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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 -- only one string
239 acpi_osi="!string2" # remove built-in string2
240 acpi_osi= # disable all strings
242 acpi_pm_good [X86]
243 Override the pmtimer bug detection: force the kernel
244 to assume that this machine's pmtimer latches its value
245 and always returns good values.
247 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
248 Format: { level | edge | high | low }
250 acpi_serialize [HW,ACPI] force serialization of AML methods
252 acpi_skip_timer_override [HW,ACPI]
253 Recognize and ignore IRQ0/pin2 Interrupt Override.
254 For broken nForce2 BIOS resulting in XT-PIC timer.
256 acpi_sleep= [HW,ACPI] Sleep options
257 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
258 old_ordering, nonvs, sci_force_enable }
259 See Documentation/power/video.txt for information on
260 s3_bios and s3_mode.
261 s3_beep is for debugging; it makes the PC's speaker beep
262 as soon as the kernel's real-mode entry point is called.
263 s4_nohwsig prevents ACPI hardware signature from being
264 used during resume from hibernation.
265 old_ordering causes the ACPI 1.0 ordering of the _PTS
266 control method, with respect to putting devices into
267 low power states, to be enforced (the ACPI 2.0 ordering
268 of _PTS is used by default).
269 nonvs prevents the kernel from saving/restoring the
270 ACPI NVS memory during suspend/hibernation and resume.
271 sci_force_enable causes the kernel to set SCI_EN directly
272 on resume from S1/S3 (which is against the ACPI spec,
273 but some broken systems don't work without it).
275 acpi_use_timer_override [HW,ACPI]
276 Use timer override. For some broken Nvidia NF5 boards
277 that require a timer override, but don't have HPET
279 acpi_enforce_resources= [ACPI]
280 { strict | lax | no }
281 Check for resource conflicts between native drivers
282 and ACPI OperationRegions (SystemIO and SystemMemory
283 only). IO ports and memory declared in ACPI might be
284 used by the ACPI subsystem in arbitrary AML code and
285 can interfere with legacy drivers.
286 strict (default): access to resources claimed by ACPI
287 is denied; legacy drivers trying to access reserved
288 resources will fail to bind to device using them.
289 lax: access to resources claimed by ACPI is allowed;
290 legacy drivers trying to access reserved resources
291 will bind successfully but a warning message is logged.
292 no: ACPI OperationRegions are not marked as reserved,
293 no further checks are performed.
295 add_efi_memmap [EFI; X86] Include EFI memory map in
296 kernel's map of available physical RAM.
298 agp= [AGP]
299 { off | try_unsupported }
300 off: disable AGP support
301 try_unsupported: try to drive unsupported chipsets
302 (may crash computer or cause data corruption)
304 ALSA [HW,ALSA]
305 See Documentation/sound/alsa/alsa-parameters.txt
307 alignment= [KNL,ARM]
308 Allow the default userspace alignment fault handler
309 behaviour to be specified. Bit 0 enables warnings,
310 bit 1 enables fixups, and bit 2 sends a segfault.
312 align_va_addr= [X86-64]
313 Align virtual addresses by clearing slice [14:12] when
314 allocating a VMA at process creation time. This option
315 gives you up to 3% performance improvement on AMD F15h
316 machines (where it is enabled by default) for a
317 CPU-intensive style benchmark, and it can vary highly in
318 a microbenchmark depending on workload and compiler.
320 32: only for 32-bit processes
321 64: only for 64-bit processes
322 on: enable for both 32- and 64-bit processes
323 off: disable for both 32- and 64-bit processes
325 alloc_snapshot [FTRACE]
326 Allocate the ftrace snapshot buffer on boot up when the
327 main buffer is allocated. This is handy if debugging
328 and you need to use tracing_snapshot() on boot up, and
329 do not want to use tracing_snapshot_alloc() as it needs
330 to be done where GFP_KERNEL allocations are allowed.
332 amd_iommu= [HW,X86-64]
333 Pass parameters to the AMD IOMMU driver in the system.
334 Possible values are:
335 fullflush - enable flushing of IO/TLB entries when
336 they are unmapped. Otherwise they are
337 flushed before they will be reused, which
338 is a lot of faster
339 off - do not initialize any AMD IOMMU found in
340 the system
341 force_isolation - Force device isolation for all
342 devices. The IOMMU driver is not
343 allowed anymore to lift isolation
344 requirements as needed. This option
345 does not override iommu=pt
347 amd_iommu_dump= [HW,X86-64]
348 Enable AMD IOMMU driver option to dump the ACPI table
349 for AMD IOMMU. With this option enabled, AMD IOMMU
350 driver will print ACPI tables for AMD IOMMU during
351 IOMMU initialization.
353 amijoy.map= [HW,JOY] Amiga joystick support
354 Map of devices attached to JOY0DAT and JOY1DAT
355 Format: <a>,<b>
356 See also Documentation/input/joystick.txt
358 analog.map= [HW,JOY] Analog joystick and gamepad support
359 Specifies type or capabilities of an analog joystick
360 connected to one of 16 gameports
361 Format: <type1>,<type2>,..<type16>
363 apc= [HW,SPARC]
364 Power management functions (SPARCstation-4/5 + deriv.)
365 Format: noidle
366 Disable APC CPU standby support. SPARCstation-Fox does
367 not play well with APC CPU idle - disable it if you have
368 APC and your system crashes randomly.
370 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
371 Change the output verbosity whilst booting
372 Format: { quiet (default) | verbose | debug }
373 Change the amount of debugging information output
374 when initialising the APIC and IO-APIC components.
376 autoconf= [IPV6]
377 See Documentation/networking/ipv6.txt.
379 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
380 Limit apic dumping. The parameter defines the maximal
381 number of local apics being dumped. Also it is possible
382 to set it to "all" by meaning -- no limit here.
383 Format: { 1 (default) | 2 | ... | all }.
384 The parameter valid if only apic=debug or
385 apic=verbose is specified.
386 Example: apic=debug show_lapic=all
388 apm= [APM] Advanced Power Management
389 See header of arch/x86/kernel/apm_32.c.
391 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
392 Format: <io>,<irq>,<nodeID>
394 ataflop= [HW,M68k]
396 atarimouse= [HW,MOUSE] Atari Mouse
398 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
399 EzKey and similar keyboards
401 atkbd.reset= [HW] Reset keyboard during initialization
403 atkbd.set= [HW] Select keyboard code set
404 Format: <int> (2 = AT (default), 3 = PS/2)
406 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
407 keyboards
409 atkbd.softraw= [HW] Choose between synthetic and real raw mode
410 Format: <bool> (0 = real, 1 = synthetic (default))
412 atkbd.softrepeat= [HW]
413 Use software keyboard repeat
415 baycom_epp= [HW,AX25]
416 Format: <io>,<mode>
418 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
419 Format: <io>,<mode>
420 See header of drivers/net/hamradio/baycom_par.c.
422 baycom_ser_fdx= [HW,AX25]
423 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
424 Format: <io>,<irq>,<mode>[,<baud>]
425 See header of drivers/net/hamradio/baycom_ser_fdx.c.
427 baycom_ser_hdx= [HW,AX25]
428 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
429 Format: <io>,<irq>,<mode>
430 See header of drivers/net/hamradio/baycom_ser_hdx.c.
432 boot_delay= Milliseconds to delay each printk during boot.
433 Values larger than 10 seconds (10000) are changed to
434 no delay (0).
435 Format: integer
437 bootmem_debug [KNL] Enable bootmem allocator debug messages.
439 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
440 bttv.radio= Most important insmod options are available as
441 kernel args too.
442 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
443 bttv.tuner=
445 bulk_remove=off [PPC] This parameter disables the use of the pSeries
446 firmware feature for flushing multiple hpte entries
447 at a time.
449 c101= [NET] Moxa C101 synchronous serial card
451 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
452 Sometimes CPU hardware bugs make them report the cache
453 size incorrectly. The kernel will attempt work arounds
454 to fix known problems, but for some CPUs it is not
455 possible to determine what the correct size should be.
456 This option provides an override for these situations.
458 ccw_timeout_log [S390]
459 See Documentation/s390/CommonIO for details.
461 cgroup_disable= [KNL] Disable a particular controller
462 Format: {name of the controller(s) to disable}
463 {Currently supported controllers - "memory"}
465 checkreqprot [SELINUX] Set initial checkreqprot flag value.
466 Format: { "0" | "1" }
467 See security/selinux/Kconfig help text.
468 0 -- check protection applied by kernel (includes
469 any implied execute protection).
470 1 -- check protection requested by application.
471 Default value is set via a kernel config option.
472 Value can be changed at runtime via
473 /selinux/checkreqprot.
475 cio_ignore= [S390]
476 See Documentation/s390/CommonIO for details.
477 clk_ignore_unused
478 [CLK]
479 Keep all clocks already enabled by bootloader on,
480 even if no driver has claimed them. This is useful
481 for debug and development, but should not be
482 needed on a platform with proper driver support.
483 For more information, see Documentation/clk.txt.
485 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
486 [Deprecated]
487 Forces specified clocksource (if available) to be used
488 when calculating gettimeofday(). If specified
489 clocksource is not available, it defaults to PIT.
490 Format: { pit | tsc | cyclone | pmtmr }
492 clocksource= Override the default clocksource
493 Format: <string>
494 Override the default clocksource and use the clocksource
495 with the name specified.
496 Some clocksource names to choose from, depending on
497 the platform:
498 [all] jiffies (this is the base, fallback clocksource)
499 [ACPI] acpi_pm
500 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
501 pxa_timer,timer3,32k_counter,timer0_1
502 [AVR32] avr32
503 [X86-32] pit,hpet,tsc;
504 scx200_hrt on Geode; cyclone on IBM x440
505 [MIPS] MIPS
506 [PARISC] cr16
507 [S390] tod
508 [SH] SuperH
509 [SPARC64] tick
510 [X86-64] hpet,tsc
512 clearcpuid=BITNUM [X86]
513 Disable CPUID feature X for the kernel. See
514 arch/x86/include/asm/cpufeature.h for the valid bit
515 numbers. Note the Linux specific bits are not necessarily
516 stable over kernel options, but the vendor specific
517 ones should be.
518 Also note that user programs calling CPUID directly
519 or using the feature without checking anything
520 will still see it. This just prevents it from
521 being used by the kernel or shown in /proc/cpuinfo.
522 Also note the kernel might malfunction if you disable
523 some critical bits.
525 cma=nn[MG] [ARM,KNL]
526 Sets the size of kernel global memory area for contiguous
527 memory allocations. For more information, see
528 include/linux/dma-contiguous.h
530 cmo_free_hint= [PPC] Format: { yes | no }
531 Specify whether pages are marked as being inactive
532 when they are freed. This is used in CMO environments
533 to determine OS memory pressure for page stealing by
534 a hypervisor.
535 Default: yes
537 coherent_pool=nn[KMG] [ARM,KNL]
538 Sets the size of memory pool for coherent, atomic dma
539 allocations, by default set to 256K.
541 code_bytes [X86] How many bytes of object code to print
542 in an oops report.
543 Range: 0 - 8192
544 Default: 64
546 com20020= [HW,NET] ARCnet - COM20020 chipset
547 Format:
548 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
550 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
551 Format: <io>[,<irq>]
553 com90xx= [HW,NET]
554 ARCnet - COM90xx chipset (memory-mapped buffers)
555 Format: <io>[,<irq>[,<memstart>]]
557 condev= [HW,S390] console device
558 conmode=
560 console= [KNL] Output console device and options.
562 tty<n> Use the virtual console device <n>.
564 ttyS<n>[,options]
565 ttyUSB0[,options]
566 Use the specified serial port. The options are of
567 the form "bbbbpnf", where "bbbb" is the baud rate,
568 "p" is parity ("n", "o", or "e"), "n" is number of
569 bits, and "f" is flow control ("r" for RTS or
570 omit it). Default is "9600n8".
572 See Documentation/serial-console.txt for more
573 information. See
574 Documentation/networking/netconsole.txt for an
575 alternative.
577 uart[8250],io,<addr>[,options]
578 uart[8250],mmio,<addr>[,options]
579 Start an early, polled-mode console on the 8250/16550
580 UART at the specified I/O port or MMIO address,
581 switching to the matching ttyS device later. The
582 options are the same as for ttyS, above.
583 hvc<n> Use the hypervisor console device <n>. This is for
584 both Xen and PowerPC hypervisors.
586 If the device connected to the port is not a TTY but a braille
587 device, prepend "brl," before the device type, for instance
588 console=brl,ttyS0
589 For now, only VisioBraille is supported.
591 consoleblank= [KNL] The console blank (screen saver) timeout in
592 seconds. Defaults to 10*60 = 10mins. A value of 0
593 disables the blank timer.
595 coredump_filter=
596 [KNL] Change the default value for
597 /proc/<pid>/coredump_filter.
598 See also Documentation/filesystems/proc.txt.
600 cpuidle.off=1 [CPU_IDLE]
601 disable the cpuidle sub-system
603 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
604 Format:
605 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
607 crashkernel=size[KMG][@offset[KMG]]
608 [KNL] Using kexec, Linux can switch to a 'crash kernel'
609 upon panic. This parameter reserves the physical
610 memory region [offset, offset + size] for that kernel
611 image. If '@offset' is omitted, then a suitable offset
612 is selected automatically. Check
613 Documentation/kdump/kdump.txt for further details.
615 crashkernel=range1:size1[,range2:size2,...][@offset]
616 [KNL] Same as above, but depends on the memory
617 in the running system. The syntax of range is
618 start-[end] where start and end are both
619 a memory unit (amount[KMG]). See also
620 Documentation/kdump/kdump.txt for an example.
622 crashkernel=size[KMG],high
623 [KNL, x86_64] range could be above 4G. Allow kernel
624 to allocate physical memory region from top, so could
625 be above 4G if system have more than 4G ram installed.
626 Otherwise memory region will be allocated below 4G, if
627 available.
628 It will be ignored if crashkernel=X is specified.
629 crashkernel=size[KMG],low
630 [KNL, x86_64] range under 4G. When crashkernel=X,high
631 is passed, kernel could allocate physical memory region
632 above 4G, that cause second kernel crash on system
633 that require some amount of low memory, e.g. swiotlb
634 requires at least 64M+32K low memory. Kernel would
635 try to allocate 72M below 4G automatically.
636 This one let user to specify own low range under 4G
637 for second kernel instead.
638 0: to disable low allocation.
639 It will be ignored when crashkernel=X,high is not used
640 or memory reserved is below 4G.
642 cs89x0_dma= [HW,NET]
643 Format: <dma>
645 cs89x0_media= [HW,NET]
646 Format: { rj45 | aui | bnc }
648 dasd= [HW,NET]
649 See header of drivers/s390/block/dasd_devmap.c.
651 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
652 (one device per port)
653 Format: <port#>,<type>
654 See also Documentation/input/joystick-parport.txt
656 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
657 time. See Documentation/dynamic-debug-howto.txt for
658 details. Deprecated, see dyndbg.
660 debug [KNL] Enable kernel debugging (events log level).
662 debug_locks_verbose=
663 [KNL] verbose self-tests
664 Format=<0|1>
665 Print debugging info while doing the locking API
666 self-tests.
667 We default to 0 (no extra messages), setting it to
668 1 will print _a lot_ more information - normally
669 only useful to kernel developers.
671 debug_objects [KNL] Enable object debugging
673 no_debug_objects
674 [KNL] Disable object debugging
676 debug_guardpage_minorder=
677 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
678 parameter allows control of the order of pages that will
679 be intentionally kept free (and hence protected) by the
680 buddy allocator. Bigger value increase the probability
681 of catching random memory corruption, but reduce the
682 amount of memory for normal system use. The maximum
683 possible value is MAX_ORDER/2. Setting this parameter
684 to 1 or 2 should be enough to identify most random
685 memory corruption problems caused by bugs in kernel or
686 driver code when a CPU writes to (or reads from) a
687 random memory location. Note that there exists a class
688 of memory corruptions problems caused by buggy H/W or
689 F/W or by drivers badly programing DMA (basically when
690 memory is written at bus level and the CPU MMU is
691 bypassed) which are not detectable by
692 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
693 tracking down these problems.
695 debugpat [X86] Enable PAT debugging
697 decnet.addr= [HW,NET]
698 Format: <area>[,<node>]
699 See also Documentation/networking/decnet.txt.
701 default_hugepagesz=
702 [same as hugepagesz=] The size of the default
703 HugeTLB page size. This is the size represented by
704 the legacy /proc/ hugepages APIs, used for SHM, and
705 default size when mounting hugetlbfs filesystems.
706 Defaults to the default architecture's huge page size
707 if not specified.
709 dhash_entries= [KNL]
710 Set number of hash buckets for dentry cache.
712 digi= [HW,SERIAL]
713 IO parameters + enable/disable command.
715 digiepca= [HW,SERIAL]
716 See drivers/char/README.epca and
717 Documentation/serial/digiepca.txt.
719 disable= [IPV6]
720 See Documentation/networking/ipv6.txt.
722 disable_ddw [PPC/PSERIES]
723 Disable Dynamic DMA Window support. Use this if
724 to workaround buggy firmware.
726 disable_ipv6= [IPV6]
727 See Documentation/networking/ipv6.txt.
729 disable_mtrr_cleanup [X86]
730 The kernel tries to adjust MTRR layout from continuous
731 to discrete, to make X server driver able to add WB
732 entry later. This parameter disables that.
734 disable_mtrr_trim [X86, Intel and AMD only]
735 By default the kernel will trim any uncacheable
736 memory out of your available memory pool based on
737 MTRR settings. This parameter disables that behavior,
738 possibly causing your machine to run very slowly.
740 disable_timer_pin_1 [X86]
741 Disable PIN 1 of APIC timer
742 Can be useful to work around chipset bugs.
744 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
745 this option disables the debugging code at boot.
747 dma_debug_entries=<number>
748 This option allows to tune the number of preallocated
749 entries for DMA-API debugging code. One entry is
750 required per DMA-API allocation. Use this if the
751 DMA-API debugging code disables itself because the
752 architectural default is too low.
754 dma_debug_driver=<driver_name>
755 With this option the DMA-API debugging driver
756 filter feature can be enabled at boot time. Just
757 pass the driver to filter for as the parameter.
758 The filter can be disabled or changed to another
759 driver later using sysfs.
761 drm_kms_helper.edid_firmware=[<connector>:]<file>
762 Broken monitors, graphic adapters and KVMs may
763 send no or incorrect EDID data sets. This parameter
764 allows to specify an EDID data set in the
765 /lib/firmware directory that is used instead.
766 Generic built-in EDID data sets are used, if one of
767 edid/1024x768.bin, edid/1280x1024.bin,
768 edid/1680x1050.bin, or edid/1920x1080.bin is given
769 and no file with the same name exists. Details and
770 instructions how to build your own EDID data are
771 available in Documentation/EDID/HOWTO.txt. An EDID
772 data set will only be used for a particular connector,
773 if its name and a colon are prepended to the EDID
774 name.
776 dscc4.setup= [NET]
778 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
779 module.dyndbg[="val"]
780 Enable debug messages at boot time. See
781 Documentation/dynamic-debug-howto.txt for details.
783 earlycon= [KNL] Output early console device and options.
784 uart[8250],io,<addr>[,options]
785 uart[8250],mmio,<addr>[,options]
786 uart[8250],mmio32,<addr>[,options]
787 Start an early, polled-mode console on the 8250/16550
788 UART at the specified I/O port or MMIO address.
789 MMIO inter-register address stride is either 8-bit
790 (mmio) or 32-bit (mmio32).
791 The options are the same as for ttyS, above.
793 earlyprintk= [X86,SH,BLACKFIN,ARM]
794 earlyprintk=vga
795 earlyprintk=xen
796 earlyprintk=serial[,ttySn[,baudrate]]
797 earlyprintk=serial[,0x...[,baudrate]]
798 earlyprintk=ttySn[,baudrate]
799 earlyprintk=dbgp[debugController#]
801 earlyprintk is useful when the kernel crashes before
802 the normal console is initialized. It is not enabled by
803 default because it has some cosmetic problems.
805 Append ",keep" to not disable it when the real console
806 takes over.
808 Only vga or serial or usb debug port at a time.
810 Currently only ttyS0 and ttyS1 may be specified by
811 name. Other I/O ports may be explicitly specified
812 on some architectures (x86 and arm at least) by
813 replacing ttySn with an I/O port address, like this:
814 earlyprintk=serial,0x1008,115200
815 You can find the port for a given device in
816 /proc/tty/driver/serial:
817 2: uart:ST16650V2 port:00001008 irq:18 ...
819 Interaction with the standard serial driver is not
820 very good.
822 The VGA output is eventually overwritten by the real
823 console.
825 The xen output can only be used by Xen PV guests.
827 ekgdboc= [X86,KGDB] Allow early kernel console debugging
828 ekgdboc=kbd
830 This is designed to be used in conjunction with
831 the boot argument: earlyprintk=vga
833 edd= [EDD]
834 Format: {"off" | "on" | "skip[mbr]"}
836 efi_no_storage_paranoia [EFI; X86]
837 Using this parameter you can use more than 50% of
838 your efi variable storage. Use this parameter only if
839 you are really sure that your UEFI does sane gc and
840 fulfills the spec otherwise your board may brick.
842 eisa_irq_edge= [PARISC,HW]
843 See header of drivers/parisc/eisa.c.
845 elanfreq= [X86-32]
846 See comment before function elanfreq_setup() in
847 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
849 elevator= [IOSCHED]
850 Format: {"cfq" | "deadline" | "noop"}
851 See Documentation/block/cfq-iosched.txt and
852 Documentation/block/deadline-iosched.txt for details.
854 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
855 Specifies physical address of start of kernel core
856 image elf header and optionally the size. Generally
857 kexec loader will pass this option to capture kernel.
858 See Documentation/kdump/kdump.txt for details.
860 enable_mtrr_cleanup [X86]
861 The kernel tries to adjust MTRR layout from continuous
862 to discrete, to make X server driver able to add WB
863 entry later. This parameter enables that.
865 enable_timer_pin_1 [X86]
866 Enable PIN 1 of APIC timer
867 Can be useful to work around chipset bugs
868 (in particular on some ATI chipsets).
869 The kernel tries to set a reasonable default.
871 enforcing [SELINUX] Set initial enforcing status.
872 Format: {"0" | "1"}
873 See security/selinux/Kconfig help text.
874 0 -- permissive (log only, no denials).
875 1 -- enforcing (deny and log).
876 Default value is 0.
877 Value can be changed at runtime via /selinux/enforce.
879 erst_disable [ACPI]
880 Disable Error Record Serialization Table (ERST)
881 support.
883 ether= [HW,NET] Ethernet cards parameters
884 This option is obsoleted by the "netdev=" option, which
885 has equivalent usage. See its documentation for details.
887 evm= [EVM]
888 Format: { "fix" }
889 Permit 'security.evm' to be updated regardless of
890 current integrity status.
892 failslab=
893 fail_page_alloc=
894 fail_make_request=[KNL]
895 General fault injection mechanism.
896 Format: <interval>,<probability>,<space>,<times>
897 See also Documentation/fault-injection/.
899 floppy= [HW]
900 See Documentation/blockdev/floppy.txt.
902 force_pal_cache_flush
903 [IA-64] Avoid check_sal_cache_flush which may hang on
904 buggy SAL_CACHE_FLUSH implementations. Using this
905 parameter will force ia64_sal_cache_flush to call
906 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
908 ftrace=[tracer]
909 [FTRACE] will set and start the specified tracer
910 as early as possible in order to facilitate early
911 boot debugging.
913 ftrace_dump_on_oops[=orig_cpu]
914 [FTRACE] will dump the trace buffers on oops.
915 If no parameter is passed, ftrace will dump
916 buffers of all CPUs, but if you pass orig_cpu, it will
917 dump only the buffer of the CPU that triggered the
918 oops.
920 ftrace_filter=[function-list]
921 [FTRACE] Limit the functions traced by the function
922 tracer at boot up. function-list is a comma separated
923 list of functions. This list can be changed at run
924 time by the set_ftrace_filter file in the debugfs
925 tracing directory.
927 ftrace_notrace=[function-list]
928 [FTRACE] Do not trace the functions specified in
929 function-list. This list can be changed at run time
930 by the set_ftrace_notrace file in the debugfs
931 tracing directory.
933 ftrace_graph_filter=[function-list]
934 [FTRACE] Limit the top level callers functions traced
935 by the function graph tracer at boot up.
936 function-list is a comma separated list of functions
937 that can be changed at run time by the
938 set_graph_function file in the debugfs tracing directory.
940 gamecon.map[2|3]=
941 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
942 support via parallel port (up to 5 devices per port)
943 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
944 See also Documentation/input/joystick-parport.txt
946 gamma= [HW,DRM]
948 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
949 Format: off | on
950 default: on
952 gcov_persist= [GCOV] When non-zero (default), profiling data for
953 kernel modules is saved and remains accessible via
954 debugfs, even when the module is unloaded/reloaded.
955 When zero, profiling data is discarded and associated
956 debugfs files are removed at module unload time.
958 gpt [EFI] Forces disk with valid GPT signature but
959 invalid Protective MBR to be treated as GPT.
961 grcan.enable0= [HW] Configuration of physical interface 0. Determines
962 the "Enable 0" bit of the configuration register.
963 Format: 0 | 1
964 Default: 0
965 grcan.enable1= [HW] Configuration of physical interface 1. Determines
966 the "Enable 0" bit of the configuration register.
967 Format: 0 | 1
968 Default: 0
969 grcan.select= [HW] Select which physical interface to use.
970 Format: 0 | 1
971 Default: 0
972 grcan.txsize= [HW] Sets the size of the tx buffer.
973 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
974 Default: 1024
975 grcan.rxsize= [HW] Sets the size of the rx buffer.
976 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
977 Default: 1024
979 hashdist= [KNL,NUMA] Large hashes allocated during boot
980 are distributed across NUMA nodes. Defaults on
981 for 64-bit NUMA, off otherwise.
982 Format: 0 | 1 (for off | on)
984 hcl= [IA-64] SGI's Hardware Graph compatibility layer
986 hd= [EIDE] (E)IDE hard drive subsystem geometry
987 Format: <cyl>,<head>,<sect>
989 hest_disable [ACPI]
990 Disable Hardware Error Source Table (HEST) support;
991 corresponding firmware-first mode error processing
992 logic will be disabled.
994 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
995 size of <nn>. This works even on boxes that have no
996 highmem otherwise. This also works to reduce highmem
997 size on bigger boxes.
999 highres= [KNL] Enable/disable high resolution timer mode.
1000 Valid parameters: "on", "off"
1001 Default: "on"
1003 hisax= [HW,ISDN]
1004 See Documentation/isdn/README.HiSax.
1006 hlt [BUGS=ARM,SH]
1008 hpet= [X86-32,HPET] option to control HPET usage
1009 Format: { enable (default) | disable | force |
1010 verbose }
1011 disable: disable HPET and use PIT instead
1012 force: allow force enabled of undocumented chips (ICH4,
1013 VIA, nVidia)
1014 verbose: show contents of HPET registers during setup
1016 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1017 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1018 On x86-64 and powerpc, this option can be specified
1019 multiple times interleaved with hugepages= to reserve
1020 huge pages of different sizes. Valid pages sizes on
1021 x86-64 are 2M (when the CPU supports "pse") and 1G
1022 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1023 Note that 1GB pages can only be allocated at boot time
1024 using hugepages= and not freed afterwards.
1026 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1027 terminal devices. Valid values: 0..8
1028 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1029 If specified, z/VM IUCV HVC accepts connections
1030 from listed z/VM user IDs only.
1032 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1033 hardware thread id mappings.
1034 Format: <cpu>:<hwthread>
1036 keep_bootcon [KNL]
1037 Do not unregister boot console at start. This is only
1038 useful for debugging when something happens in the window
1039 between unregistering the boot console and initializing
1040 the real console.
1042 i2c_bus= [HW] Override the default board specific I2C bus speed
1043 or register an additional I2C bus that is not
1044 registered from board initialization code.
1045 Format:
1046 <bus_id>,<clkrate>
1048 i8042.debug [HW] Toggle i8042 debug mode
1049 i8042.direct [HW] Put keyboard port into non-translated mode
1050 i8042.dumbkbd [HW] Pretend that controller can only read data from
1051 keyboard and cannot control its state
1052 (Don't attempt to blink the leds)
1053 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1054 i8042.nokbd [HW] Don't check/create keyboard port
1055 i8042.noloop [HW] Disable the AUX Loopback command while probing
1056 for the AUX port
1057 i8042.nomux [HW] Don't check presence of an active multiplexing
1058 controller
1059 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1060 controllers
1061 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1062 i8042.reset [HW] Reset the controller during init and cleanup
1063 i8042.unlock [HW] Unlock (ignore) the keylock
1065 i810= [HW,DRM]
1067 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1068 indicates that the driver is running on unsupported
1069 hardware.
1070 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1071 does not match list of supported models.
1072 i8k.power_status
1073 [HW] Report power status in /proc/i8k
1074 (disabled by default)
1075 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1076 capability is set.
1078 i915.invert_brightness=
1079 [DRM] Invert the sense of the variable that is used to
1080 set the brightness of the panel backlight. Normally a
1081 brightness value of 0 indicates backlight switched off,
1082 and the maximum of the brightness value sets the backlight
1083 to maximum brightness. If this parameter is set to 0
1084 (default) and the machine requires it, or this parameter
1085 is set to 1, a brightness value of 0 sets the backlight
1086 to maximum brightness, and the maximum of the brightness
1087 value switches the backlight off.
1088 -1 -- never invert brightness
1089 0 -- machine default
1090 1 -- force brightness inversion
1092 icn= [HW,ISDN]
1093 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1095 ide-core.nodma= [HW] (E)IDE subsystem
1096 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1097 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1098 .cdrom .chs .ignore_cable are additional options
1099 See Documentation/ide/ide.txt.
1101 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1102 Claim all unknown PCI IDE storage controllers.
1104 idle= [X86]
1105 Format: idle=poll, idle=halt, idle=nomwait
1106 Poll forces a polling idle loop that can slightly
1107 improve the performance of waking up a idle CPU, but
1108 will use a lot of power and make the system run hot.
1109 Not recommended.
1110 idle=halt: Halt is forced to be used for CPU idle.
1111 In such case C2/C3 won't be used again.
1112 idle=nomwait: Disable mwait for CPU C-states
1114 ignore_loglevel [KNL]
1115 Ignore loglevel setting - this will print /all/
1116 kernel messages to the console. Useful for debugging.
1117 We also add it as printk module parameter, so users
1118 could change it dynamically, usually by
1119 /sys/module/printk/parameters/ignore_loglevel.
1121 ihash_entries= [KNL]
1122 Set number of hash buckets for inode cache.
1124 ima_appraise= [IMA] appraise integrity measurements
1125 Format: { "off" | "enforce" | "fix" }
1126 default: "enforce"
1128 ima_appraise_tcb [IMA]
1129 The builtin appraise policy appraises all files
1130 owned by uid=0.
1132 ima_hash= [IMA]
1133 Format: { "sha1" | "md5" }
1134 default: "sha1"
1136 ima_tcb [IMA]
1137 Load a policy which meets the needs of the Trusted
1138 Computing Base. This means IMA will measure all
1139 programs exec'd, files mmap'd for exec, and all files
1140 opened for read by uid=0.
1142 init= [KNL]
1143 Format: <full_path>
1144 Run specified binary instead of /sbin/init as init
1145 process.
1147 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1148 for working out where the kernel is dying during
1149 startup.
1151 initrd= [BOOT] Specify the location of the initial ramdisk
1153 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1154 Format: <irq>
1156 int_pln_enable [x86] Enable power limit notification interrupt
1158 integrity_audit=[IMA]
1159 Format: { "0" | "1" }
1160 0 -- basic integrity auditing messages. (Default)
1161 1 -- additional integrity auditing messages.
1163 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1164 on
1165 Enable intel iommu driver.
1166 off
1167 Disable intel iommu driver.
1168 igfx_off [Default Off]
1169 By default, gfx is mapped as normal device. If a gfx
1170 device has a dedicated DMAR unit, the DMAR unit is
1171 bypassed by not enabling DMAR with this option. In
1172 this case, gfx device will use physical address for
1173 DMA.
1174 forcedac [x86_64]
1175 With this option iommu will not optimize to look
1176 for io virtual address below 32-bit forcing dual
1177 address cycle on pci bus for cards supporting greater
1178 than 32-bit addressing. The default is to look
1179 for translation below 32-bit and if not available
1180 then look in the higher range.
1181 strict [Default Off]
1182 With this option on every unmap_single operation will
1183 result in a hardware IOTLB flush operation as opposed
1184 to batching them for performance.
1185 sp_off [Default Off]
1186 By default, super page will be supported if Intel IOMMU
1187 has the capability. With this option, super page will
1188 not be supported.
1190 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1191 0 disables intel_idle and fall back on acpi_idle.
1192 1 to 6 specify maximum depth of C-state.
1194 intel_pstate= [X86]
1195 disable
1196 Do not enable intel_pstate as the default
1197 scaling driver for the supported processors
1199 intremap= [X86-64, Intel-IOMMU]
1200 on enable Interrupt Remapping (default)
1201 off disable Interrupt Remapping
1202 nosid disable Source ID checking
1203 no_x2apic_optout
1204 BIOS x2APIC opt-out request will be ignored
1206 iomem= Disable strict checking of access to MMIO memory
1207 strict regions from userspace.
1208 relaxed
1210 iommu= [x86]
1211 off
1212 force
1213 noforce
1214 biomerge
1215 panic
1216 nopanic
1217 merge
1218 nomerge
1219 forcesac
1220 soft
1221 pt [x86, IA-64]
1224 io7= [HW] IO7 for Marvel based alpha systems
1225 See comment before marvel_specify_io7 in
1226 arch/alpha/kernel/core_marvel.c.
1228 io_delay= [X86] I/O delay method
1229 0x80
1230 Standard port 0x80 based delay
1231 0xed
1232 Alternate port 0xed based delay (needed on some systems)
1233 udelay
1234 Simple two microseconds delay
1235 none
1236 No delay
1238 ip= [IP_PNP]
1239 See Documentation/filesystems/nfs/nfsroot.txt.
1241 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1242 See comment before ip2_setup() in
1243 drivers/char/ip2/ip2base.c.
1245 irqfixup [HW]
1246 When an interrupt is not handled search all handlers
1247 for it. Intended to get systems with badly broken
1248 firmware running.
1250 irqpoll [HW]
1251 When an interrupt is not handled search all handlers
1252 for it. Also check all handlers each timer
1253 interrupt. Intended to get systems with badly broken
1254 firmware running.
1256 isapnp= [ISAPNP]
1257 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1259 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1260 Format:
1261 <cpu number>,...,<cpu number>
1262 or
1263 <cpu number>-<cpu number>
1264 (must be a positive range in ascending order)
1265 or a mixture
1266 <cpu number>,...,<cpu number>-<cpu number>
1268 This option can be used to specify one or more CPUs
1269 to isolate from the general SMP balancing and scheduling
1270 algorithms. You can move a process onto or off an
1271 "isolated" CPU via the CPU affinity syscalls or cpuset.
1272 <cpu number> begins at 0 and the maximum value is
1273 "number of CPUs in system - 1".
1275 This option is the preferred way to isolate CPUs. The
1276 alternative -- manually setting the CPU mask of all
1277 tasks in the system -- can cause problems and
1278 suboptimal load balancer performance.
1280 iucv= [HW,NET]
1282 ivrs_ioapic [HW,X86_64]
1283 Provide an override to the IOAPIC-ID<->DEVICE-ID
1284 mapping provided in the IVRS ACPI table. For
1285 example, to map IOAPIC-ID decimal 10 to
1286 PCI device 00:14.0 write the parameter as:
1287 ivrs_ioapic[10]=00:14.0
1289 ivrs_hpet [HW,X86_64]
1290 Provide an override to the HPET-ID<->DEVICE-ID
1291 mapping provided in the IVRS ACPI table. For
1292 example, to map HPET-ID decimal 0 to
1293 PCI device 00:14.0 write the parameter as:
1294 ivrs_hpet[0]=00:14.0
1296 js= [HW,JOY] Analog joystick
1297 See Documentation/input/joystick.txt.
1299 keepinitrd [HW,ARM]
1301 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1302 specifies the amount of memory usable by the kernel
1303 for non-movable allocations. The requested amount is
1304 spread evenly throughout all nodes in the system. The
1305 remaining memory in each node is used for Movable
1306 pages. In the event, a node is too small to have both
1307 kernelcore and Movable pages, kernelcore pages will
1308 take priority and other nodes will have a larger number
1309 of kernelcore pages. The Movable zone is used for the
1310 allocation of pages that may be reclaimed or moved
1311 by the page migration subsystem. This means that
1312 HugeTLB pages may not be allocated from this zone.
1313 Note that allocations like PTEs-from-HighMem still
1314 use the HighMem zone if it exists, and the Normal
1315 zone if it does not.
1317 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1318 Format: <Controller#>[,poll interval]
1319 The controller # is the number of the ehci usb debug
1320 port as it is probed via PCI. The poll interval is
1321 optional and is the number seconds in between
1322 each poll cycle to the debug port in case you need
1323 the functionality for interrupting the kernel with
1324 gdb or control-c on the dbgp connection. When
1325 not using this parameter you use sysrq-g to break into
1326 the kernel debugger.
1328 kgdboc= [KGDB,HW] kgdb over consoles.
1329 Requires a tty driver that supports console polling,
1330 or a supported polling keyboard driver (non-usb).
1331 Serial only format: <serial_device>[,baud]
1332 keyboard only format: kbd
1333 keyboard and serial format: kbd,<serial_device>[,baud]
1334 Optional Kernel mode setting:
1335 kms, kbd format: kms,kbd
1336 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1338 kgdbwait [KGDB] Stop kernel execution and enter the
1339 kernel debugger at the earliest opportunity.
1341 kmac= [MIPS] korina ethernet MAC address.
1342 Configure the RouterBoard 532 series on-chip
1343 Ethernet adapter MAC address.
1345 kmemleak= [KNL] Boot-time kmemleak enable/disable
1346 Valid arguments: on, off
1347 Default: on
1349 kstack=N [X86] Print N words from the kernel stack
1350 in oops dumps.
1352 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1353 Default is 0 (don't ignore, but inject #GP)
1355 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1356 KVM MMU at runtime.
1357 Default is 0 (off)
1359 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1360 Default is 1 (enabled)
1362 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1363 for all guests.
1364 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1366 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1367 (virtualized MMU) support on capable Intel chips.
1368 Default is 1 (enabled)
1370 kvm-intel.emulate_invalid_guest_state=
1371 [KVM,Intel] Enable emulation of invalid guest states
1372 Default is 0 (disabled)
1374 kvm-intel.flexpriority=
1375 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1376 Default is 1 (enabled)
1378 kvm-intel.nested=
1379 [KVM,Intel] Enable VMX nesting (nVMX).
1380 Default is 0 (disabled)
1382 kvm-intel.unrestricted_guest=
1383 [KVM,Intel] Disable unrestricted guest feature
1384 (virtualized real and unpaged mode) on capable
1385 Intel chips. Default is 1 (enabled)
1387 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1388 feature (tagged TLBs) on capable Intel chips.
1389 Default is 1 (enabled)
1391 l2cr= [PPC]
1393 l3cr= [PPC]
1395 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1396 disabled it.
1398 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1399 value for LAPIC timer one-shot implementation. Default
1400 back to the programmable timer unit in the LAPIC.
1402 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1403 in C2 power state.
1405 libata.dma= [LIBATA] DMA control
1406 libata.dma=0 Disable all PATA and SATA DMA
1407 libata.dma=1 PATA and SATA Disk DMA only
1408 libata.dma=2 ATAPI (CDROM) DMA only
1409 libata.dma=4 Compact Flash DMA only
1410 Combinations also work, so libata.dma=3 enables DMA
1411 for disks and CDROMs, but not CFs.
1413 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1414 libata.ignore_hpa=0 keep BIOS limits (default)
1415 libata.ignore_hpa=1 ignore limits, using full disk
1417 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1418 when set.
1419 Format: <int>
1421 libata.force= [LIBATA] Force configurations. The format is comma
1422 separated list of "[ID:]VAL" where ID is
1423 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1424 matching port, link or device. Basically, it matches
1425 the ATA ID string printed on console by libata. If
1426 the whole ID part is omitted, the last PORT and DEVICE
1427 values are used. If ID hasn't been specified yet, the
1428 configuration applies to all ports, links and devices.
1430 If only DEVICE is omitted, the parameter applies to
1431 the port and all links and devices behind it. DEVICE
1432 number of 0 either selects the first device or the
1433 first fan-out link behind PMP device. It does not
1434 select the host link. DEVICE number of 15 selects the
1435 host link and device attached to it.
1437 The VAL specifies the configuration to force. As long
1438 as there's no ambiguity shortcut notation is allowed.
1439 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1440 The following configurations can be forced.
1442 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1443 Any ID with matching PORT is used.
1445 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1447 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1448 udma[/][16,25,33,44,66,100,133] notation is also
1449 allowed.
1451 * [no]ncq: Turn on or off NCQ.
1453 * nohrst, nosrst, norst: suppress hard, soft
1454 and both resets.
1456 * rstonce: only attempt one reset during
1457 hot-unplug link recovery
1459 * dump_id: dump IDENTIFY data.
1461 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1463 If there are multiple matching configurations changing
1464 the same attribute, the last one is used.
1466 memblock=debug [KNL] Enable memblock debug messages.
1468 load_ramdisk= [RAM] List of ramdisks to load from floppy
1469 See Documentation/blockdev/ramdisk.txt.
1471 lockd.nlm_grace_period=P [NFS] Assign grace period.
1472 Format: <integer>
1474 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1475 Format: <integer>
1477 lockd.nlm_timeout=T [NFS] Assign timeout value.
1478 Format: <integer>
1480 lockd.nlm_udpport=M [NFS] Assign UDP port.
1481 Format: <integer>
1483 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1484 Format: <irq>
1486 loglevel= All Kernel Messages with a loglevel smaller than the
1487 console loglevel will be printed to the console. It can
1488 also be changed with klogd or other programs. The
1489 loglevels are defined as follows:
1491 0 (KERN_EMERG) system is unusable
1492 1 (KERN_ALERT) action must be taken immediately
1493 2 (KERN_CRIT) critical conditions
1494 3 (KERN_ERR) error conditions
1495 4 (KERN_WARNING) warning conditions
1496 5 (KERN_NOTICE) normal but significant condition
1497 6 (KERN_INFO) informational
1498 7 (KERN_DEBUG) debug-level messages
1500 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1501 in bytes. n must be a power of two. The default
1502 size is set in the kernel config file.
1504 logo.nologo [FB] Disables display of the built-in Linux logo.
1505 This may be used to provide more screen space for
1506 kernel log messages and is useful when debugging
1507 kernel boot problems.
1509 lp=0 [LP] Specify parallel ports to use, e.g,
1510 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1511 lp=reset first parallel port). 'lp=0' disables the
1512 lp=auto printer driver. 'lp=reset' (which can be
1513 specified in addition to the ports) causes
1514 attached printers to be reset. Using
1515 lp=port1,port2,... specifies the parallel ports
1516 to associate lp devices with, starting with
1517 lp0. A port specification may be 'none' to skip
1518 that lp device, or a parport name such as
1519 'parport0'. Specifying 'lp=auto' instead of a
1520 port specification list means that device IDs
1521 from each port should be examined, to see if
1522 an IEEE 1284-compliant printer is attached; if
1523 so, the driver will manage that printer.
1524 See also header of drivers/char/lp.c.
1526 lpj=n [KNL]
1527 Sets loops_per_jiffy to given constant, thus avoiding
1528 time-consuming boot-time autodetection (up to 250 ms per
1529 CPU). 0 enables autodetection (default). To determine
1530 the correct value for your kernel, boot with normal
1531 autodetection and see what value is printed. Note that
1532 on SMP systems the preset will be applied to all CPUs,
1533 which is likely to cause problems if your CPUs need
1534 significantly divergent settings. An incorrect value
1535 will cause delays in the kernel to be wrong, leading to
1536 unpredictable I/O errors and other breakage. Although
1537 unlikely, in the extreme case this might damage your
1538 hardware.
1540 ltpc= [NET]
1541 Format: <io>,<irq>,<dma>
1543 machvec= [IA-64] Force the use of a particular machine-vector
1544 (machvec) in a generic kernel.
1545 Example: machvec=hpzx1_swiotlb
1547 machtype= [Loongson] Share the same kernel image file between different
1548 yeeloong laptop.
1549 Example: machtype=lemote-yeeloong-2f-7inch
1551 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1552 than or equal to this physical address is ignored.
1554 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1555 should make use of. maxcpus=n : n >= 0 limits the
1556 kernel to using 'n' processors. n=0 is a special case,
1557 it is equivalent to "nosmp", which also disables
1558 the IO APIC.
1560 max_loop= [LOOP] The number of loop block devices that get
1561 (loop.max_loop) unconditionally pre-created at init time. The default
1562 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1563 of statically allocating a predefined number, loop
1564 devices can be requested on-demand with the
1565 /dev/loop-control interface.
1567 mce [X86-32] Machine Check Exception
1569 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1571 md= [HW] RAID subsystems devices and level
1572 See Documentation/md.txt.
1574 mdacon= [MDA]
1575 Format: <first>,<last>
1576 Specifies range of consoles to be captured by the MDA.
1578 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1579 Amount of memory to be used when the kernel is not able
1580 to see the whole system memory or for test.
1581 [X86] Work as limiting max address. Use together
1582 with memmap= to avoid physical address space collisions.
1583 Without memmap= PCI devices could be placed at addresses
1584 belonging to unused RAM.
1586 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1587 memory.
1589 memchunk=nn[KMG]
1590 [KNL,SH] Allow user to override the default size for
1591 per-device physically contiguous DMA buffers.
1593 memmap=exactmap [KNL,X86] Enable setting of an exact
1594 E820 memory map, as specified by the user.
1595 Such memmap=exactmap lines can be constructed based on
1596 BIOS output or other requirements. See the memmap=nn@ss
1597 option description.
1599 memmap=nn[KMG]@ss[KMG]
1600 [KNL] Force usage of a specific region of memory
1601 Region of memory to be used, from ss to ss+nn.
1603 memmap=nn[KMG]#ss[KMG]
1604 [KNL,ACPI] Mark specific memory as ACPI data.
1605 Region of memory to be used, from ss to ss+nn.
1607 memmap=nn[KMG]$ss[KMG]
1608 [KNL,ACPI] Mark specific memory as reserved.
1609 Region of memory to be used, from ss to ss+nn.
1610 Example: Exclude memory from 0x18690000-0x1869ffff
1611 memmap=64K$0x18690000
1612 or
1613 memmap=0x10000$0x18690000
1615 memory_corruption_check=0/1 [X86]
1616 Some BIOSes seem to corrupt the first 64k of
1617 memory when doing things like suspend/resume.
1618 Setting this option will scan the memory
1619 looking for corruption. Enabling this will
1620 both detect corruption and prevent the kernel
1621 from using the memory being corrupted.
1622 However, its intended as a diagnostic tool; if
1623 repeatable BIOS-originated corruption always
1624 affects the same memory, you can use memmap=
1625 to prevent the kernel from using that memory.
1627 memory_corruption_check_size=size [X86]
1628 By default it checks for corruption in the low
1629 64k, making this memory unavailable for normal
1630 use. Use this parameter to scan for
1631 corruption in more or less memory.
1633 memory_corruption_check_period=seconds [X86]
1634 By default it checks for corruption every 60
1635 seconds. Use this parameter to check at some
1636 other rate. 0 disables periodic checking.
1638 memtest= [KNL,X86] Enable memtest
1639 Format: <integer>
1640 default : 0 <disable>
1641 Specifies the number of memtest passes to be
1642 performed. Each pass selects another test
1643 pattern from a given set of patterns. Memtest
1644 fills the memory with this pattern, validates
1645 memory contents and reserves bad memory
1646 regions that are detected.
1648 meye.*= [HW] Set MotionEye Camera parameters
1649 See Documentation/video4linux/meye.txt.
1651 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1652 Multi-Function General Purpose Timers on AMD Geode
1653 platforms.
1655 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1656 the BIOS has incorrectly applied a workaround. TinyBIOS
1657 version 0.98 is known to be affected, 0.99 fixes the
1658 problem by letting the user disable the workaround.
1660 mga= [HW,DRM]
1662 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1663 physical address is ignored.
1665 mini2440= [ARM,HW,KNL]
1666 Format:[0..2][b][c][t]
1667 Default: "0tb"
1668 MINI2440 configuration specification:
1669 0 - The attached screen is the 3.5" TFT
1670 1 - The attached screen is the 7" TFT
1671 2 - The VGA Shield is attached (1024x768)
1672 Leaving out the screen size parameter will not load
1673 the TFT driver, and the framebuffer will be left
1674 unconfigured.
1675 b - Enable backlight. The TFT backlight pin will be
1676 linked to the kernel VESA blanking code and a GPIO
1677 LED. This parameter is not necessary when using the
1678 VGA shield.
1679 c - Enable the s3c camera interface.
1680 t - Reserved for enabling touchscreen support. The
1681 touchscreen support is not enabled in the mainstream
1682 kernel as of 2.6.30, a preliminary port can be found
1683 in the "bleeding edge" mini2440 support kernel at
1684 http://repo.or.cz/w/linux-2.6/mini2440.git
1686 mminit_loglevel=
1687 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1688 parameter allows control of the logging verbosity for
1689 the additional memory initialisation checks. A value
1690 of 0 disables mminit logging and a level of 4 will
1691 log everything. Information is printed at KERN_DEBUG
1692 so loglevel=8 may also need to be specified.
1694 module.sig_enforce
1695 [KNL] When CONFIG_MODULE_SIG is set, this means that
1696 modules without (valid) signatures will fail to load.
1697 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1698 is always true, so this option does nothing.
1700 mousedev.tap_time=
1701 [MOUSE] Maximum time between finger touching and
1702 leaving touchpad surface for touch to be considered
1703 a tap and be reported as a left button click (for
1704 touchpads working in absolute mode only).
1705 Format: <msecs>
1706 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1707 reporting absolute coordinates, such as tablets
1708 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1709 reporting absolute coordinates, such as tablets
1711 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1712 is similar to kernelcore except it specifies the
1713 amount of memory used for migratable allocations.
1714 If both kernelcore and movablecore is specified,
1715 then kernelcore will be at *least* the specified
1716 value but may be more. If movablecore on its own
1717 is specified, the administrator must be careful
1718 that the amount of memory usable for all allocations
1719 is not too small.
1721 MTD_Partition= [MTD]
1722 Format: <name>,<region-number>,<size>,<offset>
1724 MTD_Region= [MTD] Format:
1725 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1727 mtdparts= [MTD]
1728 See drivers/mtd/cmdlinepart.c.
1730 multitce=off [PPC] This parameter disables the use of the pSeries
1731 firmware feature for updating multiple TCE entries
1732 at a time.
1734 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1736 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1738 boundary - index of last SLC block on Flex-OneNAND.
1739 The remaining blocks are configured as MLC blocks.
1740 lock - Configure if Flex-OneNAND boundary should be locked.
1741 Once locked, the boundary cannot be changed.
1742 1 indicates lock status, 0 indicates unlock status.
1744 mtdset= [ARM]
1745 ARM/S3C2412 JIVE boot control
1747 See arch/arm/mach-s3c2412/mach-jive.c
1749 mtouchusb.raw_coordinates=
1750 [HW] Make the MicroTouch USB driver use raw coordinates
1751 ('y', default) or cooked coordinates ('n')
1753 mtrr_chunk_size=nn[KMG] [X86]
1754 used for mtrr cleanup. It is largest continuous chunk
1755 that could hold holes aka. UC entries.
1757 mtrr_gran_size=nn[KMG] [X86]
1758 Used for mtrr cleanup. It is granularity of mtrr block.
1759 Default is 1.
1760 Large value could prevent small alignment from
1761 using up MTRRs.
1763 mtrr_spare_reg_nr=n [X86]
1764 Format: <integer>
1765 Range: 0,7 : spare reg number
1766 Default : 1
1767 Used for mtrr cleanup. It is spare mtrr entries number.
1768 Set to 2 or more if your graphical card needs more.
1770 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1772 netdev= [NET] Network devices parameters
1773 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1774 Note that mem_start is often overloaded to mean
1775 something different and driver-specific.
1776 This usage is only documented in each driver source
1777 file if at all.
1779 nf_conntrack.acct=
1780 [NETFILTER] Enable connection tracking flow accounting
1781 0 to disable accounting
1782 1 to enable accounting
1783 Default value is 0.
1785 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1786 See Documentation/filesystems/nfs/nfsroot.txt.
1788 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1789 See Documentation/filesystems/nfs/nfsroot.txt.
1791 nfsrootdebug [NFS] enable nfsroot debugging messages.
1792 See Documentation/filesystems/nfs/nfsroot.txt.
1794 nfs.callback_tcpport=
1795 [NFS] set the TCP port on which the NFSv4 callback
1796 channel should listen.
1798 nfs.cache_getent=
1799 [NFS] sets the pathname to the program which is used
1800 to update the NFS client cache entries.
1802 nfs.cache_getent_timeout=
1803 [NFS] sets the timeout after which an attempt to
1804 update a cache entry is deemed to have failed.
1806 nfs.idmap_cache_timeout=
1807 [NFS] set the maximum lifetime for idmapper cache
1808 entries.
1810 nfs.enable_ino64=
1811 [NFS] enable 64-bit inode numbers.
1812 If zero, the NFS client will fake up a 32-bit inode
1813 number for the readdir() and stat() syscalls instead
1814 of returning the full 64-bit number.
1815 The default is to return 64-bit inode numbers.
1817 nfs.max_session_slots=
1818 [NFSv4.1] Sets the maximum number of session slots
1819 the client will attempt to negotiate with the server.
1820 This limits the number of simultaneous RPC requests
1821 that the client can send to the NFSv4.1 server.
1822 Note that there is little point in setting this
1823 value higher than the max_tcp_slot_table_limit.
1825 nfs.nfs4_disable_idmapping=
1826 [NFSv4] When set to the default of '1', this option
1827 ensures that both the RPC level authentication
1828 scheme and the NFS level operations agree to use
1829 numeric uids/gids if the mount is using the
1830 'sec=sys' security flavour. In effect it is
1831 disabling idmapping, which can make migration from
1832 legacy NFSv2/v3 systems to NFSv4 easier.
1833 Servers that do not support this mode of operation
1834 will be autodetected by the client, and it will fall
1835 back to using the idmapper.
1836 To turn off this behaviour, set the value to '0'.
1837 nfs.nfs4_unique_id=
1838 [NFS4] Specify an additional fixed unique ident-
1839 ification string that NFSv4 clients can insert into
1840 their nfs_client_id4 string. This is typically a
1841 UUID that is generated at system install time.
1843 nfs.send_implementation_id =
1844 [NFSv4.1] Send client implementation identification
1845 information in exchange_id requests.
1846 If zero, no implementation identification information
1847 will be sent.
1848 The default is to send the implementation identification
1849 information.
1851 nfsd.nfs4_disable_idmapping=
1852 [NFSv4] When set to the default of '1', the NFSv4
1853 server will return only numeric uids and gids to
1854 clients using auth_sys, and will accept numeric uids
1855 and gids from such clients. This is intended to ease
1856 migration from NFSv2/v3.
1858 objlayoutdriver.osd_login_prog=
1859 [NFS] [OBJLAYOUT] sets the pathname to the program which
1860 is used to automatically discover and login into new
1861 osd-targets. Please see:
1862 Documentation/filesystems/pnfs.txt for more explanations
1864 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1865 when a NMI is triggered.
1866 Format: [state][,regs][,debounce][,die]
1868 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1869 Format: [panic,][nopanic,][num]
1870 Valid num: 0
1871 0 - turn nmi_watchdog off
1872 When panic is specified, panic when an NMI watchdog
1873 timeout occurs (or 'nopanic' to override the opposite
1874 default).
1875 This is useful when you use a panic=... timeout and
1876 need the box quickly up again.
1878 netpoll.carrier_timeout=
1879 [NET] Specifies amount of time (in seconds) that
1880 netpoll should wait for a carrier. By default netpoll
1881 waits 4 seconds.
1883 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1884 emulation library even if a 387 maths coprocessor
1885 is present.
1887 no_console_suspend
1888 [HW] Never suspend the console
1889 Disable suspending of consoles during suspend and
1890 hibernate operations. Once disabled, debugging
1891 messages can reach various consoles while the rest
1892 of the system is being put to sleep (ie, while
1893 debugging driver suspend/resume hooks). This may
1894 not work reliably with all consoles, but is known
1895 to work with serial and VGA consoles.
1896 To facilitate more flexible debugging, we also add
1897 console_suspend, a printk module parameter to control
1898 it. Users could use console_suspend (usually
1899 /sys/module/printk/parameters/console_suspend) to
1900 turn on/off it dynamically.
1902 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1903 caches in the slab allocator. Saves per-node memory,
1904 but will impact performance.
1906 noalign [KNL,ARM]
1908 noapic [SMP,APIC] Tells the kernel to not make use of any
1909 IOAPICs that may be present in the system.
1911 noautogroup Disable scheduler automatic task group creation.
1913 nobats [PPC] Do not use BATs for mapping kernel lowmem
1914 on "Classic" PPC cores.
1916 nocache [ARM]
1918 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1920 nodelayacct [KNL] Disable per-task delay accounting
1922 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1924 nodsp [SH] Disable hardware DSP at boot time.
1926 noefi [X86] Disable EFI runtime services support.
1928 noexec [IA-64]
1930 noexec [X86]
1931 On X86-32 available only on PAE configured kernels.
1932 noexec=on: enable non-executable mappings (default)
1933 noexec=off: disable non-executable mappings
1935 nosmap [X86]
1936 Disable SMAP (Supervisor Mode Access Prevention)
1937 even if it is supported by processor.
1939 nosmep [X86]
1940 Disable SMEP (Supervisor Mode Execution Prevention)
1941 even if it is supported by processor.
1943 noexec32 [X86-64]
1944 This affects only 32-bit executables.
1945 noexec32=on: enable non-executable mappings (default)
1946 read doesn't imply executable mappings
1947 noexec32=off: disable non-executable mappings
1948 read implies executable mappings
1950 nofpu [SH] Disable hardware FPU at boot time.
1952 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1953 register save and restore. The kernel will only save
1954 legacy floating-point registers on task switch.
1956 noxsave [BUGS=X86] Disables x86 extended register state save
1957 and restore using xsave. The kernel will fallback to
1958 enabling legacy floating-point and sse state.
1960 eagerfpu= [X86]
1961 on enable eager fpu restore
1962 off disable eager fpu restore
1963 auto selects the default scheme, which automatically
1964 enables eagerfpu restore for xsaveopt.
1966 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1967 wfi(ARM) instruction doesn't work correctly and not to
1968 use it. This is also useful when using JTAG debugger.
1970 no_file_caps Tells the kernel not to honor file capabilities. The
1971 only way then for a file to be executed with privilege
1972 is to be setuid root or executed by root.
1974 nohalt [IA-64] Tells the kernel not to use the power saving
1975 function PAL_HALT_LIGHT when idle. This increases
1976 power-consumption. On the positive side, it reduces
1977 interrupt wake-up latency, which may improve performance
1978 in certain environments such as networked servers or
1979 real-time systems.
1981 nohz= [KNL] Boottime enable/disable dynamic ticks
1982 Valid arguments: on, off
1983 Default: on
1985 nohz_full= [KNL,BOOT]
1986 In kernels built with CONFIG_NO_HZ_FULL=y, set
1987 the specified list of CPUs whose tick will be stopped
1988 whenever possible. The boot CPU will be forced outside
1989 the range to maintain the timekeeping.
1990 The CPUs in this range must also be included in the
1991 rcu_nocbs= set.
1993 noiotrap [SH] Disables trapped I/O port accesses.
1995 noirqdebug [X86-32] Disables the code which attempts to detect and
1996 disable unhandled interrupt sources.
1998 no_timer_check [X86,APIC] Disables the code which tests for
1999 broken timer IRQ sources.
2001 noisapnp [ISAPNP] Disables ISA PnP code.
2003 noinitrd [RAM] Tells the kernel not to load any configured
2004 initial RAM disk.
2006 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2007 remapping.
2008 [Deprecated - use intremap=off]
2010 nointroute [IA-64]
2012 nojitter [IA-64] Disables jitter checking for ITC timers.
2014 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2016 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2017 fault handling.
2019 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2020 steal time is computed, but won't influence scheduler
2021 behaviour
2023 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2025 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2027 noltlbs [PPC] Do not use large page/tlb entries for kernel
2028 lowmem mapping on PPC40x.
2030 nomca [IA-64] Disable machine check abort handling
2032 nomce [X86-32] Machine Check Exception
2034 nomfgpt [X86-32] Disable Multi-Function General Purpose
2035 Timer usage (for AMD Geode machines).
2037 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2038 shutdown the other cpus. Instead use the REBOOT_VECTOR
2039 irq.
2041 nomodule Disable module load
2043 nopat [X86] Disable PAT (page attribute table extension of
2044 pagetables) support.
2046 norandmaps Don't use address space randomization. Equivalent to
2047 echo 0 > /proc/sys/kernel/randomize_va_space
2049 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2051 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2052 with UP alternatives
2054 nordrand [X86] Disable the direct use of the RDRAND
2055 instruction even if it is supported by the
2056 processor. RDRAND is still available to user
2057 space applications.
2059 noresume [SWSUSP] Disables resume and restores original swap
2060 space.
2062 no-scroll [VGA] Disables scrollback.
2063 This is required for the Braillex ib80-piezo Braille
2064 reader made by F.H. Papenmeier (Germany).
2066 nosbagart [IA-64]
2068 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2070 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2071 and disable the IO APIC. legacy for "maxcpus=0".
2073 nosoftlockup [KNL] Disable the soft-lockup detector.
2075 nosync [HW,M68K] Disables sync negotiation for all devices.
2077 notsc [BUGS=X86-32] Disable Time Stamp Counter
2079 nousb [USB] Disable the USB subsystem
2081 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2083 nowb [ARM]
2085 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2087 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2088 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2089 Some features depend on CPU0. Known dependencies are:
2090 1. Resume from suspend/hibernate depends on CPU0.
2091 Suspend/hibernate will fail if CPU0 is offline and you
2092 need to online CPU0 before suspend/hibernate.
2093 2. PIC interrupts also depend on CPU0. CPU0 can't be
2094 removed if a PIC interrupt is detected.
2095 It's said poweroff/reboot may depend on CPU0 on some
2096 machines although I haven't seen such issues so far
2097 after CPU0 is offline on a few tested machines.
2098 If the dependencies are under your control, you can
2099 turn on cpu0_hotplug.
2101 nptcg= [IA-64] Override max number of concurrent global TLB
2102 purges which is reported from either PAL_VM_SUMMARY or
2103 SAL PALO.
2105 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2106 could support. nr_cpus=n : n >= 1 limits the kernel to
2107 supporting 'n' processors. Later in runtime you can not
2108 use hotplug cpu feature to put more cpu back to online.
2109 just like you compile the kernel NR_CPUS=n
2111 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2113 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2114 Allowed values are enable and disable
2116 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2117 one of ['zone', 'node', 'default'] can be specified
2118 This can be set from sysctl after boot.
2119 See Documentation/sysctl/vm.txt for details.
2121 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2122 See Documentation/debugging-via-ohci1394.txt for more
2123 info.
2125 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2126 Rather than timing out after 20 ms if an EC
2127 command is not properly ACKed, override the length
2128 of the timeout. We have interrupts disabled while
2129 waiting for the ACK, so if this is set too high
2130 interrupts *may* be lost!
2132 omap_mux= [OMAP] Override bootloader pin multiplexing.
2133 Format: <mux_mode0.mode_name=value>...
2134 For example, to override I2C bus2:
2135 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2137 oprofile.timer= [HW]
2138 Use timer interrupt instead of performance counters
2140 oprofile.cpu_type= Force an oprofile cpu type
2141 This might be useful if you have an older oprofile
2142 userland or if you want common events.
2143 Format: { arch_perfmon }
2144 arch_perfmon: [X86] Force use of architectural
2145 perfmon on Intel CPUs instead of the
2146 CPU specific event set.
2147 timer: [X86] Force use of architectural NMI
2148 timer mode (see also oprofile.timer
2149 for generic hr timer mode)
2150 [s390] Force legacy basic mode sampling
2151 (report cpu_type "timer")
2153 oops=panic Always panic on oopses. Default is to just kill the
2154 process, but there is a small probability of
2155 deadlocking the machine.
2156 This will also cause panics on machine check exceptions.
2157 Useful together with panic=30 to trigger a reboot.
2159 OSS [HW,OSS]
2160 See Documentation/sound/oss/oss-parameters.txt
2162 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2163 timeout > 0: seconds before rebooting
2164 timeout = 0: wait forever
2165 timeout < 0: reboot immediately
2166 Format: <timeout>
2168 parkbd.port= [HW] Parallel port number the keyboard adapter is
2169 connected to, default is 0.
2170 Format: <parport#>
2171 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2172 0 for XT, 1 for AT (default is AT).
2173 Format: <mode>
2175 parport= [HW,PPT] Specify parallel ports. 0 disables.
2176 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2177 Use 'auto' to force the driver to use any
2178 IRQ/DMA settings detected (the default is to
2179 ignore detected IRQ/DMA settings because of
2180 possible conflicts). You can specify the base
2181 address, IRQ, and DMA settings; IRQ and DMA
2182 should be numbers, or 'auto' (for using detected
2183 settings on that particular port), or 'nofifo'
2184 (to avoid using a FIFO even if it is detected).
2185 Parallel ports are assigned in the order they
2186 are specified on the command line, starting
2187 with parport0.
2189 parport_init_mode= [HW,PPT]
2190 Configure VIA parallel port to operate in
2191 a specific mode. This is necessary on Pegasos
2192 computer where firmware has no options for setting
2193 up parallel port mode and sets it to spp.
2194 Currently this function knows 686a and 8231 chips.
2195 Format: [spp|ps2|epp|ecp|ecpepp]
2197 pause_on_oops=
2198 Halt all CPUs after the first oops has been printed for
2199 the specified number of seconds. This is to be used if
2200 your oopses keep scrolling off the screen.
2202 pcbit= [HW,ISDN]
2204 pcd. [PARIDE]
2205 See header of drivers/block/paride/pcd.c.
2206 See also Documentation/blockdev/paride.txt.
2208 pci=option[,option...] [PCI] various PCI subsystem options:
2209 earlydump [X86] dump PCI config space before the kernel
2210 changes anything
2211 off [X86] don't probe for the PCI bus
2212 bios [X86-32] force use of PCI BIOS, don't access
2213 the hardware directly. Use this if your machine
2214 has a non-standard PCI host bridge.
2215 nobios [X86-32] disallow use of PCI BIOS, only direct
2216 hardware access methods are allowed. Use this
2217 if you experience crashes upon bootup and you
2218 suspect they are caused by the BIOS.
2219 conf1 [X86] Force use of PCI Configuration
2220 Mechanism 1.
2221 conf2 [X86] Force use of PCI Configuration
2222 Mechanism 2.
2223 noaer [PCIE] If the PCIEAER kernel config parameter is
2224 enabled, this kernel boot option can be used to
2225 disable the use of PCIE advanced error reporting.
2226 nodomains [PCI] Disable support for multiple PCI
2227 root domains (aka PCI segments, in ACPI-speak).
2228 nommconf [X86] Disable use of MMCONFIG for PCI
2229 Configuration
2230 check_enable_amd_mmconf [X86] check for and enable
2231 properly configured MMIO access to PCI
2232 config space on AMD family 10h CPU
2233 nomsi [MSI] If the PCI_MSI kernel config parameter is
2234 enabled, this kernel boot option can be used to
2235 disable the use of MSI interrupts system-wide.
2236 noioapicquirk [APIC] Disable all boot interrupt quirks.
2237 Safety option to keep boot IRQs enabled. This
2238 should never be necessary.
2239 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2240 primary IO-APIC for bridges that cannot disable
2241 boot IRQs. This fixes a source of spurious IRQs
2242 when the system masks IRQs.
2243 noioapicreroute [APIC] Disable workaround that uses the
2244 boot IRQ equivalent of an IRQ that connects to
2245 a chipset where boot IRQs cannot be disabled.
2246 The opposite of ioapicreroute.
2247 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2248 routing table. These calls are known to be buggy
2249 on several machines and they hang the machine
2250 when used, but on other computers it's the only
2251 way to get the interrupt routing table. Try
2252 this option if the kernel is unable to allocate
2253 IRQs or discover secondary PCI buses on your
2254 motherboard.
2255 rom [X86] Assign address space to expansion ROMs.
2256 Use with caution as certain devices share
2257 address decoders between ROMs and other
2258 resources.
2259 norom [X86] Do not assign address space to
2260 expansion ROMs that do not already have
2261 BIOS assigned address ranges.
2262 nobar [X86] Do not assign address space to the
2263 BARs that weren't assigned by the BIOS.
2264 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2265 assigned automatically to PCI devices. You can
2266 make the kernel exclude IRQs of your ISA cards
2267 this way.
2268 pirqaddr=0xAAAAA [X86] Specify the physical address
2269 of the PIRQ table (normally generated
2270 by the BIOS) if it is outside the
2271 F0000h-100000h range.
2272 lastbus=N [X86] Scan all buses thru bus #N. Can be
2273 useful if the kernel is unable to find your
2274 secondary buses and you want to tell it
2275 explicitly which ones they are.
2276 assign-busses [X86] Always assign all PCI bus
2277 numbers ourselves, overriding
2278 whatever the firmware may have done.
2279 usepirqmask [X86] Honor the possible IRQ mask stored
2280 in the BIOS $PIR table. This is needed on
2281 some systems with broken BIOSes, notably
2282 some HP Pavilion N5400 and Omnibook XE3
2283 notebooks. This will have no effect if ACPI
2284 IRQ routing is enabled.
2285 noacpi [X86] Do not use ACPI for IRQ routing
2286 or for PCI scanning.
2287 use_crs [X86] Use PCI host bridge window information
2288 from ACPI. On BIOSes from 2008 or later, this
2289 is enabled by default. If you need to use this,
2290 please report a bug.
2291 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2292 If you need to use this, please report a bug.
2293 routeirq Do IRQ routing for all PCI devices.
2294 This is normally done in pci_enable_device(),
2295 so this option is a temporary workaround
2296 for broken drivers that don't call it.
2297 skip_isa_align [X86] do not align io start addr, so can
2298 handle more pci cards
2299 firmware [ARM] Do not re-enumerate the bus but instead
2300 just use the configuration from the
2301 bootloader. This is currently used on
2302 IXP2000 systems where the bus has to be
2303 configured a certain way for adjunct CPUs.
2304 noearly [X86] Don't do any early type 1 scanning.
2305 This might help on some broken boards which
2306 machine check when some devices' config space
2307 is read. But various workarounds are disabled
2308 and some IOMMU drivers will not work.
2309 bfsort Sort PCI devices into breadth-first order.
2310 This sorting is done to get a device
2311 order compatible with older (<= 2.4) kernels.
2312 nobfsort Don't sort PCI devices into breadth-first order.
2313 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2314 tuning and use the BIOS-configured MPS defaults.
2315 pcie_bus_safe Set every device's MPS to the largest value
2316 supported by all devices below the root complex.
2317 pcie_bus_perf Set device MPS to the largest allowable MPS
2318 based on its parent bus. Also set MRRS (Max
2319 Read Request Size) to the largest supported
2320 value (no larger than the MPS that the device
2321 or bus can support) for best performance.
2322 pcie_bus_peer2peer Set every device's MPS to 128B, which
2323 every device is guaranteed to support. This
2324 configuration allows peer-to-peer DMA between
2325 any pair of devices, possibly at the cost of
2326 reduced performance. This also guarantees
2327 that hot-added devices will work.
2328 cbiosize=nn[KMG] The fixed amount of bus space which is
2329 reserved for the CardBus bridge's IO window.
2330 The default value is 256 bytes.
2331 cbmemsize=nn[KMG] The fixed amount of bus space which is
2332 reserved for the CardBus bridge's memory
2333 window. The default value is 64 megabytes.
2334 resource_alignment=
2335 Format:
2336 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2337 Specifies alignment and device to reassign
2338 aligned memory resources.
2339 If <order of align> is not specified,
2340 PAGE_SIZE is used as alignment.
2341 PCI-PCI bridge can be specified, if resource
2342 windows need to be expanded.
2343 ecrc= Enable/disable PCIe ECRC (transaction layer
2344 end-to-end CRC checking).
2345 bios: Use BIOS/firmware settings. This is the
2346 the default.
2347 off: Turn ECRC off
2348 on: Turn ECRC on.
2349 hpiosize=nn[KMG] The fixed amount of bus space which is
2350 reserved for hotplug bridge's IO window.
2351 Default size is 256 bytes.
2352 hpmemsize=nn[KMG] The fixed amount of bus space which is
2353 reserved for hotplug bridge's memory window.
2354 Default size is 2 megabytes.
2355 realloc= Enable/disable reallocating PCI bridge resources
2356 if allocations done by BIOS are too small to
2357 accommodate resources required by all child
2358 devices.
2359 off: Turn realloc off
2360 on: Turn realloc on
2361 realloc same as realloc=on
2362 noari do not use PCIe ARI.
2363 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2364 only look for one device below a PCIe downstream
2365 port.
2367 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2368 Management.
2369 off Disable ASPM.
2370 force Enable ASPM even on devices that claim not to support it.
2371 WARNING: Forcing ASPM on may cause system lockups.
2373 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2374 nomsi Do not use MSI for PCI Express Native Hotplug (this
2375 makes all PCIe ports use INTx for hotplug services).
2377 pcie_ports= [PCIE] PCIe ports handling:
2378 auto Ask the BIOS whether or not to use native PCIe services
2379 associated with PCIe ports (PME, hot-plug, AER). Use
2380 them only if that is allowed by the BIOS.
2381 native Use native PCIe services associated with PCIe ports
2382 unconditionally.
2383 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2384 ports driver.
2386 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2387 nomsi Do not use MSI for native PCIe PME signaling (this makes
2388 all PCIe root ports use INTx for all services).
2390 pcmv= [HW,PCMCIA] BadgePAD 4
2392 pd. [PARIDE]
2393 See Documentation/blockdev/paride.txt.
2395 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2396 boot time.
2397 Format: { 0 | 1 }
2398 See arch/parisc/kernel/pdc_chassis.c
2400 percpu_alloc= Select which percpu first chunk allocator to use.
2401 Currently supported values are "embed" and "page".
2402 Archs may support subset or none of the selections.
2403 See comments in mm/percpu.c for details on each
2404 allocator. This parameter is primarily for debugging
2405 and performance comparison.
2407 pf. [PARIDE]
2408 See Documentation/blockdev/paride.txt.
2410 pg. [PARIDE]
2411 See Documentation/blockdev/paride.txt.
2413 pirq= [SMP,APIC] Manual mp-table setup
2414 See Documentation/x86/i386/IO-APIC.txt.
2416 plip= [PPT,NET] Parallel port network link
2417 Format: { parport<nr> | timid | 0 }
2418 See also Documentation/parport.txt.
2420 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2421 Override pmtimer IOPort with a hex value.
2422 e.g. pmtmr=0x508
2424 pnp.debug=1 [PNP]
2425 Enable PNP debug messages (depends on the
2426 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2427 via /sys/module/pnp/parameters/debug. We always show
2428 current resource usage; turning this on also shows
2429 possible settings and some assignment information.
2431 pnpacpi= [ACPI]
2432 { off }
2434 pnpbios= [ISAPNP]
2435 { on | off | curr | res | no-curr | no-res }
2437 pnp_reserve_irq=
2438 [ISAPNP] Exclude IRQs for the autoconfiguration
2440 pnp_reserve_dma=
2441 [ISAPNP] Exclude DMAs for the autoconfiguration
2443 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2444 Ranges are in pairs (I/O port base and size).
2446 pnp_reserve_mem=
2447 [ISAPNP] Exclude memory regions for the
2448 autoconfiguration.
2449 Ranges are in pairs (memory base and size).
2451 ports= [IP_VS_FTP] IPVS ftp helper module
2452 Default is 21.
2453 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2454 may be specified.
2455 Format: <port>,<port>....
2457 print-fatal-signals=
2458 [KNL] debug: print fatal signals
2460 If enabled, warn about various signal handling
2461 related application anomalies: too many signals,
2462 too many POSIX.1 timers, fatal signals causing a
2463 coredump - etc.
2465 If you hit the warning due to signal overflow,
2466 you might want to try "ulimit -i unlimited".
2468 default: off.
2470 printk.always_kmsg_dump=
2471 Trigger kmsg_dump for cases other than kernel oops or
2472 panics
2473 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2474 default: disabled
2476 printk.time= Show timing data prefixed to each printk message line
2477 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2479 processor.max_cstate= [HW,ACPI]
2480 Limit processor to maximum C-state
2481 max_cstate=9 overrides any DMI blacklist limit.
2483 processor.nocst [HW,ACPI]
2484 Ignore the _CST method to determine C-states,
2485 instead using the legacy FADT method
2487 profile= [KNL] Enable kernel profiling via /proc/profile
2488 Format: [schedule,]<number>
2489 Param: "schedule" - profile schedule points.
2490 Param: <number> - step/bucket size as a power of 2 for
2491 statistical time based profiling.
2492 Param: "sleep" - profile D-state sleeping (millisecs).
2493 Requires CONFIG_SCHEDSTATS
2494 Param: "kvm" - profile VM exits.
2496 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2497 before loading.
2498 See Documentation/blockdev/ramdisk.txt.
2500 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2501 probe for; one of (bare|imps|exps|lifebook|any).
2502 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2503 per second.
2504 psmouse.resetafter= [HW,MOUSE]
2505 Try to reset the device after so many bad packets
2506 (0 = never).
2507 psmouse.resolution=
2508 [HW,MOUSE] Set desired mouse resolution, in dpi.
2509 psmouse.smartscroll=
2510 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2511 0 = disabled, 1 = enabled (default).
2513 pstore.backend= Specify the name of the pstore backend to use
2515 pt. [PARIDE]
2516 See Documentation/blockdev/paride.txt.
2518 pty.legacy_count=
2519 [KNL] Number of legacy pty's. Overwrites compiled-in
2520 default number.
2522 quiet [KNL] Disable most log messages
2524 r128= [HW,DRM]
2526 raid= [HW,RAID]
2527 See Documentation/md.txt.
2529 ramdisk_blocksize= [RAM]
2530 See Documentation/blockdev/ramdisk.txt.
2532 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2533 See Documentation/blockdev/ramdisk.txt.
2535 rcu_nocbs= [KNL,BOOT]
2536 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2537 the specified list of CPUs to be no-callback CPUs.
2538 Invocation of these CPUs' RCU callbacks will
2539 be offloaded to "rcuox/N" kthreads created for
2540 that purpose, where "x" is "b" for RCU-bh, "p"
2541 for RCU-preempt, and "s" for RCU-sched, and "N"
2542 is the CPU number. This reduces OS jitter on the
2543 offloaded CPUs, which can be useful for HPC and
2545 real-time workloads. It can also improve energy
2546 efficiency for asymmetric multiprocessors.
2548 rcu_nocb_poll [KNL,BOOT]
2549 Rather than requiring that offloaded CPUs
2550 (specified by rcu_nocbs= above) explicitly
2551 awaken the corresponding "rcuoN" kthreads,
2552 make these kthreads poll for callbacks.
2553 This improves the real-time response for the
2554 offloaded CPUs by relieving them of the need to
2555 wake up the corresponding kthread, but degrades
2556 energy efficiency by requiring that the kthreads
2557 periodically wake up to do the polling.
2559 rcutree.blimit= [KNL,BOOT]
2560 Set maximum number of finished RCU callbacks to process
2561 in one batch.
2563 rcutree.fanout_leaf= [KNL,BOOT]
2564 Increase the number of CPUs assigned to each
2565 leaf rcu_node structure. Useful for very large
2566 systems.
2568 rcutree.jiffies_till_first_fqs= [KNL,BOOT]
2569 Set delay from grace-period initialization to
2570 first attempt to force quiescent states.
2571 Units are jiffies, minimum value is zero,
2572 and maximum value is HZ.
2574 rcutree.jiffies_till_next_fqs= [KNL,BOOT]
2575 Set delay between subsequent attempts to force
2576 quiescent states. Units are jiffies, minimum
2577 value is one, and maximum value is HZ.
2579 rcutree.qhimark= [KNL,BOOT]
2580 Set threshold of queued
2581 RCU callbacks over which batch limiting is disabled.
2583 rcutree.qlowmark= [KNL,BOOT]
2584 Set threshold of queued RCU callbacks below which
2585 batch limiting is re-enabled.
2587 rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2588 Suppress RCU CPU stall warning messages.
2590 rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2591 Set timeout for RCU CPU stall warning messages.
2593 rcutree.rcu_idle_gp_delay= [KNL,BOOT]
2594 Set wakeup interval for idle CPUs that have
2595 RCU callbacks (RCU_FAST_NO_HZ=y).
2597 rcutree.rcu_idle_lazy_gp_delay= [KNL,BOOT]
2598 Set wakeup interval for idle CPUs that have
2599 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2600 Lazy RCU callbacks are those which RCU can
2601 prove do nothing more than free memory.
2603 rcutorture.fqs_duration= [KNL,BOOT]
2604 Set duration of force_quiescent_state bursts.
2606 rcutorture.fqs_holdoff= [KNL,BOOT]
2607 Set holdoff time within force_quiescent_state bursts.
2609 rcutorture.fqs_stutter= [KNL,BOOT]
2610 Set wait time between force_quiescent_state bursts.
2612 rcutorture.irqreader= [KNL,BOOT]
2613 Test RCU readers from irq handlers.
2615 rcutorture.n_barrier_cbs= [KNL,BOOT]
2616 Set callbacks/threads for rcu_barrier() testing.
2618 rcutorture.nfakewriters= [KNL,BOOT]
2619 Set number of concurrent RCU writers. These just
2620 stress RCU, they don't participate in the actual
2621 test, hence the "fake".
2623 rcutorture.nreaders= [KNL,BOOT]
2624 Set number of RCU readers.
2626 rcutorture.onoff_holdoff= [KNL,BOOT]
2627 Set time (s) after boot for CPU-hotplug testing.
2629 rcutorture.onoff_interval= [KNL,BOOT]
2630 Set time (s) between CPU-hotplug operations, or
2631 zero to disable CPU-hotplug testing.
2633 rcutorture.shuffle_interval= [KNL,BOOT]
2634 Set task-shuffle interval (s). Shuffling tasks
2635 allows some CPUs to go into dyntick-idle mode
2636 during the rcutorture test.
2638 rcutorture.shutdown_secs= [KNL,BOOT]
2639 Set time (s) after boot system shutdown. This
2640 is useful for hands-off automated testing.
2642 rcutorture.stall_cpu= [KNL,BOOT]
2643 Duration of CPU stall (s) to test RCU CPU stall
2644 warnings, zero to disable.
2646 rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2647 Time to wait (s) after boot before inducing stall.
2649 rcutorture.stat_interval= [KNL,BOOT]
2650 Time (s) between statistics printk()s.
2652 rcutorture.stutter= [KNL,BOOT]
2653 Time (s) to stutter testing, for example, specifying
2654 five seconds causes the test to run for five seconds,
2655 wait for five seconds, and so on. This tests RCU's
2656 ability to transition abruptly to and from idle.
2658 rcutorture.test_boost= [KNL,BOOT]
2659 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2660 "Maybe" means test if the RCU implementation
2661 under test support RCU priority boosting.
2663 rcutorture.test_boost_duration= [KNL,BOOT]
2664 Duration (s) of each individual boost test.
2666 rcutorture.test_boost_interval= [KNL,BOOT]
2667 Interval (s) between each boost test.
2669 rcutorture.test_no_idle_hz= [KNL,BOOT]
2670 Test RCU's dyntick-idle handling. See also the
2671 rcutorture.shuffle_interval parameter.
2673 rcutorture.torture_type= [KNL,BOOT]
2674 Specify the RCU implementation to test.
2676 rcutorture.verbose= [KNL,BOOT]
2677 Enable additional printk() statements.
2679 rdinit= [KNL]
2680 Format: <full_path>
2681 Run specified binary instead of /init from the ramdisk,
2682 used for early userspace startup. See initrd.
2684 reboot= [KNL]
2685 Format (x86 or x86_64):
2686 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2687 [[,]s[mp]#### \
2688 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2689 [[,]f[orce]
2690 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2691 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2692 reboot_force is either force or not specified,
2693 reboot_cpu is s[mp]#### with #### being the processor
2694 to be used for rebooting.
2696 relax_domain_level=
2697 [KNL, SMP] Set scheduler's default relax_domain_level.
2698 See Documentation/cgroups/cpusets.txt.
2700 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2702 reservetop= [X86-32]
2703 Format: nn[KMG]
2704 Reserves a hole at the top of the kernel virtual
2705 address space.
2707 reservelow= [X86]
2708 Format: nn[K]
2709 Set the amount of memory to reserve for BIOS at
2710 the bottom of the address space.
2712 reset_devices [KNL] Force drivers to reset the underlying device
2713 during initialization.
2715 resume= [SWSUSP]
2716 Specify the partition device for software suspend
2717 Format:
2718 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2720 resume_offset= [SWSUSP]
2721 Specify the offset from the beginning of the partition
2722 given by "resume=" at which the swap header is located,
2723 in <PAGE_SIZE> units (needed only for swap files).
2724 See Documentation/power/swsusp-and-swap-files.txt
2726 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2727 read the resume files
2729 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2730 Useful for devices that are detected asynchronously
2731 (e.g. USB and MMC devices).
2733 hibernate= [HIBERNATION]
2734 noresume Don't check if there's a hibernation image
2735 present during boot.
2736 nocompress Don't compress/decompress hibernation images.
2738 retain_initrd [RAM] Keep initrd memory after extraction
2740 rhash_entries= [KNL,NET]
2741 Set number of hash buckets for route cache
2743 riscom8= [HW,SERIAL]
2744 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2746 ro [KNL] Mount root device read-only on boot
2748 root= [KNL] Root filesystem
2749 See name_to_dev_t comment in init/do_mounts.c.
2751 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2752 mount the root filesystem
2754 rootflags= [KNL] Set root filesystem mount option string
2756 rootfstype= [KNL] Set root filesystem type
2758 rootwait [KNL] Wait (indefinitely) for root device to show up.
2759 Useful for devices that are detected asynchronously
2760 (e.g. USB and MMC devices).
2762 rproc_mem=nn[KMG][@address]
2763 [KNL,ARM,CMA] Remoteproc physical memory block.
2764 Memory area to be used by remote processor image,
2765 managed by CMA.
2767 rw [KNL] Mount root device read-write on boot
2769 S [KNL] Run init in single mode
2771 sa1100ir [NET]
2772 See drivers/net/irda/sa1100_ir.c.
2774 sbni= [NET] Granch SBNI12 leased line adapter
2776 sched_debug [KNL] Enables verbose scheduler debug messages.
2778 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2779 xtime_lock contention on larger systems, and/or RCU lock
2780 contention on all systems with CONFIG_MAXSMP set.
2781 Format: { "0" | "1" }
2782 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2783 1 -- enable.
2784 Note: increases power consumption, thus should only be
2785 enabled if running jitter sensitive (HPC/RT) workloads.
2787 security= [SECURITY] Choose a security module to enable at boot.
2788 If this boot parameter is not specified, only the first
2789 security module asking for security registration will be
2790 loaded. An invalid security module name will be treated
2791 as if no module has been chosen.
2793 selinux= [SELINUX] Disable or enable SELinux at boot time.
2794 Format: { "0" | "1" }
2795 See security/selinux/Kconfig help text.
2796 0 -- disable.
2797 1 -- enable.
2798 Default value is set via kernel config option.
2799 If enabled at boot time, /selinux/disable can be used
2800 later to disable prior to initial policy load.
2802 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2803 Format: { "0" | "1" }
2804 See security/apparmor/Kconfig help text
2805 0 -- disable.
2806 1 -- enable.
2807 Default value is set via kernel config option.
2809 serialnumber [BUGS=X86-32]
2811 shapers= [NET]
2812 Maximal number of shapers.
2814 show_msr= [x86] show boot-time MSR settings
2815 Format: { <integer> }
2816 Show boot-time (BIOS-initialized) MSR settings.
2817 The parameter means the number of CPUs to show,
2818 for example 1 means boot CPU only.
2820 simeth= [IA-64]
2821 simscsi=
2823 slram= [HW,MTD]
2825 slab_max_order= [MM, SLAB]
2826 Determines the maximum allowed order for slabs.
2827 A high setting may cause OOMs due to memory
2828 fragmentation. Defaults to 1 for systems with
2829 more than 32MB of RAM, 0 otherwise.
2831 slub_debug[=options[,slabs]] [MM, SLUB]
2832 Enabling slub_debug allows one to determine the
2833 culprit if slab objects become corrupted. Enabling
2834 slub_debug can create guard zones around objects and
2835 may poison objects when not in use. Also tracks the
2836 last alloc / free. For more information see
2837 Documentation/vm/slub.txt.
2839 slub_max_order= [MM, SLUB]
2840 Determines the maximum allowed order for slabs.
2841 A high setting may cause OOMs due to memory
2842 fragmentation. For more information see
2843 Documentation/vm/slub.txt.
2845 slub_min_objects= [MM, SLUB]
2846 The minimum number of objects per slab. SLUB will
2847 increase the slab order up to slub_max_order to
2848 generate a sufficiently large slab able to contain
2849 the number of objects indicated. The higher the number
2850 of objects the smaller the overhead of tracking slabs
2851 and the less frequently locks need to be acquired.
2852 For more information see Documentation/vm/slub.txt.
2854 slub_min_order= [MM, SLUB]
2855 Determines the minimum page order for slabs. Must be
2856 lower than slub_max_order.
2857 For more information see Documentation/vm/slub.txt.
2859 slub_nomerge [MM, SLUB]
2860 Disable merging of slabs with similar size. May be
2861 necessary if there is some reason to distinguish
2862 allocs to different slabs. Debug options disable
2863 merging on their own.
2864 For more information see Documentation/vm/slub.txt.
2866 smart2= [HW]
2867 Format: <io1>[,<io2>[,...,<io8>]]
2869 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2870 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2871 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2872 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2873 smsc-ircc2.ircc_irq= [HW] IRQ line
2874 smsc-ircc2.ircc_dma= [HW] DMA channel
2875 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2876 0: Toshiba Satellite 1800 (GP data pin select)
2877 1: Fast pin select (default)
2878 2: ATC IRMode
2880 softlockup_panic=
2881 [KNL] Should the soft-lockup detector generate panics.
2882 Format: <integer>
2884 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2885 See Documentation/laptops/sonypi.txt
2887 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2888 See Documentation/serial/specialix.txt.
2890 spia_io_base= [HW,MTD]
2891 spia_fio_base=
2892 spia_pedr=
2893 spia_peddr=
2895 stacktrace [FTRACE]
2896 Enabled the stack tracer on boot up.
2898 stacktrace_filter=[function-list]
2899 [FTRACE] Limit the functions that the stack tracer
2900 will trace at boot up. function-list is a comma separated
2901 list of functions. This list can be changed at run
2902 time by the stack_trace_filter file in the debugfs
2903 tracing directory. Note, this enables stack tracing
2904 and the stacktrace above is not needed.
2906 sti= [PARISC,HW]
2907 Format: <num>
2908 Set the STI (builtin display/keyboard on the HP-PARISC
2909 machines) console (graphic card) which should be used
2910 as the initial boot-console.
2911 See also comment in drivers/video/console/sticore.c.
2913 sti_font= [HW]
2914 See comment in drivers/video/console/sticore.c.
2916 stifb= [HW]
2917 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2919 sunrpc.min_resvport=
2920 sunrpc.max_resvport=
2921 [NFS,SUNRPC]
2922 SunRPC servers often require that client requests
2923 originate from a privileged port (i.e. a port in the
2924 range 0 < portnr < 1024).
2925 An administrator who wishes to reserve some of these
2926 ports for other uses may adjust the range that the
2927 kernel's sunrpc client considers to be privileged
2928 using these two parameters to set the minimum and
2929 maximum port values.
2931 sunrpc.pool_mode=
2932 [NFS]
2933 Control how the NFS server code allocates CPUs to
2934 service thread pools. Depending on how many NICs
2935 you have and where their interrupts are bound, this
2936 option will affect which CPUs will do NFS serving.
2937 Note: this parameter cannot be changed while the
2938 NFS server is running.
2940 auto the server chooses an appropriate mode
2941 automatically using heuristics
2942 global a single global pool contains all CPUs
2943 percpu one pool for each CPU
2944 pernode one pool for each NUMA node (equivalent
2945 to global on non-NUMA machines)
2947 sunrpc.tcp_slot_table_entries=
2948 sunrpc.udp_slot_table_entries=
2949 [NFS,SUNRPC]
2950 Sets the upper limit on the number of simultaneous
2951 RPC calls that can be sent from the client to a
2952 server. Increasing these values may allow you to
2953 improve throughput, but will also increase the
2954 amount of memory reserved for use by the client.
2956 swapaccount[=0|1]
2957 [KNL] Enable accounting of swap in memory resource
2958 controller if no parameter or 1 is given or disable
2959 it if 0 is given (See Documentation/cgroups/memory.txt)
2961 swiotlb= [IA-64] Number of I/O TLB slabs
2963 switches= [HW,M68k]
2965 sysfs.deprecated=0|1 [KNL]
2966 Enable/disable old style sysfs layout for old udev
2967 on older distributions. When this option is enabled
2968 very new udev will not work anymore. When this option
2969 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2970 in older udev will not work anymore.
2971 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2972 the kernel configuration.
2974 sysrq_always_enabled
2975 [KNL]
2976 Ignore sysrq setting - this boot parameter will
2977 neutralize any effect of /proc/sys/kernel/sysrq.
2978 Useful for debugging.
2980 tdfx= [HW,DRM]
2982 test_suspend= [SUSPEND]
2983 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2984 standby suspend) as the system sleep state to briefly
2985 enter during system startup. The system is woken from
2986 this state using a wakeup-capable RTC alarm.
2988 thash_entries= [KNL,NET]
2989 Set number of hash buckets for TCP connection
2991 thermal.act= [HW,ACPI]
2992 -1: disable all active trip points in all thermal zones
2993 <degrees C>: override all lowest active trip points
2995 thermal.crt= [HW,ACPI]
2996 -1: disable all critical trip points in all thermal zones
2997 <degrees C>: override all critical trip points
2999 thermal.nocrt= [HW,ACPI]
3000 Set to disable actions on ACPI thermal zone
3001 critical and hot trip points.
3003 thermal.off= [HW,ACPI]
3004 1: disable ACPI thermal control
3006 thermal.psv= [HW,ACPI]
3007 -1: disable all passive trip points
3008 <degrees C>: override all passive trip points to this
3009 value
3011 thermal.tzp= [HW,ACPI]
3012 Specify global default ACPI thermal zone polling rate
3013 <deci-seconds>: poll all this frequency
3014 0: no polling (default)
3016 threadirqs [KNL]
3017 Force threading of all interrupt handlers except those
3018 marked explicitly IRQF_NO_THREAD.
3020 tmem [KNL,XEN]
3021 Enable the Transcendent memory driver if built-in.
3023 tmem.cleancache=0|1 [KNL, XEN]
3024 Default is on (1). Disable the usage of the cleancache
3025 API to send anonymous pages to the hypervisor.
3027 tmem.frontswap=0|1 [KNL, XEN]
3028 Default is on (1). Disable the usage of the frontswap
3029 API to send swap pages to the hypervisor. If disabled
3030 the selfballooning and selfshrinking are force disabled.
3032 tmem.selfballooning=0|1 [KNL, XEN]
3033 Default is on (1). Disable the driving of swap pages
3034 to the hypervisor.
3036 tmem.selfshrinking=0|1 [KNL, XEN]
3037 Default is on (1). Partial swapoff that immediately
3038 transfers pages from Xen hypervisor back to the
3039 kernel based on different criteria.
3041 topology= [S390]
3042 Format: {off | on}
3043 Specify if the kernel should make use of the cpu
3044 topology information if the hardware supports this.
3045 The scheduler will make use of this information and
3046 e.g. base its process migration decisions on it.
3047 Default is on.
3049 tp720= [HW,PS2]
3051 tpm_suspend_pcr=[HW,TPM]
3052 Format: integer pcr id
3053 Specify that at suspend time, the tpm driver
3054 should extend the specified pcr with zeros,
3055 as a workaround for some chips which fail to
3056 flush the last written pcr on TPM_SaveState.
3057 This will guarantee that all the other pcrs
3058 are saved.
3060 trace_buf_size=nn[KMG]
3061 [FTRACE] will set tracing buffer size.
3063 trace_event=[event-list]
3064 [FTRACE] Set and start specified trace events in order
3065 to facilitate early boot debugging.
3066 See also Documentation/trace/events.txt
3068 trace_options=[option-list]
3069 [FTRACE] Enable or disable tracer options at boot.
3070 The option-list is a comma delimited list of options
3071 that can be enabled or disabled just as if you were
3072 to echo the option name into
3074 /sys/kernel/debug/tracing/trace_options
3076 For example, to enable stacktrace option (to dump the
3077 stack trace of each event), add to the command line:
3079 trace_options=stacktrace
3081 See also Documentation/trace/ftrace.txt "trace options"
3082 section.
3084 traceoff_on_warning
3085 [FTRACE] enable this option to disable tracing when a
3086 warning is hit. This turns off "tracing_on". Tracing can
3087 be enabled again by echoing '1' into the "tracing_on"
3088 file located in /sys/kernel/debug/tracing/
3090 This option is useful, as it disables the trace before
3091 the WARNING dump is called, which prevents the trace to
3092 be filled with content caused by the warning output.
3094 This option can also be set at run time via the sysctl
3095 option: kernel/traceoff_on_warning
3097 transparent_hugepage=
3098 [KNL]
3099 Format: [always|madvise|never]
3100 Can be used to control the default behavior of the system
3101 with respect to transparent hugepages.
3102 See Documentation/vm/transhuge.txt for more details.
3104 tsc= Disable clocksource stability checks for TSC.
3105 Format: <string>
3106 [x86] reliable: mark tsc clocksource as reliable, this
3107 disables clocksource verification at runtime, as well
3108 as the stability checks done at bootup. Used to enable
3109 high-resolution timer mode on older hardware, and in
3110 virtualized environment.
3111 [x86] noirqtime: Do not use TSC to do irq accounting.
3112 Used to run time disable IRQ_TIME_ACCOUNTING on any
3113 platforms where RDTSC is slow and this accounting
3114 can add overhead.
3116 turbografx.map[2|3]= [HW,JOY]
3117 TurboGraFX parallel port interface
3118 Format:
3119 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3120 See also Documentation/input/joystick-parport.txt
3122 udbg-immortal [PPC] When debugging early kernel crashes that
3123 happen after console_init() and before a proper
3124 console driver takes over, this boot options might
3125 help "seeing" what's going on.
3127 uhash_entries= [KNL,NET]
3128 Set number of hash buckets for UDP/UDP-Lite connections
3130 uhci-hcd.ignore_oc=
3131 [USB] Ignore overcurrent events (default N).
3132 Some badly-designed motherboards generate lots of
3133 bogus events, for ports that aren't wired to
3134 anything. Set this parameter to avoid log spamming.
3135 Note that genuine overcurrent events won't be
3136 reported either.
3138 unknown_nmi_panic
3139 [X86] Cause panic on unknown NMI.
3141 usbcore.authorized_default=
3142 [USB] Default USB device authorization:
3143 (default -1 = authorized except for wireless USB,
3144 0 = not authorized, 1 = authorized)
3146 usbcore.autosuspend=
3147 [USB] The autosuspend time delay (in seconds) used
3148 for newly-detected USB devices (default 2). This
3149 is the time required before an idle device will be
3150 autosuspended. Devices for which the delay is set
3151 to a negative value won't be autosuspended at all.
3153 usbcore.usbfs_snoop=
3154 [USB] Set to log all usbfs traffic (default 0 = off).
3156 usbcore.blinkenlights=
3157 [USB] Set to cycle leds on hubs (default 0 = off).
3159 usbcore.old_scheme_first=
3160 [USB] Start with the old device initialization
3161 scheme (default 0 = off).
3163 usbcore.usbfs_memory_mb=
3164 [USB] Memory limit (in MB) for buffers allocated by
3165 usbfs (default = 16, 0 = max = 2047).
3167 usbcore.use_both_schemes=
3168 [USB] Try the other device initialization scheme
3169 if the first one fails (default 1 = enabled).
3171 usbcore.initial_descriptor_timeout=
3172 [USB] Specifies timeout for the initial 64-byte
3173 USB_REQ_GET_DESCRIPTOR request in milliseconds
3174 (default 5000 = 5.0 seconds).
3176 usbhid.mousepoll=
3177 [USBHID] The interval which mice are to be polled at.
3179 usb-storage.delay_use=
3180 [UMS] The delay in seconds before a new device is
3181 scanned for Logical Units (default 5).
3183 usb-storage.quirks=
3184 [UMS] A list of quirks entries to supplement or
3185 override the built-in unusual_devs list. List
3186 entries are separated by commas. Each entry has
3187 the form VID:PID:Flags where VID and PID are Vendor
3188 and Product ID values (4-digit hex numbers) and
3189 Flags is a set of characters, each corresponding
3190 to a common usb-storage quirk flag as follows:
3191 a = SANE_SENSE (collect more than 18 bytes
3192 of sense data);
3193 b = BAD_SENSE (don't collect more than 18
3194 bytes of sense data);
3195 c = FIX_CAPACITY (decrease the reported
3196 device capacity by one sector);
3197 d = NO_READ_DISC_INFO (don't use
3198 READ_DISC_INFO command);
3199 e = NO_READ_CAPACITY_16 (don't use
3200 READ_CAPACITY_16 command);
3201 h = CAPACITY_HEURISTICS (decrease the
3202 reported device capacity by one
3203 sector if the number is odd);
3204 i = IGNORE_DEVICE (don't bind to this
3205 device);
3206 l = NOT_LOCKABLE (don't try to lock and
3207 unlock ejectable media);
3208 m = MAX_SECTORS_64 (don't transfer more
3209 than 64 sectors = 32 KB at a time);
3210 n = INITIAL_READ10 (force a retry of the
3211 initial READ(10) command);
3212 o = CAPACITY_OK (accept the capacity
3213 reported by the device);
3214 p = WRITE_CACHE (the device cache is ON
3215 by default);
3216 r = IGNORE_RESIDUE (the device reports
3217 bogus residue values);
3218 s = SINGLE_LUN (the device has only one
3219 Logical Unit);
3220 w = NO_WP_DETECT (don't test whether the
3221 medium is write-protected).
3222 Example: quirks=0419:aaf5:rl,0421:0433:rc
3224 user_debug= [KNL,ARM]
3225 Format: <int>
3226 See arch/arm/Kconfig.debug help text.
3227 1 - undefined instruction events
3228 2 - system calls
3229 4 - invalid data aborts
3230 8 - SIGSEGV faults
3231 16 - SIGBUS faults
3232 Example: user_debug=31
3234 userpte=
3235 [X86] Flags controlling user PTE allocations.
3237 nohigh = do not allocate PTE pages in
3238 HIGHMEM regardless of setting
3239 of CONFIG_HIGHPTE.
3241 vdso= [X86,SH]
3242 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3243 vdso=1: enable VDSO (default)
3244 vdso=0: disable VDSO mapping
3246 vdso32= [X86]
3247 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3248 vdso32=1: enable 32-bit VDSO (default)
3249 vdso32=0: disable 32-bit VDSO mapping
3251 vector= [IA-64,SMP]
3252 vector=percpu: enable percpu vector domain
3254 video= [FB] Frame buffer configuration
3255 See Documentation/fb/modedb.txt.
3257 video.brightness_switch_enabled= [0,1]
3258 If set to 1, on receiving an ACPI notify event
3259 generated by hotkey, video driver will adjust brightness
3260 level and then send out the event to user space through
3261 the allocated input device; If set to 0, video driver
3262 will only send out the event without touching backlight
3263 brightness level.
3264 default: 1
3266 virtio_mmio.device=
3267 [VMMIO] Memory mapped virtio (platform) device.
3269 <size>@<baseaddr>:<irq>[:<id>]
3270 where:
3271 <size> := size (can use standard suffixes
3272 like K, M and G)
3273 <baseaddr> := physical base address
3274 <irq> := interrupt number (as passed to
3275 request_irq())
3276 <id> := (optional) platform device id
3277 example:
3278 virtio_mmio.device=1K@0x100b0000:48:7
3280 Can be used multiple times for multiple devices.
3282 vga= [BOOT,X86-32] Select a particular video mode
3283 See Documentation/x86/boot.txt and
3284 Documentation/svga.txt.
3285 Use vga=ask for menu.
3286 This is actually a boot loader parameter; the value is
3287 passed to the kernel using a special protocol.
3289 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3290 size of <nn>. This can be used to increase the
3291 minimum size (128MB on x86). It can also be used to
3292 decrease the size and leave more room for directly
3293 mapped kernel RAM.
3295 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3296 Format: <command>
3298 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3299 Format: <command>
3301 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3302 Format: <command>
3304 vsyscall= [X86-64]
3305 Controls the behavior of vsyscalls (i.e. calls to
3306 fixed addresses of 0xffffffffff600x00 from legacy
3307 code). Most statically-linked binaries and older
3308 versions of glibc use these calls. Because these
3309 functions are at fixed addresses, they make nice
3310 targets for exploits that can control RIP.
3312 emulate [default] Vsyscalls turn into traps and are
3313 emulated reasonably safely.
3315 native Vsyscalls are native syscall instructions.
3316 This is a little bit faster than trapping
3317 and makes a few dynamic recompilers work
3318 better than they would in emulation mode.
3319 It also makes exploits much easier to write.
3321 none Vsyscalls don't work at all. This makes
3322 them quite hard to use for exploits but
3323 might break your system.
3325 vt.cur_default= [VT] Default cursor shape.
3326 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3327 the parameters of the <Esc>[?A;B;Cc escape sequence;
3328 see VGA-softcursor.txt. Default: 2 = underline.
3330 vt.default_blu= [VT]
3331 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3332 Change the default blue palette of the console.
3333 This is a 16-member array composed of values
3334 ranging from 0-255.
3336 vt.default_grn= [VT]
3337 Format: <green0>,<green1>,<green2>,...,<green15>
3338 Change the default green palette of the console.
3339 This is a 16-member array composed of values
3340 ranging from 0-255.
3342 vt.default_red= [VT]
3343 Format: <red0>,<red1>,<red2>,...,<red15>
3344 Change the default red palette of the console.
3345 This is a 16-member array composed of values
3346 ranging from 0-255.
3348 vt.default_utf8=
3349 [VT]
3350 Format=<0|1>
3351 Set system-wide default UTF-8 mode for all tty's.
3352 Default is 1, i.e. UTF-8 mode is enabled for all
3353 newly opened terminals.
3355 vt.global_cursor_default=
3356 [VT]
3357 Format=<-1|0|1>
3358 Set system-wide default for whether a cursor
3359 is shown on new VTs. Default is -1,
3360 i.e. cursors will be created by default unless
3361 overridden by individual drivers. 0 will hide
3362 cursors, 1 will display them.
3364 watchdog timers [HW,WDT] For information on watchdog timers,
3365 see Documentation/watchdog/watchdog-parameters.txt
3366 or other driver-specific files in the
3367 Documentation/watchdog/ directory.
3369 workqueue.disable_numa
3370 By default, all work items queued to unbound
3371 workqueues are affine to the NUMA nodes they're
3372 issued on, which results in better behavior in
3373 general. If NUMA affinity needs to be disabled for
3374 whatever reason, this option can be used. Note
3375 that this also can be controlled per-workqueue for
3376 workqueues visible under /sys/bus/workqueue/.
3378 workqueue.power_efficient
3379 Per-cpu workqueues are generally preferred because
3380 they show better performance thanks to cache
3381 locality; unfortunately, per-cpu workqueues tend to
3382 be more power hungry than unbound workqueues.
3384 Enabling this makes the per-cpu workqueues which
3385 were observed to contribute significantly to power
3386 consumption unbound, leading to measurably lower
3387 power usage at the cost of small performance
3388 overhead.
3390 The default value of this parameter is determined by
3391 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3393 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3394 default x2apic cluster mode on platforms
3395 supporting x2apic.
3397 x86_mrst_timer= [X86-32,APBT]
3398 Choose timer option for x86 Moorestown MID platform.
3399 Two valid options are apbt timer only and lapic timer
3400 plus one apbt timer for broadcast timer.
3401 x86_mrst_timer=apbt_only | lapic_and_apbt
3403 xen_emul_unplug= [HW,X86,XEN]
3404 Unplug Xen emulated devices
3405 Format: [unplug0,][unplug1]
3406 ide-disks -- unplug primary master IDE devices
3407 aux-ide-disks -- unplug non-primary-master IDE devices
3408 nics -- unplug network devices
3409 all -- unplug all emulated devices (NICs and IDE disks)
3410 unnecessary -- unplugging emulated devices is
3411 unnecessary even if the host did not respond to
3412 the unplug protocol
3413 never -- do not unplug even if version check succeeds
3415 xirc2ps_cs= [NET,PCMCIA]
3416 Format:
3417 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3419 ______________________________________________________________________
3421 TODO:
3423 Add more DRM drivers.