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 ccw_timeout_log [S390]
570 See Documentation/s390/CommonIO for details.
572 cgroup_disable= [KNL] Disable a particular controller
573 Format: {name of the controller(s) to disable}
574 The effects of cgroup_disable=foo are:
575 - foo isn't auto-mounted if you mount all cgroups in
577 - foo isn't visible as an individually mountable
579 {Currently only "memory" controller deal with this and
580 cut the overhead, others just disable the usage. So
581 only cgroup_disable=memory is actually worthy}
583 checkreqprot [SELINUX] Set initial checkreqprot flag value.
584 Format: { "0" | "1" }
585 See security/selinux/Kconfig help text.
586 0 -- check protection applied by kernel (includes
587 any implied execute protection).
588 1 -- check protection requested by application.
589 Default value is set via a kernel config option.
590 Value can be changed at runtime via
591 /selinux/checkreqprot.
594 See Documentation/s390/CommonIO for details.
597 Keep all clocks already enabled by bootloader on,
598 even if no driver has claimed them. This is useful
599 for debug and development, but should not be
600 needed on a platform with proper driver support.
601 For more information, see Documentation/clk.txt.
603 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
605 Forces specified clocksource (if available) to be used
606 when calculating gettimeofday(). If specified
607 clocksource is not available, it defaults to PIT.
608 Format: { pit | tsc | cyclone | pmtmr }
610 clocksource= Override the default clocksource
612 Override the default clocksource and use the clocksource
613 with the name specified.
614 Some clocksource names to choose from, depending on
616 [all] jiffies (this is the base, fallback clocksource)
618 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
619 pxa_timer,timer3,32k_counter,timer0_1
621 [X86-32] pit,hpet,tsc;
622 scx200_hrt on Geode; cyclone on IBM x440
630 clearcpuid=BITNUM [X86]
631 Disable CPUID feature X for the kernel. See
632 arch/x86/include/asm/cpufeature.h for the valid bit
633 numbers. Note the Linux specific bits are not necessarily
634 stable over kernel options, but the vendor specific
636 Also note that user programs calling CPUID directly
637 or using the feature without checking anything
638 will still see it. This just prevents it from
639 being used by the kernel or shown in /proc/cpuinfo.
640 Also note the kernel might malfunction if you disable
643 cma=nn[MG]@[start[MG][-end[MG]]]
645 Sets the size of kernel global memory area for
646 contiguous memory allocations and optionally the
647 placement constraint by the physical address range of
648 memory allocations. For more information, see
649 include/linux/dma-contiguous.h
651 cmo_free_hint= [PPC] Format: { yes | no }
652 Specify whether pages are marked as being inactive
653 when they are freed. This is used in CMO environments
654 to determine OS memory pressure for page stealing by
658 coherent_pool=nn[KMG] [ARM,KNL]
659 Sets the size of memory pool for coherent, atomic dma
660 allocations, by default set to 256K.
662 code_bytes [X86] How many bytes of object code to print
667 com20020= [HW,NET] ARCnet - COM20020 chipset
669 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
671 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
675 ARCnet - COM90xx chipset (memory-mapped buffers)
676 Format: <io>[,<irq>[,<memstart>]]
678 condev= [HW,S390] console device
681 console= [KNL] Output console device and options.
683 tty<n> Use the virtual console device <n>.
687 Use the specified serial port. The options are of
688 the form "bbbbpnf", where "bbbb" is the baud rate,
689 "p" is parity ("n", "o", or "e"), "n" is number of
690 bits, and "f" is flow control ("r" for RTS or
691 omit it). Default is "9600n8".
693 See Documentation/serial-console.txt for more
695 Documentation/networking/netconsole.txt for an
698 uart[8250],io,<addr>[,options]
699 uart[8250],mmio,<addr>[,options]
700 Start an early, polled-mode console on the 8250/16550
701 UART at the specified I/O port or MMIO address,
702 switching to the matching ttyS device later. The
703 options are the same as for ttyS, above.
704 hvc<n> Use the hypervisor console device <n>. This is for
705 both Xen and PowerPC hypervisors.
707 If the device connected to the port is not a TTY but a braille
708 device, prepend "brl," before the device type, for instance
710 For now, only VisioBraille is supported.
712 consoleblank= [KNL] The console blank (screen saver) timeout in
713 seconds. Defaults to 10*60 = 10mins. A value of 0
714 disables the blank timer.
717 [KNL] Change the default value for
718 /proc/<pid>/coredump_filter.
719 See also Documentation/filesystems/proc.txt.
721 cpuidle.off=1 [CPU_IDLE]
722 disable the cpuidle sub-system
724 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
726 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
728 crashkernel=size[KMG][@offset[KMG]]
729 [KNL] Using kexec, Linux can switch to a 'crash kernel'
730 upon panic. This parameter reserves the physical
731 memory region [offset, offset + size] for that kernel
732 image. If '@offset' is omitted, then a suitable offset
733 is selected automatically. Check
734 Documentation/kdump/kdump.txt for further details.
736 crashkernel=range1:size1[,range2:size2,...][@offset]
737 [KNL] Same as above, but depends on the memory
738 in the running system. The syntax of range is
739 start-[end] where start and end are both
740 a memory unit (amount[KMG]). See also
741 Documentation/kdump/kdump.txt for an example.
743 crashkernel=size[KMG],high
744 [KNL, x86_64] range could be above 4G. Allow kernel
745 to allocate physical memory region from top, so could
746 be above 4G if system have more than 4G ram installed.
747 Otherwise memory region will be allocated below 4G, if
749 It will be ignored if crashkernel=X is specified.
750 crashkernel=size[KMG],low
751 [KNL, x86_64] range under 4G. When crashkernel=X,high
752 is passed, kernel could allocate physical memory region
753 above 4G, that cause second kernel crash on system
754 that require some amount of low memory, e.g. swiotlb
755 requires at least 64M+32K low memory. Kernel would
756 try to allocate 72M below 4G automatically.
757 This one let user to specify own low range under 4G
758 for second kernel instead.
759 0: to disable low allocation.
760 It will be ignored when crashkernel=X,high is not used
761 or memory reserved is below 4G.
766 cs89x0_media= [HW,NET]
767 Format: { rj45 | aui | bnc }
770 See header of drivers/s390/block/dasd_devmap.c.
772 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
773 (one device per port)
774 Format: <port#>,<type>
775 See also Documentation/input/joystick-parport.txt
777 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
778 time. See Documentation/dynamic-debug-howto.txt for
779 details. Deprecated, see dyndbg.
781 debug [KNL] Enable kernel debugging (events log level).
784 [KNL] verbose self-tests
786 Print debugging info while doing the locking API
788 We default to 0 (no extra messages), setting it to
789 1 will print _a lot_ more information - normally
790 only useful to kernel developers.
792 debug_objects [KNL] Enable object debugging
795 [KNL] Disable object debugging
797 debug_guardpage_minorder=
798 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
799 parameter allows control of the order of pages that will
800 be intentionally kept free (and hence protected) by the
801 buddy allocator. Bigger value increase the probability
802 of catching random memory corruption, but reduce the
803 amount of memory for normal system use. The maximum
804 possible value is MAX_ORDER/2. Setting this parameter
805 to 1 or 2 should be enough to identify most random
806 memory corruption problems caused by bugs in kernel or
807 driver code when a CPU writes to (or reads from) a
808 random memory location. Note that there exists a class
809 of memory corruptions problems caused by buggy H/W or
810 F/W or by drivers badly programing DMA (basically when
811 memory is written at bus level and the CPU MMU is
812 bypassed) which are not detectable by
813 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
814 tracking down these problems.
816 debugpat [X86] Enable PAT debugging
818 decnet.addr= [HW,NET]
819 Format: <area>[,<node>]
820 See also Documentation/networking/decnet.txt.
823 [same as hugepagesz=] The size of the default
824 HugeTLB page size. This is the size represented by
825 the legacy /proc/ hugepages APIs, used for SHM, and
826 default size when mounting hugetlbfs filesystems.
827 Defaults to the default architecture's huge page size
831 Set number of hash buckets for dentry cache.
834 See Documentation/networking/ipv6.txt.
836 disable_cpu_apicid= [X86,APIC,SMP]
838 The number of initial APIC ID for the
839 corresponding CPU to be disabled at boot,
840 mostly used for the kdump 2nd kernel to
841 disable BSP to wake up multiple CPUs without
842 causing system reset or hang due to sending
845 disable_ddw [PPC/PSERIES]
846 Disable Dynamic DMA Window support. Use this if
847 to workaround buggy firmware.
850 See Documentation/networking/ipv6.txt.
852 disable_mtrr_cleanup [X86]
853 The kernel tries to adjust MTRR layout from continuous
854 to discrete, to make X server driver able to add WB
855 entry later. This parameter disables that.
857 disable_mtrr_trim [X86, Intel and AMD only]
858 By default the kernel will trim any uncacheable
859 memory out of your available memory pool based on
860 MTRR settings. This parameter disables that behavior,
861 possibly causing your machine to run very slowly.
863 disable_timer_pin_1 [X86]
864 Disable PIN 1 of APIC timer
865 Can be useful to work around chipset bugs.
867 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
868 this option disables the debugging code at boot.
870 dma_debug_entries=<number>
871 This option allows to tune the number of preallocated
872 entries for DMA-API debugging code. One entry is
873 required per DMA-API allocation. Use this if the
874 DMA-API debugging code disables itself because the
875 architectural default is too low.
877 dma_debug_driver=<driver_name>
878 With this option the DMA-API debugging driver
879 filter feature can be enabled at boot time. Just
880 pass the driver to filter for as the parameter.
881 The filter can be disabled or changed to another
882 driver later using sysfs.
884 drm_kms_helper.edid_firmware=[<connector>:]<file>
885 Broken monitors, graphic adapters and KVMs may
886 send no or incorrect EDID data sets. This parameter
887 allows to specify an EDID data set in the
888 /lib/firmware directory that is used instead.
889 Generic built-in EDID data sets are used, if one of
890 edid/1024x768.bin, edid/1280x1024.bin,
891 edid/1680x1050.bin, or edid/1920x1080.bin is given
892 and no file with the same name exists. Details and
893 instructions how to build your own EDID data are
894 available in Documentation/EDID/HOWTO.txt. An EDID
895 data set will only be used for a particular connector,
896 if its name and a colon are prepended to the EDID
901 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
902 module.dyndbg[="val"]
903 Enable debug messages at boot time. See
904 Documentation/dynamic-debug-howto.txt for details.
906 early_ioremap_debug [KNL]
907 Enable debug messages in early_ioremap support. This
908 is useful for tracking down temporary early mappings
909 which are not unmapped.
911 earlycon= [KNL] Output early console device and options.
913 uart[8250],io,<addr>[,options]
914 uart[8250],mmio,<addr>[,options]
915 uart[8250],mmio32,<addr>[,options]
916 Start an early, polled-mode console on the 8250/16550
917 UART at the specified I/O port or MMIO address.
918 MMIO inter-register address stride is either 8-bit
919 (mmio) or 32-bit (mmio32).
920 The options are the same as for ttyS, above.
923 Start an early, polled-mode console on a pl011 serial
924 port at the specified address. The pl011 serial port
925 must already be setup and configured. Options are not
928 smh Use ARM semihosting calls for early console.
930 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
934 earlyprintk=serial[,ttySn[,baudrate]]
935 earlyprintk=serial[,0x...[,baudrate]]
936 earlyprintk=ttySn[,baudrate]
937 earlyprintk=dbgp[debugController#]
939 earlyprintk is useful when the kernel crashes before
940 the normal console is initialized. It is not enabled by
941 default because it has some cosmetic problems.
943 Append ",keep" to not disable it when the real console
946 Only one of vga, efi, serial, or usb debug port can
949 Currently only ttyS0 and ttyS1 may be specified by
950 name. Other I/O ports may be explicitly specified
951 on some architectures (x86 and arm at least) by
952 replacing ttySn with an I/O port address, like this:
953 earlyprintk=serial,0x1008,115200
954 You can find the port for a given device in
955 /proc/tty/driver/serial:
956 2: uart:ST16650V2 port:00001008 irq:18 ...
958 Interaction with the standard serial driver is not
961 The VGA and EFI output is eventually overwritten by
964 The xen output can only be used by Xen PV guests.
966 edac_report= [HW,EDAC] Control how to report EDAC event
967 Format: {"on" | "off" | "force"}
968 on: enable EDAC to report H/W event. May be overridden
969 by other higher priority error reporting module.
970 off: disable H/W event reporting through EDAC.
971 force: enforce the use of EDAC to report H/W event.
974 ekgdboc= [X86,KGDB] Allow early kernel console debugging
977 This is designed to be used in conjunction with
978 the boot argument: earlyprintk=vga
981 Format: {"off" | "on" | "skip[mbr]"}
984 Format: { "old_map" }
985 old_map [X86-64]: switch to the old ioremap-based EFI
986 runtime services mapping. 32-bit still uses this one by
989 efi_no_storage_paranoia [EFI; X86]
990 Using this parameter you can use more than 50% of
991 your efi variable storage. Use this parameter only if
992 you are really sure that your UEFI does sane gc and
993 fulfills the spec otherwise your board may brick.
995 eisa_irq_edge= [PARISC,HW]
996 See header of drivers/parisc/eisa.c.
999 See comment before function elanfreq_setup() in
1000 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1003 Format: {"cfq" | "deadline" | "noop"}
1004 See Documentation/block/cfq-iosched.txt and
1005 Documentation/block/deadline-iosched.txt for details.
1007 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1008 Specifies physical address of start of kernel core
1009 image elf header and optionally the size. Generally
1010 kexec loader will pass this option to capture kernel.
1011 See Documentation/kdump/kdump.txt for details.
1013 enable_mtrr_cleanup [X86]
1014 The kernel tries to adjust MTRR layout from continuous
1015 to discrete, to make X server driver able to add WB
1016 entry later. This parameter enables that.
1018 enable_timer_pin_1 [X86]
1019 Enable PIN 1 of APIC timer
1020 Can be useful to work around chipset bugs
1021 (in particular on some ATI chipsets).
1022 The kernel tries to set a reasonable default.
1024 enforcing [SELINUX] Set initial enforcing status.
1026 See security/selinux/Kconfig help text.
1027 0 -- permissive (log only, no denials).
1028 1 -- enforcing (deny and log).
1030 Value can be changed at runtime via /selinux/enforce.
1033 Disable Error Record Serialization Table (ERST)
1036 ether= [HW,NET] Ethernet cards parameters
1037 This option is obsoleted by the "netdev=" option, which
1038 has equivalent usage. See its documentation for details.
1042 Permit 'security.evm' to be updated regardless of
1043 current integrity status.
1047 fail_make_request=[KNL]
1048 General fault injection mechanism.
1049 Format: <interval>,<probability>,<space>,<times>
1050 See also Documentation/fault-injection/.
1053 See Documentation/blockdev/floppy.txt.
1055 force_pal_cache_flush
1056 [IA-64] Avoid check_sal_cache_flush which may hang on
1057 buggy SAL_CACHE_FLUSH implementations. Using this
1058 parameter will force ia64_sal_cache_flush to call
1059 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1062 Forcefully enable Physical Address Extension (PAE).
1063 Many Pentium M systems disable PAE but may have a
1064 functionally usable PAE implementation.
1065 Warning: use of this parameter will taint the kernel
1066 and may cause unknown problems.
1069 [FTRACE] will set and start the specified tracer
1070 as early as possible in order to facilitate early
1073 ftrace_dump_on_oops[=orig_cpu]
1074 [FTRACE] will dump the trace buffers on oops.
1075 If no parameter is passed, ftrace will dump
1076 buffers of all CPUs, but if you pass orig_cpu, it will
1077 dump only the buffer of the CPU that triggered the
1080 ftrace_filter=[function-list]
1081 [FTRACE] Limit the functions traced by the function
1082 tracer at boot up. function-list is a comma separated
1083 list of functions. This list can be changed at run
1084 time by the set_ftrace_filter file in the debugfs
1087 ftrace_notrace=[function-list]
1088 [FTRACE] Do not trace the functions specified in
1089 function-list. This list can be changed at run time
1090 by the set_ftrace_notrace file in the debugfs
1093 ftrace_graph_filter=[function-list]
1094 [FTRACE] Limit the top level callers functions traced
1095 by the function graph tracer at boot up.
1096 function-list is a comma separated list of functions
1097 that can be changed at run time by the
1098 set_graph_function file in the debugfs tracing directory.
1100 ftrace_graph_notrace=[function-list]
1101 [FTRACE] Do not trace from the functions specified in
1102 function-list. This list is a comma separated list of
1103 functions that can be changed at run time by the
1104 set_graph_notrace file in the debugfs tracing directory.
1107 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1108 support via parallel port (up to 5 devices per port)
1109 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1110 See also Documentation/input/joystick-parport.txt
1114 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1118 gcov_persist= [GCOV] When non-zero (default), profiling data for
1119 kernel modules is saved and remains accessible via
1120 debugfs, even when the module is unloaded/reloaded.
1121 When zero, profiling data is discarded and associated
1122 debugfs files are removed at module unload time.
1124 gpt [EFI] Forces disk with valid GPT signature but
1125 invalid Protective MBR to be treated as GPT. If the
1126 primary GPT is corrupted, it enables the backup/alternate
1127 GPT to be used instead.
1129 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1130 the "Enable 0" bit of the configuration register.
1133 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1134 the "Enable 0" bit of the configuration register.
1137 grcan.select= [HW] Select which physical interface to use.
1140 grcan.txsize= [HW] Sets the size of the tx buffer.
1141 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1143 grcan.rxsize= [HW] Sets the size of the rx buffer.
1144 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1147 hashdist= [KNL,NUMA] Large hashes allocated during boot
1148 are distributed across NUMA nodes. Defaults on
1149 for 64-bit NUMA, off otherwise.
1150 Format: 0 | 1 (for off | on)
1152 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1154 hd= [EIDE] (E)IDE hard drive subsystem geometry
1155 Format: <cyl>,<head>,<sect>
1158 Disable Hardware Error Source Table (HEST) support;
1159 corresponding firmware-first mode error processing
1160 logic will be disabled.
1162 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1163 size of <nn>. This works even on boxes that have no
1164 highmem otherwise. This also works to reduce highmem
1165 size on bigger boxes.
1167 highres= [KNL] Enable/disable high resolution timer mode.
1168 Valid parameters: "on", "off"
1172 See Documentation/isdn/README.HiSax.
1176 hpet= [X86-32,HPET] option to control HPET usage
1177 Format: { enable (default) | disable | force |
1179 disable: disable HPET and use PIT instead
1180 force: allow force enabled of undocumented chips (ICH4,
1182 verbose: show contents of HPET registers during setup
1184 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1185 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1187 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1188 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1189 On x86-64 and powerpc, this option can be specified
1190 multiple times interleaved with hugepages= to reserve
1191 huge pages of different sizes. Valid pages sizes on
1192 x86-64 are 2M (when the CPU supports "pse") and 1G
1193 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1194 Note that 1GB pages can only be allocated at boot time
1195 using hugepages= and not freed afterwards.
1197 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1198 terminal devices. Valid values: 0..8
1199 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1200 If specified, z/VM IUCV HVC accepts connections
1201 from listed z/VM user IDs only.
1203 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1204 hardware thread id mappings.
1205 Format: <cpu>:<hwthread>
1208 Do not unregister boot console at start. This is only
1209 useful for debugging when something happens in the window
1210 between unregistering the boot console and initializing
1213 i2c_bus= [HW] Override the default board specific I2C bus speed
1214 or register an additional I2C bus that is not
1215 registered from board initialization code.
1219 i8042.debug [HW] Toggle i8042 debug mode
1220 i8042.direct [HW] Put keyboard port into non-translated mode
1221 i8042.dumbkbd [HW] Pretend that controller can only read data from
1222 keyboard and cannot control its state
1223 (Don't attempt to blink the leds)
1224 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1225 i8042.nokbd [HW] Don't check/create keyboard port
1226 i8042.noloop [HW] Disable the AUX Loopback command while probing
1228 i8042.nomux [HW] Don't check presence of an active multiplexing
1230 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1232 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1233 i8042.reset [HW] Reset the controller during init and cleanup
1234 i8042.unlock [HW] Unlock (ignore) the keylock
1238 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1239 indicates that the driver is running on unsupported
1241 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1242 does not match list of supported models.
1244 [HW] Report power status in /proc/i8k
1245 (disabled by default)
1246 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1249 i915.invert_brightness=
1250 [DRM] Invert the sense of the variable that is used to
1251 set the brightness of the panel backlight. Normally a
1252 brightness value of 0 indicates backlight switched off,
1253 and the maximum of the brightness value sets the backlight
1254 to maximum brightness. If this parameter is set to 0
1255 (default) and the machine requires it, or this parameter
1256 is set to 1, a brightness value of 0 sets the backlight
1257 to maximum brightness, and the maximum of the brightness
1258 value switches the backlight off.
1259 -1 -- never invert brightness
1260 0 -- machine default
1261 1 -- force brightness inversion
1264 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1266 ide-core.nodma= [HW] (E)IDE subsystem
1267 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1268 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1269 .cdrom .chs .ignore_cable are additional options
1270 See Documentation/ide/ide.txt.
1272 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1273 Claim all unknown PCI IDE storage controllers.
1276 Format: idle=poll, idle=halt, idle=nomwait
1277 Poll forces a polling idle loop that can slightly
1278 improve the performance of waking up a idle CPU, but
1279 will use a lot of power and make the system run hot.
1281 idle=halt: Halt is forced to be used for CPU idle.
1282 In such case C2/C3 won't be used again.
1283 idle=nomwait: Disable mwait for CPU C-states
1285 ignore_loglevel [KNL]
1286 Ignore loglevel setting - this will print /all/
1287 kernel messages to the console. Useful for debugging.
1288 We also add it as printk module parameter, so users
1289 could change it dynamically, usually by
1290 /sys/module/printk/parameters/ignore_loglevel.
1292 ihash_entries= [KNL]
1293 Set number of hash buckets for inode cache.
1295 ima_appraise= [IMA] appraise integrity measurements
1296 Format: { "off" | "enforce" | "fix" }
1299 ima_appraise_tcb [IMA]
1300 The builtin appraise policy appraises all files
1304 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1308 The list of supported hash algorithms is defined
1309 in crypto/hash_info.h.
1312 Load a policy which meets the needs of the Trusted
1313 Computing Base. This means IMA will measure all
1314 programs exec'd, files mmap'd for exec, and all files
1315 opened for read by uid=0.
1318 Select one of defined IMA measurements template formats.
1319 Formats: { "ima" | "ima-ng" }
1324 Run specified binary instead of /sbin/init as init
1327 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1328 for working out where the kernel is dying during
1331 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1332 initcall functions. Useful for debugging built-in
1333 modules and initcalls.
1335 initrd= [BOOT] Specify the location of the initial ramdisk
1337 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1340 int_pln_enable [x86] Enable power limit notification interrupt
1342 integrity_audit=[IMA]
1343 Format: { "0" | "1" }
1344 0 -- basic integrity auditing messages. (Default)
1345 1 -- additional integrity auditing messages.
1347 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1349 Enable intel iommu driver.
1351 Disable intel iommu driver.
1352 igfx_off [Default Off]
1353 By default, gfx is mapped as normal device. If a gfx
1354 device has a dedicated DMAR unit, the DMAR unit is
1355 bypassed by not enabling DMAR with this option. In
1356 this case, gfx device will use physical address for
1359 With this option iommu will not optimize to look
1360 for io virtual address below 32-bit forcing dual
1361 address cycle on pci bus for cards supporting greater
1362 than 32-bit addressing. The default is to look
1363 for translation below 32-bit and if not available
1364 then look in the higher range.
1365 strict [Default Off]
1366 With this option on every unmap_single operation will
1367 result in a hardware IOTLB flush operation as opposed
1368 to batching them for performance.
1369 sp_off [Default Off]
1370 By default, super page will be supported if Intel IOMMU
1371 has the capability. With this option, super page will
1374 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1375 0 disables intel_idle and fall back on acpi_idle.
1376 1 to 6 specify maximum depth of C-state.
1380 Do not enable intel_pstate as the default
1381 scaling driver for the supported processors
1383 intremap= [X86-64, Intel-IOMMU]
1384 on enable Interrupt Remapping (default)
1385 off disable Interrupt Remapping
1386 nosid disable Source ID checking
1388 BIOS x2APIC opt-out request will be ignored
1390 iomem= Disable strict checking of access to MMIO memory
1391 strict regions from userspace.
1408 io7= [HW] IO7 for Marvel based alpha systems
1409 See comment before marvel_specify_io7 in
1410 arch/alpha/kernel/core_marvel.c.
1412 io_delay= [X86] I/O delay method
1414 Standard port 0x80 based delay
1416 Alternate port 0xed based delay (needed on some systems)
1418 Simple two microseconds delay
1423 See Documentation/filesystems/nfs/nfsroot.txt.
1425 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1426 See comment before ip2_setup() in
1427 drivers/char/ip2/ip2base.c.
1430 When an interrupt is not handled search all handlers
1431 for it. Intended to get systems with badly broken
1435 When an interrupt is not handled search all handlers
1436 for it. Also check all handlers each timer
1437 interrupt. Intended to get systems with badly broken
1441 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1443 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1445 <cpu number>,...,<cpu number>
1447 <cpu number>-<cpu number>
1448 (must be a positive range in ascending order)
1450 <cpu number>,...,<cpu number>-<cpu number>
1452 This option can be used to specify one or more CPUs
1453 to isolate from the general SMP balancing and scheduling
1454 algorithms. You can move a process onto or off an
1455 "isolated" CPU via the CPU affinity syscalls or cpuset.
1456 <cpu number> begins at 0 and the maximum value is
1457 "number of CPUs in system - 1".
1459 This option is the preferred way to isolate CPUs. The
1460 alternative -- manually setting the CPU mask of all
1461 tasks in the system -- can cause problems and
1462 suboptimal load balancer performance.
1466 ivrs_ioapic [HW,X86_64]
1467 Provide an override to the IOAPIC-ID<->DEVICE-ID
1468 mapping provided in the IVRS ACPI table. For
1469 example, to map IOAPIC-ID decimal 10 to
1470 PCI device 00:14.0 write the parameter as:
1471 ivrs_ioapic[10]=00:14.0
1473 ivrs_hpet [HW,X86_64]
1474 Provide an override to the HPET-ID<->DEVICE-ID
1475 mapping provided in the IVRS ACPI table. For
1476 example, to map HPET-ID decimal 0 to
1477 PCI device 00:14.0 write the parameter as:
1478 ivrs_hpet[0]=00:14.0
1480 js= [HW,JOY] Analog joystick
1481 See Documentation/input/joystick.txt.
1484 Enable/disable kernel and module base offset ASLR
1485 (Address Space Layout Randomization) if built into
1486 the kernel. When CONFIG_HIBERNATION is selected,
1487 kASLR is disabled by default. When kASLR is enabled,
1488 hibernation will be disabled.
1492 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1493 specifies the amount of memory usable by the kernel
1494 for non-movable allocations. The requested amount is
1495 spread evenly throughout all nodes in the system. The
1496 remaining memory in each node is used for Movable
1497 pages. In the event, a node is too small to have both
1498 kernelcore and Movable pages, kernelcore pages will
1499 take priority and other nodes will have a larger number
1500 of Movable pages. The Movable zone is used for the
1501 allocation of pages that may be reclaimed or moved
1502 by the page migration subsystem. This means that
1503 HugeTLB pages may not be allocated from this zone.
1504 Note that allocations like PTEs-from-HighMem still
1505 use the HighMem zone if it exists, and the Normal
1506 zone if it does not.
1508 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1509 Format: <Controller#>[,poll interval]
1510 The controller # is the number of the ehci usb debug
1511 port as it is probed via PCI. The poll interval is
1512 optional and is the number seconds in between
1513 each poll cycle to the debug port in case you need
1514 the functionality for interrupting the kernel with
1515 gdb or control-c on the dbgp connection. When
1516 not using this parameter you use sysrq-g to break into
1517 the kernel debugger.
1519 kgdboc= [KGDB,HW] kgdb over consoles.
1520 Requires a tty driver that supports console polling,
1521 or a supported polling keyboard driver (non-usb).
1522 Serial only format: <serial_device>[,baud]
1523 keyboard only format: kbd
1524 keyboard and serial format: kbd,<serial_device>[,baud]
1525 Optional Kernel mode setting:
1526 kms, kbd format: kms,kbd
1527 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1529 kgdbwait [KGDB] Stop kernel execution and enter the
1530 kernel debugger at the earliest opportunity.
1532 kmac= [MIPS] korina ethernet MAC address.
1533 Configure the RouterBoard 532 series on-chip
1534 Ethernet adapter MAC address.
1536 kmemleak= [KNL] Boot-time kmemleak enable/disable
1537 Valid arguments: on, off
1540 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1541 Valid arguments: 0, 1, 2
1542 kmemcheck=0 (disabled)
1543 kmemcheck=1 (enabled)
1544 kmemcheck=2 (one-shot mode)
1545 Default: 2 (one-shot mode)
1547 kstack=N [X86] Print N words from the kernel stack
1550 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1551 Default is 0 (don't ignore, but inject #GP)
1553 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1557 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1558 Default is 1 (enabled)
1560 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1562 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1564 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1565 (virtualized MMU) support on capable Intel chips.
1566 Default is 1 (enabled)
1568 kvm-intel.emulate_invalid_guest_state=
1569 [KVM,Intel] Enable emulation of invalid guest states
1570 Default is 0 (disabled)
1572 kvm-intel.flexpriority=
1573 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1574 Default is 1 (enabled)
1577 [KVM,Intel] Enable VMX nesting (nVMX).
1578 Default is 0 (disabled)
1580 kvm-intel.unrestricted_guest=
1581 [KVM,Intel] Disable unrestricted guest feature
1582 (virtualized real and unpaged mode) on capable
1583 Intel chips. Default is 1 (enabled)
1585 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1586 feature (tagged TLBs) on capable Intel chips.
1587 Default is 1 (enabled)
1593 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1596 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1597 value for LAPIC timer one-shot implementation. Default
1598 back to the programmable timer unit in the LAPIC.
1600 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1603 libata.dma= [LIBATA] DMA control
1604 libata.dma=0 Disable all PATA and SATA DMA
1605 libata.dma=1 PATA and SATA Disk DMA only
1606 libata.dma=2 ATAPI (CDROM) DMA only
1607 libata.dma=4 Compact Flash DMA only
1608 Combinations also work, so libata.dma=3 enables DMA
1609 for disks and CDROMs, but not CFs.
1611 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1612 libata.ignore_hpa=0 keep BIOS limits (default)
1613 libata.ignore_hpa=1 ignore limits, using full disk
1615 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1619 libata.force= [LIBATA] Force configurations. The format is comma
1620 separated list of "[ID:]VAL" where ID is
1621 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1622 matching port, link or device. Basically, it matches
1623 the ATA ID string printed on console by libata. If
1624 the whole ID part is omitted, the last PORT and DEVICE
1625 values are used. If ID hasn't been specified yet, the
1626 configuration applies to all ports, links and devices.
1628 If only DEVICE is omitted, the parameter applies to
1629 the port and all links and devices behind it. DEVICE
1630 number of 0 either selects the first device or the
1631 first fan-out link behind PMP device. It does not
1632 select the host link. DEVICE number of 15 selects the
1633 host link and device attached to it.
1635 The VAL specifies the configuration to force. As long
1636 as there's no ambiguity shortcut notation is allowed.
1637 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1638 The following configurations can be forced.
1640 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1641 Any ID with matching PORT is used.
1643 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1645 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1646 udma[/][16,25,33,44,66,100,133] notation is also
1649 * [no]ncq: Turn on or off NCQ.
1651 * nohrst, nosrst, norst: suppress hard, soft
1654 * rstonce: only attempt one reset during
1655 hot-unplug link recovery
1657 * dump_id: dump IDENTIFY data.
1659 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1661 * disable: Disable this device.
1663 If there are multiple matching configurations changing
1664 the same attribute, the last one is used.
1666 memblock=debug [KNL] Enable memblock debug messages.
1668 load_ramdisk= [RAM] List of ramdisks to load from floppy
1669 See Documentation/blockdev/ramdisk.txt.
1671 lockd.nlm_grace_period=P [NFS] Assign grace period.
1674 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1677 lockd.nlm_timeout=T [NFS] Assign timeout value.
1680 lockd.nlm_udpport=M [NFS] Assign UDP port.
1683 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1686 loglevel= All Kernel Messages with a loglevel smaller than the
1687 console loglevel will be printed to the console. It can
1688 also be changed with klogd or other programs. The
1689 loglevels are defined as follows:
1691 0 (KERN_EMERG) system is unusable
1692 1 (KERN_ALERT) action must be taken immediately
1693 2 (KERN_CRIT) critical conditions
1694 3 (KERN_ERR) error conditions
1695 4 (KERN_WARNING) warning conditions
1696 5 (KERN_NOTICE) normal but significant condition
1697 6 (KERN_INFO) informational
1698 7 (KERN_DEBUG) debug-level messages
1700 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1701 in bytes. n must be a power of two. The default
1702 size is set in the kernel config file.
1704 logo.nologo [FB] Disables display of the built-in Linux logo.
1705 This may be used to provide more screen space for
1706 kernel log messages and is useful when debugging
1707 kernel boot problems.
1709 lp=0 [LP] Specify parallel ports to use, e.g,
1710 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1711 lp=reset first parallel port). 'lp=0' disables the
1712 lp=auto printer driver. 'lp=reset' (which can be
1713 specified in addition to the ports) causes
1714 attached printers to be reset. Using
1715 lp=port1,port2,... specifies the parallel ports
1716 to associate lp devices with, starting with
1717 lp0. A port specification may be 'none' to skip
1718 that lp device, or a parport name such as
1719 'parport0'. Specifying 'lp=auto' instead of a
1720 port specification list means that device IDs
1721 from each port should be examined, to see if
1722 an IEEE 1284-compliant printer is attached; if
1723 so, the driver will manage that printer.
1724 See also header of drivers/char/lp.c.
1727 Sets loops_per_jiffy to given constant, thus avoiding
1728 time-consuming boot-time autodetection (up to 250 ms per
1729 CPU). 0 enables autodetection (default). To determine
1730 the correct value for your kernel, boot with normal
1731 autodetection and see what value is printed. Note that
1732 on SMP systems the preset will be applied to all CPUs,
1733 which is likely to cause problems if your CPUs need
1734 significantly divergent settings. An incorrect value
1735 will cause delays in the kernel to be wrong, leading to
1736 unpredictable I/O errors and other breakage. Although
1737 unlikely, in the extreme case this might damage your
1741 Format: <io>,<irq>,<dma>
1743 machvec= [IA-64] Force the use of a particular machine-vector
1744 (machvec) in a generic kernel.
1745 Example: machvec=hpzx1_swiotlb
1747 machtype= [Loongson] Share the same kernel image file between different
1749 Example: machtype=lemote-yeeloong-2f-7inch
1751 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1752 than or equal to this physical address is ignored.
1754 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1755 should make use of. maxcpus=n : n >= 0 limits the
1756 kernel to using 'n' processors. n=0 is a special case,
1757 it is equivalent to "nosmp", which also disables
1760 max_loop= [LOOP] The number of loop block devices that get
1761 (loop.max_loop) unconditionally pre-created at init time. The default
1762 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1763 of statically allocating a predefined number, loop
1764 devices can be requested on-demand with the
1765 /dev/loop-control interface.
1767 mce [X86-32] Machine Check Exception
1769 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1771 md= [HW] RAID subsystems devices and level
1772 See Documentation/md.txt.
1775 Format: <first>,<last>
1776 Specifies range of consoles to be captured by the MDA.
1778 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1779 Amount of memory to be used when the kernel is not able
1780 to see the whole system memory or for test.
1781 [X86] Work as limiting max address. Use together
1782 with memmap= to avoid physical address space collisions.
1783 Without memmap= PCI devices could be placed at addresses
1784 belonging to unused RAM.
1786 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1790 [KNL,SH] Allow user to override the default size for
1791 per-device physically contiguous DMA buffers.
1793 memmap=exactmap [KNL,X86] Enable setting of an exact
1794 E820 memory map, as specified by the user.
1795 Such memmap=exactmap lines can be constructed based on
1796 BIOS output or other requirements. See the memmap=nn@ss
1799 memmap=nn[KMG]@ss[KMG]
1800 [KNL] Force usage of a specific region of memory.
1801 Region of memory to be used is from ss to ss+nn.
1803 memmap=nn[KMG]#ss[KMG]
1804 [KNL,ACPI] Mark specific memory as ACPI data.
1805 Region of memory to be marked is from ss to ss+nn.
1807 memmap=nn[KMG]$ss[KMG]
1808 [KNL,ACPI] Mark specific memory as reserved.
1809 Region of memory to be reserved is from ss to ss+nn.
1810 Example: Exclude memory from 0x18690000-0x1869ffff
1811 memmap=64K$0x18690000
1813 memmap=0x10000$0x18690000
1815 memory_corruption_check=0/1 [X86]
1816 Some BIOSes seem to corrupt the first 64k of
1817 memory when doing things like suspend/resume.
1818 Setting this option will scan the memory
1819 looking for corruption. Enabling this will
1820 both detect corruption and prevent the kernel
1821 from using the memory being corrupted.
1822 However, its intended as a diagnostic tool; if
1823 repeatable BIOS-originated corruption always
1824 affects the same memory, you can use memmap=
1825 to prevent the kernel from using that memory.
1827 memory_corruption_check_size=size [X86]
1828 By default it checks for corruption in the low
1829 64k, making this memory unavailable for normal
1830 use. Use this parameter to scan for
1831 corruption in more or less memory.
1833 memory_corruption_check_period=seconds [X86]
1834 By default it checks for corruption every 60
1835 seconds. Use this parameter to check at some
1836 other rate. 0 disables periodic checking.
1838 memtest= [KNL,X86] Enable memtest
1840 default : 0 <disable>
1841 Specifies the number of memtest passes to be
1842 performed. Each pass selects another test
1843 pattern from a given set of patterns. Memtest
1844 fills the memory with this pattern, validates
1845 memory contents and reserves bad memory
1846 regions that are detected.
1848 meye.*= [HW] Set MotionEye Camera parameters
1849 See Documentation/video4linux/meye.txt.
1851 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1852 Multi-Function General Purpose Timers on AMD Geode
1855 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1856 the BIOS has incorrectly applied a workaround. TinyBIOS
1857 version 0.98 is known to be affected, 0.99 fixes the
1858 problem by letting the user disable the workaround.
1862 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1863 physical address is ignored.
1865 mini2440= [ARM,HW,KNL]
1866 Format:[0..2][b][c][t]
1868 MINI2440 configuration specification:
1869 0 - The attached screen is the 3.5" TFT
1870 1 - The attached screen is the 7" TFT
1871 2 - The VGA Shield is attached (1024x768)
1872 Leaving out the screen size parameter will not load
1873 the TFT driver, and the framebuffer will be left
1875 b - Enable backlight. The TFT backlight pin will be
1876 linked to the kernel VESA blanking code and a GPIO
1877 LED. This parameter is not necessary when using the
1879 c - Enable the s3c camera interface.
1880 t - Reserved for enabling touchscreen support. The
1881 touchscreen support is not enabled in the mainstream
1882 kernel as of 2.6.30, a preliminary port can be found
1883 in the "bleeding edge" mini2440 support kernel at
1884 http://repo.or.cz/w/linux-2.6/mini2440.git
1887 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1888 parameter allows control of the logging verbosity for
1889 the additional memory initialisation checks. A value
1890 of 0 disables mminit logging and a level of 4 will
1891 log everything. Information is printed at KERN_DEBUG
1892 so loglevel=8 may also need to be specified.
1895 [KNL] When CONFIG_MODULE_SIG is set, this means that
1896 modules without (valid) signatures will fail to load.
1897 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1898 is always true, so this option does nothing.
1901 [MOUSE] Maximum time between finger touching and
1902 leaving touchpad surface for touch to be considered
1903 a tap and be reported as a left button click (for
1904 touchpads working in absolute mode only).
1906 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1907 reporting absolute coordinates, such as tablets
1908 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1909 reporting absolute coordinates, such as tablets
1911 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1912 is similar to kernelcore except it specifies the
1913 amount of memory used for migratable allocations.
1914 If both kernelcore and movablecore is specified,
1915 then kernelcore will be at *least* the specified
1916 value but may be more. If movablecore on its own
1917 is specified, the administrator must be careful
1918 that the amount of memory usable for all allocations
1921 movable_node [KNL,X86] Boot-time switch to enable the effects
1922 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
1924 MTD_Partition= [MTD]
1925 Format: <name>,<region-number>,<size>,<offset>
1927 MTD_Region= [MTD] Format:
1928 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1931 See drivers/mtd/cmdlinepart.c.
1933 multitce=off [PPC] This parameter disables the use of the pSeries
1934 firmware feature for updating multiple TCE entries
1937 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1939 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1941 boundary - index of last SLC block on Flex-OneNAND.
1942 The remaining blocks are configured as MLC blocks.
1943 lock - Configure if Flex-OneNAND boundary should be locked.
1944 Once locked, the boundary cannot be changed.
1945 1 indicates lock status, 0 indicates unlock status.
1948 ARM/S3C2412 JIVE boot control
1950 See arch/arm/mach-s3c2412/mach-jive.c
1952 mtouchusb.raw_coordinates=
1953 [HW] Make the MicroTouch USB driver use raw coordinates
1954 ('y', default) or cooked coordinates ('n')
1956 mtrr_chunk_size=nn[KMG] [X86]
1957 used for mtrr cleanup. It is largest continuous chunk
1958 that could hold holes aka. UC entries.
1960 mtrr_gran_size=nn[KMG] [X86]
1961 Used for mtrr cleanup. It is granularity of mtrr block.
1963 Large value could prevent small alignment from
1966 mtrr_spare_reg_nr=n [X86]
1968 Range: 0,7 : spare reg number
1970 Used for mtrr cleanup. It is spare mtrr entries number.
1971 Set to 2 or more if your graphical card needs more.
1973 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1975 netdev= [NET] Network devices parameters
1976 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1977 Note that mem_start is often overloaded to mean
1978 something different and driver-specific.
1979 This usage is only documented in each driver source
1983 [NETFILTER] Enable connection tracking flow accounting
1984 0 to disable accounting
1985 1 to enable accounting
1988 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1989 See Documentation/filesystems/nfs/nfsroot.txt.
1991 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1992 See Documentation/filesystems/nfs/nfsroot.txt.
1994 nfsrootdebug [NFS] enable nfsroot debugging messages.
1995 See Documentation/filesystems/nfs/nfsroot.txt.
1997 nfs.callback_tcpport=
1998 [NFS] set the TCP port on which the NFSv4 callback
1999 channel should listen.
2002 [NFS] sets the pathname to the program which is used
2003 to update the NFS client cache entries.
2005 nfs.cache_getent_timeout=
2006 [NFS] sets the timeout after which an attempt to
2007 update a cache entry is deemed to have failed.
2009 nfs.idmap_cache_timeout=
2010 [NFS] set the maximum lifetime for idmapper cache
2014 [NFS] enable 64-bit inode numbers.
2015 If zero, the NFS client will fake up a 32-bit inode
2016 number for the readdir() and stat() syscalls instead
2017 of returning the full 64-bit number.
2018 The default is to return 64-bit inode numbers.
2020 nfs.max_session_slots=
2021 [NFSv4.1] Sets the maximum number of session slots
2022 the client will attempt to negotiate with the server.
2023 This limits the number of simultaneous RPC requests
2024 that the client can send to the NFSv4.1 server.
2025 Note that there is little point in setting this
2026 value higher than the max_tcp_slot_table_limit.
2028 nfs.nfs4_disable_idmapping=
2029 [NFSv4] When set to the default of '1', this option
2030 ensures that both the RPC level authentication
2031 scheme and the NFS level operations agree to use
2032 numeric uids/gids if the mount is using the
2033 'sec=sys' security flavour. In effect it is
2034 disabling idmapping, which can make migration from
2035 legacy NFSv2/v3 systems to NFSv4 easier.
2036 Servers that do not support this mode of operation
2037 will be autodetected by the client, and it will fall
2038 back to using the idmapper.
2039 To turn off this behaviour, set the value to '0'.
2041 [NFS4] Specify an additional fixed unique ident-
2042 ification string that NFSv4 clients can insert into
2043 their nfs_client_id4 string. This is typically a
2044 UUID that is generated at system install time.
2046 nfs.send_implementation_id =
2047 [NFSv4.1] Send client implementation identification
2048 information in exchange_id requests.
2049 If zero, no implementation identification information
2051 The default is to send the implementation identification
2054 nfs.recover_lost_locks =
2055 [NFSv4] Attempt to recover locks that were lost due
2056 to a lease timeout on the server. Please note that
2057 doing this risks data corruption, since there are
2058 no guarantees that the file will remain unchanged
2059 after the locks are lost.
2060 If you want to enable the kernel legacy behaviour of
2061 attempting to recover these locks, then set this
2063 The default parameter value of '0' causes the kernel
2064 not to attempt recovery of lost locks.
2066 nfsd.nfs4_disable_idmapping=
2067 [NFSv4] When set to the default of '1', the NFSv4
2068 server will return only numeric uids and gids to
2069 clients using auth_sys, and will accept numeric uids
2070 and gids from such clients. This is intended to ease
2071 migration from NFSv2/v3.
2073 objlayoutdriver.osd_login_prog=
2074 [NFS] [OBJLAYOUT] sets the pathname to the program which
2075 is used to automatically discover and login into new
2076 osd-targets. Please see:
2077 Documentation/filesystems/pnfs.txt for more explanations
2079 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2080 when a NMI is triggered.
2081 Format: [state][,regs][,debounce][,die]
2083 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2084 Format: [panic,][nopanic,][num]
2086 0 - turn nmi_watchdog off
2087 When panic is specified, panic when an NMI watchdog
2088 timeout occurs (or 'nopanic' to override the opposite
2090 This is useful when you use a panic=... timeout and
2091 need the box quickly up again.
2093 netpoll.carrier_timeout=
2094 [NET] Specifies amount of time (in seconds) that
2095 netpoll should wait for a carrier. By default netpoll
2098 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2099 emulation library even if a 387 maths coprocessor
2103 [HW] Never suspend the console
2104 Disable suspending of consoles during suspend and
2105 hibernate operations. Once disabled, debugging
2106 messages can reach various consoles while the rest
2107 of the system is being put to sleep (ie, while
2108 debugging driver suspend/resume hooks). This may
2109 not work reliably with all consoles, but is known
2110 to work with serial and VGA consoles.
2111 To facilitate more flexible debugging, we also add
2112 console_suspend, a printk module parameter to control
2113 it. Users could use console_suspend (usually
2114 /sys/module/printk/parameters/console_suspend) to
2115 turn on/off it dynamically.
2117 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2118 caches in the slab allocator. Saves per-node memory,
2119 but will impact performance.
2123 noapic [SMP,APIC] Tells the kernel to not make use of any
2124 IOAPICs that may be present in the system.
2126 noautogroup Disable scheduler automatic task group creation.
2128 nobats [PPC] Do not use BATs for mapping kernel lowmem
2129 on "Classic" PPC cores.
2133 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2135 nodelayacct [KNL] Disable per-task delay accounting
2137 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2139 nodsp [SH] Disable hardware DSP at boot time.
2141 noefi [X86] Disable EFI runtime services support.
2146 On X86-32 available only on PAE configured kernels.
2147 noexec=on: enable non-executable mappings (default)
2148 noexec=off: disable non-executable mappings
2151 Disable SMAP (Supervisor Mode Access Prevention)
2152 even if it is supported by processor.
2155 Disable SMEP (Supervisor Mode Execution Prevention)
2156 even if it is supported by processor.
2159 This affects only 32-bit executables.
2160 noexec32=on: enable non-executable mappings (default)
2161 read doesn't imply executable mappings
2162 noexec32=off: disable non-executable mappings
2163 read implies executable mappings
2165 nofpu [SH] Disable hardware FPU at boot time.
2167 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2168 register save and restore. The kernel will only save
2169 legacy floating-point registers on task switch.
2171 noxsave [BUGS=X86] Disables x86 extended register state save
2172 and restore using xsave. The kernel will fallback to
2173 enabling legacy floating-point and sse state.
2176 on enable eager fpu restore
2177 off disable eager fpu restore
2178 auto selects the default scheme, which automatically
2179 enables eagerfpu restore for xsaveopt.
2181 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2182 wfi(ARM) instruction doesn't work correctly and not to
2183 use it. This is also useful when using JTAG debugger.
2185 no_file_caps Tells the kernel not to honor file capabilities. The
2186 only way then for a file to be executed with privilege
2187 is to be setuid root or executed by root.
2189 nohalt [IA-64] Tells the kernel not to use the power saving
2190 function PAL_HALT_LIGHT when idle. This increases
2191 power-consumption. On the positive side, it reduces
2192 interrupt wake-up latency, which may improve performance
2193 in certain environments such as networked servers or
2196 nohibernate [HIBERNATION] Disable hibernation and resume.
2198 nohz= [KNL] Boottime enable/disable dynamic ticks
2199 Valid arguments: on, off
2202 nohz_full= [KNL,BOOT]
2203 In kernels built with CONFIG_NO_HZ_FULL=y, set
2204 the specified list of CPUs whose tick will be stopped
2205 whenever possible. The boot CPU will be forced outside
2206 the range to maintain the timekeeping.
2207 The CPUs in this range must also be included in the
2210 noiotrap [SH] Disables trapped I/O port accesses.
2212 noirqdebug [X86-32] Disables the code which attempts to detect and
2213 disable unhandled interrupt sources.
2215 no_timer_check [X86,APIC] Disables the code which tests for
2216 broken timer IRQ sources.
2218 noisapnp [ISAPNP] Disables ISA PnP code.
2220 noinitrd [RAM] Tells the kernel not to load any configured
2223 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2225 [Deprecated - use intremap=off]
2229 nojitter [IA-64] Disables jitter checking for ITC timers.
2231 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2233 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2236 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2237 steal time is computed, but won't influence scheduler
2240 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2242 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2244 noltlbs [PPC] Do not use large page/tlb entries for kernel
2245 lowmem mapping on PPC40x.
2247 nomca [IA-64] Disable machine check abort handling
2249 nomce [X86-32] Machine Check Exception
2251 nomfgpt [X86-32] Disable Multi-Function General Purpose
2252 Timer usage (for AMD Geode machines).
2254 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2255 shutdown the other cpus. Instead use the REBOOT_VECTOR
2258 nomodule Disable module load
2260 nopat [X86] Disable PAT (page attribute table extension of
2261 pagetables) support.
2263 norandmaps Don't use address space randomization. Equivalent to
2264 echo 0 > /proc/sys/kernel/randomize_va_space
2266 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2268 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2269 with UP alternatives
2271 nordrand [X86] Disable kernel use of the RDRAND and
2272 RDSEED instructions even if they are supported
2273 by the processor. RDRAND and RDSEED are still
2274 available to user space applications.
2276 noresume [SWSUSP] Disables resume and restores original swap
2279 no-scroll [VGA] Disables scrollback.
2280 This is required for the Braillex ib80-piezo Braille
2281 reader made by F.H. Papenmeier (Germany).
2285 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2287 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2288 and disable the IO APIC. legacy for "maxcpus=0".
2290 nosoftlockup [KNL] Disable the soft-lockup detector.
2292 nosync [HW,M68K] Disables sync negotiation for all devices.
2294 notsc [BUGS=X86-32] Disable Time Stamp Counter
2296 nousb [USB] Disable the USB subsystem
2298 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2302 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2304 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2305 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2306 Some features depend on CPU0. Known dependencies are:
2307 1. Resume from suspend/hibernate depends on CPU0.
2308 Suspend/hibernate will fail if CPU0 is offline and you
2309 need to online CPU0 before suspend/hibernate.
2310 2. PIC interrupts also depend on CPU0. CPU0 can't be
2311 removed if a PIC interrupt is detected.
2312 It's said poweroff/reboot may depend on CPU0 on some
2313 machines although I haven't seen such issues so far
2314 after CPU0 is offline on a few tested machines.
2315 If the dependencies are under your control, you can
2316 turn on cpu0_hotplug.
2318 nptcg= [IA-64] Override max number of concurrent global TLB
2319 purges which is reported from either PAL_VM_SUMMARY or
2322 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2323 could support. nr_cpus=n : n >= 1 limits the kernel to
2324 supporting 'n' processors. Later in runtime you can not
2325 use hotplug cpu feature to put more cpu back to online.
2326 just like you compile the kernel NR_CPUS=n
2328 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2330 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2331 Allowed values are enable and disable
2333 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2334 one of ['zone', 'node', 'default'] can be specified
2335 This can be set from sysctl after boot.
2336 See Documentation/sysctl/vm.txt for details.
2338 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2339 See Documentation/debugging-via-ohci1394.txt for more
2342 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2343 Rather than timing out after 20 ms if an EC
2344 command is not properly ACKed, override the length
2345 of the timeout. We have interrupts disabled while
2346 waiting for the ACK, so if this is set too high
2347 interrupts *may* be lost!
2349 omap_mux= [OMAP] Override bootloader pin multiplexing.
2350 Format: <mux_mode0.mode_name=value>...
2351 For example, to override I2C bus2:
2352 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2354 oprofile.timer= [HW]
2355 Use timer interrupt instead of performance counters
2357 oprofile.cpu_type= Force an oprofile cpu type
2358 This might be useful if you have an older oprofile
2359 userland or if you want common events.
2360 Format: { arch_perfmon }
2361 arch_perfmon: [X86] Force use of architectural
2362 perfmon on Intel CPUs instead of the
2363 CPU specific event set.
2364 timer: [X86] Force use of architectural NMI
2365 timer mode (see also oprofile.timer
2366 for generic hr timer mode)
2367 [s390] Force legacy basic mode sampling
2368 (report cpu_type "timer")
2370 oops=panic Always panic on oopses. Default is to just kill the
2371 process, but there is a small probability of
2372 deadlocking the machine.
2373 This will also cause panics on machine check exceptions.
2374 Useful together with panic=30 to trigger a reboot.
2377 See Documentation/sound/oss/oss-parameters.txt
2379 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2380 timeout > 0: seconds before rebooting
2381 timeout = 0: wait forever
2382 timeout < 0: reboot immediately
2385 crash_kexec_post_notifiers
2386 Run kdump after running panic-notifiers and dumping
2387 kmsg. This only for the users who doubt kdump always
2388 succeeds in any situation.
2389 Note that this also increases risks of kdump failure,
2390 because some panic notifiers can make the crashed
2391 kernel more unstable.
2393 parkbd.port= [HW] Parallel port number the keyboard adapter is
2394 connected to, default is 0.
2396 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2397 0 for XT, 1 for AT (default is AT).
2400 parport= [HW,PPT] Specify parallel ports. 0 disables.
2401 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2402 Use 'auto' to force the driver to use any
2403 IRQ/DMA settings detected (the default is to
2404 ignore detected IRQ/DMA settings because of
2405 possible conflicts). You can specify the base
2406 address, IRQ, and DMA settings; IRQ and DMA
2407 should be numbers, or 'auto' (for using detected
2408 settings on that particular port), or 'nofifo'
2409 (to avoid using a FIFO even if it is detected).
2410 Parallel ports are assigned in the order they
2411 are specified on the command line, starting
2414 parport_init_mode= [HW,PPT]
2415 Configure VIA parallel port to operate in
2416 a specific mode. This is necessary on Pegasos
2417 computer where firmware has no options for setting
2418 up parallel port mode and sets it to spp.
2419 Currently this function knows 686a and 8231 chips.
2420 Format: [spp|ps2|epp|ecp|ecpepp]
2423 Halt all CPUs after the first oops has been printed for
2424 the specified number of seconds. This is to be used if
2425 your oopses keep scrolling off the screen.
2430 See header of drivers/block/paride/pcd.c.
2431 See also Documentation/blockdev/paride.txt.
2433 pci=option[,option...] [PCI] various PCI subsystem options:
2434 earlydump [X86] dump PCI config space before the kernel
2436 off [X86] don't probe for the PCI bus
2437 bios [X86-32] force use of PCI BIOS, don't access
2438 the hardware directly. Use this if your machine
2439 has a non-standard PCI host bridge.
2440 nobios [X86-32] disallow use of PCI BIOS, only direct
2441 hardware access methods are allowed. Use this
2442 if you experience crashes upon bootup and you
2443 suspect they are caused by the BIOS.
2444 conf1 [X86] Force use of PCI Configuration
2446 conf2 [X86] Force use of PCI Configuration
2448 noaer [PCIE] If the PCIEAER kernel config parameter is
2449 enabled, this kernel boot option can be used to
2450 disable the use of PCIE advanced error reporting.
2451 nodomains [PCI] Disable support for multiple PCI
2452 root domains (aka PCI segments, in ACPI-speak).
2453 nommconf [X86] Disable use of MMCONFIG for PCI
2455 check_enable_amd_mmconf [X86] check for and enable
2456 properly configured MMIO access to PCI
2457 config space on AMD family 10h CPU
2458 nomsi [MSI] If the PCI_MSI kernel config parameter is
2459 enabled, this kernel boot option can be used to
2460 disable the use of MSI interrupts system-wide.
2461 noioapicquirk [APIC] Disable all boot interrupt quirks.
2462 Safety option to keep boot IRQs enabled. This
2463 should never be necessary.
2464 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2465 primary IO-APIC for bridges that cannot disable
2466 boot IRQs. This fixes a source of spurious IRQs
2467 when the system masks IRQs.
2468 noioapicreroute [APIC] Disable workaround that uses the
2469 boot IRQ equivalent of an IRQ that connects to
2470 a chipset where boot IRQs cannot be disabled.
2471 The opposite of ioapicreroute.
2472 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2473 routing table. These calls are known to be buggy
2474 on several machines and they hang the machine
2475 when used, but on other computers it's the only
2476 way to get the interrupt routing table. Try
2477 this option if the kernel is unable to allocate
2478 IRQs or discover secondary PCI buses on your
2480 rom [X86] Assign address space to expansion ROMs.
2481 Use with caution as certain devices share
2482 address decoders between ROMs and other
2484 norom [X86] Do not assign address space to
2485 expansion ROMs that do not already have
2486 BIOS assigned address ranges.
2487 nobar [X86] Do not assign address space to the
2488 BARs that weren't assigned by the BIOS.
2489 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2490 assigned automatically to PCI devices. You can
2491 make the kernel exclude IRQs of your ISA cards
2493 pirqaddr=0xAAAAA [X86] Specify the physical address
2494 of the PIRQ table (normally generated
2495 by the BIOS) if it is outside the
2496 F0000h-100000h range.
2497 lastbus=N [X86] Scan all buses thru bus #N. Can be
2498 useful if the kernel is unable to find your
2499 secondary buses and you want to tell it
2500 explicitly which ones they are.
2501 assign-busses [X86] Always assign all PCI bus
2502 numbers ourselves, overriding
2503 whatever the firmware may have done.
2504 usepirqmask [X86] Honor the possible IRQ mask stored
2505 in the BIOS $PIR table. This is needed on
2506 some systems with broken BIOSes, notably
2507 some HP Pavilion N5400 and Omnibook XE3
2508 notebooks. This will have no effect if ACPI
2509 IRQ routing is enabled.
2510 noacpi [X86] Do not use ACPI for IRQ routing
2511 or for PCI scanning.
2512 use_crs [X86] Use PCI host bridge window information
2513 from ACPI. On BIOSes from 2008 or later, this
2514 is enabled by default. If you need to use this,
2515 please report a bug.
2516 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2517 If you need to use this, please report a bug.
2518 routeirq Do IRQ routing for all PCI devices.
2519 This is normally done in pci_enable_device(),
2520 so this option is a temporary workaround
2521 for broken drivers that don't call it.
2522 skip_isa_align [X86] do not align io start addr, so can
2523 handle more pci cards
2524 firmware [ARM] Do not re-enumerate the bus but instead
2525 just use the configuration from the
2526 bootloader. This is currently used on
2527 IXP2000 systems where the bus has to be
2528 configured a certain way for adjunct CPUs.
2529 noearly [X86] Don't do any early type 1 scanning.
2530 This might help on some broken boards which
2531 machine check when some devices' config space
2532 is read. But various workarounds are disabled
2533 and some IOMMU drivers will not work.
2534 bfsort Sort PCI devices into breadth-first order.
2535 This sorting is done to get a device
2536 order compatible with older (<= 2.4) kernels.
2537 nobfsort Don't sort PCI devices into breadth-first order.
2538 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2539 tuning and use the BIOS-configured MPS defaults.
2540 pcie_bus_safe Set every device's MPS to the largest value
2541 supported by all devices below the root complex.
2542 pcie_bus_perf Set device MPS to the largest allowable MPS
2543 based on its parent bus. Also set MRRS (Max
2544 Read Request Size) to the largest supported
2545 value (no larger than the MPS that the device
2546 or bus can support) for best performance.
2547 pcie_bus_peer2peer Set every device's MPS to 128B, which
2548 every device is guaranteed to support. This
2549 configuration allows peer-to-peer DMA between
2550 any pair of devices, possibly at the cost of
2551 reduced performance. This also guarantees
2552 that hot-added devices will work.
2553 cbiosize=nn[KMG] The fixed amount of bus space which is
2554 reserved for the CardBus bridge's IO window.
2555 The default value is 256 bytes.
2556 cbmemsize=nn[KMG] The fixed amount of bus space which is
2557 reserved for the CardBus bridge's memory
2558 window. The default value is 64 megabytes.
2561 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2562 Specifies alignment and device to reassign
2563 aligned memory resources.
2564 If <order of align> is not specified,
2565 PAGE_SIZE is used as alignment.
2566 PCI-PCI bridge can be specified, if resource
2567 windows need to be expanded.
2568 ecrc= Enable/disable PCIe ECRC (transaction layer
2569 end-to-end CRC checking).
2570 bios: Use BIOS/firmware settings. This is the
2574 hpiosize=nn[KMG] The fixed amount of bus space which is
2575 reserved for hotplug bridge's IO window.
2576 Default size is 256 bytes.
2577 hpmemsize=nn[KMG] The fixed amount of bus space which is
2578 reserved for hotplug bridge's memory window.
2579 Default size is 2 megabytes.
2580 realloc= Enable/disable reallocating PCI bridge resources
2581 if allocations done by BIOS are too small to
2582 accommodate resources required by all child
2584 off: Turn realloc off
2586 realloc same as realloc=on
2587 noari do not use PCIe ARI.
2588 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2589 only look for one device below a PCIe downstream
2592 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2595 force Enable ASPM even on devices that claim not to support it.
2596 WARNING: Forcing ASPM on may cause system lockups.
2598 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2599 nomsi Do not use MSI for PCI Express Native Hotplug (this
2600 makes all PCIe ports use INTx for hotplug services).
2602 pcie_ports= [PCIE] PCIe ports handling:
2603 auto Ask the BIOS whether or not to use native PCIe services
2604 associated with PCIe ports (PME, hot-plug, AER). Use
2605 them only if that is allowed by the BIOS.
2606 native Use native PCIe services associated with PCIe ports
2608 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2611 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2612 nomsi Do not use MSI for native PCIe PME signaling (this makes
2613 all PCIe root ports use INTx for all services).
2615 pcmv= [HW,PCMCIA] BadgePAD 4
2619 Keep all power-domains already enabled by bootloader on,
2620 even if no driver has claimed them. This is useful
2621 for debug and development, but should not be
2622 needed on a platform with proper driver support.
2625 See Documentation/blockdev/paride.txt.
2627 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2630 See arch/parisc/kernel/pdc_chassis.c
2632 percpu_alloc= Select which percpu first chunk allocator to use.
2633 Currently supported values are "embed" and "page".
2634 Archs may support subset or none of the selections.
2635 See comments in mm/percpu.c for details on each
2636 allocator. This parameter is primarily for debugging
2637 and performance comparison.
2640 See Documentation/blockdev/paride.txt.
2643 See Documentation/blockdev/paride.txt.
2645 pirq= [SMP,APIC] Manual mp-table setup
2646 See Documentation/x86/i386/IO-APIC.txt.
2648 plip= [PPT,NET] Parallel port network link
2649 Format: { parport<nr> | timid | 0 }
2650 See also Documentation/parport.txt.
2652 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2653 Override pmtimer IOPort with a hex value.
2657 Enable PNP debug messages (depends on the
2658 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2659 via /sys/module/pnp/parameters/debug. We always show
2660 current resource usage; turning this on also shows
2661 possible settings and some assignment information.
2667 { on | off | curr | res | no-curr | no-res }
2670 [ISAPNP] Exclude IRQs for the autoconfiguration
2673 [ISAPNP] Exclude DMAs for the autoconfiguration
2675 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2676 Ranges are in pairs (I/O port base and size).
2679 [ISAPNP] Exclude memory regions for the
2681 Ranges are in pairs (memory base and size).
2683 ports= [IP_VS_FTP] IPVS ftp helper module
2685 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2687 Format: <port>,<port>....
2689 print-fatal-signals=
2690 [KNL] debug: print fatal signals
2692 If enabled, warn about various signal handling
2693 related application anomalies: too many signals,
2694 too many POSIX.1 timers, fatal signals causing a
2697 If you hit the warning due to signal overflow,
2698 you might want to try "ulimit -i unlimited".
2702 printk.always_kmsg_dump=
2703 Trigger kmsg_dump for cases other than kernel oops or
2705 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2708 printk.time= Show timing data prefixed to each printk message line
2709 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2711 processor.max_cstate= [HW,ACPI]
2712 Limit processor to maximum C-state
2713 max_cstate=9 overrides any DMI blacklist limit.
2715 processor.nocst [HW,ACPI]
2716 Ignore the _CST method to determine C-states,
2717 instead using the legacy FADT method
2719 profile= [KNL] Enable kernel profiling via /proc/profile
2720 Format: [schedule,]<number>
2721 Param: "schedule" - profile schedule points.
2722 Param: <number> - step/bucket size as a power of 2 for
2723 statistical time based profiling.
2724 Param: "sleep" - profile D-state sleeping (millisecs).
2725 Requires CONFIG_SCHEDSTATS
2726 Param: "kvm" - profile VM exits.
2728 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2730 See Documentation/blockdev/ramdisk.txt.
2732 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2733 probe for; one of (bare|imps|exps|lifebook|any).
2734 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2736 psmouse.resetafter= [HW,MOUSE]
2737 Try to reset the device after so many bad packets
2740 [HW,MOUSE] Set desired mouse resolution, in dpi.
2741 psmouse.smartscroll=
2742 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2743 0 = disabled, 1 = enabled (default).
2745 pstore.backend= Specify the name of the pstore backend to use
2748 See Documentation/blockdev/paride.txt.
2751 [KNL] Number of legacy pty's. Overwrites compiled-in
2754 quiet [KNL] Disable most log messages
2759 See Documentation/md.txt.
2761 ramdisk_blocksize= [RAM]
2762 See Documentation/blockdev/ramdisk.txt.
2764 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2765 See Documentation/blockdev/ramdisk.txt.
2768 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2769 the specified list of CPUs to be no-callback CPUs.
2770 Invocation of these CPUs' RCU callbacks will
2771 be offloaded to "rcuox/N" kthreads created for
2772 that purpose, where "x" is "b" for RCU-bh, "p"
2773 for RCU-preempt, and "s" for RCU-sched, and "N"
2774 is the CPU number. This reduces OS jitter on the
2775 offloaded CPUs, which can be useful for HPC and
2776 real-time workloads. It can also improve energy
2777 efficiency for asymmetric multiprocessors.
2780 Rather than requiring that offloaded CPUs
2781 (specified by rcu_nocbs= above) explicitly
2782 awaken the corresponding "rcuoN" kthreads,
2783 make these kthreads poll for callbacks.
2784 This improves the real-time response for the
2785 offloaded CPUs by relieving them of the need to
2786 wake up the corresponding kthread, but degrades
2787 energy efficiency by requiring that the kthreads
2788 periodically wake up to do the polling.
2790 rcutree.blimit= [KNL]
2791 Set maximum number of finished RCU callbacks to
2792 process in one batch.
2794 rcutree.rcu_fanout_leaf= [KNL]
2795 Increase the number of CPUs assigned to each
2796 leaf rcu_node structure. Useful for very large
2799 rcutree.jiffies_till_sched_qs= [KNL]
2800 Set required age in jiffies for a
2801 given grace period before RCU starts
2802 soliciting quiescent-state help from
2803 rcu_note_context_switch().
2805 rcutree.jiffies_till_first_fqs= [KNL]
2806 Set delay from grace-period initialization to
2807 first attempt to force quiescent states.
2808 Units are jiffies, minimum value is zero,
2809 and maximum value is HZ.
2811 rcutree.jiffies_till_next_fqs= [KNL]
2812 Set delay between subsequent attempts to force
2813 quiescent states. Units are jiffies, minimum
2814 value is one, and maximum value is HZ.
2816 rcutree.rcu_nocb_leader_stride= [KNL]
2817 Set the number of NOCB kthread groups, which
2818 defaults to the square root of the number of
2819 CPUs. Larger numbers reduces the wakeup overhead
2820 on the per-CPU grace-period kthreads, but increases
2821 that same overhead on each group's leader.
2823 rcutree.qhimark= [KNL]
2824 Set threshold of queued RCU callbacks beyond which
2825 batch limiting is disabled.
2827 rcutree.qlowmark= [KNL]
2828 Set threshold of queued RCU callbacks below which
2829 batch limiting is re-enabled.
2831 rcutree.rcu_idle_gp_delay= [KNL]
2832 Set wakeup interval for idle CPUs that have
2833 RCU callbacks (RCU_FAST_NO_HZ=y).
2835 rcutree.rcu_idle_lazy_gp_delay= [KNL]
2836 Set wakeup interval for idle CPUs that have
2837 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2838 Lazy RCU callbacks are those which RCU can
2839 prove do nothing more than free memory.
2841 rcutorture.fqs_duration= [KNL]
2842 Set duration of force_quiescent_state bursts.
2844 rcutorture.fqs_holdoff= [KNL]
2845 Set holdoff time within force_quiescent_state bursts.
2847 rcutorture.fqs_stutter= [KNL]
2848 Set wait time between force_quiescent_state bursts.
2850 rcutorture.gp_exp= [KNL]
2851 Use expedited update-side primitives.
2853 rcutorture.gp_normal= [KNL]
2854 Use normal (non-expedited) update-side primitives.
2855 If both gp_exp and gp_normal are set, do both.
2856 If neither gp_exp nor gp_normal are set, still
2859 rcutorture.n_barrier_cbs= [KNL]
2860 Set callbacks/threads for rcu_barrier() testing.
2862 rcutorture.nfakewriters= [KNL]
2863 Set number of concurrent RCU writers. These just
2864 stress RCU, they don't participate in the actual
2865 test, hence the "fake".
2867 rcutorture.nreaders= [KNL]
2868 Set number of RCU readers.
2870 rcutorture.object_debug= [KNL]
2871 Enable debug-object double-call_rcu() testing.
2873 rcutorture.onoff_holdoff= [KNL]
2874 Set time (s) after boot for CPU-hotplug testing.
2876 rcutorture.onoff_interval= [KNL]
2877 Set time (s) between CPU-hotplug operations, or
2878 zero to disable CPU-hotplug testing.
2880 rcutorture.rcutorture_runnable= [BOOT]
2881 Start rcutorture running at boot time.
2883 rcutorture.shuffle_interval= [KNL]
2884 Set task-shuffle interval (s). Shuffling tasks
2885 allows some CPUs to go into dyntick-idle mode
2886 during the rcutorture test.
2888 rcutorture.shutdown_secs= [KNL]
2889 Set time (s) after boot system shutdown. This
2890 is useful for hands-off automated testing.
2892 rcutorture.stall_cpu= [KNL]
2893 Duration of CPU stall (s) to test RCU CPU stall
2894 warnings, zero to disable.
2896 rcutorture.stall_cpu_holdoff= [KNL]
2897 Time to wait (s) after boot before inducing stall.
2899 rcutorture.stat_interval= [KNL]
2900 Time (s) between statistics printk()s.
2902 rcutorture.stutter= [KNL]
2903 Time (s) to stutter testing, for example, specifying
2904 five seconds causes the test to run for five seconds,
2905 wait for five seconds, and so on. This tests RCU's
2906 ability to transition abruptly to and from idle.
2908 rcutorture.test_boost= [KNL]
2909 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2910 "Maybe" means test if the RCU implementation
2911 under test support RCU priority boosting.
2913 rcutorture.test_boost_duration= [KNL]
2914 Duration (s) of each individual boost test.
2916 rcutorture.test_boost_interval= [KNL]
2917 Interval (s) between each boost test.
2919 rcutorture.test_no_idle_hz= [KNL]
2920 Test RCU's dyntick-idle handling. See also the
2921 rcutorture.shuffle_interval parameter.
2923 rcutorture.torture_type= [KNL]
2924 Specify the RCU implementation to test.
2926 rcutorture.verbose= [KNL]
2927 Enable additional printk() statements.
2929 rcupdate.rcu_expedited= [KNL]
2930 Use expedited grace-period primitives, for
2931 example, synchronize_rcu_expedited() instead
2932 of synchronize_rcu(). This reduces latency,
2933 but can increase CPU utilization, degrade
2934 real-time latency, and degrade energy efficiency.
2936 rcupdate.rcu_cpu_stall_suppress= [KNL]
2937 Suppress RCU CPU stall warning messages.
2939 rcupdate.rcu_cpu_stall_timeout= [KNL]
2940 Set timeout for RCU CPU stall warning messages.
2944 Run specified binary instead of /init from the ramdisk,
2945 used for early userspace startup. See initrd.
2948 Format (x86 or x86_64):
2949 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2951 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2953 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2954 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2955 reboot_force is either force or not specified,
2956 reboot_cpu is s[mp]#### with #### being the processor
2957 to be used for rebooting.
2960 [KNL, SMP] Set scheduler's default relax_domain_level.
2961 See Documentation/cgroups/cpusets.txt.
2963 relative_sleep_states=
2964 [SUSPEND] Use sleep state labeling where the deepest
2965 state available other than hibernation is always "mem".
2966 Format: { "0" | "1" }
2967 0 -- Traditional sleep state labels.
2968 1 -- Relative sleep state labels.
2970 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2972 reservetop= [X86-32]
2974 Reserves a hole at the top of the kernel virtual
2979 Set the amount of memory to reserve for BIOS at
2980 the bottom of the address space.
2982 reset_devices [KNL] Force drivers to reset the underlying device
2983 during initialization.
2986 Specify the partition device for software suspend
2988 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2990 resume_offset= [SWSUSP]
2991 Specify the offset from the beginning of the partition
2992 given by "resume=" at which the swap header is located,
2993 in <PAGE_SIZE> units (needed only for swap files).
2994 See Documentation/power/swsusp-and-swap-files.txt
2996 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2997 read the resume files
2999 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3000 Useful for devices that are detected asynchronously
3001 (e.g. USB and MMC devices).
3003 hibernate= [HIBERNATION]
3004 noresume Don't check if there's a hibernation image
3005 present during boot.
3006 nocompress Don't compress/decompress hibernation images.
3007 no Disable hibernation and resume.
3009 retain_initrd [RAM] Keep initrd memory after extraction
3011 rhash_entries= [KNL,NET]
3012 Set number of hash buckets for route cache
3014 ro [KNL] Mount root device read-only on boot
3016 root= [KNL] Root filesystem
3017 See name_to_dev_t comment in init/do_mounts.c.
3019 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3020 mount the root filesystem
3022 rootflags= [KNL] Set root filesystem mount option string
3024 rootfstype= [KNL] Set root filesystem type
3026 rootwait [KNL] Wait (indefinitely) for root device to show up.
3027 Useful for devices that are detected asynchronously
3028 (e.g. USB and MMC devices).
3030 rproc_mem=nn[KMG][@address]
3031 [KNL,ARM,CMA] Remoteproc physical memory block.
3032 Memory area to be used by remote processor image,
3035 rw [KNL] Mount root device read-write on boot
3037 S [KNL] Run init in single mode
3040 See drivers/net/irda/sa1100_ir.c.
3042 sbni= [NET] Granch SBNI12 leased line adapter
3044 sched_debug [KNL] Enables verbose scheduler debug messages.
3046 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3047 xtime_lock contention on larger systems, and/or RCU lock
3048 contention on all systems with CONFIG_MAXSMP set.
3049 Format: { "0" | "1" }
3050 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3052 Note: increases power consumption, thus should only be
3053 enabled if running jitter sensitive (HPC/RT) workloads.
3055 security= [SECURITY] Choose a security module to enable at boot.
3056 If this boot parameter is not specified, only the first
3057 security module asking for security registration will be
3058 loaded. An invalid security module name will be treated
3059 as if no module has been chosen.
3061 selinux= [SELINUX] Disable or enable SELinux at boot time.
3062 Format: { "0" | "1" }
3063 See security/selinux/Kconfig help text.
3066 Default value is set via kernel config option.
3067 If enabled at boot time, /selinux/disable can be used
3068 later to disable prior to initial policy load.
3070 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3071 Format: { "0" | "1" }
3072 See security/apparmor/Kconfig help text
3075 Default value is set via kernel config option.
3077 serialnumber [BUGS=X86-32]
3080 Maximal number of shapers.
3082 show_msr= [x86] show boot-time MSR settings
3083 Format: { <integer> }
3084 Show boot-time (BIOS-initialized) MSR settings.
3085 The parameter means the number of CPUs to show,
3086 for example 1 means boot CPU only.
3093 slab_max_order= [MM, SLAB]
3094 Determines the maximum allowed order for slabs.
3095 A high setting may cause OOMs due to memory
3096 fragmentation. Defaults to 1 for systems with
3097 more than 32MB of RAM, 0 otherwise.
3099 slub_debug[=options[,slabs]] [MM, SLUB]
3100 Enabling slub_debug allows one to determine the
3101 culprit if slab objects become corrupted. Enabling
3102 slub_debug can create guard zones around objects and
3103 may poison objects when not in use. Also tracks the
3104 last alloc / free. For more information see
3105 Documentation/vm/slub.txt.
3107 slub_max_order= [MM, SLUB]
3108 Determines the maximum allowed order for slabs.
3109 A high setting may cause OOMs due to memory
3110 fragmentation. For more information see
3111 Documentation/vm/slub.txt.
3113 slub_min_objects= [MM, SLUB]
3114 The minimum number of objects per slab. SLUB will
3115 increase the slab order up to slub_max_order to
3116 generate a sufficiently large slab able to contain
3117 the number of objects indicated. The higher the number
3118 of objects the smaller the overhead of tracking slabs
3119 and the less frequently locks need to be acquired.
3120 For more information see Documentation/vm/slub.txt.
3122 slub_min_order= [MM, SLUB]
3123 Determines the minimum page order for slabs. Must be
3124 lower than slub_max_order.
3125 For more information see Documentation/vm/slub.txt.
3127 slub_nomerge [MM, SLUB]
3128 Disable merging of slabs with similar size. May be
3129 necessary if there is some reason to distinguish
3130 allocs to different slabs. Debug options disable
3131 merging on their own.
3132 For more information see Documentation/vm/slub.txt.
3135 Format: <io1>[,<io2>[,...,<io8>]]
3137 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3138 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3139 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3140 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3141 smsc-ircc2.ircc_irq= [HW] IRQ line
3142 smsc-ircc2.ircc_dma= [HW] DMA channel
3143 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3144 0: Toshiba Satellite 1800 (GP data pin select)
3145 1: Fast pin select (default)
3149 [KNL] Should the soft-lockup detector generate panics.
3152 softlockup_all_cpu_backtrace=
3153 [KNL] Should the soft-lockup detector generate
3154 backtraces on all cpus.
3157 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3158 See Documentation/laptops/sonypi.txt
3160 spia_io_base= [HW,MTD]
3166 Enabled the stack tracer on boot up.
3168 stacktrace_filter=[function-list]
3169 [FTRACE] Limit the functions that the stack tracer
3170 will trace at boot up. function-list is a comma separated
3171 list of functions. This list can be changed at run
3172 time by the stack_trace_filter file in the debugfs
3173 tracing directory. Note, this enables stack tracing
3174 and the stacktrace above is not needed.
3178 Set the STI (builtin display/keyboard on the HP-PARISC
3179 machines) console (graphic card) which should be used
3180 as the initial boot-console.
3181 See also comment in drivers/video/console/sticore.c.
3184 See comment in drivers/video/console/sticore.c.
3187 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3189 sunrpc.min_resvport=
3190 sunrpc.max_resvport=
3192 SunRPC servers often require that client requests
3193 originate from a privileged port (i.e. a port in the
3194 range 0 < portnr < 1024).
3195 An administrator who wishes to reserve some of these
3196 ports for other uses may adjust the range that the
3197 kernel's sunrpc client considers to be privileged
3198 using these two parameters to set the minimum and
3199 maximum port values.
3203 Control how the NFS server code allocates CPUs to
3204 service thread pools. Depending on how many NICs
3205 you have and where their interrupts are bound, this
3206 option will affect which CPUs will do NFS serving.
3207 Note: this parameter cannot be changed while the
3208 NFS server is running.
3210 auto the server chooses an appropriate mode
3211 automatically using heuristics
3212 global a single global pool contains all CPUs
3213 percpu one pool for each CPU
3214 pernode one pool for each NUMA node (equivalent
3215 to global on non-NUMA machines)
3217 sunrpc.tcp_slot_table_entries=
3218 sunrpc.udp_slot_table_entries=
3220 Sets the upper limit on the number of simultaneous
3221 RPC calls that can be sent from the client to a
3222 server. Increasing these values may allow you to
3223 improve throughput, but will also increase the
3224 amount of memory reserved for use by the client.
3227 [KNL] Enable accounting of swap in memory resource
3228 controller if no parameter or 1 is given or disable
3229 it if 0 is given (See Documentation/cgroups/memory.txt)
3231 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3232 Format: { <int> | force }
3233 <int> -- Number of I/O TLB slabs
3234 force -- force using of bounce buffers even if they
3235 wouldn't be automatically used by the kernel
3239 sysfs.deprecated=0|1 [KNL]
3240 Enable/disable old style sysfs layout for old udev
3241 on older distributions. When this option is enabled
3242 very new udev will not work anymore. When this option
3243 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3244 in older udev will not work anymore.
3245 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3246 the kernel configuration.
3248 sysrq_always_enabled
3250 Ignore sysrq setting - this boot parameter will
3251 neutralize any effect of /proc/sys/kernel/sysrq.
3252 Useful for debugging.
3256 test_suspend= [SUSPEND]
3257 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3258 standby suspend) as the system sleep state to briefly
3259 enter during system startup. The system is woken from
3260 this state using a wakeup-capable RTC alarm.
3262 thash_entries= [KNL,NET]
3263 Set number of hash buckets for TCP connection
3265 thermal.act= [HW,ACPI]
3266 -1: disable all active trip points in all thermal zones
3267 <degrees C>: override all lowest active trip points
3269 thermal.crt= [HW,ACPI]
3270 -1: disable all critical trip points in all thermal zones
3271 <degrees C>: override all critical trip points
3273 thermal.nocrt= [HW,ACPI]
3274 Set to disable actions on ACPI thermal zone
3275 critical and hot trip points.
3277 thermal.off= [HW,ACPI]
3278 1: disable ACPI thermal control
3280 thermal.psv= [HW,ACPI]
3281 -1: disable all passive trip points
3282 <degrees C>: override all passive trip points to this
3285 thermal.tzp= [HW,ACPI]
3286 Specify global default ACPI thermal zone polling rate
3287 <deci-seconds>: poll all this frequency
3288 0: no polling (default)
3291 Force threading of all interrupt handlers except those
3292 marked explicitly IRQF_NO_THREAD.
3295 Enable the Transcendent memory driver if built-in.
3297 tmem.cleancache=0|1 [KNL, XEN]
3298 Default is on (1). Disable the usage of the cleancache
3299 API to send anonymous pages to the hypervisor.
3301 tmem.frontswap=0|1 [KNL, XEN]
3302 Default is on (1). Disable the usage of the frontswap
3303 API to send swap pages to the hypervisor. If disabled
3304 the selfballooning and selfshrinking are force disabled.
3306 tmem.selfballooning=0|1 [KNL, XEN]
3307 Default is on (1). Disable the driving of swap pages
3310 tmem.selfshrinking=0|1 [KNL, XEN]
3311 Default is on (1). Partial swapoff that immediately
3312 transfers pages from Xen hypervisor back to the
3313 kernel based on different criteria.
3317 Specify if the kernel should make use of the cpu
3318 topology information if the hardware supports this.
3319 The scheduler will make use of this information and
3320 e.g. base its process migration decisions on it.
3325 tpm_suspend_pcr=[HW,TPM]
3326 Format: integer pcr id
3327 Specify that at suspend time, the tpm driver
3328 should extend the specified pcr with zeros,
3329 as a workaround for some chips which fail to
3330 flush the last written pcr on TPM_SaveState.
3331 This will guarantee that all the other pcrs
3334 trace_buf_size=nn[KMG]
3335 [FTRACE] will set tracing buffer size.
3337 trace_event=[event-list]
3338 [FTRACE] Set and start specified trace events in order
3339 to facilitate early boot debugging.
3340 See also Documentation/trace/events.txt
3342 trace_options=[option-list]
3343 [FTRACE] Enable or disable tracer options at boot.
3344 The option-list is a comma delimited list of options
3345 that can be enabled or disabled just as if you were
3346 to echo the option name into
3348 /sys/kernel/debug/tracing/trace_options
3350 For example, to enable stacktrace option (to dump the
3351 stack trace of each event), add to the command line:
3353 trace_options=stacktrace
3355 See also Documentation/trace/ftrace.txt "trace options"
3359 [FTRACE] enable this option to disable tracing when a
3360 warning is hit. This turns off "tracing_on". Tracing can
3361 be enabled again by echoing '1' into the "tracing_on"
3362 file located in /sys/kernel/debug/tracing/
3364 This option is useful, as it disables the trace before
3365 the WARNING dump is called, which prevents the trace to
3366 be filled with content caused by the warning output.
3368 This option can also be set at run time via the sysctl
3369 option: kernel/traceoff_on_warning
3371 transparent_hugepage=
3373 Format: [always|madvise|never]
3374 Can be used to control the default behavior of the system
3375 with respect to transparent hugepages.
3376 See Documentation/vm/transhuge.txt for more details.
3378 tsc= Disable clocksource stability checks for TSC.
3380 [x86] reliable: mark tsc clocksource as reliable, this
3381 disables clocksource verification at runtime, as well
3382 as the stability checks done at bootup. Used to enable
3383 high-resolution timer mode on older hardware, and in
3384 virtualized environment.
3385 [x86] noirqtime: Do not use TSC to do irq accounting.
3386 Used to run time disable IRQ_TIME_ACCOUNTING on any
3387 platforms where RDTSC is slow and this accounting
3390 turbografx.map[2|3]= [HW,JOY]
3391 TurboGraFX parallel port interface
3393 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3394 See also Documentation/input/joystick-parport.txt
3396 udbg-immortal [PPC] When debugging early kernel crashes that
3397 happen after console_init() and before a proper
3398 console driver takes over, this boot options might
3399 help "seeing" what's going on.
3401 uhash_entries= [KNL,NET]
3402 Set number of hash buckets for UDP/UDP-Lite connections
3405 [USB] Ignore overcurrent events (default N).
3406 Some badly-designed motherboards generate lots of
3407 bogus events, for ports that aren't wired to
3408 anything. Set this parameter to avoid log spamming.
3409 Note that genuine overcurrent events won't be
3413 [X86] Cause panic on unknown NMI.
3415 usbcore.authorized_default=
3416 [USB] Default USB device authorization:
3417 (default -1 = authorized except for wireless USB,
3418 0 = not authorized, 1 = authorized)
3420 usbcore.autosuspend=
3421 [USB] The autosuspend time delay (in seconds) used
3422 for newly-detected USB devices (default 2). This
3423 is the time required before an idle device will be
3424 autosuspended. Devices for which the delay is set
3425 to a negative value won't be autosuspended at all.
3427 usbcore.usbfs_snoop=
3428 [USB] Set to log all usbfs traffic (default 0 = off).
3430 usbcore.blinkenlights=
3431 [USB] Set to cycle leds on hubs (default 0 = off).
3433 usbcore.old_scheme_first=
3434 [USB] Start with the old device initialization
3435 scheme (default 0 = off).
3437 usbcore.usbfs_memory_mb=
3438 [USB] Memory limit (in MB) for buffers allocated by
3439 usbfs (default = 16, 0 = max = 2047).
3441 usbcore.use_both_schemes=
3442 [USB] Try the other device initialization scheme
3443 if the first one fails (default 1 = enabled).
3445 usbcore.initial_descriptor_timeout=
3446 [USB] Specifies timeout for the initial 64-byte
3447 USB_REQ_GET_DESCRIPTOR request in milliseconds
3448 (default 5000 = 5.0 seconds).
3451 [USBHID] The interval which mice are to be polled at.
3453 usb-storage.delay_use=
3454 [UMS] The delay in seconds before a new device is
3455 scanned for Logical Units (default 5).
3458 [UMS] A list of quirks entries to supplement or
3459 override the built-in unusual_devs list. List
3460 entries are separated by commas. Each entry has
3461 the form VID:PID:Flags where VID and PID are Vendor
3462 and Product ID values (4-digit hex numbers) and
3463 Flags is a set of characters, each corresponding
3464 to a common usb-storage quirk flag as follows:
3465 a = SANE_SENSE (collect more than 18 bytes
3467 b = BAD_SENSE (don't collect more than 18
3468 bytes of sense data);
3469 c = FIX_CAPACITY (decrease the reported
3470 device capacity by one sector);
3471 d = NO_READ_DISC_INFO (don't use
3472 READ_DISC_INFO command);
3473 e = NO_READ_CAPACITY_16 (don't use
3474 READ_CAPACITY_16 command);
3475 h = CAPACITY_HEURISTICS (decrease the
3476 reported device capacity by one
3477 sector if the number is odd);
3478 i = IGNORE_DEVICE (don't bind to this
3480 l = NOT_LOCKABLE (don't try to lock and
3481 unlock ejectable media);
3482 m = MAX_SECTORS_64 (don't transfer more
3483 than 64 sectors = 32 KB at a time);
3484 n = INITIAL_READ10 (force a retry of the
3485 initial READ(10) command);
3486 o = CAPACITY_OK (accept the capacity
3487 reported by the device);
3488 p = WRITE_CACHE (the device cache is ON
3490 r = IGNORE_RESIDUE (the device reports
3491 bogus residue values);
3492 s = SINGLE_LUN (the device has only one
3494 w = NO_WP_DETECT (don't test whether the
3495 medium is write-protected).
3496 Example: quirks=0419:aaf5:rl,0421:0433:rc
3498 user_debug= [KNL,ARM]
3500 See arch/arm/Kconfig.debug help text.
3501 1 - undefined instruction events
3503 4 - invalid data aborts
3506 Example: user_debug=31
3509 [X86] Flags controlling user PTE allocations.
3511 nohigh = do not allocate PTE pages in
3512 HIGHMEM regardless of setting
3516 On X86_32, this is an alias for vdso32=. Otherwise:
3518 vdso=1: enable VDSO (the default)
3519 vdso=0: disable VDSO mapping
3521 vdso32= [X86] Control the 32-bit vDSO
3522 vdso32=1: enable 32-bit VDSO
3523 vdso32=0 or vdso32=2: disable 32-bit VDSO
3525 See the help text for CONFIG_COMPAT_VDSO for more
3526 details. If CONFIG_COMPAT_VDSO is set, the default is
3527 vdso32=0; otherwise, the default is vdso32=1.
3529 For compatibility with older kernels, vdso32=2 is an
3532 Try vdso32=0 if you encounter an error that says:
3533 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3536 vector=percpu: enable percpu vector domain
3538 video= [FB] Frame buffer configuration
3539 See Documentation/fb/modedb.txt.
3541 video.brightness_switch_enabled= [0,1]
3542 If set to 1, on receiving an ACPI notify event
3543 generated by hotkey, video driver will adjust brightness
3544 level and then send out the event to user space through
3545 the allocated input device; If set to 0, video driver
3546 will only send out the event without touching backlight
3551 [VMMIO] Memory mapped virtio (platform) device.
3553 <size>@<baseaddr>:<irq>[:<id>]
3555 <size> := size (can use standard suffixes
3557 <baseaddr> := physical base address
3558 <irq> := interrupt number (as passed to
3560 <id> := (optional) platform device id
3562 virtio_mmio.device=1K@0x100b0000:48:7
3564 Can be used multiple times for multiple devices.
3566 vga= [BOOT,X86-32] Select a particular video mode
3567 See Documentation/x86/boot.txt and
3568 Documentation/svga.txt.
3569 Use vga=ask for menu.
3570 This is actually a boot loader parameter; the value is
3571 passed to the kernel using a special protocol.
3573 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3574 size of <nn>. This can be used to increase the
3575 minimum size (128MB on x86). It can also be used to
3576 decrease the size and leave more room for directly
3579 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3582 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3585 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3589 Controls the behavior of vsyscalls (i.e. calls to
3590 fixed addresses of 0xffffffffff600x00 from legacy
3591 code). Most statically-linked binaries and older
3592 versions of glibc use these calls. Because these
3593 functions are at fixed addresses, they make nice
3594 targets for exploits that can control RIP.
3596 emulate [default] Vsyscalls turn into traps and are
3597 emulated reasonably safely.
3599 native Vsyscalls are native syscall instructions.
3600 This is a little bit faster than trapping
3601 and makes a few dynamic recompilers work
3602 better than they would in emulation mode.
3603 It also makes exploits much easier to write.
3605 none Vsyscalls don't work at all. This makes
3606 them quite hard to use for exploits but
3607 might break your system.
3609 vt.color= [VT] Default text color.
3610 Format: 0xYX, X = foreground, Y = background.
3611 Default: 0x07 = light gray on black.
3613 vt.cur_default= [VT] Default cursor shape.
3614 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3615 the parameters of the <Esc>[?A;B;Cc escape sequence;
3616 see VGA-softcursor.txt. Default: 2 = underline.
3618 vt.default_blu= [VT]
3619 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3620 Change the default blue palette of the console.
3621 This is a 16-member array composed of values
3624 vt.default_grn= [VT]
3625 Format: <green0>,<green1>,<green2>,...,<green15>
3626 Change the default green palette of the console.
3627 This is a 16-member array composed of values
3630 vt.default_red= [VT]
3631 Format: <red0>,<red1>,<red2>,...,<red15>
3632 Change the default red palette of the console.
3633 This is a 16-member array composed of values
3639 Set system-wide default UTF-8 mode for all tty's.
3640 Default is 1, i.e. UTF-8 mode is enabled for all
3641 newly opened terminals.
3643 vt.global_cursor_default=
3646 Set system-wide default for whether a cursor
3647 is shown on new VTs. Default is -1,
3648 i.e. cursors will be created by default unless
3649 overridden by individual drivers. 0 will hide
3650 cursors, 1 will display them.
3652 vt.italic= [VT] Default color for italic text; 0-15.
3655 vt.underline= [VT] Default color for underlined text; 0-15.
3658 watchdog timers [HW,WDT] For information on watchdog timers,
3659 see Documentation/watchdog/watchdog-parameters.txt
3660 or other driver-specific files in the
3661 Documentation/watchdog/ directory.
3663 workqueue.disable_numa
3664 By default, all work items queued to unbound
3665 workqueues are affine to the NUMA nodes they're
3666 issued on, which results in better behavior in
3667 general. If NUMA affinity needs to be disabled for
3668 whatever reason, this option can be used. Note
3669 that this also can be controlled per-workqueue for
3670 workqueues visible under /sys/bus/workqueue/.
3672 workqueue.power_efficient
3673 Per-cpu workqueues are generally preferred because
3674 they show better performance thanks to cache
3675 locality; unfortunately, per-cpu workqueues tend to
3676 be more power hungry than unbound workqueues.
3678 Enabling this makes the per-cpu workqueues which
3679 were observed to contribute significantly to power
3680 consumption unbound, leading to measurably lower
3681 power usage at the cost of small performance
3684 The default value of this parameter is determined by
3685 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3687 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3688 default x2apic cluster mode on platforms
3691 x86_intel_mid_timer= [X86-32,APBT]
3692 Choose timer option for x86 Intel MID platform.
3693 Two valid options are apbt timer only and lapic timer
3694 plus one apbt timer for broadcast timer.
3695 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3697 xen_emul_unplug= [HW,X86,XEN]
3698 Unplug Xen emulated devices
3699 Format: [unplug0,][unplug1]
3700 ide-disks -- unplug primary master IDE devices
3701 aux-ide-disks -- unplug non-primary-master IDE devices
3702 nics -- unplug network devices
3703 all -- unplug all emulated devices (NICs and IDE disks)
3704 unnecessary -- unplugging emulated devices is
3705 unnecessary even if the host did not respond to
3707 never -- do not unplug even if version check succeeds
3709 xen_nopvspin [X86,XEN]
3710 Disables the ticketlock slowpath using Xen PV
3713 xirc2ps_cs= [NET,PCMCIA]
3715 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3717 ______________________________________________________________________
3721 Add more DRM drivers.
projects / cascardo / linux.git / blob