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=!! # enable all built-in OS vendor
320 acpi_osi= # disable all strings
322 'acpi_osi=!' can be used in combination with single or
323 multiple 'acpi_osi="string1"' to support specific OS
324 vendor string(s). Note that such command can only
325 affect the default state of the OS vendor strings, thus
326 it cannot affect the default state of the feature group
327 strings and the current state of the OS vendor strings,
328 specifying it multiple times through kernel command line
329 is meaningless. This command is useful when one do not
330 care about the state of the feature group strings which
331 should be controlled by the OSPM.
333 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
334 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
335 can make '_OSI("Windows 2000")' TRUE.
337 'acpi_osi=' cannot be used in combination with other
338 'acpi_osi=' command lines, the _OSI method will not
339 exist in the ACPI namespace. NOTE that such command can
340 only affect the _OSI support state, thus specifying it
341 multiple times through kernel command line is also
344 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
347 'acpi_osi=!*' can be used in combination with single or
348 multiple 'acpi_osi="string1"' to support specific
349 string(s). Note that such command can affect the
350 current state of both the OS vendor strings and the
351 feature group strings, thus specifying it multiple times
352 through kernel command line is meaningful. But it may
353 still not able to affect the final state of a string if
354 there are quirks related to this string. This command
355 is useful when one want to control the state of the
356 feature group strings to debug BIOS issues related to
359 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
360 '_OSI("Module Device")' FALSE.
361 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
362 '_OSI("Module Device")' TRUE.
363 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
365 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
367 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
368 they all will make '_OSI("Windows 2000")' TRUE.
371 Override the pmtimer bug detection: force the kernel
372 to assume that this machine's pmtimer latches its value
373 and always returns good values.
375 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
376 Format: { level | edge | high | low }
378 acpi_skip_timer_override [HW,ACPI]
379 Recognize and ignore IRQ0/pin2 Interrupt Override.
380 For broken nForce2 BIOS resulting in XT-PIC timer.
382 acpi_sleep= [HW,ACPI] Sleep options
383 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
384 old_ordering, nonvs, sci_force_enable }
385 See Documentation/power/video.txt for information on
387 s3_beep is for debugging; it makes the PC's speaker beep
388 as soon as the kernel's real-mode entry point is called.
389 s4_nohwsig prevents ACPI hardware signature from being
390 used during resume from hibernation.
391 old_ordering causes the ACPI 1.0 ordering of the _PTS
392 control method, with respect to putting devices into
393 low power states, to be enforced (the ACPI 2.0 ordering
394 of _PTS is used by default).
395 nonvs prevents the kernel from saving/restoring the
396 ACPI NVS memory during suspend/hibernation and resume.
397 sci_force_enable causes the kernel to set SCI_EN directly
398 on resume from S1/S3 (which is against the ACPI spec,
399 but some broken systems don't work without it).
401 acpi_use_timer_override [HW,ACPI]
402 Use timer override. For some broken Nvidia NF5 boards
403 that require a timer override, but don't have HPET
405 add_efi_memmap [EFI; X86] Include EFI memory map in
406 kernel's map of available physical RAM.
409 { off | try_unsupported }
410 off: disable AGP support
411 try_unsupported: try to drive unsupported chipsets
412 (may crash computer or cause data corruption)
415 See Documentation/sound/alsa/alsa-parameters.txt
418 Allow the default userspace alignment fault handler
419 behaviour to be specified. Bit 0 enables warnings,
420 bit 1 enables fixups, and bit 2 sends a segfault.
422 align_va_addr= [X86-64]
423 Align virtual addresses by clearing slice [14:12] when
424 allocating a VMA at process creation time. This option
425 gives you up to 3% performance improvement on AMD F15h
426 machines (where it is enabled by default) for a
427 CPU-intensive style benchmark, and it can vary highly in
428 a microbenchmark depending on workload and compiler.
430 32: only for 32-bit processes
431 64: only for 64-bit processes
432 on: enable for both 32- and 64-bit processes
433 off: disable for both 32- and 64-bit processes
435 alloc_snapshot [FTRACE]
436 Allocate the ftrace snapshot buffer on boot up when the
437 main buffer is allocated. This is handy if debugging
438 and you need to use tracing_snapshot() on boot up, and
439 do not want to use tracing_snapshot_alloc() as it needs
440 to be done where GFP_KERNEL allocations are allowed.
442 amd_iommu= [HW,X86-64]
443 Pass parameters to the AMD IOMMU driver in the system.
445 fullflush - enable flushing of IO/TLB entries when
446 they are unmapped. Otherwise they are
447 flushed before they will be reused, which
449 off - do not initialize any AMD IOMMU found in
451 force_isolation - Force device isolation for all
452 devices. The IOMMU driver is not
453 allowed anymore to lift isolation
454 requirements as needed. This option
455 does not override iommu=pt
457 amd_iommu_dump= [HW,X86-64]
458 Enable AMD IOMMU driver option to dump the ACPI table
459 for AMD IOMMU. With this option enabled, AMD IOMMU
460 driver will print ACPI tables for AMD IOMMU during
461 IOMMU initialization.
463 amijoy.map= [HW,JOY] Amiga joystick support
464 Map of devices attached to JOY0DAT and JOY1DAT
466 See also Documentation/input/joystick.txt
468 analog.map= [HW,JOY] Analog joystick and gamepad support
469 Specifies type or capabilities of an analog joystick
470 connected to one of 16 gameports
471 Format: <type1>,<type2>,..<type16>
474 Power management functions (SPARCstation-4/5 + deriv.)
476 Disable APC CPU standby support. SPARCstation-Fox does
477 not play well with APC CPU idle - disable it if you have
478 APC and your system crashes randomly.
480 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
481 Change the output verbosity whilst booting
482 Format: { quiet (default) | verbose | debug }
483 Change the amount of debugging information output
484 when initialising the APIC and IO-APIC components.
486 apic_extnmi= [APIC,X86] External NMI delivery setting
487 Format: { bsp (default) | all | none }
488 bsp: External NMI is delivered only to CPU 0
489 all: External NMIs are broadcast to all CPUs as a
491 none: External NMI is masked for all CPUs. This is
492 useful so that a dump capture kernel won't be
496 See Documentation/networking/ipv6.txt.
498 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
499 Limit apic dumping. The parameter defines the maximal
500 number of local apics being dumped. Also it is possible
501 to set it to "all" by meaning -- no limit here.
502 Format: { 1 (default) | 2 | ... | all }.
503 The parameter valid if only apic=debug or
504 apic=verbose is specified.
505 Example: apic=debug show_lapic=all
507 apm= [APM] Advanced Power Management
508 See header of arch/x86/kernel/apm_32.c.
510 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
511 Format: <io>,<irq>,<nodeID>
515 atarimouse= [HW,MOUSE] Atari Mouse
517 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
518 EzKey and similar keyboards
520 atkbd.reset= [HW] Reset keyboard during initialization
522 atkbd.set= [HW] Select keyboard code set
523 Format: <int> (2 = AT (default), 3 = PS/2)
525 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
528 atkbd.softraw= [HW] Choose between synthetic and real raw mode
529 Format: <bool> (0 = real, 1 = synthetic (default))
531 atkbd.softrepeat= [HW]
532 Use software keyboard repeat
534 audit= [KNL] Enable the audit sub-system
535 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
536 0 - kernel audit is disabled and can not be enabled
537 until the next reboot
538 unset - kernel audit is initialized but disabled and
539 will be fully enabled by the userspace auditd.
540 1 - kernel audit is initialized and partially enabled,
541 storing at most audit_backlog_limit messages in
542 RAM until it is fully enabled by the userspace
546 audit_backlog_limit= [KNL] Set the audit queue size limit.
547 Format: <int> (must be >=0)
550 bau= [X86_UV] Enable the BAU on SGI UV. The default
551 behavior is to disable the BAU (i.e. bau=0).
552 Format: { "0" | "1" }
555 unset - Disable the BAU.
557 baycom_epp= [HW,AX25]
560 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
562 See header of drivers/net/hamradio/baycom_par.c.
564 baycom_ser_fdx= [HW,AX25]
565 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
566 Format: <io>,<irq>,<mode>[,<baud>]
567 See header of drivers/net/hamradio/baycom_ser_fdx.c.
569 baycom_ser_hdx= [HW,AX25]
570 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
571 Format: <io>,<irq>,<mode>
572 See header of drivers/net/hamradio/baycom_ser_hdx.c.
574 blkdevparts= Manual partition parsing of block device(s) for
575 embedded devices based on command line input.
576 See Documentation/block/cmdline-partition.txt
578 boot_delay= Milliseconds to delay each printk during boot.
579 Values larger than 10 seconds (10000) are changed to
583 bootmem_debug [KNL] Enable bootmem allocator debug messages.
585 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
586 bttv.radio= Most important insmod options are available as
588 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
591 bulk_remove=off [PPC] This parameter disables the use of the pSeries
592 firmware feature for flushing multiple hpte entries
595 c101= [NET] Moxa C101 synchronous serial card
597 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
598 Sometimes CPU hardware bugs make them report the cache
599 size incorrectly. The kernel will attempt work arounds
600 to fix known problems, but for some CPUs it is not
601 possible to determine what the correct size should be.
602 This option provides an override for these situations.
604 ca_keys= [KEYS] This parameter identifies a specific key(s) on
605 the system trusted keyring to be used for certificate
607 format: { id:<keyid> | builtin }
609 cca= [MIPS] Override the kernel pages' cache coherency
610 algorithm. Accepted values range from 0 to 7
611 inclusive. See arch/mips/include/asm/pgtable-bits.h
612 for platform specific values (SB1, Loongson3 and
615 ccw_timeout_log [S390]
616 See Documentation/s390/CommonIO for details.
618 cgroup_disable= [KNL] Disable a particular controller
619 Format: {name of the controller(s) to disable}
620 The effects of cgroup_disable=foo are:
621 - foo isn't auto-mounted if you mount all cgroups in
623 - foo isn't visible as an individually mountable
625 {Currently only "memory" controller deal with this and
626 cut the overhead, others just disable the usage. So
627 only cgroup_disable=memory is actually worthy}
629 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
630 Format: { controller[,controller...] | "all" }
631 Like cgroup_disable, but only applies to cgroup v1;
632 the blacklisted controllers remain available in cgroup2.
634 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
636 nosocket -- Disable socket memory accounting.
637 nokmem -- Disable kernel memory accounting.
639 checkreqprot [SELINUX] Set initial checkreqprot flag value.
640 Format: { "0" | "1" }
641 See security/selinux/Kconfig help text.
642 0 -- check protection applied by kernel (includes
643 any implied execute protection).
644 1 -- check protection requested by application.
645 Default value is set via a kernel config option.
646 Value can be changed at runtime via
647 /selinux/checkreqprot.
650 See Documentation/s390/CommonIO for details.
653 Prevents the clock framework from automatically gating
654 clocks that have not been explicitly enabled by a Linux
655 device driver but are enabled in hardware at reset or
656 by the bootloader/firmware. Note that this does not
657 force such clocks to be always-on nor does it reserve
658 those clocks in any way. This parameter is useful for
659 debug and development, but should not be needed on a
660 platform with proper driver support. For more
661 information, see Documentation/clk.txt.
663 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
665 Forces specified clocksource (if available) to be used
666 when calculating gettimeofday(). If specified
667 clocksource is not available, it defaults to PIT.
668 Format: { pit | tsc | cyclone | pmtmr }
670 clocksource= Override the default clocksource
672 Override the default clocksource and use the clocksource
673 with the name specified.
674 Some clocksource names to choose from, depending on
676 [all] jiffies (this is the base, fallback clocksource)
678 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
679 pxa_timer,timer3,32k_counter,timer0_1
681 [X86-32] pit,hpet,tsc;
682 scx200_hrt on Geode; cyclone on IBM x440
690 clearcpuid=BITNUM [X86]
691 Disable CPUID feature X for the kernel. See
692 arch/x86/include/asm/cpufeatures.h for the valid bit
693 numbers. Note the Linux specific bits are not necessarily
694 stable over kernel options, but the vendor specific
696 Also note that user programs calling CPUID directly
697 or using the feature without checking anything
698 will still see it. This just prevents it from
699 being used by the kernel or shown in /proc/cpuinfo.
700 Also note the kernel might malfunction if you disable
703 cma=nn[MG]@[start[MG][-end[MG]]]
705 Sets the size of kernel global memory area for
706 contiguous memory allocations and optionally the
707 placement constraint by the physical address range of
708 memory allocations. A value of 0 disables CMA
709 altogether. For more information, see
710 include/linux/dma-contiguous.h
712 cmo_free_hint= [PPC] Format: { yes | no }
713 Specify whether pages are marked as being inactive
714 when they are freed. This is used in CMO environments
715 to determine OS memory pressure for page stealing by
719 coherent_pool=nn[KMG] [ARM,KNL]
720 Sets the size of memory pool for coherent, atomic dma
721 allocations, by default set to 256K.
723 code_bytes [X86] How many bytes of object code to print
728 com20020= [HW,NET] ARCnet - COM20020 chipset
730 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
732 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
736 ARCnet - COM90xx chipset (memory-mapped buffers)
737 Format: <io>[,<irq>[,<memstart>]]
739 condev= [HW,S390] console device
742 console= [KNL] Output console device and options.
744 tty<n> Use the virtual console device <n>.
748 Use the specified serial port. The options are of
749 the form "bbbbpnf", where "bbbb" is the baud rate,
750 "p" is parity ("n", "o", or "e"), "n" is number of
751 bits, and "f" is flow control ("r" for RTS or
752 omit it). Default is "9600n8".
754 See Documentation/serial-console.txt for more
756 Documentation/networking/netconsole.txt for an
759 uart[8250],io,<addr>[,options]
760 uart[8250],mmio,<addr>[,options]
761 uart[8250],mmio16,<addr>[,options]
762 uart[8250],mmio32,<addr>[,options]
763 uart[8250],0x<addr>[,options]
764 Start an early, polled-mode console on the 8250/16550
765 UART at the specified I/O port or MMIO address,
766 switching to the matching ttyS device later.
767 MMIO inter-register address stride is either 8-bit
768 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
769 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
770 to be equivalent to 'mmio'. 'options' are specified in
771 the same format described for ttyS above; if unspecified,
772 the h/w is not re-initialized.
774 hvc<n> Use the hypervisor console device <n>. This is for
775 both Xen and PowerPC hypervisors.
777 If the device connected to the port is not a TTY but a braille
778 device, prepend "brl," before the device type, for instance
780 For now, only VisioBraille is supported.
782 consoleblank= [KNL] The console blank (screen saver) timeout in
783 seconds. Defaults to 10*60 = 10mins. A value of 0
784 disables the blank timer.
787 [KNL] Change the default value for
788 /proc/<pid>/coredump_filter.
789 See also Documentation/filesystems/proc.txt.
791 cpuidle.off=1 [CPU_IDLE]
792 disable the cpuidle sub-system
795 [X86] Delay for N microsec between assert and de-assert
796 of APIC INIT to start processors. This delay occurs
797 on every CPU online, such as boot, and resume from suspend.
800 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
802 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
804 crashkernel=size[KMG][@offset[KMG]]
805 [KNL] Using kexec, Linux can switch to a 'crash kernel'
806 upon panic. This parameter reserves the physical
807 memory region [offset, offset + size] for that kernel
808 image. If '@offset' is omitted, then a suitable offset
809 is selected automatically. Check
810 Documentation/kdump/kdump.txt for further details.
812 crashkernel=range1:size1[,range2:size2,...][@offset]
813 [KNL] Same as above, but depends on the memory
814 in the running system. The syntax of range is
815 start-[end] where start and end are both
816 a memory unit (amount[KMG]). See also
817 Documentation/kdump/kdump.txt for an example.
819 crashkernel=size[KMG],high
820 [KNL, x86_64] range could be above 4G. Allow kernel
821 to allocate physical memory region from top, so could
822 be above 4G if system have more than 4G ram installed.
823 Otherwise memory region will be allocated below 4G, if
825 It will be ignored if crashkernel=X is specified.
826 crashkernel=size[KMG],low
827 [KNL, x86_64] range under 4G. When crashkernel=X,high
828 is passed, kernel could allocate physical memory region
829 above 4G, that cause second kernel crash on system
830 that require some amount of low memory, e.g. swiotlb
831 requires at least 64M+32K low memory, also enough extra
832 low memory is needed to make sure DMA buffers for 32-bit
833 devices won't run out. Kernel would try to allocate at
834 at least 256M below 4G automatically.
835 This one let user to specify own low range under 4G
836 for second kernel instead.
837 0: to disable low allocation.
838 It will be ignored when crashkernel=X,high is not used
839 or memory reserved is below 4G.
842 [KNL] Disable crypto self-tests
847 cs89x0_media= [HW,NET]
848 Format: { rj45 | aui | bnc }
851 See header of drivers/s390/block/dasd_devmap.c.
853 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
854 (one device per port)
855 Format: <port#>,<type>
856 See also Documentation/input/joystick-parport.txt
858 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
859 time. See Documentation/dynamic-debug-howto.txt for
860 details. Deprecated, see dyndbg.
862 debug [KNL] Enable kernel debugging (events log level).
865 [KNL] verbose self-tests
867 Print debugging info while doing the locking API
869 We default to 0 (no extra messages), setting it to
870 1 will print _a lot_ more information - normally
871 only useful to kernel developers.
873 debug_objects [KNL] Enable object debugging
876 [KNL] Disable object debugging
878 debug_guardpage_minorder=
879 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
880 parameter allows control of the order of pages that will
881 be intentionally kept free (and hence protected) by the
882 buddy allocator. Bigger value increase the probability
883 of catching random memory corruption, but reduce the
884 amount of memory for normal system use. The maximum
885 possible value is MAX_ORDER/2. Setting this parameter
886 to 1 or 2 should be enough to identify most random
887 memory corruption problems caused by bugs in kernel or
888 driver code when a CPU writes to (or reads from) a
889 random memory location. Note that there exists a class
890 of memory corruptions problems caused by buggy H/W or
891 F/W or by drivers badly programing DMA (basically when
892 memory is written at bus level and the CPU MMU is
893 bypassed) which are not detectable by
894 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
895 tracking down these problems.
898 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
899 parameter enables the feature at boot time. In
900 default, it is disabled. We can avoid allocating huge
901 chunk of memory for debug pagealloc if we don't enable
902 it at boot time and the system will work mostly same
903 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
904 on: enable the feature
906 debugpat [X86] Enable PAT debugging
908 decnet.addr= [HW,NET]
909 Format: <area>[,<node>]
910 See also Documentation/networking/decnet.txt.
913 [same as hugepagesz=] The size of the default
914 HugeTLB page size. This is the size represented by
915 the legacy /proc/ hugepages APIs, used for SHM, and
916 default size when mounting hugetlbfs filesystems.
917 Defaults to the default architecture's huge page size
921 Set number of hash buckets for dentry cache.
924 See Documentation/networking/ipv6.txt.
926 disable_cpu_apicid= [X86,APIC,SMP]
928 The number of initial APIC ID for the
929 corresponding CPU to be disabled at boot,
930 mostly used for the kdump 2nd kernel to
931 disable BSP to wake up multiple CPUs without
932 causing system reset or hang due to sending
935 disable_ddw [PPC/PSERIES]
936 Disable Dynamic DMA Window support. Use this if
937 to workaround buggy firmware.
940 See Documentation/networking/ipv6.txt.
942 disable_mtrr_cleanup [X86]
943 The kernel tries to adjust MTRR layout from continuous
944 to discrete, to make X server driver able to add WB
945 entry later. This parameter disables that.
947 disable_mtrr_trim [X86, Intel and AMD only]
948 By default the kernel will trim any uncacheable
949 memory out of your available memory pool based on
950 MTRR settings. This parameter disables that behavior,
951 possibly causing your machine to run very slowly.
953 disable_timer_pin_1 [X86]
954 Disable PIN 1 of APIC timer
955 Can be useful to work around chipset bugs.
957 dis_ucode_ldr [X86] Disable the microcode loader.
959 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
960 this option disables the debugging code at boot.
962 dma_debug_entries=<number>
963 This option allows to tune the number of preallocated
964 entries for DMA-API debugging code. One entry is
965 required per DMA-API allocation. Use this if the
966 DMA-API debugging code disables itself because the
967 architectural default is too low.
969 dma_debug_driver=<driver_name>
970 With this option the DMA-API debugging driver
971 filter feature can be enabled at boot time. Just
972 pass the driver to filter for as the parameter.
973 The filter can be disabled or changed to another
974 driver later using sysfs.
976 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
977 Broken monitors, graphic adapters, KVMs and EDIDless
978 panels may send no or incorrect EDID data sets.
979 This parameter allows to specify an EDID data sets
980 in the /lib/firmware directory that are used instead.
981 Generic built-in EDID data sets are used, if one of
982 edid/1024x768.bin, edid/1280x1024.bin,
983 edid/1680x1050.bin, or edid/1920x1080.bin is given
984 and no file with the same name exists. Details and
985 instructions how to build your own EDID data are
986 available in Documentation/EDID/HOWTO.txt. An EDID
987 data set will only be used for a particular connector,
988 if its name and a colon are prepended to the EDID
989 name. Each connector may use a unique EDID data
990 set by separating the files with a comma. An EDID
991 data set with no connector name will be used for
992 any connectors not explicitly specified.
996 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
997 module.dyndbg[="val"]
998 Enable debug messages at boot time. See
999 Documentation/dynamic-debug-howto.txt for details.
1001 nompx [X86] Disables Intel Memory Protection Extensions.
1002 See Documentation/x86/intel_mpx.txt for more
1003 information about the feature.
1005 nopku [X86] Disable Memory Protection Keys CPU feature found
1009 on enable eager fpu restore
1010 off disable eager fpu restore
1011 auto selects the default scheme, which automatically
1012 enables eagerfpu restore for xsaveopt.
1014 module.async_probe [KNL]
1015 Enable asynchronous probe on this module.
1017 early_ioremap_debug [KNL]
1018 Enable debug messages in early_ioremap support. This
1019 is useful for tracking down temporary early mappings
1020 which are not unmapped.
1022 earlycon= [KNL] Output early console device and options.
1024 When used with no options, the early console is
1025 determined by the stdout-path property in device
1029 Start an early, polled-mode console on a cadence serial
1030 port at the specified address. The cadence serial port
1031 must already be setup and configured. Options are not
1034 uart[8250],io,<addr>[,options]
1035 uart[8250],mmio,<addr>[,options]
1036 uart[8250],mmio32,<addr>[,options]
1037 uart[8250],mmio32be,<addr>[,options]
1038 uart[8250],0x<addr>[,options]
1039 Start an early, polled-mode console on the 8250/16550
1040 UART at the specified I/O port or MMIO address.
1041 MMIO inter-register address stride is either 8-bit
1042 (mmio) or 32-bit (mmio32 or mmio32be).
1043 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1044 to be equivalent to 'mmio'. 'options' are specified
1045 in the same format described for "console=ttyS<n>"; if
1046 unspecified, the h/w is not initialized.
1050 Start an early, polled-mode console on a pl011 serial
1051 port at the specified address. The pl011 serial port
1052 must already be setup and configured. Options are not
1053 yet supported. If 'mmio32' is specified, then only
1054 the driver will use only 32-bit accessors to read/write
1055 the device registers.
1058 Start an early, polled-mode console on an msm serial
1059 port at the specified address. The serial port
1060 must already be setup and configured. Options are not
1063 msm_serial_dm,<addr>
1064 Start an early, polled-mode console on an msm serial
1065 dm port at the specified address. The serial port
1066 must already be setup and configured. Options are not
1069 smh Use ARM semihosting calls for early console.
1077 Use early console provided by serial driver available
1078 on Samsung SoCs, requires selecting proper type and
1079 a correct base address of the selected UART port. The
1080 serial port must already be setup and configured.
1081 Options are not yet supported.
1085 Use early console provided by Freescale LP UART driver
1086 found on Freescale Vybrid and QorIQ LS1021A processors.
1087 A valid base address must be provided, and the serial
1088 port must already be setup and configured.
1090 armada3700_uart,<addr>
1091 Start an early, polled-mode console on the
1092 Armada 3700 serial port at the specified
1093 address. The serial port must already be setup
1094 and configured. Options are not yet supported.
1096 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1100 earlyprintk=serial[,ttySn[,baudrate]]
1101 earlyprintk=serial[,0x...[,baudrate]]
1102 earlyprintk=ttySn[,baudrate]
1103 earlyprintk=dbgp[debugController#]
1104 earlyprintk=pciserial,bus:device.function[,baudrate]
1106 earlyprintk is useful when the kernel crashes before
1107 the normal console is initialized. It is not enabled by
1108 default because it has some cosmetic problems.
1110 Append ",keep" to not disable it when the real console
1113 Only one of vga, efi, serial, or usb debug port can
1116 Currently only ttyS0 and ttyS1 may be specified by
1117 name. Other I/O ports may be explicitly specified
1118 on some architectures (x86 and arm at least) by
1119 replacing ttySn with an I/O port address, like this:
1120 earlyprintk=serial,0x1008,115200
1121 You can find the port for a given device in
1122 /proc/tty/driver/serial:
1123 2: uart:ST16650V2 port:00001008 irq:18 ...
1125 Interaction with the standard serial driver is not
1128 The VGA and EFI output is eventually overwritten by
1131 The xen output can only be used by Xen PV guests.
1133 edac_report= [HW,EDAC] Control how to report EDAC event
1134 Format: {"on" | "off" | "force"}
1135 on: enable EDAC to report H/W event. May be overridden
1136 by other higher priority error reporting module.
1137 off: disable H/W event reporting through EDAC.
1138 force: enforce the use of EDAC to report H/W event.
1141 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1144 This is designed to be used in conjunction with
1145 the boot argument: earlyprintk=vga
1148 Format: {"off" | "on" | "skip[mbr]"}
1151 Format: { "old_map", "nochunk", "noruntime", "debug" }
1152 old_map [X86-64]: switch to the old ioremap-based EFI
1153 runtime services mapping. 32-bit still uses this one by
1155 nochunk: disable reading files in "chunks" in the EFI
1156 boot stub, as chunking can cause problems with some
1157 firmware implementations.
1158 noruntime : disable EFI runtime services support
1159 debug: enable misc debug output
1161 efi_no_storage_paranoia [EFI; X86]
1162 Using this parameter you can use more than 50% of
1163 your efi variable storage. Use this parameter only if
1164 you are really sure that your UEFI does sane gc and
1165 fulfills the spec otherwise your board may brick.
1167 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1168 Add arbitrary attribute to specific memory range by
1169 updating original EFI memory map.
1170 Region of memory which aa attribute is added to is
1172 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1173 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1174 attribute is added to range 0x100000000-0x180000000 and
1175 0x10a0000000-0x1120000000.
1177 Using this parameter you can do debugging of EFI memmap
1178 related feature. For example, you can do debugging of
1179 Address Range Mirroring feature even if your box
1182 eisa_irq_edge= [PARISC,HW]
1183 See header of drivers/parisc/eisa.c.
1186 See comment before function elanfreq_setup() in
1187 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1190 Format: {"cfq" | "deadline" | "noop"}
1191 See Documentation/block/cfq-iosched.txt and
1192 Documentation/block/deadline-iosched.txt for details.
1194 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1195 Specifies physical address of start of kernel core
1196 image elf header and optionally the size. Generally
1197 kexec loader will pass this option to capture kernel.
1198 See Documentation/kdump/kdump.txt for details.
1200 enable_mtrr_cleanup [X86]
1201 The kernel tries to adjust MTRR layout from continuous
1202 to discrete, to make X server driver able to add WB
1203 entry later. This parameter enables that.
1205 enable_timer_pin_1 [X86]
1206 Enable PIN 1 of APIC timer
1207 Can be useful to work around chipset bugs
1208 (in particular on some ATI chipsets).
1209 The kernel tries to set a reasonable default.
1211 enforcing [SELINUX] Set initial enforcing status.
1213 See security/selinux/Kconfig help text.
1214 0 -- permissive (log only, no denials).
1215 1 -- enforcing (deny and log).
1217 Value can be changed at runtime via /selinux/enforce.
1220 Disable Error Record Serialization Table (ERST)
1223 ether= [HW,NET] Ethernet cards parameters
1224 This option is obsoleted by the "netdev=" option, which
1225 has equivalent usage. See its documentation for details.
1229 Permit 'security.evm' to be updated regardless of
1230 current integrity status.
1234 fail_make_request=[KNL]
1235 General fault injection mechanism.
1236 Format: <interval>,<probability>,<space>,<times>
1237 See also Documentation/fault-injection/.
1240 See Documentation/blockdev/floppy.txt.
1242 force_pal_cache_flush
1243 [IA-64] Avoid check_sal_cache_flush which may hang on
1244 buggy SAL_CACHE_FLUSH implementations. Using this
1245 parameter will force ia64_sal_cache_flush to call
1246 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1249 Forcefully enable Physical Address Extension (PAE).
1250 Many Pentium M systems disable PAE but may have a
1251 functionally usable PAE implementation.
1252 Warning: use of this parameter will taint the kernel
1253 and may cause unknown problems.
1256 [FTRACE] will set and start the specified tracer
1257 as early as possible in order to facilitate early
1260 ftrace_dump_on_oops[=orig_cpu]
1261 [FTRACE] will dump the trace buffers on oops.
1262 If no parameter is passed, ftrace will dump
1263 buffers of all CPUs, but if you pass orig_cpu, it will
1264 dump only the buffer of the CPU that triggered the
1267 ftrace_filter=[function-list]
1268 [FTRACE] Limit the functions traced by the function
1269 tracer at boot up. function-list is a comma separated
1270 list of functions. This list can be changed at run
1271 time by the set_ftrace_filter file in the debugfs
1274 ftrace_notrace=[function-list]
1275 [FTRACE] Do not trace the functions specified in
1276 function-list. This list can be changed at run time
1277 by the set_ftrace_notrace file in the debugfs
1280 ftrace_graph_filter=[function-list]
1281 [FTRACE] Limit the top level callers functions traced
1282 by the function graph tracer at boot up.
1283 function-list is a comma separated list of functions
1284 that can be changed at run time by the
1285 set_graph_function file in the debugfs tracing directory.
1287 ftrace_graph_notrace=[function-list]
1288 [FTRACE] Do not trace from the functions specified in
1289 function-list. This list is a comma separated list of
1290 functions that can be changed at run time by the
1291 set_graph_notrace file in the debugfs tracing directory.
1294 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1295 support via parallel port (up to 5 devices per port)
1296 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1297 See also Documentation/input/joystick-parport.txt
1301 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1305 gcov_persist= [GCOV] When non-zero (default), profiling data for
1306 kernel modules is saved and remains accessible via
1307 debugfs, even when the module is unloaded/reloaded.
1308 When zero, profiling data is discarded and associated
1309 debugfs files are removed at module unload time.
1311 gpt [EFI] Forces disk with valid GPT signature but
1312 invalid Protective MBR to be treated as GPT. If the
1313 primary GPT is corrupted, it enables the backup/alternate
1314 GPT to be used instead.
1316 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1317 the "Enable 0" bit of the configuration register.
1320 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1321 the "Enable 0" bit of the configuration register.
1324 grcan.select= [HW] Select which physical interface to use.
1327 grcan.txsize= [HW] Sets the size of the tx buffer.
1328 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1330 grcan.rxsize= [HW] Sets the size of the rx buffer.
1331 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1334 hardlockup_all_cpu_backtrace=
1335 [KNL] Should the hard-lockup detector generate
1336 backtraces on all cpus.
1339 hashdist= [KNL,NUMA] Large hashes allocated during boot
1340 are distributed across NUMA nodes. Defaults on
1341 for 64-bit NUMA, off otherwise.
1342 Format: 0 | 1 (for off | on)
1344 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1346 hd= [EIDE] (E)IDE hard drive subsystem geometry
1347 Format: <cyl>,<head>,<sect>
1350 Disable Hardware Error Source Table (HEST) support;
1351 corresponding firmware-first mode error processing
1352 logic will be disabled.
1354 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1355 size of <nn>. This works even on boxes that have no
1356 highmem otherwise. This also works to reduce highmem
1357 size on bigger boxes.
1359 highres= [KNL] Enable/disable high resolution timer mode.
1360 Valid parameters: "on", "off"
1364 See Documentation/isdn/README.HiSax.
1368 hpet= [X86-32,HPET] option to control HPET usage
1369 Format: { enable (default) | disable | force |
1371 disable: disable HPET and use PIT instead
1372 force: allow force enabled of undocumented chips (ICH4,
1374 verbose: show contents of HPET registers during setup
1376 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1377 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1379 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1380 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1381 On x86-64 and powerpc, this option can be specified
1382 multiple times interleaved with hugepages= to reserve
1383 huge pages of different sizes. Valid pages sizes on
1384 x86-64 are 2M (when the CPU supports "pse") and 1G
1385 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1387 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1388 terminal devices. Valid values: 0..8
1389 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1390 If specified, z/VM IUCV HVC accepts connections
1391 from listed z/VM user IDs only.
1393 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1394 hardware thread id mappings.
1395 Format: <cpu>:<hwthread>
1398 Do not unregister boot console at start. This is only
1399 useful for debugging when something happens in the window
1400 between unregistering the boot console and initializing
1403 i2c_bus= [HW] Override the default board specific I2C bus speed
1404 or register an additional I2C bus that is not
1405 registered from board initialization code.
1409 i8042.debug [HW] Toggle i8042 debug mode
1410 i8042.unmask_kbd_data
1411 [HW] Enable printing of interrupt data from the KBD port
1412 (disabled by default, and as a pre-condition
1413 requires that i8042.debug=1 be enabled)
1414 i8042.direct [HW] Put keyboard port into non-translated mode
1415 i8042.dumbkbd [HW] Pretend that controller can only read data from
1416 keyboard and cannot control its state
1417 (Don't attempt to blink the leds)
1418 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1419 i8042.nokbd [HW] Don't check/create keyboard port
1420 i8042.noloop [HW] Disable the AUX Loopback command while probing
1422 i8042.nomux [HW] Don't check presence of an active multiplexing
1424 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1426 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1427 i8042.reset [HW] Reset the controller during init and cleanup
1428 i8042.unlock [HW] Unlock (ignore) the keylock
1429 i8042.kbdreset [HW] Reset device connected to KBD port
1433 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1434 indicates that the driver is running on unsupported
1436 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1437 does not match list of supported models.
1439 [HW] Report power status in /proc/i8k
1440 (disabled by default)
1441 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1444 i915.invert_brightness=
1445 [DRM] Invert the sense of the variable that is used to
1446 set the brightness of the panel backlight. Normally a
1447 brightness value of 0 indicates backlight switched off,
1448 and the maximum of the brightness value sets the backlight
1449 to maximum brightness. If this parameter is set to 0
1450 (default) and the machine requires it, or this parameter
1451 is set to 1, a brightness value of 0 sets the backlight
1452 to maximum brightness, and the maximum of the brightness
1453 value switches the backlight off.
1454 -1 -- never invert brightness
1455 0 -- machine default
1456 1 -- force brightness inversion
1459 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1461 ide-core.nodma= [HW] (E)IDE subsystem
1462 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1463 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1464 .cdrom .chs .ignore_cable are additional options
1465 See Documentation/ide/ide.txt.
1467 ide-generic.probe-mask= [HW] (E)IDE subsystem
1469 Probe mask for legacy ISA IDE ports. Depending on
1470 platform up to 6 ports are supported, enabled by
1471 setting corresponding bits in the mask to 1. The
1472 default value is 0x0, which has a special meaning.
1473 On systems that have PCI, it triggers scanning the
1474 PCI bus for the first and the second port, which
1475 are then probed. On systems without PCI the value
1476 of 0x0 enables probing the two first ports as if it
1479 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1480 Claim all unknown PCI IDE storage controllers.
1483 Format: idle=poll, idle=halt, idle=nomwait
1484 Poll forces a polling idle loop that can slightly
1485 improve the performance of waking up a idle CPU, but
1486 will use a lot of power and make the system run hot.
1488 idle=halt: Halt is forced to be used for CPU idle.
1489 In such case C2/C3 won't be used again.
1490 idle=nomwait: Disable mwait for CPU C-states
1492 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1493 Format: { strict | legacy | 2008 | relaxed }
1496 Choose which programs will be accepted for execution
1497 based on the IEEE 754 NaN encoding(s) supported by
1498 the FPU and the NaN encoding requested with the value
1499 of an ELF file header flag individually set by each
1500 binary. Hardware implementations are permitted to
1501 support either or both of the legacy and the 2008 NaN
1504 Available settings are as follows:
1505 strict accept binaries that request a NaN encoding
1506 supported by the FPU
1507 legacy only accept legacy-NaN binaries, if supported
1509 2008 only accept 2008-NaN binaries, if supported
1511 relaxed accept any binaries regardless of whether
1512 supported by the FPU
1514 The FPU emulator is always able to support both NaN
1515 encodings, so if no FPU hardware is present or it has
1516 been disabled with 'nofpu', then the settings of
1517 'legacy' and '2008' strap the emulator accordingly,
1518 'relaxed' straps the emulator for both legacy-NaN and
1519 2008-NaN, whereas 'strict' enables legacy-NaN only on
1520 legacy processors and both NaN encodings on MIPS32 or
1523 The setting for ABS.fmt/NEG.fmt instruction execution
1524 mode generally follows that for the NaN encoding,
1525 except where unsupported by hardware.
1527 ignore_loglevel [KNL]
1528 Ignore loglevel setting - this will print /all/
1529 kernel messages to the console. Useful for debugging.
1530 We also add it as printk module parameter, so users
1531 could change it dynamically, usually by
1532 /sys/module/printk/parameters/ignore_loglevel.
1535 Ignore RLIMIT_DATA setting for data mappings,
1536 print warning at first misuse. Can be changed via
1537 /sys/module/kernel/parameters/ignore_rlimit_data.
1539 ihash_entries= [KNL]
1540 Set number of hash buckets for inode cache.
1542 ima_appraise= [IMA] appraise integrity measurements
1543 Format: { "off" | "enforce" | "fix" | "log" }
1546 ima_appraise_tcb [IMA]
1547 The builtin appraise policy appraises all files
1551 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1555 The list of supported hash algorithms is defined
1556 in crypto/hash_info.h.
1559 The builtin measurement policy to load during IMA
1560 setup. Specyfing "tcb" as the value, measures all
1561 programs exec'd, files mmap'd for exec, and all files
1562 opened with the read mode bit set by either the
1563 effective uid (euid=0) or uid=0.
1566 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1567 Load a policy which meets the needs of the Trusted
1568 Computing Base. This means IMA will measure all
1569 programs exec'd, files mmap'd for exec, and all files
1570 opened for read by uid=0.
1573 Select one of defined IMA measurements template formats.
1574 Formats: { "ima" | "ima-ng" | "ima-sig" }
1578 [IMA] Define a custom template format.
1579 Format: { "field1|...|fieldN" }
1581 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1582 Format: <min_file_size>
1583 Set the minimal file size for using asynchronous hash.
1584 If left unspecified, ahash usage is disabled.
1586 ahash performance varies for different data sizes on
1587 different crypto accelerators. This option can be used
1588 to achieve the best performance for a particular HW.
1590 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1592 Set hashing buffer size. Default: 4k.
1594 ahash performance varies for different chunk sizes on
1595 different crypto accelerators. This option can be used
1596 to achieve best performance for particular HW.
1600 Run specified binary instead of /sbin/init as init
1603 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1604 for working out where the kernel is dying during
1607 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1608 initcall functions. Useful for debugging built-in
1609 modules and initcalls.
1611 initrd= [BOOT] Specify the location of the initial ramdisk
1613 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1616 int_pln_enable [x86] Enable power limit notification interrupt
1618 integrity_audit=[IMA]
1619 Format: { "0" | "1" }
1620 0 -- basic integrity auditing messages. (Default)
1621 1 -- additional integrity auditing messages.
1623 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1625 Enable intel iommu driver.
1627 Disable intel iommu driver.
1628 igfx_off [Default Off]
1629 By default, gfx is mapped as normal device. If a gfx
1630 device has a dedicated DMAR unit, the DMAR unit is
1631 bypassed by not enabling DMAR with this option. In
1632 this case, gfx device will use physical address for
1635 With this option iommu will not optimize to look
1636 for io virtual address below 32-bit forcing dual
1637 address cycle on pci bus for cards supporting greater
1638 than 32-bit addressing. The default is to look
1639 for translation below 32-bit and if not available
1640 then look in the higher range.
1641 strict [Default Off]
1642 With this option on every unmap_single operation will
1643 result in a hardware IOTLB flush operation as opposed
1644 to batching them for performance.
1645 sp_off [Default Off]
1646 By default, super page will be supported if Intel IOMMU
1647 has the capability. With this option, super page will
1649 ecs_off [Default Off]
1650 By default, extended context tables will be supported if
1651 the hardware advertises that it has support both for the
1652 extended tables themselves, and also PASID support. With
1653 this option set, extended tables will not be used even
1654 on hardware which claims to support them.
1656 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1657 0 disables intel_idle and fall back on acpi_idle.
1658 1 to 6 specify maximum depth of C-state.
1662 Do not enable intel_pstate as the default
1663 scaling driver for the supported processors
1665 Enable intel_pstate on systems that prohibit it by default
1666 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1667 instead of acpi-cpufreq may disable platform features, such
1668 as thermal controls and power capping, that rely on ACPI
1669 P-States information being indicated to OSPM and therefore
1670 should be used with caution. This option does not work with
1671 processors that aren't supported by the intel_pstate driver
1672 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1674 Do not enable hardware P state control (HWP)
1677 Only load intel_pstate on systems which support
1678 hardware P state control (HWP) if available.
1680 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1681 Description Table, specifies preferred power management
1682 profile as "Enterprise Server" or "Performance Server",
1683 then this feature is turned on by default.
1685 intremap= [X86-64, Intel-IOMMU]
1686 on enable Interrupt Remapping (default)
1687 off disable Interrupt Remapping
1688 nosid disable Source ID checking
1690 BIOS x2APIC opt-out request will be ignored
1691 nopost disable Interrupt Posting
1693 iomem= Disable strict checking of access to MMIO memory
1694 strict regions from userspace.
1709 nobypass [PPC/POWERNV]
1710 Disable IOMMU bypass, using IOMMU for PCI devices.
1713 io7= [HW] IO7 for Marvel based alpha systems
1714 See comment before marvel_specify_io7 in
1715 arch/alpha/kernel/core_marvel.c.
1717 io_delay= [X86] I/O delay method
1719 Standard port 0x80 based delay
1721 Alternate port 0xed based delay (needed on some systems)
1723 Simple two microseconds delay
1728 See Documentation/filesystems/nfs/nfsroot.txt.
1730 irqaffinity= [SMP] Set the default irq affinity mask
1732 <cpu number>,...,<cpu number>
1734 <cpu number>-<cpu number>
1735 (must be a positive range in ascending order)
1737 <cpu number>,...,<cpu number>-<cpu number>
1740 When an interrupt is not handled search all handlers
1741 for it. Intended to get systems with badly broken
1745 When an interrupt is not handled search all handlers
1746 for it. Also check all handlers each timer
1747 interrupt. Intended to get systems with badly broken
1751 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1753 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1755 <cpu number>,...,<cpu number>
1757 <cpu number>-<cpu number>
1758 (must be a positive range in ascending order)
1760 <cpu number>,...,<cpu number>-<cpu number>
1762 This option can be used to specify one or more CPUs
1763 to isolate from the general SMP balancing and scheduling
1764 algorithms. You can move a process onto or off an
1765 "isolated" CPU via the CPU affinity syscalls or cpuset.
1766 <cpu number> begins at 0 and the maximum value is
1767 "number of CPUs in system - 1".
1769 This option is the preferred way to isolate CPUs. The
1770 alternative -- manually setting the CPU mask of all
1771 tasks in the system -- can cause problems and
1772 suboptimal load balancer performance.
1776 ivrs_ioapic [HW,X86_64]
1777 Provide an override to the IOAPIC-ID<->DEVICE-ID
1778 mapping provided in the IVRS ACPI table. For
1779 example, to map IOAPIC-ID decimal 10 to
1780 PCI device 00:14.0 write the parameter as:
1781 ivrs_ioapic[10]=00:14.0
1783 ivrs_hpet [HW,X86_64]
1784 Provide an override to the HPET-ID<->DEVICE-ID
1785 mapping provided in the IVRS ACPI table. For
1786 example, to map HPET-ID decimal 0 to
1787 PCI device 00:14.0 write the parameter as:
1788 ivrs_hpet[0]=00:14.0
1790 ivrs_acpihid [HW,X86_64]
1791 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1792 mapping provided in the IVRS ACPI table. For
1793 example, to map UART-HID:UID AMD0020:0 to
1794 PCI device 00:14.5 write the parameter as:
1795 ivrs_acpihid[00:14.5]=AMD0020:0
1797 js= [HW,JOY] Analog joystick
1798 See Documentation/input/joystick.txt.
1801 Enable/disable kernel and module base offset ASLR
1802 (Address Space Layout Randomization) if built into
1803 the kernel. When CONFIG_HIBERNATION is selected,
1804 kASLR is disabled by default. When kASLR is enabled,
1805 hibernation will be disabled.
1809 kernelcore= [KNL,X86,IA-64,PPC]
1810 Format: nn[KMGTPE] | "mirror"
1812 specifies the amount of memory usable by the kernel
1813 for non-movable allocations. The requested amount is
1814 spread evenly throughout all nodes in the system. The
1815 remaining memory in each node is used for Movable
1816 pages. In the event, a node is too small to have both
1817 kernelcore and Movable pages, kernelcore pages will
1818 take priority and other nodes will have a larger number
1819 of Movable pages. The Movable zone is used for the
1820 allocation of pages that may be reclaimed or moved
1821 by the page migration subsystem. This means that
1822 HugeTLB pages may not be allocated from this zone.
1823 Note that allocations like PTEs-from-HighMem still
1824 use the HighMem zone if it exists, and the Normal
1825 zone if it does not.
1827 Instead of specifying the amount of memory (nn[KMGTPE]),
1828 you can specify "mirror" option. In case "mirror"
1829 option is specified, mirrored (reliable) memory is used
1830 for non-movable allocations and remaining memory is used
1831 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1832 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1835 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1836 Format: <Controller#>[,poll interval]
1837 The controller # is the number of the ehci usb debug
1838 port as it is probed via PCI. The poll interval is
1839 optional and is the number seconds in between
1840 each poll cycle to the debug port in case you need
1841 the functionality for interrupting the kernel with
1842 gdb or control-c on the dbgp connection. When
1843 not using this parameter you use sysrq-g to break into
1844 the kernel debugger.
1846 kgdboc= [KGDB,HW] kgdb over consoles.
1847 Requires a tty driver that supports console polling,
1848 or a supported polling keyboard driver (non-usb).
1849 Serial only format: <serial_device>[,baud]
1850 keyboard only format: kbd
1851 keyboard and serial format: kbd,<serial_device>[,baud]
1852 Optional Kernel mode setting:
1853 kms, kbd format: kms,kbd
1854 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1856 kgdbwait [KGDB] Stop kernel execution and enter the
1857 kernel debugger at the earliest opportunity.
1859 kmac= [MIPS] korina ethernet MAC address.
1860 Configure the RouterBoard 532 series on-chip
1861 Ethernet adapter MAC address.
1863 kmemleak= [KNL] Boot-time kmemleak enable/disable
1864 Valid arguments: on, off
1866 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1869 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1870 Valid arguments: 0, 1, 2
1871 kmemcheck=0 (disabled)
1872 kmemcheck=1 (enabled)
1873 kmemcheck=2 (one-shot mode)
1874 Default: 2 (one-shot mode)
1876 kstack=N [X86] Print N words from the kernel stack
1879 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1880 Default is 0 (don't ignore, but inject #GP)
1882 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1886 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1887 Default is 1 (enabled)
1889 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1891 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1893 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1894 (virtualized MMU) support on capable Intel chips.
1895 Default is 1 (enabled)
1897 kvm-intel.emulate_invalid_guest_state=
1898 [KVM,Intel] Enable emulation of invalid guest states
1899 Default is 0 (disabled)
1901 kvm-intel.flexpriority=
1902 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1903 Default is 1 (enabled)
1906 [KVM,Intel] Enable VMX nesting (nVMX).
1907 Default is 0 (disabled)
1909 kvm-intel.unrestricted_guest=
1910 [KVM,Intel] Disable unrestricted guest feature
1911 (virtualized real and unpaged mode) on capable
1912 Intel chips. Default is 1 (enabled)
1914 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1915 feature (tagged TLBs) on capable Intel chips.
1916 Default is 1 (enabled)
1922 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1925 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1926 value for LAPIC timer one-shot implementation. Default
1927 back to the programmable timer unit in the LAPIC.
1929 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1932 libata.dma= [LIBATA] DMA control
1933 libata.dma=0 Disable all PATA and SATA DMA
1934 libata.dma=1 PATA and SATA Disk DMA only
1935 libata.dma=2 ATAPI (CDROM) DMA only
1936 libata.dma=4 Compact Flash DMA only
1937 Combinations also work, so libata.dma=3 enables DMA
1938 for disks and CDROMs, but not CFs.
1940 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1941 libata.ignore_hpa=0 keep BIOS limits (default)
1942 libata.ignore_hpa=1 ignore limits, using full disk
1944 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1948 libata.force= [LIBATA] Force configurations. The format is comma
1949 separated list of "[ID:]VAL" where ID is
1950 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1951 matching port, link or device. Basically, it matches
1952 the ATA ID string printed on console by libata. If
1953 the whole ID part is omitted, the last PORT and DEVICE
1954 values are used. If ID hasn't been specified yet, the
1955 configuration applies to all ports, links and devices.
1957 If only DEVICE is omitted, the parameter applies to
1958 the port and all links and devices behind it. DEVICE
1959 number of 0 either selects the first device or the
1960 first fan-out link behind PMP device. It does not
1961 select the host link. DEVICE number of 15 selects the
1962 host link and device attached to it.
1964 The VAL specifies the configuration to force. As long
1965 as there's no ambiguity shortcut notation is allowed.
1966 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1967 The following configurations can be forced.
1969 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1970 Any ID with matching PORT is used.
1972 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1974 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1975 udma[/][16,25,33,44,66,100,133] notation is also
1978 * [no]ncq: Turn on or off NCQ.
1980 * [no]ncqtrim: Turn off queued DSM TRIM.
1982 * nohrst, nosrst, norst: suppress hard, soft
1985 * rstonce: only attempt one reset during
1986 hot-unplug link recovery
1988 * dump_id: dump IDENTIFY data.
1990 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1992 * disable: Disable this device.
1994 If there are multiple matching configurations changing
1995 the same attribute, the last one is used.
1997 memblock=debug [KNL] Enable memblock debug messages.
1999 load_ramdisk= [RAM] List of ramdisks to load from floppy
2000 See Documentation/blockdev/ramdisk.txt.
2002 lockd.nlm_grace_period=P [NFS] Assign grace period.
2005 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2008 lockd.nlm_timeout=T [NFS] Assign timeout value.
2011 lockd.nlm_udpport=M [NFS] Assign UDP port.
2014 locktorture.nreaders_stress= [KNL]
2015 Set the number of locking read-acquisition kthreads.
2016 Defaults to being automatically set based on the
2017 number of online CPUs.
2019 locktorture.nwriters_stress= [KNL]
2020 Set the number of locking write-acquisition kthreads.
2022 locktorture.onoff_holdoff= [KNL]
2023 Set time (s) after boot for CPU-hotplug testing.
2025 locktorture.onoff_interval= [KNL]
2026 Set time (s) between CPU-hotplug operations, or
2027 zero to disable CPU-hotplug testing.
2029 locktorture.shuffle_interval= [KNL]
2030 Set task-shuffle interval (jiffies). Shuffling
2031 tasks allows some CPUs to go into dyntick-idle
2032 mode during the locktorture test.
2034 locktorture.shutdown_secs= [KNL]
2035 Set time (s) after boot system shutdown. This
2036 is useful for hands-off automated testing.
2038 locktorture.stat_interval= [KNL]
2039 Time (s) between statistics printk()s.
2041 locktorture.stutter= [KNL]
2042 Time (s) to stutter testing, for example,
2043 specifying five seconds causes the test to run for
2044 five seconds, wait for five seconds, and so on.
2045 This tests the locking primitive's ability to
2046 transition abruptly to and from idle.
2048 locktorture.torture_runnable= [BOOT]
2049 Start locktorture running at boot time.
2051 locktorture.torture_type= [KNL]
2052 Specify the locking implementation to test.
2054 locktorture.verbose= [KNL]
2055 Enable additional printk() statements.
2057 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2060 loglevel= All Kernel Messages with a loglevel smaller than the
2061 console loglevel will be printed to the console. It can
2062 also be changed with klogd or other programs. The
2063 loglevels are defined as follows:
2065 0 (KERN_EMERG) system is unusable
2066 1 (KERN_ALERT) action must be taken immediately
2067 2 (KERN_CRIT) critical conditions
2068 3 (KERN_ERR) error conditions
2069 4 (KERN_WARNING) warning conditions
2070 5 (KERN_NOTICE) normal but significant condition
2071 6 (KERN_INFO) informational
2072 7 (KERN_DEBUG) debug-level messages
2074 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2075 in bytes. n must be a power of two and greater
2076 than the minimal size. The minimal size is defined
2077 by LOG_BUF_SHIFT kernel config parameter. There is
2078 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2079 that allows to increase the default size depending on
2080 the number of CPUs. See init/Kconfig for more details.
2082 logo.nologo [FB] Disables display of the built-in Linux logo.
2083 This may be used to provide more screen space for
2084 kernel log messages and is useful when debugging
2085 kernel boot problems.
2087 lp=0 [LP] Specify parallel ports to use, e.g,
2088 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2089 lp=reset first parallel port). 'lp=0' disables the
2090 lp=auto printer driver. 'lp=reset' (which can be
2091 specified in addition to the ports) causes
2092 attached printers to be reset. Using
2093 lp=port1,port2,... specifies the parallel ports
2094 to associate lp devices with, starting with
2095 lp0. A port specification may be 'none' to skip
2096 that lp device, or a parport name such as
2097 'parport0'. Specifying 'lp=auto' instead of a
2098 port specification list means that device IDs
2099 from each port should be examined, to see if
2100 an IEEE 1284-compliant printer is attached; if
2101 so, the driver will manage that printer.
2102 See also header of drivers/char/lp.c.
2105 Sets loops_per_jiffy to given constant, thus avoiding
2106 time-consuming boot-time autodetection (up to 250 ms per
2107 CPU). 0 enables autodetection (default). To determine
2108 the correct value for your kernel, boot with normal
2109 autodetection and see what value is printed. Note that
2110 on SMP systems the preset will be applied to all CPUs,
2111 which is likely to cause problems if your CPUs need
2112 significantly divergent settings. An incorrect value
2113 will cause delays in the kernel to be wrong, leading to
2114 unpredictable I/O errors and other breakage. Although
2115 unlikely, in the extreme case this might damage your
2119 Format: <io>,<irq>,<dma>
2121 machvec= [IA-64] Force the use of a particular machine-vector
2122 (machvec) in a generic kernel.
2123 Example: machvec=hpzx1_swiotlb
2125 machtype= [Loongson] Share the same kernel image file between different
2127 Example: machtype=lemote-yeeloong-2f-7inch
2129 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2130 than or equal to this physical address is ignored.
2132 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2133 should make use of. maxcpus=n : n >= 0 limits the
2134 kernel to using 'n' processors. n=0 is a special case,
2135 it is equivalent to "nosmp", which also disables
2138 max_loop= [LOOP] The number of loop block devices that get
2139 (loop.max_loop) unconditionally pre-created at init time. The default
2140 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2141 of statically allocating a predefined number, loop
2142 devices can be requested on-demand with the
2143 /dev/loop-control interface.
2145 mce [X86-32] Machine Check Exception
2147 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2149 md= [HW] RAID subsystems devices and level
2150 See Documentation/md.txt.
2153 Format: <first>,<last>
2154 Specifies range of consoles to be captured by the MDA.
2156 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2157 Amount of memory to be used when the kernel is not able
2158 to see the whole system memory or for test.
2159 [X86] Work as limiting max address. Use together
2160 with memmap= to avoid physical address space collisions.
2161 Without memmap= PCI devices could be placed at addresses
2162 belonging to unused RAM.
2164 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2168 [KNL,SH] Allow user to override the default size for
2169 per-device physically contiguous DMA buffers.
2171 memhp_default_state=online/offline
2172 [KNL] Set the initial state for the memory hotplug
2173 onlining policy. If not specified, the default value is
2174 set according to the
2175 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2177 See Documentation/memory-hotplug.txt.
2179 memmap=exactmap [KNL,X86] Enable setting of an exact
2180 E820 memory map, as specified by the user.
2181 Such memmap=exactmap lines can be constructed based on
2182 BIOS output or other requirements. See the memmap=nn@ss
2185 memmap=nn[KMG]@ss[KMG]
2186 [KNL] Force usage of a specific region of memory.
2187 Region of memory to be used is from ss to ss+nn.
2189 memmap=nn[KMG]#ss[KMG]
2190 [KNL,ACPI] Mark specific memory as ACPI data.
2191 Region of memory to be marked is from ss to ss+nn.
2193 memmap=nn[KMG]$ss[KMG]
2194 [KNL,ACPI] Mark specific memory as reserved.
2195 Region of memory to be reserved is from ss to ss+nn.
2196 Example: Exclude memory from 0x18690000-0x1869ffff
2197 memmap=64K$0x18690000
2199 memmap=0x10000$0x18690000
2201 memmap=nn[KMG]!ss[KMG]
2202 [KNL,X86] Mark specific memory as protected.
2203 Region of memory to be used, from ss to ss+nn.
2204 The memory region may be marked as e820 type 12 (0xc)
2205 and is NVDIMM or ADR memory.
2207 memory_corruption_check=0/1 [X86]
2208 Some BIOSes seem to corrupt the first 64k of
2209 memory when doing things like suspend/resume.
2210 Setting this option will scan the memory
2211 looking for corruption. Enabling this will
2212 both detect corruption and prevent the kernel
2213 from using the memory being corrupted.
2214 However, its intended as a diagnostic tool; if
2215 repeatable BIOS-originated corruption always
2216 affects the same memory, you can use memmap=
2217 to prevent the kernel from using that memory.
2219 memory_corruption_check_size=size [X86]
2220 By default it checks for corruption in the low
2221 64k, making this memory unavailable for normal
2222 use. Use this parameter to scan for
2223 corruption in more or less memory.
2225 memory_corruption_check_period=seconds [X86]
2226 By default it checks for corruption every 60
2227 seconds. Use this parameter to check at some
2228 other rate. 0 disables periodic checking.
2230 memtest= [KNL,X86,ARM] Enable memtest
2232 default : 0 <disable>
2233 Specifies the number of memtest passes to be
2234 performed. Each pass selects another test
2235 pattern from a given set of patterns. Memtest
2236 fills the memory with this pattern, validates
2237 memory contents and reserves bad memory
2238 regions that are detected.
2240 meye.*= [HW] Set MotionEye Camera parameters
2241 See Documentation/video4linux/meye.txt.
2243 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2244 Multi-Function General Purpose Timers on AMD Geode
2247 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2248 the BIOS has incorrectly applied a workaround. TinyBIOS
2249 version 0.98 is known to be affected, 0.99 fixes the
2250 problem by letting the user disable the workaround.
2254 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2255 physical address is ignored.
2257 mini2440= [ARM,HW,KNL]
2258 Format:[0..2][b][c][t]
2260 MINI2440 configuration specification:
2261 0 - The attached screen is the 3.5" TFT
2262 1 - The attached screen is the 7" TFT
2263 2 - The VGA Shield is attached (1024x768)
2264 Leaving out the screen size parameter will not load
2265 the TFT driver, and the framebuffer will be left
2267 b - Enable backlight. The TFT backlight pin will be
2268 linked to the kernel VESA blanking code and a GPIO
2269 LED. This parameter is not necessary when using the
2271 c - Enable the s3c camera interface.
2272 t - Reserved for enabling touchscreen support. The
2273 touchscreen support is not enabled in the mainstream
2274 kernel as of 2.6.30, a preliminary port can be found
2275 in the "bleeding edge" mini2440 support kernel at
2276 http://repo.or.cz/w/linux-2.6/mini2440.git
2279 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2280 parameter allows control of the logging verbosity for
2281 the additional memory initialisation checks. A value
2282 of 0 disables mminit logging and a level of 4 will
2283 log everything. Information is printed at KERN_DEBUG
2284 so loglevel=8 may also need to be specified.
2287 [KNL] When CONFIG_MODULE_SIG is set, this means that
2288 modules without (valid) signatures will fail to load.
2289 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2290 is always true, so this option does nothing.
2293 [MOUSE] Maximum time between finger touching and
2294 leaving touchpad surface for touch to be considered
2295 a tap and be reported as a left button click (for
2296 touchpads working in absolute mode only).
2298 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2299 reporting absolute coordinates, such as tablets
2300 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2301 reporting absolute coordinates, such as tablets
2303 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2304 is similar to kernelcore except it specifies the
2305 amount of memory used for migratable allocations.
2306 If both kernelcore and movablecore is specified,
2307 then kernelcore will be at *least* the specified
2308 value but may be more. If movablecore on its own
2309 is specified, the administrator must be careful
2310 that the amount of memory usable for all allocations
2313 movable_node [KNL,X86] Boot-time switch to enable the effects
2314 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2316 MTD_Partition= [MTD]
2317 Format: <name>,<region-number>,<size>,<offset>
2319 MTD_Region= [MTD] Format:
2320 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2323 See drivers/mtd/cmdlinepart.c.
2325 multitce=off [PPC] This parameter disables the use of the pSeries
2326 firmware feature for updating multiple TCE entries
2329 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2331 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2333 boundary - index of last SLC block on Flex-OneNAND.
2334 The remaining blocks are configured as MLC blocks.
2335 lock - Configure if Flex-OneNAND boundary should be locked.
2336 Once locked, the boundary cannot be changed.
2337 1 indicates lock status, 0 indicates unlock status.
2340 ARM/S3C2412 JIVE boot control
2342 See arch/arm/mach-s3c2412/mach-jive.c
2344 mtouchusb.raw_coordinates=
2345 [HW] Make the MicroTouch USB driver use raw coordinates
2346 ('y', default) or cooked coordinates ('n')
2348 mtrr_chunk_size=nn[KMG] [X86]
2349 used for mtrr cleanup. It is largest continuous chunk
2350 that could hold holes aka. UC entries.
2352 mtrr_gran_size=nn[KMG] [X86]
2353 Used for mtrr cleanup. It is granularity of mtrr block.
2355 Large value could prevent small alignment from
2358 mtrr_spare_reg_nr=n [X86]
2360 Range: 0,7 : spare reg number
2362 Used for mtrr cleanup. It is spare mtrr entries number.
2363 Set to 2 or more if your graphical card needs more.
2365 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2367 netdev= [NET] Network devices parameters
2368 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2369 Note that mem_start is often overloaded to mean
2370 something different and driver-specific.
2371 This usage is only documented in each driver source
2375 [NETFILTER] Enable connection tracking flow accounting
2376 0 to disable accounting
2377 1 to enable accounting
2380 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2381 See Documentation/filesystems/nfs/nfsroot.txt.
2383 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2384 See Documentation/filesystems/nfs/nfsroot.txt.
2386 nfsrootdebug [NFS] enable nfsroot debugging messages.
2387 See Documentation/filesystems/nfs/nfsroot.txt.
2389 nfs.callback_tcpport=
2390 [NFS] set the TCP port on which the NFSv4 callback
2391 channel should listen.
2394 [NFS] sets the pathname to the program which is used
2395 to update the NFS client cache entries.
2397 nfs.cache_getent_timeout=
2398 [NFS] sets the timeout after which an attempt to
2399 update a cache entry is deemed to have failed.
2401 nfs.idmap_cache_timeout=
2402 [NFS] set the maximum lifetime for idmapper cache
2406 [NFS] enable 64-bit inode numbers.
2407 If zero, the NFS client will fake up a 32-bit inode
2408 number for the readdir() and stat() syscalls instead
2409 of returning the full 64-bit number.
2410 The default is to return 64-bit inode numbers.
2412 nfs.max_session_slots=
2413 [NFSv4.1] Sets the maximum number of session slots
2414 the client will attempt to negotiate with the server.
2415 This limits the number of simultaneous RPC requests
2416 that the client can send to the NFSv4.1 server.
2417 Note that there is little point in setting this
2418 value higher than the max_tcp_slot_table_limit.
2420 nfs.nfs4_disable_idmapping=
2421 [NFSv4] When set to the default of '1', this option
2422 ensures that both the RPC level authentication
2423 scheme and the NFS level operations agree to use
2424 numeric uids/gids if the mount is using the
2425 'sec=sys' security flavour. In effect it is
2426 disabling idmapping, which can make migration from
2427 legacy NFSv2/v3 systems to NFSv4 easier.
2428 Servers that do not support this mode of operation
2429 will be autodetected by the client, and it will fall
2430 back to using the idmapper.
2431 To turn off this behaviour, set the value to '0'.
2433 [NFS4] Specify an additional fixed unique ident-
2434 ification string that NFSv4 clients can insert into
2435 their nfs_client_id4 string. This is typically a
2436 UUID that is generated at system install time.
2438 nfs.send_implementation_id =
2439 [NFSv4.1] Send client implementation identification
2440 information in exchange_id requests.
2441 If zero, no implementation identification information
2443 The default is to send the implementation identification
2446 nfs.recover_lost_locks =
2447 [NFSv4] Attempt to recover locks that were lost due
2448 to a lease timeout on the server. Please note that
2449 doing this risks data corruption, since there are
2450 no guarantees that the file will remain unchanged
2451 after the locks are lost.
2452 If you want to enable the kernel legacy behaviour of
2453 attempting to recover these locks, then set this
2455 The default parameter value of '0' causes the kernel
2456 not to attempt recovery of lost locks.
2458 nfs4.layoutstats_timer =
2459 [NFSv4.2] Change the rate at which the kernel sends
2460 layoutstats to the pNFS metadata server.
2462 Setting this to value to 0 causes the kernel to use
2463 whatever value is the default set by the layout
2464 driver. A non-zero value sets the minimum interval
2465 in seconds between layoutstats transmissions.
2467 nfsd.nfs4_disable_idmapping=
2468 [NFSv4] When set to the default of '1', the NFSv4
2469 server will return only numeric uids and gids to
2470 clients using auth_sys, and will accept numeric uids
2471 and gids from such clients. This is intended to ease
2472 migration from NFSv2/v3.
2474 objlayoutdriver.osd_login_prog=
2475 [NFS] [OBJLAYOUT] sets the pathname to the program which
2476 is used to automatically discover and login into new
2477 osd-targets. Please see:
2478 Documentation/filesystems/pnfs.txt for more explanations
2480 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2481 when a NMI is triggered.
2482 Format: [state][,regs][,debounce][,die]
2484 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2485 Format: [panic,][nopanic,][num]
2487 0 - turn hardlockup detector in nmi_watchdog off
2488 1 - turn hardlockup detector in nmi_watchdog on
2489 When panic is specified, panic when an NMI watchdog
2490 timeout occurs (or 'nopanic' to override the opposite
2491 default). To disable both hard and soft lockup detectors,
2492 please see 'nowatchdog'.
2493 This is useful when you use a panic=... timeout and
2494 need the box quickly up again.
2496 netpoll.carrier_timeout=
2497 [NET] Specifies amount of time (in seconds) that
2498 netpoll should wait for a carrier. By default netpoll
2501 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2502 emulation library even if a 387 maths coprocessor
2506 [HW] Never suspend the console
2507 Disable suspending of consoles during suspend and
2508 hibernate operations. Once disabled, debugging
2509 messages can reach various consoles while the rest
2510 of the system is being put to sleep (ie, while
2511 debugging driver suspend/resume hooks). This may
2512 not work reliably with all consoles, but is known
2513 to work with serial and VGA consoles.
2514 To facilitate more flexible debugging, we also add
2515 console_suspend, a printk module parameter to control
2516 it. Users could use console_suspend (usually
2517 /sys/module/printk/parameters/console_suspend) to
2518 turn on/off it dynamically.
2520 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2521 caches in the slab allocator. Saves per-node memory,
2522 but will impact performance.
2526 noapic [SMP,APIC] Tells the kernel to not make use of any
2527 IOAPICs that may be present in the system.
2529 noautogroup Disable scheduler automatic task group creation.
2531 nobats [PPC] Do not use BATs for mapping kernel lowmem
2532 on "Classic" PPC cores.
2536 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2538 nodelayacct [KNL] Disable per-task delay accounting
2540 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2542 nodsp [SH] Disable hardware DSP at boot time.
2544 noefi Disable EFI runtime services support.
2549 On X86-32 available only on PAE configured kernels.
2550 noexec=on: enable non-executable mappings (default)
2551 noexec=off: disable non-executable mappings
2554 Disable SMAP (Supervisor Mode Access Prevention)
2555 even if it is supported by processor.
2558 Disable SMEP (Supervisor Mode Execution Prevention)
2559 even if it is supported by processor.
2562 This affects only 32-bit executables.
2563 noexec32=on: enable non-executable mappings (default)
2564 read doesn't imply executable mappings
2565 noexec32=off: disable non-executable mappings
2566 read implies executable mappings
2568 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2570 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2571 register save and restore. The kernel will only save
2572 legacy floating-point registers on task switch.
2574 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2576 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2577 Equivalent to smt=1.
2579 noxsave [BUGS=X86] Disables x86 extended register state save
2580 and restore using xsave. The kernel will fallback to
2581 enabling legacy floating-point and sse state.
2583 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2584 register states. The kernel will fall back to use
2585 xsave to save the states. By using this parameter,
2586 performance of saving the states is degraded because
2587 xsave doesn't support modified optimization while
2588 xsaveopt supports it on xsaveopt enabled systems.
2590 noxsaves [X86] Disables xsaves and xrstors used in saving and
2591 restoring x86 extended register state in compacted
2592 form of xsave area. The kernel will fall back to use
2593 xsaveopt and xrstor to save and restore the states
2594 in standard form of xsave area. By using this
2595 parameter, xsave area per process might occupy more
2596 memory on xsaves enabled systems.
2598 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2599 wfi(ARM) instruction doesn't work correctly and not to
2600 use it. This is also useful when using JTAG debugger.
2602 no_file_caps Tells the kernel not to honor file capabilities. The
2603 only way then for a file to be executed with privilege
2604 is to be setuid root or executed by root.
2606 nohalt [IA-64] Tells the kernel not to use the power saving
2607 function PAL_HALT_LIGHT when idle. This increases
2608 power-consumption. On the positive side, it reduces
2609 interrupt wake-up latency, which may improve performance
2610 in certain environments such as networked servers or
2613 nohibernate [HIBERNATION] Disable hibernation and resume.
2615 nohz= [KNL] Boottime enable/disable dynamic ticks
2616 Valid arguments: on, off
2619 nohz_full= [KNL,BOOT]
2620 In kernels built with CONFIG_NO_HZ_FULL=y, set
2621 the specified list of CPUs whose tick will be stopped
2622 whenever possible. The boot CPU will be forced outside
2623 the range to maintain the timekeeping.
2624 The CPUs in this range must also be included in the
2627 noiotrap [SH] Disables trapped I/O port accesses.
2629 noirqdebug [X86-32] Disables the code which attempts to detect and
2630 disable unhandled interrupt sources.
2632 no_timer_check [X86,APIC] Disables the code which tests for
2633 broken timer IRQ sources.
2635 noisapnp [ISAPNP] Disables ISA PnP code.
2637 noinitrd [RAM] Tells the kernel not to load any configured
2640 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2642 [Deprecated - use intremap=off]
2646 noinvpcid [X86] Disable the INVPCID cpu feature.
2648 nojitter [IA-64] Disables jitter checking for ITC timers.
2650 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2652 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2655 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2656 steal time is computed, but won't influence scheduler
2659 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2661 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2663 noltlbs [PPC] Do not use large page/tlb entries for kernel
2664 lowmem mapping on PPC40x and PPC8xx
2666 nomca [IA-64] Disable machine check abort handling
2668 nomce [X86-32] Disable Machine Check Exception
2670 nomfgpt [X86-32] Disable Multi-Function General Purpose
2671 Timer usage (for AMD Geode machines).
2673 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2674 shutdown the other cpus. Instead use the REBOOT_VECTOR
2677 nomodule Disable module load
2679 nopat [X86] Disable PAT (page attribute table extension of
2680 pagetables) support.
2682 norandmaps Don't use address space randomization. Equivalent to
2683 echo 0 > /proc/sys/kernel/randomize_va_space
2685 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2687 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2688 with UP alternatives
2690 nordrand [X86] Disable kernel use of the RDRAND and
2691 RDSEED instructions even if they are supported
2692 by the processor. RDRAND and RDSEED are still
2693 available to user space applications.
2695 noresume [SWSUSP] Disables resume and restores original swap
2698 no-scroll [VGA] Disables scrollback.
2699 This is required for the Braillex ib80-piezo Braille
2700 reader made by F.H. Papenmeier (Germany).
2704 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2706 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2707 and disable the IO APIC. legacy for "maxcpus=0".
2709 nosoftlockup [KNL] Disable the soft-lockup detector.
2711 nosync [HW,M68K] Disables sync negotiation for all devices.
2713 notsc [BUGS=X86-32] Disable Time Stamp Counter
2715 nowatchdog [KNL] Disable both lockup detectors, i.e.
2716 soft-lockup and NMI watchdog (hard-lockup).
2720 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2722 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2723 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2724 Some features depend on CPU0. Known dependencies are:
2725 1. Resume from suspend/hibernate depends on CPU0.
2726 Suspend/hibernate will fail if CPU0 is offline and you
2727 need to online CPU0 before suspend/hibernate.
2728 2. PIC interrupts also depend on CPU0. CPU0 can't be
2729 removed if a PIC interrupt is detected.
2730 It's said poweroff/reboot may depend on CPU0 on some
2731 machines although I haven't seen such issues so far
2732 after CPU0 is offline on a few tested machines.
2733 If the dependencies are under your control, you can
2734 turn on cpu0_hotplug.
2736 nptcg= [IA-64] Override max number of concurrent global TLB
2737 purges which is reported from either PAL_VM_SUMMARY or
2740 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2741 could support. nr_cpus=n : n >= 1 limits the kernel to
2742 supporting 'n' processors. Later in runtime you can not
2743 use hotplug cpu feature to put more cpu back to online.
2744 just like you compile the kernel NR_CPUS=n
2746 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2748 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2749 Allowed values are enable and disable
2751 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2752 one of ['zone', 'node', 'default'] can be specified
2753 This can be set from sysctl after boot.
2754 See Documentation/sysctl/vm.txt for details.
2756 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2757 See Documentation/debugging-via-ohci1394.txt for more
2760 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2761 Rather than timing out after 20 ms if an EC
2762 command is not properly ACKed, override the length
2763 of the timeout. We have interrupts disabled while
2764 waiting for the ACK, so if this is set too high
2765 interrupts *may* be lost!
2767 omap_mux= [OMAP] Override bootloader pin multiplexing.
2768 Format: <mux_mode0.mode_name=value>...
2769 For example, to override I2C bus2:
2770 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2772 oprofile.timer= [HW]
2773 Use timer interrupt instead of performance counters
2775 oprofile.cpu_type= Force an oprofile cpu type
2776 This might be useful if you have an older oprofile
2777 userland or if you want common events.
2778 Format: { arch_perfmon }
2779 arch_perfmon: [X86] Force use of architectural
2780 perfmon on Intel CPUs instead of the
2781 CPU specific event set.
2782 timer: [X86] Force use of architectural NMI
2783 timer mode (see also oprofile.timer
2784 for generic hr timer mode)
2785 [s390] Force legacy basic mode sampling
2786 (report cpu_type "timer")
2788 oops=panic Always panic on oopses. Default is to just kill the
2789 process, but there is a small probability of
2790 deadlocking the machine.
2791 This will also cause panics on machine check exceptions.
2792 Useful together with panic=30 to trigger a reboot.
2795 See Documentation/sound/oss/oss-parameters.txt
2797 page_owner= [KNL] Boot-time page_owner enabling option.
2798 Storage of the information about who allocated
2799 each page is disabled in default. With this switch,
2801 on: enable the feature
2803 page_poison= [KNL] Boot-time parameter changing the state of
2804 poisoning on the buddy allocator.
2805 off: turn off poisoning
2806 on: turn on poisoning
2808 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2809 timeout > 0: seconds before rebooting
2810 timeout = 0: wait forever
2811 timeout < 0: reboot immediately
2814 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2817 crash_kexec_post_notifiers
2818 Run kdump after running panic-notifiers and dumping
2819 kmsg. This only for the users who doubt kdump always
2820 succeeds in any situation.
2821 Note that this also increases risks of kdump failure,
2822 because some panic notifiers can make the crashed
2823 kernel more unstable.
2825 parkbd.port= [HW] Parallel port number the keyboard adapter is
2826 connected to, default is 0.
2828 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2829 0 for XT, 1 for AT (default is AT).
2832 parport= [HW,PPT] Specify parallel ports. 0 disables.
2833 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2834 Use 'auto' to force the driver to use any
2835 IRQ/DMA settings detected (the default is to
2836 ignore detected IRQ/DMA settings because of
2837 possible conflicts). You can specify the base
2838 address, IRQ, and DMA settings; IRQ and DMA
2839 should be numbers, or 'auto' (for using detected
2840 settings on that particular port), or 'nofifo'
2841 (to avoid using a FIFO even if it is detected).
2842 Parallel ports are assigned in the order they
2843 are specified on the command line, starting
2846 parport_init_mode= [HW,PPT]
2847 Configure VIA parallel port to operate in
2848 a specific mode. This is necessary on Pegasos
2849 computer where firmware has no options for setting
2850 up parallel port mode and sets it to spp.
2851 Currently this function knows 686a and 8231 chips.
2852 Format: [spp|ps2|epp|ecp|ecpepp]
2855 Halt all CPUs after the first oops has been printed for
2856 the specified number of seconds. This is to be used if
2857 your oopses keep scrolling off the screen.
2862 See header of drivers/block/paride/pcd.c.
2863 See also Documentation/blockdev/paride.txt.
2865 pci=option[,option...] [PCI] various PCI subsystem options:
2866 earlydump [X86] dump PCI config space before the kernel
2868 off [X86] don't probe for the PCI bus
2869 bios [X86-32] force use of PCI BIOS, don't access
2870 the hardware directly. Use this if your machine
2871 has a non-standard PCI host bridge.
2872 nobios [X86-32] disallow use of PCI BIOS, only direct
2873 hardware access methods are allowed. Use this
2874 if you experience crashes upon bootup and you
2875 suspect they are caused by the BIOS.
2876 conf1 [X86] Force use of PCI Configuration Access
2877 Mechanism 1 (config address in IO port 0xCF8,
2878 data in IO port 0xCFC, both 32-bit).
2879 conf2 [X86] Force use of PCI Configuration Access
2880 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2881 the function, IO port 0xCFA, also 8-bit, sets
2882 bus number. The config space is then accessed
2883 through ports 0xC000-0xCFFF).
2884 See http://wiki.osdev.org/PCI for more info
2885 on the configuration access mechanisms.
2886 noaer [PCIE] If the PCIEAER kernel config parameter is
2887 enabled, this kernel boot option can be used to
2888 disable the use of PCIE advanced error reporting.
2889 nodomains [PCI] Disable support for multiple PCI
2890 root domains (aka PCI segments, in ACPI-speak).
2891 nommconf [X86] Disable use of MMCONFIG for PCI
2893 check_enable_amd_mmconf [X86] check for and enable
2894 properly configured MMIO access to PCI
2895 config space on AMD family 10h CPU
2896 nomsi [MSI] If the PCI_MSI kernel config parameter is
2897 enabled, this kernel boot option can be used to
2898 disable the use of MSI interrupts system-wide.
2899 noioapicquirk [APIC] Disable all boot interrupt quirks.
2900 Safety option to keep boot IRQs enabled. This
2901 should never be necessary.
2902 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2903 primary IO-APIC for bridges that cannot disable
2904 boot IRQs. This fixes a source of spurious IRQs
2905 when the system masks IRQs.
2906 noioapicreroute [APIC] Disable workaround that uses the
2907 boot IRQ equivalent of an IRQ that connects to
2908 a chipset where boot IRQs cannot be disabled.
2909 The opposite of ioapicreroute.
2910 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2911 routing table. These calls are known to be buggy
2912 on several machines and they hang the machine
2913 when used, but on other computers it's the only
2914 way to get the interrupt routing table. Try
2915 this option if the kernel is unable to allocate
2916 IRQs or discover secondary PCI buses on your
2918 rom [X86] Assign address space to expansion ROMs.
2919 Use with caution as certain devices share
2920 address decoders between ROMs and other
2922 norom [X86] Do not assign address space to
2923 expansion ROMs that do not already have
2924 BIOS assigned address ranges.
2925 nobar [X86] Do not assign address space to the
2926 BARs that weren't assigned by the BIOS.
2927 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2928 assigned automatically to PCI devices. You can
2929 make the kernel exclude IRQs of your ISA cards
2931 pirqaddr=0xAAAAA [X86] Specify the physical address
2932 of the PIRQ table (normally generated
2933 by the BIOS) if it is outside the
2934 F0000h-100000h range.
2935 lastbus=N [X86] Scan all buses thru bus #N. Can be
2936 useful if the kernel is unable to find your
2937 secondary buses and you want to tell it
2938 explicitly which ones they are.
2939 assign-busses [X86] Always assign all PCI bus
2940 numbers ourselves, overriding
2941 whatever the firmware may have done.
2942 usepirqmask [X86] Honor the possible IRQ mask stored
2943 in the BIOS $PIR table. This is needed on
2944 some systems with broken BIOSes, notably
2945 some HP Pavilion N5400 and Omnibook XE3
2946 notebooks. This will have no effect if ACPI
2947 IRQ routing is enabled.
2948 noacpi [X86] Do not use ACPI for IRQ routing
2949 or for PCI scanning.
2950 use_crs [X86] Use PCI host bridge window information
2951 from ACPI. On BIOSes from 2008 or later, this
2952 is enabled by default. If you need to use this,
2953 please report a bug.
2954 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2955 If you need to use this, please report a bug.
2956 routeirq Do IRQ routing for all PCI devices.
2957 This is normally done in pci_enable_device(),
2958 so this option is a temporary workaround
2959 for broken drivers that don't call it.
2960 skip_isa_align [X86] do not align io start addr, so can
2961 handle more pci cards
2962 firmware [ARM] Do not re-enumerate the bus but instead
2963 just use the configuration from the
2964 bootloader. This is currently used on
2965 IXP2000 systems where the bus has to be
2966 configured a certain way for adjunct CPUs.
2967 noearly [X86] Don't do any early type 1 scanning.
2968 This might help on some broken boards which
2969 machine check when some devices' config space
2970 is read. But various workarounds are disabled
2971 and some IOMMU drivers will not work.
2972 bfsort Sort PCI devices into breadth-first order.
2973 This sorting is done to get a device
2974 order compatible with older (<= 2.4) kernels.
2975 nobfsort Don't sort PCI devices into breadth-first order.
2976 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2977 tuning and use the BIOS-configured MPS defaults.
2978 pcie_bus_safe Set every device's MPS to the largest value
2979 supported by all devices below the root complex.
2980 pcie_bus_perf Set device MPS to the largest allowable MPS
2981 based on its parent bus. Also set MRRS (Max
2982 Read Request Size) to the largest supported
2983 value (no larger than the MPS that the device
2984 or bus can support) for best performance.
2985 pcie_bus_peer2peer Set every device's MPS to 128B, which
2986 every device is guaranteed to support. This
2987 configuration allows peer-to-peer DMA between
2988 any pair of devices, possibly at the cost of
2989 reduced performance. This also guarantees
2990 that hot-added devices will work.
2991 cbiosize=nn[KMG] The fixed amount of bus space which is
2992 reserved for the CardBus bridge's IO window.
2993 The default value is 256 bytes.
2994 cbmemsize=nn[KMG] The fixed amount of bus space which is
2995 reserved for the CardBus bridge's memory
2996 window. The default value is 64 megabytes.
2999 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3000 Specifies alignment and device to reassign
3001 aligned memory resources.
3002 If <order of align> is not specified,
3003 PAGE_SIZE is used as alignment.
3004 PCI-PCI bridge can be specified, if resource
3005 windows need to be expanded.
3006 ecrc= Enable/disable PCIe ECRC (transaction layer
3007 end-to-end CRC checking).
3008 bios: Use BIOS/firmware settings. This is the
3012 hpiosize=nn[KMG] The fixed amount of bus space which is
3013 reserved for hotplug bridge's IO window.
3014 Default size is 256 bytes.
3015 hpmemsize=nn[KMG] The fixed amount of bus space which is
3016 reserved for hotplug bridge's memory window.
3017 Default size is 2 megabytes.
3018 realloc= Enable/disable reallocating PCI bridge resources
3019 if allocations done by BIOS are too small to
3020 accommodate resources required by all child
3022 off: Turn realloc off
3024 realloc same as realloc=on
3025 noari do not use PCIe ARI.
3026 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3027 only look for one device below a PCIe downstream
3030 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3033 force Enable ASPM even on devices that claim not to support it.
3034 WARNING: Forcing ASPM on may cause system lockups.
3036 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3037 nomsi Do not use MSI for PCI Express Native Hotplug (this
3038 makes all PCIe ports use INTx for hotplug services).
3040 pcie_ports= [PCIE] PCIe ports handling:
3041 auto Ask the BIOS whether or not to use native PCIe services
3042 associated with PCIe ports (PME, hot-plug, AER). Use
3043 them only if that is allowed by the BIOS.
3044 native Use native PCIe services associated with PCIe ports
3046 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3049 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3050 nomsi Do not use MSI for native PCIe PME signaling (this makes
3051 all PCIe root ports use INTx for all services).
3053 pcmv= [HW,PCMCIA] BadgePAD 4
3057 Keep all power-domains already enabled by bootloader on,
3058 even if no driver has claimed them. This is useful
3059 for debug and development, but should not be
3060 needed on a platform with proper driver support.
3063 See Documentation/blockdev/paride.txt.
3065 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3068 See arch/parisc/kernel/pdc_chassis.c
3070 percpu_alloc= Select which percpu first chunk allocator to use.
3071 Currently supported values are "embed" and "page".
3072 Archs may support subset or none of the selections.
3073 See comments in mm/percpu.c for details on each
3074 allocator. This parameter is primarily for debugging
3075 and performance comparison.
3078 See Documentation/blockdev/paride.txt.
3081 See Documentation/blockdev/paride.txt.
3083 pirq= [SMP,APIC] Manual mp-table setup
3084 See Documentation/x86/i386/IO-APIC.txt.
3086 plip= [PPT,NET] Parallel port network link
3087 Format: { parport<nr> | timid | 0 }
3088 See also Documentation/parport.txt.
3090 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3091 Override pmtimer IOPort with a hex value.
3095 Enable PNP debug messages (depends on the
3096 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3097 via /sys/module/pnp/parameters/debug. We always show
3098 current resource usage; turning this on also shows
3099 possible settings and some assignment information.
3105 { on | off | curr | res | no-curr | no-res }
3108 [ISAPNP] Exclude IRQs for the autoconfiguration
3111 [ISAPNP] Exclude DMAs for the autoconfiguration
3113 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3114 Ranges are in pairs (I/O port base and size).
3117 [ISAPNP] Exclude memory regions for the
3119 Ranges are in pairs (memory base and size).
3121 ports= [IP_VS_FTP] IPVS ftp helper module
3123 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3125 Format: <port>,<port>....
3127 ppc_strict_facility_enable
3128 [PPC] This option catches any kernel floating point,
3129 Altivec, VSX and SPE outside of regions specifically
3130 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3131 There is some performance impact when enabling this.
3133 print-fatal-signals=
3134 [KNL] debug: print fatal signals
3136 If enabled, warn about various signal handling
3137 related application anomalies: too many signals,
3138 too many POSIX.1 timers, fatal signals causing a
3141 If you hit the warning due to signal overflow,
3142 you might want to try "ulimit -i unlimited".
3146 printk.always_kmsg_dump=
3147 Trigger kmsg_dump for cases other than kernel oops or
3149 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3152 printk.time= Show timing data prefixed to each printk message line
3153 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3155 processor.max_cstate= [HW,ACPI]
3156 Limit processor to maximum C-state
3157 max_cstate=9 overrides any DMI blacklist limit.
3159 processor.nocst [HW,ACPI]
3160 Ignore the _CST method to determine C-states,
3161 instead using the legacy FADT method
3163 profile= [KNL] Enable kernel profiling via /proc/profile
3164 Format: [schedule,]<number>
3165 Param: "schedule" - profile schedule points.
3166 Param: <number> - step/bucket size as a power of 2 for
3167 statistical time based profiling.
3168 Param: "sleep" - profile D-state sleeping (millisecs).
3169 Requires CONFIG_SCHEDSTATS
3170 Param: "kvm" - profile VM exits.
3172 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3174 See Documentation/blockdev/ramdisk.txt.
3176 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3177 probe for; one of (bare|imps|exps|lifebook|any).
3178 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3180 psmouse.resetafter= [HW,MOUSE]
3181 Try to reset the device after so many bad packets
3184 [HW,MOUSE] Set desired mouse resolution, in dpi.
3185 psmouse.smartscroll=
3186 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3187 0 = disabled, 1 = enabled (default).
3189 pstore.backend= Specify the name of the pstore backend to use
3192 See Documentation/blockdev/paride.txt.
3195 [KNL] Number of legacy pty's. Overwrites compiled-in
3198 quiet [KNL] Disable most log messages
3203 See Documentation/md.txt.
3205 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3206 See Documentation/blockdev/ramdisk.txt.
3209 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3210 the specified list of CPUs to be no-callback CPUs.
3211 Invocation of these CPUs' RCU callbacks will
3212 be offloaded to "rcuox/N" kthreads created for
3213 that purpose, where "x" is "b" for RCU-bh, "p"
3214 for RCU-preempt, and "s" for RCU-sched, and "N"
3215 is the CPU number. This reduces OS jitter on the
3216 offloaded CPUs, which can be useful for HPC and
3217 real-time workloads. It can also improve energy
3218 efficiency for asymmetric multiprocessors.
3221 Rather than requiring that offloaded CPUs
3222 (specified by rcu_nocbs= above) explicitly
3223 awaken the corresponding "rcuoN" kthreads,
3224 make these kthreads poll for callbacks.
3225 This improves the real-time response for the
3226 offloaded CPUs by relieving them of the need to
3227 wake up the corresponding kthread, but degrades
3228 energy efficiency by requiring that the kthreads
3229 periodically wake up to do the polling.
3231 rcutree.blimit= [KNL]
3232 Set maximum number of finished RCU callbacks to
3233 process in one batch.
3235 rcutree.dump_tree= [KNL]
3236 Dump the structure of the rcu_node combining tree
3237 out at early boot. This is used for diagnostic
3238 purposes, to verify correct tree setup.
3240 rcutree.gp_cleanup_delay= [KNL]
3241 Set the number of jiffies to delay each step of
3242 RCU grace-period cleanup. This only has effect
3243 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3245 rcutree.gp_init_delay= [KNL]
3246 Set the number of jiffies to delay each step of
3247 RCU grace-period initialization. This only has
3248 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3251 rcutree.gp_preinit_delay= [KNL]
3252 Set the number of jiffies to delay each step of
3253 RCU grace-period pre-initialization, that is,
3254 the propagation of recent CPU-hotplug changes up
3255 the rcu_node combining tree. This only has effect
3256 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3258 rcutree.rcu_fanout_exact= [KNL]
3259 Disable autobalancing of the rcu_node combining
3260 tree. This is used by rcutorture, and might
3261 possibly be useful for architectures having high
3262 cache-to-cache transfer latencies.
3264 rcutree.rcu_fanout_leaf= [KNL]
3265 Change the number of CPUs assigned to each
3266 leaf rcu_node structure. Useful for very
3267 large systems, which will choose the value 64,
3268 and for NUMA systems with large remote-access
3269 latencies, which will choose a value aligned
3270 with the appropriate hardware boundaries.
3272 rcutree.jiffies_till_sched_qs= [KNL]
3273 Set required age in jiffies for a
3274 given grace period before RCU starts
3275 soliciting quiescent-state help from
3276 rcu_note_context_switch().
3278 rcutree.jiffies_till_first_fqs= [KNL]
3279 Set delay from grace-period initialization to
3280 first attempt to force quiescent states.
3281 Units are jiffies, minimum value is zero,
3282 and maximum value is HZ.
3284 rcutree.jiffies_till_next_fqs= [KNL]
3285 Set delay between subsequent attempts to force
3286 quiescent states. Units are jiffies, minimum
3287 value is one, and maximum value is HZ.
3289 rcutree.kthread_prio= [KNL,BOOT]
3290 Set the SCHED_FIFO priority of the RCU per-CPU
3291 kthreads (rcuc/N). This value is also used for
3292 the priority of the RCU boost threads (rcub/N)
3293 and for the RCU grace-period kthreads (rcu_bh,
3294 rcu_preempt, and rcu_sched). If RCU_BOOST is
3295 set, valid values are 1-99 and the default is 1
3296 (the least-favored priority). Otherwise, when
3297 RCU_BOOST is not set, valid values are 0-99 and
3298 the default is zero (non-realtime operation).
3300 rcutree.rcu_nocb_leader_stride= [KNL]
3301 Set the number of NOCB kthread groups, which
3302 defaults to the square root of the number of
3303 CPUs. Larger numbers reduces the wakeup overhead
3304 on the per-CPU grace-period kthreads, but increases
3305 that same overhead on each group's leader.
3307 rcutree.qhimark= [KNL]
3308 Set threshold of queued RCU callbacks beyond which
3309 batch limiting is disabled.
3311 rcutree.qlowmark= [KNL]
3312 Set threshold of queued RCU callbacks below which
3313 batch limiting is re-enabled.
3315 rcutree.rcu_idle_gp_delay= [KNL]
3316 Set wakeup interval for idle CPUs that have
3317 RCU callbacks (RCU_FAST_NO_HZ=y).
3319 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3320 Set wakeup interval for idle CPUs that have
3321 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3322 Lazy RCU callbacks are those which RCU can
3323 prove do nothing more than free memory.
3325 rcuperf.gp_exp= [KNL]
3326 Measure performance of expedited synchronous
3327 grace-period primitives.
3329 rcuperf.holdoff= [KNL]
3330 Set test-start holdoff period. The purpose of
3331 this parameter is to delay the start of the
3332 test until boot completes in order to avoid
3335 rcuperf.nreaders= [KNL]
3336 Set number of RCU readers. The value -1 selects
3337 N, where N is the number of CPUs. A value
3338 "n" less than -1 selects N-n+1, where N is again
3339 the number of CPUs. For example, -2 selects N
3340 (the number of CPUs), -3 selects N+1, and so on.
3341 A value of "n" less than or equal to -N selects
3344 rcuperf.nwriters= [KNL]
3345 Set number of RCU writers. The values operate
3346 the same as for rcuperf.nreaders.
3347 N, where N is the number of CPUs
3349 rcuperf.perf_runnable= [BOOT]
3350 Start rcuperf running at boot time.
3352 rcuperf.shutdown= [KNL]
3353 Shut the system down after performance tests
3354 complete. This is useful for hands-off automated
3357 rcuperf.perf_type= [KNL]
3358 Specify the RCU implementation to test.
3360 rcuperf.verbose= [KNL]
3361 Enable additional printk() statements.
3363 rcutorture.cbflood_inter_holdoff= [KNL]
3364 Set holdoff time (jiffies) between successive
3365 callback-flood tests.
3367 rcutorture.cbflood_intra_holdoff= [KNL]
3368 Set holdoff time (jiffies) between successive
3369 bursts of callbacks within a given callback-flood
3372 rcutorture.cbflood_n_burst= [KNL]
3373 Set the number of bursts making up a given
3374 callback-flood test. Set this to zero to
3375 disable callback-flood testing.
3377 rcutorture.cbflood_n_per_burst= [KNL]
3378 Set the number of callbacks to be registered
3379 in a given burst of a callback-flood test.
3381 rcutorture.fqs_duration= [KNL]
3382 Set duration of force_quiescent_state bursts
3385 rcutorture.fqs_holdoff= [KNL]
3386 Set holdoff time within force_quiescent_state bursts
3389 rcutorture.fqs_stutter= [KNL]
3390 Set wait time between force_quiescent_state bursts
3393 rcutorture.gp_cond= [KNL]
3394 Use conditional/asynchronous update-side
3395 primitives, if available.
3397 rcutorture.gp_exp= [KNL]
3398 Use expedited update-side primitives, if available.
3400 rcutorture.gp_normal= [KNL]
3401 Use normal (non-expedited) asynchronous
3402 update-side primitives, if available.
3404 rcutorture.gp_sync= [KNL]
3405 Use normal (non-expedited) synchronous
3406 update-side primitives, if available. If all
3407 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3408 rcutorture.gp_normal=, and rcutorture.gp_sync=
3409 are zero, rcutorture acts as if is interpreted
3410 they are all non-zero.
3412 rcutorture.n_barrier_cbs= [KNL]
3413 Set callbacks/threads for rcu_barrier() testing.
3415 rcutorture.nfakewriters= [KNL]
3416 Set number of concurrent RCU writers. These just
3417 stress RCU, they don't participate in the actual
3418 test, hence the "fake".
3420 rcutorture.nreaders= [KNL]
3421 Set number of RCU readers. The value -1 selects
3422 N-1, where N is the number of CPUs. A value
3423 "n" less than -1 selects N-n-2, where N is again
3424 the number of CPUs. For example, -2 selects N
3425 (the number of CPUs), -3 selects N+1, and so on.
3427 rcutorture.object_debug= [KNL]
3428 Enable debug-object double-call_rcu() testing.
3430 rcutorture.onoff_holdoff= [KNL]
3431 Set time (s) after boot for CPU-hotplug testing.
3433 rcutorture.onoff_interval= [KNL]
3434 Set time (s) between CPU-hotplug operations, or
3435 zero to disable CPU-hotplug testing.
3437 rcutorture.shuffle_interval= [KNL]
3438 Set task-shuffle interval (s). Shuffling tasks
3439 allows some CPUs to go into dyntick-idle mode
3440 during the rcutorture test.
3442 rcutorture.shutdown_secs= [KNL]
3443 Set time (s) after boot system shutdown. This
3444 is useful for hands-off automated testing.
3446 rcutorture.stall_cpu= [KNL]
3447 Duration of CPU stall (s) to test RCU CPU stall
3448 warnings, zero to disable.
3450 rcutorture.stall_cpu_holdoff= [KNL]
3451 Time to wait (s) after boot before inducing stall.
3453 rcutorture.stat_interval= [KNL]
3454 Time (s) between statistics printk()s.
3456 rcutorture.stutter= [KNL]
3457 Time (s) to stutter testing, for example, specifying
3458 five seconds causes the test to run for five seconds,
3459 wait for five seconds, and so on. This tests RCU's
3460 ability to transition abruptly to and from idle.
3462 rcutorture.test_boost= [KNL]
3463 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3464 "Maybe" means test if the RCU implementation
3465 under test support RCU priority boosting.
3467 rcutorture.test_boost_duration= [KNL]
3468 Duration (s) of each individual boost test.
3470 rcutorture.test_boost_interval= [KNL]
3471 Interval (s) between each boost test.
3473 rcutorture.test_no_idle_hz= [KNL]
3474 Test RCU's dyntick-idle handling. See also the
3475 rcutorture.shuffle_interval parameter.
3477 rcutorture.torture_runnable= [BOOT]
3478 Start rcutorture running at boot time.
3480 rcutorture.torture_type= [KNL]
3481 Specify the RCU implementation to test.
3483 rcutorture.verbose= [KNL]
3484 Enable additional printk() statements.
3486 rcupdate.rcu_cpu_stall_suppress= [KNL]
3487 Suppress RCU CPU stall warning messages.
3489 rcupdate.rcu_cpu_stall_timeout= [KNL]
3490 Set timeout for RCU CPU stall warning messages.
3492 rcupdate.rcu_expedited= [KNL]
3493 Use expedited grace-period primitives, for
3494 example, synchronize_rcu_expedited() instead
3495 of synchronize_rcu(). This reduces latency,
3496 but can increase CPU utilization, degrade
3497 real-time latency, and degrade energy efficiency.
3498 No effect on CONFIG_TINY_RCU kernels.
3500 rcupdate.rcu_normal= [KNL]
3501 Use only normal grace-period primitives,
3502 for example, synchronize_rcu() instead of
3503 synchronize_rcu_expedited(). This improves
3504 real-time latency, CPU utilization, and
3505 energy efficiency, but can expose users to
3506 increased grace-period latency. This parameter
3507 overrides rcupdate.rcu_expedited. No effect on
3508 CONFIG_TINY_RCU kernels.
3510 rcupdate.rcu_normal_after_boot= [KNL]
3511 Once boot has completed (that is, after
3512 rcu_end_inkernel_boot() has been invoked), use
3513 only normal grace-period primitives. No effect
3514 on CONFIG_TINY_RCU kernels.
3516 rcupdate.rcu_task_stall_timeout= [KNL]
3517 Set timeout in jiffies for RCU task stall warning
3518 messages. Disable with a value less than or equal
3521 rcupdate.rcu_self_test= [KNL]
3522 Run the RCU early boot self tests
3524 rcupdate.rcu_self_test_bh= [KNL]
3525 Run the RCU bh early boot self tests
3527 rcupdate.rcu_self_test_sched= [KNL]
3528 Run the RCU sched early boot self tests
3532 Run specified binary instead of /init from the ramdisk,
3533 used for early userspace startup. See initrd.
3536 Format (x86 or x86_64):
3537 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3539 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3541 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3542 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3543 reboot_force is either force or not specified,
3544 reboot_cpu is s[mp]#### with #### being the processor
3545 to be used for rebooting.
3548 [KNL, SMP] Set scheduler's default relax_domain_level.
3549 See Documentation/cgroups/cpusets.txt.
3551 relative_sleep_states=
3552 [SUSPEND] Use sleep state labeling where the deepest
3553 state available other than hibernation is always "mem".
3554 Format: { "0" | "1" }
3555 0 -- Traditional sleep state labels.
3556 1 -- Relative sleep state labels.
3558 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3560 reservetop= [X86-32]
3562 Reserves a hole at the top of the kernel virtual
3567 Set the amount of memory to reserve for BIOS at
3568 the bottom of the address space.
3570 reset_devices [KNL] Force drivers to reset the underlying device
3571 during initialization.
3574 Specify the partition device for software suspend
3576 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3578 resume_offset= [SWSUSP]
3579 Specify the offset from the beginning of the partition
3580 given by "resume=" at which the swap header is located,
3581 in <PAGE_SIZE> units (needed only for swap files).
3582 See Documentation/power/swsusp-and-swap-files.txt
3584 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3585 read the resume files
3587 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3588 Useful for devices that are detected asynchronously
3589 (e.g. USB and MMC devices).
3591 hibernate= [HIBERNATION]
3592 noresume Don't check if there's a hibernation image
3593 present during boot.
3594 nocompress Don't compress/decompress hibernation images.
3595 no Disable hibernation and resume.
3597 retain_initrd [RAM] Keep initrd memory after extraction
3599 rfkill.default_state=
3600 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3601 etc. communication is blocked by default.
3604 rfkill.master_switch_mode=
3605 0 The "airplane mode" button does nothing.
3606 1 The "airplane mode" button toggles between everything
3607 blocked and the previous configuration.
3608 2 The "airplane mode" button toggles between everything
3609 blocked and everything unblocked.
3611 rhash_entries= [KNL,NET]
3612 Set number of hash buckets for route cache
3614 ro [KNL] Mount root device read-only on boot
3617 on Mark read-only kernel memory as read-only (default).
3618 off Leave read-only kernel memory writable for debugging.
3621 Enable the uart passthrough on the designated usb port
3622 on Rockchip SoCs. When active, the signals of the
3623 debug-uart get routed to the D+ and D- pins of the usb
3624 port and the regular usb controller gets disabled.
3626 root= [KNL] Root filesystem
3627 See name_to_dev_t comment in init/do_mounts.c.
3629 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3630 mount the root filesystem
3632 rootflags= [KNL] Set root filesystem mount option string
3634 rootfstype= [KNL] Set root filesystem type
3636 rootwait [KNL] Wait (indefinitely) for root device to show up.
3637 Useful for devices that are detected asynchronously
3638 (e.g. USB and MMC devices).
3640 rproc_mem=nn[KMG][@address]
3641 [KNL,ARM,CMA] Remoteproc physical memory block.
3642 Memory area to be used by remote processor image,
3645 rw [KNL] Mount root device read-write on boot
3647 S [KNL] Run init in single mode
3649 s390_iommu= [HW,S390]
3650 Set s390 IOTLB flushing mode
3652 With strict flushing every unmap operation will result in
3653 an IOTLB flush. Default is lazy flushing before reuse,
3657 See drivers/net/irda/sa1100_ir.c.
3659 sbni= [NET] Granch SBNI12 leased line adapter
3661 sched_debug [KNL] Enables verbose scheduler debug messages.
3663 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3664 Allowed values are enable and disable. This feature
3665 incurs a small amount of overhead in the scheduler
3666 but is useful for debugging and performance tuning.
3668 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3669 xtime_lock contention on larger systems, and/or RCU lock
3670 contention on all systems with CONFIG_MAXSMP set.
3671 Format: { "0" | "1" }
3672 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3674 Note: increases power consumption, thus should only be
3675 enabled if running jitter sensitive (HPC/RT) workloads.
3677 security= [SECURITY] Choose a security module to enable at boot.
3678 If this boot parameter is not specified, only the first
3679 security module asking for security registration will be
3680 loaded. An invalid security module name will be treated
3681 as if no module has been chosen.
3683 selinux= [SELINUX] Disable or enable SELinux at boot time.
3684 Format: { "0" | "1" }
3685 See security/selinux/Kconfig help text.
3688 Default value is set via kernel config option.
3689 If enabled at boot time, /selinux/disable can be used
3690 later to disable prior to initial policy load.
3692 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3693 Format: { "0" | "1" }
3694 See security/apparmor/Kconfig help text
3697 Default value is set via kernel config option.
3699 serialnumber [BUGS=X86-32]
3702 Maximal number of shapers.
3704 show_msr= [x86] show boot-time MSR settings
3705 Format: { <integer> }
3706 Show boot-time (BIOS-initialized) MSR settings.
3707 The parameter means the number of CPUs to show,
3708 for example 1 means boot CPU only.
3716 Disable merging of slabs with similar size. May be
3717 necessary if there is some reason to distinguish
3718 allocs to different slabs. Debug options disable
3719 merging on their own.
3720 For more information see Documentation/vm/slub.txt.
3722 slab_max_order= [MM, SLAB]
3723 Determines the maximum allowed order for slabs.
3724 A high setting may cause OOMs due to memory
3725 fragmentation. Defaults to 1 for systems with
3726 more than 32MB of RAM, 0 otherwise.
3728 slub_debug[=options[,slabs]] [MM, SLUB]
3729 Enabling slub_debug allows one to determine the
3730 culprit if slab objects become corrupted. Enabling
3731 slub_debug can create guard zones around objects and
3732 may poison objects when not in use. Also tracks the
3733 last alloc / free. For more information see
3734 Documentation/vm/slub.txt.
3736 slub_max_order= [MM, SLUB]
3737 Determines the maximum allowed order for slabs.
3738 A high setting may cause OOMs due to memory
3739 fragmentation. For more information see
3740 Documentation/vm/slub.txt.
3742 slub_min_objects= [MM, SLUB]
3743 The minimum number of objects per slab. SLUB will
3744 increase the slab order up to slub_max_order to
3745 generate a sufficiently large slab able to contain
3746 the number of objects indicated. The higher the number
3747 of objects the smaller the overhead of tracking slabs
3748 and the less frequently locks need to be acquired.
3749 For more information see Documentation/vm/slub.txt.
3751 slub_min_order= [MM, SLUB]
3752 Determines the minimum page order for slabs. Must be
3753 lower than slub_max_order.
3754 For more information see Documentation/vm/slub.txt.
3756 slub_nomerge [MM, SLUB]
3757 Same with slab_nomerge. This is supported for legacy.
3758 See slab_nomerge for more information.
3761 Format: <io1>[,<io2>[,...,<io8>]]
3763 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3764 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3765 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3766 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3767 smsc-ircc2.ircc_irq= [HW] IRQ line
3768 smsc-ircc2.ircc_dma= [HW] DMA channel
3769 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3770 0: Toshiba Satellite 1800 (GP data pin select)
3771 1: Fast pin select (default)
3774 smt [KNL,S390] Set the maximum number of threads (logical
3775 CPUs) to use per physical CPU on systems capable of
3776 symmetric multithreading (SMT). Will be capped to the
3777 actual hardware limit.
3779 Default: -1 (no limit)
3782 [KNL] Should the soft-lockup detector generate panics.
3785 softlockup_all_cpu_backtrace=
3786 [KNL] Should the soft-lockup detector generate
3787 backtraces on all cpus.
3790 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3791 See Documentation/laptops/sonypi.txt
3793 spia_io_base= [HW,MTD]
3799 Enabled the stack tracer on boot up.
3801 stacktrace_filter=[function-list]
3802 [FTRACE] Limit the functions that the stack tracer
3803 will trace at boot up. function-list is a comma separated
3804 list of functions. This list can be changed at run
3805 time by the stack_trace_filter file in the debugfs
3806 tracing directory. Note, this enables stack tracing
3807 and the stacktrace above is not needed.
3811 Set the STI (builtin display/keyboard on the HP-PARISC
3812 machines) console (graphic card) which should be used
3813 as the initial boot-console.
3814 See also comment in drivers/video/console/sticore.c.
3817 See comment in drivers/video/console/sticore.c.
3820 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3822 sunrpc.min_resvport=
3823 sunrpc.max_resvport=
3825 SunRPC servers often require that client requests
3826 originate from a privileged port (i.e. a port in the
3827 range 0 < portnr < 1024).
3828 An administrator who wishes to reserve some of these
3829 ports for other uses may adjust the range that the
3830 kernel's sunrpc client considers to be privileged
3831 using these two parameters to set the minimum and
3832 maximum port values.
3836 Control how the NFS server code allocates CPUs to
3837 service thread pools. Depending on how many NICs
3838 you have and where their interrupts are bound, this
3839 option will affect which CPUs will do NFS serving.
3840 Note: this parameter cannot be changed while the
3841 NFS server is running.
3843 auto the server chooses an appropriate mode
3844 automatically using heuristics
3845 global a single global pool contains all CPUs
3846 percpu one pool for each CPU
3847 pernode one pool for each NUMA node (equivalent
3848 to global on non-NUMA machines)
3850 sunrpc.tcp_slot_table_entries=
3851 sunrpc.udp_slot_table_entries=
3853 Sets the upper limit on the number of simultaneous
3854 RPC calls that can be sent from the client to a
3855 server. Increasing these values may allow you to
3856 improve throughput, but will also increase the
3857 amount of memory reserved for use by the client.
3859 suspend.pm_test_delay=
3861 Sets the number of seconds to remain in a suspend test
3862 mode before resuming the system (see
3863 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3864 is set. Default value is 5.
3867 [KNL] Enable accounting of swap in memory resource
3868 controller if no parameter or 1 is given or disable
3869 it if 0 is given (See Documentation/cgroups/memory.txt)
3871 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3872 Format: { <int> | force }
3873 <int> -- Number of I/O TLB slabs
3874 force -- force using of bounce buffers even if they
3875 wouldn't be automatically used by the kernel
3879 sysfs.deprecated=0|1 [KNL]
3880 Enable/disable old style sysfs layout for old udev
3881 on older distributions. When this option is enabled
3882 very new udev will not work anymore. When this option
3883 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3884 in older udev will not work anymore.
3885 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3886 the kernel configuration.
3888 sysrq_always_enabled
3890 Ignore sysrq setting - this boot parameter will
3891 neutralize any effect of /proc/sys/kernel/sysrq.
3892 Useful for debugging.
3894 tcpmhash_entries= [KNL,NET]
3895 Set the number of tcp_metrics_hash slots.
3896 Default value is 8192 or 16384 depending on total
3897 ram pages. This is used to specify the TCP metrics
3898 cache size. See Documentation/networking/ip-sysctl.txt
3899 "tcp_no_metrics_save" section for more details.
3903 test_suspend= [SUSPEND][,N]
3904 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3905 standby suspend) or "freeze" (for suspend type freeze)
3906 as the system sleep state during system startup with
3907 the optional capability to repeat N number of times.
3908 The system is woken from this state using a
3909 wakeup-capable RTC alarm.
3911 thash_entries= [KNL,NET]
3912 Set number of hash buckets for TCP connection
3914 thermal.act= [HW,ACPI]
3915 -1: disable all active trip points in all thermal zones
3916 <degrees C>: override all lowest active trip points
3918 thermal.crt= [HW,ACPI]
3919 -1: disable all critical trip points in all thermal zones
3920 <degrees C>: override all critical trip points
3922 thermal.nocrt= [HW,ACPI]
3923 Set to disable actions on ACPI thermal zone
3924 critical and hot trip points.
3926 thermal.off= [HW,ACPI]
3927 1: disable ACPI thermal control
3929 thermal.psv= [HW,ACPI]
3930 -1: disable all passive trip points
3931 <degrees C>: override all passive trip points to this
3934 thermal.tzp= [HW,ACPI]
3935 Specify global default ACPI thermal zone polling rate
3936 <deci-seconds>: poll all this frequency
3937 0: no polling (default)
3940 Force threading of all interrupt handlers except those
3941 marked explicitly IRQF_NO_THREAD.
3944 Enable the Transcendent memory driver if built-in.
3946 tmem.cleancache=0|1 [KNL, XEN]
3947 Default is on (1). Disable the usage of the cleancache
3948 API to send anonymous pages to the hypervisor.
3950 tmem.frontswap=0|1 [KNL, XEN]
3951 Default is on (1). Disable the usage of the frontswap
3952 API to send swap pages to the hypervisor. If disabled
3953 the selfballooning and selfshrinking are force disabled.
3955 tmem.selfballooning=0|1 [KNL, XEN]
3956 Default is on (1). Disable the driving of swap pages
3959 tmem.selfshrinking=0|1 [KNL, XEN]
3960 Default is on (1). Partial swapoff that immediately
3961 transfers pages from Xen hypervisor back to the
3962 kernel based on different criteria.
3966 Specify if the kernel should make use of the cpu
3967 topology information if the hardware supports this.
3968 The scheduler will make use of this information and
3969 e.g. base its process migration decisions on it.
3972 topology_updates= [KNL, PPC, NUMA]
3974 Specify if the kernel should ignore (off)
3975 topology updates sent by the hypervisor to this
3980 tpm_suspend_pcr=[HW,TPM]
3981 Format: integer pcr id
3982 Specify that at suspend time, the tpm driver
3983 should extend the specified pcr with zeros,
3984 as a workaround for some chips which fail to
3985 flush the last written pcr on TPM_SaveState.
3986 This will guarantee that all the other pcrs
3989 trace_buf_size=nn[KMG]
3990 [FTRACE] will set tracing buffer size on each cpu.
3992 trace_event=[event-list]
3993 [FTRACE] Set and start specified trace events in order
3994 to facilitate early boot debugging.
3995 See also Documentation/trace/events.txt
3997 trace_options=[option-list]
3998 [FTRACE] Enable or disable tracer options at boot.
3999 The option-list is a comma delimited list of options
4000 that can be enabled or disabled just as if you were
4001 to echo the option name into
4003 /sys/kernel/debug/tracing/trace_options
4005 For example, to enable stacktrace option (to dump the
4006 stack trace of each event), add to the command line:
4008 trace_options=stacktrace
4010 See also Documentation/trace/ftrace.txt "trace options"
4014 Have the tracepoints sent to printk as well as the
4015 tracing ring buffer. This is useful for early boot up
4016 where the system hangs or reboots and does not give the
4017 option for reading the tracing buffer or performing a
4018 ftrace_dump_on_oops.
4020 To turn off having tracepoints sent to printk,
4021 echo 0 > /proc/sys/kernel/tracepoint_printk
4022 Note, echoing 1 into this file without the
4023 tracepoint_printk kernel cmdline option has no effect.
4027 Having tracepoints sent to printk() and activating high
4028 frequency tracepoints such as irq or sched, can cause
4029 the system to live lock.
4032 [FTRACE] enable this option to disable tracing when a
4033 warning is hit. This turns off "tracing_on". Tracing can
4034 be enabled again by echoing '1' into the "tracing_on"
4035 file located in /sys/kernel/debug/tracing/
4037 This option is useful, as it disables the trace before
4038 the WARNING dump is called, which prevents the trace to
4039 be filled with content caused by the warning output.
4041 This option can also be set at run time via the sysctl
4042 option: kernel/traceoff_on_warning
4044 transparent_hugepage=
4046 Format: [always|madvise|never]
4047 Can be used to control the default behavior of the system
4048 with respect to transparent hugepages.
4049 See Documentation/vm/transhuge.txt for more details.
4051 tsc= Disable clocksource stability checks for TSC.
4053 [x86] reliable: mark tsc clocksource as reliable, this
4054 disables clocksource verification at runtime, as well
4055 as the stability checks done at bootup. Used to enable
4056 high-resolution timer mode on older hardware, and in
4057 virtualized environment.
4058 [x86] noirqtime: Do not use TSC to do irq accounting.
4059 Used to run time disable IRQ_TIME_ACCOUNTING on any
4060 platforms where RDTSC is slow and this accounting
4063 turbografx.map[2|3]= [HW,JOY]
4064 TurboGraFX parallel port interface
4066 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4067 See also Documentation/input/joystick-parport.txt
4069 udbg-immortal [PPC] When debugging early kernel crashes that
4070 happen after console_init() and before a proper
4071 console driver takes over, this boot options might
4072 help "seeing" what's going on.
4074 uhash_entries= [KNL,NET]
4075 Set number of hash buckets for UDP/UDP-Lite connections
4078 [USB] Ignore overcurrent events (default N).
4079 Some badly-designed motherboards generate lots of
4080 bogus events, for ports that aren't wired to
4081 anything. Set this parameter to avoid log spamming.
4082 Note that genuine overcurrent events won't be
4086 [X86] Cause panic on unknown NMI.
4088 usbcore.authorized_default=
4089 [USB] Default USB device authorization:
4090 (default -1 = authorized except for wireless USB,
4091 0 = not authorized, 1 = authorized)
4093 usbcore.autosuspend=
4094 [USB] The autosuspend time delay (in seconds) used
4095 for newly-detected USB devices (default 2). This
4096 is the time required before an idle device will be
4097 autosuspended. Devices for which the delay is set
4098 to a negative value won't be autosuspended at all.
4100 usbcore.usbfs_snoop=
4101 [USB] Set to log all usbfs traffic (default 0 = off).
4103 usbcore.usbfs_snoop_max=
4104 [USB] Maximum number of bytes to snoop in each URB
4107 usbcore.blinkenlights=
4108 [USB] Set to cycle leds on hubs (default 0 = off).
4110 usbcore.old_scheme_first=
4111 [USB] Start with the old device initialization
4112 scheme (default 0 = off).
4114 usbcore.usbfs_memory_mb=
4115 [USB] Memory limit (in MB) for buffers allocated by
4116 usbfs (default = 16, 0 = max = 2047).
4118 usbcore.use_both_schemes=
4119 [USB] Try the other device initialization scheme
4120 if the first one fails (default 1 = enabled).
4122 usbcore.initial_descriptor_timeout=
4123 [USB] Specifies timeout for the initial 64-byte
4124 USB_REQ_GET_DESCRIPTOR request in milliseconds
4125 (default 5000 = 5.0 seconds).
4127 usbcore.nousb [USB] Disable the USB subsystem
4130 [USBHID] The interval which mice are to be polled at.
4132 usb-storage.delay_use=
4133 [UMS] The delay in seconds before a new device is
4134 scanned for Logical Units (default 1).
4137 [UMS] A list of quirks entries to supplement or
4138 override the built-in unusual_devs list. List
4139 entries are separated by commas. Each entry has
4140 the form VID:PID:Flags where VID and PID are Vendor
4141 and Product ID values (4-digit hex numbers) and
4142 Flags is a set of characters, each corresponding
4143 to a common usb-storage quirk flag as follows:
4144 a = SANE_SENSE (collect more than 18 bytes
4146 b = BAD_SENSE (don't collect more than 18
4147 bytes of sense data);
4148 c = FIX_CAPACITY (decrease the reported
4149 device capacity by one sector);
4150 d = NO_READ_DISC_INFO (don't use
4151 READ_DISC_INFO command);
4152 e = NO_READ_CAPACITY_16 (don't use
4153 READ_CAPACITY_16 command);
4154 f = NO_REPORT_OPCODES (don't use report opcodes
4156 g = MAX_SECTORS_240 (don't transfer more than
4157 240 sectors at a time, uas only);
4158 h = CAPACITY_HEURISTICS (decrease the
4159 reported device capacity by one
4160 sector if the number is odd);
4161 i = IGNORE_DEVICE (don't bind to this
4163 j = NO_REPORT_LUNS (don't use report luns
4165 l = NOT_LOCKABLE (don't try to lock and
4166 unlock ejectable media);
4167 m = MAX_SECTORS_64 (don't transfer more
4168 than 64 sectors = 32 KB at a time);
4169 n = INITIAL_READ10 (force a retry of the
4170 initial READ(10) command);
4171 o = CAPACITY_OK (accept the capacity
4172 reported by the device);
4173 p = WRITE_CACHE (the device cache is ON
4175 r = IGNORE_RESIDUE (the device reports
4176 bogus residue values);
4177 s = SINGLE_LUN (the device has only one
4179 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4180 commands, uas only);
4181 u = IGNORE_UAS (don't bind to the uas driver);
4182 w = NO_WP_DETECT (don't test whether the
4183 medium is write-protected).
4184 Example: quirks=0419:aaf5:rl,0421:0433:rc
4186 user_debug= [KNL,ARM]
4188 See arch/arm/Kconfig.debug help text.
4189 1 - undefined instruction events
4191 4 - invalid data aborts
4194 Example: user_debug=31
4197 [X86] Flags controlling user PTE allocations.
4199 nohigh = do not allocate PTE pages in
4200 HIGHMEM regardless of setting
4204 On X86_32, this is an alias for vdso32=. Otherwise:
4206 vdso=1: enable VDSO (the default)
4207 vdso=0: disable VDSO mapping
4209 vdso32= [X86] Control the 32-bit vDSO
4210 vdso32=1: enable 32-bit VDSO
4211 vdso32=0 or vdso32=2: disable 32-bit VDSO
4213 See the help text for CONFIG_COMPAT_VDSO for more
4214 details. If CONFIG_COMPAT_VDSO is set, the default is
4215 vdso32=0; otherwise, the default is vdso32=1.
4217 For compatibility with older kernels, vdso32=2 is an
4220 Try vdso32=0 if you encounter an error that says:
4221 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4224 vector=percpu: enable percpu vector domain
4226 video= [FB] Frame buffer configuration
4227 See Documentation/fb/modedb.txt.
4229 video.brightness_switch_enabled= [0,1]
4230 If set to 1, on receiving an ACPI notify event
4231 generated by hotkey, video driver will adjust brightness
4232 level and then send out the event to user space through
4233 the allocated input device; If set to 0, video driver
4234 will only send out the event without touching backlight
4239 [VMMIO] Memory mapped virtio (platform) device.
4241 <size>@<baseaddr>:<irq>[:<id>]
4243 <size> := size (can use standard suffixes
4245 <baseaddr> := physical base address
4246 <irq> := interrupt number (as passed to
4248 <id> := (optional) platform device id
4250 virtio_mmio.device=1K@0x100b0000:48:7
4252 Can be used multiple times for multiple devices.
4254 vga= [BOOT,X86-32] Select a particular video mode
4255 See Documentation/x86/boot.txt and
4256 Documentation/svga.txt.
4257 Use vga=ask for menu.
4258 This is actually a boot loader parameter; the value is
4259 passed to the kernel using a special protocol.
4261 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4262 size of <nn>. This can be used to increase the
4263 minimum size (128MB on x86). It can also be used to
4264 decrease the size and leave more room for directly
4267 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4270 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4273 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4277 Controls the behavior of vsyscalls (i.e. calls to
4278 fixed addresses of 0xffffffffff600x00 from legacy
4279 code). Most statically-linked binaries and older
4280 versions of glibc use these calls. Because these
4281 functions are at fixed addresses, they make nice
4282 targets for exploits that can control RIP.
4284 emulate [default] Vsyscalls turn into traps and are
4285 emulated reasonably safely.
4287 native Vsyscalls are native syscall instructions.
4288 This is a little bit faster than trapping
4289 and makes a few dynamic recompilers work
4290 better than they would in emulation mode.
4291 It also makes exploits much easier to write.
4293 none Vsyscalls don't work at all. This makes
4294 them quite hard to use for exploits but
4295 might break your system.
4297 vt.color= [VT] Default text color.
4298 Format: 0xYX, X = foreground, Y = background.
4299 Default: 0x07 = light gray on black.
4301 vt.cur_default= [VT] Default cursor shape.
4302 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4303 the parameters of the <Esc>[?A;B;Cc escape sequence;
4304 see VGA-softcursor.txt. Default: 2 = underline.
4306 vt.default_blu= [VT]
4307 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4308 Change the default blue palette of the console.
4309 This is a 16-member array composed of values
4312 vt.default_grn= [VT]
4313 Format: <green0>,<green1>,<green2>,...,<green15>
4314 Change the default green palette of the console.
4315 This is a 16-member array composed of values
4318 vt.default_red= [VT]
4319 Format: <red0>,<red1>,<red2>,...,<red15>
4320 Change the default red palette of the console.
4321 This is a 16-member array composed of values
4327 Set system-wide default UTF-8 mode for all tty's.
4328 Default is 1, i.e. UTF-8 mode is enabled for all
4329 newly opened terminals.
4331 vt.global_cursor_default=
4334 Set system-wide default for whether a cursor
4335 is shown on new VTs. Default is -1,
4336 i.e. cursors will be created by default unless
4337 overridden by individual drivers. 0 will hide
4338 cursors, 1 will display them.
4340 vt.italic= [VT] Default color for italic text; 0-15.
4343 vt.underline= [VT] Default color for underlined text; 0-15.
4346 watchdog timers [HW,WDT] For information on watchdog timers,
4347 see Documentation/watchdog/watchdog-parameters.txt
4348 or other driver-specific files in the
4349 Documentation/watchdog/ directory.
4351 workqueue.watchdog_thresh=
4352 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4353 warn stall conditions and dump internal state to
4354 help debugging. 0 disables workqueue stall
4355 detection; otherwise, it's the stall threshold
4356 duration in seconds. The default value is 30 and
4357 it can be updated at runtime by writing to the
4358 corresponding sysfs file.
4360 workqueue.disable_numa
4361 By default, all work items queued to unbound
4362 workqueues are affine to the NUMA nodes they're
4363 issued on, which results in better behavior in
4364 general. If NUMA affinity needs to be disabled for
4365 whatever reason, this option can be used. Note
4366 that this also can be controlled per-workqueue for
4367 workqueues visible under /sys/bus/workqueue/.
4369 workqueue.power_efficient
4370 Per-cpu workqueues are generally preferred because
4371 they show better performance thanks to cache
4372 locality; unfortunately, per-cpu workqueues tend to
4373 be more power hungry than unbound workqueues.
4375 Enabling this makes the per-cpu workqueues which
4376 were observed to contribute significantly to power
4377 consumption unbound, leading to measurably lower
4378 power usage at the cost of small performance
4381 The default value of this parameter is determined by
4382 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4384 workqueue.debug_force_rr_cpu
4385 Workqueue used to implicitly guarantee that work
4386 items queued without explicit CPU specified are put
4387 on the local CPU. This guarantee is no longer true
4388 and while local CPU is still preferred work items
4389 may be put on foreign CPUs. This debug option
4390 forces round-robin CPU selection to flush out
4391 usages which depend on the now broken guarantee.
4392 When enabled, memory and cache locality will be
4395 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4396 default x2apic cluster mode on platforms
4399 x86_intel_mid_timer= [X86-32,APBT]
4400 Choose timer option for x86 Intel MID platform.
4401 Two valid options are apbt timer only and lapic timer
4402 plus one apbt timer for broadcast timer.
4403 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4405 xen_512gb_limit [KNL,X86-64,XEN]
4406 Restricts the kernel running paravirtualized under Xen
4407 to use only up to 512 GB of RAM. The reason to do so is
4408 crash analysis tools and Xen tools for doing domain
4409 save/restore/migration must be enabled to handle larger
4412 xen_emul_unplug= [HW,X86,XEN]
4413 Unplug Xen emulated devices
4414 Format: [unplug0,][unplug1]
4415 ide-disks -- unplug primary master IDE devices
4416 aux-ide-disks -- unplug non-primary-master IDE devices
4417 nics -- unplug network devices
4418 all -- unplug all emulated devices (NICs and IDE disks)
4419 unnecessary -- unplugging emulated devices is
4420 unnecessary even if the host did not respond to
4422 never -- do not unplug even if version check succeeds
4424 xen_nopvspin [X86,XEN]
4425 Disables the ticketlock slowpath using Xen PV
4429 Disables the PV optimizations forcing the HVM guest to
4430 run as generic HVM guest with no PV drivers.
4432 xirc2ps_cs= [NET,PCMCIA]
4434 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4436 ______________________________________________________________________
4440 Add more DRM drivers.
projects / deliverable / linux.git / blob