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
1064 i8042.kbdreset [HW] Reset device connected to KBD port
1068 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1069 indicates that the driver is running on unsupported
1071 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1072 does not match list of supported models.
1074 [HW] Report power status in /proc/i8k
1075 (disabled by default)
1076 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1079 i915.invert_brightness=
1080 [DRM] Invert the sense of the variable that is used to
1081 set the brightness of the panel backlight. Normally a
1082 brightness value of 0 indicates backlight switched off,
1083 and the maximum of the brightness value sets the backlight
1084 to maximum brightness. If this parameter is set to 0
1085 (default) and the machine requires it, or this parameter
1086 is set to 1, a brightness value of 0 sets the backlight
1087 to maximum brightness, and the maximum of the brightness
1088 value switches the backlight off.
1089 -1 -- never invert brightness
1090 0 -- machine default
1091 1 -- force brightness inversion
1094 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1096 ide-core.nodma= [HW] (E)IDE subsystem
1097 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1098 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1099 .cdrom .chs .ignore_cable are additional options
1100 See Documentation/ide/ide.txt.
1102 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1103 Claim all unknown PCI IDE storage controllers.
1106 Format: idle=poll, idle=halt, idle=nomwait
1107 Poll forces a polling idle loop that can slightly
1108 improve the performance of waking up a idle CPU, but
1109 will use a lot of power and make the system run hot.
1111 idle=halt: Halt is forced to be used for CPU idle.
1112 In such case C2/C3 won't be used again.
1113 idle=nomwait: Disable mwait for CPU C-states
1115 ignore_loglevel [KNL]
1116 Ignore loglevel setting - this will print /all/
1117 kernel messages to the console. Useful for debugging.
1118 We also add it as printk module parameter, so users
1119 could change it dynamically, usually by
1120 /sys/module/printk/parameters/ignore_loglevel.
1122 ihash_entries= [KNL]
1123 Set number of hash buckets for inode cache.
1125 ima_appraise= [IMA] appraise integrity measurements
1126 Format: { "off" | "enforce" | "fix" }
1129 ima_appraise_tcb [IMA]
1130 The builtin appraise policy appraises all files
1134 Format: { "0" | "1" }
1135 0 -- integrity auditing messages. (Default)
1136 1 -- enable informational integrity auditing messages.
1139 Format: { "sha1" | "md5" }
1143 Load a policy which meets the needs of the Trusted
1144 Computing Base. This means IMA will measure all
1145 programs exec'd, files mmap'd for exec, and all files
1146 opened for read by uid=0.
1150 Run specified binary instead of /sbin/init as init
1153 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1154 for working out where the kernel is dying during
1157 initrd= [BOOT] Specify the location of the initial ramdisk
1159 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1162 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1164 Enable intel iommu driver.
1166 Disable intel iommu driver.
1167 igfx_off [Default Off]
1168 By default, gfx is mapped as normal device. If a gfx
1169 device has a dedicated DMAR unit, the DMAR unit is
1170 bypassed by not enabling DMAR with this option. In
1171 this case, gfx device will use physical address for
1174 With this option iommu will not optimize to look
1175 for io virtual address below 32-bit forcing dual
1176 address cycle on pci bus for cards supporting greater
1177 than 32-bit addressing. The default is to look
1178 for translation below 32-bit and if not available
1179 then look in the higher range.
1180 strict [Default Off]
1181 With this option on every unmap_single operation will
1182 result in a hardware IOTLB flush operation as opposed
1183 to batching them for performance.
1184 sp_off [Default Off]
1185 By default, super page will be supported if Intel IOMMU
1186 has the capability. With this option, super page will
1189 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1190 0 disables intel_idle and fall back on acpi_idle.
1191 1 to 6 specify maximum depth of C-state.
1195 Do not enable intel_pstate as the default
1196 scaling driver for the supported processors
1198 intremap= [X86-64, Intel-IOMMU]
1199 on enable Interrupt Remapping (default)
1200 off disable Interrupt Remapping
1201 nosid disable Source ID checking
1203 BIOS x2APIC opt-out request will be ignored
1205 iomem= Disable strict checking of access to MMIO memory
1206 strict regions from userspace.
1223 io7= [HW] IO7 for Marvel based alpha systems
1224 See comment before marvel_specify_io7 in
1225 arch/alpha/kernel/core_marvel.c.
1227 io_delay= [X86] I/O delay method
1229 Standard port 0x80 based delay
1231 Alternate port 0xed based delay (needed on some systems)
1233 Simple two microseconds delay
1238 See Documentation/filesystems/nfs/nfsroot.txt.
1240 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1241 See comment before ip2_setup() in
1242 drivers/char/ip2/ip2base.c.
1245 When an interrupt is not handled search all handlers
1246 for it. Intended to get systems with badly broken
1250 When an interrupt is not handled search all handlers
1251 for it. Also check all handlers each timer
1252 interrupt. Intended to get systems with badly broken
1256 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1258 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1260 <cpu number>,...,<cpu number>
1262 <cpu number>-<cpu number>
1263 (must be a positive range in ascending order)
1265 <cpu number>,...,<cpu number>-<cpu number>
1267 This option can be used to specify one or more CPUs
1268 to isolate from the general SMP balancing and scheduling
1269 algorithms. You can move a process onto or off an
1270 "isolated" CPU via the CPU affinity syscalls or cpuset.
1271 <cpu number> begins at 0 and the maximum value is
1272 "number of CPUs in system - 1".
1274 This option is the preferred way to isolate CPUs. The
1275 alternative -- manually setting the CPU mask of all
1276 tasks in the system -- can cause problems and
1277 suboptimal load balancer performance.
1281 ivrs_ioapic [HW,X86_64]
1282 Provide an override to the IOAPIC-ID<->DEVICE-ID
1283 mapping provided in the IVRS ACPI table. For
1284 example, to map IOAPIC-ID decimal 10 to
1285 PCI device 00:14.0 write the parameter as:
1286 ivrs_ioapic[10]=00:14.0
1288 ivrs_hpet [HW,X86_64]
1289 Provide an override to the HPET-ID<->DEVICE-ID
1290 mapping provided in the IVRS ACPI table. For
1291 example, to map HPET-ID decimal 0 to
1292 PCI device 00:14.0 write the parameter as:
1293 ivrs_hpet[0]=00:14.0
1295 js= [HW,JOY] Analog joystick
1296 See Documentation/input/joystick.txt.
1300 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1301 specifies the amount of memory usable by the kernel
1302 for non-movable allocations. The requested amount is
1303 spread evenly throughout all nodes in the system. The
1304 remaining memory in each node is used for Movable
1305 pages. In the event, a node is too small to have both
1306 kernelcore and Movable pages, kernelcore pages will
1307 take priority and other nodes will have a larger number
1308 of kernelcore pages. The Movable zone is used for the
1309 allocation of pages that may be reclaimed or moved
1310 by the page migration subsystem. This means that
1311 HugeTLB pages may not be allocated from this zone.
1312 Note that allocations like PTEs-from-HighMem still
1313 use the HighMem zone if it exists, and the Normal
1314 zone if it does not.
1316 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1317 Format: <Controller#>[,poll interval]
1318 The controller # is the number of the ehci usb debug
1319 port as it is probed via PCI. The poll interval is
1320 optional and is the number seconds in between
1321 each poll cycle to the debug port in case you need
1322 the functionality for interrupting the kernel with
1323 gdb or control-c on the dbgp connection. When
1324 not using this parameter you use sysrq-g to break into
1325 the kernel debugger.
1327 kgdboc= [KGDB,HW] kgdb over consoles.
1328 Requires a tty driver that supports console polling,
1329 or a supported polling keyboard driver (non-usb).
1330 Serial only format: <serial_device>[,baud]
1331 keyboard only format: kbd
1332 keyboard and serial format: kbd,<serial_device>[,baud]
1333 Optional Kernel mode setting:
1334 kms, kbd format: kms,kbd
1335 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1337 kgdbwait [KGDB] Stop kernel execution and enter the
1338 kernel debugger at the earliest opportunity.
1340 kmac= [MIPS] korina ethernet MAC address.
1341 Configure the RouterBoard 532 series on-chip
1342 Ethernet adapter MAC address.
1344 kmemleak= [KNL] Boot-time kmemleak enable/disable
1345 Valid arguments: on, off
1348 kstack=N [X86] Print N words from the kernel stack
1351 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1352 Default is 0 (don't ignore, but inject #GP)
1354 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1358 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1359 Default is 1 (enabled)
1361 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1363 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1365 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1366 (virtualized MMU) support on capable Intel chips.
1367 Default is 1 (enabled)
1369 kvm-intel.emulate_invalid_guest_state=
1370 [KVM,Intel] Enable emulation of invalid guest states
1371 Default is 0 (disabled)
1373 kvm-intel.flexpriority=
1374 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1375 Default is 1 (enabled)
1378 [KVM,Intel] Enable VMX nesting (nVMX).
1379 Default is 0 (disabled)
1381 kvm-intel.unrestricted_guest=
1382 [KVM,Intel] Disable unrestricted guest feature
1383 (virtualized real and unpaged mode) on capable
1384 Intel chips. Default is 1 (enabled)
1386 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1387 feature (tagged TLBs) on capable Intel chips.
1388 Default is 1 (enabled)
1394 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1397 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1398 value for LAPIC timer one-shot implementation. Default
1399 back to the programmable timer unit in the LAPIC.
1401 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1404 libata.dma= [LIBATA] DMA control
1405 libata.dma=0 Disable all PATA and SATA DMA
1406 libata.dma=1 PATA and SATA Disk DMA only
1407 libata.dma=2 ATAPI (CDROM) DMA only
1408 libata.dma=4 Compact Flash DMA only
1409 Combinations also work, so libata.dma=3 enables DMA
1410 for disks and CDROMs, but not CFs.
1412 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1413 libata.ignore_hpa=0 keep BIOS limits (default)
1414 libata.ignore_hpa=1 ignore limits, using full disk
1416 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1420 libata.force= [LIBATA] Force configurations. The format is comma
1421 separated list of "[ID:]VAL" where ID is
1422 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1423 matching port, link or device. Basically, it matches
1424 the ATA ID string printed on console by libata. If
1425 the whole ID part is omitted, the last PORT and DEVICE
1426 values are used. If ID hasn't been specified yet, the
1427 configuration applies to all ports, links and devices.
1429 If only DEVICE is omitted, the parameter applies to
1430 the port and all links and devices behind it. DEVICE
1431 number of 0 either selects the first device or the
1432 first fan-out link behind PMP device. It does not
1433 select the host link. DEVICE number of 15 selects the
1434 host link and device attached to it.
1436 The VAL specifies the configuration to force. As long
1437 as there's no ambiguity shortcut notation is allowed.
1438 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1439 The following configurations can be forced.
1441 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1442 Any ID with matching PORT is used.
1444 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1446 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1447 udma[/][16,25,33,44,66,100,133] notation is also
1450 * [no]ncq: Turn on or off NCQ.
1452 * nohrst, nosrst, norst: suppress hard, soft
1455 * rstonce: only attempt one reset during
1456 hot-unplug link recovery
1458 * dump_id: dump IDENTIFY data.
1460 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1462 * disable: Disable this device.
1464 If there are multiple matching configurations changing
1465 the same attribute, the last one is used.
1467 memblock=debug [KNL] Enable memblock debug messages.
1469 load_ramdisk= [RAM] List of ramdisks to load from floppy
1470 See Documentation/blockdev/ramdisk.txt.
1472 lockd.nlm_grace_period=P [NFS] Assign grace period.
1475 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1478 lockd.nlm_timeout=T [NFS] Assign timeout value.
1481 lockd.nlm_udpport=M [NFS] Assign UDP port.
1484 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1487 loglevel= All Kernel Messages with a loglevel smaller than the
1488 console loglevel will be printed to the console. It can
1489 also be changed with klogd or other programs. The
1490 loglevels are defined as follows:
1492 0 (KERN_EMERG) system is unusable
1493 1 (KERN_ALERT) action must be taken immediately
1494 2 (KERN_CRIT) critical conditions
1495 3 (KERN_ERR) error conditions
1496 4 (KERN_WARNING) warning conditions
1497 5 (KERN_NOTICE) normal but significant condition
1498 6 (KERN_INFO) informational
1499 7 (KERN_DEBUG) debug-level messages
1501 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1502 in bytes. n must be a power of two. The default
1503 size is set in the kernel config file.
1505 logo.nologo [FB] Disables display of the built-in Linux logo.
1506 This may be used to provide more screen space for
1507 kernel log messages and is useful when debugging
1508 kernel boot problems.
1510 lp=0 [LP] Specify parallel ports to use, e.g,
1511 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1512 lp=reset first parallel port). 'lp=0' disables the
1513 lp=auto printer driver. 'lp=reset' (which can be
1514 specified in addition to the ports) causes
1515 attached printers to be reset. Using
1516 lp=port1,port2,... specifies the parallel ports
1517 to associate lp devices with, starting with
1518 lp0. A port specification may be 'none' to skip
1519 that lp device, or a parport name such as
1520 'parport0'. Specifying 'lp=auto' instead of a
1521 port specification list means that device IDs
1522 from each port should be examined, to see if
1523 an IEEE 1284-compliant printer is attached; if
1524 so, the driver will manage that printer.
1525 See also header of drivers/char/lp.c.
1528 Sets loops_per_jiffy to given constant, thus avoiding
1529 time-consuming boot-time autodetection (up to 250 ms per
1530 CPU). 0 enables autodetection (default). To determine
1531 the correct value for your kernel, boot with normal
1532 autodetection and see what value is printed. Note that
1533 on SMP systems the preset will be applied to all CPUs,
1534 which is likely to cause problems if your CPUs need
1535 significantly divergent settings. An incorrect value
1536 will cause delays in the kernel to be wrong, leading to
1537 unpredictable I/O errors and other breakage. Although
1538 unlikely, in the extreme case this might damage your
1542 Format: <io>,<irq>,<dma>
1544 machvec= [IA-64] Force the use of a particular machine-vector
1545 (machvec) in a generic kernel.
1546 Example: machvec=hpzx1_swiotlb
1548 machtype= [Loongson] Share the same kernel image file between different
1550 Example: machtype=lemote-yeeloong-2f-7inch
1552 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1553 than or equal to this physical address is ignored.
1555 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1556 should make use of. maxcpus=n : n >= 0 limits the
1557 kernel to using 'n' processors. n=0 is a special case,
1558 it is equivalent to "nosmp", which also disables
1561 max_loop= [LOOP] The number of loop block devices that get
1562 (loop.max_loop) unconditionally pre-created at init time. The default
1563 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1564 of statically allocating a predefined number, loop
1565 devices can be requested on-demand with the
1566 /dev/loop-control interface.
1568 mce [X86-32] Machine Check Exception
1570 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1572 md= [HW] RAID subsystems devices and level
1573 See Documentation/md.txt.
1576 Format: <first>,<last>
1577 Specifies range of consoles to be captured by the MDA.
1579 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1580 Amount of memory to be used when the kernel is not able
1581 to see the whole system memory or for test.
1582 [X86] Work as limiting max address. Use together
1583 with memmap= to avoid physical address space collisions.
1584 Without memmap= PCI devices could be placed at addresses
1585 belonging to unused RAM.
1587 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1591 [KNL,SH] Allow user to override the default size for
1592 per-device physically contiguous DMA buffers.
1594 memmap=exactmap [KNL,X86] Enable setting of an exact
1595 E820 memory map, as specified by the user.
1596 Such memmap=exactmap lines can be constructed based on
1597 BIOS output or other requirements. See the memmap=nn@ss
1600 memmap=nn[KMG]@ss[KMG]
1601 [KNL] Force usage of a specific region of memory
1602 Region of memory to be used, from ss to ss+nn.
1604 memmap=nn[KMG]#ss[KMG]
1605 [KNL,ACPI] Mark specific memory as ACPI data.
1606 Region of memory to be used, from ss to ss+nn.
1608 memmap=nn[KMG]$ss[KMG]
1609 [KNL,ACPI] Mark specific memory as reserved.
1610 Region of memory to be used, from ss to ss+nn.
1611 Example: Exclude memory from 0x18690000-0x1869ffff
1612 memmap=64K$0x18690000
1614 memmap=0x10000$0x18690000
1616 memory_corruption_check=0/1 [X86]
1617 Some BIOSes seem to corrupt the first 64k of
1618 memory when doing things like suspend/resume.
1619 Setting this option will scan the memory
1620 looking for corruption. Enabling this will
1621 both detect corruption and prevent the kernel
1622 from using the memory being corrupted.
1623 However, its intended as a diagnostic tool; if
1624 repeatable BIOS-originated corruption always
1625 affects the same memory, you can use memmap=
1626 to prevent the kernel from using that memory.
1628 memory_corruption_check_size=size [X86]
1629 By default it checks for corruption in the low
1630 64k, making this memory unavailable for normal
1631 use. Use this parameter to scan for
1632 corruption in more or less memory.
1634 memory_corruption_check_period=seconds [X86]
1635 By default it checks for corruption every 60
1636 seconds. Use this parameter to check at some
1637 other rate. 0 disables periodic checking.
1639 memtest= [KNL,X86] Enable memtest
1641 default : 0 <disable>
1642 Specifies the number of memtest passes to be
1643 performed. Each pass selects another test
1644 pattern from a given set of patterns. Memtest
1645 fills the memory with this pattern, validates
1646 memory contents and reserves bad memory
1647 regions that are detected.
1649 meye.*= [HW] Set MotionEye Camera parameters
1650 See Documentation/video4linux/meye.txt.
1652 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1653 Multi-Function General Purpose Timers on AMD Geode
1656 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1657 the BIOS has incorrectly applied a workaround. TinyBIOS
1658 version 0.98 is known to be affected, 0.99 fixes the
1659 problem by letting the user disable the workaround.
1663 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1664 physical address is ignored.
1666 mini2440= [ARM,HW,KNL]
1667 Format:[0..2][b][c][t]
1669 MINI2440 configuration specification:
1670 0 - The attached screen is the 3.5" TFT
1671 1 - The attached screen is the 7" TFT
1672 2 - The VGA Shield is attached (1024x768)
1673 Leaving out the screen size parameter will not load
1674 the TFT driver, and the framebuffer will be left
1676 b - Enable backlight. The TFT backlight pin will be
1677 linked to the kernel VESA blanking code and a GPIO
1678 LED. This parameter is not necessary when using the
1680 c - Enable the s3c camera interface.
1681 t - Reserved for enabling touchscreen support. The
1682 touchscreen support is not enabled in the mainstream
1683 kernel as of 2.6.30, a preliminary port can be found
1684 in the "bleeding edge" mini2440 support kernel at
1685 http://repo.or.cz/w/linux-2.6/mini2440.git
1688 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1689 parameter allows control of the logging verbosity for
1690 the additional memory initialisation checks. A value
1691 of 0 disables mminit logging and a level of 4 will
1692 log everything. Information is printed at KERN_DEBUG
1693 so loglevel=8 may also need to be specified.
1696 [KNL] When CONFIG_MODULE_SIG is set, this means that
1697 modules without (valid) signatures will fail to load.
1698 Note that if CONFIG_MODULE_SIG_FORCE is set, that
1699 is always true, so this option does nothing.
1702 [MOUSE] Maximum time between finger touching and
1703 leaving touchpad surface for touch to be considered
1704 a tap and be reported as a left button click (for
1705 touchpads working in absolute mode only).
1707 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1708 reporting absolute coordinates, such as tablets
1709 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1710 reporting absolute coordinates, such as tablets
1712 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1713 is similar to kernelcore except it specifies the
1714 amount of memory used for migratable allocations.
1715 If both kernelcore and movablecore is specified,
1716 then kernelcore will be at *least* the specified
1717 value but may be more. If movablecore on its own
1718 is specified, the administrator must be careful
1719 that the amount of memory usable for all allocations
1722 MTD_Partition= [MTD]
1723 Format: <name>,<region-number>,<size>,<offset>
1725 MTD_Region= [MTD] Format:
1726 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1729 See drivers/mtd/cmdlinepart.c.
1731 multitce=off [PPC] This parameter disables the use of the pSeries
1732 firmware feature for updating multiple TCE entries
1735 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1737 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1739 boundary - index of last SLC block on Flex-OneNAND.
1740 The remaining blocks are configured as MLC blocks.
1741 lock - Configure if Flex-OneNAND boundary should be locked.
1742 Once locked, the boundary cannot be changed.
1743 1 indicates lock status, 0 indicates unlock status.
1746 ARM/S3C2412 JIVE boot control
1748 See arch/arm/mach-s3c2412/mach-jive.c
1750 mtouchusb.raw_coordinates=
1751 [HW] Make the MicroTouch USB driver use raw coordinates
1752 ('y', default) or cooked coordinates ('n')
1754 mtrr_chunk_size=nn[KMG] [X86]
1755 used for mtrr cleanup. It is largest continuous chunk
1756 that could hold holes aka. UC entries.
1758 mtrr_gran_size=nn[KMG] [X86]
1759 Used for mtrr cleanup. It is granularity of mtrr block.
1761 Large value could prevent small alignment from
1764 mtrr_spare_reg_nr=n [X86]
1766 Range: 0,7 : spare reg number
1768 Used for mtrr cleanup. It is spare mtrr entries number.
1769 Set to 2 or more if your graphical card needs more.
1771 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1773 netdev= [NET] Network devices parameters
1774 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1775 Note that mem_start is often overloaded to mean
1776 something different and driver-specific.
1777 This usage is only documented in each driver source
1781 [NETFILTER] Enable connection tracking flow accounting
1782 0 to disable accounting
1783 1 to enable accounting
1786 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1787 See Documentation/filesystems/nfs/nfsroot.txt.
1789 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1790 See Documentation/filesystems/nfs/nfsroot.txt.
1792 nfsrootdebug [NFS] enable nfsroot debugging messages.
1793 See Documentation/filesystems/nfs/nfsroot.txt.
1795 nfs.callback_tcpport=
1796 [NFS] set the TCP port on which the NFSv4 callback
1797 channel should listen.
1800 [NFS] sets the pathname to the program which is used
1801 to update the NFS client cache entries.
1803 nfs.cache_getent_timeout=
1804 [NFS] sets the timeout after which an attempt to
1805 update a cache entry is deemed to have failed.
1807 nfs.idmap_cache_timeout=
1808 [NFS] set the maximum lifetime for idmapper cache
1812 [NFS] enable 64-bit inode numbers.
1813 If zero, the NFS client will fake up a 32-bit inode
1814 number for the readdir() and stat() syscalls instead
1815 of returning the full 64-bit number.
1816 The default is to return 64-bit inode numbers.
1818 nfs.max_session_slots=
1819 [NFSv4.1] Sets the maximum number of session slots
1820 the client will attempt to negotiate with the server.
1821 This limits the number of simultaneous RPC requests
1822 that the client can send to the NFSv4.1 server.
1823 Note that there is little point in setting this
1824 value higher than the max_tcp_slot_table_limit.
1826 nfs.nfs4_disable_idmapping=
1827 [NFSv4] When set to the default of '1', this option
1828 ensures that both the RPC level authentication
1829 scheme and the NFS level operations agree to use
1830 numeric uids/gids if the mount is using the
1831 'sec=sys' security flavour. In effect it is
1832 disabling idmapping, which can make migration from
1833 legacy NFSv2/v3 systems to NFSv4 easier.
1834 Servers that do not support this mode of operation
1835 will be autodetected by the client, and it will fall
1836 back to using the idmapper.
1837 To turn off this behaviour, set the value to '0'.
1839 [NFS4] Specify an additional fixed unique ident-
1840 ification string that NFSv4 clients can insert into
1841 their nfs_client_id4 string. This is typically a
1842 UUID that is generated at system install time.
1844 nfs.send_implementation_id =
1845 [NFSv4.1] Send client implementation identification
1846 information in exchange_id requests.
1847 If zero, no implementation identification information
1849 The default is to send the implementation identification
1852 nfsd.nfs4_disable_idmapping=
1853 [NFSv4] When set to the default of '1', the NFSv4
1854 server will return only numeric uids and gids to
1855 clients using auth_sys, and will accept numeric uids
1856 and gids from such clients. This is intended to ease
1857 migration from NFSv2/v3.
1859 objlayoutdriver.osd_login_prog=
1860 [NFS] [OBJLAYOUT] sets the pathname to the program which
1861 is used to automatically discover and login into new
1862 osd-targets. Please see:
1863 Documentation/filesystems/pnfs.txt for more explanations
1865 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1866 when a NMI is triggered.
1867 Format: [state][,regs][,debounce][,die]
1869 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1870 Format: [panic,][nopanic,][num]
1872 0 - turn nmi_watchdog off
1873 When panic is specified, panic when an NMI watchdog
1874 timeout occurs (or 'nopanic' to override the opposite
1876 This is useful when you use a panic=... timeout and
1877 need the box quickly up again.
1879 netpoll.carrier_timeout=
1880 [NET] Specifies amount of time (in seconds) that
1881 netpoll should wait for a carrier. By default netpoll
1884 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1885 emulation library even if a 387 maths coprocessor
1889 [HW] Never suspend the console
1890 Disable suspending of consoles during suspend and
1891 hibernate operations. Once disabled, debugging
1892 messages can reach various consoles while the rest
1893 of the system is being put to sleep (ie, while
1894 debugging driver suspend/resume hooks). This may
1895 not work reliably with all consoles, but is known
1896 to work with serial and VGA consoles.
1897 To facilitate more flexible debugging, we also add
1898 console_suspend, a printk module parameter to control
1899 it. Users could use console_suspend (usually
1900 /sys/module/printk/parameters/console_suspend) to
1901 turn on/off it dynamically.
1903 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1904 caches in the slab allocator. Saves per-node memory,
1905 but will impact performance.
1909 noapic [SMP,APIC] Tells the kernel to not make use of any
1910 IOAPICs that may be present in the system.
1912 noautogroup Disable scheduler automatic task group creation.
1914 nobats [PPC] Do not use BATs for mapping kernel lowmem
1915 on "Classic" PPC cores.
1919 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1921 nodelayacct [KNL] Disable per-task delay accounting
1923 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1925 nodsp [SH] Disable hardware DSP at boot time.
1927 noefi [X86] Disable EFI runtime services support.
1932 On X86-32 available only on PAE configured kernels.
1933 noexec=on: enable non-executable mappings (default)
1934 noexec=off: disable non-executable mappings
1937 Disable SMAP (Supervisor Mode Access Prevention)
1938 even if it is supported by processor.
1941 Disable SMEP (Supervisor Mode Execution Prevention)
1942 even if it is supported by processor.
1945 This affects only 32-bit executables.
1946 noexec32=on: enable non-executable mappings (default)
1947 read doesn't imply executable mappings
1948 noexec32=off: disable non-executable mappings
1949 read implies executable mappings
1951 nofpu [SH] Disable hardware FPU at boot time.
1953 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1954 register save and restore. The kernel will only save
1955 legacy floating-point registers on task switch.
1957 noxsave [BUGS=X86] Disables x86 extended register state save
1958 and restore using xsave. The kernel will fallback to
1959 enabling legacy floating-point and sse state.
1962 on enable eager fpu restore
1963 off disable eager fpu restore
1964 auto selects the default scheme, which automatically
1965 enables eagerfpu restore for xsaveopt.
1967 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1968 wfi(ARM) instruction doesn't work correctly and not to
1969 use it. This is also useful when using JTAG debugger.
1971 no_file_caps Tells the kernel not to honor file capabilities. The
1972 only way then for a file to be executed with privilege
1973 is to be setuid root or executed by root.
1975 nohalt [IA-64] Tells the kernel not to use the power saving
1976 function PAL_HALT_LIGHT when idle. This increases
1977 power-consumption. On the positive side, it reduces
1978 interrupt wake-up latency, which may improve performance
1979 in certain environments such as networked servers or
1982 nohz= [KNL] Boottime enable/disable dynamic ticks
1983 Valid arguments: on, off
1986 nohz_full= [KNL,BOOT]
1987 In kernels built with CONFIG_NO_HZ_FULL=y, set
1988 the specified list of CPUs whose tick will be stopped
1989 whenever possible. The boot CPU will be forced outside
1990 the range to maintain the timekeeping.
1991 The CPUs in this range must also be included in the
1994 noiotrap [SH] Disables trapped I/O port accesses.
1996 noirqdebug [X86-32] Disables the code which attempts to detect and
1997 disable unhandled interrupt sources.
1999 no_timer_check [X86,APIC] Disables the code which tests for
2000 broken timer IRQ sources.
2002 noisapnp [ISAPNP] Disables ISA PnP code.
2004 noinitrd [RAM] Tells the kernel not to load any configured
2007 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2009 [Deprecated - use intremap=off]
2013 nojitter [IA-64] Disables jitter checking for ITC timers.
2015 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2017 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2020 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2021 steal time is computed, but won't influence scheduler
2024 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2026 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2028 noltlbs [PPC] Do not use large page/tlb entries for kernel
2029 lowmem mapping on PPC40x.
2031 nomca [IA-64] Disable machine check abort handling
2033 nomce [X86-32] Machine Check Exception
2035 nomfgpt [X86-32] Disable Multi-Function General Purpose
2036 Timer usage (for AMD Geode machines).
2038 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2039 shutdown the other cpus. Instead use the REBOOT_VECTOR
2042 nomodule Disable module load
2044 nopat [X86] Disable PAT (page attribute table extension of
2045 pagetables) support.
2047 norandmaps Don't use address space randomization. Equivalent to
2048 echo 0 > /proc/sys/kernel/randomize_va_space
2050 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2052 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2053 with UP alternatives
2055 nordrand [X86] Disable the direct use of the RDRAND
2056 instruction even if it is supported by the
2057 processor. RDRAND is still available to user
2060 noresume [SWSUSP] Disables resume and restores original swap
2063 no-scroll [VGA] Disables scrollback.
2064 This is required for the Braillex ib80-piezo Braille
2065 reader made by F.H. Papenmeier (Germany).
2069 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2071 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2072 and disable the IO APIC. legacy for "maxcpus=0".
2074 nosoftlockup [KNL] Disable the soft-lockup detector.
2076 nosync [HW,M68K] Disables sync negotiation for all devices.
2078 notsc [BUGS=X86-32] Disable Time Stamp Counter
2080 nousb [USB] Disable the USB subsystem
2082 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2086 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2088 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2089 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2090 Some features depend on CPU0. Known dependencies are:
2091 1. Resume from suspend/hibernate depends on CPU0.
2092 Suspend/hibernate will fail if CPU0 is offline and you
2093 need to online CPU0 before suspend/hibernate.
2094 2. PIC interrupts also depend on CPU0. CPU0 can't be
2095 removed if a PIC interrupt is detected.
2096 It's said poweroff/reboot may depend on CPU0 on some
2097 machines although I haven't seen such issues so far
2098 after CPU0 is offline on a few tested machines.
2099 If the dependencies are under your control, you can
2100 turn on cpu0_hotplug.
2102 nptcg= [IA-64] Override max number of concurrent global TLB
2103 purges which is reported from either PAL_VM_SUMMARY or
2106 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2107 could support. nr_cpus=n : n >= 1 limits the kernel to
2108 supporting 'n' processors. Later in runtime you can not
2109 use hotplug cpu feature to put more cpu back to online.
2110 just like you compile the kernel NR_CPUS=n
2112 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2114 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2115 Allowed values are enable and disable
2117 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2118 one of ['zone', 'node', 'default'] can be specified
2119 This can be set from sysctl after boot.
2120 See Documentation/sysctl/vm.txt for details.
2122 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2123 See Documentation/debugging-via-ohci1394.txt for more
2126 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2127 Rather than timing out after 20 ms if an EC
2128 command is not properly ACKed, override the length
2129 of the timeout. We have interrupts disabled while
2130 waiting for the ACK, so if this is set too high
2131 interrupts *may* be lost!
2133 omap_mux= [OMAP] Override bootloader pin multiplexing.
2134 Format: <mux_mode0.mode_name=value>...
2135 For example, to override I2C bus2:
2136 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2138 oprofile.timer= [HW]
2139 Use timer interrupt instead of performance counters
2141 oprofile.cpu_type= Force an oprofile cpu type
2142 This might be useful if you have an older oprofile
2143 userland or if you want common events.
2144 Format: { arch_perfmon }
2145 arch_perfmon: [X86] Force use of architectural
2146 perfmon on Intel CPUs instead of the
2147 CPU specific event set.
2148 timer: [X86] Force use of architectural NMI
2149 timer mode (see also oprofile.timer
2150 for generic hr timer mode)
2151 [s390] Force legacy basic mode sampling
2152 (report cpu_type "timer")
2154 oops=panic Always panic on oopses. Default is to just kill the
2155 process, but there is a small probability of
2156 deadlocking the machine.
2157 This will also cause panics on machine check exceptions.
2158 Useful together with panic=30 to trigger a reboot.
2161 See Documentation/sound/oss/oss-parameters.txt
2163 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2164 timeout > 0: seconds before rebooting
2165 timeout = 0: wait forever
2166 timeout < 0: reboot immediately
2169 parkbd.port= [HW] Parallel port number the keyboard adapter is
2170 connected to, default is 0.
2172 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2173 0 for XT, 1 for AT (default is AT).
2176 parport= [HW,PPT] Specify parallel ports. 0 disables.
2177 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2178 Use 'auto' to force the driver to use any
2179 IRQ/DMA settings detected (the default is to
2180 ignore detected IRQ/DMA settings because of
2181 possible conflicts). You can specify the base
2182 address, IRQ, and DMA settings; IRQ and DMA
2183 should be numbers, or 'auto' (for using detected
2184 settings on that particular port), or 'nofifo'
2185 (to avoid using a FIFO even if it is detected).
2186 Parallel ports are assigned in the order they
2187 are specified on the command line, starting
2190 parport_init_mode= [HW,PPT]
2191 Configure VIA parallel port to operate in
2192 a specific mode. This is necessary on Pegasos
2193 computer where firmware has no options for setting
2194 up parallel port mode and sets it to spp.
2195 Currently this function knows 686a and 8231 chips.
2196 Format: [spp|ps2|epp|ecp|ecpepp]
2199 Halt all CPUs after the first oops has been printed for
2200 the specified number of seconds. This is to be used if
2201 your oopses keep scrolling off the screen.
2206 See header of drivers/block/paride/pcd.c.
2207 See also Documentation/blockdev/paride.txt.
2209 pci=option[,option...] [PCI] various PCI subsystem options:
2210 earlydump [X86] dump PCI config space before the kernel
2212 off [X86] don't probe for the PCI bus
2213 bios [X86-32] force use of PCI BIOS, don't access
2214 the hardware directly. Use this if your machine
2215 has a non-standard PCI host bridge.
2216 nobios [X86-32] disallow use of PCI BIOS, only direct
2217 hardware access methods are allowed. Use this
2218 if you experience crashes upon bootup and you
2219 suspect they are caused by the BIOS.
2220 conf1 [X86] Force use of PCI Configuration
2222 conf2 [X86] Force use of PCI Configuration
2224 noaer [PCIE] If the PCIEAER kernel config parameter is
2225 enabled, this kernel boot option can be used to
2226 disable the use of PCIE advanced error reporting.
2227 nodomains [PCI] Disable support for multiple PCI
2228 root domains (aka PCI segments, in ACPI-speak).
2229 nommconf [X86] Disable use of MMCONFIG for PCI
2231 check_enable_amd_mmconf [X86] check for and enable
2232 properly configured MMIO access to PCI
2233 config space on AMD family 10h CPU
2234 nomsi [MSI] If the PCI_MSI kernel config parameter is
2235 enabled, this kernel boot option can be used to
2236 disable the use of MSI interrupts system-wide.
2237 noioapicquirk [APIC] Disable all boot interrupt quirks.
2238 Safety option to keep boot IRQs enabled. This
2239 should never be necessary.
2240 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2241 primary IO-APIC for bridges that cannot disable
2242 boot IRQs. This fixes a source of spurious IRQs
2243 when the system masks IRQs.
2244 noioapicreroute [APIC] Disable workaround that uses the
2245 boot IRQ equivalent of an IRQ that connects to
2246 a chipset where boot IRQs cannot be disabled.
2247 The opposite of ioapicreroute.
2248 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2249 routing table. These calls are known to be buggy
2250 on several machines and they hang the machine
2251 when used, but on other computers it's the only
2252 way to get the interrupt routing table. Try
2253 this option if the kernel is unable to allocate
2254 IRQs or discover secondary PCI buses on your
2256 rom [X86] Assign address space to expansion ROMs.
2257 Use with caution as certain devices share
2258 address decoders between ROMs and other
2260 norom [X86] Do not assign address space to
2261 expansion ROMs that do not already have
2262 BIOS assigned address ranges.
2263 nobar [X86] Do not assign address space to the
2264 BARs that weren't assigned by the BIOS.
2265 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2266 assigned automatically to PCI devices. You can
2267 make the kernel exclude IRQs of your ISA cards
2269 pirqaddr=0xAAAAA [X86] Specify the physical address
2270 of the PIRQ table (normally generated
2271 by the BIOS) if it is outside the
2272 F0000h-100000h range.
2273 lastbus=N [X86] Scan all buses thru bus #N. Can be
2274 useful if the kernel is unable to find your
2275 secondary buses and you want to tell it
2276 explicitly which ones they are.
2277 assign-busses [X86] Always assign all PCI bus
2278 numbers ourselves, overriding
2279 whatever the firmware may have done.
2280 usepirqmask [X86] Honor the possible IRQ mask stored
2281 in the BIOS $PIR table. This is needed on
2282 some systems with broken BIOSes, notably
2283 some HP Pavilion N5400 and Omnibook XE3
2284 notebooks. This will have no effect if ACPI
2285 IRQ routing is enabled.
2286 noacpi [X86] Do not use ACPI for IRQ routing
2287 or for PCI scanning.
2288 use_crs [X86] Use PCI host bridge window information
2289 from ACPI. On BIOSes from 2008 or later, this
2290 is enabled by default. If you need to use this,
2291 please report a bug.
2292 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2293 If you need to use this, please report a bug.
2294 routeirq Do IRQ routing for all PCI devices.
2295 This is normally done in pci_enable_device(),
2296 so this option is a temporary workaround
2297 for broken drivers that don't call it.
2298 skip_isa_align [X86] do not align io start addr, so can
2299 handle more pci cards
2300 firmware [ARM] Do not re-enumerate the bus but instead
2301 just use the configuration from the
2302 bootloader. This is currently used on
2303 IXP2000 systems where the bus has to be
2304 configured a certain way for adjunct CPUs.
2305 noearly [X86] Don't do any early type 1 scanning.
2306 This might help on some broken boards which
2307 machine check when some devices' config space
2308 is read. But various workarounds are disabled
2309 and some IOMMU drivers will not work.
2310 bfsort Sort PCI devices into breadth-first order.
2311 This sorting is done to get a device
2312 order compatible with older (<= 2.4) kernels.
2313 nobfsort Don't sort PCI devices into breadth-first order.
2314 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2315 tuning and use the BIOS-configured MPS defaults.
2316 pcie_bus_safe Set every device's MPS to the largest value
2317 supported by all devices below the root complex.
2318 pcie_bus_perf Set device MPS to the largest allowable MPS
2319 based on its parent bus. Also set MRRS (Max
2320 Read Request Size) to the largest supported
2321 value (no larger than the MPS that the device
2322 or bus can support) for best performance.
2323 pcie_bus_peer2peer Set every device's MPS to 128B, which
2324 every device is guaranteed to support. This
2325 configuration allows peer-to-peer DMA between
2326 any pair of devices, possibly at the cost of
2327 reduced performance. This also guarantees
2328 that hot-added devices will work.
2329 cbiosize=nn[KMG] The fixed amount of bus space which is
2330 reserved for the CardBus bridge's IO window.
2331 The default value is 256 bytes.
2332 cbmemsize=nn[KMG] The fixed amount of bus space which is
2333 reserved for the CardBus bridge's memory
2334 window. The default value is 64 megabytes.
2337 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2338 Specifies alignment and device to reassign
2339 aligned memory resources.
2340 If <order of align> is not specified,
2341 PAGE_SIZE is used as alignment.
2342 PCI-PCI bridge can be specified, if resource
2343 windows need to be expanded.
2344 ecrc= Enable/disable PCIe ECRC (transaction layer
2345 end-to-end CRC checking).
2346 bios: Use BIOS/firmware settings. This is the
2350 hpiosize=nn[KMG] The fixed amount of bus space which is
2351 reserved for hotplug bridge's IO window.
2352 Default size is 256 bytes.
2353 hpmemsize=nn[KMG] The fixed amount of bus space which is
2354 reserved for hotplug bridge's memory window.
2355 Default size is 2 megabytes.
2356 realloc= Enable/disable reallocating PCI bridge resources
2357 if allocations done by BIOS are too small to
2358 accommodate resources required by all child
2360 off: Turn realloc off
2362 realloc same as realloc=on
2363 noari do not use PCIe ARI.
2364 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2365 only look for one device below a PCIe downstream
2368 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2371 force Enable ASPM even on devices that claim not to support it.
2372 WARNING: Forcing ASPM on may cause system lockups.
2374 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2375 nomsi Do not use MSI for PCI Express Native Hotplug (this
2376 makes all PCIe ports use INTx for hotplug services).
2378 pcie_ports= [PCIE] PCIe ports handling:
2379 auto Ask the BIOS whether or not to use native PCIe services
2380 associated with PCIe ports (PME, hot-plug, AER). Use
2381 them only if that is allowed by the BIOS.
2382 native Use native PCIe services associated with PCIe ports
2384 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2387 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2388 nomsi Do not use MSI for native PCIe PME signaling (this makes
2389 all PCIe root ports use INTx for all services).
2391 pcmv= [HW,PCMCIA] BadgePAD 4
2394 See Documentation/blockdev/paride.txt.
2396 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2399 See arch/parisc/kernel/pdc_chassis.c
2401 percpu_alloc= Select which percpu first chunk allocator to use.
2402 Currently supported values are "embed" and "page".
2403 Archs may support subset or none of the selections.
2404 See comments in mm/percpu.c for details on each
2405 allocator. This parameter is primarily for debugging
2406 and performance comparison.
2409 See Documentation/blockdev/paride.txt.
2412 See Documentation/blockdev/paride.txt.
2414 pirq= [SMP,APIC] Manual mp-table setup
2415 See Documentation/x86/i386/IO-APIC.txt.
2417 plip= [PPT,NET] Parallel port network link
2418 Format: { parport<nr> | timid | 0 }
2419 See also Documentation/parport.txt.
2421 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2422 Override pmtimer IOPort with a hex value.
2426 Enable PNP debug messages (depends on the
2427 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2428 via /sys/module/pnp/parameters/debug. We always show
2429 current resource usage; turning this on also shows
2430 possible settings and some assignment information.
2436 { on | off | curr | res | no-curr | no-res }
2439 [ISAPNP] Exclude IRQs for the autoconfiguration
2442 [ISAPNP] Exclude DMAs for the autoconfiguration
2444 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2445 Ranges are in pairs (I/O port base and size).
2448 [ISAPNP] Exclude memory regions for the
2450 Ranges are in pairs (memory base and size).
2452 ports= [IP_VS_FTP] IPVS ftp helper module
2454 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2456 Format: <port>,<port>....
2458 print-fatal-signals=
2459 [KNL] debug: print fatal signals
2461 If enabled, warn about various signal handling
2462 related application anomalies: too many signals,
2463 too many POSIX.1 timers, fatal signals causing a
2466 If you hit the warning due to signal overflow,
2467 you might want to try "ulimit -i unlimited".
2471 printk.always_kmsg_dump=
2472 Trigger kmsg_dump for cases other than kernel oops or
2474 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2477 printk.time= Show timing data prefixed to each printk message line
2478 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2480 processor.max_cstate= [HW,ACPI]
2481 Limit processor to maximum C-state
2482 max_cstate=9 overrides any DMI blacklist limit.
2484 processor.nocst [HW,ACPI]
2485 Ignore the _CST method to determine C-states,
2486 instead using the legacy FADT method
2488 profile= [KNL] Enable kernel profiling via /proc/profile
2489 Format: [schedule,]<number>
2490 Param: "schedule" - profile schedule points.
2491 Param: <number> - step/bucket size as a power of 2 for
2492 statistical time based profiling.
2493 Param: "sleep" - profile D-state sleeping (millisecs).
2494 Requires CONFIG_SCHEDSTATS
2495 Param: "kvm" - profile VM exits.
2497 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2499 See Documentation/blockdev/ramdisk.txt.
2501 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2502 probe for; one of (bare|imps|exps|lifebook|any).
2503 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2505 psmouse.resetafter= [HW,MOUSE]
2506 Try to reset the device after so many bad packets
2509 [HW,MOUSE] Set desired mouse resolution, in dpi.
2510 psmouse.smartscroll=
2511 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2512 0 = disabled, 1 = enabled (default).
2514 pstore.backend= Specify the name of the pstore backend to use
2517 See Documentation/blockdev/paride.txt.
2520 [KNL] Number of legacy pty's. Overwrites compiled-in
2523 quiet [KNL] Disable most log messages
2528 See Documentation/md.txt.
2530 ramdisk_blocksize= [RAM]
2531 See Documentation/blockdev/ramdisk.txt.
2533 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2534 See Documentation/blockdev/ramdisk.txt.
2536 rcu_nocbs= [KNL,BOOT]
2537 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2538 the specified list of CPUs to be no-callback CPUs.
2539 Invocation of these CPUs' RCU callbacks will
2540 be offloaded to "rcuox/N" kthreads created for
2541 that purpose, where "x" is "b" for RCU-bh, "p"
2542 for RCU-preempt, and "s" for RCU-sched, and "N"
2543 is the CPU number. This reduces OS jitter on the
2544 offloaded CPUs, which can be useful for HPC and
2546 real-time workloads. It can also improve energy
2547 efficiency for asymmetric multiprocessors.
2549 rcu_nocb_poll [KNL,BOOT]
2550 Rather than requiring that offloaded CPUs
2551 (specified by rcu_nocbs= above) explicitly
2552 awaken the corresponding "rcuoN" kthreads,
2553 make these kthreads poll for callbacks.
2554 This improves the real-time response for the
2555 offloaded CPUs by relieving them of the need to
2556 wake up the corresponding kthread, but degrades
2557 energy efficiency by requiring that the kthreads
2558 periodically wake up to do the polling.
2560 rcutree.blimit= [KNL,BOOT]
2561 Set maximum number of finished RCU callbacks to process
2564 rcutree.fanout_leaf= [KNL,BOOT]
2565 Increase the number of CPUs assigned to each
2566 leaf rcu_node structure. Useful for very large
2569 rcutree.jiffies_till_first_fqs= [KNL,BOOT]
2570 Set delay from grace-period initialization to
2571 first attempt to force quiescent states.
2572 Units are jiffies, minimum value is zero,
2573 and maximum value is HZ.
2575 rcutree.jiffies_till_next_fqs= [KNL,BOOT]
2576 Set delay between subsequent attempts to force
2577 quiescent states. Units are jiffies, minimum
2578 value is one, and maximum value is HZ.
2580 rcutree.qhimark= [KNL,BOOT]
2581 Set threshold of queued
2582 RCU callbacks over which batch limiting is disabled.
2584 rcutree.qlowmark= [KNL,BOOT]
2585 Set threshold of queued RCU callbacks below which
2586 batch limiting is re-enabled.
2588 rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2589 Suppress RCU CPU stall warning messages.
2591 rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2592 Set timeout for RCU CPU stall warning messages.
2594 rcutree.rcu_idle_gp_delay= [KNL,BOOT]
2595 Set wakeup interval for idle CPUs that have
2596 RCU callbacks (RCU_FAST_NO_HZ=y).
2598 rcutree.rcu_idle_lazy_gp_delay= [KNL,BOOT]
2599 Set wakeup interval for idle CPUs that have
2600 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2601 Lazy RCU callbacks are those which RCU can
2602 prove do nothing more than free memory.
2604 rcutorture.fqs_duration= [KNL,BOOT]
2605 Set duration of force_quiescent_state bursts.
2607 rcutorture.fqs_holdoff= [KNL,BOOT]
2608 Set holdoff time within force_quiescent_state bursts.
2610 rcutorture.fqs_stutter= [KNL,BOOT]
2611 Set wait time between force_quiescent_state bursts.
2613 rcutorture.irqreader= [KNL,BOOT]
2614 Test RCU readers from irq handlers.
2616 rcutorture.n_barrier_cbs= [KNL,BOOT]
2617 Set callbacks/threads for rcu_barrier() testing.
2619 rcutorture.nfakewriters= [KNL,BOOT]
2620 Set number of concurrent RCU writers. These just
2621 stress RCU, they don't participate in the actual
2622 test, hence the "fake".
2624 rcutorture.nreaders= [KNL,BOOT]
2625 Set number of RCU readers.
2627 rcutorture.onoff_holdoff= [KNL,BOOT]
2628 Set time (s) after boot for CPU-hotplug testing.
2630 rcutorture.onoff_interval= [KNL,BOOT]
2631 Set time (s) between CPU-hotplug operations, or
2632 zero to disable CPU-hotplug testing.
2634 rcutorture.shuffle_interval= [KNL,BOOT]
2635 Set task-shuffle interval (s). Shuffling tasks
2636 allows some CPUs to go into dyntick-idle mode
2637 during the rcutorture test.
2639 rcutorture.shutdown_secs= [KNL,BOOT]
2640 Set time (s) after boot system shutdown. This
2641 is useful for hands-off automated testing.
2643 rcutorture.stall_cpu= [KNL,BOOT]
2644 Duration of CPU stall (s) to test RCU CPU stall
2645 warnings, zero to disable.
2647 rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2648 Time to wait (s) after boot before inducing stall.
2650 rcutorture.stat_interval= [KNL,BOOT]
2651 Time (s) between statistics printk()s.
2653 rcutorture.stutter= [KNL,BOOT]
2654 Time (s) to stutter testing, for example, specifying
2655 five seconds causes the test to run for five seconds,
2656 wait for five seconds, and so on. This tests RCU's
2657 ability to transition abruptly to and from idle.
2659 rcutorture.test_boost= [KNL,BOOT]
2660 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2661 "Maybe" means test if the RCU implementation
2662 under test support RCU priority boosting.
2664 rcutorture.test_boost_duration= [KNL,BOOT]
2665 Duration (s) of each individual boost test.
2667 rcutorture.test_boost_interval= [KNL,BOOT]
2668 Interval (s) between each boost test.
2670 rcutorture.test_no_idle_hz= [KNL,BOOT]
2671 Test RCU's dyntick-idle handling. See also the
2672 rcutorture.shuffle_interval parameter.
2674 rcutorture.torture_type= [KNL,BOOT]
2675 Specify the RCU implementation to test.
2677 rcutorture.verbose= [KNL,BOOT]
2678 Enable additional printk() statements.
2682 Run specified binary instead of /init from the ramdisk,
2683 used for early userspace startup. See initrd.
2685 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2686 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2687 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2690 [KNL, SMP] Set scheduler's default relax_domain_level.
2691 See Documentation/cgroups/cpusets.txt.
2693 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2695 reservetop= [X86-32]
2697 Reserves a hole at the top of the kernel virtual
2702 Set the amount of memory to reserve for BIOS at
2703 the bottom of the address space.
2705 reset_devices [KNL] Force drivers to reset the underlying device
2706 during initialization.
2709 Specify the partition device for software suspend
2711 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2713 resume_offset= [SWSUSP]
2714 Specify the offset from the beginning of the partition
2715 given by "resume=" at which the swap header is located,
2716 in <PAGE_SIZE> units (needed only for swap files).
2717 See Documentation/power/swsusp-and-swap-files.txt
2719 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2720 read the resume files
2722 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2723 Useful for devices that are detected asynchronously
2724 (e.g. USB and MMC devices).
2726 hibernate= [HIBERNATION]
2727 noresume Don't check if there's a hibernation image
2728 present during boot.
2729 nocompress Don't compress/decompress hibernation images.
2731 retain_initrd [RAM] Keep initrd memory after extraction
2733 rhash_entries= [KNL,NET]
2734 Set number of hash buckets for route cache
2736 riscom8= [HW,SERIAL]
2737 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2739 ro [KNL] Mount root device read-only on boot
2741 root= [KNL] Root filesystem
2742 See name_to_dev_t comment in init/do_mounts.c.
2744 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2745 mount the root filesystem
2747 rootflags= [KNL] Set root filesystem mount option string
2749 rootfstype= [KNL] Set root filesystem type
2751 rootwait [KNL] Wait (indefinitely) for root device to show up.
2752 Useful for devices that are detected asynchronously
2753 (e.g. USB and MMC devices).
2755 rproc_mem=nn[KMG][@address]
2756 [KNL,ARM,CMA] Remoteproc physical memory block.
2757 Memory area to be used by remote processor image,
2760 rw [KNL] Mount root device read-write on boot
2762 S [KNL] Run init in single mode
2765 See drivers/net/irda/sa1100_ir.c.
2767 sbni= [NET] Granch SBNI12 leased line adapter
2769 sched_debug [KNL] Enables verbose scheduler debug messages.
2771 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2772 xtime_lock contention on larger systems, and/or RCU lock
2773 contention on all systems with CONFIG_MAXSMP set.
2774 Format: { "0" | "1" }
2775 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2777 Note: increases power consumption, thus should only be
2778 enabled if running jitter sensitive (HPC/RT) workloads.
2780 security= [SECURITY] Choose a security module to enable at boot.
2781 If this boot parameter is not specified, only the first
2782 security module asking for security registration will be
2783 loaded. An invalid security module name will be treated
2784 as if no module has been chosen.
2786 selinux= [SELINUX] Disable or enable SELinux at boot time.
2787 Format: { "0" | "1" }
2788 See security/selinux/Kconfig help text.
2791 Default value is set via kernel config option.
2792 If enabled at boot time, /selinux/disable can be used
2793 later to disable prior to initial policy load.
2795 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2796 Format: { "0" | "1" }
2797 See security/apparmor/Kconfig help text
2800 Default value is set via kernel config option.
2802 serialnumber [BUGS=X86-32]
2805 Maximal number of shapers.
2807 show_msr= [x86] show boot-time MSR settings
2808 Format: { <integer> }
2809 Show boot-time (BIOS-initialized) MSR settings.
2810 The parameter means the number of CPUs to show,
2811 for example 1 means boot CPU only.
2818 slab_max_order= [MM, SLAB]
2819 Determines the maximum allowed order for slabs.
2820 A high setting may cause OOMs due to memory
2821 fragmentation. Defaults to 1 for systems with
2822 more than 32MB of RAM, 0 otherwise.
2824 slub_debug[=options[,slabs]] [MM, SLUB]
2825 Enabling slub_debug allows one to determine the
2826 culprit if slab objects become corrupted. Enabling
2827 slub_debug can create guard zones around objects and
2828 may poison objects when not in use. Also tracks the
2829 last alloc / free. For more information see
2830 Documentation/vm/slub.txt.
2832 slub_max_order= [MM, SLUB]
2833 Determines the maximum allowed order for slabs.
2834 A high setting may cause OOMs due to memory
2835 fragmentation. For more information see
2836 Documentation/vm/slub.txt.
2838 slub_min_objects= [MM, SLUB]
2839 The minimum number of objects per slab. SLUB will
2840 increase the slab order up to slub_max_order to
2841 generate a sufficiently large slab able to contain
2842 the number of objects indicated. The higher the number
2843 of objects the smaller the overhead of tracking slabs
2844 and the less frequently locks need to be acquired.
2845 For more information see Documentation/vm/slub.txt.
2847 slub_min_order= [MM, SLUB]
2848 Determines the minimum page order for slabs. Must be
2849 lower than slub_max_order.
2850 For more information see Documentation/vm/slub.txt.
2852 slub_nomerge [MM, SLUB]
2853 Disable merging of slabs with similar size. May be
2854 necessary if there is some reason to distinguish
2855 allocs to different slabs. Debug options disable
2856 merging on their own.
2857 For more information see Documentation/vm/slub.txt.
2860 Format: <io1>[,<io2>[,...,<io8>]]
2862 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2863 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2864 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2865 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2866 smsc-ircc2.ircc_irq= [HW] IRQ line
2867 smsc-ircc2.ircc_dma= [HW] DMA channel
2868 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2869 0: Toshiba Satellite 1800 (GP data pin select)
2870 1: Fast pin select (default)
2874 [KNL] Should the soft-lockup detector generate panics.
2877 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2878 See Documentation/laptops/sonypi.txt
2880 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2881 See Documentation/serial/specialix.txt.
2883 spia_io_base= [HW,MTD]
2889 Enabled the stack tracer on boot up.
2891 stacktrace_filter=[function-list]
2892 [FTRACE] Limit the functions that the stack tracer
2893 will trace at boot up. function-list is a comma separated
2894 list of functions. This list can be changed at run
2895 time by the stack_trace_filter file in the debugfs
2896 tracing directory. Note, this enables stack tracing
2897 and the stacktrace above is not needed.
2901 Set the STI (builtin display/keyboard on the HP-PARISC
2902 machines) console (graphic card) which should be used
2903 as the initial boot-console.
2904 See also comment in drivers/video/console/sticore.c.
2907 See comment in drivers/video/console/sticore.c.
2910 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2912 sunrpc.min_resvport=
2913 sunrpc.max_resvport=
2915 SunRPC servers often require that client requests
2916 originate from a privileged port (i.e. a port in the
2917 range 0 < portnr < 1024).
2918 An administrator who wishes to reserve some of these
2919 ports for other uses may adjust the range that the
2920 kernel's sunrpc client considers to be privileged
2921 using these two parameters to set the minimum and
2922 maximum port values.
2926 Control how the NFS server code allocates CPUs to
2927 service thread pools. Depending on how many NICs
2928 you have and where their interrupts are bound, this
2929 option will affect which CPUs will do NFS serving.
2930 Note: this parameter cannot be changed while the
2931 NFS server is running.
2933 auto the server chooses an appropriate mode
2934 automatically using heuristics
2935 global a single global pool contains all CPUs
2936 percpu one pool for each CPU
2937 pernode one pool for each NUMA node (equivalent
2938 to global on non-NUMA machines)
2940 sunrpc.tcp_slot_table_entries=
2941 sunrpc.udp_slot_table_entries=
2943 Sets the upper limit on the number of simultaneous
2944 RPC calls that can be sent from the client to a
2945 server. Increasing these values may allow you to
2946 improve throughput, but will also increase the
2947 amount of memory reserved for use by the client.
2950 [KNL] Enable accounting of swap in memory resource
2951 controller if no parameter or 1 is given or disable
2952 it if 0 is given (See Documentation/cgroups/memory.txt)
2954 swiotlb= [IA-64] Number of I/O TLB slabs
2958 sysfs.deprecated=0|1 [KNL]
2959 Enable/disable old style sysfs layout for old udev
2960 on older distributions. When this option is enabled
2961 very new udev will not work anymore. When this option
2962 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2963 in older udev will not work anymore.
2964 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2965 the kernel configuration.
2967 sysrq_always_enabled
2969 Ignore sysrq setting - this boot parameter will
2970 neutralize any effect of /proc/sys/kernel/sysrq.
2971 Useful for debugging.
2975 test_suspend= [SUSPEND]
2976 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2977 standby suspend) as the system sleep state to briefly
2978 enter during system startup. The system is woken from
2979 this state using a wakeup-capable RTC alarm.
2981 thash_entries= [KNL,NET]
2982 Set number of hash buckets for TCP connection
2984 thermal.act= [HW,ACPI]
2985 -1: disable all active trip points in all thermal zones
2986 <degrees C>: override all lowest active trip points
2988 thermal.crt= [HW,ACPI]
2989 -1: disable all critical trip points in all thermal zones
2990 <degrees C>: override all critical trip points
2992 thermal.nocrt= [HW,ACPI]
2993 Set to disable actions on ACPI thermal zone
2994 critical and hot trip points.
2996 thermal.off= [HW,ACPI]
2997 1: disable ACPI thermal control
2999 thermal.psv= [HW,ACPI]
3000 -1: disable all passive trip points
3001 <degrees C>: override all passive trip points to this
3004 thermal.tzp= [HW,ACPI]
3005 Specify global default ACPI thermal zone polling rate
3006 <deci-seconds>: poll all this frequency
3007 0: no polling (default)
3010 Force threading of all interrupt handlers except those
3011 marked explicitly IRQF_NO_THREAD.
3014 Enable the Transcendent memory driver if built-in.
3016 tmem.cleancache=0|1 [KNL, XEN]
3017 Default is on (1). Disable the usage of the cleancache
3018 API to send anonymous pages to the hypervisor.
3020 tmem.frontswap=0|1 [KNL, XEN]
3021 Default is on (1). Disable the usage of the frontswap
3022 API to send swap pages to the hypervisor. If disabled
3023 the selfballooning and selfshrinking are force disabled.
3025 tmem.selfballooning=0|1 [KNL, XEN]
3026 Default is on (1). Disable the driving of swap pages
3029 tmem.selfshrinking=0|1 [KNL, XEN]
3030 Default is on (1). Partial swapoff that immediately
3031 transfers pages from Xen hypervisor back to the
3032 kernel based on different criteria.
3036 Specify if the kernel should make use of the cpu
3037 topology information if the hardware supports this.
3038 The scheduler will make use of this information and
3039 e.g. base its process migration decisions on it.
3044 tpm_suspend_pcr=[HW,TPM]
3045 Format: integer pcr id
3046 Specify that at suspend time, the tpm driver
3047 should extend the specified pcr with zeros,
3048 as a workaround for some chips which fail to
3049 flush the last written pcr on TPM_SaveState.
3050 This will guarantee that all the other pcrs
3053 trace_buf_size=nn[KMG]
3054 [FTRACE] will set tracing buffer size.
3056 trace_event=[event-list]
3057 [FTRACE] Set and start specified trace events in order
3058 to facilitate early boot debugging.
3059 See also Documentation/trace/events.txt
3061 trace_options=[option-list]
3062 [FTRACE] Enable or disable tracer options at boot.
3063 The option-list is a comma delimited list of options
3064 that can be enabled or disabled just as if you were
3065 to echo the option name into
3067 /sys/kernel/debug/tracing/trace_options
3069 For example, to enable stacktrace option (to dump the
3070 stack trace of each event), add to the command line:
3072 trace_options=stacktrace
3074 See also Documentation/trace/ftrace.txt "trace options"
3077 transparent_hugepage=
3079 Format: [always|madvise|never]
3080 Can be used to control the default behavior of the system
3081 with respect to transparent hugepages.
3082 See Documentation/vm/transhuge.txt for more details.
3084 tsc= Disable clocksource stability checks for TSC.
3086 [x86] reliable: mark tsc clocksource as reliable, this
3087 disables clocksource verification at runtime, as well
3088 as the stability checks done at bootup. Used to enable
3089 high-resolution timer mode on older hardware, and in
3090 virtualized environment.
3091 [x86] noirqtime: Do not use TSC to do irq accounting.
3092 Used to run time disable IRQ_TIME_ACCOUNTING on any
3093 platforms where RDTSC is slow and this accounting
3096 turbografx.map[2|3]= [HW,JOY]
3097 TurboGraFX parallel port interface
3099 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3100 See also Documentation/input/joystick-parport.txt
3102 udbg-immortal [PPC] When debugging early kernel crashes that
3103 happen after console_init() and before a proper
3104 console driver takes over, this boot options might
3105 help "seeing" what's going on.
3107 uhash_entries= [KNL,NET]
3108 Set number of hash buckets for UDP/UDP-Lite connections
3111 [USB] Ignore overcurrent events (default N).
3112 Some badly-designed motherboards generate lots of
3113 bogus events, for ports that aren't wired to
3114 anything. Set this parameter to avoid log spamming.
3115 Note that genuine overcurrent events won't be
3119 [X86] Cause panic on unknown NMI.
3121 usbcore.authorized_default=
3122 [USB] Default USB device authorization:
3123 (default -1 = authorized except for wireless USB,
3124 0 = not authorized, 1 = authorized)
3126 usbcore.autosuspend=
3127 [USB] The autosuspend time delay (in seconds) used
3128 for newly-detected USB devices (default 2). This
3129 is the time required before an idle device will be
3130 autosuspended. Devices for which the delay is set
3131 to a negative value won't be autosuspended at all.
3133 usbcore.usbfs_snoop=
3134 [USB] Set to log all usbfs traffic (default 0 = off).
3136 usbcore.blinkenlights=
3137 [USB] Set to cycle leds on hubs (default 0 = off).
3139 usbcore.old_scheme_first=
3140 [USB] Start with the old device initialization
3141 scheme (default 0 = off).
3143 usbcore.usbfs_memory_mb=
3144 [USB] Memory limit (in MB) for buffers allocated by
3145 usbfs (default = 16, 0 = max = 2047).
3147 usbcore.use_both_schemes=
3148 [USB] Try the other device initialization scheme
3149 if the first one fails (default 1 = enabled).
3151 usbcore.initial_descriptor_timeout=
3152 [USB] Specifies timeout for the initial 64-byte
3153 USB_REQ_GET_DESCRIPTOR request in milliseconds
3154 (default 5000 = 5.0 seconds).
3157 [USBHID] The interval which mice are to be polled at.
3159 usb-storage.delay_use=
3160 [UMS] The delay in seconds before a new device is
3161 scanned for Logical Units (default 5).
3164 [UMS] A list of quirks entries to supplement or
3165 override the built-in unusual_devs list. List
3166 entries are separated by commas. Each entry has
3167 the form VID:PID:Flags where VID and PID are Vendor
3168 and Product ID values (4-digit hex numbers) and
3169 Flags is a set of characters, each corresponding
3170 to a common usb-storage quirk flag as follows:
3171 a = SANE_SENSE (collect more than 18 bytes
3173 b = BAD_SENSE (don't collect more than 18
3174 bytes of sense data);
3175 c = FIX_CAPACITY (decrease the reported
3176 device capacity by one sector);
3177 d = NO_READ_DISC_INFO (don't use
3178 READ_DISC_INFO command);
3179 e = NO_READ_CAPACITY_16 (don't use
3180 READ_CAPACITY_16 command);
3181 h = CAPACITY_HEURISTICS (decrease the
3182 reported device capacity by one
3183 sector if the number is odd);
3184 i = IGNORE_DEVICE (don't bind to this
3186 l = NOT_LOCKABLE (don't try to lock and
3187 unlock ejectable media);
3188 m = MAX_SECTORS_64 (don't transfer more
3189 than 64 sectors = 32 KB at a time);
3190 n = INITIAL_READ10 (force a retry of the
3191 initial READ(10) command);
3192 o = CAPACITY_OK (accept the capacity
3193 reported by the device);
3194 p = WRITE_CACHE (the device cache is ON
3196 r = IGNORE_RESIDUE (the device reports
3197 bogus residue values);
3198 s = SINGLE_LUN (the device has only one
3200 w = NO_WP_DETECT (don't test whether the
3201 medium is write-protected).
3202 Example: quirks=0419:aaf5:rl,0421:0433:rc
3204 user_debug= [KNL,ARM]
3206 See arch/arm/Kconfig.debug help text.
3207 1 - undefined instruction events
3209 4 - invalid data aborts
3212 Example: user_debug=31
3215 [X86] Flags controlling user PTE allocations.
3217 nohigh = do not allocate PTE pages in
3218 HIGHMEM regardless of setting
3222 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3223 vdso=1: enable VDSO (default)
3224 vdso=0: disable VDSO mapping
3227 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3228 vdso32=1: enable 32-bit VDSO (default)
3229 vdso32=0: disable 32-bit VDSO mapping
3232 vector=percpu: enable percpu vector domain
3234 video= [FB] Frame buffer configuration
3235 See Documentation/fb/modedb.txt.
3238 [VMMIO] Memory mapped virtio (platform) device.
3240 <size>@<baseaddr>:<irq>[:<id>]
3242 <size> := size (can use standard suffixes
3244 <baseaddr> := physical base address
3245 <irq> := interrupt number (as passed to
3247 <id> := (optional) platform device id
3249 virtio_mmio.device=1K@0x100b0000:48:7
3251 Can be used multiple times for multiple devices.
3253 vga= [BOOT,X86-32] Select a particular video mode
3254 See Documentation/x86/boot.txt and
3255 Documentation/svga.txt.
3256 Use vga=ask for menu.
3257 This is actually a boot loader parameter; the value is
3258 passed to the kernel using a special protocol.
3260 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3261 size of <nn>. This can be used to increase the
3262 minimum size (128MB on x86). It can also be used to
3263 decrease the size and leave more room for directly
3266 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3269 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3272 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3276 Controls the behavior of vsyscalls (i.e. calls to
3277 fixed addresses of 0xffffffffff600x00 from legacy
3278 code). Most statically-linked binaries and older
3279 versions of glibc use these calls. Because these
3280 functions are at fixed addresses, they make nice
3281 targets for exploits that can control RIP.
3283 emulate [default] Vsyscalls turn into traps and are
3284 emulated reasonably safely.
3286 native Vsyscalls are native syscall instructions.
3287 This is a little bit faster than trapping
3288 and makes a few dynamic recompilers work
3289 better than they would in emulation mode.
3290 It also makes exploits much easier to write.
3292 none Vsyscalls don't work at all. This makes
3293 them quite hard to use for exploits but
3294 might break your system.
3296 vt.cur_default= [VT] Default cursor shape.
3297 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3298 the parameters of the <Esc>[?A;B;Cc escape sequence;
3299 see VGA-softcursor.txt. Default: 2 = underline.
3301 vt.default_blu= [VT]
3302 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3303 Change the default blue palette of the console.
3304 This is a 16-member array composed of values
3307 vt.default_grn= [VT]
3308 Format: <green0>,<green1>,<green2>,...,<green15>
3309 Change the default green palette of the console.
3310 This is a 16-member array composed of values
3313 vt.default_red= [VT]
3314 Format: <red0>,<red1>,<red2>,...,<red15>
3315 Change the default red palette of the console.
3316 This is a 16-member array composed of values
3322 Set system-wide default UTF-8 mode for all tty's.
3323 Default is 1, i.e. UTF-8 mode is enabled for all
3324 newly opened terminals.
3326 vt.global_cursor_default=
3329 Set system-wide default for whether a cursor
3330 is shown on new VTs. Default is -1,
3331 i.e. cursors will be created by default unless
3332 overridden by individual drivers. 0 will hide
3333 cursors, 1 will display them.
3335 watchdog timers [HW,WDT] For information on watchdog timers,
3336 see Documentation/watchdog/watchdog-parameters.txt
3337 or other driver-specific files in the
3338 Documentation/watchdog/ directory.
3340 workqueue.disable_numa
3341 By default, all work items queued to unbound
3342 workqueues are affine to the NUMA nodes they're
3343 issued on, which results in better behavior in
3344 general. If NUMA affinity needs to be disabled for
3345 whatever reason, this option can be used. Note
3346 that this also can be controlled per-workqueue for
3347 workqueues visible under /sys/bus/workqueue/.
3349 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3350 default x2apic cluster mode on platforms
3353 x86_mrst_timer= [X86-32,APBT]
3354 Choose timer option for x86 Moorestown MID platform.
3355 Two valid options are apbt timer only and lapic timer
3356 plus one apbt timer for broadcast timer.
3357 x86_mrst_timer=apbt_only | lapic_and_apbt
3359 xen_emul_unplug= [HW,X86,XEN]
3360 Unplug Xen emulated devices
3361 Format: [unplug0,][unplug1]
3362 ide-disks -- unplug primary master IDE devices
3363 aux-ide-disks -- unplug non-primary-master IDE devices
3364 nics -- unplug network devices
3365 all -- unplug all emulated devices (NICs and IDE disks)
3366 unnecessary -- unplugging emulated devices is
3367 unnecessary even if the host did not respond to
3369 never -- do not unplug even if version check succeeds
3371 xirc2ps_cs= [NET,PCMCIA]
3373 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3375 ______________________________________________________________________
3379 Add more DRM drivers.
projects / firefly-linux-kernel-4.4.55.git / blob