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 amd_iommu_intr= [HW,X86-64]
464 Specifies one of the following AMD IOMMU interrupt
466 legacy - Use legacy interrupt remapping mode.
467 vapic - Use virtual APIC mode, which allows IOMMU
468 to inject interrupts directly into guest.
469 This mode requires kvm-amd.avic=1.
470 (Default when IOMMU HW support is present.)
472 amijoy.map= [HW,JOY] Amiga joystick support
473 Map of devices attached to JOY0DAT and JOY1DAT
475 See also Documentation/input/joystick.txt
477 analog.map= [HW,JOY] Analog joystick and gamepad support
478 Specifies type or capabilities of an analog joystick
479 connected to one of 16 gameports
480 Format: <type1>,<type2>,..<type16>
483 Power management functions (SPARCstation-4/5 + deriv.)
485 Disable APC CPU standby support. SPARCstation-Fox does
486 not play well with APC CPU idle - disable it if you have
487 APC and your system crashes randomly.
489 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
490 Change the output verbosity whilst booting
491 Format: { quiet (default) | verbose | debug }
492 Change the amount of debugging information output
493 when initialising the APIC and IO-APIC components.
495 apic_extnmi= [APIC,X86] External NMI delivery setting
496 Format: { bsp (default) | all | none }
497 bsp: External NMI is delivered only to CPU 0
498 all: External NMIs are broadcast to all CPUs as a
500 none: External NMI is masked for all CPUs. This is
501 useful so that a dump capture kernel won't be
505 See Documentation/networking/ipv6.txt.
507 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
508 Limit apic dumping. The parameter defines the maximal
509 number of local apics being dumped. Also it is possible
510 to set it to "all" by meaning -- no limit here.
511 Format: { 1 (default) | 2 | ... | all }.
512 The parameter valid if only apic=debug or
513 apic=verbose is specified.
514 Example: apic=debug show_lapic=all
516 apm= [APM] Advanced Power Management
517 See header of arch/x86/kernel/apm_32.c.
519 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
520 Format: <io>,<irq>,<nodeID>
524 atarimouse= [HW,MOUSE] Atari Mouse
526 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
527 EzKey and similar keyboards
529 atkbd.reset= [HW] Reset keyboard during initialization
531 atkbd.set= [HW] Select keyboard code set
532 Format: <int> (2 = AT (default), 3 = PS/2)
534 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
537 atkbd.softraw= [HW] Choose between synthetic and real raw mode
538 Format: <bool> (0 = real, 1 = synthetic (default))
540 atkbd.softrepeat= [HW]
541 Use software keyboard repeat
543 audit= [KNL] Enable the audit sub-system
544 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
545 0 - kernel audit is disabled and can not be enabled
546 until the next reboot
547 unset - kernel audit is initialized but disabled and
548 will be fully enabled by the userspace auditd.
549 1 - kernel audit is initialized and partially enabled,
550 storing at most audit_backlog_limit messages in
551 RAM until it is fully enabled by the userspace
555 audit_backlog_limit= [KNL] Set the audit queue size limit.
556 Format: <int> (must be >=0)
559 bau= [X86_UV] Enable the BAU on SGI UV. The default
560 behavior is to disable the BAU (i.e. bau=0).
561 Format: { "0" | "1" }
564 unset - Disable the BAU.
566 baycom_epp= [HW,AX25]
569 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
571 See header of drivers/net/hamradio/baycom_par.c.
573 baycom_ser_fdx= [HW,AX25]
574 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
575 Format: <io>,<irq>,<mode>[,<baud>]
576 See header of drivers/net/hamradio/baycom_ser_fdx.c.
578 baycom_ser_hdx= [HW,AX25]
579 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
580 Format: <io>,<irq>,<mode>
581 See header of drivers/net/hamradio/baycom_ser_hdx.c.
583 blkdevparts= Manual partition parsing of block device(s) for
584 embedded devices based on command line input.
585 See Documentation/block/cmdline-partition.txt
587 boot_delay= Milliseconds to delay each printk during boot.
588 Values larger than 10 seconds (10000) are changed to
592 bootmem_debug [KNL] Enable bootmem allocator debug messages.
595 Disable BERT OS support on buggy BIOSes.
597 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
598 bttv.radio= Most important insmod options are available as
600 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
603 bulk_remove=off [PPC] This parameter disables the use of the pSeries
604 firmware feature for flushing multiple hpte entries
607 c101= [NET] Moxa C101 synchronous serial card
609 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
610 Sometimes CPU hardware bugs make them report the cache
611 size incorrectly. The kernel will attempt work arounds
612 to fix known problems, but for some CPUs it is not
613 possible to determine what the correct size should be.
614 This option provides an override for these situations.
616 ca_keys= [KEYS] This parameter identifies a specific key(s) on
617 the system trusted keyring to be used for certificate
619 format: { id:<keyid> | builtin }
621 cca= [MIPS] Override the kernel pages' cache coherency
622 algorithm. Accepted values range from 0 to 7
623 inclusive. See arch/mips/include/asm/pgtable-bits.h
624 for platform specific values (SB1, Loongson3 and
627 ccw_timeout_log [S390]
628 See Documentation/s390/CommonIO for details.
630 cgroup_disable= [KNL] Disable a particular controller
631 Format: {name of the controller(s) to disable}
632 The effects of cgroup_disable=foo are:
633 - foo isn't auto-mounted if you mount all cgroups in
635 - foo isn't visible as an individually mountable
637 {Currently only "memory" controller deal with this and
638 cut the overhead, others just disable the usage. So
639 only cgroup_disable=memory is actually worthy}
641 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
642 Format: { controller[,controller...] | "all" }
643 Like cgroup_disable, but only applies to cgroup v1;
644 the blacklisted controllers remain available in cgroup2.
646 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
648 nosocket -- Disable socket memory accounting.
649 nokmem -- Disable kernel memory accounting.
651 checkreqprot [SELINUX] Set initial checkreqprot flag value.
652 Format: { "0" | "1" }
653 See security/selinux/Kconfig help text.
654 0 -- check protection applied by kernel (includes
655 any implied execute protection).
656 1 -- check protection requested by application.
657 Default value is set via a kernel config option.
658 Value can be changed at runtime via
659 /selinux/checkreqprot.
662 See Documentation/s390/CommonIO for details.
665 Prevents the clock framework from automatically gating
666 clocks that have not been explicitly enabled by a Linux
667 device driver but are enabled in hardware at reset or
668 by the bootloader/firmware. Note that this does not
669 force such clocks to be always-on nor does it reserve
670 those clocks in any way. This parameter is useful for
671 debug and development, but should not be needed on a
672 platform with proper driver support. For more
673 information, see Documentation/clk.txt.
675 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
677 Forces specified clocksource (if available) to be used
678 when calculating gettimeofday(). If specified
679 clocksource is not available, it defaults to PIT.
680 Format: { pit | tsc | cyclone | pmtmr }
682 clocksource= Override the default clocksource
684 Override the default clocksource and use the clocksource
685 with the name specified.
686 Some clocksource names to choose from, depending on
688 [all] jiffies (this is the base, fallback clocksource)
690 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
691 pxa_timer,timer3,32k_counter,timer0_1
693 [X86-32] pit,hpet,tsc;
694 scx200_hrt on Geode; cyclone on IBM x440
702 clocksource.arm_arch_timer.evtstrm=
705 Enable/disable the eventstream feature of the ARM
706 architected timer so that code using WFE-based polling
707 loops can be debugged more effectively on production
710 clocksource.arm_arch_timer.fsl-a008585=
713 Enable/disable the workaround of Freescale/NXP
714 erratum A-008585. This can be useful for KVM
715 guests, if the guest device tree doesn't show the
716 erratum. If unspecified, the workaround is
717 enabled based on the device tree.
719 clearcpuid=BITNUM [X86]
720 Disable CPUID feature X for the kernel. See
721 arch/x86/include/asm/cpufeatures.h for the valid bit
722 numbers. Note the Linux specific bits are not necessarily
723 stable over kernel options, but the vendor specific
725 Also note that user programs calling CPUID directly
726 or using the feature without checking anything
727 will still see it. This just prevents it from
728 being used by the kernel or shown in /proc/cpuinfo.
729 Also note the kernel might malfunction if you disable
732 cma=nn[MG]@[start[MG][-end[MG]]]
734 Sets the size of kernel global memory area for
735 contiguous memory allocations and optionally the
736 placement constraint by the physical address range of
737 memory allocations. A value of 0 disables CMA
738 altogether. For more information, see
739 include/linux/dma-contiguous.h
741 cmo_free_hint= [PPC] Format: { yes | no }
742 Specify whether pages are marked as being inactive
743 when they are freed. This is used in CMO environments
744 to determine OS memory pressure for page stealing by
748 coherent_pool=nn[KMG] [ARM,KNL]
749 Sets the size of memory pool for coherent, atomic dma
750 allocations, by default set to 256K.
752 code_bytes [X86] How many bytes of object code to print
757 com20020= [HW,NET] ARCnet - COM20020 chipset
759 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
761 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
765 ARCnet - COM90xx chipset (memory-mapped buffers)
766 Format: <io>[,<irq>[,<memstart>]]
768 condev= [HW,S390] console device
771 console= [KNL] Output console device and options.
773 tty<n> Use the virtual console device <n>.
777 Use the specified serial port. The options are of
778 the form "bbbbpnf", where "bbbb" is the baud rate,
779 "p" is parity ("n", "o", or "e"), "n" is number of
780 bits, and "f" is flow control ("r" for RTS or
781 omit it). Default is "9600n8".
783 See Documentation/serial-console.txt for more
785 Documentation/networking/netconsole.txt for an
788 uart[8250],io,<addr>[,options]
789 uart[8250],mmio,<addr>[,options]
790 uart[8250],mmio16,<addr>[,options]
791 uart[8250],mmio32,<addr>[,options]
792 uart[8250],0x<addr>[,options]
793 Start an early, polled-mode console on the 8250/16550
794 UART at the specified I/O port or MMIO address,
795 switching to the matching ttyS device later.
796 MMIO inter-register address stride is either 8-bit
797 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
798 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
799 to be equivalent to 'mmio'. 'options' are specified in
800 the same format described for ttyS above; if unspecified,
801 the h/w is not re-initialized.
803 hvc<n> Use the hypervisor console device <n>. This is for
804 both Xen and PowerPC hypervisors.
806 If the device connected to the port is not a TTY but a braille
807 device, prepend "brl," before the device type, for instance
809 For now, only VisioBraille is supported.
811 consoleblank= [KNL] The console blank (screen saver) timeout in
812 seconds. Defaults to 10*60 = 10mins. A value of 0
813 disables the blank timer.
816 [KNL] Change the default value for
817 /proc/<pid>/coredump_filter.
818 See also Documentation/filesystems/proc.txt.
820 cpuidle.off=1 [CPU_IDLE]
821 disable the cpuidle sub-system
824 [X86] Delay for N microsec between assert and de-assert
825 of APIC INIT to start processors. This delay occurs
826 on every CPU online, such as boot, and resume from suspend.
829 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
831 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
833 crashkernel=size[KMG][@offset[KMG]]
834 [KNL] Using kexec, Linux can switch to a 'crash kernel'
835 upon panic. This parameter reserves the physical
836 memory region [offset, offset + size] for that kernel
837 image. If '@offset' is omitted, then a suitable offset
838 is selected automatically. Check
839 Documentation/kdump/kdump.txt for further details.
841 crashkernel=range1:size1[,range2:size2,...][@offset]
842 [KNL] Same as above, but depends on the memory
843 in the running system. The syntax of range is
844 start-[end] where start and end are both
845 a memory unit (amount[KMG]). See also
846 Documentation/kdump/kdump.txt for an example.
848 crashkernel=size[KMG],high
849 [KNL, x86_64] range could be above 4G. Allow kernel
850 to allocate physical memory region from top, so could
851 be above 4G if system have more than 4G ram installed.
852 Otherwise memory region will be allocated below 4G, if
854 It will be ignored if crashkernel=X is specified.
855 crashkernel=size[KMG],low
856 [KNL, x86_64] range under 4G. When crashkernel=X,high
857 is passed, kernel could allocate physical memory region
858 above 4G, that cause second kernel crash on system
859 that require some amount of low memory, e.g. swiotlb
860 requires at least 64M+32K low memory, also enough extra
861 low memory is needed to make sure DMA buffers for 32-bit
862 devices won't run out. Kernel would try to allocate at
863 at least 256M below 4G automatically.
864 This one let user to specify own low range under 4G
865 for second kernel instead.
866 0: to disable low allocation.
867 It will be ignored when crashkernel=X,high is not used
868 or memory reserved is below 4G.
871 [KNL] Disable crypto self-tests
876 cs89x0_media= [HW,NET]
877 Format: { rj45 | aui | bnc }
880 See header of drivers/s390/block/dasd_devmap.c.
882 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
883 (one device per port)
884 Format: <port#>,<type>
885 See also Documentation/input/joystick-parport.txt
887 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
888 time. See Documentation/dynamic-debug-howto.txt for
889 details. Deprecated, see dyndbg.
891 debug [KNL] Enable kernel debugging (events log level).
894 [KNL] verbose self-tests
896 Print debugging info while doing the locking API
898 We default to 0 (no extra messages), setting it to
899 1 will print _a lot_ more information - normally
900 only useful to kernel developers.
902 debug_objects [KNL] Enable object debugging
905 [KNL] Disable object debugging
907 debug_guardpage_minorder=
908 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
909 parameter allows control of the order of pages that will
910 be intentionally kept free (and hence protected) by the
911 buddy allocator. Bigger value increase the probability
912 of catching random memory corruption, but reduce the
913 amount of memory for normal system use. The maximum
914 possible value is MAX_ORDER/2. Setting this parameter
915 to 1 or 2 should be enough to identify most random
916 memory corruption problems caused by bugs in kernel or
917 driver code when a CPU writes to (or reads from) a
918 random memory location. Note that there exists a class
919 of memory corruptions problems caused by buggy H/W or
920 F/W or by drivers badly programing DMA (basically when
921 memory is written at bus level and the CPU MMU is
922 bypassed) which are not detectable by
923 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
924 tracking down these problems.
927 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
928 parameter enables the feature at boot time. In
929 default, it is disabled. We can avoid allocating huge
930 chunk of memory for debug pagealloc if we don't enable
931 it at boot time and the system will work mostly same
932 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
933 on: enable the feature
935 debugpat [X86] Enable PAT debugging
937 decnet.addr= [HW,NET]
938 Format: <area>[,<node>]
939 See also Documentation/networking/decnet.txt.
942 [same as hugepagesz=] The size of the default
943 HugeTLB page size. This is the size represented by
944 the legacy /proc/ hugepages APIs, used for SHM, and
945 default size when mounting hugetlbfs filesystems.
946 Defaults to the default architecture's huge page size
950 Set number of hash buckets for dentry cache.
952 disable_1tb_segments [PPC]
953 Disables the use of 1TB hash page table segments. This
954 causes the kernel to fall back to 256MB segments which
955 can be useful when debugging issues that require an SLB
959 See Documentation/networking/ipv6.txt.
962 Disable RADIX MMU mode on POWER9
964 disable_cpu_apicid= [X86,APIC,SMP]
966 The number of initial APIC ID for the
967 corresponding CPU to be disabled at boot,
968 mostly used for the kdump 2nd kernel to
969 disable BSP to wake up multiple CPUs without
970 causing system reset or hang due to sending
973 disable_ddw [PPC/PSERIES]
974 Disable Dynamic DMA Window support. Use this if
975 to workaround buggy firmware.
978 See Documentation/networking/ipv6.txt.
980 disable_mtrr_cleanup [X86]
981 The kernel tries to adjust MTRR layout from continuous
982 to discrete, to make X server driver able to add WB
983 entry later. This parameter disables that.
985 disable_mtrr_trim [X86, Intel and AMD only]
986 By default the kernel will trim any uncacheable
987 memory out of your available memory pool based on
988 MTRR settings. This parameter disables that behavior,
989 possibly causing your machine to run very slowly.
991 disable_timer_pin_1 [X86]
992 Disable PIN 1 of APIC timer
993 Can be useful to work around chipset bugs.
995 dis_ucode_ldr [X86] Disable the microcode loader.
997 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
998 this option disables the debugging code at boot.
1000 dma_debug_entries=<number>
1001 This option allows to tune the number of preallocated
1002 entries for DMA-API debugging code. One entry is
1003 required per DMA-API allocation. Use this if the
1004 DMA-API debugging code disables itself because the
1005 architectural default is too low.
1007 dma_debug_driver=<driver_name>
1008 With this option the DMA-API debugging driver
1009 filter feature can be enabled at boot time. Just
1010 pass the driver to filter for as the parameter.
1011 The filter can be disabled or changed to another
1012 driver later using sysfs.
1014 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1015 Broken monitors, graphic adapters, KVMs and EDIDless
1016 panels may send no or incorrect EDID data sets.
1017 This parameter allows to specify an EDID data sets
1018 in the /lib/firmware directory that are used instead.
1019 Generic built-in EDID data sets are used, if one of
1020 edid/1024x768.bin, edid/1280x1024.bin,
1021 edid/1680x1050.bin, or edid/1920x1080.bin is given
1022 and no file with the same name exists. Details and
1023 instructions how to build your own EDID data are
1024 available in Documentation/EDID/HOWTO.txt. An EDID
1025 data set will only be used for a particular connector,
1026 if its name and a colon are prepended to the EDID
1027 name. Each connector may use a unique EDID data
1028 set by separating the files with a comma. An EDID
1029 data set with no connector name will be used for
1030 any connectors not explicitly specified.
1034 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1035 module.dyndbg[="val"]
1036 Enable debug messages at boot time. See
1037 Documentation/dynamic-debug-howto.txt for details.
1039 nompx [X86] Disables Intel Memory Protection Extensions.
1040 See Documentation/x86/intel_mpx.txt for more
1041 information about the feature.
1043 nopku [X86] Disable Memory Protection Keys CPU feature found
1047 on enable eager fpu restore
1048 off disable eager fpu restore
1049 auto selects the default scheme, which automatically
1050 enables eagerfpu restore for xsaveopt.
1052 module.async_probe [KNL]
1053 Enable asynchronous probe on this module.
1055 early_ioremap_debug [KNL]
1056 Enable debug messages in early_ioremap support. This
1057 is useful for tracking down temporary early mappings
1058 which are not unmapped.
1060 earlycon= [KNL] Output early console device and options.
1062 When used with no options, the early console is
1063 determined by the stdout-path property in device
1066 cdns,<addr>[,options]
1067 Start an early, polled-mode console on a Cadence
1068 (xuartps) serial port at the specified address. Only
1069 supported option is baud rate. If baud rate is not
1070 specified, the serial port must already be setup and
1073 uart[8250],io,<addr>[,options]
1074 uart[8250],mmio,<addr>[,options]
1075 uart[8250],mmio32,<addr>[,options]
1076 uart[8250],mmio32be,<addr>[,options]
1077 uart[8250],0x<addr>[,options]
1078 Start an early, polled-mode console on the 8250/16550
1079 UART at the specified I/O port or MMIO address.
1080 MMIO inter-register address stride is either 8-bit
1081 (mmio) or 32-bit (mmio32 or mmio32be).
1082 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1083 to be equivalent to 'mmio'. 'options' are specified
1084 in the same format described for "console=ttyS<n>"; if
1085 unspecified, the h/w is not initialized.
1089 Start an early, polled-mode console on a pl011 serial
1090 port at the specified address. The pl011 serial port
1091 must already be setup and configured. Options are not
1092 yet supported. If 'mmio32' is specified, then only
1093 the driver will use only 32-bit accessors to read/write
1094 the device registers.
1097 Start an early, polled-mode console on a meson serial
1098 port at the specified address. The serial port must
1099 already be setup and configured. Options are not yet
1103 Start an early, polled-mode console on an msm serial
1104 port at the specified address. The serial port
1105 must already be setup and configured. Options are not
1108 msm_serial_dm,<addr>
1109 Start an early, polled-mode console on an msm serial
1110 dm port at the specified address. The serial port
1111 must already be setup and configured. Options are not
1114 smh Use ARM semihosting calls for early console.
1122 Use early console provided by serial driver available
1123 on Samsung SoCs, requires selecting proper type and
1124 a correct base address of the selected UART port. The
1125 serial port must already be setup and configured.
1126 Options are not yet supported.
1130 Use early console provided by Freescale LP UART driver
1131 found on Freescale Vybrid and QorIQ LS1021A processors.
1132 A valid base address must be provided, and the serial
1133 port must already be setup and configured.
1135 armada3700_uart,<addr>
1136 Start an early, polled-mode console on the
1137 Armada 3700 serial port at the specified
1138 address. The serial port must already be setup
1139 and configured. Options are not yet supported.
1141 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1145 earlyprintk=serial[,ttySn[,baudrate]]
1146 earlyprintk=serial[,0x...[,baudrate]]
1147 earlyprintk=ttySn[,baudrate]
1148 earlyprintk=dbgp[debugController#]
1149 earlyprintk=pciserial,bus:device.function[,baudrate]
1151 earlyprintk is useful when the kernel crashes before
1152 the normal console is initialized. It is not enabled by
1153 default because it has some cosmetic problems.
1155 Append ",keep" to not disable it when the real console
1158 Only one of vga, efi, serial, or usb debug port can
1161 Currently only ttyS0 and ttyS1 may be specified by
1162 name. Other I/O ports may be explicitly specified
1163 on some architectures (x86 and arm at least) by
1164 replacing ttySn with an I/O port address, like this:
1165 earlyprintk=serial,0x1008,115200
1166 You can find the port for a given device in
1167 /proc/tty/driver/serial:
1168 2: uart:ST16650V2 port:00001008 irq:18 ...
1170 Interaction with the standard serial driver is not
1173 The VGA and EFI output is eventually overwritten by
1176 The xen output can only be used by Xen PV guests.
1178 edac_report= [HW,EDAC] Control how to report EDAC event
1179 Format: {"on" | "off" | "force"}
1180 on: enable EDAC to report H/W event. May be overridden
1181 by other higher priority error reporting module.
1182 off: disable H/W event reporting through EDAC.
1183 force: enforce the use of EDAC to report H/W event.
1186 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1189 This is designed to be used in conjunction with
1190 the boot argument: earlyprintk=vga
1193 Format: {"off" | "on" | "skip[mbr]"}
1196 Format: { "old_map", "nochunk", "noruntime", "debug" }
1197 old_map [X86-64]: switch to the old ioremap-based EFI
1198 runtime services mapping. 32-bit still uses this one by
1200 nochunk: disable reading files in "chunks" in the EFI
1201 boot stub, as chunking can cause problems with some
1202 firmware implementations.
1203 noruntime : disable EFI runtime services support
1204 debug: enable misc debug output
1206 efi_no_storage_paranoia [EFI; X86]
1207 Using this parameter you can use more than 50% of
1208 your efi variable storage. Use this parameter only if
1209 you are really sure that your UEFI does sane gc and
1210 fulfills the spec otherwise your board may brick.
1212 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1213 Add arbitrary attribute to specific memory range by
1214 updating original EFI memory map.
1215 Region of memory which aa attribute is added to is
1217 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1218 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1219 attribute is added to range 0x100000000-0x180000000 and
1220 0x10a0000000-0x1120000000.
1222 Using this parameter you can do debugging of EFI memmap
1223 related feature. For example, you can do debugging of
1224 Address Range Mirroring feature even if your box
1227 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1228 that is to be dynamically loaded by Linux. If there are
1229 multiple variables with the same name but with different
1230 vendor GUIDs, all of them will be loaded. See
1231 Documentation/acpi/ssdt-overlays.txt for details.
1234 eisa_irq_edge= [PARISC,HW]
1235 See header of drivers/parisc/eisa.c.
1238 See comment before function elanfreq_setup() in
1239 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1242 Format: {"cfq" | "deadline" | "noop"}
1243 See Documentation/block/cfq-iosched.txt and
1244 Documentation/block/deadline-iosched.txt for details.
1246 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1247 Specifies physical address of start of kernel core
1248 image elf header and optionally the size. Generally
1249 kexec loader will pass this option to capture kernel.
1250 See Documentation/kdump/kdump.txt for details.
1252 enable_mtrr_cleanup [X86]
1253 The kernel tries to adjust MTRR layout from continuous
1254 to discrete, to make X server driver able to add WB
1255 entry later. This parameter enables that.
1257 enable_timer_pin_1 [X86]
1258 Enable PIN 1 of APIC timer
1259 Can be useful to work around chipset bugs
1260 (in particular on some ATI chipsets).
1261 The kernel tries to set a reasonable default.
1263 enforcing [SELINUX] Set initial enforcing status.
1265 See security/selinux/Kconfig help text.
1266 0 -- permissive (log only, no denials).
1267 1 -- enforcing (deny and log).
1269 Value can be changed at runtime via /selinux/enforce.
1272 Disable Error Record Serialization Table (ERST)
1275 ether= [HW,NET] Ethernet cards parameters
1276 This option is obsoleted by the "netdev=" option, which
1277 has equivalent usage. See its documentation for details.
1281 Permit 'security.evm' to be updated regardless of
1282 current integrity status.
1286 fail_make_request=[KNL]
1287 General fault injection mechanism.
1288 Format: <interval>,<probability>,<space>,<times>
1289 See also Documentation/fault-injection/.
1292 See Documentation/blockdev/floppy.txt.
1294 force_pal_cache_flush
1295 [IA-64] Avoid check_sal_cache_flush which may hang on
1296 buggy SAL_CACHE_FLUSH implementations. Using this
1297 parameter will force ia64_sal_cache_flush to call
1298 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1301 Forcefully enable Physical Address Extension (PAE).
1302 Many Pentium M systems disable PAE but may have a
1303 functionally usable PAE implementation.
1304 Warning: use of this parameter will taint the kernel
1305 and may cause unknown problems.
1308 [FTRACE] will set and start the specified tracer
1309 as early as possible in order to facilitate early
1312 ftrace_dump_on_oops[=orig_cpu]
1313 [FTRACE] will dump the trace buffers on oops.
1314 If no parameter is passed, ftrace will dump
1315 buffers of all CPUs, but if you pass orig_cpu, it will
1316 dump only the buffer of the CPU that triggered the
1319 ftrace_filter=[function-list]
1320 [FTRACE] Limit the functions traced by the function
1321 tracer at boot up. function-list is a comma separated
1322 list of functions. This list can be changed at run
1323 time by the set_ftrace_filter file in the debugfs
1326 ftrace_notrace=[function-list]
1327 [FTRACE] Do not trace the functions specified in
1328 function-list. This list can be changed at run time
1329 by the set_ftrace_notrace file in the debugfs
1332 ftrace_graph_filter=[function-list]
1333 [FTRACE] Limit the top level callers functions traced
1334 by the function graph tracer at boot up.
1335 function-list is a comma separated list of functions
1336 that can be changed at run time by the
1337 set_graph_function file in the debugfs tracing directory.
1339 ftrace_graph_notrace=[function-list]
1340 [FTRACE] Do not trace from the functions specified in
1341 function-list. This list is a comma separated list of
1342 functions that can be changed at run time by the
1343 set_graph_notrace file in the debugfs tracing directory.
1346 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1347 support via parallel port (up to 5 devices per port)
1348 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1349 See also Documentation/input/joystick-parport.txt
1353 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1357 gcov_persist= [GCOV] When non-zero (default), profiling data for
1358 kernel modules is saved and remains accessible via
1359 debugfs, even when the module is unloaded/reloaded.
1360 When zero, profiling data is discarded and associated
1361 debugfs files are removed at module unload time.
1363 gpt [EFI] Forces disk with valid GPT signature but
1364 invalid Protective MBR to be treated as GPT. If the
1365 primary GPT is corrupted, it enables the backup/alternate
1366 GPT to be used instead.
1368 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1369 the "Enable 0" bit of the configuration register.
1372 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1373 the "Enable 0" bit of the configuration register.
1376 grcan.select= [HW] Select which physical interface to use.
1379 grcan.txsize= [HW] Sets the size of the tx buffer.
1380 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1382 grcan.rxsize= [HW] Sets the size of the rx buffer.
1383 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1386 gpio-mockup.gpio_mockup_ranges
1387 [HW] Sets the ranges of gpiochip of for this device.
1388 Format: <start1>,<end1>,<start2>,<end2>...
1390 hardlockup_all_cpu_backtrace=
1391 [KNL] Should the hard-lockup detector generate
1392 backtraces on all cpus.
1395 hashdist= [KNL,NUMA] Large hashes allocated during boot
1396 are distributed across NUMA nodes. Defaults on
1397 for 64-bit NUMA, off otherwise.
1398 Format: 0 | 1 (for off | on)
1400 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1402 hd= [EIDE] (E)IDE hard drive subsystem geometry
1403 Format: <cyl>,<head>,<sect>
1406 Disable Hardware Error Source Table (HEST) support;
1407 corresponding firmware-first mode error processing
1408 logic will be disabled.
1410 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1411 size of <nn>. This works even on boxes that have no
1412 highmem otherwise. This also works to reduce highmem
1413 size on bigger boxes.
1415 highres= [KNL] Enable/disable high resolution timer mode.
1416 Valid parameters: "on", "off"
1420 See Documentation/isdn/README.HiSax.
1424 hpet= [X86-32,HPET] option to control HPET usage
1425 Format: { enable (default) | disable | force |
1427 disable: disable HPET and use PIT instead
1428 force: allow force enabled of undocumented chips (ICH4,
1430 verbose: show contents of HPET registers during setup
1432 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1433 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1435 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1436 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1437 On x86-64 and powerpc, this option can be specified
1438 multiple times interleaved with hugepages= to reserve
1439 huge pages of different sizes. Valid pages sizes on
1440 x86-64 are 2M (when the CPU supports "pse") and 1G
1441 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1443 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1444 terminal devices. Valid values: 0..8
1445 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1446 If specified, z/VM IUCV HVC accepts connections
1447 from listed z/VM user IDs only.
1449 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1450 hardware thread id mappings.
1451 Format: <cpu>:<hwthread>
1454 Do not unregister boot console at start. This is only
1455 useful for debugging when something happens in the window
1456 between unregistering the boot console and initializing
1459 i2c_bus= [HW] Override the default board specific I2C bus speed
1460 or register an additional I2C bus that is not
1461 registered from board initialization code.
1465 i8042.debug [HW] Toggle i8042 debug mode
1466 i8042.unmask_kbd_data
1467 [HW] Enable printing of interrupt data from the KBD port
1468 (disabled by default, and as a pre-condition
1469 requires that i8042.debug=1 be enabled)
1470 i8042.direct [HW] Put keyboard port into non-translated mode
1471 i8042.dumbkbd [HW] Pretend that controller can only read data from
1472 keyboard and cannot control its state
1473 (Don't attempt to blink the leds)
1474 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1475 i8042.nokbd [HW] Don't check/create keyboard port
1476 i8042.noloop [HW] Disable the AUX Loopback command while probing
1478 i8042.nomux [HW] Don't check presence of an active multiplexing
1480 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1482 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1483 i8042.reset [HW] Reset the controller during init and cleanup
1484 i8042.unlock [HW] Unlock (ignore) the keylock
1485 i8042.kbdreset [HW] Reset device connected to KBD port
1489 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1490 indicates that the driver is running on unsupported
1492 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1493 does not match list of supported models.
1495 [HW] Report power status in /proc/i8k
1496 (disabled by default)
1497 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1500 i915.invert_brightness=
1501 [DRM] Invert the sense of the variable that is used to
1502 set the brightness of the panel backlight. Normally a
1503 brightness value of 0 indicates backlight switched off,
1504 and the maximum of the brightness value sets the backlight
1505 to maximum brightness. If this parameter is set to 0
1506 (default) and the machine requires it, or this parameter
1507 is set to 1, a brightness value of 0 sets the backlight
1508 to maximum brightness, and the maximum of the brightness
1509 value switches the backlight off.
1510 -1 -- never invert brightness
1511 0 -- machine default
1512 1 -- force brightness inversion
1515 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1517 ide-core.nodma= [HW] (E)IDE subsystem
1518 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1519 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1520 .cdrom .chs .ignore_cable are additional options
1521 See Documentation/ide/ide.txt.
1523 ide-generic.probe-mask= [HW] (E)IDE subsystem
1525 Probe mask for legacy ISA IDE ports. Depending on
1526 platform up to 6 ports are supported, enabled by
1527 setting corresponding bits in the mask to 1. The
1528 default value is 0x0, which has a special meaning.
1529 On systems that have PCI, it triggers scanning the
1530 PCI bus for the first and the second port, which
1531 are then probed. On systems without PCI the value
1532 of 0x0 enables probing the two first ports as if it
1535 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1536 Claim all unknown PCI IDE storage controllers.
1539 Format: idle=poll, idle=halt, idle=nomwait
1540 Poll forces a polling idle loop that can slightly
1541 improve the performance of waking up a idle CPU, but
1542 will use a lot of power and make the system run hot.
1544 idle=halt: Halt is forced to be used for CPU idle.
1545 In such case C2/C3 won't be used again.
1546 idle=nomwait: Disable mwait for CPU C-states
1548 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1549 Format: { strict | legacy | 2008 | relaxed }
1552 Choose which programs will be accepted for execution
1553 based on the IEEE 754 NaN encoding(s) supported by
1554 the FPU and the NaN encoding requested with the value
1555 of an ELF file header flag individually set by each
1556 binary. Hardware implementations are permitted to
1557 support either or both of the legacy and the 2008 NaN
1560 Available settings are as follows:
1561 strict accept binaries that request a NaN encoding
1562 supported by the FPU
1563 legacy only accept legacy-NaN binaries, if supported
1565 2008 only accept 2008-NaN binaries, if supported
1567 relaxed accept any binaries regardless of whether
1568 supported by the FPU
1570 The FPU emulator is always able to support both NaN
1571 encodings, so if no FPU hardware is present or it has
1572 been disabled with 'nofpu', then the settings of
1573 'legacy' and '2008' strap the emulator accordingly,
1574 'relaxed' straps the emulator for both legacy-NaN and
1575 2008-NaN, whereas 'strict' enables legacy-NaN only on
1576 legacy processors and both NaN encodings on MIPS32 or
1579 The setting for ABS.fmt/NEG.fmt instruction execution
1580 mode generally follows that for the NaN encoding,
1581 except where unsupported by hardware.
1583 ignore_loglevel [KNL]
1584 Ignore loglevel setting - this will print /all/
1585 kernel messages to the console. Useful for debugging.
1586 We also add it as printk module parameter, so users
1587 could change it dynamically, usually by
1588 /sys/module/printk/parameters/ignore_loglevel.
1591 Ignore RLIMIT_DATA setting for data mappings,
1592 print warning at first misuse. Can be changed via
1593 /sys/module/kernel/parameters/ignore_rlimit_data.
1595 ihash_entries= [KNL]
1596 Set number of hash buckets for inode cache.
1598 ima_appraise= [IMA] appraise integrity measurements
1599 Format: { "off" | "enforce" | "fix" | "log" }
1602 ima_appraise_tcb [IMA]
1603 The builtin appraise policy appraises all files
1607 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1611 The list of supported hash algorithms is defined
1612 in crypto/hash_info.h.
1615 The builtin measurement policy to load during IMA
1616 setup. Specyfing "tcb" as the value, measures all
1617 programs exec'd, files mmap'd for exec, and all files
1618 opened with the read mode bit set by either the
1619 effective uid (euid=0) or uid=0.
1622 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1623 Load a policy which meets the needs of the Trusted
1624 Computing Base. This means IMA will measure all
1625 programs exec'd, files mmap'd for exec, and all files
1626 opened for read by uid=0.
1629 Select one of defined IMA measurements template formats.
1630 Formats: { "ima" | "ima-ng" | "ima-sig" }
1634 [IMA] Define a custom template format.
1635 Format: { "field1|...|fieldN" }
1637 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1638 Format: <min_file_size>
1639 Set the minimal file size for using asynchronous hash.
1640 If left unspecified, ahash usage is disabled.
1642 ahash performance varies for different data sizes on
1643 different crypto accelerators. This option can be used
1644 to achieve the best performance for a particular HW.
1646 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1648 Set hashing buffer size. Default: 4k.
1650 ahash performance varies for different chunk sizes on
1651 different crypto accelerators. This option can be used
1652 to achieve best performance for particular HW.
1656 Run specified binary instead of /sbin/init as init
1659 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1660 for working out where the kernel is dying during
1663 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1664 initcall functions. Useful for debugging built-in
1665 modules and initcalls.
1667 initrd= [BOOT] Specify the location of the initial ramdisk
1669 init_pkru= [x86] Specify the default memory protection keys rights
1670 register contents for all processes. 0x55555554 by
1671 default (disallow access to all but pkey 0). Can
1672 override in debugfs after boot.
1674 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1677 int_pln_enable [x86] Enable power limit notification interrupt
1679 integrity_audit=[IMA]
1680 Format: { "0" | "1" }
1681 0 -- basic integrity auditing messages. (Default)
1682 1 -- additional integrity auditing messages.
1684 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1686 Enable intel iommu driver.
1688 Disable intel iommu driver.
1689 igfx_off [Default Off]
1690 By default, gfx is mapped as normal device. If a gfx
1691 device has a dedicated DMAR unit, the DMAR unit is
1692 bypassed by not enabling DMAR with this option. In
1693 this case, gfx device will use physical address for
1696 With this option iommu will not optimize to look
1697 for io virtual address below 32-bit forcing dual
1698 address cycle on pci bus for cards supporting greater
1699 than 32-bit addressing. The default is to look
1700 for translation below 32-bit and if not available
1701 then look in the higher range.
1702 strict [Default Off]
1703 With this option on every unmap_single operation will
1704 result in a hardware IOTLB flush operation as opposed
1705 to batching them for performance.
1706 sp_off [Default Off]
1707 By default, super page will be supported if Intel IOMMU
1708 has the capability. With this option, super page will
1710 ecs_off [Default Off]
1711 By default, extended context tables will be supported if
1712 the hardware advertises that it has support both for the
1713 extended tables themselves, and also PASID support. With
1714 this option set, extended tables will not be used even
1715 on hardware which claims to support them.
1717 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1718 0 disables intel_idle and fall back on acpi_idle.
1719 1 to 9 specify maximum depth of C-state.
1723 Do not enable intel_pstate as the default
1724 scaling driver for the supported processors
1726 Enable intel_pstate on systems that prohibit it by default
1727 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1728 instead of acpi-cpufreq may disable platform features, such
1729 as thermal controls and power capping, that rely on ACPI
1730 P-States information being indicated to OSPM and therefore
1731 should be used with caution. This option does not work with
1732 processors that aren't supported by the intel_pstate driver
1733 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1735 Do not enable hardware P state control (HWP)
1738 Only load intel_pstate on systems which support
1739 hardware P state control (HWP) if available.
1741 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1742 Description Table, specifies preferred power management
1743 profile as "Enterprise Server" or "Performance Server",
1744 then this feature is turned on by default.
1746 intremap= [X86-64, Intel-IOMMU]
1747 on enable Interrupt Remapping (default)
1748 off disable Interrupt Remapping
1749 nosid disable Source ID checking
1751 BIOS x2APIC opt-out request will be ignored
1752 nopost disable Interrupt Posting
1754 iomem= Disable strict checking of access to MMIO memory
1755 strict regions from userspace.
1770 nobypass [PPC/POWERNV]
1771 Disable IOMMU bypass, using IOMMU for PCI devices.
1774 io7= [HW] IO7 for Marvel based alpha systems
1775 See comment before marvel_specify_io7 in
1776 arch/alpha/kernel/core_marvel.c.
1778 io_delay= [X86] I/O delay method
1780 Standard port 0x80 based delay
1782 Alternate port 0xed based delay (needed on some systems)
1784 Simple two microseconds delay
1789 See Documentation/filesystems/nfs/nfsroot.txt.
1791 irqaffinity= [SMP] Set the default irq affinity mask
1793 <cpu number>,...,<cpu number>
1795 <cpu number>-<cpu number>
1796 (must be a positive range in ascending order)
1798 <cpu number>,...,<cpu number>-<cpu number>
1801 When an interrupt is not handled search all handlers
1802 for it. Intended to get systems with badly broken
1806 When an interrupt is not handled search all handlers
1807 for it. Also check all handlers each timer
1808 interrupt. Intended to get systems with badly broken
1812 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1814 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1816 <cpu number>,...,<cpu number>
1818 <cpu number>-<cpu number>
1819 (must be a positive range in ascending order)
1821 <cpu number>,...,<cpu number>-<cpu number>
1823 This option can be used to specify one or more CPUs
1824 to isolate from the general SMP balancing and scheduling
1825 algorithms. You can move a process onto or off an
1826 "isolated" CPU via the CPU affinity syscalls or cpuset.
1827 <cpu number> begins at 0 and the maximum value is
1828 "number of CPUs in system - 1".
1830 This option is the preferred way to isolate CPUs. The
1831 alternative -- manually setting the CPU mask of all
1832 tasks in the system -- can cause problems and
1833 suboptimal load balancer performance.
1837 ivrs_ioapic [HW,X86_64]
1838 Provide an override to the IOAPIC-ID<->DEVICE-ID
1839 mapping provided in the IVRS ACPI table. For
1840 example, to map IOAPIC-ID decimal 10 to
1841 PCI device 00:14.0 write the parameter as:
1842 ivrs_ioapic[10]=00:14.0
1844 ivrs_hpet [HW,X86_64]
1845 Provide an override to the HPET-ID<->DEVICE-ID
1846 mapping provided in the IVRS ACPI table. For
1847 example, to map HPET-ID decimal 0 to
1848 PCI device 00:14.0 write the parameter as:
1849 ivrs_hpet[0]=00:14.0
1851 ivrs_acpihid [HW,X86_64]
1852 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1853 mapping provided in the IVRS ACPI table. For
1854 example, to map UART-HID:UID AMD0020:0 to
1855 PCI device 00:14.5 write the parameter as:
1856 ivrs_acpihid[00:14.5]=AMD0020:0
1858 js= [HW,JOY] Analog joystick
1859 See Documentation/input/joystick.txt.
1862 When CONFIG_RANDOMIZE_BASE is set, this disables
1863 kernel and module base offset ASLR (Address Space
1864 Layout Randomization).
1868 kernelcore= [KNL,X86,IA-64,PPC]
1869 Format: nn[KMGTPE] | "mirror"
1871 specifies the amount of memory usable by the kernel
1872 for non-movable allocations. The requested amount is
1873 spread evenly throughout all nodes in the system. The
1874 remaining memory in each node is used for Movable
1875 pages. In the event, a node is too small to have both
1876 kernelcore and Movable pages, kernelcore pages will
1877 take priority and other nodes will have a larger number
1878 of Movable pages. The Movable zone is used for the
1879 allocation of pages that may be reclaimed or moved
1880 by the page migration subsystem. This means that
1881 HugeTLB pages may not be allocated from this zone.
1882 Note that allocations like PTEs-from-HighMem still
1883 use the HighMem zone if it exists, and the Normal
1884 zone if it does not.
1886 Instead of specifying the amount of memory (nn[KMGTPE]),
1887 you can specify "mirror" option. In case "mirror"
1888 option is specified, mirrored (reliable) memory is used
1889 for non-movable allocations and remaining memory is used
1890 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1891 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1894 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1895 Format: <Controller#>[,poll interval]
1896 The controller # is the number of the ehci usb debug
1897 port as it is probed via PCI. The poll interval is
1898 optional and is the number seconds in between
1899 each poll cycle to the debug port in case you need
1900 the functionality for interrupting the kernel with
1901 gdb or control-c on the dbgp connection. When
1902 not using this parameter you use sysrq-g to break into
1903 the kernel debugger.
1905 kgdboc= [KGDB,HW] kgdb over consoles.
1906 Requires a tty driver that supports console polling,
1907 or a supported polling keyboard driver (non-usb).
1908 Serial only format: <serial_device>[,baud]
1909 keyboard only format: kbd
1910 keyboard and serial format: kbd,<serial_device>[,baud]
1911 Optional Kernel mode setting:
1912 kms, kbd format: kms,kbd
1913 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1915 kgdbwait [KGDB] Stop kernel execution and enter the
1916 kernel debugger at the earliest opportunity.
1918 kmac= [MIPS] korina ethernet MAC address.
1919 Configure the RouterBoard 532 series on-chip
1920 Ethernet adapter MAC address.
1922 kmemleak= [KNL] Boot-time kmemleak enable/disable
1923 Valid arguments: on, off
1925 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1928 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1929 Valid arguments: 0, 1, 2
1930 kmemcheck=0 (disabled)
1931 kmemcheck=1 (enabled)
1932 kmemcheck=2 (one-shot mode)
1933 Default: 2 (one-shot mode)
1935 kstack=N [X86] Print N words from the kernel stack
1938 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1939 Default is 0 (don't ignore, but inject #GP)
1941 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1945 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1946 Default is 1 (enabled)
1948 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1950 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1952 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1953 (virtualized MMU) support on capable Intel chips.
1954 Default is 1 (enabled)
1956 kvm-intel.emulate_invalid_guest_state=
1957 [KVM,Intel] Enable emulation of invalid guest states
1958 Default is 0 (disabled)
1960 kvm-intel.flexpriority=
1961 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1962 Default is 1 (enabled)
1965 [KVM,Intel] Enable VMX nesting (nVMX).
1966 Default is 0 (disabled)
1968 kvm-intel.unrestricted_guest=
1969 [KVM,Intel] Disable unrestricted guest feature
1970 (virtualized real and unpaged mode) on capable
1971 Intel chips. Default is 1 (enabled)
1973 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1974 feature (tagged TLBs) on capable Intel chips.
1975 Default is 1 (enabled)
1981 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1984 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1985 value for LAPIC timer one-shot implementation. Default
1986 back to the programmable timer unit in the LAPIC.
1988 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1991 libata.dma= [LIBATA] DMA control
1992 libata.dma=0 Disable all PATA and SATA DMA
1993 libata.dma=1 PATA and SATA Disk DMA only
1994 libata.dma=2 ATAPI (CDROM) DMA only
1995 libata.dma=4 Compact Flash DMA only
1996 Combinations also work, so libata.dma=3 enables DMA
1997 for disks and CDROMs, but not CFs.
1999 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2000 libata.ignore_hpa=0 keep BIOS limits (default)
2001 libata.ignore_hpa=1 ignore limits, using full disk
2003 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2007 libata.force= [LIBATA] Force configurations. The format is comma
2008 separated list of "[ID:]VAL" where ID is
2009 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2010 matching port, link or device. Basically, it matches
2011 the ATA ID string printed on console by libata. If
2012 the whole ID part is omitted, the last PORT and DEVICE
2013 values are used. If ID hasn't been specified yet, the
2014 configuration applies to all ports, links and devices.
2016 If only DEVICE is omitted, the parameter applies to
2017 the port and all links and devices behind it. DEVICE
2018 number of 0 either selects the first device or the
2019 first fan-out link behind PMP device. It does not
2020 select the host link. DEVICE number of 15 selects the
2021 host link and device attached to it.
2023 The VAL specifies the configuration to force. As long
2024 as there's no ambiguity shortcut notation is allowed.
2025 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2026 The following configurations can be forced.
2028 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2029 Any ID with matching PORT is used.
2031 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2033 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2034 udma[/][16,25,33,44,66,100,133] notation is also
2037 * [no]ncq: Turn on or off NCQ.
2039 * [no]ncqtrim: Turn off queued DSM TRIM.
2041 * nohrst, nosrst, norst: suppress hard, soft
2044 * rstonce: only attempt one reset during
2045 hot-unplug link recovery
2047 * dump_id: dump IDENTIFY data.
2049 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2051 * disable: Disable this device.
2053 If there are multiple matching configurations changing
2054 the same attribute, the last one is used.
2056 memblock=debug [KNL] Enable memblock debug messages.
2058 load_ramdisk= [RAM] List of ramdisks to load from floppy
2059 See Documentation/blockdev/ramdisk.txt.
2061 lockd.nlm_grace_period=P [NFS] Assign grace period.
2064 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2067 lockd.nlm_timeout=T [NFS] Assign timeout value.
2070 lockd.nlm_udpport=M [NFS] Assign UDP port.
2073 locktorture.nreaders_stress= [KNL]
2074 Set the number of locking read-acquisition kthreads.
2075 Defaults to being automatically set based on the
2076 number of online CPUs.
2078 locktorture.nwriters_stress= [KNL]
2079 Set the number of locking write-acquisition kthreads.
2081 locktorture.onoff_holdoff= [KNL]
2082 Set time (s) after boot for CPU-hotplug testing.
2084 locktorture.onoff_interval= [KNL]
2085 Set time (s) between CPU-hotplug operations, or
2086 zero to disable CPU-hotplug testing.
2088 locktorture.shuffle_interval= [KNL]
2089 Set task-shuffle interval (jiffies). Shuffling
2090 tasks allows some CPUs to go into dyntick-idle
2091 mode during the locktorture test.
2093 locktorture.shutdown_secs= [KNL]
2094 Set time (s) after boot system shutdown. This
2095 is useful for hands-off automated testing.
2097 locktorture.stat_interval= [KNL]
2098 Time (s) between statistics printk()s.
2100 locktorture.stutter= [KNL]
2101 Time (s) to stutter testing, for example,
2102 specifying five seconds causes the test to run for
2103 five seconds, wait for five seconds, and so on.
2104 This tests the locking primitive's ability to
2105 transition abruptly to and from idle.
2107 locktorture.torture_runnable= [BOOT]
2108 Start locktorture running at boot time.
2110 locktorture.torture_type= [KNL]
2111 Specify the locking implementation to test.
2113 locktorture.verbose= [KNL]
2114 Enable additional printk() statements.
2116 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2119 loglevel= All Kernel Messages with a loglevel smaller than the
2120 console loglevel will be printed to the console. It can
2121 also be changed with klogd or other programs. The
2122 loglevels are defined as follows:
2124 0 (KERN_EMERG) system is unusable
2125 1 (KERN_ALERT) action must be taken immediately
2126 2 (KERN_CRIT) critical conditions
2127 3 (KERN_ERR) error conditions
2128 4 (KERN_WARNING) warning conditions
2129 5 (KERN_NOTICE) normal but significant condition
2130 6 (KERN_INFO) informational
2131 7 (KERN_DEBUG) debug-level messages
2133 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2134 in bytes. n must be a power of two and greater
2135 than the minimal size. The minimal size is defined
2136 by LOG_BUF_SHIFT kernel config parameter. There is
2137 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2138 that allows to increase the default size depending on
2139 the number of CPUs. See init/Kconfig for more details.
2141 logo.nologo [FB] Disables display of the built-in Linux logo.
2142 This may be used to provide more screen space for
2143 kernel log messages and is useful when debugging
2144 kernel boot problems.
2146 lp=0 [LP] Specify parallel ports to use, e.g,
2147 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2148 lp=reset first parallel port). 'lp=0' disables the
2149 lp=auto printer driver. 'lp=reset' (which can be
2150 specified in addition to the ports) causes
2151 attached printers to be reset. Using
2152 lp=port1,port2,... specifies the parallel ports
2153 to associate lp devices with, starting with
2154 lp0. A port specification may be 'none' to skip
2155 that lp device, or a parport name such as
2156 'parport0'. Specifying 'lp=auto' instead of a
2157 port specification list means that device IDs
2158 from each port should be examined, to see if
2159 an IEEE 1284-compliant printer is attached; if
2160 so, the driver will manage that printer.
2161 See also header of drivers/char/lp.c.
2164 Sets loops_per_jiffy to given constant, thus avoiding
2165 time-consuming boot-time autodetection (up to 250 ms per
2166 CPU). 0 enables autodetection (default). To determine
2167 the correct value for your kernel, boot with normal
2168 autodetection and see what value is printed. Note that
2169 on SMP systems the preset will be applied to all CPUs,
2170 which is likely to cause problems if your CPUs need
2171 significantly divergent settings. An incorrect value
2172 will cause delays in the kernel to be wrong, leading to
2173 unpredictable I/O errors and other breakage. Although
2174 unlikely, in the extreme case this might damage your
2178 Format: <io>,<irq>,<dma>
2180 machvec= [IA-64] Force the use of a particular machine-vector
2181 (machvec) in a generic kernel.
2182 Example: machvec=hpzx1_swiotlb
2184 machtype= [Loongson] Share the same kernel image file between different
2186 Example: machtype=lemote-yeeloong-2f-7inch
2188 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2189 than or equal to this physical address is ignored.
2191 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2192 will bring up during bootup. maxcpus=n : n >= 0 limits
2193 the kernel to bring up 'n' processors. Surely after
2194 bootup you can bring up the other plugged cpu by executing
2195 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2196 only takes effect during system bootup.
2197 While n=0 is a special case, it is equivalent to "nosmp",
2198 which also disables the IO APIC.
2200 max_loop= [LOOP] The number of loop block devices that get
2201 (loop.max_loop) unconditionally pre-created at init time. The default
2202 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2203 of statically allocating a predefined number, loop
2204 devices can be requested on-demand with the
2205 /dev/loop-control interface.
2207 mce [X86-32] Machine Check Exception
2209 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2211 md= [HW] RAID subsystems devices and level
2212 See Documentation/md.txt.
2215 Format: <first>,<last>
2216 Specifies range of consoles to be captured by the MDA.
2218 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2219 Amount of memory to be used when the kernel is not able
2220 to see the whole system memory or for test.
2221 [X86] Work as limiting max address. Use together
2222 with memmap= to avoid physical address space collisions.
2223 Without memmap= PCI devices could be placed at addresses
2224 belonging to unused RAM.
2226 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2230 [KNL,SH] Allow user to override the default size for
2231 per-device physically contiguous DMA buffers.
2233 memhp_default_state=online/offline
2234 [KNL] Set the initial state for the memory hotplug
2235 onlining policy. If not specified, the default value is
2236 set according to the
2237 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2239 See Documentation/memory-hotplug.txt.
2241 memmap=exactmap [KNL,X86] Enable setting of an exact
2242 E820 memory map, as specified by the user.
2243 Such memmap=exactmap lines can be constructed based on
2244 BIOS output or other requirements. See the memmap=nn@ss
2247 memmap=nn[KMG]@ss[KMG]
2248 [KNL] Force usage of a specific region of memory.
2249 Region of memory to be used is from ss to ss+nn.
2251 memmap=nn[KMG]#ss[KMG]
2252 [KNL,ACPI] Mark specific memory as ACPI data.
2253 Region of memory to be marked is from ss to ss+nn.
2255 memmap=nn[KMG]$ss[KMG]
2256 [KNL,ACPI] Mark specific memory as reserved.
2257 Region of memory to be reserved is from ss to ss+nn.
2258 Example: Exclude memory from 0x18690000-0x1869ffff
2259 memmap=64K$0x18690000
2261 memmap=0x10000$0x18690000
2263 memmap=nn[KMG]!ss[KMG]
2264 [KNL,X86] Mark specific memory as protected.
2265 Region of memory to be used, from ss to ss+nn.
2266 The memory region may be marked as e820 type 12 (0xc)
2267 and is NVDIMM or ADR memory.
2269 memory_corruption_check=0/1 [X86]
2270 Some BIOSes seem to corrupt the first 64k of
2271 memory when doing things like suspend/resume.
2272 Setting this option will scan the memory
2273 looking for corruption. Enabling this will
2274 both detect corruption and prevent the kernel
2275 from using the memory being corrupted.
2276 However, its intended as a diagnostic tool; if
2277 repeatable BIOS-originated corruption always
2278 affects the same memory, you can use memmap=
2279 to prevent the kernel from using that memory.
2281 memory_corruption_check_size=size [X86]
2282 By default it checks for corruption in the low
2283 64k, making this memory unavailable for normal
2284 use. Use this parameter to scan for
2285 corruption in more or less memory.
2287 memory_corruption_check_period=seconds [X86]
2288 By default it checks for corruption every 60
2289 seconds. Use this parameter to check at some
2290 other rate. 0 disables periodic checking.
2292 memtest= [KNL,X86,ARM] Enable memtest
2294 default : 0 <disable>
2295 Specifies the number of memtest passes to be
2296 performed. Each pass selects another test
2297 pattern from a given set of patterns. Memtest
2298 fills the memory with this pattern, validates
2299 memory contents and reserves bad memory
2300 regions that are detected.
2302 meye.*= [HW] Set MotionEye Camera parameters
2303 See Documentation/video4linux/meye.txt.
2305 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2306 Multi-Function General Purpose Timers on AMD Geode
2309 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2310 the BIOS has incorrectly applied a workaround. TinyBIOS
2311 version 0.98 is known to be affected, 0.99 fixes the
2312 problem by letting the user disable the workaround.
2316 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2317 physical address is ignored.
2319 mini2440= [ARM,HW,KNL]
2320 Format:[0..2][b][c][t]
2322 MINI2440 configuration specification:
2323 0 - The attached screen is the 3.5" TFT
2324 1 - The attached screen is the 7" TFT
2325 2 - The VGA Shield is attached (1024x768)
2326 Leaving out the screen size parameter will not load
2327 the TFT driver, and the framebuffer will be left
2329 b - Enable backlight. The TFT backlight pin will be
2330 linked to the kernel VESA blanking code and a GPIO
2331 LED. This parameter is not necessary when using the
2333 c - Enable the s3c camera interface.
2334 t - Reserved for enabling touchscreen support. The
2335 touchscreen support is not enabled in the mainstream
2336 kernel as of 2.6.30, a preliminary port can be found
2337 in the "bleeding edge" mini2440 support kernel at
2338 http://repo.or.cz/w/linux-2.6/mini2440.git
2341 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2342 parameter allows control of the logging verbosity for
2343 the additional memory initialisation checks. A value
2344 of 0 disables mminit logging and a level of 4 will
2345 log everything. Information is printed at KERN_DEBUG
2346 so loglevel=8 may also need to be specified.
2349 [KNL] When CONFIG_MODULE_SIG is set, this means that
2350 modules without (valid) signatures will fail to load.
2351 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2352 is always true, so this option does nothing.
2354 module_blacklist= [KNL] Do not load a comma-separated list of
2355 modules. Useful for debugging problem modules.
2358 [MOUSE] Maximum time between finger touching and
2359 leaving touchpad surface for touch to be considered
2360 a tap and be reported as a left button click (for
2361 touchpads working in absolute mode only).
2363 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2364 reporting absolute coordinates, such as tablets
2365 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2366 reporting absolute coordinates, such as tablets
2368 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2369 is similar to kernelcore except it specifies the
2370 amount of memory used for migratable allocations.
2371 If both kernelcore and movablecore is specified,
2372 then kernelcore will be at *least* the specified
2373 value but may be more. If movablecore on its own
2374 is specified, the administrator must be careful
2375 that the amount of memory usable for all allocations
2378 movable_node [KNL,X86] Boot-time switch to enable the effects
2379 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2381 MTD_Partition= [MTD]
2382 Format: <name>,<region-number>,<size>,<offset>
2384 MTD_Region= [MTD] Format:
2385 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2388 See drivers/mtd/cmdlinepart.c.
2390 multitce=off [PPC] This parameter disables the use of the pSeries
2391 firmware feature for updating multiple TCE entries
2394 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2396 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2398 boundary - index of last SLC block on Flex-OneNAND.
2399 The remaining blocks are configured as MLC blocks.
2400 lock - Configure if Flex-OneNAND boundary should be locked.
2401 Once locked, the boundary cannot be changed.
2402 1 indicates lock status, 0 indicates unlock status.
2405 ARM/S3C2412 JIVE boot control
2407 See arch/arm/mach-s3c2412/mach-jive.c
2409 mtouchusb.raw_coordinates=
2410 [HW] Make the MicroTouch USB driver use raw coordinates
2411 ('y', default) or cooked coordinates ('n')
2413 mtrr_chunk_size=nn[KMG] [X86]
2414 used for mtrr cleanup. It is largest continuous chunk
2415 that could hold holes aka. UC entries.
2417 mtrr_gran_size=nn[KMG] [X86]
2418 Used for mtrr cleanup. It is granularity of mtrr block.
2420 Large value could prevent small alignment from
2423 mtrr_spare_reg_nr=n [X86]
2425 Range: 0,7 : spare reg number
2427 Used for mtrr cleanup. It is spare mtrr entries number.
2428 Set to 2 or more if your graphical card needs more.
2430 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2432 netdev= [NET] Network devices parameters
2433 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2434 Note that mem_start is often overloaded to mean
2435 something different and driver-specific.
2436 This usage is only documented in each driver source
2440 [NETFILTER] Enable connection tracking flow accounting
2441 0 to disable accounting
2442 1 to enable accounting
2445 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2446 See Documentation/filesystems/nfs/nfsroot.txt.
2448 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2449 See Documentation/filesystems/nfs/nfsroot.txt.
2451 nfsrootdebug [NFS] enable nfsroot debugging messages.
2452 See Documentation/filesystems/nfs/nfsroot.txt.
2454 nfs.callback_tcpport=
2455 [NFS] set the TCP port on which the NFSv4 callback
2456 channel should listen.
2459 [NFS] sets the pathname to the program which is used
2460 to update the NFS client cache entries.
2462 nfs.cache_getent_timeout=
2463 [NFS] sets the timeout after which an attempt to
2464 update a cache entry is deemed to have failed.
2466 nfs.idmap_cache_timeout=
2467 [NFS] set the maximum lifetime for idmapper cache
2471 [NFS] enable 64-bit inode numbers.
2472 If zero, the NFS client will fake up a 32-bit inode
2473 number for the readdir() and stat() syscalls instead
2474 of returning the full 64-bit number.
2475 The default is to return 64-bit inode numbers.
2477 nfs.max_session_slots=
2478 [NFSv4.1] Sets the maximum number of session slots
2479 the client will attempt to negotiate with the server.
2480 This limits the number of simultaneous RPC requests
2481 that the client can send to the NFSv4.1 server.
2482 Note that there is little point in setting this
2483 value higher than the max_tcp_slot_table_limit.
2485 nfs.nfs4_disable_idmapping=
2486 [NFSv4] When set to the default of '1', this option
2487 ensures that both the RPC level authentication
2488 scheme and the NFS level operations agree to use
2489 numeric uids/gids if the mount is using the
2490 'sec=sys' security flavour. In effect it is
2491 disabling idmapping, which can make migration from
2492 legacy NFSv2/v3 systems to NFSv4 easier.
2493 Servers that do not support this mode of operation
2494 will be autodetected by the client, and it will fall
2495 back to using the idmapper.
2496 To turn off this behaviour, set the value to '0'.
2498 [NFS4] Specify an additional fixed unique ident-
2499 ification string that NFSv4 clients can insert into
2500 their nfs_client_id4 string. This is typically a
2501 UUID that is generated at system install time.
2503 nfs.send_implementation_id =
2504 [NFSv4.1] Send client implementation identification
2505 information in exchange_id requests.
2506 If zero, no implementation identification information
2508 The default is to send the implementation identification
2511 nfs.recover_lost_locks =
2512 [NFSv4] Attempt to recover locks that were lost due
2513 to a lease timeout on the server. Please note that
2514 doing this risks data corruption, since there are
2515 no guarantees that the file will remain unchanged
2516 after the locks are lost.
2517 If you want to enable the kernel legacy behaviour of
2518 attempting to recover these locks, then set this
2520 The default parameter value of '0' causes the kernel
2521 not to attempt recovery of lost locks.
2523 nfs4.layoutstats_timer =
2524 [NFSv4.2] Change the rate at which the kernel sends
2525 layoutstats to the pNFS metadata server.
2527 Setting this to value to 0 causes the kernel to use
2528 whatever value is the default set by the layout
2529 driver. A non-zero value sets the minimum interval
2530 in seconds between layoutstats transmissions.
2532 nfsd.nfs4_disable_idmapping=
2533 [NFSv4] When set to the default of '1', the NFSv4
2534 server will return only numeric uids and gids to
2535 clients using auth_sys, and will accept numeric uids
2536 and gids from such clients. This is intended to ease
2537 migration from NFSv2/v3.
2539 objlayoutdriver.osd_login_prog=
2540 [NFS] [OBJLAYOUT] sets the pathname to the program which
2541 is used to automatically discover and login into new
2542 osd-targets. Please see:
2543 Documentation/filesystems/pnfs.txt for more explanations
2545 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2546 when a NMI is triggered.
2547 Format: [state][,regs][,debounce][,die]
2549 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2550 Format: [panic,][nopanic,][num]
2552 0 - turn hardlockup detector in nmi_watchdog off
2553 1 - turn hardlockup detector in nmi_watchdog on
2554 When panic is specified, panic when an NMI watchdog
2555 timeout occurs (or 'nopanic' to override the opposite
2556 default). To disable both hard and soft lockup detectors,
2557 please see 'nowatchdog'.
2558 This is useful when you use a panic=... timeout and
2559 need the box quickly up again.
2561 netpoll.carrier_timeout=
2562 [NET] Specifies amount of time (in seconds) that
2563 netpoll should wait for a carrier. By default netpoll
2566 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2567 emulation library even if a 387 maths coprocessor
2571 [HW] Never suspend the console
2572 Disable suspending of consoles during suspend and
2573 hibernate operations. Once disabled, debugging
2574 messages can reach various consoles while the rest
2575 of the system is being put to sleep (ie, while
2576 debugging driver suspend/resume hooks). This may
2577 not work reliably with all consoles, but is known
2578 to work with serial and VGA consoles.
2579 To facilitate more flexible debugging, we also add
2580 console_suspend, a printk module parameter to control
2581 it. Users could use console_suspend (usually
2582 /sys/module/printk/parameters/console_suspend) to
2583 turn on/off it dynamically.
2585 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2586 caches in the slab allocator. Saves per-node memory,
2587 but will impact performance.
2591 noapic [SMP,APIC] Tells the kernel to not make use of any
2592 IOAPICs that may be present in the system.
2594 noautogroup Disable scheduler automatic task group creation.
2596 nobats [PPC] Do not use BATs for mapping kernel lowmem
2597 on "Classic" PPC cores.
2601 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2603 nodelayacct [KNL] Disable per-task delay accounting
2605 nodsp [SH] Disable hardware DSP at boot time.
2607 noefi Disable EFI runtime services support.
2612 On X86-32 available only on PAE configured kernels.
2613 noexec=on: enable non-executable mappings (default)
2614 noexec=off: disable non-executable mappings
2617 Disable SMAP (Supervisor Mode Access Prevention)
2618 even if it is supported by processor.
2621 Disable SMEP (Supervisor Mode Execution Prevention)
2622 even if it is supported by processor.
2625 This affects only 32-bit executables.
2626 noexec32=on: enable non-executable mappings (default)
2627 read doesn't imply executable mappings
2628 noexec32=off: disable non-executable mappings
2629 read implies executable mappings
2631 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2633 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2634 register save and restore. The kernel will only save
2635 legacy floating-point registers on task switch.
2637 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2639 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2640 Equivalent to smt=1.
2642 noxsave [BUGS=X86] Disables x86 extended register state save
2643 and restore using xsave. The kernel will fallback to
2644 enabling legacy floating-point and sse state.
2646 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2647 register states. The kernel will fall back to use
2648 xsave to save the states. By using this parameter,
2649 performance of saving the states is degraded because
2650 xsave doesn't support modified optimization while
2651 xsaveopt supports it on xsaveopt enabled systems.
2653 noxsaves [X86] Disables xsaves and xrstors used in saving and
2654 restoring x86 extended register state in compacted
2655 form of xsave area. The kernel will fall back to use
2656 xsaveopt and xrstor to save and restore the states
2657 in standard form of xsave area. By using this
2658 parameter, xsave area per process might occupy more
2659 memory on xsaves enabled systems.
2661 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2662 wfi(ARM) instruction doesn't work correctly and not to
2663 use it. This is also useful when using JTAG debugger.
2665 no_file_caps Tells the kernel not to honor file capabilities. The
2666 only way then for a file to be executed with privilege
2667 is to be setuid root or executed by root.
2669 nohalt [IA-64] Tells the kernel not to use the power saving
2670 function PAL_HALT_LIGHT when idle. This increases
2671 power-consumption. On the positive side, it reduces
2672 interrupt wake-up latency, which may improve performance
2673 in certain environments such as networked servers or
2676 nohibernate [HIBERNATION] Disable hibernation and resume.
2678 nohz= [KNL] Boottime enable/disable dynamic ticks
2679 Valid arguments: on, off
2682 nohz_full= [KNL,BOOT]
2683 In kernels built with CONFIG_NO_HZ_FULL=y, set
2684 the specified list of CPUs whose tick will be stopped
2685 whenever possible. The boot CPU will be forced outside
2686 the range to maintain the timekeeping.
2687 The CPUs in this range must also be included in the
2690 noiotrap [SH] Disables trapped I/O port accesses.
2692 noirqdebug [X86-32] Disables the code which attempts to detect and
2693 disable unhandled interrupt sources.
2695 no_timer_check [X86,APIC] Disables the code which tests for
2696 broken timer IRQ sources.
2698 noisapnp [ISAPNP] Disables ISA PnP code.
2700 noinitrd [RAM] Tells the kernel not to load any configured
2703 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2705 [Deprecated - use intremap=off]
2709 noinvpcid [X86] Disable the INVPCID cpu feature.
2711 nojitter [IA-64] Disables jitter checking for ITC timers.
2713 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2715 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2718 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2719 steal time is computed, but won't influence scheduler
2722 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2724 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2726 noltlbs [PPC] Do not use large page/tlb entries for kernel
2727 lowmem mapping on PPC40x and PPC8xx
2729 nomca [IA-64] Disable machine check abort handling
2731 nomce [X86-32] Disable Machine Check Exception
2733 nomfgpt [X86-32] Disable Multi-Function General Purpose
2734 Timer usage (for AMD Geode machines).
2736 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2737 shutdown the other cpus. Instead use the REBOOT_VECTOR
2740 nomodule Disable module load
2742 nopat [X86] Disable PAT (page attribute table extension of
2743 pagetables) support.
2745 norandmaps Don't use address space randomization. Equivalent to
2746 echo 0 > /proc/sys/kernel/randomize_va_space
2748 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2750 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2751 with UP alternatives
2753 nordrand [X86] Disable kernel use of the RDRAND and
2754 RDSEED instructions even if they are supported
2755 by the processor. RDRAND and RDSEED are still
2756 available to user space applications.
2758 noresume [SWSUSP] Disables resume and restores original swap
2761 no-scroll [VGA] Disables scrollback.
2762 This is required for the Braillex ib80-piezo Braille
2763 reader made by F.H. Papenmeier (Germany).
2767 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2769 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2770 and disable the IO APIC. legacy for "maxcpus=0".
2772 nosoftlockup [KNL] Disable the soft-lockup detector.
2774 nosync [HW,M68K] Disables sync negotiation for all devices.
2776 notsc [BUGS=X86-32] Disable Time Stamp Counter
2778 nowatchdog [KNL] Disable both lockup detectors, i.e.
2779 soft-lockup and NMI watchdog (hard-lockup).
2783 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2785 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2786 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2787 Some features depend on CPU0. Known dependencies are:
2788 1. Resume from suspend/hibernate depends on CPU0.
2789 Suspend/hibernate will fail if CPU0 is offline and you
2790 need to online CPU0 before suspend/hibernate.
2791 2. PIC interrupts also depend on CPU0. CPU0 can't be
2792 removed if a PIC interrupt is detected.
2793 It's said poweroff/reboot may depend on CPU0 on some
2794 machines although I haven't seen such issues so far
2795 after CPU0 is offline on a few tested machines.
2796 If the dependencies are under your control, you can
2797 turn on cpu0_hotplug.
2799 nptcg= [IA-64] Override max number of concurrent global TLB
2800 purges which is reported from either PAL_VM_SUMMARY or
2803 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2804 could support. nr_cpus=n : n >= 1 limits the kernel to
2805 support 'n' processors. It could be larger than the
2806 number of already plugged CPU during bootup, later in
2807 runtime you can physically add extra cpu until it reaches
2808 n. So during boot up some boot time memory for per-cpu
2809 variables need be pre-allocated for later physical cpu
2812 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2814 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2815 Allowed values are enable and disable
2817 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2818 one of ['zone', 'node', 'default'] can be specified
2819 This can be set from sysctl after boot.
2820 See Documentation/sysctl/vm.txt for details.
2822 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2823 See Documentation/debugging-via-ohci1394.txt for more
2826 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2827 Rather than timing out after 20 ms if an EC
2828 command is not properly ACKed, override the length
2829 of the timeout. We have interrupts disabled while
2830 waiting for the ACK, so if this is set too high
2831 interrupts *may* be lost!
2833 omap_mux= [OMAP] Override bootloader pin multiplexing.
2834 Format: <mux_mode0.mode_name=value>...
2835 For example, to override I2C bus2:
2836 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2838 oprofile.timer= [HW]
2839 Use timer interrupt instead of performance counters
2841 oprofile.cpu_type= Force an oprofile cpu type
2842 This might be useful if you have an older oprofile
2843 userland or if you want common events.
2844 Format: { arch_perfmon }
2845 arch_perfmon: [X86] Force use of architectural
2846 perfmon on Intel CPUs instead of the
2847 CPU specific event set.
2848 timer: [X86] Force use of architectural NMI
2849 timer mode (see also oprofile.timer
2850 for generic hr timer mode)
2852 oops=panic Always panic on oopses. Default is to just kill the
2853 process, but there is a small probability of
2854 deadlocking the machine.
2855 This will also cause panics on machine check exceptions.
2856 Useful together with panic=30 to trigger a reboot.
2859 See Documentation/sound/oss/oss-parameters.txt
2861 page_owner= [KNL] Boot-time page_owner enabling option.
2862 Storage of the information about who allocated
2863 each page is disabled in default. With this switch,
2865 on: enable the feature
2867 page_poison= [KNL] Boot-time parameter changing the state of
2868 poisoning on the buddy allocator.
2869 off: turn off poisoning
2870 on: turn on poisoning
2872 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2873 timeout > 0: seconds before rebooting
2874 timeout = 0: wait forever
2875 timeout < 0: reboot immediately
2878 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2881 crash_kexec_post_notifiers
2882 Run kdump after running panic-notifiers and dumping
2883 kmsg. This only for the users who doubt kdump always
2884 succeeds in any situation.
2885 Note that this also increases risks of kdump failure,
2886 because some panic notifiers can make the crashed
2887 kernel more unstable.
2889 parkbd.port= [HW] Parallel port number the keyboard adapter is
2890 connected to, default is 0.
2892 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2893 0 for XT, 1 for AT (default is AT).
2896 parport= [HW,PPT] Specify parallel ports. 0 disables.
2897 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2898 Use 'auto' to force the driver to use any
2899 IRQ/DMA settings detected (the default is to
2900 ignore detected IRQ/DMA settings because of
2901 possible conflicts). You can specify the base
2902 address, IRQ, and DMA settings; IRQ and DMA
2903 should be numbers, or 'auto' (for using detected
2904 settings on that particular port), or 'nofifo'
2905 (to avoid using a FIFO even if it is detected).
2906 Parallel ports are assigned in the order they
2907 are specified on the command line, starting
2910 parport_init_mode= [HW,PPT]
2911 Configure VIA parallel port to operate in
2912 a specific mode. This is necessary on Pegasos
2913 computer where firmware has no options for setting
2914 up parallel port mode and sets it to spp.
2915 Currently this function knows 686a and 8231 chips.
2916 Format: [spp|ps2|epp|ecp|ecpepp]
2919 Halt all CPUs after the first oops has been printed for
2920 the specified number of seconds. This is to be used if
2921 your oopses keep scrolling off the screen.
2926 See header of drivers/block/paride/pcd.c.
2927 See also Documentation/blockdev/paride.txt.
2929 pci=option[,option...] [PCI] various PCI subsystem options:
2930 earlydump [X86] dump PCI config space before the kernel
2932 off [X86] don't probe for the PCI bus
2933 bios [X86-32] force use of PCI BIOS, don't access
2934 the hardware directly. Use this if your machine
2935 has a non-standard PCI host bridge.
2936 nobios [X86-32] disallow use of PCI BIOS, only direct
2937 hardware access methods are allowed. Use this
2938 if you experience crashes upon bootup and you
2939 suspect they are caused by the BIOS.
2940 conf1 [X86] Force use of PCI Configuration Access
2941 Mechanism 1 (config address in IO port 0xCF8,
2942 data in IO port 0xCFC, both 32-bit).
2943 conf2 [X86] Force use of PCI Configuration Access
2944 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2945 the function, IO port 0xCFA, also 8-bit, sets
2946 bus number. The config space is then accessed
2947 through ports 0xC000-0xCFFF).
2948 See http://wiki.osdev.org/PCI for more info
2949 on the configuration access mechanisms.
2950 noaer [PCIE] If the PCIEAER kernel config parameter is
2951 enabled, this kernel boot option can be used to
2952 disable the use of PCIE advanced error reporting.
2953 nodomains [PCI] Disable support for multiple PCI
2954 root domains (aka PCI segments, in ACPI-speak).
2955 nommconf [X86] Disable use of MMCONFIG for PCI
2957 check_enable_amd_mmconf [X86] check for and enable
2958 properly configured MMIO access to PCI
2959 config space on AMD family 10h CPU
2960 nomsi [MSI] If the PCI_MSI kernel config parameter is
2961 enabled, this kernel boot option can be used to
2962 disable the use of MSI interrupts system-wide.
2963 noioapicquirk [APIC] Disable all boot interrupt quirks.
2964 Safety option to keep boot IRQs enabled. This
2965 should never be necessary.
2966 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2967 primary IO-APIC for bridges that cannot disable
2968 boot IRQs. This fixes a source of spurious IRQs
2969 when the system masks IRQs.
2970 noioapicreroute [APIC] Disable workaround that uses the
2971 boot IRQ equivalent of an IRQ that connects to
2972 a chipset where boot IRQs cannot be disabled.
2973 The opposite of ioapicreroute.
2974 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2975 routing table. These calls are known to be buggy
2976 on several machines and they hang the machine
2977 when used, but on other computers it's the only
2978 way to get the interrupt routing table. Try
2979 this option if the kernel is unable to allocate
2980 IRQs or discover secondary PCI buses on your
2982 rom [X86] Assign address space to expansion ROMs.
2983 Use with caution as certain devices share
2984 address decoders between ROMs and other
2986 norom [X86] Do not assign address space to
2987 expansion ROMs that do not already have
2988 BIOS assigned address ranges.
2989 nobar [X86] Do not assign address space to the
2990 BARs that weren't assigned by the BIOS.
2991 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2992 assigned automatically to PCI devices. You can
2993 make the kernel exclude IRQs of your ISA cards
2995 pirqaddr=0xAAAAA [X86] Specify the physical address
2996 of the PIRQ table (normally generated
2997 by the BIOS) if it is outside the
2998 F0000h-100000h range.
2999 lastbus=N [X86] Scan all buses thru bus #N. Can be
3000 useful if the kernel is unable to find your
3001 secondary buses and you want to tell it
3002 explicitly which ones they are.
3003 assign-busses [X86] Always assign all PCI bus
3004 numbers ourselves, overriding
3005 whatever the firmware may have done.
3006 usepirqmask [X86] Honor the possible IRQ mask stored
3007 in the BIOS $PIR table. This is needed on
3008 some systems with broken BIOSes, notably
3009 some HP Pavilion N5400 and Omnibook XE3
3010 notebooks. This will have no effect if ACPI
3011 IRQ routing is enabled.
3012 noacpi [X86] Do not use ACPI for IRQ routing
3013 or for PCI scanning.
3014 use_crs [X86] Use PCI host bridge window information
3015 from ACPI. On BIOSes from 2008 or later, this
3016 is enabled by default. If you need to use this,
3017 please report a bug.
3018 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3019 If you need to use this, please report a bug.
3020 routeirq Do IRQ routing for all PCI devices.
3021 This is normally done in pci_enable_device(),
3022 so this option is a temporary workaround
3023 for broken drivers that don't call it.
3024 skip_isa_align [X86] do not align io start addr, so can
3025 handle more pci cards
3026 noearly [X86] Don't do any early type 1 scanning.
3027 This might help on some broken boards which
3028 machine check when some devices' config space
3029 is read. But various workarounds are disabled
3030 and some IOMMU drivers will not work.
3031 bfsort Sort PCI devices into breadth-first order.
3032 This sorting is done to get a device
3033 order compatible with older (<= 2.4) kernels.
3034 nobfsort Don't sort PCI devices into breadth-first order.
3035 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3036 tuning and use the BIOS-configured MPS defaults.
3037 pcie_bus_safe Set every device's MPS to the largest value
3038 supported by all devices below the root complex.
3039 pcie_bus_perf Set device MPS to the largest allowable MPS
3040 based on its parent bus. Also set MRRS (Max
3041 Read Request Size) to the largest supported
3042 value (no larger than the MPS that the device
3043 or bus can support) for best performance.
3044 pcie_bus_peer2peer Set every device's MPS to 128B, which
3045 every device is guaranteed to support. This
3046 configuration allows peer-to-peer DMA between
3047 any pair of devices, possibly at the cost of
3048 reduced performance. This also guarantees
3049 that hot-added devices will work.
3050 cbiosize=nn[KMG] The fixed amount of bus space which is
3051 reserved for the CardBus bridge's IO window.
3052 The default value is 256 bytes.
3053 cbmemsize=nn[KMG] The fixed amount of bus space which is
3054 reserved for the CardBus bridge's memory
3055 window. The default value is 64 megabytes.
3058 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3059 [<order of align>@]pci:<vendor>:<device>\
3060 [:<subvendor>:<subdevice>][; ...]
3061 Specifies alignment and device to reassign
3062 aligned memory resources.
3063 If <order of align> is not specified,
3064 PAGE_SIZE is used as alignment.
3065 PCI-PCI bridge can be specified, if resource
3066 windows need to be expanded.
3067 To specify the alignment for several
3068 instances of a device, the PCI vendor,
3069 device, subvendor, and subdevice may be
3070 specified, e.g., 4096@pci:8086:9c22:103c:198f
3071 ecrc= Enable/disable PCIe ECRC (transaction layer
3072 end-to-end CRC checking).
3073 bios: Use BIOS/firmware settings. This is the
3077 hpiosize=nn[KMG] The fixed amount of bus space which is
3078 reserved for hotplug bridge's IO window.
3079 Default size is 256 bytes.
3080 hpmemsize=nn[KMG] The fixed amount of bus space which is
3081 reserved for hotplug bridge's memory window.
3082 Default size is 2 megabytes.
3083 hpbussize=nn The minimum amount of additional bus numbers
3084 reserved for buses below a hotplug bridge.
3086 realloc= Enable/disable reallocating PCI bridge resources
3087 if allocations done by BIOS are too small to
3088 accommodate resources required by all child
3090 off: Turn realloc off
3092 realloc same as realloc=on
3093 noari do not use PCIe ARI.
3094 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3095 only look for one device below a PCIe downstream
3098 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3101 force Enable ASPM even on devices that claim not to support it.
3102 WARNING: Forcing ASPM on may cause system lockups.
3104 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3105 nomsi Do not use MSI for PCI Express Native Hotplug (this
3106 makes all PCIe ports use INTx for hotplug services).
3108 pcie_ports= [PCIE] PCIe ports handling:
3109 auto Ask the BIOS whether or not to use native PCIe services
3110 associated with PCIe ports (PME, hot-plug, AER). Use
3111 them only if that is allowed by the BIOS.
3112 native Use native PCIe services associated with PCIe ports
3114 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3117 pcie_port_pm= [PCIE] PCIe port power management handling:
3118 off Disable power management of all PCIe ports
3119 force Forcibly enable power management of all PCIe ports
3121 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3122 nomsi Do not use MSI for native PCIe PME signaling (this makes
3123 all PCIe root ports use INTx for all services).
3125 pcmv= [HW,PCMCIA] BadgePAD 4
3129 Keep all power-domains already enabled by bootloader on,
3130 even if no driver has claimed them. This is useful
3131 for debug and development, but should not be
3132 needed on a platform with proper driver support.
3135 See Documentation/blockdev/paride.txt.
3137 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3140 See arch/parisc/kernel/pdc_chassis.c
3142 percpu_alloc= Select which percpu first chunk allocator to use.
3143 Currently supported values are "embed" and "page".
3144 Archs may support subset or none of the selections.
3145 See comments in mm/percpu.c for details on each
3146 allocator. This parameter is primarily for debugging
3147 and performance comparison.
3150 See Documentation/blockdev/paride.txt.
3153 See Documentation/blockdev/paride.txt.
3155 pirq= [SMP,APIC] Manual mp-table setup
3156 See Documentation/x86/i386/IO-APIC.txt.
3158 plip= [PPT,NET] Parallel port network link
3159 Format: { parport<nr> | timid | 0 }
3160 See also Documentation/parport.txt.
3162 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3163 Override pmtimer IOPort with a hex value.
3167 Enable PNP debug messages (depends on the
3168 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3169 via /sys/module/pnp/parameters/debug. We always show
3170 current resource usage; turning this on also shows
3171 possible settings and some assignment information.
3177 { on | off | curr | res | no-curr | no-res }
3180 [ISAPNP] Exclude IRQs for the autoconfiguration
3183 [ISAPNP] Exclude DMAs for the autoconfiguration
3185 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3186 Ranges are in pairs (I/O port base and size).
3189 [ISAPNP] Exclude memory regions for the
3191 Ranges are in pairs (memory base and size).
3193 ports= [IP_VS_FTP] IPVS ftp helper module
3195 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3197 Format: <port>,<port>....
3199 ppc_strict_facility_enable
3200 [PPC] This option catches any kernel floating point,
3201 Altivec, VSX and SPE outside of regions specifically
3202 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3203 There is some performance impact when enabling this.
3205 print-fatal-signals=
3206 [KNL] debug: print fatal signals
3208 If enabled, warn about various signal handling
3209 related application anomalies: too many signals,
3210 too many POSIX.1 timers, fatal signals causing a
3213 If you hit the warning due to signal overflow,
3214 you might want to try "ulimit -i unlimited".
3218 printk.always_kmsg_dump=
3219 Trigger kmsg_dump for cases other than kernel oops or
3221 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3224 printk.devkmsg={on,off,ratelimit}
3225 Control writing to /dev/kmsg.
3226 on - unlimited logging to /dev/kmsg from userspace
3227 off - logging to /dev/kmsg disabled
3228 ratelimit - ratelimit the logging
3231 printk.time= Show timing data prefixed to each printk message line
3232 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3234 processor.max_cstate= [HW,ACPI]
3235 Limit processor to maximum C-state
3236 max_cstate=9 overrides any DMI blacklist limit.
3238 processor.nocst [HW,ACPI]
3239 Ignore the _CST method to determine C-states,
3240 instead using the legacy FADT method
3242 profile= [KNL] Enable kernel profiling via /proc/profile
3243 Format: [schedule,]<number>
3244 Param: "schedule" - profile schedule points.
3245 Param: <number> - step/bucket size as a power of 2 for
3246 statistical time based profiling.
3247 Param: "sleep" - profile D-state sleeping (millisecs).
3248 Requires CONFIG_SCHEDSTATS
3249 Param: "kvm" - profile VM exits.
3251 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3253 See Documentation/blockdev/ramdisk.txt.
3255 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3256 probe for; one of (bare|imps|exps|lifebook|any).
3257 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3259 psmouse.resetafter= [HW,MOUSE]
3260 Try to reset the device after so many bad packets
3263 [HW,MOUSE] Set desired mouse resolution, in dpi.
3264 psmouse.smartscroll=
3265 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3266 0 = disabled, 1 = enabled (default).
3268 pstore.backend= Specify the name of the pstore backend to use
3271 See Documentation/blockdev/paride.txt.
3274 [KNL] Number of legacy pty's. Overwrites compiled-in
3277 quiet [KNL] Disable most log messages
3282 See Documentation/md.txt.
3284 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3285 See Documentation/blockdev/ramdisk.txt.
3288 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3289 the specified list of CPUs to be no-callback CPUs.
3290 Invocation of these CPUs' RCU callbacks will
3291 be offloaded to "rcuox/N" kthreads created for
3292 that purpose, where "x" is "b" for RCU-bh, "p"
3293 for RCU-preempt, and "s" for RCU-sched, and "N"
3294 is the CPU number. This reduces OS jitter on the
3295 offloaded CPUs, which can be useful for HPC and
3296 real-time workloads. It can also improve energy
3297 efficiency for asymmetric multiprocessors.
3300 Rather than requiring that offloaded CPUs
3301 (specified by rcu_nocbs= above) explicitly
3302 awaken the corresponding "rcuoN" kthreads,
3303 make these kthreads poll for callbacks.
3304 This improves the real-time response for the
3305 offloaded CPUs by relieving them of the need to
3306 wake up the corresponding kthread, but degrades
3307 energy efficiency by requiring that the kthreads
3308 periodically wake up to do the polling.
3310 rcutree.blimit= [KNL]
3311 Set maximum number of finished RCU callbacks to
3312 process in one batch.
3314 rcutree.dump_tree= [KNL]
3315 Dump the structure of the rcu_node combining tree
3316 out at early boot. This is used for diagnostic
3317 purposes, to verify correct tree setup.
3319 rcutree.gp_cleanup_delay= [KNL]
3320 Set the number of jiffies to delay each step of
3321 RCU grace-period cleanup. This only has effect
3322 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3324 rcutree.gp_init_delay= [KNL]
3325 Set the number of jiffies to delay each step of
3326 RCU grace-period initialization. This only has
3327 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3330 rcutree.gp_preinit_delay= [KNL]
3331 Set the number of jiffies to delay each step of
3332 RCU grace-period pre-initialization, that is,
3333 the propagation of recent CPU-hotplug changes up
3334 the rcu_node combining tree. This only has effect
3335 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3337 rcutree.rcu_fanout_exact= [KNL]
3338 Disable autobalancing of the rcu_node combining
3339 tree. This is used by rcutorture, and might
3340 possibly be useful for architectures having high
3341 cache-to-cache transfer latencies.
3343 rcutree.rcu_fanout_leaf= [KNL]
3344 Change the number of CPUs assigned to each
3345 leaf rcu_node structure. Useful for very
3346 large systems, which will choose the value 64,
3347 and for NUMA systems with large remote-access
3348 latencies, which will choose a value aligned
3349 with the appropriate hardware boundaries.
3351 rcutree.jiffies_till_sched_qs= [KNL]
3352 Set required age in jiffies for a
3353 given grace period before RCU starts
3354 soliciting quiescent-state help from
3355 rcu_note_context_switch().
3357 rcutree.jiffies_till_first_fqs= [KNL]
3358 Set delay from grace-period initialization to
3359 first attempt to force quiescent states.
3360 Units are jiffies, minimum value is zero,
3361 and maximum value is HZ.
3363 rcutree.jiffies_till_next_fqs= [KNL]
3364 Set delay between subsequent attempts to force
3365 quiescent states. Units are jiffies, minimum
3366 value is one, and maximum value is HZ.
3368 rcutree.kthread_prio= [KNL,BOOT]
3369 Set the SCHED_FIFO priority of the RCU per-CPU
3370 kthreads (rcuc/N). This value is also used for
3371 the priority of the RCU boost threads (rcub/N)
3372 and for the RCU grace-period kthreads (rcu_bh,
3373 rcu_preempt, and rcu_sched). If RCU_BOOST is
3374 set, valid values are 1-99 and the default is 1
3375 (the least-favored priority). Otherwise, when
3376 RCU_BOOST is not set, valid values are 0-99 and
3377 the default is zero (non-realtime operation).
3379 rcutree.rcu_nocb_leader_stride= [KNL]
3380 Set the number of NOCB kthread groups, which
3381 defaults to the square root of the number of
3382 CPUs. Larger numbers reduces the wakeup overhead
3383 on the per-CPU grace-period kthreads, but increases
3384 that same overhead on each group's leader.
3386 rcutree.qhimark= [KNL]
3387 Set threshold of queued RCU callbacks beyond which
3388 batch limiting is disabled.
3390 rcutree.qlowmark= [KNL]
3391 Set threshold of queued RCU callbacks below which
3392 batch limiting is re-enabled.
3394 rcutree.rcu_idle_gp_delay= [KNL]
3395 Set wakeup interval for idle CPUs that have
3396 RCU callbacks (RCU_FAST_NO_HZ=y).
3398 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3399 Set wakeup interval for idle CPUs that have
3400 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3401 Lazy RCU callbacks are those which RCU can
3402 prove do nothing more than free memory.
3404 rcuperf.gp_exp= [KNL]
3405 Measure performance of expedited synchronous
3406 grace-period primitives.
3408 rcuperf.holdoff= [KNL]
3409 Set test-start holdoff period. The purpose of
3410 this parameter is to delay the start of the
3411 test until boot completes in order to avoid
3414 rcuperf.nreaders= [KNL]
3415 Set number of RCU readers. The value -1 selects
3416 N, where N is the number of CPUs. A value
3417 "n" less than -1 selects N-n+1, where N is again
3418 the number of CPUs. For example, -2 selects N
3419 (the number of CPUs), -3 selects N+1, and so on.
3420 A value of "n" less than or equal to -N selects
3423 rcuperf.nwriters= [KNL]
3424 Set number of RCU writers. The values operate
3425 the same as for rcuperf.nreaders.
3426 N, where N is the number of CPUs
3428 rcuperf.perf_runnable= [BOOT]
3429 Start rcuperf running at boot time.
3431 rcuperf.shutdown= [KNL]
3432 Shut the system down after performance tests
3433 complete. This is useful for hands-off automated
3436 rcuperf.perf_type= [KNL]
3437 Specify the RCU implementation to test.
3439 rcuperf.verbose= [KNL]
3440 Enable additional printk() statements.
3442 rcutorture.cbflood_inter_holdoff= [KNL]
3443 Set holdoff time (jiffies) between successive
3444 callback-flood tests.
3446 rcutorture.cbflood_intra_holdoff= [KNL]
3447 Set holdoff time (jiffies) between successive
3448 bursts of callbacks within a given callback-flood
3451 rcutorture.cbflood_n_burst= [KNL]
3452 Set the number of bursts making up a given
3453 callback-flood test. Set this to zero to
3454 disable callback-flood testing.
3456 rcutorture.cbflood_n_per_burst= [KNL]
3457 Set the number of callbacks to be registered
3458 in a given burst of a callback-flood test.
3460 rcutorture.fqs_duration= [KNL]
3461 Set duration of force_quiescent_state bursts
3464 rcutorture.fqs_holdoff= [KNL]
3465 Set holdoff time within force_quiescent_state bursts
3468 rcutorture.fqs_stutter= [KNL]
3469 Set wait time between force_quiescent_state bursts
3472 rcutorture.gp_cond= [KNL]
3473 Use conditional/asynchronous update-side
3474 primitives, if available.
3476 rcutorture.gp_exp= [KNL]
3477 Use expedited update-side primitives, if available.
3479 rcutorture.gp_normal= [KNL]
3480 Use normal (non-expedited) asynchronous
3481 update-side primitives, if available.
3483 rcutorture.gp_sync= [KNL]
3484 Use normal (non-expedited) synchronous
3485 update-side primitives, if available. If all
3486 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3487 rcutorture.gp_normal=, and rcutorture.gp_sync=
3488 are zero, rcutorture acts as if is interpreted
3489 they are all non-zero.
3491 rcutorture.n_barrier_cbs= [KNL]
3492 Set callbacks/threads for rcu_barrier() testing.
3494 rcutorture.nfakewriters= [KNL]
3495 Set number of concurrent RCU writers. These just
3496 stress RCU, they don't participate in the actual
3497 test, hence the "fake".
3499 rcutorture.nreaders= [KNL]
3500 Set number of RCU readers. The value -1 selects
3501 N-1, where N is the number of CPUs. A value
3502 "n" less than -1 selects N-n-2, where N is again
3503 the number of CPUs. For example, -2 selects N
3504 (the number of CPUs), -3 selects N+1, and so on.
3506 rcutorture.object_debug= [KNL]
3507 Enable debug-object double-call_rcu() testing.
3509 rcutorture.onoff_holdoff= [KNL]
3510 Set time (s) after boot for CPU-hotplug testing.
3512 rcutorture.onoff_interval= [KNL]
3513 Set time (s) between CPU-hotplug operations, or
3514 zero to disable CPU-hotplug testing.
3516 rcutorture.shuffle_interval= [KNL]
3517 Set task-shuffle interval (s). Shuffling tasks
3518 allows some CPUs to go into dyntick-idle mode
3519 during the rcutorture test.
3521 rcutorture.shutdown_secs= [KNL]
3522 Set time (s) after boot system shutdown. This
3523 is useful for hands-off automated testing.
3525 rcutorture.stall_cpu= [KNL]
3526 Duration of CPU stall (s) to test RCU CPU stall
3527 warnings, zero to disable.
3529 rcutorture.stall_cpu_holdoff= [KNL]
3530 Time to wait (s) after boot before inducing stall.
3532 rcutorture.stat_interval= [KNL]
3533 Time (s) between statistics printk()s.
3535 rcutorture.stutter= [KNL]
3536 Time (s) to stutter testing, for example, specifying
3537 five seconds causes the test to run for five seconds,
3538 wait for five seconds, and so on. This tests RCU's
3539 ability to transition abruptly to and from idle.
3541 rcutorture.test_boost= [KNL]
3542 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3543 "Maybe" means test if the RCU implementation
3544 under test support RCU priority boosting.
3546 rcutorture.test_boost_duration= [KNL]
3547 Duration (s) of each individual boost test.
3549 rcutorture.test_boost_interval= [KNL]
3550 Interval (s) between each boost test.
3552 rcutorture.test_no_idle_hz= [KNL]
3553 Test RCU's dyntick-idle handling. See also the
3554 rcutorture.shuffle_interval parameter.
3556 rcutorture.torture_runnable= [BOOT]
3557 Start rcutorture running at boot time.
3559 rcutorture.torture_type= [KNL]
3560 Specify the RCU implementation to test.
3562 rcutorture.verbose= [KNL]
3563 Enable additional printk() statements.
3565 rcupdate.rcu_cpu_stall_suppress= [KNL]
3566 Suppress RCU CPU stall warning messages.
3568 rcupdate.rcu_cpu_stall_timeout= [KNL]
3569 Set timeout for RCU CPU stall warning messages.
3571 rcupdate.rcu_expedited= [KNL]
3572 Use expedited grace-period primitives, for
3573 example, synchronize_rcu_expedited() instead
3574 of synchronize_rcu(). This reduces latency,
3575 but can increase CPU utilization, degrade
3576 real-time latency, and degrade energy efficiency.
3577 No effect on CONFIG_TINY_RCU kernels.
3579 rcupdate.rcu_normal= [KNL]
3580 Use only normal grace-period primitives,
3581 for example, synchronize_rcu() instead of
3582 synchronize_rcu_expedited(). This improves
3583 real-time latency, CPU utilization, and
3584 energy efficiency, but can expose users to
3585 increased grace-period latency. This parameter
3586 overrides rcupdate.rcu_expedited. No effect on
3587 CONFIG_TINY_RCU kernels.
3589 rcupdate.rcu_normal_after_boot= [KNL]
3590 Once boot has completed (that is, after
3591 rcu_end_inkernel_boot() has been invoked), use
3592 only normal grace-period primitives. No effect
3593 on CONFIG_TINY_RCU kernels.
3595 rcupdate.rcu_task_stall_timeout= [KNL]
3596 Set timeout in jiffies for RCU task stall warning
3597 messages. Disable with a value less than or equal
3600 rcupdate.rcu_self_test= [KNL]
3601 Run the RCU early boot self tests
3603 rcupdate.rcu_self_test_bh= [KNL]
3604 Run the RCU bh early boot self tests
3606 rcupdate.rcu_self_test_sched= [KNL]
3607 Run the RCU sched early boot self tests
3611 Run specified binary instead of /init from the ramdisk,
3612 used for early userspace startup. See initrd.
3615 Format (x86 or x86_64):
3616 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3618 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3620 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3621 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3622 reboot_force is either force or not specified,
3623 reboot_cpu is s[mp]#### with #### being the processor
3624 to be used for rebooting.
3627 [KNL, SMP] Set scheduler's default relax_domain_level.
3628 See Documentation/cgroup-v1/cpusets.txt.
3630 relative_sleep_states=
3631 [SUSPEND] Use sleep state labeling where the deepest
3632 state available other than hibernation is always "mem".
3633 Format: { "0" | "1" }
3634 0 -- Traditional sleep state labels.
3635 1 -- Relative sleep state labels.
3637 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3639 reservetop= [X86-32]
3641 Reserves a hole at the top of the kernel virtual
3646 Set the amount of memory to reserve for BIOS at
3647 the bottom of the address space.
3649 reset_devices [KNL] Force drivers to reset the underlying device
3650 during initialization.
3653 Specify the partition device for software suspend
3655 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3657 resume_offset= [SWSUSP]
3658 Specify the offset from the beginning of the partition
3659 given by "resume=" at which the swap header is located,
3660 in <PAGE_SIZE> units (needed only for swap files).
3661 See Documentation/power/swsusp-and-swap-files.txt
3663 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3664 read the resume files
3666 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3667 Useful for devices that are detected asynchronously
3668 (e.g. USB and MMC devices).
3670 hibernate= [HIBERNATION]
3671 noresume Don't check if there's a hibernation image
3672 present during boot.
3673 nocompress Don't compress/decompress hibernation images.
3674 no Disable hibernation and resume.
3675 protect_image Turn on image protection during restoration
3676 (that will set all pages holding image data
3677 during restoration read-only).
3679 retain_initrd [RAM] Keep initrd memory after extraction
3681 rfkill.default_state=
3682 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3683 etc. communication is blocked by default.
3686 rfkill.master_switch_mode=
3687 0 The "airplane mode" button does nothing.
3688 1 The "airplane mode" button toggles between everything
3689 blocked and the previous configuration.
3690 2 The "airplane mode" button toggles between everything
3691 blocked and everything unblocked.
3693 rhash_entries= [KNL,NET]
3694 Set number of hash buckets for route cache
3696 ro [KNL] Mount root device read-only on boot
3699 on Mark read-only kernel memory as read-only (default).
3700 off Leave read-only kernel memory writable for debugging.
3703 Enable the uart passthrough on the designated usb port
3704 on Rockchip SoCs. When active, the signals of the
3705 debug-uart get routed to the D+ and D- pins of the usb
3706 port and the regular usb controller gets disabled.
3708 root= [KNL] Root filesystem
3709 See name_to_dev_t comment in init/do_mounts.c.
3711 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3712 mount the root filesystem
3714 rootflags= [KNL] Set root filesystem mount option string
3716 rootfstype= [KNL] Set root filesystem type
3718 rootwait [KNL] Wait (indefinitely) for root device to show up.
3719 Useful for devices that are detected asynchronously
3720 (e.g. USB and MMC devices).
3722 rproc_mem=nn[KMG][@address]
3723 [KNL,ARM,CMA] Remoteproc physical memory block.
3724 Memory area to be used by remote processor image,
3727 rw [KNL] Mount root device read-write on boot
3729 S [KNL] Run init in single mode
3731 s390_iommu= [HW,S390]
3732 Set s390 IOTLB flushing mode
3734 With strict flushing every unmap operation will result in
3735 an IOTLB flush. Default is lazy flushing before reuse,
3739 See drivers/net/irda/sa1100_ir.c.
3741 sbni= [NET] Granch SBNI12 leased line adapter
3743 sched_debug [KNL] Enables verbose scheduler debug messages.
3745 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3746 Allowed values are enable and disable. This feature
3747 incurs a small amount of overhead in the scheduler
3748 but is useful for debugging and performance tuning.
3750 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3751 xtime_lock contention on larger systems, and/or RCU lock
3752 contention on all systems with CONFIG_MAXSMP set.
3753 Format: { "0" | "1" }
3754 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3756 Note: increases power consumption, thus should only be
3757 enabled if running jitter sensitive (HPC/RT) workloads.
3759 security= [SECURITY] Choose a security module to enable at boot.
3760 If this boot parameter is not specified, only the first
3761 security module asking for security registration will be
3762 loaded. An invalid security module name will be treated
3763 as if no module has been chosen.
3765 selinux= [SELINUX] Disable or enable SELinux at boot time.
3766 Format: { "0" | "1" }
3767 See security/selinux/Kconfig help text.
3770 Default value is set via kernel config option.
3771 If enabled at boot time, /selinux/disable can be used
3772 later to disable prior to initial policy load.
3774 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3775 Format: { "0" | "1" }
3776 See security/apparmor/Kconfig help text
3779 Default value is set via kernel config option.
3781 serialnumber [BUGS=X86-32]
3784 Maximal number of shapers.
3786 show_msr= [x86] show boot-time MSR settings
3787 Format: { <integer> }
3788 Show boot-time (BIOS-initialized) MSR settings.
3789 The parameter means the number of CPUs to show,
3790 for example 1 means boot CPU only.
3798 Disable merging of slabs with similar size. May be
3799 necessary if there is some reason to distinguish
3800 allocs to different slabs. Debug options disable
3801 merging on their own.
3802 For more information see Documentation/vm/slub.txt.
3804 slab_max_order= [MM, SLAB]
3805 Determines the maximum allowed order for slabs.
3806 A high setting may cause OOMs due to memory
3807 fragmentation. Defaults to 1 for systems with
3808 more than 32MB of RAM, 0 otherwise.
3810 slub_debug[=options[,slabs]] [MM, SLUB]
3811 Enabling slub_debug allows one to determine the
3812 culprit if slab objects become corrupted. Enabling
3813 slub_debug can create guard zones around objects and
3814 may poison objects when not in use. Also tracks the
3815 last alloc / free. For more information see
3816 Documentation/vm/slub.txt.
3818 slub_max_order= [MM, SLUB]
3819 Determines the maximum allowed order for slabs.
3820 A high setting may cause OOMs due to memory
3821 fragmentation. For more information see
3822 Documentation/vm/slub.txt.
3824 slub_min_objects= [MM, SLUB]
3825 The minimum number of objects per slab. SLUB will
3826 increase the slab order up to slub_max_order to
3827 generate a sufficiently large slab able to contain
3828 the number of objects indicated. The higher the number
3829 of objects the smaller the overhead of tracking slabs
3830 and the less frequently locks need to be acquired.
3831 For more information see Documentation/vm/slub.txt.
3833 slub_min_order= [MM, SLUB]
3834 Determines the minimum page order for slabs. Must be
3835 lower than slub_max_order.
3836 For more information see Documentation/vm/slub.txt.
3838 slub_nomerge [MM, SLUB]
3839 Same with slab_nomerge. This is supported for legacy.
3840 See slab_nomerge for more information.
3843 Format: <io1>[,<io2>[,...,<io8>]]
3845 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3846 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3847 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3848 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3849 smsc-ircc2.ircc_irq= [HW] IRQ line
3850 smsc-ircc2.ircc_dma= [HW] DMA channel
3851 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3852 0: Toshiba Satellite 1800 (GP data pin select)
3853 1: Fast pin select (default)
3856 smt [KNL,S390] Set the maximum number of threads (logical
3857 CPUs) to use per physical CPU on systems capable of
3858 symmetric multithreading (SMT). Will be capped to the
3859 actual hardware limit.
3861 Default: -1 (no limit)
3864 [KNL] Should the soft-lockup detector generate panics.
3867 softlockup_all_cpu_backtrace=
3868 [KNL] Should the soft-lockup detector generate
3869 backtraces on all cpus.
3872 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3873 See Documentation/laptops/sonypi.txt
3875 spia_io_base= [HW,MTD]
3881 Enabled the stack tracer on boot up.
3883 stacktrace_filter=[function-list]
3884 [FTRACE] Limit the functions that the stack tracer
3885 will trace at boot up. function-list is a comma separated
3886 list of functions. This list can be changed at run
3887 time by the stack_trace_filter file in the debugfs
3888 tracing directory. Note, this enables stack tracing
3889 and the stacktrace above is not needed.
3893 Set the STI (builtin display/keyboard on the HP-PARISC
3894 machines) console (graphic card) which should be used
3895 as the initial boot-console.
3896 See also comment in drivers/video/console/sticore.c.
3899 See comment in drivers/video/console/sticore.c.
3902 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3904 sunrpc.min_resvport=
3905 sunrpc.max_resvport=
3907 SunRPC servers often require that client requests
3908 originate from a privileged port (i.e. a port in the
3909 range 0 < portnr < 1024).
3910 An administrator who wishes to reserve some of these
3911 ports for other uses may adjust the range that the
3912 kernel's sunrpc client considers to be privileged
3913 using these two parameters to set the minimum and
3914 maximum port values.
3916 sunrpc.svc_rpc_per_connection_limit=
3918 Limit the number of requests that the server will
3919 process in parallel from a single connection.
3920 The default value is 0 (no limit).
3924 Control how the NFS server code allocates CPUs to
3925 service thread pools. Depending on how many NICs
3926 you have and where their interrupts are bound, this
3927 option will affect which CPUs will do NFS serving.
3928 Note: this parameter cannot be changed while the
3929 NFS server is running.
3931 auto the server chooses an appropriate mode
3932 automatically using heuristics
3933 global a single global pool contains all CPUs
3934 percpu one pool for each CPU
3935 pernode one pool for each NUMA node (equivalent
3936 to global on non-NUMA machines)
3938 sunrpc.tcp_slot_table_entries=
3939 sunrpc.udp_slot_table_entries=
3941 Sets the upper limit on the number of simultaneous
3942 RPC calls that can be sent from the client to a
3943 server. Increasing these values may allow you to
3944 improve throughput, but will also increase the
3945 amount of memory reserved for use by the client.
3947 suspend.pm_test_delay=
3949 Sets the number of seconds to remain in a suspend test
3950 mode before resuming the system (see
3951 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3952 is set. Default value is 5.
3955 [KNL] Enable accounting of swap in memory resource
3956 controller if no parameter or 1 is given or disable
3957 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
3959 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3960 Format: { <int> | force }
3961 <int> -- Number of I/O TLB slabs
3962 force -- force using of bounce buffers even if they
3963 wouldn't be automatically used by the kernel
3967 sysfs.deprecated=0|1 [KNL]
3968 Enable/disable old style sysfs layout for old udev
3969 on older distributions. When this option is enabled
3970 very new udev will not work anymore. When this option
3971 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3972 in older udev will not work anymore.
3973 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3974 the kernel configuration.
3976 sysrq_always_enabled
3978 Ignore sysrq setting - this boot parameter will
3979 neutralize any effect of /proc/sys/kernel/sysrq.
3980 Useful for debugging.
3982 tcpmhash_entries= [KNL,NET]
3983 Set the number of tcp_metrics_hash slots.
3984 Default value is 8192 or 16384 depending on total
3985 ram pages. This is used to specify the TCP metrics
3986 cache size. See Documentation/networking/ip-sysctl.txt
3987 "tcp_no_metrics_save" section for more details.
3991 test_suspend= [SUSPEND][,N]
3992 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3993 standby suspend) or "freeze" (for suspend type freeze)
3994 as the system sleep state during system startup with
3995 the optional capability to repeat N number of times.
3996 The system is woken from this state using a
3997 wakeup-capable RTC alarm.
3999 thash_entries= [KNL,NET]
4000 Set number of hash buckets for TCP connection
4002 thermal.act= [HW,ACPI]
4003 -1: disable all active trip points in all thermal zones
4004 <degrees C>: override all lowest active trip points
4006 thermal.crt= [HW,ACPI]
4007 -1: disable all critical trip points in all thermal zones
4008 <degrees C>: override all critical trip points
4010 thermal.nocrt= [HW,ACPI]
4011 Set to disable actions on ACPI thermal zone
4012 critical and hot trip points.
4014 thermal.off= [HW,ACPI]
4015 1: disable ACPI thermal control
4017 thermal.psv= [HW,ACPI]
4018 -1: disable all passive trip points
4019 <degrees C>: override all passive trip points to this
4022 thermal.tzp= [HW,ACPI]
4023 Specify global default ACPI thermal zone polling rate
4024 <deci-seconds>: poll all this frequency
4025 0: no polling (default)
4028 Force threading of all interrupt handlers except those
4029 marked explicitly IRQF_NO_THREAD.
4032 Enable the Transcendent memory driver if built-in.
4034 tmem.cleancache=0|1 [KNL, XEN]
4035 Default is on (1). Disable the usage of the cleancache
4036 API to send anonymous pages to the hypervisor.
4038 tmem.frontswap=0|1 [KNL, XEN]
4039 Default is on (1). Disable the usage of the frontswap
4040 API to send swap pages to the hypervisor. If disabled
4041 the selfballooning and selfshrinking are force disabled.
4043 tmem.selfballooning=0|1 [KNL, XEN]
4044 Default is on (1). Disable the driving of swap pages
4047 tmem.selfshrinking=0|1 [KNL, XEN]
4048 Default is on (1). Partial swapoff that immediately
4049 transfers pages from Xen hypervisor back to the
4050 kernel based on different criteria.
4054 Specify if the kernel should make use of the cpu
4055 topology information if the hardware supports this.
4056 The scheduler will make use of this information and
4057 e.g. base its process migration decisions on it.
4060 topology_updates= [KNL, PPC, NUMA]
4062 Specify if the kernel should ignore (off)
4063 topology updates sent by the hypervisor to this
4068 tpm_suspend_pcr=[HW,TPM]
4069 Format: integer pcr id
4070 Specify that at suspend time, the tpm driver
4071 should extend the specified pcr with zeros,
4072 as a workaround for some chips which fail to
4073 flush the last written pcr on TPM_SaveState.
4074 This will guarantee that all the other pcrs
4077 trace_buf_size=nn[KMG]
4078 [FTRACE] will set tracing buffer size on each cpu.
4080 trace_event=[event-list]
4081 [FTRACE] Set and start specified trace events in order
4082 to facilitate early boot debugging. The event-list is a
4083 comma separated list of trace events to enable. See
4084 also Documentation/trace/events.txt
4086 trace_options=[option-list]
4087 [FTRACE] Enable or disable tracer options at boot.
4088 The option-list is a comma delimited list of options
4089 that can be enabled or disabled just as if you were
4090 to echo the option name into
4092 /sys/kernel/debug/tracing/trace_options
4094 For example, to enable stacktrace option (to dump the
4095 stack trace of each event), add to the command line:
4097 trace_options=stacktrace
4099 See also Documentation/trace/ftrace.txt "trace options"
4103 Have the tracepoints sent to printk as well as the
4104 tracing ring buffer. This is useful for early boot up
4105 where the system hangs or reboots and does not give the
4106 option for reading the tracing buffer or performing a
4107 ftrace_dump_on_oops.
4109 To turn off having tracepoints sent to printk,
4110 echo 0 > /proc/sys/kernel/tracepoint_printk
4111 Note, echoing 1 into this file without the
4112 tracepoint_printk kernel cmdline option has no effect.
4116 Having tracepoints sent to printk() and activating high
4117 frequency tracepoints such as irq or sched, can cause
4118 the system to live lock.
4121 [FTRACE] enable this option to disable tracing when a
4122 warning is hit. This turns off "tracing_on". Tracing can
4123 be enabled again by echoing '1' into the "tracing_on"
4124 file located in /sys/kernel/debug/tracing/
4126 This option is useful, as it disables the trace before
4127 the WARNING dump is called, which prevents the trace to
4128 be filled with content caused by the warning output.
4130 This option can also be set at run time via the sysctl
4131 option: kernel/traceoff_on_warning
4133 transparent_hugepage=
4135 Format: [always|madvise|never]
4136 Can be used to control the default behavior of the system
4137 with respect to transparent hugepages.
4138 See Documentation/vm/transhuge.txt for more details.
4140 tsc= Disable clocksource stability checks for TSC.
4142 [x86] reliable: mark tsc clocksource as reliable, this
4143 disables clocksource verification at runtime, as well
4144 as the stability checks done at bootup. Used to enable
4145 high-resolution timer mode on older hardware, and in
4146 virtualized environment.
4147 [x86] noirqtime: Do not use TSC to do irq accounting.
4148 Used to run time disable IRQ_TIME_ACCOUNTING on any
4149 platforms where RDTSC is slow and this accounting
4152 turbografx.map[2|3]= [HW,JOY]
4153 TurboGraFX parallel port interface
4155 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4156 See also Documentation/input/joystick-parport.txt
4158 udbg-immortal [PPC] When debugging early kernel crashes that
4159 happen after console_init() and before a proper
4160 console driver takes over, this boot options might
4161 help "seeing" what's going on.
4163 uhash_entries= [KNL,NET]
4164 Set number of hash buckets for UDP/UDP-Lite connections
4167 [USB] Ignore overcurrent events (default N).
4168 Some badly-designed motherboards generate lots of
4169 bogus events, for ports that aren't wired to
4170 anything. Set this parameter to avoid log spamming.
4171 Note that genuine overcurrent events won't be
4175 [X86] Cause panic on unknown NMI.
4177 usbcore.authorized_default=
4178 [USB] Default USB device authorization:
4179 (default -1 = authorized except for wireless USB,
4180 0 = not authorized, 1 = authorized)
4182 usbcore.autosuspend=
4183 [USB] The autosuspend time delay (in seconds) used
4184 for newly-detected USB devices (default 2). This
4185 is the time required before an idle device will be
4186 autosuspended. Devices for which the delay is set
4187 to a negative value won't be autosuspended at all.
4189 usbcore.usbfs_snoop=
4190 [USB] Set to log all usbfs traffic (default 0 = off).
4192 usbcore.usbfs_snoop_max=
4193 [USB] Maximum number of bytes to snoop in each URB
4196 usbcore.blinkenlights=
4197 [USB] Set to cycle leds on hubs (default 0 = off).
4199 usbcore.old_scheme_first=
4200 [USB] Start with the old device initialization
4201 scheme (default 0 = off).
4203 usbcore.usbfs_memory_mb=
4204 [USB] Memory limit (in MB) for buffers allocated by
4205 usbfs (default = 16, 0 = max = 2047).
4207 usbcore.use_both_schemes=
4208 [USB] Try the other device initialization scheme
4209 if the first one fails (default 1 = enabled).
4211 usbcore.initial_descriptor_timeout=
4212 [USB] Specifies timeout for the initial 64-byte
4213 USB_REQ_GET_DESCRIPTOR request in milliseconds
4214 (default 5000 = 5.0 seconds).
4216 usbcore.nousb [USB] Disable the USB subsystem
4219 [USBHID] The interval which mice are to be polled at.
4221 usb-storage.delay_use=
4222 [UMS] The delay in seconds before a new device is
4223 scanned for Logical Units (default 1).
4226 [UMS] A list of quirks entries to supplement or
4227 override the built-in unusual_devs list. List
4228 entries are separated by commas. Each entry has
4229 the form VID:PID:Flags where VID and PID are Vendor
4230 and Product ID values (4-digit hex numbers) and
4231 Flags is a set of characters, each corresponding
4232 to a common usb-storage quirk flag as follows:
4233 a = SANE_SENSE (collect more than 18 bytes
4235 b = BAD_SENSE (don't collect more than 18
4236 bytes of sense data);
4237 c = FIX_CAPACITY (decrease the reported
4238 device capacity by one sector);
4239 d = NO_READ_DISC_INFO (don't use
4240 READ_DISC_INFO command);
4241 e = NO_READ_CAPACITY_16 (don't use
4242 READ_CAPACITY_16 command);
4243 f = NO_REPORT_OPCODES (don't use report opcodes
4245 g = MAX_SECTORS_240 (don't transfer more than
4246 240 sectors at a time, uas only);
4247 h = CAPACITY_HEURISTICS (decrease the
4248 reported device capacity by one
4249 sector if the number is odd);
4250 i = IGNORE_DEVICE (don't bind to this
4252 j = NO_REPORT_LUNS (don't use report luns
4254 l = NOT_LOCKABLE (don't try to lock and
4255 unlock ejectable media);
4256 m = MAX_SECTORS_64 (don't transfer more
4257 than 64 sectors = 32 KB at a time);
4258 n = INITIAL_READ10 (force a retry of the
4259 initial READ(10) command);
4260 o = CAPACITY_OK (accept the capacity
4261 reported by the device);
4262 p = WRITE_CACHE (the device cache is ON
4264 r = IGNORE_RESIDUE (the device reports
4265 bogus residue values);
4266 s = SINGLE_LUN (the device has only one
4268 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4269 commands, uas only);
4270 u = IGNORE_UAS (don't bind to the uas driver);
4271 w = NO_WP_DETECT (don't test whether the
4272 medium is write-protected).
4273 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4274 even if the device claims no cache)
4275 Example: quirks=0419:aaf5:rl,0421:0433:rc
4277 user_debug= [KNL,ARM]
4279 See arch/arm/Kconfig.debug help text.
4280 1 - undefined instruction events
4282 4 - invalid data aborts
4285 Example: user_debug=31
4288 [X86] Flags controlling user PTE allocations.
4290 nohigh = do not allocate PTE pages in
4291 HIGHMEM regardless of setting
4295 On X86_32, this is an alias for vdso32=. Otherwise:
4297 vdso=1: enable VDSO (the default)
4298 vdso=0: disable VDSO mapping
4300 vdso32= [X86] Control the 32-bit vDSO
4301 vdso32=1: enable 32-bit VDSO
4302 vdso32=0 or vdso32=2: disable 32-bit VDSO
4304 See the help text for CONFIG_COMPAT_VDSO for more
4305 details. If CONFIG_COMPAT_VDSO is set, the default is
4306 vdso32=0; otherwise, the default is vdso32=1.
4308 For compatibility with older kernels, vdso32=2 is an
4311 Try vdso32=0 if you encounter an error that says:
4312 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4315 vector=percpu: enable percpu vector domain
4317 video= [FB] Frame buffer configuration
4318 See Documentation/fb/modedb.txt.
4320 video.brightness_switch_enabled= [0,1]
4321 If set to 1, on receiving an ACPI notify event
4322 generated by hotkey, video driver will adjust brightness
4323 level and then send out the event to user space through
4324 the allocated input device; If set to 0, video driver
4325 will only send out the event without touching backlight
4330 [VMMIO] Memory mapped virtio (platform) device.
4332 <size>@<baseaddr>:<irq>[:<id>]
4334 <size> := size (can use standard suffixes
4336 <baseaddr> := physical base address
4337 <irq> := interrupt number (as passed to
4339 <id> := (optional) platform device id
4341 virtio_mmio.device=1K@0x100b0000:48:7
4343 Can be used multiple times for multiple devices.
4345 vga= [BOOT,X86-32] Select a particular video mode
4346 See Documentation/x86/boot.txt and
4347 Documentation/svga.txt.
4348 Use vga=ask for menu.
4349 This is actually a boot loader parameter; the value is
4350 passed to the kernel using a special protocol.
4352 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4353 size of <nn>. This can be used to increase the
4354 minimum size (128MB on x86). It can also be used to
4355 decrease the size and leave more room for directly
4358 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4361 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4364 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4368 Controls the behavior of vsyscalls (i.e. calls to
4369 fixed addresses of 0xffffffffff600x00 from legacy
4370 code). Most statically-linked binaries and older
4371 versions of glibc use these calls. Because these
4372 functions are at fixed addresses, they make nice
4373 targets for exploits that can control RIP.
4375 emulate [default] Vsyscalls turn into traps and are
4376 emulated reasonably safely.
4378 native Vsyscalls are native syscall instructions.
4379 This is a little bit faster than trapping
4380 and makes a few dynamic recompilers work
4381 better than they would in emulation mode.
4382 It also makes exploits much easier to write.
4384 none Vsyscalls don't work at all. This makes
4385 them quite hard to use for exploits but
4386 might break your system.
4388 vt.color= [VT] Default text color.
4389 Format: 0xYX, X = foreground, Y = background.
4390 Default: 0x07 = light gray on black.
4392 vt.cur_default= [VT] Default cursor shape.
4393 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4394 the parameters of the <Esc>[?A;B;Cc escape sequence;
4395 see VGA-softcursor.txt. Default: 2 = underline.
4397 vt.default_blu= [VT]
4398 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4399 Change the default blue palette of the console.
4400 This is a 16-member array composed of values
4403 vt.default_grn= [VT]
4404 Format: <green0>,<green1>,<green2>,...,<green15>
4405 Change the default green palette of the console.
4406 This is a 16-member array composed of values
4409 vt.default_red= [VT]
4410 Format: <red0>,<red1>,<red2>,...,<red15>
4411 Change the default red palette of the console.
4412 This is a 16-member array composed of values
4418 Set system-wide default UTF-8 mode for all tty's.
4419 Default is 1, i.e. UTF-8 mode is enabled for all
4420 newly opened terminals.
4422 vt.global_cursor_default=
4425 Set system-wide default for whether a cursor
4426 is shown on new VTs. Default is -1,
4427 i.e. cursors will be created by default unless
4428 overridden by individual drivers. 0 will hide
4429 cursors, 1 will display them.
4431 vt.italic= [VT] Default color for italic text; 0-15.
4434 vt.underline= [VT] Default color for underlined text; 0-15.
4437 watchdog timers [HW,WDT] For information on watchdog timers,
4438 see Documentation/watchdog/watchdog-parameters.txt
4439 or other driver-specific files in the
4440 Documentation/watchdog/ directory.
4442 workqueue.watchdog_thresh=
4443 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4444 warn stall conditions and dump internal state to
4445 help debugging. 0 disables workqueue stall
4446 detection; otherwise, it's the stall threshold
4447 duration in seconds. The default value is 30 and
4448 it can be updated at runtime by writing to the
4449 corresponding sysfs file.
4451 workqueue.disable_numa
4452 By default, all work items queued to unbound
4453 workqueues are affine to the NUMA nodes they're
4454 issued on, which results in better behavior in
4455 general. If NUMA affinity needs to be disabled for
4456 whatever reason, this option can be used. Note
4457 that this also can be controlled per-workqueue for
4458 workqueues visible under /sys/bus/workqueue/.
4460 workqueue.power_efficient
4461 Per-cpu workqueues are generally preferred because
4462 they show better performance thanks to cache
4463 locality; unfortunately, per-cpu workqueues tend to
4464 be more power hungry than unbound workqueues.
4466 Enabling this makes the per-cpu workqueues which
4467 were observed to contribute significantly to power
4468 consumption unbound, leading to measurably lower
4469 power usage at the cost of small performance
4472 The default value of this parameter is determined by
4473 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4475 workqueue.debug_force_rr_cpu
4476 Workqueue used to implicitly guarantee that work
4477 items queued without explicit CPU specified are put
4478 on the local CPU. This guarantee is no longer true
4479 and while local CPU is still preferred work items
4480 may be put on foreign CPUs. This debug option
4481 forces round-robin CPU selection to flush out
4482 usages which depend on the now broken guarantee.
4483 When enabled, memory and cache locality will be
4486 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4487 default x2apic cluster mode on platforms
4490 x86_intel_mid_timer= [X86-32,APBT]
4491 Choose timer option for x86 Intel MID platform.
4492 Two valid options are apbt timer only and lapic timer
4493 plus one apbt timer for broadcast timer.
4494 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4496 xen_512gb_limit [KNL,X86-64,XEN]
4497 Restricts the kernel running paravirtualized under Xen
4498 to use only up to 512 GB of RAM. The reason to do so is
4499 crash analysis tools and Xen tools for doing domain
4500 save/restore/migration must be enabled to handle larger
4503 xen_emul_unplug= [HW,X86,XEN]
4504 Unplug Xen emulated devices
4505 Format: [unplug0,][unplug1]
4506 ide-disks -- unplug primary master IDE devices
4507 aux-ide-disks -- unplug non-primary-master IDE devices
4508 nics -- unplug network devices
4509 all -- unplug all emulated devices (NICs and IDE disks)
4510 unnecessary -- unplugging emulated devices is
4511 unnecessary even if the host did not respond to
4513 never -- do not unplug even if version check succeeds
4515 xen_nopvspin [X86,XEN]
4516 Disables the ticketlock slowpath using Xen PV
4520 Disables the PV optimizations forcing the HVM guest to
4521 run as generic HVM guest with no PV drivers.
4523 xirc2ps_cs= [NET,PCMCIA]
4525 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4527 ______________________________________________________________________
4531 Add more DRM drivers.
projects / cascardo / linux.git / blob