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/cpufeatures.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 noaltinstr [S390] Disables alternative instructions patching
2447 (CPU alternatives feature).
2449 noapic [SMP,APIC] Tells the kernel to not make use of any
2450 IOAPICs that may be present in the system.
2452 noautogroup Disable scheduler automatic task group creation.
2454 nobats [PPC] Do not use BATs for mapping kernel lowmem
2455 on "Classic" PPC cores.
2459 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2461 nodelayacct [KNL] Disable per-task delay accounting
2463 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2465 nodsp [SH] Disable hardware DSP at boot time.
2467 noefi Disable EFI runtime services support.
2472 On X86-32 available only on PAE configured kernels.
2473 noexec=on: enable non-executable mappings (default)
2474 noexec=off: disable non-executable mappings
2477 Force indicating stack and heap as non-executable or
2478 executable regardless of PT_GNU_STACK entry or CPU XI
2479 (execute inhibit) support. Valid valuess are: on, off.
2480 noexec=on: force indicating non-executable
2482 noexec=off: force indicating executable
2484 If this parameter is omitted, stack and heap will be
2485 indicated non-executable or executable as they are
2486 actually set up, which depends on PT_GNU_STACK entry
2487 and possibly other factors (for instance, CPU XI
2489 NOTE: Using noexec=on on a system without CPU XI
2490 support is not recommended since there is no actual
2491 HW support that provide non-executable stack/heap.
2492 Use only for debugging purposes and not in a
2493 production environment.
2496 Disable SMAP (Supervisor Mode Access Prevention)
2497 even if it is supported by processor.
2500 Disable SMEP (Supervisor Mode Execution Prevention)
2501 even if it is supported by processor.
2504 This affects only 32-bit executables.
2505 noexec32=on: enable non-executable mappings (default)
2506 read doesn't imply executable mappings
2507 noexec32=off: disable non-executable mappings
2508 read implies executable mappings
2510 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2512 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2513 register save and restore. The kernel will only save
2514 legacy floating-point registers on task switch.
2516 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2518 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2519 (indirect branch prediction) vulnerability. System may
2520 allow data leaks with this option, which is equivalent
2523 nospec_store_bypass_disable
2524 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2526 noxsave [BUGS=X86] Disables x86 extended register state save
2527 and restore using xsave. The kernel will fallback to
2528 enabling legacy floating-point and sse state.
2530 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2531 register states. The kernel will fall back to use
2532 xsave to save the states. By using this parameter,
2533 performance of saving the states is degraded because
2534 xsave doesn't support modified optimization while
2535 xsaveopt supports it on xsaveopt enabled systems.
2537 noxsaves [X86] Disables xsaves and xrstors used in saving and
2538 restoring x86 extended register state in compacted
2539 form of xsave area. The kernel will fall back to use
2540 xsaveopt and xrstor to save and restore the states
2541 in standard form of xsave area. By using this
2542 parameter, xsave area per process might occupy more
2543 memory on xsaves enabled systems.
2545 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2546 wfi(ARM) instruction doesn't work correctly and not to
2547 use it. This is also useful when using JTAG debugger.
2549 no_file_caps Tells the kernel not to honor file capabilities. The
2550 only way then for a file to be executed with privilege
2551 is to be setuid root or executed by root.
2553 nohalt [IA-64] Tells the kernel not to use the power saving
2554 function PAL_HALT_LIGHT when idle. This increases
2555 power-consumption. On the positive side, it reduces
2556 interrupt wake-up latency, which may improve performance
2557 in certain environments such as networked servers or
2560 nohibernate [HIBERNATION] Disable hibernation and resume.
2562 nohz= [KNL] Boottime enable/disable dynamic ticks
2563 Valid arguments: on, off
2566 nohz_full= [KNL,BOOT]
2567 In kernels built with CONFIG_NO_HZ_FULL=y, set
2568 the specified list of CPUs whose tick will be stopped
2569 whenever possible. The boot CPU will be forced outside
2570 the range to maintain the timekeeping.
2571 The CPUs in this range must also be included in the
2574 noiotrap [SH] Disables trapped I/O port accesses.
2576 noirqdebug [X86-32] Disables the code which attempts to detect and
2577 disable unhandled interrupt sources.
2579 no_timer_check [X86,APIC] Disables the code which tests for
2580 broken timer IRQ sources.
2582 noisapnp [ISAPNP] Disables ISA PnP code.
2584 noinitrd [RAM] Tells the kernel not to load any configured
2587 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2589 [Deprecated - use intremap=off]
2593 noinvpcid [X86] Disable the INVPCID cpu feature.
2595 nojitter [IA-64] Disables jitter checking for ITC timers.
2597 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2599 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2602 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2603 steal time is computed, but won't influence scheduler
2606 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2608 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2610 noltlbs [PPC] Do not use large page/tlb entries for kernel
2611 lowmem mapping on PPC40x.
2613 nomca [IA-64] Disable machine check abort handling
2615 nomce [X86-32] Disable Machine Check Exception
2617 nomfgpt [X86-32] Disable Multi-Function General Purpose
2618 Timer usage (for AMD Geode machines).
2620 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2621 shutdown the other cpus. Instead use the REBOOT_VECTOR
2624 nomodule Disable module load
2626 nopat [X86] Disable PAT (page attribute table extension of
2627 pagetables) support.
2629 nopcid [X86-64] Disable the PCID cpu feature.
2631 norandmaps Don't use address space randomization. Equivalent to
2632 echo 0 > /proc/sys/kernel/randomize_va_space
2634 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2635 with UP alternatives
2637 nordrand [X86] Disable kernel use of the RDRAND and
2638 RDSEED instructions even if they are supported
2639 by the processor. RDRAND and RDSEED are still
2640 available to user space applications.
2642 noresume [SWSUSP] Disables resume and restores original swap
2645 no-scroll [VGA] Disables scrollback.
2646 This is required for the Braillex ib80-piezo Braille
2647 reader made by F.H. Papenmeier (Germany).
2651 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2653 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2654 and disable the IO APIC. legacy for "maxcpus=0".
2656 nosoftlockup [KNL] Disable the soft-lockup detector.
2658 nosync [HW,M68K] Disables sync negotiation for all devices.
2660 notsc [BUGS=X86-32] Disable Time Stamp Counter
2662 nousb [USB] Disable the USB subsystem
2664 nowatchdog [KNL] Disable both lockup detectors, i.e.
2665 soft-lockup and NMI watchdog (hard-lockup).
2669 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2671 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2672 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2673 Some features depend on CPU0. Known dependencies are:
2674 1. Resume from suspend/hibernate depends on CPU0.
2675 Suspend/hibernate will fail if CPU0 is offline and you
2676 need to online CPU0 before suspend/hibernate.
2677 2. PIC interrupts also depend on CPU0. CPU0 can't be
2678 removed if a PIC interrupt is detected.
2679 It's said poweroff/reboot may depend on CPU0 on some
2680 machines although I haven't seen such issues so far
2681 after CPU0 is offline on a few tested machines.
2682 If the dependencies are under your control, you can
2683 turn on cpu0_hotplug.
2685 nptcg= [IA-64] Override max number of concurrent global TLB
2686 purges which is reported from either PAL_VM_SUMMARY or
2689 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2690 could support. nr_cpus=n : n >= 1 limits the kernel to
2691 supporting 'n' processors. Later in runtime you can not
2692 use hotplug cpu feature to put more cpu back to online.
2693 just like you compile the kernel NR_CPUS=n
2695 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2697 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2698 Allowed values are enable and disable
2700 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2701 one of ['zone', 'node', 'default'] can be specified
2702 This can be set from sysctl after boot.
2703 See Documentation/sysctl/vm.txt for details.
2705 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2706 See Documentation/debugging-via-ohci1394.txt for more
2709 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2710 Rather than timing out after 20 ms if an EC
2711 command is not properly ACKed, override the length
2712 of the timeout. We have interrupts disabled while
2713 waiting for the ACK, so if this is set too high
2714 interrupts *may* be lost!
2716 omap_mux= [OMAP] Override bootloader pin multiplexing.
2717 Format: <mux_mode0.mode_name=value>...
2718 For example, to override I2C bus2:
2719 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2721 oprofile.timer= [HW]
2722 Use timer interrupt instead of performance counters
2724 oprofile.cpu_type= Force an oprofile cpu type
2725 This might be useful if you have an older oprofile
2726 userland or if you want common events.
2727 Format: { arch_perfmon }
2728 arch_perfmon: [X86] Force use of architectural
2729 perfmon on Intel CPUs instead of the
2730 CPU specific event set.
2731 timer: [X86] Force use of architectural NMI
2732 timer mode (see also oprofile.timer
2733 for generic hr timer mode)
2734 [s390] Force legacy basic mode sampling
2735 (report cpu_type "timer")
2737 oops=panic Always panic on oopses. Default is to just kill the
2738 process, but there is a small probability of
2739 deadlocking the machine.
2740 This will also cause panics on machine check exceptions.
2741 Useful together with panic=30 to trigger a reboot.
2744 See Documentation/sound/oss/oss-parameters.txt
2746 page_owner= [KNL] Boot-time page_owner enabling option.
2747 Storage of the information about who allocated
2748 each page is disabled in default. With this switch,
2750 on: enable the feature
2752 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2753 timeout > 0: seconds before rebooting
2754 timeout = 0: wait forever
2755 timeout < 0: reboot immediately
2758 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2761 crash_kexec_post_notifiers
2762 Run kdump after running panic-notifiers and dumping
2763 kmsg. This only for the users who doubt kdump always
2764 succeeds in any situation.
2765 Note that this also increases risks of kdump failure,
2766 because some panic notifiers can make the crashed
2767 kernel more unstable.
2769 parkbd.port= [HW] Parallel port number the keyboard adapter is
2770 connected to, default is 0.
2772 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2773 0 for XT, 1 for AT (default is AT).
2776 parport= [HW,PPT] Specify parallel ports. 0 disables.
2777 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2778 Use 'auto' to force the driver to use any
2779 IRQ/DMA settings detected (the default is to
2780 ignore detected IRQ/DMA settings because of
2781 possible conflicts). You can specify the base
2782 address, IRQ, and DMA settings; IRQ and DMA
2783 should be numbers, or 'auto' (for using detected
2784 settings on that particular port), or 'nofifo'
2785 (to avoid using a FIFO even if it is detected).
2786 Parallel ports are assigned in the order they
2787 are specified on the command line, starting
2790 parport_init_mode= [HW,PPT]
2791 Configure VIA parallel port to operate in
2792 a specific mode. This is necessary on Pegasos
2793 computer where firmware has no options for setting
2794 up parallel port mode and sets it to spp.
2795 Currently this function knows 686a and 8231 chips.
2796 Format: [spp|ps2|epp|ecp|ecpepp]
2799 Halt all CPUs after the first oops has been printed for
2800 the specified number of seconds. This is to be used if
2801 your oopses keep scrolling off the screen.
2806 See header of drivers/block/paride/pcd.c.
2807 See also Documentation/blockdev/paride.txt.
2809 pci=option[,option...] [PCI] various PCI subsystem options:
2810 earlydump [X86] dump PCI config space before the kernel
2812 off [X86] don't probe for the PCI bus
2813 bios [X86-32] force use of PCI BIOS, don't access
2814 the hardware directly. Use this if your machine
2815 has a non-standard PCI host bridge.
2816 nobios [X86-32] disallow use of PCI BIOS, only direct
2817 hardware access methods are allowed. Use this
2818 if you experience crashes upon bootup and you
2819 suspect they are caused by the BIOS.
2820 conf1 [X86] Force use of PCI Configuration
2822 conf2 [X86] Force use of PCI Configuration
2824 noaer [PCIE] If the PCIEAER kernel config parameter is
2825 enabled, this kernel boot option can be used to
2826 disable the use of PCIE advanced error reporting.
2827 nodomains [PCI] Disable support for multiple PCI
2828 root domains (aka PCI segments, in ACPI-speak).
2829 nommconf [X86] Disable use of MMCONFIG for PCI
2831 check_enable_amd_mmconf [X86] check for and enable
2832 properly configured MMIO access to PCI
2833 config space on AMD family 10h CPU
2834 nomsi [MSI] If the PCI_MSI kernel config parameter is
2835 enabled, this kernel boot option can be used to
2836 disable the use of MSI interrupts system-wide.
2837 noioapicquirk [APIC] Disable all boot interrupt quirks.
2838 Safety option to keep boot IRQs enabled. This
2839 should never be necessary.
2840 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2841 primary IO-APIC for bridges that cannot disable
2842 boot IRQs. This fixes a source of spurious IRQs
2843 when the system masks IRQs.
2844 noioapicreroute [APIC] Disable workaround that uses the
2845 boot IRQ equivalent of an IRQ that connects to
2846 a chipset where boot IRQs cannot be disabled.
2847 The opposite of ioapicreroute.
2848 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2849 routing table. These calls are known to be buggy
2850 on several machines and they hang the machine
2851 when used, but on other computers it's the only
2852 way to get the interrupt routing table. Try
2853 this option if the kernel is unable to allocate
2854 IRQs or discover secondary PCI buses on your
2856 rom [X86] Assign address space to expansion ROMs.
2857 Use with caution as certain devices share
2858 address decoders between ROMs and other
2860 norom [X86] Do not assign address space to
2861 expansion ROMs that do not already have
2862 BIOS assigned address ranges.
2863 nobar [X86] Do not assign address space to the
2864 BARs that weren't assigned by the BIOS.
2865 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2866 assigned automatically to PCI devices. You can
2867 make the kernel exclude IRQs of your ISA cards
2869 pirqaddr=0xAAAAA [X86] Specify the physical address
2870 of the PIRQ table (normally generated
2871 by the BIOS) if it is outside the
2872 F0000h-100000h range.
2873 lastbus=N [X86] Scan all buses thru bus #N. Can be
2874 useful if the kernel is unable to find your
2875 secondary buses and you want to tell it
2876 explicitly which ones they are.
2877 assign-busses [X86] Always assign all PCI bus
2878 numbers ourselves, overriding
2879 whatever the firmware may have done.
2880 usepirqmask [X86] Honor the possible IRQ mask stored
2881 in the BIOS $PIR table. This is needed on
2882 some systems with broken BIOSes, notably
2883 some HP Pavilion N5400 and Omnibook XE3
2884 notebooks. This will have no effect if ACPI
2885 IRQ routing is enabled.
2886 noacpi [X86] Do not use ACPI for IRQ routing
2887 or for PCI scanning.
2888 use_crs [X86] Use PCI host bridge window information
2889 from ACPI. On BIOSes from 2008 or later, this
2890 is enabled by default. If you need to use this,
2891 please report a bug.
2892 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2893 If you need to use this, please report a bug.
2894 routeirq Do IRQ routing for all PCI devices.
2895 This is normally done in pci_enable_device(),
2896 so this option is a temporary workaround
2897 for broken drivers that don't call it.
2898 skip_isa_align [X86] do not align io start addr, so can
2899 handle more pci cards
2900 firmware [ARM] Do not re-enumerate the bus but instead
2901 just use the configuration from the
2902 bootloader. This is currently used on
2903 IXP2000 systems where the bus has to be
2904 configured a certain way for adjunct CPUs.
2905 noearly [X86] Don't do any early type 1 scanning.
2906 This might help on some broken boards which
2907 machine check when some devices' config space
2908 is read. But various workarounds are disabled
2909 and some IOMMU drivers will not work.
2910 bfsort Sort PCI devices into breadth-first order.
2911 This sorting is done to get a device
2912 order compatible with older (<= 2.4) kernels.
2913 nobfsort Don't sort PCI devices into breadth-first order.
2914 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2915 tuning and use the BIOS-configured MPS defaults.
2916 pcie_bus_safe Set every device's MPS to the largest value
2917 supported by all devices below the root complex.
2918 pcie_bus_perf Set device MPS to the largest allowable MPS
2919 based on its parent bus. Also set MRRS (Max
2920 Read Request Size) to the largest supported
2921 value (no larger than the MPS that the device
2922 or bus can support) for best performance.
2923 pcie_bus_peer2peer Set every device's MPS to 128B, which
2924 every device is guaranteed to support. This
2925 configuration allows peer-to-peer DMA between
2926 any pair of devices, possibly at the cost of
2927 reduced performance. This also guarantees
2928 that hot-added devices will work.
2929 cbiosize=nn[KMG] The fixed amount of bus space which is
2930 reserved for the CardBus bridge's IO window.
2931 The default value is 256 bytes.
2932 cbmemsize=nn[KMG] The fixed amount of bus space which is
2933 reserved for the CardBus bridge's memory
2934 window. The default value is 64 megabytes.
2937 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2938 Specifies alignment and device to reassign
2939 aligned memory resources.
2940 If <order of align> is not specified,
2941 PAGE_SIZE is used as alignment.
2942 PCI-PCI bridge can be specified, if resource
2943 windows need to be expanded.
2944 ecrc= Enable/disable PCIe ECRC (transaction layer
2945 end-to-end CRC checking).
2946 bios: Use BIOS/firmware settings. This is the
2950 hpiosize=nn[KMG] The fixed amount of bus space which is
2951 reserved for hotplug bridge's IO window.
2952 Default size is 256 bytes.
2953 hpmemsize=nn[KMG] The fixed amount of bus space which is
2954 reserved for hotplug bridge's memory window.
2955 Default size is 2 megabytes.
2956 realloc= Enable/disable reallocating PCI bridge resources
2957 if allocations done by BIOS are too small to
2958 accommodate resources required by all child
2960 off: Turn realloc off
2962 realloc same as realloc=on
2963 noari do not use PCIe ARI.
2964 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2965 only look for one device below a PCIe downstream
2968 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2971 force Enable ASPM even on devices that claim not to support it.
2972 WARNING: Forcing ASPM on may cause system lockups.
2974 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2975 nomsi Do not use MSI for PCI Express Native Hotplug (this
2976 makes all PCIe ports use INTx for hotplug services).
2978 pcie_ports= [PCIE] PCIe ports handling:
2979 auto Ask the BIOS whether or not to use native PCIe services
2980 associated with PCIe ports (PME, hot-plug, AER). Use
2981 them only if that is allowed by the BIOS.
2982 native Use native PCIe services associated with PCIe ports
2984 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2987 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2988 nomsi Do not use MSI for native PCIe PME signaling (this makes
2989 all PCIe root ports use INTx for all services).
2991 pcmv= [HW,PCMCIA] BadgePAD 4
2995 Keep all power-domains already enabled by bootloader on,
2996 even if no driver has claimed them. This is useful
2997 for debug and development, but should not be
2998 needed on a platform with proper driver support.
3001 See Documentation/blockdev/paride.txt.
3003 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3006 See arch/parisc/kernel/pdc_chassis.c
3008 percpu_alloc= Select which percpu first chunk allocator to use.
3009 Currently supported values are "embed" and "page".
3010 Archs may support subset or none of the selections.
3011 See comments in mm/percpu.c for details on each
3012 allocator. This parameter is primarily for debugging
3013 and performance comparison.
3016 See Documentation/blockdev/paride.txt.
3019 See Documentation/blockdev/paride.txt.
3021 pirq= [SMP,APIC] Manual mp-table setup
3022 See Documentation/x86/i386/IO-APIC.txt.
3024 plip= [PPT,NET] Parallel port network link
3025 Format: { parport<nr> | timid | 0 }
3026 See also Documentation/parport.txt.
3028 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3029 Override pmtimer IOPort with a hex value.
3033 Enable PNP debug messages (depends on the
3034 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3035 via /sys/module/pnp/parameters/debug. We always show
3036 current resource usage; turning this on also shows
3037 possible settings and some assignment information.
3043 { on | off | curr | res | no-curr | no-res }
3046 [ISAPNP] Exclude IRQs for the autoconfiguration
3049 [ISAPNP] Exclude DMAs for the autoconfiguration
3051 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3052 Ranges are in pairs (I/O port base and size).
3055 [ISAPNP] Exclude memory regions for the
3057 Ranges are in pairs (memory base and size).
3059 ports= [IP_VS_FTP] IPVS ftp helper module
3061 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3063 Format: <port>,<port>....
3065 print-fatal-signals=
3066 [KNL] debug: print fatal signals
3068 If enabled, warn about various signal handling
3069 related application anomalies: too many signals,
3070 too many POSIX.1 timers, fatal signals causing a
3073 If you hit the warning due to signal overflow,
3074 you might want to try "ulimit -i unlimited".
3078 printk.always_kmsg_dump=
3079 Trigger kmsg_dump for cases other than kernel oops or
3081 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3084 printk.time= Show timing data prefixed to each printk message line
3085 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3087 processor.max_cstate= [HW,ACPI]
3088 Limit processor to maximum C-state
3089 max_cstate=9 overrides any DMI blacklist limit.
3091 processor.nocst [HW,ACPI]
3092 Ignore the _CST method to determine C-states,
3093 instead using the legacy FADT method
3095 profile= [KNL] Enable kernel profiling via /proc/profile
3096 Format: [schedule,]<number>
3097 Param: "schedule" - profile schedule points.
3098 Param: <number> - step/bucket size as a power of 2 for
3099 statistical time based profiling.
3100 Param: "sleep" - profile D-state sleeping (millisecs).
3101 Requires CONFIG_SCHEDSTATS
3102 Param: "kvm" - profile VM exits.
3104 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3106 See Documentation/blockdev/ramdisk.txt.
3108 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3109 probe for; one of (bare|imps|exps|lifebook|any).
3110 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3112 psmouse.resetafter= [HW,MOUSE]
3113 Try to reset the device after so many bad packets
3116 [HW,MOUSE] Set desired mouse resolution, in dpi.
3117 psmouse.smartscroll=
3118 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3119 0 = disabled, 1 = enabled (default).
3121 pstore.backend= Specify the name of the pstore backend to use
3124 See Documentation/blockdev/paride.txt.
3126 pti= [X86_64] Control Page Table Isolation of user and
3127 kernel address spaces. Disabling this feature
3128 removes hardening, but improves performance of
3129 system calls and interrupts.
3131 on - unconditionally enable
3132 off - unconditionally disable
3133 auto - kernel detects whether your CPU model is
3134 vulnerable to issues that PTI mitigates
3136 Not specifying this option is equivalent to pti=auto.
3139 Equivalent to pti=off
3142 [KNL] Number of legacy pty's. Overwrites compiled-in
3145 quiet [KNL] Disable most log messages
3150 See Documentation/md.txt.
3152 ramdisk_blocksize= [RAM]
3153 See Documentation/blockdev/ramdisk.txt.
3155 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3156 See Documentation/blockdev/ramdisk.txt.
3159 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3160 the specified list of CPUs to be no-callback CPUs.
3161 Invocation of these CPUs' RCU callbacks will
3162 be offloaded to "rcuox/N" kthreads created for
3163 that purpose, where "x" is "b" for RCU-bh, "p"
3164 for RCU-preempt, and "s" for RCU-sched, and "N"
3165 is the CPU number. This reduces OS jitter on the
3166 offloaded CPUs, which can be useful for HPC and
3167 real-time workloads. It can also improve energy
3168 efficiency for asymmetric multiprocessors.
3171 Rather than requiring that offloaded CPUs
3172 (specified by rcu_nocbs= above) explicitly
3173 awaken the corresponding "rcuoN" kthreads,
3174 make these kthreads poll for callbacks.
3175 This improves the real-time response for the
3176 offloaded CPUs by relieving them of the need to
3177 wake up the corresponding kthread, but degrades
3178 energy efficiency by requiring that the kthreads
3179 periodically wake up to do the polling.
3181 rcutree.blimit= [KNL]
3182 Set maximum number of finished RCU callbacks to
3183 process in one batch.
3185 rcutree.dump_tree= [KNL]
3186 Dump the structure of the rcu_node combining tree
3187 out at early boot. This is used for diagnostic
3188 purposes, to verify correct tree setup.
3190 rcutree.gp_cleanup_delay= [KNL]
3191 Set the number of jiffies to delay each step of
3192 RCU grace-period cleanup. This only has effect
3193 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3195 rcutree.gp_init_delay= [KNL]
3196 Set the number of jiffies to delay each step of
3197 RCU grace-period initialization. This only has
3198 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3201 rcutree.gp_preinit_delay= [KNL]
3202 Set the number of jiffies to delay each step of
3203 RCU grace-period pre-initialization, that is,
3204 the propagation of recent CPU-hotplug changes up
3205 the rcu_node combining tree. This only has effect
3206 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3208 rcutree.rcu_fanout_exact= [KNL]
3209 Disable autobalancing of the rcu_node combining
3210 tree. This is used by rcutorture, and might
3211 possibly be useful for architectures having high
3212 cache-to-cache transfer latencies.
3214 rcutree.rcu_fanout_leaf= [KNL]
3215 Change the number of CPUs assigned to each
3216 leaf rcu_node structure. Useful for very
3217 large systems, which will choose the value 64,
3218 and for NUMA systems with large remote-access
3219 latencies, which will choose a value aligned
3220 with the appropriate hardware boundaries.
3222 rcutree.jiffies_till_sched_qs= [KNL]
3223 Set required age in jiffies for a
3224 given grace period before RCU starts
3225 soliciting quiescent-state help from
3226 rcu_note_context_switch().
3228 rcutree.jiffies_till_first_fqs= [KNL]
3229 Set delay from grace-period initialization to
3230 first attempt to force quiescent states.
3231 Units are jiffies, minimum value is zero,
3232 and maximum value is HZ.
3234 rcutree.jiffies_till_next_fqs= [KNL]
3235 Set delay between subsequent attempts to force
3236 quiescent states. Units are jiffies, minimum
3237 value is one, and maximum value is HZ.
3239 rcutree.kthread_prio= [KNL,BOOT]
3240 Set the SCHED_FIFO priority of the RCU per-CPU
3241 kthreads (rcuc/N). This value is also used for
3242 the priority of the RCU boost threads (rcub/N)
3243 and for the RCU grace-period kthreads (rcu_bh,
3244 rcu_preempt, and rcu_sched). If RCU_BOOST is
3245 set, valid values are 1-99 and the default is 1
3246 (the least-favored priority). Otherwise, when
3247 RCU_BOOST is not set, valid values are 0-99 and
3248 the default is zero (non-realtime operation).
3250 rcutree.rcu_nocb_leader_stride= [KNL]
3251 Set the number of NOCB kthread groups, which
3252 defaults to the square root of the number of
3253 CPUs. Larger numbers reduces the wakeup overhead
3254 on the per-CPU grace-period kthreads, but increases
3255 that same overhead on each group's leader.
3257 rcutree.qhimark= [KNL]
3258 Set threshold of queued RCU callbacks beyond which
3259 batch limiting is disabled.
3261 rcutree.qlowmark= [KNL]
3262 Set threshold of queued RCU callbacks below which
3263 batch limiting is re-enabled.
3265 rcutree.rcu_idle_gp_delay= [KNL]
3266 Set wakeup interval for idle CPUs that have
3267 RCU callbacks (RCU_FAST_NO_HZ=y).
3269 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3270 Set wakeup interval for idle CPUs that have
3271 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3272 Lazy RCU callbacks are those which RCU can
3273 prove do nothing more than free memory.
3275 rcutorture.cbflood_inter_holdoff= [KNL]
3276 Set holdoff time (jiffies) between successive
3277 callback-flood tests.
3279 rcutorture.cbflood_intra_holdoff= [KNL]
3280 Set holdoff time (jiffies) between successive
3281 bursts of callbacks within a given callback-flood
3284 rcutorture.cbflood_n_burst= [KNL]
3285 Set the number of bursts making up a given
3286 callback-flood test. Set this to zero to
3287 disable callback-flood testing.
3289 rcutorture.cbflood_n_per_burst= [KNL]
3290 Set the number of callbacks to be registered
3291 in a given burst of a callback-flood test.
3293 rcutorture.fqs_duration= [KNL]
3294 Set duration of force_quiescent_state bursts
3297 rcutorture.fqs_holdoff= [KNL]
3298 Set holdoff time within force_quiescent_state bursts
3301 rcutorture.fqs_stutter= [KNL]
3302 Set wait time between force_quiescent_state bursts
3305 rcutorture.gp_cond= [KNL]
3306 Use conditional/asynchronous update-side
3307 primitives, if available.
3309 rcutorture.gp_exp= [KNL]
3310 Use expedited update-side primitives, if available.
3312 rcutorture.gp_normal= [KNL]
3313 Use normal (non-expedited) asynchronous
3314 update-side primitives, if available.
3316 rcutorture.gp_sync= [KNL]
3317 Use normal (non-expedited) synchronous
3318 update-side primitives, if available. If all
3319 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3320 rcutorture.gp_normal=, and rcutorture.gp_sync=
3321 are zero, rcutorture acts as if is interpreted
3322 they are all non-zero.
3324 rcutorture.n_barrier_cbs= [KNL]
3325 Set callbacks/threads for rcu_barrier() testing.
3327 rcutorture.nfakewriters= [KNL]
3328 Set number of concurrent RCU writers. These just
3329 stress RCU, they don't participate in the actual
3330 test, hence the "fake".
3332 rcutorture.nreaders= [KNL]
3333 Set number of RCU readers. The value -1 selects
3334 N-1, where N is the number of CPUs. A value
3335 "n" less than -1 selects N-n-2, where N is again
3336 the number of CPUs. For example, -2 selects N
3337 (the number of CPUs), -3 selects N+1, and so on.
3339 rcutorture.object_debug= [KNL]
3340 Enable debug-object double-call_rcu() testing.
3342 rcutorture.onoff_holdoff= [KNL]
3343 Set time (s) after boot for CPU-hotplug testing.
3345 rcutorture.onoff_interval= [KNL]
3346 Set time (s) between CPU-hotplug operations, or
3347 zero to disable CPU-hotplug testing.
3349 rcutorture.shuffle_interval= [KNL]
3350 Set task-shuffle interval (s). Shuffling tasks
3351 allows some CPUs to go into dyntick-idle mode
3352 during the rcutorture test.
3354 rcutorture.shutdown_secs= [KNL]
3355 Set time (s) after boot system shutdown. This
3356 is useful for hands-off automated testing.
3358 rcutorture.stall_cpu= [KNL]
3359 Duration of CPU stall (s) to test RCU CPU stall
3360 warnings, zero to disable.
3362 rcutorture.stall_cpu_holdoff= [KNL]
3363 Time to wait (s) after boot before inducing stall.
3365 rcutorture.stat_interval= [KNL]
3366 Time (s) between statistics printk()s.
3368 rcutorture.stutter= [KNL]
3369 Time (s) to stutter testing, for example, specifying
3370 five seconds causes the test to run for five seconds,
3371 wait for five seconds, and so on. This tests RCU's
3372 ability to transition abruptly to and from idle.
3374 rcutorture.test_boost= [KNL]
3375 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3376 "Maybe" means test if the RCU implementation
3377 under test support RCU priority boosting.
3379 rcutorture.test_boost_duration= [KNL]
3380 Duration (s) of each individual boost test.
3382 rcutorture.test_boost_interval= [KNL]
3383 Interval (s) between each boost test.
3385 rcutorture.test_no_idle_hz= [KNL]
3386 Test RCU's dyntick-idle handling. See also the
3387 rcutorture.shuffle_interval parameter.
3389 rcutorture.torture_runnable= [BOOT]
3390 Start rcutorture running at boot time.
3392 rcutorture.torture_type= [KNL]
3393 Specify the RCU implementation to test.
3395 rcutorture.verbose= [KNL]
3396 Enable additional printk() statements.
3398 rcupdate.rcu_expedited= [KNL]
3399 Use expedited grace-period primitives, for
3400 example, synchronize_rcu_expedited() instead
3401 of synchronize_rcu(). This reduces latency,
3402 but can increase CPU utilization, degrade
3403 real-time latency, and degrade energy efficiency.
3405 rcupdate.rcu_cpu_stall_suppress= [KNL]
3406 Suppress RCU CPU stall warning messages.
3408 rcupdate.rcu_cpu_stall_timeout= [KNL]
3409 Set timeout for RCU CPU stall warning messages.
3411 rcupdate.rcu_task_stall_timeout= [KNL]
3412 Set timeout in jiffies for RCU task stall warning
3413 messages. Disable with a value less than or equal
3416 rcupdate.rcu_self_test= [KNL]
3417 Run the RCU early boot self tests
3419 rcupdate.rcu_self_test_bh= [KNL]
3420 Run the RCU bh early boot self tests
3422 rcupdate.rcu_self_test_sched= [KNL]
3423 Run the RCU sched early boot self tests
3427 Run specified binary instead of /init from the ramdisk,
3428 used for early userspace startup. See initrd.
3431 Format (x86 or x86_64):
3432 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3434 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3436 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3437 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3438 reboot_force is either force or not specified,
3439 reboot_cpu is s[mp]#### with #### being the processor
3440 to be used for rebooting.
3443 [KNL, SMP] Set scheduler's default relax_domain_level.
3444 See Documentation/cgroups/cpusets.txt.
3446 relative_sleep_states=
3447 [SUSPEND] Use sleep state labeling where the deepest
3448 state available other than hibernation is always "mem".
3449 Format: { "0" | "1" }
3450 0 -- Traditional sleep state labels.
3451 1 -- Relative sleep state labels.
3453 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3455 reservetop= [X86-32]
3457 Reserves a hole at the top of the kernel virtual
3462 Set the amount of memory to reserve for BIOS at
3463 the bottom of the address space.
3465 reset_devices [KNL] Force drivers to reset the underlying device
3466 during initialization.
3469 Specify the partition device for software suspend
3471 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3473 resume_offset= [SWSUSP]
3474 Specify the offset from the beginning of the partition
3475 given by "resume=" at which the swap header is located,
3476 in <PAGE_SIZE> units (needed only for swap files).
3477 See Documentation/power/swsusp-and-swap-files.txt
3479 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3480 read the resume files
3482 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3483 Useful for devices that are detected asynchronously
3484 (e.g. USB and MMC devices).
3486 hibernate= [HIBERNATION]
3487 noresume Don't check if there's a hibernation image
3488 present during boot.
3489 nocompress Don't compress/decompress hibernation images.
3490 no Disable hibernation and resume.
3492 retain_initrd [RAM] Keep initrd memory after extraction
3494 rfkill.default_state=
3495 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3496 etc. communication is blocked by default.
3499 rfkill.master_switch_mode=
3500 0 The "airplane mode" button does nothing.
3501 1 The "airplane mode" button toggles between everything
3502 blocked and the previous configuration.
3503 2 The "airplane mode" button toggles between everything
3504 blocked and everything unblocked.
3506 rhash_entries= [KNL,NET]
3507 Set number of hash buckets for route cache
3509 ro [KNL] Mount root device read-only on boot
3512 on Mark read-only kernel memory as read-only (default).
3513 off Leave read-only kernel memory writable for debugging.
3515 root= [KNL] Root filesystem
3516 See name_to_dev_t comment in init/do_mounts.c.
3518 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3519 mount the root filesystem
3521 rootflags= [KNL] Set root filesystem mount option string
3523 rootfstype= [KNL] Set root filesystem type
3525 rootwait [KNL] Wait (indefinitely) for root device to show up.
3526 Useful for devices that are detected asynchronously
3527 (e.g. USB and MMC devices).
3529 rproc_mem=nn[KMG][@address]
3530 [KNL,ARM,CMA] Remoteproc physical memory block.
3531 Memory area to be used by remote processor image,
3534 rw [KNL] Mount root device read-write on boot
3536 S [KNL] Run init in single mode
3538 s390_iommu= [HW,S390]
3539 Set s390 IOTLB flushing mode
3541 With strict flushing every unmap operation will result in
3542 an IOTLB flush. Default is lazy flushing before reuse,
3546 See drivers/net/irda/sa1100_ir.c.
3548 sbni= [NET] Granch SBNI12 leased line adapter
3550 sched_debug [KNL] Enables verbose scheduler debug messages.
3552 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3553 xtime_lock contention on larger systems, and/or RCU lock
3554 contention on all systems with CONFIG_MAXSMP set.
3555 Format: { "0" | "1" }
3556 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3558 Note: increases power consumption, thus should only be
3559 enabled if running jitter sensitive (HPC/RT) workloads.
3561 security= [SECURITY] Choose a security module to enable at boot.
3562 If this boot parameter is not specified, only the first
3563 security module asking for security registration will be
3564 loaded. An invalid security module name will be treated
3565 as if no module has been chosen.
3567 selinux= [SELINUX] Disable or enable SELinux at boot time.
3568 Format: { "0" | "1" }
3569 See security/selinux/Kconfig help text.
3572 Default value is set via kernel config option.
3573 If enabled at boot time, /selinux/disable can be used
3574 later to disable prior to initial policy load.
3576 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3577 Format: { "0" | "1" }
3578 See security/apparmor/Kconfig help text
3581 Default value is set via kernel config option.
3583 serialnumber [BUGS=X86-32]
3586 Maximal number of shapers.
3588 show_msr= [x86] show boot-time MSR settings
3589 Format: { <integer> }
3590 Show boot-time (BIOS-initialized) MSR settings.
3591 The parameter means the number of CPUs to show,
3592 for example 1 means boot CPU only.
3600 Disable merging of slabs with similar size. May be
3601 necessary if there is some reason to distinguish
3602 allocs to different slabs. Debug options disable
3603 merging on their own.
3604 For more information see Documentation/vm/slub.txt.
3606 slab_max_order= [MM, SLAB]
3607 Determines the maximum allowed order for slabs.
3608 A high setting may cause OOMs due to memory
3609 fragmentation. Defaults to 1 for systems with
3610 more than 32MB of RAM, 0 otherwise.
3612 slub_debug[=options[,slabs]] [MM, SLUB]
3613 Enabling slub_debug allows one to determine the
3614 culprit if slab objects become corrupted. Enabling
3615 slub_debug can create guard zones around objects and
3616 may poison objects when not in use. Also tracks the
3617 last alloc / free. For more information see
3618 Documentation/vm/slub.txt.
3620 slub_max_order= [MM, SLUB]
3621 Determines the maximum allowed order for slabs.
3622 A high setting may cause OOMs due to memory
3623 fragmentation. For more information see
3624 Documentation/vm/slub.txt.
3626 slub_min_objects= [MM, SLUB]
3627 The minimum number of objects per slab. SLUB will
3628 increase the slab order up to slub_max_order to
3629 generate a sufficiently large slab able to contain
3630 the number of objects indicated. The higher the number
3631 of objects the smaller the overhead of tracking slabs
3632 and the less frequently locks need to be acquired.
3633 For more information see Documentation/vm/slub.txt.
3635 slub_min_order= [MM, SLUB]
3636 Determines the minimum page order for slabs. Must be
3637 lower than slub_max_order.
3638 For more information see Documentation/vm/slub.txt.
3640 slub_nomerge [MM, SLUB]
3641 Same with slab_nomerge. This is supported for legacy.
3642 See slab_nomerge for more information.
3645 Format: <io1>[,<io2>[,...,<io8>]]
3647 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3648 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3649 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3650 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3651 smsc-ircc2.ircc_irq= [HW] IRQ line
3652 smsc-ircc2.ircc_dma= [HW] DMA channel
3653 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3654 0: Toshiba Satellite 1800 (GP data pin select)
3655 1: Fast pin select (default)
3659 [KNL] Should the soft-lockup detector generate panics.
3662 softlockup_all_cpu_backtrace=
3663 [KNL] Should the soft-lockup detector generate
3664 backtraces on all cpus.
3667 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3668 See Documentation/laptops/sonypi.txt
3670 spectre_v2= [X86] Control mitigation of Spectre variant 2
3671 (indirect branch speculation) vulnerability.
3673 on - unconditionally enable
3674 off - unconditionally disable
3675 auto - kernel detects whether your CPU model is
3678 Selecting 'on' will, and 'auto' may, choose a
3679 mitigation method at run time according to the
3680 CPU, the available microcode, the setting of the
3681 CONFIG_RETPOLINE configuration option, and the
3682 compiler with which the kernel was built.
3684 Specific mitigations can also be selected manually:
3686 retpoline - replace indirect branches
3687 retpoline,generic - google's original retpoline
3688 retpoline,amd - AMD-specific minimal thunk
3690 Not specifying this option is equivalent to
3693 spec_store_bypass_disable=
3694 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
3695 (Speculative Store Bypass vulnerability)
3697 Certain CPUs are vulnerable to an exploit against a
3698 a common industry wide performance optimization known
3699 as "Speculative Store Bypass" in which recent stores
3700 to the same memory location may not be observed by
3701 later loads during speculative execution. The idea
3702 is that such stores are unlikely and that they can
3703 be detected prior to instruction retirement at the
3704 end of a particular speculation execution window.
3706 In vulnerable processors, the speculatively forwarded
3707 store can be used in a cache side channel attack, for
3708 example to read memory to which the attacker does not
3709 directly have access (e.g. inside sandboxed code).
3711 This parameter controls whether the Speculative Store
3712 Bypass optimization is used.
3714 on - Unconditionally disable Speculative Store Bypass
3715 off - Unconditionally enable Speculative Store Bypass
3716 auto - Kernel detects whether the CPU model contains an
3717 implementation of Speculative Store Bypass and
3718 picks the most appropriate mitigation. If the
3719 CPU is not vulnerable, "off" is selected. If the
3720 CPU is vulnerable the default mitigation is
3721 architecture and Kconfig dependent. See below.
3722 prctl - Control Speculative Store Bypass per thread
3723 via prctl. Speculative Store Bypass is enabled
3724 for a process by default. The state of the control
3725 is inherited on fork.
3726 seccomp - Same as "prctl" above, but all seccomp threads
3727 will disable SSB unless they explicitly opt out.
3729 Not specifying this option is equivalent to
3730 spec_store_bypass_disable=auto.
3732 Default mitigations:
3733 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
3735 spia_io_base= [HW,MTD]
3740 stack_guard_gap= [MM]
3741 override the default stack gap protection. The value
3742 is in page units and it defines how many pages prior
3743 to (for stacks growing down) resp. after (for stacks
3744 growing up) the main stack are reserved for no other
3745 mapping. Default value is 256 pages.
3748 Enabled the stack tracer on boot up.
3750 stacktrace_filter=[function-list]
3751 [FTRACE] Limit the functions that the stack tracer
3752 will trace at boot up. function-list is a comma separated
3753 list of functions. This list can be changed at run
3754 time by the stack_trace_filter file in the debugfs
3755 tracing directory. Note, this enables stack tracing
3756 and the stacktrace above is not needed.
3760 Set the STI (builtin display/keyboard on the HP-PARISC
3761 machines) console (graphic card) which should be used
3762 as the initial boot-console.
3763 See also comment in drivers/video/console/sticore.c.
3766 See comment in drivers/video/console/sticore.c.
3769 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3771 sunrpc.min_resvport=
3772 sunrpc.max_resvport=
3774 SunRPC servers often require that client requests
3775 originate from a privileged port (i.e. a port in the
3776 range 0 < portnr < 1024).
3777 An administrator who wishes to reserve some of these
3778 ports for other uses may adjust the range that the
3779 kernel's sunrpc client considers to be privileged
3780 using these two parameters to set the minimum and
3781 maximum port values.
3785 Control how the NFS server code allocates CPUs to
3786 service thread pools. Depending on how many NICs
3787 you have and where their interrupts are bound, this
3788 option will affect which CPUs will do NFS serving.
3789 Note: this parameter cannot be changed while the
3790 NFS server is running.
3792 auto the server chooses an appropriate mode
3793 automatically using heuristics
3794 global a single global pool contains all CPUs
3795 percpu one pool for each CPU
3796 pernode one pool for each NUMA node (equivalent
3797 to global on non-NUMA machines)
3799 sunrpc.tcp_slot_table_entries=
3800 sunrpc.udp_slot_table_entries=
3802 Sets the upper limit on the number of simultaneous
3803 RPC calls that can be sent from the client to a
3804 server. Increasing these values may allow you to
3805 improve throughput, but will also increase the
3806 amount of memory reserved for use by the client.
3808 suspend.pm_test_delay=
3810 Sets the number of seconds to remain in a suspend test
3811 mode before resuming the system (see
3812 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3813 is set. Default value is 5.
3816 [KNL] Enable accounting of swap in memory resource
3817 controller if no parameter or 1 is given or disable
3818 it if 0 is given (See Documentation/cgroups/memory.txt)
3820 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3821 Format: { <int> | force }
3822 <int> -- Number of I/O TLB slabs
3823 force -- force using of bounce buffers even if they
3824 wouldn't be automatically used by the kernel
3828 sysfs.deprecated=0|1 [KNL]
3829 Enable/disable old style sysfs layout for old udev
3830 on older distributions. When this option is enabled
3831 very new udev will not work anymore. When this option
3832 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3833 in older udev will not work anymore.
3834 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3835 the kernel configuration.
3837 sysrq_always_enabled
3839 Ignore sysrq setting - this boot parameter will
3840 neutralize any effect of /proc/sys/kernel/sysrq.
3841 Useful for debugging.
3843 tcpmhash_entries= [KNL,NET]
3844 Set the number of tcp_metrics_hash slots.
3845 Default value is 8192 or 16384 depending on total
3846 ram pages. This is used to specify the TCP metrics
3847 cache size. See Documentation/networking/ip-sysctl.txt
3848 "tcp_no_metrics_save" section for more details.
3852 test_suspend= [SUSPEND][,N]
3853 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3854 standby suspend) or "freeze" (for suspend type freeze)
3855 as the system sleep state during system startup with
3856 the optional capability to repeat N number of times.
3857 The system is woken from this state using a
3858 wakeup-capable RTC alarm.
3860 thash_entries= [KNL,NET]
3861 Set number of hash buckets for TCP connection
3863 thermal.act= [HW,ACPI]
3864 -1: disable all active trip points in all thermal zones
3865 <degrees C>: override all lowest active trip points
3867 thermal.crt= [HW,ACPI]
3868 -1: disable all critical trip points in all thermal zones
3869 <degrees C>: override all critical trip points
3871 thermal.nocrt= [HW,ACPI]
3872 Set to disable actions on ACPI thermal zone
3873 critical and hot trip points.
3875 thermal.off= [HW,ACPI]
3876 1: disable ACPI thermal control
3878 thermal.psv= [HW,ACPI]
3879 -1: disable all passive trip points
3880 <degrees C>: override all passive trip points to this
3883 thermal.tzp= [HW,ACPI]
3884 Specify global default ACPI thermal zone polling rate
3885 <deci-seconds>: poll all this frequency
3886 0: no polling (default)
3889 Force threading of all interrupt handlers except those
3890 marked explicitly IRQF_NO_THREAD.
3893 Enable the Transcendent memory driver if built-in.
3895 tmem.cleancache=0|1 [KNL, XEN]
3896 Default is on (1). Disable the usage of the cleancache
3897 API to send anonymous pages to the hypervisor.
3899 tmem.frontswap=0|1 [KNL, XEN]
3900 Default is on (1). Disable the usage of the frontswap
3901 API to send swap pages to the hypervisor. If disabled
3902 the selfballooning and selfshrinking are force disabled.
3904 tmem.selfballooning=0|1 [KNL, XEN]
3905 Default is on (1). Disable the driving of swap pages
3908 tmem.selfshrinking=0|1 [KNL, XEN]
3909 Default is on (1). Partial swapoff that immediately
3910 transfers pages from Xen hypervisor back to the
3911 kernel based on different criteria.
3915 Specify if the kernel should make use of the cpu
3916 topology information if the hardware supports this.
3917 The scheduler will make use of this information and
3918 e.g. base its process migration decisions on it.
3921 topology_updates= [KNL, PPC, NUMA]
3923 Specify if the kernel should ignore (off)
3924 topology updates sent by the hypervisor to this
3929 tpm_suspend_pcr=[HW,TPM]
3930 Format: integer pcr id
3931 Specify that at suspend time, the tpm driver
3932 should extend the specified pcr with zeros,
3933 as a workaround for some chips which fail to
3934 flush the last written pcr on TPM_SaveState.
3935 This will guarantee that all the other pcrs
3938 trace_buf_size=nn[KMG]
3939 [FTRACE] will set tracing buffer size on each cpu.
3941 trace_event=[event-list]
3942 [FTRACE] Set and start specified trace events in order
3943 to facilitate early boot debugging.
3944 See also Documentation/trace/events.txt
3946 trace_options=[option-list]
3947 [FTRACE] Enable or disable tracer options at boot.
3948 The option-list is a comma delimited list of options
3949 that can be enabled or disabled just as if you were
3950 to echo the option name into
3952 /sys/kernel/debug/tracing/trace_options
3954 For example, to enable stacktrace option (to dump the
3955 stack trace of each event), add to the command line:
3957 trace_options=stacktrace
3959 See also Documentation/trace/ftrace.txt "trace options"
3963 Have the tracepoints sent to printk as well as the
3964 tracing ring buffer. This is useful for early boot up
3965 where the system hangs or reboots and does not give the
3966 option for reading the tracing buffer or performing a
3967 ftrace_dump_on_oops.
3969 To turn off having tracepoints sent to printk,
3970 echo 0 > /proc/sys/kernel/tracepoint_printk
3971 Note, echoing 1 into this file without the
3972 tracepoint_printk kernel cmdline option has no effect.
3976 Having tracepoints sent to printk() and activating high
3977 frequency tracepoints such as irq or sched, can cause
3978 the system to live lock.
3981 [FTRACE] enable this option to disable tracing when a
3982 warning is hit. This turns off "tracing_on". Tracing can
3983 be enabled again by echoing '1' into the "tracing_on"
3984 file located in /sys/kernel/debug/tracing/
3986 This option is useful, as it disables the trace before
3987 the WARNING dump is called, which prevents the trace to
3988 be filled with content caused by the warning output.
3990 This option can also be set at run time via the sysctl
3991 option: kernel/traceoff_on_warning
3993 transparent_hugepage=
3995 Format: [always|madvise|never]
3996 Can be used to control the default behavior of the system
3997 with respect to transparent hugepages.
3998 See Documentation/vm/transhuge.txt for more details.
4000 tsc= Disable clocksource stability checks for TSC.
4002 [x86] reliable: mark tsc clocksource as reliable, this
4003 disables clocksource verification at runtime, as well
4004 as the stability checks done at bootup. Used to enable
4005 high-resolution timer mode on older hardware, and in
4006 virtualized environment.
4007 [x86] noirqtime: Do not use TSC to do irq accounting.
4008 Used to run time disable IRQ_TIME_ACCOUNTING on any
4009 platforms where RDTSC is slow and this accounting
4012 turbografx.map[2|3]= [HW,JOY]
4013 TurboGraFX parallel port interface
4015 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4016 See also Documentation/input/joystick-parport.txt
4018 udbg-immortal [PPC] When debugging early kernel crashes that
4019 happen after console_init() and before a proper
4020 console driver takes over, this boot options might
4021 help "seeing" what's going on.
4023 uhash_entries= [KNL,NET]
4024 Set number of hash buckets for UDP/UDP-Lite connections
4027 [USB] Ignore overcurrent events (default N).
4028 Some badly-designed motherboards generate lots of
4029 bogus events, for ports that aren't wired to
4030 anything. Set this parameter to avoid log spamming.
4031 Note that genuine overcurrent events won't be
4035 [X86] Cause panic on unknown NMI.
4037 usbcore.authorized_default=
4038 [USB] Default USB device authorization:
4039 (default -1 = authorized except for wireless USB,
4040 0 = not authorized, 1 = authorized)
4042 usbcore.autosuspend=
4043 [USB] The autosuspend time delay (in seconds) used
4044 for newly-detected USB devices (default 2). This
4045 is the time required before an idle device will be
4046 autosuspended. Devices for which the delay is set
4047 to a negative value won't be autosuspended at all.
4049 usbcore.usbfs_snoop=
4050 [USB] Set to log all usbfs traffic (default 0 = off).
4052 usbcore.blinkenlights=
4053 [USB] Set to cycle leds on hubs (default 0 = off).
4055 usbcore.old_scheme_first=
4056 [USB] Start with the old device initialization
4057 scheme (default 0 = off).
4059 usbcore.usbfs_memory_mb=
4060 [USB] Memory limit (in MB) for buffers allocated by
4061 usbfs (default = 16, 0 = max = 2047).
4063 usbcore.use_both_schemes=
4064 [USB] Try the other device initialization scheme
4065 if the first one fails (default 1 = enabled).
4067 usbcore.initial_descriptor_timeout=
4068 [USB] Specifies timeout for the initial 64-byte
4069 USB_REQ_GET_DESCRIPTOR request in milliseconds
4070 (default 5000 = 5.0 seconds).
4073 [USBHID] The interval which mice are to be polled at.
4075 usb-storage.delay_use=
4076 [UMS] The delay in seconds before a new device is
4077 scanned for Logical Units (default 1).
4080 [UMS] A list of quirks entries to supplement or
4081 override the built-in unusual_devs list. List
4082 entries are separated by commas. Each entry has
4083 the form VID:PID:Flags where VID and PID are Vendor
4084 and Product ID values (4-digit hex numbers) and
4085 Flags is a set of characters, each corresponding
4086 to a common usb-storage quirk flag as follows:
4087 a = SANE_SENSE (collect more than 18 bytes
4089 b = BAD_SENSE (don't collect more than 18
4090 bytes of sense data);
4091 c = FIX_CAPACITY (decrease the reported
4092 device capacity by one sector);
4093 d = NO_READ_DISC_INFO (don't use
4094 READ_DISC_INFO command);
4095 e = NO_READ_CAPACITY_16 (don't use
4096 READ_CAPACITY_16 command);
4097 f = NO_REPORT_OPCODES (don't use report opcodes
4099 g = MAX_SECTORS_240 (don't transfer more than
4100 240 sectors at a time, uas only);
4101 h = CAPACITY_HEURISTICS (decrease the
4102 reported device capacity by one
4103 sector if the number is odd);
4104 i = IGNORE_DEVICE (don't bind to this
4106 j = NO_REPORT_LUNS (don't use report luns
4108 l = NOT_LOCKABLE (don't try to lock and
4109 unlock ejectable media);
4110 m = MAX_SECTORS_64 (don't transfer more
4111 than 64 sectors = 32 KB at a time);
4112 n = INITIAL_READ10 (force a retry of the
4113 initial READ(10) command);
4114 o = CAPACITY_OK (accept the capacity
4115 reported by the device);
4116 p = WRITE_CACHE (the device cache is ON
4118 r = IGNORE_RESIDUE (the device reports
4119 bogus residue values);
4120 s = SINGLE_LUN (the device has only one
4122 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4123 commands, uas only);
4124 u = IGNORE_UAS (don't bind to the uas driver);
4125 w = NO_WP_DETECT (don't test whether the
4126 medium is write-protected).
4127 Example: quirks=0419:aaf5:rl,0421:0433:rc
4129 user_debug= [KNL,ARM]
4131 See arch/arm/Kconfig.debug help text.
4132 1 - undefined instruction events
4134 4 - invalid data aborts
4137 Example: user_debug=31
4140 [X86] Flags controlling user PTE allocations.
4142 nohigh = do not allocate PTE pages in
4143 HIGHMEM regardless of setting
4147 On X86_32, this is an alias for vdso32=. Otherwise:
4149 vdso=1: enable VDSO (the default)
4150 vdso=0: disable VDSO mapping
4152 vdso32= [X86] Control the 32-bit vDSO
4153 vdso32=1: enable 32-bit VDSO
4154 vdso32=0 or vdso32=2: disable 32-bit VDSO
4156 See the help text for CONFIG_COMPAT_VDSO for more
4157 details. If CONFIG_COMPAT_VDSO is set, the default is
4158 vdso32=0; otherwise, the default is vdso32=1.
4160 For compatibility with older kernels, vdso32=2 is an
4163 Try vdso32=0 if you encounter an error that says:
4164 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4167 vector=percpu: enable percpu vector domain
4169 video= [FB] Frame buffer configuration
4170 See Documentation/fb/modedb.txt.
4172 video.brightness_switch_enabled= [0,1]
4173 If set to 1, on receiving an ACPI notify event
4174 generated by hotkey, video driver will adjust brightness
4175 level and then send out the event to user space through
4176 the allocated input device; If set to 0, video driver
4177 will only send out the event without touching backlight
4182 [VMMIO] Memory mapped virtio (platform) device.
4184 <size>@<baseaddr>:<irq>[:<id>]
4186 <size> := size (can use standard suffixes
4188 <baseaddr> := physical base address
4189 <irq> := interrupt number (as passed to
4191 <id> := (optional) platform device id
4193 virtio_mmio.device=1K@0x100b0000:48:7
4195 Can be used multiple times for multiple devices.
4197 vga= [BOOT,X86-32] Select a particular video mode
4198 See Documentation/x86/boot.txt and
4199 Documentation/svga.txt.
4200 Use vga=ask for menu.
4201 This is actually a boot loader parameter; the value is
4202 passed to the kernel using a special protocol.
4204 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4205 size of <nn>. This can be used to increase the
4206 minimum size (128MB on x86). It can also be used to
4207 decrease the size and leave more room for directly
4210 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4213 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4216 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4220 Controls the behavior of vsyscalls (i.e. calls to
4221 fixed addresses of 0xffffffffff600x00 from legacy
4222 code). Most statically-linked binaries and older
4223 versions of glibc use these calls. Because these
4224 functions are at fixed addresses, they make nice
4225 targets for exploits that can control RIP.
4227 emulate [default] Vsyscalls turn into traps and are
4228 emulated reasonably safely.
4230 native Vsyscalls are native syscall instructions.
4231 This is a little bit faster than trapping
4232 and makes a few dynamic recompilers work
4233 better than they would in emulation mode.
4234 It also makes exploits much easier to write.
4236 none Vsyscalls don't work at all. This makes
4237 them quite hard to use for exploits but
4238 might break your system.
4240 vt.color= [VT] Default text color.
4241 Format: 0xYX, X = foreground, Y = background.
4242 Default: 0x07 = light gray on black.
4244 vt.cur_default= [VT] Default cursor shape.
4245 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4246 the parameters of the <Esc>[?A;B;Cc escape sequence;
4247 see VGA-softcursor.txt. Default: 2 = underline.
4249 vt.default_blu= [VT]
4250 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4251 Change the default blue palette of the console.
4252 This is a 16-member array composed of values
4255 vt.default_grn= [VT]
4256 Format: <green0>,<green1>,<green2>,...,<green15>
4257 Change the default green palette of the console.
4258 This is a 16-member array composed of values
4261 vt.default_red= [VT]
4262 Format: <red0>,<red1>,<red2>,...,<red15>
4263 Change the default red palette of the console.
4264 This is a 16-member array composed of values
4270 Set system-wide default UTF-8 mode for all tty's.
4271 Default is 1, i.e. UTF-8 mode is enabled for all
4272 newly opened terminals.
4274 vt.global_cursor_default=
4277 Set system-wide default for whether a cursor
4278 is shown on new VTs. Default is -1,
4279 i.e. cursors will be created by default unless
4280 overridden by individual drivers. 0 will hide
4281 cursors, 1 will display them.
4283 vt.italic= [VT] Default color for italic text; 0-15.
4286 vt.underline= [VT] Default color for underlined text; 0-15.
4289 watchdog timers [HW,WDT] For information on watchdog timers,
4290 see Documentation/watchdog/watchdog-parameters.txt
4291 or other driver-specific files in the
4292 Documentation/watchdog/ directory.
4294 workqueue.disable_numa
4295 By default, all work items queued to unbound
4296 workqueues are affine to the NUMA nodes they're
4297 issued on, which results in better behavior in
4298 general. If NUMA affinity needs to be disabled for
4299 whatever reason, this option can be used. Note
4300 that this also can be controlled per-workqueue for
4301 workqueues visible under /sys/bus/workqueue/.
4303 workqueue.power_efficient
4304 Per-cpu workqueues are generally preferred because
4305 they show better performance thanks to cache
4306 locality; unfortunately, per-cpu workqueues tend to
4307 be more power hungry than unbound workqueues.
4309 Enabling this makes the per-cpu workqueues which
4310 were observed to contribute significantly to power
4311 consumption unbound, leading to measurably lower
4312 power usage at the cost of small performance
4315 The default value of this parameter is determined by
4316 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4318 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4319 default x2apic cluster mode on platforms
4322 x86_intel_mid_timer= [X86-32,APBT]
4323 Choose timer option for x86 Intel MID platform.
4324 Two valid options are apbt timer only and lapic timer
4325 plus one apbt timer for broadcast timer.
4326 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4328 xen_512gb_limit [KNL,X86-64,XEN]
4329 Restricts the kernel running paravirtualized under Xen
4330 to use only up to 512 GB of RAM. The reason to do so is
4331 crash analysis tools and Xen tools for doing domain
4332 save/restore/migration must be enabled to handle larger
4335 xen_emul_unplug= [HW,X86,XEN]
4336 Unplug Xen emulated devices
4337 Format: [unplug0,][unplug1]
4338 ide-disks -- unplug primary master IDE devices
4339 aux-ide-disks -- unplug non-primary-master IDE devices
4340 nics -- unplug network devices
4341 all -- unplug all emulated devices (NICs and IDE disks)
4342 unnecessary -- unplugging emulated devices is
4343 unnecessary even if the host did not respond to
4345 never -- do not unplug even if version check succeeds
4347 xen_nopvspin [X86,XEN]
4348 Disables the ticketlock slowpath using Xen PV
4352 Disables the PV optimizations forcing the HVM guest to
4353 run as generic HVM guest with no PV drivers.
4355 xirc2ps_cs= [NET,PCMCIA]
4357 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4359 ______________________________________________________________________
4363 Add more DRM drivers.