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 alloc_snapshot [FTRACE]
324 Allocate the ftrace snapshot buffer on boot up when the
325 main buffer is allocated. This is handy if debugging
326 and you need to use tracing_snapshot() on boot up, and
327 do not want to use tracing_snapshot_alloc() as it needs
328 to be done where GFP_KERNEL allocations are allowed.
330 amd_iommu= [HW,X86-64]
331 Pass parameters to the AMD IOMMU driver in the system.
333 fullflush - enable flushing of IO/TLB entries when
334 they are unmapped. Otherwise they are
335 flushed before they will be reused, which
337 off - do not initialize any AMD IOMMU found in
339 force_isolation - Force device isolation for all
340 devices. The IOMMU driver is not
341 allowed anymore to lift isolation
342 requirements as needed. This option
343 does not override iommu=pt
345 amd_iommu_dump= [HW,X86-64]
346 Enable AMD IOMMU driver option to dump the ACPI table
347 for AMD IOMMU. With this option enabled, AMD IOMMU
348 driver will print ACPI tables for AMD IOMMU during
349 IOMMU initialization.
351 amijoy.map= [HW,JOY] Amiga joystick support
352 Map of devices attached to JOY0DAT and JOY1DAT
354 See also Documentation/input/joystick.txt
356 analog.map= [HW,JOY] Analog joystick and gamepad support
357 Specifies type or capabilities of an analog joystick
358 connected to one of 16 gameports
359 Format: <type1>,<type2>,..<type16>
362 Power management functions (SPARCstation-4/5 + deriv.)
364 Disable APC CPU standby support. SPARCstation-Fox does
365 not play well with APC CPU idle - disable it if you have
366 APC and your system crashes randomly.
368 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
369 Change the output verbosity whilst booting
370 Format: { quiet (default) | verbose | debug }
371 Change the amount of debugging information output
372 when initialising the APIC and IO-APIC components.
375 See Documentation/networking/ipv6.txt.
377 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
378 Limit apic dumping. The parameter defines the maximal
379 number of local apics being dumped. Also it is possible
380 to set it to "all" by meaning -- no limit here.
381 Format: { 1 (default) | 2 | ... | all }.
382 The parameter valid if only apic=debug or
383 apic=verbose is specified.
384 Example: apic=debug show_lapic=all
386 apm= [APM] Advanced Power Management
387 See header of arch/x86/kernel/apm_32.c.
389 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
390 Format: <io>,<irq>,<nodeID>
394 atarimouse= [HW,MOUSE] Atari Mouse
396 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
397 EzKey and similar keyboards
399 atkbd.reset= [HW] Reset keyboard during initialization
401 atkbd.set= [HW] Select keyboard code set
402 Format: <int> (2 = AT (default), 3 = PS/2)
404 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
407 atkbd.softraw= [HW] Choose between synthetic and real raw mode
408 Format: <bool> (0 = real, 1 = synthetic (default))
410 atkbd.softrepeat= [HW]
411 Use software keyboard repeat
413 baycom_epp= [HW,AX25]
416 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
418 See header of drivers/net/hamradio/baycom_par.c.
420 baycom_ser_fdx= [HW,AX25]
421 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
422 Format: <io>,<irq>,<mode>[,<baud>]
423 See header of drivers/net/hamradio/baycom_ser_fdx.c.
425 baycom_ser_hdx= [HW,AX25]
426 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
427 Format: <io>,<irq>,<mode>
428 See header of drivers/net/hamradio/baycom_ser_hdx.c.
430 boot_delay= Milliseconds to delay each printk during boot.
431 Values larger than 10 seconds (10000) are changed to
435 bootmem_debug [KNL] Enable bootmem allocator debug messages.
437 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
438 bttv.radio= Most important insmod options are available as
440 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
443 bulk_remove=off [PPC] This parameter disables the use of the pSeries
444 firmware feature for flushing multiple hpte entries
447 c101= [NET] Moxa C101 synchronous serial card
449 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
450 Sometimes CPU hardware bugs make them report the cache
451 size incorrectly. The kernel will attempt work arounds
452 to fix known problems, but for some CPUs it is not
453 possible to determine what the correct size should be.
454 This option provides an override for these situations.
456 ccw_timeout_log [S390]
457 See Documentation/s390/CommonIO for details.
459 cgroup_disable= [KNL] Disable a particular controller
460 Format: {name of the controller(s) to disable}
461 {Currently supported controllers - "memory"}
463 checkreqprot [SELINUX] Set initial checkreqprot flag value.
464 Format: { "0" | "1" }
465 See security/selinux/Kconfig help text.
466 0 -- check protection applied by kernel (includes
467 any implied execute protection).
468 1 -- check protection requested by application.
469 Default value is set via a kernel config option.
470 Value can be changed at runtime via
471 /selinux/checkreqprot.
474 See Documentation/s390/CommonIO for details.
476 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
478 Forces specified clocksource (if available) to be used
479 when calculating gettimeofday(). If specified
480 clocksource is not available, it defaults to PIT.
481 Format: { pit | tsc | cyclone | pmtmr }
483 clocksource= Override the default clocksource
485 Override the default clocksource and use the clocksource
486 with the name specified.
487 Some clocksource names to choose from, depending on
489 [all] jiffies (this is the base, fallback clocksource)
491 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
492 pxa_timer,timer3,32k_counter,timer0_1
494 [X86-32] pit,hpet,tsc;
495 scx200_hrt on Geode; cyclone on IBM x440
503 clearcpuid=BITNUM [X86]
504 Disable CPUID feature X for the kernel. See
505 arch/x86/include/asm/cpufeature.h for the valid bit
506 numbers. Note the Linux specific bits are not necessarily
507 stable over kernel options, but the vendor specific
509 Also note that user programs calling CPUID directly
510 or using the feature without checking anything
511 will still see it. This just prevents it from
512 being used by the kernel or shown in /proc/cpuinfo.
513 Also note the kernel might malfunction if you disable
517 Sets the size of kernel global memory area for contiguous
518 memory allocations. For more information, see
519 include/linux/dma-contiguous.h
521 cmo_free_hint= [PPC] Format: { yes | no }
522 Specify whether pages are marked as being inactive
523 when they are freed. This is used in CMO environments
524 to determine OS memory pressure for page stealing by
528 coherent_pool=nn[KMG] [ARM,KNL]
529 Sets the size of memory pool for coherent, atomic dma
530 allocations, by default set to 256K.
532 code_bytes [X86] How many bytes of object code to print
537 com20020= [HW,NET] ARCnet - COM20020 chipset
539 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
541 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
545 ARCnet - COM90xx chipset (memory-mapped buffers)
546 Format: <io>[,<irq>[,<memstart>]]
548 condev= [HW,S390] console device
551 console= [KNL] Output console device and options.
553 tty<n> Use the virtual console device <n>.
557 Use the specified serial port. The options are of
558 the form "bbbbpnf", where "bbbb" is the baud rate,
559 "p" is parity ("n", "o", or "e"), "n" is number of
560 bits, and "f" is flow control ("r" for RTS or
561 omit it). Default is "9600n8".
563 See Documentation/serial-console.txt for more
565 Documentation/networking/netconsole.txt for an
568 uart[8250],io,<addr>[,options]
569 uart[8250],mmio,<addr>[,options]
570 Start an early, polled-mode console on the 8250/16550
571 UART at the specified I/O port or MMIO address,
572 switching to the matching ttyS device later. The
573 options are the same as for ttyS, above.
574 hvc<n> Use the hypervisor console device <n>. This is for
575 both Xen and PowerPC hypervisors.
577 If the device connected to the port is not a TTY but a braille
578 device, prepend "brl," before the device type, for instance
580 For now, only VisioBraille is supported.
582 consoleblank= [KNL] The console blank (screen saver) timeout in
583 seconds. Defaults to 10*60 = 10mins. A value of 0
584 disables the blank timer.
587 [KNL] Change the default value for
588 /proc/<pid>/coredump_filter.
589 See also Documentation/filesystems/proc.txt.
591 cpuidle.off=1 [CPU_IDLE]
592 disable the cpuidle sub-system
594 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
596 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
598 crashkernel=size[KMG][@offset[KMG]]
599 [KNL] Using kexec, Linux can switch to a 'crash kernel'
600 upon panic. This parameter reserves the physical
601 memory region [offset, offset + size] for that kernel
602 image. If '@offset' is omitted, then a suitable offset
603 is selected automatically. Check
604 Documentation/kdump/kdump.txt for further details.
606 crashkernel=range1:size1[,range2:size2,...][@offset]
607 [KNL] Same as above, but depends on the memory
608 in the running system. The syntax of range is
609 start-[end] where start and end are both
610 a memory unit (amount[KMG]). See also
611 Documentation/kdump/kdump.txt for an example.
613 crashkernel=size[KMG],high
614 [KNL, x86_64] range could be above 4G. Allow kernel
615 to allocate physical memory region from top, so could
616 be above 4G if system have more than 4G ram installed.
617 Otherwise memory region will be allocated below 4G, if
619 It will be ignored if crashkernel=X is specified.
620 crashkernel=size[KMG],low
621 [KNL, x86_64] range under 4G. When crashkernel=X,high
622 is passed, kernel could allocate physical memory region
623 above 4G, that cause second kernel crash on system
624 that require some amount of low memory, e.g. swiotlb
625 requires at least 64M+32K low memory. Kernel would
626 try to allocate 72M below 4G automatically.
627 This one let user to specify own low range under 4G
628 for second kernel instead.
629 0: to disable low allocation.
630 It will be ignored when crashkernel=X,high is not used
631 or memory reserved is below 4G.
636 cs89x0_media= [HW,NET]
637 Format: { rj45 | aui | bnc }
640 See header of drivers/s390/block/dasd_devmap.c.
642 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
643 (one device per port)
644 Format: <port#>,<type>
645 See also Documentation/input/joystick-parport.txt
647 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
648 time. See Documentation/dynamic-debug-howto.txt for
649 details. Deprecated, see dyndbg.
651 debug [KNL] Enable kernel debugging (events log level).
654 [KNL] verbose self-tests
656 Print debugging info while doing the locking API
658 We default to 0 (no extra messages), setting it to
659 1 will print _a lot_ more information - normally
660 only useful to kernel developers.
662 debug_objects [KNL] Enable object debugging
665 [KNL] Disable object debugging
667 debug_guardpage_minorder=
668 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
669 parameter allows control of the order of pages that will
670 be intentionally kept free (and hence protected) by the
671 buddy allocator. Bigger value increase the probability
672 of catching random memory corruption, but reduce the
673 amount of memory for normal system use. The maximum
674 possible value is MAX_ORDER/2. Setting this parameter
675 to 1 or 2 should be enough to identify most random
676 memory corruption problems caused by bugs in kernel or
677 driver code when a CPU writes to (or reads from) a
678 random memory location. Note that there exists a class
679 of memory corruptions problems caused by buggy H/W or
680 F/W or by drivers badly programing DMA (basically when
681 memory is written at bus level and the CPU MMU is
682 bypassed) which are not detectable by
683 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
684 tracking down these problems.
686 debugpat [X86] Enable PAT debugging
688 decnet.addr= [HW,NET]
689 Format: <area>[,<node>]
690 See also Documentation/networking/decnet.txt.
693 [same as hugepagesz=] The size of the default
694 HugeTLB page size. This is the size represented by
695 the legacy /proc/ hugepages APIs, used for SHM, and
696 default size when mounting hugetlbfs filesystems.
697 Defaults to the default architecture's huge page size
701 Set number of hash buckets for dentry cache.
704 IO parameters + enable/disable command.
706 digiepca= [HW,SERIAL]
707 See drivers/char/README.epca and
708 Documentation/serial/digiepca.txt.
711 See Documentation/networking/ipv6.txt.
713 disable_ddw [PPC/PSERIES]
714 Disable Dynamic DMA Window support. Use this if
715 to workaround buggy firmware.
718 See Documentation/networking/ipv6.txt.
720 disable_mtrr_cleanup [X86]
721 The kernel tries to adjust MTRR layout from continuous
722 to discrete, to make X server driver able to add WB
723 entry later. This parameter disables that.
725 disable_mtrr_trim [X86, Intel and AMD only]
726 By default the kernel will trim any uncacheable
727 memory out of your available memory pool based on
728 MTRR settings. This parameter disables that behavior,
729 possibly causing your machine to run very slowly.
731 disable_timer_pin_1 [X86]
732 Disable PIN 1 of APIC timer
733 Can be useful to work around chipset bugs.
735 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
736 this option disables the debugging code at boot.
738 dma_debug_entries=<number>
739 This option allows to tune the number of preallocated
740 entries for DMA-API debugging code. One entry is
741 required per DMA-API allocation. Use this if the
742 DMA-API debugging code disables itself because the
743 architectural default is too low.
745 dma_debug_driver=<driver_name>
746 With this option the DMA-API debugging driver
747 filter feature can be enabled at boot time. Just
748 pass the driver to filter for as the parameter.
749 The filter can be disabled or changed to another
750 driver later using sysfs.
752 drm_kms_helper.edid_firmware=[<connector>:]<file>
753 Broken monitors, graphic adapters and KVMs may
754 send no or incorrect EDID data sets. This parameter
755 allows to specify an EDID data set in the
756 /lib/firmware directory that is used instead.
757 Generic built-in EDID data sets are used, if one of
758 edid/1024x768.bin, edid/1280x1024.bin,
759 edid/1680x1050.bin, or edid/1920x1080.bin is given
760 and no file with the same name exists. Details and
761 instructions how to build your own EDID data are
762 available in Documentation/EDID/HOWTO.txt. An EDID
763 data set will only be used for a particular connector,
764 if its name and a colon are prepended to the EDID
769 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
770 module.dyndbg[="val"]
771 Enable debug messages at boot time. See
772 Documentation/dynamic-debug-howto.txt for details.
774 earlycon= [KNL] Output early console device and options.
775 uart[8250],io,<addr>[,options]
776 uart[8250],mmio,<addr>[,options]
777 uart[8250],mmio32,<addr>[,options]
778 Start an early, polled-mode console on the 8250/16550
779 UART at the specified I/O port or MMIO address.
780 MMIO inter-register address stride is either 8-bit
781 (mmio) or 32-bit (mmio32).
782 The options are the same as for ttyS, above.
784 earlyprintk= [X86,SH,BLACKFIN]
787 earlyprintk=serial[,ttySn[,baudrate]]
788 earlyprintk=ttySn[,baudrate]
789 earlyprintk=dbgp[debugController#]
791 Append ",keep" to not disable it when the real console
794 Only vga or serial or usb debug port at a time.
796 Currently only ttyS0 and ttyS1 are supported.
798 Interaction with the standard serial driver is not
801 The VGA output is eventually overwritten by the real
804 The xen output can only be used by Xen PV guests.
806 ekgdboc= [X86,KGDB] Allow early kernel console debugging
809 This is designed to be used in conjunction with
810 the boot argument: earlyprintk=vga
813 Format: {"off" | "on" | "skip[mbr]"}
815 efi_no_storage_paranoia [EFI; X86]
816 Using this parameter you can use more than 50% of
817 your efi variable storage. Use this parameter only if
818 you are really sure that your UEFI does sane gc and
819 fulfills the spec otherwise your board may brick.
821 eisa_irq_edge= [PARISC,HW]
822 See header of drivers/parisc/eisa.c.
825 See comment before function elanfreq_setup() in
826 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
829 Format: {"cfq" | "deadline" | "noop"}
830 See Documentation/block/cfq-iosched.txt and
831 Documentation/block/deadline-iosched.txt for details.
833 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
834 Specifies physical address of start of kernel core
835 image elf header and optionally the size. Generally
836 kexec loader will pass this option to capture kernel.
837 See Documentation/kdump/kdump.txt for details.
839 enable_mtrr_cleanup [X86]
840 The kernel tries to adjust MTRR layout from continuous
841 to discrete, to make X server driver able to add WB
842 entry later. This parameter enables that.
844 enable_timer_pin_1 [X86]
845 Enable PIN 1 of APIC timer
846 Can be useful to work around chipset bugs
847 (in particular on some ATI chipsets).
848 The kernel tries to set a reasonable default.
850 enforcing [SELINUX] Set initial enforcing status.
852 See security/selinux/Kconfig help text.
853 0 -- permissive (log only, no denials).
854 1 -- enforcing (deny and log).
856 Value can be changed at runtime via /selinux/enforce.
859 Disable Error Record Serialization Table (ERST)
862 ether= [HW,NET] Ethernet cards parameters
863 This option is obsoleted by the "netdev=" option, which
864 has equivalent usage. See its documentation for details.
868 Permit 'security.evm' to be updated regardless of
869 current integrity status.
873 fail_make_request=[KNL]
874 General fault injection mechanism.
875 Format: <interval>,<probability>,<space>,<times>
876 See also Documentation/fault-injection/.
879 See Documentation/blockdev/floppy.txt.
881 force_pal_cache_flush
882 [IA-64] Avoid check_sal_cache_flush which may hang on
883 buggy SAL_CACHE_FLUSH implementations. Using this
884 parameter will force ia64_sal_cache_flush to call
885 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
888 [FTRACE] will set and start the specified tracer
889 as early as possible in order to facilitate early
892 ftrace_dump_on_oops[=orig_cpu]
893 [FTRACE] will dump the trace buffers on oops.
894 If no parameter is passed, ftrace will dump
895 buffers of all CPUs, but if you pass orig_cpu, it will
896 dump only the buffer of the CPU that triggered the
899 ftrace_filter=[function-list]
900 [FTRACE] Limit the functions traced by the function
901 tracer at boot up. function-list is a comma separated
902 list of functions. This list can be changed at run
903 time by the set_ftrace_filter file in the debugfs
906 ftrace_notrace=[function-list]
907 [FTRACE] Do not trace the functions specified in
908 function-list. This list can be changed at run time
909 by the set_ftrace_notrace file in the debugfs
912 ftrace_graph_filter=[function-list]
913 [FTRACE] Limit the top level callers functions traced
914 by the function graph tracer at boot up.
915 function-list is a comma separated list of functions
916 that can be changed at run time by the
917 set_graph_function file in the debugfs tracing directory.
920 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
921 support via parallel port (up to 5 devices per port)
922 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
923 See also Documentation/input/joystick-parport.txt
927 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
931 gcov_persist= [GCOV] When non-zero (default), profiling data for
932 kernel modules is saved and remains accessible via
933 debugfs, even when the module is unloaded/reloaded.
934 When zero, profiling data is discarded and associated
935 debugfs files are removed at module unload time.
937 gpt [EFI] Forces disk with valid GPT signature but
938 invalid Protective MBR to be treated as GPT.
940 grcan.enable0= [HW] Configuration of physical interface 0. Determines
941 the "Enable 0" bit of the configuration register.
944 grcan.enable1= [HW] Configuration of physical interface 1. Determines
945 the "Enable 0" bit of the configuration register.
948 grcan.select= [HW] Select which physical interface to use.
951 grcan.txsize= [HW] Sets the size of the tx buffer.
952 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
954 grcan.rxsize= [HW] Sets the size of the rx buffer.
955 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
958 hashdist= [KNL,NUMA] Large hashes allocated during boot
959 are distributed across NUMA nodes. Defaults on
960 for 64-bit NUMA, off otherwise.
961 Format: 0 | 1 (for off | on)
963 hcl= [IA-64] SGI's Hardware Graph compatibility layer
965 hd= [EIDE] (E)IDE hard drive subsystem geometry
966 Format: <cyl>,<head>,<sect>
969 Disable Hardware Error Source Table (HEST) support;
970 corresponding firmware-first mode error processing
971 logic will be disabled.
973 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
974 size of <nn>. This works even on boxes that have no
975 highmem otherwise. This also works to reduce highmem
976 size on bigger boxes.
978 highres= [KNL] Enable/disable high resolution timer mode.
979 Valid parameters: "on", "off"
983 See Documentation/isdn/README.HiSax.
987 hpet= [X86-32,HPET] option to control HPET usage
988 Format: { enable (default) | disable | force |
990 disable: disable HPET and use PIT instead
991 force: allow force enabled of undocumented chips (ICH4,
993 verbose: show contents of HPET registers during setup
995 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
996 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
997 On x86-64 and powerpc, this option can be specified
998 multiple times interleaved with hugepages= to reserve
999 huge pages of different sizes. Valid pages sizes on
1000 x86-64 are 2M (when the CPU supports "pse") and 1G
1001 (when the CPU supports the "pdpe1gb" cpuinfo flag)
1002 Note that 1GB pages can only be allocated at boot time
1003 using hugepages= and not freed afterwards.
1005 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1006 terminal devices. Valid values: 0..8
1007 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1008 If specified, z/VM IUCV HVC accepts connections
1009 from listed z/VM user IDs only.
1011 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1012 hardware thread id mappings.
1013 Format: <cpu>:<hwthread>
1016 Do not unregister boot console at start. This is only
1017 useful for debugging when something happens in the window
1018 between unregistering the boot console and initializing
1021 i2c_bus= [HW] Override the default board specific I2C bus speed
1022 or register an additional I2C bus that is not
1023 registered from board initialization code.
1027 i8042.debug [HW] Toggle i8042 debug mode
1028 i8042.direct [HW] Put keyboard port into non-translated mode
1029 i8042.dumbkbd [HW] Pretend that controller can only read data from
1030 keyboard and cannot control its state
1031 (Don't attempt to blink the leds)
1032 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1033 i8042.nokbd [HW] Don't check/create keyboard port
1034 i8042.noloop [HW] Disable the AUX Loopback command while probing
1036 i8042.nomux [HW] Don't check presence of an active multiplexing
1038 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1040 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1041 i8042.reset [HW] Reset the controller during init and cleanup
1042 i8042.unlock [HW] Unlock (ignore) the keylock
1046 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1047 indicates that the driver is running on unsupported
1049 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1050 does not match list of supported models.
1052 [HW] Report power status in /proc/i8k
1053 (disabled by default)
1054 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1057 i915.invert_brightness=
1058 [DRM] Invert the sense of the variable that is used to
1059 set the brightness of the panel backlight. Normally a
1060 brightness value of 0 indicates backlight switched off,
1061 and the maximum of the brightness value sets the backlight
1062 to maximum brightness. If this parameter is set to 0
1063 (default) and the machine requires it, or this parameter
1064 is set to 1, a brightness value of 0 sets the backlight
1065 to maximum brightness, and the maximum of the brightness
1066 value switches the backlight off.
1067 -1 -- never invert brightness
1068 0 -- machine default
1069 1 -- force brightness inversion
1072 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1074 ide-core.nodma= [HW] (E)IDE subsystem
1075 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1076 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1077 .cdrom .chs .ignore_cable are additional options
1078 See Documentation/ide/ide.txt.
1080 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1081 Claim all unknown PCI IDE storage controllers.
1084 Format: idle=poll, idle=halt, idle=nomwait
1085 Poll forces a polling idle loop that can slightly
1086 improve the performance of waking up a idle CPU, but
1087 will use a lot of power and make the system run hot.
1089 idle=halt: Halt is forced to be used for CPU idle.
1090 In such case C2/C3 won't be used again.
1091 idle=nomwait: Disable mwait for CPU C-states
1093 ignore_loglevel [KNL]
1094 Ignore loglevel setting - this will print /all/
1095 kernel messages to the console. Useful for debugging.
1096 We also add it as printk module parameter, so users
1097 could change it dynamically, usually by
1098 /sys/module/printk/parameters/ignore_loglevel.
1100 ihash_entries= [KNL]
1101 Set number of hash buckets for inode cache.
1103 ima_appraise= [IMA] appraise integrity measurements
1104 Format: { "off" | "enforce" | "fix" }
1107 ima_appraise_tcb [IMA]
1108 The builtin appraise policy appraises all files
1112 Format: { "0" | "1" }
1113 0 -- integrity auditing messages. (Default)
1114 1 -- enable informational integrity auditing messages.
1117 Format: { "sha1" | "md5" }
1121 Load a policy which meets the needs of the Trusted
1122 Computing Base. This means IMA will measure all
1123 programs exec'd, files mmap'd for exec, and all files
1124 opened for read by uid=0.
1128 Run specified binary instead of /sbin/init as init
1131 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1132 for working out where the kernel is dying during
1135 initrd= [BOOT] Specify the location of the initial ramdisk
1137 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1140 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1142 Enable intel iommu driver.
1144 Disable intel iommu driver.
1145 igfx_off [Default Off]
1146 By default, gfx is mapped as normal device. If a gfx
1147 device has a dedicated DMAR unit, the DMAR unit is
1148 bypassed by not enabling DMAR with this option. In
1149 this case, gfx device will use physical address for
1152 With this option iommu will not optimize to look
1153 for io virtual address below 32-bit forcing dual
1154 address cycle on pci bus for cards supporting greater
1155 than 32-bit addressing. The default is to look
1156 for translation below 32-bit and if not available
1157 then look in the higher range.
1158 strict [Default Off]
1159 With this option on every unmap_single operation will
1160 result in a hardware IOTLB flush operation as opposed
1161 to batching them for performance.
1162 sp_off [Default Off]
1163 By default, super page will be supported if Intel IOMMU
1164 has the capability. With this option, super page will
1167 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1168 0 disables intel_idle and fall back on acpi_idle.
1169 1 to 6 specify maximum depth of C-state.
1173 Do not enable intel_pstate as the default
1174 scaling driver for the supported processors
1176 intremap= [X86-64, Intel-IOMMU]
1177 on enable Interrupt Remapping (default)
1178 off disable Interrupt Remapping
1179 nosid disable Source ID checking
1181 BIOS x2APIC opt-out request will be ignored
1183 iomem= Disable strict checking of access to MMIO memory
1184 strict regions from userspace.
1201 io7= [HW] IO7 for Marvel based alpha systems
1202 See comment before marvel_specify_io7 in
1203 arch/alpha/kernel/core_marvel.c.
1205 io_delay= [X86] I/O delay method
1207 Standard port 0x80 based delay
1209 Alternate port 0xed based delay (needed on some systems)
1211 Simple two microseconds delay
1216 See Documentation/filesystems/nfs/nfsroot.txt.
1218 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1219 See comment before ip2_setup() in
1220 drivers/char/ip2/ip2base.c.
1223 When an interrupt is not handled search all handlers
1224 for it. Intended to get systems with badly broken
1228 When an interrupt is not handled search all handlers
1229 for it. Also check all handlers each timer
1230 interrupt. Intended to get systems with badly broken
1234 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1236 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1238 <cpu number>,...,<cpu number>
1240 <cpu number>-<cpu number>
1241 (must be a positive range in ascending order)
1243 <cpu number>,...,<cpu number>-<cpu number>
1245 This option can be used to specify one or more CPUs
1246 to isolate from the general SMP balancing and scheduling
1247 algorithms. You can move a process onto or off an
1248 "isolated" CPU via the CPU affinity syscalls or cpuset.
1249 <cpu number> begins at 0 and the maximum value is
1250 "number of CPUs in system - 1".
1252 This option is the preferred way to isolate CPUs. The
1253 alternative -- manually setting the CPU mask of all
1254 tasks in the system -- can cause problems and
1255 suboptimal load balancer performance.
1259 js= [HW,JOY] Analog joystick
1260 See Documentation/input/joystick.txt.
1264 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1265 specifies the amount of memory usable by the kernel
1266 for non-movable allocations. The requested amount is
1267 spread evenly throughout all nodes in the system. The
1268 remaining memory in each node is used for Movable
1269 pages. In the event, a node is too small to have both
1270 kernelcore and Movable pages, kernelcore pages will
1271 take priority and other nodes will have a larger number
1272 of kernelcore pages. The Movable zone is used for the
1273 allocation of pages that may be reclaimed or moved
1274 by the page migration subsystem. This means that
1275 HugeTLB pages may not be allocated from this zone.
1276 Note that allocations like PTEs-from-HighMem still
1277 use the HighMem zone if it exists, and the Normal
1278 zone if it does not.
1280 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1281 Format: <Controller#>[,poll interval]
1282 The controller # is the number of the ehci usb debug
1283 port as it is probed via PCI. The poll interval is
1284 optional and is the number seconds in between
1285 each poll cycle to the debug port in case you need
1286 the functionality for interrupting the kernel with
1287 gdb or control-c on the dbgp connection. When
1288 not using this parameter you use sysrq-g to break into
1289 the kernel debugger.
1291 kgdboc= [KGDB,HW] kgdb over consoles.
1292 Requires a tty driver that supports console polling,
1293 or a supported polling keyboard driver (non-usb).
1294 Serial only format: <serial_device>[,baud]
1295 keyboard only format: kbd
1296 keyboard and serial format: kbd,<serial_device>[,baud]
1297 Optional Kernel mode setting:
1298 kms, kbd format: kms,kbd
1299 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1301 kgdbwait [KGDB] Stop kernel execution and enter the
1302 kernel debugger at the earliest opportunity.
1304 kmac= [MIPS] korina ethernet MAC address.
1305 Configure the RouterBoard 532 series on-chip
1306 Ethernet adapter MAC address.
1308 kmemleak= [KNL] Boot-time kmemleak enable/disable
1309 Valid arguments: on, off
1312 kstack=N [X86] Print N words from the kernel stack
1315 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1316 Default is 0 (don't ignore, but inject #GP)
1318 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1322 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1323 Default is 1 (enabled)
1325 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1327 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1329 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1330 (virtualized MMU) support on capable Intel chips.
1331 Default is 1 (enabled)
1333 kvm-intel.emulate_invalid_guest_state=
1334 [KVM,Intel] Enable emulation of invalid guest states
1335 Default is 0 (disabled)
1337 kvm-intel.flexpriority=
1338 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1339 Default is 1 (enabled)
1342 [KVM,Intel] Enable VMX nesting (nVMX).
1343 Default is 0 (disabled)
1345 kvm-intel.unrestricted_guest=
1346 [KVM,Intel] Disable unrestricted guest feature
1347 (virtualized real and unpaged mode) on capable
1348 Intel chips. Default is 1 (enabled)
1350 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1351 feature (tagged TLBs) on capable Intel chips.
1352 Default is 1 (enabled)
1358 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1361 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1362 value for LAPIC timer one-shot implementation. Default
1363 back to the programmable timer unit in the LAPIC.
1365 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1368 libata.dma= [LIBATA] DMA control
1369 libata.dma=0 Disable all PATA and SATA DMA
1370 libata.dma=1 PATA and SATA Disk DMA only
1371 libata.dma=2 ATAPI (CDROM) DMA only
1372 libata.dma=4 Compact Flash DMA only
1373 Combinations also work, so libata.dma=3 enables DMA
1374 for disks and CDROMs, but not CFs.
1376 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1377 libata.ignore_hpa=0 keep BIOS limits (default)
1378 libata.ignore_hpa=1 ignore limits, using full disk
1380 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1384 libata.force= [LIBATA] Force configurations. The format is comma
1385 separated list of "[ID:]VAL" where ID is
1386 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1387 matching port, link or device. Basically, it matches
1388 the ATA ID string printed on console by libata. If
1389 the whole ID part is omitted, the last PORT and DEVICE
1390 values are used. If ID hasn't been specified yet, the
1391 configuration applies to all ports, links and devices.
1393 If only DEVICE is omitted, the parameter applies to
1394 the port and all links and devices behind it. DEVICE
1395 number of 0 either selects the first device or the
1396 first fan-out link behind PMP device. It does not
1397 select the host link. DEVICE number of 15 selects the
1398 host link and device attached to it.
1400 The VAL specifies the configuration to force. As long
1401 as there's no ambiguity shortcut notation is allowed.
1402 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1403 The following configurations can be forced.
1405 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1406 Any ID with matching PORT is used.
1408 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1410 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1411 udma[/][16,25,33,44,66,100,133] notation is also
1414 * [no]ncq: Turn on or off NCQ.
1416 * nohrst, nosrst, norst: suppress hard, soft
1419 * rstonce: only attempt one reset during
1420 hot-unplug link recovery
1422 * dump_id: dump IDENTIFY data.
1424 If there are multiple matching configurations changing
1425 the same attribute, the last one is used.
1427 memblock=debug [KNL] Enable memblock debug messages.
1429 load_ramdisk= [RAM] List of ramdisks to load from floppy
1430 See Documentation/blockdev/ramdisk.txt.
1432 lockd.nlm_grace_period=P [NFS] Assign grace period.
1435 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1438 lockd.nlm_timeout=T [NFS] Assign timeout value.
1441 lockd.nlm_udpport=M [NFS] Assign UDP port.
1444 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1447 loglevel= All Kernel Messages with a loglevel smaller than the
1448 console loglevel will be printed to the console. It can
1449 also be changed with klogd or other programs. The
1450 loglevels are defined as follows:
1452 0 (KERN_EMERG) system is unusable
1453 1 (KERN_ALERT) action must be taken immediately
1454 2 (KERN_CRIT) critical conditions
1455 3 (KERN_ERR) error conditions
1456 4 (KERN_WARNING) warning conditions
1457 5 (KERN_NOTICE) normal but significant condition
1458 6 (KERN_INFO) informational
1459 7 (KERN_DEBUG) debug-level messages
1461 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1462 in bytes. n must be a power of two. The default
1463 size is set in the kernel config file.
1465 logo.nologo [FB] Disables display of the built-in Linux logo.
1466 This may be used to provide more screen space for
1467 kernel log messages and is useful when debugging
1468 kernel boot problems.
1470 lp=0 [LP] Specify parallel ports to use, e.g,
1471 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1472 lp=reset first parallel port). 'lp=0' disables the
1473 lp=auto printer driver. 'lp=reset' (which can be
1474 specified in addition to the ports) causes
1475 attached printers to be reset. Using
1476 lp=port1,port2,... specifies the parallel ports
1477 to associate lp devices with, starting with
1478 lp0. A port specification may be 'none' to skip
1479 that lp device, or a parport name such as
1480 'parport0'. Specifying 'lp=auto' instead of a
1481 port specification list means that device IDs
1482 from each port should be examined, to see if
1483 an IEEE 1284-compliant printer is attached; if
1484 so, the driver will manage that printer.
1485 See also header of drivers/char/lp.c.
1488 Sets loops_per_jiffy to given constant, thus avoiding
1489 time-consuming boot-time autodetection (up to 250 ms per
1490 CPU). 0 enables autodetection (default). To determine
1491 the correct value for your kernel, boot with normal
1492 autodetection and see what value is printed. Note that
1493 on SMP systems the preset will be applied to all CPUs,
1494 which is likely to cause problems if your CPUs need
1495 significantly divergent settings. An incorrect value
1496 will cause delays in the kernel to be wrong, leading to
1497 unpredictable I/O errors and other breakage. Although
1498 unlikely, in the extreme case this might damage your
1502 Format: <io>,<irq>,<dma>
1504 machvec= [IA-64] Force the use of a particular machine-vector
1505 (machvec) in a generic kernel.
1506 Example: machvec=hpzx1_swiotlb
1508 machtype= [Loongson] Share the same kernel image file between different
1510 Example: machtype=lemote-yeeloong-2f-7inch
1512 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1513 than or equal to this physical address is ignored.
1515 maxcpus= [SMP] Maximum number of processors that an SMP kernel
1516 should make use of. maxcpus=n : n >= 0 limits the
1517 kernel to using 'n' processors. n=0 is a special case,
1518 it is equivalent to "nosmp", which also disables
1521 max_loop= [LOOP] The number of loop block devices that get
1522 (loop.max_loop) unconditionally pre-created at init time. The default
1523 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1524 of statically allocating a predefined number, loop
1525 devices can be requested on-demand with the
1526 /dev/loop-control interface.
1528 mce [X86-32] Machine Check Exception
1530 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1532 md= [HW] RAID subsystems devices and level
1533 See Documentation/md.txt.
1536 Format: <first>,<last>
1537 Specifies range of consoles to be captured by the MDA.
1539 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1540 Amount of memory to be used when the kernel is not able
1541 to see the whole system memory or for test.
1542 [X86] Work as limiting max address. Use together
1543 with memmap= to avoid physical address space collisions.
1544 Without memmap= PCI devices could be placed at addresses
1545 belonging to unused RAM.
1547 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1551 [KNL,SH] Allow user to override the default size for
1552 per-device physically contiguous DMA buffers.
1554 memmap=exactmap [KNL,X86] Enable setting of an exact
1555 E820 memory map, as specified by the user.
1556 Such memmap=exactmap lines can be constructed based on
1557 BIOS output or other requirements. See the memmap=nn@ss
1560 memmap=nn[KMG]@ss[KMG]
1561 [KNL] Force usage of a specific region of memory
1562 Region of memory to be used, from ss to ss+nn.
1564 memmap=nn[KMG]#ss[KMG]
1565 [KNL,ACPI] Mark specific memory as ACPI data.
1566 Region of memory to be used, from ss to ss+nn.
1568 memmap=nn[KMG]$ss[KMG]
1569 [KNL,ACPI] Mark specific memory as reserved.
1570 Region of memory to be used, from ss to ss+nn.
1571 Example: Exclude memory from 0x18690000-0x1869ffff
1572 memmap=64K$0x18690000
1574 memmap=0x10000$0x18690000
1576 memory_corruption_check=0/1 [X86]
1577 Some BIOSes seem to corrupt the first 64k of
1578 memory when doing things like suspend/resume.
1579 Setting this option will scan the memory
1580 looking for corruption. Enabling this will
1581 both detect corruption and prevent the kernel
1582 from using the memory being corrupted.
1583 However, its intended as a diagnostic tool; if
1584 repeatable BIOS-originated corruption always
1585 affects the same memory, you can use memmap=
1586 to prevent the kernel from using that memory.
1588 memory_corruption_check_size=size [X86]
1589 By default it checks for corruption in the low
1590 64k, making this memory unavailable for normal
1591 use. Use this parameter to scan for
1592 corruption in more or less memory.
1594 memory_corruption_check_period=seconds [X86]
1595 By default it checks for corruption every 60
1596 seconds. Use this parameter to check at some
1597 other rate. 0 disables periodic checking.
1599 memtest= [KNL,X86] Enable memtest
1601 default : 0 <disable>
1602 Specifies the number of memtest passes to be
1603 performed. Each pass selects another test
1604 pattern from a given set of patterns. Memtest
1605 fills the memory with this pattern, validates
1606 memory contents and reserves bad memory
1607 regions that are detected.
1609 meye.*= [HW] Set MotionEye Camera parameters
1610 See Documentation/video4linux/meye.txt.
1612 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1613 Multi-Function General Purpose Timers on AMD Geode
1616 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1617 the BIOS has incorrectly applied a workaround. TinyBIOS
1618 version 0.98 is known to be affected, 0.99 fixes the
1619 problem by letting the user disable the workaround.
1623 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1624 physical address is ignored.
1626 mini2440= [ARM,HW,KNL]
1627 Format:[0..2][b][c][t]
1629 MINI2440 configuration specification:
1630 0 - The attached screen is the 3.5" TFT
1631 1 - The attached screen is the 7" TFT
1632 2 - The VGA Shield is attached (1024x768)
1633 Leaving out the screen size parameter will not load
1634 the TFT driver, and the framebuffer will be left
1636 b - Enable backlight. The TFT backlight pin will be
1637 linked to the kernel VESA blanking code and a GPIO
1638 LED. This parameter is not necessary when using the
1640 c - Enable the s3c camera interface.
1641 t - Reserved for enabling touchscreen support. The
1642 touchscreen support is not enabled in the mainstream
1643 kernel as of 2.6.30, a preliminary port can be found
1644 in the "bleeding edge" mini2440 support kernel at
1645 http://repo.or.cz/w/linux-2.6/mini2440.git
1648 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1649 parameter allows control of the logging verbosity for
1650 the additional memory initialisation checks. A value
1651 of 0 disables mminit logging and a level of 4 will
1652 log everything. Information is printed at KERN_DEBUG
1653 so loglevel=8 may also need to be specified.
1656 [KNL] When CONFIG_MODULE_SIG is set, this means that
1657 modules without (valid) signatures will fail to load.
1658 Note that if CONFIG_MODULE_SIG_ENFORCE is set, that
1659 is always true, so this option does nothing.
1662 [MOUSE] Maximum time between finger touching and
1663 leaving touchpad surface for touch to be considered
1664 a tap and be reported as a left button click (for
1665 touchpads working in absolute mode only).
1667 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1668 reporting absolute coordinates, such as tablets
1669 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1670 reporting absolute coordinates, such as tablets
1672 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1673 is similar to kernelcore except it specifies the
1674 amount of memory used for migratable allocations.
1675 If both kernelcore and movablecore is specified,
1676 then kernelcore will be at *least* the specified
1677 value but may be more. If movablecore on its own
1678 is specified, the administrator must be careful
1679 that the amount of memory usable for all allocations
1682 MTD_Partition= [MTD]
1683 Format: <name>,<region-number>,<size>,<offset>
1685 MTD_Region= [MTD] Format:
1686 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1689 See drivers/mtd/cmdlinepart.c.
1691 multitce=off [PPC] This parameter disables the use of the pSeries
1692 firmware feature for updating multiple TCE entries
1695 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1697 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1699 boundary - index of last SLC block on Flex-OneNAND.
1700 The remaining blocks are configured as MLC blocks.
1701 lock - Configure if Flex-OneNAND boundary should be locked.
1702 Once locked, the boundary cannot be changed.
1703 1 indicates lock status, 0 indicates unlock status.
1706 ARM/S3C2412 JIVE boot control
1708 See arch/arm/mach-s3c2412/mach-jive.c
1710 mtouchusb.raw_coordinates=
1711 [HW] Make the MicroTouch USB driver use raw coordinates
1712 ('y', default) or cooked coordinates ('n')
1714 mtrr_chunk_size=nn[KMG] [X86]
1715 used for mtrr cleanup. It is largest continuous chunk
1716 that could hold holes aka. UC entries.
1718 mtrr_gran_size=nn[KMG] [X86]
1719 Used for mtrr cleanup. It is granularity of mtrr block.
1721 Large value could prevent small alignment from
1724 mtrr_spare_reg_nr=n [X86]
1726 Range: 0,7 : spare reg number
1728 Used for mtrr cleanup. It is spare mtrr entries number.
1729 Set to 2 or more if your graphical card needs more.
1731 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1733 netdev= [NET] Network devices parameters
1734 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1735 Note that mem_start is often overloaded to mean
1736 something different and driver-specific.
1737 This usage is only documented in each driver source
1741 [NETFILTER] Enable connection tracking flow accounting
1742 0 to disable accounting
1743 1 to enable accounting
1746 nfsaddrs= [NFS] Deprecated. Use ip= instead.
1747 See Documentation/filesystems/nfs/nfsroot.txt.
1749 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1750 See Documentation/filesystems/nfs/nfsroot.txt.
1752 nfsrootdebug [NFS] enable nfsroot debugging messages.
1753 See Documentation/filesystems/nfs/nfsroot.txt.
1755 nfs.callback_tcpport=
1756 [NFS] set the TCP port on which the NFSv4 callback
1757 channel should listen.
1760 [NFS] sets the pathname to the program which is used
1761 to update the NFS client cache entries.
1763 nfs.cache_getent_timeout=
1764 [NFS] sets the timeout after which an attempt to
1765 update a cache entry is deemed to have failed.
1767 nfs.idmap_cache_timeout=
1768 [NFS] set the maximum lifetime for idmapper cache
1772 [NFS] enable 64-bit inode numbers.
1773 If zero, the NFS client will fake up a 32-bit inode
1774 number for the readdir() and stat() syscalls instead
1775 of returning the full 64-bit number.
1776 The default is to return 64-bit inode numbers.
1778 nfs.max_session_slots=
1779 [NFSv4.1] Sets the maximum number of session slots
1780 the client will attempt to negotiate with the server.
1781 This limits the number of simultaneous RPC requests
1782 that the client can send to the NFSv4.1 server.
1783 Note that there is little point in setting this
1784 value higher than the max_tcp_slot_table_limit.
1786 nfs.nfs4_disable_idmapping=
1787 [NFSv4] When set to the default of '1', this option
1788 ensures that both the RPC level authentication
1789 scheme and the NFS level operations agree to use
1790 numeric uids/gids if the mount is using the
1791 'sec=sys' security flavour. In effect it is
1792 disabling idmapping, which can make migration from
1793 legacy NFSv2/v3 systems to NFSv4 easier.
1794 Servers that do not support this mode of operation
1795 will be autodetected by the client, and it will fall
1796 back to using the idmapper.
1797 To turn off this behaviour, set the value to '0'.
1799 [NFS4] Specify an additional fixed unique ident-
1800 ification string that NFSv4 clients can insert into
1801 their nfs_client_id4 string. This is typically a
1802 UUID that is generated at system install time.
1804 nfs.send_implementation_id =
1805 [NFSv4.1] Send client implementation identification
1806 information in exchange_id requests.
1807 If zero, no implementation identification information
1809 The default is to send the implementation identification
1812 nfsd.nfs4_disable_idmapping=
1813 [NFSv4] When set to the default of '1', the NFSv4
1814 server will return only numeric uids and gids to
1815 clients using auth_sys, and will accept numeric uids
1816 and gids from such clients. This is intended to ease
1817 migration from NFSv2/v3.
1819 objlayoutdriver.osd_login_prog=
1820 [NFS] [OBJLAYOUT] sets the pathname to the program which
1821 is used to automatically discover and login into new
1822 osd-targets. Please see:
1823 Documentation/filesystems/pnfs.txt for more explanations
1825 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1826 when a NMI is triggered.
1827 Format: [state][,regs][,debounce][,die]
1829 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1830 Format: [panic,][nopanic,][num]
1832 0 - turn nmi_watchdog off
1833 When panic is specified, panic when an NMI watchdog
1834 timeout occurs (or 'nopanic' to override the opposite
1836 This is useful when you use a panic=... timeout and
1837 need the box quickly up again.
1839 netpoll.carrier_timeout=
1840 [NET] Specifies amount of time (in seconds) that
1841 netpoll should wait for a carrier. By default netpoll
1844 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1845 emulation library even if a 387 maths coprocessor
1849 [HW] Never suspend the console
1850 Disable suspending of consoles during suspend and
1851 hibernate operations. Once disabled, debugging
1852 messages can reach various consoles while the rest
1853 of the system is being put to sleep (ie, while
1854 debugging driver suspend/resume hooks). This may
1855 not work reliably with all consoles, but is known
1856 to work with serial and VGA consoles.
1857 To facilitate more flexible debugging, we also add
1858 console_suspend, a printk module parameter to control
1859 it. Users could use console_suspend (usually
1860 /sys/module/printk/parameters/console_suspend) to
1861 turn on/off it dynamically.
1863 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1864 caches in the slab allocator. Saves per-node memory,
1865 but will impact performance.
1869 noapic [SMP,APIC] Tells the kernel to not make use of any
1870 IOAPICs that may be present in the system.
1872 noautogroup Disable scheduler automatic task group creation.
1874 nobats [PPC] Do not use BATs for mapping kernel lowmem
1875 on "Classic" PPC cores.
1879 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1881 nodelayacct [KNL] Disable per-task delay accounting
1883 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1885 nodsp [SH] Disable hardware DSP at boot time.
1887 noefi [X86] Disable EFI runtime services support.
1892 On X86-32 available only on PAE configured kernels.
1893 noexec=on: enable non-executable mappings (default)
1894 noexec=off: disable non-executable mappings
1897 Disable SMAP (Supervisor Mode Access Prevention)
1898 even if it is supported by processor.
1901 Disable SMEP (Supervisor Mode Execution Prevention)
1902 even if it is supported by processor.
1905 This affects only 32-bit executables.
1906 noexec32=on: enable non-executable mappings (default)
1907 read doesn't imply executable mappings
1908 noexec32=off: disable non-executable mappings
1909 read implies executable mappings
1911 nofpu [SH] Disable hardware FPU at boot time.
1913 nofxsr [BUGS=X86-32] Disables x86 floating point extended
1914 register save and restore. The kernel will only save
1915 legacy floating-point registers on task switch.
1917 noxsave [BUGS=X86] Disables x86 extended register state save
1918 and restore using xsave. The kernel will fallback to
1919 enabling legacy floating-point and sse state.
1922 on enable eager fpu restore
1923 off disable eager fpu restore
1924 auto selects the default scheme, which automatically
1925 enables eagerfpu restore for xsaveopt.
1927 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1928 wfi(ARM) instruction doesn't work correctly and not to
1929 use it. This is also useful when using JTAG debugger.
1931 no_file_caps Tells the kernel not to honor file capabilities. The
1932 only way then for a file to be executed with privilege
1933 is to be setuid root or executed by root.
1935 nohalt [IA-64] Tells the kernel not to use the power saving
1936 function PAL_HALT_LIGHT when idle. This increases
1937 power-consumption. On the positive side, it reduces
1938 interrupt wake-up latency, which may improve performance
1939 in certain environments such as networked servers or
1942 nohz= [KNL] Boottime enable/disable dynamic ticks
1943 Valid arguments: on, off
1946 noiotrap [SH] Disables trapped I/O port accesses.
1948 noirqdebug [X86-32] Disables the code which attempts to detect and
1949 disable unhandled interrupt sources.
1951 no_timer_check [X86,APIC] Disables the code which tests for
1952 broken timer IRQ sources.
1954 noisapnp [ISAPNP] Disables ISA PnP code.
1956 noinitrd [RAM] Tells the kernel not to load any configured
1959 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1961 [Deprecated - use intremap=off]
1965 nojitter [IA-64] Disables jitter checking for ITC timers.
1967 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1969 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1972 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1973 steal time is computed, but won't influence scheduler
1976 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1978 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1980 noltlbs [PPC] Do not use large page/tlb entries for kernel
1981 lowmem mapping on PPC40x.
1983 nomca [IA-64] Disable machine check abort handling
1985 nomce [X86-32] Machine Check Exception
1987 nomfgpt [X86-32] Disable Multi-Function General Purpose
1988 Timer usage (for AMD Geode machines).
1990 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
1991 shutdown the other cpus. Instead use the REBOOT_VECTOR
1994 nomodule Disable module load
1996 nopat [X86] Disable PAT (page attribute table extension of
1997 pagetables) support.
1999 norandmaps Don't use address space randomization. Equivalent to
2000 echo 0 > /proc/sys/kernel/randomize_va_space
2002 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2004 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2005 with UP alternatives
2007 noresidual [PPC] Don't use residual data on PReP machines.
2009 nordrand [X86] Disable the direct use of the RDRAND
2010 instruction even if it is supported by the
2011 processor. RDRAND is still available to user
2014 noresume [SWSUSP] Disables resume and restores original swap
2017 no-scroll [VGA] Disables scrollback.
2018 This is required for the Braillex ib80-piezo Braille
2019 reader made by F.H. Papenmeier (Germany).
2023 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2025 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2026 and disable the IO APIC. legacy for "maxcpus=0".
2028 nosoftlockup [KNL] Disable the soft-lockup detector.
2030 nosync [HW,M68K] Disables sync negotiation for all devices.
2032 notsc [BUGS=X86-32] Disable Time Stamp Counter
2034 nousb [USB] Disable the USB subsystem
2036 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2040 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2042 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2043 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2044 Some features depend on CPU0. Known dependencies are:
2045 1. Resume from suspend/hibernate depends on CPU0.
2046 Suspend/hibernate will fail if CPU0 is offline and you
2047 need to online CPU0 before suspend/hibernate.
2048 2. PIC interrupts also depend on CPU0. CPU0 can't be
2049 removed if a PIC interrupt is detected.
2050 It's said poweroff/reboot may depend on CPU0 on some
2051 machines although I haven't seen such issues so far
2052 after CPU0 is offline on a few tested machines.
2053 If the dependencies are under your control, you can
2054 turn on cpu0_hotplug.
2056 nptcg= [IA-64] Override max number of concurrent global TLB
2057 purges which is reported from either PAL_VM_SUMMARY or
2060 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2061 could support. nr_cpus=n : n >= 1 limits the kernel to
2062 supporting 'n' processors. Later in runtime you can not
2063 use hotplug cpu feature to put more cpu back to online.
2064 just like you compile the kernel NR_CPUS=n
2066 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2068 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2069 Allowed values are enable and disable
2071 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2072 one of ['zone', 'node', 'default'] can be specified
2073 This can be set from sysctl after boot.
2074 See Documentation/sysctl/vm.txt for details.
2076 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2077 See Documentation/debugging-via-ohci1394.txt for more
2080 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2081 Rather than timing out after 20 ms if an EC
2082 command is not properly ACKed, override the length
2083 of the timeout. We have interrupts disabled while
2084 waiting for the ACK, so if this is set too high
2085 interrupts *may* be lost!
2087 omap_mux= [OMAP] Override bootloader pin multiplexing.
2088 Format: <mux_mode0.mode_name=value>...
2089 For example, to override I2C bus2:
2090 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2092 oprofile.timer= [HW]
2093 Use timer interrupt instead of performance counters
2095 oprofile.cpu_type= Force an oprofile cpu type
2096 This might be useful if you have an older oprofile
2097 userland or if you want common events.
2098 Format: { arch_perfmon }
2099 arch_perfmon: [X86] Force use of architectural
2100 perfmon on Intel CPUs instead of the
2101 CPU specific event set.
2102 timer: [X86] Force use of architectural NMI
2103 timer mode (see also oprofile.timer
2104 for generic hr timer mode)
2105 [s390] Force legacy basic mode sampling
2106 (report cpu_type "timer")
2108 oops=panic Always panic on oopses. Default is to just kill the
2109 process, but there is a small probability of
2110 deadlocking the machine.
2111 This will also cause panics on machine check exceptions.
2112 Useful together with panic=30 to trigger a reboot.
2115 See Documentation/sound/oss/oss-parameters.txt
2117 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2118 timeout > 0: seconds before rebooting
2119 timeout = 0: wait forever
2120 timeout < 0: reboot immediately
2123 parkbd.port= [HW] Parallel port number the keyboard adapter is
2124 connected to, default is 0.
2126 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2127 0 for XT, 1 for AT (default is AT).
2130 parport= [HW,PPT] Specify parallel ports. 0 disables.
2131 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2132 Use 'auto' to force the driver to use any
2133 IRQ/DMA settings detected (the default is to
2134 ignore detected IRQ/DMA settings because of
2135 possible conflicts). You can specify the base
2136 address, IRQ, and DMA settings; IRQ and DMA
2137 should be numbers, or 'auto' (for using detected
2138 settings on that particular port), or 'nofifo'
2139 (to avoid using a FIFO even if it is detected).
2140 Parallel ports are assigned in the order they
2141 are specified on the command line, starting
2144 parport_init_mode= [HW,PPT]
2145 Configure VIA parallel port to operate in
2146 a specific mode. This is necessary on Pegasos
2147 computer where firmware has no options for setting
2148 up parallel port mode and sets it to spp.
2149 Currently this function knows 686a and 8231 chips.
2150 Format: [spp|ps2|epp|ecp|ecpepp]
2153 Halt all CPUs after the first oops has been printed for
2154 the specified number of seconds. This is to be used if
2155 your oopses keep scrolling off the screen.
2160 See header of drivers/block/paride/pcd.c.
2161 See also Documentation/blockdev/paride.txt.
2163 pci=option[,option...] [PCI] various PCI subsystem options:
2164 earlydump [X86] dump PCI config space before the kernel
2166 off [X86] don't probe for the PCI bus
2167 bios [X86-32] force use of PCI BIOS, don't access
2168 the hardware directly. Use this if your machine
2169 has a non-standard PCI host bridge.
2170 nobios [X86-32] disallow use of PCI BIOS, only direct
2171 hardware access methods are allowed. Use this
2172 if you experience crashes upon bootup and you
2173 suspect they are caused by the BIOS.
2174 conf1 [X86] Force use of PCI Configuration
2176 conf2 [X86] Force use of PCI Configuration
2178 noaer [PCIE] If the PCIEAER kernel config parameter is
2179 enabled, this kernel boot option can be used to
2180 disable the use of PCIE advanced error reporting.
2181 nodomains [PCI] Disable support for multiple PCI
2182 root domains (aka PCI segments, in ACPI-speak).
2183 nommconf [X86] Disable use of MMCONFIG for PCI
2185 check_enable_amd_mmconf [X86] check for and enable
2186 properly configured MMIO access to PCI
2187 config space on AMD family 10h CPU
2188 nomsi [MSI] If the PCI_MSI kernel config parameter is
2189 enabled, this kernel boot option can be used to
2190 disable the use of MSI interrupts system-wide.
2191 noioapicquirk [APIC] Disable all boot interrupt quirks.
2192 Safety option to keep boot IRQs enabled. This
2193 should never be necessary.
2194 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2195 primary IO-APIC for bridges that cannot disable
2196 boot IRQs. This fixes a source of spurious IRQs
2197 when the system masks IRQs.
2198 noioapicreroute [APIC] Disable workaround that uses the
2199 boot IRQ equivalent of an IRQ that connects to
2200 a chipset where boot IRQs cannot be disabled.
2201 The opposite of ioapicreroute.
2202 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2203 routing table. These calls are known to be buggy
2204 on several machines and they hang the machine
2205 when used, but on other computers it's the only
2206 way to get the interrupt routing table. Try
2207 this option if the kernel is unable to allocate
2208 IRQs or discover secondary PCI buses on your
2210 rom [X86] Assign address space to expansion ROMs.
2211 Use with caution as certain devices share
2212 address decoders between ROMs and other
2214 norom [X86] Do not assign address space to
2215 expansion ROMs that do not already have
2216 BIOS assigned address ranges.
2217 nobar [X86] Do not assign address space to the
2218 BARs that weren't assigned by the BIOS.
2219 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2220 assigned automatically to PCI devices. You can
2221 make the kernel exclude IRQs of your ISA cards
2223 pirqaddr=0xAAAAA [X86] Specify the physical address
2224 of the PIRQ table (normally generated
2225 by the BIOS) if it is outside the
2226 F0000h-100000h range.
2227 lastbus=N [X86] Scan all buses thru bus #N. Can be
2228 useful if the kernel is unable to find your
2229 secondary buses and you want to tell it
2230 explicitly which ones they are.
2231 assign-busses [X86] Always assign all PCI bus
2232 numbers ourselves, overriding
2233 whatever the firmware may have done.
2234 usepirqmask [X86] Honor the possible IRQ mask stored
2235 in the BIOS $PIR table. This is needed on
2236 some systems with broken BIOSes, notably
2237 some HP Pavilion N5400 and Omnibook XE3
2238 notebooks. This will have no effect if ACPI
2239 IRQ routing is enabled.
2240 noacpi [X86] Do not use ACPI for IRQ routing
2241 or for PCI scanning.
2242 use_crs [X86] Use PCI host bridge window information
2243 from ACPI. On BIOSes from 2008 or later, this
2244 is enabled by default. If you need to use this,
2245 please report a bug.
2246 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2247 If you need to use this, please report a bug.
2248 routeirq Do IRQ routing for all PCI devices.
2249 This is normally done in pci_enable_device(),
2250 so this option is a temporary workaround
2251 for broken drivers that don't call it.
2252 skip_isa_align [X86] do not align io start addr, so can
2253 handle more pci cards
2254 firmware [ARM] Do not re-enumerate the bus but instead
2255 just use the configuration from the
2256 bootloader. This is currently used on
2257 IXP2000 systems where the bus has to be
2258 configured a certain way for adjunct CPUs.
2259 noearly [X86] Don't do any early type 1 scanning.
2260 This might help on some broken boards which
2261 machine check when some devices' config space
2262 is read. But various workarounds are disabled
2263 and some IOMMU drivers will not work.
2264 bfsort Sort PCI devices into breadth-first order.
2265 This sorting is done to get a device
2266 order compatible with older (<= 2.4) kernels.
2267 nobfsort Don't sort PCI devices into breadth-first order.
2268 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2269 tuning and use the BIOS-configured MPS defaults.
2270 pcie_bus_safe Set every device's MPS to the largest value
2271 supported by all devices below the root complex.
2272 pcie_bus_perf Set device MPS to the largest allowable MPS
2273 based on its parent bus. Also set MRRS (Max
2274 Read Request Size) to the largest supported
2275 value (no larger than the MPS that the device
2276 or bus can support) for best performance.
2277 pcie_bus_peer2peer Set every device's MPS to 128B, which
2278 every device is guaranteed to support. This
2279 configuration allows peer-to-peer DMA between
2280 any pair of devices, possibly at the cost of
2281 reduced performance. This also guarantees
2282 that hot-added devices will work.
2283 cbiosize=nn[KMG] The fixed amount of bus space which is
2284 reserved for the CardBus bridge's IO window.
2285 The default value is 256 bytes.
2286 cbmemsize=nn[KMG] The fixed amount of bus space which is
2287 reserved for the CardBus bridge's memory
2288 window. The default value is 64 megabytes.
2291 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2292 Specifies alignment and device to reassign
2293 aligned memory resources.
2294 If <order of align> is not specified,
2295 PAGE_SIZE is used as alignment.
2296 PCI-PCI bridge can be specified, if resource
2297 windows need to be expanded.
2298 ecrc= Enable/disable PCIe ECRC (transaction layer
2299 end-to-end CRC checking).
2300 bios: Use BIOS/firmware settings. This is the
2304 hpiosize=nn[KMG] The fixed amount of bus space which is
2305 reserved for hotplug bridge's IO window.
2306 Default size is 256 bytes.
2307 hpmemsize=nn[KMG] The fixed amount of bus space which is
2308 reserved for hotplug bridge's memory window.
2309 Default size is 2 megabytes.
2310 realloc= Enable/disable reallocating PCI bridge resources
2311 if allocations done by BIOS are too small to
2312 accommodate resources required by all child
2314 off: Turn realloc off
2316 realloc same as realloc=on
2317 noari do not use PCIe ARI.
2318 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2319 only look for one device below a PCIe downstream
2322 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2325 force Enable ASPM even on devices that claim not to support it.
2326 WARNING: Forcing ASPM on may cause system lockups.
2328 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2329 nomsi Do not use MSI for PCI Express Native Hotplug (this
2330 makes all PCIe ports use INTx for hotplug services).
2332 pcie_ports= [PCIE] PCIe ports handling:
2333 auto Ask the BIOS whether or not to use native PCIe services
2334 associated with PCIe ports (PME, hot-plug, AER). Use
2335 them only if that is allowed by the BIOS.
2336 native Use native PCIe services associated with PCIe ports
2338 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2341 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2342 nomsi Do not use MSI for native PCIe PME signaling (this makes
2343 all PCIe root ports use INTx for all services).
2345 pcmv= [HW,PCMCIA] BadgePAD 4
2348 See Documentation/blockdev/paride.txt.
2350 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2353 See arch/parisc/kernel/pdc_chassis.c
2355 percpu_alloc= Select which percpu first chunk allocator to use.
2356 Currently supported values are "embed" and "page".
2357 Archs may support subset or none of the selections.
2358 See comments in mm/percpu.c for details on each
2359 allocator. This parameter is primarily for debugging
2360 and performance comparison.
2363 See Documentation/blockdev/paride.txt.
2366 See Documentation/blockdev/paride.txt.
2368 pirq= [SMP,APIC] Manual mp-table setup
2369 See Documentation/x86/i386/IO-APIC.txt.
2371 plip= [PPT,NET] Parallel port network link
2372 Format: { parport<nr> | timid | 0 }
2373 See also Documentation/parport.txt.
2375 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2376 Override pmtimer IOPort with a hex value.
2380 Enable PNP debug messages (depends on the
2381 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2382 via /sys/module/pnp/parameters/debug. We always show
2383 current resource usage; turning this on also shows
2384 possible settings and some assignment information.
2390 { on | off | curr | res | no-curr | no-res }
2393 [ISAPNP] Exclude IRQs for the autoconfiguration
2396 [ISAPNP] Exclude DMAs for the autoconfiguration
2398 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2399 Ranges are in pairs (I/O port base and size).
2402 [ISAPNP] Exclude memory regions for the
2404 Ranges are in pairs (memory base and size).
2406 ports= [IP_VS_FTP] IPVS ftp helper module
2408 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2410 Format: <port>,<port>....
2412 print-fatal-signals=
2413 [KNL] debug: print fatal signals
2415 If enabled, warn about various signal handling
2416 related application anomalies: too many signals,
2417 too many POSIX.1 timers, fatal signals causing a
2420 If you hit the warning due to signal overflow,
2421 you might want to try "ulimit -i unlimited".
2425 printk.always_kmsg_dump=
2426 Trigger kmsg_dump for cases other than kernel oops or
2428 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2431 printk.time= Show timing data prefixed to each printk message line
2432 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2434 processor.max_cstate= [HW,ACPI]
2435 Limit processor to maximum C-state
2436 max_cstate=9 overrides any DMI blacklist limit.
2438 processor.nocst [HW,ACPI]
2439 Ignore the _CST method to determine C-states,
2440 instead using the legacy FADT method
2442 profile= [KNL] Enable kernel profiling via /proc/profile
2443 Format: [schedule,]<number>
2444 Param: "schedule" - profile schedule points.
2445 Param: <number> - step/bucket size as a power of 2 for
2446 statistical time based profiling.
2447 Param: "sleep" - profile D-state sleeping (millisecs).
2448 Requires CONFIG_SCHEDSTATS
2449 Param: "kvm" - profile VM exits.
2451 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2453 See Documentation/blockdev/ramdisk.txt.
2455 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2456 probe for; one of (bare|imps|exps|lifebook|any).
2457 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2459 psmouse.resetafter= [HW,MOUSE]
2460 Try to reset the device after so many bad packets
2463 [HW,MOUSE] Set desired mouse resolution, in dpi.
2464 psmouse.smartscroll=
2465 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2466 0 = disabled, 1 = enabled (default).
2468 pstore.backend= Specify the name of the pstore backend to use
2471 See Documentation/blockdev/paride.txt.
2474 [KNL] Number of legacy pty's. Overwrites compiled-in
2477 quiet [KNL] Disable most log messages
2482 See Documentation/md.txt.
2484 ramdisk_blocksize= [RAM]
2485 See Documentation/blockdev/ramdisk.txt.
2487 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2488 See Documentation/blockdev/ramdisk.txt.
2490 rcu_nocbs= [KNL,BOOT]
2491 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2492 the specified list of CPUs to be no-callback CPUs.
2493 Invocation of these CPUs' RCU callbacks will
2494 be offloaded to "rcuoN" kthreads created for
2495 that purpose. This reduces OS jitter on the
2496 offloaded CPUs, which can be useful for HPC and
2497 real-time workloads. It can also improve energy
2498 efficiency for asymmetric multiprocessors.
2500 rcu_nocb_poll [KNL,BOOT]
2501 Rather than requiring that offloaded CPUs
2502 (specified by rcu_nocbs= above) explicitly
2503 awaken the corresponding "rcuoN" kthreads,
2504 make these kthreads poll for callbacks.
2505 This improves the real-time response for the
2506 offloaded CPUs by relieving them of the need to
2507 wake up the corresponding kthread, but degrades
2508 energy efficiency by requiring that the kthreads
2509 periodically wake up to do the polling.
2511 rcutree.blimit= [KNL,BOOT]
2512 Set maximum number of finished RCU callbacks to process
2515 rcutree.fanout_leaf= [KNL,BOOT]
2516 Increase the number of CPUs assigned to each
2517 leaf rcu_node structure. Useful for very large
2520 rcutree.qhimark= [KNL,BOOT]
2521 Set threshold of queued
2522 RCU callbacks over which batch limiting is disabled.
2524 rcutree.qlowmark= [KNL,BOOT]
2525 Set threshold of queued RCU callbacks below which
2526 batch limiting is re-enabled.
2528 rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2529 Suppress RCU CPU stall warning messages.
2531 rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2532 Set timeout for RCU CPU stall warning messages.
2534 rcutree.jiffies_till_first_fqs= [KNL,BOOT]
2535 Set delay from grace-period initialization to
2536 first attempt to force quiescent states.
2537 Units are jiffies, minimum value is zero,
2538 and maximum value is HZ.
2540 rcutree.jiffies_till_next_fqs= [KNL,BOOT]
2541 Set delay between subsequent attempts to force
2542 quiescent states. Units are jiffies, minimum
2543 value is one, and maximum value is HZ.
2545 rcutorture.fqs_duration= [KNL,BOOT]
2546 Set duration of force_quiescent_state bursts.
2548 rcutorture.fqs_holdoff= [KNL,BOOT]
2549 Set holdoff time within force_quiescent_state bursts.
2551 rcutorture.fqs_stutter= [KNL,BOOT]
2552 Set wait time between force_quiescent_state bursts.
2554 rcutorture.irqreader= [KNL,BOOT]
2555 Test RCU readers from irq handlers.
2557 rcutorture.n_barrier_cbs= [KNL,BOOT]
2558 Set callbacks/threads for rcu_barrier() testing.
2560 rcutorture.nfakewriters= [KNL,BOOT]
2561 Set number of concurrent RCU writers. These just
2562 stress RCU, they don't participate in the actual
2563 test, hence the "fake".
2565 rcutorture.nreaders= [KNL,BOOT]
2566 Set number of RCU readers.
2568 rcutorture.onoff_holdoff= [KNL,BOOT]
2569 Set time (s) after boot for CPU-hotplug testing.
2571 rcutorture.onoff_interval= [KNL,BOOT]
2572 Set time (s) between CPU-hotplug operations, or
2573 zero to disable CPU-hotplug testing.
2575 rcutorture.shuffle_interval= [KNL,BOOT]
2576 Set task-shuffle interval (s). Shuffling tasks
2577 allows some CPUs to go into dyntick-idle mode
2578 during the rcutorture test.
2580 rcutorture.shutdown_secs= [KNL,BOOT]
2581 Set time (s) after boot system shutdown. This
2582 is useful for hands-off automated testing.
2584 rcutorture.stall_cpu= [KNL,BOOT]
2585 Duration of CPU stall (s) to test RCU CPU stall
2586 warnings, zero to disable.
2588 rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2589 Time to wait (s) after boot before inducing stall.
2591 rcutorture.stat_interval= [KNL,BOOT]
2592 Time (s) between statistics printk()s.
2594 rcutorture.stutter= [KNL,BOOT]
2595 Time (s) to stutter testing, for example, specifying
2596 five seconds causes the test to run for five seconds,
2597 wait for five seconds, and so on. This tests RCU's
2598 ability to transition abruptly to and from idle.
2600 rcutorture.test_boost= [KNL,BOOT]
2601 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2602 "Maybe" means test if the RCU implementation
2603 under test support RCU priority boosting.
2605 rcutorture.test_boost_duration= [KNL,BOOT]
2606 Duration (s) of each individual boost test.
2608 rcutorture.test_boost_interval= [KNL,BOOT]
2609 Interval (s) between each boost test.
2611 rcutorture.test_no_idle_hz= [KNL,BOOT]
2612 Test RCU's dyntick-idle handling. See also the
2613 rcutorture.shuffle_interval parameter.
2615 rcutorture.torture_type= [KNL,BOOT]
2616 Specify the RCU implementation to test.
2618 rcutorture.verbose= [KNL,BOOT]
2619 Enable additional printk() statements.
2623 Run specified binary instead of /init from the ramdisk,
2624 used for early userspace startup. See initrd.
2626 reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2627 Format: <reboot_mode>[,<reboot_mode2>[,...]]
2628 See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2631 [KNL, SMP] Set scheduler's default relax_domain_level.
2632 See Documentation/cgroups/cpusets.txt.
2634 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2636 reservetop= [X86-32]
2638 Reserves a hole at the top of the kernel virtual
2643 Set the amount of memory to reserve for BIOS at
2644 the bottom of the address space.
2646 reset_devices [KNL] Force drivers to reset the underlying device
2647 during initialization.
2650 Specify the partition device for software suspend
2652 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2654 resume_offset= [SWSUSP]
2655 Specify the offset from the beginning of the partition
2656 given by "resume=" at which the swap header is located,
2657 in <PAGE_SIZE> units (needed only for swap files).
2658 See Documentation/power/swsusp-and-swap-files.txt
2660 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2661 read the resume files
2663 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2664 Useful for devices that are detected asynchronously
2665 (e.g. USB and MMC devices).
2667 hibernate= [HIBERNATION]
2668 noresume Don't check if there's a hibernation image
2669 present during boot.
2670 nocompress Don't compress/decompress hibernation images.
2672 retain_initrd [RAM] Keep initrd memory after extraction
2674 rhash_entries= [KNL,NET]
2675 Set number of hash buckets for route cache
2677 riscom8= [HW,SERIAL]
2678 Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2680 ro [KNL] Mount root device read-only on boot
2682 root= [KNL] Root filesystem
2683 See name_to_dev_t comment in init/do_mounts.c.
2685 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2686 mount the root filesystem
2688 rootflags= [KNL] Set root filesystem mount option string
2690 rootfstype= [KNL] Set root filesystem type
2692 rootwait [KNL] Wait (indefinitely) for root device to show up.
2693 Useful for devices that are detected asynchronously
2694 (e.g. USB and MMC devices).
2696 rw [KNL] Mount root device read-write on boot
2698 S [KNL] Run init in single mode
2701 See drivers/net/irda/sa1100_ir.c.
2703 sbni= [NET] Granch SBNI12 leased line adapter
2705 sched_debug [KNL] Enables verbose scheduler debug messages.
2707 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2708 xtime_lock contention on larger systems, and/or RCU lock
2709 contention on all systems with CONFIG_MAXSMP set.
2710 Format: { "0" | "1" }
2711 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2713 Note: increases power consumption, thus should only be
2714 enabled if running jitter sensitive (HPC/RT) workloads.
2716 security= [SECURITY] Choose a security module to enable at boot.
2717 If this boot parameter is not specified, only the first
2718 security module asking for security registration will be
2719 loaded. An invalid security module name will be treated
2720 as if no module has been chosen.
2722 selinux= [SELINUX] Disable or enable SELinux at boot time.
2723 Format: { "0" | "1" }
2724 See security/selinux/Kconfig help text.
2727 Default value is set via kernel config option.
2728 If enabled at boot time, /selinux/disable can be used
2729 later to disable prior to initial policy load.
2731 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2732 Format: { "0" | "1" }
2733 See security/apparmor/Kconfig help text
2736 Default value is set via kernel config option.
2738 serialnumber [BUGS=X86-32]
2741 Maximal number of shapers.
2743 show_msr= [x86] show boot-time MSR settings
2744 Format: { <integer> }
2745 Show boot-time (BIOS-initialized) MSR settings.
2746 The parameter means the number of CPUs to show,
2747 for example 1 means boot CPU only.
2754 slab_max_order= [MM, SLAB]
2755 Determines the maximum allowed order for slabs.
2756 A high setting may cause OOMs due to memory
2757 fragmentation. Defaults to 1 for systems with
2758 more than 32MB of RAM, 0 otherwise.
2760 slub_debug[=options[,slabs]] [MM, SLUB]
2761 Enabling slub_debug allows one to determine the
2762 culprit if slab objects become corrupted. Enabling
2763 slub_debug can create guard zones around objects and
2764 may poison objects when not in use. Also tracks the
2765 last alloc / free. For more information see
2766 Documentation/vm/slub.txt.
2768 slub_max_order= [MM, SLUB]
2769 Determines the maximum allowed order for slabs.
2770 A high setting may cause OOMs due to memory
2771 fragmentation. For more information see
2772 Documentation/vm/slub.txt.
2774 slub_min_objects= [MM, SLUB]
2775 The minimum number of objects per slab. SLUB will
2776 increase the slab order up to slub_max_order to
2777 generate a sufficiently large slab able to contain
2778 the number of objects indicated. The higher the number
2779 of objects the smaller the overhead of tracking slabs
2780 and the less frequently locks need to be acquired.
2781 For more information see Documentation/vm/slub.txt.
2783 slub_min_order= [MM, SLUB]
2784 Determines the minimum page order for slabs. Must be
2785 lower than slub_max_order.
2786 For more information see Documentation/vm/slub.txt.
2788 slub_nomerge [MM, SLUB]
2789 Disable merging of slabs with similar size. May be
2790 necessary if there is some reason to distinguish
2791 allocs to different slabs. Debug options disable
2792 merging on their own.
2793 For more information see Documentation/vm/slub.txt.
2796 Format: <io1>[,<io2>[,...,<io8>]]
2798 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2799 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2800 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2801 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2802 smsc-ircc2.ircc_irq= [HW] IRQ line
2803 smsc-ircc2.ircc_dma= [HW] DMA channel
2804 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2805 0: Toshiba Satellite 1800 (GP data pin select)
2806 1: Fast pin select (default)
2810 [KNL] Should the soft-lockup detector generate panics.
2813 sonypi.*= [HW] Sony Programmable I/O Control Device driver
2814 See Documentation/laptops/sonypi.txt
2816 specialix= [HW,SERIAL] Specialix multi-serial port adapter
2817 See Documentation/serial/specialix.txt.
2819 spia_io_base= [HW,MTD]
2825 Enabled the stack tracer on boot up.
2827 stacktrace_filter=[function-list]
2828 [FTRACE] Limit the functions that the stack tracer
2829 will trace at boot up. function-list is a comma separated
2830 list of functions. This list can be changed at run
2831 time by the stack_trace_filter file in the debugfs
2832 tracing directory. Note, this enables stack tracing
2833 and the stacktrace above is not needed.
2837 Set the STI (builtin display/keyboard on the HP-PARISC
2838 machines) console (graphic card) which should be used
2839 as the initial boot-console.
2840 See also comment in drivers/video/console/sticore.c.
2843 See comment in drivers/video/console/sticore.c.
2846 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2848 sunrpc.min_resvport=
2849 sunrpc.max_resvport=
2851 SunRPC servers often require that client requests
2852 originate from a privileged port (i.e. a port in the
2853 range 0 < portnr < 1024).
2854 An administrator who wishes to reserve some of these
2855 ports for other uses may adjust the range that the
2856 kernel's sunrpc client considers to be privileged
2857 using these two parameters to set the minimum and
2858 maximum port values.
2862 Control how the NFS server code allocates CPUs to
2863 service thread pools. Depending on how many NICs
2864 you have and where their interrupts are bound, this
2865 option will affect which CPUs will do NFS serving.
2866 Note: this parameter cannot be changed while the
2867 NFS server is running.
2869 auto the server chooses an appropriate mode
2870 automatically using heuristics
2871 global a single global pool contains all CPUs
2872 percpu one pool for each CPU
2873 pernode one pool for each NUMA node (equivalent
2874 to global on non-NUMA machines)
2876 sunrpc.tcp_slot_table_entries=
2877 sunrpc.udp_slot_table_entries=
2879 Sets the upper limit on the number of simultaneous
2880 RPC calls that can be sent from the client to a
2881 server. Increasing these values may allow you to
2882 improve throughput, but will also increase the
2883 amount of memory reserved for use by the client.
2886 [KNL] Enable accounting of swap in memory resource
2887 controller if no parameter or 1 is given or disable
2888 it if 0 is given (See Documentation/cgroups/memory.txt)
2890 swiotlb= [IA-64] Number of I/O TLB slabs
2894 sysfs.deprecated=0|1 [KNL]
2895 Enable/disable old style sysfs layout for old udev
2896 on older distributions. When this option is enabled
2897 very new udev will not work anymore. When this option
2898 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2899 in older udev will not work anymore.
2900 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2901 the kernel configuration.
2903 sysrq_always_enabled
2905 Ignore sysrq setting - this boot parameter will
2906 neutralize any effect of /proc/sys/kernel/sysrq.
2907 Useful for debugging.
2911 test_suspend= [SUSPEND]
2912 Specify "mem" (for Suspend-to-RAM) or "standby" (for
2913 standby suspend) as the system sleep state to briefly
2914 enter during system startup. The system is woken from
2915 this state using a wakeup-capable RTC alarm.
2917 thash_entries= [KNL,NET]
2918 Set number of hash buckets for TCP connection
2920 thermal.act= [HW,ACPI]
2921 -1: disable all active trip points in all thermal zones
2922 <degrees C>: override all lowest active trip points
2924 thermal.crt= [HW,ACPI]
2925 -1: disable all critical trip points in all thermal zones
2926 <degrees C>: override all critical trip points
2928 thermal.nocrt= [HW,ACPI]
2929 Set to disable actions on ACPI thermal zone
2930 critical and hot trip points.
2932 thermal.off= [HW,ACPI]
2933 1: disable ACPI thermal control
2935 thermal.psv= [HW,ACPI]
2936 -1: disable all passive trip points
2937 <degrees C>: override all passive trip points to this
2940 thermal.tzp= [HW,ACPI]
2941 Specify global default ACPI thermal zone polling rate
2942 <deci-seconds>: poll all this frequency
2943 0: no polling (default)
2946 Force threading of all interrupt handlers except those
2947 marked explicitly IRQF_NO_THREAD.
2951 Specify if the kernel should make use of the cpu
2952 topology information if the hardware supports this.
2953 The scheduler will make use of this information and
2954 e.g. base its process migration decisions on it.
2959 tpm_suspend_pcr=[HW,TPM]
2960 Format: integer pcr id
2961 Specify that at suspend time, the tpm driver
2962 should extend the specified pcr with zeros,
2963 as a workaround for some chips which fail to
2964 flush the last written pcr on TPM_SaveState.
2965 This will guarantee that all the other pcrs
2968 trace_buf_size=nn[KMG]
2969 [FTRACE] will set tracing buffer size.
2971 trace_event=[event-list]
2972 [FTRACE] Set and start specified trace events in order
2973 to facilitate early boot debugging.
2974 See also Documentation/trace/events.txt
2976 trace_options=[option-list]
2977 [FTRACE] Enable or disable tracer options at boot.
2978 The option-list is a comma delimited list of options
2979 that can be enabled or disabled just as if you were
2980 to echo the option name into
2982 /sys/kernel/debug/tracing/trace_options
2984 For example, to enable stacktrace option (to dump the
2985 stack trace of each event), add to the command line:
2987 trace_options=stacktrace
2989 See also Documentation/trace/ftrace.txt "trace options"
2992 transparent_hugepage=
2994 Format: [always|madvise|never]
2995 Can be used to control the default behavior of the system
2996 with respect to transparent hugepages.
2997 See Documentation/vm/transhuge.txt for more details.
2999 tsc= Disable clocksource stability checks for TSC.
3001 [x86] reliable: mark tsc clocksource as reliable, this
3002 disables clocksource verification at runtime, as well
3003 as the stability checks done at bootup. Used to enable
3004 high-resolution timer mode on older hardware, and in
3005 virtualized environment.
3006 [x86] noirqtime: Do not use TSC to do irq accounting.
3007 Used to run time disable IRQ_TIME_ACCOUNTING on any
3008 platforms where RDTSC is slow and this accounting
3011 turbografx.map[2|3]= [HW,JOY]
3012 TurboGraFX parallel port interface
3014 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3015 See also Documentation/input/joystick-parport.txt
3017 udbg-immortal [PPC] When debugging early kernel crashes that
3018 happen after console_init() and before a proper
3019 console driver takes over, this boot options might
3020 help "seeing" what's going on.
3022 uhash_entries= [KNL,NET]
3023 Set number of hash buckets for UDP/UDP-Lite connections
3026 [USB] Ignore overcurrent events (default N).
3027 Some badly-designed motherboards generate lots of
3028 bogus events, for ports that aren't wired to
3029 anything. Set this parameter to avoid log spamming.
3030 Note that genuine overcurrent events won't be
3034 [X86] Cause panic on unknown NMI.
3036 usbcore.authorized_default=
3037 [USB] Default USB device authorization:
3038 (default -1 = authorized except for wireless USB,
3039 0 = not authorized, 1 = authorized)
3041 usbcore.autosuspend=
3042 [USB] The autosuspend time delay (in seconds) used
3043 for newly-detected USB devices (default 2). This
3044 is the time required before an idle device will be
3045 autosuspended. Devices for which the delay is set
3046 to a negative value won't be autosuspended at all.
3048 usbcore.usbfs_snoop=
3049 [USB] Set to log all usbfs traffic (default 0 = off).
3051 usbcore.blinkenlights=
3052 [USB] Set to cycle leds on hubs (default 0 = off).
3054 usbcore.old_scheme_first=
3055 [USB] Start with the old device initialization
3056 scheme (default 0 = off).
3058 usbcore.usbfs_memory_mb=
3059 [USB] Memory limit (in MB) for buffers allocated by
3060 usbfs (default = 16, 0 = max = 2047).
3062 usbcore.use_both_schemes=
3063 [USB] Try the other device initialization scheme
3064 if the first one fails (default 1 = enabled).
3066 usbcore.initial_descriptor_timeout=
3067 [USB] Specifies timeout for the initial 64-byte
3068 USB_REQ_GET_DESCRIPTOR request in milliseconds
3069 (default 5000 = 5.0 seconds).
3072 [USBHID] The interval which mice are to be polled at.
3074 usb-storage.delay_use=
3075 [UMS] The delay in seconds before a new device is
3076 scanned for Logical Units (default 5).
3079 [UMS] A list of quirks entries to supplement or
3080 override the built-in unusual_devs list. List
3081 entries are separated by commas. Each entry has
3082 the form VID:PID:Flags where VID and PID are Vendor
3083 and Product ID values (4-digit hex numbers) and
3084 Flags is a set of characters, each corresponding
3085 to a common usb-storage quirk flag as follows:
3086 a = SANE_SENSE (collect more than 18 bytes
3088 b = BAD_SENSE (don't collect more than 18
3089 bytes of sense data);
3090 c = FIX_CAPACITY (decrease the reported
3091 device capacity by one sector);
3092 d = NO_READ_DISC_INFO (don't use
3093 READ_DISC_INFO command);
3094 e = NO_READ_CAPACITY_16 (don't use
3095 READ_CAPACITY_16 command);
3096 h = CAPACITY_HEURISTICS (decrease the
3097 reported device capacity by one
3098 sector if the number is odd);
3099 i = IGNORE_DEVICE (don't bind to this
3101 l = NOT_LOCKABLE (don't try to lock and
3102 unlock ejectable media);
3103 m = MAX_SECTORS_64 (don't transfer more
3104 than 64 sectors = 32 KB at a time);
3105 n = INITIAL_READ10 (force a retry of the
3106 initial READ(10) command);
3107 o = CAPACITY_OK (accept the capacity
3108 reported by the device);
3109 p = WRITE_CACHE (the device cache is ON
3111 r = IGNORE_RESIDUE (the device reports
3112 bogus residue values);
3113 s = SINGLE_LUN (the device has only one
3115 w = NO_WP_DETECT (don't test whether the
3116 medium is write-protected).
3117 Example: quirks=0419:aaf5:rl,0421:0433:rc
3119 user_debug= [KNL,ARM]
3121 See arch/arm/Kconfig.debug help text.
3122 1 - undefined instruction events
3124 4 - invalid data aborts
3127 Example: user_debug=31
3130 [X86] Flags controlling user PTE allocations.
3132 nohigh = do not allocate PTE pages in
3133 HIGHMEM regardless of setting
3137 vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3138 vdso=1: enable VDSO (default)
3139 vdso=0: disable VDSO mapping
3142 vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3143 vdso32=1: enable 32-bit VDSO (default)
3144 vdso32=0: disable 32-bit VDSO mapping
3147 vector=percpu: enable percpu vector domain
3149 video= [FB] Frame buffer configuration
3150 See Documentation/fb/modedb.txt.
3153 [VMMIO] Memory mapped virtio (platform) device.
3155 <size>@<baseaddr>:<irq>[:<id>]
3157 <size> := size (can use standard suffixes
3159 <baseaddr> := physical base address
3160 <irq> := interrupt number (as passed to
3162 <id> := (optional) platform device id
3164 virtio_mmio.device=1K@0x100b0000:48:7
3166 Can be used multiple times for multiple devices.
3168 vga= [BOOT,X86-32] Select a particular video mode
3169 See Documentation/x86/boot.txt and
3170 Documentation/svga.txt.
3171 Use vga=ask for menu.
3172 This is actually a boot loader parameter; the value is
3173 passed to the kernel using a special protocol.
3175 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3176 size of <nn>. This can be used to increase the
3177 minimum size (128MB on x86). It can also be used to
3178 decrease the size and leave more room for directly
3181 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3184 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3187 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3191 Controls the behavior of vsyscalls (i.e. calls to
3192 fixed addresses of 0xffffffffff600x00 from legacy
3193 code). Most statically-linked binaries and older
3194 versions of glibc use these calls. Because these
3195 functions are at fixed addresses, they make nice
3196 targets for exploits that can control RIP.
3198 emulate [default] Vsyscalls turn into traps and are
3199 emulated reasonably safely.
3201 native Vsyscalls are native syscall instructions.
3202 This is a little bit faster than trapping
3203 and makes a few dynamic recompilers work
3204 better than they would in emulation mode.
3205 It also makes exploits much easier to write.
3207 none Vsyscalls don't work at all. This makes
3208 them quite hard to use for exploits but
3209 might break your system.
3211 vt.cur_default= [VT] Default cursor shape.
3212 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3213 the parameters of the <Esc>[?A;B;Cc escape sequence;
3214 see VGA-softcursor.txt. Default: 2 = underline.
3216 vt.default_blu= [VT]
3217 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3218 Change the default blue palette of the console.
3219 This is a 16-member array composed of values
3222 vt.default_grn= [VT]
3223 Format: <green0>,<green1>,<green2>,...,<green15>
3224 Change the default green palette of the console.
3225 This is a 16-member array composed of values
3228 vt.default_red= [VT]
3229 Format: <red0>,<red1>,<red2>,...,<red15>
3230 Change the default red palette of the console.
3231 This is a 16-member array composed of values
3237 Set system-wide default UTF-8 mode for all tty's.
3238 Default is 1, i.e. UTF-8 mode is enabled for all
3239 newly opened terminals.
3241 vt.global_cursor_default=
3244 Set system-wide default for whether a cursor
3245 is shown on new VTs. Default is -1,
3246 i.e. cursors will be created by default unless
3247 overridden by individual drivers. 0 will hide
3248 cursors, 1 will display them.
3250 watchdog timers [HW,WDT] For information on watchdog timers,
3251 see Documentation/watchdog/watchdog-parameters.txt
3252 or other driver-specific files in the
3253 Documentation/watchdog/ directory.
3255 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3256 default x2apic cluster mode on platforms
3259 x86_mrst_timer= [X86-32,APBT]
3260 Choose timer option for x86 Moorestown MID platform.
3261 Two valid options are apbt timer only and lapic timer
3262 plus one apbt timer for broadcast timer.
3263 x86_mrst_timer=apbt_only | lapic_and_apbt
3265 xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
3266 xd_geo= See header of drivers/block/xd.c.
3268 xen_emul_unplug= [HW,X86,XEN]
3269 Unplug Xen emulated devices
3270 Format: [unplug0,][unplug1]
3271 ide-disks -- unplug primary master IDE devices
3272 aux-ide-disks -- unplug non-primary-master IDE devices
3273 nics -- unplug network devices
3274 all -- unplug all emulated devices (NICs and IDE disks)
3275 unnecessary -- unplugging emulated devices is
3276 unnecessary even if the host did not respond to
3278 never -- do not unplug even if version check succeeds
3280 xirc2ps_cs= [NET,PCMCIA]
3282 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3284 ______________________________________________________________________
3288 Add more DRM drivers.
git.samba.org / sfrench / cifs-2.6.git / blob