4 The following is a consolidated list of the kernel parameters as
5 implemented by the __setup(), core_param() and module_param() macros
6 and sorted into English Dictionary order (defined as ignoring all
7 punctuation and sorting digits before letters in a case insensitive
8 manner), and with descriptions where known.
10 The kernel parses parameters from the kernel command line up to "--";
11 if it doesn't recognize a parameter and it doesn't contain a '.', the
12 parameter gets passed to init: parameters with '=' go into init's
13 environment, others are passed as command line arguments to init.
14 Everything after "--" is passed as an argument to init.
16 Module parameters can be specified in two ways: via the kernel command
17 line with a module name prefix, or via modprobe, e.g.:
19 (kernel command line) usbcore.blinkenlights=1
20 (modprobe command line) modprobe usbcore blinkenlights=1
22 Parameters for modules which are built into the kernel need to be
23 specified on the kernel command line. modprobe looks through the
24 kernel command line (/proc/cmdline) and collects module parameters
25 when it loads a module, so the kernel command line can be used for
28 Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30 can also be entered as
31 log-buf-len=1M print_fatal_signals=1
33 Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
36 This document may not be entirely up to date and comprehensive. The command
37 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
38 module. Loadable modules, after being loaded into the running kernel, also
39 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
40 parameters may be changed at runtime by the command
41 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
43 The parameters listed below are only valid if certain kernel build options were
44 enabled and if respective hardware is present. The text in square brackets at
45 the beginning of each description states the restrictions within which a
46 parameter is applicable:
48 ACPI ACPI support is enabled.
49 AGP AGP (Accelerated Graphics Port) is enabled.
50 ALSA ALSA sound support is enabled.
51 APIC APIC support is enabled.
52 APM Advanced Power Management support is enabled.
53 ARM ARM architecture is enabled.
54 AVR32 AVR32 architecture is enabled.
55 AX25 Appropriate AX.25 support is enabled.
56 BLACKFIN Blackfin architecture is enabled.
57 CLK Common clock infrastructure is enabled.
58 CMA Contiguous Memory Area support is enabled.
59 DRM Direct Rendering Management support is enabled.
60 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
61 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
62 EFI EFI Partitioning (GPT) is enabled
63 EIDE EIDE/ATAPI support is enabled.
64 EVM Extended Verification Module
65 FB The frame buffer device is enabled.
66 FTRACE Function tracing enabled.
67 GCOV GCOV profiling is enabled.
68 HW Appropriate hardware is enabled.
69 IA-64 IA-64 architecture is enabled.
70 IMA Integrity measurement architecture is enabled.
71 IOSCHED More than one I/O scheduler is enabled.
72 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
73 IPV6 IPv6 support is enabled.
74 ISAPNP ISA PnP code is enabled.
75 ISDN Appropriate ISDN support is enabled.
76 JOY Appropriate joystick support is enabled.
77 KGDB Kernel debugger support is enabled.
78 KVM Kernel Virtual Machine support is enabled.
79 LIBATA Libata driver is enabled
80 LP Printer support is enabled.
81 LOOP Loopback device support is enabled.
82 M68k M68k architecture is enabled.
83 These options have more detailed description inside of
84 Documentation/m68k/kernel-options.txt.
85 MDA MDA console support is enabled.
86 MIPS MIPS architecture is enabled.
87 MOUSE Appropriate mouse support is enabled.
88 MSI Message Signaled Interrupts (PCI).
89 MTD MTD (Memory Technology Device) support is enabled.
90 NET Appropriate network support is enabled.
91 NUMA NUMA support is enabled.
92 NFS Appropriate NFS support is enabled.
93 OSS OSS sound support is enabled.
94 PV_OPS A paravirtualized kernel is enabled.
95 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
96 PARISC The PA-RISC architecture is enabled.
97 PCI PCI bus support is enabled.
98 PCIE PCI Express support is enabled.
99 PCMCIA The PCMCIA subsystem is enabled.
100 PNP Plug & Play support is enabled.
101 PPC PowerPC architecture is enabled.
102 PPT Parallel port support is enabled.
103 PS2 Appropriate PS/2 support is enabled.
104 RAM RAM disk support is enabled.
105 S390 S390 architecture is enabled.
106 SCSI Appropriate SCSI support is enabled.
107 A lot of drivers have their options described inside
108 the Documentation/scsi/ sub-directory.
109 SECURITY Different security models are enabled.
110 SELINUX SELinux support is enabled.
111 APPARMOR AppArmor support is enabled.
112 SERIAL Serial support is enabled.
113 SH SuperH architecture is enabled.
114 SMP The kernel is an SMP kernel.
115 SPARC Sparc architecture is enabled.
116 SWSUSP Software suspend (hibernation) is enabled.
117 SUSPEND System suspend states are enabled.
118 TPM TPM drivers are enabled.
119 TS Appropriate touchscreen support is enabled.
120 UMS USB Mass Storage support is enabled.
121 USB USB support is enabled.
122 USBHID USB Human Interface Device support is enabled.
123 V4L Video For Linux support is enabled.
124 VMMIO Driver for memory mapped virtio devices is enabled.
125 VGA The VGA console has been enabled.
126 VT Virtual terminal support is enabled.
127 WDT Watchdog support is enabled.
128 XT IBM PC/XT MFM hard disk support is enabled.
129 X86-32 X86-32, aka i386 architecture is enabled.
130 X86-64 X86-64 architecture is enabled.
131 More X86-64 boot options can be found in
132 Documentation/x86/x86_64/boot-options.txt .
133 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
134 XEN Xen support is enabled
136 In addition, the following text indicates that the option:
138 BUGS= Relates to possible processor bugs on the said processor.
139 KNL Is a kernel start-up parameter.
140 BOOT Is a boot loader parameter.
142 Parameters denoted with BOOT are actually interpreted by the boot
143 loader, and have no meaning to the kernel directly.
144 Do not modify the syntax of boot loader parameters without extreme
145 need or coordination with <Documentation/x86/boot.txt>.
147 There are also arch-specific kernel-parameters not documented here.
148 See for example <Documentation/x86/x86_64/boot-options.txt>.
150 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
151 a trailing = on the name of any parameter states that that parameter will
152 be entered as an environment variable, whereas its absence indicates that
153 it will appear as a kernel argument readable via /proc/cmdline by programs
154 running once the system is up.
156 The number of kernel parameters is not limited, but the length of the
157 complete command line (parameters including spaces etc.) is limited to
158 a fixed number of characters. This limit depends on the architecture
159 and is between 256 and 4096 characters. It is defined in the file
160 ./include/asm/setup.h as COMMAND_LINE_SIZE.
162 Finally, the [KMG] suffix is commonly described after a number of kernel
163 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
164 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
165 bytes respectively. Such letter suffixes can also be entirely omitted.
169 Advanced Configuration and Power Interface
170 Format: { force | off | strict | noirq | rsdt }
171 force -- enable ACPI if default was off
172 off -- disable ACPI if default was on
173 noirq -- do not use ACPI for IRQ routing
174 strict -- Be less tolerant of platforms that are not
175 strictly ACPI specification compliant.
176 rsdt -- prefer RSDT over (default) XSDT
177 copy_dsdt -- copy DSDT to memory
179 See also Documentation/power/runtime_pm.txt, pci=noacpi
181 acpi_rsdp= [ACPI,EFI,KEXEC]
182 Pass the RSDP address to the kernel, mostly used
183 on machines running EFI runtime service to boot the
184 second kernel for kdump.
186 acpi_apic_instance= [ACPI, IOAPIC]
188 2: use 2nd APIC table, if available
189 1,0: use 1st APIC table
192 acpi_backlight= [HW,ACPI]
193 acpi_backlight=vendor
195 If set to vendor, prefer vendor specific driver
196 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
197 of the ACPI video.ko driver.
199 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
200 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
202 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
203 debug output. Bits in debug_layer correspond to a
204 _COMPONENT in an ACPI source file, e.g.,
205 #define _COMPONENT ACPI_PCI_COMPONENT
206 Bits in debug_level correspond to a level in
207 ACPI_DEBUG_PRINT statements, e.g.,
208 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
209 The debug_level mask defaults to "info". See
210 Documentation/acpi/debug.txt for more information about
211 debug layers and levels.
213 Enable processor driver info messages:
214 acpi.debug_layer=0x20000000
215 Enable PCI/PCI interrupt routing info messages:
216 acpi.debug_layer=0x400000
217 Enable AML "Debug" output, i.e., stores to the Debug
218 object while interpreting AML:
219 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
220 Enable all messages related to ACPI hardware:
221 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
223 Some values produce so much output that the system is
224 unusable. The "log_buf_len" parameter may be useful
225 if you need to capture more output.
227 acpi_force_table_verification [HW,ACPI]
228 Enable table checksum verification during early stage.
229 By default, this is disabled due to x86 early mapping
232 acpi_irq_balance [HW,ACPI]
233 ACPI will balance active IRQs
236 acpi_irq_nobalance [HW,ACPI]
237 ACPI will not move active IRQs (default)
240 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
241 Format: <irq>,<irq>...
243 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
245 Format: <irq>,<irq>...
247 acpi_no_auto_serialize [HW,ACPI]
248 Disable auto-serialization of AML methods
249 AML control methods that contain the opcodes to create
250 named objects will be marked as "Serialized" by the
251 auto-serialization feature.
252 This feature is enabled by default.
253 This option allows to turn off the feature.
255 acpi_no_static_ssdt [HW,ACPI]
256 Disable installation of static SSDTs at early boot time
257 By default, SSDTs contained in the RSDT/XSDT will be
258 installed automatically and they will appear under
259 /sys/firmware/acpi/tables.
260 This option turns off this feature.
261 Note that specifying this option does not affect
262 dynamic table installation which will install SSDT
263 tables to /sys/firmware/acpi/tables/dynamic.
265 acpica_no_return_repair [HW, ACPI]
266 Disable AML predefined validation mechanism
267 This mechanism can repair the evaluation result to make
268 the return objects more ACPI specification compliant.
269 This option is useful for developers to identify the
270 root cause of an AML interpreter issue when the issue
271 has something to do with the repair mechanism.
273 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
274 Format: To spoof as Windows 98: ="Microsoft Windows"
276 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
277 acpi_osi="string1" # add string1
278 acpi_osi="!string2" # remove string2
279 acpi_osi=!* # remove all strings
280 acpi_osi=! # disable all built-in OS vendor
282 acpi_osi= # disable all strings
284 'acpi_osi=!' can be used in combination with single or
285 multiple 'acpi_osi="string1"' to support specific OS
286 vendor string(s). Note that such command can only
287 affect the default state of the OS vendor strings, thus
288 it cannot affect the default state of the feature group
289 strings and the current state of the OS vendor strings,
290 specifying it multiple times through kernel command line
291 is meaningless. This command is useful when one do not
292 care about the state of the feature group strings which
293 should be controlled by the OSPM.
295 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
296 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
297 can make '_OSI("Windows 2000")' TRUE.
299 'acpi_osi=' cannot be used in combination with other
300 'acpi_osi=' command lines, the _OSI method will not
301 exist in the ACPI namespace. NOTE that such command can
302 only affect the _OSI support state, thus specifying it
303 multiple times through kernel command line is also
306 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
309 'acpi_osi=!*' can be used in combination with single or
310 multiple 'acpi_osi="string1"' to support specific
311 string(s). Note that such command can affect the
312 current state of both the OS vendor strings and the
313 feature group strings, thus specifying it multiple times
314 through kernel command line is meaningful. But it may
315 still not able to affect the final state of a string if
316 there are quirks related to this string. This command
317 is useful when one want to control the state of the
318 feature group strings to debug BIOS issues related to
321 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
322 '_OSI("Module Device")' FALSE.
323 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
324 '_OSI("Module Device")' TRUE.
325 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
327 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
329 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
330 they all will make '_OSI("Windows 2000")' TRUE.
333 Override the pmtimer bug detection: force the kernel
334 to assume that this machine's pmtimer latches its value
335 and always returns good values.
337 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
338 Format: { level | edge | high | low }
340 acpi_skip_timer_override [HW,ACPI]
341 Recognize and ignore IRQ0/pin2 Interrupt Override.
342 For broken nForce2 BIOS resulting in XT-PIC timer.
344 acpi_sleep= [HW,ACPI] Sleep options
345 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
346 old_ordering, nonvs, sci_force_enable }
347 See Documentation/power/video.txt for information on
349 s3_beep is for debugging; it makes the PC's speaker beep
350 as soon as the kernel's real-mode entry point is called.
351 s4_nohwsig prevents ACPI hardware signature from being
352 used during resume from hibernation.
353 old_ordering causes the ACPI 1.0 ordering of the _PTS
354 control method, with respect to putting devices into
355 low power states, to be enforced (the ACPI 2.0 ordering
356 of _PTS is used by default).
357 nonvs prevents the kernel from saving/restoring the
358 ACPI NVS memory during suspend/hibernation and resume.
359 sci_force_enable causes the kernel to set SCI_EN directly
360 on resume from S1/S3 (which is against the ACPI spec,
361 but some broken systems don't work without it).
363 acpi_use_timer_override [HW,ACPI]
364 Use timer override. For some broken Nvidia NF5 boards
365 that require a timer override, but don't have HPET
367 acpi_enforce_resources= [ACPI]
368 { strict | lax | no }
369 Check for resource conflicts between native drivers
370 and ACPI OperationRegions (SystemIO and SystemMemory
371 only). IO ports and memory declared in ACPI might be
372 used by the ACPI subsystem in arbitrary AML code and
373 can interfere with legacy drivers.
374 strict (default): access to resources claimed by ACPI
375 is denied; legacy drivers trying to access reserved
376 resources will fail to bind to device using them.
377 lax: access to resources claimed by ACPI is allowed;
378 legacy drivers trying to access reserved resources
379 will bind successfully but a warning message is logged.
380 no: ACPI OperationRegions are not marked as reserved,
381 no further checks are performed.
383 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
386 add_efi_memmap [EFI; X86] Include EFI memory map in
387 kernel's map of available physical RAM.
390 { off | try_unsupported }
391 off: disable AGP support
392 try_unsupported: try to drive unsupported chipsets
393 (may crash computer or cause data corruption)
396 See Documentation/sound/alsa/alsa-parameters.txt
399 Allow the default userspace alignment fault handler
400 behaviour to be specified. Bit 0 enables warnings,
401 bit 1 enables fixups, and bit 2 sends a segfault.
403 align_va_addr= [X86-64]
404 Align virtual addresses by clearing slice [14:12] when
405 allocating a VMA at process creation time. This option
406 gives you up to 3% performance improvement on AMD F15h
407 machines (where it is enabled by default) for a
408 CPU-intensive style benchmark, and it can vary highly in
409 a microbenchmark depending on workload and compiler.
411 32: only for 32-bit processes
412 64: only for 64-bit processes
413 on: enable for both 32- and 64-bit processes
414 off: disable for both 32- and 64-bit processes
416 alloc_snapshot [FTRACE]
417 Allocate the ftrace snapshot buffer on boot up when the
418 main buffer is allocated. This is handy if debugging
419 and you need to use tracing_snapshot() on boot up, and
420 do not want to use tracing_snapshot_alloc() as it needs
421 to be done where GFP_KERNEL allocations are allowed.
423 amd_iommu= [HW,X86-64]
424 Pass parameters to the AMD IOMMU driver in the system.
426 fullflush - enable flushing of IO/TLB entries when
427 they are unmapped. Otherwise they are
428 flushed before they will be reused, which
430 off - do not initialize any AMD IOMMU found in
432 force_isolation - Force device isolation for all
433 devices. The IOMMU driver is not
434 allowed anymore to lift isolation
435 requirements as needed. This option
436 does not override iommu=pt
438 amd_iommu_dump= [HW,X86-64]
439 Enable AMD IOMMU driver option to dump the ACPI table
440 for AMD IOMMU. With this option enabled, AMD IOMMU
441 driver will print ACPI tables for AMD IOMMU during
442 IOMMU initialization.
444 amijoy.map= [HW,JOY] Amiga joystick support
445 Map of devices attached to JOY0DAT and JOY1DAT
447 See also Documentation/input/joystick.txt
449 analog.map= [HW,JOY] Analog joystick and gamepad support
450 Specifies type or capabilities of an analog joystick
451 connected to one of 16 gameports
452 Format: <type1>,<type2>,..<type16>
455 Power management functions (SPARCstation-4/5 + deriv.)
457 Disable APC CPU standby support. SPARCstation-Fox does
458 not play well with APC CPU idle - disable it if you have
459 APC and your system crashes randomly.
461 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
462 Change the output verbosity whilst booting
463 Format: { quiet (default) | verbose | debug }
464 Change the amount of debugging information output
465 when initialising the APIC and IO-APIC components.
468 See Documentation/networking/ipv6.txt.
470 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
471 Limit apic dumping. The parameter defines the maximal
472 number of local apics being dumped. Also it is possible
473 to set it to "all" by meaning -- no limit here.
474 Format: { 1 (default) | 2 | ... | all }.
475 The parameter valid if only apic=debug or
476 apic=verbose is specified.
477 Example: apic=debug show_lapic=all
479 apm= [APM] Advanced Power Management
480 See header of arch/x86/kernel/apm_32.c.
482 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
483 Format: <io>,<irq>,<nodeID>
487 atarimouse= [HW,MOUSE] Atari Mouse
489 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
490 EzKey and similar keyboards
492 atkbd.reset= [HW] Reset keyboard during initialization
494 atkbd.set= [HW] Select keyboard code set
495 Format: <int> (2 = AT (default), 3 = PS/2)
497 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
500 atkbd.softraw= [HW] Choose between synthetic and real raw mode
501 Format: <bool> (0 = real, 1 = synthetic (default))
503 atkbd.softrepeat= [HW]
504 Use software keyboard repeat
506 audit= [KNL] Enable the audit sub-system
507 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
508 0 - kernel audit is disabled and can not be enabled
509 until the next reboot
510 unset - kernel audit is initialized but disabled and
511 will be fully enabled by the userspace auditd.
512 1 - kernel audit is initialized and partially enabled,
513 storing at most audit_backlog_limit messages in
514 RAM until it is fully enabled by the userspace
518 audit_backlog_limit= [KNL] Set the audit queue size limit.
519 Format: <int> (must be >=0)
522 baycom_epp= [HW,AX25]
525 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
527 See header of drivers/net/hamradio/baycom_par.c.
529 baycom_ser_fdx= [HW,AX25]
530 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
531 Format: <io>,<irq>,<mode>[,<baud>]
532 See header of drivers/net/hamradio/baycom_ser_fdx.c.
534 baycom_ser_hdx= [HW,AX25]
535 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
536 Format: <io>,<irq>,<mode>
537 See header of drivers/net/hamradio/baycom_ser_hdx.c.
539 blkdevparts= Manual partition parsing of block device(s) for
540 embedded devices based on command line input.
541 See Documentation/block/cmdline-partition.txt
543 boot_delay= Milliseconds to delay each printk during boot.
544 Values larger than 10 seconds (10000) are changed to
548 bootmem_debug [KNL] Enable bootmem allocator debug messages.
550 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
551 bttv.radio= Most important insmod options are available as
553 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
556 bulk_remove=off [PPC] This parameter disables the use of the pSeries
557 firmware feature for flushing multiple hpte entries
560 c101= [NET] Moxa C101 synchronous serial card
562 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
563 Sometimes CPU hardware bugs make them report the cache
564 size incorrectly. The kernel will attempt work arounds
565 to fix known problems, but for some CPUs it is not
566 possible to determine what the correct size should be.
567 This option provides an override for these situations.
569 ca_keys= [KEYS] This parameter identifies a specific key(s) on
570 the system trusted keyring to be used for certificate
572 format: { id:<keyid> | builtin }
574 cca= [MIPS] Override the kernel pages' cache coherency
575 algorithm. Accepted values range from 0 to 7
576 inclusive. See arch/mips/include/asm/pgtable-bits.h
577 for platform specific values (SB1, Loongson3 and
580 ccw_timeout_log [S390]
581 See Documentation/s390/CommonIO for details.
583 cgroup_disable= [KNL] Disable a particular controller
584 Format: {name of the controller(s) to disable}
585 The effects of cgroup_disable=foo are:
586 - foo isn't auto-mounted if you mount all cgroups in
588 - foo isn't visible as an individually mountable
590 {Currently only "memory" controller deal with this and
591 cut the overhead, others just disable the usage. So
592 only cgroup_disable=memory is actually worthy}
594 checkreqprot [SELINUX] Set initial checkreqprot flag value.
595 Format: { "0" | "1" }
596 See security/selinux/Kconfig help text.
597 0 -- check protection applied by kernel (includes
598 any implied execute protection).
599 1 -- check protection requested by application.
600 Default value is set via a kernel config option.
601 Value can be changed at runtime via
602 /selinux/checkreqprot.
605 See Documentation/s390/CommonIO for details.
608 Keep all clocks already enabled by bootloader on,
609 even if no driver has claimed them. This is useful
610 for debug and development, but should not be
611 needed on a platform with proper driver support.
612 For more information, see Documentation/clk.txt.
614 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
616 Forces specified clocksource (if available) to be used
617 when calculating gettimeofday(). If specified
618 clocksource is not available, it defaults to PIT.
619 Format: { pit | tsc | cyclone | pmtmr }
621 clocksource= Override the default clocksource
623 Override the default clocksource and use the clocksource
624 with the name specified.
625 Some clocksource names to choose from, depending on
627 [all] jiffies (this is the base, fallback clocksource)
629 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
630 pxa_timer,timer3,32k_counter,timer0_1
632 [X86-32] pit,hpet,tsc;
633 scx200_hrt on Geode; cyclone on IBM x440
641 clearcpuid=BITNUM [X86]
642 Disable CPUID feature X for the kernel. See
643 arch/x86/include/asm/cpufeature.h for the valid bit
644 numbers. Note the Linux specific bits are not necessarily
645 stable over kernel options, but the vendor specific
647 Also note that user programs calling CPUID directly
648 or using the feature without checking anything
649 will still see it. This just prevents it from
650 being used by the kernel or shown in /proc/cpuinfo.
651 Also note the kernel might malfunction if you disable
654 cma=nn[MG]@[start[MG][-end[MG]]]
656 Sets the size of kernel global memory area for
657 contiguous memory allocations and optionally the
658 placement constraint by the physical address range of
659 memory allocations. For more information, see
660 include/linux/dma-contiguous.h
662 cmo_free_hint= [PPC] Format: { yes | no }
663 Specify whether pages are marked as being inactive
664 when they are freed. This is used in CMO environments
665 to determine OS memory pressure for page stealing by
669 coherent_pool=nn[KMG] [ARM,KNL]
670 Sets the size of memory pool for coherent, atomic dma
671 allocations, by default set to 256K.
673 code_bytes [X86] How many bytes of object code to print
678 com20020= [HW,NET] ARCnet - COM20020 chipset
680 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
682 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
686 ARCnet - COM90xx chipset (memory-mapped buffers)
687 Format: <io>[,<irq>[,<memstart>]]
689 condev= [HW,S390] console device
692 console= [KNL] Output console device and options.
694 tty<n> Use the virtual console device <n>.
698 Use the specified serial port. The options are of
699 the form "bbbbpnf", where "bbbb" is the baud rate,
700 "p" is parity ("n", "o", or "e"), "n" is number of
701 bits, and "f" is flow control ("r" for RTS or
702 omit it). Default is "9600n8".
704 See Documentation/serial-console.txt for more
706 Documentation/networking/netconsole.txt for an
709 uart[8250],io,<addr>[,options]
710 uart[8250],mmio,<addr>[,options]
711 Start an early, polled-mode console on the 8250/16550
712 UART at the specified I/O port or MMIO address,
713 switching to the matching ttyS device later. The
714 options are the same as for ttyS, above.
715 hvc<n> Use the hypervisor console device <n>. This is for
716 both Xen and PowerPC hypervisors.
718 If the device connected to the port is not a TTY but a braille
719 device, prepend "brl," before the device type, for instance
721 For now, only VisioBraille is supported.
723 consoleblank= [KNL] The console blank (screen saver) timeout in
724 seconds. Defaults to 10*60 = 10mins. A value of 0
725 disables the blank timer.
728 [KNL] Change the default value for
729 /proc/<pid>/coredump_filter.
730 See also Documentation/filesystems/proc.txt.
732 cpuidle.off=1 [CPU_IDLE]
733 disable the cpuidle sub-system
735 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
737 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
739 crashkernel=size[KMG][@offset[KMG]]
740 [KNL] Using kexec, Linux can switch to a 'crash kernel'
741 upon panic. This parameter reserves the physical
742 memory region [offset, offset + size] for that kernel
743 image. If '@offset' is omitted, then a suitable offset
744 is selected automatically. Check
745 Documentation/kdump/kdump.txt for further details.
747 crashkernel=range1:size1[,range2:size2,...][@offset]
748 [KNL] Same as above, but depends on the memory
749 in the running system. The syntax of range is
750 start-[end] where start and end are both
751 a memory unit (amount[KMG]). See also
752 Documentation/kdump/kdump.txt for an example.
754 crashkernel=size[KMG],high
755 [KNL, x86_64] range could be above 4G. Allow kernel
756 to allocate physical memory region from top, so could
757 be above 4G if system have more than 4G ram installed.
758 Otherwise memory region will be allocated below 4G, if
760 It will be ignored if crashkernel=X is specified.
761 crashkernel=size[KMG],low
762 [KNL, x86_64] range under 4G. When crashkernel=X,high
763 is passed, kernel could allocate physical memory region
764 above 4G, that cause second kernel crash on system
765 that require some amount of low memory, e.g. swiotlb
766 requires at least 64M+32K low memory. Kernel would
767 try to allocate 72M below 4G automatically.
768 This one let user to specify own low range under 4G
769 for second kernel instead.
770 0: to disable low allocation.
771 It will be ignored when crashkernel=X,high is not used
772 or memory reserved is below 4G.
777 cs89x0_media= [HW,NET]
778 Format: { rj45 | aui | bnc }
781 See header of drivers/s390/block/dasd_devmap.c.
783 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
784 (one device per port)
785 Format: <port#>,<type>
786 See also Documentation/input/joystick-parport.txt
788 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
789 time. See Documentation/dynamic-debug-howto.txt for
790 details. Deprecated, see dyndbg.
792 debug [KNL] Enable kernel debugging (events log level).
795 [KNL] verbose self-tests
797 Print debugging info while doing the locking API
799 We default to 0 (no extra messages), setting it to
800 1 will print _a lot_ more information - normally
801 only useful to kernel developers.
803 debug_objects [KNL] Enable object debugging
806 [KNL] Disable object debugging
808 debug_guardpage_minorder=
809 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
810 parameter allows control of the order of pages that will
811 be intentionally kept free (and hence protected) by the
812 buddy allocator. Bigger value increase the probability
813 of catching random memory corruption, but reduce the
814 amount of memory for normal system use. The maximum
815 possible value is MAX_ORDER/2. Setting this parameter
816 to 1 or 2 should be enough to identify most random
817 memory corruption problems caused by bugs in kernel or
818 driver code when a CPU writes to (or reads from) a
819 random memory location. Note that there exists a class
820 of memory corruptions problems caused by buggy H/W or
821 F/W or by drivers badly programing DMA (basically when
822 memory is written at bus level and the CPU MMU is
823 bypassed) which are not detectable by
824 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
825 tracking down these problems.
827 debugpat [X86] Enable PAT debugging
829 decnet.addr= [HW,NET]
830 Format: <area>[,<node>]
831 See also Documentation/networking/decnet.txt.
834 [same as hugepagesz=] The size of the default
835 HugeTLB page size. This is the size represented by
836 the legacy /proc/ hugepages APIs, used for SHM, and
837 default size when mounting hugetlbfs filesystems.
838 Defaults to the default architecture's huge page size
842 Set number of hash buckets for dentry cache.
845 See Documentation/networking/ipv6.txt.
847 disable_cpu_apicid= [X86,APIC,SMP]
849 The number of initial APIC ID for the
850 corresponding CPU to be disabled at boot,
851 mostly used for the kdump 2nd kernel to
852 disable BSP to wake up multiple CPUs without
853 causing system reset or hang due to sending
856 disable_ddw [PPC/PSERIES]
857 Disable Dynamic DMA Window support. Use this if
858 to workaround buggy firmware.
861 See Documentation/networking/ipv6.txt.
863 disable_mtrr_cleanup [X86]
864 The kernel tries to adjust MTRR layout from continuous
865 to discrete, to make X server driver able to add WB
866 entry later. This parameter disables that.
868 disable_mtrr_trim [X86, Intel and AMD only]
869 By default the kernel will trim any uncacheable
870 memory out of your available memory pool based on
871 MTRR settings. This parameter disables that behavior,
872 possibly causing your machine to run very slowly.
874 disable_timer_pin_1 [X86]
875 Disable PIN 1 of APIC timer
876 Can be useful to work around chipset bugs.
878 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
879 this option disables the debugging code at boot.
881 dma_debug_entries=<number>
882 This option allows to tune the number of preallocated
883 entries for DMA-API debugging code. One entry is
884 required per DMA-API allocation. Use this if the
885 DMA-API debugging code disables itself because the
886 architectural default is too low.
888 dma_debug_driver=<driver_name>
889 With this option the DMA-API debugging driver
890 filter feature can be enabled at boot time. Just
891 pass the driver to filter for as the parameter.
892 The filter can be disabled or changed to another
893 driver later using sysfs.
895 drm_kms_helper.edid_firmware=[<connector>:]<file>
896 Broken monitors, graphic adapters and KVMs may
897 send no or incorrect EDID data sets. This parameter
898 allows to specify an EDID data set in the
899 /lib/firmware directory that is used instead.
900 Generic built-in EDID data sets are used, if one of
901 edid/1024x768.bin, edid/1280x1024.bin,
902 edid/1680x1050.bin, or edid/1920x1080.bin is given
903 and no file with the same name exists. Details and
904 instructions how to build your own EDID data are
905 available in Documentation/EDID/HOWTO.txt. An EDID
906 data set will only be used for a particular connector,
907 if its name and a colon are prepended to the EDID
912 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
913 module.dyndbg[="val"]
914 Enable debug messages at boot time. See
915 Documentation/dynamic-debug-howto.txt for details.
917 early_ioremap_debug [KNL]
918 Enable debug messages in early_ioremap support. This
919 is useful for tracking down temporary early mappings
920 which are not unmapped.
922 earlycon= [KNL] Output early console device and options.
924 uart[8250],io,<addr>[,options]
925 uart[8250],mmio,<addr>[,options]
926 uart[8250],mmio32,<addr>[,options]
927 Start an early, polled-mode console on the 8250/16550
928 UART at the specified I/O port or MMIO address.
929 MMIO inter-register address stride is either 8-bit
930 (mmio) or 32-bit (mmio32).
931 The options are the same as for ttyS, above.
934 Start an early, polled-mode console on a pl011 serial
935 port at the specified address. The pl011 serial port
936 must already be setup and configured. Options are not
939 smh Use ARM semihosting calls for early console.
941 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
945 earlyprintk=serial[,ttySn[,baudrate]]
946 earlyprintk=serial[,0x...[,baudrate]]
947 earlyprintk=ttySn[,baudrate]
948 earlyprintk=dbgp[debugController#]
950 earlyprintk is useful when the kernel crashes before
951 the normal console is initialized. It is not enabled by
952 default because it has some cosmetic problems.
954 Append ",keep" to not disable it when the real console
957 Only one of vga, efi, serial, or usb debug port can
960 Currently only ttyS0 and ttyS1 may be specified by
961 name. Other I/O ports may be explicitly specified
962 on some architectures (x86 and arm at least) by
963 replacing ttySn with an I/O port address, like this:
964 earlyprintk=serial,0x1008,115200
965 You can find the port for a given device in
966 /proc/tty/driver/serial:
967 2: uart:ST16650V2 port:00001008 irq:18 ...
969 Interaction with the standard serial driver is not
972 The VGA and EFI output is eventually overwritten by
975 The xen output can only be used by Xen PV guests.
977 edac_report= [HW,EDAC] Control how to report EDAC event
978 Format: {"on" | "off" | "force"}
979 on: enable EDAC to report H/W event. May be overridden
980 by other higher priority error reporting module.
981 off: disable H/W event reporting through EDAC.
982 force: enforce the use of EDAC to report H/W event.
985 ekgdboc= [X86,KGDB] Allow early kernel console debugging
988 This is designed to be used in conjunction with
989 the boot argument: earlyprintk=vga
992 Format: {"off" | "on" | "skip[mbr]"}
995 Format: { "old_map" }
996 old_map [X86-64]: switch to the old ioremap-based EFI
997 runtime services mapping. 32-bit still uses this one by
1000 efi_no_storage_paranoia [EFI; X86]
1001 Using this parameter you can use more than 50% of
1002 your efi variable storage. Use this parameter only if
1003 you are really sure that your UEFI does sane gc and
1004 fulfills the spec otherwise your board may brick.
1006 eisa_irq_edge= [PARISC,HW]
1007 See header of drivers/parisc/eisa.c.
1010 See comment before function elanfreq_setup() in
1011 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1014 Format: {"cfq" | "deadline" | "noop"}
1015 See Documentation/block/cfq-iosched.txt and
1016 Documentation/block/deadline-iosched.txt for details.
1018 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1019 Specifies physical address of start of kernel core
1020 image elf header and optionally the size. Generally
1021 kexec loader will pass this option to capture kernel.
1022 See Documentation/kdump/kdump.txt for details.
1024 enable_mtrr_cleanup [X86]
1025 The kernel tries to adjust MTRR layout from continuous
1026 to discrete, to make X server driver able to add WB
1027 entry later. This parameter enables that.
1029 enable_timer_pin_1 [X86]
1030 Enable PIN 1 of APIC timer
1031 Can be useful to work around chipset bugs
1032 (in particular on some ATI chipsets).
1033 The kernel tries to set a reasonable default.
1035 enforcing [SELINUX] Set initial enforcing status.
1037 See security/selinux/Kconfig help text.
1038 0 -- permissive (log only, no denials).
1039 1 -- enforcing (deny and log).
1041 Value can be changed at runtime via /selinux/enforce.
1044 Disable Error Record Serialization Table (ERST)
1047 ether= [HW,NET] Ethernet cards parameters
1048 This option is obsoleted by the "netdev=" option, which
1049 has equivalent usage. See its documentation for details.
1053 Permit 'security.evm' to be updated regardless of
1054 current integrity status.
1058 fail_make_request=[KNL]
1059 General fault injection mechanism.
1060 Format: <interval>,<probability>,<space>,<times>
1061 See also Documentation/fault-injection/.
1064 See Documentation/blockdev/floppy.txt.
1066 force_pal_cache_flush
1067 [IA-64] Avoid check_sal_cache_flush which may hang on
1068 buggy SAL_CACHE_FLUSH implementations. Using this
1069 parameter will force ia64_sal_cache_flush to call
1070 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1073 Forcefully enable Physical Address Extension (PAE).
1074 Many Pentium M systems disable PAE but may have a
1075 functionally usable PAE implementation.
1076 Warning: use of this parameter will taint the kernel
1077 and may cause unknown problems.
1080 [FTRACE] will set and start the specified tracer
1081 as early as possible in order to facilitate early
1084 ftrace_dump_on_oops[=orig_cpu]
1085 [FTRACE] will dump the trace buffers on oops.
1086 If no parameter is passed, ftrace will dump
1087 buffers of all CPUs, but if you pass orig_cpu, it will
1088 dump only the buffer of the CPU that triggered the
1091 ftrace_filter=[function-list]
1092 [FTRACE] Limit the functions traced by the function
1093 tracer at boot up. function-list is a comma separated
1094 list of functions. This list can be changed at run
1095 time by the set_ftrace_filter file in the debugfs
1098 ftrace_notrace=[function-list]
1099 [FTRACE] Do not trace the functions specified in
1100 function-list. This list can be changed at run time
1101 by the set_ftrace_notrace file in the debugfs
1104 ftrace_graph_filter=[function-list]
1105 [FTRACE] Limit the top level callers functions traced
1106 by the function graph tracer at boot up.
1107 function-list is a comma separated list of functions
1108 that can be changed at run time by the
1109 set_graph_function file in the debugfs tracing directory.
1111 ftrace_graph_notrace=[function-list]
1112 [FTRACE] Do not trace from the functions specified in
1113 function-list. This list is a comma separated list of
1114 functions that can be changed at run time by the
1115 set_graph_notrace file in the debugfs tracing directory.
1118 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1119 support via parallel port (up to 5 devices per port)
1120 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1121 See also Documentation/input/joystick-parport.txt
1125 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1129 gcov_persist= [GCOV] When non-zero (default), profiling data for
1130 kernel modules is saved and remains accessible via
1131 debugfs, even when the module is unloaded/reloaded.
1132 When zero, profiling data is discarded and associated
1133 debugfs files are removed at module unload time.
1135 gpt [EFI] Forces disk with valid GPT signature but
1136 invalid Protective MBR to be treated as GPT. If the
1137 primary GPT is corrupted, it enables the backup/alternate
1138 GPT to be used instead.
1140 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1141 the "Enable 0" bit of the configuration register.
1144 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1145 the "Enable 0" bit of the configuration register.
1148 grcan.select= [HW] Select which physical interface to use.
1151 grcan.txsize= [HW] Sets the size of the tx buffer.
1152 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1154 grcan.rxsize= [HW] Sets the size of the rx buffer.
1155 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1158 hashdist= [KNL,NUMA] Large hashes allocated during boot
1159 are distributed across NUMA nodes. Defaults on
1160 for 64-bit NUMA, off otherwise.
1161 Format: 0 | 1 (for off | on)
1163 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1165 hd= [EIDE] (E)IDE hard drive subsystem geometry
1166 Format: <cyl>,<head>,<sect>
1169 Disable Hardware Error Source Table (HEST) support;
1170 corresponding firmware-first mode error processing
1171 logic will be disabled.
1173 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1174 size of <nn>. This works even on boxes that have no
1175 highmem otherwise. This also works to reduce highmem
1176 size on bigger boxes.
1178 highres= [KNL] Enable/disable high resolution timer mode.
1179 Valid parameters: "on", "off"
1183 See Documentation/isdn/README.HiSax.
1187 hpet= [X86-32,HPET] option to control HPET usage
1188 Format: { enable (default) | disable | force |
1190 disable: disable HPET and use PIT instead
1191 force: allow force enabled of undocumented chips (ICH4,
1193 verbose: show contents of HPET registers during setup
1195 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1196 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1198 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1199 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1200 On x86-64 and powerpc, this option can be specified
1201 multiple times interleaved with hugepages= to reserve
1202 huge pages of different sizes. Valid pages sizes on
1203 x86-64 are 2M (when the CPU supports "pse") and 1G
1204 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1205 Note that 1GB pages can only be allocated at boot time
1206 using hugepages= and not freed afterwards.
1208 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1209 terminal devices. Valid values: 0..8
1210 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1211 If specified, z/VM IUCV HVC accepts connections
1212 from listed z/VM user IDs only.
1214 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1215 hardware thread id mappings.
1216 Format: <cpu>:<hwthread>
1219 Do not unregister boot console at start. This is only
1220 useful for debugging when something happens in the window
1221 between unregistering the boot console and initializing
1224 i2c_bus= [HW] Override the default board specific I2C bus speed
1225 or register an additional I2C bus that is not
1226 registered from board initialization code.
1230 i8042.debug [HW] Toggle i8042 debug mode
1231 i8042.direct [HW] Put keyboard port into non-translated mode
1232 i8042.dumbkbd [HW] Pretend that controller can only read data from
1233 keyboard and cannot control its state
1234 (Don't attempt to blink the leds)
1235 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1236 i8042.nokbd [HW] Don't check/create keyboard port
1237 i8042.noloop [HW] Disable the AUX Loopback command while probing
1239 i8042.nomux [HW] Don't check presence of an active multiplexing
1241 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1243 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1244 i8042.reset [HW] Reset the controller during init and cleanup
1245 i8042.unlock [HW] Unlock (ignore) the keylock
1246 i8042.kbdreset [HW] Reset device connected to KBD port
1250 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1251 indicates that the driver is running on unsupported
1253 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1254 does not match list of supported models.
1256 [HW] Report power status in /proc/i8k
1257 (disabled by default)
1258 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1261 i915.invert_brightness=
1262 [DRM] Invert the sense of the variable that is used to
1263 set the brightness of the panel backlight. Normally a
1264 brightness value of 0 indicates backlight switched off,
1265 and the maximum of the brightness value sets the backlight
1266 to maximum brightness. If this parameter is set to 0
1267 (default) and the machine requires it, or this parameter
1268 is set to 1, a brightness value of 0 sets the backlight
1269 to maximum brightness, and the maximum of the brightness
1270 value switches the backlight off.
1271 -1 -- never invert brightness
1272 0 -- machine default
1273 1 -- force brightness inversion
1276 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1278 ide-core.nodma= [HW] (E)IDE subsystem
1279 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1280 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1281 .cdrom .chs .ignore_cable are additional options
1282 See Documentation/ide/ide.txt.
1284 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1285 Claim all unknown PCI IDE storage controllers.
1288 Format: idle=poll, idle=halt, idle=nomwait
1289 Poll forces a polling idle loop that can slightly
1290 improve the performance of waking up a idle CPU, but
1291 will use a lot of power and make the system run hot.
1293 idle=halt: Halt is forced to be used for CPU idle.
1294 In such case C2/C3 won't be used again.
1295 idle=nomwait: Disable mwait for CPU C-states
1297 ignore_loglevel [KNL]
1298 Ignore loglevel setting - this will print /all/
1299 kernel messages to the console. Useful for debugging.
1300 We also add it as printk module parameter, so users
1301 could change it dynamically, usually by
1302 /sys/module/printk/parameters/ignore_loglevel.
1304 ihash_entries= [KNL]
1305 Set number of hash buckets for inode cache.
1307 ima_appraise= [IMA] appraise integrity measurements
1308 Format: { "off" | "enforce" | "fix" }
1311 ima_appraise_tcb [IMA]
1312 The builtin appraise policy appraises all files
1316 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1320 The list of supported hash algorithms is defined
1321 in crypto/hash_info.h.
1324 Load a policy which meets the needs of the Trusted
1325 Computing Base. This means IMA will measure all
1326 programs exec'd, files mmap'd for exec, and all files
1327 opened for read by uid=0.
1330 Select one of defined IMA measurements template formats.
1331 Formats: { "ima" | "ima-ng" }
1334 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1335 Format: <min_file_size>
1336 Set the minimal file size for using asynchronous hash.
1337 If left unspecified, ahash usage is disabled.
1339 ahash performance varies for different data sizes on
1340 different crypto accelerators. This option can be used
1341 to achieve the best performance for a particular HW.
1343 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1345 Set hashing buffer size. Default: 4k.
1347 ahash performance varies for different chunk sizes on
1348 different crypto accelerators. This option can be used
1349 to achieve best performance for particular HW.
1353 Run specified binary instead of /sbin/init as init
1356 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1357 for working out where the kernel is dying during
1360 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1361 initcall functions. Useful for debugging built-in
1362 modules and initcalls.
1364 initrd= [BOOT] Specify the location of the initial ramdisk
1366 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1369 int_pln_enable [x86] Enable power limit notification interrupt
1371 integrity_audit=[IMA]
1372 Format: { "0" | "1" }
1373 0 -- basic integrity auditing messages. (Default)
1374 1 -- additional integrity auditing messages.
1376 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1378 Enable intel iommu driver.
1380 Disable intel iommu driver.
1381 igfx_off [Default Off]
1382 By default, gfx is mapped as normal device. If a gfx
1383 device has a dedicated DMAR unit, the DMAR unit is
1384 bypassed by not enabling DMAR with this option. In
1385 this case, gfx device will use physical address for
1388 With this option iommu will not optimize to look
1389 for io virtual address below 32-bit forcing dual
1390 address cycle on pci bus for cards supporting greater
1391 than 32-bit addressing. The default is to look
1392 for translation below 32-bit and if not available
1393 then look in the higher range.
1394 strict [Default Off]
1395 With this option on every unmap_single operation will
1396 result in a hardware IOTLB flush operation as opposed
1397 to batching them for performance.
1398 sp_off [Default Off]
1399 By default, super page will be supported if Intel IOMMU
1400 has the capability. With this option, super page will
1403 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1404 0 disables intel_idle and fall back on acpi_idle.
1405 1 to 6 specify maximum depth of C-state.
1409 Do not enable intel_pstate as the default
1410 scaling driver for the supported processors
1412 intremap= [X86-64, Intel-IOMMU]
1413 on enable Interrupt Remapping (default)
1414 off disable Interrupt Remapping
1415 nosid disable Source ID checking
1417 BIOS x2APIC opt-out request will be ignored
1419 iomem= Disable strict checking of access to MMIO memory
1420 strict regions from userspace.
1437 io7= [HW] IO7 for Marvel based alpha systems
1438 See comment before marvel_specify_io7 in
1439 arch/alpha/kernel/core_marvel.c.
1441 io_delay= [X86] I/O delay method
1443 Standard port 0x80 based delay
1445 Alternate port 0xed based delay (needed on some systems)
1447 Simple two microseconds delay
1452 See Documentation/filesystems/nfs/nfsroot.txt.
1455 When an interrupt is not handled search all handlers
1456 for it. Intended to get systems with badly broken
1460 When an interrupt is not handled search all handlers
1461 for it. Also check all handlers each timer
1462 interrupt. Intended to get systems with badly broken
1466 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1468 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1470 <cpu number>,...,<cpu number>
1472 <cpu number>-<cpu number>
1473 (must be a positive range in ascending order)
1475 <cpu number>,...,<cpu number>-<cpu number>
1477 This option can be used to specify one or more CPUs
1478 to isolate from the general SMP balancing and scheduling
1479 algorithms. You can move a process onto or off an
1480 "isolated" CPU via the CPU affinity syscalls or cpuset.
1481 <cpu number> begins at 0 and the maximum value is
1482 "number of CPUs in system - 1".
1484 This option is the preferred way to isolate CPUs. The
1485 alternative -- manually setting the CPU mask of all
1486 tasks in the system -- can cause problems and
1487 suboptimal load balancer performance.
1491 ivrs_ioapic [HW,X86_64]
1492 Provide an override to the IOAPIC-ID<->DEVICE-ID
1493 mapping provided in the IVRS ACPI table. For
1494 example, to map IOAPIC-ID decimal 10 to
1495 PCI device 00:14.0 write the parameter as:
1496 ivrs_ioapic[10]=00:14.0
1498 ivrs_hpet [HW,X86_64]
1499 Provide an override to the HPET-ID<->DEVICE-ID
1500 mapping provided in the IVRS ACPI table. For
1501 example, to map HPET-ID decimal 0 to
1502 PCI device 00:14.0 write the parameter as:
1503 ivrs_hpet[0]=00:14.0
1505 js= [HW,JOY] Analog joystick
1506 See Documentation/input/joystick.txt.
1509 Enable/disable kernel and module base offset ASLR
1510 (Address Space Layout Randomization) if built into
1511 the kernel. When CONFIG_HIBERNATION is selected,
1512 kASLR is disabled by default. When kASLR is enabled,
1513 hibernation will be disabled.
1517 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1518 specifies the amount of memory usable by the kernel
1519 for non-movable allocations. The requested amount is
1520 spread evenly throughout all nodes in the system. The
1521 remaining memory in each node is used for Movable
1522 pages. In the event, a node is too small to have both
1523 kernelcore and Movable pages, kernelcore pages will
1524 take priority and other nodes will have a larger number
1525 of Movable pages. The Movable zone is used for the
1526 allocation of pages that may be reclaimed or moved
1527 by the page migration subsystem. This means that
1528 HugeTLB pages may not be allocated from this zone.
1529 Note that allocations like PTEs-from-HighMem still
1530 use the HighMem zone if it exists, and the Normal
1531 zone if it does not.
1533 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1534 Format: <Controller#>[,poll interval]
1535 The controller # is the number of the ehci usb debug
1536 port as it is probed via PCI. The poll interval is
1537 optional and is the number seconds in between
1538 each poll cycle to the debug port in case you need
1539 the functionality for interrupting the kernel with
1540 gdb or control-c on the dbgp connection. When
1541 not using this parameter you use sysrq-g to break into
1542 the kernel debugger.
1544 kgdboc= [KGDB,HW] kgdb over consoles.
1545 Requires a tty driver that supports console polling,
1546 or a supported polling keyboard driver (non-usb).
1547 Serial only format: <serial_device>[,baud]
1548 keyboard only format: kbd
1549 keyboard and serial format: kbd,<serial_device>[,baud]
1550 Optional Kernel mode setting:
1551 kms, kbd format: kms,kbd
1552 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1554 kgdbwait [KGDB] Stop kernel execution and enter the
1555 kernel debugger at the earliest opportunity.
1557 kmac= [MIPS] korina ethernet MAC address.
1558 Configure the RouterBoard 532 series on-chip
1559 Ethernet adapter MAC address.
1561 kmemleak= [KNL] Boot-time kmemleak enable/disable
1562 Valid arguments: on, off
1565 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1566 Valid arguments: 0, 1, 2
1567 kmemcheck=0 (disabled)
1568 kmemcheck=1 (enabled)
1569 kmemcheck=2 (one-shot mode)
1570 Default: 2 (one-shot mode)
1572 kstack=N [X86] Print N words from the kernel stack
1575 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1576 Default is 0 (don't ignore, but inject #GP)
1578 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1582 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1583 Default is 1 (enabled)
1585 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1587 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1589 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1590 (virtualized MMU) support on capable Intel chips.
1591 Default is 1 (enabled)
1593 kvm-intel.emulate_invalid_guest_state=
1594 [KVM,Intel] Enable emulation of invalid guest states
1595 Default is 0 (disabled)
1597 kvm-intel.flexpriority=
1598 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1599 Default is 1 (enabled)
1602 [KVM,Intel] Enable VMX nesting (nVMX).
1603 Default is 0 (disabled)
1605 kvm-intel.unrestricted_guest=
1606 [KVM,Intel] Disable unrestricted guest feature
1607 (virtualized real and unpaged mode) on capable
1608 Intel chips. Default is 1 (enabled)
1610 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1611 feature (tagged TLBs) on capable Intel chips.
1612 Default is 1 (enabled)
1618 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1621 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1622 value for LAPIC timer one-shot implementation. Default
1623 back to the programmable timer unit in the LAPIC.
1625 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1628 libata.dma= [LIBATA] DMA control
1629 libata.dma=0 Disable all PATA and SATA DMA
1630 libata.dma=1 PATA and SATA Disk DMA only
1631 libata.dma=2 ATAPI (CDROM) DMA only
1632 libata.dma=4 Compact Flash DMA only
1633 Combinations also work, so libata.dma=3 enables DMA
1634 for disks and CDROMs, but not CFs.
1636 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1637 libata.ignore_hpa=0 keep BIOS limits (default)
1638 libata.ignore_hpa=1 ignore limits, using full disk
1640 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1644 libata.force= [LIBATA] Force configurations. The format is comma
1645 separated list of "[ID:]VAL" where ID is
1646 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1647 matching port, link or device. Basically, it matches
1648 the ATA ID string printed on console by libata. If
1649 the whole ID part is omitted, the last PORT and DEVICE
1650 values are used. If ID hasn't been specified yet, the
1651 configuration applies to all ports, links and devices.
1653 If only DEVICE is omitted, the parameter applies to
1654 the port and all links and devices behind it. DEVICE
1655 number of 0 either selects the first device or the
1656 first fan-out link behind PMP device. It does not
1657 select the host link. DEVICE number of 15 selects the
1658 host link and device attached to it.
1660 The VAL specifies the configuration to force. As long
1661 as there's no ambiguity shortcut notation is allowed.
1662 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1663 The following configurations can be forced.
1665 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1666 Any ID with matching PORT is used.
1668 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1670 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1671 udma[/][16,25,33,44,66,100,133] notation is also
1674 * [no]ncq: Turn on or off NCQ.
1676 * nohrst, nosrst, norst: suppress hard, soft
1679 * rstonce: only attempt one reset during
1680 hot-unplug link recovery
1682 * dump_id: dump IDENTIFY data.
1684 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1686 * disable: Disable this device.
1688 If there are multiple matching configurations changing
1689 the same attribute, the last one is used.
1691 memblock=debug [KNL] Enable memblock debug messages.
1693 load_ramdisk= [RAM] List of ramdisks to load from floppy
1694 See Documentation/blockdev/ramdisk.txt.
1696 lockd.nlm_grace_period=P [NFS] Assign grace period.
1699 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1702 lockd.nlm_timeout=T [NFS] Assign timeout value.
1705 lockd.nlm_udpport=M [NFS] Assign UDP port.
1708 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1711 loglevel= All Kernel Messages with a loglevel smaller than the
1712 console loglevel will be printed to the console. It can
1713 also be changed with klogd or other programs. The
1714 loglevels are defined as follows:
1716 0 (KERN_EMERG) system is unusable
1717 1 (KERN_ALERT) action must be taken immediately
1718 2 (KERN_CRIT) critical conditions
1719 3 (KERN_ERR) error conditions
1720 4 (KERN_WARNING) warning conditions
1721 5 (KERN_NOTICE) normal but significant condition
1722 6 (KERN_INFO) informational
1723 7 (KERN_DEBUG) debug-level messages
1725 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1726 in bytes. n must be a power of two and greater
1727 than the minimal size. The minimal size is defined
1728 by LOG_BUF_SHIFT kernel config parameter. There is
1729 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1730 that allows to increase the default size depending on
1731 the number of CPUs. See init/Kconfig for more details.
1733 logo.nologo [FB] Disables display of the built-in Linux logo.
1734 This may be used to provide more screen space for
1735 kernel log messages and is useful when debugging
1736 kernel boot problems.
1738 lp=0 [LP] Specify parallel ports to use, e.g,
1739 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1740 lp=reset first parallel port). 'lp=0' disables the
1741 lp=auto printer driver. 'lp=reset' (which can be
1742 specified in addition to the ports) causes
1743 attached printers to be reset. Using
1744 lp=port1,port2,... specifies the parallel ports
1745 to associate lp devices with, starting with
1746 lp0. A port specification may be 'none' to skip
1747 that lp device, or a parport name such as
1748 'parport0'. Specifying 'lp=auto' instead of a
1749 port specification list means that device IDs
1750 from each port should be examined, to see if
1751 an IEEE 1284-compliant printer is attached; if
1752 so, the driver will manage that printer.
1753 See also header of drivers/char/lp.c.
1756 Sets loops_per_jiffy to given constant, thus avoiding
1757 time-consuming boot-time autodetection (up to 250 ms per
1758 CPU). 0 enables autodetection (default). To determine
1759 the correct value for your kernel, boot with normal
1760 autodetection and see what value is printed. Note that
1761 on SMP systems the preset will be applied to all CPUs,
1762 which is likely to cause problems if your CPUs need
1763 significantly divergent settings. An incorrect value
1764 will cause delays in the kernel to be wrong, leading to
1765 unpredictable I/O errors and other breakage. Although
1766 unlikely, in the extreme case this might damage your
1770 Format: <io>,<irq>,<dma>
1772 machvec= [IA-64] Force the use of a particular machine-vector
1773 (machvec) in a generic kernel.
1774 Example: machvec=hpzx1_swiotlb
1776 machtype= [Loongson] Share the same kernel image file between different
1778 Example: machtype=lemote-yeeloong-2f-7inch
1780 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1781 than or equal to this physical address is ignored.
1783 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1784 should make use of. maxcpus=n : n >= 0 limits the
1785 kernel to using 'n' processors. n=0 is a special case,
1786 it is equivalent to "nosmp", which also disables
1789 max_loop= [LOOP] The number of loop block devices that get
1790 (loop.max_loop) unconditionally pre-created at init time. The default
1791 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1792 of statically allocating a predefined number, loop
1793 devices can be requested on-demand with the
1794 /dev/loop-control interface.
1796 mce [X86-32] Machine Check Exception
1798 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1800 md= [HW] RAID subsystems devices and level
1801 See Documentation/md.txt.
1804 Format: <first>,<last>
1805 Specifies range of consoles to be captured by the MDA.
1807 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1808 Amount of memory to be used when the kernel is not able
1809 to see the whole system memory or for test.
1810 [X86] Work as limiting max address. Use together
1811 with memmap= to avoid physical address space collisions.
1812 Without memmap= PCI devices could be placed at addresses
1813 belonging to unused RAM.
1815 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1819 [KNL,SH] Allow user to override the default size for
1820 per-device physically contiguous DMA buffers.
1822 memmap=exactmap [KNL,X86] Enable setting of an exact
1823 E820 memory map, as specified by the user.
1824 Such memmap=exactmap lines can be constructed based on
1825 BIOS output or other requirements. See the memmap=nn@ss
1828 memmap=nn[KMG]@ss[KMG]
1829 [KNL] Force usage of a specific region of memory.
1830 Region of memory to be used is from ss to ss+nn.
1832 memmap=nn[KMG]#ss[KMG]
1833 [KNL,ACPI] Mark specific memory as ACPI data.
1834 Region of memory to be marked is from ss to ss+nn.
1836 memmap=nn[KMG]$ss[KMG]
1837 [KNL,ACPI] Mark specific memory as reserved.
1838 Region of memory to be reserved is from ss to ss+nn.
1839 Example: Exclude memory from 0x18690000-0x1869ffff
1840 memmap=64K$0x18690000
1842 memmap=0x10000$0x18690000
1844 memory_corruption_check=0/1 [X86]
1845 Some BIOSes seem to corrupt the first 64k of
1846 memory when doing things like suspend/resume.
1847 Setting this option will scan the memory
1848 looking for corruption. Enabling this will
1849 both detect corruption and prevent the kernel
1850 from using the memory being corrupted.
1851 However, its intended as a diagnostic tool; if
1852 repeatable BIOS-originated corruption always
1853 affects the same memory, you can use memmap=
1854 to prevent the kernel from using that memory.
1856 memory_corruption_check_size=size [X86]
1857 By default it checks for corruption in the low
1858 64k, making this memory unavailable for normal
1859 use. Use this parameter to scan for
1860 corruption in more or less memory.
1862 memory_corruption_check_period=seconds [X86]
1863 By default it checks for corruption every 60
1864 seconds. Use this parameter to check at some
1865 other rate. 0 disables periodic checking.
1867 memtest= [KNL,X86] Enable memtest
1869 default : 0 <disable>
1870 Specifies the number of memtest passes to be
1871 performed. Each pass selects another test
1872 pattern from a given set of patterns. Memtest
1873 fills the memory with this pattern, validates
1874 memory contents and reserves bad memory
1875 regions that are detected.
1877 meye.*= [HW] Set MotionEye Camera parameters
1878 See Documentation/video4linux/meye.txt.
1880 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1881 Multi-Function General Purpose Timers on AMD Geode
1884 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1885 the BIOS has incorrectly applied a workaround. TinyBIOS
1886 version 0.98 is known to be affected, 0.99 fixes the
1887 problem by letting the user disable the workaround.
1891 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1892 physical address is ignored.
1894 mini2440= [ARM,HW,KNL]
1895 Format:[0..2][b][c][t]
1897 MINI2440 configuration specification:
1898 0 - The attached screen is the 3.5" TFT
1899 1 - The attached screen is the 7" TFT
1900 2 - The VGA Shield is attached (1024x768)
1901 Leaving out the screen size parameter will not load
1902 the TFT driver, and the framebuffer will be left
1904 b - Enable backlight. The TFT backlight pin will be
1905 linked to the kernel VESA blanking code and a GPIO
1906 LED. This parameter is not necessary when using the
1908 c - Enable the s3c camera interface.
1909 t - Reserved for enabling touchscreen support. The
1910 touchscreen support is not enabled in the mainstream
1911 kernel as of 2.6.30, a preliminary port can be found
1912 in the "bleeding edge" mini2440 support kernel at
1913 http://repo.or.cz/w/linux-2.6/mini2440.git
1916 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1917 parameter allows control of the logging verbosity for
1918 the additional memory initialisation checks. A value
1919 of 0 disables mminit logging and a level of 4 will
1920 log everything. Information is printed at KERN_DEBUG
1921 so loglevel=8 may also need to be specified.
1924 [KNL] When CONFIG_MODULE_SIG is set, this means that
1925 modules without (valid) signatures will fail to load.
1926 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1927 is always true, so this option does nothing.
1930 [MOUSE] Maximum time between finger touching and
1931 leaving touchpad surface for touch to be considered
1932 a tap and be reported as a left button click (for
1933 touchpads working in absolute mode only).
1935 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1936 reporting absolute coordinates, such as tablets
1937 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1938 reporting absolute coordinates, such as tablets
1940 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1941 is similar to kernelcore except it specifies the
1942 amount of memory used for migratable allocations.
1943 If both kernelcore and movablecore is specified,
1944 then kernelcore will be at *least* the specified
1945 value but may be more. If movablecore on its own
1946 is specified, the administrator must be careful
1947 that the amount of memory usable for all allocations
1950 movable_node [KNL,X86] Boot-time switch to enable the effects
1951 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
1953 MTD_Partition= [MTD]
1954 Format: <name>,<region-number>,<size>,<offset>
1956 MTD_Region= [MTD] Format:
1957 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1960 See drivers/mtd/cmdlinepart.c.
1962 multitce=off [PPC] This parameter disables the use of the pSeries
1963 firmware feature for updating multiple TCE entries
1966 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1968 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1970 boundary - index of last SLC block on Flex-OneNAND.
1971 The remaining blocks are configured as MLC blocks.
1972 lock - Configure if Flex-OneNAND boundary should be locked.
1973 Once locked, the boundary cannot be changed.
1974 1 indicates lock status, 0 indicates unlock status.
1977 ARM/S3C2412 JIVE boot control
1979 See arch/arm/mach-s3c2412/mach-jive.c
1981 mtouchusb.raw_coordinates=
1982 [HW] Make the MicroTouch USB driver use raw coordinates
1983 ('y', default) or cooked coordinates ('n')
1985 mtrr_chunk_size=nn[KMG] [X86]
1986 used for mtrr cleanup. It is largest continuous chunk
1987 that could hold holes aka. UC entries.
1989 mtrr_gran_size=nn[KMG] [X86]
1990 Used for mtrr cleanup. It is granularity of mtrr block.
1992 Large value could prevent small alignment from
1995 mtrr_spare_reg_nr=n [X86]
1997 Range: 0,7 : spare reg number
1999 Used for mtrr cleanup. It is spare mtrr entries number.
2000 Set to 2 or more if your graphical card needs more.
2002 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2004 netdev= [NET] Network devices parameters
2005 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2006 Note that mem_start is often overloaded to mean
2007 something different and driver-specific.
2008 This usage is only documented in each driver source
2012 [NETFILTER] Enable connection tracking flow accounting
2013 0 to disable accounting
2014 1 to enable accounting
2017 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2018 See Documentation/filesystems/nfs/nfsroot.txt.
2020 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2021 See Documentation/filesystems/nfs/nfsroot.txt.
2023 nfsrootdebug [NFS] enable nfsroot debugging messages.
2024 See Documentation/filesystems/nfs/nfsroot.txt.
2026 nfs.callback_tcpport=
2027 [NFS] set the TCP port on which the NFSv4 callback
2028 channel should listen.
2031 [NFS] sets the pathname to the program which is used
2032 to update the NFS client cache entries.
2034 nfs.cache_getent_timeout=
2035 [NFS] sets the timeout after which an attempt to
2036 update a cache entry is deemed to have failed.
2038 nfs.idmap_cache_timeout=
2039 [NFS] set the maximum lifetime for idmapper cache
2043 [NFS] enable 64-bit inode numbers.
2044 If zero, the NFS client will fake up a 32-bit inode
2045 number for the readdir() and stat() syscalls instead
2046 of returning the full 64-bit number.
2047 The default is to return 64-bit inode numbers.
2049 nfs.max_session_slots=
2050 [NFSv4.1] Sets the maximum number of session slots
2051 the client will attempt to negotiate with the server.
2052 This limits the number of simultaneous RPC requests
2053 that the client can send to the NFSv4.1 server.
2054 Note that there is little point in setting this
2055 value higher than the max_tcp_slot_table_limit.
2057 nfs.nfs4_disable_idmapping=
2058 [NFSv4] When set to the default of '1', this option
2059 ensures that both the RPC level authentication
2060 scheme and the NFS level operations agree to use
2061 numeric uids/gids if the mount is using the
2062 'sec=sys' security flavour. In effect it is
2063 disabling idmapping, which can make migration from
2064 legacy NFSv2/v3 systems to NFSv4 easier.
2065 Servers that do not support this mode of operation
2066 will be autodetected by the client, and it will fall
2067 back to using the idmapper.
2068 To turn off this behaviour, set the value to '0'.
2070 [NFS4] Specify an additional fixed unique ident-
2071 ification string that NFSv4 clients can insert into
2072 their nfs_client_id4 string. This is typically a
2073 UUID that is generated at system install time.
2075 nfs.send_implementation_id =
2076 [NFSv4.1] Send client implementation identification
2077 information in exchange_id requests.
2078 If zero, no implementation identification information
2080 The default is to send the implementation identification
2083 nfs.recover_lost_locks =
2084 [NFSv4] Attempt to recover locks that were lost due
2085 to a lease timeout on the server. Please note that
2086 doing this risks data corruption, since there are
2087 no guarantees that the file will remain unchanged
2088 after the locks are lost.
2089 If you want to enable the kernel legacy behaviour of
2090 attempting to recover these locks, then set this
2092 The default parameter value of '0' causes the kernel
2093 not to attempt recovery of lost locks.
2095 nfsd.nfs4_disable_idmapping=
2096 [NFSv4] When set to the default of '1', the NFSv4
2097 server will return only numeric uids and gids to
2098 clients using auth_sys, and will accept numeric uids
2099 and gids from such clients. This is intended to ease
2100 migration from NFSv2/v3.
2102 objlayoutdriver.osd_login_prog=
2103 [NFS] [OBJLAYOUT] sets the pathname to the program which
2104 is used to automatically discover and login into new
2105 osd-targets. Please see:
2106 Documentation/filesystems/pnfs.txt for more explanations
2108 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2109 when a NMI is triggered.
2110 Format: [state][,regs][,debounce][,die]
2112 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2113 Format: [panic,][nopanic,][num]
2115 0 - turn nmi_watchdog off
2116 When panic is specified, panic when an NMI watchdog
2117 timeout occurs (or 'nopanic' to override the opposite
2119 This is useful when you use a panic=... timeout and
2120 need the box quickly up again.
2122 netpoll.carrier_timeout=
2123 [NET] Specifies amount of time (in seconds) that
2124 netpoll should wait for a carrier. By default netpoll
2127 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2128 emulation library even if a 387 maths coprocessor
2132 [HW] Never suspend the console
2133 Disable suspending of consoles during suspend and
2134 hibernate operations. Once disabled, debugging
2135 messages can reach various consoles while the rest
2136 of the system is being put to sleep (ie, while
2137 debugging driver suspend/resume hooks). This may
2138 not work reliably with all consoles, but is known
2139 to work with serial and VGA consoles.
2140 To facilitate more flexible debugging, we also add
2141 console_suspend, a printk module parameter to control
2142 it. Users could use console_suspend (usually
2143 /sys/module/printk/parameters/console_suspend) to
2144 turn on/off it dynamically.
2146 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2147 caches in the slab allocator. Saves per-node memory,
2148 but will impact performance.
2152 noapic [SMP,APIC] Tells the kernel to not make use of any
2153 IOAPICs that may be present in the system.
2155 noautogroup Disable scheduler automatic task group creation.
2157 nobats [PPC] Do not use BATs for mapping kernel lowmem
2158 on "Classic" PPC cores.
2162 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2164 nodelayacct [KNL] Disable per-task delay accounting
2166 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2168 nodsp [SH] Disable hardware DSP at boot time.
2170 noefi [X86] Disable EFI runtime services support.
2175 On X86-32 available only on PAE configured kernels.
2176 noexec=on: enable non-executable mappings (default)
2177 noexec=off: disable non-executable mappings
2180 Disable SMAP (Supervisor Mode Access Prevention)
2181 even if it is supported by processor.
2184 Disable SMEP (Supervisor Mode Execution Prevention)
2185 even if it is supported by processor.
2188 This affects only 32-bit executables.
2189 noexec32=on: enable non-executable mappings (default)
2190 read doesn't imply executable mappings
2191 noexec32=off: disable non-executable mappings
2192 read implies executable mappings
2194 nofpu [SH] Disable hardware FPU at boot time.
2196 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2197 register save and restore. The kernel will only save
2198 legacy floating-point registers on task switch.
2200 noxsave [BUGS=X86] Disables x86 extended register state save
2201 and restore using xsave. The kernel will fallback to
2202 enabling legacy floating-point and sse state.
2204 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2205 register states. The kernel will fall back to use
2206 xsave to save the states. By using this parameter,
2207 performance of saving the states is degraded because
2208 xsave doesn't support modified optimization while
2209 xsaveopt supports it on xsaveopt enabled systems.
2211 noxsaves [X86] Disables xsaves and xrstors used in saving and
2212 restoring x86 extended register state in compacted
2213 form of xsave area. The kernel will fall back to use
2214 xsaveopt and xrstor to save and restore the states
2215 in standard form of xsave area. By using this
2216 parameter, xsave area per process might occupy more
2217 memory on xsaves enabled systems.
2220 on enable eager fpu restore
2221 off disable eager fpu restore
2222 auto selects the default scheme, which automatically
2223 enables eagerfpu restore for xsaveopt.
2225 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2226 wfi(ARM) instruction doesn't work correctly and not to
2227 use it. This is also useful when using JTAG debugger.
2229 no_file_caps Tells the kernel not to honor file capabilities. The
2230 only way then for a file to be executed with privilege
2231 is to be setuid root or executed by root.
2233 nohalt [IA-64] Tells the kernel not to use the power saving
2234 function PAL_HALT_LIGHT when idle. This increases
2235 power-consumption. On the positive side, it reduces
2236 interrupt wake-up latency, which may improve performance
2237 in certain environments such as networked servers or
2240 nohibernate [HIBERNATION] Disable hibernation and resume.
2242 nohz= [KNL] Boottime enable/disable dynamic ticks
2243 Valid arguments: on, off
2246 nohz_full= [KNL,BOOT]
2247 In kernels built with CONFIG_NO_HZ_FULL=y, set
2248 the specified list of CPUs whose tick will be stopped
2249 whenever possible. The boot CPU will be forced outside
2250 the range to maintain the timekeeping.
2251 The CPUs in this range must also be included in the
2254 noiotrap [SH] Disables trapped I/O port accesses.
2256 noirqdebug [X86-32] Disables the code which attempts to detect and
2257 disable unhandled interrupt sources.
2259 no_timer_check [X86,APIC] Disables the code which tests for
2260 broken timer IRQ sources.
2262 noisapnp [ISAPNP] Disables ISA PnP code.
2264 noinitrd [RAM] Tells the kernel not to load any configured
2267 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2269 [Deprecated - use intremap=off]
2273 nojitter [IA-64] Disables jitter checking for ITC timers.
2275 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2277 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2280 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2281 steal time is computed, but won't influence scheduler
2284 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2286 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2288 noltlbs [PPC] Do not use large page/tlb entries for kernel
2289 lowmem mapping on PPC40x.
2291 nomca [IA-64] Disable machine check abort handling
2293 nomce [X86-32] Machine Check Exception
2295 nomfgpt [X86-32] Disable Multi-Function General Purpose
2296 Timer usage (for AMD Geode machines).
2298 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2299 shutdown the other cpus. Instead use the REBOOT_VECTOR
2302 nomodule Disable module load
2304 nopat [X86] Disable PAT (page attribute table extension of
2305 pagetables) support.
2307 norandmaps Don't use address space randomization. Equivalent to
2308 echo 0 > /proc/sys/kernel/randomize_va_space
2310 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2312 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2313 with UP alternatives
2315 nordrand [X86] Disable kernel use of the RDRAND and
2316 RDSEED instructions even if they are supported
2317 by the processor. RDRAND and RDSEED are still
2318 available to user space applications.
2320 noresume [SWSUSP] Disables resume and restores original swap
2323 no-scroll [VGA] Disables scrollback.
2324 This is required for the Braillex ib80-piezo Braille
2325 reader made by F.H. Papenmeier (Germany).
2329 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2331 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2332 and disable the IO APIC. legacy for "maxcpus=0".
2334 nosoftlockup [KNL] Disable the soft-lockup detector.
2336 nosync [HW,M68K] Disables sync negotiation for all devices.
2338 notsc [BUGS=X86-32] Disable Time Stamp Counter
2340 nousb [USB] Disable the USB subsystem
2342 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2346 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2348 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2349 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2350 Some features depend on CPU0. Known dependencies are:
2351 1. Resume from suspend/hibernate depends on CPU0.
2352 Suspend/hibernate will fail if CPU0 is offline and you
2353 need to online CPU0 before suspend/hibernate.
2354 2. PIC interrupts also depend on CPU0. CPU0 can't be
2355 removed if a PIC interrupt is detected.
2356 It's said poweroff/reboot may depend on CPU0 on some
2357 machines although I haven't seen such issues so far
2358 after CPU0 is offline on a few tested machines.
2359 If the dependencies are under your control, you can
2360 turn on cpu0_hotplug.
2362 nptcg= [IA-64] Override max number of concurrent global TLB
2363 purges which is reported from either PAL_VM_SUMMARY or
2366 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2367 could support. nr_cpus=n : n >= 1 limits the kernel to
2368 supporting 'n' processors. Later in runtime you can not
2369 use hotplug cpu feature to put more cpu back to online.
2370 just like you compile the kernel NR_CPUS=n
2372 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2374 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2375 Allowed values are enable and disable
2377 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2378 one of ['zone', 'node', 'default'] can be specified
2379 This can be set from sysctl after boot.
2380 See Documentation/sysctl/vm.txt for details.
2382 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2383 See Documentation/debugging-via-ohci1394.txt for more
2386 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2387 Rather than timing out after 20 ms if an EC
2388 command is not properly ACKed, override the length
2389 of the timeout. We have interrupts disabled while
2390 waiting for the ACK, so if this is set too high
2391 interrupts *may* be lost!
2393 omap_mux= [OMAP] Override bootloader pin multiplexing.
2394 Format: <mux_mode0.mode_name=value>...
2395 For example, to override I2C bus2:
2396 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2398 oprofile.timer= [HW]
2399 Use timer interrupt instead of performance counters
2401 oprofile.cpu_type= Force an oprofile cpu type
2402 This might be useful if you have an older oprofile
2403 userland or if you want common events.
2404 Format: { arch_perfmon }
2405 arch_perfmon: [X86] Force use of architectural
2406 perfmon on Intel CPUs instead of the
2407 CPU specific event set.
2408 timer: [X86] Force use of architectural NMI
2409 timer mode (see also oprofile.timer
2410 for generic hr timer mode)
2411 [s390] Force legacy basic mode sampling
2412 (report cpu_type "timer")
2414 oops=panic Always panic on oopses. Default is to just kill the
2415 process, but there is a small probability of
2416 deadlocking the machine.
2417 This will also cause panics on machine check exceptions.
2418 Useful together with panic=30 to trigger a reboot.
2421 See Documentation/sound/oss/oss-parameters.txt
2423 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2424 timeout > 0: seconds before rebooting
2425 timeout = 0: wait forever
2426 timeout < 0: reboot immediately
2429 crash_kexec_post_notifiers
2430 Run kdump after running panic-notifiers and dumping
2431 kmsg. This only for the users who doubt kdump always
2432 succeeds in any situation.
2433 Note that this also increases risks of kdump failure,
2434 because some panic notifiers can make the crashed
2435 kernel more unstable.
2437 parkbd.port= [HW] Parallel port number the keyboard adapter is
2438 connected to, default is 0.
2440 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2441 0 for XT, 1 for AT (default is AT).
2444 parport= [HW,PPT] Specify parallel ports. 0 disables.
2445 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2446 Use 'auto' to force the driver to use any
2447 IRQ/DMA settings detected (the default is to
2448 ignore detected IRQ/DMA settings because of
2449 possible conflicts). You can specify the base
2450 address, IRQ, and DMA settings; IRQ and DMA
2451 should be numbers, or 'auto' (for using detected
2452 settings on that particular port), or 'nofifo'
2453 (to avoid using a FIFO even if it is detected).
2454 Parallel ports are assigned in the order they
2455 are specified on the command line, starting
2458 parport_init_mode= [HW,PPT]
2459 Configure VIA parallel port to operate in
2460 a specific mode. This is necessary on Pegasos
2461 computer where firmware has no options for setting
2462 up parallel port mode and sets it to spp.
2463 Currently this function knows 686a and 8231 chips.
2464 Format: [spp|ps2|epp|ecp|ecpepp]
2467 Halt all CPUs after the first oops has been printed for
2468 the specified number of seconds. This is to be used if
2469 your oopses keep scrolling off the screen.
2474 See header of drivers/block/paride/pcd.c.
2475 See also Documentation/blockdev/paride.txt.
2477 pci=option[,option...] [PCI] various PCI subsystem options:
2478 earlydump [X86] dump PCI config space before the kernel
2480 off [X86] don't probe for the PCI bus
2481 bios [X86-32] force use of PCI BIOS, don't access
2482 the hardware directly. Use this if your machine
2483 has a non-standard PCI host bridge.
2484 nobios [X86-32] disallow use of PCI BIOS, only direct
2485 hardware access methods are allowed. Use this
2486 if you experience crashes upon bootup and you
2487 suspect they are caused by the BIOS.
2488 conf1 [X86] Force use of PCI Configuration
2490 conf2 [X86] Force use of PCI Configuration
2492 noaer [PCIE] If the PCIEAER kernel config parameter is
2493 enabled, this kernel boot option can be used to
2494 disable the use of PCIE advanced error reporting.
2495 nodomains [PCI] Disable support for multiple PCI
2496 root domains (aka PCI segments, in ACPI-speak).
2497 nommconf [X86] Disable use of MMCONFIG for PCI
2499 check_enable_amd_mmconf [X86] check for and enable
2500 properly configured MMIO access to PCI
2501 config space on AMD family 10h CPU
2502 nomsi [MSI] If the PCI_MSI kernel config parameter is
2503 enabled, this kernel boot option can be used to
2504 disable the use of MSI interrupts system-wide.
2505 noioapicquirk [APIC] Disable all boot interrupt quirks.
2506 Safety option to keep boot IRQs enabled. This
2507 should never be necessary.
2508 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2509 primary IO-APIC for bridges that cannot disable
2510 boot IRQs. This fixes a source of spurious IRQs
2511 when the system masks IRQs.
2512 noioapicreroute [APIC] Disable workaround that uses the
2513 boot IRQ equivalent of an IRQ that connects to
2514 a chipset where boot IRQs cannot be disabled.
2515 The opposite of ioapicreroute.
2516 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2517 routing table. These calls are known to be buggy
2518 on several machines and they hang the machine
2519 when used, but on other computers it's the only
2520 way to get the interrupt routing table. Try
2521 this option if the kernel is unable to allocate
2522 IRQs or discover secondary PCI buses on your
2524 rom [X86] Assign address space to expansion ROMs.
2525 Use with caution as certain devices share
2526 address decoders between ROMs and other
2528 norom [X86] Do not assign address space to
2529 expansion ROMs that do not already have
2530 BIOS assigned address ranges.
2531 nobar [X86] Do not assign address space to the
2532 BARs that weren't assigned by the BIOS.
2533 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2534 assigned automatically to PCI devices. You can
2535 make the kernel exclude IRQs of your ISA cards
2537 pirqaddr=0xAAAAA [X86] Specify the physical address
2538 of the PIRQ table (normally generated
2539 by the BIOS) if it is outside the
2540 F0000h-100000h range.
2541 lastbus=N [X86] Scan all buses thru bus #N. Can be
2542 useful if the kernel is unable to find your
2543 secondary buses and you want to tell it
2544 explicitly which ones they are.
2545 assign-busses [X86] Always assign all PCI bus
2546 numbers ourselves, overriding
2547 whatever the firmware may have done.
2548 usepirqmask [X86] Honor the possible IRQ mask stored
2549 in the BIOS $PIR table. This is needed on
2550 some systems with broken BIOSes, notably
2551 some HP Pavilion N5400 and Omnibook XE3
2552 notebooks. This will have no effect if ACPI
2553 IRQ routing is enabled.
2554 noacpi [X86] Do not use ACPI for IRQ routing
2555 or for PCI scanning.
2556 use_crs [X86] Use PCI host bridge window information
2557 from ACPI. On BIOSes from 2008 or later, this
2558 is enabled by default. If you need to use this,
2559 please report a bug.
2560 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2561 If you need to use this, please report a bug.
2562 routeirq Do IRQ routing for all PCI devices.
2563 This is normally done in pci_enable_device(),
2564 so this option is a temporary workaround
2565 for broken drivers that don't call it.
2566 skip_isa_align [X86] do not align io start addr, so can
2567 handle more pci cards
2568 firmware [ARM] Do not re-enumerate the bus but instead
2569 just use the configuration from the
2570 bootloader. This is currently used on
2571 IXP2000 systems where the bus has to be
2572 configured a certain way for adjunct CPUs.
2573 noearly [X86] Don't do any early type 1 scanning.
2574 This might help on some broken boards which
2575 machine check when some devices' config space
2576 is read. But various workarounds are disabled
2577 and some IOMMU drivers will not work.
2578 bfsort Sort PCI devices into breadth-first order.
2579 This sorting is done to get a device
2580 order compatible with older (<= 2.4) kernels.
2581 nobfsort Don't sort PCI devices into breadth-first order.
2582 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2583 tuning and use the BIOS-configured MPS defaults.
2584 pcie_bus_safe Set every device's MPS to the largest value
2585 supported by all devices below the root complex.
2586 pcie_bus_perf Set device MPS to the largest allowable MPS
2587 based on its parent bus. Also set MRRS (Max
2588 Read Request Size) to the largest supported
2589 value (no larger than the MPS that the device
2590 or bus can support) for best performance.
2591 pcie_bus_peer2peer Set every device's MPS to 128B, which
2592 every device is guaranteed to support. This
2593 configuration allows peer-to-peer DMA between
2594 any pair of devices, possibly at the cost of
2595 reduced performance. This also guarantees
2596 that hot-added devices will work.
2597 cbiosize=nn[KMG] The fixed amount of bus space which is
2598 reserved for the CardBus bridge's IO window.
2599 The default value is 256 bytes.
2600 cbmemsize=nn[KMG] The fixed amount of bus space which is
2601 reserved for the CardBus bridge's memory
2602 window. The default value is 64 megabytes.
2605 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2606 Specifies alignment and device to reassign
2607 aligned memory resources.
2608 If <order of align> is not specified,
2609 PAGE_SIZE is used as alignment.
2610 PCI-PCI bridge can be specified, if resource
2611 windows need to be expanded.
2612 ecrc= Enable/disable PCIe ECRC (transaction layer
2613 end-to-end CRC checking).
2614 bios: Use BIOS/firmware settings. This is the
2618 hpiosize=nn[KMG] The fixed amount of bus space which is
2619 reserved for hotplug bridge's IO window.
2620 Default size is 256 bytes.
2621 hpmemsize=nn[KMG] The fixed amount of bus space which is
2622 reserved for hotplug bridge's memory window.
2623 Default size is 2 megabytes.
2624 realloc= Enable/disable reallocating PCI bridge resources
2625 if allocations done by BIOS are too small to
2626 accommodate resources required by all child
2628 off: Turn realloc off
2630 realloc same as realloc=on
2631 noari do not use PCIe ARI.
2632 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2633 only look for one device below a PCIe downstream
2636 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2639 force Enable ASPM even on devices that claim not to support it.
2640 WARNING: Forcing ASPM on may cause system lockups.
2642 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2643 nomsi Do not use MSI for PCI Express Native Hotplug (this
2644 makes all PCIe ports use INTx for hotplug services).
2646 pcie_ports= [PCIE] PCIe ports handling:
2647 auto Ask the BIOS whether or not to use native PCIe services
2648 associated with PCIe ports (PME, hot-plug, AER). Use
2649 them only if that is allowed by the BIOS.
2650 native Use native PCIe services associated with PCIe ports
2652 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2655 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2656 nomsi Do not use MSI for native PCIe PME signaling (this makes
2657 all PCIe root ports use INTx for all services).
2659 pcmv= [HW,PCMCIA] BadgePAD 4
2663 Keep all power-domains already enabled by bootloader on,
2664 even if no driver has claimed them. This is useful
2665 for debug and development, but should not be
2666 needed on a platform with proper driver support.
2669 See Documentation/blockdev/paride.txt.
2671 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2674 See arch/parisc/kernel/pdc_chassis.c
2676 percpu_alloc= Select which percpu first chunk allocator to use.
2677 Currently supported values are "embed" and "page".
2678 Archs may support subset or none of the selections.
2679 See comments in mm/percpu.c for details on each
2680 allocator. This parameter is primarily for debugging
2681 and performance comparison.
2684 See Documentation/blockdev/paride.txt.
2687 See Documentation/blockdev/paride.txt.
2689 pirq= [SMP,APIC] Manual mp-table setup
2690 See Documentation/x86/i386/IO-APIC.txt.
2692 plip= [PPT,NET] Parallel port network link
2693 Format: { parport<nr> | timid | 0 }
2694 See also Documentation/parport.txt.
2696 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2697 Override pmtimer IOPort with a hex value.
2701 Enable PNP debug messages (depends on the
2702 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2703 via /sys/module/pnp/parameters/debug. We always show
2704 current resource usage; turning this on also shows
2705 possible settings and some assignment information.
2711 { on | off | curr | res | no-curr | no-res }
2714 [ISAPNP] Exclude IRQs for the autoconfiguration
2717 [ISAPNP] Exclude DMAs for the autoconfiguration
2719 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2720 Ranges are in pairs (I/O port base and size).
2723 [ISAPNP] Exclude memory regions for the
2725 Ranges are in pairs (memory base and size).
2727 ports= [IP_VS_FTP] IPVS ftp helper module
2729 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2731 Format: <port>,<port>....
2733 print-fatal-signals=
2734 [KNL] debug: print fatal signals
2736 If enabled, warn about various signal handling
2737 related application anomalies: too many signals,
2738 too many POSIX.1 timers, fatal signals causing a
2741 If you hit the warning due to signal overflow,
2742 you might want to try "ulimit -i unlimited".
2746 printk.always_kmsg_dump=
2747 Trigger kmsg_dump for cases other than kernel oops or
2749 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2752 printk.time= Show timing data prefixed to each printk message line
2753 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2755 processor.max_cstate= [HW,ACPI]
2756 Limit processor to maximum C-state
2757 max_cstate=9 overrides any DMI blacklist limit.
2759 processor.nocst [HW,ACPI]
2760 Ignore the _CST method to determine C-states,
2761 instead using the legacy FADT method
2763 profile= [KNL] Enable kernel profiling via /proc/profile
2764 Format: [schedule,]<number>
2765 Param: "schedule" - profile schedule points.
2766 Param: <number> - step/bucket size as a power of 2 for
2767 statistical time based profiling.
2768 Param: "sleep" - profile D-state sleeping (millisecs).
2769 Requires CONFIG_SCHEDSTATS
2770 Param: "kvm" - profile VM exits.
2772 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2774 See Documentation/blockdev/ramdisk.txt.
2776 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2777 probe for; one of (bare|imps|exps|lifebook|any).
2778 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2780 psmouse.resetafter= [HW,MOUSE]
2781 Try to reset the device after so many bad packets
2784 [HW,MOUSE] Set desired mouse resolution, in dpi.
2785 psmouse.smartscroll=
2786 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2787 0 = disabled, 1 = enabled (default).
2789 pstore.backend= Specify the name of the pstore backend to use
2792 See Documentation/blockdev/paride.txt.
2795 [KNL] Number of legacy pty's. Overwrites compiled-in
2798 quiet [KNL] Disable most log messages
2803 See Documentation/md.txt.
2805 ramdisk_blocksize= [RAM]
2806 See Documentation/blockdev/ramdisk.txt.
2808 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2809 See Documentation/blockdev/ramdisk.txt.
2812 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2813 the specified list of CPUs to be no-callback CPUs.
2814 Invocation of these CPUs' RCU callbacks will
2815 be offloaded to "rcuox/N" kthreads created for
2816 that purpose, where "x" is "b" for RCU-bh, "p"
2817 for RCU-preempt, and "s" for RCU-sched, and "N"
2818 is the CPU number. This reduces OS jitter on the
2819 offloaded CPUs, which can be useful for HPC and
2820 real-time workloads. It can also improve energy
2821 efficiency for asymmetric multiprocessors.
2824 Rather than requiring that offloaded CPUs
2825 (specified by rcu_nocbs= above) explicitly
2826 awaken the corresponding "rcuoN" kthreads,
2827 make these kthreads poll for callbacks.
2828 This improves the real-time response for the
2829 offloaded CPUs by relieving them of the need to
2830 wake up the corresponding kthread, but degrades
2831 energy efficiency by requiring that the kthreads
2832 periodically wake up to do the polling.
2834 rcutree.blimit= [KNL]
2835 Set maximum number of finished RCU callbacks to
2836 process in one batch.
2838 rcutree.rcu_fanout_leaf= [KNL]
2839 Increase the number of CPUs assigned to each
2840 leaf rcu_node structure. Useful for very large
2843 rcutree.jiffies_till_sched_qs= [KNL]
2844 Set required age in jiffies for a
2845 given grace period before RCU starts
2846 soliciting quiescent-state help from
2847 rcu_note_context_switch().
2849 rcutree.jiffies_till_first_fqs= [KNL]
2850 Set delay from grace-period initialization to
2851 first attempt to force quiescent states.
2852 Units are jiffies, minimum value is zero,
2853 and maximum value is HZ.
2855 rcutree.jiffies_till_next_fqs= [KNL]
2856 Set delay between subsequent attempts to force
2857 quiescent states. Units are jiffies, minimum
2858 value is one, and maximum value is HZ.
2860 rcutree.rcu_nocb_leader_stride= [KNL]
2861 Set the number of NOCB kthread groups, which
2862 defaults to the square root of the number of
2863 CPUs. Larger numbers reduces the wakeup overhead
2864 on the per-CPU grace-period kthreads, but increases
2865 that same overhead on each group's leader.
2867 rcutree.qhimark= [KNL]
2868 Set threshold of queued RCU callbacks beyond which
2869 batch limiting is disabled.
2871 rcutree.qlowmark= [KNL]
2872 Set threshold of queued RCU callbacks below which
2873 batch limiting is re-enabled.
2875 rcutree.rcu_idle_gp_delay= [KNL]
2876 Set wakeup interval for idle CPUs that have
2877 RCU callbacks (RCU_FAST_NO_HZ=y).
2879 rcutree.rcu_idle_lazy_gp_delay= [KNL]
2880 Set wakeup interval for idle CPUs that have
2881 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2882 Lazy RCU callbacks are those which RCU can
2883 prove do nothing more than free memory.
2885 rcutorture.fqs_duration= [KNL]
2886 Set duration of force_quiescent_state bursts.
2888 rcutorture.fqs_holdoff= [KNL]
2889 Set holdoff time within force_quiescent_state bursts.
2891 rcutorture.fqs_stutter= [KNL]
2892 Set wait time between force_quiescent_state bursts.
2894 rcutorture.gp_exp= [KNL]
2895 Use expedited update-side primitives.
2897 rcutorture.gp_normal= [KNL]
2898 Use normal (non-expedited) update-side primitives.
2899 If both gp_exp and gp_normal are set, do both.
2900 If neither gp_exp nor gp_normal are set, still
2903 rcutorture.n_barrier_cbs= [KNL]
2904 Set callbacks/threads for rcu_barrier() testing.
2906 rcutorture.nfakewriters= [KNL]
2907 Set number of concurrent RCU writers. These just
2908 stress RCU, they don't participate in the actual
2909 test, hence the "fake".
2911 rcutorture.nreaders= [KNL]
2912 Set number of RCU readers.
2914 rcutorture.object_debug= [KNL]
2915 Enable debug-object double-call_rcu() testing.
2917 rcutorture.onoff_holdoff= [KNL]
2918 Set time (s) after boot for CPU-hotplug testing.
2920 rcutorture.onoff_interval= [KNL]
2921 Set time (s) between CPU-hotplug operations, or
2922 zero to disable CPU-hotplug testing.
2924 rcutorture.rcutorture_runnable= [BOOT]
2925 Start rcutorture running at boot time.
2927 rcutorture.shuffle_interval= [KNL]
2928 Set task-shuffle interval (s). Shuffling tasks
2929 allows some CPUs to go into dyntick-idle mode
2930 during the rcutorture test.
2932 rcutorture.shutdown_secs= [KNL]
2933 Set time (s) after boot system shutdown. This
2934 is useful for hands-off automated testing.
2936 rcutorture.stall_cpu= [KNL]
2937 Duration of CPU stall (s) to test RCU CPU stall
2938 warnings, zero to disable.
2940 rcutorture.stall_cpu_holdoff= [KNL]
2941 Time to wait (s) after boot before inducing stall.
2943 rcutorture.stat_interval= [KNL]
2944 Time (s) between statistics printk()s.
2946 rcutorture.stutter= [KNL]
2947 Time (s) to stutter testing, for example, specifying
2948 five seconds causes the test to run for five seconds,
2949 wait for five seconds, and so on. This tests RCU's
2950 ability to transition abruptly to and from idle.
2952 rcutorture.test_boost= [KNL]
2953 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2954 "Maybe" means test if the RCU implementation
2955 under test support RCU priority boosting.
2957 rcutorture.test_boost_duration= [KNL]
2958 Duration (s) of each individual boost test.
2960 rcutorture.test_boost_interval= [KNL]
2961 Interval (s) between each boost test.
2963 rcutorture.test_no_idle_hz= [KNL]
2964 Test RCU's dyntick-idle handling. See also the
2965 rcutorture.shuffle_interval parameter.
2967 rcutorture.torture_type= [KNL]
2968 Specify the RCU implementation to test.
2970 rcutorture.verbose= [KNL]
2971 Enable additional printk() statements.
2973 rcupdate.rcu_expedited= [KNL]
2974 Use expedited grace-period primitives, for
2975 example, synchronize_rcu_expedited() instead
2976 of synchronize_rcu(). This reduces latency,
2977 but can increase CPU utilization, degrade
2978 real-time latency, and degrade energy efficiency.
2980 rcupdate.rcu_cpu_stall_suppress= [KNL]
2981 Suppress RCU CPU stall warning messages.
2983 rcupdate.rcu_cpu_stall_timeout= [KNL]
2984 Set timeout for RCU CPU stall warning messages.
2988 Run specified binary instead of /init from the ramdisk,
2989 used for early userspace startup. See initrd.
2992 Format (x86 or x86_64):
2993 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2995 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2997 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2998 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2999 reboot_force is either force or not specified,
3000 reboot_cpu is s[mp]#### with #### being the processor
3001 to be used for rebooting.
3004 [KNL, SMP] Set scheduler's default relax_domain_level.
3005 See Documentation/cgroups/cpusets.txt.
3007 relative_sleep_states=
3008 [SUSPEND] Use sleep state labeling where the deepest
3009 state available other than hibernation is always "mem".
3010 Format: { "0" | "1" }
3011 0 -- Traditional sleep state labels.
3012 1 -- Relative sleep state labels.
3014 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3016 reservetop= [X86-32]
3018 Reserves a hole at the top of the kernel virtual
3023 Set the amount of memory to reserve for BIOS at
3024 the bottom of the address space.
3026 reset_devices [KNL] Force drivers to reset the underlying device
3027 during initialization.
3030 Specify the partition device for software suspend
3032 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3034 resume_offset= [SWSUSP]
3035 Specify the offset from the beginning of the partition
3036 given by "resume=" at which the swap header is located,
3037 in <PAGE_SIZE> units (needed only for swap files).
3038 See Documentation/power/swsusp-and-swap-files.txt
3040 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3041 read the resume files
3043 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3044 Useful for devices that are detected asynchronously
3045 (e.g. USB and MMC devices).
3047 hibernate= [HIBERNATION]
3048 noresume Don't check if there's a hibernation image
3049 present during boot.
3050 nocompress Don't compress/decompress hibernation images.
3051 no Disable hibernation and resume.
3053 retain_initrd [RAM] Keep initrd memory after extraction
3055 rhash_entries= [KNL,NET]
3056 Set number of hash buckets for route cache
3058 ro [KNL] Mount root device read-only on boot
3060 root= [KNL] Root filesystem
3061 See name_to_dev_t comment in init/do_mounts.c.
3063 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3064 mount the root filesystem
3066 rootflags= [KNL] Set root filesystem mount option string
3068 rootfstype= [KNL] Set root filesystem type
3070 rootwait [KNL] Wait (indefinitely) for root device to show up.
3071 Useful for devices that are detected asynchronously
3072 (e.g. USB and MMC devices).
3074 rproc_mem=nn[KMG][@address]
3075 [KNL,ARM,CMA] Remoteproc physical memory block.
3076 Memory area to be used by remote processor image,
3079 rw [KNL] Mount root device read-write on boot
3081 S [KNL] Run init in single mode
3083 s390_iommu= [HW,S390]
3084 Set s390 IOTLB flushing mode
3086 With strict flushing every unmap operation will result in
3087 an IOTLB flush. Default is lazy flushing before reuse,
3091 See drivers/net/irda/sa1100_ir.c.
3093 sbni= [NET] Granch SBNI12 leased line adapter
3095 sched_debug [KNL] Enables verbose scheduler debug messages.
3097 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3098 xtime_lock contention on larger systems, and/or RCU lock
3099 contention on all systems with CONFIG_MAXSMP set.
3100 Format: { "0" | "1" }
3101 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3103 Note: increases power consumption, thus should only be
3104 enabled if running jitter sensitive (HPC/RT) workloads.
3106 security= [SECURITY] Choose a security module to enable at boot.
3107 If this boot parameter is not specified, only the first
3108 security module asking for security registration will be
3109 loaded. An invalid security module name will be treated
3110 as if no module has been chosen.
3112 selinux= [SELINUX] Disable or enable SELinux at boot time.
3113 Format: { "0" | "1" }
3114 See security/selinux/Kconfig help text.
3117 Default value is set via kernel config option.
3118 If enabled at boot time, /selinux/disable can be used
3119 later to disable prior to initial policy load.
3121 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3122 Format: { "0" | "1" }
3123 See security/apparmor/Kconfig help text
3126 Default value is set via kernel config option.
3128 serialnumber [BUGS=X86-32]
3131 Maximal number of shapers.
3133 show_msr= [x86] show boot-time MSR settings
3134 Format: { <integer> }
3135 Show boot-time (BIOS-initialized) MSR settings.
3136 The parameter means the number of CPUs to show,
3137 for example 1 means boot CPU only.
3144 slab_max_order= [MM, SLAB]
3145 Determines the maximum allowed order for slabs.
3146 A high setting may cause OOMs due to memory
3147 fragmentation. Defaults to 1 for systems with
3148 more than 32MB of RAM, 0 otherwise.
3150 slub_debug[=options[,slabs]] [MM, SLUB]
3151 Enabling slub_debug allows one to determine the
3152 culprit if slab objects become corrupted. Enabling
3153 slub_debug can create guard zones around objects and
3154 may poison objects when not in use. Also tracks the
3155 last alloc / free. For more information see
3156 Documentation/vm/slub.txt.
3158 slub_max_order= [MM, SLUB]
3159 Determines the maximum allowed order for slabs.
3160 A high setting may cause OOMs due to memory
3161 fragmentation. For more information see
3162 Documentation/vm/slub.txt.
3164 slub_min_objects= [MM, SLUB]
3165 The minimum number of objects per slab. SLUB will
3166 increase the slab order up to slub_max_order to
3167 generate a sufficiently large slab able to contain
3168 the number of objects indicated. The higher the number
3169 of objects the smaller the overhead of tracking slabs
3170 and the less frequently locks need to be acquired.
3171 For more information see Documentation/vm/slub.txt.
3173 slub_min_order= [MM, SLUB]
3174 Determines the minimum page order for slabs. Must be
3175 lower than slub_max_order.
3176 For more information see Documentation/vm/slub.txt.
3178 slub_nomerge [MM, SLUB]
3179 Disable merging of slabs with similar size. May be
3180 necessary if there is some reason to distinguish
3181 allocs to different slabs. Debug options disable
3182 merging on their own.
3183 For more information see Documentation/vm/slub.txt.
3186 Format: <io1>[,<io2>[,...,<io8>]]
3188 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3189 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3190 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3191 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3192 smsc-ircc2.ircc_irq= [HW] IRQ line
3193 smsc-ircc2.ircc_dma= [HW] DMA channel
3194 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3195 0: Toshiba Satellite 1800 (GP data pin select)
3196 1: Fast pin select (default)
3200 [KNL] Should the soft-lockup detector generate panics.
3203 softlockup_all_cpu_backtrace=
3204 [KNL] Should the soft-lockup detector generate
3205 backtraces on all cpus.
3208 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3209 See Documentation/laptops/sonypi.txt
3211 spia_io_base= [HW,MTD]
3217 Enabled the stack tracer on boot up.
3219 stacktrace_filter=[function-list]
3220 [FTRACE] Limit the functions that the stack tracer
3221 will trace at boot up. function-list is a comma separated
3222 list of functions. This list can be changed at run
3223 time by the stack_trace_filter file in the debugfs
3224 tracing directory. Note, this enables stack tracing
3225 and the stacktrace above is not needed.
3229 Set the STI (builtin display/keyboard on the HP-PARISC
3230 machines) console (graphic card) which should be used
3231 as the initial boot-console.
3232 See also comment in drivers/video/console/sticore.c.
3235 See comment in drivers/video/console/sticore.c.
3238 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3240 sunrpc.min_resvport=
3241 sunrpc.max_resvport=
3243 SunRPC servers often require that client requests
3244 originate from a privileged port (i.e. a port in the
3245 range 0 < portnr < 1024).
3246 An administrator who wishes to reserve some of these
3247 ports for other uses may adjust the range that the
3248 kernel's sunrpc client considers to be privileged
3249 using these two parameters to set the minimum and
3250 maximum port values.
3254 Control how the NFS server code allocates CPUs to
3255 service thread pools. Depending on how many NICs
3256 you have and where their interrupts are bound, this
3257 option will affect which CPUs will do NFS serving.
3258 Note: this parameter cannot be changed while the
3259 NFS server is running.
3261 auto the server chooses an appropriate mode
3262 automatically using heuristics
3263 global a single global pool contains all CPUs
3264 percpu one pool for each CPU
3265 pernode one pool for each NUMA node (equivalent
3266 to global on non-NUMA machines)
3268 sunrpc.tcp_slot_table_entries=
3269 sunrpc.udp_slot_table_entries=
3271 Sets the upper limit on the number of simultaneous
3272 RPC calls that can be sent from the client to a
3273 server. Increasing these values may allow you to
3274 improve throughput, but will also increase the
3275 amount of memory reserved for use by the client.
3278 [KNL] Enable accounting of swap in memory resource
3279 controller if no parameter or 1 is given or disable
3280 it if 0 is given (See Documentation/cgroups/memory.txt)
3282 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3283 Format: { <int> | force }
3284 <int> -- Number of I/O TLB slabs
3285 force -- force using of bounce buffers even if they
3286 wouldn't be automatically used by the kernel
3290 sysfs.deprecated=0|1 [KNL]
3291 Enable/disable old style sysfs layout for old udev
3292 on older distributions. When this option is enabled
3293 very new udev will not work anymore. When this option
3294 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3295 in older udev will not work anymore.
3296 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3297 the kernel configuration.
3299 sysrq_always_enabled
3301 Ignore sysrq setting - this boot parameter will
3302 neutralize any effect of /proc/sys/kernel/sysrq.
3303 Useful for debugging.
3307 test_suspend= [SUSPEND]
3308 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3309 standby suspend) as the system sleep state to briefly
3310 enter during system startup. The system is woken from
3311 this state using a wakeup-capable RTC alarm.
3313 thash_entries= [KNL,NET]
3314 Set number of hash buckets for TCP connection
3316 thermal.act= [HW,ACPI]
3317 -1: disable all active trip points in all thermal zones
3318 <degrees C>: override all lowest active trip points
3320 thermal.crt= [HW,ACPI]
3321 -1: disable all critical trip points in all thermal zones
3322 <degrees C>: override all critical trip points
3324 thermal.nocrt= [HW,ACPI]
3325 Set to disable actions on ACPI thermal zone
3326 critical and hot trip points.
3328 thermal.off= [HW,ACPI]
3329 1: disable ACPI thermal control
3331 thermal.psv= [HW,ACPI]
3332 -1: disable all passive trip points
3333 <degrees C>: override all passive trip points to this
3336 thermal.tzp= [HW,ACPI]
3337 Specify global default ACPI thermal zone polling rate
3338 <deci-seconds>: poll all this frequency
3339 0: no polling (default)
3342 Force threading of all interrupt handlers except those
3343 marked explicitly IRQF_NO_THREAD.
3346 Enable the Transcendent memory driver if built-in.
3348 tmem.cleancache=0|1 [KNL, XEN]
3349 Default is on (1). Disable the usage of the cleancache
3350 API to send anonymous pages to the hypervisor.
3352 tmem.frontswap=0|1 [KNL, XEN]
3353 Default is on (1). Disable the usage of the frontswap
3354 API to send swap pages to the hypervisor. If disabled
3355 the selfballooning and selfshrinking are force disabled.
3357 tmem.selfballooning=0|1 [KNL, XEN]
3358 Default is on (1). Disable the driving of swap pages
3361 tmem.selfshrinking=0|1 [KNL, XEN]
3362 Default is on (1). Partial swapoff that immediately
3363 transfers pages from Xen hypervisor back to the
3364 kernel based on different criteria.
3368 Specify if the kernel should make use of the cpu
3369 topology information if the hardware supports this.
3370 The scheduler will make use of this information and
3371 e.g. base its process migration decisions on it.
3376 tpm_suspend_pcr=[HW,TPM]
3377 Format: integer pcr id
3378 Specify that at suspend time, the tpm driver
3379 should extend the specified pcr with zeros,
3380 as a workaround for some chips which fail to
3381 flush the last written pcr on TPM_SaveState.
3382 This will guarantee that all the other pcrs
3385 trace_buf_size=nn[KMG]
3386 [FTRACE] will set tracing buffer size.
3388 trace_event=[event-list]
3389 [FTRACE] Set and start specified trace events in order
3390 to facilitate early boot debugging.
3391 See also Documentation/trace/events.txt
3393 trace_options=[option-list]
3394 [FTRACE] Enable or disable tracer options at boot.
3395 The option-list is a comma delimited list of options
3396 that can be enabled or disabled just as if you were
3397 to echo the option name into
3399 /sys/kernel/debug/tracing/trace_options
3401 For example, to enable stacktrace option (to dump the
3402 stack trace of each event), add to the command line:
3404 trace_options=stacktrace
3406 See also Documentation/trace/ftrace.txt "trace options"
3410 [FTRACE] enable this option to disable tracing when a
3411 warning is hit. This turns off "tracing_on". Tracing can
3412 be enabled again by echoing '1' into the "tracing_on"
3413 file located in /sys/kernel/debug/tracing/
3415 This option is useful, as it disables the trace before
3416 the WARNING dump is called, which prevents the trace to
3417 be filled with content caused by the warning output.
3419 This option can also be set at run time via the sysctl
3420 option: kernel/traceoff_on_warning
3422 transparent_hugepage=
3424 Format: [always|madvise|never]
3425 Can be used to control the default behavior of the system
3426 with respect to transparent hugepages.
3427 See Documentation/vm/transhuge.txt for more details.
3429 tsc= Disable clocksource stability checks for TSC.
3431 [x86] reliable: mark tsc clocksource as reliable, this
3432 disables clocksource verification at runtime, as well
3433 as the stability checks done at bootup. Used to enable
3434 high-resolution timer mode on older hardware, and in
3435 virtualized environment.
3436 [x86] noirqtime: Do not use TSC to do irq accounting.
3437 Used to run time disable IRQ_TIME_ACCOUNTING on any
3438 platforms where RDTSC is slow and this accounting
3441 turbografx.map[2|3]= [HW,JOY]
3442 TurboGraFX parallel port interface
3444 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3445 See also Documentation/input/joystick-parport.txt
3447 udbg-immortal [PPC] When debugging early kernel crashes that
3448 happen after console_init() and before a proper
3449 console driver takes over, this boot options might
3450 help "seeing" what's going on.
3452 uhash_entries= [KNL,NET]
3453 Set number of hash buckets for UDP/UDP-Lite connections
3456 [USB] Ignore overcurrent events (default N).
3457 Some badly-designed motherboards generate lots of
3458 bogus events, for ports that aren't wired to
3459 anything. Set this parameter to avoid log spamming.
3460 Note that genuine overcurrent events won't be
3464 [X86] Cause panic on unknown NMI.
3466 usbcore.authorized_default=
3467 [USB] Default USB device authorization:
3468 (default -1 = authorized except for wireless USB,
3469 0 = not authorized, 1 = authorized)
3471 usbcore.autosuspend=
3472 [USB] The autosuspend time delay (in seconds) used
3473 for newly-detected USB devices (default 2). This
3474 is the time required before an idle device will be
3475 autosuspended. Devices for which the delay is set
3476 to a negative value won't be autosuspended at all.
3478 usbcore.usbfs_snoop=
3479 [USB] Set to log all usbfs traffic (default 0 = off).
3481 usbcore.blinkenlights=
3482 [USB] Set to cycle leds on hubs (default 0 = off).
3484 usbcore.old_scheme_first=
3485 [USB] Start with the old device initialization
3486 scheme (default 0 = off).
3488 usbcore.usbfs_memory_mb=
3489 [USB] Memory limit (in MB) for buffers allocated by
3490 usbfs (default = 16, 0 = max = 2047).
3492 usbcore.use_both_schemes=
3493 [USB] Try the other device initialization scheme
3494 if the first one fails (default 1 = enabled).
3496 usbcore.initial_descriptor_timeout=
3497 [USB] Specifies timeout for the initial 64-byte
3498 USB_REQ_GET_DESCRIPTOR request in milliseconds
3499 (default 5000 = 5.0 seconds).
3502 [USBHID] The interval which mice are to be polled at.
3504 usb-storage.delay_use=
3505 [UMS] The delay in seconds before a new device is
3506 scanned for Logical Units (default 5).
3509 [UMS] A list of quirks entries to supplement or
3510 override the built-in unusual_devs list. List
3511 entries are separated by commas. Each entry has
3512 the form VID:PID:Flags where VID and PID are Vendor
3513 and Product ID values (4-digit hex numbers) and
3514 Flags is a set of characters, each corresponding
3515 to a common usb-storage quirk flag as follows:
3516 a = SANE_SENSE (collect more than 18 bytes
3518 b = BAD_SENSE (don't collect more than 18
3519 bytes of sense data);
3520 c = FIX_CAPACITY (decrease the reported
3521 device capacity by one sector);
3522 d = NO_READ_DISC_INFO (don't use
3523 READ_DISC_INFO command);
3524 e = NO_READ_CAPACITY_16 (don't use
3525 READ_CAPACITY_16 command);
3526 h = CAPACITY_HEURISTICS (decrease the
3527 reported device capacity by one
3528 sector if the number is odd);
3529 i = IGNORE_DEVICE (don't bind to this
3531 l = NOT_LOCKABLE (don't try to lock and
3532 unlock ejectable media);
3533 m = MAX_SECTORS_64 (don't transfer more
3534 than 64 sectors = 32 KB at a time);
3535 n = INITIAL_READ10 (force a retry of the
3536 initial READ(10) command);
3537 o = CAPACITY_OK (accept the capacity
3538 reported by the device);
3539 p = WRITE_CACHE (the device cache is ON
3541 r = IGNORE_RESIDUE (the device reports
3542 bogus residue values);
3543 s = SINGLE_LUN (the device has only one
3545 u = IGNORE_UAS (don't bind to the uas driver);
3546 w = NO_WP_DETECT (don't test whether the
3547 medium is write-protected).
3548 Example: quirks=0419:aaf5:rl,0421:0433:rc
3550 user_debug= [KNL,ARM]
3552 See arch/arm/Kconfig.debug help text.
3553 1 - undefined instruction events
3555 4 - invalid data aborts
3558 Example: user_debug=31
3561 [X86] Flags controlling user PTE allocations.
3563 nohigh = do not allocate PTE pages in
3564 HIGHMEM regardless of setting
3568 On X86_32, this is an alias for vdso32=. Otherwise:
3570 vdso=1: enable VDSO (the default)
3571 vdso=0: disable VDSO mapping
3573 vdso32= [X86] Control the 32-bit vDSO
3574 vdso32=1: enable 32-bit VDSO
3575 vdso32=0 or vdso32=2: disable 32-bit VDSO
3577 See the help text for CONFIG_COMPAT_VDSO for more
3578 details. If CONFIG_COMPAT_VDSO is set, the default is
3579 vdso32=0; otherwise, the default is vdso32=1.
3581 For compatibility with older kernels, vdso32=2 is an
3584 Try vdso32=0 if you encounter an error that says:
3585 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3588 vector=percpu: enable percpu vector domain
3590 video= [FB] Frame buffer configuration
3591 See Documentation/fb/modedb.txt.
3593 video.brightness_switch_enabled= [0,1]
3594 If set to 1, on receiving an ACPI notify event
3595 generated by hotkey, video driver will adjust brightness
3596 level and then send out the event to user space through
3597 the allocated input device; If set to 0, video driver
3598 will only send out the event without touching backlight
3603 [VMMIO] Memory mapped virtio (platform) device.
3605 <size>@<baseaddr>:<irq>[:<id>]
3607 <size> := size (can use standard suffixes
3609 <baseaddr> := physical base address
3610 <irq> := interrupt number (as passed to
3612 <id> := (optional) platform device id
3614 virtio_mmio.device=1K@0x100b0000:48:7
3616 Can be used multiple times for multiple devices.
3618 vga= [BOOT,X86-32] Select a particular video mode
3619 See Documentation/x86/boot.txt and
3620 Documentation/svga.txt.
3621 Use vga=ask for menu.
3622 This is actually a boot loader parameter; the value is
3623 passed to the kernel using a special protocol.
3625 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3626 size of <nn>. This can be used to increase the
3627 minimum size (128MB on x86). It can also be used to
3628 decrease the size and leave more room for directly
3631 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3634 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3637 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3641 Controls the behavior of vsyscalls (i.e. calls to
3642 fixed addresses of 0xffffffffff600x00 from legacy
3643 code). Most statically-linked binaries and older
3644 versions of glibc use these calls. Because these
3645 functions are at fixed addresses, they make nice
3646 targets for exploits that can control RIP.
3648 emulate [default] Vsyscalls turn into traps and are
3649 emulated reasonably safely.
3651 native Vsyscalls are native syscall instructions.
3652 This is a little bit faster than trapping
3653 and makes a few dynamic recompilers work
3654 better than they would in emulation mode.
3655 It also makes exploits much easier to write.
3657 none Vsyscalls don't work at all. This makes
3658 them quite hard to use for exploits but
3659 might break your system.
3661 vt.color= [VT] Default text color.
3662 Format: 0xYX, X = foreground, Y = background.
3663 Default: 0x07 = light gray on black.
3665 vt.cur_default= [VT] Default cursor shape.
3666 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3667 the parameters of the <Esc>[?A;B;Cc escape sequence;
3668 see VGA-softcursor.txt. Default: 2 = underline.
3670 vt.default_blu= [VT]
3671 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3672 Change the default blue palette of the console.
3673 This is a 16-member array composed of values
3676 vt.default_grn= [VT]
3677 Format: <green0>,<green1>,<green2>,...,<green15>
3678 Change the default green palette of the console.
3679 This is a 16-member array composed of values
3682 vt.default_red= [VT]
3683 Format: <red0>,<red1>,<red2>,...,<red15>
3684 Change the default red palette of the console.
3685 This is a 16-member array composed of values
3691 Set system-wide default UTF-8 mode for all tty's.
3692 Default is 1, i.e. UTF-8 mode is enabled for all
3693 newly opened terminals.
3695 vt.global_cursor_default=
3698 Set system-wide default for whether a cursor
3699 is shown on new VTs. Default is -1,
3700 i.e. cursors will be created by default unless
3701 overridden by individual drivers. 0 will hide
3702 cursors, 1 will display them.
3704 vt.italic= [VT] Default color for italic text; 0-15.
3707 vt.underline= [VT] Default color for underlined text; 0-15.
3710 watchdog timers [HW,WDT] For information on watchdog timers,
3711 see Documentation/watchdog/watchdog-parameters.txt
3712 or other driver-specific files in the
3713 Documentation/watchdog/ directory.
3715 workqueue.disable_numa
3716 By default, all work items queued to unbound
3717 workqueues are affine to the NUMA nodes they're
3718 issued on, which results in better behavior in
3719 general. If NUMA affinity needs to be disabled for
3720 whatever reason, this option can be used. Note
3721 that this also can be controlled per-workqueue for
3722 workqueues visible under /sys/bus/workqueue/.
3724 workqueue.power_efficient
3725 Per-cpu workqueues are generally preferred because
3726 they show better performance thanks to cache
3727 locality; unfortunately, per-cpu workqueues tend to
3728 be more power hungry than unbound workqueues.
3730 Enabling this makes the per-cpu workqueues which
3731 were observed to contribute significantly to power
3732 consumption unbound, leading to measurably lower
3733 power usage at the cost of small performance
3736 The default value of this parameter is determined by
3737 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3739 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3740 default x2apic cluster mode on platforms
3743 x86_intel_mid_timer= [X86-32,APBT]
3744 Choose timer option for x86 Intel MID platform.
3745 Two valid options are apbt timer only and lapic timer
3746 plus one apbt timer for broadcast timer.
3747 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3749 xen_emul_unplug= [HW,X86,XEN]
3750 Unplug Xen emulated devices
3751 Format: [unplug0,][unplug1]
3752 ide-disks -- unplug primary master IDE devices
3753 aux-ide-disks -- unplug non-primary-master IDE devices
3754 nics -- unplug network devices
3755 all -- unplug all emulated devices (NICs and IDE disks)
3756 unnecessary -- unplugging emulated devices is
3757 unnecessary even if the host did not respond to
3759 never -- do not unplug even if version check succeeds
3761 xen_nopvspin [X86,XEN]
3762 Disables the ticketlock slowpath using Xen PV
3766 Disables the PV optimizations forcing the HVM guest to
3767 run as generic HVM guest with no PV drivers.
3769 xirc2ps_cs= [NET,PCMCIA]
3771 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3773 ______________________________________________________________________
3777 Add more DRM drivers.
projects / firefly-linux-kernel-4.4.55.git / blob