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 acpica_no_return_repair [HW, ACPI]
197 Disable AML predefined validation mechanism
198 This mechanism can repair the evaluation result to make
199 the return objects more ACPI specification compliant.
200 This option is useful for developers to identify the
201 root cause of an AML interpreter issue when the issue
202 has something to do with the repair mechanism.
204 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
205 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
207 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
208 debug output. Bits in debug_layer correspond to a
209 _COMPONENT in an ACPI source file, e.g.,
210 #define _COMPONENT ACPI_PCI_COMPONENT
211 Bits in debug_level correspond to a level in
212 ACPI_DEBUG_PRINT statements, e.g.,
213 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
214 The debug_level mask defaults to "info". See
215 Documentation/acpi/debug.txt for more information about
216 debug layers and levels.
218 Enable processor driver info messages:
219 acpi.debug_layer=0x20000000
220 Enable PCI/PCI interrupt routing info messages:
221 acpi.debug_layer=0x400000
222 Enable AML "Debug" output, i.e., stores to the Debug
223 object while interpreting AML:
224 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
225 Enable all messages related to ACPI hardware:
226 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
228 Some values produce so much output that the system is
229 unusable. The "log_buf_len" parameter may be useful
230 if you need to capture more output.
232 acpi_enforce_resources= [ACPI]
233 { strict | lax | no }
234 Check for resource conflicts between native drivers
235 and ACPI OperationRegions (SystemIO and SystemMemory
236 only). IO ports and memory declared in ACPI might be
237 used by the ACPI subsystem in arbitrary AML code and
238 can interfere with legacy drivers.
239 strict (default): access to resources claimed by ACPI
240 is denied; legacy drivers trying to access reserved
241 resources will fail to bind to device using them.
242 lax: access to resources claimed by ACPI is allowed;
243 legacy drivers trying to access reserved resources
244 will bind successfully but a warning message is logged.
245 no: ACPI OperationRegions are not marked as reserved,
246 no further checks are performed.
248 acpi_force_table_verification [HW,ACPI]
249 Enable table checksum verification during early stage.
250 By default, this is disabled due to x86 early mapping
253 acpi_irq_balance [HW,ACPI]
254 ACPI will balance active IRQs
257 acpi_irq_nobalance [HW,ACPI]
258 ACPI will not move active IRQs (default)
261 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
262 Format: <irq>,<irq>...
264 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
266 Format: <irq>,<irq>...
268 acpi_no_auto_serialize [HW,ACPI]
269 Disable auto-serialization of AML methods
270 AML control methods that contain the opcodes to create
271 named objects will be marked as "Serialized" by the
272 auto-serialization feature.
273 This feature is enabled by default.
274 This option allows to turn off the feature.
276 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
279 acpi_no_static_ssdt [HW,ACPI]
280 Disable installation of static SSDTs at early boot time
281 By default, SSDTs contained in the RSDT/XSDT will be
282 installed automatically and they will appear under
283 /sys/firmware/acpi/tables.
284 This option turns off this feature.
285 Note that specifying this option does not affect
286 dynamic table installation which will install SSDT
287 tables to /sys/firmware/acpi/tables/dynamic.
289 acpi_rsdp= [ACPI,EFI,KEXEC]
290 Pass the RSDP address to the kernel, mostly used
291 on machines running EFI runtime service to boot the
292 second kernel for kdump.
294 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
295 Format: To spoof as Windows 98: ="Microsoft Windows"
297 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
298 of 2 which is mandated by ACPI 6) as the supported ACPI
299 specification revision (when using this switch, it may
300 be necessary to carry out a cold reboot _twice_ in a
301 row to make it take effect on the platform firmware).
303 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
304 acpi_osi="string1" # add string1
305 acpi_osi="!string2" # remove string2
306 acpi_osi=!* # remove all strings
307 acpi_osi=! # disable all built-in OS vendor
309 acpi_osi= # disable all strings
311 'acpi_osi=!' can be used in combination with single or
312 multiple 'acpi_osi="string1"' to support specific OS
313 vendor string(s). Note that such command can only
314 affect the default state of the OS vendor strings, thus
315 it cannot affect the default state of the feature group
316 strings and the current state of the OS vendor strings,
317 specifying it multiple times through kernel command line
318 is meaningless. This command is useful when one do not
319 care about the state of the feature group strings which
320 should be controlled by the OSPM.
322 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
323 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
324 can make '_OSI("Windows 2000")' TRUE.
326 'acpi_osi=' cannot be used in combination with other
327 'acpi_osi=' command lines, the _OSI method will not
328 exist in the ACPI namespace. NOTE that such command can
329 only affect the _OSI support state, thus specifying it
330 multiple times through kernel command line is also
333 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
336 'acpi_osi=!*' can be used in combination with single or
337 multiple 'acpi_osi="string1"' to support specific
338 string(s). Note that such command can affect the
339 current state of both the OS vendor strings and the
340 feature group strings, thus specifying it multiple times
341 through kernel command line is meaningful. But it may
342 still not able to affect the final state of a string if
343 there are quirks related to this string. This command
344 is useful when one want to control the state of the
345 feature group strings to debug BIOS issues related to
348 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
349 '_OSI("Module Device")' FALSE.
350 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
351 '_OSI("Module Device")' TRUE.
352 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
354 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
356 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
357 they all will make '_OSI("Windows 2000")' TRUE.
360 Override the pmtimer bug detection: force the kernel
361 to assume that this machine's pmtimer latches its value
362 and always returns good values.
364 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
365 Format: { level | edge | high | low }
367 acpi_skip_timer_override [HW,ACPI]
368 Recognize and ignore IRQ0/pin2 Interrupt Override.
369 For broken nForce2 BIOS resulting in XT-PIC timer.
371 acpi_sleep= [HW,ACPI] Sleep options
372 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
373 old_ordering, nonvs, sci_force_enable }
374 See Documentation/power/video.txt for information on
376 s3_beep is for debugging; it makes the PC's speaker beep
377 as soon as the kernel's real-mode entry point is called.
378 s4_nohwsig prevents ACPI hardware signature from being
379 used during resume from hibernation.
380 old_ordering causes the ACPI 1.0 ordering of the _PTS
381 control method, with respect to putting devices into
382 low power states, to be enforced (the ACPI 2.0 ordering
383 of _PTS is used by default).
384 nonvs prevents the kernel from saving/restoring the
385 ACPI NVS memory during suspend/hibernation and resume.
386 sci_force_enable causes the kernel to set SCI_EN directly
387 on resume from S1/S3 (which is against the ACPI spec,
388 but some broken systems don't work without it).
390 acpi_use_timer_override [HW,ACPI]
391 Use timer override. For some broken Nvidia NF5 boards
392 that require a timer override, but don't have HPET
394 add_efi_memmap [EFI; X86] Include EFI memory map in
395 kernel's map of available physical RAM.
398 { off | try_unsupported }
399 off: disable AGP support
400 try_unsupported: try to drive unsupported chipsets
401 (may crash computer or cause data corruption)
404 See Documentation/sound/alsa/alsa-parameters.txt
407 Allow the default userspace alignment fault handler
408 behaviour to be specified. Bit 0 enables warnings,
409 bit 1 enables fixups, and bit 2 sends a segfault.
411 align_va_addr= [X86-64]
412 Align virtual addresses by clearing slice [14:12] when
413 allocating a VMA at process creation time. This option
414 gives you up to 3% performance improvement on AMD F15h
415 machines (where it is enabled by default) for a
416 CPU-intensive style benchmark, and it can vary highly in
417 a microbenchmark depending on workload and compiler.
419 32: only for 32-bit processes
420 64: only for 64-bit processes
421 on: enable for both 32- and 64-bit processes
422 off: disable for both 32- and 64-bit processes
424 alloc_snapshot [FTRACE]
425 Allocate the ftrace snapshot buffer on boot up when the
426 main buffer is allocated. This is handy if debugging
427 and you need to use tracing_snapshot() on boot up, and
428 do not want to use tracing_snapshot_alloc() as it needs
429 to be done where GFP_KERNEL allocations are allowed.
431 amd_iommu= [HW,X86-64]
432 Pass parameters to the AMD IOMMU driver in the system.
434 fullflush - enable flushing of IO/TLB entries when
435 they are unmapped. Otherwise they are
436 flushed before they will be reused, which
438 off - do not initialize any AMD IOMMU found in
440 force_isolation - Force device isolation for all
441 devices. The IOMMU driver is not
442 allowed anymore to lift isolation
443 requirements as needed. This option
444 does not override iommu=pt
446 amd_iommu_dump= [HW,X86-64]
447 Enable AMD IOMMU driver option to dump the ACPI table
448 for AMD IOMMU. With this option enabled, AMD IOMMU
449 driver will print ACPI tables for AMD IOMMU during
450 IOMMU initialization.
452 amijoy.map= [HW,JOY] Amiga joystick support
453 Map of devices attached to JOY0DAT and JOY1DAT
455 See also Documentation/input/joystick.txt
457 analog.map= [HW,JOY] Analog joystick and gamepad support
458 Specifies type or capabilities of an analog joystick
459 connected to one of 16 gameports
460 Format: <type1>,<type2>,..<type16>
463 Power management functions (SPARCstation-4/5 + deriv.)
465 Disable APC CPU standby support. SPARCstation-Fox does
466 not play well with APC CPU idle - disable it if you have
467 APC and your system crashes randomly.
469 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
470 Change the output verbosity whilst booting
471 Format: { quiet (default) | verbose | debug }
472 Change the amount of debugging information output
473 when initialising the APIC and IO-APIC components.
475 apic_extnmi= [APIC,X86] External NMI delivery setting
476 Format: { bsp (default) | all | none }
477 bsp: External NMI is delivered only to CPU 0
478 all: External NMIs are broadcast to all CPUs as a
480 none: External NMI is masked for all CPUs. This is
481 useful so that a dump capture kernel won't be
485 See Documentation/networking/ipv6.txt.
487 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
488 Limit apic dumping. The parameter defines the maximal
489 number of local apics being dumped. Also it is possible
490 to set it to "all" by meaning -- no limit here.
491 Format: { 1 (default) | 2 | ... | all }.
492 The parameter valid if only apic=debug or
493 apic=verbose is specified.
494 Example: apic=debug show_lapic=all
496 apm= [APM] Advanced Power Management
497 See header of arch/x86/kernel/apm_32.c.
499 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
500 Format: <io>,<irq>,<nodeID>
504 atarimouse= [HW,MOUSE] Atari Mouse
506 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
507 EzKey and similar keyboards
509 atkbd.reset= [HW] Reset keyboard during initialization
511 atkbd.set= [HW] Select keyboard code set
512 Format: <int> (2 = AT (default), 3 = PS/2)
514 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
517 atkbd.softraw= [HW] Choose between synthetic and real raw mode
518 Format: <bool> (0 = real, 1 = synthetic (default))
520 atkbd.softrepeat= [HW]
521 Use software keyboard repeat
523 audit= [KNL] Enable the audit sub-system
524 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
525 0 - kernel audit is disabled and can not be enabled
526 until the next reboot
527 unset - kernel audit is initialized but disabled and
528 will be fully enabled by the userspace auditd.
529 1 - kernel audit is initialized and partially enabled,
530 storing at most audit_backlog_limit messages in
531 RAM until it is fully enabled by the userspace
535 audit_backlog_limit= [KNL] Set the audit queue size limit.
536 Format: <int> (must be >=0)
539 baycom_epp= [HW,AX25]
542 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
544 See header of drivers/net/hamradio/baycom_par.c.
546 baycom_ser_fdx= [HW,AX25]
547 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
548 Format: <io>,<irq>,<mode>[,<baud>]
549 See header of drivers/net/hamradio/baycom_ser_fdx.c.
551 baycom_ser_hdx= [HW,AX25]
552 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
553 Format: <io>,<irq>,<mode>
554 See header of drivers/net/hamradio/baycom_ser_hdx.c.
556 blkdevparts= Manual partition parsing of block device(s) for
557 embedded devices based on command line input.
558 See Documentation/block/cmdline-partition.txt
560 boot_delay= Milliseconds to delay each printk during boot.
561 Values larger than 10 seconds (10000) are changed to
565 bootmem_debug [KNL] Enable bootmem allocator debug messages.
567 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
568 bttv.radio= Most important insmod options are available as
570 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
573 bulk_remove=off [PPC] This parameter disables the use of the pSeries
574 firmware feature for flushing multiple hpte entries
577 c101= [NET] Moxa C101 synchronous serial card
579 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
580 Sometimes CPU hardware bugs make them report the cache
581 size incorrectly. The kernel will attempt work arounds
582 to fix known problems, but for some CPUs it is not
583 possible to determine what the correct size should be.
584 This option provides an override for these situations.
586 ca_keys= [KEYS] This parameter identifies a specific key(s) on
587 the system trusted keyring to be used for certificate
589 format: { id:<keyid> | builtin }
591 cca= [MIPS] Override the kernel pages' cache coherency
592 algorithm. Accepted values range from 0 to 7
593 inclusive. See arch/mips/include/asm/pgtable-bits.h
594 for platform specific values (SB1, Loongson3 and
597 ccw_timeout_log [S390]
598 See Documentation/s390/CommonIO for details.
600 cgroup_disable= [KNL] Disable a particular controller
601 Format: {name of the controller(s) to disable}
602 The effects of cgroup_disable=foo are:
603 - foo isn't auto-mounted if you mount all cgroups in
605 - foo isn't visible as an individually mountable
607 {Currently only "memory" controller deal with this and
608 cut the overhead, others just disable the usage. So
609 only cgroup_disable=memory is actually worthy}
611 checkreqprot [SELINUX] Set initial checkreqprot flag value.
612 Format: { "0" | "1" }
613 See security/selinux/Kconfig help text.
614 0 -- check protection applied by kernel (includes
615 any implied execute protection).
616 1 -- check protection requested by application.
617 Default value is set via a kernel config option.
618 Value can be changed at runtime via
619 /selinux/checkreqprot.
622 See Documentation/s390/CommonIO for details.
625 Prevents the clock framework from automatically gating
626 clocks that have not been explicitly enabled by a Linux
627 device driver but are enabled in hardware at reset or
628 by the bootloader/firmware. Note that this does not
629 force such clocks to be always-on nor does it reserve
630 those clocks in any way. This parameter is useful for
631 debug and development, but should not be needed on a
632 platform with proper driver support. For more
633 information, see Documentation/clk.txt.
635 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
637 Forces specified clocksource (if available) to be used
638 when calculating gettimeofday(). If specified
639 clocksource is not available, it defaults to PIT.
640 Format: { pit | tsc | cyclone | pmtmr }
642 clocksource= Override the default clocksource
644 Override the default clocksource and use the clocksource
645 with the name specified.
646 Some clocksource names to choose from, depending on
648 [all] jiffies (this is the base, fallback clocksource)
650 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
651 pxa_timer,timer3,32k_counter,timer0_1
653 [X86-32] pit,hpet,tsc;
654 scx200_hrt on Geode; cyclone on IBM x440
662 clearcpuid=BITNUM [X86]
663 Disable CPUID feature X for the kernel. See
664 arch/x86/include/asm/cpufeature.h for the valid bit
665 numbers. Note the Linux specific bits are not necessarily
666 stable over kernel options, but the vendor specific
668 Also note that user programs calling CPUID directly
669 or using the feature without checking anything
670 will still see it. This just prevents it from
671 being used by the kernel or shown in /proc/cpuinfo.
672 Also note the kernel might malfunction if you disable
675 cma=nn[MG]@[start[MG][-end[MG]]]
677 Sets the size of kernel global memory area for
678 contiguous memory allocations and optionally the
679 placement constraint by the physical address range of
680 memory allocations. A value of 0 disables CMA
681 altogether. For more information, see
682 include/linux/dma-contiguous.h
684 cmo_free_hint= [PPC] Format: { yes | no }
685 Specify whether pages are marked as being inactive
686 when they are freed. This is used in CMO environments
687 to determine OS memory pressure for page stealing by
691 coherent_pool=nn[KMG] [ARM,KNL]
692 Sets the size of memory pool for coherent, atomic dma
693 allocations, by default set to 256K.
695 code_bytes [X86] How many bytes of object code to print
700 com20020= [HW,NET] ARCnet - COM20020 chipset
702 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
704 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
708 ARCnet - COM90xx chipset (memory-mapped buffers)
709 Format: <io>[,<irq>[,<memstart>]]
711 condev= [HW,S390] console device
714 console= [KNL] Output console device and options.
716 tty<n> Use the virtual console device <n>.
720 Use the specified serial port. The options are of
721 the form "bbbbpnf", where "bbbb" is the baud rate,
722 "p" is parity ("n", "o", or "e"), "n" is number of
723 bits, and "f" is flow control ("r" for RTS or
724 omit it). Default is "9600n8".
726 See Documentation/serial-console.txt for more
728 Documentation/networking/netconsole.txt for an
731 uart[8250],io,<addr>[,options]
732 uart[8250],mmio,<addr>[,options]
733 uart[8250],mmio32,<addr>[,options]
734 uart[8250],0x<addr>[,options]
735 Start an early, polled-mode console on the 8250/16550
736 UART at the specified I/O port or MMIO address,
737 switching to the matching ttyS device later.
738 MMIO inter-register address stride is either 8-bit
739 (mmio) or 32-bit (mmio32).
740 If none of [io|mmio|mmio32], <addr> is assumed to be
741 equivalent to 'mmio'. 'options' are specified in the
742 same format described for ttyS above; if unspecified,
743 the h/w is not re-initialized.
745 hvc<n> Use the hypervisor console device <n>. This is for
746 both Xen and PowerPC hypervisors.
748 If the device connected to the port is not a TTY but a braille
749 device, prepend "brl," before the device type, for instance
751 For now, only VisioBraille is supported.
753 consoleblank= [KNL] The console blank (screen saver) timeout in
754 seconds. Defaults to 10*60 = 10mins. A value of 0
755 disables the blank timer.
758 [KNL] Change the default value for
759 /proc/<pid>/coredump_filter.
760 See also Documentation/filesystems/proc.txt.
762 cpuidle.off=1 [CPU_IDLE]
763 disable the cpuidle sub-system
766 [X86] Delay for N microsec between assert and de-assert
767 of APIC INIT to start processors. This delay occurs
768 on every CPU online, such as boot, and resume from suspend.
771 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
773 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
775 crashkernel=size[KMG][@offset[KMG]]
776 [KNL] Using kexec, Linux can switch to a 'crash kernel'
777 upon panic. This parameter reserves the physical
778 memory region [offset, offset + size] for that kernel
779 image. If '@offset' is omitted, then a suitable offset
780 is selected automatically. Check
781 Documentation/kdump/kdump.txt for further details.
783 crashkernel=range1:size1[,range2:size2,...][@offset]
784 [KNL] Same as above, but depends on the memory
785 in the running system. The syntax of range is
786 start-[end] where start and end are both
787 a memory unit (amount[KMG]). See also
788 Documentation/kdump/kdump.txt for an example.
790 crashkernel=size[KMG],high
791 [KNL, x86_64] range could be above 4G. Allow kernel
792 to allocate physical memory region from top, so could
793 be above 4G if system have more than 4G ram installed.
794 Otherwise memory region will be allocated below 4G, if
796 It will be ignored if crashkernel=X is specified.
797 crashkernel=size[KMG],low
798 [KNL, x86_64] range under 4G. When crashkernel=X,high
799 is passed, kernel could allocate physical memory region
800 above 4G, that cause second kernel crash on system
801 that require some amount of low memory, e.g. swiotlb
802 requires at least 64M+32K low memory, also enough extra
803 low memory is needed to make sure DMA buffers for 32-bit
804 devices won't run out. Kernel would try to allocate at
805 at least 256M below 4G automatically.
806 This one let user to specify own low range under 4G
807 for second kernel instead.
808 0: to disable low allocation.
809 It will be ignored when crashkernel=X,high is not used
810 or memory reserved is below 4G.
815 cs89x0_media= [HW,NET]
816 Format: { rj45 | aui | bnc }
819 See header of drivers/s390/block/dasd_devmap.c.
821 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
822 (one device per port)
823 Format: <port#>,<type>
824 See also Documentation/input/joystick-parport.txt
826 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
827 time. See Documentation/dynamic-debug-howto.txt for
828 details. Deprecated, see dyndbg.
830 debug [KNL] Enable kernel debugging (events log level).
833 [KNL] verbose self-tests
835 Print debugging info while doing the locking API
837 We default to 0 (no extra messages), setting it to
838 1 will print _a lot_ more information - normally
839 only useful to kernel developers.
841 debug_objects [KNL] Enable object debugging
844 [KNL] Disable object debugging
846 debug_guardpage_minorder=
847 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
848 parameter allows control of the order of pages that will
849 be intentionally kept free (and hence protected) by the
850 buddy allocator. Bigger value increase the probability
851 of catching random memory corruption, but reduce the
852 amount of memory for normal system use. The maximum
853 possible value is MAX_ORDER/2. Setting this parameter
854 to 1 or 2 should be enough to identify most random
855 memory corruption problems caused by bugs in kernel or
856 driver code when a CPU writes to (or reads from) a
857 random memory location. Note that there exists a class
858 of memory corruptions problems caused by buggy H/W or
859 F/W or by drivers badly programing DMA (basically when
860 memory is written at bus level and the CPU MMU is
861 bypassed) which are not detectable by
862 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
863 tracking down these problems.
866 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
867 parameter enables the feature at boot time. In
868 default, it is disabled. We can avoid allocating huge
869 chunk of memory for debug pagealloc if we don't enable
870 it at boot time and the system will work mostly same
871 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
872 on: enable the feature
874 debugpat [X86] Enable PAT debugging
876 decnet.addr= [HW,NET]
877 Format: <area>[,<node>]
878 See also Documentation/networking/decnet.txt.
881 [same as hugepagesz=] The size of the default
882 HugeTLB page size. This is the size represented by
883 the legacy /proc/ hugepages APIs, used for SHM, and
884 default size when mounting hugetlbfs filesystems.
885 Defaults to the default architecture's huge page size
889 Set number of hash buckets for dentry cache.
892 See Documentation/networking/ipv6.txt.
894 disable_cpu_apicid= [X86,APIC,SMP]
896 The number of initial APIC ID for the
897 corresponding CPU to be disabled at boot,
898 mostly used for the kdump 2nd kernel to
899 disable BSP to wake up multiple CPUs without
900 causing system reset or hang due to sending
903 disable_ddw [PPC/PSERIES]
904 Disable Dynamic DMA Window support. Use this if
905 to workaround buggy firmware.
908 See Documentation/networking/ipv6.txt.
910 disable_mtrr_cleanup [X86]
911 The kernel tries to adjust MTRR layout from continuous
912 to discrete, to make X server driver able to add WB
913 entry later. This parameter disables that.
915 disable_mtrr_trim [X86, Intel and AMD only]
916 By default the kernel will trim any uncacheable
917 memory out of your available memory pool based on
918 MTRR settings. This parameter disables that behavior,
919 possibly causing your machine to run very slowly.
921 disable_timer_pin_1 [X86]
922 Disable PIN 1 of APIC timer
923 Can be useful to work around chipset bugs.
925 dis_ucode_ldr [X86] Disable the microcode loader.
927 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
928 this option disables the debugging code at boot.
930 dma_debug_entries=<number>
931 This option allows to tune the number of preallocated
932 entries for DMA-API debugging code. One entry is
933 required per DMA-API allocation. Use this if the
934 DMA-API debugging code disables itself because the
935 architectural default is too low.
937 dma_debug_driver=<driver_name>
938 With this option the DMA-API debugging driver
939 filter feature can be enabled at boot time. Just
940 pass the driver to filter for as the parameter.
941 The filter can be disabled or changed to another
942 driver later using sysfs.
944 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
945 Broken monitors, graphic adapters, KVMs and EDIDless
946 panels may send no or incorrect EDID data sets.
947 This parameter allows to specify an EDID data sets
948 in the /lib/firmware directory that are used instead.
949 Generic built-in EDID data sets are used, if one of
950 edid/1024x768.bin, edid/1280x1024.bin,
951 edid/1680x1050.bin, or edid/1920x1080.bin is given
952 and no file with the same name exists. Details and
953 instructions how to build your own EDID data are
954 available in Documentation/EDID/HOWTO.txt. An EDID
955 data set will only be used for a particular connector,
956 if its name and a colon are prepended to the EDID
957 name. Each connector may use a unique EDID data
958 set by separating the files with a comma. An EDID
959 data set with no connector name will be used for
960 any connectors not explicitly specified.
964 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
965 module.dyndbg[="val"]
966 Enable debug messages at boot time. See
967 Documentation/dynamic-debug-howto.txt for details.
969 nompx [X86] Disables Intel Memory Protection Extensions.
970 See Documentation/x86/intel_mpx.txt for more
971 information about the feature.
974 on enable eager fpu restore
975 off disable eager fpu restore
976 auto selects the default scheme, which automatically
977 enables eagerfpu restore for xsaveopt.
979 module.async_probe [KNL]
980 Enable asynchronous probe on this module.
982 early_ioremap_debug [KNL]
983 Enable debug messages in early_ioremap support. This
984 is useful for tracking down temporary early mappings
985 which are not unmapped.
987 earlycon= [KNL] Output early console device and options.
989 When used with no options, the early console is
990 determined by the stdout-path property in device
994 Start an early, polled-mode console on a cadence serial
995 port at the specified address. The cadence serial port
996 must already be setup and configured. Options are not
999 uart[8250],io,<addr>[,options]
1000 uart[8250],mmio,<addr>[,options]
1001 uart[8250],mmio32,<addr>[,options]
1002 uart[8250],mmio32be,<addr>[,options]
1003 uart[8250],0x<addr>[,options]
1004 Start an early, polled-mode console on the 8250/16550
1005 UART at the specified I/O port or MMIO address.
1006 MMIO inter-register address stride is either 8-bit
1007 (mmio) or 32-bit (mmio32 or mmio32be).
1008 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1009 to be equivalent to 'mmio'. 'options' are specified
1010 in the same format described for "console=ttyS<n>"; if
1011 unspecified, the h/w is not initialized.
1014 Start an early, polled-mode console on a pl011 serial
1015 port at the specified address. The pl011 serial port
1016 must already be setup and configured. Options are not
1020 Start an early, polled-mode console on an msm serial
1021 port at the specified address. The serial port
1022 must already be setup and configured. Options are not
1025 msm_serial_dm,<addr>
1026 Start an early, polled-mode console on an msm serial
1027 dm port at the specified address. The serial port
1028 must already be setup and configured. Options are not
1031 smh Use ARM semihosting calls for early console.
1039 Use early console provided by serial driver available
1040 on Samsung SoCs, requires selecting proper type and
1041 a correct base address of the selected UART port. The
1042 serial port must already be setup and configured.
1043 Options are not yet supported.
1047 Use early console provided by Freescale LP UART driver
1048 found on Freescale Vybrid and QorIQ LS1021A processors.
1049 A valid base address must be provided, and the serial
1050 port must already be setup and configured.
1052 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1056 earlyprintk=serial[,ttySn[,baudrate]]
1057 earlyprintk=serial[,0x...[,baudrate]]
1058 earlyprintk=ttySn[,baudrate]
1059 earlyprintk=dbgp[debugController#]
1060 earlyprintk=pciserial,bus:device.function[,baudrate]
1062 earlyprintk is useful when the kernel crashes before
1063 the normal console is initialized. It is not enabled by
1064 default because it has some cosmetic problems.
1066 Append ",keep" to not disable it when the real console
1069 Only one of vga, efi, serial, or usb debug port can
1072 Currently only ttyS0 and ttyS1 may be specified by
1073 name. Other I/O ports may be explicitly specified
1074 on some architectures (x86 and arm at least) by
1075 replacing ttySn with an I/O port address, like this:
1076 earlyprintk=serial,0x1008,115200
1077 You can find the port for a given device in
1078 /proc/tty/driver/serial:
1079 2: uart:ST16650V2 port:00001008 irq:18 ...
1081 Interaction with the standard serial driver is not
1084 The VGA and EFI output is eventually overwritten by
1087 The xen output can only be used by Xen PV guests.
1089 edac_report= [HW,EDAC] Control how to report EDAC event
1090 Format: {"on" | "off" | "force"}
1091 on: enable EDAC to report H/W event. May be overridden
1092 by other higher priority error reporting module.
1093 off: disable H/W event reporting through EDAC.
1094 force: enforce the use of EDAC to report H/W event.
1097 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1100 This is designed to be used in conjunction with
1101 the boot argument: earlyprintk=vga
1104 Format: {"off" | "on" | "skip[mbr]"}
1107 Format: { "old_map", "nochunk", "noruntime", "debug" }
1108 old_map [X86-64]: switch to the old ioremap-based EFI
1109 runtime services mapping. 32-bit still uses this one by
1111 nochunk: disable reading files in "chunks" in the EFI
1112 boot stub, as chunking can cause problems with some
1113 firmware implementations.
1114 noruntime : disable EFI runtime services support
1115 debug: enable misc debug output
1117 efi_no_storage_paranoia [EFI; X86]
1118 Using this parameter you can use more than 50% of
1119 your efi variable storage. Use this parameter only if
1120 you are really sure that your UEFI does sane gc and
1121 fulfills the spec otherwise your board may brick.
1123 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1124 Add arbitrary attribute to specific memory range by
1125 updating original EFI memory map.
1126 Region of memory which aa attribute is added to is
1128 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1129 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1130 attribute is added to range 0x100000000-0x180000000 and
1131 0x10a0000000-0x1120000000.
1133 Using this parameter you can do debugging of EFI memmap
1134 related feature. For example, you can do debugging of
1135 Address Range Mirroring feature even if your box
1138 eisa_irq_edge= [PARISC,HW]
1139 See header of drivers/parisc/eisa.c.
1142 See comment before function elanfreq_setup() in
1143 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1146 Format: {"cfq" | "deadline" | "noop"}
1147 See Documentation/block/cfq-iosched.txt and
1148 Documentation/block/deadline-iosched.txt for details.
1150 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1151 Specifies physical address of start of kernel core
1152 image elf header and optionally the size. Generally
1153 kexec loader will pass this option to capture kernel.
1154 See Documentation/kdump/kdump.txt for details.
1156 enable_mtrr_cleanup [X86]
1157 The kernel tries to adjust MTRR layout from continuous
1158 to discrete, to make X server driver able to add WB
1159 entry later. This parameter enables that.
1161 enable_timer_pin_1 [X86]
1162 Enable PIN 1 of APIC timer
1163 Can be useful to work around chipset bugs
1164 (in particular on some ATI chipsets).
1165 The kernel tries to set a reasonable default.
1167 enforcing [SELINUX] Set initial enforcing status.
1169 See security/selinux/Kconfig help text.
1170 0 -- permissive (log only, no denials).
1171 1 -- enforcing (deny and log).
1173 Value can be changed at runtime via /selinux/enforce.
1176 Disable Error Record Serialization Table (ERST)
1179 ether= [HW,NET] Ethernet cards parameters
1180 This option is obsoleted by the "netdev=" option, which
1181 has equivalent usage. See its documentation for details.
1185 Permit 'security.evm' to be updated regardless of
1186 current integrity status.
1190 fail_make_request=[KNL]
1191 General fault injection mechanism.
1192 Format: <interval>,<probability>,<space>,<times>
1193 See also Documentation/fault-injection/.
1196 See Documentation/blockdev/floppy.txt.
1198 force_pal_cache_flush
1199 [IA-64] Avoid check_sal_cache_flush which may hang on
1200 buggy SAL_CACHE_FLUSH implementations. Using this
1201 parameter will force ia64_sal_cache_flush to call
1202 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1205 Forcefully enable Physical Address Extension (PAE).
1206 Many Pentium M systems disable PAE but may have a
1207 functionally usable PAE implementation.
1208 Warning: use of this parameter will taint the kernel
1209 and may cause unknown problems.
1212 [FTRACE] will set and start the specified tracer
1213 as early as possible in order to facilitate early
1216 ftrace_dump_on_oops[=orig_cpu]
1217 [FTRACE] will dump the trace buffers on oops.
1218 If no parameter is passed, ftrace will dump
1219 buffers of all CPUs, but if you pass orig_cpu, it will
1220 dump only the buffer of the CPU that triggered the
1223 ftrace_filter=[function-list]
1224 [FTRACE] Limit the functions traced by the function
1225 tracer at boot up. function-list is a comma separated
1226 list of functions. This list can be changed at run
1227 time by the set_ftrace_filter file in the debugfs
1230 ftrace_notrace=[function-list]
1231 [FTRACE] Do not trace the functions specified in
1232 function-list. This list can be changed at run time
1233 by the set_ftrace_notrace file in the debugfs
1236 ftrace_graph_filter=[function-list]
1237 [FTRACE] Limit the top level callers functions traced
1238 by the function graph tracer at boot up.
1239 function-list is a comma separated list of functions
1240 that can be changed at run time by the
1241 set_graph_function file in the debugfs tracing directory.
1243 ftrace_graph_notrace=[function-list]
1244 [FTRACE] Do not trace from the functions specified in
1245 function-list. This list is a comma separated list of
1246 functions that can be changed at run time by the
1247 set_graph_notrace file in the debugfs tracing directory.
1250 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1251 support via parallel port (up to 5 devices per port)
1252 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1253 See also Documentation/input/joystick-parport.txt
1257 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1261 gcov_persist= [GCOV] When non-zero (default), profiling data for
1262 kernel modules is saved and remains accessible via
1263 debugfs, even when the module is unloaded/reloaded.
1264 When zero, profiling data is discarded and associated
1265 debugfs files are removed at module unload time.
1267 gpt [EFI] Forces disk with valid GPT signature but
1268 invalid Protective MBR to be treated as GPT. If the
1269 primary GPT is corrupted, it enables the backup/alternate
1270 GPT to be used instead.
1272 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1273 the "Enable 0" bit of the configuration register.
1276 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1277 the "Enable 0" bit of the configuration register.
1280 grcan.select= [HW] Select which physical interface to use.
1283 grcan.txsize= [HW] Sets the size of the tx buffer.
1284 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1286 grcan.rxsize= [HW] Sets the size of the rx buffer.
1287 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1290 hardlockup_all_cpu_backtrace=
1291 [KNL] Should the hard-lockup detector generate
1292 backtraces on all cpus.
1295 hashdist= [KNL,NUMA] Large hashes allocated during boot
1296 are distributed across NUMA nodes. Defaults on
1297 for 64-bit NUMA, off otherwise.
1298 Format: 0 | 1 (for off | on)
1300 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1302 hd= [EIDE] (E)IDE hard drive subsystem geometry
1303 Format: <cyl>,<head>,<sect>
1306 Disable Hardware Error Source Table (HEST) support;
1307 corresponding firmware-first mode error processing
1308 logic will be disabled.
1310 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1311 size of <nn>. This works even on boxes that have no
1312 highmem otherwise. This also works to reduce highmem
1313 size on bigger boxes.
1315 highres= [KNL] Enable/disable high resolution timer mode.
1316 Valid parameters: "on", "off"
1320 See Documentation/isdn/README.HiSax.
1324 hpet= [X86-32,HPET] option to control HPET usage
1325 Format: { enable (default) | disable | force |
1327 disable: disable HPET and use PIT instead
1328 force: allow force enabled of undocumented chips (ICH4,
1330 verbose: show contents of HPET registers during setup
1332 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1333 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1335 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1336 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1337 On x86-64 and powerpc, this option can be specified
1338 multiple times interleaved with hugepages= to reserve
1339 huge pages of different sizes. Valid pages sizes on
1340 x86-64 are 2M (when the CPU supports "pse") and 1G
1341 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1343 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1344 terminal devices. Valid values: 0..8
1345 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1346 If specified, z/VM IUCV HVC accepts connections
1347 from listed z/VM user IDs only.
1349 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1350 hardware thread id mappings.
1351 Format: <cpu>:<hwthread>
1354 Do not unregister boot console at start. This is only
1355 useful for debugging when something happens in the window
1356 between unregistering the boot console and initializing
1359 i2c_bus= [HW] Override the default board specific I2C bus speed
1360 or register an additional I2C bus that is not
1361 registered from board initialization code.
1365 i8042.debug [HW] Toggle i8042 debug mode
1366 i8042.unmask_kbd_data
1367 [HW] Enable printing of interrupt data from the KBD port
1368 (disabled by default, and as a pre-condition
1369 requires that i8042.debug=1 be enabled)
1370 i8042.direct [HW] Put keyboard port into non-translated mode
1371 i8042.dumbkbd [HW] Pretend that controller can only read data from
1372 keyboard and cannot control its state
1373 (Don't attempt to blink the leds)
1374 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1375 i8042.nokbd [HW] Don't check/create keyboard port
1376 i8042.noloop [HW] Disable the AUX Loopback command while probing
1378 i8042.nomux [HW] Don't check presence of an active multiplexing
1380 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1382 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1383 i8042.reset [HW] Reset the controller during init and cleanup
1384 i8042.unlock [HW] Unlock (ignore) the keylock
1385 i8042.kbdreset [HW] Reset device connected to KBD port
1389 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1390 indicates that the driver is running on unsupported
1392 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1393 does not match list of supported models.
1395 [HW] Report power status in /proc/i8k
1396 (disabled by default)
1397 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1400 i915.invert_brightness=
1401 [DRM] Invert the sense of the variable that is used to
1402 set the brightness of the panel backlight. Normally a
1403 brightness value of 0 indicates backlight switched off,
1404 and the maximum of the brightness value sets the backlight
1405 to maximum brightness. If this parameter is set to 0
1406 (default) and the machine requires it, or this parameter
1407 is set to 1, a brightness value of 0 sets the backlight
1408 to maximum brightness, and the maximum of the brightness
1409 value switches the backlight off.
1410 -1 -- never invert brightness
1411 0 -- machine default
1412 1 -- force brightness inversion
1415 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1417 ide-core.nodma= [HW] (E)IDE subsystem
1418 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1419 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1420 .cdrom .chs .ignore_cable are additional options
1421 See Documentation/ide/ide.txt.
1423 ide-generic.probe-mask= [HW] (E)IDE subsystem
1425 Probe mask for legacy ISA IDE ports. Depending on
1426 platform up to 6 ports are supported, enabled by
1427 setting corresponding bits in the mask to 1. The
1428 default value is 0x0, which has a special meaning.
1429 On systems that have PCI, it triggers scanning the
1430 PCI bus for the first and the second port, which
1431 are then probed. On systems without PCI the value
1432 of 0x0 enables probing the two first ports as if it
1435 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1436 Claim all unknown PCI IDE storage controllers.
1439 Format: idle=poll, idle=halt, idle=nomwait
1440 Poll forces a polling idle loop that can slightly
1441 improve the performance of waking up a idle CPU, but
1442 will use a lot of power and make the system run hot.
1444 idle=halt: Halt is forced to be used for CPU idle.
1445 In such case C2/C3 won't be used again.
1446 idle=nomwait: Disable mwait for CPU C-states
1448 ignore_loglevel [KNL]
1449 Ignore loglevel setting - this will print /all/
1450 kernel messages to the console. Useful for debugging.
1451 We also add it as printk module parameter, so users
1452 could change it dynamically, usually by
1453 /sys/module/printk/parameters/ignore_loglevel.
1455 ihash_entries= [KNL]
1456 Set number of hash buckets for inode cache.
1458 ima_appraise= [IMA] appraise integrity measurements
1459 Format: { "off" | "enforce" | "fix" | "log" }
1462 ima_appraise_tcb [IMA]
1463 The builtin appraise policy appraises all files
1467 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1471 The list of supported hash algorithms is defined
1472 in crypto/hash_info.h.
1475 The builtin measurement policy to load during IMA
1476 setup. Specyfing "tcb" as the value, measures all
1477 programs exec'd, files mmap'd for exec, and all files
1478 opened with the read mode bit set by either the
1479 effective uid (euid=0) or uid=0.
1482 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1483 Load a policy which meets the needs of the Trusted
1484 Computing Base. This means IMA will measure all
1485 programs exec'd, files mmap'd for exec, and all files
1486 opened for read by uid=0.
1489 Select one of defined IMA measurements template formats.
1490 Formats: { "ima" | "ima-ng" | "ima-sig" }
1494 [IMA] Define a custom template format.
1495 Format: { "field1|...|fieldN" }
1497 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1498 Format: <min_file_size>
1499 Set the minimal file size for using asynchronous hash.
1500 If left unspecified, ahash usage is disabled.
1502 ahash performance varies for different data sizes on
1503 different crypto accelerators. This option can be used
1504 to achieve the best performance for a particular HW.
1506 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1508 Set hashing buffer size. Default: 4k.
1510 ahash performance varies for different chunk sizes on
1511 different crypto accelerators. This option can be used
1512 to achieve best performance for particular HW.
1516 Run specified binary instead of /sbin/init as init
1519 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1520 for working out where the kernel is dying during
1523 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1524 initcall functions. Useful for debugging built-in
1525 modules and initcalls.
1527 initrd= [BOOT] Specify the location of the initial ramdisk
1529 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1532 int_pln_enable [x86] Enable power limit notification interrupt
1534 integrity_audit=[IMA]
1535 Format: { "0" | "1" }
1536 0 -- basic integrity auditing messages. (Default)
1537 1 -- additional integrity auditing messages.
1539 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1541 Enable intel iommu driver.
1543 Disable intel iommu driver.
1544 igfx_off [Default Off]
1545 By default, gfx is mapped as normal device. If a gfx
1546 device has a dedicated DMAR unit, the DMAR unit is
1547 bypassed by not enabling DMAR with this option. In
1548 this case, gfx device will use physical address for
1551 With this option iommu will not optimize to look
1552 for io virtual address below 32-bit forcing dual
1553 address cycle on pci bus for cards supporting greater
1554 than 32-bit addressing. The default is to look
1555 for translation below 32-bit and if not available
1556 then look in the higher range.
1557 strict [Default Off]
1558 With this option on every unmap_single operation will
1559 result in a hardware IOTLB flush operation as opposed
1560 to batching them for performance.
1561 sp_off [Default Off]
1562 By default, super page will be supported if Intel IOMMU
1563 has the capability. With this option, super page will
1565 ecs_off [Default Off]
1566 By default, extended context tables will be supported if
1567 the hardware advertises that it has support both for the
1568 extended tables themselves, and also PASID support. With
1569 this option set, extended tables will not be used even
1570 on hardware which claims to support them.
1572 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1573 0 disables intel_idle and fall back on acpi_idle.
1574 1 to 6 specify maximum depth of C-state.
1578 Do not enable intel_pstate as the default
1579 scaling driver for the supported processors
1581 Enable intel_pstate on systems that prohibit it by default
1582 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1583 instead of acpi-cpufreq may disable platform features, such
1584 as thermal controls and power capping, that rely on ACPI
1585 P-States information being indicated to OSPM and therefore
1586 should be used with caution. This option does not work with
1587 processors that aren't supported by the intel_pstate driver
1588 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1590 Do not enable hardware P state control (HWP)
1593 Only load intel_pstate on systems which support
1594 hardware P state control (HWP) if available.
1596 intremap= [X86-64, Intel-IOMMU]
1597 on enable Interrupt Remapping (default)
1598 off disable Interrupt Remapping
1599 nosid disable Source ID checking
1601 BIOS x2APIC opt-out request will be ignored
1602 nopost disable Interrupt Posting
1604 iomem= Disable strict checking of access to MMIO memory
1605 strict regions from userspace.
1620 nobypass [PPC/POWERNV]
1621 Disable IOMMU bypass, using IOMMU for PCI devices.
1624 io7= [HW] IO7 for Marvel based alpha systems
1625 See comment before marvel_specify_io7 in
1626 arch/alpha/kernel/core_marvel.c.
1628 io_delay= [X86] I/O delay method
1630 Standard port 0x80 based delay
1632 Alternate port 0xed based delay (needed on some systems)
1634 Simple two microseconds delay
1639 See Documentation/filesystems/nfs/nfsroot.txt.
1642 When an interrupt is not handled search all handlers
1643 for it. Intended to get systems with badly broken
1647 When an interrupt is not handled search all handlers
1648 for it. Also check all handlers each timer
1649 interrupt. Intended to get systems with badly broken
1653 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1655 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1657 <cpu number>,...,<cpu number>
1659 <cpu number>-<cpu number>
1660 (must be a positive range in ascending order)
1662 <cpu number>,...,<cpu number>-<cpu number>
1664 This option can be used to specify one or more CPUs
1665 to isolate from the general SMP balancing and scheduling
1666 algorithms. You can move a process onto or off an
1667 "isolated" CPU via the CPU affinity syscalls or cpuset.
1668 <cpu number> begins at 0 and the maximum value is
1669 "number of CPUs in system - 1".
1671 This option is the preferred way to isolate CPUs. The
1672 alternative -- manually setting the CPU mask of all
1673 tasks in the system -- can cause problems and
1674 suboptimal load balancer performance.
1678 ivrs_ioapic [HW,X86_64]
1679 Provide an override to the IOAPIC-ID<->DEVICE-ID
1680 mapping provided in the IVRS ACPI table. For
1681 example, to map IOAPIC-ID decimal 10 to
1682 PCI device 00:14.0 write the parameter as:
1683 ivrs_ioapic[10]=00:14.0
1685 ivrs_hpet [HW,X86_64]
1686 Provide an override to the HPET-ID<->DEVICE-ID
1687 mapping provided in the IVRS ACPI table. For
1688 example, to map HPET-ID decimal 0 to
1689 PCI device 00:14.0 write the parameter as:
1690 ivrs_hpet[0]=00:14.0
1692 js= [HW,JOY] Analog joystick
1693 See Documentation/input/joystick.txt.
1696 Enable/disable kernel and module base offset ASLR
1697 (Address Space Layout Randomization) if built into
1698 the kernel. When CONFIG_HIBERNATION is selected,
1699 kASLR is disabled by default. When kASLR is enabled,
1700 hibernation will be disabled.
1704 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1705 specifies the amount of memory usable by the kernel
1706 for non-movable allocations. The requested amount is
1707 spread evenly throughout all nodes in the system. The
1708 remaining memory in each node is used for Movable
1709 pages. In the event, a node is too small to have both
1710 kernelcore and Movable pages, kernelcore pages will
1711 take priority and other nodes will have a larger number
1712 of Movable pages. The Movable zone is used for the
1713 allocation of pages that may be reclaimed or moved
1714 by the page migration subsystem. This means that
1715 HugeTLB pages may not be allocated from this zone.
1716 Note that allocations like PTEs-from-HighMem still
1717 use the HighMem zone if it exists, and the Normal
1718 zone if it does not.
1720 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1721 Format: <Controller#>[,poll interval]
1722 The controller # is the number of the ehci usb debug
1723 port as it is probed via PCI. The poll interval is
1724 optional and is the number seconds in between
1725 each poll cycle to the debug port in case you need
1726 the functionality for interrupting the kernel with
1727 gdb or control-c on the dbgp connection. When
1728 not using this parameter you use sysrq-g to break into
1729 the kernel debugger.
1731 kgdboc= [KGDB,HW] kgdb over consoles.
1732 Requires a tty driver that supports console polling,
1733 or a supported polling keyboard driver (non-usb).
1734 Serial only format: <serial_device>[,baud]
1735 keyboard only format: kbd
1736 keyboard and serial format: kbd,<serial_device>[,baud]
1737 Optional Kernel mode setting:
1738 kms, kbd format: kms,kbd
1739 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1741 kgdbwait [KGDB] Stop kernel execution and enter the
1742 kernel debugger at the earliest opportunity.
1744 kmac= [MIPS] korina ethernet MAC address.
1745 Configure the RouterBoard 532 series on-chip
1746 Ethernet adapter MAC address.
1748 kmemleak= [KNL] Boot-time kmemleak enable/disable
1749 Valid arguments: on, off
1751 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1754 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1755 Valid arguments: 0, 1, 2
1756 kmemcheck=0 (disabled)
1757 kmemcheck=1 (enabled)
1758 kmemcheck=2 (one-shot mode)
1759 Default: 2 (one-shot mode)
1761 kstack=N [X86] Print N words from the kernel stack
1764 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1765 Default is 0 (don't ignore, but inject #GP)
1767 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1771 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1772 Default is 1 (enabled)
1774 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1776 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1778 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1779 (virtualized MMU) support on capable Intel chips.
1780 Default is 1 (enabled)
1782 kvm-intel.emulate_invalid_guest_state=
1783 [KVM,Intel] Enable emulation of invalid guest states
1784 Default is 0 (disabled)
1786 kvm-intel.flexpriority=
1787 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1788 Default is 1 (enabled)
1791 [KVM,Intel] Enable VMX nesting (nVMX).
1792 Default is 0 (disabled)
1794 kvm-intel.unrestricted_guest=
1795 [KVM,Intel] Disable unrestricted guest feature
1796 (virtualized real and unpaged mode) on capable
1797 Intel chips. Default is 1 (enabled)
1799 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1800 feature (tagged TLBs) on capable Intel chips.
1801 Default is 1 (enabled)
1807 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1810 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1811 value for LAPIC timer one-shot implementation. Default
1812 back to the programmable timer unit in the LAPIC.
1814 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1817 libata.dma= [LIBATA] DMA control
1818 libata.dma=0 Disable all PATA and SATA DMA
1819 libata.dma=1 PATA and SATA Disk DMA only
1820 libata.dma=2 ATAPI (CDROM) DMA only
1821 libata.dma=4 Compact Flash DMA only
1822 Combinations also work, so libata.dma=3 enables DMA
1823 for disks and CDROMs, but not CFs.
1825 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1826 libata.ignore_hpa=0 keep BIOS limits (default)
1827 libata.ignore_hpa=1 ignore limits, using full disk
1829 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1833 libata.force= [LIBATA] Force configurations. The format is comma
1834 separated list of "[ID:]VAL" where ID is
1835 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1836 matching port, link or device. Basically, it matches
1837 the ATA ID string printed on console by libata. If
1838 the whole ID part is omitted, the last PORT and DEVICE
1839 values are used. If ID hasn't been specified yet, the
1840 configuration applies to all ports, links and devices.
1842 If only DEVICE is omitted, the parameter applies to
1843 the port and all links and devices behind it. DEVICE
1844 number of 0 either selects the first device or the
1845 first fan-out link behind PMP device. It does not
1846 select the host link. DEVICE number of 15 selects the
1847 host link and device attached to it.
1849 The VAL specifies the configuration to force. As long
1850 as there's no ambiguity shortcut notation is allowed.
1851 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1852 The following configurations can be forced.
1854 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1855 Any ID with matching PORT is used.
1857 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1859 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1860 udma[/][16,25,33,44,66,100,133] notation is also
1863 * [no]ncq: Turn on or off NCQ.
1865 * [no]ncqtrim: Turn off queued DSM TRIM.
1867 * nohrst, nosrst, norst: suppress hard, soft
1870 * rstonce: only attempt one reset during
1871 hot-unplug link recovery
1873 * dump_id: dump IDENTIFY data.
1875 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1877 * disable: Disable this device.
1879 If there are multiple matching configurations changing
1880 the same attribute, the last one is used.
1882 memblock=debug [KNL] Enable memblock debug messages.
1884 load_ramdisk= [RAM] List of ramdisks to load from floppy
1885 See Documentation/blockdev/ramdisk.txt.
1887 lockd.nlm_grace_period=P [NFS] Assign grace period.
1890 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1893 lockd.nlm_timeout=T [NFS] Assign timeout value.
1896 lockd.nlm_udpport=M [NFS] Assign UDP port.
1899 locktorture.nreaders_stress= [KNL]
1900 Set the number of locking read-acquisition kthreads.
1901 Defaults to being automatically set based on the
1902 number of online CPUs.
1904 locktorture.nwriters_stress= [KNL]
1905 Set the number of locking write-acquisition kthreads.
1907 locktorture.onoff_holdoff= [KNL]
1908 Set time (s) after boot for CPU-hotplug testing.
1910 locktorture.onoff_interval= [KNL]
1911 Set time (s) between CPU-hotplug operations, or
1912 zero to disable CPU-hotplug testing.
1914 locktorture.shuffle_interval= [KNL]
1915 Set task-shuffle interval (jiffies). Shuffling
1916 tasks allows some CPUs to go into dyntick-idle
1917 mode during the locktorture test.
1919 locktorture.shutdown_secs= [KNL]
1920 Set time (s) after boot system shutdown. This
1921 is useful for hands-off automated testing.
1923 locktorture.stat_interval= [KNL]
1924 Time (s) between statistics printk()s.
1926 locktorture.stutter= [KNL]
1927 Time (s) to stutter testing, for example,
1928 specifying five seconds causes the test to run for
1929 five seconds, wait for five seconds, and so on.
1930 This tests the locking primitive's ability to
1931 transition abruptly to and from idle.
1933 locktorture.torture_runnable= [BOOT]
1934 Start locktorture running at boot time.
1936 locktorture.torture_type= [KNL]
1937 Specify the locking implementation to test.
1939 locktorture.verbose= [KNL]
1940 Enable additional printk() statements.
1942 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1945 loglevel= All Kernel Messages with a loglevel smaller than the
1946 console loglevel will be printed to the console. It can
1947 also be changed with klogd or other programs. The
1948 loglevels are defined as follows:
1950 0 (KERN_EMERG) system is unusable
1951 1 (KERN_ALERT) action must be taken immediately
1952 2 (KERN_CRIT) critical conditions
1953 3 (KERN_ERR) error conditions
1954 4 (KERN_WARNING) warning conditions
1955 5 (KERN_NOTICE) normal but significant condition
1956 6 (KERN_INFO) informational
1957 7 (KERN_DEBUG) debug-level messages
1959 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1960 in bytes. n must be a power of two and greater
1961 than the minimal size. The minimal size is defined
1962 by LOG_BUF_SHIFT kernel config parameter. There is
1963 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1964 that allows to increase the default size depending on
1965 the number of CPUs. See init/Kconfig for more details.
1967 logo.nologo [FB] Disables display of the built-in Linux logo.
1968 This may be used to provide more screen space for
1969 kernel log messages and is useful when debugging
1970 kernel boot problems.
1972 lp=0 [LP] Specify parallel ports to use, e.g,
1973 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1974 lp=reset first parallel port). 'lp=0' disables the
1975 lp=auto printer driver. 'lp=reset' (which can be
1976 specified in addition to the ports) causes
1977 attached printers to be reset. Using
1978 lp=port1,port2,... specifies the parallel ports
1979 to associate lp devices with, starting with
1980 lp0. A port specification may be 'none' to skip
1981 that lp device, or a parport name such as
1982 'parport0'. Specifying 'lp=auto' instead of a
1983 port specification list means that device IDs
1984 from each port should be examined, to see if
1985 an IEEE 1284-compliant printer is attached; if
1986 so, the driver will manage that printer.
1987 See also header of drivers/char/lp.c.
1990 Sets loops_per_jiffy to given constant, thus avoiding
1991 time-consuming boot-time autodetection (up to 250 ms per
1992 CPU). 0 enables autodetection (default). To determine
1993 the correct value for your kernel, boot with normal
1994 autodetection and see what value is printed. Note that
1995 on SMP systems the preset will be applied to all CPUs,
1996 which is likely to cause problems if your CPUs need
1997 significantly divergent settings. An incorrect value
1998 will cause delays in the kernel to be wrong, leading to
1999 unpredictable I/O errors and other breakage. Although
2000 unlikely, in the extreme case this might damage your
2004 Format: <io>,<irq>,<dma>
2006 machvec= [IA-64] Force the use of a particular machine-vector
2007 (machvec) in a generic kernel.
2008 Example: machvec=hpzx1_swiotlb
2010 machtype= [Loongson] Share the same kernel image file between different
2012 Example: machtype=lemote-yeeloong-2f-7inch
2014 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2015 than or equal to this physical address is ignored.
2017 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2018 should make use of. maxcpus=n : n >= 0 limits the
2019 kernel to using 'n' processors. n=0 is a special case,
2020 it is equivalent to "nosmp", which also disables
2023 max_loop= [LOOP] The number of loop block devices that get
2024 (loop.max_loop) unconditionally pre-created at init time. The default
2025 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2026 of statically allocating a predefined number, loop
2027 devices can be requested on-demand with the
2028 /dev/loop-control interface.
2030 mce [X86-32] Machine Check Exception
2032 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2034 md= [HW] RAID subsystems devices and level
2035 See Documentation/md.txt.
2038 Format: <first>,<last>
2039 Specifies range of consoles to be captured by the MDA.
2041 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2042 Amount of memory to be used when the kernel is not able
2043 to see the whole system memory or for test.
2044 [X86] Work as limiting max address. Use together
2045 with memmap= to avoid physical address space collisions.
2046 Without memmap= PCI devices could be placed at addresses
2047 belonging to unused RAM.
2049 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2053 [KNL,SH] Allow user to override the default size for
2054 per-device physically contiguous DMA buffers.
2056 memmap=exactmap [KNL,X86] Enable setting of an exact
2057 E820 memory map, as specified by the user.
2058 Such memmap=exactmap lines can be constructed based on
2059 BIOS output or other requirements. See the memmap=nn@ss
2062 memmap=nn[KMG]@ss[KMG]
2063 [KNL] Force usage of a specific region of memory.
2064 Region of memory to be used is from ss to ss+nn.
2066 memmap=nn[KMG]#ss[KMG]
2067 [KNL,ACPI] Mark specific memory as ACPI data.
2068 Region of memory to be marked is from ss to ss+nn.
2070 memmap=nn[KMG]$ss[KMG]
2071 [KNL,ACPI] Mark specific memory as reserved.
2072 Region of memory to be reserved is from ss to ss+nn.
2073 Example: Exclude memory from 0x18690000-0x1869ffff
2074 memmap=64K$0x18690000
2076 memmap=0x10000$0x18690000
2078 memmap=nn[KMG]!ss[KMG]
2079 [KNL,X86] Mark specific memory as protected.
2080 Region of memory to be used, from ss to ss+nn.
2081 The memory region may be marked as e820 type 12 (0xc)
2082 and is NVDIMM or ADR memory.
2084 memory_corruption_check=0/1 [X86]
2085 Some BIOSes seem to corrupt the first 64k of
2086 memory when doing things like suspend/resume.
2087 Setting this option will scan the memory
2088 looking for corruption. Enabling this will
2089 both detect corruption and prevent the kernel
2090 from using the memory being corrupted.
2091 However, its intended as a diagnostic tool; if
2092 repeatable BIOS-originated corruption always
2093 affects the same memory, you can use memmap=
2094 to prevent the kernel from using that memory.
2096 memory_corruption_check_size=size [X86]
2097 By default it checks for corruption in the low
2098 64k, making this memory unavailable for normal
2099 use. Use this parameter to scan for
2100 corruption in more or less memory.
2102 memory_corruption_check_period=seconds [X86]
2103 By default it checks for corruption every 60
2104 seconds. Use this parameter to check at some
2105 other rate. 0 disables periodic checking.
2107 memtest= [KNL,X86,ARM] Enable memtest
2109 default : 0 <disable>
2110 Specifies the number of memtest passes to be
2111 performed. Each pass selects another test
2112 pattern from a given set of patterns. Memtest
2113 fills the memory with this pattern, validates
2114 memory contents and reserves bad memory
2115 regions that are detected.
2117 meye.*= [HW] Set MotionEye Camera parameters
2118 See Documentation/video4linux/meye.txt.
2120 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2121 Multi-Function General Purpose Timers on AMD Geode
2124 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2125 the BIOS has incorrectly applied a workaround. TinyBIOS
2126 version 0.98 is known to be affected, 0.99 fixes the
2127 problem by letting the user disable the workaround.
2131 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2132 physical address is ignored.
2134 mini2440= [ARM,HW,KNL]
2135 Format:[0..2][b][c][t]
2137 MINI2440 configuration specification:
2138 0 - The attached screen is the 3.5" TFT
2139 1 - The attached screen is the 7" TFT
2140 2 - The VGA Shield is attached (1024x768)
2141 Leaving out the screen size parameter will not load
2142 the TFT driver, and the framebuffer will be left
2144 b - Enable backlight. The TFT backlight pin will be
2145 linked to the kernel VESA blanking code and a GPIO
2146 LED. This parameter is not necessary when using the
2148 c - Enable the s3c camera interface.
2149 t - Reserved for enabling touchscreen support. The
2150 touchscreen support is not enabled in the mainstream
2151 kernel as of 2.6.30, a preliminary port can be found
2152 in the "bleeding edge" mini2440 support kernel at
2153 http://repo.or.cz/w/linux-2.6/mini2440.git
2156 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2157 parameter allows control of the logging verbosity for
2158 the additional memory initialisation checks. A value
2159 of 0 disables mminit logging and a level of 4 will
2160 log everything. Information is printed at KERN_DEBUG
2161 so loglevel=8 may also need to be specified.
2164 [KNL] When CONFIG_MODULE_SIG is set, this means that
2165 modules without (valid) signatures will fail to load.
2166 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2167 is always true, so this option does nothing.
2170 [MOUSE] Maximum time between finger touching and
2171 leaving touchpad surface for touch to be considered
2172 a tap and be reported as a left button click (for
2173 touchpads working in absolute mode only).
2175 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2176 reporting absolute coordinates, such as tablets
2177 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2178 reporting absolute coordinates, such as tablets
2180 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2181 is similar to kernelcore except it specifies the
2182 amount of memory used for migratable allocations.
2183 If both kernelcore and movablecore is specified,
2184 then kernelcore will be at *least* the specified
2185 value but may be more. If movablecore on its own
2186 is specified, the administrator must be careful
2187 that the amount of memory usable for all allocations
2190 movable_node [KNL,X86] Boot-time switch to enable the effects
2191 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2193 MTD_Partition= [MTD]
2194 Format: <name>,<region-number>,<size>,<offset>
2196 MTD_Region= [MTD] Format:
2197 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2200 See drivers/mtd/cmdlinepart.c.
2202 multitce=off [PPC] This parameter disables the use of the pSeries
2203 firmware feature for updating multiple TCE entries
2206 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2208 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2210 boundary - index of last SLC block on Flex-OneNAND.
2211 The remaining blocks are configured as MLC blocks.
2212 lock - Configure if Flex-OneNAND boundary should be locked.
2213 Once locked, the boundary cannot be changed.
2214 1 indicates lock status, 0 indicates unlock status.
2217 ARM/S3C2412 JIVE boot control
2219 See arch/arm/mach-s3c2412/mach-jive.c
2221 mtouchusb.raw_coordinates=
2222 [HW] Make the MicroTouch USB driver use raw coordinates
2223 ('y', default) or cooked coordinates ('n')
2225 mtrr_chunk_size=nn[KMG] [X86]
2226 used for mtrr cleanup. It is largest continuous chunk
2227 that could hold holes aka. UC entries.
2229 mtrr_gran_size=nn[KMG] [X86]
2230 Used for mtrr cleanup. It is granularity of mtrr block.
2232 Large value could prevent small alignment from
2235 mtrr_spare_reg_nr=n [X86]
2237 Range: 0,7 : spare reg number
2239 Used for mtrr cleanup. It is spare mtrr entries number.
2240 Set to 2 or more if your graphical card needs more.
2242 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2244 netdev= [NET] Network devices parameters
2245 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2246 Note that mem_start is often overloaded to mean
2247 something different and driver-specific.
2248 This usage is only documented in each driver source
2252 [NETFILTER] Enable connection tracking flow accounting
2253 0 to disable accounting
2254 1 to enable accounting
2257 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2258 See Documentation/filesystems/nfs/nfsroot.txt.
2260 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2261 See Documentation/filesystems/nfs/nfsroot.txt.
2263 nfsrootdebug [NFS] enable nfsroot debugging messages.
2264 See Documentation/filesystems/nfs/nfsroot.txt.
2266 nfs.callback_tcpport=
2267 [NFS] set the TCP port on which the NFSv4 callback
2268 channel should listen.
2271 [NFS] sets the pathname to the program which is used
2272 to update the NFS client cache entries.
2274 nfs.cache_getent_timeout=
2275 [NFS] sets the timeout after which an attempt to
2276 update a cache entry is deemed to have failed.
2278 nfs.idmap_cache_timeout=
2279 [NFS] set the maximum lifetime for idmapper cache
2283 [NFS] enable 64-bit inode numbers.
2284 If zero, the NFS client will fake up a 32-bit inode
2285 number for the readdir() and stat() syscalls instead
2286 of returning the full 64-bit number.
2287 The default is to return 64-bit inode numbers.
2289 nfs.max_session_slots=
2290 [NFSv4.1] Sets the maximum number of session slots
2291 the client will attempt to negotiate with the server.
2292 This limits the number of simultaneous RPC requests
2293 that the client can send to the NFSv4.1 server.
2294 Note that there is little point in setting this
2295 value higher than the max_tcp_slot_table_limit.
2297 nfs.nfs4_disable_idmapping=
2298 [NFSv4] When set to the default of '1', this option
2299 ensures that both the RPC level authentication
2300 scheme and the NFS level operations agree to use
2301 numeric uids/gids if the mount is using the
2302 'sec=sys' security flavour. In effect it is
2303 disabling idmapping, which can make migration from
2304 legacy NFSv2/v3 systems to NFSv4 easier.
2305 Servers that do not support this mode of operation
2306 will be autodetected by the client, and it will fall
2307 back to using the idmapper.
2308 To turn off this behaviour, set the value to '0'.
2310 [NFS4] Specify an additional fixed unique ident-
2311 ification string that NFSv4 clients can insert into
2312 their nfs_client_id4 string. This is typically a
2313 UUID that is generated at system install time.
2315 nfs.send_implementation_id =
2316 [NFSv4.1] Send client implementation identification
2317 information in exchange_id requests.
2318 If zero, no implementation identification information
2320 The default is to send the implementation identification
2323 nfs.recover_lost_locks =
2324 [NFSv4] Attempt to recover locks that were lost due
2325 to a lease timeout on the server. Please note that
2326 doing this risks data corruption, since there are
2327 no guarantees that the file will remain unchanged
2328 after the locks are lost.
2329 If you want to enable the kernel legacy behaviour of
2330 attempting to recover these locks, then set this
2332 The default parameter value of '0' causes the kernel
2333 not to attempt recovery of lost locks.
2335 nfs4.layoutstats_timer =
2336 [NFSv4.2] Change the rate at which the kernel sends
2337 layoutstats to the pNFS metadata server.
2339 Setting this to value to 0 causes the kernel to use
2340 whatever value is the default set by the layout
2341 driver. A non-zero value sets the minimum interval
2342 in seconds between layoutstats transmissions.
2344 nfsd.nfs4_disable_idmapping=
2345 [NFSv4] When set to the default of '1', the NFSv4
2346 server will return only numeric uids and gids to
2347 clients using auth_sys, and will accept numeric uids
2348 and gids from such clients. This is intended to ease
2349 migration from NFSv2/v3.
2351 objlayoutdriver.osd_login_prog=
2352 [NFS] [OBJLAYOUT] sets the pathname to the program which
2353 is used to automatically discover and login into new
2354 osd-targets. Please see:
2355 Documentation/filesystems/pnfs.txt for more explanations
2357 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2358 when a NMI is triggered.
2359 Format: [state][,regs][,debounce][,die]
2361 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2362 Format: [panic,][nopanic,][num]
2364 0 - turn hardlockup detector in nmi_watchdog off
2365 1 - turn hardlockup detector in nmi_watchdog on
2366 When panic is specified, panic when an NMI watchdog
2367 timeout occurs (or 'nopanic' to override the opposite
2368 default). To disable both hard and soft lockup detectors,
2369 please see 'nowatchdog'.
2370 This is useful when you use a panic=... timeout and
2371 need the box quickly up again.
2373 netpoll.carrier_timeout=
2374 [NET] Specifies amount of time (in seconds) that
2375 netpoll should wait for a carrier. By default netpoll
2378 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2379 emulation library even if a 387 maths coprocessor
2383 [HW] Never suspend the console
2384 Disable suspending of consoles during suspend and
2385 hibernate operations. Once disabled, debugging
2386 messages can reach various consoles while the rest
2387 of the system is being put to sleep (ie, while
2388 debugging driver suspend/resume hooks). This may
2389 not work reliably with all consoles, but is known
2390 to work with serial and VGA consoles.
2391 To facilitate more flexible debugging, we also add
2392 console_suspend, a printk module parameter to control
2393 it. Users could use console_suspend (usually
2394 /sys/module/printk/parameters/console_suspend) to
2395 turn on/off it dynamically.
2397 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2398 caches in the slab allocator. Saves per-node memory,
2399 but will impact performance.
2403 noapic [SMP,APIC] Tells the kernel to not make use of any
2404 IOAPICs that may be present in the system.
2406 noautogroup Disable scheduler automatic task group creation.
2408 nobats [PPC] Do not use BATs for mapping kernel lowmem
2409 on "Classic" PPC cores.
2413 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2415 nodelayacct [KNL] Disable per-task delay accounting
2417 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2419 nodsp [SH] Disable hardware DSP at boot time.
2421 noefi Disable EFI runtime services support.
2426 On X86-32 available only on PAE configured kernels.
2427 noexec=on: enable non-executable mappings (default)
2428 noexec=off: disable non-executable mappings
2431 Disable SMAP (Supervisor Mode Access Prevention)
2432 even if it is supported by processor.
2435 Disable SMEP (Supervisor Mode Execution Prevention)
2436 even if it is supported by processor.
2439 This affects only 32-bit executables.
2440 noexec32=on: enable non-executable mappings (default)
2441 read doesn't imply executable mappings
2442 noexec32=off: disable non-executable mappings
2443 read implies executable mappings
2445 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2447 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2448 register save and restore. The kernel will only save
2449 legacy floating-point registers on task switch.
2451 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2453 noxsave [BUGS=X86] Disables x86 extended register state save
2454 and restore using xsave. The kernel will fallback to
2455 enabling legacy floating-point and sse state.
2457 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2458 register states. The kernel will fall back to use
2459 xsave to save the states. By using this parameter,
2460 performance of saving the states is degraded because
2461 xsave doesn't support modified optimization while
2462 xsaveopt supports it on xsaveopt enabled systems.
2464 noxsaves [X86] Disables xsaves and xrstors used in saving and
2465 restoring x86 extended register state in compacted
2466 form of xsave area. The kernel will fall back to use
2467 xsaveopt and xrstor to save and restore the states
2468 in standard form of xsave area. By using this
2469 parameter, xsave area per process might occupy more
2470 memory on xsaves enabled systems.
2472 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2473 wfi(ARM) instruction doesn't work correctly and not to
2474 use it. This is also useful when using JTAG debugger.
2476 no_file_caps Tells the kernel not to honor file capabilities. The
2477 only way then for a file to be executed with privilege
2478 is to be setuid root or executed by root.
2480 nohalt [IA-64] Tells the kernel not to use the power saving
2481 function PAL_HALT_LIGHT when idle. This increases
2482 power-consumption. On the positive side, it reduces
2483 interrupt wake-up latency, which may improve performance
2484 in certain environments such as networked servers or
2487 nohibernate [HIBERNATION] Disable hibernation and resume.
2489 nohz= [KNL] Boottime enable/disable dynamic ticks
2490 Valid arguments: on, off
2493 nohz_full= [KNL,BOOT]
2494 In kernels built with CONFIG_NO_HZ_FULL=y, set
2495 the specified list of CPUs whose tick will be stopped
2496 whenever possible. The boot CPU will be forced outside
2497 the range to maintain the timekeeping.
2498 The CPUs in this range must also be included in the
2501 noiotrap [SH] Disables trapped I/O port accesses.
2503 noirqdebug [X86-32] Disables the code which attempts to detect and
2504 disable unhandled interrupt sources.
2506 no_timer_check [X86,APIC] Disables the code which tests for
2507 broken timer IRQ sources.
2509 noisapnp [ISAPNP] Disables ISA PnP code.
2511 noinitrd [RAM] Tells the kernel not to load any configured
2514 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2516 [Deprecated - use intremap=off]
2520 nojitter [IA-64] Disables jitter checking for ITC timers.
2522 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2524 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2527 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2528 steal time is computed, but won't influence scheduler
2531 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2533 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2535 noltlbs [PPC] Do not use large page/tlb entries for kernel
2536 lowmem mapping on PPC40x.
2538 nomca [IA-64] Disable machine check abort handling
2540 nomce [X86-32] Disable Machine Check Exception
2542 nomfgpt [X86-32] Disable Multi-Function General Purpose
2543 Timer usage (for AMD Geode machines).
2545 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2546 shutdown the other cpus. Instead use the REBOOT_VECTOR
2549 nomodule Disable module load
2551 nopat [X86] Disable PAT (page attribute table extension of
2552 pagetables) support.
2554 norandmaps Don't use address space randomization. Equivalent to
2555 echo 0 > /proc/sys/kernel/randomize_va_space
2557 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2559 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2560 with UP alternatives
2562 nordrand [X86] Disable kernel use of the RDRAND and
2563 RDSEED instructions even if they are supported
2564 by the processor. RDRAND and RDSEED are still
2565 available to user space applications.
2567 noresume [SWSUSP] Disables resume and restores original swap
2570 no-scroll [VGA] Disables scrollback.
2571 This is required for the Braillex ib80-piezo Braille
2572 reader made by F.H. Papenmeier (Germany).
2576 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2578 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2579 and disable the IO APIC. legacy for "maxcpus=0".
2581 nosoftlockup [KNL] Disable the soft-lockup detector.
2583 nosync [HW,M68K] Disables sync negotiation for all devices.
2585 notsc [BUGS=X86-32] Disable Time Stamp Counter
2587 nowatchdog [KNL] Disable both lockup detectors, i.e.
2588 soft-lockup and NMI watchdog (hard-lockup).
2592 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2594 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2595 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2596 Some features depend on CPU0. Known dependencies are:
2597 1. Resume from suspend/hibernate depends on CPU0.
2598 Suspend/hibernate will fail if CPU0 is offline and you
2599 need to online CPU0 before suspend/hibernate.
2600 2. PIC interrupts also depend on CPU0. CPU0 can't be
2601 removed if a PIC interrupt is detected.
2602 It's said poweroff/reboot may depend on CPU0 on some
2603 machines although I haven't seen such issues so far
2604 after CPU0 is offline on a few tested machines.
2605 If the dependencies are under your control, you can
2606 turn on cpu0_hotplug.
2608 nptcg= [IA-64] Override max number of concurrent global TLB
2609 purges which is reported from either PAL_VM_SUMMARY or
2612 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2613 could support. nr_cpus=n : n >= 1 limits the kernel to
2614 supporting 'n' processors. Later in runtime you can not
2615 use hotplug cpu feature to put more cpu back to online.
2616 just like you compile the kernel NR_CPUS=n
2618 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2620 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2621 Allowed values are enable and disable
2623 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2624 one of ['zone', 'node', 'default'] can be specified
2625 This can be set from sysctl after boot.
2626 See Documentation/sysctl/vm.txt for details.
2628 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2629 See Documentation/debugging-via-ohci1394.txt for more
2632 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2633 Rather than timing out after 20 ms if an EC
2634 command is not properly ACKed, override the length
2635 of the timeout. We have interrupts disabled while
2636 waiting for the ACK, so if this is set too high
2637 interrupts *may* be lost!
2639 omap_mux= [OMAP] Override bootloader pin multiplexing.
2640 Format: <mux_mode0.mode_name=value>...
2641 For example, to override I2C bus2:
2642 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2644 oprofile.timer= [HW]
2645 Use timer interrupt instead of performance counters
2647 oprofile.cpu_type= Force an oprofile cpu type
2648 This might be useful if you have an older oprofile
2649 userland or if you want common events.
2650 Format: { arch_perfmon }
2651 arch_perfmon: [X86] Force use of architectural
2652 perfmon on Intel CPUs instead of the
2653 CPU specific event set.
2654 timer: [X86] Force use of architectural NMI
2655 timer mode (see also oprofile.timer
2656 for generic hr timer mode)
2657 [s390] Force legacy basic mode sampling
2658 (report cpu_type "timer")
2660 oops=panic Always panic on oopses. Default is to just kill the
2661 process, but there is a small probability of
2662 deadlocking the machine.
2663 This will also cause panics on machine check exceptions.
2664 Useful together with panic=30 to trigger a reboot.
2667 See Documentation/sound/oss/oss-parameters.txt
2669 page_owner= [KNL] Boot-time page_owner enabling option.
2670 Storage of the information about who allocated
2671 each page is disabled in default. With this switch,
2673 on: enable the feature
2675 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2676 timeout > 0: seconds before rebooting
2677 timeout = 0: wait forever
2678 timeout < 0: reboot immediately
2681 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2684 crash_kexec_post_notifiers
2685 Run kdump after running panic-notifiers and dumping
2686 kmsg. This only for the users who doubt kdump always
2687 succeeds in any situation.
2688 Note that this also increases risks of kdump failure,
2689 because some panic notifiers can make the crashed
2690 kernel more unstable.
2692 parkbd.port= [HW] Parallel port number the keyboard adapter is
2693 connected to, default is 0.
2695 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2696 0 for XT, 1 for AT (default is AT).
2699 parport= [HW,PPT] Specify parallel ports. 0 disables.
2700 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2701 Use 'auto' to force the driver to use any
2702 IRQ/DMA settings detected (the default is to
2703 ignore detected IRQ/DMA settings because of
2704 possible conflicts). You can specify the base
2705 address, IRQ, and DMA settings; IRQ and DMA
2706 should be numbers, or 'auto' (for using detected
2707 settings on that particular port), or 'nofifo'
2708 (to avoid using a FIFO even if it is detected).
2709 Parallel ports are assigned in the order they
2710 are specified on the command line, starting
2713 parport_init_mode= [HW,PPT]
2714 Configure VIA parallel port to operate in
2715 a specific mode. This is necessary on Pegasos
2716 computer where firmware has no options for setting
2717 up parallel port mode and sets it to spp.
2718 Currently this function knows 686a and 8231 chips.
2719 Format: [spp|ps2|epp|ecp|ecpepp]
2722 Halt all CPUs after the first oops has been printed for
2723 the specified number of seconds. This is to be used if
2724 your oopses keep scrolling off the screen.
2729 See header of drivers/block/paride/pcd.c.
2730 See also Documentation/blockdev/paride.txt.
2732 pci=option[,option...] [PCI] various PCI subsystem options:
2733 earlydump [X86] dump PCI config space before the kernel
2735 off [X86] don't probe for the PCI bus
2736 bios [X86-32] force use of PCI BIOS, don't access
2737 the hardware directly. Use this if your machine
2738 has a non-standard PCI host bridge.
2739 nobios [X86-32] disallow use of PCI BIOS, only direct
2740 hardware access methods are allowed. Use this
2741 if you experience crashes upon bootup and you
2742 suspect they are caused by the BIOS.
2743 conf1 [X86] Force use of PCI Configuration
2745 conf2 [X86] Force use of PCI Configuration
2747 noaer [PCIE] If the PCIEAER kernel config parameter is
2748 enabled, this kernel boot option can be used to
2749 disable the use of PCIE advanced error reporting.
2750 nodomains [PCI] Disable support for multiple PCI
2751 root domains (aka PCI segments, in ACPI-speak).
2752 nommconf [X86] Disable use of MMCONFIG for PCI
2754 check_enable_amd_mmconf [X86] check for and enable
2755 properly configured MMIO access to PCI
2756 config space on AMD family 10h CPU
2757 nomsi [MSI] If the PCI_MSI kernel config parameter is
2758 enabled, this kernel boot option can be used to
2759 disable the use of MSI interrupts system-wide.
2760 noioapicquirk [APIC] Disable all boot interrupt quirks.
2761 Safety option to keep boot IRQs enabled. This
2762 should never be necessary.
2763 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2764 primary IO-APIC for bridges that cannot disable
2765 boot IRQs. This fixes a source of spurious IRQs
2766 when the system masks IRQs.
2767 noioapicreroute [APIC] Disable workaround that uses the
2768 boot IRQ equivalent of an IRQ that connects to
2769 a chipset where boot IRQs cannot be disabled.
2770 The opposite of ioapicreroute.
2771 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2772 routing table. These calls are known to be buggy
2773 on several machines and they hang the machine
2774 when used, but on other computers it's the only
2775 way to get the interrupt routing table. Try
2776 this option if the kernel is unable to allocate
2777 IRQs or discover secondary PCI buses on your
2779 rom [X86] Assign address space to expansion ROMs.
2780 Use with caution as certain devices share
2781 address decoders between ROMs and other
2783 norom [X86] Do not assign address space to
2784 expansion ROMs that do not already have
2785 BIOS assigned address ranges.
2786 nobar [X86] Do not assign address space to the
2787 BARs that weren't assigned by the BIOS.
2788 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2789 assigned automatically to PCI devices. You can
2790 make the kernel exclude IRQs of your ISA cards
2792 pirqaddr=0xAAAAA [X86] Specify the physical address
2793 of the PIRQ table (normally generated
2794 by the BIOS) if it is outside the
2795 F0000h-100000h range.
2796 lastbus=N [X86] Scan all buses thru bus #N. Can be
2797 useful if the kernel is unable to find your
2798 secondary buses and you want to tell it
2799 explicitly which ones they are.
2800 assign-busses [X86] Always assign all PCI bus
2801 numbers ourselves, overriding
2802 whatever the firmware may have done.
2803 usepirqmask [X86] Honor the possible IRQ mask stored
2804 in the BIOS $PIR table. This is needed on
2805 some systems with broken BIOSes, notably
2806 some HP Pavilion N5400 and Omnibook XE3
2807 notebooks. This will have no effect if ACPI
2808 IRQ routing is enabled.
2809 noacpi [X86] Do not use ACPI for IRQ routing
2810 or for PCI scanning.
2811 use_crs [X86] Use PCI host bridge window information
2812 from ACPI. On BIOSes from 2008 or later, this
2813 is enabled by default. If you need to use this,
2814 please report a bug.
2815 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2816 If you need to use this, please report a bug.
2817 routeirq Do IRQ routing for all PCI devices.
2818 This is normally done in pci_enable_device(),
2819 so this option is a temporary workaround
2820 for broken drivers that don't call it.
2821 skip_isa_align [X86] do not align io start addr, so can
2822 handle more pci cards
2823 firmware [ARM] Do not re-enumerate the bus but instead
2824 just use the configuration from the
2825 bootloader. This is currently used on
2826 IXP2000 systems where the bus has to be
2827 configured a certain way for adjunct CPUs.
2828 noearly [X86] Don't do any early type 1 scanning.
2829 This might help on some broken boards which
2830 machine check when some devices' config space
2831 is read. But various workarounds are disabled
2832 and some IOMMU drivers will not work.
2833 bfsort Sort PCI devices into breadth-first order.
2834 This sorting is done to get a device
2835 order compatible with older (<= 2.4) kernels.
2836 nobfsort Don't sort PCI devices into breadth-first order.
2837 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2838 tuning and use the BIOS-configured MPS defaults.
2839 pcie_bus_safe Set every device's MPS to the largest value
2840 supported by all devices below the root complex.
2841 pcie_bus_perf Set device MPS to the largest allowable MPS
2842 based on its parent bus. Also set MRRS (Max
2843 Read Request Size) to the largest supported
2844 value (no larger than the MPS that the device
2845 or bus can support) for best performance.
2846 pcie_bus_peer2peer Set every device's MPS to 128B, which
2847 every device is guaranteed to support. This
2848 configuration allows peer-to-peer DMA between
2849 any pair of devices, possibly at the cost of
2850 reduced performance. This also guarantees
2851 that hot-added devices will work.
2852 cbiosize=nn[KMG] The fixed amount of bus space which is
2853 reserved for the CardBus bridge's IO window.
2854 The default value is 256 bytes.
2855 cbmemsize=nn[KMG] The fixed amount of bus space which is
2856 reserved for the CardBus bridge's memory
2857 window. The default value is 64 megabytes.
2860 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2861 Specifies alignment and device to reassign
2862 aligned memory resources.
2863 If <order of align> is not specified,
2864 PAGE_SIZE is used as alignment.
2865 PCI-PCI bridge can be specified, if resource
2866 windows need to be expanded.
2867 ecrc= Enable/disable PCIe ECRC (transaction layer
2868 end-to-end CRC checking).
2869 bios: Use BIOS/firmware settings. This is the
2873 hpiosize=nn[KMG] The fixed amount of bus space which is
2874 reserved for hotplug bridge's IO window.
2875 Default size is 256 bytes.
2876 hpmemsize=nn[KMG] The fixed amount of bus space which is
2877 reserved for hotplug bridge's memory window.
2878 Default size is 2 megabytes.
2879 realloc= Enable/disable reallocating PCI bridge resources
2880 if allocations done by BIOS are too small to
2881 accommodate resources required by all child
2883 off: Turn realloc off
2885 realloc same as realloc=on
2886 noari do not use PCIe ARI.
2887 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2888 only look for one device below a PCIe downstream
2891 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2894 force Enable ASPM even on devices that claim not to support it.
2895 WARNING: Forcing ASPM on may cause system lockups.
2897 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2898 nomsi Do not use MSI for PCI Express Native Hotplug (this
2899 makes all PCIe ports use INTx for hotplug services).
2901 pcie_ports= [PCIE] PCIe ports handling:
2902 auto Ask the BIOS whether or not to use native PCIe services
2903 associated with PCIe ports (PME, hot-plug, AER). Use
2904 them only if that is allowed by the BIOS.
2905 native Use native PCIe services associated with PCIe ports
2907 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2910 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2911 nomsi Do not use MSI for native PCIe PME signaling (this makes
2912 all PCIe root ports use INTx for all services).
2914 pcmv= [HW,PCMCIA] BadgePAD 4
2918 Keep all power-domains already enabled by bootloader on,
2919 even if no driver has claimed them. This is useful
2920 for debug and development, but should not be
2921 needed on a platform with proper driver support.
2924 See Documentation/blockdev/paride.txt.
2926 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2929 See arch/parisc/kernel/pdc_chassis.c
2931 percpu_alloc= Select which percpu first chunk allocator to use.
2932 Currently supported values are "embed" and "page".
2933 Archs may support subset or none of the selections.
2934 See comments in mm/percpu.c for details on each
2935 allocator. This parameter is primarily for debugging
2936 and performance comparison.
2939 See Documentation/blockdev/paride.txt.
2942 See Documentation/blockdev/paride.txt.
2944 pirq= [SMP,APIC] Manual mp-table setup
2945 See Documentation/x86/i386/IO-APIC.txt.
2947 plip= [PPT,NET] Parallel port network link
2948 Format: { parport<nr> | timid | 0 }
2949 See also Documentation/parport.txt.
2951 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2952 Override pmtimer IOPort with a hex value.
2956 Enable PNP debug messages (depends on the
2957 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2958 via /sys/module/pnp/parameters/debug. We always show
2959 current resource usage; turning this on also shows
2960 possible settings and some assignment information.
2966 { on | off | curr | res | no-curr | no-res }
2969 [ISAPNP] Exclude IRQs for the autoconfiguration
2972 [ISAPNP] Exclude DMAs for the autoconfiguration
2974 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2975 Ranges are in pairs (I/O port base and size).
2978 [ISAPNP] Exclude memory regions for the
2980 Ranges are in pairs (memory base and size).
2982 ports= [IP_VS_FTP] IPVS ftp helper module
2984 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2986 Format: <port>,<port>....
2988 print-fatal-signals=
2989 [KNL] debug: print fatal signals
2991 If enabled, warn about various signal handling
2992 related application anomalies: too many signals,
2993 too many POSIX.1 timers, fatal signals causing a
2996 If you hit the warning due to signal overflow,
2997 you might want to try "ulimit -i unlimited".
3001 printk.always_kmsg_dump=
3002 Trigger kmsg_dump for cases other than kernel oops or
3004 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3007 printk.time= Show timing data prefixed to each printk message line
3008 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3010 processor.max_cstate= [HW,ACPI]
3011 Limit processor to maximum C-state
3012 max_cstate=9 overrides any DMI blacklist limit.
3014 processor.nocst [HW,ACPI]
3015 Ignore the _CST method to determine C-states,
3016 instead using the legacy FADT method
3018 profile= [KNL] Enable kernel profiling via /proc/profile
3019 Format: [schedule,]<number>
3020 Param: "schedule" - profile schedule points.
3021 Param: <number> - step/bucket size as a power of 2 for
3022 statistical time based profiling.
3023 Param: "sleep" - profile D-state sleeping (millisecs).
3024 Requires CONFIG_SCHEDSTATS
3025 Param: "kvm" - profile VM exits.
3027 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3029 See Documentation/blockdev/ramdisk.txt.
3031 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3032 probe for; one of (bare|imps|exps|lifebook|any).
3033 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3035 psmouse.resetafter= [HW,MOUSE]
3036 Try to reset the device after so many bad packets
3039 [HW,MOUSE] Set desired mouse resolution, in dpi.
3040 psmouse.smartscroll=
3041 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3042 0 = disabled, 1 = enabled (default).
3044 pstore.backend= Specify the name of the pstore backend to use
3047 See Documentation/blockdev/paride.txt.
3050 [KNL] Number of legacy pty's. Overwrites compiled-in
3053 quiet [KNL] Disable most log messages
3058 See Documentation/md.txt.
3060 ramdisk_blocksize= [RAM]
3061 See Documentation/blockdev/ramdisk.txt.
3063 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3064 See Documentation/blockdev/ramdisk.txt.
3067 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3068 the specified list of CPUs to be no-callback CPUs.
3069 Invocation of these CPUs' RCU callbacks will
3070 be offloaded to "rcuox/N" kthreads created for
3071 that purpose, where "x" is "b" for RCU-bh, "p"
3072 for RCU-preempt, and "s" for RCU-sched, and "N"
3073 is the CPU number. This reduces OS jitter on the
3074 offloaded CPUs, which can be useful for HPC and
3075 real-time workloads. It can also improve energy
3076 efficiency for asymmetric multiprocessors.
3079 Rather than requiring that offloaded CPUs
3080 (specified by rcu_nocbs= above) explicitly
3081 awaken the corresponding "rcuoN" kthreads,
3082 make these kthreads poll for callbacks.
3083 This improves the real-time response for the
3084 offloaded CPUs by relieving them of the need to
3085 wake up the corresponding kthread, but degrades
3086 energy efficiency by requiring that the kthreads
3087 periodically wake up to do the polling.
3089 rcutree.blimit= [KNL]
3090 Set maximum number of finished RCU callbacks to
3091 process in one batch.
3093 rcutree.dump_tree= [KNL]
3094 Dump the structure of the rcu_node combining tree
3095 out at early boot. This is used for diagnostic
3096 purposes, to verify correct tree setup.
3098 rcutree.gp_cleanup_delay= [KNL]
3099 Set the number of jiffies to delay each step of
3100 RCU grace-period cleanup. This only has effect
3101 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3103 rcutree.gp_init_delay= [KNL]
3104 Set the number of jiffies to delay each step of
3105 RCU grace-period initialization. This only has
3106 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3109 rcutree.gp_preinit_delay= [KNL]
3110 Set the number of jiffies to delay each step of
3111 RCU grace-period pre-initialization, that is,
3112 the propagation of recent CPU-hotplug changes up
3113 the rcu_node combining tree. This only has effect
3114 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3116 rcutree.rcu_fanout_exact= [KNL]
3117 Disable autobalancing of the rcu_node combining
3118 tree. This is used by rcutorture, and might
3119 possibly be useful for architectures having high
3120 cache-to-cache transfer latencies.
3122 rcutree.rcu_fanout_leaf= [KNL]
3123 Change the number of CPUs assigned to each
3124 leaf rcu_node structure. Useful for very
3125 large systems, which will choose the value 64,
3126 and for NUMA systems with large remote-access
3127 latencies, which will choose a value aligned
3128 with the appropriate hardware boundaries.
3130 rcutree.jiffies_till_sched_qs= [KNL]
3131 Set required age in jiffies for a
3132 given grace period before RCU starts
3133 soliciting quiescent-state help from
3134 rcu_note_context_switch().
3136 rcutree.jiffies_till_first_fqs= [KNL]
3137 Set delay from grace-period initialization to
3138 first attempt to force quiescent states.
3139 Units are jiffies, minimum value is zero,
3140 and maximum value is HZ.
3142 rcutree.jiffies_till_next_fqs= [KNL]
3143 Set delay between subsequent attempts to force
3144 quiescent states. Units are jiffies, minimum
3145 value is one, and maximum value is HZ.
3147 rcutree.kthread_prio= [KNL,BOOT]
3148 Set the SCHED_FIFO priority of the RCU per-CPU
3149 kthreads (rcuc/N). This value is also used for
3150 the priority of the RCU boost threads (rcub/N)
3151 and for the RCU grace-period kthreads (rcu_bh,
3152 rcu_preempt, and rcu_sched). If RCU_BOOST is
3153 set, valid values are 1-99 and the default is 1
3154 (the least-favored priority). Otherwise, when
3155 RCU_BOOST is not set, valid values are 0-99 and
3156 the default is zero (non-realtime operation).
3158 rcutree.rcu_nocb_leader_stride= [KNL]
3159 Set the number of NOCB kthread groups, which
3160 defaults to the square root of the number of
3161 CPUs. Larger numbers reduces the wakeup overhead
3162 on the per-CPU grace-period kthreads, but increases
3163 that same overhead on each group's leader.
3165 rcutree.qhimark= [KNL]
3166 Set threshold of queued RCU callbacks beyond which
3167 batch limiting is disabled.
3169 rcutree.qlowmark= [KNL]
3170 Set threshold of queued RCU callbacks below which
3171 batch limiting is re-enabled.
3173 rcutree.rcu_idle_gp_delay= [KNL]
3174 Set wakeup interval for idle CPUs that have
3175 RCU callbacks (RCU_FAST_NO_HZ=y).
3177 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3178 Set wakeup interval for idle CPUs that have
3179 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3180 Lazy RCU callbacks are those which RCU can
3181 prove do nothing more than free memory.
3183 rcutorture.cbflood_inter_holdoff= [KNL]
3184 Set holdoff time (jiffies) between successive
3185 callback-flood tests.
3187 rcutorture.cbflood_intra_holdoff= [KNL]
3188 Set holdoff time (jiffies) between successive
3189 bursts of callbacks within a given callback-flood
3192 rcutorture.cbflood_n_burst= [KNL]
3193 Set the number of bursts making up a given
3194 callback-flood test. Set this to zero to
3195 disable callback-flood testing.
3197 rcutorture.cbflood_n_per_burst= [KNL]
3198 Set the number of callbacks to be registered
3199 in a given burst of a callback-flood test.
3201 rcutorture.fqs_duration= [KNL]
3202 Set duration of force_quiescent_state bursts
3205 rcutorture.fqs_holdoff= [KNL]
3206 Set holdoff time within force_quiescent_state bursts
3209 rcutorture.fqs_stutter= [KNL]
3210 Set wait time between force_quiescent_state bursts
3213 rcutorture.gp_cond= [KNL]
3214 Use conditional/asynchronous update-side
3215 primitives, if available.
3217 rcutorture.gp_exp= [KNL]
3218 Use expedited update-side primitives, if available.
3220 rcutorture.gp_normal= [KNL]
3221 Use normal (non-expedited) asynchronous
3222 update-side primitives, if available.
3224 rcutorture.gp_sync= [KNL]
3225 Use normal (non-expedited) synchronous
3226 update-side primitives, if available. If all
3227 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3228 rcutorture.gp_normal=, and rcutorture.gp_sync=
3229 are zero, rcutorture acts as if is interpreted
3230 they are all non-zero.
3232 rcutorture.n_barrier_cbs= [KNL]
3233 Set callbacks/threads for rcu_barrier() testing.
3235 rcutorture.nfakewriters= [KNL]
3236 Set number of concurrent RCU writers. These just
3237 stress RCU, they don't participate in the actual
3238 test, hence the "fake".
3240 rcutorture.nreaders= [KNL]
3241 Set number of RCU readers. The value -1 selects
3242 N-1, where N is the number of CPUs. A value
3243 "n" less than -1 selects N-n-2, where N is again
3244 the number of CPUs. For example, -2 selects N
3245 (the number of CPUs), -3 selects N+1, and so on.
3247 rcutorture.object_debug= [KNL]
3248 Enable debug-object double-call_rcu() testing.
3250 rcutorture.onoff_holdoff= [KNL]
3251 Set time (s) after boot for CPU-hotplug testing.
3253 rcutorture.onoff_interval= [KNL]
3254 Set time (s) between CPU-hotplug operations, or
3255 zero to disable CPU-hotplug testing.
3257 rcutorture.shuffle_interval= [KNL]
3258 Set task-shuffle interval (s). Shuffling tasks
3259 allows some CPUs to go into dyntick-idle mode
3260 during the rcutorture test.
3262 rcutorture.shutdown_secs= [KNL]
3263 Set time (s) after boot system shutdown. This
3264 is useful for hands-off automated testing.
3266 rcutorture.stall_cpu= [KNL]
3267 Duration of CPU stall (s) to test RCU CPU stall
3268 warnings, zero to disable.
3270 rcutorture.stall_cpu_holdoff= [KNL]
3271 Time to wait (s) after boot before inducing stall.
3273 rcutorture.stat_interval= [KNL]
3274 Time (s) between statistics printk()s.
3276 rcutorture.stutter= [KNL]
3277 Time (s) to stutter testing, for example, specifying
3278 five seconds causes the test to run for five seconds,
3279 wait for five seconds, and so on. This tests RCU's
3280 ability to transition abruptly to and from idle.
3282 rcutorture.test_boost= [KNL]
3283 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3284 "Maybe" means test if the RCU implementation
3285 under test support RCU priority boosting.
3287 rcutorture.test_boost_duration= [KNL]
3288 Duration (s) of each individual boost test.
3290 rcutorture.test_boost_interval= [KNL]
3291 Interval (s) between each boost test.
3293 rcutorture.test_no_idle_hz= [KNL]
3294 Test RCU's dyntick-idle handling. See also the
3295 rcutorture.shuffle_interval parameter.
3297 rcutorture.torture_runnable= [BOOT]
3298 Start rcutorture running at boot time.
3300 rcutorture.torture_type= [KNL]
3301 Specify the RCU implementation to test.
3303 rcutorture.verbose= [KNL]
3304 Enable additional printk() statements.
3306 rcupdate.rcu_cpu_stall_suppress= [KNL]
3307 Suppress RCU CPU stall warning messages.
3309 rcupdate.rcu_cpu_stall_timeout= [KNL]
3310 Set timeout for RCU CPU stall warning messages.
3312 rcupdate.rcu_expedited= [KNL]
3313 Use expedited grace-period primitives, for
3314 example, synchronize_rcu_expedited() instead
3315 of synchronize_rcu(). This reduces latency,
3316 but can increase CPU utilization, degrade
3317 real-time latency, and degrade energy efficiency.
3318 No effect on CONFIG_TINY_RCU kernels.
3320 rcupdate.rcu_normal= [KNL]
3321 Use only normal grace-period primitives,
3322 for example, synchronize_rcu() instead of
3323 synchronize_rcu_expedited(). This improves
3324 real-time latency, CPU utilization, and
3325 energy efficiency, but can expose users to
3326 increased grace-period latency. This parameter
3327 overrides rcupdate.rcu_expedited. No effect on
3328 CONFIG_TINY_RCU kernels.
3330 rcupdate.rcu_normal_after_boot= [KNL]
3331 Once boot has completed (that is, after
3332 rcu_end_inkernel_boot() has been invoked), use
3333 only normal grace-period primitives. No effect
3334 on CONFIG_TINY_RCU kernels.
3336 rcupdate.rcu_task_stall_timeout= [KNL]
3337 Set timeout in jiffies for RCU task stall warning
3338 messages. Disable with a value less than or equal
3341 rcupdate.rcu_self_test= [KNL]
3342 Run the RCU early boot self tests
3344 rcupdate.rcu_self_test_bh= [KNL]
3345 Run the RCU bh early boot self tests
3347 rcupdate.rcu_self_test_sched= [KNL]
3348 Run the RCU sched early boot self tests
3352 Run specified binary instead of /init from the ramdisk,
3353 used for early userspace startup. See initrd.
3356 Format (x86 or x86_64):
3357 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3359 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3361 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3362 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3363 reboot_force is either force or not specified,
3364 reboot_cpu is s[mp]#### with #### being the processor
3365 to be used for rebooting.
3368 [KNL, SMP] Set scheduler's default relax_domain_level.
3369 See Documentation/cgroups/cpusets.txt.
3371 relative_sleep_states=
3372 [SUSPEND] Use sleep state labeling where the deepest
3373 state available other than hibernation is always "mem".
3374 Format: { "0" | "1" }
3375 0 -- Traditional sleep state labels.
3376 1 -- Relative sleep state labels.
3378 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3380 reservetop= [X86-32]
3382 Reserves a hole at the top of the kernel virtual
3387 Set the amount of memory to reserve for BIOS at
3388 the bottom of the address space.
3390 reset_devices [KNL] Force drivers to reset the underlying device
3391 during initialization.
3394 Specify the partition device for software suspend
3396 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3398 resume_offset= [SWSUSP]
3399 Specify the offset from the beginning of the partition
3400 given by "resume=" at which the swap header is located,
3401 in <PAGE_SIZE> units (needed only for swap files).
3402 See Documentation/power/swsusp-and-swap-files.txt
3404 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3405 read the resume files
3407 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3408 Useful for devices that are detected asynchronously
3409 (e.g. USB and MMC devices).
3411 hibernate= [HIBERNATION]
3412 noresume Don't check if there's a hibernation image
3413 present during boot.
3414 nocompress Don't compress/decompress hibernation images.
3415 no Disable hibernation and resume.
3417 retain_initrd [RAM] Keep initrd memory after extraction
3419 rfkill.default_state=
3420 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3421 etc. communication is blocked by default.
3424 rfkill.master_switch_mode=
3425 0 The "airplane mode" button does nothing.
3426 1 The "airplane mode" button toggles between everything
3427 blocked and the previous configuration.
3428 2 The "airplane mode" button toggles between everything
3429 blocked and everything unblocked.
3431 rhash_entries= [KNL,NET]
3432 Set number of hash buckets for route cache
3434 ro [KNL] Mount root device read-only on boot
3436 root= [KNL] Root filesystem
3437 See name_to_dev_t comment in init/do_mounts.c.
3439 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3440 mount the root filesystem
3442 rootflags= [KNL] Set root filesystem mount option string
3444 rootfstype= [KNL] Set root filesystem type
3446 rootwait [KNL] Wait (indefinitely) for root device to show up.
3447 Useful for devices that are detected asynchronously
3448 (e.g. USB and MMC devices).
3450 rproc_mem=nn[KMG][@address]
3451 [KNL,ARM,CMA] Remoteproc physical memory block.
3452 Memory area to be used by remote processor image,
3455 rw [KNL] Mount root device read-write on boot
3457 S [KNL] Run init in single mode
3459 s390_iommu= [HW,S390]
3460 Set s390 IOTLB flushing mode
3462 With strict flushing every unmap operation will result in
3463 an IOTLB flush. Default is lazy flushing before reuse,
3467 See drivers/net/irda/sa1100_ir.c.
3469 sbni= [NET] Granch SBNI12 leased line adapter
3471 sched_debug [KNL] Enables verbose scheduler debug messages.
3473 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3474 xtime_lock contention on larger systems, and/or RCU lock
3475 contention on all systems with CONFIG_MAXSMP set.
3476 Format: { "0" | "1" }
3477 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3479 Note: increases power consumption, thus should only be
3480 enabled if running jitter sensitive (HPC/RT) workloads.
3482 security= [SECURITY] Choose a security module to enable at boot.
3483 If this boot parameter is not specified, only the first
3484 security module asking for security registration will be
3485 loaded. An invalid security module name will be treated
3486 as if no module has been chosen.
3488 selinux= [SELINUX] Disable or enable SELinux at boot time.
3489 Format: { "0" | "1" }
3490 See security/selinux/Kconfig help text.
3493 Default value is set via kernel config option.
3494 If enabled at boot time, /selinux/disable can be used
3495 later to disable prior to initial policy load.
3497 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3498 Format: { "0" | "1" }
3499 See security/apparmor/Kconfig help text
3502 Default value is set via kernel config option.
3504 serialnumber [BUGS=X86-32]
3507 Maximal number of shapers.
3509 show_msr= [x86] show boot-time MSR settings
3510 Format: { <integer> }
3511 Show boot-time (BIOS-initialized) MSR settings.
3512 The parameter means the number of CPUs to show,
3513 for example 1 means boot CPU only.
3521 Disable merging of slabs with similar size. May be
3522 necessary if there is some reason to distinguish
3523 allocs to different slabs. Debug options disable
3524 merging on their own.
3525 For more information see Documentation/vm/slub.txt.
3527 slab_max_order= [MM, SLAB]
3528 Determines the maximum allowed order for slabs.
3529 A high setting may cause OOMs due to memory
3530 fragmentation. Defaults to 1 for systems with
3531 more than 32MB of RAM, 0 otherwise.
3533 slub_debug[=options[,slabs]] [MM, SLUB]
3534 Enabling slub_debug allows one to determine the
3535 culprit if slab objects become corrupted. Enabling
3536 slub_debug can create guard zones around objects and
3537 may poison objects when not in use. Also tracks the
3538 last alloc / free. For more information see
3539 Documentation/vm/slub.txt.
3541 slub_max_order= [MM, SLUB]
3542 Determines the maximum allowed order for slabs.
3543 A high setting may cause OOMs due to memory
3544 fragmentation. For more information see
3545 Documentation/vm/slub.txt.
3547 slub_min_objects= [MM, SLUB]
3548 The minimum number of objects per slab. SLUB will
3549 increase the slab order up to slub_max_order to
3550 generate a sufficiently large slab able to contain
3551 the number of objects indicated. The higher the number
3552 of objects the smaller the overhead of tracking slabs
3553 and the less frequently locks need to be acquired.
3554 For more information see Documentation/vm/slub.txt.
3556 slub_min_order= [MM, SLUB]
3557 Determines the minimum page order for slabs. Must be
3558 lower than slub_max_order.
3559 For more information see Documentation/vm/slub.txt.
3561 slub_nomerge [MM, SLUB]
3562 Same with slab_nomerge. This is supported for legacy.
3563 See slab_nomerge for more information.
3566 Format: <io1>[,<io2>[,...,<io8>]]
3568 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3569 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3570 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3571 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3572 smsc-ircc2.ircc_irq= [HW] IRQ line
3573 smsc-ircc2.ircc_dma= [HW] DMA channel
3574 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3575 0: Toshiba Satellite 1800 (GP data pin select)
3576 1: Fast pin select (default)
3580 [KNL] Should the soft-lockup detector generate panics.
3583 softlockup_all_cpu_backtrace=
3584 [KNL] Should the soft-lockup detector generate
3585 backtraces on all cpus.
3588 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3589 See Documentation/laptops/sonypi.txt
3591 spia_io_base= [HW,MTD]
3597 Enabled the stack tracer on boot up.
3599 stacktrace_filter=[function-list]
3600 [FTRACE] Limit the functions that the stack tracer
3601 will trace at boot up. function-list is a comma separated
3602 list of functions. This list can be changed at run
3603 time by the stack_trace_filter file in the debugfs
3604 tracing directory. Note, this enables stack tracing
3605 and the stacktrace above is not needed.
3609 Set the STI (builtin display/keyboard on the HP-PARISC
3610 machines) console (graphic card) which should be used
3611 as the initial boot-console.
3612 See also comment in drivers/video/console/sticore.c.
3615 See comment in drivers/video/console/sticore.c.
3618 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3620 sunrpc.min_resvport=
3621 sunrpc.max_resvport=
3623 SunRPC servers often require that client requests
3624 originate from a privileged port (i.e. a port in the
3625 range 0 < portnr < 1024).
3626 An administrator who wishes to reserve some of these
3627 ports for other uses may adjust the range that the
3628 kernel's sunrpc client considers to be privileged
3629 using these two parameters to set the minimum and
3630 maximum port values.
3634 Control how the NFS server code allocates CPUs to
3635 service thread pools. Depending on how many NICs
3636 you have and where their interrupts are bound, this
3637 option will affect which CPUs will do NFS serving.
3638 Note: this parameter cannot be changed while the
3639 NFS server is running.
3641 auto the server chooses an appropriate mode
3642 automatically using heuristics
3643 global a single global pool contains all CPUs
3644 percpu one pool for each CPU
3645 pernode one pool for each NUMA node (equivalent
3646 to global on non-NUMA machines)
3648 sunrpc.tcp_slot_table_entries=
3649 sunrpc.udp_slot_table_entries=
3651 Sets the upper limit on the number of simultaneous
3652 RPC calls that can be sent from the client to a
3653 server. Increasing these values may allow you to
3654 improve throughput, but will also increase the
3655 amount of memory reserved for use by the client.
3657 suspend.pm_test_delay=
3659 Sets the number of seconds to remain in a suspend test
3660 mode before resuming the system (see
3661 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3662 is set. Default value is 5.
3665 [KNL] Enable accounting of swap in memory resource
3666 controller if no parameter or 1 is given or disable
3667 it if 0 is given (See Documentation/cgroups/memory.txt)
3669 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3670 Format: { <int> | force }
3671 <int> -- Number of I/O TLB slabs
3672 force -- force using of bounce buffers even if they
3673 wouldn't be automatically used by the kernel
3677 sysfs.deprecated=0|1 [KNL]
3678 Enable/disable old style sysfs layout for old udev
3679 on older distributions. When this option is enabled
3680 very new udev will not work anymore. When this option
3681 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3682 in older udev will not work anymore.
3683 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3684 the kernel configuration.
3686 sysrq_always_enabled
3688 Ignore sysrq setting - this boot parameter will
3689 neutralize any effect of /proc/sys/kernel/sysrq.
3690 Useful for debugging.
3692 tcpmhash_entries= [KNL,NET]
3693 Set the number of tcp_metrics_hash slots.
3694 Default value is 8192 or 16384 depending on total
3695 ram pages. This is used to specify the TCP metrics
3696 cache size. See Documentation/networking/ip-sysctl.txt
3697 "tcp_no_metrics_save" section for more details.
3701 test_suspend= [SUSPEND][,N]
3702 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3703 standby suspend) or "freeze" (for suspend type freeze)
3704 as the system sleep state during system startup with
3705 the optional capability to repeat N number of times.
3706 The system is woken from this state using a
3707 wakeup-capable RTC alarm.
3709 thash_entries= [KNL,NET]
3710 Set number of hash buckets for TCP connection
3712 thermal.act= [HW,ACPI]
3713 -1: disable all active trip points in all thermal zones
3714 <degrees C>: override all lowest active trip points
3716 thermal.crt= [HW,ACPI]
3717 -1: disable all critical trip points in all thermal zones
3718 <degrees C>: override all critical trip points
3720 thermal.nocrt= [HW,ACPI]
3721 Set to disable actions on ACPI thermal zone
3722 critical and hot trip points.
3724 thermal.off= [HW,ACPI]
3725 1: disable ACPI thermal control
3727 thermal.psv= [HW,ACPI]
3728 -1: disable all passive trip points
3729 <degrees C>: override all passive trip points to this
3732 thermal.tzp= [HW,ACPI]
3733 Specify global default ACPI thermal zone polling rate
3734 <deci-seconds>: poll all this frequency
3735 0: no polling (default)
3738 Force threading of all interrupt handlers except those
3739 marked explicitly IRQF_NO_THREAD.
3742 Enable the Transcendent memory driver if built-in.
3744 tmem.cleancache=0|1 [KNL, XEN]
3745 Default is on (1). Disable the usage of the cleancache
3746 API to send anonymous pages to the hypervisor.
3748 tmem.frontswap=0|1 [KNL, XEN]
3749 Default is on (1). Disable the usage of the frontswap
3750 API to send swap pages to the hypervisor. If disabled
3751 the selfballooning and selfshrinking are force disabled.
3753 tmem.selfballooning=0|1 [KNL, XEN]
3754 Default is on (1). Disable the driving of swap pages
3757 tmem.selfshrinking=0|1 [KNL, XEN]
3758 Default is on (1). Partial swapoff that immediately
3759 transfers pages from Xen hypervisor back to the
3760 kernel based on different criteria.
3764 Specify if the kernel should make use of the cpu
3765 topology information if the hardware supports this.
3766 The scheduler will make use of this information and
3767 e.g. base its process migration decisions on it.
3770 topology_updates= [KNL, PPC, NUMA]
3772 Specify if the kernel should ignore (off)
3773 topology updates sent by the hypervisor to this
3778 tpm_suspend_pcr=[HW,TPM]
3779 Format: integer pcr id
3780 Specify that at suspend time, the tpm driver
3781 should extend the specified pcr with zeros,
3782 as a workaround for some chips which fail to
3783 flush the last written pcr on TPM_SaveState.
3784 This will guarantee that all the other pcrs
3787 trace_buf_size=nn[KMG]
3788 [FTRACE] will set tracing buffer size on each cpu.
3790 trace_event=[event-list]
3791 [FTRACE] Set and start specified trace events in order
3792 to facilitate early boot debugging.
3793 See also Documentation/trace/events.txt
3795 trace_options=[option-list]
3796 [FTRACE] Enable or disable tracer options at boot.
3797 The option-list is a comma delimited list of options
3798 that can be enabled or disabled just as if you were
3799 to echo the option name into
3801 /sys/kernel/debug/tracing/trace_options
3803 For example, to enable stacktrace option (to dump the
3804 stack trace of each event), add to the command line:
3806 trace_options=stacktrace
3808 See also Documentation/trace/ftrace.txt "trace options"
3812 Have the tracepoints sent to printk as well as the
3813 tracing ring buffer. This is useful for early boot up
3814 where the system hangs or reboots and does not give the
3815 option for reading the tracing buffer or performing a
3816 ftrace_dump_on_oops.
3818 To turn off having tracepoints sent to printk,
3819 echo 0 > /proc/sys/kernel/tracepoint_printk
3820 Note, echoing 1 into this file without the
3821 tracepoint_printk kernel cmdline option has no effect.
3825 Having tracepoints sent to printk() and activating high
3826 frequency tracepoints such as irq or sched, can cause
3827 the system to live lock.
3830 [FTRACE] enable this option to disable tracing when a
3831 warning is hit. This turns off "tracing_on". Tracing can
3832 be enabled again by echoing '1' into the "tracing_on"
3833 file located in /sys/kernel/debug/tracing/
3835 This option is useful, as it disables the trace before
3836 the WARNING dump is called, which prevents the trace to
3837 be filled with content caused by the warning output.
3839 This option can also be set at run time via the sysctl
3840 option: kernel/traceoff_on_warning
3842 transparent_hugepage=
3844 Format: [always|madvise|never]
3845 Can be used to control the default behavior of the system
3846 with respect to transparent hugepages.
3847 See Documentation/vm/transhuge.txt for more details.
3849 tsc= Disable clocksource stability checks for TSC.
3851 [x86] reliable: mark tsc clocksource as reliable, this
3852 disables clocksource verification at runtime, as well
3853 as the stability checks done at bootup. Used to enable
3854 high-resolution timer mode on older hardware, and in
3855 virtualized environment.
3856 [x86] noirqtime: Do not use TSC to do irq accounting.
3857 Used to run time disable IRQ_TIME_ACCOUNTING on any
3858 platforms where RDTSC is slow and this accounting
3861 turbografx.map[2|3]= [HW,JOY]
3862 TurboGraFX parallel port interface
3864 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3865 See also Documentation/input/joystick-parport.txt
3867 udbg-immortal [PPC] When debugging early kernel crashes that
3868 happen after console_init() and before a proper
3869 console driver takes over, this boot options might
3870 help "seeing" what's going on.
3872 uhash_entries= [KNL,NET]
3873 Set number of hash buckets for UDP/UDP-Lite connections
3876 [USB] Ignore overcurrent events (default N).
3877 Some badly-designed motherboards generate lots of
3878 bogus events, for ports that aren't wired to
3879 anything. Set this parameter to avoid log spamming.
3880 Note that genuine overcurrent events won't be
3884 [X86] Cause panic on unknown NMI.
3886 usbcore.authorized_default=
3887 [USB] Default USB device authorization:
3888 (default -1 = authorized except for wireless USB,
3889 0 = not authorized, 1 = authorized)
3891 usbcore.autosuspend=
3892 [USB] The autosuspend time delay (in seconds) used
3893 for newly-detected USB devices (default 2). This
3894 is the time required before an idle device will be
3895 autosuspended. Devices for which the delay is set
3896 to a negative value won't be autosuspended at all.
3898 usbcore.usbfs_snoop=
3899 [USB] Set to log all usbfs traffic (default 0 = off).
3901 usbcore.usbfs_snoop_max=
3902 [USB] Maximum number of bytes to snoop in each URB
3905 usbcore.blinkenlights=
3906 [USB] Set to cycle leds on hubs (default 0 = off).
3908 usbcore.old_scheme_first=
3909 [USB] Start with the old device initialization
3910 scheme (default 0 = off).
3912 usbcore.usbfs_memory_mb=
3913 [USB] Memory limit (in MB) for buffers allocated by
3914 usbfs (default = 16, 0 = max = 2047).
3916 usbcore.use_both_schemes=
3917 [USB] Try the other device initialization scheme
3918 if the first one fails (default 1 = enabled).
3920 usbcore.initial_descriptor_timeout=
3921 [USB] Specifies timeout for the initial 64-byte
3922 USB_REQ_GET_DESCRIPTOR request in milliseconds
3923 (default 5000 = 5.0 seconds).
3925 usbcore.nousb [USB] Disable the USB subsystem
3928 [USBHID] The interval which mice are to be polled at.
3930 usb-storage.delay_use=
3931 [UMS] The delay in seconds before a new device is
3932 scanned for Logical Units (default 1).
3935 [UMS] A list of quirks entries to supplement or
3936 override the built-in unusual_devs list. List
3937 entries are separated by commas. Each entry has
3938 the form VID:PID:Flags where VID and PID are Vendor
3939 and Product ID values (4-digit hex numbers) and
3940 Flags is a set of characters, each corresponding
3941 to a common usb-storage quirk flag as follows:
3942 a = SANE_SENSE (collect more than 18 bytes
3944 b = BAD_SENSE (don't collect more than 18
3945 bytes of sense data);
3946 c = FIX_CAPACITY (decrease the reported
3947 device capacity by one sector);
3948 d = NO_READ_DISC_INFO (don't use
3949 READ_DISC_INFO command);
3950 e = NO_READ_CAPACITY_16 (don't use
3951 READ_CAPACITY_16 command);
3952 f = NO_REPORT_OPCODES (don't use report opcodes
3954 g = MAX_SECTORS_240 (don't transfer more than
3955 240 sectors at a time, uas only);
3956 h = CAPACITY_HEURISTICS (decrease the
3957 reported device capacity by one
3958 sector if the number is odd);
3959 i = IGNORE_DEVICE (don't bind to this
3961 l = NOT_LOCKABLE (don't try to lock and
3962 unlock ejectable media);
3963 m = MAX_SECTORS_64 (don't transfer more
3964 than 64 sectors = 32 KB at a time);
3965 n = INITIAL_READ10 (force a retry of the
3966 initial READ(10) command);
3967 o = CAPACITY_OK (accept the capacity
3968 reported by the device);
3969 p = WRITE_CACHE (the device cache is ON
3971 r = IGNORE_RESIDUE (the device reports
3972 bogus residue values);
3973 s = SINGLE_LUN (the device has only one
3975 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3976 commands, uas only);
3977 u = IGNORE_UAS (don't bind to the uas driver);
3978 w = NO_WP_DETECT (don't test whether the
3979 medium is write-protected).
3980 Example: quirks=0419:aaf5:rl,0421:0433:rc
3982 user_debug= [KNL,ARM]
3984 See arch/arm/Kconfig.debug help text.
3985 1 - undefined instruction events
3987 4 - invalid data aborts
3990 Example: user_debug=31
3993 [X86] Flags controlling user PTE allocations.
3995 nohigh = do not allocate PTE pages in
3996 HIGHMEM regardless of setting
4000 On X86_32, this is an alias for vdso32=. Otherwise:
4002 vdso=1: enable VDSO (the default)
4003 vdso=0: disable VDSO mapping
4005 vdso32= [X86] Control the 32-bit vDSO
4006 vdso32=1: enable 32-bit VDSO
4007 vdso32=0 or vdso32=2: disable 32-bit VDSO
4009 See the help text for CONFIG_COMPAT_VDSO for more
4010 details. If CONFIG_COMPAT_VDSO is set, the default is
4011 vdso32=0; otherwise, the default is vdso32=1.
4013 For compatibility with older kernels, vdso32=2 is an
4016 Try vdso32=0 if you encounter an error that says:
4017 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4020 vector=percpu: enable percpu vector domain
4022 video= [FB] Frame buffer configuration
4023 See Documentation/fb/modedb.txt.
4025 video.brightness_switch_enabled= [0,1]
4026 If set to 1, on receiving an ACPI notify event
4027 generated by hotkey, video driver will adjust brightness
4028 level and then send out the event to user space through
4029 the allocated input device; If set to 0, video driver
4030 will only send out the event without touching backlight
4035 [VMMIO] Memory mapped virtio (platform) device.
4037 <size>@<baseaddr>:<irq>[:<id>]
4039 <size> := size (can use standard suffixes
4041 <baseaddr> := physical base address
4042 <irq> := interrupt number (as passed to
4044 <id> := (optional) platform device id
4046 virtio_mmio.device=1K@0x100b0000:48:7
4048 Can be used multiple times for multiple devices.
4050 vga= [BOOT,X86-32] Select a particular video mode
4051 See Documentation/x86/boot.txt and
4052 Documentation/svga.txt.
4053 Use vga=ask for menu.
4054 This is actually a boot loader parameter; the value is
4055 passed to the kernel using a special protocol.
4057 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4058 size of <nn>. This can be used to increase the
4059 minimum size (128MB on x86). It can also be used to
4060 decrease the size and leave more room for directly
4063 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4066 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4069 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4073 Controls the behavior of vsyscalls (i.e. calls to
4074 fixed addresses of 0xffffffffff600x00 from legacy
4075 code). Most statically-linked binaries and older
4076 versions of glibc use these calls. Because these
4077 functions are at fixed addresses, they make nice
4078 targets for exploits that can control RIP.
4080 emulate [default] Vsyscalls turn into traps and are
4081 emulated reasonably safely.
4083 native Vsyscalls are native syscall instructions.
4084 This is a little bit faster than trapping
4085 and makes a few dynamic recompilers work
4086 better than they would in emulation mode.
4087 It also makes exploits much easier to write.
4089 none Vsyscalls don't work at all. This makes
4090 them quite hard to use for exploits but
4091 might break your system.
4093 vt.color= [VT] Default text color.
4094 Format: 0xYX, X = foreground, Y = background.
4095 Default: 0x07 = light gray on black.
4097 vt.cur_default= [VT] Default cursor shape.
4098 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4099 the parameters of the <Esc>[?A;B;Cc escape sequence;
4100 see VGA-softcursor.txt. Default: 2 = underline.
4102 vt.default_blu= [VT]
4103 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4104 Change the default blue palette of the console.
4105 This is a 16-member array composed of values
4108 vt.default_grn= [VT]
4109 Format: <green0>,<green1>,<green2>,...,<green15>
4110 Change the default green palette of the console.
4111 This is a 16-member array composed of values
4114 vt.default_red= [VT]
4115 Format: <red0>,<red1>,<red2>,...,<red15>
4116 Change the default red palette of the console.
4117 This is a 16-member array composed of values
4123 Set system-wide default UTF-8 mode for all tty's.
4124 Default is 1, i.e. UTF-8 mode is enabled for all
4125 newly opened terminals.
4127 vt.global_cursor_default=
4130 Set system-wide default for whether a cursor
4131 is shown on new VTs. Default is -1,
4132 i.e. cursors will be created by default unless
4133 overridden by individual drivers. 0 will hide
4134 cursors, 1 will display them.
4136 vt.italic= [VT] Default color for italic text; 0-15.
4139 vt.underline= [VT] Default color for underlined text; 0-15.
4142 watchdog timers [HW,WDT] For information on watchdog timers,
4143 see Documentation/watchdog/watchdog-parameters.txt
4144 or other driver-specific files in the
4145 Documentation/watchdog/ directory.
4147 workqueue.watchdog_thresh=
4148 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4149 warn stall conditions and dump internal state to
4150 help debugging. 0 disables workqueue stall
4151 detection; otherwise, it's the stall threshold
4152 duration in seconds. The default value is 30 and
4153 it can be updated at runtime by writing to the
4154 corresponding sysfs file.
4156 workqueue.disable_numa
4157 By default, all work items queued to unbound
4158 workqueues are affine to the NUMA nodes they're
4159 issued on, which results in better behavior in
4160 general. If NUMA affinity needs to be disabled for
4161 whatever reason, this option can be used. Note
4162 that this also can be controlled per-workqueue for
4163 workqueues visible under /sys/bus/workqueue/.
4165 workqueue.power_efficient
4166 Per-cpu workqueues are generally preferred because
4167 they show better performance thanks to cache
4168 locality; unfortunately, per-cpu workqueues tend to
4169 be more power hungry than unbound workqueues.
4171 Enabling this makes the per-cpu workqueues which
4172 were observed to contribute significantly to power
4173 consumption unbound, leading to measurably lower
4174 power usage at the cost of small performance
4177 The default value of this parameter is determined by
4178 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4180 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4181 default x2apic cluster mode on platforms
4184 x86_intel_mid_timer= [X86-32,APBT]
4185 Choose timer option for x86 Intel MID platform.
4186 Two valid options are apbt timer only and lapic timer
4187 plus one apbt timer for broadcast timer.
4188 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4190 xen_512gb_limit [KNL,X86-64,XEN]
4191 Restricts the kernel running paravirtualized under Xen
4192 to use only up to 512 GB of RAM. The reason to do so is
4193 crash analysis tools and Xen tools for doing domain
4194 save/restore/migration must be enabled to handle larger
4197 xen_emul_unplug= [HW,X86,XEN]
4198 Unplug Xen emulated devices
4199 Format: [unplug0,][unplug1]
4200 ide-disks -- unplug primary master IDE devices
4201 aux-ide-disks -- unplug non-primary-master IDE devices
4202 nics -- unplug network devices
4203 all -- unplug all emulated devices (NICs and IDE disks)
4204 unnecessary -- unplugging emulated devices is
4205 unnecessary even if the host did not respond to
4207 never -- do not unplug even if version check succeeds
4209 xen_nopvspin [X86,XEN]
4210 Disables the ticketlock slowpath using Xen PV
4214 Disables the PV optimizations forcing the HVM guest to
4215 run as generic HVM guest with no PV drivers.
4217 xirc2ps_cs= [NET,PCMCIA]
4219 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4221 ______________________________________________________________________
4225 Add more DRM drivers.
projects / linux-beck.git / blob