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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
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
26 loadable modules too.
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 |
172 copy_dsdt }
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"
182 are available
184 See also Documentation/power/runtime_pm.txt, pci=noacpi
186 acpi_apic_instance= [ACPI, IOAPIC]
187 Format: <int>
188 2: use 2nd APIC table, if available
189 1,0: use 1st APIC table
190 default: 0
192 acpi_backlight= [HW,ACPI]
193 acpi_backlight=vendor
194 acpi_backlight=video
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]
215 Format: <int>
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
260 size limitation.
262 acpi_irq_balance [HW,ACPI]
263 ACPI will balance active IRQs
264 default in APIC mode
266 acpi_irq_nobalance [HW,ACPI]
267 ACPI will not move active IRQs (default)
268 default in PIC mode
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
274 use by PCI
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
286 kernels.
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
317 strings
318 acpi_osi=!! # enable all built-in OS vendor
319 strings
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.
332 Examples:
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
342 meaningless.
343 Examples:
344 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
345 FALSE.
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
357 the OSPM features.
358 Examples:
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
364 equivalent to
365 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
366 and
367 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
368 they all will make '_OSI("Windows 2000")' TRUE.
370 acpi_pm_good [X86]
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
386 s3_bios and s3_mode.
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.
408 agp= [AGP]
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)
414 ALSA [HW,ALSA]
415 See Documentation/sound/alsa/alsa-parameters.txt
417 alignment= [KNL,ARM]
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.
444 Possible values are:
445 fullflush - enable flushing of IO/TLB entries when
446 they are unmapped. Otherwise they are
447 flushed before they will be reused, which
448 is a lot of faster
449 off - do not initialize any AMD IOMMU found in
450 the system
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
465 Format: <a>,<b>
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>
473 apc= [HW,SPARC]
474 Power management functions (SPARCstation-4/5 + deriv.)
475 Format: noidle
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
490 backup of CPU 0
491 none: External NMI is masked for all CPUs. This is
492 useful so that a dump capture kernel won't be
493 shot down by NMI
495 autoconf= [IPV6]
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>
513 ataflop= [HW,M68k]
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
526 keyboards
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
543 auditd.
544 Default: unset
546 audit_backlog_limit= [KNL] Set the audit queue size limit.
547 Format: <int> (must be >=0)
548 Default: 64
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" }
553 0 - Disable the BAU.
554 1 - Enable the BAU.
555 unset - Disable the BAU.
557 baycom_epp= [HW,AX25]
558 Format: <io>,<mode>
560 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
561 Format: <io>,<mode>
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
580 no delay (0).
581 Format: integer
583 bootmem_debug [KNL] Enable bootmem allocator debug messages.
585 bert_disable [ACPI]
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
590 kernel args too.
591 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
592 bttv.tuner=
594 bulk_remove=off [PPC] This parameter disables the use of the pSeries
595 firmware feature for flushing multiple hpte entries
596 at a time.
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
609 trust validation.
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
616 others).
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
625 a single hierarchy
626 - foo isn't visible as an individually mountable
627 subsystem
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.
638 Format: <string>
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.
652 cio_ignore= [S390]
653 See Documentation/s390/CommonIO for details.
654 clk_ignore_unused
655 [CLK]
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.
667 [Deprecated]
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
674 Format: <string>
675 Override the default clocksource and use the clocksource
676 with the name specified.
677 Some clocksource names to choose from, depending on
678 the platform:
679 [all] jiffies (this is the base, fallback clocksource)
680 [ACPI] acpi_pm
681 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
682 pxa_timer,timer3,32k_counter,timer0_1
683 [AVR32] avr32
684 [X86-32] pit,hpet,tsc;
685 scx200_hrt on Geode; cyclone on IBM x440
686 [MIPS] MIPS
687 [PARISC] cr16
688 [S390] tod
689 [SH] SuperH
690 [SPARC64] tick
691 [X86-64] hpet,tsc
693 clocksource.arm_arch_timer.evtstrm=
694 [ARM,ARM64]
695 Format: <bool>
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
699 systems.
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
706 ones should be.
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
712 some critical bits.
714 cma=nn[MG]@[start[MG][-end[MG]]]
715 [ARM,X86,KNL]
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
727 a hypervisor.
728 Default: yes
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
735 in an oops report.
736 Range: 0 - 8192
737 Default: 64
739 com20020= [HW,NET] ARCnet - COM20020 chipset
740 Format:
741 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
743 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
744 Format: <io>[,<irq>]
746 com90xx= [HW,NET]
747 ARCnet - COM90xx chipset (memory-mapped buffers)
748 Format: <io>[,<irq>[,<memstart>]]
750 condev= [HW,S390] console device
751 conmode=
753 console= [KNL] Output console device and options.
755 tty<n> Use the virtual console device <n>.
757 ttyS<n>[,options]
758 ttyUSB0[,options]
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
766 information. See
767 Documentation/networking/netconsole.txt for an
768 alternative.
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
790 console=brl,ttyS0
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.
797 coredump_filter=
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
805 cpu_init_udelay=N
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.
809 Default: 10000
811 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
812 Format:
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
835 available.
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.
852 cryptomgr.notests
853 [KNL] Disable crypto self-tests
855 cs89x0_dma= [HW,NET]
856 Format: <dma>
858 cs89x0_media= [HW,NET]
859 Format: { rj45 | aui | bnc }
861 dasd= [HW,NET]
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).
875 debug_locks_verbose=
876 [KNL] verbose self-tests
877 Format=<0|1>
878 Print debugging info while doing the locking API
879 self-tests.
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
886 no_debug_objects
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.
908 debug_pagealloc=
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.
923 default_hugepagesz=
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
929 if not specified.
931 dhash_entries= [KNL]
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
938 miss to occur.
940 disable= [IPV6]
941 See Documentation/networking/ipv6.txt.
943 disable_radix [PPC]
944 Disable RADIX MMU mode on POWER9
946 disable_cpu_apicid= [X86,APIC,SMP]
947 Format: <int>
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
953 INIT from AP to BSP.
955 disable_ddw [PPC/PSERIES]
956 Disable Dynamic DMA Window support. Use this if
957 to workaround buggy firmware.
959 disable_ipv6= [IPV6]
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.
1014 dscc4.setup= [NET]
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
1026 in some Intel CPUs.
1028 eagerfpu= [X86]
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
1046 tree's chosen node.
1048 cdns,<addr>
1049 Start an early, polled-mode console on a cadence serial
1050 port at the specified address. The cadence serial port
1051 must already be setup and configured. Options are not
1052 yet supported.
1054 uart[8250],io,<addr>[,options]
1055 uart[8250],mmio,<addr>[,options]
1056 uart[8250],mmio32,<addr>[,options]
1057 uart[8250],mmio32be,<addr>[,options]
1058 uart[8250],0x<addr>[,options]
1059 Start an early, polled-mode console on the 8250/16550
1060 UART at the specified I/O port or MMIO address.
1061 MMIO inter-register address stride is either 8-bit
1062 (mmio) or 32-bit (mmio32 or mmio32be).
1063 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1064 to be equivalent to 'mmio'. 'options' are specified
1065 in the same format described for "console=ttyS<n>"; if
1066 unspecified, the h/w is not initialized.
1068 pl011,<addr>
1069 pl011,mmio32,<addr>
1070 Start an early, polled-mode console on a pl011 serial
1071 port at the specified address. The pl011 serial port
1072 must already be setup and configured. Options are not
1073 yet supported. If 'mmio32' is specified, then only
1074 the driver will use only 32-bit accessors to read/write
1075 the device registers.
1077 meson,<addr>
1078 Start an early, polled-mode console on a meson serial
1079 port at the specified address. The serial port must
1080 already be setup and configured. Options are not yet
1081 supported.
1083 msm_serial,<addr>
1084 Start an early, polled-mode console on an msm serial
1085 port at the specified address. The serial port
1086 must already be setup and configured. Options are not
1087 yet supported.
1089 msm_serial_dm,<addr>
1090 Start an early, polled-mode console on an msm serial
1091 dm port at the specified address. The serial port
1092 must already be setup and configured. Options are not
1093 yet supported.
1095 smh Use ARM semihosting calls for early console.
1097 s3c2410,<addr>
1098 s3c2412,<addr>
1099 s3c2440,<addr>
1100 s3c6400,<addr>
1101 s5pv210,<addr>
1102 exynos4210,<addr>
1103 Use early console provided by serial driver available
1104 on Samsung SoCs, requires selecting proper type and
1105 a correct base address of the selected UART port. The
1106 serial port must already be setup and configured.
1107 Options are not yet supported.
1109 lpuart,<addr>
1110 lpuart32,<addr>
1111 Use early console provided by Freescale LP UART driver
1112 found on Freescale Vybrid and QorIQ LS1021A processors.
1113 A valid base address must be provided, and the serial
1114 port must already be setup and configured.
1116 armada3700_uart,<addr>
1117 Start an early, polled-mode console on the
1118 Armada 3700 serial port at the specified
1119 address. The serial port must already be setup
1120 and configured. Options are not yet supported.
1122 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1123 earlyprintk=vga
1124 earlyprintk=efi
1125 earlyprintk=xen
1126 earlyprintk=serial[,ttySn[,baudrate]]
1127 earlyprintk=serial[,0x...[,baudrate]]
1128 earlyprintk=ttySn[,baudrate]
1129 earlyprintk=dbgp[debugController#]
1130 earlyprintk=pciserial,bus:device.function[,baudrate]
1132 earlyprintk is useful when the kernel crashes before
1133 the normal console is initialized. It is not enabled by
1134 default because it has some cosmetic problems.
1136 Append ",keep" to not disable it when the real console
1137 takes over.
1139 Only one of vga, efi, serial, or usb debug port can
1140 be used at a time.
1142 Currently only ttyS0 and ttyS1 may be specified by
1143 name. Other I/O ports may be explicitly specified
1144 on some architectures (x86 and arm at least) by
1145 replacing ttySn with an I/O port address, like this:
1146 earlyprintk=serial,0x1008,115200
1147 You can find the port for a given device in
1148 /proc/tty/driver/serial:
1149 2: uart:ST16650V2 port:00001008 irq:18 ...
1151 Interaction with the standard serial driver is not
1152 very good.
1154 The VGA and EFI output is eventually overwritten by
1155 the real console.
1157 The xen output can only be used by Xen PV guests.
1159 edac_report= [HW,EDAC] Control how to report EDAC event
1160 Format: {"on" | "off" | "force"}
1161 on: enable EDAC to report H/W event. May be overridden
1162 by other higher priority error reporting module.
1163 off: disable H/W event reporting through EDAC.
1164 force: enforce the use of EDAC to report H/W event.
1165 default: on.
1167 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1168 ekgdboc=kbd
1170 This is designed to be used in conjunction with
1171 the boot argument: earlyprintk=vga
1173 edd= [EDD]
1174 Format: {"off" | "on" | "skip[mbr]"}
1176 efi= [EFI]
1177 Format: { "old_map", "nochunk", "noruntime", "debug" }
1178 old_map [X86-64]: switch to the old ioremap-based EFI
1179 runtime services mapping. 32-bit still uses this one by
1180 default.
1181 nochunk: disable reading files in "chunks" in the EFI
1182 boot stub, as chunking can cause problems with some
1183 firmware implementations.
1184 noruntime : disable EFI runtime services support
1185 debug: enable misc debug output
1187 efi_no_storage_paranoia [EFI; X86]
1188 Using this parameter you can use more than 50% of
1189 your efi variable storage. Use this parameter only if
1190 you are really sure that your UEFI does sane gc and
1191 fulfills the spec otherwise your board may brick.
1193 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1194 Add arbitrary attribute to specific memory range by
1195 updating original EFI memory map.
1196 Region of memory which aa attribute is added to is
1197 from ss to ss+nn.
1198 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1199 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1200 attribute is added to range 0x100000000-0x180000000 and
1201 0x10a0000000-0x1120000000.
1203 Using this parameter you can do debugging of EFI memmap
1204 related feature. For example, you can do debugging of
1205 Address Range Mirroring feature even if your box
1206 doesn't support it.
1208 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1209 that is to be dynamically loaded by Linux. If there are
1210 multiple variables with the same name but with different
1211 vendor GUIDs, all of them will be loaded. See
1212 Documentation/acpi/ssdt-overlays.txt for details.
1215 eisa_irq_edge= [PARISC,HW]
1216 See header of drivers/parisc/eisa.c.
1218 elanfreq= [X86-32]
1219 See comment before function elanfreq_setup() in
1220 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1222 elevator= [IOSCHED]
1223 Format: {"cfq" | "deadline" | "noop"}
1224 See Documentation/block/cfq-iosched.txt and
1225 Documentation/block/deadline-iosched.txt for details.
1227 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1228 Specifies physical address of start of kernel core
1229 image elf header and optionally the size. Generally
1230 kexec loader will pass this option to capture kernel.
1231 See Documentation/kdump/kdump.txt for details.
1233 enable_mtrr_cleanup [X86]
1234 The kernel tries to adjust MTRR layout from continuous
1235 to discrete, to make X server driver able to add WB
1236 entry later. This parameter enables that.
1238 enable_timer_pin_1 [X86]
1239 Enable PIN 1 of APIC timer
1240 Can be useful to work around chipset bugs
1241 (in particular on some ATI chipsets).
1242 The kernel tries to set a reasonable default.
1244 enforcing [SELINUX] Set initial enforcing status.
1245 Format: {"0" | "1"}
1246 See security/selinux/Kconfig help text.
1247 0 -- permissive (log only, no denials).
1248 1 -- enforcing (deny and log).
1249 Default value is 0.
1250 Value can be changed at runtime via /selinux/enforce.
1252 erst_disable [ACPI]
1253 Disable Error Record Serialization Table (ERST)
1254 support.
1256 ether= [HW,NET] Ethernet cards parameters
1257 This option is obsoleted by the "netdev=" option, which
1258 has equivalent usage. See its documentation for details.
1260 evm= [EVM]
1261 Format: { "fix" }
1262 Permit 'security.evm' to be updated regardless of
1263 current integrity status.
1265 failslab=
1266 fail_page_alloc=
1267 fail_make_request=[KNL]
1268 General fault injection mechanism.
1269 Format: <interval>,<probability>,<space>,<times>
1270 See also Documentation/fault-injection/.
1272 floppy= [HW]
1273 See Documentation/blockdev/floppy.txt.
1275 force_pal_cache_flush
1276 [IA-64] Avoid check_sal_cache_flush which may hang on
1277 buggy SAL_CACHE_FLUSH implementations. Using this
1278 parameter will force ia64_sal_cache_flush to call
1279 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1281 forcepae [X86-32]
1282 Forcefully enable Physical Address Extension (PAE).
1283 Many Pentium M systems disable PAE but may have a
1284 functionally usable PAE implementation.
1285 Warning: use of this parameter will taint the kernel
1286 and may cause unknown problems.
1288 ftrace=[tracer]
1289 [FTRACE] will set and start the specified tracer
1290 as early as possible in order to facilitate early
1291 boot debugging.
1293 ftrace_dump_on_oops[=orig_cpu]
1294 [FTRACE] will dump the trace buffers on oops.
1295 If no parameter is passed, ftrace will dump
1296 buffers of all CPUs, but if you pass orig_cpu, it will
1297 dump only the buffer of the CPU that triggered the
1298 oops.
1300 ftrace_filter=[function-list]
1301 [FTRACE] Limit the functions traced by the function
1302 tracer at boot up. function-list is a comma separated
1303 list of functions. This list can be changed at run
1304 time by the set_ftrace_filter file in the debugfs
1305 tracing directory.
1307 ftrace_notrace=[function-list]
1308 [FTRACE] Do not trace the functions specified in
1309 function-list. This list can be changed at run time
1310 by the set_ftrace_notrace file in the debugfs
1311 tracing directory.
1313 ftrace_graph_filter=[function-list]
1314 [FTRACE] Limit the top level callers functions traced
1315 by the function graph tracer at boot up.
1316 function-list is a comma separated list of functions
1317 that can be changed at run time by the
1318 set_graph_function file in the debugfs tracing directory.
1320 ftrace_graph_notrace=[function-list]
1321 [FTRACE] Do not trace from the functions specified in
1322 function-list. This list is a comma separated list of
1323 functions that can be changed at run time by the
1324 set_graph_notrace file in the debugfs tracing directory.
1326 gamecon.map[2|3]=
1327 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1328 support via parallel port (up to 5 devices per port)
1329 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1330 See also Documentation/input/joystick-parport.txt
1332 gamma= [HW,DRM]
1334 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1335 Format: off | on
1336 default: on
1338 gcov_persist= [GCOV] When non-zero (default), profiling data for
1339 kernel modules is saved and remains accessible via
1340 debugfs, even when the module is unloaded/reloaded.
1341 When zero, profiling data is discarded and associated
1342 debugfs files are removed at module unload time.
1344 gpt [EFI] Forces disk with valid GPT signature but
1345 invalid Protective MBR to be treated as GPT. If the
1346 primary GPT is corrupted, it enables the backup/alternate
1347 GPT to be used instead.
1349 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1350 the "Enable 0" bit of the configuration register.
1351 Format: 0 | 1
1352 Default: 0
1353 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1354 the "Enable 0" bit of the configuration register.
1355 Format: 0 | 1
1356 Default: 0
1357 grcan.select= [HW] Select which physical interface to use.
1358 Format: 0 | 1
1359 Default: 0
1360 grcan.txsize= [HW] Sets the size of the tx buffer.
1361 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1362 Default: 1024
1363 grcan.rxsize= [HW] Sets the size of the rx buffer.
1364 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1365 Default: 1024
1367 hardlockup_all_cpu_backtrace=
1368 [KNL] Should the hard-lockup detector generate
1369 backtraces on all cpus.
1370 Format: <integer>
1372 hashdist= [KNL,NUMA] Large hashes allocated during boot
1373 are distributed across NUMA nodes. Defaults on
1374 for 64-bit NUMA, off otherwise.
1375 Format: 0 | 1 (for off | on)
1377 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1379 hd= [EIDE] (E)IDE hard drive subsystem geometry
1380 Format: <cyl>,<head>,<sect>
1382 hest_disable [ACPI]
1383 Disable Hardware Error Source Table (HEST) support;
1384 corresponding firmware-first mode error processing
1385 logic will be disabled.
1387 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1388 size of <nn>. This works even on boxes that have no
1389 highmem otherwise. This also works to reduce highmem
1390 size on bigger boxes.
1392 highres= [KNL] Enable/disable high resolution timer mode.
1393 Valid parameters: "on", "off"
1394 Default: "on"
1396 hisax= [HW,ISDN]
1397 See Documentation/isdn/README.HiSax.
1399 hlt [BUGS=ARM,SH]
1401 hpet= [X86-32,HPET] option to control HPET usage
1402 Format: { enable (default) | disable | force |
1403 verbose }
1404 disable: disable HPET and use PIT instead
1405 force: allow force enabled of undocumented chips (ICH4,
1406 VIA, nVidia)
1407 verbose: show contents of HPET registers during setup
1409 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1410 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1412 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1413 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1414 On x86-64 and powerpc, this option can be specified
1415 multiple times interleaved with hugepages= to reserve
1416 huge pages of different sizes. Valid pages sizes on
1417 x86-64 are 2M (when the CPU supports "pse") and 1G
1418 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1420 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1421 terminal devices. Valid values: 0..8
1422 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1423 If specified, z/VM IUCV HVC accepts connections
1424 from listed z/VM user IDs only.
1426 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1427 hardware thread id mappings.
1428 Format: <cpu>:<hwthread>
1430 keep_bootcon [KNL]
1431 Do not unregister boot console at start. This is only
1432 useful for debugging when something happens in the window
1433 between unregistering the boot console and initializing
1434 the real console.
1436 i2c_bus= [HW] Override the default board specific I2C bus speed
1437 or register an additional I2C bus that is not
1438 registered from board initialization code.
1439 Format:
1440 <bus_id>,<clkrate>
1442 i8042.debug [HW] Toggle i8042 debug mode
1443 i8042.unmask_kbd_data
1444 [HW] Enable printing of interrupt data from the KBD port
1445 (disabled by default, and as a pre-condition
1446 requires that i8042.debug=1 be enabled)
1447 i8042.direct [HW] Put keyboard port into non-translated mode
1448 i8042.dumbkbd [HW] Pretend that controller can only read data from
1449 keyboard and cannot control its state
1450 (Don't attempt to blink the leds)
1451 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1452 i8042.nokbd [HW] Don't check/create keyboard port
1453 i8042.noloop [HW] Disable the AUX Loopback command while probing
1454 for the AUX port
1455 i8042.nomux [HW] Don't check presence of an active multiplexing
1456 controller
1457 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1458 controllers
1459 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1460 i8042.reset [HW] Reset the controller during init and cleanup
1461 i8042.unlock [HW] Unlock (ignore) the keylock
1462 i8042.kbdreset [HW] Reset device connected to KBD port
1464 i810= [HW,DRM]
1466 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1467 indicates that the driver is running on unsupported
1468 hardware.
1469 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1470 does not match list of supported models.
1471 i8k.power_status
1472 [HW] Report power status in /proc/i8k
1473 (disabled by default)
1474 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1475 capability is set.
1477 i915.invert_brightness=
1478 [DRM] Invert the sense of the variable that is used to
1479 set the brightness of the panel backlight. Normally a
1480 brightness value of 0 indicates backlight switched off,
1481 and the maximum of the brightness value sets the backlight
1482 to maximum brightness. If this parameter is set to 0
1483 (default) and the machine requires it, or this parameter
1484 is set to 1, a brightness value of 0 sets the backlight
1485 to maximum brightness, and the maximum of the brightness
1486 value switches the backlight off.
1487 -1 -- never invert brightness
1488 0 -- machine default
1489 1 -- force brightness inversion
1491 icn= [HW,ISDN]
1492 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1494 ide-core.nodma= [HW] (E)IDE subsystem
1495 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1496 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1497 .cdrom .chs .ignore_cable are additional options
1498 See Documentation/ide/ide.txt.
1500 ide-generic.probe-mask= [HW] (E)IDE subsystem
1501 Format: <int>
1502 Probe mask for legacy ISA IDE ports. Depending on
1503 platform up to 6 ports are supported, enabled by
1504 setting corresponding bits in the mask to 1. The
1505 default value is 0x0, which has a special meaning.
1506 On systems that have PCI, it triggers scanning the
1507 PCI bus for the first and the second port, which
1508 are then probed. On systems without PCI the value
1509 of 0x0 enables probing the two first ports as if it
1510 was 0x3.
1512 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1513 Claim all unknown PCI IDE storage controllers.
1515 idle= [X86]
1516 Format: idle=poll, idle=halt, idle=nomwait
1517 Poll forces a polling idle loop that can slightly
1518 improve the performance of waking up a idle CPU, but
1519 will use a lot of power and make the system run hot.
1520 Not recommended.
1521 idle=halt: Halt is forced to be used for CPU idle.
1522 In such case C2/C3 won't be used again.
1523 idle=nomwait: Disable mwait for CPU C-states
1525 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1526 Format: { strict | legacy | 2008 | relaxed }
1527 Default: strict
1529 Choose which programs will be accepted for execution
1530 based on the IEEE 754 NaN encoding(s) supported by
1531 the FPU and the NaN encoding requested with the value
1532 of an ELF file header flag individually set by each
1533 binary. Hardware implementations are permitted to
1534 support either or both of the legacy and the 2008 NaN
1535 encoding mode.
1537 Available settings are as follows:
1538 strict accept binaries that request a NaN encoding
1539 supported by the FPU
1540 legacy only accept legacy-NaN binaries, if supported
1541 by the FPU
1542 2008 only accept 2008-NaN binaries, if supported
1543 by the FPU
1544 relaxed accept any binaries regardless of whether
1545 supported by the FPU
1547 The FPU emulator is always able to support both NaN
1548 encodings, so if no FPU hardware is present or it has
1549 been disabled with 'nofpu', then the settings of
1550 'legacy' and '2008' strap the emulator accordingly,
1551 'relaxed' straps the emulator for both legacy-NaN and
1552 2008-NaN, whereas 'strict' enables legacy-NaN only on
1553 legacy processors and both NaN encodings on MIPS32 or
1554 MIPS64 CPUs.
1556 The setting for ABS.fmt/NEG.fmt instruction execution
1557 mode generally follows that for the NaN encoding,
1558 except where unsupported by hardware.
1560 ignore_loglevel [KNL]
1561 Ignore loglevel setting - this will print /all/
1562 kernel messages to the console. Useful for debugging.
1563 We also add it as printk module parameter, so users
1564 could change it dynamically, usually by
1565 /sys/module/printk/parameters/ignore_loglevel.
1567 ignore_rlimit_data
1568 Ignore RLIMIT_DATA setting for data mappings,
1569 print warning at first misuse. Can be changed via
1570 /sys/module/kernel/parameters/ignore_rlimit_data.
1572 ihash_entries= [KNL]
1573 Set number of hash buckets for inode cache.
1575 ima_appraise= [IMA] appraise integrity measurements
1576 Format: { "off" | "enforce" | "fix" | "log" }
1577 default: "enforce"
1579 ima_appraise_tcb [IMA]
1580 The builtin appraise policy appraises all files
1581 owned by uid=0.
1583 ima_hash= [IMA]
1584 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1585 | sha512 | ... }
1586 default: "sha1"
1588 The list of supported hash algorithms is defined
1589 in crypto/hash_info.h.
1591 ima_policy= [IMA]
1592 The builtin measurement policy to load during IMA
1593 setup. Specyfing "tcb" as the value, measures all
1594 programs exec'd, files mmap'd for exec, and all files
1595 opened with the read mode bit set by either the
1596 effective uid (euid=0) or uid=0.
1597 Format: "tcb"
1599 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1600 Load a policy which meets the needs of the Trusted
1601 Computing Base. This means IMA will measure all
1602 programs exec'd, files mmap'd for exec, and all files
1603 opened for read by uid=0.
1605 ima_template= [IMA]
1606 Select one of defined IMA measurements template formats.
1607 Formats: { "ima" | "ima-ng" | "ima-sig" }
1608 Default: "ima-ng"
1610 ima_template_fmt=
1611 [IMA] Define a custom template format.
1612 Format: { "field1|...|fieldN" }
1614 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1615 Format: <min_file_size>
1616 Set the minimal file size for using asynchronous hash.
1617 If left unspecified, ahash usage is disabled.
1619 ahash performance varies for different data sizes on
1620 different crypto accelerators. This option can be used
1621 to achieve the best performance for a particular HW.
1623 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1624 Format: <bufsize>
1625 Set hashing buffer size. Default: 4k.
1627 ahash performance varies for different chunk sizes on
1628 different crypto accelerators. This option can be used
1629 to achieve best performance for particular HW.
1631 init= [KNL]
1632 Format: <full_path>
1633 Run specified binary instead of /sbin/init as init
1634 process.
1636 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1637 for working out where the kernel is dying during
1638 startup.
1640 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1641 initcall functions. Useful for debugging built-in
1642 modules and initcalls.
1644 initrd= [BOOT] Specify the location of the initial ramdisk
1646 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1647 Format: <irq>
1649 int_pln_enable [x86] Enable power limit notification interrupt
1651 integrity_audit=[IMA]
1652 Format: { "0" | "1" }
1653 0 -- basic integrity auditing messages. (Default)
1654 1 -- additional integrity auditing messages.
1656 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1657 on
1658 Enable intel iommu driver.
1659 off
1660 Disable intel iommu driver.
1661 igfx_off [Default Off]
1662 By default, gfx is mapped as normal device. If a gfx
1663 device has a dedicated DMAR unit, the DMAR unit is
1664 bypassed by not enabling DMAR with this option. In
1665 this case, gfx device will use physical address for
1666 DMA.
1667 forcedac [x86_64]
1668 With this option iommu will not optimize to look
1669 for io virtual address below 32-bit forcing dual
1670 address cycle on pci bus for cards supporting greater
1671 than 32-bit addressing. The default is to look
1672 for translation below 32-bit and if not available
1673 then look in the higher range.
1674 strict [Default Off]
1675 With this option on every unmap_single operation will
1676 result in a hardware IOTLB flush operation as opposed
1677 to batching them for performance.
1678 sp_off [Default Off]
1679 By default, super page will be supported if Intel IOMMU
1680 has the capability. With this option, super page will
1681 not be supported.
1682 ecs_off [Default Off]
1683 By default, extended context tables will be supported if
1684 the hardware advertises that it has support both for the
1685 extended tables themselves, and also PASID support. With
1686 this option set, extended tables will not be used even
1687 on hardware which claims to support them.
1689 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1690 0 disables intel_idle and fall back on acpi_idle.
1691 1 to 6 specify maximum depth of C-state.
1693 intel_pstate= [X86]
1694 disable
1695 Do not enable intel_pstate as the default
1696 scaling driver for the supported processors
1697 force
1698 Enable intel_pstate on systems that prohibit it by default
1699 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1700 instead of acpi-cpufreq may disable platform features, such
1701 as thermal controls and power capping, that rely on ACPI
1702 P-States information being indicated to OSPM and therefore
1703 should be used with caution. This option does not work with
1704 processors that aren't supported by the intel_pstate driver
1705 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1706 no_hwp
1707 Do not enable hardware P state control (HWP)
1708 if available.
1709 hwp_only
1710 Only load intel_pstate on systems which support
1711 hardware P state control (HWP) if available.
1712 support_acpi_ppc
1713 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1714 Description Table, specifies preferred power management
1715 profile as "Enterprise Server" or "Performance Server",
1716 then this feature is turned on by default.
1718 intremap= [X86-64, Intel-IOMMU]
1719 on enable Interrupt Remapping (default)
1720 off disable Interrupt Remapping
1721 nosid disable Source ID checking
1722 no_x2apic_optout
1723 BIOS x2APIC opt-out request will be ignored
1724 nopost disable Interrupt Posting
1726 iomem= Disable strict checking of access to MMIO memory
1727 strict regions from userspace.
1728 relaxed
1730 iommu= [x86]
1731 off
1732 force
1733 noforce
1734 biomerge
1735 panic
1736 nopanic
1737 merge
1738 nomerge
1739 forcesac
1740 soft
1741 pt [x86, IA-64]
1742 nobypass [PPC/POWERNV]
1743 Disable IOMMU bypass, using IOMMU for PCI devices.
1746 io7= [HW] IO7 for Marvel based alpha systems
1747 See comment before marvel_specify_io7 in
1748 arch/alpha/kernel/core_marvel.c.
1750 io_delay= [X86] I/O delay method
1751 0x80
1752 Standard port 0x80 based delay
1753 0xed
1754 Alternate port 0xed based delay (needed on some systems)
1755 udelay
1756 Simple two microseconds delay
1757 none
1758 No delay
1760 ip= [IP_PNP]
1761 See Documentation/filesystems/nfs/nfsroot.txt.
1763 irqaffinity= [SMP] Set the default irq affinity mask
1764 Format:
1765 <cpu number>,...,<cpu number>
1766 or
1767 <cpu number>-<cpu number>
1768 (must be a positive range in ascending order)
1769 or a mixture
1770 <cpu number>,...,<cpu number>-<cpu number>
1772 irqfixup [HW]
1773 When an interrupt is not handled search all handlers
1774 for it. Intended to get systems with badly broken
1775 firmware running.
1777 irqpoll [HW]
1778 When an interrupt is not handled search all handlers
1779 for it. Also check all handlers each timer
1780 interrupt. Intended to get systems with badly broken
1781 firmware running.
1783 isapnp= [ISAPNP]
1784 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1786 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1787 Format:
1788 <cpu number>,...,<cpu number>
1789 or
1790 <cpu number>-<cpu number>
1791 (must be a positive range in ascending order)
1792 or a mixture
1793 <cpu number>,...,<cpu number>-<cpu number>
1795 This option can be used to specify one or more CPUs
1796 to isolate from the general SMP balancing and scheduling
1797 algorithms. You can move a process onto or off an
1798 "isolated" CPU via the CPU affinity syscalls or cpuset.
1799 <cpu number> begins at 0 and the maximum value is
1800 "number of CPUs in system - 1".
1802 This option is the preferred way to isolate CPUs. The
1803 alternative -- manually setting the CPU mask of all
1804 tasks in the system -- can cause problems and
1805 suboptimal load balancer performance.
1807 iucv= [HW,NET]
1809 ivrs_ioapic [HW,X86_64]
1810 Provide an override to the IOAPIC-ID<->DEVICE-ID
1811 mapping provided in the IVRS ACPI table. For
1812 example, to map IOAPIC-ID decimal 10 to
1813 PCI device 00:14.0 write the parameter as:
1814 ivrs_ioapic[10]=00:14.0
1816 ivrs_hpet [HW,X86_64]
1817 Provide an override to the HPET-ID<->DEVICE-ID
1818 mapping provided in the IVRS ACPI table. For
1819 example, to map HPET-ID decimal 0 to
1820 PCI device 00:14.0 write the parameter as:
1821 ivrs_hpet[0]=00:14.0
1823 ivrs_acpihid [HW,X86_64]
1824 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1825 mapping provided in the IVRS ACPI table. For
1826 example, to map UART-HID:UID AMD0020:0 to
1827 PCI device 00:14.5 write the parameter as:
1828 ivrs_acpihid[00:14.5]=AMD0020:0
1830 js= [HW,JOY] Analog joystick
1831 See Documentation/input/joystick.txt.
1833 nokaslr [KNL]
1834 When CONFIG_RANDOMIZE_BASE is set, this disables
1835 kernel and module base offset ASLR (Address Space
1836 Layout Randomization).
1838 keepinitrd [HW,ARM]
1840 kernelcore= [KNL,X86,IA-64,PPC]
1841 Format: nn[KMGTPE] | "mirror"
1842 This parameter
1843 specifies the amount of memory usable by the kernel
1844 for non-movable allocations. The requested amount is
1845 spread evenly throughout all nodes in the system. The
1846 remaining memory in each node is used for Movable
1847 pages. In the event, a node is too small to have both
1848 kernelcore and Movable pages, kernelcore pages will
1849 take priority and other nodes will have a larger number
1850 of Movable pages. The Movable zone is used for the
1851 allocation of pages that may be reclaimed or moved
1852 by the page migration subsystem. This means that
1853 HugeTLB pages may not be allocated from this zone.
1854 Note that allocations like PTEs-from-HighMem still
1855 use the HighMem zone if it exists, and the Normal
1856 zone if it does not.
1858 Instead of specifying the amount of memory (nn[KMGTPE]),
1859 you can specify "mirror" option. In case "mirror"
1860 option is specified, mirrored (reliable) memory is used
1861 for non-movable allocations and remaining memory is used
1862 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1863 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1864 time.
1866 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1867 Format: <Controller#>[,poll interval]
1868 The controller # is the number of the ehci usb debug
1869 port as it is probed via PCI. The poll interval is
1870 optional and is the number seconds in between
1871 each poll cycle to the debug port in case you need
1872 the functionality for interrupting the kernel with
1873 gdb or control-c on the dbgp connection. When
1874 not using this parameter you use sysrq-g to break into
1875 the kernel debugger.
1877 kgdboc= [KGDB,HW] kgdb over consoles.
1878 Requires a tty driver that supports console polling,
1879 or a supported polling keyboard driver (non-usb).
1880 Serial only format: <serial_device>[,baud]
1881 keyboard only format: kbd
1882 keyboard and serial format: kbd,<serial_device>[,baud]
1883 Optional Kernel mode setting:
1884 kms, kbd format: kms,kbd
1885 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1887 kgdbwait [KGDB] Stop kernel execution and enter the
1888 kernel debugger at the earliest opportunity.
1890 kmac= [MIPS] korina ethernet MAC address.
1891 Configure the RouterBoard 532 series on-chip
1892 Ethernet adapter MAC address.
1894 kmemleak= [KNL] Boot-time kmemleak enable/disable
1895 Valid arguments: on, off
1896 Default: on
1897 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1898 the default is off.
1900 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1901 Valid arguments: 0, 1, 2
1902 kmemcheck=0 (disabled)
1903 kmemcheck=1 (enabled)
1904 kmemcheck=2 (one-shot mode)
1905 Default: 2 (one-shot mode)
1907 kstack=N [X86] Print N words from the kernel stack
1908 in oops dumps.
1910 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1911 Default is 0 (don't ignore, but inject #GP)
1913 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1914 KVM MMU at runtime.
1915 Default is 0 (off)
1917 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1918 Default is 1 (enabled)
1920 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1921 for all guests.
1922 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1924 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1925 (virtualized MMU) support on capable Intel chips.
1926 Default is 1 (enabled)
1928 kvm-intel.emulate_invalid_guest_state=
1929 [KVM,Intel] Enable emulation of invalid guest states
1930 Default is 0 (disabled)
1932 kvm-intel.flexpriority=
1933 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1934 Default is 1 (enabled)
1936 kvm-intel.nested=
1937 [KVM,Intel] Enable VMX nesting (nVMX).
1938 Default is 0 (disabled)
1940 kvm-intel.unrestricted_guest=
1941 [KVM,Intel] Disable unrestricted guest feature
1942 (virtualized real and unpaged mode) on capable
1943 Intel chips. Default is 1 (enabled)
1945 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1946 feature (tagged TLBs) on capable Intel chips.
1947 Default is 1 (enabled)
1949 l2cr= [PPC]
1951 l3cr= [PPC]
1953 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1954 disabled it.
1956 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1957 value for LAPIC timer one-shot implementation. Default
1958 back to the programmable timer unit in the LAPIC.
1960 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1961 in C2 power state.
1963 libata.dma= [LIBATA] DMA control
1964 libata.dma=0 Disable all PATA and SATA DMA
1965 libata.dma=1 PATA and SATA Disk DMA only
1966 libata.dma=2 ATAPI (CDROM) DMA only
1967 libata.dma=4 Compact Flash DMA only
1968 Combinations also work, so libata.dma=3 enables DMA
1969 for disks and CDROMs, but not CFs.
1971 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1972 libata.ignore_hpa=0 keep BIOS limits (default)
1973 libata.ignore_hpa=1 ignore limits, using full disk
1975 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1976 when set.
1977 Format: <int>
1979 libata.force= [LIBATA] Force configurations. The format is comma
1980 separated list of "[ID:]VAL" where ID is
1981 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1982 matching port, link or device. Basically, it matches
1983 the ATA ID string printed on console by libata. If
1984 the whole ID part is omitted, the last PORT and DEVICE
1985 values are used. If ID hasn't been specified yet, the
1986 configuration applies to all ports, links and devices.
1988 If only DEVICE is omitted, the parameter applies to
1989 the port and all links and devices behind it. DEVICE
1990 number of 0 either selects the first device or the
1991 first fan-out link behind PMP device. It does not
1992 select the host link. DEVICE number of 15 selects the
1993 host link and device attached to it.
1995 The VAL specifies the configuration to force. As long
1996 as there's no ambiguity shortcut notation is allowed.
1997 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1998 The following configurations can be forced.
2000 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2001 Any ID with matching PORT is used.
2003 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2005 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2006 udma[/][16,25,33,44,66,100,133] notation is also
2007 allowed.
2009 * [no]ncq: Turn on or off NCQ.
2011 * [no]ncqtrim: Turn off queued DSM TRIM.
2013 * nohrst, nosrst, norst: suppress hard, soft
2014 and both resets.
2016 * rstonce: only attempt one reset during
2017 hot-unplug link recovery
2019 * dump_id: dump IDENTIFY data.
2021 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2023 * disable: Disable this device.
2025 If there are multiple matching configurations changing
2026 the same attribute, the last one is used.
2028 memblock=debug [KNL] Enable memblock debug messages.
2030 load_ramdisk= [RAM] List of ramdisks to load from floppy
2031 See Documentation/blockdev/ramdisk.txt.
2033 lockd.nlm_grace_period=P [NFS] Assign grace period.
2034 Format: <integer>
2036 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2037 Format: <integer>
2039 lockd.nlm_timeout=T [NFS] Assign timeout value.
2040 Format: <integer>
2042 lockd.nlm_udpport=M [NFS] Assign UDP port.
2043 Format: <integer>
2045 locktorture.nreaders_stress= [KNL]
2046 Set the number of locking read-acquisition kthreads.
2047 Defaults to being automatically set based on the
2048 number of online CPUs.
2050 locktorture.nwriters_stress= [KNL]
2051 Set the number of locking write-acquisition kthreads.
2053 locktorture.onoff_holdoff= [KNL]
2054 Set time (s) after boot for CPU-hotplug testing.
2056 locktorture.onoff_interval= [KNL]
2057 Set time (s) between CPU-hotplug operations, or
2058 zero to disable CPU-hotplug testing.
2060 locktorture.shuffle_interval= [KNL]
2061 Set task-shuffle interval (jiffies). Shuffling
2062 tasks allows some CPUs to go into dyntick-idle
2063 mode during the locktorture test.
2065 locktorture.shutdown_secs= [KNL]
2066 Set time (s) after boot system shutdown. This
2067 is useful for hands-off automated testing.
2069 locktorture.stat_interval= [KNL]
2070 Time (s) between statistics printk()s.
2072 locktorture.stutter= [KNL]
2073 Time (s) to stutter testing, for example,
2074 specifying five seconds causes the test to run for
2075 five seconds, wait for five seconds, and so on.
2076 This tests the locking primitive's ability to
2077 transition abruptly to and from idle.
2079 locktorture.torture_runnable= [BOOT]
2080 Start locktorture running at boot time.
2082 locktorture.torture_type= [KNL]
2083 Specify the locking implementation to test.
2085 locktorture.verbose= [KNL]
2086 Enable additional printk() statements.
2088 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2089 Format: <irq>
2091 loglevel= All Kernel Messages with a loglevel smaller than the
2092 console loglevel will be printed to the console. It can
2093 also be changed with klogd or other programs. The
2094 loglevels are defined as follows:
2096 0 (KERN_EMERG) system is unusable
2097 1 (KERN_ALERT) action must be taken immediately
2098 2 (KERN_CRIT) critical conditions
2099 3 (KERN_ERR) error conditions
2100 4 (KERN_WARNING) warning conditions
2101 5 (KERN_NOTICE) normal but significant condition
2102 6 (KERN_INFO) informational
2103 7 (KERN_DEBUG) debug-level messages
2105 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2106 in bytes. n must be a power of two and greater
2107 than the minimal size. The minimal size is defined
2108 by LOG_BUF_SHIFT kernel config parameter. There is
2109 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2110 that allows to increase the default size depending on
2111 the number of CPUs. See init/Kconfig for more details.
2113 logo.nologo [FB] Disables display of the built-in Linux logo.
2114 This may be used to provide more screen space for
2115 kernel log messages and is useful when debugging
2116 kernel boot problems.
2118 lp=0 [LP] Specify parallel ports to use, e.g,
2119 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2120 lp=reset first parallel port). 'lp=0' disables the
2121 lp=auto printer driver. 'lp=reset' (which can be
2122 specified in addition to the ports) causes
2123 attached printers to be reset. Using
2124 lp=port1,port2,... specifies the parallel ports
2125 to associate lp devices with, starting with
2126 lp0. A port specification may be 'none' to skip
2127 that lp device, or a parport name such as
2128 'parport0'. Specifying 'lp=auto' instead of a
2129 port specification list means that device IDs
2130 from each port should be examined, to see if
2131 an IEEE 1284-compliant printer is attached; if
2132 so, the driver will manage that printer.
2133 See also header of drivers/char/lp.c.
2135 lpj=n [KNL]
2136 Sets loops_per_jiffy to given constant, thus avoiding
2137 time-consuming boot-time autodetection (up to 250 ms per
2138 CPU). 0 enables autodetection (default). To determine
2139 the correct value for your kernel, boot with normal
2140 autodetection and see what value is printed. Note that
2141 on SMP systems the preset will be applied to all CPUs,
2142 which is likely to cause problems if your CPUs need
2143 significantly divergent settings. An incorrect value
2144 will cause delays in the kernel to be wrong, leading to
2145 unpredictable I/O errors and other breakage. Although
2146 unlikely, in the extreme case this might damage your
2147 hardware.
2149 ltpc= [NET]
2150 Format: <io>,<irq>,<dma>
2152 machvec= [IA-64] Force the use of a particular machine-vector
2153 (machvec) in a generic kernel.
2154 Example: machvec=hpzx1_swiotlb
2156 machtype= [Loongson] Share the same kernel image file between different
2157 yeeloong laptop.
2158 Example: machtype=lemote-yeeloong-2f-7inch
2160 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2161 than or equal to this physical address is ignored.
2163 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2164 should make use of. maxcpus=n : n >= 0 limits the
2165 kernel to using 'n' processors. n=0 is a special case,
2166 it is equivalent to "nosmp", which also disables
2167 the IO APIC.
2169 max_loop= [LOOP] The number of loop block devices that get
2170 (loop.max_loop) unconditionally pre-created at init time. The default
2171 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2172 of statically allocating a predefined number, loop
2173 devices can be requested on-demand with the
2174 /dev/loop-control interface.
2176 mce [X86-32] Machine Check Exception
2178 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2180 md= [HW] RAID subsystems devices and level
2181 See Documentation/md.txt.
2183 mdacon= [MDA]
2184 Format: <first>,<last>
2185 Specifies range of consoles to be captured by the MDA.
2187 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2188 Amount of memory to be used when the kernel is not able
2189 to see the whole system memory or for test.
2190 [X86] Work as limiting max address. Use together
2191 with memmap= to avoid physical address space collisions.
2192 Without memmap= PCI devices could be placed at addresses
2193 belonging to unused RAM.
2195 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2196 memory.
2198 memchunk=nn[KMG]
2199 [KNL,SH] Allow user to override the default size for
2200 per-device physically contiguous DMA buffers.
2202 memhp_default_state=online/offline
2203 [KNL] Set the initial state for the memory hotplug
2204 onlining policy. If not specified, the default value is
2205 set according to the
2206 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2207 option.
2208 See Documentation/memory-hotplug.txt.
2210 memmap=exactmap [KNL,X86] Enable setting of an exact
2211 E820 memory map, as specified by the user.
2212 Such memmap=exactmap lines can be constructed based on
2213 BIOS output or other requirements. See the memmap=nn@ss
2214 option description.
2216 memmap=nn[KMG]@ss[KMG]
2217 [KNL] Force usage of a specific region of memory.
2218 Region of memory to be used is from ss to ss+nn.
2220 memmap=nn[KMG]#ss[KMG]
2221 [KNL,ACPI] Mark specific memory as ACPI data.
2222 Region of memory to be marked is from ss to ss+nn.
2224 memmap=nn[KMG]$ss[KMG]
2225 [KNL,ACPI] Mark specific memory as reserved.
2226 Region of memory to be reserved is from ss to ss+nn.
2227 Example: Exclude memory from 0x18690000-0x1869ffff
2228 memmap=64K$0x18690000
2229 or
2230 memmap=0x10000$0x18690000
2232 memmap=nn[KMG]!ss[KMG]
2233 [KNL,X86] Mark specific memory as protected.
2234 Region of memory to be used, from ss to ss+nn.
2235 The memory region may be marked as e820 type 12 (0xc)
2236 and is NVDIMM or ADR memory.
2238 memory_corruption_check=0/1 [X86]
2239 Some BIOSes seem to corrupt the first 64k of
2240 memory when doing things like suspend/resume.
2241 Setting this option will scan the memory
2242 looking for corruption. Enabling this will
2243 both detect corruption and prevent the kernel
2244 from using the memory being corrupted.
2245 However, its intended as a diagnostic tool; if
2246 repeatable BIOS-originated corruption always
2247 affects the same memory, you can use memmap=
2248 to prevent the kernel from using that memory.
2250 memory_corruption_check_size=size [X86]
2251 By default it checks for corruption in the low
2252 64k, making this memory unavailable for normal
2253 use. Use this parameter to scan for
2254 corruption in more or less memory.
2256 memory_corruption_check_period=seconds [X86]
2257 By default it checks for corruption every 60
2258 seconds. Use this parameter to check at some
2259 other rate. 0 disables periodic checking.
2261 memtest= [KNL,X86,ARM] Enable memtest
2262 Format: <integer>
2263 default : 0 <disable>
2264 Specifies the number of memtest passes to be
2265 performed. Each pass selects another test
2266 pattern from a given set of patterns. Memtest
2267 fills the memory with this pattern, validates
2268 memory contents and reserves bad memory
2269 regions that are detected.
2271 meye.*= [HW] Set MotionEye Camera parameters
2272 See Documentation/video4linux/meye.txt.
2274 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2275 Multi-Function General Purpose Timers on AMD Geode
2276 platforms.
2278 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2279 the BIOS has incorrectly applied a workaround. TinyBIOS
2280 version 0.98 is known to be affected, 0.99 fixes the
2281 problem by letting the user disable the workaround.
2283 mga= [HW,DRM]
2285 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2286 physical address is ignored.
2288 mini2440= [ARM,HW,KNL]
2289 Format:[0..2][b][c][t]
2290 Default: "0tb"
2291 MINI2440 configuration specification:
2292 0 - The attached screen is the 3.5" TFT
2293 1 - The attached screen is the 7" TFT
2294 2 - The VGA Shield is attached (1024x768)
2295 Leaving out the screen size parameter will not load
2296 the TFT driver, and the framebuffer will be left
2297 unconfigured.
2298 b - Enable backlight. The TFT backlight pin will be
2299 linked to the kernel VESA blanking code and a GPIO
2300 LED. This parameter is not necessary when using the
2301 VGA shield.
2302 c - Enable the s3c camera interface.
2303 t - Reserved for enabling touchscreen support. The
2304 touchscreen support is not enabled in the mainstream
2305 kernel as of 2.6.30, a preliminary port can be found
2306 in the "bleeding edge" mini2440 support kernel at
2307 http://repo.or.cz/w/linux-2.6/mini2440.git
2309 mminit_loglevel=
2310 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2311 parameter allows control of the logging verbosity for
2312 the additional memory initialisation checks. A value
2313 of 0 disables mminit logging and a level of 4 will
2314 log everything. Information is printed at KERN_DEBUG
2315 so loglevel=8 may also need to be specified.
2317 module.sig_enforce
2318 [KNL] When CONFIG_MODULE_SIG is set, this means that
2319 modules without (valid) signatures will fail to load.
2320 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2321 is always true, so this option does nothing.
2323 module_blacklist= [KNL] Do not load a comma-separated list of
2324 modules. Useful for debugging problem modules.
2326 mousedev.tap_time=
2327 [MOUSE] Maximum time between finger touching and
2328 leaving touchpad surface for touch to be considered
2329 a tap and be reported as a left button click (for
2330 touchpads working in absolute mode only).
2331 Format: <msecs>
2332 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2333 reporting absolute coordinates, such as tablets
2334 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2335 reporting absolute coordinates, such as tablets
2337 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2338 is similar to kernelcore except it specifies the
2339 amount of memory used for migratable allocations.
2340 If both kernelcore and movablecore is specified,
2341 then kernelcore will be at *least* the specified
2342 value but may be more. If movablecore on its own
2343 is specified, the administrator must be careful
2344 that the amount of memory usable for all allocations
2345 is not too small.
2347 movable_node [KNL,X86] Boot-time switch to enable the effects
2348 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2350 MTD_Partition= [MTD]
2351 Format: <name>,<region-number>,<size>,<offset>
2353 MTD_Region= [MTD] Format:
2354 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2356 mtdparts= [MTD]
2357 See drivers/mtd/cmdlinepart.c.
2359 multitce=off [PPC] This parameter disables the use of the pSeries
2360 firmware feature for updating multiple TCE entries
2361 at a time.
2363 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2365 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2367 boundary - index of last SLC block on Flex-OneNAND.
2368 The remaining blocks are configured as MLC blocks.
2369 lock - Configure if Flex-OneNAND boundary should be locked.
2370 Once locked, the boundary cannot be changed.
2371 1 indicates lock status, 0 indicates unlock status.
2373 mtdset= [ARM]
2374 ARM/S3C2412 JIVE boot control
2376 See arch/arm/mach-s3c2412/mach-jive.c
2378 mtouchusb.raw_coordinates=
2379 [HW] Make the MicroTouch USB driver use raw coordinates
2380 ('y', default) or cooked coordinates ('n')
2382 mtrr_chunk_size=nn[KMG] [X86]
2383 used for mtrr cleanup. It is largest continuous chunk
2384 that could hold holes aka. UC entries.
2386 mtrr_gran_size=nn[KMG] [X86]
2387 Used for mtrr cleanup. It is granularity of mtrr block.
2388 Default is 1.
2389 Large value could prevent small alignment from
2390 using up MTRRs.
2392 mtrr_spare_reg_nr=n [X86]
2393 Format: <integer>
2394 Range: 0,7 : spare reg number
2395 Default : 1
2396 Used for mtrr cleanup. It is spare mtrr entries number.
2397 Set to 2 or more if your graphical card needs more.
2399 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2401 netdev= [NET] Network devices parameters
2402 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2403 Note that mem_start is often overloaded to mean
2404 something different and driver-specific.
2405 This usage is only documented in each driver source
2406 file if at all.
2408 nf_conntrack.acct=
2409 [NETFILTER] Enable connection tracking flow accounting
2410 0 to disable accounting
2411 1 to enable accounting
2412 Default value is 0.
2414 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2415 See Documentation/filesystems/nfs/nfsroot.txt.
2417 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2418 See Documentation/filesystems/nfs/nfsroot.txt.
2420 nfsrootdebug [NFS] enable nfsroot debugging messages.
2421 See Documentation/filesystems/nfs/nfsroot.txt.
2423 nfs.callback_tcpport=
2424 [NFS] set the TCP port on which the NFSv4 callback
2425 channel should listen.
2427 nfs.cache_getent=
2428 [NFS] sets the pathname to the program which is used
2429 to update the NFS client cache entries.
2431 nfs.cache_getent_timeout=
2432 [NFS] sets the timeout after which an attempt to
2433 update a cache entry is deemed to have failed.
2435 nfs.idmap_cache_timeout=
2436 [NFS] set the maximum lifetime for idmapper cache
2437 entries.
2439 nfs.enable_ino64=
2440 [NFS] enable 64-bit inode numbers.
2441 If zero, the NFS client will fake up a 32-bit inode
2442 number for the readdir() and stat() syscalls instead
2443 of returning the full 64-bit number.
2444 The default is to return 64-bit inode numbers.
2446 nfs.max_session_slots=
2447 [NFSv4.1] Sets the maximum number of session slots
2448 the client will attempt to negotiate with the server.
2449 This limits the number of simultaneous RPC requests
2450 that the client can send to the NFSv4.1 server.
2451 Note that there is little point in setting this
2452 value higher than the max_tcp_slot_table_limit.
2454 nfs.nfs4_disable_idmapping=
2455 [NFSv4] When set to the default of '1', this option
2456 ensures that both the RPC level authentication
2457 scheme and the NFS level operations agree to use
2458 numeric uids/gids if the mount is using the
2459 'sec=sys' security flavour. In effect it is
2460 disabling idmapping, which can make migration from
2461 legacy NFSv2/v3 systems to NFSv4 easier.
2462 Servers that do not support this mode of operation
2463 will be autodetected by the client, and it will fall
2464 back to using the idmapper.
2465 To turn off this behaviour, set the value to '0'.
2466 nfs.nfs4_unique_id=
2467 [NFS4] Specify an additional fixed unique ident-
2468 ification string that NFSv4 clients can insert into
2469 their nfs_client_id4 string. This is typically a
2470 UUID that is generated at system install time.
2472 nfs.send_implementation_id =
2473 [NFSv4.1] Send client implementation identification
2474 information in exchange_id requests.
2475 If zero, no implementation identification information
2476 will be sent.
2477 The default is to send the implementation identification
2478 information.
2480 nfs.recover_lost_locks =
2481 [NFSv4] Attempt to recover locks that were lost due
2482 to a lease timeout on the server. Please note that
2483 doing this risks data corruption, since there are
2484 no guarantees that the file will remain unchanged
2485 after the locks are lost.
2486 If you want to enable the kernel legacy behaviour of
2487 attempting to recover these locks, then set this
2488 parameter to '1'.
2489 The default parameter value of '0' causes the kernel
2490 not to attempt recovery of lost locks.
2492 nfs4.layoutstats_timer =
2493 [NFSv4.2] Change the rate at which the kernel sends
2494 layoutstats to the pNFS metadata server.
2496 Setting this to value to 0 causes the kernel to use
2497 whatever value is the default set by the layout
2498 driver. A non-zero value sets the minimum interval
2499 in seconds between layoutstats transmissions.
2501 nfsd.nfs4_disable_idmapping=
2502 [NFSv4] When set to the default of '1', the NFSv4
2503 server will return only numeric uids and gids to
2504 clients using auth_sys, and will accept numeric uids
2505 and gids from such clients. This is intended to ease
2506 migration from NFSv2/v3.
2508 objlayoutdriver.osd_login_prog=
2509 [NFS] [OBJLAYOUT] sets the pathname to the program which
2510 is used to automatically discover and login into new
2511 osd-targets. Please see:
2512 Documentation/filesystems/pnfs.txt for more explanations
2514 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2515 when a NMI is triggered.
2516 Format: [state][,regs][,debounce][,die]
2518 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2519 Format: [panic,][nopanic,][num]
2520 Valid num: 0 or 1
2521 0 - turn hardlockup detector in nmi_watchdog off
2522 1 - turn hardlockup detector in nmi_watchdog on
2523 When panic is specified, panic when an NMI watchdog
2524 timeout occurs (or 'nopanic' to override the opposite
2525 default). To disable both hard and soft lockup detectors,
2526 please see 'nowatchdog'.
2527 This is useful when you use a panic=... timeout and
2528 need the box quickly up again.
2530 netpoll.carrier_timeout=
2531 [NET] Specifies amount of time (in seconds) that
2532 netpoll should wait for a carrier. By default netpoll
2533 waits 4 seconds.
2535 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2536 emulation library even if a 387 maths coprocessor
2537 is present.
2539 no_console_suspend
2540 [HW] Never suspend the console
2541 Disable suspending of consoles during suspend and
2542 hibernate operations. Once disabled, debugging
2543 messages can reach various consoles while the rest
2544 of the system is being put to sleep (ie, while
2545 debugging driver suspend/resume hooks). This may
2546 not work reliably with all consoles, but is known
2547 to work with serial and VGA consoles.
2548 To facilitate more flexible debugging, we also add
2549 console_suspend, a printk module parameter to control
2550 it. Users could use console_suspend (usually
2551 /sys/module/printk/parameters/console_suspend) to
2552 turn on/off it dynamically.
2554 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2555 caches in the slab allocator. Saves per-node memory,
2556 but will impact performance.
2558 noalign [KNL,ARM]
2560 noapic [SMP,APIC] Tells the kernel to not make use of any
2561 IOAPICs that may be present in the system.
2563 noautogroup Disable scheduler automatic task group creation.
2565 nobats [PPC] Do not use BATs for mapping kernel lowmem
2566 on "Classic" PPC cores.
2568 nocache [ARM]
2570 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2572 nodelayacct [KNL] Disable per-task delay accounting
2574 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2576 nodsp [SH] Disable hardware DSP at boot time.
2578 noefi Disable EFI runtime services support.
2580 noexec [IA-64]
2582 noexec [X86]
2583 On X86-32 available only on PAE configured kernels.
2584 noexec=on: enable non-executable mappings (default)
2585 noexec=off: disable non-executable mappings
2587 nosmap [X86]
2588 Disable SMAP (Supervisor Mode Access Prevention)
2589 even if it is supported by processor.
2591 nosmep [X86]
2592 Disable SMEP (Supervisor Mode Execution Prevention)
2593 even if it is supported by processor.
2595 noexec32 [X86-64]
2596 This affects only 32-bit executables.
2597 noexec32=on: enable non-executable mappings (default)
2598 read doesn't imply executable mappings
2599 noexec32=off: disable non-executable mappings
2600 read implies executable mappings
2602 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2604 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2605 register save and restore. The kernel will only save
2606 legacy floating-point registers on task switch.
2608 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2610 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2611 Equivalent to smt=1.
2613 noxsave [BUGS=X86] Disables x86 extended register state save
2614 and restore using xsave. The kernel will fallback to
2615 enabling legacy floating-point and sse state.
2617 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2618 register states. The kernel will fall back to use
2619 xsave to save the states. By using this parameter,
2620 performance of saving the states is degraded because
2621 xsave doesn't support modified optimization while
2622 xsaveopt supports it on xsaveopt enabled systems.
2624 noxsaves [X86] Disables xsaves and xrstors used in saving and
2625 restoring x86 extended register state in compacted
2626 form of xsave area. The kernel will fall back to use
2627 xsaveopt and xrstor to save and restore the states
2628 in standard form of xsave area. By using this
2629 parameter, xsave area per process might occupy more
2630 memory on xsaves enabled systems.
2632 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2633 wfi(ARM) instruction doesn't work correctly and not to
2634 use it. This is also useful when using JTAG debugger.
2636 no_file_caps Tells the kernel not to honor file capabilities. The
2637 only way then for a file to be executed with privilege
2638 is to be setuid root or executed by root.
2640 nohalt [IA-64] Tells the kernel not to use the power saving
2641 function PAL_HALT_LIGHT when idle. This increases
2642 power-consumption. On the positive side, it reduces
2643 interrupt wake-up latency, which may improve performance
2644 in certain environments such as networked servers or
2645 real-time systems.
2647 nohibernate [HIBERNATION] Disable hibernation and resume.
2649 nohz= [KNL] Boottime enable/disable dynamic ticks
2650 Valid arguments: on, off
2651 Default: on
2653 nohz_full= [KNL,BOOT]
2654 In kernels built with CONFIG_NO_HZ_FULL=y, set
2655 the specified list of CPUs whose tick will be stopped
2656 whenever possible. The boot CPU will be forced outside
2657 the range to maintain the timekeeping.
2658 The CPUs in this range must also be included in the
2659 rcu_nocbs= set.
2661 noiotrap [SH] Disables trapped I/O port accesses.
2663 noirqdebug [X86-32] Disables the code which attempts to detect and
2664 disable unhandled interrupt sources.
2666 no_timer_check [X86,APIC] Disables the code which tests for
2667 broken timer IRQ sources.
2669 noisapnp [ISAPNP] Disables ISA PnP code.
2671 noinitrd [RAM] Tells the kernel not to load any configured
2672 initial RAM disk.
2674 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2675 remapping.
2676 [Deprecated - use intremap=off]
2678 nointroute [IA-64]
2680 noinvpcid [X86] Disable the INVPCID cpu feature.
2682 nojitter [IA-64] Disables jitter checking for ITC timers.
2684 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2686 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2687 fault handling.
2689 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2690 steal time is computed, but won't influence scheduler
2691 behaviour
2693 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2695 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2697 noltlbs [PPC] Do not use large page/tlb entries for kernel
2698 lowmem mapping on PPC40x and PPC8xx
2700 nomca [IA-64] Disable machine check abort handling
2702 nomce [X86-32] Disable Machine Check Exception
2704 nomfgpt [X86-32] Disable Multi-Function General Purpose
2705 Timer usage (for AMD Geode machines).
2707 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2708 shutdown the other cpus. Instead use the REBOOT_VECTOR
2709 irq.
2711 nomodule Disable module load
2713 nopat [X86] Disable PAT (page attribute table extension of
2714 pagetables) support.
2716 norandmaps Don't use address space randomization. Equivalent to
2717 echo 0 > /proc/sys/kernel/randomize_va_space
2719 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2721 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2722 with UP alternatives
2724 nordrand [X86] Disable kernel use of the RDRAND and
2725 RDSEED instructions even if they are supported
2726 by the processor. RDRAND and RDSEED are still
2727 available to user space applications.
2729 noresume [SWSUSP] Disables resume and restores original swap
2730 space.
2732 no-scroll [VGA] Disables scrollback.
2733 This is required for the Braillex ib80-piezo Braille
2734 reader made by F.H. Papenmeier (Germany).
2736 nosbagart [IA-64]
2738 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2740 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2741 and disable the IO APIC. legacy for "maxcpus=0".
2743 nosoftlockup [KNL] Disable the soft-lockup detector.
2745 nosync [HW,M68K] Disables sync negotiation for all devices.
2747 notsc [BUGS=X86-32] Disable Time Stamp Counter
2749 nowatchdog [KNL] Disable both lockup detectors, i.e.
2750 soft-lockup and NMI watchdog (hard-lockup).
2752 nowb [ARM]
2754 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2756 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2757 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2758 Some features depend on CPU0. Known dependencies are:
2759 1. Resume from suspend/hibernate depends on CPU0.
2760 Suspend/hibernate will fail if CPU0 is offline and you
2761 need to online CPU0 before suspend/hibernate.
2762 2. PIC interrupts also depend on CPU0. CPU0 can't be
2763 removed if a PIC interrupt is detected.
2764 It's said poweroff/reboot may depend on CPU0 on some
2765 machines although I haven't seen such issues so far
2766 after CPU0 is offline on a few tested machines.
2767 If the dependencies are under your control, you can
2768 turn on cpu0_hotplug.
2770 nptcg= [IA-64] Override max number of concurrent global TLB
2771 purges which is reported from either PAL_VM_SUMMARY or
2772 SAL PALO.
2774 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2775 could support. nr_cpus=n : n >= 1 limits the kernel to
2776 supporting 'n' processors. Later in runtime you can not
2777 use hotplug cpu feature to put more cpu back to online.
2778 just like you compile the kernel NR_CPUS=n
2780 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2782 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2783 Allowed values are enable and disable
2785 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2786 one of ['zone', 'node', 'default'] can be specified
2787 This can be set from sysctl after boot.
2788 See Documentation/sysctl/vm.txt for details.
2790 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2791 See Documentation/debugging-via-ohci1394.txt for more
2792 info.
2794 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2795 Rather than timing out after 20 ms if an EC
2796 command is not properly ACKed, override the length
2797 of the timeout. We have interrupts disabled while
2798 waiting for the ACK, so if this is set too high
2799 interrupts *may* be lost!
2801 omap_mux= [OMAP] Override bootloader pin multiplexing.
2802 Format: <mux_mode0.mode_name=value>...
2803 For example, to override I2C bus2:
2804 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2806 oprofile.timer= [HW]
2807 Use timer interrupt instead of performance counters
2809 oprofile.cpu_type= Force an oprofile cpu type
2810 This might be useful if you have an older oprofile
2811 userland or if you want common events.
2812 Format: { arch_perfmon }
2813 arch_perfmon: [X86] Force use of architectural
2814 perfmon on Intel CPUs instead of the
2815 CPU specific event set.
2816 timer: [X86] Force use of architectural NMI
2817 timer mode (see also oprofile.timer
2818 for generic hr timer mode)
2820 oops=panic Always panic on oopses. Default is to just kill the
2821 process, but there is a small probability of
2822 deadlocking the machine.
2823 This will also cause panics on machine check exceptions.
2824 Useful together with panic=30 to trigger a reboot.
2826 OSS [HW,OSS]
2827 See Documentation/sound/oss/oss-parameters.txt
2829 page_owner= [KNL] Boot-time page_owner enabling option.
2830 Storage of the information about who allocated
2831 each page is disabled in default. With this switch,
2832 we can turn it on.
2833 on: enable the feature
2835 page_poison= [KNL] Boot-time parameter changing the state of
2836 poisoning on the buddy allocator.
2837 off: turn off poisoning
2838 on: turn on poisoning
2840 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2841 timeout > 0: seconds before rebooting
2842 timeout = 0: wait forever
2843 timeout < 0: reboot immediately
2844 Format: <timeout>
2846 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2847 on a WARN().
2849 crash_kexec_post_notifiers
2850 Run kdump after running panic-notifiers and dumping
2851 kmsg. This only for the users who doubt kdump always
2852 succeeds in any situation.
2853 Note that this also increases risks of kdump failure,
2854 because some panic notifiers can make the crashed
2855 kernel more unstable.
2857 parkbd.port= [HW] Parallel port number the keyboard adapter is
2858 connected to, default is 0.
2859 Format: <parport#>
2860 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2861 0 for XT, 1 for AT (default is AT).
2862 Format: <mode>
2864 parport= [HW,PPT] Specify parallel ports. 0 disables.
2865 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2866 Use 'auto' to force the driver to use any
2867 IRQ/DMA settings detected (the default is to
2868 ignore detected IRQ/DMA settings because of
2869 possible conflicts). You can specify the base
2870 address, IRQ, and DMA settings; IRQ and DMA
2871 should be numbers, or 'auto' (for using detected
2872 settings on that particular port), or 'nofifo'
2873 (to avoid using a FIFO even if it is detected).
2874 Parallel ports are assigned in the order they
2875 are specified on the command line, starting
2876 with parport0.
2878 parport_init_mode= [HW,PPT]
2879 Configure VIA parallel port to operate in
2880 a specific mode. This is necessary on Pegasos
2881 computer where firmware has no options for setting
2882 up parallel port mode and sets it to spp.
2883 Currently this function knows 686a and 8231 chips.
2884 Format: [spp|ps2|epp|ecp|ecpepp]
2886 pause_on_oops=
2887 Halt all CPUs after the first oops has been printed for
2888 the specified number of seconds. This is to be used if
2889 your oopses keep scrolling off the screen.
2891 pcbit= [HW,ISDN]
2893 pcd. [PARIDE]
2894 See header of drivers/block/paride/pcd.c.
2895 See also Documentation/blockdev/paride.txt.
2897 pci=option[,option...] [PCI] various PCI subsystem options:
2898 earlydump [X86] dump PCI config space before the kernel
2899 changes anything
2900 off [X86] don't probe for the PCI bus
2901 bios [X86-32] force use of PCI BIOS, don't access
2902 the hardware directly. Use this if your machine
2903 has a non-standard PCI host bridge.
2904 nobios [X86-32] disallow use of PCI BIOS, only direct
2905 hardware access methods are allowed. Use this
2906 if you experience crashes upon bootup and you
2907 suspect they are caused by the BIOS.
2908 conf1 [X86] Force use of PCI Configuration Access
2909 Mechanism 1 (config address in IO port 0xCF8,
2910 data in IO port 0xCFC, both 32-bit).
2911 conf2 [X86] Force use of PCI Configuration Access
2912 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2913 the function, IO port 0xCFA, also 8-bit, sets
2914 bus number. The config space is then accessed
2915 through ports 0xC000-0xCFFF).
2916 See http://wiki.osdev.org/PCI for more info
2917 on the configuration access mechanisms.
2918 noaer [PCIE] If the PCIEAER kernel config parameter is
2919 enabled, this kernel boot option can be used to
2920 disable the use of PCIE advanced error reporting.
2921 nodomains [PCI] Disable support for multiple PCI
2922 root domains (aka PCI segments, in ACPI-speak).
2923 nommconf [X86] Disable use of MMCONFIG for PCI
2924 Configuration
2925 check_enable_amd_mmconf [X86] check for and enable
2926 properly configured MMIO access to PCI
2927 config space on AMD family 10h CPU
2928 nomsi [MSI] If the PCI_MSI kernel config parameter is
2929 enabled, this kernel boot option can be used to
2930 disable the use of MSI interrupts system-wide.
2931 noioapicquirk [APIC] Disable all boot interrupt quirks.
2932 Safety option to keep boot IRQs enabled. This
2933 should never be necessary.
2934 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2935 primary IO-APIC for bridges that cannot disable
2936 boot IRQs. This fixes a source of spurious IRQs
2937 when the system masks IRQs.
2938 noioapicreroute [APIC] Disable workaround that uses the
2939 boot IRQ equivalent of an IRQ that connects to
2940 a chipset where boot IRQs cannot be disabled.
2941 The opposite of ioapicreroute.
2942 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2943 routing table. These calls are known to be buggy
2944 on several machines and they hang the machine
2945 when used, but on other computers it's the only
2946 way to get the interrupt routing table. Try
2947 this option if the kernel is unable to allocate
2948 IRQs or discover secondary PCI buses on your
2949 motherboard.
2950 rom [X86] Assign address space to expansion ROMs.
2951 Use with caution as certain devices share
2952 address decoders between ROMs and other
2953 resources.
2954 norom [X86] Do not assign address space to
2955 expansion ROMs that do not already have
2956 BIOS assigned address ranges.
2957 nobar [X86] Do not assign address space to the
2958 BARs that weren't assigned by the BIOS.
2959 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2960 assigned automatically to PCI devices. You can
2961 make the kernel exclude IRQs of your ISA cards
2962 this way.
2963 pirqaddr=0xAAAAA [X86] Specify the physical address
2964 of the PIRQ table (normally generated
2965 by the BIOS) if it is outside the
2966 F0000h-100000h range.
2967 lastbus=N [X86] Scan all buses thru bus #N. Can be
2968 useful if the kernel is unable to find your
2969 secondary buses and you want to tell it
2970 explicitly which ones they are.
2971 assign-busses [X86] Always assign all PCI bus
2972 numbers ourselves, overriding
2973 whatever the firmware may have done.
2974 usepirqmask [X86] Honor the possible IRQ mask stored
2975 in the BIOS $PIR table. This is needed on
2976 some systems with broken BIOSes, notably
2977 some HP Pavilion N5400 and Omnibook XE3
2978 notebooks. This will have no effect if ACPI
2979 IRQ routing is enabled.
2980 noacpi [X86] Do not use ACPI for IRQ routing
2981 or for PCI scanning.
2982 use_crs [X86] Use PCI host bridge window information
2983 from ACPI. On BIOSes from 2008 or later, this
2984 is enabled by default. If you need to use this,
2985 please report a bug.
2986 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2987 If you need to use this, please report a bug.
2988 routeirq Do IRQ routing for all PCI devices.
2989 This is normally done in pci_enable_device(),
2990 so this option is a temporary workaround
2991 for broken drivers that don't call it.
2992 skip_isa_align [X86] do not align io start addr, so can
2993 handle more pci cards
2994 noearly [X86] Don't do any early type 1 scanning.
2995 This might help on some broken boards which
2996 machine check when some devices' config space
2997 is read. But various workarounds are disabled
2998 and some IOMMU drivers will not work.
2999 bfsort Sort PCI devices into breadth-first order.
3000 This sorting is done to get a device
3001 order compatible with older (<= 2.4) kernels.
3002 nobfsort Don't sort PCI devices into breadth-first order.
3003 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3004 tuning and use the BIOS-configured MPS defaults.
3005 pcie_bus_safe Set every device's MPS to the largest value
3006 supported by all devices below the root complex.
3007 pcie_bus_perf Set device MPS to the largest allowable MPS
3008 based on its parent bus. Also set MRRS (Max
3009 Read Request Size) to the largest supported
3010 value (no larger than the MPS that the device
3011 or bus can support) for best performance.
3012 pcie_bus_peer2peer Set every device's MPS to 128B, which
3013 every device is guaranteed to support. This
3014 configuration allows peer-to-peer DMA between
3015 any pair of devices, possibly at the cost of
3016 reduced performance. This also guarantees
3017 that hot-added devices will work.
3018 cbiosize=nn[KMG] The fixed amount of bus space which is
3019 reserved for the CardBus bridge's IO window.
3020 The default value is 256 bytes.
3021 cbmemsize=nn[KMG] The fixed amount of bus space which is
3022 reserved for the CardBus bridge's memory
3023 window. The default value is 64 megabytes.
3024 resource_alignment=
3025 Format:
3026 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3027 [<order of align>@]pci:<vendor>:<device>\
3028 [:<subvendor>:<subdevice>][; ...]
3029 Specifies alignment and device to reassign
3030 aligned memory resources.
3031 If <order of align> is not specified,
3032 PAGE_SIZE is used as alignment.
3033 PCI-PCI bridge can be specified, if resource
3034 windows need to be expanded.
3035 To specify the alignment for several
3036 instances of a device, the PCI vendor,
3037 device, subvendor, and subdevice may be
3038 specified, e.g., 4096@pci:8086:9c22:103c:198f
3039 ecrc= Enable/disable PCIe ECRC (transaction layer
3040 end-to-end CRC checking).
3041 bios: Use BIOS/firmware settings. This is the
3042 the default.
3043 off: Turn ECRC off
3044 on: Turn ECRC on.
3045 hpiosize=nn[KMG] The fixed amount of bus space which is
3046 reserved for hotplug bridge's IO window.
3047 Default size is 256 bytes.
3048 hpmemsize=nn[KMG] The fixed amount of bus space which is
3049 reserved for hotplug bridge's memory window.
3050 Default size is 2 megabytes.
3051 hpbussize=nn The minimum amount of additional bus numbers
3052 reserved for buses below a hotplug bridge.
3053 Default is 1.
3054 realloc= Enable/disable reallocating PCI bridge resources
3055 if allocations done by BIOS are too small to
3056 accommodate resources required by all child
3057 devices.
3058 off: Turn realloc off
3059 on: Turn realloc on
3060 realloc same as realloc=on
3061 noari do not use PCIe ARI.
3062 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3063 only look for one device below a PCIe downstream
3064 port.
3066 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3067 Management.
3068 off Disable ASPM.
3069 force Enable ASPM even on devices that claim not to support it.
3070 WARNING: Forcing ASPM on may cause system lockups.
3072 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3073 nomsi Do not use MSI for PCI Express Native Hotplug (this
3074 makes all PCIe ports use INTx for hotplug services).
3076 pcie_ports= [PCIE] PCIe ports handling:
3077 auto Ask the BIOS whether or not to use native PCIe services
3078 associated with PCIe ports (PME, hot-plug, AER). Use
3079 them only if that is allowed by the BIOS.
3080 native Use native PCIe services associated with PCIe ports
3081 unconditionally.
3082 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3083 ports driver.
3085 pcie_port_pm= [PCIE] PCIe port power management handling:
3086 off Disable power management of all PCIe ports
3087 force Forcibly enable power management of all PCIe ports
3089 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3090 nomsi Do not use MSI for native PCIe PME signaling (this makes
3091 all PCIe root ports use INTx for all services).
3093 pcmv= [HW,PCMCIA] BadgePAD 4
3095 pd_ignore_unused
3096 [PM]
3097 Keep all power-domains already enabled by bootloader on,
3098 even if no driver has claimed them. This is useful
3099 for debug and development, but should not be
3100 needed on a platform with proper driver support.
3102 pd. [PARIDE]
3103 See Documentation/blockdev/paride.txt.
3105 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3106 boot time.
3107 Format: { 0 | 1 }
3108 See arch/parisc/kernel/pdc_chassis.c
3110 percpu_alloc= Select which percpu first chunk allocator to use.
3111 Currently supported values are "embed" and "page".
3112 Archs may support subset or none of the selections.
3113 See comments in mm/percpu.c for details on each
3114 allocator. This parameter is primarily for debugging
3115 and performance comparison.
3117 pf. [PARIDE]
3118 See Documentation/blockdev/paride.txt.
3120 pg. [PARIDE]
3121 See Documentation/blockdev/paride.txt.
3123 pirq= [SMP,APIC] Manual mp-table setup
3124 See Documentation/x86/i386/IO-APIC.txt.
3126 plip= [PPT,NET] Parallel port network link
3127 Format: { parport<nr> | timid | 0 }
3128 See also Documentation/parport.txt.
3130 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3131 Override pmtimer IOPort with a hex value.
3132 e.g. pmtmr=0x508
3134 pnp.debug=1 [PNP]
3135 Enable PNP debug messages (depends on the
3136 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3137 via /sys/module/pnp/parameters/debug. We always show
3138 current resource usage; turning this on also shows
3139 possible settings and some assignment information.
3141 pnpacpi= [ACPI]
3142 { off }
3144 pnpbios= [ISAPNP]
3145 { on | off | curr | res | no-curr | no-res }
3147 pnp_reserve_irq=
3148 [ISAPNP] Exclude IRQs for the autoconfiguration
3150 pnp_reserve_dma=
3151 [ISAPNP] Exclude DMAs for the autoconfiguration
3153 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3154 Ranges are in pairs (I/O port base and size).
3156 pnp_reserve_mem=
3157 [ISAPNP] Exclude memory regions for the
3158 autoconfiguration.
3159 Ranges are in pairs (memory base and size).
3161 ports= [IP_VS_FTP] IPVS ftp helper module
3162 Default is 21.
3163 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3164 may be specified.
3165 Format: <port>,<port>....
3167 ppc_strict_facility_enable
3168 [PPC] This option catches any kernel floating point,
3169 Altivec, VSX and SPE outside of regions specifically
3170 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3171 There is some performance impact when enabling this.
3173 print-fatal-signals=
3174 [KNL] debug: print fatal signals
3176 If enabled, warn about various signal handling
3177 related application anomalies: too many signals,
3178 too many POSIX.1 timers, fatal signals causing a
3179 coredump - etc.
3181 If you hit the warning due to signal overflow,
3182 you might want to try "ulimit -i unlimited".
3184 default: off.
3186 printk.always_kmsg_dump=
3187 Trigger kmsg_dump for cases other than kernel oops or
3188 panics
3189 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3190 default: disabled
3192 printk.devkmsg={on,off,ratelimit}
3193 Control writing to /dev/kmsg.
3194 on - unlimited logging to /dev/kmsg from userspace
3195 off - logging to /dev/kmsg disabled
3196 ratelimit - ratelimit the logging
3197 Default: ratelimit
3199 printk.time= Show timing data prefixed to each printk message line
3200 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3202 processor.max_cstate= [HW,ACPI]
3203 Limit processor to maximum C-state
3204 max_cstate=9 overrides any DMI blacklist limit.
3206 processor.nocst [HW,ACPI]
3207 Ignore the _CST method to determine C-states,
3208 instead using the legacy FADT method
3210 profile= [KNL] Enable kernel profiling via /proc/profile
3211 Format: [schedule,]<number>
3212 Param: "schedule" - profile schedule points.
3213 Param: <number> - step/bucket size as a power of 2 for
3214 statistical time based profiling.
3215 Param: "sleep" - profile D-state sleeping (millisecs).
3216 Requires CONFIG_SCHEDSTATS
3217 Param: "kvm" - profile VM exits.
3219 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3220 before loading.
3221 See Documentation/blockdev/ramdisk.txt.
3223 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3224 probe for; one of (bare|imps|exps|lifebook|any).
3225 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3226 per second.
3227 psmouse.resetafter= [HW,MOUSE]
3228 Try to reset the device after so many bad packets
3229 (0 = never).
3230 psmouse.resolution=
3231 [HW,MOUSE] Set desired mouse resolution, in dpi.
3232 psmouse.smartscroll=
3233 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3234 0 = disabled, 1 = enabled (default).
3236 pstore.backend= Specify the name of the pstore backend to use
3238 pt. [PARIDE]
3239 See Documentation/blockdev/paride.txt.
3241 pty.legacy_count=
3242 [KNL] Number of legacy pty's. Overwrites compiled-in
3243 default number.
3245 quiet [KNL] Disable most log messages
3247 r128= [HW,DRM]
3249 raid= [HW,RAID]
3250 See Documentation/md.txt.
3252 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3253 See Documentation/blockdev/ramdisk.txt.
3255 rcu_nocbs= [KNL]
3256 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3257 the specified list of CPUs to be no-callback CPUs.
3258 Invocation of these CPUs' RCU callbacks will
3259 be offloaded to "rcuox/N" kthreads created for
3260 that purpose, where "x" is "b" for RCU-bh, "p"
3261 for RCU-preempt, and "s" for RCU-sched, and "N"
3262 is the CPU number. This reduces OS jitter on the
3263 offloaded CPUs, which can be useful for HPC and
3264 real-time workloads. It can also improve energy
3265 efficiency for asymmetric multiprocessors.
3267 rcu_nocb_poll [KNL]
3268 Rather than requiring that offloaded CPUs
3269 (specified by rcu_nocbs= above) explicitly
3270 awaken the corresponding "rcuoN" kthreads,
3271 make these kthreads poll for callbacks.
3272 This improves the real-time response for the
3273 offloaded CPUs by relieving them of the need to
3274 wake up the corresponding kthread, but degrades
3275 energy efficiency by requiring that the kthreads
3276 periodically wake up to do the polling.
3278 rcutree.blimit= [KNL]
3279 Set maximum number of finished RCU callbacks to
3280 process in one batch.
3282 rcutree.dump_tree= [KNL]
3283 Dump the structure of the rcu_node combining tree
3284 out at early boot. This is used for diagnostic
3285 purposes, to verify correct tree setup.
3287 rcutree.gp_cleanup_delay= [KNL]
3288 Set the number of jiffies to delay each step of
3289 RCU grace-period cleanup. This only has effect
3290 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3292 rcutree.gp_init_delay= [KNL]
3293 Set the number of jiffies to delay each step of
3294 RCU grace-period initialization. This only has
3295 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3296 is set.
3298 rcutree.gp_preinit_delay= [KNL]
3299 Set the number of jiffies to delay each step of
3300 RCU grace-period pre-initialization, that is,
3301 the propagation of recent CPU-hotplug changes up
3302 the rcu_node combining tree. This only has effect
3303 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3305 rcutree.rcu_fanout_exact= [KNL]
3306 Disable autobalancing of the rcu_node combining
3307 tree. This is used by rcutorture, and might
3308 possibly be useful for architectures having high
3309 cache-to-cache transfer latencies.
3311 rcutree.rcu_fanout_leaf= [KNL]
3312 Change the number of CPUs assigned to each
3313 leaf rcu_node structure. Useful for very
3314 large systems, which will choose the value 64,
3315 and for NUMA systems with large remote-access
3316 latencies, which will choose a value aligned
3317 with the appropriate hardware boundaries.
3319 rcutree.jiffies_till_sched_qs= [KNL]
3320 Set required age in jiffies for a
3321 given grace period before RCU starts
3322 soliciting quiescent-state help from
3323 rcu_note_context_switch().
3325 rcutree.jiffies_till_first_fqs= [KNL]
3326 Set delay from grace-period initialization to
3327 first attempt to force quiescent states.
3328 Units are jiffies, minimum value is zero,
3329 and maximum value is HZ.
3331 rcutree.jiffies_till_next_fqs= [KNL]
3332 Set delay between subsequent attempts to force
3333 quiescent states. Units are jiffies, minimum
3334 value is one, and maximum value is HZ.
3336 rcutree.kthread_prio= [KNL,BOOT]
3337 Set the SCHED_FIFO priority of the RCU per-CPU
3338 kthreads (rcuc/N). This value is also used for
3339 the priority of the RCU boost threads (rcub/N)
3340 and for the RCU grace-period kthreads (rcu_bh,
3341 rcu_preempt, and rcu_sched). If RCU_BOOST is
3342 set, valid values are 1-99 and the default is 1
3343 (the least-favored priority). Otherwise, when
3344 RCU_BOOST is not set, valid values are 0-99 and
3345 the default is zero (non-realtime operation).
3347 rcutree.rcu_nocb_leader_stride= [KNL]
3348 Set the number of NOCB kthread groups, which
3349 defaults to the square root of the number of
3350 CPUs. Larger numbers reduces the wakeup overhead
3351 on the per-CPU grace-period kthreads, but increases
3352 that same overhead on each group's leader.
3354 rcutree.qhimark= [KNL]
3355 Set threshold of queued RCU callbacks beyond which
3356 batch limiting is disabled.
3358 rcutree.qlowmark= [KNL]
3359 Set threshold of queued RCU callbacks below which
3360 batch limiting is re-enabled.
3362 rcutree.rcu_idle_gp_delay= [KNL]
3363 Set wakeup interval for idle CPUs that have
3364 RCU callbacks (RCU_FAST_NO_HZ=y).
3366 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3367 Set wakeup interval for idle CPUs that have
3368 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3369 Lazy RCU callbacks are those which RCU can
3370 prove do nothing more than free memory.
3372 rcuperf.gp_exp= [KNL]
3373 Measure performance of expedited synchronous
3374 grace-period primitives.
3376 rcuperf.holdoff= [KNL]
3377 Set test-start holdoff period. The purpose of
3378 this parameter is to delay the start of the
3379 test until boot completes in order to avoid
3380 interference.
3382 rcuperf.nreaders= [KNL]
3383 Set number of RCU readers. The value -1 selects
3384 N, where N is the number of CPUs. A value
3385 "n" less than -1 selects N-n+1, where N is again
3386 the number of CPUs. For example, -2 selects N
3387 (the number of CPUs), -3 selects N+1, and so on.
3388 A value of "n" less than or equal to -N selects
3389 a single reader.
3391 rcuperf.nwriters= [KNL]
3392 Set number of RCU writers. The values operate
3393 the same as for rcuperf.nreaders.
3394 N, where N is the number of CPUs
3396 rcuperf.perf_runnable= [BOOT]
3397 Start rcuperf running at boot time.
3399 rcuperf.shutdown= [KNL]
3400 Shut the system down after performance tests
3401 complete. This is useful for hands-off automated
3402 testing.
3404 rcuperf.perf_type= [KNL]
3405 Specify the RCU implementation to test.
3407 rcuperf.verbose= [KNL]
3408 Enable additional printk() statements.
3410 rcutorture.cbflood_inter_holdoff= [KNL]
3411 Set holdoff time (jiffies) between successive
3412 callback-flood tests.
3414 rcutorture.cbflood_intra_holdoff= [KNL]
3415 Set holdoff time (jiffies) between successive
3416 bursts of callbacks within a given callback-flood
3417 test.
3419 rcutorture.cbflood_n_burst= [KNL]
3420 Set the number of bursts making up a given
3421 callback-flood test. Set this to zero to
3422 disable callback-flood testing.
3424 rcutorture.cbflood_n_per_burst= [KNL]
3425 Set the number of callbacks to be registered
3426 in a given burst of a callback-flood test.
3428 rcutorture.fqs_duration= [KNL]
3429 Set duration of force_quiescent_state bursts
3430 in microseconds.
3432 rcutorture.fqs_holdoff= [KNL]
3433 Set holdoff time within force_quiescent_state bursts
3434 in microseconds.
3436 rcutorture.fqs_stutter= [KNL]
3437 Set wait time between force_quiescent_state bursts
3438 in seconds.
3440 rcutorture.gp_cond= [KNL]
3441 Use conditional/asynchronous update-side
3442 primitives, if available.
3444 rcutorture.gp_exp= [KNL]
3445 Use expedited update-side primitives, if available.
3447 rcutorture.gp_normal= [KNL]
3448 Use normal (non-expedited) asynchronous
3449 update-side primitives, if available.
3451 rcutorture.gp_sync= [KNL]
3452 Use normal (non-expedited) synchronous
3453 update-side primitives, if available. If all
3454 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3455 rcutorture.gp_normal=, and rcutorture.gp_sync=
3456 are zero, rcutorture acts as if is interpreted
3457 they are all non-zero.
3459 rcutorture.n_barrier_cbs= [KNL]
3460 Set callbacks/threads for rcu_barrier() testing.
3462 rcutorture.nfakewriters= [KNL]
3463 Set number of concurrent RCU writers. These just
3464 stress RCU, they don't participate in the actual
3465 test, hence the "fake".
3467 rcutorture.nreaders= [KNL]
3468 Set number of RCU readers. The value -1 selects
3469 N-1, where N is the number of CPUs. A value
3470 "n" less than -1 selects N-n-2, where N is again
3471 the number of CPUs. For example, -2 selects N
3472 (the number of CPUs), -3 selects N+1, and so on.
3474 rcutorture.object_debug= [KNL]
3475 Enable debug-object double-call_rcu() testing.
3477 rcutorture.onoff_holdoff= [KNL]
3478 Set time (s) after boot for CPU-hotplug testing.
3480 rcutorture.onoff_interval= [KNL]
3481 Set time (s) between CPU-hotplug operations, or
3482 zero to disable CPU-hotplug testing.
3484 rcutorture.shuffle_interval= [KNL]
3485 Set task-shuffle interval (s). Shuffling tasks
3486 allows some CPUs to go into dyntick-idle mode
3487 during the rcutorture test.
3489 rcutorture.shutdown_secs= [KNL]
3490 Set time (s) after boot system shutdown. This
3491 is useful for hands-off automated testing.
3493 rcutorture.stall_cpu= [KNL]
3494 Duration of CPU stall (s) to test RCU CPU stall
3495 warnings, zero to disable.
3497 rcutorture.stall_cpu_holdoff= [KNL]
3498 Time to wait (s) after boot before inducing stall.
3500 rcutorture.stat_interval= [KNL]
3501 Time (s) between statistics printk()s.
3503 rcutorture.stutter= [KNL]
3504 Time (s) to stutter testing, for example, specifying
3505 five seconds causes the test to run for five seconds,
3506 wait for five seconds, and so on. This tests RCU's
3507 ability to transition abruptly to and from idle.
3509 rcutorture.test_boost= [KNL]
3510 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3511 "Maybe" means test if the RCU implementation
3512 under test support RCU priority boosting.
3514 rcutorture.test_boost_duration= [KNL]
3515 Duration (s) of each individual boost test.
3517 rcutorture.test_boost_interval= [KNL]
3518 Interval (s) between each boost test.
3520 rcutorture.test_no_idle_hz= [KNL]
3521 Test RCU's dyntick-idle handling. See also the
3522 rcutorture.shuffle_interval parameter.
3524 rcutorture.torture_runnable= [BOOT]
3525 Start rcutorture running at boot time.
3527 rcutorture.torture_type= [KNL]
3528 Specify the RCU implementation to test.
3530 rcutorture.verbose= [KNL]
3531 Enable additional printk() statements.
3533 rcupdate.rcu_cpu_stall_suppress= [KNL]
3534 Suppress RCU CPU stall warning messages.
3536 rcupdate.rcu_cpu_stall_timeout= [KNL]
3537 Set timeout for RCU CPU stall warning messages.
3539 rcupdate.rcu_expedited= [KNL]
3540 Use expedited grace-period primitives, for
3541 example, synchronize_rcu_expedited() instead
3542 of synchronize_rcu(). This reduces latency,
3543 but can increase CPU utilization, degrade
3544 real-time latency, and degrade energy efficiency.
3545 No effect on CONFIG_TINY_RCU kernels.
3547 rcupdate.rcu_normal= [KNL]
3548 Use only normal grace-period primitives,
3549 for example, synchronize_rcu() instead of
3550 synchronize_rcu_expedited(). This improves
3551 real-time latency, CPU utilization, and
3552 energy efficiency, but can expose users to
3553 increased grace-period latency. This parameter
3554 overrides rcupdate.rcu_expedited. No effect on
3555 CONFIG_TINY_RCU kernels.
3557 rcupdate.rcu_normal_after_boot= [KNL]
3558 Once boot has completed (that is, after
3559 rcu_end_inkernel_boot() has been invoked), use
3560 only normal grace-period primitives. No effect
3561 on CONFIG_TINY_RCU kernels.
3563 rcupdate.rcu_task_stall_timeout= [KNL]
3564 Set timeout in jiffies for RCU task stall warning
3565 messages. Disable with a value less than or equal
3566 to zero.
3568 rcupdate.rcu_self_test= [KNL]
3569 Run the RCU early boot self tests
3571 rcupdate.rcu_self_test_bh= [KNL]
3572 Run the RCU bh early boot self tests
3574 rcupdate.rcu_self_test_sched= [KNL]
3575 Run the RCU sched early boot self tests
3577 rdinit= [KNL]
3578 Format: <full_path>
3579 Run specified binary instead of /init from the ramdisk,
3580 used for early userspace startup. See initrd.
3582 reboot= [KNL]
3583 Format (x86 or x86_64):
3584 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3585 [[,]s[mp]#### \
3586 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3587 [[,]f[orce]
3588 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3589 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3590 reboot_force is either force or not specified,
3591 reboot_cpu is s[mp]#### with #### being the processor
3592 to be used for rebooting.
3594 relax_domain_level=
3595 [KNL, SMP] Set scheduler's default relax_domain_level.
3596 See Documentation/cgroup-v1/cpusets.txt.
3598 relative_sleep_states=
3599 [SUSPEND] Use sleep state labeling where the deepest
3600 state available other than hibernation is always "mem".
3601 Format: { "0" | "1" }
3602 0 -- Traditional sleep state labels.
3603 1 -- Relative sleep state labels.
3605 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3607 reservetop= [X86-32]
3608 Format: nn[KMG]
3609 Reserves a hole at the top of the kernel virtual
3610 address space.
3612 reservelow= [X86]
3613 Format: nn[K]
3614 Set the amount of memory to reserve for BIOS at
3615 the bottom of the address space.
3617 reset_devices [KNL] Force drivers to reset the underlying device
3618 during initialization.
3620 resume= [SWSUSP]
3621 Specify the partition device for software suspend
3622 Format:
3623 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3625 resume_offset= [SWSUSP]
3626 Specify the offset from the beginning of the partition
3627 given by "resume=" at which the swap header is located,
3628 in <PAGE_SIZE> units (needed only for swap files).
3629 See Documentation/power/swsusp-and-swap-files.txt
3631 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3632 read the resume files
3634 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3635 Useful for devices that are detected asynchronously
3636 (e.g. USB and MMC devices).
3638 hibernate= [HIBERNATION]
3639 noresume Don't check if there's a hibernation image
3640 present during boot.
3641 nocompress Don't compress/decompress hibernation images.
3642 no Disable hibernation and resume.
3643 protect_image Turn on image protection during restoration
3644 (that will set all pages holding image data
3645 during restoration read-only).
3647 retain_initrd [RAM] Keep initrd memory after extraction
3649 rfkill.default_state=
3650 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3651 etc. communication is blocked by default.
3652 1 Unblocked.
3654 rfkill.master_switch_mode=
3655 0 The "airplane mode" button does nothing.
3656 1 The "airplane mode" button toggles between everything
3657 blocked and the previous configuration.
3658 2 The "airplane mode" button toggles between everything
3659 blocked and everything unblocked.
3661 rhash_entries= [KNL,NET]
3662 Set number of hash buckets for route cache
3664 ro [KNL] Mount root device read-only on boot
3666 rodata= [KNL]
3667 on Mark read-only kernel memory as read-only (default).
3668 off Leave read-only kernel memory writable for debugging.
3670 rockchip.usb_uart
3671 Enable the uart passthrough on the designated usb port
3672 on Rockchip SoCs. When active, the signals of the
3673 debug-uart get routed to the D+ and D- pins of the usb
3674 port and the regular usb controller gets disabled.
3676 root= [KNL] Root filesystem
3677 See name_to_dev_t comment in init/do_mounts.c.
3679 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3680 mount the root filesystem
3682 rootflags= [KNL] Set root filesystem mount option string
3684 rootfstype= [KNL] Set root filesystem type
3686 rootwait [KNL] Wait (indefinitely) for root device to show up.
3687 Useful for devices that are detected asynchronously
3688 (e.g. USB and MMC devices).
3690 rproc_mem=nn[KMG][@address]
3691 [KNL,ARM,CMA] Remoteproc physical memory block.
3692 Memory area to be used by remote processor image,
3693 managed by CMA.
3695 rw [KNL] Mount root device read-write on boot
3697 S [KNL] Run init in single mode
3699 s390_iommu= [HW,S390]
3700 Set s390 IOTLB flushing mode
3701 strict
3702 With strict flushing every unmap operation will result in
3703 an IOTLB flush. Default is lazy flushing before reuse,
3704 which is faster.
3706 sa1100ir [NET]
3707 See drivers/net/irda/sa1100_ir.c.
3709 sbni= [NET] Granch SBNI12 leased line adapter
3711 sched_debug [KNL] Enables verbose scheduler debug messages.
3713 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3714 Allowed values are enable and disable. This feature
3715 incurs a small amount of overhead in the scheduler
3716 but is useful for debugging and performance tuning.
3718 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3719 xtime_lock contention on larger systems, and/or RCU lock
3720 contention on all systems with CONFIG_MAXSMP set.
3721 Format: { "0" | "1" }
3722 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3723 1 -- enable.
3724 Note: increases power consumption, thus should only be
3725 enabled if running jitter sensitive (HPC/RT) workloads.
3727 security= [SECURITY] Choose a security module to enable at boot.
3728 If this boot parameter is not specified, only the first
3729 security module asking for security registration will be
3730 loaded. An invalid security module name will be treated
3731 as if no module has been chosen.
3733 selinux= [SELINUX] Disable or enable SELinux at boot time.
3734 Format: { "0" | "1" }
3735 See security/selinux/Kconfig help text.
3736 0 -- disable.
3737 1 -- enable.
3738 Default value is set via kernel config option.
3739 If enabled at boot time, /selinux/disable can be used
3740 later to disable prior to initial policy load.
3742 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3743 Format: { "0" | "1" }
3744 See security/apparmor/Kconfig help text
3745 0 -- disable.
3746 1 -- enable.
3747 Default value is set via kernel config option.
3749 serialnumber [BUGS=X86-32]
3751 shapers= [NET]
3752 Maximal number of shapers.
3754 show_msr= [x86] show boot-time MSR settings
3755 Format: { <integer> }
3756 Show boot-time (BIOS-initialized) MSR settings.
3757 The parameter means the number of CPUs to show,
3758 for example 1 means boot CPU only.
3760 simeth= [IA-64]
3761 simscsi=
3763 slram= [HW,MTD]
3765 slab_nomerge [MM]
3766 Disable merging of slabs with similar size. May be
3767 necessary if there is some reason to distinguish
3768 allocs to different slabs. Debug options disable
3769 merging on their own.
3770 For more information see Documentation/vm/slub.txt.
3772 slab_max_order= [MM, SLAB]
3773 Determines the maximum allowed order for slabs.
3774 A high setting may cause OOMs due to memory
3775 fragmentation. Defaults to 1 for systems with
3776 more than 32MB of RAM, 0 otherwise.
3778 slub_debug[=options[,slabs]] [MM, SLUB]
3779 Enabling slub_debug allows one to determine the
3780 culprit if slab objects become corrupted. Enabling
3781 slub_debug can create guard zones around objects and
3782 may poison objects when not in use. Also tracks the
3783 last alloc / free. For more information see
3784 Documentation/vm/slub.txt.
3786 slub_max_order= [MM, SLUB]
3787 Determines the maximum allowed order for slabs.
3788 A high setting may cause OOMs due to memory
3789 fragmentation. For more information see
3790 Documentation/vm/slub.txt.
3792 slub_min_objects= [MM, SLUB]
3793 The minimum number of objects per slab. SLUB will
3794 increase the slab order up to slub_max_order to
3795 generate a sufficiently large slab able to contain
3796 the number of objects indicated. The higher the number
3797 of objects the smaller the overhead of tracking slabs
3798 and the less frequently locks need to be acquired.
3799 For more information see Documentation/vm/slub.txt.
3801 slub_min_order= [MM, SLUB]
3802 Determines the minimum page order for slabs. Must be
3803 lower than slub_max_order.
3804 For more information see Documentation/vm/slub.txt.
3806 slub_nomerge [MM, SLUB]
3807 Same with slab_nomerge. This is supported for legacy.
3808 See slab_nomerge for more information.
3810 smart2= [HW]
3811 Format: <io1>[,<io2>[,...,<io8>]]
3813 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3814 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3815 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3816 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3817 smsc-ircc2.ircc_irq= [HW] IRQ line
3818 smsc-ircc2.ircc_dma= [HW] DMA channel
3819 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3820 0: Toshiba Satellite 1800 (GP data pin select)
3821 1: Fast pin select (default)
3822 2: ATC IRMode
3824 smt [KNL,S390] Set the maximum number of threads (logical
3825 CPUs) to use per physical CPU on systems capable of
3826 symmetric multithreading (SMT). Will be capped to the
3827 actual hardware limit.
3828 Format: <integer>
3829 Default: -1 (no limit)
3831 softlockup_panic=
3832 [KNL] Should the soft-lockup detector generate panics.
3833 Format: <integer>
3835 softlockup_all_cpu_backtrace=
3836 [KNL] Should the soft-lockup detector generate
3837 backtraces on all cpus.
3838 Format: <integer>
3840 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3841 See Documentation/laptops/sonypi.txt
3843 spia_io_base= [HW,MTD]
3844 spia_fio_base=
3845 spia_pedr=
3846 spia_peddr=
3848 stacktrace [FTRACE]
3849 Enabled the stack tracer on boot up.
3851 stacktrace_filter=[function-list]
3852 [FTRACE] Limit the functions that the stack tracer
3853 will trace at boot up. function-list is a comma separated
3854 list of functions. This list can be changed at run
3855 time by the stack_trace_filter file in the debugfs
3856 tracing directory. Note, this enables stack tracing
3857 and the stacktrace above is not needed.
3859 sti= [PARISC,HW]
3860 Format: <num>
3861 Set the STI (builtin display/keyboard on the HP-PARISC
3862 machines) console (graphic card) which should be used
3863 as the initial boot-console.
3864 See also comment in drivers/video/console/sticore.c.
3866 sti_font= [HW]
3867 See comment in drivers/video/console/sticore.c.
3869 stifb= [HW]
3870 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3872 sunrpc.min_resvport=
3873 sunrpc.max_resvport=
3874 [NFS,SUNRPC]
3875 SunRPC servers often require that client requests
3876 originate from a privileged port (i.e. a port in the
3877 range 0 < portnr < 1024).
3878 An administrator who wishes to reserve some of these
3879 ports for other uses may adjust the range that the
3880 kernel's sunrpc client considers to be privileged
3881 using these two parameters to set the minimum and
3882 maximum port values.
3884 sunrpc.svc_rpc_per_connection_limit=
3885 [NFS,SUNRPC]
3886 Limit the number of requests that the server will
3887 process in parallel from a single connection.
3888 The default value is 0 (no limit).
3890 sunrpc.pool_mode=
3891 [NFS]
3892 Control how the NFS server code allocates CPUs to
3893 service thread pools. Depending on how many NICs
3894 you have and where their interrupts are bound, this
3895 option will affect which CPUs will do NFS serving.
3896 Note: this parameter cannot be changed while the
3897 NFS server is running.
3899 auto the server chooses an appropriate mode
3900 automatically using heuristics
3901 global a single global pool contains all CPUs
3902 percpu one pool for each CPU
3903 pernode one pool for each NUMA node (equivalent
3904 to global on non-NUMA machines)
3906 sunrpc.tcp_slot_table_entries=
3907 sunrpc.udp_slot_table_entries=
3908 [NFS,SUNRPC]
3909 Sets the upper limit on the number of simultaneous
3910 RPC calls that can be sent from the client to a
3911 server. Increasing these values may allow you to
3912 improve throughput, but will also increase the
3913 amount of memory reserved for use by the client.
3915 suspend.pm_test_delay=
3916 [SUSPEND]
3917 Sets the number of seconds to remain in a suspend test
3918 mode before resuming the system (see
3919 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3920 is set. Default value is 5.
3922 swapaccount=[0|1]
3923 [KNL] Enable accounting of swap in memory resource
3924 controller if no parameter or 1 is given or disable
3925 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
3927 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3928 Format: { <int> | force }
3929 <int> -- Number of I/O TLB slabs
3930 force -- force using of bounce buffers even if they
3931 wouldn't be automatically used by the kernel
3933 switches= [HW,M68k]
3935 sysfs.deprecated=0|1 [KNL]
3936 Enable/disable old style sysfs layout for old udev
3937 on older distributions. When this option is enabled
3938 very new udev will not work anymore. When this option
3939 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3940 in older udev will not work anymore.
3941 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3942 the kernel configuration.
3944 sysrq_always_enabled
3945 [KNL]
3946 Ignore sysrq setting - this boot parameter will
3947 neutralize any effect of /proc/sys/kernel/sysrq.
3948 Useful for debugging.
3950 tcpmhash_entries= [KNL,NET]
3951 Set the number of tcp_metrics_hash slots.
3952 Default value is 8192 or 16384 depending on total
3953 ram pages. This is used to specify the TCP metrics
3954 cache size. See Documentation/networking/ip-sysctl.txt
3955 "tcp_no_metrics_save" section for more details.
3957 tdfx= [HW,DRM]
3959 test_suspend= [SUSPEND][,N]
3960 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3961 standby suspend) or "freeze" (for suspend type freeze)
3962 as the system sleep state during system startup with
3963 the optional capability to repeat N number of times.
3964 The system is woken from this state using a
3965 wakeup-capable RTC alarm.
3967 thash_entries= [KNL,NET]
3968 Set number of hash buckets for TCP connection
3970 thermal.act= [HW,ACPI]
3971 -1: disable all active trip points in all thermal zones
3972 <degrees C>: override all lowest active trip points
3974 thermal.crt= [HW,ACPI]
3975 -1: disable all critical trip points in all thermal zones
3976 <degrees C>: override all critical trip points
3978 thermal.nocrt= [HW,ACPI]
3979 Set to disable actions on ACPI thermal zone
3980 critical and hot trip points.
3982 thermal.off= [HW,ACPI]
3983 1: disable ACPI thermal control
3985 thermal.psv= [HW,ACPI]
3986 -1: disable all passive trip points
3987 <degrees C>: override all passive trip points to this
3988 value
3990 thermal.tzp= [HW,ACPI]
3991 Specify global default ACPI thermal zone polling rate
3992 <deci-seconds>: poll all this frequency
3993 0: no polling (default)
3995 threadirqs [KNL]
3996 Force threading of all interrupt handlers except those
3997 marked explicitly IRQF_NO_THREAD.
3999 tmem [KNL,XEN]
4000 Enable the Transcendent memory driver if built-in.
4002 tmem.cleancache=0|1 [KNL, XEN]
4003 Default is on (1). Disable the usage of the cleancache
4004 API to send anonymous pages to the hypervisor.
4006 tmem.frontswap=0|1 [KNL, XEN]
4007 Default is on (1). Disable the usage of the frontswap
4008 API to send swap pages to the hypervisor. If disabled
4009 the selfballooning and selfshrinking are force disabled.
4011 tmem.selfballooning=0|1 [KNL, XEN]
4012 Default is on (1). Disable the driving of swap pages
4013 to the hypervisor.
4015 tmem.selfshrinking=0|1 [KNL, XEN]
4016 Default is on (1). Partial swapoff that immediately
4017 transfers pages from Xen hypervisor back to the
4018 kernel based on different criteria.
4020 topology= [S390]
4021 Format: {off | on}
4022 Specify if the kernel should make use of the cpu
4023 topology information if the hardware supports this.
4024 The scheduler will make use of this information and
4025 e.g. base its process migration decisions on it.
4026 Default is on.
4028 topology_updates= [KNL, PPC, NUMA]
4029 Format: {off}
4030 Specify if the kernel should ignore (off)
4031 topology updates sent by the hypervisor to this
4032 LPAR.
4034 tp720= [HW,PS2]
4036 tpm_suspend_pcr=[HW,TPM]
4037 Format: integer pcr id
4038 Specify that at suspend time, the tpm driver
4039 should extend the specified pcr with zeros,
4040 as a workaround for some chips which fail to
4041 flush the last written pcr on TPM_SaveState.
4042 This will guarantee that all the other pcrs
4043 are saved.
4045 trace_buf_size=nn[KMG]
4046 [FTRACE] will set tracing buffer size on each cpu.
4048 trace_event=[event-list]
4049 [FTRACE] Set and start specified trace events in order
4050 to facilitate early boot debugging. The event-list is a
4051 comma separated list of trace events to enable. See
4052 also Documentation/trace/events.txt
4054 trace_options=[option-list]
4055 [FTRACE] Enable or disable tracer options at boot.
4056 The option-list is a comma delimited list of options
4057 that can be enabled or disabled just as if you were
4058 to echo the option name into
4060 /sys/kernel/debug/tracing/trace_options
4062 For example, to enable stacktrace option (to dump the
4063 stack trace of each event), add to the command line:
4065 trace_options=stacktrace
4067 See also Documentation/trace/ftrace.txt "trace options"
4068 section.
4070 tp_printk[FTRACE]
4071 Have the tracepoints sent to printk as well as the
4072 tracing ring buffer. This is useful for early boot up
4073 where the system hangs or reboots and does not give the
4074 option for reading the tracing buffer or performing a
4075 ftrace_dump_on_oops.
4077 To turn off having tracepoints sent to printk,
4078 echo 0 > /proc/sys/kernel/tracepoint_printk
4079 Note, echoing 1 into this file without the
4080 tracepoint_printk kernel cmdline option has no effect.
4082 ** CAUTION **
4084 Having tracepoints sent to printk() and activating high
4085 frequency tracepoints such as irq or sched, can cause
4086 the system to live lock.
4088 traceoff_on_warning
4089 [FTRACE] enable this option to disable tracing when a
4090 warning is hit. This turns off "tracing_on". Tracing can
4091 be enabled again by echoing '1' into the "tracing_on"
4092 file located in /sys/kernel/debug/tracing/
4094 This option is useful, as it disables the trace before
4095 the WARNING dump is called, which prevents the trace to
4096 be filled with content caused by the warning output.
4098 This option can also be set at run time via the sysctl
4099 option: kernel/traceoff_on_warning
4101 transparent_hugepage=
4102 [KNL]
4103 Format: [always|madvise|never]
4104 Can be used to control the default behavior of the system
4105 with respect to transparent hugepages.
4106 See Documentation/vm/transhuge.txt for more details.
4108 tsc= Disable clocksource stability checks for TSC.
4109 Format: <string>
4110 [x86] reliable: mark tsc clocksource as reliable, this
4111 disables clocksource verification at runtime, as well
4112 as the stability checks done at bootup. Used to enable
4113 high-resolution timer mode on older hardware, and in
4114 virtualized environment.
4115 [x86] noirqtime: Do not use TSC to do irq accounting.
4116 Used to run time disable IRQ_TIME_ACCOUNTING on any
4117 platforms where RDTSC is slow and this accounting
4118 can add overhead.
4120 turbografx.map[2|3]= [HW,JOY]
4121 TurboGraFX parallel port interface
4122 Format:
4123 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4124 See also Documentation/input/joystick-parport.txt
4126 udbg-immortal [PPC] When debugging early kernel crashes that
4127 happen after console_init() and before a proper
4128 console driver takes over, this boot options might
4129 help "seeing" what's going on.
4131 uhash_entries= [KNL,NET]
4132 Set number of hash buckets for UDP/UDP-Lite connections
4134 uhci-hcd.ignore_oc=
4135 [USB] Ignore overcurrent events (default N).
4136 Some badly-designed motherboards generate lots of
4137 bogus events, for ports that aren't wired to
4138 anything. Set this parameter to avoid log spamming.
4139 Note that genuine overcurrent events won't be
4140 reported either.
4142 unknown_nmi_panic
4143 [X86] Cause panic on unknown NMI.
4145 usbcore.authorized_default=
4146 [USB] Default USB device authorization:
4147 (default -1 = authorized except for wireless USB,
4148 0 = not authorized, 1 = authorized)
4150 usbcore.autosuspend=
4151 [USB] The autosuspend time delay (in seconds) used
4152 for newly-detected USB devices (default 2). This
4153 is the time required before an idle device will be
4154 autosuspended. Devices for which the delay is set
4155 to a negative value won't be autosuspended at all.
4157 usbcore.usbfs_snoop=
4158 [USB] Set to log all usbfs traffic (default 0 = off).
4160 usbcore.usbfs_snoop_max=
4161 [USB] Maximum number of bytes to snoop in each URB
4162 (default = 65536).
4164 usbcore.blinkenlights=
4165 [USB] Set to cycle leds on hubs (default 0 = off).
4167 usbcore.old_scheme_first=
4168 [USB] Start with the old device initialization
4169 scheme (default 0 = off).
4171 usbcore.usbfs_memory_mb=
4172 [USB] Memory limit (in MB) for buffers allocated by
4173 usbfs (default = 16, 0 = max = 2047).
4175 usbcore.use_both_schemes=
4176 [USB] Try the other device initialization scheme
4177 if the first one fails (default 1 = enabled).
4179 usbcore.initial_descriptor_timeout=
4180 [USB] Specifies timeout for the initial 64-byte
4181 USB_REQ_GET_DESCRIPTOR request in milliseconds
4182 (default 5000 = 5.0 seconds).
4184 usbcore.nousb [USB] Disable the USB subsystem
4186 usbhid.mousepoll=
4187 [USBHID] The interval which mice are to be polled at.
4189 usb-storage.delay_use=
4190 [UMS] The delay in seconds before a new device is
4191 scanned for Logical Units (default 1).
4193 usb-storage.quirks=
4194 [UMS] A list of quirks entries to supplement or
4195 override the built-in unusual_devs list. List
4196 entries are separated by commas. Each entry has
4197 the form VID:PID:Flags where VID and PID are Vendor
4198 and Product ID values (4-digit hex numbers) and
4199 Flags is a set of characters, each corresponding
4200 to a common usb-storage quirk flag as follows:
4201 a = SANE_SENSE (collect more than 18 bytes
4202 of sense data);
4203 b = BAD_SENSE (don't collect more than 18
4204 bytes of sense data);
4205 c = FIX_CAPACITY (decrease the reported
4206 device capacity by one sector);
4207 d = NO_READ_DISC_INFO (don't use
4208 READ_DISC_INFO command);
4209 e = NO_READ_CAPACITY_16 (don't use
4210 READ_CAPACITY_16 command);
4211 f = NO_REPORT_OPCODES (don't use report opcodes
4212 command, uas only);
4213 g = MAX_SECTORS_240 (don't transfer more than
4214 240 sectors at a time, uas only);
4215 h = CAPACITY_HEURISTICS (decrease the
4216 reported device capacity by one
4217 sector if the number is odd);
4218 i = IGNORE_DEVICE (don't bind to this
4219 device);
4220 j = NO_REPORT_LUNS (don't use report luns
4221 command, uas only);
4222 l = NOT_LOCKABLE (don't try to lock and
4223 unlock ejectable media);
4224 m = MAX_SECTORS_64 (don't transfer more
4225 than 64 sectors = 32 KB at a time);
4226 n = INITIAL_READ10 (force a retry of the
4227 initial READ(10) command);
4228 o = CAPACITY_OK (accept the capacity
4229 reported by the device);
4230 p = WRITE_CACHE (the device cache is ON
4231 by default);
4232 r = IGNORE_RESIDUE (the device reports
4233 bogus residue values);
4234 s = SINGLE_LUN (the device has only one
4235 Logical Unit);
4236 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4237 commands, uas only);
4238 u = IGNORE_UAS (don't bind to the uas driver);
4239 w = NO_WP_DETECT (don't test whether the
4240 medium is write-protected).
4241 Example: quirks=0419:aaf5:rl,0421:0433:rc
4243 user_debug= [KNL,ARM]
4244 Format: <int>
4245 See arch/arm/Kconfig.debug help text.
4246 1 - undefined instruction events
4247 2 - system calls
4248 4 - invalid data aborts
4249 8 - SIGSEGV faults
4250 16 - SIGBUS faults
4251 Example: user_debug=31
4253 userpte=
4254 [X86] Flags controlling user PTE allocations.
4256 nohigh = do not allocate PTE pages in
4257 HIGHMEM regardless of setting
4258 of CONFIG_HIGHPTE.
4260 vdso= [X86,SH]
4261 On X86_32, this is an alias for vdso32=. Otherwise:
4263 vdso=1: enable VDSO (the default)
4264 vdso=0: disable VDSO mapping
4266 vdso32= [X86] Control the 32-bit vDSO
4267 vdso32=1: enable 32-bit VDSO
4268 vdso32=0 or vdso32=2: disable 32-bit VDSO
4270 See the help text for CONFIG_COMPAT_VDSO for more
4271 details. If CONFIG_COMPAT_VDSO is set, the default is
4272 vdso32=0; otherwise, the default is vdso32=1.
4274 For compatibility with older kernels, vdso32=2 is an
4275 alias for vdso32=0.
4277 Try vdso32=0 if you encounter an error that says:
4278 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4280 vector= [IA-64,SMP]
4281 vector=percpu: enable percpu vector domain
4283 video= [FB] Frame buffer configuration
4284 See Documentation/fb/modedb.txt.
4286 video.brightness_switch_enabled= [0,1]
4287 If set to 1, on receiving an ACPI notify event
4288 generated by hotkey, video driver will adjust brightness
4289 level and then send out the event to user space through
4290 the allocated input device; If set to 0, video driver
4291 will only send out the event without touching backlight
4292 brightness level.
4293 default: 1
4295 virtio_mmio.device=
4296 [VMMIO] Memory mapped virtio (platform) device.
4298 <size>@<baseaddr>:<irq>[:<id>]
4299 where:
4300 <size> := size (can use standard suffixes
4301 like K, M and G)
4302 <baseaddr> := physical base address
4303 <irq> := interrupt number (as passed to
4304 request_irq())
4305 <id> := (optional) platform device id
4306 example:
4307 virtio_mmio.device=1K@0x100b0000:48:7
4309 Can be used multiple times for multiple devices.
4311 vga= [BOOT,X86-32] Select a particular video mode
4312 See Documentation/x86/boot.txt and
4313 Documentation/svga.txt.
4314 Use vga=ask for menu.
4315 This is actually a boot loader parameter; the value is
4316 passed to the kernel using a special protocol.
4318 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4319 size of <nn>. This can be used to increase the
4320 minimum size (128MB on x86). It can also be used to
4321 decrease the size and leave more room for directly
4322 mapped kernel RAM.
4324 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4325 Format: <command>
4327 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4328 Format: <command>
4330 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4331 Format: <command>
4333 vsyscall= [X86-64]
4334 Controls the behavior of vsyscalls (i.e. calls to
4335 fixed addresses of 0xffffffffff600x00 from legacy
4336 code). Most statically-linked binaries and older
4337 versions of glibc use these calls. Because these
4338 functions are at fixed addresses, they make nice
4339 targets for exploits that can control RIP.
4341 emulate [default] Vsyscalls turn into traps and are
4342 emulated reasonably safely.
4344 native Vsyscalls are native syscall instructions.
4345 This is a little bit faster than trapping
4346 and makes a few dynamic recompilers work
4347 better than they would in emulation mode.
4348 It also makes exploits much easier to write.
4350 none Vsyscalls don't work at all. This makes
4351 them quite hard to use for exploits but
4352 might break your system.
4354 vt.color= [VT] Default text color.
4355 Format: 0xYX, X = foreground, Y = background.
4356 Default: 0x07 = light gray on black.
4358 vt.cur_default= [VT] Default cursor shape.
4359 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4360 the parameters of the <Esc>[?A;B;Cc escape sequence;
4361 see VGA-softcursor.txt. Default: 2 = underline.
4363 vt.default_blu= [VT]
4364 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4365 Change the default blue palette of the console.
4366 This is a 16-member array composed of values
4367 ranging from 0-255.
4369 vt.default_grn= [VT]
4370 Format: <green0>,<green1>,<green2>,...,<green15>
4371 Change the default green palette of the console.
4372 This is a 16-member array composed of values
4373 ranging from 0-255.
4375 vt.default_red= [VT]
4376 Format: <red0>,<red1>,<red2>,...,<red15>
4377 Change the default red palette of the console.
4378 This is a 16-member array composed of values
4379 ranging from 0-255.
4381 vt.default_utf8=
4382 [VT]
4383 Format=<0|1>
4384 Set system-wide default UTF-8 mode for all tty's.
4385 Default is 1, i.e. UTF-8 mode is enabled for all
4386 newly opened terminals.
4388 vt.global_cursor_default=
4389 [VT]
4390 Format=<-1|0|1>
4391 Set system-wide default for whether a cursor
4392 is shown on new VTs. Default is -1,
4393 i.e. cursors will be created by default unless
4394 overridden by individual drivers. 0 will hide
4395 cursors, 1 will display them.
4397 vt.italic= [VT] Default color for italic text; 0-15.
4398 Default: 2 = green.
4400 vt.underline= [VT] Default color for underlined text; 0-15.
4401 Default: 3 = cyan.
4403 watchdog timers [HW,WDT] For information on watchdog timers,
4404 see Documentation/watchdog/watchdog-parameters.txt
4405 or other driver-specific files in the
4406 Documentation/watchdog/ directory.
4408 workqueue.watchdog_thresh=
4409 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4410 warn stall conditions and dump internal state to
4411 help debugging. 0 disables workqueue stall
4412 detection; otherwise, it's the stall threshold
4413 duration in seconds. The default value is 30 and
4414 it can be updated at runtime by writing to the
4415 corresponding sysfs file.
4417 workqueue.disable_numa
4418 By default, all work items queued to unbound
4419 workqueues are affine to the NUMA nodes they're
4420 issued on, which results in better behavior in
4421 general. If NUMA affinity needs to be disabled for
4422 whatever reason, this option can be used. Note
4423 that this also can be controlled per-workqueue for
4424 workqueues visible under /sys/bus/workqueue/.
4426 workqueue.power_efficient
4427 Per-cpu workqueues are generally preferred because
4428 they show better performance thanks to cache
4429 locality; unfortunately, per-cpu workqueues tend to
4430 be more power hungry than unbound workqueues.
4432 Enabling this makes the per-cpu workqueues which
4433 were observed to contribute significantly to power
4434 consumption unbound, leading to measurably lower
4435 power usage at the cost of small performance
4436 overhead.
4438 The default value of this parameter is determined by
4439 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4441 workqueue.debug_force_rr_cpu
4442 Workqueue used to implicitly guarantee that work
4443 items queued without explicit CPU specified are put
4444 on the local CPU. This guarantee is no longer true
4445 and while local CPU is still preferred work items
4446 may be put on foreign CPUs. This debug option
4447 forces round-robin CPU selection to flush out
4448 usages which depend on the now broken guarantee.
4449 When enabled, memory and cache locality will be
4450 impacted.
4452 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4453 default x2apic cluster mode on platforms
4454 supporting x2apic.
4456 x86_intel_mid_timer= [X86-32,APBT]
4457 Choose timer option for x86 Intel MID platform.
4458 Two valid options are apbt timer only and lapic timer
4459 plus one apbt timer for broadcast timer.
4460 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4462 xen_512gb_limit [KNL,X86-64,XEN]
4463 Restricts the kernel running paravirtualized under Xen
4464 to use only up to 512 GB of RAM. The reason to do so is
4465 crash analysis tools and Xen tools for doing domain
4466 save/restore/migration must be enabled to handle larger
4467 domains.
4469 xen_emul_unplug= [HW,X86,XEN]
4470 Unplug Xen emulated devices
4471 Format: [unplug0,][unplug1]
4472 ide-disks -- unplug primary master IDE devices
4473 aux-ide-disks -- unplug non-primary-master IDE devices
4474 nics -- unplug network devices
4475 all -- unplug all emulated devices (NICs and IDE disks)
4476 unnecessary -- unplugging emulated devices is
4477 unnecessary even if the host did not respond to
4478 the unplug protocol
4479 never -- do not unplug even if version check succeeds
4481 xen_nopvspin [X86,XEN]
4482 Disables the ticketlock slowpath using Xen PV
4483 optimizations.
4485 xen_nopv [X86]
4486 Disables the PV optimizations forcing the HVM guest to
4487 run as generic HVM guest with no PV drivers.
4489 xirc2ps_cs= [NET,PCMCIA]
4490 Format:
4491 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4493 ______________________________________________________________________
4495 TODO:
4497 Add more DRM drivers.