4 The following is a consolidated list of the kernel parameters as
5 implemented by the __setup(), core_param() and module_param() macros
6 and sorted into English Dictionary order (defined as ignoring all
7 punctuation and sorting digits before letters in a case insensitive
8 manner), and with descriptions where known.
10 The kernel parses parameters from the kernel command line up to "--";
11 if it doesn't recognize a parameter and it doesn't contain a '.', the
12 parameter gets passed to init: parameters with '=' go into init's
13 environment, others are passed as command line arguments to init.
14 Everything after "--" is passed as an argument to init.
16 Module parameters can be specified in two ways: via the kernel command
17 line with a module name prefix, or via modprobe, e.g.:
19 (kernel command line) usbcore.blinkenlights=1
20 (modprobe command line) modprobe usbcore blinkenlights=1
22 Parameters for modules which are built into the kernel need to be
23 specified on the kernel command line. modprobe looks through the
24 kernel command line (/proc/cmdline) and collects module parameters
25 when it loads a module, so the kernel command line can be used for
28 Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30 can also be entered as
31 log-buf-len=1M print_fatal_signals=1
33 Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
36 This document may not be entirely up to date and comprehensive. The command
37 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
38 module. Loadable modules, after being loaded into the running kernel, also
39 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
40 parameters may be changed at runtime by the command
41 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
43 The parameters listed below are only valid if certain kernel build options were
44 enabled and if respective hardware is present. The text in square brackets at
45 the beginning of each description states the restrictions within which a
46 parameter is applicable:
48 ACPI ACPI support is enabled.
49 AGP AGP (Accelerated Graphics Port) is enabled.
50 ALSA ALSA sound support is enabled.
51 APIC APIC support is enabled.
52 APM Advanced Power Management support is enabled.
53 ARM ARM architecture is enabled.
54 AVR32 AVR32 architecture is enabled.
55 AX25 Appropriate AX.25 support is enabled.
56 BLACKFIN Blackfin architecture is enabled.
57 CLK Common clock infrastructure is enabled.
58 CMA Contiguous Memory Area support is enabled.
59 DRM Direct Rendering Management support is enabled.
60 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
61 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
62 EFI EFI Partitioning (GPT) is enabled
63 EIDE EIDE/ATAPI support is enabled.
64 EVM Extended Verification Module
65 FB The frame buffer device is enabled.
66 FTRACE Function tracing enabled.
67 GCOV GCOV profiling is enabled.
68 HW Appropriate hardware is enabled.
69 IA-64 IA-64 architecture is enabled.
70 IMA Integrity measurement architecture is enabled.
71 IOSCHED More than one I/O scheduler is enabled.
72 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
73 IPV6 IPv6 support is enabled.
74 ISAPNP ISA PnP code is enabled.
75 ISDN Appropriate ISDN support is enabled.
76 JOY Appropriate joystick support is enabled.
77 KGDB Kernel debugger support is enabled.
78 KVM Kernel Virtual Machine support is enabled.
79 LIBATA Libata driver is enabled
80 LP Printer support is enabled.
81 LOOP Loopback device support is enabled.
82 M68k M68k architecture is enabled.
83 These options have more detailed description inside of
84 Documentation/m68k/kernel-options.txt.
85 MDA MDA console support is enabled.
86 MIPS MIPS architecture is enabled.
87 MOUSE Appropriate mouse support is enabled.
88 MSI Message Signaled Interrupts (PCI).
89 MTD MTD (Memory Technology Device) support is enabled.
90 NET Appropriate network support is enabled.
91 NUMA NUMA support is enabled.
92 NFS Appropriate NFS support is enabled.
93 OSS OSS sound support is enabled.
94 PV_OPS A paravirtualized kernel is enabled.
95 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
96 PARISC The PA-RISC architecture is enabled.
97 PCI PCI bus support is enabled.
98 PCIE PCI Express support is enabled.
99 PCMCIA The PCMCIA subsystem is enabled.
100 PNP Plug & Play support is enabled.
101 PPC PowerPC architecture is enabled.
102 PPT Parallel port support is enabled.
103 PS2 Appropriate PS/2 support is enabled.
104 RAM RAM disk support is enabled.
105 S390 S390 architecture is enabled.
106 SCSI Appropriate SCSI support is enabled.
107 A lot of drivers have their options described inside
108 the Documentation/scsi/ sub-directory.
109 SECURITY Different security models are enabled.
110 SELINUX SELinux support is enabled.
111 APPARMOR AppArmor support is enabled.
112 SERIAL Serial support is enabled.
113 SH SuperH architecture is enabled.
114 SMP The kernel is an SMP kernel.
115 SPARC Sparc architecture is enabled.
116 SWSUSP Software suspend (hibernation) is enabled.
117 SUSPEND System suspend states are enabled.
118 TPM TPM drivers are enabled.
119 TS Appropriate touchscreen support is enabled.
120 UMS USB Mass Storage support is enabled.
121 USB USB support is enabled.
122 USBHID USB Human Interface Device support is enabled.
123 V4L Video For Linux support is enabled.
124 VMMIO Driver for memory mapped virtio devices is enabled.
125 VGA The VGA console has been enabled.
126 VT Virtual terminal support is enabled.
127 WDT Watchdog support is enabled.
128 XT IBM PC/XT MFM hard disk support is enabled.
129 X86-32 X86-32, aka i386 architecture is enabled.
130 X86-64 X86-64 architecture is enabled.
131 More X86-64 boot options can be found in
132 Documentation/x86/x86_64/boot-options.txt .
133 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
134 X86_UV SGI UV support is enabled.
135 XEN Xen support is enabled
137 In addition, the following text indicates that the option:
139 BUGS= Relates to possible processor bugs on the said processor.
140 KNL Is a kernel start-up parameter.
141 BOOT Is a boot loader parameter.
143 Parameters denoted with BOOT are actually interpreted by the boot
144 loader, and have no meaning to the kernel directly.
145 Do not modify the syntax of boot loader parameters without extreme
146 need or coordination with <Documentation/x86/boot.txt>.
148 There are also arch-specific kernel-parameters not documented here.
149 See for example <Documentation/x86/x86_64/boot-options.txt>.
151 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
152 a trailing = on the name of any parameter states that that parameter will
153 be entered as an environment variable, whereas its absence indicates that
154 it will appear as a kernel argument readable via /proc/cmdline by programs
155 running once the system is up.
157 The number of kernel parameters is not limited, but the length of the
158 complete command line (parameters including spaces etc.) is limited to
159 a fixed number of characters. This limit depends on the architecture
160 and is between 256 and 4096 characters. It is defined in the file
161 ./include/asm/setup.h as COMMAND_LINE_SIZE.
163 Finally, the [KMG] suffix is commonly described after a number of kernel
164 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
165 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
166 bytes respectively. Such letter suffixes can also be entirely omitted.
169 acpi= [HW,ACPI,X86,ARM64]
170 Advanced Configuration and Power Interface
171 Format: { force | on | off | strict | noirq | rsdt |
173 force -- enable ACPI if default was off
174 on -- enable ACPI but allow fallback to DT [arm64]
175 off -- disable ACPI if default was on
176 noirq -- do not use ACPI for IRQ routing
177 strict -- Be less tolerant of platforms that are not
178 strictly ACPI specification compliant.
179 rsdt -- prefer RSDT over (default) XSDT
180 copy_dsdt -- copy DSDT to memory
181 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
184 See also Documentation/power/runtime_pm.txt, pci=noacpi
186 acpi_apic_instance= [ACPI, IOAPIC]
188 2: use 2nd APIC table, if available
189 1,0: use 1st APIC table
192 acpi_backlight= [HW,ACPI]
193 acpi_backlight=vendor
195 If set to vendor, prefer vendor specific driver
196 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
197 of the ACPI video.ko driver.
199 acpi_force_32bit_fadt_addr
200 force FADT to use 32 bit addresses rather than the
201 64 bit X_* addresses. Some firmware have broken 64
202 bit addresses for force ACPI ignore these and use
203 the older legacy 32 bit addresses.
205 acpica_no_return_repair [HW, ACPI]
206 Disable AML predefined validation mechanism
207 This mechanism can repair the evaluation result to make
208 the return objects more ACPI specification compliant.
209 This option is useful for developers to identify the
210 root cause of an AML interpreter issue when the issue
211 has something to do with the repair mechanism.
213 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
214 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
216 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
217 debug output. Bits in debug_layer correspond to a
218 _COMPONENT in an ACPI source file, e.g.,
219 #define _COMPONENT ACPI_PCI_COMPONENT
220 Bits in debug_level correspond to a level in
221 ACPI_DEBUG_PRINT statements, e.g.,
222 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
223 The debug_level mask defaults to "info". See
224 Documentation/acpi/debug.txt for more information about
225 debug layers and levels.
227 Enable processor driver info messages:
228 acpi.debug_layer=0x20000000
229 Enable PCI/PCI interrupt routing info messages:
230 acpi.debug_layer=0x400000
231 Enable AML "Debug" output, i.e., stores to the Debug
232 object while interpreting AML:
233 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
234 Enable all messages related to ACPI hardware:
235 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
237 Some values produce so much output that the system is
238 unusable. The "log_buf_len" parameter may be useful
239 if you need to capture more output.
241 acpi_enforce_resources= [ACPI]
242 { strict | lax | no }
243 Check for resource conflicts between native drivers
244 and ACPI OperationRegions (SystemIO and SystemMemory
245 only). IO ports and memory declared in ACPI might be
246 used by the ACPI subsystem in arbitrary AML code and
247 can interfere with legacy drivers.
248 strict (default): access to resources claimed by ACPI
249 is denied; legacy drivers trying to access reserved
250 resources will fail to bind to device using them.
251 lax: access to resources claimed by ACPI is allowed;
252 legacy drivers trying to access reserved resources
253 will bind successfully but a warning message is logged.
254 no: ACPI OperationRegions are not marked as reserved,
255 no further checks are performed.
257 acpi_force_table_verification [HW,ACPI]
258 Enable table checksum verification during early stage.
259 By default, this is disabled due to x86 early mapping
262 acpi_irq_balance [HW,ACPI]
263 ACPI will balance active IRQs
266 acpi_irq_nobalance [HW,ACPI]
267 ACPI will not move active IRQs (default)
270 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
271 Format: <irq>,<irq>...
273 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
275 Format: <irq>,<irq>...
277 acpi_no_auto_serialize [HW,ACPI]
278 Disable auto-serialization of AML methods
279 AML control methods that contain the opcodes to create
280 named objects will be marked as "Serialized" by the
281 auto-serialization feature.
282 This feature is enabled by default.
283 This option allows to turn off the feature.
285 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
288 acpi_no_static_ssdt [HW,ACPI]
289 Disable installation of static SSDTs at early boot time
290 By default, SSDTs contained in the RSDT/XSDT will be
291 installed automatically and they will appear under
292 /sys/firmware/acpi/tables.
293 This option turns off this feature.
294 Note that specifying this option does not affect
295 dynamic table installation which will install SSDT
296 tables to /sys/firmware/acpi/tables/dynamic.
298 acpi_rsdp= [ACPI,EFI,KEXEC]
299 Pass the RSDP address to the kernel, mostly used
300 on machines running EFI runtime service to boot the
301 second kernel for kdump.
303 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
304 Format: To spoof as Windows 98: ="Microsoft Windows"
306 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
307 of 2 which is mandated by ACPI 6) as the supported ACPI
308 specification revision (when using this switch, it may
309 be necessary to carry out a cold reboot _twice_ in a
310 row to make it take effect on the platform firmware).
312 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
313 acpi_osi="string1" # add string1
314 acpi_osi="!string2" # remove string2
315 acpi_osi=!* # remove all strings
316 acpi_osi=! # disable all built-in OS vendor
318 acpi_osi=!! # enable all built-in OS vendor
320 acpi_osi= # disable all strings
322 'acpi_osi=!' can be used in combination with single or
323 multiple 'acpi_osi="string1"' to support specific OS
324 vendor string(s). Note that such command can only
325 affect the default state of the OS vendor strings, thus
326 it cannot affect the default state of the feature group
327 strings and the current state of the OS vendor strings,
328 specifying it multiple times through kernel command line
329 is meaningless. This command is useful when one do not
330 care about the state of the feature group strings which
331 should be controlled by the OSPM.
333 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
334 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
335 can make '_OSI("Windows 2000")' TRUE.
337 'acpi_osi=' cannot be used in combination with other
338 'acpi_osi=' command lines, the _OSI method will not
339 exist in the ACPI namespace. NOTE that such command can
340 only affect the _OSI support state, thus specifying it
341 multiple times through kernel command line is also
344 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
347 'acpi_osi=!*' can be used in combination with single or
348 multiple 'acpi_osi="string1"' to support specific
349 string(s). Note that such command can affect the
350 current state of both the OS vendor strings and the
351 feature group strings, thus specifying it multiple times
352 through kernel command line is meaningful. But it may
353 still not able to affect the final state of a string if
354 there are quirks related to this string. This command
355 is useful when one want to control the state of the
356 feature group strings to debug BIOS issues related to
359 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
360 '_OSI("Module Device")' FALSE.
361 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
362 '_OSI("Module Device")' TRUE.
363 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
365 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
367 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
368 they all will make '_OSI("Windows 2000")' TRUE.
371 Override the pmtimer bug detection: force the kernel
372 to assume that this machine's pmtimer latches its value
373 and always returns good values.
375 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
376 Format: { level | edge | high | low }
378 acpi_skip_timer_override [HW,ACPI]
379 Recognize and ignore IRQ0/pin2 Interrupt Override.
380 For broken nForce2 BIOS resulting in XT-PIC timer.
382 acpi_sleep= [HW,ACPI] Sleep options
383 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
384 old_ordering, nonvs, sci_force_enable }
385 See Documentation/power/video.txt for information on
387 s3_beep is for debugging; it makes the PC's speaker beep
388 as soon as the kernel's real-mode entry point is called.
389 s4_nohwsig prevents ACPI hardware signature from being
390 used during resume from hibernation.
391 old_ordering causes the ACPI 1.0 ordering of the _PTS
392 control method, with respect to putting devices into
393 low power states, to be enforced (the ACPI 2.0 ordering
394 of _PTS is used by default).
395 nonvs prevents the kernel from saving/restoring the
396 ACPI NVS memory during suspend/hibernation and resume.
397 sci_force_enable causes the kernel to set SCI_EN directly
398 on resume from S1/S3 (which is against the ACPI spec,
399 but some broken systems don't work without it).
401 acpi_use_timer_override [HW,ACPI]
402 Use timer override. For some broken Nvidia NF5 boards
403 that require a timer override, but don't have HPET
405 add_efi_memmap [EFI; X86] Include EFI memory map in
406 kernel's map of available physical RAM.
409 { off | try_unsupported }
410 off: disable AGP support
411 try_unsupported: try to drive unsupported chipsets
412 (may crash computer or cause data corruption)
415 See Documentation/sound/alsa/alsa-parameters.txt
418 Allow the default userspace alignment fault handler
419 behaviour to be specified. Bit 0 enables warnings,
420 bit 1 enables fixups, and bit 2 sends a segfault.
422 align_va_addr= [X86-64]
423 Align virtual addresses by clearing slice [14:12] when
424 allocating a VMA at process creation time. This option
425 gives you up to 3% performance improvement on AMD F15h
426 machines (where it is enabled by default) for a
427 CPU-intensive style benchmark, and it can vary highly in
428 a microbenchmark depending on workload and compiler.
430 32: only for 32-bit processes
431 64: only for 64-bit processes
432 on: enable for both 32- and 64-bit processes
433 off: disable for both 32- and 64-bit processes
435 alloc_snapshot [FTRACE]
436 Allocate the ftrace snapshot buffer on boot up when the
437 main buffer is allocated. This is handy if debugging
438 and you need to use tracing_snapshot() on boot up, and
439 do not want to use tracing_snapshot_alloc() as it needs
440 to be done where GFP_KERNEL allocations are allowed.
442 amd_iommu= [HW,X86-64]
443 Pass parameters to the AMD IOMMU driver in the system.
445 fullflush - enable flushing of IO/TLB entries when
446 they are unmapped. Otherwise they are
447 flushed before they will be reused, which
449 off - do not initialize any AMD IOMMU found in
451 force_isolation - Force device isolation for all
452 devices. The IOMMU driver is not
453 allowed anymore to lift isolation
454 requirements as needed. This option
455 does not override iommu=pt
457 amd_iommu_dump= [HW,X86-64]
458 Enable AMD IOMMU driver option to dump the ACPI table
459 for AMD IOMMU. With this option enabled, AMD IOMMU
460 driver will print ACPI tables for AMD IOMMU during
461 IOMMU initialization.
463 amijoy.map= [HW,JOY] Amiga joystick support
464 Map of devices attached to JOY0DAT and JOY1DAT
466 See also Documentation/input/joystick.txt
468 analog.map= [HW,JOY] Analog joystick and gamepad support
469 Specifies type or capabilities of an analog joystick
470 connected to one of 16 gameports
471 Format: <type1>,<type2>,..<type16>
474 Power management functions (SPARCstation-4/5 + deriv.)
476 Disable APC CPU standby support. SPARCstation-Fox does
477 not play well with APC CPU idle - disable it if you have
478 APC and your system crashes randomly.
480 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
481 Change the output verbosity whilst booting
482 Format: { quiet (default) | verbose | debug }
483 Change the amount of debugging information output
484 when initialising the APIC and IO-APIC components.
486 apic_extnmi= [APIC,X86] External NMI delivery setting
487 Format: { bsp (default) | all | none }
488 bsp: External NMI is delivered only to CPU 0
489 all: External NMIs are broadcast to all CPUs as a
491 none: External NMI is masked for all CPUs. This is
492 useful so that a dump capture kernel won't be
496 See Documentation/networking/ipv6.txt.
498 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
499 Limit apic dumping. The parameter defines the maximal
500 number of local apics being dumped. Also it is possible
501 to set it to "all" by meaning -- no limit here.
502 Format: { 1 (default) | 2 | ... | all }.
503 The parameter valid if only apic=debug or
504 apic=verbose is specified.
505 Example: apic=debug show_lapic=all
507 apm= [APM] Advanced Power Management
508 See header of arch/x86/kernel/apm_32.c.
510 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
511 Format: <io>,<irq>,<nodeID>
515 atarimouse= [HW,MOUSE] Atari Mouse
517 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
518 EzKey and similar keyboards
520 atkbd.reset= [HW] Reset keyboard during initialization
522 atkbd.set= [HW] Select keyboard code set
523 Format: <int> (2 = AT (default), 3 = PS/2)
525 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
528 atkbd.softraw= [HW] Choose between synthetic and real raw mode
529 Format: <bool> (0 = real, 1 = synthetic (default))
531 atkbd.softrepeat= [HW]
532 Use software keyboard repeat
534 audit= [KNL] Enable the audit sub-system
535 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
536 0 - kernel audit is disabled and can not be enabled
537 until the next reboot
538 unset - kernel audit is initialized but disabled and
539 will be fully enabled by the userspace auditd.
540 1 - kernel audit is initialized and partially enabled,
541 storing at most audit_backlog_limit messages in
542 RAM until it is fully enabled by the userspace
546 audit_backlog_limit= [KNL] Set the audit queue size limit.
547 Format: <int> (must be >=0)
550 bau= [X86_UV] Enable the BAU on SGI UV. The default
551 behavior is to disable the BAU (i.e. bau=0).
552 Format: { "0" | "1" }
555 unset - Disable the BAU.
557 baycom_epp= [HW,AX25]
560 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
562 See header of drivers/net/hamradio/baycom_par.c.
564 baycom_ser_fdx= [HW,AX25]
565 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
566 Format: <io>,<irq>,<mode>[,<baud>]
567 See header of drivers/net/hamradio/baycom_ser_fdx.c.
569 baycom_ser_hdx= [HW,AX25]
570 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
571 Format: <io>,<irq>,<mode>
572 See header of drivers/net/hamradio/baycom_ser_hdx.c.
574 blkdevparts= Manual partition parsing of block device(s) for
575 embedded devices based on command line input.
576 See Documentation/block/cmdline-partition.txt
578 boot_delay= Milliseconds to delay each printk during boot.
579 Values larger than 10 seconds (10000) are changed to
583 bootmem_debug [KNL] Enable bootmem allocator debug messages.
585 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
586 bttv.radio= Most important insmod options are available as
588 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
591 bulk_remove=off [PPC] This parameter disables the use of the pSeries
592 firmware feature for flushing multiple hpte entries
595 c101= [NET] Moxa C101 synchronous serial card
597 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
598 Sometimes CPU hardware bugs make them report the cache
599 size incorrectly. The kernel will attempt work arounds
600 to fix known problems, but for some CPUs it is not
601 possible to determine what the correct size should be.
602 This option provides an override for these situations.
604 ca_keys= [KEYS] This parameter identifies a specific key(s) on
605 the system trusted keyring to be used for certificate
607 format: { id:<keyid> | builtin }
609 cca= [MIPS] Override the kernel pages' cache coherency
610 algorithm. Accepted values range from 0 to 7
611 inclusive. See arch/mips/include/asm/pgtable-bits.h
612 for platform specific values (SB1, Loongson3 and
615 ccw_timeout_log [S390]
616 See Documentation/s390/CommonIO for details.
618 cgroup_disable= [KNL] Disable a particular controller
619 Format: {name of the controller(s) to disable}
620 The effects of cgroup_disable=foo are:
621 - foo isn't auto-mounted if you mount all cgroups in
623 - foo isn't visible as an individually mountable
625 {Currently only "memory" controller deal with this and
626 cut the overhead, others just disable the usage. So
627 only cgroup_disable=memory is actually worthy}
629 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
630 Format: { controller[,controller...] | "all" }
631 Like cgroup_disable, but only applies to cgroup v1;
632 the blacklisted controllers remain available in cgroup2.
634 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
636 nosocket -- Disable socket memory accounting.
637 nokmem -- Disable kernel memory accounting.
639 checkreqprot [SELINUX] Set initial checkreqprot flag value.
640 Format: { "0" | "1" }
641 See security/selinux/Kconfig help text.
642 0 -- check protection applied by kernel (includes
643 any implied execute protection).
644 1 -- check protection requested by application.
645 Default value is set via a kernel config option.
646 Value can be changed at runtime via
647 /selinux/checkreqprot.
650 See Documentation/s390/CommonIO for details.
653 Prevents the clock framework from automatically gating
654 clocks that have not been explicitly enabled by a Linux
655 device driver but are enabled in hardware at reset or
656 by the bootloader/firmware. Note that this does not
657 force such clocks to be always-on nor does it reserve
658 those clocks in any way. This parameter is useful for
659 debug and development, but should not be needed on a
660 platform with proper driver support. For more
661 information, see Documentation/clk.txt.
663 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
665 Forces specified clocksource (if available) to be used
666 when calculating gettimeofday(). If specified
667 clocksource is not available, it defaults to PIT.
668 Format: { pit | tsc | cyclone | pmtmr }
670 clocksource= Override the default clocksource
672 Override the default clocksource and use the clocksource
673 with the name specified.
674 Some clocksource names to choose from, depending on
676 [all] jiffies (this is the base, fallback clocksource)
678 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
679 pxa_timer,timer3,32k_counter,timer0_1
681 [X86-32] pit,hpet,tsc;
682 scx200_hrt on Geode; cyclone on IBM x440
690 clocksource.arm_arch_timer.evtstrm=
693 Enable/disable the eventstream feature of the ARM
694 architected timer so that code using WFE-based polling
695 loops can be debugged more effectively on production
698 clearcpuid=BITNUM [X86]
699 Disable CPUID feature X for the kernel. See
700 arch/x86/include/asm/cpufeatures.h for the valid bit
701 numbers. Note the Linux specific bits are not necessarily
702 stable over kernel options, but the vendor specific
704 Also note that user programs calling CPUID directly
705 or using the feature without checking anything
706 will still see it. This just prevents it from
707 being used by the kernel or shown in /proc/cpuinfo.
708 Also note the kernel might malfunction if you disable
711 cma=nn[MG]@[start[MG][-end[MG]]]
713 Sets the size of kernel global memory area for
714 contiguous memory allocations and optionally the
715 placement constraint by the physical address range of
716 memory allocations. A value of 0 disables CMA
717 altogether. For more information, see
718 include/linux/dma-contiguous.h
720 cmo_free_hint= [PPC] Format: { yes | no }
721 Specify whether pages are marked as being inactive
722 when they are freed. This is used in CMO environments
723 to determine OS memory pressure for page stealing by
727 coherent_pool=nn[KMG] [ARM,KNL]
728 Sets the size of memory pool for coherent, atomic dma
729 allocations, by default set to 256K.
731 code_bytes [X86] How many bytes of object code to print
736 com20020= [HW,NET] ARCnet - COM20020 chipset
738 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
740 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
744 ARCnet - COM90xx chipset (memory-mapped buffers)
745 Format: <io>[,<irq>[,<memstart>]]
747 condev= [HW,S390] console device
750 console= [KNL] Output console device and options.
752 tty<n> Use the virtual console device <n>.
756 Use the specified serial port. The options are of
757 the form "bbbbpnf", where "bbbb" is the baud rate,
758 "p" is parity ("n", "o", or "e"), "n" is number of
759 bits, and "f" is flow control ("r" for RTS or
760 omit it). Default is "9600n8".
762 See Documentation/serial-console.txt for more
764 Documentation/networking/netconsole.txt for an
767 uart[8250],io,<addr>[,options]
768 uart[8250],mmio,<addr>[,options]
769 uart[8250],mmio16,<addr>[,options]
770 uart[8250],mmio32,<addr>[,options]
771 uart[8250],0x<addr>[,options]
772 Start an early, polled-mode console on the 8250/16550
773 UART at the specified I/O port or MMIO address,
774 switching to the matching ttyS device later.
775 MMIO inter-register address stride is either 8-bit
776 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
777 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
778 to be equivalent to 'mmio'. 'options' are specified in
779 the same format described for ttyS above; if unspecified,
780 the h/w is not re-initialized.
782 hvc<n> Use the hypervisor console device <n>. This is for
783 both Xen and PowerPC hypervisors.
785 If the device connected to the port is not a TTY but a braille
786 device, prepend "brl," before the device type, for instance
788 For now, only VisioBraille is supported.
790 consoleblank= [KNL] The console blank (screen saver) timeout in
791 seconds. Defaults to 10*60 = 10mins. A value of 0
792 disables the blank timer.
795 [KNL] Change the default value for
796 /proc/<pid>/coredump_filter.
797 See also Documentation/filesystems/proc.txt.
799 cpuidle.off=1 [CPU_IDLE]
800 disable the cpuidle sub-system
803 [X86] Delay for N microsec between assert and de-assert
804 of APIC INIT to start processors. This delay occurs
805 on every CPU online, such as boot, and resume from suspend.
808 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
810 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
812 crashkernel=size[KMG][@offset[KMG]]
813 [KNL] Using kexec, Linux can switch to a 'crash kernel'
814 upon panic. This parameter reserves the physical
815 memory region [offset, offset + size] for that kernel
816 image. If '@offset' is omitted, then a suitable offset
817 is selected automatically. Check
818 Documentation/kdump/kdump.txt for further details.
820 crashkernel=range1:size1[,range2:size2,...][@offset]
821 [KNL] Same as above, but depends on the memory
822 in the running system. The syntax of range is
823 start-[end] where start and end are both
824 a memory unit (amount[KMG]). See also
825 Documentation/kdump/kdump.txt for an example.
827 crashkernel=size[KMG],high
828 [KNL, x86_64] range could be above 4G. Allow kernel
829 to allocate physical memory region from top, so could
830 be above 4G if system have more than 4G ram installed.
831 Otherwise memory region will be allocated below 4G, if
833 It will be ignored if crashkernel=X is specified.
834 crashkernel=size[KMG],low
835 [KNL, x86_64] range under 4G. When crashkernel=X,high
836 is passed, kernel could allocate physical memory region
837 above 4G, that cause second kernel crash on system
838 that require some amount of low memory, e.g. swiotlb
839 requires at least 64M+32K low memory, also enough extra
840 low memory is needed to make sure DMA buffers for 32-bit
841 devices won't run out. Kernel would try to allocate at
842 at least 256M below 4G automatically.
843 This one let user to specify own low range under 4G
844 for second kernel instead.
845 0: to disable low allocation.
846 It will be ignored when crashkernel=X,high is not used
847 or memory reserved is below 4G.
850 [KNL] Disable crypto self-tests
855 cs89x0_media= [HW,NET]
856 Format: { rj45 | aui | bnc }
859 See header of drivers/s390/block/dasd_devmap.c.
861 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
862 (one device per port)
863 Format: <port#>,<type>
864 See also Documentation/input/joystick-parport.txt
866 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
867 time. See Documentation/dynamic-debug-howto.txt for
868 details. Deprecated, see dyndbg.
870 debug [KNL] Enable kernel debugging (events log level).
873 [KNL] verbose self-tests
875 Print debugging info while doing the locking API
877 We default to 0 (no extra messages), setting it to
878 1 will print _a lot_ more information - normally
879 only useful to kernel developers.
881 debug_objects [KNL] Enable object debugging
884 [KNL] Disable object debugging
886 debug_guardpage_minorder=
887 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
888 parameter allows control of the order of pages that will
889 be intentionally kept free (and hence protected) by the
890 buddy allocator. Bigger value increase the probability
891 of catching random memory corruption, but reduce the
892 amount of memory for normal system use. The maximum
893 possible value is MAX_ORDER/2. Setting this parameter
894 to 1 or 2 should be enough to identify most random
895 memory corruption problems caused by bugs in kernel or
896 driver code when a CPU writes to (or reads from) a
897 random memory location. Note that there exists a class
898 of memory corruptions problems caused by buggy H/W or
899 F/W or by drivers badly programing DMA (basically when
900 memory is written at bus level and the CPU MMU is
901 bypassed) which are not detectable by
902 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
903 tracking down these problems.
906 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
907 parameter enables the feature at boot time. In
908 default, it is disabled. We can avoid allocating huge
909 chunk of memory for debug pagealloc if we don't enable
910 it at boot time and the system will work mostly same
911 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
912 on: enable the feature
914 debugpat [X86] Enable PAT debugging
916 decnet.addr= [HW,NET]
917 Format: <area>[,<node>]
918 See also Documentation/networking/decnet.txt.
921 [same as hugepagesz=] The size of the default
922 HugeTLB page size. This is the size represented by
923 the legacy /proc/ hugepages APIs, used for SHM, and
924 default size when mounting hugetlbfs filesystems.
925 Defaults to the default architecture's huge page size
929 Set number of hash buckets for dentry cache.
932 See Documentation/networking/ipv6.txt.
934 disable_cpu_apicid= [X86,APIC,SMP]
936 The number of initial APIC ID for the
937 corresponding CPU to be disabled at boot,
938 mostly used for the kdump 2nd kernel to
939 disable BSP to wake up multiple CPUs without
940 causing system reset or hang due to sending
943 disable_ddw [PPC/PSERIES]
944 Disable Dynamic DMA Window support. Use this if
945 to workaround buggy firmware.
948 See Documentation/networking/ipv6.txt.
950 disable_mtrr_cleanup [X86]
951 The kernel tries to adjust MTRR layout from continuous
952 to discrete, to make X server driver able to add WB
953 entry later. This parameter disables that.
955 disable_mtrr_trim [X86, Intel and AMD only]
956 By default the kernel will trim any uncacheable
957 memory out of your available memory pool based on
958 MTRR settings. This parameter disables that behavior,
959 possibly causing your machine to run very slowly.
961 disable_timer_pin_1 [X86]
962 Disable PIN 1 of APIC timer
963 Can be useful to work around chipset bugs.
965 dis_ucode_ldr [X86] Disable the microcode loader.
967 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
968 this option disables the debugging code at boot.
970 dma_debug_entries=<number>
971 This option allows to tune the number of preallocated
972 entries for DMA-API debugging code. One entry is
973 required per DMA-API allocation. Use this if the
974 DMA-API debugging code disables itself because the
975 architectural default is too low.
977 dma_debug_driver=<driver_name>
978 With this option the DMA-API debugging driver
979 filter feature can be enabled at boot time. Just
980 pass the driver to filter for as the parameter.
981 The filter can be disabled or changed to another
982 driver later using sysfs.
984 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
985 Broken monitors, graphic adapters, KVMs and EDIDless
986 panels may send no or incorrect EDID data sets.
987 This parameter allows to specify an EDID data sets
988 in the /lib/firmware directory that are used instead.
989 Generic built-in EDID data sets are used, if one of
990 edid/1024x768.bin, edid/1280x1024.bin,
991 edid/1680x1050.bin, or edid/1920x1080.bin is given
992 and no file with the same name exists. Details and
993 instructions how to build your own EDID data are
994 available in Documentation/EDID/HOWTO.txt. An EDID
995 data set will only be used for a particular connector,
996 if its name and a colon are prepended to the EDID
997 name. Each connector may use a unique EDID data
998 set by separating the files with a comma. An EDID
999 data set with no connector name will be used for
1000 any connectors not explicitly specified.
1004 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1005 module.dyndbg[="val"]
1006 Enable debug messages at boot time. See
1007 Documentation/dynamic-debug-howto.txt for details.
1009 nompx [X86] Disables Intel Memory Protection Extensions.
1010 See Documentation/x86/intel_mpx.txt for more
1011 information about the feature.
1013 nopku [X86] Disable Memory Protection Keys CPU feature found
1017 on enable eager fpu restore
1018 off disable eager fpu restore
1019 auto selects the default scheme, which automatically
1020 enables eagerfpu restore for xsaveopt.
1022 module.async_probe [KNL]
1023 Enable asynchronous probe on this module.
1025 early_ioremap_debug [KNL]
1026 Enable debug messages in early_ioremap support. This
1027 is useful for tracking down temporary early mappings
1028 which are not unmapped.
1030 earlycon= [KNL] Output early console device and options.
1032 When used with no options, the early console is
1033 determined by the stdout-path property in device
1037 Start an early, polled-mode console on a cadence serial
1038 port at the specified address. The cadence serial port
1039 must already be setup and configured. Options are not
1042 uart[8250],io,<addr>[,options]
1043 uart[8250],mmio,<addr>[,options]
1044 uart[8250],mmio32,<addr>[,options]
1045 uart[8250],mmio32be,<addr>[,options]
1046 uart[8250],0x<addr>[,options]
1047 Start an early, polled-mode console on the 8250/16550
1048 UART at the specified I/O port or MMIO address.
1049 MMIO inter-register address stride is either 8-bit
1050 (mmio) or 32-bit (mmio32 or mmio32be).
1051 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1052 to be equivalent to 'mmio'. 'options' are specified
1053 in the same format described for "console=ttyS<n>"; if
1054 unspecified, the h/w is not initialized.
1058 Start an early, polled-mode console on a pl011 serial
1059 port at the specified address. The pl011 serial port
1060 must already be setup and configured. Options are not
1061 yet supported. If 'mmio32' is specified, then only
1062 the driver will use only 32-bit accessors to read/write
1063 the device registers.
1066 Start an early, polled-mode console on a meson serial
1067 port at the specified address. The serial port must
1068 already be setup and configured. Options are not yet
1072 Start an early, polled-mode console on an msm serial
1073 port at the specified address. The serial port
1074 must already be setup and configured. Options are not
1077 msm_serial_dm,<addr>
1078 Start an early, polled-mode console on an msm serial
1079 dm port at the specified address. The serial port
1080 must already be setup and configured. Options are not
1083 smh Use ARM semihosting calls for early console.
1091 Use early console provided by serial driver available
1092 on Samsung SoCs, requires selecting proper type and
1093 a correct base address of the selected UART port. The
1094 serial port must already be setup and configured.
1095 Options are not yet supported.
1099 Use early console provided by Freescale LP UART driver
1100 found on Freescale Vybrid and QorIQ LS1021A processors.
1101 A valid base address must be provided, and the serial
1102 port must already be setup and configured.
1104 armada3700_uart,<addr>
1105 Start an early, polled-mode console on the
1106 Armada 3700 serial port at the specified
1107 address. The serial port must already be setup
1108 and configured. Options are not yet supported.
1110 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1114 earlyprintk=serial[,ttySn[,baudrate]]
1115 earlyprintk=serial[,0x...[,baudrate]]
1116 earlyprintk=ttySn[,baudrate]
1117 earlyprintk=dbgp[debugController#]
1118 earlyprintk=pciserial,bus:device.function[,baudrate]
1120 earlyprintk is useful when the kernel crashes before
1121 the normal console is initialized. It is not enabled by
1122 default because it has some cosmetic problems.
1124 Append ",keep" to not disable it when the real console
1127 Only one of vga, efi, serial, or usb debug port can
1130 Currently only ttyS0 and ttyS1 may be specified by
1131 name. Other I/O ports may be explicitly specified
1132 on some architectures (x86 and arm at least) by
1133 replacing ttySn with an I/O port address, like this:
1134 earlyprintk=serial,0x1008,115200
1135 You can find the port for a given device in
1136 /proc/tty/driver/serial:
1137 2: uart:ST16650V2 port:00001008 irq:18 ...
1139 Interaction with the standard serial driver is not
1142 The VGA and EFI output is eventually overwritten by
1145 The xen output can only be used by Xen PV guests.
1147 edac_report= [HW,EDAC] Control how to report EDAC event
1148 Format: {"on" | "off" | "force"}
1149 on: enable EDAC to report H/W event. May be overridden
1150 by other higher priority error reporting module.
1151 off: disable H/W event reporting through EDAC.
1152 force: enforce the use of EDAC to report H/W event.
1155 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1158 This is designed to be used in conjunction with
1159 the boot argument: earlyprintk=vga
1162 Format: {"off" | "on" | "skip[mbr]"}
1165 Format: { "old_map", "nochunk", "noruntime", "debug" }
1166 old_map [X86-64]: switch to the old ioremap-based EFI
1167 runtime services mapping. 32-bit still uses this one by
1169 nochunk: disable reading files in "chunks" in the EFI
1170 boot stub, as chunking can cause problems with some
1171 firmware implementations.
1172 noruntime : disable EFI runtime services support
1173 debug: enable misc debug output
1175 efi_no_storage_paranoia [EFI; X86]
1176 Using this parameter you can use more than 50% of
1177 your efi variable storage. Use this parameter only if
1178 you are really sure that your UEFI does sane gc and
1179 fulfills the spec otherwise your board may brick.
1181 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1182 Add arbitrary attribute to specific memory range by
1183 updating original EFI memory map.
1184 Region of memory which aa attribute is added to is
1186 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1187 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1188 attribute is added to range 0x100000000-0x180000000 and
1189 0x10a0000000-0x1120000000.
1191 Using this parameter you can do debugging of EFI memmap
1192 related feature. For example, you can do debugging of
1193 Address Range Mirroring feature even if your box
1196 eisa_irq_edge= [PARISC,HW]
1197 See header of drivers/parisc/eisa.c.
1200 See comment before function elanfreq_setup() in
1201 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1204 Format: {"cfq" | "deadline" | "noop"}
1205 See Documentation/block/cfq-iosched.txt and
1206 Documentation/block/deadline-iosched.txt for details.
1208 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1209 Specifies physical address of start of kernel core
1210 image elf header and optionally the size. Generally
1211 kexec loader will pass this option to capture kernel.
1212 See Documentation/kdump/kdump.txt for details.
1214 enable_mtrr_cleanup [X86]
1215 The kernel tries to adjust MTRR layout from continuous
1216 to discrete, to make X server driver able to add WB
1217 entry later. This parameter enables that.
1219 enable_timer_pin_1 [X86]
1220 Enable PIN 1 of APIC timer
1221 Can be useful to work around chipset bugs
1222 (in particular on some ATI chipsets).
1223 The kernel tries to set a reasonable default.
1225 enforcing [SELINUX] Set initial enforcing status.
1227 See security/selinux/Kconfig help text.
1228 0 -- permissive (log only, no denials).
1229 1 -- enforcing (deny and log).
1231 Value can be changed at runtime via /selinux/enforce.
1234 Disable Error Record Serialization Table (ERST)
1237 ether= [HW,NET] Ethernet cards parameters
1238 This option is obsoleted by the "netdev=" option, which
1239 has equivalent usage. See its documentation for details.
1243 Permit 'security.evm' to be updated regardless of
1244 current integrity status.
1248 fail_make_request=[KNL]
1249 General fault injection mechanism.
1250 Format: <interval>,<probability>,<space>,<times>
1251 See also Documentation/fault-injection/.
1254 See Documentation/blockdev/floppy.txt.
1256 force_pal_cache_flush
1257 [IA-64] Avoid check_sal_cache_flush which may hang on
1258 buggy SAL_CACHE_FLUSH implementations. Using this
1259 parameter will force ia64_sal_cache_flush to call
1260 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1263 Forcefully enable Physical Address Extension (PAE).
1264 Many Pentium M systems disable PAE but may have a
1265 functionally usable PAE implementation.
1266 Warning: use of this parameter will taint the kernel
1267 and may cause unknown problems.
1270 [FTRACE] will set and start the specified tracer
1271 as early as possible in order to facilitate early
1274 ftrace_dump_on_oops[=orig_cpu]
1275 [FTRACE] will dump the trace buffers on oops.
1276 If no parameter is passed, ftrace will dump
1277 buffers of all CPUs, but if you pass orig_cpu, it will
1278 dump only the buffer of the CPU that triggered the
1281 ftrace_filter=[function-list]
1282 [FTRACE] Limit the functions traced by the function
1283 tracer at boot up. function-list is a comma separated
1284 list of functions. This list can be changed at run
1285 time by the set_ftrace_filter file in the debugfs
1288 ftrace_notrace=[function-list]
1289 [FTRACE] Do not trace the functions specified in
1290 function-list. This list can be changed at run time
1291 by the set_ftrace_notrace file in the debugfs
1294 ftrace_graph_filter=[function-list]
1295 [FTRACE] Limit the top level callers functions traced
1296 by the function graph tracer at boot up.
1297 function-list is a comma separated list of functions
1298 that can be changed at run time by the
1299 set_graph_function file in the debugfs tracing directory.
1301 ftrace_graph_notrace=[function-list]
1302 [FTRACE] Do not trace from the functions specified in
1303 function-list. This list is a comma separated list of
1304 functions that can be changed at run time by the
1305 set_graph_notrace file in the debugfs tracing directory.
1308 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1309 support via parallel port (up to 5 devices per port)
1310 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1311 See also Documentation/input/joystick-parport.txt
1315 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1319 gcov_persist= [GCOV] When non-zero (default), profiling data for
1320 kernel modules is saved and remains accessible via
1321 debugfs, even when the module is unloaded/reloaded.
1322 When zero, profiling data is discarded and associated
1323 debugfs files are removed at module unload time.
1325 gpt [EFI] Forces disk with valid GPT signature but
1326 invalid Protective MBR to be treated as GPT. If the
1327 primary GPT is corrupted, it enables the backup/alternate
1328 GPT to be used instead.
1330 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1331 the "Enable 0" bit of the configuration register.
1334 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1335 the "Enable 0" bit of the configuration register.
1338 grcan.select= [HW] Select which physical interface to use.
1341 grcan.txsize= [HW] Sets the size of the tx buffer.
1342 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1344 grcan.rxsize= [HW] Sets the size of the rx buffer.
1345 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1348 hardlockup_all_cpu_backtrace=
1349 [KNL] Should the hard-lockup detector generate
1350 backtraces on all cpus.
1353 hashdist= [KNL,NUMA] Large hashes allocated during boot
1354 are distributed across NUMA nodes. Defaults on
1355 for 64-bit NUMA, off otherwise.
1356 Format: 0 | 1 (for off | on)
1358 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1360 hd= [EIDE] (E)IDE hard drive subsystem geometry
1361 Format: <cyl>,<head>,<sect>
1364 Disable Hardware Error Source Table (HEST) support;
1365 corresponding firmware-first mode error processing
1366 logic will be disabled.
1368 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1369 size of <nn>. This works even on boxes that have no
1370 highmem otherwise. This also works to reduce highmem
1371 size on bigger boxes.
1373 highres= [KNL] Enable/disable high resolution timer mode.
1374 Valid parameters: "on", "off"
1378 See Documentation/isdn/README.HiSax.
1382 hpet= [X86-32,HPET] option to control HPET usage
1383 Format: { enable (default) | disable | force |
1385 disable: disable HPET and use PIT instead
1386 force: allow force enabled of undocumented chips (ICH4,
1388 verbose: show contents of HPET registers during setup
1390 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1391 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1393 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1394 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1395 On x86-64 and powerpc, this option can be specified
1396 multiple times interleaved with hugepages= to reserve
1397 huge pages of different sizes. Valid pages sizes on
1398 x86-64 are 2M (when the CPU supports "pse") and 1G
1399 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1401 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1402 terminal devices. Valid values: 0..8
1403 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1404 If specified, z/VM IUCV HVC accepts connections
1405 from listed z/VM user IDs only.
1407 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1408 hardware thread id mappings.
1409 Format: <cpu>:<hwthread>
1412 Do not unregister boot console at start. This is only
1413 useful for debugging when something happens in the window
1414 between unregistering the boot console and initializing
1417 i2c_bus= [HW] Override the default board specific I2C bus speed
1418 or register an additional I2C bus that is not
1419 registered from board initialization code.
1423 i8042.debug [HW] Toggle i8042 debug mode
1424 i8042.unmask_kbd_data
1425 [HW] Enable printing of interrupt data from the KBD port
1426 (disabled by default, and as a pre-condition
1427 requires that i8042.debug=1 be enabled)
1428 i8042.direct [HW] Put keyboard port into non-translated mode
1429 i8042.dumbkbd [HW] Pretend that controller can only read data from
1430 keyboard and cannot control its state
1431 (Don't attempt to blink the leds)
1432 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1433 i8042.nokbd [HW] Don't check/create keyboard port
1434 i8042.noloop [HW] Disable the AUX Loopback command while probing
1436 i8042.nomux [HW] Don't check presence of an active multiplexing
1438 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1440 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1441 i8042.reset [HW] Reset the controller during init and cleanup
1442 i8042.unlock [HW] Unlock (ignore) the keylock
1443 i8042.kbdreset [HW] Reset device connected to KBD port
1447 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1448 indicates that the driver is running on unsupported
1450 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1451 does not match list of supported models.
1453 [HW] Report power status in /proc/i8k
1454 (disabled by default)
1455 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1458 i915.invert_brightness=
1459 [DRM] Invert the sense of the variable that is used to
1460 set the brightness of the panel backlight. Normally a
1461 brightness value of 0 indicates backlight switched off,
1462 and the maximum of the brightness value sets the backlight
1463 to maximum brightness. If this parameter is set to 0
1464 (default) and the machine requires it, or this parameter
1465 is set to 1, a brightness value of 0 sets the backlight
1466 to maximum brightness, and the maximum of the brightness
1467 value switches the backlight off.
1468 -1 -- never invert brightness
1469 0 -- machine default
1470 1 -- force brightness inversion
1473 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1475 ide-core.nodma= [HW] (E)IDE subsystem
1476 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1477 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1478 .cdrom .chs .ignore_cable are additional options
1479 See Documentation/ide/ide.txt.
1481 ide-generic.probe-mask= [HW] (E)IDE subsystem
1483 Probe mask for legacy ISA IDE ports. Depending on
1484 platform up to 6 ports are supported, enabled by
1485 setting corresponding bits in the mask to 1. The
1486 default value is 0x0, which has a special meaning.
1487 On systems that have PCI, it triggers scanning the
1488 PCI bus for the first and the second port, which
1489 are then probed. On systems without PCI the value
1490 of 0x0 enables probing the two first ports as if it
1493 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1494 Claim all unknown PCI IDE storage controllers.
1497 Format: idle=poll, idle=halt, idle=nomwait
1498 Poll forces a polling idle loop that can slightly
1499 improve the performance of waking up a idle CPU, but
1500 will use a lot of power and make the system run hot.
1502 idle=halt: Halt is forced to be used for CPU idle.
1503 In such case C2/C3 won't be used again.
1504 idle=nomwait: Disable mwait for CPU C-states
1506 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1507 Format: { strict | legacy | 2008 | relaxed }
1510 Choose which programs will be accepted for execution
1511 based on the IEEE 754 NaN encoding(s) supported by
1512 the FPU and the NaN encoding requested with the value
1513 of an ELF file header flag individually set by each
1514 binary. Hardware implementations are permitted to
1515 support either or both of the legacy and the 2008 NaN
1518 Available settings are as follows:
1519 strict accept binaries that request a NaN encoding
1520 supported by the FPU
1521 legacy only accept legacy-NaN binaries, if supported
1523 2008 only accept 2008-NaN binaries, if supported
1525 relaxed accept any binaries regardless of whether
1526 supported by the FPU
1528 The FPU emulator is always able to support both NaN
1529 encodings, so if no FPU hardware is present or it has
1530 been disabled with 'nofpu', then the settings of
1531 'legacy' and '2008' strap the emulator accordingly,
1532 'relaxed' straps the emulator for both legacy-NaN and
1533 2008-NaN, whereas 'strict' enables legacy-NaN only on
1534 legacy processors and both NaN encodings on MIPS32 or
1537 The setting for ABS.fmt/NEG.fmt instruction execution
1538 mode generally follows that for the NaN encoding,
1539 except where unsupported by hardware.
1541 ignore_loglevel [KNL]
1542 Ignore loglevel setting - this will print /all/
1543 kernel messages to the console. Useful for debugging.
1544 We also add it as printk module parameter, so users
1545 could change it dynamically, usually by
1546 /sys/module/printk/parameters/ignore_loglevel.
1549 Ignore RLIMIT_DATA setting for data mappings,
1550 print warning at first misuse. Can be changed via
1551 /sys/module/kernel/parameters/ignore_rlimit_data.
1553 ihash_entries= [KNL]
1554 Set number of hash buckets for inode cache.
1556 ima_appraise= [IMA] appraise integrity measurements
1557 Format: { "off" | "enforce" | "fix" | "log" }
1560 ima_appraise_tcb [IMA]
1561 The builtin appraise policy appraises all files
1565 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1569 The list of supported hash algorithms is defined
1570 in crypto/hash_info.h.
1573 The builtin measurement policy to load during IMA
1574 setup. Specyfing "tcb" as the value, measures all
1575 programs exec'd, files mmap'd for exec, and all files
1576 opened with the read mode bit set by either the
1577 effective uid (euid=0) or uid=0.
1580 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1581 Load a policy which meets the needs of the Trusted
1582 Computing Base. This means IMA will measure all
1583 programs exec'd, files mmap'd for exec, and all files
1584 opened for read by uid=0.
1587 Select one of defined IMA measurements template formats.
1588 Formats: { "ima" | "ima-ng" | "ima-sig" }
1592 [IMA] Define a custom template format.
1593 Format: { "field1|...|fieldN" }
1595 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1596 Format: <min_file_size>
1597 Set the minimal file size for using asynchronous hash.
1598 If left unspecified, ahash usage is disabled.
1600 ahash performance varies for different data sizes on
1601 different crypto accelerators. This option can be used
1602 to achieve the best performance for a particular HW.
1604 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1606 Set hashing buffer size. Default: 4k.
1608 ahash performance varies for different chunk sizes on
1609 different crypto accelerators. This option can be used
1610 to achieve best performance for particular HW.
1614 Run specified binary instead of /sbin/init as init
1617 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1618 for working out where the kernel is dying during
1621 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1622 initcall functions. Useful for debugging built-in
1623 modules and initcalls.
1625 initrd= [BOOT] Specify the location of the initial ramdisk
1627 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1630 int_pln_enable [x86] Enable power limit notification interrupt
1632 integrity_audit=[IMA]
1633 Format: { "0" | "1" }
1634 0 -- basic integrity auditing messages. (Default)
1635 1 -- additional integrity auditing messages.
1637 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1639 Enable intel iommu driver.
1641 Disable intel iommu driver.
1642 igfx_off [Default Off]
1643 By default, gfx is mapped as normal device. If a gfx
1644 device has a dedicated DMAR unit, the DMAR unit is
1645 bypassed by not enabling DMAR with this option. In
1646 this case, gfx device will use physical address for
1649 With this option iommu will not optimize to look
1650 for io virtual address below 32-bit forcing dual
1651 address cycle on pci bus for cards supporting greater
1652 than 32-bit addressing. The default is to look
1653 for translation below 32-bit and if not available
1654 then look in the higher range.
1655 strict [Default Off]
1656 With this option on every unmap_single operation will
1657 result in a hardware IOTLB flush operation as opposed
1658 to batching them for performance.
1659 sp_off [Default Off]
1660 By default, super page will be supported if Intel IOMMU
1661 has the capability. With this option, super page will
1663 ecs_off [Default Off]
1664 By default, extended context tables will be supported if
1665 the hardware advertises that it has support both for the
1666 extended tables themselves, and also PASID support. With
1667 this option set, extended tables will not be used even
1668 on hardware which claims to support them.
1670 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1671 0 disables intel_idle and fall back on acpi_idle.
1672 1 to 6 specify maximum depth of C-state.
1676 Do not enable intel_pstate as the default
1677 scaling driver for the supported processors
1679 Enable intel_pstate on systems that prohibit it by default
1680 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1681 instead of acpi-cpufreq may disable platform features, such
1682 as thermal controls and power capping, that rely on ACPI
1683 P-States information being indicated to OSPM and therefore
1684 should be used with caution. This option does not work with
1685 processors that aren't supported by the intel_pstate driver
1686 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1688 Do not enable hardware P state control (HWP)
1691 Only load intel_pstate on systems which support
1692 hardware P state control (HWP) if available.
1694 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1695 Description Table, specifies preferred power management
1696 profile as "Enterprise Server" or "Performance Server",
1697 then this feature is turned on by default.
1699 intremap= [X86-64, Intel-IOMMU]
1700 on enable Interrupt Remapping (default)
1701 off disable Interrupt Remapping
1702 nosid disable Source ID checking
1704 BIOS x2APIC opt-out request will be ignored
1705 nopost disable Interrupt Posting
1707 iomem= Disable strict checking of access to MMIO memory
1708 strict regions from userspace.
1723 nobypass [PPC/POWERNV]
1724 Disable IOMMU bypass, using IOMMU for PCI devices.
1727 io7= [HW] IO7 for Marvel based alpha systems
1728 See comment before marvel_specify_io7 in
1729 arch/alpha/kernel/core_marvel.c.
1731 io_delay= [X86] I/O delay method
1733 Standard port 0x80 based delay
1735 Alternate port 0xed based delay (needed on some systems)
1737 Simple two microseconds delay
1742 See Documentation/filesystems/nfs/nfsroot.txt.
1744 irqaffinity= [SMP] Set the default irq affinity mask
1746 <cpu number>,...,<cpu number>
1748 <cpu number>-<cpu number>
1749 (must be a positive range in ascending order)
1751 <cpu number>,...,<cpu number>-<cpu number>
1754 When an interrupt is not handled search all handlers
1755 for it. Intended to get systems with badly broken
1759 When an interrupt is not handled search all handlers
1760 for it. Also check all handlers each timer
1761 interrupt. Intended to get systems with badly broken
1765 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1767 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1769 <cpu number>,...,<cpu number>
1771 <cpu number>-<cpu number>
1772 (must be a positive range in ascending order)
1774 <cpu number>,...,<cpu number>-<cpu number>
1776 This option can be used to specify one or more CPUs
1777 to isolate from the general SMP balancing and scheduling
1778 algorithms. You can move a process onto or off an
1779 "isolated" CPU via the CPU affinity syscalls or cpuset.
1780 <cpu number> begins at 0 and the maximum value is
1781 "number of CPUs in system - 1".
1783 This option is the preferred way to isolate CPUs. The
1784 alternative -- manually setting the CPU mask of all
1785 tasks in the system -- can cause problems and
1786 suboptimal load balancer performance.
1790 ivrs_ioapic [HW,X86_64]
1791 Provide an override to the IOAPIC-ID<->DEVICE-ID
1792 mapping provided in the IVRS ACPI table. For
1793 example, to map IOAPIC-ID decimal 10 to
1794 PCI device 00:14.0 write the parameter as:
1795 ivrs_ioapic[10]=00:14.0
1797 ivrs_hpet [HW,X86_64]
1798 Provide an override to the HPET-ID<->DEVICE-ID
1799 mapping provided in the IVRS ACPI table. For
1800 example, to map HPET-ID decimal 0 to
1801 PCI device 00:14.0 write the parameter as:
1802 ivrs_hpet[0]=00:14.0
1804 ivrs_acpihid [HW,X86_64]
1805 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1806 mapping provided in the IVRS ACPI table. For
1807 example, to map UART-HID:UID AMD0020:0 to
1808 PCI device 00:14.5 write the parameter as:
1809 ivrs_acpihid[00:14.5]=AMD0020:0
1811 js= [HW,JOY] Analog joystick
1812 See Documentation/input/joystick.txt.
1815 Enable/disable kernel and module base offset ASLR
1816 (Address Space Layout Randomization) if built into
1817 the kernel. When CONFIG_HIBERNATION is selected,
1818 kASLR is disabled by default. When kASLR is enabled,
1819 hibernation will be disabled.
1823 kernelcore= [KNL,X86,IA-64,PPC]
1824 Format: nn[KMGTPE] | "mirror"
1826 specifies the amount of memory usable by the kernel
1827 for non-movable allocations. The requested amount is
1828 spread evenly throughout all nodes in the system. The
1829 remaining memory in each node is used for Movable
1830 pages. In the event, a node is too small to have both
1831 kernelcore and Movable pages, kernelcore pages will
1832 take priority and other nodes will have a larger number
1833 of Movable pages. The Movable zone is used for the
1834 allocation of pages that may be reclaimed or moved
1835 by the page migration subsystem. This means that
1836 HugeTLB pages may not be allocated from this zone.
1837 Note that allocations like PTEs-from-HighMem still
1838 use the HighMem zone if it exists, and the Normal
1839 zone if it does not.
1841 Instead of specifying the amount of memory (nn[KMGTPE]),
1842 you can specify "mirror" option. In case "mirror"
1843 option is specified, mirrored (reliable) memory is used
1844 for non-movable allocations and remaining memory is used
1845 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1846 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1849 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1850 Format: <Controller#>[,poll interval]
1851 The controller # is the number of the ehci usb debug
1852 port as it is probed via PCI. The poll interval is
1853 optional and is the number seconds in between
1854 each poll cycle to the debug port in case you need
1855 the functionality for interrupting the kernel with
1856 gdb or control-c on the dbgp connection. When
1857 not using this parameter you use sysrq-g to break into
1858 the kernel debugger.
1860 kgdboc= [KGDB,HW] kgdb over consoles.
1861 Requires a tty driver that supports console polling,
1862 or a supported polling keyboard driver (non-usb).
1863 Serial only format: <serial_device>[,baud]
1864 keyboard only format: kbd
1865 keyboard and serial format: kbd,<serial_device>[,baud]
1866 Optional Kernel mode setting:
1867 kms, kbd format: kms,kbd
1868 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1870 kgdbwait [KGDB] Stop kernel execution and enter the
1871 kernel debugger at the earliest opportunity.
1873 kmac= [MIPS] korina ethernet MAC address.
1874 Configure the RouterBoard 532 series on-chip
1875 Ethernet adapter MAC address.
1877 kmemleak= [KNL] Boot-time kmemleak enable/disable
1878 Valid arguments: on, off
1880 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1883 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1884 Valid arguments: 0, 1, 2
1885 kmemcheck=0 (disabled)
1886 kmemcheck=1 (enabled)
1887 kmemcheck=2 (one-shot mode)
1888 Default: 2 (one-shot mode)
1890 kstack=N [X86] Print N words from the kernel stack
1893 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1894 Default is 0 (don't ignore, but inject #GP)
1896 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1900 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1901 Default is 1 (enabled)
1903 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1905 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1907 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1908 (virtualized MMU) support on capable Intel chips.
1909 Default is 1 (enabled)
1911 kvm-intel.emulate_invalid_guest_state=
1912 [KVM,Intel] Enable emulation of invalid guest states
1913 Default is 0 (disabled)
1915 kvm-intel.flexpriority=
1916 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1917 Default is 1 (enabled)
1920 [KVM,Intel] Enable VMX nesting (nVMX).
1921 Default is 0 (disabled)
1923 kvm-intel.unrestricted_guest=
1924 [KVM,Intel] Disable unrestricted guest feature
1925 (virtualized real and unpaged mode) on capable
1926 Intel chips. Default is 1 (enabled)
1928 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1929 feature (tagged TLBs) on capable Intel chips.
1930 Default is 1 (enabled)
1936 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1939 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1940 value for LAPIC timer one-shot implementation. Default
1941 back to the programmable timer unit in the LAPIC.
1943 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1946 libata.dma= [LIBATA] DMA control
1947 libata.dma=0 Disable all PATA and SATA DMA
1948 libata.dma=1 PATA and SATA Disk DMA only
1949 libata.dma=2 ATAPI (CDROM) DMA only
1950 libata.dma=4 Compact Flash DMA only
1951 Combinations also work, so libata.dma=3 enables DMA
1952 for disks and CDROMs, but not CFs.
1954 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1955 libata.ignore_hpa=0 keep BIOS limits (default)
1956 libata.ignore_hpa=1 ignore limits, using full disk
1958 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1962 libata.force= [LIBATA] Force configurations. The format is comma
1963 separated list of "[ID:]VAL" where ID is
1964 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1965 matching port, link or device. Basically, it matches
1966 the ATA ID string printed on console by libata. If
1967 the whole ID part is omitted, the last PORT and DEVICE
1968 values are used. If ID hasn't been specified yet, the
1969 configuration applies to all ports, links and devices.
1971 If only DEVICE is omitted, the parameter applies to
1972 the port and all links and devices behind it. DEVICE
1973 number of 0 either selects the first device or the
1974 first fan-out link behind PMP device. It does not
1975 select the host link. DEVICE number of 15 selects the
1976 host link and device attached to it.
1978 The VAL specifies the configuration to force. As long
1979 as there's no ambiguity shortcut notation is allowed.
1980 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1981 The following configurations can be forced.
1983 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1984 Any ID with matching PORT is used.
1986 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1988 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1989 udma[/][16,25,33,44,66,100,133] notation is also
1992 * [no]ncq: Turn on or off NCQ.
1994 * [no]ncqtrim: Turn off queued DSM TRIM.
1996 * nohrst, nosrst, norst: suppress hard, soft
1999 * rstonce: only attempt one reset during
2000 hot-unplug link recovery
2002 * dump_id: dump IDENTIFY data.
2004 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2006 * disable: Disable this device.
2008 If there are multiple matching configurations changing
2009 the same attribute, the last one is used.
2011 memblock=debug [KNL] Enable memblock debug messages.
2013 load_ramdisk= [RAM] List of ramdisks to load from floppy
2014 See Documentation/blockdev/ramdisk.txt.
2016 lockd.nlm_grace_period=P [NFS] Assign grace period.
2019 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2022 lockd.nlm_timeout=T [NFS] Assign timeout value.
2025 lockd.nlm_udpport=M [NFS] Assign UDP port.
2028 locktorture.nreaders_stress= [KNL]
2029 Set the number of locking read-acquisition kthreads.
2030 Defaults to being automatically set based on the
2031 number of online CPUs.
2033 locktorture.nwriters_stress= [KNL]
2034 Set the number of locking write-acquisition kthreads.
2036 locktorture.onoff_holdoff= [KNL]
2037 Set time (s) after boot for CPU-hotplug testing.
2039 locktorture.onoff_interval= [KNL]
2040 Set time (s) between CPU-hotplug operations, or
2041 zero to disable CPU-hotplug testing.
2043 locktorture.shuffle_interval= [KNL]
2044 Set task-shuffle interval (jiffies). Shuffling
2045 tasks allows some CPUs to go into dyntick-idle
2046 mode during the locktorture test.
2048 locktorture.shutdown_secs= [KNL]
2049 Set time (s) after boot system shutdown. This
2050 is useful for hands-off automated testing.
2052 locktorture.stat_interval= [KNL]
2053 Time (s) between statistics printk()s.
2055 locktorture.stutter= [KNL]
2056 Time (s) to stutter testing, for example,
2057 specifying five seconds causes the test to run for
2058 five seconds, wait for five seconds, and so on.
2059 This tests the locking primitive's ability to
2060 transition abruptly to and from idle.
2062 locktorture.torture_runnable= [BOOT]
2063 Start locktorture running at boot time.
2065 locktorture.torture_type= [KNL]
2066 Specify the locking implementation to test.
2068 locktorture.verbose= [KNL]
2069 Enable additional printk() statements.
2071 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2074 loglevel= All Kernel Messages with a loglevel smaller than the
2075 console loglevel will be printed to the console. It can
2076 also be changed with klogd or other programs. The
2077 loglevels are defined as follows:
2079 0 (KERN_EMERG) system is unusable
2080 1 (KERN_ALERT) action must be taken immediately
2081 2 (KERN_CRIT) critical conditions
2082 3 (KERN_ERR) error conditions
2083 4 (KERN_WARNING) warning conditions
2084 5 (KERN_NOTICE) normal but significant condition
2085 6 (KERN_INFO) informational
2086 7 (KERN_DEBUG) debug-level messages
2088 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2089 in bytes. n must be a power of two and greater
2090 than the minimal size. The minimal size is defined
2091 by LOG_BUF_SHIFT kernel config parameter. There is
2092 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2093 that allows to increase the default size depending on
2094 the number of CPUs. See init/Kconfig for more details.
2096 logo.nologo [FB] Disables display of the built-in Linux logo.
2097 This may be used to provide more screen space for
2098 kernel log messages and is useful when debugging
2099 kernel boot problems.
2101 lp=0 [LP] Specify parallel ports to use, e.g,
2102 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2103 lp=reset first parallel port). 'lp=0' disables the
2104 lp=auto printer driver. 'lp=reset' (which can be
2105 specified in addition to the ports) causes
2106 attached printers to be reset. Using
2107 lp=port1,port2,... specifies the parallel ports
2108 to associate lp devices with, starting with
2109 lp0. A port specification may be 'none' to skip
2110 that lp device, or a parport name such as
2111 'parport0'. Specifying 'lp=auto' instead of a
2112 port specification list means that device IDs
2113 from each port should be examined, to see if
2114 an IEEE 1284-compliant printer is attached; if
2115 so, the driver will manage that printer.
2116 See also header of drivers/char/lp.c.
2119 Sets loops_per_jiffy to given constant, thus avoiding
2120 time-consuming boot-time autodetection (up to 250 ms per
2121 CPU). 0 enables autodetection (default). To determine
2122 the correct value for your kernel, boot with normal
2123 autodetection and see what value is printed. Note that
2124 on SMP systems the preset will be applied to all CPUs,
2125 which is likely to cause problems if your CPUs need
2126 significantly divergent settings. An incorrect value
2127 will cause delays in the kernel to be wrong, leading to
2128 unpredictable I/O errors and other breakage. Although
2129 unlikely, in the extreme case this might damage your
2133 Format: <io>,<irq>,<dma>
2135 machvec= [IA-64] Force the use of a particular machine-vector
2136 (machvec) in a generic kernel.
2137 Example: machvec=hpzx1_swiotlb
2139 machtype= [Loongson] Share the same kernel image file between different
2141 Example: machtype=lemote-yeeloong-2f-7inch
2143 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2144 than or equal to this physical address is ignored.
2146 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2147 should make use of. maxcpus=n : n >= 0 limits the
2148 kernel to using 'n' processors. n=0 is a special case,
2149 it is equivalent to "nosmp", which also disables
2152 max_loop= [LOOP] The number of loop block devices that get
2153 (loop.max_loop) unconditionally pre-created at init time. The default
2154 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2155 of statically allocating a predefined number, loop
2156 devices can be requested on-demand with the
2157 /dev/loop-control interface.
2159 mce [X86-32] Machine Check Exception
2161 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2163 md= [HW] RAID subsystems devices and level
2164 See Documentation/md.txt.
2167 Format: <first>,<last>
2168 Specifies range of consoles to be captured by the MDA.
2170 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2171 Amount of memory to be used when the kernel is not able
2172 to see the whole system memory or for test.
2173 [X86] Work as limiting max address. Use together
2174 with memmap= to avoid physical address space collisions.
2175 Without memmap= PCI devices could be placed at addresses
2176 belonging to unused RAM.
2178 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2182 [KNL,SH] Allow user to override the default size for
2183 per-device physically contiguous DMA buffers.
2185 memhp_default_state=online/offline
2186 [KNL] Set the initial state for the memory hotplug
2187 onlining policy. If not specified, the default value is
2188 set according to the
2189 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2191 See Documentation/memory-hotplug.txt.
2193 memmap=exactmap [KNL,X86] Enable setting of an exact
2194 E820 memory map, as specified by the user.
2195 Such memmap=exactmap lines can be constructed based on
2196 BIOS output or other requirements. See the memmap=nn@ss
2199 memmap=nn[KMG]@ss[KMG]
2200 [KNL] Force usage of a specific region of memory.
2201 Region of memory to be used is from ss to ss+nn.
2203 memmap=nn[KMG]#ss[KMG]
2204 [KNL,ACPI] Mark specific memory as ACPI data.
2205 Region of memory to be marked is from ss to ss+nn.
2207 memmap=nn[KMG]$ss[KMG]
2208 [KNL,ACPI] Mark specific memory as reserved.
2209 Region of memory to be reserved is from ss to ss+nn.
2210 Example: Exclude memory from 0x18690000-0x1869ffff
2211 memmap=64K$0x18690000
2213 memmap=0x10000$0x18690000
2215 memmap=nn[KMG]!ss[KMG]
2216 [KNL,X86] Mark specific memory as protected.
2217 Region of memory to be used, from ss to ss+nn.
2218 The memory region may be marked as e820 type 12 (0xc)
2219 and is NVDIMM or ADR memory.
2221 memory_corruption_check=0/1 [X86]
2222 Some BIOSes seem to corrupt the first 64k of
2223 memory when doing things like suspend/resume.
2224 Setting this option will scan the memory
2225 looking for corruption. Enabling this will
2226 both detect corruption and prevent the kernel
2227 from using the memory being corrupted.
2228 However, its intended as a diagnostic tool; if
2229 repeatable BIOS-originated corruption always
2230 affects the same memory, you can use memmap=
2231 to prevent the kernel from using that memory.
2233 memory_corruption_check_size=size [X86]
2234 By default it checks for corruption in the low
2235 64k, making this memory unavailable for normal
2236 use. Use this parameter to scan for
2237 corruption in more or less memory.
2239 memory_corruption_check_period=seconds [X86]
2240 By default it checks for corruption every 60
2241 seconds. Use this parameter to check at some
2242 other rate. 0 disables periodic checking.
2244 memtest= [KNL,X86,ARM] Enable memtest
2246 default : 0 <disable>
2247 Specifies the number of memtest passes to be
2248 performed. Each pass selects another test
2249 pattern from a given set of patterns. Memtest
2250 fills the memory with this pattern, validates
2251 memory contents and reserves bad memory
2252 regions that are detected.
2254 meye.*= [HW] Set MotionEye Camera parameters
2255 See Documentation/video4linux/meye.txt.
2257 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2258 Multi-Function General Purpose Timers on AMD Geode
2261 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2262 the BIOS has incorrectly applied a workaround. TinyBIOS
2263 version 0.98 is known to be affected, 0.99 fixes the
2264 problem by letting the user disable the workaround.
2268 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2269 physical address is ignored.
2271 mini2440= [ARM,HW,KNL]
2272 Format:[0..2][b][c][t]
2274 MINI2440 configuration specification:
2275 0 - The attached screen is the 3.5" TFT
2276 1 - The attached screen is the 7" TFT
2277 2 - The VGA Shield is attached (1024x768)
2278 Leaving out the screen size parameter will not load
2279 the TFT driver, and the framebuffer will be left
2281 b - Enable backlight. The TFT backlight pin will be
2282 linked to the kernel VESA blanking code and a GPIO
2283 LED. This parameter is not necessary when using the
2285 c - Enable the s3c camera interface.
2286 t - Reserved for enabling touchscreen support. The
2287 touchscreen support is not enabled in the mainstream
2288 kernel as of 2.6.30, a preliminary port can be found
2289 in the "bleeding edge" mini2440 support kernel at
2290 http://repo.or.cz/w/linux-2.6/mini2440.git
2293 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2294 parameter allows control of the logging verbosity for
2295 the additional memory initialisation checks. A value
2296 of 0 disables mminit logging and a level of 4 will
2297 log everything. Information is printed at KERN_DEBUG
2298 so loglevel=8 may also need to be specified.
2301 [KNL] When CONFIG_MODULE_SIG is set, this means that
2302 modules without (valid) signatures will fail to load.
2303 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2304 is always true, so this option does nothing.
2307 [MOUSE] Maximum time between finger touching and
2308 leaving touchpad surface for touch to be considered
2309 a tap and be reported as a left button click (for
2310 touchpads working in absolute mode only).
2312 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2313 reporting absolute coordinates, such as tablets
2314 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2315 reporting absolute coordinates, such as tablets
2317 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2318 is similar to kernelcore except it specifies the
2319 amount of memory used for migratable allocations.
2320 If both kernelcore and movablecore is specified,
2321 then kernelcore will be at *least* the specified
2322 value but may be more. If movablecore on its own
2323 is specified, the administrator must be careful
2324 that the amount of memory usable for all allocations
2327 movable_node [KNL,X86] Boot-time switch to enable the effects
2328 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2330 MTD_Partition= [MTD]
2331 Format: <name>,<region-number>,<size>,<offset>
2333 MTD_Region= [MTD] Format:
2334 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2337 See drivers/mtd/cmdlinepart.c.
2339 multitce=off [PPC] This parameter disables the use of the pSeries
2340 firmware feature for updating multiple TCE entries
2343 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2345 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2347 boundary - index of last SLC block on Flex-OneNAND.
2348 The remaining blocks are configured as MLC blocks.
2349 lock - Configure if Flex-OneNAND boundary should be locked.
2350 Once locked, the boundary cannot be changed.
2351 1 indicates lock status, 0 indicates unlock status.
2354 ARM/S3C2412 JIVE boot control
2356 See arch/arm/mach-s3c2412/mach-jive.c
2358 mtouchusb.raw_coordinates=
2359 [HW] Make the MicroTouch USB driver use raw coordinates
2360 ('y', default) or cooked coordinates ('n')
2362 mtrr_chunk_size=nn[KMG] [X86]
2363 used for mtrr cleanup. It is largest continuous chunk
2364 that could hold holes aka. UC entries.
2366 mtrr_gran_size=nn[KMG] [X86]
2367 Used for mtrr cleanup. It is granularity of mtrr block.
2369 Large value could prevent small alignment from
2372 mtrr_spare_reg_nr=n [X86]
2374 Range: 0,7 : spare reg number
2376 Used for mtrr cleanup. It is spare mtrr entries number.
2377 Set to 2 or more if your graphical card needs more.
2379 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2381 netdev= [NET] Network devices parameters
2382 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2383 Note that mem_start is often overloaded to mean
2384 something different and driver-specific.
2385 This usage is only documented in each driver source
2389 [NETFILTER] Enable connection tracking flow accounting
2390 0 to disable accounting
2391 1 to enable accounting
2394 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2395 See Documentation/filesystems/nfs/nfsroot.txt.
2397 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2398 See Documentation/filesystems/nfs/nfsroot.txt.
2400 nfsrootdebug [NFS] enable nfsroot debugging messages.
2401 See Documentation/filesystems/nfs/nfsroot.txt.
2403 nfs.callback_tcpport=
2404 [NFS] set the TCP port on which the NFSv4 callback
2405 channel should listen.
2408 [NFS] sets the pathname to the program which is used
2409 to update the NFS client cache entries.
2411 nfs.cache_getent_timeout=
2412 [NFS] sets the timeout after which an attempt to
2413 update a cache entry is deemed to have failed.
2415 nfs.idmap_cache_timeout=
2416 [NFS] set the maximum lifetime for idmapper cache
2420 [NFS] enable 64-bit inode numbers.
2421 If zero, the NFS client will fake up a 32-bit inode
2422 number for the readdir() and stat() syscalls instead
2423 of returning the full 64-bit number.
2424 The default is to return 64-bit inode numbers.
2426 nfs.max_session_slots=
2427 [NFSv4.1] Sets the maximum number of session slots
2428 the client will attempt to negotiate with the server.
2429 This limits the number of simultaneous RPC requests
2430 that the client can send to the NFSv4.1 server.
2431 Note that there is little point in setting this
2432 value higher than the max_tcp_slot_table_limit.
2434 nfs.nfs4_disable_idmapping=
2435 [NFSv4] When set to the default of '1', this option
2436 ensures that both the RPC level authentication
2437 scheme and the NFS level operations agree to use
2438 numeric uids/gids if the mount is using the
2439 'sec=sys' security flavour. In effect it is
2440 disabling idmapping, which can make migration from
2441 legacy NFSv2/v3 systems to NFSv4 easier.
2442 Servers that do not support this mode of operation
2443 will be autodetected by the client, and it will fall
2444 back to using the idmapper.
2445 To turn off this behaviour, set the value to '0'.
2447 [NFS4] Specify an additional fixed unique ident-
2448 ification string that NFSv4 clients can insert into
2449 their nfs_client_id4 string. This is typically a
2450 UUID that is generated at system install time.
2452 nfs.send_implementation_id =
2453 [NFSv4.1] Send client implementation identification
2454 information in exchange_id requests.
2455 If zero, no implementation identification information
2457 The default is to send the implementation identification
2460 nfs.recover_lost_locks =
2461 [NFSv4] Attempt to recover locks that were lost due
2462 to a lease timeout on the server. Please note that
2463 doing this risks data corruption, since there are
2464 no guarantees that the file will remain unchanged
2465 after the locks are lost.
2466 If you want to enable the kernel legacy behaviour of
2467 attempting to recover these locks, then set this
2469 The default parameter value of '0' causes the kernel
2470 not to attempt recovery of lost locks.
2472 nfs4.layoutstats_timer =
2473 [NFSv4.2] Change the rate at which the kernel sends
2474 layoutstats to the pNFS metadata server.
2476 Setting this to value to 0 causes the kernel to use
2477 whatever value is the default set by the layout
2478 driver. A non-zero value sets the minimum interval
2479 in seconds between layoutstats transmissions.
2481 nfsd.nfs4_disable_idmapping=
2482 [NFSv4] When set to the default of '1', the NFSv4
2483 server will return only numeric uids and gids to
2484 clients using auth_sys, and will accept numeric uids
2485 and gids from such clients. This is intended to ease
2486 migration from NFSv2/v3.
2488 objlayoutdriver.osd_login_prog=
2489 [NFS] [OBJLAYOUT] sets the pathname to the program which
2490 is used to automatically discover and login into new
2491 osd-targets. Please see:
2492 Documentation/filesystems/pnfs.txt for more explanations
2494 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2495 when a NMI is triggered.
2496 Format: [state][,regs][,debounce][,die]
2498 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2499 Format: [panic,][nopanic,][num]
2501 0 - turn hardlockup detector in nmi_watchdog off
2502 1 - turn hardlockup detector in nmi_watchdog on
2503 When panic is specified, panic when an NMI watchdog
2504 timeout occurs (or 'nopanic' to override the opposite
2505 default). To disable both hard and soft lockup detectors,
2506 please see 'nowatchdog'.
2507 This is useful when you use a panic=... timeout and
2508 need the box quickly up again.
2510 netpoll.carrier_timeout=
2511 [NET] Specifies amount of time (in seconds) that
2512 netpoll should wait for a carrier. By default netpoll
2515 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2516 emulation library even if a 387 maths coprocessor
2520 [HW] Never suspend the console
2521 Disable suspending of consoles during suspend and
2522 hibernate operations. Once disabled, debugging
2523 messages can reach various consoles while the rest
2524 of the system is being put to sleep (ie, while
2525 debugging driver suspend/resume hooks). This may
2526 not work reliably with all consoles, but is known
2527 to work with serial and VGA consoles.
2528 To facilitate more flexible debugging, we also add
2529 console_suspend, a printk module parameter to control
2530 it. Users could use console_suspend (usually
2531 /sys/module/printk/parameters/console_suspend) to
2532 turn on/off it dynamically.
2534 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2535 caches in the slab allocator. Saves per-node memory,
2536 but will impact performance.
2540 noapic [SMP,APIC] Tells the kernel to not make use of any
2541 IOAPICs that may be present in the system.
2543 noautogroup Disable scheduler automatic task group creation.
2545 nobats [PPC] Do not use BATs for mapping kernel lowmem
2546 on "Classic" PPC cores.
2550 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2552 nodelayacct [KNL] Disable per-task delay accounting
2554 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2556 nodsp [SH] Disable hardware DSP at boot time.
2558 noefi Disable EFI runtime services support.
2563 On X86-32 available only on PAE configured kernels.
2564 noexec=on: enable non-executable mappings (default)
2565 noexec=off: disable non-executable mappings
2568 Disable SMAP (Supervisor Mode Access Prevention)
2569 even if it is supported by processor.
2572 Disable SMEP (Supervisor Mode Execution Prevention)
2573 even if it is supported by processor.
2576 This affects only 32-bit executables.
2577 noexec32=on: enable non-executable mappings (default)
2578 read doesn't imply executable mappings
2579 noexec32=off: disable non-executable mappings
2580 read implies executable mappings
2582 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2584 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2585 register save and restore. The kernel will only save
2586 legacy floating-point registers on task switch.
2588 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2590 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2591 Equivalent to smt=1.
2593 noxsave [BUGS=X86] Disables x86 extended register state save
2594 and restore using xsave. The kernel will fallback to
2595 enabling legacy floating-point and sse state.
2597 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2598 register states. The kernel will fall back to use
2599 xsave to save the states. By using this parameter,
2600 performance of saving the states is degraded because
2601 xsave doesn't support modified optimization while
2602 xsaveopt supports it on xsaveopt enabled systems.
2604 noxsaves [X86] Disables xsaves and xrstors used in saving and
2605 restoring x86 extended register state in compacted
2606 form of xsave area. The kernel will fall back to use
2607 xsaveopt and xrstor to save and restore the states
2608 in standard form of xsave area. By using this
2609 parameter, xsave area per process might occupy more
2610 memory on xsaves enabled systems.
2612 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2613 wfi(ARM) instruction doesn't work correctly and not to
2614 use it. This is also useful when using JTAG debugger.
2616 no_file_caps Tells the kernel not to honor file capabilities. The
2617 only way then for a file to be executed with privilege
2618 is to be setuid root or executed by root.
2620 nohalt [IA-64] Tells the kernel not to use the power saving
2621 function PAL_HALT_LIGHT when idle. This increases
2622 power-consumption. On the positive side, it reduces
2623 interrupt wake-up latency, which may improve performance
2624 in certain environments such as networked servers or
2627 nohibernate [HIBERNATION] Disable hibernation and resume.
2629 nohz= [KNL] Boottime enable/disable dynamic ticks
2630 Valid arguments: on, off
2633 nohz_full= [KNL,BOOT]
2634 In kernels built with CONFIG_NO_HZ_FULL=y, set
2635 the specified list of CPUs whose tick will be stopped
2636 whenever possible. The boot CPU will be forced outside
2637 the range to maintain the timekeeping.
2638 The CPUs in this range must also be included in the
2641 noiotrap [SH] Disables trapped I/O port accesses.
2643 noirqdebug [X86-32] Disables the code which attempts to detect and
2644 disable unhandled interrupt sources.
2646 no_timer_check [X86,APIC] Disables the code which tests for
2647 broken timer IRQ sources.
2649 noisapnp [ISAPNP] Disables ISA PnP code.
2651 noinitrd [RAM] Tells the kernel not to load any configured
2654 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2656 [Deprecated - use intremap=off]
2660 noinvpcid [X86] Disable the INVPCID cpu feature.
2662 nojitter [IA-64] Disables jitter checking for ITC timers.
2664 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2666 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2669 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2670 steal time is computed, but won't influence scheduler
2673 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2675 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2677 noltlbs [PPC] Do not use large page/tlb entries for kernel
2678 lowmem mapping on PPC40x and PPC8xx
2680 nomca [IA-64] Disable machine check abort handling
2682 nomce [X86-32] Disable Machine Check Exception
2684 nomfgpt [X86-32] Disable Multi-Function General Purpose
2685 Timer usage (for AMD Geode machines).
2687 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2688 shutdown the other cpus. Instead use the REBOOT_VECTOR
2691 nomodule Disable module load
2693 nopat [X86] Disable PAT (page attribute table extension of
2694 pagetables) support.
2696 norandmaps Don't use address space randomization. Equivalent to
2697 echo 0 > /proc/sys/kernel/randomize_va_space
2699 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2701 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2702 with UP alternatives
2704 nordrand [X86] Disable kernel use of the RDRAND and
2705 RDSEED instructions even if they are supported
2706 by the processor. RDRAND and RDSEED are still
2707 available to user space applications.
2709 noresume [SWSUSP] Disables resume and restores original swap
2712 no-scroll [VGA] Disables scrollback.
2713 This is required for the Braillex ib80-piezo Braille
2714 reader made by F.H. Papenmeier (Germany).
2718 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2720 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2721 and disable the IO APIC. legacy for "maxcpus=0".
2723 nosoftlockup [KNL] Disable the soft-lockup detector.
2725 nosync [HW,M68K] Disables sync negotiation for all devices.
2727 notsc [BUGS=X86-32] Disable Time Stamp Counter
2729 nowatchdog [KNL] Disable both lockup detectors, i.e.
2730 soft-lockup and NMI watchdog (hard-lockup).
2734 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2736 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2737 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2738 Some features depend on CPU0. Known dependencies are:
2739 1. Resume from suspend/hibernate depends on CPU0.
2740 Suspend/hibernate will fail if CPU0 is offline and you
2741 need to online CPU0 before suspend/hibernate.
2742 2. PIC interrupts also depend on CPU0. CPU0 can't be
2743 removed if a PIC interrupt is detected.
2744 It's said poweroff/reboot may depend on CPU0 on some
2745 machines although I haven't seen such issues so far
2746 after CPU0 is offline on a few tested machines.
2747 If the dependencies are under your control, you can
2748 turn on cpu0_hotplug.
2750 nptcg= [IA-64] Override max number of concurrent global TLB
2751 purges which is reported from either PAL_VM_SUMMARY or
2754 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2755 could support. nr_cpus=n : n >= 1 limits the kernel to
2756 supporting 'n' processors. Later in runtime you can not
2757 use hotplug cpu feature to put more cpu back to online.
2758 just like you compile the kernel NR_CPUS=n
2760 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2762 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2763 Allowed values are enable and disable
2765 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2766 one of ['zone', 'node', 'default'] can be specified
2767 This can be set from sysctl after boot.
2768 See Documentation/sysctl/vm.txt for details.
2770 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2771 See Documentation/debugging-via-ohci1394.txt for more
2774 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2775 Rather than timing out after 20 ms if an EC
2776 command is not properly ACKed, override the length
2777 of the timeout. We have interrupts disabled while
2778 waiting for the ACK, so if this is set too high
2779 interrupts *may* be lost!
2781 omap_mux= [OMAP] Override bootloader pin multiplexing.
2782 Format: <mux_mode0.mode_name=value>...
2783 For example, to override I2C bus2:
2784 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2786 oprofile.timer= [HW]
2787 Use timer interrupt instead of performance counters
2789 oprofile.cpu_type= Force an oprofile cpu type
2790 This might be useful if you have an older oprofile
2791 userland or if you want common events.
2792 Format: { arch_perfmon }
2793 arch_perfmon: [X86] Force use of architectural
2794 perfmon on Intel CPUs instead of the
2795 CPU specific event set.
2796 timer: [X86] Force use of architectural NMI
2797 timer mode (see also oprofile.timer
2798 for generic hr timer mode)
2799 [s390] Force legacy basic mode sampling
2800 (report cpu_type "timer")
2802 oops=panic Always panic on oopses. Default is to just kill the
2803 process, but there is a small probability of
2804 deadlocking the machine.
2805 This will also cause panics on machine check exceptions.
2806 Useful together with panic=30 to trigger a reboot.
2809 See Documentation/sound/oss/oss-parameters.txt
2811 page_owner= [KNL] Boot-time page_owner enabling option.
2812 Storage of the information about who allocated
2813 each page is disabled in default. With this switch,
2815 on: enable the feature
2817 page_poison= [KNL] Boot-time parameter changing the state of
2818 poisoning on the buddy allocator.
2819 off: turn off poisoning
2820 on: turn on poisoning
2822 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2823 timeout > 0: seconds before rebooting
2824 timeout = 0: wait forever
2825 timeout < 0: reboot immediately
2828 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2831 crash_kexec_post_notifiers
2832 Run kdump after running panic-notifiers and dumping
2833 kmsg. This only for the users who doubt kdump always
2834 succeeds in any situation.
2835 Note that this also increases risks of kdump failure,
2836 because some panic notifiers can make the crashed
2837 kernel more unstable.
2839 parkbd.port= [HW] Parallel port number the keyboard adapter is
2840 connected to, default is 0.
2842 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2843 0 for XT, 1 for AT (default is AT).
2846 parport= [HW,PPT] Specify parallel ports. 0 disables.
2847 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2848 Use 'auto' to force the driver to use any
2849 IRQ/DMA settings detected (the default is to
2850 ignore detected IRQ/DMA settings because of
2851 possible conflicts). You can specify the base
2852 address, IRQ, and DMA settings; IRQ and DMA
2853 should be numbers, or 'auto' (for using detected
2854 settings on that particular port), or 'nofifo'
2855 (to avoid using a FIFO even if it is detected).
2856 Parallel ports are assigned in the order they
2857 are specified on the command line, starting
2860 parport_init_mode= [HW,PPT]
2861 Configure VIA parallel port to operate in
2862 a specific mode. This is necessary on Pegasos
2863 computer where firmware has no options for setting
2864 up parallel port mode and sets it to spp.
2865 Currently this function knows 686a and 8231 chips.
2866 Format: [spp|ps2|epp|ecp|ecpepp]
2869 Halt all CPUs after the first oops has been printed for
2870 the specified number of seconds. This is to be used if
2871 your oopses keep scrolling off the screen.
2876 See header of drivers/block/paride/pcd.c.
2877 See also Documentation/blockdev/paride.txt.
2879 pci=option[,option...] [PCI] various PCI subsystem options:
2880 earlydump [X86] dump PCI config space before the kernel
2882 off [X86] don't probe for the PCI bus
2883 bios [X86-32] force use of PCI BIOS, don't access
2884 the hardware directly. Use this if your machine
2885 has a non-standard PCI host bridge.
2886 nobios [X86-32] disallow use of PCI BIOS, only direct
2887 hardware access methods are allowed. Use this
2888 if you experience crashes upon bootup and you
2889 suspect they are caused by the BIOS.
2890 conf1 [X86] Force use of PCI Configuration Access
2891 Mechanism 1 (config address in IO port 0xCF8,
2892 data in IO port 0xCFC, both 32-bit).
2893 conf2 [X86] Force use of PCI Configuration Access
2894 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2895 the function, IO port 0xCFA, also 8-bit, sets
2896 bus number. The config space is then accessed
2897 through ports 0xC000-0xCFFF).
2898 See http://wiki.osdev.org/PCI for more info
2899 on the configuration access mechanisms.
2900 noaer [PCIE] If the PCIEAER kernel config parameter is
2901 enabled, this kernel boot option can be used to
2902 disable the use of PCIE advanced error reporting.
2903 nodomains [PCI] Disable support for multiple PCI
2904 root domains (aka PCI segments, in ACPI-speak).
2905 nommconf [X86] Disable use of MMCONFIG for PCI
2907 check_enable_amd_mmconf [X86] check for and enable
2908 properly configured MMIO access to PCI
2909 config space on AMD family 10h CPU
2910 nomsi [MSI] If the PCI_MSI kernel config parameter is
2911 enabled, this kernel boot option can be used to
2912 disable the use of MSI interrupts system-wide.
2913 noioapicquirk [APIC] Disable all boot interrupt quirks.
2914 Safety option to keep boot IRQs enabled. This
2915 should never be necessary.
2916 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2917 primary IO-APIC for bridges that cannot disable
2918 boot IRQs. This fixes a source of spurious IRQs
2919 when the system masks IRQs.
2920 noioapicreroute [APIC] Disable workaround that uses the
2921 boot IRQ equivalent of an IRQ that connects to
2922 a chipset where boot IRQs cannot be disabled.
2923 The opposite of ioapicreroute.
2924 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2925 routing table. These calls are known to be buggy
2926 on several machines and they hang the machine
2927 when used, but on other computers it's the only
2928 way to get the interrupt routing table. Try
2929 this option if the kernel is unable to allocate
2930 IRQs or discover secondary PCI buses on your
2932 rom [X86] Assign address space to expansion ROMs.
2933 Use with caution as certain devices share
2934 address decoders between ROMs and other
2936 norom [X86] Do not assign address space to
2937 expansion ROMs that do not already have
2938 BIOS assigned address ranges.
2939 nobar [X86] Do not assign address space to the
2940 BARs that weren't assigned by the BIOS.
2941 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2942 assigned automatically to PCI devices. You can
2943 make the kernel exclude IRQs of your ISA cards
2945 pirqaddr=0xAAAAA [X86] Specify the physical address
2946 of the PIRQ table (normally generated
2947 by the BIOS) if it is outside the
2948 F0000h-100000h range.
2949 lastbus=N [X86] Scan all buses thru bus #N. Can be
2950 useful if the kernel is unable to find your
2951 secondary buses and you want to tell it
2952 explicitly which ones they are.
2953 assign-busses [X86] Always assign all PCI bus
2954 numbers ourselves, overriding
2955 whatever the firmware may have done.
2956 usepirqmask [X86] Honor the possible IRQ mask stored
2957 in the BIOS $PIR table. This is needed on
2958 some systems with broken BIOSes, notably
2959 some HP Pavilion N5400 and Omnibook XE3
2960 notebooks. This will have no effect if ACPI
2961 IRQ routing is enabled.
2962 noacpi [X86] Do not use ACPI for IRQ routing
2963 or for PCI scanning.
2964 use_crs [X86] Use PCI host bridge window information
2965 from ACPI. On BIOSes from 2008 or later, this
2966 is enabled by default. If you need to use this,
2967 please report a bug.
2968 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2969 If you need to use this, please report a bug.
2970 routeirq Do IRQ routing for all PCI devices.
2971 This is normally done in pci_enable_device(),
2972 so this option is a temporary workaround
2973 for broken drivers that don't call it.
2974 skip_isa_align [X86] do not align io start addr, so can
2975 handle more pci cards
2976 noearly [X86] Don't do any early type 1 scanning.
2977 This might help on some broken boards which
2978 machine check when some devices' config space
2979 is read. But various workarounds are disabled
2980 and some IOMMU drivers will not work.
2981 bfsort Sort PCI devices into breadth-first order.
2982 This sorting is done to get a device
2983 order compatible with older (<= 2.4) kernels.
2984 nobfsort Don't sort PCI devices into breadth-first order.
2985 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2986 tuning and use the BIOS-configured MPS defaults.
2987 pcie_bus_safe Set every device's MPS to the largest value
2988 supported by all devices below the root complex.
2989 pcie_bus_perf Set device MPS to the largest allowable MPS
2990 based on its parent bus. Also set MRRS (Max
2991 Read Request Size) to the largest supported
2992 value (no larger than the MPS that the device
2993 or bus can support) for best performance.
2994 pcie_bus_peer2peer Set every device's MPS to 128B, which
2995 every device is guaranteed to support. This
2996 configuration allows peer-to-peer DMA between
2997 any pair of devices, possibly at the cost of
2998 reduced performance. This also guarantees
2999 that hot-added devices will work.
3000 cbiosize=nn[KMG] The fixed amount of bus space which is
3001 reserved for the CardBus bridge's IO window.
3002 The default value is 256 bytes.
3003 cbmemsize=nn[KMG] The fixed amount of bus space which is
3004 reserved for the CardBus bridge's memory
3005 window. The default value is 64 megabytes.
3008 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3009 Specifies alignment and device to reassign
3010 aligned memory resources.
3011 If <order of align> is not specified,
3012 PAGE_SIZE is used as alignment.
3013 PCI-PCI bridge can be specified, if resource
3014 windows need to be expanded.
3015 ecrc= Enable/disable PCIe ECRC (transaction layer
3016 end-to-end CRC checking).
3017 bios: Use BIOS/firmware settings. This is the
3021 hpiosize=nn[KMG] The fixed amount of bus space which is
3022 reserved for hotplug bridge's IO window.
3023 Default size is 256 bytes.
3024 hpmemsize=nn[KMG] The fixed amount of bus space which is
3025 reserved for hotplug bridge's memory window.
3026 Default size is 2 megabytes.
3027 realloc= Enable/disable reallocating PCI bridge resources
3028 if allocations done by BIOS are too small to
3029 accommodate resources required by all child
3031 off: Turn realloc off
3033 realloc same as realloc=on
3034 noari do not use PCIe ARI.
3035 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3036 only look for one device below a PCIe downstream
3039 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3042 force Enable ASPM even on devices that claim not to support it.
3043 WARNING: Forcing ASPM on may cause system lockups.
3045 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3046 nomsi Do not use MSI for PCI Express Native Hotplug (this
3047 makes all PCIe ports use INTx for hotplug services).
3049 pcie_ports= [PCIE] PCIe ports handling:
3050 auto Ask the BIOS whether or not to use native PCIe services
3051 associated with PCIe ports (PME, hot-plug, AER). Use
3052 them only if that is allowed by the BIOS.
3053 native Use native PCIe services associated with PCIe ports
3055 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3058 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3059 nomsi Do not use MSI for native PCIe PME signaling (this makes
3060 all PCIe root ports use INTx for all services).
3062 pcmv= [HW,PCMCIA] BadgePAD 4
3066 Keep all power-domains already enabled by bootloader on,
3067 even if no driver has claimed them. This is useful
3068 for debug and development, but should not be
3069 needed on a platform with proper driver support.
3072 See Documentation/blockdev/paride.txt.
3074 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3077 See arch/parisc/kernel/pdc_chassis.c
3079 percpu_alloc= Select which percpu first chunk allocator to use.
3080 Currently supported values are "embed" and "page".
3081 Archs may support subset or none of the selections.
3082 See comments in mm/percpu.c for details on each
3083 allocator. This parameter is primarily for debugging
3084 and performance comparison.
3087 See Documentation/blockdev/paride.txt.
3090 See Documentation/blockdev/paride.txt.
3092 pirq= [SMP,APIC] Manual mp-table setup
3093 See Documentation/x86/i386/IO-APIC.txt.
3095 plip= [PPT,NET] Parallel port network link
3096 Format: { parport<nr> | timid | 0 }
3097 See also Documentation/parport.txt.
3099 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3100 Override pmtimer IOPort with a hex value.
3104 Enable PNP debug messages (depends on the
3105 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3106 via /sys/module/pnp/parameters/debug. We always show
3107 current resource usage; turning this on also shows
3108 possible settings and some assignment information.
3114 { on | off | curr | res | no-curr | no-res }
3117 [ISAPNP] Exclude IRQs for the autoconfiguration
3120 [ISAPNP] Exclude DMAs for the autoconfiguration
3122 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3123 Ranges are in pairs (I/O port base and size).
3126 [ISAPNP] Exclude memory regions for the
3128 Ranges are in pairs (memory base and size).
3130 ports= [IP_VS_FTP] IPVS ftp helper module
3132 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3134 Format: <port>,<port>....
3136 ppc_strict_facility_enable
3137 [PPC] This option catches any kernel floating point,
3138 Altivec, VSX and SPE outside of regions specifically
3139 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3140 There is some performance impact when enabling this.
3142 print-fatal-signals=
3143 [KNL] debug: print fatal signals
3145 If enabled, warn about various signal handling
3146 related application anomalies: too many signals,
3147 too many POSIX.1 timers, fatal signals causing a
3150 If you hit the warning due to signal overflow,
3151 you might want to try "ulimit -i unlimited".
3155 printk.always_kmsg_dump=
3156 Trigger kmsg_dump for cases other than kernel oops or
3158 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3161 printk.time= Show timing data prefixed to each printk message line
3162 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3164 processor.max_cstate= [HW,ACPI]
3165 Limit processor to maximum C-state
3166 max_cstate=9 overrides any DMI blacklist limit.
3168 processor.nocst [HW,ACPI]
3169 Ignore the _CST method to determine C-states,
3170 instead using the legacy FADT method
3172 profile= [KNL] Enable kernel profiling via /proc/profile
3173 Format: [schedule,]<number>
3174 Param: "schedule" - profile schedule points.
3175 Param: <number> - step/bucket size as a power of 2 for
3176 statistical time based profiling.
3177 Param: "sleep" - profile D-state sleeping (millisecs).
3178 Requires CONFIG_SCHEDSTATS
3179 Param: "kvm" - profile VM exits.
3181 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3183 See Documentation/blockdev/ramdisk.txt.
3185 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3186 probe for; one of (bare|imps|exps|lifebook|any).
3187 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3189 psmouse.resetafter= [HW,MOUSE]
3190 Try to reset the device after so many bad packets
3193 [HW,MOUSE] Set desired mouse resolution, in dpi.
3194 psmouse.smartscroll=
3195 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3196 0 = disabled, 1 = enabled (default).
3198 pstore.backend= Specify the name of the pstore backend to use
3201 See Documentation/blockdev/paride.txt.
3204 [KNL] Number of legacy pty's. Overwrites compiled-in
3207 quiet [KNL] Disable most log messages
3212 See Documentation/md.txt.
3214 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3215 See Documentation/blockdev/ramdisk.txt.
3218 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3219 the specified list of CPUs to be no-callback CPUs.
3220 Invocation of these CPUs' RCU callbacks will
3221 be offloaded to "rcuox/N" kthreads created for
3222 that purpose, where "x" is "b" for RCU-bh, "p"
3223 for RCU-preempt, and "s" for RCU-sched, and "N"
3224 is the CPU number. This reduces OS jitter on the
3225 offloaded CPUs, which can be useful for HPC and
3226 real-time workloads. It can also improve energy
3227 efficiency for asymmetric multiprocessors.
3230 Rather than requiring that offloaded CPUs
3231 (specified by rcu_nocbs= above) explicitly
3232 awaken the corresponding "rcuoN" kthreads,
3233 make these kthreads poll for callbacks.
3234 This improves the real-time response for the
3235 offloaded CPUs by relieving them of the need to
3236 wake up the corresponding kthread, but degrades
3237 energy efficiency by requiring that the kthreads
3238 periodically wake up to do the polling.
3240 rcutree.blimit= [KNL]
3241 Set maximum number of finished RCU callbacks to
3242 process in one batch.
3244 rcutree.dump_tree= [KNL]
3245 Dump the structure of the rcu_node combining tree
3246 out at early boot. This is used for diagnostic
3247 purposes, to verify correct tree setup.
3249 rcutree.gp_cleanup_delay= [KNL]
3250 Set the number of jiffies to delay each step of
3251 RCU grace-period cleanup. This only has effect
3252 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3254 rcutree.gp_init_delay= [KNL]
3255 Set the number of jiffies to delay each step of
3256 RCU grace-period initialization. This only has
3257 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3260 rcutree.gp_preinit_delay= [KNL]
3261 Set the number of jiffies to delay each step of
3262 RCU grace-period pre-initialization, that is,
3263 the propagation of recent CPU-hotplug changes up
3264 the rcu_node combining tree. This only has effect
3265 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3267 rcutree.rcu_fanout_exact= [KNL]
3268 Disable autobalancing of the rcu_node combining
3269 tree. This is used by rcutorture, and might
3270 possibly be useful for architectures having high
3271 cache-to-cache transfer latencies.
3273 rcutree.rcu_fanout_leaf= [KNL]
3274 Change the number of CPUs assigned to each
3275 leaf rcu_node structure. Useful for very
3276 large systems, which will choose the value 64,
3277 and for NUMA systems with large remote-access
3278 latencies, which will choose a value aligned
3279 with the appropriate hardware boundaries.
3281 rcutree.jiffies_till_sched_qs= [KNL]
3282 Set required age in jiffies for a
3283 given grace period before RCU starts
3284 soliciting quiescent-state help from
3285 rcu_note_context_switch().
3287 rcutree.jiffies_till_first_fqs= [KNL]
3288 Set delay from grace-period initialization to
3289 first attempt to force quiescent states.
3290 Units are jiffies, minimum value is zero,
3291 and maximum value is HZ.
3293 rcutree.jiffies_till_next_fqs= [KNL]
3294 Set delay between subsequent attempts to force
3295 quiescent states. Units are jiffies, minimum
3296 value is one, and maximum value is HZ.
3298 rcutree.kthread_prio= [KNL,BOOT]
3299 Set the SCHED_FIFO priority of the RCU per-CPU
3300 kthreads (rcuc/N). This value is also used for
3301 the priority of the RCU boost threads (rcub/N)
3302 and for the RCU grace-period kthreads (rcu_bh,
3303 rcu_preempt, and rcu_sched). If RCU_BOOST is
3304 set, valid values are 1-99 and the default is 1
3305 (the least-favored priority). Otherwise, when
3306 RCU_BOOST is not set, valid values are 0-99 and
3307 the default is zero (non-realtime operation).
3309 rcutree.rcu_nocb_leader_stride= [KNL]
3310 Set the number of NOCB kthread groups, which
3311 defaults to the square root of the number of
3312 CPUs. Larger numbers reduces the wakeup overhead
3313 on the per-CPU grace-period kthreads, but increases
3314 that same overhead on each group's leader.
3316 rcutree.qhimark= [KNL]
3317 Set threshold of queued RCU callbacks beyond which
3318 batch limiting is disabled.
3320 rcutree.qlowmark= [KNL]
3321 Set threshold of queued RCU callbacks below which
3322 batch limiting is re-enabled.
3324 rcutree.rcu_idle_gp_delay= [KNL]
3325 Set wakeup interval for idle CPUs that have
3326 RCU callbacks (RCU_FAST_NO_HZ=y).
3328 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3329 Set wakeup interval for idle CPUs that have
3330 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3331 Lazy RCU callbacks are those which RCU can
3332 prove do nothing more than free memory.
3334 rcuperf.gp_exp= [KNL]
3335 Measure performance of expedited synchronous
3336 grace-period primitives.
3338 rcuperf.holdoff= [KNL]
3339 Set test-start holdoff period. The purpose of
3340 this parameter is to delay the start of the
3341 test until boot completes in order to avoid
3344 rcuperf.nreaders= [KNL]
3345 Set number of RCU readers. The value -1 selects
3346 N, where N is the number of CPUs. A value
3347 "n" less than -1 selects N-n+1, where N is again
3348 the number of CPUs. For example, -2 selects N
3349 (the number of CPUs), -3 selects N+1, and so on.
3350 A value of "n" less than or equal to -N selects
3353 rcuperf.nwriters= [KNL]
3354 Set number of RCU writers. The values operate
3355 the same as for rcuperf.nreaders.
3356 N, where N is the number of CPUs
3358 rcuperf.perf_runnable= [BOOT]
3359 Start rcuperf running at boot time.
3361 rcuperf.shutdown= [KNL]
3362 Shut the system down after performance tests
3363 complete. This is useful for hands-off automated
3366 rcuperf.perf_type= [KNL]
3367 Specify the RCU implementation to test.
3369 rcuperf.verbose= [KNL]
3370 Enable additional printk() statements.
3372 rcutorture.cbflood_inter_holdoff= [KNL]
3373 Set holdoff time (jiffies) between successive
3374 callback-flood tests.
3376 rcutorture.cbflood_intra_holdoff= [KNL]
3377 Set holdoff time (jiffies) between successive
3378 bursts of callbacks within a given callback-flood
3381 rcutorture.cbflood_n_burst= [KNL]
3382 Set the number of bursts making up a given
3383 callback-flood test. Set this to zero to
3384 disable callback-flood testing.
3386 rcutorture.cbflood_n_per_burst= [KNL]
3387 Set the number of callbacks to be registered
3388 in a given burst of a callback-flood test.
3390 rcutorture.fqs_duration= [KNL]
3391 Set duration of force_quiescent_state bursts
3394 rcutorture.fqs_holdoff= [KNL]
3395 Set holdoff time within force_quiescent_state bursts
3398 rcutorture.fqs_stutter= [KNL]
3399 Set wait time between force_quiescent_state bursts
3402 rcutorture.gp_cond= [KNL]
3403 Use conditional/asynchronous update-side
3404 primitives, if available.
3406 rcutorture.gp_exp= [KNL]
3407 Use expedited update-side primitives, if available.
3409 rcutorture.gp_normal= [KNL]
3410 Use normal (non-expedited) asynchronous
3411 update-side primitives, if available.
3413 rcutorture.gp_sync= [KNL]
3414 Use normal (non-expedited) synchronous
3415 update-side primitives, if available. If all
3416 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3417 rcutorture.gp_normal=, and rcutorture.gp_sync=
3418 are zero, rcutorture acts as if is interpreted
3419 they are all non-zero.
3421 rcutorture.n_barrier_cbs= [KNL]
3422 Set callbacks/threads for rcu_barrier() testing.
3424 rcutorture.nfakewriters= [KNL]
3425 Set number of concurrent RCU writers. These just
3426 stress RCU, they don't participate in the actual
3427 test, hence the "fake".
3429 rcutorture.nreaders= [KNL]
3430 Set number of RCU readers. The value -1 selects
3431 N-1, where N is the number of CPUs. A value
3432 "n" less than -1 selects N-n-2, where N is again
3433 the number of CPUs. For example, -2 selects N
3434 (the number of CPUs), -3 selects N+1, and so on.
3436 rcutorture.object_debug= [KNL]
3437 Enable debug-object double-call_rcu() testing.
3439 rcutorture.onoff_holdoff= [KNL]
3440 Set time (s) after boot for CPU-hotplug testing.
3442 rcutorture.onoff_interval= [KNL]
3443 Set time (s) between CPU-hotplug operations, or
3444 zero to disable CPU-hotplug testing.
3446 rcutorture.shuffle_interval= [KNL]
3447 Set task-shuffle interval (s). Shuffling tasks
3448 allows some CPUs to go into dyntick-idle mode
3449 during the rcutorture test.
3451 rcutorture.shutdown_secs= [KNL]
3452 Set time (s) after boot system shutdown. This
3453 is useful for hands-off automated testing.
3455 rcutorture.stall_cpu= [KNL]
3456 Duration of CPU stall (s) to test RCU CPU stall
3457 warnings, zero to disable.
3459 rcutorture.stall_cpu_holdoff= [KNL]
3460 Time to wait (s) after boot before inducing stall.
3462 rcutorture.stat_interval= [KNL]
3463 Time (s) between statistics printk()s.
3465 rcutorture.stutter= [KNL]
3466 Time (s) to stutter testing, for example, specifying
3467 five seconds causes the test to run for five seconds,
3468 wait for five seconds, and so on. This tests RCU's
3469 ability to transition abruptly to and from idle.
3471 rcutorture.test_boost= [KNL]
3472 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3473 "Maybe" means test if the RCU implementation
3474 under test support RCU priority boosting.
3476 rcutorture.test_boost_duration= [KNL]
3477 Duration (s) of each individual boost test.
3479 rcutorture.test_boost_interval= [KNL]
3480 Interval (s) between each boost test.
3482 rcutorture.test_no_idle_hz= [KNL]
3483 Test RCU's dyntick-idle handling. See also the
3484 rcutorture.shuffle_interval parameter.
3486 rcutorture.torture_runnable= [BOOT]
3487 Start rcutorture running at boot time.
3489 rcutorture.torture_type= [KNL]
3490 Specify the RCU implementation to test.
3492 rcutorture.verbose= [KNL]
3493 Enable additional printk() statements.
3495 rcupdate.rcu_cpu_stall_suppress= [KNL]
3496 Suppress RCU CPU stall warning messages.
3498 rcupdate.rcu_cpu_stall_timeout= [KNL]
3499 Set timeout for RCU CPU stall warning messages.
3501 rcupdate.rcu_expedited= [KNL]
3502 Use expedited grace-period primitives, for
3503 example, synchronize_rcu_expedited() instead
3504 of synchronize_rcu(). This reduces latency,
3505 but can increase CPU utilization, degrade
3506 real-time latency, and degrade energy efficiency.
3507 No effect on CONFIG_TINY_RCU kernels.
3509 rcupdate.rcu_normal= [KNL]
3510 Use only normal grace-period primitives,
3511 for example, synchronize_rcu() instead of
3512 synchronize_rcu_expedited(). This improves
3513 real-time latency, CPU utilization, and
3514 energy efficiency, but can expose users to
3515 increased grace-period latency. This parameter
3516 overrides rcupdate.rcu_expedited. No effect on
3517 CONFIG_TINY_RCU kernels.
3519 rcupdate.rcu_normal_after_boot= [KNL]
3520 Once boot has completed (that is, after
3521 rcu_end_inkernel_boot() has been invoked), use
3522 only normal grace-period primitives. No effect
3523 on CONFIG_TINY_RCU kernels.
3525 rcupdate.rcu_task_stall_timeout= [KNL]
3526 Set timeout in jiffies for RCU task stall warning
3527 messages. Disable with a value less than or equal
3530 rcupdate.rcu_self_test= [KNL]
3531 Run the RCU early boot self tests
3533 rcupdate.rcu_self_test_bh= [KNL]
3534 Run the RCU bh early boot self tests
3536 rcupdate.rcu_self_test_sched= [KNL]
3537 Run the RCU sched early boot self tests
3541 Run specified binary instead of /init from the ramdisk,
3542 used for early userspace startup. See initrd.
3545 Format (x86 or x86_64):
3546 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3548 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3550 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3551 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3552 reboot_force is either force or not specified,
3553 reboot_cpu is s[mp]#### with #### being the processor
3554 to be used for rebooting.
3557 [KNL, SMP] Set scheduler's default relax_domain_level.
3558 See Documentation/cgroups/cpusets.txt.
3560 relative_sleep_states=
3561 [SUSPEND] Use sleep state labeling where the deepest
3562 state available other than hibernation is always "mem".
3563 Format: { "0" | "1" }
3564 0 -- Traditional sleep state labels.
3565 1 -- Relative sleep state labels.
3567 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3569 reservetop= [X86-32]
3571 Reserves a hole at the top of the kernel virtual
3576 Set the amount of memory to reserve for BIOS at
3577 the bottom of the address space.
3579 reset_devices [KNL] Force drivers to reset the underlying device
3580 during initialization.
3583 Specify the partition device for software suspend
3585 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3587 resume_offset= [SWSUSP]
3588 Specify the offset from the beginning of the partition
3589 given by "resume=" at which the swap header is located,
3590 in <PAGE_SIZE> units (needed only for swap files).
3591 See Documentation/power/swsusp-and-swap-files.txt
3593 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3594 read the resume files
3596 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3597 Useful for devices that are detected asynchronously
3598 (e.g. USB and MMC devices).
3600 hibernate= [HIBERNATION]
3601 noresume Don't check if there's a hibernation image
3602 present during boot.
3603 nocompress Don't compress/decompress hibernation images.
3604 no Disable hibernation and resume.
3606 retain_initrd [RAM] Keep initrd memory after extraction
3608 rfkill.default_state=
3609 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3610 etc. communication is blocked by default.
3613 rfkill.master_switch_mode=
3614 0 The "airplane mode" button does nothing.
3615 1 The "airplane mode" button toggles between everything
3616 blocked and the previous configuration.
3617 2 The "airplane mode" button toggles between everything
3618 blocked and everything unblocked.
3620 rhash_entries= [KNL,NET]
3621 Set number of hash buckets for route cache
3623 ro [KNL] Mount root device read-only on boot
3626 on Mark read-only kernel memory as read-only (default).
3627 off Leave read-only kernel memory writable for debugging.
3630 Enable the uart passthrough on the designated usb port
3631 on Rockchip SoCs. When active, the signals of the
3632 debug-uart get routed to the D+ and D- pins of the usb
3633 port and the regular usb controller gets disabled.
3635 root= [KNL] Root filesystem
3636 See name_to_dev_t comment in init/do_mounts.c.
3638 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3639 mount the root filesystem
3641 rootflags= [KNL] Set root filesystem mount option string
3643 rootfstype= [KNL] Set root filesystem type
3645 rootwait [KNL] Wait (indefinitely) for root device to show up.
3646 Useful for devices that are detected asynchronously
3647 (e.g. USB and MMC devices).
3649 rproc_mem=nn[KMG][@address]
3650 [KNL,ARM,CMA] Remoteproc physical memory block.
3651 Memory area to be used by remote processor image,
3654 rw [KNL] Mount root device read-write on boot
3656 S [KNL] Run init in single mode
3658 s390_iommu= [HW,S390]
3659 Set s390 IOTLB flushing mode
3661 With strict flushing every unmap operation will result in
3662 an IOTLB flush. Default is lazy flushing before reuse,
3666 See drivers/net/irda/sa1100_ir.c.
3668 sbni= [NET] Granch SBNI12 leased line adapter
3670 sched_debug [KNL] Enables verbose scheduler debug messages.
3672 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3673 Allowed values are enable and disable. This feature
3674 incurs a small amount of overhead in the scheduler
3675 but is useful for debugging and performance tuning.
3677 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3678 xtime_lock contention on larger systems, and/or RCU lock
3679 contention on all systems with CONFIG_MAXSMP set.
3680 Format: { "0" | "1" }
3681 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3683 Note: increases power consumption, thus should only be
3684 enabled if running jitter sensitive (HPC/RT) workloads.
3686 security= [SECURITY] Choose a security module to enable at boot.
3687 If this boot parameter is not specified, only the first
3688 security module asking for security registration will be
3689 loaded. An invalid security module name will be treated
3690 as if no module has been chosen.
3692 selinux= [SELINUX] Disable or enable SELinux at boot time.
3693 Format: { "0" | "1" }
3694 See security/selinux/Kconfig help text.
3697 Default value is set via kernel config option.
3698 If enabled at boot time, /selinux/disable can be used
3699 later to disable prior to initial policy load.
3701 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3702 Format: { "0" | "1" }
3703 See security/apparmor/Kconfig help text
3706 Default value is set via kernel config option.
3708 serialnumber [BUGS=X86-32]
3711 Maximal number of shapers.
3713 show_msr= [x86] show boot-time MSR settings
3714 Format: { <integer> }
3715 Show boot-time (BIOS-initialized) MSR settings.
3716 The parameter means the number of CPUs to show,
3717 for example 1 means boot CPU only.
3725 Disable merging of slabs with similar size. May be
3726 necessary if there is some reason to distinguish
3727 allocs to different slabs. Debug options disable
3728 merging on their own.
3729 For more information see Documentation/vm/slub.txt.
3731 slab_max_order= [MM, SLAB]
3732 Determines the maximum allowed order for slabs.
3733 A high setting may cause OOMs due to memory
3734 fragmentation. Defaults to 1 for systems with
3735 more than 32MB of RAM, 0 otherwise.
3737 slub_debug[=options[,slabs]] [MM, SLUB]
3738 Enabling slub_debug allows one to determine the
3739 culprit if slab objects become corrupted. Enabling
3740 slub_debug can create guard zones around objects and
3741 may poison objects when not in use. Also tracks the
3742 last alloc / free. For more information see
3743 Documentation/vm/slub.txt.
3745 slub_max_order= [MM, SLUB]
3746 Determines the maximum allowed order for slabs.
3747 A high setting may cause OOMs due to memory
3748 fragmentation. For more information see
3749 Documentation/vm/slub.txt.
3751 slub_min_objects= [MM, SLUB]
3752 The minimum number of objects per slab. SLUB will
3753 increase the slab order up to slub_max_order to
3754 generate a sufficiently large slab able to contain
3755 the number of objects indicated. The higher the number
3756 of objects the smaller the overhead of tracking slabs
3757 and the less frequently locks need to be acquired.
3758 For more information see Documentation/vm/slub.txt.
3760 slub_min_order= [MM, SLUB]
3761 Determines the minimum page order for slabs. Must be
3762 lower than slub_max_order.
3763 For more information see Documentation/vm/slub.txt.
3765 slub_nomerge [MM, SLUB]
3766 Same with slab_nomerge. This is supported for legacy.
3767 See slab_nomerge for more information.
3770 Format: <io1>[,<io2>[,...,<io8>]]
3772 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3773 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3774 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3775 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3776 smsc-ircc2.ircc_irq= [HW] IRQ line
3777 smsc-ircc2.ircc_dma= [HW] DMA channel
3778 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3779 0: Toshiba Satellite 1800 (GP data pin select)
3780 1: Fast pin select (default)
3783 smt [KNL,S390] Set the maximum number of threads (logical
3784 CPUs) to use per physical CPU on systems capable of
3785 symmetric multithreading (SMT). Will be capped to the
3786 actual hardware limit.
3788 Default: -1 (no limit)
3791 [KNL] Should the soft-lockup detector generate panics.
3794 softlockup_all_cpu_backtrace=
3795 [KNL] Should the soft-lockup detector generate
3796 backtraces on all cpus.
3799 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3800 See Documentation/laptops/sonypi.txt
3802 spia_io_base= [HW,MTD]
3808 Enabled the stack tracer on boot up.
3810 stacktrace_filter=[function-list]
3811 [FTRACE] Limit the functions that the stack tracer
3812 will trace at boot up. function-list is a comma separated
3813 list of functions. This list can be changed at run
3814 time by the stack_trace_filter file in the debugfs
3815 tracing directory. Note, this enables stack tracing
3816 and the stacktrace above is not needed.
3820 Set the STI (builtin display/keyboard on the HP-PARISC
3821 machines) console (graphic card) which should be used
3822 as the initial boot-console.
3823 See also comment in drivers/video/console/sticore.c.
3826 See comment in drivers/video/console/sticore.c.
3829 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3831 sunrpc.min_resvport=
3832 sunrpc.max_resvport=
3834 SunRPC servers often require that client requests
3835 originate from a privileged port (i.e. a port in the
3836 range 0 < portnr < 1024).
3837 An administrator who wishes to reserve some of these
3838 ports for other uses may adjust the range that the
3839 kernel's sunrpc client considers to be privileged
3840 using these two parameters to set the minimum and
3841 maximum port values.
3845 Control how the NFS server code allocates CPUs to
3846 service thread pools. Depending on how many NICs
3847 you have and where their interrupts are bound, this
3848 option will affect which CPUs will do NFS serving.
3849 Note: this parameter cannot be changed while the
3850 NFS server is running.
3852 auto the server chooses an appropriate mode
3853 automatically using heuristics
3854 global a single global pool contains all CPUs
3855 percpu one pool for each CPU
3856 pernode one pool for each NUMA node (equivalent
3857 to global on non-NUMA machines)
3859 sunrpc.tcp_slot_table_entries=
3860 sunrpc.udp_slot_table_entries=
3862 Sets the upper limit on the number of simultaneous
3863 RPC calls that can be sent from the client to a
3864 server. Increasing these values may allow you to
3865 improve throughput, but will also increase the
3866 amount of memory reserved for use by the client.
3868 suspend.pm_test_delay=
3870 Sets the number of seconds to remain in a suspend test
3871 mode before resuming the system (see
3872 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3873 is set. Default value is 5.
3876 [KNL] Enable accounting of swap in memory resource
3877 controller if no parameter or 1 is given or disable
3878 it if 0 is given (See Documentation/cgroups/memory.txt)
3880 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3881 Format: { <int> | force }
3882 <int> -- Number of I/O TLB slabs
3883 force -- force using of bounce buffers even if they
3884 wouldn't be automatically used by the kernel
3888 sysfs.deprecated=0|1 [KNL]
3889 Enable/disable old style sysfs layout for old udev
3890 on older distributions. When this option is enabled
3891 very new udev will not work anymore. When this option
3892 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3893 in older udev will not work anymore.
3894 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3895 the kernel configuration.
3897 sysrq_always_enabled
3899 Ignore sysrq setting - this boot parameter will
3900 neutralize any effect of /proc/sys/kernel/sysrq.
3901 Useful for debugging.
3903 tcpmhash_entries= [KNL,NET]
3904 Set the number of tcp_metrics_hash slots.
3905 Default value is 8192 or 16384 depending on total
3906 ram pages. This is used to specify the TCP metrics
3907 cache size. See Documentation/networking/ip-sysctl.txt
3908 "tcp_no_metrics_save" section for more details.
3912 test_suspend= [SUSPEND][,N]
3913 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3914 standby suspend) or "freeze" (for suspend type freeze)
3915 as the system sleep state during system startup with
3916 the optional capability to repeat N number of times.
3917 The system is woken from this state using a
3918 wakeup-capable RTC alarm.
3920 thash_entries= [KNL,NET]
3921 Set number of hash buckets for TCP connection
3923 thermal.act= [HW,ACPI]
3924 -1: disable all active trip points in all thermal zones
3925 <degrees C>: override all lowest active trip points
3927 thermal.crt= [HW,ACPI]
3928 -1: disable all critical trip points in all thermal zones
3929 <degrees C>: override all critical trip points
3931 thermal.nocrt= [HW,ACPI]
3932 Set to disable actions on ACPI thermal zone
3933 critical and hot trip points.
3935 thermal.off= [HW,ACPI]
3936 1: disable ACPI thermal control
3938 thermal.psv= [HW,ACPI]
3939 -1: disable all passive trip points
3940 <degrees C>: override all passive trip points to this
3943 thermal.tzp= [HW,ACPI]
3944 Specify global default ACPI thermal zone polling rate
3945 <deci-seconds>: poll all this frequency
3946 0: no polling (default)
3949 Force threading of all interrupt handlers except those
3950 marked explicitly IRQF_NO_THREAD.
3953 Enable the Transcendent memory driver if built-in.
3955 tmem.cleancache=0|1 [KNL, XEN]
3956 Default is on (1). Disable the usage of the cleancache
3957 API to send anonymous pages to the hypervisor.
3959 tmem.frontswap=0|1 [KNL, XEN]
3960 Default is on (1). Disable the usage of the frontswap
3961 API to send swap pages to the hypervisor. If disabled
3962 the selfballooning and selfshrinking are force disabled.
3964 tmem.selfballooning=0|1 [KNL, XEN]
3965 Default is on (1). Disable the driving of swap pages
3968 tmem.selfshrinking=0|1 [KNL, XEN]
3969 Default is on (1). Partial swapoff that immediately
3970 transfers pages from Xen hypervisor back to the
3971 kernel based on different criteria.
3975 Specify if the kernel should make use of the cpu
3976 topology information if the hardware supports this.
3977 The scheduler will make use of this information and
3978 e.g. base its process migration decisions on it.
3981 topology_updates= [KNL, PPC, NUMA]
3983 Specify if the kernel should ignore (off)
3984 topology updates sent by the hypervisor to this
3989 tpm_suspend_pcr=[HW,TPM]
3990 Format: integer pcr id
3991 Specify that at suspend time, the tpm driver
3992 should extend the specified pcr with zeros,
3993 as a workaround for some chips which fail to
3994 flush the last written pcr on TPM_SaveState.
3995 This will guarantee that all the other pcrs
3998 trace_buf_size=nn[KMG]
3999 [FTRACE] will set tracing buffer size on each cpu.
4001 trace_event=[event-list]
4002 [FTRACE] Set and start specified trace events in order
4003 to facilitate early boot debugging.
4004 See also Documentation/trace/events.txt
4006 trace_options=[option-list]
4007 [FTRACE] Enable or disable tracer options at boot.
4008 The option-list is a comma delimited list of options
4009 that can be enabled or disabled just as if you were
4010 to echo the option name into
4012 /sys/kernel/debug/tracing/trace_options
4014 For example, to enable stacktrace option (to dump the
4015 stack trace of each event), add to the command line:
4017 trace_options=stacktrace
4019 See also Documentation/trace/ftrace.txt "trace options"
4023 Have the tracepoints sent to printk as well as the
4024 tracing ring buffer. This is useful for early boot up
4025 where the system hangs or reboots and does not give the
4026 option for reading the tracing buffer or performing a
4027 ftrace_dump_on_oops.
4029 To turn off having tracepoints sent to printk,
4030 echo 0 > /proc/sys/kernel/tracepoint_printk
4031 Note, echoing 1 into this file without the
4032 tracepoint_printk kernel cmdline option has no effect.
4036 Having tracepoints sent to printk() and activating high
4037 frequency tracepoints such as irq or sched, can cause
4038 the system to live lock.
4041 [FTRACE] enable this option to disable tracing when a
4042 warning is hit. This turns off "tracing_on". Tracing can
4043 be enabled again by echoing '1' into the "tracing_on"
4044 file located in /sys/kernel/debug/tracing/
4046 This option is useful, as it disables the trace before
4047 the WARNING dump is called, which prevents the trace to
4048 be filled with content caused by the warning output.
4050 This option can also be set at run time via the sysctl
4051 option: kernel/traceoff_on_warning
4053 transparent_hugepage=
4055 Format: [always|madvise|never]
4056 Can be used to control the default behavior of the system
4057 with respect to transparent hugepages.
4058 See Documentation/vm/transhuge.txt for more details.
4060 tsc= Disable clocksource stability checks for TSC.
4062 [x86] reliable: mark tsc clocksource as reliable, this
4063 disables clocksource verification at runtime, as well
4064 as the stability checks done at bootup. Used to enable
4065 high-resolution timer mode on older hardware, and in
4066 virtualized environment.
4067 [x86] noirqtime: Do not use TSC to do irq accounting.
4068 Used to run time disable IRQ_TIME_ACCOUNTING on any
4069 platforms where RDTSC is slow and this accounting
4072 turbografx.map[2|3]= [HW,JOY]
4073 TurboGraFX parallel port interface
4075 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4076 See also Documentation/input/joystick-parport.txt
4078 udbg-immortal [PPC] When debugging early kernel crashes that
4079 happen after console_init() and before a proper
4080 console driver takes over, this boot options might
4081 help "seeing" what's going on.
4083 uhash_entries= [KNL,NET]
4084 Set number of hash buckets for UDP/UDP-Lite connections
4087 [USB] Ignore overcurrent events (default N).
4088 Some badly-designed motherboards generate lots of
4089 bogus events, for ports that aren't wired to
4090 anything. Set this parameter to avoid log spamming.
4091 Note that genuine overcurrent events won't be
4095 [X86] Cause panic on unknown NMI.
4097 usbcore.authorized_default=
4098 [USB] Default USB device authorization:
4099 (default -1 = authorized except for wireless USB,
4100 0 = not authorized, 1 = authorized)
4102 usbcore.autosuspend=
4103 [USB] The autosuspend time delay (in seconds) used
4104 for newly-detected USB devices (default 2). This
4105 is the time required before an idle device will be
4106 autosuspended. Devices for which the delay is set
4107 to a negative value won't be autosuspended at all.
4109 usbcore.usbfs_snoop=
4110 [USB] Set to log all usbfs traffic (default 0 = off).
4112 usbcore.usbfs_snoop_max=
4113 [USB] Maximum number of bytes to snoop in each URB
4116 usbcore.blinkenlights=
4117 [USB] Set to cycle leds on hubs (default 0 = off).
4119 usbcore.old_scheme_first=
4120 [USB] Start with the old device initialization
4121 scheme (default 0 = off).
4123 usbcore.usbfs_memory_mb=
4124 [USB] Memory limit (in MB) for buffers allocated by
4125 usbfs (default = 16, 0 = max = 2047).
4127 usbcore.use_both_schemes=
4128 [USB] Try the other device initialization scheme
4129 if the first one fails (default 1 = enabled).
4131 usbcore.initial_descriptor_timeout=
4132 [USB] Specifies timeout for the initial 64-byte
4133 USB_REQ_GET_DESCRIPTOR request in milliseconds
4134 (default 5000 = 5.0 seconds).
4136 usbcore.nousb [USB] Disable the USB subsystem
4139 [USBHID] The interval which mice are to be polled at.
4141 usb-storage.delay_use=
4142 [UMS] The delay in seconds before a new device is
4143 scanned for Logical Units (default 1).
4146 [UMS] A list of quirks entries to supplement or
4147 override the built-in unusual_devs list. List
4148 entries are separated by commas. Each entry has
4149 the form VID:PID:Flags where VID and PID are Vendor
4150 and Product ID values (4-digit hex numbers) and
4151 Flags is a set of characters, each corresponding
4152 to a common usb-storage quirk flag as follows:
4153 a = SANE_SENSE (collect more than 18 bytes
4155 b = BAD_SENSE (don't collect more than 18
4156 bytes of sense data);
4157 c = FIX_CAPACITY (decrease the reported
4158 device capacity by one sector);
4159 d = NO_READ_DISC_INFO (don't use
4160 READ_DISC_INFO command);
4161 e = NO_READ_CAPACITY_16 (don't use
4162 READ_CAPACITY_16 command);
4163 f = NO_REPORT_OPCODES (don't use report opcodes
4165 g = MAX_SECTORS_240 (don't transfer more than
4166 240 sectors at a time, uas only);
4167 h = CAPACITY_HEURISTICS (decrease the
4168 reported device capacity by one
4169 sector if the number is odd);
4170 i = IGNORE_DEVICE (don't bind to this
4172 j = NO_REPORT_LUNS (don't use report luns
4174 l = NOT_LOCKABLE (don't try to lock and
4175 unlock ejectable media);
4176 m = MAX_SECTORS_64 (don't transfer more
4177 than 64 sectors = 32 KB at a time);
4178 n = INITIAL_READ10 (force a retry of the
4179 initial READ(10) command);
4180 o = CAPACITY_OK (accept the capacity
4181 reported by the device);
4182 p = WRITE_CACHE (the device cache is ON
4184 r = IGNORE_RESIDUE (the device reports
4185 bogus residue values);
4186 s = SINGLE_LUN (the device has only one
4188 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4189 commands, uas only);
4190 u = IGNORE_UAS (don't bind to the uas driver);
4191 w = NO_WP_DETECT (don't test whether the
4192 medium is write-protected).
4193 Example: quirks=0419:aaf5:rl,0421:0433:rc
4195 user_debug= [KNL,ARM]
4197 See arch/arm/Kconfig.debug help text.
4198 1 - undefined instruction events
4200 4 - invalid data aborts
4203 Example: user_debug=31
4206 [X86] Flags controlling user PTE allocations.
4208 nohigh = do not allocate PTE pages in
4209 HIGHMEM regardless of setting
4213 On X86_32, this is an alias for vdso32=. Otherwise:
4215 vdso=1: enable VDSO (the default)
4216 vdso=0: disable VDSO mapping
4218 vdso32= [X86] Control the 32-bit vDSO
4219 vdso32=1: enable 32-bit VDSO
4220 vdso32=0 or vdso32=2: disable 32-bit VDSO
4222 See the help text for CONFIG_COMPAT_VDSO for more
4223 details. If CONFIG_COMPAT_VDSO is set, the default is
4224 vdso32=0; otherwise, the default is vdso32=1.
4226 For compatibility with older kernels, vdso32=2 is an
4229 Try vdso32=0 if you encounter an error that says:
4230 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4233 vector=percpu: enable percpu vector domain
4235 video= [FB] Frame buffer configuration
4236 See Documentation/fb/modedb.txt.
4238 video.brightness_switch_enabled= [0,1]
4239 If set to 1, on receiving an ACPI notify event
4240 generated by hotkey, video driver will adjust brightness
4241 level and then send out the event to user space through
4242 the allocated input device; If set to 0, video driver
4243 will only send out the event without touching backlight
4248 [VMMIO] Memory mapped virtio (platform) device.
4250 <size>@<baseaddr>:<irq>[:<id>]
4252 <size> := size (can use standard suffixes
4254 <baseaddr> := physical base address
4255 <irq> := interrupt number (as passed to
4257 <id> := (optional) platform device id
4259 virtio_mmio.device=1K@0x100b0000:48:7
4261 Can be used multiple times for multiple devices.
4263 vga= [BOOT,X86-32] Select a particular video mode
4264 See Documentation/x86/boot.txt and
4265 Documentation/svga.txt.
4266 Use vga=ask for menu.
4267 This is actually a boot loader parameter; the value is
4268 passed to the kernel using a special protocol.
4270 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4271 size of <nn>. This can be used to increase the
4272 minimum size (128MB on x86). It can also be used to
4273 decrease the size and leave more room for directly
4276 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4279 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4282 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4286 Controls the behavior of vsyscalls (i.e. calls to
4287 fixed addresses of 0xffffffffff600x00 from legacy
4288 code). Most statically-linked binaries and older
4289 versions of glibc use these calls. Because these
4290 functions are at fixed addresses, they make nice
4291 targets for exploits that can control RIP.
4293 emulate [default] Vsyscalls turn into traps and are
4294 emulated reasonably safely.
4296 native Vsyscalls are native syscall instructions.
4297 This is a little bit faster than trapping
4298 and makes a few dynamic recompilers work
4299 better than they would in emulation mode.
4300 It also makes exploits much easier to write.
4302 none Vsyscalls don't work at all. This makes
4303 them quite hard to use for exploits but
4304 might break your system.
4306 vt.color= [VT] Default text color.
4307 Format: 0xYX, X = foreground, Y = background.
4308 Default: 0x07 = light gray on black.
4310 vt.cur_default= [VT] Default cursor shape.
4311 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4312 the parameters of the <Esc>[?A;B;Cc escape sequence;
4313 see VGA-softcursor.txt. Default: 2 = underline.
4315 vt.default_blu= [VT]
4316 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4317 Change the default blue palette of the console.
4318 This is a 16-member array composed of values
4321 vt.default_grn= [VT]
4322 Format: <green0>,<green1>,<green2>,...,<green15>
4323 Change the default green palette of the console.
4324 This is a 16-member array composed of values
4327 vt.default_red= [VT]
4328 Format: <red0>,<red1>,<red2>,...,<red15>
4329 Change the default red palette of the console.
4330 This is a 16-member array composed of values
4336 Set system-wide default UTF-8 mode for all tty's.
4337 Default is 1, i.e. UTF-8 mode is enabled for all
4338 newly opened terminals.
4340 vt.global_cursor_default=
4343 Set system-wide default for whether a cursor
4344 is shown on new VTs. Default is -1,
4345 i.e. cursors will be created by default unless
4346 overridden by individual drivers. 0 will hide
4347 cursors, 1 will display them.
4349 vt.italic= [VT] Default color for italic text; 0-15.
4352 vt.underline= [VT] Default color for underlined text; 0-15.
4355 watchdog timers [HW,WDT] For information on watchdog timers,
4356 see Documentation/watchdog/watchdog-parameters.txt
4357 or other driver-specific files in the
4358 Documentation/watchdog/ directory.
4360 workqueue.watchdog_thresh=
4361 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4362 warn stall conditions and dump internal state to
4363 help debugging. 0 disables workqueue stall
4364 detection; otherwise, it's the stall threshold
4365 duration in seconds. The default value is 30 and
4366 it can be updated at runtime by writing to the
4367 corresponding sysfs file.
4369 workqueue.disable_numa
4370 By default, all work items queued to unbound
4371 workqueues are affine to the NUMA nodes they're
4372 issued on, which results in better behavior in
4373 general. If NUMA affinity needs to be disabled for
4374 whatever reason, this option can be used. Note
4375 that this also can be controlled per-workqueue for
4376 workqueues visible under /sys/bus/workqueue/.
4378 workqueue.power_efficient
4379 Per-cpu workqueues are generally preferred because
4380 they show better performance thanks to cache
4381 locality; unfortunately, per-cpu workqueues tend to
4382 be more power hungry than unbound workqueues.
4384 Enabling this makes the per-cpu workqueues which
4385 were observed to contribute significantly to power
4386 consumption unbound, leading to measurably lower
4387 power usage at the cost of small performance
4390 The default value of this parameter is determined by
4391 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4393 workqueue.debug_force_rr_cpu
4394 Workqueue used to implicitly guarantee that work
4395 items queued without explicit CPU specified are put
4396 on the local CPU. This guarantee is no longer true
4397 and while local CPU is still preferred work items
4398 may be put on foreign CPUs. This debug option
4399 forces round-robin CPU selection to flush out
4400 usages which depend on the now broken guarantee.
4401 When enabled, memory and cache locality will be
4404 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4405 default x2apic cluster mode on platforms
4408 x86_intel_mid_timer= [X86-32,APBT]
4409 Choose timer option for x86 Intel MID platform.
4410 Two valid options are apbt timer only and lapic timer
4411 plus one apbt timer for broadcast timer.
4412 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4414 xen_512gb_limit [KNL,X86-64,XEN]
4415 Restricts the kernel running paravirtualized under Xen
4416 to use only up to 512 GB of RAM. The reason to do so is
4417 crash analysis tools and Xen tools for doing domain
4418 save/restore/migration must be enabled to handle larger
4421 xen_emul_unplug= [HW,X86,XEN]
4422 Unplug Xen emulated devices
4423 Format: [unplug0,][unplug1]
4424 ide-disks -- unplug primary master IDE devices
4425 aux-ide-disks -- unplug non-primary-master IDE devices
4426 nics -- unplug network devices
4427 all -- unplug all emulated devices (NICs and IDE disks)
4428 unnecessary -- unplugging emulated devices is
4429 unnecessary even if the host did not respond to
4431 never -- do not unplug even if version check succeeds
4433 xen_nopvspin [X86,XEN]
4434 Disables the ticketlock slowpath using Xen PV
4438 Disables the PV optimizations forcing the HVM guest to
4439 run as generic HVM guest with no PV drivers.
4441 xirc2ps_cs= [NET,PCMCIA]
4443 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4445 ______________________________________________________________________
4449 Add more DRM drivers.