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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 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1074 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1075 On x86-64 and powerpc, this option can be specified
1076 multiple times interleaved with hugepages= to reserve
1077 huge pages of different sizes. Valid pages sizes on
1078 x86-64 are 2M (when the CPU supports "pse") and 1G
1079 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1080 Note that 1GB pages can only be allocated at boot time
1081 using hugepages= and not freed afterwards.
1083 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1084 terminal devices. Valid values: 0..8
1085 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1086 If specified, z/VM IUCV HVC accepts connections
1087 from listed z/VM user IDs only.
1089 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1090 hardware thread id mappings.
1091 Format: <cpu>:<hwthread>
1093 keep_bootcon [KNL]
1094 Do not unregister boot console at start. This is only
1095 useful for debugging when something happens in the window
1096 between unregistering the boot console and initializing
1097 the real console.
1099 i2c_bus= [HW] Override the default board specific I2C bus speed
1100 or register an additional I2C bus that is not
1101 registered from board initialization code.
1102 Format:
1103 <bus_id>,<clkrate>
1105 i8042.debug [HW] Toggle i8042 debug mode
1106 i8042.direct [HW] Put keyboard port into non-translated mode
1107 i8042.dumbkbd [HW] Pretend that controller can only read data from
1108 keyboard and cannot control its state
1109 (Don't attempt to blink the leds)
1110 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1111 i8042.nokbd [HW] Don't check/create keyboard port
1112 i8042.noloop [HW] Disable the AUX Loopback command while probing
1113 for the AUX port
1114 i8042.nomux [HW] Don't check presence of an active multiplexing
1115 controller
1116 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1117 controllers
1118 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1119 i8042.reset [HW] Reset the controller during init and cleanup
1120 i8042.unlock [HW] Unlock (ignore) the keylock
1122 i810= [HW,DRM]
1124 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1125 indicates that the driver is running on unsupported
1126 hardware.
1127 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1128 does not match list of supported models.
1129 i8k.power_status
1130 [HW] Report power status in /proc/i8k
1131 (disabled by default)
1132 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1133 capability is set.
1135 i915.invert_brightness=
1136 [DRM] Invert the sense of the variable that is used to
1137 set the brightness of the panel backlight. Normally a
1138 brightness value of 0 indicates backlight switched off,
1139 and the maximum of the brightness value sets the backlight
1140 to maximum brightness. If this parameter is set to 0
1141 (default) and the machine requires it, or this parameter
1142 is set to 1, a brightness value of 0 sets the backlight
1143 to maximum brightness, and the maximum of the brightness
1144 value switches the backlight off.
1145 -1 -- never invert brightness
1146 0 -- machine default
1147 1 -- force brightness inversion
1149 icn= [HW,ISDN]
1150 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1152 ide-core.nodma= [HW] (E)IDE subsystem
1153 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1154 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1155 .cdrom .chs .ignore_cable are additional options
1156 See Documentation/ide/ide.txt.
1158 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1159 Claim all unknown PCI IDE storage controllers.
1161 idle= [X86]
1162 Format: idle=poll, idle=halt, idle=nomwait
1163 Poll forces a polling idle loop that can slightly
1164 improve the performance of waking up a idle CPU, but
1165 will use a lot of power and make the system run hot.
1166 Not recommended.
1167 idle=halt: Halt is forced to be used for CPU idle.
1168 In such case C2/C3 won't be used again.
1169 idle=nomwait: Disable mwait for CPU C-states
1171 ignore_loglevel [KNL]
1172 Ignore loglevel setting - this will print /all/
1173 kernel messages to the console. Useful for debugging.
1174 We also add it as printk module parameter, so users
1175 could change it dynamically, usually by
1176 /sys/module/printk/parameters/ignore_loglevel.
1178 ihash_entries= [KNL]
1179 Set number of hash buckets for inode cache.
1181 ima_appraise= [IMA] appraise integrity measurements
1182 Format: { "off" | "enforce" | "fix" }
1183 default: "enforce"
1185 ima_appraise_tcb [IMA]
1186 The builtin appraise policy appraises all files
1187 owned by uid=0.
1189 ima_hash= [IMA]
1190 Format: { "sha1" | "md5" }
1191 default: "sha1"
1193 ima_tcb [IMA]
1194 Load a policy which meets the needs of the Trusted
1195 Computing Base. This means IMA will measure all
1196 programs exec'd, files mmap'd for exec, and all files
1197 opened for read by uid=0.
1199 init= [KNL]
1200 Format: <full_path>
1201 Run specified binary instead of /sbin/init as init
1202 process.
1204 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1205 for working out where the kernel is dying during
1206 startup.
1208 initrd= [BOOT] Specify the location of the initial ramdisk
1210 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1211 Format: <irq>
1213 int_pln_enable [x86] Enable power limit notification interrupt
1215 integrity_audit=[IMA]
1216 Format: { "0" | "1" }
1217 0 -- basic integrity auditing messages. (Default)
1218 1 -- additional integrity auditing messages.
1220 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1221 on
1222 Enable intel iommu driver.
1223 off
1224 Disable intel iommu driver.
1225 igfx_off [Default Off]
1226 By default, gfx is mapped as normal device. If a gfx
1227 device has a dedicated DMAR unit, the DMAR unit is
1228 bypassed by not enabling DMAR with this option. In
1229 this case, gfx device will use physical address for
1230 DMA.
1231 forcedac [x86_64]
1232 With this option iommu will not optimize to look
1233 for io virtual address below 32-bit forcing dual
1234 address cycle on pci bus for cards supporting greater
1235 than 32-bit addressing. The default is to look
1236 for translation below 32-bit and if not available
1237 then look in the higher range.
1238 strict [Default Off]
1239 With this option on every unmap_single operation will
1240 result in a hardware IOTLB flush operation as opposed
1241 to batching them for performance.
1242 sp_off [Default Off]
1243 By default, super page will be supported if Intel IOMMU
1244 has the capability. With this option, super page will
1245 not be supported.
1247 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1248 0 disables intel_idle and fall back on acpi_idle.
1249 1 to 6 specify maximum depth of C-state.
1251 intel_pstate= [X86]
1252 disable
1253 Do not enable intel_pstate as the default
1254 scaling driver for the supported processors
1256 intremap= [X86-64, Intel-IOMMU]
1257 on enable Interrupt Remapping (default)
1258 off disable Interrupt Remapping
1259 nosid disable Source ID checking
1260 no_x2apic_optout
1261 BIOS x2APIC opt-out request will be ignored
1263 iomem= Disable strict checking of access to MMIO memory
1264 strict regions from userspace.
1265 relaxed
1267 iommu= [x86]
1268 off
1269 force
1270 noforce
1271 biomerge
1272 panic
1273 nopanic
1274 merge
1275 nomerge
1276 forcesac
1277 soft
1278 pt [x86, IA-64]
1281 io7= [HW] IO7 for Marvel based alpha systems
1282 See comment before marvel_specify_io7 in
1283 arch/alpha/kernel/core_marvel.c.
1285 io_delay= [X86] I/O delay method
1286 0x80
1287 Standard port 0x80 based delay
1288 0xed
1289 Alternate port 0xed based delay (needed on some systems)
1290 udelay
1291 Simple two microseconds delay
1292 none
1293 No delay
1295 ip= [IP_PNP]
1296 See Documentation/filesystems/nfs/nfsroot.txt.
1298 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1299 See comment before ip2_setup() in
1300 drivers/char/ip2/ip2base.c.
1302 irqfixup [HW]
1303 When an interrupt is not handled search all handlers
1304 for it. Intended to get systems with badly broken
1305 firmware running.
1307 irqpoll [HW]
1308 When an interrupt is not handled search all handlers
1309 for it. Also check all handlers each timer
1310 interrupt. Intended to get systems with badly broken
1311 firmware running.
1313 isapnp= [ISAPNP]
1314 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1316 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1317 Format:
1318 <cpu number>,...,<cpu number>
1319 or
1320 <cpu number>-<cpu number>
1321 (must be a positive range in ascending order)
1322 or a mixture
1323 <cpu number>,...,<cpu number>-<cpu number>
1325 This option can be used to specify one or more CPUs
1326 to isolate from the general SMP balancing and scheduling
1327 algorithms. You can move a process onto or off an
1328 "isolated" CPU via the CPU affinity syscalls or cpuset.
1329 <cpu number> begins at 0 and the maximum value is
1330 "number of CPUs in system - 1".
1332 This option is the preferred way to isolate CPUs. The
1333 alternative -- manually setting the CPU mask of all
1334 tasks in the system -- can cause problems and
1335 suboptimal load balancer performance.
1337 iucv= [HW,NET]
1339 ivrs_ioapic [HW,X86_64]
1340 Provide an override to the IOAPIC-ID<->DEVICE-ID
1341 mapping provided in the IVRS ACPI table. For
1342 example, to map IOAPIC-ID decimal 10 to
1343 PCI device 00:14.0 write the parameter as:
1344 ivrs_ioapic[10]=00:14.0
1346 ivrs_hpet [HW,X86_64]
1347 Provide an override to the HPET-ID<->DEVICE-ID
1348 mapping provided in the IVRS ACPI table. For
1349 example, to map HPET-ID decimal 0 to
1350 PCI device 00:14.0 write the parameter as:
1351 ivrs_hpet[0]=00:14.0
1353 js= [HW,JOY] Analog joystick
1354 See Documentation/input/joystick.txt.
1356 keepinitrd [HW,ARM]
1358 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1359 specifies the amount of memory usable by the kernel
1360 for non-movable allocations. The requested amount is
1361 spread evenly throughout all nodes in the system. The
1362 remaining memory in each node is used for Movable
1363 pages. In the event, a node is too small to have both
1364 kernelcore and Movable pages, kernelcore pages will
1365 take priority and other nodes will have a larger number
1366 of Movable pages. The Movable zone is used for the
1367 allocation of pages that may be reclaimed or moved
1368 by the page migration subsystem. This means that
1369 HugeTLB pages may not be allocated from this zone.
1370 Note that allocations like PTEs-from-HighMem still
1371 use the HighMem zone if it exists, and the Normal
1372 zone if it does not.
1374 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1375 Format: <Controller#>[,poll interval]
1376 The controller # is the number of the ehci usb debug
1377 port as it is probed via PCI. The poll interval is
1378 optional and is the number seconds in between
1379 each poll cycle to the debug port in case you need
1380 the functionality for interrupting the kernel with
1381 gdb or control-c on the dbgp connection. When
1382 not using this parameter you use sysrq-g to break into
1383 the kernel debugger.
1385 kgdboc= [KGDB,HW] kgdb over consoles.
1386 Requires a tty driver that supports console polling,
1387 or a supported polling keyboard driver (non-usb).
1388 Serial only format: <serial_device>[,baud]
1389 keyboard only format: kbd
1390 keyboard and serial format: kbd,<serial_device>[,baud]
1391 Optional Kernel mode setting:
1392 kms, kbd format: kms,kbd
1393 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1395 kgdbwait [KGDB] Stop kernel execution and enter the
1396 kernel debugger at the earliest opportunity.
1398 kmac= [MIPS] korina ethernet MAC address.
1399 Configure the RouterBoard 532 series on-chip
1400 Ethernet adapter MAC address.
1402 kmemleak= [KNL] Boot-time kmemleak enable/disable
1403 Valid arguments: on, off
1404 Default: on
1406 kstack=N [X86] Print N words from the kernel stack
1407 in oops dumps.
1409 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1410 Default is 0 (don't ignore, but inject #GP)
1412 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1413 KVM MMU at runtime.
1414 Default is 0 (off)
1416 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1417 Default is 1 (enabled)
1419 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1420 for all guests.
1421 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1423 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1424 (virtualized MMU) support on capable Intel chips.
1425 Default is 1 (enabled)
1427 kvm-intel.emulate_invalid_guest_state=
1428 [KVM,Intel] Enable emulation of invalid guest states
1429 Default is 0 (disabled)
1431 kvm-intel.flexpriority=
1432 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1433 Default is 1 (enabled)
1435 kvm-intel.nested=
1436 [KVM,Intel] Enable VMX nesting (nVMX).
1437 Default is 0 (disabled)
1439 kvm-intel.unrestricted_guest=
1440 [KVM,Intel] Disable unrestricted guest feature
1441 (virtualized real and unpaged mode) on capable
1442 Intel chips. Default is 1 (enabled)
1444 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1445 feature (tagged TLBs) on capable Intel chips.
1446 Default is 1 (enabled)
1448 l2cr= [PPC]
1450 l3cr= [PPC]
1452 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1453 disabled it.
1455 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1456 value for LAPIC timer one-shot implementation. Default
1457 back to the programmable timer unit in the LAPIC.
1459 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1460 in C2 power state.
1462 libata.dma= [LIBATA] DMA control
1463 libata.dma=0 Disable all PATA and SATA DMA
1464 libata.dma=1 PATA and SATA Disk DMA only
1465 libata.dma=2 ATAPI (CDROM) DMA only
1466 libata.dma=4 Compact Flash DMA only
1467 Combinations also work, so libata.dma=3 enables DMA
1468 for disks and CDROMs, but not CFs.
1470 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1471 libata.ignore_hpa=0 keep BIOS limits (default)
1472 libata.ignore_hpa=1 ignore limits, using full disk
1474 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1475 when set.
1476 Format: <int>
1478 libata.force= [LIBATA] Force configurations. The format is comma
1479 separated list of "[ID:]VAL" where ID is
1480 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1481 matching port, link or device. Basically, it matches
1482 the ATA ID string printed on console by libata. If
1483 the whole ID part is omitted, the last PORT and DEVICE
1484 values are used. If ID hasn't been specified yet, the
1485 configuration applies to all ports, links and devices.
1487 If only DEVICE is omitted, the parameter applies to
1488 the port and all links and devices behind it. DEVICE
1489 number of 0 either selects the first device or the
1490 first fan-out link behind PMP device. It does not
1491 select the host link. DEVICE number of 15 selects the
1492 host link and device attached to it.
1494 The VAL specifies the configuration to force. As long
1495 as there's no ambiguity shortcut notation is allowed.
1496 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1497 The following configurations can be forced.
1499 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1500 Any ID with matching PORT is used.
1502 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1504 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1505 udma[/][16,25,33,44,66,100,133] notation is also
1506 allowed.
1508 * [no]ncq: Turn on or off NCQ.
1510 * nohrst, nosrst, norst: suppress hard, soft
1511 and both resets.
1513 * rstonce: only attempt one reset during
1514 hot-unplug link recovery
1516 * dump_id: dump IDENTIFY data.
1518 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1520 If there are multiple matching configurations changing
1521 the same attribute, the last one is used.
1523 memblock=debug [KNL] Enable memblock debug messages.
1525 load_ramdisk= [RAM] List of ramdisks to load from floppy
1526 See Documentation/blockdev/ramdisk.txt.
1528 lockd.nlm_grace_period=P [NFS] Assign grace period.
1529 Format: <integer>
1531 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1532 Format: <integer>
1534 lockd.nlm_timeout=T [NFS] Assign timeout value.
1535 Format: <integer>
1537 lockd.nlm_udpport=M [NFS] Assign UDP port.
1538 Format: <integer>
1540 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1541 Format: <irq>
1543 loglevel= All Kernel Messages with a loglevel smaller than the
1544 console loglevel will be printed to the console. It can
1545 also be changed with klogd or other programs. The
1546 loglevels are defined as follows:
1548 0 (KERN_EMERG) system is unusable
1549 1 (KERN_ALERT) action must be taken immediately
1550 2 (KERN_CRIT) critical conditions
1551 3 (KERN_ERR) error conditions
1552 4 (KERN_WARNING) warning conditions
1553 5 (KERN_NOTICE) normal but significant condition
1554 6 (KERN_INFO) informational
1555 7 (KERN_DEBUG) debug-level messages
1557 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1558 in bytes. n must be a power of two. The default
1559 size is set in the kernel config file.
1561 logo.nologo [FB] Disables display of the built-in Linux logo.
1562 This may be used to provide more screen space for
1563 kernel log messages and is useful when debugging
1564 kernel boot problems.
1566 lp=0 [LP] Specify parallel ports to use, e.g,
1567 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1568 lp=reset first parallel port). 'lp=0' disables the
1569 lp=auto printer driver. 'lp=reset' (which can be
1570 specified in addition to the ports) causes
1571 attached printers to be reset. Using
1572 lp=port1,port2,... specifies the parallel ports
1573 to associate lp devices with, starting with
1574 lp0. A port specification may be 'none' to skip
1575 that lp device, or a parport name such as
1576 'parport0'. Specifying 'lp=auto' instead of a
1577 port specification list means that device IDs
1578 from each port should be examined, to see if
1579 an IEEE 1284-compliant printer is attached; if
1580 so, the driver will manage that printer.
1581 See also header of drivers/char/lp.c.
1583 lpj=n [KNL]
1584 Sets loops_per_jiffy to given constant, thus avoiding
1585 time-consuming boot-time autodetection (up to 250 ms per
1586 CPU). 0 enables autodetection (default). To determine
1587 the correct value for your kernel, boot with normal
1588 autodetection and see what value is printed. Note that
1589 on SMP systems the preset will be applied to all CPUs,
1590 which is likely to cause problems if your CPUs need
1591 significantly divergent settings. An incorrect value
1592 will cause delays in the kernel to be wrong, leading to
1593 unpredictable I/O errors and other breakage. Although
1594 unlikely, in the extreme case this might damage your
1595 hardware.
1597 ltpc= [NET]
1598 Format: <io>,<irq>,<dma>
1600 machvec= [IA-64] Force the use of a particular machine-vector
1601 (machvec) in a generic kernel.
1602 Example: machvec=hpzx1_swiotlb
1604 machtype= [Loongson] Share the same kernel image file between different
1605 yeeloong laptop.
1606 Example: machtype=lemote-yeeloong-2f-7inch
1608 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1609 than or equal to this physical address is ignored.
1611 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1612 should make use of. maxcpus=n : n >= 0 limits the
1613 kernel to using 'n' processors. n=0 is a special case,
1614 it is equivalent to "nosmp", which also disables
1615 the IO APIC.
1617 max_loop= [LOOP] The number of loop block devices that get
1618 (loop.max_loop) unconditionally pre-created at init time. The default
1619 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1620 of statically allocating a predefined number, loop
1621 devices can be requested on-demand with the
1622 /dev/loop-control interface.
1624 mce [X86-32] Machine Check Exception
1626 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1628 md= [HW] RAID subsystems devices and level
1629 See Documentation/md.txt.
1631 mdacon= [MDA]
1632 Format: <first>,<last>
1633 Specifies range of consoles to be captured by the MDA.
1635 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1636 Amount of memory to be used when the kernel is not able
1637 to see the whole system memory or for test.
1638 [X86] Work as limiting max address. Use together
1639 with memmap= to avoid physical address space collisions.
1640 Without memmap= PCI devices could be placed at addresses
1641 belonging to unused RAM.
1643 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1644 memory.
1646 memchunk=nn[KMG]
1647 [KNL,SH] Allow user to override the default size for
1648 per-device physically contiguous DMA buffers.
1650 memmap=exactmap [KNL,X86] Enable setting of an exact
1651 E820 memory map, as specified by the user.
1652 Such memmap=exactmap lines can be constructed based on
1653 BIOS output or other requirements. See the memmap=nn@ss
1654 option description.
1656 memmap=nn[KMG]@ss[KMG]
1657 [KNL] Force usage of a specific region of memory
1658 Region of memory to be used, from ss to ss+nn.
1660 memmap=nn[KMG]#ss[KMG]
1661 [KNL,ACPI] Mark specific memory as ACPI data.
1662 Region of memory to be used, from ss to ss+nn.
1664 memmap=nn[KMG]$ss[KMG]
1665 [KNL,ACPI] Mark specific memory as reserved.
1666 Region of memory to be used, from ss to ss+nn.
1667 Example: Exclude memory from 0x18690000-0x1869ffff
1668 memmap=64K$0x18690000
1669 or
1670 memmap=0x10000$0x18690000
1672 memory_corruption_check=0/1 [X86]
1673 Some BIOSes seem to corrupt the first 64k of
1674 memory when doing things like suspend/resume.
1675 Setting this option will scan the memory
1676 looking for corruption. Enabling this will
1677 both detect corruption and prevent the kernel
1678 from using the memory being corrupted.
1679 However, its intended as a diagnostic tool; if
1680 repeatable BIOS-originated corruption always
1681 affects the same memory, you can use memmap=
1682 to prevent the kernel from using that memory.
1684 memory_corruption_check_size=size [X86]
1685 By default it checks for corruption in the low
1686 64k, making this memory unavailable for normal
1687 use. Use this parameter to scan for
1688 corruption in more or less memory.
1690 memory_corruption_check_period=seconds [X86]
1691 By default it checks for corruption every 60
1692 seconds. Use this parameter to check at some
1693 other rate. 0 disables periodic checking.
1695 memtest= [KNL,X86] Enable memtest
1696 Format: <integer>
1697 default : 0 <disable>
1698 Specifies the number of memtest passes to be
1699 performed. Each pass selects another test
1700 pattern from a given set of patterns. Memtest
1701 fills the memory with this pattern, validates
1702 memory contents and reserves bad memory
1703 regions that are detected.
1705 meye.*= [HW] Set MotionEye Camera parameters
1706 See Documentation/video4linux/meye.txt.
1708 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1709 Multi-Function General Purpose Timers on AMD Geode
1710 platforms.
1712 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1713 the BIOS has incorrectly applied a workaround. TinyBIOS
1714 version 0.98 is known to be affected, 0.99 fixes the
1715 problem by letting the user disable the workaround.
1717 mga= [HW,DRM]
1719 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1720 physical address is ignored.
1722 mini2440= [ARM,HW,KNL]
1723 Format:[0..2][b][c][t]
1724 Default: "0tb"
1725 MINI2440 configuration specification:
1726 0 - The attached screen is the 3.5" TFT
1727 1 - The attached screen is the 7" TFT
1728 2 - The VGA Shield is attached (1024x768)
1729 Leaving out the screen size parameter will not load
1730 the TFT driver, and the framebuffer will be left
1731 unconfigured.
1732 b - Enable backlight. The TFT backlight pin will be
1733 linked to the kernel VESA blanking code and a GPIO
1734 LED. This parameter is not necessary when using the
1735 VGA shield.
1736 c - Enable the s3c camera interface.
1737 t - Reserved for enabling touchscreen support. The
1738 touchscreen support is not enabled in the mainstream
1739 kernel as of 2.6.30, a preliminary port can be found
1740 in the "bleeding edge" mini2440 support kernel at
1741 http://repo.or.cz/w/linux-2.6/mini2440.git
1743 mminit_loglevel=
1744 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1745 parameter allows control of the logging verbosity for
1746 the additional memory initialisation checks. A value
1747 of 0 disables mminit logging and a level of 4 will
1748 log everything. Information is printed at KERN_DEBUG
1749 so loglevel=8 may also need to be specified.
1751 module.sig_enforce
1752 [KNL] When CONFIG_MODULE_SIG is set, this means that
1753 modules without (valid) signatures will fail to load.
1754 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1755 is always true, so this option does nothing.
1757 mousedev.tap_time=
1758 [MOUSE] Maximum time between finger touching and
1759 leaving touchpad surface for touch to be considered
1760 a tap and be reported as a left button click (for
1761 touchpads working in absolute mode only).
1762 Format: <msecs>
1763 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1764 reporting absolute coordinates, such as tablets
1765 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1766 reporting absolute coordinates, such as tablets
1768 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1769 is similar to kernelcore except it specifies the
1770 amount of memory used for migratable allocations.
1771 If both kernelcore and movablecore is specified,
1772 then kernelcore will be at *least* the specified
1773 value but may be more. If movablecore on its own
1774 is specified, the administrator must be careful
1775 that the amount of memory usable for all allocations
1776 is not too small.
1778 MTD_Partition= [MTD]
1779 Format: <name>,<region-number>,<size>,<offset>
1781 MTD_Region= [MTD] Format:
1782 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1784 mtdparts= [MTD]
1785 See drivers/mtd/cmdlinepart.c.
1787 multitce=off [PPC] This parameter disables the use of the pSeries
1788 firmware feature for updating multiple TCE entries
1789 at a time.
1791 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1793 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1795 boundary - index of last SLC block on Flex-OneNAND.
1796 The remaining blocks are configured as MLC blocks.
1797 lock - Configure if Flex-OneNAND boundary should be locked.
1798 Once locked, the boundary cannot be changed.
1799 1 indicates lock status, 0 indicates unlock status.
1801 mtdset= [ARM]
1802 ARM/S3C2412 JIVE boot control
1804 See arch/arm/mach-s3c2412/mach-jive.c
1806 mtouchusb.raw_coordinates=
1807 [HW] Make the MicroTouch USB driver use raw coordinates
1808 ('y', default) or cooked coordinates ('n')
1810 mtrr_chunk_size=nn[KMG] [X86]
1811 used for mtrr cleanup. It is largest continuous chunk
1812 that could hold holes aka. UC entries.
1814 mtrr_gran_size=nn[KMG] [X86]
1815 Used for mtrr cleanup. It is granularity of mtrr block.
1816 Default is 1.
1817 Large value could prevent small alignment from
1818 using up MTRRs.
1820 mtrr_spare_reg_nr=n [X86]
1821 Format: <integer>
1822 Range: 0,7 : spare reg number
1823 Default : 1
1824 Used for mtrr cleanup. It is spare mtrr entries number.
1825 Set to 2 or more if your graphical card needs more.
1827 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1829 netdev= [NET] Network devices parameters
1830 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1831 Note that mem_start is often overloaded to mean
1832 something different and driver-specific.
1833 This usage is only documented in each driver source
1834 file if at all.
1836 nf_conntrack.acct=
1837 [NETFILTER] Enable connection tracking flow accounting
1838 0 to disable accounting
1839 1 to enable accounting
1840 Default value is 0.
1842 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1843 See Documentation/filesystems/nfs/nfsroot.txt.
1845 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1846 See Documentation/filesystems/nfs/nfsroot.txt.
1848 nfsrootdebug [NFS] enable nfsroot debugging messages.
1849 See Documentation/filesystems/nfs/nfsroot.txt.
1851 nfs.callback_tcpport=
1852 [NFS] set the TCP port on which the NFSv4 callback
1853 channel should listen.
1855 nfs.cache_getent=
1856 [NFS] sets the pathname to the program which is used
1857 to update the NFS client cache entries.
1859 nfs.cache_getent_timeout=
1860 [NFS] sets the timeout after which an attempt to
1861 update a cache entry is deemed to have failed.
1863 nfs.idmap_cache_timeout=
1864 [NFS] set the maximum lifetime for idmapper cache
1865 entries.
1867 nfs.enable_ino64=
1868 [NFS] enable 64-bit inode numbers.
1869 If zero, the NFS client will fake up a 32-bit inode
1870 number for the readdir() and stat() syscalls instead
1871 of returning the full 64-bit number.
1872 The default is to return 64-bit inode numbers.
1874 nfs.max_session_slots=
1875 [NFSv4.1] Sets the maximum number of session slots
1876 the client will attempt to negotiate with the server.
1877 This limits the number of simultaneous RPC requests
1878 that the client can send to the NFSv4.1 server.
1879 Note that there is little point in setting this
1880 value higher than the max_tcp_slot_table_limit.
1882 nfs.nfs4_disable_idmapping=
1883 [NFSv4] When set to the default of '1', this option
1884 ensures that both the RPC level authentication
1885 scheme and the NFS level operations agree to use
1886 numeric uids/gids if the mount is using the
1887 'sec=sys' security flavour. In effect it is
1888 disabling idmapping, which can make migration from
1889 legacy NFSv2/v3 systems to NFSv4 easier.
1890 Servers that do not support this mode of operation
1891 will be autodetected by the client, and it will fall
1892 back to using the idmapper.
1893 To turn off this behaviour, set the value to '0'.
1894 nfs.nfs4_unique_id=
1895 [NFS4] Specify an additional fixed unique ident-
1896 ification string that NFSv4 clients can insert into
1897 their nfs_client_id4 string. This is typically a
1898 UUID that is generated at system install time.
1900 nfs.send_implementation_id =
1901 [NFSv4.1] Send client implementation identification
1902 information in exchange_id requests.
1903 If zero, no implementation identification information
1904 will be sent.
1905 The default is to send the implementation identification
1906 information.
1908 nfs.recover_lost_locks =
1909 [NFSv4] Attempt to recover locks that were lost due
1910 to a lease timeout on the server. Please note that
1911 doing this risks data corruption, since there are
1912 no guarantees that the file will remain unchanged
1913 after the locks are lost.
1914 If you want to enable the kernel legacy behaviour of
1915 attempting to recover these locks, then set this
1916 parameter to '1'.
1917 The default parameter value of '0' causes the kernel
1918 not to attempt recovery of lost locks.
1920 nfsd.nfs4_disable_idmapping=
1921 [NFSv4] When set to the default of '1', the NFSv4
1922 server will return only numeric uids and gids to
1923 clients using auth_sys, and will accept numeric uids
1924 and gids from such clients. This is intended to ease
1925 migration from NFSv2/v3.
1927 objlayoutdriver.osd_login_prog=
1928 [NFS] [OBJLAYOUT] sets the pathname to the program which
1929 is used to automatically discover and login into new
1930 osd-targets. Please see:
1931 Documentation/filesystems/pnfs.txt for more explanations
1933 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1934 when a NMI is triggered.
1935 Format: [state][,regs][,debounce][,die]
1937 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1938 Format: [panic,][nopanic,][num]
1939 Valid num: 0
1940 0 - turn nmi_watchdog off
1941 When panic is specified, panic when an NMI watchdog
1942 timeout occurs (or 'nopanic' to override the opposite
1943 default).
1944 This is useful when you use a panic=... timeout and
1945 need the box quickly up again.
1947 netpoll.carrier_timeout=
1948 [NET] Specifies amount of time (in seconds) that
1949 netpoll should wait for a carrier. By default netpoll
1950 waits 4 seconds.
1952 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1953 emulation library even if a 387 maths coprocessor
1954 is present.
1956 no_console_suspend
1957 [HW] Never suspend the console
1958 Disable suspending of consoles during suspend and
1959 hibernate operations. Once disabled, debugging
1960 messages can reach various consoles while the rest
1961 of the system is being put to sleep (ie, while
1962 debugging driver suspend/resume hooks). This may
1963 not work reliably with all consoles, but is known
1964 to work with serial and VGA consoles.
1965 To facilitate more flexible debugging, we also add
1966 console_suspend, a printk module parameter to control
1967 it. Users could use console_suspend (usually
1968 /sys/module/printk/parameters/console_suspend) to
1969 turn on/off it dynamically.
1971 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1972 caches in the slab allocator. Saves per-node memory,
1973 but will impact performance.
1975 noalign [KNL,ARM]
1977 noapic [SMP,APIC] Tells the kernel to not make use of any
1978 IOAPICs that may be present in the system.
1980 noautogroup Disable scheduler automatic task group creation.
1982 nobats [PPC] Do not use BATs for mapping kernel lowmem
1983 on "Classic" PPC cores.
1985 nocache [ARM]
1987 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1989 nodelayacct [KNL] Disable per-task delay accounting
1991 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1993 nodsp [SH] Disable hardware DSP at boot time.
1995 noefi [X86] Disable EFI runtime services support.
1997 noexec [IA-64]
1999 noexec [X86]
2000 On X86-32 available only on PAE configured kernels.
2001 noexec=on: enable non-executable mappings (default)
2002 noexec=off: disable non-executable mappings
2004 nosmap [X86]
2005 Disable SMAP (Supervisor Mode Access Prevention)
2006 even if it is supported by processor.
2008 nosmep [X86]
2009 Disable SMEP (Supervisor Mode Execution Prevention)
2010 even if it is supported by processor.
2012 noexec32 [X86-64]
2013 This affects only 32-bit executables.
2014 noexec32=on: enable non-executable mappings (default)
2015 read doesn't imply executable mappings
2016 noexec32=off: disable non-executable mappings
2017 read implies executable mappings
2019 nofpu [SH] Disable hardware FPU at boot time.
2021 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2022 register save and restore. The kernel will only save
2023 legacy floating-point registers on task switch.
2025 noxsave [BUGS=X86] Disables x86 extended register state save
2026 and restore using xsave. The kernel will fallback to
2027 enabling legacy floating-point and sse state.
2029 eagerfpu= [X86]
2030 on enable eager fpu restore
2031 off disable eager fpu restore
2032 auto selects the default scheme, which automatically
2033 enables eagerfpu restore for xsaveopt.
2035 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2036 wfi(ARM) instruction doesn't work correctly and not to
2037 use it. This is also useful when using JTAG debugger.
2039 no_file_caps Tells the kernel not to honor file capabilities. The
2040 only way then for a file to be executed with privilege
2041 is to be setuid root or executed by root.
2043 nohalt [IA-64] Tells the kernel not to use the power saving
2044 function PAL_HALT_LIGHT when idle. This increases
2045 power-consumption. On the positive side, it reduces
2046 interrupt wake-up latency, which may improve performance
2047 in certain environments such as networked servers or
2048 real-time systems.
2050 nohz= [KNL] Boottime enable/disable dynamic ticks
2051 Valid arguments: on, off
2052 Default: on
2054 nohz_full= [KNL,BOOT]
2055 In kernels built with CONFIG_NO_HZ_FULL=y, set
2056 the specified list of CPUs whose tick will be stopped
2057 whenever possible. The boot CPU will be forced outside
2058 the range to maintain the timekeeping.
2059 The CPUs in this range must also be included in the
2060 rcu_nocbs= set.
2062 noiotrap [SH] Disables trapped I/O port accesses.
2064 noirqdebug [X86-32] Disables the code which attempts to detect and
2065 disable unhandled interrupt sources.
2067 no_timer_check [X86,APIC] Disables the code which tests for
2068 broken timer IRQ sources.
2070 noisapnp [ISAPNP] Disables ISA PnP code.
2072 noinitrd [RAM] Tells the kernel not to load any configured
2073 initial RAM disk.
2075 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2076 remapping.
2077 [Deprecated - use intremap=off]
2079 nointroute [IA-64]
2081 nojitter [IA-64] Disables jitter checking for ITC timers.
2083 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2085 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2086 fault handling.
2088 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2089 steal time is computed, but won't influence scheduler
2090 behaviour
2092 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2094 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2096 noltlbs [PPC] Do not use large page/tlb entries for kernel
2097 lowmem mapping on PPC40x.
2099 nomca [IA-64] Disable machine check abort handling
2101 nomce [X86-32] Machine Check Exception
2103 nomfgpt [X86-32] Disable Multi-Function General Purpose
2104 Timer usage (for AMD Geode machines).
2106 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2107 shutdown the other cpus. Instead use the REBOOT_VECTOR
2108 irq.
2110 nomodule Disable module load
2112 nopat [X86] Disable PAT (page attribute table extension of
2113 pagetables) support.
2115 norandmaps Don't use address space randomization. Equivalent to
2116 echo 0 > /proc/sys/kernel/randomize_va_space
2118 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2120 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2121 with UP alternatives
2123 nordrand [X86] Disable the direct use of the RDRAND
2124 instruction even if it is supported by the
2125 processor. RDRAND is still available to user
2126 space applications.
2128 noresume [SWSUSP] Disables resume and restores original swap
2129 space.
2131 no-scroll [VGA] Disables scrollback.
2132 This is required for the Braillex ib80-piezo Braille
2133 reader made by F.H. Papenmeier (Germany).
2135 nosbagart [IA-64]
2137 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2139 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2140 and disable the IO APIC. legacy for "maxcpus=0".
2142 nosoftlockup [KNL] Disable the soft-lockup detector.
2144 nosync [HW,M68K] Disables sync negotiation for all devices.
2146 notsc [BUGS=X86-32] Disable Time Stamp Counter
2148 nousb [USB] Disable the USB subsystem
2150 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2152 nowb [ARM]
2154 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2156 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2157 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2158 Some features depend on CPU0. Known dependencies are:
2159 1. Resume from suspend/hibernate depends on CPU0.
2160 Suspend/hibernate will fail if CPU0 is offline and you
2161 need to online CPU0 before suspend/hibernate.
2162 2. PIC interrupts also depend on CPU0. CPU0 can't be
2163 removed if a PIC interrupt is detected.
2164 It's said poweroff/reboot may depend on CPU0 on some
2165 machines although I haven't seen such issues so far
2166 after CPU0 is offline on a few tested machines.
2167 If the dependencies are under your control, you can
2168 turn on cpu0_hotplug.
2170 nptcg= [IA-64] Override max number of concurrent global TLB
2171 purges which is reported from either PAL_VM_SUMMARY or
2172 SAL PALO.
2174 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2175 could support. nr_cpus=n : n >= 1 limits the kernel to
2176 supporting 'n' processors. Later in runtime you can not
2177 use hotplug cpu feature to put more cpu back to online.
2178 just like you compile the kernel NR_CPUS=n
2180 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2182 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2183 Allowed values are enable and disable
2185 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2186 one of ['zone', 'node', 'default'] can be specified
2187 This can be set from sysctl after boot.
2188 See Documentation/sysctl/vm.txt for details.
2190 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2191 See Documentation/debugging-via-ohci1394.txt for more
2192 info.
2194 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2195 Rather than timing out after 20 ms if an EC
2196 command is not properly ACKed, override the length
2197 of the timeout. We have interrupts disabled while
2198 waiting for the ACK, so if this is set too high
2199 interrupts *may* be lost!
2201 omap_mux= [OMAP] Override bootloader pin multiplexing.
2202 Format: <mux_mode0.mode_name=value>...
2203 For example, to override I2C bus2:
2204 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2206 oprofile.timer= [HW]
2207 Use timer interrupt instead of performance counters
2209 oprofile.cpu_type= Force an oprofile cpu type
2210 This might be useful if you have an older oprofile
2211 userland or if you want common events.
2212 Format: { arch_perfmon }
2213 arch_perfmon: [X86] Force use of architectural
2214 perfmon on Intel CPUs instead of the
2215 CPU specific event set.
2216 timer: [X86] Force use of architectural NMI
2217 timer mode (see also oprofile.timer
2218 for generic hr timer mode)
2219 [s390] Force legacy basic mode sampling
2220 (report cpu_type "timer")
2222 oops=panic Always panic on oopses. Default is to just kill the
2223 process, but there is a small probability of
2224 deadlocking the machine.
2225 This will also cause panics on machine check exceptions.
2226 Useful together with panic=30 to trigger a reboot.
2228 OSS [HW,OSS]
2229 See Documentation/sound/oss/oss-parameters.txt
2231 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2232 timeout > 0: seconds before rebooting
2233 timeout = 0: wait forever
2234 timeout < 0: reboot immediately
2235 Format: <timeout>
2237 parkbd.port= [HW] Parallel port number the keyboard adapter is
2238 connected to, default is 0.
2239 Format: <parport#>
2240 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2241 0 for XT, 1 for AT (default is AT).
2242 Format: <mode>
2244 parport= [HW,PPT] Specify parallel ports. 0 disables.
2245 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2246 Use 'auto' to force the driver to use any
2247 IRQ/DMA settings detected (the default is to
2248 ignore detected IRQ/DMA settings because of
2249 possible conflicts). You can specify the base
2250 address, IRQ, and DMA settings; IRQ and DMA
2251 should be numbers, or 'auto' (for using detected
2252 settings on that particular port), or 'nofifo'
2253 (to avoid using a FIFO even if it is detected).
2254 Parallel ports are assigned in the order they
2255 are specified on the command line, starting
2256 with parport0.
2258 parport_init_mode= [HW,PPT]
2259 Configure VIA parallel port to operate in
2260 a specific mode. This is necessary on Pegasos
2261 computer where firmware has no options for setting
2262 up parallel port mode and sets it to spp.
2263 Currently this function knows 686a and 8231 chips.
2264 Format: [spp|ps2|epp|ecp|ecpepp]
2266 pause_on_oops=
2267 Halt all CPUs after the first oops has been printed for
2268 the specified number of seconds. This is to be used if
2269 your oopses keep scrolling off the screen.
2271 pcbit= [HW,ISDN]
2273 pcd. [PARIDE]
2274 See header of drivers/block/paride/pcd.c.
2275 See also Documentation/blockdev/paride.txt.
2277 pci=option[,option...] [PCI] various PCI subsystem options:
2278 earlydump [X86] dump PCI config space before the kernel
2279 changes anything
2280 off [X86] don't probe for the PCI bus
2281 bios [X86-32] force use of PCI BIOS, don't access
2282 the hardware directly. Use this if your machine
2283 has a non-standard PCI host bridge.
2284 nobios [X86-32] disallow use of PCI BIOS, only direct
2285 hardware access methods are allowed. Use this
2286 if you experience crashes upon bootup and you
2287 suspect they are caused by the BIOS.
2288 conf1 [X86] Force use of PCI Configuration
2289 Mechanism 1.
2290 conf2 [X86] Force use of PCI Configuration
2291 Mechanism 2.
2292 noaer [PCIE] If the PCIEAER kernel config parameter is
2293 enabled, this kernel boot option can be used to
2294 disable the use of PCIE advanced error reporting.
2295 nodomains [PCI] Disable support for multiple PCI
2296 root domains (aka PCI segments, in ACPI-speak).
2297 nommconf [X86] Disable use of MMCONFIG for PCI
2298 Configuration
2299 check_enable_amd_mmconf [X86] check for and enable
2300 properly configured MMIO access to PCI
2301 config space on AMD family 10h CPU
2302 nomsi [MSI] If the PCI_MSI kernel config parameter is
2303 enabled, this kernel boot option can be used to
2304 disable the use of MSI interrupts system-wide.
2305 noioapicquirk [APIC] Disable all boot interrupt quirks.
2306 Safety option to keep boot IRQs enabled. This
2307 should never be necessary.
2308 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2309 primary IO-APIC for bridges that cannot disable
2310 boot IRQs. This fixes a source of spurious IRQs
2311 when the system masks IRQs.
2312 noioapicreroute [APIC] Disable workaround that uses the
2313 boot IRQ equivalent of an IRQ that connects to
2314 a chipset where boot IRQs cannot be disabled.
2315 The opposite of ioapicreroute.
2316 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2317 routing table. These calls are known to be buggy
2318 on several machines and they hang the machine
2319 when used, but on other computers it's the only
2320 way to get the interrupt routing table. Try
2321 this option if the kernel is unable to allocate
2322 IRQs or discover secondary PCI buses on your
2323 motherboard.
2324 rom [X86] Assign address space to expansion ROMs.
2325 Use with caution as certain devices share
2326 address decoders between ROMs and other
2327 resources.
2328 norom [X86] Do not assign address space to
2329 expansion ROMs that do not already have
2330 BIOS assigned address ranges.
2331 nobar [X86] Do not assign address space to the
2332 BARs that weren't assigned by the BIOS.
2333 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2334 assigned automatically to PCI devices. You can
2335 make the kernel exclude IRQs of your ISA cards
2336 this way.
2337 pirqaddr=0xAAAAA [X86] Specify the physical address
2338 of the PIRQ table (normally generated
2339 by the BIOS) if it is outside the
2340 F0000h-100000h range.
2341 lastbus=N [X86] Scan all buses thru bus #N. Can be
2342 useful if the kernel is unable to find your
2343 secondary buses and you want to tell it
2344 explicitly which ones they are.
2345 assign-busses [X86] Always assign all PCI bus
2346 numbers ourselves, overriding
2347 whatever the firmware may have done.
2348 usepirqmask [X86] Honor the possible IRQ mask stored
2349 in the BIOS $PIR table. This is needed on
2350 some systems with broken BIOSes, notably
2351 some HP Pavilion N5400 and Omnibook XE3
2352 notebooks. This will have no effect if ACPI
2353 IRQ routing is enabled.
2354 noacpi [X86] Do not use ACPI for IRQ routing
2355 or for PCI scanning.
2356 use_crs [X86] Use PCI host bridge window information
2357 from ACPI. On BIOSes from 2008 or later, this
2358 is enabled by default. If you need to use this,
2359 please report a bug.
2360 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2361 If you need to use this, please report a bug.
2362 routeirq Do IRQ routing for all PCI devices.
2363 This is normally done in pci_enable_device(),
2364 so this option is a temporary workaround
2365 for broken drivers that don't call it.
2366 skip_isa_align [X86] do not align io start addr, so can
2367 handle more pci cards
2368 firmware [ARM] Do not re-enumerate the bus but instead
2369 just use the configuration from the
2370 bootloader. This is currently used on
2371 IXP2000 systems where the bus has to be
2372 configured a certain way for adjunct CPUs.
2373 noearly [X86] Don't do any early type 1 scanning.
2374 This might help on some broken boards which
2375 machine check when some devices' config space
2376 is read. But various workarounds are disabled
2377 and some IOMMU drivers will not work.
2378 bfsort Sort PCI devices into breadth-first order.
2379 This sorting is done to get a device
2380 order compatible with older (<= 2.4) kernels.
2381 nobfsort Don't sort PCI devices into breadth-first order.
2382 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2383 tuning and use the BIOS-configured MPS defaults.
2384 pcie_bus_safe Set every device's MPS to the largest value
2385 supported by all devices below the root complex.
2386 pcie_bus_perf Set device MPS to the largest allowable MPS
2387 based on its parent bus. Also set MRRS (Max
2388 Read Request Size) to the largest supported
2389 value (no larger than the MPS that the device
2390 or bus can support) for best performance.
2391 pcie_bus_peer2peer Set every device's MPS to 128B, which
2392 every device is guaranteed to support. This
2393 configuration allows peer-to-peer DMA between
2394 any pair of devices, possibly at the cost of
2395 reduced performance. This also guarantees
2396 that hot-added devices will work.
2397 cbiosize=nn[KMG] The fixed amount of bus space which is
2398 reserved for the CardBus bridge's IO window.
2399 The default value is 256 bytes.
2400 cbmemsize=nn[KMG] The fixed amount of bus space which is
2401 reserved for the CardBus bridge's memory
2402 window. The default value is 64 megabytes.
2403 resource_alignment=
2404 Format:
2405 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2406 Specifies alignment and device to reassign
2407 aligned memory resources.
2408 If <order of align> is not specified,
2409 PAGE_SIZE is used as alignment.
2410 PCI-PCI bridge can be specified, if resource
2411 windows need to be expanded.
2412 ecrc= Enable/disable PCIe ECRC (transaction layer
2413 end-to-end CRC checking).
2414 bios: Use BIOS/firmware settings. This is the
2415 the default.
2416 off: Turn ECRC off
2417 on: Turn ECRC on.
2418 hpiosize=nn[KMG] The fixed amount of bus space which is
2419 reserved for hotplug bridge's IO window.
2420 Default size is 256 bytes.
2421 hpmemsize=nn[KMG] The fixed amount of bus space which is
2422 reserved for hotplug bridge's memory window.
2423 Default size is 2 megabytes.
2424 realloc= Enable/disable reallocating PCI bridge resources
2425 if allocations done by BIOS are too small to
2426 accommodate resources required by all child
2427 devices.
2428 off: Turn realloc off
2429 on: Turn realloc on
2430 realloc same as realloc=on
2431 noari do not use PCIe ARI.
2432 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2433 only look for one device below a PCIe downstream
2434 port.
2436 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2437 Management.
2438 off Disable ASPM.
2439 force Enable ASPM even on devices that claim not to support it.
2440 WARNING: Forcing ASPM on may cause system lockups.
2442 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2443 nomsi Do not use MSI for PCI Express Native Hotplug (this
2444 makes all PCIe ports use INTx for hotplug services).
2446 pcie_ports= [PCIE] PCIe ports handling:
2447 auto Ask the BIOS whether or not to use native PCIe services
2448 associated with PCIe ports (PME, hot-plug, AER). Use
2449 them only if that is allowed by the BIOS.
2450 native Use native PCIe services associated with PCIe ports
2451 unconditionally.
2452 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2453 ports driver.
2455 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2456 nomsi Do not use MSI for native PCIe PME signaling (this makes
2457 all PCIe root ports use INTx for all services).
2459 pcmv= [HW,PCMCIA] BadgePAD 4
2461 pd. [PARIDE]
2462 See Documentation/blockdev/paride.txt.
2464 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2465 boot time.
2466 Format: { 0 | 1 }
2467 See arch/parisc/kernel/pdc_chassis.c
2469 percpu_alloc= Select which percpu first chunk allocator to use.
2470 Currently supported values are "embed" and "page".
2471 Archs may support subset or none of the selections.
2472 See comments in mm/percpu.c for details on each
2473 allocator. This parameter is primarily for debugging
2474 and performance comparison.
2476 pf. [PARIDE]
2477 See Documentation/blockdev/paride.txt.
2479 pg. [PARIDE]
2480 See Documentation/blockdev/paride.txt.
2482 pirq= [SMP,APIC] Manual mp-table setup
2483 See Documentation/x86/i386/IO-APIC.txt.
2485 plip= [PPT,NET] Parallel port network link
2486 Format: { parport<nr> | timid | 0 }
2487 See also Documentation/parport.txt.
2489 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2490 Override pmtimer IOPort with a hex value.
2491 e.g. pmtmr=0x508
2493 pnp.debug=1 [PNP]
2494 Enable PNP debug messages (depends on the
2495 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2496 via /sys/module/pnp/parameters/debug. We always show
2497 current resource usage; turning this on also shows
2498 possible settings and some assignment information.
2500 pnpacpi= [ACPI]
2501 { off }
2503 pnpbios= [ISAPNP]
2504 { on | off | curr | res | no-curr | no-res }
2506 pnp_reserve_irq=
2507 [ISAPNP] Exclude IRQs for the autoconfiguration
2509 pnp_reserve_dma=
2510 [ISAPNP] Exclude DMAs for the autoconfiguration
2512 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2513 Ranges are in pairs (I/O port base and size).
2515 pnp_reserve_mem=
2516 [ISAPNP] Exclude memory regions for the
2517 autoconfiguration.
2518 Ranges are in pairs (memory base and size).
2520 ports= [IP_VS_FTP] IPVS ftp helper module
2521 Default is 21.
2522 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2523 may be specified.
2524 Format: <port>,<port>....
2526 print-fatal-signals=
2527 [KNL] debug: print fatal signals
2529 If enabled, warn about various signal handling
2530 related application anomalies: too many signals,
2531 too many POSIX.1 timers, fatal signals causing a
2532 coredump - etc.
2534 If you hit the warning due to signal overflow,
2535 you might want to try "ulimit -i unlimited".
2537 default: off.
2539 printk.always_kmsg_dump=
2540 Trigger kmsg_dump for cases other than kernel oops or
2541 panics
2542 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2543 default: disabled
2545 printk.time= Show timing data prefixed to each printk message line
2546 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2548 processor.max_cstate= [HW,ACPI]
2549 Limit processor to maximum C-state
2550 max_cstate=9 overrides any DMI blacklist limit.
2552 processor.nocst [HW,ACPI]
2553 Ignore the _CST method to determine C-states,
2554 instead using the legacy FADT method
2556 profile= [KNL] Enable kernel profiling via /proc/profile
2557 Format: [schedule,]<number>
2558 Param: "schedule" - profile schedule points.
2559 Param: <number> - step/bucket size as a power of 2 for
2560 statistical time based profiling.
2561 Param: "sleep" - profile D-state sleeping (millisecs).
2562 Requires CONFIG_SCHEDSTATS
2563 Param: "kvm" - profile VM exits.
2565 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2566 before loading.
2567 See Documentation/blockdev/ramdisk.txt.
2569 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2570 probe for; one of (bare|imps|exps|lifebook|any).
2571 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2572 per second.
2573 psmouse.resetafter= [HW,MOUSE]
2574 Try to reset the device after so many bad packets
2575 (0 = never).
2576 psmouse.resolution=
2577 [HW,MOUSE] Set desired mouse resolution, in dpi.
2578 psmouse.smartscroll=
2579 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2580 0 = disabled, 1 = enabled (default).
2582 pstore.backend= Specify the name of the pstore backend to use
2584 pt. [PARIDE]
2585 See Documentation/blockdev/paride.txt.
2587 pty.legacy_count=
2588 [KNL] Number of legacy pty's. Overwrites compiled-in
2589 default number.
2591 quiet [KNL] Disable most log messages
2593 r128= [HW,DRM]
2595 raid= [HW,RAID]
2596 See Documentation/md.txt.
2598 ramdisk_blocksize= [RAM]
2599 See Documentation/blockdev/ramdisk.txt.
2601 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2602 See Documentation/blockdev/ramdisk.txt.
2604 rcu_nocbs= [KNL]
2605 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2606 the specified list of CPUs to be no-callback CPUs.
2607 Invocation of these CPUs' RCU callbacks will
2608 be offloaded to "rcuox/N" kthreads created for
2609 that purpose, where "x" is "b" for RCU-bh, "p"
2610 for RCU-preempt, and "s" for RCU-sched, and "N"
2611 is the CPU number. This reduces OS jitter on the
2612 offloaded CPUs, which can be useful for HPC and
2614 real-time workloads. It can also improve energy
2615 efficiency for asymmetric multiprocessors.
2617 rcu_nocb_poll [KNL]
2618 Rather than requiring that offloaded CPUs
2619 (specified by rcu_nocbs= above) explicitly
2620 awaken the corresponding "rcuoN" kthreads,
2621 make these kthreads poll for callbacks.
2622 This improves the real-time response for the
2623 offloaded CPUs by relieving them of the need to
2624 wake up the corresponding kthread, but degrades
2625 energy efficiency by requiring that the kthreads
2626 periodically wake up to do the polling.
2628 rcutree.blimit= [KNL]
2629 Set maximum number of finished RCU callbacks to process
2630 in one batch.
2632 rcutree.rcu_fanout_leaf= [KNL]
2633 Increase the number of CPUs assigned to each
2634 leaf rcu_node structure. Useful for very large
2635 systems.
2637 rcutree.jiffies_till_first_fqs= [KNL]
2638 Set delay from grace-period initialization to
2639 first attempt to force quiescent states.
2640 Units are jiffies, minimum value is zero,
2641 and maximum value is HZ.
2643 rcutree.jiffies_till_next_fqs= [KNL]
2644 Set delay between subsequent attempts to force
2645 quiescent states. Units are jiffies, minimum
2646 value is one, and maximum value is HZ.
2648 rcutree.qhimark= [KNL]
2649 Set threshold of queued
2650 RCU callbacks over which batch limiting is disabled.
2652 rcutree.qlowmark= [KNL]
2653 Set threshold of queued RCU callbacks below which
2654 batch limiting is re-enabled.
2656 rcutree.rcu_idle_gp_delay= [KNL]
2657 Set wakeup interval for idle CPUs that have
2658 RCU callbacks (RCU_FAST_NO_HZ=y).
2660 rcutree.rcu_idle_lazy_gp_delay= [KNL]
2661 Set wakeup interval for idle CPUs that have
2662 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2663 Lazy RCU callbacks are those which RCU can
2664 prove do nothing more than free memory.
2666 rcutorture.fqs_duration= [KNL]
2667 Set duration of force_quiescent_state bursts.
2669 rcutorture.fqs_holdoff= [KNL]
2670 Set holdoff time within force_quiescent_state bursts.
2672 rcutorture.fqs_stutter= [KNL]
2673 Set wait time between force_quiescent_state bursts.
2675 rcutorture.gp_exp= [KNL]
2676 Use expedited update-side primitives.
2678 rcutorture.gp_normal= [KNL]
2679 Use normal (non-expedited) update-side primitives.
2680 If both gp_exp and gp_normal are set, do both.
2681 If neither gp_exp nor gp_normal are set, still
2682 do both.
2684 rcutorture.n_barrier_cbs= [KNL]
2685 Set callbacks/threads for rcu_barrier() testing.
2687 rcutorture.nfakewriters= [KNL]
2688 Set number of concurrent RCU writers. These just
2689 stress RCU, they don't participate in the actual
2690 test, hence the "fake".
2692 rcutorture.nreaders= [KNL]
2693 Set number of RCU readers.
2695 rcutorture.object_debug= [KNL]
2696 Enable debug-object double-call_rcu() testing.
2698 rcutorture.onoff_holdoff= [KNL]
2699 Set time (s) after boot for CPU-hotplug testing.
2701 rcutorture.onoff_interval= [KNL]
2702 Set time (s) between CPU-hotplug operations, or
2703 zero to disable CPU-hotplug testing.
2705 rcutorture.rcutorture_runnable= [BOOT]
2706 Start rcutorture running at boot time.
2708 rcutorture.shuffle_interval= [KNL]
2709 Set task-shuffle interval (s). Shuffling tasks
2710 allows some CPUs to go into dyntick-idle mode
2711 during the rcutorture test.
2713 rcutorture.shutdown_secs= [KNL]
2714 Set time (s) after boot system shutdown. This
2715 is useful for hands-off automated testing.
2717 rcutorture.stall_cpu= [KNL]
2718 Duration of CPU stall (s) to test RCU CPU stall
2719 warnings, zero to disable.
2721 rcutorture.stall_cpu_holdoff= [KNL]
2722 Time to wait (s) after boot before inducing stall.
2724 rcutorture.stat_interval= [KNL]
2725 Time (s) between statistics printk()s.
2727 rcutorture.stutter= [KNL]
2728 Time (s) to stutter testing, for example, specifying
2729 five seconds causes the test to run for five seconds,
2730 wait for five seconds, and so on. This tests RCU's
2731 ability to transition abruptly to and from idle.
2733 rcutorture.test_boost= [KNL]
2734 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2735 "Maybe" means test if the RCU implementation
2736 under test support RCU priority boosting.
2738 rcutorture.test_boost_duration= [KNL]
2739 Duration (s) of each individual boost test.
2741 rcutorture.test_boost_interval= [KNL]
2742 Interval (s) between each boost test.
2744 rcutorture.test_no_idle_hz= [KNL]
2745 Test RCU's dyntick-idle handling. See also the
2746 rcutorture.shuffle_interval parameter.
2748 rcutorture.torture_type= [KNL]
2749 Specify the RCU implementation to test.
2751 rcutorture.verbose= [KNL]
2752 Enable additional printk() statements.
2754 rcupdate.rcu_expedited= [KNL]
2755 Use expedited grace-period primitives, for
2756 example, synchronize_rcu_expedited() instead
2757 of synchronize_rcu(). This reduces latency,
2758 but can increase CPU utilization, degrade
2759 real-time latency, and degrade energy efficiency.
2761 rcupdate.rcu_cpu_stall_suppress= [KNL]
2762 Suppress RCU CPU stall warning messages.
2764 rcupdate.rcu_cpu_stall_timeout= [KNL]
2765 Set timeout for RCU CPU stall warning messages.
2767 rdinit= [KNL]
2768 Format: <full_path>
2769 Run specified binary instead of /init from the ramdisk,
2770 used for early userspace startup. See initrd.
2772 reboot= [KNL]
2773 Format (x86 or x86_64):
2774 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2775 [[,]s[mp]#### \
2776 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2777 [[,]f[orce]
2778 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2779 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2780 reboot_force is either force or not specified,
2781 reboot_cpu is s[mp]#### with #### being the processor
2782 to be used for rebooting.
2784 relax_domain_level=
2785 [KNL, SMP] Set scheduler's default relax_domain_level.
2786 See Documentation/cgroups/cpusets.txt.
2788 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2790 reservetop= [X86-32]
2791 Format: nn[KMG]
2792 Reserves a hole at the top of the kernel virtual
2793 address space.
2795 reservelow= [X86]
2796 Format: nn[K]
2797 Set the amount of memory to reserve for BIOS at
2798 the bottom of the address space.
2800 reset_devices [KNL] Force drivers to reset the underlying device
2801 during initialization.
2803 resume= [SWSUSP]
2804 Specify the partition device for software suspend
2805 Format:
2806 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2808 resume_offset= [SWSUSP]
2809 Specify the offset from the beginning of the partition
2810 given by "resume=" at which the swap header is located,
2811 in <PAGE_SIZE> units (needed only for swap files).
2812 See Documentation/power/swsusp-and-swap-files.txt
2814 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2815 read the resume files
2817 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2818 Useful for devices that are detected asynchronously
2819 (e.g. USB and MMC devices).
2821 hibernate= [HIBERNATION]
2822 noresume Don't check if there's a hibernation image
2823 present during boot.
2824 nocompress Don't compress/decompress hibernation images.
2826 retain_initrd [RAM] Keep initrd memory after extraction
2828 rhash_entries= [KNL,NET]
2829 Set number of hash buckets for route cache
2831 riscom8= [HW,SERIAL]
2832 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2834 ro [KNL] Mount root device read-only on boot
2836 root= [KNL] Root filesystem
2837 See name_to_dev_t comment in init/do_mounts.c.
2839 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2840 mount the root filesystem
2842 rootflags= [KNL] Set root filesystem mount option string
2844 rootfstype= [KNL] Set root filesystem type
2846 rootwait [KNL] Wait (indefinitely) for root device to show up.
2847 Useful for devices that are detected asynchronously
2848 (e.g. USB and MMC devices).
2850 rproc_mem=nn[KMG][@address]
2851 [KNL,ARM,CMA] Remoteproc physical memory block.
2852 Memory area to be used by remote processor image,
2853 managed by CMA.
2855 rw [KNL] Mount root device read-write on boot
2857 S [KNL] Run init in single mode
2859 sa1100ir [NET]
2860 See drivers/net/irda/sa1100_ir.c.
2862 sbni= [NET] Granch SBNI12 leased line adapter
2864 sched_debug [KNL] Enables verbose scheduler debug messages.
2866 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2867 xtime_lock contention on larger systems, and/or RCU lock
2868 contention on all systems with CONFIG_MAXSMP set.
2869 Format: { "0" | "1" }
2870 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2871 1 -- enable.
2872 Note: increases power consumption, thus should only be
2873 enabled if running jitter sensitive (HPC/RT) workloads.
2875 security= [SECURITY] Choose a security module to enable at boot.
2876 If this boot parameter is not specified, only the first
2877 security module asking for security registration will be
2878 loaded. An invalid security module name will be treated
2879 as if no module has been chosen.
2881 selinux= [SELINUX] Disable or enable SELinux at boot time.
2882 Format: { "0" | "1" }
2883 See security/selinux/Kconfig help text.
2884 0 -- disable.
2885 1 -- enable.
2886 Default value is set via kernel config option.
2887 If enabled at boot time, /selinux/disable can be used
2888 later to disable prior to initial policy load.
2890 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2891 Format: { "0" | "1" }
2892 See security/apparmor/Kconfig help text
2893 0 -- disable.
2894 1 -- enable.
2895 Default value is set via kernel config option.
2897 serialnumber [BUGS=X86-32]
2899 shapers= [NET]
2900 Maximal number of shapers.
2902 show_msr= [x86] show boot-time MSR settings
2903 Format: { <integer> }
2904 Show boot-time (BIOS-initialized) MSR settings.
2905 The parameter means the number of CPUs to show,
2906 for example 1 means boot CPU only.
2908 simeth= [IA-64]
2909 simscsi=
2911 slram= [HW,MTD]
2913 slab_max_order= [MM, SLAB]
2914 Determines the maximum allowed order for slabs.
2915 A high setting may cause OOMs due to memory
2916 fragmentation. Defaults to 1 for systems with
2917 more than 32MB of RAM, 0 otherwise.
2919 slub_debug[=options[,slabs]] [MM, SLUB]
2920 Enabling slub_debug allows one to determine the
2921 culprit if slab objects become corrupted. Enabling
2922 slub_debug can create guard zones around objects and
2923 may poison objects when not in use. Also tracks the
2924 last alloc / free. For more information see
2925 Documentation/vm/slub.txt.
2927 slub_max_order= [MM, SLUB]
2928 Determines the maximum allowed order for slabs.
2929 A high setting may cause OOMs due to memory
2930 fragmentation. For more information see
2931 Documentation/vm/slub.txt.
2933 slub_min_objects= [MM, SLUB]
2934 The minimum number of objects per slab. SLUB will
2935 increase the slab order up to slub_max_order to
2936 generate a sufficiently large slab able to contain
2937 the number of objects indicated. The higher the number
2938 of objects the smaller the overhead of tracking slabs
2939 and the less frequently locks need to be acquired.
2940 For more information see Documentation/vm/slub.txt.
2942 slub_min_order= [MM, SLUB]
2943 Determines the minimum page order for slabs. Must be
2944 lower than slub_max_order.
2945 For more information see Documentation/vm/slub.txt.
2947 slub_nomerge [MM, SLUB]
2948 Disable merging of slabs with similar size. May be
2949 necessary if there is some reason to distinguish
2950 allocs to different slabs. Debug options disable
2951 merging on their own.
2952 For more information see Documentation/vm/slub.txt.
2954 smart2= [HW]
2955 Format: <io1>[,<io2>[,...,<io8>]]
2957 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2958 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2959 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2960 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2961 smsc-ircc2.ircc_irq= [HW] IRQ line
2962 smsc-ircc2.ircc_dma= [HW] DMA channel
2963 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2964 0: Toshiba Satellite 1800 (GP data pin select)
2965 1: Fast pin select (default)
2966 2: ATC IRMode
2968 softlockup_panic=
2969 [KNL] Should the soft-lockup detector generate panics.
2970 Format: <integer>
2972 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2973 See Documentation/laptops/sonypi.txt
2975 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2976 See Documentation/serial/specialix.txt.
2978 spia_io_base= [HW,MTD]
2979 spia_fio_base=
2980 spia_pedr=
2981 spia_peddr=
2983 stacktrace [FTRACE]
2984 Enabled the stack tracer on boot up.
2986 stacktrace_filter=[function-list]
2987 [FTRACE] Limit the functions that the stack tracer
2988 will trace at boot up. function-list is a comma separated
2989 list of functions. This list can be changed at run
2990 time by the stack_trace_filter file in the debugfs
2991 tracing directory. Note, this enables stack tracing
2992 and the stacktrace above is not needed.
2994 sti= [PARISC,HW]
2995 Format: <num>
2996 Set the STI (builtin display/keyboard on the HP-PARISC
2997 machines) console (graphic card) which should be used
2998 as the initial boot-console.
2999 See also comment in drivers/video/console/sticore.c.
3001 sti_font= [HW]
3002 See comment in drivers/video/console/sticore.c.
3004 stifb= [HW]
3005 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3007 sunrpc.min_resvport=
3008 sunrpc.max_resvport=
3009 [NFS,SUNRPC]
3010 SunRPC servers often require that client requests
3011 originate from a privileged port (i.e. a port in the
3012 range 0 < portnr < 1024).
3013 An administrator who wishes to reserve some of these
3014 ports for other uses may adjust the range that the
3015 kernel's sunrpc client considers to be privileged
3016 using these two parameters to set the minimum and
3017 maximum port values.
3019 sunrpc.pool_mode=
3020 [NFS]
3021 Control how the NFS server code allocates CPUs to
3022 service thread pools. Depending on how many NICs
3023 you have and where their interrupts are bound, this
3024 option will affect which CPUs will do NFS serving.
3025 Note: this parameter cannot be changed while the
3026 NFS server is running.
3028 auto the server chooses an appropriate mode
3029 automatically using heuristics
3030 global a single global pool contains all CPUs
3031 percpu one pool for each CPU
3032 pernode one pool for each NUMA node (equivalent
3033 to global on non-NUMA machines)
3035 sunrpc.tcp_slot_table_entries=
3036 sunrpc.udp_slot_table_entries=
3037 [NFS,SUNRPC]
3038 Sets the upper limit on the number of simultaneous
3039 RPC calls that can be sent from the client to a
3040 server. Increasing these values may allow you to
3041 improve throughput, but will also increase the
3042 amount of memory reserved for use by the client.
3044 swapaccount=[0|1]
3045 [KNL] Enable accounting of swap in memory resource
3046 controller if no parameter or 1 is given or disable
3047 it if 0 is given (See Documentation/cgroups/memory.txt)
3049 swiotlb= [IA-64] Number of I/O TLB slabs
3051 switches= [HW,M68k]
3053 sysfs.deprecated=0|1 [KNL]
3054 Enable/disable old style sysfs layout for old udev
3055 on older distributions. When this option is enabled
3056 very new udev will not work anymore. When this option
3057 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3058 in older udev will not work anymore.
3059 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3060 the kernel configuration.
3062 sysrq_always_enabled
3063 [KNL]
3064 Ignore sysrq setting - this boot parameter will
3065 neutralize any effect of /proc/sys/kernel/sysrq.
3066 Useful for debugging.
3068 tdfx= [HW,DRM]
3070 test_suspend= [SUSPEND]
3071 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3072 standby suspend) as the system sleep state to briefly
3073 enter during system startup. The system is woken from
3074 this state using a wakeup-capable RTC alarm.
3076 thash_entries= [KNL,NET]
3077 Set number of hash buckets for TCP connection
3079 thermal.act= [HW,ACPI]
3080 -1: disable all active trip points in all thermal zones
3081 <degrees C>: override all lowest active trip points
3083 thermal.crt= [HW,ACPI]
3084 -1: disable all critical trip points in all thermal zones
3085 <degrees C>: override all critical trip points
3087 thermal.nocrt= [HW,ACPI]
3088 Set to disable actions on ACPI thermal zone
3089 critical and hot trip points.
3091 thermal.off= [HW,ACPI]
3092 1: disable ACPI thermal control
3094 thermal.psv= [HW,ACPI]
3095 -1: disable all passive trip points
3096 <degrees C>: override all passive trip points to this
3097 value
3099 thermal.tzp= [HW,ACPI]
3100 Specify global default ACPI thermal zone polling rate
3101 <deci-seconds>: poll all this frequency
3102 0: no polling (default)
3104 threadirqs [KNL]
3105 Force threading of all interrupt handlers except those
3106 marked explicitly IRQF_NO_THREAD.
3108 tmem [KNL,XEN]
3109 Enable the Transcendent memory driver if built-in.
3111 tmem.cleancache=0|1 [KNL, XEN]
3112 Default is on (1). Disable the usage of the cleancache
3113 API to send anonymous pages to the hypervisor.
3115 tmem.frontswap=0|1 [KNL, XEN]
3116 Default is on (1). Disable the usage of the frontswap
3117 API to send swap pages to the hypervisor. If disabled
3118 the selfballooning and selfshrinking are force disabled.
3120 tmem.selfballooning=0|1 [KNL, XEN]
3121 Default is on (1). Disable the driving of swap pages
3122 to the hypervisor.
3124 tmem.selfshrinking=0|1 [KNL, XEN]
3125 Default is on (1). Partial swapoff that immediately
3126 transfers pages from Xen hypervisor back to the
3127 kernel based on different criteria.
3129 topology= [S390]
3130 Format: {off | on}
3131 Specify if the kernel should make use of the cpu
3132 topology information if the hardware supports this.
3133 The scheduler will make use of this information and
3134 e.g. base its process migration decisions on it.
3135 Default is on.
3137 tp720= [HW,PS2]
3139 tpm_suspend_pcr=[HW,TPM]
3140 Format: integer pcr id
3141 Specify that at suspend time, the tpm driver
3142 should extend the specified pcr with zeros,
3143 as a workaround for some chips which fail to
3144 flush the last written pcr on TPM_SaveState.
3145 This will guarantee that all the other pcrs
3146 are saved.
3148 trace_buf_size=nn[KMG]
3149 [FTRACE] will set tracing buffer size.
3151 trace_event=[event-list]
3152 [FTRACE] Set and start specified trace events in order
3153 to facilitate early boot debugging.
3154 See also Documentation/trace/events.txt
3156 trace_options=[option-list]
3157 [FTRACE] Enable or disable tracer options at boot.
3158 The option-list is a comma delimited list of options
3159 that can be enabled or disabled just as if you were
3160 to echo the option name into
3162 /sys/kernel/debug/tracing/trace_options
3164 For example, to enable stacktrace option (to dump the
3165 stack trace of each event), add to the command line:
3167 trace_options=stacktrace
3169 See also Documentation/trace/ftrace.txt "trace options"
3170 section.
3172 traceoff_on_warning
3173 [FTRACE] enable this option to disable tracing when a
3174 warning is hit. This turns off "tracing_on". Tracing can
3175 be enabled again by echoing '1' into the "tracing_on"
3176 file located in /sys/kernel/debug/tracing/
3178 This option is useful, as it disables the trace before
3179 the WARNING dump is called, which prevents the trace to
3180 be filled with content caused by the warning output.
3182 This option can also be set at run time via the sysctl
3183 option: kernel/traceoff_on_warning
3185 transparent_hugepage=
3186 [KNL]
3187 Format: [always|madvise|never]
3188 Can be used to control the default behavior of the system
3189 with respect to transparent hugepages.
3190 See Documentation/vm/transhuge.txt for more details.
3192 tsc= Disable clocksource stability checks for TSC.
3193 Format: <string>
3194 [x86] reliable: mark tsc clocksource as reliable, this
3195 disables clocksource verification at runtime, as well
3196 as the stability checks done at bootup. Used to enable
3197 high-resolution timer mode on older hardware, and in
3198 virtualized environment.
3199 [x86] noirqtime: Do not use TSC to do irq accounting.
3200 Used to run time disable IRQ_TIME_ACCOUNTING on any
3201 platforms where RDTSC is slow and this accounting
3202 can add overhead.
3204 turbografx.map[2|3]= [HW,JOY]
3205 TurboGraFX parallel port interface
3206 Format:
3207 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3208 See also Documentation/input/joystick-parport.txt
3210 udbg-immortal [PPC] When debugging early kernel crashes that
3211 happen after console_init() and before a proper
3212 console driver takes over, this boot options might
3213 help "seeing" what's going on.
3215 uhash_entries= [KNL,NET]
3216 Set number of hash buckets for UDP/UDP-Lite connections
3218 uhci-hcd.ignore_oc=
3219 [USB] Ignore overcurrent events (default N).
3220 Some badly-designed motherboards generate lots of
3221 bogus events, for ports that aren't wired to
3222 anything. Set this parameter to avoid log spamming.
3223 Note that genuine overcurrent events won't be
3224 reported either.
3226 unknown_nmi_panic
3227 [X86] Cause panic on unknown NMI.
3229 usbcore.authorized_default=
3230 [USB] Default USB device authorization:
3231 (default -1 = authorized except for wireless USB,
3232 0 = not authorized, 1 = authorized)
3234 usbcore.autosuspend=
3235 [USB] The autosuspend time delay (in seconds) used
3236 for newly-detected USB devices (default 2). This
3237 is the time required before an idle device will be
3238 autosuspended. Devices for which the delay is set
3239 to a negative value won't be autosuspended at all.
3241 usbcore.usbfs_snoop=
3242 [USB] Set to log all usbfs traffic (default 0 = off).
3244 usbcore.blinkenlights=
3245 [USB] Set to cycle leds on hubs (default 0 = off).
3247 usbcore.old_scheme_first=
3248 [USB] Start with the old device initialization
3249 scheme (default 0 = off).
3251 usbcore.usbfs_memory_mb=
3252 [USB] Memory limit (in MB) for buffers allocated by
3253 usbfs (default = 16, 0 = max = 2047).
3255 usbcore.use_both_schemes=
3256 [USB] Try the other device initialization scheme
3257 if the first one fails (default 1 = enabled).
3259 usbcore.initial_descriptor_timeout=
3260 [USB] Specifies timeout for the initial 64-byte
3261 USB_REQ_GET_DESCRIPTOR request in milliseconds
3262 (default 5000 = 5.0 seconds).
3264 usbhid.mousepoll=
3265 [USBHID] The interval which mice are to be polled at.
3267 usb-storage.delay_use=
3268 [UMS] The delay in seconds before a new device is
3269 scanned for Logical Units (default 5).
3271 usb-storage.quirks=
3272 [UMS] A list of quirks entries to supplement or
3273 override the built-in unusual_devs list. List
3274 entries are separated by commas. Each entry has
3275 the form VID:PID:Flags where VID and PID are Vendor
3276 and Product ID values (4-digit hex numbers) and
3277 Flags is a set of characters, each corresponding
3278 to a common usb-storage quirk flag as follows:
3279 a = SANE_SENSE (collect more than 18 bytes
3280 of sense data);
3281 b = BAD_SENSE (don't collect more than 18
3282 bytes of sense data);
3283 c = FIX_CAPACITY (decrease the reported
3284 device capacity by one sector);
3285 d = NO_READ_DISC_INFO (don't use
3286 READ_DISC_INFO command);
3287 e = NO_READ_CAPACITY_16 (don't use
3288 READ_CAPACITY_16 command);
3289 h = CAPACITY_HEURISTICS (decrease the
3290 reported device capacity by one
3291 sector if the number is odd);
3292 i = IGNORE_DEVICE (don't bind to this
3293 device);
3294 l = NOT_LOCKABLE (don't try to lock and
3295 unlock ejectable media);
3296 m = MAX_SECTORS_64 (don't transfer more
3297 than 64 sectors = 32 KB at a time);
3298 n = INITIAL_READ10 (force a retry of the
3299 initial READ(10) command);
3300 o = CAPACITY_OK (accept the capacity
3301 reported by the device);
3302 p = WRITE_CACHE (the device cache is ON
3303 by default);
3304 r = IGNORE_RESIDUE (the device reports
3305 bogus residue values);
3306 s = SINGLE_LUN (the device has only one
3307 Logical Unit);
3308 w = NO_WP_DETECT (don't test whether the
3309 medium is write-protected).
3310 Example: quirks=0419:aaf5:rl,0421:0433:rc
3312 user_debug= [KNL,ARM]
3313 Format: <int>
3314 See arch/arm/Kconfig.debug help text.
3315 1 - undefined instruction events
3316 2 - system calls
3317 4 - invalid data aborts
3318 8 - SIGSEGV faults
3319 16 - SIGBUS faults
3320 Example: user_debug=31
3322 userpte=
3323 [X86] Flags controlling user PTE allocations.
3325 nohigh = do not allocate PTE pages in
3326 HIGHMEM regardless of setting
3327 of CONFIG_HIGHPTE.
3329 vdso= [X86,SH]
3330 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3331 vdso=1: enable VDSO (default)
3332 vdso=0: disable VDSO mapping
3334 vdso32= [X86]
3335 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3336 vdso32=1: enable 32-bit VDSO (default)
3337 vdso32=0: disable 32-bit VDSO mapping
3339 vector= [IA-64,SMP]
3340 vector=percpu: enable percpu vector domain
3342 video= [FB] Frame buffer configuration
3343 See Documentation/fb/modedb.txt.
3345 video.brightness_switch_enabled= [0,1]
3346 If set to 1, on receiving an ACPI notify event
3347 generated by hotkey, video driver will adjust brightness
3348 level and then send out the event to user space through
3349 the allocated input device; If set to 0, video driver
3350 will only send out the event without touching backlight
3351 brightness level.
3352 default: 1
3354 virtio_mmio.device=
3355 [VMMIO] Memory mapped virtio (platform) device.
3357 <size>@<baseaddr>:<irq>[:<id>]
3358 where:
3359 <size> := size (can use standard suffixes
3360 like K, M and G)
3361 <baseaddr> := physical base address
3362 <irq> := interrupt number (as passed to
3363 request_irq())
3364 <id> := (optional) platform device id
3365 example:
3366 virtio_mmio.device=1K@0x100b0000:48:7
3368 Can be used multiple times for multiple devices.
3370 vga= [BOOT,X86-32] Select a particular video mode
3371 See Documentation/x86/boot.txt and
3372 Documentation/svga.txt.
3373 Use vga=ask for menu.
3374 This is actually a boot loader parameter; the value is
3375 passed to the kernel using a special protocol.
3377 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3378 size of <nn>. This can be used to increase the
3379 minimum size (128MB on x86). It can also be used to
3380 decrease the size and leave more room for directly
3381 mapped kernel RAM.
3383 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3384 Format: <command>
3386 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3387 Format: <command>
3389 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3390 Format: <command>
3392 vsyscall= [X86-64]
3393 Controls the behavior of vsyscalls (i.e. calls to
3394 fixed addresses of 0xffffffffff600x00 from legacy
3395 code). Most statically-linked binaries and older
3396 versions of glibc use these calls. Because these
3397 functions are at fixed addresses, they make nice
3398 targets for exploits that can control RIP.
3400 emulate [default] Vsyscalls turn into traps and are
3401 emulated reasonably safely.
3403 native Vsyscalls are native syscall instructions.
3404 This is a little bit faster than trapping
3405 and makes a few dynamic recompilers work
3406 better than they would in emulation mode.
3407 It also makes exploits much easier to write.
3409 none Vsyscalls don't work at all. This makes
3410 them quite hard to use for exploits but
3411 might break your system.
3413 vt.color= [VT] Default text color.
3414 Format: 0xYX, X = foreground, Y = background.
3415 Default: 0x07 = light gray on black.
3417 vt.cur_default= [VT] Default cursor shape.
3418 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3419 the parameters of the <Esc>[?A;B;Cc escape sequence;
3420 see VGA-softcursor.txt. Default: 2 = underline.
3422 vt.default_blu= [VT]
3423 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3424 Change the default blue palette of the console.
3425 This is a 16-member array composed of values
3426 ranging from 0-255.
3428 vt.default_grn= [VT]
3429 Format: <green0>,<green1>,<green2>,...,<green15>
3430 Change the default green palette of the console.
3431 This is a 16-member array composed of values
3432 ranging from 0-255.
3434 vt.default_red= [VT]
3435 Format: <red0>,<red1>,<red2>,...,<red15>
3436 Change the default red palette of the console.
3437 This is a 16-member array composed of values
3438 ranging from 0-255.
3440 vt.default_utf8=
3441 [VT]
3442 Format=<0|1>
3443 Set system-wide default UTF-8 mode for all tty's.
3444 Default is 1, i.e. UTF-8 mode is enabled for all
3445 newly opened terminals.
3447 vt.global_cursor_default=
3448 [VT]
3449 Format=<-1|0|1>
3450 Set system-wide default for whether a cursor
3451 is shown on new VTs. Default is -1,
3452 i.e. cursors will be created by default unless
3453 overridden by individual drivers. 0 will hide
3454 cursors, 1 will display them.
3456 vt.italic= [VT] Default color for italic text; 0-15.
3457 Default: 2 = green.
3459 vt.underline= [VT] Default color for underlined text; 0-15.
3460 Default: 3 = cyan.
3462 watchdog timers [HW,WDT] For information on watchdog timers,
3463 see Documentation/watchdog/watchdog-parameters.txt
3464 or other driver-specific files in the
3465 Documentation/watchdog/ directory.
3467 workqueue.disable_numa
3468 By default, all work items queued to unbound
3469 workqueues are affine to the NUMA nodes they're
3470 issued on, which results in better behavior in
3471 general. If NUMA affinity needs to be disabled for
3472 whatever reason, this option can be used. Note
3473 that this also can be controlled per-workqueue for
3474 workqueues visible under /sys/bus/workqueue/.
3476 workqueue.power_efficient
3477 Per-cpu workqueues are generally preferred because
3478 they show better performance thanks to cache
3479 locality; unfortunately, per-cpu workqueues tend to
3480 be more power hungry than unbound workqueues.
3482 Enabling this makes the per-cpu workqueues which
3483 were observed to contribute significantly to power
3484 consumption unbound, leading to measurably lower
3485 power usage at the cost of small performance
3486 overhead.
3488 The default value of this parameter is determined by
3489 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3491 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3492 default x2apic cluster mode on platforms
3493 supporting x2apic.
3495 x86_intel_mid_timer= [X86-32,APBT]
3496 Choose timer option for x86 Intel MID platform.
3497 Two valid options are apbt timer only and lapic timer
3498 plus one apbt timer for broadcast timer.
3499 x86_intel_mid_timer=apbt_only | lapic_and_apbt
3501 xen_emul_unplug= [HW,X86,XEN]
3502 Unplug Xen emulated devices
3503 Format: [unplug0,][unplug1]
3504 ide-disks -- unplug primary master IDE devices
3505 aux-ide-disks -- unplug non-primary-master IDE devices
3506 nics -- unplug network devices
3507 all -- unplug all emulated devices (NICs and IDE disks)
3508 unnecessary -- unplugging emulated devices is
3509 unnecessary even if the host did not respond to
3510 the unplug protocol
3511 never -- do not unplug even if version check succeeds
3513 xen_nopvspin [X86,XEN]
3514 Disables the ticketlock slowpath using Xen PV
3515 optimizations.
3517 xirc2ps_cs= [NET,PCMCIA]
3518 Format:
3519 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3521 ______________________________________________________________________
3523 TODO:
3525 Add more DRM drivers.