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 goldfish [X86] Enable the goldfish android emulator platform.
1259 Don't use this when you are not running on the
1262 gpt [EFI] Forces disk with valid GPT signature but
1263 invalid Protective MBR to be treated as GPT. If the
1264 primary GPT is corrupted, it enables the backup/alternate
1265 GPT to be used instead.
1267 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1268 the "Enable 0" bit of the configuration register.
1271 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1272 the "Enable 0" bit of the configuration register.
1275 grcan.select= [HW] Select which physical interface to use.
1278 grcan.txsize= [HW] Sets the size of the tx buffer.
1279 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1281 grcan.rxsize= [HW] Sets the size of the rx buffer.
1282 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1285 hardlockup_all_cpu_backtrace=
1286 [KNL] Should the hard-lockup detector generate
1287 backtraces on all cpus.
1290 hashdist= [KNL,NUMA] Large hashes allocated during boot
1291 are distributed across NUMA nodes. Defaults on
1292 for 64-bit NUMA, off otherwise.
1293 Format: 0 | 1 (for off | on)
1295 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1297 hd= [EIDE] (E)IDE hard drive subsystem geometry
1298 Format: <cyl>,<head>,<sect>
1301 Disable Hardware Error Source Table (HEST) support;
1302 corresponding firmware-first mode error processing
1303 logic will be disabled.
1305 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1306 size of <nn>. This works even on boxes that have no
1307 highmem otherwise. This also works to reduce highmem
1308 size on bigger boxes.
1310 highres= [KNL] Enable/disable high resolution timer mode.
1311 Valid parameters: "on", "off"
1315 See Documentation/isdn/README.HiSax.
1319 hpet= [X86-32,HPET] option to control HPET usage
1320 Format: { enable (default) | disable | force |
1322 disable: disable HPET and use PIT instead
1323 force: allow force enabled of undocumented chips (ICH4,
1325 verbose: show contents of HPET registers during setup
1327 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1328 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1330 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1331 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1332 On x86-64 and powerpc, this option can be specified
1333 multiple times interleaved with hugepages= to reserve
1334 huge pages of different sizes. Valid pages sizes on
1335 x86-64 are 2M (when the CPU supports "pse") and 1G
1336 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1338 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1339 terminal devices. Valid values: 0..8
1340 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1341 If specified, z/VM IUCV HVC accepts connections
1342 from listed z/VM user IDs only.
1344 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1345 hardware thread id mappings.
1346 Format: <cpu>:<hwthread>
1349 Do not unregister boot console at start. This is only
1350 useful for debugging when something happens in the window
1351 between unregistering the boot console and initializing
1354 i2c_bus= [HW] Override the default board specific I2C bus speed
1355 or register an additional I2C bus that is not
1356 registered from board initialization code.
1360 i8042.debug [HW] Toggle i8042 debug mode
1361 i8042.unmask_kbd_data
1362 [HW] Enable printing of interrupt data from the KBD port
1363 (disabled by default, and as a pre-condition
1364 requires that i8042.debug=1 be enabled)
1365 i8042.direct [HW] Put keyboard port into non-translated mode
1366 i8042.dumbkbd [HW] Pretend that controller can only read data from
1367 keyboard and cannot control its state
1368 (Don't attempt to blink the leds)
1369 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1370 i8042.nokbd [HW] Don't check/create keyboard port
1371 i8042.noloop [HW] Disable the AUX Loopback command while probing
1373 i8042.nomux [HW] Don't check presence of an active multiplexing
1375 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1377 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1378 i8042.reset [HW] Reset the controller during init, cleanup and
1379 suspend-to-ram transitions, only during s2r
1380 transitions, or never reset
1381 Format: { 1 | Y | y | 0 | N | n }
1382 1, Y, y: always reset controller
1383 0, N, n: don't ever reset controller
1384 Default: only on s2r transitions on x86; most other
1385 architectures force reset to be always executed
1386 i8042.unlock [HW] Unlock (ignore) the keylock
1387 i8042.kbdreset [HW] Reset device connected to KBD port
1391 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1392 indicates that the driver is running on unsupported
1394 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1395 does not match list of supported models.
1397 [HW] Report power status in /proc/i8k
1398 (disabled by default)
1399 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1402 i915.invert_brightness=
1403 [DRM] Invert the sense of the variable that is used to
1404 set the brightness of the panel backlight. Normally a
1405 brightness value of 0 indicates backlight switched off,
1406 and the maximum of the brightness value sets the backlight
1407 to maximum brightness. If this parameter is set to 0
1408 (default) and the machine requires it, or this parameter
1409 is set to 1, a brightness value of 0 sets the backlight
1410 to maximum brightness, and the maximum of the brightness
1411 value switches the backlight off.
1412 -1 -- never invert brightness
1413 0 -- machine default
1414 1 -- force brightness inversion
1417 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1419 ide-core.nodma= [HW] (E)IDE subsystem
1420 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1421 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1422 .cdrom .chs .ignore_cable are additional options
1423 See Documentation/ide/ide.txt.
1425 ide-generic.probe-mask= [HW] (E)IDE subsystem
1427 Probe mask for legacy ISA IDE ports. Depending on
1428 platform up to 6 ports are supported, enabled by
1429 setting corresponding bits in the mask to 1. The
1430 default value is 0x0, which has a special meaning.
1431 On systems that have PCI, it triggers scanning the
1432 PCI bus for the first and the second port, which
1433 are then probed. On systems without PCI the value
1434 of 0x0 enables probing the two first ports as if it
1437 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1438 Claim all unknown PCI IDE storage controllers.
1441 Format: idle=poll, idle=halt, idle=nomwait
1442 Poll forces a polling idle loop that can slightly
1443 improve the performance of waking up a idle CPU, but
1444 will use a lot of power and make the system run hot.
1446 idle=halt: Halt is forced to be used for CPU idle.
1447 In such case C2/C3 won't be used again.
1448 idle=nomwait: Disable mwait for CPU C-states
1450 ignore_loglevel [KNL]
1451 Ignore loglevel setting - this will print /all/
1452 kernel messages to the console. Useful for debugging.
1453 We also add it as printk module parameter, so users
1454 could change it dynamically, usually by
1455 /sys/module/printk/parameters/ignore_loglevel.
1457 ihash_entries= [KNL]
1458 Set number of hash buckets for inode cache.
1460 ima_appraise= [IMA] appraise integrity measurements
1461 Format: { "off" | "enforce" | "fix" | "log" }
1464 ima_appraise_tcb [IMA]
1465 The builtin appraise policy appraises all files
1469 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1473 The list of supported hash algorithms is defined
1474 in crypto/hash_info.h.
1477 The builtin measurement policy to load during IMA
1478 setup. Specyfing "tcb" as the value, measures all
1479 programs exec'd, files mmap'd for exec, and all files
1480 opened with the read mode bit set by either the
1481 effective uid (euid=0) or uid=0.
1484 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1485 Load a policy which meets the needs of the Trusted
1486 Computing Base. This means IMA will measure all
1487 programs exec'd, files mmap'd for exec, and all files
1488 opened for read by uid=0.
1491 Select one of defined IMA measurements template formats.
1492 Formats: { "ima" | "ima-ng" | "ima-sig" }
1496 [IMA] Define a custom template format.
1497 Format: { "field1|...|fieldN" }
1499 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1500 Format: <min_file_size>
1501 Set the minimal file size for using asynchronous hash.
1502 If left unspecified, ahash usage is disabled.
1504 ahash performance varies for different data sizes on
1505 different crypto accelerators. This option can be used
1506 to achieve the best performance for a particular HW.
1508 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1510 Set hashing buffer size. Default: 4k.
1512 ahash performance varies for different chunk sizes on
1513 different crypto accelerators. This option can be used
1514 to achieve best performance for particular HW.
1518 Run specified binary instead of /sbin/init as init
1521 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1522 for working out where the kernel is dying during
1525 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1526 initcall functions. Useful for debugging built-in
1527 modules and initcalls.
1529 initrd= [BOOT] Specify the location of the initial ramdisk
1531 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1534 int_pln_enable [x86] Enable power limit notification interrupt
1536 integrity_audit=[IMA]
1537 Format: { "0" | "1" }
1538 0 -- basic integrity auditing messages. (Default)
1539 1 -- additional integrity auditing messages.
1541 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1543 Enable intel iommu driver.
1545 Disable intel iommu driver.
1546 igfx_off [Default Off]
1547 By default, gfx is mapped as normal device. If a gfx
1548 device has a dedicated DMAR unit, the DMAR unit is
1549 bypassed by not enabling DMAR with this option. In
1550 this case, gfx device will use physical address for
1553 With this option iommu will not optimize to look
1554 for io virtual address below 32-bit forcing dual
1555 address cycle on pci bus for cards supporting greater
1556 than 32-bit addressing. The default is to look
1557 for translation below 32-bit and if not available
1558 then look in the higher range.
1559 strict [Default Off]
1560 With this option on every unmap_single operation will
1561 result in a hardware IOTLB flush operation as opposed
1562 to batching them for performance.
1563 sp_off [Default Off]
1564 By default, super page will be supported if Intel IOMMU
1565 has the capability. With this option, super page will
1567 ecs_off [Default Off]
1568 By default, extended context tables will be supported if
1569 the hardware advertises that it has support both for the
1570 extended tables themselves, and also PASID support. With
1571 this option set, extended tables will not be used even
1572 on hardware which claims to support them.
1574 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1575 0 disables intel_idle and fall back on acpi_idle.
1576 1 to 6 specify maximum depth of C-state.
1580 Do not enable intel_pstate as the default
1581 scaling driver for the supported processors
1583 Enable intel_pstate on systems that prohibit it by default
1584 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1585 instead of acpi-cpufreq may disable platform features, such
1586 as thermal controls and power capping, that rely on ACPI
1587 P-States information being indicated to OSPM and therefore
1588 should be used with caution. This option does not work with
1589 processors that aren't supported by the intel_pstate driver
1590 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1592 Do not enable hardware P state control (HWP)
1595 Only load intel_pstate on systems which support
1596 hardware P state control (HWP) if available.
1598 intremap= [X86-64, Intel-IOMMU]
1599 on enable Interrupt Remapping (default)
1600 off disable Interrupt Remapping
1601 nosid disable Source ID checking
1603 BIOS x2APIC opt-out request will be ignored
1604 nopost disable Interrupt Posting
1606 iomem= Disable strict checking of access to MMIO memory
1607 strict regions from userspace.
1622 nobypass [PPC/POWERNV]
1623 Disable IOMMU bypass, using IOMMU for PCI devices.
1626 io7= [HW] IO7 for Marvel based alpha systems
1627 See comment before marvel_specify_io7 in
1628 arch/alpha/kernel/core_marvel.c.
1630 io_delay= [X86] I/O delay method
1632 Standard port 0x80 based delay
1634 Alternate port 0xed based delay (needed on some systems)
1636 Simple two microseconds delay
1641 See Documentation/filesystems/nfs/nfsroot.txt.
1644 When an interrupt is not handled search all handlers
1645 for it. Intended to get systems with badly broken
1649 When an interrupt is not handled search all handlers
1650 for it. Also check all handlers each timer
1651 interrupt. Intended to get systems with badly broken
1655 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1657 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1659 <cpu number>,...,<cpu number>
1661 <cpu number>-<cpu number>
1662 (must be a positive range in ascending order)
1664 <cpu number>,...,<cpu number>-<cpu number>
1666 This option can be used to specify one or more CPUs
1667 to isolate from the general SMP balancing and scheduling
1668 algorithms. You can move a process onto or off an
1669 "isolated" CPU via the CPU affinity syscalls or cpuset.
1670 <cpu number> begins at 0 and the maximum value is
1671 "number of CPUs in system - 1".
1673 This option is the preferred way to isolate CPUs. The
1674 alternative -- manually setting the CPU mask of all
1675 tasks in the system -- can cause problems and
1676 suboptimal load balancer performance.
1680 ivrs_ioapic [HW,X86_64]
1681 Provide an override to the IOAPIC-ID<->DEVICE-ID
1682 mapping provided in the IVRS ACPI table. For
1683 example, to map IOAPIC-ID decimal 10 to
1684 PCI device 00:14.0 write the parameter as:
1685 ivrs_ioapic[10]=00:14.0
1687 ivrs_hpet [HW,X86_64]
1688 Provide an override to the HPET-ID<->DEVICE-ID
1689 mapping provided in the IVRS ACPI table. For
1690 example, to map HPET-ID decimal 0 to
1691 PCI device 00:14.0 write the parameter as:
1692 ivrs_hpet[0]=00:14.0
1694 js= [HW,JOY] Analog joystick
1695 See Documentation/input/joystick.txt.
1698 Enable/disable kernel and module base offset ASLR
1699 (Address Space Layout Randomization) if built into
1700 the kernel. When CONFIG_HIBERNATION is selected,
1701 kASLR is disabled by default. When kASLR is enabled,
1702 hibernation will be disabled.
1706 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1707 specifies the amount of memory usable by the kernel
1708 for non-movable allocations. The requested amount is
1709 spread evenly throughout all nodes in the system. The
1710 remaining memory in each node is used for Movable
1711 pages. In the event, a node is too small to have both
1712 kernelcore and Movable pages, kernelcore pages will
1713 take priority and other nodes will have a larger number
1714 of Movable pages. The Movable zone is used for the
1715 allocation of pages that may be reclaimed or moved
1716 by the page migration subsystem. This means that
1717 HugeTLB pages may not be allocated from this zone.
1718 Note that allocations like PTEs-from-HighMem still
1719 use the HighMem zone if it exists, and the Normal
1720 zone if it does not.
1722 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1723 Format: <Controller#>[,poll interval]
1724 The controller # is the number of the ehci usb debug
1725 port as it is probed via PCI. The poll interval is
1726 optional and is the number seconds in between
1727 each poll cycle to the debug port in case you need
1728 the functionality for interrupting the kernel with
1729 gdb or control-c on the dbgp connection. When
1730 not using this parameter you use sysrq-g to break into
1731 the kernel debugger.
1733 kgdboc= [KGDB,HW] kgdb over consoles.
1734 Requires a tty driver that supports console polling,
1735 or a supported polling keyboard driver (non-usb).
1736 Serial only format: <serial_device>[,baud]
1737 keyboard only format: kbd
1738 keyboard and serial format: kbd,<serial_device>[,baud]
1739 Optional Kernel mode setting:
1740 kms, kbd format: kms,kbd
1741 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1743 kgdbwait [KGDB] Stop kernel execution and enter the
1744 kernel debugger at the earliest opportunity.
1746 kmac= [MIPS] korina ethernet MAC address.
1747 Configure the RouterBoard 532 series on-chip
1748 Ethernet adapter MAC address.
1750 kmemleak= [KNL] Boot-time kmemleak enable/disable
1751 Valid arguments: on, off
1753 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1756 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1757 Valid arguments: 0, 1, 2
1758 kmemcheck=0 (disabled)
1759 kmemcheck=1 (enabled)
1760 kmemcheck=2 (one-shot mode)
1761 Default: 2 (one-shot mode)
1763 kstack=N [X86] Print N words from the kernel stack
1766 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1767 Default is 0 (don't ignore, but inject #GP)
1769 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1773 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1774 Default is 1 (enabled)
1776 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1778 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1780 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1781 (virtualized MMU) support on capable Intel chips.
1782 Default is 1 (enabled)
1784 kvm-intel.emulate_invalid_guest_state=
1785 [KVM,Intel] Enable emulation of invalid guest states
1786 Default is 0 (disabled)
1788 kvm-intel.flexpriority=
1789 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1790 Default is 1 (enabled)
1793 [KVM,Intel] Enable VMX nesting (nVMX).
1794 Default is 0 (disabled)
1796 kvm-intel.unrestricted_guest=
1797 [KVM,Intel] Disable unrestricted guest feature
1798 (virtualized real and unpaged mode) on capable
1799 Intel chips. Default is 1 (enabled)
1801 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1802 feature (tagged TLBs) on capable Intel chips.
1803 Default is 1 (enabled)
1809 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1812 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1813 value for LAPIC timer one-shot implementation. Default
1814 back to the programmable timer unit in the LAPIC.
1816 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1819 libata.dma= [LIBATA] DMA control
1820 libata.dma=0 Disable all PATA and SATA DMA
1821 libata.dma=1 PATA and SATA Disk DMA only
1822 libata.dma=2 ATAPI (CDROM) DMA only
1823 libata.dma=4 Compact Flash DMA only
1824 Combinations also work, so libata.dma=3 enables DMA
1825 for disks and CDROMs, but not CFs.
1827 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1828 libata.ignore_hpa=0 keep BIOS limits (default)
1829 libata.ignore_hpa=1 ignore limits, using full disk
1831 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1835 libata.force= [LIBATA] Force configurations. The format is comma
1836 separated list of "[ID:]VAL" where ID is
1837 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1838 matching port, link or device. Basically, it matches
1839 the ATA ID string printed on console by libata. If
1840 the whole ID part is omitted, the last PORT and DEVICE
1841 values are used. If ID hasn't been specified yet, the
1842 configuration applies to all ports, links and devices.
1844 If only DEVICE is omitted, the parameter applies to
1845 the port and all links and devices behind it. DEVICE
1846 number of 0 either selects the first device or the
1847 first fan-out link behind PMP device. It does not
1848 select the host link. DEVICE number of 15 selects the
1849 host link and device attached to it.
1851 The VAL specifies the configuration to force. As long
1852 as there's no ambiguity shortcut notation is allowed.
1853 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1854 The following configurations can be forced.
1856 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1857 Any ID with matching PORT is used.
1859 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1861 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1862 udma[/][16,25,33,44,66,100,133] notation is also
1865 * [no]ncq: Turn on or off NCQ.
1867 * [no]ncqtrim: Turn off queued DSM TRIM.
1869 * nohrst, nosrst, norst: suppress hard, soft
1872 * rstonce: only attempt one reset during
1873 hot-unplug link recovery
1875 * dump_id: dump IDENTIFY data.
1877 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1879 * disable: Disable this device.
1881 If there are multiple matching configurations changing
1882 the same attribute, the last one is used.
1884 memblock=debug [KNL] Enable memblock debug messages.
1886 load_ramdisk= [RAM] List of ramdisks to load from floppy
1887 See Documentation/blockdev/ramdisk.txt.
1889 lockd.nlm_grace_period=P [NFS] Assign grace period.
1892 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1895 lockd.nlm_timeout=T [NFS] Assign timeout value.
1898 lockd.nlm_udpport=M [NFS] Assign UDP port.
1901 locktorture.nreaders_stress= [KNL]
1902 Set the number of locking read-acquisition kthreads.
1903 Defaults to being automatically set based on the
1904 number of online CPUs.
1906 locktorture.nwriters_stress= [KNL]
1907 Set the number of locking write-acquisition kthreads.
1909 locktorture.onoff_holdoff= [KNL]
1910 Set time (s) after boot for CPU-hotplug testing.
1912 locktorture.onoff_interval= [KNL]
1913 Set time (s) between CPU-hotplug operations, or
1914 zero to disable CPU-hotplug testing.
1916 locktorture.shuffle_interval= [KNL]
1917 Set task-shuffle interval (jiffies). Shuffling
1918 tasks allows some CPUs to go into dyntick-idle
1919 mode during the locktorture test.
1921 locktorture.shutdown_secs= [KNL]
1922 Set time (s) after boot system shutdown. This
1923 is useful for hands-off automated testing.
1925 locktorture.stat_interval= [KNL]
1926 Time (s) between statistics printk()s.
1928 locktorture.stutter= [KNL]
1929 Time (s) to stutter testing, for example,
1930 specifying five seconds causes the test to run for
1931 five seconds, wait for five seconds, and so on.
1932 This tests the locking primitive's ability to
1933 transition abruptly to and from idle.
1935 locktorture.torture_runnable= [BOOT]
1936 Start locktorture running at boot time.
1938 locktorture.torture_type= [KNL]
1939 Specify the locking implementation to test.
1941 locktorture.verbose= [KNL]
1942 Enable additional printk() statements.
1944 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1947 loglevel= All Kernel Messages with a loglevel smaller than the
1948 console loglevel will be printed to the console. It can
1949 also be changed with klogd or other programs. The
1950 loglevels are defined as follows:
1952 0 (KERN_EMERG) system is unusable
1953 1 (KERN_ALERT) action must be taken immediately
1954 2 (KERN_CRIT) critical conditions
1955 3 (KERN_ERR) error conditions
1956 4 (KERN_WARNING) warning conditions
1957 5 (KERN_NOTICE) normal but significant condition
1958 6 (KERN_INFO) informational
1959 7 (KERN_DEBUG) debug-level messages
1961 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1962 in bytes. n must be a power of two and greater
1963 than the minimal size. The minimal size is defined
1964 by LOG_BUF_SHIFT kernel config parameter. There is
1965 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1966 that allows to increase the default size depending on
1967 the number of CPUs. See init/Kconfig for more details.
1969 logo.nologo [FB] Disables display of the built-in Linux logo.
1970 This may be used to provide more screen space for
1971 kernel log messages and is useful when debugging
1972 kernel boot problems.
1974 lp=0 [LP] Specify parallel ports to use, e.g,
1975 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1976 lp=reset first parallel port). 'lp=0' disables the
1977 lp=auto printer driver. 'lp=reset' (which can be
1978 specified in addition to the ports) causes
1979 attached printers to be reset. Using
1980 lp=port1,port2,... specifies the parallel ports
1981 to associate lp devices with, starting with
1982 lp0. A port specification may be 'none' to skip
1983 that lp device, or a parport name such as
1984 'parport0'. Specifying 'lp=auto' instead of a
1985 port specification list means that device IDs
1986 from each port should be examined, to see if
1987 an IEEE 1284-compliant printer is attached; if
1988 so, the driver will manage that printer.
1989 See also header of drivers/char/lp.c.
1992 Sets loops_per_jiffy to given constant, thus avoiding
1993 time-consuming boot-time autodetection (up to 250 ms per
1994 CPU). 0 enables autodetection (default). To determine
1995 the correct value for your kernel, boot with normal
1996 autodetection and see what value is printed. Note that
1997 on SMP systems the preset will be applied to all CPUs,
1998 which is likely to cause problems if your CPUs need
1999 significantly divergent settings. An incorrect value
2000 will cause delays in the kernel to be wrong, leading to
2001 unpredictable I/O errors and other breakage. Although
2002 unlikely, in the extreme case this might damage your
2006 Format: <io>,<irq>,<dma>
2008 machvec= [IA-64] Force the use of a particular machine-vector
2009 (machvec) in a generic kernel.
2010 Example: machvec=hpzx1_swiotlb
2012 machtype= [Loongson] Share the same kernel image file between different
2014 Example: machtype=lemote-yeeloong-2f-7inch
2016 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2017 than or equal to this physical address is ignored.
2019 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2020 should make use of. maxcpus=n : n >= 0 limits the
2021 kernel to using 'n' processors. n=0 is a special case,
2022 it is equivalent to "nosmp", which also disables
2025 max_loop= [LOOP] The number of loop block devices that get
2026 (loop.max_loop) unconditionally pre-created at init time. The default
2027 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2028 of statically allocating a predefined number, loop
2029 devices can be requested on-demand with the
2030 /dev/loop-control interface.
2032 mce [X86-32] Machine Check Exception
2034 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2036 md= [HW] RAID subsystems devices and level
2037 See Documentation/md.txt.
2040 Format: <first>,<last>
2041 Specifies range of consoles to be captured by the MDA.
2043 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2044 Amount of memory to be used when the kernel is not able
2045 to see the whole system memory or for test.
2046 [X86] Work as limiting max address. Use together
2047 with memmap= to avoid physical address space collisions.
2048 Without memmap= PCI devices could be placed at addresses
2049 belonging to unused RAM.
2051 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2055 [KNL,SH] Allow user to override the default size for
2056 per-device physically contiguous DMA buffers.
2058 memmap=exactmap [KNL,X86] Enable setting of an exact
2059 E820 memory map, as specified by the user.
2060 Such memmap=exactmap lines can be constructed based on
2061 BIOS output or other requirements. See the memmap=nn@ss
2064 memmap=nn[KMG]@ss[KMG]
2065 [KNL] Force usage of a specific region of memory.
2066 Region of memory to be used is from ss to ss+nn.
2068 memmap=nn[KMG]#ss[KMG]
2069 [KNL,ACPI] Mark specific memory as ACPI data.
2070 Region of memory to be marked is from ss to ss+nn.
2072 memmap=nn[KMG]$ss[KMG]
2073 [KNL,ACPI] Mark specific memory as reserved.
2074 Region of memory to be reserved is from ss to ss+nn.
2075 Example: Exclude memory from 0x18690000-0x1869ffff
2076 memmap=64K$0x18690000
2078 memmap=0x10000$0x18690000
2080 memmap=nn[KMG]!ss[KMG]
2081 [KNL,X86] Mark specific memory as protected.
2082 Region of memory to be used, from ss to ss+nn.
2083 The memory region may be marked as e820 type 12 (0xc)
2084 and is NVDIMM or ADR memory.
2086 memory_corruption_check=0/1 [X86]
2087 Some BIOSes seem to corrupt the first 64k of
2088 memory when doing things like suspend/resume.
2089 Setting this option will scan the memory
2090 looking for corruption. Enabling this will
2091 both detect corruption and prevent the kernel
2092 from using the memory being corrupted.
2093 However, its intended as a diagnostic tool; if
2094 repeatable BIOS-originated corruption always
2095 affects the same memory, you can use memmap=
2096 to prevent the kernel from using that memory.
2098 memory_corruption_check_size=size [X86]
2099 By default it checks for corruption in the low
2100 64k, making this memory unavailable for normal
2101 use. Use this parameter to scan for
2102 corruption in more or less memory.
2104 memory_corruption_check_period=seconds [X86]
2105 By default it checks for corruption every 60
2106 seconds. Use this parameter to check at some
2107 other rate. 0 disables periodic checking.
2109 memtest= [KNL,X86,ARM] Enable memtest
2111 default : 0 <disable>
2112 Specifies the number of memtest passes to be
2113 performed. Each pass selects another test
2114 pattern from a given set of patterns. Memtest
2115 fills the memory with this pattern, validates
2116 memory contents and reserves bad memory
2117 regions that are detected.
2119 meye.*= [HW] Set MotionEye Camera parameters
2120 See Documentation/video4linux/meye.txt.
2122 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2123 Multi-Function General Purpose Timers on AMD Geode
2126 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2127 the BIOS has incorrectly applied a workaround. TinyBIOS
2128 version 0.98 is known to be affected, 0.99 fixes the
2129 problem by letting the user disable the workaround.
2133 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2134 physical address is ignored.
2136 mini2440= [ARM,HW,KNL]
2137 Format:[0..2][b][c][t]
2139 MINI2440 configuration specification:
2140 0 - The attached screen is the 3.5" TFT
2141 1 - The attached screen is the 7" TFT
2142 2 - The VGA Shield is attached (1024x768)
2143 Leaving out the screen size parameter will not load
2144 the TFT driver, and the framebuffer will be left
2146 b - Enable backlight. The TFT backlight pin will be
2147 linked to the kernel VESA blanking code and a GPIO
2148 LED. This parameter is not necessary when using the
2150 c - Enable the s3c camera interface.
2151 t - Reserved for enabling touchscreen support. The
2152 touchscreen support is not enabled in the mainstream
2153 kernel as of 2.6.30, a preliminary port can be found
2154 in the "bleeding edge" mini2440 support kernel at
2155 http://repo.or.cz/w/linux-2.6/mini2440.git
2158 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2159 parameter allows control of the logging verbosity for
2160 the additional memory initialisation checks. A value
2161 of 0 disables mminit logging and a level of 4 will
2162 log everything. Information is printed at KERN_DEBUG
2163 so loglevel=8 may also need to be specified.
2166 [KNL] When CONFIG_MODULE_SIG is set, this means that
2167 modules without (valid) signatures will fail to load.
2168 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2169 is always true, so this option does nothing.
2172 [MOUSE] Maximum time between finger touching and
2173 leaving touchpad surface for touch to be considered
2174 a tap and be reported as a left button click (for
2175 touchpads working in absolute mode only).
2177 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2178 reporting absolute coordinates, such as tablets
2179 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2180 reporting absolute coordinates, such as tablets
2182 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2183 is similar to kernelcore except it specifies the
2184 amount of memory used for migratable allocations.
2185 If both kernelcore and movablecore is specified,
2186 then kernelcore will be at *least* the specified
2187 value but may be more. If movablecore on its own
2188 is specified, the administrator must be careful
2189 that the amount of memory usable for all allocations
2192 movable_node [KNL,X86] Boot-time switch to enable the effects
2193 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2195 MTD_Partition= [MTD]
2196 Format: <name>,<region-number>,<size>,<offset>
2198 MTD_Region= [MTD] Format:
2199 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2202 See drivers/mtd/cmdlinepart.c.
2204 multitce=off [PPC] This parameter disables the use of the pSeries
2205 firmware feature for updating multiple TCE entries
2208 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2210 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2212 boundary - index of last SLC block on Flex-OneNAND.
2213 The remaining blocks are configured as MLC blocks.
2214 lock - Configure if Flex-OneNAND boundary should be locked.
2215 Once locked, the boundary cannot be changed.
2216 1 indicates lock status, 0 indicates unlock status.
2219 ARM/S3C2412 JIVE boot control
2221 See arch/arm/mach-s3c2412/mach-jive.c
2223 mtouchusb.raw_coordinates=
2224 [HW] Make the MicroTouch USB driver use raw coordinates
2225 ('y', default) or cooked coordinates ('n')
2227 mtrr_chunk_size=nn[KMG] [X86]
2228 used for mtrr cleanup. It is largest continuous chunk
2229 that could hold holes aka. UC entries.
2231 mtrr_gran_size=nn[KMG] [X86]
2232 Used for mtrr cleanup. It is granularity of mtrr block.
2234 Large value could prevent small alignment from
2237 mtrr_spare_reg_nr=n [X86]
2239 Range: 0,7 : spare reg number
2241 Used for mtrr cleanup. It is spare mtrr entries number.
2242 Set to 2 or more if your graphical card needs more.
2244 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2246 netdev= [NET] Network devices parameters
2247 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2248 Note that mem_start is often overloaded to mean
2249 something different and driver-specific.
2250 This usage is only documented in each driver source
2254 [NETFILTER] Enable connection tracking flow accounting
2255 0 to disable accounting
2256 1 to enable accounting
2259 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2260 See Documentation/filesystems/nfs/nfsroot.txt.
2262 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2263 See Documentation/filesystems/nfs/nfsroot.txt.
2265 nfsrootdebug [NFS] enable nfsroot debugging messages.
2266 See Documentation/filesystems/nfs/nfsroot.txt.
2268 nfs.callback_tcpport=
2269 [NFS] set the TCP port on which the NFSv4 callback
2270 channel should listen.
2273 [NFS] sets the pathname to the program which is used
2274 to update the NFS client cache entries.
2276 nfs.cache_getent_timeout=
2277 [NFS] sets the timeout after which an attempt to
2278 update a cache entry is deemed to have failed.
2280 nfs.idmap_cache_timeout=
2281 [NFS] set the maximum lifetime for idmapper cache
2285 [NFS] enable 64-bit inode numbers.
2286 If zero, the NFS client will fake up a 32-bit inode
2287 number for the readdir() and stat() syscalls instead
2288 of returning the full 64-bit number.
2289 The default is to return 64-bit inode numbers.
2291 nfs.max_session_slots=
2292 [NFSv4.1] Sets the maximum number of session slots
2293 the client will attempt to negotiate with the server.
2294 This limits the number of simultaneous RPC requests
2295 that the client can send to the NFSv4.1 server.
2296 Note that there is little point in setting this
2297 value higher than the max_tcp_slot_table_limit.
2299 nfs.nfs4_disable_idmapping=
2300 [NFSv4] When set to the default of '1', this option
2301 ensures that both the RPC level authentication
2302 scheme and the NFS level operations agree to use
2303 numeric uids/gids if the mount is using the
2304 'sec=sys' security flavour. In effect it is
2305 disabling idmapping, which can make migration from
2306 legacy NFSv2/v3 systems to NFSv4 easier.
2307 Servers that do not support this mode of operation
2308 will be autodetected by the client, and it will fall
2309 back to using the idmapper.
2310 To turn off this behaviour, set the value to '0'.
2312 [NFS4] Specify an additional fixed unique ident-
2313 ification string that NFSv4 clients can insert into
2314 their nfs_client_id4 string. This is typically a
2315 UUID that is generated at system install time.
2317 nfs.send_implementation_id =
2318 [NFSv4.1] Send client implementation identification
2319 information in exchange_id requests.
2320 If zero, no implementation identification information
2322 The default is to send the implementation identification
2325 nfs.recover_lost_locks =
2326 [NFSv4] Attempt to recover locks that were lost due
2327 to a lease timeout on the server. Please note that
2328 doing this risks data corruption, since there are
2329 no guarantees that the file will remain unchanged
2330 after the locks are lost.
2331 If you want to enable the kernel legacy behaviour of
2332 attempting to recover these locks, then set this
2334 The default parameter value of '0' causes the kernel
2335 not to attempt recovery of lost locks.
2337 nfs4.layoutstats_timer =
2338 [NFSv4.2] Change the rate at which the kernel sends
2339 layoutstats to the pNFS metadata server.
2341 Setting this to value to 0 causes the kernel to use
2342 whatever value is the default set by the layout
2343 driver. A non-zero value sets the minimum interval
2344 in seconds between layoutstats transmissions.
2346 nfsd.nfs4_disable_idmapping=
2347 [NFSv4] When set to the default of '1', the NFSv4
2348 server will return only numeric uids and gids to
2349 clients using auth_sys, and will accept numeric uids
2350 and gids from such clients. This is intended to ease
2351 migration from NFSv2/v3.
2353 objlayoutdriver.osd_login_prog=
2354 [NFS] [OBJLAYOUT] sets the pathname to the program which
2355 is used to automatically discover and login into new
2356 osd-targets. Please see:
2357 Documentation/filesystems/pnfs.txt for more explanations
2359 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2360 when a NMI is triggered.
2361 Format: [state][,regs][,debounce][,die]
2363 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2364 Format: [panic,][nopanic,][num]
2366 0 - turn hardlockup detector in nmi_watchdog off
2367 1 - turn hardlockup detector in nmi_watchdog on
2368 When panic is specified, panic when an NMI watchdog
2369 timeout occurs (or 'nopanic' to override the opposite
2370 default). To disable both hard and soft lockup detectors,
2371 please see 'nowatchdog'.
2372 This is useful when you use a panic=... timeout and
2373 need the box quickly up again.
2375 netpoll.carrier_timeout=
2376 [NET] Specifies amount of time (in seconds) that
2377 netpoll should wait for a carrier. By default netpoll
2380 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2381 emulation library even if a 387 maths coprocessor
2385 [HW] Never suspend the console
2386 Disable suspending of consoles during suspend and
2387 hibernate operations. Once disabled, debugging
2388 messages can reach various consoles while the rest
2389 of the system is being put to sleep (ie, while
2390 debugging driver suspend/resume hooks). This may
2391 not work reliably with all consoles, but is known
2392 to work with serial and VGA consoles.
2393 To facilitate more flexible debugging, we also add
2394 console_suspend, a printk module parameter to control
2395 it. Users could use console_suspend (usually
2396 /sys/module/printk/parameters/console_suspend) to
2397 turn on/off it dynamically.
2399 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2400 caches in the slab allocator. Saves per-node memory,
2401 but will impact performance.
2405 noapic [SMP,APIC] Tells the kernel to not make use of any
2406 IOAPICs that may be present in the system.
2408 noautogroup Disable scheduler automatic task group creation.
2410 nobats [PPC] Do not use BATs for mapping kernel lowmem
2411 on "Classic" PPC cores.
2415 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2417 nodelayacct [KNL] Disable per-task delay accounting
2419 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2421 nodsp [SH] Disable hardware DSP at boot time.
2423 noefi Disable EFI runtime services support.
2428 On X86-32 available only on PAE configured kernels.
2429 noexec=on: enable non-executable mappings (default)
2430 noexec=off: disable non-executable mappings
2433 Disable SMAP (Supervisor Mode Access Prevention)
2434 even if it is supported by processor.
2437 Disable SMEP (Supervisor Mode Execution Prevention)
2438 even if it is supported by processor.
2441 This affects only 32-bit executables.
2442 noexec32=on: enable non-executable mappings (default)
2443 read doesn't imply executable mappings
2444 noexec32=off: disable non-executable mappings
2445 read implies executable mappings
2447 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2449 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2450 register save and restore. The kernel will only save
2451 legacy floating-point registers on task switch.
2453 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2455 noxsave [BUGS=X86] Disables x86 extended register state save
2456 and restore using xsave. The kernel will fallback to
2457 enabling legacy floating-point and sse state.
2459 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2460 register states. The kernel will fall back to use
2461 xsave to save the states. By using this parameter,
2462 performance of saving the states is degraded because
2463 xsave doesn't support modified optimization while
2464 xsaveopt supports it on xsaveopt enabled systems.
2466 noxsaves [X86] Disables xsaves and xrstors used in saving and
2467 restoring x86 extended register state in compacted
2468 form of xsave area. The kernel will fall back to use
2469 xsaveopt and xrstor to save and restore the states
2470 in standard form of xsave area. By using this
2471 parameter, xsave area per process might occupy more
2472 memory on xsaves enabled systems.
2474 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2475 wfi(ARM) instruction doesn't work correctly and not to
2476 use it. This is also useful when using JTAG debugger.
2478 no_file_caps Tells the kernel not to honor file capabilities. The
2479 only way then for a file to be executed with privilege
2480 is to be setuid root or executed by root.
2482 nohalt [IA-64] Tells the kernel not to use the power saving
2483 function PAL_HALT_LIGHT when idle. This increases
2484 power-consumption. On the positive side, it reduces
2485 interrupt wake-up latency, which may improve performance
2486 in certain environments such as networked servers or
2489 nohibernate [HIBERNATION] Disable hibernation and resume.
2491 nohz= [KNL] Boottime enable/disable dynamic ticks
2492 Valid arguments: on, off
2495 nohz_full= [KNL,BOOT]
2496 In kernels built with CONFIG_NO_HZ_FULL=y, set
2497 the specified list of CPUs whose tick will be stopped
2498 whenever possible. The boot CPU will be forced outside
2499 the range to maintain the timekeeping.
2500 The CPUs in this range must also be included in the
2503 noiotrap [SH] Disables trapped I/O port accesses.
2505 noirqdebug [X86-32] Disables the code which attempts to detect and
2506 disable unhandled interrupt sources.
2508 no_timer_check [X86,APIC] Disables the code which tests for
2509 broken timer IRQ sources.
2511 noisapnp [ISAPNP] Disables ISA PnP code.
2513 noinitrd [RAM] Tells the kernel not to load any configured
2516 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2518 [Deprecated - use intremap=off]
2522 noinvpcid [X86] Disable the INVPCID cpu feature.
2524 nojitter [IA-64] Disables jitter checking for ITC timers.
2526 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2528 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2531 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2532 steal time is computed, but won't influence scheduler
2535 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2537 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2539 noltlbs [PPC] Do not use large page/tlb entries for kernel
2540 lowmem mapping on PPC40x.
2542 nomca [IA-64] Disable machine check abort handling
2544 nomce [X86-32] Disable Machine Check Exception
2546 nomfgpt [X86-32] Disable Multi-Function General Purpose
2547 Timer usage (for AMD Geode machines).
2549 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2550 shutdown the other cpus. Instead use the REBOOT_VECTOR
2553 nomodule Disable module load
2555 nopat [X86] Disable PAT (page attribute table extension of
2556 pagetables) support.
2558 nopcid [X86-64] Disable the PCID cpu feature.
2560 norandmaps Don't use address space randomization. Equivalent to
2561 echo 0 > /proc/sys/kernel/randomize_va_space
2563 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2565 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2566 with UP alternatives
2568 nordrand [X86] Disable kernel use of the RDRAND and
2569 RDSEED instructions even if they are supported
2570 by the processor. RDRAND and RDSEED are still
2571 available to user space applications.
2573 noresume [SWSUSP] Disables resume and restores original swap
2576 no-scroll [VGA] Disables scrollback.
2577 This is required for the Braillex ib80-piezo Braille
2578 reader made by F.H. Papenmeier (Germany).
2582 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2584 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2585 and disable the IO APIC. legacy for "maxcpus=0".
2587 nosoftlockup [KNL] Disable the soft-lockup detector.
2589 nosync [HW,M68K] Disables sync negotiation for all devices.
2591 notsc [BUGS=X86-32] Disable Time Stamp Counter
2593 nousb [USB] Disable the USB subsystem
2595 nowatchdog [KNL] Disable both lockup detectors, i.e.
2596 soft-lockup and NMI watchdog (hard-lockup).
2600 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2602 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2603 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2604 Some features depend on CPU0. Known dependencies are:
2605 1. Resume from suspend/hibernate depends on CPU0.
2606 Suspend/hibernate will fail if CPU0 is offline and you
2607 need to online CPU0 before suspend/hibernate.
2608 2. PIC interrupts also depend on CPU0. CPU0 can't be
2609 removed if a PIC interrupt is detected.
2610 It's said poweroff/reboot may depend on CPU0 on some
2611 machines although I haven't seen such issues so far
2612 after CPU0 is offline on a few tested machines.
2613 If the dependencies are under your control, you can
2614 turn on cpu0_hotplug.
2616 nptcg= [IA-64] Override max number of concurrent global TLB
2617 purges which is reported from either PAL_VM_SUMMARY or
2620 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2621 could support. nr_cpus=n : n >= 1 limits the kernel to
2622 supporting 'n' processors. Later in runtime you can not
2623 use hotplug cpu feature to put more cpu back to online.
2624 just like you compile the kernel NR_CPUS=n
2626 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2628 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2629 Allowed values are enable and disable
2631 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2632 one of ['zone', 'node', 'default'] can be specified
2633 This can be set from sysctl after boot.
2634 See Documentation/sysctl/vm.txt for details.
2636 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2637 See Documentation/debugging-via-ohci1394.txt for more
2640 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2641 Rather than timing out after 20 ms if an EC
2642 command is not properly ACKed, override the length
2643 of the timeout. We have interrupts disabled while
2644 waiting for the ACK, so if this is set too high
2645 interrupts *may* be lost!
2647 omap_mux= [OMAP] Override bootloader pin multiplexing.
2648 Format: <mux_mode0.mode_name=value>...
2649 For example, to override I2C bus2:
2650 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2652 oprofile.timer= [HW]
2653 Use timer interrupt instead of performance counters
2655 oprofile.cpu_type= Force an oprofile cpu type
2656 This might be useful if you have an older oprofile
2657 userland or if you want common events.
2658 Format: { arch_perfmon }
2659 arch_perfmon: [X86] Force use of architectural
2660 perfmon on Intel CPUs instead of the
2661 CPU specific event set.
2662 timer: [X86] Force use of architectural NMI
2663 timer mode (see also oprofile.timer
2664 for generic hr timer mode)
2665 [s390] Force legacy basic mode sampling
2666 (report cpu_type "timer")
2668 oops=panic Always panic on oopses. Default is to just kill the
2669 process, but there is a small probability of
2670 deadlocking the machine.
2671 This will also cause panics on machine check exceptions.
2672 Useful together with panic=30 to trigger a reboot.
2675 See Documentation/sound/oss/oss-parameters.txt
2677 page_owner= [KNL] Boot-time page_owner enabling option.
2678 Storage of the information about who allocated
2679 each page is disabled in default. With this switch,
2681 on: enable the feature
2683 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2684 timeout > 0: seconds before rebooting
2685 timeout = 0: wait forever
2686 timeout < 0: reboot immediately
2689 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2692 crash_kexec_post_notifiers
2693 Run kdump after running panic-notifiers and dumping
2694 kmsg. This only for the users who doubt kdump always
2695 succeeds in any situation.
2696 Note that this also increases risks of kdump failure,
2697 because some panic notifiers can make the crashed
2698 kernel more unstable.
2700 parkbd.port= [HW] Parallel port number the keyboard adapter is
2701 connected to, default is 0.
2703 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2704 0 for XT, 1 for AT (default is AT).
2707 parport= [HW,PPT] Specify parallel ports. 0 disables.
2708 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2709 Use 'auto' to force the driver to use any
2710 IRQ/DMA settings detected (the default is to
2711 ignore detected IRQ/DMA settings because of
2712 possible conflicts). You can specify the base
2713 address, IRQ, and DMA settings; IRQ and DMA
2714 should be numbers, or 'auto' (for using detected
2715 settings on that particular port), or 'nofifo'
2716 (to avoid using a FIFO even if it is detected).
2717 Parallel ports are assigned in the order they
2718 are specified on the command line, starting
2721 parport_init_mode= [HW,PPT]
2722 Configure VIA parallel port to operate in
2723 a specific mode. This is necessary on Pegasos
2724 computer where firmware has no options for setting
2725 up parallel port mode and sets it to spp.
2726 Currently this function knows 686a and 8231 chips.
2727 Format: [spp|ps2|epp|ecp|ecpepp]
2730 Halt all CPUs after the first oops has been printed for
2731 the specified number of seconds. This is to be used if
2732 your oopses keep scrolling off the screen.
2737 See header of drivers/block/paride/pcd.c.
2738 See also Documentation/blockdev/paride.txt.
2740 pci=option[,option...] [PCI] various PCI subsystem options:
2741 earlydump [X86] dump PCI config space before the kernel
2743 off [X86] don't probe for the PCI bus
2744 bios [X86-32] force use of PCI BIOS, don't access
2745 the hardware directly. Use this if your machine
2746 has a non-standard PCI host bridge.
2747 nobios [X86-32] disallow use of PCI BIOS, only direct
2748 hardware access methods are allowed. Use this
2749 if you experience crashes upon bootup and you
2750 suspect they are caused by the BIOS.
2751 conf1 [X86] Force use of PCI Configuration
2753 conf2 [X86] Force use of PCI Configuration
2755 noaer [PCIE] If the PCIEAER kernel config parameter is
2756 enabled, this kernel boot option can be used to
2757 disable the use of PCIE advanced error reporting.
2758 nodomains [PCI] Disable support for multiple PCI
2759 root domains (aka PCI segments, in ACPI-speak).
2760 nommconf [X86] Disable use of MMCONFIG for PCI
2762 check_enable_amd_mmconf [X86] check for and enable
2763 properly configured MMIO access to PCI
2764 config space on AMD family 10h CPU
2765 nomsi [MSI] If the PCI_MSI kernel config parameter is
2766 enabled, this kernel boot option can be used to
2767 disable the use of MSI interrupts system-wide.
2768 noioapicquirk [APIC] Disable all boot interrupt quirks.
2769 Safety option to keep boot IRQs enabled. This
2770 should never be necessary.
2771 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2772 primary IO-APIC for bridges that cannot disable
2773 boot IRQs. This fixes a source of spurious IRQs
2774 when the system masks IRQs.
2775 noioapicreroute [APIC] Disable workaround that uses the
2776 boot IRQ equivalent of an IRQ that connects to
2777 a chipset where boot IRQs cannot be disabled.
2778 The opposite of ioapicreroute.
2779 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2780 routing table. These calls are known to be buggy
2781 on several machines and they hang the machine
2782 when used, but on other computers it's the only
2783 way to get the interrupt routing table. Try
2784 this option if the kernel is unable to allocate
2785 IRQs or discover secondary PCI buses on your
2787 rom [X86] Assign address space to expansion ROMs.
2788 Use with caution as certain devices share
2789 address decoders between ROMs and other
2791 norom [X86] Do not assign address space to
2792 expansion ROMs that do not already have
2793 BIOS assigned address ranges.
2794 nobar [X86] Do not assign address space to the
2795 BARs that weren't assigned by the BIOS.
2796 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2797 assigned automatically to PCI devices. You can
2798 make the kernel exclude IRQs of your ISA cards
2800 pirqaddr=0xAAAAA [X86] Specify the physical address
2801 of the PIRQ table (normally generated
2802 by the BIOS) if it is outside the
2803 F0000h-100000h range.
2804 lastbus=N [X86] Scan all buses thru bus #N. Can be
2805 useful if the kernel is unable to find your
2806 secondary buses and you want to tell it
2807 explicitly which ones they are.
2808 assign-busses [X86] Always assign all PCI bus
2809 numbers ourselves, overriding
2810 whatever the firmware may have done.
2811 usepirqmask [X86] Honor the possible IRQ mask stored
2812 in the BIOS $PIR table. This is needed on
2813 some systems with broken BIOSes, notably
2814 some HP Pavilion N5400 and Omnibook XE3
2815 notebooks. This will have no effect if ACPI
2816 IRQ routing is enabled.
2817 noacpi [X86] Do not use ACPI for IRQ routing
2818 or for PCI scanning.
2819 use_crs [X86] Use PCI host bridge window information
2820 from ACPI. On BIOSes from 2008 or later, this
2821 is enabled by default. If you need to use this,
2822 please report a bug.
2823 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2824 If you need to use this, please report a bug.
2825 routeirq Do IRQ routing for all PCI devices.
2826 This is normally done in pci_enable_device(),
2827 so this option is a temporary workaround
2828 for broken drivers that don't call it.
2829 skip_isa_align [X86] do not align io start addr, so can
2830 handle more pci cards
2831 firmware [ARM] Do not re-enumerate the bus but instead
2832 just use the configuration from the
2833 bootloader. This is currently used on
2834 IXP2000 systems where the bus has to be
2835 configured a certain way for adjunct CPUs.
2836 noearly [X86] Don't do any early type 1 scanning.
2837 This might help on some broken boards which
2838 machine check when some devices' config space
2839 is read. But various workarounds are disabled
2840 and some IOMMU drivers will not work.
2841 bfsort Sort PCI devices into breadth-first order.
2842 This sorting is done to get a device
2843 order compatible with older (<= 2.4) kernels.
2844 nobfsort Don't sort PCI devices into breadth-first order.
2845 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2846 tuning and use the BIOS-configured MPS defaults.
2847 pcie_bus_safe Set every device's MPS to the largest value
2848 supported by all devices below the root complex.
2849 pcie_bus_perf Set device MPS to the largest allowable MPS
2850 based on its parent bus. Also set MRRS (Max
2851 Read Request Size) to the largest supported
2852 value (no larger than the MPS that the device
2853 or bus can support) for best performance.
2854 pcie_bus_peer2peer Set every device's MPS to 128B, which
2855 every device is guaranteed to support. This
2856 configuration allows peer-to-peer DMA between
2857 any pair of devices, possibly at the cost of
2858 reduced performance. This also guarantees
2859 that hot-added devices will work.
2860 cbiosize=nn[KMG] The fixed amount of bus space which is
2861 reserved for the CardBus bridge's IO window.
2862 The default value is 256 bytes.
2863 cbmemsize=nn[KMG] The fixed amount of bus space which is
2864 reserved for the CardBus bridge's memory
2865 window. The default value is 64 megabytes.
2868 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2869 Specifies alignment and device to reassign
2870 aligned memory resources.
2871 If <order of align> is not specified,
2872 PAGE_SIZE is used as alignment.
2873 PCI-PCI bridge can be specified, if resource
2874 windows need to be expanded.
2875 ecrc= Enable/disable PCIe ECRC (transaction layer
2876 end-to-end CRC checking).
2877 bios: Use BIOS/firmware settings. This is the
2881 hpiosize=nn[KMG] The fixed amount of bus space which is
2882 reserved for hotplug bridge's IO window.
2883 Default size is 256 bytes.
2884 hpmemsize=nn[KMG] The fixed amount of bus space which is
2885 reserved for hotplug bridge's memory window.
2886 Default size is 2 megabytes.
2887 realloc= Enable/disable reallocating PCI bridge resources
2888 if allocations done by BIOS are too small to
2889 accommodate resources required by all child
2891 off: Turn realloc off
2893 realloc same as realloc=on
2894 noari do not use PCIe ARI.
2895 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2896 only look for one device below a PCIe downstream
2899 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2902 force Enable ASPM even on devices that claim not to support it.
2903 WARNING: Forcing ASPM on may cause system lockups.
2905 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2906 nomsi Do not use MSI for PCI Express Native Hotplug (this
2907 makes all PCIe ports use INTx for hotplug services).
2909 pcie_ports= [PCIE] PCIe ports handling:
2910 auto Ask the BIOS whether or not to use native PCIe services
2911 associated with PCIe ports (PME, hot-plug, AER). Use
2912 them only if that is allowed by the BIOS.
2913 native Use native PCIe services associated with PCIe ports
2915 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2918 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2919 nomsi Do not use MSI for native PCIe PME signaling (this makes
2920 all PCIe root ports use INTx for all services).
2922 pcmv= [HW,PCMCIA] BadgePAD 4
2926 Keep all power-domains already enabled by bootloader on,
2927 even if no driver has claimed them. This is useful
2928 for debug and development, but should not be
2929 needed on a platform with proper driver support.
2932 See Documentation/blockdev/paride.txt.
2934 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2937 See arch/parisc/kernel/pdc_chassis.c
2939 percpu_alloc= Select which percpu first chunk allocator to use.
2940 Currently supported values are "embed" and "page".
2941 Archs may support subset or none of the selections.
2942 See comments in mm/percpu.c for details on each
2943 allocator. This parameter is primarily for debugging
2944 and performance comparison.
2947 See Documentation/blockdev/paride.txt.
2950 See Documentation/blockdev/paride.txt.
2952 pirq= [SMP,APIC] Manual mp-table setup
2953 See Documentation/x86/i386/IO-APIC.txt.
2955 plip= [PPT,NET] Parallel port network link
2956 Format: { parport<nr> | timid | 0 }
2957 See also Documentation/parport.txt.
2959 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2960 Override pmtimer IOPort with a hex value.
2964 Enable PNP debug messages (depends on the
2965 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2966 via /sys/module/pnp/parameters/debug. We always show
2967 current resource usage; turning this on also shows
2968 possible settings and some assignment information.
2974 { on | off | curr | res | no-curr | no-res }
2977 [ISAPNP] Exclude IRQs for the autoconfiguration
2980 [ISAPNP] Exclude DMAs for the autoconfiguration
2982 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2983 Ranges are in pairs (I/O port base and size).
2986 [ISAPNP] Exclude memory regions for the
2988 Ranges are in pairs (memory base and size).
2990 ports= [IP_VS_FTP] IPVS ftp helper module
2992 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2994 Format: <port>,<port>....
2996 print-fatal-signals=
2997 [KNL] debug: print fatal signals
2999 If enabled, warn about various signal handling
3000 related application anomalies: too many signals,
3001 too many POSIX.1 timers, fatal signals causing a
3004 If you hit the warning due to signal overflow,
3005 you might want to try "ulimit -i unlimited".
3009 printk.always_kmsg_dump=
3010 Trigger kmsg_dump for cases other than kernel oops or
3012 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3015 printk.time= Show timing data prefixed to each printk message line
3016 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3018 processor.max_cstate= [HW,ACPI]
3019 Limit processor to maximum C-state
3020 max_cstate=9 overrides any DMI blacklist limit.
3022 processor.nocst [HW,ACPI]
3023 Ignore the _CST method to determine C-states,
3024 instead using the legacy FADT method
3026 profile= [KNL] Enable kernel profiling via /proc/profile
3027 Format: [schedule,]<number>
3028 Param: "schedule" - profile schedule points.
3029 Param: <number> - step/bucket size as a power of 2 for
3030 statistical time based profiling.
3031 Param: "sleep" - profile D-state sleeping (millisecs).
3032 Requires CONFIG_SCHEDSTATS
3033 Param: "kvm" - profile VM exits.
3035 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3037 See Documentation/blockdev/ramdisk.txt.
3039 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3040 probe for; one of (bare|imps|exps|lifebook|any).
3041 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3043 psmouse.resetafter= [HW,MOUSE]
3044 Try to reset the device after so many bad packets
3047 [HW,MOUSE] Set desired mouse resolution, in dpi.
3048 psmouse.smartscroll=
3049 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3050 0 = disabled, 1 = enabled (default).
3052 pstore.backend= Specify the name of the pstore backend to use
3055 See Documentation/blockdev/paride.txt.
3057 pti= [X86_64] Control Page Table Isolation of user and
3058 kernel address spaces. Disabling this feature
3059 removes hardening, but improves performance of
3060 system calls and interrupts.
3062 on - unconditionally enable
3063 off - unconditionally disable
3064 auto - kernel detects whether your CPU model is
3065 vulnerable to issues that PTI mitigates
3067 Not specifying this option is equivalent to pti=auto.
3070 Equivalent to pti=off
3073 [KNL] Number of legacy pty's. Overwrites compiled-in
3076 quiet [KNL] Disable most log messages
3081 See Documentation/md.txt.
3083 ramdisk_blocksize= [RAM]
3084 See Documentation/blockdev/ramdisk.txt.
3086 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3087 See Documentation/blockdev/ramdisk.txt.
3090 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3091 the specified list of CPUs to be no-callback CPUs.
3092 Invocation of these CPUs' RCU callbacks will
3093 be offloaded to "rcuox/N" kthreads created for
3094 that purpose, where "x" is "b" for RCU-bh, "p"
3095 for RCU-preempt, and "s" for RCU-sched, and "N"
3096 is the CPU number. This reduces OS jitter on the
3097 offloaded CPUs, which can be useful for HPC and
3098 real-time workloads. It can also improve energy
3099 efficiency for asymmetric multiprocessors.
3102 Rather than requiring that offloaded CPUs
3103 (specified by rcu_nocbs= above) explicitly
3104 awaken the corresponding "rcuoN" kthreads,
3105 make these kthreads poll for callbacks.
3106 This improves the real-time response for the
3107 offloaded CPUs by relieving them of the need to
3108 wake up the corresponding kthread, but degrades
3109 energy efficiency by requiring that the kthreads
3110 periodically wake up to do the polling.
3112 rcutree.blimit= [KNL]
3113 Set maximum number of finished RCU callbacks to
3114 process in one batch.
3116 rcutree.dump_tree= [KNL]
3117 Dump the structure of the rcu_node combining tree
3118 out at early boot. This is used for diagnostic
3119 purposes, to verify correct tree setup.
3121 rcutree.gp_cleanup_delay= [KNL]
3122 Set the number of jiffies to delay each step of
3123 RCU grace-period cleanup. This only has effect
3124 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3126 rcutree.gp_init_delay= [KNL]
3127 Set the number of jiffies to delay each step of
3128 RCU grace-period initialization. This only has
3129 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3132 rcutree.gp_preinit_delay= [KNL]
3133 Set the number of jiffies to delay each step of
3134 RCU grace-period pre-initialization, that is,
3135 the propagation of recent CPU-hotplug changes up
3136 the rcu_node combining tree. This only has effect
3137 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3139 rcutree.rcu_fanout_exact= [KNL]
3140 Disable autobalancing of the rcu_node combining
3141 tree. This is used by rcutorture, and might
3142 possibly be useful for architectures having high
3143 cache-to-cache transfer latencies.
3145 rcutree.rcu_fanout_leaf= [KNL]
3146 Change the number of CPUs assigned to each
3147 leaf rcu_node structure. Useful for very
3148 large systems, which will choose the value 64,
3149 and for NUMA systems with large remote-access
3150 latencies, which will choose a value aligned
3151 with the appropriate hardware boundaries.
3153 rcutree.jiffies_till_sched_qs= [KNL]
3154 Set required age in jiffies for a
3155 given grace period before RCU starts
3156 soliciting quiescent-state help from
3157 rcu_note_context_switch().
3159 rcutree.jiffies_till_first_fqs= [KNL]
3160 Set delay from grace-period initialization to
3161 first attempt to force quiescent states.
3162 Units are jiffies, minimum value is zero,
3163 and maximum value is HZ.
3165 rcutree.jiffies_till_next_fqs= [KNL]
3166 Set delay between subsequent attempts to force
3167 quiescent states. Units are jiffies, minimum
3168 value is one, and maximum value is HZ.
3170 rcutree.kthread_prio= [KNL,BOOT]
3171 Set the SCHED_FIFO priority of the RCU per-CPU
3172 kthreads (rcuc/N). This value is also used for
3173 the priority of the RCU boost threads (rcub/N)
3174 and for the RCU grace-period kthreads (rcu_bh,
3175 rcu_preempt, and rcu_sched). If RCU_BOOST is
3176 set, valid values are 1-99 and the default is 1
3177 (the least-favored priority). Otherwise, when
3178 RCU_BOOST is not set, valid values are 0-99 and
3179 the default is zero (non-realtime operation).
3181 rcutree.rcu_nocb_leader_stride= [KNL]
3182 Set the number of NOCB kthread groups, which
3183 defaults to the square root of the number of
3184 CPUs. Larger numbers reduces the wakeup overhead
3185 on the per-CPU grace-period kthreads, but increases
3186 that same overhead on each group's leader.
3188 rcutree.qhimark= [KNL]
3189 Set threshold of queued RCU callbacks beyond which
3190 batch limiting is disabled.
3192 rcutree.qlowmark= [KNL]
3193 Set threshold of queued RCU callbacks below which
3194 batch limiting is re-enabled.
3196 rcutree.rcu_idle_gp_delay= [KNL]
3197 Set wakeup interval for idle CPUs that have
3198 RCU callbacks (RCU_FAST_NO_HZ=y).
3200 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3201 Set wakeup interval for idle CPUs that have
3202 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3203 Lazy RCU callbacks are those which RCU can
3204 prove do nothing more than free memory.
3206 rcutorture.cbflood_inter_holdoff= [KNL]
3207 Set holdoff time (jiffies) between successive
3208 callback-flood tests.
3210 rcutorture.cbflood_intra_holdoff= [KNL]
3211 Set holdoff time (jiffies) between successive
3212 bursts of callbacks within a given callback-flood
3215 rcutorture.cbflood_n_burst= [KNL]
3216 Set the number of bursts making up a given
3217 callback-flood test. Set this to zero to
3218 disable callback-flood testing.
3220 rcutorture.cbflood_n_per_burst= [KNL]
3221 Set the number of callbacks to be registered
3222 in a given burst of a callback-flood test.
3224 rcutorture.fqs_duration= [KNL]
3225 Set duration of force_quiescent_state bursts
3228 rcutorture.fqs_holdoff= [KNL]
3229 Set holdoff time within force_quiescent_state bursts
3232 rcutorture.fqs_stutter= [KNL]
3233 Set wait time between force_quiescent_state bursts
3236 rcutorture.gp_cond= [KNL]
3237 Use conditional/asynchronous update-side
3238 primitives, if available.
3240 rcutorture.gp_exp= [KNL]
3241 Use expedited update-side primitives, if available.
3243 rcutorture.gp_normal= [KNL]
3244 Use normal (non-expedited) asynchronous
3245 update-side primitives, if available.
3247 rcutorture.gp_sync= [KNL]
3248 Use normal (non-expedited) synchronous
3249 update-side primitives, if available. If all
3250 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3251 rcutorture.gp_normal=, and rcutorture.gp_sync=
3252 are zero, rcutorture acts as if is interpreted
3253 they are all non-zero.
3255 rcutorture.n_barrier_cbs= [KNL]
3256 Set callbacks/threads for rcu_barrier() testing.
3258 rcutorture.nfakewriters= [KNL]
3259 Set number of concurrent RCU writers. These just
3260 stress RCU, they don't participate in the actual
3261 test, hence the "fake".
3263 rcutorture.nreaders= [KNL]
3264 Set number of RCU readers. The value -1 selects
3265 N-1, where N is the number of CPUs. A value
3266 "n" less than -1 selects N-n-2, where N is again
3267 the number of CPUs. For example, -2 selects N
3268 (the number of CPUs), -3 selects N+1, and so on.
3270 rcutorture.object_debug= [KNL]
3271 Enable debug-object double-call_rcu() testing.
3273 rcutorture.onoff_holdoff= [KNL]
3274 Set time (s) after boot for CPU-hotplug testing.
3276 rcutorture.onoff_interval= [KNL]
3277 Set time (s) between CPU-hotplug operations, or
3278 zero to disable CPU-hotplug testing.
3280 rcutorture.shuffle_interval= [KNL]
3281 Set task-shuffle interval (s). Shuffling tasks
3282 allows some CPUs to go into dyntick-idle mode
3283 during the rcutorture test.
3285 rcutorture.shutdown_secs= [KNL]
3286 Set time (s) after boot system shutdown. This
3287 is useful for hands-off automated testing.
3289 rcutorture.stall_cpu= [KNL]
3290 Duration of CPU stall (s) to test RCU CPU stall
3291 warnings, zero to disable.
3293 rcutorture.stall_cpu_holdoff= [KNL]
3294 Time to wait (s) after boot before inducing stall.
3296 rcutorture.stat_interval= [KNL]
3297 Time (s) between statistics printk()s.
3299 rcutorture.stutter= [KNL]
3300 Time (s) to stutter testing, for example, specifying
3301 five seconds causes the test to run for five seconds,
3302 wait for five seconds, and so on. This tests RCU's
3303 ability to transition abruptly to and from idle.
3305 rcutorture.test_boost= [KNL]
3306 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3307 "Maybe" means test if the RCU implementation
3308 under test support RCU priority boosting.
3310 rcutorture.test_boost_duration= [KNL]
3311 Duration (s) of each individual boost test.
3313 rcutorture.test_boost_interval= [KNL]
3314 Interval (s) between each boost test.
3316 rcutorture.test_no_idle_hz= [KNL]
3317 Test RCU's dyntick-idle handling. See also the
3318 rcutorture.shuffle_interval parameter.
3320 rcutorture.torture_runnable= [BOOT]
3321 Start rcutorture running at boot time.
3323 rcutorture.torture_type= [KNL]
3324 Specify the RCU implementation to test.
3326 rcutorture.verbose= [KNL]
3327 Enable additional printk() statements.
3329 rcupdate.rcu_expedited= [KNL]
3330 Use expedited grace-period primitives, for
3331 example, synchronize_rcu_expedited() instead
3332 of synchronize_rcu(). This reduces latency,
3333 but can increase CPU utilization, degrade
3334 real-time latency, and degrade energy efficiency.
3336 rcupdate.rcu_cpu_stall_suppress= [KNL]
3337 Suppress RCU CPU stall warning messages.
3339 rcupdate.rcu_cpu_stall_timeout= [KNL]
3340 Set timeout for RCU CPU stall warning messages.
3342 rcupdate.rcu_task_stall_timeout= [KNL]
3343 Set timeout in jiffies for RCU task stall warning
3344 messages. Disable with a value less than or equal
3347 rcupdate.rcu_self_test= [KNL]
3348 Run the RCU early boot self tests
3350 rcupdate.rcu_self_test_bh= [KNL]
3351 Run the RCU bh early boot self tests
3353 rcupdate.rcu_self_test_sched= [KNL]
3354 Run the RCU sched early boot self tests
3358 Run specified binary instead of /init from the ramdisk,
3359 used for early userspace startup. See initrd.
3362 Format (x86 or x86_64):
3363 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3365 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3367 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3368 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3369 reboot_force is either force or not specified,
3370 reboot_cpu is s[mp]#### with #### being the processor
3371 to be used for rebooting.
3374 [KNL, SMP] Set scheduler's default relax_domain_level.
3375 See Documentation/cgroups/cpusets.txt.
3377 relative_sleep_states=
3378 [SUSPEND] Use sleep state labeling where the deepest
3379 state available other than hibernation is always "mem".
3380 Format: { "0" | "1" }
3381 0 -- Traditional sleep state labels.
3382 1 -- Relative sleep state labels.
3384 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3386 reservetop= [X86-32]
3388 Reserves a hole at the top of the kernel virtual
3393 Set the amount of memory to reserve for BIOS at
3394 the bottom of the address space.
3396 reset_devices [KNL] Force drivers to reset the underlying device
3397 during initialization.
3400 Specify the partition device for software suspend
3402 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3404 resume_offset= [SWSUSP]
3405 Specify the offset from the beginning of the partition
3406 given by "resume=" at which the swap header is located,
3407 in <PAGE_SIZE> units (needed only for swap files).
3408 See Documentation/power/swsusp-and-swap-files.txt
3410 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3411 read the resume files
3413 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3414 Useful for devices that are detected asynchronously
3415 (e.g. USB and MMC devices).
3417 hibernate= [HIBERNATION]
3418 noresume Don't check if there's a hibernation image
3419 present during boot.
3420 nocompress Don't compress/decompress hibernation images.
3421 no Disable hibernation and resume.
3423 retain_initrd [RAM] Keep initrd memory after extraction
3425 rfkill.default_state=
3426 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3427 etc. communication is blocked by default.
3430 rfkill.master_switch_mode=
3431 0 The "airplane mode" button does nothing.
3432 1 The "airplane mode" button toggles between everything
3433 blocked and the previous configuration.
3434 2 The "airplane mode" button toggles between everything
3435 blocked and everything unblocked.
3437 rhash_entries= [KNL,NET]
3438 Set number of hash buckets for route cache
3440 ro [KNL] Mount root device read-only on boot
3442 root= [KNL] Root filesystem
3443 See name_to_dev_t comment in init/do_mounts.c.
3445 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3446 mount the root filesystem
3448 rootflags= [KNL] Set root filesystem mount option string
3450 rootfstype= [KNL] Set root filesystem type
3452 rootwait [KNL] Wait (indefinitely) for root device to show up.
3453 Useful for devices that are detected asynchronously
3454 (e.g. USB and MMC devices).
3456 rproc_mem=nn[KMG][@address]
3457 [KNL,ARM,CMA] Remoteproc physical memory block.
3458 Memory area to be used by remote processor image,
3461 rw [KNL] Mount root device read-write on boot
3463 S [KNL] Run init in single mode
3465 s390_iommu= [HW,S390]
3466 Set s390 IOTLB flushing mode
3468 With strict flushing every unmap operation will result in
3469 an IOTLB flush. Default is lazy flushing before reuse,
3473 See drivers/net/irda/sa1100_ir.c.
3475 sbni= [NET] Granch SBNI12 leased line adapter
3477 sched_debug [KNL] Enables verbose scheduler debug messages.
3479 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3480 xtime_lock contention on larger systems, and/or RCU lock
3481 contention on all systems with CONFIG_MAXSMP set.
3482 Format: { "0" | "1" }
3483 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3485 Note: increases power consumption, thus should only be
3486 enabled if running jitter sensitive (HPC/RT) workloads.
3488 security= [SECURITY] Choose a security module to enable at boot.
3489 If this boot parameter is not specified, only the first
3490 security module asking for security registration will be
3491 loaded. An invalid security module name will be treated
3492 as if no module has been chosen.
3494 selinux= [SELINUX] Disable or enable SELinux at boot time.
3495 Format: { "0" | "1" }
3496 See security/selinux/Kconfig help text.
3499 Default value is set via kernel config option.
3500 If enabled at boot time, /selinux/disable can be used
3501 later to disable prior to initial policy load.
3503 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3504 Format: { "0" | "1" }
3505 See security/apparmor/Kconfig help text
3508 Default value is set via kernel config option.
3510 serialnumber [BUGS=X86-32]
3513 Maximal number of shapers.
3515 show_msr= [x86] show boot-time MSR settings
3516 Format: { <integer> }
3517 Show boot-time (BIOS-initialized) MSR settings.
3518 The parameter means the number of CPUs to show,
3519 for example 1 means boot CPU only.
3527 Disable merging of slabs with similar size. May be
3528 necessary if there is some reason to distinguish
3529 allocs to different slabs. Debug options disable
3530 merging on their own.
3531 For more information see Documentation/vm/slub.txt.
3533 slab_max_order= [MM, SLAB]
3534 Determines the maximum allowed order for slabs.
3535 A high setting may cause OOMs due to memory
3536 fragmentation. Defaults to 1 for systems with
3537 more than 32MB of RAM, 0 otherwise.
3539 slub_debug[=options[,slabs]] [MM, SLUB]
3540 Enabling slub_debug allows one to determine the
3541 culprit if slab objects become corrupted. Enabling
3542 slub_debug can create guard zones around objects and
3543 may poison objects when not in use. Also tracks the
3544 last alloc / free. For more information see
3545 Documentation/vm/slub.txt.
3547 slub_max_order= [MM, SLUB]
3548 Determines the maximum allowed order for slabs.
3549 A high setting may cause OOMs due to memory
3550 fragmentation. For more information see
3551 Documentation/vm/slub.txt.
3553 slub_min_objects= [MM, SLUB]
3554 The minimum number of objects per slab. SLUB will
3555 increase the slab order up to slub_max_order to
3556 generate a sufficiently large slab able to contain
3557 the number of objects indicated. The higher the number
3558 of objects the smaller the overhead of tracking slabs
3559 and the less frequently locks need to be acquired.
3560 For more information see Documentation/vm/slub.txt.
3562 slub_min_order= [MM, SLUB]
3563 Determines the minimum page order for slabs. Must be
3564 lower than slub_max_order.
3565 For more information see Documentation/vm/slub.txt.
3567 slub_nomerge [MM, SLUB]
3568 Same with slab_nomerge. This is supported for legacy.
3569 See slab_nomerge for more information.
3572 Format: <io1>[,<io2>[,...,<io8>]]
3574 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3575 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3576 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3577 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3578 smsc-ircc2.ircc_irq= [HW] IRQ line
3579 smsc-ircc2.ircc_dma= [HW] DMA channel
3580 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3581 0: Toshiba Satellite 1800 (GP data pin select)
3582 1: Fast pin select (default)
3586 [KNL] Should the soft-lockup detector generate panics.
3589 softlockup_all_cpu_backtrace=
3590 [KNL] Should the soft-lockup detector generate
3591 backtraces on all cpus.
3594 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3595 See Documentation/laptops/sonypi.txt
3597 spia_io_base= [HW,MTD]
3602 stack_guard_gap= [MM]
3603 override the default stack gap protection. The value
3604 is in page units and it defines how many pages prior
3605 to (for stacks growing down) resp. after (for stacks
3606 growing up) the main stack are reserved for no other
3607 mapping. Default value is 256 pages.
3610 Enabled the stack tracer on boot up.
3612 stacktrace_filter=[function-list]
3613 [FTRACE] Limit the functions that the stack tracer
3614 will trace at boot up. function-list is a comma separated
3615 list of functions. This list can be changed at run
3616 time by the stack_trace_filter file in the debugfs
3617 tracing directory. Note, this enables stack tracing
3618 and the stacktrace above is not needed.
3622 Set the STI (builtin display/keyboard on the HP-PARISC
3623 machines) console (graphic card) which should be used
3624 as the initial boot-console.
3625 See also comment in drivers/video/console/sticore.c.
3628 See comment in drivers/video/console/sticore.c.
3631 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3633 sunrpc.min_resvport=
3634 sunrpc.max_resvport=
3636 SunRPC servers often require that client requests
3637 originate from a privileged port (i.e. a port in the
3638 range 0 < portnr < 1024).
3639 An administrator who wishes to reserve some of these
3640 ports for other uses may adjust the range that the
3641 kernel's sunrpc client considers to be privileged
3642 using these two parameters to set the minimum and
3643 maximum port values.
3647 Control how the NFS server code allocates CPUs to
3648 service thread pools. Depending on how many NICs
3649 you have and where their interrupts are bound, this
3650 option will affect which CPUs will do NFS serving.
3651 Note: this parameter cannot be changed while the
3652 NFS server is running.
3654 auto the server chooses an appropriate mode
3655 automatically using heuristics
3656 global a single global pool contains all CPUs
3657 percpu one pool for each CPU
3658 pernode one pool for each NUMA node (equivalent
3659 to global on non-NUMA machines)
3661 sunrpc.tcp_slot_table_entries=
3662 sunrpc.udp_slot_table_entries=
3664 Sets the upper limit on the number of simultaneous
3665 RPC calls that can be sent from the client to a
3666 server. Increasing these values may allow you to
3667 improve throughput, but will also increase the
3668 amount of memory reserved for use by the client.
3670 suspend.pm_test_delay=
3672 Sets the number of seconds to remain in a suspend test
3673 mode before resuming the system (see
3674 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3675 is set. Default value is 5.
3678 [KNL] Enable accounting of swap in memory resource
3679 controller if no parameter or 1 is given or disable
3680 it if 0 is given (See Documentation/cgroups/memory.txt)
3682 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3683 Format: { <int> | force }
3684 <int> -- Number of I/O TLB slabs
3685 force -- force using of bounce buffers even if they
3686 wouldn't be automatically used by the kernel
3690 sysfs.deprecated=0|1 [KNL]
3691 Enable/disable old style sysfs layout for old udev
3692 on older distributions. When this option is enabled
3693 very new udev will not work anymore. When this option
3694 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3695 in older udev will not work anymore.
3696 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3697 the kernel configuration.
3699 sysrq_always_enabled
3701 Ignore sysrq setting - this boot parameter will
3702 neutralize any effect of /proc/sys/kernel/sysrq.
3703 Useful for debugging.
3705 tcpmhash_entries= [KNL,NET]
3706 Set the number of tcp_metrics_hash slots.
3707 Default value is 8192 or 16384 depending on total
3708 ram pages. This is used to specify the TCP metrics
3709 cache size. See Documentation/networking/ip-sysctl.txt
3710 "tcp_no_metrics_save" section for more details.
3714 test_suspend= [SUSPEND][,N]
3715 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3716 standby suspend) or "freeze" (for suspend type freeze)
3717 as the system sleep state during system startup with
3718 the optional capability to repeat N number of times.
3719 The system is woken from this state using a
3720 wakeup-capable RTC alarm.
3722 thash_entries= [KNL,NET]
3723 Set number of hash buckets for TCP connection
3725 thermal.act= [HW,ACPI]
3726 -1: disable all active trip points in all thermal zones
3727 <degrees C>: override all lowest active trip points
3729 thermal.crt= [HW,ACPI]
3730 -1: disable all critical trip points in all thermal zones
3731 <degrees C>: override all critical trip points
3733 thermal.nocrt= [HW,ACPI]
3734 Set to disable actions on ACPI thermal zone
3735 critical and hot trip points.
3737 thermal.off= [HW,ACPI]
3738 1: disable ACPI thermal control
3740 thermal.psv= [HW,ACPI]
3741 -1: disable all passive trip points
3742 <degrees C>: override all passive trip points to this
3745 thermal.tzp= [HW,ACPI]
3746 Specify global default ACPI thermal zone polling rate
3747 <deci-seconds>: poll all this frequency
3748 0: no polling (default)
3751 Force threading of all interrupt handlers except those
3752 marked explicitly IRQF_NO_THREAD.
3755 Enable the Transcendent memory driver if built-in.
3757 tmem.cleancache=0|1 [KNL, XEN]
3758 Default is on (1). Disable the usage of the cleancache
3759 API to send anonymous pages to the hypervisor.
3761 tmem.frontswap=0|1 [KNL, XEN]
3762 Default is on (1). Disable the usage of the frontswap
3763 API to send swap pages to the hypervisor. If disabled
3764 the selfballooning and selfshrinking are force disabled.
3766 tmem.selfballooning=0|1 [KNL, XEN]
3767 Default is on (1). Disable the driving of swap pages
3770 tmem.selfshrinking=0|1 [KNL, XEN]
3771 Default is on (1). Partial swapoff that immediately
3772 transfers pages from Xen hypervisor back to the
3773 kernel based on different criteria.
3777 Specify if the kernel should make use of the cpu
3778 topology information if the hardware supports this.
3779 The scheduler will make use of this information and
3780 e.g. base its process migration decisions on it.
3783 topology_updates= [KNL, PPC, NUMA]
3785 Specify if the kernel should ignore (off)
3786 topology updates sent by the hypervisor to this
3791 tpm_suspend_pcr=[HW,TPM]
3792 Format: integer pcr id
3793 Specify that at suspend time, the tpm driver
3794 should extend the specified pcr with zeros,
3795 as a workaround for some chips which fail to
3796 flush the last written pcr on TPM_SaveState.
3797 This will guarantee that all the other pcrs
3800 trace_buf_size=nn[KMG]
3801 [FTRACE] will set tracing buffer size on each cpu.
3803 trace_event=[event-list]
3804 [FTRACE] Set and start specified trace events in order
3805 to facilitate early boot debugging.
3806 See also Documentation/trace/events.txt
3808 trace_options=[option-list]
3809 [FTRACE] Enable or disable tracer options at boot.
3810 The option-list is a comma delimited list of options
3811 that can be enabled or disabled just as if you were
3812 to echo the option name into
3814 /sys/kernel/debug/tracing/trace_options
3816 For example, to enable stacktrace option (to dump the
3817 stack trace of each event), add to the command line:
3819 trace_options=stacktrace
3821 See also Documentation/trace/ftrace.txt "trace options"
3825 Have the tracepoints sent to printk as well as the
3826 tracing ring buffer. This is useful for early boot up
3827 where the system hangs or reboots and does not give the
3828 option for reading the tracing buffer or performing a
3829 ftrace_dump_on_oops.
3831 To turn off having tracepoints sent to printk,
3832 echo 0 > /proc/sys/kernel/tracepoint_printk
3833 Note, echoing 1 into this file without the
3834 tracepoint_printk kernel cmdline option has no effect.
3838 Having tracepoints sent to printk() and activating high
3839 frequency tracepoints such as irq or sched, can cause
3840 the system to live lock.
3843 [FTRACE] enable this option to disable tracing when a
3844 warning is hit. This turns off "tracing_on". Tracing can
3845 be enabled again by echoing '1' into the "tracing_on"
3846 file located in /sys/kernel/debug/tracing/
3848 This option is useful, as it disables the trace before
3849 the WARNING dump is called, which prevents the trace to
3850 be filled with content caused by the warning output.
3852 This option can also be set at run time via the sysctl
3853 option: kernel/traceoff_on_warning
3855 transparent_hugepage=
3857 Format: [always|madvise|never]
3858 Can be used to control the default behavior of the system
3859 with respect to transparent hugepages.
3860 See Documentation/vm/transhuge.txt for more details.
3862 tsc= Disable clocksource stability checks for TSC.
3864 [x86] reliable: mark tsc clocksource as reliable, this
3865 disables clocksource verification at runtime, as well
3866 as the stability checks done at bootup. Used to enable
3867 high-resolution timer mode on older hardware, and in
3868 virtualized environment.
3869 [x86] noirqtime: Do not use TSC to do irq accounting.
3870 Used to run time disable IRQ_TIME_ACCOUNTING on any
3871 platforms where RDTSC is slow and this accounting
3874 turbografx.map[2|3]= [HW,JOY]
3875 TurboGraFX parallel port interface
3877 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3878 See also Documentation/input/joystick-parport.txt
3880 udbg-immortal [PPC] When debugging early kernel crashes that
3881 happen after console_init() and before a proper
3882 console driver takes over, this boot options might
3883 help "seeing" what's going on.
3885 uhash_entries= [KNL,NET]
3886 Set number of hash buckets for UDP/UDP-Lite connections
3889 [USB] Ignore overcurrent events (default N).
3890 Some badly-designed motherboards generate lots of
3891 bogus events, for ports that aren't wired to
3892 anything. Set this parameter to avoid log spamming.
3893 Note that genuine overcurrent events won't be
3897 [X86] Cause panic on unknown NMI.
3899 usbcore.authorized_default=
3900 [USB] Default USB device authorization:
3901 (default -1 = authorized except for wireless USB,
3902 0 = not authorized, 1 = authorized)
3904 usbcore.autosuspend=
3905 [USB] The autosuspend time delay (in seconds) used
3906 for newly-detected USB devices (default 2). This
3907 is the time required before an idle device will be
3908 autosuspended. Devices for which the delay is set
3909 to a negative value won't be autosuspended at all.
3911 usbcore.usbfs_snoop=
3912 [USB] Set to log all usbfs traffic (default 0 = off).
3914 usbcore.blinkenlights=
3915 [USB] Set to cycle leds on hubs (default 0 = off).
3917 usbcore.old_scheme_first=
3918 [USB] Start with the old device initialization
3919 scheme (default 0 = off).
3921 usbcore.usbfs_memory_mb=
3922 [USB] Memory limit (in MB) for buffers allocated by
3923 usbfs (default = 16, 0 = max = 2047).
3925 usbcore.use_both_schemes=
3926 [USB] Try the other device initialization scheme
3927 if the first one fails (default 1 = enabled).
3929 usbcore.initial_descriptor_timeout=
3930 [USB] Specifies timeout for the initial 64-byte
3931 USB_REQ_GET_DESCRIPTOR request in milliseconds
3932 (default 5000 = 5.0 seconds).
3935 [USBHID] The interval which mice are to be polled at.
3937 usb-storage.delay_use=
3938 [UMS] The delay in seconds before a new device is
3939 scanned for Logical Units (default 1).
3942 [UMS] A list of quirks entries to supplement or
3943 override the built-in unusual_devs list. List
3944 entries are separated by commas. Each entry has
3945 the form VID:PID:Flags where VID and PID are Vendor
3946 and Product ID values (4-digit hex numbers) and
3947 Flags is a set of characters, each corresponding
3948 to a common usb-storage quirk flag as follows:
3949 a = SANE_SENSE (collect more than 18 bytes
3951 b = BAD_SENSE (don't collect more than 18
3952 bytes of sense data);
3953 c = FIX_CAPACITY (decrease the reported
3954 device capacity by one sector);
3955 d = NO_READ_DISC_INFO (don't use
3956 READ_DISC_INFO command);
3957 e = NO_READ_CAPACITY_16 (don't use
3958 READ_CAPACITY_16 command);
3959 f = NO_REPORT_OPCODES (don't use report opcodes
3961 g = MAX_SECTORS_240 (don't transfer more than
3962 240 sectors at a time, uas only);
3963 h = CAPACITY_HEURISTICS (decrease the
3964 reported device capacity by one
3965 sector if the number is odd);
3966 i = IGNORE_DEVICE (don't bind to this
3968 j = NO_REPORT_LUNS (don't use report luns
3970 l = NOT_LOCKABLE (don't try to lock and
3971 unlock ejectable media);
3972 m = MAX_SECTORS_64 (don't transfer more
3973 than 64 sectors = 32 KB at a time);
3974 n = INITIAL_READ10 (force a retry of the
3975 initial READ(10) command);
3976 o = CAPACITY_OK (accept the capacity
3977 reported by the device);
3978 p = WRITE_CACHE (the device cache is ON
3980 r = IGNORE_RESIDUE (the device reports
3981 bogus residue values);
3982 s = SINGLE_LUN (the device has only one
3984 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3985 commands, uas only);
3986 u = IGNORE_UAS (don't bind to the uas driver);
3987 w = NO_WP_DETECT (don't test whether the
3988 medium is write-protected).
3989 Example: quirks=0419:aaf5:rl,0421:0433:rc
3991 user_debug= [KNL,ARM]
3993 See arch/arm/Kconfig.debug help text.
3994 1 - undefined instruction events
3996 4 - invalid data aborts
3999 Example: user_debug=31
4002 [X86] Flags controlling user PTE allocations.
4004 nohigh = do not allocate PTE pages in
4005 HIGHMEM regardless of setting
4009 On X86_32, this is an alias for vdso32=. Otherwise:
4011 vdso=1: enable VDSO (the default)
4012 vdso=0: disable VDSO mapping
4014 vdso32= [X86] Control the 32-bit vDSO
4015 vdso32=1: enable 32-bit VDSO
4016 vdso32=0 or vdso32=2: disable 32-bit VDSO
4018 See the help text for CONFIG_COMPAT_VDSO for more
4019 details. If CONFIG_COMPAT_VDSO is set, the default is
4020 vdso32=0; otherwise, the default is vdso32=1.
4022 For compatibility with older kernels, vdso32=2 is an
4025 Try vdso32=0 if you encounter an error that says:
4026 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4029 vector=percpu: enable percpu vector domain
4031 video= [FB] Frame buffer configuration
4032 See Documentation/fb/modedb.txt.
4034 video.brightness_switch_enabled= [0,1]
4035 If set to 1, on receiving an ACPI notify event
4036 generated by hotkey, video driver will adjust brightness
4037 level and then send out the event to user space through
4038 the allocated input device; If set to 0, video driver
4039 will only send out the event without touching backlight
4044 [VMMIO] Memory mapped virtio (platform) device.
4046 <size>@<baseaddr>:<irq>[:<id>]
4048 <size> := size (can use standard suffixes
4050 <baseaddr> := physical base address
4051 <irq> := interrupt number (as passed to
4053 <id> := (optional) platform device id
4055 virtio_mmio.device=1K@0x100b0000:48:7
4057 Can be used multiple times for multiple devices.
4059 vga= [BOOT,X86-32] Select a particular video mode
4060 See Documentation/x86/boot.txt and
4061 Documentation/svga.txt.
4062 Use vga=ask for menu.
4063 This is actually a boot loader parameter; the value is
4064 passed to the kernel using a special protocol.
4066 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4067 size of <nn>. This can be used to increase the
4068 minimum size (128MB on x86). It can also be used to
4069 decrease the size and leave more room for directly
4072 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4075 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4078 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4082 Controls the behavior of vsyscalls (i.e. calls to
4083 fixed addresses of 0xffffffffff600x00 from legacy
4084 code). Most statically-linked binaries and older
4085 versions of glibc use these calls. Because these
4086 functions are at fixed addresses, they make nice
4087 targets for exploits that can control RIP.
4089 emulate [default] Vsyscalls turn into traps and are
4090 emulated reasonably safely.
4092 native Vsyscalls are native syscall instructions.
4093 This is a little bit faster than trapping
4094 and makes a few dynamic recompilers work
4095 better than they would in emulation mode.
4096 It also makes exploits much easier to write.
4098 none Vsyscalls don't work at all. This makes
4099 them quite hard to use for exploits but
4100 might break your system.
4102 vt.color= [VT] Default text color.
4103 Format: 0xYX, X = foreground, Y = background.
4104 Default: 0x07 = light gray on black.
4106 vt.cur_default= [VT] Default cursor shape.
4107 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4108 the parameters of the <Esc>[?A;B;Cc escape sequence;
4109 see VGA-softcursor.txt. Default: 2 = underline.
4111 vt.default_blu= [VT]
4112 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4113 Change the default blue palette of the console.
4114 This is a 16-member array composed of values
4117 vt.default_grn= [VT]
4118 Format: <green0>,<green1>,<green2>,...,<green15>
4119 Change the default green palette of the console.
4120 This is a 16-member array composed of values
4123 vt.default_red= [VT]
4124 Format: <red0>,<red1>,<red2>,...,<red15>
4125 Change the default red palette of the console.
4126 This is a 16-member array composed of values
4132 Set system-wide default UTF-8 mode for all tty's.
4133 Default is 1, i.e. UTF-8 mode is enabled for all
4134 newly opened terminals.
4136 vt.global_cursor_default=
4139 Set system-wide default for whether a cursor
4140 is shown on new VTs. Default is -1,
4141 i.e. cursors will be created by default unless
4142 overridden by individual drivers. 0 will hide
4143 cursors, 1 will display them.
4145 vt.italic= [VT] Default color for italic text; 0-15.
4148 vt.underline= [VT] Default color for underlined text; 0-15.
4151 watchdog timers [HW,WDT] For information on watchdog timers,
4152 see Documentation/watchdog/watchdog-parameters.txt
4153 or other driver-specific files in the
4154 Documentation/watchdog/ directory.
4156 workqueue.disable_numa
4157 By default, all work items queued to unbound
4158 workqueues are affine to the NUMA nodes they're
4159 issued on, which results in better behavior in
4160 general. If NUMA affinity needs to be disabled for
4161 whatever reason, this option can be used. Note
4162 that this also can be controlled per-workqueue for
4163 workqueues visible under /sys/bus/workqueue/.
4165 workqueue.power_efficient
4166 Per-cpu workqueues are generally preferred because
4167 they show better performance thanks to cache
4168 locality; unfortunately, per-cpu workqueues tend to
4169 be more power hungry than unbound workqueues.
4171 Enabling this makes the per-cpu workqueues which
4172 were observed to contribute significantly to power
4173 consumption unbound, leading to measurably lower
4174 power usage at the cost of small performance
4177 The default value of this parameter is determined by
4178 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4180 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4181 default x2apic cluster mode on platforms
4184 x86_intel_mid_timer= [X86-32,APBT]
4185 Choose timer option for x86 Intel MID platform.
4186 Two valid options are apbt timer only and lapic timer
4187 plus one apbt timer for broadcast timer.
4188 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4190 xen_512gb_limit [KNL,X86-64,XEN]
4191 Restricts the kernel running paravirtualized under Xen
4192 to use only up to 512 GB of RAM. The reason to do so is
4193 crash analysis tools and Xen tools for doing domain
4194 save/restore/migration must be enabled to handle larger
4197 xen_emul_unplug= [HW,X86,XEN]
4198 Unplug Xen emulated devices
4199 Format: [unplug0,][unplug1]
4200 ide-disks -- unplug primary master IDE devices
4201 aux-ide-disks -- unplug non-primary-master IDE devices
4202 nics -- unplug network devices
4203 all -- unplug all emulated devices (NICs and IDE disks)
4204 unnecessary -- unplugging emulated devices is
4205 unnecessary even if the host did not respond to
4207 never -- do not unplug even if version check succeeds
4209 xen_nopvspin [X86,XEN]
4210 Disables the ticketlock slowpath using Xen PV
4214 Disables the PV optimizations forcing the HVM guest to
4215 run as generic HVM guest with no PV drivers.
4217 xirc2ps_cs= [NET,PCMCIA]
4219 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4221 ______________________________________________________________________
4225 Add more DRM drivers.
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