| blob | 789b8941a0c603ab4595e032d2aac7b16ae61750 |
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 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
347 kernels.
349 add_efi_memmap [EFI; X86] Include EFI memory map in
350 kernel's map of available physical RAM.
352 agp= [AGP]
353 { off | try_unsupported }
354 off: disable AGP support
355 try_unsupported: try to drive unsupported chipsets
356 (may crash computer or cause data corruption)
358 ALSA [HW,ALSA]
359 See Documentation/sound/alsa/alsa-parameters.txt
361 alignment= [KNL,ARM]
362 Allow the default userspace alignment fault handler
363 behaviour to be specified. Bit 0 enables warnings,
364 bit 1 enables fixups, and bit 2 sends a segfault.
366 align_va_addr= [X86-64]
367 Align virtual addresses by clearing slice [14:12] when
368 allocating a VMA at process creation time. This option
369 gives you up to 3% performance improvement on AMD F15h
370 machines (where it is enabled by default) for a
371 CPU-intensive style benchmark, and it can vary highly in
372 a microbenchmark depending on workload and compiler.
374 32: only for 32-bit processes
375 64: only for 64-bit processes
376 on: enable for both 32- and 64-bit processes
377 off: disable for both 32- and 64-bit processes
379 alloc_snapshot [FTRACE]
380 Allocate the ftrace snapshot buffer on boot up when the
381 main buffer is allocated. This is handy if debugging
382 and you need to use tracing_snapshot() on boot up, and
383 do not want to use tracing_snapshot_alloc() as it needs
384 to be done where GFP_KERNEL allocations are allowed.
386 amd_iommu= [HW,X86-64]
387 Pass parameters to the AMD IOMMU driver in the system.
388 Possible values are:
389 fullflush - enable flushing of IO/TLB entries when
390 they are unmapped. Otherwise they are
391 flushed before they will be reused, which
392 is a lot of faster
393 off - do not initialize any AMD IOMMU found in
394 the system
395 force_isolation - Force device isolation for all
396 devices. The IOMMU driver is not
397 allowed anymore to lift isolation
398 requirements as needed. This option
399 does not override iommu=pt
401 amd_iommu_dump= [HW,X86-64]
402 Enable AMD IOMMU driver option to dump the ACPI table
403 for AMD IOMMU. With this option enabled, AMD IOMMU
404 driver will print ACPI tables for AMD IOMMU during
405 IOMMU initialization.
407 amijoy.map= [HW,JOY] Amiga joystick support
408 Map of devices attached to JOY0DAT and JOY1DAT
409 Format: <a>,<b>
410 See also Documentation/input/joystick.txt
412 analog.map= [HW,JOY] Analog joystick and gamepad support
413 Specifies type or capabilities of an analog joystick
414 connected to one of 16 gameports
415 Format: <type1>,<type2>,..<type16>
417 apc= [HW,SPARC]
418 Power management functions (SPARCstation-4/5 + deriv.)
419 Format: noidle
420 Disable APC CPU standby support. SPARCstation-Fox does
421 not play well with APC CPU idle - disable it if you have
422 APC and your system crashes randomly.
424 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
425 Change the output verbosity whilst booting
426 Format: { quiet (default) | verbose | debug }
427 Change the amount of debugging information output
428 when initialising the APIC and IO-APIC components.
430 autoconf= [IPV6]
431 See Documentation/networking/ipv6.txt.
433 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
434 Limit apic dumping. The parameter defines the maximal
435 number of local apics being dumped. Also it is possible
436 to set it to "all" by meaning -- no limit here.
437 Format: { 1 (default) | 2 | ... | all }.
438 The parameter valid if only apic=debug or
439 apic=verbose is specified.
440 Example: apic=debug show_lapic=all
442 apm= [APM] Advanced Power Management
443 See header of arch/x86/kernel/apm_32.c.
445 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
446 Format: <io>,<irq>,<nodeID>
448 ataflop= [HW,M68k]
450 atarimouse= [HW,MOUSE] Atari Mouse
452 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
453 EzKey and similar keyboards
455 atkbd.reset= [HW] Reset keyboard during initialization
457 atkbd.set= [HW] Select keyboard code set
458 Format: <int> (2 = AT (default), 3 = PS/2)
460 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
461 keyboards
463 atkbd.softraw= [HW] Choose between synthetic and real raw mode
464 Format: <bool> (0 = real, 1 = synthetic (default))
466 atkbd.softrepeat= [HW]
467 Use software keyboard repeat
469 baycom_epp= [HW,AX25]
470 Format: <io>,<mode>
472 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
473 Format: <io>,<mode>
474 See header of drivers/net/hamradio/baycom_par.c.
476 baycom_ser_fdx= [HW,AX25]
477 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
478 Format: <io>,<irq>,<mode>[,<baud>]
479 See header of drivers/net/hamradio/baycom_ser_fdx.c.
481 baycom_ser_hdx= [HW,AX25]
482 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
483 Format: <io>,<irq>,<mode>
484 See header of drivers/net/hamradio/baycom_ser_hdx.c.
486 blkdevparts= Manual partition parsing of block device(s) for
487 embedded devices based on command line input.
488 See Documentation/block/cmdline-partition.txt
490 boot_delay= Milliseconds to delay each printk during boot.
491 Values larger than 10 seconds (10000) are changed to
492 no delay (0).
493 Format: integer
495 bootmem_debug [KNL] Enable bootmem allocator debug messages.
497 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
498 bttv.radio= Most important insmod options are available as
499 kernel args too.
500 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
501 bttv.tuner=
503 bulk_remove=off [PPC] This parameter disables the use of the pSeries
504 firmware feature for flushing multiple hpte entries
505 at a time.
507 c101= [NET] Moxa C101 synchronous serial card
509 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
510 Sometimes CPU hardware bugs make them report the cache
511 size incorrectly. The kernel will attempt work arounds
512 to fix known problems, but for some CPUs it is not
513 possible to determine what the correct size should be.
514 This option provides an override for these situations.
516 ccw_timeout_log [S390]
517 See Documentation/s390/CommonIO for details.
519 cgroup_disable= [KNL] Disable a particular controller
520 Format: {name of the controller(s) to disable}
521 {Currently supported controllers - "memory"}
523 checkreqprot [SELINUX] Set initial checkreqprot flag value.
524 Format: { "0" | "1" }
525 See security/selinux/Kconfig help text.
526 0 -- check protection applied by kernel (includes
527 any implied execute protection).
528 1 -- check protection requested by application.
529 Default value is set via a kernel config option.
530 Value can be changed at runtime via
531 /selinux/checkreqprot.
533 cio_ignore= [S390]
534 See Documentation/s390/CommonIO for details.
535 clk_ignore_unused
536 [CLK]
537 Keep all clocks already enabled by bootloader on,
538 even if no driver has claimed them. This is useful
539 for debug and development, but should not be
540 needed on a platform with proper driver support.
541 For more information, see Documentation/clk.txt.
543 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
544 [Deprecated]
545 Forces specified clocksource (if available) to be used
546 when calculating gettimeofday(). If specified
547 clocksource is not available, it defaults to PIT.
548 Format: { pit | tsc | cyclone | pmtmr }
550 clocksource= Override the default clocksource
551 Format: <string>
552 Override the default clocksource and use the clocksource
553 with the name specified.
554 Some clocksource names to choose from, depending on
555 the platform:
556 [all] jiffies (this is the base, fallback clocksource)
557 [ACPI] acpi_pm
558 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
559 pxa_timer,timer3,32k_counter,timer0_1
560 [AVR32] avr32
561 [X86-32] pit,hpet,tsc;
562 scx200_hrt on Geode; cyclone on IBM x440
563 [MIPS] MIPS
564 [PARISC] cr16
565 [S390] tod
566 [SH] SuperH
567 [SPARC64] tick
568 [X86-64] hpet,tsc
570 clearcpuid=BITNUM [X86]
571 Disable CPUID feature X for the kernel. See
572 arch/x86/include/asm/cpufeature.h for the valid bit
573 numbers. Note the Linux specific bits are not necessarily
574 stable over kernel options, but the vendor specific
575 ones should be.
576 Also note that user programs calling CPUID directly
577 or using the feature without checking anything
578 will still see it. This just prevents it from
579 being used by the kernel or shown in /proc/cpuinfo.
580 Also note the kernel might malfunction if you disable
581 some critical bits.
583 cma=nn[MG] [ARM,KNL]
584 Sets the size of kernel global memory area for contiguous
585 memory allocations. For more information, see
586 include/linux/dma-contiguous.h
588 cmo_free_hint= [PPC] Format: { yes | no }
589 Specify whether pages are marked as being inactive
590 when they are freed. This is used in CMO environments
591 to determine OS memory pressure for page stealing by
592 a hypervisor.
593 Default: yes
595 coherent_pool=nn[KMG] [ARM,KNL]
596 Sets the size of memory pool for coherent, atomic dma
597 allocations, by default set to 256K.
599 code_bytes [X86] How many bytes of object code to print
600 in an oops report.
601 Range: 0 - 8192
602 Default: 64
604 com20020= [HW,NET] ARCnet - COM20020 chipset
605 Format:
606 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
608 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
609 Format: <io>[,<irq>]
611 com90xx= [HW,NET]
612 ARCnet - COM90xx chipset (memory-mapped buffers)
613 Format: <io>[,<irq>[,<memstart>]]
615 condev= [HW,S390] console device
616 conmode=
618 console= [KNL] Output console device and options.
620 tty<n> Use the virtual console device <n>.
622 ttyS<n>[,options]
623 ttyUSB0[,options]
624 Use the specified serial port. The options are of
625 the form "bbbbpnf", where "bbbb" is the baud rate,
626 "p" is parity ("n", "o", or "e"), "n" is number of
627 bits, and "f" is flow control ("r" for RTS or
628 omit it). Default is "9600n8".
630 See Documentation/serial-console.txt for more
631 information. See
632 Documentation/networking/netconsole.txt for an
633 alternative.
635 uart[8250],io,<addr>[,options]
636 uart[8250],mmio,<addr>[,options]
637 Start an early, polled-mode console on the 8250/16550
638 UART at the specified I/O port or MMIO address,
639 switching to the matching ttyS device later. The
640 options are the same as for ttyS, above.
641 hvc<n> Use the hypervisor console device <n>. This is for
642 both Xen and PowerPC hypervisors.
644 If the device connected to the port is not a TTY but a braille
645 device, prepend "brl," before the device type, for instance
646 console=brl,ttyS0
647 For now, only VisioBraille is supported.
649 consoleblank= [KNL] The console blank (screen saver) timeout in
650 seconds. Defaults to 10*60 = 10mins. A value of 0
651 disables the blank timer.
653 coredump_filter=
654 [KNL] Change the default value for
655 /proc/<pid>/coredump_filter.
656 See also Documentation/filesystems/proc.txt.
658 cpuidle.off=1 [CPU_IDLE]
659 disable the cpuidle sub-system
661 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
662 Format:
663 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
665 crashkernel=size[KMG][@offset[KMG]]
666 [KNL] Using kexec, Linux can switch to a 'crash kernel'
667 upon panic. This parameter reserves the physical
668 memory region [offset, offset + size] for that kernel
669 image. If '@offset' is omitted, then a suitable offset
670 is selected automatically. Check
671 Documentation/kdump/kdump.txt for further details.
673 crashkernel=range1:size1[,range2:size2,...][@offset]
674 [KNL] Same as above, but depends on the memory
675 in the running system. The syntax of range is
676 start-[end] where start and end are both
677 a memory unit (amount[KMG]). See also
678 Documentation/kdump/kdump.txt for an example.
680 crashkernel=size[KMG],high
681 [KNL, x86_64] range could be above 4G. Allow kernel
682 to allocate physical memory region from top, so could
683 be above 4G if system have more than 4G ram installed.
684 Otherwise memory region will be allocated below 4G, if
685 available.
686 It will be ignored if crashkernel=X is specified.
687 crashkernel=size[KMG],low
688 [KNL, x86_64] range under 4G. When crashkernel=X,high
689 is passed, kernel could allocate physical memory region
690 above 4G, that cause second kernel crash on system
691 that require some amount of low memory, e.g. swiotlb
692 requires at least 64M+32K low memory. Kernel would
693 try to allocate 72M below 4G automatically.
694 This one let user to specify own low range under 4G
695 for second kernel instead.
696 0: to disable low allocation.
697 It will be ignored when crashkernel=X,high is not used
698 or memory reserved is below 4G.
700 cs89x0_dma= [HW,NET]
701 Format: <dma>
703 cs89x0_media= [HW,NET]
704 Format: { rj45 | aui | bnc }
706 dasd= [HW,NET]
707 See header of drivers/s390/block/dasd_devmap.c.
709 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
710 (one device per port)
711 Format: <port#>,<type>
712 See also Documentation/input/joystick-parport.txt
714 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
715 time. See Documentation/dynamic-debug-howto.txt for
716 details. Deprecated, see dyndbg.
718 debug [KNL] Enable kernel debugging (events log level).
720 debug_locks_verbose=
721 [KNL] verbose self-tests
722 Format=<0|1>
723 Print debugging info while doing the locking API
724 self-tests.
725 We default to 0 (no extra messages), setting it to
726 1 will print _a lot_ more information - normally
727 only useful to kernel developers.
729 debug_objects [KNL] Enable object debugging
731 no_debug_objects
732 [KNL] Disable object debugging
734 debug_guardpage_minorder=
735 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
736 parameter allows control of the order of pages that will
737 be intentionally kept free (and hence protected) by the
738 buddy allocator. Bigger value increase the probability
739 of catching random memory corruption, but reduce the
740 amount of memory for normal system use. The maximum
741 possible value is MAX_ORDER/2. Setting this parameter
742 to 1 or 2 should be enough to identify most random
743 memory corruption problems caused by bugs in kernel or
744 driver code when a CPU writes to (or reads from) a
745 random memory location. Note that there exists a class
746 of memory corruptions problems caused by buggy H/W or
747 F/W or by drivers badly programing DMA (basically when
748 memory is written at bus level and the CPU MMU is
749 bypassed) which are not detectable by
750 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
751 tracking down these problems.
753 debugpat [X86] Enable PAT debugging
755 decnet.addr= [HW,NET]
756 Format: <area>[,<node>]
757 See also Documentation/networking/decnet.txt.
759 default_hugepagesz=
760 [same as hugepagesz=] The size of the default
761 HugeTLB page size. This is the size represented by
762 the legacy /proc/ hugepages APIs, used for SHM, and
763 default size when mounting hugetlbfs filesystems.
764 Defaults to the default architecture's huge page size
765 if not specified.
767 dhash_entries= [KNL]
768 Set number of hash buckets for dentry cache.
770 digi= [HW,SERIAL]
771 IO parameters + enable/disable command.
773 digiepca= [HW,SERIAL]
774 See drivers/char/README.epca and
775 Documentation/serial/digiepca.txt.
777 disable= [IPV6]
778 See Documentation/networking/ipv6.txt.
780 disable_ddw [PPC/PSERIES]
781 Disable Dynamic DMA Window support. Use this if
782 to workaround buggy firmware.
784 disable_ipv6= [IPV6]
785 See Documentation/networking/ipv6.txt.
787 disable_mtrr_cleanup [X86]
788 The kernel tries to adjust MTRR layout from continuous
789 to discrete, to make X server driver able to add WB
790 entry later. This parameter disables that.
792 disable_mtrr_trim [X86, Intel and AMD only]
793 By default the kernel will trim any uncacheable
794 memory out of your available memory pool based on
795 MTRR settings. This parameter disables that behavior,
796 possibly causing your machine to run very slowly.
798 disable_timer_pin_1 [X86]
799 Disable PIN 1 of APIC timer
800 Can be useful to work around chipset bugs.
802 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
803 this option disables the debugging code at boot.
805 dma_debug_entries=<number>
806 This option allows to tune the number of preallocated
807 entries for DMA-API debugging code. One entry is
808 required per DMA-API allocation. Use this if the
809 DMA-API debugging code disables itself because the
810 architectural default is too low.
812 dma_debug_driver=<driver_name>
813 With this option the DMA-API debugging driver
814 filter feature can be enabled at boot time. Just
815 pass the driver to filter for as the parameter.
816 The filter can be disabled or changed to another
817 driver later using sysfs.
819 drm_kms_helper.edid_firmware=[<connector>:]<file>
820 Broken monitors, graphic adapters and KVMs may
821 send no or incorrect EDID data sets. This parameter
822 allows to specify an EDID data set in the
823 /lib/firmware directory that is used instead.
824 Generic built-in EDID data sets are used, if one of
825 edid/1024x768.bin, edid/1280x1024.bin,
826 edid/1680x1050.bin, or edid/1920x1080.bin is given
827 and no file with the same name exists. Details and
828 instructions how to build your own EDID data are
829 available in Documentation/EDID/HOWTO.txt. An EDID
830 data set will only be used for a particular connector,
831 if its name and a colon are prepended to the EDID
832 name.
834 dscc4.setup= [NET]
836 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
837 module.dyndbg[="val"]
838 Enable debug messages at boot time. See
839 Documentation/dynamic-debug-howto.txt for details.
841 earlycon= [KNL] Output early console device and options.
842 uart[8250],io,<addr>[,options]
843 uart[8250],mmio,<addr>[,options]
844 uart[8250],mmio32,<addr>[,options]
845 Start an early, polled-mode console on the 8250/16550
846 UART at the specified I/O port or MMIO address.
847 MMIO inter-register address stride is either 8-bit
848 (mmio) or 32-bit (mmio32).
849 The options are the same as for ttyS, above.
851 earlyprintk= [X86,SH,BLACKFIN,ARM]
852 earlyprintk=vga
853 earlyprintk=xen
854 earlyprintk=serial[,ttySn[,baudrate]]
855 earlyprintk=serial[,0x...[,baudrate]]
856 earlyprintk=ttySn[,baudrate]
857 earlyprintk=dbgp[debugController#]
859 earlyprintk is useful when the kernel crashes before
860 the normal console is initialized. It is not enabled by
861 default because it has some cosmetic problems.
863 Append ",keep" to not disable it when the real console
864 takes over.
866 Only vga or serial or usb debug port at a time.
868 Currently only ttyS0 and ttyS1 may be specified by
869 name. Other I/O ports may be explicitly specified
870 on some architectures (x86 and arm at least) by
871 replacing ttySn with an I/O port address, like this:
872 earlyprintk=serial,0x1008,115200
873 You can find the port for a given device in
874 /proc/tty/driver/serial:
875 2: uart:ST16650V2 port:00001008 irq:18 ...
877 Interaction with the standard serial driver is not
878 very good.
880 The VGA output is eventually overwritten by the real
881 console.
883 The xen output can only be used by Xen PV guests.
885 ekgdboc= [X86,KGDB] Allow early kernel console debugging
886 ekgdboc=kbd
888 This is designed to be used in conjunction with
889 the boot argument: earlyprintk=vga
891 edd= [EDD]
892 Format: {"off" | "on" | "skip[mbr]"}
894 efi_no_storage_paranoia [EFI; X86]
895 Using this parameter you can use more than 50% of
896 your efi variable storage. Use this parameter only if
897 you are really sure that your UEFI does sane gc and
898 fulfills the spec otherwise your board may brick.
900 eisa_irq_edge= [PARISC,HW]
901 See header of drivers/parisc/eisa.c.
903 elanfreq= [X86-32]
904 See comment before function elanfreq_setup() in
905 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
907 elevator= [IOSCHED]
908 Format: {"cfq" | "deadline" | "noop"}
909 See Documentation/block/cfq-iosched.txt and
910 Documentation/block/deadline-iosched.txt for details.
912 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
913 Specifies physical address of start of kernel core
914 image elf header and optionally the size. Generally
915 kexec loader will pass this option to capture kernel.
916 See Documentation/kdump/kdump.txt for details.
918 enable_mtrr_cleanup [X86]
919 The kernel tries to adjust MTRR layout from continuous
920 to discrete, to make X server driver able to add WB
921 entry later. This parameter enables that.
923 enable_timer_pin_1 [X86]
924 Enable PIN 1 of APIC timer
925 Can be useful to work around chipset bugs
926 (in particular on some ATI chipsets).
927 The kernel tries to set a reasonable default.
929 enforcing [SELINUX] Set initial enforcing status.
930 Format: {"0" | "1"}
931 See security/selinux/Kconfig help text.
932 0 -- permissive (log only, no denials).
933 1 -- enforcing (deny and log).
934 Default value is 0.
935 Value can be changed at runtime via /selinux/enforce.
937 erst_disable [ACPI]
938 Disable Error Record Serialization Table (ERST)
939 support.
941 ether= [HW,NET] Ethernet cards parameters
942 This option is obsoleted by the "netdev=" option, which
943 has equivalent usage. See its documentation for details.
945 evm= [EVM]
946 Format: { "fix" }
947 Permit 'security.evm' to be updated regardless of
948 current integrity status.
950 failslab=
951 fail_page_alloc=
952 fail_make_request=[KNL]
953 General fault injection mechanism.
954 Format: <interval>,<probability>,<space>,<times>
955 See also Documentation/fault-injection/.
957 floppy= [HW]
958 See Documentation/blockdev/floppy.txt.
960 force_pal_cache_flush
961 [IA-64] Avoid check_sal_cache_flush which may hang on
962 buggy SAL_CACHE_FLUSH implementations. Using this
963 parameter will force ia64_sal_cache_flush to call
964 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
966 ftrace=[tracer]
967 [FTRACE] will set and start the specified tracer
968 as early as possible in order to facilitate early
969 boot debugging.
971 ftrace_dump_on_oops[=orig_cpu]
972 [FTRACE] will dump the trace buffers on oops.
973 If no parameter is passed, ftrace will dump
974 buffers of all CPUs, but if you pass orig_cpu, it will
975 dump only the buffer of the CPU that triggered the
976 oops.
978 ftrace_filter=[function-list]
979 [FTRACE] Limit the functions traced by the function
980 tracer at boot up. function-list is a comma separated
981 list of functions. This list can be changed at run
982 time by the set_ftrace_filter file in the debugfs
983 tracing directory.
985 ftrace_notrace=[function-list]
986 [FTRACE] Do not trace the functions specified in
987 function-list. This list can be changed at run time
988 by the set_ftrace_notrace file in the debugfs
989 tracing directory.
991 ftrace_graph_filter=[function-list]
992 [FTRACE] Limit the top level callers functions traced
993 by the function graph tracer at boot up.
994 function-list is a comma separated list of functions
995 that can be changed at run time by the
996 set_graph_function file in the debugfs tracing directory.
998 gamecon.map[2|3]=
999 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1000 support via parallel port (up to 5 devices per port)
1001 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1002 See also Documentation/input/joystick-parport.txt
1004 gamma= [HW,DRM]
1006 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1007 Format: off | on
1008 default: on
1010 gcov_persist= [GCOV] When non-zero (default), profiling data for
1011 kernel modules is saved and remains accessible via
1012 debugfs, even when the module is unloaded/reloaded.
1013 When zero, profiling data is discarded and associated
1014 debugfs files are removed at module unload time.
1016 gpt [EFI] Forces disk with valid GPT signature but
1017 invalid Protective MBR to be treated as GPT.
1019 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1020 the "Enable 0" bit of the configuration register.
1021 Format: 0 | 1
1022 Default: 0
1023 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1024 the "Enable 0" bit of the configuration register.
1025 Format: 0 | 1
1026 Default: 0
1027 grcan.select= [HW] Select which physical interface to use.
1028 Format: 0 | 1
1029 Default: 0
1030 grcan.txsize= [HW] Sets the size of the tx buffer.
1031 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1032 Default: 1024
1033 grcan.rxsize= [HW] Sets the size of the rx buffer.
1034 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1035 Default: 1024
1037 hashdist= [KNL,NUMA] Large hashes allocated during boot
1038 are distributed across NUMA nodes. Defaults on
1039 for 64-bit NUMA, off otherwise.
1040 Format: 0 | 1 (for off | on)
1042 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1044 hd= [EIDE] (E)IDE hard drive subsystem geometry
1045 Format: <cyl>,<head>,<sect>
1047 hest_disable [ACPI]
1048 Disable Hardware Error Source Table (HEST) support;
1049 corresponding firmware-first mode error processing
1050 logic will be disabled.
1052 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1053 size of <nn>. This works even on boxes that have no
1054 highmem otherwise. This also works to reduce highmem
1055 size on bigger boxes.
1057 highres= [KNL] Enable/disable high resolution timer mode.
1058 Valid parameters: "on", "off"
1059 Default: "on"
1061 hisax= [HW,ISDN]
1062 See Documentation/isdn/README.HiSax.
1064 hlt [BUGS=ARM,SH]
1066 hpet= [X86-32,HPET] option to control HPET usage
1067 Format: { enable (default) | disable | force |
1068 verbose }
1069 disable: disable HPET and use PIT instead
1070 force: allow force enabled of undocumented chips (ICH4,
1071 VIA, nVidia)
1072 verbose: show contents of HPET registers during setup
1074 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1075 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1076 On x86-64 and powerpc, this option can be specified
1077 multiple times interleaved with hugepages= to reserve
1078 huge pages of different sizes. Valid pages sizes on
1079 x86-64 are 2M (when the CPU supports "pse") and 1G
1080 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1081 Note that 1GB pages can only be allocated at boot time
1082 using hugepages= and not freed afterwards.
1084 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1085 terminal devices. Valid values: 0..8
1086 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1087 If specified, z/VM IUCV HVC accepts connections
1088 from listed z/VM user IDs only.
1090 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1091 hardware thread id mappings.
1092 Format: <cpu>:<hwthread>
1094 keep_bootcon [KNL]
1095 Do not unregister boot console at start. This is only
1096 useful for debugging when something happens in the window
1097 between unregistering the boot console and initializing
1098 the real console.
1100 i2c_bus= [HW] Override the default board specific I2C bus speed
1101 or register an additional I2C bus that is not
1102 registered from board initialization code.
1103 Format:
1104 <bus_id>,<clkrate>
1106 i8042.debug [HW] Toggle i8042 debug mode
1107 i8042.direct [HW] Put keyboard port into non-translated mode
1108 i8042.dumbkbd [HW] Pretend that controller can only read data from
1109 keyboard and cannot control its state
1110 (Don't attempt to blink the leds)
1111 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1112 i8042.nokbd [HW] Don't check/create keyboard port
1113 i8042.noloop [HW] Disable the AUX Loopback command while probing
1114 for the AUX port
1115 i8042.nomux [HW] Don't check presence of an active multiplexing
1116 controller
1117 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1118 controllers
1119 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1120 i8042.reset [HW] Reset the controller during init and cleanup
1121 i8042.unlock [HW] Unlock (ignore) the keylock
1123 i810= [HW,DRM]
1125 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1126 indicates that the driver is running on unsupported
1127 hardware.
1128 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1129 does not match list of supported models.
1130 i8k.power_status
1131 [HW] Report power status in /proc/i8k
1132 (disabled by default)
1133 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1134 capability is set.
1136 i915.invert_brightness=
1137 [DRM] Invert the sense of the variable that is used to
1138 set the brightness of the panel backlight. Normally a
1139 brightness value of 0 indicates backlight switched off,
1140 and the maximum of the brightness value sets the backlight
1141 to maximum brightness. If this parameter is set to 0
1142 (default) and the machine requires it, or this parameter
1143 is set to 1, a brightness value of 0 sets the backlight
1144 to maximum brightness, and the maximum of the brightness
1145 value switches the backlight off.
1146 -1 -- never invert brightness
1147 0 -- machine default
1148 1 -- force brightness inversion
1150 icn= [HW,ISDN]
1151 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1153 ide-core.nodma= [HW] (E)IDE subsystem
1154 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1155 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1156 .cdrom .chs .ignore_cable are additional options
1157 See Documentation/ide/ide.txt.
1159 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1160 Claim all unknown PCI IDE storage controllers.
1162 idle= [X86]
1163 Format: idle=poll, idle=halt, idle=nomwait
1164 Poll forces a polling idle loop that can slightly
1165 improve the performance of waking up a idle CPU, but
1166 will use a lot of power and make the system run hot.
1167 Not recommended.
1168 idle=halt: Halt is forced to be used for CPU idle.
1169 In such case C2/C3 won't be used again.
1170 idle=nomwait: Disable mwait for CPU C-states
1172 ignore_loglevel [KNL]
1173 Ignore loglevel setting - this will print /all/
1174 kernel messages to the console. Useful for debugging.
1175 We also add it as printk module parameter, so users
1176 could change it dynamically, usually by
1177 /sys/module/printk/parameters/ignore_loglevel.
1179 ihash_entries= [KNL]
1180 Set number of hash buckets for inode cache.
1182 ima_appraise= [IMA] appraise integrity measurements
1183 Format: { "off" | "enforce" | "fix" }
1184 default: "enforce"
1186 ima_appraise_tcb [IMA]
1187 The builtin appraise policy appraises all files
1188 owned by uid=0.
1190 ima_hash= [IMA]
1191 Format: { "sha1" | "md5" }
1192 default: "sha1"
1194 ima_tcb [IMA]
1195 Load a policy which meets the needs of the Trusted
1196 Computing Base. This means IMA will measure all
1197 programs exec'd, files mmap'd for exec, and all files
1198 opened for read by uid=0.
1200 init= [KNL]
1201 Format: <full_path>
1202 Run specified binary instead of /sbin/init as init
1203 process.
1205 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1206 for working out where the kernel is dying during
1207 startup.
1209 initrd= [BOOT] Specify the location of the initial ramdisk
1211 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1212 Format: <irq>
1214 int_pln_enable [x86] Enable power limit notification interrupt
1216 integrity_audit=[IMA]
1217 Format: { "0" | "1" }
1218 0 -- basic integrity auditing messages. (Default)
1219 1 -- additional integrity auditing messages.
1221 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1222 on
1223 Enable intel iommu driver.
1224 off
1225 Disable intel iommu driver.
1226 igfx_off [Default Off]
1227 By default, gfx is mapped as normal device. If a gfx
1228 device has a dedicated DMAR unit, the DMAR unit is
1229 bypassed by not enabling DMAR with this option. In
1230 this case, gfx device will use physical address for
1231 DMA.
1232 forcedac [x86_64]
1233 With this option iommu will not optimize to look
1234 for io virtual address below 32-bit forcing dual
1235 address cycle on pci bus for cards supporting greater
1236 than 32-bit addressing. The default is to look
1237 for translation below 32-bit and if not available
1238 then look in the higher range.
1239 strict [Default Off]
1240 With this option on every unmap_single operation will
1241 result in a hardware IOTLB flush operation as opposed
1242 to batching them for performance.
1243 sp_off [Default Off]
1244 By default, super page will be supported if Intel IOMMU
1245 has the capability. With this option, super page will
1246 not be supported.
1248 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1249 0 disables intel_idle and fall back on acpi_idle.
1250 1 to 6 specify maximum depth of C-state.
1252 intel_pstate= [X86]
1253 disable
1254 Do not enable intel_pstate as the default
1255 scaling driver for the supported processors
1257 intremap= [X86-64, Intel-IOMMU]
1258 on enable Interrupt Remapping (default)
1259 off disable Interrupt Remapping
1260 nosid disable Source ID checking
1261 no_x2apic_optout
1262 BIOS x2APIC opt-out request will be ignored
1264 iomem= Disable strict checking of access to MMIO memory
1265 strict regions from userspace.
1266 relaxed
1268 iommu= [x86]
1269 off
1270 force
1271 noforce
1272 biomerge
1273 panic
1274 nopanic
1275 merge
1276 nomerge
1277 forcesac
1278 soft
1279 pt [x86, IA-64]
1282 io7= [HW] IO7 for Marvel based alpha systems
1283 See comment before marvel_specify_io7 in
1284 arch/alpha/kernel/core_marvel.c.
1286 io_delay= [X86] I/O delay method
1287 0x80
1288 Standard port 0x80 based delay
1289 0xed
1290 Alternate port 0xed based delay (needed on some systems)
1291 udelay
1292 Simple two microseconds delay
1293 none
1294 No delay
1296 ip= [IP_PNP]
1297 See Documentation/filesystems/nfs/nfsroot.txt.
1299 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1300 See comment before ip2_setup() in
1301 drivers/char/ip2/ip2base.c.
1303 irqfixup [HW]
1304 When an interrupt is not handled search all handlers
1305 for it. Intended to get systems with badly broken
1306 firmware running.
1308 irqpoll [HW]
1309 When an interrupt is not handled search all handlers
1310 for it. Also check all handlers each timer
1311 interrupt. Intended to get systems with badly broken
1312 firmware running.
1314 isapnp= [ISAPNP]
1315 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1317 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1318 Format:
1319 <cpu number>,...,<cpu number>
1320 or
1321 <cpu number>-<cpu number>
1322 (must be a positive range in ascending order)
1323 or a mixture
1324 <cpu number>,...,<cpu number>-<cpu number>
1326 This option can be used to specify one or more CPUs
1327 to isolate from the general SMP balancing and scheduling
1328 algorithms. You can move a process onto or off an
1329 "isolated" CPU via the CPU affinity syscalls or cpuset.
1330 <cpu number> begins at 0 and the maximum value is
1331 "number of CPUs in system - 1".
1333 This option is the preferred way to isolate CPUs. The
1334 alternative -- manually setting the CPU mask of all
1335 tasks in the system -- can cause problems and
1336 suboptimal load balancer performance.
1338 iucv= [HW,NET]
1340 ivrs_ioapic [HW,X86_64]
1341 Provide an override to the IOAPIC-ID<->DEVICE-ID
1342 mapping provided in the IVRS ACPI table. For
1343 example, to map IOAPIC-ID decimal 10 to
1344 PCI device 00:14.0 write the parameter as:
1345 ivrs_ioapic[10]=00:14.0
1347 ivrs_hpet [HW,X86_64]
1348 Provide an override to the HPET-ID<->DEVICE-ID
1349 mapping provided in the IVRS ACPI table. For
1350 example, to map HPET-ID decimal 0 to
1351 PCI device 00:14.0 write the parameter as:
1352 ivrs_hpet[0]=00:14.0
1354 js= [HW,JOY] Analog joystick
1355 See Documentation/input/joystick.txt.
1357 keepinitrd [HW,ARM]
1359 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1360 specifies the amount of memory usable by the kernel
1361 for non-movable allocations. The requested amount is
1362 spread evenly throughout all nodes in the system. The
1363 remaining memory in each node is used for Movable
1364 pages. In the event, a node is too small to have both
1365 kernelcore and Movable pages, kernelcore pages will
1366 take priority and other nodes will have a larger number
1367 of Movable pages. The Movable zone is used for the
1368 allocation of pages that may be reclaimed or moved
1369 by the page migration subsystem. This means that
1370 HugeTLB pages may not be allocated from this zone.
1371 Note that allocations like PTEs-from-HighMem still
1372 use the HighMem zone if it exists, and the Normal
1373 zone if it does not.
1375 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1376 Format: <Controller#>[,poll interval]
1377 The controller # is the number of the ehci usb debug
1378 port as it is probed via PCI. The poll interval is
1379 optional and is the number seconds in between
1380 each poll cycle to the debug port in case you need
1381 the functionality for interrupting the kernel with
1382 gdb or control-c on the dbgp connection. When
1383 not using this parameter you use sysrq-g to break into
1384 the kernel debugger.
1386 kgdboc= [KGDB,HW] kgdb over consoles.
1387 Requires a tty driver that supports console polling,
1388 or a supported polling keyboard driver (non-usb).
1389 Serial only format: <serial_device>[,baud]
1390 keyboard only format: kbd
1391 keyboard and serial format: kbd,<serial_device>[,baud]
1392 Optional Kernel mode setting:
1393 kms, kbd format: kms,kbd
1394 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1396 kgdbwait [KGDB] Stop kernel execution and enter the
1397 kernel debugger at the earliest opportunity.
1399 kmac= [MIPS] korina ethernet MAC address.
1400 Configure the RouterBoard 532 series on-chip
1401 Ethernet adapter MAC address.
1403 kmemleak= [KNL] Boot-time kmemleak enable/disable
1404 Valid arguments: on, off
1405 Default: on
1407 kstack=N [X86] Print N words from the kernel stack
1408 in oops dumps.
1410 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1411 Default is 0 (don't ignore, but inject #GP)
1413 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1414 KVM MMU at runtime.
1415 Default is 0 (off)
1417 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1418 Default is 1 (enabled)
1420 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1421 for all guests.
1422 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1424 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1425 (virtualized MMU) support on capable Intel chips.
1426 Default is 1 (enabled)
1428 kvm-intel.emulate_invalid_guest_state=
1429 [KVM,Intel] Enable emulation of invalid guest states
1430 Default is 0 (disabled)
1432 kvm-intel.flexpriority=
1433 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1434 Default is 1 (enabled)
1436 kvm-intel.nested=
1437 [KVM,Intel] Enable VMX nesting (nVMX).
1438 Default is 0 (disabled)
1440 kvm-intel.unrestricted_guest=
1441 [KVM,Intel] Disable unrestricted guest feature
1442 (virtualized real and unpaged mode) on capable
1443 Intel chips. Default is 1 (enabled)
1445 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1446 feature (tagged TLBs) on capable Intel chips.
1447 Default is 1 (enabled)
1449 l2cr= [PPC]
1451 l3cr= [PPC]
1453 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1454 disabled it.
1456 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1457 value for LAPIC timer one-shot implementation. Default
1458 back to the programmable timer unit in the LAPIC.
1460 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1461 in C2 power state.
1463 libata.dma= [LIBATA] DMA control
1464 libata.dma=0 Disable all PATA and SATA DMA
1465 libata.dma=1 PATA and SATA Disk DMA only
1466 libata.dma=2 ATAPI (CDROM) DMA only
1467 libata.dma=4 Compact Flash DMA only
1468 Combinations also work, so libata.dma=3 enables DMA
1469 for disks and CDROMs, but not CFs.
1471 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1472 libata.ignore_hpa=0 keep BIOS limits (default)
1473 libata.ignore_hpa=1 ignore limits, using full disk
1475 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1476 when set.
1477 Format: <int>
1479 libata.force= [LIBATA] Force configurations. The format is comma
1480 separated list of "[ID:]VAL" where ID is
1481 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1482 matching port, link or device. Basically, it matches
1483 the ATA ID string printed on console by libata. If
1484 the whole ID part is omitted, the last PORT and DEVICE
1485 values are used. If ID hasn't been specified yet, the
1486 configuration applies to all ports, links and devices.
1488 If only DEVICE is omitted, the parameter applies to
1489 the port and all links and devices behind it. DEVICE
1490 number of 0 either selects the first device or the
1491 first fan-out link behind PMP device. It does not
1492 select the host link. DEVICE number of 15 selects the
1493 host link and device attached to it.
1495 The VAL specifies the configuration to force. As long
1496 as there's no ambiguity shortcut notation is allowed.
1497 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1498 The following configurations can be forced.
1500 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1501 Any ID with matching PORT is used.
1503 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1505 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1506 udma[/][16,25,33,44,66,100,133] notation is also
1507 allowed.
1509 * [no]ncq: Turn on or off NCQ.
1511 * nohrst, nosrst, norst: suppress hard, soft
1512 and both resets.
1514 * rstonce: only attempt one reset during
1515 hot-unplug link recovery
1517 * dump_id: dump IDENTIFY data.
1519 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1521 * disable: Disable this device.
1523 If there are multiple matching configurations changing
1524 the same attribute, the last one is used.
1526 memblock=debug [KNL] Enable memblock debug messages.
1528 load_ramdisk= [RAM] List of ramdisks to load from floppy
1529 See Documentation/blockdev/ramdisk.txt.
1531 lockd.nlm_grace_period=P [NFS] Assign grace period.
1532 Format: <integer>
1534 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1535 Format: <integer>
1537 lockd.nlm_timeout=T [NFS] Assign timeout value.
1538 Format: <integer>
1540 lockd.nlm_udpport=M [NFS] Assign UDP port.
1541 Format: <integer>
1543 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1544 Format: <irq>
1546 loglevel= All Kernel Messages with a loglevel smaller than the
1547 console loglevel will be printed to the console. It can
1548 also be changed with klogd or other programs. The
1549 loglevels are defined as follows:
1551 0 (KERN_EMERG) system is unusable
1552 1 (KERN_ALERT) action must be taken immediately
1553 2 (KERN_CRIT) critical conditions
1554 3 (KERN_ERR) error conditions
1555 4 (KERN_WARNING) warning conditions
1556 5 (KERN_NOTICE) normal but significant condition
1557 6 (KERN_INFO) informational
1558 7 (KERN_DEBUG) debug-level messages
1560 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1561 in bytes. n must be a power of two. The default
1562 size is set in the kernel config file.
1564 logo.nologo [FB] Disables display of the built-in Linux logo.
1565 This may be used to provide more screen space for
1566 kernel log messages and is useful when debugging
1567 kernel boot problems.
1569 lp=0 [LP] Specify parallel ports to use, e.g,
1570 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1571 lp=reset first parallel port). 'lp=0' disables the
1572 lp=auto printer driver. 'lp=reset' (which can be
1573 specified in addition to the ports) causes
1574 attached printers to be reset. Using
1575 lp=port1,port2,... specifies the parallel ports
1576 to associate lp devices with, starting with
1577 lp0. A port specification may be 'none' to skip
1578 that lp device, or a parport name such as
1579 'parport0'. Specifying 'lp=auto' instead of a
1580 port specification list means that device IDs
1581 from each port should be examined, to see if
1582 an IEEE 1284-compliant printer is attached; if
1583 so, the driver will manage that printer.
1584 See also header of drivers/char/lp.c.
1586 lpj=n [KNL]
1587 Sets loops_per_jiffy to given constant, thus avoiding
1588 time-consuming boot-time autodetection (up to 250 ms per
1589 CPU). 0 enables autodetection (default). To determine
1590 the correct value for your kernel, boot with normal
1591 autodetection and see what value is printed. Note that
1592 on SMP systems the preset will be applied to all CPUs,
1593 which is likely to cause problems if your CPUs need
1594 significantly divergent settings. An incorrect value
1595 will cause delays in the kernel to be wrong, leading to
1596 unpredictable I/O errors and other breakage. Although
1597 unlikely, in the extreme case this might damage your
1598 hardware.
1600 ltpc= [NET]
1601 Format: <io>,<irq>,<dma>
1603 machvec= [IA-64] Force the use of a particular machine-vector
1604 (machvec) in a generic kernel.
1605 Example: machvec=hpzx1_swiotlb
1607 machtype= [Loongson] Share the same kernel image file between different
1608 yeeloong laptop.
1609 Example: machtype=lemote-yeeloong-2f-7inch
1611 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1612 than or equal to this physical address is ignored.
1614 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1615 should make use of. maxcpus=n : n >= 0 limits the
1616 kernel to using 'n' processors. n=0 is a special case,
1617 it is equivalent to "nosmp", which also disables
1618 the IO APIC.
1620 max_loop= [LOOP] The number of loop block devices that get
1621 (loop.max_loop) unconditionally pre-created at init time. The default
1622 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1623 of statically allocating a predefined number, loop
1624 devices can be requested on-demand with the
1625 /dev/loop-control interface.
1627 mce [X86-32] Machine Check Exception
1629 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1631 md= [HW] RAID subsystems devices and level
1632 See Documentation/md.txt.
1634 mdacon= [MDA]
1635 Format: <first>,<last>
1636 Specifies range of consoles to be captured by the MDA.
1638 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1639 Amount of memory to be used when the kernel is not able
1640 to see the whole system memory or for test.
1641 [X86] Work as limiting max address. Use together
1642 with memmap= to avoid physical address space collisions.
1643 Without memmap= PCI devices could be placed at addresses
1644 belonging to unused RAM.
1646 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1647 memory.
1649 memchunk=nn[KMG]
1650 [KNL,SH] Allow user to override the default size for
1651 per-device physically contiguous DMA buffers.
1653 memmap=exactmap [KNL,X86] Enable setting of an exact
1654 E820 memory map, as specified by the user.
1655 Such memmap=exactmap lines can be constructed based on
1656 BIOS output or other requirements. See the memmap=nn@ss
1657 option description.
1659 memmap=nn[KMG]@ss[KMG]
1660 [KNL] Force usage of a specific region of memory
1661 Region of memory to be used, from ss to ss+nn.
1663 memmap=nn[KMG]#ss[KMG]
1664 [KNL,ACPI] Mark specific memory as ACPI data.
1665 Region of memory to be used, from ss to ss+nn.
1667 memmap=nn[KMG]$ss[KMG]
1668 [KNL,ACPI] Mark specific memory as reserved.
1669 Region of memory to be used, from ss to ss+nn.
1670 Example: Exclude memory from 0x18690000-0x1869ffff
1671 memmap=64K$0x18690000
1672 or
1673 memmap=0x10000$0x18690000
1675 memory_corruption_check=0/1 [X86]
1676 Some BIOSes seem to corrupt the first 64k of
1677 memory when doing things like suspend/resume.
1678 Setting this option will scan the memory
1679 looking for corruption. Enabling this will
1680 both detect corruption and prevent the kernel
1681 from using the memory being corrupted.
1682 However, its intended as a diagnostic tool; if
1683 repeatable BIOS-originated corruption always
1684 affects the same memory, you can use memmap=
1685 to prevent the kernel from using that memory.
1687 memory_corruption_check_size=size [X86]
1688 By default it checks for corruption in the low
1689 64k, making this memory unavailable for normal
1690 use. Use this parameter to scan for
1691 corruption in more or less memory.
1693 memory_corruption_check_period=seconds [X86]
1694 By default it checks for corruption every 60
1695 seconds. Use this parameter to check at some
1696 other rate. 0 disables periodic checking.
1698 memtest= [KNL,X86] Enable memtest
1699 Format: <integer>
1700 default : 0 <disable>
1701 Specifies the number of memtest passes to be
1702 performed. Each pass selects another test
1703 pattern from a given set of patterns. Memtest
1704 fills the memory with this pattern, validates
1705 memory contents and reserves bad memory
1706 regions that are detected.
1708 meye.*= [HW] Set MotionEye Camera parameters
1709 See Documentation/video4linux/meye.txt.
1711 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1712 Multi-Function General Purpose Timers on AMD Geode
1713 platforms.
1715 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1716 the BIOS has incorrectly applied a workaround. TinyBIOS
1717 version 0.98 is known to be affected, 0.99 fixes the
1718 problem by letting the user disable the workaround.
1720 mga= [HW,DRM]
1722 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1723 physical address is ignored.
1725 mini2440= [ARM,HW,KNL]
1726 Format:[0..2][b][c][t]
1727 Default: "0tb"
1728 MINI2440 configuration specification:
1729 0 - The attached screen is the 3.5" TFT
1730 1 - The attached screen is the 7" TFT
1731 2 - The VGA Shield is attached (1024x768)
1732 Leaving out the screen size parameter will not load
1733 the TFT driver, and the framebuffer will be left
1734 unconfigured.
1735 b - Enable backlight. The TFT backlight pin will be
1736 linked to the kernel VESA blanking code and a GPIO
1737 LED. This parameter is not necessary when using the
1738 VGA shield.
1739 c - Enable the s3c camera interface.
1740 t - Reserved for enabling touchscreen support. The
1741 touchscreen support is not enabled in the mainstream
1742 kernel as of 2.6.30, a preliminary port can be found
1743 in the "bleeding edge" mini2440 support kernel at
1744 http://repo.or.cz/w/linux-2.6/mini2440.git
1746 mminit_loglevel=
1747 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1748 parameter allows control of the logging verbosity for
1749 the additional memory initialisation checks. A value
1750 of 0 disables mminit logging and a level of 4 will
1751 log everything. Information is printed at KERN_DEBUG
1752 so loglevel=8 may also need to be specified.
1754 module.sig_enforce
1755 [KNL] When CONFIG_MODULE_SIG is set, this means that
1756 modules without (valid) signatures will fail to load.
1757 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1758 is always true, so this option does nothing.
1760 mousedev.tap_time=
1761 [MOUSE] Maximum time between finger touching and
1762 leaving touchpad surface for touch to be considered
1763 a tap and be reported as a left button click (for
1764 touchpads working in absolute mode only).
1765 Format: <msecs>
1766 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1767 reporting absolute coordinates, such as tablets
1768 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1769 reporting absolute coordinates, such as tablets
1771 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1772 is similar to kernelcore except it specifies the
1773 amount of memory used for migratable allocations.
1774 If both kernelcore and movablecore is specified,
1775 then kernelcore will be at *least* the specified
1776 value but may be more. If movablecore on its own
1777 is specified, the administrator must be careful
1778 that the amount of memory usable for all allocations
1779 is not too small.
1781 MTD_Partition= [MTD]
1782 Format: <name>,<region-number>,<size>,<offset>
1784 MTD_Region= [MTD] Format:
1785 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1787 mtdparts= [MTD]
1788 See drivers/mtd/cmdlinepart.c.
1790 multitce=off [PPC] This parameter disables the use of the pSeries
1791 firmware feature for updating multiple TCE entries
1792 at a time.
1794 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1796 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1798 boundary - index of last SLC block on Flex-OneNAND.
1799 The remaining blocks are configured as MLC blocks.
1800 lock - Configure if Flex-OneNAND boundary should be locked.
1801 Once locked, the boundary cannot be changed.
1802 1 indicates lock status, 0 indicates unlock status.
1804 mtdset= [ARM]
1805 ARM/S3C2412 JIVE boot control
1807 See arch/arm/mach-s3c2412/mach-jive.c
1809 mtouchusb.raw_coordinates=
1810 [HW] Make the MicroTouch USB driver use raw coordinates
1811 ('y', default) or cooked coordinates ('n')
1813 mtrr_chunk_size=nn[KMG] [X86]
1814 used for mtrr cleanup. It is largest continuous chunk
1815 that could hold holes aka. UC entries.
1817 mtrr_gran_size=nn[KMG] [X86]
1818 Used for mtrr cleanup. It is granularity of mtrr block.
1819 Default is 1.
1820 Large value could prevent small alignment from
1821 using up MTRRs.
1823 mtrr_spare_reg_nr=n [X86]
1824 Format: <integer>
1825 Range: 0,7 : spare reg number
1826 Default : 1
1827 Used for mtrr cleanup. It is spare mtrr entries number.
1828 Set to 2 or more if your graphical card needs more.
1830 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1832 netdev= [NET] Network devices parameters
1833 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1834 Note that mem_start is often overloaded to mean
1835 something different and driver-specific.
1836 This usage is only documented in each driver source
1837 file if at all.
1839 nf_conntrack.acct=
1840 [NETFILTER] Enable connection tracking flow accounting
1841 0 to disable accounting
1842 1 to enable accounting
1843 Default value is 0.
1845 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1846 See Documentation/filesystems/nfs/nfsroot.txt.
1848 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1849 See Documentation/filesystems/nfs/nfsroot.txt.
1851 nfsrootdebug [NFS] enable nfsroot debugging messages.
1852 See Documentation/filesystems/nfs/nfsroot.txt.
1854 nfs.callback_tcpport=
1855 [NFS] set the TCP port on which the NFSv4 callback
1856 channel should listen.
1858 nfs.cache_getent=
1859 [NFS] sets the pathname to the program which is used
1860 to update the NFS client cache entries.
1862 nfs.cache_getent_timeout=
1863 [NFS] sets the timeout after which an attempt to
1864 update a cache entry is deemed to have failed.
1866 nfs.idmap_cache_timeout=
1867 [NFS] set the maximum lifetime for idmapper cache
1868 entries.
1870 nfs.enable_ino64=
1871 [NFS] enable 64-bit inode numbers.
1872 If zero, the NFS client will fake up a 32-bit inode
1873 number for the readdir() and stat() syscalls instead
1874 of returning the full 64-bit number.
1875 The default is to return 64-bit inode numbers.
1877 nfs.max_session_slots=
1878 [NFSv4.1] Sets the maximum number of session slots
1879 the client will attempt to negotiate with the server.
1880 This limits the number of simultaneous RPC requests
1881 that the client can send to the NFSv4.1 server.
1882 Note that there is little point in setting this
1883 value higher than the max_tcp_slot_table_limit.
1885 nfs.nfs4_disable_idmapping=
1886 [NFSv4] When set to the default of '1', this option
1887 ensures that both the RPC level authentication
1888 scheme and the NFS level operations agree to use
1889 numeric uids/gids if the mount is using the
1890 'sec=sys' security flavour. In effect it is
1891 disabling idmapping, which can make migration from
1892 legacy NFSv2/v3 systems to NFSv4 easier.
1893 Servers that do not support this mode of operation
1894 will be autodetected by the client, and it will fall
1895 back to using the idmapper.
1896 To turn off this behaviour, set the value to '0'.
1897 nfs.nfs4_unique_id=
1898 [NFS4] Specify an additional fixed unique ident-
1899 ification string that NFSv4 clients can insert into
1900 their nfs_client_id4 string. This is typically a
1901 UUID that is generated at system install time.
1903 nfs.send_implementation_id =
1904 [NFSv4.1] Send client implementation identification
1905 information in exchange_id requests.
1906 If zero, no implementation identification information
1907 will be sent.
1908 The default is to send the implementation identification
1909 information.
1911 nfs.recover_lost_locks =
1912 [NFSv4] Attempt to recover locks that were lost due
1913 to a lease timeout on the server. Please note that
1914 doing this risks data corruption, since there are
1915 no guarantees that the file will remain unchanged
1916 after the locks are lost.
1917 If you want to enable the kernel legacy behaviour of
1918 attempting to recover these locks, then set this
1919 parameter to '1'.
1920 The default parameter value of '0' causes the kernel
1921 not to attempt recovery of lost locks.
1923 nfsd.nfs4_disable_idmapping=
1924 [NFSv4] When set to the default of '1', the NFSv4
1925 server will return only numeric uids and gids to
1926 clients using auth_sys, and will accept numeric uids
1927 and gids from such clients. This is intended to ease
1928 migration from NFSv2/v3.
1930 objlayoutdriver.osd_login_prog=
1931 [NFS] [OBJLAYOUT] sets the pathname to the program which
1932 is used to automatically discover and login into new
1933 osd-targets. Please see:
1934 Documentation/filesystems/pnfs.txt for more explanations
1936 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1937 when a NMI is triggered.
1938 Format: [state][,regs][,debounce][,die]
1940 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1941 Format: [panic,][nopanic,][num]
1942 Valid num: 0
1943 0 - turn nmi_watchdog off
1944 When panic is specified, panic when an NMI watchdog
1945 timeout occurs (or 'nopanic' to override the opposite
1946 default).
1947 This is useful when you use a panic=... timeout and
1948 need the box quickly up again.
1950 netpoll.carrier_timeout=
1951 [NET] Specifies amount of time (in seconds) that
1952 netpoll should wait for a carrier. By default netpoll
1953 waits 4 seconds.
1955 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1956 emulation library even if a 387 maths coprocessor
1957 is present.
1959 no_console_suspend
1960 [HW] Never suspend the console
1961 Disable suspending of consoles during suspend and
1962 hibernate operations. Once disabled, debugging
1963 messages can reach various consoles while the rest
1964 of the system is being put to sleep (ie, while
1965 debugging driver suspend/resume hooks). This may
1966 not work reliably with all consoles, but is known
1967 to work with serial and VGA consoles.
1968 To facilitate more flexible debugging, we also add
1969 console_suspend, a printk module parameter to control
1970 it. Users could use console_suspend (usually
1971 /sys/module/printk/parameters/console_suspend) to
1972 turn on/off it dynamically.
1974 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1975 caches in the slab allocator. Saves per-node memory,
1976 but will impact performance.
1978 noalign [KNL,ARM]
1980 noapic [SMP,APIC] Tells the kernel to not make use of any
1981 IOAPICs that may be present in the system.
1983 noautogroup Disable scheduler automatic task group creation.
1985 nobats [PPC] Do not use BATs for mapping kernel lowmem
1986 on "Classic" PPC cores.
1988 nocache [ARM]
1990 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1992 nodelayacct [KNL] Disable per-task delay accounting
1994 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1996 nodsp [SH] Disable hardware DSP at boot time.
1998 noefi [X86] Disable EFI runtime services support.
2000 noexec [IA-64]
2002 noexec [X86]
2003 On X86-32 available only on PAE configured kernels.
2004 noexec=on: enable non-executable mappings (default)
2005 noexec=off: disable non-executable mappings
2007 nosmap [X86]
2008 Disable SMAP (Supervisor Mode Access Prevention)
2009 even if it is supported by processor.
2011 nosmep [X86]
2012 Disable SMEP (Supervisor Mode Execution Prevention)
2013 even if it is supported by processor.
2015 noexec32 [X86-64]
2016 This affects only 32-bit executables.
2017 noexec32=on: enable non-executable mappings (default)
2018 read doesn't imply executable mappings
2019 noexec32=off: disable non-executable mappings
2020 read implies executable mappings
2022 nofpu [SH] Disable hardware FPU at boot time.
2024 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2025 register save and restore. The kernel will only save
2026 legacy floating-point registers on task switch.
2028 noxsave [BUGS=X86] Disables x86 extended register state save
2029 and restore using xsave. The kernel will fallback to
2030 enabling legacy floating-point and sse state.
2032 eagerfpu= [X86]
2033 on enable eager fpu restore
2034 off disable eager fpu restore
2035 auto selects the default scheme, which automatically
2036 enables eagerfpu restore for xsaveopt.
2038 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2039 wfi(ARM) instruction doesn't work correctly and not to
2040 use it. This is also useful when using JTAG debugger.
2042 no_file_caps Tells the kernel not to honor file capabilities. The
2043 only way then for a file to be executed with privilege
2044 is to be setuid root or executed by root.
2046 nohalt [IA-64] Tells the kernel not to use the power saving
2047 function PAL_HALT_LIGHT when idle. This increases
2048 power-consumption. On the positive side, it reduces
2049 interrupt wake-up latency, which may improve performance
2050 in certain environments such as networked servers or
2051 real-time systems.
2053 nohz= [KNL] Boottime enable/disable dynamic ticks
2054 Valid arguments: on, off
2055 Default: on
2057 nohz_full= [KNL,BOOT]
2058 In kernels built with CONFIG_NO_HZ_FULL=y, set
2059 the specified list of CPUs whose tick will be stopped
2060 whenever possible. The boot CPU will be forced outside
2061 the range to maintain the timekeeping.
2062 The CPUs in this range must also be included in the
2063 rcu_nocbs= set.
2065 noiotrap [SH] Disables trapped I/O port accesses.
2067 noirqdebug [X86-32] Disables the code which attempts to detect and
2068 disable unhandled interrupt sources.
2070 no_timer_check [X86,APIC] Disables the code which tests for
2071 broken timer IRQ sources.
2073 noisapnp [ISAPNP] Disables ISA PnP code.
2075 noinitrd [RAM] Tells the kernel not to load any configured
2076 initial RAM disk.
2078 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2079 remapping.
2080 [Deprecated - use intremap=off]
2082 nointroute [IA-64]
2084 nojitter [IA-64] Disables jitter checking for ITC timers.
2086 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2088 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2089 fault handling.
2091 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2092 steal time is computed, but won't influence scheduler
2093 behaviour
2095 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2097 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2099 noltlbs [PPC] Do not use large page/tlb entries for kernel
2100 lowmem mapping on PPC40x.
2102 nomca [IA-64] Disable machine check abort handling
2104 nomce [X86-32] Machine Check Exception
2106 nomfgpt [X86-32] Disable Multi-Function General Purpose
2107 Timer usage (for AMD Geode machines).
2109 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2110 shutdown the other cpus. Instead use the REBOOT_VECTOR
2111 irq.
2113 nomodule Disable module load
2115 nopat [X86] Disable PAT (page attribute table extension of
2116 pagetables) support.
2118 norandmaps Don't use address space randomization. Equivalent to
2119 echo 0 > /proc/sys/kernel/randomize_va_space
2121 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2123 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2124 with UP alternatives
2126 nordrand [X86] Disable the direct use of the RDRAND
2127 instruction even if it is supported by the
2128 processor. RDRAND is still available to user
2129 space applications.
2131 noresume [SWSUSP] Disables resume and restores original swap
2132 space.
2134 no-scroll [VGA] Disables scrollback.
2135 This is required for the Braillex ib80-piezo Braille
2136 reader made by F.H. Papenmeier (Germany).
2138 nosbagart [IA-64]
2140 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2142 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2143 and disable the IO APIC. legacy for "maxcpus=0".
2145 nosoftlockup [KNL] Disable the soft-lockup detector.
2147 nosync [HW,M68K] Disables sync negotiation for all devices.
2149 notsc [BUGS=X86-32] Disable Time Stamp Counter
2151 nousb [USB] Disable the USB subsystem
2153 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2155 nowb [ARM]
2157 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2159 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2160 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2161 Some features depend on CPU0. Known dependencies are:
2162 1. Resume from suspend/hibernate depends on CPU0.
2163 Suspend/hibernate will fail if CPU0 is offline and you
2164 need to online CPU0 before suspend/hibernate.
2165 2. PIC interrupts also depend on CPU0. CPU0 can't be
2166 removed if a PIC interrupt is detected.
2167 It's said poweroff/reboot may depend on CPU0 on some
2168 machines although I haven't seen such issues so far
2169 after CPU0 is offline on a few tested machines.
2170 If the dependencies are under your control, you can
2171 turn on cpu0_hotplug.
2173 nptcg= [IA-64] Override max number of concurrent global TLB
2174 purges which is reported from either PAL_VM_SUMMARY or
2175 SAL PALO.
2177 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2178 could support. nr_cpus=n : n >= 1 limits the kernel to
2179 supporting 'n' processors. Later in runtime you can not
2180 use hotplug cpu feature to put more cpu back to online.
2181 just like you compile the kernel NR_CPUS=n
2183 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2185 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2186 Allowed values are enable and disable
2188 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2189 one of ['zone', 'node', 'default'] can be specified
2190 This can be set from sysctl after boot.
2191 See Documentation/sysctl/vm.txt for details.
2193 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2194 See Documentation/debugging-via-ohci1394.txt for more
2195 info.
2197 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2198 Rather than timing out after 20 ms if an EC
2199 command is not properly ACKed, override the length
2200 of the timeout. We have interrupts disabled while
2201 waiting for the ACK, so if this is set too high
2202 interrupts *may* be lost!
2204 omap_mux= [OMAP] Override bootloader pin multiplexing.
2205 Format: <mux_mode0.mode_name=value>...
2206 For example, to override I2C bus2:
2207 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2209 oprofile.timer= [HW]
2210 Use timer interrupt instead of performance counters
2212 oprofile.cpu_type= Force an oprofile cpu type
2213 This might be useful if you have an older oprofile
2214 userland or if you want common events.
2215 Format: { arch_perfmon }
2216 arch_perfmon: [X86] Force use of architectural
2217 perfmon on Intel CPUs instead of the
2218 CPU specific event set.
2219 timer: [X86] Force use of architectural NMI
2220 timer mode (see also oprofile.timer
2221 for generic hr timer mode)
2222 [s390] Force legacy basic mode sampling
2223 (report cpu_type "timer")
2225 oops=panic Always panic on oopses. Default is to just kill the
2226 process, but there is a small probability of
2227 deadlocking the machine.
2228 This will also cause panics on machine check exceptions.
2229 Useful together with panic=30 to trigger a reboot.
2231 OSS [HW,OSS]
2232 See Documentation/sound/oss/oss-parameters.txt
2234 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2235 timeout > 0: seconds before rebooting
2236 timeout = 0: wait forever
2237 timeout < 0: reboot immediately
2238 Format: <timeout>
2240 parkbd.port= [HW] Parallel port number the keyboard adapter is
2241 connected to, default is 0.
2242 Format: <parport#>
2243 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2244 0 for XT, 1 for AT (default is AT).
2245 Format: <mode>
2247 parport= [HW,PPT] Specify parallel ports. 0 disables.
2248 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2249 Use 'auto' to force the driver to use any
2250 IRQ/DMA settings detected (the default is to
2251 ignore detected IRQ/DMA settings because of
2252 possible conflicts). You can specify the base
2253 address, IRQ, and DMA settings; IRQ and DMA
2254 should be numbers, or 'auto' (for using detected
2255 settings on that particular port), or 'nofifo'
2256 (to avoid using a FIFO even if it is detected).
2257 Parallel ports are assigned in the order they
2258 are specified on the command line, starting
2259 with parport0.
2261 parport_init_mode= [HW,PPT]
2262 Configure VIA parallel port to operate in
2263 a specific mode. This is necessary on Pegasos
2264 computer where firmware has no options for setting
2265 up parallel port mode and sets it to spp.
2266 Currently this function knows 686a and 8231 chips.
2267 Format: [spp|ps2|epp|ecp|ecpepp]
2269 pause_on_oops=
2270 Halt all CPUs after the first oops has been printed for
2271 the specified number of seconds. This is to be used if
2272 your oopses keep scrolling off the screen.
2274 pcbit= [HW,ISDN]
2276 pcd. [PARIDE]
2277 See header of drivers/block/paride/pcd.c.
2278 See also Documentation/blockdev/paride.txt.
2280 pci=option[,option...] [PCI] various PCI subsystem options:
2281 earlydump [X86] dump PCI config space before the kernel
2282 changes anything
2283 off [X86] don't probe for the PCI bus
2284 bios [X86-32] force use of PCI BIOS, don't access
2285 the hardware directly. Use this if your machine
2286 has a non-standard PCI host bridge.
2287 nobios [X86-32] disallow use of PCI BIOS, only direct
2288 hardware access methods are allowed. Use this
2289 if you experience crashes upon bootup and you
2290 suspect they are caused by the BIOS.
2291 conf1 [X86] Force use of PCI Configuration
2292 Mechanism 1.
2293 conf2 [X86] Force use of PCI Configuration
2294 Mechanism 2.
2295 noaer [PCIE] If the PCIEAER kernel config parameter is
2296 enabled, this kernel boot option can be used to
2297 disable the use of PCIE advanced error reporting.
2298 nodomains [PCI] Disable support for multiple PCI
2299 root domains (aka PCI segments, in ACPI-speak).
2300 nommconf [X86] Disable use of MMCONFIG for PCI
2301 Configuration
2302 check_enable_amd_mmconf [X86] check for and enable
2303 properly configured MMIO access to PCI
2304 config space on AMD family 10h CPU
2305 nomsi [MSI] If the PCI_MSI kernel config parameter is
2306 enabled, this kernel boot option can be used to
2307 disable the use of MSI interrupts system-wide.
2308 noioapicquirk [APIC] Disable all boot interrupt quirks.
2309 Safety option to keep boot IRQs enabled. This
2310 should never be necessary.
2311 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2312 primary IO-APIC for bridges that cannot disable
2313 boot IRQs. This fixes a source of spurious IRQs
2314 when the system masks IRQs.
2315 noioapicreroute [APIC] Disable workaround that uses the
2316 boot IRQ equivalent of an IRQ that connects to
2317 a chipset where boot IRQs cannot be disabled.
2318 The opposite of ioapicreroute.
2319 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2320 routing table. These calls are known to be buggy
2321 on several machines and they hang the machine
2322 when used, but on other computers it's the only
2323 way to get the interrupt routing table. Try
2324 this option if the kernel is unable to allocate
2325 IRQs or discover secondary PCI buses on your
2326 motherboard.
2327 rom [X86] Assign address space to expansion ROMs.
2328 Use with caution as certain devices share
2329 address decoders between ROMs and other
2330 resources.
2331 norom [X86] Do not assign address space to
2332 expansion ROMs that do not already have
2333 BIOS assigned address ranges.
2334 nobar [X86] Do not assign address space to the
2335 BARs that weren't assigned by the BIOS.
2336 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2337 assigned automatically to PCI devices. You can
2338 make the kernel exclude IRQs of your ISA cards
2339 this way.
2340 pirqaddr=0xAAAAA [X86] Specify the physical address
2341 of the PIRQ table (normally generated
2342 by the BIOS) if it is outside the
2343 F0000h-100000h range.
2344 lastbus=N [X86] Scan all buses thru bus #N. Can be
2345 useful if the kernel is unable to find your
2346 secondary buses and you want to tell it
2347 explicitly which ones they are.
2348 assign-busses [X86] Always assign all PCI bus
2349 numbers ourselves, overriding
2350 whatever the firmware may have done.
2351 usepirqmask [X86] Honor the possible IRQ mask stored
2352 in the BIOS $PIR table. This is needed on
2353 some systems with broken BIOSes, notably
2354 some HP Pavilion N5400 and Omnibook XE3
2355 notebooks. This will have no effect if ACPI
2356 IRQ routing is enabled.
2357 noacpi [X86] Do not use ACPI for IRQ routing
2358 or for PCI scanning.
2359 use_crs [X86] Use PCI host bridge window information
2360 from ACPI. On BIOSes from 2008 or later, this
2361 is enabled by default. If you need to use this,
2362 please report a bug.
2363 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2364 If you need to use this, please report a bug.
2365 routeirq Do IRQ routing for all PCI devices.
2366 This is normally done in pci_enable_device(),
2367 so this option is a temporary workaround
2368 for broken drivers that don't call it.
2369 skip_isa_align [X86] do not align io start addr, so can
2370 handle more pci cards
2371 firmware [ARM] Do not re-enumerate the bus but instead
2372 just use the configuration from the
2373 bootloader. This is currently used on
2374 IXP2000 systems where the bus has to be
2375 configured a certain way for adjunct CPUs.
2376 noearly [X86] Don't do any early type 1 scanning.
2377 This might help on some broken boards which
2378 machine check when some devices' config space
2379 is read. But various workarounds are disabled
2380 and some IOMMU drivers will not work.
2381 bfsort Sort PCI devices into breadth-first order.
2382 This sorting is done to get a device
2383 order compatible with older (<= 2.4) kernels.
2384 nobfsort Don't sort PCI devices into breadth-first order.
2385 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2386 tuning and use the BIOS-configured MPS defaults.
2387 pcie_bus_safe Set every device's MPS to the largest value
2388 supported by all devices below the root complex.
2389 pcie_bus_perf Set device MPS to the largest allowable MPS
2390 based on its parent bus. Also set MRRS (Max
2391 Read Request Size) to the largest supported
2392 value (no larger than the MPS that the device
2393 or bus can support) for best performance.
2394 pcie_bus_peer2peer Set every device's MPS to 128B, which
2395 every device is guaranteed to support. This
2396 configuration allows peer-to-peer DMA between
2397 any pair of devices, possibly at the cost of
2398 reduced performance. This also guarantees
2399 that hot-added devices will work.
2400 cbiosize=nn[KMG] The fixed amount of bus space which is
2401 reserved for the CardBus bridge's IO window.
2402 The default value is 256 bytes.
2403 cbmemsize=nn[KMG] The fixed amount of bus space which is
2404 reserved for the CardBus bridge's memory
2405 window. The default value is 64 megabytes.
2406 resource_alignment=
2407 Format:
2408 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2409 Specifies alignment and device to reassign
2410 aligned memory resources.
2411 If <order of align> is not specified,
2412 PAGE_SIZE is used as alignment.
2413 PCI-PCI bridge can be specified, if resource
2414 windows need to be expanded.
2415 ecrc= Enable/disable PCIe ECRC (transaction layer
2416 end-to-end CRC checking).
2417 bios: Use BIOS/firmware settings. This is the
2418 the default.
2419 off: Turn ECRC off
2420 on: Turn ECRC on.
2421 hpiosize=nn[KMG] The fixed amount of bus space which is
2422 reserved for hotplug bridge's IO window.
2423 Default size is 256 bytes.
2424 hpmemsize=nn[KMG] The fixed amount of bus space which is
2425 reserved for hotplug bridge's memory window.
2426 Default size is 2 megabytes.
2427 realloc= Enable/disable reallocating PCI bridge resources
2428 if allocations done by BIOS are too small to
2429 accommodate resources required by all child
2430 devices.
2431 off: Turn realloc off
2432 on: Turn realloc on
2433 realloc same as realloc=on
2434 noari do not use PCIe ARI.
2435 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2436 only look for one device below a PCIe downstream
2437 port.
2439 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2440 Management.
2441 off Disable ASPM.
2442 force Enable ASPM even on devices that claim not to support it.
2443 WARNING: Forcing ASPM on may cause system lockups.
2445 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2446 nomsi Do not use MSI for PCI Express Native Hotplug (this
2447 makes all PCIe ports use INTx for hotplug services).
2449 pcie_ports= [PCIE] PCIe ports handling:
2450 auto Ask the BIOS whether or not to use native PCIe services
2451 associated with PCIe ports (PME, hot-plug, AER). Use
2452 them only if that is allowed by the BIOS.
2453 native Use native PCIe services associated with PCIe ports
2454 unconditionally.
2455 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2456 ports driver.
2458 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2459 nomsi Do not use MSI for native PCIe PME signaling (this makes
2460 all PCIe root ports use INTx for all services).
2462 pcmv= [HW,PCMCIA] BadgePAD 4
2464 pd. [PARIDE]
2465 See Documentation/blockdev/paride.txt.
2467 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2468 boot time.
2469 Format: { 0 | 1 }
2470 See arch/parisc/kernel/pdc_chassis.c
2472 percpu_alloc= Select which percpu first chunk allocator to use.
2473 Currently supported values are "embed" and "page".
2474 Archs may support subset or none of the selections.
2475 See comments in mm/percpu.c for details on each
2476 allocator. This parameter is primarily for debugging
2477 and performance comparison.
2479 pf. [PARIDE]
2480 See Documentation/blockdev/paride.txt.
2482 pg. [PARIDE]
2483 See Documentation/blockdev/paride.txt.
2485 pirq= [SMP,APIC] Manual mp-table setup
2486 See Documentation/x86/i386/IO-APIC.txt.
2488 plip= [PPT,NET] Parallel port network link
2489 Format: { parport<nr> | timid | 0 }
2490 See also Documentation/parport.txt.
2492 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2493 Override pmtimer IOPort with a hex value.
2494 e.g. pmtmr=0x508
2496 pnp.debug=1 [PNP]
2497 Enable PNP debug messages (depends on the
2498 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2499 via /sys/module/pnp/parameters/debug. We always show
2500 current resource usage; turning this on also shows
2501 possible settings and some assignment information.
2503 pnpacpi= [ACPI]
2504 { off }
2506 pnpbios= [ISAPNP]
2507 { on | off | curr | res | no-curr | no-res }
2509 pnp_reserve_irq=
2510 [ISAPNP] Exclude IRQs for the autoconfiguration
2512 pnp_reserve_dma=
2513 [ISAPNP] Exclude DMAs for the autoconfiguration
2515 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2516 Ranges are in pairs (I/O port base and size).
2518 pnp_reserve_mem=
2519 [ISAPNP] Exclude memory regions for the
2520 autoconfiguration.
2521 Ranges are in pairs (memory base and size).
2523 ports= [IP_VS_FTP] IPVS ftp helper module
2524 Default is 21.
2525 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2526 may be specified.
2527 Format: <port>,<port>....
2529 print-fatal-signals=
2530 [KNL] debug: print fatal signals
2532 If enabled, warn about various signal handling
2533 related application anomalies: too many signals,
2534 too many POSIX.1 timers, fatal signals causing a
2535 coredump - etc.
2537 If you hit the warning due to signal overflow,
2538 you might want to try "ulimit -i unlimited".
2540 default: off.
2542 printk.always_kmsg_dump=
2543 Trigger kmsg_dump for cases other than kernel oops or
2544 panics
2545 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2546 default: disabled
2548 printk.time= Show timing data prefixed to each printk message line
2549 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2551 processor.max_cstate= [HW,ACPI]
2552 Limit processor to maximum C-state
2553 max_cstate=9 overrides any DMI blacklist limit.
2555 processor.nocst [HW,ACPI]
2556 Ignore the _CST method to determine C-states,
2557 instead using the legacy FADT method
2559 profile= [KNL] Enable kernel profiling via /proc/profile
2560 Format: [schedule,]<number>
2561 Param: "schedule" - profile schedule points.
2562 Param: <number> - step/bucket size as a power of 2 for
2563 statistical time based profiling.
2564 Param: "sleep" - profile D-state sleeping (millisecs).
2565 Requires CONFIG_SCHEDSTATS
2566 Param: "kvm" - profile VM exits.
2568 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2569 before loading.
2570 See Documentation/blockdev/ramdisk.txt.
2572 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2573 probe for; one of (bare|imps|exps|lifebook|any).
2574 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2575 per second.
2576 psmouse.resetafter= [HW,MOUSE]
2577 Try to reset the device after so many bad packets
2578 (0 = never).
2579 psmouse.resolution=
2580 [HW,MOUSE] Set desired mouse resolution, in dpi.
2581 psmouse.smartscroll=
2582 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2583 0 = disabled, 1 = enabled (default).
2585 pstore.backend= Specify the name of the pstore backend to use
2587 pt. [PARIDE]
2588 See Documentation/blockdev/paride.txt.
2590 pty.legacy_count=
2591 [KNL] Number of legacy pty's. Overwrites compiled-in
2592 default number.
2594 quiet [KNL] Disable most log messages
2596 r128= [HW,DRM]
2598 raid= [HW,RAID]
2599 See Documentation/md.txt.
2601 ramdisk_blocksize= [RAM]
2602 See Documentation/blockdev/ramdisk.txt.
2604 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2605 See Documentation/blockdev/ramdisk.txt.
2607 rcu_nocbs= [KNL,BOOT]
2608 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2609 the specified list of CPUs to be no-callback CPUs.
2610 Invocation of these CPUs' RCU callbacks will
2611 be offloaded to "rcuox/N" kthreads created for
2612 that purpose, where "x" is "b" for RCU-bh, "p"
2613 for RCU-preempt, and "s" for RCU-sched, and "N"
2614 is the CPU number. This reduces OS jitter on the
2615 offloaded CPUs, which can be useful for HPC and
2617 real-time workloads. It can also improve energy
2618 efficiency for asymmetric multiprocessors.
2620 rcu_nocb_poll [KNL,BOOT]
2621 Rather than requiring that offloaded CPUs
2622 (specified by rcu_nocbs= above) explicitly
2623 awaken the corresponding "rcuoN" kthreads,
2624 make these kthreads poll for callbacks.
2625 This improves the real-time response for the
2626 offloaded CPUs by relieving them of the need to
2627 wake up the corresponding kthread, but degrades
2628 energy efficiency by requiring that the kthreads
2629 periodically wake up to do the polling.
2631 rcutree.blimit= [KNL,BOOT]
2632 Set maximum number of finished RCU callbacks to process
2633 in one batch.
2635 rcutree.fanout_leaf= [KNL,BOOT]
2636 Increase the number of CPUs assigned to each
2637 leaf rcu_node structure. Useful for very large
2638 systems.
2640 rcutree.jiffies_till_first_fqs= [KNL,BOOT]
2641 Set delay from grace-period initialization to
2642 first attempt to force quiescent states.
2643 Units are jiffies, minimum value is zero,
2644 and maximum value is HZ.
2646 rcutree.jiffies_till_next_fqs= [KNL,BOOT]
2647 Set delay between subsequent attempts to force
2648 quiescent states. Units are jiffies, minimum
2649 value is one, and maximum value is HZ.
2651 rcutree.qhimark= [KNL,BOOT]
2652 Set threshold of queued
2653 RCU callbacks over which batch limiting is disabled.
2655 rcutree.qlowmark= [KNL,BOOT]
2656 Set threshold of queued RCU callbacks below which
2657 batch limiting is re-enabled.
2659 rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2660 Suppress RCU CPU stall warning messages.
2662 rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2663 Set timeout for RCU CPU stall warning messages.
2665 rcutree.rcu_idle_gp_delay= [KNL,BOOT]
2666 Set wakeup interval for idle CPUs that have
2667 RCU callbacks (RCU_FAST_NO_HZ=y).
2669 rcutree.rcu_idle_lazy_gp_delay= [KNL,BOOT]
2670 Set wakeup interval for idle CPUs that have
2671 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2672 Lazy RCU callbacks are those which RCU can
2673 prove do nothing more than free memory.
2675 rcutorture.fqs_duration= [KNL,BOOT]
2676 Set duration of force_quiescent_state bursts.
2678 rcutorture.fqs_holdoff= [KNL,BOOT]
2679 Set holdoff time within force_quiescent_state bursts.
2681 rcutorture.fqs_stutter= [KNL,BOOT]
2682 Set wait time between force_quiescent_state bursts.
2684 rcutorture.irqreader= [KNL,BOOT]
2685 Test RCU readers from irq handlers.
2687 rcutorture.n_barrier_cbs= [KNL,BOOT]
2688 Set callbacks/threads for rcu_barrier() testing.
2690 rcutorture.nfakewriters= [KNL,BOOT]
2691 Set number of concurrent RCU writers. These just
2692 stress RCU, they don't participate in the actual
2693 test, hence the "fake".
2695 rcutorture.nreaders= [KNL,BOOT]
2696 Set number of RCU readers.
2698 rcutorture.onoff_holdoff= [KNL,BOOT]
2699 Set time (s) after boot for CPU-hotplug testing.
2701 rcutorture.onoff_interval= [KNL,BOOT]
2702 Set time (s) between CPU-hotplug operations, or
2703 zero to disable CPU-hotplug testing.
2705 rcutorture.shuffle_interval= [KNL,BOOT]
2706 Set task-shuffle interval (s). Shuffling tasks
2707 allows some CPUs to go into dyntick-idle mode
2708 during the rcutorture test.
2710 rcutorture.shutdown_secs= [KNL,BOOT]
2711 Set time (s) after boot system shutdown. This
2712 is useful for hands-off automated testing.
2714 rcutorture.stall_cpu= [KNL,BOOT]
2715 Duration of CPU stall (s) to test RCU CPU stall
2716 warnings, zero to disable.
2718 rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2719 Time to wait (s) after boot before inducing stall.
2721 rcutorture.stat_interval= [KNL,BOOT]
2722 Time (s) between statistics printk()s.
2724 rcutorture.stutter= [KNL,BOOT]
2725 Time (s) to stutter testing, for example, specifying
2726 five seconds causes the test to run for five seconds,
2727 wait for five seconds, and so on. This tests RCU's
2728 ability to transition abruptly to and from idle.
2730 rcutorture.test_boost= [KNL,BOOT]
2731 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2732 "Maybe" means test if the RCU implementation
2733 under test support RCU priority boosting.
2735 rcutorture.test_boost_duration= [KNL,BOOT]
2736 Duration (s) of each individual boost test.
2738 rcutorture.test_boost_interval= [KNL,BOOT]
2739 Interval (s) between each boost test.
2741 rcutorture.test_no_idle_hz= [KNL,BOOT]
2742 Test RCU's dyntick-idle handling. See also the
2743 rcutorture.shuffle_interval parameter.
2745 rcutorture.torture_type= [KNL,BOOT]
2746 Specify the RCU implementation to test.
2748 rcutorture.verbose= [KNL,BOOT]
2749 Enable additional printk() statements.
2751 rdinit= [KNL]
2752 Format: <full_path>
2753 Run specified binary instead of /init from the ramdisk,
2754 used for early userspace startup. See initrd.
2756 reboot= [KNL]
2757 Format (x86 or x86_64):
2758 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2759 [[,]s[mp]#### \
2760 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2761 [[,]f[orce]
2762 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2763 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2764 reboot_force is either force or not specified,
2765 reboot_cpu is s[mp]#### with #### being the processor
2766 to be used for rebooting.
2768 relax_domain_level=
2769 [KNL, SMP] Set scheduler's default relax_domain_level.
2770 See Documentation/cgroups/cpusets.txt.
2772 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2774 reservetop= [X86-32]
2775 Format: nn[KMG]
2776 Reserves a hole at the top of the kernel virtual
2777 address space.
2779 reservelow= [X86]
2780 Format: nn[K]
2781 Set the amount of memory to reserve for BIOS at
2782 the bottom of the address space.
2784 reset_devices [KNL] Force drivers to reset the underlying device
2785 during initialization.
2787 resume= [SWSUSP]
2788 Specify the partition device for software suspend
2789 Format:
2790 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2792 resume_offset= [SWSUSP]
2793 Specify the offset from the beginning of the partition
2794 given by "resume=" at which the swap header is located,
2795 in <PAGE_SIZE> units (needed only for swap files).
2796 See Documentation/power/swsusp-and-swap-files.txt
2798 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2799 read the resume files
2801 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2802 Useful for devices that are detected asynchronously
2803 (e.g. USB and MMC devices).
2805 hibernate= [HIBERNATION]
2806 noresume Don't check if there's a hibernation image
2807 present during boot.
2808 nocompress Don't compress/decompress hibernation images.
2810 retain_initrd [RAM] Keep initrd memory after extraction
2812 rhash_entries= [KNL,NET]
2813 Set number of hash buckets for route cache
2815 riscom8= [HW,SERIAL]
2816 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2818 ro [KNL] Mount root device read-only on boot
2820 root= [KNL] Root filesystem
2821 See name_to_dev_t comment in init/do_mounts.c.
2823 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2824 mount the root filesystem
2826 rootflags= [KNL] Set root filesystem mount option string
2828 rootfstype= [KNL] Set root filesystem type
2830 rootwait [KNL] Wait (indefinitely) for root device to show up.
2831 Useful for devices that are detected asynchronously
2832 (e.g. USB and MMC devices).
2834 rproc_mem=nn[KMG][@address]
2835 [KNL,ARM,CMA] Remoteproc physical memory block.
2836 Memory area to be used by remote processor image,
2837 managed by CMA.
2839 rw [KNL] Mount root device read-write on boot
2841 S [KNL] Run init in single mode
2843 sa1100ir [NET]
2844 See drivers/net/irda/sa1100_ir.c.
2846 sbni= [NET] Granch SBNI12 leased line adapter
2848 sched_debug [KNL] Enables verbose scheduler debug messages.
2850 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2851 xtime_lock contention on larger systems, and/or RCU lock
2852 contention on all systems with CONFIG_MAXSMP set.
2853 Format: { "0" | "1" }
2854 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2855 1 -- enable.
2856 Note: increases power consumption, thus should only be
2857 enabled if running jitter sensitive (HPC/RT) workloads.
2859 security= [SECURITY] Choose a security module to enable at boot.
2860 If this boot parameter is not specified, only the first
2861 security module asking for security registration will be
2862 loaded. An invalid security module name will be treated
2863 as if no module has been chosen.
2865 selinux= [SELINUX] Disable or enable SELinux at boot time.
2866 Format: { "0" | "1" }
2867 See security/selinux/Kconfig help text.
2868 0 -- disable.
2869 1 -- enable.
2870 Default value is set via kernel config option.
2871 If enabled at boot time, /selinux/disable can be used
2872 later to disable prior to initial policy load.
2874 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2875 Format: { "0" | "1" }
2876 See security/apparmor/Kconfig help text
2877 0 -- disable.
2878 1 -- enable.
2879 Default value is set via kernel config option.
2881 serialnumber [BUGS=X86-32]
2883 shapers= [NET]
2884 Maximal number of shapers.
2886 show_msr= [x86] show boot-time MSR settings
2887 Format: { <integer> }
2888 Show boot-time (BIOS-initialized) MSR settings.
2889 The parameter means the number of CPUs to show,
2890 for example 1 means boot CPU only.
2892 simeth= [IA-64]
2893 simscsi=
2895 slram= [HW,MTD]
2897 slab_max_order= [MM, SLAB]
2898 Determines the maximum allowed order for slabs.
2899 A high setting may cause OOMs due to memory
2900 fragmentation. Defaults to 1 for systems with
2901 more than 32MB of RAM, 0 otherwise.
2903 slub_debug[=options[,slabs]] [MM, SLUB]
2904 Enabling slub_debug allows one to determine the
2905 culprit if slab objects become corrupted. Enabling
2906 slub_debug can create guard zones around objects and
2907 may poison objects when not in use. Also tracks the
2908 last alloc / free. For more information see
2909 Documentation/vm/slub.txt.
2911 slub_max_order= [MM, SLUB]
2912 Determines the maximum allowed order for slabs.
2913 A high setting may cause OOMs due to memory
2914 fragmentation. For more information see
2915 Documentation/vm/slub.txt.
2917 slub_min_objects= [MM, SLUB]
2918 The minimum number of objects per slab. SLUB will
2919 increase the slab order up to slub_max_order to
2920 generate a sufficiently large slab able to contain
2921 the number of objects indicated. The higher the number
2922 of objects the smaller the overhead of tracking slabs
2923 and the less frequently locks need to be acquired.
2924 For more information see Documentation/vm/slub.txt.
2926 slub_min_order= [MM, SLUB]
2927 Determines the minimum page order for slabs. Must be
2928 lower than slub_max_order.
2929 For more information see Documentation/vm/slub.txt.
2931 slub_nomerge [MM, SLUB]
2932 Disable merging of slabs with similar size. May be
2933 necessary if there is some reason to distinguish
2934 allocs to different slabs. Debug options disable
2935 merging on their own.
2936 For more information see Documentation/vm/slub.txt.
2938 smart2= [HW]
2939 Format: <io1>[,<io2>[,...,<io8>]]
2941 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2942 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2943 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2944 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2945 smsc-ircc2.ircc_irq= [HW] IRQ line
2946 smsc-ircc2.ircc_dma= [HW] DMA channel
2947 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2948 0: Toshiba Satellite 1800 (GP data pin select)
2949 1: Fast pin select (default)
2950 2: ATC IRMode
2952 softlockup_panic=
2953 [KNL] Should the soft-lockup detector generate panics.
2954 Format: <integer>
2956 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2957 See Documentation/laptops/sonypi.txt
2959 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2960 See Documentation/serial/specialix.txt.
2962 spia_io_base= [HW,MTD]
2963 spia_fio_base=
2964 spia_pedr=
2965 spia_peddr=
2967 stacktrace [FTRACE]
2968 Enabled the stack tracer on boot up.
2970 stacktrace_filter=[function-list]
2971 [FTRACE] Limit the functions that the stack tracer
2972 will trace at boot up. function-list is a comma separated
2973 list of functions. This list can be changed at run
2974 time by the stack_trace_filter file in the debugfs
2975 tracing directory. Note, this enables stack tracing
2976 and the stacktrace above is not needed.
2978 sti= [PARISC,HW]
2979 Format: <num>
2980 Set the STI (builtin display/keyboard on the HP-PARISC
2981 machines) console (graphic card) which should be used
2982 as the initial boot-console.
2983 See also comment in drivers/video/console/sticore.c.
2985 sti_font= [HW]
2986 See comment in drivers/video/console/sticore.c.
2988 stifb= [HW]
2989 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2991 sunrpc.min_resvport=
2992 sunrpc.max_resvport=
2993 [NFS,SUNRPC]
2994 SunRPC servers often require that client requests
2995 originate from a privileged port (i.e. a port in the
2996 range 0 < portnr < 1024).
2997 An administrator who wishes to reserve some of these
2998 ports for other uses may adjust the range that the
2999 kernel's sunrpc client considers to be privileged
3000 using these two parameters to set the minimum and
3001 maximum port values.
3003 sunrpc.pool_mode=
3004 [NFS]
3005 Control how the NFS server code allocates CPUs to
3006 service thread pools. Depending on how many NICs
3007 you have and where their interrupts are bound, this
3008 option will affect which CPUs will do NFS serving.
3009 Note: this parameter cannot be changed while the
3010 NFS server is running.
3012 auto the server chooses an appropriate mode
3013 automatically using heuristics
3014 global a single global pool contains all CPUs
3015 percpu one pool for each CPU
3016 pernode one pool for each NUMA node (equivalent
3017 to global on non-NUMA machines)
3019 sunrpc.tcp_slot_table_entries=
3020 sunrpc.udp_slot_table_entries=
3021 [NFS,SUNRPC]
3022 Sets the upper limit on the number of simultaneous
3023 RPC calls that can be sent from the client to a
3024 server. Increasing these values may allow you to
3025 improve throughput, but will also increase the
3026 amount of memory reserved for use by the client.
3028 swapaccount=[0|1]
3029 [KNL] Enable accounting of swap in memory resource
3030 controller if no parameter or 1 is given or disable
3031 it if 0 is given (See Documentation/cgroups/memory.txt)
3033 swiotlb= [IA-64] Number of I/O TLB slabs
3035 switches= [HW,M68k]
3037 sysfs.deprecated=0|1 [KNL]
3038 Enable/disable old style sysfs layout for old udev
3039 on older distributions. When this option is enabled
3040 very new udev will not work anymore. When this option
3041 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3042 in older udev will not work anymore.
3043 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3044 the kernel configuration.
3046 sysrq_always_enabled
3047 [KNL]
3048 Ignore sysrq setting - this boot parameter will
3049 neutralize any effect of /proc/sys/kernel/sysrq.
3050 Useful for debugging.
3052 tdfx= [HW,DRM]
3054 test_suspend= [SUSPEND]
3055 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3056 standby suspend) as the system sleep state to briefly
3057 enter during system startup. The system is woken from
3058 this state using a wakeup-capable RTC alarm.
3060 thash_entries= [KNL,NET]
3061 Set number of hash buckets for TCP connection
3063 thermal.act= [HW,ACPI]
3064 -1: disable all active trip points in all thermal zones
3065 <degrees C>: override all lowest active trip points
3067 thermal.crt= [HW,ACPI]
3068 -1: disable all critical trip points in all thermal zones
3069 <degrees C>: override all critical trip points
3071 thermal.nocrt= [HW,ACPI]
3072 Set to disable actions on ACPI thermal zone
3073 critical and hot trip points.
3075 thermal.off= [HW,ACPI]
3076 1: disable ACPI thermal control
3078 thermal.psv= [HW,ACPI]
3079 -1: disable all passive trip points
3080 <degrees C>: override all passive trip points to this
3081 value
3083 thermal.tzp= [HW,ACPI]
3084 Specify global default ACPI thermal zone polling rate
3085 <deci-seconds>: poll all this frequency
3086 0: no polling (default)
3088 threadirqs [KNL]
3089 Force threading of all interrupt handlers except those
3090 marked explicitly IRQF_NO_THREAD.
3092 tmem [KNL,XEN]
3093 Enable the Transcendent memory driver if built-in.
3095 tmem.cleancache=0|1 [KNL, XEN]
3096 Default is on (1). Disable the usage of the cleancache
3097 API to send anonymous pages to the hypervisor.
3099 tmem.frontswap=0|1 [KNL, XEN]
3100 Default is on (1). Disable the usage of the frontswap
3101 API to send swap pages to the hypervisor. If disabled
3102 the selfballooning and selfshrinking are force disabled.
3104 tmem.selfballooning=0|1 [KNL, XEN]
3105 Default is on (1). Disable the driving of swap pages
3106 to the hypervisor.
3108 tmem.selfshrinking=0|1 [KNL, XEN]
3109 Default is on (1). Partial swapoff that immediately
3110 transfers pages from Xen hypervisor back to the
3111 kernel based on different criteria.
3113 topology= [S390]
3114 Format: {off | on}
3115 Specify if the kernel should make use of the cpu
3116 topology information if the hardware supports this.
3117 The scheduler will make use of this information and
3118 e.g. base its process migration decisions on it.
3119 Default is on.
3121 tp720= [HW,PS2]
3123 tpm_suspend_pcr=[HW,TPM]
3124 Format: integer pcr id
3125 Specify that at suspend time, the tpm driver
3126 should extend the specified pcr with zeros,
3127 as a workaround for some chips which fail to
3128 flush the last written pcr on TPM_SaveState.
3129 This will guarantee that all the other pcrs
3130 are saved.
3132 trace_buf_size=nn[KMG]
3133 [FTRACE] will set tracing buffer size.
3135 trace_event=[event-list]
3136 [FTRACE] Set and start specified trace events in order
3137 to facilitate early boot debugging.
3138 See also Documentation/trace/events.txt
3140 trace_options=[option-list]
3141 [FTRACE] Enable or disable tracer options at boot.
3142 The option-list is a comma delimited list of options
3143 that can be enabled or disabled just as if you were
3144 to echo the option name into
3146 /sys/kernel/debug/tracing/trace_options
3148 For example, to enable stacktrace option (to dump the
3149 stack trace of each event), add to the command line:
3151 trace_options=stacktrace
3153 See also Documentation/trace/ftrace.txt "trace options"
3154 section.
3156 traceoff_on_warning
3157 [FTRACE] enable this option to disable tracing when a
3158 warning is hit. This turns off "tracing_on". Tracing can
3159 be enabled again by echoing '1' into the "tracing_on"
3160 file located in /sys/kernel/debug/tracing/
3162 This option is useful, as it disables the trace before
3163 the WARNING dump is called, which prevents the trace to
3164 be filled with content caused by the warning output.
3166 This option can also be set at run time via the sysctl
3167 option: kernel/traceoff_on_warning
3169 transparent_hugepage=
3170 [KNL]
3171 Format: [always|madvise|never]
3172 Can be used to control the default behavior of the system
3173 with respect to transparent hugepages.
3174 See Documentation/vm/transhuge.txt for more details.
3176 tsc= Disable clocksource stability checks for TSC.
3177 Format: <string>
3178 [x86] reliable: mark tsc clocksource as reliable, this
3179 disables clocksource verification at runtime, as well
3180 as the stability checks done at bootup. Used to enable
3181 high-resolution timer mode on older hardware, and in
3182 virtualized environment.
3183 [x86] noirqtime: Do not use TSC to do irq accounting.
3184 Used to run time disable IRQ_TIME_ACCOUNTING on any
3185 platforms where RDTSC is slow and this accounting
3186 can add overhead.
3188 turbografx.map[2|3]= [HW,JOY]
3189 TurboGraFX parallel port interface
3190 Format:
3191 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3192 See also Documentation/input/joystick-parport.txt
3194 udbg-immortal [PPC] When debugging early kernel crashes that
3195 happen after console_init() and before a proper
3196 console driver takes over, this boot options might
3197 help "seeing" what's going on.
3199 uhash_entries= [KNL,NET]
3200 Set number of hash buckets for UDP/UDP-Lite connections
3202 uhci-hcd.ignore_oc=
3203 [USB] Ignore overcurrent events (default N).
3204 Some badly-designed motherboards generate lots of
3205 bogus events, for ports that aren't wired to
3206 anything. Set this parameter to avoid log spamming.
3207 Note that genuine overcurrent events won't be
3208 reported either.
3210 unknown_nmi_panic
3211 [X86] Cause panic on unknown NMI.
3213 usbcore.authorized_default=
3214 [USB] Default USB device authorization:
3215 (default -1 = authorized except for wireless USB,
3216 0 = not authorized, 1 = authorized)
3218 usbcore.autosuspend=
3219 [USB] The autosuspend time delay (in seconds) used
3220 for newly-detected USB devices (default 2). This
3221 is the time required before an idle device will be
3222 autosuspended. Devices for which the delay is set
3223 to a negative value won't be autosuspended at all.
3225 usbcore.usbfs_snoop=
3226 [USB] Set to log all usbfs traffic (default 0 = off).
3228 usbcore.blinkenlights=
3229 [USB] Set to cycle leds on hubs (default 0 = off).
3231 usbcore.old_scheme_first=
3232 [USB] Start with the old device initialization
3233 scheme (default 0 = off).
3235 usbcore.usbfs_memory_mb=
3236 [USB] Memory limit (in MB) for buffers allocated by
3237 usbfs (default = 16, 0 = max = 2047).
3239 usbcore.use_both_schemes=
3240 [USB] Try the other device initialization scheme
3241 if the first one fails (default 1 = enabled).
3243 usbcore.initial_descriptor_timeout=
3244 [USB] Specifies timeout for the initial 64-byte
3245 USB_REQ_GET_DESCRIPTOR request in milliseconds
3246 (default 5000 = 5.0 seconds).
3248 usbhid.mousepoll=
3249 [USBHID] The interval which mice are to be polled at.
3251 usb-storage.delay_use=
3252 [UMS] The delay in seconds before a new device is
3253 scanned for Logical Units (default 5).
3255 usb-storage.quirks=
3256 [UMS] A list of quirks entries to supplement or
3257 override the built-in unusual_devs list. List
3258 entries are separated by commas. Each entry has
3259 the form VID:PID:Flags where VID and PID are Vendor
3260 and Product ID values (4-digit hex numbers) and
3261 Flags is a set of characters, each corresponding
3262 to a common usb-storage quirk flag as follows:
3263 a = SANE_SENSE (collect more than 18 bytes
3264 of sense data);
3265 b = BAD_SENSE (don't collect more than 18
3266 bytes of sense data);
3267 c = FIX_CAPACITY (decrease the reported
3268 device capacity by one sector);
3269 d = NO_READ_DISC_INFO (don't use
3270 READ_DISC_INFO command);
3271 e = NO_READ_CAPACITY_16 (don't use
3272 READ_CAPACITY_16 command);
3273 h = CAPACITY_HEURISTICS (decrease the
3274 reported device capacity by one
3275 sector if the number is odd);
3276 i = IGNORE_DEVICE (don't bind to this
3277 device);
3278 l = NOT_LOCKABLE (don't try to lock and
3279 unlock ejectable media);
3280 m = MAX_SECTORS_64 (don't transfer more
3281 than 64 sectors = 32 KB at a time);
3282 n = INITIAL_READ10 (force a retry of the
3283 initial READ(10) command);
3284 o = CAPACITY_OK (accept the capacity
3285 reported by the device);
3286 p = WRITE_CACHE (the device cache is ON
3287 by default);
3288 r = IGNORE_RESIDUE (the device reports
3289 bogus residue values);
3290 s = SINGLE_LUN (the device has only one
3291 Logical Unit);
3292 w = NO_WP_DETECT (don't test whether the
3293 medium is write-protected).
3294 Example: quirks=0419:aaf5:rl,0421:0433:rc
3296 user_debug= [KNL,ARM]
3297 Format: <int>
3298 See arch/arm/Kconfig.debug help text.
3299 1 - undefined instruction events
3300 2 - system calls
3301 4 - invalid data aborts
3302 8 - SIGSEGV faults
3303 16 - SIGBUS faults
3304 Example: user_debug=31
3306 userpte=
3307 [X86] Flags controlling user PTE allocations.
3309 nohigh = do not allocate PTE pages in
3310 HIGHMEM regardless of setting
3311 of CONFIG_HIGHPTE.
3313 vdso= [X86,SH]
3314 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3315 vdso=1: enable VDSO (default)
3316 vdso=0: disable VDSO mapping
3318 vdso32= [X86]
3319 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3320 vdso32=1: enable 32-bit VDSO (default)
3321 vdso32=0: disable 32-bit VDSO mapping
3323 vector= [IA-64,SMP]
3324 vector=percpu: enable percpu vector domain
3326 video= [FB] Frame buffer configuration
3327 See Documentation/fb/modedb.txt.
3329 video.brightness_switch_enabled= [0,1]
3330 If set to 1, on receiving an ACPI notify event
3331 generated by hotkey, video driver will adjust brightness
3332 level and then send out the event to user space through
3333 the allocated input device; If set to 0, video driver
3334 will only send out the event without touching backlight
3335 brightness level.
3336 default: 1
3338 virtio_mmio.device=
3339 [VMMIO] Memory mapped virtio (platform) device.
3341 <size>@<baseaddr>:<irq>[:<id>]
3342 where:
3343 <size> := size (can use standard suffixes
3344 like K, M and G)
3345 <baseaddr> := physical base address
3346 <irq> := interrupt number (as passed to
3347 request_irq())
3348 <id> := (optional) platform device id
3349 example:
3350 virtio_mmio.device=1K@0x100b0000:48:7
3352 Can be used multiple times for multiple devices.
3354 vga= [BOOT,X86-32] Select a particular video mode
3355 See Documentation/x86/boot.txt and
3356 Documentation/svga.txt.
3357 Use vga=ask for menu.
3358 This is actually a boot loader parameter; the value is
3359 passed to the kernel using a special protocol.
3361 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3362 size of <nn>. This can be used to increase the
3363 minimum size (128MB on x86). It can also be used to
3364 decrease the size and leave more room for directly
3365 mapped kernel RAM.
3367 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3368 Format: <command>
3370 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3371 Format: <command>
3373 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3374 Format: <command>
3376 vsyscall= [X86-64]
3377 Controls the behavior of vsyscalls (i.e. calls to
3378 fixed addresses of 0xffffffffff600x00 from legacy
3379 code). Most statically-linked binaries and older
3380 versions of glibc use these calls. Because these
3381 functions are at fixed addresses, they make nice
3382 targets for exploits that can control RIP.
3384 emulate [default] Vsyscalls turn into traps and are
3385 emulated reasonably safely.
3387 native Vsyscalls are native syscall instructions.
3388 This is a little bit faster than trapping
3389 and makes a few dynamic recompilers work
3390 better than they would in emulation mode.
3391 It also makes exploits much easier to write.
3393 none Vsyscalls don't work at all. This makes
3394 them quite hard to use for exploits but
3395 might break your system.
3397 vt.color= [VT] Default text color.
3398 Format: 0xYX, X = foreground, Y = background.
3399 Default: 0x07 = light gray on black.
3401 vt.cur_default= [VT] Default cursor shape.
3402 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3403 the parameters of the <Esc>[?A;B;Cc escape sequence;
3404 see VGA-softcursor.txt. Default: 2 = underline.
3406 vt.default_blu= [VT]
3407 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3408 Change the default blue palette of the console.
3409 This is a 16-member array composed of values
3410 ranging from 0-255.
3412 vt.default_grn= [VT]
3413 Format: <green0>,<green1>,<green2>,...,<green15>
3414 Change the default green palette of the console.
3415 This is a 16-member array composed of values
3416 ranging from 0-255.
3418 vt.default_red= [VT]
3419 Format: <red0>,<red1>,<red2>,...,<red15>
3420 Change the default red palette of the console.
3421 This is a 16-member array composed of values
3422 ranging from 0-255.
3424 vt.default_utf8=
3425 [VT]
3426 Format=<0|1>
3427 Set system-wide default UTF-8 mode for all tty's.
3428 Default is 1, i.e. UTF-8 mode is enabled for all
3429 newly opened terminals.
3431 vt.global_cursor_default=
3432 [VT]
3433 Format=<-1|0|1>
3434 Set system-wide default for whether a cursor
3435 is shown on new VTs. Default is -1,
3436 i.e. cursors will be created by default unless
3437 overridden by individual drivers. 0 will hide
3438 cursors, 1 will display them.
3440 vt.italic= [VT] Default color for italic text; 0-15.
3441 Default: 2 = green.
3443 vt.underline= [VT] Default color for underlined text; 0-15.
3444 Default: 3 = cyan.
3446 watchdog timers [HW,WDT] For information on watchdog timers,
3447 see Documentation/watchdog/watchdog-parameters.txt
3448 or other driver-specific files in the
3449 Documentation/watchdog/ directory.
3451 workqueue.disable_numa
3452 By default, all work items queued to unbound
3453 workqueues are affine to the NUMA nodes they're
3454 issued on, which results in better behavior in
3455 general. If NUMA affinity needs to be disabled for
3456 whatever reason, this option can be used. Note
3457 that this also can be controlled per-workqueue for
3458 workqueues visible under /sys/bus/workqueue/.
3460 workqueue.power_efficient
3461 Per-cpu workqueues are generally preferred because
3462 they show better performance thanks to cache
3463 locality; unfortunately, per-cpu workqueues tend to
3464 be more power hungry than unbound workqueues.
3466 Enabling this makes the per-cpu workqueues which
3467 were observed to contribute significantly to power
3468 consumption unbound, leading to measurably lower
3469 power usage at the cost of small performance
3470 overhead.
3472 The default value of this parameter is determined by
3473 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3475 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3476 default x2apic cluster mode on platforms
3477 supporting x2apic.
3479 x86_mrst_timer= [X86-32,APBT]
3480 Choose timer option for x86 Moorestown MID platform.
3481 Two valid options are apbt timer only and lapic timer
3482 plus one apbt timer for broadcast timer.
3483 x86_mrst_timer=apbt_only | lapic_and_apbt
3485 xen_emul_unplug= [HW,X86,XEN]
3486 Unplug Xen emulated devices
3487 Format: [unplug0,][unplug1]
3488 ide-disks -- unplug primary master IDE devices
3489 aux-ide-disks -- unplug non-primary-master IDE devices
3490 nics -- unplug network devices
3491 all -- unplug all emulated devices (NICs and IDE disks)
3492 unnecessary -- unplugging emulated devices is
3493 unnecessary even if the host did not respond to
3494 the unplug protocol
3495 never -- do not unplug even if version check succeeds
3497 xen_nopvspin [X86,XEN]
3498 Disables the ticketlock slowpath using Xen PV
3499 optimizations.
3501 xirc2ps_cs= [NET,PCMCIA]
3502 Format:
3503 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3505 ______________________________________________________________________
3507 TODO:
3509 Add more DRM drivers.