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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
4 The following is a consolidated list of the kernel parameters as implemented
5 (mostly) by the __setup() macro and sorted into English Dictionary order
6 (defined as ignoring all punctuation and sorting digits before letters in a
7 case insensitive manner), and with descriptions where known.
9 Module parameters for loadable modules are specified only as the
10 parameter name with optional '=' and value as appropriate, such as:
12 modprobe usbcore blinkenlights=1
14 Module parameters for modules that are built into the kernel image
15 are specified on the kernel command line with the module name plus
16 '.' plus parameter name, with '=' and value if appropriate, such as:
18 usbcore.blinkenlights=1
20 Hyphens (dashes) and underscores are equivalent in parameter names, so
21 log_buf_len=1M print-fatal-signals=1
22 can also be entered as
23 log-buf-len=1M print_fatal_signals=1
26 This document may not be entirely up to date and comprehensive. The command
27 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
28 module. Loadable modules, after being loaded into the running kernel, also
29 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
30 parameters may be changed at runtime by the command
31 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
33 The parameters listed below are only valid if certain kernel build options were
34 enabled and if respective hardware is present. The text in square brackets at
35 the beginning of each description states the restrictions within which a
36 parameter is applicable:
38 ACPI ACPI support is enabled.
39 AGP AGP (Accelerated Graphics Port) is enabled.
40 ALSA ALSA sound support is enabled.
41 APIC APIC support is enabled.
42 APM Advanced Power Management support is enabled.
43 ARM ARM architecture is enabled.
44 AVR32 AVR32 architecture is enabled.
45 AX25 Appropriate AX.25 support is enabled.
46 BLACKFIN Blackfin architecture is enabled.
47 CLK Common clock infrastructure is enabled.
48 CMA Contiguous Memory Area support is enabled.
49 DRM Direct Rendering Management support is enabled.
50 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
51 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
52 EFI EFI Partitioning (GPT) is enabled
53 EIDE EIDE/ATAPI support is enabled.
54 EVM Extended Verification Module
55 FB The frame buffer device is enabled.
56 FTRACE Function tracing enabled.
57 GCOV GCOV profiling is enabled.
58 HW Appropriate hardware is enabled.
59 IA-64 IA-64 architecture is enabled.
60 IMA Integrity measurement architecture is enabled.
61 IOSCHED More than one I/O scheduler is enabled.
62 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
63 IPV6 IPv6 support is enabled.
64 ISAPNP ISA PnP code is enabled.
65 ISDN Appropriate ISDN support is enabled.
66 JOY Appropriate joystick support is enabled.
67 KGDB Kernel debugger support is enabled.
68 KVM Kernel Virtual Machine support is enabled.
69 LIBATA Libata driver is enabled
70 LP Printer support is enabled.
71 LOOP Loopback device support is enabled.
72 M68k M68k architecture is enabled.
73 These options have more detailed description inside of
74 Documentation/m68k/kernel-options.txt.
75 MDA MDA console support is enabled.
76 MIPS MIPS architecture is enabled.
77 MOUSE Appropriate mouse support is enabled.
78 MSI Message Signaled Interrupts (PCI).
79 MTD MTD (Memory Technology Device) support is enabled.
80 NET Appropriate network support is enabled.
81 NUMA NUMA support is enabled.
82 NFS Appropriate NFS support is enabled.
83 OSS OSS sound support is enabled.
84 PV_OPS A paravirtualized kernel is enabled.
85 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
86 PARISC The PA-RISC architecture is enabled.
87 PCI PCI bus support is enabled.
88 PCIE PCI Express support is enabled.
89 PCMCIA The PCMCIA subsystem is enabled.
90 PNP Plug & Play support is enabled.
91 PPC PowerPC architecture is enabled.
92 PPT Parallel port support is enabled.
93 PS2 Appropriate PS/2 support is enabled.
94 RAM RAM disk support is enabled.
95 S390 S390 architecture is enabled.
96 SCSI Appropriate SCSI support is enabled.
97 A lot of drivers have their options described inside
98 the Documentation/scsi/ sub-directory.
99 SECURITY Different security models are enabled.
100 SELINUX SELinux support is enabled.
101 APPARMOR AppArmor support is enabled.
102 SERIAL Serial support is enabled.
103 SH SuperH architecture is enabled.
104 SMP The kernel is an SMP kernel.
105 SPARC Sparc architecture is enabled.
106 SWSUSP Software suspend (hibernation) is enabled.
107 SUSPEND System suspend states are enabled.
108 TPM TPM drivers are enabled.
109 TS Appropriate touchscreen support is enabled.
110 UMS USB Mass Storage support is enabled.
111 USB USB support is enabled.
112 USBHID USB Human Interface Device support is enabled.
113 V4L Video For Linux support is enabled.
114 VMMIO Driver for memory mapped virtio devices is enabled.
115 VGA The VGA console has been enabled.
116 VT Virtual terminal support is enabled.
117 WDT Watchdog support is enabled.
118 XT IBM PC/XT MFM hard disk support is enabled.
119 X86-32 X86-32, aka i386 architecture is enabled.
120 X86-64 X86-64 architecture is enabled.
121 More X86-64 boot options can be found in
122 Documentation/x86/x86_64/boot-options.txt .
123 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
124 XEN Xen support is enabled
126 In addition, the following text indicates that the option:
128 BUGS= Relates to possible processor bugs on the said processor.
129 KNL Is a kernel start-up parameter.
130 BOOT Is a boot loader parameter.
132 Parameters denoted with BOOT are actually interpreted by the boot
133 loader, and have no meaning to the kernel directly.
134 Do not modify the syntax of boot loader parameters without extreme
135 need or coordination with <Documentation/x86/boot.txt>.
137 There are also arch-specific kernel-parameters not documented here.
138 See for example <Documentation/x86/x86_64/boot-options.txt>.
140 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
141 a trailing = on the name of any parameter states that that parameter will
142 be entered as an environment variable, whereas its absence indicates that
143 it will appear as a kernel argument readable via /proc/cmdline by programs
144 running once the system is up.
146 The number of kernel parameters is not limited, but the length of the
147 complete command line (parameters including spaces etc.) is limited to
148 a fixed number of characters. This limit depends on the architecture
149 and is between 256 and 4096 characters. It is defined in the file
150 ./include/asm/setup.h as COMMAND_LINE_SIZE.
152 Finally, the [KMG] suffix is commonly described after a number of kernel
153 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
154 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
155 bytes respectively. Such letter suffixes can also be entirely omitted.
158 acpi= [HW,ACPI,X86]
159 Advanced Configuration and Power Interface
160 Format: { force | off | strict | noirq | rsdt }
161 force -- enable ACPI if default was off
162 off -- disable ACPI if default was on
163 noirq -- do not use ACPI for IRQ routing
164 strict -- Be less tolerant of platforms that are not
165 strictly ACPI specification compliant.
166 rsdt -- prefer RSDT over (default) XSDT
167 copy_dsdt -- copy DSDT to memory
169 See also Documentation/power/runtime_pm.txt, pci=noacpi
171 acpi_rsdp= [ACPI,EFI,KEXEC]
172 Pass the RSDP address to the kernel, mostly used
173 on machines running EFI runtime service to boot the
174 second kernel for kdump.
176 acpi_apic_instance= [ACPI, IOAPIC]
177 Format: <int>
178 2: use 2nd APIC table, if available
179 1,0: use 1st APIC table
180 default: 0
182 acpi_backlight= [HW,ACPI]
183 acpi_backlight=vendor
184 acpi_backlight=video
185 If set to vendor, prefer vendor specific driver
186 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
187 of the ACPI video.ko driver.
189 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
190 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
191 Format: <int>
192 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
193 debug output. Bits in debug_layer correspond to a
194 _COMPONENT in an ACPI source file, e.g.,
195 #define _COMPONENT ACPI_PCI_COMPONENT
196 Bits in debug_level correspond to a level in
197 ACPI_DEBUG_PRINT statements, e.g.,
198 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
199 The debug_level mask defaults to "info". See
200 Documentation/acpi/debug.txt for more information about
201 debug layers and levels.
203 Enable processor driver info messages:
204 acpi.debug_layer=0x20000000
205 Enable PCI/PCI interrupt routing info messages:
206 acpi.debug_layer=0x400000
207 Enable AML "Debug" output, i.e., stores to the Debug
208 object while interpreting AML:
209 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
210 Enable all messages related to ACPI hardware:
211 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
213 Some values produce so much output that the system is
214 unusable. The "log_buf_len" parameter may be useful
215 if you need to capture more output.
217 acpi_irq_balance [HW,ACPI]
218 ACPI will balance active IRQs
219 default in APIC mode
221 acpi_irq_nobalance [HW,ACPI]
222 ACPI will not move active IRQs (default)
223 default in PIC mode
225 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
226 Format: <irq>,<irq>...
228 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
229 use by PCI
230 Format: <irq>,<irq>...
232 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
234 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
235 Format: To spoof as Windows 98: ="Microsoft Windows"
237 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
238 acpi_osi="string1" # add string1
239 acpi_osi="!string2" # remove string2
240 acpi_osi=!* # remove all strings
241 acpi_osi=! # disable all built-in OS vendor
242 strings
243 acpi_osi= # disable all strings
245 'acpi_osi=!' can be used in combination with single or
246 multiple 'acpi_osi="string1"' to support specific OS
247 vendor string(s). Note that such command can only
248 affect the default state of the OS vendor strings, thus
249 it cannot affect the default state of the feature group
250 strings and the current state of the OS vendor strings,
251 specifying it multiple times through kernel command line
252 is meaningless. This command is useful when one do not
253 care about the state of the feature group strings which
254 should be controlled by the OSPM.
255 Examples:
256 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
257 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
258 can make '_OSI("Windows 2000")' TRUE.
260 'acpi_osi=' cannot be used in combination with other
261 'acpi_osi=' command lines, the _OSI method will not
262 exist in the ACPI namespace. NOTE that such command can
263 only affect the _OSI support state, thus specifying it
264 multiple times through kernel command line is also
265 meaningless.
266 Examples:
267 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
268 FALSE.
270 'acpi_osi=!*' can be used in combination with single or
271 multiple 'acpi_osi="string1"' to support specific
272 string(s). Note that such command can affect the
273 current state of both the OS vendor strings and the
274 feature group strings, thus specifying it multiple times
275 through kernel command line is meaningful. But it may
276 still not able to affect the final state of a string if
277 there are quirks related to this string. This command
278 is useful when one want to control the state of the
279 feature group strings to debug BIOS issues related to
280 the OSPM features.
281 Examples:
282 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
283 '_OSI("Module Device")' FALSE.
284 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
285 '_OSI("Module Device")' TRUE.
286 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
287 equivalent to
288 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
289 and
290 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
291 they all will make '_OSI("Windows 2000")' TRUE.
293 acpi_pm_good [X86]
294 Override the pmtimer bug detection: force the kernel
295 to assume that this machine's pmtimer latches its value
296 and always returns good values.
298 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
299 Format: { level | edge | high | low }
301 acpi_serialize [HW,ACPI] force serialization of AML methods
303 acpi_skip_timer_override [HW,ACPI]
304 Recognize and ignore IRQ0/pin2 Interrupt Override.
305 For broken nForce2 BIOS resulting in XT-PIC timer.
307 acpi_sleep= [HW,ACPI] Sleep options
308 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
309 old_ordering, nonvs, sci_force_enable }
310 See Documentation/power/video.txt for information on
311 s3_bios and s3_mode.
312 s3_beep is for debugging; it makes the PC's speaker beep
313 as soon as the kernel's real-mode entry point is called.
314 s4_nohwsig prevents ACPI hardware signature from being
315 used during resume from hibernation.
316 old_ordering causes the ACPI 1.0 ordering of the _PTS
317 control method, with respect to putting devices into
318 low power states, to be enforced (the ACPI 2.0 ordering
319 of _PTS is used by default).
320 nonvs prevents the kernel from saving/restoring the
321 ACPI NVS memory during suspend/hibernation and resume.
322 sci_force_enable causes the kernel to set SCI_EN directly
323 on resume from S1/S3 (which is against the ACPI spec,
324 but some broken systems don't work without it).
326 acpi_use_timer_override [HW,ACPI]
327 Use timer override. For some broken Nvidia NF5 boards
328 that require a timer override, but don't have HPET
330 acpi_enforce_resources= [ACPI]
331 { strict | lax | no }
332 Check for resource conflicts between native drivers
333 and ACPI OperationRegions (SystemIO and SystemMemory
334 only). IO ports and memory declared in ACPI might be
335 used by the ACPI subsystem in arbitrary AML code and
336 can interfere with legacy drivers.
337 strict (default): access to resources claimed by ACPI
338 is denied; legacy drivers trying to access reserved
339 resources will fail to bind to device using them.
340 lax: access to resources claimed by ACPI is allowed;
341 legacy drivers trying to access reserved resources
342 will bind successfully but a warning message is logged.
343 no: ACPI OperationRegions are not marked as reserved,
344 no further checks are performed.
346 add_efi_memmap [EFI; X86] Include EFI memory map in
347 kernel's map of available physical RAM.
349 agp= [AGP]
350 { off | try_unsupported }
351 off: disable AGP support
352 try_unsupported: try to drive unsupported chipsets
353 (may crash computer or cause data corruption)
355 ALSA [HW,ALSA]
356 See Documentation/sound/alsa/alsa-parameters.txt
358 alignment= [KNL,ARM]
359 Allow the default userspace alignment fault handler
360 behaviour to be specified. Bit 0 enables warnings,
361 bit 1 enables fixups, and bit 2 sends a segfault.
363 align_va_addr= [X86-64]
364 Align virtual addresses by clearing slice [14:12] when
365 allocating a VMA at process creation time. This option
366 gives you up to 3% performance improvement on AMD F15h
367 machines (where it is enabled by default) for a
368 CPU-intensive style benchmark, and it can vary highly in
369 a microbenchmark depending on workload and compiler.
371 32: only for 32-bit processes
372 64: only for 64-bit processes
373 on: enable for both 32- and 64-bit processes
374 off: disable for both 32- and 64-bit processes
376 alloc_snapshot [FTRACE]
377 Allocate the ftrace snapshot buffer on boot up when the
378 main buffer is allocated. This is handy if debugging
379 and you need to use tracing_snapshot() on boot up, and
380 do not want to use tracing_snapshot_alloc() as it needs
381 to be done where GFP_KERNEL allocations are allowed.
383 amd_iommu= [HW,X86-64]
384 Pass parameters to the AMD IOMMU driver in the system.
385 Possible values are:
386 fullflush - enable flushing of IO/TLB entries when
387 they are unmapped. Otherwise they are
388 flushed before they will be reused, which
389 is a lot of faster
390 off - do not initialize any AMD IOMMU found in
391 the system
392 force_isolation - Force device isolation for all
393 devices. The IOMMU driver is not
394 allowed anymore to lift isolation
395 requirements as needed. This option
396 does not override iommu=pt
398 amd_iommu_dump= [HW,X86-64]
399 Enable AMD IOMMU driver option to dump the ACPI table
400 for AMD IOMMU. With this option enabled, AMD IOMMU
401 driver will print ACPI tables for AMD IOMMU during
402 IOMMU initialization.
404 amijoy.map= [HW,JOY] Amiga joystick support
405 Map of devices attached to JOY0DAT and JOY1DAT
406 Format: <a>,<b>
407 See also Documentation/input/joystick.txt
409 analog.map= [HW,JOY] Analog joystick and gamepad support
410 Specifies type or capabilities of an analog joystick
411 connected to one of 16 gameports
412 Format: <type1>,<type2>,..<type16>
414 apc= [HW,SPARC]
415 Power management functions (SPARCstation-4/5 + deriv.)
416 Format: noidle
417 Disable APC CPU standby support. SPARCstation-Fox does
418 not play well with APC CPU idle - disable it if you have
419 APC and your system crashes randomly.
421 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
422 Change the output verbosity whilst booting
423 Format: { quiet (default) | verbose | debug }
424 Change the amount of debugging information output
425 when initialising the APIC and IO-APIC components.
427 autoconf= [IPV6]
428 See Documentation/networking/ipv6.txt.
430 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
431 Limit apic dumping. The parameter defines the maximal
432 number of local apics being dumped. Also it is possible
433 to set it to "all" by meaning -- no limit here.
434 Format: { 1 (default) | 2 | ... | all }.
435 The parameter valid if only apic=debug or
436 apic=verbose is specified.
437 Example: apic=debug show_lapic=all
439 apm= [APM] Advanced Power Management
440 See header of arch/x86/kernel/apm_32.c.
442 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
443 Format: <io>,<irq>,<nodeID>
445 ataflop= [HW,M68k]
447 atarimouse= [HW,MOUSE] Atari Mouse
449 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
450 EzKey and similar keyboards
452 atkbd.reset= [HW] Reset keyboard during initialization
454 atkbd.set= [HW] Select keyboard code set
455 Format: <int> (2 = AT (default), 3 = PS/2)
457 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
458 keyboards
460 atkbd.softraw= [HW] Choose between synthetic and real raw mode
461 Format: <bool> (0 = real, 1 = synthetic (default))
463 atkbd.softrepeat= [HW]
464 Use software keyboard repeat
466 baycom_epp= [HW,AX25]
467 Format: <io>,<mode>
469 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
470 Format: <io>,<mode>
471 See header of drivers/net/hamradio/baycom_par.c.
473 baycom_ser_fdx= [HW,AX25]
474 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
475 Format: <io>,<irq>,<mode>[,<baud>]
476 See header of drivers/net/hamradio/baycom_ser_fdx.c.
478 baycom_ser_hdx= [HW,AX25]
479 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
480 Format: <io>,<irq>,<mode>
481 See header of drivers/net/hamradio/baycom_ser_hdx.c.
483 blkdevparts= Manual partition parsing of block device(s) for
484 embedded devices based on command line input.
485 See Documentation/block/cmdline-partition.txt
487 boot_delay= Milliseconds to delay each printk during boot.
488 Values larger than 10 seconds (10000) are changed to
489 no delay (0).
490 Format: integer
492 bootmem_debug [KNL] Enable bootmem allocator debug messages.
494 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
495 bttv.radio= Most important insmod options are available as
496 kernel args too.
497 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
498 bttv.tuner=
500 bulk_remove=off [PPC] This parameter disables the use of the pSeries
501 firmware feature for flushing multiple hpte entries
502 at a time.
504 c101= [NET] Moxa C101 synchronous serial card
506 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
507 Sometimes CPU hardware bugs make them report the cache
508 size incorrectly. The kernel will attempt work arounds
509 to fix known problems, but for some CPUs it is not
510 possible to determine what the correct size should be.
511 This option provides an override for these situations.
513 ccw_timeout_log [S390]
514 See Documentation/s390/CommonIO for details.
516 cgroup_disable= [KNL] Disable a particular controller
517 Format: {name of the controller(s) to disable}
518 {Currently supported controllers - "memory"}
520 checkreqprot [SELINUX] Set initial checkreqprot flag value.
521 Format: { "0" | "1" }
522 See security/selinux/Kconfig help text.
523 0 -- check protection applied by kernel (includes
524 any implied execute protection).
525 1 -- check protection requested by application.
526 Default value is set via a kernel config option.
527 Value can be changed at runtime via
528 /selinux/checkreqprot.
530 cio_ignore= [S390]
531 See Documentation/s390/CommonIO for details.
532 clk_ignore_unused
533 [CLK]
534 Keep all clocks already enabled by bootloader on,
535 even if no driver has claimed them. This is useful
536 for debug and development, but should not be
537 needed on a platform with proper driver support.
538 For more information, see Documentation/clk.txt.
540 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
541 [Deprecated]
542 Forces specified clocksource (if available) to be used
543 when calculating gettimeofday(). If specified
544 clocksource is not available, it defaults to PIT.
545 Format: { pit | tsc | cyclone | pmtmr }
547 clocksource= Override the default clocksource
548 Format: <string>
549 Override the default clocksource and use the clocksource
550 with the name specified.
551 Some clocksource names to choose from, depending on
552 the platform:
553 [all] jiffies (this is the base, fallback clocksource)
554 [ACPI] acpi_pm
555 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
556 pxa_timer,timer3,32k_counter,timer0_1
557 [AVR32] avr32
558 [X86-32] pit,hpet,tsc;
559 scx200_hrt on Geode; cyclone on IBM x440
560 [MIPS] MIPS
561 [PARISC] cr16
562 [S390] tod
563 [SH] SuperH
564 [SPARC64] tick
565 [X86-64] hpet,tsc
567 clearcpuid=BITNUM [X86]
568 Disable CPUID feature X for the kernel. See
569 arch/x86/include/asm/cpufeature.h for the valid bit
570 numbers. Note the Linux specific bits are not necessarily
571 stable over kernel options, but the vendor specific
572 ones should be.
573 Also note that user programs calling CPUID directly
574 or using the feature without checking anything
575 will still see it. This just prevents it from
576 being used by the kernel or shown in /proc/cpuinfo.
577 Also note the kernel might malfunction if you disable
578 some critical bits.
580 cma=nn[MG] [ARM,KNL]
581 Sets the size of kernel global memory area for contiguous
582 memory allocations. For more information, see
583 include/linux/dma-contiguous.h
585 cmo_free_hint= [PPC] Format: { yes | no }
586 Specify whether pages are marked as being inactive
587 when they are freed. This is used in CMO environments
588 to determine OS memory pressure for page stealing by
589 a hypervisor.
590 Default: yes
592 coherent_pool=nn[KMG] [ARM,KNL]
593 Sets the size of memory pool for coherent, atomic dma
594 allocations, by default set to 256K.
596 code_bytes [X86] How many bytes of object code to print
597 in an oops report.
598 Range: 0 - 8192
599 Default: 64
601 com20020= [HW,NET] ARCnet - COM20020 chipset
602 Format:
603 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
605 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
606 Format: <io>[,<irq>]
608 com90xx= [HW,NET]
609 ARCnet - COM90xx chipset (memory-mapped buffers)
610 Format: <io>[,<irq>[,<memstart>]]
612 condev= [HW,S390] console device
613 conmode=
615 console= [KNL] Output console device and options.
617 tty<n> Use the virtual console device <n>.
619 ttyS<n>[,options]
620 ttyUSB0[,options]
621 Use the specified serial port. The options are of
622 the form "bbbbpnf", where "bbbb" is the baud rate,
623 "p" is parity ("n", "o", or "e"), "n" is number of
624 bits, and "f" is flow control ("r" for RTS or
625 omit it). Default is "9600n8".
627 See Documentation/serial-console.txt for more
628 information. See
629 Documentation/networking/netconsole.txt for an
630 alternative.
632 uart[8250],io,<addr>[,options]
633 uart[8250],mmio,<addr>[,options]
634 Start an early, polled-mode console on the 8250/16550
635 UART at the specified I/O port or MMIO address,
636 switching to the matching ttyS device later. The
637 options are the same as for ttyS, above.
638 hvc<n> Use the hypervisor console device <n>. This is for
639 both Xen and PowerPC hypervisors.
641 If the device connected to the port is not a TTY but a braille
642 device, prepend "brl," before the device type, for instance
643 console=brl,ttyS0
644 For now, only VisioBraille is supported.
646 consoleblank= [KNL] The console blank (screen saver) timeout in
647 seconds. Defaults to 10*60 = 10mins. A value of 0
648 disables the blank timer.
650 coredump_filter=
651 [KNL] Change the default value for
652 /proc/<pid>/coredump_filter.
653 See also Documentation/filesystems/proc.txt.
655 cpuidle.off=1 [CPU_IDLE]
656 disable the cpuidle sub-system
658 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
659 Format:
660 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
662 crashkernel=size[KMG][@offset[KMG]]
663 [KNL] Using kexec, Linux can switch to a 'crash kernel'
664 upon panic. This parameter reserves the physical
665 memory region [offset, offset + size] for that kernel
666 image. If '@offset' is omitted, then a suitable offset
667 is selected automatically. Check
668 Documentation/kdump/kdump.txt for further details.
670 crashkernel=range1:size1[,range2:size2,...][@offset]
671 [KNL] Same as above, but depends on the memory
672 in the running system. The syntax of range is
673 start-[end] where start and end are both
674 a memory unit (amount[KMG]). See also
675 Documentation/kdump/kdump.txt for an example.
677 crashkernel=size[KMG],high
678 [KNL, x86_64] range could be above 4G. Allow kernel
679 to allocate physical memory region from top, so could
680 be above 4G if system have more than 4G ram installed.
681 Otherwise memory region will be allocated below 4G, if
682 available.
683 It will be ignored if crashkernel=X is specified.
684 crashkernel=size[KMG],low
685 [KNL, x86_64] range under 4G. When crashkernel=X,high
686 is passed, kernel could allocate physical memory region
687 above 4G, that cause second kernel crash on system
688 that require some amount of low memory, e.g. swiotlb
689 requires at least 64M+32K low memory. Kernel would
690 try to allocate 72M below 4G automatically.
691 This one let user to specify own low range under 4G
692 for second kernel instead.
693 0: to disable low allocation.
694 It will be ignored when crashkernel=X,high is not used
695 or memory reserved is below 4G.
697 cs89x0_dma= [HW,NET]
698 Format: <dma>
700 cs89x0_media= [HW,NET]
701 Format: { rj45 | aui | bnc }
703 dasd= [HW,NET]
704 See header of drivers/s390/block/dasd_devmap.c.
706 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
707 (one device per port)
708 Format: <port#>,<type>
709 See also Documentation/input/joystick-parport.txt
711 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
712 time. See Documentation/dynamic-debug-howto.txt for
713 details. Deprecated, see dyndbg.
715 debug [KNL] Enable kernel debugging (events log level).
717 debug_locks_verbose=
718 [KNL] verbose self-tests
719 Format=<0|1>
720 Print debugging info while doing the locking API
721 self-tests.
722 We default to 0 (no extra messages), setting it to
723 1 will print _a lot_ more information - normally
724 only useful to kernel developers.
726 debug_objects [KNL] Enable object debugging
728 no_debug_objects
729 [KNL] Disable object debugging
731 debug_guardpage_minorder=
732 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
733 parameter allows control of the order of pages that will
734 be intentionally kept free (and hence protected) by the
735 buddy allocator. Bigger value increase the probability
736 of catching random memory corruption, but reduce the
737 amount of memory for normal system use. The maximum
738 possible value is MAX_ORDER/2. Setting this parameter
739 to 1 or 2 should be enough to identify most random
740 memory corruption problems caused by bugs in kernel or
741 driver code when a CPU writes to (or reads from) a
742 random memory location. Note that there exists a class
743 of memory corruptions problems caused by buggy H/W or
744 F/W or by drivers badly programing DMA (basically when
745 memory is written at bus level and the CPU MMU is
746 bypassed) which are not detectable by
747 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
748 tracking down these problems.
750 debugpat [X86] Enable PAT debugging
752 decnet.addr= [HW,NET]
753 Format: <area>[,<node>]
754 See also Documentation/networking/decnet.txt.
756 default_hugepagesz=
757 [same as hugepagesz=] The size of the default
758 HugeTLB page size. This is the size represented by
759 the legacy /proc/ hugepages APIs, used for SHM, and
760 default size when mounting hugetlbfs filesystems.
761 Defaults to the default architecture's huge page size
762 if not specified.
764 dhash_entries= [KNL]
765 Set number of hash buckets for dentry cache.
767 digi= [HW,SERIAL]
768 IO parameters + enable/disable command.
770 digiepca= [HW,SERIAL]
771 See drivers/char/README.epca and
772 Documentation/serial/digiepca.txt.
774 disable= [IPV6]
775 See Documentation/networking/ipv6.txt.
777 disable_ddw [PPC/PSERIES]
778 Disable Dynamic DMA Window support. Use this if
779 to workaround buggy firmware.
781 disable_ipv6= [IPV6]
782 See Documentation/networking/ipv6.txt.
784 disable_mtrr_cleanup [X86]
785 The kernel tries to adjust MTRR layout from continuous
786 to discrete, to make X server driver able to add WB
787 entry later. This parameter disables that.
789 disable_mtrr_trim [X86, Intel and AMD only]
790 By default the kernel will trim any uncacheable
791 memory out of your available memory pool based on
792 MTRR settings. This parameter disables that behavior,
793 possibly causing your machine to run very slowly.
795 disable_timer_pin_1 [X86]
796 Disable PIN 1 of APIC timer
797 Can be useful to work around chipset bugs.
799 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
800 this option disables the debugging code at boot.
802 dma_debug_entries=<number>
803 This option allows to tune the number of preallocated
804 entries for DMA-API debugging code. One entry is
805 required per DMA-API allocation. Use this if the
806 DMA-API debugging code disables itself because the
807 architectural default is too low.
809 dma_debug_driver=<driver_name>
810 With this option the DMA-API debugging driver
811 filter feature can be enabled at boot time. Just
812 pass the driver to filter for as the parameter.
813 The filter can be disabled or changed to another
814 driver later using sysfs.
816 drm_kms_helper.edid_firmware=[<connector>:]<file>
817 Broken monitors, graphic adapters and KVMs may
818 send no or incorrect EDID data sets. This parameter
819 allows to specify an EDID data set in the
820 /lib/firmware directory that is used instead.
821 Generic built-in EDID data sets are used, if one of
822 edid/1024x768.bin, edid/1280x1024.bin,
823 edid/1680x1050.bin, or edid/1920x1080.bin is given
824 and no file with the same name exists. Details and
825 instructions how to build your own EDID data are
826 available in Documentation/EDID/HOWTO.txt. An EDID
827 data set will only be used for a particular connector,
828 if its name and a colon are prepended to the EDID
829 name.
831 dscc4.setup= [NET]
833 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
834 module.dyndbg[="val"]
835 Enable debug messages at boot time. See
836 Documentation/dynamic-debug-howto.txt for details.
838 earlycon= [KNL] Output early console device and options.
839 uart[8250],io,<addr>[,options]
840 uart[8250],mmio,<addr>[,options]
841 uart[8250],mmio32,<addr>[,options]
842 Start an early, polled-mode console on the 8250/16550
843 UART at the specified I/O port or MMIO address.
844 MMIO inter-register address stride is either 8-bit
845 (mmio) or 32-bit (mmio32).
846 The options are the same as for ttyS, above.
848 earlyprintk= [X86,SH,BLACKFIN,ARM]
849 earlyprintk=vga
850 earlyprintk=xen
851 earlyprintk=serial[,ttySn[,baudrate]]
852 earlyprintk=serial[,0x...[,baudrate]]
853 earlyprintk=ttySn[,baudrate]
854 earlyprintk=dbgp[debugController#]
856 earlyprintk is useful when the kernel crashes before
857 the normal console is initialized. It is not enabled by
858 default because it has some cosmetic problems.
860 Append ",keep" to not disable it when the real console
861 takes over.
863 Only vga or serial or usb debug port at a time.
865 Currently only ttyS0 and ttyS1 may be specified by
866 name. Other I/O ports may be explicitly specified
867 on some architectures (x86 and arm at least) by
868 replacing ttySn with an I/O port address, like this:
869 earlyprintk=serial,0x1008,115200
870 You can find the port for a given device in
871 /proc/tty/driver/serial:
872 2: uart:ST16650V2 port:00001008 irq:18 ...
874 Interaction with the standard serial driver is not
875 very good.
877 The VGA output is eventually overwritten by the real
878 console.
880 The xen output can only be used by Xen PV guests.
882 ekgdboc= [X86,KGDB] Allow early kernel console debugging
883 ekgdboc=kbd
885 This is designed to be used in conjunction with
886 the boot argument: earlyprintk=vga
888 edd= [EDD]
889 Format: {"off" | "on" | "skip[mbr]"}
891 efi_no_storage_paranoia [EFI; X86]
892 Using this parameter you can use more than 50% of
893 your efi variable storage. Use this parameter only if
894 you are really sure that your UEFI does sane gc and
895 fulfills the spec otherwise your board may brick.
897 eisa_irq_edge= [PARISC,HW]
898 See header of drivers/parisc/eisa.c.
900 elanfreq= [X86-32]
901 See comment before function elanfreq_setup() in
902 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
904 elevator= [IOSCHED]
905 Format: {"cfq" | "deadline" | "noop"}
906 See Documentation/block/cfq-iosched.txt and
907 Documentation/block/deadline-iosched.txt for details.
909 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
910 Specifies physical address of start of kernel core
911 image elf header and optionally the size. Generally
912 kexec loader will pass this option to capture kernel.
913 See Documentation/kdump/kdump.txt for details.
915 enable_mtrr_cleanup [X86]
916 The kernel tries to adjust MTRR layout from continuous
917 to discrete, to make X server driver able to add WB
918 entry later. This parameter enables that.
920 enable_timer_pin_1 [X86]
921 Enable PIN 1 of APIC timer
922 Can be useful to work around chipset bugs
923 (in particular on some ATI chipsets).
924 The kernel tries to set a reasonable default.
926 enforcing [SELINUX] Set initial enforcing status.
927 Format: {"0" | "1"}
928 See security/selinux/Kconfig help text.
929 0 -- permissive (log only, no denials).
930 1 -- enforcing (deny and log).
931 Default value is 0.
932 Value can be changed at runtime via /selinux/enforce.
934 erst_disable [ACPI]
935 Disable Error Record Serialization Table (ERST)
936 support.
938 ether= [HW,NET] Ethernet cards parameters
939 This option is obsoleted by the "netdev=" option, which
940 has equivalent usage. See its documentation for details.
942 evm= [EVM]
943 Format: { "fix" }
944 Permit 'security.evm' to be updated regardless of
945 current integrity status.
947 failslab=
948 fail_page_alloc=
949 fail_make_request=[KNL]
950 General fault injection mechanism.
951 Format: <interval>,<probability>,<space>,<times>
952 See also Documentation/fault-injection/.
954 floppy= [HW]
955 See Documentation/blockdev/floppy.txt.
957 force_pal_cache_flush
958 [IA-64] Avoid check_sal_cache_flush which may hang on
959 buggy SAL_CACHE_FLUSH implementations. Using this
960 parameter will force ia64_sal_cache_flush to call
961 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
963 ftrace=[tracer]
964 [FTRACE] will set and start the specified tracer
965 as early as possible in order to facilitate early
966 boot debugging.
968 ftrace_dump_on_oops[=orig_cpu]
969 [FTRACE] will dump the trace buffers on oops.
970 If no parameter is passed, ftrace will dump
971 buffers of all CPUs, but if you pass orig_cpu, it will
972 dump only the buffer of the CPU that triggered the
973 oops.
975 ftrace_filter=[function-list]
976 [FTRACE] Limit the functions traced by the function
977 tracer at boot up. function-list is a comma separated
978 list of functions. This list can be changed at run
979 time by the set_ftrace_filter file in the debugfs
980 tracing directory.
982 ftrace_notrace=[function-list]
983 [FTRACE] Do not trace the functions specified in
984 function-list. This list can be changed at run time
985 by the set_ftrace_notrace file in the debugfs
986 tracing directory.
988 ftrace_graph_filter=[function-list]
989 [FTRACE] Limit the top level callers functions traced
990 by the function graph tracer at boot up.
991 function-list is a comma separated list of functions
992 that can be changed at run time by the
993 set_graph_function file in the debugfs tracing directory.
995 gamecon.map[2|3]=
996 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
997 support via parallel port (up to 5 devices per port)
998 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
999 See also Documentation/input/joystick-parport.txt
1001 gamma= [HW,DRM]
1003 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1004 Format: off | on
1005 default: on
1007 gcov_persist= [GCOV] When non-zero (default), profiling data for
1008 kernel modules is saved and remains accessible via
1009 debugfs, even when the module is unloaded/reloaded.
1010 When zero, profiling data is discarded and associated
1011 debugfs files are removed at module unload time.
1013 gpt [EFI] Forces disk with valid GPT signature but
1014 invalid Protective MBR to be treated as GPT.
1016 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1017 the "Enable 0" bit of the configuration register.
1018 Format: 0 | 1
1019 Default: 0
1020 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1021 the "Enable 0" bit of the configuration register.
1022 Format: 0 | 1
1023 Default: 0
1024 grcan.select= [HW] Select which physical interface to use.
1025 Format: 0 | 1
1026 Default: 0
1027 grcan.txsize= [HW] Sets the size of the tx buffer.
1028 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1029 Default: 1024
1030 grcan.rxsize= [HW] Sets the size of the rx buffer.
1031 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1032 Default: 1024
1034 hashdist= [KNL,NUMA] Large hashes allocated during boot
1035 are distributed across NUMA nodes. Defaults on
1036 for 64-bit NUMA, off otherwise.
1037 Format: 0 | 1 (for off | on)
1039 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1041 hd= [EIDE] (E)IDE hard drive subsystem geometry
1042 Format: <cyl>,<head>,<sect>
1044 hest_disable [ACPI]
1045 Disable Hardware Error Source Table (HEST) support;
1046 corresponding firmware-first mode error processing
1047 logic will be disabled.
1049 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1050 size of <nn>. This works even on boxes that have no
1051 highmem otherwise. This also works to reduce highmem
1052 size on bigger boxes.
1054 highres= [KNL] Enable/disable high resolution timer mode.
1055 Valid parameters: "on", "off"
1056 Default: "on"
1058 hisax= [HW,ISDN]
1059 See Documentation/isdn/README.HiSax.
1061 hlt [BUGS=ARM,SH]
1063 hpet= [X86-32,HPET] option to control HPET usage
1064 Format: { enable (default) | disable | force |
1065 verbose }
1066 disable: disable HPET and use PIT instead
1067 force: allow force enabled of undocumented chips (ICH4,
1068 VIA, nVidia)
1069 verbose: show contents of HPET registers during setup
1071 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1072 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1073 On x86-64 and powerpc, this option can be specified
1074 multiple times interleaved with hugepages= to reserve
1075 huge pages of different sizes. Valid pages sizes on
1076 x86-64 are 2M (when the CPU supports "pse") and 1G
1077 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1078 Note that 1GB pages can only be allocated at boot time
1079 using hugepages= and not freed afterwards.
1081 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1082 terminal devices. Valid values: 0..8
1083 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1084 If specified, z/VM IUCV HVC accepts connections
1085 from listed z/VM user IDs only.
1087 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1088 hardware thread id mappings.
1089 Format: <cpu>:<hwthread>
1091 keep_bootcon [KNL]
1092 Do not unregister boot console at start. This is only
1093 useful for debugging when something happens in the window
1094 between unregistering the boot console and initializing
1095 the real console.
1097 i2c_bus= [HW] Override the default board specific I2C bus speed
1098 or register an additional I2C bus that is not
1099 registered from board initialization code.
1100 Format:
1101 <bus_id>,<clkrate>
1103 i8042.debug [HW] Toggle i8042 debug mode
1104 i8042.direct [HW] Put keyboard port into non-translated mode
1105 i8042.dumbkbd [HW] Pretend that controller can only read data from
1106 keyboard and cannot control its state
1107 (Don't attempt to blink the leds)
1108 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1109 i8042.nokbd [HW] Don't check/create keyboard port
1110 i8042.noloop [HW] Disable the AUX Loopback command while probing
1111 for the AUX port
1112 i8042.nomux [HW] Don't check presence of an active multiplexing
1113 controller
1114 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1115 controllers
1116 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1117 i8042.reset [HW] Reset the controller during init and cleanup
1118 i8042.unlock [HW] Unlock (ignore) the keylock
1120 i810= [HW,DRM]
1122 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1123 indicates that the driver is running on unsupported
1124 hardware.
1125 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1126 does not match list of supported models.
1127 i8k.power_status
1128 [HW] Report power status in /proc/i8k
1129 (disabled by default)
1130 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1131 capability is set.
1133 i915.invert_brightness=
1134 [DRM] Invert the sense of the variable that is used to
1135 set the brightness of the panel backlight. Normally a
1136 brightness value of 0 indicates backlight switched off,
1137 and the maximum of the brightness value sets the backlight
1138 to maximum brightness. If this parameter is set to 0
1139 (default) and the machine requires it, or this parameter
1140 is set to 1, a brightness value of 0 sets the backlight
1141 to maximum brightness, and the maximum of the brightness
1142 value switches the backlight off.
1143 -1 -- never invert brightness
1144 0 -- machine default
1145 1 -- force brightness inversion
1147 icn= [HW,ISDN]
1148 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1150 ide-core.nodma= [HW] (E)IDE subsystem
1151 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1152 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1153 .cdrom .chs .ignore_cable are additional options
1154 See Documentation/ide/ide.txt.
1156 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1157 Claim all unknown PCI IDE storage controllers.
1159 idle= [X86]
1160 Format: idle=poll, idle=halt, idle=nomwait
1161 Poll forces a polling idle loop that can slightly
1162 improve the performance of waking up a idle CPU, but
1163 will use a lot of power and make the system run hot.
1164 Not recommended.
1165 idle=halt: Halt is forced to be used for CPU idle.
1166 In such case C2/C3 won't be used again.
1167 idle=nomwait: Disable mwait for CPU C-states
1169 ignore_loglevel [KNL]
1170 Ignore loglevel setting - this will print /all/
1171 kernel messages to the console. Useful for debugging.
1172 We also add it as printk module parameter, so users
1173 could change it dynamically, usually by
1174 /sys/module/printk/parameters/ignore_loglevel.
1176 ihash_entries= [KNL]
1177 Set number of hash buckets for inode cache.
1179 ima_appraise= [IMA] appraise integrity measurements
1180 Format: { "off" | "enforce" | "fix" }
1181 default: "enforce"
1183 ima_appraise_tcb [IMA]
1184 The builtin appraise policy appraises all files
1185 owned by uid=0.
1187 ima_hash= [IMA]
1188 Format: { "sha1" | "md5" }
1189 default: "sha1"
1191 ima_tcb [IMA]
1192 Load a policy which meets the needs of the Trusted
1193 Computing Base. This means IMA will measure all
1194 programs exec'd, files mmap'd for exec, and all files
1195 opened for read by uid=0.
1197 init= [KNL]
1198 Format: <full_path>
1199 Run specified binary instead of /sbin/init as init
1200 process.
1202 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1203 for working out where the kernel is dying during
1204 startup.
1206 initrd= [BOOT] Specify the location of the initial ramdisk
1208 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1209 Format: <irq>
1211 int_pln_enable [x86] Enable power limit notification interrupt
1213 integrity_audit=[IMA]
1214 Format: { "0" | "1" }
1215 0 -- basic integrity auditing messages. (Default)
1216 1 -- additional integrity auditing messages.
1218 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1219 on
1220 Enable intel iommu driver.
1221 off
1222 Disable intel iommu driver.
1223 igfx_off [Default Off]
1224 By default, gfx is mapped as normal device. If a gfx
1225 device has a dedicated DMAR unit, the DMAR unit is
1226 bypassed by not enabling DMAR with this option. In
1227 this case, gfx device will use physical address for
1228 DMA.
1229 forcedac [x86_64]
1230 With this option iommu will not optimize to look
1231 for io virtual address below 32-bit forcing dual
1232 address cycle on pci bus for cards supporting greater
1233 than 32-bit addressing. The default is to look
1234 for translation below 32-bit and if not available
1235 then look in the higher range.
1236 strict [Default Off]
1237 With this option on every unmap_single operation will
1238 result in a hardware IOTLB flush operation as opposed
1239 to batching them for performance.
1240 sp_off [Default Off]
1241 By default, super page will be supported if Intel IOMMU
1242 has the capability. With this option, super page will
1243 not be supported.
1245 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1246 0 disables intel_idle and fall back on acpi_idle.
1247 1 to 6 specify maximum depth of C-state.
1249 intel_pstate= [X86]
1250 disable
1251 Do not enable intel_pstate as the default
1252 scaling driver for the supported processors
1254 intremap= [X86-64, Intel-IOMMU]
1255 on enable Interrupt Remapping (default)
1256 off disable Interrupt Remapping
1257 nosid disable Source ID checking
1258 no_x2apic_optout
1259 BIOS x2APIC opt-out request will be ignored
1261 iomem= Disable strict checking of access to MMIO memory
1262 strict regions from userspace.
1263 relaxed
1265 iommu= [x86]
1266 off
1267 force
1268 noforce
1269 biomerge
1270 panic
1271 nopanic
1272 merge
1273 nomerge
1274 forcesac
1275 soft
1276 pt [x86, IA-64]
1279 io7= [HW] IO7 for Marvel based alpha systems
1280 See comment before marvel_specify_io7 in
1281 arch/alpha/kernel/core_marvel.c.
1283 io_delay= [X86] I/O delay method
1284 0x80
1285 Standard port 0x80 based delay
1286 0xed
1287 Alternate port 0xed based delay (needed on some systems)
1288 udelay
1289 Simple two microseconds delay
1290 none
1291 No delay
1293 ip= [IP_PNP]
1294 See Documentation/filesystems/nfs/nfsroot.txt.
1296 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1297 See comment before ip2_setup() in
1298 drivers/char/ip2/ip2base.c.
1300 irqfixup [HW]
1301 When an interrupt is not handled search all handlers
1302 for it. Intended to get systems with badly broken
1303 firmware running.
1305 irqpoll [HW]
1306 When an interrupt is not handled search all handlers
1307 for it. Also check all handlers each timer
1308 interrupt. Intended to get systems with badly broken
1309 firmware running.
1311 isapnp= [ISAPNP]
1312 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1314 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1315 Format:
1316 <cpu number>,...,<cpu number>
1317 or
1318 <cpu number>-<cpu number>
1319 (must be a positive range in ascending order)
1320 or a mixture
1321 <cpu number>,...,<cpu number>-<cpu number>
1323 This option can be used to specify one or more CPUs
1324 to isolate from the general SMP balancing and scheduling
1325 algorithms. You can move a process onto or off an
1326 "isolated" CPU via the CPU affinity syscalls or cpuset.
1327 <cpu number> begins at 0 and the maximum value is
1328 "number of CPUs in system - 1".
1330 This option is the preferred way to isolate CPUs. The
1331 alternative -- manually setting the CPU mask of all
1332 tasks in the system -- can cause problems and
1333 suboptimal load balancer performance.
1335 iucv= [HW,NET]
1337 ivrs_ioapic [HW,X86_64]
1338 Provide an override to the IOAPIC-ID<->DEVICE-ID
1339 mapping provided in the IVRS ACPI table. For
1340 example, to map IOAPIC-ID decimal 10 to
1341 PCI device 00:14.0 write the parameter as:
1342 ivrs_ioapic[10]=00:14.0
1344 ivrs_hpet [HW,X86_64]
1345 Provide an override to the HPET-ID<->DEVICE-ID
1346 mapping provided in the IVRS ACPI table. For
1347 example, to map HPET-ID decimal 0 to
1348 PCI device 00:14.0 write the parameter as:
1349 ivrs_hpet[0]=00:14.0
1351 js= [HW,JOY] Analog joystick
1352 See Documentation/input/joystick.txt.
1354 keepinitrd [HW,ARM]
1356 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1357 specifies the amount of memory usable by the kernel
1358 for non-movable allocations. The requested amount is
1359 spread evenly throughout all nodes in the system. The
1360 remaining memory in each node is used for Movable
1361 pages. In the event, a node is too small to have both
1362 kernelcore and Movable pages, kernelcore pages will
1363 take priority and other nodes will have a larger number
1364 of Movable pages. The Movable zone is used for the
1365 allocation of pages that may be reclaimed or moved
1366 by the page migration subsystem. This means that
1367 HugeTLB pages may not be allocated from this zone.
1368 Note that allocations like PTEs-from-HighMem still
1369 use the HighMem zone if it exists, and the Normal
1370 zone if it does not.
1372 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1373 Format: <Controller#>[,poll interval]
1374 The controller # is the number of the ehci usb debug
1375 port as it is probed via PCI. The poll interval is
1376 optional and is the number seconds in between
1377 each poll cycle to the debug port in case you need
1378 the functionality for interrupting the kernel with
1379 gdb or control-c on the dbgp connection. When
1380 not using this parameter you use sysrq-g to break into
1381 the kernel debugger.
1383 kgdboc= [KGDB,HW] kgdb over consoles.
1384 Requires a tty driver that supports console polling,
1385 or a supported polling keyboard driver (non-usb).
1386 Serial only format: <serial_device>[,baud]
1387 keyboard only format: kbd
1388 keyboard and serial format: kbd,<serial_device>[,baud]
1389 Optional Kernel mode setting:
1390 kms, kbd format: kms,kbd
1391 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1393 kgdbwait [KGDB] Stop kernel execution and enter the
1394 kernel debugger at the earliest opportunity.
1396 kmac= [MIPS] korina ethernet MAC address.
1397 Configure the RouterBoard 532 series on-chip
1398 Ethernet adapter MAC address.
1400 kmemleak= [KNL] Boot-time kmemleak enable/disable
1401 Valid arguments: on, off
1402 Default: on
1404 kstack=N [X86] Print N words from the kernel stack
1405 in oops dumps.
1407 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1408 Default is 0 (don't ignore, but inject #GP)
1410 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1411 KVM MMU at runtime.
1412 Default is 0 (off)
1414 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1415 Default is 1 (enabled)
1417 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1418 for all guests.
1419 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1421 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1422 (virtualized MMU) support on capable Intel chips.
1423 Default is 1 (enabled)
1425 kvm-intel.emulate_invalid_guest_state=
1426 [KVM,Intel] Enable emulation of invalid guest states
1427 Default is 0 (disabled)
1429 kvm-intel.flexpriority=
1430 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1431 Default is 1 (enabled)
1433 kvm-intel.nested=
1434 [KVM,Intel] Enable VMX nesting (nVMX).
1435 Default is 0 (disabled)
1437 kvm-intel.unrestricted_guest=
1438 [KVM,Intel] Disable unrestricted guest feature
1439 (virtualized real and unpaged mode) on capable
1440 Intel chips. Default is 1 (enabled)
1442 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1443 feature (tagged TLBs) on capable Intel chips.
1444 Default is 1 (enabled)
1446 l2cr= [PPC]
1448 l3cr= [PPC]
1450 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1451 disabled it.
1453 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1454 value for LAPIC timer one-shot implementation. Default
1455 back to the programmable timer unit in the LAPIC.
1457 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1458 in C2 power state.
1460 libata.dma= [LIBATA] DMA control
1461 libata.dma=0 Disable all PATA and SATA DMA
1462 libata.dma=1 PATA and SATA Disk DMA only
1463 libata.dma=2 ATAPI (CDROM) DMA only
1464 libata.dma=4 Compact Flash DMA only
1465 Combinations also work, so libata.dma=3 enables DMA
1466 for disks and CDROMs, but not CFs.
1468 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1469 libata.ignore_hpa=0 keep BIOS limits (default)
1470 libata.ignore_hpa=1 ignore limits, using full disk
1472 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1473 when set.
1474 Format: <int>
1476 libata.force= [LIBATA] Force configurations. The format is comma
1477 separated list of "[ID:]VAL" where ID is
1478 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1479 matching port, link or device. Basically, it matches
1480 the ATA ID string printed on console by libata. If
1481 the whole ID part is omitted, the last PORT and DEVICE
1482 values are used. If ID hasn't been specified yet, the
1483 configuration applies to all ports, links and devices.
1485 If only DEVICE is omitted, the parameter applies to
1486 the port and all links and devices behind it. DEVICE
1487 number of 0 either selects the first device or the
1488 first fan-out link behind PMP device. It does not
1489 select the host link. DEVICE number of 15 selects the
1490 host link and device attached to it.
1492 The VAL specifies the configuration to force. As long
1493 as there's no ambiguity shortcut notation is allowed.
1494 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1495 The following configurations can be forced.
1497 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1498 Any ID with matching PORT is used.
1500 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1502 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1503 udma[/][16,25,33,44,66,100,133] notation is also
1504 allowed.
1506 * [no]ncq: Turn on or off NCQ.
1508 * nohrst, nosrst, norst: suppress hard, soft
1509 and both resets.
1511 * rstonce: only attempt one reset during
1512 hot-unplug link recovery
1514 * dump_id: dump IDENTIFY data.
1516 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1518 If there are multiple matching configurations changing
1519 the same attribute, the last one is used.
1521 memblock=debug [KNL] Enable memblock debug messages.
1523 load_ramdisk= [RAM] List of ramdisks to load from floppy
1524 See Documentation/blockdev/ramdisk.txt.
1526 lockd.nlm_grace_period=P [NFS] Assign grace period.
1527 Format: <integer>
1529 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1530 Format: <integer>
1532 lockd.nlm_timeout=T [NFS] Assign timeout value.
1533 Format: <integer>
1535 lockd.nlm_udpport=M [NFS] Assign UDP port.
1536 Format: <integer>
1538 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1539 Format: <irq>
1541 loglevel= All Kernel Messages with a loglevel smaller than the
1542 console loglevel will be printed to the console. It can
1543 also be changed with klogd or other programs. The
1544 loglevels are defined as follows:
1546 0 (KERN_EMERG) system is unusable
1547 1 (KERN_ALERT) action must be taken immediately
1548 2 (KERN_CRIT) critical conditions
1549 3 (KERN_ERR) error conditions
1550 4 (KERN_WARNING) warning conditions
1551 5 (KERN_NOTICE) normal but significant condition
1552 6 (KERN_INFO) informational
1553 7 (KERN_DEBUG) debug-level messages
1555 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1556 in bytes. n must be a power of two. The default
1557 size is set in the kernel config file.
1559 logo.nologo [FB] Disables display of the built-in Linux logo.
1560 This may be used to provide more screen space for
1561 kernel log messages and is useful when debugging
1562 kernel boot problems.
1564 lp=0 [LP] Specify parallel ports to use, e.g,
1565 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1566 lp=reset first parallel port). 'lp=0' disables the
1567 lp=auto printer driver. 'lp=reset' (which can be
1568 specified in addition to the ports) causes
1569 attached printers to be reset. Using
1570 lp=port1,port2,... specifies the parallel ports
1571 to associate lp devices with, starting with
1572 lp0. A port specification may be 'none' to skip
1573 that lp device, or a parport name such as
1574 'parport0'. Specifying 'lp=auto' instead of a
1575 port specification list means that device IDs
1576 from each port should be examined, to see if
1577 an IEEE 1284-compliant printer is attached; if
1578 so, the driver will manage that printer.
1579 See also header of drivers/char/lp.c.
1581 lpj=n [KNL]
1582 Sets loops_per_jiffy to given constant, thus avoiding
1583 time-consuming boot-time autodetection (up to 250 ms per
1584 CPU). 0 enables autodetection (default). To determine
1585 the correct value for your kernel, boot with normal
1586 autodetection and see what value is printed. Note that
1587 on SMP systems the preset will be applied to all CPUs,
1588 which is likely to cause problems if your CPUs need
1589 significantly divergent settings. An incorrect value
1590 will cause delays in the kernel to be wrong, leading to
1591 unpredictable I/O errors and other breakage. Although
1592 unlikely, in the extreme case this might damage your
1593 hardware.
1595 ltpc= [NET]
1596 Format: <io>,<irq>,<dma>
1598 machvec= [IA-64] Force the use of a particular machine-vector
1599 (machvec) in a generic kernel.
1600 Example: machvec=hpzx1_swiotlb
1602 machtype= [Loongson] Share the same kernel image file between different
1603 yeeloong laptop.
1604 Example: machtype=lemote-yeeloong-2f-7inch
1606 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1607 than or equal to this physical address is ignored.
1609 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1610 should make use of. maxcpus=n : n >= 0 limits the
1611 kernel to using 'n' processors. n=0 is a special case,
1612 it is equivalent to "nosmp", which also disables
1613 the IO APIC.
1615 max_loop= [LOOP] The number of loop block devices that get
1616 (loop.max_loop) unconditionally pre-created at init time. The default
1617 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1618 of statically allocating a predefined number, loop
1619 devices can be requested on-demand with the
1620 /dev/loop-control interface.
1622 mce [X86-32] Machine Check Exception
1624 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1626 md= [HW] RAID subsystems devices and level
1627 See Documentation/md.txt.
1629 mdacon= [MDA]
1630 Format: <first>,<last>
1631 Specifies range of consoles to be captured by the MDA.
1633 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1634 Amount of memory to be used when the kernel is not able
1635 to see the whole system memory or for test.
1636 [X86] Work as limiting max address. Use together
1637 with memmap= to avoid physical address space collisions.
1638 Without memmap= PCI devices could be placed at addresses
1639 belonging to unused RAM.
1641 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1642 memory.
1644 memchunk=nn[KMG]
1645 [KNL,SH] Allow user to override the default size for
1646 per-device physically contiguous DMA buffers.
1648 memmap=exactmap [KNL,X86] Enable setting of an exact
1649 E820 memory map, as specified by the user.
1650 Such memmap=exactmap lines can be constructed based on
1651 BIOS output or other requirements. See the memmap=nn@ss
1652 option description.
1654 memmap=nn[KMG]@ss[KMG]
1655 [KNL] Force usage of a specific region of memory
1656 Region of memory to be used, from ss to ss+nn.
1658 memmap=nn[KMG]#ss[KMG]
1659 [KNL,ACPI] Mark specific memory as ACPI data.
1660 Region of memory to be used, from ss to ss+nn.
1662 memmap=nn[KMG]$ss[KMG]
1663 [KNL,ACPI] Mark specific memory as reserved.
1664 Region of memory to be used, from ss to ss+nn.
1665 Example: Exclude memory from 0x18690000-0x1869ffff
1666 memmap=64K$0x18690000
1667 or
1668 memmap=0x10000$0x18690000
1670 memory_corruption_check=0/1 [X86]
1671 Some BIOSes seem to corrupt the first 64k of
1672 memory when doing things like suspend/resume.
1673 Setting this option will scan the memory
1674 looking for corruption. Enabling this will
1675 both detect corruption and prevent the kernel
1676 from using the memory being corrupted.
1677 However, its intended as a diagnostic tool; if
1678 repeatable BIOS-originated corruption always
1679 affects the same memory, you can use memmap=
1680 to prevent the kernel from using that memory.
1682 memory_corruption_check_size=size [X86]
1683 By default it checks for corruption in the low
1684 64k, making this memory unavailable for normal
1685 use. Use this parameter to scan for
1686 corruption in more or less memory.
1688 memory_corruption_check_period=seconds [X86]
1689 By default it checks for corruption every 60
1690 seconds. Use this parameter to check at some
1691 other rate. 0 disables periodic checking.
1693 memtest= [KNL,X86] Enable memtest
1694 Format: <integer>
1695 default : 0 <disable>
1696 Specifies the number of memtest passes to be
1697 performed. Each pass selects another test
1698 pattern from a given set of patterns. Memtest
1699 fills the memory with this pattern, validates
1700 memory contents and reserves bad memory
1701 regions that are detected.
1703 meye.*= [HW] Set MotionEye Camera parameters
1704 See Documentation/video4linux/meye.txt.
1706 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1707 Multi-Function General Purpose Timers on AMD Geode
1708 platforms.
1710 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1711 the BIOS has incorrectly applied a workaround. TinyBIOS
1712 version 0.98 is known to be affected, 0.99 fixes the
1713 problem by letting the user disable the workaround.
1715 mga= [HW,DRM]
1717 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1718 physical address is ignored.
1720 mini2440= [ARM,HW,KNL]
1721 Format:[0..2][b][c][t]
1722 Default: "0tb"
1723 MINI2440 configuration specification:
1724 0 - The attached screen is the 3.5" TFT
1725 1 - The attached screen is the 7" TFT
1726 2 - The VGA Shield is attached (1024x768)
1727 Leaving out the screen size parameter will not load
1728 the TFT driver, and the framebuffer will be left
1729 unconfigured.
1730 b - Enable backlight. The TFT backlight pin will be
1731 linked to the kernel VESA blanking code and a GPIO
1732 LED. This parameter is not necessary when using the
1733 VGA shield.
1734 c - Enable the s3c camera interface.
1735 t - Reserved for enabling touchscreen support. The
1736 touchscreen support is not enabled in the mainstream
1737 kernel as of 2.6.30, a preliminary port can be found
1738 in the "bleeding edge" mini2440 support kernel at
1739 http://repo.or.cz/w/linux-2.6/mini2440.git
1741 mminit_loglevel=
1742 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1743 parameter allows control of the logging verbosity for
1744 the additional memory initialisation checks. A value
1745 of 0 disables mminit logging and a level of 4 will
1746 log everything. Information is printed at KERN_DEBUG
1747 so loglevel=8 may also need to be specified.
1749 module.sig_enforce
1750 [KNL] When CONFIG_MODULE_SIG is set, this means that
1751 modules without (valid) signatures will fail to load.
1752 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1753 is always true, so this option does nothing.
1755 mousedev.tap_time=
1756 [MOUSE] Maximum time between finger touching and
1757 leaving touchpad surface for touch to be considered
1758 a tap and be reported as a left button click (for
1759 touchpads working in absolute mode only).
1760 Format: <msecs>
1761 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1762 reporting absolute coordinates, such as tablets
1763 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1764 reporting absolute coordinates, such as tablets
1766 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1767 is similar to kernelcore except it specifies the
1768 amount of memory used for migratable allocations.
1769 If both kernelcore and movablecore is specified,
1770 then kernelcore will be at *least* the specified
1771 value but may be more. If movablecore on its own
1772 is specified, the administrator must be careful
1773 that the amount of memory usable for all allocations
1774 is not too small.
1776 MTD_Partition= [MTD]
1777 Format: <name>,<region-number>,<size>,<offset>
1779 MTD_Region= [MTD] Format:
1780 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1782 mtdparts= [MTD]
1783 See drivers/mtd/cmdlinepart.c.
1785 multitce=off [PPC] This parameter disables the use of the pSeries
1786 firmware feature for updating multiple TCE entries
1787 at a time.
1789 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1791 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1793 boundary - index of last SLC block on Flex-OneNAND.
1794 The remaining blocks are configured as MLC blocks.
1795 lock - Configure if Flex-OneNAND boundary should be locked.
1796 Once locked, the boundary cannot be changed.
1797 1 indicates lock status, 0 indicates unlock status.
1799 mtdset= [ARM]
1800 ARM/S3C2412 JIVE boot control
1802 See arch/arm/mach-s3c2412/mach-jive.c
1804 mtouchusb.raw_coordinates=
1805 [HW] Make the MicroTouch USB driver use raw coordinates
1806 ('y', default) or cooked coordinates ('n')
1808 mtrr_chunk_size=nn[KMG] [X86]
1809 used for mtrr cleanup. It is largest continuous chunk
1810 that could hold holes aka. UC entries.
1812 mtrr_gran_size=nn[KMG] [X86]
1813 Used for mtrr cleanup. It is granularity of mtrr block.
1814 Default is 1.
1815 Large value could prevent small alignment from
1816 using up MTRRs.
1818 mtrr_spare_reg_nr=n [X86]
1819 Format: <integer>
1820 Range: 0,7 : spare reg number
1821 Default : 1
1822 Used for mtrr cleanup. It is spare mtrr entries number.
1823 Set to 2 or more if your graphical card needs more.
1825 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1827 netdev= [NET] Network devices parameters
1828 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1829 Note that mem_start is often overloaded to mean
1830 something different and driver-specific.
1831 This usage is only documented in each driver source
1832 file if at all.
1834 nf_conntrack.acct=
1835 [NETFILTER] Enable connection tracking flow accounting
1836 0 to disable accounting
1837 1 to enable accounting
1838 Default value is 0.
1840 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1841 See Documentation/filesystems/nfs/nfsroot.txt.
1843 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1844 See Documentation/filesystems/nfs/nfsroot.txt.
1846 nfsrootdebug [NFS] enable nfsroot debugging messages.
1847 See Documentation/filesystems/nfs/nfsroot.txt.
1849 nfs.callback_tcpport=
1850 [NFS] set the TCP port on which the NFSv4 callback
1851 channel should listen.
1853 nfs.cache_getent=
1854 [NFS] sets the pathname to the program which is used
1855 to update the NFS client cache entries.
1857 nfs.cache_getent_timeout=
1858 [NFS] sets the timeout after which an attempt to
1859 update a cache entry is deemed to have failed.
1861 nfs.idmap_cache_timeout=
1862 [NFS] set the maximum lifetime for idmapper cache
1863 entries.
1865 nfs.enable_ino64=
1866 [NFS] enable 64-bit inode numbers.
1867 If zero, the NFS client will fake up a 32-bit inode
1868 number for the readdir() and stat() syscalls instead
1869 of returning the full 64-bit number.
1870 The default is to return 64-bit inode numbers.
1872 nfs.max_session_slots=
1873 [NFSv4.1] Sets the maximum number of session slots
1874 the client will attempt to negotiate with the server.
1875 This limits the number of simultaneous RPC requests
1876 that the client can send to the NFSv4.1 server.
1877 Note that there is little point in setting this
1878 value higher than the max_tcp_slot_table_limit.
1880 nfs.nfs4_disable_idmapping=
1881 [NFSv4] When set to the default of '1', this option
1882 ensures that both the RPC level authentication
1883 scheme and the NFS level operations agree to use
1884 numeric uids/gids if the mount is using the
1885 'sec=sys' security flavour. In effect it is
1886 disabling idmapping, which can make migration from
1887 legacy NFSv2/v3 systems to NFSv4 easier.
1888 Servers that do not support this mode of operation
1889 will be autodetected by the client, and it will fall
1890 back to using the idmapper.
1891 To turn off this behaviour, set the value to '0'.
1892 nfs.nfs4_unique_id=
1893 [NFS4] Specify an additional fixed unique ident-
1894 ification string that NFSv4 clients can insert into
1895 their nfs_client_id4 string. This is typically a
1896 UUID that is generated at system install time.
1898 nfs.send_implementation_id =
1899 [NFSv4.1] Send client implementation identification
1900 information in exchange_id requests.
1901 If zero, no implementation identification information
1902 will be sent.
1903 The default is to send the implementation identification
1904 information.
1906 nfs.recover_lost_locks =
1907 [NFSv4] Attempt to recover locks that were lost due
1908 to a lease timeout on the server. Please note that
1909 doing this risks data corruption, since there are
1910 no guarantees that the file will remain unchanged
1911 after the locks are lost.
1912 If you want to enable the kernel legacy behaviour of
1913 attempting to recover these locks, then set this
1914 parameter to '1'.
1915 The default parameter value of '0' causes the kernel
1916 not to attempt recovery of lost locks.
1918 nfsd.nfs4_disable_idmapping=
1919 [NFSv4] When set to the default of '1', the NFSv4
1920 server will return only numeric uids and gids to
1921 clients using auth_sys, and will accept numeric uids
1922 and gids from such clients. This is intended to ease
1923 migration from NFSv2/v3.
1925 objlayoutdriver.osd_login_prog=
1926 [NFS] [OBJLAYOUT] sets the pathname to the program which
1927 is used to automatically discover and login into new
1928 osd-targets. Please see:
1929 Documentation/filesystems/pnfs.txt for more explanations
1931 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1932 when a NMI is triggered.
1933 Format: [state][,regs][,debounce][,die]
1935 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1936 Format: [panic,][nopanic,][num]
1937 Valid num: 0
1938 0 - turn nmi_watchdog off
1939 When panic is specified, panic when an NMI watchdog
1940 timeout occurs (or 'nopanic' to override the opposite
1941 default).
1942 This is useful when you use a panic=... timeout and
1943 need the box quickly up again.
1945 netpoll.carrier_timeout=
1946 [NET] Specifies amount of time (in seconds) that
1947 netpoll should wait for a carrier. By default netpoll
1948 waits 4 seconds.
1950 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1951 emulation library even if a 387 maths coprocessor
1952 is present.
1954 no_console_suspend
1955 [HW] Never suspend the console
1956 Disable suspending of consoles during suspend and
1957 hibernate operations. Once disabled, debugging
1958 messages can reach various consoles while the rest
1959 of the system is being put to sleep (ie, while
1960 debugging driver suspend/resume hooks). This may
1961 not work reliably with all consoles, but is known
1962 to work with serial and VGA consoles.
1963 To facilitate more flexible debugging, we also add
1964 console_suspend, a printk module parameter to control
1965 it. Users could use console_suspend (usually
1966 /sys/module/printk/parameters/console_suspend) to
1967 turn on/off it dynamically.
1969 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1970 caches in the slab allocator. Saves per-node memory,
1971 but will impact performance.
1973 noalign [KNL,ARM]
1975 noapic [SMP,APIC] Tells the kernel to not make use of any
1976 IOAPICs that may be present in the system.
1978 noautogroup Disable scheduler automatic task group creation.
1980 nobats [PPC] Do not use BATs for mapping kernel lowmem
1981 on "Classic" PPC cores.
1983 nocache [ARM]
1985 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1987 nodelayacct [KNL] Disable per-task delay accounting
1989 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1991 nodsp [SH] Disable hardware DSP at boot time.
1993 noefi [X86] Disable EFI runtime services support.
1995 noexec [IA-64]
1997 noexec [X86]
1998 On X86-32 available only on PAE configured kernels.
1999 noexec=on: enable non-executable mappings (default)
2000 noexec=off: disable non-executable mappings
2002 nosmap [X86]
2003 Disable SMAP (Supervisor Mode Access Prevention)
2004 even if it is supported by processor.
2006 nosmep [X86]
2007 Disable SMEP (Supervisor Mode Execution Prevention)
2008 even if it is supported by processor.
2010 noexec32 [X86-64]
2011 This affects only 32-bit executables.
2012 noexec32=on: enable non-executable mappings (default)
2013 read doesn't imply executable mappings
2014 noexec32=off: disable non-executable mappings
2015 read implies executable mappings
2017 nofpu [SH] Disable hardware FPU at boot time.
2019 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2020 register save and restore. The kernel will only save
2021 legacy floating-point registers on task switch.
2023 noxsave [BUGS=X86] Disables x86 extended register state save
2024 and restore using xsave. The kernel will fallback to
2025 enabling legacy floating-point and sse state.
2027 eagerfpu= [X86]
2028 on enable eager fpu restore
2029 off disable eager fpu restore
2030 auto selects the default scheme, which automatically
2031 enables eagerfpu restore for xsaveopt.
2033 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2034 wfi(ARM) instruction doesn't work correctly and not to
2035 use it. This is also useful when using JTAG debugger.
2037 no_file_caps Tells the kernel not to honor file capabilities. The
2038 only way then for a file to be executed with privilege
2039 is to be setuid root or executed by root.
2041 nohalt [IA-64] Tells the kernel not to use the power saving
2042 function PAL_HALT_LIGHT when idle. This increases
2043 power-consumption. On the positive side, it reduces
2044 interrupt wake-up latency, which may improve performance
2045 in certain environments such as networked servers or
2046 real-time systems.
2048 nohz= [KNL] Boottime enable/disable dynamic ticks
2049 Valid arguments: on, off
2050 Default: on
2052 nohz_full= [KNL,BOOT]
2053 In kernels built with CONFIG_NO_HZ_FULL=y, set
2054 the specified list of CPUs whose tick will be stopped
2055 whenever possible. The boot CPU will be forced outside
2056 the range to maintain the timekeeping.
2057 The CPUs in this range must also be included in the
2058 rcu_nocbs= set.
2060 noiotrap [SH] Disables trapped I/O port accesses.
2062 noirqdebug [X86-32] Disables the code which attempts to detect and
2063 disable unhandled interrupt sources.
2065 no_timer_check [X86,APIC] Disables the code which tests for
2066 broken timer IRQ sources.
2068 noisapnp [ISAPNP] Disables ISA PnP code.
2070 noinitrd [RAM] Tells the kernel not to load any configured
2071 initial RAM disk.
2073 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2074 remapping.
2075 [Deprecated - use intremap=off]
2077 nointroute [IA-64]
2079 nojitter [IA-64] Disables jitter checking for ITC timers.
2081 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2083 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2084 fault handling.
2086 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2087 steal time is computed, but won't influence scheduler
2088 behaviour
2090 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2092 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2094 noltlbs [PPC] Do not use large page/tlb entries for kernel
2095 lowmem mapping on PPC40x.
2097 nomca [IA-64] Disable machine check abort handling
2099 nomce [X86-32] Machine Check Exception
2101 nomfgpt [X86-32] Disable Multi-Function General Purpose
2102 Timer usage (for AMD Geode machines).
2104 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2105 shutdown the other cpus. Instead use the REBOOT_VECTOR
2106 irq.
2108 nomodule Disable module load
2110 nopat [X86] Disable PAT (page attribute table extension of
2111 pagetables) support.
2113 norandmaps Don't use address space randomization. Equivalent to
2114 echo 0 > /proc/sys/kernel/randomize_va_space
2116 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2118 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2119 with UP alternatives
2121 nordrand [X86] Disable the direct use of the RDRAND
2122 instruction even if it is supported by the
2123 processor. RDRAND is still available to user
2124 space applications.
2126 noresume [SWSUSP] Disables resume and restores original swap
2127 space.
2129 no-scroll [VGA] Disables scrollback.
2130 This is required for the Braillex ib80-piezo Braille
2131 reader made by F.H. Papenmeier (Germany).
2133 nosbagart [IA-64]
2135 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2137 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2138 and disable the IO APIC. legacy for "maxcpus=0".
2140 nosoftlockup [KNL] Disable the soft-lockup detector.
2142 nosync [HW,M68K] Disables sync negotiation for all devices.
2144 notsc [BUGS=X86-32] Disable Time Stamp Counter
2146 nousb [USB] Disable the USB subsystem
2148 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2150 nowb [ARM]
2152 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2154 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2155 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2156 Some features depend on CPU0. Known dependencies are:
2157 1. Resume from suspend/hibernate depends on CPU0.
2158 Suspend/hibernate will fail if CPU0 is offline and you
2159 need to online CPU0 before suspend/hibernate.
2160 2. PIC interrupts also depend on CPU0. CPU0 can't be
2161 removed if a PIC interrupt is detected.
2162 It's said poweroff/reboot may depend on CPU0 on some
2163 machines although I haven't seen such issues so far
2164 after CPU0 is offline on a few tested machines.
2165 If the dependencies are under your control, you can
2166 turn on cpu0_hotplug.
2168 nptcg= [IA-64] Override max number of concurrent global TLB
2169 purges which is reported from either PAL_VM_SUMMARY or
2170 SAL PALO.
2172 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2173 could support. nr_cpus=n : n >= 1 limits the kernel to
2174 supporting 'n' processors. Later in runtime you can not
2175 use hotplug cpu feature to put more cpu back to online.
2176 just like you compile the kernel NR_CPUS=n
2178 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2180 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2181 Allowed values are enable and disable
2183 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2184 one of ['zone', 'node', 'default'] can be specified
2185 This can be set from sysctl after boot.
2186 See Documentation/sysctl/vm.txt for details.
2188 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2189 See Documentation/debugging-via-ohci1394.txt for more
2190 info.
2192 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2193 Rather than timing out after 20 ms if an EC
2194 command is not properly ACKed, override the length
2195 of the timeout. We have interrupts disabled while
2196 waiting for the ACK, so if this is set too high
2197 interrupts *may* be lost!
2199 omap_mux= [OMAP] Override bootloader pin multiplexing.
2200 Format: <mux_mode0.mode_name=value>...
2201 For example, to override I2C bus2:
2202 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2204 oprofile.timer= [HW]
2205 Use timer interrupt instead of performance counters
2207 oprofile.cpu_type= Force an oprofile cpu type
2208 This might be useful if you have an older oprofile
2209 userland or if you want common events.
2210 Format: { arch_perfmon }
2211 arch_perfmon: [X86] Force use of architectural
2212 perfmon on Intel CPUs instead of the
2213 CPU specific event set.
2214 timer: [X86] Force use of architectural NMI
2215 timer mode (see also oprofile.timer
2216 for generic hr timer mode)
2217 [s390] Force legacy basic mode sampling
2218 (report cpu_type "timer")
2220 oops=panic Always panic on oopses. Default is to just kill the
2221 process, but there is a small probability of
2222 deadlocking the machine.
2223 This will also cause panics on machine check exceptions.
2224 Useful together with panic=30 to trigger a reboot.
2226 OSS [HW,OSS]
2227 See Documentation/sound/oss/oss-parameters.txt
2229 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2230 timeout > 0: seconds before rebooting
2231 timeout = 0: wait forever
2232 timeout < 0: reboot immediately
2233 Format: <timeout>
2235 parkbd.port= [HW] Parallel port number the keyboard adapter is
2236 connected to, default is 0.
2237 Format: <parport#>
2238 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2239 0 for XT, 1 for AT (default is AT).
2240 Format: <mode>
2242 parport= [HW,PPT] Specify parallel ports. 0 disables.
2243 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2244 Use 'auto' to force the driver to use any
2245 IRQ/DMA settings detected (the default is to
2246 ignore detected IRQ/DMA settings because of
2247 possible conflicts). You can specify the base
2248 address, IRQ, and DMA settings; IRQ and DMA
2249 should be numbers, or 'auto' (for using detected
2250 settings on that particular port), or 'nofifo'
2251 (to avoid using a FIFO even if it is detected).
2252 Parallel ports are assigned in the order they
2253 are specified on the command line, starting
2254 with parport0.
2256 parport_init_mode= [HW,PPT]
2257 Configure VIA parallel port to operate in
2258 a specific mode. This is necessary on Pegasos
2259 computer where firmware has no options for setting
2260 up parallel port mode and sets it to spp.
2261 Currently this function knows 686a and 8231 chips.
2262 Format: [spp|ps2|epp|ecp|ecpepp]
2264 pause_on_oops=
2265 Halt all CPUs after the first oops has been printed for
2266 the specified number of seconds. This is to be used if
2267 your oopses keep scrolling off the screen.
2269 pcbit= [HW,ISDN]
2271 pcd. [PARIDE]
2272 See header of drivers/block/paride/pcd.c.
2273 See also Documentation/blockdev/paride.txt.
2275 pci=option[,option...] [PCI] various PCI subsystem options:
2276 earlydump [X86] dump PCI config space before the kernel
2277 changes anything
2278 off [X86] don't probe for the PCI bus
2279 bios [X86-32] force use of PCI BIOS, don't access
2280 the hardware directly. Use this if your machine
2281 has a non-standard PCI host bridge.
2282 nobios [X86-32] disallow use of PCI BIOS, only direct
2283 hardware access methods are allowed. Use this
2284 if you experience crashes upon bootup and you
2285 suspect they are caused by the BIOS.
2286 conf1 [X86] Force use of PCI Configuration
2287 Mechanism 1.
2288 conf2 [X86] Force use of PCI Configuration
2289 Mechanism 2.
2290 noaer [PCIE] If the PCIEAER kernel config parameter is
2291 enabled, this kernel boot option can be used to
2292 disable the use of PCIE advanced error reporting.
2293 nodomains [PCI] Disable support for multiple PCI
2294 root domains (aka PCI segments, in ACPI-speak).
2295 nommconf [X86] Disable use of MMCONFIG for PCI
2296 Configuration
2297 check_enable_amd_mmconf [X86] check for and enable
2298 properly configured MMIO access to PCI
2299 config space on AMD family 10h CPU
2300 nomsi [MSI] If the PCI_MSI kernel config parameter is
2301 enabled, this kernel boot option can be used to
2302 disable the use of MSI interrupts system-wide.
2303 noioapicquirk [APIC] Disable all boot interrupt quirks.
2304 Safety option to keep boot IRQs enabled. This
2305 should never be necessary.
2306 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2307 primary IO-APIC for bridges that cannot disable
2308 boot IRQs. This fixes a source of spurious IRQs
2309 when the system masks IRQs.
2310 noioapicreroute [APIC] Disable workaround that uses the
2311 boot IRQ equivalent of an IRQ that connects to
2312 a chipset where boot IRQs cannot be disabled.
2313 The opposite of ioapicreroute.
2314 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2315 routing table. These calls are known to be buggy
2316 on several machines and they hang the machine
2317 when used, but on other computers it's the only
2318 way to get the interrupt routing table. Try
2319 this option if the kernel is unable to allocate
2320 IRQs or discover secondary PCI buses on your
2321 motherboard.
2322 rom [X86] Assign address space to expansion ROMs.
2323 Use with caution as certain devices share
2324 address decoders between ROMs and other
2325 resources.
2326 norom [X86] Do not assign address space to
2327 expansion ROMs that do not already have
2328 BIOS assigned address ranges.
2329 nobar [X86] Do not assign address space to the
2330 BARs that weren't assigned by the BIOS.
2331 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2332 assigned automatically to PCI devices. You can
2333 make the kernel exclude IRQs of your ISA cards
2334 this way.
2335 pirqaddr=0xAAAAA [X86] Specify the physical address
2336 of the PIRQ table (normally generated
2337 by the BIOS) if it is outside the
2338 F0000h-100000h range.
2339 lastbus=N [X86] Scan all buses thru bus #N. Can be
2340 useful if the kernel is unable to find your
2341 secondary buses and you want to tell it
2342 explicitly which ones they are.
2343 assign-busses [X86] Always assign all PCI bus
2344 numbers ourselves, overriding
2345 whatever the firmware may have done.
2346 usepirqmask [X86] Honor the possible IRQ mask stored
2347 in the BIOS $PIR table. This is needed on
2348 some systems with broken BIOSes, notably
2349 some HP Pavilion N5400 and Omnibook XE3
2350 notebooks. This will have no effect if ACPI
2351 IRQ routing is enabled.
2352 noacpi [X86] Do not use ACPI for IRQ routing
2353 or for PCI scanning.
2354 use_crs [X86] Use PCI host bridge window information
2355 from ACPI. On BIOSes from 2008 or later, this
2356 is enabled by default. If you need to use this,
2357 please report a bug.
2358 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2359 If you need to use this, please report a bug.
2360 routeirq Do IRQ routing for all PCI devices.
2361 This is normally done in pci_enable_device(),
2362 so this option is a temporary workaround
2363 for broken drivers that don't call it.
2364 skip_isa_align [X86] do not align io start addr, so can
2365 handle more pci cards
2366 firmware [ARM] Do not re-enumerate the bus but instead
2367 just use the configuration from the
2368 bootloader. This is currently used on
2369 IXP2000 systems where the bus has to be
2370 configured a certain way for adjunct CPUs.
2371 noearly [X86] Don't do any early type 1 scanning.
2372 This might help on some broken boards which
2373 machine check when some devices' config space
2374 is read. But various workarounds are disabled
2375 and some IOMMU drivers will not work.
2376 bfsort Sort PCI devices into breadth-first order.
2377 This sorting is done to get a device
2378 order compatible with older (<= 2.4) kernels.
2379 nobfsort Don't sort PCI devices into breadth-first order.
2380 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2381 tuning and use the BIOS-configured MPS defaults.
2382 pcie_bus_safe Set every device's MPS to the largest value
2383 supported by all devices below the root complex.
2384 pcie_bus_perf Set device MPS to the largest allowable MPS
2385 based on its parent bus. Also set MRRS (Max
2386 Read Request Size) to the largest supported
2387 value (no larger than the MPS that the device
2388 or bus can support) for best performance.
2389 pcie_bus_peer2peer Set every device's MPS to 128B, which
2390 every device is guaranteed to support. This
2391 configuration allows peer-to-peer DMA between
2392 any pair of devices, possibly at the cost of
2393 reduced performance. This also guarantees
2394 that hot-added devices will work.
2395 cbiosize=nn[KMG] The fixed amount of bus space which is
2396 reserved for the CardBus bridge's IO window.
2397 The default value is 256 bytes.
2398 cbmemsize=nn[KMG] The fixed amount of bus space which is
2399 reserved for the CardBus bridge's memory
2400 window. The default value is 64 megabytes.
2401 resource_alignment=
2402 Format:
2403 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2404 Specifies alignment and device to reassign
2405 aligned memory resources.
2406 If <order of align> is not specified,
2407 PAGE_SIZE is used as alignment.
2408 PCI-PCI bridge can be specified, if resource
2409 windows need to be expanded.
2410 ecrc= Enable/disable PCIe ECRC (transaction layer
2411 end-to-end CRC checking).
2412 bios: Use BIOS/firmware settings. This is the
2413 the default.
2414 off: Turn ECRC off
2415 on: Turn ECRC on.
2416 hpiosize=nn[KMG] The fixed amount of bus space which is
2417 reserved for hotplug bridge's IO window.
2418 Default size is 256 bytes.
2419 hpmemsize=nn[KMG] The fixed amount of bus space which is
2420 reserved for hotplug bridge's memory window.
2421 Default size is 2 megabytes.
2422 realloc= Enable/disable reallocating PCI bridge resources
2423 if allocations done by BIOS are too small to
2424 accommodate resources required by all child
2425 devices.
2426 off: Turn realloc off
2427 on: Turn realloc on
2428 realloc same as realloc=on
2429 noari do not use PCIe ARI.
2430 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2431 only look for one device below a PCIe downstream
2432 port.
2434 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2435 Management.
2436 off Disable ASPM.
2437 force Enable ASPM even on devices that claim not to support it.
2438 WARNING: Forcing ASPM on may cause system lockups.
2440 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2441 nomsi Do not use MSI for PCI Express Native Hotplug (this
2442 makes all PCIe ports use INTx for hotplug services).
2444 pcie_ports= [PCIE] PCIe ports handling:
2445 auto Ask the BIOS whether or not to use native PCIe services
2446 associated with PCIe ports (PME, hot-plug, AER). Use
2447 them only if that is allowed by the BIOS.
2448 native Use native PCIe services associated with PCIe ports
2449 unconditionally.
2450 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2451 ports driver.
2453 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2454 nomsi Do not use MSI for native PCIe PME signaling (this makes
2455 all PCIe root ports use INTx for all services).
2457 pcmv= [HW,PCMCIA] BadgePAD 4
2459 pd. [PARIDE]
2460 See Documentation/blockdev/paride.txt.
2462 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2463 boot time.
2464 Format: { 0 | 1 }
2465 See arch/parisc/kernel/pdc_chassis.c
2467 percpu_alloc= Select which percpu first chunk allocator to use.
2468 Currently supported values are "embed" and "page".
2469 Archs may support subset or none of the selections.
2470 See comments in mm/percpu.c for details on each
2471 allocator. This parameter is primarily for debugging
2472 and performance comparison.
2474 pf. [PARIDE]
2475 See Documentation/blockdev/paride.txt.
2477 pg. [PARIDE]
2478 See Documentation/blockdev/paride.txt.
2480 pirq= [SMP,APIC] Manual mp-table setup
2481 See Documentation/x86/i386/IO-APIC.txt.
2483 plip= [PPT,NET] Parallel port network link
2484 Format: { parport<nr> | timid | 0 }
2485 See also Documentation/parport.txt.
2487 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2488 Override pmtimer IOPort with a hex value.
2489 e.g. pmtmr=0x508
2491 pnp.debug=1 [PNP]
2492 Enable PNP debug messages (depends on the
2493 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2494 via /sys/module/pnp/parameters/debug. We always show
2495 current resource usage; turning this on also shows
2496 possible settings and some assignment information.
2498 pnpacpi= [ACPI]
2499 { off }
2501 pnpbios= [ISAPNP]
2502 { on | off | curr | res | no-curr | no-res }
2504 pnp_reserve_irq=
2505 [ISAPNP] Exclude IRQs for the autoconfiguration
2507 pnp_reserve_dma=
2508 [ISAPNP] Exclude DMAs for the autoconfiguration
2510 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2511 Ranges are in pairs (I/O port base and size).
2513 pnp_reserve_mem=
2514 [ISAPNP] Exclude memory regions for the
2515 autoconfiguration.
2516 Ranges are in pairs (memory base and size).
2518 ports= [IP_VS_FTP] IPVS ftp helper module
2519 Default is 21.
2520 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2521 may be specified.
2522 Format: <port>,<port>....
2524 print-fatal-signals=
2525 [KNL] debug: print fatal signals
2527 If enabled, warn about various signal handling
2528 related application anomalies: too many signals,
2529 too many POSIX.1 timers, fatal signals causing a
2530 coredump - etc.
2532 If you hit the warning due to signal overflow,
2533 you might want to try "ulimit -i unlimited".
2535 default: off.
2537 printk.always_kmsg_dump=
2538 Trigger kmsg_dump for cases other than kernel oops or
2539 panics
2540 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2541 default: disabled
2543 printk.time= Show timing data prefixed to each printk message line
2544 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2546 processor.max_cstate= [HW,ACPI]
2547 Limit processor to maximum C-state
2548 max_cstate=9 overrides any DMI blacklist limit.
2550 processor.nocst [HW,ACPI]
2551 Ignore the _CST method to determine C-states,
2552 instead using the legacy FADT method
2554 profile= [KNL] Enable kernel profiling via /proc/profile
2555 Format: [schedule,]<number>
2556 Param: "schedule" - profile schedule points.
2557 Param: <number> - step/bucket size as a power of 2 for
2558 statistical time based profiling.
2559 Param: "sleep" - profile D-state sleeping (millisecs).
2560 Requires CONFIG_SCHEDSTATS
2561 Param: "kvm" - profile VM exits.
2563 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2564 before loading.
2565 See Documentation/blockdev/ramdisk.txt.
2567 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2568 probe for; one of (bare|imps|exps|lifebook|any).
2569 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2570 per second.
2571 psmouse.resetafter= [HW,MOUSE]
2572 Try to reset the device after so many bad packets
2573 (0 = never).
2574 psmouse.resolution=
2575 [HW,MOUSE] Set desired mouse resolution, in dpi.
2576 psmouse.smartscroll=
2577 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2578 0 = disabled, 1 = enabled (default).
2580 pstore.backend= Specify the name of the pstore backend to use
2582 pt. [PARIDE]
2583 See Documentation/blockdev/paride.txt.
2585 pty.legacy_count=
2586 [KNL] Number of legacy pty's. Overwrites compiled-in
2587 default number.
2589 quiet [KNL] Disable most log messages
2591 r128= [HW,DRM]
2593 raid= [HW,RAID]
2594 See Documentation/md.txt.
2596 ramdisk_blocksize= [RAM]
2597 See Documentation/blockdev/ramdisk.txt.
2599 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2600 See Documentation/blockdev/ramdisk.txt.
2602 rcu_nocbs= [KNL,BOOT]
2603 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2604 the specified list of CPUs to be no-callback CPUs.
2605 Invocation of these CPUs' RCU callbacks will
2606 be offloaded to "rcuox/N" kthreads created for
2607 that purpose, where "x" is "b" for RCU-bh, "p"
2608 for RCU-preempt, and "s" for RCU-sched, and "N"
2609 is the CPU number. This reduces OS jitter on the
2610 offloaded CPUs, which can be useful for HPC and
2612 real-time workloads. It can also improve energy
2613 efficiency for asymmetric multiprocessors.
2615 rcu_nocb_poll [KNL,BOOT]
2616 Rather than requiring that offloaded CPUs
2617 (specified by rcu_nocbs= above) explicitly
2618 awaken the corresponding "rcuoN" kthreads,
2619 make these kthreads poll for callbacks.
2620 This improves the real-time response for the
2621 offloaded CPUs by relieving them of the need to
2622 wake up the corresponding kthread, but degrades
2623 energy efficiency by requiring that the kthreads
2624 periodically wake up to do the polling.
2626 rcutree.blimit= [KNL,BOOT]
2627 Set maximum number of finished RCU callbacks to process
2628 in one batch.
2630 rcutree.fanout_leaf= [KNL,BOOT]
2631 Increase the number of CPUs assigned to each
2632 leaf rcu_node structure. Useful for very large
2633 systems.
2635 rcutree.jiffies_till_first_fqs= [KNL,BOOT]
2636 Set delay from grace-period initialization to
2637 first attempt to force quiescent states.
2638 Units are jiffies, minimum value is zero,
2639 and maximum value is HZ.
2641 rcutree.jiffies_till_next_fqs= [KNL,BOOT]
2642 Set delay between subsequent attempts to force
2643 quiescent states. Units are jiffies, minimum
2644 value is one, and maximum value is HZ.
2646 rcutree.qhimark= [KNL,BOOT]
2647 Set threshold of queued
2648 RCU callbacks over which batch limiting is disabled.
2650 rcutree.qlowmark= [KNL,BOOT]
2651 Set threshold of queued RCU callbacks below which
2652 batch limiting is re-enabled.
2654 rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2655 Suppress RCU CPU stall warning messages.
2657 rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2658 Set timeout for RCU CPU stall warning messages.
2660 rcutree.rcu_idle_gp_delay= [KNL,BOOT]
2661 Set wakeup interval for idle CPUs that have
2662 RCU callbacks (RCU_FAST_NO_HZ=y).
2664 rcutree.rcu_idle_lazy_gp_delay= [KNL,BOOT]
2665 Set wakeup interval for idle CPUs that have
2666 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2667 Lazy RCU callbacks are those which RCU can
2668 prove do nothing more than free memory.
2670 rcutorture.fqs_duration= [KNL,BOOT]
2671 Set duration of force_quiescent_state bursts.
2673 rcutorture.fqs_holdoff= [KNL,BOOT]
2674 Set holdoff time within force_quiescent_state bursts.
2676 rcutorture.fqs_stutter= [KNL,BOOT]
2677 Set wait time between force_quiescent_state bursts.
2679 rcutorture.irqreader= [KNL,BOOT]
2680 Test RCU readers from irq handlers.
2682 rcutorture.n_barrier_cbs= [KNL,BOOT]
2683 Set callbacks/threads for rcu_barrier() testing.
2685 rcutorture.nfakewriters= [KNL,BOOT]
2686 Set number of concurrent RCU writers. These just
2687 stress RCU, they don't participate in the actual
2688 test, hence the "fake".
2690 rcutorture.nreaders= [KNL,BOOT]
2691 Set number of RCU readers.
2693 rcutorture.onoff_holdoff= [KNL,BOOT]
2694 Set time (s) after boot for CPU-hotplug testing.
2696 rcutorture.onoff_interval= [KNL,BOOT]
2697 Set time (s) between CPU-hotplug operations, or
2698 zero to disable CPU-hotplug testing.
2700 rcutorture.shuffle_interval= [KNL,BOOT]
2701 Set task-shuffle interval (s). Shuffling tasks
2702 allows some CPUs to go into dyntick-idle mode
2703 during the rcutorture test.
2705 rcutorture.shutdown_secs= [KNL,BOOT]
2706 Set time (s) after boot system shutdown. This
2707 is useful for hands-off automated testing.
2709 rcutorture.stall_cpu= [KNL,BOOT]
2710 Duration of CPU stall (s) to test RCU CPU stall
2711 warnings, zero to disable.
2713 rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2714 Time to wait (s) after boot before inducing stall.
2716 rcutorture.stat_interval= [KNL,BOOT]
2717 Time (s) between statistics printk()s.
2719 rcutorture.stutter= [KNL,BOOT]
2720 Time (s) to stutter testing, for example, specifying
2721 five seconds causes the test to run for five seconds,
2722 wait for five seconds, and so on. This tests RCU's
2723 ability to transition abruptly to and from idle.
2725 rcutorture.test_boost= [KNL,BOOT]
2726 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2727 "Maybe" means test if the RCU implementation
2728 under test support RCU priority boosting.
2730 rcutorture.test_boost_duration= [KNL,BOOT]
2731 Duration (s) of each individual boost test.
2733 rcutorture.test_boost_interval= [KNL,BOOT]
2734 Interval (s) between each boost test.
2736 rcutorture.test_no_idle_hz= [KNL,BOOT]
2737 Test RCU's dyntick-idle handling. See also the
2738 rcutorture.shuffle_interval parameter.
2740 rcutorture.torture_type= [KNL,BOOT]
2741 Specify the RCU implementation to test.
2743 rcutorture.verbose= [KNL,BOOT]
2744 Enable additional printk() statements.
2746 rdinit= [KNL]
2747 Format: <full_path>
2748 Run specified binary instead of /init from the ramdisk,
2749 used for early userspace startup. See initrd.
2751 reboot= [KNL]
2752 Format (x86 or x86_64):
2753 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2754 [[,]s[mp]#### \
2755 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2756 [[,]f[orce]
2757 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2758 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2759 reboot_force is either force or not specified,
2760 reboot_cpu is s[mp]#### with #### being the processor
2761 to be used for rebooting.
2763 relax_domain_level=
2764 [KNL, SMP] Set scheduler's default relax_domain_level.
2765 See Documentation/cgroups/cpusets.txt.
2767 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2769 reservetop= [X86-32]
2770 Format: nn[KMG]
2771 Reserves a hole at the top of the kernel virtual
2772 address space.
2774 reservelow= [X86]
2775 Format: nn[K]
2776 Set the amount of memory to reserve for BIOS at
2777 the bottom of the address space.
2779 reset_devices [KNL] Force drivers to reset the underlying device
2780 during initialization.
2782 resume= [SWSUSP]
2783 Specify the partition device for software suspend
2784 Format:
2785 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2787 resume_offset= [SWSUSP]
2788 Specify the offset from the beginning of the partition
2789 given by "resume=" at which the swap header is located,
2790 in <PAGE_SIZE> units (needed only for swap files).
2791 See Documentation/power/swsusp-and-swap-files.txt
2793 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2794 read the resume files
2796 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2797 Useful for devices that are detected asynchronously
2798 (e.g. USB and MMC devices).
2800 hibernate= [HIBERNATION]
2801 noresume Don't check if there's a hibernation image
2802 present during boot.
2803 nocompress Don't compress/decompress hibernation images.
2805 retain_initrd [RAM] Keep initrd memory after extraction
2807 rhash_entries= [KNL,NET]
2808 Set number of hash buckets for route cache
2810 riscom8= [HW,SERIAL]
2811 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2813 ro [KNL] Mount root device read-only on boot
2815 root= [KNL] Root filesystem
2816 See name_to_dev_t comment in init/do_mounts.c.
2818 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2819 mount the root filesystem
2821 rootflags= [KNL] Set root filesystem mount option string
2823 rootfstype= [KNL] Set root filesystem type
2825 rootwait [KNL] Wait (indefinitely) for root device to show up.
2826 Useful for devices that are detected asynchronously
2827 (e.g. USB and MMC devices).
2829 rproc_mem=nn[KMG][@address]
2830 [KNL,ARM,CMA] Remoteproc physical memory block.
2831 Memory area to be used by remote processor image,
2832 managed by CMA.
2834 rw [KNL] Mount root device read-write on boot
2836 S [KNL] Run init in single mode
2838 sa1100ir [NET]
2839 See drivers/net/irda/sa1100_ir.c.
2841 sbni= [NET] Granch SBNI12 leased line adapter
2843 sched_debug [KNL] Enables verbose scheduler debug messages.
2845 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2846 xtime_lock contention on larger systems, and/or RCU lock
2847 contention on all systems with CONFIG_MAXSMP set.
2848 Format: { "0" | "1" }
2849 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2850 1 -- enable.
2851 Note: increases power consumption, thus should only be
2852 enabled if running jitter sensitive (HPC/RT) workloads.
2854 security= [SECURITY] Choose a security module to enable at boot.
2855 If this boot parameter is not specified, only the first
2856 security module asking for security registration will be
2857 loaded. An invalid security module name will be treated
2858 as if no module has been chosen.
2860 selinux= [SELINUX] Disable or enable SELinux at boot time.
2861 Format: { "0" | "1" }
2862 See security/selinux/Kconfig help text.
2863 0 -- disable.
2864 1 -- enable.
2865 Default value is set via kernel config option.
2866 If enabled at boot time, /selinux/disable can be used
2867 later to disable prior to initial policy load.
2869 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2870 Format: { "0" | "1" }
2871 See security/apparmor/Kconfig help text
2872 0 -- disable.
2873 1 -- enable.
2874 Default value is set via kernel config option.
2876 serialnumber [BUGS=X86-32]
2878 shapers= [NET]
2879 Maximal number of shapers.
2881 show_msr= [x86] show boot-time MSR settings
2882 Format: { <integer> }
2883 Show boot-time (BIOS-initialized) MSR settings.
2884 The parameter means the number of CPUs to show,
2885 for example 1 means boot CPU only.
2887 simeth= [IA-64]
2888 simscsi=
2890 slram= [HW,MTD]
2892 slab_max_order= [MM, SLAB]
2893 Determines the maximum allowed order for slabs.
2894 A high setting may cause OOMs due to memory
2895 fragmentation. Defaults to 1 for systems with
2896 more than 32MB of RAM, 0 otherwise.
2898 slub_debug[=options[,slabs]] [MM, SLUB]
2899 Enabling slub_debug allows one to determine the
2900 culprit if slab objects become corrupted. Enabling
2901 slub_debug can create guard zones around objects and
2902 may poison objects when not in use. Also tracks the
2903 last alloc / free. For more information see
2904 Documentation/vm/slub.txt.
2906 slub_max_order= [MM, SLUB]
2907 Determines the maximum allowed order for slabs.
2908 A high setting may cause OOMs due to memory
2909 fragmentation. For more information see
2910 Documentation/vm/slub.txt.
2912 slub_min_objects= [MM, SLUB]
2913 The minimum number of objects per slab. SLUB will
2914 increase the slab order up to slub_max_order to
2915 generate a sufficiently large slab able to contain
2916 the number of objects indicated. The higher the number
2917 of objects the smaller the overhead of tracking slabs
2918 and the less frequently locks need to be acquired.
2919 For more information see Documentation/vm/slub.txt.
2921 slub_min_order= [MM, SLUB]
2922 Determines the minimum page order for slabs. Must be
2923 lower than slub_max_order.
2924 For more information see Documentation/vm/slub.txt.
2926 slub_nomerge [MM, SLUB]
2927 Disable merging of slabs with similar size. May be
2928 necessary if there is some reason to distinguish
2929 allocs to different slabs. Debug options disable
2930 merging on their own.
2931 For more information see Documentation/vm/slub.txt.
2933 smart2= [HW]
2934 Format: <io1>[,<io2>[,...,<io8>]]
2936 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2937 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2938 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2939 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2940 smsc-ircc2.ircc_irq= [HW] IRQ line
2941 smsc-ircc2.ircc_dma= [HW] DMA channel
2942 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2943 0: Toshiba Satellite 1800 (GP data pin select)
2944 1: Fast pin select (default)
2945 2: ATC IRMode
2947 softlockup_panic=
2948 [KNL] Should the soft-lockup detector generate panics.
2949 Format: <integer>
2951 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2952 See Documentation/laptops/sonypi.txt
2954 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2955 See Documentation/serial/specialix.txt.
2957 spia_io_base= [HW,MTD]
2958 spia_fio_base=
2959 spia_pedr=
2960 spia_peddr=
2962 stacktrace [FTRACE]
2963 Enabled the stack tracer on boot up.
2965 stacktrace_filter=[function-list]
2966 [FTRACE] Limit the functions that the stack tracer
2967 will trace at boot up. function-list is a comma separated
2968 list of functions. This list can be changed at run
2969 time by the stack_trace_filter file in the debugfs
2970 tracing directory. Note, this enables stack tracing
2971 and the stacktrace above is not needed.
2973 sti= [PARISC,HW]
2974 Format: <num>
2975 Set the STI (builtin display/keyboard on the HP-PARISC
2976 machines) console (graphic card) which should be used
2977 as the initial boot-console.
2978 See also comment in drivers/video/console/sticore.c.
2980 sti_font= [HW]
2981 See comment in drivers/video/console/sticore.c.
2983 stifb= [HW]
2984 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2986 sunrpc.min_resvport=
2987 sunrpc.max_resvport=
2988 [NFS,SUNRPC]
2989 SunRPC servers often require that client requests
2990 originate from a privileged port (i.e. a port in the
2991 range 0 < portnr < 1024).
2992 An administrator who wishes to reserve some of these
2993 ports for other uses may adjust the range that the
2994 kernel's sunrpc client considers to be privileged
2995 using these two parameters to set the minimum and
2996 maximum port values.
2998 sunrpc.pool_mode=
2999 [NFS]
3000 Control how the NFS server code allocates CPUs to
3001 service thread pools. Depending on how many NICs
3002 you have and where their interrupts are bound, this
3003 option will affect which CPUs will do NFS serving.
3004 Note: this parameter cannot be changed while the
3005 NFS server is running.
3007 auto the server chooses an appropriate mode
3008 automatically using heuristics
3009 global a single global pool contains all CPUs
3010 percpu one pool for each CPU
3011 pernode one pool for each NUMA node (equivalent
3012 to global on non-NUMA machines)
3014 sunrpc.tcp_slot_table_entries=
3015 sunrpc.udp_slot_table_entries=
3016 [NFS,SUNRPC]
3017 Sets the upper limit on the number of simultaneous
3018 RPC calls that can be sent from the client to a
3019 server. Increasing these values may allow you to
3020 improve throughput, but will also increase the
3021 amount of memory reserved for use by the client.
3023 swapaccount=[0|1]
3024 [KNL] Enable accounting of swap in memory resource
3025 controller if no parameter or 1 is given or disable
3026 it if 0 is given (See Documentation/cgroups/memory.txt)
3028 swiotlb= [IA-64] Number of I/O TLB slabs
3030 switches= [HW,M68k]
3032 sysfs.deprecated=0|1 [KNL]
3033 Enable/disable old style sysfs layout for old udev
3034 on older distributions. When this option is enabled
3035 very new udev will not work anymore. When this option
3036 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3037 in older udev will not work anymore.
3038 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3039 the kernel configuration.
3041 sysrq_always_enabled
3042 [KNL]
3043 Ignore sysrq setting - this boot parameter will
3044 neutralize any effect of /proc/sys/kernel/sysrq.
3045 Useful for debugging.
3047 tdfx= [HW,DRM]
3049 test_suspend= [SUSPEND]
3050 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3051 standby suspend) as the system sleep state to briefly
3052 enter during system startup. The system is woken from
3053 this state using a wakeup-capable RTC alarm.
3055 thash_entries= [KNL,NET]
3056 Set number of hash buckets for TCP connection
3058 thermal.act= [HW,ACPI]
3059 -1: disable all active trip points in all thermal zones
3060 <degrees C>: override all lowest active trip points
3062 thermal.crt= [HW,ACPI]
3063 -1: disable all critical trip points in all thermal zones
3064 <degrees C>: override all critical trip points
3066 thermal.nocrt= [HW,ACPI]
3067 Set to disable actions on ACPI thermal zone
3068 critical and hot trip points.
3070 thermal.off= [HW,ACPI]
3071 1: disable ACPI thermal control
3073 thermal.psv= [HW,ACPI]
3074 -1: disable all passive trip points
3075 <degrees C>: override all passive trip points to this
3076 value
3078 thermal.tzp= [HW,ACPI]
3079 Specify global default ACPI thermal zone polling rate
3080 <deci-seconds>: poll all this frequency
3081 0: no polling (default)
3083 threadirqs [KNL]
3084 Force threading of all interrupt handlers except those
3085 marked explicitly IRQF_NO_THREAD.
3087 tmem [KNL,XEN]
3088 Enable the Transcendent memory driver if built-in.
3090 tmem.cleancache=0|1 [KNL, XEN]
3091 Default is on (1). Disable the usage of the cleancache
3092 API to send anonymous pages to the hypervisor.
3094 tmem.frontswap=0|1 [KNL, XEN]
3095 Default is on (1). Disable the usage of the frontswap
3096 API to send swap pages to the hypervisor. If disabled
3097 the selfballooning and selfshrinking are force disabled.
3099 tmem.selfballooning=0|1 [KNL, XEN]
3100 Default is on (1). Disable the driving of swap pages
3101 to the hypervisor.
3103 tmem.selfshrinking=0|1 [KNL, XEN]
3104 Default is on (1). Partial swapoff that immediately
3105 transfers pages from Xen hypervisor back to the
3106 kernel based on different criteria.
3108 topology= [S390]
3109 Format: {off | on}
3110 Specify if the kernel should make use of the cpu
3111 topology information if the hardware supports this.
3112 The scheduler will make use of this information and
3113 e.g. base its process migration decisions on it.
3114 Default is on.
3116 tp720= [HW,PS2]
3118 tpm_suspend_pcr=[HW,TPM]
3119 Format: integer pcr id
3120 Specify that at suspend time, the tpm driver
3121 should extend the specified pcr with zeros,
3122 as a workaround for some chips which fail to
3123 flush the last written pcr on TPM_SaveState.
3124 This will guarantee that all the other pcrs
3125 are saved.
3127 trace_buf_size=nn[KMG]
3128 [FTRACE] will set tracing buffer size.
3130 trace_event=[event-list]
3131 [FTRACE] Set and start specified trace events in order
3132 to facilitate early boot debugging.
3133 See also Documentation/trace/events.txt
3135 trace_options=[option-list]
3136 [FTRACE] Enable or disable tracer options at boot.
3137 The option-list is a comma delimited list of options
3138 that can be enabled or disabled just as if you were
3139 to echo the option name into
3141 /sys/kernel/debug/tracing/trace_options
3143 For example, to enable stacktrace option (to dump the
3144 stack trace of each event), add to the command line:
3146 trace_options=stacktrace
3148 See also Documentation/trace/ftrace.txt "trace options"
3149 section.
3151 traceoff_on_warning
3152 [FTRACE] enable this option to disable tracing when a
3153 warning is hit. This turns off "tracing_on". Tracing can
3154 be enabled again by echoing '1' into the "tracing_on"
3155 file located in /sys/kernel/debug/tracing/
3157 This option is useful, as it disables the trace before
3158 the WARNING dump is called, which prevents the trace to
3159 be filled with content caused by the warning output.
3161 This option can also be set at run time via the sysctl
3162 option: kernel/traceoff_on_warning
3164 transparent_hugepage=
3165 [KNL]
3166 Format: [always|madvise|never]
3167 Can be used to control the default behavior of the system
3168 with respect to transparent hugepages.
3169 See Documentation/vm/transhuge.txt for more details.
3171 tsc= Disable clocksource stability checks for TSC.
3172 Format: <string>
3173 [x86] reliable: mark tsc clocksource as reliable, this
3174 disables clocksource verification at runtime, as well
3175 as the stability checks done at bootup. Used to enable
3176 high-resolution timer mode on older hardware, and in
3177 virtualized environment.
3178 [x86] noirqtime: Do not use TSC to do irq accounting.
3179 Used to run time disable IRQ_TIME_ACCOUNTING on any
3180 platforms where RDTSC is slow and this accounting
3181 can add overhead.
3183 turbografx.map[2|3]= [HW,JOY]
3184 TurboGraFX parallel port interface
3185 Format:
3186 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3187 See also Documentation/input/joystick-parport.txt
3189 udbg-immortal [PPC] When debugging early kernel crashes that
3190 happen after console_init() and before a proper
3191 console driver takes over, this boot options might
3192 help "seeing" what's going on.
3194 uhash_entries= [KNL,NET]
3195 Set number of hash buckets for UDP/UDP-Lite connections
3197 uhci-hcd.ignore_oc=
3198 [USB] Ignore overcurrent events (default N).
3199 Some badly-designed motherboards generate lots of
3200 bogus events, for ports that aren't wired to
3201 anything. Set this parameter to avoid log spamming.
3202 Note that genuine overcurrent events won't be
3203 reported either.
3205 unknown_nmi_panic
3206 [X86] Cause panic on unknown NMI.
3208 usbcore.authorized_default=
3209 [USB] Default USB device authorization:
3210 (default -1 = authorized except for wireless USB,
3211 0 = not authorized, 1 = authorized)
3213 usbcore.autosuspend=
3214 [USB] The autosuspend time delay (in seconds) used
3215 for newly-detected USB devices (default 2). This
3216 is the time required before an idle device will be
3217 autosuspended. Devices for which the delay is set
3218 to a negative value won't be autosuspended at all.
3220 usbcore.usbfs_snoop=
3221 [USB] Set to log all usbfs traffic (default 0 = off).
3223 usbcore.blinkenlights=
3224 [USB] Set to cycle leds on hubs (default 0 = off).
3226 usbcore.old_scheme_first=
3227 [USB] Start with the old device initialization
3228 scheme (default 0 = off).
3230 usbcore.usbfs_memory_mb=
3231 [USB] Memory limit (in MB) for buffers allocated by
3232 usbfs (default = 16, 0 = max = 2047).
3234 usbcore.use_both_schemes=
3235 [USB] Try the other device initialization scheme
3236 if the first one fails (default 1 = enabled).
3238 usbcore.initial_descriptor_timeout=
3239 [USB] Specifies timeout for the initial 64-byte
3240 USB_REQ_GET_DESCRIPTOR request in milliseconds
3241 (default 5000 = 5.0 seconds).
3243 usbhid.mousepoll=
3244 [USBHID] The interval which mice are to be polled at.
3246 usb-storage.delay_use=
3247 [UMS] The delay in seconds before a new device is
3248 scanned for Logical Units (default 5).
3250 usb-storage.quirks=
3251 [UMS] A list of quirks entries to supplement or
3252 override the built-in unusual_devs list. List
3253 entries are separated by commas. Each entry has
3254 the form VID:PID:Flags where VID and PID are Vendor
3255 and Product ID values (4-digit hex numbers) and
3256 Flags is a set of characters, each corresponding
3257 to a common usb-storage quirk flag as follows:
3258 a = SANE_SENSE (collect more than 18 bytes
3259 of sense data);
3260 b = BAD_SENSE (don't collect more than 18
3261 bytes of sense data);
3262 c = FIX_CAPACITY (decrease the reported
3263 device capacity by one sector);
3264 d = NO_READ_DISC_INFO (don't use
3265 READ_DISC_INFO command);
3266 e = NO_READ_CAPACITY_16 (don't use
3267 READ_CAPACITY_16 command);
3268 h = CAPACITY_HEURISTICS (decrease the
3269 reported device capacity by one
3270 sector if the number is odd);
3271 i = IGNORE_DEVICE (don't bind to this
3272 device);
3273 l = NOT_LOCKABLE (don't try to lock and
3274 unlock ejectable media);
3275 m = MAX_SECTORS_64 (don't transfer more
3276 than 64 sectors = 32 KB at a time);
3277 n = INITIAL_READ10 (force a retry of the
3278 initial READ(10) command);
3279 o = CAPACITY_OK (accept the capacity
3280 reported by the device);
3281 p = WRITE_CACHE (the device cache is ON
3282 by default);
3283 r = IGNORE_RESIDUE (the device reports
3284 bogus residue values);
3285 s = SINGLE_LUN (the device has only one
3286 Logical Unit);
3287 w = NO_WP_DETECT (don't test whether the
3288 medium is write-protected).
3289 Example: quirks=0419:aaf5:rl,0421:0433:rc
3291 user_debug= [KNL,ARM]
3292 Format: <int>
3293 See arch/arm/Kconfig.debug help text.
3294 1 - undefined instruction events
3295 2 - system calls
3296 4 - invalid data aborts
3297 8 - SIGSEGV faults
3298 16 - SIGBUS faults
3299 Example: user_debug=31
3301 userpte=
3302 [X86] Flags controlling user PTE allocations.
3304 nohigh = do not allocate PTE pages in
3305 HIGHMEM regardless of setting
3306 of CONFIG_HIGHPTE.
3308 vdso= [X86,SH]
3309 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3310 vdso=1: enable VDSO (default)
3311 vdso=0: disable VDSO mapping
3313 vdso32= [X86]
3314 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3315 vdso32=1: enable 32-bit VDSO (default)
3316 vdso32=0: disable 32-bit VDSO mapping
3318 vector= [IA-64,SMP]
3319 vector=percpu: enable percpu vector domain
3321 video= [FB] Frame buffer configuration
3322 See Documentation/fb/modedb.txt.
3324 video.brightness_switch_enabled= [0,1]
3325 If set to 1, on receiving an ACPI notify event
3326 generated by hotkey, video driver will adjust brightness
3327 level and then send out the event to user space through
3328 the allocated input device; If set to 0, video driver
3329 will only send out the event without touching backlight
3330 brightness level.
3331 default: 1
3333 virtio_mmio.device=
3334 [VMMIO] Memory mapped virtio (platform) device.
3336 <size>@<baseaddr>:<irq>[:<id>]
3337 where:
3338 <size> := size (can use standard suffixes
3339 like K, M and G)
3340 <baseaddr> := physical base address
3341 <irq> := interrupt number (as passed to
3342 request_irq())
3343 <id> := (optional) platform device id
3344 example:
3345 virtio_mmio.device=1K@0x100b0000:48:7
3347 Can be used multiple times for multiple devices.
3349 vga= [BOOT,X86-32] Select a particular video mode
3350 See Documentation/x86/boot.txt and
3351 Documentation/svga.txt.
3352 Use vga=ask for menu.
3353 This is actually a boot loader parameter; the value is
3354 passed to the kernel using a special protocol.
3356 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3357 size of <nn>. This can be used to increase the
3358 minimum size (128MB on x86). It can also be used to
3359 decrease the size and leave more room for directly
3360 mapped kernel RAM.
3362 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3363 Format: <command>
3365 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3366 Format: <command>
3368 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3369 Format: <command>
3371 vsyscall= [X86-64]
3372 Controls the behavior of vsyscalls (i.e. calls to
3373 fixed addresses of 0xffffffffff600x00 from legacy
3374 code). Most statically-linked binaries and older
3375 versions of glibc use these calls. Because these
3376 functions are at fixed addresses, they make nice
3377 targets for exploits that can control RIP.
3379 emulate [default] Vsyscalls turn into traps and are
3380 emulated reasonably safely.
3382 native Vsyscalls are native syscall instructions.
3383 This is a little bit faster than trapping
3384 and makes a few dynamic recompilers work
3385 better than they would in emulation mode.
3386 It also makes exploits much easier to write.
3388 none Vsyscalls don't work at all. This makes
3389 them quite hard to use for exploits but
3390 might break your system.
3392 vt.color= [VT] Default text color.
3393 Format: 0xYX, X = foreground, Y = background.
3394 Default: 0x07 = light gray on black.
3396 vt.cur_default= [VT] Default cursor shape.
3397 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3398 the parameters of the <Esc>[?A;B;Cc escape sequence;
3399 see VGA-softcursor.txt. Default: 2 = underline.
3401 vt.default_blu= [VT]
3402 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3403 Change the default blue palette of the console.
3404 This is a 16-member array composed of values
3405 ranging from 0-255.
3407 vt.default_grn= [VT]
3408 Format: <green0>,<green1>,<green2>,...,<green15>
3409 Change the default green palette of the console.
3410 This is a 16-member array composed of values
3411 ranging from 0-255.
3413 vt.default_red= [VT]
3414 Format: <red0>,<red1>,<red2>,...,<red15>
3415 Change the default red palette of the console.
3416 This is a 16-member array composed of values
3417 ranging from 0-255.
3419 vt.default_utf8=
3420 [VT]
3421 Format=<0|1>
3422 Set system-wide default UTF-8 mode for all tty's.
3423 Default is 1, i.e. UTF-8 mode is enabled for all
3424 newly opened terminals.
3426 vt.global_cursor_default=
3427 [VT]
3428 Format=<-1|0|1>
3429 Set system-wide default for whether a cursor
3430 is shown on new VTs. Default is -1,
3431 i.e. cursors will be created by default unless
3432 overridden by individual drivers. 0 will hide
3433 cursors, 1 will display them.
3435 vt.italic= [VT] Default color for italic text; 0-15.
3436 Default: 2 = green.
3438 vt.underline= [VT] Default color for underlined text; 0-15.
3439 Default: 3 = cyan.
3441 watchdog timers [HW,WDT] For information on watchdog timers,
3442 see Documentation/watchdog/watchdog-parameters.txt
3443 or other driver-specific files in the
3444 Documentation/watchdog/ directory.
3446 workqueue.disable_numa
3447 By default, all work items queued to unbound
3448 workqueues are affine to the NUMA nodes they're
3449 issued on, which results in better behavior in
3450 general. If NUMA affinity needs to be disabled for
3451 whatever reason, this option can be used. Note
3452 that this also can be controlled per-workqueue for
3453 workqueues visible under /sys/bus/workqueue/.
3455 workqueue.power_efficient
3456 Per-cpu workqueues are generally preferred because
3457 they show better performance thanks to cache
3458 locality; unfortunately, per-cpu workqueues tend to
3459 be more power hungry than unbound workqueues.
3461 Enabling this makes the per-cpu workqueues which
3462 were observed to contribute significantly to power
3463 consumption unbound, leading to measurably lower
3464 power usage at the cost of small performance
3465 overhead.
3467 The default value of this parameter is determined by
3468 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3470 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3471 default x2apic cluster mode on platforms
3472 supporting x2apic.
3474 x86_mrst_timer= [X86-32,APBT]
3475 Choose timer option for x86 Moorestown MID platform.
3476 Two valid options are apbt timer only and lapic timer
3477 plus one apbt timer for broadcast timer.
3478 x86_mrst_timer=apbt_only | lapic_and_apbt
3480 xen_emul_unplug= [HW,X86,XEN]
3481 Unplug Xen emulated devices
3482 Format: [unplug0,][unplug1]
3483 ide-disks -- unplug primary master IDE devices
3484 aux-ide-disks -- unplug non-primary-master IDE devices
3485 nics -- unplug network devices
3486 all -- unplug all emulated devices (NICs and IDE disks)
3487 unnecessary -- unplugging emulated devices is
3488 unnecessary even if the host did not respond to
3489 the unplug protocol
3490 never -- do not unplug even if version check succeeds
3492 xen_nopvspin [X86,XEN]
3493 Disables the ticketlock slowpath using Xen PV
3494 optimizations.
3496 xirc2ps_cs= [NET,PCMCIA]
3497 Format:
3498 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3500 ______________________________________________________________________
3502 TODO:
3504 Add more DRM drivers.