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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
4 The following is a consolidated list of the kernel parameters as implemented
5 (mostly) by the __setup() macro and sorted into English Dictionary order
6 (defined as ignoring all punctuation and sorting digits before letters in a
7 case insensitive manner), and with descriptions where known.
9 Module parameters for loadable modules are specified only as the
10 parameter name with optional '=' and value as appropriate, such as:
12 modprobe usbcore blinkenlights=1
14 Module parameters for modules that are built into the kernel image
15 are specified on the kernel command line with the module name plus
16 '.' plus parameter name, with '=' and value if appropriate, such as:
18 usbcore.blinkenlights=1
20 Hyphens (dashes) and underscores are equivalent in parameter names, so
21 log_buf_len=1M print-fatal-signals=1
22 can also be entered as
23 log-buf-len=1M print_fatal_signals=1
26 This document may not be entirely up to date and comprehensive. The command
27 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
28 module. Loadable modules, after being loaded into the running kernel, also
29 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
30 parameters may be changed at runtime by the command
31 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
33 The parameters listed below are only valid if certain kernel build options were
34 enabled and if respective hardware is present. The text in square brackets at
35 the beginning of each description states the restrictions within which a
36 parameter is applicable:
38 ACPI ACPI support is enabled.
39 AGP AGP (Accelerated Graphics Port) is enabled.
40 ALSA ALSA sound support is enabled.
41 APIC APIC support is enabled.
42 APM Advanced Power Management support is enabled.
43 ARM ARM architecture is enabled.
44 AVR32 AVR32 architecture is enabled.
45 AX25 Appropriate AX.25 support is enabled.
46 BLACKFIN Blackfin architecture is enabled.
47 CLK Common clock infrastructure is enabled.
48 CMA Contiguous Memory Area support is enabled.
49 DRM Direct Rendering Management support is enabled.
50 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
51 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
52 EFI EFI Partitioning (GPT) is enabled
53 EIDE EIDE/ATAPI support is enabled.
54 EVM Extended Verification Module
55 FB The frame buffer device is enabled.
56 FTRACE Function tracing enabled.
57 GCOV GCOV profiling is enabled.
58 HW Appropriate hardware is enabled.
59 IA-64 IA-64 architecture is enabled.
60 IMA Integrity measurement architecture is enabled.
61 IOSCHED More than one I/O scheduler is enabled.
62 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
63 IPV6 IPv6 support is enabled.
64 ISAPNP ISA PnP code is enabled.
65 ISDN Appropriate ISDN support is enabled.
66 JOY Appropriate joystick support is enabled.
67 KGDB Kernel debugger support is enabled.
68 KVM Kernel Virtual Machine support is enabled.
69 LIBATA Libata driver is enabled
70 LP Printer support is enabled.
71 LOOP Loopback device support is enabled.
72 M68k M68k architecture is enabled.
73 These options have more detailed description inside of
74 Documentation/m68k/kernel-options.txt.
75 MDA MDA console support is enabled.
76 MIPS MIPS architecture is enabled.
77 MOUSE Appropriate mouse support is enabled.
78 MSI Message Signaled Interrupts (PCI).
79 MTD MTD (Memory Technology Device) support is enabled.
80 NET Appropriate network support is enabled.
81 NUMA NUMA support is enabled.
82 NFS Appropriate NFS support is enabled.
83 OSS OSS sound support is enabled.
84 PV_OPS A paravirtualized kernel is enabled.
85 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
86 PARISC The PA-RISC architecture is enabled.
87 PCI PCI bus support is enabled.
88 PCIE PCI Express support is enabled.
89 PCMCIA The PCMCIA subsystem is enabled.
90 PNP Plug & Play support is enabled.
91 PPC PowerPC architecture is enabled.
92 PPT Parallel port support is enabled.
93 PS2 Appropriate PS/2 support is enabled.
94 RAM RAM disk support is enabled.
95 S390 S390 architecture is enabled.
96 SCSI Appropriate SCSI support is enabled.
97 A lot of drivers have their options described inside
98 the Documentation/scsi/ sub-directory.
99 SECURITY Different security models are enabled.
100 SELINUX SELinux support is enabled.
101 APPARMOR AppArmor support is enabled.
102 SERIAL Serial support is enabled.
103 SH SuperH architecture is enabled.
104 SMP The kernel is an SMP kernel.
105 SPARC Sparc architecture is enabled.
106 SWSUSP Software suspend (hibernation) is enabled.
107 SUSPEND System suspend states are enabled.
108 TPM TPM drivers are enabled.
109 TS Appropriate touchscreen support is enabled.
110 UMS USB Mass Storage support is enabled.
111 USB USB support is enabled.
112 USBHID USB Human Interface Device support is enabled.
113 V4L Video For Linux support is enabled.
114 VMMIO Driver for memory mapped virtio devices is enabled.
115 VGA The VGA console has been enabled.
116 VT Virtual terminal support is enabled.
117 WDT Watchdog support is enabled.
118 XT IBM PC/XT MFM hard disk support is enabled.
119 X86-32 X86-32, aka i386 architecture is enabled.
120 X86-64 X86-64 architecture is enabled.
121 More X86-64 boot options can be found in
122 Documentation/x86/x86_64/boot-options.txt .
123 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
124 XEN Xen support is enabled
126 In addition, the following text indicates that the option:
128 BUGS= Relates to possible processor bugs on the said processor.
129 KNL Is a kernel start-up parameter.
130 BOOT Is a boot loader parameter.
132 Parameters denoted with BOOT are actually interpreted by the boot
133 loader, and have no meaning to the kernel directly.
134 Do not modify the syntax of boot loader parameters without extreme
135 need or coordination with <Documentation/x86/boot.txt>.
137 There are also arch-specific kernel-parameters not documented here.
138 See for example <Documentation/x86/x86_64/boot-options.txt>.
140 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
141 a trailing = on the name of any parameter states that that parameter will
142 be entered as an environment variable, whereas its absence indicates that
143 it will appear as a kernel argument readable via /proc/cmdline by programs
144 running once the system is up.
146 The number of kernel parameters is not limited, but the length of the
147 complete command line (parameters including spaces etc.) is limited to
148 a fixed number of characters. This limit depends on the architecture
149 and is between 256 and 4096 characters. It is defined in the file
150 ./include/asm/setup.h as COMMAND_LINE_SIZE.
152 Finally, the [KMG] suffix is commonly described after a number of kernel
153 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
154 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
155 bytes respectively. Such letter suffixes can also be entirely omitted.
158 acpi= [HW,ACPI,X86]
159 Advanced Configuration and Power Interface
160 Format: { force | off | strict | noirq | rsdt }
161 force -- enable ACPI if default was off
162 off -- disable ACPI if default was on
163 noirq -- do not use ACPI for IRQ routing
164 strict -- Be less tolerant of platforms that are not
165 strictly ACPI specification compliant.
166 rsdt -- prefer RSDT over (default) XSDT
167 copy_dsdt -- copy DSDT to memory
169 See also Documentation/power/runtime_pm.txt, pci=noacpi
171 acpi_rsdp= [ACPI,EFI,KEXEC]
172 Pass the RSDP address to the kernel, mostly used
173 on machines running EFI runtime service to boot the
174 second kernel for kdump.
176 acpi_apic_instance= [ACPI, IOAPIC]
177 Format: <int>
178 2: use 2nd APIC table, if available
179 1,0: use 1st APIC table
180 default: 0
182 acpi_backlight= [HW,ACPI]
183 acpi_backlight=vendor
184 acpi_backlight=video
185 If set to vendor, prefer vendor specific driver
186 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
187 of the ACPI video.ko driver.
189 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
190 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
191 Format: <int>
192 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
193 debug output. Bits in debug_layer correspond to a
194 _COMPONENT in an ACPI source file, e.g.,
195 #define _COMPONENT ACPI_PCI_COMPONENT
196 Bits in debug_level correspond to a level in
197 ACPI_DEBUG_PRINT statements, e.g.,
198 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
199 The debug_level mask defaults to "info". See
200 Documentation/acpi/debug.txt for more information about
201 debug layers and levels.
203 Enable processor driver info messages:
204 acpi.debug_layer=0x20000000
205 Enable PCI/PCI interrupt routing info messages:
206 acpi.debug_layer=0x400000
207 Enable AML "Debug" output, i.e., stores to the Debug
208 object while interpreting AML:
209 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
210 Enable all messages related to ACPI hardware:
211 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
213 Some values produce so much output that the system is
214 unusable. The "log_buf_len" parameter may be useful
215 if you need to capture more output.
217 acpi_irq_balance [HW,ACPI]
218 ACPI will balance active IRQs
219 default in APIC mode
221 acpi_irq_nobalance [HW,ACPI]
222 ACPI will not move active IRQs (default)
223 default in PIC mode
225 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
226 Format: <irq>,<irq>...
228 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
229 use by PCI
230 Format: <irq>,<irq>...
232 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
234 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
235 Format: To spoof as Windows 98: ="Microsoft Windows"
237 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
238 acpi_osi="string1" # add string1
239 acpi_osi="!string2" # remove string2
240 acpi_osi=!* # remove all strings
241 acpi_osi=! # disable all built-in OS vendor
242 strings
243 acpi_osi= # disable all strings
245 'acpi_osi=!' can be used in combination with single or
246 multiple 'acpi_osi="string1"' to support specific OS
247 vendor string(s). Note that such command can only
248 affect the default state of the OS vendor strings, thus
249 it cannot affect the default state of the feature group
250 strings and the current state of the OS vendor strings,
251 specifying it multiple times through kernel command line
252 is meaningless. This command is useful when one do not
253 care about the state of the feature group strings which
254 should be controlled by the OSPM.
255 Examples:
256 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
257 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
258 can make '_OSI("Windows 2000")' TRUE.
260 'acpi_osi=' cannot be used in combination with other
261 'acpi_osi=' command lines, the _OSI method will not
262 exist in the ACPI namespace. NOTE that such command can
263 only affect the _OSI support state, thus specifying it
264 multiple times through kernel command line is also
265 meaningless.
266 Examples:
267 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
268 FALSE.
270 'acpi_osi=!*' can be used in combination with single or
271 multiple 'acpi_osi="string1"' to support specific
272 string(s). Note that such command can affect the
273 current state of both the OS vendor strings and the
274 feature group strings, thus specifying it multiple times
275 through kernel command line is meaningful. But it may
276 still not able to affect the final state of a string if
277 there are quirks related to this string. This command
278 is useful when one want to control the state of the
279 feature group strings to debug BIOS issues related to
280 the OSPM features.
281 Examples:
282 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
283 '_OSI("Module Device")' FALSE.
284 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
285 '_OSI("Module Device")' TRUE.
286 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
287 equivalent to
288 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
289 and
290 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
291 they all will make '_OSI("Windows 2000")' TRUE.
293 acpi_pm_good [X86]
294 Override the pmtimer bug detection: force the kernel
295 to assume that this machine's pmtimer latches its value
296 and always returns good values.
298 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
299 Format: { level | edge | high | low }
301 acpi_serialize [HW,ACPI] force serialization of AML methods
303 acpi_skip_timer_override [HW,ACPI]
304 Recognize and ignore IRQ0/pin2 Interrupt Override.
305 For broken nForce2 BIOS resulting in XT-PIC timer.
307 acpi_sleep= [HW,ACPI] Sleep options
308 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
309 old_ordering, nonvs, sci_force_enable }
310 See Documentation/power/video.txt for information on
311 s3_bios and s3_mode.
312 s3_beep is for debugging; it makes the PC's speaker beep
313 as soon as the kernel's real-mode entry point is called.
314 s4_nohwsig prevents ACPI hardware signature from being
315 used during resume from hibernation.
316 old_ordering causes the ACPI 1.0 ordering of the _PTS
317 control method, with respect to putting devices into
318 low power states, to be enforced (the ACPI 2.0 ordering
319 of _PTS is used by default).
320 nonvs prevents the kernel from saving/restoring the
321 ACPI NVS memory during suspend/hibernation and resume.
322 sci_force_enable causes the kernel to set SCI_EN directly
323 on resume from S1/S3 (which is against the ACPI spec,
324 but some broken systems don't work without it).
326 acpi_use_timer_override [HW,ACPI]
327 Use timer override. For some broken Nvidia NF5 boards
328 that require a timer override, but don't have HPET
330 acpi_enforce_resources= [ACPI]
331 { strict | lax | no }
332 Check for resource conflicts between native drivers
333 and ACPI OperationRegions (SystemIO and SystemMemory
334 only). IO ports and memory declared in ACPI might be
335 used by the ACPI subsystem in arbitrary AML code and
336 can interfere with legacy drivers.
337 strict (default): access to resources claimed by ACPI
338 is denied; legacy drivers trying to access reserved
339 resources will fail to bind to device using them.
340 lax: access to resources claimed by ACPI is allowed;
341 legacy drivers trying to access reserved resources
342 will bind successfully but a warning message is logged.
343 no: ACPI OperationRegions are not marked as reserved,
344 no further checks are performed.
346 add_efi_memmap [EFI; X86] Include EFI memory map in
347 kernel's map of available physical RAM.
349 agp= [AGP]
350 { off | try_unsupported }
351 off: disable AGP support
352 try_unsupported: try to drive unsupported chipsets
353 (may crash computer or cause data corruption)
355 ALSA [HW,ALSA]
356 See Documentation/sound/alsa/alsa-parameters.txt
358 alignment= [KNL,ARM]
359 Allow the default userspace alignment fault handler
360 behaviour to be specified. Bit 0 enables warnings,
361 bit 1 enables fixups, and bit 2 sends a segfault.
363 align_va_addr= [X86-64]
364 Align virtual addresses by clearing slice [14:12] when
365 allocating a VMA at process creation time. This option
366 gives you up to 3% performance improvement on AMD F15h
367 machines (where it is enabled by default) for a
368 CPU-intensive style benchmark, and it can vary highly in
369 a microbenchmark depending on workload and compiler.
371 32: only for 32-bit processes
372 64: only for 64-bit processes
373 on: enable for both 32- and 64-bit processes
374 off: disable for both 32- and 64-bit processes
376 alloc_snapshot [FTRACE]
377 Allocate the ftrace snapshot buffer on boot up when the
378 main buffer is allocated. This is handy if debugging
379 and you need to use tracing_snapshot() on boot up, and
380 do not want to use tracing_snapshot_alloc() as it needs
381 to be done where GFP_KERNEL allocations are allowed.
383 amd_iommu= [HW,X86-64]
384 Pass parameters to the AMD IOMMU driver in the system.
385 Possible values are:
386 fullflush - enable flushing of IO/TLB entries when
387 they are unmapped. Otherwise they are
388 flushed before they will be reused, which
389 is a lot of faster
390 off - do not initialize any AMD IOMMU found in
391 the system
392 force_isolation - Force device isolation for all
393 devices. The IOMMU driver is not
394 allowed anymore to lift isolation
395 requirements as needed. This option
396 does not override iommu=pt
398 amd_iommu_dump= [HW,X86-64]
399 Enable AMD IOMMU driver option to dump the ACPI table
400 for AMD IOMMU. With this option enabled, AMD IOMMU
401 driver will print ACPI tables for AMD IOMMU during
402 IOMMU initialization.
404 amijoy.map= [HW,JOY] Amiga joystick support
405 Map of devices attached to JOY0DAT and JOY1DAT
406 Format: <a>,<b>
407 See also Documentation/input/joystick.txt
409 analog.map= [HW,JOY] Analog joystick and gamepad support
410 Specifies type or capabilities of an analog joystick
411 connected to one of 16 gameports
412 Format: <type1>,<type2>,..<type16>
414 apc= [HW,SPARC]
415 Power management functions (SPARCstation-4/5 + deriv.)
416 Format: noidle
417 Disable APC CPU standby support. SPARCstation-Fox does
418 not play well with APC CPU idle - disable it if you have
419 APC and your system crashes randomly.
421 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
422 Change the output verbosity whilst booting
423 Format: { quiet (default) | verbose | debug }
424 Change the amount of debugging information output
425 when initialising the APIC and IO-APIC components.
427 autoconf= [IPV6]
428 See Documentation/networking/ipv6.txt.
430 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
431 Limit apic dumping. The parameter defines the maximal
432 number of local apics being dumped. Also it is possible
433 to set it to "all" by meaning -- no limit here.
434 Format: { 1 (default) | 2 | ... | all }.
435 The parameter valid if only apic=debug or
436 apic=verbose is specified.
437 Example: apic=debug show_lapic=all
439 apm= [APM] Advanced Power Management
440 See header of arch/x86/kernel/apm_32.c.
442 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
443 Format: <io>,<irq>,<nodeID>
445 ataflop= [HW,M68k]
447 atarimouse= [HW,MOUSE] Atari Mouse
449 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
450 EzKey and similar keyboards
452 atkbd.reset= [HW] Reset keyboard during initialization
454 atkbd.set= [HW] Select keyboard code set
455 Format: <int> (2 = AT (default), 3 = PS/2)
457 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
458 keyboards
460 atkbd.softraw= [HW] Choose between synthetic and real raw mode
461 Format: <bool> (0 = real, 1 = synthetic (default))
463 atkbd.softrepeat= [HW]
464 Use software keyboard repeat
466 baycom_epp= [HW,AX25]
467 Format: <io>,<mode>
469 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
470 Format: <io>,<mode>
471 See header of drivers/net/hamradio/baycom_par.c.
473 baycom_ser_fdx= [HW,AX25]
474 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
475 Format: <io>,<irq>,<mode>[,<baud>]
476 See header of drivers/net/hamradio/baycom_ser_fdx.c.
478 baycom_ser_hdx= [HW,AX25]
479 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
480 Format: <io>,<irq>,<mode>
481 See header of drivers/net/hamradio/baycom_ser_hdx.c.
483 blkdevparts= Manual partition parsing of block device(s) for
484 embedded devices based on command line input.
485 See Documentation/block/cmdline-partition.txt
487 boot_delay= Milliseconds to delay each printk during boot.
488 Values larger than 10 seconds (10000) are changed to
489 no delay (0).
490 Format: integer
492 bootmem_debug [KNL] Enable bootmem allocator debug messages.
494 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
495 bttv.radio= Most important insmod options are available as
496 kernel args too.
497 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
498 bttv.tuner=
500 bulk_remove=off [PPC] This parameter disables the use of the pSeries
501 firmware feature for flushing multiple hpte entries
502 at a time.
504 c101= [NET] Moxa C101 synchronous serial card
506 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
507 Sometimes CPU hardware bugs make them report the cache
508 size incorrectly. The kernel will attempt work arounds
509 to fix known problems, but for some CPUs it is not
510 possible to determine what the correct size should be.
511 This option provides an override for these situations.
513 ccw_timeout_log [S390]
514 See Documentation/s390/CommonIO for details.
516 cgroup_disable= [KNL] Disable a particular controller
517 Format: {name of the controller(s) to disable}
518 {Currently supported controllers - "memory"}
520 checkreqprot [SELINUX] Set initial checkreqprot flag value.
521 Format: { "0" | "1" }
522 See security/selinux/Kconfig help text.
523 0 -- check protection applied by kernel (includes
524 any implied execute protection).
525 1 -- check protection requested by application.
526 Default value is set via a kernel config option.
527 Value can be changed at runtime via
528 /selinux/checkreqprot.
530 cio_ignore= [S390]
531 See Documentation/s390/CommonIO for details.
532 clk_ignore_unused
533 [CLK]
534 Keep all clocks already enabled by bootloader on,
535 even if no driver has claimed them. This is useful
536 for debug and development, but should not be
537 needed on a platform with proper driver support.
538 For more information, see Documentation/clk.txt.
540 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
541 [Deprecated]
542 Forces specified clocksource (if available) to be used
543 when calculating gettimeofday(). If specified
544 clocksource is not available, it defaults to PIT.
545 Format: { pit | tsc | cyclone | pmtmr }
547 clocksource= Override the default clocksource
548 Format: <string>
549 Override the default clocksource and use the clocksource
550 with the name specified.
551 Some clocksource names to choose from, depending on
552 the platform:
553 [all] jiffies (this is the base, fallback clocksource)
554 [ACPI] acpi_pm
555 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
556 pxa_timer,timer3,32k_counter,timer0_1
557 [AVR32] avr32
558 [X86-32] pit,hpet,tsc;
559 scx200_hrt on Geode; cyclone on IBM x440
560 [MIPS] MIPS
561 [PARISC] cr16
562 [S390] tod
563 [SH] SuperH
564 [SPARC64] tick
565 [X86-64] hpet,tsc
567 clearcpuid=BITNUM [X86]
568 Disable CPUID feature X for the kernel. See
569 arch/x86/include/asm/cpufeature.h for the valid bit
570 numbers. Note the Linux specific bits are not necessarily
571 stable over kernel options, but the vendor specific
572 ones should be.
573 Also note that user programs calling CPUID directly
574 or using the feature without checking anything
575 will still see it. This just prevents it from
576 being used by the kernel or shown in /proc/cpuinfo.
577 Also note the kernel might malfunction if you disable
578 some critical bits.
580 cma=nn[MG] [ARM,KNL]
581 Sets the size of kernel global memory area for contiguous
582 memory allocations. For more information, see
583 include/linux/dma-contiguous.h
585 cmo_free_hint= [PPC] Format: { yes | no }
586 Specify whether pages are marked as being inactive
587 when they are freed. This is used in CMO environments
588 to determine OS memory pressure for page stealing by
589 a hypervisor.
590 Default: yes
592 coherent_pool=nn[KMG] [ARM,KNL]
593 Sets the size of memory pool for coherent, atomic dma
594 allocations, by default set to 256K.
596 code_bytes [X86] How many bytes of object code to print
597 in an oops report.
598 Range: 0 - 8192
599 Default: 64
601 com20020= [HW,NET] ARCnet - COM20020 chipset
602 Format:
603 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
605 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
606 Format: <io>[,<irq>]
608 com90xx= [HW,NET]
609 ARCnet - COM90xx chipset (memory-mapped buffers)
610 Format: <io>[,<irq>[,<memstart>]]
612 condev= [HW,S390] console device
613 conmode=
615 console= [KNL] Output console device and options.
617 tty<n> Use the virtual console device <n>.
619 ttyS<n>[,options]
620 ttyUSB0[,options]
621 Use the specified serial port. The options are of
622 the form "bbbbpnf", where "bbbb" is the baud rate,
623 "p" is parity ("n", "o", or "e"), "n" is number of
624 bits, and "f" is flow control ("r" for RTS or
625 omit it). Default is "9600n8".
627 See Documentation/serial-console.txt for more
628 information. See
629 Documentation/networking/netconsole.txt for an
630 alternative.
632 uart[8250],io,<addr>[,options]
633 uart[8250],mmio,<addr>[,options]
634 Start an early, polled-mode console on the 8250/16550
635 UART at the specified I/O port or MMIO address,
636 switching to the matching ttyS device later. The
637 options are the same as for ttyS, above.
638 hvc<n> Use the hypervisor console device <n>. This is for
639 both Xen and PowerPC hypervisors.
641 If the device connected to the port is not a TTY but a braille
642 device, prepend "brl," before the device type, for instance
643 console=brl,ttyS0
644 For now, only VisioBraille is supported.
646 consoleblank= [KNL] The console blank (screen saver) timeout in
647 seconds. Defaults to 10*60 = 10mins. A value of 0
648 disables the blank timer.
650 coredump_filter=
651 [KNL] Change the default value for
652 /proc/<pid>/coredump_filter.
653 See also Documentation/filesystems/proc.txt.
655 cpuidle.off=1 [CPU_IDLE]
656 disable the cpuidle sub-system
658 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
659 Format:
660 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
662 crashkernel=size[KMG][@offset[KMG]]
663 [KNL] Using kexec, Linux can switch to a 'crash kernel'
664 upon panic. This parameter reserves the physical
665 memory region [offset, offset + size] for that kernel
666 image. If '@offset' is omitted, then a suitable offset
667 is selected automatically. Check
668 Documentation/kdump/kdump.txt for further details.
670 crashkernel=range1:size1[,range2:size2,...][@offset]
671 [KNL] Same as above, but depends on the memory
672 in the running system. The syntax of range is
673 start-[end] where start and end are both
674 a memory unit (amount[KMG]). See also
675 Documentation/kdump/kdump.txt for an example.
677 crashkernel=size[KMG],high
678 [KNL, x86_64] range could be above 4G. Allow kernel
679 to allocate physical memory region from top, so could
680 be above 4G if system have more than 4G ram installed.
681 Otherwise memory region will be allocated below 4G, if
682 available.
683 It will be ignored if crashkernel=X is specified.
684 crashkernel=size[KMG],low
685 [KNL, x86_64] range under 4G. When crashkernel=X,high
686 is passed, kernel could allocate physical memory region
687 above 4G, that cause second kernel crash on system
688 that require some amount of low memory, e.g. swiotlb
689 requires at least 64M+32K low memory. Kernel would
690 try to allocate 72M below 4G automatically.
691 This one let user to specify own low range under 4G
692 for second kernel instead.
693 0: to disable low allocation.
694 It will be ignored when crashkernel=X,high is not used
695 or memory reserved is below 4G.
697 cs89x0_dma= [HW,NET]
698 Format: <dma>
700 cs89x0_media= [HW,NET]
701 Format: { rj45 | aui | bnc }
703 dasd= [HW,NET]
704 See header of drivers/s390/block/dasd_devmap.c.
706 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
707 (one device per port)
708 Format: <port#>,<type>
709 See also Documentation/input/joystick-parport.txt
711 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
712 time. See Documentation/dynamic-debug-howto.txt for
713 details. Deprecated, see dyndbg.
715 debug [KNL] Enable kernel debugging (events log level).
717 debug_locks_verbose=
718 [KNL] verbose self-tests
719 Format=<0|1>
720 Print debugging info while doing the locking API
721 self-tests.
722 We default to 0 (no extra messages), setting it to
723 1 will print _a lot_ more information - normally
724 only useful to kernel developers.
726 debug_objects [KNL] Enable object debugging
728 no_debug_objects
729 [KNL] Disable object debugging
731 debug_guardpage_minorder=
732 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
733 parameter allows control of the order of pages that will
734 be intentionally kept free (and hence protected) by the
735 buddy allocator. Bigger value increase the probability
736 of catching random memory corruption, but reduce the
737 amount of memory for normal system use. The maximum
738 possible value is MAX_ORDER/2. Setting this parameter
739 to 1 or 2 should be enough to identify most random
740 memory corruption problems caused by bugs in kernel or
741 driver code when a CPU writes to (or reads from) a
742 random memory location. Note that there exists a class
743 of memory corruptions problems caused by buggy H/W or
744 F/W or by drivers badly programing DMA (basically when
745 memory is written at bus level and the CPU MMU is
746 bypassed) which are not detectable by
747 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
748 tracking down these problems.
750 debugpat [X86] Enable PAT debugging
752 decnet.addr= [HW,NET]
753 Format: <area>[,<node>]
754 See also Documentation/networking/decnet.txt.
756 default_hugepagesz=
757 [same as hugepagesz=] The size of the default
758 HugeTLB page size. This is the size represented by
759 the legacy /proc/ hugepages APIs, used for SHM, and
760 default size when mounting hugetlbfs filesystems.
761 Defaults to the default architecture's huge page size
762 if not specified.
764 dhash_entries= [KNL]
765 Set number of hash buckets for dentry cache.
767 digi= [HW,SERIAL]
768 IO parameters + enable/disable command.
770 digiepca= [HW,SERIAL]
771 See drivers/char/README.epca and
772 Documentation/serial/digiepca.txt.
774 disable= [IPV6]
775 See Documentation/networking/ipv6.txt.
777 disable_ddw [PPC/PSERIES]
778 Disable Dynamic DMA Window support. Use this if
779 to workaround buggy firmware.
781 disable_ipv6= [IPV6]
782 See Documentation/networking/ipv6.txt.
784 disable_mtrr_cleanup [X86]
785 The kernel tries to adjust MTRR layout from continuous
786 to discrete, to make X server driver able to add WB
787 entry later. This parameter disables that.
789 disable_mtrr_trim [X86, Intel and AMD only]
790 By default the kernel will trim any uncacheable
791 memory out of your available memory pool based on
792 MTRR settings. This parameter disables that behavior,
793 possibly causing your machine to run very slowly.
795 disable_timer_pin_1 [X86]
796 Disable PIN 1 of APIC timer
797 Can be useful to work around chipset bugs.
799 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
800 this option disables the debugging code at boot.
802 dma_debug_entries=<number>
803 This option allows to tune the number of preallocated
804 entries for DMA-API debugging code. One entry is
805 required per DMA-API allocation. Use this if the
806 DMA-API debugging code disables itself because the
807 architectural default is too low.
809 dma_debug_driver=<driver_name>
810 With this option the DMA-API debugging driver
811 filter feature can be enabled at boot time. Just
812 pass the driver to filter for as the parameter.
813 The filter can be disabled or changed to another
814 driver later using sysfs.
816 drm_kms_helper.edid_firmware=[<connector>:]<file>
817 Broken monitors, graphic adapters and KVMs may
818 send no or incorrect EDID data sets. This parameter
819 allows to specify an EDID data set in the
820 /lib/firmware directory that is used instead.
821 Generic built-in EDID data sets are used, if one of
822 edid/1024x768.bin, edid/1280x1024.bin,
823 edid/1680x1050.bin, or edid/1920x1080.bin is given
824 and no file with the same name exists. Details and
825 instructions how to build your own EDID data are
826 available in Documentation/EDID/HOWTO.txt. An EDID
827 data set will only be used for a particular connector,
828 if its name and a colon are prepended to the EDID
829 name.
831 dscc4.setup= [NET]
833 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
834 module.dyndbg[="val"]
835 Enable debug messages at boot time. See
836 Documentation/dynamic-debug-howto.txt for details.
838 earlycon= [KNL] Output early console device and options.
839 uart[8250],io,<addr>[,options]
840 uart[8250],mmio,<addr>[,options]
841 uart[8250],mmio32,<addr>[,options]
842 Start an early, polled-mode console on the 8250/16550
843 UART at the specified I/O port or MMIO address.
844 MMIO inter-register address stride is either 8-bit
845 (mmio) or 32-bit (mmio32).
846 The options are the same as for ttyS, above.
848 earlyprintk= [X86,SH,BLACKFIN,ARM]
849 earlyprintk=vga
850 earlyprintk=efi
851 earlyprintk=xen
852 earlyprintk=serial[,ttySn[,baudrate]]
853 earlyprintk=serial[,0x...[,baudrate]]
854 earlyprintk=ttySn[,baudrate]
855 earlyprintk=dbgp[debugController#]
857 earlyprintk is useful when the kernel crashes before
858 the normal console is initialized. It is not enabled by
859 default because it has some cosmetic problems.
861 Append ",keep" to not disable it when the real console
862 takes over.
864 Only one of vga, efi, serial, or usb debug port can
865 be used at a time.
867 Currently only ttyS0 and ttyS1 may be specified by
868 name. Other I/O ports may be explicitly specified
869 on some architectures (x86 and arm at least) by
870 replacing ttySn with an I/O port address, like this:
871 earlyprintk=serial,0x1008,115200
872 You can find the port for a given device in
873 /proc/tty/driver/serial:
874 2: uart:ST16650V2 port:00001008 irq:18 ...
876 Interaction with the standard serial driver is not
877 very good.
879 The VGA and EFI output is eventually overwritten by
880 the real console.
882 The xen output can only be used by Xen PV guests.
884 ekgdboc= [X86,KGDB] Allow early kernel console debugging
885 ekgdboc=kbd
887 This is designed to be used in conjunction with
888 the boot argument: earlyprintk=vga
890 edd= [EDD]
891 Format: {"off" | "on" | "skip[mbr]"}
893 efi_no_storage_paranoia [EFI; X86]
894 Using this parameter you can use more than 50% of
895 your efi variable storage. Use this parameter only if
896 you are really sure that your UEFI does sane gc and
897 fulfills the spec otherwise your board may brick.
899 eisa_irq_edge= [PARISC,HW]
900 See header of drivers/parisc/eisa.c.
902 elanfreq= [X86-32]
903 See comment before function elanfreq_setup() in
904 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
906 elevator= [IOSCHED]
907 Format: {"cfq" | "deadline" | "noop"}
908 See Documentation/block/cfq-iosched.txt and
909 Documentation/block/deadline-iosched.txt for details.
911 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
912 Specifies physical address of start of kernel core
913 image elf header and optionally the size. Generally
914 kexec loader will pass this option to capture kernel.
915 See Documentation/kdump/kdump.txt for details.
917 enable_mtrr_cleanup [X86]
918 The kernel tries to adjust MTRR layout from continuous
919 to discrete, to make X server driver able to add WB
920 entry later. This parameter enables that.
922 enable_timer_pin_1 [X86]
923 Enable PIN 1 of APIC timer
924 Can be useful to work around chipset bugs
925 (in particular on some ATI chipsets).
926 The kernel tries to set a reasonable default.
928 enforcing [SELINUX] Set initial enforcing status.
929 Format: {"0" | "1"}
930 See security/selinux/Kconfig help text.
931 0 -- permissive (log only, no denials).
932 1 -- enforcing (deny and log).
933 Default value is 0.
934 Value can be changed at runtime via /selinux/enforce.
936 erst_disable [ACPI]
937 Disable Error Record Serialization Table (ERST)
938 support.
940 ether= [HW,NET] Ethernet cards parameters
941 This option is obsoleted by the "netdev=" option, which
942 has equivalent usage. See its documentation for details.
944 evm= [EVM]
945 Format: { "fix" }
946 Permit 'security.evm' to be updated regardless of
947 current integrity status.
949 failslab=
950 fail_page_alloc=
951 fail_make_request=[KNL]
952 General fault injection mechanism.
953 Format: <interval>,<probability>,<space>,<times>
954 See also Documentation/fault-injection/.
956 floppy= [HW]
957 See Documentation/blockdev/floppy.txt.
959 force_pal_cache_flush
960 [IA-64] Avoid check_sal_cache_flush which may hang on
961 buggy SAL_CACHE_FLUSH implementations. Using this
962 parameter will force ia64_sal_cache_flush to call
963 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
965 ftrace=[tracer]
966 [FTRACE] will set and start the specified tracer
967 as early as possible in order to facilitate early
968 boot debugging.
970 ftrace_dump_on_oops[=orig_cpu]
971 [FTRACE] will dump the trace buffers on oops.
972 If no parameter is passed, ftrace will dump
973 buffers of all CPUs, but if you pass orig_cpu, it will
974 dump only the buffer of the CPU that triggered the
975 oops.
977 ftrace_filter=[function-list]
978 [FTRACE] Limit the functions traced by the function
979 tracer at boot up. function-list is a comma separated
980 list of functions. This list can be changed at run
981 time by the set_ftrace_filter file in the debugfs
982 tracing directory.
984 ftrace_notrace=[function-list]
985 [FTRACE] Do not trace the functions specified in
986 function-list. This list can be changed at run time
987 by the set_ftrace_notrace file in the debugfs
988 tracing directory.
990 ftrace_graph_filter=[function-list]
991 [FTRACE] Limit the top level callers functions traced
992 by the function graph tracer at boot up.
993 function-list is a comma separated list of functions
994 that can be changed at run time by the
995 set_graph_function file in the debugfs tracing directory.
997 gamecon.map[2|3]=
998 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
999 support via parallel port (up to 5 devices per port)
1000 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1001 See also Documentation/input/joystick-parport.txt
1003 gamma= [HW,DRM]
1005 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1006 Format: off | on
1007 default: on
1009 gcov_persist= [GCOV] When non-zero (default), profiling data for
1010 kernel modules is saved and remains accessible via
1011 debugfs, even when the module is unloaded/reloaded.
1012 When zero, profiling data is discarded and associated
1013 debugfs files are removed at module unload time.
1015 gpt [EFI] Forces disk with valid GPT signature but
1016 invalid Protective MBR to be treated as GPT.
1018 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1019 the "Enable 0" bit of the configuration register.
1020 Format: 0 | 1
1021 Default: 0
1022 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1023 the "Enable 0" bit of the configuration register.
1024 Format: 0 | 1
1025 Default: 0
1026 grcan.select= [HW] Select which physical interface to use.
1027 Format: 0 | 1
1028 Default: 0
1029 grcan.txsize= [HW] Sets the size of the tx buffer.
1030 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1031 Default: 1024
1032 grcan.rxsize= [HW] Sets the size of the rx buffer.
1033 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1034 Default: 1024
1036 hashdist= [KNL,NUMA] Large hashes allocated during boot
1037 are distributed across NUMA nodes. Defaults on
1038 for 64-bit NUMA, off otherwise.
1039 Format: 0 | 1 (for off | on)
1041 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1043 hd= [EIDE] (E)IDE hard drive subsystem geometry
1044 Format: <cyl>,<head>,<sect>
1046 hest_disable [ACPI]
1047 Disable Hardware Error Source Table (HEST) support;
1048 corresponding firmware-first mode error processing
1049 logic will be disabled.
1051 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1052 size of <nn>. This works even on boxes that have no
1053 highmem otherwise. This also works to reduce highmem
1054 size on bigger boxes.
1056 highres= [KNL] Enable/disable high resolution timer mode.
1057 Valid parameters: "on", "off"
1058 Default: "on"
1060 hisax= [HW,ISDN]
1061 See Documentation/isdn/README.HiSax.
1063 hlt [BUGS=ARM,SH]
1065 hpet= [X86-32,HPET] option to control HPET usage
1066 Format: { enable (default) | disable | force |
1067 verbose }
1068 disable: disable HPET and use PIT instead
1069 force: allow force enabled of undocumented chips (ICH4,
1070 VIA, nVidia)
1071 verbose: show contents of HPET registers during setup
1073 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1074 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1076 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1077 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1078 On x86-64 and powerpc, this option can be specified
1079 multiple times interleaved with hugepages= to reserve
1080 huge pages of different sizes. Valid pages sizes on
1081 x86-64 are 2M (when the CPU supports "pse") and 1G
1082 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1083 Note that 1GB pages can only be allocated at boot time
1084 using hugepages= and not freed afterwards.
1086 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1087 terminal devices. Valid values: 0..8
1088 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1089 If specified, z/VM IUCV HVC accepts connections
1090 from listed z/VM user IDs only.
1092 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1093 hardware thread id mappings.
1094 Format: <cpu>:<hwthread>
1096 keep_bootcon [KNL]
1097 Do not unregister boot console at start. This is only
1098 useful for debugging when something happens in the window
1099 between unregistering the boot console and initializing
1100 the real console.
1102 i2c_bus= [HW] Override the default board specific I2C bus speed
1103 or register an additional I2C bus that is not
1104 registered from board initialization code.
1105 Format:
1106 <bus_id>,<clkrate>
1108 i8042.debug [HW] Toggle i8042 debug mode
1109 i8042.direct [HW] Put keyboard port into non-translated mode
1110 i8042.dumbkbd [HW] Pretend that controller can only read data from
1111 keyboard and cannot control its state
1112 (Don't attempt to blink the leds)
1113 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1114 i8042.nokbd [HW] Don't check/create keyboard port
1115 i8042.noloop [HW] Disable the AUX Loopback command while probing
1116 for the AUX port
1117 i8042.nomux [HW] Don't check presence of an active multiplexing
1118 controller
1119 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1120 controllers
1121 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1122 i8042.reset [HW] Reset the controller during init and cleanup
1123 i8042.unlock [HW] Unlock (ignore) the keylock
1125 i810= [HW,DRM]
1127 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1128 indicates that the driver is running on unsupported
1129 hardware.
1130 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1131 does not match list of supported models.
1132 i8k.power_status
1133 [HW] Report power status in /proc/i8k
1134 (disabled by default)
1135 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1136 capability is set.
1138 i915.invert_brightness=
1139 [DRM] Invert the sense of the variable that is used to
1140 set the brightness of the panel backlight. Normally a
1141 brightness value of 0 indicates backlight switched off,
1142 and the maximum of the brightness value sets the backlight
1143 to maximum brightness. If this parameter is set to 0
1144 (default) and the machine requires it, or this parameter
1145 is set to 1, a brightness value of 0 sets the backlight
1146 to maximum brightness, and the maximum of the brightness
1147 value switches the backlight off.
1148 -1 -- never invert brightness
1149 0 -- machine default
1150 1 -- force brightness inversion
1152 icn= [HW,ISDN]
1153 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1155 ide-core.nodma= [HW] (E)IDE subsystem
1156 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1157 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1158 .cdrom .chs .ignore_cable are additional options
1159 See Documentation/ide/ide.txt.
1161 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1162 Claim all unknown PCI IDE storage controllers.
1164 idle= [X86]
1165 Format: idle=poll, idle=halt, idle=nomwait
1166 Poll forces a polling idle loop that can slightly
1167 improve the performance of waking up a idle CPU, but
1168 will use a lot of power and make the system run hot.
1169 Not recommended.
1170 idle=halt: Halt is forced to be used for CPU idle.
1171 In such case C2/C3 won't be used again.
1172 idle=nomwait: Disable mwait for CPU C-states
1174 ignore_loglevel [KNL]
1175 Ignore loglevel setting - this will print /all/
1176 kernel messages to the console. Useful for debugging.
1177 We also add it as printk module parameter, so users
1178 could change it dynamically, usually by
1179 /sys/module/printk/parameters/ignore_loglevel.
1181 ihash_entries= [KNL]
1182 Set number of hash buckets for inode cache.
1184 ima_appraise= [IMA] appraise integrity measurements
1185 Format: { "off" | "enforce" | "fix" }
1186 default: "enforce"
1188 ima_appraise_tcb [IMA]
1189 The builtin appraise policy appraises all files
1190 owned by uid=0.
1192 ima_hash= [IMA]
1193 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1194 | sha512 | ... }
1195 default: "sha1"
1197 The list of supported hash algorithms is defined
1198 in crypto/hash_info.h.
1200 ima_tcb [IMA]
1201 Load a policy which meets the needs of the Trusted
1202 Computing Base. This means IMA will measure all
1203 programs exec'd, files mmap'd for exec, and all files
1204 opened for read by uid=0.
1206 ima_template= [IMA]
1207 Select one of defined IMA measurements template formats.
1208 Formats: { "ima" | "ima-ng" }
1209 Default: "ima-ng"
1211 init= [KNL]
1212 Format: <full_path>
1213 Run specified binary instead of /sbin/init as init
1214 process.
1216 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1217 for working out where the kernel is dying during
1218 startup.
1220 initrd= [BOOT] Specify the location of the initial ramdisk
1222 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1223 Format: <irq>
1225 int_pln_enable [x86] Enable power limit notification interrupt
1227 integrity_audit=[IMA]
1228 Format: { "0" | "1" }
1229 0 -- basic integrity auditing messages. (Default)
1230 1 -- additional integrity auditing messages.
1232 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1233 on
1234 Enable intel iommu driver.
1235 off
1236 Disable intel iommu driver.
1237 igfx_off [Default Off]
1238 By default, gfx is mapped as normal device. If a gfx
1239 device has a dedicated DMAR unit, the DMAR unit is
1240 bypassed by not enabling DMAR with this option. In
1241 this case, gfx device will use physical address for
1242 DMA.
1243 forcedac [x86_64]
1244 With this option iommu will not optimize to look
1245 for io virtual address below 32-bit forcing dual
1246 address cycle on pci bus for cards supporting greater
1247 than 32-bit addressing. The default is to look
1248 for translation below 32-bit and if not available
1249 then look in the higher range.
1250 strict [Default Off]
1251 With this option on every unmap_single operation will
1252 result in a hardware IOTLB flush operation as opposed
1253 to batching them for performance.
1254 sp_off [Default Off]
1255 By default, super page will be supported if Intel IOMMU
1256 has the capability. With this option, super page will
1257 not be supported.
1259 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1260 0 disables intel_idle and fall back on acpi_idle.
1261 1 to 6 specify maximum depth of C-state.
1263 intel_pstate= [X86]
1264 disable
1265 Do not enable intel_pstate as the default
1266 scaling driver for the supported processors
1268 intremap= [X86-64, Intel-IOMMU]
1269 on enable Interrupt Remapping (default)
1270 off disable Interrupt Remapping
1271 nosid disable Source ID checking
1272 no_x2apic_optout
1273 BIOS x2APIC opt-out request will be ignored
1275 iomem= Disable strict checking of access to MMIO memory
1276 strict regions from userspace.
1277 relaxed
1279 iommu= [x86]
1280 off
1281 force
1282 noforce
1283 biomerge
1284 panic
1285 nopanic
1286 merge
1287 nomerge
1288 forcesac
1289 soft
1290 pt [x86, IA-64]
1293 io7= [HW] IO7 for Marvel based alpha systems
1294 See comment before marvel_specify_io7 in
1295 arch/alpha/kernel/core_marvel.c.
1297 io_delay= [X86] I/O delay method
1298 0x80
1299 Standard port 0x80 based delay
1300 0xed
1301 Alternate port 0xed based delay (needed on some systems)
1302 udelay
1303 Simple two microseconds delay
1304 none
1305 No delay
1307 ip= [IP_PNP]
1308 See Documentation/filesystems/nfs/nfsroot.txt.
1310 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1311 See comment before ip2_setup() in
1312 drivers/char/ip2/ip2base.c.
1314 irqfixup [HW]
1315 When an interrupt is not handled search all handlers
1316 for it. Intended to get systems with badly broken
1317 firmware running.
1319 irqpoll [HW]
1320 When an interrupt is not handled search all handlers
1321 for it. Also check all handlers each timer
1322 interrupt. Intended to get systems with badly broken
1323 firmware running.
1325 isapnp= [ISAPNP]
1326 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1328 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1329 Format:
1330 <cpu number>,...,<cpu number>
1331 or
1332 <cpu number>-<cpu number>
1333 (must be a positive range in ascending order)
1334 or a mixture
1335 <cpu number>,...,<cpu number>-<cpu number>
1337 This option can be used to specify one or more CPUs
1338 to isolate from the general SMP balancing and scheduling
1339 algorithms. You can move a process onto or off an
1340 "isolated" CPU via the CPU affinity syscalls or cpuset.
1341 <cpu number> begins at 0 and the maximum value is
1342 "number of CPUs in system - 1".
1344 This option is the preferred way to isolate CPUs. The
1345 alternative -- manually setting the CPU mask of all
1346 tasks in the system -- can cause problems and
1347 suboptimal load balancer performance.
1349 iucv= [HW,NET]
1351 ivrs_ioapic [HW,X86_64]
1352 Provide an override to the IOAPIC-ID<->DEVICE-ID
1353 mapping provided in the IVRS ACPI table. For
1354 example, to map IOAPIC-ID decimal 10 to
1355 PCI device 00:14.0 write the parameter as:
1356 ivrs_ioapic[10]=00:14.0
1358 ivrs_hpet [HW,X86_64]
1359 Provide an override to the HPET-ID<->DEVICE-ID
1360 mapping provided in the IVRS ACPI table. For
1361 example, to map HPET-ID decimal 0 to
1362 PCI device 00:14.0 write the parameter as:
1363 ivrs_hpet[0]=00:14.0
1365 js= [HW,JOY] Analog joystick
1366 See Documentation/input/joystick.txt.
1368 keepinitrd [HW,ARM]
1370 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1371 specifies the amount of memory usable by the kernel
1372 for non-movable allocations. The requested amount is
1373 spread evenly throughout all nodes in the system. The
1374 remaining memory in each node is used for Movable
1375 pages. In the event, a node is too small to have both
1376 kernelcore and Movable pages, kernelcore pages will
1377 take priority and other nodes will have a larger number
1378 of Movable pages. The Movable zone is used for the
1379 allocation of pages that may be reclaimed or moved
1380 by the page migration subsystem. This means that
1381 HugeTLB pages may not be allocated from this zone.
1382 Note that allocations like PTEs-from-HighMem still
1383 use the HighMem zone if it exists, and the Normal
1384 zone if it does not.
1386 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1387 Format: <Controller#>[,poll interval]
1388 The controller # is the number of the ehci usb debug
1389 port as it is probed via PCI. The poll interval is
1390 optional and is the number seconds in between
1391 each poll cycle to the debug port in case you need
1392 the functionality for interrupting the kernel with
1393 gdb or control-c on the dbgp connection. When
1394 not using this parameter you use sysrq-g to break into
1395 the kernel debugger.
1397 kgdboc= [KGDB,HW] kgdb over consoles.
1398 Requires a tty driver that supports console polling,
1399 or a supported polling keyboard driver (non-usb).
1400 Serial only format: <serial_device>[,baud]
1401 keyboard only format: kbd
1402 keyboard and serial format: kbd,<serial_device>[,baud]
1403 Optional Kernel mode setting:
1404 kms, kbd format: kms,kbd
1405 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1407 kgdbwait [KGDB] Stop kernel execution and enter the
1408 kernel debugger at the earliest opportunity.
1410 kmac= [MIPS] korina ethernet MAC address.
1411 Configure the RouterBoard 532 series on-chip
1412 Ethernet adapter MAC address.
1414 kmemleak= [KNL] Boot-time kmemleak enable/disable
1415 Valid arguments: on, off
1416 Default: on
1418 kstack=N [X86] Print N words from the kernel stack
1419 in oops dumps.
1421 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1422 Default is 0 (don't ignore, but inject #GP)
1424 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1425 KVM MMU at runtime.
1426 Default is 0 (off)
1428 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1429 Default is 1 (enabled)
1431 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1432 for all guests.
1433 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1435 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1436 (virtualized MMU) support on capable Intel chips.
1437 Default is 1 (enabled)
1439 kvm-intel.emulate_invalid_guest_state=
1440 [KVM,Intel] Enable emulation of invalid guest states
1441 Default is 0 (disabled)
1443 kvm-intel.flexpriority=
1444 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1445 Default is 1 (enabled)
1447 kvm-intel.nested=
1448 [KVM,Intel] Enable VMX nesting (nVMX).
1449 Default is 0 (disabled)
1451 kvm-intel.unrestricted_guest=
1452 [KVM,Intel] Disable unrestricted guest feature
1453 (virtualized real and unpaged mode) on capable
1454 Intel chips. Default is 1 (enabled)
1456 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1457 feature (tagged TLBs) on capable Intel chips.
1458 Default is 1 (enabled)
1460 l2cr= [PPC]
1462 l3cr= [PPC]
1464 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1465 disabled it.
1467 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1468 value for LAPIC timer one-shot implementation. Default
1469 back to the programmable timer unit in the LAPIC.
1471 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1472 in C2 power state.
1474 libata.dma= [LIBATA] DMA control
1475 libata.dma=0 Disable all PATA and SATA DMA
1476 libata.dma=1 PATA and SATA Disk DMA only
1477 libata.dma=2 ATAPI (CDROM) DMA only
1478 libata.dma=4 Compact Flash DMA only
1479 Combinations also work, so libata.dma=3 enables DMA
1480 for disks and CDROMs, but not CFs.
1482 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1483 libata.ignore_hpa=0 keep BIOS limits (default)
1484 libata.ignore_hpa=1 ignore limits, using full disk
1486 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1487 when set.
1488 Format: <int>
1490 libata.force= [LIBATA] Force configurations. The format is comma
1491 separated list of "[ID:]VAL" where ID is
1492 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1493 matching port, link or device. Basically, it matches
1494 the ATA ID string printed on console by libata. If
1495 the whole ID part is omitted, the last PORT and DEVICE
1496 values are used. If ID hasn't been specified yet, the
1497 configuration applies to all ports, links and devices.
1499 If only DEVICE is omitted, the parameter applies to
1500 the port and all links and devices behind it. DEVICE
1501 number of 0 either selects the first device or the
1502 first fan-out link behind PMP device. It does not
1503 select the host link. DEVICE number of 15 selects the
1504 host link and device attached to it.
1506 The VAL specifies the configuration to force. As long
1507 as there's no ambiguity shortcut notation is allowed.
1508 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1509 The following configurations can be forced.
1511 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1512 Any ID with matching PORT is used.
1514 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1516 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1517 udma[/][16,25,33,44,66,100,133] notation is also
1518 allowed.
1520 * [no]ncq: Turn on or off NCQ.
1522 * nohrst, nosrst, norst: suppress hard, soft
1523 and both resets.
1525 * rstonce: only attempt one reset during
1526 hot-unplug link recovery
1528 * dump_id: dump IDENTIFY data.
1530 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1532 If there are multiple matching configurations changing
1533 the same attribute, the last one is used.
1535 memblock=debug [KNL] Enable memblock debug messages.
1537 load_ramdisk= [RAM] List of ramdisks to load from floppy
1538 See Documentation/blockdev/ramdisk.txt.
1540 lockd.nlm_grace_period=P [NFS] Assign grace period.
1541 Format: <integer>
1543 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1544 Format: <integer>
1546 lockd.nlm_timeout=T [NFS] Assign timeout value.
1547 Format: <integer>
1549 lockd.nlm_udpport=M [NFS] Assign UDP port.
1550 Format: <integer>
1552 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1553 Format: <irq>
1555 loglevel= All Kernel Messages with a loglevel smaller than the
1556 console loglevel will be printed to the console. It can
1557 also be changed with klogd or other programs. The
1558 loglevels are defined as follows:
1560 0 (KERN_EMERG) system is unusable
1561 1 (KERN_ALERT) action must be taken immediately
1562 2 (KERN_CRIT) critical conditions
1563 3 (KERN_ERR) error conditions
1564 4 (KERN_WARNING) warning conditions
1565 5 (KERN_NOTICE) normal but significant condition
1566 6 (KERN_INFO) informational
1567 7 (KERN_DEBUG) debug-level messages
1569 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1570 in bytes. n must be a power of two. The default
1571 size is set in the kernel config file.
1573 logo.nologo [FB] Disables display of the built-in Linux logo.
1574 This may be used to provide more screen space for
1575 kernel log messages and is useful when debugging
1576 kernel boot problems.
1578 lp=0 [LP] Specify parallel ports to use, e.g,
1579 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1580 lp=reset first parallel port). 'lp=0' disables the
1581 lp=auto printer driver. 'lp=reset' (which can be
1582 specified in addition to the ports) causes
1583 attached printers to be reset. Using
1584 lp=port1,port2,... specifies the parallel ports
1585 to associate lp devices with, starting with
1586 lp0. A port specification may be 'none' to skip
1587 that lp device, or a parport name such as
1588 'parport0'. Specifying 'lp=auto' instead of a
1589 port specification list means that device IDs
1590 from each port should be examined, to see if
1591 an IEEE 1284-compliant printer is attached; if
1592 so, the driver will manage that printer.
1593 See also header of drivers/char/lp.c.
1595 lpj=n [KNL]
1596 Sets loops_per_jiffy to given constant, thus avoiding
1597 time-consuming boot-time autodetection (up to 250 ms per
1598 CPU). 0 enables autodetection (default). To determine
1599 the correct value for your kernel, boot with normal
1600 autodetection and see what value is printed. Note that
1601 on SMP systems the preset will be applied to all CPUs,
1602 which is likely to cause problems if your CPUs need
1603 significantly divergent settings. An incorrect value
1604 will cause delays in the kernel to be wrong, leading to
1605 unpredictable I/O errors and other breakage. Although
1606 unlikely, in the extreme case this might damage your
1607 hardware.
1609 ltpc= [NET]
1610 Format: <io>,<irq>,<dma>
1612 machvec= [IA-64] Force the use of a particular machine-vector
1613 (machvec) in a generic kernel.
1614 Example: machvec=hpzx1_swiotlb
1616 machtype= [Loongson] Share the same kernel image file between different
1617 yeeloong laptop.
1618 Example: machtype=lemote-yeeloong-2f-7inch
1620 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1621 than or equal to this physical address is ignored.
1623 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1624 should make use of. maxcpus=n : n >= 0 limits the
1625 kernel to using 'n' processors. n=0 is a special case,
1626 it is equivalent to "nosmp", which also disables
1627 the IO APIC.
1629 max_loop= [LOOP] The number of loop block devices that get
1630 (loop.max_loop) unconditionally pre-created at init time. The default
1631 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1632 of statically allocating a predefined number, loop
1633 devices can be requested on-demand with the
1634 /dev/loop-control interface.
1636 mce [X86-32] Machine Check Exception
1638 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1640 md= [HW] RAID subsystems devices and level
1641 See Documentation/md.txt.
1643 mdacon= [MDA]
1644 Format: <first>,<last>
1645 Specifies range of consoles to be captured by the MDA.
1647 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1648 Amount of memory to be used when the kernel is not able
1649 to see the whole system memory or for test.
1650 [X86] Work as limiting max address. Use together
1651 with memmap= to avoid physical address space collisions.
1652 Without memmap= PCI devices could be placed at addresses
1653 belonging to unused RAM.
1655 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1656 memory.
1658 memchunk=nn[KMG]
1659 [KNL,SH] Allow user to override the default size for
1660 per-device physically contiguous DMA buffers.
1662 memmap=exactmap [KNL,X86] Enable setting of an exact
1663 E820 memory map, as specified by the user.
1664 Such memmap=exactmap lines can be constructed based on
1665 BIOS output or other requirements. See the memmap=nn@ss
1666 option description.
1668 memmap=nn[KMG]@ss[KMG]
1669 [KNL] Force usage of a specific region of memory
1670 Region of memory to be used, from ss to ss+nn.
1672 memmap=nn[KMG]#ss[KMG]
1673 [KNL,ACPI] Mark specific memory as ACPI data.
1674 Region of memory to be used, from ss to ss+nn.
1676 memmap=nn[KMG]$ss[KMG]
1677 [KNL,ACPI] Mark specific memory as reserved.
1678 Region of memory to be used, from ss to ss+nn.
1679 Example: Exclude memory from 0x18690000-0x1869ffff
1680 memmap=64K$0x18690000
1681 or
1682 memmap=0x10000$0x18690000
1684 memory_corruption_check=0/1 [X86]
1685 Some BIOSes seem to corrupt the first 64k of
1686 memory when doing things like suspend/resume.
1687 Setting this option will scan the memory
1688 looking for corruption. Enabling this will
1689 both detect corruption and prevent the kernel
1690 from using the memory being corrupted.
1691 However, its intended as a diagnostic tool; if
1692 repeatable BIOS-originated corruption always
1693 affects the same memory, you can use memmap=
1694 to prevent the kernel from using that memory.
1696 memory_corruption_check_size=size [X86]
1697 By default it checks for corruption in the low
1698 64k, making this memory unavailable for normal
1699 use. Use this parameter to scan for
1700 corruption in more or less memory.
1702 memory_corruption_check_period=seconds [X86]
1703 By default it checks for corruption every 60
1704 seconds. Use this parameter to check at some
1705 other rate. 0 disables periodic checking.
1707 memtest= [KNL,X86] Enable memtest
1708 Format: <integer>
1709 default : 0 <disable>
1710 Specifies the number of memtest passes to be
1711 performed. Each pass selects another test
1712 pattern from a given set of patterns. Memtest
1713 fills the memory with this pattern, validates
1714 memory contents and reserves bad memory
1715 regions that are detected.
1717 meye.*= [HW] Set MotionEye Camera parameters
1718 See Documentation/video4linux/meye.txt.
1720 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1721 Multi-Function General Purpose Timers on AMD Geode
1722 platforms.
1724 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1725 the BIOS has incorrectly applied a workaround. TinyBIOS
1726 version 0.98 is known to be affected, 0.99 fixes the
1727 problem by letting the user disable the workaround.
1729 mga= [HW,DRM]
1731 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1732 physical address is ignored.
1734 mini2440= [ARM,HW,KNL]
1735 Format:[0..2][b][c][t]
1736 Default: "0tb"
1737 MINI2440 configuration specification:
1738 0 - The attached screen is the 3.5" TFT
1739 1 - The attached screen is the 7" TFT
1740 2 - The VGA Shield is attached (1024x768)
1741 Leaving out the screen size parameter will not load
1742 the TFT driver, and the framebuffer will be left
1743 unconfigured.
1744 b - Enable backlight. The TFT backlight pin will be
1745 linked to the kernel VESA blanking code and a GPIO
1746 LED. This parameter is not necessary when using the
1747 VGA shield.
1748 c - Enable the s3c camera interface.
1749 t - Reserved for enabling touchscreen support. The
1750 touchscreen support is not enabled in the mainstream
1751 kernel as of 2.6.30, a preliminary port can be found
1752 in the "bleeding edge" mini2440 support kernel at
1753 http://repo.or.cz/w/linux-2.6/mini2440.git
1755 mminit_loglevel=
1756 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1757 parameter allows control of the logging verbosity for
1758 the additional memory initialisation checks. A value
1759 of 0 disables mminit logging and a level of 4 will
1760 log everything. Information is printed at KERN_DEBUG
1761 so loglevel=8 may also need to be specified.
1763 module.sig_enforce
1764 [KNL] When CONFIG_MODULE_SIG is set, this means that
1765 modules without (valid) signatures will fail to load.
1766 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1767 is always true, so this option does nothing.
1769 mousedev.tap_time=
1770 [MOUSE] Maximum time between finger touching and
1771 leaving touchpad surface for touch to be considered
1772 a tap and be reported as a left button click (for
1773 touchpads working in absolute mode only).
1774 Format: <msecs>
1775 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1776 reporting absolute coordinates, such as tablets
1777 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1778 reporting absolute coordinates, such as tablets
1780 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1781 is similar to kernelcore except it specifies the
1782 amount of memory used for migratable allocations.
1783 If both kernelcore and movablecore is specified,
1784 then kernelcore will be at *least* the specified
1785 value but may be more. If movablecore on its own
1786 is specified, the administrator must be careful
1787 that the amount of memory usable for all allocations
1788 is not too small.
1790 movable_node [KNL,X86] Boot-time switch to enable the effects
1791 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
1793 MTD_Partition= [MTD]
1794 Format: <name>,<region-number>,<size>,<offset>
1796 MTD_Region= [MTD] Format:
1797 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1799 mtdparts= [MTD]
1800 See drivers/mtd/cmdlinepart.c.
1802 multitce=off [PPC] This parameter disables the use of the pSeries
1803 firmware feature for updating multiple TCE entries
1804 at a time.
1806 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1808 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1810 boundary - index of last SLC block on Flex-OneNAND.
1811 The remaining blocks are configured as MLC blocks.
1812 lock - Configure if Flex-OneNAND boundary should be locked.
1813 Once locked, the boundary cannot be changed.
1814 1 indicates lock status, 0 indicates unlock status.
1816 mtdset= [ARM]
1817 ARM/S3C2412 JIVE boot control
1819 See arch/arm/mach-s3c2412/mach-jive.c
1821 mtouchusb.raw_coordinates=
1822 [HW] Make the MicroTouch USB driver use raw coordinates
1823 ('y', default) or cooked coordinates ('n')
1825 mtrr_chunk_size=nn[KMG] [X86]
1826 used for mtrr cleanup. It is largest continuous chunk
1827 that could hold holes aka. UC entries.
1829 mtrr_gran_size=nn[KMG] [X86]
1830 Used for mtrr cleanup. It is granularity of mtrr block.
1831 Default is 1.
1832 Large value could prevent small alignment from
1833 using up MTRRs.
1835 mtrr_spare_reg_nr=n [X86]
1836 Format: <integer>
1837 Range: 0,7 : spare reg number
1838 Default : 1
1839 Used for mtrr cleanup. It is spare mtrr entries number.
1840 Set to 2 or more if your graphical card needs more.
1842 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1844 netdev= [NET] Network devices parameters
1845 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1846 Note that mem_start is often overloaded to mean
1847 something different and driver-specific.
1848 This usage is only documented in each driver source
1849 file if at all.
1851 nf_conntrack.acct=
1852 [NETFILTER] Enable connection tracking flow accounting
1853 0 to disable accounting
1854 1 to enable accounting
1855 Default value is 0.
1857 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1858 See Documentation/filesystems/nfs/nfsroot.txt.
1860 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1861 See Documentation/filesystems/nfs/nfsroot.txt.
1863 nfsrootdebug [NFS] enable nfsroot debugging messages.
1864 See Documentation/filesystems/nfs/nfsroot.txt.
1866 nfs.callback_tcpport=
1867 [NFS] set the TCP port on which the NFSv4 callback
1868 channel should listen.
1870 nfs.cache_getent=
1871 [NFS] sets the pathname to the program which is used
1872 to update the NFS client cache entries.
1874 nfs.cache_getent_timeout=
1875 [NFS] sets the timeout after which an attempt to
1876 update a cache entry is deemed to have failed.
1878 nfs.idmap_cache_timeout=
1879 [NFS] set the maximum lifetime for idmapper cache
1880 entries.
1882 nfs.enable_ino64=
1883 [NFS] enable 64-bit inode numbers.
1884 If zero, the NFS client will fake up a 32-bit inode
1885 number for the readdir() and stat() syscalls instead
1886 of returning the full 64-bit number.
1887 The default is to return 64-bit inode numbers.
1889 nfs.max_session_slots=
1890 [NFSv4.1] Sets the maximum number of session slots
1891 the client will attempt to negotiate with the server.
1892 This limits the number of simultaneous RPC requests
1893 that the client can send to the NFSv4.1 server.
1894 Note that there is little point in setting this
1895 value higher than the max_tcp_slot_table_limit.
1897 nfs.nfs4_disable_idmapping=
1898 [NFSv4] When set to the default of '1', this option
1899 ensures that both the RPC level authentication
1900 scheme and the NFS level operations agree to use
1901 numeric uids/gids if the mount is using the
1902 'sec=sys' security flavour. In effect it is
1903 disabling idmapping, which can make migration from
1904 legacy NFSv2/v3 systems to NFSv4 easier.
1905 Servers that do not support this mode of operation
1906 will be autodetected by the client, and it will fall
1907 back to using the idmapper.
1908 To turn off this behaviour, set the value to '0'.
1909 nfs.nfs4_unique_id=
1910 [NFS4] Specify an additional fixed unique ident-
1911 ification string that NFSv4 clients can insert into
1912 their nfs_client_id4 string. This is typically a
1913 UUID that is generated at system install time.
1915 nfs.send_implementation_id =
1916 [NFSv4.1] Send client implementation identification
1917 information in exchange_id requests.
1918 If zero, no implementation identification information
1919 will be sent.
1920 The default is to send the implementation identification
1921 information.
1923 nfs.recover_lost_locks =
1924 [NFSv4] Attempt to recover locks that were lost due
1925 to a lease timeout on the server. Please note that
1926 doing this risks data corruption, since there are
1927 no guarantees that the file will remain unchanged
1928 after the locks are lost.
1929 If you want to enable the kernel legacy behaviour of
1930 attempting to recover these locks, then set this
1931 parameter to '1'.
1932 The default parameter value of '0' causes the kernel
1933 not to attempt recovery of lost locks.
1935 nfsd.nfs4_disable_idmapping=
1936 [NFSv4] When set to the default of '1', the NFSv4
1937 server will return only numeric uids and gids to
1938 clients using auth_sys, and will accept numeric uids
1939 and gids from such clients. This is intended to ease
1940 migration from NFSv2/v3.
1942 objlayoutdriver.osd_login_prog=
1943 [NFS] [OBJLAYOUT] sets the pathname to the program which
1944 is used to automatically discover and login into new
1945 osd-targets. Please see:
1946 Documentation/filesystems/pnfs.txt for more explanations
1948 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1949 when a NMI is triggered.
1950 Format: [state][,regs][,debounce][,die]
1952 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1953 Format: [panic,][nopanic,][num]
1954 Valid num: 0
1955 0 - turn nmi_watchdog off
1956 When panic is specified, panic when an NMI watchdog
1957 timeout occurs (or 'nopanic' to override the opposite
1958 default).
1959 This is useful when you use a panic=... timeout and
1960 need the box quickly up again.
1962 netpoll.carrier_timeout=
1963 [NET] Specifies amount of time (in seconds) that
1964 netpoll should wait for a carrier. By default netpoll
1965 waits 4 seconds.
1967 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1968 emulation library even if a 387 maths coprocessor
1969 is present.
1971 no_console_suspend
1972 [HW] Never suspend the console
1973 Disable suspending of consoles during suspend and
1974 hibernate operations. Once disabled, debugging
1975 messages can reach various consoles while the rest
1976 of the system is being put to sleep (ie, while
1977 debugging driver suspend/resume hooks). This may
1978 not work reliably with all consoles, but is known
1979 to work with serial and VGA consoles.
1980 To facilitate more flexible debugging, we also add
1981 console_suspend, a printk module parameter to control
1982 it. Users could use console_suspend (usually
1983 /sys/module/printk/parameters/console_suspend) to
1984 turn on/off it dynamically.
1986 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1987 caches in the slab allocator. Saves per-node memory,
1988 but will impact performance.
1990 noalign [KNL,ARM]
1992 noapic [SMP,APIC] Tells the kernel to not make use of any
1993 IOAPICs that may be present in the system.
1995 noautogroup Disable scheduler automatic task group creation.
1997 nobats [PPC] Do not use BATs for mapping kernel lowmem
1998 on "Classic" PPC cores.
2000 nocache [ARM]
2002 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2004 nodelayacct [KNL] Disable per-task delay accounting
2006 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2008 nodsp [SH] Disable hardware DSP at boot time.
2010 noefi [X86] Disable EFI runtime services support.
2012 noexec [IA-64]
2014 noexec [X86]
2015 On X86-32 available only on PAE configured kernels.
2016 noexec=on: enable non-executable mappings (default)
2017 noexec=off: disable non-executable mappings
2019 nosmap [X86]
2020 Disable SMAP (Supervisor Mode Access Prevention)
2021 even if it is supported by processor.
2023 nosmep [X86]
2024 Disable SMEP (Supervisor Mode Execution Prevention)
2025 even if it is supported by processor.
2027 noexec32 [X86-64]
2028 This affects only 32-bit executables.
2029 noexec32=on: enable non-executable mappings (default)
2030 read doesn't imply executable mappings
2031 noexec32=off: disable non-executable mappings
2032 read implies executable mappings
2034 nofpu [SH] Disable hardware FPU at boot time.
2036 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2037 register save and restore. The kernel will only save
2038 legacy floating-point registers on task switch.
2040 noxsave [BUGS=X86] Disables x86 extended register state save
2041 and restore using xsave. The kernel will fallback to
2042 enabling legacy floating-point and sse state.
2044 eagerfpu= [X86]
2045 on enable eager fpu restore
2046 off disable eager fpu restore
2047 auto selects the default scheme, which automatically
2048 enables eagerfpu restore for xsaveopt.
2050 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2051 wfi(ARM) instruction doesn't work correctly and not to
2052 use it. This is also useful when using JTAG debugger.
2054 no_file_caps Tells the kernel not to honor file capabilities. The
2055 only way then for a file to be executed with privilege
2056 is to be setuid root or executed by root.
2058 nohalt [IA-64] Tells the kernel not to use the power saving
2059 function PAL_HALT_LIGHT when idle. This increases
2060 power-consumption. On the positive side, it reduces
2061 interrupt wake-up latency, which may improve performance
2062 in certain environments such as networked servers or
2063 real-time systems.
2065 nohz= [KNL] Boottime enable/disable dynamic ticks
2066 Valid arguments: on, off
2067 Default: on
2069 nohz_full= [KNL,BOOT]
2070 In kernels built with CONFIG_NO_HZ_FULL=y, set
2071 the specified list of CPUs whose tick will be stopped
2072 whenever possible. The boot CPU will be forced outside
2073 the range to maintain the timekeeping.
2074 The CPUs in this range must also be included in the
2075 rcu_nocbs= set.
2077 noiotrap [SH] Disables trapped I/O port accesses.
2079 noirqdebug [X86-32] Disables the code which attempts to detect and
2080 disable unhandled interrupt sources.
2082 no_timer_check [X86,APIC] Disables the code which tests for
2083 broken timer IRQ sources.
2085 noisapnp [ISAPNP] Disables ISA PnP code.
2087 noinitrd [RAM] Tells the kernel not to load any configured
2088 initial RAM disk.
2090 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2091 remapping.
2092 [Deprecated - use intremap=off]
2094 nointroute [IA-64]
2096 nojitter [IA-64] Disables jitter checking for ITC timers.
2098 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2100 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2101 fault handling.
2103 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2104 steal time is computed, but won't influence scheduler
2105 behaviour
2107 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2109 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2111 noltlbs [PPC] Do not use large page/tlb entries for kernel
2112 lowmem mapping on PPC40x.
2114 nomca [IA-64] Disable machine check abort handling
2116 nomce [X86-32] Machine Check Exception
2118 nomfgpt [X86-32] Disable Multi-Function General Purpose
2119 Timer usage (for AMD Geode machines).
2121 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2122 shutdown the other cpus. Instead use the REBOOT_VECTOR
2123 irq.
2125 nomodule Disable module load
2127 nopat [X86] Disable PAT (page attribute table extension of
2128 pagetables) support.
2130 norandmaps Don't use address space randomization. Equivalent to
2131 echo 0 > /proc/sys/kernel/randomize_va_space
2133 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2135 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2136 with UP alternatives
2138 nordrand [X86] Disable the direct use of the RDRAND
2139 instruction even if it is supported by the
2140 processor. RDRAND is still available to user
2141 space applications.
2143 noresume [SWSUSP] Disables resume and restores original swap
2144 space.
2146 no-scroll [VGA] Disables scrollback.
2147 This is required for the Braillex ib80-piezo Braille
2148 reader made by F.H. Papenmeier (Germany).
2150 nosbagart [IA-64]
2152 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2154 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2155 and disable the IO APIC. legacy for "maxcpus=0".
2157 nosoftlockup [KNL] Disable the soft-lockup detector.
2159 nosync [HW,M68K] Disables sync negotiation for all devices.
2161 notsc [BUGS=X86-32] Disable Time Stamp Counter
2163 nousb [USB] Disable the USB subsystem
2165 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2167 nowb [ARM]
2169 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2171 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2172 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2173 Some features depend on CPU0. Known dependencies are:
2174 1. Resume from suspend/hibernate depends on CPU0.
2175 Suspend/hibernate will fail if CPU0 is offline and you
2176 need to online CPU0 before suspend/hibernate.
2177 2. PIC interrupts also depend on CPU0. CPU0 can't be
2178 removed if a PIC interrupt is detected.
2179 It's said poweroff/reboot may depend on CPU0 on some
2180 machines although I haven't seen such issues so far
2181 after CPU0 is offline on a few tested machines.
2182 If the dependencies are under your control, you can
2183 turn on cpu0_hotplug.
2185 nptcg= [IA-64] Override max number of concurrent global TLB
2186 purges which is reported from either PAL_VM_SUMMARY or
2187 SAL PALO.
2189 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2190 could support. nr_cpus=n : n >= 1 limits the kernel to
2191 supporting 'n' processors. Later in runtime you can not
2192 use hotplug cpu feature to put more cpu back to online.
2193 just like you compile the kernel NR_CPUS=n
2195 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2197 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2198 Allowed values are enable and disable
2200 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2201 one of ['zone', 'node', 'default'] can be specified
2202 This can be set from sysctl after boot.
2203 See Documentation/sysctl/vm.txt for details.
2205 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2206 See Documentation/debugging-via-ohci1394.txt for more
2207 info.
2209 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2210 Rather than timing out after 20 ms if an EC
2211 command is not properly ACKed, override the length
2212 of the timeout. We have interrupts disabled while
2213 waiting for the ACK, so if this is set too high
2214 interrupts *may* be lost!
2216 omap_mux= [OMAP] Override bootloader pin multiplexing.
2217 Format: <mux_mode0.mode_name=value>...
2218 For example, to override I2C bus2:
2219 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2221 oprofile.timer= [HW]
2222 Use timer interrupt instead of performance counters
2224 oprofile.cpu_type= Force an oprofile cpu type
2225 This might be useful if you have an older oprofile
2226 userland or if you want common events.
2227 Format: { arch_perfmon }
2228 arch_perfmon: [X86] Force use of architectural
2229 perfmon on Intel CPUs instead of the
2230 CPU specific event set.
2231 timer: [X86] Force use of architectural NMI
2232 timer mode (see also oprofile.timer
2233 for generic hr timer mode)
2234 [s390] Force legacy basic mode sampling
2235 (report cpu_type "timer")
2237 oops=panic Always panic on oopses. Default is to just kill the
2238 process, but there is a small probability of
2239 deadlocking the machine.
2240 This will also cause panics on machine check exceptions.
2241 Useful together with panic=30 to trigger a reboot.
2243 OSS [HW,OSS]
2244 See Documentation/sound/oss/oss-parameters.txt
2246 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2247 timeout > 0: seconds before rebooting
2248 timeout = 0: wait forever
2249 timeout < 0: reboot immediately
2250 Format: <timeout>
2252 parkbd.port= [HW] Parallel port number the keyboard adapter is
2253 connected to, default is 0.
2254 Format: <parport#>
2255 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2256 0 for XT, 1 for AT (default is AT).
2257 Format: <mode>
2259 parport= [HW,PPT] Specify parallel ports. 0 disables.
2260 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2261 Use 'auto' to force the driver to use any
2262 IRQ/DMA settings detected (the default is to
2263 ignore detected IRQ/DMA settings because of
2264 possible conflicts). You can specify the base
2265 address, IRQ, and DMA settings; IRQ and DMA
2266 should be numbers, or 'auto' (for using detected
2267 settings on that particular port), or 'nofifo'
2268 (to avoid using a FIFO even if it is detected).
2269 Parallel ports are assigned in the order they
2270 are specified on the command line, starting
2271 with parport0.
2273 parport_init_mode= [HW,PPT]
2274 Configure VIA parallel port to operate in
2275 a specific mode. This is necessary on Pegasos
2276 computer where firmware has no options for setting
2277 up parallel port mode and sets it to spp.
2278 Currently this function knows 686a and 8231 chips.
2279 Format: [spp|ps2|epp|ecp|ecpepp]
2281 pause_on_oops=
2282 Halt all CPUs after the first oops has been printed for
2283 the specified number of seconds. This is to be used if
2284 your oopses keep scrolling off the screen.
2286 pcbit= [HW,ISDN]
2288 pcd. [PARIDE]
2289 See header of drivers/block/paride/pcd.c.
2290 See also Documentation/blockdev/paride.txt.
2292 pci=option[,option...] [PCI] various PCI subsystem options:
2293 earlydump [X86] dump PCI config space before the kernel
2294 changes anything
2295 off [X86] don't probe for the PCI bus
2296 bios [X86-32] force use of PCI BIOS, don't access
2297 the hardware directly. Use this if your machine
2298 has a non-standard PCI host bridge.
2299 nobios [X86-32] disallow use of PCI BIOS, only direct
2300 hardware access methods are allowed. Use this
2301 if you experience crashes upon bootup and you
2302 suspect they are caused by the BIOS.
2303 conf1 [X86] Force use of PCI Configuration
2304 Mechanism 1.
2305 conf2 [X86] Force use of PCI Configuration
2306 Mechanism 2.
2307 noaer [PCIE] If the PCIEAER kernel config parameter is
2308 enabled, this kernel boot option can be used to
2309 disable the use of PCIE advanced error reporting.
2310 nodomains [PCI] Disable support for multiple PCI
2311 root domains (aka PCI segments, in ACPI-speak).
2312 nommconf [X86] Disable use of MMCONFIG for PCI
2313 Configuration
2314 check_enable_amd_mmconf [X86] check for and enable
2315 properly configured MMIO access to PCI
2316 config space on AMD family 10h CPU
2317 nomsi [MSI] If the PCI_MSI kernel config parameter is
2318 enabled, this kernel boot option can be used to
2319 disable the use of MSI interrupts system-wide.
2320 noioapicquirk [APIC] Disable all boot interrupt quirks.
2321 Safety option to keep boot IRQs enabled. This
2322 should never be necessary.
2323 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2324 primary IO-APIC for bridges that cannot disable
2325 boot IRQs. This fixes a source of spurious IRQs
2326 when the system masks IRQs.
2327 noioapicreroute [APIC] Disable workaround that uses the
2328 boot IRQ equivalent of an IRQ that connects to
2329 a chipset where boot IRQs cannot be disabled.
2330 The opposite of ioapicreroute.
2331 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2332 routing table. These calls are known to be buggy
2333 on several machines and they hang the machine
2334 when used, but on other computers it's the only
2335 way to get the interrupt routing table. Try
2336 this option if the kernel is unable to allocate
2337 IRQs or discover secondary PCI buses on your
2338 motherboard.
2339 rom [X86] Assign address space to expansion ROMs.
2340 Use with caution as certain devices share
2341 address decoders between ROMs and other
2342 resources.
2343 norom [X86] Do not assign address space to
2344 expansion ROMs that do not already have
2345 BIOS assigned address ranges.
2346 nobar [X86] Do not assign address space to the
2347 BARs that weren't assigned by the BIOS.
2348 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2349 assigned automatically to PCI devices. You can
2350 make the kernel exclude IRQs of your ISA cards
2351 this way.
2352 pirqaddr=0xAAAAA [X86] Specify the physical address
2353 of the PIRQ table (normally generated
2354 by the BIOS) if it is outside the
2355 F0000h-100000h range.
2356 lastbus=N [X86] Scan all buses thru bus #N. Can be
2357 useful if the kernel is unable to find your
2358 secondary buses and you want to tell it
2359 explicitly which ones they are.
2360 assign-busses [X86] Always assign all PCI bus
2361 numbers ourselves, overriding
2362 whatever the firmware may have done.
2363 usepirqmask [X86] Honor the possible IRQ mask stored
2364 in the BIOS $PIR table. This is needed on
2365 some systems with broken BIOSes, notably
2366 some HP Pavilion N5400 and Omnibook XE3
2367 notebooks. This will have no effect if ACPI
2368 IRQ routing is enabled.
2369 noacpi [X86] Do not use ACPI for IRQ routing
2370 or for PCI scanning.
2371 use_crs [X86] Use PCI host bridge window information
2372 from ACPI. On BIOSes from 2008 or later, this
2373 is enabled by default. If you need to use this,
2374 please report a bug.
2375 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2376 If you need to use this, please report a bug.
2377 routeirq Do IRQ routing for all PCI devices.
2378 This is normally done in pci_enable_device(),
2379 so this option is a temporary workaround
2380 for broken drivers that don't call it.
2381 skip_isa_align [X86] do not align io start addr, so can
2382 handle more pci cards
2383 firmware [ARM] Do not re-enumerate the bus but instead
2384 just use the configuration from the
2385 bootloader. This is currently used on
2386 IXP2000 systems where the bus has to be
2387 configured a certain way for adjunct CPUs.
2388 noearly [X86] Don't do any early type 1 scanning.
2389 This might help on some broken boards which
2390 machine check when some devices' config space
2391 is read. But various workarounds are disabled
2392 and some IOMMU drivers will not work.
2393 bfsort Sort PCI devices into breadth-first order.
2394 This sorting is done to get a device
2395 order compatible with older (<= 2.4) kernels.
2396 nobfsort Don't sort PCI devices into breadth-first order.
2397 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2398 tuning and use the BIOS-configured MPS defaults.
2399 pcie_bus_safe Set every device's MPS to the largest value
2400 supported by all devices below the root complex.
2401 pcie_bus_perf Set device MPS to the largest allowable MPS
2402 based on its parent bus. Also set MRRS (Max
2403 Read Request Size) to the largest supported
2404 value (no larger than the MPS that the device
2405 or bus can support) for best performance.
2406 pcie_bus_peer2peer Set every device's MPS to 128B, which
2407 every device is guaranteed to support. This
2408 configuration allows peer-to-peer DMA between
2409 any pair of devices, possibly at the cost of
2410 reduced performance. This also guarantees
2411 that hot-added devices will work.
2412 cbiosize=nn[KMG] The fixed amount of bus space which is
2413 reserved for the CardBus bridge's IO window.
2414 The default value is 256 bytes.
2415 cbmemsize=nn[KMG] The fixed amount of bus space which is
2416 reserved for the CardBus bridge's memory
2417 window. The default value is 64 megabytes.
2418 resource_alignment=
2419 Format:
2420 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2421 Specifies alignment and device to reassign
2422 aligned memory resources.
2423 If <order of align> is not specified,
2424 PAGE_SIZE is used as alignment.
2425 PCI-PCI bridge can be specified, if resource
2426 windows need to be expanded.
2427 ecrc= Enable/disable PCIe ECRC (transaction layer
2428 end-to-end CRC checking).
2429 bios: Use BIOS/firmware settings. This is the
2430 the default.
2431 off: Turn ECRC off
2432 on: Turn ECRC on.
2433 hpiosize=nn[KMG] The fixed amount of bus space which is
2434 reserved for hotplug bridge's IO window.
2435 Default size is 256 bytes.
2436 hpmemsize=nn[KMG] The fixed amount of bus space which is
2437 reserved for hotplug bridge's memory window.
2438 Default size is 2 megabytes.
2439 realloc= Enable/disable reallocating PCI bridge resources
2440 if allocations done by BIOS are too small to
2441 accommodate resources required by all child
2442 devices.
2443 off: Turn realloc off
2444 on: Turn realloc on
2445 realloc same as realloc=on
2446 noari do not use PCIe ARI.
2447 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2448 only look for one device below a PCIe downstream
2449 port.
2451 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2452 Management.
2453 off Disable ASPM.
2454 force Enable ASPM even on devices that claim not to support it.
2455 WARNING: Forcing ASPM on may cause system lockups.
2457 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2458 nomsi Do not use MSI for PCI Express Native Hotplug (this
2459 makes all PCIe ports use INTx for hotplug services).
2461 pcie_ports= [PCIE] PCIe ports handling:
2462 auto Ask the BIOS whether or not to use native PCIe services
2463 associated with PCIe ports (PME, hot-plug, AER). Use
2464 them only if that is allowed by the BIOS.
2465 native Use native PCIe services associated with PCIe ports
2466 unconditionally.
2467 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2468 ports driver.
2470 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2471 nomsi Do not use MSI for native PCIe PME signaling (this makes
2472 all PCIe root ports use INTx for all services).
2474 pcmv= [HW,PCMCIA] BadgePAD 4
2476 pd. [PARIDE]
2477 See Documentation/blockdev/paride.txt.
2479 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2480 boot time.
2481 Format: { 0 | 1 }
2482 See arch/parisc/kernel/pdc_chassis.c
2484 percpu_alloc= Select which percpu first chunk allocator to use.
2485 Currently supported values are "embed" and "page".
2486 Archs may support subset or none of the selections.
2487 See comments in mm/percpu.c for details on each
2488 allocator. This parameter is primarily for debugging
2489 and performance comparison.
2491 pf. [PARIDE]
2492 See Documentation/blockdev/paride.txt.
2494 pg. [PARIDE]
2495 See Documentation/blockdev/paride.txt.
2497 pirq= [SMP,APIC] Manual mp-table setup
2498 See Documentation/x86/i386/IO-APIC.txt.
2500 plip= [PPT,NET] Parallel port network link
2501 Format: { parport<nr> | timid | 0 }
2502 See also Documentation/parport.txt.
2504 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2505 Override pmtimer IOPort with a hex value.
2506 e.g. pmtmr=0x508
2508 pnp.debug=1 [PNP]
2509 Enable PNP debug messages (depends on the
2510 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2511 via /sys/module/pnp/parameters/debug. We always show
2512 current resource usage; turning this on also shows
2513 possible settings and some assignment information.
2515 pnpacpi= [ACPI]
2516 { off }
2518 pnpbios= [ISAPNP]
2519 { on | off | curr | res | no-curr | no-res }
2521 pnp_reserve_irq=
2522 [ISAPNP] Exclude IRQs for the autoconfiguration
2524 pnp_reserve_dma=
2525 [ISAPNP] Exclude DMAs for the autoconfiguration
2527 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2528 Ranges are in pairs (I/O port base and size).
2530 pnp_reserve_mem=
2531 [ISAPNP] Exclude memory regions for the
2532 autoconfiguration.
2533 Ranges are in pairs (memory base and size).
2535 ports= [IP_VS_FTP] IPVS ftp helper module
2536 Default is 21.
2537 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2538 may be specified.
2539 Format: <port>,<port>....
2541 print-fatal-signals=
2542 [KNL] debug: print fatal signals
2544 If enabled, warn about various signal handling
2545 related application anomalies: too many signals,
2546 too many POSIX.1 timers, fatal signals causing a
2547 coredump - etc.
2549 If you hit the warning due to signal overflow,
2550 you might want to try "ulimit -i unlimited".
2552 default: off.
2554 printk.always_kmsg_dump=
2555 Trigger kmsg_dump for cases other than kernel oops or
2556 panics
2557 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2558 default: disabled
2560 printk.time= Show timing data prefixed to each printk message line
2561 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2563 processor.max_cstate= [HW,ACPI]
2564 Limit processor to maximum C-state
2565 max_cstate=9 overrides any DMI blacklist limit.
2567 processor.nocst [HW,ACPI]
2568 Ignore the _CST method to determine C-states,
2569 instead using the legacy FADT method
2571 profile= [KNL] Enable kernel profiling via /proc/profile
2572 Format: [schedule,]<number>
2573 Param: "schedule" - profile schedule points.
2574 Param: <number> - step/bucket size as a power of 2 for
2575 statistical time based profiling.
2576 Param: "sleep" - profile D-state sleeping (millisecs).
2577 Requires CONFIG_SCHEDSTATS
2578 Param: "kvm" - profile VM exits.
2580 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2581 before loading.
2582 See Documentation/blockdev/ramdisk.txt.
2584 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2585 probe for; one of (bare|imps|exps|lifebook|any).
2586 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2587 per second.
2588 psmouse.resetafter= [HW,MOUSE]
2589 Try to reset the device after so many bad packets
2590 (0 = never).
2591 psmouse.resolution=
2592 [HW,MOUSE] Set desired mouse resolution, in dpi.
2593 psmouse.smartscroll=
2594 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2595 0 = disabled, 1 = enabled (default).
2597 pstore.backend= Specify the name of the pstore backend to use
2599 pt. [PARIDE]
2600 See Documentation/blockdev/paride.txt.
2602 pty.legacy_count=
2603 [KNL] Number of legacy pty's. Overwrites compiled-in
2604 default number.
2606 quiet [KNL] Disable most log messages
2608 r128= [HW,DRM]
2610 raid= [HW,RAID]
2611 See Documentation/md.txt.
2613 ramdisk_blocksize= [RAM]
2614 See Documentation/blockdev/ramdisk.txt.
2616 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2617 See Documentation/blockdev/ramdisk.txt.
2619 rcu_nocbs= [KNL]
2620 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2621 the specified list of CPUs to be no-callback CPUs.
2622 Invocation of these CPUs' RCU callbacks will
2623 be offloaded to "rcuox/N" kthreads created for
2624 that purpose, where "x" is "b" for RCU-bh, "p"
2625 for RCU-preempt, and "s" for RCU-sched, and "N"
2626 is the CPU number. This reduces OS jitter on the
2627 offloaded CPUs, which can be useful for HPC and
2629 real-time workloads. It can also improve energy
2630 efficiency for asymmetric multiprocessors.
2632 rcu_nocb_poll [KNL]
2633 Rather than requiring that offloaded CPUs
2634 (specified by rcu_nocbs= above) explicitly
2635 awaken the corresponding "rcuoN" kthreads,
2636 make these kthreads poll for callbacks.
2637 This improves the real-time response for the
2638 offloaded CPUs by relieving them of the need to
2639 wake up the corresponding kthread, but degrades
2640 energy efficiency by requiring that the kthreads
2641 periodically wake up to do the polling.
2643 rcutree.blimit= [KNL]
2644 Set maximum number of finished RCU callbacks to process
2645 in one batch.
2647 rcutree.rcu_fanout_leaf= [KNL]
2648 Increase the number of CPUs assigned to each
2649 leaf rcu_node structure. Useful for very large
2650 systems.
2652 rcutree.jiffies_till_first_fqs= [KNL]
2653 Set delay from grace-period initialization to
2654 first attempt to force quiescent states.
2655 Units are jiffies, minimum value is zero,
2656 and maximum value is HZ.
2658 rcutree.jiffies_till_next_fqs= [KNL]
2659 Set delay between subsequent attempts to force
2660 quiescent states. Units are jiffies, minimum
2661 value is one, and maximum value is HZ.
2663 rcutree.qhimark= [KNL]
2664 Set threshold of queued
2665 RCU callbacks over which batch limiting is disabled.
2667 rcutree.qlowmark= [KNL]
2668 Set threshold of queued RCU callbacks below which
2669 batch limiting is re-enabled.
2671 rcutree.rcu_idle_gp_delay= [KNL]
2672 Set wakeup interval for idle CPUs that have
2673 RCU callbacks (RCU_FAST_NO_HZ=y).
2675 rcutree.rcu_idle_lazy_gp_delay= [KNL]
2676 Set wakeup interval for idle CPUs that have
2677 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2678 Lazy RCU callbacks are those which RCU can
2679 prove do nothing more than free memory.
2681 rcutorture.fqs_duration= [KNL]
2682 Set duration of force_quiescent_state bursts.
2684 rcutorture.fqs_holdoff= [KNL]
2685 Set holdoff time within force_quiescent_state bursts.
2687 rcutorture.fqs_stutter= [KNL]
2688 Set wait time between force_quiescent_state bursts.
2690 rcutorture.gp_exp= [KNL]
2691 Use expedited update-side primitives.
2693 rcutorture.gp_normal= [KNL]
2694 Use normal (non-expedited) update-side primitives.
2695 If both gp_exp and gp_normal are set, do both.
2696 If neither gp_exp nor gp_normal are set, still
2697 do both.
2699 rcutorture.n_barrier_cbs= [KNL]
2700 Set callbacks/threads for rcu_barrier() testing.
2702 rcutorture.nfakewriters= [KNL]
2703 Set number of concurrent RCU writers. These just
2704 stress RCU, they don't participate in the actual
2705 test, hence the "fake".
2707 rcutorture.nreaders= [KNL]
2708 Set number of RCU readers.
2710 rcutorture.object_debug= [KNL]
2711 Enable debug-object double-call_rcu() testing.
2713 rcutorture.onoff_holdoff= [KNL]
2714 Set time (s) after boot for CPU-hotplug testing.
2716 rcutorture.onoff_interval= [KNL]
2717 Set time (s) between CPU-hotplug operations, or
2718 zero to disable CPU-hotplug testing.
2720 rcutorture.rcutorture_runnable= [BOOT]
2721 Start rcutorture running at boot time.
2723 rcutorture.shuffle_interval= [KNL]
2724 Set task-shuffle interval (s). Shuffling tasks
2725 allows some CPUs to go into dyntick-idle mode
2726 during the rcutorture test.
2728 rcutorture.shutdown_secs= [KNL]
2729 Set time (s) after boot system shutdown. This
2730 is useful for hands-off automated testing.
2732 rcutorture.stall_cpu= [KNL]
2733 Duration of CPU stall (s) to test RCU CPU stall
2734 warnings, zero to disable.
2736 rcutorture.stall_cpu_holdoff= [KNL]
2737 Time to wait (s) after boot before inducing stall.
2739 rcutorture.stat_interval= [KNL]
2740 Time (s) between statistics printk()s.
2742 rcutorture.stutter= [KNL]
2743 Time (s) to stutter testing, for example, specifying
2744 five seconds causes the test to run for five seconds,
2745 wait for five seconds, and so on. This tests RCU's
2746 ability to transition abruptly to and from idle.
2748 rcutorture.test_boost= [KNL]
2749 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2750 "Maybe" means test if the RCU implementation
2751 under test support RCU priority boosting.
2753 rcutorture.test_boost_duration= [KNL]
2754 Duration (s) of each individual boost test.
2756 rcutorture.test_boost_interval= [KNL]
2757 Interval (s) between each boost test.
2759 rcutorture.test_no_idle_hz= [KNL]
2760 Test RCU's dyntick-idle handling. See also the
2761 rcutorture.shuffle_interval parameter.
2763 rcutorture.torture_type= [KNL]
2764 Specify the RCU implementation to test.
2766 rcutorture.verbose= [KNL]
2767 Enable additional printk() statements.
2769 rcupdate.rcu_expedited= [KNL]
2770 Use expedited grace-period primitives, for
2771 example, synchronize_rcu_expedited() instead
2772 of synchronize_rcu(). This reduces latency,
2773 but can increase CPU utilization, degrade
2774 real-time latency, and degrade energy efficiency.
2776 rcupdate.rcu_cpu_stall_suppress= [KNL]
2777 Suppress RCU CPU stall warning messages.
2779 rcupdate.rcu_cpu_stall_timeout= [KNL]
2780 Set timeout for RCU CPU stall warning messages.
2782 rdinit= [KNL]
2783 Format: <full_path>
2784 Run specified binary instead of /init from the ramdisk,
2785 used for early userspace startup. See initrd.
2787 reboot= [KNL]
2788 Format (x86 or x86_64):
2789 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2790 [[,]s[mp]#### \
2791 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2792 [[,]f[orce]
2793 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2794 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2795 reboot_force is either force or not specified,
2796 reboot_cpu is s[mp]#### with #### being the processor
2797 to be used for rebooting.
2799 relax_domain_level=
2800 [KNL, SMP] Set scheduler's default relax_domain_level.
2801 See Documentation/cgroups/cpusets.txt.
2803 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2805 reservetop= [X86-32]
2806 Format: nn[KMG]
2807 Reserves a hole at the top of the kernel virtual
2808 address space.
2810 reservelow= [X86]
2811 Format: nn[K]
2812 Set the amount of memory to reserve for BIOS at
2813 the bottom of the address space.
2815 reset_devices [KNL] Force drivers to reset the underlying device
2816 during initialization.
2818 resume= [SWSUSP]
2819 Specify the partition device for software suspend
2820 Format:
2821 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2823 resume_offset= [SWSUSP]
2824 Specify the offset from the beginning of the partition
2825 given by "resume=" at which the swap header is located,
2826 in <PAGE_SIZE> units (needed only for swap files).
2827 See Documentation/power/swsusp-and-swap-files.txt
2829 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2830 read the resume files
2832 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2833 Useful for devices that are detected asynchronously
2834 (e.g. USB and MMC devices).
2836 hibernate= [HIBERNATION]
2837 noresume Don't check if there's a hibernation image
2838 present during boot.
2839 nocompress Don't compress/decompress hibernation images.
2841 retain_initrd [RAM] Keep initrd memory after extraction
2843 rhash_entries= [KNL,NET]
2844 Set number of hash buckets for route cache
2846 riscom8= [HW,SERIAL]
2847 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2849 ro [KNL] Mount root device read-only on boot
2851 root= [KNL] Root filesystem
2852 See name_to_dev_t comment in init/do_mounts.c.
2854 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2855 mount the root filesystem
2857 rootflags= [KNL] Set root filesystem mount option string
2859 rootfstype= [KNL] Set root filesystem type
2861 rootwait [KNL] Wait (indefinitely) for root device to show up.
2862 Useful for devices that are detected asynchronously
2863 (e.g. USB and MMC devices).
2865 rproc_mem=nn[KMG][@address]
2866 [KNL,ARM,CMA] Remoteproc physical memory block.
2867 Memory area to be used by remote processor image,
2868 managed by CMA.
2870 rw [KNL] Mount root device read-write on boot
2872 S [KNL] Run init in single mode
2874 sa1100ir [NET]
2875 See drivers/net/irda/sa1100_ir.c.
2877 sbni= [NET] Granch SBNI12 leased line adapter
2879 sched_debug [KNL] Enables verbose scheduler debug messages.
2881 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2882 xtime_lock contention on larger systems, and/or RCU lock
2883 contention on all systems with CONFIG_MAXSMP set.
2884 Format: { "0" | "1" }
2885 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2886 1 -- enable.
2887 Note: increases power consumption, thus should only be
2888 enabled if running jitter sensitive (HPC/RT) workloads.
2890 security= [SECURITY] Choose a security module to enable at boot.
2891 If this boot parameter is not specified, only the first
2892 security module asking for security registration will be
2893 loaded. An invalid security module name will be treated
2894 as if no module has been chosen.
2896 selinux= [SELINUX] Disable or enable SELinux at boot time.
2897 Format: { "0" | "1" }
2898 See security/selinux/Kconfig help text.
2899 0 -- disable.
2900 1 -- enable.
2901 Default value is set via kernel config option.
2902 If enabled at boot time, /selinux/disable can be used
2903 later to disable prior to initial policy load.
2905 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2906 Format: { "0" | "1" }
2907 See security/apparmor/Kconfig help text
2908 0 -- disable.
2909 1 -- enable.
2910 Default value is set via kernel config option.
2912 serialnumber [BUGS=X86-32]
2914 shapers= [NET]
2915 Maximal number of shapers.
2917 show_msr= [x86] show boot-time MSR settings
2918 Format: { <integer> }
2919 Show boot-time (BIOS-initialized) MSR settings.
2920 The parameter means the number of CPUs to show,
2921 for example 1 means boot CPU only.
2923 simeth= [IA-64]
2924 simscsi=
2926 slram= [HW,MTD]
2928 slab_max_order= [MM, SLAB]
2929 Determines the maximum allowed order for slabs.
2930 A high setting may cause OOMs due to memory
2931 fragmentation. Defaults to 1 for systems with
2932 more than 32MB of RAM, 0 otherwise.
2934 slub_debug[=options[,slabs]] [MM, SLUB]
2935 Enabling slub_debug allows one to determine the
2936 culprit if slab objects become corrupted. Enabling
2937 slub_debug can create guard zones around objects and
2938 may poison objects when not in use. Also tracks the
2939 last alloc / free. For more information see
2940 Documentation/vm/slub.txt.
2942 slub_max_order= [MM, SLUB]
2943 Determines the maximum allowed order for slabs.
2944 A high setting may cause OOMs due to memory
2945 fragmentation. For more information see
2946 Documentation/vm/slub.txt.
2948 slub_min_objects= [MM, SLUB]
2949 The minimum number of objects per slab. SLUB will
2950 increase the slab order up to slub_max_order to
2951 generate a sufficiently large slab able to contain
2952 the number of objects indicated. The higher the number
2953 of objects the smaller the overhead of tracking slabs
2954 and the less frequently locks need to be acquired.
2955 For more information see Documentation/vm/slub.txt.
2957 slub_min_order= [MM, SLUB]
2958 Determines the minimum page order for slabs. Must be
2959 lower than slub_max_order.
2960 For more information see Documentation/vm/slub.txt.
2962 slub_nomerge [MM, SLUB]
2963 Disable merging of slabs with similar size. May be
2964 necessary if there is some reason to distinguish
2965 allocs to different slabs. Debug options disable
2966 merging on their own.
2967 For more information see Documentation/vm/slub.txt.
2969 smart2= [HW]
2970 Format: <io1>[,<io2>[,...,<io8>]]
2972 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2973 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2974 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2975 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2976 smsc-ircc2.ircc_irq= [HW] IRQ line
2977 smsc-ircc2.ircc_dma= [HW] DMA channel
2978 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2979 0: Toshiba Satellite 1800 (GP data pin select)
2980 1: Fast pin select (default)
2981 2: ATC IRMode
2983 softlockup_panic=
2984 [KNL] Should the soft-lockup detector generate panics.
2985 Format: <integer>
2987 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2988 See Documentation/laptops/sonypi.txt
2990 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2991 See Documentation/serial/specialix.txt.
2993 spia_io_base= [HW,MTD]
2994 spia_fio_base=
2995 spia_pedr=
2996 spia_peddr=
2998 stacktrace [FTRACE]
2999 Enabled the stack tracer on boot up.
3001 stacktrace_filter=[function-list]
3002 [FTRACE] Limit the functions that the stack tracer
3003 will trace at boot up. function-list is a comma separated
3004 list of functions. This list can be changed at run
3005 time by the stack_trace_filter file in the debugfs
3006 tracing directory. Note, this enables stack tracing
3007 and the stacktrace above is not needed.
3009 sti= [PARISC,HW]
3010 Format: <num>
3011 Set the STI (builtin display/keyboard on the HP-PARISC
3012 machines) console (graphic card) which should be used
3013 as the initial boot-console.
3014 See also comment in drivers/video/console/sticore.c.
3016 sti_font= [HW]
3017 See comment in drivers/video/console/sticore.c.
3019 stifb= [HW]
3020 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3022 sunrpc.min_resvport=
3023 sunrpc.max_resvport=
3024 [NFS,SUNRPC]
3025 SunRPC servers often require that client requests
3026 originate from a privileged port (i.e. a port in the
3027 range 0 < portnr < 1024).
3028 An administrator who wishes to reserve some of these
3029 ports for other uses may adjust the range that the
3030 kernel's sunrpc client considers to be privileged
3031 using these two parameters to set the minimum and
3032 maximum port values.
3034 sunrpc.pool_mode=
3035 [NFS]
3036 Control how the NFS server code allocates CPUs to
3037 service thread pools. Depending on how many NICs
3038 you have and where their interrupts are bound, this
3039 option will affect which CPUs will do NFS serving.
3040 Note: this parameter cannot be changed while the
3041 NFS server is running.
3043 auto the server chooses an appropriate mode
3044 automatically using heuristics
3045 global a single global pool contains all CPUs
3046 percpu one pool for each CPU
3047 pernode one pool for each NUMA node (equivalent
3048 to global on non-NUMA machines)
3050 sunrpc.tcp_slot_table_entries=
3051 sunrpc.udp_slot_table_entries=
3052 [NFS,SUNRPC]
3053 Sets the upper limit on the number of simultaneous
3054 RPC calls that can be sent from the client to a
3055 server. Increasing these values may allow you to
3056 improve throughput, but will also increase the
3057 amount of memory reserved for use by the client.
3059 swapaccount=[0|1]
3060 [KNL] Enable accounting of swap in memory resource
3061 controller if no parameter or 1 is given or disable
3062 it if 0 is given (See Documentation/cgroups/memory.txt)
3064 swiotlb= [IA-64] Number of I/O TLB slabs
3066 switches= [HW,M68k]
3068 sysfs.deprecated=0|1 [KNL]
3069 Enable/disable old style sysfs layout for old udev
3070 on older distributions. When this option is enabled
3071 very new udev will not work anymore. When this option
3072 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3073 in older udev will not work anymore.
3074 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3075 the kernel configuration.
3077 sysrq_always_enabled
3078 [KNL]
3079 Ignore sysrq setting - this boot parameter will
3080 neutralize any effect of /proc/sys/kernel/sysrq.
3081 Useful for debugging.
3083 tdfx= [HW,DRM]
3085 test_suspend= [SUSPEND]
3086 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3087 standby suspend) as the system sleep state to briefly
3088 enter during system startup. The system is woken from
3089 this state using a wakeup-capable RTC alarm.
3091 thash_entries= [KNL,NET]
3092 Set number of hash buckets for TCP connection
3094 thermal.act= [HW,ACPI]
3095 -1: disable all active trip points in all thermal zones
3096 <degrees C>: override all lowest active trip points
3098 thermal.crt= [HW,ACPI]
3099 -1: disable all critical trip points in all thermal zones
3100 <degrees C>: override all critical trip points
3102 thermal.nocrt= [HW,ACPI]
3103 Set to disable actions on ACPI thermal zone
3104 critical and hot trip points.
3106 thermal.off= [HW,ACPI]
3107 1: disable ACPI thermal control
3109 thermal.psv= [HW,ACPI]
3110 -1: disable all passive trip points
3111 <degrees C>: override all passive trip points to this
3112 value
3114 thermal.tzp= [HW,ACPI]
3115 Specify global default ACPI thermal zone polling rate
3116 <deci-seconds>: poll all this frequency
3117 0: no polling (default)
3119 threadirqs [KNL]
3120 Force threading of all interrupt handlers except those
3121 marked explicitly IRQF_NO_THREAD.
3123 tmem [KNL,XEN]
3124 Enable the Transcendent memory driver if built-in.
3126 tmem.cleancache=0|1 [KNL, XEN]
3127 Default is on (1). Disable the usage of the cleancache
3128 API to send anonymous pages to the hypervisor.
3130 tmem.frontswap=0|1 [KNL, XEN]
3131 Default is on (1). Disable the usage of the frontswap
3132 API to send swap pages to the hypervisor. If disabled
3133 the selfballooning and selfshrinking are force disabled.
3135 tmem.selfballooning=0|1 [KNL, XEN]
3136 Default is on (1). Disable the driving of swap pages
3137 to the hypervisor.
3139 tmem.selfshrinking=0|1 [KNL, XEN]
3140 Default is on (1). Partial swapoff that immediately
3141 transfers pages from Xen hypervisor back to the
3142 kernel based on different criteria.
3144 topology= [S390]
3145 Format: {off | on}
3146 Specify if the kernel should make use of the cpu
3147 topology information if the hardware supports this.
3148 The scheduler will make use of this information and
3149 e.g. base its process migration decisions on it.
3150 Default is on.
3152 tp720= [HW,PS2]
3154 tpm_suspend_pcr=[HW,TPM]
3155 Format: integer pcr id
3156 Specify that at suspend time, the tpm driver
3157 should extend the specified pcr with zeros,
3158 as a workaround for some chips which fail to
3159 flush the last written pcr on TPM_SaveState.
3160 This will guarantee that all the other pcrs
3161 are saved.
3163 trace_buf_size=nn[KMG]
3164 [FTRACE] will set tracing buffer size.
3166 trace_event=[event-list]
3167 [FTRACE] Set and start specified trace events in order
3168 to facilitate early boot debugging.
3169 See also Documentation/trace/events.txt
3171 trace_options=[option-list]
3172 [FTRACE] Enable or disable tracer options at boot.
3173 The option-list is a comma delimited list of options
3174 that can be enabled or disabled just as if you were
3175 to echo the option name into
3177 /sys/kernel/debug/tracing/trace_options
3179 For example, to enable stacktrace option (to dump the
3180 stack trace of each event), add to the command line:
3182 trace_options=stacktrace
3184 See also Documentation/trace/ftrace.txt "trace options"
3185 section.
3187 traceoff_on_warning
3188 [FTRACE] enable this option to disable tracing when a
3189 warning is hit. This turns off "tracing_on". Tracing can
3190 be enabled again by echoing '1' into the "tracing_on"
3191 file located in /sys/kernel/debug/tracing/
3193 This option is useful, as it disables the trace before
3194 the WARNING dump is called, which prevents the trace to
3195 be filled with content caused by the warning output.
3197 This option can also be set at run time via the sysctl
3198 option: kernel/traceoff_on_warning
3200 transparent_hugepage=
3201 [KNL]
3202 Format: [always|madvise|never]
3203 Can be used to control the default behavior of the system
3204 with respect to transparent hugepages.
3205 See Documentation/vm/transhuge.txt for more details.
3207 tsc= Disable clocksource stability checks for TSC.
3208 Format: <string>
3209 [x86] reliable: mark tsc clocksource as reliable, this
3210 disables clocksource verification at runtime, as well
3211 as the stability checks done at bootup. Used to enable
3212 high-resolution timer mode on older hardware, and in
3213 virtualized environment.
3214 [x86] noirqtime: Do not use TSC to do irq accounting.
3215 Used to run time disable IRQ_TIME_ACCOUNTING on any
3216 platforms where RDTSC is slow and this accounting
3217 can add overhead.
3219 turbografx.map[2|3]= [HW,JOY]
3220 TurboGraFX parallel port interface
3221 Format:
3222 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3223 See also Documentation/input/joystick-parport.txt
3225 udbg-immortal [PPC] When debugging early kernel crashes that
3226 happen after console_init() and before a proper
3227 console driver takes over, this boot options might
3228 help "seeing" what's going on.
3230 uhash_entries= [KNL,NET]
3231 Set number of hash buckets for UDP/UDP-Lite connections
3233 uhci-hcd.ignore_oc=
3234 [USB] Ignore overcurrent events (default N).
3235 Some badly-designed motherboards generate lots of
3236 bogus events, for ports that aren't wired to
3237 anything. Set this parameter to avoid log spamming.
3238 Note that genuine overcurrent events won't be
3239 reported either.
3241 unknown_nmi_panic
3242 [X86] Cause panic on unknown NMI.
3244 usbcore.authorized_default=
3245 [USB] Default USB device authorization:
3246 (default -1 = authorized except for wireless USB,
3247 0 = not authorized, 1 = authorized)
3249 usbcore.autosuspend=
3250 [USB] The autosuspend time delay (in seconds) used
3251 for newly-detected USB devices (default 2). This
3252 is the time required before an idle device will be
3253 autosuspended. Devices for which the delay is set
3254 to a negative value won't be autosuspended at all.
3256 usbcore.usbfs_snoop=
3257 [USB] Set to log all usbfs traffic (default 0 = off).
3259 usbcore.blinkenlights=
3260 [USB] Set to cycle leds on hubs (default 0 = off).
3262 usbcore.old_scheme_first=
3263 [USB] Start with the old device initialization
3264 scheme (default 0 = off).
3266 usbcore.usbfs_memory_mb=
3267 [USB] Memory limit (in MB) for buffers allocated by
3268 usbfs (default = 16, 0 = max = 2047).
3270 usbcore.use_both_schemes=
3271 [USB] Try the other device initialization scheme
3272 if the first one fails (default 1 = enabled).
3274 usbcore.initial_descriptor_timeout=
3275 [USB] Specifies timeout for the initial 64-byte
3276 USB_REQ_GET_DESCRIPTOR request in milliseconds
3277 (default 5000 = 5.0 seconds).
3279 usbhid.mousepoll=
3280 [USBHID] The interval which mice are to be polled at.
3282 usb-storage.delay_use=
3283 [UMS] The delay in seconds before a new device is
3284 scanned for Logical Units (default 5).
3286 usb-storage.quirks=
3287 [UMS] A list of quirks entries to supplement or
3288 override the built-in unusual_devs list. List
3289 entries are separated by commas. Each entry has
3290 the form VID:PID:Flags where VID and PID are Vendor
3291 and Product ID values (4-digit hex numbers) and
3292 Flags is a set of characters, each corresponding
3293 to a common usb-storage quirk flag as follows:
3294 a = SANE_SENSE (collect more than 18 bytes
3295 of sense data);
3296 b = BAD_SENSE (don't collect more than 18
3297 bytes of sense data);
3298 c = FIX_CAPACITY (decrease the reported
3299 device capacity by one sector);
3300 d = NO_READ_DISC_INFO (don't use
3301 READ_DISC_INFO command);
3302 e = NO_READ_CAPACITY_16 (don't use
3303 READ_CAPACITY_16 command);
3304 h = CAPACITY_HEURISTICS (decrease the
3305 reported device capacity by one
3306 sector if the number is odd);
3307 i = IGNORE_DEVICE (don't bind to this
3308 device);
3309 l = NOT_LOCKABLE (don't try to lock and
3310 unlock ejectable media);
3311 m = MAX_SECTORS_64 (don't transfer more
3312 than 64 sectors = 32 KB at a time);
3313 n = INITIAL_READ10 (force a retry of the
3314 initial READ(10) command);
3315 o = CAPACITY_OK (accept the capacity
3316 reported by the device);
3317 p = WRITE_CACHE (the device cache is ON
3318 by default);
3319 r = IGNORE_RESIDUE (the device reports
3320 bogus residue values);
3321 s = SINGLE_LUN (the device has only one
3322 Logical Unit);
3323 w = NO_WP_DETECT (don't test whether the
3324 medium is write-protected).
3325 Example: quirks=0419:aaf5:rl,0421:0433:rc
3327 user_debug= [KNL,ARM]
3328 Format: <int>
3329 See arch/arm/Kconfig.debug help text.
3330 1 - undefined instruction events
3331 2 - system calls
3332 4 - invalid data aborts
3333 8 - SIGSEGV faults
3334 16 - SIGBUS faults
3335 Example: user_debug=31
3337 userpte=
3338 [X86] Flags controlling user PTE allocations.
3340 nohigh = do not allocate PTE pages in
3341 HIGHMEM regardless of setting
3342 of CONFIG_HIGHPTE.
3344 vdso= [X86,SH]
3345 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3346 vdso=1: enable VDSO (default)
3347 vdso=0: disable VDSO mapping
3349 vdso32= [X86]
3350 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3351 vdso32=1: enable 32-bit VDSO (default)
3352 vdso32=0: disable 32-bit VDSO mapping
3354 vector= [IA-64,SMP]
3355 vector=percpu: enable percpu vector domain
3357 video= [FB] Frame buffer configuration
3358 See Documentation/fb/modedb.txt.
3360 video.brightness_switch_enabled= [0,1]
3361 If set to 1, on receiving an ACPI notify event
3362 generated by hotkey, video driver will adjust brightness
3363 level and then send out the event to user space through
3364 the allocated input device; If set to 0, video driver
3365 will only send out the event without touching backlight
3366 brightness level.
3367 default: 1
3369 virtio_mmio.device=
3370 [VMMIO] Memory mapped virtio (platform) device.
3372 <size>@<baseaddr>:<irq>[:<id>]
3373 where:
3374 <size> := size (can use standard suffixes
3375 like K, M and G)
3376 <baseaddr> := physical base address
3377 <irq> := interrupt number (as passed to
3378 request_irq())
3379 <id> := (optional) platform device id
3380 example:
3381 virtio_mmio.device=1K@0x100b0000:48:7
3383 Can be used multiple times for multiple devices.
3385 vga= [BOOT,X86-32] Select a particular video mode
3386 See Documentation/x86/boot.txt and
3387 Documentation/svga.txt.
3388 Use vga=ask for menu.
3389 This is actually a boot loader parameter; the value is
3390 passed to the kernel using a special protocol.
3392 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3393 size of <nn>. This can be used to increase the
3394 minimum size (128MB on x86). It can also be used to
3395 decrease the size and leave more room for directly
3396 mapped kernel RAM.
3398 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3399 Format: <command>
3401 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3402 Format: <command>
3404 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3405 Format: <command>
3407 vsyscall= [X86-64]
3408 Controls the behavior of vsyscalls (i.e. calls to
3409 fixed addresses of 0xffffffffff600x00 from legacy
3410 code). Most statically-linked binaries and older
3411 versions of glibc use these calls. Because these
3412 functions are at fixed addresses, they make nice
3413 targets for exploits that can control RIP.
3415 emulate [default] Vsyscalls turn into traps and are
3416 emulated reasonably safely.
3418 native Vsyscalls are native syscall instructions.
3419 This is a little bit faster than trapping
3420 and makes a few dynamic recompilers work
3421 better than they would in emulation mode.
3422 It also makes exploits much easier to write.
3424 none Vsyscalls don't work at all. This makes
3425 them quite hard to use for exploits but
3426 might break your system.
3428 vt.color= [VT] Default text color.
3429 Format: 0xYX, X = foreground, Y = background.
3430 Default: 0x07 = light gray on black.
3432 vt.cur_default= [VT] Default cursor shape.
3433 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3434 the parameters of the <Esc>[?A;B;Cc escape sequence;
3435 see VGA-softcursor.txt. Default: 2 = underline.
3437 vt.default_blu= [VT]
3438 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3439 Change the default blue palette of the console.
3440 This is a 16-member array composed of values
3441 ranging from 0-255.
3443 vt.default_grn= [VT]
3444 Format: <green0>,<green1>,<green2>,...,<green15>
3445 Change the default green palette of the console.
3446 This is a 16-member array composed of values
3447 ranging from 0-255.
3449 vt.default_red= [VT]
3450 Format: <red0>,<red1>,<red2>,...,<red15>
3451 Change the default red palette of the console.
3452 This is a 16-member array composed of values
3453 ranging from 0-255.
3455 vt.default_utf8=
3456 [VT]
3457 Format=<0|1>
3458 Set system-wide default UTF-8 mode for all tty's.
3459 Default is 1, i.e. UTF-8 mode is enabled for all
3460 newly opened terminals.
3462 vt.global_cursor_default=
3463 [VT]
3464 Format=<-1|0|1>
3465 Set system-wide default for whether a cursor
3466 is shown on new VTs. Default is -1,
3467 i.e. cursors will be created by default unless
3468 overridden by individual drivers. 0 will hide
3469 cursors, 1 will display them.
3471 vt.italic= [VT] Default color for italic text; 0-15.
3472 Default: 2 = green.
3474 vt.underline= [VT] Default color for underlined text; 0-15.
3475 Default: 3 = cyan.
3477 watchdog timers [HW,WDT] For information on watchdog timers,
3478 see Documentation/watchdog/watchdog-parameters.txt
3479 or other driver-specific files in the
3480 Documentation/watchdog/ directory.
3482 workqueue.disable_numa
3483 By default, all work items queued to unbound
3484 workqueues are affine to the NUMA nodes they're
3485 issued on, which results in better behavior in
3486 general. If NUMA affinity needs to be disabled for
3487 whatever reason, this option can be used. Note
3488 that this also can be controlled per-workqueue for
3489 workqueues visible under /sys/bus/workqueue/.
3491 workqueue.power_efficient
3492 Per-cpu workqueues are generally preferred because
3493 they show better performance thanks to cache
3494 locality; unfortunately, per-cpu workqueues tend to
3495 be more power hungry than unbound workqueues.
3497 Enabling this makes the per-cpu workqueues which
3498 were observed to contribute significantly to power
3499 consumption unbound, leading to measurably lower
3500 power usage at the cost of small performance
3501 overhead.
3503 The default value of this parameter is determined by
3504 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3506 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3507 default x2apic cluster mode on platforms
3508 supporting x2apic.
3510 x86_intel_mid_timer= [X86-32,APBT]
3511 Choose timer option for x86 Intel MID platform.
3512 Two valid options are apbt timer only and lapic timer
3513 plus one apbt timer for broadcast timer.
3514 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3516 xen_emul_unplug= [HW,X86,XEN]
3517 Unplug Xen emulated devices
3518 Format: [unplug0,][unplug1]
3519 ide-disks -- unplug primary master IDE devices
3520 aux-ide-disks -- unplug non-primary-master IDE devices
3521 nics -- unplug network devices
3522 all -- unplug all emulated devices (NICs and IDE disks)
3523 unnecessary -- unplugging emulated devices is
3524 unnecessary even if the host did not respond to
3525 the unplug protocol
3526 never -- do not unplug even if version check succeeds
3528 xen_nopvspin [X86,XEN]
3529 Disables the ticketlock slowpath using Xen PV
3530 optimizations.
3532 xirc2ps_cs= [NET,PCMCIA]
3533 Format:
3534 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3536 ______________________________________________________________________
3538 TODO:
3540 Add more DRM drivers.