given (See Documentation/cgroups/memory.txt)
3285 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3286 Format: { <int> | force }
3287 <int> -- Number of I/O TLB slabs
3288 force -- force using of bounce buffers even if they
3289 wouldn't be automatically used by the kernel
3293 sysfs.deprecated=0|1 [KNL]
3294 Enable/disable old style sysfs layout for old udev
3295 on older distributions. When this option is enabled
3296 very new udev will not work anymore. When this option
3297 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3298 in older udev will not work anymore.
3299 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3300 the kernel configuration.
3302 sysrq_always_enabled
3304 Ignore sysrq setting - this boot parameter will
3305 neutralize any effect of /proc/sys/kernel/sysrq.
3306 Useful for debugging.
3310 test_suspend= [SUSPEND]
3311 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3312 standby suspend) as the system sleep state to briefly
3313 enter during system startup. The system is woken from
3314 this state using a wakeup-capable RTC alarm.
3316 thash_entries= [KNL,NET]
3317 Set number of hash buckets for TCP connection
3319 thermal.act= [HW,ACPI]
3320 -1: disable all active trip points in all thermal zones
3321 <degrees C>: override all lowest active trip points
3323 thermal.crt= [HW,ACPI]
3324 -1: disable all critical trip points in all thermal zones
3325 <degrees C>: override all critical trip points
3327 thermal.nocrt= [HW,ACPI]
3328 Set to disable actions on ACPI thermal zone
3329 critical and hot trip points.
3331 thermal.off= [HW,ACPI]
3332 1: disable ACPI thermal control
3334 thermal.psv= [HW,ACPI]
3335 -1: disable all passive trip points
3336 <degrees C>: override all passive trip points to this
3339 thermal.tzp= [HW,ACPI]
3340 Specify global default ACPI thermal zone polling rate
3341 <deci-seconds>: poll all this frequency
3342 0: no polling (default)
3345 Force threading of all interrupt handlers except those
3346 marked explicitly IRQF_NO_THREAD.
3349 Enable the Transcendent memory driver if built-in.
3351 tmem.cleancache=0|1 [KNL, XEN]
3352 Default is on (1). Disable the usage of the cleancache
3353 API to send anonymous pages to the hypervisor.
3355 tmem.frontswap=0|1 [KNL, XEN]
3356 Default is on (1). Disable the usage of the frontswap
3357 API to send swap pages to the hypervisor. If disabled
3358 the selfballooning and selfshrinking are force disabled.
3360 tmem.selfballooning=0|1 [KNL, XEN]
3361 Default is on (1). Disable the driving of swap pages
3364 tmem.selfshrinking=0|1 [KNL, XEN]
3365 Default is on (1). Partial swapoff that immediately
3366 transfers pages from Xen hypervisor back to the
3367 kernel based on different criteria.
3371 Specify if the kernel should make use of the cpu
3372 topology information if the hardware supports this.
3373 The scheduler will make use of this information and
3374 e.g. base its process migration decisions on it.
3379 tpm_suspend_pcr=[HW,TPM]
3380 Format: integer pcr id
3381 Specify that at suspend time, the tpm driver
3382 should extend the specified pcr with zeros,
3383 as a workaround for some chips which fail to
3384 flush the last written pcr on TPM_SaveState.
3385 This will guarantee that all the other pcrs
3388 trace_buf_size=nn[KMG]
3389 [FTRACE] will set tracing buffer size.
3391 trace_event=[event-list]
3392 [FTRACE] Set and start specified trace events in order
3393 to facilitate early boot debugging.
3394 See also Documentation/trace/events.txt
3396 trace_options=[option-list]
3397 [FTRACE] Enable or disable tracer options at boot.
3398 The option-list is a comma delimited list of options
3399 that can be enabled or disabled just as if you were
3400 to echo the option name into
3402 /sys/kernel/debug/tracing/trace_options
3404 For example, to enable stacktrace option (to dump the
3405 stack trace of each event), add to the command line:
3407 trace_options=stacktrace
3409 See also Documentation/trace/ftrace.txt "trace options"
3413 [FTRACE] enable this option to disable tracing when a
3414 warning is hit. This turns off "tracing_on". Tracing can
3415 be enabled again by echoing '1' into the "tracing_on"
3416 file located in /sys/kernel/debug/tracing/
3418 This option is useful, as it disables the trace before
3419 the WARNING dump is called, which prevents the trace to
3420 be filled with content caused by the warning output.
3422 This option can also be set at run time via the sysctl
3423 option: kernel/traceoff_on_warning
3425 transparent_hugepage=
3427 Format: [always|madvise|never]
3428 Can be used to control the default behavior of the system
3429 with respect to transparent hugepages.
3430 See Documentation/vm/transhuge.txt for more details.
3432 tsc= Disable clocksource stability checks for TSC.
3434 [x86] reliable: mark tsc clocksource as reliable, this
3435 disables clocksource verification at runtime, as well
3436 as the stability checks done at bootup. Used to enable
3437 high-resolution timer mode on older hardware, and in
3438 virtualized environment.
3439 [x86] noirqtime: Do not use TSC to do irq accounting.
3440 Used to run time disable IRQ_TIME_ACCOUNTING on any
3441 platforms where RDTSC is slow and this accounting
3444 turbografx.map[2|3]= [HW,JOY]
3445 TurboGraFX parallel port interface
3447 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3448 See also Documentation/input/joystick-parport.txt
3450 udbg-immortal [PPC] When debugging early kernel crashes that
3451 happen after console_init() and before a proper
3452 console driver takes over, this boot options might
3453 help "seeing" what's going on.
3455 uhash_entries= [KNL,NET]
3456 Set number of hash buckets for UDP/UDP-Lite connections
3459 [USB] Ignore overcurrent events (default N).
3460 Some badly-designed motherboards generate lots of
3461 bogus events, for ports that aren't wired to
3462 anything. Set this parameter to avoid log spamming.
3463 Note that genuine overcurrent events won't be
3467 [X86] Cause panic on unknown NMI.
3469 usbcore.authorized_default=
3470 [USB] Default USB device authorization:
3471 (default -1 = authorized except for wireless USB,
3472 0 = not authorized, 1 = authorized)
3474 usbcore.autosuspend=
3475 [USB] The autosuspend time delay (in seconds) used
3476 for newly-detected USB devices (default 2). This
3477 is the time required before an idle device will be
3478 autosuspended. Devices for which the delay is set
3479 to a negative value won't be autosuspended at all.
3481 usbcore.usbfs_snoop=
3482 [USB] Set to log all usbfs traffic (default 0 = off).
3484 usbcore.blinkenlights=
3485 [USB] Set to cycle leds on hubs (default 0 = off).
3487 usbcore.old_scheme_first=
3488 [USB] Start with the old device initialization
3489 scheme (default 0 = off).
3491 usbcore.usbfs_memory_mb=
3492 [USB] Memory limit (in MB) for buffers allocated by
3493 usbfs (default = 16, 0 = max = 2047).
3495 usbcore.use_both_schemes=
3496 [USB] Try the other device initialization scheme
3497 if the first one fails (default 1 = enabled).
3499 usbcore.initial_descriptor_timeout=
3500 [USB] Specifies timeout for the initial 64-byte
3501 USB_REQ_GET_DESCRIPTOR request in milliseconds
3502 (default 5000 = 5.0 seconds).
3505 [USBHID] The interval which mice are to be polled at.
3507 usb-storage.delay_use=
3508 [UMS] The delay in seconds before a new device is
3509 scanned for Logical Units (default 5).
3512 [UMS] A list of quirks entries to supplement or
3513 override the built-in unusual_devs list. List
3514 entries are separated by commas. Each entry has
3515 the form VID:PID:Flags where VID and PID are Vendor
3516 and Product ID values (4-digit hex numbers) and
3517 Flags is a set of characters, each corresponding
3518 to a common usb-storage quirk flag as follows:
3519 a = SANE_SENSE (collect more than 18 bytes
3521 b = BAD_SENSE (don't collect more than 18
3522 bytes of sense data);
3523 c = FIX_CAPACITY (decrease the reported
3524 device capacity by one sector);
3525 d = NO_READ_DISC_INFO (don't use
3526 READ_DISC_INFO command);
3527 e = NO_READ_CAPACITY_16 (don't use
3528 READ_CAPACITY_16 command);
3529 h = CAPACITY_HEURISTICS (decrease the
3530 reported device capacity by one
3531 sector if the number is odd);
3532 i = IGNORE_DEVICE (don't bind to this
3534 l = NOT_LOCKABLE (don't try to lock and
3535 unlock ejectable media);
3536 m = MAX_SECTORS_64 (don't transfer more
3537 than 64 sectors = 32 KB at a time);
3538 n = INITIAL_READ10 (force a retry of the
3539 initial READ(10) command);
3540 o = CAPACITY_OK (accept the capacity
3541 reported by the device);
3542 p = WRITE_CACHE (the device cache is ON
3544 r = IGNORE_RESIDUE (the device reports
3545 bogus residue values);
3546 s = SINGLE_LUN (the device has only one
3548 u = IGNORE_UAS (don't bind to the uas driver);
3549 w = NO_WP_DETECT (don't test whether the
3550 medium is write-protected).
3551 Example: quirks=0419:aaf5:rl,0421:0433:rc
3553 user_debug= [KNL,ARM]
3555 See arch/arm/Kconfig.debug help text.
3556 1 - undefined instruction events
3558 4 - invalid data aborts
3561 Example: user_debug=31
3564 [X86] Flags controlling user PTE allocations.
3566 nohigh = do not allocate PTE pages in
3567 HIGHMEM regardless of setting
3571 On X86_32, this is an alias for vdso32=. Otherwise:
3573 vdso=1: enable VDSO (the default)
3574 vdso=0: disable VDSO mapping
3576 vdso32= [X86] Control the 32-bit vDSO
3577 vdso32=1: enable 32-bit VDSO
3578 vdso32=0 or vdso32=2: disable 32-bit VDSO
3580 See the help text for CONFIG_COMPAT_VDSO for more
3581 details. If CONFIG_COMPAT_VDSO is set, the default is
3582 vdso32=0; otherwise, the default is vdso32=1.
3584 For compatibility with older kernels, vdso32=2 is an
3587 Try vdso32=0 if you encounter an error that says:
3588 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3591 vector=percpu: enable percpu vector domain
3593 video= [FB] Frame buffer configuration
3594 See Documentation/fb/modedb.txt.
3596 video.brightness_switch_enabled= [0,1]
3597 If set to 1, on receiving an ACPI notify event
3598 generated by hotkey, video driver will adjust brightness
3599 level and then send out the event to user space through
3600 the allocated input device; If set to 0, video driver
3601 will only send out the event without touching backlight
3606 [VMMIO] Memory mapped virtio (platform) device.
3608 <size>@<baseaddr>:<irq>[:<id>]
3610 <size> := size (can use standard suffixes
3612 <baseaddr> := physical base address
3613 <irq> := interrupt number (as passed to
3615 <id> := (optional) platform device id
3617 virtio_mmio.device=1K@0x100b0000:48:7
3619 Can be used multiple times for multiple devices.
3621 vga= [BOOT,X86-32] Select a particular video mode
3622 See Documentation/x86/boot.txt and
3623 Documentation/svga.txt.
3624 Use vga=ask for menu.
3625 This is actually a boot loader parameter; the value is
3626 passed to the kernel using a special protocol.
3628 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3629 size of <nn>. This can be used to increase the
3630 minimum size (128MB on x86). It can also be used to
3631 decrease the size and leave more room for directly
3634 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3637 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3640 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3644 Controls the behavior of vsyscalls (i.e. calls to
3645 fixed addresses of 0xffffffffff600x00 from legacy
3646 code). Most statically-linked binaries and older
3647 versions of glibc use these calls. Because these
3648 functions are at fixed addresses, they make nice
3649 targets for exploits that can control RIP.
3651 emulate [default] Vsyscalls turn into traps and are
3652 emulated reasonably safely.
3654 native Vsyscalls are native syscall instructions.
3655 This is a little bit faster than trapping
3656 and makes a few dynamic recompilers work
3657 better than they would in emulation mode.
3658 It also makes exploits much easier to write.
3660 none Vsyscalls don't work at all. This makes
3661 them quite hard to use for exploits but
3662 might break your system.
3664 vt.color= [VT] Default text color.
3665 Format: 0xYX, X = foreground, Y = background.
3666 Default: 0x07 = light gray on black.
3668 vt.cur_default= [VT] Default cursor shape.
3669 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3670 the parameters of the <Esc>[?A;B;Cc escape sequence;
3671 see VGA-softcursor.txt. Default: 2 = underline.
3673 vt.default_blu= [VT]
3674 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3675 Change the default blue palette of the console.
3676 This is a 16-member array composed of values
3679 vt.default_grn= [VT]
3680 Format: <green0>,<green1>,<green2>,...,<green15>
3681 Change the default green palette of the console.
3682 This is a 16-member array composed of values
3685 vt.default_red= [VT]
3686 Format: <red0>,<red1>,<red2>,...,<red15>
3687 Change the default red palette of the console.
3688 This is a 16-member array composed of values
3694 Set system-wide default UTF-8 mode for all tty's.
3695 Default is 1, i.e. UTF-8 mode is enabled for all
3696 newly opened terminals.
3698 vt.global_cursor_default=
3701 Set system-wide default for whether a cursor
3702 is shown on new VTs. Default is -1,
3703 i.e. cursors will be created by default unless
3704 overridden by individual drivers. 0 will hide
3705 cursors, 1 will display them.
3707 vt.italic= [VT] Default color for italic text; 0-15.
3710 vt.underline= [VT] Default color for underlined text; 0-15.
3713 watchdog timers [HW,WDT] For information on watchdog timers,
3714 see Documentation/watchdog/watchdog-parameters.txt
3715 or other driver-specific files in the
3716 Documentation/watchdog/ directory.
3718 workqueue.disable_numa
3719 By default, all work items queued to unbound
3720 workqueues are affine to the NUMA nodes they're
3721 issued on, which results in better behavior in
3722 general. If NUMA affinity needs to be disabled for
3723 whatever reason, this option can be used. Note
3724 that this also can be controlled per-workqueue for
3725 workqueues visible under /sys/bus/workqueue/.
3727 workqueue.power_efficient
3728 Per-cpu workqueues are generally preferred because
3729 they show better performance thanks to cache
3730 locality; unfortunately, per-cpu workqueues tend to
3731 be more power hungry than unbound workqueues.
3733 Enabling this makes the per-cpu workqueues which
3734 were observed to contribute significantly to power
3735 consumption unbound, leading to measurably lower
3736 power usage at the cost of small performance
3739 The default value of this parameter is determined by
3740 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3742 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3743 default x2apic cluster mode on platforms
3746 x86_intel_mid_timer= [X86-32,APBT]
3747 Choose timer option for x86 Intel MID platform.
3748 Two valid options are apbt timer only and lapic timer
3749 plus one apbt timer for broadcast timer.
3750 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3752 xen_emul_unplug= [HW,X86,XEN]
3753 Unplug Xen emulated devices
3754 Format: [unplug0,][unplug1]
3755 ide-disks -- unplug primary master IDE devices
3756 aux-ide-disks -- unplug non-primary-master IDE devices
3757 nics -- unplug network devices
3758 all -- unplug all emulated devices (NICs and IDE disks)
3759 unnecessary -- unplugging emulated devices is
3760 unnecessary even if the host did not respond to
3762 never -- do not unplug even if version check succeeds
3764 xen_nopvspin [X86,XEN]
3765 Disables the ticketlock slowpath using Xen PV
3769 Disables the PV optimizations forcing the HVM guest to
3770 run as generic HVM guest with no PV drivers.
3772 xirc2ps_cs= [NET,PCMCIA]
3774 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3776 ______________________________________________________________________
3780 Add more DRM drivers.
projects / cascardo / linux.git / blob