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 X86_UV SGI UV support is enabled.
135 XEN Xen support is enabled
137 In addition, the following text indicates that the option:
139 BUGS= Relates to possible processor bugs on the said processor.
140 KNL Is a kernel start-up parameter.
141 BOOT Is a boot loader parameter.
143 Parameters denoted with BOOT are actually interpreted by the boot
144 loader, and have no meaning to the kernel directly.
145 Do not modify the syntax of boot loader parameters without extreme
146 need or coordination with <Documentation/x86/boot.txt>.
148 There are also arch-specific kernel-parameters not documented here.
149 See for example <Documentation/x86/x86_64/boot-options.txt>.
151 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
152 a trailing = on the name of any parameter states that that parameter will
153 be entered as an environment variable, whereas its absence indicates that
154 it will appear as a kernel argument readable via /proc/cmdline by programs
155 running once the system is up.
157 The number of kernel parameters is not limited, but the length of the
158 complete command line (parameters including spaces etc.) is limited to
159 a fixed number of characters. This limit depends on the architecture
160 and is between 256 and 4096 characters. It is defined in the file
161 ./include/asm/setup.h as COMMAND_LINE_SIZE.
163 Finally, the [KMG] suffix is commonly described after a number of kernel
164 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
165 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
166 bytes respectively. Such letter suffixes can also be entirely omitted.
169 acpi= [HW,ACPI,X86,ARM64]
170 Advanced Configuration and Power Interface
171 Format: { force | on | off | strict | noirq | rsdt |
173 force -- enable ACPI if default was off
174 on -- enable ACPI but allow fallback to DT [arm64]
175 off -- disable ACPI if default was on
176 noirq -- do not use ACPI for IRQ routing
177 strict -- Be less tolerant of platforms that are not
178 strictly ACPI specification compliant.
179 rsdt -- prefer RSDT over (default) XSDT
180 copy_dsdt -- copy DSDT to memory
181 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
184 See also Documentation/power/runtime_pm.txt, pci=noacpi
186 acpi_apic_instance= [ACPI, IOAPIC]
188 2: use 2nd APIC table, if available
189 1,0: use 1st APIC table
192 acpi_backlight= [HW,ACPI]
193 acpi_backlight=vendor
195 If set to vendor, prefer vendor specific driver
196 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
197 of the ACPI video.ko driver.
199 acpi_force_32bit_fadt_addr
200 force FADT to use 32 bit addresses rather than the
201 64 bit X_* addresses. Some firmware have broken 64
202 bit addresses for force ACPI ignore these and use
203 the older legacy 32 bit addresses.
205 acpica_no_return_repair [HW, ACPI]
206 Disable AML predefined validation mechanism
207 This mechanism can repair the evaluation result to make
208 the return objects more ACPI specification compliant.
209 This option is useful for developers to identify the
210 root cause of an AML interpreter issue when the issue
211 has something to do with the repair mechanism.
213 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
214 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
216 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
217 debug output. Bits in debug_layer correspond to a
218 _COMPONENT in an ACPI source file, e.g.,
219 #define _COMPONENT ACPI_PCI_COMPONENT
220 Bits in debug_level correspond to a level in
221 ACPI_DEBUG_PRINT statements, e.g.,
222 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
223 The debug_level mask defaults to "info". See
224 Documentation/acpi/debug.txt for more information about
225 debug layers and levels.
227 Enable processor driver info messages:
228 acpi.debug_layer=0x20000000
229 Enable PCI/PCI interrupt routing info messages:
230 acpi.debug_layer=0x400000
231 Enable AML "Debug" output, i.e., stores to the Debug
232 object while interpreting AML:
233 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
234 Enable all messages related to ACPI hardware:
235 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
237 Some values produce so much output that the system is
238 unusable. The "log_buf_len" parameter may be useful
239 if you need to capture more output.
241 acpi_enforce_resources= [ACPI]
242 { strict | lax | no }
243 Check for resource conflicts between native drivers
244 and ACPI OperationRegions (SystemIO and SystemMemory
245 only). IO ports and memory declared in ACPI might be
246 used by the ACPI subsystem in arbitrary AML code and
247 can interfere with legacy drivers.
248 strict (default): access to resources claimed by ACPI
249 is denied; legacy drivers trying to access reserved
250 resources will fail to bind to device using them.
251 lax: access to resources claimed by ACPI is allowed;
252 legacy drivers trying to access reserved resources
253 will bind successfully but a warning message is logged.
254 no: ACPI OperationRegions are not marked as reserved,
255 no further checks are performed.
257 acpi_force_table_verification [HW,ACPI]
258 Enable table checksum verification during early stage.
259 By default, this is disabled due to x86 early mapping
262 acpi_irq_balance [HW,ACPI]
263 ACPI will balance active IRQs
266 acpi_irq_nobalance [HW,ACPI]
267 ACPI will not move active IRQs (default)
270 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
271 Format: <irq>,<irq>...
273 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
275 Format: <irq>,<irq>...
277 acpi_no_auto_serialize [HW,ACPI]
278 Disable auto-serialization of AML methods
279 AML control methods that contain the opcodes to create
280 named objects will be marked as "Serialized" by the
281 auto-serialization feature.
282 This feature is enabled by default.
283 This option allows to turn off the feature.
285 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
288 acpi_no_static_ssdt [HW,ACPI]
289 Disable installation of static SSDTs at early boot time
290 By default, SSDTs contained in the RSDT/XSDT will be
291 installed automatically and they will appear under
292 /sys/firmware/acpi/tables.
293 This option turns off this feature.
294 Note that specifying this option does not affect
295 dynamic table installation which will install SSDT
296 tables to /sys/firmware/acpi/tables/dynamic.
298 acpi_rsdp= [ACPI,EFI,KEXEC]
299 Pass the RSDP address to the kernel, mostly used
300 on machines running EFI runtime service to boot the
301 second kernel for kdump.
303 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
304 Format: To spoof as Windows 98: ="Microsoft Windows"
306 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
307 of 2 which is mandated by ACPI 6) as the supported ACPI
308 specification revision (when using this switch, it may
309 be necessary to carry out a cold reboot _twice_ in a
310 row to make it take effect on the platform firmware).
312 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
313 acpi_osi="string1" # add string1
314 acpi_osi="!string2" # remove string2
315 acpi_osi=!* # remove all strings
316 acpi_osi=! # disable all built-in OS vendor
318 acpi_osi= # disable all strings
320 'acpi_osi=!' can be used in combination with single or
321 multiple 'acpi_osi="string1"' to support specific OS
322 vendor string(s). Note that such command can only
323 affect the default state of the OS vendor strings, thus
324 it cannot affect the default state of the feature group
325 strings and the current state of the OS vendor strings,
326 specifying it multiple times through kernel command line
327 is meaningless. This command is useful when one do not
328 care about the state of the feature group strings which
329 should be controlled by the OSPM.
331 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
332 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
333 can make '_OSI("Windows 2000")' TRUE.
335 'acpi_osi=' cannot be used in combination with other
336 'acpi_osi=' command lines, the _OSI method will not
337 exist in the ACPI namespace. NOTE that such command can
338 only affect the _OSI support state, thus specifying it
339 multiple times through kernel command line is also
342 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
345 'acpi_osi=!*' can be used in combination with single or
346 multiple 'acpi_osi="string1"' to support specific
347 string(s). Note that such command can affect the
348 current state of both the OS vendor strings and the
349 feature group strings, thus specifying it multiple times
350 through kernel command line is meaningful. But it may
351 still not able to affect the final state of a string if
352 there are quirks related to this string. This command
353 is useful when one want to control the state of the
354 feature group strings to debug BIOS issues related to
357 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
358 '_OSI("Module Device")' FALSE.
359 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
360 '_OSI("Module Device")' TRUE.
361 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
363 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
365 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
366 they all will make '_OSI("Windows 2000")' TRUE.
369 Override the pmtimer bug detection: force the kernel
370 to assume that this machine's pmtimer latches its value
371 and always returns good values.
373 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
374 Format: { level | edge | high | low }
376 acpi_skip_timer_override [HW,ACPI]
377 Recognize and ignore IRQ0/pin2 Interrupt Override.
378 For broken nForce2 BIOS resulting in XT-PIC timer.
380 acpi_sleep= [HW,ACPI] Sleep options
381 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
382 old_ordering, nonvs, sci_force_enable }
383 See Documentation/power/video.txt for information on
385 s3_beep is for debugging; it makes the PC's speaker beep
386 as soon as the kernel's real-mode entry point is called.
387 s4_nohwsig prevents ACPI hardware signature from being
388 used during resume from hibernation.
389 old_ordering causes the ACPI 1.0 ordering of the _PTS
390 control method, with respect to putting devices into
391 low power states, to be enforced (the ACPI 2.0 ordering
392 of _PTS is used by default).
393 nonvs prevents the kernel from saving/restoring the
394 ACPI NVS memory during suspend/hibernation and resume.
395 sci_force_enable causes the kernel to set SCI_EN directly
396 on resume from S1/S3 (which is against the ACPI spec,
397 but some broken systems don't work without it).
399 acpi_use_timer_override [HW,ACPI]
400 Use timer override. For some broken Nvidia NF5 boards
401 that require a timer override, but don't have HPET
403 add_efi_memmap [EFI; X86] Include EFI memory map in
404 kernel's map of available physical RAM.
407 { off | try_unsupported }
408 off: disable AGP support
409 try_unsupported: try to drive unsupported chipsets
410 (may crash computer or cause data corruption)
413 See Documentation/sound/alsa/alsa-parameters.txt
416 Allow the default userspace alignment fault handler
417 behaviour to be specified. Bit 0 enables warnings,
418 bit 1 enables fixups, and bit 2 sends a segfault.
420 align_va_addr= [X86-64]
421 Align virtual addresses by clearing slice [14:12] when
422 allocating a VMA at process creation time. This option
423 gives you up to 3% performance improvement on AMD F15h
424 machines (where it is enabled by default) for a
425 CPU-intensive style benchmark, and it can vary highly in
426 a microbenchmark depending on workload and compiler.
428 32: only for 32-bit processes
429 64: only for 64-bit processes
430 on: enable for both 32- and 64-bit processes
431 off: disable for both 32- and 64-bit processes
433 alloc_snapshot [FTRACE]
434 Allocate the ftrace snapshot buffer on boot up when the
435 main buffer is allocated. This is handy if debugging
436 and you need to use tracing_snapshot() on boot up, and
437 do not want to use tracing_snapshot_alloc() as it needs
438 to be done where GFP_KERNEL allocations are allowed.
440 amd_iommu= [HW,X86-64]
441 Pass parameters to the AMD IOMMU driver in the system.
443 fullflush - enable flushing of IO/TLB entries when
444 they are unmapped. Otherwise they are
445 flushed before they will be reused, which
447 off - do not initialize any AMD IOMMU found in
449 force_isolation - Force device isolation for all
450 devices. The IOMMU driver is not
451 allowed anymore to lift isolation
452 requirements as needed. This option
453 does not override iommu=pt
455 amd_iommu_dump= [HW,X86-64]
456 Enable AMD IOMMU driver option to dump the ACPI table
457 for AMD IOMMU. With this option enabled, AMD IOMMU
458 driver will print ACPI tables for AMD IOMMU during
459 IOMMU initialization.
461 amijoy.map= [HW,JOY] Amiga joystick support
462 Map of devices attached to JOY0DAT and JOY1DAT
464 See also Documentation/input/joystick.txt
466 analog.map= [HW,JOY] Analog joystick and gamepad support
467 Specifies type or capabilities of an analog joystick
468 connected to one of 16 gameports
469 Format: <type1>,<type2>,..<type16>
472 Power management functions (SPARCstation-4/5 + deriv.)
474 Disable APC CPU standby support. SPARCstation-Fox does
475 not play well with APC CPU idle - disable it if you have
476 APC and your system crashes randomly.
478 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
479 Change the output verbosity whilst booting
480 Format: { quiet (default) | verbose | debug }
481 Change the amount of debugging information output
482 when initialising the APIC and IO-APIC components.
484 apic_extnmi= [APIC,X86] External NMI delivery setting
485 Format: { bsp (default) | all | none }
486 bsp: External NMI is delivered only to CPU 0
487 all: External NMIs are broadcast to all CPUs as a
489 none: External NMI is masked for all CPUs. This is
490 useful so that a dump capture kernel won't be
494 See Documentation/networking/ipv6.txt.
496 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
497 Limit apic dumping. The parameter defines the maximal
498 number of local apics being dumped. Also it is possible
499 to set it to "all" by meaning -- no limit here.
500 Format: { 1 (default) | 2 | ... | all }.
501 The parameter valid if only apic=debug or
502 apic=verbose is specified.
503 Example: apic=debug show_lapic=all
505 apm= [APM] Advanced Power Management
506 See header of arch/x86/kernel/apm_32.c.
508 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
509 Format: <io>,<irq>,<nodeID>
513 atarimouse= [HW,MOUSE] Atari Mouse
515 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
516 EzKey and similar keyboards
518 atkbd.reset= [HW] Reset keyboard during initialization
520 atkbd.set= [HW] Select keyboard code set
521 Format: <int> (2 = AT (default), 3 = PS/2)
523 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
526 atkbd.softraw= [HW] Choose between synthetic and real raw mode
527 Format: <bool> (0 = real, 1 = synthetic (default))
529 atkbd.softrepeat= [HW]
530 Use software keyboard repeat
532 audit= [KNL] Enable the audit sub-system
533 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
534 0 - kernel audit is disabled and can not be enabled
535 until the next reboot
536 unset - kernel audit is initialized but disabled and
537 will be fully enabled by the userspace auditd.
538 1 - kernel audit is initialized and partially enabled,
539 storing at most audit_backlog_limit messages in
540 RAM until it is fully enabled by the userspace
544 audit_backlog_limit= [KNL] Set the audit queue size limit.
545 Format: <int> (must be >=0)
548 bau= [X86_UV] Enable the BAU on SGI UV. The default
549 behavior is to disable the BAU (i.e. bau=0).
550 Format: { "0" | "1" }
553 unset - Disable the BAU.
555 baycom_epp= [HW,AX25]
558 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
560 See header of drivers/net/hamradio/baycom_par.c.
562 baycom_ser_fdx= [HW,AX25]
563 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
564 Format: <io>,<irq>,<mode>[,<baud>]
565 See header of drivers/net/hamradio/baycom_ser_fdx.c.
567 baycom_ser_hdx= [HW,AX25]
568 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
569 Format: <io>,<irq>,<mode>
570 See header of drivers/net/hamradio/baycom_ser_hdx.c.
572 blkdevparts= Manual partition parsing of block device(s) for
573 embedded devices based on command line input.
574 See Documentation/block/cmdline-partition.txt
576 boot_delay= Milliseconds to delay each printk during boot.
577 Values larger than 10 seconds (10000) are changed to
581 bootmem_debug [KNL] Enable bootmem allocator debug messages.
583 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
584 bttv.radio= Most important insmod options are available as
586 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
589 bulk_remove=off [PPC] This parameter disables the use of the pSeries
590 firmware feature for flushing multiple hpte entries
593 c101= [NET] Moxa C101 synchronous serial card
595 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
596 Sometimes CPU hardware bugs make them report the cache
597 size incorrectly. The kernel will attempt work arounds
598 to fix known problems, but for some CPUs it is not
599 possible to determine what the correct size should be.
600 This option provides an override for these situations.
602 ca_keys= [KEYS] This parameter identifies a specific key(s) on
603 the system trusted keyring to be used for certificate
605 format: { id:<keyid> | builtin }
607 cca= [MIPS] Override the kernel pages' cache coherency
608 algorithm. Accepted values range from 0 to 7
609 inclusive. See arch/mips/include/asm/pgtable-bits.h
610 for platform specific values (SB1, Loongson3 and
613 ccw_timeout_log [S390]
614 See Documentation/s390/CommonIO for details.
616 cgroup_disable= [KNL] Disable a particular controller
617 Format: {name of the controller(s) to disable}
618 The effects of cgroup_disable=foo are:
619 - foo isn't auto-mounted if you mount all cgroups in
621 - foo isn't visible as an individually mountable
623 {Currently only "memory" controller deal with this and
624 cut the overhead, others just disable the usage. So
625 only cgroup_disable=memory is actually worthy}
627 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
628 Format: { controller[,controller...] | "all" }
629 Like cgroup_disable, but only applies to cgroup v1;
630 the blacklisted controllers remain available in cgroup2.
632 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
634 nosocket -- Disable socket memory accounting.
635 nokmem -- Disable kernel memory accounting.
637 checkreqprot [SELINUX] Set initial checkreqprot flag value.
638 Format: { "0" | "1" }
639 See security/selinux/Kconfig help text.
640 0 -- check protection applied by kernel (includes
641 any implied execute protection).
642 1 -- check protection requested by application.
643 Default value is set via a kernel config option.
644 Value can be changed at runtime via
645 /selinux/checkreqprot.
648 See Documentation/s390/CommonIO for details.
651 Prevents the clock framework from automatically gating
652 clocks that have not been explicitly enabled by a Linux
653 device driver but are enabled in hardware at reset or
654 by the bootloader/firmware. Note that this does not
655 force such clocks to be always-on nor does it reserve
656 those clocks in any way. This parameter is useful for
657 debug and development, but should not be needed on a
658 platform with proper driver support. For more
659 information, see Documentation/clk.txt.
661 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
663 Forces specified clocksource (if available) to be used
664 when calculating gettimeofday(). If specified
665 clocksource is not available, it defaults to PIT.
666 Format: { pit | tsc | cyclone | pmtmr }
668 clocksource= Override the default clocksource
670 Override the default clocksource and use the clocksource
671 with the name specified.
672 Some clocksource names to choose from, depending on
674 [all] jiffies (this is the base, fallback clocksource)
676 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
677 pxa_timer,timer3,32k_counter,timer0_1
679 [X86-32] pit,hpet,tsc;
680 scx200_hrt on Geode; cyclone on IBM x440
688 clearcpuid=BITNUM [X86]
689 Disable CPUID feature X for the kernel. See
690 arch/x86/include/asm/cpufeatures.h for the valid bit
691 numbers. Note the Linux specific bits are not necessarily
692 stable over kernel options, but the vendor specific
694 Also note that user programs calling CPUID directly
695 or using the feature without checking anything
696 will still see it. This just prevents it from
697 being used by the kernel or shown in /proc/cpuinfo.
698 Also note the kernel might malfunction if you disable
701 cma=nn[MG]@[start[MG][-end[MG]]]
703 Sets the size of kernel global memory area for
704 contiguous memory allocations and optionally the
705 placement constraint by the physical address range of
706 memory allocations. A value of 0 disables CMA
707 altogether. For more information, see
708 include/linux/dma-contiguous.h
710 cmo_free_hint= [PPC] Format: { yes | no }
711 Specify whether pages are marked as being inactive
712 when they are freed. This is used in CMO environments
713 to determine OS memory pressure for page stealing by
717 coherent_pool=nn[KMG] [ARM,KNL]
718 Sets the size of memory pool for coherent, atomic dma
719 allocations, by default set to 256K.
721 code_bytes [X86] How many bytes of object code to print
726 com20020= [HW,NET] ARCnet - COM20020 chipset
728 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
730 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
734 ARCnet - COM90xx chipset (memory-mapped buffers)
735 Format: <io>[,<irq>[,<memstart>]]
737 condev= [HW,S390] console device
740 console= [KNL] Output console device and options.
742 tty<n> Use the virtual console device <n>.
746 Use the specified serial port. The options are of
747 the form "bbbbpnf", where "bbbb" is the baud rate,
748 "p" is parity ("n", "o", or "e"), "n" is number of
749 bits, and "f" is flow control ("r" for RTS or
750 omit it). Default is "9600n8".
752 See Documentation/serial-console.txt for more
754 Documentation/networking/netconsole.txt for an
757 uart[8250],io,<addr>[,options]
758 uart[8250],mmio,<addr>[,options]
759 uart[8250],mmio16,<addr>[,options]
760 uart[8250],mmio32,<addr>[,options]
761 uart[8250],0x<addr>[,options]
762 Start an early, polled-mode console on the 8250/16550
763 UART at the specified I/O port or MMIO address,
764 switching to the matching ttyS device later.
765 MMIO inter-register address stride is either 8-bit
766 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
767 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
768 to be equivalent to 'mmio'. 'options' are specified in
769 the same format described for ttyS above; if unspecified,
770 the h/w is not re-initialized.
772 hvc<n> Use the hypervisor console device <n>. This is for
773 both Xen and PowerPC hypervisors.
775 If the device connected to the port is not a TTY but a braille
776 device, prepend "brl," before the device type, for instance
778 For now, only VisioBraille is supported.
780 consoleblank= [KNL] The console blank (screen saver) timeout in
781 seconds. Defaults to 10*60 = 10mins. A value of 0
782 disables the blank timer.
785 [KNL] Change the default value for
786 /proc/<pid>/coredump_filter.
787 See also Documentation/filesystems/proc.txt.
789 cpuidle.off=1 [CPU_IDLE]
790 disable the cpuidle sub-system
793 [X86] Delay for N microsec between assert and de-assert
794 of APIC INIT to start processors. This delay occurs
795 on every CPU online, such as boot, and resume from suspend.
798 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
800 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
802 crashkernel=size[KMG][@offset[KMG]]
803 [KNL] Using kexec, Linux can switch to a 'crash kernel'
804 upon panic. This parameter reserves the physical
805 memory region [offset, offset + size] for that kernel
806 image. If '@offset' is omitted, then a suitable offset
807 is selected automatically. Check
808 Documentation/kdump/kdump.txt for further details.
810 crashkernel=range1:size1[,range2:size2,...][@offset]
811 [KNL] Same as above, but depends on the memory
812 in the running system. The syntax of range is
813 start-[end] where start and end are both
814 a memory unit (amount[KMG]). See also
815 Documentation/kdump/kdump.txt for an example.
817 crashkernel=size[KMG],high
818 [KNL, x86_64] range could be above 4G. Allow kernel
819 to allocate physical memory region from top, so could
820 be above 4G if system have more than 4G ram installed.
821 Otherwise memory region will be allocated below 4G, if
823 It will be ignored if crashkernel=X is specified.
824 crashkernel=size[KMG],low
825 [KNL, x86_64] range under 4G. When crashkernel=X,high
826 is passed, kernel could allocate physical memory region
827 above 4G, that cause second kernel crash on system
828 that require some amount of low memory, e.g. swiotlb
829 requires at least 64M+32K low memory, also enough extra
830 low memory is needed to make sure DMA buffers for 32-bit
831 devices won't run out. Kernel would try to allocate at
832 at least 256M below 4G automatically.
833 This one let user to specify own low range under 4G
834 for second kernel instead.
835 0: to disable low allocation.
836 It will be ignored when crashkernel=X,high is not used
837 or memory reserved is below 4G.
842 cs89x0_media= [HW,NET]
843 Format: { rj45 | aui | bnc }
846 See header of drivers/s390/block/dasd_devmap.c.
848 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
849 (one device per port)
850 Format: <port#>,<type>
851 See also Documentation/input/joystick-parport.txt
853 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
854 time. See Documentation/dynamic-debug-howto.txt for
855 details. Deprecated, see dyndbg.
857 debug [KNL] Enable kernel debugging (events log level).
860 [KNL] verbose self-tests
862 Print debugging info while doing the locking API
864 We default to 0 (no extra messages), setting it to
865 1 will print _a lot_ more information - normally
866 only useful to kernel developers.
868 debug_objects [KNL] Enable object debugging
871 [KNL] Disable object debugging
873 debug_guardpage_minorder=
874 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
875 parameter allows control of the order of pages that will
876 be intentionally kept free (and hence protected) by the
877 buddy allocator. Bigger value increase the probability
878 of catching random memory corruption, but reduce the
879 amount of memory for normal system use. The maximum
880 possible value is MAX_ORDER/2. Setting this parameter
881 to 1 or 2 should be enough to identify most random
882 memory corruption problems caused by bugs in kernel or
883 driver code when a CPU writes to (or reads from) a
884 random memory location. Note that there exists a class
885 of memory corruptions problems caused by buggy H/W or
886 F/W or by drivers badly programing DMA (basically when
887 memory is written at bus level and the CPU MMU is
888 bypassed) which are not detectable by
889 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
890 tracking down these problems.
893 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
894 parameter enables the feature at boot time. In
895 default, it is disabled. We can avoid allocating huge
896 chunk of memory for debug pagealloc if we don't enable
897 it at boot time and the system will work mostly same
898 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
899 on: enable the feature
901 debugpat [X86] Enable PAT debugging
903 decnet.addr= [HW,NET]
904 Format: <area>[,<node>]
905 See also Documentation/networking/decnet.txt.
908 [same as hugepagesz=] The size of the default
909 HugeTLB page size. This is the size represented by
910 the legacy /proc/ hugepages APIs, used for SHM, and
911 default size when mounting hugetlbfs filesystems.
912 Defaults to the default architecture's huge page size
916 Set number of hash buckets for dentry cache.
919 See Documentation/networking/ipv6.txt.
921 disable_cpu_apicid= [X86,APIC,SMP]
923 The number of initial APIC ID for the
924 corresponding CPU to be disabled at boot,
925 mostly used for the kdump 2nd kernel to
926 disable BSP to wake up multiple CPUs without
927 causing system reset or hang due to sending
930 disable_ddw [PPC/PSERIES]
931 Disable Dynamic DMA Window support. Use this if
932 to workaround buggy firmware.
935 See Documentation/networking/ipv6.txt.
937 disable_mtrr_cleanup [X86]
938 The kernel tries to adjust MTRR layout from continuous
939 to discrete, to make X server driver able to add WB
940 entry later. This parameter disables that.
942 disable_mtrr_trim [X86, Intel and AMD only]
943 By default the kernel will trim any uncacheable
944 memory out of your available memory pool based on
945 MTRR settings. This parameter disables that behavior,
946 possibly causing your machine to run very slowly.
948 disable_timer_pin_1 [X86]
949 Disable PIN 1 of APIC timer
950 Can be useful to work around chipset bugs.
952 dis_ucode_ldr [X86] Disable the microcode loader.
954 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
955 this option disables the debugging code at boot.
957 dma_debug_entries=<number>
958 This option allows to tune the number of preallocated
959 entries for DMA-API debugging code. One entry is
960 required per DMA-API allocation. Use this if the
961 DMA-API debugging code disables itself because the
962 architectural default is too low.
964 dma_debug_driver=<driver_name>
965 With this option the DMA-API debugging driver
966 filter feature can be enabled at boot time. Just
967 pass the driver to filter for as the parameter.
968 The filter can be disabled or changed to another
969 driver later using sysfs.
971 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
972 Broken monitors, graphic adapters, KVMs and EDIDless
973 panels may send no or incorrect EDID data sets.
974 This parameter allows to specify an EDID data sets
975 in the /lib/firmware directory that are used instead.
976 Generic built-in EDID data sets are used, if one of
977 edid/1024x768.bin, edid/1280x1024.bin,
978 edid/1680x1050.bin, or edid/1920x1080.bin is given
979 and no file with the same name exists. Details and
980 instructions how to build your own EDID data are
981 available in Documentation/EDID/HOWTO.txt. An EDID
982 data set will only be used for a particular connector,
983 if its name and a colon are prepended to the EDID
984 name. Each connector may use a unique EDID data
985 set by separating the files with a comma. An EDID
986 data set with no connector name will be used for
987 any connectors not explicitly specified.
991 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
992 module.dyndbg[="val"]
993 Enable debug messages at boot time. See
994 Documentation/dynamic-debug-howto.txt for details.
996 nompx [X86] Disables Intel Memory Protection Extensions.
997 See Documentation/x86/intel_mpx.txt for more
998 information about the feature.
1000 nopku [X86] Disable Memory Protection Keys CPU feature found
1004 on enable eager fpu restore
1005 off disable eager fpu restore
1006 auto selects the default scheme, which automatically
1007 enables eagerfpu restore for xsaveopt.
1009 module.async_probe [KNL]
1010 Enable asynchronous probe on this module.
1012 early_ioremap_debug [KNL]
1013 Enable debug messages in early_ioremap support. This
1014 is useful for tracking down temporary early mappings
1015 which are not unmapped.
1017 earlycon= [KNL] Output early console device and options.
1019 When used with no options, the early console is
1020 determined by the stdout-path property in device
1024 Start an early, polled-mode console on a cadence serial
1025 port at the specified address. The cadence serial port
1026 must already be setup and configured. Options are not
1029 uart[8250],io,<addr>[,options]
1030 uart[8250],mmio,<addr>[,options]
1031 uart[8250],mmio32,<addr>[,options]
1032 uart[8250],mmio32be,<addr>[,options]
1033 uart[8250],0x<addr>[,options]
1034 Start an early, polled-mode console on the 8250/16550
1035 UART at the specified I/O port or MMIO address.
1036 MMIO inter-register address stride is either 8-bit
1037 (mmio) or 32-bit (mmio32 or mmio32be).
1038 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1039 to be equivalent to 'mmio'. 'options' are specified
1040 in the same format described for "console=ttyS<n>"; if
1041 unspecified, the h/w is not initialized.
1045 Start an early, polled-mode console on a pl011 serial
1046 port at the specified address. The pl011 serial port
1047 must already be setup and configured. Options are not
1048 yet supported. If 'mmio32' is specified, then only
1049 the driver will use only 32-bit accessors to read/write
1050 the device registers.
1053 Start an early, polled-mode console on an msm serial
1054 port at the specified address. The serial port
1055 must already be setup and configured. Options are not
1058 msm_serial_dm,<addr>
1059 Start an early, polled-mode console on an msm serial
1060 dm port at the specified address. The serial port
1061 must already be setup and configured. Options are not
1064 smh Use ARM semihosting calls for early console.
1072 Use early console provided by serial driver available
1073 on Samsung SoCs, requires selecting proper type and
1074 a correct base address of the selected UART port. The
1075 serial port must already be setup and configured.
1076 Options are not yet supported.
1080 Use early console provided by Freescale LP UART driver
1081 found on Freescale Vybrid and QorIQ LS1021A processors.
1082 A valid base address must be provided, and the serial
1083 port must already be setup and configured.
1085 armada3700_uart,<addr>
1086 Start an early, polled-mode console on the
1087 Armada 3700 serial port at the specified
1088 address. The serial port must already be setup
1089 and configured. Options are not yet supported.
1091 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1095 earlyprintk=serial[,ttySn[,baudrate]]
1096 earlyprintk=serial[,0x...[,baudrate]]
1097 earlyprintk=ttySn[,baudrate]
1098 earlyprintk=dbgp[debugController#]
1099 earlyprintk=pciserial,bus:device.function[,baudrate]
1101 earlyprintk is useful when the kernel crashes before
1102 the normal console is initialized. It is not enabled by
1103 default because it has some cosmetic problems.
1105 Append ",keep" to not disable it when the real console
1108 Only one of vga, efi, serial, or usb debug port can
1111 Currently only ttyS0 and ttyS1 may be specified by
1112 name. Other I/O ports may be explicitly specified
1113 on some architectures (x86 and arm at least) by
1114 replacing ttySn with an I/O port address, like this:
1115 earlyprintk=serial,0x1008,115200
1116 You can find the port for a given device in
1117 /proc/tty/driver/serial:
1118 2: uart:ST16650V2 port:00001008 irq:18 ...
1120 Interaction with the standard serial driver is not
1123 The VGA and EFI output is eventually overwritten by
1126 The xen output can only be used by Xen PV guests.
1128 edac_report= [HW,EDAC] Control how to report EDAC event
1129 Format: {"on" | "off" | "force"}
1130 on: enable EDAC to report H/W event. May be overridden
1131 by other higher priority error reporting module.
1132 off: disable H/W event reporting through EDAC.
1133 force: enforce the use of EDAC to report H/W event.
1136 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1139 This is designed to be used in conjunction with
1140 the boot argument: earlyprintk=vga
1143 Format: {"off" | "on" | "skip[mbr]"}
1146 Format: { "old_map", "nochunk", "noruntime", "debug" }
1147 old_map [X86-64]: switch to the old ioremap-based EFI
1148 runtime services mapping. 32-bit still uses this one by
1150 nochunk: disable reading files in "chunks" in the EFI
1151 boot stub, as chunking can cause problems with some
1152 firmware implementations.
1153 noruntime : disable EFI runtime services support
1154 debug: enable misc debug output
1156 efi_no_storage_paranoia [EFI; X86]
1157 Using this parameter you can use more than 50% of
1158 your efi variable storage. Use this parameter only if
1159 you are really sure that your UEFI does sane gc and
1160 fulfills the spec otherwise your board may brick.
1162 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1163 Add arbitrary attribute to specific memory range by
1164 updating original EFI memory map.
1165 Region of memory which aa attribute is added to is
1167 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1168 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1169 attribute is added to range 0x100000000-0x180000000 and
1170 0x10a0000000-0x1120000000.
1172 Using this parameter you can do debugging of EFI memmap
1173 related feature. For example, you can do debugging of
1174 Address Range Mirroring feature even if your box
1177 eisa_irq_edge= [PARISC,HW]
1178 See header of drivers/parisc/eisa.c.
1181 See comment before function elanfreq_setup() in
1182 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1185 Format: {"cfq" | "deadline" | "noop"}
1186 See Documentation/block/cfq-iosched.txt and
1187 Documentation/block/deadline-iosched.txt for details.
1189 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1190 Specifies physical address of start of kernel core
1191 image elf header and optionally the size. Generally
1192 kexec loader will pass this option to capture kernel.
1193 See Documentation/kdump/kdump.txt for details.
1195 enable_mtrr_cleanup [X86]
1196 The kernel tries to adjust MTRR layout from continuous
1197 to discrete, to make X server driver able to add WB
1198 entry later. This parameter enables that.
1200 enable_timer_pin_1 [X86]
1201 Enable PIN 1 of APIC timer
1202 Can be useful to work around chipset bugs
1203 (in particular on some ATI chipsets).
1204 The kernel tries to set a reasonable default.
1206 enforcing [SELINUX] Set initial enforcing status.
1208 See security/selinux/Kconfig help text.
1209 0 -- permissive (log only, no denials).
1210 1 -- enforcing (deny and log).
1212 Value can be changed at runtime via /selinux/enforce.
1215 Disable Error Record Serialization Table (ERST)
1218 ether= [HW,NET] Ethernet cards parameters
1219 This option is obsoleted by the "netdev=" option, which
1220 has equivalent usage. See its documentation for details.
1224 Permit 'security.evm' to be updated regardless of
1225 current integrity status.
1229 fail_make_request=[KNL]
1230 General fault injection mechanism.
1231 Format: <interval>,<probability>,<space>,<times>
1232 See also Documentation/fault-injection/.
1235 See Documentation/blockdev/floppy.txt.
1237 force_pal_cache_flush
1238 [IA-64] Avoid check_sal_cache_flush which may hang on
1239 buggy SAL_CACHE_FLUSH implementations. Using this
1240 parameter will force ia64_sal_cache_flush to call
1241 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1244 Forcefully enable Physical Address Extension (PAE).
1245 Many Pentium M systems disable PAE but may have a
1246 functionally usable PAE implementation.
1247 Warning: use of this parameter will taint the kernel
1248 and may cause unknown problems.
1251 [FTRACE] will set and start the specified tracer
1252 as early as possible in order to facilitate early
1255 ftrace_dump_on_oops[=orig_cpu]
1256 [FTRACE] will dump the trace buffers on oops.
1257 If no parameter is passed, ftrace will dump
1258 buffers of all CPUs, but if you pass orig_cpu, it will
1259 dump only the buffer of the CPU that triggered the
1262 ftrace_filter=[function-list]
1263 [FTRACE] Limit the functions traced by the function
1264 tracer at boot up. function-list is a comma separated
1265 list of functions. This list can be changed at run
1266 time by the set_ftrace_filter file in the debugfs
1269 ftrace_notrace=[function-list]
1270 [FTRACE] Do not trace the functions specified in
1271 function-list. This list can be changed at run time
1272 by the set_ftrace_notrace file in the debugfs
1275 ftrace_graph_filter=[function-list]
1276 [FTRACE] Limit the top level callers functions traced
1277 by the function graph tracer at boot up.
1278 function-list is a comma separated list of functions
1279 that can be changed at run time by the
1280 set_graph_function file in the debugfs tracing directory.
1282 ftrace_graph_notrace=[function-list]
1283 [FTRACE] Do not trace from the functions specified in
1284 function-list. This list is a comma separated list of
1285 functions that can be changed at run time by the
1286 set_graph_notrace file in the debugfs tracing directory.
1289 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1290 support via parallel port (up to 5 devices per port)
1291 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1292 See also Documentation/input/joystick-parport.txt
1296 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1300 gcov_persist= [GCOV] When non-zero (default), profiling data for
1301 kernel modules is saved and remains accessible via
1302 debugfs, even when the module is unloaded/reloaded.
1303 When zero, profiling data is discarded and associated
1304 debugfs files are removed at module unload time.
1306 gpt [EFI] Forces disk with valid GPT signature but
1307 invalid Protective MBR to be treated as GPT. If the
1308 primary GPT is corrupted, it enables the backup/alternate
1309 GPT to be used instead.
1311 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1312 the "Enable 0" bit of the configuration register.
1315 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1316 the "Enable 0" bit of the configuration register.
1319 grcan.select= [HW] Select which physical interface to use.
1322 grcan.txsize= [HW] Sets the size of the tx buffer.
1323 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1325 grcan.rxsize= [HW] Sets the size of the rx buffer.
1326 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1329 hardlockup_all_cpu_backtrace=
1330 [KNL] Should the hard-lockup detector generate
1331 backtraces on all cpus.
1334 hashdist= [KNL,NUMA] Large hashes allocated during boot
1335 are distributed across NUMA nodes. Defaults on
1336 for 64-bit NUMA, off otherwise.
1337 Format: 0 | 1 (for off | on)
1339 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1341 hd= [EIDE] (E)IDE hard drive subsystem geometry
1342 Format: <cyl>,<head>,<sect>
1345 Disable Hardware Error Source Table (HEST) support;
1346 corresponding firmware-first mode error processing
1347 logic will be disabled.
1349 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1350 size of <nn>. This works even on boxes that have no
1351 highmem otherwise. This also works to reduce highmem
1352 size on bigger boxes.
1354 highres= [KNL] Enable/disable high resolution timer mode.
1355 Valid parameters: "on", "off"
1359 See Documentation/isdn/README.HiSax.
1363 hpet= [X86-32,HPET] option to control HPET usage
1364 Format: { enable (default) | disable | force |
1366 disable: disable HPET and use PIT instead
1367 force: allow force enabled of undocumented chips (ICH4,
1369 verbose: show contents of HPET registers during setup
1371 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1372 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1374 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1375 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1376 On x86-64 and powerpc, this option can be specified
1377 multiple times interleaved with hugepages= to reserve
1378 huge pages of different sizes. Valid pages sizes on
1379 x86-64 are 2M (when the CPU supports "pse") and 1G
1380 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1382 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1383 terminal devices. Valid values: 0..8
1384 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1385 If specified, z/VM IUCV HVC accepts connections
1386 from listed z/VM user IDs only.
1388 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1389 hardware thread id mappings.
1390 Format: <cpu>:<hwthread>
1393 Do not unregister boot console at start. This is only
1394 useful for debugging when something happens in the window
1395 between unregistering the boot console and initializing
1398 i2c_bus= [HW] Override the default board specific I2C bus speed
1399 or register an additional I2C bus that is not
1400 registered from board initialization code.
1404 i8042.debug [HW] Toggle i8042 debug mode
1405 i8042.unmask_kbd_data
1406 [HW] Enable printing of interrupt data from the KBD port
1407 (disabled by default, and as a pre-condition
1408 requires that i8042.debug=1 be enabled)
1409 i8042.direct [HW] Put keyboard port into non-translated mode
1410 i8042.dumbkbd [HW] Pretend that controller can only read data from
1411 keyboard and cannot control its state
1412 (Don't attempt to blink the leds)
1413 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1414 i8042.nokbd [HW] Don't check/create keyboard port
1415 i8042.noloop [HW] Disable the AUX Loopback command while probing
1417 i8042.nomux [HW] Don't check presence of an active multiplexing
1419 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1421 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1422 i8042.reset [HW] Reset the controller during init and cleanup
1423 i8042.unlock [HW] Unlock (ignore) the keylock
1424 i8042.kbdreset [HW] Reset device connected to KBD port
1428 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1429 indicates that the driver is running on unsupported
1431 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1432 does not match list of supported models.
1434 [HW] Report power status in /proc/i8k
1435 (disabled by default)
1436 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1439 i915.invert_brightness=
1440 [DRM] Invert the sense of the variable that is used to
1441 set the brightness of the panel backlight. Normally a
1442 brightness value of 0 indicates backlight switched off,
1443 and the maximum of the brightness value sets the backlight
1444 to maximum brightness. If this parameter is set to 0
1445 (default) and the machine requires it, or this parameter
1446 is set to 1, a brightness value of 0 sets the backlight
1447 to maximum brightness, and the maximum of the brightness
1448 value switches the backlight off.
1449 -1 -- never invert brightness
1450 0 -- machine default
1451 1 -- force brightness inversion
1454 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1456 ide-core.nodma= [HW] (E)IDE subsystem
1457 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1458 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1459 .cdrom .chs .ignore_cable are additional options
1460 See Documentation/ide/ide.txt.
1462 ide-generic.probe-mask= [HW] (E)IDE subsystem
1464 Probe mask for legacy ISA IDE ports. Depending on
1465 platform up to 6 ports are supported, enabled by
1466 setting corresponding bits in the mask to 1. The
1467 default value is 0x0, which has a special meaning.
1468 On systems that have PCI, it triggers scanning the
1469 PCI bus for the first and the second port, which
1470 are then probed. On systems without PCI the value
1471 of 0x0 enables probing the two first ports as if it
1474 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1475 Claim all unknown PCI IDE storage controllers.
1478 Format: idle=poll, idle=halt, idle=nomwait
1479 Poll forces a polling idle loop that can slightly
1480 improve the performance of waking up a idle CPU, but
1481 will use a lot of power and make the system run hot.
1483 idle=halt: Halt is forced to be used for CPU idle.
1484 In such case C2/C3 won't be used again.
1485 idle=nomwait: Disable mwait for CPU C-states
1487 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1488 Format: { strict | legacy | 2008 | relaxed }
1491 Choose which programs will be accepted for execution
1492 based on the IEEE 754 NaN encoding(s) supported by
1493 the FPU and the NaN encoding requested with the value
1494 of an ELF file header flag individually set by each
1495 binary. Hardware implementations are permitted to
1496 support either or both of the legacy and the 2008 NaN
1499 Available settings are as follows:
1500 strict accept binaries that request a NaN encoding
1501 supported by the FPU
1502 legacy only accept legacy-NaN binaries, if supported
1504 2008 only accept 2008-NaN binaries, if supported
1506 relaxed accept any binaries regardless of whether
1507 supported by the FPU
1509 The FPU emulator is always able to support both NaN
1510 encodings, so if no FPU hardware is present or it has
1511 been disabled with 'nofpu', then the settings of
1512 'legacy' and '2008' strap the emulator accordingly,
1513 'relaxed' straps the emulator for both legacy-NaN and
1514 2008-NaN, whereas 'strict' enables legacy-NaN only on
1515 legacy processors and both NaN encodings on MIPS32 or
1518 The setting for ABS.fmt/NEG.fmt instruction execution
1519 mode generally follows that for the NaN encoding,
1520 except where unsupported by hardware.
1522 ignore_loglevel [KNL]
1523 Ignore loglevel setting - this will print /all/
1524 kernel messages to the console. Useful for debugging.
1525 We also add it as printk module parameter, so users
1526 could change it dynamically, usually by
1527 /sys/module/printk/parameters/ignore_loglevel.
1530 Ignore RLIMIT_DATA setting for data mappings,
1531 print warning at first misuse. Can be changed via
1532 /sys/module/kernel/parameters/ignore_rlimit_data.
1534 ihash_entries= [KNL]
1535 Set number of hash buckets for inode cache.
1537 ima_appraise= [IMA] appraise integrity measurements
1538 Format: { "off" | "enforce" | "fix" | "log" }
1541 ima_appraise_tcb [IMA]
1542 The builtin appraise policy appraises all files
1546 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1550 The list of supported hash algorithms is defined
1551 in crypto/hash_info.h.
1554 The builtin measurement policy to load during IMA
1555 setup. Specyfing "tcb" as the value, measures all
1556 programs exec'd, files mmap'd for exec, and all files
1557 opened with the read mode bit set by either the
1558 effective uid (euid=0) or uid=0.
1561 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1562 Load a policy which meets the needs of the Trusted
1563 Computing Base. This means IMA will measure all
1564 programs exec'd, files mmap'd for exec, and all files
1565 opened for read by uid=0.
1568 Select one of defined IMA measurements template formats.
1569 Formats: { "ima" | "ima-ng" | "ima-sig" }
1573 [IMA] Define a custom template format.
1574 Format: { "field1|...|fieldN" }
1576 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1577 Format: <min_file_size>
1578 Set the minimal file size for using asynchronous hash.
1579 If left unspecified, ahash usage is disabled.
1581 ahash performance varies for different data sizes on
1582 different crypto accelerators. This option can be used
1583 to achieve the best performance for a particular HW.
1585 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1587 Set hashing buffer size. Default: 4k.
1589 ahash performance varies for different chunk sizes on
1590 different crypto accelerators. This option can be used
1591 to achieve best performance for particular HW.
1595 Run specified binary instead of /sbin/init as init
1598 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1599 for working out where the kernel is dying during
1602 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1603 initcall functions. Useful for debugging built-in
1604 modules and initcalls.
1606 initrd= [BOOT] Specify the location of the initial ramdisk
1608 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1611 int_pln_enable [x86] Enable power limit notification interrupt
1613 integrity_audit=[IMA]
1614 Format: { "0" | "1" }
1615 0 -- basic integrity auditing messages. (Default)
1616 1 -- additional integrity auditing messages.
1618 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1620 Enable intel iommu driver.
1622 Disable intel iommu driver.
1623 igfx_off [Default Off]
1624 By default, gfx is mapped as normal device. If a gfx
1625 device has a dedicated DMAR unit, the DMAR unit is
1626 bypassed by not enabling DMAR with this option. In
1627 this case, gfx device will use physical address for
1630 With this option iommu will not optimize to look
1631 for io virtual address below 32-bit forcing dual
1632 address cycle on pci bus for cards supporting greater
1633 than 32-bit addressing. The default is to look
1634 for translation below 32-bit and if not available
1635 then look in the higher range.
1636 strict [Default Off]
1637 With this option on every unmap_single operation will
1638 result in a hardware IOTLB flush operation as opposed
1639 to batching them for performance.
1640 sp_off [Default Off]
1641 By default, super page will be supported if Intel IOMMU
1642 has the capability. With this option, super page will
1644 ecs_off [Default Off]
1645 By default, extended context tables will be supported if
1646 the hardware advertises that it has support both for the
1647 extended tables themselves, and also PASID support. With
1648 this option set, extended tables will not be used even
1649 on hardware which claims to support them.
1651 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1652 0 disables intel_idle and fall back on acpi_idle.
1653 1 to 6 specify maximum depth of C-state.
1657 Do not enable intel_pstate as the default
1658 scaling driver for the supported processors
1660 Enable intel_pstate on systems that prohibit it by default
1661 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1662 instead of acpi-cpufreq may disable platform features, such
1663 as thermal controls and power capping, that rely on ACPI
1664 P-States information being indicated to OSPM and therefore
1665 should be used with caution. This option does not work with
1666 processors that aren't supported by the intel_pstate driver
1667 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1669 Do not enable hardware P state control (HWP)
1672 Only load intel_pstate on systems which support
1673 hardware P state control (HWP) if available.
1675 intremap= [X86-64, Intel-IOMMU]
1676 on enable Interrupt Remapping (default)
1677 off disable Interrupt Remapping
1678 nosid disable Source ID checking
1680 BIOS x2APIC opt-out request will be ignored
1681 nopost disable Interrupt Posting
1683 iomem= Disable strict checking of access to MMIO memory
1684 strict regions from userspace.
1699 nobypass [PPC/POWERNV]
1700 Disable IOMMU bypass, using IOMMU for PCI devices.
1703 io7= [HW] IO7 for Marvel based alpha systems
1704 See comment before marvel_specify_io7 in
1705 arch/alpha/kernel/core_marvel.c.
1707 io_delay= [X86] I/O delay method
1709 Standard port 0x80 based delay
1711 Alternate port 0xed based delay (needed on some systems)
1713 Simple two microseconds delay
1718 See Documentation/filesystems/nfs/nfsroot.txt.
1720 irqaffinity= [SMP] Set the default irq affinity mask
1722 <cpu number>,...,<cpu number>
1724 <cpu number>-<cpu number>
1725 (must be a positive range in ascending order)
1727 <cpu number>,...,<cpu number>-<cpu number>
1730 When an interrupt is not handled search all handlers
1731 for it. Intended to get systems with badly broken
1735 When an interrupt is not handled search all handlers
1736 for it. Also check all handlers each timer
1737 interrupt. Intended to get systems with badly broken
1741 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1743 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1745 <cpu number>,...,<cpu number>
1747 <cpu number>-<cpu number>
1748 (must be a positive range in ascending order)
1750 <cpu number>,...,<cpu number>-<cpu number>
1752 This option can be used to specify one or more CPUs
1753 to isolate from the general SMP balancing and scheduling
1754 algorithms. You can move a process onto or off an
1755 "isolated" CPU via the CPU affinity syscalls or cpuset.
1756 <cpu number> begins at 0 and the maximum value is
1757 "number of CPUs in system - 1".
1759 This option is the preferred way to isolate CPUs. The
1760 alternative -- manually setting the CPU mask of all
1761 tasks in the system -- can cause problems and
1762 suboptimal load balancer performance.
1766 ivrs_ioapic [HW,X86_64]
1767 Provide an override to the IOAPIC-ID<->DEVICE-ID
1768 mapping provided in the IVRS ACPI table. For
1769 example, to map IOAPIC-ID decimal 10 to
1770 PCI device 00:14.0 write the parameter as:
1771 ivrs_ioapic[10]=00:14.0
1773 ivrs_hpet [HW,X86_64]
1774 Provide an override to the HPET-ID<->DEVICE-ID
1775 mapping provided in the IVRS ACPI table. For
1776 example, to map HPET-ID decimal 0 to
1777 PCI device 00:14.0 write the parameter as:
1778 ivrs_hpet[0]=00:14.0
1780 js= [HW,JOY] Analog joystick
1781 See Documentation/input/joystick.txt.
1784 Enable/disable kernel and module base offset ASLR
1785 (Address Space Layout Randomization) if built into
1786 the kernel. When CONFIG_HIBERNATION is selected,
1787 kASLR is disabled by default. When kASLR is enabled,
1788 hibernation will be disabled.
1792 kernelcore= [KNL,X86,IA-64,PPC]
1793 Format: nn[KMGTPE] | "mirror"
1795 specifies the amount of memory usable by the kernel
1796 for non-movable allocations. The requested amount is
1797 spread evenly throughout all nodes in the system. The
1798 remaining memory in each node is used for Movable
1799 pages. In the event, a node is too small to have both
1800 kernelcore and Movable pages, kernelcore pages will
1801 take priority and other nodes will have a larger number
1802 of Movable pages. The Movable zone is used for the
1803 allocation of pages that may be reclaimed or moved
1804 by the page migration subsystem. This means that
1805 HugeTLB pages may not be allocated from this zone.
1806 Note that allocations like PTEs-from-HighMem still
1807 use the HighMem zone if it exists, and the Normal
1808 zone if it does not.
1810 Instead of specifying the amount of memory (nn[KMGTPE]),
1811 you can specify "mirror" option. In case "mirror"
1812 option is specified, mirrored (reliable) memory is used
1813 for non-movable allocations and remaining memory is used
1814 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1815 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1818 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1819 Format: <Controller#>[,poll interval]
1820 The controller # is the number of the ehci usb debug
1821 port as it is probed via PCI. The poll interval is
1822 optional and is the number seconds in between
1823 each poll cycle to the debug port in case you need
1824 the functionality for interrupting the kernel with
1825 gdb or control-c on the dbgp connection. When
1826 not using this parameter you use sysrq-g to break into
1827 the kernel debugger.
1829 kgdboc= [KGDB,HW] kgdb over consoles.
1830 Requires a tty driver that supports console polling,
1831 or a supported polling keyboard driver (non-usb).
1832 Serial only format: <serial_device>[,baud]
1833 keyboard only format: kbd
1834 keyboard and serial format: kbd,<serial_device>[,baud]
1835 Optional Kernel mode setting:
1836 kms, kbd format: kms,kbd
1837 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1839 kgdbwait [KGDB] Stop kernel execution and enter the
1840 kernel debugger at the earliest opportunity.
1842 kmac= [MIPS] korina ethernet MAC address.
1843 Configure the RouterBoard 532 series on-chip
1844 Ethernet adapter MAC address.
1846 kmemleak= [KNL] Boot-time kmemleak enable/disable
1847 Valid arguments: on, off
1849 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1852 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1853 Valid arguments: 0, 1, 2
1854 kmemcheck=0 (disabled)
1855 kmemcheck=1 (enabled)
1856 kmemcheck=2 (one-shot mode)
1857 Default: 2 (one-shot mode)
1859 kstack=N [X86] Print N words from the kernel stack
1862 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1863 Default is 0 (don't ignore, but inject #GP)
1865 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1869 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1870 Default is 1 (enabled)
1872 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1874 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1876 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1877 (virtualized MMU) support on capable Intel chips.
1878 Default is 1 (enabled)
1880 kvm-intel.emulate_invalid_guest_state=
1881 [KVM,Intel] Enable emulation of invalid guest states
1882 Default is 0 (disabled)
1884 kvm-intel.flexpriority=
1885 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1886 Default is 1 (enabled)
1889 [KVM,Intel] Enable VMX nesting (nVMX).
1890 Default is 0 (disabled)
1892 kvm-intel.unrestricted_guest=
1893 [KVM,Intel] Disable unrestricted guest feature
1894 (virtualized real and unpaged mode) on capable
1895 Intel chips. Default is 1 (enabled)
1897 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1898 feature (tagged TLBs) on capable Intel chips.
1899 Default is 1 (enabled)
1905 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1908 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1909 value for LAPIC timer one-shot implementation. Default
1910 back to the programmable timer unit in the LAPIC.
1912 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1915 libata.dma= [LIBATA] DMA control
1916 libata.dma=0 Disable all PATA and SATA DMA
1917 libata.dma=1 PATA and SATA Disk DMA only
1918 libata.dma=2 ATAPI (CDROM) DMA only
1919 libata.dma=4 Compact Flash DMA only
1920 Combinations also work, so libata.dma=3 enables DMA
1921 for disks and CDROMs, but not CFs.
1923 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1924 libata.ignore_hpa=0 keep BIOS limits (default)
1925 libata.ignore_hpa=1 ignore limits, using full disk
1927 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1931 libata.force= [LIBATA] Force configurations. The format is comma
1932 separated list of "[ID:]VAL" where ID is
1933 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1934 matching port, link or device. Basically, it matches
1935 the ATA ID string printed on console by libata. If
1936 the whole ID part is omitted, the last PORT and DEVICE
1937 values are used. If ID hasn't been specified yet, the
1938 configuration applies to all ports, links and devices.
1940 If only DEVICE is omitted, the parameter applies to
1941 the port and all links and devices behind it. DEVICE
1942 number of 0 either selects the first device or the
1943 first fan-out link behind PMP device. It does not
1944 select the host link. DEVICE number of 15 selects the
1945 host link and device attached to it.
1947 The VAL specifies the configuration to force. As long
1948 as there's no ambiguity shortcut notation is allowed.
1949 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1950 The following configurations can be forced.
1952 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1953 Any ID with matching PORT is used.
1955 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1957 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1958 udma[/][16,25,33,44,66,100,133] notation is also
1961 * [no]ncq: Turn on or off NCQ.
1963 * [no]ncqtrim: Turn off queued DSM TRIM.
1965 * nohrst, nosrst, norst: suppress hard, soft
1968 * rstonce: only attempt one reset during
1969 hot-unplug link recovery
1971 * dump_id: dump IDENTIFY data.
1973 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1975 * disable: Disable this device.
1977 If there are multiple matching configurations changing
1978 the same attribute, the last one is used.
1980 memblock=debug [KNL] Enable memblock debug messages.
1982 load_ramdisk= [RAM] List of ramdisks to load from floppy
1983 See Documentation/blockdev/ramdisk.txt.
1985 lockd.nlm_grace_period=P [NFS] Assign grace period.
1988 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1991 lockd.nlm_timeout=T [NFS] Assign timeout value.
1994 lockd.nlm_udpport=M [NFS] Assign UDP port.
1997 locktorture.nreaders_stress= [KNL]
1998 Set the number of locking read-acquisition kthreads.
1999 Defaults to being automatically set based on the
2000 number of online CPUs.
2002 locktorture.nwriters_stress= [KNL]
2003 Set the number of locking write-acquisition kthreads.
2005 locktorture.onoff_holdoff= [KNL]
2006 Set time (s) after boot for CPU-hotplug testing.
2008 locktorture.onoff_interval= [KNL]
2009 Set time (s) between CPU-hotplug operations, or
2010 zero to disable CPU-hotplug testing.
2012 locktorture.shuffle_interval= [KNL]
2013 Set task-shuffle interval (jiffies). Shuffling
2014 tasks allows some CPUs to go into dyntick-idle
2015 mode during the locktorture test.
2017 locktorture.shutdown_secs= [KNL]
2018 Set time (s) after boot system shutdown. This
2019 is useful for hands-off automated testing.
2021 locktorture.stat_interval= [KNL]
2022 Time (s) between statistics printk()s.
2024 locktorture.stutter= [KNL]
2025 Time (s) to stutter testing, for example,
2026 specifying five seconds causes the test to run for
2027 five seconds, wait for five seconds, and so on.
2028 This tests the locking primitive's ability to
2029 transition abruptly to and from idle.
2031 locktorture.torture_runnable= [BOOT]
2032 Start locktorture running at boot time.
2034 locktorture.torture_type= [KNL]
2035 Specify the locking implementation to test.
2037 locktorture.verbose= [KNL]
2038 Enable additional printk() statements.
2040 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2043 loglevel= All Kernel Messages with a loglevel smaller than the
2044 console loglevel will be printed to the console. It can
2045 also be changed with klogd or other programs. The
2046 loglevels are defined as follows:
2048 0 (KERN_EMERG) system is unusable
2049 1 (KERN_ALERT) action must be taken immediately
2050 2 (KERN_CRIT) critical conditions
2051 3 (KERN_ERR) error conditions
2052 4 (KERN_WARNING) warning conditions
2053 5 (KERN_NOTICE) normal but significant condition
2054 6 (KERN_INFO) informational
2055 7 (KERN_DEBUG) debug-level messages
2057 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2058 in bytes. n must be a power of two and greater
2059 than the minimal size. The minimal size is defined
2060 by LOG_BUF_SHIFT kernel config parameter. There is
2061 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2062 that allows to increase the default size depending on
2063 the number of CPUs. See init/Kconfig for more details.
2065 logo.nologo [FB] Disables display of the built-in Linux logo.
2066 This may be used to provide more screen space for
2067 kernel log messages and is useful when debugging
2068 kernel boot problems.
2070 lp=0 [LP] Specify parallel ports to use, e.g,
2071 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2072 lp=reset first parallel port). 'lp=0' disables the
2073 lp=auto printer driver. 'lp=reset' (which can be
2074 specified in addition to the ports) causes
2075 attached printers to be reset. Using
2076 lp=port1,port2,... specifies the parallel ports
2077 to associate lp devices with, starting with
2078 lp0. A port specification may be 'none' to skip
2079 that lp device, or a parport name such as
2080 'parport0'. Specifying 'lp=auto' instead of a
2081 port specification list means that device IDs
2082 from each port should be examined, to see if
2083 an IEEE 1284-compliant printer is attached; if
2084 so, the driver will manage that printer.
2085 See also header of drivers/char/lp.c.
2088 Sets loops_per_jiffy to given constant, thus avoiding
2089 time-consuming boot-time autodetection (up to 250 ms per
2090 CPU). 0 enables autodetection (default). To determine
2091 the correct value for your kernel, boot with normal
2092 autodetection and see what value is printed. Note that
2093 on SMP systems the preset will be applied to all CPUs,
2094 which is likely to cause problems if your CPUs need
2095 significantly divergent settings. An incorrect value
2096 will cause delays in the kernel to be wrong, leading to
2097 unpredictable I/O errors and other breakage. Although
2098 unlikely, in the extreme case this might damage your
2102 Format: <io>,<irq>,<dma>
2104 machvec= [IA-64] Force the use of a particular machine-vector
2105 (machvec) in a generic kernel.
2106 Example: machvec=hpzx1_swiotlb
2108 machtype= [Loongson] Share the same kernel image file between different
2110 Example: machtype=lemote-yeeloong-2f-7inch
2112 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2113 than or equal to this physical address is ignored.
2115 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2116 should make use of. maxcpus=n : n >= 0 limits the
2117 kernel to using 'n' processors. n=0 is a special case,
2118 it is equivalent to "nosmp", which also disables
2121 max_loop= [LOOP] The number of loop block devices that get
2122 (loop.max_loop) unconditionally pre-created at init time. The default
2123 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2124 of statically allocating a predefined number, loop
2125 devices can be requested on-demand with the
2126 /dev/loop-control interface.
2128 mce [X86-32] Machine Check Exception
2130 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2132 md= [HW] RAID subsystems devices and level
2133 See Documentation/md.txt.
2136 Format: <first>,<last>
2137 Specifies range of consoles to be captured by the MDA.
2139 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2140 Amount of memory to be used when the kernel is not able
2141 to see the whole system memory or for test.
2142 [X86] Work as limiting max address. Use together
2143 with memmap= to avoid physical address space collisions.
2144 Without memmap= PCI devices could be placed at addresses
2145 belonging to unused RAM.
2147 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2151 [KNL,SH] Allow user to override the default size for
2152 per-device physically contiguous DMA buffers.
2154 memmap=exactmap [KNL,X86] Enable setting of an exact
2155 E820 memory map, as specified by the user.
2156 Such memmap=exactmap lines can be constructed based on
2157 BIOS output or other requirements. See the memmap=nn@ss
2160 memmap=nn[KMG]@ss[KMG]
2161 [KNL] Force usage of a specific region of memory.
2162 Region of memory to be used is from ss to ss+nn.
2164 memmap=nn[KMG]#ss[KMG]
2165 [KNL,ACPI] Mark specific memory as ACPI data.
2166 Region of memory to be marked is from ss to ss+nn.
2168 memmap=nn[KMG]$ss[KMG]
2169 [KNL,ACPI] Mark specific memory as reserved.
2170 Region of memory to be reserved is from ss to ss+nn.
2171 Example: Exclude memory from 0x18690000-0x1869ffff
2172 memmap=64K$0x18690000
2174 memmap=0x10000$0x18690000
2176 memmap=nn[KMG]!ss[KMG]
2177 [KNL,X86] Mark specific memory as protected.
2178 Region of memory to be used, from ss to ss+nn.
2179 The memory region may be marked as e820 type 12 (0xc)
2180 and is NVDIMM or ADR memory.
2182 memory_corruption_check=0/1 [X86]
2183 Some BIOSes seem to corrupt the first 64k of
2184 memory when doing things like suspend/resume.
2185 Setting this option will scan the memory
2186 looking for corruption. Enabling this will
2187 both detect corruption and prevent the kernel
2188 from using the memory being corrupted.
2189 However, its intended as a diagnostic tool; if
2190 repeatable BIOS-originated corruption always
2191 affects the same memory, you can use memmap=
2192 to prevent the kernel from using that memory.
2194 memory_corruption_check_size=size [X86]
2195 By default it checks for corruption in the low
2196 64k, making this memory unavailable for normal
2197 use. Use this parameter to scan for
2198 corruption in more or less memory.
2200 memory_corruption_check_period=seconds [X86]
2201 By default it checks for corruption every 60
2202 seconds. Use this parameter to check at some
2203 other rate. 0 disables periodic checking.
2205 memtest= [KNL,X86,ARM] Enable memtest
2207 default : 0 <disable>
2208 Specifies the number of memtest passes to be
2209 performed. Each pass selects another test
2210 pattern from a given set of patterns. Memtest
2211 fills the memory with this pattern, validates
2212 memory contents and reserves bad memory
2213 regions that are detected.
2215 meye.*= [HW] Set MotionEye Camera parameters
2216 See Documentation/video4linux/meye.txt.
2218 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2219 Multi-Function General Purpose Timers on AMD Geode
2222 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2223 the BIOS has incorrectly applied a workaround. TinyBIOS
2224 version 0.98 is known to be affected, 0.99 fixes the
2225 problem by letting the user disable the workaround.
2229 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2230 physical address is ignored.
2232 mini2440= [ARM,HW,KNL]
2233 Format:[0..2][b][c][t]
2235 MINI2440 configuration specification:
2236 0 - The attached screen is the 3.5" TFT
2237 1 - The attached screen is the 7" TFT
2238 2 - The VGA Shield is attached (1024x768)
2239 Leaving out the screen size parameter will not load
2240 the TFT driver, and the framebuffer will be left
2242 b - Enable backlight. The TFT backlight pin will be
2243 linked to the kernel VESA blanking code and a GPIO
2244 LED. This parameter is not necessary when using the
2246 c - Enable the s3c camera interface.
2247 t - Reserved for enabling touchscreen support. The
2248 touchscreen support is not enabled in the mainstream
2249 kernel as of 2.6.30, a preliminary port can be found
2250 in the "bleeding edge" mini2440 support kernel at
2251 http://repo.or.cz/w/linux-2.6/mini2440.git
2254 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2255 parameter allows control of the logging verbosity for
2256 the additional memory initialisation checks. A value
2257 of 0 disables mminit logging and a level of 4 will
2258 log everything. Information is printed at KERN_DEBUG
2259 so loglevel=8 may also need to be specified.
2262 [KNL] When CONFIG_MODULE_SIG is set, this means that
2263 modules without (valid) signatures will fail to load.
2264 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2265 is always true, so this option does nothing.
2268 [MOUSE] Maximum time between finger touching and
2269 leaving touchpad surface for touch to be considered
2270 a tap and be reported as a left button click (for
2271 touchpads working in absolute mode only).
2273 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2274 reporting absolute coordinates, such as tablets
2275 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2276 reporting absolute coordinates, such as tablets
2278 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2279 is similar to kernelcore except it specifies the
2280 amount of memory used for migratable allocations.
2281 If both kernelcore and movablecore is specified,
2282 then kernelcore will be at *least* the specified
2283 value but may be more. If movablecore on its own
2284 is specified, the administrator must be careful
2285 that the amount of memory usable for all allocations
2288 movable_node [KNL,X86] Boot-time switch to enable the effects
2289 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2291 MTD_Partition= [MTD]
2292 Format: <name>,<region-number>,<size>,<offset>
2294 MTD_Region= [MTD] Format:
2295 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2298 See drivers/mtd/cmdlinepart.c.
2300 multitce=off [PPC] This parameter disables the use of the pSeries
2301 firmware feature for updating multiple TCE entries
2304 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2306 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2308 boundary - index of last SLC block on Flex-OneNAND.
2309 The remaining blocks are configured as MLC blocks.
2310 lock - Configure if Flex-OneNAND boundary should be locked.
2311 Once locked, the boundary cannot be changed.
2312 1 indicates lock status, 0 indicates unlock status.
2315 ARM/S3C2412 JIVE boot control
2317 See arch/arm/mach-s3c2412/mach-jive.c
2319 mtouchusb.raw_coordinates=
2320 [HW] Make the MicroTouch USB driver use raw coordinates
2321 ('y', default) or cooked coordinates ('n')
2323 mtrr_chunk_size=nn[KMG] [X86]
2324 used for mtrr cleanup. It is largest continuous chunk
2325 that could hold holes aka. UC entries.
2327 mtrr_gran_size=nn[KMG] [X86]
2328 Used for mtrr cleanup. It is granularity of mtrr block.
2330 Large value could prevent small alignment from
2333 mtrr_spare_reg_nr=n [X86]
2335 Range: 0,7 : spare reg number
2337 Used for mtrr cleanup. It is spare mtrr entries number.
2338 Set to 2 or more if your graphical card needs more.
2340 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2342 netdev= [NET] Network devices parameters
2343 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2344 Note that mem_start is often overloaded to mean
2345 something different and driver-specific.
2346 This usage is only documented in each driver source
2350 [NETFILTER] Enable connection tracking flow accounting
2351 0 to disable accounting
2352 1 to enable accounting
2355 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2356 See Documentation/filesystems/nfs/nfsroot.txt.
2358 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2359 See Documentation/filesystems/nfs/nfsroot.txt.
2361 nfsrootdebug [NFS] enable nfsroot debugging messages.
2362 See Documentation/filesystems/nfs/nfsroot.txt.
2364 nfs.callback_tcpport=
2365 [NFS] set the TCP port on which the NFSv4 callback
2366 channel should listen.
2369 [NFS] sets the pathname to the program which is used
2370 to update the NFS client cache entries.
2372 nfs.cache_getent_timeout=
2373 [NFS] sets the timeout after which an attempt to
2374 update a cache entry is deemed to have failed.
2376 nfs.idmap_cache_timeout=
2377 [NFS] set the maximum lifetime for idmapper cache
2381 [NFS] enable 64-bit inode numbers.
2382 If zero, the NFS client will fake up a 32-bit inode
2383 number for the readdir() and stat() syscalls instead
2384 of returning the full 64-bit number.
2385 The default is to return 64-bit inode numbers.
2387 nfs.max_session_slots=
2388 [NFSv4.1] Sets the maximum number of session slots
2389 the client will attempt to negotiate with the server.
2390 This limits the number of simultaneous RPC requests
2391 that the client can send to the NFSv4.1 server.
2392 Note that there is little point in setting this
2393 value higher than the max_tcp_slot_table_limit.
2395 nfs.nfs4_disable_idmapping=
2396 [NFSv4] When set to the default of '1', this option
2397 ensures that both the RPC level authentication
2398 scheme and the NFS level operations agree to use
2399 numeric uids/gids if the mount is using the
2400 'sec=sys' security flavour. In effect it is
2401 disabling idmapping, which can make migration from
2402 legacy NFSv2/v3 systems to NFSv4 easier.
2403 Servers that do not support this mode of operation
2404 will be autodetected by the client, and it will fall
2405 back to using the idmapper.
2406 To turn off this behaviour, set the value to '0'.
2408 [NFS4] Specify an additional fixed unique ident-
2409 ification string that NFSv4 clients can insert into
2410 their nfs_client_id4 string. This is typically a
2411 UUID that is generated at system install time.
2413 nfs.send_implementation_id =
2414 [NFSv4.1] Send client implementation identification
2415 information in exchange_id requests.
2416 If zero, no implementation identification information
2418 The default is to send the implementation identification
2421 nfs.recover_lost_locks =
2422 [NFSv4] Attempt to recover locks that were lost due
2423 to a lease timeout on the server. Please note that
2424 doing this risks data corruption, since there are
2425 no guarantees that the file will remain unchanged
2426 after the locks are lost.
2427 If you want to enable the kernel legacy behaviour of
2428 attempting to recover these locks, then set this
2430 The default parameter value of '0' causes the kernel
2431 not to attempt recovery of lost locks.
2433 nfs4.layoutstats_timer =
2434 [NFSv4.2] Change the rate at which the kernel sends
2435 layoutstats to the pNFS metadata server.
2437 Setting this to value to 0 causes the kernel to use
2438 whatever value is the default set by the layout
2439 driver. A non-zero value sets the minimum interval
2440 in seconds between layoutstats transmissions.
2442 nfsd.nfs4_disable_idmapping=
2443 [NFSv4] When set to the default of '1', the NFSv4
2444 server will return only numeric uids and gids to
2445 clients using auth_sys, and will accept numeric uids
2446 and gids from such clients. This is intended to ease
2447 migration from NFSv2/v3.
2449 objlayoutdriver.osd_login_prog=
2450 [NFS] [OBJLAYOUT] sets the pathname to the program which
2451 is used to automatically discover and login into new
2452 osd-targets. Please see:
2453 Documentation/filesystems/pnfs.txt for more explanations
2455 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2456 when a NMI is triggered.
2457 Format: [state][,regs][,debounce][,die]
2459 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2460 Format: [panic,][nopanic,][num]
2462 0 - turn hardlockup detector in nmi_watchdog off
2463 1 - turn hardlockup detector in nmi_watchdog on
2464 When panic is specified, panic when an NMI watchdog
2465 timeout occurs (or 'nopanic' to override the opposite
2466 default). To disable both hard and soft lockup detectors,
2467 please see 'nowatchdog'.
2468 This is useful when you use a panic=... timeout and
2469 need the box quickly up again.
2471 netpoll.carrier_timeout=
2472 [NET] Specifies amount of time (in seconds) that
2473 netpoll should wait for a carrier. By default netpoll
2476 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2477 emulation library even if a 387 maths coprocessor
2481 [HW] Never suspend the console
2482 Disable suspending of consoles during suspend and
2483 hibernate operations. Once disabled, debugging
2484 messages can reach various consoles while the rest
2485 of the system is being put to sleep (ie, while
2486 debugging driver suspend/resume hooks). This may
2487 not work reliably with all consoles, but is known
2488 to work with serial and VGA consoles.
2489 To facilitate more flexible debugging, we also add
2490 console_suspend, a printk module parameter to control
2491 it. Users could use console_suspend (usually
2492 /sys/module/printk/parameters/console_suspend) to
2493 turn on/off it dynamically.
2495 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2496 caches in the slab allocator. Saves per-node memory,
2497 but will impact performance.
2501 noapic [SMP,APIC] Tells the kernel to not make use of any
2502 IOAPICs that may be present in the system.
2504 noautogroup Disable scheduler automatic task group creation.
2506 nobats [PPC] Do not use BATs for mapping kernel lowmem
2507 on "Classic" PPC cores.
2511 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2513 nodelayacct [KNL] Disable per-task delay accounting
2515 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2517 nodsp [SH] Disable hardware DSP at boot time.
2519 noefi Disable EFI runtime services support.
2524 On X86-32 available only on PAE configured kernels.
2525 noexec=on: enable non-executable mappings (default)
2526 noexec=off: disable non-executable mappings
2529 Disable SMAP (Supervisor Mode Access Prevention)
2530 even if it is supported by processor.
2533 Disable SMEP (Supervisor Mode Execution Prevention)
2534 even if it is supported by processor.
2537 This affects only 32-bit executables.
2538 noexec32=on: enable non-executable mappings (default)
2539 read doesn't imply executable mappings
2540 noexec32=off: disable non-executable mappings
2541 read implies executable mappings
2543 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2545 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2546 register save and restore. The kernel will only save
2547 legacy floating-point registers on task switch.
2549 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2551 noxsave [BUGS=X86] Disables x86 extended register state save
2552 and restore using xsave. The kernel will fallback to
2553 enabling legacy floating-point and sse state.
2555 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2556 register states. The kernel will fall back to use
2557 xsave to save the states. By using this parameter,
2558 performance of saving the states is degraded because
2559 xsave doesn't support modified optimization while
2560 xsaveopt supports it on xsaveopt enabled systems.
2562 noxsaves [X86] Disables xsaves and xrstors used in saving and
2563 restoring x86 extended register state in compacted
2564 form of xsave area. The kernel will fall back to use
2565 xsaveopt and xrstor to save and restore the states
2566 in standard form of xsave area. By using this
2567 parameter, xsave area per process might occupy more
2568 memory on xsaves enabled systems.
2570 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2571 wfi(ARM) instruction doesn't work correctly and not to
2572 use it. This is also useful when using JTAG debugger.
2574 no_file_caps Tells the kernel not to honor file capabilities. The
2575 only way then for a file to be executed with privilege
2576 is to be setuid root or executed by root.
2578 nohalt [IA-64] Tells the kernel not to use the power saving
2579 function PAL_HALT_LIGHT when idle. This increases
2580 power-consumption. On the positive side, it reduces
2581 interrupt wake-up latency, which may improve performance
2582 in certain environments such as networked servers or
2585 nohibernate [HIBERNATION] Disable hibernation and resume.
2587 nohz= [KNL] Boottime enable/disable dynamic ticks
2588 Valid arguments: on, off
2591 nohz_full= [KNL,BOOT]
2592 In kernels built with CONFIG_NO_HZ_FULL=y, set
2593 the specified list of CPUs whose tick will be stopped
2594 whenever possible. The boot CPU will be forced outside
2595 the range to maintain the timekeeping.
2596 The CPUs in this range must also be included in the
2599 noiotrap [SH] Disables trapped I/O port accesses.
2601 noirqdebug [X86-32] Disables the code which attempts to detect and
2602 disable unhandled interrupt sources.
2604 no_timer_check [X86,APIC] Disables the code which tests for
2605 broken timer IRQ sources.
2607 noisapnp [ISAPNP] Disables ISA PnP code.
2609 noinitrd [RAM] Tells the kernel not to load any configured
2612 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2614 [Deprecated - use intremap=off]
2618 noinvpcid [X86] Disable the INVPCID cpu feature.
2620 nojitter [IA-64] Disables jitter checking for ITC timers.
2622 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2624 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2627 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2628 steal time is computed, but won't influence scheduler
2631 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2633 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2635 noltlbs [PPC] Do not use large page/tlb entries for kernel
2636 lowmem mapping on PPC40x and PPC8xx
2638 nomca [IA-64] Disable machine check abort handling
2640 nomce [X86-32] Disable Machine Check Exception
2642 nomfgpt [X86-32] Disable Multi-Function General Purpose
2643 Timer usage (for AMD Geode machines).
2645 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2646 shutdown the other cpus. Instead use the REBOOT_VECTOR
2649 nomodule Disable module load
2651 nopat [X86] Disable PAT (page attribute table extension of
2652 pagetables) support.
2654 norandmaps Don't use address space randomization. Equivalent to
2655 echo 0 > /proc/sys/kernel/randomize_va_space
2657 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2659 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2660 with UP alternatives
2662 nordrand [X86] Disable kernel use of the RDRAND and
2663 RDSEED instructions even if they are supported
2664 by the processor. RDRAND and RDSEED are still
2665 available to user space applications.
2667 noresume [SWSUSP] Disables resume and restores original swap
2670 no-scroll [VGA] Disables scrollback.
2671 This is required for the Braillex ib80-piezo Braille
2672 reader made by F.H. Papenmeier (Germany).
2676 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2678 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2679 and disable the IO APIC. legacy for "maxcpus=0".
2681 nosoftlockup [KNL] Disable the soft-lockup detector.
2683 nosync [HW,M68K] Disables sync negotiation for all devices.
2685 notsc [BUGS=X86-32] Disable Time Stamp Counter
2687 nowatchdog [KNL] Disable both lockup detectors, i.e.
2688 soft-lockup and NMI watchdog (hard-lockup).
2692 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2694 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2695 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2696 Some features depend on CPU0. Known dependencies are:
2697 1. Resume from suspend/hibernate depends on CPU0.
2698 Suspend/hibernate will fail if CPU0 is offline and you
2699 need to online CPU0 before suspend/hibernate.
2700 2. PIC interrupts also depend on CPU0. CPU0 can't be
2701 removed if a PIC interrupt is detected.
2702 It's said poweroff/reboot may depend on CPU0 on some
2703 machines although I haven't seen such issues so far
2704 after CPU0 is offline on a few tested machines.
2705 If the dependencies are under your control, you can
2706 turn on cpu0_hotplug.
2708 nptcg= [IA-64] Override max number of concurrent global TLB
2709 purges which is reported from either PAL_VM_SUMMARY or
2712 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2713 could support. nr_cpus=n : n >= 1 limits the kernel to
2714 supporting 'n' processors. Later in runtime you can not
2715 use hotplug cpu feature to put more cpu back to online.
2716 just like you compile the kernel NR_CPUS=n
2718 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2720 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2721 Allowed values are enable and disable
2723 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2724 one of ['zone', 'node', 'default'] can be specified
2725 This can be set from sysctl after boot.
2726 See Documentation/sysctl/vm.txt for details.
2728 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2729 See Documentation/debugging-via-ohci1394.txt for more
2732 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2733 Rather than timing out after 20 ms if an EC
2734 command is not properly ACKed, override the length
2735 of the timeout. We have interrupts disabled while
2736 waiting for the ACK, so if this is set too high
2737 interrupts *may* be lost!
2739 omap_mux= [OMAP] Override bootloader pin multiplexing.
2740 Format: <mux_mode0.mode_name=value>...
2741 For example, to override I2C bus2:
2742 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2744 oprofile.timer= [HW]
2745 Use timer interrupt instead of performance counters
2747 oprofile.cpu_type= Force an oprofile cpu type
2748 This might be useful if you have an older oprofile
2749 userland or if you want common events.
2750 Format: { arch_perfmon }
2751 arch_perfmon: [X86] Force use of architectural
2752 perfmon on Intel CPUs instead of the
2753 CPU specific event set.
2754 timer: [X86] Force use of architectural NMI
2755 timer mode (see also oprofile.timer
2756 for generic hr timer mode)
2757 [s390] Force legacy basic mode sampling
2758 (report cpu_type "timer")
2760 oops=panic Always panic on oopses. Default is to just kill the
2761 process, but there is a small probability of
2762 deadlocking the machine.
2763 This will also cause panics on machine check exceptions.
2764 Useful together with panic=30 to trigger a reboot.
2767 See Documentation/sound/oss/oss-parameters.txt
2769 page_owner= [KNL] Boot-time page_owner enabling option.
2770 Storage of the information about who allocated
2771 each page is disabled in default. With this switch,
2773 on: enable the feature
2775 page_poison= [KNL] Boot-time parameter changing the state of
2776 poisoning on the buddy allocator.
2777 off: turn off poisoning
2778 on: turn on poisoning
2780 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2781 timeout > 0: seconds before rebooting
2782 timeout = 0: wait forever
2783 timeout < 0: reboot immediately
2786 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2789 crash_kexec_post_notifiers
2790 Run kdump after running panic-notifiers and dumping
2791 kmsg. This only for the users who doubt kdump always
2792 succeeds in any situation.
2793 Note that this also increases risks of kdump failure,
2794 because some panic notifiers can make the crashed
2795 kernel more unstable.
2797 parkbd.port= [HW] Parallel port number the keyboard adapter is
2798 connected to, default is 0.
2800 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2801 0 for XT, 1 for AT (default is AT).
2804 parport= [HW,PPT] Specify parallel ports. 0 disables.
2805 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2806 Use 'auto' to force the driver to use any
2807 IRQ/DMA settings detected (the default is to
2808 ignore detected IRQ/DMA settings because of
2809 possible conflicts). You can specify the base
2810 address, IRQ, and DMA settings; IRQ and DMA
2811 should be numbers, or 'auto' (for using detected
2812 settings on that particular port), or 'nofifo'
2813 (to avoid using a FIFO even if it is detected).
2814 Parallel ports are assigned in the order they
2815 are specified on the command line, starting
2818 parport_init_mode= [HW,PPT]
2819 Configure VIA parallel port to operate in
2820 a specific mode. This is necessary on Pegasos
2821 computer where firmware has no options for setting
2822 up parallel port mode and sets it to spp.
2823 Currently this function knows 686a and 8231 chips.
2824 Format: [spp|ps2|epp|ecp|ecpepp]
2827 Halt all CPUs after the first oops has been printed for
2828 the specified number of seconds. This is to be used if
2829 your oopses keep scrolling off the screen.
2834 See header of drivers/block/paride/pcd.c.
2835 See also Documentation/blockdev/paride.txt.
2837 pci=option[,option...] [PCI] various PCI subsystem options:
2838 earlydump [X86] dump PCI config space before the kernel
2840 off [X86] don't probe for the PCI bus
2841 bios [X86-32] force use of PCI BIOS, don't access
2842 the hardware directly. Use this if your machine
2843 has a non-standard PCI host bridge.
2844 nobios [X86-32] disallow use of PCI BIOS, only direct
2845 hardware access methods are allowed. Use this
2846 if you experience crashes upon bootup and you
2847 suspect they are caused by the BIOS.
2848 conf1 [X86] Force use of PCI Configuration Access
2849 Mechanism 1 (config address in IO port 0xCF8,
2850 data in IO port 0xCFC, both 32-bit).
2851 conf2 [X86] Force use of PCI Configuration Access
2852 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2853 the function, IO port 0xCFA, also 8-bit, sets
2854 bus number. The config space is then accessed
2855 through ports 0xC000-0xCFFF).
2856 See http://wiki.osdev.org/PCI for more info
2857 on the configuration access mechanisms.
2858 noaer [PCIE] If the PCIEAER kernel config parameter is
2859 enabled, this kernel boot option can be used to
2860 disable the use of PCIE advanced error reporting.
2861 nodomains [PCI] Disable support for multiple PCI
2862 root domains (aka PCI segments, in ACPI-speak).
2863 nommconf [X86] Disable use of MMCONFIG for PCI
2865 check_enable_amd_mmconf [X86] check for and enable
2866 properly configured MMIO access to PCI
2867 config space on AMD family 10h CPU
2868 nomsi [MSI] If the PCI_MSI kernel config parameter is
2869 enabled, this kernel boot option can be used to
2870 disable the use of MSI interrupts system-wide.
2871 noioapicquirk [APIC] Disable all boot interrupt quirks.
2872 Safety option to keep boot IRQs enabled. This
2873 should never be necessary.
2874 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2875 primary IO-APIC for bridges that cannot disable
2876 boot IRQs. This fixes a source of spurious IRQs
2877 when the system masks IRQs.
2878 noioapicreroute [APIC] Disable workaround that uses the
2879 boot IRQ equivalent of an IRQ that connects to
2880 a chipset where boot IRQs cannot be disabled.
2881 The opposite of ioapicreroute.
2882 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2883 routing table. These calls are known to be buggy
2884 on several machines and they hang the machine
2885 when used, but on other computers it's the only
2886 way to get the interrupt routing table. Try
2887 this option if the kernel is unable to allocate
2888 IRQs or discover secondary PCI buses on your
2890 rom [X86] Assign address space to expansion ROMs.
2891 Use with caution as certain devices share
2892 address decoders between ROMs and other
2894 norom [X86] Do not assign address space to
2895 expansion ROMs that do not already have
2896 BIOS assigned address ranges.
2897 nobar [X86] Do not assign address space to the
2898 BARs that weren't assigned by the BIOS.
2899 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2900 assigned automatically to PCI devices. You can
2901 make the kernel exclude IRQs of your ISA cards
2903 pirqaddr=0xAAAAA [X86] Specify the physical address
2904 of the PIRQ table (normally generated
2905 by the BIOS) if it is outside the
2906 F0000h-100000h range.
2907 lastbus=N [X86] Scan all buses thru bus #N. Can be
2908 useful if the kernel is unable to find your
2909 secondary buses and you want to tell it
2910 explicitly which ones they are.
2911 assign-busses [X86] Always assign all PCI bus
2912 numbers ourselves, overriding
2913 whatever the firmware may have done.
2914 usepirqmask [X86] Honor the possible IRQ mask stored
2915 in the BIOS $PIR table. This is needed on
2916 some systems with broken BIOSes, notably
2917 some HP Pavilion N5400 and Omnibook XE3
2918 notebooks. This will have no effect if ACPI
2919 IRQ routing is enabled.
2920 noacpi [X86] Do not use ACPI for IRQ routing
2921 or for PCI scanning.
2922 use_crs [X86] Use PCI host bridge window information
2923 from ACPI. On BIOSes from 2008 or later, this
2924 is enabled by default. If you need to use this,
2925 please report a bug.
2926 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2927 If you need to use this, please report a bug.
2928 routeirq Do IRQ routing for all PCI devices.
2929 This is normally done in pci_enable_device(),
2930 so this option is a temporary workaround
2931 for broken drivers that don't call it.
2932 skip_isa_align [X86] do not align io start addr, so can
2933 handle more pci cards
2934 firmware [ARM] Do not re-enumerate the bus but instead
2935 just use the configuration from the
2936 bootloader. This is currently used on
2937 IXP2000 systems where the bus has to be
2938 configured a certain way for adjunct CPUs.
2939 noearly [X86] Don't do any early type 1 scanning.
2940 This might help on some broken boards which
2941 machine check when some devices' config space
2942 is read. But various workarounds are disabled
2943 and some IOMMU drivers will not work.
2944 bfsort Sort PCI devices into breadth-first order.
2945 This sorting is done to get a device
2946 order compatible with older (<= 2.4) kernels.
2947 nobfsort Don't sort PCI devices into breadth-first order.
2948 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2949 tuning and use the BIOS-configured MPS defaults.
2950 pcie_bus_safe Set every device's MPS to the largest value
2951 supported by all devices below the root complex.
2952 pcie_bus_perf Set device MPS to the largest allowable MPS
2953 based on its parent bus. Also set MRRS (Max
2954 Read Request Size) to the largest supported
2955 value (no larger than the MPS that the device
2956 or bus can support) for best performance.
2957 pcie_bus_peer2peer Set every device's MPS to 128B, which
2958 every device is guaranteed to support. This
2959 configuration allows peer-to-peer DMA between
2960 any pair of devices, possibly at the cost of
2961 reduced performance. This also guarantees
2962 that hot-added devices will work.
2963 cbiosize=nn[KMG] The fixed amount of bus space which is
2964 reserved for the CardBus bridge's IO window.
2965 The default value is 256 bytes.
2966 cbmemsize=nn[KMG] The fixed amount of bus space which is
2967 reserved for the CardBus bridge's memory
2968 window. The default value is 64 megabytes.
2971 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2972 Specifies alignment and device to reassign
2973 aligned memory resources.
2974 If <order of align> is not specified,
2975 PAGE_SIZE is used as alignment.
2976 PCI-PCI bridge can be specified, if resource
2977 windows need to be expanded.
2978 ecrc= Enable/disable PCIe ECRC (transaction layer
2979 end-to-end CRC checking).
2980 bios: Use BIOS/firmware settings. This is the
2984 hpiosize=nn[KMG] The fixed amount of bus space which is
2985 reserved for hotplug bridge's IO window.
2986 Default size is 256 bytes.
2987 hpmemsize=nn[KMG] The fixed amount of bus space which is
2988 reserved for hotplug bridge's memory window.
2989 Default size is 2 megabytes.
2990 realloc= Enable/disable reallocating PCI bridge resources
2991 if allocations done by BIOS are too small to
2992 accommodate resources required by all child
2994 off: Turn realloc off
2996 realloc same as realloc=on
2997 noari do not use PCIe ARI.
2998 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2999 only look for one device below a PCIe downstream
3002 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3005 force Enable ASPM even on devices that claim not to support it.
3006 WARNING: Forcing ASPM on may cause system lockups.
3008 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3009 nomsi Do not use MSI for PCI Express Native Hotplug (this
3010 makes all PCIe ports use INTx for hotplug services).
3012 pcie_ports= [PCIE] PCIe ports handling:
3013 auto Ask the BIOS whether or not to use native PCIe services
3014 associated with PCIe ports (PME, hot-plug, AER). Use
3015 them only if that is allowed by the BIOS.
3016 native Use native PCIe services associated with PCIe ports
3018 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3021 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3022 nomsi Do not use MSI for native PCIe PME signaling (this makes
3023 all PCIe root ports use INTx for all services).
3025 pcmv= [HW,PCMCIA] BadgePAD 4
3029 Keep all power-domains already enabled by bootloader on,
3030 even if no driver has claimed them. This is useful
3031 for debug and development, but should not be
3032 needed on a platform with proper driver support.
3035 See Documentation/blockdev/paride.txt.
3037 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3040 See arch/parisc/kernel/pdc_chassis.c
3042 percpu_alloc= Select which percpu first chunk allocator to use.
3043 Currently supported values are "embed" and "page".
3044 Archs may support subset or none of the selections.
3045 See comments in mm/percpu.c for details on each
3046 allocator. This parameter is primarily for debugging
3047 and performance comparison.
3050 See Documentation/blockdev/paride.txt.
3053 See Documentation/blockdev/paride.txt.
3055 pirq= [SMP,APIC] Manual mp-table setup
3056 See Documentation/x86/i386/IO-APIC.txt.
3058 plip= [PPT,NET] Parallel port network link
3059 Format: { parport<nr> | timid | 0 }
3060 See also Documentation/parport.txt.
3062 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3063 Override pmtimer IOPort with a hex value.
3067 Enable PNP debug messages (depends on the
3068 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3069 via /sys/module/pnp/parameters/debug. We always show
3070 current resource usage; turning this on also shows
3071 possible settings and some assignment information.
3077 { on | off | curr | res | no-curr | no-res }
3080 [ISAPNP] Exclude IRQs for the autoconfiguration
3083 [ISAPNP] Exclude DMAs for the autoconfiguration
3085 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3086 Ranges are in pairs (I/O port base and size).
3089 [ISAPNP] Exclude memory regions for the
3091 Ranges are in pairs (memory base and size).
3093 ports= [IP_VS_FTP] IPVS ftp helper module
3095 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3097 Format: <port>,<port>....
3099 ppc_strict_facility_enable
3100 [PPC] This option catches any kernel floating point,
3101 Altivec, VSX and SPE outside of regions specifically
3102 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3103 There is some performance impact when enabling this.
3105 print-fatal-signals=
3106 [KNL] debug: print fatal signals
3108 If enabled, warn about various signal handling
3109 related application anomalies: too many signals,
3110 too many POSIX.1 timers, fatal signals causing a
3113 If you hit the warning due to signal overflow,
3114 you might want to try "ulimit -i unlimited".
3118 printk.always_kmsg_dump=
3119 Trigger kmsg_dump for cases other than kernel oops or
3121 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3124 printk.time= Show timing data prefixed to each printk message line
3125 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3127 processor.max_cstate= [HW,ACPI]
3128 Limit processor to maximum C-state
3129 max_cstate=9 overrides any DMI blacklist limit.
3131 processor.nocst [HW,ACPI]
3132 Ignore the _CST method to determine C-states,
3133 instead using the legacy FADT method
3135 profile= [KNL] Enable kernel profiling via /proc/profile
3136 Format: [schedule,]<number>
3137 Param: "schedule" - profile schedule points.
3138 Param: <number> - step/bucket size as a power of 2 for
3139 statistical time based profiling.
3140 Param: "sleep" - profile D-state sleeping (millisecs).
3141 Requires CONFIG_SCHEDSTATS
3142 Param: "kvm" - profile VM exits.
3144 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3146 See Documentation/blockdev/ramdisk.txt.
3148 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3149 probe for; one of (bare|imps|exps|lifebook|any).
3150 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3152 psmouse.resetafter= [HW,MOUSE]
3153 Try to reset the device after so many bad packets
3156 [HW,MOUSE] Set desired mouse resolution, in dpi.
3157 psmouse.smartscroll=
3158 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3159 0 = disabled, 1 = enabled (default).
3161 pstore.backend= Specify the name of the pstore backend to use
3164 See Documentation/blockdev/paride.txt.
3167 [KNL] Number of legacy pty's. Overwrites compiled-in
3170 quiet [KNL] Disable most log messages
3175 See Documentation/md.txt.
3177 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3178 See Documentation/blockdev/ramdisk.txt.
3181 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3182 the specified list of CPUs to be no-callback CPUs.
3183 Invocation of these CPUs' RCU callbacks will
3184 be offloaded to "rcuox/N" kthreads created for
3185 that purpose, where "x" is "b" for RCU-bh, "p"
3186 for RCU-preempt, and "s" for RCU-sched, and "N"
3187 is the CPU number. This reduces OS jitter on the
3188 offloaded CPUs, which can be useful for HPC and
3189 real-time workloads. It can also improve energy
3190 efficiency for asymmetric multiprocessors.
3193 Rather than requiring that offloaded CPUs
3194 (specified by rcu_nocbs= above) explicitly
3195 awaken the corresponding "rcuoN" kthreads,
3196 make these kthreads poll for callbacks.
3197 This improves the real-time response for the
3198 offloaded CPUs by relieving them of the need to
3199 wake up the corresponding kthread, but degrades
3200 energy efficiency by requiring that the kthreads
3201 periodically wake up to do the polling.
3203 rcutree.blimit= [KNL]
3204 Set maximum number of finished RCU callbacks to
3205 process in one batch.
3207 rcutree.dump_tree= [KNL]
3208 Dump the structure of the rcu_node combining tree
3209 out at early boot. This is used for diagnostic
3210 purposes, to verify correct tree setup.
3212 rcutree.gp_cleanup_delay= [KNL]
3213 Set the number of jiffies to delay each step of
3214 RCU grace-period cleanup. This only has effect
3215 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3217 rcutree.gp_init_delay= [KNL]
3218 Set the number of jiffies to delay each step of
3219 RCU grace-period initialization. This only has
3220 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3223 rcutree.gp_preinit_delay= [KNL]
3224 Set the number of jiffies to delay each step of
3225 RCU grace-period pre-initialization, that is,
3226 the propagation of recent CPU-hotplug changes up
3227 the rcu_node combining tree. This only has effect
3228 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3230 rcutree.rcu_fanout_exact= [KNL]
3231 Disable autobalancing of the rcu_node combining
3232 tree. This is used by rcutorture, and might
3233 possibly be useful for architectures having high
3234 cache-to-cache transfer latencies.
3236 rcutree.rcu_fanout_leaf= [KNL]
3237 Change the number of CPUs assigned to each
3238 leaf rcu_node structure. Useful for very
3239 large systems, which will choose the value 64,
3240 and for NUMA systems with large remote-access
3241 latencies, which will choose a value aligned
3242 with the appropriate hardware boundaries.
3244 rcutree.jiffies_till_sched_qs= [KNL]
3245 Set required age in jiffies for a
3246 given grace period before RCU starts
3247 soliciting quiescent-state help from
3248 rcu_note_context_switch().
3250 rcutree.jiffies_till_first_fqs= [KNL]
3251 Set delay from grace-period initialization to
3252 first attempt to force quiescent states.
3253 Units are jiffies, minimum value is zero,
3254 and maximum value is HZ.
3256 rcutree.jiffies_till_next_fqs= [KNL]
3257 Set delay between subsequent attempts to force
3258 quiescent states. Units are jiffies, minimum
3259 value is one, and maximum value is HZ.
3261 rcutree.kthread_prio= [KNL,BOOT]
3262 Set the SCHED_FIFO priority of the RCU per-CPU
3263 kthreads (rcuc/N). This value is also used for
3264 the priority of the RCU boost threads (rcub/N)
3265 and for the RCU grace-period kthreads (rcu_bh,
3266 rcu_preempt, and rcu_sched). If RCU_BOOST is
3267 set, valid values are 1-99 and the default is 1
3268 (the least-favored priority). Otherwise, when
3269 RCU_BOOST is not set, valid values are 0-99 and
3270 the default is zero (non-realtime operation).
3272 rcutree.rcu_nocb_leader_stride= [KNL]
3273 Set the number of NOCB kthread groups, which
3274 defaults to the square root of the number of
3275 CPUs. Larger numbers reduces the wakeup overhead
3276 on the per-CPU grace-period kthreads, but increases
3277 that same overhead on each group's leader.
3279 rcutree.qhimark= [KNL]
3280 Set threshold of queued RCU callbacks beyond which
3281 batch limiting is disabled.
3283 rcutree.qlowmark= [KNL]
3284 Set threshold of queued RCU callbacks below which
3285 batch limiting is re-enabled.
3287 rcutree.rcu_idle_gp_delay= [KNL]
3288 Set wakeup interval for idle CPUs that have
3289 RCU callbacks (RCU_FAST_NO_HZ=y).
3291 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3292 Set wakeup interval for idle CPUs that have
3293 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3294 Lazy RCU callbacks are those which RCU can
3295 prove do nothing more than free memory.
3297 rcuperf.gp_exp= [KNL]
3298 Measure performance of expedited synchronous
3299 grace-period primitives.
3301 rcuperf.holdoff= [KNL]
3302 Set test-start holdoff period. The purpose of
3303 this parameter is to delay the start of the
3304 test until boot completes in order to avoid
3307 rcuperf.nreaders= [KNL]
3308 Set number of RCU readers. The value -1 selects
3309 N, where N is the number of CPUs. A value
3310 "n" less than -1 selects N-n+1, where N is again
3311 the number of CPUs. For example, -2 selects N
3312 (the number of CPUs), -3 selects N+1, and so on.
3313 A value of "n" less than or equal to -N selects
3316 rcuperf.nwriters= [KNL]
3317 Set number of RCU writers. The values operate
3318 the same as for rcuperf.nreaders.
3319 N, where N is the number of CPUs
3321 rcuperf.perf_runnable= [BOOT]
3322 Start rcuperf running at boot time.
3324 rcuperf.shutdown= [KNL]
3325 Shut the system down after performance tests
3326 complete. This is useful for hands-off automated
3329 rcuperf.perf_type= [KNL]
3330 Specify the RCU implementation to test.
3332 rcuperf.verbose= [KNL]
3333 Enable additional printk() statements.
3335 rcutorture.cbflood_inter_holdoff= [KNL]
3336 Set holdoff time (jiffies) between successive
3337 callback-flood tests.
3339 rcutorture.cbflood_intra_holdoff= [KNL]
3340 Set holdoff time (jiffies) between successive
3341 bursts of callbacks within a given callback-flood
3344 rcutorture.cbflood_n_burst= [KNL]
3345 Set the number of bursts making up a given
3346 callback-flood test. Set this to zero to
3347 disable callback-flood testing.
3349 rcutorture.cbflood_n_per_burst= [KNL]
3350 Set the number of callbacks to be registered
3351 in a given burst of a callback-flood test.
3353 rcutorture.fqs_duration= [KNL]
3354 Set duration of force_quiescent_state bursts
3357 rcutorture.fqs_holdoff= [KNL]
3358 Set holdoff time within force_quiescent_state bursts
3361 rcutorture.fqs_stutter= [KNL]
3362 Set wait time between force_quiescent_state bursts
3365 rcutorture.gp_cond= [KNL]
3366 Use conditional/asynchronous update-side
3367 primitives, if available.
3369 rcutorture.gp_exp= [KNL]
3370 Use expedited update-side primitives, if available.
3372 rcutorture.gp_normal= [KNL]
3373 Use normal (non-expedited) asynchronous
3374 update-side primitives, if available.
3376 rcutorture.gp_sync= [KNL]
3377 Use normal (non-expedited) synchronous
3378 update-side primitives, if available. If all
3379 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3380 rcutorture.gp_normal=, and rcutorture.gp_sync=
3381 are zero, rcutorture acts as if is interpreted
3382 they are all non-zero.
3384 rcutorture.n_barrier_cbs= [KNL]
3385 Set callbacks/threads for rcu_barrier() testing.
3387 rcutorture.nfakewriters= [KNL]
3388 Set number of concurrent RCU writers. These just
3389 stress RCU, they don't participate in the actual
3390 test, hence the "fake".
3392 rcutorture.nreaders= [KNL]
3393 Set number of RCU readers. The value -1 selects
3394 N-1, where N is the number of CPUs. A value
3395 "n" less than -1 selects N-n-2, where N is again
3396 the number of CPUs. For example, -2 selects N
3397 (the number of CPUs), -3 selects N+1, and so on.
3399 rcutorture.object_debug= [KNL]
3400 Enable debug-object double-call_rcu() testing.
3402 rcutorture.onoff_holdoff= [KNL]
3403 Set time (s) after boot for CPU-hotplug testing.
3405 rcutorture.onoff_interval= [KNL]
3406 Set time (s) between CPU-hotplug operations, or
3407 zero to disable CPU-hotplug testing.
3409 rcutorture.shuffle_interval= [KNL]
3410 Set task-shuffle interval (s). Shuffling tasks
3411 allows some CPUs to go into dyntick-idle mode
3412 during the rcutorture test.
3414 rcutorture.shutdown_secs= [KNL]
3415 Set time (s) after boot system shutdown. This
3416 is useful for hands-off automated testing.
3418 rcutorture.stall_cpu= [KNL]
3419 Duration of CPU stall (s) to test RCU CPU stall
3420 warnings, zero to disable.
3422 rcutorture.stall_cpu_holdoff= [KNL]
3423 Time to wait (s) after boot before inducing stall.
3425 rcutorture.stat_interval= [KNL]
3426 Time (s) between statistics printk()s.
3428 rcutorture.stutter= [KNL]
3429 Time (s) to stutter testing, for example, specifying
3430 five seconds causes the test to run for five seconds,
3431 wait for five seconds, and so on. This tests RCU's
3432 ability to transition abruptly to and from idle.
3434 rcutorture.test_boost= [KNL]
3435 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3436 "Maybe" means test if the RCU implementation
3437 under test support RCU priority boosting.
3439 rcutorture.test_boost_duration= [KNL]
3440 Duration (s) of each individual boost test.
3442 rcutorture.test_boost_interval= [KNL]
3443 Interval (s) between each boost test.
3445 rcutorture.test_no_idle_hz= [KNL]
3446 Test RCU's dyntick-idle handling. See also the
3447 rcutorture.shuffle_interval parameter.
3449 rcutorture.torture_runnable= [BOOT]
3450 Start rcutorture running at boot time.
3452 rcutorture.torture_type= [KNL]
3453 Specify the RCU implementation to test.
3455 rcutorture.verbose= [KNL]
3456 Enable additional printk() statements.
3458 rcupdate.rcu_cpu_stall_suppress= [KNL]
3459 Suppress RCU CPU stall warning messages.
3461 rcupdate.rcu_cpu_stall_timeout= [KNL]
3462 Set timeout for RCU CPU stall warning messages.
3464 rcupdate.rcu_expedited= [KNL]
3465 Use expedited grace-period primitives, for
3466 example, synchronize_rcu_expedited() instead
3467 of synchronize_rcu(). This reduces latency,
3468 but can increase CPU utilization, degrade
3469 real-time latency, and degrade energy efficiency.
3470 No effect on CONFIG_TINY_RCU kernels.
3472 rcupdate.rcu_normal= [KNL]
3473 Use only normal grace-period primitives,
3474 for example, synchronize_rcu() instead of
3475 synchronize_rcu_expedited(). This improves
3476 real-time latency, CPU utilization, and
3477 energy efficiency, but can expose users to
3478 increased grace-period latency. This parameter
3479 overrides rcupdate.rcu_expedited. No effect on
3480 CONFIG_TINY_RCU kernels.
3482 rcupdate.rcu_normal_after_boot= [KNL]
3483 Once boot has completed (that is, after
3484 rcu_end_inkernel_boot() has been invoked), use
3485 only normal grace-period primitives. No effect
3486 on CONFIG_TINY_RCU kernels.
3488 rcupdate.rcu_task_stall_timeout= [KNL]
3489 Set timeout in jiffies for RCU task stall warning
3490 messages. Disable with a value less than or equal
3493 rcupdate.rcu_self_test= [KNL]
3494 Run the RCU early boot self tests
3496 rcupdate.rcu_self_test_bh= [KNL]
3497 Run the RCU bh early boot self tests
3499 rcupdate.rcu_self_test_sched= [KNL]
3500 Run the RCU sched early boot self tests
3504 Run specified binary instead of /init from the ramdisk,
3505 used for early userspace startup. See initrd.
3508 Format (x86 or x86_64):
3509 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3511 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3513 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3514 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3515 reboot_force is either force or not specified,
3516 reboot_cpu is s[mp]#### with #### being the processor
3517 to be used for rebooting.
3520 [KNL, SMP] Set scheduler's default relax_domain_level.
3521 See Documentation/cgroups/cpusets.txt.
3523 relative_sleep_states=
3524 [SUSPEND] Use sleep state labeling where the deepest
3525 state available other than hibernation is always "mem".
3526 Format: { "0" | "1" }
3527 0 -- Traditional sleep state labels.
3528 1 -- Relative sleep state labels.
3530 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3532 reservetop= [X86-32]
3534 Reserves a hole at the top of the kernel virtual
3539 Set the amount of memory to reserve for BIOS at
3540 the bottom of the address space.
3542 reset_devices [KNL] Force drivers to reset the underlying device
3543 during initialization.
3546 Specify the partition device for software suspend
3548 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3550 resume_offset= [SWSUSP]
3551 Specify the offset from the beginning of the partition
3552 given by "resume=" at which the swap header is located,
3553 in <PAGE_SIZE> units (needed only for swap files).
3554 See Documentation/power/swsusp-and-swap-files.txt
3556 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3557 read the resume files
3559 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3560 Useful for devices that are detected asynchronously
3561 (e.g. USB and MMC devices).
3563 hibernate= [HIBERNATION]
3564 noresume Don't check if there's a hibernation image
3565 present during boot.
3566 nocompress Don't compress/decompress hibernation images.
3567 no Disable hibernation and resume.
3569 retain_initrd [RAM] Keep initrd memory after extraction
3571 rfkill.default_state=
3572 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3573 etc. communication is blocked by default.
3576 rfkill.master_switch_mode=
3577 0 The "airplane mode" button does nothing.
3578 1 The "airplane mode" button toggles between everything
3579 blocked and the previous configuration.
3580 2 The "airplane mode" button toggles between everything
3581 blocked and everything unblocked.
3583 rhash_entries= [KNL,NET]
3584 Set number of hash buckets for route cache
3586 ro [KNL] Mount root device read-only on boot
3589 on Mark read-only kernel memory as read-only (default).
3590 off Leave read-only kernel memory writable for debugging.
3593 Enable the uart passthrough on the designated usb port
3594 on Rockchip SoCs. When active, the signals of the
3595 debug-uart get routed to the D+ and D- pins of the usb
3596 port and the regular usb controller gets disabled.
3598 root= [KNL] Root filesystem
3599 See name_to_dev_t comment in init/do_mounts.c.
3601 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3602 mount the root filesystem
3604 rootflags= [KNL] Set root filesystem mount option string
3606 rootfstype= [KNL] Set root filesystem type
3608 rootwait [KNL] Wait (indefinitely) for root device to show up.
3609 Useful for devices that are detected asynchronously
3610 (e.g. USB and MMC devices).
3612 rproc_mem=nn[KMG][@address]
3613 [KNL,ARM,CMA] Remoteproc physical memory block.
3614 Memory area to be used by remote processor image,
3617 rw [KNL] Mount root device read-write on boot
3619 S [KNL] Run init in single mode
3621 s390_iommu= [HW,S390]
3622 Set s390 IOTLB flushing mode
3624 With strict flushing every unmap operation will result in
3625 an IOTLB flush. Default is lazy flushing before reuse,
3629 See drivers/net/irda/sa1100_ir.c.
3631 sbni= [NET] Granch SBNI12 leased line adapter
3633 sched_debug [KNL] Enables verbose scheduler debug messages.
3635 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3636 Allowed values are enable and disable. This feature
3637 incurs a small amount of overhead in the scheduler
3638 but is useful for debugging and performance tuning.
3640 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3641 xtime_lock contention on larger systems, and/or RCU lock
3642 contention on all systems with CONFIG_MAXSMP set.
3643 Format: { "0" | "1" }
3644 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3646 Note: increases power consumption, thus should only be
3647 enabled if running jitter sensitive (HPC/RT) workloads.
3649 security= [SECURITY] Choose a security module to enable at boot.
3650 If this boot parameter is not specified, only the first
3651 security module asking for security registration will be
3652 loaded. An invalid security module name will be treated
3653 as if no module has been chosen.
3655 selinux= [SELINUX] Disable or enable SELinux at boot time.
3656 Format: { "0" | "1" }
3657 See security/selinux/Kconfig help text.
3660 Default value is set via kernel config option.
3661 If enabled at boot time, /selinux/disable can be used
3662 later to disable prior to initial policy load.
3664 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3665 Format: { "0" | "1" }
3666 See security/apparmor/Kconfig help text
3669 Default value is set via kernel config option.
3671 serialnumber [BUGS=X86-32]
3674 Maximal number of shapers.
3676 show_msr= [x86] show boot-time MSR settings
3677 Format: { <integer> }
3678 Show boot-time (BIOS-initialized) MSR settings.
3679 The parameter means the number of CPUs to show,
3680 for example 1 means boot CPU only.
3688 Disable merging of slabs with similar size. May be
3689 necessary if there is some reason to distinguish
3690 allocs to different slabs. Debug options disable
3691 merging on their own.
3692 For more information see Documentation/vm/slub.txt.
3694 slab_max_order= [MM, SLAB]
3695 Determines the maximum allowed order for slabs.
3696 A high setting may cause OOMs due to memory
3697 fragmentation. Defaults to 1 for systems with
3698 more than 32MB of RAM, 0 otherwise.
3700 slub_debug[=options[,slabs]] [MM, SLUB]
3701 Enabling slub_debug allows one to determine the
3702 culprit if slab objects become corrupted. Enabling
3703 slub_debug can create guard zones around objects and
3704 may poison objects when not in use. Also tracks the
3705 last alloc / free. For more information see
3706 Documentation/vm/slub.txt.
3708 slub_max_order= [MM, SLUB]
3709 Determines the maximum allowed order for slabs.
3710 A high setting may cause OOMs due to memory
3711 fragmentation. For more information see
3712 Documentation/vm/slub.txt.
3714 slub_min_objects= [MM, SLUB]
3715 The minimum number of objects per slab. SLUB will
3716 increase the slab order up to slub_max_order to
3717 generate a sufficiently large slab able to contain
3718 the number of objects indicated. The higher the number
3719 of objects the smaller the overhead of tracking slabs
3720 and the less frequently locks need to be acquired.
3721 For more information see Documentation/vm/slub.txt.
3723 slub_min_order= [MM, SLUB]
3724 Determines the minimum page order for slabs. Must be
3725 lower than slub_max_order.
3726 For more information see Documentation/vm/slub.txt.
3728 slub_nomerge [MM, SLUB]
3729 Same with slab_nomerge. This is supported for legacy.
3730 See slab_nomerge for more information.
3733 Format: <io1>[,<io2>[,...,<io8>]]
3735 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3736 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3737 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3738 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3739 smsc-ircc2.ircc_irq= [HW] IRQ line
3740 smsc-ircc2.ircc_dma= [HW] DMA channel
3741 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3742 0: Toshiba Satellite 1800 (GP data pin select)
3743 1: Fast pin select (default)
3747 [KNL] Should the soft-lockup detector generate panics.
3750 softlockup_all_cpu_backtrace=
3751 [KNL] Should the soft-lockup detector generate
3752 backtraces on all cpus.
3755 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3756 See Documentation/laptops/sonypi.txt
3758 spia_io_base= [HW,MTD]
3764 Enabled the stack tracer on boot up.
3766 stacktrace_filter=[function-list]
3767 [FTRACE] Limit the functions that the stack tracer
3768 will trace at boot up. function-list is a comma separated
3769 list of functions. This list can be changed at run
3770 time by the stack_trace_filter file in the debugfs
3771 tracing directory. Note, this enables stack tracing
3772 and the stacktrace above is not needed.
3776 Set the STI (builtin display/keyboard on the HP-PARISC
3777 machines) console (graphic card) which should be used
3778 as the initial boot-console.
3779 See also comment in drivers/video/console/sticore.c.
3782 See comment in drivers/video/console/sticore.c.
3785 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3787 sunrpc.min_resvport=
3788 sunrpc.max_resvport=
3790 SunRPC servers often require that client requests
3791 originate from a privileged port (i.e. a port in the
3792 range 0 < portnr < 1024).
3793 An administrator who wishes to reserve some of these
3794 ports for other uses may adjust the range that the
3795 kernel's sunrpc client considers to be privileged
3796 using these two parameters to set the minimum and
3797 maximum port values.
3801 Control how the NFS server code allocates CPUs to
3802 service thread pools. Depending on how many NICs
3803 you have and where their interrupts are bound, this
3804 option will affect which CPUs will do NFS serving.
3805 Note: this parameter cannot be changed while the
3806 NFS server is running.
3808 auto the server chooses an appropriate mode
3809 automatically using heuristics
3810 global a single global pool contains all CPUs
3811 percpu one pool for each CPU
3812 pernode one pool for each NUMA node (equivalent
3813 to global on non-NUMA machines)
3815 sunrpc.tcp_slot_table_entries=
3816 sunrpc.udp_slot_table_entries=
3818 Sets the upper limit on the number of simultaneous
3819 RPC calls that can be sent from the client to a
3820 server. Increasing these values may allow you to
3821 improve throughput, but will also increase the
3822 amount of memory reserved for use by the client.
3824 suspend.pm_test_delay=
3826 Sets the number of seconds to remain in a suspend test
3827 mode before resuming the system (see
3828 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3829 is set. Default value is 5.
3832 [KNL] Enable accounting of swap in memory resource
3833 controller if no parameter or 1 is given or disable
3834 it if 0 is given (See Documentation/cgroups/memory.txt)
3836 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3837 Format: { <int> | force }
3838 <int> -- Number of I/O TLB slabs
3839 force -- force using of bounce buffers even if they
3840 wouldn't be automatically used by the kernel
3844 sysfs.deprecated=0|1 [KNL]
3845 Enable/disable old style sysfs layout for old udev
3846 on older distributions. When this option is enabled
3847 very new udev will not work anymore. When this option
3848 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3849 in older udev will not work anymore.
3850 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3851 the kernel configuration.
3853 sysrq_always_enabled
3855 Ignore sysrq setting - this boot parameter will
3856 neutralize any effect of /proc/sys/kernel/sysrq.
3857 Useful for debugging.
3859 tcpmhash_entries= [KNL,NET]
3860 Set the number of tcp_metrics_hash slots.
3861 Default value is 8192 or 16384 depending on total
3862 ram pages. This is used to specify the TCP metrics
3863 cache size. See Documentation/networking/ip-sysctl.txt
3864 "tcp_no_metrics_save" section for more details.
3868 test_suspend= [SUSPEND][,N]
3869 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3870 standby suspend) or "freeze" (for suspend type freeze)
3871 as the system sleep state during system startup with
3872 the optional capability to repeat N number of times.
3873 The system is woken from this state using a
3874 wakeup-capable RTC alarm.
3876 thash_entries= [KNL,NET]
3877 Set number of hash buckets for TCP connection
3879 thermal.act= [HW,ACPI]
3880 -1: disable all active trip points in all thermal zones
3881 <degrees C>: override all lowest active trip points
3883 thermal.crt= [HW,ACPI]
3884 -1: disable all critical trip points in all thermal zones
3885 <degrees C>: override all critical trip points
3887 thermal.nocrt= [HW,ACPI]
3888 Set to disable actions on ACPI thermal zone
3889 critical and hot trip points.
3891 thermal.off= [HW,ACPI]
3892 1: disable ACPI thermal control
3894 thermal.psv= [HW,ACPI]
3895 -1: disable all passive trip points
3896 <degrees C>: override all passive trip points to this
3899 thermal.tzp= [HW,ACPI]
3900 Specify global default ACPI thermal zone polling rate
3901 <deci-seconds>: poll all this frequency
3902 0: no polling (default)
3905 Force threading of all interrupt handlers except those
3906 marked explicitly IRQF_NO_THREAD.
3909 Enable the Transcendent memory driver if built-in.
3911 tmem.cleancache=0|1 [KNL, XEN]
3912 Default is on (1). Disable the usage of the cleancache
3913 API to send anonymous pages to the hypervisor.
3915 tmem.frontswap=0|1 [KNL, XEN]
3916 Default is on (1). Disable the usage of the frontswap
3917 API to send swap pages to the hypervisor. If disabled
3918 the selfballooning and selfshrinking are force disabled.
3920 tmem.selfballooning=0|1 [KNL, XEN]
3921 Default is on (1). Disable the driving of swap pages
3924 tmem.selfshrinking=0|1 [KNL, XEN]
3925 Default is on (1). Partial swapoff that immediately
3926 transfers pages from Xen hypervisor back to the
3927 kernel based on different criteria.
3931 Specify if the kernel should make use of the cpu
3932 topology information if the hardware supports this.
3933 The scheduler will make use of this information and
3934 e.g. base its process migration decisions on it.
3937 topology_updates= [KNL, PPC, NUMA]
3939 Specify if the kernel should ignore (off)
3940 topology updates sent by the hypervisor to this
3945 tpm_suspend_pcr=[HW,TPM]
3946 Format: integer pcr id
3947 Specify that at suspend time, the tpm driver
3948 should extend the specified pcr with zeros,
3949 as a workaround for some chips which fail to
3950 flush the last written pcr on TPM_SaveState.
3951 This will guarantee that all the other pcrs
3954 trace_buf_size=nn[KMG]
3955 [FTRACE] will set tracing buffer size on each cpu.
3957 trace_event=[event-list]
3958 [FTRACE] Set and start specified trace events in order
3959 to facilitate early boot debugging.
3960 See also Documentation/trace/events.txt
3962 trace_options=[option-list]
3963 [FTRACE] Enable or disable tracer options at boot.
3964 The option-list is a comma delimited list of options
3965 that can be enabled or disabled just as if you were
3966 to echo the option name into
3968 /sys/kernel/debug/tracing/trace_options
3970 For example, to enable stacktrace option (to dump the
3971 stack trace of each event), add to the command line:
3973 trace_options=stacktrace
3975 See also Documentation/trace/ftrace.txt "trace options"
3979 Have the tracepoints sent to printk as well as the
3980 tracing ring buffer. This is useful for early boot up
3981 where the system hangs or reboots and does not give the
3982 option for reading the tracing buffer or performing a
3983 ftrace_dump_on_oops.
3985 To turn off having tracepoints sent to printk,
3986 echo 0 > /proc/sys/kernel/tracepoint_printk
3987 Note, echoing 1 into this file without the
3988 tracepoint_printk kernel cmdline option has no effect.
3992 Having tracepoints sent to printk() and activating high
3993 frequency tracepoints such as irq or sched, can cause
3994 the system to live lock.
3997 [FTRACE] enable this option to disable tracing when a
3998 warning is hit. This turns off "tracing_on". Tracing can
3999 be enabled again by echoing '1' into the "tracing_on"
4000 file located in /sys/kernel/debug/tracing/
4002 This option is useful, as it disables the trace before
4003 the WARNING dump is called, which prevents the trace to
4004 be filled with content caused by the warning output.
4006 This option can also be set at run time via the sysctl
4007 option: kernel/traceoff_on_warning
4009 transparent_hugepage=
4011 Format: [always|madvise|never]
4012 Can be used to control the default behavior of the system
4013 with respect to transparent hugepages.
4014 See Documentation/vm/transhuge.txt for more details.
4016 tsc= Disable clocksource stability checks for TSC.
4018 [x86] reliable: mark tsc clocksource as reliable, this
4019 disables clocksource verification at runtime, as well
4020 as the stability checks done at bootup. Used to enable
4021 high-resolution timer mode on older hardware, and in
4022 virtualized environment.
4023 [x86] noirqtime: Do not use TSC to do irq accounting.
4024 Used to run time disable IRQ_TIME_ACCOUNTING on any
4025 platforms where RDTSC is slow and this accounting
4028 turbografx.map[2|3]= [HW,JOY]
4029 TurboGraFX parallel port interface
4031 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4032 See also Documentation/input/joystick-parport.txt
4034 udbg-immortal [PPC] When debugging early kernel crashes that
4035 happen after console_init() and before a proper
4036 console driver takes over, this boot options might
4037 help "seeing" what's going on.
4039 uhash_entries= [KNL,NET]
4040 Set number of hash buckets for UDP/UDP-Lite connections
4043 [USB] Ignore overcurrent events (default N).
4044 Some badly-designed motherboards generate lots of
4045 bogus events, for ports that aren't wired to
4046 anything. Set this parameter to avoid log spamming.
4047 Note that genuine overcurrent events won't be
4051 [X86] Cause panic on unknown NMI.
4053 usbcore.authorized_default=
4054 [USB] Default USB device authorization:
4055 (default -1 = authorized except for wireless USB,
4056 0 = not authorized, 1 = authorized)
4058 usbcore.autosuspend=
4059 [USB] The autosuspend time delay (in seconds) used
4060 for newly-detected USB devices (default 2). This
4061 is the time required before an idle device will be
4062 autosuspended. Devices for which the delay is set
4063 to a negative value won't be autosuspended at all.
4065 usbcore.usbfs_snoop=
4066 [USB] Set to log all usbfs traffic (default 0 = off).
4068 usbcore.usbfs_snoop_max=
4069 [USB] Maximum number of bytes to snoop in each URB
4072 usbcore.blinkenlights=
4073 [USB] Set to cycle leds on hubs (default 0 = off).
4075 usbcore.old_scheme_first=
4076 [USB] Start with the old device initialization
4077 scheme (default 0 = off).
4079 usbcore.usbfs_memory_mb=
4080 [USB] Memory limit (in MB) for buffers allocated by
4081 usbfs (default = 16, 0 = max = 2047).
4083 usbcore.use_both_schemes=
4084 [USB] Try the other device initialization scheme
4085 if the first one fails (default 1 = enabled).
4087 usbcore.initial_descriptor_timeout=
4088 [USB] Specifies timeout for the initial 64-byte
4089 USB_REQ_GET_DESCRIPTOR request in milliseconds
4090 (default 5000 = 5.0 seconds).
4092 usbcore.nousb [USB] Disable the USB subsystem
4095 [USBHID] The interval which mice are to be polled at.
4097 usb-storage.delay_use=
4098 [UMS] The delay in seconds before a new device is
4099 scanned for Logical Units (default 1).
4102 [UMS] A list of quirks entries to supplement or
4103 override the built-in unusual_devs list. List
4104 entries are separated by commas. Each entry has
4105 the form VID:PID:Flags where VID and PID are Vendor
4106 and Product ID values (4-digit hex numbers) and
4107 Flags is a set of characters, each corresponding
4108 to a common usb-storage quirk flag as follows:
4109 a = SANE_SENSE (collect more than 18 bytes
4111 b = BAD_SENSE (don't collect more than 18
4112 bytes of sense data);
4113 c = FIX_CAPACITY (decrease the reported
4114 device capacity by one sector);
4115 d = NO_READ_DISC_INFO (don't use
4116 READ_DISC_INFO command);
4117 e = NO_READ_CAPACITY_16 (don't use
4118 READ_CAPACITY_16 command);
4119 f = NO_REPORT_OPCODES (don't use report opcodes
4121 g = MAX_SECTORS_240 (don't transfer more than
4122 240 sectors at a time, uas only);
4123 h = CAPACITY_HEURISTICS (decrease the
4124 reported device capacity by one
4125 sector if the number is odd);
4126 i = IGNORE_DEVICE (don't bind to this
4128 j = NO_REPORT_LUNS (don't use report luns
4130 l = NOT_LOCKABLE (don't try to lock and
4131 unlock ejectable media);
4132 m = MAX_SECTORS_64 (don't transfer more
4133 than 64 sectors = 32 KB at a time);
4134 n = INITIAL_READ10 (force a retry of the
4135 initial READ(10) command);
4136 o = CAPACITY_OK (accept the capacity
4137 reported by the device);
4138 p = WRITE_CACHE (the device cache is ON
4140 r = IGNORE_RESIDUE (the device reports
4141 bogus residue values);
4142 s = SINGLE_LUN (the device has only one
4144 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4145 commands, uas only);
4146 u = IGNORE_UAS (don't bind to the uas driver);
4147 w = NO_WP_DETECT (don't test whether the
4148 medium is write-protected).
4149 Example: quirks=0419:aaf5:rl,0421:0433:rc
4151 user_debug= [KNL,ARM]
4153 See arch/arm/Kconfig.debug help text.
4154 1 - undefined instruction events
4156 4 - invalid data aborts
4159 Example: user_debug=31
4162 [X86] Flags controlling user PTE allocations.
4164 nohigh = do not allocate PTE pages in
4165 HIGHMEM regardless of setting
4169 On X86_32, this is an alias for vdso32=. Otherwise:
4171 vdso=1: enable VDSO (the default)
4172 vdso=0: disable VDSO mapping
4174 vdso32= [X86] Control the 32-bit vDSO
4175 vdso32=1: enable 32-bit VDSO
4176 vdso32=0 or vdso32=2: disable 32-bit VDSO
4178 See the help text for CONFIG_COMPAT_VDSO for more
4179 details. If CONFIG_COMPAT_VDSO is set, the default is
4180 vdso32=0; otherwise, the default is vdso32=1.
4182 For compatibility with older kernels, vdso32=2 is an
4185 Try vdso32=0 if you encounter an error that says:
4186 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4189 vector=percpu: enable percpu vector domain
4191 video= [FB] Frame buffer configuration
4192 See Documentation/fb/modedb.txt.
4194 video.brightness_switch_enabled= [0,1]
4195 If set to 1, on receiving an ACPI notify event
4196 generated by hotkey, video driver will adjust brightness
4197 level and then send out the event to user space through
4198 the allocated input device; If set to 0, video driver
4199 will only send out the event without touching backlight
4204 [VMMIO] Memory mapped virtio (platform) device.
4206 <size>@<baseaddr>:<irq>[:<id>]
4208 <size> := size (can use standard suffixes
4210 <baseaddr> := physical base address
4211 <irq> := interrupt number (as passed to
4213 <id> := (optional) platform device id
4215 virtio_mmio.device=1K@0x100b0000:48:7
4217 Can be used multiple times for multiple devices.
4219 vga= [BOOT,X86-32] Select a particular video mode
4220 See Documentation/x86/boot.txt and
4221 Documentation/svga.txt.
4222 Use vga=ask for menu.
4223 This is actually a boot loader parameter; the value is
4224 passed to the kernel using a special protocol.
4226 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4227 size of <nn>. This can be used to increase the
4228 minimum size (128MB on x86). It can also be used to
4229 decrease the size and leave more room for directly
4232 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4235 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4238 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4242 Controls the behavior of vsyscalls (i.e. calls to
4243 fixed addresses of 0xffffffffff600x00 from legacy
4244 code). Most statically-linked binaries and older
4245 versions of glibc use these calls. Because these
4246 functions are at fixed addresses, they make nice
4247 targets for exploits that can control RIP.
4249 emulate [default] Vsyscalls turn into traps and are
4250 emulated reasonably safely.
4252 native Vsyscalls are native syscall instructions.
4253 This is a little bit faster than trapping
4254 and makes a few dynamic recompilers work
4255 better than they would in emulation mode.
4256 It also makes exploits much easier to write.
4258 none Vsyscalls don't work at all. This makes
4259 them quite hard to use for exploits but
4260 might break your system.
4262 vt.color= [VT] Default text color.
4263 Format: 0xYX, X = foreground, Y = background.
4264 Default: 0x07 = light gray on black.
4266 vt.cur_default= [VT] Default cursor shape.
4267 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4268 the parameters of the <Esc>[?A;B;Cc escape sequence;
4269 see VGA-softcursor.txt. Default: 2 = underline.
4271 vt.default_blu= [VT]
4272 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4273 Change the default blue palette of the console.
4274 This is a 16-member array composed of values
4277 vt.default_grn= [VT]
4278 Format: <green0>,<green1>,<green2>,...,<green15>
4279 Change the default green palette of the console.
4280 This is a 16-member array composed of values
4283 vt.default_red= [VT]
4284 Format: <red0>,<red1>,<red2>,...,<red15>
4285 Change the default red palette of the console.
4286 This is a 16-member array composed of values
4292 Set system-wide default UTF-8 mode for all tty's.
4293 Default is 1, i.e. UTF-8 mode is enabled for all
4294 newly opened terminals.
4296 vt.global_cursor_default=
4299 Set system-wide default for whether a cursor
4300 is shown on new VTs. Default is -1,
4301 i.e. cursors will be created by default unless
4302 overridden by individual drivers. 0 will hide
4303 cursors, 1 will display them.
4305 vt.italic= [VT] Default color for italic text; 0-15.
4308 vt.underline= [VT] Default color for underlined text; 0-15.
4311 watchdog timers [HW,WDT] For information on watchdog timers,
4312 see Documentation/watchdog/watchdog-parameters.txt
4313 or other driver-specific files in the
4314 Documentation/watchdog/ directory.
4316 workqueue.watchdog_thresh=
4317 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4318 warn stall conditions and dump internal state to
4319 help debugging. 0 disables workqueue stall
4320 detection; otherwise, it's the stall threshold
4321 duration in seconds. The default value is 30 and
4322 it can be updated at runtime by writing to the
4323 corresponding sysfs file.
4325 workqueue.disable_numa
4326 By default, all work items queued to unbound
4327 workqueues are affine to the NUMA nodes they're
4328 issued on, which results in better behavior in
4329 general. If NUMA affinity needs to be disabled for
4330 whatever reason, this option can be used. Note
4331 that this also can be controlled per-workqueue for
4332 workqueues visible under /sys/bus/workqueue/.
4334 workqueue.power_efficient
4335 Per-cpu workqueues are generally preferred because
4336 they show better performance thanks to cache
4337 locality; unfortunately, per-cpu workqueues tend to
4338 be more power hungry than unbound workqueues.
4340 Enabling this makes the per-cpu workqueues which
4341 were observed to contribute significantly to power
4342 consumption unbound, leading to measurably lower
4343 power usage at the cost of small performance
4346 The default value of this parameter is determined by
4347 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4349 workqueue.debug_force_rr_cpu
4350 Workqueue used to implicitly guarantee that work
4351 items queued without explicit CPU specified are put
4352 on the local CPU. This guarantee is no longer true
4353 and while local CPU is still preferred work items
4354 may be put on foreign CPUs. This debug option
4355 forces round-robin CPU selection to flush out
4356 usages which depend on the now broken guarantee.
4357 When enabled, memory and cache locality will be
4360 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4361 default x2apic cluster mode on platforms
4364 x86_intel_mid_timer= [X86-32,APBT]
4365 Choose timer option for x86 Intel MID platform.
4366 Two valid options are apbt timer only and lapic timer
4367 plus one apbt timer for broadcast timer.
4368 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4370 xen_512gb_limit [KNL,X86-64,XEN]
4371 Restricts the kernel running paravirtualized under Xen
4372 to use only up to 512 GB of RAM. The reason to do so is
4373 crash analysis tools and Xen tools for doing domain
4374 save/restore/migration must be enabled to handle larger
4377 xen_emul_unplug= [HW,X86,XEN]
4378 Unplug Xen emulated devices
4379 Format: [unplug0,][unplug1]
4380 ide-disks -- unplug primary master IDE devices
4381 aux-ide-disks -- unplug non-primary-master IDE devices
4382 nics -- unplug network devices
4383 all -- unplug all emulated devices (NICs and IDE disks)
4384 unnecessary -- unplugging emulated devices is
4385 unnecessary even if the host did not respond to
4387 never -- do not unplug even if version check succeeds
4389 xen_nopvspin [X86,XEN]
4390 Disables the ticketlock slowpath using Xen PV
4394 Disables the PV optimizations forcing the HVM guest to
4395 run as generic HVM guest with no PV drivers.
4397 xirc2ps_cs= [NET,PCMCIA]
4399 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4401 ______________________________________________________________________
4405 Add more DRM drivers.
projects / linux-2.6-block.git / blob