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 DM Device mapper support is enabled.
60 DRM Direct Rendering Management support is enabled.
61 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
62 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
63 EFI EFI Partitioning (GPT) is enabled
64 EIDE EIDE/ATAPI support is enabled.
65 EVM Extended Verification Module
66 FB The frame buffer device is enabled.
67 FTRACE Function tracing enabled.
68 GCOV GCOV profiling is enabled.
69 HW Appropriate hardware is enabled.
70 IA-64 IA-64 architecture is enabled.
71 IMA Integrity measurement architecture is enabled.
72 IOSCHED More than one I/O scheduler is enabled.
73 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
74 IPV6 IPv6 support is enabled.
75 ISAPNP ISA PnP code is enabled.
76 ISDN Appropriate ISDN support is enabled.
77 JOY Appropriate joystick support is enabled.
78 KGDB Kernel debugger support is enabled.
79 KVM Kernel Virtual Machine support is enabled.
80 LIBATA Libata driver is enabled
81 LP Printer support is enabled.
82 LOOP Loopback device support is enabled.
83 M68k M68k architecture is enabled.
84 These options have more detailed description inside of
85 Documentation/m68k/kernel-options.txt.
86 MDA MDA console support is enabled.
87 MIPS MIPS architecture is enabled.
88 MOUSE Appropriate mouse support is enabled.
89 MSI Message Signaled Interrupts (PCI).
90 MTD MTD (Memory Technology Device) support is enabled.
91 NET Appropriate network support is enabled.
92 NUMA NUMA support is enabled.
93 NFS Appropriate NFS support is enabled.
94 OSS OSS sound support is enabled.
95 PV_OPS A paravirtualized kernel is enabled.
96 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
97 PARISC The PA-RISC architecture is enabled.
98 PCI PCI bus support is enabled.
99 PCIE PCI Express support is enabled.
100 PCMCIA The PCMCIA subsystem is enabled.
101 PNP Plug & Play support is enabled.
102 PPC PowerPC architecture is enabled.
103 PPT Parallel port support is enabled.
104 PS2 Appropriate PS/2 support is enabled.
105 RAM RAM disk support is enabled.
106 S390 S390 architecture is enabled.
107 SCSI Appropriate SCSI support is enabled.
108 A lot of drivers have their options described inside
109 the Documentation/scsi/ sub-directory.
110 SECURITY Different security models are enabled.
111 SELINUX SELinux support is enabled.
112 APPARMOR AppArmor support is enabled.
113 SERIAL Serial support is enabled.
114 SH SuperH architecture is enabled.
115 SMP The kernel is an SMP kernel.
116 SPARC Sparc architecture is enabled.
117 SWSUSP Software suspend (hibernation) is enabled.
118 SUSPEND System suspend states are enabled.
119 TPM TPM drivers are enabled.
120 TS Appropriate touchscreen support is enabled.
121 UMS USB Mass Storage support is enabled.
122 USB USB support is enabled.
123 USBHID USB Human Interface Device support is enabled.
124 V4L Video For Linux support is enabled.
125 VMMIO Driver for memory mapped virtio devices is enabled.
126 VGA The VGA console has been enabled.
127 VT Virtual terminal support is enabled.
128 WDT Watchdog support is enabled.
129 XT IBM PC/XT MFM hard disk support is enabled.
130 X86-32 X86-32, aka i386 architecture is enabled.
131 X86-64 X86-64 architecture is enabled.
132 More X86-64 boot options can be found in
133 Documentation/x86/x86_64/boot-options.txt .
134 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
135 XEN Xen support is enabled
137 In addition, the following text indicates that the option:
139 BUGS= Relates to possible processor bugs on the said processor.
140 KNL Is a kernel start-up parameter.
141 BOOT Is a boot loader parameter.
143 Parameters denoted with BOOT are actually interpreted by the boot
144 loader, and have no meaning to the kernel directly.
145 Do not modify the syntax of boot loader parameters without extreme
146 need or coordination with <Documentation/x86/boot.txt>.
148 There are also arch-specific kernel-parameters not documented here.
149 See for example <Documentation/x86/x86_64/boot-options.txt>.
151 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
152 a trailing = on the name of any parameter states that that parameter will
153 be entered as an environment variable, whereas its absence indicates that
154 it will appear as a kernel argument readable via /proc/cmdline by programs
155 running once the system is up.
157 The number of kernel parameters is not limited, but the length of the
158 complete command line (parameters including spaces etc.) is limited to
159 a fixed number of characters. This limit depends on the architecture
160 and is between 256 and 4096 characters. It is defined in the file
161 ./include/asm/setup.h as COMMAND_LINE_SIZE.
163 Finally, the [KMG] suffix is commonly described after a number of kernel
164 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
165 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
166 bytes respectively. Such letter suffixes can also be entirely omitted.
169 acpi= [HW,ACPI,X86,ARM64]
170 Advanced Configuration and Power Interface
171 Format: { force | off | strict | noirq | rsdt |
173 force -- enable ACPI if default was off
174 off -- disable ACPI if default was on
175 noirq -- do not use ACPI for IRQ routing
176 strict -- Be less tolerant of platforms that are not
177 strictly ACPI specification compliant.
178 rsdt -- prefer RSDT over (default) XSDT
179 copy_dsdt -- copy DSDT to memory
180 For ARM64, ONLY "acpi=off" or "acpi=force" are available
182 See also Documentation/power/runtime_pm.txt, pci=noacpi
184 acpi_apic_instance= [ACPI, IOAPIC]
186 2: use 2nd APIC table, if available
187 1,0: use 1st APIC table
190 acpi_backlight= [HW,ACPI]
191 acpi_backlight=vendor
193 If set to vendor, prefer vendor specific driver
194 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
195 of the ACPI video.ko driver.
197 acpica_no_return_repair [HW, ACPI]
198 Disable AML predefined validation mechanism
199 This mechanism can repair the evaluation result to make
200 the return objects more ACPI specification compliant.
201 This option is useful for developers to identify the
202 root cause of an AML interpreter issue when the issue
203 has something to do with the repair mechanism.
205 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
206 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
208 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
209 debug output. Bits in debug_layer correspond to a
210 _COMPONENT in an ACPI source file, e.g.,
211 #define _COMPONENT ACPI_PCI_COMPONENT
212 Bits in debug_level correspond to a level in
213 ACPI_DEBUG_PRINT statements, e.g.,
214 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
215 The debug_level mask defaults to "info". See
216 Documentation/acpi/debug.txt for more information about
217 debug layers and levels.
219 Enable processor driver info messages:
220 acpi.debug_layer=0x20000000
221 Enable PCI/PCI interrupt routing info messages:
222 acpi.debug_layer=0x400000
223 Enable AML "Debug" output, i.e., stores to the Debug
224 object while interpreting AML:
225 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
226 Enable all messages related to ACPI hardware:
227 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
229 Some values produce so much output that the system is
230 unusable. The "log_buf_len" parameter may be useful
231 if you need to capture more output.
233 acpi_enforce_resources= [ACPI]
234 { strict | lax | no }
235 Check for resource conflicts between native drivers
236 and ACPI OperationRegions (SystemIO and SystemMemory
237 only). IO ports and memory declared in ACPI might be
238 used by the ACPI subsystem in arbitrary AML code and
239 can interfere with legacy drivers.
240 strict (default): access to resources claimed by ACPI
241 is denied; legacy drivers trying to access reserved
242 resources will fail to bind to device using them.
243 lax: access to resources claimed by ACPI is allowed;
244 legacy drivers trying to access reserved resources
245 will bind successfully but a warning message is logged.
246 no: ACPI OperationRegions are not marked as reserved,
247 no further checks are performed.
249 acpi_force_table_verification [HW,ACPI]
250 Enable table checksum verification during early stage.
251 By default, this is disabled due to x86 early mapping
254 acpi_irq_balance [HW,ACPI]
255 ACPI will balance active IRQs
258 acpi_irq_nobalance [HW,ACPI]
259 ACPI will not move active IRQs (default)
262 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
263 Format: <irq>,<irq>...
265 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
267 Format: <irq>,<irq>...
269 acpi_no_auto_serialize [HW,ACPI]
270 Disable auto-serialization of AML methods
271 AML control methods that contain the opcodes to create
272 named objects will be marked as "Serialized" by the
273 auto-serialization feature.
274 This feature is enabled by default.
275 This option allows to turn off the feature.
277 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
280 acpi_no_static_ssdt [HW,ACPI]
281 Disable installation of static SSDTs at early boot time
282 By default, SSDTs contained in the RSDT/XSDT will be
283 installed automatically and they will appear under
284 /sys/firmware/acpi/tables.
285 This option turns off this feature.
286 Note that specifying this option does not affect
287 dynamic table installation which will install SSDT
288 tables to /sys/firmware/acpi/tables/dynamic.
290 acpi_rsdp= [ACPI,EFI,KEXEC]
291 Pass the RSDP address to the kernel, mostly used
292 on machines running EFI runtime service to boot the
293 second kernel for kdump.
295 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
296 Format: To spoof as Windows 98: ="Microsoft Windows"
298 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
299 of 2 which is mandated by ACPI 6) as the supported ACPI
300 specification revision (when using this switch, it may
301 be necessary to carry out a cold reboot _twice_ in a
302 row to make it take effect on the platform firmware).
304 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
305 acpi_osi="string1" # add string1
306 acpi_osi="!string2" # remove string2
307 acpi_osi=!* # remove all strings
308 acpi_osi=! # disable all built-in OS vendor
310 acpi_osi= # disable all strings
312 'acpi_osi=!' can be used in combination with single or
313 multiple 'acpi_osi="string1"' to support specific OS
314 vendor string(s). Note that such command can only
315 affect the default state of the OS vendor strings, thus
316 it cannot affect the default state of the feature group
317 strings and the current state of the OS vendor strings,
318 specifying it multiple times through kernel command line
319 is meaningless. This command is useful when one do not
320 care about the state of the feature group strings which
321 should be controlled by the OSPM.
323 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
324 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
325 can make '_OSI("Windows 2000")' TRUE.
327 'acpi_osi=' cannot be used in combination with other
328 'acpi_osi=' command lines, the _OSI method will not
329 exist in the ACPI namespace. NOTE that such command can
330 only affect the _OSI support state, thus specifying it
331 multiple times through kernel command line is also
334 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
337 'acpi_osi=!*' can be used in combination with single or
338 multiple 'acpi_osi="string1"' to support specific
339 string(s). Note that such command can affect the
340 current state of both the OS vendor strings and the
341 feature group strings, thus specifying it multiple times
342 through kernel command line is meaningful. But it may
343 still not able to affect the final state of a string if
344 there are quirks related to this string. This command
345 is useful when one want to control the state of the
346 feature group strings to debug BIOS issues related to
349 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
350 '_OSI("Module Device")' FALSE.
351 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
352 '_OSI("Module Device")' TRUE.
353 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
355 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
357 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
358 they all will make '_OSI("Windows 2000")' TRUE.
361 Override the pmtimer bug detection: force the kernel
362 to assume that this machine's pmtimer latches its value
363 and always returns good values.
365 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
366 Format: { level | edge | high | low }
368 acpi_skip_timer_override [HW,ACPI]
369 Recognize and ignore IRQ0/pin2 Interrupt Override.
370 For broken nForce2 BIOS resulting in XT-PIC timer.
372 acpi_sleep= [HW,ACPI] Sleep options
373 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
374 old_ordering, nonvs, sci_force_enable }
375 See Documentation/power/video.txt for information on
377 s3_beep is for debugging; it makes the PC's speaker beep
378 as soon as the kernel's real-mode entry point is called.
379 s4_nohwsig prevents ACPI hardware signature from being
380 used during resume from hibernation.
381 old_ordering causes the ACPI 1.0 ordering of the _PTS
382 control method, with respect to putting devices into
383 low power states, to be enforced (the ACPI 2.0 ordering
384 of _PTS is used by default).
385 nonvs prevents the kernel from saving/restoring the
386 ACPI NVS memory during suspend/hibernation and resume.
387 sci_force_enable causes the kernel to set SCI_EN directly
388 on resume from S1/S3 (which is against the ACPI spec,
389 but some broken systems don't work without it).
391 acpi_use_timer_override [HW,ACPI]
392 Use timer override. For some broken Nvidia NF5 boards
393 that require a timer override, but don't have HPET
395 add_efi_memmap [EFI; X86] Include EFI memory map in
396 kernel's map of available physical RAM.
399 { off | try_unsupported }
400 off: disable AGP support
401 try_unsupported: try to drive unsupported chipsets
402 (may crash computer or cause data corruption)
405 See Documentation/sound/alsa/alsa-parameters.txt
408 Allow the default userspace alignment fault handler
409 behaviour to be specified. Bit 0 enables warnings,
410 bit 1 enables fixups, and bit 2 sends a segfault.
412 align_va_addr= [X86-64]
413 Align virtual addresses by clearing slice [14:12] when
414 allocating a VMA at process creation time. This option
415 gives you up to 3% performance improvement on AMD F15h
416 machines (where it is enabled by default) for a
417 CPU-intensive style benchmark, and it can vary highly in
418 a microbenchmark depending on workload and compiler.
420 32: only for 32-bit processes
421 64: only for 64-bit processes
422 on: enable for both 32- and 64-bit processes
423 off: disable for both 32- and 64-bit processes
425 alloc_snapshot [FTRACE]
426 Allocate the ftrace snapshot buffer on boot up when the
427 main buffer is allocated. This is handy if debugging
428 and you need to use tracing_snapshot() on boot up, and
429 do not want to use tracing_snapshot_alloc() as it needs
430 to be done where GFP_KERNEL allocations are allowed.
432 amd_iommu= [HW,X86-64]
433 Pass parameters to the AMD IOMMU driver in the system.
435 fullflush - enable flushing of IO/TLB entries when
436 they are unmapped. Otherwise they are
437 flushed before they will be reused, which
439 off - do not initialize any AMD IOMMU found in
441 force_isolation - Force device isolation for all
442 devices. The IOMMU driver is not
443 allowed anymore to lift isolation
444 requirements as needed. This option
445 does not override iommu=pt
447 amd_iommu_dump= [HW,X86-64]
448 Enable AMD IOMMU driver option to dump the ACPI table
449 for AMD IOMMU. With this option enabled, AMD IOMMU
450 driver will print ACPI tables for AMD IOMMU during
451 IOMMU initialization.
453 amijoy.map= [HW,JOY] Amiga joystick support
454 Map of devices attached to JOY0DAT and JOY1DAT
456 See also Documentation/input/joystick.txt
458 analog.map= [HW,JOY] Analog joystick and gamepad support
459 Specifies type or capabilities of an analog joystick
460 connected to one of 16 gameports
461 Format: <type1>,<type2>,..<type16>
464 Power management functions (SPARCstation-4/5 + deriv.)
466 Disable APC CPU standby support. SPARCstation-Fox does
467 not play well with APC CPU idle - disable it if you have
468 APC and your system crashes randomly.
470 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
471 Change the output verbosity whilst booting
472 Format: { quiet (default) | verbose | debug }
473 Change the amount of debugging information output
474 when initialising the APIC and IO-APIC components.
477 See Documentation/networking/ipv6.txt.
479 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
480 Limit apic dumping. The parameter defines the maximal
481 number of local apics being dumped. Also it is possible
482 to set it to "all" by meaning -- no limit here.
483 Format: { 1 (default) | 2 | ... | all }.
484 The parameter valid if only apic=debug or
485 apic=verbose is specified.
486 Example: apic=debug show_lapic=all
488 apm= [APM] Advanced Power Management
489 See header of arch/x86/kernel/apm_32.c.
491 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
492 Format: <io>,<irq>,<nodeID>
496 atarimouse= [HW,MOUSE] Atari Mouse
498 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
499 EzKey and similar keyboards
501 atkbd.reset= [HW] Reset keyboard during initialization
503 atkbd.set= [HW] Select keyboard code set
504 Format: <int> (2 = AT (default), 3 = PS/2)
506 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
509 atkbd.softraw= [HW] Choose between synthetic and real raw mode
510 Format: <bool> (0 = real, 1 = synthetic (default))
512 atkbd.softrepeat= [HW]
513 Use software keyboard repeat
515 audit= [KNL] Enable the audit sub-system
516 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
517 0 - kernel audit is disabled and can not be enabled
518 until the next reboot
519 unset - kernel audit is initialized but disabled and
520 will be fully enabled by the userspace auditd.
521 1 - kernel audit is initialized and partially enabled,
522 storing at most audit_backlog_limit messages in
523 RAM until it is fully enabled by the userspace
527 audit_backlog_limit= [KNL] Set the audit queue size limit.
528 Format: <int> (must be >=0)
531 baycom_epp= [HW,AX25]
534 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
536 See header of drivers/net/hamradio/baycom_par.c.
538 baycom_ser_fdx= [HW,AX25]
539 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
540 Format: <io>,<irq>,<mode>[,<baud>]
541 See header of drivers/net/hamradio/baycom_ser_fdx.c.
543 baycom_ser_hdx= [HW,AX25]
544 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
545 Format: <io>,<irq>,<mode>
546 See header of drivers/net/hamradio/baycom_ser_hdx.c.
548 blkdevparts= Manual partition parsing of block device(s) for
549 embedded devices based on command line input.
550 See Documentation/block/cmdline-partition.txt
552 boot_delay= Milliseconds to delay each printk during boot.
553 Values larger than 10 seconds (10000) are changed to
557 bootmem_debug [KNL] Enable bootmem allocator debug messages.
559 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
560 bttv.radio= Most important insmod options are available as
562 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
565 bulk_remove=off [PPC] This parameter disables the use of the pSeries
566 firmware feature for flushing multiple hpte entries
569 c101= [NET] Moxa C101 synchronous serial card
571 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
572 Sometimes CPU hardware bugs make them report the cache
573 size incorrectly. The kernel will attempt work arounds
574 to fix known problems, but for some CPUs it is not
575 possible to determine what the correct size should be.
576 This option provides an override for these situations.
578 ca_keys= [KEYS] This parameter identifies a specific key(s) on
579 the system trusted keyring to be used for certificate
581 format: { id:<keyid> | builtin }
583 cca= [MIPS] Override the kernel pages' cache coherency
584 algorithm. Accepted values range from 0 to 7
585 inclusive. See arch/mips/include/asm/pgtable-bits.h
586 for platform specific values (SB1, Loongson3 and
589 ccw_timeout_log [S390]
590 See Documentation/s390/CommonIO for details.
592 cgroup_disable= [KNL] Disable a particular controller
593 Format: {name of the controller(s) to disable}
594 The effects of cgroup_disable=foo are:
595 - foo isn't auto-mounted if you mount all cgroups in
597 - foo isn't visible as an individually mountable
599 {Currently only "memory" controller deal with this and
600 cut the overhead, others just disable the usage. So
601 only cgroup_disable=memory is actually worthy}
603 checkreqprot [SELINUX] Set initial checkreqprot flag value.
604 Format: { "0" | "1" }
605 See security/selinux/Kconfig help text.
606 0 -- check protection applied by kernel (includes
607 any implied execute protection).
608 1 -- check protection requested by application.
609 Default value is set via a kernel config option.
610 Value can be changed at runtime via
611 /selinux/checkreqprot.
614 See Documentation/s390/CommonIO for details.
617 Prevents the clock framework from automatically gating
618 clocks that have not been explicitly enabled by a Linux
619 device driver but are enabled in hardware at reset or
620 by the bootloader/firmware. Note that this does not
621 force such clocks to be always-on nor does it reserve
622 those clocks in any way. This parameter is useful for
623 debug and development, but should not be needed on a
624 platform with proper driver support. For more
625 information, see Documentation/clk.txt.
627 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
629 Forces specified clocksource (if available) to be used
630 when calculating gettimeofday(). If specified
631 clocksource is not available, it defaults to PIT.
632 Format: { pit | tsc | cyclone | pmtmr }
634 clocksource= Override the default clocksource
636 Override the default clocksource and use the clocksource
637 with the name specified.
638 Some clocksource names to choose from, depending on
640 [all] jiffies (this is the base, fallback clocksource)
642 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
643 pxa_timer,timer3,32k_counter,timer0_1
645 [X86-32] pit,hpet,tsc;
646 scx200_hrt on Geode; cyclone on IBM x440
654 clearcpuid=BITNUM [X86]
655 Disable CPUID feature X for the kernel. See
656 arch/x86/include/asm/cpufeature.h for the valid bit
657 numbers. Note the Linux specific bits are not necessarily
658 stable over kernel options, but the vendor specific
660 Also note that user programs calling CPUID directly
661 or using the feature without checking anything
662 will still see it. This just prevents it from
663 being used by the kernel or shown in /proc/cpuinfo.
664 Also note the kernel might malfunction if you disable
667 cma=nn[MG]@[start[MG][-end[MG]]]
669 Sets the size of kernel global memory area for
670 contiguous memory allocations and optionally the
671 placement constraint by the physical address range of
672 memory allocations. A value of 0 disables CMA
673 altogether. For more information, see
674 include/linux/dma-contiguous.h
676 cmo_free_hint= [PPC] Format: { yes | no }
677 Specify whether pages are marked as being inactive
678 when they are freed. This is used in CMO environments
679 to determine OS memory pressure for page stealing by
683 coherent_pool=nn[KMG] [ARM,KNL]
684 Sets the size of memory pool for coherent, atomic dma
685 allocations, by default set to 256K.
687 code_bytes [X86] How many bytes of object code to print
692 com20020= [HW,NET] ARCnet - COM20020 chipset
694 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
696 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
700 ARCnet - COM90xx chipset (memory-mapped buffers)
701 Format: <io>[,<irq>[,<memstart>]]
703 condev= [HW,S390] console device
706 console= [KNL] Output console device and options.
708 tty<n> Use the virtual console device <n>.
712 Use the specified serial port. The options are of
713 the form "bbbbpnf", where "bbbb" is the baud rate,
714 "p" is parity ("n", "o", or "e"), "n" is number of
715 bits, and "f" is flow control ("r" for RTS or
716 omit it). Default is "9600n8".
718 See Documentation/serial-console.txt for more
720 Documentation/networking/netconsole.txt for an
723 uart[8250],io,<addr>[,options]
724 uart[8250],mmio,<addr>[,options]
725 uart[8250],mmio32,<addr>[,options]
726 uart[8250],0x<addr>[,options]
727 Start an early, polled-mode console on the 8250/16550
728 UART at the specified I/O port or MMIO address,
729 switching to the matching ttyS device later.
730 MMIO inter-register address stride is either 8-bit
731 (mmio) or 32-bit (mmio32).
732 If none of [io|mmio|mmio32], <addr> is assumed to be
733 equivalent to 'mmio'. 'options' are specified in the
734 same format described for ttyS above; if unspecified,
735 the h/w is not re-initialized.
737 hvc<n> Use the hypervisor console device <n>. This is for
738 both Xen and PowerPC hypervisors.
740 If the device connected to the port is not a TTY but a braille
741 device, prepend "brl," before the device type, for instance
743 For now, only VisioBraille is supported.
745 consoleblank= [KNL] The console blank (screen saver) timeout in
746 seconds. Defaults to 10*60 = 10mins. A value of 0
747 disables the blank timer.
750 [KNL] Change the default value for
751 /proc/<pid>/coredump_filter.
752 See also Documentation/filesystems/proc.txt.
754 cpuidle.off=1 [CPU_IDLE]
755 disable the cpuidle sub-system
758 [X86] Delay for N microsec between assert and de-assert
759 of APIC INIT to start processors. This delay occurs
760 on every CPU online, such as boot, and resume from suspend.
763 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
765 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
767 crashkernel=size[KMG][@offset[KMG]]
768 [KNL] Using kexec, Linux can switch to a 'crash kernel'
769 upon panic. This parameter reserves the physical
770 memory region [offset, offset + size] for that kernel
771 image. If '@offset' is omitted, then a suitable offset
772 is selected automatically. Check
773 Documentation/kdump/kdump.txt for further details.
775 crashkernel=range1:size1[,range2:size2,...][@offset]
776 [KNL] Same as above, but depends on the memory
777 in the running system. The syntax of range is
778 start-[end] where start and end are both
779 a memory unit (amount[KMG]). See also
780 Documentation/kdump/kdump.txt for an example.
782 crashkernel=size[KMG],high
783 [KNL, x86_64] range could be above 4G. Allow kernel
784 to allocate physical memory region from top, so could
785 be above 4G if system have more than 4G ram installed.
786 Otherwise memory region will be allocated below 4G, if
788 It will be ignored if crashkernel=X is specified.
789 crashkernel=size[KMG],low
790 [KNL, x86_64] range under 4G. When crashkernel=X,high
791 is passed, kernel could allocate physical memory region
792 above 4G, that cause second kernel crash on system
793 that require some amount of low memory, e.g. swiotlb
794 requires at least 64M+32K low memory, also enough extra
795 low memory is needed to make sure DMA buffers for 32-bit
796 devices won't run out. Kernel would try to allocate at
797 at least 256M below 4G automatically.
798 This one let user to specify own low range under 4G
799 for second kernel instead.
800 0: to disable low allocation.
801 It will be ignored when crashkernel=X,high is not used
802 or memory reserved is below 4G.
807 cs89x0_media= [HW,NET]
808 Format: { rj45 | aui | bnc }
811 See header of drivers/s390/block/dasd_devmap.c.
813 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
814 (one device per port)
815 Format: <port#>,<type>
816 See also Documentation/input/joystick-parport.txt
818 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
819 time. See Documentation/dynamic-debug-howto.txt for
820 details. Deprecated, see dyndbg.
822 debug [KNL] Enable kernel debugging (events log level).
825 [KNL] verbose self-tests
827 Print debugging info while doing the locking API
829 We default to 0 (no extra messages), setting it to
830 1 will print _a lot_ more information - normally
831 only useful to kernel developers.
833 debug_objects [KNL] Enable object debugging
836 [KNL] Disable object debugging
838 debug_guardpage_minorder=
839 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
840 parameter allows control of the order of pages that will
841 be intentionally kept free (and hence protected) by the
842 buddy allocator. Bigger value increase the probability
843 of catching random memory corruption, but reduce the
844 amount of memory for normal system use. The maximum
845 possible value is MAX_ORDER/2. Setting this parameter
846 to 1 or 2 should be enough to identify most random
847 memory corruption problems caused by bugs in kernel or
848 driver code when a CPU writes to (or reads from) a
849 random memory location. Note that there exists a class
850 of memory corruptions problems caused by buggy H/W or
851 F/W or by drivers badly programing DMA (basically when
852 memory is written at bus level and the CPU MMU is
853 bypassed) which are not detectable by
854 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
855 tracking down these problems.
858 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
859 parameter enables the feature at boot time. In
860 default, it is disabled. We can avoid allocating huge
861 chunk of memory for debug pagealloc if we don't enable
862 it at boot time and the system will work mostly same
863 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
864 on: enable the feature
866 debugpat [X86] Enable PAT debugging
868 decnet.addr= [HW,NET]
869 Format: <area>[,<node>]
870 See also Documentation/networking/decnet.txt.
873 [same as hugepagesz=] The size of the default
874 HugeTLB page size. This is the size represented by
875 the legacy /proc/ hugepages APIs, used for SHM, and
876 default size when mounting hugetlbfs filesystems.
877 Defaults to the default architecture's huge page size
881 Set number of hash buckets for dentry cache.
884 See Documentation/networking/ipv6.txt.
886 disable_cpu_apicid= [X86,APIC,SMP]
888 The number of initial APIC ID for the
889 corresponding CPU to be disabled at boot,
890 mostly used for the kdump 2nd kernel to
891 disable BSP to wake up multiple CPUs without
892 causing system reset or hang due to sending
895 disable_ddw [PPC/PSERIES]
896 Disable Dynamic DMA Window support. Use this if
897 to workaround buggy firmware.
900 See Documentation/networking/ipv6.txt.
902 disable_mtrr_cleanup [X86]
903 The kernel tries to adjust MTRR layout from continuous
904 to discrete, to make X server driver able to add WB
905 entry later. This parameter disables that.
907 disable_mtrr_trim [X86, Intel and AMD only]
908 By default the kernel will trim any uncacheable
909 memory out of your available memory pool based on
910 MTRR settings. This parameter disables that behavior,
911 possibly causing your machine to run very slowly.
913 disable_timer_pin_1 [X86]
914 Disable PIN 1 of APIC timer
915 Can be useful to work around chipset bugs.
917 dis_ucode_ldr [X86] Disable the microcode loader.
919 dm= [DM] Allows early creation of a device-mapper device.
920 See Documentation/device-mapper/boot.txt.
922 dmasound= [HW,OSS] Sound subsystem buff
924 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
925 this option disables the debugging code at boot.
927 dma_debug_entries=<number>
928 This option allows to tune the number of preallocated
929 entries for DMA-API debugging code. One entry is
930 required per DMA-API allocation. Use this if the
931 DMA-API debugging code disables itself because the
932 architectural default is too low.
934 dma_debug_driver=<driver_name>
935 With this option the DMA-API debugging driver
936 filter feature can be enabled at boot time. Just
937 pass the driver to filter for as the parameter.
938 The filter can be disabled or changed to another
939 driver later using sysfs.
941 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
942 Broken monitors, graphic adapters, KVMs and EDIDless
943 panels may send no or incorrect EDID data sets.
944 This parameter allows to specify an EDID data sets
945 in the /lib/firmware directory that are used instead.
946 Generic built-in EDID data sets are used, if one of
947 edid/1024x768.bin, edid/1280x1024.bin,
948 edid/1680x1050.bin, or edid/1920x1080.bin is given
949 and no file with the same name exists. Details and
950 instructions how to build your own EDID data are
951 available in Documentation/EDID/HOWTO.txt. An EDID
952 data set will only be used for a particular connector,
953 if its name and a colon are prepended to the EDID
954 name. Each connector may use a unique EDID data
955 set by separating the files with a comma. An EDID
956 data set with no connector name will be used for
957 any connectors not explicitly specified.
961 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
962 module.dyndbg[="val"]
963 Enable debug messages at boot time. See
964 Documentation/dynamic-debug-howto.txt for details.
966 nompx [X86] Disables Intel Memory Protection Extensions.
967 See Documentation/x86/intel_mpx.txt for more
968 information about the feature.
971 on enable eager fpu restore
972 off disable eager fpu restore
973 auto selects the default scheme, which automatically
974 enables eagerfpu restore for xsaveopt.
976 module.async_probe [KNL]
977 Enable asynchronous probe on this module.
979 early_ioremap_debug [KNL]
980 Enable debug messages in early_ioremap support. This
981 is useful for tracking down temporary early mappings
982 which are not unmapped.
984 earlycon= [KNL] Output early console device and options.
986 When used with no options, the early console is
987 determined by the stdout-path property in device
991 Start an early, polled-mode console on a cadence serial
992 port at the specified address. The cadence serial port
993 must already be setup and configured. Options are not
996 uart[8250],io,<addr>[,options]
997 uart[8250],mmio,<addr>[,options]
998 uart[8250],mmio32,<addr>[,options]
999 uart[8250],mmio32be,<addr>[,options]
1000 uart[8250],0x<addr>[,options]
1001 Start an early, polled-mode console on the 8250/16550
1002 UART at the specified I/O port or MMIO address.
1003 MMIO inter-register address stride is either 8-bit
1004 (mmio) or 32-bit (mmio32 or mmio32be).
1005 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1006 to be equivalent to 'mmio'. 'options' are specified
1007 in the same format described for "console=ttyS<n>"; if
1008 unspecified, the h/w is not initialized.
1011 Start an early, polled-mode console on a pl011 serial
1012 port at the specified address. The pl011 serial port
1013 must already be setup and configured. Options are not
1017 Start an early, polled-mode console on an msm serial
1018 port at the specified address. The serial port
1019 must already be setup and configured. Options are not
1022 msm_serial_dm,<addr>
1023 Start an early, polled-mode console on an msm serial
1024 dm port at the specified address. The serial port
1025 must already be setup and configured. Options are not
1028 smh Use ARM semihosting calls for early console.
1036 Use early console provided by serial driver available
1037 on Samsung SoCs, requires selecting proper type and
1038 a correct base address of the selected UART port. The
1039 serial port must already be setup and configured.
1040 Options are not yet supported.
1044 Use early console provided by Freescale LP UART driver
1045 found on Freescale Vybrid and QorIQ LS1021A processors.
1046 A valid base address must be provided, and the serial
1047 port must already be setup and configured.
1049 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1053 earlyprintk=serial[,ttySn[,baudrate]]
1054 earlyprintk=serial[,0x...[,baudrate]]
1055 earlyprintk=ttySn[,baudrate]
1056 earlyprintk=dbgp[debugController#]
1057 earlyprintk=pciserial,bus:device.function[,baudrate]
1059 earlyprintk is useful when the kernel crashes before
1060 the normal console is initialized. It is not enabled by
1061 default because it has some cosmetic problems.
1063 Append ",keep" to not disable it when the real console
1066 Only one of vga, efi, serial, or usb debug port can
1069 Currently only ttyS0 and ttyS1 may be specified by
1070 name. Other I/O ports may be explicitly specified
1071 on some architectures (x86 and arm at least) by
1072 replacing ttySn with an I/O port address, like this:
1073 earlyprintk=serial,0x1008,115200
1074 You can find the port for a given device in
1075 /proc/tty/driver/serial:
1076 2: uart:ST16650V2 port:00001008 irq:18 ...
1078 Interaction with the standard serial driver is not
1081 The VGA and EFI output is eventually overwritten by
1084 The xen output can only be used by Xen PV guests.
1086 edac_report= [HW,EDAC] Control how to report EDAC event
1087 Format: {"on" | "off" | "force"}
1088 on: enable EDAC to report H/W event. May be overridden
1089 by other higher priority error reporting module.
1090 off: disable H/W event reporting through EDAC.
1091 force: enforce the use of EDAC to report H/W event.
1094 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1097 This is designed to be used in conjunction with
1098 the boot argument: earlyprintk=vga
1101 Format: {"off" | "on" | "skip[mbr]"}
1104 Format: { "old_map", "nochunk", "noruntime", "debug" }
1105 old_map [X86-64]: switch to the old ioremap-based EFI
1106 runtime services mapping. 32-bit still uses this one by
1108 nochunk: disable reading files in "chunks" in the EFI
1109 boot stub, as chunking can cause problems with some
1110 firmware implementations.
1111 noruntime : disable EFI runtime services support
1112 debug: enable misc debug output
1114 efi_no_storage_paranoia [EFI; X86]
1115 Using this parameter you can use more than 50% of
1116 your efi variable storage. Use this parameter only if
1117 you are really sure that your UEFI does sane gc and
1118 fulfills the spec otherwise your board may brick.
1120 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1121 Add arbitrary attribute to specific memory range by
1122 updating original EFI memory map.
1123 Region of memory which aa attribute is added to is
1125 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1126 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1127 attribute is added to range 0x100000000-0x180000000 and
1128 0x10a0000000-0x1120000000.
1130 Using this parameter you can do debugging of EFI memmap
1131 related feature. For example, you can do debugging of
1132 Address Range Mirroring feature even if your box
1135 eisa_irq_edge= [PARISC,HW]
1136 See header of drivers/parisc/eisa.c.
1139 See comment before function elanfreq_setup() in
1140 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1143 Format: {"cfq" | "deadline" | "noop"}
1144 See Documentation/block/cfq-iosched.txt and
1145 Documentation/block/deadline-iosched.txt for details.
1147 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1148 Specifies physical address of start of kernel core
1149 image elf header and optionally the size. Generally
1150 kexec loader will pass this option to capture kernel.
1151 See Documentation/kdump/kdump.txt for details.
1153 enable_mtrr_cleanup [X86]
1154 The kernel tries to adjust MTRR layout from continuous
1155 to discrete, to make X server driver able to add WB
1156 entry later. This parameter enables that.
1158 enable_timer_pin_1 [X86]
1159 Enable PIN 1 of APIC timer
1160 Can be useful to work around chipset bugs
1161 (in particular on some ATI chipsets).
1162 The kernel tries to set a reasonable default.
1164 enforcing [SELINUX] Set initial enforcing status.
1166 See security/selinux/Kconfig help text.
1167 0 -- permissive (log only, no denials).
1168 1 -- enforcing (deny and log).
1170 Value can be changed at runtime via /selinux/enforce.
1173 Disable Error Record Serialization Table (ERST)
1176 ether= [HW,NET] Ethernet cards parameters
1177 This option is obsoleted by the "netdev=" option, which
1178 has equivalent usage. See its documentation for details.
1182 Permit 'security.evm' to be updated regardless of
1183 current integrity status.
1187 fail_make_request=[KNL]
1188 General fault injection mechanism.
1189 Format: <interval>,<probability>,<space>,<times>
1190 See also Documentation/fault-injection/.
1193 See Documentation/blockdev/floppy.txt.
1195 force_pal_cache_flush
1196 [IA-64] Avoid check_sal_cache_flush which may hang on
1197 buggy SAL_CACHE_FLUSH implementations. Using this
1198 parameter will force ia64_sal_cache_flush to call
1199 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1202 Forcefully enable Physical Address Extension (PAE).
1203 Many Pentium M systems disable PAE but may have a
1204 functionally usable PAE implementation.
1205 Warning: use of this parameter will taint the kernel
1206 and may cause unknown problems.
1209 [FTRACE] will set and start the specified tracer
1210 as early as possible in order to facilitate early
1213 ftrace_dump_on_oops[=orig_cpu]
1214 [FTRACE] will dump the trace buffers on oops.
1215 If no parameter is passed, ftrace will dump
1216 buffers of all CPUs, but if you pass orig_cpu, it will
1217 dump only the buffer of the CPU that triggered the
1220 ftrace_filter=[function-list]
1221 [FTRACE] Limit the functions traced by the function
1222 tracer at boot up. function-list is a comma separated
1223 list of functions. This list can be changed at run
1224 time by the set_ftrace_filter file in the debugfs
1227 ftrace_notrace=[function-list]
1228 [FTRACE] Do not trace the functions specified in
1229 function-list. This list can be changed at run time
1230 by the set_ftrace_notrace file in the debugfs
1233 ftrace_graph_filter=[function-list]
1234 [FTRACE] Limit the top level callers functions traced
1235 by the function graph tracer at boot up.
1236 function-list is a comma separated list of functions
1237 that can be changed at run time by the
1238 set_graph_function file in the debugfs tracing directory.
1240 ftrace_graph_notrace=[function-list]
1241 [FTRACE] Do not trace from the functions specified in
1242 function-list. This list is a comma separated list of
1243 functions that can be changed at run time by the
1244 set_graph_notrace file in the debugfs tracing directory.
1247 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1248 support via parallel port (up to 5 devices per port)
1249 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1250 See also Documentation/input/joystick-parport.txt
1254 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1258 gcov_persist= [GCOV] When non-zero (default), profiling data for
1259 kernel modules is saved and remains accessible via
1260 debugfs, even when the module is unloaded/reloaded.
1261 When zero, profiling data is discarded and associated
1262 debugfs files are removed at module unload time.
1264 gpt [EFI] Forces disk with valid GPT signature but
1265 invalid Protective MBR to be treated as GPT. If the
1266 primary GPT is corrupted, it enables the backup/alternate
1267 GPT to be used instead.
1269 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1270 the "Enable 0" bit of the configuration register.
1273 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1274 the "Enable 0" bit of the configuration register.
1277 grcan.select= [HW] Select which physical interface to use.
1280 grcan.txsize= [HW] Sets the size of the tx buffer.
1281 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1283 grcan.rxsize= [HW] Sets the size of the rx buffer.
1284 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1287 hardlockup_all_cpu_backtrace=
1288 [KNL] Should the hard-lockup detector generate
1289 backtraces on all cpus.
1292 hashdist= [KNL,NUMA] Large hashes allocated during boot
1293 are distributed across NUMA nodes. Defaults on
1294 for 64-bit NUMA, off otherwise.
1295 Format: 0 | 1 (for off | on)
1297 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1299 hd= [EIDE] (E)IDE hard drive subsystem geometry
1300 Format: <cyl>,<head>,<sect>
1303 Disable Hardware Error Source Table (HEST) support;
1304 corresponding firmware-first mode error processing
1305 logic will be disabled.
1307 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1308 size of <nn>. This works even on boxes that have no
1309 highmem otherwise. This also works to reduce highmem
1310 size on bigger boxes.
1312 highres= [KNL] Enable/disable high resolution timer mode.
1313 Valid parameters: "on", "off"
1317 See Documentation/isdn/README.HiSax.
1321 hpet= [X86-32,HPET] option to control HPET usage
1322 Format: { enable (default) | disable | force |
1324 disable: disable HPET and use PIT instead
1325 force: allow force enabled of undocumented chips (ICH4,
1327 verbose: show contents of HPET registers during setup
1329 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1330 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1332 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1333 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1334 On x86-64 and powerpc, this option can be specified
1335 multiple times interleaved with hugepages= to reserve
1336 huge pages of different sizes. Valid pages sizes on
1337 x86-64 are 2M (when the CPU supports "pse") and 1G
1338 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1340 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1341 terminal devices. Valid values: 0..8
1342 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1343 If specified, z/VM IUCV HVC accepts connections
1344 from listed z/VM user IDs only.
1346 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1347 hardware thread id mappings.
1348 Format: <cpu>:<hwthread>
1351 Do not unregister boot console at start. This is only
1352 useful for debugging when something happens in the window
1353 between unregistering the boot console and initializing
1356 i2c_bus= [HW] Override the default board specific I2C bus speed
1357 or register an additional I2C bus that is not
1358 registered from board initialization code.
1362 i8042.debug [HW] Toggle i8042 debug mode
1363 i8042.unmask_kbd_data
1364 [HW] Enable printing of interrupt data from the KBD port
1365 (disabled by default, and as a pre-condition
1366 requires that i8042.debug=1 be enabled)
1367 i8042.direct [HW] Put keyboard port into non-translated mode
1368 i8042.dumbkbd [HW] Pretend that controller can only read data from
1369 keyboard and cannot control its state
1370 (Don't attempt to blink the leds)
1371 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1372 i8042.nokbd [HW] Don't check/create keyboard port
1373 i8042.noloop [HW] Disable the AUX Loopback command while probing
1375 i8042.nomux [HW] Don't check presence of an active multiplexing
1377 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1379 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1380 i8042.reset [HW] Reset the controller during init, cleanup and
1381 suspend-to-ram transitions, only during s2r
1382 transitions, or never reset
1383 Format: { 1 | Y | y | 0 | N | n }
1384 1, Y, y: always reset controller
1385 0, N, n: don't ever reset controller
1386 Default: only on s2r transitions on x86; most other
1387 architectures force reset to be always executed
1388 i8042.unlock [HW] Unlock (ignore) the keylock
1389 i8042.kbdreset [HW] Reset device connected to KBD port
1393 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1394 indicates that the driver is running on unsupported
1396 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1397 does not match list of supported models.
1399 [HW] Report power status in /proc/i8k
1400 (disabled by default)
1401 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1404 i915.invert_brightness=
1405 [DRM] Invert the sense of the variable that is used to
1406 set the brightness of the panel backlight. Normally a
1407 brightness value of 0 indicates backlight switched off,
1408 and the maximum of the brightness value sets the backlight
1409 to maximum brightness. If this parameter is set to 0
1410 (default) and the machine requires it, or this parameter
1411 is set to 1, a brightness value of 0 sets the backlight
1412 to maximum brightness, and the maximum of the brightness
1413 value switches the backlight off.
1414 -1 -- never invert brightness
1415 0 -- machine default
1416 1 -- force brightness inversion
1419 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1421 ide-core.nodma= [HW] (E)IDE subsystem
1422 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1423 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1424 .cdrom .chs .ignore_cable are additional options
1425 See Documentation/ide/ide.txt.
1427 ide-generic.probe-mask= [HW] (E)IDE subsystem
1429 Probe mask for legacy ISA IDE ports. Depending on
1430 platform up to 6 ports are supported, enabled by
1431 setting corresponding bits in the mask to 1. The
1432 default value is 0x0, which has a special meaning.
1433 On systems that have PCI, it triggers scanning the
1434 PCI bus for the first and the second port, which
1435 are then probed. On systems without PCI the value
1436 of 0x0 enables probing the two first ports as if it
1439 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1440 Claim all unknown PCI IDE storage controllers.
1443 Format: idle=poll, idle=halt, idle=nomwait
1444 Poll forces a polling idle loop that can slightly
1445 improve the performance of waking up a idle CPU, but
1446 will use a lot of power and make the system run hot.
1448 idle=halt: Halt is forced to be used for CPU idle.
1449 In such case C2/C3 won't be used again.
1450 idle=nomwait: Disable mwait for CPU C-states
1452 ignore_loglevel [KNL]
1453 Ignore loglevel setting - this will print /all/
1454 kernel messages to the console. Useful for debugging.
1455 We also add it as printk module parameter, so users
1456 could change it dynamically, usually by
1457 /sys/module/printk/parameters/ignore_loglevel.
1459 ihash_entries= [KNL]
1460 Set number of hash buckets for inode cache.
1462 ima_appraise= [IMA] appraise integrity measurements
1463 Format: { "off" | "enforce" | "fix" | "log" }
1466 ima_appraise_tcb [IMA]
1467 The builtin appraise policy appraises all files
1471 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1475 The list of supported hash algorithms is defined
1476 in crypto/hash_info.h.
1479 The builtin measurement policy to load during IMA
1480 setup. Specyfing "tcb" as the value, measures all
1481 programs exec'd, files mmap'd for exec, and all files
1482 opened with the read mode bit set by either the
1483 effective uid (euid=0) or uid=0.
1486 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1487 Load a policy which meets the needs of the Trusted
1488 Computing Base. This means IMA will measure all
1489 programs exec'd, files mmap'd for exec, and all files
1490 opened for read by uid=0.
1493 Select one of defined IMA measurements template formats.
1494 Formats: { "ima" | "ima-ng" | "ima-sig" }
1498 [IMA] Define a custom template format.
1499 Format: { "field1|...|fieldN" }
1501 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1502 Format: <min_file_size>
1503 Set the minimal file size for using asynchronous hash.
1504 If left unspecified, ahash usage is disabled.
1506 ahash performance varies for different data sizes on
1507 different crypto accelerators. This option can be used
1508 to achieve the best performance for a particular HW.
1510 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1512 Set hashing buffer size. Default: 4k.
1514 ahash performance varies for different chunk sizes on
1515 different crypto accelerators. This option can be used
1516 to achieve best performance for particular HW.
1520 Run specified binary instead of /sbin/init as init
1523 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1524 for working out where the kernel is dying during
1527 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1528 initcall functions. Useful for debugging built-in
1529 modules and initcalls.
1531 initrd= [BOOT] Specify the location of the initial ramdisk
1533 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1536 int_pln_enable [x86] Enable power limit notification interrupt
1538 integrity_audit=[IMA]
1539 Format: { "0" | "1" }
1540 0 -- basic integrity auditing messages. (Default)
1541 1 -- additional integrity auditing messages.
1543 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1545 Enable intel iommu driver.
1547 Disable intel iommu driver.
1548 igfx_off [Default Off]
1549 By default, gfx is mapped as normal device. If a gfx
1550 device has a dedicated DMAR unit, the DMAR unit is
1551 bypassed by not enabling DMAR with this option. In
1552 this case, gfx device will use physical address for
1555 With this option iommu will not optimize to look
1556 for io virtual address below 32-bit forcing dual
1557 address cycle on pci bus for cards supporting greater
1558 than 32-bit addressing. The default is to look
1559 for translation below 32-bit and if not available
1560 then look in the higher range.
1561 strict [Default Off]
1562 With this option on every unmap_single operation will
1563 result in a hardware IOTLB flush operation as opposed
1564 to batching them for performance.
1565 sp_off [Default Off]
1566 By default, super page will be supported if Intel IOMMU
1567 has the capability. With this option, super page will
1569 ecs_off [Default Off]
1570 By default, extended context tables will be supported if
1571 the hardware advertises that it has support both for the
1572 extended tables themselves, and also PASID support. With
1573 this option set, extended tables will not be used even
1574 on hardware which claims to support them.
1576 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1577 0 disables intel_idle and fall back on acpi_idle.
1578 1 to 6 specify maximum depth of C-state.
1582 Do not enable intel_pstate as the default
1583 scaling driver for the supported processors
1585 Enable intel_pstate on systems that prohibit it by default
1586 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1587 instead of acpi-cpufreq may disable platform features, such
1588 as thermal controls and power capping, that rely on ACPI
1589 P-States information being indicated to OSPM and therefore
1590 should be used with caution. This option does not work with
1591 processors that aren't supported by the intel_pstate driver
1592 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1594 Do not enable hardware P state control (HWP)
1597 Only load intel_pstate on systems which support
1598 hardware P state control (HWP) if available.
1600 intremap= [X86-64, Intel-IOMMU]
1601 on enable Interrupt Remapping (default)
1602 off disable Interrupt Remapping
1603 nosid disable Source ID checking
1605 BIOS x2APIC opt-out request will be ignored
1606 nopost disable Interrupt Posting
1608 iomem= Disable strict checking of access to MMIO memory
1609 strict regions from userspace.
1624 nobypass [PPC/POWERNV]
1625 Disable IOMMU bypass, using IOMMU for PCI devices.
1628 io7= [HW] IO7 for Marvel based alpha systems
1629 See comment before marvel_specify_io7 in
1630 arch/alpha/kernel/core_marvel.c.
1632 io_delay= [X86] I/O delay method
1634 Standard port 0x80 based delay
1636 Alternate port 0xed based delay (needed on some systems)
1638 Simple two microseconds delay
1643 See Documentation/filesystems/nfs/nfsroot.txt.
1646 When an interrupt is not handled search all handlers
1647 for it. Intended to get systems with badly broken
1651 When an interrupt is not handled search all handlers
1652 for it. Also check all handlers each timer
1653 interrupt. Intended to get systems with badly broken
1657 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1659 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1661 <cpu number>,...,<cpu number>
1663 <cpu number>-<cpu number>
1664 (must be a positive range in ascending order)
1666 <cpu number>,...,<cpu number>-<cpu number>
1668 This option can be used to specify one or more CPUs
1669 to isolate from the general SMP balancing and scheduling
1670 algorithms. You can move a process onto or off an
1671 "isolated" CPU via the CPU affinity syscalls or cpuset.
1672 <cpu number> begins at 0 and the maximum value is
1673 "number of CPUs in system - 1".
1675 This option is the preferred way to isolate CPUs. The
1676 alternative -- manually setting the CPU mask of all
1677 tasks in the system -- can cause problems and
1678 suboptimal load balancer performance.
1682 ivrs_ioapic [HW,X86_64]
1683 Provide an override to the IOAPIC-ID<->DEVICE-ID
1684 mapping provided in the IVRS ACPI table. For
1685 example, to map IOAPIC-ID decimal 10 to
1686 PCI device 00:14.0 write the parameter as:
1687 ivrs_ioapic[10]=00:14.0
1689 ivrs_hpet [HW,X86_64]
1690 Provide an override to the HPET-ID<->DEVICE-ID
1691 mapping provided in the IVRS ACPI table. For
1692 example, to map HPET-ID decimal 0 to
1693 PCI device 00:14.0 write the parameter as:
1694 ivrs_hpet[0]=00:14.0
1696 js= [HW,JOY] Analog joystick
1697 See Documentation/input/joystick.txt.
1700 Enable/disable kernel and module base offset ASLR
1701 (Address Space Layout Randomization) if built into
1702 the kernel. When CONFIG_HIBERNATION is selected,
1703 kASLR is disabled by default. When kASLR is enabled,
1704 hibernation will be disabled.
1708 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1709 specifies the amount of memory usable by the kernel
1710 for non-movable allocations. The requested amount is
1711 spread evenly throughout all nodes in the system. The
1712 remaining memory in each node is used for Movable
1713 pages. In the event, a node is too small to have both
1714 kernelcore and Movable pages, kernelcore pages will
1715 take priority and other nodes will have a larger number
1716 of Movable pages. The Movable zone is used for the
1717 allocation of pages that may be reclaimed or moved
1718 by the page migration subsystem. This means that
1719 HugeTLB pages may not be allocated from this zone.
1720 Note that allocations like PTEs-from-HighMem still
1721 use the HighMem zone if it exists, and the Normal
1722 zone if it does not.
1724 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1725 Format: <Controller#>[,poll interval]
1726 The controller # is the number of the ehci usb debug
1727 port as it is probed via PCI. The poll interval is
1728 optional and is the number seconds in between
1729 each poll cycle to the debug port in case you need
1730 the functionality for interrupting the kernel with
1731 gdb or control-c on the dbgp connection. When
1732 not using this parameter you use sysrq-g to break into
1733 the kernel debugger.
1735 kgdboc= [KGDB,HW] kgdb over consoles.
1736 Requires a tty driver that supports console polling,
1737 or a supported polling keyboard driver (non-usb).
1738 Serial only format: <serial_device>[,baud]
1739 keyboard only format: kbd
1740 keyboard and serial format: kbd,<serial_device>[,baud]
1741 Optional Kernel mode setting:
1742 kms, kbd format: kms,kbd
1743 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1745 kgdbwait [KGDB] Stop kernel execution and enter the
1746 kernel debugger at the earliest opportunity.
1748 kmac= [MIPS] korina ethernet MAC address.
1749 Configure the RouterBoard 532 series on-chip
1750 Ethernet adapter MAC address.
1752 kmemleak= [KNL] Boot-time kmemleak enable/disable
1753 Valid arguments: on, off
1755 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1758 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1759 Valid arguments: 0, 1, 2
1760 kmemcheck=0 (disabled)
1761 kmemcheck=1 (enabled)
1762 kmemcheck=2 (one-shot mode)
1763 Default: 2 (one-shot mode)
1765 kstack=N [X86] Print N words from the kernel stack
1768 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1769 Default is 0 (don't ignore, but inject #GP)
1771 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1775 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1776 Default is 1 (enabled)
1778 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1780 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1782 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1783 (virtualized MMU) support on capable Intel chips.
1784 Default is 1 (enabled)
1786 kvm-intel.emulate_invalid_guest_state=
1787 [KVM,Intel] Enable emulation of invalid guest states
1788 Default is 0 (disabled)
1790 kvm-intel.flexpriority=
1791 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1792 Default is 1 (enabled)
1795 [KVM,Intel] Enable VMX nesting (nVMX).
1796 Default is 0 (disabled)
1798 kvm-intel.unrestricted_guest=
1799 [KVM,Intel] Disable unrestricted guest feature
1800 (virtualized real and unpaged mode) on capable
1801 Intel chips. Default is 1 (enabled)
1803 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1804 feature (tagged TLBs) on capable Intel chips.
1805 Default is 1 (enabled)
1811 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1814 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1815 value for LAPIC timer one-shot implementation. Default
1816 back to the programmable timer unit in the LAPIC.
1818 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1821 libata.dma= [LIBATA] DMA control
1822 libata.dma=0 Disable all PATA and SATA DMA
1823 libata.dma=1 PATA and SATA Disk DMA only
1824 libata.dma=2 ATAPI (CDROM) DMA only
1825 libata.dma=4 Compact Flash DMA only
1826 Combinations also work, so libata.dma=3 enables DMA
1827 for disks and CDROMs, but not CFs.
1829 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1830 libata.ignore_hpa=0 keep BIOS limits (default)
1831 libata.ignore_hpa=1 ignore limits, using full disk
1833 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1837 libata.force= [LIBATA] Force configurations. The format is comma
1838 separated list of "[ID:]VAL" where ID is
1839 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1840 matching port, link or device. Basically, it matches
1841 the ATA ID string printed on console by libata. If
1842 the whole ID part is omitted, the last PORT and DEVICE
1843 values are used. If ID hasn't been specified yet, the
1844 configuration applies to all ports, links and devices.
1846 If only DEVICE is omitted, the parameter applies to
1847 the port and all links and devices behind it. DEVICE
1848 number of 0 either selects the first device or the
1849 first fan-out link behind PMP device. It does not
1850 select the host link. DEVICE number of 15 selects the
1851 host link and device attached to it.
1853 The VAL specifies the configuration to force. As long
1854 as there's no ambiguity shortcut notation is allowed.
1855 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1856 The following configurations can be forced.
1858 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1859 Any ID with matching PORT is used.
1861 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1863 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1864 udma[/][16,25,33,44,66,100,133] notation is also
1867 * [no]ncq: Turn on or off NCQ.
1869 * [no]ncqtrim: Turn off queued DSM TRIM.
1871 * nohrst, nosrst, norst: suppress hard, soft
1874 * rstonce: only attempt one reset during
1875 hot-unplug link recovery
1877 * dump_id: dump IDENTIFY data.
1879 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1881 * disable: Disable this device.
1883 If there are multiple matching configurations changing
1884 the same attribute, the last one is used.
1886 memblock=debug [KNL] Enable memblock debug messages.
1888 load_ramdisk= [RAM] List of ramdisks to load from floppy
1889 See Documentation/blockdev/ramdisk.txt.
1891 lockd.nlm_grace_period=P [NFS] Assign grace period.
1894 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1897 lockd.nlm_timeout=T [NFS] Assign timeout value.
1900 lockd.nlm_udpport=M [NFS] Assign UDP port.
1903 locktorture.nreaders_stress= [KNL]
1904 Set the number of locking read-acquisition kthreads.
1905 Defaults to being automatically set based on the
1906 number of online CPUs.
1908 locktorture.nwriters_stress= [KNL]
1909 Set the number of locking write-acquisition kthreads.
1911 locktorture.onoff_holdoff= [KNL]
1912 Set time (s) after boot for CPU-hotplug testing.
1914 locktorture.onoff_interval= [KNL]
1915 Set time (s) between CPU-hotplug operations, or
1916 zero to disable CPU-hotplug testing.
1918 locktorture.shuffle_interval= [KNL]
1919 Set task-shuffle interval (jiffies). Shuffling
1920 tasks allows some CPUs to go into dyntick-idle
1921 mode during the locktorture test.
1923 locktorture.shutdown_secs= [KNL]
1924 Set time (s) after boot system shutdown. This
1925 is useful for hands-off automated testing.
1927 locktorture.stat_interval= [KNL]
1928 Time (s) between statistics printk()s.
1930 locktorture.stutter= [KNL]
1931 Time (s) to stutter testing, for example,
1932 specifying five seconds causes the test to run for
1933 five seconds, wait for five seconds, and so on.
1934 This tests the locking primitive's ability to
1935 transition abruptly to and from idle.
1937 locktorture.torture_runnable= [BOOT]
1938 Start locktorture running at boot time.
1940 locktorture.torture_type= [KNL]
1941 Specify the locking implementation to test.
1943 locktorture.verbose= [KNL]
1944 Enable additional printk() statements.
1946 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1949 loglevel= All Kernel Messages with a loglevel smaller than the
1950 console loglevel will be printed to the console. It can
1951 also be changed with klogd or other programs. The
1952 loglevels are defined as follows:
1954 0 (KERN_EMERG) system is unusable
1955 1 (KERN_ALERT) action must be taken immediately
1956 2 (KERN_CRIT) critical conditions
1957 3 (KERN_ERR) error conditions
1958 4 (KERN_WARNING) warning conditions
1959 5 (KERN_NOTICE) normal but significant condition
1960 6 (KERN_INFO) informational
1961 7 (KERN_DEBUG) debug-level messages
1963 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1964 in bytes. n must be a power of two and greater
1965 than the minimal size. The minimal size is defined
1966 by LOG_BUF_SHIFT kernel config parameter. There is
1967 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1968 that allows to increase the default size depending on
1969 the number of CPUs. See init/Kconfig for more details.
1971 logo.nologo [FB] Disables display of the built-in Linux logo.
1972 This may be used to provide more screen space for
1973 kernel log messages and is useful when debugging
1974 kernel boot problems.
1976 lp=0 [LP] Specify parallel ports to use, e.g,
1977 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1978 lp=reset first parallel port). 'lp=0' disables the
1979 lp=auto printer driver. 'lp=reset' (which can be
1980 specified in addition to the ports) causes
1981 attached printers to be reset. Using
1982 lp=port1,port2,... specifies the parallel ports
1983 to associate lp devices with, starting with
1984 lp0. A port specification may be 'none' to skip
1985 that lp device, or a parport name such as
1986 'parport0'. Specifying 'lp=auto' instead of a
1987 port specification list means that device IDs
1988 from each port should be examined, to see if
1989 an IEEE 1284-compliant printer is attached; if
1990 so, the driver will manage that printer.
1991 See also header of drivers/char/lp.c.
1994 Sets loops_per_jiffy to given constant, thus avoiding
1995 time-consuming boot-time autodetection (up to 250 ms per
1996 CPU). 0 enables autodetection (default). To determine
1997 the correct value for your kernel, boot with normal
1998 autodetection and see what value is printed. Note that
1999 on SMP systems the preset will be applied to all CPUs,
2000 which is likely to cause problems if your CPUs need
2001 significantly divergent settings. An incorrect value
2002 will cause delays in the kernel to be wrong, leading to
2003 unpredictable I/O errors and other breakage. Although
2004 unlikely, in the extreme case this might damage your
2008 Format: <io>,<irq>,<dma>
2010 machvec= [IA-64] Force the use of a particular machine-vector
2011 (machvec) in a generic kernel.
2012 Example: machvec=hpzx1_swiotlb
2014 machtype= [Loongson] Share the same kernel image file between different
2016 Example: machtype=lemote-yeeloong-2f-7inch
2018 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2019 than or equal to this physical address is ignored.
2021 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2022 should make use of. maxcpus=n : n >= 0 limits the
2023 kernel to using 'n' processors. n=0 is a special case,
2024 it is equivalent to "nosmp", which also disables
2027 max_loop= [LOOP] The number of loop block devices that get
2028 (loop.max_loop) unconditionally pre-created at init time. The default
2029 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2030 of statically allocating a predefined number, loop
2031 devices can be requested on-demand with the
2032 /dev/loop-control interface.
2034 mce [X86-32] Machine Check Exception
2036 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2038 md= [HW] RAID subsystems devices and level
2039 See Documentation/md.txt.
2042 Format: <first>,<last>
2043 Specifies range of consoles to be captured by the MDA.
2045 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2046 Amount of memory to be used when the kernel is not able
2047 to see the whole system memory or for test.
2048 [X86] Work as limiting max address. Use together
2049 with memmap= to avoid physical address space collisions.
2050 Without memmap= PCI devices could be placed at addresses
2051 belonging to unused RAM.
2053 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2057 [KNL,SH] Allow user to override the default size for
2058 per-device physically contiguous DMA buffers.
2060 memmap=exactmap [KNL,X86] Enable setting of an exact
2061 E820 memory map, as specified by the user.
2062 Such memmap=exactmap lines can be constructed based on
2063 BIOS output or other requirements. See the memmap=nn@ss
2066 memmap=nn[KMG]@ss[KMG]
2067 [KNL] Force usage of a specific region of memory.
2068 Region of memory to be used is from ss to ss+nn.
2070 memmap=nn[KMG]#ss[KMG]
2071 [KNL,ACPI] Mark specific memory as ACPI data.
2072 Region of memory to be marked is from ss to ss+nn.
2074 memmap=nn[KMG]$ss[KMG]
2075 [KNL,ACPI] Mark specific memory as reserved.
2076 Region of memory to be reserved is from ss to ss+nn.
2077 Example: Exclude memory from 0x18690000-0x1869ffff
2078 memmap=64K$0x18690000
2080 memmap=0x10000$0x18690000
2082 memmap=nn[KMG]!ss[KMG]
2083 [KNL,X86] Mark specific memory as protected.
2084 Region of memory to be used, from ss to ss+nn.
2085 The memory region may be marked as e820 type 12 (0xc)
2086 and is NVDIMM or ADR memory.
2088 memory_corruption_check=0/1 [X86]
2089 Some BIOSes seem to corrupt the first 64k of
2090 memory when doing things like suspend/resume.
2091 Setting this option will scan the memory
2092 looking for corruption. Enabling this will
2093 both detect corruption and prevent the kernel
2094 from using the memory being corrupted.
2095 However, its intended as a diagnostic tool; if
2096 repeatable BIOS-originated corruption always
2097 affects the same memory, you can use memmap=
2098 to prevent the kernel from using that memory.
2100 memory_corruption_check_size=size [X86]
2101 By default it checks for corruption in the low
2102 64k, making this memory unavailable for normal
2103 use. Use this parameter to scan for
2104 corruption in more or less memory.
2106 memory_corruption_check_period=seconds [X86]
2107 By default it checks for corruption every 60
2108 seconds. Use this parameter to check at some
2109 other rate. 0 disables periodic checking.
2111 memtest= [KNL,X86,ARM] Enable memtest
2113 default : 0 <disable>
2114 Specifies the number of memtest passes to be
2115 performed. Each pass selects another test
2116 pattern from a given set of patterns. Memtest
2117 fills the memory with this pattern, validates
2118 memory contents and reserves bad memory
2119 regions that are detected.
2121 meye.*= [HW] Set MotionEye Camera parameters
2122 See Documentation/video4linux/meye.txt.
2124 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2125 Multi-Function General Purpose Timers on AMD Geode
2128 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2129 the BIOS has incorrectly applied a workaround. TinyBIOS
2130 version 0.98 is known to be affected, 0.99 fixes the
2131 problem by letting the user disable the workaround.
2135 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2136 physical address is ignored.
2138 mini2440= [ARM,HW,KNL]
2139 Format:[0..2][b][c][t]
2141 MINI2440 configuration specification:
2142 0 - The attached screen is the 3.5" TFT
2143 1 - The attached screen is the 7" TFT
2144 2 - The VGA Shield is attached (1024x768)
2145 Leaving out the screen size parameter will not load
2146 the TFT driver, and the framebuffer will be left
2148 b - Enable backlight. The TFT backlight pin will be
2149 linked to the kernel VESA blanking code and a GPIO
2150 LED. This parameter is not necessary when using the
2152 c - Enable the s3c camera interface.
2153 t - Reserved for enabling touchscreen support. The
2154 touchscreen support is not enabled in the mainstream
2155 kernel as of 2.6.30, a preliminary port can be found
2156 in the "bleeding edge" mini2440 support kernel at
2157 http://repo.or.cz/w/linux-2.6/mini2440.git
2160 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2161 parameter allows control of the logging verbosity for
2162 the additional memory initialisation checks. A value
2163 of 0 disables mminit logging and a level of 4 will
2164 log everything. Information is printed at KERN_DEBUG
2165 so loglevel=8 may also need to be specified.
2168 [KNL] When CONFIG_MODULE_SIG is set, this means that
2169 modules without (valid) signatures will fail to load.
2170 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2171 is always true, so this option does nothing.
2174 [MOUSE] Maximum time between finger touching and
2175 leaving touchpad surface for touch to be considered
2176 a tap and be reported as a left button click (for
2177 touchpads working in absolute mode only).
2179 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2180 reporting absolute coordinates, such as tablets
2181 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2182 reporting absolute coordinates, such as tablets
2184 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2185 is similar to kernelcore except it specifies the
2186 amount of memory used for migratable allocations.
2187 If both kernelcore and movablecore is specified,
2188 then kernelcore will be at *least* the specified
2189 value but may be more. If movablecore on its own
2190 is specified, the administrator must be careful
2191 that the amount of memory usable for all allocations
2194 movable_node [KNL,X86] Boot-time switch to enable the effects
2195 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2197 MTD_Partition= [MTD]
2198 Format: <name>,<region-number>,<size>,<offset>
2200 MTD_Region= [MTD] Format:
2201 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2204 See drivers/mtd/cmdlinepart.c.
2206 multitce=off [PPC] This parameter disables the use of the pSeries
2207 firmware feature for updating multiple TCE entries
2210 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2212 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2214 boundary - index of last SLC block on Flex-OneNAND.
2215 The remaining blocks are configured as MLC blocks.
2216 lock - Configure if Flex-OneNAND boundary should be locked.
2217 Once locked, the boundary cannot be changed.
2218 1 indicates lock status, 0 indicates unlock status.
2221 ARM/S3C2412 JIVE boot control
2223 See arch/arm/mach-s3c2412/mach-jive.c
2225 mtouchusb.raw_coordinates=
2226 [HW] Make the MicroTouch USB driver use raw coordinates
2227 ('y', default) or cooked coordinates ('n')
2229 mtrr_chunk_size=nn[KMG] [X86]
2230 used for mtrr cleanup. It is largest continuous chunk
2231 that could hold holes aka. UC entries.
2233 mtrr_gran_size=nn[KMG] [X86]
2234 Used for mtrr cleanup. It is granularity of mtrr block.
2236 Large value could prevent small alignment from
2239 mtrr_spare_reg_nr=n [X86]
2241 Range: 0,7 : spare reg number
2243 Used for mtrr cleanup. It is spare mtrr entries number.
2244 Set to 2 or more if your graphical card needs more.
2246 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2248 netdev= [NET] Network devices parameters
2249 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2250 Note that mem_start is often overloaded to mean
2251 something different and driver-specific.
2252 This usage is only documented in each driver source
2256 [NETFILTER] Enable connection tracking flow accounting
2257 0 to disable accounting
2258 1 to enable accounting
2261 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2262 See Documentation/filesystems/nfs/nfsroot.txt.
2264 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2265 See Documentation/filesystems/nfs/nfsroot.txt.
2267 nfsrootdebug [NFS] enable nfsroot debugging messages.
2268 See Documentation/filesystems/nfs/nfsroot.txt.
2270 nfs.callback_tcpport=
2271 [NFS] set the TCP port on which the NFSv4 callback
2272 channel should listen.
2275 [NFS] sets the pathname to the program which is used
2276 to update the NFS client cache entries.
2278 nfs.cache_getent_timeout=
2279 [NFS] sets the timeout after which an attempt to
2280 update a cache entry is deemed to have failed.
2282 nfs.idmap_cache_timeout=
2283 [NFS] set the maximum lifetime for idmapper cache
2287 [NFS] enable 64-bit inode numbers.
2288 If zero, the NFS client will fake up a 32-bit inode
2289 number for the readdir() and stat() syscalls instead
2290 of returning the full 64-bit number.
2291 The default is to return 64-bit inode numbers.
2293 nfs.max_session_slots=
2294 [NFSv4.1] Sets the maximum number of session slots
2295 the client will attempt to negotiate with the server.
2296 This limits the number of simultaneous RPC requests
2297 that the client can send to the NFSv4.1 server.
2298 Note that there is little point in setting this
2299 value higher than the max_tcp_slot_table_limit.
2301 nfs.nfs4_disable_idmapping=
2302 [NFSv4] When set to the default of '1', this option
2303 ensures that both the RPC level authentication
2304 scheme and the NFS level operations agree to use
2305 numeric uids/gids if the mount is using the
2306 'sec=sys' security flavour. In effect it is
2307 disabling idmapping, which can make migration from
2308 legacy NFSv2/v3 systems to NFSv4 easier.
2309 Servers that do not support this mode of operation
2310 will be autodetected by the client, and it will fall
2311 back to using the idmapper.
2312 To turn off this behaviour, set the value to '0'.
2314 [NFS4] Specify an additional fixed unique ident-
2315 ification string that NFSv4 clients can insert into
2316 their nfs_client_id4 string. This is typically a
2317 UUID that is generated at system install time.
2319 nfs.send_implementation_id =
2320 [NFSv4.1] Send client implementation identification
2321 information in exchange_id requests.
2322 If zero, no implementation identification information
2324 The default is to send the implementation identification
2327 nfs.recover_lost_locks =
2328 [NFSv4] Attempt to recover locks that were lost due
2329 to a lease timeout on the server. Please note that
2330 doing this risks data corruption, since there are
2331 no guarantees that the file will remain unchanged
2332 after the locks are lost.
2333 If you want to enable the kernel legacy behaviour of
2334 attempting to recover these locks, then set this
2336 The default parameter value of '0' causes the kernel
2337 not to attempt recovery of lost locks.
2339 nfs4.layoutstats_timer =
2340 [NFSv4.2] Change the rate at which the kernel sends
2341 layoutstats to the pNFS metadata server.
2343 Setting this to value to 0 causes the kernel to use
2344 whatever value is the default set by the layout
2345 driver. A non-zero value sets the minimum interval
2346 in seconds between layoutstats transmissions.
2348 nfsd.nfs4_disable_idmapping=
2349 [NFSv4] When set to the default of '1', the NFSv4
2350 server will return only numeric uids and gids to
2351 clients using auth_sys, and will accept numeric uids
2352 and gids from such clients. This is intended to ease
2353 migration from NFSv2/v3.
2355 objlayoutdriver.osd_login_prog=
2356 [NFS] [OBJLAYOUT] sets the pathname to the program which
2357 is used to automatically discover and login into new
2358 osd-targets. Please see:
2359 Documentation/filesystems/pnfs.txt for more explanations
2361 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2362 when a NMI is triggered.
2363 Format: [state][,regs][,debounce][,die]
2365 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2366 Format: [panic,][nopanic,][num]
2368 0 - turn hardlockup detector in nmi_watchdog off
2369 1 - turn hardlockup detector in nmi_watchdog on
2370 When panic is specified, panic when an NMI watchdog
2371 timeout occurs (or 'nopanic' to override the opposite
2372 default). To disable both hard and soft lockup detectors,
2373 please see 'nowatchdog'.
2374 This is useful when you use a panic=... timeout and
2375 need the box quickly up again.
2377 netpoll.carrier_timeout=
2378 [NET] Specifies amount of time (in seconds) that
2379 netpoll should wait for a carrier. By default netpoll
2382 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2383 emulation library even if a 387 maths coprocessor
2387 [HW] Never suspend the console
2388 Disable suspending of consoles during suspend and
2389 hibernate operations. Once disabled, debugging
2390 messages can reach various consoles while the rest
2391 of the system is being put to sleep (ie, while
2392 debugging driver suspend/resume hooks). This may
2393 not work reliably with all consoles, but is known
2394 to work with serial and VGA consoles.
2395 To facilitate more flexible debugging, we also add
2396 console_suspend, a printk module parameter to control
2397 it. Users could use console_suspend (usually
2398 /sys/module/printk/parameters/console_suspend) to
2399 turn on/off it dynamically.
2401 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2402 caches in the slab allocator. Saves per-node memory,
2403 but will impact performance.
2407 noapic [SMP,APIC] Tells the kernel to not make use of any
2408 IOAPICs that may be present in the system.
2410 noautogroup Disable scheduler automatic task group creation.
2412 nobats [PPC] Do not use BATs for mapping kernel lowmem
2413 on "Classic" PPC cores.
2417 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2419 nodelayacct [KNL] Disable per-task delay accounting
2421 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2423 nodsp [SH] Disable hardware DSP at boot time.
2425 noefi Disable EFI runtime services support.
2430 On X86-32 available only on PAE configured kernels.
2431 noexec=on: enable non-executable mappings (default)
2432 noexec=off: disable non-executable mappings
2435 Disable SMAP (Supervisor Mode Access Prevention)
2436 even if it is supported by processor.
2439 Disable SMEP (Supervisor Mode Execution Prevention)
2440 even if it is supported by processor.
2443 This affects only 32-bit executables.
2444 noexec32=on: enable non-executable mappings (default)
2445 read doesn't imply executable mappings
2446 noexec32=off: disable non-executable mappings
2447 read implies executable mappings
2449 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2451 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2452 register save and restore. The kernel will only save
2453 legacy floating-point registers on task switch.
2455 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2457 noxsave [BUGS=X86] Disables x86 extended register state save
2458 and restore using xsave. The kernel will fallback to
2459 enabling legacy floating-point and sse state.
2461 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2462 register states. The kernel will fall back to use
2463 xsave to save the states. By using this parameter,
2464 performance of saving the states is degraded because
2465 xsave doesn't support modified optimization while
2466 xsaveopt supports it on xsaveopt enabled systems.
2468 noxsaves [X86] Disables xsaves and xrstors used in saving and
2469 restoring x86 extended register state in compacted
2470 form of xsave area. The kernel will fall back to use
2471 xsaveopt and xrstor to save and restore the states
2472 in standard form of xsave area. By using this
2473 parameter, xsave area per process might occupy more
2474 memory on xsaves enabled systems.
2476 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2477 wfi(ARM) instruction doesn't work correctly and not to
2478 use it. This is also useful when using JTAG debugger.
2480 no_file_caps Tells the kernel not to honor file capabilities. The
2481 only way then for a file to be executed with privilege
2482 is to be setuid root or executed by root.
2484 nohalt [IA-64] Tells the kernel not to use the power saving
2485 function PAL_HALT_LIGHT when idle. This increases
2486 power-consumption. On the positive side, it reduces
2487 interrupt wake-up latency, which may improve performance
2488 in certain environments such as networked servers or
2491 nohibernate [HIBERNATION] Disable hibernation and resume.
2493 nohz= [KNL] Boottime enable/disable dynamic ticks
2494 Valid arguments: on, off
2497 nohz_full= [KNL,BOOT]
2498 In kernels built with CONFIG_NO_HZ_FULL=y, set
2499 the specified list of CPUs whose tick will be stopped
2500 whenever possible. The boot CPU will be forced outside
2501 the range to maintain the timekeeping.
2502 The CPUs in this range must also be included in the
2505 noiotrap [SH] Disables trapped I/O port accesses.
2507 noirqdebug [X86-32] Disables the code which attempts to detect and
2508 disable unhandled interrupt sources.
2510 no_timer_check [X86,APIC] Disables the code which tests for
2511 broken timer IRQ sources.
2513 noisapnp [ISAPNP] Disables ISA PnP code.
2515 noinitrd [RAM] Tells the kernel not to load any configured
2518 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2520 [Deprecated - use intremap=off]
2524 nojitter [IA-64] Disables jitter checking for ITC timers.
2526 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2528 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2531 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2532 steal time is computed, but won't influence scheduler
2535 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2537 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2539 noltlbs [PPC] Do not use large page/tlb entries for kernel
2540 lowmem mapping on PPC40x.
2542 nomca [IA-64] Disable machine check abort handling
2544 nomce [X86-32] Disable Machine Check Exception
2546 nomfgpt [X86-32] Disable Multi-Function General Purpose
2547 Timer usage (for AMD Geode machines).
2549 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2550 shutdown the other cpus. Instead use the REBOOT_VECTOR
2553 nomodule Disable module load
2555 nopat [X86] Disable PAT (page attribute table extension of
2556 pagetables) support.
2558 norandmaps Don't use address space randomization. Equivalent to
2559 echo 0 > /proc/sys/kernel/randomize_va_space
2561 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2563 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2564 with UP alternatives
2566 nordrand [X86] Disable kernel use of the RDRAND and
2567 RDSEED instructions even if they are supported
2568 by the processor. RDRAND and RDSEED are still
2569 available to user space applications.
2571 noresume [SWSUSP] Disables resume and restores original swap
2574 no-scroll [VGA] Disables scrollback.
2575 This is required for the Braillex ib80-piezo Braille
2576 reader made by F.H. Papenmeier (Germany).
2580 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2582 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2583 and disable the IO APIC. legacy for "maxcpus=0".
2585 nosoftlockup [KNL] Disable the soft-lockup detector.
2587 nosync [HW,M68K] Disables sync negotiation for all devices.
2589 notsc [BUGS=X86-32] Disable Time Stamp Counter
2591 nousb [USB] Disable the USB subsystem
2593 nowatchdog [KNL] Disable both lockup detectors, i.e.
2594 soft-lockup and NMI watchdog (hard-lockup).
2598 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2600 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2601 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2602 Some features depend on CPU0. Known dependencies are:
2603 1. Resume from suspend/hibernate depends on CPU0.
2604 Suspend/hibernate will fail if CPU0 is offline and you
2605 need to online CPU0 before suspend/hibernate.
2606 2. PIC interrupts also depend on CPU0. CPU0 can't be
2607 removed if a PIC interrupt is detected.
2608 It's said poweroff/reboot may depend on CPU0 on some
2609 machines although I haven't seen such issues so far
2610 after CPU0 is offline on a few tested machines.
2611 If the dependencies are under your control, you can
2612 turn on cpu0_hotplug.
2614 nptcg= [IA-64] Override max number of concurrent global TLB
2615 purges which is reported from either PAL_VM_SUMMARY or
2618 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2619 could support. nr_cpus=n : n >= 1 limits the kernel to
2620 supporting 'n' processors. Later in runtime you can not
2621 use hotplug cpu feature to put more cpu back to online.
2622 just like you compile the kernel NR_CPUS=n
2624 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2626 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2627 Allowed values are enable and disable
2629 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2630 one of ['zone', 'node', 'default'] can be specified
2631 This can be set from sysctl after boot.
2632 See Documentation/sysctl/vm.txt for details.
2634 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2635 See Documentation/debugging-via-ohci1394.txt for more
2638 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2639 Rather than timing out after 20 ms if an EC
2640 command is not properly ACKed, override the length
2641 of the timeout. We have interrupts disabled while
2642 waiting for the ACK, so if this is set too high
2643 interrupts *may* be lost!
2645 omap_mux= [OMAP] Override bootloader pin multiplexing.
2646 Format: <mux_mode0.mode_name=value>...
2647 For example, to override I2C bus2:
2648 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2650 oprofile.timer= [HW]
2651 Use timer interrupt instead of performance counters
2653 oprofile.cpu_type= Force an oprofile cpu type
2654 This might be useful if you have an older oprofile
2655 userland or if you want common events.
2656 Format: { arch_perfmon }
2657 arch_perfmon: [X86] Force use of architectural
2658 perfmon on Intel CPUs instead of the
2659 CPU specific event set.
2660 timer: [X86] Force use of architectural NMI
2661 timer mode (see also oprofile.timer
2662 for generic hr timer mode)
2663 [s390] Force legacy basic mode sampling
2664 (report cpu_type "timer")
2666 oops=panic Always panic on oopses. Default is to just kill the
2667 process, but there is a small probability of
2668 deadlocking the machine.
2669 This will also cause panics on machine check exceptions.
2670 Useful together with panic=30 to trigger a reboot.
2673 See Documentation/sound/oss/oss-parameters.txt
2675 page_owner= [KNL] Boot-time page_owner enabling option.
2676 Storage of the information about who allocated
2677 each page is disabled in default. With this switch,
2679 on: enable the feature
2681 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2682 timeout > 0: seconds before rebooting
2683 timeout = 0: wait forever
2684 timeout < 0: reboot immediately
2687 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2690 crash_kexec_post_notifiers
2691 Run kdump after running panic-notifiers and dumping
2692 kmsg. This only for the users who doubt kdump always
2693 succeeds in any situation.
2694 Note that this also increases risks of kdump failure,
2695 because some panic notifiers can make the crashed
2696 kernel more unstable.
2698 parkbd.port= [HW] Parallel port number the keyboard adapter is
2699 connected to, default is 0.
2701 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2702 0 for XT, 1 for AT (default is AT).
2705 parport= [HW,PPT] Specify parallel ports. 0 disables.
2706 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2707 Use 'auto' to force the driver to use any
2708 IRQ/DMA settings detected (the default is to
2709 ignore detected IRQ/DMA settings because of
2710 possible conflicts). You can specify the base
2711 address, IRQ, and DMA settings; IRQ and DMA
2712 should be numbers, or 'auto' (for using detected
2713 settings on that particular port), or 'nofifo'
2714 (to avoid using a FIFO even if it is detected).
2715 Parallel ports are assigned in the order they
2716 are specified on the command line, starting
2719 parport_init_mode= [HW,PPT]
2720 Configure VIA parallel port to operate in
2721 a specific mode. This is necessary on Pegasos
2722 computer where firmware has no options for setting
2723 up parallel port mode and sets it to spp.
2724 Currently this function knows 686a and 8231 chips.
2725 Format: [spp|ps2|epp|ecp|ecpepp]
2728 Halt all CPUs after the first oops has been printed for
2729 the specified number of seconds. This is to be used if
2730 your oopses keep scrolling off the screen.
2735 See header of drivers/block/paride/pcd.c.
2736 See also Documentation/blockdev/paride.txt.
2738 pci=option[,option...] [PCI] various PCI subsystem options:
2739 earlydump [X86] dump PCI config space before the kernel
2741 off [X86] don't probe for the PCI bus
2742 bios [X86-32] force use of PCI BIOS, don't access
2743 the hardware directly. Use this if your machine
2744 has a non-standard PCI host bridge.
2745 nobios [X86-32] disallow use of PCI BIOS, only direct
2746 hardware access methods are allowed. Use this
2747 if you experience crashes upon bootup and you
2748 suspect they are caused by the BIOS.
2749 conf1 [X86] Force use of PCI Configuration
2751 conf2 [X86] Force use of PCI Configuration
2753 noaer [PCIE] If the PCIEAER kernel config parameter is
2754 enabled, this kernel boot option can be used to
2755 disable the use of PCIE advanced error reporting.
2756 nodomains [PCI] Disable support for multiple PCI
2757 root domains (aka PCI segments, in ACPI-speak).
2758 nommconf [X86] Disable use of MMCONFIG for PCI
2760 check_enable_amd_mmconf [X86] check for and enable
2761 properly configured MMIO access to PCI
2762 config space on AMD family 10h CPU
2763 nomsi [MSI] If the PCI_MSI kernel config parameter is
2764 enabled, this kernel boot option can be used to
2765 disable the use of MSI interrupts system-wide.
2766 noioapicquirk [APIC] Disable all boot interrupt quirks.
2767 Safety option to keep boot IRQs enabled. This
2768 should never be necessary.
2769 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2770 primary IO-APIC for bridges that cannot disable
2771 boot IRQs. This fixes a source of spurious IRQs
2772 when the system masks IRQs.
2773 noioapicreroute [APIC] Disable workaround that uses the
2774 boot IRQ equivalent of an IRQ that connects to
2775 a chipset where boot IRQs cannot be disabled.
2776 The opposite of ioapicreroute.
2777 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2778 routing table. These calls are known to be buggy
2779 on several machines and they hang the machine
2780 when used, but on other computers it's the only
2781 way to get the interrupt routing table. Try
2782 this option if the kernel is unable to allocate
2783 IRQs or discover secondary PCI buses on your
2785 rom [X86] Assign address space to expansion ROMs.
2786 Use with caution as certain devices share
2787 address decoders between ROMs and other
2789 norom [X86] Do not assign address space to
2790 expansion ROMs that do not already have
2791 BIOS assigned address ranges.
2792 nobar [X86] Do not assign address space to the
2793 BARs that weren't assigned by the BIOS.
2794 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2795 assigned automatically to PCI devices. You can
2796 make the kernel exclude IRQs of your ISA cards
2798 pirqaddr=0xAAAAA [X86] Specify the physical address
2799 of the PIRQ table (normally generated
2800 by the BIOS) if it is outside the
2801 F0000h-100000h range.
2802 lastbus=N [X86] Scan all buses thru bus #N. Can be
2803 useful if the kernel is unable to find your
2804 secondary buses and you want to tell it
2805 explicitly which ones they are.
2806 assign-busses [X86] Always assign all PCI bus
2807 numbers ourselves, overriding
2808 whatever the firmware may have done.
2809 usepirqmask [X86] Honor the possible IRQ mask stored
2810 in the BIOS $PIR table. This is needed on
2811 some systems with broken BIOSes, notably
2812 some HP Pavilion N5400 and Omnibook XE3
2813 notebooks. This will have no effect if ACPI
2814 IRQ routing is enabled.
2815 noacpi [X86] Do not use ACPI for IRQ routing
2816 or for PCI scanning.
2817 use_crs [X86] Use PCI host bridge window information
2818 from ACPI. On BIOSes from 2008 or later, this
2819 is enabled by default. If you need to use this,
2820 please report a bug.
2821 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2822 If you need to use this, please report a bug.
2823 routeirq Do IRQ routing for all PCI devices.
2824 This is normally done in pci_enable_device(),
2825 so this option is a temporary workaround
2826 for broken drivers that don't call it.
2827 skip_isa_align [X86] do not align io start addr, so can
2828 handle more pci cards
2829 firmware [ARM] Do not re-enumerate the bus but instead
2830 just use the configuration from the
2831 bootloader. This is currently used on
2832 IXP2000 systems where the bus has to be
2833 configured a certain way for adjunct CPUs.
2834 noearly [X86] Don't do any early type 1 scanning.
2835 This might help on some broken boards which
2836 machine check when some devices' config space
2837 is read. But various workarounds are disabled
2838 and some IOMMU drivers will not work.
2839 bfsort Sort PCI devices into breadth-first order.
2840 This sorting is done to get a device
2841 order compatible with older (<= 2.4) kernels.
2842 nobfsort Don't sort PCI devices into breadth-first order.
2843 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2844 tuning and use the BIOS-configured MPS defaults.
2845 pcie_bus_safe Set every device's MPS to the largest value
2846 supported by all devices below the root complex.
2847 pcie_bus_perf Set device MPS to the largest allowable MPS
2848 based on its parent bus. Also set MRRS (Max
2849 Read Request Size) to the largest supported
2850 value (no larger than the MPS that the device
2851 or bus can support) for best performance.
2852 pcie_bus_peer2peer Set every device's MPS to 128B, which
2853 every device is guaranteed to support. This
2854 configuration allows peer-to-peer DMA between
2855 any pair of devices, possibly at the cost of
2856 reduced performance. This also guarantees
2857 that hot-added devices will work.
2858 cbiosize=nn[KMG] The fixed amount of bus space which is
2859 reserved for the CardBus bridge's IO window.
2860 The default value is 256 bytes.
2861 cbmemsize=nn[KMG] The fixed amount of bus space which is
2862 reserved for the CardBus bridge's memory
2863 window. The default value is 64 megabytes.
2866 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2867 Specifies alignment and device to reassign
2868 aligned memory resources.
2869 If <order of align> is not specified,
2870 PAGE_SIZE is used as alignment.
2871 PCI-PCI bridge can be specified, if resource
2872 windows need to be expanded.
2873 ecrc= Enable/disable PCIe ECRC (transaction layer
2874 end-to-end CRC checking).
2875 bios: Use BIOS/firmware settings. This is the
2879 hpiosize=nn[KMG] The fixed amount of bus space which is
2880 reserved for hotplug bridge's IO window.
2881 Default size is 256 bytes.
2882 hpmemsize=nn[KMG] The fixed amount of bus space which is
2883 reserved for hotplug bridge's memory window.
2884 Default size is 2 megabytes.
2885 realloc= Enable/disable reallocating PCI bridge resources
2886 if allocations done by BIOS are too small to
2887 accommodate resources required by all child
2889 off: Turn realloc off
2891 realloc same as realloc=on
2892 noari do not use PCIe ARI.
2893 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2894 only look for one device below a PCIe downstream
2897 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2900 force Enable ASPM even on devices that claim not to support it.
2901 WARNING: Forcing ASPM on may cause system lockups.
2903 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2904 nomsi Do not use MSI for PCI Express Native Hotplug (this
2905 makes all PCIe ports use INTx for hotplug services).
2907 pcie_ports= [PCIE] PCIe ports handling:
2908 auto Ask the BIOS whether or not to use native PCIe services
2909 associated with PCIe ports (PME, hot-plug, AER). Use
2910 them only if that is allowed by the BIOS.
2911 native Use native PCIe services associated with PCIe ports
2913 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2916 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2917 nomsi Do not use MSI for native PCIe PME signaling (this makes
2918 all PCIe root ports use INTx for all services).
2920 pcmv= [HW,PCMCIA] BadgePAD 4
2924 Keep all power-domains already enabled by bootloader on,
2925 even if no driver has claimed them. This is useful
2926 for debug and development, but should not be
2927 needed on a platform with proper driver support.
2930 See Documentation/blockdev/paride.txt.
2932 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2935 See arch/parisc/kernel/pdc_chassis.c
2937 percpu_alloc= Select which percpu first chunk allocator to use.
2938 Currently supported values are "embed" and "page".
2939 Archs may support subset or none of the selections.
2940 See comments in mm/percpu.c for details on each
2941 allocator. This parameter is primarily for debugging
2942 and performance comparison.
2945 See Documentation/blockdev/paride.txt.
2948 See Documentation/blockdev/paride.txt.
2950 pirq= [SMP,APIC] Manual mp-table setup
2951 See Documentation/x86/i386/IO-APIC.txt.
2953 plip= [PPT,NET] Parallel port network link
2954 Format: { parport<nr> | timid | 0 }
2955 See also Documentation/parport.txt.
2957 pmtmr= [X86] Manual setup of pmtmr I/O Port.
2958 Override pmtimer IOPort with a hex value.
2962 Enable PNP debug messages (depends on the
2963 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2964 via /sys/module/pnp/parameters/debug. We always show
2965 current resource usage; turning this on also shows
2966 possible settings and some assignment information.
2972 { on | off | curr | res | no-curr | no-res }
2975 [ISAPNP] Exclude IRQs for the autoconfiguration
2978 [ISAPNP] Exclude DMAs for the autoconfiguration
2980 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2981 Ranges are in pairs (I/O port base and size).
2984 [ISAPNP] Exclude memory regions for the
2986 Ranges are in pairs (memory base and size).
2988 ports= [IP_VS_FTP] IPVS ftp helper module
2990 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2992 Format: <port>,<port>....
2994 print-fatal-signals=
2995 [KNL] debug: print fatal signals
2997 If enabled, warn about various signal handling
2998 related application anomalies: too many signals,
2999 too many POSIX.1 timers, fatal signals causing a
3002 If you hit the warning due to signal overflow,
3003 you might want to try "ulimit -i unlimited".
3007 printk.always_kmsg_dump=
3008 Trigger kmsg_dump for cases other than kernel oops or
3010 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3013 printk.time= Show timing data prefixed to each printk message line
3014 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3016 processor.max_cstate= [HW,ACPI]
3017 Limit processor to maximum C-state
3018 max_cstate=9 overrides any DMI blacklist limit.
3020 processor.nocst [HW,ACPI]
3021 Ignore the _CST method to determine C-states,
3022 instead using the legacy FADT method
3024 profile= [KNL] Enable kernel profiling via /proc/profile
3025 Format: [schedule,]<number>
3026 Param: "schedule" - profile schedule points.
3027 Param: <number> - step/bucket size as a power of 2 for
3028 statistical time based profiling.
3029 Param: "sleep" - profile D-state sleeping (millisecs).
3030 Requires CONFIG_SCHEDSTATS
3031 Param: "kvm" - profile VM exits.
3033 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3035 See Documentation/blockdev/ramdisk.txt.
3037 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3038 probe for; one of (bare|imps|exps|lifebook|any).
3039 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3041 psmouse.resetafter= [HW,MOUSE]
3042 Try to reset the device after so many bad packets
3045 [HW,MOUSE] Set desired mouse resolution, in dpi.
3046 psmouse.smartscroll=
3047 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3048 0 = disabled, 1 = enabled (default).
3050 pstore.backend= Specify the name of the pstore backend to use
3053 See Documentation/blockdev/paride.txt.
3056 [KNL] Number of legacy pty's. Overwrites compiled-in
3059 quiet [KNL] Disable most log messages
3064 See Documentation/md.txt.
3066 ramdisk_blocksize= [RAM]
3067 See Documentation/blockdev/ramdisk.txt.
3069 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3070 See Documentation/blockdev/ramdisk.txt.
3073 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3074 the specified list of CPUs to be no-callback CPUs.
3075 Invocation of these CPUs' RCU callbacks will
3076 be offloaded to "rcuox/N" kthreads created for
3077 that purpose, where "x" is "b" for RCU-bh, "p"
3078 for RCU-preempt, and "s" for RCU-sched, and "N"
3079 is the CPU number. This reduces OS jitter on the
3080 offloaded CPUs, which can be useful for HPC and
3081 real-time workloads. It can also improve energy
3082 efficiency for asymmetric multiprocessors.
3085 Rather than requiring that offloaded CPUs
3086 (specified by rcu_nocbs= above) explicitly
3087 awaken the corresponding "rcuoN" kthreads,
3088 make these kthreads poll for callbacks.
3089 This improves the real-time response for the
3090 offloaded CPUs by relieving them of the need to
3091 wake up the corresponding kthread, but degrades
3092 energy efficiency by requiring that the kthreads
3093 periodically wake up to do the polling.
3095 rcutree.blimit= [KNL]
3096 Set maximum number of finished RCU callbacks to
3097 process in one batch.
3099 rcutree.dump_tree= [KNL]
3100 Dump the structure of the rcu_node combining tree
3101 out at early boot. This is used for diagnostic
3102 purposes, to verify correct tree setup.
3104 rcutree.gp_cleanup_delay= [KNL]
3105 Set the number of jiffies to delay each step of
3106 RCU grace-period cleanup. This only has effect
3107 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3109 rcutree.gp_init_delay= [KNL]
3110 Set the number of jiffies to delay each step of
3111 RCU grace-period initialization. This only has
3112 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3115 rcutree.gp_preinit_delay= [KNL]
3116 Set the number of jiffies to delay each step of
3117 RCU grace-period pre-initialization, that is,
3118 the propagation of recent CPU-hotplug changes up
3119 the rcu_node combining tree. This only has effect
3120 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3122 rcutree.rcu_fanout_exact= [KNL]
3123 Disable autobalancing of the rcu_node combining
3124 tree. This is used by rcutorture, and might
3125 possibly be useful for architectures having high
3126 cache-to-cache transfer latencies.
3128 rcutree.rcu_fanout_leaf= [KNL]
3129 Change the number of CPUs assigned to each
3130 leaf rcu_node structure. Useful for very
3131 large systems, which will choose the value 64,
3132 and for NUMA systems with large remote-access
3133 latencies, which will choose a value aligned
3134 with the appropriate hardware boundaries.
3136 rcutree.jiffies_till_sched_qs= [KNL]
3137 Set required age in jiffies for a
3138 given grace period before RCU starts
3139 soliciting quiescent-state help from
3140 rcu_note_context_switch().
3142 rcutree.jiffies_till_first_fqs= [KNL]
3143 Set delay from grace-period initialization to
3144 first attempt to force quiescent states.
3145 Units are jiffies, minimum value is zero,
3146 and maximum value is HZ.
3148 rcutree.jiffies_till_next_fqs= [KNL]
3149 Set delay between subsequent attempts to force
3150 quiescent states. Units are jiffies, minimum
3151 value is one, and maximum value is HZ.
3153 rcutree.kthread_prio= [KNL,BOOT]
3154 Set the SCHED_FIFO priority of the RCU per-CPU
3155 kthreads (rcuc/N). This value is also used for
3156 the priority of the RCU boost threads (rcub/N)
3157 and for the RCU grace-period kthreads (rcu_bh,
3158 rcu_preempt, and rcu_sched). If RCU_BOOST is
3159 set, valid values are 1-99 and the default is 1
3160 (the least-favored priority). Otherwise, when
3161 RCU_BOOST is not set, valid values are 0-99 and
3162 the default is zero (non-realtime operation).
3164 rcutree.rcu_nocb_leader_stride= [KNL]
3165 Set the number of NOCB kthread groups, which
3166 defaults to the square root of the number of
3167 CPUs. Larger numbers reduces the wakeup overhead
3168 on the per-CPU grace-period kthreads, but increases
3169 that same overhead on each group's leader.
3171 rcutree.qhimark= [KNL]
3172 Set threshold of queued RCU callbacks beyond which
3173 batch limiting is disabled.
3175 rcutree.qlowmark= [KNL]
3176 Set threshold of queued RCU callbacks below which
3177 batch limiting is re-enabled.
3179 rcutree.rcu_idle_gp_delay= [KNL]
3180 Set wakeup interval for idle CPUs that have
3181 RCU callbacks (RCU_FAST_NO_HZ=y).
3183 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3184 Set wakeup interval for idle CPUs that have
3185 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3186 Lazy RCU callbacks are those which RCU can
3187 prove do nothing more than free memory.
3189 rcutorture.cbflood_inter_holdoff= [KNL]
3190 Set holdoff time (jiffies) between successive
3191 callback-flood tests.
3193 rcutorture.cbflood_intra_holdoff= [KNL]
3194 Set holdoff time (jiffies) between successive
3195 bursts of callbacks within a given callback-flood
3198 rcutorture.cbflood_n_burst= [KNL]
3199 Set the number of bursts making up a given
3200 callback-flood test. Set this to zero to
3201 disable callback-flood testing.
3203 rcutorture.cbflood_n_per_burst= [KNL]
3204 Set the number of callbacks to be registered
3205 in a given burst of a callback-flood test.
3207 rcutorture.fqs_duration= [KNL]
3208 Set duration of force_quiescent_state bursts
3211 rcutorture.fqs_holdoff= [KNL]
3212 Set holdoff time within force_quiescent_state bursts
3215 rcutorture.fqs_stutter= [KNL]
3216 Set wait time between force_quiescent_state bursts
3219 rcutorture.gp_cond= [KNL]
3220 Use conditional/asynchronous update-side
3221 primitives, if available.
3223 rcutorture.gp_exp= [KNL]
3224 Use expedited update-side primitives, if available.
3226 rcutorture.gp_normal= [KNL]
3227 Use normal (non-expedited) asynchronous
3228 update-side primitives, if available.
3230 rcutorture.gp_sync= [KNL]
3231 Use normal (non-expedited) synchronous
3232 update-side primitives, if available. If all
3233 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3234 rcutorture.gp_normal=, and rcutorture.gp_sync=
3235 are zero, rcutorture acts as if is interpreted
3236 they are all non-zero.
3238 rcutorture.n_barrier_cbs= [KNL]
3239 Set callbacks/threads for rcu_barrier() testing.
3241 rcutorture.nfakewriters= [KNL]
3242 Set number of concurrent RCU writers. These just
3243 stress RCU, they don't participate in the actual
3244 test, hence the "fake".
3246 rcutorture.nreaders= [KNL]
3247 Set number of RCU readers. The value -1 selects
3248 N-1, where N is the number of CPUs. A value
3249 "n" less than -1 selects N-n-2, where N is again
3250 the number of CPUs. For example, -2 selects N
3251 (the number of CPUs), -3 selects N+1, and so on.
3253 rcutorture.object_debug= [KNL]
3254 Enable debug-object double-call_rcu() testing.
3256 rcutorture.onoff_holdoff= [KNL]
3257 Set time (s) after boot for CPU-hotplug testing.
3259 rcutorture.onoff_interval= [KNL]
3260 Set time (s) between CPU-hotplug operations, or
3261 zero to disable CPU-hotplug testing.
3263 rcutorture.shuffle_interval= [KNL]
3264 Set task-shuffle interval (s). Shuffling tasks
3265 allows some CPUs to go into dyntick-idle mode
3266 during the rcutorture test.
3268 rcutorture.shutdown_secs= [KNL]
3269 Set time (s) after boot system shutdown. This
3270 is useful for hands-off automated testing.
3272 rcutorture.stall_cpu= [KNL]
3273 Duration of CPU stall (s) to test RCU CPU stall
3274 warnings, zero to disable.
3276 rcutorture.stall_cpu_holdoff= [KNL]
3277 Time to wait (s) after boot before inducing stall.
3279 rcutorture.stat_interval= [KNL]
3280 Time (s) between statistics printk()s.
3282 rcutorture.stutter= [KNL]
3283 Time (s) to stutter testing, for example, specifying
3284 five seconds causes the test to run for five seconds,
3285 wait for five seconds, and so on. This tests RCU's
3286 ability to transition abruptly to and from idle.
3288 rcutorture.test_boost= [KNL]
3289 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3290 "Maybe" means test if the RCU implementation
3291 under test support RCU priority boosting.
3293 rcutorture.test_boost_duration= [KNL]
3294 Duration (s) of each individual boost test.
3296 rcutorture.test_boost_interval= [KNL]
3297 Interval (s) between each boost test.
3299 rcutorture.test_no_idle_hz= [KNL]
3300 Test RCU's dyntick-idle handling. See also the
3301 rcutorture.shuffle_interval parameter.
3303 rcutorture.torture_runnable= [BOOT]
3304 Start rcutorture running at boot time.
3306 rcutorture.torture_type= [KNL]
3307 Specify the RCU implementation to test.
3309 rcutorture.verbose= [KNL]
3310 Enable additional printk() statements.
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.
3319 rcupdate.rcu_cpu_stall_suppress= [KNL]
3320 Suppress RCU CPU stall warning messages.
3322 rcupdate.rcu_cpu_stall_timeout= [KNL]
3323 Set timeout for RCU CPU stall warning messages.
3325 rcupdate.rcu_task_stall_timeout= [KNL]
3326 Set timeout in jiffies for RCU task stall warning
3327 messages. Disable with a value less than or equal
3330 rcupdate.rcu_self_test= [KNL]
3331 Run the RCU early boot self tests
3333 rcupdate.rcu_self_test_bh= [KNL]
3334 Run the RCU bh early boot self tests
3336 rcupdate.rcu_self_test_sched= [KNL]
3337 Run the RCU sched early boot self tests
3341 Run specified binary instead of /init from the ramdisk,
3342 used for early userspace startup. See initrd.
3345 Format (x86 or x86_64):
3346 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3348 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3350 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3351 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3352 reboot_force is either force or not specified,
3353 reboot_cpu is s[mp]#### with #### being the processor
3354 to be used for rebooting.
3357 [KNL, SMP] Set scheduler's default relax_domain_level.
3358 See Documentation/cgroups/cpusets.txt.
3360 relative_sleep_states=
3361 [SUSPEND] Use sleep state labeling where the deepest
3362 state available other than hibernation is always "mem".
3363 Format: { "0" | "1" }
3364 0 -- Traditional sleep state labels.
3365 1 -- Relative sleep state labels.
3367 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3369 reservetop= [X86-32]
3371 Reserves a hole at the top of the kernel virtual
3376 Set the amount of memory to reserve for BIOS at
3377 the bottom of the address space.
3379 reset_devices [KNL] Force drivers to reset the underlying device
3380 during initialization.
3383 Specify the partition device for software suspend
3385 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3387 resume_offset= [SWSUSP]
3388 Specify the offset from the beginning of the partition
3389 given by "resume=" at which the swap header is located,
3390 in <PAGE_SIZE> units (needed only for swap files).
3391 See Documentation/power/swsusp-and-swap-files.txt
3393 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3394 read the resume files
3396 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3397 Useful for devices that are detected asynchronously
3398 (e.g. USB and MMC devices).
3400 hibernate= [HIBERNATION]
3401 noresume Don't check if there's a hibernation image
3402 present during boot.
3403 nocompress Don't compress/decompress hibernation images.
3404 no Disable hibernation and resume.
3406 retain_initrd [RAM] Keep initrd memory after extraction
3408 rfkill.default_state=
3409 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3410 etc. communication is blocked by default.
3413 rfkill.master_switch_mode=
3414 0 The "airplane mode" button does nothing.
3415 1 The "airplane mode" button toggles between everything
3416 blocked and the previous configuration.
3417 2 The "airplane mode" button toggles between everything
3418 blocked and everything unblocked.
3420 rhash_entries= [KNL,NET]
3421 Set number of hash buckets for route cache
3423 ro [KNL] Mount root device read-only on boot
3426 on Mark read-only kernel memory as read-only (default).
3427 off Leave read-only kernel memory writable for debugging.
3429 root= [KNL] Root filesystem
3430 See name_to_dev_t comment in init/do_mounts.c.
3432 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3433 mount the root filesystem
3435 rootflags= [KNL] Set root filesystem mount option string
3437 rootfstype= [KNL] Set root filesystem type
3439 rootwait [KNL] Wait (indefinitely) for root device to show up.
3440 Useful for devices that are detected asynchronously
3441 (e.g. USB and MMC devices).
3443 rproc_mem=nn[KMG][@address]
3444 [KNL,ARM,CMA] Remoteproc physical memory block.
3445 Memory area to be used by remote processor image,
3448 rw [KNL] Mount root device read-write on boot
3450 S [KNL] Run init in single mode
3452 s390_iommu= [HW,S390]
3453 Set s390 IOTLB flushing mode
3455 With strict flushing every unmap operation will result in
3456 an IOTLB flush. Default is lazy flushing before reuse,
3460 See drivers/net/irda/sa1100_ir.c.
3462 sbni= [NET] Granch SBNI12 leased line adapter
3464 sched_debug [KNL] Enables verbose scheduler debug messages.
3466 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3467 xtime_lock contention on larger systems, and/or RCU lock
3468 contention on all systems with CONFIG_MAXSMP set.
3469 Format: { "0" | "1" }
3470 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3472 Note: increases power consumption, thus should only be
3473 enabled if running jitter sensitive (HPC/RT) workloads.
3475 security= [SECURITY] Choose a security module to enable at boot.
3476 If this boot parameter is not specified, only the first
3477 security module asking for security registration will be
3478 loaded. An invalid security module name will be treated
3479 as if no module has been chosen.
3481 selinux= [SELINUX] Disable or enable SELinux at boot time.
3482 Format: { "0" | "1" }
3483 See security/selinux/Kconfig help text.
3486 Default value is set via kernel config option.
3487 If enabled at boot time, /selinux/disable can be used
3488 later to disable prior to initial policy load.
3490 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3491 Format: { "0" | "1" }
3492 See security/apparmor/Kconfig help text
3495 Default value is set via kernel config option.
3497 serialnumber [BUGS=X86-32]
3500 Maximal number of shapers.
3502 show_msr= [x86] show boot-time MSR settings
3503 Format: { <integer> }
3504 Show boot-time (BIOS-initialized) MSR settings.
3505 The parameter means the number of CPUs to show,
3506 for example 1 means boot CPU only.
3514 Disable merging of slabs with similar size. May be
3515 necessary if there is some reason to distinguish
3516 allocs to different slabs. Debug options disable
3517 merging on their own.
3518 For more information see Documentation/vm/slub.txt.
3520 slab_max_order= [MM, SLAB]
3521 Determines the maximum allowed order for slabs.
3522 A high setting may cause OOMs due to memory
3523 fragmentation. Defaults to 1 for systems with
3524 more than 32MB of RAM, 0 otherwise.
3526 slub_debug[=options[,slabs]] [MM, SLUB]
3527 Enabling slub_debug allows one to determine the
3528 culprit if slab objects become corrupted. Enabling
3529 slub_debug can create guard zones around objects and
3530 may poison objects when not in use. Also tracks the
3531 last alloc / free. For more information see
3532 Documentation/vm/slub.txt.
3534 slub_max_order= [MM, SLUB]
3535 Determines the maximum allowed order for slabs.
3536 A high setting may cause OOMs due to memory
3537 fragmentation. For more information see
3538 Documentation/vm/slub.txt.
3540 slub_min_objects= [MM, SLUB]
3541 The minimum number of objects per slab. SLUB will
3542 increase the slab order up to slub_max_order to
3543 generate a sufficiently large slab able to contain
3544 the number of objects indicated. The higher the number
3545 of objects the smaller the overhead of tracking slabs
3546 and the less frequently locks need to be acquired.
3547 For more information see Documentation/vm/slub.txt.
3549 slub_min_order= [MM, SLUB]
3550 Determines the minimum page order for slabs. Must be
3551 lower than slub_max_order.
3552 For more information see Documentation/vm/slub.txt.
3554 slub_nomerge [MM, SLUB]
3555 Same with slab_nomerge. This is supported for legacy.
3556 See slab_nomerge for more information.
3559 Format: <io1>[,<io2>[,...,<io8>]]
3561 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3562 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3563 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3564 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3565 smsc-ircc2.ircc_irq= [HW] IRQ line
3566 smsc-ircc2.ircc_dma= [HW] DMA channel
3567 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3568 0: Toshiba Satellite 1800 (GP data pin select)
3569 1: Fast pin select (default)
3573 [KNL] Should the soft-lockup detector generate panics.
3576 softlockup_all_cpu_backtrace=
3577 [KNL] Should the soft-lockup detector generate
3578 backtraces on all cpus.
3581 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3582 See Documentation/laptops/sonypi.txt
3584 spia_io_base= [HW,MTD]
3590 Enabled the stack tracer on boot up.
3592 stacktrace_filter=[function-list]
3593 [FTRACE] Limit the functions that the stack tracer
3594 will trace at boot up. function-list is a comma separated
3595 list of functions. This list can be changed at run
3596 time by the stack_trace_filter file in the debugfs
3597 tracing directory. Note, this enables stack tracing
3598 and the stacktrace above is not needed.
3602 Set the STI (builtin display/keyboard on the HP-PARISC
3603 machines) console (graphic card) which should be used
3604 as the initial boot-console.
3605 See also comment in drivers/video/console/sticore.c.
3608 See comment in drivers/video/console/sticore.c.
3611 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3613 sunrpc.min_resvport=
3614 sunrpc.max_resvport=
3616 SunRPC servers often require that client requests
3617 originate from a privileged port (i.e. a port in the
3618 range 0 < portnr < 1024).
3619 An administrator who wishes to reserve some of these
3620 ports for other uses may adjust the range that the
3621 kernel's sunrpc client considers to be privileged
3622 using these two parameters to set the minimum and
3623 maximum port values.
3627 Control how the NFS server code allocates CPUs to
3628 service thread pools. Depending on how many NICs
3629 you have and where their interrupts are bound, this
3630 option will affect which CPUs will do NFS serving.
3631 Note: this parameter cannot be changed while the
3632 NFS server is running.
3634 auto the server chooses an appropriate mode
3635 automatically using heuristics
3636 global a single global pool contains all CPUs
3637 percpu one pool for each CPU
3638 pernode one pool for each NUMA node (equivalent
3639 to global on non-NUMA machines)
3641 sunrpc.tcp_slot_table_entries=
3642 sunrpc.udp_slot_table_entries=
3644 Sets the upper limit on the number of simultaneous
3645 RPC calls that can be sent from the client to a
3646 server. Increasing these values may allow you to
3647 improve throughput, but will also increase the
3648 amount of memory reserved for use by the client.
3650 suspend.pm_test_delay=
3652 Sets the number of seconds to remain in a suspend test
3653 mode before resuming the system (see
3654 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3655 is set. Default value is 5.
3658 [KNL] Enable accounting of swap in memory resource
3659 controller if no parameter or 1 is given or disable
3660 it if 0 is given (See Documentation/cgroups/memory.txt)
3662 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3663 Format: { <int> | force }
3664 <int> -- Number of I/O TLB slabs
3665 force -- force using of bounce buffers even if they
3666 wouldn't be automatically used by the kernel
3670 sysfs.deprecated=0|1 [KNL]
3671 Enable/disable old style sysfs layout for old udev
3672 on older distributions. When this option is enabled
3673 very new udev will not work anymore. When this option
3674 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3675 in older udev will not work anymore.
3676 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3677 the kernel configuration.
3679 sysrq_always_enabled
3681 Ignore sysrq setting - this boot parameter will
3682 neutralize any effect of /proc/sys/kernel/sysrq.
3683 Useful for debugging.
3685 tcpmhash_entries= [KNL,NET]
3686 Set the number of tcp_metrics_hash slots.
3687 Default value is 8192 or 16384 depending on total
3688 ram pages. This is used to specify the TCP metrics
3689 cache size. See Documentation/networking/ip-sysctl.txt
3690 "tcp_no_metrics_save" section for more details.
3694 test_suspend= [SUSPEND][,N]
3695 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3696 standby suspend) or "freeze" (for suspend type freeze)
3697 as the system sleep state during system startup with
3698 the optional capability to repeat N number of times.
3699 The system is woken from this state using a
3700 wakeup-capable RTC alarm.
3702 thash_entries= [KNL,NET]
3703 Set number of hash buckets for TCP connection
3705 thermal.act= [HW,ACPI]
3706 -1: disable all active trip points in all thermal zones
3707 <degrees C>: override all lowest active trip points
3709 thermal.crt= [HW,ACPI]
3710 -1: disable all critical trip points in all thermal zones
3711 <degrees C>: override all critical trip points
3713 thermal.nocrt= [HW,ACPI]
3714 Set to disable actions on ACPI thermal zone
3715 critical and hot trip points.
3717 thermal.off= [HW,ACPI]
3718 1: disable ACPI thermal control
3720 thermal.psv= [HW,ACPI]
3721 -1: disable all passive trip points
3722 <degrees C>: override all passive trip points to this
3725 thermal.tzp= [HW,ACPI]
3726 Specify global default ACPI thermal zone polling rate
3727 <deci-seconds>: poll all this frequency
3728 0: no polling (default)
3731 Force threading of all interrupt handlers except those
3732 marked explicitly IRQF_NO_THREAD.
3735 Enable the Transcendent memory driver if built-in.
3737 tmem.cleancache=0|1 [KNL, XEN]
3738 Default is on (1). Disable the usage of the cleancache
3739 API to send anonymous pages to the hypervisor.
3741 tmem.frontswap=0|1 [KNL, XEN]
3742 Default is on (1). Disable the usage of the frontswap
3743 API to send swap pages to the hypervisor. If disabled
3744 the selfballooning and selfshrinking are force disabled.
3746 tmem.selfballooning=0|1 [KNL, XEN]
3747 Default is on (1). Disable the driving of swap pages
3750 tmem.selfshrinking=0|1 [KNL, XEN]
3751 Default is on (1). Partial swapoff that immediately
3752 transfers pages from Xen hypervisor back to the
3753 kernel based on different criteria.
3757 Specify if the kernel should make use of the cpu
3758 topology information if the hardware supports this.
3759 The scheduler will make use of this information and
3760 e.g. base its process migration decisions on it.
3763 topology_updates= [KNL, PPC, NUMA]
3765 Specify if the kernel should ignore (off)
3766 topology updates sent by the hypervisor to this
3771 tpm_suspend_pcr=[HW,TPM]
3772 Format: integer pcr id
3773 Specify that at suspend time, the tpm driver
3774 should extend the specified pcr with zeros,
3775 as a workaround for some chips which fail to
3776 flush the last written pcr on TPM_SaveState.
3777 This will guarantee that all the other pcrs
3780 trace_buf_size=nn[KMG]
3781 [FTRACE] will set tracing buffer size on each cpu.
3783 trace_event=[event-list]
3784 [FTRACE] Set and start specified trace events in order
3785 to facilitate early boot debugging.
3786 See also Documentation/trace/events.txt
3788 trace_options=[option-list]
3789 [FTRACE] Enable or disable tracer options at boot.
3790 The option-list is a comma delimited list of options
3791 that can be enabled or disabled just as if you were
3792 to echo the option name into
3794 /sys/kernel/debug/tracing/trace_options
3796 For example, to enable stacktrace option (to dump the
3797 stack trace of each event), add to the command line:
3799 trace_options=stacktrace
3801 See also Documentation/trace/ftrace.txt "trace options"
3805 Have the tracepoints sent to printk as well as the
3806 tracing ring buffer. This is useful for early boot up
3807 where the system hangs or reboots and does not give the
3808 option for reading the tracing buffer or performing a
3809 ftrace_dump_on_oops.
3811 To turn off having tracepoints sent to printk,
3812 echo 0 > /proc/sys/kernel/tracepoint_printk
3813 Note, echoing 1 into this file without the
3814 tracepoint_printk kernel cmdline option has no effect.
3818 Having tracepoints sent to printk() and activating high
3819 frequency tracepoints such as irq or sched, can cause
3820 the system to live lock.
3823 [FTRACE] enable this option to disable tracing when a
3824 warning is hit. This turns off "tracing_on". Tracing can
3825 be enabled again by echoing '1' into the "tracing_on"
3826 file located in /sys/kernel/debug/tracing/
3828 This option is useful, as it disables the trace before
3829 the WARNING dump is called, which prevents the trace to
3830 be filled with content caused by the warning output.
3832 This option can also be set at run time via the sysctl
3833 option: kernel/traceoff_on_warning
3835 transparent_hugepage=
3837 Format: [always|madvise|never]
3838 Can be used to control the default behavior of the system
3839 with respect to transparent hugepages.
3840 See Documentation/vm/transhuge.txt for more details.
3842 tsc= Disable clocksource stability checks for TSC.
3844 [x86] reliable: mark tsc clocksource as reliable, this
3845 disables clocksource verification at runtime, as well
3846 as the stability checks done at bootup. Used to enable
3847 high-resolution timer mode on older hardware, and in
3848 virtualized environment.
3849 [x86] noirqtime: Do not use TSC to do irq accounting.
3850 Used to run time disable IRQ_TIME_ACCOUNTING on any
3851 platforms where RDTSC is slow and this accounting
3854 turbografx.map[2|3]= [HW,JOY]
3855 TurboGraFX parallel port interface
3857 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3858 See also Documentation/input/joystick-parport.txt
3860 udbg-immortal [PPC] When debugging early kernel crashes that
3861 happen after console_init() and before a proper
3862 console driver takes over, this boot options might
3863 help "seeing" what's going on.
3865 uhash_entries= [KNL,NET]
3866 Set number of hash buckets for UDP/UDP-Lite connections
3869 [USB] Ignore overcurrent events (default N).
3870 Some badly-designed motherboards generate lots of
3871 bogus events, for ports that aren't wired to
3872 anything. Set this parameter to avoid log spamming.
3873 Note that genuine overcurrent events won't be
3877 [X86] Cause panic on unknown NMI.
3879 usbcore.authorized_default=
3880 [USB] Default USB device authorization:
3881 (default -1 = authorized except for wireless USB,
3882 0 = not authorized, 1 = authorized)
3884 usbcore.autosuspend=
3885 [USB] The autosuspend time delay (in seconds) used
3886 for newly-detected USB devices (default 2). This
3887 is the time required before an idle device will be
3888 autosuspended. Devices for which the delay is set
3889 to a negative value won't be autosuspended at all.
3891 usbcore.usbfs_snoop=
3892 [USB] Set to log all usbfs traffic (default 0 = off).
3894 usbcore.blinkenlights=
3895 [USB] Set to cycle leds on hubs (default 0 = off).
3897 usbcore.old_scheme_first=
3898 [USB] Start with the old device initialization
3899 scheme (default 0 = off).
3901 usbcore.usbfs_memory_mb=
3902 [USB] Memory limit (in MB) for buffers allocated by
3903 usbfs (default = 16, 0 = max = 2047).
3905 usbcore.use_both_schemes=
3906 [USB] Try the other device initialization scheme
3907 if the first one fails (default 1 = enabled).
3909 usbcore.initial_descriptor_timeout=
3910 [USB] Specifies timeout for the initial 64-byte
3911 USB_REQ_GET_DESCRIPTOR request in milliseconds
3912 (default 5000 = 5.0 seconds).
3915 [USBHID] The interval which mice are to be polled at.
3917 usb-storage.delay_use=
3918 [UMS] The delay in seconds before a new device is
3919 scanned for Logical Units (default 1).
3922 [UMS] A list of quirks entries to supplement or
3923 override the built-in unusual_devs list. List
3924 entries are separated by commas. Each entry has
3925 the form VID:PID:Flags where VID and PID are Vendor
3926 and Product ID values (4-digit hex numbers) and
3927 Flags is a set of characters, each corresponding
3928 to a common usb-storage quirk flag as follows:
3929 a = SANE_SENSE (collect more than 18 bytes
3931 b = BAD_SENSE (don't collect more than 18
3932 bytes of sense data);
3933 c = FIX_CAPACITY (decrease the reported
3934 device capacity by one sector);
3935 d = NO_READ_DISC_INFO (don't use
3936 READ_DISC_INFO command);
3937 e = NO_READ_CAPACITY_16 (don't use
3938 READ_CAPACITY_16 command);
3939 f = NO_REPORT_OPCODES (don't use report opcodes
3941 g = MAX_SECTORS_240 (don't transfer more than
3942 240 sectors at a time, uas only);
3943 h = CAPACITY_HEURISTICS (decrease the
3944 reported device capacity by one
3945 sector if the number is odd);
3946 i = IGNORE_DEVICE (don't bind to this
3948 j = NO_REPORT_LUNS (don't use report luns
3950 l = NOT_LOCKABLE (don't try to lock and
3951 unlock ejectable media);
3952 m = MAX_SECTORS_64 (don't transfer more
3953 than 64 sectors = 32 KB at a time);
3954 n = INITIAL_READ10 (force a retry of the
3955 initial READ(10) command);
3956 o = CAPACITY_OK (accept the capacity
3957 reported by the device);
3958 p = WRITE_CACHE (the device cache is ON
3960 r = IGNORE_RESIDUE (the device reports
3961 bogus residue values);
3962 s = SINGLE_LUN (the device has only one
3964 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3965 commands, uas only);
3966 u = IGNORE_UAS (don't bind to the uas driver);
3967 w = NO_WP_DETECT (don't test whether the
3968 medium is write-protected).
3969 Example: quirks=0419:aaf5:rl,0421:0433:rc
3971 user_debug= [KNL,ARM]
3973 See arch/arm/Kconfig.debug help text.
3974 1 - undefined instruction events
3976 4 - invalid data aborts
3979 Example: user_debug=31
3982 [X86] Flags controlling user PTE allocations.
3984 nohigh = do not allocate PTE pages in
3985 HIGHMEM regardless of setting
3989 On X86_32, this is an alias for vdso32=. Otherwise:
3991 vdso=1: enable VDSO (the default)
3992 vdso=0: disable VDSO mapping
3994 vdso32= [X86] Control the 32-bit vDSO
3995 vdso32=1: enable 32-bit VDSO
3996 vdso32=0 or vdso32=2: disable 32-bit VDSO
3998 See the help text for CONFIG_COMPAT_VDSO for more
3999 details. If CONFIG_COMPAT_VDSO is set, the default is
4000 vdso32=0; otherwise, the default is vdso32=1.
4002 For compatibility with older kernels, vdso32=2 is an
4005 Try vdso32=0 if you encounter an error that says:
4006 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4009 vector=percpu: enable percpu vector domain
4011 video= [FB] Frame buffer configuration
4012 See Documentation/fb/modedb.txt.
4014 video.brightness_switch_enabled= [0,1]
4015 If set to 1, on receiving an ACPI notify event
4016 generated by hotkey, video driver will adjust brightness
4017 level and then send out the event to user space through
4018 the allocated input device; If set to 0, video driver
4019 will only send out the event without touching backlight
4024 [VMMIO] Memory mapped virtio (platform) device.
4026 <size>@<baseaddr>:<irq>[:<id>]
4028 <size> := size (can use standard suffixes
4030 <baseaddr> := physical base address
4031 <irq> := interrupt number (as passed to
4033 <id> := (optional) platform device id
4035 virtio_mmio.device=1K@0x100b0000:48:7
4037 Can be used multiple times for multiple devices.
4039 vga= [BOOT,X86-32] Select a particular video mode
4040 See Documentation/x86/boot.txt and
4041 Documentation/svga.txt.
4042 Use vga=ask for menu.
4043 This is actually a boot loader parameter; the value is
4044 passed to the kernel using a special protocol.
4046 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4047 size of <nn>. This can be used to increase the
4048 minimum size (128MB on x86). It can also be used to
4049 decrease the size and leave more room for directly
4052 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4055 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4058 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4062 Controls the behavior of vsyscalls (i.e. calls to
4063 fixed addresses of 0xffffffffff600x00 from legacy
4064 code). Most statically-linked binaries and older
4065 versions of glibc use these calls. Because these
4066 functions are at fixed addresses, they make nice
4067 targets for exploits that can control RIP.
4069 emulate [default] Vsyscalls turn into traps and are
4070 emulated reasonably safely.
4072 native Vsyscalls are native syscall instructions.
4073 This is a little bit faster than trapping
4074 and makes a few dynamic recompilers work
4075 better than they would in emulation mode.
4076 It also makes exploits much easier to write.
4078 none Vsyscalls don't work at all. This makes
4079 them quite hard to use for exploits but
4080 might break your system.
4082 vt.color= [VT] Default text color.
4083 Format: 0xYX, X = foreground, Y = background.
4084 Default: 0x07 = light gray on black.
4086 vt.cur_default= [VT] Default cursor shape.
4087 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4088 the parameters of the <Esc>[?A;B;Cc escape sequence;
4089 see VGA-softcursor.txt. Default: 2 = underline.
4091 vt.default_blu= [VT]
4092 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4093 Change the default blue palette of the console.
4094 This is a 16-member array composed of values
4097 vt.default_grn= [VT]
4098 Format: <green0>,<green1>,<green2>,...,<green15>
4099 Change the default green palette of the console.
4100 This is a 16-member array composed of values
4103 vt.default_red= [VT]
4104 Format: <red0>,<red1>,<red2>,...,<red15>
4105 Change the default red palette of the console.
4106 This is a 16-member array composed of values
4112 Set system-wide default UTF-8 mode for all tty's.
4113 Default is 1, i.e. UTF-8 mode is enabled for all
4114 newly opened terminals.
4116 vt.global_cursor_default=
4119 Set system-wide default for whether a cursor
4120 is shown on new VTs. Default is -1,
4121 i.e. cursors will be created by default unless
4122 overridden by individual drivers. 0 will hide
4123 cursors, 1 will display them.
4125 vt.italic= [VT] Default color for italic text; 0-15.
4128 vt.underline= [VT] Default color for underlined text; 0-15.
4131 watchdog timers [HW,WDT] For information on watchdog timers,
4132 see Documentation/watchdog/watchdog-parameters.txt
4133 or other driver-specific files in the
4134 Documentation/watchdog/ directory.
4136 workqueue.disable_numa
4137 By default, all work items queued to unbound
4138 workqueues are affine to the NUMA nodes they're
4139 issued on, which results in better behavior in
4140 general. If NUMA affinity needs to be disabled for
4141 whatever reason, this option can be used. Note
4142 that this also can be controlled per-workqueue for
4143 workqueues visible under /sys/bus/workqueue/.
4145 workqueue.power_efficient
4146 Per-cpu workqueues are generally preferred because
4147 they show better performance thanks to cache
4148 locality; unfortunately, per-cpu workqueues tend to
4149 be more power hungry than unbound workqueues.
4151 Enabling this makes the per-cpu workqueues which
4152 were observed to contribute significantly to power
4153 consumption unbound, leading to measurably lower
4154 power usage at the cost of small performance
4157 The default value of this parameter is determined by
4158 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4160 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4161 default x2apic cluster mode on platforms
4164 x86_intel_mid_timer= [X86-32,APBT]
4165 Choose timer option for x86 Intel MID platform.
4166 Two valid options are apbt timer only and lapic timer
4167 plus one apbt timer for broadcast timer.
4168 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4170 xen_512gb_limit [KNL,X86-64,XEN]
4171 Restricts the kernel running paravirtualized under Xen
4172 to use only up to 512 GB of RAM. The reason to do so is
4173 crash analysis tools and Xen tools for doing domain
4174 save/restore/migration must be enabled to handle larger
4177 xen_emul_unplug= [HW,X86,XEN]
4178 Unplug Xen emulated devices
4179 Format: [unplug0,][unplug1]
4180 ide-disks -- unplug primary master IDE devices
4181 aux-ide-disks -- unplug non-primary-master IDE devices
4182 nics -- unplug network devices
4183 all -- unplug all emulated devices (NICs and IDE disks)
4184 unnecessary -- unplugging emulated devices is
4185 unnecessary even if the host did not respond to
4187 never -- do not unplug even if version check succeeds
4189 xen_nopvspin [X86,XEN]
4190 Disables the ticketlock slowpath using Xen PV
4194 Disables the PV optimizations forcing the HVM guest to
4195 run as generic HVM guest with no PV drivers.
4197 xirc2ps_cs= [NET,PCMCIA]
4199 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4201 ______________________________________________________________________
4205 Add more DRM drivers.