4 The following is a consolidated list of the kernel parameters as
5 implemented by the __setup(), core_param() and module_param() macros
6 and sorted into English Dictionary order (defined as ignoring all
7 punctuation and sorting digits before letters in a case insensitive
8 manner), and with descriptions where known.
10 The kernel parses parameters from the kernel command line up to "--";
11 if it doesn't recognize a parameter and it doesn't contain a '.', the
12 parameter gets passed to init: parameters with '=' go into init's
13 environment, others are passed as command line arguments to init.
14 Everything after "--" is passed as an argument to init.
16 Module parameters can be specified in two ways: via the kernel command
17 line with a module name prefix, or via modprobe, e.g.:
19 (kernel command line) usbcore.blinkenlights=1
20 (modprobe command line) modprobe usbcore blinkenlights=1
22 Parameters for modules which are built into the kernel need to be
23 specified on the kernel command line. modprobe looks through the
24 kernel command line (/proc/cmdline) and collects module parameters
25 when it loads a module, so the kernel command line can be used for
28 Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30 can also be entered as
31 log-buf-len=1M print_fatal_signals=1
33 Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
36 This document may not be entirely up to date and comprehensive. The command
37 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
38 module. Loadable modules, after being loaded into the running kernel, also
39 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
40 parameters may be changed at runtime by the command
41 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
43 The parameters listed below are only valid if certain kernel build options were
44 enabled and if respective hardware is present. The text in square brackets at
45 the beginning of each description states the restrictions within which a
46 parameter is applicable:
48 ACPI ACPI support is enabled.
49 AGP AGP (Accelerated Graphics Port) is enabled.
50 ALSA ALSA sound support is enabled.
51 APIC APIC support is enabled.
52 APM Advanced Power Management support is enabled.
53 ARM ARM architecture is enabled.
54 AVR32 AVR32 architecture is enabled.
55 AX25 Appropriate AX.25 support is enabled.
56 BLACKFIN Blackfin architecture is enabled.
57 CLK Common clock infrastructure is enabled.
58 CMA Contiguous Memory Area support is enabled.
59 DRM Direct Rendering Management support is enabled.
60 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
61 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
62 EFI EFI Partitioning (GPT) is enabled
63 EIDE EIDE/ATAPI support is enabled.
64 EVM Extended Verification Module
65 FB The frame buffer device is enabled.
66 FTRACE Function tracing enabled.
67 GCOV GCOV profiling is enabled.
68 HW Appropriate hardware is enabled.
69 IA-64 IA-64 architecture is enabled.
70 IMA Integrity measurement architecture is enabled.
71 IOSCHED More than one I/O scheduler is enabled.
72 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
73 IPV6 IPv6 support is enabled.
74 ISAPNP ISA PnP code is enabled.
75 ISDN Appropriate ISDN support is enabled.
76 JOY Appropriate joystick support is enabled.
77 KGDB Kernel debugger support is enabled.
78 KVM Kernel Virtual Machine support is enabled.
79 LIBATA Libata driver is enabled
80 LP Printer support is enabled.
81 LOOP Loopback device support is enabled.
82 M68k M68k architecture is enabled.
83 These options have more detailed description inside of
84 Documentation/m68k/kernel-options.txt.
85 MDA MDA console support is enabled.
86 MIPS MIPS architecture is enabled.
87 MOUSE Appropriate mouse support is enabled.
88 MSI Message Signaled Interrupts (PCI).
89 MTD MTD (Memory Technology Device) support is enabled.
90 NET Appropriate network support is enabled.
91 NUMA NUMA support is enabled.
92 NFS Appropriate NFS support is enabled.
93 OSS OSS sound support is enabled.
94 PV_OPS A paravirtualized kernel is enabled.
95 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
96 PARISC The PA-RISC architecture is enabled.
97 PCI PCI bus support is enabled.
98 PCIE PCI Express support is enabled.
99 PCMCIA The PCMCIA subsystem is enabled.
100 PNP Plug & Play support is enabled.
101 PPC PowerPC architecture is enabled.
102 PPT Parallel port support is enabled.
103 PS2 Appropriate PS/2 support is enabled.
104 RAM RAM disk support is enabled.
105 S390 S390 architecture is enabled.
106 SCSI Appropriate SCSI support is enabled.
107 A lot of drivers have their options described inside
108 the Documentation/scsi/ sub-directory.
109 SECURITY Different security models are enabled.
110 SELINUX SELinux support is enabled.
111 APPARMOR AppArmor support is enabled.
112 SERIAL Serial support is enabled.
113 SH SuperH architecture is enabled.
114 SMP The kernel is an SMP kernel.
115 SPARC Sparc architecture is enabled.
116 SWSUSP Software suspend (hibernation) is enabled.
117 SUSPEND System suspend states are enabled.
118 TPM TPM drivers are enabled.
119 TS Appropriate touchscreen support is enabled.
120 UMS USB Mass Storage support is enabled.
121 USB USB support is enabled.
122 USBHID USB Human Interface Device support is enabled.
123 V4L Video For Linux support is enabled.
124 VMMIO Driver for memory mapped virtio devices is enabled.
125 VGA The VGA console has been enabled.
126 VT Virtual terminal support is enabled.
127 WDT Watchdog support is enabled.
128 XT IBM PC/XT MFM hard disk support is enabled.
129 X86-32 X86-32, aka i386 architecture is enabled.
130 X86-64 X86-64 architecture is enabled.
131 More X86-64 boot options can be found in
132 Documentation/x86/x86_64/boot-options.txt .
133 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
134 XEN Xen support is enabled
136 In addition, the following text indicates that the option:
138 BUGS= Relates to possible processor bugs on the said processor.
139 KNL Is a kernel start-up parameter.
140 BOOT Is a boot loader parameter.
142 Parameters denoted with BOOT are actually interpreted by the boot
143 loader, and have no meaning to the kernel directly.
144 Do not modify the syntax of boot loader parameters without extreme
145 need or coordination with <Documentation/x86/boot.txt>.
147 There are also arch-specific kernel-parameters not documented here.
148 See for example <Documentation/x86/x86_64/boot-options.txt>.
150 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
151 a trailing = on the name of any parameter states that that parameter will
152 be entered as an environment variable, whereas its absence indicates that
153 it will appear as a kernel argument readable via /proc/cmdline by programs
154 running once the system is up.
156 The number of kernel parameters is not limited, but the length of the
157 complete command line (parameters including spaces etc.) is limited to
158 a fixed number of characters. This limit depends on the architecture
159 and is between 256 and 4096 characters. It is defined in the file
160 ./include/asm/setup.h as COMMAND_LINE_SIZE.
162 Finally, the [KMG] suffix is commonly described after a number of kernel
163 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
164 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
165 bytes respectively. Such letter suffixes can also be entirely omitted.
168 acpi= [HW,ACPI,X86,ARM64]
169 Advanced Configuration and Power Interface
170 Format: { force | off | strict | noirq | rsdt |
172 force -- enable ACPI if default was off
173 off -- disable ACPI if default was on
174 noirq -- do not use ACPI for IRQ routing
175 strict -- Be less tolerant of platforms that are not
176 strictly ACPI specification compliant.
177 rsdt -- prefer RSDT over (default) XSDT
178 copy_dsdt -- copy DSDT to memory
179 For ARM64, ONLY "acpi=off" or "acpi=force" are available
181 See also Documentation/power/runtime_pm.txt, pci=noacpi
183 acpi_apic_instance= [ACPI, IOAPIC]
185 2: use 2nd APIC table, if available
186 1,0: use 1st APIC table
189 acpi_backlight= [HW,ACPI]
190 acpi_backlight=vendor
192 If set to vendor, prefer vendor specific driver
193 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
194 of the ACPI video.ko driver.
196 acpi_force_32bit_fadt_addr
197 force FADT to use 32 bit addresses rather than the
198 64 bit X_* addresses. Some firmware have broken 64
199 bit addresses for force ACPI ignore these and use
200 the older legacy 32 bit addresss.
202 acpica_no_return_repair [HW, ACPI]
203 Disable AML predefined validation mechanism
204 This mechanism can repair the evaluation result to make
205 the return objects more ACPI specification compliant.
206 This option is useful for developers to identify the
207 root cause of an AML interpreter issue when the issue
208 has something to do with the repair mechanism.
210 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
211 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
213 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
214 debug output. Bits in debug_layer correspond to a
215 _COMPONENT in an ACPI source file, e.g.,
216 #define _COMPONENT ACPI_PCI_COMPONENT
217 Bits in debug_level correspond to a level in
218 ACPI_DEBUG_PRINT statements, e.g.,
219 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
220 The debug_level mask defaults to "info". See
221 Documentation/acpi/debug.txt for more information about
222 debug layers and levels.
224 Enable processor driver info messages:
225 acpi.debug_layer=0x20000000
226 Enable PCI/PCI interrupt routing info messages:
227 acpi.debug_layer=0x400000
228 Enable AML "Debug" output, i.e., stores to the Debug
229 object while interpreting AML:
230 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
231 Enable all messages related to ACPI hardware:
232 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
234 Some values produce so much output that the system is
235 unusable. The "log_buf_len" parameter may be useful
236 if you need to capture more output.
238 acpi_enforce_resources= [ACPI]
239 { strict | lax | no }
240 Check for resource conflicts between native drivers
241 and ACPI OperationRegions (SystemIO and SystemMemory
242 only). IO ports and memory declared in ACPI might be
243 used by the ACPI subsystem in arbitrary AML code and
244 can interfere with legacy drivers.
245 strict (default): access to resources claimed by ACPI
246 is denied; legacy drivers trying to access reserved
247 resources will fail to bind to device using them.
248 lax: access to resources claimed by ACPI is allowed;
249 legacy drivers trying to access reserved resources
250 will bind successfully but a warning message is logged.
251 no: ACPI OperationRegions are not marked as reserved,
252 no further checks are performed.
254 acpi_force_table_verification [HW,ACPI]
255 Enable table checksum verification during early stage.
256 By default, this is disabled due to x86 early mapping
259 acpi_irq_balance [HW,ACPI]
260 ACPI will balance active IRQs
263 acpi_irq_nobalance [HW,ACPI]
264 ACPI will not move active IRQs (default)
267 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
268 Format: <irq>,<irq>...
270 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
272 Format: <irq>,<irq>...
274 acpi_no_auto_serialize [HW,ACPI]
275 Disable auto-serialization of AML methods
276 AML control methods that contain the opcodes to create
277 named objects will be marked as "Serialized" by the
278 auto-serialization feature.
279 This feature is enabled by default.
280 This option allows to turn off the feature.
282 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
285 acpi_no_static_ssdt [HW,ACPI]
286 Disable installation of static SSDTs at early boot time
287 By default, SSDTs contained in the RSDT/XSDT will be
288 installed automatically and they will appear under
289 /sys/firmware/acpi/tables.
290 This option turns off this feature.
291 Note that specifying this option does not affect
292 dynamic table installation which will install SSDT
293 tables to /sys/firmware/acpi/tables/dynamic.
295 acpi_rsdp= [ACPI,EFI,KEXEC]
296 Pass the RSDP address to the kernel, mostly used
297 on machines running EFI runtime service to boot the
298 second kernel for kdump.
300 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
301 Format: To spoof as Windows 98: ="Microsoft Windows"
303 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
304 of 2 which is mandated by ACPI 6) as the supported ACPI
305 specification revision (when using this switch, it may
306 be necessary to carry out a cold reboot _twice_ in a
307 row to make it take effect on the platform firmware).
309 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
310 acpi_osi="string1" # add string1
311 acpi_osi="!string2" # remove string2
312 acpi_osi=!* # remove all strings
313 acpi_osi=! # disable all built-in OS vendor
315 acpi_osi= # disable all strings
317 'acpi_osi=!' can be used in combination with single or
318 multiple 'acpi_osi="string1"' to support specific OS
319 vendor string(s). Note that such command can only
320 affect the default state of the OS vendor strings, thus
321 it cannot affect the default state of the feature group
322 strings and the current state of the OS vendor strings,
323 specifying it multiple times through kernel command line
324 is meaningless. This command is useful when one do not
325 care about the state of the feature group strings which
326 should be controlled by the OSPM.
328 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
329 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
330 can make '_OSI("Windows 2000")' TRUE.
332 'acpi_osi=' cannot be used in combination with other
333 'acpi_osi=' command lines, the _OSI method will not
334 exist in the ACPI namespace. NOTE that such command can
335 only affect the _OSI support state, thus specifying it
336 multiple times through kernel command line is also
339 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
342 'acpi_osi=!*' can be used in combination with single or
343 multiple 'acpi_osi="string1"' to support specific
344 string(s). Note that such command can affect the
345 current state of both the OS vendor strings and the
346 feature group strings, thus specifying it multiple times
347 through kernel command line is meaningful. But it may
348 still not able to affect the final state of a string if
349 there are quirks related to this string. This command
350 is useful when one want to control the state of the
351 feature group strings to debug BIOS issues related to
354 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
355 '_OSI("Module Device")' FALSE.
356 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
357 '_OSI("Module Device")' TRUE.
358 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
360 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
362 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
363 they all will make '_OSI("Windows 2000")' TRUE.
366 Override the pmtimer bug detection: force the kernel
367 to assume that this machine's pmtimer latches its value
368 and always returns good values.
370 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
371 Format: { level | edge | high | low }
373 acpi_skip_timer_override [HW,ACPI]
374 Recognize and ignore IRQ0/pin2 Interrupt Override.
375 For broken nForce2 BIOS resulting in XT-PIC timer.
377 acpi_sleep= [HW,ACPI] Sleep options
378 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
379 old_ordering, nonvs, sci_force_enable }
380 See Documentation/power/video.txt for information on
382 s3_beep is for debugging; it makes the PC's speaker beep
383 as soon as the kernel's real-mode entry point is called.
384 s4_nohwsig prevents ACPI hardware signature from being
385 used during resume from hibernation.
386 old_ordering causes the ACPI 1.0 ordering of the _PTS
387 control method, with respect to putting devices into
388 low power states, to be enforced (the ACPI 2.0 ordering
389 of _PTS is used by default).
390 nonvs prevents the kernel from saving/restoring the
391 ACPI NVS memory during suspend/hibernation and resume.
392 sci_force_enable causes the kernel to set SCI_EN directly
393 on resume from S1/S3 (which is against the ACPI spec,
394 but some broken systems don't work without it).
396 acpi_use_timer_override [HW,ACPI]
397 Use timer override. For some broken Nvidia NF5 boards
398 that require a timer override, but don't have HPET
400 add_efi_memmap [EFI; X86] Include EFI memory map in
401 kernel's map of available physical RAM.
404 { off | try_unsupported }
405 off: disable AGP support
406 try_unsupported: try to drive unsupported chipsets
407 (may crash computer or cause data corruption)
410 See Documentation/sound/alsa/alsa-parameters.txt
413 Allow the default userspace alignment fault handler
414 behaviour to be specified. Bit 0 enables warnings,
415 bit 1 enables fixups, and bit 2 sends a segfault.
417 align_va_addr= [X86-64]
418 Align virtual addresses by clearing slice [14:12] when
419 allocating a VMA at process creation time. This option
420 gives you up to 3% performance improvement on AMD F15h
421 machines (where it is enabled by default) for a
422 CPU-intensive style benchmark, and it can vary highly in
423 a microbenchmark depending on workload and compiler.
425 32: only for 32-bit processes
426 64: only for 64-bit processes
427 on: enable for both 32- and 64-bit processes
428 off: disable for both 32- and 64-bit processes
430 alloc_snapshot [FTRACE]
431 Allocate the ftrace snapshot buffer on boot up when the
432 main buffer is allocated. This is handy if debugging
433 and you need to use tracing_snapshot() on boot up, and
434 do not want to use tracing_snapshot_alloc() as it needs
435 to be done where GFP_KERNEL allocations are allowed.
437 amd_iommu= [HW,X86-64]
438 Pass parameters to the AMD IOMMU driver in the system.
440 fullflush - enable flushing of IO/TLB entries when
441 they are unmapped. Otherwise they are
442 flushed before they will be reused, which
444 off - do not initialize any AMD IOMMU found in
446 force_isolation - Force device isolation for all
447 devices. The IOMMU driver is not
448 allowed anymore to lift isolation
449 requirements as needed. This option
450 does not override iommu=pt
452 amd_iommu_dump= [HW,X86-64]
453 Enable AMD IOMMU driver option to dump the ACPI table
454 for AMD IOMMU. With this option enabled, AMD IOMMU
455 driver will print ACPI tables for AMD IOMMU during
456 IOMMU initialization.
458 amijoy.map= [HW,JOY] Amiga joystick support
459 Map of devices attached to JOY0DAT and JOY1DAT
461 See also Documentation/input/joystick.txt
463 analog.map= [HW,JOY] Analog joystick and gamepad support
464 Specifies type or capabilities of an analog joystick
465 connected to one of 16 gameports
466 Format: <type1>,<type2>,..<type16>
469 Power management functions (SPARCstation-4/5 + deriv.)
471 Disable APC CPU standby support. SPARCstation-Fox does
472 not play well with APC CPU idle - disable it if you have
473 APC and your system crashes randomly.
475 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
476 Change the output verbosity whilst booting
477 Format: { quiet (default) | verbose | debug }
478 Change the amount of debugging information output
479 when initialising the APIC and IO-APIC components.
482 See Documentation/networking/ipv6.txt.
484 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
485 Limit apic dumping. The parameter defines the maximal
486 number of local apics being dumped. Also it is possible
487 to set it to "all" by meaning -- no limit here.
488 Format: { 1 (default) | 2 | ... | all }.
489 The parameter valid if only apic=debug or
490 apic=verbose is specified.
491 Example: apic=debug show_lapic=all
493 apm= [APM] Advanced Power Management
494 See header of arch/x86/kernel/apm_32.c.
496 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
497 Format: <io>,<irq>,<nodeID>
501 atarimouse= [HW,MOUSE] Atari Mouse
503 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
504 EzKey and similar keyboards
506 atkbd.reset= [HW] Reset keyboard during initialization
508 atkbd.set= [HW] Select keyboard code set
509 Format: <int> (2 = AT (default), 3 = PS/2)
511 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
514 atkbd.softraw= [HW] Choose between synthetic and real raw mode
515 Format: <bool> (0 = real, 1 = synthetic (default))
517 atkbd.softrepeat= [HW]
518 Use software keyboard repeat
520 audit= [KNL] Enable the audit sub-system
521 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
522 0 - kernel audit is disabled and can not be enabled
523 until the next reboot
524 unset - kernel audit is initialized but disabled and
525 will be fully enabled by the userspace auditd.
526 1 - kernel audit is initialized and partially enabled,
527 storing at most audit_backlog_limit messages in
528 RAM until it is fully enabled by the userspace
532 audit_backlog_limit= [KNL] Set the audit queue size limit.
533 Format: <int> (must be >=0)
536 baycom_epp= [HW,AX25]
539 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
541 See header of drivers/net/hamradio/baycom_par.c.
543 baycom_ser_fdx= [HW,AX25]
544 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
545 Format: <io>,<irq>,<mode>[,<baud>]
546 See header of drivers/net/hamradio/baycom_ser_fdx.c.
548 baycom_ser_hdx= [HW,AX25]
549 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
550 Format: <io>,<irq>,<mode>
551 See header of drivers/net/hamradio/baycom_ser_hdx.c.
553 blkdevparts= Manual partition parsing of block device(s) for
554 embedded devices based on command line input.
555 See Documentation/block/cmdline-partition.txt
557 boot_delay= Milliseconds to delay each printk during boot.
558 Values larger than 10 seconds (10000) are changed to
562 bootmem_debug [KNL] Enable bootmem allocator debug messages.
564 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
565 bttv.radio= Most important insmod options are available as
567 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
570 bulk_remove=off [PPC] This parameter disables the use of the pSeries
571 firmware feature for flushing multiple hpte entries
574 c101= [NET] Moxa C101 synchronous serial card
576 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
577 Sometimes CPU hardware bugs make them report the cache
578 size incorrectly. The kernel will attempt work arounds
579 to fix known problems, but for some CPUs it is not
580 possible to determine what the correct size should be.
581 This option provides an override for these situations.
583 ca_keys= [KEYS] This parameter identifies a specific key(s) on
584 the system trusted keyring to be used for certificate
586 format: { id:<keyid> | builtin }
588 cca= [MIPS] Override the kernel pages' cache coherency
589 algorithm. Accepted values range from 0 to 7
590 inclusive. See arch/mips/include/asm/pgtable-bits.h
591 for platform specific values (SB1, Loongson3 and
594 ccw_timeout_log [S390]
595 See Documentation/s390/CommonIO for details.
597 cgroup_disable= [KNL] Disable a particular controller
598 Format: {name of the controller(s) to disable}
599 The effects of cgroup_disable=foo are:
600 - foo isn't auto-mounted if you mount all cgroups in
602 - foo isn't visible as an individually mountable
604 {Currently only "memory" controller deal with this and
605 cut the overhead, others just disable the usage. So
606 only cgroup_disable=memory is actually worthy}
608 checkreqprot [SELINUX] Set initial checkreqprot flag value.
609 Format: { "0" | "1" }
610 See security/selinux/Kconfig help text.
611 0 -- check protection applied by kernel (includes
612 any implied execute protection).
613 1 -- check protection requested by application.
614 Default value is set via a kernel config option.
615 Value can be changed at runtime via
616 /selinux/checkreqprot.
619 See Documentation/s390/CommonIO for details.
622 Prevents the clock framework from automatically gating
623 clocks that have not been explicitly enabled by a Linux
624 device driver but are enabled in hardware at reset or
625 by the bootloader/firmware. Note that this does not
626 force such clocks to be always-on nor does it reserve
627 those clocks in any way. This parameter is useful for
628 debug and development, but should not be needed on a
629 platform with proper driver support. For more
630 information, see Documentation/clk.txt.
632 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
634 Forces specified clocksource (if available) to be used
635 when calculating gettimeofday(). If specified
636 clocksource is not available, it defaults to PIT.
637 Format: { pit | tsc | cyclone | pmtmr }
639 clocksource= Override the default clocksource
641 Override the default clocksource and use the clocksource
642 with the name specified.
643 Some clocksource names to choose from, depending on
645 [all] jiffies (this is the base, fallback clocksource)
647 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
648 pxa_timer,timer3,32k_counter,timer0_1
650 [X86-32] pit,hpet,tsc;
651 scx200_hrt on Geode; cyclone on IBM x440
659 clearcpuid=BITNUM [X86]
660 Disable CPUID feature X for the kernel. See
661 arch/x86/include/asm/cpufeatures.h for the valid bit
662 numbers. Note the Linux specific bits are not necessarily
663 stable over kernel options, but the vendor specific
665 Also note that user programs calling CPUID directly
666 or using the feature without checking anything
667 will still see it. This just prevents it from
668 being used by the kernel or shown in /proc/cpuinfo.
669 Also note the kernel might malfunction if you disable
672 cma=nn[MG]@[start[MG][-end[MG]]]
674 Sets the size of kernel global memory area for
675 contiguous memory allocations and optionally the
676 placement constraint by the physical address range of
677 memory allocations. A value of 0 disables CMA
678 altogether. For more information, see
679 include/linux/dma-contiguous.h
681 cmo_free_hint= [PPC] Format: { yes | no }
682 Specify whether pages are marked as being inactive
683 when they are freed. This is used in CMO environments
684 to determine OS memory pressure for page stealing by
688 coherent_pool=nn[KMG] [ARM,KNL]
689 Sets the size of memory pool for coherent, atomic dma
690 allocations, by default set to 256K.
692 code_bytes [X86] How many bytes of object code to print
697 com20020= [HW,NET] ARCnet - COM20020 chipset
699 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
701 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
705 ARCnet - COM90xx chipset (memory-mapped buffers)
706 Format: <io>[,<irq>[,<memstart>]]
708 condev= [HW,S390] console device
711 console= [KNL] Output console device and options.
713 tty<n> Use the virtual console device <n>.
717 Use the specified serial port. The options are of
718 the form "bbbbpnf", where "bbbb" is the baud rate,
719 "p" is parity ("n", "o", or "e"), "n" is number of
720 bits, and "f" is flow control ("r" for RTS or
721 omit it). Default is "9600n8".
723 See Documentation/serial-console.txt for more
725 Documentation/networking/netconsole.txt for an
728 uart[8250],io,<addr>[,options]
729 uart[8250],mmio,<addr>[,options]
730 uart[8250],mmio32,<addr>[,options]
731 uart[8250],0x<addr>[,options]
732 Start an early, polled-mode console on the 8250/16550
733 UART at the specified I/O port or MMIO address,
734 switching to the matching ttyS device later.
735 MMIO inter-register address stride is either 8-bit
736 (mmio) or 32-bit (mmio32).
737 If none of [io|mmio|mmio32], <addr> is assumed to be
738 equivalent to 'mmio'. 'options' are specified in the
739 same format described for ttyS above; if unspecified,
740 the h/w is not re-initialized.
742 hvc<n> Use the hypervisor console device <n>. This is for
743 both Xen and PowerPC hypervisors.
745 If the device connected to the port is not a TTY but a braille
746 device, prepend "brl," before the device type, for instance
748 For now, only VisioBraille is supported.
750 consoleblank= [KNL] The console blank (screen saver) timeout in
751 seconds. Defaults to 10*60 = 10mins. A value of 0
752 disables the blank timer.
755 [KNL] Change the default value for
756 /proc/<pid>/coredump_filter.
757 See also Documentation/filesystems/proc.txt.
759 cpufreq_driver= [X86] Allow only the named cpu frequency scaling driver
760 to register. Example: cpufreq_driver=powernow-k8
761 Format: { none | STRING }
763 cpuidle.off=1 [CPU_IDLE]
764 disable the cpuidle sub-system
767 [X86] Delay for N microsec between assert and de-assert
768 of APIC INIT to start processors. This delay occurs
769 on every CPU online, such as boot, and resume from suspend.
772 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
774 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
776 crashkernel=size[KMG][@offset[KMG]]
777 [KNL] Using kexec, Linux can switch to a 'crash kernel'
778 upon panic. This parameter reserves the physical
779 memory region [offset, offset + size] for that kernel
780 image. If '@offset' is omitted, then a suitable offset
781 is selected automatically. Check
782 Documentation/kdump/kdump.txt for further details.
784 crashkernel=range1:size1[,range2:size2,...][@offset]
785 [KNL] Same as above, but depends on the memory
786 in the running system. The syntax of range is
787 start-[end] where start and end are both
788 a memory unit (amount[KMG]). See also
789 Documentation/kdump/kdump.txt for an example.
791 crashkernel=size[KMG],high
792 [KNL, x86_64] range could be above 4G. Allow kernel
793 to allocate physical memory region from top, so could
794 be above 4G if system have more than 4G ram installed.
795 Otherwise memory region will be allocated below 4G, if
797 It will be ignored if crashkernel=X is specified.
798 crashkernel=size[KMG],low
799 [KNL, x86_64] range under 4G. When crashkernel=X,high
800 is passed, kernel could allocate physical memory region
801 above 4G, that cause second kernel crash on system
802 that require some amount of low memory, e.g. swiotlb
803 requires at least 64M+32K low memory, also enough extra
804 low memory is needed to make sure DMA buffers for 32-bit
805 devices won't run out. Kernel would try to allocate at
806 at least 256M below 4G automatically.
807 This one let user to specify own low range under 4G
808 for second kernel instead.
809 0: to disable low allocation.
810 It will be ignored when crashkernel=X,high is not used
811 or memory reserved is below 4G.
816 cs89x0_media= [HW,NET]
817 Format: { rj45 | aui | bnc }
820 See header of drivers/s390/block/dasd_devmap.c.
822 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
823 (one device per port)
824 Format: <port#>,<type>
825 See also Documentation/input/joystick-parport.txt
827 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
828 time. See Documentation/dynamic-debug-howto.txt for
829 details. Deprecated, see dyndbg.
831 debug [KNL] Enable kernel debugging (events log level).
834 [KNL] verbose self-tests
836 Print debugging info while doing the locking API
838 We default to 0 (no extra messages), setting it to
839 1 will print _a lot_ more information - normally
840 only useful to kernel developers.
842 debug_objects [KNL] Enable object debugging
845 [KNL] Disable object debugging
847 debug_guardpage_minorder=
848 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
849 parameter allows control of the order of pages that will
850 be intentionally kept free (and hence protected) by the
851 buddy allocator. Bigger value increase the probability
852 of catching random memory corruption, but reduce the
853 amount of memory for normal system use. The maximum
854 possible value is MAX_ORDER/2. Setting this parameter
855 to 1 or 2 should be enough to identify most random
856 memory corruption problems caused by bugs in kernel or
857 driver code when a CPU writes to (or reads from) a
858 random memory location. Note that there exists a class
859 of memory corruptions problems caused by buggy H/W or
860 F/W or by drivers badly programing DMA (basically when
861 memory is written at bus level and the CPU MMU is
862 bypassed) which are not detectable by
863 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
864 tracking down these problems.
867 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
868 parameter enables the feature at boot time. In
869 default, it is disabled. We can avoid allocating huge
870 chunk of memory for debug pagealloc if we don't enable
871 it at boot time and the system will work mostly same
872 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
873 on: enable the feature
875 debugpat [X86] Enable PAT debugging
877 decnet.addr= [HW,NET]
878 Format: <area>[,<node>]
879 See also Documentation/networking/decnet.txt.
882 [same as hugepagesz=] The size of the default
883 HugeTLB page size. This is the size represented by
884 the legacy /proc/ hugepages APIs, used for SHM, and
885 default size when mounting hugetlbfs filesystems.
886 Defaults to the default architecture's huge page size
890 Set number of hash buckets for dentry cache.
893 See Documentation/networking/ipv6.txt.
895 disable_cpu_apicid= [X86,APIC,SMP]
897 The number of initial APIC ID for the
898 corresponding CPU to be disabled at boot,
899 mostly used for the kdump 2nd kernel to
900 disable BSP to wake up multiple CPUs without
901 causing system reset or hang due to sending
904 disable_ddw [PPC/PSERIES]
905 Disable Dynamic DMA Window support. Use this if
906 to workaround buggy firmware.
909 See Documentation/networking/ipv6.txt.
911 disable_mtrr_cleanup [X86]
912 The kernel tries to adjust MTRR layout from continuous
913 to discrete, to make X server driver able to add WB
914 entry later. This parameter disables that.
916 disable_mtrr_trim [X86, Intel and AMD only]
917 By default the kernel will trim any uncacheable
918 memory out of your available memory pool based on
919 MTRR settings. This parameter disables that behavior,
920 possibly causing your machine to run very slowly.
922 disable_timer_pin_1 [X86]
923 Disable PIN 1 of APIC timer
924 Can be useful to work around chipset bugs.
926 dis_ucode_ldr [X86] Disable the microcode loader.
928 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
929 this option disables the debugging code at boot.
931 dma_debug_entries=<number>
932 This option allows to tune the number of preallocated
933 entries for DMA-API debugging code. One entry is
934 required per DMA-API allocation. Use this if the
935 DMA-API debugging code disables itself because the
936 architectural default is too low.
938 dma_debug_driver=<driver_name>
939 With this option the DMA-API debugging driver
940 filter feature can be enabled at boot time. Just
941 pass the driver to filter for as the parameter.
942 The filter can be disabled or changed to another
943 driver later using sysfs.
945 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
946 Broken monitors, graphic adapters, KVMs and EDIDless
947 panels may send no or incorrect EDID data sets.
948 This parameter allows to specify an EDID data sets
949 in the /lib/firmware directory that are used instead.
950 Generic built-in EDID data sets are used, if one of
951 edid/1024x768.bin, edid/1280x1024.bin,
952 edid/1680x1050.bin, or edid/1920x1080.bin is given
953 and no file with the same name exists. Details and
954 instructions how to build your own EDID data are
955 available in Documentation/EDID/HOWTO.txt. An EDID
956 data set will only be used for a particular connector,
957 if its name and a colon are prepended to the EDID
958 name. Each connector may use a unique EDID data
959 set by separating the files with a comma. An EDID
960 data set with no connector name will be used for
961 any connectors not explicitly specified.
965 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
966 module.dyndbg[="val"]
967 Enable debug messages at boot time. See
968 Documentation/dynamic-debug-howto.txt for details.
970 nompx [X86] Disables Intel Memory Protection Extensions.
971 See Documentation/x86/intel_mpx.txt for more
972 information about the feature.
975 on enable eager fpu restore
976 off disable eager fpu restore
977 auto selects the default scheme, which automatically
978 enables eagerfpu restore for xsaveopt.
980 module.async_probe [KNL]
981 Enable asynchronous probe on this module.
983 early_ioremap_debug [KNL]
984 Enable debug messages in early_ioremap support. This
985 is useful for tracking down temporary early mappings
986 which are not unmapped.
988 earlycon= [KNL] Output early console device and options.
990 When used with no options, the early console is
991 determined by the stdout-path property in device
995 Start an early, polled-mode console on a cadence serial
996 port at the specified address. The cadence serial port
997 must already be setup and configured. Options are not
1000 uart[8250],io,<addr>[,options]
1001 uart[8250],mmio,<addr>[,options]
1002 uart[8250],mmio32,<addr>[,options]
1003 uart[8250],mmio32be,<addr>[,options]
1004 uart[8250],0x<addr>[,options]
1005 Start an early, polled-mode console on the 8250/16550
1006 UART at the specified I/O port or MMIO address.
1007 MMIO inter-register address stride is either 8-bit
1008 (mmio) or 32-bit (mmio32 or mmio32be).
1009 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1010 to be equivalent to 'mmio'. 'options' are specified
1011 in the same format described for "console=ttyS<n>"; if
1012 unspecified, the h/w is not initialized.
1015 Start an early, polled-mode console on a pl011 serial
1016 port at the specified address. The pl011 serial port
1017 must already be setup and configured. Options are not
1021 Start an early, polled-mode console on an msm serial
1022 port at the specified address. The serial port
1023 must already be setup and configured. Options are not
1026 msm_serial_dm,<addr>
1027 Start an early, polled-mode console on an msm serial
1028 dm port at the specified address. The serial port
1029 must already be setup and configured. Options are not
1032 smh Use ARM semihosting calls for early console.
1040 Use early console provided by serial driver available
1041 on Samsung SoCs, requires selecting proper type and
1042 a correct base address of the selected UART port. The
1043 serial port must already be setup and configured.
1044 Options are not yet supported.
1048 Use early console provided by Freescale LP UART driver
1049 found on Freescale Vybrid and QorIQ LS1021A processors.
1050 A valid base address must be provided, and the serial
1051 port must already be setup and configured.
1053 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1057 earlyprintk=serial[,ttySn[,baudrate]]
1058 earlyprintk=serial[,0x...[,baudrate]]
1059 earlyprintk=ttySn[,baudrate]
1060 earlyprintk=dbgp[debugController#]
1061 earlyprintk=pciserial,bus:device.function[,baudrate]
1063 earlyprintk is useful when the kernel crashes before
1064 the normal console is initialized. It is not enabled by
1065 default because it has some cosmetic problems.
1067 Append ",keep" to not disable it when the real console
1070 Only one of vga, efi, serial, or usb debug port can
1073 Currently only ttyS0 and ttyS1 may be specified by
1074 name. Other I/O ports may be explicitly specified
1075 on some architectures (x86 and arm at least) by
1076 replacing ttySn with an I/O port address, like this:
1077 earlyprintk=serial,0x1008,115200
1078 You can find the port for a given device in
1079 /proc/tty/driver/serial:
1080 2: uart:ST16650V2 port:00001008 irq:18 ...
1082 Interaction with the standard serial driver is not
1085 The VGA and EFI output is eventually overwritten by
1088 The xen output can only be used by Xen PV guests.
1090 edac_report= [HW,EDAC] Control how to report EDAC event
1091 Format: {"on" | "off" | "force"}
1092 on: enable EDAC to report H/W event. May be overridden
1093 by other higher priority error reporting module.
1094 off: disable H/W event reporting through EDAC.
1095 force: enforce the use of EDAC to report H/W event.
1098 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1101 This is designed to be used in conjunction with
1102 the boot argument: earlyprintk=vga
1105 Format: {"off" | "on" | "skip[mbr]"}
1108 Format: { "old_map", "nochunk", "noruntime", "debug" }
1109 old_map [X86-64]: switch to the old ioremap-based EFI
1110 runtime services mapping. 32-bit still uses this one by
1112 nochunk: disable reading files in "chunks" in the EFI
1113 boot stub, as chunking can cause problems with some
1114 firmware implementations.
1115 noruntime : disable EFI runtime services support
1116 debug: enable misc debug output
1118 efi_no_storage_paranoia [EFI; X86]
1119 Using this parameter you can use more than 50% of
1120 your efi variable storage. Use this parameter only if
1121 you are really sure that your UEFI does sane gc and
1122 fulfills the spec otherwise your board may brick.
1124 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1125 Add arbitrary attribute to specific memory range by
1126 updating original EFI memory map.
1127 Region of memory which aa attribute is added to is
1129 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1130 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1131 attribute is added to range 0x100000000-0x180000000 and
1132 0x10a0000000-0x1120000000.
1134 Using this parameter you can do debugging of EFI memmap
1135 related feature. For example, you can do debugging of
1136 Address Range Mirroring feature even if your box
1139 eisa_irq_edge= [PARISC,HW]
1140 See header of drivers/parisc/eisa.c.
1143 See comment before function elanfreq_setup() in
1144 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1147 Format: {"cfq" | "deadline" | "noop"}
1148 See Documentation/block/cfq-iosched.txt and
1149 Documentation/block/deadline-iosched.txt for details.
1151 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1152 Specifies physical address of start of kernel core
1153 image elf header and optionally the size. Generally
1154 kexec loader will pass this option to capture kernel.
1155 See Documentation/kdump/kdump.txt for details.
1157 enable_mtrr_cleanup [X86]
1158 The kernel tries to adjust MTRR layout from continuous
1159 to discrete, to make X server driver able to add WB
1160 entry later. This parameter enables that.
1162 enable_timer_pin_1 [X86]
1163 Enable PIN 1 of APIC timer
1164 Can be useful to work around chipset bugs
1165 (in particular on some ATI chipsets).
1166 The kernel tries to set a reasonable default.
1168 enforcing [SELINUX] Set initial enforcing status.
1170 See security/selinux/Kconfig help text.
1171 0 -- permissive (log only, no denials).
1172 1 -- enforcing (deny and log).
1174 Value can be changed at runtime via /selinux/enforce.
1177 Disable Error Record Serialization Table (ERST)
1180 ether= [HW,NET] Ethernet cards parameters
1181 This option is obsoleted by the "netdev=" option, which
1182 has equivalent usage. See its documentation for details.
1186 Permit 'security.evm' to be updated regardless of
1187 current integrity status.
1191 fail_make_request=[KNL]
1192 General fault injection mechanism.
1193 Format: <interval>,<probability>,<space>,<times>
1194 See also Documentation/fault-injection/.
1197 See Documentation/blockdev/floppy.txt.
1199 force_pal_cache_flush
1200 [IA-64] Avoid check_sal_cache_flush which may hang on
1201 buggy SAL_CACHE_FLUSH implementations. Using this
1202 parameter will force ia64_sal_cache_flush to call
1203 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1206 Forcefully enable Physical Address Extension (PAE).
1207 Many Pentium M systems disable PAE but may have a
1208 functionally usable PAE implementation.
1209 Warning: use of this parameter will taint the kernel
1210 and may cause unknown problems.
1213 [FTRACE] will set and start the specified tracer
1214 as early as possible in order to facilitate early
1217 ftrace_dump_on_oops[=orig_cpu]
1218 [FTRACE] will dump the trace buffers on oops.
1219 If no parameter is passed, ftrace will dump
1220 buffers of all CPUs, but if you pass orig_cpu, it will
1221 dump only the buffer of the CPU that triggered the
1224 ftrace_filter=[function-list]
1225 [FTRACE] Limit the functions traced by the function
1226 tracer at boot up. function-list is a comma separated
1227 list of functions. This list can be changed at run
1228 time by the set_ftrace_filter file in the debugfs
1231 ftrace_notrace=[function-list]
1232 [FTRACE] Do not trace the functions specified in
1233 function-list. This list can be changed at run time
1234 by the set_ftrace_notrace file in the debugfs
1237 ftrace_graph_filter=[function-list]
1238 [FTRACE] Limit the top level callers functions traced
1239 by the function graph tracer at boot up.
1240 function-list is a comma separated list of functions
1241 that can be changed at run time by the
1242 set_graph_function file in the debugfs tracing directory.
1244 ftrace_graph_notrace=[function-list]
1245 [FTRACE] Do not trace from the functions specified in
1246 function-list. This list is a comma separated list of
1247 functions that can be changed at run time by the
1248 set_graph_notrace file in the debugfs tracing directory.
1251 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1252 support via parallel port (up to 5 devices per port)
1253 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1254 See also Documentation/input/joystick-parport.txt
1258 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1262 gcov_persist= [GCOV] When non-zero (default), profiling data for
1263 kernel modules is saved and remains accessible via
1264 debugfs, even when the module is unloaded/reloaded.
1265 When zero, profiling data is discarded and associated
1266 debugfs files are removed at module unload time.
1268 goldfish [X86] Enable the goldfish android emulator platform.
1269 Don't use this when you are not running on the
1272 gpt [EFI] Forces disk with valid GPT signature but
1273 invalid Protective MBR to be treated as GPT. If the
1274 primary GPT is corrupted, it enables the backup/alternate
1275 GPT to be used instead.
1277 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1278 the "Enable 0" bit of the configuration register.
1281 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1282 the "Enable 0" bit of the configuration register.
1285 grcan.select= [HW] Select which physical interface to use.
1288 grcan.txsize= [HW] Sets the size of the tx buffer.
1289 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1291 grcan.rxsize= [HW] Sets the size of the rx buffer.
1292 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1295 hardlockup_all_cpu_backtrace=
1296 [KNL] Should the hard-lockup detector generate
1297 backtraces on all cpus.
1300 hashdist= [KNL,NUMA] Large hashes allocated during boot
1301 are distributed across NUMA nodes. Defaults on
1302 for 64-bit NUMA, off otherwise.
1303 Format: 0 | 1 (for off | on)
1305 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1307 hd= [EIDE] (E)IDE hard drive subsystem geometry
1308 Format: <cyl>,<head>,<sect>
1311 Disable Hardware Error Source Table (HEST) support;
1312 corresponding firmware-first mode error processing
1313 logic will be disabled.
1315 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1316 size of <nn>. This works even on boxes that have no
1317 highmem otherwise. This also works to reduce highmem
1318 size on bigger boxes.
1320 highres= [KNL] Enable/disable high resolution timer mode.
1321 Valid parameters: "on", "off"
1325 See Documentation/isdn/README.HiSax.
1329 hpet= [X86-32,HPET] option to control HPET usage
1330 Format: { enable (default) | disable | force |
1332 disable: disable HPET and use PIT instead
1333 force: allow force enabled of undocumented chips (ICH4,
1335 verbose: show contents of HPET registers during setup
1337 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1338 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1340 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1341 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1342 On x86-64 and powerpc, this option can be specified
1343 multiple times interleaved with hugepages= to reserve
1344 huge pages of different sizes. Valid pages sizes on
1345 x86-64 are 2M (when the CPU supports "pse") and 1G
1346 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1348 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1349 terminal devices. Valid values: 0..8
1350 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1351 If specified, z/VM IUCV HVC accepts connections
1352 from listed z/VM user IDs only.
1354 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1355 hardware thread id mappings.
1356 Format: <cpu>:<hwthread>
1359 Do not unregister boot console at start. This is only
1360 useful for debugging when something happens in the window
1361 between unregistering the boot console and initializing
1364 i2c_bus= [HW] Override the default board specific I2C bus speed
1365 or register an additional I2C bus that is not
1366 registered from board initialization code.
1370 i8042.debug [HW] Toggle i8042 debug mode
1371 i8042.unmask_kbd_data
1372 [HW] Enable printing of interrupt data from the KBD port
1373 (disabled by default, and as a pre-condition
1374 requires that i8042.debug=1 be enabled)
1375 i8042.direct [HW] Put keyboard port into non-translated mode
1376 i8042.dumbkbd [HW] Pretend that controller can only read data from
1377 keyboard and cannot control its state
1378 (Don't attempt to blink the leds)
1379 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1380 i8042.nokbd [HW] Don't check/create keyboard port
1381 i8042.noloop [HW] Disable the AUX Loopback command while probing
1383 i8042.nomux [HW] Don't check presence of an active multiplexing
1385 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1387 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1388 i8042.reset [HW] Reset the controller during init, cleanup and
1389 suspend-to-ram transitions, only during s2r
1390 transitions, or never reset
1391 Format: { 1 | Y | y | 0 | N | n }
1392 1, Y, y: always reset controller
1393 0, N, n: don't ever reset controller
1394 Default: only on s2r transitions on x86; most other
1395 architectures force reset to be always executed
1396 i8042.unlock [HW] Unlock (ignore) the keylock
1397 i8042.kbdreset [HW] Reset device connected to KBD port
1401 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1402 indicates that the driver is running on unsupported
1404 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1405 does not match list of supported models.
1407 [HW] Report power status in /proc/i8k
1408 (disabled by default)
1409 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1412 i915.invert_brightness=
1413 [DRM] Invert the sense of the variable that is used to
1414 set the brightness of the panel backlight. Normally a
1415 brightness value of 0 indicates backlight switched off,
1416 and the maximum of the brightness value sets the backlight
1417 to maximum brightness. If this parameter is set to 0
1418 (default) and the machine requires it, or this parameter
1419 is set to 1, a brightness value of 0 sets the backlight
1420 to maximum brightness, and the maximum of the brightness
1421 value switches the backlight off.
1422 -1 -- never invert brightness
1423 0 -- machine default
1424 1 -- force brightness inversion
1427 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1429 ide-core.nodma= [HW] (E)IDE subsystem
1430 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1431 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1432 .cdrom .chs .ignore_cable are additional options
1433 See Documentation/ide/ide.txt.
1435 ide-generic.probe-mask= [HW] (E)IDE subsystem
1437 Probe mask for legacy ISA IDE ports. Depending on
1438 platform up to 6 ports are supported, enabled by
1439 setting corresponding bits in the mask to 1. The
1440 default value is 0x0, which has a special meaning.
1441 On systems that have PCI, it triggers scanning the
1442 PCI bus for the first and the second port, which
1443 are then probed. On systems without PCI the value
1444 of 0x0 enables probing the two first ports as if it
1447 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1448 Claim all unknown PCI IDE storage controllers.
1451 Format: idle=poll, idle=halt, idle=nomwait
1452 Poll forces a polling idle loop that can slightly
1453 improve the performance of waking up a idle CPU, but
1454 will use a lot of power and make the system run hot.
1456 idle=halt: Halt is forced to be used for CPU idle.
1457 In such case C2/C3 won't be used again.
1458 idle=nomwait: Disable mwait for CPU C-states
1460 ignore_loglevel [KNL]
1461 Ignore loglevel setting - this will print /all/
1462 kernel messages to the console. Useful for debugging.
1463 We also add it as printk module parameter, so users
1464 could change it dynamically, usually by
1465 /sys/module/printk/parameters/ignore_loglevel.
1467 ihash_entries= [KNL]
1468 Set number of hash buckets for inode cache.
1470 ima_appraise= [IMA] appraise integrity measurements
1471 Format: { "off" | "enforce" | "fix" | "log" }
1474 ima_appraise_tcb [IMA]
1475 The builtin appraise policy appraises all files
1479 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1483 The list of supported hash algorithms is defined
1484 in crypto/hash_info.h.
1487 The builtin measurement policy to load during IMA
1488 setup. Specyfing "tcb" as the value, measures all
1489 programs exec'd, files mmap'd for exec, and all files
1490 opened with the read mode bit set by either the
1491 effective uid (euid=0) or uid=0.
1494 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1495 Load a policy which meets the needs of the Trusted
1496 Computing Base. This means IMA will measure all
1497 programs exec'd, files mmap'd for exec, and all files
1498 opened for read by uid=0.
1501 Select one of defined IMA measurements template formats.
1502 Formats: { "ima" | "ima-ng" | "ima-sig" }
1506 [IMA] Define a custom template format.
1507 Format: { "field1|...|fieldN" }
1509 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1510 Format: <min_file_size>
1511 Set the minimal file size for using asynchronous hash.
1512 If left unspecified, ahash usage is disabled.
1514 ahash performance varies for different data sizes on
1515 different crypto accelerators. This option can be used
1516 to achieve the best performance for a particular HW.
1518 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1520 Set hashing buffer size. Default: 4k.
1522 ahash performance varies for different chunk sizes on
1523 different crypto accelerators. This option can be used
1524 to achieve best performance for particular HW.
1528 Run specified binary instead of /sbin/init as init
1531 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1532 for working out where the kernel is dying during
1535 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1536 initcall functions. Useful for debugging built-in
1537 modules and initcalls.
1539 initrd= [BOOT] Specify the location of the initial ramdisk
1541 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1544 int_pln_enable [x86] Enable power limit notification interrupt
1546 integrity_audit=[IMA]
1547 Format: { "0" | "1" }
1548 0 -- basic integrity auditing messages. (Default)
1549 1 -- additional integrity auditing messages.
1551 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1553 Enable intel iommu driver.
1555 Disable intel iommu driver.
1556 igfx_off [Default Off]
1557 By default, gfx is mapped as normal device. If a gfx
1558 device has a dedicated DMAR unit, the DMAR unit is
1559 bypassed by not enabling DMAR with this option. In
1560 this case, gfx device will use physical address for
1563 With this option iommu will not optimize to look
1564 for io virtual address below 32-bit forcing dual
1565 address cycle on pci bus for cards supporting greater
1566 than 32-bit addressing. The default is to look
1567 for translation below 32-bit and if not available
1568 then look in the higher range.
1569 strict [Default Off]
1570 With this option on every unmap_single operation will
1571 result in a hardware IOTLB flush operation as opposed
1572 to batching them for performance.
1573 sp_off [Default Off]
1574 By default, super page will be supported if Intel IOMMU
1575 has the capability. With this option, super page will
1577 ecs_off [Default Off]
1578 By default, extended context tables will be supported if
1579 the hardware advertises that it has support both for the
1580 extended tables themselves, and also PASID support. With
1581 this option set, extended tables will not be used even
1582 on hardware which claims to support them.
1584 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1585 0 disables intel_idle and fall back on acpi_idle.
1586 1 to 6 specify maximum depth of C-state.
1590 Do not enable intel_pstate as the default
1591 scaling driver for the supported processors
1593 Enable intel_pstate on systems that prohibit it by default
1594 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1595 instead of acpi-cpufreq may disable platform features, such
1596 as thermal controls and power capping, that rely on ACPI
1597 P-States information being indicated to OSPM and therefore
1598 should be used with caution. This option does not work with
1599 processors that aren't supported by the intel_pstate driver
1600 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1602 Do not enable hardware P state control (HWP)
1605 Only load intel_pstate on systems which support
1606 hardware P state control (HWP) if available.
1608 intremap= [X86-64, Intel-IOMMU]
1609 on enable Interrupt Remapping (default)
1610 off disable Interrupt Remapping
1611 nosid disable Source ID checking
1613 BIOS x2APIC opt-out request will be ignored
1614 nopost disable Interrupt Posting
1616 iomem= Disable strict checking of access to MMIO memory
1617 strict regions from userspace.
1632 nobypass [PPC/POWERNV]
1633 Disable IOMMU bypass, using IOMMU for PCI devices.
1636 io7= [HW] IO7 for Marvel based alpha systems
1637 See comment before marvel_specify_io7 in
1638 arch/alpha/kernel/core_marvel.c.
1640 io_delay= [X86] I/O delay method
1642 Standard port 0x80 based delay
1644 Alternate port 0xed based delay (needed on some systems)
1646 Simple two microseconds delay
1651 See Documentation/filesystems/nfs/nfsroot.txt.
1654 When an interrupt is not handled search all handlers
1655 for it. Intended to get systems with badly broken
1659 When an interrupt is not handled search all handlers
1660 for it. Also check all handlers each timer
1661 interrupt. Intended to get systems with badly broken
1665 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1667 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1669 <cpu number>,...,<cpu number>
1671 <cpu number>-<cpu number>
1672 (must be a positive range in ascending order)
1674 <cpu number>,...,<cpu number>-<cpu number>
1676 This option can be used to specify one or more CPUs
1677 to isolate from the general SMP balancing and scheduling
1678 algorithms. You can move a process onto or off an
1679 "isolated" CPU via the CPU affinity syscalls or cpuset.
1680 <cpu number> begins at 0 and the maximum value is
1681 "number of CPUs in system - 1".
1683 This option is the preferred way to isolate CPUs. The
1684 alternative -- manually setting the CPU mask of all
1685 tasks in the system -- can cause problems and
1686 suboptimal load balancer performance.
1690 ivrs_ioapic [HW,X86_64]
1691 Provide an override to the IOAPIC-ID<->DEVICE-ID
1692 mapping provided in the IVRS ACPI table. For
1693 example, to map IOAPIC-ID decimal 10 to
1694 PCI device 00:14.0 write the parameter as:
1695 ivrs_ioapic[10]=00:14.0
1697 ivrs_hpet [HW,X86_64]
1698 Provide an override to the HPET-ID<->DEVICE-ID
1699 mapping provided in the IVRS ACPI table. For
1700 example, to map HPET-ID decimal 0 to
1701 PCI device 00:14.0 write the parameter as:
1702 ivrs_hpet[0]=00:14.0
1704 js= [HW,JOY] Analog joystick
1705 See Documentation/input/joystick.txt.
1708 Enable/disable kernel and module base offset ASLR
1709 (Address Space Layout Randomization) if built into
1710 the kernel. When CONFIG_HIBERNATION is selected,
1711 kASLR is disabled by default. When kASLR is enabled,
1712 hibernation will be disabled.
1716 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1717 specifies the amount of memory usable by the kernel
1718 for non-movable allocations. The requested amount is
1719 spread evenly throughout all nodes in the system. The
1720 remaining memory in each node is used for Movable
1721 pages. In the event, a node is too small to have both
1722 kernelcore and Movable pages, kernelcore pages will
1723 take priority and other nodes will have a larger number
1724 of Movable pages. The Movable zone is used for the
1725 allocation of pages that may be reclaimed or moved
1726 by the page migration subsystem. This means that
1727 HugeTLB pages may not be allocated from this zone.
1728 Note that allocations like PTEs-from-HighMem still
1729 use the HighMem zone if it exists, and the Normal
1730 zone if it does not.
1732 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1733 Format: <Controller#>[,poll interval]
1734 The controller # is the number of the ehci usb debug
1735 port as it is probed via PCI. The poll interval is
1736 optional and is the number seconds in between
1737 each poll cycle to the debug port in case you need
1738 the functionality for interrupting the kernel with
1739 gdb or control-c on the dbgp connection. When
1740 not using this parameter you use sysrq-g to break into
1741 the kernel debugger.
1743 kgdboc= [KGDB,HW] kgdb over consoles.
1744 Requires a tty driver that supports console polling,
1745 or a supported polling keyboard driver (non-usb).
1746 Serial only format: <serial_device>[,baud]
1747 keyboard only format: kbd
1748 keyboard and serial format: kbd,<serial_device>[,baud]
1749 Optional Kernel mode setting:
1750 kms, kbd format: kms,kbd
1751 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1753 kgdbwait [KGDB] Stop kernel execution and enter the
1754 kernel debugger at the earliest opportunity.
1756 kmac= [MIPS] korina ethernet MAC address.
1757 Configure the RouterBoard 532 series on-chip
1758 Ethernet adapter MAC address.
1760 kmemleak= [KNL] Boot-time kmemleak enable/disable
1761 Valid arguments: on, off
1763 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1766 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1767 Valid arguments: 0, 1, 2
1768 kmemcheck=0 (disabled)
1769 kmemcheck=1 (enabled)
1770 kmemcheck=2 (one-shot mode)
1771 Default: 2 (one-shot mode)
1773 kstack=N [X86] Print N words from the kernel stack
1776 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1777 Default is 0 (don't ignore, but inject #GP)
1779 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1783 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1784 Default is 1 (enabled)
1786 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1788 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1790 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1791 (virtualized MMU) support on capable Intel chips.
1792 Default is 1 (enabled)
1794 kvm-intel.emulate_invalid_guest_state=
1795 [KVM,Intel] Enable emulation of invalid guest states
1796 Default is 0 (disabled)
1798 kvm-intel.flexpriority=
1799 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1800 Default is 1 (enabled)
1803 [KVM,Intel] Enable VMX nesting (nVMX).
1804 Default is 0 (disabled)
1806 kvm-intel.unrestricted_guest=
1807 [KVM,Intel] Disable unrestricted guest feature
1808 (virtualized real and unpaged mode) on capable
1809 Intel chips. Default is 1 (enabled)
1811 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1812 feature (tagged TLBs) on capable Intel chips.
1813 Default is 1 (enabled)
1819 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1822 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1823 value for LAPIC timer one-shot implementation. Default
1824 back to the programmable timer unit in the LAPIC.
1826 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1829 libata.dma= [LIBATA] DMA control
1830 libata.dma=0 Disable all PATA and SATA DMA
1831 libata.dma=1 PATA and SATA Disk DMA only
1832 libata.dma=2 ATAPI (CDROM) DMA only
1833 libata.dma=4 Compact Flash DMA only
1834 Combinations also work, so libata.dma=3 enables DMA
1835 for disks and CDROMs, but not CFs.
1837 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1838 libata.ignore_hpa=0 keep BIOS limits (default)
1839 libata.ignore_hpa=1 ignore limits, using full disk
1841 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1845 libata.force= [LIBATA] Force configurations. The format is comma
1846 separated list of "[ID:]VAL" where ID is
1847 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1848 matching port, link or device. Basically, it matches
1849 the ATA ID string printed on console by libata. If
1850 the whole ID part is omitted, the last PORT and DEVICE
1851 values are used. If ID hasn't been specified yet, the
1852 configuration applies to all ports, links and devices.
1854 If only DEVICE is omitted, the parameter applies to
1855 the port and all links and devices behind it. DEVICE
1856 number of 0 either selects the first device or the
1857 first fan-out link behind PMP device. It does not
1858 select the host link. DEVICE number of 15 selects the
1859 host link and device attached to it.
1861 The VAL specifies the configuration to force. As long
1862 as there's no ambiguity shortcut notation is allowed.
1863 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1864 The following configurations can be forced.
1866 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1867 Any ID with matching PORT is used.
1869 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1871 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1872 udma[/][16,25,33,44,66,100,133] notation is also
1875 * [no]ncq: Turn on or off NCQ.
1877 * [no]ncqtrim: Turn off queued DSM TRIM.
1879 * nohrst, nosrst, norst: suppress hard, soft
1882 * rstonce: only attempt one reset during
1883 hot-unplug link recovery
1885 * dump_id: dump IDENTIFY data.
1887 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1889 * disable: Disable this device.
1891 If there are multiple matching configurations changing
1892 the same attribute, the last one is used.
1894 memblock=debug [KNL] Enable memblock debug messages.
1896 load_ramdisk= [RAM] List of ramdisks to load from floppy
1897 See Documentation/blockdev/ramdisk.txt.
1899 lockd.nlm_grace_period=P [NFS] Assign grace period.
1902 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1905 lockd.nlm_timeout=T [NFS] Assign timeout value.
1908 lockd.nlm_udpport=M [NFS] Assign UDP port.
1911 locktorture.nreaders_stress= [KNL]
1912 Set the number of locking read-acquisition kthreads.
1913 Defaults to being automatically set based on the
1914 number of online CPUs.
1916 locktorture.nwriters_stress= [KNL]
1917 Set the number of locking write-acquisition kthreads.
1919 locktorture.onoff_holdoff= [KNL]
1920 Set time (s) after boot for CPU-hotplug testing.
1922 locktorture.onoff_interval= [KNL]
1923 Set time (s) between CPU-hotplug operations, or
1924 zero to disable CPU-hotplug testing.
1926 locktorture.shuffle_interval= [KNL]
1927 Set task-shuffle interval (jiffies). Shuffling
1928 tasks allows some CPUs to go into dyntick-idle
1929 mode during the locktorture test.
1931 locktorture.shutdown_secs= [KNL]
1932 Set time (s) after boot system shutdown. This
1933 is useful for hands-off automated testing.
1935 locktorture.stat_interval= [KNL]
1936 Time (s) between statistics printk()s.
1938 locktorture.stutter= [KNL]
1939 Time (s) to stutter testing, for example,
1940 specifying five seconds causes the test to run for
1941 five seconds, wait for five seconds, and so on.
1942 This tests the locking primitive's ability to
1943 transition abruptly to and from idle.
1945 locktorture.torture_runnable= [BOOT]
1946 Start locktorture running at boot time.
1948 locktorture.torture_type= [KNL]
1949 Specify the locking implementation to test.
1951 locktorture.verbose= [KNL]
1952 Enable additional printk() statements.
1954 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1957 loglevel= All Kernel Messages with a loglevel smaller than the
1958 console loglevel will be printed to the console. It can
1959 also be changed with klogd or other programs. The
1960 loglevels are defined as follows:
1962 0 (KERN_EMERG) system is unusable
1963 1 (KERN_ALERT) action must be taken immediately
1964 2 (KERN_CRIT) critical conditions
1965 3 (KERN_ERR) error conditions
1966 4 (KERN_WARNING) warning conditions
1967 5 (KERN_NOTICE) normal but significant condition
1968 6 (KERN_INFO) informational
1969 7 (KERN_DEBUG) debug-level messages
1971 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1972 in bytes. n must be a power of two and greater
1973 than the minimal size. The minimal size is defined
1974 by LOG_BUF_SHIFT kernel config parameter. There is
1975 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1976 that allows to increase the default size depending on
1977 the number of CPUs. See init/Kconfig for more details.
1979 logo.nologo [FB] Disables display of the built-in Linux logo.
1980 This may be used to provide more screen space for
1981 kernel log messages and is useful when debugging
1982 kernel boot problems.
1984 lp=0 [LP] Specify parallel ports to use, e.g,
1985 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1986 lp=reset first parallel port). 'lp=0' disables the
1987 lp=auto printer driver. 'lp=reset' (which can be
1988 specified in addition to the ports) causes
1989 attached printers to be reset. Using
1990 lp=port1,port2,... specifies the parallel ports
1991 to associate lp devices with, starting with
1992 lp0. A port specification may be 'none' to skip
1993 that lp device, or a parport name such as
1994 'parport0'. Specifying 'lp=auto' instead of a
1995 port specification list means that device IDs
1996 from each port should be examined, to see if
1997 an IEEE 1284-compliant printer is attached; if
1998 so, the driver will manage that printer.
1999 See also header of drivers/char/lp.c.
2002 Sets loops_per_jiffy to given constant, thus avoiding
2003 time-consuming boot-time autodetection (up to 250 ms per
2004 CPU). 0 enables autodetection (default). To determine
2005 the correct value for your kernel, boot with normal
2006 autodetection and see what value is printed. Note that
2007 on SMP systems the preset will be applied to all CPUs,
2008 which is likely to cause problems if your CPUs need
2009 significantly divergent settings. An incorrect value
2010 will cause delays in the kernel to be wrong, leading to
2011 unpredictable I/O errors and other breakage. Although
2012 unlikely, in the extreme case this might damage your
2016 Format: <io>,<irq>,<dma>
2018 machvec= [IA-64] Force the use of a particular machine-vector
2019 (machvec) in a generic kernel.
2020 Example: machvec=hpzx1_swiotlb
2022 machtype= [Loongson] Share the same kernel image file between different
2024 Example: machtype=lemote-yeeloong-2f-7inch
2026 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2027 than or equal to this physical address is ignored.
2029 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2030 should make use of. maxcpus=n : n >= 0 limits the
2031 kernel to using 'n' processors. n=0 is a special case,
2032 it is equivalent to "nosmp", which also disables
2035 max_loop= [LOOP] The number of loop block devices that get
2036 (loop.max_loop) unconditionally pre-created at init time. The default
2037 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2038 of statically allocating a predefined number, loop
2039 devices can be requested on-demand with the
2040 /dev/loop-control interface.
2042 mce [X86-32] Machine Check Exception
2044 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2046 md= [HW] RAID subsystems devices and level
2047 See Documentation/md.txt.
2050 Format: <first>,<last>
2051 Specifies range of consoles to be captured by the MDA.
2053 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2054 Amount of memory to be used when the kernel is not able
2055 to see the whole system memory or for test.
2056 [X86] Work as limiting max address. Use together
2057 with memmap= to avoid physical address space collisions.
2058 Without memmap= PCI devices could be placed at addresses
2059 belonging to unused RAM.
2061 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2065 [KNL,SH] Allow user to override the default size for
2066 per-device physically contiguous DMA buffers.
2068 memmap=exactmap [KNL,X86] Enable setting of an exact
2069 E820 memory map, as specified by the user.
2070 Such memmap=exactmap lines can be constructed based on
2071 BIOS output or other requirements. See the memmap=nn@ss
2074 memmap=nn[KMG]@ss[KMG]
2075 [KNL] Force usage of a specific region of memory.
2076 Region of memory to be used is from ss to ss+nn.
2078 memmap=nn[KMG]#ss[KMG]
2079 [KNL,ACPI] Mark specific memory as ACPI data.
2080 Region of memory to be marked is from ss to ss+nn.
2082 memmap=nn[KMG]$ss[KMG]
2083 [KNL,ACPI] Mark specific memory as reserved.
2084 Region of memory to be reserved is from ss to ss+nn.
2085 Example: Exclude memory from 0x18690000-0x1869ffff
2086 memmap=64K$0x18690000
2088 memmap=0x10000$0x18690000
2090 memmap=nn[KMG]!ss[KMG]
2091 [KNL,X86] Mark specific memory as protected.
2092 Region of memory to be used, from ss to ss+nn.
2093 The memory region may be marked as e820 type 12 (0xc)
2094 and is NVDIMM or ADR memory.
2096 memory_corruption_check=0/1 [X86]
2097 Some BIOSes seem to corrupt the first 64k of
2098 memory when doing things like suspend/resume.
2099 Setting this option will scan the memory
2100 looking for corruption. Enabling this will
2101 both detect corruption and prevent the kernel
2102 from using the memory being corrupted.
2103 However, its intended as a diagnostic tool; if
2104 repeatable BIOS-originated corruption always
2105 affects the same memory, you can use memmap=
2106 to prevent the kernel from using that memory.
2108 memory_corruption_check_size=size [X86]
2109 By default it checks for corruption in the low
2110 64k, making this memory unavailable for normal
2111 use. Use this parameter to scan for
2112 corruption in more or less memory.
2114 memory_corruption_check_period=seconds [X86]
2115 By default it checks for corruption every 60
2116 seconds. Use this parameter to check at some
2117 other rate. 0 disables periodic checking.
2119 memtest= [KNL,X86,ARM] Enable memtest
2121 default : 0 <disable>
2122 Specifies the number of memtest passes to be
2123 performed. Each pass selects another test
2124 pattern from a given set of patterns. Memtest
2125 fills the memory with this pattern, validates
2126 memory contents and reserves bad memory
2127 regions that are detected.
2129 meye.*= [HW] Set MotionEye Camera parameters
2130 See Documentation/video4linux/meye.txt.
2132 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2133 Multi-Function General Purpose Timers on AMD Geode
2136 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2137 the BIOS has incorrectly applied a workaround. TinyBIOS
2138 version 0.98 is known to be affected, 0.99 fixes the
2139 problem by letting the user disable the workaround.
2143 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2144 physical address is ignored.
2146 mini2440= [ARM,HW,KNL]
2147 Format:[0..2][b][c][t]
2149 MINI2440 configuration specification:
2150 0 - The attached screen is the 3.5" TFT
2151 1 - The attached screen is the 7" TFT
2152 2 - The VGA Shield is attached (1024x768)
2153 Leaving out the screen size parameter will not load
2154 the TFT driver, and the framebuffer will be left
2156 b - Enable backlight. The TFT backlight pin will be
2157 linked to the kernel VESA blanking code and a GPIO
2158 LED. This parameter is not necessary when using the
2160 c - Enable the s3c camera interface.
2161 t - Reserved for enabling touchscreen support. The
2162 touchscreen support is not enabled in the mainstream
2163 kernel as of 2.6.30, a preliminary port can be found
2164 in the "bleeding edge" mini2440 support kernel at
2165 http://repo.or.cz/w/linux-2.6/mini2440.git
2168 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2169 parameter allows control of the logging verbosity for
2170 the additional memory initialisation checks. A value
2171 of 0 disables mminit logging and a level of 4 will
2172 log everything. Information is printed at KERN_DEBUG
2173 so loglevel=8 may also need to be specified.
2176 [KNL] When CONFIG_MODULE_SIG is set, this means that
2177 modules without (valid) signatures will fail to load.
2178 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2179 is always true, so this option does nothing.
2182 [MOUSE] Maximum time between finger touching and
2183 leaving touchpad surface for touch to be considered
2184 a tap and be reported as a left button click (for
2185 touchpads working in absolute mode only).
2187 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2188 reporting absolute coordinates, such as tablets
2189 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2190 reporting absolute coordinates, such as tablets
2192 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2193 is similar to kernelcore except it specifies the
2194 amount of memory used for migratable allocations.
2195 If both kernelcore and movablecore is specified,
2196 then kernelcore will be at *least* the specified
2197 value but may be more. If movablecore on its own
2198 is specified, the administrator must be careful
2199 that the amount of memory usable for all allocations
2202 movable_node [KNL,X86] Boot-time switch to enable the effects
2203 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2205 MTD_Partition= [MTD]
2206 Format: <name>,<region-number>,<size>,<offset>
2208 MTD_Region= [MTD] Format:
2209 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2212 See drivers/mtd/cmdlinepart.c.
2214 multitce=off [PPC] This parameter disables the use of the pSeries
2215 firmware feature for updating multiple TCE entries
2218 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2220 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2222 boundary - index of last SLC block on Flex-OneNAND.
2223 The remaining blocks are configured as MLC blocks.
2224 lock - Configure if Flex-OneNAND boundary should be locked.
2225 Once locked, the boundary cannot be changed.
2226 1 indicates lock status, 0 indicates unlock status.
2229 ARM/S3C2412 JIVE boot control
2231 See arch/arm/mach-s3c2412/mach-jive.c
2233 mtouchusb.raw_coordinates=
2234 [HW] Make the MicroTouch USB driver use raw coordinates
2235 ('y', default) or cooked coordinates ('n')
2237 mtrr_chunk_size=nn[KMG] [X86]
2238 used for mtrr cleanup. It is largest continuous chunk
2239 that could hold holes aka. UC entries.
2241 mtrr_gran_size=nn[KMG] [X86]
2242 Used for mtrr cleanup. It is granularity of mtrr block.
2244 Large value could prevent small alignment from
2247 mtrr_spare_reg_nr=n [X86]
2249 Range: 0,7 : spare reg number
2251 Used for mtrr cleanup. It is spare mtrr entries number.
2252 Set to 2 or more if your graphical card needs more.
2254 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2256 netdev= [NET] Network devices parameters
2257 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2258 Note that mem_start is often overloaded to mean
2259 something different and driver-specific.
2260 This usage is only documented in each driver source
2264 [NETFILTER] Enable connection tracking flow accounting
2265 0 to disable accounting
2266 1 to enable accounting
2269 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2270 See Documentation/filesystems/nfs/nfsroot.txt.
2272 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2273 See Documentation/filesystems/nfs/nfsroot.txt.
2275 nfsrootdebug [NFS] enable nfsroot debugging messages.
2276 See Documentation/filesystems/nfs/nfsroot.txt.
2278 nfs.callback_tcpport=
2279 [NFS] set the TCP port on which the NFSv4 callback
2280 channel should listen.
2283 [NFS] sets the pathname to the program which is used
2284 to update the NFS client cache entries.
2286 nfs.cache_getent_timeout=
2287 [NFS] sets the timeout after which an attempt to
2288 update a cache entry is deemed to have failed.
2290 nfs.idmap_cache_timeout=
2291 [NFS] set the maximum lifetime for idmapper cache
2295 [NFS] enable 64-bit inode numbers.
2296 If zero, the NFS client will fake up a 32-bit inode
2297 number for the readdir() and stat() syscalls instead
2298 of returning the full 64-bit number.
2299 The default is to return 64-bit inode numbers.
2301 nfs.max_session_slots=
2302 [NFSv4.1] Sets the maximum number of session slots
2303 the client will attempt to negotiate with the server.
2304 This limits the number of simultaneous RPC requests
2305 that the client can send to the NFSv4.1 server.
2306 Note that there is little point in setting this
2307 value higher than the max_tcp_slot_table_limit.
2309 nfs.nfs4_disable_idmapping=
2310 [NFSv4] When set to the default of '1', this option
2311 ensures that both the RPC level authentication
2312 scheme and the NFS level operations agree to use
2313 numeric uids/gids if the mount is using the
2314 'sec=sys' security flavour. In effect it is
2315 disabling idmapping, which can make migration from
2316 legacy NFSv2/v3 systems to NFSv4 easier.
2317 Servers that do not support this mode of operation
2318 will be autodetected by the client, and it will fall
2319 back to using the idmapper.
2320 To turn off this behaviour, set the value to '0'.
2322 [NFS4] Specify an additional fixed unique ident-
2323 ification string that NFSv4 clients can insert into
2324 their nfs_client_id4 string. This is typically a
2325 UUID that is generated at system install time.
2327 nfs.send_implementation_id =
2328 [NFSv4.1] Send client implementation identification
2329 information in exchange_id requests.
2330 If zero, no implementation identification information
2332 The default is to send the implementation identification
2335 nfs.recover_lost_locks =
2336 [NFSv4] Attempt to recover locks that were lost due
2337 to a lease timeout on the server. Please note that
2338 doing this risks data corruption, since there are
2339 no guarantees that the file will remain unchanged
2340 after the locks are lost.
2341 If you want to enable the kernel legacy behaviour of
2342 attempting to recover these locks, then set this
2344 The default parameter value of '0' causes the kernel
2345 not to attempt recovery of lost locks.
2347 nfs4.layoutstats_timer =
2348 [NFSv4.2] Change the rate at which the kernel sends
2349 layoutstats to the pNFS metadata server.
2351 Setting this to value to 0 causes the kernel to use
2352 whatever value is the default set by the layout
2353 driver. A non-zero value sets the minimum interval
2354 in seconds between layoutstats transmissions.
2356 nfsd.nfs4_disable_idmapping=
2357 [NFSv4] When set to the default of '1', the NFSv4
2358 server will return only numeric uids and gids to
2359 clients using auth_sys, and will accept numeric uids
2360 and gids from such clients. This is intended to ease
2361 migration from NFSv2/v3.
2363 objlayoutdriver.osd_login_prog=
2364 [NFS] [OBJLAYOUT] sets the pathname to the program which
2365 is used to automatically discover and login into new
2366 osd-targets. Please see:
2367 Documentation/filesystems/pnfs.txt for more explanations
2369 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2370 when a NMI is triggered.
2371 Format: [state][,regs][,debounce][,die]
2373 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2374 Format: [panic,][nopanic,][num]
2376 0 - turn hardlockup detector in nmi_watchdog off
2377 1 - turn hardlockup detector in nmi_watchdog on
2378 When panic is specified, panic when an NMI watchdog
2379 timeout occurs (or 'nopanic' to override the opposite
2380 default). To disable both hard and soft lockup detectors,
2381 please see 'nowatchdog'.
2382 This is useful when you use a panic=... timeout and
2383 need the box quickly up again.
2385 netpoll.carrier_timeout=
2386 [NET] Specifies amount of time (in seconds) that
2387 netpoll should wait for a carrier. By default netpoll
2390 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2391 emulation library even if a 387 maths coprocessor
2395 [HW] Never suspend the console
2396 Disable suspending of consoles during suspend and
2397 hibernate operations. Once disabled, debugging
2398 messages can reach various consoles while the rest
2399 of the system is being put to sleep (ie, while
2400 debugging driver suspend/resume hooks). This may
2401 not work reliably with all consoles, but is known
2402 to work with serial and VGA consoles.
2403 To facilitate more flexible debugging, we also add
2404 console_suspend, a printk module parameter to control
2405 it. Users could use console_suspend (usually
2406 /sys/module/printk/parameters/console_suspend) to
2407 turn on/off it dynamically.
2409 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2410 caches in the slab allocator. Saves per-node memory,
2411 but will impact performance.
2415 noapic [SMP,APIC] Tells the kernel to not make use of any
2416 IOAPICs that may be present in the system.
2418 noautogroup Disable scheduler automatic task group creation.
2420 nobats [PPC] Do not use BATs for mapping kernel lowmem
2421 on "Classic" PPC cores.
2425 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2427 nodelayacct [KNL] Disable per-task delay accounting
2429 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2431 nodsp [SH] Disable hardware DSP at boot time.
2433 noefi Disable EFI runtime services support.
2438 On X86-32 available only on PAE configured kernels.
2439 noexec=on: enable non-executable mappings (default)
2440 noexec=off: disable non-executable mappings
2443 Disable SMAP (Supervisor Mode Access Prevention)
2444 even if it is supported by processor.
2447 Disable SMEP (Supervisor Mode Execution Prevention)
2448 even if it is supported by processor.
2451 This affects only 32-bit executables.
2452 noexec32=on: enable non-executable mappings (default)
2453 read doesn't imply executable mappings
2454 noexec32=off: disable non-executable mappings
2455 read implies executable mappings
2457 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2459 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2460 register save and restore. The kernel will only save
2461 legacy floating-point registers on task switch.
2463 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2465 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2466 (indirect branch prediction) vulnerability. System may
2467 allow data leaks with this option, which is equivalent
2470 noxsave [BUGS=X86] Disables x86 extended register state save
2471 and restore using xsave. The kernel will fallback to
2472 enabling legacy floating-point and sse state.
2474 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2475 register states. The kernel will fall back to use
2476 xsave to save the states. By using this parameter,
2477 performance of saving the states is degraded because
2478 xsave doesn't support modified optimization while
2479 xsaveopt supports it on xsaveopt enabled systems.
2481 noxsaves [X86] Disables xsaves and xrstors used in saving and
2482 restoring x86 extended register state in compacted
2483 form of xsave area. The kernel will fall back to use
2484 xsaveopt and xrstor to save and restore the states
2485 in standard form of xsave area. By using this
2486 parameter, xsave area per process might occupy more
2487 memory on xsaves enabled systems.
2489 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2490 wfi(ARM) instruction doesn't work correctly and not to
2491 use it. This is also useful when using JTAG debugger.
2493 no_file_caps Tells the kernel not to honor file capabilities. The
2494 only way then for a file to be executed with privilege
2495 is to be setuid root or executed by root.
2497 nohalt [IA-64] Tells the kernel not to use the power saving
2498 function PAL_HALT_LIGHT when idle. This increases
2499 power-consumption. On the positive side, it reduces
2500 interrupt wake-up latency, which may improve performance
2501 in certain environments such as networked servers or
2504 nohibernate [HIBERNATION] Disable hibernation and resume.
2506 nohz= [KNL] Boottime enable/disable dynamic ticks
2507 Valid arguments: on, off
2510 nohz_full= [KNL,BOOT]
2511 In kernels built with CONFIG_NO_HZ_FULL=y, set
2512 the specified list of CPUs whose tick will be stopped
2513 whenever possible. The boot CPU will be forced outside
2514 the range to maintain the timekeeping.
2515 The CPUs in this range must also be included in the
2518 noiotrap [SH] Disables trapped I/O port accesses.
2520 noirqdebug [X86-32] Disables the code which attempts to detect and
2521 disable unhandled interrupt sources.
2523 no_timer_check [X86,APIC] Disables the code which tests for
2524 broken timer IRQ sources.
2526 noisapnp [ISAPNP] Disables ISA PnP code.
2528 noinitrd [RAM] Tells the kernel not to load any configured
2531 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2533 [Deprecated - use intremap=off]
2537 noinvpcid [X86] Disable the INVPCID cpu feature.
2539 nojitter [IA-64] Disables jitter checking for ITC timers.
2541 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2543 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2546 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2547 steal time is computed, but won't influence scheduler
2550 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2552 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2554 noltlbs [PPC] Do not use large page/tlb entries for kernel
2555 lowmem mapping on PPC40x.
2557 nomca [IA-64] Disable machine check abort handling
2559 nomce [X86-32] Disable Machine Check Exception
2561 nomfgpt [X86-32] Disable Multi-Function General Purpose
2562 Timer usage (for AMD Geode machines).
2564 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2565 shutdown the other cpus. Instead use the REBOOT_VECTOR
2568 nomodule Disable module load
2570 nopat [X86] Disable PAT (page attribute table extension of
2571 pagetables) support.
2573 nopcid [X86-64] Disable the PCID cpu feature.
2575 norandmaps Don't use address space randomization. Equivalent to
2576 echo 0 > /proc/sys/kernel/randomize_va_space
2578 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2580 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2581 with UP alternatives
2583 nordrand [X86] Disable kernel use of the RDRAND and
2584 RDSEED instructions even if they are supported
2585 by the processor. RDRAND and RDSEED are still
2586 available to user space applications.
2588 noresume [SWSUSP] Disables resume and restores original swap
2591 no-scroll [VGA] Disables scrollback.
2592 This is required for the Braillex ib80-piezo Braille
2593 reader made by F.H. Papenmeier (Germany).
2597 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2599 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2600 and disable the IO APIC. legacy for "maxcpus=0".
2602 nosoftlockup [KNL] Disable the soft-lockup detector.
2604 nosync [HW,M68K] Disables sync negotiation for all devices.
2606 notsc [BUGS=X86-32] Disable Time Stamp Counter
2608 nousb [USB] Disable the USB subsystem
2610 nowatchdog [KNL] Disable both lockup detectors, i.e.
2611 soft-lockup and NMI watchdog (hard-lockup).
2615 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2617 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2618 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2619 Some features depend on CPU0. Known dependencies are:
2620 1. Resume from suspend/hibernate depends on CPU0.
2621 Suspend/hibernate will fail if CPU0 is offline and you
2622 need to online CPU0 before suspend/hibernate.
2623 2. PIC interrupts also depend on CPU0. CPU0 can't be
2624 removed if a PIC interrupt is detected.
2625 It's said poweroff/reboot may depend on CPU0 on some
2626 machines although I haven't seen such issues so far
2627 after CPU0 is offline on a few tested machines.
2628 If the dependencies are under your control, you can
2629 turn on cpu0_hotplug.
2631 nptcg= [IA-64] Override max number of concurrent global TLB
2632 purges which is reported from either PAL_VM_SUMMARY or
2635 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2636 could support. nr_cpus=n : n >= 1 limits the kernel to
2637 supporting 'n' processors. Later in runtime you can not
2638 use hotplug cpu feature to put more cpu back to online.
2639 just like you compile the kernel NR_CPUS=n
2641 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2643 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2644 Allowed values are enable and disable
2646 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2647 one of ['zone', 'node', 'default'] can be specified
2648 This can be set from sysctl after boot.
2649 See Documentation/sysctl/vm.txt for details.
2651 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2652 See Documentation/debugging-via-ohci1394.txt for more
2655 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2656 Rather than timing out after 20 ms if an EC
2657 command is not properly ACKed, override the length
2658 of the timeout. We have interrupts disabled while
2659 waiting for the ACK, so if this is set too high
2660 interrupts *may* be lost!
2662 omap_mux= [OMAP] Override bootloader pin multiplexing.
2663 Format: <mux_mode0.mode_name=value>...
2664 For example, to override I2C bus2:
2665 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2667 oprofile.timer= [HW]
2668 Use timer interrupt instead of performance counters
2670 oprofile.cpu_type= Force an oprofile cpu type
2671 This might be useful if you have an older oprofile
2672 userland or if you want common events.
2673 Format: { arch_perfmon }
2674 arch_perfmon: [X86] Force use of architectural
2675 perfmon on Intel CPUs instead of the
2676 CPU specific event set.
2677 timer: [X86] Force use of architectural NMI
2678 timer mode (see also oprofile.timer
2679 for generic hr timer mode)
2680 [s390] Force legacy basic mode sampling
2681 (report cpu_type "timer")
2683 oops=panic Always panic on oopses. Default is to just kill the
2684 process, but there is a small probability of
2685 deadlocking the machine.
2686 This will also cause panics on machine check exceptions.
2687 Useful together with panic=30 to trigger a reboot.
2690 See Documentation/sound/oss/oss-parameters.txt
2692 page_owner= [KNL] Boot-time page_owner enabling option.
2693 Storage of the information about who allocated
2694 each page is disabled in default. With this switch,
2696 on: enable the feature
2698 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2699 timeout > 0: seconds before rebooting
2700 timeout = 0: wait forever
2701 timeout < 0: reboot immediately
2704 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2707 crash_kexec_post_notifiers
2708 Run kdump after running panic-notifiers and dumping
2709 kmsg. This only for the users who doubt kdump always
2710 succeeds in any situation.
2711 Note that this also increases risks of kdump failure,
2712 because some panic notifiers can make the crashed
2713 kernel more unstable.
2715 parkbd.port= [HW] Parallel port number the keyboard adapter is
2716 connected to, default is 0.
2718 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2719 0 for XT, 1 for AT (default is AT).
2722 parport= [HW,PPT] Specify parallel ports. 0 disables.
2723 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2724 Use 'auto' to force the driver to use any
2725 IRQ/DMA settings detected (the default is to
2726 ignore detected IRQ/DMA settings because of
2727 possible conflicts). You can specify the base
2728 address, IRQ, and DMA settings; IRQ and DMA
2729 should be numbers, or 'auto' (for using detected
2730 settings on that particular port), or 'nofifo'
2731 (to avoid using a FIFO even if it is detected).
2732 Parallel ports are assigned in the order they
2733 are specified on the command line, starting
2736 parport_init_mode= [HW,PPT]
2737 Configure VIA parallel port to operate in
2738 a specific mode. This is necessary on Pegasos
2739 computer where firmware has no options for setting
2740 up parallel port mode and sets it to spp.
2741 Currently this function knows 686a and 8231 chips.
2742 Format: [spp|ps2|epp|ecp|ecpepp]
2745 Halt all CPUs after the first oops has been printed for
2746 the specified number of seconds. This is to be used if
2747 your oopses keep scrolling off the screen.
2752 See header of drivers/block/paride/pcd.c.
2753 See also Documentation/blockdev/paride.txt.
2755 pci=option[,option...] [PCI] various PCI subsystem options:
2756 earlydump [X86] dump PCI config space before the kernel
2758 off [X86] don't probe for the PCI bus
2759 bios [X86-32] force use of PCI BIOS, don't access
2760 the hardware directly. Use this if your machine
2761 has a non-standard PCI host bridge.
2762 nobios [X86-32] disallow use of PCI BIOS, only direct
2763 hardware access methods are allowed. Use this
2764 if you experience crashes upon bootup and you
2765 suspect they are caused by the BIOS.
2766 conf1 [X86] Force use of PCI Configuration
2768 conf2 [X86] Force use of PCI Configuration
2770 noaer [PCIE] If the PCIEAER kernel config parameter is
2771 enabled, this kernel boot option can be used to
2772 disable the use of PCIE advanced error reporting.
2773 nodomains [PCI] Disable support for multiple PCI
2774 root domains (aka PCI segments, in ACPI-speak).
2775 nommconf [X86] Disable use of MMCONFIG for PCI
2777 check_enable_amd_mmconf [X86] check for and enable
2778 properly configured MMIO access to PCI
2779 config space on AMD family 10h CPU
2780 nomsi [MSI] If the PCI_MSI kernel config parameter is
2781 enabled, this kernel boot option can be used to
2782 disable the use of MSI interrupts system-wide.
2783 noioapicquirk [APIC] Disable all boot interrupt quirks.
2784 Safety option to keep boot IRQs enabled. This
2785 should never be necessary.
2786 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2787 primary IO-APIC for bridges that cannot disable
2788 boot IRQs. This fixes a source of spurious IRQs
2789 when the system masks IRQs.
2790 noioapicreroute [APIC] Disable workaround that uses the
2791 boot IRQ equivalent of an IRQ that connects to
2792 a chipset where boot IRQs cannot be disabled.
2793 The opposite of ioapicreroute.
2794 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2795 routing table. These calls are known to be buggy
2796 on several machines and they hang the machine
2797 when used, but on other computers it's the only
2798 way to get the interrupt routing table. Try
2799 this option if the kernel is unable to allocate
2800 IRQs or discover secondary PCI buses on your
2802 rom [X86] Assign address space to expansion ROMs.
2803 Use with caution as certain devices share
2804 address decoders between ROMs and other
2806 norom [X86] Do not assign address space to
2807 expansion ROMs that do not already have
2808 BIOS assigned address ranges.
2809 nobar [X86] Do not assign address space to the
2810 BARs that weren't assigned by the BIOS.
2811 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2812 assigned automatically to PCI devices. You can
2813 make the kernel exclude IRQs of your ISA cards
2815 pirqaddr=0xAAAAA [X86] Specify the physical address
2816 of the PIRQ table (normally generated
2817 by the BIOS) if it is outside the
2818 F0000h-100000h range.
2819 lastbus=N [X86] Scan all buses thru bus #N. Can be
2820 useful if the kernel is unable to find your
2821 secondary buses and you want to tell it
2822 explicitly which ones they are.
2823 assign-busses [X86] Always assign all PCI bus
2824 numbers ourselves, overriding
2825 whatever the firmware may have done.
2826 usepirqmask [X86] Honor the possible IRQ mask stored
2827 in the BIOS $PIR table. This is needed on
2828 some systems with broken BIOSes, notably
2829 some HP Pavilion N5400 and Omnibook XE3
2830 notebooks. This will have no effect if ACPI
2831 IRQ routing is enabled.
2832 noacpi [X86] Do not use ACPI for IRQ routing
2833 or for PCI scanning.
2834 use_crs [X86] Use PCI host bridge window information
2835 from ACPI. On BIOSes from 2008 or later, this
2836 is enabled by default. If you need to use this,
2837 please report a bug.
2838 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2839 If you need to use this, please report a bug.
2840 routeirq Do IRQ routing for all PCI devices.
2841 This is normally done in pci_enable_device(),
2842 so this option is a temporary workaround
2843 for broken drivers that don't call it.
2844 skip_isa_align [X86] do not align io start addr, so can
2845 handle more pci cards
2846 firmware [ARM] Do not re-enumerate the bus but instead
2847 just use the configuration from the
2848 bootloader. This is currently used on
2849 IXP2000 systems where the bus has to be
2850 configured a certain way for adjunct CPUs.
2851 noearly [X86] Don't do any early type 1 scanning.
2852 This might help on some broken boards which
2853 machine check when some devices' config space
2854 is read. But various workarounds are disabled
2855 and some IOMMU drivers will not work.
2856 bfsort Sort PCI devices into breadth-first order.
2857 This sorting is done to get a device
2858 order compatible with older (<= 2.4) kernels.
2859 nobfsort Don't sort PCI devices into breadth-first order.
2860 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2861 tuning and use the BIOS-configured MPS defaults.
2862 pcie_bus_safe Set every device's MPS to the largest value
2863 supported by all devices below the root complex.
2864 pcie_bus_perf Set device MPS to the largest allowable MPS
2865 based on its parent bus. Also set MRRS (Max
2866 Read Request Size) to the largest supported
2867 value (no larger than the MPS that the device
2868 or bus can support) for best performance.
2869 pcie_bus_peer2peer Set every device's MPS to 128B, which
2870 every device is guaranteed to support. This
2871 configuration allows peer-to-peer DMA between
2872 any pair of devices, possibly at the cost of
2873 reduced performance. This also guarantees
2874 that hot-added devices will work.
2875 cbiosize=nn[KMG] The fixed amount of bus space which is
2876 reserved for the CardBus bridge's IO window.
2877 The default value is 256 bytes.
2878 cbmemsize=nn[KMG] The fixed amount of bus space which is
2879 reserved for the CardBus bridge's memory
2880 window. The default value is 64 megabytes.
2883 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2884 Specifies alignment and device to reassign
2885 aligned memory resources.
2886 If <order of align> is not specified,
2887 PAGE_SIZE is used as alignment.
2888 PCI-PCI bridge can be specified, if resource
2889 windows need to be expanded.
2890 ecrc= Enable/disable PCIe ECRC (transaction layer
2891 end-to-end CRC checking).
2892 bios: Use BIOS/firmware settings. This is the
2896 hpiosize=nn[KMG] The fixed amount of bus space which is
2897 reserved for hotplug bridge's IO window.
2898 Default size is 256 bytes.
2899 hpmemsize=nn[KMG] The fixed amount of bus space which is
2900 reserved for hotplug bridge's memory window.
2901 Default size is 2 megabytes.
2902 realloc= Enable/disable reallocating PCI bridge resources
2903 if allocations done by BIOS are too small to
2904 accommodate resources required by all child
2906 off: Turn realloc off
2908 realloc same as realloc=on
2909 noari do not use PCIe ARI.
2910 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2911 only look for one device below a PCIe downstream
2914 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2917 force Enable ASPM even on devices that claim not to support it.
2918 WARNING: Forcing ASPM on may cause system lockups.
2920 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2921 nomsi Do not use MSI for PCI Express Native Hotplug (this
2922 makes all PCIe ports use INTx for hotplug services).
2924 pcie_ports= [PCIE] PCIe ports handling:
2925 auto Ask the BIOS whether or not to use native PCIe services
2926 associated with PCIe ports (PME, hot-plug, AER). Use
2927 them only if that is allowed by the BIOS.
2928 native Use native PCIe services associated with PCIe ports
2930 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2933 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2934 nomsi Do not use MSI for native PCIe PME signaling (this makes
2935 all PCIe root ports use INTx for all services).
2937 pcmv= [HW,PCMCIA] BadgePAD 4
2941 Keep all power-domains already enabled by bootloader on,
2942 even if no driver has claimed them. This is useful
2943 for debug and development, but should not be
2944 needed on a platform with proper driver support.
2947 See Documentation/blockdev/paride.txt.
2949 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2952 See arch/parisc/kernel/pdc_chassis.c
2954 percpu_alloc= Select which percpu first chunk allocator to use.
2955 Currently supported values are "embed" and "page".
2956 Archs may support subset or none of the selections.
2957 See comments in mm/percpu.c for details on each
2958 allocator. This parameter is primarily for debugging
2959 and performance comparison.
2962 See Documentation/blockdev/paride.txt.
2965 See Documentation/blockdev/paride.txt.
2967 pirq= [SMP,APIC] Manual mp-table setup
2968 See Documentation/x86/i386/IO-APIC.txt.
2970 plip= [PPT,NET] Parallel port network link
2971 Format: { parport<nr> | timid | 0 }
2972 See also Documentation/parport.txt.
2974 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2975 Override pmtimer IOPort with a hex value.
2979 Enable PNP debug messages (depends on the
2980 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2981 via /sys/module/pnp/parameters/debug. We always show
2982 current resource usage; turning this on also shows
2983 possible settings and some assignment information.
2989 { on | off | curr | res | no-curr | no-res }
2992 [ISAPNP] Exclude IRQs for the autoconfiguration
2995 [ISAPNP] Exclude DMAs for the autoconfiguration
2997 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2998 Ranges are in pairs (I/O port base and size).
3001 [ISAPNP] Exclude memory regions for the
3003 Ranges are in pairs (memory base and size).
3005 ports= [IP_VS_FTP] IPVS ftp helper module
3007 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3009 Format: <port>,<port>....
3011 print-fatal-signals=
3012 [KNL] debug: print fatal signals
3014 If enabled, warn about various signal handling
3015 related application anomalies: too many signals,
3016 too many POSIX.1 timers, fatal signals causing a
3019 If you hit the warning due to signal overflow,
3020 you might want to try "ulimit -i unlimited".
3024 printk.always_kmsg_dump=
3025 Trigger kmsg_dump for cases other than kernel oops or
3027 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3030 printk.time= Show timing data prefixed to each printk message line
3031 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3033 processor.max_cstate= [HW,ACPI]
3034 Limit processor to maximum C-state
3035 max_cstate=9 overrides any DMI blacklist limit.
3037 processor.nocst [HW,ACPI]
3038 Ignore the _CST method to determine C-states,
3039 instead using the legacy FADT method
3041 profile= [KNL] Enable kernel profiling via /proc/profile
3042 Format: [schedule,]<number>
3043 Param: "schedule" - profile schedule points.
3044 Param: <number> - step/bucket size as a power of 2 for
3045 statistical time based profiling.
3046 Param: "sleep" - profile D-state sleeping (millisecs).
3047 Requires CONFIG_SCHEDSTATS
3048 Param: "kvm" - profile VM exits.
3050 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3052 See Documentation/blockdev/ramdisk.txt.
3054 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3055 probe for; one of (bare|imps|exps|lifebook|any).
3056 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3058 psmouse.resetafter= [HW,MOUSE]
3059 Try to reset the device after so many bad packets
3062 [HW,MOUSE] Set desired mouse resolution, in dpi.
3063 psmouse.smartscroll=
3064 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3065 0 = disabled, 1 = enabled (default).
3067 pstore.backend= Specify the name of the pstore backend to use
3070 See Documentation/blockdev/paride.txt.
3072 pti= [X86_64] Control Page Table Isolation of user and
3073 kernel address spaces. Disabling this feature
3074 removes hardening, but improves performance of
3075 system calls and interrupts.
3077 on - unconditionally enable
3078 off - unconditionally disable
3079 auto - kernel detects whether your CPU model is
3080 vulnerable to issues that PTI mitigates
3082 Not specifying this option is equivalent to pti=auto.
3085 Equivalent to pti=off
3088 [KNL] Number of legacy pty's. Overwrites compiled-in
3091 quiet [KNL] Disable most log messages
3096 See Documentation/md.txt.
3098 ramdisk_blocksize= [RAM]
3099 See Documentation/blockdev/ramdisk.txt.
3101 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3102 See Documentation/blockdev/ramdisk.txt.
3105 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3106 the specified list of CPUs to be no-callback CPUs.
3107 Invocation of these CPUs' RCU callbacks will
3108 be offloaded to "rcuox/N" kthreads created for
3109 that purpose, where "x" is "b" for RCU-bh, "p"
3110 for RCU-preempt, and "s" for RCU-sched, and "N"
3111 is the CPU number. This reduces OS jitter on the
3112 offloaded CPUs, which can be useful for HPC and
3113 real-time workloads. It can also improve energy
3114 efficiency for asymmetric multiprocessors.
3117 Rather than requiring that offloaded CPUs
3118 (specified by rcu_nocbs= above) explicitly
3119 awaken the corresponding "rcuoN" kthreads,
3120 make these kthreads poll for callbacks.
3121 This improves the real-time response for the
3122 offloaded CPUs by relieving them of the need to
3123 wake up the corresponding kthread, but degrades
3124 energy efficiency by requiring that the kthreads
3125 periodically wake up to do the polling.
3127 rcutree.blimit= [KNL]
3128 Set maximum number of finished RCU callbacks to
3129 process in one batch.
3131 rcutree.dump_tree= [KNL]
3132 Dump the structure of the rcu_node combining tree
3133 out at early boot. This is used for diagnostic
3134 purposes, to verify correct tree setup.
3136 rcutree.gp_cleanup_delay= [KNL]
3137 Set the number of jiffies to delay each step of
3138 RCU grace-period cleanup. This only has effect
3139 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3141 rcutree.gp_init_delay= [KNL]
3142 Set the number of jiffies to delay each step of
3143 RCU grace-period initialization. This only has
3144 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3147 rcutree.gp_preinit_delay= [KNL]
3148 Set the number of jiffies to delay each step of
3149 RCU grace-period pre-initialization, that is,
3150 the propagation of recent CPU-hotplug changes up
3151 the rcu_node combining tree. This only has effect
3152 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3154 rcutree.rcu_fanout_exact= [KNL]
3155 Disable autobalancing of the rcu_node combining
3156 tree. This is used by rcutorture, and might
3157 possibly be useful for architectures having high
3158 cache-to-cache transfer latencies.
3160 rcutree.rcu_fanout_leaf= [KNL]
3161 Change the number of CPUs assigned to each
3162 leaf rcu_node structure. Useful for very
3163 large systems, which will choose the value 64,
3164 and for NUMA systems with large remote-access
3165 latencies, which will choose a value aligned
3166 with the appropriate hardware boundaries.
3168 rcutree.jiffies_till_sched_qs= [KNL]
3169 Set required age in jiffies for a
3170 given grace period before RCU starts
3171 soliciting quiescent-state help from
3172 rcu_note_context_switch().
3174 rcutree.jiffies_till_first_fqs= [KNL]
3175 Set delay from grace-period initialization to
3176 first attempt to force quiescent states.
3177 Units are jiffies, minimum value is zero,
3178 and maximum value is HZ.
3180 rcutree.jiffies_till_next_fqs= [KNL]
3181 Set delay between subsequent attempts to force
3182 quiescent states. Units are jiffies, minimum
3183 value is one, and maximum value is HZ.
3185 rcutree.kthread_prio= [KNL,BOOT]
3186 Set the SCHED_FIFO priority of the RCU per-CPU
3187 kthreads (rcuc/N). This value is also used for
3188 the priority of the RCU boost threads (rcub/N)
3189 and for the RCU grace-period kthreads (rcu_bh,
3190 rcu_preempt, and rcu_sched). If RCU_BOOST is
3191 set, valid values are 1-99 and the default is 1
3192 (the least-favored priority). Otherwise, when
3193 RCU_BOOST is not set, valid values are 0-99 and
3194 the default is zero (non-realtime operation).
3196 rcutree.rcu_nocb_leader_stride= [KNL]
3197 Set the number of NOCB kthread groups, which
3198 defaults to the square root of the number of
3199 CPUs. Larger numbers reduces the wakeup overhead
3200 on the per-CPU grace-period kthreads, but increases
3201 that same overhead on each group's leader.
3203 rcutree.qhimark= [KNL]
3204 Set threshold of queued RCU callbacks beyond which
3205 batch limiting is disabled.
3207 rcutree.qlowmark= [KNL]
3208 Set threshold of queued RCU callbacks below which
3209 batch limiting is re-enabled.
3211 rcutree.rcu_idle_gp_delay= [KNL]
3212 Set wakeup interval for idle CPUs that have
3213 RCU callbacks (RCU_FAST_NO_HZ=y).
3215 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3216 Set wakeup interval for idle CPUs that have
3217 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3218 Lazy RCU callbacks are those which RCU can
3219 prove do nothing more than free memory.
3221 rcutorture.cbflood_inter_holdoff= [KNL]
3222 Set holdoff time (jiffies) between successive
3223 callback-flood tests.
3225 rcutorture.cbflood_intra_holdoff= [KNL]
3226 Set holdoff time (jiffies) between successive
3227 bursts of callbacks within a given callback-flood
3230 rcutorture.cbflood_n_burst= [KNL]
3231 Set the number of bursts making up a given
3232 callback-flood test. Set this to zero to
3233 disable callback-flood testing.
3235 rcutorture.cbflood_n_per_burst= [KNL]
3236 Set the number of callbacks to be registered
3237 in a given burst of a callback-flood test.
3239 rcutorture.fqs_duration= [KNL]
3240 Set duration of force_quiescent_state bursts
3243 rcutorture.fqs_holdoff= [KNL]
3244 Set holdoff time within force_quiescent_state bursts
3247 rcutorture.fqs_stutter= [KNL]
3248 Set wait time between force_quiescent_state bursts
3251 rcutorture.gp_cond= [KNL]
3252 Use conditional/asynchronous update-side
3253 primitives, if available.
3255 rcutorture.gp_exp= [KNL]
3256 Use expedited update-side primitives, if available.
3258 rcutorture.gp_normal= [KNL]
3259 Use normal (non-expedited) asynchronous
3260 update-side primitives, if available.
3262 rcutorture.gp_sync= [KNL]
3263 Use normal (non-expedited) synchronous
3264 update-side primitives, if available. If all
3265 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3266 rcutorture.gp_normal=, and rcutorture.gp_sync=
3267 are zero, rcutorture acts as if is interpreted
3268 they are all non-zero.
3270 rcutorture.n_barrier_cbs= [KNL]
3271 Set callbacks/threads for rcu_barrier() testing.
3273 rcutorture.nfakewriters= [KNL]
3274 Set number of concurrent RCU writers. These just
3275 stress RCU, they don't participate in the actual
3276 test, hence the "fake".
3278 rcutorture.nreaders= [KNL]
3279 Set number of RCU readers. The value -1 selects
3280 N-1, where N is the number of CPUs. A value
3281 "n" less than -1 selects N-n-2, where N is again
3282 the number of CPUs. For example, -2 selects N
3283 (the number of CPUs), -3 selects N+1, and so on.
3285 rcutorture.object_debug= [KNL]
3286 Enable debug-object double-call_rcu() testing.
3288 rcutorture.onoff_holdoff= [KNL]
3289 Set time (s) after boot for CPU-hotplug testing.
3291 rcutorture.onoff_interval= [KNL]
3292 Set time (s) between CPU-hotplug operations, or
3293 zero to disable CPU-hotplug testing.
3295 rcutorture.shuffle_interval= [KNL]
3296 Set task-shuffle interval (s). Shuffling tasks
3297 allows some CPUs to go into dyntick-idle mode
3298 during the rcutorture test.
3300 rcutorture.shutdown_secs= [KNL]
3301 Set time (s) after boot system shutdown. This
3302 is useful for hands-off automated testing.
3304 rcutorture.stall_cpu= [KNL]
3305 Duration of CPU stall (s) to test RCU CPU stall
3306 warnings, zero to disable.
3308 rcutorture.stall_cpu_holdoff= [KNL]
3309 Time to wait (s) after boot before inducing stall.
3311 rcutorture.stat_interval= [KNL]
3312 Time (s) between statistics printk()s.
3314 rcutorture.stutter= [KNL]
3315 Time (s) to stutter testing, for example, specifying
3316 five seconds causes the test to run for five seconds,
3317 wait for five seconds, and so on. This tests RCU's
3318 ability to transition abruptly to and from idle.
3320 rcutorture.test_boost= [KNL]
3321 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3322 "Maybe" means test if the RCU implementation
3323 under test support RCU priority boosting.
3325 rcutorture.test_boost_duration= [KNL]
3326 Duration (s) of each individual boost test.
3328 rcutorture.test_boost_interval= [KNL]
3329 Interval (s) between each boost test.
3331 rcutorture.test_no_idle_hz= [KNL]
3332 Test RCU's dyntick-idle handling. See also the
3333 rcutorture.shuffle_interval parameter.
3335 rcutorture.torture_runnable= [BOOT]
3336 Start rcutorture running at boot time.
3338 rcutorture.torture_type= [KNL]
3339 Specify the RCU implementation to test.
3341 rcutorture.verbose= [KNL]
3342 Enable additional printk() statements.
3344 rcupdate.rcu_expedited= [KNL]
3345 Use expedited grace-period primitives, for
3346 example, synchronize_rcu_expedited() instead
3347 of synchronize_rcu(). This reduces latency,
3348 but can increase CPU utilization, degrade
3349 real-time latency, and degrade energy efficiency.
3351 rcupdate.rcu_cpu_stall_suppress= [KNL]
3352 Suppress RCU CPU stall warning messages.
3354 rcupdate.rcu_cpu_stall_timeout= [KNL]
3355 Set timeout for RCU CPU stall warning messages.
3357 rcupdate.rcu_task_stall_timeout= [KNL]
3358 Set timeout in jiffies for RCU task stall warning
3359 messages. Disable with a value less than or equal
3362 rcupdate.rcu_self_test= [KNL]
3363 Run the RCU early boot self tests
3365 rcupdate.rcu_self_test_bh= [KNL]
3366 Run the RCU bh early boot self tests
3368 rcupdate.rcu_self_test_sched= [KNL]
3369 Run the RCU sched early boot self tests
3373 Run specified binary instead of /init from the ramdisk,
3374 used for early userspace startup. See initrd.
3377 Format (x86 or x86_64):
3378 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3380 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3382 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3383 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3384 reboot_force is either force or not specified,
3385 reboot_cpu is s[mp]#### with #### being the processor
3386 to be used for rebooting.
3389 [KNL, SMP] Set scheduler's default relax_domain_level.
3390 See Documentation/cgroups/cpusets.txt.
3392 relative_sleep_states=
3393 [SUSPEND] Use sleep state labeling where the deepest
3394 state available other than hibernation is always "mem".
3395 Format: { "0" | "1" }
3396 0 -- Traditional sleep state labels.
3397 1 -- Relative sleep state labels.
3399 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3401 reservetop= [X86-32]
3403 Reserves a hole at the top of the kernel virtual
3408 Set the amount of memory to reserve for BIOS at
3409 the bottom of the address space.
3411 reset_devices [KNL] Force drivers to reset the underlying device
3412 during initialization.
3415 Specify the partition device for software suspend
3417 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3419 resume_offset= [SWSUSP]
3420 Specify the offset from the beginning of the partition
3421 given by "resume=" at which the swap header is located,
3422 in <PAGE_SIZE> units (needed only for swap files).
3423 See Documentation/power/swsusp-and-swap-files.txt
3425 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3426 read the resume files
3428 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3429 Useful for devices that are detected asynchronously
3430 (e.g. USB and MMC devices).
3432 hibernate= [HIBERNATION]
3433 noresume Don't check if there's a hibernation image
3434 present during boot.
3435 nocompress Don't compress/decompress hibernation images.
3436 no Disable hibernation and resume.
3438 retain_initrd [RAM] Keep initrd memory after extraction
3440 rfkill.default_state=
3441 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3442 etc. communication is blocked by default.
3445 rfkill.master_switch_mode=
3446 0 The "airplane mode" button does nothing.
3447 1 The "airplane mode" button toggles between everything
3448 blocked and the previous configuration.
3449 2 The "airplane mode" button toggles between everything
3450 blocked and everything unblocked.
3452 rhash_entries= [KNL,NET]
3453 Set number of hash buckets for route cache
3455 ro [KNL] Mount root device read-only on boot
3457 root= [KNL] Root filesystem
3458 See name_to_dev_t comment in init/do_mounts.c.
3460 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3461 mount the root filesystem
3463 rootflags= [KNL] Set root filesystem mount option string
3465 rootfstype= [KNL] Set root filesystem type
3467 rootwait [KNL] Wait (indefinitely) for root device to show up.
3468 Useful for devices that are detected asynchronously
3469 (e.g. USB and MMC devices).
3471 rproc_mem=nn[KMG][@address]
3472 [KNL,ARM,CMA] Remoteproc physical memory block.
3473 Memory area to be used by remote processor image,
3476 rw [KNL] Mount root device read-write on boot
3478 S [KNL] Run init in single mode
3480 s390_iommu= [HW,S390]
3481 Set s390 IOTLB flushing mode
3483 With strict flushing every unmap operation will result in
3484 an IOTLB flush. Default is lazy flushing before reuse,
3488 See drivers/net/irda/sa1100_ir.c.
3490 sbni= [NET] Granch SBNI12 leased line adapter
3492 sched_debug [KNL] Enables verbose scheduler debug messages.
3494 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3495 xtime_lock contention on larger systems, and/or RCU lock
3496 contention on all systems with CONFIG_MAXSMP set.
3497 Format: { "0" | "1" }
3498 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3500 Note: increases power consumption, thus should only be
3501 enabled if running jitter sensitive (HPC/RT) workloads.
3503 security= [SECURITY] Choose a security module to enable at boot.
3504 If this boot parameter is not specified, only the first
3505 security module asking for security registration will be
3506 loaded. An invalid security module name will be treated
3507 as if no module has been chosen.
3509 selinux= [SELINUX] Disable or enable SELinux at boot time.
3510 Format: { "0" | "1" }
3511 See security/selinux/Kconfig help text.
3514 Default value is set via kernel config option.
3515 If enabled at boot time, /selinux/disable can be used
3516 later to disable prior to initial policy load.
3518 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3519 Format: { "0" | "1" }
3520 See security/apparmor/Kconfig help text
3523 Default value is set via kernel config option.
3525 serialnumber [BUGS=X86-32]
3528 Maximal number of shapers.
3530 show_msr= [x86] show boot-time MSR settings
3531 Format: { <integer> }
3532 Show boot-time (BIOS-initialized) MSR settings.
3533 The parameter means the number of CPUs to show,
3534 for example 1 means boot CPU only.
3542 Disable merging of slabs with similar size. May be
3543 necessary if there is some reason to distinguish
3544 allocs to different slabs. Debug options disable
3545 merging on their own.
3546 For more information see Documentation/vm/slub.txt.
3548 slab_max_order= [MM, SLAB]
3549 Determines the maximum allowed order for slabs.
3550 A high setting may cause OOMs due to memory
3551 fragmentation. Defaults to 1 for systems with
3552 more than 32MB of RAM, 0 otherwise.
3554 slub_debug[=options[,slabs]] [MM, SLUB]
3555 Enabling slub_debug allows one to determine the
3556 culprit if slab objects become corrupted. Enabling
3557 slub_debug can create guard zones around objects and
3558 may poison objects when not in use. Also tracks the
3559 last alloc / free. For more information see
3560 Documentation/vm/slub.txt.
3562 slub_max_order= [MM, SLUB]
3563 Determines the maximum allowed order for slabs.
3564 A high setting may cause OOMs due to memory
3565 fragmentation. For more information see
3566 Documentation/vm/slub.txt.
3568 slub_min_objects= [MM, SLUB]
3569 The minimum number of objects per slab. SLUB will
3570 increase the slab order up to slub_max_order to
3571 generate a sufficiently large slab able to contain
3572 the number of objects indicated. The higher the number
3573 of objects the smaller the overhead of tracking slabs
3574 and the less frequently locks need to be acquired.
3575 For more information see Documentation/vm/slub.txt.
3577 slub_min_order= [MM, SLUB]
3578 Determines the minimum page order for slabs. Must be
3579 lower than slub_max_order.
3580 For more information see Documentation/vm/slub.txt.
3582 slub_nomerge [MM, SLUB]
3583 Same with slab_nomerge. This is supported for legacy.
3584 See slab_nomerge for more information.
3587 Format: <io1>[,<io2>[,...,<io8>]]
3589 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3590 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3591 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3592 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3593 smsc-ircc2.ircc_irq= [HW] IRQ line
3594 smsc-ircc2.ircc_dma= [HW] DMA channel
3595 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3596 0: Toshiba Satellite 1800 (GP data pin select)
3597 1: Fast pin select (default)
3601 [KNL] Should the soft-lockup detector generate panics.
3604 softlockup_all_cpu_backtrace=
3605 [KNL] Should the soft-lockup detector generate
3606 backtraces on all cpus.
3609 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3610 See Documentation/laptops/sonypi.txt
3612 spectre_v2= [X86] Control mitigation of Spectre variant 2
3613 (indirect branch speculation) vulnerability.
3615 on - unconditionally enable
3616 off - unconditionally disable
3617 auto - kernel detects whether your CPU model is
3620 Selecting 'on' will, and 'auto' may, choose a
3621 mitigation method at run time according to the
3622 CPU, the available microcode, the setting of the
3623 CONFIG_RETPOLINE configuration option, and the
3624 compiler with which the kernel was built.
3626 Specific mitigations can also be selected manually:
3628 retpoline - replace indirect branches
3629 retpoline,generic - google's original retpoline
3630 retpoline,amd - AMD-specific minimal thunk
3632 Not specifying this option is equivalent to
3635 spia_io_base= [HW,MTD]
3640 stack_guard_gap= [MM]
3641 override the default stack gap protection. The value
3642 is in page units and it defines how many pages prior
3643 to (for stacks growing down) resp. after (for stacks
3644 growing up) the main stack are reserved for no other
3645 mapping. Default value is 256 pages.
3648 Enabled the stack tracer on boot up.
3650 stacktrace_filter=[function-list]
3651 [FTRACE] Limit the functions that the stack tracer
3652 will trace at boot up. function-list is a comma separated
3653 list of functions. This list can be changed at run
3654 time by the stack_trace_filter file in the debugfs
3655 tracing directory. Note, this enables stack tracing
3656 and the stacktrace above is not needed.
3660 Set the STI (builtin display/keyboard on the HP-PARISC
3661 machines) console (graphic card) which should be used
3662 as the initial boot-console.
3663 See also comment in drivers/video/console/sticore.c.
3666 See comment in drivers/video/console/sticore.c.
3669 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3671 sunrpc.min_resvport=
3672 sunrpc.max_resvport=
3674 SunRPC servers often require that client requests
3675 originate from a privileged port (i.e. a port in the
3676 range 0 < portnr < 1024).
3677 An administrator who wishes to reserve some of these
3678 ports for other uses may adjust the range that the
3679 kernel's sunrpc client considers to be privileged
3680 using these two parameters to set the minimum and
3681 maximum port values.
3685 Control how the NFS server code allocates CPUs to
3686 service thread pools. Depending on how many NICs
3687 you have and where their interrupts are bound, this
3688 option will affect which CPUs will do NFS serving.
3689 Note: this parameter cannot be changed while the
3690 NFS server is running.
3692 auto the server chooses an appropriate mode
3693 automatically using heuristics
3694 global a single global pool contains all CPUs
3695 percpu one pool for each CPU
3696 pernode one pool for each NUMA node (equivalent
3697 to global on non-NUMA machines)
3699 sunrpc.tcp_slot_table_entries=
3700 sunrpc.udp_slot_table_entries=
3702 Sets the upper limit on the number of simultaneous
3703 RPC calls that can be sent from the client to a
3704 server. Increasing these values may allow you to
3705 improve throughput, but will also increase the
3706 amount of memory reserved for use by the client.
3708 suspend.pm_test_delay=
3710 Sets the number of seconds to remain in a suspend test
3711 mode before resuming the system (see
3712 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3713 is set. Default value is 5.
3716 [KNL] Enable accounting of swap in memory resource
3717 controller if no parameter or 1 is given or disable
3718 it if 0 is given (See Documentation/cgroups/memory.txt)
3720 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3721 Format: { <int> | force }
3722 <int> -- Number of I/O TLB slabs
3723 force -- force using of bounce buffers even if they
3724 wouldn't be automatically used by the kernel
3728 sysfs.deprecated=0|1 [KNL]
3729 Enable/disable old style sysfs layout for old udev
3730 on older distributions. When this option is enabled
3731 very new udev will not work anymore. When this option
3732 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3733 in older udev will not work anymore.
3734 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3735 the kernel configuration.
3737 sysrq_always_enabled
3739 Ignore sysrq setting - this boot parameter will
3740 neutralize any effect of /proc/sys/kernel/sysrq.
3741 Useful for debugging.
3743 tcpmhash_entries= [KNL,NET]
3744 Set the number of tcp_metrics_hash slots.
3745 Default value is 8192 or 16384 depending on total
3746 ram pages. This is used to specify the TCP metrics
3747 cache size. See Documentation/networking/ip-sysctl.txt
3748 "tcp_no_metrics_save" section for more details.
3752 test_suspend= [SUSPEND][,N]
3753 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3754 standby suspend) or "freeze" (for suspend type freeze)
3755 as the system sleep state during system startup with
3756 the optional capability to repeat N number of times.
3757 The system is woken from this state using a
3758 wakeup-capable RTC alarm.
3760 thash_entries= [KNL,NET]
3761 Set number of hash buckets for TCP connection
3763 thermal.act= [HW,ACPI]
3764 -1: disable all active trip points in all thermal zones
3765 <degrees C>: override all lowest active trip points
3767 thermal.crt= [HW,ACPI]
3768 -1: disable all critical trip points in all thermal zones
3769 <degrees C>: override all critical trip points
3771 thermal.nocrt= [HW,ACPI]
3772 Set to disable actions on ACPI thermal zone
3773 critical and hot trip points.
3775 thermal.off= [HW,ACPI]
3776 1: disable ACPI thermal control
3778 thermal.psv= [HW,ACPI]
3779 -1: disable all passive trip points
3780 <degrees C>: override all passive trip points to this
3783 thermal.tzp= [HW,ACPI]
3784 Specify global default ACPI thermal zone polling rate
3785 <deci-seconds>: poll all this frequency
3786 0: no polling (default)
3789 Force threading of all interrupt handlers except those
3790 marked explicitly IRQF_NO_THREAD.
3793 Enable the Transcendent memory driver if built-in.
3795 tmem.cleancache=0|1 [KNL, XEN]
3796 Default is on (1). Disable the usage of the cleancache
3797 API to send anonymous pages to the hypervisor.
3799 tmem.frontswap=0|1 [KNL, XEN]
3800 Default is on (1). Disable the usage of the frontswap
3801 API to send swap pages to the hypervisor. If disabled
3802 the selfballooning and selfshrinking are force disabled.
3804 tmem.selfballooning=0|1 [KNL, XEN]
3805 Default is on (1). Disable the driving of swap pages
3808 tmem.selfshrinking=0|1 [KNL, XEN]
3809 Default is on (1). Partial swapoff that immediately
3810 transfers pages from Xen hypervisor back to the
3811 kernel based on different criteria.
3815 Specify if the kernel should make use of the cpu
3816 topology information if the hardware supports this.
3817 The scheduler will make use of this information and
3818 e.g. base its process migration decisions on it.
3821 topology_updates= [KNL, PPC, NUMA]
3823 Specify if the kernel should ignore (off)
3824 topology updates sent by the hypervisor to this
3829 tpm_suspend_pcr=[HW,TPM]
3830 Format: integer pcr id
3831 Specify that at suspend time, the tpm driver
3832 should extend the specified pcr with zeros,
3833 as a workaround for some chips which fail to
3834 flush the last written pcr on TPM_SaveState.
3835 This will guarantee that all the other pcrs
3838 trace_buf_size=nn[KMG]
3839 [FTRACE] will set tracing buffer size on each cpu.
3841 trace_event=[event-list]
3842 [FTRACE] Set and start specified trace events in order
3843 to facilitate early boot debugging.
3844 See also Documentation/trace/events.txt
3846 trace_options=[option-list]
3847 [FTRACE] Enable or disable tracer options at boot.
3848 The option-list is a comma delimited list of options
3849 that can be enabled or disabled just as if you were
3850 to echo the option name into
3852 /sys/kernel/debug/tracing/trace_options
3854 For example, to enable stacktrace option (to dump the
3855 stack trace of each event), add to the command line:
3857 trace_options=stacktrace
3859 See also Documentation/trace/ftrace.txt "trace options"
3863 Have the tracepoints sent to printk as well as the
3864 tracing ring buffer. This is useful for early boot up
3865 where the system hangs or reboots and does not give the
3866 option for reading the tracing buffer or performing a
3867 ftrace_dump_on_oops.
3869 To turn off having tracepoints sent to printk,
3870 echo 0 > /proc/sys/kernel/tracepoint_printk
3871 Note, echoing 1 into this file without the
3872 tracepoint_printk kernel cmdline option has no effect.
3876 Having tracepoints sent to printk() and activating high
3877 frequency tracepoints such as irq or sched, can cause
3878 the system to live lock.
3881 [FTRACE] enable this option to disable tracing when a
3882 warning is hit. This turns off "tracing_on". Tracing can
3883 be enabled again by echoing '1' into the "tracing_on"
3884 file located in /sys/kernel/debug/tracing/
3886 This option is useful, as it disables the trace before
3887 the WARNING dump is called, which prevents the trace to
3888 be filled with content caused by the warning output.
3890 This option can also be set at run time via the sysctl
3891 option: kernel/traceoff_on_warning
3893 transparent_hugepage=
3895 Format: [always|madvise|never]
3896 Can be used to control the default behavior of the system
3897 with respect to transparent hugepages.
3898 See Documentation/vm/transhuge.txt for more details.
3900 tsc= Disable clocksource stability checks for TSC.
3902 [x86] reliable: mark tsc clocksource as reliable, this
3903 disables clocksource verification at runtime, as well
3904 as the stability checks done at bootup. Used to enable
3905 high-resolution timer mode on older hardware, and in
3906 virtualized environment.
3907 [x86] noirqtime: Do not use TSC to do irq accounting.
3908 Used to run time disable IRQ_TIME_ACCOUNTING on any
3909 platforms where RDTSC is slow and this accounting
3912 turbografx.map[2|3]= [HW,JOY]
3913 TurboGraFX parallel port interface
3915 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3916 See also Documentation/input/joystick-parport.txt
3918 udbg-immortal [PPC] When debugging early kernel crashes that
3919 happen after console_init() and before a proper
3920 console driver takes over, this boot options might
3921 help "seeing" what's going on.
3923 uhash_entries= [KNL,NET]
3924 Set number of hash buckets for UDP/UDP-Lite connections
3927 [USB] Ignore overcurrent events (default N).
3928 Some badly-designed motherboards generate lots of
3929 bogus events, for ports that aren't wired to
3930 anything. Set this parameter to avoid log spamming.
3931 Note that genuine overcurrent events won't be
3935 [X86] Cause panic on unknown NMI.
3937 usbcore.authorized_default=
3938 [USB] Default USB device authorization:
3939 (default -1 = authorized except for wireless USB,
3940 0 = not authorized, 1 = authorized)
3942 usbcore.autosuspend=
3943 [USB] The autosuspend time delay (in seconds) used
3944 for newly-detected USB devices (default 2). This
3945 is the time required before an idle device will be
3946 autosuspended. Devices for which the delay is set
3947 to a negative value won't be autosuspended at all.
3949 usbcore.usbfs_snoop=
3950 [USB] Set to log all usbfs traffic (default 0 = off).
3952 usbcore.blinkenlights=
3953 [USB] Set to cycle leds on hubs (default 0 = off).
3955 usbcore.old_scheme_first=
3956 [USB] Start with the old device initialization
3957 scheme (default 0 = off).
3959 usbcore.usbfs_memory_mb=
3960 [USB] Memory limit (in MB) for buffers allocated by
3961 usbfs (default = 16, 0 = max = 2047).
3963 usbcore.use_both_schemes=
3964 [USB] Try the other device initialization scheme
3965 if the first one fails (default 1 = enabled).
3967 usbcore.initial_descriptor_timeout=
3968 [USB] Specifies timeout for the initial 64-byte
3969 USB_REQ_GET_DESCRIPTOR request in milliseconds
3970 (default 5000 = 5.0 seconds).
3973 [USBHID] The interval which mice are to be polled at.
3975 usb-storage.delay_use=
3976 [UMS] The delay in seconds before a new device is
3977 scanned for Logical Units (default 1).
3980 [UMS] A list of quirks entries to supplement or
3981 override the built-in unusual_devs list. List
3982 entries are separated by commas. Each entry has
3983 the form VID:PID:Flags where VID and PID are Vendor
3984 and Product ID values (4-digit hex numbers) and
3985 Flags is a set of characters, each corresponding
3986 to a common usb-storage quirk flag as follows:
3987 a = SANE_SENSE (collect more than 18 bytes
3989 b = BAD_SENSE (don't collect more than 18
3990 bytes of sense data);
3991 c = FIX_CAPACITY (decrease the reported
3992 device capacity by one sector);
3993 d = NO_READ_DISC_INFO (don't use
3994 READ_DISC_INFO command);
3995 e = NO_READ_CAPACITY_16 (don't use
3996 READ_CAPACITY_16 command);
3997 f = NO_REPORT_OPCODES (don't use report opcodes
3999 g = MAX_SECTORS_240 (don't transfer more than
4000 240 sectors at a time, uas only);
4001 h = CAPACITY_HEURISTICS (decrease the
4002 reported device capacity by one
4003 sector if the number is odd);
4004 i = IGNORE_DEVICE (don't bind to this
4006 j = NO_REPORT_LUNS (don't use report luns
4008 l = NOT_LOCKABLE (don't try to lock and
4009 unlock ejectable media);
4010 m = MAX_SECTORS_64 (don't transfer more
4011 than 64 sectors = 32 KB at a time);
4012 n = INITIAL_READ10 (force a retry of the
4013 initial READ(10) command);
4014 o = CAPACITY_OK (accept the capacity
4015 reported by the device);
4016 p = WRITE_CACHE (the device cache is ON
4018 r = IGNORE_RESIDUE (the device reports
4019 bogus residue values);
4020 s = SINGLE_LUN (the device has only one
4022 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4023 commands, uas only);
4024 u = IGNORE_UAS (don't bind to the uas driver);
4025 w = NO_WP_DETECT (don't test whether the
4026 medium is write-protected).
4027 Example: quirks=0419:aaf5:rl,0421:0433:rc
4029 user_debug= [KNL,ARM]
4031 See arch/arm/Kconfig.debug help text.
4032 1 - undefined instruction events
4034 4 - invalid data aborts
4037 Example: user_debug=31
4040 [X86] Flags controlling user PTE allocations.
4042 nohigh = do not allocate PTE pages in
4043 HIGHMEM regardless of setting
4047 On X86_32, this is an alias for vdso32=. Otherwise:
4049 vdso=1: enable VDSO (the default)
4050 vdso=0: disable VDSO mapping
4052 vdso32= [X86] Control the 32-bit vDSO
4053 vdso32=1: enable 32-bit VDSO
4054 vdso32=0 or vdso32=2: disable 32-bit VDSO
4056 See the help text for CONFIG_COMPAT_VDSO for more
4057 details. If CONFIG_COMPAT_VDSO is set, the default is
4058 vdso32=0; otherwise, the default is vdso32=1.
4060 For compatibility with older kernels, vdso32=2 is an
4063 Try vdso32=0 if you encounter an error that says:
4064 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4067 vector=percpu: enable percpu vector domain
4069 video= [FB] Frame buffer configuration
4070 See Documentation/fb/modedb.txt.
4072 video.brightness_switch_enabled= [0,1]
4073 If set to 1, on receiving an ACPI notify event
4074 generated by hotkey, video driver will adjust brightness
4075 level and then send out the event to user space through
4076 the allocated input device; If set to 0, video driver
4077 will only send out the event without touching backlight
4082 [VMMIO] Memory mapped virtio (platform) device.
4084 <size>@<baseaddr>:<irq>[:<id>]
4086 <size> := size (can use standard suffixes
4088 <baseaddr> := physical base address
4089 <irq> := interrupt number (as passed to
4091 <id> := (optional) platform device id
4093 virtio_mmio.device=1K@0x100b0000:48:7
4095 Can be used multiple times for multiple devices.
4097 vga= [BOOT,X86-32] Select a particular video mode
4098 See Documentation/x86/boot.txt and
4099 Documentation/svga.txt.
4100 Use vga=ask for menu.
4101 This is actually a boot loader parameter; the value is
4102 passed to the kernel using a special protocol.
4104 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4105 size of <nn>. This can be used to increase the
4106 minimum size (128MB on x86). It can also be used to
4107 decrease the size and leave more room for directly
4110 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4113 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4116 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4120 Controls the behavior of vsyscalls (i.e. calls to
4121 fixed addresses of 0xffffffffff600x00 from legacy
4122 code). Most statically-linked binaries and older
4123 versions of glibc use these calls. Because these
4124 functions are at fixed addresses, they make nice
4125 targets for exploits that can control RIP.
4127 emulate [default] Vsyscalls turn into traps and are
4128 emulated reasonably safely.
4130 native Vsyscalls are native syscall instructions.
4131 This is a little bit faster than trapping
4132 and makes a few dynamic recompilers work
4133 better than they would in emulation mode.
4134 It also makes exploits much easier to write.
4136 none Vsyscalls don't work at all. This makes
4137 them quite hard to use for exploits but
4138 might break your system.
4140 vt.color= [VT] Default text color.
4141 Format: 0xYX, X = foreground, Y = background.
4142 Default: 0x07 = light gray on black.
4144 vt.cur_default= [VT] Default cursor shape.
4145 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4146 the parameters of the <Esc>[?A;B;Cc escape sequence;
4147 see VGA-softcursor.txt. Default: 2 = underline.
4149 vt.default_blu= [VT]
4150 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4151 Change the default blue palette of the console.
4152 This is a 16-member array composed of values
4155 vt.default_grn= [VT]
4156 Format: <green0>,<green1>,<green2>,...,<green15>
4157 Change the default green palette of the console.
4158 This is a 16-member array composed of values
4161 vt.default_red= [VT]
4162 Format: <red0>,<red1>,<red2>,...,<red15>
4163 Change the default red palette of the console.
4164 This is a 16-member array composed of values
4170 Set system-wide default UTF-8 mode for all tty's.
4171 Default is 1, i.e. UTF-8 mode is enabled for all
4172 newly opened terminals.
4174 vt.global_cursor_default=
4177 Set system-wide default for whether a cursor
4178 is shown on new VTs. Default is -1,
4179 i.e. cursors will be created by default unless
4180 overridden by individual drivers. 0 will hide
4181 cursors, 1 will display them.
4183 vt.italic= [VT] Default color for italic text; 0-15.
4186 vt.underline= [VT] Default color for underlined text; 0-15.
4189 watchdog timers [HW,WDT] For information on watchdog timers,
4190 see Documentation/watchdog/watchdog-parameters.txt
4191 or other driver-specific files in the
4192 Documentation/watchdog/ directory.
4194 workqueue.disable_numa
4195 By default, all work items queued to unbound
4196 workqueues are affine to the NUMA nodes they're
4197 issued on, which results in better behavior in
4198 general. If NUMA affinity needs to be disabled for
4199 whatever reason, this option can be used. Note
4200 that this also can be controlled per-workqueue for
4201 workqueues visible under /sys/bus/workqueue/.
4203 workqueue.power_efficient
4204 Per-cpu workqueues are generally preferred because
4205 they show better performance thanks to cache
4206 locality; unfortunately, per-cpu workqueues tend to
4207 be more power hungry than unbound workqueues.
4209 Enabling this makes the per-cpu workqueues which
4210 were observed to contribute significantly to power
4211 consumption unbound, leading to measurably lower
4212 power usage at the cost of small performance
4215 The default value of this parameter is determined by
4216 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4218 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4219 default x2apic cluster mode on platforms
4222 x86_intel_mid_timer= [X86-32,APBT]
4223 Choose timer option for x86 Intel MID platform.
4224 Two valid options are apbt timer only and lapic timer
4225 plus one apbt timer for broadcast timer.
4226 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4228 xen_512gb_limit [KNL,X86-64,XEN]
4229 Restricts the kernel running paravirtualized under Xen
4230 to use only up to 512 GB of RAM. The reason to do so is
4231 crash analysis tools and Xen tools for doing domain
4232 save/restore/migration must be enabled to handle larger
4235 xen_emul_unplug= [HW,X86,XEN]
4236 Unplug Xen emulated devices
4237 Format: [unplug0,][unplug1]
4238 ide-disks -- unplug primary master IDE devices
4239 aux-ide-disks -- unplug non-primary-master IDE devices
4240 nics -- unplug network devices
4241 all -- unplug all emulated devices (NICs and IDE disks)
4242 unnecessary -- unplugging emulated devices is
4243 unnecessary even if the host did not respond to
4245 never -- do not unplug even if version check succeeds
4247 xen_nopvspin [X86,XEN]
4248 Disables the ticketlock slowpath using Xen PV
4252 Disables the PV optimizations forcing the HVM guest to
4253 run as generic HVM guest with no PV drivers.
4255 xirc2ps_cs= [NET,PCMCIA]
4257 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4259 ______________________________________________________________________
4263 Add more DRM drivers.