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.
925 Start an early, polled-mode console on a cadence serial
926 port at the specified address. The cadence serial port
927 must already be setup and configured. Options are not
930 uart[8250],io,<addr>[,options]
931 uart[8250],mmio,<addr>[,options]
932 uart[8250],mmio32,<addr>[,options]
933 Start an early, polled-mode console on the 8250/16550
934 UART at the specified I/O port or MMIO address.
935 MMIO inter-register address stride is either 8-bit
936 (mmio) or 32-bit (mmio32).
937 The options are the same as for ttyS, above.
940 Start an early, polled-mode console on a pl011 serial
941 port at the specified address. The pl011 serial port
942 must already be setup and configured. Options are not
945 smh Use ARM semihosting calls for early console.
947 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
951 earlyprintk=serial[,ttySn[,baudrate]]
952 earlyprintk=serial[,0x...[,baudrate]]
953 earlyprintk=ttySn[,baudrate]
954 earlyprintk=dbgp[debugController#]
956 earlyprintk is useful when the kernel crashes before
957 the normal console is initialized. It is not enabled by
958 default because it has some cosmetic problems.
960 Append ",keep" to not disable it when the real console
963 Only one of vga, efi, serial, or usb debug port can
966 Currently only ttyS0 and ttyS1 may be specified by
967 name. Other I/O ports may be explicitly specified
968 on some architectures (x86 and arm at least) by
969 replacing ttySn with an I/O port address, like this:
970 earlyprintk=serial,0x1008,115200
971 You can find the port for a given device in
972 /proc/tty/driver/serial:
973 2: uart:ST16650V2 port:00001008 irq:18 ...
975 Interaction with the standard serial driver is not
978 The VGA and EFI output is eventually overwritten by
981 The xen output can only be used by Xen PV guests.
983 edac_report= [HW,EDAC] Control how to report EDAC event
984 Format: {"on" | "off" | "force"}
985 on: enable EDAC to report H/W event. May be overridden
986 by other higher priority error reporting module.
987 off: disable H/W event reporting through EDAC.
988 force: enforce the use of EDAC to report H/W event.
991 ekgdboc= [X86,KGDB] Allow early kernel console debugging
994 This is designed to be used in conjunction with
995 the boot argument: earlyprintk=vga
998 Format: {"off" | "on" | "skip[mbr]"}
1001 Format: { "old_map" }
1002 old_map [X86-64]: switch to the old ioremap-based EFI
1003 runtime services mapping. 32-bit still uses this one by
1006 efi_no_storage_paranoia [EFI; X86]
1007 Using this parameter you can use more than 50% of
1008 your efi variable storage. Use this parameter only if
1009 you are really sure that your UEFI does sane gc and
1010 fulfills the spec otherwise your board may brick.
1012 eisa_irq_edge= [PARISC,HW]
1013 See header of drivers/parisc/eisa.c.
1016 See comment before function elanfreq_setup() in
1017 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1020 Format: {"cfq" | "deadline" | "noop"}
1021 See Documentation/block/cfq-iosched.txt and
1022 Documentation/block/deadline-iosched.txt for details.
1024 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1025 Specifies physical address of start of kernel core
1026 image elf header and optionally the size. Generally
1027 kexec loader will pass this option to capture kernel.
1028 See Documentation/kdump/kdump.txt for details.
1030 enable_mtrr_cleanup [X86]
1031 The kernel tries to adjust MTRR layout from continuous
1032 to discrete, to make X server driver able to add WB
1033 entry later. This parameter enables that.
1035 enable_timer_pin_1 [X86]
1036 Enable PIN 1 of APIC timer
1037 Can be useful to work around chipset bugs
1038 (in particular on some ATI chipsets).
1039 The kernel tries to set a reasonable default.
1041 enforcing [SELINUX] Set initial enforcing status.
1043 See security/selinux/Kconfig help text.
1044 0 -- permissive (log only, no denials).
1045 1 -- enforcing (deny and log).
1047 Value can be changed at runtime via /selinux/enforce.
1050 Disable Error Record Serialization Table (ERST)
1053 ether= [HW,NET] Ethernet cards parameters
1054 This option is obsoleted by the "netdev=" option, which
1055 has equivalent usage. See its documentation for details.
1059 Permit 'security.evm' to be updated regardless of
1060 current integrity status.
1064 fail_make_request=[KNL]
1065 General fault injection mechanism.
1066 Format: <interval>,<probability>,<space>,<times>
1067 See also Documentation/fault-injection/.
1070 See Documentation/blockdev/floppy.txt.
1072 force_pal_cache_flush
1073 [IA-64] Avoid check_sal_cache_flush which may hang on
1074 buggy SAL_CACHE_FLUSH implementations. Using this
1075 parameter will force ia64_sal_cache_flush to call
1076 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1079 Forcefully enable Physical Address Extension (PAE).
1080 Many Pentium M systems disable PAE but may have a
1081 functionally usable PAE implementation.
1082 Warning: use of this parameter will taint the kernel
1083 and may cause unknown problems.
1086 [FTRACE] will set and start the specified tracer
1087 as early as possible in order to facilitate early
1090 ftrace_dump_on_oops[=orig_cpu]
1091 [FTRACE] will dump the trace buffers on oops.
1092 If no parameter is passed, ftrace will dump
1093 buffers of all CPUs, but if you pass orig_cpu, it will
1094 dump only the buffer of the CPU that triggered the
1097 ftrace_filter=[function-list]
1098 [FTRACE] Limit the functions traced by the function
1099 tracer at boot up. function-list is a comma separated
1100 list of functions. This list can be changed at run
1101 time by the set_ftrace_filter file in the debugfs
1104 ftrace_notrace=[function-list]
1105 [FTRACE] Do not trace the functions specified in
1106 function-list. This list can be changed at run time
1107 by the set_ftrace_notrace file in the debugfs
1110 ftrace_graph_filter=[function-list]
1111 [FTRACE] Limit the top level callers functions traced
1112 by the function graph tracer at boot up.
1113 function-list is a comma separated list of functions
1114 that can be changed at run time by the
1115 set_graph_function file in the debugfs tracing directory.
1117 ftrace_graph_notrace=[function-list]
1118 [FTRACE] Do not trace from the functions specified in
1119 function-list. This list is a comma separated list of
1120 functions that can be changed at run time by the
1121 set_graph_notrace file in the debugfs tracing directory.
1124 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1125 support via parallel port (up to 5 devices per port)
1126 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1127 See also Documentation/input/joystick-parport.txt
1131 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1135 gcov_persist= [GCOV] When non-zero (default), profiling data for
1136 kernel modules is saved and remains accessible via
1137 debugfs, even when the module is unloaded/reloaded.
1138 When zero, profiling data is discarded and associated
1139 debugfs files are removed at module unload time.
1141 gpt [EFI] Forces disk with valid GPT signature but
1142 invalid Protective MBR to be treated as GPT. If the
1143 primary GPT is corrupted, it enables the backup/alternate
1144 GPT to be used instead.
1146 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1147 the "Enable 0" bit of the configuration register.
1150 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1151 the "Enable 0" bit of the configuration register.
1154 grcan.select= [HW] Select which physical interface to use.
1157 grcan.txsize= [HW] Sets the size of the tx buffer.
1158 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1160 grcan.rxsize= [HW] Sets the size of the rx buffer.
1161 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1164 hashdist= [KNL,NUMA] Large hashes allocated during boot
1165 are distributed across NUMA nodes. Defaults on
1166 for 64-bit NUMA, off otherwise.
1167 Format: 0 | 1 (for off | on)
1169 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1171 hd= [EIDE] (E)IDE hard drive subsystem geometry
1172 Format: <cyl>,<head>,<sect>
1175 Disable Hardware Error Source Table (HEST) support;
1176 corresponding firmware-first mode error processing
1177 logic will be disabled.
1179 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1180 size of <nn>. This works even on boxes that have no
1181 highmem otherwise. This also works to reduce highmem
1182 size on bigger boxes.
1184 highres= [KNL] Enable/disable high resolution timer mode.
1185 Valid parameters: "on", "off"
1189 See Documentation/isdn/README.HiSax.
1193 hpet= [X86-32,HPET] option to control HPET usage
1194 Format: { enable (default) | disable | force |
1196 disable: disable HPET and use PIT instead
1197 force: allow force enabled of undocumented chips (ICH4,
1199 verbose: show contents of HPET registers during setup
1201 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1202 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1204 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1205 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1206 On x86-64 and powerpc, this option can be specified
1207 multiple times interleaved with hugepages= to reserve
1208 huge pages of different sizes. Valid pages sizes on
1209 x86-64 are 2M (when the CPU supports "pse") and 1G
1210 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1211 Note that 1GB pages can only be allocated at boot time
1212 using hugepages= and not freed afterwards.
1214 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1215 terminal devices. Valid values: 0..8
1216 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1217 If specified, z/VM IUCV HVC accepts connections
1218 from listed z/VM user IDs only.
1220 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1221 hardware thread id mappings.
1222 Format: <cpu>:<hwthread>
1225 Do not unregister boot console at start. This is only
1226 useful for debugging when something happens in the window
1227 between unregistering the boot console and initializing
1230 i2c_bus= [HW] Override the default board specific I2C bus speed
1231 or register an additional I2C bus that is not
1232 registered from board initialization code.
1236 i8042.debug [HW] Toggle i8042 debug mode
1237 i8042.direct [HW] Put keyboard port into non-translated mode
1238 i8042.dumbkbd [HW] Pretend that controller can only read data from
1239 keyboard and cannot control its state
1240 (Don't attempt to blink the leds)
1241 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1242 i8042.nokbd [HW] Don't check/create keyboard port
1243 i8042.noloop [HW] Disable the AUX Loopback command while probing
1245 i8042.nomux [HW] Don't check presence of an active multiplexing
1247 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1249 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1250 i8042.reset [HW] Reset the controller during init and cleanup
1251 i8042.unlock [HW] Unlock (ignore) the keylock
1255 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1256 indicates that the driver is running on unsupported
1258 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1259 does not match list of supported models.
1261 [HW] Report power status in /proc/i8k
1262 (disabled by default)
1263 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1266 i915.invert_brightness=
1267 [DRM] Invert the sense of the variable that is used to
1268 set the brightness of the panel backlight. Normally a
1269 brightness value of 0 indicates backlight switched off,
1270 and the maximum of the brightness value sets the backlight
1271 to maximum brightness. If this parameter is set to 0
1272 (default) and the machine requires it, or this parameter
1273 is set to 1, a brightness value of 0 sets the backlight
1274 to maximum brightness, and the maximum of the brightness
1275 value switches the backlight off.
1276 -1 -- never invert brightness
1277 0 -- machine default
1278 1 -- force brightness inversion
1281 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1283 ide-core.nodma= [HW] (E)IDE subsystem
1284 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1285 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1286 .cdrom .chs .ignore_cable are additional options
1287 See Documentation/ide/ide.txt.
1289 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1290 Claim all unknown PCI IDE storage controllers.
1293 Format: idle=poll, idle=halt, idle=nomwait
1294 Poll forces a polling idle loop that can slightly
1295 improve the performance of waking up a idle CPU, but
1296 will use a lot of power and make the system run hot.
1298 idle=halt: Halt is forced to be used for CPU idle.
1299 In such case C2/C3 won't be used again.
1300 idle=nomwait: Disable mwait for CPU C-states
1302 ignore_loglevel [KNL]
1303 Ignore loglevel setting - this will print /all/
1304 kernel messages to the console. Useful for debugging.
1305 We also add it as printk module parameter, so users
1306 could change it dynamically, usually by
1307 /sys/module/printk/parameters/ignore_loglevel.
1309 ihash_entries= [KNL]
1310 Set number of hash buckets for inode cache.
1312 ima_appraise= [IMA] appraise integrity measurements
1313 Format: { "off" | "enforce" | "fix" }
1316 ima_appraise_tcb [IMA]
1317 The builtin appraise policy appraises all files
1321 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1325 The list of supported hash algorithms is defined
1326 in crypto/hash_info.h.
1329 Load a policy which meets the needs of the Trusted
1330 Computing Base. This means IMA will measure all
1331 programs exec'd, files mmap'd for exec, and all files
1332 opened for read by uid=0.
1335 Select one of defined IMA measurements template formats.
1336 Formats: { "ima" | "ima-ng" }
1339 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1340 Format: <min_file_size>
1341 Set the minimal file size for using asynchronous hash.
1342 If left unspecified, ahash usage is disabled.
1344 ahash performance varies for different data sizes on
1345 different crypto accelerators. This option can be used
1346 to achieve the best performance for a particular HW.
1348 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1350 Set hashing buffer size. Default: 4k.
1352 ahash performance varies for different chunk sizes on
1353 different crypto accelerators. This option can be used
1354 to achieve best performance for particular HW.
1358 Run specified binary instead of /sbin/init as init
1361 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1362 for working out where the kernel is dying during
1365 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1366 initcall functions. Useful for debugging built-in
1367 modules and initcalls.
1369 initrd= [BOOT] Specify the location of the initial ramdisk
1371 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1374 int_pln_enable [x86] Enable power limit notification interrupt
1376 integrity_audit=[IMA]
1377 Format: { "0" | "1" }
1378 0 -- basic integrity auditing messages. (Default)
1379 1 -- additional integrity auditing messages.
1381 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1383 Enable intel iommu driver.
1385 Disable intel iommu driver.
1386 igfx_off [Default Off]
1387 By default, gfx is mapped as normal device. If a gfx
1388 device has a dedicated DMAR unit, the DMAR unit is
1389 bypassed by not enabling DMAR with this option. In
1390 this case, gfx device will use physical address for
1393 With this option iommu will not optimize to look
1394 for io virtual address below 32-bit forcing dual
1395 address cycle on pci bus for cards supporting greater
1396 than 32-bit addressing. The default is to look
1397 for translation below 32-bit and if not available
1398 then look in the higher range.
1399 strict [Default Off]
1400 With this option on every unmap_single operation will
1401 result in a hardware IOTLB flush operation as opposed
1402 to batching them for performance.
1403 sp_off [Default Off]
1404 By default, super page will be supported if Intel IOMMU
1405 has the capability. With this option, super page will
1408 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1409 0 disables intel_idle and fall back on acpi_idle.
1410 1 to 6 specify maximum depth of C-state.
1414 Do not enable intel_pstate as the default
1415 scaling driver for the supported processors
1417 intremap= [X86-64, Intel-IOMMU]
1418 on enable Interrupt Remapping (default)
1419 off disable Interrupt Remapping
1420 nosid disable Source ID checking
1422 BIOS x2APIC opt-out request will be ignored
1424 iomem= Disable strict checking of access to MMIO memory
1425 strict regions from userspace.
1442 io7= [HW] IO7 for Marvel based alpha systems
1443 See comment before marvel_specify_io7 in
1444 arch/alpha/kernel/core_marvel.c.
1446 io_delay= [X86] I/O delay method
1448 Standard port 0x80 based delay
1450 Alternate port 0xed based delay (needed on some systems)
1452 Simple two microseconds delay
1457 See Documentation/filesystems/nfs/nfsroot.txt.
1460 When an interrupt is not handled search all handlers
1461 for it. Intended to get systems with badly broken
1465 When an interrupt is not handled search all handlers
1466 for it. Also check all handlers each timer
1467 interrupt. Intended to get systems with badly broken
1471 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1473 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1475 <cpu number>,...,<cpu number>
1477 <cpu number>-<cpu number>
1478 (must be a positive range in ascending order)
1480 <cpu number>,...,<cpu number>-<cpu number>
1482 This option can be used to specify one or more CPUs
1483 to isolate from the general SMP balancing and scheduling
1484 algorithms. You can move a process onto or off an
1485 "isolated" CPU via the CPU affinity syscalls or cpuset.
1486 <cpu number> begins at 0 and the maximum value is
1487 "number of CPUs in system - 1".
1489 This option is the preferred way to isolate CPUs. The
1490 alternative -- manually setting the CPU mask of all
1491 tasks in the system -- can cause problems and
1492 suboptimal load balancer performance.
1496 ivrs_ioapic [HW,X86_64]
1497 Provide an override to the IOAPIC-ID<->DEVICE-ID
1498 mapping provided in the IVRS ACPI table. For
1499 example, to map IOAPIC-ID decimal 10 to
1500 PCI device 00:14.0 write the parameter as:
1501 ivrs_ioapic[10]=00:14.0
1503 ivrs_hpet [HW,X86_64]
1504 Provide an override to the HPET-ID<->DEVICE-ID
1505 mapping provided in the IVRS ACPI table. For
1506 example, to map HPET-ID decimal 0 to
1507 PCI device 00:14.0 write the parameter as:
1508 ivrs_hpet[0]=00:14.0
1510 js= [HW,JOY] Analog joystick
1511 See Documentation/input/joystick.txt.
1514 Enable/disable kernel and module base offset ASLR
1515 (Address Space Layout Randomization) if built into
1516 the kernel. When CONFIG_HIBERNATION is selected,
1517 kASLR is disabled by default. When kASLR is enabled,
1518 hibernation will be disabled.
1522 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1523 specifies the amount of memory usable by the kernel
1524 for non-movable allocations. The requested amount is
1525 spread evenly throughout all nodes in the system. The
1526 remaining memory in each node is used for Movable
1527 pages. In the event, a node is too small to have both
1528 kernelcore and Movable pages, kernelcore pages will
1529 take priority and other nodes will have a larger number
1530 of Movable pages. The Movable zone is used for the
1531 allocation of pages that may be reclaimed or moved
1532 by the page migration subsystem. This means that
1533 HugeTLB pages may not be allocated from this zone.
1534 Note that allocations like PTEs-from-HighMem still
1535 use the HighMem zone if it exists, and the Normal
1536 zone if it does not.
1538 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1539 Format: <Controller#>[,poll interval]
1540 The controller # is the number of the ehci usb debug
1541 port as it is probed via PCI. The poll interval is
1542 optional and is the number seconds in between
1543 each poll cycle to the debug port in case you need
1544 the functionality for interrupting the kernel with
1545 gdb or control-c on the dbgp connection. When
1546 not using this parameter you use sysrq-g to break into
1547 the kernel debugger.
1549 kgdboc= [KGDB,HW] kgdb over consoles.
1550 Requires a tty driver that supports console polling,
1551 or a supported polling keyboard driver (non-usb).
1552 Serial only format: <serial_device>[,baud]
1553 keyboard only format: kbd
1554 keyboard and serial format: kbd,<serial_device>[,baud]
1555 Optional Kernel mode setting:
1556 kms, kbd format: kms,kbd
1557 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1559 kgdbwait [KGDB] Stop kernel execution and enter the
1560 kernel debugger at the earliest opportunity.
1562 kmac= [MIPS] korina ethernet MAC address.
1563 Configure the RouterBoard 532 series on-chip
1564 Ethernet adapter MAC address.
1566 kmemleak= [KNL] Boot-time kmemleak enable/disable
1567 Valid arguments: on, off
1570 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1571 Valid arguments: 0, 1, 2
1572 kmemcheck=0 (disabled)
1573 kmemcheck=1 (enabled)
1574 kmemcheck=2 (one-shot mode)
1575 Default: 2 (one-shot mode)
1577 kstack=N [X86] Print N words from the kernel stack
1580 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1581 Default is 0 (don't ignore, but inject #GP)
1583 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1587 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1588 Default is 1 (enabled)
1590 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1592 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1594 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1595 (virtualized MMU) support on capable Intel chips.
1596 Default is 1 (enabled)
1598 kvm-intel.emulate_invalid_guest_state=
1599 [KVM,Intel] Enable emulation of invalid guest states
1600 Default is 0 (disabled)
1602 kvm-intel.flexpriority=
1603 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1604 Default is 1 (enabled)
1607 [KVM,Intel] Enable VMX nesting (nVMX).
1608 Default is 0 (disabled)
1610 kvm-intel.unrestricted_guest=
1611 [KVM,Intel] Disable unrestricted guest feature
1612 (virtualized real and unpaged mode) on capable
1613 Intel chips. Default is 1 (enabled)
1615 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1616 feature (tagged TLBs) on capable Intel chips.
1617 Default is 1 (enabled)
1623 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1626 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1627 value for LAPIC timer one-shot implementation. Default
1628 back to the programmable timer unit in the LAPIC.
1630 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1633 libata.dma= [LIBATA] DMA control
1634 libata.dma=0 Disable all PATA and SATA DMA
1635 libata.dma=1 PATA and SATA Disk DMA only
1636 libata.dma=2 ATAPI (CDROM) DMA only
1637 libata.dma=4 Compact Flash DMA only
1638 Combinations also work, so libata.dma=3 enables DMA
1639 for disks and CDROMs, but not CFs.
1641 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1642 libata.ignore_hpa=0 keep BIOS limits (default)
1643 libata.ignore_hpa=1 ignore limits, using full disk
1645 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1649 libata.force= [LIBATA] Force configurations. The format is comma
1650 separated list of "[ID:]VAL" where ID is
1651 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1652 matching port, link or device. Basically, it matches
1653 the ATA ID string printed on console by libata. If
1654 the whole ID part is omitted, the last PORT and DEVICE
1655 values are used. If ID hasn't been specified yet, the
1656 configuration applies to all ports, links and devices.
1658 If only DEVICE is omitted, the parameter applies to
1659 the port and all links and devices behind it. DEVICE
1660 number of 0 either selects the first device or the
1661 first fan-out link behind PMP device. It does not
1662 select the host link. DEVICE number of 15 selects the
1663 host link and device attached to it.
1665 The VAL specifies the configuration to force. As long
1666 as there's no ambiguity shortcut notation is allowed.
1667 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1668 The following configurations can be forced.
1670 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1671 Any ID with matching PORT is used.
1673 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1675 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1676 udma[/][16,25,33,44,66,100,133] notation is also
1679 * [no]ncq: Turn on or off NCQ.
1681 * nohrst, nosrst, norst: suppress hard, soft
1684 * rstonce: only attempt one reset during
1685 hot-unplug link recovery
1687 * dump_id: dump IDENTIFY data.
1689 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1691 * disable: Disable this device.
1693 If there are multiple matching configurations changing
1694 the same attribute, the last one is used.
1696 memblock=debug [KNL] Enable memblock debug messages.
1698 load_ramdisk= [RAM] List of ramdisks to load from floppy
1699 See Documentation/blockdev/ramdisk.txt.
1701 lockd.nlm_grace_period=P [NFS] Assign grace period.
1704 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1707 lockd.nlm_timeout=T [NFS] Assign timeout value.
1710 lockd.nlm_udpport=M [NFS] Assign UDP port.
1713 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1716 loglevel= All Kernel Messages with a loglevel smaller than the
1717 console loglevel will be printed to the console. It can
1718 also be changed with klogd or other programs. The
1719 loglevels are defined as follows:
1721 0 (KERN_EMERG) system is unusable
1722 1 (KERN_ALERT) action must be taken immediately
1723 2 (KERN_CRIT) critical conditions
1724 3 (KERN_ERR) error conditions
1725 4 (KERN_WARNING) warning conditions
1726 5 (KERN_NOTICE) normal but significant condition
1727 6 (KERN_INFO) informational
1728 7 (KERN_DEBUG) debug-level messages
1730 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1731 in bytes. n must be a power of two and greater
1732 than the minimal size. The minimal size is defined
1733 by LOG_BUF_SHIFT kernel config parameter. There is
1734 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1735 that allows to increase the default size depending on
1736 the number of CPUs. See init/Kconfig for more details.
1738 logo.nologo [FB] Disables display of the built-in Linux logo.
1739 This may be used to provide more screen space for
1740 kernel log messages and is useful when debugging
1741 kernel boot problems.
1743 lp=0 [LP] Specify parallel ports to use, e.g,
1744 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1745 lp=reset first parallel port). 'lp=0' disables the
1746 lp=auto printer driver. 'lp=reset' (which can be
1747 specified in addition to the ports) causes
1748 attached printers to be reset. Using
1749 lp=port1,port2,... specifies the parallel ports
1750 to associate lp devices with, starting with
1751 lp0. A port specification may be 'none' to skip
1752 that lp device, or a parport name such as
1753 'parport0'. Specifying 'lp=auto' instead of a
1754 port specification list means that device IDs
1755 from each port should be examined, to see if
1756 an IEEE 1284-compliant printer is attached; if
1757 so, the driver will manage that printer.
1758 See also header of drivers/char/lp.c.
1761 Sets loops_per_jiffy to given constant, thus avoiding
1762 time-consuming boot-time autodetection (up to 250 ms per
1763 CPU). 0 enables autodetection (default). To determine
1764 the correct value for your kernel, boot with normal
1765 autodetection and see what value is printed. Note that
1766 on SMP systems the preset will be applied to all CPUs,
1767 which is likely to cause problems if your CPUs need
1768 significantly divergent settings. An incorrect value
1769 will cause delays in the kernel to be wrong, leading to
1770 unpredictable I/O errors and other breakage. Although
1771 unlikely, in the extreme case this might damage your
1775 Format: <io>,<irq>,<dma>
1777 machvec= [IA-64] Force the use of a particular machine-vector
1778 (machvec) in a generic kernel.
1779 Example: machvec=hpzx1_swiotlb
1781 machtype= [Loongson] Share the same kernel image file between different
1783 Example: machtype=lemote-yeeloong-2f-7inch
1785 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1786 than or equal to this physical address is ignored.
1788 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1789 should make use of. maxcpus=n : n >= 0 limits the
1790 kernel to using 'n' processors. n=0 is a special case,
1791 it is equivalent to "nosmp", which also disables
1794 max_loop= [LOOP] The number of loop block devices that get
1795 (loop.max_loop) unconditionally pre-created at init time. The default
1796 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1797 of statically allocating a predefined number, loop
1798 devices can be requested on-demand with the
1799 /dev/loop-control interface.
1801 mce [X86-32] Machine Check Exception
1803 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1805 md= [HW] RAID subsystems devices and level
1806 See Documentation/md.txt.
1809 Format: <first>,<last>
1810 Specifies range of consoles to be captured by the MDA.
1812 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1813 Amount of memory to be used when the kernel is not able
1814 to see the whole system memory or for test.
1815 [X86] Work as limiting max address. Use together
1816 with memmap= to avoid physical address space collisions.
1817 Without memmap= PCI devices could be placed at addresses
1818 belonging to unused RAM.
1820 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1824 [KNL,SH] Allow user to override the default size for
1825 per-device physically contiguous DMA buffers.
1827 memmap=exactmap [KNL,X86] Enable setting of an exact
1828 E820 memory map, as specified by the user.
1829 Such memmap=exactmap lines can be constructed based on
1830 BIOS output or other requirements. See the memmap=nn@ss
1833 memmap=nn[KMG]@ss[KMG]
1834 [KNL] Force usage of a specific region of memory.
1835 Region of memory to be used is from ss to ss+nn.
1837 memmap=nn[KMG]#ss[KMG]
1838 [KNL,ACPI] Mark specific memory as ACPI data.
1839 Region of memory to be marked is from ss to ss+nn.
1841 memmap=nn[KMG]$ss[KMG]
1842 [KNL,ACPI] Mark specific memory as reserved.
1843 Region of memory to be reserved is from ss to ss+nn.
1844 Example: Exclude memory from 0x18690000-0x1869ffff
1845 memmap=64K$0x18690000
1847 memmap=0x10000$0x18690000
1849 memory_corruption_check=0/1 [X86]
1850 Some BIOSes seem to corrupt the first 64k of
1851 memory when doing things like suspend/resume.
1852 Setting this option will scan the memory
1853 looking for corruption. Enabling this will
1854 both detect corruption and prevent the kernel
1855 from using the memory being corrupted.
1856 However, its intended as a diagnostic tool; if
1857 repeatable BIOS-originated corruption always
1858 affects the same memory, you can use memmap=
1859 to prevent the kernel from using that memory.
1861 memory_corruption_check_size=size [X86]
1862 By default it checks for corruption in the low
1863 64k, making this memory unavailable for normal
1864 use. Use this parameter to scan for
1865 corruption in more or less memory.
1867 memory_corruption_check_period=seconds [X86]
1868 By default it checks for corruption every 60
1869 seconds. Use this parameter to check at some
1870 other rate. 0 disables periodic checking.
1872 memtest= [KNL,X86] Enable memtest
1874 default : 0 <disable>
1875 Specifies the number of memtest passes to be
1876 performed. Each pass selects another test
1877 pattern from a given set of patterns. Memtest
1878 fills the memory with this pattern, validates
1879 memory contents and reserves bad memory
1880 regions that are detected.
1882 meye.*= [HW] Set MotionEye Camera parameters
1883 See Documentation/video4linux/meye.txt.
1885 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1886 Multi-Function General Purpose Timers on AMD Geode
1889 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1890 the BIOS has incorrectly applied a workaround. TinyBIOS
1891 version 0.98 is known to be affected, 0.99 fixes the
1892 problem by letting the user disable the workaround.
1896 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1897 physical address is ignored.
1899 mini2440= [ARM,HW,KNL]
1900 Format:[0..2][b][c][t]
1902 MINI2440 configuration specification:
1903 0 - The attached screen is the 3.5" TFT
1904 1 - The attached screen is the 7" TFT
1905 2 - The VGA Shield is attached (1024x768)
1906 Leaving out the screen size parameter will not load
1907 the TFT driver, and the framebuffer will be left
1909 b - Enable backlight. The TFT backlight pin will be
1910 linked to the kernel VESA blanking code and a GPIO
1911 LED. This parameter is not necessary when using the
1913 c - Enable the s3c camera interface.
1914 t - Reserved for enabling touchscreen support. The
1915 touchscreen support is not enabled in the mainstream
1916 kernel as of 2.6.30, a preliminary port can be found
1917 in the "bleeding edge" mini2440 support kernel at
1918 http://repo.or.cz/w/linux-2.6/mini2440.git
1921 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1922 parameter allows control of the logging verbosity for
1923 the additional memory initialisation checks. A value
1924 of 0 disables mminit logging and a level of 4 will
1925 log everything. Information is printed at KERN_DEBUG
1926 so loglevel=8 may also need to be specified.
1929 [KNL] When CONFIG_MODULE_SIG is set, this means that
1930 modules without (valid) signatures will fail to load.
1931 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1932 is always true, so this option does nothing.
1935 [MOUSE] Maximum time between finger touching and
1936 leaving touchpad surface for touch to be considered
1937 a tap and be reported as a left button click (for
1938 touchpads working in absolute mode only).
1940 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1941 reporting absolute coordinates, such as tablets
1942 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1943 reporting absolute coordinates, such as tablets
1945 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1946 is similar to kernelcore except it specifies the
1947 amount of memory used for migratable allocations.
1948 If both kernelcore and movablecore is specified,
1949 then kernelcore will be at *least* the specified
1950 value but may be more. If movablecore on its own
1951 is specified, the administrator must be careful
1952 that the amount of memory usable for all allocations
1955 movable_node [KNL,X86] Boot-time switch to enable the effects
1956 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
1958 MTD_Partition= [MTD]
1959 Format: <name>,<region-number>,<size>,<offset>
1961 MTD_Region= [MTD] Format:
1962 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1965 See drivers/mtd/cmdlinepart.c.
1967 multitce=off [PPC] This parameter disables the use of the pSeries
1968 firmware feature for updating multiple TCE entries
1971 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1973 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1975 boundary - index of last SLC block on Flex-OneNAND.
1976 The remaining blocks are configured as MLC blocks.
1977 lock - Configure if Flex-OneNAND boundary should be locked.
1978 Once locked, the boundary cannot be changed.
1979 1 indicates lock status, 0 indicates unlock status.
1982 ARM/S3C2412 JIVE boot control
1984 See arch/arm/mach-s3c2412/mach-jive.c
1986 mtouchusb.raw_coordinates=
1987 [HW] Make the MicroTouch USB driver use raw coordinates
1988 ('y', default) or cooked coordinates ('n')
1990 mtrr_chunk_size=nn[KMG] [X86]
1991 used for mtrr cleanup. It is largest continuous chunk
1992 that could hold holes aka. UC entries.
1994 mtrr_gran_size=nn[KMG] [X86]
1995 Used for mtrr cleanup. It is granularity of mtrr block.
1997 Large value could prevent small alignment from
2000 mtrr_spare_reg_nr=n [X86]
2002 Range: 0,7 : spare reg number
2004 Used for mtrr cleanup. It is spare mtrr entries number.
2005 Set to 2 or more if your graphical card needs more.
2007 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2009 netdev= [NET] Network devices parameters
2010 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2011 Note that mem_start is often overloaded to mean
2012 something different and driver-specific.
2013 This usage is only documented in each driver source
2017 [NETFILTER] Enable connection tracking flow accounting
2018 0 to disable accounting
2019 1 to enable accounting
2022 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2023 See Documentation/filesystems/nfs/nfsroot.txt.
2025 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2026 See Documentation/filesystems/nfs/nfsroot.txt.
2028 nfsrootdebug [NFS] enable nfsroot debugging messages.
2029 See Documentation/filesystems/nfs/nfsroot.txt.
2031 nfs.callback_tcpport=
2032 [NFS] set the TCP port on which the NFSv4 callback
2033 channel should listen.
2036 [NFS] sets the pathname to the program which is used
2037 to update the NFS client cache entries.
2039 nfs.cache_getent_timeout=
2040 [NFS] sets the timeout after which an attempt to
2041 update a cache entry is deemed to have failed.
2043 nfs.idmap_cache_timeout=
2044 [NFS] set the maximum lifetime for idmapper cache
2048 [NFS] enable 64-bit inode numbers.
2049 If zero, the NFS client will fake up a 32-bit inode
2050 number for the readdir() and stat() syscalls instead
2051 of returning the full 64-bit number.
2052 The default is to return 64-bit inode numbers.
2054 nfs.max_session_slots=
2055 [NFSv4.1] Sets the maximum number of session slots
2056 the client will attempt to negotiate with the server.
2057 This limits the number of simultaneous RPC requests
2058 that the client can send to the NFSv4.1 server.
2059 Note that there is little point in setting this
2060 value higher than the max_tcp_slot_table_limit.
2062 nfs.nfs4_disable_idmapping=
2063 [NFSv4] When set to the default of '1', this option
2064 ensures that both the RPC level authentication
2065 scheme and the NFS level operations agree to use
2066 numeric uids/gids if the mount is using the
2067 'sec=sys' security flavour. In effect it is
2068 disabling idmapping, which can make migration from
2069 legacy NFSv2/v3 systems to NFSv4 easier.
2070 Servers that do not support this mode of operation
2071 will be autodetected by the client, and it will fall
2072 back to using the idmapper.
2073 To turn off this behaviour, set the value to '0'.
2075 [NFS4] Specify an additional fixed unique ident-
2076 ification string that NFSv4 clients can insert into
2077 their nfs_client_id4 string. This is typically a
2078 UUID that is generated at system install time.
2080 nfs.send_implementation_id =
2081 [NFSv4.1] Send client implementation identification
2082 information in exchange_id requests.
2083 If zero, no implementation identification information
2085 The default is to send the implementation identification
2088 nfs.recover_lost_locks =
2089 [NFSv4] Attempt to recover locks that were lost due
2090 to a lease timeout on the server. Please note that
2091 doing this risks data corruption, since there are
2092 no guarantees that the file will remain unchanged
2093 after the locks are lost.
2094 If you want to enable the kernel legacy behaviour of
2095 attempting to recover these locks, then set this
2097 The default parameter value of '0' causes the kernel
2098 not to attempt recovery of lost locks.
2100 nfsd.nfs4_disable_idmapping=
2101 [NFSv4] When set to the default of '1', the NFSv4
2102 server will return only numeric uids and gids to
2103 clients using auth_sys, and will accept numeric uids
2104 and gids from such clients. This is intended to ease
2105 migration from NFSv2/v3.
2107 objlayoutdriver.osd_login_prog=
2108 [NFS] [OBJLAYOUT] sets the pathname to the program which
2109 is used to automatically discover and login into new
2110 osd-targets. Please see:
2111 Documentation/filesystems/pnfs.txt for more explanations
2113 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2114 when a NMI is triggered.
2115 Format: [state][,regs][,debounce][,die]
2117 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2118 Format: [panic,][nopanic,][num]
2120 0 - turn nmi_watchdog off
2121 When panic is specified, panic when an NMI watchdog
2122 timeout occurs (or 'nopanic' to override the opposite
2124 This is useful when you use a panic=... timeout and
2125 need the box quickly up again.
2127 netpoll.carrier_timeout=
2128 [NET] Specifies amount of time (in seconds) that
2129 netpoll should wait for a carrier. By default netpoll
2132 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2133 emulation library even if a 387 maths coprocessor
2137 [HW] Never suspend the console
2138 Disable suspending of consoles during suspend and
2139 hibernate operations. Once disabled, debugging
2140 messages can reach various consoles while the rest
2141 of the system is being put to sleep (ie, while
2142 debugging driver suspend/resume hooks). This may
2143 not work reliably with all consoles, but is known
2144 to work with serial and VGA consoles.
2145 To facilitate more flexible debugging, we also add
2146 console_suspend, a printk module parameter to control
2147 it. Users could use console_suspend (usually
2148 /sys/module/printk/parameters/console_suspend) to
2149 turn on/off it dynamically.
2151 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2152 caches in the slab allocator. Saves per-node memory,
2153 but will impact performance.
2157 noapic [SMP,APIC] Tells the kernel to not make use of any
2158 IOAPICs that may be present in the system.
2160 noautogroup Disable scheduler automatic task group creation.
2162 nobats [PPC] Do not use BATs for mapping kernel lowmem
2163 on "Classic" PPC cores.
2167 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2169 nodelayacct [KNL] Disable per-task delay accounting
2171 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2173 nodsp [SH] Disable hardware DSP at boot time.
2175 noefi [X86] Disable EFI runtime services support.
2180 On X86-32 available only on PAE configured kernels.
2181 noexec=on: enable non-executable mappings (default)
2182 noexec=off: disable non-executable mappings
2185 Disable SMAP (Supervisor Mode Access Prevention)
2186 even if it is supported by processor.
2189 Disable SMEP (Supervisor Mode Execution Prevention)
2190 even if it is supported by processor.
2193 This affects only 32-bit executables.
2194 noexec32=on: enable non-executable mappings (default)
2195 read doesn't imply executable mappings
2196 noexec32=off: disable non-executable mappings
2197 read implies executable mappings
2199 nofpu [SH] Disable hardware FPU at boot time.
2201 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2202 register save and restore. The kernel will only save
2203 legacy floating-point registers on task switch.
2205 noxsave [BUGS=X86] Disables x86 extended register state save
2206 and restore using xsave. The kernel will fallback to
2207 enabling legacy floating-point and sse state.
2209 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2210 register states. The kernel will fall back to use
2211 xsave to save the states. By using this parameter,
2212 performance of saving the states is degraded because
2213 xsave doesn't support modified optimization while
2214 xsaveopt supports it on xsaveopt enabled systems.
2216 noxsaves [X86] Disables xsaves and xrstors used in saving and
2217 restoring x86 extended register state in compacted
2218 form of xsave area. The kernel will fall back to use
2219 xsaveopt and xrstor to save and restore the states
2220 in standard form of xsave area. By using this
2221 parameter, xsave area per process might occupy more
2222 memory on xsaves enabled systems.
2225 on enable eager fpu restore
2226 off disable eager fpu restore
2227 auto selects the default scheme, which automatically
2228 enables eagerfpu restore for xsaveopt.
2230 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2231 wfi(ARM) instruction doesn't work correctly and not to
2232 use it. This is also useful when using JTAG debugger.
2234 no_file_caps Tells the kernel not to honor file capabilities. The
2235 only way then for a file to be executed with privilege
2236 is to be setuid root or executed by root.
2238 nohalt [IA-64] Tells the kernel not to use the power saving
2239 function PAL_HALT_LIGHT when idle. This increases
2240 power-consumption. On the positive side, it reduces
2241 interrupt wake-up latency, which may improve performance
2242 in certain environments such as networked servers or
2245 nohibernate [HIBERNATION] Disable hibernation and resume.
2247 nohz= [KNL] Boottime enable/disable dynamic ticks
2248 Valid arguments: on, off
2251 nohz_full= [KNL,BOOT]
2252 In kernels built with CONFIG_NO_HZ_FULL=y, set
2253 the specified list of CPUs whose tick will be stopped
2254 whenever possible. The boot CPU will be forced outside
2255 the range to maintain the timekeeping.
2256 The CPUs in this range must also be included in the
2259 noiotrap [SH] Disables trapped I/O port accesses.
2261 noirqdebug [X86-32] Disables the code which attempts to detect and
2262 disable unhandled interrupt sources.
2264 no_timer_check [X86,APIC] Disables the code which tests for
2265 broken timer IRQ sources.
2267 noisapnp [ISAPNP] Disables ISA PnP code.
2269 noinitrd [RAM] Tells the kernel not to load any configured
2272 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2274 [Deprecated - use intremap=off]
2278 nojitter [IA-64] Disables jitter checking for ITC timers.
2280 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2282 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2285 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2286 steal time is computed, but won't influence scheduler
2289 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2291 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2293 noltlbs [PPC] Do not use large page/tlb entries for kernel
2294 lowmem mapping on PPC40x.
2296 nomca [IA-64] Disable machine check abort handling
2298 nomce [X86-32] Machine Check Exception
2300 nomfgpt [X86-32] Disable Multi-Function General Purpose
2301 Timer usage (for AMD Geode machines).
2303 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2304 shutdown the other cpus. Instead use the REBOOT_VECTOR
2307 nomodule Disable module load
2309 nopat [X86] Disable PAT (page attribute table extension of
2310 pagetables) support.
2312 norandmaps Don't use address space randomization. Equivalent to
2313 echo 0 > /proc/sys/kernel/randomize_va_space
2315 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2317 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2318 with UP alternatives
2320 nordrand [X86] Disable kernel use of the RDRAND and
2321 RDSEED instructions even if they are supported
2322 by the processor. RDRAND and RDSEED are still
2323 available to user space applications.
2325 noresume [SWSUSP] Disables resume and restores original swap
2328 no-scroll [VGA] Disables scrollback.
2329 This is required for the Braillex ib80-piezo Braille
2330 reader made by F.H. Papenmeier (Germany).
2334 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2336 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2337 and disable the IO APIC. legacy for "maxcpus=0".
2339 nosoftlockup [KNL] Disable the soft-lockup detector.
2341 nosync [HW,M68K] Disables sync negotiation for all devices.
2343 notsc [BUGS=X86-32] Disable Time Stamp Counter
2345 nousb [USB] Disable the USB subsystem
2347 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2351 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2353 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2354 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2355 Some features depend on CPU0. Known dependencies are:
2356 1. Resume from suspend/hibernate depends on CPU0.
2357 Suspend/hibernate will fail if CPU0 is offline and you
2358 need to online CPU0 before suspend/hibernate.
2359 2. PIC interrupts also depend on CPU0. CPU0 can't be
2360 removed if a PIC interrupt is detected.
2361 It's said poweroff/reboot may depend on CPU0 on some
2362 machines although I haven't seen such issues so far
2363 after CPU0 is offline on a few tested machines.
2364 If the dependencies are under your control, you can
2365 turn on cpu0_hotplug.
2367 nptcg= [IA-64] Override max number of concurrent global TLB
2368 purges which is reported from either PAL_VM_SUMMARY or
2371 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2372 could support. nr_cpus=n : n >= 1 limits the kernel to
2373 supporting 'n' processors. Later in runtime you can not
2374 use hotplug cpu feature to put more cpu back to online.
2375 just like you compile the kernel NR_CPUS=n
2377 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2379 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2380 Allowed values are enable and disable
2382 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2383 one of ['zone', 'node', 'default'] can be specified
2384 This can be set from sysctl after boot.
2385 See Documentation/sysctl/vm.txt for details.
2387 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2388 See Documentation/debugging-via-ohci1394.txt for more
2391 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2392 Rather than timing out after 20 ms if an EC
2393 command is not properly ACKed, override the length
2394 of the timeout. We have interrupts disabled while
2395 waiting for the ACK, so if this is set too high
2396 interrupts *may* be lost!
2398 omap_mux= [OMAP] Override bootloader pin multiplexing.
2399 Format: <mux_mode0.mode_name=value>...
2400 For example, to override I2C bus2:
2401 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2403 oprofile.timer= [HW]
2404 Use timer interrupt instead of performance counters
2406 oprofile.cpu_type= Force an oprofile cpu type
2407 This might be useful if you have an older oprofile
2408 userland or if you want common events.
2409 Format: { arch_perfmon }
2410 arch_perfmon: [X86] Force use of architectural
2411 perfmon on Intel CPUs instead of the
2412 CPU specific event set.
2413 timer: [X86] Force use of architectural NMI
2414 timer mode (see also oprofile.timer
2415 for generic hr timer mode)
2416 [s390] Force legacy basic mode sampling
2417 (report cpu_type "timer")
2419 oops=panic Always panic on oopses. Default is to just kill the
2420 process, but there is a small probability of
2421 deadlocking the machine.
2422 This will also cause panics on machine check exceptions.
2423 Useful together with panic=30 to trigger a reboot.
2426 See Documentation/sound/oss/oss-parameters.txt
2428 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2429 timeout > 0: seconds before rebooting
2430 timeout = 0: wait forever
2431 timeout < 0: reboot immediately
2434 crash_kexec_post_notifiers
2435 Run kdump after running panic-notifiers and dumping
2436 kmsg. This only for the users who doubt kdump always
2437 succeeds in any situation.
2438 Note that this also increases risks of kdump failure,
2439 because some panic notifiers can make the crashed
2440 kernel more unstable.
2442 parkbd.port= [HW] Parallel port number the keyboard adapter is
2443 connected to, default is 0.
2445 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2446 0 for XT, 1 for AT (default is AT).
2449 parport= [HW,PPT] Specify parallel ports. 0 disables.
2450 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2451 Use 'auto' to force the driver to use any
2452 IRQ/DMA settings detected (the default is to
2453 ignore detected IRQ/DMA settings because of
2454 possible conflicts). You can specify the base
2455 address, IRQ, and DMA settings; IRQ and DMA
2456 should be numbers, or 'auto' (for using detected
2457 settings on that particular port), or 'nofifo'
2458 (to avoid using a FIFO even if it is detected).
2459 Parallel ports are assigned in the order they
2460 are specified on the command line, starting
2463 parport_init_mode= [HW,PPT]
2464 Configure VIA parallel port to operate in
2465 a specific mode. This is necessary on Pegasos
2466 computer where firmware has no options for setting
2467 up parallel port mode and sets it to spp.
2468 Currently this function knows 686a and 8231 chips.
2469 Format: [spp|ps2|epp|ecp|ecpepp]
2472 Halt all CPUs after the first oops has been printed for
2473 the specified number of seconds. This is to be used if
2474 your oopses keep scrolling off the screen.
2479 See header of drivers/block/paride/pcd.c.
2480 See also Documentation/blockdev/paride.txt.
2482 pci=option[,option...] [PCI] various PCI subsystem options:
2483 earlydump [X86] dump PCI config space before the kernel
2485 off [X86] don't probe for the PCI bus
2486 bios [X86-32] force use of PCI BIOS, don't access
2487 the hardware directly. Use this if your machine
2488 has a non-standard PCI host bridge.
2489 nobios [X86-32] disallow use of PCI BIOS, only direct
2490 hardware access methods are allowed. Use this
2491 if you experience crashes upon bootup and you
2492 suspect they are caused by the BIOS.
2493 conf1 [X86] Force use of PCI Configuration
2495 conf2 [X86] Force use of PCI Configuration
2497 noaer [PCIE] If the PCIEAER kernel config parameter is
2498 enabled, this kernel boot option can be used to
2499 disable the use of PCIE advanced error reporting.
2500 nodomains [PCI] Disable support for multiple PCI
2501 root domains (aka PCI segments, in ACPI-speak).
2502 nommconf [X86] Disable use of MMCONFIG for PCI
2504 check_enable_amd_mmconf [X86] check for and enable
2505 properly configured MMIO access to PCI
2506 config space on AMD family 10h CPU
2507 nomsi [MSI] If the PCI_MSI kernel config parameter is
2508 enabled, this kernel boot option can be used to
2509 disable the use of MSI interrupts system-wide.
2510 noioapicquirk [APIC] Disable all boot interrupt quirks.
2511 Safety option to keep boot IRQs enabled. This
2512 should never be necessary.
2513 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2514 primary IO-APIC for bridges that cannot disable
2515 boot IRQs. This fixes a source of spurious IRQs
2516 when the system masks IRQs.
2517 noioapicreroute [APIC] Disable workaround that uses the
2518 boot IRQ equivalent of an IRQ that connects to
2519 a chipset where boot IRQs cannot be disabled.
2520 The opposite of ioapicreroute.
2521 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2522 routing table. These calls are known to be buggy
2523 on several machines and they hang the machine
2524 when used, but on other computers it's the only
2525 way to get the interrupt routing table. Try
2526 this option if the kernel is unable to allocate
2527 IRQs or discover secondary PCI buses on your
2529 rom [X86] Assign address space to expansion ROMs.
2530 Use with caution as certain devices share
2531 address decoders between ROMs and other
2533 norom [X86] Do not assign address space to
2534 expansion ROMs that do not already have
2535 BIOS assigned address ranges.
2536 nobar [X86] Do not assign address space to the
2537 BARs that weren't assigned by the BIOS.
2538 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2539 assigned automatically to PCI devices. You can
2540 make the kernel exclude IRQs of your ISA cards
2542 pirqaddr=0xAAAAA [X86] Specify the physical address
2543 of the PIRQ table (normally generated
2544 by the BIOS) if it is outside the
2545 F0000h-100000h range.
2546 lastbus=N [X86] Scan all buses thru bus #N. Can be
2547 useful if the kernel is unable to find your
2548 secondary buses and you want to tell it
2549 explicitly which ones they are.
2550 assign-busses [X86] Always assign all PCI bus
2551 numbers ourselves, overriding
2552 whatever the firmware may have done.
2553 usepirqmask [X86] Honor the possible IRQ mask stored
2554 in the BIOS $PIR table. This is needed on
2555 some systems with broken BIOSes, notably
2556 some HP Pavilion N5400 and Omnibook XE3
2557 notebooks. This will have no effect if ACPI
2558 IRQ routing is enabled.
2559 noacpi [X86] Do not use ACPI for IRQ routing
2560 or for PCI scanning.
2561 use_crs [X86] Use PCI host bridge window information
2562 from ACPI. On BIOSes from 2008 or later, this
2563 is enabled by default. If you need to use this,
2564 please report a bug.
2565 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2566 If you need to use this, please report a bug.
2567 routeirq Do IRQ routing for all PCI devices.
2568 This is normally done in pci_enable_device(),
2569 so this option is a temporary workaround
2570 for broken drivers that don't call it.
2571 skip_isa_align [X86] do not align io start addr, so can
2572 handle more pci cards
2573 firmware [ARM] Do not re-enumerate the bus but instead
2574 just use the configuration from the
2575 bootloader. This is currently used on
2576 IXP2000 systems where the bus has to be
2577 configured a certain way for adjunct CPUs.
2578 noearly [X86] Don't do any early type 1 scanning.
2579 This might help on some broken boards which
2580 machine check when some devices' config space
2581 is read. But various workarounds are disabled
2582 and some IOMMU drivers will not work.
2583 bfsort Sort PCI devices into breadth-first order.
2584 This sorting is done to get a device
2585 order compatible with older (<= 2.4) kernels.
2586 nobfsort Don't sort PCI devices into breadth-first order.
2587 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2588 tuning and use the BIOS-configured MPS defaults.
2589 pcie_bus_safe Set every device's MPS to the largest value
2590 supported by all devices below the root complex.
2591 pcie_bus_perf Set device MPS to the largest allowable MPS
2592 based on its parent bus. Also set MRRS (Max
2593 Read Request Size) to the largest supported
2594 value (no larger than the MPS that the device
2595 or bus can support) for best performance.
2596 pcie_bus_peer2peer Set every device's MPS to 128B, which
2597 every device is guaranteed to support. This
2598 configuration allows peer-to-peer DMA between
2599 any pair of devices, possibly at the cost of
2600 reduced performance. This also guarantees
2601 that hot-added devices will work.
2602 cbiosize=nn[KMG] The fixed amount of bus space which is
2603 reserved for the CardBus bridge's IO window.
2604 The default value is 256 bytes.
2605 cbmemsize=nn[KMG] The fixed amount of bus space which is
2606 reserved for the CardBus bridge's memory
2607 window. The default value is 64 megabytes.
2610 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2611 Specifies alignment and device to reassign
2612 aligned memory resources.
2613 If <order of align> is not specified,
2614 PAGE_SIZE is used as alignment.
2615 PCI-PCI bridge can be specified, if resource
2616 windows need to be expanded.
2617 ecrc= Enable/disable PCIe ECRC (transaction layer
2618 end-to-end CRC checking).
2619 bios: Use BIOS/firmware settings. This is the
2623 hpiosize=nn[KMG] The fixed amount of bus space which is
2624 reserved for hotplug bridge's IO window.
2625 Default size is 256 bytes.
2626 hpmemsize=nn[KMG] The fixed amount of bus space which is
2627 reserved for hotplug bridge's memory window.
2628 Default size is 2 megabytes.
2629 realloc= Enable/disable reallocating PCI bridge resources
2630 if allocations done by BIOS are too small to
2631 accommodate resources required by all child
2633 off: Turn realloc off
2635 realloc same as realloc=on
2636 noari do not use PCIe ARI.
2637 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2638 only look for one device below a PCIe downstream
2641 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2644 force Enable ASPM even on devices that claim not to support it.
2645 WARNING: Forcing ASPM on may cause system lockups.
2647 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2648 nomsi Do not use MSI for PCI Express Native Hotplug (this
2649 makes all PCIe ports use INTx for hotplug services).
2651 pcie_ports= [PCIE] PCIe ports handling:
2652 auto Ask the BIOS whether or not to use native PCIe services
2653 associated with PCIe ports (PME, hot-plug, AER). Use
2654 them only if that is allowed by the BIOS.
2655 native Use native PCIe services associated with PCIe ports
2657 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2660 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2661 nomsi Do not use MSI for native PCIe PME signaling (this makes
2662 all PCIe root ports use INTx for all services).
2664 pcmv= [HW,PCMCIA] BadgePAD 4
2668 Keep all power-domains already enabled by bootloader on,
2669 even if no driver has claimed them. This is useful
2670 for debug and development, but should not be
2671 needed on a platform with proper driver support.
2674 See Documentation/blockdev/paride.txt.
2676 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2679 See arch/parisc/kernel/pdc_chassis.c
2681 percpu_alloc= Select which percpu first chunk allocator to use.
2682 Currently supported values are "embed" and "page".
2683 Archs may support subset or none of the selections.
2684 See comments in mm/percpu.c for details on each
2685 allocator. This parameter is primarily for debugging
2686 and performance comparison.
2689 See Documentation/blockdev/paride.txt.
2692 See Documentation/blockdev/paride.txt.
2694 pirq= [SMP,APIC] Manual mp-table setup
2695 See Documentation/x86/i386/IO-APIC.txt.
2697 plip= [PPT,NET] Parallel port network link
2698 Format: { parport<nr> | timid | 0 }
2699 See also Documentation/parport.txt.
2701 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2702 Override pmtimer IOPort with a hex value.
2706 Enable PNP debug messages (depends on the
2707 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2708 via /sys/module/pnp/parameters/debug. We always show
2709 current resource usage; turning this on also shows
2710 possible settings and some assignment information.
2716 { on | off | curr | res | no-curr | no-res }
2719 [ISAPNP] Exclude IRQs for the autoconfiguration
2722 [ISAPNP] Exclude DMAs for the autoconfiguration
2724 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2725 Ranges are in pairs (I/O port base and size).
2728 [ISAPNP] Exclude memory regions for the
2730 Ranges are in pairs (memory base and size).
2732 ports= [IP_VS_FTP] IPVS ftp helper module
2734 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2736 Format: <port>,<port>....
2738 print-fatal-signals=
2739 [KNL] debug: print fatal signals
2741 If enabled, warn about various signal handling
2742 related application anomalies: too many signals,
2743 too many POSIX.1 timers, fatal signals causing a
2746 If you hit the warning due to signal overflow,
2747 you might want to try "ulimit -i unlimited".
2751 printk.always_kmsg_dump=
2752 Trigger kmsg_dump for cases other than kernel oops or
2754 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2757 printk.time= Show timing data prefixed to each printk message line
2758 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2760 processor.max_cstate= [HW,ACPI]
2761 Limit processor to maximum C-state
2762 max_cstate=9 overrides any DMI blacklist limit.
2764 processor.nocst [HW,ACPI]
2765 Ignore the _CST method to determine C-states,
2766 instead using the legacy FADT method
2768 profile= [KNL] Enable kernel profiling via /proc/profile
2769 Format: [schedule,]<number>
2770 Param: "schedule" - profile schedule points.
2771 Param: <number> - step/bucket size as a power of 2 for
2772 statistical time based profiling.
2773 Param: "sleep" - profile D-state sleeping (millisecs).
2774 Requires CONFIG_SCHEDSTATS
2775 Param: "kvm" - profile VM exits.
2777 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2779 See Documentation/blockdev/ramdisk.txt.
2781 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2782 probe for; one of (bare|imps|exps|lifebook|any).
2783 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2785 psmouse.resetafter= [HW,MOUSE]
2786 Try to reset the device after so many bad packets
2789 [HW,MOUSE] Set desired mouse resolution, in dpi.
2790 psmouse.smartscroll=
2791 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2792 0 = disabled, 1 = enabled (default).
2794 pstore.backend= Specify the name of the pstore backend to use
2797 See Documentation/blockdev/paride.txt.
2800 [KNL] Number of legacy pty's. Overwrites compiled-in
2803 quiet [KNL] Disable most log messages
2808 See Documentation/md.txt.
2810 ramdisk_blocksize= [RAM]
2811 See Documentation/blockdev/ramdisk.txt.
2813 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2814 See Documentation/blockdev/ramdisk.txt.
2817 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2818 the specified list of CPUs to be no-callback CPUs.
2819 Invocation of these CPUs' RCU callbacks will
2820 be offloaded to "rcuox/N" kthreads created for
2821 that purpose, where "x" is "b" for RCU-bh, "p"
2822 for RCU-preempt, and "s" for RCU-sched, and "N"
2823 is the CPU number. This reduces OS jitter on the
2824 offloaded CPUs, which can be useful for HPC and
2825 real-time workloads. It can also improve energy
2826 efficiency for asymmetric multiprocessors.
2829 Rather than requiring that offloaded CPUs
2830 (specified by rcu_nocbs= above) explicitly
2831 awaken the corresponding "rcuoN" kthreads,
2832 make these kthreads poll for callbacks.
2833 This improves the real-time response for the
2834 offloaded CPUs by relieving them of the need to
2835 wake up the corresponding kthread, but degrades
2836 energy efficiency by requiring that the kthreads
2837 periodically wake up to do the polling.
2839 rcutree.blimit= [KNL]
2840 Set maximum number of finished RCU callbacks to
2841 process in one batch.
2843 rcutree.rcu_fanout_leaf= [KNL]
2844 Increase the number of CPUs assigned to each
2845 leaf rcu_node structure. Useful for very large
2848 rcutree.jiffies_till_sched_qs= [KNL]
2849 Set required age in jiffies for a
2850 given grace period before RCU starts
2851 soliciting quiescent-state help from
2852 rcu_note_context_switch().
2854 rcutree.jiffies_till_first_fqs= [KNL]
2855 Set delay from grace-period initialization to
2856 first attempt to force quiescent states.
2857 Units are jiffies, minimum value is zero,
2858 and maximum value is HZ.
2860 rcutree.jiffies_till_next_fqs= [KNL]
2861 Set delay between subsequent attempts to force
2862 quiescent states. Units are jiffies, minimum
2863 value is one, and maximum value is HZ.
2865 rcutree.rcu_nocb_leader_stride= [KNL]
2866 Set the number of NOCB kthread groups, which
2867 defaults to the square root of the number of
2868 CPUs. Larger numbers reduces the wakeup overhead
2869 on the per-CPU grace-period kthreads, but increases
2870 that same overhead on each group's leader.
2872 rcutree.qhimark= [KNL]
2873 Set threshold of queued RCU callbacks beyond which
2874 batch limiting is disabled.
2876 rcutree.qlowmark= [KNL]
2877 Set threshold of queued RCU callbacks below which
2878 batch limiting is re-enabled.
2880 rcutree.rcu_idle_gp_delay= [KNL]
2881 Set wakeup interval for idle CPUs that have
2882 RCU callbacks (RCU_FAST_NO_HZ=y).
2884 rcutree.rcu_idle_lazy_gp_delay= [KNL]
2885 Set wakeup interval for idle CPUs that have
2886 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2887 Lazy RCU callbacks are those which RCU can
2888 prove do nothing more than free memory.
2890 rcutorture.fqs_duration= [KNL]
2891 Set duration of force_quiescent_state bursts.
2893 rcutorture.fqs_holdoff= [KNL]
2894 Set holdoff time within force_quiescent_state bursts.
2896 rcutorture.fqs_stutter= [KNL]
2897 Set wait time between force_quiescent_state bursts.
2899 rcutorture.gp_exp= [KNL]
2900 Use expedited update-side primitives.
2902 rcutorture.gp_normal= [KNL]
2903 Use normal (non-expedited) update-side primitives.
2904 If both gp_exp and gp_normal are set, do both.
2905 If neither gp_exp nor gp_normal are set, still
2908 rcutorture.n_barrier_cbs= [KNL]
2909 Set callbacks/threads for rcu_barrier() testing.
2911 rcutorture.nfakewriters= [KNL]
2912 Set number of concurrent RCU writers. These just
2913 stress RCU, they don't participate in the actual
2914 test, hence the "fake".
2916 rcutorture.nreaders= [KNL]
2917 Set number of RCU readers.
2919 rcutorture.object_debug= [KNL]
2920 Enable debug-object double-call_rcu() testing.
2922 rcutorture.onoff_holdoff= [KNL]
2923 Set time (s) after boot for CPU-hotplug testing.
2925 rcutorture.onoff_interval= [KNL]
2926 Set time (s) between CPU-hotplug operations, or
2927 zero to disable CPU-hotplug testing.
2929 rcutorture.rcutorture_runnable= [BOOT]
2930 Start rcutorture running at boot time.
2932 rcutorture.shuffle_interval= [KNL]
2933 Set task-shuffle interval (s). Shuffling tasks
2934 allows some CPUs to go into dyntick-idle mode
2935 during the rcutorture test.
2937 rcutorture.shutdown_secs= [KNL]
2938 Set time (s) after boot system shutdown. This
2939 is useful for hands-off automated testing.
2941 rcutorture.stall_cpu= [KNL]
2942 Duration of CPU stall (s) to test RCU CPU stall
2943 warnings, zero to disable.
2945 rcutorture.stall_cpu_holdoff= [KNL]
2946 Time to wait (s) after boot before inducing stall.
2948 rcutorture.stat_interval= [KNL]
2949 Time (s) between statistics printk()s.
2951 rcutorture.stutter= [KNL]
2952 Time (s) to stutter testing, for example, specifying
2953 five seconds causes the test to run for five seconds,
2954 wait for five seconds, and so on. This tests RCU's
2955 ability to transition abruptly to and from idle.
2957 rcutorture.test_boost= [KNL]
2958 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2959 "Maybe" means test if the RCU implementation
2960 under test support RCU priority boosting.
2962 rcutorture.test_boost_duration= [KNL]
2963 Duration (s) of each individual boost test.
2965 rcutorture.test_boost_interval= [KNL]
2966 Interval (s) between each boost test.
2968 rcutorture.test_no_idle_hz= [KNL]
2969 Test RCU's dyntick-idle handling. See also the
2970 rcutorture.shuffle_interval parameter.
2972 rcutorture.torture_type= [KNL]
2973 Specify the RCU implementation to test.
2975 rcutorture.verbose= [KNL]
2976 Enable additional printk() statements.
2978 rcupdate.rcu_expedited= [KNL]
2979 Use expedited grace-period primitives, for
2980 example, synchronize_rcu_expedited() instead
2981 of synchronize_rcu(). This reduces latency,
2982 but can increase CPU utilization, degrade
2983 real-time latency, and degrade energy efficiency.
2985 rcupdate.rcu_cpu_stall_suppress= [KNL]
2986 Suppress RCU CPU stall warning messages.
2988 rcupdate.rcu_cpu_stall_timeout= [KNL]
2989 Set timeout for RCU CPU stall warning messages.
2993 Run specified binary instead of /init from the ramdisk,
2994 used for early userspace startup. See initrd.
2997 Format (x86 or x86_64):
2998 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3000 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3002 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3003 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3004 reboot_force is either force or not specified,
3005 reboot_cpu is s[mp]#### with #### being the processor
3006 to be used for rebooting.
3009 [KNL, SMP] Set scheduler's default relax_domain_level.
3010 See Documentation/cgroups/cpusets.txt.
3012 relative_sleep_states=
3013 [SUSPEND] Use sleep state labeling where the deepest
3014 state available other than hibernation is always "mem".
3015 Format: { "0" | "1" }
3016 0 -- Traditional sleep state labels.
3017 1 -- Relative sleep state labels.
3019 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3021 reservetop= [X86-32]
3023 Reserves a hole at the top of the kernel virtual
3028 Set the amount of memory to reserve for BIOS at
3029 the bottom of the address space.
3031 reset_devices [KNL] Force drivers to reset the underlying device
3032 during initialization.
3035 Specify the partition device for software suspend
3037 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3039 resume_offset= [SWSUSP]
3040 Specify the offset from the beginning of the partition
3041 given by "resume=" at which the swap header is located,
3042 in <PAGE_SIZE> units (needed only for swap files).
3043 See Documentation/power/swsusp-and-swap-files.txt
3045 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3046 read the resume files
3048 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3049 Useful for devices that are detected asynchronously
3050 (e.g. USB and MMC devices).
3052 hibernate= [HIBERNATION]
3053 noresume Don't check if there's a hibernation image
3054 present during boot.
3055 nocompress Don't compress/decompress hibernation images.
3056 no Disable hibernation and resume.
3058 retain_initrd [RAM] Keep initrd memory after extraction
3060 rhash_entries= [KNL,NET]
3061 Set number of hash buckets for route cache
3063 ro [KNL] Mount root device read-only on boot
3065 root= [KNL] Root filesystem
3066 See name_to_dev_t comment in init/do_mounts.c.
3068 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3069 mount the root filesystem
3071 rootflags= [KNL] Set root filesystem mount option string
3073 rootfstype= [KNL] Set root filesystem type
3075 rootwait [KNL] Wait (indefinitely) for root device to show up.
3076 Useful for devices that are detected asynchronously
3077 (e.g. USB and MMC devices).
3079 rproc_mem=nn[KMG][@address]
3080 [KNL,ARM,CMA] Remoteproc physical memory block.
3081 Memory area to be used by remote processor image,
3084 rw [KNL] Mount root device read-write on boot
3086 S [KNL] Run init in single mode
3088 s390_iommu= [HW,S390]
3089 Set s390 IOTLB flushing mode
3091 With strict flushing every unmap operation will result in
3092 an IOTLB flush. Default is lazy flushing before reuse,
3096 See drivers/net/irda/sa1100_ir.c.
3098 sbni= [NET] Granch SBNI12 leased line adapter
3100 sched_debug [KNL] Enables verbose scheduler debug messages.
3102 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3103 xtime_lock contention on larger systems, and/or RCU lock
3104 contention on all systems with CONFIG_MAXSMP set.
3105 Format: { "0" | "1" }
3106 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3108 Note: increases power consumption, thus should only be
3109 enabled if running jitter sensitive (HPC/RT) workloads.
3111 security= [SECURITY] Choose a security module to enable at boot.
3112 If this boot parameter is not specified, only the first
3113 security module asking for security registration will be
3114 loaded. An invalid security module name will be treated
3115 as if no module has been chosen.
3117 selinux= [SELINUX] Disable or enable SELinux at boot time.
3118 Format: { "0" | "1" }
3119 See security/selinux/Kconfig help text.
3122 Default value is set via kernel config option.
3123 If enabled at boot time, /selinux/disable can be used
3124 later to disable prior to initial policy load.
3126 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3127 Format: { "0" | "1" }
3128 See security/apparmor/Kconfig help text
3131 Default value is set via kernel config option.
3133 serialnumber [BUGS=X86-32]
3136 Maximal number of shapers.
3138 show_msr= [x86] show boot-time MSR settings
3139 Format: { <integer> }
3140 Show boot-time (BIOS-initialized) MSR settings.
3141 The parameter means the number of CPUs to show,
3142 for example 1 means boot CPU only.
3149 slab_max_order= [MM, SLAB]
3150 Determines the maximum allowed order for slabs.
3151 A high setting may cause OOMs due to memory
3152 fragmentation. Defaults to 1 for systems with
3153 more than 32MB of RAM, 0 otherwise.
3155 slub_debug[=options[,slabs]] [MM, SLUB]
3156 Enabling slub_debug allows one to determine the
3157 culprit if slab objects become corrupted. Enabling
3158 slub_debug can create guard zones around objects and
3159 may poison objects when not in use. Also tracks the
3160 last alloc / free. For more information see
3161 Documentation/vm/slub.txt.
3163 slub_max_order= [MM, SLUB]
3164 Determines the maximum allowed order for slabs.
3165 A high setting may cause OOMs due to memory
3166 fragmentation. For more information see
3167 Documentation/vm/slub.txt.
3169 slub_min_objects= [MM, SLUB]
3170 The minimum number of objects per slab. SLUB will
3171 increase the slab order up to slub_max_order to
3172 generate a sufficiently large slab able to contain
3173 the number of objects indicated. The higher the number
3174 of objects the smaller the overhead of tracking slabs
3175 and the less frequently locks need to be acquired.
3176 For more information see Documentation/vm/slub.txt.
3178 slub_min_order= [MM, SLUB]
3179 Determines the minimum page order for slabs. Must be
3180 lower than slub_max_order.
3181 For more information see Documentation/vm/slub.txt.
3183 slub_nomerge [MM, SLUB]
3184 Disable merging of slabs with similar size. May be
3185 necessary if there is some reason to distinguish
3186 allocs to different slabs. Debug options disable
3187 merging on their own.
3188 For more information see Documentation/vm/slub.txt.
3191 Format: <io1>[,<io2>[,...,<io8>]]
3193 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3194 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3195 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3196 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3197 smsc-ircc2.ircc_irq= [HW] IRQ line
3198 smsc-ircc2.ircc_dma= [HW] DMA channel
3199 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3200 0: Toshiba Satellite 1800 (GP data pin select)
3201 1: Fast pin select (default)
3205 [KNL] Should the soft-lockup detector generate panics.
3208 softlockup_all_cpu_backtrace=
3209 [KNL] Should the soft-lockup detector generate
3210 backtraces on all cpus.
3213 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3214 See Documentation/laptops/sonypi.txt
3216 spia_io_base= [HW,MTD]
3222 Enabled the stack tracer on boot up.
3224 stacktrace_filter=[function-list]
3225 [FTRACE] Limit the functions that the stack tracer
3226 will trace at boot up. function-list is a comma separated
3227 list of functions. This list can be changed at run
3228 time by the stack_trace_filter file in the debugfs
3229 tracing directory. Note, this enables stack tracing
3230 and the stacktrace above is not needed.
3234 Set the STI (builtin display/keyboard on the HP-PARISC
3235 machines) console (graphic card) which should be used
3236 as the initial boot-console.
3237 See also comment in drivers/video/console/sticore.c.
3240 See comment in drivers/video/console/sticore.c.
3243 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3245 sunrpc.min_resvport=
3246 sunrpc.max_resvport=
3248 SunRPC servers often require that client requests
3249 originate from a privileged port (i.e. a port in the
3250 range 0 < portnr < 1024).
3251 An administrator who wishes to reserve some of these
3252 ports for other uses may adjust the range that the
3253 kernel's sunrpc client considers to be privileged
3254 using these two parameters to set the minimum and
3255 maximum port values.
3259 Control how the NFS server code allocates CPUs to
3260 service thread pools. Depending on how many NICs
3261 you have and where their interrupts are bound, this
3262 option will affect which CPUs will do NFS serving.
3263 Note: this parameter cannot be changed while the
3264 NFS server is running.
3266 auto the server chooses an appropriate mode
3267 automatically using heuristics
3268 global a single global pool contains all CPUs
3269 percpu one pool for each CPU
3270 pernode one pool for each NUMA node (equivalent
3271 to global on non-NUMA machines)
3273 sunrpc.tcp_slot_table_entries=
3274 sunrpc.udp_slot_table_entries=
3276 Sets the upper limit on the number of simultaneous
3277 RPC calls that can be sent from the client to a
3278 server. Increasing these values may allow you to
3279 improve throughput, but will also increase the
3280 amount of memory reserved for use by the client.
3283 [KNL] Enable accounting of swap in memory resource
3284 controller if no parameter or 1 is given or disable
3285 it if 0 is given (See Documentation/cgroups/memory.txt)
3287 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3288 Format: { <int> | force }
3289 <int> -- Number of I/O TLB slabs
3290 force -- force using of bounce buffers even if they
3291 wouldn't be automatically used by the kernel
3295 sysfs.deprecated=0|1 [KNL]
3296 Enable/disable old style sysfs layout for old udev
3297 on older distributions. When this option is enabled
3298 very new udev will not work anymore. When this option
3299 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3300 in older udev will not work anymore.
3301 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3302 the kernel configuration.
3304 sysrq_always_enabled
3306 Ignore sysrq setting - this boot parameter will
3307 neutralize any effect of /proc/sys/kernel/sysrq.
3308 Useful for debugging.
3312 test_suspend= [SUSPEND]
3313 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3314 standby suspend) as the system sleep state to briefly
3315 enter during system startup. The system is woken from
3316 this state using a wakeup-capable RTC alarm.
3318 thash_entries= [KNL,NET]
3319 Set number of hash buckets for TCP connection
3321 thermal.act= [HW,ACPI]
3322 -1: disable all active trip points in all thermal zones
3323 <degrees C>: override all lowest active trip points
3325 thermal.crt= [HW,ACPI]
3326 -1: disable all critical trip points in all thermal zones
3327 <degrees C>: override all critical trip points
3329 thermal.nocrt= [HW,ACPI]
3330 Set to disable actions on ACPI thermal zone
3331 critical and hot trip points.
3333 thermal.off= [HW,ACPI]
3334 1: disable ACPI thermal control
3336 thermal.psv= [HW,ACPI]
3337 -1: disable all passive trip points
3338 <degrees C>: override all passive trip points to this
3341 thermal.tzp= [HW,ACPI]
3342 Specify global default ACPI thermal zone polling rate
3343 <deci-seconds>: poll all this frequency
3344 0: no polling (default)
3347 Force threading of all interrupt handlers except those
3348 marked explicitly IRQF_NO_THREAD.
3351 Enable the Transcendent memory driver if built-in.
3353 tmem.cleancache=0|1 [KNL, XEN]
3354 Default is on (1). Disable the usage of the cleancache
3355 API to send anonymous pages to the hypervisor.
3357 tmem.frontswap=0|1 [KNL, XEN]
3358 Default is on (1). Disable the usage of the frontswap
3359 API to send swap pages to the hypervisor. If disabled
3360 the selfballooning and selfshrinking are force disabled.
3362 tmem.selfballooning=0|1 [KNL, XEN]
3363 Default is on (1). Disable the driving of swap pages
3366 tmem.selfshrinking=0|1 [KNL, XEN]
3367 Default is on (1). Partial swapoff that immediately
3368 transfers pages from Xen hypervisor back to the
3369 kernel based on different criteria.
3373 Specify if the kernel should make use of the cpu
3374 topology information if the hardware supports this.
3375 The scheduler will make use of this information and
3376 e.g. base its process migration decisions on it.
3381 tpm_suspend_pcr=[HW,TPM]
3382 Format: integer pcr id
3383 Specify that at suspend time, the tpm driver
3384 should extend the specified pcr with zeros,
3385 as a workaround for some chips which fail to
3386 flush the last written pcr on TPM_SaveState.
3387 This will guarantee that all the other pcrs
3390 trace_buf_size=nn[KMG]
3391 [FTRACE] will set tracing buffer size.
3393 trace_event=[event-list]
3394 [FTRACE] Set and start specified trace events in order
3395 to facilitate early boot debugging.
3396 See also Documentation/trace/events.txt
3398 trace_options=[option-list]
3399 [FTRACE] Enable or disable tracer options at boot.
3400 The option-list is a comma delimited list of options
3401 that can be enabled or disabled just as if you were
3402 to echo the option name into
3404 /sys/kernel/debug/tracing/trace_options
3406 For example, to enable stacktrace option (to dump the
3407 stack trace of each event), add to the command line:
3409 trace_options=stacktrace
3411 See also Documentation/trace/ftrace.txt "trace options"
3415 [FTRACE] enable this option to disable tracing when a
3416 warning is hit. This turns off "tracing_on". Tracing can
3417 be enabled again by echoing '1' into the "tracing_on"
3418 file located in /sys/kernel/debug/tracing/
3420 This option is useful, as it disables the trace before
3421 the WARNING dump is called, which prevents the trace to
3422 be filled with content caused by the warning output.
3424 This option can also be set at run time via the sysctl
3425 option: kernel/traceoff_on_warning
3427 transparent_hugepage=
3429 Format: [always|madvise|never]
3430 Can be used to control the default behavior of the system
3431 with respect to transparent hugepages.
3432 See Documentation/vm/transhuge.txt for more details.
3434 tsc= Disable clocksource stability checks for TSC.
3436 [x86] reliable: mark tsc clocksource as reliable, this
3437 disables clocksource verification at runtime, as well
3438 as the stability checks done at bootup. Used to enable
3439 high-resolution timer mode on older hardware, and in
3440 virtualized environment.
3441 [x86] noirqtime: Do not use TSC to do irq accounting.
3442 Used to run time disable IRQ_TIME_ACCOUNTING on any
3443 platforms where RDTSC is slow and this accounting
3446 turbografx.map[2|3]= [HW,JOY]
3447 TurboGraFX parallel port interface
3449 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3450 See also Documentation/input/joystick-parport.txt
3452 udbg-immortal [PPC] When debugging early kernel crashes that
3453 happen after console_init() and before a proper
3454 console driver takes over, this boot options might
3455 help "seeing" what's going on.
3457 uhash_entries= [KNL,NET]
3458 Set number of hash buckets for UDP/UDP-Lite connections
3461 [USB] Ignore overcurrent events (default N).
3462 Some badly-designed motherboards generate lots of
3463 bogus events, for ports that aren't wired to
3464 anything. Set this parameter to avoid log spamming.
3465 Note that genuine overcurrent events won't be
3469 [X86] Cause panic on unknown NMI.
3471 usbcore.authorized_default=
3472 [USB] Default USB device authorization:
3473 (default -1 = authorized except for wireless USB,
3474 0 = not authorized, 1 = authorized)
3476 usbcore.autosuspend=
3477 [USB] The autosuspend time delay (in seconds) used
3478 for newly-detected USB devices (default 2). This
3479 is the time required before an idle device will be
3480 autosuspended. Devices for which the delay is set
3481 to a negative value won't be autosuspended at all.
3483 usbcore.usbfs_snoop=
3484 [USB] Set to log all usbfs traffic (default 0 = off).
3486 usbcore.blinkenlights=
3487 [USB] Set to cycle leds on hubs (default 0 = off).
3489 usbcore.old_scheme_first=
3490 [USB] Start with the old device initialization
3491 scheme (default 0 = off).
3493 usbcore.usbfs_memory_mb=
3494 [USB] Memory limit (in MB) for buffers allocated by
3495 usbfs (default = 16, 0 = max = 2047).
3497 usbcore.use_both_schemes=
3498 [USB] Try the other device initialization scheme
3499 if the first one fails (default 1 = enabled).
3501 usbcore.initial_descriptor_timeout=
3502 [USB] Specifies timeout for the initial 64-byte
3503 USB_REQ_GET_DESCRIPTOR request in milliseconds
3504 (default 5000 = 5.0 seconds).
3507 [USBHID] The interval which mice are to be polled at.
3509 usb-storage.delay_use=
3510 [UMS] The delay in seconds before a new device is
3511 scanned for Logical Units (default 5).
3514 [UMS] A list of quirks entries to supplement or
3515 override the built-in unusual_devs list. List
3516 entries are separated by commas. Each entry has
3517 the form VID:PID:Flags where VID and PID are Vendor
3518 and Product ID values (4-digit hex numbers) and
3519 Flags is a set of characters, each corresponding
3520 to a common usb-storage quirk flag as follows:
3521 a = SANE_SENSE (collect more than 18 bytes
3523 b = BAD_SENSE (don't collect more than 18
3524 bytes of sense data);
3525 c = FIX_CAPACITY (decrease the reported
3526 device capacity by one sector);
3527 d = NO_READ_DISC_INFO (don't use
3528 READ_DISC_INFO command);
3529 e = NO_READ_CAPACITY_16 (don't use
3530 READ_CAPACITY_16 command);
3531 h = CAPACITY_HEURISTICS (decrease the
3532 reported device capacity by one
3533 sector if the number is odd);
3534 i = IGNORE_DEVICE (don't bind to this
3536 l = NOT_LOCKABLE (don't try to lock and
3537 unlock ejectable media);
3538 m = MAX_SECTORS_64 (don't transfer more
3539 than 64 sectors = 32 KB at a time);
3540 n = INITIAL_READ10 (force a retry of the
3541 initial READ(10) command);
3542 o = CAPACITY_OK (accept the capacity
3543 reported by the device);
3544 p = WRITE_CACHE (the device cache is ON
3546 r = IGNORE_RESIDUE (the device reports
3547 bogus residue values);
3548 s = SINGLE_LUN (the device has only one
3550 u = IGNORE_UAS (don't bind to the uas driver);
3551 w = NO_WP_DETECT (don't test whether the
3552 medium is write-protected).
3553 Example: quirks=0419:aaf5:rl,0421:0433:rc
3555 user_debug= [KNL,ARM]
3557 See arch/arm/Kconfig.debug help text.
3558 1 - undefined instruction events
3560 4 - invalid data aborts
3563 Example: user_debug=31
3566 [X86] Flags controlling user PTE allocations.
3568 nohigh = do not allocate PTE pages in
3569 HIGHMEM regardless of setting
3573 On X86_32, this is an alias for vdso32=. Otherwise:
3575 vdso=1: enable VDSO (the default)
3576 vdso=0: disable VDSO mapping
3578 vdso32= [X86] Control the 32-bit vDSO
3579 vdso32=1: enable 32-bit VDSO
3580 vdso32=0 or vdso32=2: disable 32-bit VDSO
3582 See the help text for CONFIG_COMPAT_VDSO for more
3583 details. If CONFIG_COMPAT_VDSO is set, the default is
3584 vdso32=0; otherwise, the default is vdso32=1.
3586 For compatibility with older kernels, vdso32=2 is an
3589 Try vdso32=0 if you encounter an error that says:
3590 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3593 vector=percpu: enable percpu vector domain
3595 video= [FB] Frame buffer configuration
3596 See Documentation/fb/modedb.txt.
3598 video.brightness_switch_enabled= [0,1]
3599 If set to 1, on receiving an ACPI notify event
3600 generated by hotkey, video driver will adjust brightness
3601 level and then send out the event to user space through
3602 the allocated input device; If set to 0, video driver
3603 will only send out the event without touching backlight
3608 [VMMIO] Memory mapped virtio (platform) device.
3610 <size>@<baseaddr>:<irq>[:<id>]
3612 <size> := size (can use standard suffixes
3614 <baseaddr> := physical base address
3615 <irq> := interrupt number (as passed to
3617 <id> := (optional) platform device id
3619 virtio_mmio.device=1K@0x100b0000:48:7
3621 Can be used multiple times for multiple devices.
3623 vga= [BOOT,X86-32] Select a particular video mode
3624 See Documentation/x86/boot.txt and
3625 Documentation/svga.txt.
3626 Use vga=ask for menu.
3627 This is actually a boot loader parameter; the value is
3628 passed to the kernel using a special protocol.
3630 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3631 size of <nn>. This can be used to increase the
3632 minimum size (128MB on x86). It can also be used to
3633 decrease the size and leave more room for directly
3636 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3639 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3642 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3646 Controls the behavior of vsyscalls (i.e. calls to
3647 fixed addresses of 0xffffffffff600x00 from legacy
3648 code). Most statically-linked binaries and older
3649 versions of glibc use these calls. Because these
3650 functions are at fixed addresses, they make nice
3651 targets for exploits that can control RIP.
3653 emulate [default] Vsyscalls turn into traps and are
3654 emulated reasonably safely.
3656 native Vsyscalls are native syscall instructions.
3657 This is a little bit faster than trapping
3658 and makes a few dynamic recompilers work
3659 better than they would in emulation mode.
3660 It also makes exploits much easier to write.
3662 none Vsyscalls don't work at all. This makes
3663 them quite hard to use for exploits but
3664 might break your system.
3666 vt.color= [VT] Default text color.
3667 Format: 0xYX, X = foreground, Y = background.
3668 Default: 0x07 = light gray on black.
3670 vt.cur_default= [VT] Default cursor shape.
3671 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3672 the parameters of the <Esc>[?A;B;Cc escape sequence;
3673 see VGA-softcursor.txt. Default: 2 = underline.
3675 vt.default_blu= [VT]
3676 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3677 Change the default blue palette of the console.
3678 This is a 16-member array composed of values
3681 vt.default_grn= [VT]
3682 Format: <green0>,<green1>,<green2>,...,<green15>
3683 Change the default green palette of the console.
3684 This is a 16-member array composed of values
3687 vt.default_red= [VT]
3688 Format: <red0>,<red1>,<red2>,...,<red15>
3689 Change the default red palette of the console.
3690 This is a 16-member array composed of values
3696 Set system-wide default UTF-8 mode for all tty's.
3697 Default is 1, i.e. UTF-8 mode is enabled for all
3698 newly opened terminals.
3700 vt.global_cursor_default=
3703 Set system-wide default for whether a cursor
3704 is shown on new VTs. Default is -1,
3705 i.e. cursors will be created by default unless
3706 overridden by individual drivers. 0 will hide
3707 cursors, 1 will display them.
3709 vt.italic= [VT] Default color for italic text; 0-15.
3712 vt.underline= [VT] Default color for underlined text; 0-15.
3715 watchdog timers [HW,WDT] For information on watchdog timers,
3716 see Documentation/watchdog/watchdog-parameters.txt
3717 or other driver-specific files in the
3718 Documentation/watchdog/ directory.
3720 workqueue.disable_numa
3721 By default, all work items queued to unbound
3722 workqueues are affine to the NUMA nodes they're
3723 issued on, which results in better behavior in
3724 general. If NUMA affinity needs to be disabled for
3725 whatever reason, this option can be used. Note
3726 that this also can be controlled per-workqueue for
3727 workqueues visible under /sys/bus/workqueue/.
3729 workqueue.power_efficient
3730 Per-cpu workqueues are generally preferred because
3731 they show better performance thanks to cache
3732 locality; unfortunately, per-cpu workqueues tend to
3733 be more power hungry than unbound workqueues.
3735 Enabling this makes the per-cpu workqueues which
3736 were observed to contribute significantly to power
3737 consumption unbound, leading to measurably lower
3738 power usage at the cost of small performance
3741 The default value of this parameter is determined by
3742 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3744 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3745 default x2apic cluster mode on platforms
3748 x86_intel_mid_timer= [X86-32,APBT]
3749 Choose timer option for x86 Intel MID platform.
3750 Two valid options are apbt timer only and lapic timer
3751 plus one apbt timer for broadcast timer.
3752 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3754 xen_emul_unplug= [HW,X86,XEN]
3755 Unplug Xen emulated devices
3756 Format: [unplug0,][unplug1]
3757 ide-disks -- unplug primary master IDE devices
3758 aux-ide-disks -- unplug non-primary-master IDE devices
3759 nics -- unplug network devices
3760 all -- unplug all emulated devices (NICs and IDE disks)
3761 unnecessary -- unplugging emulated devices is
3762 unnecessary even if the host did not respond to
3764 never -- do not unplug even if version check succeeds
3766 xen_nopvspin [X86,XEN]
3767 Disables the ticketlock slowpath using Xen PV
3771 Disables the PV optimizations forcing the HVM guest to
3772 run as generic HVM guest with no PV drivers.
3774 xirc2ps_cs= [NET,PCMCIA]
3776 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3778 ______________________________________________________________________
3782 Add more DRM drivers.
projects / firefly-linux-kernel-4.4.55.git / blob