4 The following is a consolidated list of the kernel parameters as
5 implemented by the __setup(), core_param() and module_param() macros
6 and sorted into English Dictionary order (defined as ignoring all
7 punctuation and sorting digits before letters in a case insensitive
8 manner), and with descriptions where known.
10 The kernel parses parameters from the kernel command line up to "--";
11 if it doesn't recognize a parameter and it doesn't contain a '.', the
12 parameter gets passed to init: parameters with '=' go into init's
13 environment, others are passed as command line arguments to init.
14 Everything after "--" is passed as an argument to init.
16 Module parameters can be specified in two ways: via the kernel command
17 line with a module name prefix, or via modprobe, e.g.:
19 (kernel command line) usbcore.blinkenlights=1
20 (modprobe command line) modprobe usbcore blinkenlights=1
22 Parameters for modules which are built into the kernel need to be
23 specified on the kernel command line. modprobe looks through the
24 kernel command line (/proc/cmdline) and collects module parameters
25 when it loads a module, so the kernel command line can be used for
28 Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30 can also be entered as
31 log-buf-len=1M print_fatal_signals=1
33 Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
36 This document may not be entirely up to date and comprehensive. The command
37 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
38 module. Loadable modules, after being loaded into the running kernel, also
39 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
40 parameters may be changed at runtime by the command
41 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
43 The parameters listed below are only valid if certain kernel build options were
44 enabled and if respective hardware is present. The text in square brackets at
45 the beginning of each description states the restrictions within which a
46 parameter is applicable:
48 ACPI ACPI support is enabled.
49 AGP AGP (Accelerated Graphics Port) is enabled.
50 ALSA ALSA sound support is enabled.
51 APIC APIC support is enabled.
52 APM Advanced Power Management support is enabled.
53 ARM ARM architecture is enabled.
54 AVR32 AVR32 architecture is enabled.
55 AX25 Appropriate AX.25 support is enabled.
56 BLACKFIN Blackfin architecture is enabled.
57 CLK Common clock infrastructure is enabled.
58 CMA Contiguous Memory Area support is enabled.
59 DRM Direct Rendering Management support is enabled.
60 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
61 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
62 EFI EFI Partitioning (GPT) is enabled
63 EIDE EIDE/ATAPI support is enabled.
64 EVM Extended Verification Module
65 FB The frame buffer device is enabled.
66 FTRACE Function tracing enabled.
67 GCOV GCOV profiling is enabled.
68 HW Appropriate hardware is enabled.
69 IA-64 IA-64 architecture is enabled.
70 IMA Integrity measurement architecture is enabled.
71 IOSCHED More than one I/O scheduler is enabled.
72 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
73 IPV6 IPv6 support is enabled.
74 ISAPNP ISA PnP code is enabled.
75 ISDN Appropriate ISDN support is enabled.
76 JOY Appropriate joystick support is enabled.
77 KGDB Kernel debugger support is enabled.
78 KVM Kernel Virtual Machine support is enabled.
79 LIBATA Libata driver is enabled
80 LP Printer support is enabled.
81 LOOP Loopback device support is enabled.
82 M68k M68k architecture is enabled.
83 These options have more detailed description inside of
84 Documentation/m68k/kernel-options.txt.
85 MDA MDA console support is enabled.
86 MIPS MIPS architecture is enabled.
87 MOUSE Appropriate mouse support is enabled.
88 MSI Message Signaled Interrupts (PCI).
89 MTD MTD (Memory Technology Device) support is enabled.
90 NET Appropriate network support is enabled.
91 NUMA NUMA support is enabled.
92 NFS Appropriate NFS support is enabled.
93 OSS OSS sound support is enabled.
94 PV_OPS A paravirtualized kernel is enabled.
95 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
96 PARISC The PA-RISC architecture is enabled.
97 PCI PCI bus support is enabled.
98 PCIE PCI Express support is enabled.
99 PCMCIA The PCMCIA subsystem is enabled.
100 PNP Plug & Play support is enabled.
101 PPC PowerPC architecture is enabled.
102 PPT Parallel port support is enabled.
103 PS2 Appropriate PS/2 support is enabled.
104 RAM RAM disk support is enabled.
105 S390 S390 architecture is enabled.
106 SCSI Appropriate SCSI support is enabled.
107 A lot of drivers have their options described inside
108 the Documentation/scsi/ sub-directory.
109 SECURITY Different security models are enabled.
110 SELINUX SELinux support is enabled.
111 APPARMOR AppArmor support is enabled.
112 SERIAL Serial support is enabled.
113 SH SuperH architecture is enabled.
114 SMP The kernel is an SMP kernel.
115 SPARC Sparc architecture is enabled.
116 SWSUSP Software suspend (hibernation) is enabled.
117 SUSPEND System suspend states are enabled.
118 TPM TPM drivers are enabled.
119 TS Appropriate touchscreen support is enabled.
120 UMS USB Mass Storage support is enabled.
121 USB USB support is enabled.
122 USBHID USB Human Interface Device support is enabled.
123 V4L Video For Linux support is enabled.
124 VMMIO Driver for memory mapped virtio devices is enabled.
125 VGA The VGA console has been enabled.
126 VT Virtual terminal support is enabled.
127 WDT Watchdog support is enabled.
128 XT IBM PC/XT MFM hard disk support is enabled.
129 X86-32 X86-32, aka i386 architecture is enabled.
130 X86-64 X86-64 architecture is enabled.
131 More X86-64 boot options can be found in
132 Documentation/x86/x86_64/boot-options.txt .
133 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
134 XEN Xen support is enabled
136 In addition, the following text indicates that the option:
138 BUGS= Relates to possible processor bugs on the said processor.
139 KNL Is a kernel start-up parameter.
140 BOOT Is a boot loader parameter.
142 Parameters denoted with BOOT are actually interpreted by the boot
143 loader, and have no meaning to the kernel directly.
144 Do not modify the syntax of boot loader parameters without extreme
145 need or coordination with <Documentation/x86/boot.txt>.
147 There are also arch-specific kernel-parameters not documented here.
148 See for example <Documentation/x86/x86_64/boot-options.txt>.
150 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
151 a trailing = on the name of any parameter states that that parameter will
152 be entered as an environment variable, whereas its absence indicates that
153 it will appear as a kernel argument readable via /proc/cmdline by programs
154 running once the system is up.
156 The number of kernel parameters is not limited, but the length of the
157 complete command line (parameters including spaces etc.) is limited to
158 a fixed number of characters. This limit depends on the architecture
159 and is between 256 and 4096 characters. It is defined in the file
160 ./include/asm/setup.h as COMMAND_LINE_SIZE.
162 Finally, the [KMG] suffix is commonly described after a number of kernel
163 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
164 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
165 bytes respectively. Such letter suffixes can also be entirely omitted.
168 acpi= [HW,ACPI,X86,ARM64]
169 Advanced Configuration and Power Interface
170 Format: { force | off | strict | noirq | rsdt |
172 force -- enable ACPI if default was off
173 off -- disable ACPI if default was on
174 noirq -- do not use ACPI for IRQ routing
175 strict -- Be less tolerant of platforms that are not
176 strictly ACPI specification compliant.
177 rsdt -- prefer RSDT over (default) XSDT
178 copy_dsdt -- copy DSDT to memory
179 For ARM64, ONLY "acpi=off" or "acpi=force" are available
181 See also Documentation/power/runtime_pm.txt, pci=noacpi
183 acpi_apic_instance= [ACPI, IOAPIC]
185 2: use 2nd APIC table, if available
186 1,0: use 1st APIC table
189 acpi_backlight= [HW,ACPI]
190 acpi_backlight=vendor
192 If set to vendor, prefer vendor specific driver
193 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
194 of the ACPI video.ko driver.
196 acpica_no_return_repair [HW, ACPI]
197 Disable AML predefined validation mechanism
198 This mechanism can repair the evaluation result to make
199 the return objects more ACPI specification compliant.
200 This option is useful for developers to identify the
201 root cause of an AML interpreter issue when the issue
202 has something to do with the repair mechanism.
204 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
205 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
207 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
208 debug output. Bits in debug_layer correspond to a
209 _COMPONENT in an ACPI source file, e.g.,
210 #define _COMPONENT ACPI_PCI_COMPONENT
211 Bits in debug_level correspond to a level in
212 ACPI_DEBUG_PRINT statements, e.g.,
213 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
214 The debug_level mask defaults to "info". See
215 Documentation/acpi/debug.txt for more information about
216 debug layers and levels.
218 Enable processor driver info messages:
219 acpi.debug_layer=0x20000000
220 Enable PCI/PCI interrupt routing info messages:
221 acpi.debug_layer=0x400000
222 Enable AML "Debug" output, i.e., stores to the Debug
223 object while interpreting AML:
224 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
225 Enable all messages related to ACPI hardware:
226 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
228 Some values produce so much output that the system is
229 unusable. The "log_buf_len" parameter may be useful
230 if you need to capture more output.
232 acpi_enforce_resources= [ACPI]
233 { strict | lax | no }
234 Check for resource conflicts between native drivers
235 and ACPI OperationRegions (SystemIO and SystemMemory
236 only). IO ports and memory declared in ACPI might be
237 used by the ACPI subsystem in arbitrary AML code and
238 can interfere with legacy drivers.
239 strict (default): access to resources claimed by ACPI
240 is denied; legacy drivers trying to access reserved
241 resources will fail to bind to device using them.
242 lax: access to resources claimed by ACPI is allowed;
243 legacy drivers trying to access reserved resources
244 will bind successfully but a warning message is logged.
245 no: ACPI OperationRegions are not marked as reserved,
246 no further checks are performed.
248 acpi_force_table_verification [HW,ACPI]
249 Enable table checksum verification during early stage.
250 By default, this is disabled due to x86 early mapping
253 acpi_irq_balance [HW,ACPI]
254 ACPI will balance active IRQs
257 acpi_irq_nobalance [HW,ACPI]
258 ACPI will not move active IRQs (default)
261 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
262 Format: <irq>,<irq>...
264 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
266 Format: <irq>,<irq>...
268 acpi_no_auto_serialize [HW,ACPI]
269 Disable auto-serialization of AML methods
270 AML control methods that contain the opcodes to create
271 named objects will be marked as "Serialized" by the
272 auto-serialization feature.
273 This feature is enabled by default.
274 This option allows to turn off the feature.
276 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
279 acpi_no_static_ssdt [HW,ACPI]
280 Disable installation of static SSDTs at early boot time
281 By default, SSDTs contained in the RSDT/XSDT will be
282 installed automatically and they will appear under
283 /sys/firmware/acpi/tables.
284 This option turns off this feature.
285 Note that specifying this option does not affect
286 dynamic table installation which will install SSDT
287 tables to /sys/firmware/acpi/tables/dynamic.
289 acpi_rsdp= [ACPI,EFI,KEXEC]
290 Pass the RSDP address to the kernel, mostly used
291 on machines running EFI runtime service to boot the
292 second kernel for kdump.
294 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
295 Format: To spoof as Windows 98: ="Microsoft Windows"
297 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
298 of 2 which is mandated by ACPI 6) as the supported ACPI
299 specification revision (when using this switch, it may
300 be necessary to carry out a cold reboot _twice_ in a
301 row to make it take effect on the platform firmware).
303 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
304 acpi_osi="string1" # add string1
305 acpi_osi="!string2" # remove string2
306 acpi_osi=!* # remove all strings
307 acpi_osi=! # disable all built-in OS vendor
309 acpi_osi= # disable all strings
311 'acpi_osi=!' can be used in combination with single or
312 multiple 'acpi_osi="string1"' to support specific OS
313 vendor string(s). Note that such command can only
314 affect the default state of the OS vendor strings, thus
315 it cannot affect the default state of the feature group
316 strings and the current state of the OS vendor strings,
317 specifying it multiple times through kernel command line
318 is meaningless. This command is useful when one do not
319 care about the state of the feature group strings which
320 should be controlled by the OSPM.
322 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
323 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
324 can make '_OSI("Windows 2000")' TRUE.
326 'acpi_osi=' cannot be used in combination with other
327 'acpi_osi=' command lines, the _OSI method will not
328 exist in the ACPI namespace. NOTE that such command can
329 only affect the _OSI support state, thus specifying it
330 multiple times through kernel command line is also
333 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
336 'acpi_osi=!*' can be used in combination with single or
337 multiple 'acpi_osi="string1"' to support specific
338 string(s). Note that such command can affect the
339 current state of both the OS vendor strings and the
340 feature group strings, thus specifying it multiple times
341 through kernel command line is meaningful. But it may
342 still not able to affect the final state of a string if
343 there are quirks related to this string. This command
344 is useful when one want to control the state of the
345 feature group strings to debug BIOS issues related to
348 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
349 '_OSI("Module Device")' FALSE.
350 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
351 '_OSI("Module Device")' TRUE.
352 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
354 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
356 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
357 they all will make '_OSI("Windows 2000")' TRUE.
360 Override the pmtimer bug detection: force the kernel
361 to assume that this machine's pmtimer latches its value
362 and always returns good values.
364 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
365 Format: { level | edge | high | low }
367 acpi_skip_timer_override [HW,ACPI]
368 Recognize and ignore IRQ0/pin2 Interrupt Override.
369 For broken nForce2 BIOS resulting in XT-PIC timer.
371 acpi_sleep= [HW,ACPI] Sleep options
372 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
373 old_ordering, nonvs, sci_force_enable }
374 See Documentation/power/video.txt for information on
376 s3_beep is for debugging; it makes the PC's speaker beep
377 as soon as the kernel's real-mode entry point is called.
378 s4_nohwsig prevents ACPI hardware signature from being
379 used during resume from hibernation.
380 old_ordering causes the ACPI 1.0 ordering of the _PTS
381 control method, with respect to putting devices into
382 low power states, to be enforced (the ACPI 2.0 ordering
383 of _PTS is used by default).
384 nonvs prevents the kernel from saving/restoring the
385 ACPI NVS memory during suspend/hibernation and resume.
386 sci_force_enable causes the kernel to set SCI_EN directly
387 on resume from S1/S3 (which is against the ACPI spec,
388 but some broken systems don't work without it).
390 acpi_use_timer_override [HW,ACPI]
391 Use timer override. For some broken Nvidia NF5 boards
392 that require a timer override, but don't have HPET
394 add_efi_memmap [EFI; X86] Include EFI memory map in
395 kernel's map of available physical RAM.
398 { off | try_unsupported }
399 off: disable AGP support
400 try_unsupported: try to drive unsupported chipsets
401 (may crash computer or cause data corruption)
404 See Documentation/sound/alsa/alsa-parameters.txt
407 Allow the default userspace alignment fault handler
408 behaviour to be specified. Bit 0 enables warnings,
409 bit 1 enables fixups, and bit 2 sends a segfault.
411 align_va_addr= [X86-64]
412 Align virtual addresses by clearing slice [14:12] when
413 allocating a VMA at process creation time. This option
414 gives you up to 3% performance improvement on AMD F15h
415 machines (where it is enabled by default) for a
416 CPU-intensive style benchmark, and it can vary highly in
417 a microbenchmark depending on workload and compiler.
419 32: only for 32-bit processes
420 64: only for 64-bit processes
421 on: enable for both 32- and 64-bit processes
422 off: disable for both 32- and 64-bit processes
424 alloc_snapshot [FTRACE]
425 Allocate the ftrace snapshot buffer on boot up when the
426 main buffer is allocated. This is handy if debugging
427 and you need to use tracing_snapshot() on boot up, and
428 do not want to use tracing_snapshot_alloc() as it needs
429 to be done where GFP_KERNEL allocations are allowed.
431 amd_iommu= [HW,X86-64]
432 Pass parameters to the AMD IOMMU driver in the system.
434 fullflush - enable flushing of IO/TLB entries when
435 they are unmapped. Otherwise they are
436 flushed before they will be reused, which
438 off - do not initialize any AMD IOMMU found in
440 force_isolation - Force device isolation for all
441 devices. The IOMMU driver is not
442 allowed anymore to lift isolation
443 requirements as needed. This option
444 does not override iommu=pt
446 amd_iommu_dump= [HW,X86-64]
447 Enable AMD IOMMU driver option to dump the ACPI table
448 for AMD IOMMU. With this option enabled, AMD IOMMU
449 driver will print ACPI tables for AMD IOMMU during
450 IOMMU initialization.
452 amijoy.map= [HW,JOY] Amiga joystick support
453 Map of devices attached to JOY0DAT and JOY1DAT
455 See also Documentation/input/joystick.txt
457 analog.map= [HW,JOY] Analog joystick and gamepad support
458 Specifies type or capabilities of an analog joystick
459 connected to one of 16 gameports
460 Format: <type1>,<type2>,..<type16>
463 Power management functions (SPARCstation-4/5 + deriv.)
465 Disable APC CPU standby support. SPARCstation-Fox does
466 not play well with APC CPU idle - disable it if you have
467 APC and your system crashes randomly.
469 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
470 Change the output verbosity whilst booting
471 Format: { quiet (default) | verbose | debug }
472 Change the amount of debugging information output
473 when initialising the APIC and IO-APIC components.
475 apic_extnmi= [APIC,X86] External NMI delivery setting
476 Format: { bsp (default) | all | none }
477 bsp: External NMI is delivered only to CPU 0
478 all: External NMIs are broadcast to all CPUs as a
480 none: External NMI is masked for all CPUs. This is
481 useful so that a dump capture kernel won't be
485 See Documentation/networking/ipv6.txt.
487 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
488 Limit apic dumping. The parameter defines the maximal
489 number of local apics being dumped. Also it is possible
490 to set it to "all" by meaning -- no limit here.
491 Format: { 1 (default) | 2 | ... | all }.
492 The parameter valid if only apic=debug or
493 apic=verbose is specified.
494 Example: apic=debug show_lapic=all
496 apm= [APM] Advanced Power Management
497 See header of arch/x86/kernel/apm_32.c.
499 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
500 Format: <io>,<irq>,<nodeID>
504 atarimouse= [HW,MOUSE] Atari Mouse
506 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
507 EzKey and similar keyboards
509 atkbd.reset= [HW] Reset keyboard during initialization
511 atkbd.set= [HW] Select keyboard code set
512 Format: <int> (2 = AT (default), 3 = PS/2)
514 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
517 atkbd.softraw= [HW] Choose between synthetic and real raw mode
518 Format: <bool> (0 = real, 1 = synthetic (default))
520 atkbd.softrepeat= [HW]
521 Use software keyboard repeat
523 audit= [KNL] Enable the audit sub-system
524 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
525 0 - kernel audit is disabled and can not be enabled
526 until the next reboot
527 unset - kernel audit is initialized but disabled and
528 will be fully enabled by the userspace auditd.
529 1 - kernel audit is initialized and partially enabled,
530 storing at most audit_backlog_limit messages in
531 RAM until it is fully enabled by the userspace
535 audit_backlog_limit= [KNL] Set the audit queue size limit.
536 Format: <int> (must be >=0)
539 baycom_epp= [HW,AX25]
542 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
544 See header of drivers/net/hamradio/baycom_par.c.
546 baycom_ser_fdx= [HW,AX25]
547 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
548 Format: <io>,<irq>,<mode>[,<baud>]
549 See header of drivers/net/hamradio/baycom_ser_fdx.c.
551 baycom_ser_hdx= [HW,AX25]
552 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
553 Format: <io>,<irq>,<mode>
554 See header of drivers/net/hamradio/baycom_ser_hdx.c.
556 blkdevparts= Manual partition parsing of block device(s) for
557 embedded devices based on command line input.
558 See Documentation/block/cmdline-partition.txt
560 boot_delay= Milliseconds to delay each printk during boot.
561 Values larger than 10 seconds (10000) are changed to
565 bootmem_debug [KNL] Enable bootmem allocator debug messages.
567 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
568 bttv.radio= Most important insmod options are available as
570 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
573 bulk_remove=off [PPC] This parameter disables the use of the pSeries
574 firmware feature for flushing multiple hpte entries
577 c101= [NET] Moxa C101 synchronous serial card
579 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
580 Sometimes CPU hardware bugs make them report the cache
581 size incorrectly. The kernel will attempt work arounds
582 to fix known problems, but for some CPUs it is not
583 possible to determine what the correct size should be.
584 This option provides an override for these situations.
586 ca_keys= [KEYS] This parameter identifies a specific key(s) on
587 the system trusted keyring to be used for certificate
589 format: { id:<keyid> | builtin }
591 cca= [MIPS] Override the kernel pages' cache coherency
592 algorithm. Accepted values range from 0 to 7
593 inclusive. See arch/mips/include/asm/pgtable-bits.h
594 for platform specific values (SB1, Loongson3 and
597 ccw_timeout_log [S390]
598 See Documentation/s390/CommonIO for details.
600 cgroup_disable= [KNL] Disable a particular controller
601 Format: {name of the controller(s) to disable}
602 The effects of cgroup_disable=foo are:
603 - foo isn't auto-mounted if you mount all cgroups in
605 - foo isn't visible as an individually mountable
607 {Currently only "memory" controller deal with this and
608 cut the overhead, others just disable the usage. So
609 only cgroup_disable=memory is actually worthy}
611 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
613 nosocket -- Disable socket memory accounting.
614 nokmem -- Disable kernel memory accounting.
616 checkreqprot [SELINUX] Set initial checkreqprot flag value.
617 Format: { "0" | "1" }
618 See security/selinux/Kconfig help text.
619 0 -- check protection applied by kernel (includes
620 any implied execute protection).
621 1 -- check protection requested by application.
622 Default value is set via a kernel config option.
623 Value can be changed at runtime via
624 /selinux/checkreqprot.
627 See Documentation/s390/CommonIO for details.
630 Prevents the clock framework from automatically gating
631 clocks that have not been explicitly enabled by a Linux
632 device driver but are enabled in hardware at reset or
633 by the bootloader/firmware. Note that this does not
634 force such clocks to be always-on nor does it reserve
635 those clocks in any way. This parameter is useful for
636 debug and development, but should not be needed on a
637 platform with proper driver support. For more
638 information, see Documentation/clk.txt.
640 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
642 Forces specified clocksource (if available) to be used
643 when calculating gettimeofday(). If specified
644 clocksource is not available, it defaults to PIT.
645 Format: { pit | tsc | cyclone | pmtmr }
647 clocksource= Override the default clocksource
649 Override the default clocksource and use the clocksource
650 with the name specified.
651 Some clocksource names to choose from, depending on
653 [all] jiffies (this is the base, fallback clocksource)
655 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
656 pxa_timer,timer3,32k_counter,timer0_1
658 [X86-32] pit,hpet,tsc;
659 scx200_hrt on Geode; cyclone on IBM x440
667 clearcpuid=BITNUM [X86]
668 Disable CPUID feature X for the kernel. See
669 arch/x86/include/asm/cpufeature.h for the valid bit
670 numbers. Note the Linux specific bits are not necessarily
671 stable over kernel options, but the vendor specific
673 Also note that user programs calling CPUID directly
674 or using the feature without checking anything
675 will still see it. This just prevents it from
676 being used by the kernel or shown in /proc/cpuinfo.
677 Also note the kernel might malfunction if you disable
680 cma=nn[MG]@[start[MG][-end[MG]]]
682 Sets the size of kernel global memory area for
683 contiguous memory allocations and optionally the
684 placement constraint by the physical address range of
685 memory allocations. A value of 0 disables CMA
686 altogether. For more information, see
687 include/linux/dma-contiguous.h
689 cmo_free_hint= [PPC] Format: { yes | no }
690 Specify whether pages are marked as being inactive
691 when they are freed. This is used in CMO environments
692 to determine OS memory pressure for page stealing by
696 coherent_pool=nn[KMG] [ARM,KNL]
697 Sets the size of memory pool for coherent, atomic dma
698 allocations, by default set to 256K.
700 code_bytes [X86] How many bytes of object code to print
705 com20020= [HW,NET] ARCnet - COM20020 chipset
707 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
709 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
713 ARCnet - COM90xx chipset (memory-mapped buffers)
714 Format: <io>[,<irq>[,<memstart>]]
716 condev= [HW,S390] console device
719 console= [KNL] Output console device and options.
721 tty<n> Use the virtual console device <n>.
725 Use the specified serial port. The options are of
726 the form "bbbbpnf", where "bbbb" is the baud rate,
727 "p" is parity ("n", "o", or "e"), "n" is number of
728 bits, and "f" is flow control ("r" for RTS or
729 omit it). Default is "9600n8".
731 See Documentation/serial-console.txt for more
733 Documentation/networking/netconsole.txt for an
736 uart[8250],io,<addr>[,options]
737 uart[8250],mmio,<addr>[,options]
738 uart[8250],mmio16,<addr>[,options]
739 uart[8250],mmio32,<addr>[,options]
740 uart[8250],0x<addr>[,options]
741 Start an early, polled-mode console on the 8250/16550
742 UART at the specified I/O port or MMIO address,
743 switching to the matching ttyS device later.
744 MMIO inter-register address stride is either 8-bit
745 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
746 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
747 to be equivalent to 'mmio'. 'options' are specified in
748 the same format described for ttyS above; if unspecified,
749 the h/w is not re-initialized.
751 hvc<n> Use the hypervisor console device <n>. This is for
752 both Xen and PowerPC hypervisors.
754 If the device connected to the port is not a TTY but a braille
755 device, prepend "brl," before the device type, for instance
757 For now, only VisioBraille is supported.
759 consoleblank= [KNL] The console blank (screen saver) timeout in
760 seconds. Defaults to 10*60 = 10mins. A value of 0
761 disables the blank timer.
764 [KNL] Change the default value for
765 /proc/<pid>/coredump_filter.
766 See also Documentation/filesystems/proc.txt.
768 cpuidle.off=1 [CPU_IDLE]
769 disable the cpuidle sub-system
772 [X86] Delay for N microsec between assert and de-assert
773 of APIC INIT to start processors. This delay occurs
774 on every CPU online, such as boot, and resume from suspend.
777 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
779 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
781 crashkernel=size[KMG][@offset[KMG]]
782 [KNL] Using kexec, Linux can switch to a 'crash kernel'
783 upon panic. This parameter reserves the physical
784 memory region [offset, offset + size] for that kernel
785 image. If '@offset' is omitted, then a suitable offset
786 is selected automatically. Check
787 Documentation/kdump/kdump.txt for further details.
789 crashkernel=range1:size1[,range2:size2,...][@offset]
790 [KNL] Same as above, but depends on the memory
791 in the running system. The syntax of range is
792 start-[end] where start and end are both
793 a memory unit (amount[KMG]). See also
794 Documentation/kdump/kdump.txt for an example.
796 crashkernel=size[KMG],high
797 [KNL, x86_64] range could be above 4G. Allow kernel
798 to allocate physical memory region from top, so could
799 be above 4G if system have more than 4G ram installed.
800 Otherwise memory region will be allocated below 4G, if
802 It will be ignored if crashkernel=X is specified.
803 crashkernel=size[KMG],low
804 [KNL, x86_64] range under 4G. When crashkernel=X,high
805 is passed, kernel could allocate physical memory region
806 above 4G, that cause second kernel crash on system
807 that require some amount of low memory, e.g. swiotlb
808 requires at least 64M+32K low memory, also enough extra
809 low memory is needed to make sure DMA buffers for 32-bit
810 devices won't run out. Kernel would try to allocate at
811 at least 256M below 4G automatically.
812 This one let user to specify own low range under 4G
813 for second kernel instead.
814 0: to disable low allocation.
815 It will be ignored when crashkernel=X,high is not used
816 or memory reserved is below 4G.
821 cs89x0_media= [HW,NET]
822 Format: { rj45 | aui | bnc }
825 See header of drivers/s390/block/dasd_devmap.c.
827 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
828 (one device per port)
829 Format: <port#>,<type>
830 See also Documentation/input/joystick-parport.txt
832 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
833 time. See Documentation/dynamic-debug-howto.txt for
834 details. Deprecated, see dyndbg.
836 debug [KNL] Enable kernel debugging (events log level).
839 [KNL] verbose self-tests
841 Print debugging info while doing the locking API
843 We default to 0 (no extra messages), setting it to
844 1 will print _a lot_ more information - normally
845 only useful to kernel developers.
847 debug_objects [KNL] Enable object debugging
850 [KNL] Disable object debugging
852 debug_guardpage_minorder=
853 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
854 parameter allows control of the order of pages that will
855 be intentionally kept free (and hence protected) by the
856 buddy allocator. Bigger value increase the probability
857 of catching random memory corruption, but reduce the
858 amount of memory for normal system use. The maximum
859 possible value is MAX_ORDER/2. Setting this parameter
860 to 1 or 2 should be enough to identify most random
861 memory corruption problems caused by bugs in kernel or
862 driver code when a CPU writes to (or reads from) a
863 random memory location. Note that there exists a class
864 of memory corruptions problems caused by buggy H/W or
865 F/W or by drivers badly programing DMA (basically when
866 memory is written at bus level and the CPU MMU is
867 bypassed) which are not detectable by
868 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
869 tracking down these problems.
872 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
873 parameter enables the feature at boot time. In
874 default, it is disabled. We can avoid allocating huge
875 chunk of memory for debug pagealloc if we don't enable
876 it at boot time and the system will work mostly same
877 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
878 on: enable the feature
880 debugpat [X86] Enable PAT debugging
882 decnet.addr= [HW,NET]
883 Format: <area>[,<node>]
884 See also Documentation/networking/decnet.txt.
887 [same as hugepagesz=] The size of the default
888 HugeTLB page size. This is the size represented by
889 the legacy /proc/ hugepages APIs, used for SHM, and
890 default size when mounting hugetlbfs filesystems.
891 Defaults to the default architecture's huge page size
895 Set number of hash buckets for dentry cache.
898 See Documentation/networking/ipv6.txt.
900 disable_cpu_apicid= [X86,APIC,SMP]
902 The number of initial APIC ID for the
903 corresponding CPU to be disabled at boot,
904 mostly used for the kdump 2nd kernel to
905 disable BSP to wake up multiple CPUs without
906 causing system reset or hang due to sending
909 disable_ddw [PPC/PSERIES]
910 Disable Dynamic DMA Window support. Use this if
911 to workaround buggy firmware.
914 See Documentation/networking/ipv6.txt.
916 disable_mtrr_cleanup [X86]
917 The kernel tries to adjust MTRR layout from continuous
918 to discrete, to make X server driver able to add WB
919 entry later. This parameter disables that.
921 disable_mtrr_trim [X86, Intel and AMD only]
922 By default the kernel will trim any uncacheable
923 memory out of your available memory pool based on
924 MTRR settings. This parameter disables that behavior,
925 possibly causing your machine to run very slowly.
927 disable_timer_pin_1 [X86]
928 Disable PIN 1 of APIC timer
929 Can be useful to work around chipset bugs.
931 dis_ucode_ldr [X86] Disable the microcode loader.
933 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
934 this option disables the debugging code at boot.
936 dma_debug_entries=<number>
937 This option allows to tune the number of preallocated
938 entries for DMA-API debugging code. One entry is
939 required per DMA-API allocation. Use this if the
940 DMA-API debugging code disables itself because the
941 architectural default is too low.
943 dma_debug_driver=<driver_name>
944 With this option the DMA-API debugging driver
945 filter feature can be enabled at boot time. Just
946 pass the driver to filter for as the parameter.
947 The filter can be disabled or changed to another
948 driver later using sysfs.
950 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
951 Broken monitors, graphic adapters, KVMs and EDIDless
952 panels may send no or incorrect EDID data sets.
953 This parameter allows to specify an EDID data sets
954 in the /lib/firmware directory that are used instead.
955 Generic built-in EDID data sets are used, if one of
956 edid/1024x768.bin, edid/1280x1024.bin,
957 edid/1680x1050.bin, or edid/1920x1080.bin is given
958 and no file with the same name exists. Details and
959 instructions how to build your own EDID data are
960 available in Documentation/EDID/HOWTO.txt. An EDID
961 data set will only be used for a particular connector,
962 if its name and a colon are prepended to the EDID
963 name. Each connector may use a unique EDID data
964 set by separating the files with a comma. An EDID
965 data set with no connector name will be used for
966 any connectors not explicitly specified.
970 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
971 module.dyndbg[="val"]
972 Enable debug messages at boot time. See
973 Documentation/dynamic-debug-howto.txt for details.
975 nompx [X86] Disables Intel Memory Protection Extensions.
976 See Documentation/x86/intel_mpx.txt for more
977 information about the feature.
980 on enable eager fpu restore
981 off disable eager fpu restore
982 auto selects the default scheme, which automatically
983 enables eagerfpu restore for xsaveopt.
985 module.async_probe [KNL]
986 Enable asynchronous probe on this module.
988 early_ioremap_debug [KNL]
989 Enable debug messages in early_ioremap support. This
990 is useful for tracking down temporary early mappings
991 which are not unmapped.
993 earlycon= [KNL] Output early console device and options.
995 When used with no options, the early console is
996 determined by the stdout-path property in device
1000 Start an early, polled-mode console on a cadence serial
1001 port at the specified address. The cadence serial port
1002 must already be setup and configured. Options are not
1005 uart[8250],io,<addr>[,options]
1006 uart[8250],mmio,<addr>[,options]
1007 uart[8250],mmio32,<addr>[,options]
1008 uart[8250],mmio32be,<addr>[,options]
1009 uart[8250],0x<addr>[,options]
1010 Start an early, polled-mode console on the 8250/16550
1011 UART at the specified I/O port or MMIO address.
1012 MMIO inter-register address stride is either 8-bit
1013 (mmio) or 32-bit (mmio32 or mmio32be).
1014 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1015 to be equivalent to 'mmio'. 'options' are specified
1016 in the same format described for "console=ttyS<n>"; if
1017 unspecified, the h/w is not initialized.
1021 Start an early, polled-mode console on a pl011 serial
1022 port at the specified address. The pl011 serial port
1023 must already be setup and configured. Options are not
1024 yet supported. If 'mmio32' is specified, then only
1025 the driver will use only 32-bit accessors to read/write
1026 the device registers.
1029 Start an early, polled-mode console on an msm serial
1030 port at the specified address. The serial port
1031 must already be setup and configured. Options are not
1034 msm_serial_dm,<addr>
1035 Start an early, polled-mode console on an msm serial
1036 dm port at the specified address. The serial port
1037 must already be setup and configured. Options are not
1040 smh Use ARM semihosting calls for early console.
1048 Use early console provided by serial driver available
1049 on Samsung SoCs, requires selecting proper type and
1050 a correct base address of the selected UART port. The
1051 serial port must already be setup and configured.
1052 Options are not yet supported.
1056 Use early console provided by Freescale LP UART driver
1057 found on Freescale Vybrid and QorIQ LS1021A processors.
1058 A valid base address must be provided, and the serial
1059 port must already be setup and configured.
1061 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1065 earlyprintk=serial[,ttySn[,baudrate]]
1066 earlyprintk=serial[,0x...[,baudrate]]
1067 earlyprintk=ttySn[,baudrate]
1068 earlyprintk=dbgp[debugController#]
1069 earlyprintk=pciserial,bus:device.function[,baudrate]
1071 earlyprintk is useful when the kernel crashes before
1072 the normal console is initialized. It is not enabled by
1073 default because it has some cosmetic problems.
1075 Append ",keep" to not disable it when the real console
1078 Only one of vga, efi, serial, or usb debug port can
1081 Currently only ttyS0 and ttyS1 may be specified by
1082 name. Other I/O ports may be explicitly specified
1083 on some architectures (x86 and arm at least) by
1084 replacing ttySn with an I/O port address, like this:
1085 earlyprintk=serial,0x1008,115200
1086 You can find the port for a given device in
1087 /proc/tty/driver/serial:
1088 2: uart:ST16650V2 port:00001008 irq:18 ...
1090 Interaction with the standard serial driver is not
1093 The VGA and EFI output is eventually overwritten by
1096 The xen output can only be used by Xen PV guests.
1098 edac_report= [HW,EDAC] Control how to report EDAC event
1099 Format: {"on" | "off" | "force"}
1100 on: enable EDAC to report H/W event. May be overridden
1101 by other higher priority error reporting module.
1102 off: disable H/W event reporting through EDAC.
1103 force: enforce the use of EDAC to report H/W event.
1106 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1109 This is designed to be used in conjunction with
1110 the boot argument: earlyprintk=vga
1113 Format: {"off" | "on" | "skip[mbr]"}
1116 Format: { "old_map", "nochunk", "noruntime", "debug" }
1117 old_map [X86-64]: switch to the old ioremap-based EFI
1118 runtime services mapping. 32-bit still uses this one by
1120 nochunk: disable reading files in "chunks" in the EFI
1121 boot stub, as chunking can cause problems with some
1122 firmware implementations.
1123 noruntime : disable EFI runtime services support
1124 debug: enable misc debug output
1126 efi_no_storage_paranoia [EFI; X86]
1127 Using this parameter you can use more than 50% of
1128 your efi variable storage. Use this parameter only if
1129 you are really sure that your UEFI does sane gc and
1130 fulfills the spec otherwise your board may brick.
1132 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1133 Add arbitrary attribute to specific memory range by
1134 updating original EFI memory map.
1135 Region of memory which aa attribute is added to is
1137 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1138 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1139 attribute is added to range 0x100000000-0x180000000 and
1140 0x10a0000000-0x1120000000.
1142 Using this parameter you can do debugging of EFI memmap
1143 related feature. For example, you can do debugging of
1144 Address Range Mirroring feature even if your box
1147 eisa_irq_edge= [PARISC,HW]
1148 See header of drivers/parisc/eisa.c.
1151 See comment before function elanfreq_setup() in
1152 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1155 Format: {"cfq" | "deadline" | "noop"}
1156 See Documentation/block/cfq-iosched.txt and
1157 Documentation/block/deadline-iosched.txt for details.
1159 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1160 Specifies physical address of start of kernel core
1161 image elf header and optionally the size. Generally
1162 kexec loader will pass this option to capture kernel.
1163 See Documentation/kdump/kdump.txt for details.
1165 enable_mtrr_cleanup [X86]
1166 The kernel tries to adjust MTRR layout from continuous
1167 to discrete, to make X server driver able to add WB
1168 entry later. This parameter enables that.
1170 enable_timer_pin_1 [X86]
1171 Enable PIN 1 of APIC timer
1172 Can be useful to work around chipset bugs
1173 (in particular on some ATI chipsets).
1174 The kernel tries to set a reasonable default.
1176 enforcing [SELINUX] Set initial enforcing status.
1178 See security/selinux/Kconfig help text.
1179 0 -- permissive (log only, no denials).
1180 1 -- enforcing (deny and log).
1182 Value can be changed at runtime via /selinux/enforce.
1185 Disable Error Record Serialization Table (ERST)
1188 ether= [HW,NET] Ethernet cards parameters
1189 This option is obsoleted by the "netdev=" option, which
1190 has equivalent usage. See its documentation for details.
1194 Permit 'security.evm' to be updated regardless of
1195 current integrity status.
1199 fail_make_request=[KNL]
1200 General fault injection mechanism.
1201 Format: <interval>,<probability>,<space>,<times>
1202 See also Documentation/fault-injection/.
1205 See Documentation/blockdev/floppy.txt.
1207 force_pal_cache_flush
1208 [IA-64] Avoid check_sal_cache_flush which may hang on
1209 buggy SAL_CACHE_FLUSH implementations. Using this
1210 parameter will force ia64_sal_cache_flush to call
1211 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1214 Forcefully enable Physical Address Extension (PAE).
1215 Many Pentium M systems disable PAE but may have a
1216 functionally usable PAE implementation.
1217 Warning: use of this parameter will taint the kernel
1218 and may cause unknown problems.
1221 [FTRACE] will set and start the specified tracer
1222 as early as possible in order to facilitate early
1225 ftrace_dump_on_oops[=orig_cpu]
1226 [FTRACE] will dump the trace buffers on oops.
1227 If no parameter is passed, ftrace will dump
1228 buffers of all CPUs, but if you pass orig_cpu, it will
1229 dump only the buffer of the CPU that triggered the
1232 ftrace_filter=[function-list]
1233 [FTRACE] Limit the functions traced by the function
1234 tracer at boot up. function-list is a comma separated
1235 list of functions. This list can be changed at run
1236 time by the set_ftrace_filter file in the debugfs
1239 ftrace_notrace=[function-list]
1240 [FTRACE] Do not trace the functions specified in
1241 function-list. This list can be changed at run time
1242 by the set_ftrace_notrace file in the debugfs
1245 ftrace_graph_filter=[function-list]
1246 [FTRACE] Limit the top level callers functions traced
1247 by the function graph tracer at boot up.
1248 function-list is a comma separated list of functions
1249 that can be changed at run time by the
1250 set_graph_function file in the debugfs tracing directory.
1252 ftrace_graph_notrace=[function-list]
1253 [FTRACE] Do not trace from the functions specified in
1254 function-list. This list is a comma separated list of
1255 functions that can be changed at run time by the
1256 set_graph_notrace file in the debugfs tracing directory.
1259 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1260 support via parallel port (up to 5 devices per port)
1261 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1262 See also Documentation/input/joystick-parport.txt
1266 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1270 gcov_persist= [GCOV] When non-zero (default), profiling data for
1271 kernel modules is saved and remains accessible via
1272 debugfs, even when the module is unloaded/reloaded.
1273 When zero, profiling data is discarded and associated
1274 debugfs files are removed at module unload time.
1276 gpt [EFI] Forces disk with valid GPT signature but
1277 invalid Protective MBR to be treated as GPT. If the
1278 primary GPT is corrupted, it enables the backup/alternate
1279 GPT to be used instead.
1281 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1282 the "Enable 0" bit of the configuration register.
1285 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1286 the "Enable 0" bit of the configuration register.
1289 grcan.select= [HW] Select which physical interface to use.
1292 grcan.txsize= [HW] Sets the size of the tx buffer.
1293 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1295 grcan.rxsize= [HW] Sets the size of the rx buffer.
1296 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1299 hardlockup_all_cpu_backtrace=
1300 [KNL] Should the hard-lockup detector generate
1301 backtraces on all cpus.
1304 hashdist= [KNL,NUMA] Large hashes allocated during boot
1305 are distributed across NUMA nodes. Defaults on
1306 for 64-bit NUMA, off otherwise.
1307 Format: 0 | 1 (for off | on)
1309 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1311 hd= [EIDE] (E)IDE hard drive subsystem geometry
1312 Format: <cyl>,<head>,<sect>
1315 Disable Hardware Error Source Table (HEST) support;
1316 corresponding firmware-first mode error processing
1317 logic will be disabled.
1319 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1320 size of <nn>. This works even on boxes that have no
1321 highmem otherwise. This also works to reduce highmem
1322 size on bigger boxes.
1324 highres= [KNL] Enable/disable high resolution timer mode.
1325 Valid parameters: "on", "off"
1329 See Documentation/isdn/README.HiSax.
1333 hpet= [X86-32,HPET] option to control HPET usage
1334 Format: { enable (default) | disable | force |
1336 disable: disable HPET and use PIT instead
1337 force: allow force enabled of undocumented chips (ICH4,
1339 verbose: show contents of HPET registers during setup
1341 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1342 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1344 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1345 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1346 On x86-64 and powerpc, this option can be specified
1347 multiple times interleaved with hugepages= to reserve
1348 huge pages of different sizes. Valid pages sizes on
1349 x86-64 are 2M (when the CPU supports "pse") and 1G
1350 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1352 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1353 terminal devices. Valid values: 0..8
1354 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1355 If specified, z/VM IUCV HVC accepts connections
1356 from listed z/VM user IDs only.
1358 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1359 hardware thread id mappings.
1360 Format: <cpu>:<hwthread>
1363 Do not unregister boot console at start. This is only
1364 useful for debugging when something happens in the window
1365 between unregistering the boot console and initializing
1368 i2c_bus= [HW] Override the default board specific I2C bus speed
1369 or register an additional I2C bus that is not
1370 registered from board initialization code.
1374 i8042.debug [HW] Toggle i8042 debug mode
1375 i8042.unmask_kbd_data
1376 [HW] Enable printing of interrupt data from the KBD port
1377 (disabled by default, and as a pre-condition
1378 requires that i8042.debug=1 be enabled)
1379 i8042.direct [HW] Put keyboard port into non-translated mode
1380 i8042.dumbkbd [HW] Pretend that controller can only read data from
1381 keyboard and cannot control its state
1382 (Don't attempt to blink the leds)
1383 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1384 i8042.nokbd [HW] Don't check/create keyboard port
1385 i8042.noloop [HW] Disable the AUX Loopback command while probing
1387 i8042.nomux [HW] Don't check presence of an active multiplexing
1389 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1391 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1392 i8042.reset [HW] Reset the controller during init and cleanup
1393 i8042.unlock [HW] Unlock (ignore) the keylock
1394 i8042.kbdreset [HW] Reset device connected to KBD port
1398 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1399 indicates that the driver is running on unsupported
1401 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1402 does not match list of supported models.
1404 [HW] Report power status in /proc/i8k
1405 (disabled by default)
1406 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1409 i915.invert_brightness=
1410 [DRM] Invert the sense of the variable that is used to
1411 set the brightness of the panel backlight. Normally a
1412 brightness value of 0 indicates backlight switched off,
1413 and the maximum of the brightness value sets the backlight
1414 to maximum brightness. If this parameter is set to 0
1415 (default) and the machine requires it, or this parameter
1416 is set to 1, a brightness value of 0 sets the backlight
1417 to maximum brightness, and the maximum of the brightness
1418 value switches the backlight off.
1419 -1 -- never invert brightness
1420 0 -- machine default
1421 1 -- force brightness inversion
1424 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1426 ide-core.nodma= [HW] (E)IDE subsystem
1427 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1428 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1429 .cdrom .chs .ignore_cable are additional options
1430 See Documentation/ide/ide.txt.
1432 ide-generic.probe-mask= [HW] (E)IDE subsystem
1434 Probe mask for legacy ISA IDE ports. Depending on
1435 platform up to 6 ports are supported, enabled by
1436 setting corresponding bits in the mask to 1. The
1437 default value is 0x0, which has a special meaning.
1438 On systems that have PCI, it triggers scanning the
1439 PCI bus for the first and the second port, which
1440 are then probed. On systems without PCI the value
1441 of 0x0 enables probing the two first ports as if it
1444 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1445 Claim all unknown PCI IDE storage controllers.
1448 Format: idle=poll, idle=halt, idle=nomwait
1449 Poll forces a polling idle loop that can slightly
1450 improve the performance of waking up a idle CPU, but
1451 will use a lot of power and make the system run hot.
1453 idle=halt: Halt is forced to be used for CPU idle.
1454 In such case C2/C3 won't be used again.
1455 idle=nomwait: Disable mwait for CPU C-states
1457 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1458 Format: { strict | legacy | 2008 | relaxed }
1461 Choose which programs will be accepted for execution
1462 based on the IEEE 754 NaN encoding(s) supported by
1463 the FPU and the NaN encoding requested with the value
1464 of an ELF file header flag individually set by each
1465 binary. Hardware implementations are permitted to
1466 support either or both of the legacy and the 2008 NaN
1469 Available settings are as follows:
1470 strict accept binaries that request a NaN encoding
1471 supported by the FPU
1472 legacy only accept legacy-NaN binaries, if supported
1474 2008 only accept 2008-NaN binaries, if supported
1476 relaxed accept any binaries regardless of whether
1477 supported by the FPU
1479 The FPU emulator is always able to support both NaN
1480 encodings, so if no FPU hardware is present or it has
1481 been disabled with 'nofpu', then the settings of
1482 'legacy' and '2008' strap the emulator accordingly,
1483 'relaxed' straps the emulator for both legacy-NaN and
1484 2008-NaN, whereas 'strict' enables legacy-NaN only on
1485 legacy processors and both NaN encodings on MIPS32 or
1488 The setting for ABS.fmt/NEG.fmt instruction execution
1489 mode generally follows that for the NaN encoding,
1490 except where unsupported by hardware.
1492 ignore_loglevel [KNL]
1493 Ignore loglevel setting - this will print /all/
1494 kernel messages to the console. Useful for debugging.
1495 We also add it as printk module parameter, so users
1496 could change it dynamically, usually by
1497 /sys/module/printk/parameters/ignore_loglevel.
1500 Ignore RLIMIT_DATA setting for data mappings,
1501 print warning at first misuse. Can be changed via
1502 /sys/module/kernel/parameters/ignore_rlimit_data.
1504 ihash_entries= [KNL]
1505 Set number of hash buckets for inode cache.
1507 ima_appraise= [IMA] appraise integrity measurements
1508 Format: { "off" | "enforce" | "fix" | "log" }
1511 ima_appraise_tcb [IMA]
1512 The builtin appraise policy appraises all files
1516 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1520 The list of supported hash algorithms is defined
1521 in crypto/hash_info.h.
1524 The builtin measurement policy to load during IMA
1525 setup. Specyfing "tcb" as the value, measures all
1526 programs exec'd, files mmap'd for exec, and all files
1527 opened with the read mode bit set by either the
1528 effective uid (euid=0) or uid=0.
1531 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1532 Load a policy which meets the needs of the Trusted
1533 Computing Base. This means IMA will measure all
1534 programs exec'd, files mmap'd for exec, and all files
1535 opened for read by uid=0.
1538 Select one of defined IMA measurements template formats.
1539 Formats: { "ima" | "ima-ng" | "ima-sig" }
1543 [IMA] Define a custom template format.
1544 Format: { "field1|...|fieldN" }
1546 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1547 Format: <min_file_size>
1548 Set the minimal file size for using asynchronous hash.
1549 If left unspecified, ahash usage is disabled.
1551 ahash performance varies for different data sizes on
1552 different crypto accelerators. This option can be used
1553 to achieve the best performance for a particular HW.
1555 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1557 Set hashing buffer size. Default: 4k.
1559 ahash performance varies for different chunk sizes on
1560 different crypto accelerators. This option can be used
1561 to achieve best performance for particular HW.
1565 Run specified binary instead of /sbin/init as init
1568 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1569 for working out where the kernel is dying during
1572 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1573 initcall functions. Useful for debugging built-in
1574 modules and initcalls.
1576 initrd= [BOOT] Specify the location of the initial ramdisk
1578 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1581 int_pln_enable [x86] Enable power limit notification interrupt
1583 integrity_audit=[IMA]
1584 Format: { "0" | "1" }
1585 0 -- basic integrity auditing messages. (Default)
1586 1 -- additional integrity auditing messages.
1588 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1590 Enable intel iommu driver.
1592 Disable intel iommu driver.
1593 igfx_off [Default Off]
1594 By default, gfx is mapped as normal device. If a gfx
1595 device has a dedicated DMAR unit, the DMAR unit is
1596 bypassed by not enabling DMAR with this option. In
1597 this case, gfx device will use physical address for
1600 With this option iommu will not optimize to look
1601 for io virtual address below 32-bit forcing dual
1602 address cycle on pci bus for cards supporting greater
1603 than 32-bit addressing. The default is to look
1604 for translation below 32-bit and if not available
1605 then look in the higher range.
1606 strict [Default Off]
1607 With this option on every unmap_single operation will
1608 result in a hardware IOTLB flush operation as opposed
1609 to batching them for performance.
1610 sp_off [Default Off]
1611 By default, super page will be supported if Intel IOMMU
1612 has the capability. With this option, super page will
1614 ecs_off [Default Off]
1615 By default, extended context tables will be supported if
1616 the hardware advertises that it has support both for the
1617 extended tables themselves, and also PASID support. With
1618 this option set, extended tables will not be used even
1619 on hardware which claims to support them.
1621 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1622 0 disables intel_idle and fall back on acpi_idle.
1623 1 to 6 specify maximum depth of C-state.
1627 Do not enable intel_pstate as the default
1628 scaling driver for the supported processors
1630 Enable intel_pstate on systems that prohibit it by default
1631 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1632 instead of acpi-cpufreq may disable platform features, such
1633 as thermal controls and power capping, that rely on ACPI
1634 P-States information being indicated to OSPM and therefore
1635 should be used with caution. This option does not work with
1636 processors that aren't supported by the intel_pstate driver
1637 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1639 Do not enable hardware P state control (HWP)
1642 Only load intel_pstate on systems which support
1643 hardware P state control (HWP) if available.
1645 intremap= [X86-64, Intel-IOMMU]
1646 on enable Interrupt Remapping (default)
1647 off disable Interrupt Remapping
1648 nosid disable Source ID checking
1650 BIOS x2APIC opt-out request will be ignored
1651 nopost disable Interrupt Posting
1653 iomem= Disable strict checking of access to MMIO memory
1654 strict regions from userspace.
1669 nobypass [PPC/POWERNV]
1670 Disable IOMMU bypass, using IOMMU for PCI devices.
1673 io7= [HW] IO7 for Marvel based alpha systems
1674 See comment before marvel_specify_io7 in
1675 arch/alpha/kernel/core_marvel.c.
1677 io_delay= [X86] I/O delay method
1679 Standard port 0x80 based delay
1681 Alternate port 0xed based delay (needed on some systems)
1683 Simple two microseconds delay
1688 See Documentation/filesystems/nfs/nfsroot.txt.
1691 When an interrupt is not handled search all handlers
1692 for it. Intended to get systems with badly broken
1696 When an interrupt is not handled search all handlers
1697 for it. Also check all handlers each timer
1698 interrupt. Intended to get systems with badly broken
1702 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1704 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1706 <cpu number>,...,<cpu number>
1708 <cpu number>-<cpu number>
1709 (must be a positive range in ascending order)
1711 <cpu number>,...,<cpu number>-<cpu number>
1713 This option can be used to specify one or more CPUs
1714 to isolate from the general SMP balancing and scheduling
1715 algorithms. You can move a process onto or off an
1716 "isolated" CPU via the CPU affinity syscalls or cpuset.
1717 <cpu number> begins at 0 and the maximum value is
1718 "number of CPUs in system - 1".
1720 This option is the preferred way to isolate CPUs. The
1721 alternative -- manually setting the CPU mask of all
1722 tasks in the system -- can cause problems and
1723 suboptimal load balancer performance.
1727 ivrs_ioapic [HW,X86_64]
1728 Provide an override to the IOAPIC-ID<->DEVICE-ID
1729 mapping provided in the IVRS ACPI table. For
1730 example, to map IOAPIC-ID decimal 10 to
1731 PCI device 00:14.0 write the parameter as:
1732 ivrs_ioapic[10]=00:14.0
1734 ivrs_hpet [HW,X86_64]
1735 Provide an override to the HPET-ID<->DEVICE-ID
1736 mapping provided in the IVRS ACPI table. For
1737 example, to map HPET-ID decimal 0 to
1738 PCI device 00:14.0 write the parameter as:
1739 ivrs_hpet[0]=00:14.0
1741 js= [HW,JOY] Analog joystick
1742 See Documentation/input/joystick.txt.
1745 Enable/disable kernel and module base offset ASLR
1746 (Address Space Layout Randomization) if built into
1747 the kernel. When CONFIG_HIBERNATION is selected,
1748 kASLR is disabled by default. When kASLR is enabled,
1749 hibernation will be disabled.
1753 kernelcore= [KNL,X86,IA-64,PPC]
1754 Format: nn[KMGTPE] | "mirror"
1756 specifies the amount of memory usable by the kernel
1757 for non-movable allocations. The requested amount is
1758 spread evenly throughout all nodes in the system. The
1759 remaining memory in each node is used for Movable
1760 pages. In the event, a node is too small to have both
1761 kernelcore and Movable pages, kernelcore pages will
1762 take priority and other nodes will have a larger number
1763 of Movable pages. The Movable zone is used for the
1764 allocation of pages that may be reclaimed or moved
1765 by the page migration subsystem. This means that
1766 HugeTLB pages may not be allocated from this zone.
1767 Note that allocations like PTEs-from-HighMem still
1768 use the HighMem zone if it exists, and the Normal
1769 zone if it does not.
1771 Instead of specifying the amount of memory (nn[KMGTPE]),
1772 you can specify "mirror" option. In case "mirror"
1773 option is specified, mirrored (reliable) memory is used
1774 for non-movable allocations and remaining memory is used
1775 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1776 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1779 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1780 Format: <Controller#>[,poll interval]
1781 The controller # is the number of the ehci usb debug
1782 port as it is probed via PCI. The poll interval is
1783 optional and is the number seconds in between
1784 each poll cycle to the debug port in case you need
1785 the functionality for interrupting the kernel with
1786 gdb or control-c on the dbgp connection. When
1787 not using this parameter you use sysrq-g to break into
1788 the kernel debugger.
1790 kgdboc= [KGDB,HW] kgdb over consoles.
1791 Requires a tty driver that supports console polling,
1792 or a supported polling keyboard driver (non-usb).
1793 Serial only format: <serial_device>[,baud]
1794 keyboard only format: kbd
1795 keyboard and serial format: kbd,<serial_device>[,baud]
1796 Optional Kernel mode setting:
1797 kms, kbd format: kms,kbd
1798 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1800 kgdbwait [KGDB] Stop kernel execution and enter the
1801 kernel debugger at the earliest opportunity.
1803 kmac= [MIPS] korina ethernet MAC address.
1804 Configure the RouterBoard 532 series on-chip
1805 Ethernet adapter MAC address.
1807 kmemleak= [KNL] Boot-time kmemleak enable/disable
1808 Valid arguments: on, off
1810 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1813 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1814 Valid arguments: 0, 1, 2
1815 kmemcheck=0 (disabled)
1816 kmemcheck=1 (enabled)
1817 kmemcheck=2 (one-shot mode)
1818 Default: 2 (one-shot mode)
1820 kstack=N [X86] Print N words from the kernel stack
1823 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1824 Default is 0 (don't ignore, but inject #GP)
1826 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1830 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1831 Default is 1 (enabled)
1833 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1835 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1837 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1838 (virtualized MMU) support on capable Intel chips.
1839 Default is 1 (enabled)
1841 kvm-intel.emulate_invalid_guest_state=
1842 [KVM,Intel] Enable emulation of invalid guest states
1843 Default is 0 (disabled)
1845 kvm-intel.flexpriority=
1846 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1847 Default is 1 (enabled)
1850 [KVM,Intel] Enable VMX nesting (nVMX).
1851 Default is 0 (disabled)
1853 kvm-intel.unrestricted_guest=
1854 [KVM,Intel] Disable unrestricted guest feature
1855 (virtualized real and unpaged mode) on capable
1856 Intel chips. Default is 1 (enabled)
1858 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1859 feature (tagged TLBs) on capable Intel chips.
1860 Default is 1 (enabled)
1866 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1869 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1870 value for LAPIC timer one-shot implementation. Default
1871 back to the programmable timer unit in the LAPIC.
1873 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1876 libata.dma= [LIBATA] DMA control
1877 libata.dma=0 Disable all PATA and SATA DMA
1878 libata.dma=1 PATA and SATA Disk DMA only
1879 libata.dma=2 ATAPI (CDROM) DMA only
1880 libata.dma=4 Compact Flash DMA only
1881 Combinations also work, so libata.dma=3 enables DMA
1882 for disks and CDROMs, but not CFs.
1884 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1885 libata.ignore_hpa=0 keep BIOS limits (default)
1886 libata.ignore_hpa=1 ignore limits, using full disk
1888 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1892 libata.force= [LIBATA] Force configurations. The format is comma
1893 separated list of "[ID:]VAL" where ID is
1894 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1895 matching port, link or device. Basically, it matches
1896 the ATA ID string printed on console by libata. If
1897 the whole ID part is omitted, the last PORT and DEVICE
1898 values are used. If ID hasn't been specified yet, the
1899 configuration applies to all ports, links and devices.
1901 If only DEVICE is omitted, the parameter applies to
1902 the port and all links and devices behind it. DEVICE
1903 number of 0 either selects the first device or the
1904 first fan-out link behind PMP device. It does not
1905 select the host link. DEVICE number of 15 selects the
1906 host link and device attached to it.
1908 The VAL specifies the configuration to force. As long
1909 as there's no ambiguity shortcut notation is allowed.
1910 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1911 The following configurations can be forced.
1913 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1914 Any ID with matching PORT is used.
1916 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1918 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1919 udma[/][16,25,33,44,66,100,133] notation is also
1922 * [no]ncq: Turn on or off NCQ.
1924 * [no]ncqtrim: Turn off queued DSM TRIM.
1926 * nohrst, nosrst, norst: suppress hard, soft
1929 * rstonce: only attempt one reset during
1930 hot-unplug link recovery
1932 * dump_id: dump IDENTIFY data.
1934 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1936 * disable: Disable this device.
1938 If there are multiple matching configurations changing
1939 the same attribute, the last one is used.
1941 memblock=debug [KNL] Enable memblock debug messages.
1943 load_ramdisk= [RAM] List of ramdisks to load from floppy
1944 See Documentation/blockdev/ramdisk.txt.
1946 lockd.nlm_grace_period=P [NFS] Assign grace period.
1949 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1952 lockd.nlm_timeout=T [NFS] Assign timeout value.
1955 lockd.nlm_udpport=M [NFS] Assign UDP port.
1958 locktorture.nreaders_stress= [KNL]
1959 Set the number of locking read-acquisition kthreads.
1960 Defaults to being automatically set based on the
1961 number of online CPUs.
1963 locktorture.nwriters_stress= [KNL]
1964 Set the number of locking write-acquisition kthreads.
1966 locktorture.onoff_holdoff= [KNL]
1967 Set time (s) after boot for CPU-hotplug testing.
1969 locktorture.onoff_interval= [KNL]
1970 Set time (s) between CPU-hotplug operations, or
1971 zero to disable CPU-hotplug testing.
1973 locktorture.shuffle_interval= [KNL]
1974 Set task-shuffle interval (jiffies). Shuffling
1975 tasks allows some CPUs to go into dyntick-idle
1976 mode during the locktorture test.
1978 locktorture.shutdown_secs= [KNL]
1979 Set time (s) after boot system shutdown. This
1980 is useful for hands-off automated testing.
1982 locktorture.stat_interval= [KNL]
1983 Time (s) between statistics printk()s.
1985 locktorture.stutter= [KNL]
1986 Time (s) to stutter testing, for example,
1987 specifying five seconds causes the test to run for
1988 five seconds, wait for five seconds, and so on.
1989 This tests the locking primitive's ability to
1990 transition abruptly to and from idle.
1992 locktorture.torture_runnable= [BOOT]
1993 Start locktorture running at boot time.
1995 locktorture.torture_type= [KNL]
1996 Specify the locking implementation to test.
1998 locktorture.verbose= [KNL]
1999 Enable additional printk() statements.
2001 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2004 loglevel= All Kernel Messages with a loglevel smaller than the
2005 console loglevel will be printed to the console. It can
2006 also be changed with klogd or other programs. The
2007 loglevels are defined as follows:
2009 0 (KERN_EMERG) system is unusable
2010 1 (KERN_ALERT) action must be taken immediately
2011 2 (KERN_CRIT) critical conditions
2012 3 (KERN_ERR) error conditions
2013 4 (KERN_WARNING) warning conditions
2014 5 (KERN_NOTICE) normal but significant condition
2015 6 (KERN_INFO) informational
2016 7 (KERN_DEBUG) debug-level messages
2018 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2019 in bytes. n must be a power of two and greater
2020 than the minimal size. The minimal size is defined
2021 by LOG_BUF_SHIFT kernel config parameter. There is
2022 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2023 that allows to increase the default size depending on
2024 the number of CPUs. See init/Kconfig for more details.
2026 logo.nologo [FB] Disables display of the built-in Linux logo.
2027 This may be used to provide more screen space for
2028 kernel log messages and is useful when debugging
2029 kernel boot problems.
2031 lp=0 [LP] Specify parallel ports to use, e.g,
2032 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2033 lp=reset first parallel port). 'lp=0' disables the
2034 lp=auto printer driver. 'lp=reset' (which can be
2035 specified in addition to the ports) causes
2036 attached printers to be reset. Using
2037 lp=port1,port2,... specifies the parallel ports
2038 to associate lp devices with, starting with
2039 lp0. A port specification may be 'none' to skip
2040 that lp device, or a parport name such as
2041 'parport0'. Specifying 'lp=auto' instead of a
2042 port specification list means that device IDs
2043 from each port should be examined, to see if
2044 an IEEE 1284-compliant printer is attached; if
2045 so, the driver will manage that printer.
2046 See also header of drivers/char/lp.c.
2049 Sets loops_per_jiffy to given constant, thus avoiding
2050 time-consuming boot-time autodetection (up to 250 ms per
2051 CPU). 0 enables autodetection (default). To determine
2052 the correct value for your kernel, boot with normal
2053 autodetection and see what value is printed. Note that
2054 on SMP systems the preset will be applied to all CPUs,
2055 which is likely to cause problems if your CPUs need
2056 significantly divergent settings. An incorrect value
2057 will cause delays in the kernel to be wrong, leading to
2058 unpredictable I/O errors and other breakage. Although
2059 unlikely, in the extreme case this might damage your
2063 Format: <io>,<irq>,<dma>
2065 machvec= [IA-64] Force the use of a particular machine-vector
2066 (machvec) in a generic kernel.
2067 Example: machvec=hpzx1_swiotlb
2069 machtype= [Loongson] Share the same kernel image file between different
2071 Example: machtype=lemote-yeeloong-2f-7inch
2073 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2074 than or equal to this physical address is ignored.
2076 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2077 should make use of. maxcpus=n : n >= 0 limits the
2078 kernel to using 'n' processors. n=0 is a special case,
2079 it is equivalent to "nosmp", which also disables
2082 max_loop= [LOOP] The number of loop block devices that get
2083 (loop.max_loop) unconditionally pre-created at init time. The default
2084 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2085 of statically allocating a predefined number, loop
2086 devices can be requested on-demand with the
2087 /dev/loop-control interface.
2089 mce [X86-32] Machine Check Exception
2091 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2093 md= [HW] RAID subsystems devices and level
2094 See Documentation/md.txt.
2097 Format: <first>,<last>
2098 Specifies range of consoles to be captured by the MDA.
2100 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2101 Amount of memory to be used when the kernel is not able
2102 to see the whole system memory or for test.
2103 [X86] Work as limiting max address. Use together
2104 with memmap= to avoid physical address space collisions.
2105 Without memmap= PCI devices could be placed at addresses
2106 belonging to unused RAM.
2108 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2112 [KNL,SH] Allow user to override the default size for
2113 per-device physically contiguous DMA buffers.
2115 memmap=exactmap [KNL,X86] Enable setting of an exact
2116 E820 memory map, as specified by the user.
2117 Such memmap=exactmap lines can be constructed based on
2118 BIOS output or other requirements. See the memmap=nn@ss
2121 memmap=nn[KMG]@ss[KMG]
2122 [KNL] Force usage of a specific region of memory.
2123 Region of memory to be used is from ss to ss+nn.
2125 memmap=nn[KMG]#ss[KMG]
2126 [KNL,ACPI] Mark specific memory as ACPI data.
2127 Region of memory to be marked is from ss to ss+nn.
2129 memmap=nn[KMG]$ss[KMG]
2130 [KNL,ACPI] Mark specific memory as reserved.
2131 Region of memory to be reserved is from ss to ss+nn.
2132 Example: Exclude memory from 0x18690000-0x1869ffff
2133 memmap=64K$0x18690000
2135 memmap=0x10000$0x18690000
2137 memmap=nn[KMG]!ss[KMG]
2138 [KNL,X86] Mark specific memory as protected.
2139 Region of memory to be used, from ss to ss+nn.
2140 The memory region may be marked as e820 type 12 (0xc)
2141 and is NVDIMM or ADR memory.
2143 memory_corruption_check=0/1 [X86]
2144 Some BIOSes seem to corrupt the first 64k of
2145 memory when doing things like suspend/resume.
2146 Setting this option will scan the memory
2147 looking for corruption. Enabling this will
2148 both detect corruption and prevent the kernel
2149 from using the memory being corrupted.
2150 However, its intended as a diagnostic tool; if
2151 repeatable BIOS-originated corruption always
2152 affects the same memory, you can use memmap=
2153 to prevent the kernel from using that memory.
2155 memory_corruption_check_size=size [X86]
2156 By default it checks for corruption in the low
2157 64k, making this memory unavailable for normal
2158 use. Use this parameter to scan for
2159 corruption in more or less memory.
2161 memory_corruption_check_period=seconds [X86]
2162 By default it checks for corruption every 60
2163 seconds. Use this parameter to check at some
2164 other rate. 0 disables periodic checking.
2166 memtest= [KNL,X86,ARM] Enable memtest
2168 default : 0 <disable>
2169 Specifies the number of memtest passes to be
2170 performed. Each pass selects another test
2171 pattern from a given set of patterns. Memtest
2172 fills the memory with this pattern, validates
2173 memory contents and reserves bad memory
2174 regions that are detected.
2176 meye.*= [HW] Set MotionEye Camera parameters
2177 See Documentation/video4linux/meye.txt.
2179 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2180 Multi-Function General Purpose Timers on AMD Geode
2183 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2184 the BIOS has incorrectly applied a workaround. TinyBIOS
2185 version 0.98 is known to be affected, 0.99 fixes the
2186 problem by letting the user disable the workaround.
2190 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2191 physical address is ignored.
2193 mini2440= [ARM,HW,KNL]
2194 Format:[0..2][b][c][t]
2196 MINI2440 configuration specification:
2197 0 - The attached screen is the 3.5" TFT
2198 1 - The attached screen is the 7" TFT
2199 2 - The VGA Shield is attached (1024x768)
2200 Leaving out the screen size parameter will not load
2201 the TFT driver, and the framebuffer will be left
2203 b - Enable backlight. The TFT backlight pin will be
2204 linked to the kernel VESA blanking code and a GPIO
2205 LED. This parameter is not necessary when using the
2207 c - Enable the s3c camera interface.
2208 t - Reserved for enabling touchscreen support. The
2209 touchscreen support is not enabled in the mainstream
2210 kernel as of 2.6.30, a preliminary port can be found
2211 in the "bleeding edge" mini2440 support kernel at
2212 http://repo.or.cz/w/linux-2.6/mini2440.git
2215 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2216 parameter allows control of the logging verbosity for
2217 the additional memory initialisation checks. A value
2218 of 0 disables mminit logging and a level of 4 will
2219 log everything. Information is printed at KERN_DEBUG
2220 so loglevel=8 may also need to be specified.
2223 [KNL] When CONFIG_MODULE_SIG is set, this means that
2224 modules without (valid) signatures will fail to load.
2225 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2226 is always true, so this option does nothing.
2229 [MOUSE] Maximum time between finger touching and
2230 leaving touchpad surface for touch to be considered
2231 a tap and be reported as a left button click (for
2232 touchpads working in absolute mode only).
2234 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2235 reporting absolute coordinates, such as tablets
2236 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2237 reporting absolute coordinates, such as tablets
2239 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2240 is similar to kernelcore except it specifies the
2241 amount of memory used for migratable allocations.
2242 If both kernelcore and movablecore is specified,
2243 then kernelcore will be at *least* the specified
2244 value but may be more. If movablecore on its own
2245 is specified, the administrator must be careful
2246 that the amount of memory usable for all allocations
2249 movable_node [KNL,X86] Boot-time switch to enable the effects
2250 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2252 MTD_Partition= [MTD]
2253 Format: <name>,<region-number>,<size>,<offset>
2255 MTD_Region= [MTD] Format:
2256 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2259 See drivers/mtd/cmdlinepart.c.
2261 multitce=off [PPC] This parameter disables the use of the pSeries
2262 firmware feature for updating multiple TCE entries
2265 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2267 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2269 boundary - index of last SLC block on Flex-OneNAND.
2270 The remaining blocks are configured as MLC blocks.
2271 lock - Configure if Flex-OneNAND boundary should be locked.
2272 Once locked, the boundary cannot be changed.
2273 1 indicates lock status, 0 indicates unlock status.
2276 ARM/S3C2412 JIVE boot control
2278 See arch/arm/mach-s3c2412/mach-jive.c
2280 mtouchusb.raw_coordinates=
2281 [HW] Make the MicroTouch USB driver use raw coordinates
2282 ('y', default) or cooked coordinates ('n')
2284 mtrr_chunk_size=nn[KMG] [X86]
2285 used for mtrr cleanup. It is largest continuous chunk
2286 that could hold holes aka. UC entries.
2288 mtrr_gran_size=nn[KMG] [X86]
2289 Used for mtrr cleanup. It is granularity of mtrr block.
2291 Large value could prevent small alignment from
2294 mtrr_spare_reg_nr=n [X86]
2296 Range: 0,7 : spare reg number
2298 Used for mtrr cleanup. It is spare mtrr entries number.
2299 Set to 2 or more if your graphical card needs more.
2301 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2303 netdev= [NET] Network devices parameters
2304 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2305 Note that mem_start is often overloaded to mean
2306 something different and driver-specific.
2307 This usage is only documented in each driver source
2311 [NETFILTER] Enable connection tracking flow accounting
2312 0 to disable accounting
2313 1 to enable accounting
2316 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2317 See Documentation/filesystems/nfs/nfsroot.txt.
2319 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2320 See Documentation/filesystems/nfs/nfsroot.txt.
2322 nfsrootdebug [NFS] enable nfsroot debugging messages.
2323 See Documentation/filesystems/nfs/nfsroot.txt.
2325 nfs.callback_tcpport=
2326 [NFS] set the TCP port on which the NFSv4 callback
2327 channel should listen.
2330 [NFS] sets the pathname to the program which is used
2331 to update the NFS client cache entries.
2333 nfs.cache_getent_timeout=
2334 [NFS] sets the timeout after which an attempt to
2335 update a cache entry is deemed to have failed.
2337 nfs.idmap_cache_timeout=
2338 [NFS] set the maximum lifetime for idmapper cache
2342 [NFS] enable 64-bit inode numbers.
2343 If zero, the NFS client will fake up a 32-bit inode
2344 number for the readdir() and stat() syscalls instead
2345 of returning the full 64-bit number.
2346 The default is to return 64-bit inode numbers.
2348 nfs.max_session_slots=
2349 [NFSv4.1] Sets the maximum number of session slots
2350 the client will attempt to negotiate with the server.
2351 This limits the number of simultaneous RPC requests
2352 that the client can send to the NFSv4.1 server.
2353 Note that there is little point in setting this
2354 value higher than the max_tcp_slot_table_limit.
2356 nfs.nfs4_disable_idmapping=
2357 [NFSv4] When set to the default of '1', this option
2358 ensures that both the RPC level authentication
2359 scheme and the NFS level operations agree to use
2360 numeric uids/gids if the mount is using the
2361 'sec=sys' security flavour. In effect it is
2362 disabling idmapping, which can make migration from
2363 legacy NFSv2/v3 systems to NFSv4 easier.
2364 Servers that do not support this mode of operation
2365 will be autodetected by the client, and it will fall
2366 back to using the idmapper.
2367 To turn off this behaviour, set the value to '0'.
2369 [NFS4] Specify an additional fixed unique ident-
2370 ification string that NFSv4 clients can insert into
2371 their nfs_client_id4 string. This is typically a
2372 UUID that is generated at system install time.
2374 nfs.send_implementation_id =
2375 [NFSv4.1] Send client implementation identification
2376 information in exchange_id requests.
2377 If zero, no implementation identification information
2379 The default is to send the implementation identification
2382 nfs.recover_lost_locks =
2383 [NFSv4] Attempt to recover locks that were lost due
2384 to a lease timeout on the server. Please note that
2385 doing this risks data corruption, since there are
2386 no guarantees that the file will remain unchanged
2387 after the locks are lost.
2388 If you want to enable the kernel legacy behaviour of
2389 attempting to recover these locks, then set this
2391 The default parameter value of '0' causes the kernel
2392 not to attempt recovery of lost locks.
2394 nfs4.layoutstats_timer =
2395 [NFSv4.2] Change the rate at which the kernel sends
2396 layoutstats to the pNFS metadata server.
2398 Setting this to value to 0 causes the kernel to use
2399 whatever value is the default set by the layout
2400 driver. A non-zero value sets the minimum interval
2401 in seconds between layoutstats transmissions.
2403 nfsd.nfs4_disable_idmapping=
2404 [NFSv4] When set to the default of '1', the NFSv4
2405 server will return only numeric uids and gids to
2406 clients using auth_sys, and will accept numeric uids
2407 and gids from such clients. This is intended to ease
2408 migration from NFSv2/v3.
2410 objlayoutdriver.osd_login_prog=
2411 [NFS] [OBJLAYOUT] sets the pathname to the program which
2412 is used to automatically discover and login into new
2413 osd-targets. Please see:
2414 Documentation/filesystems/pnfs.txt for more explanations
2416 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2417 when a NMI is triggered.
2418 Format: [state][,regs][,debounce][,die]
2420 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2421 Format: [panic,][nopanic,][num]
2423 0 - turn hardlockup detector in nmi_watchdog off
2424 1 - turn hardlockup detector in nmi_watchdog on
2425 When panic is specified, panic when an NMI watchdog
2426 timeout occurs (or 'nopanic' to override the opposite
2427 default). To disable both hard and soft lockup detectors,
2428 please see 'nowatchdog'.
2429 This is useful when you use a panic=... timeout and
2430 need the box quickly up again.
2432 netpoll.carrier_timeout=
2433 [NET] Specifies amount of time (in seconds) that
2434 netpoll should wait for a carrier. By default netpoll
2437 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2438 emulation library even if a 387 maths coprocessor
2442 [HW] Never suspend the console
2443 Disable suspending of consoles during suspend and
2444 hibernate operations. Once disabled, debugging
2445 messages can reach various consoles while the rest
2446 of the system is being put to sleep (ie, while
2447 debugging driver suspend/resume hooks). This may
2448 not work reliably with all consoles, but is known
2449 to work with serial and VGA consoles.
2450 To facilitate more flexible debugging, we also add
2451 console_suspend, a printk module parameter to control
2452 it. Users could use console_suspend (usually
2453 /sys/module/printk/parameters/console_suspend) to
2454 turn on/off it dynamically.
2456 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2457 caches in the slab allocator. Saves per-node memory,
2458 but will impact performance.
2462 noapic [SMP,APIC] Tells the kernel to not make use of any
2463 IOAPICs that may be present in the system.
2465 noautogroup Disable scheduler automatic task group creation.
2467 nobats [PPC] Do not use BATs for mapping kernel lowmem
2468 on "Classic" PPC cores.
2472 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2474 nodelayacct [KNL] Disable per-task delay accounting
2476 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2478 nodsp [SH] Disable hardware DSP at boot time.
2480 noefi Disable EFI runtime services support.
2485 On X86-32 available only on PAE configured kernels.
2486 noexec=on: enable non-executable mappings (default)
2487 noexec=off: disable non-executable mappings
2490 Disable SMAP (Supervisor Mode Access Prevention)
2491 even if it is supported by processor.
2494 Disable SMEP (Supervisor Mode Execution Prevention)
2495 even if it is supported by processor.
2498 This affects only 32-bit executables.
2499 noexec32=on: enable non-executable mappings (default)
2500 read doesn't imply executable mappings
2501 noexec32=off: disable non-executable mappings
2502 read implies executable mappings
2504 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2506 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2507 register save and restore. The kernel will only save
2508 legacy floating-point registers on task switch.
2510 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2512 noxsave [BUGS=X86] Disables x86 extended register state save
2513 and restore using xsave. The kernel will fallback to
2514 enabling legacy floating-point and sse state.
2516 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2517 register states. The kernel will fall back to use
2518 xsave to save the states. By using this parameter,
2519 performance of saving the states is degraded because
2520 xsave doesn't support modified optimization while
2521 xsaveopt supports it on xsaveopt enabled systems.
2523 noxsaves [X86] Disables xsaves and xrstors used in saving and
2524 restoring x86 extended register state in compacted
2525 form of xsave area. The kernel will fall back to use
2526 xsaveopt and xrstor to save and restore the states
2527 in standard form of xsave area. By using this
2528 parameter, xsave area per process might occupy more
2529 memory on xsaves enabled systems.
2531 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2532 wfi(ARM) instruction doesn't work correctly and not to
2533 use it. This is also useful when using JTAG debugger.
2535 no_file_caps Tells the kernel not to honor file capabilities. The
2536 only way then for a file to be executed with privilege
2537 is to be setuid root or executed by root.
2539 nohalt [IA-64] Tells the kernel not to use the power saving
2540 function PAL_HALT_LIGHT when idle. This increases
2541 power-consumption. On the positive side, it reduces
2542 interrupt wake-up latency, which may improve performance
2543 in certain environments such as networked servers or
2546 nohibernate [HIBERNATION] Disable hibernation and resume.
2548 nohz= [KNL] Boottime enable/disable dynamic ticks
2549 Valid arguments: on, off
2552 nohz_full= [KNL,BOOT]
2553 In kernels built with CONFIG_NO_HZ_FULL=y, set
2554 the specified list of CPUs whose tick will be stopped
2555 whenever possible. The boot CPU will be forced outside
2556 the range to maintain the timekeeping.
2557 The CPUs in this range must also be included in the
2560 noiotrap [SH] Disables trapped I/O port accesses.
2562 noirqdebug [X86-32] Disables the code which attempts to detect and
2563 disable unhandled interrupt sources.
2565 no_timer_check [X86,APIC] Disables the code which tests for
2566 broken timer IRQ sources.
2568 noisapnp [ISAPNP] Disables ISA PnP code.
2570 noinitrd [RAM] Tells the kernel not to load any configured
2573 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2575 [Deprecated - use intremap=off]
2579 nojitter [IA-64] Disables jitter checking for ITC timers.
2581 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2583 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2586 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2587 steal time is computed, but won't influence scheduler
2590 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2592 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2594 noltlbs [PPC] Do not use large page/tlb entries for kernel
2595 lowmem mapping on PPC40x.
2597 nomca [IA-64] Disable machine check abort handling
2599 nomce [X86-32] Disable Machine Check Exception
2601 nomfgpt [X86-32] Disable Multi-Function General Purpose
2602 Timer usage (for AMD Geode machines).
2604 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2605 shutdown the other cpus. Instead use the REBOOT_VECTOR
2608 nomodule Disable module load
2610 nopat [X86] Disable PAT (page attribute table extension of
2611 pagetables) support.
2613 norandmaps Don't use address space randomization. Equivalent to
2614 echo 0 > /proc/sys/kernel/randomize_va_space
2616 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2618 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2619 with UP alternatives
2621 nordrand [X86] Disable kernel use of the RDRAND and
2622 RDSEED instructions even if they are supported
2623 by the processor. RDRAND and RDSEED are still
2624 available to user space applications.
2626 noresume [SWSUSP] Disables resume and restores original swap
2629 no-scroll [VGA] Disables scrollback.
2630 This is required for the Braillex ib80-piezo Braille
2631 reader made by F.H. Papenmeier (Germany).
2635 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2637 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2638 and disable the IO APIC. legacy for "maxcpus=0".
2640 nosoftlockup [KNL] Disable the soft-lockup detector.
2642 nosync [HW,M68K] Disables sync negotiation for all devices.
2644 notsc [BUGS=X86-32] Disable Time Stamp Counter
2646 nowatchdog [KNL] Disable both lockup detectors, i.e.
2647 soft-lockup and NMI watchdog (hard-lockup).
2651 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2653 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2654 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2655 Some features depend on CPU0. Known dependencies are:
2656 1. Resume from suspend/hibernate depends on CPU0.
2657 Suspend/hibernate will fail if CPU0 is offline and you
2658 need to online CPU0 before suspend/hibernate.
2659 2. PIC interrupts also depend on CPU0. CPU0 can't be
2660 removed if a PIC interrupt is detected.
2661 It's said poweroff/reboot may depend on CPU0 on some
2662 machines although I haven't seen such issues so far
2663 after CPU0 is offline on a few tested machines.
2664 If the dependencies are under your control, you can
2665 turn on cpu0_hotplug.
2667 nptcg= [IA-64] Override max number of concurrent global TLB
2668 purges which is reported from either PAL_VM_SUMMARY or
2671 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2672 could support. nr_cpus=n : n >= 1 limits the kernel to
2673 supporting 'n' processors. Later in runtime you can not
2674 use hotplug cpu feature to put more cpu back to online.
2675 just like you compile the kernel NR_CPUS=n
2677 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2679 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2680 Allowed values are enable and disable
2682 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2683 one of ['zone', 'node', 'default'] can be specified
2684 This can be set from sysctl after boot.
2685 See Documentation/sysctl/vm.txt for details.
2687 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2688 See Documentation/debugging-via-ohci1394.txt for more
2691 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2692 Rather than timing out after 20 ms if an EC
2693 command is not properly ACKed, override the length
2694 of the timeout. We have interrupts disabled while
2695 waiting for the ACK, so if this is set too high
2696 interrupts *may* be lost!
2698 omap_mux= [OMAP] Override bootloader pin multiplexing.
2699 Format: <mux_mode0.mode_name=value>...
2700 For example, to override I2C bus2:
2701 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2703 oprofile.timer= [HW]
2704 Use timer interrupt instead of performance counters
2706 oprofile.cpu_type= Force an oprofile cpu type
2707 This might be useful if you have an older oprofile
2708 userland or if you want common events.
2709 Format: { arch_perfmon }
2710 arch_perfmon: [X86] Force use of architectural
2711 perfmon on Intel CPUs instead of the
2712 CPU specific event set.
2713 timer: [X86] Force use of architectural NMI
2714 timer mode (see also oprofile.timer
2715 for generic hr timer mode)
2716 [s390] Force legacy basic mode sampling
2717 (report cpu_type "timer")
2719 oops=panic Always panic on oopses. Default is to just kill the
2720 process, but there is a small probability of
2721 deadlocking the machine.
2722 This will also cause panics on machine check exceptions.
2723 Useful together with panic=30 to trigger a reboot.
2726 See Documentation/sound/oss/oss-parameters.txt
2728 page_owner= [KNL] Boot-time page_owner enabling option.
2729 Storage of the information about who allocated
2730 each page is disabled in default. With this switch,
2732 on: enable the feature
2734 page_poison= [KNL] Boot-time parameter changing the state of
2735 poisoning on the buddy allocator.
2736 off: turn off poisoning
2737 on: turn on poisoning
2739 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2740 timeout > 0: seconds before rebooting
2741 timeout = 0: wait forever
2742 timeout < 0: reboot immediately
2745 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2748 crash_kexec_post_notifiers
2749 Run kdump after running panic-notifiers and dumping
2750 kmsg. This only for the users who doubt kdump always
2751 succeeds in any situation.
2752 Note that this also increases risks of kdump failure,
2753 because some panic notifiers can make the crashed
2754 kernel more unstable.
2756 parkbd.port= [HW] Parallel port number the keyboard adapter is
2757 connected to, default is 0.
2759 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2760 0 for XT, 1 for AT (default is AT).
2763 parport= [HW,PPT] Specify parallel ports. 0 disables.
2764 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2765 Use 'auto' to force the driver to use any
2766 IRQ/DMA settings detected (the default is to
2767 ignore detected IRQ/DMA settings because of
2768 possible conflicts). You can specify the base
2769 address, IRQ, and DMA settings; IRQ and DMA
2770 should be numbers, or 'auto' (for using detected
2771 settings on that particular port), or 'nofifo'
2772 (to avoid using a FIFO even if it is detected).
2773 Parallel ports are assigned in the order they
2774 are specified on the command line, starting
2777 parport_init_mode= [HW,PPT]
2778 Configure VIA parallel port to operate in
2779 a specific mode. This is necessary on Pegasos
2780 computer where firmware has no options for setting
2781 up parallel port mode and sets it to spp.
2782 Currently this function knows 686a and 8231 chips.
2783 Format: [spp|ps2|epp|ecp|ecpepp]
2786 Halt all CPUs after the first oops has been printed for
2787 the specified number of seconds. This is to be used if
2788 your oopses keep scrolling off the screen.
2793 See header of drivers/block/paride/pcd.c.
2794 See also Documentation/blockdev/paride.txt.
2796 pci=option[,option...] [PCI] various PCI subsystem options:
2797 earlydump [X86] dump PCI config space before the kernel
2799 off [X86] don't probe for the PCI bus
2800 bios [X86-32] force use of PCI BIOS, don't access
2801 the hardware directly. Use this if your machine
2802 has a non-standard PCI host bridge.
2803 nobios [X86-32] disallow use of PCI BIOS, only direct
2804 hardware access methods are allowed. Use this
2805 if you experience crashes upon bootup and you
2806 suspect they are caused by the BIOS.
2807 conf1 [X86] Force use of PCI Configuration Access
2808 Mechanism 1 (config address in IO port 0xCF8,
2809 data in IO port 0xCFC, both 32-bit).
2810 conf2 [X86] Force use of PCI Configuration Access
2811 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2812 the function, IO port 0xCFA, also 8-bit, sets
2813 bus number. The config space is then accessed
2814 through ports 0xC000-0xCFFF).
2815 See http://wiki.osdev.org/PCI for more info
2816 on the configuration access mechanisms.
2817 noaer [PCIE] If the PCIEAER kernel config parameter is
2818 enabled, this kernel boot option can be used to
2819 disable the use of PCIE advanced error reporting.
2820 nodomains [PCI] Disable support for multiple PCI
2821 root domains (aka PCI segments, in ACPI-speak).
2822 nommconf [X86] Disable use of MMCONFIG for PCI
2824 check_enable_amd_mmconf [X86] check for and enable
2825 properly configured MMIO access to PCI
2826 config space on AMD family 10h CPU
2827 nomsi [MSI] If the PCI_MSI kernel config parameter is
2828 enabled, this kernel boot option can be used to
2829 disable the use of MSI interrupts system-wide.
2830 noioapicquirk [APIC] Disable all boot interrupt quirks.
2831 Safety option to keep boot IRQs enabled. This
2832 should never be necessary.
2833 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2834 primary IO-APIC for bridges that cannot disable
2835 boot IRQs. This fixes a source of spurious IRQs
2836 when the system masks IRQs.
2837 noioapicreroute [APIC] Disable workaround that uses the
2838 boot IRQ equivalent of an IRQ that connects to
2839 a chipset where boot IRQs cannot be disabled.
2840 The opposite of ioapicreroute.
2841 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2842 routing table. These calls are known to be buggy
2843 on several machines and they hang the machine
2844 when used, but on other computers it's the only
2845 way to get the interrupt routing table. Try
2846 this option if the kernel is unable to allocate
2847 IRQs or discover secondary PCI buses on your
2849 rom [X86] Assign address space to expansion ROMs.
2850 Use with caution as certain devices share
2851 address decoders between ROMs and other
2853 norom [X86] Do not assign address space to
2854 expansion ROMs that do not already have
2855 BIOS assigned address ranges.
2856 nobar [X86] Do not assign address space to the
2857 BARs that weren't assigned by the BIOS.
2858 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2859 assigned automatically to PCI devices. You can
2860 make the kernel exclude IRQs of your ISA cards
2862 pirqaddr=0xAAAAA [X86] Specify the physical address
2863 of the PIRQ table (normally generated
2864 by the BIOS) if it is outside the
2865 F0000h-100000h range.
2866 lastbus=N [X86] Scan all buses thru bus #N. Can be
2867 useful if the kernel is unable to find your
2868 secondary buses and you want to tell it
2869 explicitly which ones they are.
2870 assign-busses [X86] Always assign all PCI bus
2871 numbers ourselves, overriding
2872 whatever the firmware may have done.
2873 usepirqmask [X86] Honor the possible IRQ mask stored
2874 in the BIOS $PIR table. This is needed on
2875 some systems with broken BIOSes, notably
2876 some HP Pavilion N5400 and Omnibook XE3
2877 notebooks. This will have no effect if ACPI
2878 IRQ routing is enabled.
2879 noacpi [X86] Do not use ACPI for IRQ routing
2880 or for PCI scanning.
2881 use_crs [X86] Use PCI host bridge window information
2882 from ACPI. On BIOSes from 2008 or later, this
2883 is enabled by default. If you need to use this,
2884 please report a bug.
2885 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2886 If you need to use this, please report a bug.
2887 routeirq Do IRQ routing for all PCI devices.
2888 This is normally done in pci_enable_device(),
2889 so this option is a temporary workaround
2890 for broken drivers that don't call it.
2891 skip_isa_align [X86] do not align io start addr, so can
2892 handle more pci cards
2893 firmware [ARM] Do not re-enumerate the bus but instead
2894 just use the configuration from the
2895 bootloader. This is currently used on
2896 IXP2000 systems where the bus has to be
2897 configured a certain way for adjunct CPUs.
2898 noearly [X86] Don't do any early type 1 scanning.
2899 This might help on some broken boards which
2900 machine check when some devices' config space
2901 is read. But various workarounds are disabled
2902 and some IOMMU drivers will not work.
2903 bfsort Sort PCI devices into breadth-first order.
2904 This sorting is done to get a device
2905 order compatible with older (<= 2.4) kernels.
2906 nobfsort Don't sort PCI devices into breadth-first order.
2907 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2908 tuning and use the BIOS-configured MPS defaults.
2909 pcie_bus_safe Set every device's MPS to the largest value
2910 supported by all devices below the root complex.
2911 pcie_bus_perf Set device MPS to the largest allowable MPS
2912 based on its parent bus. Also set MRRS (Max
2913 Read Request Size) to the largest supported
2914 value (no larger than the MPS that the device
2915 or bus can support) for best performance.
2916 pcie_bus_peer2peer Set every device's MPS to 128B, which
2917 every device is guaranteed to support. This
2918 configuration allows peer-to-peer DMA between
2919 any pair of devices, possibly at the cost of
2920 reduced performance. This also guarantees
2921 that hot-added devices will work.
2922 cbiosize=nn[KMG] The fixed amount of bus space which is
2923 reserved for the CardBus bridge's IO window.
2924 The default value is 256 bytes.
2925 cbmemsize=nn[KMG] The fixed amount of bus space which is
2926 reserved for the CardBus bridge's memory
2927 window. The default value is 64 megabytes.
2930 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2931 Specifies alignment and device to reassign
2932 aligned memory resources.
2933 If <order of align> is not specified,
2934 PAGE_SIZE is used as alignment.
2935 PCI-PCI bridge can be specified, if resource
2936 windows need to be expanded.
2937 ecrc= Enable/disable PCIe ECRC (transaction layer
2938 end-to-end CRC checking).
2939 bios: Use BIOS/firmware settings. This is the
2943 hpiosize=nn[KMG] The fixed amount of bus space which is
2944 reserved for hotplug bridge's IO window.
2945 Default size is 256 bytes.
2946 hpmemsize=nn[KMG] The fixed amount of bus space which is
2947 reserved for hotplug bridge's memory window.
2948 Default size is 2 megabytes.
2949 realloc= Enable/disable reallocating PCI bridge resources
2950 if allocations done by BIOS are too small to
2951 accommodate resources required by all child
2953 off: Turn realloc off
2955 realloc same as realloc=on
2956 noari do not use PCIe ARI.
2957 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2958 only look for one device below a PCIe downstream
2961 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2964 force Enable ASPM even on devices that claim not to support it.
2965 WARNING: Forcing ASPM on may cause system lockups.
2967 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2968 nomsi Do not use MSI for PCI Express Native Hotplug (this
2969 makes all PCIe ports use INTx for hotplug services).
2971 pcie_ports= [PCIE] PCIe ports handling:
2972 auto Ask the BIOS whether or not to use native PCIe services
2973 associated with PCIe ports (PME, hot-plug, AER). Use
2974 them only if that is allowed by the BIOS.
2975 native Use native PCIe services associated with PCIe ports
2977 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2980 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2981 nomsi Do not use MSI for native PCIe PME signaling (this makes
2982 all PCIe root ports use INTx for all services).
2984 pcmv= [HW,PCMCIA] BadgePAD 4
2988 Keep all power-domains already enabled by bootloader on,
2989 even if no driver has claimed them. This is useful
2990 for debug and development, but should not be
2991 needed on a platform with proper driver support.
2994 See Documentation/blockdev/paride.txt.
2996 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2999 See arch/parisc/kernel/pdc_chassis.c
3001 percpu_alloc= Select which percpu first chunk allocator to use.
3002 Currently supported values are "embed" and "page".
3003 Archs may support subset or none of the selections.
3004 See comments in mm/percpu.c for details on each
3005 allocator. This parameter is primarily for debugging
3006 and performance comparison.
3009 See Documentation/blockdev/paride.txt.
3012 See Documentation/blockdev/paride.txt.
3014 pirq= [SMP,APIC] Manual mp-table setup
3015 See Documentation/x86/i386/IO-APIC.txt.
3017 plip= [PPT,NET] Parallel port network link
3018 Format: { parport<nr> | timid | 0 }
3019 See also Documentation/parport.txt.
3021 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3022 Override pmtimer IOPort with a hex value.
3026 Enable PNP debug messages (depends on the
3027 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3028 via /sys/module/pnp/parameters/debug. We always show
3029 current resource usage; turning this on also shows
3030 possible settings and some assignment information.
3036 { on | off | curr | res | no-curr | no-res }
3039 [ISAPNP] Exclude IRQs for the autoconfiguration
3042 [ISAPNP] Exclude DMAs for the autoconfiguration
3044 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3045 Ranges are in pairs (I/O port base and size).
3048 [ISAPNP] Exclude memory regions for the
3050 Ranges are in pairs (memory base and size).
3052 ports= [IP_VS_FTP] IPVS ftp helper module
3054 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3056 Format: <port>,<port>....
3058 ppc_strict_facility_enable
3059 [PPC] This option catches any kernel floating point,
3060 Altivec, VSX and SPE outside of regions specifically
3061 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3062 There is some performance impact when enabling this.
3064 print-fatal-signals=
3065 [KNL] debug: print fatal signals
3067 If enabled, warn about various signal handling
3068 related application anomalies: too many signals,
3069 too many POSIX.1 timers, fatal signals causing a
3072 If you hit the warning due to signal overflow,
3073 you might want to try "ulimit -i unlimited".
3077 printk.always_kmsg_dump=
3078 Trigger kmsg_dump for cases other than kernel oops or
3080 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3083 printk.time= Show timing data prefixed to each printk message line
3084 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3086 processor.max_cstate= [HW,ACPI]
3087 Limit processor to maximum C-state
3088 max_cstate=9 overrides any DMI blacklist limit.
3090 processor.nocst [HW,ACPI]
3091 Ignore the _CST method to determine C-states,
3092 instead using the legacy FADT method
3094 profile= [KNL] Enable kernel profiling via /proc/profile
3095 Format: [schedule,]<number>
3096 Param: "schedule" - profile schedule points.
3097 Param: <number> - step/bucket size as a power of 2 for
3098 statistical time based profiling.
3099 Param: "sleep" - profile D-state sleeping (millisecs).
3100 Requires CONFIG_SCHEDSTATS
3101 Param: "kvm" - profile VM exits.
3103 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3105 See Documentation/blockdev/ramdisk.txt.
3107 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3108 probe for; one of (bare|imps|exps|lifebook|any).
3109 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3111 psmouse.resetafter= [HW,MOUSE]
3112 Try to reset the device after so many bad packets
3115 [HW,MOUSE] Set desired mouse resolution, in dpi.
3116 psmouse.smartscroll=
3117 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3118 0 = disabled, 1 = enabled (default).
3120 pstore.backend= Specify the name of the pstore backend to use
3123 See Documentation/blockdev/paride.txt.
3126 [KNL] Number of legacy pty's. Overwrites compiled-in
3129 quiet [KNL] Disable most log messages
3134 See Documentation/md.txt.
3136 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3137 See Documentation/blockdev/ramdisk.txt.
3140 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3141 the specified list of CPUs to be no-callback CPUs.
3142 Invocation of these CPUs' RCU callbacks will
3143 be offloaded to "rcuox/N" kthreads created for
3144 that purpose, where "x" is "b" for RCU-bh, "p"
3145 for RCU-preempt, and "s" for RCU-sched, and "N"
3146 is the CPU number. This reduces OS jitter on the
3147 offloaded CPUs, which can be useful for HPC and
3148 real-time workloads. It can also improve energy
3149 efficiency for asymmetric multiprocessors.
3152 Rather than requiring that offloaded CPUs
3153 (specified by rcu_nocbs= above) explicitly
3154 awaken the corresponding "rcuoN" kthreads,
3155 make these kthreads poll for callbacks.
3156 This improves the real-time response for the
3157 offloaded CPUs by relieving them of the need to
3158 wake up the corresponding kthread, but degrades
3159 energy efficiency by requiring that the kthreads
3160 periodically wake up to do the polling.
3162 rcutree.blimit= [KNL]
3163 Set maximum number of finished RCU callbacks to
3164 process in one batch.
3166 rcutree.dump_tree= [KNL]
3167 Dump the structure of the rcu_node combining tree
3168 out at early boot. This is used for diagnostic
3169 purposes, to verify correct tree setup.
3171 rcutree.gp_cleanup_delay= [KNL]
3172 Set the number of jiffies to delay each step of
3173 RCU grace-period cleanup. This only has effect
3174 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3176 rcutree.gp_init_delay= [KNL]
3177 Set the number of jiffies to delay each step of
3178 RCU grace-period initialization. This only has
3179 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3182 rcutree.gp_preinit_delay= [KNL]
3183 Set the number of jiffies to delay each step of
3184 RCU grace-period pre-initialization, that is,
3185 the propagation of recent CPU-hotplug changes up
3186 the rcu_node combining tree. This only has effect
3187 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3189 rcutree.rcu_fanout_exact= [KNL]
3190 Disable autobalancing of the rcu_node combining
3191 tree. This is used by rcutorture, and might
3192 possibly be useful for architectures having high
3193 cache-to-cache transfer latencies.
3195 rcutree.rcu_fanout_leaf= [KNL]
3196 Change the number of CPUs assigned to each
3197 leaf rcu_node structure. Useful for very
3198 large systems, which will choose the value 64,
3199 and for NUMA systems with large remote-access
3200 latencies, which will choose a value aligned
3201 with the appropriate hardware boundaries.
3203 rcutree.jiffies_till_sched_qs= [KNL]
3204 Set required age in jiffies for a
3205 given grace period before RCU starts
3206 soliciting quiescent-state help from
3207 rcu_note_context_switch().
3209 rcutree.jiffies_till_first_fqs= [KNL]
3210 Set delay from grace-period initialization to
3211 first attempt to force quiescent states.
3212 Units are jiffies, minimum value is zero,
3213 and maximum value is HZ.
3215 rcutree.jiffies_till_next_fqs= [KNL]
3216 Set delay between subsequent attempts to force
3217 quiescent states. Units are jiffies, minimum
3218 value is one, and maximum value is HZ.
3220 rcutree.kthread_prio= [KNL,BOOT]
3221 Set the SCHED_FIFO priority of the RCU per-CPU
3222 kthreads (rcuc/N). This value is also used for
3223 the priority of the RCU boost threads (rcub/N)
3224 and for the RCU grace-period kthreads (rcu_bh,
3225 rcu_preempt, and rcu_sched). If RCU_BOOST is
3226 set, valid values are 1-99 and the default is 1
3227 (the least-favored priority). Otherwise, when
3228 RCU_BOOST is not set, valid values are 0-99 and
3229 the default is zero (non-realtime operation).
3231 rcutree.rcu_nocb_leader_stride= [KNL]
3232 Set the number of NOCB kthread groups, which
3233 defaults to the square root of the number of
3234 CPUs. Larger numbers reduces the wakeup overhead
3235 on the per-CPU grace-period kthreads, but increases
3236 that same overhead on each group's leader.
3238 rcutree.qhimark= [KNL]
3239 Set threshold of queued RCU callbacks beyond which
3240 batch limiting is disabled.
3242 rcutree.qlowmark= [KNL]
3243 Set threshold of queued RCU callbacks below which
3244 batch limiting is re-enabled.
3246 rcutree.rcu_idle_gp_delay= [KNL]
3247 Set wakeup interval for idle CPUs that have
3248 RCU callbacks (RCU_FAST_NO_HZ=y).
3250 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3251 Set wakeup interval for idle CPUs that have
3252 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3253 Lazy RCU callbacks are those which RCU can
3254 prove do nothing more than free memory.
3256 rcutorture.cbflood_inter_holdoff= [KNL]
3257 Set holdoff time (jiffies) between successive
3258 callback-flood tests.
3260 rcutorture.cbflood_intra_holdoff= [KNL]
3261 Set holdoff time (jiffies) between successive
3262 bursts of callbacks within a given callback-flood
3265 rcutorture.cbflood_n_burst= [KNL]
3266 Set the number of bursts making up a given
3267 callback-flood test. Set this to zero to
3268 disable callback-flood testing.
3270 rcutorture.cbflood_n_per_burst= [KNL]
3271 Set the number of callbacks to be registered
3272 in a given burst of a callback-flood test.
3274 rcutorture.fqs_duration= [KNL]
3275 Set duration of force_quiescent_state bursts
3278 rcutorture.fqs_holdoff= [KNL]
3279 Set holdoff time within force_quiescent_state bursts
3282 rcutorture.fqs_stutter= [KNL]
3283 Set wait time between force_quiescent_state bursts
3286 rcutorture.gp_cond= [KNL]
3287 Use conditional/asynchronous update-side
3288 primitives, if available.
3290 rcutorture.gp_exp= [KNL]
3291 Use expedited update-side primitives, if available.
3293 rcutorture.gp_normal= [KNL]
3294 Use normal (non-expedited) asynchronous
3295 update-side primitives, if available.
3297 rcutorture.gp_sync= [KNL]
3298 Use normal (non-expedited) synchronous
3299 update-side primitives, if available. If all
3300 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3301 rcutorture.gp_normal=, and rcutorture.gp_sync=
3302 are zero, rcutorture acts as if is interpreted
3303 they are all non-zero.
3305 rcutorture.n_barrier_cbs= [KNL]
3306 Set callbacks/threads for rcu_barrier() testing.
3308 rcutorture.nfakewriters= [KNL]
3309 Set number of concurrent RCU writers. These just
3310 stress RCU, they don't participate in the actual
3311 test, hence the "fake".
3313 rcutorture.nreaders= [KNL]
3314 Set number of RCU readers. The value -1 selects
3315 N-1, where N is the number of CPUs. A value
3316 "n" less than -1 selects N-n-2, where N is again
3317 the number of CPUs. For example, -2 selects N
3318 (the number of CPUs), -3 selects N+1, and so on.
3320 rcutorture.object_debug= [KNL]
3321 Enable debug-object double-call_rcu() testing.
3323 rcutorture.onoff_holdoff= [KNL]
3324 Set time (s) after boot for CPU-hotplug testing.
3326 rcutorture.onoff_interval= [KNL]
3327 Set time (s) between CPU-hotplug operations, or
3328 zero to disable CPU-hotplug testing.
3330 rcutorture.shuffle_interval= [KNL]
3331 Set task-shuffle interval (s). Shuffling tasks
3332 allows some CPUs to go into dyntick-idle mode
3333 during the rcutorture test.
3335 rcutorture.shutdown_secs= [KNL]
3336 Set time (s) after boot system shutdown. This
3337 is useful for hands-off automated testing.
3339 rcutorture.stall_cpu= [KNL]
3340 Duration of CPU stall (s) to test RCU CPU stall
3341 warnings, zero to disable.
3343 rcutorture.stall_cpu_holdoff= [KNL]
3344 Time to wait (s) after boot before inducing stall.
3346 rcutorture.stat_interval= [KNL]
3347 Time (s) between statistics printk()s.
3349 rcutorture.stutter= [KNL]
3350 Time (s) to stutter testing, for example, specifying
3351 five seconds causes the test to run for five seconds,
3352 wait for five seconds, and so on. This tests RCU's
3353 ability to transition abruptly to and from idle.
3355 rcutorture.test_boost= [KNL]
3356 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3357 "Maybe" means test if the RCU implementation
3358 under test support RCU priority boosting.
3360 rcutorture.test_boost_duration= [KNL]
3361 Duration (s) of each individual boost test.
3363 rcutorture.test_boost_interval= [KNL]
3364 Interval (s) between each boost test.
3366 rcutorture.test_no_idle_hz= [KNL]
3367 Test RCU's dyntick-idle handling. See also the
3368 rcutorture.shuffle_interval parameter.
3370 rcutorture.torture_runnable= [BOOT]
3371 Start rcutorture running at boot time.
3373 rcutorture.torture_type= [KNL]
3374 Specify the RCU implementation to test.
3376 rcutorture.verbose= [KNL]
3377 Enable additional printk() statements.
3379 rcupdate.rcu_cpu_stall_suppress= [KNL]
3380 Suppress RCU CPU stall warning messages.
3382 rcupdate.rcu_cpu_stall_timeout= [KNL]
3383 Set timeout for RCU CPU stall warning messages.
3385 rcupdate.rcu_expedited= [KNL]
3386 Use expedited grace-period primitives, for
3387 example, synchronize_rcu_expedited() instead
3388 of synchronize_rcu(). This reduces latency,
3389 but can increase CPU utilization, degrade
3390 real-time latency, and degrade energy efficiency.
3391 No effect on CONFIG_TINY_RCU kernels.
3393 rcupdate.rcu_normal= [KNL]
3394 Use only normal grace-period primitives,
3395 for example, synchronize_rcu() instead of
3396 synchronize_rcu_expedited(). This improves
3397 real-time latency, CPU utilization, and
3398 energy efficiency, but can expose users to
3399 increased grace-period latency. This parameter
3400 overrides rcupdate.rcu_expedited. No effect on
3401 CONFIG_TINY_RCU kernels.
3403 rcupdate.rcu_normal_after_boot= [KNL]
3404 Once boot has completed (that is, after
3405 rcu_end_inkernel_boot() has been invoked), use
3406 only normal grace-period primitives. No effect
3407 on CONFIG_TINY_RCU kernels.
3409 rcupdate.rcu_task_stall_timeout= [KNL]
3410 Set timeout in jiffies for RCU task stall warning
3411 messages. Disable with a value less than or equal
3414 rcupdate.rcu_self_test= [KNL]
3415 Run the RCU early boot self tests
3417 rcupdate.rcu_self_test_bh= [KNL]
3418 Run the RCU bh early boot self tests
3420 rcupdate.rcu_self_test_sched= [KNL]
3421 Run the RCU sched early boot self tests
3425 Run specified binary instead of /init from the ramdisk,
3426 used for early userspace startup. See initrd.
3429 Format (x86 or x86_64):
3430 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3432 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3434 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3435 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3436 reboot_force is either force or not specified,
3437 reboot_cpu is s[mp]#### with #### being the processor
3438 to be used for rebooting.
3441 [KNL, SMP] Set scheduler's default relax_domain_level.
3442 See Documentation/cgroups/cpusets.txt.
3444 relative_sleep_states=
3445 [SUSPEND] Use sleep state labeling where the deepest
3446 state available other than hibernation is always "mem".
3447 Format: { "0" | "1" }
3448 0 -- Traditional sleep state labels.
3449 1 -- Relative sleep state labels.
3451 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3453 reservetop= [X86-32]
3455 Reserves a hole at the top of the kernel virtual
3460 Set the amount of memory to reserve for BIOS at
3461 the bottom of the address space.
3463 reset_devices [KNL] Force drivers to reset the underlying device
3464 during initialization.
3467 Specify the partition device for software suspend
3469 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3471 resume_offset= [SWSUSP]
3472 Specify the offset from the beginning of the partition
3473 given by "resume=" at which the swap header is located,
3474 in <PAGE_SIZE> units (needed only for swap files).
3475 See Documentation/power/swsusp-and-swap-files.txt
3477 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3478 read the resume files
3480 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3481 Useful for devices that are detected asynchronously
3482 (e.g. USB and MMC devices).
3484 hibernate= [HIBERNATION]
3485 noresume Don't check if there's a hibernation image
3486 present during boot.
3487 nocompress Don't compress/decompress hibernation images.
3488 no Disable hibernation and resume.
3490 retain_initrd [RAM] Keep initrd memory after extraction
3492 rfkill.default_state=
3493 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3494 etc. communication is blocked by default.
3497 rfkill.master_switch_mode=
3498 0 The "airplane mode" button does nothing.
3499 1 The "airplane mode" button toggles between everything
3500 blocked and the previous configuration.
3501 2 The "airplane mode" button toggles between everything
3502 blocked and everything unblocked.
3504 rhash_entries= [KNL,NET]
3505 Set number of hash buckets for route cache
3507 ro [KNL] Mount root device read-only on boot
3510 on Mark read-only kernel memory as read-only (default).
3511 off Leave read-only kernel memory writable for debugging.
3513 root= [KNL] Root filesystem
3514 See name_to_dev_t comment in init/do_mounts.c.
3516 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3517 mount the root filesystem
3519 rootflags= [KNL] Set root filesystem mount option string
3521 rootfstype= [KNL] Set root filesystem type
3523 rootwait [KNL] Wait (indefinitely) for root device to show up.
3524 Useful for devices that are detected asynchronously
3525 (e.g. USB and MMC devices).
3527 rproc_mem=nn[KMG][@address]
3528 [KNL,ARM,CMA] Remoteproc physical memory block.
3529 Memory area to be used by remote processor image,
3532 rw [KNL] Mount root device read-write on boot
3534 S [KNL] Run init in single mode
3536 s390_iommu= [HW,S390]
3537 Set s390 IOTLB flushing mode
3539 With strict flushing every unmap operation will result in
3540 an IOTLB flush. Default is lazy flushing before reuse,
3544 See drivers/net/irda/sa1100_ir.c.
3546 sbni= [NET] Granch SBNI12 leased line adapter
3548 sched_debug [KNL] Enables verbose scheduler debug messages.
3550 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3551 Allowed values are enable and disable. This feature
3552 incurs a small amount of overhead in the scheduler
3553 but is useful for debugging and performance tuning.
3555 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3556 xtime_lock contention on larger systems, and/or RCU lock
3557 contention on all systems with CONFIG_MAXSMP set.
3558 Format: { "0" | "1" }
3559 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3561 Note: increases power consumption, thus should only be
3562 enabled if running jitter sensitive (HPC/RT) workloads.
3564 security= [SECURITY] Choose a security module to enable at boot.
3565 If this boot parameter is not specified, only the first
3566 security module asking for security registration will be
3567 loaded. An invalid security module name will be treated
3568 as if no module has been chosen.
3570 selinux= [SELINUX] Disable or enable SELinux at boot time.
3571 Format: { "0" | "1" }
3572 See security/selinux/Kconfig help text.
3575 Default value is set via kernel config option.
3576 If enabled at boot time, /selinux/disable can be used
3577 later to disable prior to initial policy load.
3579 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3580 Format: { "0" | "1" }
3581 See security/apparmor/Kconfig help text
3584 Default value is set via kernel config option.
3586 serialnumber [BUGS=X86-32]
3589 Maximal number of shapers.
3591 show_msr= [x86] show boot-time MSR settings
3592 Format: { <integer> }
3593 Show boot-time (BIOS-initialized) MSR settings.
3594 The parameter means the number of CPUs to show,
3595 for example 1 means boot CPU only.
3603 Disable merging of slabs with similar size. May be
3604 necessary if there is some reason to distinguish
3605 allocs to different slabs. Debug options disable
3606 merging on their own.
3607 For more information see Documentation/vm/slub.txt.
3609 slab_max_order= [MM, SLAB]
3610 Determines the maximum allowed order for slabs.
3611 A high setting may cause OOMs due to memory
3612 fragmentation. Defaults to 1 for systems with
3613 more than 32MB of RAM, 0 otherwise.
3615 slub_debug[=options[,slabs]] [MM, SLUB]
3616 Enabling slub_debug allows one to determine the
3617 culprit if slab objects become corrupted. Enabling
3618 slub_debug can create guard zones around objects and
3619 may poison objects when not in use. Also tracks the
3620 last alloc / free. For more information see
3621 Documentation/vm/slub.txt.
3623 slub_max_order= [MM, SLUB]
3624 Determines the maximum allowed order for slabs.
3625 A high setting may cause OOMs due to memory
3626 fragmentation. For more information see
3627 Documentation/vm/slub.txt.
3629 slub_min_objects= [MM, SLUB]
3630 The minimum number of objects per slab. SLUB will
3631 increase the slab order up to slub_max_order to
3632 generate a sufficiently large slab able to contain
3633 the number of objects indicated. The higher the number
3634 of objects the smaller the overhead of tracking slabs
3635 and the less frequently locks need to be acquired.
3636 For more information see Documentation/vm/slub.txt.
3638 slub_min_order= [MM, SLUB]
3639 Determines the minimum page order for slabs. Must be
3640 lower than slub_max_order.
3641 For more information see Documentation/vm/slub.txt.
3643 slub_nomerge [MM, SLUB]
3644 Same with slab_nomerge. This is supported for legacy.
3645 See slab_nomerge for more information.
3648 Format: <io1>[,<io2>[,...,<io8>]]
3650 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3651 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3652 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3653 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3654 smsc-ircc2.ircc_irq= [HW] IRQ line
3655 smsc-ircc2.ircc_dma= [HW] DMA channel
3656 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3657 0: Toshiba Satellite 1800 (GP data pin select)
3658 1: Fast pin select (default)
3662 [KNL] Should the soft-lockup detector generate panics.
3665 softlockup_all_cpu_backtrace=
3666 [KNL] Should the soft-lockup detector generate
3667 backtraces on all cpus.
3670 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3671 See Documentation/laptops/sonypi.txt
3673 spia_io_base= [HW,MTD]
3679 Enabled the stack tracer on boot up.
3681 stacktrace_filter=[function-list]
3682 [FTRACE] Limit the functions that the stack tracer
3683 will trace at boot up. function-list is a comma separated
3684 list of functions. This list can be changed at run
3685 time by the stack_trace_filter file in the debugfs
3686 tracing directory. Note, this enables stack tracing
3687 and the stacktrace above is not needed.
3691 Set the STI (builtin display/keyboard on the HP-PARISC
3692 machines) console (graphic card) which should be used
3693 as the initial boot-console.
3694 See also comment in drivers/video/console/sticore.c.
3697 See comment in drivers/video/console/sticore.c.
3700 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3702 sunrpc.min_resvport=
3703 sunrpc.max_resvport=
3705 SunRPC servers often require that client requests
3706 originate from a privileged port (i.e. a port in the
3707 range 0 < portnr < 1024).
3708 An administrator who wishes to reserve some of these
3709 ports for other uses may adjust the range that the
3710 kernel's sunrpc client considers to be privileged
3711 using these two parameters to set the minimum and
3712 maximum port values.
3716 Control how the NFS server code allocates CPUs to
3717 service thread pools. Depending on how many NICs
3718 you have and where their interrupts are bound, this
3719 option will affect which CPUs will do NFS serving.
3720 Note: this parameter cannot be changed while the
3721 NFS server is running.
3723 auto the server chooses an appropriate mode
3724 automatically using heuristics
3725 global a single global pool contains all CPUs
3726 percpu one pool for each CPU
3727 pernode one pool for each NUMA node (equivalent
3728 to global on non-NUMA machines)
3730 sunrpc.tcp_slot_table_entries=
3731 sunrpc.udp_slot_table_entries=
3733 Sets the upper limit on the number of simultaneous
3734 RPC calls that can be sent from the client to a
3735 server. Increasing these values may allow you to
3736 improve throughput, but will also increase the
3737 amount of memory reserved for use by the client.
3739 suspend.pm_test_delay=
3741 Sets the number of seconds to remain in a suspend test
3742 mode before resuming the system (see
3743 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3744 is set. Default value is 5.
3747 [KNL] Enable accounting of swap in memory resource
3748 controller if no parameter or 1 is given or disable
3749 it if 0 is given (See Documentation/cgroups/memory.txt)
3751 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3752 Format: { <int> | force }
3753 <int> -- Number of I/O TLB slabs
3754 force -- force using of bounce buffers even if they
3755 wouldn't be automatically used by the kernel
3759 sysfs.deprecated=0|1 [KNL]
3760 Enable/disable old style sysfs layout for old udev
3761 on older distributions. When this option is enabled
3762 very new udev will not work anymore. When this option
3763 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3764 in older udev will not work anymore.
3765 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3766 the kernel configuration.
3768 sysrq_always_enabled
3770 Ignore sysrq setting - this boot parameter will
3771 neutralize any effect of /proc/sys/kernel/sysrq.
3772 Useful for debugging.
3774 tcpmhash_entries= [KNL,NET]
3775 Set the number of tcp_metrics_hash slots.
3776 Default value is 8192 or 16384 depending on total
3777 ram pages. This is used to specify the TCP metrics
3778 cache size. See Documentation/networking/ip-sysctl.txt
3779 "tcp_no_metrics_save" section for more details.
3783 test_suspend= [SUSPEND][,N]
3784 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3785 standby suspend) or "freeze" (for suspend type freeze)
3786 as the system sleep state during system startup with
3787 the optional capability to repeat N number of times.
3788 The system is woken from this state using a
3789 wakeup-capable RTC alarm.
3791 thash_entries= [KNL,NET]
3792 Set number of hash buckets for TCP connection
3794 thermal.act= [HW,ACPI]
3795 -1: disable all active trip points in all thermal zones
3796 <degrees C>: override all lowest active trip points
3798 thermal.crt= [HW,ACPI]
3799 -1: disable all critical trip points in all thermal zones
3800 <degrees C>: override all critical trip points
3802 thermal.nocrt= [HW,ACPI]
3803 Set to disable actions on ACPI thermal zone
3804 critical and hot trip points.
3806 thermal.off= [HW,ACPI]
3807 1: disable ACPI thermal control
3809 thermal.psv= [HW,ACPI]
3810 -1: disable all passive trip points
3811 <degrees C>: override all passive trip points to this
3814 thermal.tzp= [HW,ACPI]
3815 Specify global default ACPI thermal zone polling rate
3816 <deci-seconds>: poll all this frequency
3817 0: no polling (default)
3820 Force threading of all interrupt handlers except those
3821 marked explicitly IRQF_NO_THREAD.
3824 Enable the Transcendent memory driver if built-in.
3826 tmem.cleancache=0|1 [KNL, XEN]
3827 Default is on (1). Disable the usage of the cleancache
3828 API to send anonymous pages to the hypervisor.
3830 tmem.frontswap=0|1 [KNL, XEN]
3831 Default is on (1). Disable the usage of the frontswap
3832 API to send swap pages to the hypervisor. If disabled
3833 the selfballooning and selfshrinking are force disabled.
3835 tmem.selfballooning=0|1 [KNL, XEN]
3836 Default is on (1). Disable the driving of swap pages
3839 tmem.selfshrinking=0|1 [KNL, XEN]
3840 Default is on (1). Partial swapoff that immediately
3841 transfers pages from Xen hypervisor back to the
3842 kernel based on different criteria.
3846 Specify if the kernel should make use of the cpu
3847 topology information if the hardware supports this.
3848 The scheduler will make use of this information and
3849 e.g. base its process migration decisions on it.
3852 topology_updates= [KNL, PPC, NUMA]
3854 Specify if the kernel should ignore (off)
3855 topology updates sent by the hypervisor to this
3860 tpm_suspend_pcr=[HW,TPM]
3861 Format: integer pcr id
3862 Specify that at suspend time, the tpm driver
3863 should extend the specified pcr with zeros,
3864 as a workaround for some chips which fail to
3865 flush the last written pcr on TPM_SaveState.
3866 This will guarantee that all the other pcrs
3869 trace_buf_size=nn[KMG]
3870 [FTRACE] will set tracing buffer size on each cpu.
3872 trace_event=[event-list]
3873 [FTRACE] Set and start specified trace events in order
3874 to facilitate early boot debugging.
3875 See also Documentation/trace/events.txt
3877 trace_options=[option-list]
3878 [FTRACE] Enable or disable tracer options at boot.
3879 The option-list is a comma delimited list of options
3880 that can be enabled or disabled just as if you were
3881 to echo the option name into
3883 /sys/kernel/debug/tracing/trace_options
3885 For example, to enable stacktrace option (to dump the
3886 stack trace of each event), add to the command line:
3888 trace_options=stacktrace
3890 See also Documentation/trace/ftrace.txt "trace options"
3894 Have the tracepoints sent to printk as well as the
3895 tracing ring buffer. This is useful for early boot up
3896 where the system hangs or reboots and does not give the
3897 option for reading the tracing buffer or performing a
3898 ftrace_dump_on_oops.
3900 To turn off having tracepoints sent to printk,
3901 echo 0 > /proc/sys/kernel/tracepoint_printk
3902 Note, echoing 1 into this file without the
3903 tracepoint_printk kernel cmdline option has no effect.
3907 Having tracepoints sent to printk() and activating high
3908 frequency tracepoints such as irq or sched, can cause
3909 the system to live lock.
3912 [FTRACE] enable this option to disable tracing when a
3913 warning is hit. This turns off "tracing_on". Tracing can
3914 be enabled again by echoing '1' into the "tracing_on"
3915 file located in /sys/kernel/debug/tracing/
3917 This option is useful, as it disables the trace before
3918 the WARNING dump is called, which prevents the trace to
3919 be filled with content caused by the warning output.
3921 This option can also be set at run time via the sysctl
3922 option: kernel/traceoff_on_warning
3924 transparent_hugepage=
3926 Format: [always|madvise|never]
3927 Can be used to control the default behavior of the system
3928 with respect to transparent hugepages.
3929 See Documentation/vm/transhuge.txt for more details.
3931 tsc= Disable clocksource stability checks for TSC.
3933 [x86] reliable: mark tsc clocksource as reliable, this
3934 disables clocksource verification at runtime, as well
3935 as the stability checks done at bootup. Used to enable
3936 high-resolution timer mode on older hardware, and in
3937 virtualized environment.
3938 [x86] noirqtime: Do not use TSC to do irq accounting.
3939 Used to run time disable IRQ_TIME_ACCOUNTING on any
3940 platforms where RDTSC is slow and this accounting
3943 turbografx.map[2|3]= [HW,JOY]
3944 TurboGraFX parallel port interface
3946 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3947 See also Documentation/input/joystick-parport.txt
3949 udbg-immortal [PPC] When debugging early kernel crashes that
3950 happen after console_init() and before a proper
3951 console driver takes over, this boot options might
3952 help "seeing" what's going on.
3954 uhash_entries= [KNL,NET]
3955 Set number of hash buckets for UDP/UDP-Lite connections
3958 [USB] Ignore overcurrent events (default N).
3959 Some badly-designed motherboards generate lots of
3960 bogus events, for ports that aren't wired to
3961 anything. Set this parameter to avoid log spamming.
3962 Note that genuine overcurrent events won't be
3966 [X86] Cause panic on unknown NMI.
3968 usbcore.authorized_default=
3969 [USB] Default USB device authorization:
3970 (default -1 = authorized except for wireless USB,
3971 0 = not authorized, 1 = authorized)
3973 usbcore.autosuspend=
3974 [USB] The autosuspend time delay (in seconds) used
3975 for newly-detected USB devices (default 2). This
3976 is the time required before an idle device will be
3977 autosuspended. Devices for which the delay is set
3978 to a negative value won't be autosuspended at all.
3980 usbcore.usbfs_snoop=
3981 [USB] Set to log all usbfs traffic (default 0 = off).
3983 usbcore.usbfs_snoop_max=
3984 [USB] Maximum number of bytes to snoop in each URB
3987 usbcore.blinkenlights=
3988 [USB] Set to cycle leds on hubs (default 0 = off).
3990 usbcore.old_scheme_first=
3991 [USB] Start with the old device initialization
3992 scheme (default 0 = off).
3994 usbcore.usbfs_memory_mb=
3995 [USB] Memory limit (in MB) for buffers allocated by
3996 usbfs (default = 16, 0 = max = 2047).
3998 usbcore.use_both_schemes=
3999 [USB] Try the other device initialization scheme
4000 if the first one fails (default 1 = enabled).
4002 usbcore.initial_descriptor_timeout=
4003 [USB] Specifies timeout for the initial 64-byte
4004 USB_REQ_GET_DESCRIPTOR request in milliseconds
4005 (default 5000 = 5.0 seconds).
4007 usbcore.nousb [USB] Disable the USB subsystem
4010 [USBHID] The interval which mice are to be polled at.
4012 usb-storage.delay_use=
4013 [UMS] The delay in seconds before a new device is
4014 scanned for Logical Units (default 1).
4017 [UMS] A list of quirks entries to supplement or
4018 override the built-in unusual_devs list. List
4019 entries are separated by commas. Each entry has
4020 the form VID:PID:Flags where VID and PID are Vendor
4021 and Product ID values (4-digit hex numbers) and
4022 Flags is a set of characters, each corresponding
4023 to a common usb-storage quirk flag as follows:
4024 a = SANE_SENSE (collect more than 18 bytes
4026 b = BAD_SENSE (don't collect more than 18
4027 bytes of sense data);
4028 c = FIX_CAPACITY (decrease the reported
4029 device capacity by one sector);
4030 d = NO_READ_DISC_INFO (don't use
4031 READ_DISC_INFO command);
4032 e = NO_READ_CAPACITY_16 (don't use
4033 READ_CAPACITY_16 command);
4034 f = NO_REPORT_OPCODES (don't use report opcodes
4036 g = MAX_SECTORS_240 (don't transfer more than
4037 240 sectors at a time, uas only);
4038 h = CAPACITY_HEURISTICS (decrease the
4039 reported device capacity by one
4040 sector if the number is odd);
4041 i = IGNORE_DEVICE (don't bind to this
4043 l = NOT_LOCKABLE (don't try to lock and
4044 unlock ejectable media);
4045 m = MAX_SECTORS_64 (don't transfer more
4046 than 64 sectors = 32 KB at a time);
4047 n = INITIAL_READ10 (force a retry of the
4048 initial READ(10) command);
4049 o = CAPACITY_OK (accept the capacity
4050 reported by the device);
4051 p = WRITE_CACHE (the device cache is ON
4053 r = IGNORE_RESIDUE (the device reports
4054 bogus residue values);
4055 s = SINGLE_LUN (the device has only one
4057 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4058 commands, uas only);
4059 u = IGNORE_UAS (don't bind to the uas driver);
4060 w = NO_WP_DETECT (don't test whether the
4061 medium is write-protected).
4062 Example: quirks=0419:aaf5:rl,0421:0433:rc
4064 user_debug= [KNL,ARM]
4066 See arch/arm/Kconfig.debug help text.
4067 1 - undefined instruction events
4069 4 - invalid data aborts
4072 Example: user_debug=31
4075 [X86] Flags controlling user PTE allocations.
4077 nohigh = do not allocate PTE pages in
4078 HIGHMEM regardless of setting
4082 On X86_32, this is an alias for vdso32=. Otherwise:
4084 vdso=1: enable VDSO (the default)
4085 vdso=0: disable VDSO mapping
4087 vdso32= [X86] Control the 32-bit vDSO
4088 vdso32=1: enable 32-bit VDSO
4089 vdso32=0 or vdso32=2: disable 32-bit VDSO
4091 See the help text for CONFIG_COMPAT_VDSO for more
4092 details. If CONFIG_COMPAT_VDSO is set, the default is
4093 vdso32=0; otherwise, the default is vdso32=1.
4095 For compatibility with older kernels, vdso32=2 is an
4098 Try vdso32=0 if you encounter an error that says:
4099 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4102 vector=percpu: enable percpu vector domain
4104 video= [FB] Frame buffer configuration
4105 See Documentation/fb/modedb.txt.
4107 video.brightness_switch_enabled= [0,1]
4108 If set to 1, on receiving an ACPI notify event
4109 generated by hotkey, video driver will adjust brightness
4110 level and then send out the event to user space through
4111 the allocated input device; If set to 0, video driver
4112 will only send out the event without touching backlight
4117 [VMMIO] Memory mapped virtio (platform) device.
4119 <size>@<baseaddr>:<irq>[:<id>]
4121 <size> := size (can use standard suffixes
4123 <baseaddr> := physical base address
4124 <irq> := interrupt number (as passed to
4126 <id> := (optional) platform device id
4128 virtio_mmio.device=1K@0x100b0000:48:7
4130 Can be used multiple times for multiple devices.
4132 vga= [BOOT,X86-32] Select a particular video mode
4133 See Documentation/x86/boot.txt and
4134 Documentation/svga.txt.
4135 Use vga=ask for menu.
4136 This is actually a boot loader parameter; the value is
4137 passed to the kernel using a special protocol.
4139 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4140 size of <nn>. This can be used to increase the
4141 minimum size (128MB on x86). It can also be used to
4142 decrease the size and leave more room for directly
4145 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4148 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4151 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4155 Controls the behavior of vsyscalls (i.e. calls to
4156 fixed addresses of 0xffffffffff600x00 from legacy
4157 code). Most statically-linked binaries and older
4158 versions of glibc use these calls. Because these
4159 functions are at fixed addresses, they make nice
4160 targets for exploits that can control RIP.
4162 emulate [default] Vsyscalls turn into traps and are
4163 emulated reasonably safely.
4165 native Vsyscalls are native syscall instructions.
4166 This is a little bit faster than trapping
4167 and makes a few dynamic recompilers work
4168 better than they would in emulation mode.
4169 It also makes exploits much easier to write.
4171 none Vsyscalls don't work at all. This makes
4172 them quite hard to use for exploits but
4173 might break your system.
4175 vt.color= [VT] Default text color.
4176 Format: 0xYX, X = foreground, Y = background.
4177 Default: 0x07 = light gray on black.
4179 vt.cur_default= [VT] Default cursor shape.
4180 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4181 the parameters of the <Esc>[?A;B;Cc escape sequence;
4182 see VGA-softcursor.txt. Default: 2 = underline.
4184 vt.default_blu= [VT]
4185 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4186 Change the default blue palette of the console.
4187 This is a 16-member array composed of values
4190 vt.default_grn= [VT]
4191 Format: <green0>,<green1>,<green2>,...,<green15>
4192 Change the default green palette of the console.
4193 This is a 16-member array composed of values
4196 vt.default_red= [VT]
4197 Format: <red0>,<red1>,<red2>,...,<red15>
4198 Change the default red palette of the console.
4199 This is a 16-member array composed of values
4205 Set system-wide default UTF-8 mode for all tty's.
4206 Default is 1, i.e. UTF-8 mode is enabled for all
4207 newly opened terminals.
4209 vt.global_cursor_default=
4212 Set system-wide default for whether a cursor
4213 is shown on new VTs. Default is -1,
4214 i.e. cursors will be created by default unless
4215 overridden by individual drivers. 0 will hide
4216 cursors, 1 will display them.
4218 vt.italic= [VT] Default color for italic text; 0-15.
4221 vt.underline= [VT] Default color for underlined text; 0-15.
4224 watchdog timers [HW,WDT] For information on watchdog timers,
4225 see Documentation/watchdog/watchdog-parameters.txt
4226 or other driver-specific files in the
4227 Documentation/watchdog/ directory.
4229 workqueue.watchdog_thresh=
4230 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4231 warn stall conditions and dump internal state to
4232 help debugging. 0 disables workqueue stall
4233 detection; otherwise, it's the stall threshold
4234 duration in seconds. The default value is 30 and
4235 it can be updated at runtime by writing to the
4236 corresponding sysfs file.
4238 workqueue.disable_numa
4239 By default, all work items queued to unbound
4240 workqueues are affine to the NUMA nodes they're
4241 issued on, which results in better behavior in
4242 general. If NUMA affinity needs to be disabled for
4243 whatever reason, this option can be used. Note
4244 that this also can be controlled per-workqueue for
4245 workqueues visible under /sys/bus/workqueue/.
4247 workqueue.power_efficient
4248 Per-cpu workqueues are generally preferred because
4249 they show better performance thanks to cache
4250 locality; unfortunately, per-cpu workqueues tend to
4251 be more power hungry than unbound workqueues.
4253 Enabling this makes the per-cpu workqueues which
4254 were observed to contribute significantly to power
4255 consumption unbound, leading to measurably lower
4256 power usage at the cost of small performance
4259 The default value of this parameter is determined by
4260 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4262 workqueue.debug_force_rr_cpu
4263 Workqueue used to implicitly guarantee that work
4264 items queued without explicit CPU specified are put
4265 on the local CPU. This guarantee is no longer true
4266 and while local CPU is still preferred work items
4267 may be put on foreign CPUs. This debug option
4268 forces round-robin CPU selection to flush out
4269 usages which depend on the now broken guarantee.
4270 When enabled, memory and cache locality will be
4273 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4274 default x2apic cluster mode on platforms
4277 x86_intel_mid_timer= [X86-32,APBT]
4278 Choose timer option for x86 Intel MID platform.
4279 Two valid options are apbt timer only and lapic timer
4280 plus one apbt timer for broadcast timer.
4281 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4283 xen_512gb_limit [KNL,X86-64,XEN]
4284 Restricts the kernel running paravirtualized under Xen
4285 to use only up to 512 GB of RAM. The reason to do so is
4286 crash analysis tools and Xen tools for doing domain
4287 save/restore/migration must be enabled to handle larger
4290 xen_emul_unplug= [HW,X86,XEN]
4291 Unplug Xen emulated devices
4292 Format: [unplug0,][unplug1]
4293 ide-disks -- unplug primary master IDE devices
4294 aux-ide-disks -- unplug non-primary-master IDE devices
4295 nics -- unplug network devices
4296 all -- unplug all emulated devices (NICs and IDE disks)
4297 unnecessary -- unplugging emulated devices is
4298 unnecessary even if the host did not respond to
4300 never -- do not unplug even if version check succeeds
4302 xen_nopvspin [X86,XEN]
4303 Disables the ticketlock slowpath using Xen PV
4307 Disables the PV optimizations forcing the HVM guest to
4308 run as generic HVM guest with no PV drivers.
4310 xirc2ps_cs= [NET,PCMCIA]
4312 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4314 ______________________________________________________________________
4318 Add more DRM drivers.
projects / cascardo / linux.git / blob