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 DM Device mapper support is enabled.
60 DRM Direct Rendering Management support is enabled.
61 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
62 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
63 EFI EFI Partitioning (GPT) is enabled
64 EIDE EIDE/ATAPI support is enabled.
65 EVM Extended Verification Module
66 FB The frame buffer device is enabled.
67 FTRACE Function tracing enabled.
68 GCOV GCOV profiling is enabled.
69 HW Appropriate hardware is enabled.
70 IA-64 IA-64 architecture is enabled.
71 IMA Integrity measurement architecture is enabled.
72 IOSCHED More than one I/O scheduler is enabled.
73 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
74 IPV6 IPv6 support is enabled.
75 ISAPNP ISA PnP code is enabled.
76 ISDN Appropriate ISDN support is enabled.
77 JOY Appropriate joystick support is enabled.
78 KGDB Kernel debugger support is enabled.
79 KVM Kernel Virtual Machine support is enabled.
80 LIBATA Libata driver is enabled
81 LP Printer support is enabled.
82 LOOP Loopback device support is enabled.
83 M68k M68k architecture is enabled.
84 These options have more detailed description inside of
85 Documentation/m68k/kernel-options.txt.
86 MDA MDA console support is enabled.
87 MIPS MIPS architecture is enabled.
88 MOUSE Appropriate mouse support is enabled.
89 MSI Message Signaled Interrupts (PCI).
90 MTD MTD (Memory Technology Device) support is enabled.
91 NET Appropriate network support is enabled.
92 NUMA NUMA support is enabled.
93 NFS Appropriate NFS support is enabled.
94 OSS OSS sound support is enabled.
95 PV_OPS A paravirtualized kernel is enabled.
96 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
97 PARISC The PA-RISC architecture is enabled.
98 PCI PCI bus support is enabled.
99 PCIE PCI Express support is enabled.
100 PCMCIA The PCMCIA subsystem is enabled.
101 PNP Plug & Play support is enabled.
102 PPC PowerPC architecture is enabled.
103 PPT Parallel port support is enabled.
104 PS2 Appropriate PS/2 support is enabled.
105 RAM RAM disk support is enabled.
106 S390 S390 architecture is enabled.
107 SCSI Appropriate SCSI support is enabled.
108 A lot of drivers have their options described inside
109 the Documentation/scsi/ sub-directory.
110 SECURITY Different security models are enabled.
111 SELINUX SELinux support is enabled.
112 APPARMOR AppArmor support is enabled.
113 SERIAL Serial support is enabled.
114 SH SuperH architecture is enabled.
115 SMP The kernel is an SMP kernel.
116 SPARC Sparc architecture is enabled.
117 SWSUSP Software suspend (hibernation) is enabled.
118 SUSPEND System suspend states are enabled.
119 TPM TPM drivers are enabled.
120 TS Appropriate touchscreen support is enabled.
121 UMS USB Mass Storage support is enabled.
122 USB USB support is enabled.
123 USBHID USB Human Interface Device support is enabled.
124 V4L Video For Linux support is enabled.
125 VMMIO Driver for memory mapped virtio devices is enabled.
126 VGA The VGA console has been enabled.
127 VT Virtual terminal support is enabled.
128 WDT Watchdog support is enabled.
129 XT IBM PC/XT MFM hard disk support is enabled.
130 X86-32 X86-32, aka i386 architecture is enabled.
131 X86-64 X86-64 architecture is enabled.
132 More X86-64 boot options can be found in
133 Documentation/x86/x86_64/boot-options.txt .
134 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
135 XEN Xen support is enabled
137 In addition, the following text indicates that the option:
139 BUGS= Relates to possible processor bugs on the said processor.
140 KNL Is a kernel start-up parameter.
141 BOOT Is a boot loader parameter.
143 Parameters denoted with BOOT are actually interpreted by the boot
144 loader, and have no meaning to the kernel directly.
145 Do not modify the syntax of boot loader parameters without extreme
146 need or coordination with <Documentation/x86/boot.txt>.
148 There are also arch-specific kernel-parameters not documented here.
149 See for example <Documentation/x86/x86_64/boot-options.txt>.
151 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
152 a trailing = on the name of any parameter states that that parameter will
153 be entered as an environment variable, whereas its absence indicates that
154 it will appear as a kernel argument readable via /proc/cmdline by programs
155 running once the system is up.
157 The number of kernel parameters is not limited, but the length of the
158 complete command line (parameters including spaces etc.) is limited to
159 a fixed number of characters. This limit depends on the architecture
160 and is between 256 and 4096 characters. It is defined in the file
161 ./include/asm/setup.h as COMMAND_LINE_SIZE.
163 Finally, the [KMG] suffix is commonly described after a number of kernel
164 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
165 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
166 bytes respectively. Such letter suffixes can also be entirely omitted.
169 acpi= [HW,ACPI,X86,ARM64]
170 Advanced Configuration and Power Interface
171 Format: { force | off | strict | noirq | rsdt |
173 force -- enable ACPI if default was off
174 off -- disable ACPI if default was on
175 noirq -- do not use ACPI for IRQ routing
176 strict -- Be less tolerant of platforms that are not
177 strictly ACPI specification compliant.
178 rsdt -- prefer RSDT over (default) XSDT
179 copy_dsdt -- copy DSDT to memory
180 For ARM64, ONLY "acpi=off" or "acpi=force" are available
182 See also Documentation/power/runtime_pm.txt, pci=noacpi
184 acpi_apic_instance= [ACPI, IOAPIC]
186 2: use 2nd APIC table, if available
187 1,0: use 1st APIC table
190 acpi_backlight= [HW,ACPI]
191 acpi_backlight=vendor
193 If set to vendor, prefer vendor specific driver
194 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
195 of the ACPI video.ko driver.
197 acpica_no_return_repair [HW, ACPI]
198 Disable AML predefined validation mechanism
199 This mechanism can repair the evaluation result to make
200 the return objects more ACPI specification compliant.
201 This option is useful for developers to identify the
202 root cause of an AML interpreter issue when the issue
203 has something to do with the repair mechanism.
205 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
206 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
208 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
209 debug output. Bits in debug_layer correspond to a
210 _COMPONENT in an ACPI source file, e.g.,
211 #define _COMPONENT ACPI_PCI_COMPONENT
212 Bits in debug_level correspond to a level in
213 ACPI_DEBUG_PRINT statements, e.g.,
214 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
215 The debug_level mask defaults to "info". See
216 Documentation/acpi/debug.txt for more information about
217 debug layers and levels.
219 Enable processor driver info messages:
220 acpi.debug_layer=0x20000000
221 Enable PCI/PCI interrupt routing info messages:
222 acpi.debug_layer=0x400000
223 Enable AML "Debug" output, i.e., stores to the Debug
224 object while interpreting AML:
225 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
226 Enable all messages related to ACPI hardware:
227 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
229 Some values produce so much output that the system is
230 unusable. The "log_buf_len" parameter may be useful
231 if you need to capture more output.
233 acpi_enforce_resources= [ACPI]
234 { strict | lax | no }
235 Check for resource conflicts between native drivers
236 and ACPI OperationRegions (SystemIO and SystemMemory
237 only). IO ports and memory declared in ACPI might be
238 used by the ACPI subsystem in arbitrary AML code and
239 can interfere with legacy drivers.
240 strict (default): access to resources claimed by ACPI
241 is denied; legacy drivers trying to access reserved
242 resources will fail to bind to device using them.
243 lax: access to resources claimed by ACPI is allowed;
244 legacy drivers trying to access reserved resources
245 will bind successfully but a warning message is logged.
246 no: ACPI OperationRegions are not marked as reserved,
247 no further checks are performed.
249 acpi_force_table_verification [HW,ACPI]
250 Enable table checksum verification during early stage.
251 By default, this is disabled due to x86 early mapping
254 acpi_irq_balance [HW,ACPI]
255 ACPI will balance active IRQs
258 acpi_irq_nobalance [HW,ACPI]
259 ACPI will not move active IRQs (default)
262 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
263 Format: <irq>,<irq>...
265 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
267 Format: <irq>,<irq>...
269 acpi_no_auto_serialize [HW,ACPI]
270 Disable auto-serialization of AML methods
271 AML control methods that contain the opcodes to create
272 named objects will be marked as "Serialized" by the
273 auto-serialization feature.
274 This feature is enabled by default.
275 This option allows to turn off the feature.
277 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
280 acpi_no_static_ssdt [HW,ACPI]
281 Disable installation of static SSDTs at early boot time
282 By default, SSDTs contained in the RSDT/XSDT will be
283 installed automatically and they will appear under
284 /sys/firmware/acpi/tables.
285 This option turns off this feature.
286 Note that specifying this option does not affect
287 dynamic table installation which will install SSDT
288 tables to /sys/firmware/acpi/tables/dynamic.
290 acpi_rsdp= [ACPI,EFI,KEXEC]
291 Pass the RSDP address to the kernel, mostly used
292 on machines running EFI runtime service to boot the
293 second kernel for kdump.
295 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
296 Format: To spoof as Windows 98: ="Microsoft Windows"
298 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
299 of 2 which is mandated by ACPI 6) as the supported ACPI
300 specification revision (when using this switch, it may
301 be necessary to carry out a cold reboot _twice_ in a
302 row to make it take effect on the platform firmware).
304 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
305 acpi_osi="string1" # add string1
306 acpi_osi="!string2" # remove string2
307 acpi_osi=!* # remove all strings
308 acpi_osi=! # disable all built-in OS vendor
310 acpi_osi= # disable all strings
312 'acpi_osi=!' can be used in combination with single or
313 multiple 'acpi_osi="string1"' to support specific OS
314 vendor string(s). Note that such command can only
315 affect the default state of the OS vendor strings, thus
316 it cannot affect the default state of the feature group
317 strings and the current state of the OS vendor strings,
318 specifying it multiple times through kernel command line
319 is meaningless. This command is useful when one do not
320 care about the state of the feature group strings which
321 should be controlled by the OSPM.
323 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
324 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
325 can make '_OSI("Windows 2000")' TRUE.
327 'acpi_osi=' cannot be used in combination with other
328 'acpi_osi=' command lines, the _OSI method will not
329 exist in the ACPI namespace. NOTE that such command can
330 only affect the _OSI support state, thus specifying it
331 multiple times through kernel command line is also
334 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
337 'acpi_osi=!*' can be used in combination with single or
338 multiple 'acpi_osi="string1"' to support specific
339 string(s). Note that such command can affect the
340 current state of both the OS vendor strings and the
341 feature group strings, thus specifying it multiple times
342 through kernel command line is meaningful. But it may
343 still not able to affect the final state of a string if
344 there are quirks related to this string. This command
345 is useful when one want to control the state of the
346 feature group strings to debug BIOS issues related to
349 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
350 '_OSI("Module Device")' FALSE.
351 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
352 '_OSI("Module Device")' TRUE.
353 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
355 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
357 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
358 they all will make '_OSI("Windows 2000")' TRUE.
361 Override the pmtimer bug detection: force the kernel
362 to assume that this machine's pmtimer latches its value
363 and always returns good values.
365 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
366 Format: { level | edge | high | low }
368 acpi_skip_timer_override [HW,ACPI]
369 Recognize and ignore IRQ0/pin2 Interrupt Override.
370 For broken nForce2 BIOS resulting in XT-PIC timer.
372 acpi_sleep= [HW,ACPI] Sleep options
373 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
374 old_ordering, nonvs, sci_force_enable }
375 See Documentation/power/video.txt for information on
377 s3_beep is for debugging; it makes the PC's speaker beep
378 as soon as the kernel's real-mode entry point is called.
379 s4_nohwsig prevents ACPI hardware signature from being
380 used during resume from hibernation.
381 old_ordering causes the ACPI 1.0 ordering of the _PTS
382 control method, with respect to putting devices into
383 low power states, to be enforced (the ACPI 2.0 ordering
384 of _PTS is used by default).
385 nonvs prevents the kernel from saving/restoring the
386 ACPI NVS memory during suspend/hibernation and resume.
387 sci_force_enable causes the kernel to set SCI_EN directly
388 on resume from S1/S3 (which is against the ACPI spec,
389 but some broken systems don't work without it).
391 acpi_use_timer_override [HW,ACPI]
392 Use timer override. For some broken Nvidia NF5 boards
393 that require a timer override, but don't have HPET
395 add_efi_memmap [EFI; X86] Include EFI memory map in
396 kernel's map of available physical RAM.
399 { off | try_unsupported }
400 off: disable AGP support
401 try_unsupported: try to drive unsupported chipsets
402 (may crash computer or cause data corruption)
405 See Documentation/sound/alsa/alsa-parameters.txt
408 Allow the default userspace alignment fault handler
409 behaviour to be specified. Bit 0 enables warnings,
410 bit 1 enables fixups, and bit 2 sends a segfault.
412 align_va_addr= [X86-64]
413 Align virtual addresses by clearing slice [14:12] when
414 allocating a VMA at process creation time. This option
415 gives you up to 3% performance improvement on AMD F15h
416 machines (where it is enabled by default) for a
417 CPU-intensive style benchmark, and it can vary highly in
418 a microbenchmark depending on workload and compiler.
420 32: only for 32-bit processes
421 64: only for 64-bit processes
422 on: enable for both 32- and 64-bit processes
423 off: disable for both 32- and 64-bit processes
425 alloc_snapshot [FTRACE]
426 Allocate the ftrace snapshot buffer on boot up when the
427 main buffer is allocated. This is handy if debugging
428 and you need to use tracing_snapshot() on boot up, and
429 do not want to use tracing_snapshot_alloc() as it needs
430 to be done where GFP_KERNEL allocations are allowed.
432 amd_iommu= [HW,X86-64]
433 Pass parameters to the AMD IOMMU driver in the system.
435 fullflush - enable flushing of IO/TLB entries when
436 they are unmapped. Otherwise they are
437 flushed before they will be reused, which
439 off - do not initialize any AMD IOMMU found in
441 force_isolation - Force device isolation for all
442 devices. The IOMMU driver is not
443 allowed anymore to lift isolation
444 requirements as needed. This option
445 does not override iommu=pt
447 amd_iommu_dump= [HW,X86-64]
448 Enable AMD IOMMU driver option to dump the ACPI table
449 for AMD IOMMU. With this option enabled, AMD IOMMU
450 driver will print ACPI tables for AMD IOMMU during
451 IOMMU initialization.
453 amijoy.map= [HW,JOY] Amiga joystick support
454 Map of devices attached to JOY0DAT and JOY1DAT
456 See also Documentation/input/joystick.txt
458 analog.map= [HW,JOY] Analog joystick and gamepad support
459 Specifies type or capabilities of an analog joystick
460 connected to one of 16 gameports
461 Format: <type1>,<type2>,..<type16>
464 Power management functions (SPARCstation-4/5 + deriv.)
466 Disable APC CPU standby support. SPARCstation-Fox does
467 not play well with APC CPU idle - disable it if you have
468 APC and your system crashes randomly.
470 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
471 Change the output verbosity whilst booting
472 Format: { quiet (default) | verbose | debug }
473 Change the amount of debugging information output
474 when initialising the APIC and IO-APIC components.
477 See Documentation/networking/ipv6.txt.
479 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
480 Limit apic dumping. The parameter defines the maximal
481 number of local apics being dumped. Also it is possible
482 to set it to "all" by meaning -- no limit here.
483 Format: { 1 (default) | 2 | ... | all }.
484 The parameter valid if only apic=debug or
485 apic=verbose is specified.
486 Example: apic=debug show_lapic=all
488 apm= [APM] Advanced Power Management
489 See header of arch/x86/kernel/apm_32.c.
491 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
492 Format: <io>,<irq>,<nodeID>
496 atarimouse= [HW,MOUSE] Atari Mouse
498 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
499 EzKey and similar keyboards
501 atkbd.reset= [HW] Reset keyboard during initialization
503 atkbd.set= [HW] Select keyboard code set
504 Format: <int> (2 = AT (default), 3 = PS/2)
506 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
509 atkbd.softraw= [HW] Choose between synthetic and real raw mode
510 Format: <bool> (0 = real, 1 = synthetic (default))
512 atkbd.softrepeat= [HW]
513 Use software keyboard repeat
515 audit= [KNL] Enable the audit sub-system
516 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
517 0 - kernel audit is disabled and can not be enabled
518 until the next reboot
519 unset - kernel audit is initialized but disabled and
520 will be fully enabled by the userspace auditd.
521 1 - kernel audit is initialized and partially enabled,
522 storing at most audit_backlog_limit messages in
523 RAM until it is fully enabled by the userspace
527 audit_backlog_limit= [KNL] Set the audit queue size limit.
528 Format: <int> (must be >=0)
531 baycom_epp= [HW,AX25]
534 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
536 See header of drivers/net/hamradio/baycom_par.c.
538 baycom_ser_fdx= [HW,AX25]
539 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
540 Format: <io>,<irq>,<mode>[,<baud>]
541 See header of drivers/net/hamradio/baycom_ser_fdx.c.
543 baycom_ser_hdx= [HW,AX25]
544 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
545 Format: <io>,<irq>,<mode>
546 See header of drivers/net/hamradio/baycom_ser_hdx.c.
548 blkdevparts= Manual partition parsing of block device(s) for
549 embedded devices based on command line input.
550 See Documentation/block/cmdline-partition.txt
552 boot_delay= Milliseconds to delay each printk during boot.
553 Values larger than 10 seconds (10000) are changed to
557 bootmem_debug [KNL] Enable bootmem allocator debug messages.
559 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
560 bttv.radio= Most important insmod options are available as
562 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
565 bulk_remove=off [PPC] This parameter disables the use of the pSeries
566 firmware feature for flushing multiple hpte entries
569 c101= [NET] Moxa C101 synchronous serial card
571 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
572 Sometimes CPU hardware bugs make them report the cache
573 size incorrectly. The kernel will attempt work arounds
574 to fix known problems, but for some CPUs it is not
575 possible to determine what the correct size should be.
576 This option provides an override for these situations.
578 ca_keys= [KEYS] This parameter identifies a specific key(s) on
579 the system trusted keyring to be used for certificate
581 format: { id:<keyid> | builtin }
583 cca= [MIPS] Override the kernel pages' cache coherency
584 algorithm. Accepted values range from 0 to 7
585 inclusive. See arch/mips/include/asm/pgtable-bits.h
586 for platform specific values (SB1, Loongson3 and
589 ccw_timeout_log [S390]
590 See Documentation/s390/CommonIO for details.
592 cgroup_disable= [KNL] Disable a particular controller
593 Format: {name of the controller(s) to disable}
594 The effects of cgroup_disable=foo are:
595 - foo isn't auto-mounted if you mount all cgroups in
597 - foo isn't visible as an individually mountable
599 {Currently only "memory" controller deal with this and
600 cut the overhead, others just disable the usage. So
601 only cgroup_disable=memory is actually worthy}
603 checkreqprot [SELINUX] Set initial checkreqprot flag value.
604 Format: { "0" | "1" }
605 See security/selinux/Kconfig help text.
606 0 -- check protection applied by kernel (includes
607 any implied execute protection).
608 1 -- check protection requested by application.
609 Default value is set via a kernel config option.
610 Value can be changed at runtime via
611 /selinux/checkreqprot.
614 See Documentation/s390/CommonIO for details.
617 Prevents the clock framework from automatically gating
618 clocks that have not been explicitly enabled by a Linux
619 device driver but are enabled in hardware at reset or
620 by the bootloader/firmware. Note that this does not
621 force such clocks to be always-on nor does it reserve
622 those clocks in any way. This parameter is useful for
623 debug and development, but should not be needed on a
624 platform with proper driver support. For more
625 information, see Documentation/clk.txt.
627 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
629 Forces specified clocksource (if available) to be used
630 when calculating gettimeofday(). If specified
631 clocksource is not available, it defaults to PIT.
632 Format: { pit | tsc | cyclone | pmtmr }
634 clocksource= Override the default clocksource
636 Override the default clocksource and use the clocksource
637 with the name specified.
638 Some clocksource names to choose from, depending on
640 [all] jiffies (this is the base, fallback clocksource)
642 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
643 pxa_timer,timer3,32k_counter,timer0_1
645 [X86-32] pit,hpet,tsc;
646 scx200_hrt on Geode; cyclone on IBM x440
654 clearcpuid=BITNUM [X86]
655 Disable CPUID feature X for the kernel. See
656 arch/x86/include/asm/cpufeature.h for the valid bit
657 numbers. Note the Linux specific bits are not necessarily
658 stable over kernel options, but the vendor specific
660 Also note that user programs calling CPUID directly
661 or using the feature without checking anything
662 will still see it. This just prevents it from
663 being used by the kernel or shown in /proc/cpuinfo.
664 Also note the kernel might malfunction if you disable
667 cma=nn[MG]@[start[MG][-end[MG]]]
669 Sets the size of kernel global memory area for
670 contiguous memory allocations and optionally the
671 placement constraint by the physical address range of
672 memory allocations. A value of 0 disables CMA
673 altogether. For more information, see
674 include/linux/dma-contiguous.h
676 cmo_free_hint= [PPC] Format: { yes | no }
677 Specify whether pages are marked as being inactive
678 when they are freed. This is used in CMO environments
679 to determine OS memory pressure for page stealing by
683 coherent_pool=nn[KMG] [ARM,KNL]
684 Sets the size of memory pool for coherent, atomic dma
685 allocations, by default set to 256K.
687 code_bytes [X86] How many bytes of object code to print
692 com20020= [HW,NET] ARCnet - COM20020 chipset
694 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
696 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
700 ARCnet - COM90xx chipset (memory-mapped buffers)
701 Format: <io>[,<irq>[,<memstart>]]
703 condev= [HW,S390] console device
706 console= [KNL] Output console device and options.
708 tty<n> Use the virtual console device <n>.
712 Use the specified serial port. The options are of
713 the form "bbbbpnf", where "bbbb" is the baud rate,
714 "p" is parity ("n", "o", or "e"), "n" is number of
715 bits, and "f" is flow control ("r" for RTS or
716 omit it). Default is "9600n8".
718 See Documentation/serial-console.txt for more
720 Documentation/networking/netconsole.txt for an
723 uart[8250],io,<addr>[,options]
724 uart[8250],mmio,<addr>[,options]
725 uart[8250],mmio32,<addr>[,options]
726 uart[8250],0x<addr>[,options]
727 Start an early, polled-mode console on the 8250/16550
728 UART at the specified I/O port or MMIO address,
729 switching to the matching ttyS device later.
730 MMIO inter-register address stride is either 8-bit
731 (mmio) or 32-bit (mmio32).
732 If none of [io|mmio|mmio32], <addr> is assumed to be
733 equivalent to 'mmio'. 'options' are specified in the
734 same format described for ttyS above; if unspecified,
735 the h/w is not re-initialized.
737 hvc<n> Use the hypervisor console device <n>. This is for
738 both Xen and PowerPC hypervisors.
740 If the device connected to the port is not a TTY but a braille
741 device, prepend "brl," before the device type, for instance
743 For now, only VisioBraille is supported.
745 consoleblank= [KNL] The console blank (screen saver) timeout in
746 seconds. Defaults to 10*60 = 10mins. A value of 0
747 disables the blank timer.
750 [KNL] Change the default value for
751 /proc/<pid>/coredump_filter.
752 See also Documentation/filesystems/proc.txt.
754 cpuidle.off=1 [CPU_IDLE]
755 disable the cpuidle sub-system
758 [X86] Delay for N microsec between assert and de-assert
759 of APIC INIT to start processors. This delay occurs
760 on every CPU online, such as boot, and resume from suspend.
763 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
765 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
767 crashkernel=size[KMG][@offset[KMG]]
768 [KNL] Using kexec, Linux can switch to a 'crash kernel'
769 upon panic. This parameter reserves the physical
770 memory region [offset, offset + size] for that kernel
771 image. If '@offset' is omitted, then a suitable offset
772 is selected automatically. Check
773 Documentation/kdump/kdump.txt for further details.
775 crashkernel=range1:size1[,range2:size2,...][@offset]
776 [KNL] Same as above, but depends on the memory
777 in the running system. The syntax of range is
778 start-[end] where start and end are both
779 a memory unit (amount[KMG]). See also
780 Documentation/kdump/kdump.txt for an example.
782 crashkernel=size[KMG],high
783 [KNL, x86_64] range could be above 4G. Allow kernel
784 to allocate physical memory region from top, so could
785 be above 4G if system have more than 4G ram installed.
786 Otherwise memory region will be allocated below 4G, if
788 It will be ignored if crashkernel=X is specified.
789 crashkernel=size[KMG],low
790 [KNL, x86_64] range under 4G. When crashkernel=X,high
791 is passed, kernel could allocate physical memory region
792 above 4G, that cause second kernel crash on system
793 that require some amount of low memory, e.g. swiotlb
794 requires at least 64M+32K low memory, also enough extra
795 low memory is needed to make sure DMA buffers for 32-bit
796 devices won't run out. Kernel would try to allocate at
797 at least 256M below 4G automatically.
798 This one let user to specify own low range under 4G
799 for second kernel instead.
800 0: to disable low allocation.
801 It will be ignored when crashkernel=X,high is not used
802 or memory reserved is below 4G.
807 cs89x0_media= [HW,NET]
808 Format: { rj45 | aui | bnc }
811 See header of drivers/s390/block/dasd_devmap.c.
813 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
814 (one device per port)
815 Format: <port#>,<type>
816 See also Documentation/input/joystick-parport.txt
818 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
819 time. See Documentation/dynamic-debug-howto.txt for
820 details. Deprecated, see dyndbg.
822 debug [KNL] Enable kernel debugging (events log level).
825 [KNL] verbose self-tests
827 Print debugging info while doing the locking API
829 We default to 0 (no extra messages), setting it to
830 1 will print _a lot_ more information - normally
831 only useful to kernel developers.
833 debug_objects [KNL] Enable object debugging
836 [KNL] Disable object debugging
838 debug_guardpage_minorder=
839 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
840 parameter allows control of the order of pages that will
841 be intentionally kept free (and hence protected) by the
842 buddy allocator. Bigger value increase the probability
843 of catching random memory corruption, but reduce the
844 amount of memory for normal system use. The maximum
845 possible value is MAX_ORDER/2. Setting this parameter
846 to 1 or 2 should be enough to identify most random
847 memory corruption problems caused by bugs in kernel or
848 driver code when a CPU writes to (or reads from) a
849 random memory location. Note that there exists a class
850 of memory corruptions problems caused by buggy H/W or
851 F/W or by drivers badly programing DMA (basically when
852 memory is written at bus level and the CPU MMU is
853 bypassed) which are not detectable by
854 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
855 tracking down these problems.
858 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
859 parameter enables the feature at boot time. In
860 default, it is disabled. We can avoid allocating huge
861 chunk of memory for debug pagealloc if we don't enable
862 it at boot time and the system will work mostly same
863 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
864 on: enable the feature
866 debugpat [X86] Enable PAT debugging
868 decnet.addr= [HW,NET]
869 Format: <area>[,<node>]
870 See also Documentation/networking/decnet.txt.
873 [same as hugepagesz=] The size of the default
874 HugeTLB page size. This is the size represented by
875 the legacy /proc/ hugepages APIs, used for SHM, and
876 default size when mounting hugetlbfs filesystems.
877 Defaults to the default architecture's huge page size
881 Set number of hash buckets for dentry cache.
884 See Documentation/networking/ipv6.txt.
886 disable_cpu_apicid= [X86,APIC,SMP]
888 The number of initial APIC ID for the
889 corresponding CPU to be disabled at boot,
890 mostly used for the kdump 2nd kernel to
891 disable BSP to wake up multiple CPUs without
892 causing system reset or hang due to sending
895 disable_ddw [PPC/PSERIES]
896 Disable Dynamic DMA Window support. Use this if
897 to workaround buggy firmware.
900 See Documentation/networking/ipv6.txt.
902 disable_mtrr_cleanup [X86]
903 The kernel tries to adjust MTRR layout from continuous
904 to discrete, to make X server driver able to add WB
905 entry later. This parameter disables that.
907 disable_mtrr_trim [X86, Intel and AMD only]
908 By default the kernel will trim any uncacheable
909 memory out of your available memory pool based on
910 MTRR settings. This parameter disables that behavior,
911 possibly causing your machine to run very slowly.
913 disable_timer_pin_1 [X86]
914 Disable PIN 1 of APIC timer
915 Can be useful to work around chipset bugs.
917 dis_ucode_ldr [X86] Disable the microcode loader.
919 dm= [DM] Allows early creation of a device-mapper device.
920 See Documentation/device-mapper/boot.txt.
922 dmasound= [HW,OSS] Sound subsystem buff
924 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
925 this option disables the debugging code at boot.
927 dma_debug_entries=<number>
928 This option allows to tune the number of preallocated
929 entries for DMA-API debugging code. One entry is
930 required per DMA-API allocation. Use this if the
931 DMA-API debugging code disables itself because the
932 architectural default is too low.
934 dma_debug_driver=<driver_name>
935 With this option the DMA-API debugging driver
936 filter feature can be enabled at boot time. Just
937 pass the driver to filter for as the parameter.
938 The filter can be disabled or changed to another
939 driver later using sysfs.
941 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
942 Broken monitors, graphic adapters, KVMs and EDIDless
943 panels may send no or incorrect EDID data sets.
944 This parameter allows to specify an EDID data sets
945 in the /lib/firmware directory that are used instead.
946 Generic built-in EDID data sets are used, if one of
947 edid/1024x768.bin, edid/1280x1024.bin,
948 edid/1680x1050.bin, or edid/1920x1080.bin is given
949 and no file with the same name exists. Details and
950 instructions how to build your own EDID data are
951 available in Documentation/EDID/HOWTO.txt. An EDID
952 data set will only be used for a particular connector,
953 if its name and a colon are prepended to the EDID
954 name. Each connector may use a unique EDID data
955 set by separating the files with a comma. An EDID
956 data set with no connector name will be used for
957 any connectors not explicitly specified.
961 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
962 module.dyndbg[="val"]
963 Enable debug messages at boot time. See
964 Documentation/dynamic-debug-howto.txt for details.
966 nompx [X86] Disables Intel Memory Protection Extensions.
967 See Documentation/x86/intel_mpx.txt for more
968 information about the feature.
971 on enable eager fpu restore
972 off disable eager fpu restore
973 auto selects the default scheme, which automatically
974 enables eagerfpu restore for xsaveopt.
976 module.async_probe [KNL]
977 Enable asynchronous probe on this module.
979 early_ioremap_debug [KNL]
980 Enable debug messages in early_ioremap support. This
981 is useful for tracking down temporary early mappings
982 which are not unmapped.
984 earlycon= [KNL] Output early console device and options.
986 When used with no options, the early console is
987 determined by the stdout-path property in device
991 Start an early, polled-mode console on a cadence serial
992 port at the specified address. The cadence serial port
993 must already be setup and configured. Options are not
996 uart[8250],io,<addr>[,options]
997 uart[8250],mmio,<addr>[,options]
998 uart[8250],mmio32,<addr>[,options]
999 uart[8250],mmio32be,<addr>[,options]
1000 uart[8250],0x<addr>[,options]
1001 Start an early, polled-mode console on the 8250/16550
1002 UART at the specified I/O port or MMIO address.
1003 MMIO inter-register address stride is either 8-bit
1004 (mmio) or 32-bit (mmio32 or mmio32be).
1005 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1006 to be equivalent to 'mmio'. 'options' are specified
1007 in the same format described for "console=ttyS<n>"; if
1008 unspecified, the h/w is not initialized.
1011 Start an early, polled-mode console on a pl011 serial
1012 port at the specified address. The pl011 serial port
1013 must already be setup and configured. Options are not
1017 Start an early, polled-mode console on an msm serial
1018 port at the specified address. The serial port
1019 must already be setup and configured. Options are not
1022 msm_serial_dm,<addr>
1023 Start an early, polled-mode console on an msm serial
1024 dm port at the specified address. The serial port
1025 must already be setup and configured. Options are not
1028 smh Use ARM semihosting calls for early console.
1036 Use early console provided by serial driver available
1037 on Samsung SoCs, requires selecting proper type and
1038 a correct base address of the selected UART port. The
1039 serial port must already be setup and configured.
1040 Options are not yet supported.
1044 Use early console provided by Freescale LP UART driver
1045 found on Freescale Vybrid and QorIQ LS1021A processors.
1046 A valid base address must be provided, and the serial
1047 port must already be setup and configured.
1049 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1053 earlyprintk=serial[,ttySn[,baudrate]]
1054 earlyprintk=serial[,0x...[,baudrate]]
1055 earlyprintk=ttySn[,baudrate]
1056 earlyprintk=dbgp[debugController#]
1057 earlyprintk=pciserial,bus:device.function[,baudrate]
1059 earlyprintk is useful when the kernel crashes before
1060 the normal console is initialized. It is not enabled by
1061 default because it has some cosmetic problems.
1063 Append ",keep" to not disable it when the real console
1066 Only one of vga, efi, serial, or usb debug port can
1069 Currently only ttyS0 and ttyS1 may be specified by
1070 name. Other I/O ports may be explicitly specified
1071 on some architectures (x86 and arm at least) by
1072 replacing ttySn with an I/O port address, like this:
1073 earlyprintk=serial,0x1008,115200
1074 You can find the port for a given device in
1075 /proc/tty/driver/serial:
1076 2: uart:ST16650V2 port:00001008 irq:18 ...
1078 Interaction with the standard serial driver is not
1081 The VGA and EFI output is eventually overwritten by
1084 The xen output can only be used by Xen PV guests.
1086 edac_report= [HW,EDAC] Control how to report EDAC event
1087 Format: {"on" | "off" | "force"}
1088 on: enable EDAC to report H/W event. May be overridden
1089 by other higher priority error reporting module.
1090 off: disable H/W event reporting through EDAC.
1091 force: enforce the use of EDAC to report H/W event.
1094 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1097 This is designed to be used in conjunction with
1098 the boot argument: earlyprintk=vga
1101 Format: {"off" | "on" | "skip[mbr]"}
1104 Format: { "old_map", "nochunk", "noruntime", "debug" }
1105 old_map [X86-64]: switch to the old ioremap-based EFI
1106 runtime services mapping. 32-bit still uses this one by
1108 nochunk: disable reading files in "chunks" in the EFI
1109 boot stub, as chunking can cause problems with some
1110 firmware implementations.
1111 noruntime : disable EFI runtime services support
1112 debug: enable misc debug output
1114 efi_no_storage_paranoia [EFI; X86]
1115 Using this parameter you can use more than 50% of
1116 your efi variable storage. Use this parameter only if
1117 you are really sure that your UEFI does sane gc and
1118 fulfills the spec otherwise your board may brick.
1120 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1121 Add arbitrary attribute to specific memory range by
1122 updating original EFI memory map.
1123 Region of memory which aa attribute is added to is
1125 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1126 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1127 attribute is added to range 0x100000000-0x180000000 and
1128 0x10a0000000-0x1120000000.
1130 Using this parameter you can do debugging of EFI memmap
1131 related feature. For example, you can do debugging of
1132 Address Range Mirroring feature even if your box
1135 eisa_irq_edge= [PARISC,HW]
1136 See header of drivers/parisc/eisa.c.
1139 See comment before function elanfreq_setup() in
1140 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1143 Format: {"cfq" | "deadline" | "noop"}
1144 See Documentation/block/cfq-iosched.txt and
1145 Documentation/block/deadline-iosched.txt for details.
1147 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1148 Specifies physical address of start of kernel core
1149 image elf header and optionally the size. Generally
1150 kexec loader will pass this option to capture kernel.
1151 See Documentation/kdump/kdump.txt for details.
1153 enable_mtrr_cleanup [X86]
1154 The kernel tries to adjust MTRR layout from continuous
1155 to discrete, to make X server driver able to add WB
1156 entry later. This parameter enables that.
1158 enable_timer_pin_1 [X86]
1159 Enable PIN 1 of APIC timer
1160 Can be useful to work around chipset bugs
1161 (in particular on some ATI chipsets).
1162 The kernel tries to set a reasonable default.
1164 enforcing [SELINUX] Set initial enforcing status.
1166 See security/selinux/Kconfig help text.
1167 0 -- permissive (log only, no denials).
1168 1 -- enforcing (deny and log).
1170 Value can be changed at runtime via /selinux/enforce.
1173 Disable Error Record Serialization Table (ERST)
1176 ether= [HW,NET] Ethernet cards parameters
1177 This option is obsoleted by the "netdev=" option, which
1178 has equivalent usage. See its documentation for details.
1182 Permit 'security.evm' to be updated regardless of
1183 current integrity status.
1187 fail_make_request=[KNL]
1188 General fault injection mechanism.
1189 Format: <interval>,<probability>,<space>,<times>
1190 See also Documentation/fault-injection/.
1193 See Documentation/blockdev/floppy.txt.
1195 force_pal_cache_flush
1196 [IA-64] Avoid check_sal_cache_flush which may hang on
1197 buggy SAL_CACHE_FLUSH implementations. Using this
1198 parameter will force ia64_sal_cache_flush to call
1199 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1202 Forcefully enable Physical Address Extension (PAE).
1203 Many Pentium M systems disable PAE but may have a
1204 functionally usable PAE implementation.
1205 Warning: use of this parameter will taint the kernel
1206 and may cause unknown problems.
1209 [FTRACE] will set and start the specified tracer
1210 as early as possible in order to facilitate early
1213 ftrace_dump_on_oops[=orig_cpu]
1214 [FTRACE] will dump the trace buffers on oops.
1215 If no parameter is passed, ftrace will dump
1216 buffers of all CPUs, but if you pass orig_cpu, it will
1217 dump only the buffer of the CPU that triggered the
1220 ftrace_filter=[function-list]
1221 [FTRACE] Limit the functions traced by the function
1222 tracer at boot up. function-list is a comma separated
1223 list of functions. This list can be changed at run
1224 time by the set_ftrace_filter file in the debugfs
1227 ftrace_notrace=[function-list]
1228 [FTRACE] Do not trace the functions specified in
1229 function-list. This list can be changed at run time
1230 by the set_ftrace_notrace file in the debugfs
1233 ftrace_graph_filter=[function-list]
1234 [FTRACE] Limit the top level callers functions traced
1235 by the function graph tracer at boot up.
1236 function-list is a comma separated list of functions
1237 that can be changed at run time by the
1238 set_graph_function file in the debugfs tracing directory.
1240 ftrace_graph_notrace=[function-list]
1241 [FTRACE] Do not trace from the functions specified in
1242 function-list. This list is a comma separated list of
1243 functions that can be changed at run time by the
1244 set_graph_notrace file in the debugfs tracing directory.
1247 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1248 support via parallel port (up to 5 devices per port)
1249 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1250 See also Documentation/input/joystick-parport.txt
1254 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1258 gcov_persist= [GCOV] When non-zero (default), profiling data for
1259 kernel modules is saved and remains accessible via
1260 debugfs, even when the module is unloaded/reloaded.
1261 When zero, profiling data is discarded and associated
1262 debugfs files are removed at module unload time.
1264 goldfish [X86] Enable the goldfish android emulator platform.
1265 Don't use this when you are not running on the
1268 gpt [EFI] Forces disk with valid GPT signature but
1269 invalid Protective MBR to be treated as GPT. If the
1270 primary GPT is corrupted, it enables the backup/alternate
1271 GPT to be used instead.
1273 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1274 the "Enable 0" bit of the configuration register.
1277 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1278 the "Enable 0" bit of the configuration register.
1281 grcan.select= [HW] Select which physical interface to use.
1284 grcan.txsize= [HW] Sets the size of the tx buffer.
1285 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1287 grcan.rxsize= [HW] Sets the size of the rx buffer.
1288 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1291 hardlockup_all_cpu_backtrace=
1292 [KNL] Should the hard-lockup detector generate
1293 backtraces on all cpus.
1296 hashdist= [KNL,NUMA] Large hashes allocated during boot
1297 are distributed across NUMA nodes. Defaults on
1298 for 64-bit NUMA, off otherwise.
1299 Format: 0 | 1 (for off | on)
1301 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1303 hd= [EIDE] (E)IDE hard drive subsystem geometry
1304 Format: <cyl>,<head>,<sect>
1307 Disable Hardware Error Source Table (HEST) support;
1308 corresponding firmware-first mode error processing
1309 logic will be disabled.
1311 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1312 size of <nn>. This works even on boxes that have no
1313 highmem otherwise. This also works to reduce highmem
1314 size on bigger boxes.
1316 highres= [KNL] Enable/disable high resolution timer mode.
1317 Valid parameters: "on", "off"
1321 See Documentation/isdn/README.HiSax.
1325 hpet= [X86-32,HPET] option to control HPET usage
1326 Format: { enable (default) | disable | force |
1328 disable: disable HPET and use PIT instead
1329 force: allow force enabled of undocumented chips (ICH4,
1331 verbose: show contents of HPET registers during setup
1333 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1334 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1336 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1337 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1338 On x86-64 and powerpc, this option can be specified
1339 multiple times interleaved with hugepages= to reserve
1340 huge pages of different sizes. Valid pages sizes on
1341 x86-64 are 2M (when the CPU supports "pse") and 1G
1342 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1344 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1345 terminal devices. Valid values: 0..8
1346 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1347 If specified, z/VM IUCV HVC accepts connections
1348 from listed z/VM user IDs only.
1350 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1351 hardware thread id mappings.
1352 Format: <cpu>:<hwthread>
1355 Do not unregister boot console at start. This is only
1356 useful for debugging when something happens in the window
1357 between unregistering the boot console and initializing
1360 i2c_bus= [HW] Override the default board specific I2C bus speed
1361 or register an additional I2C bus that is not
1362 registered from board initialization code.
1366 i8042.debug [HW] Toggle i8042 debug mode
1367 i8042.unmask_kbd_data
1368 [HW] Enable printing of interrupt data from the KBD port
1369 (disabled by default, and as a pre-condition
1370 requires that i8042.debug=1 be enabled)
1371 i8042.direct [HW] Put keyboard port into non-translated mode
1372 i8042.dumbkbd [HW] Pretend that controller can only read data from
1373 keyboard and cannot control its state
1374 (Don't attempt to blink the leds)
1375 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1376 i8042.nokbd [HW] Don't check/create keyboard port
1377 i8042.noloop [HW] Disable the AUX Loopback command while probing
1379 i8042.nomux [HW] Don't check presence of an active multiplexing
1381 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1383 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1384 i8042.reset [HW] Reset the controller during init, cleanup and
1385 suspend-to-ram transitions, only during s2r
1386 transitions, or never reset
1387 Format: { 1 | Y | y | 0 | N | n }
1388 1, Y, y: always reset controller
1389 0, N, n: don't ever reset controller
1390 Default: only on s2r transitions on x86; most other
1391 architectures force reset to be always executed
1392 i8042.unlock [HW] Unlock (ignore) the keylock
1393 i8042.kbdreset [HW] Reset device connected to KBD port
1397 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1398 indicates that the driver is running on unsupported
1400 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1401 does not match list of supported models.
1403 [HW] Report power status in /proc/i8k
1404 (disabled by default)
1405 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1408 i915.invert_brightness=
1409 [DRM] Invert the sense of the variable that is used to
1410 set the brightness of the panel backlight. Normally a
1411 brightness value of 0 indicates backlight switched off,
1412 and the maximum of the brightness value sets the backlight
1413 to maximum brightness. If this parameter is set to 0
1414 (default) and the machine requires it, or this parameter
1415 is set to 1, a brightness value of 0 sets the backlight
1416 to maximum brightness, and the maximum of the brightness
1417 value switches the backlight off.
1418 -1 -- never invert brightness
1419 0 -- machine default
1420 1 -- force brightness inversion
1423 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1425 ide-core.nodma= [HW] (E)IDE subsystem
1426 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1427 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1428 .cdrom .chs .ignore_cable are additional options
1429 See Documentation/ide/ide.txt.
1431 ide-generic.probe-mask= [HW] (E)IDE subsystem
1433 Probe mask for legacy ISA IDE ports. Depending on
1434 platform up to 6 ports are supported, enabled by
1435 setting corresponding bits in the mask to 1. The
1436 default value is 0x0, which has a special meaning.
1437 On systems that have PCI, it triggers scanning the
1438 PCI bus for the first and the second port, which
1439 are then probed. On systems without PCI the value
1440 of 0x0 enables probing the two first ports as if it
1443 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1444 Claim all unknown PCI IDE storage controllers.
1447 Format: idle=poll, idle=halt, idle=nomwait
1448 Poll forces a polling idle loop that can slightly
1449 improve the performance of waking up a idle CPU, but
1450 will use a lot of power and make the system run hot.
1452 idle=halt: Halt is forced to be used for CPU idle.
1453 In such case C2/C3 won't be used again.
1454 idle=nomwait: Disable mwait for CPU C-states
1456 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1457 Format: { strict | legacy | 2008 | relaxed }
1460 Choose which programs will be accepted for execution
1461 based on the IEEE 754 NaN encoding(s) supported by
1462 the FPU and the NaN encoding requested with the value
1463 of an ELF file header flag individually set by each
1464 binary. Hardware implementations are permitted to
1465 support either or both of the legacy and the 2008 NaN
1468 Available settings are as follows:
1469 strict accept binaries that request a NaN encoding
1470 supported by the FPU
1471 legacy only accept legacy-NaN binaries, if supported
1473 2008 only accept 2008-NaN binaries, if supported
1475 relaxed accept any binaries regardless of whether
1476 supported by the FPU
1478 The FPU emulator is always able to support both NaN
1479 encodings, so if no FPU hardware is present or it has
1480 been disabled with 'nofpu', then the settings of
1481 'legacy' and '2008' strap the emulator accordingly,
1482 'relaxed' straps the emulator for both legacy-NaN and
1483 2008-NaN, whereas 'strict' enables legacy-NaN only on
1484 legacy processors and both NaN encodings on MIPS32 or
1487 The setting for ABS.fmt/NEG.fmt instruction execution
1488 mode generally follows that for the NaN encoding,
1489 except where unsupported by hardware.
1491 ignore_loglevel [KNL]
1492 Ignore loglevel setting - this will print /all/
1493 kernel messages to the console. Useful for debugging.
1494 We also add it as printk module parameter, so users
1495 could change it dynamically, usually by
1496 /sys/module/printk/parameters/ignore_loglevel.
1498 ihash_entries= [KNL]
1499 Set number of hash buckets for inode cache.
1501 ima_appraise= [IMA] appraise integrity measurements
1502 Format: { "off" | "enforce" | "fix" | "log" }
1505 ima_appraise_tcb [IMA]
1506 The builtin appraise policy appraises all files
1510 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1514 The list of supported hash algorithms is defined
1515 in crypto/hash_info.h.
1518 The builtin measurement policy to load during IMA
1519 setup. Specyfing "tcb" as the value, measures all
1520 programs exec'd, files mmap'd for exec, and all files
1521 opened with the read mode bit set by either the
1522 effective uid (euid=0) or uid=0.
1525 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1526 Load a policy which meets the needs of the Trusted
1527 Computing Base. This means IMA will measure all
1528 programs exec'd, files mmap'd for exec, and all files
1529 opened for read by uid=0.
1532 Select one of defined IMA measurements template formats.
1533 Formats: { "ima" | "ima-ng" | "ima-sig" }
1537 [IMA] Define a custom template format.
1538 Format: { "field1|...|fieldN" }
1540 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1541 Format: <min_file_size>
1542 Set the minimal file size for using asynchronous hash.
1543 If left unspecified, ahash usage is disabled.
1545 ahash performance varies for different data sizes on
1546 different crypto accelerators. This option can be used
1547 to achieve the best performance for a particular HW.
1549 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1551 Set hashing buffer size. Default: 4k.
1553 ahash performance varies for different chunk sizes on
1554 different crypto accelerators. This option can be used
1555 to achieve best performance for particular HW.
1559 Run specified binary instead of /sbin/init as init
1562 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1563 for working out where the kernel is dying during
1566 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1567 initcall functions. Useful for debugging built-in
1568 modules and initcalls.
1570 initrd= [BOOT] Specify the location of the initial ramdisk
1572 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1575 int_pln_enable [x86] Enable power limit notification interrupt
1577 integrity_audit=[IMA]
1578 Format: { "0" | "1" }
1579 0 -- basic integrity auditing messages. (Default)
1580 1 -- additional integrity auditing messages.
1582 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1584 Enable intel iommu driver.
1586 Disable intel iommu driver.
1587 igfx_off [Default Off]
1588 By default, gfx is mapped as normal device. If a gfx
1589 device has a dedicated DMAR unit, the DMAR unit is
1590 bypassed by not enabling DMAR with this option. In
1591 this case, gfx device will use physical address for
1594 With this option iommu will not optimize to look
1595 for io virtual address below 32-bit forcing dual
1596 address cycle on pci bus for cards supporting greater
1597 than 32-bit addressing. The default is to look
1598 for translation below 32-bit and if not available
1599 then look in the higher range.
1600 strict [Default Off]
1601 With this option on every unmap_single operation will
1602 result in a hardware IOTLB flush operation as opposed
1603 to batching them for performance.
1604 sp_off [Default Off]
1605 By default, super page will be supported if Intel IOMMU
1606 has the capability. With this option, super page will
1608 ecs_off [Default Off]
1609 By default, extended context tables will be supported if
1610 the hardware advertises that it has support both for the
1611 extended tables themselves, and also PASID support. With
1612 this option set, extended tables will not be used even
1613 on hardware which claims to support them.
1615 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1616 0 disables intel_idle and fall back on acpi_idle.
1617 1 to 6 specify maximum depth of C-state.
1621 Do not enable intel_pstate as the default
1622 scaling driver for the supported processors
1624 Enable intel_pstate on systems that prohibit it by default
1625 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1626 instead of acpi-cpufreq may disable platform features, such
1627 as thermal controls and power capping, that rely on ACPI
1628 P-States information being indicated to OSPM and therefore
1629 should be used with caution. This option does not work with
1630 processors that aren't supported by the intel_pstate driver
1631 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1633 Do not enable hardware P state control (HWP)
1636 Only load intel_pstate on systems which support
1637 hardware P state control (HWP) if available.
1639 intremap= [X86-64, Intel-IOMMU]
1640 on enable Interrupt Remapping (default)
1641 off disable Interrupt Remapping
1642 nosid disable Source ID checking
1644 BIOS x2APIC opt-out request will be ignored
1645 nopost disable Interrupt Posting
1647 iomem= Disable strict checking of access to MMIO memory
1648 strict regions from userspace.
1663 nobypass [PPC/POWERNV]
1664 Disable IOMMU bypass, using IOMMU for PCI devices.
1667 io7= [HW] IO7 for Marvel based alpha systems
1668 See comment before marvel_specify_io7 in
1669 arch/alpha/kernel/core_marvel.c.
1671 io_delay= [X86] I/O delay method
1673 Standard port 0x80 based delay
1675 Alternate port 0xed based delay (needed on some systems)
1677 Simple two microseconds delay
1682 See Documentation/filesystems/nfs/nfsroot.txt.
1685 When an interrupt is not handled search all handlers
1686 for it. Intended to get systems with badly broken
1690 When an interrupt is not handled search all handlers
1691 for it. Also check all handlers each timer
1692 interrupt. Intended to get systems with badly broken
1696 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1698 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1700 <cpu number>,...,<cpu number>
1702 <cpu number>-<cpu number>
1703 (must be a positive range in ascending order)
1705 <cpu number>,...,<cpu number>-<cpu number>
1707 This option can be used to specify one or more CPUs
1708 to isolate from the general SMP balancing and scheduling
1709 algorithms. You can move a process onto or off an
1710 "isolated" CPU via the CPU affinity syscalls or cpuset.
1711 <cpu number> begins at 0 and the maximum value is
1712 "number of CPUs in system - 1".
1714 This option is the preferred way to isolate CPUs. The
1715 alternative -- manually setting the CPU mask of all
1716 tasks in the system -- can cause problems and
1717 suboptimal load balancer performance.
1721 ivrs_ioapic [HW,X86_64]
1722 Provide an override to the IOAPIC-ID<->DEVICE-ID
1723 mapping provided in the IVRS ACPI table. For
1724 example, to map IOAPIC-ID decimal 10 to
1725 PCI device 00:14.0 write the parameter as:
1726 ivrs_ioapic[10]=00:14.0
1728 ivrs_hpet [HW,X86_64]
1729 Provide an override to the HPET-ID<->DEVICE-ID
1730 mapping provided in the IVRS ACPI table. For
1731 example, to map HPET-ID decimal 0 to
1732 PCI device 00:14.0 write the parameter as:
1733 ivrs_hpet[0]=00:14.0
1735 js= [HW,JOY] Analog joystick
1736 See Documentation/input/joystick.txt.
1739 Enable/disable kernel and module base offset ASLR
1740 (Address Space Layout Randomization) if built into
1741 the kernel. When CONFIG_HIBERNATION is selected,
1742 kASLR is disabled by default. When kASLR is enabled,
1743 hibernation will be disabled.
1747 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1748 specifies the amount of memory usable by the kernel
1749 for non-movable allocations. The requested amount is
1750 spread evenly throughout all nodes in the system. The
1751 remaining memory in each node is used for Movable
1752 pages. In the event, a node is too small to have both
1753 kernelcore and Movable pages, kernelcore pages will
1754 take priority and other nodes will have a larger number
1755 of Movable pages. The Movable zone is used for the
1756 allocation of pages that may be reclaimed or moved
1757 by the page migration subsystem. This means that
1758 HugeTLB pages may not be allocated from this zone.
1759 Note that allocations like PTEs-from-HighMem still
1760 use the HighMem zone if it exists, and the Normal
1761 zone if it does not.
1763 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1764 Format: <Controller#>[,poll interval]
1765 The controller # is the number of the ehci usb debug
1766 port as it is probed via PCI. The poll interval is
1767 optional and is the number seconds in between
1768 each poll cycle to the debug port in case you need
1769 the functionality for interrupting the kernel with
1770 gdb or control-c on the dbgp connection. When
1771 not using this parameter you use sysrq-g to break into
1772 the kernel debugger.
1774 kgdboc= [KGDB,HW] kgdb over consoles.
1775 Requires a tty driver that supports console polling,
1776 or a supported polling keyboard driver (non-usb).
1777 Serial only format: <serial_device>[,baud]
1778 keyboard only format: kbd
1779 keyboard and serial format: kbd,<serial_device>[,baud]
1780 Optional Kernel mode setting:
1781 kms, kbd format: kms,kbd
1782 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1784 kgdbwait [KGDB] Stop kernel execution and enter the
1785 kernel debugger at the earliest opportunity.
1787 kmac= [MIPS] korina ethernet MAC address.
1788 Configure the RouterBoard 532 series on-chip
1789 Ethernet adapter MAC address.
1791 kmemleak= [KNL] Boot-time kmemleak enable/disable
1792 Valid arguments: on, off
1794 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1797 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1798 Valid arguments: 0, 1, 2
1799 kmemcheck=0 (disabled)
1800 kmemcheck=1 (enabled)
1801 kmemcheck=2 (one-shot mode)
1802 Default: 2 (one-shot mode)
1804 kstack=N [X86] Print N words from the kernel stack
1807 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1808 Default is 0 (don't ignore, but inject #GP)
1810 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1814 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1815 Default is 1 (enabled)
1817 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1819 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1821 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1822 (virtualized MMU) support on capable Intel chips.
1823 Default is 1 (enabled)
1825 kvm-intel.emulate_invalid_guest_state=
1826 [KVM,Intel] Enable emulation of invalid guest states
1827 Default is 0 (disabled)
1829 kvm-intel.flexpriority=
1830 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1831 Default is 1 (enabled)
1834 [KVM,Intel] Enable VMX nesting (nVMX).
1835 Default is 0 (disabled)
1837 kvm-intel.unrestricted_guest=
1838 [KVM,Intel] Disable unrestricted guest feature
1839 (virtualized real and unpaged mode) on capable
1840 Intel chips. Default is 1 (enabled)
1842 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1843 feature (tagged TLBs) on capable Intel chips.
1844 Default is 1 (enabled)
1850 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1853 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1854 value for LAPIC timer one-shot implementation. Default
1855 back to the programmable timer unit in the LAPIC.
1857 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1860 libata.dma= [LIBATA] DMA control
1861 libata.dma=0 Disable all PATA and SATA DMA
1862 libata.dma=1 PATA and SATA Disk DMA only
1863 libata.dma=2 ATAPI (CDROM) DMA only
1864 libata.dma=4 Compact Flash DMA only
1865 Combinations also work, so libata.dma=3 enables DMA
1866 for disks and CDROMs, but not CFs.
1868 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1869 libata.ignore_hpa=0 keep BIOS limits (default)
1870 libata.ignore_hpa=1 ignore limits, using full disk
1872 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1876 libata.force= [LIBATA] Force configurations. The format is comma
1877 separated list of "[ID:]VAL" where ID is
1878 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1879 matching port, link or device. Basically, it matches
1880 the ATA ID string printed on console by libata. If
1881 the whole ID part is omitted, the last PORT and DEVICE
1882 values are used. If ID hasn't been specified yet, the
1883 configuration applies to all ports, links and devices.
1885 If only DEVICE is omitted, the parameter applies to
1886 the port and all links and devices behind it. DEVICE
1887 number of 0 either selects the first device or the
1888 first fan-out link behind PMP device. It does not
1889 select the host link. DEVICE number of 15 selects the
1890 host link and device attached to it.
1892 The VAL specifies the configuration to force. As long
1893 as there's no ambiguity shortcut notation is allowed.
1894 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1895 The following configurations can be forced.
1897 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1898 Any ID with matching PORT is used.
1900 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1902 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1903 udma[/][16,25,33,44,66,100,133] notation is also
1906 * [no]ncq: Turn on or off NCQ.
1908 * [no]ncqtrim: Turn off queued DSM TRIM.
1910 * nohrst, nosrst, norst: suppress hard, soft
1913 * rstonce: only attempt one reset during
1914 hot-unplug link recovery
1916 * dump_id: dump IDENTIFY data.
1918 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1920 * disable: Disable this device.
1922 If there are multiple matching configurations changing
1923 the same attribute, the last one is used.
1925 memblock=debug [KNL] Enable memblock debug messages.
1927 load_ramdisk= [RAM] List of ramdisks to load from floppy
1928 See Documentation/blockdev/ramdisk.txt.
1930 lockd.nlm_grace_period=P [NFS] Assign grace period.
1933 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1936 lockd.nlm_timeout=T [NFS] Assign timeout value.
1939 lockd.nlm_udpport=M [NFS] Assign UDP port.
1942 locktorture.nreaders_stress= [KNL]
1943 Set the number of locking read-acquisition kthreads.
1944 Defaults to being automatically set based on the
1945 number of online CPUs.
1947 locktorture.nwriters_stress= [KNL]
1948 Set the number of locking write-acquisition kthreads.
1950 locktorture.onoff_holdoff= [KNL]
1951 Set time (s) after boot for CPU-hotplug testing.
1953 locktorture.onoff_interval= [KNL]
1954 Set time (s) between CPU-hotplug operations, or
1955 zero to disable CPU-hotplug testing.
1957 locktorture.shuffle_interval= [KNL]
1958 Set task-shuffle interval (jiffies). Shuffling
1959 tasks allows some CPUs to go into dyntick-idle
1960 mode during the locktorture test.
1962 locktorture.shutdown_secs= [KNL]
1963 Set time (s) after boot system shutdown. This
1964 is useful for hands-off automated testing.
1966 locktorture.stat_interval= [KNL]
1967 Time (s) between statistics printk()s.
1969 locktorture.stutter= [KNL]
1970 Time (s) to stutter testing, for example,
1971 specifying five seconds causes the test to run for
1972 five seconds, wait for five seconds, and so on.
1973 This tests the locking primitive's ability to
1974 transition abruptly to and from idle.
1976 locktorture.torture_runnable= [BOOT]
1977 Start locktorture running at boot time.
1979 locktorture.torture_type= [KNL]
1980 Specify the locking implementation to test.
1982 locktorture.verbose= [KNL]
1983 Enable additional printk() statements.
1985 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1988 loglevel= All Kernel Messages with a loglevel smaller than the
1989 console loglevel will be printed to the console. It can
1990 also be changed with klogd or other programs. The
1991 loglevels are defined as follows:
1993 0 (KERN_EMERG) system is unusable
1994 1 (KERN_ALERT) action must be taken immediately
1995 2 (KERN_CRIT) critical conditions
1996 3 (KERN_ERR) error conditions
1997 4 (KERN_WARNING) warning conditions
1998 5 (KERN_NOTICE) normal but significant condition
1999 6 (KERN_INFO) informational
2000 7 (KERN_DEBUG) debug-level messages
2002 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2003 in bytes. n must be a power of two and greater
2004 than the minimal size. The minimal size is defined
2005 by LOG_BUF_SHIFT kernel config parameter. There is
2006 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2007 that allows to increase the default size depending on
2008 the number of CPUs. See init/Kconfig for more details.
2010 logo.nologo [FB] Disables display of the built-in Linux logo.
2011 This may be used to provide more screen space for
2012 kernel log messages and is useful when debugging
2013 kernel boot problems.
2015 lp=0 [LP] Specify parallel ports to use, e.g,
2016 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2017 lp=reset first parallel port). 'lp=0' disables the
2018 lp=auto printer driver. 'lp=reset' (which can be
2019 specified in addition to the ports) causes
2020 attached printers to be reset. Using
2021 lp=port1,port2,... specifies the parallel ports
2022 to associate lp devices with, starting with
2023 lp0. A port specification may be 'none' to skip
2024 that lp device, or a parport name such as
2025 'parport0'. Specifying 'lp=auto' instead of a
2026 port specification list means that device IDs
2027 from each port should be examined, to see if
2028 an IEEE 1284-compliant printer is attached; if
2029 so, the driver will manage that printer.
2030 See also header of drivers/char/lp.c.
2033 Sets loops_per_jiffy to given constant, thus avoiding
2034 time-consuming boot-time autodetection (up to 250 ms per
2035 CPU). 0 enables autodetection (default). To determine
2036 the correct value for your kernel, boot with normal
2037 autodetection and see what value is printed. Note that
2038 on SMP systems the preset will be applied to all CPUs,
2039 which is likely to cause problems if your CPUs need
2040 significantly divergent settings. An incorrect value
2041 will cause delays in the kernel to be wrong, leading to
2042 unpredictable I/O errors and other breakage. Although
2043 unlikely, in the extreme case this might damage your
2047 Format: <io>,<irq>,<dma>
2049 machvec= [IA-64] Force the use of a particular machine-vector
2050 (machvec) in a generic kernel.
2051 Example: machvec=hpzx1_swiotlb
2053 machtype= [Loongson] Share the same kernel image file between different
2055 Example: machtype=lemote-yeeloong-2f-7inch
2057 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2058 than or equal to this physical address is ignored.
2060 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2061 should make use of. maxcpus=n : n >= 0 limits the
2062 kernel to using 'n' processors. n=0 is a special case,
2063 it is equivalent to "nosmp", which also disables
2066 max_loop= [LOOP] The number of loop block devices that get
2067 (loop.max_loop) unconditionally pre-created at init time. The default
2068 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2069 of statically allocating a predefined number, loop
2070 devices can be requested on-demand with the
2071 /dev/loop-control interface.
2073 mce [X86-32] Machine Check Exception
2075 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2077 md= [HW] RAID subsystems devices and level
2078 See Documentation/md.txt.
2081 Format: <first>,<last>
2082 Specifies range of consoles to be captured by the MDA.
2084 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2085 Amount of memory to be used when the kernel is not able
2086 to see the whole system memory or for test.
2087 [X86] Work as limiting max address. Use together
2088 with memmap= to avoid physical address space collisions.
2089 Without memmap= PCI devices could be placed at addresses
2090 belonging to unused RAM.
2092 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2096 [KNL,SH] Allow user to override the default size for
2097 per-device physically contiguous DMA buffers.
2099 memmap=exactmap [KNL,X86] Enable setting of an exact
2100 E820 memory map, as specified by the user.
2101 Such memmap=exactmap lines can be constructed based on
2102 BIOS output or other requirements. See the memmap=nn@ss
2105 memmap=nn[KMG]@ss[KMG]
2106 [KNL] Force usage of a specific region of memory.
2107 Region of memory to be used is from ss to ss+nn.
2109 memmap=nn[KMG]#ss[KMG]
2110 [KNL,ACPI] Mark specific memory as ACPI data.
2111 Region of memory to be marked is from ss to ss+nn.
2113 memmap=nn[KMG]$ss[KMG]
2114 [KNL,ACPI] Mark specific memory as reserved.
2115 Region of memory to be reserved is from ss to ss+nn.
2116 Example: Exclude memory from 0x18690000-0x1869ffff
2117 memmap=64K$0x18690000
2119 memmap=0x10000$0x18690000
2121 memmap=nn[KMG]!ss[KMG]
2122 [KNL,X86] Mark specific memory as protected.
2123 Region of memory to be used, from ss to ss+nn.
2124 The memory region may be marked as e820 type 12 (0xc)
2125 and is NVDIMM or ADR memory.
2127 memory_corruption_check=0/1 [X86]
2128 Some BIOSes seem to corrupt the first 64k of
2129 memory when doing things like suspend/resume.
2130 Setting this option will scan the memory
2131 looking for corruption. Enabling this will
2132 both detect corruption and prevent the kernel
2133 from using the memory being corrupted.
2134 However, its intended as a diagnostic tool; if
2135 repeatable BIOS-originated corruption always
2136 affects the same memory, you can use memmap=
2137 to prevent the kernel from using that memory.
2139 memory_corruption_check_size=size [X86]
2140 By default it checks for corruption in the low
2141 64k, making this memory unavailable for normal
2142 use. Use this parameter to scan for
2143 corruption in more or less memory.
2145 memory_corruption_check_period=seconds [X86]
2146 By default it checks for corruption every 60
2147 seconds. Use this parameter to check at some
2148 other rate. 0 disables periodic checking.
2150 memtest= [KNL,X86,ARM] Enable memtest
2152 default : 0 <disable>
2153 Specifies the number of memtest passes to be
2154 performed. Each pass selects another test
2155 pattern from a given set of patterns. Memtest
2156 fills the memory with this pattern, validates
2157 memory contents and reserves bad memory
2158 regions that are detected.
2160 meye.*= [HW] Set MotionEye Camera parameters
2161 See Documentation/video4linux/meye.txt.
2163 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2164 Multi-Function General Purpose Timers on AMD Geode
2167 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2168 the BIOS has incorrectly applied a workaround. TinyBIOS
2169 version 0.98 is known to be affected, 0.99 fixes the
2170 problem by letting the user disable the workaround.
2174 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2175 physical address is ignored.
2177 mini2440= [ARM,HW,KNL]
2178 Format:[0..2][b][c][t]
2180 MINI2440 configuration specification:
2181 0 - The attached screen is the 3.5" TFT
2182 1 - The attached screen is the 7" TFT
2183 2 - The VGA Shield is attached (1024x768)
2184 Leaving out the screen size parameter will not load
2185 the TFT driver, and the framebuffer will be left
2187 b - Enable backlight. The TFT backlight pin will be
2188 linked to the kernel VESA blanking code and a GPIO
2189 LED. This parameter is not necessary when using the
2191 c - Enable the s3c camera interface.
2192 t - Reserved for enabling touchscreen support. The
2193 touchscreen support is not enabled in the mainstream
2194 kernel as of 2.6.30, a preliminary port can be found
2195 in the "bleeding edge" mini2440 support kernel at
2196 http://repo.or.cz/w/linux-2.6/mini2440.git
2199 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2200 parameter allows control of the logging verbosity for
2201 the additional memory initialisation checks. A value
2202 of 0 disables mminit logging and a level of 4 will
2203 log everything. Information is printed at KERN_DEBUG
2204 so loglevel=8 may also need to be specified.
2207 [KNL] When CONFIG_MODULE_SIG is set, this means that
2208 modules without (valid) signatures will fail to load.
2209 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2210 is always true, so this option does nothing.
2213 [MOUSE] Maximum time between finger touching and
2214 leaving touchpad surface for touch to be considered
2215 a tap and be reported as a left button click (for
2216 touchpads working in absolute mode only).
2218 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2219 reporting absolute coordinates, such as tablets
2220 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2221 reporting absolute coordinates, such as tablets
2223 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2224 is similar to kernelcore except it specifies the
2225 amount of memory used for migratable allocations.
2226 If both kernelcore and movablecore is specified,
2227 then kernelcore will be at *least* the specified
2228 value but may be more. If movablecore on its own
2229 is specified, the administrator must be careful
2230 that the amount of memory usable for all allocations
2233 movable_node [KNL,X86] Boot-time switch to enable the effects
2234 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2236 MTD_Partition= [MTD]
2237 Format: <name>,<region-number>,<size>,<offset>
2239 MTD_Region= [MTD] Format:
2240 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2243 See drivers/mtd/cmdlinepart.c.
2245 multitce=off [PPC] This parameter disables the use of the pSeries
2246 firmware feature for updating multiple TCE entries
2249 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2251 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2253 boundary - index of last SLC block on Flex-OneNAND.
2254 The remaining blocks are configured as MLC blocks.
2255 lock - Configure if Flex-OneNAND boundary should be locked.
2256 Once locked, the boundary cannot be changed.
2257 1 indicates lock status, 0 indicates unlock status.
2260 ARM/S3C2412 JIVE boot control
2262 See arch/arm/mach-s3c2412/mach-jive.c
2264 mtouchusb.raw_coordinates=
2265 [HW] Make the MicroTouch USB driver use raw coordinates
2266 ('y', default) or cooked coordinates ('n')
2268 mtrr_chunk_size=nn[KMG] [X86]
2269 used for mtrr cleanup. It is largest continuous chunk
2270 that could hold holes aka. UC entries.
2272 mtrr_gran_size=nn[KMG] [X86]
2273 Used for mtrr cleanup. It is granularity of mtrr block.
2275 Large value could prevent small alignment from
2278 mtrr_spare_reg_nr=n [X86]
2280 Range: 0,7 : spare reg number
2282 Used for mtrr cleanup. It is spare mtrr entries number.
2283 Set to 2 or more if your graphical card needs more.
2285 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2287 netdev= [NET] Network devices parameters
2288 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2289 Note that mem_start is often overloaded to mean
2290 something different and driver-specific.
2291 This usage is only documented in each driver source
2295 [NETFILTER] Enable connection tracking flow accounting
2296 0 to disable accounting
2297 1 to enable accounting
2300 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2301 See Documentation/filesystems/nfs/nfsroot.txt.
2303 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2304 See Documentation/filesystems/nfs/nfsroot.txt.
2306 nfsrootdebug [NFS] enable nfsroot debugging messages.
2307 See Documentation/filesystems/nfs/nfsroot.txt.
2309 nfs.callback_tcpport=
2310 [NFS] set the TCP port on which the NFSv4 callback
2311 channel should listen.
2314 [NFS] sets the pathname to the program which is used
2315 to update the NFS client cache entries.
2317 nfs.cache_getent_timeout=
2318 [NFS] sets the timeout after which an attempt to
2319 update a cache entry is deemed to have failed.
2321 nfs.idmap_cache_timeout=
2322 [NFS] set the maximum lifetime for idmapper cache
2326 [NFS] enable 64-bit inode numbers.
2327 If zero, the NFS client will fake up a 32-bit inode
2328 number for the readdir() and stat() syscalls instead
2329 of returning the full 64-bit number.
2330 The default is to return 64-bit inode numbers.
2332 nfs.max_session_slots=
2333 [NFSv4.1] Sets the maximum number of session slots
2334 the client will attempt to negotiate with the server.
2335 This limits the number of simultaneous RPC requests
2336 that the client can send to the NFSv4.1 server.
2337 Note that there is little point in setting this
2338 value higher than the max_tcp_slot_table_limit.
2340 nfs.nfs4_disable_idmapping=
2341 [NFSv4] When set to the default of '1', this option
2342 ensures that both the RPC level authentication
2343 scheme and the NFS level operations agree to use
2344 numeric uids/gids if the mount is using the
2345 'sec=sys' security flavour. In effect it is
2346 disabling idmapping, which can make migration from
2347 legacy NFSv2/v3 systems to NFSv4 easier.
2348 Servers that do not support this mode of operation
2349 will be autodetected by the client, and it will fall
2350 back to using the idmapper.
2351 To turn off this behaviour, set the value to '0'.
2353 [NFS4] Specify an additional fixed unique ident-
2354 ification string that NFSv4 clients can insert into
2355 their nfs_client_id4 string. This is typically a
2356 UUID that is generated at system install time.
2358 nfs.send_implementation_id =
2359 [NFSv4.1] Send client implementation identification
2360 information in exchange_id requests.
2361 If zero, no implementation identification information
2363 The default is to send the implementation identification
2366 nfs.recover_lost_locks =
2367 [NFSv4] Attempt to recover locks that were lost due
2368 to a lease timeout on the server. Please note that
2369 doing this risks data corruption, since there are
2370 no guarantees that the file will remain unchanged
2371 after the locks are lost.
2372 If you want to enable the kernel legacy behaviour of
2373 attempting to recover these locks, then set this
2375 The default parameter value of '0' causes the kernel
2376 not to attempt recovery of lost locks.
2378 nfs4.layoutstats_timer =
2379 [NFSv4.2] Change the rate at which the kernel sends
2380 layoutstats to the pNFS metadata server.
2382 Setting this to value to 0 causes the kernel to use
2383 whatever value is the default set by the layout
2384 driver. A non-zero value sets the minimum interval
2385 in seconds between layoutstats transmissions.
2387 nfsd.nfs4_disable_idmapping=
2388 [NFSv4] When set to the default of '1', the NFSv4
2389 server will return only numeric uids and gids to
2390 clients using auth_sys, and will accept numeric uids
2391 and gids from such clients. This is intended to ease
2392 migration from NFSv2/v3.
2394 objlayoutdriver.osd_login_prog=
2395 [NFS] [OBJLAYOUT] sets the pathname to the program which
2396 is used to automatically discover and login into new
2397 osd-targets. Please see:
2398 Documentation/filesystems/pnfs.txt for more explanations
2400 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2401 when a NMI is triggered.
2402 Format: [state][,regs][,debounce][,die]
2404 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2405 Format: [panic,][nopanic,][num]
2407 0 - turn hardlockup detector in nmi_watchdog off
2408 1 - turn hardlockup detector in nmi_watchdog on
2409 When panic is specified, panic when an NMI watchdog
2410 timeout occurs (or 'nopanic' to override the opposite
2411 default). To disable both hard and soft lockup detectors,
2412 please see 'nowatchdog'.
2413 This is useful when you use a panic=... timeout and
2414 need the box quickly up again.
2416 netpoll.carrier_timeout=
2417 [NET] Specifies amount of time (in seconds) that
2418 netpoll should wait for a carrier. By default netpoll
2421 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2422 emulation library even if a 387 maths coprocessor
2426 [HW] Never suspend the console
2427 Disable suspending of consoles during suspend and
2428 hibernate operations. Once disabled, debugging
2429 messages can reach various consoles while the rest
2430 of the system is being put to sleep (ie, while
2431 debugging driver suspend/resume hooks). This may
2432 not work reliably with all consoles, but is known
2433 to work with serial and VGA consoles.
2434 To facilitate more flexible debugging, we also add
2435 console_suspend, a printk module parameter to control
2436 it. Users could use console_suspend (usually
2437 /sys/module/printk/parameters/console_suspend) to
2438 turn on/off it dynamically.
2440 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2441 caches in the slab allocator. Saves per-node memory,
2442 but will impact performance.
2446 noapic [SMP,APIC] Tells the kernel to not make use of any
2447 IOAPICs that may be present in the system.
2449 noautogroup Disable scheduler automatic task group creation.
2451 nobats [PPC] Do not use BATs for mapping kernel lowmem
2452 on "Classic" PPC cores.
2456 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2458 nodelayacct [KNL] Disable per-task delay accounting
2460 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2462 nodsp [SH] Disable hardware DSP at boot time.
2464 noefi Disable EFI runtime services support.
2469 On X86-32 available only on PAE configured kernels.
2470 noexec=on: enable non-executable mappings (default)
2471 noexec=off: disable non-executable mappings
2474 Force indicating stack and heap as non-executable or
2475 executable regardless of PT_GNU_STACK entry or CPU XI
2476 (execute inhibit) support. Valid valuess are: on, off.
2477 noexec=on: force indicating non-executable
2479 noexec=off: force indicating executable
2481 If this parameter is omitted, stack and heap will be
2482 indicated non-executable or executable as they are
2483 actually set up, which depends on PT_GNU_STACK entry
2484 and possibly other factors (for instance, CPU XI
2486 NOTE: Using noexec=on on a system without CPU XI
2487 support is not recommended since there is no actual
2488 HW support that provide non-executable stack/heap.
2489 Use only for debugging purposes and not in a
2490 production environment.
2493 Disable SMAP (Supervisor Mode Access Prevention)
2494 even if it is supported by processor.
2497 Disable SMEP (Supervisor Mode Execution Prevention)
2498 even if it is supported by processor.
2501 This affects only 32-bit executables.
2502 noexec32=on: enable non-executable mappings (default)
2503 read doesn't imply executable mappings
2504 noexec32=off: disable non-executable mappings
2505 read implies executable mappings
2507 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2509 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2510 register save and restore. The kernel will only save
2511 legacy floating-point registers on task switch.
2513 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2515 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2516 (indirect branch prediction) vulnerability. System may
2517 allow data leaks with this option, which is equivalent
2520 noxsave [BUGS=X86] Disables x86 extended register state save
2521 and restore using xsave. The kernel will fallback to
2522 enabling legacy floating-point and sse state.
2524 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2525 register states. The kernel will fall back to use
2526 xsave to save the states. By using this parameter,
2527 performance of saving the states is degraded because
2528 xsave doesn't support modified optimization while
2529 xsaveopt supports it on xsaveopt enabled systems.
2531 noxsaves [X86] Disables xsaves and xrstors used in saving and
2532 restoring x86 extended register state in compacted
2533 form of xsave area. The kernel will fall back to use
2534 xsaveopt and xrstor to save and restore the states
2535 in standard form of xsave area. By using this
2536 parameter, xsave area per process might occupy more
2537 memory on xsaves enabled systems.
2539 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2540 wfi(ARM) instruction doesn't work correctly and not to
2541 use it. This is also useful when using JTAG debugger.
2543 no_file_caps Tells the kernel not to honor file capabilities. The
2544 only way then for a file to be executed with privilege
2545 is to be setuid root or executed by root.
2547 nohalt [IA-64] Tells the kernel not to use the power saving
2548 function PAL_HALT_LIGHT when idle. This increases
2549 power-consumption. On the positive side, it reduces
2550 interrupt wake-up latency, which may improve performance
2551 in certain environments such as networked servers or
2554 nohibernate [HIBERNATION] Disable hibernation and resume.
2556 nohz= [KNL] Boottime enable/disable dynamic ticks
2557 Valid arguments: on, off
2560 nohz_full= [KNL,BOOT]
2561 In kernels built with CONFIG_NO_HZ_FULL=y, set
2562 the specified list of CPUs whose tick will be stopped
2563 whenever possible. The boot CPU will be forced outside
2564 the range to maintain the timekeeping.
2565 The CPUs in this range must also be included in the
2568 noiotrap [SH] Disables trapped I/O port accesses.
2570 noirqdebug [X86-32] Disables the code which attempts to detect and
2571 disable unhandled interrupt sources.
2573 no_timer_check [X86,APIC] Disables the code which tests for
2574 broken timer IRQ sources.
2576 noisapnp [ISAPNP] Disables ISA PnP code.
2578 noinitrd [RAM] Tells the kernel not to load any configured
2581 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2583 [Deprecated - use intremap=off]
2587 noinvpcid [X86] Disable the INVPCID cpu feature.
2589 nojitter [IA-64] Disables jitter checking for ITC timers.
2591 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2593 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2596 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2597 steal time is computed, but won't influence scheduler
2600 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2602 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2604 noltlbs [PPC] Do not use large page/tlb entries for kernel
2605 lowmem mapping on PPC40x.
2607 nomca [IA-64] Disable machine check abort handling
2609 nomce [X86-32] Disable Machine Check Exception
2611 nomfgpt [X86-32] Disable Multi-Function General Purpose
2612 Timer usage (for AMD Geode machines).
2614 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2615 shutdown the other cpus. Instead use the REBOOT_VECTOR
2618 nomodule Disable module load
2620 nopat [X86] Disable PAT (page attribute table extension of
2621 pagetables) support.
2623 nopcid [X86-64] Disable the PCID cpu feature.
2625 norandmaps Don't use address space randomization. Equivalent to
2626 echo 0 > /proc/sys/kernel/randomize_va_space
2628 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2629 with UP alternatives
2631 nordrand [X86] Disable kernel use of the RDRAND and
2632 RDSEED instructions even if they are supported
2633 by the processor. RDRAND and RDSEED are still
2634 available to user space applications.
2636 noresume [SWSUSP] Disables resume and restores original swap
2639 no-scroll [VGA] Disables scrollback.
2640 This is required for the Braillex ib80-piezo Braille
2641 reader made by F.H. Papenmeier (Germany).
2645 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2647 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2648 and disable the IO APIC. legacy for "maxcpus=0".
2650 nosoftlockup [KNL] Disable the soft-lockup detector.
2652 nosync [HW,M68K] Disables sync negotiation for all devices.
2654 notsc [BUGS=X86-32] Disable Time Stamp Counter
2656 nousb [USB] Disable the USB subsystem
2658 nowatchdog [KNL] Disable both lockup detectors, i.e.
2659 soft-lockup and NMI watchdog (hard-lockup).
2663 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2665 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2666 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2667 Some features depend on CPU0. Known dependencies are:
2668 1. Resume from suspend/hibernate depends on CPU0.
2669 Suspend/hibernate will fail if CPU0 is offline and you
2670 need to online CPU0 before suspend/hibernate.
2671 2. PIC interrupts also depend on CPU0. CPU0 can't be
2672 removed if a PIC interrupt is detected.
2673 It's said poweroff/reboot may depend on CPU0 on some
2674 machines although I haven't seen such issues so far
2675 after CPU0 is offline on a few tested machines.
2676 If the dependencies are under your control, you can
2677 turn on cpu0_hotplug.
2679 nptcg= [IA-64] Override max number of concurrent global TLB
2680 purges which is reported from either PAL_VM_SUMMARY or
2683 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2684 could support. nr_cpus=n : n >= 1 limits the kernel to
2685 supporting 'n' processors. Later in runtime you can not
2686 use hotplug cpu feature to put more cpu back to online.
2687 just like you compile the kernel NR_CPUS=n
2689 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2691 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2692 Allowed values are enable and disable
2694 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2695 one of ['zone', 'node', 'default'] can be specified
2696 This can be set from sysctl after boot.
2697 See Documentation/sysctl/vm.txt for details.
2699 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2700 See Documentation/debugging-via-ohci1394.txt for more
2703 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2704 Rather than timing out after 20 ms if an EC
2705 command is not properly ACKed, override the length
2706 of the timeout. We have interrupts disabled while
2707 waiting for the ACK, so if this is set too high
2708 interrupts *may* be lost!
2710 omap_mux= [OMAP] Override bootloader pin multiplexing.
2711 Format: <mux_mode0.mode_name=value>...
2712 For example, to override I2C bus2:
2713 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2715 oprofile.timer= [HW]
2716 Use timer interrupt instead of performance counters
2718 oprofile.cpu_type= Force an oprofile cpu type
2719 This might be useful if you have an older oprofile
2720 userland or if you want common events.
2721 Format: { arch_perfmon }
2722 arch_perfmon: [X86] Force use of architectural
2723 perfmon on Intel CPUs instead of the
2724 CPU specific event set.
2725 timer: [X86] Force use of architectural NMI
2726 timer mode (see also oprofile.timer
2727 for generic hr timer mode)
2728 [s390] Force legacy basic mode sampling
2729 (report cpu_type "timer")
2731 oops=panic Always panic on oopses. Default is to just kill the
2732 process, but there is a small probability of
2733 deadlocking the machine.
2734 This will also cause panics on machine check exceptions.
2735 Useful together with panic=30 to trigger a reboot.
2738 See Documentation/sound/oss/oss-parameters.txt
2740 page_owner= [KNL] Boot-time page_owner enabling option.
2741 Storage of the information about who allocated
2742 each page is disabled in default. With this switch,
2744 on: enable the feature
2746 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2747 timeout > 0: seconds before rebooting
2748 timeout = 0: wait forever
2749 timeout < 0: reboot immediately
2752 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2755 crash_kexec_post_notifiers
2756 Run kdump after running panic-notifiers and dumping
2757 kmsg. This only for the users who doubt kdump always
2758 succeeds in any situation.
2759 Note that this also increases risks of kdump failure,
2760 because some panic notifiers can make the crashed
2761 kernel more unstable.
2763 parkbd.port= [HW] Parallel port number the keyboard adapter is
2764 connected to, default is 0.
2766 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2767 0 for XT, 1 for AT (default is AT).
2770 parport= [HW,PPT] Specify parallel ports. 0 disables.
2771 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2772 Use 'auto' to force the driver to use any
2773 IRQ/DMA settings detected (the default is to
2774 ignore detected IRQ/DMA settings because of
2775 possible conflicts). You can specify the base
2776 address, IRQ, and DMA settings; IRQ and DMA
2777 should be numbers, or 'auto' (for using detected
2778 settings on that particular port), or 'nofifo'
2779 (to avoid using a FIFO even if it is detected).
2780 Parallel ports are assigned in the order they
2781 are specified on the command line, starting
2784 parport_init_mode= [HW,PPT]
2785 Configure VIA parallel port to operate in
2786 a specific mode. This is necessary on Pegasos
2787 computer where firmware has no options for setting
2788 up parallel port mode and sets it to spp.
2789 Currently this function knows 686a and 8231 chips.
2790 Format: [spp|ps2|epp|ecp|ecpepp]
2793 Halt all CPUs after the first oops has been printed for
2794 the specified number of seconds. This is to be used if
2795 your oopses keep scrolling off the screen.
2800 See header of drivers/block/paride/pcd.c.
2801 See also Documentation/blockdev/paride.txt.
2803 pci=option[,option...] [PCI] various PCI subsystem options:
2804 earlydump [X86] dump PCI config space before the kernel
2806 off [X86] don't probe for the PCI bus
2807 bios [X86-32] force use of PCI BIOS, don't access
2808 the hardware directly. Use this if your machine
2809 has a non-standard PCI host bridge.
2810 nobios [X86-32] disallow use of PCI BIOS, only direct
2811 hardware access methods are allowed. Use this
2812 if you experience crashes upon bootup and you
2813 suspect they are caused by the BIOS.
2814 conf1 [X86] Force use of PCI Configuration
2816 conf2 [X86] Force use of PCI Configuration
2818 noaer [PCIE] If the PCIEAER kernel config parameter is
2819 enabled, this kernel boot option can be used to
2820 disable the use of PCIE advanced error reporting.
2821 nodomains [PCI] Disable support for multiple PCI
2822 root domains (aka PCI segments, in ACPI-speak).
2823 nommconf [X86] Disable use of MMCONFIG for PCI
2825 check_enable_amd_mmconf [X86] check for and enable
2826 properly configured MMIO access to PCI
2827 config space on AMD family 10h CPU
2828 nomsi [MSI] If the PCI_MSI kernel config parameter is
2829 enabled, this kernel boot option can be used to
2830 disable the use of MSI interrupts system-wide.
2831 noioapicquirk [APIC] Disable all boot interrupt quirks.
2832 Safety option to keep boot IRQs enabled. This
2833 should never be necessary.
2834 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2835 primary IO-APIC for bridges that cannot disable
2836 boot IRQs. This fixes a source of spurious IRQs
2837 when the system masks IRQs.
2838 noioapicreroute [APIC] Disable workaround that uses the
2839 boot IRQ equivalent of an IRQ that connects to
2840 a chipset where boot IRQs cannot be disabled.
2841 The opposite of ioapicreroute.
2842 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2843 routing table. These calls are known to be buggy
2844 on several machines and they hang the machine
2845 when used, but on other computers it's the only
2846 way to get the interrupt routing table. Try
2847 this option if the kernel is unable to allocate
2848 IRQs or discover secondary PCI buses on your
2850 rom [X86] Assign address space to expansion ROMs.
2851 Use with caution as certain devices share
2852 address decoders between ROMs and other
2854 norom [X86] Do not assign address space to
2855 expansion ROMs that do not already have
2856 BIOS assigned address ranges.
2857 nobar [X86] Do not assign address space to the
2858 BARs that weren't assigned by the BIOS.
2859 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2860 assigned automatically to PCI devices. You can
2861 make the kernel exclude IRQs of your ISA cards
2863 pirqaddr=0xAAAAA [X86] Specify the physical address
2864 of the PIRQ table (normally generated
2865 by the BIOS) if it is outside the
2866 F0000h-100000h range.
2867 lastbus=N [X86] Scan all buses thru bus #N. Can be
2868 useful if the kernel is unable to find your
2869 secondary buses and you want to tell it
2870 explicitly which ones they are.
2871 assign-busses [X86] Always assign all PCI bus
2872 numbers ourselves, overriding
2873 whatever the firmware may have done.
2874 usepirqmask [X86] Honor the possible IRQ mask stored
2875 in the BIOS $PIR table. This is needed on
2876 some systems with broken BIOSes, notably
2877 some HP Pavilion N5400 and Omnibook XE3
2878 notebooks. This will have no effect if ACPI
2879 IRQ routing is enabled.
2880 noacpi [X86] Do not use ACPI for IRQ routing
2881 or for PCI scanning.
2882 use_crs [X86] Use PCI host bridge window information
2883 from ACPI. On BIOSes from 2008 or later, this
2884 is enabled by default. If you need to use this,
2885 please report a bug.
2886 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2887 If you need to use this, please report a bug.
2888 routeirq Do IRQ routing for all PCI devices.
2889 This is normally done in pci_enable_device(),
2890 so this option is a temporary workaround
2891 for broken drivers that don't call it.
2892 skip_isa_align [X86] do not align io start addr, so can
2893 handle more pci cards
2894 firmware [ARM] Do not re-enumerate the bus but instead
2895 just use the configuration from the
2896 bootloader. This is currently used on
2897 IXP2000 systems where the bus has to be
2898 configured a certain way for adjunct CPUs.
2899 noearly [X86] Don't do any early type 1 scanning.
2900 This might help on some broken boards which
2901 machine check when some devices' config space
2902 is read. But various workarounds are disabled
2903 and some IOMMU drivers will not work.
2904 bfsort Sort PCI devices into breadth-first order.
2905 This sorting is done to get a device
2906 order compatible with older (<= 2.4) kernels.
2907 nobfsort Don't sort PCI devices into breadth-first order.
2908 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2909 tuning and use the BIOS-configured MPS defaults.
2910 pcie_bus_safe Set every device's MPS to the largest value
2911 supported by all devices below the root complex.
2912 pcie_bus_perf Set device MPS to the largest allowable MPS
2913 based on its parent bus. Also set MRRS (Max
2914 Read Request Size) to the largest supported
2915 value (no larger than the MPS that the device
2916 or bus can support) for best performance.
2917 pcie_bus_peer2peer Set every device's MPS to 128B, which
2918 every device is guaranteed to support. This
2919 configuration allows peer-to-peer DMA between
2920 any pair of devices, possibly at the cost of
2921 reduced performance. This also guarantees
2922 that hot-added devices will work.
2923 cbiosize=nn[KMG] The fixed amount of bus space which is
2924 reserved for the CardBus bridge's IO window.
2925 The default value is 256 bytes.
2926 cbmemsize=nn[KMG] The fixed amount of bus space which is
2927 reserved for the CardBus bridge's memory
2928 window. The default value is 64 megabytes.
2931 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2932 Specifies alignment and device to reassign
2933 aligned memory resources.
2934 If <order of align> is not specified,
2935 PAGE_SIZE is used as alignment.
2936 PCI-PCI bridge can be specified, if resource
2937 windows need to be expanded.
2938 ecrc= Enable/disable PCIe ECRC (transaction layer
2939 end-to-end CRC checking).
2940 bios: Use BIOS/firmware settings. This is the
2944 hpiosize=nn[KMG] The fixed amount of bus space which is
2945 reserved for hotplug bridge's IO window.
2946 Default size is 256 bytes.
2947 hpmemsize=nn[KMG] The fixed amount of bus space which is
2948 reserved for hotplug bridge's memory window.
2949 Default size is 2 megabytes.
2950 realloc= Enable/disable reallocating PCI bridge resources
2951 if allocations done by BIOS are too small to
2952 accommodate resources required by all child
2954 off: Turn realloc off
2956 realloc same as realloc=on
2957 noari do not use PCIe ARI.
2958 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2959 only look for one device below a PCIe downstream
2962 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2965 force Enable ASPM even on devices that claim not to support it.
2966 WARNING: Forcing ASPM on may cause system lockups.
2968 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2969 nomsi Do not use MSI for PCI Express Native Hotplug (this
2970 makes all PCIe ports use INTx for hotplug services).
2972 pcie_ports= [PCIE] PCIe ports handling:
2973 auto Ask the BIOS whether or not to use native PCIe services
2974 associated with PCIe ports (PME, hot-plug, AER). Use
2975 them only if that is allowed by the BIOS.
2976 native Use native PCIe services associated with PCIe ports
2978 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2981 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2982 nomsi Do not use MSI for native PCIe PME signaling (this makes
2983 all PCIe root ports use INTx for all services).
2985 pcmv= [HW,PCMCIA] BadgePAD 4
2989 Keep all power-domains already enabled by bootloader on,
2990 even if no driver has claimed them. This is useful
2991 for debug and development, but should not be
2992 needed on a platform with proper driver support.
2995 See Documentation/blockdev/paride.txt.
2997 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3000 See arch/parisc/kernel/pdc_chassis.c
3002 percpu_alloc= Select which percpu first chunk allocator to use.
3003 Currently supported values are "embed" and "page".
3004 Archs may support subset or none of the selections.
3005 See comments in mm/percpu.c for details on each
3006 allocator. This parameter is primarily for debugging
3007 and performance comparison.
3010 See Documentation/blockdev/paride.txt.
3013 See Documentation/blockdev/paride.txt.
3015 pirq= [SMP,APIC] Manual mp-table setup
3016 See Documentation/x86/i386/IO-APIC.txt.
3018 plip= [PPT,NET] Parallel port network link
3019 Format: { parport<nr> | timid | 0 }
3020 See also Documentation/parport.txt.
3022 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3023 Override pmtimer IOPort with a hex value.
3027 Enable PNP debug messages (depends on the
3028 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3029 via /sys/module/pnp/parameters/debug. We always show
3030 current resource usage; turning this on also shows
3031 possible settings and some assignment information.
3037 { on | off | curr | res | no-curr | no-res }
3040 [ISAPNP] Exclude IRQs for the autoconfiguration
3043 [ISAPNP] Exclude DMAs for the autoconfiguration
3045 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3046 Ranges are in pairs (I/O port base and size).
3049 [ISAPNP] Exclude memory regions for the
3051 Ranges are in pairs (memory base and size).
3053 ports= [IP_VS_FTP] IPVS ftp helper module
3055 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3057 Format: <port>,<port>....
3059 print-fatal-signals=
3060 [KNL] debug: print fatal signals
3062 If enabled, warn about various signal handling
3063 related application anomalies: too many signals,
3064 too many POSIX.1 timers, fatal signals causing a
3067 If you hit the warning due to signal overflow,
3068 you might want to try "ulimit -i unlimited".
3072 printk.always_kmsg_dump=
3073 Trigger kmsg_dump for cases other than kernel oops or
3075 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3078 printk.time= Show timing data prefixed to each printk message line
3079 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3081 processor.max_cstate= [HW,ACPI]
3082 Limit processor to maximum C-state
3083 max_cstate=9 overrides any DMI blacklist limit.
3085 processor.nocst [HW,ACPI]
3086 Ignore the _CST method to determine C-states,
3087 instead using the legacy FADT method
3089 profile= [KNL] Enable kernel profiling via /proc/profile
3090 Format: [schedule,]<number>
3091 Param: "schedule" - profile schedule points.
3092 Param: <number> - step/bucket size as a power of 2 for
3093 statistical time based profiling.
3094 Param: "sleep" - profile D-state sleeping (millisecs).
3095 Requires CONFIG_SCHEDSTATS
3096 Param: "kvm" - profile VM exits.
3098 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3100 See Documentation/blockdev/ramdisk.txt.
3102 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3103 probe for; one of (bare|imps|exps|lifebook|any).
3104 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3106 psmouse.resetafter= [HW,MOUSE]
3107 Try to reset the device after so many bad packets
3110 [HW,MOUSE] Set desired mouse resolution, in dpi.
3111 psmouse.smartscroll=
3112 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3113 0 = disabled, 1 = enabled (default).
3115 pstore.backend= Specify the name of the pstore backend to use
3118 See Documentation/blockdev/paride.txt.
3120 pti= [X86_64] Control Page Table Isolation of user and
3121 kernel address spaces. Disabling this feature
3122 removes hardening, but improves performance of
3123 system calls and interrupts.
3125 on - unconditionally enable
3126 off - unconditionally disable
3127 auto - kernel detects whether your CPU model is
3128 vulnerable to issues that PTI mitigates
3130 Not specifying this option is equivalent to pti=auto.
3133 Equivalent to pti=off
3136 [KNL] Number of legacy pty's. Overwrites compiled-in
3139 quiet [KNL] Disable most log messages
3144 See Documentation/md.txt.
3146 ramdisk_blocksize= [RAM]
3147 See Documentation/blockdev/ramdisk.txt.
3149 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3150 See Documentation/blockdev/ramdisk.txt.
3153 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3154 the specified list of CPUs to be no-callback CPUs.
3155 Invocation of these CPUs' RCU callbacks will
3156 be offloaded to "rcuox/N" kthreads created for
3157 that purpose, where "x" is "b" for RCU-bh, "p"
3158 for RCU-preempt, and "s" for RCU-sched, and "N"
3159 is the CPU number. This reduces OS jitter on the
3160 offloaded CPUs, which can be useful for HPC and
3161 real-time workloads. It can also improve energy
3162 efficiency for asymmetric multiprocessors.
3165 Rather than requiring that offloaded CPUs
3166 (specified by rcu_nocbs= above) explicitly
3167 awaken the corresponding "rcuoN" kthreads,
3168 make these kthreads poll for callbacks.
3169 This improves the real-time response for the
3170 offloaded CPUs by relieving them of the need to
3171 wake up the corresponding kthread, but degrades
3172 energy efficiency by requiring that the kthreads
3173 periodically wake up to do the polling.
3175 rcutree.blimit= [KNL]
3176 Set maximum number of finished RCU callbacks to
3177 process in one batch.
3179 rcutree.dump_tree= [KNL]
3180 Dump the structure of the rcu_node combining tree
3181 out at early boot. This is used for diagnostic
3182 purposes, to verify correct tree setup.
3184 rcutree.gp_cleanup_delay= [KNL]
3185 Set the number of jiffies to delay each step of
3186 RCU grace-period cleanup. This only has effect
3187 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3189 rcutree.gp_init_delay= [KNL]
3190 Set the number of jiffies to delay each step of
3191 RCU grace-period initialization. This only has
3192 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3195 rcutree.gp_preinit_delay= [KNL]
3196 Set the number of jiffies to delay each step of
3197 RCU grace-period pre-initialization, that is,
3198 the propagation of recent CPU-hotplug changes up
3199 the rcu_node combining tree. This only has effect
3200 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3202 rcutree.rcu_fanout_exact= [KNL]
3203 Disable autobalancing of the rcu_node combining
3204 tree. This is used by rcutorture, and might
3205 possibly be useful for architectures having high
3206 cache-to-cache transfer latencies.
3208 rcutree.rcu_fanout_leaf= [KNL]
3209 Change the number of CPUs assigned to each
3210 leaf rcu_node structure. Useful for very
3211 large systems, which will choose the value 64,
3212 and for NUMA systems with large remote-access
3213 latencies, which will choose a value aligned
3214 with the appropriate hardware boundaries.
3216 rcutree.jiffies_till_sched_qs= [KNL]
3217 Set required age in jiffies for a
3218 given grace period before RCU starts
3219 soliciting quiescent-state help from
3220 rcu_note_context_switch().
3222 rcutree.jiffies_till_first_fqs= [KNL]
3223 Set delay from grace-period initialization to
3224 first attempt to force quiescent states.
3225 Units are jiffies, minimum value is zero,
3226 and maximum value is HZ.
3228 rcutree.jiffies_till_next_fqs= [KNL]
3229 Set delay between subsequent attempts to force
3230 quiescent states. Units are jiffies, minimum
3231 value is one, and maximum value is HZ.
3233 rcutree.kthread_prio= [KNL,BOOT]
3234 Set the SCHED_FIFO priority of the RCU per-CPU
3235 kthreads (rcuc/N). This value is also used for
3236 the priority of the RCU boost threads (rcub/N)
3237 and for the RCU grace-period kthreads (rcu_bh,
3238 rcu_preempt, and rcu_sched). If RCU_BOOST is
3239 set, valid values are 1-99 and the default is 1
3240 (the least-favored priority). Otherwise, when
3241 RCU_BOOST is not set, valid values are 0-99 and
3242 the default is zero (non-realtime operation).
3244 rcutree.rcu_nocb_leader_stride= [KNL]
3245 Set the number of NOCB kthread groups, which
3246 defaults to the square root of the number of
3247 CPUs. Larger numbers reduces the wakeup overhead
3248 on the per-CPU grace-period kthreads, but increases
3249 that same overhead on each group's leader.
3251 rcutree.qhimark= [KNL]
3252 Set threshold of queued RCU callbacks beyond which
3253 batch limiting is disabled.
3255 rcutree.qlowmark= [KNL]
3256 Set threshold of queued RCU callbacks below which
3257 batch limiting is re-enabled.
3259 rcutree.rcu_idle_gp_delay= [KNL]
3260 Set wakeup interval for idle CPUs that have
3261 RCU callbacks (RCU_FAST_NO_HZ=y).
3263 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3264 Set wakeup interval for idle CPUs that have
3265 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3266 Lazy RCU callbacks are those which RCU can
3267 prove do nothing more than free memory.
3269 rcutorture.cbflood_inter_holdoff= [KNL]
3270 Set holdoff time (jiffies) between successive
3271 callback-flood tests.
3273 rcutorture.cbflood_intra_holdoff= [KNL]
3274 Set holdoff time (jiffies) between successive
3275 bursts of callbacks within a given callback-flood
3278 rcutorture.cbflood_n_burst= [KNL]
3279 Set the number of bursts making up a given
3280 callback-flood test. Set this to zero to
3281 disable callback-flood testing.
3283 rcutorture.cbflood_n_per_burst= [KNL]
3284 Set the number of callbacks to be registered
3285 in a given burst of a callback-flood test.
3287 rcutorture.fqs_duration= [KNL]
3288 Set duration of force_quiescent_state bursts
3291 rcutorture.fqs_holdoff= [KNL]
3292 Set holdoff time within force_quiescent_state bursts
3295 rcutorture.fqs_stutter= [KNL]
3296 Set wait time between force_quiescent_state bursts
3299 rcutorture.gp_cond= [KNL]
3300 Use conditional/asynchronous update-side
3301 primitives, if available.
3303 rcutorture.gp_exp= [KNL]
3304 Use expedited update-side primitives, if available.
3306 rcutorture.gp_normal= [KNL]
3307 Use normal (non-expedited) asynchronous
3308 update-side primitives, if available.
3310 rcutorture.gp_sync= [KNL]
3311 Use normal (non-expedited) synchronous
3312 update-side primitives, if available. If all
3313 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3314 rcutorture.gp_normal=, and rcutorture.gp_sync=
3315 are zero, rcutorture acts as if is interpreted
3316 they are all non-zero.
3318 rcutorture.n_barrier_cbs= [KNL]
3319 Set callbacks/threads for rcu_barrier() testing.
3321 rcutorture.nfakewriters= [KNL]
3322 Set number of concurrent RCU writers. These just
3323 stress RCU, they don't participate in the actual
3324 test, hence the "fake".
3326 rcutorture.nreaders= [KNL]
3327 Set number of RCU readers. The value -1 selects
3328 N-1, where N is the number of CPUs. A value
3329 "n" less than -1 selects N-n-2, where N is again
3330 the number of CPUs. For example, -2 selects N
3331 (the number of CPUs), -3 selects N+1, and so on.
3333 rcutorture.object_debug= [KNL]
3334 Enable debug-object double-call_rcu() testing.
3336 rcutorture.onoff_holdoff= [KNL]
3337 Set time (s) after boot for CPU-hotplug testing.
3339 rcutorture.onoff_interval= [KNL]
3340 Set time (s) between CPU-hotplug operations, or
3341 zero to disable CPU-hotplug testing.
3343 rcutorture.shuffle_interval= [KNL]
3344 Set task-shuffle interval (s). Shuffling tasks
3345 allows some CPUs to go into dyntick-idle mode
3346 during the rcutorture test.
3348 rcutorture.shutdown_secs= [KNL]
3349 Set time (s) after boot system shutdown. This
3350 is useful for hands-off automated testing.
3352 rcutorture.stall_cpu= [KNL]
3353 Duration of CPU stall (s) to test RCU CPU stall
3354 warnings, zero to disable.
3356 rcutorture.stall_cpu_holdoff= [KNL]
3357 Time to wait (s) after boot before inducing stall.
3359 rcutorture.stat_interval= [KNL]
3360 Time (s) between statistics printk()s.
3362 rcutorture.stutter= [KNL]
3363 Time (s) to stutter testing, for example, specifying
3364 five seconds causes the test to run for five seconds,
3365 wait for five seconds, and so on. This tests RCU's
3366 ability to transition abruptly to and from idle.
3368 rcutorture.test_boost= [KNL]
3369 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3370 "Maybe" means test if the RCU implementation
3371 under test support RCU priority boosting.
3373 rcutorture.test_boost_duration= [KNL]
3374 Duration (s) of each individual boost test.
3376 rcutorture.test_boost_interval= [KNL]
3377 Interval (s) between each boost test.
3379 rcutorture.test_no_idle_hz= [KNL]
3380 Test RCU's dyntick-idle handling. See also the
3381 rcutorture.shuffle_interval parameter.
3383 rcutorture.torture_runnable= [BOOT]
3384 Start rcutorture running at boot time.
3386 rcutorture.torture_type= [KNL]
3387 Specify the RCU implementation to test.
3389 rcutorture.verbose= [KNL]
3390 Enable additional printk() statements.
3392 rcupdate.rcu_expedited= [KNL]
3393 Use expedited grace-period primitives, for
3394 example, synchronize_rcu_expedited() instead
3395 of synchronize_rcu(). This reduces latency,
3396 but can increase CPU utilization, degrade
3397 real-time latency, and degrade energy efficiency.
3399 rcupdate.rcu_cpu_stall_suppress= [KNL]
3400 Suppress RCU CPU stall warning messages.
3402 rcupdate.rcu_cpu_stall_timeout= [KNL]
3403 Set timeout for RCU CPU stall warning messages.
3405 rcupdate.rcu_task_stall_timeout= [KNL]
3406 Set timeout in jiffies for RCU task stall warning
3407 messages. Disable with a value less than or equal
3410 rcupdate.rcu_self_test= [KNL]
3411 Run the RCU early boot self tests
3413 rcupdate.rcu_self_test_bh= [KNL]
3414 Run the RCU bh early boot self tests
3416 rcupdate.rcu_self_test_sched= [KNL]
3417 Run the RCU sched early boot self tests
3421 Run specified binary instead of /init from the ramdisk,
3422 used for early userspace startup. See initrd.
3425 Format (x86 or x86_64):
3426 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3428 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3430 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3431 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3432 reboot_force is either force or not specified,
3433 reboot_cpu is s[mp]#### with #### being the processor
3434 to be used for rebooting.
3437 [KNL, SMP] Set scheduler's default relax_domain_level.
3438 See Documentation/cgroups/cpusets.txt.
3440 relative_sleep_states=
3441 [SUSPEND] Use sleep state labeling where the deepest
3442 state available other than hibernation is always "mem".
3443 Format: { "0" | "1" }
3444 0 -- Traditional sleep state labels.
3445 1 -- Relative sleep state labels.
3447 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3449 reservetop= [X86-32]
3451 Reserves a hole at the top of the kernel virtual
3456 Set the amount of memory to reserve for BIOS at
3457 the bottom of the address space.
3459 reset_devices [KNL] Force drivers to reset the underlying device
3460 during initialization.
3463 Specify the partition device for software suspend
3465 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3467 resume_offset= [SWSUSP]
3468 Specify the offset from the beginning of the partition
3469 given by "resume=" at which the swap header is located,
3470 in <PAGE_SIZE> units (needed only for swap files).
3471 See Documentation/power/swsusp-and-swap-files.txt
3473 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3474 read the resume files
3476 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3477 Useful for devices that are detected asynchronously
3478 (e.g. USB and MMC devices).
3480 hibernate= [HIBERNATION]
3481 noresume Don't check if there's a hibernation image
3482 present during boot.
3483 nocompress Don't compress/decompress hibernation images.
3484 no Disable hibernation and resume.
3486 retain_initrd [RAM] Keep initrd memory after extraction
3488 rfkill.default_state=
3489 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3490 etc. communication is blocked by default.
3493 rfkill.master_switch_mode=
3494 0 The "airplane mode" button does nothing.
3495 1 The "airplane mode" button toggles between everything
3496 blocked and the previous configuration.
3497 2 The "airplane mode" button toggles between everything
3498 blocked and everything unblocked.
3500 rhash_entries= [KNL,NET]
3501 Set number of hash buckets for route cache
3503 ro [KNL] Mount root device read-only on boot
3506 on Mark read-only kernel memory as read-only (default).
3507 off Leave read-only kernel memory writable for debugging.
3509 root= [KNL] Root filesystem
3510 See name_to_dev_t comment in init/do_mounts.c.
3512 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3513 mount the root filesystem
3515 rootflags= [KNL] Set root filesystem mount option string
3517 rootfstype= [KNL] Set root filesystem type
3519 rootwait [KNL] Wait (indefinitely) for root device to show up.
3520 Useful for devices that are detected asynchronously
3521 (e.g. USB and MMC devices).
3523 rproc_mem=nn[KMG][@address]
3524 [KNL,ARM,CMA] Remoteproc physical memory block.
3525 Memory area to be used by remote processor image,
3528 rw [KNL] Mount root device read-write on boot
3530 S [KNL] Run init in single mode
3532 s390_iommu= [HW,S390]
3533 Set s390 IOTLB flushing mode
3535 With strict flushing every unmap operation will result in
3536 an IOTLB flush. Default is lazy flushing before reuse,
3540 See drivers/net/irda/sa1100_ir.c.
3542 sbni= [NET] Granch SBNI12 leased line adapter
3544 sched_debug [KNL] Enables verbose scheduler debug messages.
3546 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3547 xtime_lock contention on larger systems, and/or RCU lock
3548 contention on all systems with CONFIG_MAXSMP set.
3549 Format: { "0" | "1" }
3550 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3552 Note: increases power consumption, thus should only be
3553 enabled if running jitter sensitive (HPC/RT) workloads.
3555 security= [SECURITY] Choose a security module to enable at boot.
3556 If this boot parameter is not specified, only the first
3557 security module asking for security registration will be
3558 loaded. An invalid security module name will be treated
3559 as if no module has been chosen.
3561 selinux= [SELINUX] Disable or enable SELinux at boot time.
3562 Format: { "0" | "1" }
3563 See security/selinux/Kconfig help text.
3566 Default value is set via kernel config option.
3567 If enabled at boot time, /selinux/disable can be used
3568 later to disable prior to initial policy load.
3570 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3571 Format: { "0" | "1" }
3572 See security/apparmor/Kconfig help text
3575 Default value is set via kernel config option.
3577 serialnumber [BUGS=X86-32]
3580 Maximal number of shapers.
3582 show_msr= [x86] show boot-time MSR settings
3583 Format: { <integer> }
3584 Show boot-time (BIOS-initialized) MSR settings.
3585 The parameter means the number of CPUs to show,
3586 for example 1 means boot CPU only.
3594 Disable merging of slabs with similar size. May be
3595 necessary if there is some reason to distinguish
3596 allocs to different slabs. Debug options disable
3597 merging on their own.
3598 For more information see Documentation/vm/slub.txt.
3600 slab_max_order= [MM, SLAB]
3601 Determines the maximum allowed order for slabs.
3602 A high setting may cause OOMs due to memory
3603 fragmentation. Defaults to 1 for systems with
3604 more than 32MB of RAM, 0 otherwise.
3606 slub_debug[=options[,slabs]] [MM, SLUB]
3607 Enabling slub_debug allows one to determine the
3608 culprit if slab objects become corrupted. Enabling
3609 slub_debug can create guard zones around objects and
3610 may poison objects when not in use. Also tracks the
3611 last alloc / free. For more information see
3612 Documentation/vm/slub.txt.
3614 slub_max_order= [MM, SLUB]
3615 Determines the maximum allowed order for slabs.
3616 A high setting may cause OOMs due to memory
3617 fragmentation. For more information see
3618 Documentation/vm/slub.txt.
3620 slub_min_objects= [MM, SLUB]
3621 The minimum number of objects per slab. SLUB will
3622 increase the slab order up to slub_max_order to
3623 generate a sufficiently large slab able to contain
3624 the number of objects indicated. The higher the number
3625 of objects the smaller the overhead of tracking slabs
3626 and the less frequently locks need to be acquired.
3627 For more information see Documentation/vm/slub.txt.
3629 slub_min_order= [MM, SLUB]
3630 Determines the minimum page order for slabs. Must be
3631 lower than slub_max_order.
3632 For more information see Documentation/vm/slub.txt.
3634 slub_nomerge [MM, SLUB]
3635 Same with slab_nomerge. This is supported for legacy.
3636 See slab_nomerge for more information.
3639 Format: <io1>[,<io2>[,...,<io8>]]
3641 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3642 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3643 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3644 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3645 smsc-ircc2.ircc_irq= [HW] IRQ line
3646 smsc-ircc2.ircc_dma= [HW] DMA channel
3647 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3648 0: Toshiba Satellite 1800 (GP data pin select)
3649 1: Fast pin select (default)
3653 [KNL] Should the soft-lockup detector generate panics.
3656 softlockup_all_cpu_backtrace=
3657 [KNL] Should the soft-lockup detector generate
3658 backtraces on all cpus.
3661 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3662 See Documentation/laptops/sonypi.txt
3664 spectre_v2= [X86] Control mitigation of Spectre variant 2
3665 (indirect branch speculation) vulnerability.
3667 on - unconditionally enable
3668 off - unconditionally disable
3669 auto - kernel detects whether your CPU model is
3672 Selecting 'on' will, and 'auto' may, choose a
3673 mitigation method at run time according to the
3674 CPU, the available microcode, the setting of the
3675 CONFIG_RETPOLINE configuration option, and the
3676 compiler with which the kernel was built.
3678 Specific mitigations can also be selected manually:
3680 retpoline - replace indirect branches
3681 retpoline,generic - google's original retpoline
3682 retpoline,amd - AMD-specific minimal thunk
3684 Not specifying this option is equivalent to
3687 spia_io_base= [HW,MTD]
3692 stack_guard_gap= [MM]
3693 override the default stack gap protection. The value
3694 is in page units and it defines how many pages prior
3695 to (for stacks growing down) resp. after (for stacks
3696 growing up) the main stack are reserved for no other
3697 mapping. Default value is 256 pages.
3700 Enabled the stack tracer on boot up.
3702 stacktrace_filter=[function-list]
3703 [FTRACE] Limit the functions that the stack tracer
3704 will trace at boot up. function-list is a comma separated
3705 list of functions. This list can be changed at run
3706 time by the stack_trace_filter file in the debugfs
3707 tracing directory. Note, this enables stack tracing
3708 and the stacktrace above is not needed.
3712 Set the STI (builtin display/keyboard on the HP-PARISC
3713 machines) console (graphic card) which should be used
3714 as the initial boot-console.
3715 See also comment in drivers/video/console/sticore.c.
3718 See comment in drivers/video/console/sticore.c.
3721 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3723 sunrpc.min_resvport=
3724 sunrpc.max_resvport=
3726 SunRPC servers often require that client requests
3727 originate from a privileged port (i.e. a port in the
3728 range 0 < portnr < 1024).
3729 An administrator who wishes to reserve some of these
3730 ports for other uses may adjust the range that the
3731 kernel's sunrpc client considers to be privileged
3732 using these two parameters to set the minimum and
3733 maximum port values.
3737 Control how the NFS server code allocates CPUs to
3738 service thread pools. Depending on how many NICs
3739 you have and where their interrupts are bound, this
3740 option will affect which CPUs will do NFS serving.
3741 Note: this parameter cannot be changed while the
3742 NFS server is running.
3744 auto the server chooses an appropriate mode
3745 automatically using heuristics
3746 global a single global pool contains all CPUs
3747 percpu one pool for each CPU
3748 pernode one pool for each NUMA node (equivalent
3749 to global on non-NUMA machines)
3751 sunrpc.tcp_slot_table_entries=
3752 sunrpc.udp_slot_table_entries=
3754 Sets the upper limit on the number of simultaneous
3755 RPC calls that can be sent from the client to a
3756 server. Increasing these values may allow you to
3757 improve throughput, but will also increase the
3758 amount of memory reserved for use by the client.
3760 suspend.pm_test_delay=
3762 Sets the number of seconds to remain in a suspend test
3763 mode before resuming the system (see
3764 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3765 is set. Default value is 5.
3768 [KNL] Enable accounting of swap in memory resource
3769 controller if no parameter or 1 is given or disable
3770 it if 0 is given (See Documentation/cgroups/memory.txt)
3772 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3773 Format: { <int> | force }
3774 <int> -- Number of I/O TLB slabs
3775 force -- force using of bounce buffers even if they
3776 wouldn't be automatically used by the kernel
3780 sysfs.deprecated=0|1 [KNL]
3781 Enable/disable old style sysfs layout for old udev
3782 on older distributions. When this option is enabled
3783 very new udev will not work anymore. When this option
3784 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3785 in older udev will not work anymore.
3786 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3787 the kernel configuration.
3789 sysrq_always_enabled
3791 Ignore sysrq setting - this boot parameter will
3792 neutralize any effect of /proc/sys/kernel/sysrq.
3793 Useful for debugging.
3795 tcpmhash_entries= [KNL,NET]
3796 Set the number of tcp_metrics_hash slots.
3797 Default value is 8192 or 16384 depending on total
3798 ram pages. This is used to specify the TCP metrics
3799 cache size. See Documentation/networking/ip-sysctl.txt
3800 "tcp_no_metrics_save" section for more details.
3804 test_suspend= [SUSPEND][,N]
3805 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3806 standby suspend) or "freeze" (for suspend type freeze)
3807 as the system sleep state during system startup with
3808 the optional capability to repeat N number of times.
3809 The system is woken from this state using a
3810 wakeup-capable RTC alarm.
3812 thash_entries= [KNL,NET]
3813 Set number of hash buckets for TCP connection
3815 thermal.act= [HW,ACPI]
3816 -1: disable all active trip points in all thermal zones
3817 <degrees C>: override all lowest active trip points
3819 thermal.crt= [HW,ACPI]
3820 -1: disable all critical trip points in all thermal zones
3821 <degrees C>: override all critical trip points
3823 thermal.nocrt= [HW,ACPI]
3824 Set to disable actions on ACPI thermal zone
3825 critical and hot trip points.
3827 thermal.off= [HW,ACPI]
3828 1: disable ACPI thermal control
3830 thermal.psv= [HW,ACPI]
3831 -1: disable all passive trip points
3832 <degrees C>: override all passive trip points to this
3835 thermal.tzp= [HW,ACPI]
3836 Specify global default ACPI thermal zone polling rate
3837 <deci-seconds>: poll all this frequency
3838 0: no polling (default)
3841 Force threading of all interrupt handlers except those
3842 marked explicitly IRQF_NO_THREAD.
3845 Enable the Transcendent memory driver if built-in.
3847 tmem.cleancache=0|1 [KNL, XEN]
3848 Default is on (1). Disable the usage of the cleancache
3849 API to send anonymous pages to the hypervisor.
3851 tmem.frontswap=0|1 [KNL, XEN]
3852 Default is on (1). Disable the usage of the frontswap
3853 API to send swap pages to the hypervisor. If disabled
3854 the selfballooning and selfshrinking are force disabled.
3856 tmem.selfballooning=0|1 [KNL, XEN]
3857 Default is on (1). Disable the driving of swap pages
3860 tmem.selfshrinking=0|1 [KNL, XEN]
3861 Default is on (1). Partial swapoff that immediately
3862 transfers pages from Xen hypervisor back to the
3863 kernel based on different criteria.
3867 Specify if the kernel should make use of the cpu
3868 topology information if the hardware supports this.
3869 The scheduler will make use of this information and
3870 e.g. base its process migration decisions on it.
3873 topology_updates= [KNL, PPC, NUMA]
3875 Specify if the kernel should ignore (off)
3876 topology updates sent by the hypervisor to this
3881 tpm_suspend_pcr=[HW,TPM]
3882 Format: integer pcr id
3883 Specify that at suspend time, the tpm driver
3884 should extend the specified pcr with zeros,
3885 as a workaround for some chips which fail to
3886 flush the last written pcr on TPM_SaveState.
3887 This will guarantee that all the other pcrs
3890 trace_buf_size=nn[KMG]
3891 [FTRACE] will set tracing buffer size on each cpu.
3893 trace_event=[event-list]
3894 [FTRACE] Set and start specified trace events in order
3895 to facilitate early boot debugging.
3896 See also Documentation/trace/events.txt
3898 trace_options=[option-list]
3899 [FTRACE] Enable or disable tracer options at boot.
3900 The option-list is a comma delimited list of options
3901 that can be enabled or disabled just as if you were
3902 to echo the option name into
3904 /sys/kernel/debug/tracing/trace_options
3906 For example, to enable stacktrace option (to dump the
3907 stack trace of each event), add to the command line:
3909 trace_options=stacktrace
3911 See also Documentation/trace/ftrace.txt "trace options"
3915 Have the tracepoints sent to printk as well as the
3916 tracing ring buffer. This is useful for early boot up
3917 where the system hangs or reboots and does not give the
3918 option for reading the tracing buffer or performing a
3919 ftrace_dump_on_oops.
3921 To turn off having tracepoints sent to printk,
3922 echo 0 > /proc/sys/kernel/tracepoint_printk
3923 Note, echoing 1 into this file without the
3924 tracepoint_printk kernel cmdline option has no effect.
3928 Having tracepoints sent to printk() and activating high
3929 frequency tracepoints such as irq or sched, can cause
3930 the system to live lock.
3933 [FTRACE] enable this option to disable tracing when a
3934 warning is hit. This turns off "tracing_on". Tracing can
3935 be enabled again by echoing '1' into the "tracing_on"
3936 file located in /sys/kernel/debug/tracing/
3938 This option is useful, as it disables the trace before
3939 the WARNING dump is called, which prevents the trace to
3940 be filled with content caused by the warning output.
3942 This option can also be set at run time via the sysctl
3943 option: kernel/traceoff_on_warning
3945 transparent_hugepage=
3947 Format: [always|madvise|never]
3948 Can be used to control the default behavior of the system
3949 with respect to transparent hugepages.
3950 See Documentation/vm/transhuge.txt for more details.
3952 tsc= Disable clocksource stability checks for TSC.
3954 [x86] reliable: mark tsc clocksource as reliable, this
3955 disables clocksource verification at runtime, as well
3956 as the stability checks done at bootup. Used to enable
3957 high-resolution timer mode on older hardware, and in
3958 virtualized environment.
3959 [x86] noirqtime: Do not use TSC to do irq accounting.
3960 Used to run time disable IRQ_TIME_ACCOUNTING on any
3961 platforms where RDTSC is slow and this accounting
3964 turbografx.map[2|3]= [HW,JOY]
3965 TurboGraFX parallel port interface
3967 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3968 See also Documentation/input/joystick-parport.txt
3970 udbg-immortal [PPC] When debugging early kernel crashes that
3971 happen after console_init() and before a proper
3972 console driver takes over, this boot options might
3973 help "seeing" what's going on.
3975 uhash_entries= [KNL,NET]
3976 Set number of hash buckets for UDP/UDP-Lite connections
3979 [USB] Ignore overcurrent events (default N).
3980 Some badly-designed motherboards generate lots of
3981 bogus events, for ports that aren't wired to
3982 anything. Set this parameter to avoid log spamming.
3983 Note that genuine overcurrent events won't be
3987 [X86] Cause panic on unknown NMI.
3989 usbcore.authorized_default=
3990 [USB] Default USB device authorization:
3991 (default -1 = authorized except for wireless USB,
3992 0 = not authorized, 1 = authorized)
3994 usbcore.autosuspend=
3995 [USB] The autosuspend time delay (in seconds) used
3996 for newly-detected USB devices (default 2). This
3997 is the time required before an idle device will be
3998 autosuspended. Devices for which the delay is set
3999 to a negative value won't be autosuspended at all.
4001 usbcore.usbfs_snoop=
4002 [USB] Set to log all usbfs traffic (default 0 = off).
4004 usbcore.blinkenlights=
4005 [USB] Set to cycle leds on hubs (default 0 = off).
4007 usbcore.old_scheme_first=
4008 [USB] Start with the old device initialization
4009 scheme (default 0 = off).
4011 usbcore.usbfs_memory_mb=
4012 [USB] Memory limit (in MB) for buffers allocated by
4013 usbfs (default = 16, 0 = max = 2047).
4015 usbcore.use_both_schemes=
4016 [USB] Try the other device initialization scheme
4017 if the first one fails (default 1 = enabled).
4019 usbcore.initial_descriptor_timeout=
4020 [USB] Specifies timeout for the initial 64-byte
4021 USB_REQ_GET_DESCRIPTOR request in milliseconds
4022 (default 5000 = 5.0 seconds).
4025 [USBHID] The interval which mice are to be polled at.
4027 usb-storage.delay_use=
4028 [UMS] The delay in seconds before a new device is
4029 scanned for Logical Units (default 1).
4032 [UMS] A list of quirks entries to supplement or
4033 override the built-in unusual_devs list. List
4034 entries are separated by commas. Each entry has
4035 the form VID:PID:Flags where VID and PID are Vendor
4036 and Product ID values (4-digit hex numbers) and
4037 Flags is a set of characters, each corresponding
4038 to a common usb-storage quirk flag as follows:
4039 a = SANE_SENSE (collect more than 18 bytes
4041 b = BAD_SENSE (don't collect more than 18
4042 bytes of sense data);
4043 c = FIX_CAPACITY (decrease the reported
4044 device capacity by one sector);
4045 d = NO_READ_DISC_INFO (don't use
4046 READ_DISC_INFO command);
4047 e = NO_READ_CAPACITY_16 (don't use
4048 READ_CAPACITY_16 command);
4049 f = NO_REPORT_OPCODES (don't use report opcodes
4051 g = MAX_SECTORS_240 (don't transfer more than
4052 240 sectors at a time, uas only);
4053 h = CAPACITY_HEURISTICS (decrease the
4054 reported device capacity by one
4055 sector if the number is odd);
4056 i = IGNORE_DEVICE (don't bind to this
4058 j = NO_REPORT_LUNS (don't use report luns
4060 l = NOT_LOCKABLE (don't try to lock and
4061 unlock ejectable media);
4062 m = MAX_SECTORS_64 (don't transfer more
4063 than 64 sectors = 32 KB at a time);
4064 n = INITIAL_READ10 (force a retry of the
4065 initial READ(10) command);
4066 o = CAPACITY_OK (accept the capacity
4067 reported by the device);
4068 p = WRITE_CACHE (the device cache is ON
4070 r = IGNORE_RESIDUE (the device reports
4071 bogus residue values);
4072 s = SINGLE_LUN (the device has only one
4074 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4075 commands, uas only);
4076 u = IGNORE_UAS (don't bind to the uas driver);
4077 w = NO_WP_DETECT (don't test whether the
4078 medium is write-protected).
4079 Example: quirks=0419:aaf5:rl,0421:0433:rc
4081 user_debug= [KNL,ARM]
4083 See arch/arm/Kconfig.debug help text.
4084 1 - undefined instruction events
4086 4 - invalid data aborts
4089 Example: user_debug=31
4092 [X86] Flags controlling user PTE allocations.
4094 nohigh = do not allocate PTE pages in
4095 HIGHMEM regardless of setting
4099 On X86_32, this is an alias for vdso32=. Otherwise:
4101 vdso=1: enable VDSO (the default)
4102 vdso=0: disable VDSO mapping
4104 vdso32= [X86] Control the 32-bit vDSO
4105 vdso32=1: enable 32-bit VDSO
4106 vdso32=0 or vdso32=2: disable 32-bit VDSO
4108 See the help text for CONFIG_COMPAT_VDSO for more
4109 details. If CONFIG_COMPAT_VDSO is set, the default is
4110 vdso32=0; otherwise, the default is vdso32=1.
4112 For compatibility with older kernels, vdso32=2 is an
4115 Try vdso32=0 if you encounter an error that says:
4116 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4119 vector=percpu: enable percpu vector domain
4121 video= [FB] Frame buffer configuration
4122 See Documentation/fb/modedb.txt.
4124 video.brightness_switch_enabled= [0,1]
4125 If set to 1, on receiving an ACPI notify event
4126 generated by hotkey, video driver will adjust brightness
4127 level and then send out the event to user space through
4128 the allocated input device; If set to 0, video driver
4129 will only send out the event without touching backlight
4134 [VMMIO] Memory mapped virtio (platform) device.
4136 <size>@<baseaddr>:<irq>[:<id>]
4138 <size> := size (can use standard suffixes
4140 <baseaddr> := physical base address
4141 <irq> := interrupt number (as passed to
4143 <id> := (optional) platform device id
4145 virtio_mmio.device=1K@0x100b0000:48:7
4147 Can be used multiple times for multiple devices.
4149 vga= [BOOT,X86-32] Select a particular video mode
4150 See Documentation/x86/boot.txt and
4151 Documentation/svga.txt.
4152 Use vga=ask for menu.
4153 This is actually a boot loader parameter; the value is
4154 passed to the kernel using a special protocol.
4156 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4157 size of <nn>. This can be used to increase the
4158 minimum size (128MB on x86). It can also be used to
4159 decrease the size and leave more room for directly
4162 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4165 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4168 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4172 Controls the behavior of vsyscalls (i.e. calls to
4173 fixed addresses of 0xffffffffff600x00 from legacy
4174 code). Most statically-linked binaries and older
4175 versions of glibc use these calls. Because these
4176 functions are at fixed addresses, they make nice
4177 targets for exploits that can control RIP.
4179 emulate [default] Vsyscalls turn into traps and are
4180 emulated reasonably safely.
4182 native Vsyscalls are native syscall instructions.
4183 This is a little bit faster than trapping
4184 and makes a few dynamic recompilers work
4185 better than they would in emulation mode.
4186 It also makes exploits much easier to write.
4188 none Vsyscalls don't work at all. This makes
4189 them quite hard to use for exploits but
4190 might break your system.
4192 vt.color= [VT] Default text color.
4193 Format: 0xYX, X = foreground, Y = background.
4194 Default: 0x07 = light gray on black.
4196 vt.cur_default= [VT] Default cursor shape.
4197 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4198 the parameters of the <Esc>[?A;B;Cc escape sequence;
4199 see VGA-softcursor.txt. Default: 2 = underline.
4201 vt.default_blu= [VT]
4202 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4203 Change the default blue palette of the console.
4204 This is a 16-member array composed of values
4207 vt.default_grn= [VT]
4208 Format: <green0>,<green1>,<green2>,...,<green15>
4209 Change the default green palette of the console.
4210 This is a 16-member array composed of values
4213 vt.default_red= [VT]
4214 Format: <red0>,<red1>,<red2>,...,<red15>
4215 Change the default red palette of the console.
4216 This is a 16-member array composed of values
4222 Set system-wide default UTF-8 mode for all tty's.
4223 Default is 1, i.e. UTF-8 mode is enabled for all
4224 newly opened terminals.
4226 vt.global_cursor_default=
4229 Set system-wide default for whether a cursor
4230 is shown on new VTs. Default is -1,
4231 i.e. cursors will be created by default unless
4232 overridden by individual drivers. 0 will hide
4233 cursors, 1 will display them.
4235 vt.italic= [VT] Default color for italic text; 0-15.
4238 vt.underline= [VT] Default color for underlined text; 0-15.
4241 watchdog timers [HW,WDT] For information on watchdog timers,
4242 see Documentation/watchdog/watchdog-parameters.txt
4243 or other driver-specific files in the
4244 Documentation/watchdog/ directory.
4246 workqueue.disable_numa
4247 By default, all work items queued to unbound
4248 workqueues are affine to the NUMA nodes they're
4249 issued on, which results in better behavior in
4250 general. If NUMA affinity needs to be disabled for
4251 whatever reason, this option can be used. Note
4252 that this also can be controlled per-workqueue for
4253 workqueues visible under /sys/bus/workqueue/.
4255 workqueue.power_efficient
4256 Per-cpu workqueues are generally preferred because
4257 they show better performance thanks to cache
4258 locality; unfortunately, per-cpu workqueues tend to
4259 be more power hungry than unbound workqueues.
4261 Enabling this makes the per-cpu workqueues which
4262 were observed to contribute significantly to power
4263 consumption unbound, leading to measurably lower
4264 power usage at the cost of small performance
4267 The default value of this parameter is determined by
4268 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4270 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4271 default x2apic cluster mode on platforms
4274 x86_intel_mid_timer= [X86-32,APBT]
4275 Choose timer option for x86 Intel MID platform.
4276 Two valid options are apbt timer only and lapic timer
4277 plus one apbt timer for broadcast timer.
4278 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4280 xen_512gb_limit [KNL,X86-64,XEN]
4281 Restricts the kernel running paravirtualized under Xen
4282 to use only up to 512 GB of RAM. The reason to do so is
4283 crash analysis tools and Xen tools for doing domain
4284 save/restore/migration must be enabled to handle larger
4287 xen_emul_unplug= [HW,X86,XEN]
4288 Unplug Xen emulated devices
4289 Format: [unplug0,][unplug1]
4290 ide-disks -- unplug primary master IDE devices
4291 aux-ide-disks -- unplug non-primary-master IDE devices
4292 nics -- unplug network devices
4293 all -- unplug all emulated devices (NICs and IDE disks)
4294 unnecessary -- unplugging emulated devices is
4295 unnecessary even if the host did not respond to
4297 never -- do not unplug even if version check succeeds
4299 xen_nopvspin [X86,XEN]
4300 Disables the ticketlock slowpath using Xen PV
4304 Disables the PV optimizations forcing the HVM guest to
4305 run as generic HVM guest with no PV drivers.
4307 xirc2ps_cs= [NET,PCMCIA]
4309 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4311 ______________________________________________________________________
4315 Add more DRM drivers.