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.
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]
178 2: use 2nd APIC table, if available
179 1,0: use 1st APIC table
182 acpi_backlight= [HW,ACPI]
183 acpi_backlight=vendor
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]
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
221 acpi_irq_nobalance [HW,ACPI]
222 ACPI will not move active IRQs (default)
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
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
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
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.
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)
305 See Documentation/sound/alsa/alsa-parameters.txt
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.
335 fullflush - enable flushing of IO/TLB entries when
336 they are unmapped. Otherwise they are
337 flushed before they will be reused, which
339 off - do not initialize any AMD IOMMU found in
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
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>
364 Power management functions (SPARCstation-4/5 + deriv.)
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.
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>
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
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]
418 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
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
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
442 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
445 bulk_remove=off [PPC] This parameter disables the use of the pSeries
446 firmware feature for flushing multiple hpte entries
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.
476 See Documentation/s390/CommonIO for details.
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.
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
494 Override the default clocksource and use the clocksource
495 with the name specified.
496 Some clocksource names to choose from, depending on
498 [all] jiffies (this is the base, fallback clocksource)
500 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
501 pxa_timer,timer3,32k_counter,timer0_1
503 [X86-32] pit,hpet,tsc;
504 scx200_hrt on Geode; cyclone on IBM x440
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
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
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
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
546 com20020= [HW,NET] ARCnet - COM20020 chipset
548 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
550 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
554 ARCnet - COM90xx chipset (memory-mapped buffers)
555 Format: <io>[,<irq>[,<memstart>]]
557 condev= [HW,S390] console device
560 console= [KNL] Output console device and options.
562 tty<n> Use the virtual console device <n>.
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
574 Documentation/networking/netconsole.txt for an
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
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.
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
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
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.
645 cs89x0_media= [HW,NET]
646 Format: { rj45 | aui | bnc }
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).
663 [KNL] verbose self-tests
665 Print debugging info while doing the locking API
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
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.
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
710 Set number of hash buckets for dentry cache.
713 IO parameters + enable/disable command.
715 digiepca= [HW,SERIAL]
716 See drivers/char/README.epca and
717 Documentation/serial/digiepca.txt.
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.
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
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]
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
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
822 The VGA output is eventually overwritten by the real
825 The xen output can only be used by Xen PV guests.
827 ekgdboc= [X86,KGDB] Allow early kernel console debugging
830 This is designed to be used in conjunction with
831 the boot argument: earlyprintk=vga
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.
846 See comment before function elanfreq_setup() in
847 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
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.
873 See security/selinux/Kconfig help text.
874 0 -- permissive (log only, no denials).
875 1 -- enforcing (deny and log).
877 Value can be changed at runtime via /selinux/enforce.
880 Disable Error Record Serialization Table (ERST)
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.
889 Permit 'security.evm' to be updated regardless of
890 current integrity status.
894 fail_make_request=[KNL]
895 General fault injection mechanism.
896 Format: <interval>,<probability>,<space>,<times>
897 See also Documentation/fault-injection/.
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.
909 [FTRACE] will set and start the specified tracer
910 as early as possible in order to facilitate early
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
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
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
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.
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
948 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
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.
965 grcan.enable1= [HW] Configuration of physical interface 1. Determines
966 the "Enable 0" bit of the configuration register.
969 grcan.select= [HW] Select which physical interface to use.
972 grcan.txsize= [HW] Sets the size of the tx buffer.
973 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
975 grcan.rxsize= [HW] Sets the size of the rx buffer.
976 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
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>
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"
1004 See Documentation/isdn/README.HiSax.
1008 hpet= [X86-32,HPET] option to control HPET usage
1009 Format: { enable (default) | disable | force |
1011 disable: disable HPET and use PIT instead
1012 force: allow force enabled of undocumented chips (ICH4,
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>
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
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.
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
1057 i8042.nomux [HW] Don't check presence of an active multiplexing
1059 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
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
1067 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1068 indicates that the driver is running on unsupported
1070 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1071 does not match list of supported models.
1073 [HW] Report power status in /proc/i8k
1074 (disabled by default)
1075 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
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
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.
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.
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" }
1128 ima_appraise_tcb [IMA]
1129 The builtin appraise policy appraises all files
1133 Format: { "0" | "1" }
1134 0 -- integrity auditing messages. (Default)
1135 1 -- enable informational integrity auditing messages.
1138 Format: { "sha1" | "md5" }
1142 Load a policy which meets the needs of the Trusted
1143 Computing Base. This means IMA will measure all
1144 programs exec'd, files mmap'd for exec, and all files
1145 opened for read by uid=0.
1149 Run specified binary instead of /sbin/init as init
1152 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1153 for working out where the kernel is dying during
1156 initrd= [BOOT] Specify the location of the initial ramdisk
1158 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1161 int_pln_enable [x86] Enable power limit notification interrupt
1163 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1165 Enable intel iommu driver.
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
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
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.
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
1204 BIOS x2APIC opt-out request will be ignored
1206 iomem= Disable strict checking of access to MMIO memory
1207 strict regions from userspace.
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
1230 Standard port 0x80 based delay
1232 Alternate port 0xed based delay (needed on some systems)
1234 Simple two microseconds delay
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.
1246 When an interrupt is not handled search all handlers
1247 for it. Intended to get systems with badly broken
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
1257 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1259 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1261 <cpu number>,...,<cpu number>
1263 <cpu number>-<cpu number>
1264 (must be a positive range in ascending order)
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.
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.
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
1349 kstack=N [X86] Print N words from the kernel stack
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
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)
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)
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)
1395 lapic [X86-32,APIC] Enable the local APIC even if BIOS
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
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
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
1451 * [no]ncq: Turn on or off NCQ.
1453 * nohrst, nosrst, norst: suppress hard, soft
1456 * rstonce: only attempt one reset during
1457 hot-unplug link recovery
1459 * dump_id: dump IDENTIFY data.
1461 If there are multiple matching configurations changing
1462 the same attribute, the last one is used.
1464 memblock=debug [KNL] Enable memblock debug messages.
1466 load_ramdisk= [RAM] List of ramdisks to load from floppy
1467 See Documentation/blockdev/ramdisk.txt.
1469 lockd.nlm_grace_period=P [NFS] Assign grace period.
1472 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1475 lockd.nlm_timeout=T [NFS] Assign timeout value.
1478 lockd.nlm_udpport=M [NFS] Assign UDP port.
1481 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1484 loglevel= All Kernel Messages with a loglevel smaller than the
1485 console loglevel will be printed to the console. It can
1486 also be changed with klogd or other programs. The
1487 loglevels are defined as follows:
1489 0 (KERN_EMERG) system is unusable
1490 1 (KERN_ALERT) action must be taken immediately
1491 2 (KERN_CRIT) critical conditions
1492 3 (KERN_ERR) error conditions
1493 4 (KERN_WARNING) warning conditions
1494 5 (KERN_NOTICE) normal but significant condition
1495 6 (KERN_INFO) informational
1496 7 (KERN_DEBUG) debug-level messages
1498 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1499 in bytes. n must be a power of two. The default
1500 size is set in the kernel config file.
1502 logo.nologo [FB] Disables display of the built-in Linux logo.
1503 This may be used to provide more screen space for
1504 kernel log messages and is useful when debugging
1505 kernel boot problems.
1507 lp=0 [LP] Specify parallel ports to use, e.g,
1508 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1509 lp=reset first parallel port). 'lp=0' disables the
1510 lp=auto printer driver. 'lp=reset' (which can be
1511 specified in addition to the ports) causes
1512 attached printers to be reset. Using
1513 lp=port1,port2,... specifies the parallel ports
1514 to associate lp devices with, starting with
1515 lp0. A port specification may be 'none' to skip
1516 that lp device, or a parport name such as
1517 'parport0'. Specifying 'lp=auto' instead of a
1518 port specification list means that device IDs
1519 from each port should be examined, to see if
1520 an IEEE 1284-compliant printer is attached; if
1521 so, the driver will manage that printer.
1522 See also header of drivers/char/lp.c.
1525 Sets loops_per_jiffy to given constant, thus avoiding
1526 time-consuming boot-time autodetection (up to 250 ms per
1527 CPU). 0 enables autodetection (default). To determine
1528 the correct value for your kernel, boot with normal
1529 autodetection and see what value is printed. Note that
1530 on SMP systems the preset will be applied to all CPUs,
1531 which is likely to cause problems if your CPUs need
1532 significantly divergent settings. An incorrect value
1533 will cause delays in the kernel to be wrong, leading to
1534 unpredictable I/O errors and other breakage. Although
1535 unlikely, in the extreme case this might damage your
1539 Format: <io>,<irq>,<dma>
1541 machvec= [IA-64] Force the use of a particular machine-vector
1542 (machvec) in a generic kernel.
1543 Example: machvec=hpzx1_swiotlb
1545 machtype= [Loongson] Share the same kernel image file between different
1547 Example: machtype=lemote-yeeloong-2f-7inch
1549 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1550 than or equal to this physical address is ignored.
1552 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1553 should make use of. maxcpus=n : n >= 0 limits the
1554 kernel to using 'n' processors. n=0 is a special case,
1555 it is equivalent to "nosmp", which also disables
1558 max_loop= [LOOP] The number of loop block devices that get
1559 (loop.max_loop) unconditionally pre-created at init time. The default
1560 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1561 of statically allocating a predefined number, loop
1562 devices can be requested on-demand with the
1563 /dev/loop-control interface.
1565 mce [X86-32] Machine Check Exception
1567 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1569 md= [HW] RAID subsystems devices and level
1570 See Documentation/md.txt.
1573 Format: <first>,<last>
1574 Specifies range of consoles to be captured by the MDA.
1576 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1577 Amount of memory to be used when the kernel is not able
1578 to see the whole system memory or for test.
1579 [X86] Work as limiting max address. Use together
1580 with memmap= to avoid physical address space collisions.
1581 Without memmap= PCI devices could be placed at addresses
1582 belonging to unused RAM.
1584 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1588 [KNL,SH] Allow user to override the default size for
1589 per-device physically contiguous DMA buffers.
1591 memmap=exactmap [KNL,X86] Enable setting of an exact
1592 E820 memory map, as specified by the user.
1593 Such memmap=exactmap lines can be constructed based on
1594 BIOS output or other requirements. See the memmap=nn@ss
1597 memmap=nn[KMG]@ss[KMG]
1598 [KNL] Force usage of a specific region of memory
1599 Region of memory to be used, from ss to ss+nn.
1601 memmap=nn[KMG]#ss[KMG]
1602 [KNL,ACPI] Mark specific memory as ACPI data.
1603 Region of memory to be used, from ss to ss+nn.
1605 memmap=nn[KMG]$ss[KMG]
1606 [KNL,ACPI] Mark specific memory as reserved.
1607 Region of memory to be used, from ss to ss+nn.
1608 Example: Exclude memory from 0x18690000-0x1869ffff
1609 memmap=64K$0x18690000
1611 memmap=0x10000$0x18690000
1613 memory_corruption_check=0/1 [X86]
1614 Some BIOSes seem to corrupt the first 64k of
1615 memory when doing things like suspend/resume.
1616 Setting this option will scan the memory
1617 looking for corruption. Enabling this will
1618 both detect corruption and prevent the kernel
1619 from using the memory being corrupted.
1620 However, its intended as a diagnostic tool; if
1621 repeatable BIOS-originated corruption always
1622 affects the same memory, you can use memmap=
1623 to prevent the kernel from using that memory.
1625 memory_corruption_check_size=size [X86]
1626 By default it checks for corruption in the low
1627 64k, making this memory unavailable for normal
1628 use. Use this parameter to scan for
1629 corruption in more or less memory.
1631 memory_corruption_check_period=seconds [X86]
1632 By default it checks for corruption every 60
1633 seconds. Use this parameter to check at some
1634 other rate. 0 disables periodic checking.
1636 memtest= [KNL,X86] Enable memtest
1638 default : 0 <disable>
1639 Specifies the number of memtest passes to be
1640 performed. Each pass selects another test
1641 pattern from a given set of patterns. Memtest
1642 fills the memory with this pattern, validates
1643 memory contents and reserves bad memory
1644 regions that are detected.
1646 meye.*= [HW] Set MotionEye Camera parameters
1647 See Documentation/video4linux/meye.txt.
1649 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1650 Multi-Function General Purpose Timers on AMD Geode
1653 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1654 the BIOS has incorrectly applied a workaround. TinyBIOS
1655 version 0.98 is known to be affected, 0.99 fixes the
1656 problem by letting the user disable the workaround.
1660 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1661 physical address is ignored.
1663 mini2440= [ARM,HW,KNL]
1664 Format:[0..2][b][c][t]
1666 MINI2440 configuration specification:
1667 0 - The attached screen is the 3.5" TFT
1668 1 - The attached screen is the 7" TFT
1669 2 - The VGA Shield is attached (1024x768)
1670 Leaving out the screen size parameter will not load
1671 the TFT driver, and the framebuffer will be left
1673 b - Enable backlight. The TFT backlight pin will be
1674 linked to the kernel VESA blanking code and a GPIO
1675 LED. This parameter is not necessary when using the
1677 c - Enable the s3c camera interface.
1678 t - Reserved for enabling touchscreen support. The
1679 touchscreen support is not enabled in the mainstream
1680 kernel as of 2.6.30, a preliminary port can be found
1681 in the "bleeding edge" mini2440 support kernel at
1682 http://repo.or.cz/w/linux-2.6/mini2440.git
1685 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1686 parameter allows control of the logging verbosity for
1687 the additional memory initialisation checks. A value
1688 of 0 disables mminit logging and a level of 4 will
1689 log everything. Information is printed at KERN_DEBUG
1690 so loglevel=8 may also need to be specified.
1693 [KNL] When CONFIG_MODULE_SIG is set, this means that
1694 modules without (valid) signatures will fail to load.
1695 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1696 is always true, so this option does nothing.
1699 [MOUSE] Maximum time between finger touching and
1700 leaving touchpad surface for touch to be considered
1701 a tap and be reported as a left button click (for
1702 touchpads working in absolute mode only).
1704 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1705 reporting absolute coordinates, such as tablets
1706 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1707 reporting absolute coordinates, such as tablets
1709 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1710 is similar to kernelcore except it specifies the
1711 amount of memory used for migratable allocations.
1712 If both kernelcore and movablecore is specified,
1713 then kernelcore will be at *least* the specified
1714 value but may be more. If movablecore on its own
1715 is specified, the administrator must be careful
1716 that the amount of memory usable for all allocations
1719 MTD_Partition= [MTD]
1720 Format: <name>,<region-number>,<size>,<offset>
1722 MTD_Region= [MTD] Format:
1723 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1726 See drivers/mtd/cmdlinepart.c.
1728 multitce=off [PPC] This parameter disables the use of the pSeries
1729 firmware feature for updating multiple TCE entries
1732 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1734 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1736 boundary - index of last SLC block on Flex-OneNAND.
1737 The remaining blocks are configured as MLC blocks.
1738 lock - Configure if Flex-OneNAND boundary should be locked.
1739 Once locked, the boundary cannot be changed.
1740 1 indicates lock status, 0 indicates unlock status.
1743 ARM/S3C2412 JIVE boot control
1745 See arch/arm/mach-s3c2412/mach-jive.c
1747 mtouchusb.raw_coordinates=
1748 [HW] Make the MicroTouch USB driver use raw coordinates
1749 ('y', default) or cooked coordinates ('n')
1751 mtrr_chunk_size=nn[KMG] [X86]
1752 used for mtrr cleanup. It is largest continuous chunk
1753 that could hold holes aka. UC entries.
1755 mtrr_gran_size=nn[KMG] [X86]
1756 Used for mtrr cleanup. It is granularity of mtrr block.
1758 Large value could prevent small alignment from
1761 mtrr_spare_reg_nr=n [X86]
1763 Range: 0,7 : spare reg number
1765 Used for mtrr cleanup. It is spare mtrr entries number.
1766 Set to 2 or more if your graphical card needs more.
1768 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1770 netdev= [NET] Network devices parameters
1771 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1772 Note that mem_start is often overloaded to mean
1773 something different and driver-specific.
1774 This usage is only documented in each driver source
1778 [NETFILTER] Enable connection tracking flow accounting
1779 0 to disable accounting
1780 1 to enable accounting
1783 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1784 See Documentation/filesystems/nfs/nfsroot.txt.
1786 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1787 See Documentation/filesystems/nfs/nfsroot.txt.
1789 nfsrootdebug [NFS] enable nfsroot debugging messages.
1790 See Documentation/filesystems/nfs/nfsroot.txt.
1792 nfs.callback_tcpport=
1793 [NFS] set the TCP port on which the NFSv4 callback
1794 channel should listen.
1797 [NFS] sets the pathname to the program which is used
1798 to update the NFS client cache entries.
1800 nfs.cache_getent_timeout=
1801 [NFS] sets the timeout after which an attempt to
1802 update a cache entry is deemed to have failed.
1804 nfs.idmap_cache_timeout=
1805 [NFS] set the maximum lifetime for idmapper cache
1809 [NFS] enable 64-bit inode numbers.
1810 If zero, the NFS client will fake up a 32-bit inode
1811 number for the readdir() and stat() syscalls instead
1812 of returning the full 64-bit number.
1813 The default is to return 64-bit inode numbers.
1815 nfs.max_session_slots=
1816 [NFSv4.1] Sets the maximum number of session slots
1817 the client will attempt to negotiate with the server.
1818 This limits the number of simultaneous RPC requests
1819 that the client can send to the NFSv4.1 server.
1820 Note that there is little point in setting this
1821 value higher than the max_tcp_slot_table_limit.
1823 nfs.nfs4_disable_idmapping=
1824 [NFSv4] When set to the default of '1', this option
1825 ensures that both the RPC level authentication
1826 scheme and the NFS level operations agree to use
1827 numeric uids/gids if the mount is using the
1828 'sec=sys' security flavour. In effect it is
1829 disabling idmapping, which can make migration from
1830 legacy NFSv2/v3 systems to NFSv4 easier.
1831 Servers that do not support this mode of operation
1832 will be autodetected by the client, and it will fall
1833 back to using the idmapper.
1834 To turn off this behaviour, set the value to '0'.
1836 [NFS4] Specify an additional fixed unique ident-
1837 ification string that NFSv4 clients can insert into
1838 their nfs_client_id4 string. This is typically a
1839 UUID that is generated at system install time.
1841 nfs.send_implementation_id =
1842 [NFSv4.1] Send client implementation identification
1843 information in exchange_id requests.
1844 If zero, no implementation identification information
1846 The default is to send the implementation identification
1849 nfsd.nfs4_disable_idmapping=
1850 [NFSv4] When set to the default of '1', the NFSv4
1851 server will return only numeric uids and gids to
1852 clients using auth_sys, and will accept numeric uids
1853 and gids from such clients. This is intended to ease
1854 migration from NFSv2/v3.
1856 objlayoutdriver.osd_login_prog=
1857 [NFS] [OBJLAYOUT] sets the pathname to the program which
1858 is used to automatically discover and login into new
1859 osd-targets. Please see:
1860 Documentation/filesystems/pnfs.txt for more explanations
1862 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1863 when a NMI is triggered.
1864 Format: [state][,regs][,debounce][,die]
1866 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1867 Format: [panic,][nopanic,][num]
1869 0 - turn nmi_watchdog off
1870 When panic is specified, panic when an NMI watchdog
1871 timeout occurs (or 'nopanic' to override the opposite
1873 This is useful when you use a panic=... timeout and
1874 need the box quickly up again.
1876 netpoll.carrier_timeout=
1877 [NET] Specifies amount of time (in seconds) that
1878 netpoll should wait for a carrier. By default netpoll
1881 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1882 emulation library even if a 387 maths coprocessor
1886 [HW] Never suspend the console
1887 Disable suspending of consoles during suspend and
1888 hibernate operations. Once disabled, debugging
1889 messages can reach various consoles while the rest
1890 of the system is being put to sleep (ie, while
1891 debugging driver suspend/resume hooks). This may
1892 not work reliably with all consoles, but is known
1893 to work with serial and VGA consoles.
1894 To facilitate more flexible debugging, we also add
1895 console_suspend, a printk module parameter to control
1896 it. Users could use console_suspend (usually
1897 /sys/module/printk/parameters/console_suspend) to
1898 turn on/off it dynamically.
1900 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1901 caches in the slab allocator. Saves per-node memory,
1902 but will impact performance.
1906 noapic [SMP,APIC] Tells the kernel to not make use of any
1907 IOAPICs that may be present in the system.
1909 noautogroup Disable scheduler automatic task group creation.
1911 nobats [PPC] Do not use BATs for mapping kernel lowmem
1912 on "Classic" PPC cores.
1916 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1918 nodelayacct [KNL] Disable per-task delay accounting
1920 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1922 nodsp [SH] Disable hardware DSP at boot time.
1924 noefi [X86] Disable EFI runtime services support.
1929 On X86-32 available only on PAE configured kernels.
1930 noexec=on: enable non-executable mappings (default)
1931 noexec=off: disable non-executable mappings
1934 Disable SMAP (Supervisor Mode Access Prevention)
1935 even if it is supported by processor.
1938 Disable SMEP (Supervisor Mode Execution Prevention)
1939 even if it is supported by processor.
1942 This affects only 32-bit executables.
1943 noexec32=on: enable non-executable mappings (default)
1944 read doesn't imply executable mappings
1945 noexec32=off: disable non-executable mappings
1946 read implies executable mappings
1948 nofpu [SH] Disable hardware FPU at boot time.
1950 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1951 register save and restore. The kernel will only save
1952 legacy floating-point registers on task switch.
1954 noxsave [BUGS=X86] Disables x86 extended register state save
1955 and restore using xsave. The kernel will fallback to
1956 enabling legacy floating-point and sse state.
1959 on enable eager fpu restore
1960 off disable eager fpu restore
1961 auto selects the default scheme, which automatically
1962 enables eagerfpu restore for xsaveopt.
1964 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1965 wfi(ARM) instruction doesn't work correctly and not to
1966 use it. This is also useful when using JTAG debugger.
1968 no_file_caps Tells the kernel not to honor file capabilities. The
1969 only way then for a file to be executed with privilege
1970 is to be setuid root or executed by root.
1972 nohalt [IA-64] Tells the kernel not to use the power saving
1973 function PAL_HALT_LIGHT when idle. This increases
1974 power-consumption. On the positive side, it reduces
1975 interrupt wake-up latency, which may improve performance
1976 in certain environments such as networked servers or
1979 nohz= [KNL] Boottime enable/disable dynamic ticks
1980 Valid arguments: on, off
1983 nohz_full= [KNL,BOOT]
1984 In kernels built with CONFIG_NO_HZ_FULL=y, set
1985 the specified list of CPUs whose tick will be stopped
1986 whenever possible. The boot CPU will be forced outside
1987 the range to maintain the timekeeping.
1988 The CPUs in this range must also be included in the
1991 noiotrap [SH] Disables trapped I/O port accesses.
1993 noirqdebug [X86-32] Disables the code which attempts to detect and
1994 disable unhandled interrupt sources.
1996 no_timer_check [X86,APIC] Disables the code which tests for
1997 broken timer IRQ sources.
1999 noisapnp [ISAPNP] Disables ISA PnP code.
2001 noinitrd [RAM] Tells the kernel not to load any configured
2004 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2006 [Deprecated - use intremap=off]
2010 nojitter [IA-64] Disables jitter checking for ITC timers.
2012 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2014 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2017 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2018 steal time is computed, but won't influence scheduler
2021 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2023 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2025 noltlbs [PPC] Do not use large page/tlb entries for kernel
2026 lowmem mapping on PPC40x.
2028 nomca [IA-64] Disable machine check abort handling
2030 nomce [X86-32] Machine Check Exception
2032 nomfgpt [X86-32] Disable Multi-Function General Purpose
2033 Timer usage (for AMD Geode machines).
2035 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2036 shutdown the other cpus. Instead use the REBOOT_VECTOR
2039 nomodule Disable module load
2041 nopat [X86] Disable PAT (page attribute table extension of
2042 pagetables) support.
2044 norandmaps Don't use address space randomization. Equivalent to
2045 echo 0 > /proc/sys/kernel/randomize_va_space
2047 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2049 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2050 with UP alternatives
2052 nordrand [X86] Disable the direct use of the RDRAND
2053 instruction even if it is supported by the
2054 processor. RDRAND is still available to user
2057 noresume [SWSUSP] Disables resume and restores original swap
2060 no-scroll [VGA] Disables scrollback.
2061 This is required for the Braillex ib80-piezo Braille
2062 reader made by F.H. Papenmeier (Germany).
2066 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2068 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2069 and disable the IO APIC. legacy for "maxcpus=0".
2071 nosoftlockup [KNL] Disable the soft-lockup detector.
2073 nosync [HW,M68K] Disables sync negotiation for all devices.
2075 notsc [BUGS=X86-32] Disable Time Stamp Counter
2077 nousb [USB] Disable the USB subsystem
2079 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2083 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2085 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2086 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2087 Some features depend on CPU0. Known dependencies are:
2088 1. Resume from suspend/hibernate depends on CPU0.
2089 Suspend/hibernate will fail if CPU0 is offline and you
2090 need to online CPU0 before suspend/hibernate.
2091 2. PIC interrupts also depend on CPU0. CPU0 can't be
2092 removed if a PIC interrupt is detected.
2093 It's said poweroff/reboot may depend on CPU0 on some
2094 machines although I haven't seen such issues so far
2095 after CPU0 is offline on a few tested machines.
2096 If the dependencies are under your control, you can
2097 turn on cpu0_hotplug.
2099 nptcg= [IA-64] Override max number of concurrent global TLB
2100 purges which is reported from either PAL_VM_SUMMARY or
2103 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2104 could support. nr_cpus=n : n >= 1 limits the kernel to
2105 supporting 'n' processors. Later in runtime you can not
2106 use hotplug cpu feature to put more cpu back to online.
2107 just like you compile the kernel NR_CPUS=n
2109 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2111 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2112 Allowed values are enable and disable
2114 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2115 one of ['zone', 'node', 'default'] can be specified
2116 This can be set from sysctl after boot.
2117 See Documentation/sysctl/vm.txt for details.
2119 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2120 See Documentation/debugging-via-ohci1394.txt for more
2123 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2124 Rather than timing out after 20 ms if an EC
2125 command is not properly ACKed, override the length
2126 of the timeout. We have interrupts disabled while
2127 waiting for the ACK, so if this is set too high
2128 interrupts *may* be lost!
2130 omap_mux= [OMAP] Override bootloader pin multiplexing.
2131 Format: <mux_mode0.mode_name=value>...
2132 For example, to override I2C bus2:
2133 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2135 oprofile.timer= [HW]
2136 Use timer interrupt instead of performance counters
2138 oprofile.cpu_type= Force an oprofile cpu type
2139 This might be useful if you have an older oprofile
2140 userland or if you want common events.
2141 Format: { arch_perfmon }
2142 arch_perfmon: [X86] Force use of architectural
2143 perfmon on Intel CPUs instead of the
2144 CPU specific event set.
2145 timer: [X86] Force use of architectural NMI
2146 timer mode (see also oprofile.timer
2147 for generic hr timer mode)
2148 [s390] Force legacy basic mode sampling
2149 (report cpu_type "timer")
2151 oops=panic Always panic on oopses. Default is to just kill the
2152 process, but there is a small probability of
2153 deadlocking the machine.
2154 This will also cause panics on machine check exceptions.
2155 Useful together with panic=30 to trigger a reboot.
2158 See Documentation/sound/oss/oss-parameters.txt
2160 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2161 timeout > 0: seconds before rebooting
2162 timeout = 0: wait forever
2163 timeout < 0: reboot immediately
2166 parkbd.port= [HW] Parallel port number the keyboard adapter is
2167 connected to, default is 0.
2169 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2170 0 for XT, 1 for AT (default is AT).
2173 parport= [HW,PPT] Specify parallel ports. 0 disables.
2174 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2175 Use 'auto' to force the driver to use any
2176 IRQ/DMA settings detected (the default is to
2177 ignore detected IRQ/DMA settings because of
2178 possible conflicts). You can specify the base
2179 address, IRQ, and DMA settings; IRQ and DMA
2180 should be numbers, or 'auto' (for using detected
2181 settings on that particular port), or 'nofifo'
2182 (to avoid using a FIFO even if it is detected).
2183 Parallel ports are assigned in the order they
2184 are specified on the command line, starting
2187 parport_init_mode= [HW,PPT]
2188 Configure VIA parallel port to operate in
2189 a specific mode. This is necessary on Pegasos
2190 computer where firmware has no options for setting
2191 up parallel port mode and sets it to spp.
2192 Currently this function knows 686a and 8231 chips.
2193 Format: [spp|ps2|epp|ecp|ecpepp]
2196 Halt all CPUs after the first oops has been printed for
2197 the specified number of seconds. This is to be used if
2198 your oopses keep scrolling off the screen.
2203 See header of drivers/block/paride/pcd.c.
2204 See also Documentation/blockdev/paride.txt.
2206 pci=option[,option...] [PCI] various PCI subsystem options:
2207 earlydump [X86] dump PCI config space before the kernel
2209 off [X86] don't probe for the PCI bus
2210 bios [X86-32] force use of PCI BIOS, don't access
2211 the hardware directly. Use this if your machine
2212 has a non-standard PCI host bridge.
2213 nobios [X86-32] disallow use of PCI BIOS, only direct
2214 hardware access methods are allowed. Use this
2215 if you experience crashes upon bootup and you
2216 suspect they are caused by the BIOS.
2217 conf1 [X86] Force use of PCI Configuration
2219 conf2 [X86] Force use of PCI Configuration
2221 noaer [PCIE] If the PCIEAER kernel config parameter is
2222 enabled, this kernel boot option can be used to
2223 disable the use of PCIE advanced error reporting.
2224 nodomains [PCI] Disable support for multiple PCI
2225 root domains (aka PCI segments, in ACPI-speak).
2226 nommconf [X86] Disable use of MMCONFIG for PCI
2228 check_enable_amd_mmconf [X86] check for and enable
2229 properly configured MMIO access to PCI
2230 config space on AMD family 10h CPU
2231 nomsi [MSI] If the PCI_MSI kernel config parameter is
2232 enabled, this kernel boot option can be used to
2233 disable the use of MSI interrupts system-wide.
2234 noioapicquirk [APIC] Disable all boot interrupt quirks.
2235 Safety option to keep boot IRQs enabled. This
2236 should never be necessary.
2237 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2238 primary IO-APIC for bridges that cannot disable
2239 boot IRQs. This fixes a source of spurious IRQs
2240 when the system masks IRQs.
2241 noioapicreroute [APIC] Disable workaround that uses the
2242 boot IRQ equivalent of an IRQ that connects to
2243 a chipset where boot IRQs cannot be disabled.
2244 The opposite of ioapicreroute.
2245 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2246 routing table. These calls are known to be buggy
2247 on several machines and they hang the machine
2248 when used, but on other computers it's the only
2249 way to get the interrupt routing table. Try
2250 this option if the kernel is unable to allocate
2251 IRQs or discover secondary PCI buses on your
2253 rom [X86] Assign address space to expansion ROMs.
2254 Use with caution as certain devices share
2255 address decoders between ROMs and other
2257 norom [X86] Do not assign address space to
2258 expansion ROMs that do not already have
2259 BIOS assigned address ranges.
2260 nobar [X86] Do not assign address space to the
2261 BARs that weren't assigned by the BIOS.
2262 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2263 assigned automatically to PCI devices. You can
2264 make the kernel exclude IRQs of your ISA cards
2266 pirqaddr=0xAAAAA [X86] Specify the physical address
2267 of the PIRQ table (normally generated
2268 by the BIOS) if it is outside the
2269 F0000h-100000h range.
2270 lastbus=N [X86] Scan all buses thru bus #N. Can be
2271 useful if the kernel is unable to find your
2272 secondary buses and you want to tell it
2273 explicitly which ones they are.
2274 assign-busses [X86] Always assign all PCI bus
2275 numbers ourselves, overriding
2276 whatever the firmware may have done.
2277 usepirqmask [X86] Honor the possible IRQ mask stored
2278 in the BIOS $PIR table. This is needed on
2279 some systems with broken BIOSes, notably
2280 some HP Pavilion N5400 and Omnibook XE3
2281 notebooks. This will have no effect if ACPI
2282 IRQ routing is enabled.
2283 noacpi [X86] Do not use ACPI for IRQ routing
2284 or for PCI scanning.
2285 use_crs [X86] Use PCI host bridge window information
2286 from ACPI. On BIOSes from 2008 or later, this
2287 is enabled by default. If you need to use this,
2288 please report a bug.
2289 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2290 If you need to use this, please report a bug.
2291 routeirq Do IRQ routing for all PCI devices.
2292 This is normally done in pci_enable_device(),
2293 so this option is a temporary workaround
2294 for broken drivers that don't call it.
2295 skip_isa_align [X86] do not align io start addr, so can
2296 handle more pci cards
2297 firmware [ARM] Do not re-enumerate the bus but instead
2298 just use the configuration from the
2299 bootloader. This is currently used on
2300 IXP2000 systems where the bus has to be
2301 configured a certain way for adjunct CPUs.
2302 noearly [X86] Don't do any early type 1 scanning.
2303 This might help on some broken boards which
2304 machine check when some devices' config space
2305 is read. But various workarounds are disabled
2306 and some IOMMU drivers will not work.
2307 bfsort Sort PCI devices into breadth-first order.
2308 This sorting is done to get a device
2309 order compatible with older (<= 2.4) kernels.
2310 nobfsort Don't sort PCI devices into breadth-first order.
2311 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2312 tuning and use the BIOS-configured MPS defaults.
2313 pcie_bus_safe Set every device's MPS to the largest value
2314 supported by all devices below the root complex.
2315 pcie_bus_perf Set device MPS to the largest allowable MPS
2316 based on its parent bus. Also set MRRS (Max
2317 Read Request Size) to the largest supported
2318 value (no larger than the MPS that the device
2319 or bus can support) for best performance.
2320 pcie_bus_peer2peer Set every device's MPS to 128B, which
2321 every device is guaranteed to support. This
2322 configuration allows peer-to-peer DMA between
2323 any pair of devices, possibly at the cost of
2324 reduced performance. This also guarantees
2325 that hot-added devices will work.
2326 cbiosize=nn[KMG] The fixed amount of bus space which is
2327 reserved for the CardBus bridge's IO window.
2328 The default value is 256 bytes.
2329 cbmemsize=nn[KMG] The fixed amount of bus space which is
2330 reserved for the CardBus bridge's memory
2331 window. The default value is 64 megabytes.
2334 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2335 Specifies alignment and device to reassign
2336 aligned memory resources.
2337 If <order of align> is not specified,
2338 PAGE_SIZE is used as alignment.
2339 PCI-PCI bridge can be specified, if resource
2340 windows need to be expanded.
2341 ecrc= Enable/disable PCIe ECRC (transaction layer
2342 end-to-end CRC checking).
2343 bios: Use BIOS/firmware settings. This is the
2347 hpiosize=nn[KMG] The fixed amount of bus space which is
2348 reserved for hotplug bridge's IO window.
2349 Default size is 256 bytes.
2350 hpmemsize=nn[KMG] The fixed amount of bus space which is
2351 reserved for hotplug bridge's memory window.
2352 Default size is 2 megabytes.
2353 realloc= Enable/disable reallocating PCI bridge resources
2354 if allocations done by BIOS are too small to
2355 accommodate resources required by all child
2357 off: Turn realloc off
2359 realloc same as realloc=on
2360 noari do not use PCIe ARI.
2361 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2362 only look for one device below a PCIe downstream
2365 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2368 force Enable ASPM even on devices that claim not to support it.
2369 WARNING: Forcing ASPM on may cause system lockups.
2371 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2372 nomsi Do not use MSI for PCI Express Native Hotplug (this
2373 makes all PCIe ports use INTx for hotplug services).
2375 pcie_ports= [PCIE] PCIe ports handling:
2376 auto Ask the BIOS whether or not to use native PCIe services
2377 associated with PCIe ports (PME, hot-plug, AER). Use
2378 them only if that is allowed by the BIOS.
2379 native Use native PCIe services associated with PCIe ports
2381 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2384 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2385 nomsi Do not use MSI for native PCIe PME signaling (this makes
2386 all PCIe root ports use INTx for all services).
2388 pcmv= [HW,PCMCIA] BadgePAD 4
2391 See Documentation/blockdev/paride.txt.
2393 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2396 See arch/parisc/kernel/pdc_chassis.c
2398 percpu_alloc= Select which percpu first chunk allocator to use.
2399 Currently supported values are "embed" and "page".
2400 Archs may support subset or none of the selections.
2401 See comments in mm/percpu.c for details on each
2402 allocator. This parameter is primarily for debugging
2403 and performance comparison.
2406 See Documentation/blockdev/paride.txt.
2409 See Documentation/blockdev/paride.txt.
2411 pirq= [SMP,APIC] Manual mp-table setup
2412 See Documentation/x86/i386/IO-APIC.txt.
2414 plip= [PPT,NET] Parallel port network link
2415 Format: { parport<nr> | timid | 0 }
2416 See also Documentation/parport.txt.
2418 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2419 Override pmtimer IOPort with a hex value.
2423 Enable PNP debug messages (depends on the
2424 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2425 via /sys/module/pnp/parameters/debug. We always show
2426 current resource usage; turning this on also shows
2427 possible settings and some assignment information.
2433 { on | off | curr | res | no-curr | no-res }
2436 [ISAPNP] Exclude IRQs for the autoconfiguration
2439 [ISAPNP] Exclude DMAs for the autoconfiguration
2441 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2442 Ranges are in pairs (I/O port base and size).
2445 [ISAPNP] Exclude memory regions for the
2447 Ranges are in pairs (memory base and size).
2449 ports= [IP_VS_FTP] IPVS ftp helper module
2451 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2453 Format: <port>,<port>....
2455 print-fatal-signals=
2456 [KNL] debug: print fatal signals
2458 If enabled, warn about various signal handling
2459 related application anomalies: too many signals,
2460 too many POSIX.1 timers, fatal signals causing a
2463 If you hit the warning due to signal overflow,
2464 you might want to try "ulimit -i unlimited".
2468 printk.always_kmsg_dump=
2469 Trigger kmsg_dump for cases other than kernel oops or
2471 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2474 printk.time= Show timing data prefixed to each printk message line
2475 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2477 processor.max_cstate= [HW,ACPI]
2478 Limit processor to maximum C-state
2479 max_cstate=9 overrides any DMI blacklist limit.
2481 processor.nocst [HW,ACPI]
2482 Ignore the _CST method to determine C-states,
2483 instead using the legacy FADT method
2485 profile= [KNL] Enable kernel profiling via /proc/profile
2486 Format: [schedule,]<number>
2487 Param: "schedule" - profile schedule points.
2488 Param: <number> - step/bucket size as a power of 2 for
2489 statistical time based profiling.
2490 Param: "sleep" - profile D-state sleeping (millisecs).
2491 Requires CONFIG_SCHEDSTATS
2492 Param: "kvm" - profile VM exits.
2494 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2496 See Documentation/blockdev/ramdisk.txt.
2498 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2499 probe for; one of (bare|imps|exps|lifebook|any).
2500 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2502 psmouse.resetafter= [HW,MOUSE]
2503 Try to reset the device after so many bad packets
2506 [HW,MOUSE] Set desired mouse resolution, in dpi.
2507 psmouse.smartscroll=
2508 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2509 0 = disabled, 1 = enabled (default).
2511 pstore.backend= Specify the name of the pstore backend to use
2514 See Documentation/blockdev/paride.txt.
2517 [KNL] Number of legacy pty's. Overwrites compiled-in
2520 quiet [KNL] Disable most log messages
2525 See Documentation/md.txt.
2527 ramdisk_blocksize= [RAM]
2528 See Documentation/blockdev/ramdisk.txt.
2530 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2531 See Documentation/blockdev/ramdisk.txt.
2533 rcu_nocbs= [KNL,BOOT]
2534 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2535 the specified list of CPUs to be no-callback CPUs.
2536 Invocation of these CPUs' RCU callbacks will
2537 be offloaded to "rcuox/N" kthreads created for
2538 that purpose, where "x" is "b" for RCU-bh, "p"
2539 for RCU-preempt, and "s" for RCU-sched, and "N"
2540 is the CPU number. This reduces OS jitter on the
2541 offloaded CPUs, which can be useful for HPC and
2543 real-time workloads. It can also improve energy
2544 efficiency for asymmetric multiprocessors.
2546 rcu_nocb_poll [KNL,BOOT]
2547 Rather than requiring that offloaded CPUs
2548 (specified by rcu_nocbs= above) explicitly
2549 awaken the corresponding "rcuoN" kthreads,
2550 make these kthreads poll for callbacks.
2551 This improves the real-time response for the
2552 offloaded CPUs by relieving them of the need to
2553 wake up the corresponding kthread, but degrades
2554 energy efficiency by requiring that the kthreads
2555 periodically wake up to do the polling.
2557 rcutree.blimit= [KNL,BOOT]
2558 Set maximum number of finished RCU callbacks to process
2561 rcutree.fanout_leaf= [KNL,BOOT]
2562 Increase the number of CPUs assigned to each
2563 leaf rcu_node structure. Useful for very large
2566 rcutree.jiffies_till_first_fqs= [KNL,BOOT]
2567 Set delay from grace-period initialization to
2568 first attempt to force quiescent states.
2569 Units are jiffies, minimum value is zero,
2570 and maximum value is HZ.
2572 rcutree.jiffies_till_next_fqs= [KNL,BOOT]
2573 Set delay between subsequent attempts to force
2574 quiescent states. Units are jiffies, minimum
2575 value is one, and maximum value is HZ.
2577 rcutree.qhimark= [KNL,BOOT]
2578 Set threshold of queued
2579 RCU callbacks over which batch limiting is disabled.
2581 rcutree.qlowmark= [KNL,BOOT]
2582 Set threshold of queued RCU callbacks below which
2583 batch limiting is re-enabled.
2585 rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2586 Suppress RCU CPU stall warning messages.
2588 rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2589 Set timeout for RCU CPU stall warning messages.
2591 rcutree.rcu_idle_gp_delay= [KNL,BOOT]
2592 Set wakeup interval for idle CPUs that have
2593 RCU callbacks (RCU_FAST_NO_HZ=y).
2595 rcutree.rcu_idle_lazy_gp_delay= [KNL,BOOT]
2596 Set wakeup interval for idle CPUs that have
2597 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2598 Lazy RCU callbacks are those which RCU can
2599 prove do nothing more than free memory.
2601 rcutorture.fqs_duration= [KNL,BOOT]
2602 Set duration of force_quiescent_state bursts.
2604 rcutorture.fqs_holdoff= [KNL,BOOT]
2605 Set holdoff time within force_quiescent_state bursts.
2607 rcutorture.fqs_stutter= [KNL,BOOT]
2608 Set wait time between force_quiescent_state bursts.
2610 rcutorture.irqreader= [KNL,BOOT]
2611 Test RCU readers from irq handlers.
2613 rcutorture.n_barrier_cbs= [KNL,BOOT]
2614 Set callbacks/threads for rcu_barrier() testing.
2616 rcutorture.nfakewriters= [KNL,BOOT]
2617 Set number of concurrent RCU writers. These just
2618 stress RCU, they don't participate in the actual
2619 test, hence the "fake".
2621 rcutorture.nreaders= [KNL,BOOT]
2622 Set number of RCU readers.
2624 rcutorture.onoff_holdoff= [KNL,BOOT]
2625 Set time (s) after boot for CPU-hotplug testing.
2627 rcutorture.onoff_interval= [KNL,BOOT]
2628 Set time (s) between CPU-hotplug operations, or
2629 zero to disable CPU-hotplug testing.
2631 rcutorture.shuffle_interval= [KNL,BOOT]
2632 Set task-shuffle interval (s). Shuffling tasks
2633 allows some CPUs to go into dyntick-idle mode
2634 during the rcutorture test.
2636 rcutorture.shutdown_secs= [KNL,BOOT]
2637 Set time (s) after boot system shutdown. This
2638 is useful for hands-off automated testing.
2640 rcutorture.stall_cpu= [KNL,BOOT]
2641 Duration of CPU stall (s) to test RCU CPU stall
2642 warnings, zero to disable.
2644 rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2645 Time to wait (s) after boot before inducing stall.
2647 rcutorture.stat_interval= [KNL,BOOT]
2648 Time (s) between statistics printk()s.
2650 rcutorture.stutter= [KNL,BOOT]
2651 Time (s) to stutter testing, for example, specifying
2652 five seconds causes the test to run for five seconds,
2653 wait for five seconds, and so on. This tests RCU's
2654 ability to transition abruptly to and from idle.
2656 rcutorture.test_boost= [KNL,BOOT]
2657 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2658 "Maybe" means test if the RCU implementation
2659 under test support RCU priority boosting.
2661 rcutorture.test_boost_duration= [KNL,BOOT]
2662 Duration (s) of each individual boost test.
2664 rcutorture.test_boost_interval= [KNL,BOOT]
2665 Interval (s) between each boost test.
2667 rcutorture.test_no_idle_hz= [KNL,BOOT]
2668 Test RCU's dyntick-idle handling. See also the
2669 rcutorture.shuffle_interval parameter.
2671 rcutorture.torture_type= [KNL,BOOT]
2672 Specify the RCU implementation to test.
2674 rcutorture.verbose= [KNL,BOOT]
2675 Enable additional printk() statements.
2679 Run specified binary instead of /init from the ramdisk,
2680 used for early userspace startup. See initrd.
2682 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2683 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2684 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2687 [KNL, SMP] Set scheduler's default relax_domain_level.
2688 See Documentation/cgroups/cpusets.txt.
2690 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2692 reservetop= [X86-32]
2694 Reserves a hole at the top of the kernel virtual
2699 Set the amount of memory to reserve for BIOS at
2700 the bottom of the address space.
2702 reset_devices [KNL] Force drivers to reset the underlying device
2703 during initialization.
2706 Specify the partition device for software suspend
2708 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2710 resume_offset= [SWSUSP]
2711 Specify the offset from the beginning of the partition
2712 given by "resume=" at which the swap header is located,
2713 in <PAGE_SIZE> units (needed only for swap files).
2714 See Documentation/power/swsusp-and-swap-files.txt
2716 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2717 read the resume files
2719 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2720 Useful for devices that are detected asynchronously
2721 (e.g. USB and MMC devices).
2723 hibernate= [HIBERNATION]
2724 noresume Don't check if there's a hibernation image
2725 present during boot.
2726 nocompress Don't compress/decompress hibernation images.
2728 retain_initrd [RAM] Keep initrd memory after extraction
2730 rhash_entries= [KNL,NET]
2731 Set number of hash buckets for route cache
2733 riscom8= [HW,SERIAL]
2734 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2736 ro [KNL] Mount root device read-only on boot
2738 root= [KNL] Root filesystem
2739 See name_to_dev_t comment in init/do_mounts.c.
2741 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2742 mount the root filesystem
2744 rootflags= [KNL] Set root filesystem mount option string
2746 rootfstype= [KNL] Set root filesystem type
2748 rootwait [KNL] Wait (indefinitely) for root device to show up.
2749 Useful for devices that are detected asynchronously
2750 (e.g. USB and MMC devices).
2752 rproc_mem=nn[KMG][@address]
2753 [KNL,ARM,CMA] Remoteproc physical memory block.
2754 Memory area to be used by remote processor image,
2757 rw [KNL] Mount root device read-write on boot
2759 S [KNL] Run init in single mode
2762 See drivers/net/irda/sa1100_ir.c.
2764 sbni= [NET] Granch SBNI12 leased line adapter
2766 sched_debug [KNL] Enables verbose scheduler debug messages.
2768 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2769 xtime_lock contention on larger systems, and/or RCU lock
2770 contention on all systems with CONFIG_MAXSMP set.
2771 Format: { "0" | "1" }
2772 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2774 Note: increases power consumption, thus should only be
2775 enabled if running jitter sensitive (HPC/RT) workloads.
2777 security= [SECURITY] Choose a security module to enable at boot.
2778 If this boot parameter is not specified, only the first
2779 security module asking for security registration will be
2780 loaded. An invalid security module name will be treated
2781 as if no module has been chosen.
2783 selinux= [SELINUX] Disable or enable SELinux at boot time.
2784 Format: { "0" | "1" }
2785 See security/selinux/Kconfig help text.
2788 Default value is set via kernel config option.
2789 If enabled at boot time, /selinux/disable can be used
2790 later to disable prior to initial policy load.
2792 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2793 Format: { "0" | "1" }
2794 See security/apparmor/Kconfig help text
2797 Default value is set via kernel config option.
2799 serialnumber [BUGS=X86-32]
2802 Maximal number of shapers.
2804 show_msr= [x86] show boot-time MSR settings
2805 Format: { <integer> }
2806 Show boot-time (BIOS-initialized) MSR settings.
2807 The parameter means the number of CPUs to show,
2808 for example 1 means boot CPU only.
2815 slab_max_order= [MM, SLAB]
2816 Determines the maximum allowed order for slabs.
2817 A high setting may cause OOMs due to memory
2818 fragmentation. Defaults to 1 for systems with
2819 more than 32MB of RAM, 0 otherwise.
2821 slub_debug[=options[,slabs]] [MM, SLUB]
2822 Enabling slub_debug allows one to determine the
2823 culprit if slab objects become corrupted. Enabling
2824 slub_debug can create guard zones around objects and
2825 may poison objects when not in use. Also tracks the
2826 last alloc / free. For more information see
2827 Documentation/vm/slub.txt.
2829 slub_max_order= [MM, SLUB]
2830 Determines the maximum allowed order for slabs.
2831 A high setting may cause OOMs due to memory
2832 fragmentation. For more information see
2833 Documentation/vm/slub.txt.
2835 slub_min_objects= [MM, SLUB]
2836 The minimum number of objects per slab. SLUB will
2837 increase the slab order up to slub_max_order to
2838 generate a sufficiently large slab able to contain
2839 the number of objects indicated. The higher the number
2840 of objects the smaller the overhead of tracking slabs
2841 and the less frequently locks need to be acquired.
2842 For more information see Documentation/vm/slub.txt.
2844 slub_min_order= [MM, SLUB]
2845 Determines the minimum page order for slabs. Must be
2846 lower than slub_max_order.
2847 For more information see Documentation/vm/slub.txt.
2849 slub_nomerge [MM, SLUB]
2850 Disable merging of slabs with similar size. May be
2851 necessary if there is some reason to distinguish
2852 allocs to different slabs. Debug options disable
2853 merging on their own.
2854 For more information see Documentation/vm/slub.txt.
2857 Format: <io1>[,<io2>[,...,<io8>]]
2859 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2860 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2861 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2862 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2863 smsc-ircc2.ircc_irq= [HW] IRQ line
2864 smsc-ircc2.ircc_dma= [HW] DMA channel
2865 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2866 0: Toshiba Satellite 1800 (GP data pin select)
2867 1: Fast pin select (default)
2871 [KNL] Should the soft-lockup detector generate panics.
2874 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2875 See Documentation/laptops/sonypi.txt
2877 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2878 See Documentation/serial/specialix.txt.
2880 spia_io_base= [HW,MTD]
2886 Enabled the stack tracer on boot up.
2888 stacktrace_filter=[function-list]
2889 [FTRACE] Limit the functions that the stack tracer
2890 will trace at boot up. function-list is a comma separated
2891 list of functions. This list can be changed at run
2892 time by the stack_trace_filter file in the debugfs
2893 tracing directory. Note, this enables stack tracing
2894 and the stacktrace above is not needed.
2898 Set the STI (builtin display/keyboard on the HP-PARISC
2899 machines) console (graphic card) which should be used
2900 as the initial boot-console.
2901 See also comment in drivers/video/console/sticore.c.
2904 See comment in drivers/video/console/sticore.c.
2907 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2909 sunrpc.min_resvport=
2910 sunrpc.max_resvport=
2912 SunRPC servers often require that client requests
2913 originate from a privileged port (i.e. a port in the
2914 range 0 < portnr < 1024).
2915 An administrator who wishes to reserve some of these
2916 ports for other uses may adjust the range that the
2917 kernel's sunrpc client considers to be privileged
2918 using these two parameters to set the minimum and
2919 maximum port values.
2923 Control how the NFS server code allocates CPUs to
2924 service thread pools. Depending on how many NICs
2925 you have and where their interrupts are bound, this
2926 option will affect which CPUs will do NFS serving.
2927 Note: this parameter cannot be changed while the
2928 NFS server is running.
2930 auto the server chooses an appropriate mode
2931 automatically using heuristics
2932 global a single global pool contains all CPUs
2933 percpu one pool for each CPU
2934 pernode one pool for each NUMA node (equivalent
2935 to global on non-NUMA machines)
2937 sunrpc.tcp_slot_table_entries=
2938 sunrpc.udp_slot_table_entries=
2940 Sets the upper limit on the number of simultaneous
2941 RPC calls that can be sent from the client to a
2942 server. Increasing these values may allow you to
2943 improve throughput, but will also increase the
2944 amount of memory reserved for use by the client.
2947 [KNL] Enable accounting of swap in memory resource
2948 controller if no parameter or 1 is given or disable
2949 it if 0 is given (See Documentation/cgroups/memory.txt)
2951 swiotlb= [IA-64] Number of I/O TLB slabs
2955 sysfs.deprecated=0|1 [KNL]
2956 Enable/disable old style sysfs layout for old udev
2957 on older distributions. When this option is enabled
2958 very new udev will not work anymore. When this option
2959 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2960 in older udev will not work anymore.
2961 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2962 the kernel configuration.
2964 sysrq_always_enabled
2966 Ignore sysrq setting - this boot parameter will
2967 neutralize any effect of /proc/sys/kernel/sysrq.
2968 Useful for debugging.
2972 test_suspend= [SUSPEND]
2973 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2974 standby suspend) as the system sleep state to briefly
2975 enter during system startup. The system is woken from
2976 this state using a wakeup-capable RTC alarm.
2978 thash_entries= [KNL,NET]
2979 Set number of hash buckets for TCP connection
2981 thermal.act= [HW,ACPI]
2982 -1: disable all active trip points in all thermal zones
2983 <degrees C>: override all lowest active trip points
2985 thermal.crt= [HW,ACPI]
2986 -1: disable all critical trip points in all thermal zones
2987 <degrees C>: override all critical trip points
2989 thermal.nocrt= [HW,ACPI]
2990 Set to disable actions on ACPI thermal zone
2991 critical and hot trip points.
2993 thermal.off= [HW,ACPI]
2994 1: disable ACPI thermal control
2996 thermal.psv= [HW,ACPI]
2997 -1: disable all passive trip points
2998 <degrees C>: override all passive trip points to this
3001 thermal.tzp= [HW,ACPI]
3002 Specify global default ACPI thermal zone polling rate
3003 <deci-seconds>: poll all this frequency
3004 0: no polling (default)
3007 Force threading of all interrupt handlers except those
3008 marked explicitly IRQF_NO_THREAD.
3011 Enable the Transcendent memory driver if built-in.
3013 tmem.cleancache=0|1 [KNL, XEN]
3014 Default is on (1). Disable the usage of the cleancache
3015 API to send anonymous pages to the hypervisor.
3017 tmem.frontswap=0|1 [KNL, XEN]
3018 Default is on (1). Disable the usage of the frontswap
3019 API to send swap pages to the hypervisor. If disabled
3020 the selfballooning and selfshrinking are force disabled.
3022 tmem.selfballooning=0|1 [KNL, XEN]
3023 Default is on (1). Disable the driving of swap pages
3026 tmem.selfshrinking=0|1 [KNL, XEN]
3027 Default is on (1). Partial swapoff that immediately
3028 transfers pages from Xen hypervisor back to the
3029 kernel based on different criteria.
3033 Specify if the kernel should make use of the cpu
3034 topology information if the hardware supports this.
3035 The scheduler will make use of this information and
3036 e.g. base its process migration decisions on it.
3041 tpm_suspend_pcr=[HW,TPM]
3042 Format: integer pcr id
3043 Specify that at suspend time, the tpm driver
3044 should extend the specified pcr with zeros,
3045 as a workaround for some chips which fail to
3046 flush the last written pcr on TPM_SaveState.
3047 This will guarantee that all the other pcrs
3050 trace_buf_size=nn[KMG]
3051 [FTRACE] will set tracing buffer size.
3053 trace_event=[event-list]
3054 [FTRACE] Set and start specified trace events in order
3055 to facilitate early boot debugging.
3056 See also Documentation/trace/events.txt
3058 trace_options=[option-list]
3059 [FTRACE] Enable or disable tracer options at boot.
3060 The option-list is a comma delimited list of options
3061 that can be enabled or disabled just as if you were
3062 to echo the option name into
3064 /sys/kernel/debug/tracing/trace_options
3066 For example, to enable stacktrace option (to dump the
3067 stack trace of each event), add to the command line:
3069 trace_options=stacktrace
3071 See also Documentation/trace/ftrace.txt "trace options"
3074 transparent_hugepage=
3076 Format: [always|madvise|never]
3077 Can be used to control the default behavior of the system
3078 with respect to transparent hugepages.
3079 See Documentation/vm/transhuge.txt for more details.
3081 tsc= Disable clocksource stability checks for TSC.
3083 [x86] reliable: mark tsc clocksource as reliable, this
3084 disables clocksource verification at runtime, as well
3085 as the stability checks done at bootup. Used to enable
3086 high-resolution timer mode on older hardware, and in
3087 virtualized environment.
3088 [x86] noirqtime: Do not use TSC to do irq accounting.
3089 Used to run time disable IRQ_TIME_ACCOUNTING on any
3090 platforms where RDTSC is slow and this accounting
3093 turbografx.map[2|3]= [HW,JOY]
3094 TurboGraFX parallel port interface
3096 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3097 See also Documentation/input/joystick-parport.txt
3099 udbg-immortal [PPC] When debugging early kernel crashes that
3100 happen after console_init() and before a proper
3101 console driver takes over, this boot options might
3102 help "seeing" what's going on.
3104 uhash_entries= [KNL,NET]
3105 Set number of hash buckets for UDP/UDP-Lite connections
3108 [USB] Ignore overcurrent events (default N).
3109 Some badly-designed motherboards generate lots of
3110 bogus events, for ports that aren't wired to
3111 anything. Set this parameter to avoid log spamming.
3112 Note that genuine overcurrent events won't be
3116 [X86] Cause panic on unknown NMI.
3118 usbcore.authorized_default=
3119 [USB] Default USB device authorization:
3120 (default -1 = authorized except for wireless USB,
3121 0 = not authorized, 1 = authorized)
3123 usbcore.autosuspend=
3124 [USB] The autosuspend time delay (in seconds) used
3125 for newly-detected USB devices (default 2). This
3126 is the time required before an idle device will be
3127 autosuspended. Devices for which the delay is set
3128 to a negative value won't be autosuspended at all.
3130 usbcore.usbfs_snoop=
3131 [USB] Set to log all usbfs traffic (default 0 = off).
3133 usbcore.blinkenlights=
3134 [USB] Set to cycle leds on hubs (default 0 = off).
3136 usbcore.old_scheme_first=
3137 [USB] Start with the old device initialization
3138 scheme (default 0 = off).
3140 usbcore.usbfs_memory_mb=
3141 [USB] Memory limit (in MB) for buffers allocated by
3142 usbfs (default = 16, 0 = max = 2047).
3144 usbcore.use_both_schemes=
3145 [USB] Try the other device initialization scheme
3146 if the first one fails (default 1 = enabled).
3148 usbcore.initial_descriptor_timeout=
3149 [USB] Specifies timeout for the initial 64-byte
3150 USB_REQ_GET_DESCRIPTOR request in milliseconds
3151 (default 5000 = 5.0 seconds).
3154 [USBHID] The interval which mice are to be polled at.
3156 usb-storage.delay_use=
3157 [UMS] The delay in seconds before a new device is
3158 scanned for Logical Units (default 5).
3161 [UMS] A list of quirks entries to supplement or
3162 override the built-in unusual_devs list. List
3163 entries are separated by commas. Each entry has
3164 the form VID:PID:Flags where VID and PID are Vendor
3165 and Product ID values (4-digit hex numbers) and
3166 Flags is a set of characters, each corresponding
3167 to a common usb-storage quirk flag as follows:
3168 a = SANE_SENSE (collect more than 18 bytes
3170 b = BAD_SENSE (don't collect more than 18
3171 bytes of sense data);
3172 c = FIX_CAPACITY (decrease the reported
3173 device capacity by one sector);
3174 d = NO_READ_DISC_INFO (don't use
3175 READ_DISC_INFO command);
3176 e = NO_READ_CAPACITY_16 (don't use
3177 READ_CAPACITY_16 command);
3178 h = CAPACITY_HEURISTICS (decrease the
3179 reported device capacity by one
3180 sector if the number is odd);
3181 i = IGNORE_DEVICE (don't bind to this
3183 l = NOT_LOCKABLE (don't try to lock and
3184 unlock ejectable media);
3185 m = MAX_SECTORS_64 (don't transfer more
3186 than 64 sectors = 32 KB at a time);
3187 n = INITIAL_READ10 (force a retry of the
3188 initial READ(10) command);
3189 o = CAPACITY_OK (accept the capacity
3190 reported by the device);
3191 p = WRITE_CACHE (the device cache is ON
3193 r = IGNORE_RESIDUE (the device reports
3194 bogus residue values);
3195 s = SINGLE_LUN (the device has only one
3197 w = NO_WP_DETECT (don't test whether the
3198 medium is write-protected).
3199 Example: quirks=0419:aaf5:rl,0421:0433:rc
3201 user_debug= [KNL,ARM]
3203 See arch/arm/Kconfig.debug help text.
3204 1 - undefined instruction events
3206 4 - invalid data aborts
3209 Example: user_debug=31
3212 [X86] Flags controlling user PTE allocations.
3214 nohigh = do not allocate PTE pages in
3215 HIGHMEM regardless of setting
3219 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3220 vdso=1: enable VDSO (default)
3221 vdso=0: disable VDSO mapping
3224 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3225 vdso32=1: enable 32-bit VDSO (default)
3226 vdso32=0: disable 32-bit VDSO mapping
3229 vector=percpu: enable percpu vector domain
3231 video= [FB] Frame buffer configuration
3232 See Documentation/fb/modedb.txt.
3235 [VMMIO] Memory mapped virtio (platform) device.
3237 <size>@<baseaddr>:<irq>[:<id>]
3239 <size> := size (can use standard suffixes
3241 <baseaddr> := physical base address
3242 <irq> := interrupt number (as passed to
3244 <id> := (optional) platform device id
3246 virtio_mmio.device=1K@0x100b0000:48:7
3248 Can be used multiple times for multiple devices.
3250 vga= [BOOT,X86-32] Select a particular video mode
3251 See Documentation/x86/boot.txt and
3252 Documentation/svga.txt.
3253 Use vga=ask for menu.
3254 This is actually a boot loader parameter; the value is
3255 passed to the kernel using a special protocol.
3257 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3258 size of <nn>. This can be used to increase the
3259 minimum size (128MB on x86). It can also be used to
3260 decrease the size and leave more room for directly
3263 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3266 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3269 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3273 Controls the behavior of vsyscalls (i.e. calls to
3274 fixed addresses of 0xffffffffff600x00 from legacy
3275 code). Most statically-linked binaries and older
3276 versions of glibc use these calls. Because these
3277 functions are at fixed addresses, they make nice
3278 targets for exploits that can control RIP.
3280 emulate [default] Vsyscalls turn into traps and are
3281 emulated reasonably safely.
3283 native Vsyscalls are native syscall instructions.
3284 This is a little bit faster than trapping
3285 and makes a few dynamic recompilers work
3286 better than they would in emulation mode.
3287 It also makes exploits much easier to write.
3289 none Vsyscalls don't work at all. This makes
3290 them quite hard to use for exploits but
3291 might break your system.
3293 vt.cur_default= [VT] Default cursor shape.
3294 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3295 the parameters of the <Esc>[?A;B;Cc escape sequence;
3296 see VGA-softcursor.txt. Default: 2 = underline.
3298 vt.default_blu= [VT]
3299 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3300 Change the default blue palette of the console.
3301 This is a 16-member array composed of values
3304 vt.default_grn= [VT]
3305 Format: <green0>,<green1>,<green2>,...,<green15>
3306 Change the default green palette of the console.
3307 This is a 16-member array composed of values
3310 vt.default_red= [VT]
3311 Format: <red0>,<red1>,<red2>,...,<red15>
3312 Change the default red palette of the console.
3313 This is a 16-member array composed of values
3319 Set system-wide default UTF-8 mode for all tty's.
3320 Default is 1, i.e. UTF-8 mode is enabled for all
3321 newly opened terminals.
3323 vt.global_cursor_default=
3326 Set system-wide default for whether a cursor
3327 is shown on new VTs. Default is -1,
3328 i.e. cursors will be created by default unless
3329 overridden by individual drivers. 0 will hide
3330 cursors, 1 will display them.
3332 watchdog timers [HW,WDT] For information on watchdog timers,
3333 see Documentation/watchdog/watchdog-parameters.txt
3334 or other driver-specific files in the
3335 Documentation/watchdog/ directory.
3337 workqueue.disable_numa
3338 By default, all work items queued to unbound
3339 workqueues are affine to the NUMA nodes they're
3340 issued on, which results in better behavior in
3341 general. If NUMA affinity needs to be disabled for
3342 whatever reason, this option can be used. Note
3343 that this also can be controlled per-workqueue for
3344 workqueues visible under /sys/bus/workqueue/.
3346 workqueue.power_efficient
3347 Per-cpu workqueues are generally preferred because
3348 they show better performance thanks to cache
3349 locality; unfortunately, per-cpu workqueues tend to
3350 be more power hungry than unbound workqueues.
3352 Enabling this makes the per-cpu workqueues which
3353 were observed to contribute significantly to power
3354 consumption unbound, leading to measurably lower
3355 power usage at the cost of small performance
3358 The default value of this parameter is determined by
3359 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3361 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3362 default x2apic cluster mode on platforms
3365 x86_mrst_timer= [X86-32,APBT]
3366 Choose timer option for x86 Moorestown MID platform.
3367 Two valid options are apbt timer only and lapic timer
3368 plus one apbt timer for broadcast timer.
3369 x86_mrst_timer=apbt_only | lapic_and_apbt
3371 xen_emul_unplug= [HW,X86,XEN]
3372 Unplug Xen emulated devices
3373 Format: [unplug0,][unplug1]
3374 ide-disks -- unplug primary master IDE devices
3375 aux-ide-disks -- unplug non-primary-master IDE devices
3376 nics -- unplug network devices
3377 all -- unplug all emulated devices (NICs and IDE disks)
3378 unnecessary -- unplugging emulated devices is
3379 unnecessary even if the host did not respond to
3381 never -- do not unplug even if version check succeeds
3383 xirc2ps_cs= [NET,PCMCIA]
3385 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3387 ______________________________________________________________________
3391 Add more DRM drivers.
projects / cascardo / linux.git / blob