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 DRM Direct Rendering Management support is enabled.
48 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
49 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
50 EFI EFI Partitioning (GPT) is enabled
51 EIDE EIDE/ATAPI support is enabled.
52 EVM Extended Verification Module
53 FB The frame buffer device is enabled.
54 FTRACE Function tracing enabled.
55 GCOV GCOV profiling is enabled.
56 HW Appropriate hardware is enabled.
57 IA-64 IA-64 architecture is enabled.
58 IMA Integrity measurement architecture is enabled.
59 IOSCHED More than one I/O scheduler is enabled.
60 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
61 IPV6 IPv6 support is enabled.
62 ISAPNP ISA PnP code is enabled.
63 ISDN Appropriate ISDN support is enabled.
64 JOY Appropriate joystick support is enabled.
65 KGDB Kernel debugger support is enabled.
66 KVM Kernel Virtual Machine support is enabled.
67 LIBATA Libata driver is enabled
68 LP Printer support is enabled.
69 LOOP Loopback device support is enabled.
70 M68k M68k architecture is enabled.
71 These options have more detailed description inside of
72 Documentation/m68k/kernel-options.txt.
73 MDA MDA console support is enabled.
74 MIPS MIPS architecture is enabled.
75 MOUSE Appropriate mouse support is enabled.
76 MSI Message Signaled Interrupts (PCI).
77 MTD MTD (Memory Technology Device) support is enabled.
78 NET Appropriate network support is enabled.
79 NUMA NUMA support is enabled.
80 NFS Appropriate NFS support is enabled.
81 OSS OSS sound support is enabled.
82 PV_OPS A paravirtualized kernel is enabled.
83 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
84 PARISC The PA-RISC architecture is enabled.
85 PCI PCI bus support is enabled.
86 PCIE PCI Express support is enabled.
87 PCMCIA The PCMCIA subsystem is enabled.
88 PNP Plug & Play support is enabled.
89 PPC PowerPC architecture is enabled.
90 PPT Parallel port support is enabled.
91 PS2 Appropriate PS/2 support is enabled.
92 RAM RAM disk support is enabled.
93 S390 S390 architecture is enabled.
94 SCSI Appropriate SCSI support is enabled.
95 A lot of drivers have their options described inside
96 the Documentation/scsi/ sub-directory.
97 SECURITY Different security models are enabled.
98 SELINUX SELinux support is enabled.
99 APPARMOR AppArmor support is enabled.
100 SERIAL Serial support is enabled.
101 SH SuperH architecture is enabled.
102 SMP The kernel is an SMP kernel.
103 SPARC Sparc architecture is enabled.
104 SWSUSP Software suspend (hibernation) is enabled.
105 SUSPEND System suspend states are enabled.
106 TPM TPM drivers are enabled.
107 TS Appropriate touchscreen support is enabled.
108 UMS USB Mass Storage support is enabled.
109 USB USB support is enabled.
110 USBHID USB Human Interface Device support is enabled.
111 V4L Video For Linux support is enabled.
112 VMMIO Driver for memory mapped virtio devices is enabled.
113 VGA The VGA console has been enabled.
114 VT Virtual terminal support is enabled.
115 WDT Watchdog support is enabled.
116 XT IBM PC/XT MFM hard disk support is enabled.
117 X86-32 X86-32, aka i386 architecture is enabled.
118 X86-64 X86-64 architecture is enabled.
119 More X86-64 boot options can be found in
120 Documentation/x86/x86_64/boot-options.txt .
121 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
122 XEN Xen support is enabled
124 In addition, the following text indicates that the option:
126 BUGS= Relates to possible processor bugs on the said processor.
127 KNL Is a kernel start-up parameter.
128 BOOT Is a boot loader parameter.
130 Parameters denoted with BOOT are actually interpreted by the boot
131 loader, and have no meaning to the kernel directly.
132 Do not modify the syntax of boot loader parameters without extreme
133 need or coordination with <Documentation/x86/boot.txt>.
135 There are also arch-specific kernel-parameters not documented here.
136 See for example <Documentation/x86/x86_64/boot-options.txt>.
138 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
139 a trailing = on the name of any parameter states that that parameter will
140 be entered as an environment variable, whereas its absence indicates that
141 it will appear as a kernel argument readable via /proc/cmdline by programs
142 running once the system is up.
144 The number of kernel parameters is not limited, but the length of the
145 complete command line (parameters including spaces etc.) is limited to
146 a fixed number of characters. This limit depends on the architecture
147 and is between 256 and 4096 characters. It is defined in the file
148 ./include/asm/setup.h as COMMAND_LINE_SIZE.
150 Finally, the [KMG] suffix is commonly described after a number of kernel
151 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
152 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
153 bytes respectively. Such letter suffixes can also be entirely omitted.
157 Advanced Configuration and Power Interface
158 Format: { force | off | strict | noirq | rsdt }
159 force -- enable ACPI if default was off
160 off -- disable ACPI if default was on
161 noirq -- do not use ACPI for IRQ routing
162 strict -- Be less tolerant of platforms that are not
163 strictly ACPI specification compliant.
164 rsdt -- prefer RSDT over (default) XSDT
165 copy_dsdt -- copy DSDT to memory
167 See also Documentation/power/runtime_pm.txt, pci=noacpi
169 acpi_rsdp= [ACPI,EFI,KEXEC]
170 Pass the RSDP address to the kernel, mostly used
171 on machines running EFI runtime service to boot the
172 second kernel for kdump.
174 acpi_apic_instance= [ACPI, IOAPIC]
176 2: use 2nd APIC table, if available
177 1,0: use 1st APIC table
180 acpi_backlight= [HW,ACPI]
181 acpi_backlight=vendor
183 If set to vendor, prefer vendor specific driver
184 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
185 of the ACPI video.ko driver.
187 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
188 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
190 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
191 debug output. Bits in debug_layer correspond to a
192 _COMPONENT in an ACPI source file, e.g.,
193 #define _COMPONENT ACPI_PCI_COMPONENT
194 Bits in debug_level correspond to a level in
195 ACPI_DEBUG_PRINT statements, e.g.,
196 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
197 The debug_level mask defaults to "info". See
198 Documentation/acpi/debug.txt for more information about
199 debug layers and levels.
201 Enable processor driver info messages:
202 acpi.debug_layer=0x20000000
203 Enable PCI/PCI interrupt routing info messages:
204 acpi.debug_layer=0x400000
205 Enable AML "Debug" output, i.e., stores to the Debug
206 object while interpreting AML:
207 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
208 Enable all messages related to ACPI hardware:
209 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
211 Some values produce so much output that the system is
212 unusable. The "log_buf_len" parameter may be useful
213 if you need to capture more output.
215 acpi_irq_balance [HW,ACPI]
216 ACPI will balance active IRQs
219 acpi_irq_nobalance [HW,ACPI]
220 ACPI will not move active IRQs (default)
223 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
224 Format: <irq>,<irq>...
226 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
228 Format: <irq>,<irq>...
230 acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
232 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
233 Format: To spoof as Windows 98: ="Microsoft Windows"
235 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
236 acpi_osi="string1" # add string1 -- only one string
237 acpi_osi="!string2" # remove built-in string2
238 acpi_osi= # disable all strings
241 Override the pmtimer bug detection: force the kernel
242 to assume that this machine's pmtimer latches its value
243 and always returns good values.
245 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
246 Format: { level | edge | high | low }
248 acpi_serialize [HW,ACPI] force serialization of AML methods
250 acpi_skip_timer_override [HW,ACPI]
251 Recognize and ignore IRQ0/pin2 Interrupt Override.
252 For broken nForce2 BIOS resulting in XT-PIC timer.
254 acpi_sleep= [HW,ACPI] Sleep options
255 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
256 old_ordering, nonvs, sci_force_enable }
257 See Documentation/power/video.txt for information on
259 s3_beep is for debugging; it makes the PC's speaker beep
260 as soon as the kernel's real-mode entry point is called.
261 s4_nohwsig prevents ACPI hardware signature from being
262 used during resume from hibernation.
263 old_ordering causes the ACPI 1.0 ordering of the _PTS
264 control method, with respect to putting devices into
265 low power states, to be enforced (the ACPI 2.0 ordering
266 of _PTS is used by default).
267 nonvs prevents the kernel from saving/restoring the
268 ACPI NVS memory during suspend/hibernation and resume.
269 sci_force_enable causes the kernel to set SCI_EN directly
270 on resume from S1/S3 (which is against the ACPI spec,
271 but some broken systems don't work without it).
273 acpi_use_timer_override [HW,ACPI]
274 Use timer override. For some broken Nvidia NF5 boards
275 that require a timer override, but don't have HPET
277 acpi_enforce_resources= [ACPI]
278 { strict | lax | no }
279 Check for resource conflicts between native drivers
280 and ACPI OperationRegions (SystemIO and SystemMemory
281 only). IO ports and memory declared in ACPI might be
282 used by the ACPI subsystem in arbitrary AML code and
283 can interfere with legacy drivers.
284 strict (default): access to resources claimed by ACPI
285 is denied; legacy drivers trying to access reserved
286 resources will fail to bind to device using them.
287 lax: access to resources claimed by ACPI is allowed;
288 legacy drivers trying to access reserved resources
289 will bind successfully but a warning message is logged.
290 no: ACPI OperationRegions are not marked as reserved,
291 no further checks are performed.
293 add_efi_memmap [EFI; X86] Include EFI memory map in
294 kernel's map of available physical RAM.
297 { off | try_unsupported }
298 off: disable AGP support
299 try_unsupported: try to drive unsupported chipsets
300 (may crash computer or cause data corruption)
303 See Documentation/sound/alsa/alsa-parameters.txt
306 Allow the default userspace alignment fault handler
307 behaviour to be specified. Bit 0 enables warnings,
308 bit 1 enables fixups, and bit 2 sends a segfault.
310 align_va_addr= [X86-64]
311 Align virtual addresses by clearing slice [14:12] when
312 allocating a VMA at process creation time. This option
313 gives you up to 3% performance improvement on AMD F15h
314 machines (where it is enabled by default) for a
315 CPU-intensive style benchmark, and it can vary highly in
316 a microbenchmark depending on workload and compiler.
318 32: only for 32-bit processes
319 64: only for 64-bit processes
320 on: enable for both 32- and 64-bit processes
321 off: disable for both 32- and 64-bit processes
323 amd_iommu= [HW,X86-64]
324 Pass parameters to the AMD IOMMU driver in the system.
326 fullflush - enable flushing of IO/TLB entries when
327 they are unmapped. Otherwise they are
328 flushed before they will be reused, which
330 off - do not initialize any AMD IOMMU found in
332 force_isolation - Force device isolation for all
333 devices. The IOMMU driver is not
334 allowed anymore to lift isolation
335 requirements as needed. This option
336 does not override iommu=pt
338 amd_iommu_dump= [HW,X86-64]
339 Enable AMD IOMMU driver option to dump the ACPI table
340 for AMD IOMMU. With this option enabled, AMD IOMMU
341 driver will print ACPI tables for AMD IOMMU during
342 IOMMU initialization.
344 amijoy.map= [HW,JOY] Amiga joystick support
345 Map of devices attached to JOY0DAT and JOY1DAT
347 See also Documentation/input/joystick.txt
349 analog.map= [HW,JOY] Analog joystick and gamepad support
350 Specifies type or capabilities of an analog joystick
351 connected to one of 16 gameports
352 Format: <type1>,<type2>,..<type16>
355 Power management functions (SPARCstation-4/5 + deriv.)
357 Disable APC CPU standby support. SPARCstation-Fox does
358 not play well with APC CPU idle - disable it if you have
359 APC and your system crashes randomly.
361 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
362 Change the output verbosity whilst booting
363 Format: { quiet (default) | verbose | debug }
364 Change the amount of debugging information output
365 when initialising the APIC and IO-APIC components.
368 See Documentation/networking/ipv6.txt.
370 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
371 Limit apic dumping. The parameter defines the maximal
372 number of local apics being dumped. Also it is possible
373 to set it to "all" by meaning -- no limit here.
374 Format: { 1 (default) | 2 | ... | all }.
375 The parameter valid if only apic=debug or
376 apic=verbose is specified.
377 Example: apic=debug show_lapic=all
379 apm= [APM] Advanced Power Management
380 See header of arch/x86/kernel/apm_32.c.
382 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
383 Format: <io>,<irq>,<nodeID>
387 atarimouse= [HW,MOUSE] Atari Mouse
389 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
390 EzKey and similar keyboards
392 atkbd.reset= [HW] Reset keyboard during initialization
394 atkbd.set= [HW] Select keyboard code set
395 Format: <int> (2 = AT (default), 3 = PS/2)
397 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
400 atkbd.softraw= [HW] Choose between synthetic and real raw mode
401 Format: <bool> (0 = real, 1 = synthetic (default))
403 atkbd.softrepeat= [HW]
404 Use software keyboard repeat
406 baycom_epp= [HW,AX25]
409 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
411 See header of drivers/net/hamradio/baycom_par.c.
413 baycom_ser_fdx= [HW,AX25]
414 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
415 Format: <io>,<irq>,<mode>[,<baud>]
416 See header of drivers/net/hamradio/baycom_ser_fdx.c.
418 baycom_ser_hdx= [HW,AX25]
419 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
420 Format: <io>,<irq>,<mode>
421 See header of drivers/net/hamradio/baycom_ser_hdx.c.
423 boot_delay= Milliseconds to delay each printk during boot.
424 Values larger than 10 seconds (10000) are changed to
428 bootmem_debug [KNL] Enable bootmem allocator debug messages.
430 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
431 bttv.radio= Most important insmod options are available as
433 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
436 bulk_remove=off [PPC] This parameter disables the use of the pSeries
437 firmware feature for flushing multiple hpte entries
440 c101= [NET] Moxa C101 synchronous serial card
442 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
443 Sometimes CPU hardware bugs make them report the cache
444 size incorrectly. The kernel will attempt work arounds
445 to fix known problems, but for some CPUs it is not
446 possible to determine what the correct size should be.
447 This option provides an override for these situations.
449 ccw_timeout_log [S390]
450 See Documentation/s390/CommonIO for details.
452 cgroup_disable= [KNL] Disable a particular controller
453 Format: {name of the controller(s) to disable}
454 {Currently supported controllers - "memory"}
456 checkreqprot [SELINUX] Set initial checkreqprot flag value.
457 Format: { "0" | "1" }
458 See security/selinux/Kconfig help text.
459 0 -- check protection applied by kernel (includes
460 any implied execute protection).
461 1 -- check protection requested by application.
462 Default value is set via a kernel config option.
463 Value can be changed at runtime via
464 /selinux/checkreqprot.
467 See Documentation/s390/CommonIO for details.
469 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
471 Forces specified clocksource (if available) to be used
472 when calculating gettimeofday(). If specified
473 clocksource is not available, it defaults to PIT.
474 Format: { pit | tsc | cyclone | pmtmr }
476 clocksource= Override the default clocksource
478 Override the default clocksource and use the clocksource
479 with the name specified.
480 Some clocksource names to choose from, depending on
482 [all] jiffies (this is the base, fallback clocksource)
484 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
485 pxa_timer,timer3,32k_counter,timer0_1
487 [X86-32] pit,hpet,tsc;
488 scx200_hrt on Geode; cyclone on IBM x440
496 clearcpuid=BITNUM [X86]
497 Disable CPUID feature X for the kernel. See
498 arch/x86/include/asm/cpufeature.h for the valid bit
499 numbers. Note the Linux specific bits are not necessarily
500 stable over kernel options, but the vendor specific
502 Also note that user programs calling CPUID directly
503 or using the feature without checking anything
504 will still see it. This just prevents it from
505 being used by the kernel or shown in /proc/cpuinfo.
506 Also note the kernel might malfunction if you disable
510 Sets the size of kernel global memory area for contiguous
511 memory allocations. For more information, see
512 include/linux/dma-contiguous.h
514 cmo_free_hint= [PPC] Format: { yes | no }
515 Specify whether pages are marked as being inactive
516 when they are freed. This is used in CMO environments
517 to determine OS memory pressure for page stealing by
521 coherent_pool=nn[KMG] [ARM,KNL]
522 Sets the size of memory pool for coherent, atomic dma
523 allocations, by default set to 256K.
525 code_bytes [X86] How many bytes of object code to print
530 com20020= [HW,NET] ARCnet - COM20020 chipset
532 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
534 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
538 ARCnet - COM90xx chipset (memory-mapped buffers)
539 Format: <io>[,<irq>[,<memstart>]]
541 condev= [HW,S390] console device
544 console= [KNL] Output console device and options.
546 tty<n> Use the virtual console device <n>.
550 Use the specified serial port. The options are of
551 the form "bbbbpnf", where "bbbb" is the baud rate,
552 "p" is parity ("n", "o", or "e"), "n" is number of
553 bits, and "f" is flow control ("r" for RTS or
554 omit it). Default is "9600n8".
556 See Documentation/serial-console.txt for more
558 Documentation/networking/netconsole.txt for an
561 uart[8250],io,<addr>[,options]
562 uart[8250],mmio,<addr>[,options]
563 Start an early, polled-mode console on the 8250/16550
564 UART at the specified I/O port or MMIO address,
565 switching to the matching ttyS device later. The
566 options are the same as for ttyS, above.
567 hvc<n> Use the hypervisor console device <n>. This is for
568 both Xen and PowerPC hypervisors.
570 If the device connected to the port is not a TTY but a braille
571 device, prepend "brl," before the device type, for instance
573 For now, only VisioBraille is supported.
575 consoleblank= [KNL] The console blank (screen saver) timeout in
576 seconds. Defaults to 10*60 = 10mins. A value of 0
577 disables the blank timer.
580 [KNL] Change the default value for
581 /proc/<pid>/coredump_filter.
582 See also Documentation/filesystems/proc.txt.
584 cpuidle.off=1 [CPU_IDLE]
585 disable the cpuidle sub-system
587 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
589 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
591 crashkernel=size[KMG][@offset[KMG]]
592 [KNL] Using kexec, Linux can switch to a 'crash kernel'
593 upon panic. This parameter reserves the physical
594 memory region [offset, offset + size] for that kernel
595 image. If '@offset' is omitted, then a suitable offset
596 is selected automatically. Check
597 Documentation/kdump/kdump.txt for further details.
599 crashkernel_low=size[KMG]
600 [KNL, x86] parts under 4G.
602 crashkernel=range1:size1[,range2:size2,...][@offset]
603 [KNL] Same as above, but depends on the memory
604 in the running system. The syntax of range is
605 start-[end] where start and end are both
606 a memory unit (amount[KMG]). See also
607 Documentation/kdump/kdump.txt for an example.
612 cs89x0_media= [HW,NET]
613 Format: { rj45 | aui | bnc }
616 See header of drivers/s390/block/dasd_devmap.c.
618 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
619 (one device per port)
620 Format: <port#>,<type>
621 See also Documentation/input/joystick-parport.txt
623 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
624 time. See Documentation/dynamic-debug-howto.txt for
625 details. Deprecated, see dyndbg.
627 debug [KNL] Enable kernel debugging (events log level).
630 [KNL] verbose self-tests
632 Print debugging info while doing the locking API
634 We default to 0 (no extra messages), setting it to
635 1 will print _a lot_ more information - normally
636 only useful to kernel developers.
638 debug_objects [KNL] Enable object debugging
641 [KNL] Disable object debugging
643 debug_guardpage_minorder=
644 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
645 parameter allows control of the order of pages that will
646 be intentionally kept free (and hence protected) by the
647 buddy allocator. Bigger value increase the probability
648 of catching random memory corruption, but reduce the
649 amount of memory for normal system use. The maximum
650 possible value is MAX_ORDER/2. Setting this parameter
651 to 1 or 2 should be enough to identify most random
652 memory corruption problems caused by bugs in kernel or
653 driver code when a CPU writes to (or reads from) a
654 random memory location. Note that there exists a class
655 of memory corruptions problems caused by buggy H/W or
656 F/W or by drivers badly programing DMA (basically when
657 memory is written at bus level and the CPU MMU is
658 bypassed) which are not detectable by
659 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
660 tracking down these problems.
662 debugpat [X86] Enable PAT debugging
664 decnet.addr= [HW,NET]
665 Format: <area>[,<node>]
666 See also Documentation/networking/decnet.txt.
669 [same as hugepagesz=] The size of the default
670 HugeTLB page size. This is the size represented by
671 the legacy /proc/ hugepages APIs, used for SHM, and
672 default size when mounting hugetlbfs filesystems.
673 Defaults to the default architecture's huge page size
677 Set number of hash buckets for dentry cache.
680 IO parameters + enable/disable command.
682 digiepca= [HW,SERIAL]
683 See drivers/char/README.epca and
684 Documentation/serial/digiepca.txt.
687 See Documentation/networking/ipv6.txt.
689 disable_ddw [PPC/PSERIES]
690 Disable Dynamic DMA Window support. Use this if
691 to workaround buggy firmware.
694 See Documentation/networking/ipv6.txt.
696 disable_mtrr_cleanup [X86]
697 The kernel tries to adjust MTRR layout from continuous
698 to discrete, to make X server driver able to add WB
699 entry later. This parameter disables that.
701 disable_mtrr_trim [X86, Intel and AMD only]
702 By default the kernel will trim any uncacheable
703 memory out of your available memory pool based on
704 MTRR settings. This parameter disables that behavior,
705 possibly causing your machine to run very slowly.
707 disable_timer_pin_1 [X86]
708 Disable PIN 1 of APIC timer
709 Can be useful to work around chipset bugs.
711 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
712 this option disables the debugging code at boot.
714 dma_debug_entries=<number>
715 This option allows to tune the number of preallocated
716 entries for DMA-API debugging code. One entry is
717 required per DMA-API allocation. Use this if the
718 DMA-API debugging code disables itself because the
719 architectural default is too low.
721 dma_debug_driver=<driver_name>
722 With this option the DMA-API debugging driver
723 filter feature can be enabled at boot time. Just
724 pass the driver to filter for as the parameter.
725 The filter can be disabled or changed to another
726 driver later using sysfs.
728 drm_kms_helper.edid_firmware=[<connector>:]<file>
729 Broken monitors, graphic adapters and KVMs may
730 send no or incorrect EDID data sets. This parameter
731 allows to specify an EDID data set in the
732 /lib/firmware directory that is used instead.
733 Generic built-in EDID data sets are used, if one of
734 edid/1024x768.bin, edid/1280x1024.bin,
735 edid/1680x1050.bin, or edid/1920x1080.bin is given
736 and no file with the same name exists. Details and
737 instructions how to build your own EDID data are
738 available in Documentation/EDID/HOWTO.txt. An EDID
739 data set will only be used for a particular connector,
740 if its name and a colon are prepended to the EDID
745 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
746 module.dyndbg[="val"]
747 Enable debug messages at boot time. See
748 Documentation/dynamic-debug-howto.txt for details.
750 earlycon= [KNL] Output early console device and options.
751 uart[8250],io,<addr>[,options]
752 uart[8250],mmio,<addr>[,options]
753 uart[8250],mmio32,<addr>[,options]
754 Start an early, polled-mode console on the 8250/16550
755 UART at the specified I/O port or MMIO address.
756 MMIO inter-register address stride is either 8-bit
757 (mmio) or 32-bit (mmio32).
758 The options are the same as for ttyS, above.
760 earlyprintk= [X86,SH,BLACKFIN]
763 earlyprintk=serial[,ttySn[,baudrate]]
764 earlyprintk=ttySn[,baudrate]
765 earlyprintk=dbgp[debugController#]
767 Append ",keep" to not disable it when the real console
770 Only vga or serial or usb debug port at a time.
772 Currently only ttyS0 and ttyS1 are supported.
774 Interaction with the standard serial driver is not
777 The VGA output is eventually overwritten by the real
780 The xen output can only be used by Xen PV guests.
782 ekgdboc= [X86,KGDB] Allow early kernel console debugging
785 This is designed to be used in conjunction with
786 the boot argument: earlyprintk=vga
789 Format: {"off" | "on" | "skip[mbr]"}
791 eisa_irq_edge= [PARISC,HW]
792 See header of drivers/parisc/eisa.c.
795 See comment before function elanfreq_setup() in
796 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
799 Format: {"cfq" | "deadline" | "noop"}
800 See Documentation/block/cfq-iosched.txt and
801 Documentation/block/deadline-iosched.txt for details.
803 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
804 Specifies physical address of start of kernel core
805 image elf header and optionally the size. Generally
806 kexec loader will pass this option to capture kernel.
807 See Documentation/kdump/kdump.txt for details.
809 enable_mtrr_cleanup [X86]
810 The kernel tries to adjust MTRR layout from continuous
811 to discrete, to make X server driver able to add WB
812 entry later. This parameter enables that.
814 enable_timer_pin_1 [X86]
815 Enable PIN 1 of APIC timer
816 Can be useful to work around chipset bugs
817 (in particular on some ATI chipsets).
818 The kernel tries to set a reasonable default.
820 enforcing [SELINUX] Set initial enforcing status.
822 See security/selinux/Kconfig help text.
823 0 -- permissive (log only, no denials).
824 1 -- enforcing (deny and log).
826 Value can be changed at runtime via /selinux/enforce.
829 Disable Error Record Serialization Table (ERST)
832 ether= [HW,NET] Ethernet cards parameters
833 This option is obsoleted by the "netdev=" option, which
834 has equivalent usage. See its documentation for details.
838 Permit 'security.evm' to be updated regardless of
839 current integrity status.
843 fail_make_request=[KNL]
844 General fault injection mechanism.
845 Format: <interval>,<probability>,<space>,<times>
846 See also Documentation/fault-injection/.
849 See Documentation/blockdev/floppy.txt.
851 force_pal_cache_flush
852 [IA-64] Avoid check_sal_cache_flush which may hang on
853 buggy SAL_CACHE_FLUSH implementations. Using this
854 parameter will force ia64_sal_cache_flush to call
855 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
858 [FTRACE] will set and start the specified tracer
859 as early as possible in order to facilitate early
862 ftrace_dump_on_oops[=orig_cpu]
863 [FTRACE] will dump the trace buffers on oops.
864 If no parameter is passed, ftrace will dump
865 buffers of all CPUs, but if you pass orig_cpu, it will
866 dump only the buffer of the CPU that triggered the
869 ftrace_filter=[function-list]
870 [FTRACE] Limit the functions traced by the function
871 tracer at boot up. function-list is a comma separated
872 list of functions. This list can be changed at run
873 time by the set_ftrace_filter file in the debugfs
876 ftrace_notrace=[function-list]
877 [FTRACE] Do not trace the functions specified in
878 function-list. This list can be changed at run time
879 by the set_ftrace_notrace file in the debugfs
882 ftrace_graph_filter=[function-list]
883 [FTRACE] Limit the top level callers functions traced
884 by the function graph tracer at boot up.
885 function-list is a comma separated list of functions
886 that can be changed at run time by the
887 set_graph_function file in the debugfs tracing directory.
890 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
891 support via parallel port (up to 5 devices per port)
892 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
893 See also Documentation/input/joystick-parport.txt
897 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
901 gcov_persist= [GCOV] When non-zero (default), profiling data for
902 kernel modules is saved and remains accessible via
903 debugfs, even when the module is unloaded/reloaded.
904 When zero, profiling data is discarded and associated
905 debugfs files are removed at module unload time.
907 gpt [EFI] Forces disk with valid GPT signature but
908 invalid Protective MBR to be treated as GPT.
910 grcan.enable0= [HW] Configuration of physical interface 0. Determines
911 the "Enable 0" bit of the configuration register.
914 grcan.enable1= [HW] Configuration of physical interface 1. Determines
915 the "Enable 0" bit of the configuration register.
918 grcan.select= [HW] Select which physical interface to use.
921 grcan.txsize= [HW] Sets the size of the tx buffer.
922 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
924 grcan.rxsize= [HW] Sets the size of the rx buffer.
925 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
928 hashdist= [KNL,NUMA] Large hashes allocated during boot
929 are distributed across NUMA nodes. Defaults on
930 for 64-bit NUMA, off otherwise.
931 Format: 0 | 1 (for off | on)
933 hcl= [IA-64] SGI's Hardware Graph compatibility layer
935 hd= [EIDE] (E)IDE hard drive subsystem geometry
936 Format: <cyl>,<head>,<sect>
939 Disable Hardware Error Source Table (HEST) support;
940 corresponding firmware-first mode error processing
941 logic will be disabled.
943 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
944 size of <nn>. This works even on boxes that have no
945 highmem otherwise. This also works to reduce highmem
946 size on bigger boxes.
948 highres= [KNL] Enable/disable high resolution timer mode.
949 Valid parameters: "on", "off"
953 See Documentation/isdn/README.HiSax.
957 hpet= [X86-32,HPET] option to control HPET usage
958 Format: { enable (default) | disable | force |
960 disable: disable HPET and use PIT instead
961 force: allow force enabled of undocumented chips (ICH4,
963 verbose: show contents of HPET registers during setup
965 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
966 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
967 On x86-64 and powerpc, this option can be specified
968 multiple times interleaved with hugepages= to reserve
969 huge pages of different sizes. Valid pages sizes on
970 x86-64 are 2M (when the CPU supports "pse") and 1G
971 (when the CPU supports the "pdpe1gb" cpuinfo flag)
972 Note that 1GB pages can only be allocated at boot time
973 using hugepages= and not freed afterwards.
975 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
976 terminal devices. Valid values: 0..8
977 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
978 If specified, z/VM IUCV HVC accepts connections
979 from listed z/VM user IDs only.
982 Do not unregister boot console at start. This is only
983 useful for debugging when something happens in the window
984 between unregistering the boot console and initializing
987 i2c_bus= [HW] Override the default board specific I2C bus speed
988 or register an additional I2C bus that is not
989 registered from board initialization code.
993 i8042.debug [HW] Toggle i8042 debug mode
994 i8042.direct [HW] Put keyboard port into non-translated mode
995 i8042.dumbkbd [HW] Pretend that controller can only read data from
996 keyboard and cannot control its state
997 (Don't attempt to blink the leds)
998 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
999 i8042.nokbd [HW] Don't check/create keyboard port
1000 i8042.noloop [HW] Disable the AUX Loopback command while probing
1002 i8042.nomux [HW] Don't check presence of an active multiplexing
1004 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1006 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1007 i8042.reset [HW] Reset the controller during init and cleanup
1008 i8042.unlock [HW] Unlock (ignore) the keylock
1012 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1013 indicates that the driver is running on unsupported
1015 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1016 does not match list of supported models.
1018 [HW] Report power status in /proc/i8k
1019 (disabled by default)
1020 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1023 i915.invert_brightness=
1024 [DRM] Invert the sense of the variable that is used to
1025 set the brightness of the panel backlight. Normally a
1026 brightness value of 0 indicates backlight switched off,
1027 and the maximum of the brightness value sets the backlight
1028 to maximum brightness. If this parameter is set to 0
1029 (default) and the machine requires it, or this parameter
1030 is set to 1, a brightness value of 0 sets the backlight
1031 to maximum brightness, and the maximum of the brightness
1032 value switches the backlight off.
1033 -1 -- never invert brightness
1034 0 -- machine default
1035 1 -- force brightness inversion
1038 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1040 ide-core.nodma= [HW] (E)IDE subsystem
1041 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1042 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1043 .cdrom .chs .ignore_cable are additional options
1044 See Documentation/ide/ide.txt.
1046 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1047 Claim all unknown PCI IDE storage controllers.
1050 Format: idle=poll, idle=halt, idle=nomwait
1051 Poll forces a polling idle loop that can slightly
1052 improve the performance of waking up a idle CPU, but
1053 will use a lot of power and make the system run hot.
1055 idle=halt: Halt is forced to be used for CPU idle.
1056 In such case C2/C3 won't be used again.
1057 idle=nomwait: Disable mwait for CPU C-states
1059 ignore_loglevel [KNL]
1060 Ignore loglevel setting - this will print /all/
1061 kernel messages to the console. Useful for debugging.
1062 We also add it as printk module parameter, so users
1063 could change it dynamically, usually by
1064 /sys/module/printk/parameters/ignore_loglevel.
1066 ihash_entries= [KNL]
1067 Set number of hash buckets for inode cache.
1069 ima_appraise= [IMA] appraise integrity measurements
1070 Format: { "off" | "enforce" | "fix" }
1073 ima_appraise_tcb [IMA]
1074 The builtin appraise policy appraises all files
1078 Format: { "0" | "1" }
1079 0 -- integrity auditing messages. (Default)
1080 1 -- enable informational integrity auditing messages.
1083 Format: { "sha1" | "md5" }
1087 Load a policy which meets the needs of the Trusted
1088 Computing Base. This means IMA will measure all
1089 programs exec'd, files mmap'd for exec, and all files
1090 opened for read by uid=0.
1094 Run specified binary instead of /sbin/init as init
1097 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1098 for working out where the kernel is dying during
1101 initrd= [BOOT] Specify the location of the initial ramdisk
1103 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1106 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1108 Enable intel iommu driver.
1110 Disable intel iommu driver.
1111 igfx_off [Default Off]
1112 By default, gfx is mapped as normal device. If a gfx
1113 device has a dedicated DMAR unit, the DMAR unit is
1114 bypassed by not enabling DMAR with this option. In
1115 this case, gfx device will use physical address for
1118 With this option iommu will not optimize to look
1119 for io virtual address below 32-bit forcing dual
1120 address cycle on pci bus for cards supporting greater
1121 than 32-bit addressing. The default is to look
1122 for translation below 32-bit and if not available
1123 then look in the higher range.
1124 strict [Default Off]
1125 With this option on every unmap_single operation will
1126 result in a hardware IOTLB flush operation as opposed
1127 to batching them for performance.
1128 sp_off [Default Off]
1129 By default, super page will be supported if Intel IOMMU
1130 has the capability. With this option, super page will
1133 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1134 0 disables intel_idle and fall back on acpi_idle.
1135 1 to 6 specify maximum depth of C-state.
1139 Do not enable intel_pstate as the default
1140 scaling driver for the supported processors
1142 intremap= [X86-64, Intel-IOMMU]
1143 on enable Interrupt Remapping (default)
1144 off disable Interrupt Remapping
1145 nosid disable Source ID checking
1147 BIOS x2APIC opt-out request will be ignored
1149 iomem= Disable strict checking of access to MMIO memory
1150 strict regions from userspace.
1167 io7= [HW] IO7 for Marvel based alpha systems
1168 See comment before marvel_specify_io7 in
1169 arch/alpha/kernel/core_marvel.c.
1171 io_delay= [X86] I/O delay method
1173 Standard port 0x80 based delay
1175 Alternate port 0xed based delay (needed on some systems)
1177 Simple two microseconds delay
1182 See Documentation/filesystems/nfs/nfsroot.txt.
1184 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1185 See comment before ip2_setup() in
1186 drivers/char/ip2/ip2base.c.
1189 When an interrupt is not handled search all handlers
1190 for it. Intended to get systems with badly broken
1194 When an interrupt is not handled search all handlers
1195 for it. Also check all handlers each timer
1196 interrupt. Intended to get systems with badly broken
1200 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1202 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1204 <cpu number>,...,<cpu number>
1206 <cpu number>-<cpu number>
1207 (must be a positive range in ascending order)
1209 <cpu number>,...,<cpu number>-<cpu number>
1211 This option can be used to specify one or more CPUs
1212 to isolate from the general SMP balancing and scheduling
1213 algorithms. You can move a process onto or off an
1214 "isolated" CPU via the CPU affinity syscalls or cpuset.
1215 <cpu number> begins at 0 and the maximum value is
1216 "number of CPUs in system - 1".
1218 This option is the preferred way to isolate CPUs. The
1219 alternative -- manually setting the CPU mask of all
1220 tasks in the system -- can cause problems and
1221 suboptimal load balancer performance.
1225 js= [HW,JOY] Analog joystick
1226 See Documentation/input/joystick.txt.
1230 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1231 specifies the amount of memory usable by the kernel
1232 for non-movable allocations. The requested amount is
1233 spread evenly throughout all nodes in the system. The
1234 remaining memory in each node is used for Movable
1235 pages. In the event, a node is too small to have both
1236 kernelcore and Movable pages, kernelcore pages will
1237 take priority and other nodes will have a larger number
1238 of kernelcore pages. The Movable zone is used for the
1239 allocation of pages that may be reclaimed or moved
1240 by the page migration subsystem. This means that
1241 HugeTLB pages may not be allocated from this zone.
1242 Note that allocations like PTEs-from-HighMem still
1243 use the HighMem zone if it exists, and the Normal
1244 zone if it does not.
1246 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1247 Format: <Controller#>[,poll interval]
1248 The controller # is the number of the ehci usb debug
1249 port as it is probed via PCI. The poll interval is
1250 optional and is the number seconds in between
1251 each poll cycle to the debug port in case you need
1252 the functionality for interrupting the kernel with
1253 gdb or control-c on the dbgp connection. When
1254 not using this parameter you use sysrq-g to break into
1255 the kernel debugger.
1257 kgdboc= [KGDB,HW] kgdb over consoles.
1258 Requires a tty driver that supports console polling,
1259 or a supported polling keyboard driver (non-usb).
1260 Serial only format: <serial_device>[,baud]
1261 keyboard only format: kbd
1262 keyboard and serial format: kbd,<serial_device>[,baud]
1263 Optional Kernel mode setting:
1264 kms, kbd format: kms,kbd
1265 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1267 kgdbwait [KGDB] Stop kernel execution and enter the
1268 kernel debugger at the earliest opportunity.
1270 kmac= [MIPS] korina ethernet MAC address.
1271 Configure the RouterBoard 532 series on-chip
1272 Ethernet adapter MAC address.
1274 kmemleak= [KNL] Boot-time kmemleak enable/disable
1275 Valid arguments: on, off
1278 kstack=N [X86] Print N words from the kernel stack
1281 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1282 Default is 0 (don't ignore, but inject #GP)
1284 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1288 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1289 Default is 1 (enabled)
1291 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1293 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1295 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1296 (virtualized MMU) support on capable Intel chips.
1297 Default is 1 (enabled)
1299 kvm-intel.emulate_invalid_guest_state=
1300 [KVM,Intel] Enable emulation of invalid guest states
1301 Default is 0 (disabled)
1303 kvm-intel.flexpriority=
1304 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1305 Default is 1 (enabled)
1308 [KVM,Intel] Enable VMX nesting (nVMX).
1309 Default is 0 (disabled)
1311 kvm-intel.unrestricted_guest=
1312 [KVM,Intel] Disable unrestricted guest feature
1313 (virtualized real and unpaged mode) on capable
1314 Intel chips. Default is 1 (enabled)
1316 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1317 feature (tagged TLBs) on capable Intel chips.
1318 Default is 1 (enabled)
1324 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1327 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1328 value for LAPIC timer one-shot implementation. Default
1329 back to the programmable timer unit in the LAPIC.
1331 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1334 libata.dma= [LIBATA] DMA control
1335 libata.dma=0 Disable all PATA and SATA DMA
1336 libata.dma=1 PATA and SATA Disk DMA only
1337 libata.dma=2 ATAPI (CDROM) DMA only
1338 libata.dma=4 Compact Flash DMA only
1339 Combinations also work, so libata.dma=3 enables DMA
1340 for disks and CDROMs, but not CFs.
1342 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1343 libata.ignore_hpa=0 keep BIOS limits (default)
1344 libata.ignore_hpa=1 ignore limits, using full disk
1346 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1350 libata.force= [LIBATA] Force configurations. The format is comma
1351 separated list of "[ID:]VAL" where ID is
1352 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1353 matching port, link or device. Basically, it matches
1354 the ATA ID string printed on console by libata. If
1355 the whole ID part is omitted, the last PORT and DEVICE
1356 values are used. If ID hasn't been specified yet, the
1357 configuration applies to all ports, links and devices.
1359 If only DEVICE is omitted, the parameter applies to
1360 the port and all links and devices behind it. DEVICE
1361 number of 0 either selects the first device or the
1362 first fan-out link behind PMP device. It does not
1363 select the host link. DEVICE number of 15 selects the
1364 host link and device attached to it.
1366 The VAL specifies the configuration to force. As long
1367 as there's no ambiguity shortcut notation is allowed.
1368 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1369 The following configurations can be forced.
1371 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1372 Any ID with matching PORT is used.
1374 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1376 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1377 udma[/][16,25,33,44,66,100,133] notation is also
1380 * [no]ncq: Turn on or off NCQ.
1382 * nohrst, nosrst, norst: suppress hard, soft
1385 * rstonce: only attempt one reset during
1386 hot-unplug link recovery
1388 * dump_id: dump IDENTIFY data.
1390 If there are multiple matching configurations changing
1391 the same attribute, the last one is used.
1393 memblock=debug [KNL] Enable memblock debug messages.
1395 load_ramdisk= [RAM] List of ramdisks to load from floppy
1396 See Documentation/blockdev/ramdisk.txt.
1398 lockd.nlm_grace_period=P [NFS] Assign grace period.
1401 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1404 lockd.nlm_timeout=T [NFS] Assign timeout value.
1407 lockd.nlm_udpport=M [NFS] Assign UDP port.
1410 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1413 loglevel= All Kernel Messages with a loglevel smaller than the
1414 console loglevel will be printed to the console. It can
1415 also be changed with klogd or other programs. The
1416 loglevels are defined as follows:
1418 0 (KERN_EMERG) system is unusable
1419 1 (KERN_ALERT) action must be taken immediately
1420 2 (KERN_CRIT) critical conditions
1421 3 (KERN_ERR) error conditions
1422 4 (KERN_WARNING) warning conditions
1423 5 (KERN_NOTICE) normal but significant condition
1424 6 (KERN_INFO) informational
1425 7 (KERN_DEBUG) debug-level messages
1427 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1428 in bytes. n must be a power of two. The default
1429 size is set in the kernel config file.
1431 logo.nologo [FB] Disables display of the built-in Linux logo.
1432 This may be used to provide more screen space for
1433 kernel log messages and is useful when debugging
1434 kernel boot problems.
1436 lp=0 [LP] Specify parallel ports to use, e.g,
1437 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1438 lp=reset first parallel port). 'lp=0' disables the
1439 lp=auto printer driver. 'lp=reset' (which can be
1440 specified in addition to the ports) causes
1441 attached printers to be reset. Using
1442 lp=port1,port2,... specifies the parallel ports
1443 to associate lp devices with, starting with
1444 lp0. A port specification may be 'none' to skip
1445 that lp device, or a parport name such as
1446 'parport0'. Specifying 'lp=auto' instead of a
1447 port specification list means that device IDs
1448 from each port should be examined, to see if
1449 an IEEE 1284-compliant printer is attached; if
1450 so, the driver will manage that printer.
1451 See also header of drivers/char/lp.c.
1454 Sets loops_per_jiffy to given constant, thus avoiding
1455 time-consuming boot-time autodetection (up to 250 ms per
1456 CPU). 0 enables autodetection (default). To determine
1457 the correct value for your kernel, boot with normal
1458 autodetection and see what value is printed. Note that
1459 on SMP systems the preset will be applied to all CPUs,
1460 which is likely to cause problems if your CPUs need
1461 significantly divergent settings. An incorrect value
1462 will cause delays in the kernel to be wrong, leading to
1463 unpredictable I/O errors and other breakage. Although
1464 unlikely, in the extreme case this might damage your
1468 Format: <io>,<irq>,<dma>
1470 machvec= [IA-64] Force the use of a particular machine-vector
1471 (machvec) in a generic kernel.
1472 Example: machvec=hpzx1_swiotlb
1474 machtype= [Loongson] Share the same kernel image file between different
1476 Example: machtype=lemote-yeeloong-2f-7inch
1478 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1479 than or equal to this physical address is ignored.
1481 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1482 should make use of. maxcpus=n : n >= 0 limits the
1483 kernel to using 'n' processors. n=0 is a special case,
1484 it is equivalent to "nosmp", which also disables
1487 max_loop= [LOOP] The number of loop block devices that get
1488 (loop.max_loop) unconditionally pre-created at init time. The default
1489 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1490 of statically allocating a predefined number, loop
1491 devices can be requested on-demand with the
1492 /dev/loop-control interface.
1494 mce [X86-32] Machine Check Exception
1496 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1498 md= [HW] RAID subsystems devices and level
1499 See Documentation/md.txt.
1502 Format: <first>,<last>
1503 Specifies range of consoles to be captured by the MDA.
1505 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1506 Amount of memory to be used when the kernel is not able
1507 to see the whole system memory or for test.
1508 [X86] Work as limiting max address. Use together
1509 with memmap= to avoid physical address space collisions.
1510 Without memmap= PCI devices could be placed at addresses
1511 belonging to unused RAM.
1513 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1517 [KNL,SH] Allow user to override the default size for
1518 per-device physically contiguous DMA buffers.
1520 memmap=exactmap [KNL,X86] Enable setting of an exact
1521 E820 memory map, as specified by the user.
1522 Such memmap=exactmap lines can be constructed based on
1523 BIOS output or other requirements. See the memmap=nn@ss
1526 memmap=nn[KMG]@ss[KMG]
1527 [KNL] Force usage of a specific region of memory
1528 Region of memory to be used, from ss to ss+nn.
1530 memmap=nn[KMG]#ss[KMG]
1531 [KNL,ACPI] Mark specific memory as ACPI data.
1532 Region of memory to be used, from ss to ss+nn.
1534 memmap=nn[KMG]$ss[KMG]
1535 [KNL,ACPI] Mark specific memory as reserved.
1536 Region of memory to be used, from ss to ss+nn.
1537 Example: Exclude memory from 0x18690000-0x1869ffff
1538 memmap=64K$0x18690000
1540 memmap=0x10000$0x18690000
1542 memory_corruption_check=0/1 [X86]
1543 Some BIOSes seem to corrupt the first 64k of
1544 memory when doing things like suspend/resume.
1545 Setting this option will scan the memory
1546 looking for corruption. Enabling this will
1547 both detect corruption and prevent the kernel
1548 from using the memory being corrupted.
1549 However, its intended as a diagnostic tool; if
1550 repeatable BIOS-originated corruption always
1551 affects the same memory, you can use memmap=
1552 to prevent the kernel from using that memory.
1554 memory_corruption_check_size=size [X86]
1555 By default it checks for corruption in the low
1556 64k, making this memory unavailable for normal
1557 use. Use this parameter to scan for
1558 corruption in more or less memory.
1560 memory_corruption_check_period=seconds [X86]
1561 By default it checks for corruption every 60
1562 seconds. Use this parameter to check at some
1563 other rate. 0 disables periodic checking.
1565 memtest= [KNL,X86] Enable memtest
1567 default : 0 <disable>
1568 Specifies the number of memtest passes to be
1569 performed. Each pass selects another test
1570 pattern from a given set of patterns. Memtest
1571 fills the memory with this pattern, validates
1572 memory contents and reserves bad memory
1573 regions that are detected.
1575 meye.*= [HW] Set MotionEye Camera parameters
1576 See Documentation/video4linux/meye.txt.
1578 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1579 Multi-Function General Purpose Timers on AMD Geode
1582 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1583 the BIOS has incorrectly applied a workaround. TinyBIOS
1584 version 0.98 is known to be affected, 0.99 fixes the
1585 problem by letting the user disable the workaround.
1589 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1590 physical address is ignored.
1592 mini2440= [ARM,HW,KNL]
1593 Format:[0..2][b][c][t]
1595 MINI2440 configuration specification:
1596 0 - The attached screen is the 3.5" TFT
1597 1 - The attached screen is the 7" TFT
1598 2 - The VGA Shield is attached (1024x768)
1599 Leaving out the screen size parameter will not load
1600 the TFT driver, and the framebuffer will be left
1602 b - Enable backlight. The TFT backlight pin will be
1603 linked to the kernel VESA blanking code and a GPIO
1604 LED. This parameter is not necessary when using the
1606 c - Enable the s3c camera interface.
1607 t - Reserved for enabling touchscreen support. The
1608 touchscreen support is not enabled in the mainstream
1609 kernel as of 2.6.30, a preliminary port can be found
1610 in the "bleeding edge" mini2440 support kernel at
1611 http://repo.or.cz/w/linux-2.6/mini2440.git
1614 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1615 parameter allows control of the logging verbosity for
1616 the additional memory initialisation checks. A value
1617 of 0 disables mminit logging and a level of 4 will
1618 log everything. Information is printed at KERN_DEBUG
1619 so loglevel=8 may also need to be specified.
1622 [KNL] When CONFIG_MODULE_SIG is set, this means that
1623 modules without (valid) signatures will fail to load.
1624 Note that if CONFIG_MODULE_SIG_ENFORCE is set, that
1625 is always true, so this option does nothing.
1628 [MOUSE] Maximum time between finger touching and
1629 leaving touchpad surface for touch to be considered
1630 a tap and be reported as a left button click (for
1631 touchpads working in absolute mode only).
1633 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1634 reporting absolute coordinates, such as tablets
1635 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1636 reporting absolute coordinates, such as tablets
1638 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1639 is similar to kernelcore except it specifies the
1640 amount of memory used for migratable allocations.
1641 If both kernelcore and movablecore is specified,
1642 then kernelcore will be at *least* the specified
1643 value but may be more. If movablecore on its own
1644 is specified, the administrator must be careful
1645 that the amount of memory usable for all allocations
1649 [KNL,X86,IA-64,PPC] This parameter is similar to
1650 memmap except it specifies the memory map of
1652 This option inform the kernel to use Hot Pluggable bit
1653 in flags from SRAT from ACPI BIOS to determine which
1654 memory devices could be hotplugged. The corresponding
1655 memory ranges will be set as ZONE_MOVABLE.
1656 NOTE: Whatever node the kernel resides in will always
1659 movablemem_map=nn[KMG]@ss[KMG]
1660 [KNL,X86,IA-64,PPC] This parameter is similar to
1661 memmap except it specifies the memory map of
1663 If user specifies memory ranges, the info in SRAT will
1664 be ingored. And it works like the following:
1665 - If more ranges are all within one node, then from
1666 lowest ss to the end of the node will be ZONE_MOVABLE.
1667 - If a range is within a node, then from ss to the end
1668 of the node will be ZONE_MOVABLE.
1669 - If a range covers two or more nodes, then from ss to
1670 the end of the 1st node will be ZONE_MOVABLE, and all
1671 the rest nodes will only have ZONE_MOVABLE.
1672 If memmap is specified at the same time, the
1673 movablemem_map will be limited within the memmap
1674 areas. If kernelcore or movablecore is also specified,
1675 movablemem_map will have higher priority to be
1676 satisfied. So the administrator should be careful that
1677 the amount of movablemem_map areas are not too large.
1678 Otherwise kernel won't have enough memory to start.
1679 NOTE: We don't stop users specifying the node the
1680 kernel resides in as hotpluggable so that this
1681 option can be used as a workaround of firmware
1684 MTD_Partition= [MTD]
1685 Format: <name>,<region-number>,<size>,<offset>
1687 MTD_Region= [MTD] Format:
1688 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1691 See drivers/mtd/cmdlinepart.c.
1693 multitce=off [PPC] This parameter disables the use of the pSeries
1694 firmware feature for updating multiple TCE entries
1697 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1699 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1701 boundary - index of last SLC block on Flex-OneNAND.
1702 The remaining blocks are configured as MLC blocks.
1703 lock - Configure if Flex-OneNAND boundary should be locked.
1704 Once locked, the boundary cannot be changed.
1705 1 indicates lock status, 0 indicates unlock status.
1708 ARM/S3C2412 JIVE boot control
1710 See arch/arm/mach-s3c2412/mach-jive.c
1712 mtouchusb.raw_coordinates=
1713 [HW] Make the MicroTouch USB driver use raw coordinates
1714 ('y', default) or cooked coordinates ('n')
1716 mtrr_chunk_size=nn[KMG] [X86]
1717 used for mtrr cleanup. It is largest continuous chunk
1718 that could hold holes aka. UC entries.
1720 mtrr_gran_size=nn[KMG] [X86]
1721 Used for mtrr cleanup. It is granularity of mtrr block.
1723 Large value could prevent small alignment from
1726 mtrr_spare_reg_nr=n [X86]
1728 Range: 0,7 : spare reg number
1730 Used for mtrr cleanup. It is spare mtrr entries number.
1731 Set to 2 or more if your graphical card needs more.
1733 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1735 netdev= [NET] Network devices parameters
1736 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1737 Note that mem_start is often overloaded to mean
1738 something different and driver-specific.
1739 This usage is only documented in each driver source
1743 [NETFILTER] Enable connection tracking flow accounting
1744 0 to disable accounting
1745 1 to enable accounting
1748 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1749 See Documentation/filesystems/nfs/nfsroot.txt.
1751 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1752 See Documentation/filesystems/nfs/nfsroot.txt.
1754 nfsrootdebug [NFS] enable nfsroot debugging messages.
1755 See Documentation/filesystems/nfs/nfsroot.txt.
1757 nfs.callback_tcpport=
1758 [NFS] set the TCP port on which the NFSv4 callback
1759 channel should listen.
1762 [NFS] sets the pathname to the program which is used
1763 to update the NFS client cache entries.
1765 nfs.cache_getent_timeout=
1766 [NFS] sets the timeout after which an attempt to
1767 update a cache entry is deemed to have failed.
1769 nfs.idmap_cache_timeout=
1770 [NFS] set the maximum lifetime for idmapper cache
1774 [NFS] enable 64-bit inode numbers.
1775 If zero, the NFS client will fake up a 32-bit inode
1776 number for the readdir() and stat() syscalls instead
1777 of returning the full 64-bit number.
1778 The default is to return 64-bit inode numbers.
1780 nfs.max_session_slots=
1781 [NFSv4.1] Sets the maximum number of session slots
1782 the client will attempt to negotiate with the server.
1783 This limits the number of simultaneous RPC requests
1784 that the client can send to the NFSv4.1 server.
1785 Note that there is little point in setting this
1786 value higher than the max_tcp_slot_table_limit.
1788 nfs.nfs4_disable_idmapping=
1789 [NFSv4] When set to the default of '1', this option
1790 ensures that both the RPC level authentication
1791 scheme and the NFS level operations agree to use
1792 numeric uids/gids if the mount is using the
1793 'sec=sys' security flavour. In effect it is
1794 disabling idmapping, which can make migration from
1795 legacy NFSv2/v3 systems to NFSv4 easier.
1796 Servers that do not support this mode of operation
1797 will be autodetected by the client, and it will fall
1798 back to using the idmapper.
1799 To turn off this behaviour, set the value to '0'.
1801 [NFS4] Specify an additional fixed unique ident-
1802 ification string that NFSv4 clients can insert into
1803 their nfs_client_id4 string. This is typically a
1804 UUID that is generated at system install time.
1806 nfs.send_implementation_id =
1807 [NFSv4.1] Send client implementation identification
1808 information in exchange_id requests.
1809 If zero, no implementation identification information
1811 The default is to send the implementation identification
1814 nfsd.nfs4_disable_idmapping=
1815 [NFSv4] When set to the default of '1', the NFSv4
1816 server will return only numeric uids and gids to
1817 clients using auth_sys, and will accept numeric uids
1818 and gids from such clients. This is intended to ease
1819 migration from NFSv2/v3.
1821 objlayoutdriver.osd_login_prog=
1822 [NFS] [OBJLAYOUT] sets the pathname to the program which
1823 is used to automatically discover and login into new
1824 osd-targets. Please see:
1825 Documentation/filesystems/pnfs.txt for more explanations
1827 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1828 when a NMI is triggered.
1829 Format: [state][,regs][,debounce][,die]
1831 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1832 Format: [panic,][nopanic,][num]
1834 0 - turn nmi_watchdog off
1835 When panic is specified, panic when an NMI watchdog
1836 timeout occurs (or 'nopanic' to override the opposite
1838 This is useful when you use a panic=... timeout and
1839 need the box quickly up again.
1841 netpoll.carrier_timeout=
1842 [NET] Specifies amount of time (in seconds) that
1843 netpoll should wait for a carrier. By default netpoll
1846 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1847 emulation library even if a 387 maths coprocessor
1851 [HW] Never suspend the console
1852 Disable suspending of consoles during suspend and
1853 hibernate operations. Once disabled, debugging
1854 messages can reach various consoles while the rest
1855 of the system is being put to sleep (ie, while
1856 debugging driver suspend/resume hooks). This may
1857 not work reliably with all consoles, but is known
1858 to work with serial and VGA consoles.
1859 To facilitate more flexible debugging, we also add
1860 console_suspend, a printk module parameter to control
1861 it. Users could use console_suspend (usually
1862 /sys/module/printk/parameters/console_suspend) to
1863 turn on/off it dynamically.
1865 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1866 caches in the slab allocator. Saves per-node memory,
1867 but will impact performance.
1871 noapic [SMP,APIC] Tells the kernel to not make use of any
1872 IOAPICs that may be present in the system.
1874 noautogroup Disable scheduler automatic task group creation.
1876 nobats [PPC] Do not use BATs for mapping kernel lowmem
1877 on "Classic" PPC cores.
1881 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1883 nodelayacct [KNL] Disable per-task delay accounting
1885 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1887 nodsp [SH] Disable hardware DSP at boot time.
1889 noefi [X86] Disable EFI runtime services support.
1894 On X86-32 available only on PAE configured kernels.
1895 noexec=on: enable non-executable mappings (default)
1896 noexec=off: disable non-executable mappings
1899 Disable SMAP (Supervisor Mode Access Prevention)
1900 even if it is supported by processor.
1903 Disable SMEP (Supervisor Mode Execution Prevention)
1904 even if it is supported by processor.
1907 This affects only 32-bit executables.
1908 noexec32=on: enable non-executable mappings (default)
1909 read doesn't imply executable mappings
1910 noexec32=off: disable non-executable mappings
1911 read implies executable mappings
1913 nofpu [SH] Disable hardware FPU at boot time.
1915 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1916 register save and restore. The kernel will only save
1917 legacy floating-point registers on task switch.
1919 noxsave [BUGS=X86] Disables x86 extended register state save
1920 and restore using xsave. The kernel will fallback to
1921 enabling legacy floating-point and sse state.
1924 on enable eager fpu restore
1925 off disable eager fpu restore
1926 auto selects the default scheme, which automatically
1927 enables eagerfpu restore for xsaveopt.
1929 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1930 wfi(ARM) instruction doesn't work correctly and not to
1931 use it. This is also useful when using JTAG debugger.
1933 no_file_caps Tells the kernel not to honor file capabilities. The
1934 only way then for a file to be executed with privilege
1935 is to be setuid root or executed by root.
1937 nohalt [IA-64] Tells the kernel not to use the power saving
1938 function PAL_HALT_LIGHT when idle. This increases
1939 power-consumption. On the positive side, it reduces
1940 interrupt wake-up latency, which may improve performance
1941 in certain environments such as networked servers or
1944 nohz= [KNL] Boottime enable/disable dynamic ticks
1945 Valid arguments: on, off
1948 noiotrap [SH] Disables trapped I/O port accesses.
1950 noirqdebug [X86-32] Disables the code which attempts to detect and
1951 disable unhandled interrupt sources.
1953 no_timer_check [X86,APIC] Disables the code which tests for
1954 broken timer IRQ sources.
1956 noisapnp [ISAPNP] Disables ISA PnP code.
1958 noinitrd [RAM] Tells the kernel not to load any configured
1961 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1963 [Deprecated - use intremap=off]
1967 nojitter [IA-64] Disables jitter checking for ITC timers.
1969 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1971 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1974 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1975 steal time is computed, but won't influence scheduler
1978 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1980 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1982 noltlbs [PPC] Do not use large page/tlb entries for kernel
1983 lowmem mapping on PPC40x.
1985 nomca [IA-64] Disable machine check abort handling
1987 nomce [X86-32] Machine Check Exception
1989 nomfgpt [X86-32] Disable Multi-Function General Purpose
1990 Timer usage (for AMD Geode machines).
1992 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
1993 shutdown the other cpus. Instead use the REBOOT_VECTOR
1996 nomodule Disable module load
1998 nopat [X86] Disable PAT (page attribute table extension of
1999 pagetables) support.
2001 norandmaps Don't use address space randomization. Equivalent to
2002 echo 0 > /proc/sys/kernel/randomize_va_space
2004 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2006 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2007 with UP alternatives
2009 noresidual [PPC] Don't use residual data on PReP machines.
2011 nordrand [X86] Disable the direct use of the RDRAND
2012 instruction even if it is supported by the
2013 processor. RDRAND is still available to user
2016 noresume [SWSUSP] Disables resume and restores original swap
2019 no-scroll [VGA] Disables scrollback.
2020 This is required for the Braillex ib80-piezo Braille
2021 reader made by F.H. Papenmeier (Germany).
2025 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2027 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2028 and disable the IO APIC. legacy for "maxcpus=0".
2030 nosoftlockup [KNL] Disable the soft-lockup detector.
2032 nosync [HW,M68K] Disables sync negotiation for all devices.
2034 notsc [BUGS=X86-32] Disable Time Stamp Counter
2036 nousb [USB] Disable the USB subsystem
2038 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2042 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2044 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2045 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2046 Some features depend on CPU0. Known dependencies are:
2047 1. Resume from suspend/hibernate depends on CPU0.
2048 Suspend/hibernate will fail if CPU0 is offline and you
2049 need to online CPU0 before suspend/hibernate.
2050 2. PIC interrupts also depend on CPU0. CPU0 can't be
2051 removed if a PIC interrupt is detected.
2052 It's said poweroff/reboot may depend on CPU0 on some
2053 machines although I haven't seen such issues so far
2054 after CPU0 is offline on a few tested machines.
2055 If the dependencies are under your control, you can
2056 turn on cpu0_hotplug.
2058 nptcg= [IA-64] Override max number of concurrent global TLB
2059 purges which is reported from either PAL_VM_SUMMARY or
2062 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2063 could support. nr_cpus=n : n >= 1 limits the kernel to
2064 supporting 'n' processors. Later in runtime you can not
2065 use hotplug cpu feature to put more cpu back to online.
2066 just like you compile the kernel NR_CPUS=n
2068 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2070 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2071 Allowed values are enable and disable
2073 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2074 one of ['zone', 'node', 'default'] can be specified
2075 This can be set from sysctl after boot.
2076 See Documentation/sysctl/vm.txt for details.
2078 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2079 See Documentation/debugging-via-ohci1394.txt for more
2082 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2083 Rather than timing out after 20 ms if an EC
2084 command is not properly ACKed, override the length
2085 of the timeout. We have interrupts disabled while
2086 waiting for the ACK, so if this is set too high
2087 interrupts *may* be lost!
2089 omap_mux= [OMAP] Override bootloader pin multiplexing.
2090 Format: <mux_mode0.mode_name=value>...
2091 For example, to override I2C bus2:
2092 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2094 oprofile.timer= [HW]
2095 Use timer interrupt instead of performance counters
2097 oprofile.cpu_type= Force an oprofile cpu type
2098 This might be useful if you have an older oprofile
2099 userland or if you want common events.
2100 Format: { arch_perfmon }
2101 arch_perfmon: [X86] Force use of architectural
2102 perfmon on Intel CPUs instead of the
2103 CPU specific event set.
2104 timer: [X86] Force use of architectural NMI
2105 timer mode (see also oprofile.timer
2106 for generic hr timer mode)
2107 [s390] Force legacy basic mode sampling
2108 (report cpu_type "timer")
2110 oops=panic Always panic on oopses. Default is to just kill the
2111 process, but there is a small probability of
2112 deadlocking the machine.
2113 This will also cause panics on machine check exceptions.
2114 Useful together with panic=30 to trigger a reboot.
2117 See Documentation/sound/oss/oss-parameters.txt
2119 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2120 timeout > 0: seconds before rebooting
2121 timeout = 0: wait forever
2122 timeout < 0: reboot immediately
2125 parkbd.port= [HW] Parallel port number the keyboard adapter is
2126 connected to, default is 0.
2128 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2129 0 for XT, 1 for AT (default is AT).
2132 parport= [HW,PPT] Specify parallel ports. 0 disables.
2133 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2134 Use 'auto' to force the driver to use any
2135 IRQ/DMA settings detected (the default is to
2136 ignore detected IRQ/DMA settings because of
2137 possible conflicts). You can specify the base
2138 address, IRQ, and DMA settings; IRQ and DMA
2139 should be numbers, or 'auto' (for using detected
2140 settings on that particular port), or 'nofifo'
2141 (to avoid using a FIFO even if it is detected).
2142 Parallel ports are assigned in the order they
2143 are specified on the command line, starting
2146 parport_init_mode= [HW,PPT]
2147 Configure VIA parallel port to operate in
2148 a specific mode. This is necessary on Pegasos
2149 computer where firmware has no options for setting
2150 up parallel port mode and sets it to spp.
2151 Currently this function knows 686a and 8231 chips.
2152 Format: [spp|ps2|epp|ecp|ecpepp]
2155 Halt all CPUs after the first oops has been printed for
2156 the specified number of seconds. This is to be used if
2157 your oopses keep scrolling off the screen.
2162 See header of drivers/block/paride/pcd.c.
2163 See also Documentation/blockdev/paride.txt.
2165 pci=option[,option...] [PCI] various PCI subsystem options:
2166 earlydump [X86] dump PCI config space before the kernel
2168 off [X86] don't probe for the PCI bus
2169 bios [X86-32] force use of PCI BIOS, don't access
2170 the hardware directly. Use this if your machine
2171 has a non-standard PCI host bridge.
2172 nobios [X86-32] disallow use of PCI BIOS, only direct
2173 hardware access methods are allowed. Use this
2174 if you experience crashes upon bootup and you
2175 suspect they are caused by the BIOS.
2176 conf1 [X86] Force use of PCI Configuration
2178 conf2 [X86] Force use of PCI Configuration
2180 noaer [PCIE] If the PCIEAER kernel config parameter is
2181 enabled, this kernel boot option can be used to
2182 disable the use of PCIE advanced error reporting.
2183 nodomains [PCI] Disable support for multiple PCI
2184 root domains (aka PCI segments, in ACPI-speak).
2185 nommconf [X86] Disable use of MMCONFIG for PCI
2187 check_enable_amd_mmconf [X86] check for and enable
2188 properly configured MMIO access to PCI
2189 config space on AMD family 10h CPU
2190 nomsi [MSI] If the PCI_MSI kernel config parameter is
2191 enabled, this kernel boot option can be used to
2192 disable the use of MSI interrupts system-wide.
2193 noioapicquirk [APIC] Disable all boot interrupt quirks.
2194 Safety option to keep boot IRQs enabled. This
2195 should never be necessary.
2196 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2197 primary IO-APIC for bridges that cannot disable
2198 boot IRQs. This fixes a source of spurious IRQs
2199 when the system masks IRQs.
2200 noioapicreroute [APIC] Disable workaround that uses the
2201 boot IRQ equivalent of an IRQ that connects to
2202 a chipset where boot IRQs cannot be disabled.
2203 The opposite of ioapicreroute.
2204 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2205 routing table. These calls are known to be buggy
2206 on several machines and they hang the machine
2207 when used, but on other computers it's the only
2208 way to get the interrupt routing table. Try
2209 this option if the kernel is unable to allocate
2210 IRQs or discover secondary PCI buses on your
2212 rom [X86] Assign address space to expansion ROMs.
2213 Use with caution as certain devices share
2214 address decoders between ROMs and other
2216 norom [X86] Do not assign address space to
2217 expansion ROMs that do not already have
2218 BIOS assigned address ranges.
2219 nobar [X86] Do not assign address space to the
2220 BARs that weren't assigned by the BIOS.
2221 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2222 assigned automatically to PCI devices. You can
2223 make the kernel exclude IRQs of your ISA cards
2225 pirqaddr=0xAAAAA [X86] Specify the physical address
2226 of the PIRQ table (normally generated
2227 by the BIOS) if it is outside the
2228 F0000h-100000h range.
2229 lastbus=N [X86] Scan all buses thru bus #N. Can be
2230 useful if the kernel is unable to find your
2231 secondary buses and you want to tell it
2232 explicitly which ones they are.
2233 assign-busses [X86] Always assign all PCI bus
2234 numbers ourselves, overriding
2235 whatever the firmware may have done.
2236 usepirqmask [X86] Honor the possible IRQ mask stored
2237 in the BIOS $PIR table. This is needed on
2238 some systems with broken BIOSes, notably
2239 some HP Pavilion N5400 and Omnibook XE3
2240 notebooks. This will have no effect if ACPI
2241 IRQ routing is enabled.
2242 noacpi [X86] Do not use ACPI for IRQ routing
2243 or for PCI scanning.
2244 use_crs [X86] Use PCI host bridge window information
2245 from ACPI. On BIOSes from 2008 or later, this
2246 is enabled by default. If you need to use this,
2247 please report a bug.
2248 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2249 If you need to use this, please report a bug.
2250 routeirq Do IRQ routing for all PCI devices.
2251 This is normally done in pci_enable_device(),
2252 so this option is a temporary workaround
2253 for broken drivers that don't call it.
2254 skip_isa_align [X86] do not align io start addr, so can
2255 handle more pci cards
2256 firmware [ARM] Do not re-enumerate the bus but instead
2257 just use the configuration from the
2258 bootloader. This is currently used on
2259 IXP2000 systems where the bus has to be
2260 configured a certain way for adjunct CPUs.
2261 noearly [X86] Don't do any early type 1 scanning.
2262 This might help on some broken boards which
2263 machine check when some devices' config space
2264 is read. But various workarounds are disabled
2265 and some IOMMU drivers will not work.
2266 bfsort Sort PCI devices into breadth-first order.
2267 This sorting is done to get a device
2268 order compatible with older (<= 2.4) kernels.
2269 nobfsort Don't sort PCI devices into breadth-first order.
2270 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2271 tuning and use the BIOS-configured MPS defaults.
2272 pcie_bus_safe Set every device's MPS to the largest value
2273 supported by all devices below the root complex.
2274 pcie_bus_perf Set device MPS to the largest allowable MPS
2275 based on its parent bus. Also set MRRS (Max
2276 Read Request Size) to the largest supported
2277 value (no larger than the MPS that the device
2278 or bus can support) for best performance.
2279 pcie_bus_peer2peer Set every device's MPS to 128B, which
2280 every device is guaranteed to support. This
2281 configuration allows peer-to-peer DMA between
2282 any pair of devices, possibly at the cost of
2283 reduced performance. This also guarantees
2284 that hot-added devices will work.
2285 cbiosize=nn[KMG] The fixed amount of bus space which is
2286 reserved for the CardBus bridge's IO window.
2287 The default value is 256 bytes.
2288 cbmemsize=nn[KMG] The fixed amount of bus space which is
2289 reserved for the CardBus bridge's memory
2290 window. The default value is 64 megabytes.
2293 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2294 Specifies alignment and device to reassign
2295 aligned memory resources.
2296 If <order of align> is not specified,
2297 PAGE_SIZE is used as alignment.
2298 PCI-PCI bridge can be specified, if resource
2299 windows need to be expanded.
2300 ecrc= Enable/disable PCIe ECRC (transaction layer
2301 end-to-end CRC checking).
2302 bios: Use BIOS/firmware settings. This is the
2306 hpiosize=nn[KMG] The fixed amount of bus space which is
2307 reserved for hotplug bridge's IO window.
2308 Default size is 256 bytes.
2309 hpmemsize=nn[KMG] The fixed amount of bus space which is
2310 reserved for hotplug bridge's memory window.
2311 Default size is 2 megabytes.
2312 realloc= Enable/disable reallocating PCI bridge resources
2313 if allocations done by BIOS are too small to
2314 accommodate resources required by all child
2316 off: Turn realloc off
2318 realloc same as realloc=on
2319 noari do not use PCIe ARI.
2320 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2321 only look for one device below a PCIe downstream
2324 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2327 force Enable ASPM even on devices that claim not to support it.
2328 WARNING: Forcing ASPM on may cause system lockups.
2330 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2331 nomsi Do not use MSI for PCI Express Native Hotplug (this
2332 makes all PCIe ports use INTx for hotplug services).
2334 pcie_ports= [PCIE] PCIe ports handling:
2335 auto Ask the BIOS whether or not to use native PCIe services
2336 associated with PCIe ports (PME, hot-plug, AER). Use
2337 them only if that is allowed by the BIOS.
2338 native Use native PCIe services associated with PCIe ports
2340 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2343 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2344 nomsi Do not use MSI for native PCIe PME signaling (this makes
2345 all PCIe root ports use INTx for all services).
2347 pcmv= [HW,PCMCIA] BadgePAD 4
2350 See Documentation/blockdev/paride.txt.
2352 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2355 See arch/parisc/kernel/pdc_chassis.c
2357 percpu_alloc= Select which percpu first chunk allocator to use.
2358 Currently supported values are "embed" and "page".
2359 Archs may support subset or none of the selections.
2360 See comments in mm/percpu.c for details on each
2361 allocator. This parameter is primarily for debugging
2362 and performance comparison.
2365 See Documentation/blockdev/paride.txt.
2368 See Documentation/blockdev/paride.txt.
2370 pirq= [SMP,APIC] Manual mp-table setup
2371 See Documentation/x86/i386/IO-APIC.txt.
2373 plip= [PPT,NET] Parallel port network link
2374 Format: { parport<nr> | timid | 0 }
2375 See also Documentation/parport.txt.
2377 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2378 Override pmtimer IOPort with a hex value.
2382 Enable PNP debug messages (depends on the
2383 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2384 via /sys/module/pnp/parameters/debug. We always show
2385 current resource usage; turning this on also shows
2386 possible settings and some assignment information.
2392 { on | off | curr | res | no-curr | no-res }
2395 [ISAPNP] Exclude IRQs for the autoconfiguration
2398 [ISAPNP] Exclude DMAs for the autoconfiguration
2400 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2401 Ranges are in pairs (I/O port base and size).
2404 [ISAPNP] Exclude memory regions for the
2406 Ranges are in pairs (memory base and size).
2408 ports= [IP_VS_FTP] IPVS ftp helper module
2410 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2412 Format: <port>,<port>....
2414 print-fatal-signals=
2415 [KNL] debug: print fatal signals
2417 If enabled, warn about various signal handling
2418 related application anomalies: too many signals,
2419 too many POSIX.1 timers, fatal signals causing a
2422 If you hit the warning due to signal overflow,
2423 you might want to try "ulimit -i unlimited".
2427 printk.always_kmsg_dump=
2428 Trigger kmsg_dump for cases other than kernel oops or
2430 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2433 printk.time= Show timing data prefixed to each printk message line
2434 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2436 processor.max_cstate= [HW,ACPI]
2437 Limit processor to maximum C-state
2438 max_cstate=9 overrides any DMI blacklist limit.
2440 processor.nocst [HW,ACPI]
2441 Ignore the _CST method to determine C-states,
2442 instead using the legacy FADT method
2444 profile= [KNL] Enable kernel profiling via /proc/profile
2445 Format: [schedule,]<number>
2446 Param: "schedule" - profile schedule points.
2447 Param: <number> - step/bucket size as a power of 2 for
2448 statistical time based profiling.
2449 Param: "sleep" - profile D-state sleeping (millisecs).
2450 Requires CONFIG_SCHEDSTATS
2451 Param: "kvm" - profile VM exits.
2453 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2455 See Documentation/blockdev/ramdisk.txt.
2457 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2458 probe for; one of (bare|imps|exps|lifebook|any).
2459 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2461 psmouse.resetafter= [HW,MOUSE]
2462 Try to reset the device after so many bad packets
2465 [HW,MOUSE] Set desired mouse resolution, in dpi.
2466 psmouse.smartscroll=
2467 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2468 0 = disabled, 1 = enabled (default).
2470 pstore.backend= Specify the name of the pstore backend to use
2473 See Documentation/blockdev/paride.txt.
2476 [KNL] Number of legacy pty's. Overwrites compiled-in
2479 quiet [KNL] Disable most log messages
2484 See Documentation/md.txt.
2486 ramdisk_blocksize= [RAM]
2487 See Documentation/blockdev/ramdisk.txt.
2489 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2490 See Documentation/blockdev/ramdisk.txt.
2492 rcu_nocbs= [KNL,BOOT]
2493 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2494 the specified list of CPUs to be no-callback CPUs.
2495 Invocation of these CPUs' RCU callbacks will
2496 be offloaded to "rcuoN" kthreads created for
2497 that purpose. This reduces OS jitter on the
2498 offloaded CPUs, which can be useful for HPC and
2499 real-time workloads. It can also improve energy
2500 efficiency for asymmetric multiprocessors.
2502 rcu_nocb_poll [KNL,BOOT]
2503 Rather than requiring that offloaded CPUs
2504 (specified by rcu_nocbs= above) explicitly
2505 awaken the corresponding "rcuoN" kthreads,
2506 make these kthreads poll for callbacks.
2507 This improves the real-time response for the
2508 offloaded CPUs by relieving them of the need to
2509 wake up the corresponding kthread, but degrades
2510 energy efficiency by requiring that the kthreads
2511 periodically wake up to do the polling.
2513 rcutree.blimit= [KNL,BOOT]
2514 Set maximum number of finished RCU callbacks to process
2517 rcutree.fanout_leaf= [KNL,BOOT]
2518 Increase the number of CPUs assigned to each
2519 leaf rcu_node structure. Useful for very large
2522 rcutree.qhimark= [KNL,BOOT]
2523 Set threshold of queued
2524 RCU callbacks over which batch limiting is disabled.
2526 rcutree.qlowmark= [KNL,BOOT]
2527 Set threshold of queued RCU callbacks below which
2528 batch limiting is re-enabled.
2530 rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2531 Suppress RCU CPU stall warning messages.
2533 rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2534 Set timeout for RCU CPU stall warning messages.
2536 rcutree.jiffies_till_first_fqs= [KNL,BOOT]
2537 Set delay from grace-period initialization to
2538 first attempt to force quiescent states.
2539 Units are jiffies, minimum value is zero,
2540 and maximum value is HZ.
2542 rcutree.jiffies_till_next_fqs= [KNL,BOOT]
2543 Set delay between subsequent attempts to force
2544 quiescent states. Units are jiffies, minimum
2545 value is one, and maximum value is HZ.
2547 rcutorture.fqs_duration= [KNL,BOOT]
2548 Set duration of force_quiescent_state bursts.
2550 rcutorture.fqs_holdoff= [KNL,BOOT]
2551 Set holdoff time within force_quiescent_state bursts.
2553 rcutorture.fqs_stutter= [KNL,BOOT]
2554 Set wait time between force_quiescent_state bursts.
2556 rcutorture.irqreader= [KNL,BOOT]
2557 Test RCU readers from irq handlers.
2559 rcutorture.n_barrier_cbs= [KNL,BOOT]
2560 Set callbacks/threads for rcu_barrier() testing.
2562 rcutorture.nfakewriters= [KNL,BOOT]
2563 Set number of concurrent RCU writers. These just
2564 stress RCU, they don't participate in the actual
2565 test, hence the "fake".
2567 rcutorture.nreaders= [KNL,BOOT]
2568 Set number of RCU readers.
2570 rcutorture.onoff_holdoff= [KNL,BOOT]
2571 Set time (s) after boot for CPU-hotplug testing.
2573 rcutorture.onoff_interval= [KNL,BOOT]
2574 Set time (s) between CPU-hotplug operations, or
2575 zero to disable CPU-hotplug testing.
2577 rcutorture.shuffle_interval= [KNL,BOOT]
2578 Set task-shuffle interval (s). Shuffling tasks
2579 allows some CPUs to go into dyntick-idle mode
2580 during the rcutorture test.
2582 rcutorture.shutdown_secs= [KNL,BOOT]
2583 Set time (s) after boot system shutdown. This
2584 is useful for hands-off automated testing.
2586 rcutorture.stall_cpu= [KNL,BOOT]
2587 Duration of CPU stall (s) to test RCU CPU stall
2588 warnings, zero to disable.
2590 rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2591 Time to wait (s) after boot before inducing stall.
2593 rcutorture.stat_interval= [KNL,BOOT]
2594 Time (s) between statistics printk()s.
2596 rcutorture.stutter= [KNL,BOOT]
2597 Time (s) to stutter testing, for example, specifying
2598 five seconds causes the test to run for five seconds,
2599 wait for five seconds, and so on. This tests RCU's
2600 ability to transition abruptly to and from idle.
2602 rcutorture.test_boost= [KNL,BOOT]
2603 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2604 "Maybe" means test if the RCU implementation
2605 under test support RCU priority boosting.
2607 rcutorture.test_boost_duration= [KNL,BOOT]
2608 Duration (s) of each individual boost test.
2610 rcutorture.test_boost_interval= [KNL,BOOT]
2611 Interval (s) between each boost test.
2613 rcutorture.test_no_idle_hz= [KNL,BOOT]
2614 Test RCU's dyntick-idle handling. See also the
2615 rcutorture.shuffle_interval parameter.
2617 rcutorture.torture_type= [KNL,BOOT]
2618 Specify the RCU implementation to test.
2620 rcutorture.verbose= [KNL,BOOT]
2621 Enable additional printk() statements.
2625 Run specified binary instead of /init from the ramdisk,
2626 used for early userspace startup. See initrd.
2628 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2629 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2630 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2633 [KNL, SMP] Set scheduler's default relax_domain_level.
2634 See Documentation/cgroups/cpusets.txt.
2636 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2638 reservetop= [X86-32]
2640 Reserves a hole at the top of the kernel virtual
2645 Set the amount of memory to reserve for BIOS at
2646 the bottom of the address space.
2648 reset_devices [KNL] Force drivers to reset the underlying device
2649 during initialization.
2652 Specify the partition device for software suspend
2654 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2656 resume_offset= [SWSUSP]
2657 Specify the offset from the beginning of the partition
2658 given by "resume=" at which the swap header is located,
2659 in <PAGE_SIZE> units (needed only for swap files).
2660 See Documentation/power/swsusp-and-swap-files.txt
2662 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2663 read the resume files
2665 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2666 Useful for devices that are detected asynchronously
2667 (e.g. USB and MMC devices).
2669 hibernate= [HIBERNATION]
2670 noresume Don't check if there's a hibernation image
2671 present during boot.
2672 nocompress Don't compress/decompress hibernation images.
2674 retain_initrd [RAM] Keep initrd memory after extraction
2676 rhash_entries= [KNL,NET]
2677 Set number of hash buckets for route cache
2679 riscom8= [HW,SERIAL]
2680 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2682 ro [KNL] Mount root device read-only on boot
2684 root= [KNL] Root filesystem
2685 See name_to_dev_t comment in init/do_mounts.c.
2687 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2688 mount the root filesystem
2690 rootflags= [KNL] Set root filesystem mount option string
2692 rootfstype= [KNL] Set root filesystem type
2694 rootwait [KNL] Wait (indefinitely) for root device to show up.
2695 Useful for devices that are detected asynchronously
2696 (e.g. USB and MMC devices).
2698 rw [KNL] Mount root device read-write on boot
2700 S [KNL] Run init in single mode
2703 See drivers/net/irda/sa1100_ir.c.
2705 sbni= [NET] Granch SBNI12 leased line adapter
2707 sched_debug [KNL] Enables verbose scheduler debug messages.
2709 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2710 xtime_lock contention on larger systems, and/or RCU lock
2711 contention on all systems with CONFIG_MAXSMP set.
2712 Format: { "0" | "1" }
2713 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2715 Note: increases power consumption, thus should only be
2716 enabled if running jitter sensitive (HPC/RT) workloads.
2718 security= [SECURITY] Choose a security module to enable at boot.
2719 If this boot parameter is not specified, only the first
2720 security module asking for security registration will be
2721 loaded. An invalid security module name will be treated
2722 as if no module has been chosen.
2724 selinux= [SELINUX] Disable or enable SELinux at boot time.
2725 Format: { "0" | "1" }
2726 See security/selinux/Kconfig help text.
2729 Default value is set via kernel config option.
2730 If enabled at boot time, /selinux/disable can be used
2731 later to disable prior to initial policy load.
2733 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2734 Format: { "0" | "1" }
2735 See security/apparmor/Kconfig help text
2738 Default value is set via kernel config option.
2740 serialnumber [BUGS=X86-32]
2743 Maximal number of shapers.
2745 show_msr= [x86] show boot-time MSR settings
2746 Format: { <integer> }
2747 Show boot-time (BIOS-initialized) MSR settings.
2748 The parameter means the number of CPUs to show,
2749 for example 1 means boot CPU only.
2756 slab_max_order= [MM, SLAB]
2757 Determines the maximum allowed order for slabs.
2758 A high setting may cause OOMs due to memory
2759 fragmentation. Defaults to 1 for systems with
2760 more than 32MB of RAM, 0 otherwise.
2762 slub_debug[=options[,slabs]] [MM, SLUB]
2763 Enabling slub_debug allows one to determine the
2764 culprit if slab objects become corrupted. Enabling
2765 slub_debug can create guard zones around objects and
2766 may poison objects when not in use. Also tracks the
2767 last alloc / free. For more information see
2768 Documentation/vm/slub.txt.
2770 slub_max_order= [MM, SLUB]
2771 Determines the maximum allowed order for slabs.
2772 A high setting may cause OOMs due to memory
2773 fragmentation. For more information see
2774 Documentation/vm/slub.txt.
2776 slub_min_objects= [MM, SLUB]
2777 The minimum number of objects per slab. SLUB will
2778 increase the slab order up to slub_max_order to
2779 generate a sufficiently large slab able to contain
2780 the number of objects indicated. The higher the number
2781 of objects the smaller the overhead of tracking slabs
2782 and the less frequently locks need to be acquired.
2783 For more information see Documentation/vm/slub.txt.
2785 slub_min_order= [MM, SLUB]
2786 Determines the minimum page order for slabs. Must be
2787 lower than slub_max_order.
2788 For more information see Documentation/vm/slub.txt.
2790 slub_nomerge [MM, SLUB]
2791 Disable merging of slabs with similar size. May be
2792 necessary if there is some reason to distinguish
2793 allocs to different slabs. Debug options disable
2794 merging on their own.
2795 For more information see Documentation/vm/slub.txt.
2798 Format: <io1>[,<io2>[,...,<io8>]]
2800 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2801 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2802 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2803 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2804 smsc-ircc2.ircc_irq= [HW] IRQ line
2805 smsc-ircc2.ircc_dma= [HW] DMA channel
2806 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2807 0: Toshiba Satellite 1800 (GP data pin select)
2808 1: Fast pin select (default)
2812 [KNL] Should the soft-lockup detector generate panics.
2815 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2816 See Documentation/laptops/sonypi.txt
2818 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2819 See Documentation/serial/specialix.txt.
2821 spia_io_base= [HW,MTD]
2827 Enabled the stack tracer on boot up.
2829 stacktrace_filter=[function-list]
2830 [FTRACE] Limit the functions that the stack tracer
2831 will trace at boot up. function-list is a comma separated
2832 list of functions. This list can be changed at run
2833 time by the stack_trace_filter file in the debugfs
2834 tracing directory. Note, this enables stack tracing
2835 and the stacktrace above is not needed.
2839 Set the STI (builtin display/keyboard on the HP-PARISC
2840 machines) console (graphic card) which should be used
2841 as the initial boot-console.
2842 See also comment in drivers/video/console/sticore.c.
2845 See comment in drivers/video/console/sticore.c.
2848 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2850 sunrpc.min_resvport=
2851 sunrpc.max_resvport=
2853 SunRPC servers often require that client requests
2854 originate from a privileged port (i.e. a port in the
2855 range 0 < portnr < 1024).
2856 An administrator who wishes to reserve some of these
2857 ports for other uses may adjust the range that the
2858 kernel's sunrpc client considers to be privileged
2859 using these two parameters to set the minimum and
2860 maximum port values.
2864 Control how the NFS server code allocates CPUs to
2865 service thread pools. Depending on how many NICs
2866 you have and where their interrupts are bound, this
2867 option will affect which CPUs will do NFS serving.
2868 Note: this parameter cannot be changed while the
2869 NFS server is running.
2871 auto the server chooses an appropriate mode
2872 automatically using heuristics
2873 global a single global pool contains all CPUs
2874 percpu one pool for each CPU
2875 pernode one pool for each NUMA node (equivalent
2876 to global on non-NUMA machines)
2878 sunrpc.tcp_slot_table_entries=
2879 sunrpc.udp_slot_table_entries=
2881 Sets the upper limit on the number of simultaneous
2882 RPC calls that can be sent from the client to a
2883 server. Increasing these values may allow you to
2884 improve throughput, but will also increase the
2885 amount of memory reserved for use by the client.
2888 [KNL] Enable accounting of swap in memory resource
2889 controller if no parameter or 1 is given or disable
2890 it if 0 is given (See Documentation/cgroups/memory.txt)
2892 swiotlb= [IA-64] Number of I/O TLB slabs
2896 sysfs.deprecated=0|1 [KNL]
2897 Enable/disable old style sysfs layout for old udev
2898 on older distributions. When this option is enabled
2899 very new udev will not work anymore. When this option
2900 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2901 in older udev will not work anymore.
2902 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2903 the kernel configuration.
2905 sysrq_always_enabled
2907 Ignore sysrq setting - this boot parameter will
2908 neutralize any effect of /proc/sys/kernel/sysrq.
2909 Useful for debugging.
2913 test_suspend= [SUSPEND]
2914 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2915 standby suspend) as the system sleep state to briefly
2916 enter during system startup. The system is woken from
2917 this state using a wakeup-capable RTC alarm.
2919 thash_entries= [KNL,NET]
2920 Set number of hash buckets for TCP connection
2922 thermal.act= [HW,ACPI]
2923 -1: disable all active trip points in all thermal zones
2924 <degrees C>: override all lowest active trip points
2926 thermal.crt= [HW,ACPI]
2927 -1: disable all critical trip points in all thermal zones
2928 <degrees C>: override all critical trip points
2930 thermal.nocrt= [HW,ACPI]
2931 Set to disable actions on ACPI thermal zone
2932 critical and hot trip points.
2934 thermal.off= [HW,ACPI]
2935 1: disable ACPI thermal control
2937 thermal.psv= [HW,ACPI]
2938 -1: disable all passive trip points
2939 <degrees C>: override all passive trip points to this
2942 thermal.tzp= [HW,ACPI]
2943 Specify global default ACPI thermal zone polling rate
2944 <deci-seconds>: poll all this frequency
2945 0: no polling (default)
2948 Force threading of all interrupt handlers except those
2949 marked explicitly IRQF_NO_THREAD.
2953 Specify if the kernel should make use of the cpu
2954 topology information if the hardware supports this.
2955 The scheduler will make use of this information and
2956 e.g. base its process migration decisions on it.
2961 tpm_suspend_pcr=[HW,TPM]
2962 Format: integer pcr id
2963 Specify that at suspend time, the tpm driver
2964 should extend the specified pcr with zeros,
2965 as a workaround for some chips which fail to
2966 flush the last written pcr on TPM_SaveState.
2967 This will guarantee that all the other pcrs
2970 trace_buf_size=nn[KMG]
2971 [FTRACE] will set tracing buffer size.
2973 trace_event=[event-list]
2974 [FTRACE] Set and start specified trace events in order
2975 to facilitate early boot debugging.
2976 See also Documentation/trace/events.txt
2978 trace_options=[option-list]
2979 [FTRACE] Enable or disable tracer options at boot.
2980 The option-list is a comma delimited list of options
2981 that can be enabled or disabled just as if you were
2982 to echo the option name into
2984 /sys/kernel/debug/tracing/trace_options
2986 For example, to enable stacktrace option (to dump the
2987 stack trace of each event), add to the command line:
2989 trace_options=stacktrace
2991 See also Documentation/trace/ftrace.txt "trace options"
2994 transparent_hugepage=
2996 Format: [always|madvise|never]
2997 Can be used to control the default behavior of the system
2998 with respect to transparent hugepages.
2999 See Documentation/vm/transhuge.txt for more details.
3001 tsc= Disable clocksource stability checks for TSC.
3003 [x86] reliable: mark tsc clocksource as reliable, this
3004 disables clocksource verification at runtime, as well
3005 as the stability checks done at bootup. Used to enable
3006 high-resolution timer mode on older hardware, and in
3007 virtualized environment.
3008 [x86] noirqtime: Do not use TSC to do irq accounting.
3009 Used to run time disable IRQ_TIME_ACCOUNTING on any
3010 platforms where RDTSC is slow and this accounting
3013 turbografx.map[2|3]= [HW,JOY]
3014 TurboGraFX parallel port interface
3016 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3017 See also Documentation/input/joystick-parport.txt
3019 udbg-immortal [PPC] When debugging early kernel crashes that
3020 happen after console_init() and before a proper
3021 console driver takes over, this boot options might
3022 help "seeing" what's going on.
3024 uhash_entries= [KNL,NET]
3025 Set number of hash buckets for UDP/UDP-Lite connections
3028 [USB] Ignore overcurrent events (default N).
3029 Some badly-designed motherboards generate lots of
3030 bogus events, for ports that aren't wired to
3031 anything. Set this parameter to avoid log spamming.
3032 Note that genuine overcurrent events won't be
3036 [X86] Cause panic on unknown NMI.
3038 usbcore.authorized_default=
3039 [USB] Default USB device authorization:
3040 (default -1 = authorized except for wireless USB,
3041 0 = not authorized, 1 = authorized)
3043 usbcore.autosuspend=
3044 [USB] The autosuspend time delay (in seconds) used
3045 for newly-detected USB devices (default 2). This
3046 is the time required before an idle device will be
3047 autosuspended. Devices for which the delay is set
3048 to a negative value won't be autosuspended at all.
3050 usbcore.usbfs_snoop=
3051 [USB] Set to log all usbfs traffic (default 0 = off).
3053 usbcore.blinkenlights=
3054 [USB] Set to cycle leds on hubs (default 0 = off).
3056 usbcore.old_scheme_first=
3057 [USB] Start with the old device initialization
3058 scheme (default 0 = off).
3060 usbcore.usbfs_memory_mb=
3061 [USB] Memory limit (in MB) for buffers allocated by
3062 usbfs (default = 16, 0 = max = 2047).
3064 usbcore.use_both_schemes=
3065 [USB] Try the other device initialization scheme
3066 if the first one fails (default 1 = enabled).
3068 usbcore.initial_descriptor_timeout=
3069 [USB] Specifies timeout for the initial 64-byte
3070 USB_REQ_GET_DESCRIPTOR request in milliseconds
3071 (default 5000 = 5.0 seconds).
3074 [USBHID] The interval which mice are to be polled at.
3076 usb-storage.delay_use=
3077 [UMS] The delay in seconds before a new device is
3078 scanned for Logical Units (default 5).
3081 [UMS] A list of quirks entries to supplement or
3082 override the built-in unusual_devs list. List
3083 entries are separated by commas. Each entry has
3084 the form VID:PID:Flags where VID and PID are Vendor
3085 and Product ID values (4-digit hex numbers) and
3086 Flags is a set of characters, each corresponding
3087 to a common usb-storage quirk flag as follows:
3088 a = SANE_SENSE (collect more than 18 bytes
3090 b = BAD_SENSE (don't collect more than 18
3091 bytes of sense data);
3092 c = FIX_CAPACITY (decrease the reported
3093 device capacity by one sector);
3094 d = NO_READ_DISC_INFO (don't use
3095 READ_DISC_INFO command);
3096 e = NO_READ_CAPACITY_16 (don't use
3097 READ_CAPACITY_16 command);
3098 h = CAPACITY_HEURISTICS (decrease the
3099 reported device capacity by one
3100 sector if the number is odd);
3101 i = IGNORE_DEVICE (don't bind to this
3103 l = NOT_LOCKABLE (don't try to lock and
3104 unlock ejectable media);
3105 m = MAX_SECTORS_64 (don't transfer more
3106 than 64 sectors = 32 KB at a time);
3107 n = INITIAL_READ10 (force a retry of the
3108 initial READ(10) command);
3109 o = CAPACITY_OK (accept the capacity
3110 reported by the device);
3111 p = WRITE_CACHE (the device cache is ON
3113 r = IGNORE_RESIDUE (the device reports
3114 bogus residue values);
3115 s = SINGLE_LUN (the device has only one
3117 w = NO_WP_DETECT (don't test whether the
3118 medium is write-protected).
3119 Example: quirks=0419:aaf5:rl,0421:0433:rc
3121 user_debug= [KNL,ARM]
3123 See arch/arm/Kconfig.debug help text.
3124 1 - undefined instruction events
3126 4 - invalid data aborts
3129 Example: user_debug=31
3132 [X86] Flags controlling user PTE allocations.
3134 nohigh = do not allocate PTE pages in
3135 HIGHMEM regardless of setting
3139 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3140 vdso=1: enable VDSO (default)
3141 vdso=0: disable VDSO mapping
3144 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3145 vdso32=1: enable 32-bit VDSO (default)
3146 vdso32=0: disable 32-bit VDSO mapping
3149 vector=percpu: enable percpu vector domain
3151 video= [FB] Frame buffer configuration
3152 See Documentation/fb/modedb.txt.
3155 [VMMIO] Memory mapped virtio (platform) device.
3157 <size>@<baseaddr>:<irq>[:<id>]
3159 <size> := size (can use standard suffixes
3161 <baseaddr> := physical base address
3162 <irq> := interrupt number (as passed to
3164 <id> := (optional) platform device id
3166 virtio_mmio.device=1K@0x100b0000:48:7
3168 Can be used multiple times for multiple devices.
3170 vga= [BOOT,X86-32] Select a particular video mode
3171 See Documentation/x86/boot.txt and
3172 Documentation/svga.txt.
3173 Use vga=ask for menu.
3174 This is actually a boot loader parameter; the value is
3175 passed to the kernel using a special protocol.
3177 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3178 size of <nn>. This can be used to increase the
3179 minimum size (128MB on x86). It can also be used to
3180 decrease the size and leave more room for directly
3183 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3186 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3189 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3193 Controls the behavior of vsyscalls (i.e. calls to
3194 fixed addresses of 0xffffffffff600x00 from legacy
3195 code). Most statically-linked binaries and older
3196 versions of glibc use these calls. Because these
3197 functions are at fixed addresses, they make nice
3198 targets for exploits that can control RIP.
3200 emulate [default] Vsyscalls turn into traps and are
3201 emulated reasonably safely.
3203 native Vsyscalls are native syscall instructions.
3204 This is a little bit faster than trapping
3205 and makes a few dynamic recompilers work
3206 better than they would in emulation mode.
3207 It also makes exploits much easier to write.
3209 none Vsyscalls don't work at all. This makes
3210 them quite hard to use for exploits but
3211 might break your system.
3213 vt.cur_default= [VT] Default cursor shape.
3214 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3215 the parameters of the <Esc>[?A;B;Cc escape sequence;
3216 see VGA-softcursor.txt. Default: 2 = underline.
3218 vt.default_blu= [VT]
3219 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3220 Change the default blue palette of the console.
3221 This is a 16-member array composed of values
3224 vt.default_grn= [VT]
3225 Format: <green0>,<green1>,<green2>,...,<green15>
3226 Change the default green palette of the console.
3227 This is a 16-member array composed of values
3230 vt.default_red= [VT]
3231 Format: <red0>,<red1>,<red2>,...,<red15>
3232 Change the default red palette of the console.
3233 This is a 16-member array composed of values
3239 Set system-wide default UTF-8 mode for all tty's.
3240 Default is 1, i.e. UTF-8 mode is enabled for all
3241 newly opened terminals.
3243 vt.global_cursor_default=
3246 Set system-wide default for whether a cursor
3247 is shown on new VTs. Default is -1,
3248 i.e. cursors will be created by default unless
3249 overridden by individual drivers. 0 will hide
3250 cursors, 1 will display them.
3252 watchdog timers [HW,WDT] For information on watchdog timers,
3253 see Documentation/watchdog/watchdog-parameters.txt
3254 or other driver-specific files in the
3255 Documentation/watchdog/ directory.
3257 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3258 default x2apic cluster mode on platforms
3261 x86_mrst_timer= [X86-32,APBT]
3262 Choose timer option for x86 Moorestown MID platform.
3263 Two valid options are apbt timer only and lapic timer
3264 plus one apbt timer for broadcast timer.
3265 x86_mrst_timer=apbt_only | lapic_and_apbt
3267 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
3268 xd_geo= See header of drivers/block/xd.c.
3270 xen_emul_unplug= [HW,X86,XEN]
3271 Unplug Xen emulated devices
3272 Format: [unplug0,][unplug1]
3273 ide-disks -- unplug primary master IDE devices
3274 aux-ide-disks -- unplug non-primary-master IDE devices
3275 nics -- unplug network devices
3276 all -- unplug all emulated devices (NICs and IDE disks)
3277 unnecessary -- unplugging emulated devices is
3278 unnecessary even if the host did not respond to
3280 never -- do not unplug even if version check succeeds
3282 xirc2ps_cs= [NET,PCMCIA]
3284 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3286 ______________________________________________________________________
3290 Add more DRM drivers.
projects / mirror_ubuntu-artful-kernel.git / blob