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 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1672 int_pln_enable [x86] Enable power limit notification interrupt
1674 integrity_audit=[IMA]
1675 Format: { "0" | "1" }
1676 0 -- basic integrity auditing messages. (Default)
1677 1 -- additional integrity auditing messages.
1679 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1681 Enable intel iommu driver.
1683 Disable intel iommu driver.
1684 igfx_off [Default Off]
1685 By default, gfx is mapped as normal device. If a gfx
1686 device has a dedicated DMAR unit, the DMAR unit is
1687 bypassed by not enabling DMAR with this option. In
1688 this case, gfx device will use physical address for
1691 With this option iommu will not optimize to look
1692 for io virtual address below 32-bit forcing dual
1693 address cycle on pci bus for cards supporting greater
1694 than 32-bit addressing. The default is to look
1695 for translation below 32-bit and if not available
1696 then look in the higher range.
1697 strict [Default Off]
1698 With this option on every unmap_single operation will
1699 result in a hardware IOTLB flush operation as opposed
1700 to batching them for performance.
1701 sp_off [Default Off]
1702 By default, super page will be supported if Intel IOMMU
1703 has the capability. With this option, super page will
1705 ecs_off [Default Off]
1706 By default, extended context tables will be supported if
1707 the hardware advertises that it has support both for the
1708 extended tables themselves, and also PASID support. With
1709 this option set, extended tables will not be used even
1710 on hardware which claims to support them.
1712 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1713 0 disables intel_idle and fall back on acpi_idle.
1714 1 to 9 specify maximum depth of C-state.
1718 Do not enable intel_pstate as the default
1719 scaling driver for the supported processors
1721 Enable intel_pstate on systems that prohibit it by default
1722 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1723 instead of acpi-cpufreq may disable platform features, such
1724 as thermal controls and power capping, that rely on ACPI
1725 P-States information being indicated to OSPM and therefore
1726 should be used with caution. This option does not work with
1727 processors that aren't supported by the intel_pstate driver
1728 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1730 Do not enable hardware P state control (HWP)
1733 Only load intel_pstate on systems which support
1734 hardware P state control (HWP) if available.
1736 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1737 Description Table, specifies preferred power management
1738 profile as "Enterprise Server" or "Performance Server",
1739 then this feature is turned on by default.
1741 intremap= [X86-64, Intel-IOMMU]
1742 on enable Interrupt Remapping (default)
1743 off disable Interrupt Remapping
1744 nosid disable Source ID checking
1746 BIOS x2APIC opt-out request will be ignored
1747 nopost disable Interrupt Posting
1749 iomem= Disable strict checking of access to MMIO memory
1750 strict regions from userspace.
1765 nobypass [PPC/POWERNV]
1766 Disable IOMMU bypass, using IOMMU for PCI devices.
1769 io7= [HW] IO7 for Marvel based alpha systems
1770 See comment before marvel_specify_io7 in
1771 arch/alpha/kernel/core_marvel.c.
1773 io_delay= [X86] I/O delay method
1775 Standard port 0x80 based delay
1777 Alternate port 0xed based delay (needed on some systems)
1779 Simple two microseconds delay
1784 See Documentation/filesystems/nfs/nfsroot.txt.
1786 irqaffinity= [SMP] Set the default irq affinity mask
1788 <cpu number>,...,<cpu number>
1790 <cpu number>-<cpu number>
1791 (must be a positive range in ascending order)
1793 <cpu number>,...,<cpu number>-<cpu number>
1796 When an interrupt is not handled search all handlers
1797 for it. Intended to get systems with badly broken
1801 When an interrupt is not handled search all handlers
1802 for it. Also check all handlers each timer
1803 interrupt. Intended to get systems with badly broken
1807 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1809 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1811 <cpu number>,...,<cpu number>
1813 <cpu number>-<cpu number>
1814 (must be a positive range in ascending order)
1816 <cpu number>,...,<cpu number>-<cpu number>
1818 This option can be used to specify one or more CPUs
1819 to isolate from the general SMP balancing and scheduling
1820 algorithms. You can move a process onto or off an
1821 "isolated" CPU via the CPU affinity syscalls or cpuset.
1822 <cpu number> begins at 0 and the maximum value is
1823 "number of CPUs in system - 1".
1825 This option is the preferred way to isolate CPUs. The
1826 alternative -- manually setting the CPU mask of all
1827 tasks in the system -- can cause problems and
1828 suboptimal load balancer performance.
1832 ivrs_ioapic [HW,X86_64]
1833 Provide an override to the IOAPIC-ID<->DEVICE-ID
1834 mapping provided in the IVRS ACPI table. For
1835 example, to map IOAPIC-ID decimal 10 to
1836 PCI device 00:14.0 write the parameter as:
1837 ivrs_ioapic[10]=00:14.0
1839 ivrs_hpet [HW,X86_64]
1840 Provide an override to the HPET-ID<->DEVICE-ID
1841 mapping provided in the IVRS ACPI table. For
1842 example, to map HPET-ID decimal 0 to
1843 PCI device 00:14.0 write the parameter as:
1844 ivrs_hpet[0]=00:14.0
1846 ivrs_acpihid [HW,X86_64]
1847 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1848 mapping provided in the IVRS ACPI table. For
1849 example, to map UART-HID:UID AMD0020:0 to
1850 PCI device 00:14.5 write the parameter as:
1851 ivrs_acpihid[00:14.5]=AMD0020:0
1853 js= [HW,JOY] Analog joystick
1854 See Documentation/input/joystick.txt.
1857 When CONFIG_RANDOMIZE_BASE is set, this disables
1858 kernel and module base offset ASLR (Address Space
1859 Layout Randomization).
1863 kernelcore= [KNL,X86,IA-64,PPC]
1864 Format: nn[KMGTPE] | "mirror"
1866 specifies the amount of memory usable by the kernel
1867 for non-movable allocations. The requested amount is
1868 spread evenly throughout all nodes in the system. The
1869 remaining memory in each node is used for Movable
1870 pages. In the event, a node is too small to have both
1871 kernelcore and Movable pages, kernelcore pages will
1872 take priority and other nodes will have a larger number
1873 of Movable pages. The Movable zone is used for the
1874 allocation of pages that may be reclaimed or moved
1875 by the page migration subsystem. This means that
1876 HugeTLB pages may not be allocated from this zone.
1877 Note that allocations like PTEs-from-HighMem still
1878 use the HighMem zone if it exists, and the Normal
1879 zone if it does not.
1881 Instead of specifying the amount of memory (nn[KMGTPE]),
1882 you can specify "mirror" option. In case "mirror"
1883 option is specified, mirrored (reliable) memory is used
1884 for non-movable allocations and remaining memory is used
1885 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1886 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1889 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1890 Format: <Controller#>[,poll interval]
1891 The controller # is the number of the ehci usb debug
1892 port as it is probed via PCI. The poll interval is
1893 optional and is the number seconds in between
1894 each poll cycle to the debug port in case you need
1895 the functionality for interrupting the kernel with
1896 gdb or control-c on the dbgp connection. When
1897 not using this parameter you use sysrq-g to break into
1898 the kernel debugger.
1900 kgdboc= [KGDB,HW] kgdb over consoles.
1901 Requires a tty driver that supports console polling,
1902 or a supported polling keyboard driver (non-usb).
1903 Serial only format: <serial_device>[,baud]
1904 keyboard only format: kbd
1905 keyboard and serial format: kbd,<serial_device>[,baud]
1906 Optional Kernel mode setting:
1907 kms, kbd format: kms,kbd
1908 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1910 kgdbwait [KGDB] Stop kernel execution and enter the
1911 kernel debugger at the earliest opportunity.
1913 kmac= [MIPS] korina ethernet MAC address.
1914 Configure the RouterBoard 532 series on-chip
1915 Ethernet adapter MAC address.
1917 kmemleak= [KNL] Boot-time kmemleak enable/disable
1918 Valid arguments: on, off
1920 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1923 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1924 Valid arguments: 0, 1, 2
1925 kmemcheck=0 (disabled)
1926 kmemcheck=1 (enabled)
1927 kmemcheck=2 (one-shot mode)
1928 Default: 2 (one-shot mode)
1930 kstack=N [X86] Print N words from the kernel stack
1933 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1934 Default is 0 (don't ignore, but inject #GP)
1936 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1940 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1941 Default is 1 (enabled)
1943 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1945 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1947 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1948 (virtualized MMU) support on capable Intel chips.
1949 Default is 1 (enabled)
1951 kvm-intel.emulate_invalid_guest_state=
1952 [KVM,Intel] Enable emulation of invalid guest states
1953 Default is 0 (disabled)
1955 kvm-intel.flexpriority=
1956 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1957 Default is 1 (enabled)
1960 [KVM,Intel] Enable VMX nesting (nVMX).
1961 Default is 0 (disabled)
1963 kvm-intel.unrestricted_guest=
1964 [KVM,Intel] Disable unrestricted guest feature
1965 (virtualized real and unpaged mode) on capable
1966 Intel chips. Default is 1 (enabled)
1968 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1969 feature (tagged TLBs) on capable Intel chips.
1970 Default is 1 (enabled)
1976 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1979 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1980 value for LAPIC timer one-shot implementation. Default
1981 back to the programmable timer unit in the LAPIC.
1983 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1986 libata.dma= [LIBATA] DMA control
1987 libata.dma=0 Disable all PATA and SATA DMA
1988 libata.dma=1 PATA and SATA Disk DMA only
1989 libata.dma=2 ATAPI (CDROM) DMA only
1990 libata.dma=4 Compact Flash DMA only
1991 Combinations also work, so libata.dma=3 enables DMA
1992 for disks and CDROMs, but not CFs.
1994 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1995 libata.ignore_hpa=0 keep BIOS limits (default)
1996 libata.ignore_hpa=1 ignore limits, using full disk
1998 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2002 libata.force= [LIBATA] Force configurations. The format is comma
2003 separated list of "[ID:]VAL" where ID is
2004 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2005 matching port, link or device. Basically, it matches
2006 the ATA ID string printed on console by libata. If
2007 the whole ID part is omitted, the last PORT and DEVICE
2008 values are used. If ID hasn't been specified yet, the
2009 configuration applies to all ports, links and devices.
2011 If only DEVICE is omitted, the parameter applies to
2012 the port and all links and devices behind it. DEVICE
2013 number of 0 either selects the first device or the
2014 first fan-out link behind PMP device. It does not
2015 select the host link. DEVICE number of 15 selects the
2016 host link and device attached to it.
2018 The VAL specifies the configuration to force. As long
2019 as there's no ambiguity shortcut notation is allowed.
2020 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2021 The following configurations can be forced.
2023 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2024 Any ID with matching PORT is used.
2026 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2028 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2029 udma[/][16,25,33,44,66,100,133] notation is also
2032 * [no]ncq: Turn on or off NCQ.
2034 * [no]ncqtrim: Turn off queued DSM TRIM.
2036 * nohrst, nosrst, norst: suppress hard, soft
2039 * rstonce: only attempt one reset during
2040 hot-unplug link recovery
2042 * dump_id: dump IDENTIFY data.
2044 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2046 * disable: Disable this device.
2048 If there are multiple matching configurations changing
2049 the same attribute, the last one is used.
2051 memblock=debug [KNL] Enable memblock debug messages.
2053 load_ramdisk= [RAM] List of ramdisks to load from floppy
2054 See Documentation/blockdev/ramdisk.txt.
2056 lockd.nlm_grace_period=P [NFS] Assign grace period.
2059 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2062 lockd.nlm_timeout=T [NFS] Assign timeout value.
2065 lockd.nlm_udpport=M [NFS] Assign UDP port.
2068 locktorture.nreaders_stress= [KNL]
2069 Set the number of locking read-acquisition kthreads.
2070 Defaults to being automatically set based on the
2071 number of online CPUs.
2073 locktorture.nwriters_stress= [KNL]
2074 Set the number of locking write-acquisition kthreads.
2076 locktorture.onoff_holdoff= [KNL]
2077 Set time (s) after boot for CPU-hotplug testing.
2079 locktorture.onoff_interval= [KNL]
2080 Set time (s) between CPU-hotplug operations, or
2081 zero to disable CPU-hotplug testing.
2083 locktorture.shuffle_interval= [KNL]
2084 Set task-shuffle interval (jiffies). Shuffling
2085 tasks allows some CPUs to go into dyntick-idle
2086 mode during the locktorture test.
2088 locktorture.shutdown_secs= [KNL]
2089 Set time (s) after boot system shutdown. This
2090 is useful for hands-off automated testing.
2092 locktorture.stat_interval= [KNL]
2093 Time (s) between statistics printk()s.
2095 locktorture.stutter= [KNL]
2096 Time (s) to stutter testing, for example,
2097 specifying five seconds causes the test to run for
2098 five seconds, wait for five seconds, and so on.
2099 This tests the locking primitive's ability to
2100 transition abruptly to and from idle.
2102 locktorture.torture_runnable= [BOOT]
2103 Start locktorture running at boot time.
2105 locktorture.torture_type= [KNL]
2106 Specify the locking implementation to test.
2108 locktorture.verbose= [KNL]
2109 Enable additional printk() statements.
2111 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2114 loglevel= All Kernel Messages with a loglevel smaller than the
2115 console loglevel will be printed to the console. It can
2116 also be changed with klogd or other programs. The
2117 loglevels are defined as follows:
2119 0 (KERN_EMERG) system is unusable
2120 1 (KERN_ALERT) action must be taken immediately
2121 2 (KERN_CRIT) critical conditions
2122 3 (KERN_ERR) error conditions
2123 4 (KERN_WARNING) warning conditions
2124 5 (KERN_NOTICE) normal but significant condition
2125 6 (KERN_INFO) informational
2126 7 (KERN_DEBUG) debug-level messages
2128 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2129 in bytes. n must be a power of two and greater
2130 than the minimal size. The minimal size is defined
2131 by LOG_BUF_SHIFT kernel config parameter. There is
2132 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2133 that allows to increase the default size depending on
2134 the number of CPUs. See init/Kconfig for more details.
2136 logo.nologo [FB] Disables display of the built-in Linux logo.
2137 This may be used to provide more screen space for
2138 kernel log messages and is useful when debugging
2139 kernel boot problems.
2141 lp=0 [LP] Specify parallel ports to use, e.g,
2142 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2143 lp=reset first parallel port). 'lp=0' disables the
2144 lp=auto printer driver. 'lp=reset' (which can be
2145 specified in addition to the ports) causes
2146 attached printers to be reset. Using
2147 lp=port1,port2,... specifies the parallel ports
2148 to associate lp devices with, starting with
2149 lp0. A port specification may be 'none' to skip
2150 that lp device, or a parport name such as
2151 'parport0'. Specifying 'lp=auto' instead of a
2152 port specification list means that device IDs
2153 from each port should be examined, to see if
2154 an IEEE 1284-compliant printer is attached; if
2155 so, the driver will manage that printer.
2156 See also header of drivers/char/lp.c.
2159 Sets loops_per_jiffy to given constant, thus avoiding
2160 time-consuming boot-time autodetection (up to 250 ms per
2161 CPU). 0 enables autodetection (default). To determine
2162 the correct value for your kernel, boot with normal
2163 autodetection and see what value is printed. Note that
2164 on SMP systems the preset will be applied to all CPUs,
2165 which is likely to cause problems if your CPUs need
2166 significantly divergent settings. An incorrect value
2167 will cause delays in the kernel to be wrong, leading to
2168 unpredictable I/O errors and other breakage. Although
2169 unlikely, in the extreme case this might damage your
2173 Format: <io>,<irq>,<dma>
2175 machvec= [IA-64] Force the use of a particular machine-vector
2176 (machvec) in a generic kernel.
2177 Example: machvec=hpzx1_swiotlb
2179 machtype= [Loongson] Share the same kernel image file between different
2181 Example: machtype=lemote-yeeloong-2f-7inch
2183 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2184 than or equal to this physical address is ignored.
2186 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2187 will bring up during bootup. maxcpus=n : n >= 0 limits
2188 the kernel to bring up 'n' processors. Surely after
2189 bootup you can bring up the other plugged cpu by executing
2190 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2191 only takes effect during system bootup.
2192 While n=0 is a special case, it is equivalent to "nosmp",
2193 which also disables the IO APIC.
2195 max_loop= [LOOP] The number of loop block devices that get
2196 (loop.max_loop) unconditionally pre-created at init time. The default
2197 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2198 of statically allocating a predefined number, loop
2199 devices can be requested on-demand with the
2200 /dev/loop-control interface.
2202 mce [X86-32] Machine Check Exception
2204 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2206 md= [HW] RAID subsystems devices and level
2207 See Documentation/md.txt.
2210 Format: <first>,<last>
2211 Specifies range of consoles to be captured by the MDA.
2213 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2214 Amount of memory to be used when the kernel is not able
2215 to see the whole system memory or for test.
2216 [X86] Work as limiting max address. Use together
2217 with memmap= to avoid physical address space collisions.
2218 Without memmap= PCI devices could be placed at addresses
2219 belonging to unused RAM.
2221 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2225 [KNL,SH] Allow user to override the default size for
2226 per-device physically contiguous DMA buffers.
2228 memhp_default_state=online/offline
2229 [KNL] Set the initial state for the memory hotplug
2230 onlining policy. If not specified, the default value is
2231 set according to the
2232 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2234 See Documentation/memory-hotplug.txt.
2236 memmap=exactmap [KNL,X86] Enable setting of an exact
2237 E820 memory map, as specified by the user.
2238 Such memmap=exactmap lines can be constructed based on
2239 BIOS output or other requirements. See the memmap=nn@ss
2242 memmap=nn[KMG]@ss[KMG]
2243 [KNL] Force usage of a specific region of memory.
2244 Region of memory to be used is from ss to ss+nn.
2246 memmap=nn[KMG]#ss[KMG]
2247 [KNL,ACPI] Mark specific memory as ACPI data.
2248 Region of memory to be marked is from ss to ss+nn.
2250 memmap=nn[KMG]$ss[KMG]
2251 [KNL,ACPI] Mark specific memory as reserved.
2252 Region of memory to be reserved is from ss to ss+nn.
2253 Example: Exclude memory from 0x18690000-0x1869ffff
2254 memmap=64K$0x18690000
2256 memmap=0x10000$0x18690000
2258 memmap=nn[KMG]!ss[KMG]
2259 [KNL,X86] Mark specific memory as protected.
2260 Region of memory to be used, from ss to ss+nn.
2261 The memory region may be marked as e820 type 12 (0xc)
2262 and is NVDIMM or ADR memory.
2264 memory_corruption_check=0/1 [X86]
2265 Some BIOSes seem to corrupt the first 64k of
2266 memory when doing things like suspend/resume.
2267 Setting this option will scan the memory
2268 looking for corruption. Enabling this will
2269 both detect corruption and prevent the kernel
2270 from using the memory being corrupted.
2271 However, its intended as a diagnostic tool; if
2272 repeatable BIOS-originated corruption always
2273 affects the same memory, you can use memmap=
2274 to prevent the kernel from using that memory.
2276 memory_corruption_check_size=size [X86]
2277 By default it checks for corruption in the low
2278 64k, making this memory unavailable for normal
2279 use. Use this parameter to scan for
2280 corruption in more or less memory.
2282 memory_corruption_check_period=seconds [X86]
2283 By default it checks for corruption every 60
2284 seconds. Use this parameter to check at some
2285 other rate. 0 disables periodic checking.
2287 memtest= [KNL,X86,ARM] Enable memtest
2289 default : 0 <disable>
2290 Specifies the number of memtest passes to be
2291 performed. Each pass selects another test
2292 pattern from a given set of patterns. Memtest
2293 fills the memory with this pattern, validates
2294 memory contents and reserves bad memory
2295 regions that are detected.
2297 meye.*= [HW] Set MotionEye Camera parameters
2298 See Documentation/video4linux/meye.txt.
2300 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2301 Multi-Function General Purpose Timers on AMD Geode
2304 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2305 the BIOS has incorrectly applied a workaround. TinyBIOS
2306 version 0.98 is known to be affected, 0.99 fixes the
2307 problem by letting the user disable the workaround.
2311 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2312 physical address is ignored.
2314 mini2440= [ARM,HW,KNL]
2315 Format:[0..2][b][c][t]
2317 MINI2440 configuration specification:
2318 0 - The attached screen is the 3.5" TFT
2319 1 - The attached screen is the 7" TFT
2320 2 - The VGA Shield is attached (1024x768)
2321 Leaving out the screen size parameter will not load
2322 the TFT driver, and the framebuffer will be left
2324 b - Enable backlight. The TFT backlight pin will be
2325 linked to the kernel VESA blanking code and a GPIO
2326 LED. This parameter is not necessary when using the
2328 c - Enable the s3c camera interface.
2329 t - Reserved for enabling touchscreen support. The
2330 touchscreen support is not enabled in the mainstream
2331 kernel as of 2.6.30, a preliminary port can be found
2332 in the "bleeding edge" mini2440 support kernel at
2333 http://repo.or.cz/w/linux-2.6/mini2440.git
2336 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2337 parameter allows control of the logging verbosity for
2338 the additional memory initialisation checks. A value
2339 of 0 disables mminit logging and a level of 4 will
2340 log everything. Information is printed at KERN_DEBUG
2341 so loglevel=8 may also need to be specified.
2344 [KNL] When CONFIG_MODULE_SIG is set, this means that
2345 modules without (valid) signatures will fail to load.
2346 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2347 is always true, so this option does nothing.
2349 module_blacklist= [KNL] Do not load a comma-separated list of
2350 modules. Useful for debugging problem modules.
2353 [MOUSE] Maximum time between finger touching and
2354 leaving touchpad surface for touch to be considered
2355 a tap and be reported as a left button click (for
2356 touchpads working in absolute mode only).
2358 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2359 reporting absolute coordinates, such as tablets
2360 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2361 reporting absolute coordinates, such as tablets
2363 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2364 is similar to kernelcore except it specifies the
2365 amount of memory used for migratable allocations.
2366 If both kernelcore and movablecore is specified,
2367 then kernelcore will be at *least* the specified
2368 value but may be more. If movablecore on its own
2369 is specified, the administrator must be careful
2370 that the amount of memory usable for all allocations
2373 movable_node [KNL,X86] Boot-time switch to enable the effects
2374 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2376 MTD_Partition= [MTD]
2377 Format: <name>,<region-number>,<size>,<offset>
2379 MTD_Region= [MTD] Format:
2380 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2383 See drivers/mtd/cmdlinepart.c.
2385 multitce=off [PPC] This parameter disables the use of the pSeries
2386 firmware feature for updating multiple TCE entries
2389 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2391 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2393 boundary - index of last SLC block on Flex-OneNAND.
2394 The remaining blocks are configured as MLC blocks.
2395 lock - Configure if Flex-OneNAND boundary should be locked.
2396 Once locked, the boundary cannot be changed.
2397 1 indicates lock status, 0 indicates unlock status.
2400 ARM/S3C2412 JIVE boot control
2402 See arch/arm/mach-s3c2412/mach-jive.c
2404 mtouchusb.raw_coordinates=
2405 [HW] Make the MicroTouch USB driver use raw coordinates
2406 ('y', default) or cooked coordinates ('n')
2408 mtrr_chunk_size=nn[KMG] [X86]
2409 used for mtrr cleanup. It is largest continuous chunk
2410 that could hold holes aka. UC entries.
2412 mtrr_gran_size=nn[KMG] [X86]
2413 Used for mtrr cleanup. It is granularity of mtrr block.
2415 Large value could prevent small alignment from
2418 mtrr_spare_reg_nr=n [X86]
2420 Range: 0,7 : spare reg number
2422 Used for mtrr cleanup. It is spare mtrr entries number.
2423 Set to 2 or more if your graphical card needs more.
2425 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2427 netdev= [NET] Network devices parameters
2428 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2429 Note that mem_start is often overloaded to mean
2430 something different and driver-specific.
2431 This usage is only documented in each driver source
2435 [NETFILTER] Enable connection tracking flow accounting
2436 0 to disable accounting
2437 1 to enable accounting
2440 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2441 See Documentation/filesystems/nfs/nfsroot.txt.
2443 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2444 See Documentation/filesystems/nfs/nfsroot.txt.
2446 nfsrootdebug [NFS] enable nfsroot debugging messages.
2447 See Documentation/filesystems/nfs/nfsroot.txt.
2449 nfs.callback_tcpport=
2450 [NFS] set the TCP port on which the NFSv4 callback
2451 channel should listen.
2454 [NFS] sets the pathname to the program which is used
2455 to update the NFS client cache entries.
2457 nfs.cache_getent_timeout=
2458 [NFS] sets the timeout after which an attempt to
2459 update a cache entry is deemed to have failed.
2461 nfs.idmap_cache_timeout=
2462 [NFS] set the maximum lifetime for idmapper cache
2466 [NFS] enable 64-bit inode numbers.
2467 If zero, the NFS client will fake up a 32-bit inode
2468 number for the readdir() and stat() syscalls instead
2469 of returning the full 64-bit number.
2470 The default is to return 64-bit inode numbers.
2472 nfs.max_session_slots=
2473 [NFSv4.1] Sets the maximum number of session slots
2474 the client will attempt to negotiate with the server.
2475 This limits the number of simultaneous RPC requests
2476 that the client can send to the NFSv4.1 server.
2477 Note that there is little point in setting this
2478 value higher than the max_tcp_slot_table_limit.
2480 nfs.nfs4_disable_idmapping=
2481 [NFSv4] When set to the default of '1', this option
2482 ensures that both the RPC level authentication
2483 scheme and the NFS level operations agree to use
2484 numeric uids/gids if the mount is using the
2485 'sec=sys' security flavour. In effect it is
2486 disabling idmapping, which can make migration from
2487 legacy NFSv2/v3 systems to NFSv4 easier.
2488 Servers that do not support this mode of operation
2489 will be autodetected by the client, and it will fall
2490 back to using the idmapper.
2491 To turn off this behaviour, set the value to '0'.
2493 [NFS4] Specify an additional fixed unique ident-
2494 ification string that NFSv4 clients can insert into
2495 their nfs_client_id4 string. This is typically a
2496 UUID that is generated at system install time.
2498 nfs.send_implementation_id =
2499 [NFSv4.1] Send client implementation identification
2500 information in exchange_id requests.
2501 If zero, no implementation identification information
2503 The default is to send the implementation identification
2506 nfs.recover_lost_locks =
2507 [NFSv4] Attempt to recover locks that were lost due
2508 to a lease timeout on the server. Please note that
2509 doing this risks data corruption, since there are
2510 no guarantees that the file will remain unchanged
2511 after the locks are lost.
2512 If you want to enable the kernel legacy behaviour of
2513 attempting to recover these locks, then set this
2515 The default parameter value of '0' causes the kernel
2516 not to attempt recovery of lost locks.
2518 nfs4.layoutstats_timer =
2519 [NFSv4.2] Change the rate at which the kernel sends
2520 layoutstats to the pNFS metadata server.
2522 Setting this to value to 0 causes the kernel to use
2523 whatever value is the default set by the layout
2524 driver. A non-zero value sets the minimum interval
2525 in seconds between layoutstats transmissions.
2527 nfsd.nfs4_disable_idmapping=
2528 [NFSv4] When set to the default of '1', the NFSv4
2529 server will return only numeric uids and gids to
2530 clients using auth_sys, and will accept numeric uids
2531 and gids from such clients. This is intended to ease
2532 migration from NFSv2/v3.
2534 objlayoutdriver.osd_login_prog=
2535 [NFS] [OBJLAYOUT] sets the pathname to the program which
2536 is used to automatically discover and login into new
2537 osd-targets. Please see:
2538 Documentation/filesystems/pnfs.txt for more explanations
2540 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2541 when a NMI is triggered.
2542 Format: [state][,regs][,debounce][,die]
2544 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2545 Format: [panic,][nopanic,][num]
2547 0 - turn hardlockup detector in nmi_watchdog off
2548 1 - turn hardlockup detector in nmi_watchdog on
2549 When panic is specified, panic when an NMI watchdog
2550 timeout occurs (or 'nopanic' to override the opposite
2551 default). To disable both hard and soft lockup detectors,
2552 please see 'nowatchdog'.
2553 This is useful when you use a panic=... timeout and
2554 need the box quickly up again.
2556 netpoll.carrier_timeout=
2557 [NET] Specifies amount of time (in seconds) that
2558 netpoll should wait for a carrier. By default netpoll
2561 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2562 emulation library even if a 387 maths coprocessor
2566 [HW] Never suspend the console
2567 Disable suspending of consoles during suspend and
2568 hibernate operations. Once disabled, debugging
2569 messages can reach various consoles while the rest
2570 of the system is being put to sleep (ie, while
2571 debugging driver suspend/resume hooks). This may
2572 not work reliably with all consoles, but is known
2573 to work with serial and VGA consoles.
2574 To facilitate more flexible debugging, we also add
2575 console_suspend, a printk module parameter to control
2576 it. Users could use console_suspend (usually
2577 /sys/module/printk/parameters/console_suspend) to
2578 turn on/off it dynamically.
2580 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2581 caches in the slab allocator. Saves per-node memory,
2582 but will impact performance.
2586 noapic [SMP,APIC] Tells the kernel to not make use of any
2587 IOAPICs that may be present in the system.
2589 noautogroup Disable scheduler automatic task group creation.
2591 nobats [PPC] Do not use BATs for mapping kernel lowmem
2592 on "Classic" PPC cores.
2596 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2598 nodelayacct [KNL] Disable per-task delay accounting
2600 nodsp [SH] Disable hardware DSP at boot time.
2602 noefi Disable EFI runtime services support.
2607 On X86-32 available only on PAE configured kernels.
2608 noexec=on: enable non-executable mappings (default)
2609 noexec=off: disable non-executable mappings
2612 Disable SMAP (Supervisor Mode Access Prevention)
2613 even if it is supported by processor.
2616 Disable SMEP (Supervisor Mode Execution Prevention)
2617 even if it is supported by processor.
2620 This affects only 32-bit executables.
2621 noexec32=on: enable non-executable mappings (default)
2622 read doesn't imply executable mappings
2623 noexec32=off: disable non-executable mappings
2624 read implies executable mappings
2626 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2628 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2629 register save and restore. The kernel will only save
2630 legacy floating-point registers on task switch.
2632 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2634 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2635 Equivalent to smt=1.
2637 noxsave [BUGS=X86] Disables x86 extended register state save
2638 and restore using xsave. The kernel will fallback to
2639 enabling legacy floating-point and sse state.
2641 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2642 register states. The kernel will fall back to use
2643 xsave to save the states. By using this parameter,
2644 performance of saving the states is degraded because
2645 xsave doesn't support modified optimization while
2646 xsaveopt supports it on xsaveopt enabled systems.
2648 noxsaves [X86] Disables xsaves and xrstors used in saving and
2649 restoring x86 extended register state in compacted
2650 form of xsave area. The kernel will fall back to use
2651 xsaveopt and xrstor to save and restore the states
2652 in standard form of xsave area. By using this
2653 parameter, xsave area per process might occupy more
2654 memory on xsaves enabled systems.
2656 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2657 wfi(ARM) instruction doesn't work correctly and not to
2658 use it. This is also useful when using JTAG debugger.
2660 no_file_caps Tells the kernel not to honor file capabilities. The
2661 only way then for a file to be executed with privilege
2662 is to be setuid root or executed by root.
2664 nohalt [IA-64] Tells the kernel not to use the power saving
2665 function PAL_HALT_LIGHT when idle. This increases
2666 power-consumption. On the positive side, it reduces
2667 interrupt wake-up latency, which may improve performance
2668 in certain environments such as networked servers or
2671 nohibernate [HIBERNATION] Disable hibernation and resume.
2673 nohz= [KNL] Boottime enable/disable dynamic ticks
2674 Valid arguments: on, off
2677 nohz_full= [KNL,BOOT]
2678 In kernels built with CONFIG_NO_HZ_FULL=y, set
2679 the specified list of CPUs whose tick will be stopped
2680 whenever possible. The boot CPU will be forced outside
2681 the range to maintain the timekeeping.
2682 The CPUs in this range must also be included in the
2685 noiotrap [SH] Disables trapped I/O port accesses.
2687 noirqdebug [X86-32] Disables the code which attempts to detect and
2688 disable unhandled interrupt sources.
2690 no_timer_check [X86,APIC] Disables the code which tests for
2691 broken timer IRQ sources.
2693 noisapnp [ISAPNP] Disables ISA PnP code.
2695 noinitrd [RAM] Tells the kernel not to load any configured
2698 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2700 [Deprecated - use intremap=off]
2704 noinvpcid [X86] Disable the INVPCID cpu feature.
2706 nojitter [IA-64] Disables jitter checking for ITC timers.
2708 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2710 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2713 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2714 steal time is computed, but won't influence scheduler
2717 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2719 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2721 noltlbs [PPC] Do not use large page/tlb entries for kernel
2722 lowmem mapping on PPC40x and PPC8xx
2724 nomca [IA-64] Disable machine check abort handling
2726 nomce [X86-32] Disable Machine Check Exception
2728 nomfgpt [X86-32] Disable Multi-Function General Purpose
2729 Timer usage (for AMD Geode machines).
2731 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2732 shutdown the other cpus. Instead use the REBOOT_VECTOR
2735 nomodule Disable module load
2737 nopat [X86] Disable PAT (page attribute table extension of
2738 pagetables) support.
2740 norandmaps Don't use address space randomization. Equivalent to
2741 echo 0 > /proc/sys/kernel/randomize_va_space
2743 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2745 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2746 with UP alternatives
2748 nordrand [X86] Disable kernel use of the RDRAND and
2749 RDSEED instructions even if they are supported
2750 by the processor. RDRAND and RDSEED are still
2751 available to user space applications.
2753 noresume [SWSUSP] Disables resume and restores original swap
2756 no-scroll [VGA] Disables scrollback.
2757 This is required for the Braillex ib80-piezo Braille
2758 reader made by F.H. Papenmeier (Germany).
2762 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2764 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2765 and disable the IO APIC. legacy for "maxcpus=0".
2767 nosoftlockup [KNL] Disable the soft-lockup detector.
2769 nosync [HW,M68K] Disables sync negotiation for all devices.
2771 notsc [BUGS=X86-32] Disable Time Stamp Counter
2773 nowatchdog [KNL] Disable both lockup detectors, i.e.
2774 soft-lockup and NMI watchdog (hard-lockup).
2778 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2780 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2781 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2782 Some features depend on CPU0. Known dependencies are:
2783 1. Resume from suspend/hibernate depends on CPU0.
2784 Suspend/hibernate will fail if CPU0 is offline and you
2785 need to online CPU0 before suspend/hibernate.
2786 2. PIC interrupts also depend on CPU0. CPU0 can't be
2787 removed if a PIC interrupt is detected.
2788 It's said poweroff/reboot may depend on CPU0 on some
2789 machines although I haven't seen such issues so far
2790 after CPU0 is offline on a few tested machines.
2791 If the dependencies are under your control, you can
2792 turn on cpu0_hotplug.
2794 nptcg= [IA-64] Override max number of concurrent global TLB
2795 purges which is reported from either PAL_VM_SUMMARY or
2798 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2799 could support. nr_cpus=n : n >= 1 limits the kernel to
2800 support 'n' processors. It could be larger than the
2801 number of already plugged CPU during bootup, later in
2802 runtime you can physically add extra cpu until it reaches
2803 n. So during boot up some boot time memory for per-cpu
2804 variables need be pre-allocated for later physical cpu
2807 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2809 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2810 Allowed values are enable and disable
2812 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2813 one of ['zone', 'node', 'default'] can be specified
2814 This can be set from sysctl after boot.
2815 See Documentation/sysctl/vm.txt for details.
2817 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2818 See Documentation/debugging-via-ohci1394.txt for more
2821 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2822 Rather than timing out after 20 ms if an EC
2823 command is not properly ACKed, override the length
2824 of the timeout. We have interrupts disabled while
2825 waiting for the ACK, so if this is set too high
2826 interrupts *may* be lost!
2828 omap_mux= [OMAP] Override bootloader pin multiplexing.
2829 Format: <mux_mode0.mode_name=value>...
2830 For example, to override I2C bus2:
2831 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2833 oprofile.timer= [HW]
2834 Use timer interrupt instead of performance counters
2836 oprofile.cpu_type= Force an oprofile cpu type
2837 This might be useful if you have an older oprofile
2838 userland or if you want common events.
2839 Format: { arch_perfmon }
2840 arch_perfmon: [X86] Force use of architectural
2841 perfmon on Intel CPUs instead of the
2842 CPU specific event set.
2843 timer: [X86] Force use of architectural NMI
2844 timer mode (see also oprofile.timer
2845 for generic hr timer mode)
2847 oops=panic Always panic on oopses. Default is to just kill the
2848 process, but there is a small probability of
2849 deadlocking the machine.
2850 This will also cause panics on machine check exceptions.
2851 Useful together with panic=30 to trigger a reboot.
2854 See Documentation/sound/oss/oss-parameters.txt
2856 page_owner= [KNL] Boot-time page_owner enabling option.
2857 Storage of the information about who allocated
2858 each page is disabled in default. With this switch,
2860 on: enable the feature
2862 page_poison= [KNL] Boot-time parameter changing the state of
2863 poisoning on the buddy allocator.
2864 off: turn off poisoning
2865 on: turn on poisoning
2867 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2868 timeout > 0: seconds before rebooting
2869 timeout = 0: wait forever
2870 timeout < 0: reboot immediately
2873 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2876 crash_kexec_post_notifiers
2877 Run kdump after running panic-notifiers and dumping
2878 kmsg. This only for the users who doubt kdump always
2879 succeeds in any situation.
2880 Note that this also increases risks of kdump failure,
2881 because some panic notifiers can make the crashed
2882 kernel more unstable.
2884 parkbd.port= [HW] Parallel port number the keyboard adapter is
2885 connected to, default is 0.
2887 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2888 0 for XT, 1 for AT (default is AT).
2891 parport= [HW,PPT] Specify parallel ports. 0 disables.
2892 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2893 Use 'auto' to force the driver to use any
2894 IRQ/DMA settings detected (the default is to
2895 ignore detected IRQ/DMA settings because of
2896 possible conflicts). You can specify the base
2897 address, IRQ, and DMA settings; IRQ and DMA
2898 should be numbers, or 'auto' (for using detected
2899 settings on that particular port), or 'nofifo'
2900 (to avoid using a FIFO even if it is detected).
2901 Parallel ports are assigned in the order they
2902 are specified on the command line, starting
2905 parport_init_mode= [HW,PPT]
2906 Configure VIA parallel port to operate in
2907 a specific mode. This is necessary on Pegasos
2908 computer where firmware has no options for setting
2909 up parallel port mode and sets it to spp.
2910 Currently this function knows 686a and 8231 chips.
2911 Format: [spp|ps2|epp|ecp|ecpepp]
2914 Halt all CPUs after the first oops has been printed for
2915 the specified number of seconds. This is to be used if
2916 your oopses keep scrolling off the screen.
2921 See header of drivers/block/paride/pcd.c.
2922 See also Documentation/blockdev/paride.txt.
2924 pci=option[,option...] [PCI] various PCI subsystem options:
2925 earlydump [X86] dump PCI config space before the kernel
2927 off [X86] don't probe for the PCI bus
2928 bios [X86-32] force use of PCI BIOS, don't access
2929 the hardware directly. Use this if your machine
2930 has a non-standard PCI host bridge.
2931 nobios [X86-32] disallow use of PCI BIOS, only direct
2932 hardware access methods are allowed. Use this
2933 if you experience crashes upon bootup and you
2934 suspect they are caused by the BIOS.
2935 conf1 [X86] Force use of PCI Configuration Access
2936 Mechanism 1 (config address in IO port 0xCF8,
2937 data in IO port 0xCFC, both 32-bit).
2938 conf2 [X86] Force use of PCI Configuration Access
2939 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2940 the function, IO port 0xCFA, also 8-bit, sets
2941 bus number. The config space is then accessed
2942 through ports 0xC000-0xCFFF).
2943 See http://wiki.osdev.org/PCI for more info
2944 on the configuration access mechanisms.
2945 noaer [PCIE] If the PCIEAER kernel config parameter is
2946 enabled, this kernel boot option can be used to
2947 disable the use of PCIE advanced error reporting.
2948 nodomains [PCI] Disable support for multiple PCI
2949 root domains (aka PCI segments, in ACPI-speak).
2950 nommconf [X86] Disable use of MMCONFIG for PCI
2952 check_enable_amd_mmconf [X86] check for and enable
2953 properly configured MMIO access to PCI
2954 config space on AMD family 10h CPU
2955 nomsi [MSI] If the PCI_MSI kernel config parameter is
2956 enabled, this kernel boot option can be used to
2957 disable the use of MSI interrupts system-wide.
2958 noioapicquirk [APIC] Disable all boot interrupt quirks.
2959 Safety option to keep boot IRQs enabled. This
2960 should never be necessary.
2961 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2962 primary IO-APIC for bridges that cannot disable
2963 boot IRQs. This fixes a source of spurious IRQs
2964 when the system masks IRQs.
2965 noioapicreroute [APIC] Disable workaround that uses the
2966 boot IRQ equivalent of an IRQ that connects to
2967 a chipset where boot IRQs cannot be disabled.
2968 The opposite of ioapicreroute.
2969 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2970 routing table. These calls are known to be buggy
2971 on several machines and they hang the machine
2972 when used, but on other computers it's the only
2973 way to get the interrupt routing table. Try
2974 this option if the kernel is unable to allocate
2975 IRQs or discover secondary PCI buses on your
2977 rom [X86] Assign address space to expansion ROMs.
2978 Use with caution as certain devices share
2979 address decoders between ROMs and other
2981 norom [X86] Do not assign address space to
2982 expansion ROMs that do not already have
2983 BIOS assigned address ranges.
2984 nobar [X86] Do not assign address space to the
2985 BARs that weren't assigned by the BIOS.
2986 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2987 assigned automatically to PCI devices. You can
2988 make the kernel exclude IRQs of your ISA cards
2990 pirqaddr=0xAAAAA [X86] Specify the physical address
2991 of the PIRQ table (normally generated
2992 by the BIOS) if it is outside the
2993 F0000h-100000h range.
2994 lastbus=N [X86] Scan all buses thru bus #N. Can be
2995 useful if the kernel is unable to find your
2996 secondary buses and you want to tell it
2997 explicitly which ones they are.
2998 assign-busses [X86] Always assign all PCI bus
2999 numbers ourselves, overriding
3000 whatever the firmware may have done.
3001 usepirqmask [X86] Honor the possible IRQ mask stored
3002 in the BIOS $PIR table. This is needed on
3003 some systems with broken BIOSes, notably
3004 some HP Pavilion N5400 and Omnibook XE3
3005 notebooks. This will have no effect if ACPI
3006 IRQ routing is enabled.
3007 noacpi [X86] Do not use ACPI for IRQ routing
3008 or for PCI scanning.
3009 use_crs [X86] Use PCI host bridge window information
3010 from ACPI. On BIOSes from 2008 or later, this
3011 is enabled by default. If you need to use this,
3012 please report a bug.
3013 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3014 If you need to use this, please report a bug.
3015 routeirq Do IRQ routing for all PCI devices.
3016 This is normally done in pci_enable_device(),
3017 so this option is a temporary workaround
3018 for broken drivers that don't call it.
3019 skip_isa_align [X86] do not align io start addr, so can
3020 handle more pci cards
3021 noearly [X86] Don't do any early type 1 scanning.
3022 This might help on some broken boards which
3023 machine check when some devices' config space
3024 is read. But various workarounds are disabled
3025 and some IOMMU drivers will not work.
3026 bfsort Sort PCI devices into breadth-first order.
3027 This sorting is done to get a device
3028 order compatible with older (<= 2.4) kernels.
3029 nobfsort Don't sort PCI devices into breadth-first order.
3030 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3031 tuning and use the BIOS-configured MPS defaults.
3032 pcie_bus_safe Set every device's MPS to the largest value
3033 supported by all devices below the root complex.
3034 pcie_bus_perf Set device MPS to the largest allowable MPS
3035 based on its parent bus. Also set MRRS (Max
3036 Read Request Size) to the largest supported
3037 value (no larger than the MPS that the device
3038 or bus can support) for best performance.
3039 pcie_bus_peer2peer Set every device's MPS to 128B, which
3040 every device is guaranteed to support. This
3041 configuration allows peer-to-peer DMA between
3042 any pair of devices, possibly at the cost of
3043 reduced performance. This also guarantees
3044 that hot-added devices will work.
3045 cbiosize=nn[KMG] The fixed amount of bus space which is
3046 reserved for the CardBus bridge's IO window.
3047 The default value is 256 bytes.
3048 cbmemsize=nn[KMG] The fixed amount of bus space which is
3049 reserved for the CardBus bridge's memory
3050 window. The default value is 64 megabytes.
3053 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3054 [<order of align>@]pci:<vendor>:<device>\
3055 [:<subvendor>:<subdevice>][; ...]
3056 Specifies alignment and device to reassign
3057 aligned memory resources.
3058 If <order of align> is not specified,
3059 PAGE_SIZE is used as alignment.
3060 PCI-PCI bridge can be specified, if resource
3061 windows need to be expanded.
3062 To specify the alignment for several
3063 instances of a device, the PCI vendor,
3064 device, subvendor, and subdevice may be
3065 specified, e.g., 4096@pci:8086:9c22:103c:198f
3066 ecrc= Enable/disable PCIe ECRC (transaction layer
3067 end-to-end CRC checking).
3068 bios: Use BIOS/firmware settings. This is the
3072 hpiosize=nn[KMG] The fixed amount of bus space which is
3073 reserved for hotplug bridge's IO window.
3074 Default size is 256 bytes.
3075 hpmemsize=nn[KMG] The fixed amount of bus space which is
3076 reserved for hotplug bridge's memory window.
3077 Default size is 2 megabytes.
3078 hpbussize=nn The minimum amount of additional bus numbers
3079 reserved for buses below a hotplug bridge.
3081 realloc= Enable/disable reallocating PCI bridge resources
3082 if allocations done by BIOS are too small to
3083 accommodate resources required by all child
3085 off: Turn realloc off
3087 realloc same as realloc=on
3088 noari do not use PCIe ARI.
3089 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3090 only look for one device below a PCIe downstream
3093 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3096 force Enable ASPM even on devices that claim not to support it.
3097 WARNING: Forcing ASPM on may cause system lockups.
3099 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3100 nomsi Do not use MSI for PCI Express Native Hotplug (this
3101 makes all PCIe ports use INTx for hotplug services).
3103 pcie_ports= [PCIE] PCIe ports handling:
3104 auto Ask the BIOS whether or not to use native PCIe services
3105 associated with PCIe ports (PME, hot-plug, AER). Use
3106 them only if that is allowed by the BIOS.
3107 native Use native PCIe services associated with PCIe ports
3109 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3112 pcie_port_pm= [PCIE] PCIe port power management handling:
3113 off Disable power management of all PCIe ports
3114 force Forcibly enable power management of all PCIe ports
3116 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3117 nomsi Do not use MSI for native PCIe PME signaling (this makes
3118 all PCIe root ports use INTx for all services).
3120 pcmv= [HW,PCMCIA] BadgePAD 4
3124 Keep all power-domains already enabled by bootloader on,
3125 even if no driver has claimed them. This is useful
3126 for debug and development, but should not be
3127 needed on a platform with proper driver support.
3130 See Documentation/blockdev/paride.txt.
3132 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3135 See arch/parisc/kernel/pdc_chassis.c
3137 percpu_alloc= Select which percpu first chunk allocator to use.
3138 Currently supported values are "embed" and "page".
3139 Archs may support subset or none of the selections.
3140 See comments in mm/percpu.c for details on each
3141 allocator. This parameter is primarily for debugging
3142 and performance comparison.
3145 See Documentation/blockdev/paride.txt.
3148 See Documentation/blockdev/paride.txt.
3150 pirq= [SMP,APIC] Manual mp-table setup
3151 See Documentation/x86/i386/IO-APIC.txt.
3153 plip= [PPT,NET] Parallel port network link
3154 Format: { parport<nr> | timid | 0 }
3155 See also Documentation/parport.txt.
3157 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3158 Override pmtimer IOPort with a hex value.
3162 Enable PNP debug messages (depends on the
3163 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3164 via /sys/module/pnp/parameters/debug. We always show
3165 current resource usage; turning this on also shows
3166 possible settings and some assignment information.
3172 { on | off | curr | res | no-curr | no-res }
3175 [ISAPNP] Exclude IRQs for the autoconfiguration
3178 [ISAPNP] Exclude DMAs for the autoconfiguration
3180 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3181 Ranges are in pairs (I/O port base and size).
3184 [ISAPNP] Exclude memory regions for the
3186 Ranges are in pairs (memory base and size).
3188 ports= [IP_VS_FTP] IPVS ftp helper module
3190 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3192 Format: <port>,<port>....
3194 ppc_strict_facility_enable
3195 [PPC] This option catches any kernel floating point,
3196 Altivec, VSX and SPE outside of regions specifically
3197 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3198 There is some performance impact when enabling this.
3200 print-fatal-signals=
3201 [KNL] debug: print fatal signals
3203 If enabled, warn about various signal handling
3204 related application anomalies: too many signals,
3205 too many POSIX.1 timers, fatal signals causing a
3208 If you hit the warning due to signal overflow,
3209 you might want to try "ulimit -i unlimited".
3213 printk.always_kmsg_dump=
3214 Trigger kmsg_dump for cases other than kernel oops or
3216 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3219 printk.devkmsg={on,off,ratelimit}
3220 Control writing to /dev/kmsg.
3221 on - unlimited logging to /dev/kmsg from userspace
3222 off - logging to /dev/kmsg disabled
3223 ratelimit - ratelimit the logging
3226 printk.time= Show timing data prefixed to each printk message line
3227 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3229 processor.max_cstate= [HW,ACPI]
3230 Limit processor to maximum C-state
3231 max_cstate=9 overrides any DMI blacklist limit.
3233 processor.nocst [HW,ACPI]
3234 Ignore the _CST method to determine C-states,
3235 instead using the legacy FADT method
3237 profile= [KNL] Enable kernel profiling via /proc/profile
3238 Format: [schedule,]<number>
3239 Param: "schedule" - profile schedule points.
3240 Param: <number> - step/bucket size as a power of 2 for
3241 statistical time based profiling.
3242 Param: "sleep" - profile D-state sleeping (millisecs).
3243 Requires CONFIG_SCHEDSTATS
3244 Param: "kvm" - profile VM exits.
3246 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3248 See Documentation/blockdev/ramdisk.txt.
3250 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3251 probe for; one of (bare|imps|exps|lifebook|any).
3252 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3254 psmouse.resetafter= [HW,MOUSE]
3255 Try to reset the device after so many bad packets
3258 [HW,MOUSE] Set desired mouse resolution, in dpi.
3259 psmouse.smartscroll=
3260 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3261 0 = disabled, 1 = enabled (default).
3263 pstore.backend= Specify the name of the pstore backend to use
3266 See Documentation/blockdev/paride.txt.
3269 [KNL] Number of legacy pty's. Overwrites compiled-in
3272 quiet [KNL] Disable most log messages
3277 See Documentation/md.txt.
3279 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3280 See Documentation/blockdev/ramdisk.txt.
3283 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3284 the specified list of CPUs to be no-callback CPUs.
3285 Invocation of these CPUs' RCU callbacks will
3286 be offloaded to "rcuox/N" kthreads created for
3287 that purpose, where "x" is "b" for RCU-bh, "p"
3288 for RCU-preempt, and "s" for RCU-sched, and "N"
3289 is the CPU number. This reduces OS jitter on the
3290 offloaded CPUs, which can be useful for HPC and
3291 real-time workloads. It can also improve energy
3292 efficiency for asymmetric multiprocessors.
3295 Rather than requiring that offloaded CPUs
3296 (specified by rcu_nocbs= above) explicitly
3297 awaken the corresponding "rcuoN" kthreads,
3298 make these kthreads poll for callbacks.
3299 This improves the real-time response for the
3300 offloaded CPUs by relieving them of the need to
3301 wake up the corresponding kthread, but degrades
3302 energy efficiency by requiring that the kthreads
3303 periodically wake up to do the polling.
3305 rcutree.blimit= [KNL]
3306 Set maximum number of finished RCU callbacks to
3307 process in one batch.
3309 rcutree.dump_tree= [KNL]
3310 Dump the structure of the rcu_node combining tree
3311 out at early boot. This is used for diagnostic
3312 purposes, to verify correct tree setup.
3314 rcutree.gp_cleanup_delay= [KNL]
3315 Set the number of jiffies to delay each step of
3316 RCU grace-period cleanup. This only has effect
3317 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3319 rcutree.gp_init_delay= [KNL]
3320 Set the number of jiffies to delay each step of
3321 RCU grace-period initialization. This only has
3322 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3325 rcutree.gp_preinit_delay= [KNL]
3326 Set the number of jiffies to delay each step of
3327 RCU grace-period pre-initialization, that is,
3328 the propagation of recent CPU-hotplug changes up
3329 the rcu_node combining tree. This only has effect
3330 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3332 rcutree.rcu_fanout_exact= [KNL]
3333 Disable autobalancing of the rcu_node combining
3334 tree. This is used by rcutorture, and might
3335 possibly be useful for architectures having high
3336 cache-to-cache transfer latencies.
3338 rcutree.rcu_fanout_leaf= [KNL]
3339 Change the number of CPUs assigned to each
3340 leaf rcu_node structure. Useful for very
3341 large systems, which will choose the value 64,
3342 and for NUMA systems with large remote-access
3343 latencies, which will choose a value aligned
3344 with the appropriate hardware boundaries.
3346 rcutree.jiffies_till_sched_qs= [KNL]
3347 Set required age in jiffies for a
3348 given grace period before RCU starts
3349 soliciting quiescent-state help from
3350 rcu_note_context_switch().
3352 rcutree.jiffies_till_first_fqs= [KNL]
3353 Set delay from grace-period initialization to
3354 first attempt to force quiescent states.
3355 Units are jiffies, minimum value is zero,
3356 and maximum value is HZ.
3358 rcutree.jiffies_till_next_fqs= [KNL]
3359 Set delay between subsequent attempts to force
3360 quiescent states. Units are jiffies, minimum
3361 value is one, and maximum value is HZ.
3363 rcutree.kthread_prio= [KNL,BOOT]
3364 Set the SCHED_FIFO priority of the RCU per-CPU
3365 kthreads (rcuc/N). This value is also used for
3366 the priority of the RCU boost threads (rcub/N)
3367 and for the RCU grace-period kthreads (rcu_bh,
3368 rcu_preempt, and rcu_sched). If RCU_BOOST is
3369 set, valid values are 1-99 and the default is 1
3370 (the least-favored priority). Otherwise, when
3371 RCU_BOOST is not set, valid values are 0-99 and
3372 the default is zero (non-realtime operation).
3374 rcutree.rcu_nocb_leader_stride= [KNL]
3375 Set the number of NOCB kthread groups, which
3376 defaults to the square root of the number of
3377 CPUs. Larger numbers reduces the wakeup overhead
3378 on the per-CPU grace-period kthreads, but increases
3379 that same overhead on each group's leader.
3381 rcutree.qhimark= [KNL]
3382 Set threshold of queued RCU callbacks beyond which
3383 batch limiting is disabled.
3385 rcutree.qlowmark= [KNL]
3386 Set threshold of queued RCU callbacks below which
3387 batch limiting is re-enabled.
3389 rcutree.rcu_idle_gp_delay= [KNL]
3390 Set wakeup interval for idle CPUs that have
3391 RCU callbacks (RCU_FAST_NO_HZ=y).
3393 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3394 Set wakeup interval for idle CPUs that have
3395 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3396 Lazy RCU callbacks are those which RCU can
3397 prove do nothing more than free memory.
3399 rcuperf.gp_exp= [KNL]
3400 Measure performance of expedited synchronous
3401 grace-period primitives.
3403 rcuperf.holdoff= [KNL]
3404 Set test-start holdoff period. The purpose of
3405 this parameter is to delay the start of the
3406 test until boot completes in order to avoid
3409 rcuperf.nreaders= [KNL]
3410 Set number of RCU readers. The value -1 selects
3411 N, where N is the number of CPUs. A value
3412 "n" less than -1 selects N-n+1, where N is again
3413 the number of CPUs. For example, -2 selects N
3414 (the number of CPUs), -3 selects N+1, and so on.
3415 A value of "n" less than or equal to -N selects
3418 rcuperf.nwriters= [KNL]
3419 Set number of RCU writers. The values operate
3420 the same as for rcuperf.nreaders.
3421 N, where N is the number of CPUs
3423 rcuperf.perf_runnable= [BOOT]
3424 Start rcuperf running at boot time.
3426 rcuperf.shutdown= [KNL]
3427 Shut the system down after performance tests
3428 complete. This is useful for hands-off automated
3431 rcuperf.perf_type= [KNL]
3432 Specify the RCU implementation to test.
3434 rcuperf.verbose= [KNL]
3435 Enable additional printk() statements.
3437 rcutorture.cbflood_inter_holdoff= [KNL]
3438 Set holdoff time (jiffies) between successive
3439 callback-flood tests.
3441 rcutorture.cbflood_intra_holdoff= [KNL]
3442 Set holdoff time (jiffies) between successive
3443 bursts of callbacks within a given callback-flood
3446 rcutorture.cbflood_n_burst= [KNL]
3447 Set the number of bursts making up a given
3448 callback-flood test. Set this to zero to
3449 disable callback-flood testing.
3451 rcutorture.cbflood_n_per_burst= [KNL]
3452 Set the number of callbacks to be registered
3453 in a given burst of a callback-flood test.
3455 rcutorture.fqs_duration= [KNL]
3456 Set duration of force_quiescent_state bursts
3459 rcutorture.fqs_holdoff= [KNL]
3460 Set holdoff time within force_quiescent_state bursts
3463 rcutorture.fqs_stutter= [KNL]
3464 Set wait time between force_quiescent_state bursts
3467 rcutorture.gp_cond= [KNL]
3468 Use conditional/asynchronous update-side
3469 primitives, if available.
3471 rcutorture.gp_exp= [KNL]
3472 Use expedited update-side primitives, if available.
3474 rcutorture.gp_normal= [KNL]
3475 Use normal (non-expedited) asynchronous
3476 update-side primitives, if available.
3478 rcutorture.gp_sync= [KNL]
3479 Use normal (non-expedited) synchronous
3480 update-side primitives, if available. If all
3481 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3482 rcutorture.gp_normal=, and rcutorture.gp_sync=
3483 are zero, rcutorture acts as if is interpreted
3484 they are all non-zero.
3486 rcutorture.n_barrier_cbs= [KNL]
3487 Set callbacks/threads for rcu_barrier() testing.
3489 rcutorture.nfakewriters= [KNL]
3490 Set number of concurrent RCU writers. These just
3491 stress RCU, they don't participate in the actual
3492 test, hence the "fake".
3494 rcutorture.nreaders= [KNL]
3495 Set number of RCU readers. The value -1 selects
3496 N-1, where N is the number of CPUs. A value
3497 "n" less than -1 selects N-n-2, where N is again
3498 the number of CPUs. For example, -2 selects N
3499 (the number of CPUs), -3 selects N+1, and so on.
3501 rcutorture.object_debug= [KNL]
3502 Enable debug-object double-call_rcu() testing.
3504 rcutorture.onoff_holdoff= [KNL]
3505 Set time (s) after boot for CPU-hotplug testing.
3507 rcutorture.onoff_interval= [KNL]
3508 Set time (s) between CPU-hotplug operations, or
3509 zero to disable CPU-hotplug testing.
3511 rcutorture.shuffle_interval= [KNL]
3512 Set task-shuffle interval (s). Shuffling tasks
3513 allows some CPUs to go into dyntick-idle mode
3514 during the rcutorture test.
3516 rcutorture.shutdown_secs= [KNL]
3517 Set time (s) after boot system shutdown. This
3518 is useful for hands-off automated testing.
3520 rcutorture.stall_cpu= [KNL]
3521 Duration of CPU stall (s) to test RCU CPU stall
3522 warnings, zero to disable.
3524 rcutorture.stall_cpu_holdoff= [KNL]
3525 Time to wait (s) after boot before inducing stall.
3527 rcutorture.stat_interval= [KNL]
3528 Time (s) between statistics printk()s.
3530 rcutorture.stutter= [KNL]
3531 Time (s) to stutter testing, for example, specifying
3532 five seconds causes the test to run for five seconds,
3533 wait for five seconds, and so on. This tests RCU's
3534 ability to transition abruptly to and from idle.
3536 rcutorture.test_boost= [KNL]
3537 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3538 "Maybe" means test if the RCU implementation
3539 under test support RCU priority boosting.
3541 rcutorture.test_boost_duration= [KNL]
3542 Duration (s) of each individual boost test.
3544 rcutorture.test_boost_interval= [KNL]
3545 Interval (s) between each boost test.
3547 rcutorture.test_no_idle_hz= [KNL]
3548 Test RCU's dyntick-idle handling. See also the
3549 rcutorture.shuffle_interval parameter.
3551 rcutorture.torture_runnable= [BOOT]
3552 Start rcutorture running at boot time.
3554 rcutorture.torture_type= [KNL]
3555 Specify the RCU implementation to test.
3557 rcutorture.verbose= [KNL]
3558 Enable additional printk() statements.
3560 rcupdate.rcu_cpu_stall_suppress= [KNL]
3561 Suppress RCU CPU stall warning messages.
3563 rcupdate.rcu_cpu_stall_timeout= [KNL]
3564 Set timeout for RCU CPU stall warning messages.
3566 rcupdate.rcu_expedited= [KNL]
3567 Use expedited grace-period primitives, for
3568 example, synchronize_rcu_expedited() instead
3569 of synchronize_rcu(). This reduces latency,
3570 but can increase CPU utilization, degrade
3571 real-time latency, and degrade energy efficiency.
3572 No effect on CONFIG_TINY_RCU kernels.
3574 rcupdate.rcu_normal= [KNL]
3575 Use only normal grace-period primitives,
3576 for example, synchronize_rcu() instead of
3577 synchronize_rcu_expedited(). This improves
3578 real-time latency, CPU utilization, and
3579 energy efficiency, but can expose users to
3580 increased grace-period latency. This parameter
3581 overrides rcupdate.rcu_expedited. No effect on
3582 CONFIG_TINY_RCU kernels.
3584 rcupdate.rcu_normal_after_boot= [KNL]
3585 Once boot has completed (that is, after
3586 rcu_end_inkernel_boot() has been invoked), use
3587 only normal grace-period primitives. No effect
3588 on CONFIG_TINY_RCU kernels.
3590 rcupdate.rcu_task_stall_timeout= [KNL]
3591 Set timeout in jiffies for RCU task stall warning
3592 messages. Disable with a value less than or equal
3595 rcupdate.rcu_self_test= [KNL]
3596 Run the RCU early boot self tests
3598 rcupdate.rcu_self_test_bh= [KNL]
3599 Run the RCU bh early boot self tests
3601 rcupdate.rcu_self_test_sched= [KNL]
3602 Run the RCU sched early boot self tests
3606 Run specified binary instead of /init from the ramdisk,
3607 used for early userspace startup. See initrd.
3610 Format (x86 or x86_64):
3611 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3613 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3615 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3616 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3617 reboot_force is either force or not specified,
3618 reboot_cpu is s[mp]#### with #### being the processor
3619 to be used for rebooting.
3622 [KNL, SMP] Set scheduler's default relax_domain_level.
3623 See Documentation/cgroup-v1/cpusets.txt.
3625 relative_sleep_states=
3626 [SUSPEND] Use sleep state labeling where the deepest
3627 state available other than hibernation is always "mem".
3628 Format: { "0" | "1" }
3629 0 -- Traditional sleep state labels.
3630 1 -- Relative sleep state labels.
3632 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3634 reservetop= [X86-32]
3636 Reserves a hole at the top of the kernel virtual
3641 Set the amount of memory to reserve for BIOS at
3642 the bottom of the address space.
3644 reset_devices [KNL] Force drivers to reset the underlying device
3645 during initialization.
3648 Specify the partition device for software suspend
3650 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3652 resume_offset= [SWSUSP]
3653 Specify the offset from the beginning of the partition
3654 given by "resume=" at which the swap header is located,
3655 in <PAGE_SIZE> units (needed only for swap files).
3656 See Documentation/power/swsusp-and-swap-files.txt
3658 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3659 read the resume files
3661 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3662 Useful for devices that are detected asynchronously
3663 (e.g. USB and MMC devices).
3665 hibernate= [HIBERNATION]
3666 noresume Don't check if there's a hibernation image
3667 present during boot.
3668 nocompress Don't compress/decompress hibernation images.
3669 no Disable hibernation and resume.
3670 protect_image Turn on image protection during restoration
3671 (that will set all pages holding image data
3672 during restoration read-only).
3674 retain_initrd [RAM] Keep initrd memory after extraction
3676 rfkill.default_state=
3677 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3678 etc. communication is blocked by default.
3681 rfkill.master_switch_mode=
3682 0 The "airplane mode" button does nothing.
3683 1 The "airplane mode" button toggles between everything
3684 blocked and the previous configuration.
3685 2 The "airplane mode" button toggles between everything
3686 blocked and everything unblocked.
3688 rhash_entries= [KNL,NET]
3689 Set number of hash buckets for route cache
3691 ro [KNL] Mount root device read-only on boot
3694 on Mark read-only kernel memory as read-only (default).
3695 off Leave read-only kernel memory writable for debugging.
3698 Enable the uart passthrough on the designated usb port
3699 on Rockchip SoCs. When active, the signals of the
3700 debug-uart get routed to the D+ and D- pins of the usb
3701 port and the regular usb controller gets disabled.
3703 root= [KNL] Root filesystem
3704 See name_to_dev_t comment in init/do_mounts.c.
3706 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3707 mount the root filesystem
3709 rootflags= [KNL] Set root filesystem mount option string
3711 rootfstype= [KNL] Set root filesystem type
3713 rootwait [KNL] Wait (indefinitely) for root device to show up.
3714 Useful for devices that are detected asynchronously
3715 (e.g. USB and MMC devices).
3717 rproc_mem=nn[KMG][@address]
3718 [KNL,ARM,CMA] Remoteproc physical memory block.
3719 Memory area to be used by remote processor image,
3722 rw [KNL] Mount root device read-write on boot
3724 S [KNL] Run init in single mode
3726 s390_iommu= [HW,S390]
3727 Set s390 IOTLB flushing mode
3729 With strict flushing every unmap operation will result in
3730 an IOTLB flush. Default is lazy flushing before reuse,
3734 See drivers/net/irda/sa1100_ir.c.
3736 sbni= [NET] Granch SBNI12 leased line adapter
3738 sched_debug [KNL] Enables verbose scheduler debug messages.
3740 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3741 Allowed values are enable and disable. This feature
3742 incurs a small amount of overhead in the scheduler
3743 but is useful for debugging and performance tuning.
3745 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3746 xtime_lock contention on larger systems, and/or RCU lock
3747 contention on all systems with CONFIG_MAXSMP set.
3748 Format: { "0" | "1" }
3749 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3751 Note: increases power consumption, thus should only be
3752 enabled if running jitter sensitive (HPC/RT) workloads.
3754 security= [SECURITY] Choose a security module to enable at boot.
3755 If this boot parameter is not specified, only the first
3756 security module asking for security registration will be
3757 loaded. An invalid security module name will be treated
3758 as if no module has been chosen.
3760 selinux= [SELINUX] Disable or enable SELinux at boot time.
3761 Format: { "0" | "1" }
3762 See security/selinux/Kconfig help text.
3765 Default value is set via kernel config option.
3766 If enabled at boot time, /selinux/disable can be used
3767 later to disable prior to initial policy load.
3769 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3770 Format: { "0" | "1" }
3771 See security/apparmor/Kconfig help text
3774 Default value is set via kernel config option.
3776 serialnumber [BUGS=X86-32]
3779 Maximal number of shapers.
3781 show_msr= [x86] show boot-time MSR settings
3782 Format: { <integer> }
3783 Show boot-time (BIOS-initialized) MSR settings.
3784 The parameter means the number of CPUs to show,
3785 for example 1 means boot CPU only.
3793 Disable merging of slabs with similar size. May be
3794 necessary if there is some reason to distinguish
3795 allocs to different slabs. Debug options disable
3796 merging on their own.
3797 For more information see Documentation/vm/slub.txt.
3799 slab_max_order= [MM, SLAB]
3800 Determines the maximum allowed order for slabs.
3801 A high setting may cause OOMs due to memory
3802 fragmentation. Defaults to 1 for systems with
3803 more than 32MB of RAM, 0 otherwise.
3805 slub_debug[=options[,slabs]] [MM, SLUB]
3806 Enabling slub_debug allows one to determine the
3807 culprit if slab objects become corrupted. Enabling
3808 slub_debug can create guard zones around objects and
3809 may poison objects when not in use. Also tracks the
3810 last alloc / free. For more information see
3811 Documentation/vm/slub.txt.
3813 slub_max_order= [MM, SLUB]
3814 Determines the maximum allowed order for slabs.
3815 A high setting may cause OOMs due to memory
3816 fragmentation. For more information see
3817 Documentation/vm/slub.txt.
3819 slub_min_objects= [MM, SLUB]
3820 The minimum number of objects per slab. SLUB will
3821 increase the slab order up to slub_max_order to
3822 generate a sufficiently large slab able to contain
3823 the number of objects indicated. The higher the number
3824 of objects the smaller the overhead of tracking slabs
3825 and the less frequently locks need to be acquired.
3826 For more information see Documentation/vm/slub.txt.
3828 slub_min_order= [MM, SLUB]
3829 Determines the minimum page order for slabs. Must be
3830 lower than slub_max_order.
3831 For more information see Documentation/vm/slub.txt.
3833 slub_nomerge [MM, SLUB]
3834 Same with slab_nomerge. This is supported for legacy.
3835 See slab_nomerge for more information.
3838 Format: <io1>[,<io2>[,...,<io8>]]
3840 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3841 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3842 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3843 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3844 smsc-ircc2.ircc_irq= [HW] IRQ line
3845 smsc-ircc2.ircc_dma= [HW] DMA channel
3846 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3847 0: Toshiba Satellite 1800 (GP data pin select)
3848 1: Fast pin select (default)
3851 smt [KNL,S390] Set the maximum number of threads (logical
3852 CPUs) to use per physical CPU on systems capable of
3853 symmetric multithreading (SMT). Will be capped to the
3854 actual hardware limit.
3856 Default: -1 (no limit)
3859 [KNL] Should the soft-lockup detector generate panics.
3862 softlockup_all_cpu_backtrace=
3863 [KNL] Should the soft-lockup detector generate
3864 backtraces on all cpus.
3867 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3868 See Documentation/laptops/sonypi.txt
3870 spia_io_base= [HW,MTD]
3876 Enabled the stack tracer on boot up.
3878 stacktrace_filter=[function-list]
3879 [FTRACE] Limit the functions that the stack tracer
3880 will trace at boot up. function-list is a comma separated
3881 list of functions. This list can be changed at run
3882 time by the stack_trace_filter file in the debugfs
3883 tracing directory. Note, this enables stack tracing
3884 and the stacktrace above is not needed.
3888 Set the STI (builtin display/keyboard on the HP-PARISC
3889 machines) console (graphic card) which should be used
3890 as the initial boot-console.
3891 See also comment in drivers/video/console/sticore.c.
3894 See comment in drivers/video/console/sticore.c.
3897 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3899 sunrpc.min_resvport=
3900 sunrpc.max_resvport=
3902 SunRPC servers often require that client requests
3903 originate from a privileged port (i.e. a port in the
3904 range 0 < portnr < 1024).
3905 An administrator who wishes to reserve some of these
3906 ports for other uses may adjust the range that the
3907 kernel's sunrpc client considers to be privileged
3908 using these two parameters to set the minimum and
3909 maximum port values.
3911 sunrpc.svc_rpc_per_connection_limit=
3913 Limit the number of requests that the server will
3914 process in parallel from a single connection.
3915 The default value is 0 (no limit).
3919 Control how the NFS server code allocates CPUs to
3920 service thread pools. Depending on how many NICs
3921 you have and where their interrupts are bound, this
3922 option will affect which CPUs will do NFS serving.
3923 Note: this parameter cannot be changed while the
3924 NFS server is running.
3926 auto the server chooses an appropriate mode
3927 automatically using heuristics
3928 global a single global pool contains all CPUs
3929 percpu one pool for each CPU
3930 pernode one pool for each NUMA node (equivalent
3931 to global on non-NUMA machines)
3933 sunrpc.tcp_slot_table_entries=
3934 sunrpc.udp_slot_table_entries=
3936 Sets the upper limit on the number of simultaneous
3937 RPC calls that can be sent from the client to a
3938 server. Increasing these values may allow you to
3939 improve throughput, but will also increase the
3940 amount of memory reserved for use by the client.
3942 suspend.pm_test_delay=
3944 Sets the number of seconds to remain in a suspend test
3945 mode before resuming the system (see
3946 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3947 is set. Default value is 5.
3950 [KNL] Enable accounting of swap in memory resource
3951 controller if no parameter or 1 is given or disable
3952 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
3954 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3955 Format: { <int> | force }
3956 <int> -- Number of I/O TLB slabs
3957 force -- force using of bounce buffers even if they
3958 wouldn't be automatically used by the kernel
3962 sysfs.deprecated=0|1 [KNL]
3963 Enable/disable old style sysfs layout for old udev
3964 on older distributions. When this option is enabled
3965 very new udev will not work anymore. When this option
3966 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3967 in older udev will not work anymore.
3968 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3969 the kernel configuration.
3971 sysrq_always_enabled
3973 Ignore sysrq setting - this boot parameter will
3974 neutralize any effect of /proc/sys/kernel/sysrq.
3975 Useful for debugging.
3977 tcpmhash_entries= [KNL,NET]
3978 Set the number of tcp_metrics_hash slots.
3979 Default value is 8192 or 16384 depending on total
3980 ram pages. This is used to specify the TCP metrics
3981 cache size. See Documentation/networking/ip-sysctl.txt
3982 "tcp_no_metrics_save" section for more details.
3986 test_suspend= [SUSPEND][,N]
3987 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3988 standby suspend) or "freeze" (for suspend type freeze)
3989 as the system sleep state during system startup with
3990 the optional capability to repeat N number of times.
3991 The system is woken from this state using a
3992 wakeup-capable RTC alarm.
3994 thash_entries= [KNL,NET]
3995 Set number of hash buckets for TCP connection
3997 thermal.act= [HW,ACPI]
3998 -1: disable all active trip points in all thermal zones
3999 <degrees C>: override all lowest active trip points
4001 thermal.crt= [HW,ACPI]
4002 -1: disable all critical trip points in all thermal zones
4003 <degrees C>: override all critical trip points
4005 thermal.nocrt= [HW,ACPI]
4006 Set to disable actions on ACPI thermal zone
4007 critical and hot trip points.
4009 thermal.off= [HW,ACPI]
4010 1: disable ACPI thermal control
4012 thermal.psv= [HW,ACPI]
4013 -1: disable all passive trip points
4014 <degrees C>: override all passive trip points to this
4017 thermal.tzp= [HW,ACPI]
4018 Specify global default ACPI thermal zone polling rate
4019 <deci-seconds>: poll all this frequency
4020 0: no polling (default)
4023 Force threading of all interrupt handlers except those
4024 marked explicitly IRQF_NO_THREAD.
4027 Enable the Transcendent memory driver if built-in.
4029 tmem.cleancache=0|1 [KNL, XEN]
4030 Default is on (1). Disable the usage of the cleancache
4031 API to send anonymous pages to the hypervisor.
4033 tmem.frontswap=0|1 [KNL, XEN]
4034 Default is on (1). Disable the usage of the frontswap
4035 API to send swap pages to the hypervisor. If disabled
4036 the selfballooning and selfshrinking are force disabled.
4038 tmem.selfballooning=0|1 [KNL, XEN]
4039 Default is on (1). Disable the driving of swap pages
4042 tmem.selfshrinking=0|1 [KNL, XEN]
4043 Default is on (1). Partial swapoff that immediately
4044 transfers pages from Xen hypervisor back to the
4045 kernel based on different criteria.
4049 Specify if the kernel should make use of the cpu
4050 topology information if the hardware supports this.
4051 The scheduler will make use of this information and
4052 e.g. base its process migration decisions on it.
4055 topology_updates= [KNL, PPC, NUMA]
4057 Specify if the kernel should ignore (off)
4058 topology updates sent by the hypervisor to this
4063 tpm_suspend_pcr=[HW,TPM]
4064 Format: integer pcr id
4065 Specify that at suspend time, the tpm driver
4066 should extend the specified pcr with zeros,
4067 as a workaround for some chips which fail to
4068 flush the last written pcr on TPM_SaveState.
4069 This will guarantee that all the other pcrs
4072 trace_buf_size=nn[KMG]
4073 [FTRACE] will set tracing buffer size on each cpu.
4075 trace_event=[event-list]
4076 [FTRACE] Set and start specified trace events in order
4077 to facilitate early boot debugging. The event-list is a
4078 comma separated list of trace events to enable. See
4079 also Documentation/trace/events.txt
4081 trace_options=[option-list]
4082 [FTRACE] Enable or disable tracer options at boot.
4083 The option-list is a comma delimited list of options
4084 that can be enabled or disabled just as if you were
4085 to echo the option name into
4087 /sys/kernel/debug/tracing/trace_options
4089 For example, to enable stacktrace option (to dump the
4090 stack trace of each event), add to the command line:
4092 trace_options=stacktrace
4094 See also Documentation/trace/ftrace.txt "trace options"
4098 Have the tracepoints sent to printk as well as the
4099 tracing ring buffer. This is useful for early boot up
4100 where the system hangs or reboots and does not give the
4101 option for reading the tracing buffer or performing a
4102 ftrace_dump_on_oops.
4104 To turn off having tracepoints sent to printk,
4105 echo 0 > /proc/sys/kernel/tracepoint_printk
4106 Note, echoing 1 into this file without the
4107 tracepoint_printk kernel cmdline option has no effect.
4111 Having tracepoints sent to printk() and activating high
4112 frequency tracepoints such as irq or sched, can cause
4113 the system to live lock.
4116 [FTRACE] enable this option to disable tracing when a
4117 warning is hit. This turns off "tracing_on". Tracing can
4118 be enabled again by echoing '1' into the "tracing_on"
4119 file located in /sys/kernel/debug/tracing/
4121 This option is useful, as it disables the trace before
4122 the WARNING dump is called, which prevents the trace to
4123 be filled with content caused by the warning output.
4125 This option can also be set at run time via the sysctl
4126 option: kernel/traceoff_on_warning
4128 transparent_hugepage=
4130 Format: [always|madvise|never]
4131 Can be used to control the default behavior of the system
4132 with respect to transparent hugepages.
4133 See Documentation/vm/transhuge.txt for more details.
4135 tsc= Disable clocksource stability checks for TSC.
4137 [x86] reliable: mark tsc clocksource as reliable, this
4138 disables clocksource verification at runtime, as well
4139 as the stability checks done at bootup. Used to enable
4140 high-resolution timer mode on older hardware, and in
4141 virtualized environment.
4142 [x86] noirqtime: Do not use TSC to do irq accounting.
4143 Used to run time disable IRQ_TIME_ACCOUNTING on any
4144 platforms where RDTSC is slow and this accounting
4147 turbografx.map[2|3]= [HW,JOY]
4148 TurboGraFX parallel port interface
4150 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4151 See also Documentation/input/joystick-parport.txt
4153 udbg-immortal [PPC] When debugging early kernel crashes that
4154 happen after console_init() and before a proper
4155 console driver takes over, this boot options might
4156 help "seeing" what's going on.
4158 uhash_entries= [KNL,NET]
4159 Set number of hash buckets for UDP/UDP-Lite connections
4162 [USB] Ignore overcurrent events (default N).
4163 Some badly-designed motherboards generate lots of
4164 bogus events, for ports that aren't wired to
4165 anything. Set this parameter to avoid log spamming.
4166 Note that genuine overcurrent events won't be
4170 [X86] Cause panic on unknown NMI.
4172 usbcore.authorized_default=
4173 [USB] Default USB device authorization:
4174 (default -1 = authorized except for wireless USB,
4175 0 = not authorized, 1 = authorized)
4177 usbcore.autosuspend=
4178 [USB] The autosuspend time delay (in seconds) used
4179 for newly-detected USB devices (default 2). This
4180 is the time required before an idle device will be
4181 autosuspended. Devices for which the delay is set
4182 to a negative value won't be autosuspended at all.
4184 usbcore.usbfs_snoop=
4185 [USB] Set to log all usbfs traffic (default 0 = off).
4187 usbcore.usbfs_snoop_max=
4188 [USB] Maximum number of bytes to snoop in each URB
4191 usbcore.blinkenlights=
4192 [USB] Set to cycle leds on hubs (default 0 = off).
4194 usbcore.old_scheme_first=
4195 [USB] Start with the old device initialization
4196 scheme (default 0 = off).
4198 usbcore.usbfs_memory_mb=
4199 [USB] Memory limit (in MB) for buffers allocated by
4200 usbfs (default = 16, 0 = max = 2047).
4202 usbcore.use_both_schemes=
4203 [USB] Try the other device initialization scheme
4204 if the first one fails (default 1 = enabled).
4206 usbcore.initial_descriptor_timeout=
4207 [USB] Specifies timeout for the initial 64-byte
4208 USB_REQ_GET_DESCRIPTOR request in milliseconds
4209 (default 5000 = 5.0 seconds).
4211 usbcore.nousb [USB] Disable the USB subsystem
4214 [USBHID] The interval which mice are to be polled at.
4216 usb-storage.delay_use=
4217 [UMS] The delay in seconds before a new device is
4218 scanned for Logical Units (default 1).
4221 [UMS] A list of quirks entries to supplement or
4222 override the built-in unusual_devs list. List
4223 entries are separated by commas. Each entry has
4224 the form VID:PID:Flags where VID and PID are Vendor
4225 and Product ID values (4-digit hex numbers) and
4226 Flags is a set of characters, each corresponding
4227 to a common usb-storage quirk flag as follows:
4228 a = SANE_SENSE (collect more than 18 bytes
4230 b = BAD_SENSE (don't collect more than 18
4231 bytes of sense data);
4232 c = FIX_CAPACITY (decrease the reported
4233 device capacity by one sector);
4234 d = NO_READ_DISC_INFO (don't use
4235 READ_DISC_INFO command);
4236 e = NO_READ_CAPACITY_16 (don't use
4237 READ_CAPACITY_16 command);
4238 f = NO_REPORT_OPCODES (don't use report opcodes
4240 g = MAX_SECTORS_240 (don't transfer more than
4241 240 sectors at a time, uas only);
4242 h = CAPACITY_HEURISTICS (decrease the
4243 reported device capacity by one
4244 sector if the number is odd);
4245 i = IGNORE_DEVICE (don't bind to this
4247 j = NO_REPORT_LUNS (don't use report luns
4249 l = NOT_LOCKABLE (don't try to lock and
4250 unlock ejectable media);
4251 m = MAX_SECTORS_64 (don't transfer more
4252 than 64 sectors = 32 KB at a time);
4253 n = INITIAL_READ10 (force a retry of the
4254 initial READ(10) command);
4255 o = CAPACITY_OK (accept the capacity
4256 reported by the device);
4257 p = WRITE_CACHE (the device cache is ON
4259 r = IGNORE_RESIDUE (the device reports
4260 bogus residue values);
4261 s = SINGLE_LUN (the device has only one
4263 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4264 commands, uas only);
4265 u = IGNORE_UAS (don't bind to the uas driver);
4266 w = NO_WP_DETECT (don't test whether the
4267 medium is write-protected).
4268 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4269 even if the device claims no cache)
4270 Example: quirks=0419:aaf5:rl,0421:0433:rc
4272 user_debug= [KNL,ARM]
4274 See arch/arm/Kconfig.debug help text.
4275 1 - undefined instruction events
4277 4 - invalid data aborts
4280 Example: user_debug=31
4283 [X86] Flags controlling user PTE allocations.
4285 nohigh = do not allocate PTE pages in
4286 HIGHMEM regardless of setting
4290 On X86_32, this is an alias for vdso32=. Otherwise:
4292 vdso=1: enable VDSO (the default)
4293 vdso=0: disable VDSO mapping
4295 vdso32= [X86] Control the 32-bit vDSO
4296 vdso32=1: enable 32-bit VDSO
4297 vdso32=0 or vdso32=2: disable 32-bit VDSO
4299 See the help text for CONFIG_COMPAT_VDSO for more
4300 details. If CONFIG_COMPAT_VDSO is set, the default is
4301 vdso32=0; otherwise, the default is vdso32=1.
4303 For compatibility with older kernels, vdso32=2 is an
4306 Try vdso32=0 if you encounter an error that says:
4307 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4310 vector=percpu: enable percpu vector domain
4312 video= [FB] Frame buffer configuration
4313 See Documentation/fb/modedb.txt.
4315 video.brightness_switch_enabled= [0,1]
4316 If set to 1, on receiving an ACPI notify event
4317 generated by hotkey, video driver will adjust brightness
4318 level and then send out the event to user space through
4319 the allocated input device; If set to 0, video driver
4320 will only send out the event without touching backlight
4325 [VMMIO] Memory mapped virtio (platform) device.
4327 <size>@<baseaddr>:<irq>[:<id>]
4329 <size> := size (can use standard suffixes
4331 <baseaddr> := physical base address
4332 <irq> := interrupt number (as passed to
4334 <id> := (optional) platform device id
4336 virtio_mmio.device=1K@0x100b0000:48:7
4338 Can be used multiple times for multiple devices.
4340 vga= [BOOT,X86-32] Select a particular video mode
4341 See Documentation/x86/boot.txt and
4342 Documentation/svga.txt.
4343 Use vga=ask for menu.
4344 This is actually a boot loader parameter; the value is
4345 passed to the kernel using a special protocol.
4347 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4348 size of <nn>. This can be used to increase the
4349 minimum size (128MB on x86). It can also be used to
4350 decrease the size and leave more room for directly
4353 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4356 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4359 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4363 Controls the behavior of vsyscalls (i.e. calls to
4364 fixed addresses of 0xffffffffff600x00 from legacy
4365 code). Most statically-linked binaries and older
4366 versions of glibc use these calls. Because these
4367 functions are at fixed addresses, they make nice
4368 targets for exploits that can control RIP.
4370 emulate [default] Vsyscalls turn into traps and are
4371 emulated reasonably safely.
4373 native Vsyscalls are native syscall instructions.
4374 This is a little bit faster than trapping
4375 and makes a few dynamic recompilers work
4376 better than they would in emulation mode.
4377 It also makes exploits much easier to write.
4379 none Vsyscalls don't work at all. This makes
4380 them quite hard to use for exploits but
4381 might break your system.
4383 vt.color= [VT] Default text color.
4384 Format: 0xYX, X = foreground, Y = background.
4385 Default: 0x07 = light gray on black.
4387 vt.cur_default= [VT] Default cursor shape.
4388 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4389 the parameters of the <Esc>[?A;B;Cc escape sequence;
4390 see VGA-softcursor.txt. Default: 2 = underline.
4392 vt.default_blu= [VT]
4393 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4394 Change the default blue palette of the console.
4395 This is a 16-member array composed of values
4398 vt.default_grn= [VT]
4399 Format: <green0>,<green1>,<green2>,...,<green15>
4400 Change the default green palette of the console.
4401 This is a 16-member array composed of values
4404 vt.default_red= [VT]
4405 Format: <red0>,<red1>,<red2>,...,<red15>
4406 Change the default red palette of the console.
4407 This is a 16-member array composed of values
4413 Set system-wide default UTF-8 mode for all tty's.
4414 Default is 1, i.e. UTF-8 mode is enabled for all
4415 newly opened terminals.
4417 vt.global_cursor_default=
4420 Set system-wide default for whether a cursor
4421 is shown on new VTs. Default is -1,
4422 i.e. cursors will be created by default unless
4423 overridden by individual drivers. 0 will hide
4424 cursors, 1 will display them.
4426 vt.italic= [VT] Default color for italic text; 0-15.
4429 vt.underline= [VT] Default color for underlined text; 0-15.
4432 watchdog timers [HW,WDT] For information on watchdog timers,
4433 see Documentation/watchdog/watchdog-parameters.txt
4434 or other driver-specific files in the
4435 Documentation/watchdog/ directory.
4437 workqueue.watchdog_thresh=
4438 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4439 warn stall conditions and dump internal state to
4440 help debugging. 0 disables workqueue stall
4441 detection; otherwise, it's the stall threshold
4442 duration in seconds. The default value is 30 and
4443 it can be updated at runtime by writing to the
4444 corresponding sysfs file.
4446 workqueue.disable_numa
4447 By default, all work items queued to unbound
4448 workqueues are affine to the NUMA nodes they're
4449 issued on, which results in better behavior in
4450 general. If NUMA affinity needs to be disabled for
4451 whatever reason, this option can be used. Note
4452 that this also can be controlled per-workqueue for
4453 workqueues visible under /sys/bus/workqueue/.
4455 workqueue.power_efficient
4456 Per-cpu workqueues are generally preferred because
4457 they show better performance thanks to cache
4458 locality; unfortunately, per-cpu workqueues tend to
4459 be more power hungry than unbound workqueues.
4461 Enabling this makes the per-cpu workqueues which
4462 were observed to contribute significantly to power
4463 consumption unbound, leading to measurably lower
4464 power usage at the cost of small performance
4467 The default value of this parameter is determined by
4468 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4470 workqueue.debug_force_rr_cpu
4471 Workqueue used to implicitly guarantee that work
4472 items queued without explicit CPU specified are put
4473 on the local CPU. This guarantee is no longer true
4474 and while local CPU is still preferred work items
4475 may be put on foreign CPUs. This debug option
4476 forces round-robin CPU selection to flush out
4477 usages which depend on the now broken guarantee.
4478 When enabled, memory and cache locality will be
4481 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4482 default x2apic cluster mode on platforms
4485 x86_intel_mid_timer= [X86-32,APBT]
4486 Choose timer option for x86 Intel MID platform.
4487 Two valid options are apbt timer only and lapic timer
4488 plus one apbt timer for broadcast timer.
4489 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4491 xen_512gb_limit [KNL,X86-64,XEN]
4492 Restricts the kernel running paravirtualized under Xen
4493 to use only up to 512 GB of RAM. The reason to do so is
4494 crash analysis tools and Xen tools for doing domain
4495 save/restore/migration must be enabled to handle larger
4498 xen_emul_unplug= [HW,X86,XEN]
4499 Unplug Xen emulated devices
4500 Format: [unplug0,][unplug1]
4501 ide-disks -- unplug primary master IDE devices
4502 aux-ide-disks -- unplug non-primary-master IDE devices
4503 nics -- unplug network devices
4504 all -- unplug all emulated devices (NICs and IDE disks)
4505 unnecessary -- unplugging emulated devices is
4506 unnecessary even if the host did not respond to
4508 never -- do not unplug even if version check succeeds
4510 xen_nopvspin [X86,XEN]
4511 Disables the ticketlock slowpath using Xen PV
4515 Disables the PV optimizations forcing the HVM guest to
4516 run as generic HVM guest with no PV drivers.
4518 xirc2ps_cs= [NET,PCMCIA]
4520 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4522 ______________________________________________________________________
4526 Add more DRM drivers.
git.samba.org / sfrench / cifs-2.6.git / blob