4 The following is a consolidated list of the kernel parameters as
5 implemented by the __setup(), core_param() and module_param() macros
6 and sorted into English Dictionary order (defined as ignoring all
7 punctuation and sorting digits before letters in a case insensitive
8 manner), and with descriptions where known.
10 The kernel parses parameters from the kernel command line up to "--";
11 if it doesn't recognize a parameter and it doesn't contain a '.', the
12 parameter gets passed to init: parameters with '=' go into init's
13 environment, others are passed as command line arguments to init.
14 Everything after "--" is passed as an argument to init.
16 Module parameters can be specified in two ways: via the kernel command
17 line with a module name prefix, or via modprobe, e.g.:
19 (kernel command line) usbcore.blinkenlights=1
20 (modprobe command line) modprobe usbcore blinkenlights=1
22 Parameters for modules which are built into the kernel need to be
23 specified on the kernel command line. modprobe looks through the
24 kernel command line (/proc/cmdline) and collects module parameters
25 when it loads a module, so the kernel command line can be used for
28 Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30 can also be entered as
31 log-buf-len=1M print_fatal_signals=1
33 Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
36 This document may not be entirely up to date and comprehensive. The command
37 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
38 module. Loadable modules, after being loaded into the running kernel, also
39 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
40 parameters may be changed at runtime by the command
41 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
43 The parameters listed below are only valid if certain kernel build options were
44 enabled and if respective hardware is present. The text in square brackets at
45 the beginning of each description states the restrictions within which a
46 parameter is applicable:
48 ACPI ACPI support is enabled.
49 AGP AGP (Accelerated Graphics Port) is enabled.
50 ALSA ALSA sound support is enabled.
51 APIC APIC support is enabled.
52 APM Advanced Power Management support is enabled.
53 ARM ARM architecture is enabled.
54 AVR32 AVR32 architecture is enabled.
55 AX25 Appropriate AX.25 support is enabled.
56 BLACKFIN Blackfin architecture is enabled.
57 CLK Common clock infrastructure is enabled.
58 CMA Contiguous Memory Area support is enabled.
59 DRM Direct Rendering Management support is enabled.
60 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
61 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
62 EFI EFI Partitioning (GPT) is enabled
63 EIDE EIDE/ATAPI support is enabled.
64 EVM Extended Verification Module
65 FB The frame buffer device is enabled.
66 FTRACE Function tracing enabled.
67 GCOV GCOV profiling is enabled.
68 HW Appropriate hardware is enabled.
69 IA-64 IA-64 architecture is enabled.
70 IMA Integrity measurement architecture is enabled.
71 IOSCHED More than one I/O scheduler is enabled.
72 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
73 IPV6 IPv6 support is enabled.
74 ISAPNP ISA PnP code is enabled.
75 ISDN Appropriate ISDN support is enabled.
76 JOY Appropriate joystick support is enabled.
77 KGDB Kernel debugger support is enabled.
78 KVM Kernel Virtual Machine support is enabled.
79 LIBATA Libata driver is enabled
80 LP Printer support is enabled.
81 LOOP Loopback device support is enabled.
82 M68k M68k architecture is enabled.
83 These options have more detailed description inside of
84 Documentation/m68k/kernel-options.txt.
85 MDA MDA console support is enabled.
86 MIPS MIPS architecture is enabled.
87 MOUSE Appropriate mouse support is enabled.
88 MSI Message Signaled Interrupts (PCI).
89 MTD MTD (Memory Technology Device) support is enabled.
90 NET Appropriate network support is enabled.
91 NUMA NUMA support is enabled.
92 NFS Appropriate NFS support is enabled.
93 OSS OSS sound support is enabled.
94 PV_OPS A paravirtualized kernel is enabled.
95 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
96 PARISC The PA-RISC architecture is enabled.
97 PCI PCI bus support is enabled.
98 PCIE PCI Express support is enabled.
99 PCMCIA The PCMCIA subsystem is enabled.
100 PNP Plug & Play support is enabled.
101 PPC PowerPC architecture is enabled.
102 PPT Parallel port support is enabled.
103 PS2 Appropriate PS/2 support is enabled.
104 RAM RAM disk support is enabled.
105 S390 S390 architecture is enabled.
106 SCSI Appropriate SCSI support is enabled.
107 A lot of drivers have their options described inside
108 the Documentation/scsi/ sub-directory.
109 SECURITY Different security models are enabled.
110 SELINUX SELinux support is enabled.
111 APPARMOR AppArmor support is enabled.
112 SERIAL Serial support is enabled.
113 SH SuperH architecture is enabled.
114 SMP The kernel is an SMP kernel.
115 SPARC Sparc architecture is enabled.
116 SWSUSP Software suspend (hibernation) is enabled.
117 SUSPEND System suspend states are enabled.
118 TPM TPM drivers are enabled.
119 TS Appropriate touchscreen support is enabled.
120 UMS USB Mass Storage support is enabled.
121 USB USB support is enabled.
122 USBHID USB Human Interface Device support is enabled.
123 V4L Video For Linux support is enabled.
124 VMMIO Driver for memory mapped virtio devices is enabled.
125 VGA The VGA console has been enabled.
126 VT Virtual terminal support is enabled.
127 WDT Watchdog support is enabled.
128 XT IBM PC/XT MFM hard disk support is enabled.
129 X86-32 X86-32, aka i386 architecture is enabled.
130 X86-64 X86-64 architecture is enabled.
131 More X86-64 boot options can be found in
132 Documentation/x86/x86_64/boot-options.txt .
133 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
134 X86_UV SGI UV support is enabled.
135 XEN Xen support is enabled
137 In addition, the following text indicates that the option:
139 BUGS= Relates to possible processor bugs on the said processor.
140 KNL Is a kernel start-up parameter.
141 BOOT Is a boot loader parameter.
143 Parameters denoted with BOOT are actually interpreted by the boot
144 loader, and have no meaning to the kernel directly.
145 Do not modify the syntax of boot loader parameters without extreme
146 need or coordination with <Documentation/x86/boot.txt>.
148 There are also arch-specific kernel-parameters not documented here.
149 See for example <Documentation/x86/x86_64/boot-options.txt>.
151 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
152 a trailing = on the name of any parameter states that that parameter will
153 be entered as an environment variable, whereas its absence indicates that
154 it will appear as a kernel argument readable via /proc/cmdline by programs
155 running once the system is up.
157 The number of kernel parameters is not limited, but the length of the
158 complete command line (parameters including spaces etc.) is limited to
159 a fixed number of characters. This limit depends on the architecture
160 and is between 256 and 4096 characters. It is defined in the file
161 ./include/asm/setup.h as COMMAND_LINE_SIZE.
163 Finally, the [KMG] suffix is commonly described after a number of kernel
164 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
165 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
166 bytes respectively. Such letter suffixes can also be entirely omitted.
169 acpi= [HW,ACPI,X86,ARM64]
170 Advanced Configuration and Power Interface
171 Format: { force | on | off | strict | noirq | rsdt |
173 force -- enable ACPI if default was off
174 on -- enable ACPI but allow fallback to DT [arm64]
175 off -- disable ACPI if default was on
176 noirq -- do not use ACPI for IRQ routing
177 strict -- Be less tolerant of platforms that are not
178 strictly ACPI specification compliant.
179 rsdt -- prefer RSDT over (default) XSDT
180 copy_dsdt -- copy DSDT to memory
181 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
184 See also Documentation/power/runtime_pm.txt, pci=noacpi
186 acpi_apic_instance= [ACPI, IOAPIC]
188 2: use 2nd APIC table, if available
189 1,0: use 1st APIC table
192 acpi_backlight= [HW,ACPI]
193 acpi_backlight=vendor
195 If set to vendor, prefer vendor specific driver
196 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
197 of the ACPI video.ko driver.
199 acpi_force_32bit_fadt_addr
200 force FADT to use 32 bit addresses rather than the
201 64 bit X_* addresses. Some firmware have broken 64
202 bit addresses for force ACPI ignore these and use
203 the older legacy 32 bit addresses.
205 acpica_no_return_repair [HW, ACPI]
206 Disable AML predefined validation mechanism
207 This mechanism can repair the evaluation result to make
208 the return objects more ACPI specification compliant.
209 This option is useful for developers to identify the
210 root cause of an AML interpreter issue when the issue
211 has something to do with the repair mechanism.
213 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
214 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
216 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
217 debug output. Bits in debug_layer correspond to a
218 _COMPONENT in an ACPI source file, e.g.,
219 #define _COMPONENT ACPI_PCI_COMPONENT
220 Bits in debug_level correspond to a level in
221 ACPI_DEBUG_PRINT statements, e.g.,
222 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
223 The debug_level mask defaults to "info". See
224 Documentation/acpi/debug.txt for more information about
225 debug layers and levels.
227 Enable processor driver info messages:
228 acpi.debug_layer=0x20000000
229 Enable PCI/PCI interrupt routing info messages:
230 acpi.debug_layer=0x400000
231 Enable AML "Debug" output, i.e., stores to the Debug
232 object while interpreting AML:
233 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
234 Enable all messages related to ACPI hardware:
235 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
237 Some values produce so much output that the system is
238 unusable. The "log_buf_len" parameter may be useful
239 if you need to capture more output.
241 acpi_enforce_resources= [ACPI]
242 { strict | lax | no }
243 Check for resource conflicts between native drivers
244 and ACPI OperationRegions (SystemIO and SystemMemory
245 only). IO ports and memory declared in ACPI might be
246 used by the ACPI subsystem in arbitrary AML code and
247 can interfere with legacy drivers.
248 strict (default): access to resources claimed by ACPI
249 is denied; legacy drivers trying to access reserved
250 resources will fail to bind to device using them.
251 lax: access to resources claimed by ACPI is allowed;
252 legacy drivers trying to access reserved resources
253 will bind successfully but a warning message is logged.
254 no: ACPI OperationRegions are not marked as reserved,
255 no further checks are performed.
257 acpi_force_table_verification [HW,ACPI]
258 Enable table checksum verification during early stage.
259 By default, this is disabled due to x86 early mapping
262 acpi_irq_balance [HW,ACPI]
263 ACPI will balance active IRQs
266 acpi_irq_nobalance [HW,ACPI]
267 ACPI will not move active IRQs (default)
270 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
271 Format: <irq>,<irq>...
273 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
275 Format: <irq>,<irq>...
277 acpi_no_auto_serialize [HW,ACPI]
278 Disable auto-serialization of AML methods
279 AML control methods that contain the opcodes to create
280 named objects will be marked as "Serialized" by the
281 auto-serialization feature.
282 This feature is enabled by default.
283 This option allows to turn off the feature.
285 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
288 acpi_no_static_ssdt [HW,ACPI]
289 Disable installation of static SSDTs at early boot time
290 By default, SSDTs contained in the RSDT/XSDT will be
291 installed automatically and they will appear under
292 /sys/firmware/acpi/tables.
293 This option turns off this feature.
294 Note that specifying this option does not affect
295 dynamic table installation which will install SSDT
296 tables to /sys/firmware/acpi/tables/dynamic.
298 acpi_rsdp= [ACPI,EFI,KEXEC]
299 Pass the RSDP address to the kernel, mostly used
300 on machines running EFI runtime service to boot the
301 second kernel for kdump.
303 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
304 Format: To spoof as Windows 98: ="Microsoft Windows"
306 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
307 of 2 which is mandated by ACPI 6) as the supported ACPI
308 specification revision (when using this switch, it may
309 be necessary to carry out a cold reboot _twice_ in a
310 row to make it take effect on the platform firmware).
312 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
313 acpi_osi="string1" # add string1
314 acpi_osi="!string2" # remove string2
315 acpi_osi=!* # remove all strings
316 acpi_osi=! # disable all built-in OS vendor
318 acpi_osi=!! # enable all built-in OS vendor
320 acpi_osi= # disable all strings
322 'acpi_osi=!' can be used in combination with single or
323 multiple 'acpi_osi="string1"' to support specific OS
324 vendor string(s). Note that such command can only
325 affect the default state of the OS vendor strings, thus
326 it cannot affect the default state of the feature group
327 strings and the current state of the OS vendor strings,
328 specifying it multiple times through kernel command line
329 is meaningless. This command is useful when one do not
330 care about the state of the feature group strings which
331 should be controlled by the OSPM.
333 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
334 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
335 can make '_OSI("Windows 2000")' TRUE.
337 'acpi_osi=' cannot be used in combination with other
338 'acpi_osi=' command lines, the _OSI method will not
339 exist in the ACPI namespace. NOTE that such command can
340 only affect the _OSI support state, thus specifying it
341 multiple times through kernel command line is also
344 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
347 'acpi_osi=!*' can be used in combination with single or
348 multiple 'acpi_osi="string1"' to support specific
349 string(s). Note that such command can affect the
350 current state of both the OS vendor strings and the
351 feature group strings, thus specifying it multiple times
352 through kernel command line is meaningful. But it may
353 still not able to affect the final state of a string if
354 there are quirks related to this string. This command
355 is useful when one want to control the state of the
356 feature group strings to debug BIOS issues related to
359 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
360 '_OSI("Module Device")' FALSE.
361 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
362 '_OSI("Module Device")' TRUE.
363 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
365 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
367 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
368 they all will make '_OSI("Windows 2000")' TRUE.
371 Override the pmtimer bug detection: force the kernel
372 to assume that this machine's pmtimer latches its value
373 and always returns good values.
375 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
376 Format: { level | edge | high | low }
378 acpi_skip_timer_override [HW,ACPI]
379 Recognize and ignore IRQ0/pin2 Interrupt Override.
380 For broken nForce2 BIOS resulting in XT-PIC timer.
382 acpi_sleep= [HW,ACPI] Sleep options
383 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
384 old_ordering, nonvs, sci_force_enable }
385 See Documentation/power/video.txt for information on
387 s3_beep is for debugging; it makes the PC's speaker beep
388 as soon as the kernel's real-mode entry point is called.
389 s4_nohwsig prevents ACPI hardware signature from being
390 used during resume from hibernation.
391 old_ordering causes the ACPI 1.0 ordering of the _PTS
392 control method, with respect to putting devices into
393 low power states, to be enforced (the ACPI 2.0 ordering
394 of _PTS is used by default).
395 nonvs prevents the kernel from saving/restoring the
396 ACPI NVS memory during suspend/hibernation and resume.
397 sci_force_enable causes the kernel to set SCI_EN directly
398 on resume from S1/S3 (which is against the ACPI spec,
399 but some broken systems don't work without it).
401 acpi_use_timer_override [HW,ACPI]
402 Use timer override. For some broken Nvidia NF5 boards
403 that require a timer override, but don't have HPET
405 add_efi_memmap [EFI; X86] Include EFI memory map in
406 kernel's map of available physical RAM.
409 { off | try_unsupported }
410 off: disable AGP support
411 try_unsupported: try to drive unsupported chipsets
412 (may crash computer or cause data corruption)
415 See Documentation/sound/alsa/alsa-parameters.txt
418 Allow the default userspace alignment fault handler
419 behaviour to be specified. Bit 0 enables warnings,
420 bit 1 enables fixups, and bit 2 sends a segfault.
422 align_va_addr= [X86-64]
423 Align virtual addresses by clearing slice [14:12] when
424 allocating a VMA at process creation time. This option
425 gives you up to 3% performance improvement on AMD F15h
426 machines (where it is enabled by default) for a
427 CPU-intensive style benchmark, and it can vary highly in
428 a microbenchmark depending on workload and compiler.
430 32: only for 32-bit processes
431 64: only for 64-bit processes
432 on: enable for both 32- and 64-bit processes
433 off: disable for both 32- and 64-bit processes
435 alloc_snapshot [FTRACE]
436 Allocate the ftrace snapshot buffer on boot up when the
437 main buffer is allocated. This is handy if debugging
438 and you need to use tracing_snapshot() on boot up, and
439 do not want to use tracing_snapshot_alloc() as it needs
440 to be done where GFP_KERNEL allocations are allowed.
442 amd_iommu= [HW,X86-64]
443 Pass parameters to the AMD IOMMU driver in the system.
445 fullflush - enable flushing of IO/TLB entries when
446 they are unmapped. Otherwise they are
447 flushed before they will be reused, which
449 off - do not initialize any AMD IOMMU found in
451 force_isolation - Force device isolation for all
452 devices. The IOMMU driver is not
453 allowed anymore to lift isolation
454 requirements as needed. This option
455 does not override iommu=pt
457 amd_iommu_dump= [HW,X86-64]
458 Enable AMD IOMMU driver option to dump the ACPI table
459 for AMD IOMMU. With this option enabled, AMD IOMMU
460 driver will print ACPI tables for AMD IOMMU during
461 IOMMU initialization.
463 amijoy.map= [HW,JOY] Amiga joystick support
464 Map of devices attached to JOY0DAT and JOY1DAT
466 See also Documentation/input/joystick.txt
468 analog.map= [HW,JOY] Analog joystick and gamepad support
469 Specifies type or capabilities of an analog joystick
470 connected to one of 16 gameports
471 Format: <type1>,<type2>,..<type16>
474 Power management functions (SPARCstation-4/5 + deriv.)
476 Disable APC CPU standby support. SPARCstation-Fox does
477 not play well with APC CPU idle - disable it if you have
478 APC and your system crashes randomly.
480 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
481 Change the output verbosity whilst booting
482 Format: { quiet (default) | verbose | debug }
483 Change the amount of debugging information output
484 when initialising the APIC and IO-APIC components.
486 apic_extnmi= [APIC,X86] External NMI delivery setting
487 Format: { bsp (default) | all | none }
488 bsp: External NMI is delivered only to CPU 0
489 all: External NMIs are broadcast to all CPUs as a
491 none: External NMI is masked for all CPUs. This is
492 useful so that a dump capture kernel won't be
496 See Documentation/networking/ipv6.txt.
498 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
499 Limit apic dumping. The parameter defines the maximal
500 number of local apics being dumped. Also it is possible
501 to set it to "all" by meaning -- no limit here.
502 Format: { 1 (default) | 2 | ... | all }.
503 The parameter valid if only apic=debug or
504 apic=verbose is specified.
505 Example: apic=debug show_lapic=all
507 apm= [APM] Advanced Power Management
508 See header of arch/x86/kernel/apm_32.c.
510 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
511 Format: <io>,<irq>,<nodeID>
515 atarimouse= [HW,MOUSE] Atari Mouse
517 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
518 EzKey and similar keyboards
520 atkbd.reset= [HW] Reset keyboard during initialization
522 atkbd.set= [HW] Select keyboard code set
523 Format: <int> (2 = AT (default), 3 = PS/2)
525 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
528 atkbd.softraw= [HW] Choose between synthetic and real raw mode
529 Format: <bool> (0 = real, 1 = synthetic (default))
531 atkbd.softrepeat= [HW]
532 Use software keyboard repeat
534 audit= [KNL] Enable the audit sub-system
535 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
536 0 - kernel audit is disabled and can not be enabled
537 until the next reboot
538 unset - kernel audit is initialized but disabled and
539 will be fully enabled by the userspace auditd.
540 1 - kernel audit is initialized and partially enabled,
541 storing at most audit_backlog_limit messages in
542 RAM until it is fully enabled by the userspace
546 audit_backlog_limit= [KNL] Set the audit queue size limit.
547 Format: <int> (must be >=0)
550 bau= [X86_UV] Enable the BAU on SGI UV. The default
551 behavior is to disable the BAU (i.e. bau=0).
552 Format: { "0" | "1" }
555 unset - Disable the BAU.
557 baycom_epp= [HW,AX25]
560 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
562 See header of drivers/net/hamradio/baycom_par.c.
564 baycom_ser_fdx= [HW,AX25]
565 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
566 Format: <io>,<irq>,<mode>[,<baud>]
567 See header of drivers/net/hamradio/baycom_ser_fdx.c.
569 baycom_ser_hdx= [HW,AX25]
570 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
571 Format: <io>,<irq>,<mode>
572 See header of drivers/net/hamradio/baycom_ser_hdx.c.
574 blkdevparts= Manual partition parsing of block device(s) for
575 embedded devices based on command line input.
576 See Documentation/block/cmdline-partition.txt
578 boot_delay= Milliseconds to delay each printk during boot.
579 Values larger than 10 seconds (10000) are changed to
583 bootmem_debug [KNL] Enable bootmem allocator debug messages.
586 Disable BERT OS support on buggy BIOSes.
588 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
589 bttv.radio= Most important insmod options are available as
591 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
594 bulk_remove=off [PPC] This parameter disables the use of the pSeries
595 firmware feature for flushing multiple hpte entries
598 c101= [NET] Moxa C101 synchronous serial card
600 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
601 Sometimes CPU hardware bugs make them report the cache
602 size incorrectly. The kernel will attempt work arounds
603 to fix known problems, but for some CPUs it is not
604 possible to determine what the correct size should be.
605 This option provides an override for these situations.
607 ca_keys= [KEYS] This parameter identifies a specific key(s) on
608 the system trusted keyring to be used for certificate
610 format: { id:<keyid> | builtin }
612 cca= [MIPS] Override the kernel pages' cache coherency
613 algorithm. Accepted values range from 0 to 7
614 inclusive. See arch/mips/include/asm/pgtable-bits.h
615 for platform specific values (SB1, Loongson3 and
618 ccw_timeout_log [S390]
619 See Documentation/s390/CommonIO for details.
621 cgroup_disable= [KNL] Disable a particular controller
622 Format: {name of the controller(s) to disable}
623 The effects of cgroup_disable=foo are:
624 - foo isn't auto-mounted if you mount all cgroups in
626 - foo isn't visible as an individually mountable
628 {Currently only "memory" controller deal with this and
629 cut the overhead, others just disable the usage. So
630 only cgroup_disable=memory is actually worthy}
632 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
633 Format: { controller[,controller...] | "all" }
634 Like cgroup_disable, but only applies to cgroup v1;
635 the blacklisted controllers remain available in cgroup2.
637 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
639 nosocket -- Disable socket memory accounting.
640 nokmem -- Disable kernel memory accounting.
642 checkreqprot [SELINUX] Set initial checkreqprot flag value.
643 Format: { "0" | "1" }
644 See security/selinux/Kconfig help text.
645 0 -- check protection applied by kernel (includes
646 any implied execute protection).
647 1 -- check protection requested by application.
648 Default value is set via a kernel config option.
649 Value can be changed at runtime via
650 /selinux/checkreqprot.
653 See Documentation/s390/CommonIO for details.
656 Prevents the clock framework from automatically gating
657 clocks that have not been explicitly enabled by a Linux
658 device driver but are enabled in hardware at reset or
659 by the bootloader/firmware. Note that this does not
660 force such clocks to be always-on nor does it reserve
661 those clocks in any way. This parameter is useful for
662 debug and development, but should not be needed on a
663 platform with proper driver support. For more
664 information, see Documentation/clk.txt.
666 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
668 Forces specified clocksource (if available) to be used
669 when calculating gettimeofday(). If specified
670 clocksource is not available, it defaults to PIT.
671 Format: { pit | tsc | cyclone | pmtmr }
673 clocksource= Override the default clocksource
675 Override the default clocksource and use the clocksource
676 with the name specified.
677 Some clocksource names to choose from, depending on
679 [all] jiffies (this is the base, fallback clocksource)
681 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
682 pxa_timer,timer3,32k_counter,timer0_1
684 [X86-32] pit,hpet,tsc;
685 scx200_hrt on Geode; cyclone on IBM x440
693 clocksource.arm_arch_timer.evtstrm=
696 Enable/disable the eventstream feature of the ARM
697 architected timer so that code using WFE-based polling
698 loops can be debugged more effectively on production
701 clearcpuid=BITNUM [X86]
702 Disable CPUID feature X for the kernel. See
703 arch/x86/include/asm/cpufeatures.h for the valid bit
704 numbers. Note the Linux specific bits are not necessarily
705 stable over kernel options, but the vendor specific
707 Also note that user programs calling CPUID directly
708 or using the feature without checking anything
709 will still see it. This just prevents it from
710 being used by the kernel or shown in /proc/cpuinfo.
711 Also note the kernel might malfunction if you disable
714 cma=nn[MG]@[start[MG][-end[MG]]]
716 Sets the size of kernel global memory area for
717 contiguous memory allocations and optionally the
718 placement constraint by the physical address range of
719 memory allocations. A value of 0 disables CMA
720 altogether. For more information, see
721 include/linux/dma-contiguous.h
723 cmo_free_hint= [PPC] Format: { yes | no }
724 Specify whether pages are marked as being inactive
725 when they are freed. This is used in CMO environments
726 to determine OS memory pressure for page stealing by
730 coherent_pool=nn[KMG] [ARM,KNL]
731 Sets the size of memory pool for coherent, atomic dma
732 allocations, by default set to 256K.
734 code_bytes [X86] How many bytes of object code to print
739 com20020= [HW,NET] ARCnet - COM20020 chipset
741 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
743 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
747 ARCnet - COM90xx chipset (memory-mapped buffers)
748 Format: <io>[,<irq>[,<memstart>]]
750 condev= [HW,S390] console device
753 console= [KNL] Output console device and options.
755 tty<n> Use the virtual console device <n>.
759 Use the specified serial port. The options are of
760 the form "bbbbpnf", where "bbbb" is the baud rate,
761 "p" is parity ("n", "o", or "e"), "n" is number of
762 bits, and "f" is flow control ("r" for RTS or
763 omit it). Default is "9600n8".
765 See Documentation/serial-console.txt for more
767 Documentation/networking/netconsole.txt for an
770 uart[8250],io,<addr>[,options]
771 uart[8250],mmio,<addr>[,options]
772 uart[8250],mmio16,<addr>[,options]
773 uart[8250],mmio32,<addr>[,options]
774 uart[8250],0x<addr>[,options]
775 Start an early, polled-mode console on the 8250/16550
776 UART at the specified I/O port or MMIO address,
777 switching to the matching ttyS device later.
778 MMIO inter-register address stride is either 8-bit
779 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
780 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
781 to be equivalent to 'mmio'. 'options' are specified in
782 the same format described for ttyS above; if unspecified,
783 the h/w is not re-initialized.
785 hvc<n> Use the hypervisor console device <n>. This is for
786 both Xen and PowerPC hypervisors.
788 If the device connected to the port is not a TTY but a braille
789 device, prepend "brl," before the device type, for instance
791 For now, only VisioBraille is supported.
793 consoleblank= [KNL] The console blank (screen saver) timeout in
794 seconds. Defaults to 10*60 = 10mins. A value of 0
795 disables the blank timer.
798 [KNL] Change the default value for
799 /proc/<pid>/coredump_filter.
800 See also Documentation/filesystems/proc.txt.
802 cpuidle.off=1 [CPU_IDLE]
803 disable the cpuidle sub-system
806 [X86] Delay for N microsec between assert and de-assert
807 of APIC INIT to start processors. This delay occurs
808 on every CPU online, such as boot, and resume from suspend.
811 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
813 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
815 crashkernel=size[KMG][@offset[KMG]]
816 [KNL] Using kexec, Linux can switch to a 'crash kernel'
817 upon panic. This parameter reserves the physical
818 memory region [offset, offset + size] for that kernel
819 image. If '@offset' is omitted, then a suitable offset
820 is selected automatically. Check
821 Documentation/kdump/kdump.txt for further details.
823 crashkernel=range1:size1[,range2:size2,...][@offset]
824 [KNL] Same as above, but depends on the memory
825 in the running system. The syntax of range is
826 start-[end] where start and end are both
827 a memory unit (amount[KMG]). See also
828 Documentation/kdump/kdump.txt for an example.
830 crashkernel=size[KMG],high
831 [KNL, x86_64] range could be above 4G. Allow kernel
832 to allocate physical memory region from top, so could
833 be above 4G if system have more than 4G ram installed.
834 Otherwise memory region will be allocated below 4G, if
836 It will be ignored if crashkernel=X is specified.
837 crashkernel=size[KMG],low
838 [KNL, x86_64] range under 4G. When crashkernel=X,high
839 is passed, kernel could allocate physical memory region
840 above 4G, that cause second kernel crash on system
841 that require some amount of low memory, e.g. swiotlb
842 requires at least 64M+32K low memory, also enough extra
843 low memory is needed to make sure DMA buffers for 32-bit
844 devices won't run out. Kernel would try to allocate at
845 at least 256M below 4G automatically.
846 This one let user to specify own low range under 4G
847 for second kernel instead.
848 0: to disable low allocation.
849 It will be ignored when crashkernel=X,high is not used
850 or memory reserved is below 4G.
853 [KNL] Disable crypto self-tests
858 cs89x0_media= [HW,NET]
859 Format: { rj45 | aui | bnc }
862 See header of drivers/s390/block/dasd_devmap.c.
864 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
865 (one device per port)
866 Format: <port#>,<type>
867 See also Documentation/input/joystick-parport.txt
869 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
870 time. See Documentation/dynamic-debug-howto.txt for
871 details. Deprecated, see dyndbg.
873 debug [KNL] Enable kernel debugging (events log level).
876 [KNL] verbose self-tests
878 Print debugging info while doing the locking API
880 We default to 0 (no extra messages), setting it to
881 1 will print _a lot_ more information - normally
882 only useful to kernel developers.
884 debug_objects [KNL] Enable object debugging
887 [KNL] Disable object debugging
889 debug_guardpage_minorder=
890 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
891 parameter allows control of the order of pages that will
892 be intentionally kept free (and hence protected) by the
893 buddy allocator. Bigger value increase the probability
894 of catching random memory corruption, but reduce the
895 amount of memory for normal system use. The maximum
896 possible value is MAX_ORDER/2. Setting this parameter
897 to 1 or 2 should be enough to identify most random
898 memory corruption problems caused by bugs in kernel or
899 driver code when a CPU writes to (or reads from) a
900 random memory location. Note that there exists a class
901 of memory corruptions problems caused by buggy H/W or
902 F/W or by drivers badly programing DMA (basically when
903 memory is written at bus level and the CPU MMU is
904 bypassed) which are not detectable by
905 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
906 tracking down these problems.
909 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
910 parameter enables the feature at boot time. In
911 default, it is disabled. We can avoid allocating huge
912 chunk of memory for debug pagealloc if we don't enable
913 it at boot time and the system will work mostly same
914 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
915 on: enable the feature
917 debugpat [X86] Enable PAT debugging
919 decnet.addr= [HW,NET]
920 Format: <area>[,<node>]
921 See also Documentation/networking/decnet.txt.
924 [same as hugepagesz=] The size of the default
925 HugeTLB page size. This is the size represented by
926 the legacy /proc/ hugepages APIs, used for SHM, and
927 default size when mounting hugetlbfs filesystems.
928 Defaults to the default architecture's huge page size
932 Set number of hash buckets for dentry cache.
934 disable_1tb_segments [PPC]
935 Disables the use of 1TB hash page table segments. This
936 causes the kernel to fall back to 256MB segments which
937 can be useful when debugging issues that require an SLB
941 See Documentation/networking/ipv6.txt.
944 Disable RADIX MMU mode on POWER9
946 disable_cpu_apicid= [X86,APIC,SMP]
948 The number of initial APIC ID for the
949 corresponding CPU to be disabled at boot,
950 mostly used for the kdump 2nd kernel to
951 disable BSP to wake up multiple CPUs without
952 causing system reset or hang due to sending
955 disable_ddw [PPC/PSERIES]
956 Disable Dynamic DMA Window support. Use this if
957 to workaround buggy firmware.
960 See Documentation/networking/ipv6.txt.
962 disable_mtrr_cleanup [X86]
963 The kernel tries to adjust MTRR layout from continuous
964 to discrete, to make X server driver able to add WB
965 entry later. This parameter disables that.
967 disable_mtrr_trim [X86, Intel and AMD only]
968 By default the kernel will trim any uncacheable
969 memory out of your available memory pool based on
970 MTRR settings. This parameter disables that behavior,
971 possibly causing your machine to run very slowly.
973 disable_timer_pin_1 [X86]
974 Disable PIN 1 of APIC timer
975 Can be useful to work around chipset bugs.
977 dis_ucode_ldr [X86] Disable the microcode loader.
979 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
980 this option disables the debugging code at boot.
982 dma_debug_entries=<number>
983 This option allows to tune the number of preallocated
984 entries for DMA-API debugging code. One entry is
985 required per DMA-API allocation. Use this if the
986 DMA-API debugging code disables itself because the
987 architectural default is too low.
989 dma_debug_driver=<driver_name>
990 With this option the DMA-API debugging driver
991 filter feature can be enabled at boot time. Just
992 pass the driver to filter for as the parameter.
993 The filter can be disabled or changed to another
994 driver later using sysfs.
996 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
997 Broken monitors, graphic adapters, KVMs and EDIDless
998 panels may send no or incorrect EDID data sets.
999 This parameter allows to specify an EDID data sets
1000 in the /lib/firmware directory that are used instead.
1001 Generic built-in EDID data sets are used, if one of
1002 edid/1024x768.bin, edid/1280x1024.bin,
1003 edid/1680x1050.bin, or edid/1920x1080.bin is given
1004 and no file with the same name exists. Details and
1005 instructions how to build your own EDID data are
1006 available in Documentation/EDID/HOWTO.txt. An EDID
1007 data set will only be used for a particular connector,
1008 if its name and a colon are prepended to the EDID
1009 name. Each connector may use a unique EDID data
1010 set by separating the files with a comma. An EDID
1011 data set with no connector name will be used for
1012 any connectors not explicitly specified.
1016 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1017 module.dyndbg[="val"]
1018 Enable debug messages at boot time. See
1019 Documentation/dynamic-debug-howto.txt for details.
1021 nompx [X86] Disables Intel Memory Protection Extensions.
1022 See Documentation/x86/intel_mpx.txt for more
1023 information about the feature.
1025 nopku [X86] Disable Memory Protection Keys CPU feature found
1029 on enable eager fpu restore
1030 off disable eager fpu restore
1031 auto selects the default scheme, which automatically
1032 enables eagerfpu restore for xsaveopt.
1034 module.async_probe [KNL]
1035 Enable asynchronous probe on this module.
1037 early_ioremap_debug [KNL]
1038 Enable debug messages in early_ioremap support. This
1039 is useful for tracking down temporary early mappings
1040 which are not unmapped.
1042 earlycon= [KNL] Output early console device and options.
1044 When used with no options, the early console is
1045 determined by the stdout-path property in device
1048 cdns,<addr>[,options]
1049 Start an early, polled-mode console on a Cadence
1050 (xuartps) serial port at the specified address. Only
1051 supported option is baud rate. If baud rate is not
1052 specified, the serial port must already be setup and
1055 uart[8250],io,<addr>[,options]
1056 uart[8250],mmio,<addr>[,options]
1057 uart[8250],mmio32,<addr>[,options]
1058 uart[8250],mmio32be,<addr>[,options]
1059 uart[8250],0x<addr>[,options]
1060 Start an early, polled-mode console on the 8250/16550
1061 UART at the specified I/O port or MMIO address.
1062 MMIO inter-register address stride is either 8-bit
1063 (mmio) or 32-bit (mmio32 or mmio32be).
1064 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1065 to be equivalent to 'mmio'. 'options' are specified
1066 in the same format described for "console=ttyS<n>"; if
1067 unspecified, the h/w is not initialized.
1071 Start an early, polled-mode console on a pl011 serial
1072 port at the specified address. The pl011 serial port
1073 must already be setup and configured. Options are not
1074 yet supported. If 'mmio32' is specified, then only
1075 the driver will use only 32-bit accessors to read/write
1076 the device registers.
1079 Start an early, polled-mode console on a meson serial
1080 port at the specified address. The serial port must
1081 already be setup and configured. Options are not yet
1085 Start an early, polled-mode console on an msm serial
1086 port at the specified address. The serial port
1087 must already be setup and configured. Options are not
1090 msm_serial_dm,<addr>
1091 Start an early, polled-mode console on an msm serial
1092 dm port at the specified address. The serial port
1093 must already be setup and configured. Options are not
1096 smh Use ARM semihosting calls for early console.
1104 Use early console provided by serial driver available
1105 on Samsung SoCs, requires selecting proper type and
1106 a correct base address of the selected UART port. The
1107 serial port must already be setup and configured.
1108 Options are not yet supported.
1112 Use early console provided by Freescale LP UART driver
1113 found on Freescale Vybrid and QorIQ LS1021A processors.
1114 A valid base address must be provided, and the serial
1115 port must already be setup and configured.
1117 armada3700_uart,<addr>
1118 Start an early, polled-mode console on the
1119 Armada 3700 serial port at the specified
1120 address. The serial port must already be setup
1121 and configured. Options are not yet supported.
1123 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1127 earlyprintk=serial[,ttySn[,baudrate]]
1128 earlyprintk=serial[,0x...[,baudrate]]
1129 earlyprintk=ttySn[,baudrate]
1130 earlyprintk=dbgp[debugController#]
1131 earlyprintk=pciserial,bus:device.function[,baudrate]
1133 earlyprintk is useful when the kernel crashes before
1134 the normal console is initialized. It is not enabled by
1135 default because it has some cosmetic problems.
1137 Append ",keep" to not disable it when the real console
1140 Only one of vga, efi, serial, or usb debug port can
1143 Currently only ttyS0 and ttyS1 may be specified by
1144 name. Other I/O ports may be explicitly specified
1145 on some architectures (x86 and arm at least) by
1146 replacing ttySn with an I/O port address, like this:
1147 earlyprintk=serial,0x1008,115200
1148 You can find the port for a given device in
1149 /proc/tty/driver/serial:
1150 2: uart:ST16650V2 port:00001008 irq:18 ...
1152 Interaction with the standard serial driver is not
1155 The VGA and EFI output is eventually overwritten by
1158 The xen output can only be used by Xen PV guests.
1160 edac_report= [HW,EDAC] Control how to report EDAC event
1161 Format: {"on" | "off" | "force"}
1162 on: enable EDAC to report H/W event. May be overridden
1163 by other higher priority error reporting module.
1164 off: disable H/W event reporting through EDAC.
1165 force: enforce the use of EDAC to report H/W event.
1168 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1171 This is designed to be used in conjunction with
1172 the boot argument: earlyprintk=vga
1175 Format: {"off" | "on" | "skip[mbr]"}
1178 Format: { "old_map", "nochunk", "noruntime", "debug" }
1179 old_map [X86-64]: switch to the old ioremap-based EFI
1180 runtime services mapping. 32-bit still uses this one by
1182 nochunk: disable reading files in "chunks" in the EFI
1183 boot stub, as chunking can cause problems with some
1184 firmware implementations.
1185 noruntime : disable EFI runtime services support
1186 debug: enable misc debug output
1188 efi_no_storage_paranoia [EFI; X86]
1189 Using this parameter you can use more than 50% of
1190 your efi variable storage. Use this parameter only if
1191 you are really sure that your UEFI does sane gc and
1192 fulfills the spec otherwise your board may brick.
1194 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1195 Add arbitrary attribute to specific memory range by
1196 updating original EFI memory map.
1197 Region of memory which aa attribute is added to is
1199 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1200 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1201 attribute is added to range 0x100000000-0x180000000 and
1202 0x10a0000000-0x1120000000.
1204 Using this parameter you can do debugging of EFI memmap
1205 related feature. For example, you can do debugging of
1206 Address Range Mirroring feature even if your box
1209 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1210 that is to be dynamically loaded by Linux. If there are
1211 multiple variables with the same name but with different
1212 vendor GUIDs, all of them will be loaded. See
1213 Documentation/acpi/ssdt-overlays.txt for details.
1216 eisa_irq_edge= [PARISC,HW]
1217 See header of drivers/parisc/eisa.c.
1220 See comment before function elanfreq_setup() in
1221 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1224 Format: {"cfq" | "deadline" | "noop"}
1225 See Documentation/block/cfq-iosched.txt and
1226 Documentation/block/deadline-iosched.txt for details.
1228 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1229 Specifies physical address of start of kernel core
1230 image elf header and optionally the size. Generally
1231 kexec loader will pass this option to capture kernel.
1232 See Documentation/kdump/kdump.txt for details.
1234 enable_mtrr_cleanup [X86]
1235 The kernel tries to adjust MTRR layout from continuous
1236 to discrete, to make X server driver able to add WB
1237 entry later. This parameter enables that.
1239 enable_timer_pin_1 [X86]
1240 Enable PIN 1 of APIC timer
1241 Can be useful to work around chipset bugs
1242 (in particular on some ATI chipsets).
1243 The kernel tries to set a reasonable default.
1245 enforcing [SELINUX] Set initial enforcing status.
1247 See security/selinux/Kconfig help text.
1248 0 -- permissive (log only, no denials).
1249 1 -- enforcing (deny and log).
1251 Value can be changed at runtime via /selinux/enforce.
1254 Disable Error Record Serialization Table (ERST)
1257 ether= [HW,NET] Ethernet cards parameters
1258 This option is obsoleted by the "netdev=" option, which
1259 has equivalent usage. See its documentation for details.
1263 Permit 'security.evm' to be updated regardless of
1264 current integrity status.
1268 fail_make_request=[KNL]
1269 General fault injection mechanism.
1270 Format: <interval>,<probability>,<space>,<times>
1271 See also Documentation/fault-injection/.
1274 See Documentation/blockdev/floppy.txt.
1276 force_pal_cache_flush
1277 [IA-64] Avoid check_sal_cache_flush which may hang on
1278 buggy SAL_CACHE_FLUSH implementations. Using this
1279 parameter will force ia64_sal_cache_flush to call
1280 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1283 Forcefully enable Physical Address Extension (PAE).
1284 Many Pentium M systems disable PAE but may have a
1285 functionally usable PAE implementation.
1286 Warning: use of this parameter will taint the kernel
1287 and may cause unknown problems.
1290 [FTRACE] will set and start the specified tracer
1291 as early as possible in order to facilitate early
1294 ftrace_dump_on_oops[=orig_cpu]
1295 [FTRACE] will dump the trace buffers on oops.
1296 If no parameter is passed, ftrace will dump
1297 buffers of all CPUs, but if you pass orig_cpu, it will
1298 dump only the buffer of the CPU that triggered the
1301 ftrace_filter=[function-list]
1302 [FTRACE] Limit the functions traced by the function
1303 tracer at boot up. function-list is a comma separated
1304 list of functions. This list can be changed at run
1305 time by the set_ftrace_filter file in the debugfs
1308 ftrace_notrace=[function-list]
1309 [FTRACE] Do not trace the functions specified in
1310 function-list. This list can be changed at run time
1311 by the set_ftrace_notrace file in the debugfs
1314 ftrace_graph_filter=[function-list]
1315 [FTRACE] Limit the top level callers functions traced
1316 by the function graph tracer at boot up.
1317 function-list is a comma separated list of functions
1318 that can be changed at run time by the
1319 set_graph_function file in the debugfs tracing directory.
1321 ftrace_graph_notrace=[function-list]
1322 [FTRACE] Do not trace from the functions specified in
1323 function-list. This list is a comma separated list of
1324 functions that can be changed at run time by the
1325 set_graph_notrace file in the debugfs tracing directory.
1328 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1329 support via parallel port (up to 5 devices per port)
1330 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1331 See also Documentation/input/joystick-parport.txt
1335 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1339 gcov_persist= [GCOV] When non-zero (default), profiling data for
1340 kernel modules is saved and remains accessible via
1341 debugfs, even when the module is unloaded/reloaded.
1342 When zero, profiling data is discarded and associated
1343 debugfs files are removed at module unload time.
1345 gpt [EFI] Forces disk with valid GPT signature but
1346 invalid Protective MBR to be treated as GPT. If the
1347 primary GPT is corrupted, it enables the backup/alternate
1348 GPT to be used instead.
1350 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1351 the "Enable 0" bit of the configuration register.
1354 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1355 the "Enable 0" bit of the configuration register.
1358 grcan.select= [HW] Select which physical interface to use.
1361 grcan.txsize= [HW] Sets the size of the tx buffer.
1362 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1364 grcan.rxsize= [HW] Sets the size of the rx buffer.
1365 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1368 hardlockup_all_cpu_backtrace=
1369 [KNL] Should the hard-lockup detector generate
1370 backtraces on all cpus.
1373 hashdist= [KNL,NUMA] Large hashes allocated during boot
1374 are distributed across NUMA nodes. Defaults on
1375 for 64-bit NUMA, off otherwise.
1376 Format: 0 | 1 (for off | on)
1378 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1380 hd= [EIDE] (E)IDE hard drive subsystem geometry
1381 Format: <cyl>,<head>,<sect>
1384 Disable Hardware Error Source Table (HEST) support;
1385 corresponding firmware-first mode error processing
1386 logic will be disabled.
1388 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1389 size of <nn>. This works even on boxes that have no
1390 highmem otherwise. This also works to reduce highmem
1391 size on bigger boxes.
1393 highres= [KNL] Enable/disable high resolution timer mode.
1394 Valid parameters: "on", "off"
1398 See Documentation/isdn/README.HiSax.
1402 hpet= [X86-32,HPET] option to control HPET usage
1403 Format: { enable (default) | disable | force |
1405 disable: disable HPET and use PIT instead
1406 force: allow force enabled of undocumented chips (ICH4,
1408 verbose: show contents of HPET registers during setup
1410 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1411 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1413 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1414 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1415 On x86-64 and powerpc, this option can be specified
1416 multiple times interleaved with hugepages= to reserve
1417 huge pages of different sizes. Valid pages sizes on
1418 x86-64 are 2M (when the CPU supports "pse") and 1G
1419 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1421 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1422 terminal devices. Valid values: 0..8
1423 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1424 If specified, z/VM IUCV HVC accepts connections
1425 from listed z/VM user IDs only.
1427 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1428 hardware thread id mappings.
1429 Format: <cpu>:<hwthread>
1432 Do not unregister boot console at start. This is only
1433 useful for debugging when something happens in the window
1434 between unregistering the boot console and initializing
1437 i2c_bus= [HW] Override the default board specific I2C bus speed
1438 or register an additional I2C bus that is not
1439 registered from board initialization code.
1443 i8042.debug [HW] Toggle i8042 debug mode
1444 i8042.unmask_kbd_data
1445 [HW] Enable printing of interrupt data from the KBD port
1446 (disabled by default, and as a pre-condition
1447 requires that i8042.debug=1 be enabled)
1448 i8042.direct [HW] Put keyboard port into non-translated mode
1449 i8042.dumbkbd [HW] Pretend that controller can only read data from
1450 keyboard and cannot control its state
1451 (Don't attempt to blink the leds)
1452 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1453 i8042.nokbd [HW] Don't check/create keyboard port
1454 i8042.noloop [HW] Disable the AUX Loopback command while probing
1456 i8042.nomux [HW] Don't check presence of an active multiplexing
1458 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1460 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1461 i8042.reset [HW] Reset the controller during init and cleanup
1462 i8042.unlock [HW] Unlock (ignore) the keylock
1463 i8042.kbdreset [HW] Reset device connected to KBD port
1467 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1468 indicates that the driver is running on unsupported
1470 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1471 does not match list of supported models.
1473 [HW] Report power status in /proc/i8k
1474 (disabled by default)
1475 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1478 i915.invert_brightness=
1479 [DRM] Invert the sense of the variable that is used to
1480 set the brightness of the panel backlight. Normally a
1481 brightness value of 0 indicates backlight switched off,
1482 and the maximum of the brightness value sets the backlight
1483 to maximum brightness. If this parameter is set to 0
1484 (default) and the machine requires it, or this parameter
1485 is set to 1, a brightness value of 0 sets the backlight
1486 to maximum brightness, and the maximum of the brightness
1487 value switches the backlight off.
1488 -1 -- never invert brightness
1489 0 -- machine default
1490 1 -- force brightness inversion
1493 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1495 ide-core.nodma= [HW] (E)IDE subsystem
1496 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1497 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1498 .cdrom .chs .ignore_cable are additional options
1499 See Documentation/ide/ide.txt.
1501 ide-generic.probe-mask= [HW] (E)IDE subsystem
1503 Probe mask for legacy ISA IDE ports. Depending on
1504 platform up to 6 ports are supported, enabled by
1505 setting corresponding bits in the mask to 1. The
1506 default value is 0x0, which has a special meaning.
1507 On systems that have PCI, it triggers scanning the
1508 PCI bus for the first and the second port, which
1509 are then probed. On systems without PCI the value
1510 of 0x0 enables probing the two first ports as if it
1513 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1514 Claim all unknown PCI IDE storage controllers.
1517 Format: idle=poll, idle=halt, idle=nomwait
1518 Poll forces a polling idle loop that can slightly
1519 improve the performance of waking up a idle CPU, but
1520 will use a lot of power and make the system run hot.
1522 idle=halt: Halt is forced to be used for CPU idle.
1523 In such case C2/C3 won't be used again.
1524 idle=nomwait: Disable mwait for CPU C-states
1526 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1527 Format: { strict | legacy | 2008 | relaxed }
1530 Choose which programs will be accepted for execution
1531 based on the IEEE 754 NaN encoding(s) supported by
1532 the FPU and the NaN encoding requested with the value
1533 of an ELF file header flag individually set by each
1534 binary. Hardware implementations are permitted to
1535 support either or both of the legacy and the 2008 NaN
1538 Available settings are as follows:
1539 strict accept binaries that request a NaN encoding
1540 supported by the FPU
1541 legacy only accept legacy-NaN binaries, if supported
1543 2008 only accept 2008-NaN binaries, if supported
1545 relaxed accept any binaries regardless of whether
1546 supported by the FPU
1548 The FPU emulator is always able to support both NaN
1549 encodings, so if no FPU hardware is present or it has
1550 been disabled with 'nofpu', then the settings of
1551 'legacy' and '2008' strap the emulator accordingly,
1552 'relaxed' straps the emulator for both legacy-NaN and
1553 2008-NaN, whereas 'strict' enables legacy-NaN only on
1554 legacy processors and both NaN encodings on MIPS32 or
1557 The setting for ABS.fmt/NEG.fmt instruction execution
1558 mode generally follows that for the NaN encoding,
1559 except where unsupported by hardware.
1561 ignore_loglevel [KNL]
1562 Ignore loglevel setting - this will print /all/
1563 kernel messages to the console. Useful for debugging.
1564 We also add it as printk module parameter, so users
1565 could change it dynamically, usually by
1566 /sys/module/printk/parameters/ignore_loglevel.
1569 Ignore RLIMIT_DATA setting for data mappings,
1570 print warning at first misuse. Can be changed via
1571 /sys/module/kernel/parameters/ignore_rlimit_data.
1573 ihash_entries= [KNL]
1574 Set number of hash buckets for inode cache.
1576 ima_appraise= [IMA] appraise integrity measurements
1577 Format: { "off" | "enforce" | "fix" | "log" }
1580 ima_appraise_tcb [IMA]
1581 The builtin appraise policy appraises all files
1585 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1589 The list of supported hash algorithms is defined
1590 in crypto/hash_info.h.
1593 The builtin measurement policy to load during IMA
1594 setup. Specyfing "tcb" as the value, measures all
1595 programs exec'd, files mmap'd for exec, and all files
1596 opened with the read mode bit set by either the
1597 effective uid (euid=0) or uid=0.
1600 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1601 Load a policy which meets the needs of the Trusted
1602 Computing Base. This means IMA will measure all
1603 programs exec'd, files mmap'd for exec, and all files
1604 opened for read by uid=0.
1607 Select one of defined IMA measurements template formats.
1608 Formats: { "ima" | "ima-ng" | "ima-sig" }
1612 [IMA] Define a custom template format.
1613 Format: { "field1|...|fieldN" }
1615 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1616 Format: <min_file_size>
1617 Set the minimal file size for using asynchronous hash.
1618 If left unspecified, ahash usage is disabled.
1620 ahash performance varies for different data sizes on
1621 different crypto accelerators. This option can be used
1622 to achieve the best performance for a particular HW.
1624 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1626 Set hashing buffer size. Default: 4k.
1628 ahash performance varies for different chunk sizes on
1629 different crypto accelerators. This option can be used
1630 to achieve best performance for particular HW.
1634 Run specified binary instead of /sbin/init as init
1637 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1638 for working out where the kernel is dying during
1641 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1642 initcall functions. Useful for debugging built-in
1643 modules and initcalls.
1645 initrd= [BOOT] Specify the location of the initial ramdisk
1647 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1650 int_pln_enable [x86] Enable power limit notification interrupt
1652 integrity_audit=[IMA]
1653 Format: { "0" | "1" }
1654 0 -- basic integrity auditing messages. (Default)
1655 1 -- additional integrity auditing messages.
1657 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1659 Enable intel iommu driver.
1661 Disable intel iommu driver.
1662 igfx_off [Default Off]
1663 By default, gfx is mapped as normal device. If a gfx
1664 device has a dedicated DMAR unit, the DMAR unit is
1665 bypassed by not enabling DMAR with this option. In
1666 this case, gfx device will use physical address for
1669 With this option iommu will not optimize to look
1670 for io virtual address below 32-bit forcing dual
1671 address cycle on pci bus for cards supporting greater
1672 than 32-bit addressing. The default is to look
1673 for translation below 32-bit and if not available
1674 then look in the higher range.
1675 strict [Default Off]
1676 With this option on every unmap_single operation will
1677 result in a hardware IOTLB flush operation as opposed
1678 to batching them for performance.
1679 sp_off [Default Off]
1680 By default, super page will be supported if Intel IOMMU
1681 has the capability. With this option, super page will
1683 ecs_off [Default Off]
1684 By default, extended context tables will be supported if
1685 the hardware advertises that it has support both for the
1686 extended tables themselves, and also PASID support. With
1687 this option set, extended tables will not be used even
1688 on hardware which claims to support them.
1690 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1691 0 disables intel_idle and fall back on acpi_idle.
1692 1 to 6 specify maximum depth of C-state.
1696 Do not enable intel_pstate as the default
1697 scaling driver for the supported processors
1699 Enable intel_pstate on systems that prohibit it by default
1700 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1701 instead of acpi-cpufreq may disable platform features, such
1702 as thermal controls and power capping, that rely on ACPI
1703 P-States information being indicated to OSPM and therefore
1704 should be used with caution. This option does not work with
1705 processors that aren't supported by the intel_pstate driver
1706 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1708 Do not enable hardware P state control (HWP)
1711 Only load intel_pstate on systems which support
1712 hardware P state control (HWP) if available.
1714 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1715 Description Table, specifies preferred power management
1716 profile as "Enterprise Server" or "Performance Server",
1717 then this feature is turned on by default.
1719 intremap= [X86-64, Intel-IOMMU]
1720 on enable Interrupt Remapping (default)
1721 off disable Interrupt Remapping
1722 nosid disable Source ID checking
1724 BIOS x2APIC opt-out request will be ignored
1725 nopost disable Interrupt Posting
1727 iomem= Disable strict checking of access to MMIO memory
1728 strict regions from userspace.
1743 nobypass [PPC/POWERNV]
1744 Disable IOMMU bypass, using IOMMU for PCI devices.
1747 io7= [HW] IO7 for Marvel based alpha systems
1748 See comment before marvel_specify_io7 in
1749 arch/alpha/kernel/core_marvel.c.
1751 io_delay= [X86] I/O delay method
1753 Standard port 0x80 based delay
1755 Alternate port 0xed based delay (needed on some systems)
1757 Simple two microseconds delay
1762 See Documentation/filesystems/nfs/nfsroot.txt.
1764 irqaffinity= [SMP] Set the default irq affinity mask
1766 <cpu number>,...,<cpu number>
1768 <cpu number>-<cpu number>
1769 (must be a positive range in ascending order)
1771 <cpu number>,...,<cpu number>-<cpu number>
1774 When an interrupt is not handled search all handlers
1775 for it. Intended to get systems with badly broken
1779 When an interrupt is not handled search all handlers
1780 for it. Also check all handlers each timer
1781 interrupt. Intended to get systems with badly broken
1785 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1787 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1789 <cpu number>,...,<cpu number>
1791 <cpu number>-<cpu number>
1792 (must be a positive range in ascending order)
1794 <cpu number>,...,<cpu number>-<cpu number>
1796 This option can be used to specify one or more CPUs
1797 to isolate from the general SMP balancing and scheduling
1798 algorithms. You can move a process onto or off an
1799 "isolated" CPU via the CPU affinity syscalls or cpuset.
1800 <cpu number> begins at 0 and the maximum value is
1801 "number of CPUs in system - 1".
1803 This option is the preferred way to isolate CPUs. The
1804 alternative -- manually setting the CPU mask of all
1805 tasks in the system -- can cause problems and
1806 suboptimal load balancer performance.
1810 ivrs_ioapic [HW,X86_64]
1811 Provide an override to the IOAPIC-ID<->DEVICE-ID
1812 mapping provided in the IVRS ACPI table. For
1813 example, to map IOAPIC-ID decimal 10 to
1814 PCI device 00:14.0 write the parameter as:
1815 ivrs_ioapic[10]=00:14.0
1817 ivrs_hpet [HW,X86_64]
1818 Provide an override to the HPET-ID<->DEVICE-ID
1819 mapping provided in the IVRS ACPI table. For
1820 example, to map HPET-ID decimal 0 to
1821 PCI device 00:14.0 write the parameter as:
1822 ivrs_hpet[0]=00:14.0
1824 ivrs_acpihid [HW,X86_64]
1825 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1826 mapping provided in the IVRS ACPI table. For
1827 example, to map UART-HID:UID AMD0020:0 to
1828 PCI device 00:14.5 write the parameter as:
1829 ivrs_acpihid[00:14.5]=AMD0020:0
1831 js= [HW,JOY] Analog joystick
1832 See Documentation/input/joystick.txt.
1835 When CONFIG_RANDOMIZE_BASE is set, this disables
1836 kernel and module base offset ASLR (Address Space
1837 Layout Randomization).
1841 kernelcore= [KNL,X86,IA-64,PPC]
1842 Format: nn[KMGTPE] | "mirror"
1844 specifies the amount of memory usable by the kernel
1845 for non-movable allocations. The requested amount is
1846 spread evenly throughout all nodes in the system. The
1847 remaining memory in each node is used for Movable
1848 pages. In the event, a node is too small to have both
1849 kernelcore and Movable pages, kernelcore pages will
1850 take priority and other nodes will have a larger number
1851 of Movable pages. The Movable zone is used for the
1852 allocation of pages that may be reclaimed or moved
1853 by the page migration subsystem. This means that
1854 HugeTLB pages may not be allocated from this zone.
1855 Note that allocations like PTEs-from-HighMem still
1856 use the HighMem zone if it exists, and the Normal
1857 zone if it does not.
1859 Instead of specifying the amount of memory (nn[KMGTPE]),
1860 you can specify "mirror" option. In case "mirror"
1861 option is specified, mirrored (reliable) memory is used
1862 for non-movable allocations and remaining memory is used
1863 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1864 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1867 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1868 Format: <Controller#>[,poll interval]
1869 The controller # is the number of the ehci usb debug
1870 port as it is probed via PCI. The poll interval is
1871 optional and is the number seconds in between
1872 each poll cycle to the debug port in case you need
1873 the functionality for interrupting the kernel with
1874 gdb or control-c on the dbgp connection. When
1875 not using this parameter you use sysrq-g to break into
1876 the kernel debugger.
1878 kgdboc= [KGDB,HW] kgdb over consoles.
1879 Requires a tty driver that supports console polling,
1880 or a supported polling keyboard driver (non-usb).
1881 Serial only format: <serial_device>[,baud]
1882 keyboard only format: kbd
1883 keyboard and serial format: kbd,<serial_device>[,baud]
1884 Optional Kernel mode setting:
1885 kms, kbd format: kms,kbd
1886 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1888 kgdbwait [KGDB] Stop kernel execution and enter the
1889 kernel debugger at the earliest opportunity.
1891 kmac= [MIPS] korina ethernet MAC address.
1892 Configure the RouterBoard 532 series on-chip
1893 Ethernet adapter MAC address.
1895 kmemleak= [KNL] Boot-time kmemleak enable/disable
1896 Valid arguments: on, off
1898 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1901 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1902 Valid arguments: 0, 1, 2
1903 kmemcheck=0 (disabled)
1904 kmemcheck=1 (enabled)
1905 kmemcheck=2 (one-shot mode)
1906 Default: 2 (one-shot mode)
1908 kstack=N [X86] Print N words from the kernel stack
1911 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1912 Default is 0 (don't ignore, but inject #GP)
1914 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1918 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1919 Default is 1 (enabled)
1921 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1923 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1925 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1926 (virtualized MMU) support on capable Intel chips.
1927 Default is 1 (enabled)
1929 kvm-intel.emulate_invalid_guest_state=
1930 [KVM,Intel] Enable emulation of invalid guest states
1931 Default is 0 (disabled)
1933 kvm-intel.flexpriority=
1934 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1935 Default is 1 (enabled)
1938 [KVM,Intel] Enable VMX nesting (nVMX).
1939 Default is 0 (disabled)
1941 kvm-intel.unrestricted_guest=
1942 [KVM,Intel] Disable unrestricted guest feature
1943 (virtualized real and unpaged mode) on capable
1944 Intel chips. Default is 1 (enabled)
1946 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1947 feature (tagged TLBs) on capable Intel chips.
1948 Default is 1 (enabled)
1954 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1957 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1958 value for LAPIC timer one-shot implementation. Default
1959 back to the programmable timer unit in the LAPIC.
1961 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1964 libata.dma= [LIBATA] DMA control
1965 libata.dma=0 Disable all PATA and SATA DMA
1966 libata.dma=1 PATA and SATA Disk DMA only
1967 libata.dma=2 ATAPI (CDROM) DMA only
1968 libata.dma=4 Compact Flash DMA only
1969 Combinations also work, so libata.dma=3 enables DMA
1970 for disks and CDROMs, but not CFs.
1972 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1973 libata.ignore_hpa=0 keep BIOS limits (default)
1974 libata.ignore_hpa=1 ignore limits, using full disk
1976 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1980 libata.force= [LIBATA] Force configurations. The format is comma
1981 separated list of "[ID:]VAL" where ID is
1982 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1983 matching port, link or device. Basically, it matches
1984 the ATA ID string printed on console by libata. If
1985 the whole ID part is omitted, the last PORT and DEVICE
1986 values are used. If ID hasn't been specified yet, the
1987 configuration applies to all ports, links and devices.
1989 If only DEVICE is omitted, the parameter applies to
1990 the port and all links and devices behind it. DEVICE
1991 number of 0 either selects the first device or the
1992 first fan-out link behind PMP device. It does not
1993 select the host link. DEVICE number of 15 selects the
1994 host link and device attached to it.
1996 The VAL specifies the configuration to force. As long
1997 as there's no ambiguity shortcut notation is allowed.
1998 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1999 The following configurations can be forced.
2001 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2002 Any ID with matching PORT is used.
2004 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2006 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2007 udma[/][16,25,33,44,66,100,133] notation is also
2010 * [no]ncq: Turn on or off NCQ.
2012 * [no]ncqtrim: Turn off queued DSM TRIM.
2014 * nohrst, nosrst, norst: suppress hard, soft
2017 * rstonce: only attempt one reset during
2018 hot-unplug link recovery
2020 * dump_id: dump IDENTIFY data.
2022 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2024 * disable: Disable this device.
2026 If there are multiple matching configurations changing
2027 the same attribute, the last one is used.
2029 memblock=debug [KNL] Enable memblock debug messages.
2031 load_ramdisk= [RAM] List of ramdisks to load from floppy
2032 See Documentation/blockdev/ramdisk.txt.
2034 lockd.nlm_grace_period=P [NFS] Assign grace period.
2037 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2040 lockd.nlm_timeout=T [NFS] Assign timeout value.
2043 lockd.nlm_udpport=M [NFS] Assign UDP port.
2046 locktorture.nreaders_stress= [KNL]
2047 Set the number of locking read-acquisition kthreads.
2048 Defaults to being automatically set based on the
2049 number of online CPUs.
2051 locktorture.nwriters_stress= [KNL]
2052 Set the number of locking write-acquisition kthreads.
2054 locktorture.onoff_holdoff= [KNL]
2055 Set time (s) after boot for CPU-hotplug testing.
2057 locktorture.onoff_interval= [KNL]
2058 Set time (s) between CPU-hotplug operations, or
2059 zero to disable CPU-hotplug testing.
2061 locktorture.shuffle_interval= [KNL]
2062 Set task-shuffle interval (jiffies). Shuffling
2063 tasks allows some CPUs to go into dyntick-idle
2064 mode during the locktorture test.
2066 locktorture.shutdown_secs= [KNL]
2067 Set time (s) after boot system shutdown. This
2068 is useful for hands-off automated testing.
2070 locktorture.stat_interval= [KNL]
2071 Time (s) between statistics printk()s.
2073 locktorture.stutter= [KNL]
2074 Time (s) to stutter testing, for example,
2075 specifying five seconds causes the test to run for
2076 five seconds, wait for five seconds, and so on.
2077 This tests the locking primitive's ability to
2078 transition abruptly to and from idle.
2080 locktorture.torture_runnable= [BOOT]
2081 Start locktorture running at boot time.
2083 locktorture.torture_type= [KNL]
2084 Specify the locking implementation to test.
2086 locktorture.verbose= [KNL]
2087 Enable additional printk() statements.
2089 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2092 loglevel= All Kernel Messages with a loglevel smaller than the
2093 console loglevel will be printed to the console. It can
2094 also be changed with klogd or other programs. The
2095 loglevels are defined as follows:
2097 0 (KERN_EMERG) system is unusable
2098 1 (KERN_ALERT) action must be taken immediately
2099 2 (KERN_CRIT) critical conditions
2100 3 (KERN_ERR) error conditions
2101 4 (KERN_WARNING) warning conditions
2102 5 (KERN_NOTICE) normal but significant condition
2103 6 (KERN_INFO) informational
2104 7 (KERN_DEBUG) debug-level messages
2106 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2107 in bytes. n must be a power of two and greater
2108 than the minimal size. The minimal size is defined
2109 by LOG_BUF_SHIFT kernel config parameter. There is
2110 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2111 that allows to increase the default size depending on
2112 the number of CPUs. See init/Kconfig for more details.
2114 logo.nologo [FB] Disables display of the built-in Linux logo.
2115 This may be used to provide more screen space for
2116 kernel log messages and is useful when debugging
2117 kernel boot problems.
2119 lp=0 [LP] Specify parallel ports to use, e.g,
2120 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2121 lp=reset first parallel port). 'lp=0' disables the
2122 lp=auto printer driver. 'lp=reset' (which can be
2123 specified in addition to the ports) causes
2124 attached printers to be reset. Using
2125 lp=port1,port2,... specifies the parallel ports
2126 to associate lp devices with, starting with
2127 lp0. A port specification may be 'none' to skip
2128 that lp device, or a parport name such as
2129 'parport0'. Specifying 'lp=auto' instead of a
2130 port specification list means that device IDs
2131 from each port should be examined, to see if
2132 an IEEE 1284-compliant printer is attached; if
2133 so, the driver will manage that printer.
2134 See also header of drivers/char/lp.c.
2137 Sets loops_per_jiffy to given constant, thus avoiding
2138 time-consuming boot-time autodetection (up to 250 ms per
2139 CPU). 0 enables autodetection (default). To determine
2140 the correct value for your kernel, boot with normal
2141 autodetection and see what value is printed. Note that
2142 on SMP systems the preset will be applied to all CPUs,
2143 which is likely to cause problems if your CPUs need
2144 significantly divergent settings. An incorrect value
2145 will cause delays in the kernel to be wrong, leading to
2146 unpredictable I/O errors and other breakage. Although
2147 unlikely, in the extreme case this might damage your
2151 Format: <io>,<irq>,<dma>
2153 machvec= [IA-64] Force the use of a particular machine-vector
2154 (machvec) in a generic kernel.
2155 Example: machvec=hpzx1_swiotlb
2157 machtype= [Loongson] Share the same kernel image file between different
2159 Example: machtype=lemote-yeeloong-2f-7inch
2161 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2162 than or equal to this physical address is ignored.
2164 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2165 should make use of. maxcpus=n : n >= 0 limits the
2166 kernel to using 'n' processors. n=0 is a special case,
2167 it is equivalent to "nosmp", which also disables
2170 max_loop= [LOOP] The number of loop block devices that get
2171 (loop.max_loop) unconditionally pre-created at init time. The default
2172 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2173 of statically allocating a predefined number, loop
2174 devices can be requested on-demand with the
2175 /dev/loop-control interface.
2177 mce [X86-32] Machine Check Exception
2179 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2181 md= [HW] RAID subsystems devices and level
2182 See Documentation/md.txt.
2185 Format: <first>,<last>
2186 Specifies range of consoles to be captured by the MDA.
2188 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2189 Amount of memory to be used when the kernel is not able
2190 to see the whole system memory or for test.
2191 [X86] Work as limiting max address. Use together
2192 with memmap= to avoid physical address space collisions.
2193 Without memmap= PCI devices could be placed at addresses
2194 belonging to unused RAM.
2196 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2200 [KNL,SH] Allow user to override the default size for
2201 per-device physically contiguous DMA buffers.
2203 memhp_default_state=online/offline
2204 [KNL] Set the initial state for the memory hotplug
2205 onlining policy. If not specified, the default value is
2206 set according to the
2207 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2209 See Documentation/memory-hotplug.txt.
2211 memmap=exactmap [KNL,X86] Enable setting of an exact
2212 E820 memory map, as specified by the user.
2213 Such memmap=exactmap lines can be constructed based on
2214 BIOS output or other requirements. See the memmap=nn@ss
2217 memmap=nn[KMG]@ss[KMG]
2218 [KNL] Force usage of a specific region of memory.
2219 Region of memory to be used is from ss to ss+nn.
2221 memmap=nn[KMG]#ss[KMG]
2222 [KNL,ACPI] Mark specific memory as ACPI data.
2223 Region of memory to be marked is from ss to ss+nn.
2225 memmap=nn[KMG]$ss[KMG]
2226 [KNL,ACPI] Mark specific memory as reserved.
2227 Region of memory to be reserved is from ss to ss+nn.
2228 Example: Exclude memory from 0x18690000-0x1869ffff
2229 memmap=64K$0x18690000
2231 memmap=0x10000$0x18690000
2233 memmap=nn[KMG]!ss[KMG]
2234 [KNL,X86] Mark specific memory as protected.
2235 Region of memory to be used, from ss to ss+nn.
2236 The memory region may be marked as e820 type 12 (0xc)
2237 and is NVDIMM or ADR memory.
2239 memory_corruption_check=0/1 [X86]
2240 Some BIOSes seem to corrupt the first 64k of
2241 memory when doing things like suspend/resume.
2242 Setting this option will scan the memory
2243 looking for corruption. Enabling this will
2244 both detect corruption and prevent the kernel
2245 from using the memory being corrupted.
2246 However, its intended as a diagnostic tool; if
2247 repeatable BIOS-originated corruption always
2248 affects the same memory, you can use memmap=
2249 to prevent the kernel from using that memory.
2251 memory_corruption_check_size=size [X86]
2252 By default it checks for corruption in the low
2253 64k, making this memory unavailable for normal
2254 use. Use this parameter to scan for
2255 corruption in more or less memory.
2257 memory_corruption_check_period=seconds [X86]
2258 By default it checks for corruption every 60
2259 seconds. Use this parameter to check at some
2260 other rate. 0 disables periodic checking.
2262 memtest= [KNL,X86,ARM] Enable memtest
2264 default : 0 <disable>
2265 Specifies the number of memtest passes to be
2266 performed. Each pass selects another test
2267 pattern from a given set of patterns. Memtest
2268 fills the memory with this pattern, validates
2269 memory contents and reserves bad memory
2270 regions that are detected.
2272 meye.*= [HW] Set MotionEye Camera parameters
2273 See Documentation/video4linux/meye.txt.
2275 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2276 Multi-Function General Purpose Timers on AMD Geode
2279 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2280 the BIOS has incorrectly applied a workaround. TinyBIOS
2281 version 0.98 is known to be affected, 0.99 fixes the
2282 problem by letting the user disable the workaround.
2286 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2287 physical address is ignored.
2289 mini2440= [ARM,HW,KNL]
2290 Format:[0..2][b][c][t]
2292 MINI2440 configuration specification:
2293 0 - The attached screen is the 3.5" TFT
2294 1 - The attached screen is the 7" TFT
2295 2 - The VGA Shield is attached (1024x768)
2296 Leaving out the screen size parameter will not load
2297 the TFT driver, and the framebuffer will be left
2299 b - Enable backlight. The TFT backlight pin will be
2300 linked to the kernel VESA blanking code and a GPIO
2301 LED. This parameter is not necessary when using the
2303 c - Enable the s3c camera interface.
2304 t - Reserved for enabling touchscreen support. The
2305 touchscreen support is not enabled in the mainstream
2306 kernel as of 2.6.30, a preliminary port can be found
2307 in the "bleeding edge" mini2440 support kernel at
2308 http://repo.or.cz/w/linux-2.6/mini2440.git
2311 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2312 parameter allows control of the logging verbosity for
2313 the additional memory initialisation checks. A value
2314 of 0 disables mminit logging and a level of 4 will
2315 log everything. Information is printed at KERN_DEBUG
2316 so loglevel=8 may also need to be specified.
2319 [KNL] When CONFIG_MODULE_SIG is set, this means that
2320 modules without (valid) signatures will fail to load.
2321 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2322 is always true, so this option does nothing.
2324 module_blacklist= [KNL] Do not load a comma-separated list of
2325 modules. Useful for debugging problem modules.
2328 [MOUSE] Maximum time between finger touching and
2329 leaving touchpad surface for touch to be considered
2330 a tap and be reported as a left button click (for
2331 touchpads working in absolute mode only).
2333 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2334 reporting absolute coordinates, such as tablets
2335 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2336 reporting absolute coordinates, such as tablets
2338 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2339 is similar to kernelcore except it specifies the
2340 amount of memory used for migratable allocations.
2341 If both kernelcore and movablecore is specified,
2342 then kernelcore will be at *least* the specified
2343 value but may be more. If movablecore on its own
2344 is specified, the administrator must be careful
2345 that the amount of memory usable for all allocations
2348 movable_node [KNL,X86] Boot-time switch to enable the effects
2349 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2351 MTD_Partition= [MTD]
2352 Format: <name>,<region-number>,<size>,<offset>
2354 MTD_Region= [MTD] Format:
2355 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2358 See drivers/mtd/cmdlinepart.c.
2360 multitce=off [PPC] This parameter disables the use of the pSeries
2361 firmware feature for updating multiple TCE entries
2364 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2366 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2368 boundary - index of last SLC block on Flex-OneNAND.
2369 The remaining blocks are configured as MLC blocks.
2370 lock - Configure if Flex-OneNAND boundary should be locked.
2371 Once locked, the boundary cannot be changed.
2372 1 indicates lock status, 0 indicates unlock status.
2375 ARM/S3C2412 JIVE boot control
2377 See arch/arm/mach-s3c2412/mach-jive.c
2379 mtouchusb.raw_coordinates=
2380 [HW] Make the MicroTouch USB driver use raw coordinates
2381 ('y', default) or cooked coordinates ('n')
2383 mtrr_chunk_size=nn[KMG] [X86]
2384 used for mtrr cleanup. It is largest continuous chunk
2385 that could hold holes aka. UC entries.
2387 mtrr_gran_size=nn[KMG] [X86]
2388 Used for mtrr cleanup. It is granularity of mtrr block.
2390 Large value could prevent small alignment from
2393 mtrr_spare_reg_nr=n [X86]
2395 Range: 0,7 : spare reg number
2397 Used for mtrr cleanup. It is spare mtrr entries number.
2398 Set to 2 or more if your graphical card needs more.
2400 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2402 netdev= [NET] Network devices parameters
2403 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2404 Note that mem_start is often overloaded to mean
2405 something different and driver-specific.
2406 This usage is only documented in each driver source
2410 [NETFILTER] Enable connection tracking flow accounting
2411 0 to disable accounting
2412 1 to enable accounting
2415 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2416 See Documentation/filesystems/nfs/nfsroot.txt.
2418 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2419 See Documentation/filesystems/nfs/nfsroot.txt.
2421 nfsrootdebug [NFS] enable nfsroot debugging messages.
2422 See Documentation/filesystems/nfs/nfsroot.txt.
2424 nfs.callback_tcpport=
2425 [NFS] set the TCP port on which the NFSv4 callback
2426 channel should listen.
2429 [NFS] sets the pathname to the program which is used
2430 to update the NFS client cache entries.
2432 nfs.cache_getent_timeout=
2433 [NFS] sets the timeout after which an attempt to
2434 update a cache entry is deemed to have failed.
2436 nfs.idmap_cache_timeout=
2437 [NFS] set the maximum lifetime for idmapper cache
2441 [NFS] enable 64-bit inode numbers.
2442 If zero, the NFS client will fake up a 32-bit inode
2443 number for the readdir() and stat() syscalls instead
2444 of returning the full 64-bit number.
2445 The default is to return 64-bit inode numbers.
2447 nfs.max_session_slots=
2448 [NFSv4.1] Sets the maximum number of session slots
2449 the client will attempt to negotiate with the server.
2450 This limits the number of simultaneous RPC requests
2451 that the client can send to the NFSv4.1 server.
2452 Note that there is little point in setting this
2453 value higher than the max_tcp_slot_table_limit.
2455 nfs.nfs4_disable_idmapping=
2456 [NFSv4] When set to the default of '1', this option
2457 ensures that both the RPC level authentication
2458 scheme and the NFS level operations agree to use
2459 numeric uids/gids if the mount is using the
2460 'sec=sys' security flavour. In effect it is
2461 disabling idmapping, which can make migration from
2462 legacy NFSv2/v3 systems to NFSv4 easier.
2463 Servers that do not support this mode of operation
2464 will be autodetected by the client, and it will fall
2465 back to using the idmapper.
2466 To turn off this behaviour, set the value to '0'.
2468 [NFS4] Specify an additional fixed unique ident-
2469 ification string that NFSv4 clients can insert into
2470 their nfs_client_id4 string. This is typically a
2471 UUID that is generated at system install time.
2473 nfs.send_implementation_id =
2474 [NFSv4.1] Send client implementation identification
2475 information in exchange_id requests.
2476 If zero, no implementation identification information
2478 The default is to send the implementation identification
2481 nfs.recover_lost_locks =
2482 [NFSv4] Attempt to recover locks that were lost due
2483 to a lease timeout on the server. Please note that
2484 doing this risks data corruption, since there are
2485 no guarantees that the file will remain unchanged
2486 after the locks are lost.
2487 If you want to enable the kernel legacy behaviour of
2488 attempting to recover these locks, then set this
2490 The default parameter value of '0' causes the kernel
2491 not to attempt recovery of lost locks.
2493 nfs4.layoutstats_timer =
2494 [NFSv4.2] Change the rate at which the kernel sends
2495 layoutstats to the pNFS metadata server.
2497 Setting this to value to 0 causes the kernel to use
2498 whatever value is the default set by the layout
2499 driver. A non-zero value sets the minimum interval
2500 in seconds between layoutstats transmissions.
2502 nfsd.nfs4_disable_idmapping=
2503 [NFSv4] When set to the default of '1', the NFSv4
2504 server will return only numeric uids and gids to
2505 clients using auth_sys, and will accept numeric uids
2506 and gids from such clients. This is intended to ease
2507 migration from NFSv2/v3.
2509 objlayoutdriver.osd_login_prog=
2510 [NFS] [OBJLAYOUT] sets the pathname to the program which
2511 is used to automatically discover and login into new
2512 osd-targets. Please see:
2513 Documentation/filesystems/pnfs.txt for more explanations
2515 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2516 when a NMI is triggered.
2517 Format: [state][,regs][,debounce][,die]
2519 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2520 Format: [panic,][nopanic,][num]
2522 0 - turn hardlockup detector in nmi_watchdog off
2523 1 - turn hardlockup detector in nmi_watchdog on
2524 When panic is specified, panic when an NMI watchdog
2525 timeout occurs (or 'nopanic' to override the opposite
2526 default). To disable both hard and soft lockup detectors,
2527 please see 'nowatchdog'.
2528 This is useful when you use a panic=... timeout and
2529 need the box quickly up again.
2531 netpoll.carrier_timeout=
2532 [NET] Specifies amount of time (in seconds) that
2533 netpoll should wait for a carrier. By default netpoll
2536 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2537 emulation library even if a 387 maths coprocessor
2541 [HW] Never suspend the console
2542 Disable suspending of consoles during suspend and
2543 hibernate operations. Once disabled, debugging
2544 messages can reach various consoles while the rest
2545 of the system is being put to sleep (ie, while
2546 debugging driver suspend/resume hooks). This may
2547 not work reliably with all consoles, but is known
2548 to work with serial and VGA consoles.
2549 To facilitate more flexible debugging, we also add
2550 console_suspend, a printk module parameter to control
2551 it. Users could use console_suspend (usually
2552 /sys/module/printk/parameters/console_suspend) to
2553 turn on/off it dynamically.
2555 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2556 caches in the slab allocator. Saves per-node memory,
2557 but will impact performance.
2561 noapic [SMP,APIC] Tells the kernel to not make use of any
2562 IOAPICs that may be present in the system.
2564 noautogroup Disable scheduler automatic task group creation.
2566 nobats [PPC] Do not use BATs for mapping kernel lowmem
2567 on "Classic" PPC cores.
2571 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2573 nodelayacct [KNL] Disable per-task delay accounting
2575 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2577 nodsp [SH] Disable hardware DSP at boot time.
2579 noefi Disable EFI runtime services support.
2584 On X86-32 available only on PAE configured kernels.
2585 noexec=on: enable non-executable mappings (default)
2586 noexec=off: disable non-executable mappings
2589 Disable SMAP (Supervisor Mode Access Prevention)
2590 even if it is supported by processor.
2593 Disable SMEP (Supervisor Mode Execution Prevention)
2594 even if it is supported by processor.
2597 This affects only 32-bit executables.
2598 noexec32=on: enable non-executable mappings (default)
2599 read doesn't imply executable mappings
2600 noexec32=off: disable non-executable mappings
2601 read implies executable mappings
2603 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2605 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2606 register save and restore. The kernel will only save
2607 legacy floating-point registers on task switch.
2609 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2611 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2612 Equivalent to smt=1.
2614 noxsave [BUGS=X86] Disables x86 extended register state save
2615 and restore using xsave. The kernel will fallback to
2616 enabling legacy floating-point and sse state.
2618 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2619 register states. The kernel will fall back to use
2620 xsave to save the states. By using this parameter,
2621 performance of saving the states is degraded because
2622 xsave doesn't support modified optimization while
2623 xsaveopt supports it on xsaveopt enabled systems.
2625 noxsaves [X86] Disables xsaves and xrstors used in saving and
2626 restoring x86 extended register state in compacted
2627 form of xsave area. The kernel will fall back to use
2628 xsaveopt and xrstor to save and restore the states
2629 in standard form of xsave area. By using this
2630 parameter, xsave area per process might occupy more
2631 memory on xsaves enabled systems.
2633 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2634 wfi(ARM) instruction doesn't work correctly and not to
2635 use it. This is also useful when using JTAG debugger.
2637 no_file_caps Tells the kernel not to honor file capabilities. The
2638 only way then for a file to be executed with privilege
2639 is to be setuid root or executed by root.
2641 nohalt [IA-64] Tells the kernel not to use the power saving
2642 function PAL_HALT_LIGHT when idle. This increases
2643 power-consumption. On the positive side, it reduces
2644 interrupt wake-up latency, which may improve performance
2645 in certain environments such as networked servers or
2648 nohibernate [HIBERNATION] Disable hibernation and resume.
2650 nohz= [KNL] Boottime enable/disable dynamic ticks
2651 Valid arguments: on, off
2654 nohz_full= [KNL,BOOT]
2655 In kernels built with CONFIG_NO_HZ_FULL=y, set
2656 the specified list of CPUs whose tick will be stopped
2657 whenever possible. The boot CPU will be forced outside
2658 the range to maintain the timekeeping.
2659 The CPUs in this range must also be included in the
2662 noiotrap [SH] Disables trapped I/O port accesses.
2664 noirqdebug [X86-32] Disables the code which attempts to detect and
2665 disable unhandled interrupt sources.
2667 no_timer_check [X86,APIC] Disables the code which tests for
2668 broken timer IRQ sources.
2670 noisapnp [ISAPNP] Disables ISA PnP code.
2672 noinitrd [RAM] Tells the kernel not to load any configured
2675 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2677 [Deprecated - use intremap=off]
2681 noinvpcid [X86] Disable the INVPCID cpu feature.
2683 nojitter [IA-64] Disables jitter checking for ITC timers.
2685 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2687 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2690 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2691 steal time is computed, but won't influence scheduler
2694 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2696 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2698 noltlbs [PPC] Do not use large page/tlb entries for kernel
2699 lowmem mapping on PPC40x and PPC8xx
2701 nomca [IA-64] Disable machine check abort handling
2703 nomce [X86-32] Disable Machine Check Exception
2705 nomfgpt [X86-32] Disable Multi-Function General Purpose
2706 Timer usage (for AMD Geode machines).
2708 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2709 shutdown the other cpus. Instead use the REBOOT_VECTOR
2712 nomodule Disable module load
2714 nopat [X86] Disable PAT (page attribute table extension of
2715 pagetables) support.
2717 norandmaps Don't use address space randomization. Equivalent to
2718 echo 0 > /proc/sys/kernel/randomize_va_space
2720 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2722 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2723 with UP alternatives
2725 nordrand [X86] Disable kernel use of the RDRAND and
2726 RDSEED instructions even if they are supported
2727 by the processor. RDRAND and RDSEED are still
2728 available to user space applications.
2730 noresume [SWSUSP] Disables resume and restores original swap
2733 no-scroll [VGA] Disables scrollback.
2734 This is required for the Braillex ib80-piezo Braille
2735 reader made by F.H. Papenmeier (Germany).
2739 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2741 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2742 and disable the IO APIC. legacy for "maxcpus=0".
2744 nosoftlockup [KNL] Disable the soft-lockup detector.
2746 nosync [HW,M68K] Disables sync negotiation for all devices.
2748 notsc [BUGS=X86-32] Disable Time Stamp Counter
2750 nowatchdog [KNL] Disable both lockup detectors, i.e.
2751 soft-lockup and NMI watchdog (hard-lockup).
2755 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2757 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2758 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2759 Some features depend on CPU0. Known dependencies are:
2760 1. Resume from suspend/hibernate depends on CPU0.
2761 Suspend/hibernate will fail if CPU0 is offline and you
2762 need to online CPU0 before suspend/hibernate.
2763 2. PIC interrupts also depend on CPU0. CPU0 can't be
2764 removed if a PIC interrupt is detected.
2765 It's said poweroff/reboot may depend on CPU0 on some
2766 machines although I haven't seen such issues so far
2767 after CPU0 is offline on a few tested machines.
2768 If the dependencies are under your control, you can
2769 turn on cpu0_hotplug.
2771 nptcg= [IA-64] Override max number of concurrent global TLB
2772 purges which is reported from either PAL_VM_SUMMARY or
2775 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2776 could support. nr_cpus=n : n >= 1 limits the kernel to
2777 supporting 'n' processors. Later in runtime you can not
2778 use hotplug cpu feature to put more cpu back to online.
2779 just like you compile the kernel NR_CPUS=n
2781 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2783 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2784 Allowed values are enable and disable
2786 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2787 one of ['zone', 'node', 'default'] can be specified
2788 This can be set from sysctl after boot.
2789 See Documentation/sysctl/vm.txt for details.
2791 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2792 See Documentation/debugging-via-ohci1394.txt for more
2795 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2796 Rather than timing out after 20 ms if an EC
2797 command is not properly ACKed, override the length
2798 of the timeout. We have interrupts disabled while
2799 waiting for the ACK, so if this is set too high
2800 interrupts *may* be lost!
2802 omap_mux= [OMAP] Override bootloader pin multiplexing.
2803 Format: <mux_mode0.mode_name=value>...
2804 For example, to override I2C bus2:
2805 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2807 oprofile.timer= [HW]
2808 Use timer interrupt instead of performance counters
2810 oprofile.cpu_type= Force an oprofile cpu type
2811 This might be useful if you have an older oprofile
2812 userland or if you want common events.
2813 Format: { arch_perfmon }
2814 arch_perfmon: [X86] Force use of architectural
2815 perfmon on Intel CPUs instead of the
2816 CPU specific event set.
2817 timer: [X86] Force use of architectural NMI
2818 timer mode (see also oprofile.timer
2819 for generic hr timer mode)
2821 oops=panic Always panic on oopses. Default is to just kill the
2822 process, but there is a small probability of
2823 deadlocking the machine.
2824 This will also cause panics on machine check exceptions.
2825 Useful together with panic=30 to trigger a reboot.
2828 See Documentation/sound/oss/oss-parameters.txt
2830 page_owner= [KNL] Boot-time page_owner enabling option.
2831 Storage of the information about who allocated
2832 each page is disabled in default. With this switch,
2834 on: enable the feature
2836 page_poison= [KNL] Boot-time parameter changing the state of
2837 poisoning on the buddy allocator.
2838 off: turn off poisoning
2839 on: turn on poisoning
2841 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2842 timeout > 0: seconds before rebooting
2843 timeout = 0: wait forever
2844 timeout < 0: reboot immediately
2847 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2850 crash_kexec_post_notifiers
2851 Run kdump after running panic-notifiers and dumping
2852 kmsg. This only for the users who doubt kdump always
2853 succeeds in any situation.
2854 Note that this also increases risks of kdump failure,
2855 because some panic notifiers can make the crashed
2856 kernel more unstable.
2858 parkbd.port= [HW] Parallel port number the keyboard adapter is
2859 connected to, default is 0.
2861 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2862 0 for XT, 1 for AT (default is AT).
2865 parport= [HW,PPT] Specify parallel ports. 0 disables.
2866 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2867 Use 'auto' to force the driver to use any
2868 IRQ/DMA settings detected (the default is to
2869 ignore detected IRQ/DMA settings because of
2870 possible conflicts). You can specify the base
2871 address, IRQ, and DMA settings; IRQ and DMA
2872 should be numbers, or 'auto' (for using detected
2873 settings on that particular port), or 'nofifo'
2874 (to avoid using a FIFO even if it is detected).
2875 Parallel ports are assigned in the order they
2876 are specified on the command line, starting
2879 parport_init_mode= [HW,PPT]
2880 Configure VIA parallel port to operate in
2881 a specific mode. This is necessary on Pegasos
2882 computer where firmware has no options for setting
2883 up parallel port mode and sets it to spp.
2884 Currently this function knows 686a and 8231 chips.
2885 Format: [spp|ps2|epp|ecp|ecpepp]
2888 Halt all CPUs after the first oops has been printed for
2889 the specified number of seconds. This is to be used if
2890 your oopses keep scrolling off the screen.
2895 See header of drivers/block/paride/pcd.c.
2896 See also Documentation/blockdev/paride.txt.
2898 pci=option[,option...] [PCI] various PCI subsystem options:
2899 earlydump [X86] dump PCI config space before the kernel
2901 off [X86] don't probe for the PCI bus
2902 bios [X86-32] force use of PCI BIOS, don't access
2903 the hardware directly. Use this if your machine
2904 has a non-standard PCI host bridge.
2905 nobios [X86-32] disallow use of PCI BIOS, only direct
2906 hardware access methods are allowed. Use this
2907 if you experience crashes upon bootup and you
2908 suspect they are caused by the BIOS.
2909 conf1 [X86] Force use of PCI Configuration Access
2910 Mechanism 1 (config address in IO port 0xCF8,
2911 data in IO port 0xCFC, both 32-bit).
2912 conf2 [X86] Force use of PCI Configuration Access
2913 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2914 the function, IO port 0xCFA, also 8-bit, sets
2915 bus number. The config space is then accessed
2916 through ports 0xC000-0xCFFF).
2917 See http://wiki.osdev.org/PCI for more info
2918 on the configuration access mechanisms.
2919 noaer [PCIE] If the PCIEAER kernel config parameter is
2920 enabled, this kernel boot option can be used to
2921 disable the use of PCIE advanced error reporting.
2922 nodomains [PCI] Disable support for multiple PCI
2923 root domains (aka PCI segments, in ACPI-speak).
2924 nommconf [X86] Disable use of MMCONFIG for PCI
2926 check_enable_amd_mmconf [X86] check for and enable
2927 properly configured MMIO access to PCI
2928 config space on AMD family 10h CPU
2929 nomsi [MSI] If the PCI_MSI kernel config parameter is
2930 enabled, this kernel boot option can be used to
2931 disable the use of MSI interrupts system-wide.
2932 noioapicquirk [APIC] Disable all boot interrupt quirks.
2933 Safety option to keep boot IRQs enabled. This
2934 should never be necessary.
2935 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2936 primary IO-APIC for bridges that cannot disable
2937 boot IRQs. This fixes a source of spurious IRQs
2938 when the system masks IRQs.
2939 noioapicreroute [APIC] Disable workaround that uses the
2940 boot IRQ equivalent of an IRQ that connects to
2941 a chipset where boot IRQs cannot be disabled.
2942 The opposite of ioapicreroute.
2943 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2944 routing table. These calls are known to be buggy
2945 on several machines and they hang the machine
2946 when used, but on other computers it's the only
2947 way to get the interrupt routing table. Try
2948 this option if the kernel is unable to allocate
2949 IRQs or discover secondary PCI buses on your
2951 rom [X86] Assign address space to expansion ROMs.
2952 Use with caution as certain devices share
2953 address decoders between ROMs and other
2955 norom [X86] Do not assign address space to
2956 expansion ROMs that do not already have
2957 BIOS assigned address ranges.
2958 nobar [X86] Do not assign address space to the
2959 BARs that weren't assigned by the BIOS.
2960 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2961 assigned automatically to PCI devices. You can
2962 make the kernel exclude IRQs of your ISA cards
2964 pirqaddr=0xAAAAA [X86] Specify the physical address
2965 of the PIRQ table (normally generated
2966 by the BIOS) if it is outside the
2967 F0000h-100000h range.
2968 lastbus=N [X86] Scan all buses thru bus #N. Can be
2969 useful if the kernel is unable to find your
2970 secondary buses and you want to tell it
2971 explicitly which ones they are.
2972 assign-busses [X86] Always assign all PCI bus
2973 numbers ourselves, overriding
2974 whatever the firmware may have done.
2975 usepirqmask [X86] Honor the possible IRQ mask stored
2976 in the BIOS $PIR table. This is needed on
2977 some systems with broken BIOSes, notably
2978 some HP Pavilion N5400 and Omnibook XE3
2979 notebooks. This will have no effect if ACPI
2980 IRQ routing is enabled.
2981 noacpi [X86] Do not use ACPI for IRQ routing
2982 or for PCI scanning.
2983 use_crs [X86] Use PCI host bridge window information
2984 from ACPI. On BIOSes from 2008 or later, this
2985 is enabled by default. If you need to use this,
2986 please report a bug.
2987 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2988 If you need to use this, please report a bug.
2989 routeirq Do IRQ routing for all PCI devices.
2990 This is normally done in pci_enable_device(),
2991 so this option is a temporary workaround
2992 for broken drivers that don't call it.
2993 skip_isa_align [X86] do not align io start addr, so can
2994 handle more pci cards
2995 noearly [X86] Don't do any early type 1 scanning.
2996 This might help on some broken boards which
2997 machine check when some devices' config space
2998 is read. But various workarounds are disabled
2999 and some IOMMU drivers will not work.
3000 bfsort Sort PCI devices into breadth-first order.
3001 This sorting is done to get a device
3002 order compatible with older (<= 2.4) kernels.
3003 nobfsort Don't sort PCI devices into breadth-first order.
3004 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3005 tuning and use the BIOS-configured MPS defaults.
3006 pcie_bus_safe Set every device's MPS to the largest value
3007 supported by all devices below the root complex.
3008 pcie_bus_perf Set device MPS to the largest allowable MPS
3009 based on its parent bus. Also set MRRS (Max
3010 Read Request Size) to the largest supported
3011 value (no larger than the MPS that the device
3012 or bus can support) for best performance.
3013 pcie_bus_peer2peer Set every device's MPS to 128B, which
3014 every device is guaranteed to support. This
3015 configuration allows peer-to-peer DMA between
3016 any pair of devices, possibly at the cost of
3017 reduced performance. This also guarantees
3018 that hot-added devices will work.
3019 cbiosize=nn[KMG] The fixed amount of bus space which is
3020 reserved for the CardBus bridge's IO window.
3021 The default value is 256 bytes.
3022 cbmemsize=nn[KMG] The fixed amount of bus space which is
3023 reserved for the CardBus bridge's memory
3024 window. The default value is 64 megabytes.
3027 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3028 [<order of align>@]pci:<vendor>:<device>\
3029 [:<subvendor>:<subdevice>][; ...]
3030 Specifies alignment and device to reassign
3031 aligned memory resources.
3032 If <order of align> is not specified,
3033 PAGE_SIZE is used as alignment.
3034 PCI-PCI bridge can be specified, if resource
3035 windows need to be expanded.
3036 To specify the alignment for several
3037 instances of a device, the PCI vendor,
3038 device, subvendor, and subdevice may be
3039 specified, e.g., 4096@pci:8086:9c22:103c:198f
3040 ecrc= Enable/disable PCIe ECRC (transaction layer
3041 end-to-end CRC checking).
3042 bios: Use BIOS/firmware settings. This is the
3046 hpiosize=nn[KMG] The fixed amount of bus space which is
3047 reserved for hotplug bridge's IO window.
3048 Default size is 256 bytes.
3049 hpmemsize=nn[KMG] The fixed amount of bus space which is
3050 reserved for hotplug bridge's memory window.
3051 Default size is 2 megabytes.
3052 hpbussize=nn The minimum amount of additional bus numbers
3053 reserved for buses below a hotplug bridge.
3055 realloc= Enable/disable reallocating PCI bridge resources
3056 if allocations done by BIOS are too small to
3057 accommodate resources required by all child
3059 off: Turn realloc off
3061 realloc same as realloc=on
3062 noari do not use PCIe ARI.
3063 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3064 only look for one device below a PCIe downstream
3067 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3070 force Enable ASPM even on devices that claim not to support it.
3071 WARNING: Forcing ASPM on may cause system lockups.
3073 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3074 nomsi Do not use MSI for PCI Express Native Hotplug (this
3075 makes all PCIe ports use INTx for hotplug services).
3077 pcie_ports= [PCIE] PCIe ports handling:
3078 auto Ask the BIOS whether or not to use native PCIe services
3079 associated with PCIe ports (PME, hot-plug, AER). Use
3080 them only if that is allowed by the BIOS.
3081 native Use native PCIe services associated with PCIe ports
3083 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3086 pcie_port_pm= [PCIE] PCIe port power management handling:
3087 off Disable power management of all PCIe ports
3088 force Forcibly enable power management of all PCIe ports
3090 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3091 nomsi Do not use MSI for native PCIe PME signaling (this makes
3092 all PCIe root ports use INTx for all services).
3094 pcmv= [HW,PCMCIA] BadgePAD 4
3098 Keep all power-domains already enabled by bootloader on,
3099 even if no driver has claimed them. This is useful
3100 for debug and development, but should not be
3101 needed on a platform with proper driver support.
3104 See Documentation/blockdev/paride.txt.
3106 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3109 See arch/parisc/kernel/pdc_chassis.c
3111 percpu_alloc= Select which percpu first chunk allocator to use.
3112 Currently supported values are "embed" and "page".
3113 Archs may support subset or none of the selections.
3114 See comments in mm/percpu.c for details on each
3115 allocator. This parameter is primarily for debugging
3116 and performance comparison.
3119 See Documentation/blockdev/paride.txt.
3122 See Documentation/blockdev/paride.txt.
3124 pirq= [SMP,APIC] Manual mp-table setup
3125 See Documentation/x86/i386/IO-APIC.txt.
3127 plip= [PPT,NET] Parallel port network link
3128 Format: { parport<nr> | timid | 0 }
3129 See also Documentation/parport.txt.
3131 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3132 Override pmtimer IOPort with a hex value.
3136 Enable PNP debug messages (depends on the
3137 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3138 via /sys/module/pnp/parameters/debug. We always show
3139 current resource usage; turning this on also shows
3140 possible settings and some assignment information.
3146 { on | off | curr | res | no-curr | no-res }
3149 [ISAPNP] Exclude IRQs for the autoconfiguration
3152 [ISAPNP] Exclude DMAs for the autoconfiguration
3154 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3155 Ranges are in pairs (I/O port base and size).
3158 [ISAPNP] Exclude memory regions for the
3160 Ranges are in pairs (memory base and size).
3162 ports= [IP_VS_FTP] IPVS ftp helper module
3164 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3166 Format: <port>,<port>....
3168 ppc_strict_facility_enable
3169 [PPC] This option catches any kernel floating point,
3170 Altivec, VSX and SPE outside of regions specifically
3171 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3172 There is some performance impact when enabling this.
3174 print-fatal-signals=
3175 [KNL] debug: print fatal signals
3177 If enabled, warn about various signal handling
3178 related application anomalies: too many signals,
3179 too many POSIX.1 timers, fatal signals causing a
3182 If you hit the warning due to signal overflow,
3183 you might want to try "ulimit -i unlimited".
3187 printk.always_kmsg_dump=
3188 Trigger kmsg_dump for cases other than kernel oops or
3190 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3193 printk.devkmsg={on,off,ratelimit}
3194 Control writing to /dev/kmsg.
3195 on - unlimited logging to /dev/kmsg from userspace
3196 off - logging to /dev/kmsg disabled
3197 ratelimit - ratelimit the logging
3200 printk.time= Show timing data prefixed to each printk message line
3201 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3203 processor.max_cstate= [HW,ACPI]
3204 Limit processor to maximum C-state
3205 max_cstate=9 overrides any DMI blacklist limit.
3207 processor.nocst [HW,ACPI]
3208 Ignore the _CST method to determine C-states,
3209 instead using the legacy FADT method
3211 profile= [KNL] Enable kernel profiling via /proc/profile
3212 Format: [schedule,]<number>
3213 Param: "schedule" - profile schedule points.
3214 Param: <number> - step/bucket size as a power of 2 for
3215 statistical time based profiling.
3216 Param: "sleep" - profile D-state sleeping (millisecs).
3217 Requires CONFIG_SCHEDSTATS
3218 Param: "kvm" - profile VM exits.
3220 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3222 See Documentation/blockdev/ramdisk.txt.
3224 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3225 probe for; one of (bare|imps|exps|lifebook|any).
3226 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3228 psmouse.resetafter= [HW,MOUSE]
3229 Try to reset the device after so many bad packets
3232 [HW,MOUSE] Set desired mouse resolution, in dpi.
3233 psmouse.smartscroll=
3234 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3235 0 = disabled, 1 = enabled (default).
3237 pstore.backend= Specify the name of the pstore backend to use
3240 See Documentation/blockdev/paride.txt.
3243 [KNL] Number of legacy pty's. Overwrites compiled-in
3246 quiet [KNL] Disable most log messages
3251 See Documentation/md.txt.
3253 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3254 See Documentation/blockdev/ramdisk.txt.
3257 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3258 the specified list of CPUs to be no-callback CPUs.
3259 Invocation of these CPUs' RCU callbacks will
3260 be offloaded to "rcuox/N" kthreads created for
3261 that purpose, where "x" is "b" for RCU-bh, "p"
3262 for RCU-preempt, and "s" for RCU-sched, and "N"
3263 is the CPU number. This reduces OS jitter on the
3264 offloaded CPUs, which can be useful for HPC and
3265 real-time workloads. It can also improve energy
3266 efficiency for asymmetric multiprocessors.
3269 Rather than requiring that offloaded CPUs
3270 (specified by rcu_nocbs= above) explicitly
3271 awaken the corresponding "rcuoN" kthreads,
3272 make these kthreads poll for callbacks.
3273 This improves the real-time response for the
3274 offloaded CPUs by relieving them of the need to
3275 wake up the corresponding kthread, but degrades
3276 energy efficiency by requiring that the kthreads
3277 periodically wake up to do the polling.
3279 rcutree.blimit= [KNL]
3280 Set maximum number of finished RCU callbacks to
3281 process in one batch.
3283 rcutree.dump_tree= [KNL]
3284 Dump the structure of the rcu_node combining tree
3285 out at early boot. This is used for diagnostic
3286 purposes, to verify correct tree setup.
3288 rcutree.gp_cleanup_delay= [KNL]
3289 Set the number of jiffies to delay each step of
3290 RCU grace-period cleanup. This only has effect
3291 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3293 rcutree.gp_init_delay= [KNL]
3294 Set the number of jiffies to delay each step of
3295 RCU grace-period initialization. This only has
3296 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3299 rcutree.gp_preinit_delay= [KNL]
3300 Set the number of jiffies to delay each step of
3301 RCU grace-period pre-initialization, that is,
3302 the propagation of recent CPU-hotplug changes up
3303 the rcu_node combining tree. This only has effect
3304 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3306 rcutree.rcu_fanout_exact= [KNL]
3307 Disable autobalancing of the rcu_node combining
3308 tree. This is used by rcutorture, and might
3309 possibly be useful for architectures having high
3310 cache-to-cache transfer latencies.
3312 rcutree.rcu_fanout_leaf= [KNL]
3313 Change the number of CPUs assigned to each
3314 leaf rcu_node structure. Useful for very
3315 large systems, which will choose the value 64,
3316 and for NUMA systems with large remote-access
3317 latencies, which will choose a value aligned
3318 with the appropriate hardware boundaries.
3320 rcutree.jiffies_till_sched_qs= [KNL]
3321 Set required age in jiffies for a
3322 given grace period before RCU starts
3323 soliciting quiescent-state help from
3324 rcu_note_context_switch().
3326 rcutree.jiffies_till_first_fqs= [KNL]
3327 Set delay from grace-period initialization to
3328 first attempt to force quiescent states.
3329 Units are jiffies, minimum value is zero,
3330 and maximum value is HZ.
3332 rcutree.jiffies_till_next_fqs= [KNL]
3333 Set delay between subsequent attempts to force
3334 quiescent states. Units are jiffies, minimum
3335 value is one, and maximum value is HZ.
3337 rcutree.kthread_prio= [KNL,BOOT]
3338 Set the SCHED_FIFO priority of the RCU per-CPU
3339 kthreads (rcuc/N). This value is also used for
3340 the priority of the RCU boost threads (rcub/N)
3341 and for the RCU grace-period kthreads (rcu_bh,
3342 rcu_preempt, and rcu_sched). If RCU_BOOST is
3343 set, valid values are 1-99 and the default is 1
3344 (the least-favored priority). Otherwise, when
3345 RCU_BOOST is not set, valid values are 0-99 and
3346 the default is zero (non-realtime operation).
3348 rcutree.rcu_nocb_leader_stride= [KNL]
3349 Set the number of NOCB kthread groups, which
3350 defaults to the square root of the number of
3351 CPUs. Larger numbers reduces the wakeup overhead
3352 on the per-CPU grace-period kthreads, but increases
3353 that same overhead on each group's leader.
3355 rcutree.qhimark= [KNL]
3356 Set threshold of queued RCU callbacks beyond which
3357 batch limiting is disabled.
3359 rcutree.qlowmark= [KNL]
3360 Set threshold of queued RCU callbacks below which
3361 batch limiting is re-enabled.
3363 rcutree.rcu_idle_gp_delay= [KNL]
3364 Set wakeup interval for idle CPUs that have
3365 RCU callbacks (RCU_FAST_NO_HZ=y).
3367 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3368 Set wakeup interval for idle CPUs that have
3369 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3370 Lazy RCU callbacks are those which RCU can
3371 prove do nothing more than free memory.
3373 rcuperf.gp_exp= [KNL]
3374 Measure performance of expedited synchronous
3375 grace-period primitives.
3377 rcuperf.holdoff= [KNL]
3378 Set test-start holdoff period. The purpose of
3379 this parameter is to delay the start of the
3380 test until boot completes in order to avoid
3383 rcuperf.nreaders= [KNL]
3384 Set number of RCU readers. The value -1 selects
3385 N, where N is the number of CPUs. A value
3386 "n" less than -1 selects N-n+1, where N is again
3387 the number of CPUs. For example, -2 selects N
3388 (the number of CPUs), -3 selects N+1, and so on.
3389 A value of "n" less than or equal to -N selects
3392 rcuperf.nwriters= [KNL]
3393 Set number of RCU writers. The values operate
3394 the same as for rcuperf.nreaders.
3395 N, where N is the number of CPUs
3397 rcuperf.perf_runnable= [BOOT]
3398 Start rcuperf running at boot time.
3400 rcuperf.shutdown= [KNL]
3401 Shut the system down after performance tests
3402 complete. This is useful for hands-off automated
3405 rcuperf.perf_type= [KNL]
3406 Specify the RCU implementation to test.
3408 rcuperf.verbose= [KNL]
3409 Enable additional printk() statements.
3411 rcutorture.cbflood_inter_holdoff= [KNL]
3412 Set holdoff time (jiffies) between successive
3413 callback-flood tests.
3415 rcutorture.cbflood_intra_holdoff= [KNL]
3416 Set holdoff time (jiffies) between successive
3417 bursts of callbacks within a given callback-flood
3420 rcutorture.cbflood_n_burst= [KNL]
3421 Set the number of bursts making up a given
3422 callback-flood test. Set this to zero to
3423 disable callback-flood testing.
3425 rcutorture.cbflood_n_per_burst= [KNL]
3426 Set the number of callbacks to be registered
3427 in a given burst of a callback-flood test.
3429 rcutorture.fqs_duration= [KNL]
3430 Set duration of force_quiescent_state bursts
3433 rcutorture.fqs_holdoff= [KNL]
3434 Set holdoff time within force_quiescent_state bursts
3437 rcutorture.fqs_stutter= [KNL]
3438 Set wait time between force_quiescent_state bursts
3441 rcutorture.gp_cond= [KNL]
3442 Use conditional/asynchronous update-side
3443 primitives, if available.
3445 rcutorture.gp_exp= [KNL]
3446 Use expedited update-side primitives, if available.
3448 rcutorture.gp_normal= [KNL]
3449 Use normal (non-expedited) asynchronous
3450 update-side primitives, if available.
3452 rcutorture.gp_sync= [KNL]
3453 Use normal (non-expedited) synchronous
3454 update-side primitives, if available. If all
3455 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3456 rcutorture.gp_normal=, and rcutorture.gp_sync=
3457 are zero, rcutorture acts as if is interpreted
3458 they are all non-zero.
3460 rcutorture.n_barrier_cbs= [KNL]
3461 Set callbacks/threads for rcu_barrier() testing.
3463 rcutorture.nfakewriters= [KNL]
3464 Set number of concurrent RCU writers. These just
3465 stress RCU, they don't participate in the actual
3466 test, hence the "fake".
3468 rcutorture.nreaders= [KNL]
3469 Set number of RCU readers. The value -1 selects
3470 N-1, where N is the number of CPUs. A value
3471 "n" less than -1 selects N-n-2, where N is again
3472 the number of CPUs. For example, -2 selects N
3473 (the number of CPUs), -3 selects N+1, and so on.
3475 rcutorture.object_debug= [KNL]
3476 Enable debug-object double-call_rcu() testing.
3478 rcutorture.onoff_holdoff= [KNL]
3479 Set time (s) after boot for CPU-hotplug testing.
3481 rcutorture.onoff_interval= [KNL]
3482 Set time (s) between CPU-hotplug operations, or
3483 zero to disable CPU-hotplug testing.
3485 rcutorture.shuffle_interval= [KNL]
3486 Set task-shuffle interval (s). Shuffling tasks
3487 allows some CPUs to go into dyntick-idle mode
3488 during the rcutorture test.
3490 rcutorture.shutdown_secs= [KNL]
3491 Set time (s) after boot system shutdown. This
3492 is useful for hands-off automated testing.
3494 rcutorture.stall_cpu= [KNL]
3495 Duration of CPU stall (s) to test RCU CPU stall
3496 warnings, zero to disable.
3498 rcutorture.stall_cpu_holdoff= [KNL]
3499 Time to wait (s) after boot before inducing stall.
3501 rcutorture.stat_interval= [KNL]
3502 Time (s) between statistics printk()s.
3504 rcutorture.stutter= [KNL]
3505 Time (s) to stutter testing, for example, specifying
3506 five seconds causes the test to run for five seconds,
3507 wait for five seconds, and so on. This tests RCU's
3508 ability to transition abruptly to and from idle.
3510 rcutorture.test_boost= [KNL]
3511 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3512 "Maybe" means test if the RCU implementation
3513 under test support RCU priority boosting.
3515 rcutorture.test_boost_duration= [KNL]
3516 Duration (s) of each individual boost test.
3518 rcutorture.test_boost_interval= [KNL]
3519 Interval (s) between each boost test.
3521 rcutorture.test_no_idle_hz= [KNL]
3522 Test RCU's dyntick-idle handling. See also the
3523 rcutorture.shuffle_interval parameter.
3525 rcutorture.torture_runnable= [BOOT]
3526 Start rcutorture running at boot time.
3528 rcutorture.torture_type= [KNL]
3529 Specify the RCU implementation to test.
3531 rcutorture.verbose= [KNL]
3532 Enable additional printk() statements.
3534 rcupdate.rcu_cpu_stall_suppress= [KNL]
3535 Suppress RCU CPU stall warning messages.
3537 rcupdate.rcu_cpu_stall_timeout= [KNL]
3538 Set timeout for RCU CPU stall warning messages.
3540 rcupdate.rcu_expedited= [KNL]
3541 Use expedited grace-period primitives, for
3542 example, synchronize_rcu_expedited() instead
3543 of synchronize_rcu(). This reduces latency,
3544 but can increase CPU utilization, degrade
3545 real-time latency, and degrade energy efficiency.
3546 No effect on CONFIG_TINY_RCU kernels.
3548 rcupdate.rcu_normal= [KNL]
3549 Use only normal grace-period primitives,
3550 for example, synchronize_rcu() instead of
3551 synchronize_rcu_expedited(). This improves
3552 real-time latency, CPU utilization, and
3553 energy efficiency, but can expose users to
3554 increased grace-period latency. This parameter
3555 overrides rcupdate.rcu_expedited. No effect on
3556 CONFIG_TINY_RCU kernels.
3558 rcupdate.rcu_normal_after_boot= [KNL]
3559 Once boot has completed (that is, after
3560 rcu_end_inkernel_boot() has been invoked), use
3561 only normal grace-period primitives. No effect
3562 on CONFIG_TINY_RCU kernels.
3564 rcupdate.rcu_task_stall_timeout= [KNL]
3565 Set timeout in jiffies for RCU task stall warning
3566 messages. Disable with a value less than or equal
3569 rcupdate.rcu_self_test= [KNL]
3570 Run the RCU early boot self tests
3572 rcupdate.rcu_self_test_bh= [KNL]
3573 Run the RCU bh early boot self tests
3575 rcupdate.rcu_self_test_sched= [KNL]
3576 Run the RCU sched early boot self tests
3580 Run specified binary instead of /init from the ramdisk,
3581 used for early userspace startup. See initrd.
3584 Format (x86 or x86_64):
3585 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3587 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3589 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3590 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3591 reboot_force is either force or not specified,
3592 reboot_cpu is s[mp]#### with #### being the processor
3593 to be used for rebooting.
3596 [KNL, SMP] Set scheduler's default relax_domain_level.
3597 See Documentation/cgroup-v1/cpusets.txt.
3599 relative_sleep_states=
3600 [SUSPEND] Use sleep state labeling where the deepest
3601 state available other than hibernation is always "mem".
3602 Format: { "0" | "1" }
3603 0 -- Traditional sleep state labels.
3604 1 -- Relative sleep state labels.
3606 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3608 reservetop= [X86-32]
3610 Reserves a hole at the top of the kernel virtual
3615 Set the amount of memory to reserve for BIOS at
3616 the bottom of the address space.
3618 reset_devices [KNL] Force drivers to reset the underlying device
3619 during initialization.
3622 Specify the partition device for software suspend
3624 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3626 resume_offset= [SWSUSP]
3627 Specify the offset from the beginning of the partition
3628 given by "resume=" at which the swap header is located,
3629 in <PAGE_SIZE> units (needed only for swap files).
3630 See Documentation/power/swsusp-and-swap-files.txt
3632 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3633 read the resume files
3635 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3636 Useful for devices that are detected asynchronously
3637 (e.g. USB and MMC devices).
3639 hibernate= [HIBERNATION]
3640 noresume Don't check if there's a hibernation image
3641 present during boot.
3642 nocompress Don't compress/decompress hibernation images.
3643 no Disable hibernation and resume.
3644 protect_image Turn on image protection during restoration
3645 (that will set all pages holding image data
3646 during restoration read-only).
3648 retain_initrd [RAM] Keep initrd memory after extraction
3650 rfkill.default_state=
3651 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3652 etc. communication is blocked by default.
3655 rfkill.master_switch_mode=
3656 0 The "airplane mode" button does nothing.
3657 1 The "airplane mode" button toggles between everything
3658 blocked and the previous configuration.
3659 2 The "airplane mode" button toggles between everything
3660 blocked and everything unblocked.
3662 rhash_entries= [KNL,NET]
3663 Set number of hash buckets for route cache
3665 ro [KNL] Mount root device read-only on boot
3668 on Mark read-only kernel memory as read-only (default).
3669 off Leave read-only kernel memory writable for debugging.
3672 Enable the uart passthrough on the designated usb port
3673 on Rockchip SoCs. When active, the signals of the
3674 debug-uart get routed to the D+ and D- pins of the usb
3675 port and the regular usb controller gets disabled.
3677 root= [KNL] Root filesystem
3678 See name_to_dev_t comment in init/do_mounts.c.
3680 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3681 mount the root filesystem
3683 rootflags= [KNL] Set root filesystem mount option string
3685 rootfstype= [KNL] Set root filesystem type
3687 rootwait [KNL] Wait (indefinitely) for root device to show up.
3688 Useful for devices that are detected asynchronously
3689 (e.g. USB and MMC devices).
3691 rproc_mem=nn[KMG][@address]
3692 [KNL,ARM,CMA] Remoteproc physical memory block.
3693 Memory area to be used by remote processor image,
3696 rw [KNL] Mount root device read-write on boot
3698 S [KNL] Run init in single mode
3700 s390_iommu= [HW,S390]
3701 Set s390 IOTLB flushing mode
3703 With strict flushing every unmap operation will result in
3704 an IOTLB flush. Default is lazy flushing before reuse,
3708 See drivers/net/irda/sa1100_ir.c.
3710 sbni= [NET] Granch SBNI12 leased line adapter
3712 sched_debug [KNL] Enables verbose scheduler debug messages.
3714 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3715 Allowed values are enable and disable. This feature
3716 incurs a small amount of overhead in the scheduler
3717 but is useful for debugging and performance tuning.
3719 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3720 xtime_lock contention on larger systems, and/or RCU lock
3721 contention on all systems with CONFIG_MAXSMP set.
3722 Format: { "0" | "1" }
3723 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3725 Note: increases power consumption, thus should only be
3726 enabled if running jitter sensitive (HPC/RT) workloads.
3728 security= [SECURITY] Choose a security module to enable at boot.
3729 If this boot parameter is not specified, only the first
3730 security module asking for security registration will be
3731 loaded. An invalid security module name will be treated
3732 as if no module has been chosen.
3734 selinux= [SELINUX] Disable or enable SELinux at boot time.
3735 Format: { "0" | "1" }
3736 See security/selinux/Kconfig help text.
3739 Default value is set via kernel config option.
3740 If enabled at boot time, /selinux/disable can be used
3741 later to disable prior to initial policy load.
3743 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3744 Format: { "0" | "1" }
3745 See security/apparmor/Kconfig help text
3748 Default value is set via kernel config option.
3750 serialnumber [BUGS=X86-32]
3753 Maximal number of shapers.
3755 show_msr= [x86] show boot-time MSR settings
3756 Format: { <integer> }
3757 Show boot-time (BIOS-initialized) MSR settings.
3758 The parameter means the number of CPUs to show,
3759 for example 1 means boot CPU only.
3767 Disable merging of slabs with similar size. May be
3768 necessary if there is some reason to distinguish
3769 allocs to different slabs. Debug options disable
3770 merging on their own.
3771 For more information see Documentation/vm/slub.txt.
3773 slab_max_order= [MM, SLAB]
3774 Determines the maximum allowed order for slabs.
3775 A high setting may cause OOMs due to memory
3776 fragmentation. Defaults to 1 for systems with
3777 more than 32MB of RAM, 0 otherwise.
3779 slub_debug[=options[,slabs]] [MM, SLUB]
3780 Enabling slub_debug allows one to determine the
3781 culprit if slab objects become corrupted. Enabling
3782 slub_debug can create guard zones around objects and
3783 may poison objects when not in use. Also tracks the
3784 last alloc / free. For more information see
3785 Documentation/vm/slub.txt.
3787 slub_max_order= [MM, SLUB]
3788 Determines the maximum allowed order for slabs.
3789 A high setting may cause OOMs due to memory
3790 fragmentation. For more information see
3791 Documentation/vm/slub.txt.
3793 slub_min_objects= [MM, SLUB]
3794 The minimum number of objects per slab. SLUB will
3795 increase the slab order up to slub_max_order to
3796 generate a sufficiently large slab able to contain
3797 the number of objects indicated. The higher the number
3798 of objects the smaller the overhead of tracking slabs
3799 and the less frequently locks need to be acquired.
3800 For more information see Documentation/vm/slub.txt.
3802 slub_min_order= [MM, SLUB]
3803 Determines the minimum page order for slabs. Must be
3804 lower than slub_max_order.
3805 For more information see Documentation/vm/slub.txt.
3807 slub_nomerge [MM, SLUB]
3808 Same with slab_nomerge. This is supported for legacy.
3809 See slab_nomerge for more information.
3812 Format: <io1>[,<io2>[,...,<io8>]]
3814 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3815 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3816 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3817 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3818 smsc-ircc2.ircc_irq= [HW] IRQ line
3819 smsc-ircc2.ircc_dma= [HW] DMA channel
3820 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3821 0: Toshiba Satellite 1800 (GP data pin select)
3822 1: Fast pin select (default)
3825 smt [KNL,S390] Set the maximum number of threads (logical
3826 CPUs) to use per physical CPU on systems capable of
3827 symmetric multithreading (SMT). Will be capped to the
3828 actual hardware limit.
3830 Default: -1 (no limit)
3833 [KNL] Should the soft-lockup detector generate panics.
3836 softlockup_all_cpu_backtrace=
3837 [KNL] Should the soft-lockup detector generate
3838 backtraces on all cpus.
3841 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3842 See Documentation/laptops/sonypi.txt
3844 spia_io_base= [HW,MTD]
3850 Enabled the stack tracer on boot up.
3852 stacktrace_filter=[function-list]
3853 [FTRACE] Limit the functions that the stack tracer
3854 will trace at boot up. function-list is a comma separated
3855 list of functions. This list can be changed at run
3856 time by the stack_trace_filter file in the debugfs
3857 tracing directory. Note, this enables stack tracing
3858 and the stacktrace above is not needed.
3862 Set the STI (builtin display/keyboard on the HP-PARISC
3863 machines) console (graphic card) which should be used
3864 as the initial boot-console.
3865 See also comment in drivers/video/console/sticore.c.
3868 See comment in drivers/video/console/sticore.c.
3871 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3873 sunrpc.min_resvport=
3874 sunrpc.max_resvport=
3876 SunRPC servers often require that client requests
3877 originate from a privileged port (i.e. a port in the
3878 range 0 < portnr < 1024).
3879 An administrator who wishes to reserve some of these
3880 ports for other uses may adjust the range that the
3881 kernel's sunrpc client considers to be privileged
3882 using these two parameters to set the minimum and
3883 maximum port values.
3885 sunrpc.svc_rpc_per_connection_limit=
3887 Limit the number of requests that the server will
3888 process in parallel from a single connection.
3889 The default value is 0 (no limit).
3893 Control how the NFS server code allocates CPUs to
3894 service thread pools. Depending on how many NICs
3895 you have and where their interrupts are bound, this
3896 option will affect which CPUs will do NFS serving.
3897 Note: this parameter cannot be changed while the
3898 NFS server is running.
3900 auto the server chooses an appropriate mode
3901 automatically using heuristics
3902 global a single global pool contains all CPUs
3903 percpu one pool for each CPU
3904 pernode one pool for each NUMA node (equivalent
3905 to global on non-NUMA machines)
3907 sunrpc.tcp_slot_table_entries=
3908 sunrpc.udp_slot_table_entries=
3910 Sets the upper limit on the number of simultaneous
3911 RPC calls that can be sent from the client to a
3912 server. Increasing these values may allow you to
3913 improve throughput, but will also increase the
3914 amount of memory reserved for use by the client.
3916 suspend.pm_test_delay=
3918 Sets the number of seconds to remain in a suspend test
3919 mode before resuming the system (see
3920 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3921 is set. Default value is 5.
3924 [KNL] Enable accounting of swap in memory resource
3925 controller if no parameter or 1 is given or disable
3926 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
3928 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3929 Format: { <int> | force }
3930 <int> -- Number of I/O TLB slabs
3931 force -- force using of bounce buffers even if they
3932 wouldn't be automatically used by the kernel
3936 sysfs.deprecated=0|1 [KNL]
3937 Enable/disable old style sysfs layout for old udev
3938 on older distributions. When this option is enabled
3939 very new udev will not work anymore. When this option
3940 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3941 in older udev will not work anymore.
3942 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3943 the kernel configuration.
3945 sysrq_always_enabled
3947 Ignore sysrq setting - this boot parameter will
3948 neutralize any effect of /proc/sys/kernel/sysrq.
3949 Useful for debugging.
3951 tcpmhash_entries= [KNL,NET]
3952 Set the number of tcp_metrics_hash slots.
3953 Default value is 8192 or 16384 depending on total
3954 ram pages. This is used to specify the TCP metrics
3955 cache size. See Documentation/networking/ip-sysctl.txt
3956 "tcp_no_metrics_save" section for more details.
3960 test_suspend= [SUSPEND][,N]
3961 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3962 standby suspend) or "freeze" (for suspend type freeze)
3963 as the system sleep state during system startup with
3964 the optional capability to repeat N number of times.
3965 The system is woken from this state using a
3966 wakeup-capable RTC alarm.
3968 thash_entries= [KNL,NET]
3969 Set number of hash buckets for TCP connection
3971 thermal.act= [HW,ACPI]
3972 -1: disable all active trip points in all thermal zones
3973 <degrees C>: override all lowest active trip points
3975 thermal.crt= [HW,ACPI]
3976 -1: disable all critical trip points in all thermal zones
3977 <degrees C>: override all critical trip points
3979 thermal.nocrt= [HW,ACPI]
3980 Set to disable actions on ACPI thermal zone
3981 critical and hot trip points.
3983 thermal.off= [HW,ACPI]
3984 1: disable ACPI thermal control
3986 thermal.psv= [HW,ACPI]
3987 -1: disable all passive trip points
3988 <degrees C>: override all passive trip points to this
3991 thermal.tzp= [HW,ACPI]
3992 Specify global default ACPI thermal zone polling rate
3993 <deci-seconds>: poll all this frequency
3994 0: no polling (default)
3997 Force threading of all interrupt handlers except those
3998 marked explicitly IRQF_NO_THREAD.
4001 Enable the Transcendent memory driver if built-in.
4003 tmem.cleancache=0|1 [KNL, XEN]
4004 Default is on (1). Disable the usage of the cleancache
4005 API to send anonymous pages to the hypervisor.
4007 tmem.frontswap=0|1 [KNL, XEN]
4008 Default is on (1). Disable the usage of the frontswap
4009 API to send swap pages to the hypervisor. If disabled
4010 the selfballooning and selfshrinking are force disabled.
4012 tmem.selfballooning=0|1 [KNL, XEN]
4013 Default is on (1). Disable the driving of swap pages
4016 tmem.selfshrinking=0|1 [KNL, XEN]
4017 Default is on (1). Partial swapoff that immediately
4018 transfers pages from Xen hypervisor back to the
4019 kernel based on different criteria.
4023 Specify if the kernel should make use of the cpu
4024 topology information if the hardware supports this.
4025 The scheduler will make use of this information and
4026 e.g. base its process migration decisions on it.
4029 topology_updates= [KNL, PPC, NUMA]
4031 Specify if the kernel should ignore (off)
4032 topology updates sent by the hypervisor to this
4037 tpm_suspend_pcr=[HW,TPM]
4038 Format: integer pcr id
4039 Specify that at suspend time, the tpm driver
4040 should extend the specified pcr with zeros,
4041 as a workaround for some chips which fail to
4042 flush the last written pcr on TPM_SaveState.
4043 This will guarantee that all the other pcrs
4046 trace_buf_size=nn[KMG]
4047 [FTRACE] will set tracing buffer size on each cpu.
4049 trace_event=[event-list]
4050 [FTRACE] Set and start specified trace events in order
4051 to facilitate early boot debugging. The event-list is a
4052 comma separated list of trace events to enable. See
4053 also Documentation/trace/events.txt
4055 trace_options=[option-list]
4056 [FTRACE] Enable or disable tracer options at boot.
4057 The option-list is a comma delimited list of options
4058 that can be enabled or disabled just as if you were
4059 to echo the option name into
4061 /sys/kernel/debug/tracing/trace_options
4063 For example, to enable stacktrace option (to dump the
4064 stack trace of each event), add to the command line:
4066 trace_options=stacktrace
4068 See also Documentation/trace/ftrace.txt "trace options"
4072 Have the tracepoints sent to printk as well as the
4073 tracing ring buffer. This is useful for early boot up
4074 where the system hangs or reboots and does not give the
4075 option for reading the tracing buffer or performing a
4076 ftrace_dump_on_oops.
4078 To turn off having tracepoints sent to printk,
4079 echo 0 > /proc/sys/kernel/tracepoint_printk
4080 Note, echoing 1 into this file without the
4081 tracepoint_printk kernel cmdline option has no effect.
4085 Having tracepoints sent to printk() and activating high
4086 frequency tracepoints such as irq or sched, can cause
4087 the system to live lock.
4090 [FTRACE] enable this option to disable tracing when a
4091 warning is hit. This turns off "tracing_on". Tracing can
4092 be enabled again by echoing '1' into the "tracing_on"
4093 file located in /sys/kernel/debug/tracing/
4095 This option is useful, as it disables the trace before
4096 the WARNING dump is called, which prevents the trace to
4097 be filled with content caused by the warning output.
4099 This option can also be set at run time via the sysctl
4100 option: kernel/traceoff_on_warning
4102 transparent_hugepage=
4104 Format: [always|madvise|never]
4105 Can be used to control the default behavior of the system
4106 with respect to transparent hugepages.
4107 See Documentation/vm/transhuge.txt for more details.
4109 tsc= Disable clocksource stability checks for TSC.
4111 [x86] reliable: mark tsc clocksource as reliable, this
4112 disables clocksource verification at runtime, as well
4113 as the stability checks done at bootup. Used to enable
4114 high-resolution timer mode on older hardware, and in
4115 virtualized environment.
4116 [x86] noirqtime: Do not use TSC to do irq accounting.
4117 Used to run time disable IRQ_TIME_ACCOUNTING on any
4118 platforms where RDTSC is slow and this accounting
4121 turbografx.map[2|3]= [HW,JOY]
4122 TurboGraFX parallel port interface
4124 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4125 See also Documentation/input/joystick-parport.txt
4127 udbg-immortal [PPC] When debugging early kernel crashes that
4128 happen after console_init() and before a proper
4129 console driver takes over, this boot options might
4130 help "seeing" what's going on.
4132 uhash_entries= [KNL,NET]
4133 Set number of hash buckets for UDP/UDP-Lite connections
4136 [USB] Ignore overcurrent events (default N).
4137 Some badly-designed motherboards generate lots of
4138 bogus events, for ports that aren't wired to
4139 anything. Set this parameter to avoid log spamming.
4140 Note that genuine overcurrent events won't be
4144 [X86] Cause panic on unknown NMI.
4146 usbcore.authorized_default=
4147 [USB] Default USB device authorization:
4148 (default -1 = authorized except for wireless USB,
4149 0 = not authorized, 1 = authorized)
4151 usbcore.autosuspend=
4152 [USB] The autosuspend time delay (in seconds) used
4153 for newly-detected USB devices (default 2). This
4154 is the time required before an idle device will be
4155 autosuspended. Devices for which the delay is set
4156 to a negative value won't be autosuspended at all.
4158 usbcore.usbfs_snoop=
4159 [USB] Set to log all usbfs traffic (default 0 = off).
4161 usbcore.usbfs_snoop_max=
4162 [USB] Maximum number of bytes to snoop in each URB
4165 usbcore.blinkenlights=
4166 [USB] Set to cycle leds on hubs (default 0 = off).
4168 usbcore.old_scheme_first=
4169 [USB] Start with the old device initialization
4170 scheme (default 0 = off).
4172 usbcore.usbfs_memory_mb=
4173 [USB] Memory limit (in MB) for buffers allocated by
4174 usbfs (default = 16, 0 = max = 2047).
4176 usbcore.use_both_schemes=
4177 [USB] Try the other device initialization scheme
4178 if the first one fails (default 1 = enabled).
4180 usbcore.initial_descriptor_timeout=
4181 [USB] Specifies timeout for the initial 64-byte
4182 USB_REQ_GET_DESCRIPTOR request in milliseconds
4183 (default 5000 = 5.0 seconds).
4185 usbcore.nousb [USB] Disable the USB subsystem
4188 [USBHID] The interval which mice are to be polled at.
4190 usb-storage.delay_use=
4191 [UMS] The delay in seconds before a new device is
4192 scanned for Logical Units (default 1).
4195 [UMS] A list of quirks entries to supplement or
4196 override the built-in unusual_devs list. List
4197 entries are separated by commas. Each entry has
4198 the form VID:PID:Flags where VID and PID are Vendor
4199 and Product ID values (4-digit hex numbers) and
4200 Flags is a set of characters, each corresponding
4201 to a common usb-storage quirk flag as follows:
4202 a = SANE_SENSE (collect more than 18 bytes
4204 b = BAD_SENSE (don't collect more than 18
4205 bytes of sense data);
4206 c = FIX_CAPACITY (decrease the reported
4207 device capacity by one sector);
4208 d = NO_READ_DISC_INFO (don't use
4209 READ_DISC_INFO command);
4210 e = NO_READ_CAPACITY_16 (don't use
4211 READ_CAPACITY_16 command);
4212 f = NO_REPORT_OPCODES (don't use report opcodes
4214 g = MAX_SECTORS_240 (don't transfer more than
4215 240 sectors at a time, uas only);
4216 h = CAPACITY_HEURISTICS (decrease the
4217 reported device capacity by one
4218 sector if the number is odd);
4219 i = IGNORE_DEVICE (don't bind to this
4221 j = NO_REPORT_LUNS (don't use report luns
4223 l = NOT_LOCKABLE (don't try to lock and
4224 unlock ejectable media);
4225 m = MAX_SECTORS_64 (don't transfer more
4226 than 64 sectors = 32 KB at a time);
4227 n = INITIAL_READ10 (force a retry of the
4228 initial READ(10) command);
4229 o = CAPACITY_OK (accept the capacity
4230 reported by the device);
4231 p = WRITE_CACHE (the device cache is ON
4233 r = IGNORE_RESIDUE (the device reports
4234 bogus residue values);
4235 s = SINGLE_LUN (the device has only one
4237 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4238 commands, uas only);
4239 u = IGNORE_UAS (don't bind to the uas driver);
4240 w = NO_WP_DETECT (don't test whether the
4241 medium is write-protected).
4242 Example: quirks=0419:aaf5:rl,0421:0433:rc
4244 user_debug= [KNL,ARM]
4246 See arch/arm/Kconfig.debug help text.
4247 1 - undefined instruction events
4249 4 - invalid data aborts
4252 Example: user_debug=31
4255 [X86] Flags controlling user PTE allocations.
4257 nohigh = do not allocate PTE pages in
4258 HIGHMEM regardless of setting
4262 On X86_32, this is an alias for vdso32=. Otherwise:
4264 vdso=1: enable VDSO (the default)
4265 vdso=0: disable VDSO mapping
4267 vdso32= [X86] Control the 32-bit vDSO
4268 vdso32=1: enable 32-bit VDSO
4269 vdso32=0 or vdso32=2: disable 32-bit VDSO
4271 See the help text for CONFIG_COMPAT_VDSO for more
4272 details. If CONFIG_COMPAT_VDSO is set, the default is
4273 vdso32=0; otherwise, the default is vdso32=1.
4275 For compatibility with older kernels, vdso32=2 is an
4278 Try vdso32=0 if you encounter an error that says:
4279 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4282 vector=percpu: enable percpu vector domain
4284 video= [FB] Frame buffer configuration
4285 See Documentation/fb/modedb.txt.
4287 video.brightness_switch_enabled= [0,1]
4288 If set to 1, on receiving an ACPI notify event
4289 generated by hotkey, video driver will adjust brightness
4290 level and then send out the event to user space through
4291 the allocated input device; If set to 0, video driver
4292 will only send out the event without touching backlight
4297 [VMMIO] Memory mapped virtio (platform) device.
4299 <size>@<baseaddr>:<irq>[:<id>]
4301 <size> := size (can use standard suffixes
4303 <baseaddr> := physical base address
4304 <irq> := interrupt number (as passed to
4306 <id> := (optional) platform device id
4308 virtio_mmio.device=1K@0x100b0000:48:7
4310 Can be used multiple times for multiple devices.
4312 vga= [BOOT,X86-32] Select a particular video mode
4313 See Documentation/x86/boot.txt and
4314 Documentation/svga.txt.
4315 Use vga=ask for menu.
4316 This is actually a boot loader parameter; the value is
4317 passed to the kernel using a special protocol.
4319 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4320 size of <nn>. This can be used to increase the
4321 minimum size (128MB on x86). It can also be used to
4322 decrease the size and leave more room for directly
4325 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4328 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4331 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4335 Controls the behavior of vsyscalls (i.e. calls to
4336 fixed addresses of 0xffffffffff600x00 from legacy
4337 code). Most statically-linked binaries and older
4338 versions of glibc use these calls. Because these
4339 functions are at fixed addresses, they make nice
4340 targets for exploits that can control RIP.
4342 emulate [default] Vsyscalls turn into traps and are
4343 emulated reasonably safely.
4345 native Vsyscalls are native syscall instructions.
4346 This is a little bit faster than trapping
4347 and makes a few dynamic recompilers work
4348 better than they would in emulation mode.
4349 It also makes exploits much easier to write.
4351 none Vsyscalls don't work at all. This makes
4352 them quite hard to use for exploits but
4353 might break your system.
4355 vt.color= [VT] Default text color.
4356 Format: 0xYX, X = foreground, Y = background.
4357 Default: 0x07 = light gray on black.
4359 vt.cur_default= [VT] Default cursor shape.
4360 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4361 the parameters of the <Esc>[?A;B;Cc escape sequence;
4362 see VGA-softcursor.txt. Default: 2 = underline.
4364 vt.default_blu= [VT]
4365 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4366 Change the default blue palette of the console.
4367 This is a 16-member array composed of values
4370 vt.default_grn= [VT]
4371 Format: <green0>,<green1>,<green2>,...,<green15>
4372 Change the default green palette of the console.
4373 This is a 16-member array composed of values
4376 vt.default_red= [VT]
4377 Format: <red0>,<red1>,<red2>,...,<red15>
4378 Change the default red palette of the console.
4379 This is a 16-member array composed of values
4385 Set system-wide default UTF-8 mode for all tty's.
4386 Default is 1, i.e. UTF-8 mode is enabled for all
4387 newly opened terminals.
4389 vt.global_cursor_default=
4392 Set system-wide default for whether a cursor
4393 is shown on new VTs. Default is -1,
4394 i.e. cursors will be created by default unless
4395 overridden by individual drivers. 0 will hide
4396 cursors, 1 will display them.
4398 vt.italic= [VT] Default color for italic text; 0-15.
4401 vt.underline= [VT] Default color for underlined text; 0-15.
4404 watchdog timers [HW,WDT] For information on watchdog timers,
4405 see Documentation/watchdog/watchdog-parameters.txt
4406 or other driver-specific files in the
4407 Documentation/watchdog/ directory.
4409 workqueue.watchdog_thresh=
4410 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4411 warn stall conditions and dump internal state to
4412 help debugging. 0 disables workqueue stall
4413 detection; otherwise, it's the stall threshold
4414 duration in seconds. The default value is 30 and
4415 it can be updated at runtime by writing to the
4416 corresponding sysfs file.
4418 workqueue.disable_numa
4419 By default, all work items queued to unbound
4420 workqueues are affine to the NUMA nodes they're
4421 issued on, which results in better behavior in
4422 general. If NUMA affinity needs to be disabled for
4423 whatever reason, this option can be used. Note
4424 that this also can be controlled per-workqueue for
4425 workqueues visible under /sys/bus/workqueue/.
4427 workqueue.power_efficient
4428 Per-cpu workqueues are generally preferred because
4429 they show better performance thanks to cache
4430 locality; unfortunately, per-cpu workqueues tend to
4431 be more power hungry than unbound workqueues.
4433 Enabling this makes the per-cpu workqueues which
4434 were observed to contribute significantly to power
4435 consumption unbound, leading to measurably lower
4436 power usage at the cost of small performance
4439 The default value of this parameter is determined by
4440 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4442 workqueue.debug_force_rr_cpu
4443 Workqueue used to implicitly guarantee that work
4444 items queued without explicit CPU specified are put
4445 on the local CPU. This guarantee is no longer true
4446 and while local CPU is still preferred work items
4447 may be put on foreign CPUs. This debug option
4448 forces round-robin CPU selection to flush out
4449 usages which depend on the now broken guarantee.
4450 When enabled, memory and cache locality will be
4453 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4454 default x2apic cluster mode on platforms
4457 x86_intel_mid_timer= [X86-32,APBT]
4458 Choose timer option for x86 Intel MID platform.
4459 Two valid options are apbt timer only and lapic timer
4460 plus one apbt timer for broadcast timer.
4461 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4463 xen_512gb_limit [KNL,X86-64,XEN]
4464 Restricts the kernel running paravirtualized under Xen
4465 to use only up to 512 GB of RAM. The reason to do so is
4466 crash analysis tools and Xen tools for doing domain
4467 save/restore/migration must be enabled to handle larger
4470 xen_emul_unplug= [HW,X86,XEN]
4471 Unplug Xen emulated devices
4472 Format: [unplug0,][unplug1]
4473 ide-disks -- unplug primary master IDE devices
4474 aux-ide-disks -- unplug non-primary-master IDE devices
4475 nics -- unplug network devices
4476 all -- unplug all emulated devices (NICs and IDE disks)
4477 unnecessary -- unplugging emulated devices is
4478 unnecessary even if the host did not respond to
4480 never -- do not unplug even if version check succeeds
4482 xen_nopvspin [X86,XEN]
4483 Disables the ticketlock slowpath using Xen PV
4487 Disables the PV optimizations forcing the HVM guest to
4488 run as generic HVM guest with no PV drivers.
4490 xirc2ps_cs= [NET,PCMCIA]
4492 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4494 ______________________________________________________________________
4498 Add more DRM drivers.
projects / cascardo / linux.git / blob