4 The following is a consolidated list of the kernel parameters as
5 implemented by the __setup(), core_param() and module_param() macros
6 and sorted into English Dictionary order (defined as ignoring all
7 punctuation and sorting digits before letters in a case insensitive
8 manner), and with descriptions where known.
10 The kernel parses parameters from the kernel command line up to "--";
11 if it doesn't recognize a parameter and it doesn't contain a '.', the
12 parameter gets passed to init: parameters with '=' go into init's
13 environment, others are passed as command line arguments to init.
14 Everything after "--" is passed as an argument to init.
16 Module parameters can be specified in two ways: via the kernel command
17 line with a module name prefix, or via modprobe, e.g.:
19 (kernel command line) usbcore.blinkenlights=1
20 (modprobe command line) modprobe usbcore blinkenlights=1
22 Parameters for modules which are built into the kernel need to be
23 specified on the kernel command line. modprobe looks through the
24 kernel command line (/proc/cmdline) and collects module parameters
25 when it loads a module, so the kernel command line can be used for
28 Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30 can also be entered as
31 log-buf-len=1M print_fatal_signals=1
33 Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
36 This document may not be entirely up to date and comprehensive. The command
37 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
38 module. Loadable modules, after being loaded into the running kernel, also
39 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
40 parameters may be changed at runtime by the command
41 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
43 The parameters listed below are only valid if certain kernel build options were
44 enabled and if respective hardware is present. The text in square brackets at
45 the beginning of each description states the restrictions within which a
46 parameter is applicable:
48 ACPI ACPI support is enabled.
49 AGP AGP (Accelerated Graphics Port) is enabled.
50 ALSA ALSA sound support is enabled.
51 APIC APIC support is enabled.
52 APM Advanced Power Management support is enabled.
53 ARM ARM architecture is enabled.
54 AVR32 AVR32 architecture is enabled.
55 AX25 Appropriate AX.25 support is enabled.
56 BLACKFIN Blackfin architecture is enabled.
57 CLK Common clock infrastructure is enabled.
58 CMA Contiguous Memory Area support is enabled.
59 DRM Direct Rendering Management support is enabled.
60 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
61 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
62 EFI EFI Partitioning (GPT) is enabled
63 EIDE EIDE/ATAPI support is enabled.
64 EVM Extended Verification Module
65 FB The frame buffer device is enabled.
66 FTRACE Function tracing enabled.
67 GCOV GCOV profiling is enabled.
68 HW Appropriate hardware is enabled.
69 IA-64 IA-64 architecture is enabled.
70 IMA Integrity measurement architecture is enabled.
71 IOSCHED More than one I/O scheduler is enabled.
72 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
73 IPV6 IPv6 support is enabled.
74 ISAPNP ISA PnP code is enabled.
75 ISDN Appropriate ISDN support is enabled.
76 JOY Appropriate joystick support is enabled.
77 KGDB Kernel debugger support is enabled.
78 KVM Kernel Virtual Machine support is enabled.
79 LIBATA Libata driver is enabled
80 LP Printer support is enabled.
81 LOOP Loopback device support is enabled.
82 M68k M68k architecture is enabled.
83 These options have more detailed description inside of
84 Documentation/m68k/kernel-options.txt.
85 MDA MDA console support is enabled.
86 MIPS MIPS architecture is enabled.
87 MOUSE Appropriate mouse support is enabled.
88 MSI Message Signaled Interrupts (PCI).
89 MTD MTD (Memory Technology Device) support is enabled.
90 NET Appropriate network support is enabled.
91 NUMA NUMA support is enabled.
92 NFS Appropriate NFS support is enabled.
93 OSS OSS sound support is enabled.
94 PV_OPS A paravirtualized kernel is enabled.
95 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
96 PARISC The PA-RISC architecture is enabled.
97 PCI PCI bus support is enabled.
98 PCIE PCI Express support is enabled.
99 PCMCIA The PCMCIA subsystem is enabled.
100 PNP Plug & Play support is enabled.
101 PPC PowerPC architecture is enabled.
102 PPT Parallel port support is enabled.
103 PS2 Appropriate PS/2 support is enabled.
104 RAM RAM disk support is enabled.
105 S390 S390 architecture is enabled.
106 SCSI Appropriate SCSI support is enabled.
107 A lot of drivers have their options described inside
108 the Documentation/scsi/ sub-directory.
109 SECURITY Different security models are enabled.
110 SELINUX SELinux support is enabled.
111 APPARMOR AppArmor support is enabled.
112 SERIAL Serial support is enabled.
113 SH SuperH architecture is enabled.
114 SMP The kernel is an SMP kernel.
115 SPARC Sparc architecture is enabled.
116 SWSUSP Software suspend (hibernation) is enabled.
117 SUSPEND System suspend states are enabled.
118 TPM TPM drivers are enabled.
119 TS Appropriate touchscreen support is enabled.
120 UMS USB Mass Storage support is enabled.
121 USB USB support is enabled.
122 USBHID USB Human Interface Device support is enabled.
123 V4L Video For Linux support is enabled.
124 VMMIO Driver for memory mapped virtio devices is enabled.
125 VGA The VGA console has been enabled.
126 VT Virtual terminal support is enabled.
127 WDT Watchdog support is enabled.
128 XT IBM PC/XT MFM hard disk support is enabled.
129 X86-32 X86-32, aka i386 architecture is enabled.
130 X86-64 X86-64 architecture is enabled.
131 More X86-64 boot options can be found in
132 Documentation/x86/x86_64/boot-options.txt .
133 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
134 XEN Xen support is enabled
136 In addition, the following text indicates that the option:
138 BUGS= Relates to possible processor bugs on the said processor.
139 KNL Is a kernel start-up parameter.
140 BOOT Is a boot loader parameter.
142 Parameters denoted with BOOT are actually interpreted by the boot
143 loader, and have no meaning to the kernel directly.
144 Do not modify the syntax of boot loader parameters without extreme
145 need or coordination with <Documentation/x86/boot.txt>.
147 There are also arch-specific kernel-parameters not documented here.
148 See for example <Documentation/x86/x86_64/boot-options.txt>.
150 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
151 a trailing = on the name of any parameter states that that parameter will
152 be entered as an environment variable, whereas its absence indicates that
153 it will appear as a kernel argument readable via /proc/cmdline by programs
154 running once the system is up.
156 The number of kernel parameters is not limited, but the length of the
157 complete command line (parameters including spaces etc.) is limited to
158 a fixed number of characters. This limit depends on the architecture
159 and is between 256 and 4096 characters. It is defined in the file
160 ./include/asm/setup.h as COMMAND_LINE_SIZE.
162 Finally, the [KMG] suffix is commonly described after a number of kernel
163 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
164 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
165 bytes respectively. Such letter suffixes can also be entirely omitted.
168 acpi= [HW,ACPI,X86,ARM64]
169 Advanced Configuration and Power Interface
170 Format: { force | off | strict | noirq | rsdt |
172 force -- enable ACPI if default was off
173 off -- disable ACPI if default was on
174 noirq -- do not use ACPI for IRQ routing
175 strict -- Be less tolerant of platforms that are not
176 strictly ACPI specification compliant.
177 rsdt -- prefer RSDT over (default) XSDT
178 copy_dsdt -- copy DSDT to memory
179 For ARM64, ONLY "acpi=off" or "acpi=force" are available
181 See also Documentation/power/runtime_pm.txt, pci=noacpi
183 acpi_apic_instance= [ACPI, IOAPIC]
185 2: use 2nd APIC table, if available
186 1,0: use 1st APIC table
189 acpi_backlight= [HW,ACPI]
190 acpi_backlight=vendor
192 If set to vendor, prefer vendor specific driver
193 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
194 of the ACPI video.ko driver.
196 acpica_no_return_repair [HW, ACPI]
197 Disable AML predefined validation mechanism
198 This mechanism can repair the evaluation result to make
199 the return objects more ACPI specification compliant.
200 This option is useful for developers to identify the
201 root cause of an AML interpreter issue when the issue
202 has something to do with the repair mechanism.
204 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
205 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
207 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
208 debug output. Bits in debug_layer correspond to a
209 _COMPONENT in an ACPI source file, e.g.,
210 #define _COMPONENT ACPI_PCI_COMPONENT
211 Bits in debug_level correspond to a level in
212 ACPI_DEBUG_PRINT statements, e.g.,
213 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
214 The debug_level mask defaults to "info". See
215 Documentation/acpi/debug.txt for more information about
216 debug layers and levels.
218 Enable processor driver info messages:
219 acpi.debug_layer=0x20000000
220 Enable PCI/PCI interrupt routing info messages:
221 acpi.debug_layer=0x400000
222 Enable AML "Debug" output, i.e., stores to the Debug
223 object while interpreting AML:
224 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
225 Enable all messages related to ACPI hardware:
226 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
228 Some values produce so much output that the system is
229 unusable. The "log_buf_len" parameter may be useful
230 if you need to capture more output.
232 acpi_enforce_resources= [ACPI]
233 { strict | lax | no }
234 Check for resource conflicts between native drivers
235 and ACPI OperationRegions (SystemIO and SystemMemory
236 only). IO ports and memory declared in ACPI might be
237 used by the ACPI subsystem in arbitrary AML code and
238 can interfere with legacy drivers.
239 strict (default): access to resources claimed by ACPI
240 is denied; legacy drivers trying to access reserved
241 resources will fail to bind to device using them.
242 lax: access to resources claimed by ACPI is allowed;
243 legacy drivers trying to access reserved resources
244 will bind successfully but a warning message is logged.
245 no: ACPI OperationRegions are not marked as reserved,
246 no further checks are performed.
248 acpi_force_table_verification [HW,ACPI]
249 Enable table checksum verification during early stage.
250 By default, this is disabled due to x86 early mapping
253 acpi_irq_balance [HW,ACPI]
254 ACPI will balance active IRQs
257 acpi_irq_nobalance [HW,ACPI]
258 ACPI will not move active IRQs (default)
261 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
262 Format: <irq>,<irq>...
264 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
266 Format: <irq>,<irq>...
268 acpi_no_auto_serialize [HW,ACPI]
269 Disable auto-serialization of AML methods
270 AML control methods that contain the opcodes to create
271 named objects will be marked as "Serialized" by the
272 auto-serialization feature.
273 This feature is enabled by default.
274 This option allows to turn off the feature.
276 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
279 acpi_no_static_ssdt [HW,ACPI]
280 Disable installation of static SSDTs at early boot time
281 By default, SSDTs contained in the RSDT/XSDT will be
282 installed automatically and they will appear under
283 /sys/firmware/acpi/tables.
284 This option turns off this feature.
285 Note that specifying this option does not affect
286 dynamic table installation which will install SSDT
287 tables to /sys/firmware/acpi/tables/dynamic.
289 acpi_rsdp= [ACPI,EFI,KEXEC]
290 Pass the RSDP address to the kernel, mostly used
291 on machines running EFI runtime service to boot the
292 second kernel for kdump.
294 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
295 Format: To spoof as Windows 98: ="Microsoft Windows"
297 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
298 of 2 which is mandated by ACPI 6) as the supported ACPI
299 specification revision (when using this switch, it may
300 be necessary to carry out a cold reboot _twice_ in a
301 row to make it take effect on the platform firmware).
303 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
304 acpi_osi="string1" # add string1
305 acpi_osi="!string2" # remove string2
306 acpi_osi=!* # remove all strings
307 acpi_osi=! # disable all built-in OS vendor
309 acpi_osi= # disable all strings
311 'acpi_osi=!' can be used in combination with single or
312 multiple 'acpi_osi="string1"' to support specific OS
313 vendor string(s). Note that such command can only
314 affect the default state of the OS vendor strings, thus
315 it cannot affect the default state of the feature group
316 strings and the current state of the OS vendor strings,
317 specifying it multiple times through kernel command line
318 is meaningless. This command is useful when one do not
319 care about the state of the feature group strings which
320 should be controlled by the OSPM.
322 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
323 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
324 can make '_OSI("Windows 2000")' TRUE.
326 'acpi_osi=' cannot be used in combination with other
327 'acpi_osi=' command lines, the _OSI method will not
328 exist in the ACPI namespace. NOTE that such command can
329 only affect the _OSI support state, thus specifying it
330 multiple times through kernel command line is also
333 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
336 'acpi_osi=!*' can be used in combination with single or
337 multiple 'acpi_osi="string1"' to support specific
338 string(s). Note that such command can affect the
339 current state of both the OS vendor strings and the
340 feature group strings, thus specifying it multiple times
341 through kernel command line is meaningful. But it may
342 still not able to affect the final state of a string if
343 there are quirks related to this string. This command
344 is useful when one want to control the state of the
345 feature group strings to debug BIOS issues related to
348 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
349 '_OSI("Module Device")' FALSE.
350 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
351 '_OSI("Module Device")' TRUE.
352 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
354 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
356 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
357 they all will make '_OSI("Windows 2000")' TRUE.
360 Override the pmtimer bug detection: force the kernel
361 to assume that this machine's pmtimer latches its value
362 and always returns good values.
364 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
365 Format: { level | edge | high | low }
367 acpi_skip_timer_override [HW,ACPI]
368 Recognize and ignore IRQ0/pin2 Interrupt Override.
369 For broken nForce2 BIOS resulting in XT-PIC timer.
371 acpi_sleep= [HW,ACPI] Sleep options
372 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
373 old_ordering, nonvs, sci_force_enable }
374 See Documentation/power/video.txt for information on
376 s3_beep is for debugging; it makes the PC's speaker beep
377 as soon as the kernel's real-mode entry point is called.
378 s4_nohwsig prevents ACPI hardware signature from being
379 used during resume from hibernation.
380 old_ordering causes the ACPI 1.0 ordering of the _PTS
381 control method, with respect to putting devices into
382 low power states, to be enforced (the ACPI 2.0 ordering
383 of _PTS is used by default).
384 nonvs prevents the kernel from saving/restoring the
385 ACPI NVS memory during suspend/hibernation and resume.
386 sci_force_enable causes the kernel to set SCI_EN directly
387 on resume from S1/S3 (which is against the ACPI spec,
388 but some broken systems don't work without it).
390 acpi_use_timer_override [HW,ACPI]
391 Use timer override. For some broken Nvidia NF5 boards
392 that require a timer override, but don't have HPET
394 add_efi_memmap [EFI; X86] Include EFI memory map in
395 kernel's map of available physical RAM.
398 { off | try_unsupported }
399 off: disable AGP support
400 try_unsupported: try to drive unsupported chipsets
401 (may crash computer or cause data corruption)
404 See Documentation/sound/alsa/alsa-parameters.txt
407 Allow the default userspace alignment fault handler
408 behaviour to be specified. Bit 0 enables warnings,
409 bit 1 enables fixups, and bit 2 sends a segfault.
411 align_va_addr= [X86-64]
412 Align virtual addresses by clearing slice [14:12] when
413 allocating a VMA at process creation time. This option
414 gives you up to 3% performance improvement on AMD F15h
415 machines (where it is enabled by default) for a
416 CPU-intensive style benchmark, and it can vary highly in
417 a microbenchmark depending on workload and compiler.
419 32: only for 32-bit processes
420 64: only for 64-bit processes
421 on: enable for both 32- and 64-bit processes
422 off: disable for both 32- and 64-bit processes
424 alloc_snapshot [FTRACE]
425 Allocate the ftrace snapshot buffer on boot up when the
426 main buffer is allocated. This is handy if debugging
427 and you need to use tracing_snapshot() on boot up, and
428 do not want to use tracing_snapshot_alloc() as it needs
429 to be done where GFP_KERNEL allocations are allowed.
431 amd_iommu= [HW,X86-64]
432 Pass parameters to the AMD IOMMU driver in the system.
434 fullflush - enable flushing of IO/TLB entries when
435 they are unmapped. Otherwise they are
436 flushed before they will be reused, which
438 off - do not initialize any AMD IOMMU found in
440 force_isolation - Force device isolation for all
441 devices. The IOMMU driver is not
442 allowed anymore to lift isolation
443 requirements as needed. This option
444 does not override iommu=pt
446 amd_iommu_dump= [HW,X86-64]
447 Enable AMD IOMMU driver option to dump the ACPI table
448 for AMD IOMMU. With this option enabled, AMD IOMMU
449 driver will print ACPI tables for AMD IOMMU during
450 IOMMU initialization.
452 amijoy.map= [HW,JOY] Amiga joystick support
453 Map of devices attached to JOY0DAT and JOY1DAT
455 See also Documentation/input/joystick.txt
457 analog.map= [HW,JOY] Analog joystick and gamepad support
458 Specifies type or capabilities of an analog joystick
459 connected to one of 16 gameports
460 Format: <type1>,<type2>,..<type16>
463 Power management functions (SPARCstation-4/5 + deriv.)
465 Disable APC CPU standby support. SPARCstation-Fox does
466 not play well with APC CPU idle - disable it if you have
467 APC and your system crashes randomly.
469 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
470 Change the output verbosity whilst booting
471 Format: { quiet (default) | verbose | debug }
472 Change the amount of debugging information output
473 when initialising the APIC and IO-APIC components.
476 See Documentation/networking/ipv6.txt.
478 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
479 Limit apic dumping. The parameter defines the maximal
480 number of local apics being dumped. Also it is possible
481 to set it to "all" by meaning -- no limit here.
482 Format: { 1 (default) | 2 | ... | all }.
483 The parameter valid if only apic=debug or
484 apic=verbose is specified.
485 Example: apic=debug show_lapic=all
487 apm= [APM] Advanced Power Management
488 See header of arch/x86/kernel/apm_32.c.
490 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
491 Format: <io>,<irq>,<nodeID>
495 atarimouse= [HW,MOUSE] Atari Mouse
497 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
498 EzKey and similar keyboards
500 atkbd.reset= [HW] Reset keyboard during initialization
502 atkbd.set= [HW] Select keyboard code set
503 Format: <int> (2 = AT (default), 3 = PS/2)
505 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
508 atkbd.softraw= [HW] Choose between synthetic and real raw mode
509 Format: <bool> (0 = real, 1 = synthetic (default))
511 atkbd.softrepeat= [HW]
512 Use software keyboard repeat
514 audit= [KNL] Enable the audit sub-system
515 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
516 0 - kernel audit is disabled and can not be enabled
517 until the next reboot
518 unset - kernel audit is initialized but disabled and
519 will be fully enabled by the userspace auditd.
520 1 - kernel audit is initialized and partially enabled,
521 storing at most audit_backlog_limit messages in
522 RAM until it is fully enabled by the userspace
526 audit_backlog_limit= [KNL] Set the audit queue size limit.
527 Format: <int> (must be >=0)
530 baycom_epp= [HW,AX25]
533 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
535 See header of drivers/net/hamradio/baycom_par.c.
537 baycom_ser_fdx= [HW,AX25]
538 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
539 Format: <io>,<irq>,<mode>[,<baud>]
540 See header of drivers/net/hamradio/baycom_ser_fdx.c.
542 baycom_ser_hdx= [HW,AX25]
543 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
544 Format: <io>,<irq>,<mode>
545 See header of drivers/net/hamradio/baycom_ser_hdx.c.
547 blkdevparts= Manual partition parsing of block device(s) for
548 embedded devices based on command line input.
549 See Documentation/block/cmdline-partition.txt
551 boot_delay= Milliseconds to delay each printk during boot.
552 Values larger than 10 seconds (10000) are changed to
556 bootmem_debug [KNL] Enable bootmem allocator debug messages.
558 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
559 bttv.radio= Most important insmod options are available as
561 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
564 bulk_remove=off [PPC] This parameter disables the use of the pSeries
565 firmware feature for flushing multiple hpte entries
568 c101= [NET] Moxa C101 synchronous serial card
570 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
571 Sometimes CPU hardware bugs make them report the cache
572 size incorrectly. The kernel will attempt work arounds
573 to fix known problems, but for some CPUs it is not
574 possible to determine what the correct size should be.
575 This option provides an override for these situations.
577 ca_keys= [KEYS] This parameter identifies a specific key(s) on
578 the system trusted keyring to be used for certificate
580 format: { id:<keyid> | builtin }
582 cca= [MIPS] Override the kernel pages' cache coherency
583 algorithm. Accepted values range from 0 to 7
584 inclusive. See arch/mips/include/asm/pgtable-bits.h
585 for platform specific values (SB1, Loongson3 and
588 ccw_timeout_log [S390]
589 See Documentation/s390/CommonIO for details.
591 cgroup_disable= [KNL] Disable a particular controller
592 Format: {name of the controller(s) to disable}
593 The effects of cgroup_disable=foo are:
594 - foo isn't auto-mounted if you mount all cgroups in
596 - foo isn't visible as an individually mountable
598 {Currently only "memory" controller deal with this and
599 cut the overhead, others just disable the usage. So
600 only cgroup_disable=memory is actually worthy}
602 checkreqprot [SELINUX] Set initial checkreqprot flag value.
603 Format: { "0" | "1" }
604 See security/selinux/Kconfig help text.
605 0 -- check protection applied by kernel (includes
606 any implied execute protection).
607 1 -- check protection requested by application.
608 Default value is set via a kernel config option.
609 Value can be changed at runtime via
610 /selinux/checkreqprot.
613 See Documentation/s390/CommonIO for details.
616 Prevents the clock framework from automatically gating
617 clocks that have not been explicitly enabled by a Linux
618 device driver but are enabled in hardware at reset or
619 by the bootloader/firmware. Note that this does not
620 force such clocks to be always-on nor does it reserve
621 those clocks in any way. This parameter is useful for
622 debug and development, but should not be needed on a
623 platform with proper driver support. For more
624 information, see Documentation/clk.txt.
626 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
628 Forces specified clocksource (if available) to be used
629 when calculating gettimeofday(). If specified
630 clocksource is not available, it defaults to PIT.
631 Format: { pit | tsc | cyclone | pmtmr }
633 clocksource= Override the default clocksource
635 Override the default clocksource and use the clocksource
636 with the name specified.
637 Some clocksource names to choose from, depending on
639 [all] jiffies (this is the base, fallback clocksource)
641 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
642 pxa_timer,timer3,32k_counter,timer0_1
644 [X86-32] pit,hpet,tsc;
645 scx200_hrt on Geode; cyclone on IBM x440
653 clearcpuid=BITNUM [X86]
654 Disable CPUID feature X for the kernel. See
655 arch/x86/include/asm/cpufeature.h for the valid bit
656 numbers. Note the Linux specific bits are not necessarily
657 stable over kernel options, but the vendor specific
659 Also note that user programs calling CPUID directly
660 or using the feature without checking anything
661 will still see it. This just prevents it from
662 being used by the kernel or shown in /proc/cpuinfo.
663 Also note the kernel might malfunction if you disable
666 cma=nn[MG]@[start[MG][-end[MG]]]
668 Sets the size of kernel global memory area for
669 contiguous memory allocations and optionally the
670 placement constraint by the physical address range of
671 memory allocations. A value of 0 disables CMA
672 altogether. For more information, see
673 include/linux/dma-contiguous.h
675 cmo_free_hint= [PPC] Format: { yes | no }
676 Specify whether pages are marked as being inactive
677 when they are freed. This is used in CMO environments
678 to determine OS memory pressure for page stealing by
682 coherent_pool=nn[KMG] [ARM,KNL]
683 Sets the size of memory pool for coherent, atomic dma
684 allocations, by default set to 256K.
686 code_bytes [X86] How many bytes of object code to print
691 com20020= [HW,NET] ARCnet - COM20020 chipset
693 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
695 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
699 ARCnet - COM90xx chipset (memory-mapped buffers)
700 Format: <io>[,<irq>[,<memstart>]]
702 condev= [HW,S390] console device
705 console= [KNL] Output console device and options.
707 tty<n> Use the virtual console device <n>.
711 Use the specified serial port. The options are of
712 the form "bbbbpnf", where "bbbb" is the baud rate,
713 "p" is parity ("n", "o", or "e"), "n" is number of
714 bits, and "f" is flow control ("r" for RTS or
715 omit it). Default is "9600n8".
717 See Documentation/serial-console.txt for more
719 Documentation/networking/netconsole.txt for an
722 uart[8250],io,<addr>[,options]
723 uart[8250],mmio,<addr>[,options]
724 uart[8250],mmio32,<addr>[,options]
725 uart[8250],0x<addr>[,options]
726 Start an early, polled-mode console on the 8250/16550
727 UART at the specified I/O port or MMIO address,
728 switching to the matching ttyS device later.
729 MMIO inter-register address stride is either 8-bit
730 (mmio) or 32-bit (mmio32).
731 If none of [io|mmio|mmio32], <addr> is assumed to be
732 equivalent to 'mmio'. 'options' are specified in the
733 same format described for ttyS above; if unspecified,
734 the h/w is not re-initialized.
736 hvc<n> Use the hypervisor console device <n>. This is for
737 both Xen and PowerPC hypervisors.
739 If the device connected to the port is not a TTY but a braille
740 device, prepend "brl," before the device type, for instance
742 For now, only VisioBraille is supported.
744 consoleblank= [KNL] The console blank (screen saver) timeout in
745 seconds. Defaults to 10*60 = 10mins. A value of 0
746 disables the blank timer.
749 [KNL] Change the default value for
750 /proc/<pid>/coredump_filter.
751 See also Documentation/filesystems/proc.txt.
753 cpuidle.off=1 [CPU_IDLE]
754 disable the cpuidle sub-system
757 [X86] Delay for N microsec between assert and de-assert
758 of APIC INIT to start processors. This delay occurs
759 on every CPU online, such as boot, and resume from suspend.
762 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
764 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
766 crashkernel=size[KMG][@offset[KMG]]
767 [KNL] Using kexec, Linux can switch to a 'crash kernel'
768 upon panic. This parameter reserves the physical
769 memory region [offset, offset + size] for that kernel
770 image. If '@offset' is omitted, then a suitable offset
771 is selected automatically. Check
772 Documentation/kdump/kdump.txt for further details.
774 crashkernel=range1:size1[,range2:size2,...][@offset]
775 [KNL] Same as above, but depends on the memory
776 in the running system. The syntax of range is
777 start-[end] where start and end are both
778 a memory unit (amount[KMG]). See also
779 Documentation/kdump/kdump.txt for an example.
781 crashkernel=size[KMG],high
782 [KNL, x86_64] range could be above 4G. Allow kernel
783 to allocate physical memory region from top, so could
784 be above 4G if system have more than 4G ram installed.
785 Otherwise memory region will be allocated below 4G, if
787 It will be ignored if crashkernel=X is specified.
788 crashkernel=size[KMG],low
789 [KNL, x86_64] range under 4G. When crashkernel=X,high
790 is passed, kernel could allocate physical memory region
791 above 4G, that cause second kernel crash on system
792 that require some amount of low memory, e.g. swiotlb
793 requires at least 64M+32K low memory, also enough extra
794 low memory is needed to make sure DMA buffers for 32-bit
795 devices won't run out. Kernel would try to allocate at
796 at least 256M below 4G automatically.
797 This one let user to specify own low range under 4G
798 for second kernel instead.
799 0: to disable low allocation.
800 It will be ignored when crashkernel=X,high is not used
801 or memory reserved is below 4G.
806 cs89x0_media= [HW,NET]
807 Format: { rj45 | aui | bnc }
810 See header of drivers/s390/block/dasd_devmap.c.
812 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
813 (one device per port)
814 Format: <port#>,<type>
815 See also Documentation/input/joystick-parport.txt
817 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
818 time. See Documentation/dynamic-debug-howto.txt for
819 details. Deprecated, see dyndbg.
821 debug [KNL] Enable kernel debugging (events log level).
824 [KNL] verbose self-tests
826 Print debugging info while doing the locking API
828 We default to 0 (no extra messages), setting it to
829 1 will print _a lot_ more information - normally
830 only useful to kernel developers.
832 debug_objects [KNL] Enable object debugging
835 [KNL] Disable object debugging
837 debug_guardpage_minorder=
838 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
839 parameter allows control of the order of pages that will
840 be intentionally kept free (and hence protected) by the
841 buddy allocator. Bigger value increase the probability
842 of catching random memory corruption, but reduce the
843 amount of memory for normal system use. The maximum
844 possible value is MAX_ORDER/2. Setting this parameter
845 to 1 or 2 should be enough to identify most random
846 memory corruption problems caused by bugs in kernel or
847 driver code when a CPU writes to (or reads from) a
848 random memory location. Note that there exists a class
849 of memory corruptions problems caused by buggy H/W or
850 F/W or by drivers badly programing DMA (basically when
851 memory is written at bus level and the CPU MMU is
852 bypassed) which are not detectable by
853 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
854 tracking down these problems.
857 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
858 parameter enables the feature at boot time. In
859 default, it is disabled. We can avoid allocating huge
860 chunk of memory for debug pagealloc if we don't enable
861 it at boot time and the system will work mostly same
862 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
863 on: enable the feature
865 debugpat [X86] Enable PAT debugging
867 decnet.addr= [HW,NET]
868 Format: <area>[,<node>]
869 See also Documentation/networking/decnet.txt.
872 [same as hugepagesz=] The size of the default
873 HugeTLB page size. This is the size represented by
874 the legacy /proc/ hugepages APIs, used for SHM, and
875 default size when mounting hugetlbfs filesystems.
876 Defaults to the default architecture's huge page size
880 Set number of hash buckets for dentry cache.
883 See Documentation/networking/ipv6.txt.
885 disable_cpu_apicid= [X86,APIC,SMP]
887 The number of initial APIC ID for the
888 corresponding CPU to be disabled at boot,
889 mostly used for the kdump 2nd kernel to
890 disable BSP to wake up multiple CPUs without
891 causing system reset or hang due to sending
894 disable_ddw [PPC/PSERIES]
895 Disable Dynamic DMA Window support. Use this if
896 to workaround buggy firmware.
899 See Documentation/networking/ipv6.txt.
901 disable_mtrr_cleanup [X86]
902 The kernel tries to adjust MTRR layout from continuous
903 to discrete, to make X server driver able to add WB
904 entry later. This parameter disables that.
906 disable_mtrr_trim [X86, Intel and AMD only]
907 By default the kernel will trim any uncacheable
908 memory out of your available memory pool based on
909 MTRR settings. This parameter disables that behavior,
910 possibly causing your machine to run very slowly.
912 disable_timer_pin_1 [X86]
913 Disable PIN 1 of APIC timer
914 Can be useful to work around chipset bugs.
916 dis_ucode_ldr [X86] Disable the microcode loader.
918 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
919 this option disables the debugging code at boot.
921 dma_debug_entries=<number>
922 This option allows to tune the number of preallocated
923 entries for DMA-API debugging code. One entry is
924 required per DMA-API allocation. Use this if the
925 DMA-API debugging code disables itself because the
926 architectural default is too low.
928 dma_debug_driver=<driver_name>
929 With this option the DMA-API debugging driver
930 filter feature can be enabled at boot time. Just
931 pass the driver to filter for as the parameter.
932 The filter can be disabled or changed to another
933 driver later using sysfs.
935 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
936 Broken monitors, graphic adapters, KVMs and EDIDless
937 panels may send no or incorrect EDID data sets.
938 This parameter allows to specify an EDID data sets
939 in the /lib/firmware directory that are used instead.
940 Generic built-in EDID data sets are used, if one of
941 edid/1024x768.bin, edid/1280x1024.bin,
942 edid/1680x1050.bin, or edid/1920x1080.bin is given
943 and no file with the same name exists. Details and
944 instructions how to build your own EDID data are
945 available in Documentation/EDID/HOWTO.txt. An EDID
946 data set will only be used for a particular connector,
947 if its name and a colon are prepended to the EDID
948 name. Each connector may use a unique EDID data
949 set by separating the files with a comma. An EDID
950 data set with no connector name will be used for
951 any connectors not explicitly specified.
955 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
956 module.dyndbg[="val"]
957 Enable debug messages at boot time. See
958 Documentation/dynamic-debug-howto.txt for details.
960 nompx [X86] Disables Intel Memory Protection Extensions.
961 See Documentation/x86/intel_mpx.txt for more
962 information about the feature.
965 on enable eager fpu restore
966 off disable eager fpu restore
967 auto selects the default scheme, which automatically
968 enables eagerfpu restore for xsaveopt.
970 module.async_probe [KNL]
971 Enable asynchronous probe on this module.
973 early_ioremap_debug [KNL]
974 Enable debug messages in early_ioremap support. This
975 is useful for tracking down temporary early mappings
976 which are not unmapped.
978 earlycon= [KNL] Output early console device and options.
980 When used with no options, the early console is
981 determined by the stdout-path property in device
985 Start an early, polled-mode console on a cadence serial
986 port at the specified address. The cadence serial port
987 must already be setup and configured. Options are not
990 uart[8250],io,<addr>[,options]
991 uart[8250],mmio,<addr>[,options]
992 uart[8250],mmio32,<addr>[,options]
993 uart[8250],mmio32be,<addr>[,options]
994 uart[8250],0x<addr>[,options]
995 Start an early, polled-mode console on the 8250/16550
996 UART at the specified I/O port or MMIO address.
997 MMIO inter-register address stride is either 8-bit
998 (mmio) or 32-bit (mmio32 or mmio32be).
999 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1000 to be equivalent to 'mmio'. 'options' are specified
1001 in the same format described for "console=ttyS<n>"; if
1002 unspecified, the h/w is not initialized.
1005 Start an early, polled-mode console on a pl011 serial
1006 port at the specified address. The pl011 serial port
1007 must already be setup and configured. Options are not
1011 Start an early, polled-mode console on an msm serial
1012 port at the specified address. The serial port
1013 must already be setup and configured. Options are not
1016 msm_serial_dm,<addr>
1017 Start an early, polled-mode console on an msm serial
1018 dm port at the specified address. The serial port
1019 must already be setup and configured. Options are not
1022 smh Use ARM semihosting calls for early console.
1030 Use early console provided by serial driver available
1031 on Samsung SoCs, requires selecting proper type and
1032 a correct base address of the selected UART port. The
1033 serial port must already be setup and configured.
1034 Options are not yet supported.
1038 Use early console provided by Freescale LP UART driver
1039 found on Freescale Vybrid and QorIQ LS1021A processors.
1040 A valid base address must be provided, and the serial
1041 port must already be setup and configured.
1043 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1047 earlyprintk=serial[,ttySn[,baudrate]]
1048 earlyprintk=serial[,0x...[,baudrate]]
1049 earlyprintk=ttySn[,baudrate]
1050 earlyprintk=dbgp[debugController#]
1051 earlyprintk=pciserial,bus:device.function[,baudrate]
1053 earlyprintk is useful when the kernel crashes before
1054 the normal console is initialized. It is not enabled by
1055 default because it has some cosmetic problems.
1057 Append ",keep" to not disable it when the real console
1060 Only one of vga, efi, serial, or usb debug port can
1063 Currently only ttyS0 and ttyS1 may be specified by
1064 name. Other I/O ports may be explicitly specified
1065 on some architectures (x86 and arm at least) by
1066 replacing ttySn with an I/O port address, like this:
1067 earlyprintk=serial,0x1008,115200
1068 You can find the port for a given device in
1069 /proc/tty/driver/serial:
1070 2: uart:ST16650V2 port:00001008 irq:18 ...
1072 Interaction with the standard serial driver is not
1075 The VGA and EFI output is eventually overwritten by
1078 The xen output can only be used by Xen PV guests.
1080 edac_report= [HW,EDAC] Control how to report EDAC event
1081 Format: {"on" | "off" | "force"}
1082 on: enable EDAC to report H/W event. May be overridden
1083 by other higher priority error reporting module.
1084 off: disable H/W event reporting through EDAC.
1085 force: enforce the use of EDAC to report H/W event.
1088 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1091 This is designed to be used in conjunction with
1092 the boot argument: earlyprintk=vga
1095 Format: {"off" | "on" | "skip[mbr]"}
1098 Format: { "old_map", "nochunk", "noruntime", "debug" }
1099 old_map [X86-64]: switch to the old ioremap-based EFI
1100 runtime services mapping. 32-bit still uses this one by
1102 nochunk: disable reading files in "chunks" in the EFI
1103 boot stub, as chunking can cause problems with some
1104 firmware implementations.
1105 noruntime : disable EFI runtime services support
1106 debug: enable misc debug output
1108 efi_no_storage_paranoia [EFI; X86]
1109 Using this parameter you can use more than 50% of
1110 your efi variable storage. Use this parameter only if
1111 you are really sure that your UEFI does sane gc and
1112 fulfills the spec otherwise your board may brick.
1114 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1115 Add arbitrary attribute to specific memory range by
1116 updating original EFI memory map.
1117 Region of memory which aa attribute is added to is
1119 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1120 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1121 attribute is added to range 0x100000000-0x180000000 and
1122 0x10a0000000-0x1120000000.
1124 Using this parameter you can do debugging of EFI memmap
1125 related feature. For example, you can do debugging of
1126 Address Range Mirroring feature even if your box
1129 eisa_irq_edge= [PARISC,HW]
1130 See header of drivers/parisc/eisa.c.
1133 See comment before function elanfreq_setup() in
1134 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1137 Format: {"cfq" | "deadline" | "noop"}
1138 See Documentation/block/cfq-iosched.txt and
1139 Documentation/block/deadline-iosched.txt for details.
1141 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1142 Specifies physical address of start of kernel core
1143 image elf header and optionally the size. Generally
1144 kexec loader will pass this option to capture kernel.
1145 See Documentation/kdump/kdump.txt for details.
1147 enable_mtrr_cleanup [X86]
1148 The kernel tries to adjust MTRR layout from continuous
1149 to discrete, to make X server driver able to add WB
1150 entry later. This parameter enables that.
1152 enable_timer_pin_1 [X86]
1153 Enable PIN 1 of APIC timer
1154 Can be useful to work around chipset bugs
1155 (in particular on some ATI chipsets).
1156 The kernel tries to set a reasonable default.
1158 enforcing [SELINUX] Set initial enforcing status.
1160 See security/selinux/Kconfig help text.
1161 0 -- permissive (log only, no denials).
1162 1 -- enforcing (deny and log).
1164 Value can be changed at runtime via /selinux/enforce.
1167 Disable Error Record Serialization Table (ERST)
1170 ether= [HW,NET] Ethernet cards parameters
1171 This option is obsoleted by the "netdev=" option, which
1172 has equivalent usage. See its documentation for details.
1176 Permit 'security.evm' to be updated regardless of
1177 current integrity status.
1181 fail_make_request=[KNL]
1182 General fault injection mechanism.
1183 Format: <interval>,<probability>,<space>,<times>
1184 See also Documentation/fault-injection/.
1187 See Documentation/blockdev/floppy.txt.
1189 force_pal_cache_flush
1190 [IA-64] Avoid check_sal_cache_flush which may hang on
1191 buggy SAL_CACHE_FLUSH implementations. Using this
1192 parameter will force ia64_sal_cache_flush to call
1193 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1196 Forcefully enable Physical Address Extension (PAE).
1197 Many Pentium M systems disable PAE but may have a
1198 functionally usable PAE implementation.
1199 Warning: use of this parameter will taint the kernel
1200 and may cause unknown problems.
1203 [FTRACE] will set and start the specified tracer
1204 as early as possible in order to facilitate early
1207 ftrace_dump_on_oops[=orig_cpu]
1208 [FTRACE] will dump the trace buffers on oops.
1209 If no parameter is passed, ftrace will dump
1210 buffers of all CPUs, but if you pass orig_cpu, it will
1211 dump only the buffer of the CPU that triggered the
1214 ftrace_filter=[function-list]
1215 [FTRACE] Limit the functions traced by the function
1216 tracer at boot up. function-list is a comma separated
1217 list of functions. This list can be changed at run
1218 time by the set_ftrace_filter file in the debugfs
1221 ftrace_notrace=[function-list]
1222 [FTRACE] Do not trace the functions specified in
1223 function-list. This list can be changed at run time
1224 by the set_ftrace_notrace file in the debugfs
1227 ftrace_graph_filter=[function-list]
1228 [FTRACE] Limit the top level callers functions traced
1229 by the function graph tracer at boot up.
1230 function-list is a comma separated list of functions
1231 that can be changed at run time by the
1232 set_graph_function file in the debugfs tracing directory.
1234 ftrace_graph_notrace=[function-list]
1235 [FTRACE] Do not trace from the functions specified in
1236 function-list. This list is a comma separated list of
1237 functions that can be changed at run time by the
1238 set_graph_notrace file in the debugfs tracing directory.
1241 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1242 support via parallel port (up to 5 devices per port)
1243 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1244 See also Documentation/input/joystick-parport.txt
1248 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1252 gcov_persist= [GCOV] When non-zero (default), profiling data for
1253 kernel modules is saved and remains accessible via
1254 debugfs, even when the module is unloaded/reloaded.
1255 When zero, profiling data is discarded and associated
1256 debugfs files are removed at module unload time.
1258 gpt [EFI] Forces disk with valid GPT signature but
1259 invalid Protective MBR to be treated as GPT. If the
1260 primary GPT is corrupted, it enables the backup/alternate
1261 GPT to be used instead.
1263 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1264 the "Enable 0" bit of the configuration register.
1267 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1268 the "Enable 0" bit of the configuration register.
1271 grcan.select= [HW] Select which physical interface to use.
1274 grcan.txsize= [HW] Sets the size of the tx buffer.
1275 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1277 grcan.rxsize= [HW] Sets the size of the rx buffer.
1278 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1281 hardlockup_all_cpu_backtrace=
1282 [KNL] Should the hard-lockup detector generate
1283 backtraces on all cpus.
1286 hashdist= [KNL,NUMA] Large hashes allocated during boot
1287 are distributed across NUMA nodes. Defaults on
1288 for 64-bit NUMA, off otherwise.
1289 Format: 0 | 1 (for off | on)
1291 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1293 hd= [EIDE] (E)IDE hard drive subsystem geometry
1294 Format: <cyl>,<head>,<sect>
1297 Disable Hardware Error Source Table (HEST) support;
1298 corresponding firmware-first mode error processing
1299 logic will be disabled.
1301 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1302 size of <nn>. This works even on boxes that have no
1303 highmem otherwise. This also works to reduce highmem
1304 size on bigger boxes.
1306 highres= [KNL] Enable/disable high resolution timer mode.
1307 Valid parameters: "on", "off"
1311 See Documentation/isdn/README.HiSax.
1315 hpet= [X86-32,HPET] option to control HPET usage
1316 Format: { enable (default) | disable | force |
1318 disable: disable HPET and use PIT instead
1319 force: allow force enabled of undocumented chips (ICH4,
1321 verbose: show contents of HPET registers during setup
1323 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1324 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1326 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1327 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1328 On x86-64 and powerpc, this option can be specified
1329 multiple times interleaved with hugepages= to reserve
1330 huge pages of different sizes. Valid pages sizes on
1331 x86-64 are 2M (when the CPU supports "pse") and 1G
1332 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1334 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1335 terminal devices. Valid values: 0..8
1336 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1337 If specified, z/VM IUCV HVC accepts connections
1338 from listed z/VM user IDs only.
1340 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1341 hardware thread id mappings.
1342 Format: <cpu>:<hwthread>
1345 Do not unregister boot console at start. This is only
1346 useful for debugging when something happens in the window
1347 between unregistering the boot console and initializing
1350 i2c_bus= [HW] Override the default board specific I2C bus speed
1351 or register an additional I2C bus that is not
1352 registered from board initialization code.
1356 i8042.debug [HW] Toggle i8042 debug mode
1357 i8042.unmask_kbd_data
1358 [HW] Enable printing of interrupt data from the KBD port
1359 (disabled by default, and as a pre-condition
1360 requires that i8042.debug=1 be enabled)
1361 i8042.direct [HW] Put keyboard port into non-translated mode
1362 i8042.dumbkbd [HW] Pretend that controller can only read data from
1363 keyboard and cannot control its state
1364 (Don't attempt to blink the leds)
1365 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1366 i8042.nokbd [HW] Don't check/create keyboard port
1367 i8042.noloop [HW] Disable the AUX Loopback command while probing
1369 i8042.nomux [HW] Don't check presence of an active multiplexing
1371 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1373 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1374 i8042.reset [HW] Reset the controller during init, cleanup and
1375 suspend-to-ram transitions, only during s2r
1376 transitions, or never reset
1377 Format: { 1 | Y | y | 0 | N | n }
1378 1, Y, y: always reset controller
1379 0, N, n: don't ever reset controller
1380 Default: only on s2r transitions on x86; most other
1381 architectures force reset to be always executed
1382 i8042.unlock [HW] Unlock (ignore) the keylock
1383 i8042.kbdreset [HW] Reset device connected to KBD port
1387 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1388 indicates that the driver is running on unsupported
1390 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1391 does not match list of supported models.
1393 [HW] Report power status in /proc/i8k
1394 (disabled by default)
1395 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1398 i915.invert_brightness=
1399 [DRM] Invert the sense of the variable that is used to
1400 set the brightness of the panel backlight. Normally a
1401 brightness value of 0 indicates backlight switched off,
1402 and the maximum of the brightness value sets the backlight
1403 to maximum brightness. If this parameter is set to 0
1404 (default) and the machine requires it, or this parameter
1405 is set to 1, a brightness value of 0 sets the backlight
1406 to maximum brightness, and the maximum of the brightness
1407 value switches the backlight off.
1408 -1 -- never invert brightness
1409 0 -- machine default
1410 1 -- force brightness inversion
1413 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1415 ide-core.nodma= [HW] (E)IDE subsystem
1416 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1417 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1418 .cdrom .chs .ignore_cable are additional options
1419 See Documentation/ide/ide.txt.
1421 ide-generic.probe-mask= [HW] (E)IDE subsystem
1423 Probe mask for legacy ISA IDE ports. Depending on
1424 platform up to 6 ports are supported, enabled by
1425 setting corresponding bits in the mask to 1. The
1426 default value is 0x0, which has a special meaning.
1427 On systems that have PCI, it triggers scanning the
1428 PCI bus for the first and the second port, which
1429 are then probed. On systems without PCI the value
1430 of 0x0 enables probing the two first ports as if it
1433 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1434 Claim all unknown PCI IDE storage controllers.
1437 Format: idle=poll, idle=halt, idle=nomwait
1438 Poll forces a polling idle loop that can slightly
1439 improve the performance of waking up a idle CPU, but
1440 will use a lot of power and make the system run hot.
1442 idle=halt: Halt is forced to be used for CPU idle.
1443 In such case C2/C3 won't be used again.
1444 idle=nomwait: Disable mwait for CPU C-states
1446 ignore_loglevel [KNL]
1447 Ignore loglevel setting - this will print /all/
1448 kernel messages to the console. Useful for debugging.
1449 We also add it as printk module parameter, so users
1450 could change it dynamically, usually by
1451 /sys/module/printk/parameters/ignore_loglevel.
1453 ihash_entries= [KNL]
1454 Set number of hash buckets for inode cache.
1456 ima_appraise= [IMA] appraise integrity measurements
1457 Format: { "off" | "enforce" | "fix" | "log" }
1460 ima_appraise_tcb [IMA]
1461 The builtin appraise policy appraises all files
1465 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1469 The list of supported hash algorithms is defined
1470 in crypto/hash_info.h.
1473 The builtin measurement policy to load during IMA
1474 setup. Specyfing "tcb" as the value, measures all
1475 programs exec'd, files mmap'd for exec, and all files
1476 opened with the read mode bit set by either the
1477 effective uid (euid=0) or uid=0.
1480 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1481 Load a policy which meets the needs of the Trusted
1482 Computing Base. This means IMA will measure all
1483 programs exec'd, files mmap'd for exec, and all files
1484 opened for read by uid=0.
1487 Select one of defined IMA measurements template formats.
1488 Formats: { "ima" | "ima-ng" | "ima-sig" }
1492 [IMA] Define a custom template format.
1493 Format: { "field1|...|fieldN" }
1495 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1496 Format: <min_file_size>
1497 Set the minimal file size for using asynchronous hash.
1498 If left unspecified, ahash usage is disabled.
1500 ahash performance varies for different data sizes on
1501 different crypto accelerators. This option can be used
1502 to achieve the best performance for a particular HW.
1504 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1506 Set hashing buffer size. Default: 4k.
1508 ahash performance varies for different chunk sizes on
1509 different crypto accelerators. This option can be used
1510 to achieve best performance for particular HW.
1514 Run specified binary instead of /sbin/init as init
1517 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1518 for working out where the kernel is dying during
1521 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1522 initcall functions. Useful for debugging built-in
1523 modules and initcalls.
1525 initrd= [BOOT] Specify the location of the initial ramdisk
1527 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1530 int_pln_enable [x86] Enable power limit notification interrupt
1532 integrity_audit=[IMA]
1533 Format: { "0" | "1" }
1534 0 -- basic integrity auditing messages. (Default)
1535 1 -- additional integrity auditing messages.
1537 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1539 Enable intel iommu driver.
1541 Disable intel iommu driver.
1542 igfx_off [Default Off]
1543 By default, gfx is mapped as normal device. If a gfx
1544 device has a dedicated DMAR unit, the DMAR unit is
1545 bypassed by not enabling DMAR with this option. In
1546 this case, gfx device will use physical address for
1549 With this option iommu will not optimize to look
1550 for io virtual address below 32-bit forcing dual
1551 address cycle on pci bus for cards supporting greater
1552 than 32-bit addressing. The default is to look
1553 for translation below 32-bit and if not available
1554 then look in the higher range.
1555 strict [Default Off]
1556 With this option on every unmap_single operation will
1557 result in a hardware IOTLB flush operation as opposed
1558 to batching them for performance.
1559 sp_off [Default Off]
1560 By default, super page will be supported if Intel IOMMU
1561 has the capability. With this option, super page will
1563 ecs_off [Default Off]
1564 By default, extended context tables will be supported if
1565 the hardware advertises that it has support both for the
1566 extended tables themselves, and also PASID support. With
1567 this option set, extended tables will not be used even
1568 on hardware which claims to support them.
1570 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1571 0 disables intel_idle and fall back on acpi_idle.
1572 1 to 6 specify maximum depth of C-state.
1576 Do not enable intel_pstate as the default
1577 scaling driver for the supported processors
1579 Enable intel_pstate on systems that prohibit it by default
1580 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1581 instead of acpi-cpufreq may disable platform features, such
1582 as thermal controls and power capping, that rely on ACPI
1583 P-States information being indicated to OSPM and therefore
1584 should be used with caution. This option does not work with
1585 processors that aren't supported by the intel_pstate driver
1586 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1588 Do not enable hardware P state control (HWP)
1591 Only load intel_pstate on systems which support
1592 hardware P state control (HWP) if available.
1594 intremap= [X86-64, Intel-IOMMU]
1595 on enable Interrupt Remapping (default)
1596 off disable Interrupt Remapping
1597 nosid disable Source ID checking
1599 BIOS x2APIC opt-out request will be ignored
1600 nopost disable Interrupt Posting
1602 iomem= Disable strict checking of access to MMIO memory
1603 strict regions from userspace.
1618 nobypass [PPC/POWERNV]
1619 Disable IOMMU bypass, using IOMMU for PCI devices.
1622 io7= [HW] IO7 for Marvel based alpha systems
1623 See comment before marvel_specify_io7 in
1624 arch/alpha/kernel/core_marvel.c.
1626 io_delay= [X86] I/O delay method
1628 Standard port 0x80 based delay
1630 Alternate port 0xed based delay (needed on some systems)
1632 Simple two microseconds delay
1637 See Documentation/filesystems/nfs/nfsroot.txt.
1639 irqaffinity= [SMP] Set the default irq affinity mask
1641 <cpu number>,...,<cpu number>
1643 <cpu number>-<cpu number>
1644 (must be a positive range in ascending order)
1646 <cpu number>,...,<cpu number>-<cpu number>
1649 When an interrupt is not handled search all handlers
1650 for it. Intended to get systems with badly broken
1654 When an interrupt is not handled search all handlers
1655 for it. Also check all handlers each timer
1656 interrupt. Intended to get systems with badly broken
1660 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1662 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1664 <cpu number>,...,<cpu number>
1666 <cpu number>-<cpu number>
1667 (must be a positive range in ascending order)
1669 <cpu number>,...,<cpu number>-<cpu number>
1671 This option can be used to specify one or more CPUs
1672 to isolate from the general SMP balancing and scheduling
1673 algorithms. You can move a process onto or off an
1674 "isolated" CPU via the CPU affinity syscalls or cpuset.
1675 <cpu number> begins at 0 and the maximum value is
1676 "number of CPUs in system - 1".
1678 This option is the preferred way to isolate CPUs. The
1679 alternative -- manually setting the CPU mask of all
1680 tasks in the system -- can cause problems and
1681 suboptimal load balancer performance.
1685 ivrs_ioapic [HW,X86_64]
1686 Provide an override to the IOAPIC-ID<->DEVICE-ID
1687 mapping provided in the IVRS ACPI table. For
1688 example, to map IOAPIC-ID decimal 10 to
1689 PCI device 00:14.0 write the parameter as:
1690 ivrs_ioapic[10]=00:14.0
1692 ivrs_hpet [HW,X86_64]
1693 Provide an override to the HPET-ID<->DEVICE-ID
1694 mapping provided in the IVRS ACPI table. For
1695 example, to map HPET-ID decimal 0 to
1696 PCI device 00:14.0 write the parameter as:
1697 ivrs_hpet[0]=00:14.0
1699 js= [HW,JOY] Analog joystick
1700 See Documentation/input/joystick.txt.
1703 Enable/disable kernel and module base offset ASLR
1704 (Address Space Layout Randomization) if built into
1705 the kernel. When CONFIG_HIBERNATION is selected,
1706 kASLR is disabled by default. When kASLR is enabled,
1707 hibernation will be disabled.
1711 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1712 specifies the amount of memory usable by the kernel
1713 for non-movable allocations. The requested amount is
1714 spread evenly throughout all nodes in the system. The
1715 remaining memory in each node is used for Movable
1716 pages. In the event, a node is too small to have both
1717 kernelcore and Movable pages, kernelcore pages will
1718 take priority and other nodes will have a larger number
1719 of Movable pages. The Movable zone is used for the
1720 allocation of pages that may be reclaimed or moved
1721 by the page migration subsystem. This means that
1722 HugeTLB pages may not be allocated from this zone.
1723 Note that allocations like PTEs-from-HighMem still
1724 use the HighMem zone if it exists, and the Normal
1725 zone if it does not.
1727 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1728 Format: <Controller#>[,poll interval]
1729 The controller # is the number of the ehci usb debug
1730 port as it is probed via PCI. The poll interval is
1731 optional and is the number seconds in between
1732 each poll cycle to the debug port in case you need
1733 the functionality for interrupting the kernel with
1734 gdb or control-c on the dbgp connection. When
1735 not using this parameter you use sysrq-g to break into
1736 the kernel debugger.
1738 kgdboc= [KGDB,HW] kgdb over consoles.
1739 Requires a tty driver that supports console polling,
1740 or a supported polling keyboard driver (non-usb).
1741 Serial only format: <serial_device>[,baud]
1742 keyboard only format: kbd
1743 keyboard and serial format: kbd,<serial_device>[,baud]
1744 Optional Kernel mode setting:
1745 kms, kbd format: kms,kbd
1746 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1748 kgdbwait [KGDB] Stop kernel execution and enter the
1749 kernel debugger at the earliest opportunity.
1751 kmac= [MIPS] korina ethernet MAC address.
1752 Configure the RouterBoard 532 series on-chip
1753 Ethernet adapter MAC address.
1755 kmemleak= [KNL] Boot-time kmemleak enable/disable
1756 Valid arguments: on, off
1758 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1761 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1762 Valid arguments: 0, 1, 2
1763 kmemcheck=0 (disabled)
1764 kmemcheck=1 (enabled)
1765 kmemcheck=2 (one-shot mode)
1766 Default: 2 (one-shot mode)
1768 kstack=N [X86] Print N words from the kernel stack
1771 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1772 Default is 0 (don't ignore, but inject #GP)
1774 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1778 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1779 Default is 1 (enabled)
1781 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1783 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1785 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1786 (virtualized MMU) support on capable Intel chips.
1787 Default is 1 (enabled)
1789 kvm-intel.emulate_invalid_guest_state=
1790 [KVM,Intel] Enable emulation of invalid guest states
1791 Default is 0 (disabled)
1793 kvm-intel.flexpriority=
1794 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1795 Default is 1 (enabled)
1798 [KVM,Intel] Enable VMX nesting (nVMX).
1799 Default is 0 (disabled)
1801 kvm-intel.unrestricted_guest=
1802 [KVM,Intel] Disable unrestricted guest feature
1803 (virtualized real and unpaged mode) on capable
1804 Intel chips. Default is 1 (enabled)
1806 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1807 feature (tagged TLBs) on capable Intel chips.
1808 Default is 1 (enabled)
1814 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1817 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1818 value for LAPIC timer one-shot implementation. Default
1819 back to the programmable timer unit in the LAPIC.
1821 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1824 libata.dma= [LIBATA] DMA control
1825 libata.dma=0 Disable all PATA and SATA DMA
1826 libata.dma=1 PATA and SATA Disk DMA only
1827 libata.dma=2 ATAPI (CDROM) DMA only
1828 libata.dma=4 Compact Flash DMA only
1829 Combinations also work, so libata.dma=3 enables DMA
1830 for disks and CDROMs, but not CFs.
1832 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1833 libata.ignore_hpa=0 keep BIOS limits (default)
1834 libata.ignore_hpa=1 ignore limits, using full disk
1836 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1840 libata.force= [LIBATA] Force configurations. The format is comma
1841 separated list of "[ID:]VAL" where ID is
1842 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1843 matching port, link or device. Basically, it matches
1844 the ATA ID string printed on console by libata. If
1845 the whole ID part is omitted, the last PORT and DEVICE
1846 values are used. If ID hasn't been specified yet, the
1847 configuration applies to all ports, links and devices.
1849 If only DEVICE is omitted, the parameter applies to
1850 the port and all links and devices behind it. DEVICE
1851 number of 0 either selects the first device or the
1852 first fan-out link behind PMP device. It does not
1853 select the host link. DEVICE number of 15 selects the
1854 host link and device attached to it.
1856 The VAL specifies the configuration to force. As long
1857 as there's no ambiguity shortcut notation is allowed.
1858 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1859 The following configurations can be forced.
1861 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1862 Any ID with matching PORT is used.
1864 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1866 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1867 udma[/][16,25,33,44,66,100,133] notation is also
1870 * [no]ncq: Turn on or off NCQ.
1872 * [no]ncqtrim: Turn off queued DSM TRIM.
1874 * nohrst, nosrst, norst: suppress hard, soft
1877 * rstonce: only attempt one reset during
1878 hot-unplug link recovery
1880 * dump_id: dump IDENTIFY data.
1882 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1884 * disable: Disable this device.
1886 If there are multiple matching configurations changing
1887 the same attribute, the last one is used.
1889 memblock=debug [KNL] Enable memblock debug messages.
1891 load_ramdisk= [RAM] List of ramdisks to load from floppy
1892 See Documentation/blockdev/ramdisk.txt.
1894 lockd.nlm_grace_period=P [NFS] Assign grace period.
1897 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1900 lockd.nlm_timeout=T [NFS] Assign timeout value.
1903 lockd.nlm_udpport=M [NFS] Assign UDP port.
1906 locktorture.nreaders_stress= [KNL]
1907 Set the number of locking read-acquisition kthreads.
1908 Defaults to being automatically set based on the
1909 number of online CPUs.
1911 locktorture.nwriters_stress= [KNL]
1912 Set the number of locking write-acquisition kthreads.
1914 locktorture.onoff_holdoff= [KNL]
1915 Set time (s) after boot for CPU-hotplug testing.
1917 locktorture.onoff_interval= [KNL]
1918 Set time (s) between CPU-hotplug operations, or
1919 zero to disable CPU-hotplug testing.
1921 locktorture.shuffle_interval= [KNL]
1922 Set task-shuffle interval (jiffies). Shuffling
1923 tasks allows some CPUs to go into dyntick-idle
1924 mode during the locktorture test.
1926 locktorture.shutdown_secs= [KNL]
1927 Set time (s) after boot system shutdown. This
1928 is useful for hands-off automated testing.
1930 locktorture.stat_interval= [KNL]
1931 Time (s) between statistics printk()s.
1933 locktorture.stutter= [KNL]
1934 Time (s) to stutter testing, for example,
1935 specifying five seconds causes the test to run for
1936 five seconds, wait for five seconds, and so on.
1937 This tests the locking primitive's ability to
1938 transition abruptly to and from idle.
1940 locktorture.torture_runnable= [BOOT]
1941 Start locktorture running at boot time.
1943 locktorture.torture_type= [KNL]
1944 Specify the locking implementation to test.
1946 locktorture.verbose= [KNL]
1947 Enable additional printk() statements.
1949 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1952 loglevel= All Kernel Messages with a loglevel smaller than the
1953 console loglevel will be printed to the console. It can
1954 also be changed with klogd or other programs. The
1955 loglevels are defined as follows:
1957 0 (KERN_EMERG) system is unusable
1958 1 (KERN_ALERT) action must be taken immediately
1959 2 (KERN_CRIT) critical conditions
1960 3 (KERN_ERR) error conditions
1961 4 (KERN_WARNING) warning conditions
1962 5 (KERN_NOTICE) normal but significant condition
1963 6 (KERN_INFO) informational
1964 7 (KERN_DEBUG) debug-level messages
1966 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1967 in bytes. n must be a power of two and greater
1968 than the minimal size. The minimal size is defined
1969 by LOG_BUF_SHIFT kernel config parameter. There is
1970 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1971 that allows to increase the default size depending on
1972 the number of CPUs. See init/Kconfig for more details.
1974 logo.nologo [FB] Disables display of the built-in Linux logo.
1975 This may be used to provide more screen space for
1976 kernel log messages and is useful when debugging
1977 kernel boot problems.
1979 lp=0 [LP] Specify parallel ports to use, e.g,
1980 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1981 lp=reset first parallel port). 'lp=0' disables the
1982 lp=auto printer driver. 'lp=reset' (which can be
1983 specified in addition to the ports) causes
1984 attached printers to be reset. Using
1985 lp=port1,port2,... specifies the parallel ports
1986 to associate lp devices with, starting with
1987 lp0. A port specification may be 'none' to skip
1988 that lp device, or a parport name such as
1989 'parport0'. Specifying 'lp=auto' instead of a
1990 port specification list means that device IDs
1991 from each port should be examined, to see if
1992 an IEEE 1284-compliant printer is attached; if
1993 so, the driver will manage that printer.
1994 See also header of drivers/char/lp.c.
1997 Sets loops_per_jiffy to given constant, thus avoiding
1998 time-consuming boot-time autodetection (up to 250 ms per
1999 CPU). 0 enables autodetection (default). To determine
2000 the correct value for your kernel, boot with normal
2001 autodetection and see what value is printed. Note that
2002 on SMP systems the preset will be applied to all CPUs,
2003 which is likely to cause problems if your CPUs need
2004 significantly divergent settings. An incorrect value
2005 will cause delays in the kernel to be wrong, leading to
2006 unpredictable I/O errors and other breakage. Although
2007 unlikely, in the extreme case this might damage your
2011 Format: <io>,<irq>,<dma>
2013 machvec= [IA-64] Force the use of a particular machine-vector
2014 (machvec) in a generic kernel.
2015 Example: machvec=hpzx1_swiotlb
2017 machtype= [Loongson] Share the same kernel image file between different
2019 Example: machtype=lemote-yeeloong-2f-7inch
2021 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2022 than or equal to this physical address is ignored.
2024 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2025 should make use of. maxcpus=n : n >= 0 limits the
2026 kernel to using 'n' processors. n=0 is a special case,
2027 it is equivalent to "nosmp", which also disables
2030 max_loop= [LOOP] The number of loop block devices that get
2031 (loop.max_loop) unconditionally pre-created at init time. The default
2032 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2033 of statically allocating a predefined number, loop
2034 devices can be requested on-demand with the
2035 /dev/loop-control interface.
2037 mce [X86-32] Machine Check Exception
2039 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2041 md= [HW] RAID subsystems devices and level
2042 See Documentation/md.txt.
2045 Format: <first>,<last>
2046 Specifies range of consoles to be captured by the MDA.
2048 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2049 Amount of memory to be used when the kernel is not able
2050 to see the whole system memory or for test.
2051 [X86] Work as limiting max address. Use together
2052 with memmap= to avoid physical address space collisions.
2053 Without memmap= PCI devices could be placed at addresses
2054 belonging to unused RAM.
2056 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2060 [KNL,SH] Allow user to override the default size for
2061 per-device physically contiguous DMA buffers.
2063 memmap=exactmap [KNL,X86] Enable setting of an exact
2064 E820 memory map, as specified by the user.
2065 Such memmap=exactmap lines can be constructed based on
2066 BIOS output or other requirements. See the memmap=nn@ss
2069 memmap=nn[KMG]@ss[KMG]
2070 [KNL] Force usage of a specific region of memory.
2071 Region of memory to be used is from ss to ss+nn.
2073 memmap=nn[KMG]#ss[KMG]
2074 [KNL,ACPI] Mark specific memory as ACPI data.
2075 Region of memory to be marked is from ss to ss+nn.
2077 memmap=nn[KMG]$ss[KMG]
2078 [KNL,ACPI] Mark specific memory as reserved.
2079 Region of memory to be reserved is from ss to ss+nn.
2080 Example: Exclude memory from 0x18690000-0x1869ffff
2081 memmap=64K$0x18690000
2083 memmap=0x10000$0x18690000
2085 memmap=nn[KMG]!ss[KMG]
2086 [KNL,X86] Mark specific memory as protected.
2087 Region of memory to be used, from ss to ss+nn.
2088 The memory region may be marked as e820 type 12 (0xc)
2089 and is NVDIMM or ADR memory.
2091 memory_corruption_check=0/1 [X86]
2092 Some BIOSes seem to corrupt the first 64k of
2093 memory when doing things like suspend/resume.
2094 Setting this option will scan the memory
2095 looking for corruption. Enabling this will
2096 both detect corruption and prevent the kernel
2097 from using the memory being corrupted.
2098 However, its intended as a diagnostic tool; if
2099 repeatable BIOS-originated corruption always
2100 affects the same memory, you can use memmap=
2101 to prevent the kernel from using that memory.
2103 memory_corruption_check_size=size [X86]
2104 By default it checks for corruption in the low
2105 64k, making this memory unavailable for normal
2106 use. Use this parameter to scan for
2107 corruption in more or less memory.
2109 memory_corruption_check_period=seconds [X86]
2110 By default it checks for corruption every 60
2111 seconds. Use this parameter to check at some
2112 other rate. 0 disables periodic checking.
2114 memtest= [KNL,X86,ARM] Enable memtest
2116 default : 0 <disable>
2117 Specifies the number of memtest passes to be
2118 performed. Each pass selects another test
2119 pattern from a given set of patterns. Memtest
2120 fills the memory with this pattern, validates
2121 memory contents and reserves bad memory
2122 regions that are detected.
2124 meye.*= [HW] Set MotionEye Camera parameters
2125 See Documentation/video4linux/meye.txt.
2127 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2128 Multi-Function General Purpose Timers on AMD Geode
2131 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2132 the BIOS has incorrectly applied a workaround. TinyBIOS
2133 version 0.98 is known to be affected, 0.99 fixes the
2134 problem by letting the user disable the workaround.
2138 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2139 physical address is ignored.
2141 mini2440= [ARM,HW,KNL]
2142 Format:[0..2][b][c][t]
2144 MINI2440 configuration specification:
2145 0 - The attached screen is the 3.5" TFT
2146 1 - The attached screen is the 7" TFT
2147 2 - The VGA Shield is attached (1024x768)
2148 Leaving out the screen size parameter will not load
2149 the TFT driver, and the framebuffer will be left
2151 b - Enable backlight. The TFT backlight pin will be
2152 linked to the kernel VESA blanking code and a GPIO
2153 LED. This parameter is not necessary when using the
2155 c - Enable the s3c camera interface.
2156 t - Reserved for enabling touchscreen support. The
2157 touchscreen support is not enabled in the mainstream
2158 kernel as of 2.6.30, a preliminary port can be found
2159 in the "bleeding edge" mini2440 support kernel at
2160 http://repo.or.cz/w/linux-2.6/mini2440.git
2163 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2164 parameter allows control of the logging verbosity for
2165 the additional memory initialisation checks. A value
2166 of 0 disables mminit logging and a level of 4 will
2167 log everything. Information is printed at KERN_DEBUG
2168 so loglevel=8 may also need to be specified.
2171 [KNL] When CONFIG_MODULE_SIG is set, this means that
2172 modules without (valid) signatures will fail to load.
2173 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2174 is always true, so this option does nothing.
2177 [MOUSE] Maximum time between finger touching and
2178 leaving touchpad surface for touch to be considered
2179 a tap and be reported as a left button click (for
2180 touchpads working in absolute mode only).
2182 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2183 reporting absolute coordinates, such as tablets
2184 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2185 reporting absolute coordinates, such as tablets
2187 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2188 is similar to kernelcore except it specifies the
2189 amount of memory used for migratable allocations.
2190 If both kernelcore and movablecore is specified,
2191 then kernelcore will be at *least* the specified
2192 value but may be more. If movablecore on its own
2193 is specified, the administrator must be careful
2194 that the amount of memory usable for all allocations
2197 movable_node [KNL,X86] Boot-time switch to enable the effects
2198 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2200 MTD_Partition= [MTD]
2201 Format: <name>,<region-number>,<size>,<offset>
2203 MTD_Region= [MTD] Format:
2204 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2207 See drivers/mtd/cmdlinepart.c.
2209 multitce=off [PPC] This parameter disables the use of the pSeries
2210 firmware feature for updating multiple TCE entries
2213 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2215 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2217 boundary - index of last SLC block on Flex-OneNAND.
2218 The remaining blocks are configured as MLC blocks.
2219 lock - Configure if Flex-OneNAND boundary should be locked.
2220 Once locked, the boundary cannot be changed.
2221 1 indicates lock status, 0 indicates unlock status.
2224 ARM/S3C2412 JIVE boot control
2226 See arch/arm/mach-s3c2412/mach-jive.c
2228 mtouchusb.raw_coordinates=
2229 [HW] Make the MicroTouch USB driver use raw coordinates
2230 ('y', default) or cooked coordinates ('n')
2232 mtrr_chunk_size=nn[KMG] [X86]
2233 used for mtrr cleanup. It is largest continuous chunk
2234 that could hold holes aka. UC entries.
2236 mtrr_gran_size=nn[KMG] [X86]
2237 Used for mtrr cleanup. It is granularity of mtrr block.
2239 Large value could prevent small alignment from
2242 mtrr_spare_reg_nr=n [X86]
2244 Range: 0,7 : spare reg number
2246 Used for mtrr cleanup. It is spare mtrr entries number.
2247 Set to 2 or more if your graphical card needs more.
2249 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2251 netdev= [NET] Network devices parameters
2252 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2253 Note that mem_start is often overloaded to mean
2254 something different and driver-specific.
2255 This usage is only documented in each driver source
2259 [NETFILTER] Enable connection tracking flow accounting
2260 0 to disable accounting
2261 1 to enable accounting
2264 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2265 See Documentation/filesystems/nfs/nfsroot.txt.
2267 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2268 See Documentation/filesystems/nfs/nfsroot.txt.
2270 nfsrootdebug [NFS] enable nfsroot debugging messages.
2271 See Documentation/filesystems/nfs/nfsroot.txt.
2273 nfs.callback_tcpport=
2274 [NFS] set the TCP port on which the NFSv4 callback
2275 channel should listen.
2278 [NFS] sets the pathname to the program which is used
2279 to update the NFS client cache entries.
2281 nfs.cache_getent_timeout=
2282 [NFS] sets the timeout after which an attempt to
2283 update a cache entry is deemed to have failed.
2285 nfs.idmap_cache_timeout=
2286 [NFS] set the maximum lifetime for idmapper cache
2290 [NFS] enable 64-bit inode numbers.
2291 If zero, the NFS client will fake up a 32-bit inode
2292 number for the readdir() and stat() syscalls instead
2293 of returning the full 64-bit number.
2294 The default is to return 64-bit inode numbers.
2296 nfs.max_session_slots=
2297 [NFSv4.1] Sets the maximum number of session slots
2298 the client will attempt to negotiate with the server.
2299 This limits the number of simultaneous RPC requests
2300 that the client can send to the NFSv4.1 server.
2301 Note that there is little point in setting this
2302 value higher than the max_tcp_slot_table_limit.
2304 nfs.nfs4_disable_idmapping=
2305 [NFSv4] When set to the default of '1', this option
2306 ensures that both the RPC level authentication
2307 scheme and the NFS level operations agree to use
2308 numeric uids/gids if the mount is using the
2309 'sec=sys' security flavour. In effect it is
2310 disabling idmapping, which can make migration from
2311 legacy NFSv2/v3 systems to NFSv4 easier.
2312 Servers that do not support this mode of operation
2313 will be autodetected by the client, and it will fall
2314 back to using the idmapper.
2315 To turn off this behaviour, set the value to '0'.
2317 [NFS4] Specify an additional fixed unique ident-
2318 ification string that NFSv4 clients can insert into
2319 their nfs_client_id4 string. This is typically a
2320 UUID that is generated at system install time.
2322 nfs.send_implementation_id =
2323 [NFSv4.1] Send client implementation identification
2324 information in exchange_id requests.
2325 If zero, no implementation identification information
2327 The default is to send the implementation identification
2330 nfs.recover_lost_locks =
2331 [NFSv4] Attempt to recover locks that were lost due
2332 to a lease timeout on the server. Please note that
2333 doing this risks data corruption, since there are
2334 no guarantees that the file will remain unchanged
2335 after the locks are lost.
2336 If you want to enable the kernel legacy behaviour of
2337 attempting to recover these locks, then set this
2339 The default parameter value of '0' causes the kernel
2340 not to attempt recovery of lost locks.
2342 nfs4.layoutstats_timer =
2343 [NFSv4.2] Change the rate at which the kernel sends
2344 layoutstats to the pNFS metadata server.
2346 Setting this to value to 0 causes the kernel to use
2347 whatever value is the default set by the layout
2348 driver. A non-zero value sets the minimum interval
2349 in seconds between layoutstats transmissions.
2351 nfsd.nfs4_disable_idmapping=
2352 [NFSv4] When set to the default of '1', the NFSv4
2353 server will return only numeric uids and gids to
2354 clients using auth_sys, and will accept numeric uids
2355 and gids from such clients. This is intended to ease
2356 migration from NFSv2/v3.
2358 objlayoutdriver.osd_login_prog=
2359 [NFS] [OBJLAYOUT] sets the pathname to the program which
2360 is used to automatically discover and login into new
2361 osd-targets. Please see:
2362 Documentation/filesystems/pnfs.txt for more explanations
2364 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2365 when a NMI is triggered.
2366 Format: [state][,regs][,debounce][,die]
2368 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2369 Format: [panic,][nopanic,][num]
2371 0 - turn hardlockup detector in nmi_watchdog off
2372 1 - turn hardlockup detector in nmi_watchdog on
2373 When panic is specified, panic when an NMI watchdog
2374 timeout occurs (or 'nopanic' to override the opposite
2375 default). To disable both hard and soft lockup detectors,
2376 please see 'nowatchdog'.
2377 This is useful when you use a panic=... timeout and
2378 need the box quickly up again.
2380 netpoll.carrier_timeout=
2381 [NET] Specifies amount of time (in seconds) that
2382 netpoll should wait for a carrier. By default netpoll
2385 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2386 emulation library even if a 387 maths coprocessor
2390 [HW] Never suspend the console
2391 Disable suspending of consoles during suspend and
2392 hibernate operations. Once disabled, debugging
2393 messages can reach various consoles while the rest
2394 of the system is being put to sleep (ie, while
2395 debugging driver suspend/resume hooks). This may
2396 not work reliably with all consoles, but is known
2397 to work with serial and VGA consoles.
2398 To facilitate more flexible debugging, we also add
2399 console_suspend, a printk module parameter to control
2400 it. Users could use console_suspend (usually
2401 /sys/module/printk/parameters/console_suspend) to
2402 turn on/off it dynamically.
2404 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2405 caches in the slab allocator. Saves per-node memory,
2406 but will impact performance.
2410 noapic [SMP,APIC] Tells the kernel to not make use of any
2411 IOAPICs that may be present in the system.
2413 noautogroup Disable scheduler automatic task group creation.
2415 nobats [PPC] Do not use BATs for mapping kernel lowmem
2416 on "Classic" PPC cores.
2420 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2422 nodelayacct [KNL] Disable per-task delay accounting
2424 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2426 nodsp [SH] Disable hardware DSP at boot time.
2428 noefi Disable EFI runtime services support.
2433 On X86-32 available only on PAE configured kernels.
2434 noexec=on: enable non-executable mappings (default)
2435 noexec=off: disable non-executable mappings
2438 Disable SMAP (Supervisor Mode Access Prevention)
2439 even if it is supported by processor.
2442 Disable SMEP (Supervisor Mode Execution Prevention)
2443 even if it is supported by processor.
2446 This affects only 32-bit executables.
2447 noexec32=on: enable non-executable mappings (default)
2448 read doesn't imply executable mappings
2449 noexec32=off: disable non-executable mappings
2450 read implies executable mappings
2452 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2454 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2455 register save and restore. The kernel will only save
2456 legacy floating-point registers on task switch.
2458 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2460 noxsave [BUGS=X86] Disables x86 extended register state save
2461 and restore using xsave. The kernel will fallback to
2462 enabling legacy floating-point and sse state.
2464 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2465 register states. The kernel will fall back to use
2466 xsave to save the states. By using this parameter,
2467 performance of saving the states is degraded because
2468 xsave doesn't support modified optimization while
2469 xsaveopt supports it on xsaveopt enabled systems.
2471 noxsaves [X86] Disables xsaves and xrstors used in saving and
2472 restoring x86 extended register state in compacted
2473 form of xsave area. The kernel will fall back to use
2474 xsaveopt and xrstor to save and restore the states
2475 in standard form of xsave area. By using this
2476 parameter, xsave area per process might occupy more
2477 memory on xsaves enabled systems.
2479 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2480 wfi(ARM) instruction doesn't work correctly and not to
2481 use it. This is also useful when using JTAG debugger.
2483 no_file_caps Tells the kernel not to honor file capabilities. The
2484 only way then for a file to be executed with privilege
2485 is to be setuid root or executed by root.
2487 nohalt [IA-64] Tells the kernel not to use the power saving
2488 function PAL_HALT_LIGHT when idle. This increases
2489 power-consumption. On the positive side, it reduces
2490 interrupt wake-up latency, which may improve performance
2491 in certain environments such as networked servers or
2494 nohibernate [HIBERNATION] Disable hibernation and resume.
2496 nohz= [KNL] Boottime enable/disable dynamic ticks
2497 Valid arguments: on, off
2500 nohz_full= [KNL,BOOT]
2501 In kernels built with CONFIG_NO_HZ_FULL=y, set
2502 the specified list of CPUs whose tick will be stopped
2503 whenever possible. The boot CPU will be forced outside
2504 the range to maintain the timekeeping.
2505 The CPUs in this range must also be included in the
2508 noiotrap [SH] Disables trapped I/O port accesses.
2510 noirqdebug [X86-32] Disables the code which attempts to detect and
2511 disable unhandled interrupt sources.
2513 no_timer_check [X86,APIC] Disables the code which tests for
2514 broken timer IRQ sources.
2516 noisapnp [ISAPNP] Disables ISA PnP code.
2518 noinitrd [RAM] Tells the kernel not to load any configured
2521 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2523 [Deprecated - use intremap=off]
2527 nojitter [IA-64] Disables jitter checking for ITC timers.
2529 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2531 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2534 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2535 steal time is computed, but won't influence scheduler
2538 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2540 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2542 noltlbs [PPC] Do not use large page/tlb entries for kernel
2543 lowmem mapping on PPC40x.
2545 nomca [IA-64] Disable machine check abort handling
2547 nomce [X86-32] Disable Machine Check Exception
2549 nomfgpt [X86-32] Disable Multi-Function General Purpose
2550 Timer usage (for AMD Geode machines).
2552 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2553 shutdown the other cpus. Instead use the REBOOT_VECTOR
2556 nomodule Disable module load
2558 nopat [X86] Disable PAT (page attribute table extension of
2559 pagetables) support.
2561 norandmaps Don't use address space randomization. Equivalent to
2562 echo 0 > /proc/sys/kernel/randomize_va_space
2564 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2566 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2567 with UP alternatives
2569 nordrand [X86] Disable kernel use of the RDRAND and
2570 RDSEED instructions even if they are supported
2571 by the processor. RDRAND and RDSEED are still
2572 available to user space applications.
2574 noresume [SWSUSP] Disables resume and restores original swap
2577 no-scroll [VGA] Disables scrollback.
2578 This is required for the Braillex ib80-piezo Braille
2579 reader made by F.H. Papenmeier (Germany).
2583 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2585 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2586 and disable the IO APIC. legacy for "maxcpus=0".
2588 nosoftlockup [KNL] Disable the soft-lockup detector.
2590 nosync [HW,M68K] Disables sync negotiation for all devices.
2592 notsc [BUGS=X86-32] Disable Time Stamp Counter
2594 nousb [USB] Disable the USB subsystem
2596 nowatchdog [KNL] Disable both lockup detectors, i.e.
2597 soft-lockup and NMI watchdog (hard-lockup).
2601 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2603 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2604 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2605 Some features depend on CPU0. Known dependencies are:
2606 1. Resume from suspend/hibernate depends on CPU0.
2607 Suspend/hibernate will fail if CPU0 is offline and you
2608 need to online CPU0 before suspend/hibernate.
2609 2. PIC interrupts also depend on CPU0. CPU0 can't be
2610 removed if a PIC interrupt is detected.
2611 It's said poweroff/reboot may depend on CPU0 on some
2612 machines although I haven't seen such issues so far
2613 after CPU0 is offline on a few tested machines.
2614 If the dependencies are under your control, you can
2615 turn on cpu0_hotplug.
2617 nptcg= [IA-64] Override max number of concurrent global TLB
2618 purges which is reported from either PAL_VM_SUMMARY or
2621 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2622 could support. nr_cpus=n : n >= 1 limits the kernel to
2623 supporting 'n' processors. Later in runtime you can not
2624 use hotplug cpu feature to put more cpu back to online.
2625 just like you compile the kernel NR_CPUS=n
2627 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2629 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2630 Allowed values are enable and disable
2632 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2633 one of ['zone', 'node', 'default'] can be specified
2634 This can be set from sysctl after boot.
2635 See Documentation/sysctl/vm.txt for details.
2637 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2638 See Documentation/debugging-via-ohci1394.txt for more
2641 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2642 Rather than timing out after 20 ms if an EC
2643 command is not properly ACKed, override the length
2644 of the timeout. We have interrupts disabled while
2645 waiting for the ACK, so if this is set too high
2646 interrupts *may* be lost!
2648 omap_mux= [OMAP] Override bootloader pin multiplexing.
2649 Format: <mux_mode0.mode_name=value>...
2650 For example, to override I2C bus2:
2651 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2653 oprofile.timer= [HW]
2654 Use timer interrupt instead of performance counters
2656 oprofile.cpu_type= Force an oprofile cpu type
2657 This might be useful if you have an older oprofile
2658 userland or if you want common events.
2659 Format: { arch_perfmon }
2660 arch_perfmon: [X86] Force use of architectural
2661 perfmon on Intel CPUs instead of the
2662 CPU specific event set.
2663 timer: [X86] Force use of architectural NMI
2664 timer mode (see also oprofile.timer
2665 for generic hr timer mode)
2666 [s390] Force legacy basic mode sampling
2667 (report cpu_type "timer")
2669 oops=panic Always panic on oopses. Default is to just kill the
2670 process, but there is a small probability of
2671 deadlocking the machine.
2672 This will also cause panics on machine check exceptions.
2673 Useful together with panic=30 to trigger a reboot.
2676 See Documentation/sound/oss/oss-parameters.txt
2678 page_owner= [KNL] Boot-time page_owner enabling option.
2679 Storage of the information about who allocated
2680 each page is disabled in default. With this switch,
2682 on: enable the feature
2684 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2685 timeout > 0: seconds before rebooting
2686 timeout = 0: wait forever
2687 timeout < 0: reboot immediately
2690 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2693 crash_kexec_post_notifiers
2694 Run kdump after running panic-notifiers and dumping
2695 kmsg. This only for the users who doubt kdump always
2696 succeeds in any situation.
2697 Note that this also increases risks of kdump failure,
2698 because some panic notifiers can make the crashed
2699 kernel more unstable.
2701 parkbd.port= [HW] Parallel port number the keyboard adapter is
2702 connected to, default is 0.
2704 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2705 0 for XT, 1 for AT (default is AT).
2708 parport= [HW,PPT] Specify parallel ports. 0 disables.
2709 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2710 Use 'auto' to force the driver to use any
2711 IRQ/DMA settings detected (the default is to
2712 ignore detected IRQ/DMA settings because of
2713 possible conflicts). You can specify the base
2714 address, IRQ, and DMA settings; IRQ and DMA
2715 should be numbers, or 'auto' (for using detected
2716 settings on that particular port), or 'nofifo'
2717 (to avoid using a FIFO even if it is detected).
2718 Parallel ports are assigned in the order they
2719 are specified on the command line, starting
2722 parport_init_mode= [HW,PPT]
2723 Configure VIA parallel port to operate in
2724 a specific mode. This is necessary on Pegasos
2725 computer where firmware has no options for setting
2726 up parallel port mode and sets it to spp.
2727 Currently this function knows 686a and 8231 chips.
2728 Format: [spp|ps2|epp|ecp|ecpepp]
2731 Halt all CPUs after the first oops has been printed for
2732 the specified number of seconds. This is to be used if
2733 your oopses keep scrolling off the screen.
2738 See header of drivers/block/paride/pcd.c.
2739 See also Documentation/blockdev/paride.txt.
2741 pci=option[,option...] [PCI] various PCI subsystem options:
2742 earlydump [X86] dump PCI config space before the kernel
2744 off [X86] don't probe for the PCI bus
2745 bios [X86-32] force use of PCI BIOS, don't access
2746 the hardware directly. Use this if your machine
2747 has a non-standard PCI host bridge.
2748 nobios [X86-32] disallow use of PCI BIOS, only direct
2749 hardware access methods are allowed. Use this
2750 if you experience crashes upon bootup and you
2751 suspect they are caused by the BIOS.
2752 conf1 [X86] Force use of PCI Configuration
2754 conf2 [X86] Force use of PCI Configuration
2756 noaer [PCIE] If the PCIEAER kernel config parameter is
2757 enabled, this kernel boot option can be used to
2758 disable the use of PCIE advanced error reporting.
2759 nodomains [PCI] Disable support for multiple PCI
2760 root domains (aka PCI segments, in ACPI-speak).
2761 nommconf [X86] Disable use of MMCONFIG for PCI
2763 check_enable_amd_mmconf [X86] check for and enable
2764 properly configured MMIO access to PCI
2765 config space on AMD family 10h CPU
2766 nomsi [MSI] If the PCI_MSI kernel config parameter is
2767 enabled, this kernel boot option can be used to
2768 disable the use of MSI interrupts system-wide.
2769 noioapicquirk [APIC] Disable all boot interrupt quirks.
2770 Safety option to keep boot IRQs enabled. This
2771 should never be necessary.
2772 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2773 primary IO-APIC for bridges that cannot disable
2774 boot IRQs. This fixes a source of spurious IRQs
2775 when the system masks IRQs.
2776 noioapicreroute [APIC] Disable workaround that uses the
2777 boot IRQ equivalent of an IRQ that connects to
2778 a chipset where boot IRQs cannot be disabled.
2779 The opposite of ioapicreroute.
2780 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2781 routing table. These calls are known to be buggy
2782 on several machines and they hang the machine
2783 when used, but on other computers it's the only
2784 way to get the interrupt routing table. Try
2785 this option if the kernel is unable to allocate
2786 IRQs or discover secondary PCI buses on your
2788 rom [X86] Assign address space to expansion ROMs.
2789 Use with caution as certain devices share
2790 address decoders between ROMs and other
2792 norom [X86] Do not assign address space to
2793 expansion ROMs that do not already have
2794 BIOS assigned address ranges.
2795 nobar [X86] Do not assign address space to the
2796 BARs that weren't assigned by the BIOS.
2797 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2798 assigned automatically to PCI devices. You can
2799 make the kernel exclude IRQs of your ISA cards
2801 pirqaddr=0xAAAAA [X86] Specify the physical address
2802 of the PIRQ table (normally generated
2803 by the BIOS) if it is outside the
2804 F0000h-100000h range.
2805 lastbus=N [X86] Scan all buses thru bus #N. Can be
2806 useful if the kernel is unable to find your
2807 secondary buses and you want to tell it
2808 explicitly which ones they are.
2809 assign-busses [X86] Always assign all PCI bus
2810 numbers ourselves, overriding
2811 whatever the firmware may have done.
2812 usepirqmask [X86] Honor the possible IRQ mask stored
2813 in the BIOS $PIR table. This is needed on
2814 some systems with broken BIOSes, notably
2815 some HP Pavilion N5400 and Omnibook XE3
2816 notebooks. This will have no effect if ACPI
2817 IRQ routing is enabled.
2818 noacpi [X86] Do not use ACPI for IRQ routing
2819 or for PCI scanning.
2820 use_crs [X86] Use PCI host bridge window information
2821 from ACPI. On BIOSes from 2008 or later, this
2822 is enabled by default. If you need to use this,
2823 please report a bug.
2824 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2825 If you need to use this, please report a bug.
2826 routeirq Do IRQ routing for all PCI devices.
2827 This is normally done in pci_enable_device(),
2828 so this option is a temporary workaround
2829 for broken drivers that don't call it.
2830 skip_isa_align [X86] do not align io start addr, so can
2831 handle more pci cards
2832 firmware [ARM] Do not re-enumerate the bus but instead
2833 just use the configuration from the
2834 bootloader. This is currently used on
2835 IXP2000 systems where the bus has to be
2836 configured a certain way for adjunct CPUs.
2837 noearly [X86] Don't do any early type 1 scanning.
2838 This might help on some broken boards which
2839 machine check when some devices' config space
2840 is read. But various workarounds are disabled
2841 and some IOMMU drivers will not work.
2842 bfsort Sort PCI devices into breadth-first order.
2843 This sorting is done to get a device
2844 order compatible with older (<= 2.4) kernels.
2845 nobfsort Don't sort PCI devices into breadth-first order.
2846 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2847 tuning and use the BIOS-configured MPS defaults.
2848 pcie_bus_safe Set every device's MPS to the largest value
2849 supported by all devices below the root complex.
2850 pcie_bus_perf Set device MPS to the largest allowable MPS
2851 based on its parent bus. Also set MRRS (Max
2852 Read Request Size) to the largest supported
2853 value (no larger than the MPS that the device
2854 or bus can support) for best performance.
2855 pcie_bus_peer2peer Set every device's MPS to 128B, which
2856 every device is guaranteed to support. This
2857 configuration allows peer-to-peer DMA between
2858 any pair of devices, possibly at the cost of
2859 reduced performance. This also guarantees
2860 that hot-added devices will work.
2861 cbiosize=nn[KMG] The fixed amount of bus space which is
2862 reserved for the CardBus bridge's IO window.
2863 The default value is 256 bytes.
2864 cbmemsize=nn[KMG] The fixed amount of bus space which is
2865 reserved for the CardBus bridge's memory
2866 window. The default value is 64 megabytes.
2869 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2870 Specifies alignment and device to reassign
2871 aligned memory resources.
2872 If <order of align> is not specified,
2873 PAGE_SIZE is used as alignment.
2874 PCI-PCI bridge can be specified, if resource
2875 windows need to be expanded.
2876 ecrc= Enable/disable PCIe ECRC (transaction layer
2877 end-to-end CRC checking).
2878 bios: Use BIOS/firmware settings. This is the
2882 hpiosize=nn[KMG] The fixed amount of bus space which is
2883 reserved for hotplug bridge's IO window.
2884 Default size is 256 bytes.
2885 hpmemsize=nn[KMG] The fixed amount of bus space which is
2886 reserved for hotplug bridge's memory window.
2887 Default size is 2 megabytes.
2888 realloc= Enable/disable reallocating PCI bridge resources
2889 if allocations done by BIOS are too small to
2890 accommodate resources required by all child
2892 off: Turn realloc off
2894 realloc same as realloc=on
2895 noari do not use PCIe ARI.
2896 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2897 only look for one device below a PCIe downstream
2900 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2903 force Enable ASPM even on devices that claim not to support it.
2904 WARNING: Forcing ASPM on may cause system lockups.
2906 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2907 nomsi Do not use MSI for PCI Express Native Hotplug (this
2908 makes all PCIe ports use INTx for hotplug services).
2910 pcie_ports= [PCIE] PCIe ports handling:
2911 auto Ask the BIOS whether or not to use native PCIe services
2912 associated with PCIe ports (PME, hot-plug, AER). Use
2913 them only if that is allowed by the BIOS.
2914 native Use native PCIe services associated with PCIe ports
2916 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2919 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2920 nomsi Do not use MSI for native PCIe PME signaling (this makes
2921 all PCIe root ports use INTx for all services).
2923 pcmv= [HW,PCMCIA] BadgePAD 4
2927 Keep all power-domains already enabled by bootloader on,
2928 even if no driver has claimed them. This is useful
2929 for debug and development, but should not be
2930 needed on a platform with proper driver support.
2933 See Documentation/blockdev/paride.txt.
2935 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2938 See arch/parisc/kernel/pdc_chassis.c
2940 percpu_alloc= Select which percpu first chunk allocator to use.
2941 Currently supported values are "embed" and "page".
2942 Archs may support subset or none of the selections.
2943 See comments in mm/percpu.c for details on each
2944 allocator. This parameter is primarily for debugging
2945 and performance comparison.
2948 See Documentation/blockdev/paride.txt.
2951 See Documentation/blockdev/paride.txt.
2953 pirq= [SMP,APIC] Manual mp-table setup
2954 See Documentation/x86/i386/IO-APIC.txt.
2956 plip= [PPT,NET] Parallel port network link
2957 Format: { parport<nr> | timid | 0 }
2958 See also Documentation/parport.txt.
2960 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2961 Override pmtimer IOPort with a hex value.
2965 Enable PNP debug messages (depends on the
2966 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2967 via /sys/module/pnp/parameters/debug. We always show
2968 current resource usage; turning this on also shows
2969 possible settings and some assignment information.
2975 { on | off | curr | res | no-curr | no-res }
2978 [ISAPNP] Exclude IRQs for the autoconfiguration
2981 [ISAPNP] Exclude DMAs for the autoconfiguration
2983 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2984 Ranges are in pairs (I/O port base and size).
2987 [ISAPNP] Exclude memory regions for the
2989 Ranges are in pairs (memory base and size).
2991 ports= [IP_VS_FTP] IPVS ftp helper module
2993 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2995 Format: <port>,<port>....
2997 print-fatal-signals=
2998 [KNL] debug: print fatal signals
3000 If enabled, warn about various signal handling
3001 related application anomalies: too many signals,
3002 too many POSIX.1 timers, fatal signals causing a
3005 If you hit the warning due to signal overflow,
3006 you might want to try "ulimit -i unlimited".
3010 printk.always_kmsg_dump=
3011 Trigger kmsg_dump for cases other than kernel oops or
3013 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3016 printk.time= Show timing data prefixed to each printk message line
3017 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3019 processor.max_cstate= [HW,ACPI]
3020 Limit processor to maximum C-state
3021 max_cstate=9 overrides any DMI blacklist limit.
3023 processor.nocst [HW,ACPI]
3024 Ignore the _CST method to determine C-states,
3025 instead using the legacy FADT method
3027 profile= [KNL] Enable kernel profiling via /proc/profile
3028 Format: [schedule,]<number>
3029 Param: "schedule" - profile schedule points.
3030 Param: <number> - step/bucket size as a power of 2 for
3031 statistical time based profiling.
3032 Param: "sleep" - profile D-state sleeping (millisecs).
3033 Requires CONFIG_SCHEDSTATS
3034 Param: "kvm" - profile VM exits.
3036 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3038 See Documentation/blockdev/ramdisk.txt.
3040 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3041 probe for; one of (bare|imps|exps|lifebook|any).
3042 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3044 psmouse.resetafter= [HW,MOUSE]
3045 Try to reset the device after so many bad packets
3048 [HW,MOUSE] Set desired mouse resolution, in dpi.
3049 psmouse.smartscroll=
3050 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3051 0 = disabled, 1 = enabled (default).
3053 pstore.backend= Specify the name of the pstore backend to use
3056 See Documentation/blockdev/paride.txt.
3059 [KNL] Number of legacy pty's. Overwrites compiled-in
3062 quiet [KNL] Disable most log messages
3067 See Documentation/md.txt.
3069 ramdisk_blocksize= [RAM]
3070 See Documentation/blockdev/ramdisk.txt.
3072 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3073 See Documentation/blockdev/ramdisk.txt.
3076 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3077 the specified list of CPUs to be no-callback CPUs.
3078 Invocation of these CPUs' RCU callbacks will
3079 be offloaded to "rcuox/N" kthreads created for
3080 that purpose, where "x" is "b" for RCU-bh, "p"
3081 for RCU-preempt, and "s" for RCU-sched, and "N"
3082 is the CPU number. This reduces OS jitter on the
3083 offloaded CPUs, which can be useful for HPC and
3084 real-time workloads. It can also improve energy
3085 efficiency for asymmetric multiprocessors.
3088 Rather than requiring that offloaded CPUs
3089 (specified by rcu_nocbs= above) explicitly
3090 awaken the corresponding "rcuoN" kthreads,
3091 make these kthreads poll for callbacks.
3092 This improves the real-time response for the
3093 offloaded CPUs by relieving them of the need to
3094 wake up the corresponding kthread, but degrades
3095 energy efficiency by requiring that the kthreads
3096 periodically wake up to do the polling.
3098 rcutree.blimit= [KNL]
3099 Set maximum number of finished RCU callbacks to
3100 process in one batch.
3102 rcutree.dump_tree= [KNL]
3103 Dump the structure of the rcu_node combining tree
3104 out at early boot. This is used for diagnostic
3105 purposes, to verify correct tree setup.
3107 rcutree.gp_cleanup_delay= [KNL]
3108 Set the number of jiffies to delay each step of
3109 RCU grace-period cleanup. This only has effect
3110 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3112 rcutree.gp_init_delay= [KNL]
3113 Set the number of jiffies to delay each step of
3114 RCU grace-period initialization. This only has
3115 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3118 rcutree.gp_preinit_delay= [KNL]
3119 Set the number of jiffies to delay each step of
3120 RCU grace-period pre-initialization, that is,
3121 the propagation of recent CPU-hotplug changes up
3122 the rcu_node combining tree. This only has effect
3123 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3125 rcutree.rcu_fanout_exact= [KNL]
3126 Disable autobalancing of the rcu_node combining
3127 tree. This is used by rcutorture, and might
3128 possibly be useful for architectures having high
3129 cache-to-cache transfer latencies.
3131 rcutree.rcu_fanout_leaf= [KNL]
3132 Change the number of CPUs assigned to each
3133 leaf rcu_node structure. Useful for very
3134 large systems, which will choose the value 64,
3135 and for NUMA systems with large remote-access
3136 latencies, which will choose a value aligned
3137 with the appropriate hardware boundaries.
3139 rcutree.jiffies_till_sched_qs= [KNL]
3140 Set required age in jiffies for a
3141 given grace period before RCU starts
3142 soliciting quiescent-state help from
3143 rcu_note_context_switch().
3145 rcutree.jiffies_till_first_fqs= [KNL]
3146 Set delay from grace-period initialization to
3147 first attempt to force quiescent states.
3148 Units are jiffies, minimum value is zero,
3149 and maximum value is HZ.
3151 rcutree.jiffies_till_next_fqs= [KNL]
3152 Set delay between subsequent attempts to force
3153 quiescent states. Units are jiffies, minimum
3154 value is one, and maximum value is HZ.
3156 rcutree.kthread_prio= [KNL,BOOT]
3157 Set the SCHED_FIFO priority of the RCU per-CPU
3158 kthreads (rcuc/N). This value is also used for
3159 the priority of the RCU boost threads (rcub/N)
3160 and for the RCU grace-period kthreads (rcu_bh,
3161 rcu_preempt, and rcu_sched). If RCU_BOOST is
3162 set, valid values are 1-99 and the default is 1
3163 (the least-favored priority). Otherwise, when
3164 RCU_BOOST is not set, valid values are 0-99 and
3165 the default is zero (non-realtime operation).
3167 rcutree.rcu_nocb_leader_stride= [KNL]
3168 Set the number of NOCB kthread groups, which
3169 defaults to the square root of the number of
3170 CPUs. Larger numbers reduces the wakeup overhead
3171 on the per-CPU grace-period kthreads, but increases
3172 that same overhead on each group's leader.
3174 rcutree.qhimark= [KNL]
3175 Set threshold of queued RCU callbacks beyond which
3176 batch limiting is disabled.
3178 rcutree.qlowmark= [KNL]
3179 Set threshold of queued RCU callbacks below which
3180 batch limiting is re-enabled.
3182 rcutree.rcu_idle_gp_delay= [KNL]
3183 Set wakeup interval for idle CPUs that have
3184 RCU callbacks (RCU_FAST_NO_HZ=y).
3186 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3187 Set wakeup interval for idle CPUs that have
3188 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3189 Lazy RCU callbacks are those which RCU can
3190 prove do nothing more than free memory.
3192 rcutorture.cbflood_inter_holdoff= [KNL]
3193 Set holdoff time (jiffies) between successive
3194 callback-flood tests.
3196 rcutorture.cbflood_intra_holdoff= [KNL]
3197 Set holdoff time (jiffies) between successive
3198 bursts of callbacks within a given callback-flood
3201 rcutorture.cbflood_n_burst= [KNL]
3202 Set the number of bursts making up a given
3203 callback-flood test. Set this to zero to
3204 disable callback-flood testing.
3206 rcutorture.cbflood_n_per_burst= [KNL]
3207 Set the number of callbacks to be registered
3208 in a given burst of a callback-flood test.
3210 rcutorture.fqs_duration= [KNL]
3211 Set duration of force_quiescent_state bursts
3214 rcutorture.fqs_holdoff= [KNL]
3215 Set holdoff time within force_quiescent_state bursts
3218 rcutorture.fqs_stutter= [KNL]
3219 Set wait time between force_quiescent_state bursts
3222 rcutorture.gp_cond= [KNL]
3223 Use conditional/asynchronous update-side
3224 primitives, if available.
3226 rcutorture.gp_exp= [KNL]
3227 Use expedited update-side primitives, if available.
3229 rcutorture.gp_normal= [KNL]
3230 Use normal (non-expedited) asynchronous
3231 update-side primitives, if available.
3233 rcutorture.gp_sync= [KNL]
3234 Use normal (non-expedited) synchronous
3235 update-side primitives, if available. If all
3236 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3237 rcutorture.gp_normal=, and rcutorture.gp_sync=
3238 are zero, rcutorture acts as if is interpreted
3239 they are all non-zero.
3241 rcutorture.n_barrier_cbs= [KNL]
3242 Set callbacks/threads for rcu_barrier() testing.
3244 rcutorture.nfakewriters= [KNL]
3245 Set number of concurrent RCU writers. These just
3246 stress RCU, they don't participate in the actual
3247 test, hence the "fake".
3249 rcutorture.nreaders= [KNL]
3250 Set number of RCU readers. The value -1 selects
3251 N-1, where N is the number of CPUs. A value
3252 "n" less than -1 selects N-n-2, where N is again
3253 the number of CPUs. For example, -2 selects N
3254 (the number of CPUs), -3 selects N+1, and so on.
3256 rcutorture.object_debug= [KNL]
3257 Enable debug-object double-call_rcu() testing.
3259 rcutorture.onoff_holdoff= [KNL]
3260 Set time (s) after boot for CPU-hotplug testing.
3262 rcutorture.onoff_interval= [KNL]
3263 Set time (s) between CPU-hotplug operations, or
3264 zero to disable CPU-hotplug testing.
3266 rcutorture.shuffle_interval= [KNL]
3267 Set task-shuffle interval (s). Shuffling tasks
3268 allows some CPUs to go into dyntick-idle mode
3269 during the rcutorture test.
3271 rcutorture.shutdown_secs= [KNL]
3272 Set time (s) after boot system shutdown. This
3273 is useful for hands-off automated testing.
3275 rcutorture.stall_cpu= [KNL]
3276 Duration of CPU stall (s) to test RCU CPU stall
3277 warnings, zero to disable.
3279 rcutorture.stall_cpu_holdoff= [KNL]
3280 Time to wait (s) after boot before inducing stall.
3282 rcutorture.stat_interval= [KNL]
3283 Time (s) between statistics printk()s.
3285 rcutorture.stutter= [KNL]
3286 Time (s) to stutter testing, for example, specifying
3287 five seconds causes the test to run for five seconds,
3288 wait for five seconds, and so on. This tests RCU's
3289 ability to transition abruptly to and from idle.
3291 rcutorture.test_boost= [KNL]
3292 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3293 "Maybe" means test if the RCU implementation
3294 under test support RCU priority boosting.
3296 rcutorture.test_boost_duration= [KNL]
3297 Duration (s) of each individual boost test.
3299 rcutorture.test_boost_interval= [KNL]
3300 Interval (s) between each boost test.
3302 rcutorture.test_no_idle_hz= [KNL]
3303 Test RCU's dyntick-idle handling. See also the
3304 rcutorture.shuffle_interval parameter.
3306 rcutorture.torture_runnable= [BOOT]
3307 Start rcutorture running at boot time.
3309 rcutorture.torture_type= [KNL]
3310 Specify the RCU implementation to test.
3312 rcutorture.verbose= [KNL]
3313 Enable additional printk() statements.
3315 rcupdate.rcu_expedited= [KNL]
3316 Use expedited grace-period primitives, for
3317 example, synchronize_rcu_expedited() instead
3318 of synchronize_rcu(). This reduces latency,
3319 but can increase CPU utilization, degrade
3320 real-time latency, and degrade energy efficiency.
3322 rcupdate.rcu_cpu_stall_suppress= [KNL]
3323 Suppress RCU CPU stall warning messages.
3325 rcupdate.rcu_cpu_stall_timeout= [KNL]
3326 Set timeout for RCU CPU stall warning messages.
3328 rcupdate.rcu_task_stall_timeout= [KNL]
3329 Set timeout in jiffies for RCU task stall warning
3330 messages. Disable with a value less than or equal
3333 rcupdate.rcu_self_test= [KNL]
3334 Run the RCU early boot self tests
3336 rcupdate.rcu_self_test_bh= [KNL]
3337 Run the RCU bh early boot self tests
3339 rcupdate.rcu_self_test_sched= [KNL]
3340 Run the RCU sched early boot self tests
3344 Run specified binary instead of /init from the ramdisk,
3345 used for early userspace startup. See initrd.
3348 Format (x86 or x86_64):
3349 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3351 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3353 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3354 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3355 reboot_force is either force or not specified,
3356 reboot_cpu is s[mp]#### with #### being the processor
3357 to be used for rebooting.
3360 [KNL, SMP] Set scheduler's default relax_domain_level.
3361 See Documentation/cgroups/cpusets.txt.
3363 relative_sleep_states=
3364 [SUSPEND] Use sleep state labeling where the deepest
3365 state available other than hibernation is always "mem".
3366 Format: { "0" | "1" }
3367 0 -- Traditional sleep state labels.
3368 1 -- Relative sleep state labels.
3370 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3372 reservetop= [X86-32]
3374 Reserves a hole at the top of the kernel virtual
3379 Set the amount of memory to reserve for BIOS at
3380 the bottom of the address space.
3382 reset_devices [KNL] Force drivers to reset the underlying device
3383 during initialization.
3386 Specify the partition device for software suspend
3388 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3390 resume_offset= [SWSUSP]
3391 Specify the offset from the beginning of the partition
3392 given by "resume=" at which the swap header is located,
3393 in <PAGE_SIZE> units (needed only for swap files).
3394 See Documentation/power/swsusp-and-swap-files.txt
3396 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3397 read the resume files
3399 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3400 Useful for devices that are detected asynchronously
3401 (e.g. USB and MMC devices).
3403 hibernate= [HIBERNATION]
3404 noresume Don't check if there's a hibernation image
3405 present during boot.
3406 nocompress Don't compress/decompress hibernation images.
3407 no Disable hibernation and resume.
3409 retain_initrd [RAM] Keep initrd memory after extraction
3411 rfkill.default_state=
3412 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3413 etc. communication is blocked by default.
3416 rfkill.master_switch_mode=
3417 0 The "airplane mode" button does nothing.
3418 1 The "airplane mode" button toggles between everything
3419 blocked and the previous configuration.
3420 2 The "airplane mode" button toggles between everything
3421 blocked and everything unblocked.
3423 rhash_entries= [KNL,NET]
3424 Set number of hash buckets for route cache
3426 ro [KNL] Mount root device read-only on boot
3428 root= [KNL] Root filesystem
3429 See name_to_dev_t comment in init/do_mounts.c.
3431 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3432 mount the root filesystem
3434 rootflags= [KNL] Set root filesystem mount option string
3436 rootfstype= [KNL] Set root filesystem type
3438 rootwait [KNL] Wait (indefinitely) for root device to show up.
3439 Useful for devices that are detected asynchronously
3440 (e.g. USB and MMC devices).
3442 rproc_mem=nn[KMG][@address]
3443 [KNL,ARM,CMA] Remoteproc physical memory block.
3444 Memory area to be used by remote processor image,
3447 rw [KNL] Mount root device read-write on boot
3449 S [KNL] Run init in single mode
3451 s390_iommu= [HW,S390]
3452 Set s390 IOTLB flushing mode
3454 With strict flushing every unmap operation will result in
3455 an IOTLB flush. Default is lazy flushing before reuse,
3459 See drivers/net/irda/sa1100_ir.c.
3461 sbni= [NET] Granch SBNI12 leased line adapter
3463 sched_debug [KNL] Enables verbose scheduler debug messages.
3465 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3466 xtime_lock contention on larger systems, and/or RCU lock
3467 contention on all systems with CONFIG_MAXSMP set.
3468 Format: { "0" | "1" }
3469 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3471 Note: increases power consumption, thus should only be
3472 enabled if running jitter sensitive (HPC/RT) workloads.
3474 security= [SECURITY] Choose a security module to enable at boot.
3475 If this boot parameter is not specified, only the first
3476 security module asking for security registration will be
3477 loaded. An invalid security module name will be treated
3478 as if no module has been chosen.
3480 selinux= [SELINUX] Disable or enable SELinux at boot time.
3481 Format: { "0" | "1" }
3482 See security/selinux/Kconfig help text.
3485 Default value is set via kernel config option.
3486 If enabled at boot time, /selinux/disable can be used
3487 later to disable prior to initial policy load.
3489 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3490 Format: { "0" | "1" }
3491 See security/apparmor/Kconfig help text
3494 Default value is set via kernel config option.
3496 serialnumber [BUGS=X86-32]
3499 Maximal number of shapers.
3501 show_msr= [x86] show boot-time MSR settings
3502 Format: { <integer> }
3503 Show boot-time (BIOS-initialized) MSR settings.
3504 The parameter means the number of CPUs to show,
3505 for example 1 means boot CPU only.
3513 Disable merging of slabs with similar size. May be
3514 necessary if there is some reason to distinguish
3515 allocs to different slabs. Debug options disable
3516 merging on their own.
3517 For more information see Documentation/vm/slub.txt.
3519 slab_max_order= [MM, SLAB]
3520 Determines the maximum allowed order for slabs.
3521 A high setting may cause OOMs due to memory
3522 fragmentation. Defaults to 1 for systems with
3523 more than 32MB of RAM, 0 otherwise.
3525 slub_debug[=options[,slabs]] [MM, SLUB]
3526 Enabling slub_debug allows one to determine the
3527 culprit if slab objects become corrupted. Enabling
3528 slub_debug can create guard zones around objects and
3529 may poison objects when not in use. Also tracks the
3530 last alloc / free. For more information see
3531 Documentation/vm/slub.txt.
3533 slub_max_order= [MM, SLUB]
3534 Determines the maximum allowed order for slabs.
3535 A high setting may cause OOMs due to memory
3536 fragmentation. For more information see
3537 Documentation/vm/slub.txt.
3539 slub_min_objects= [MM, SLUB]
3540 The minimum number of objects per slab. SLUB will
3541 increase the slab order up to slub_max_order to
3542 generate a sufficiently large slab able to contain
3543 the number of objects indicated. The higher the number
3544 of objects the smaller the overhead of tracking slabs
3545 and the less frequently locks need to be acquired.
3546 For more information see Documentation/vm/slub.txt.
3548 slub_min_order= [MM, SLUB]
3549 Determines the minimum page order for slabs. Must be
3550 lower than slub_max_order.
3551 For more information see Documentation/vm/slub.txt.
3553 slub_nomerge [MM, SLUB]
3554 Same with slab_nomerge. This is supported for legacy.
3555 See slab_nomerge for more information.
3558 Format: <io1>[,<io2>[,...,<io8>]]
3560 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3561 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3562 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3563 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3564 smsc-ircc2.ircc_irq= [HW] IRQ line
3565 smsc-ircc2.ircc_dma= [HW] DMA channel
3566 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3567 0: Toshiba Satellite 1800 (GP data pin select)
3568 1: Fast pin select (default)
3572 [KNL] Should the soft-lockup detector generate panics.
3575 softlockup_all_cpu_backtrace=
3576 [KNL] Should the soft-lockup detector generate
3577 backtraces on all cpus.
3580 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3581 See Documentation/laptops/sonypi.txt
3583 spia_io_base= [HW,MTD]
3589 Enabled the stack tracer on boot up.
3591 stacktrace_filter=[function-list]
3592 [FTRACE] Limit the functions that the stack tracer
3593 will trace at boot up. function-list is a comma separated
3594 list of functions. This list can be changed at run
3595 time by the stack_trace_filter file in the debugfs
3596 tracing directory. Note, this enables stack tracing
3597 and the stacktrace above is not needed.
3601 Set the STI (builtin display/keyboard on the HP-PARISC
3602 machines) console (graphic card) which should be used
3603 as the initial boot-console.
3604 See also comment in drivers/video/console/sticore.c.
3607 See comment in drivers/video/console/sticore.c.
3610 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3612 sunrpc.min_resvport=
3613 sunrpc.max_resvport=
3615 SunRPC servers often require that client requests
3616 originate from a privileged port (i.e. a port in the
3617 range 0 < portnr < 1024).
3618 An administrator who wishes to reserve some of these
3619 ports for other uses may adjust the range that the
3620 kernel's sunrpc client considers to be privileged
3621 using these two parameters to set the minimum and
3622 maximum port values.
3626 Control how the NFS server code allocates CPUs to
3627 service thread pools. Depending on how many NICs
3628 you have and where their interrupts are bound, this
3629 option will affect which CPUs will do NFS serving.
3630 Note: this parameter cannot be changed while the
3631 NFS server is running.
3633 auto the server chooses an appropriate mode
3634 automatically using heuristics
3635 global a single global pool contains all CPUs
3636 percpu one pool for each CPU
3637 pernode one pool for each NUMA node (equivalent
3638 to global on non-NUMA machines)
3640 sunrpc.tcp_slot_table_entries=
3641 sunrpc.udp_slot_table_entries=
3643 Sets the upper limit on the number of simultaneous
3644 RPC calls that can be sent from the client to a
3645 server. Increasing these values may allow you to
3646 improve throughput, but will also increase the
3647 amount of memory reserved for use by the client.
3649 suspend.pm_test_delay=
3651 Sets the number of seconds to remain in a suspend test
3652 mode before resuming the system (see
3653 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3654 is set. Default value is 5.
3657 [KNL] Enable accounting of swap in memory resource
3658 controller if no parameter or 1 is given or disable
3659 it if 0 is given (See Documentation/cgroups/memory.txt)
3661 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3662 Format: { <int> | force }
3663 <int> -- Number of I/O TLB slabs
3664 force -- force using of bounce buffers even if they
3665 wouldn't be automatically used by the kernel
3669 sysfs.deprecated=0|1 [KNL]
3670 Enable/disable old style sysfs layout for old udev
3671 on older distributions. When this option is enabled
3672 very new udev will not work anymore. When this option
3673 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3674 in older udev will not work anymore.
3675 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3676 the kernel configuration.
3678 sysrq_always_enabled
3680 Ignore sysrq setting - this boot parameter will
3681 neutralize any effect of /proc/sys/kernel/sysrq.
3682 Useful for debugging.
3684 tcpmhash_entries= [KNL,NET]
3685 Set the number of tcp_metrics_hash slots.
3686 Default value is 8192 or 16384 depending on total
3687 ram pages. This is used to specify the TCP metrics
3688 cache size. See Documentation/networking/ip-sysctl.txt
3689 "tcp_no_metrics_save" section for more details.
3693 test_suspend= [SUSPEND][,N]
3694 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3695 standby suspend) or "freeze" (for suspend type freeze)
3696 as the system sleep state during system startup with
3697 the optional capability to repeat N number of times.
3698 The system is woken from this state using a
3699 wakeup-capable RTC alarm.
3701 thash_entries= [KNL,NET]
3702 Set number of hash buckets for TCP connection
3704 thermal.act= [HW,ACPI]
3705 -1: disable all active trip points in all thermal zones
3706 <degrees C>: override all lowest active trip points
3708 thermal.crt= [HW,ACPI]
3709 -1: disable all critical trip points in all thermal zones
3710 <degrees C>: override all critical trip points
3712 thermal.nocrt= [HW,ACPI]
3713 Set to disable actions on ACPI thermal zone
3714 critical and hot trip points.
3716 thermal.off= [HW,ACPI]
3717 1: disable ACPI thermal control
3719 thermal.psv= [HW,ACPI]
3720 -1: disable all passive trip points
3721 <degrees C>: override all passive trip points to this
3724 thermal.tzp= [HW,ACPI]
3725 Specify global default ACPI thermal zone polling rate
3726 <deci-seconds>: poll all this frequency
3727 0: no polling (default)
3730 Force threading of all interrupt handlers except those
3731 marked explicitly IRQF_NO_THREAD.
3734 Enable the Transcendent memory driver if built-in.
3736 tmem.cleancache=0|1 [KNL, XEN]
3737 Default is on (1). Disable the usage of the cleancache
3738 API to send anonymous pages to the hypervisor.
3740 tmem.frontswap=0|1 [KNL, XEN]
3741 Default is on (1). Disable the usage of the frontswap
3742 API to send swap pages to the hypervisor. If disabled
3743 the selfballooning and selfshrinking are force disabled.
3745 tmem.selfballooning=0|1 [KNL, XEN]
3746 Default is on (1). Disable the driving of swap pages
3749 tmem.selfshrinking=0|1 [KNL, XEN]
3750 Default is on (1). Partial swapoff that immediately
3751 transfers pages from Xen hypervisor back to the
3752 kernel based on different criteria.
3756 Specify if the kernel should make use of the cpu
3757 topology information if the hardware supports this.
3758 The scheduler will make use of this information and
3759 e.g. base its process migration decisions on it.
3762 topology_updates= [KNL, PPC, NUMA]
3764 Specify if the kernel should ignore (off)
3765 topology updates sent by the hypervisor to this
3770 tpm_suspend_pcr=[HW,TPM]
3771 Format: integer pcr id
3772 Specify that at suspend time, the tpm driver
3773 should extend the specified pcr with zeros,
3774 as a workaround for some chips which fail to
3775 flush the last written pcr on TPM_SaveState.
3776 This will guarantee that all the other pcrs
3779 trace_buf_size=nn[KMG]
3780 [FTRACE] will set tracing buffer size on each cpu.
3782 trace_event=[event-list]
3783 [FTRACE] Set and start specified trace events in order
3784 to facilitate early boot debugging.
3785 See also Documentation/trace/events.txt
3787 trace_options=[option-list]
3788 [FTRACE] Enable or disable tracer options at boot.
3789 The option-list is a comma delimited list of options
3790 that can be enabled or disabled just as if you were
3791 to echo the option name into
3793 /sys/kernel/debug/tracing/trace_options
3795 For example, to enable stacktrace option (to dump the
3796 stack trace of each event), add to the command line:
3798 trace_options=stacktrace
3800 See also Documentation/trace/ftrace.txt "trace options"
3804 Have the tracepoints sent to printk as well as the
3805 tracing ring buffer. This is useful for early boot up
3806 where the system hangs or reboots and does not give the
3807 option for reading the tracing buffer or performing a
3808 ftrace_dump_on_oops.
3810 To turn off having tracepoints sent to printk,
3811 echo 0 > /proc/sys/kernel/tracepoint_printk
3812 Note, echoing 1 into this file without the
3813 tracepoint_printk kernel cmdline option has no effect.
3817 Having tracepoints sent to printk() and activating high
3818 frequency tracepoints such as irq or sched, can cause
3819 the system to live lock.
3822 [FTRACE] enable this option to disable tracing when a
3823 warning is hit. This turns off "tracing_on". Tracing can
3824 be enabled again by echoing '1' into the "tracing_on"
3825 file located in /sys/kernel/debug/tracing/
3827 This option is useful, as it disables the trace before
3828 the WARNING dump is called, which prevents the trace to
3829 be filled with content caused by the warning output.
3831 This option can also be set at run time via the sysctl
3832 option: kernel/traceoff_on_warning
3834 transparent_hugepage=
3836 Format: [always|madvise|never]
3837 Can be used to control the default behavior of the system
3838 with respect to transparent hugepages.
3839 See Documentation/vm/transhuge.txt for more details.
3841 tsc= Disable clocksource stability checks for TSC.
3843 [x86] reliable: mark tsc clocksource as reliable, this
3844 disables clocksource verification at runtime, as well
3845 as the stability checks done at bootup. Used to enable
3846 high-resolution timer mode on older hardware, and in
3847 virtualized environment.
3848 [x86] noirqtime: Do not use TSC to do irq accounting.
3849 Used to run time disable IRQ_TIME_ACCOUNTING on any
3850 platforms where RDTSC is slow and this accounting
3853 turbografx.map[2|3]= [HW,JOY]
3854 TurboGraFX parallel port interface
3856 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3857 See also Documentation/input/joystick-parport.txt
3859 udbg-immortal [PPC] When debugging early kernel crashes that
3860 happen after console_init() and before a proper
3861 console driver takes over, this boot options might
3862 help "seeing" what's going on.
3864 uhash_entries= [KNL,NET]
3865 Set number of hash buckets for UDP/UDP-Lite connections
3868 [USB] Ignore overcurrent events (default N).
3869 Some badly-designed motherboards generate lots of
3870 bogus events, for ports that aren't wired to
3871 anything. Set this parameter to avoid log spamming.
3872 Note that genuine overcurrent events won't be
3876 [X86] Cause panic on unknown NMI.
3878 usbcore.authorized_default=
3879 [USB] Default USB device authorization:
3880 (default -1 = authorized except for wireless USB,
3881 0 = not authorized, 1 = authorized)
3883 usbcore.autosuspend=
3884 [USB] The autosuspend time delay (in seconds) used
3885 for newly-detected USB devices (default 2). This
3886 is the time required before an idle device will be
3887 autosuspended. Devices for which the delay is set
3888 to a negative value won't be autosuspended at all.
3890 usbcore.usbfs_snoop=
3891 [USB] Set to log all usbfs traffic (default 0 = off).
3893 usbcore.blinkenlights=
3894 [USB] Set to cycle leds on hubs (default 0 = off).
3896 usbcore.old_scheme_first=
3897 [USB] Start with the old device initialization
3898 scheme (default 0 = off).
3900 usbcore.usbfs_memory_mb=
3901 [USB] Memory limit (in MB) for buffers allocated by
3902 usbfs (default = 16, 0 = max = 2047).
3904 usbcore.use_both_schemes=
3905 [USB] Try the other device initialization scheme
3906 if the first one fails (default 1 = enabled).
3908 usbcore.initial_descriptor_timeout=
3909 [USB] Specifies timeout for the initial 64-byte
3910 USB_REQ_GET_DESCRIPTOR request in milliseconds
3911 (default 5000 = 5.0 seconds).
3914 [USBHID] The interval which mice are to be polled at.
3916 usb-storage.delay_use=
3917 [UMS] The delay in seconds before a new device is
3918 scanned for Logical Units (default 1).
3921 [UMS] A list of quirks entries to supplement or
3922 override the built-in unusual_devs list. List
3923 entries are separated by commas. Each entry has
3924 the form VID:PID:Flags where VID and PID are Vendor
3925 and Product ID values (4-digit hex numbers) and
3926 Flags is a set of characters, each corresponding
3927 to a common usb-storage quirk flag as follows:
3928 a = SANE_SENSE (collect more than 18 bytes
3930 b = BAD_SENSE (don't collect more than 18
3931 bytes of sense data);
3932 c = FIX_CAPACITY (decrease the reported
3933 device capacity by one sector);
3934 d = NO_READ_DISC_INFO (don't use
3935 READ_DISC_INFO command);
3936 e = NO_READ_CAPACITY_16 (don't use
3937 READ_CAPACITY_16 command);
3938 f = NO_REPORT_OPCODES (don't use report opcodes
3940 g = MAX_SECTORS_240 (don't transfer more than
3941 240 sectors at a time, uas only);
3942 h = CAPACITY_HEURISTICS (decrease the
3943 reported device capacity by one
3944 sector if the number is odd);
3945 i = IGNORE_DEVICE (don't bind to this
3947 j = NO_REPORT_LUNS (don't use report luns
3949 l = NOT_LOCKABLE (don't try to lock and
3950 unlock ejectable media);
3951 m = MAX_SECTORS_64 (don't transfer more
3952 than 64 sectors = 32 KB at a time);
3953 n = INITIAL_READ10 (force a retry of the
3954 initial READ(10) command);
3955 o = CAPACITY_OK (accept the capacity
3956 reported by the device);
3957 p = WRITE_CACHE (the device cache is ON
3959 r = IGNORE_RESIDUE (the device reports
3960 bogus residue values);
3961 s = SINGLE_LUN (the device has only one
3963 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3964 commands, uas only);
3965 u = IGNORE_UAS (don't bind to the uas driver);
3966 w = NO_WP_DETECT (don't test whether the
3967 medium is write-protected).
3968 Example: quirks=0419:aaf5:rl,0421:0433:rc
3970 user_debug= [KNL,ARM]
3972 See arch/arm/Kconfig.debug help text.
3973 1 - undefined instruction events
3975 4 - invalid data aborts
3978 Example: user_debug=31
3981 [X86] Flags controlling user PTE allocations.
3983 nohigh = do not allocate PTE pages in
3984 HIGHMEM regardless of setting
3988 On X86_32, this is an alias for vdso32=. Otherwise:
3990 vdso=1: enable VDSO (the default)
3991 vdso=0: disable VDSO mapping
3993 vdso32= [X86] Control the 32-bit vDSO
3994 vdso32=1: enable 32-bit VDSO
3995 vdso32=0 or vdso32=2: disable 32-bit VDSO
3997 See the help text for CONFIG_COMPAT_VDSO for more
3998 details. If CONFIG_COMPAT_VDSO is set, the default is
3999 vdso32=0; otherwise, the default is vdso32=1.
4001 For compatibility with older kernels, vdso32=2 is an
4004 Try vdso32=0 if you encounter an error that says:
4005 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4008 vector=percpu: enable percpu vector domain
4010 video= [FB] Frame buffer configuration
4011 See Documentation/fb/modedb.txt.
4013 video.brightness_switch_enabled= [0,1]
4014 If set to 1, on receiving an ACPI notify event
4015 generated by hotkey, video driver will adjust brightness
4016 level and then send out the event to user space through
4017 the allocated input device; If set to 0, video driver
4018 will only send out the event without touching backlight
4023 [VMMIO] Memory mapped virtio (platform) device.
4025 <size>@<baseaddr>:<irq>[:<id>]
4027 <size> := size (can use standard suffixes
4029 <baseaddr> := physical base address
4030 <irq> := interrupt number (as passed to
4032 <id> := (optional) platform device id
4034 virtio_mmio.device=1K@0x100b0000:48:7
4036 Can be used multiple times for multiple devices.
4038 vga= [BOOT,X86-32] Select a particular video mode
4039 See Documentation/x86/boot.txt and
4040 Documentation/svga.txt.
4041 Use vga=ask for menu.
4042 This is actually a boot loader parameter; the value is
4043 passed to the kernel using a special protocol.
4045 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4046 size of <nn>. This can be used to increase the
4047 minimum size (128MB on x86). It can also be used to
4048 decrease the size and leave more room for directly
4051 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4054 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4057 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4061 Controls the behavior of vsyscalls (i.e. calls to
4062 fixed addresses of 0xffffffffff600x00 from legacy
4063 code). Most statically-linked binaries and older
4064 versions of glibc use these calls. Because these
4065 functions are at fixed addresses, they make nice
4066 targets for exploits that can control RIP.
4068 emulate [default] Vsyscalls turn into traps and are
4069 emulated reasonably safely.
4071 native Vsyscalls are native syscall instructions.
4072 This is a little bit faster than trapping
4073 and makes a few dynamic recompilers work
4074 better than they would in emulation mode.
4075 It also makes exploits much easier to write.
4077 none Vsyscalls don't work at all. This makes
4078 them quite hard to use for exploits but
4079 might break your system.
4081 vt.color= [VT] Default text color.
4082 Format: 0xYX, X = foreground, Y = background.
4083 Default: 0x07 = light gray on black.
4085 vt.cur_default= [VT] Default cursor shape.
4086 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4087 the parameters of the <Esc>[?A;B;Cc escape sequence;
4088 see VGA-softcursor.txt. Default: 2 = underline.
4090 vt.default_blu= [VT]
4091 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4092 Change the default blue palette of the console.
4093 This is a 16-member array composed of values
4096 vt.default_grn= [VT]
4097 Format: <green0>,<green1>,<green2>,...,<green15>
4098 Change the default green palette of the console.
4099 This is a 16-member array composed of values
4102 vt.default_red= [VT]
4103 Format: <red0>,<red1>,<red2>,...,<red15>
4104 Change the default red palette of the console.
4105 This is a 16-member array composed of values
4111 Set system-wide default UTF-8 mode for all tty's.
4112 Default is 1, i.e. UTF-8 mode is enabled for all
4113 newly opened terminals.
4115 vt.global_cursor_default=
4118 Set system-wide default for whether a cursor
4119 is shown on new VTs. Default is -1,
4120 i.e. cursors will be created by default unless
4121 overridden by individual drivers. 0 will hide
4122 cursors, 1 will display them.
4124 vt.italic= [VT] Default color for italic text; 0-15.
4127 vt.underline= [VT] Default color for underlined text; 0-15.
4130 watchdog timers [HW,WDT] For information on watchdog timers,
4131 see Documentation/watchdog/watchdog-parameters.txt
4132 or other driver-specific files in the
4133 Documentation/watchdog/ directory.
4135 workqueue.disable_numa
4136 By default, all work items queued to unbound
4137 workqueues are affine to the NUMA nodes they're
4138 issued on, which results in better behavior in
4139 general. If NUMA affinity needs to be disabled for
4140 whatever reason, this option can be used. Note
4141 that this also can be controlled per-workqueue for
4142 workqueues visible under /sys/bus/workqueue/.
4144 workqueue.power_efficient
4145 Per-cpu workqueues are generally preferred because
4146 they show better performance thanks to cache
4147 locality; unfortunately, per-cpu workqueues tend to
4148 be more power hungry than unbound workqueues.
4150 Enabling this makes the per-cpu workqueues which
4151 were observed to contribute significantly to power
4152 consumption unbound, leading to measurably lower
4153 power usage at the cost of small performance
4156 The default value of this parameter is determined by
4157 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4159 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4160 default x2apic cluster mode on platforms
4163 x86_intel_mid_timer= [X86-32,APBT]
4164 Choose timer option for x86 Intel MID platform.
4165 Two valid options are apbt timer only and lapic timer
4166 plus one apbt timer for broadcast timer.
4167 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4169 xen_512gb_limit [KNL,X86-64,XEN]
4170 Restricts the kernel running paravirtualized under Xen
4171 to use only up to 512 GB of RAM. The reason to do so is
4172 crash analysis tools and Xen tools for doing domain
4173 save/restore/migration must be enabled to handle larger
4176 xen_emul_unplug= [HW,X86,XEN]
4177 Unplug Xen emulated devices
4178 Format: [unplug0,][unplug1]
4179 ide-disks -- unplug primary master IDE devices
4180 aux-ide-disks -- unplug non-primary-master IDE devices
4181 nics -- unplug network devices
4182 all -- unplug all emulated devices (NICs and IDE disks)
4183 unnecessary -- unplugging emulated devices is
4184 unnecessary even if the host did not respond to
4186 never -- do not unplug even if version check succeeds
4188 xen_nopvspin [X86,XEN]
4189 Disables the ticketlock slowpath using Xen PV
4193 Disables the PV optimizations forcing the HVM guest to
4194 run as generic HVM guest with no PV drivers.
4196 xirc2ps_cs= [NET,PCMCIA]
4198 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4200 ______________________________________________________________________
4204 Add more DRM drivers.
Code Review / kvmfornfv.git / blob