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 clearcpuid=BITNUM [X86]
691 Disable CPUID feature X for the kernel. See
692 arch/x86/include/asm/cpufeatures.h for the valid bit
693 numbers. Note the Linux specific bits are not necessarily
694 stable over kernel options, but the vendor specific
696 Also note that user programs calling CPUID directly
697 or using the feature without checking anything
698 will still see it. This just prevents it from
699 being used by the kernel or shown in /proc/cpuinfo.
700 Also note the kernel might malfunction if you disable
703 cma=nn[MG]@[start[MG][-end[MG]]]
705 Sets the size of kernel global memory area for
706 contiguous memory allocations and optionally the
707 placement constraint by the physical address range of
708 memory allocations. A value of 0 disables CMA
709 altogether. For more information, see
710 include/linux/dma-contiguous.h
712 cmo_free_hint= [PPC] Format: { yes | no }
713 Specify whether pages are marked as being inactive
714 when they are freed. This is used in CMO environments
715 to determine OS memory pressure for page stealing by
719 coherent_pool=nn[KMG] [ARM,KNL]
720 Sets the size of memory pool for coherent, atomic dma
721 allocations, by default set to 256K.
723 code_bytes [X86] How many bytes of object code to print
728 com20020= [HW,NET] ARCnet - COM20020 chipset
730 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
732 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
736 ARCnet - COM90xx chipset (memory-mapped buffers)
737 Format: <io>[,<irq>[,<memstart>]]
739 condev= [HW,S390] console device
742 console= [KNL] Output console device and options.
744 tty<n> Use the virtual console device <n>.
748 Use the specified serial port. The options are of
749 the form "bbbbpnf", where "bbbb" is the baud rate,
750 "p" is parity ("n", "o", or "e"), "n" is number of
751 bits, and "f" is flow control ("r" for RTS or
752 omit it). Default is "9600n8".
754 See Documentation/serial-console.txt for more
756 Documentation/networking/netconsole.txt for an
759 uart[8250],io,<addr>[,options]
760 uart[8250],mmio,<addr>[,options]
761 uart[8250],mmio16,<addr>[,options]
762 uart[8250],mmio32,<addr>[,options]
763 uart[8250],0x<addr>[,options]
764 Start an early, polled-mode console on the 8250/16550
765 UART at the specified I/O port or MMIO address,
766 switching to the matching ttyS device later.
767 MMIO inter-register address stride is either 8-bit
768 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
769 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
770 to be equivalent to 'mmio'. 'options' are specified in
771 the same format described for ttyS above; if unspecified,
772 the h/w is not re-initialized.
774 hvc<n> Use the hypervisor console device <n>. This is for
775 both Xen and PowerPC hypervisors.
777 If the device connected to the port is not a TTY but a braille
778 device, prepend "brl," before the device type, for instance
780 For now, only VisioBraille is supported.
782 consoleblank= [KNL] The console blank (screen saver) timeout in
783 seconds. Defaults to 10*60 = 10mins. A value of 0
784 disables the blank timer.
787 [KNL] Change the default value for
788 /proc/<pid>/coredump_filter.
789 See also Documentation/filesystems/proc.txt.
791 cpuidle.off=1 [CPU_IDLE]
792 disable the cpuidle sub-system
795 [X86] Delay for N microsec between assert and de-assert
796 of APIC INIT to start processors. This delay occurs
797 on every CPU online, such as boot, and resume from suspend.
800 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
802 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
804 crashkernel=size[KMG][@offset[KMG]]
805 [KNL] Using kexec, Linux can switch to a 'crash kernel'
806 upon panic. This parameter reserves the physical
807 memory region [offset, offset + size] for that kernel
808 image. If '@offset' is omitted, then a suitable offset
809 is selected automatically. Check
810 Documentation/kdump/kdump.txt for further details.
812 crashkernel=range1:size1[,range2:size2,...][@offset]
813 [KNL] Same as above, but depends on the memory
814 in the running system. The syntax of range is
815 start-[end] where start and end are both
816 a memory unit (amount[KMG]). See also
817 Documentation/kdump/kdump.txt for an example.
819 crashkernel=size[KMG],high
820 [KNL, x86_64] range could be above 4G. Allow kernel
821 to allocate physical memory region from top, so could
822 be above 4G if system have more than 4G ram installed.
823 Otherwise memory region will be allocated below 4G, if
825 It will be ignored if crashkernel=X is specified.
826 crashkernel=size[KMG],low
827 [KNL, x86_64] range under 4G. When crashkernel=X,high
828 is passed, kernel could allocate physical memory region
829 above 4G, that cause second kernel crash on system
830 that require some amount of low memory, e.g. swiotlb
831 requires at least 64M+32K low memory, also enough extra
832 low memory is needed to make sure DMA buffers for 32-bit
833 devices won't run out. Kernel would try to allocate at
834 at least 256M below 4G automatically.
835 This one let user to specify own low range under 4G
836 for second kernel instead.
837 0: to disable low allocation.
838 It will be ignored when crashkernel=X,high is not used
839 or memory reserved is below 4G.
842 [KNL] Disable crypto self-tests
847 cs89x0_media= [HW,NET]
848 Format: { rj45 | aui | bnc }
851 See header of drivers/s390/block/dasd_devmap.c.
853 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
854 (one device per port)
855 Format: <port#>,<type>
856 See also Documentation/input/joystick-parport.txt
858 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
859 time. See Documentation/dynamic-debug-howto.txt for
860 details. Deprecated, see dyndbg.
862 debug [KNL] Enable kernel debugging (events log level).
865 [KNL] verbose self-tests
867 Print debugging info while doing the locking API
869 We default to 0 (no extra messages), setting it to
870 1 will print _a lot_ more information - normally
871 only useful to kernel developers.
873 debug_objects [KNL] Enable object debugging
876 [KNL] Disable object debugging
878 debug_guardpage_minorder=
879 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
880 parameter allows control of the order of pages that will
881 be intentionally kept free (and hence protected) by the
882 buddy allocator. Bigger value increase the probability
883 of catching random memory corruption, but reduce the
884 amount of memory for normal system use. The maximum
885 possible value is MAX_ORDER/2. Setting this parameter
886 to 1 or 2 should be enough to identify most random
887 memory corruption problems caused by bugs in kernel or
888 driver code when a CPU writes to (or reads from) a
889 random memory location. Note that there exists a class
890 of memory corruptions problems caused by buggy H/W or
891 F/W or by drivers badly programing DMA (basically when
892 memory is written at bus level and the CPU MMU is
893 bypassed) which are not detectable by
894 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
895 tracking down these problems.
898 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
899 parameter enables the feature at boot time. In
900 default, it is disabled. We can avoid allocating huge
901 chunk of memory for debug pagealloc if we don't enable
902 it at boot time and the system will work mostly same
903 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
904 on: enable the feature
906 debugpat [X86] Enable PAT debugging
908 decnet.addr= [HW,NET]
909 Format: <area>[,<node>]
910 See also Documentation/networking/decnet.txt.
913 [same as hugepagesz=] The size of the default
914 HugeTLB page size. This is the size represented by
915 the legacy /proc/ hugepages APIs, used for SHM, and
916 default size when mounting hugetlbfs filesystems.
917 Defaults to the default architecture's huge page size
921 Set number of hash buckets for dentry cache.
924 See Documentation/networking/ipv6.txt.
926 disable_cpu_apicid= [X86,APIC,SMP]
928 The number of initial APIC ID for the
929 corresponding CPU to be disabled at boot,
930 mostly used for the kdump 2nd kernel to
931 disable BSP to wake up multiple CPUs without
932 causing system reset or hang due to sending
935 disable_ddw [PPC/PSERIES]
936 Disable Dynamic DMA Window support. Use this if
937 to workaround buggy firmware.
940 See Documentation/networking/ipv6.txt.
942 disable_mtrr_cleanup [X86]
943 The kernel tries to adjust MTRR layout from continuous
944 to discrete, to make X server driver able to add WB
945 entry later. This parameter disables that.
947 disable_mtrr_trim [X86, Intel and AMD only]
948 By default the kernel will trim any uncacheable
949 memory out of your available memory pool based on
950 MTRR settings. This parameter disables that behavior,
951 possibly causing your machine to run very slowly.
953 disable_timer_pin_1 [X86]
954 Disable PIN 1 of APIC timer
955 Can be useful to work around chipset bugs.
957 dis_ucode_ldr [X86] Disable the microcode loader.
959 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
960 this option disables the debugging code at boot.
962 dma_debug_entries=<number>
963 This option allows to tune the number of preallocated
964 entries for DMA-API debugging code. One entry is
965 required per DMA-API allocation. Use this if the
966 DMA-API debugging code disables itself because the
967 architectural default is too low.
969 dma_debug_driver=<driver_name>
970 With this option the DMA-API debugging driver
971 filter feature can be enabled at boot time. Just
972 pass the driver to filter for as the parameter.
973 The filter can be disabled or changed to another
974 driver later using sysfs.
976 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
977 Broken monitors, graphic adapters, KVMs and EDIDless
978 panels may send no or incorrect EDID data sets.
979 This parameter allows to specify an EDID data sets
980 in the /lib/firmware directory that are used instead.
981 Generic built-in EDID data sets are used, if one of
982 edid/1024x768.bin, edid/1280x1024.bin,
983 edid/1680x1050.bin, or edid/1920x1080.bin is given
984 and no file with the same name exists. Details and
985 instructions how to build your own EDID data are
986 available in Documentation/EDID/HOWTO.txt. An EDID
987 data set will only be used for a particular connector,
988 if its name and a colon are prepended to the EDID
989 name. Each connector may use a unique EDID data
990 set by separating the files with a comma. An EDID
991 data set with no connector name will be used for
992 any connectors not explicitly specified.
996 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
997 module.dyndbg[="val"]
998 Enable debug messages at boot time. See
999 Documentation/dynamic-debug-howto.txt for details.
1001 nompx [X86] Disables Intel Memory Protection Extensions.
1002 See Documentation/x86/intel_mpx.txt for more
1003 information about the feature.
1005 nopku [X86] Disable Memory Protection Keys CPU feature found
1009 on enable eager fpu restore
1010 off disable eager fpu restore
1011 auto selects the default scheme, which automatically
1012 enables eagerfpu restore for xsaveopt.
1014 module.async_probe [KNL]
1015 Enable asynchronous probe on this module.
1017 early_ioremap_debug [KNL]
1018 Enable debug messages in early_ioremap support. This
1019 is useful for tracking down temporary early mappings
1020 which are not unmapped.
1022 earlycon= [KNL] Output early console device and options.
1024 When used with no options, the early console is
1025 determined by the stdout-path property in device
1029 Start an early, polled-mode console on a cadence serial
1030 port at the specified address. The cadence serial port
1031 must already be setup and configured. Options are not
1034 uart[8250],io,<addr>[,options]
1035 uart[8250],mmio,<addr>[,options]
1036 uart[8250],mmio32,<addr>[,options]
1037 uart[8250],mmio32be,<addr>[,options]
1038 uart[8250],0x<addr>[,options]
1039 Start an early, polled-mode console on the 8250/16550
1040 UART at the specified I/O port or MMIO address.
1041 MMIO inter-register address stride is either 8-bit
1042 (mmio) or 32-bit (mmio32 or mmio32be).
1043 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1044 to be equivalent to 'mmio'. 'options' are specified
1045 in the same format described for "console=ttyS<n>"; if
1046 unspecified, the h/w is not initialized.
1050 Start an early, polled-mode console on a pl011 serial
1051 port at the specified address. The pl011 serial port
1052 must already be setup and configured. Options are not
1053 yet supported. If 'mmio32' is specified, then only
1054 the driver will use only 32-bit accessors to read/write
1055 the device registers.
1058 Start an early, polled-mode console on a meson serial
1059 port at the specified address. The serial port must
1060 already be setup and configured. Options are not yet
1064 Start an early, polled-mode console on an msm serial
1065 port at the specified address. The serial port
1066 must already be setup and configured. Options are not
1069 msm_serial_dm,<addr>
1070 Start an early, polled-mode console on an msm serial
1071 dm port at the specified address. The serial port
1072 must already be setup and configured. Options are not
1075 smh Use ARM semihosting calls for early console.
1083 Use early console provided by serial driver available
1084 on Samsung SoCs, requires selecting proper type and
1085 a correct base address of the selected UART port. The
1086 serial port must already be setup and configured.
1087 Options are not yet supported.
1091 Use early console provided by Freescale LP UART driver
1092 found on Freescale Vybrid and QorIQ LS1021A processors.
1093 A valid base address must be provided, and the serial
1094 port must already be setup and configured.
1096 armada3700_uart,<addr>
1097 Start an early, polled-mode console on the
1098 Armada 3700 serial port at the specified
1099 address. The serial port must already be setup
1100 and configured. Options are not yet supported.
1102 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1106 earlyprintk=serial[,ttySn[,baudrate]]
1107 earlyprintk=serial[,0x...[,baudrate]]
1108 earlyprintk=ttySn[,baudrate]
1109 earlyprintk=dbgp[debugController#]
1110 earlyprintk=pciserial,bus:device.function[,baudrate]
1112 earlyprintk is useful when the kernel crashes before
1113 the normal console is initialized. It is not enabled by
1114 default because it has some cosmetic problems.
1116 Append ",keep" to not disable it when the real console
1119 Only one of vga, efi, serial, or usb debug port can
1122 Currently only ttyS0 and ttyS1 may be specified by
1123 name. Other I/O ports may be explicitly specified
1124 on some architectures (x86 and arm at least) by
1125 replacing ttySn with an I/O port address, like this:
1126 earlyprintk=serial,0x1008,115200
1127 You can find the port for a given device in
1128 /proc/tty/driver/serial:
1129 2: uart:ST16650V2 port:00001008 irq:18 ...
1131 Interaction with the standard serial driver is not
1134 The VGA and EFI output is eventually overwritten by
1137 The xen output can only be used by Xen PV guests.
1139 edac_report= [HW,EDAC] Control how to report EDAC event
1140 Format: {"on" | "off" | "force"}
1141 on: enable EDAC to report H/W event. May be overridden
1142 by other higher priority error reporting module.
1143 off: disable H/W event reporting through EDAC.
1144 force: enforce the use of EDAC to report H/W event.
1147 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1150 This is designed to be used in conjunction with
1151 the boot argument: earlyprintk=vga
1154 Format: {"off" | "on" | "skip[mbr]"}
1157 Format: { "old_map", "nochunk", "noruntime", "debug" }
1158 old_map [X86-64]: switch to the old ioremap-based EFI
1159 runtime services mapping. 32-bit still uses this one by
1161 nochunk: disable reading files in "chunks" in the EFI
1162 boot stub, as chunking can cause problems with some
1163 firmware implementations.
1164 noruntime : disable EFI runtime services support
1165 debug: enable misc debug output
1167 efi_no_storage_paranoia [EFI; X86]
1168 Using this parameter you can use more than 50% of
1169 your efi variable storage. Use this parameter only if
1170 you are really sure that your UEFI does sane gc and
1171 fulfills the spec otherwise your board may brick.
1173 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1174 Add arbitrary attribute to specific memory range by
1175 updating original EFI memory map.
1176 Region of memory which aa attribute is added to is
1178 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1179 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1180 attribute is added to range 0x100000000-0x180000000 and
1181 0x10a0000000-0x1120000000.
1183 Using this parameter you can do debugging of EFI memmap
1184 related feature. For example, you can do debugging of
1185 Address Range Mirroring feature even if your box
1188 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1189 that is to be dynamically loaded by Linux. If there are
1190 multiple variables with the same name but with different
1191 vendor GUIDs, all of them will be loaded. See
1192 Documentation/acpi/ssdt-overlays.txt for details.
1195 eisa_irq_edge= [PARISC,HW]
1196 See header of drivers/parisc/eisa.c.
1199 See comment before function elanfreq_setup() in
1200 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1203 Format: {"cfq" | "deadline" | "noop"}
1204 See Documentation/block/cfq-iosched.txt and
1205 Documentation/block/deadline-iosched.txt for details.
1207 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1208 Specifies physical address of start of kernel core
1209 image elf header and optionally the size. Generally
1210 kexec loader will pass this option to capture kernel.
1211 See Documentation/kdump/kdump.txt for details.
1213 enable_mtrr_cleanup [X86]
1214 The kernel tries to adjust MTRR layout from continuous
1215 to discrete, to make X server driver able to add WB
1216 entry later. This parameter enables that.
1218 enable_timer_pin_1 [X86]
1219 Enable PIN 1 of APIC timer
1220 Can be useful to work around chipset bugs
1221 (in particular on some ATI chipsets).
1222 The kernel tries to set a reasonable default.
1224 enforcing [SELINUX] Set initial enforcing status.
1226 See security/selinux/Kconfig help text.
1227 0 -- permissive (log only, no denials).
1228 1 -- enforcing (deny and log).
1230 Value can be changed at runtime via /selinux/enforce.
1233 Disable Error Record Serialization Table (ERST)
1236 ether= [HW,NET] Ethernet cards parameters
1237 This option is obsoleted by the "netdev=" option, which
1238 has equivalent usage. See its documentation for details.
1242 Permit 'security.evm' to be updated regardless of
1243 current integrity status.
1247 fail_make_request=[KNL]
1248 General fault injection mechanism.
1249 Format: <interval>,<probability>,<space>,<times>
1250 See also Documentation/fault-injection/.
1253 See Documentation/blockdev/floppy.txt.
1255 force_pal_cache_flush
1256 [IA-64] Avoid check_sal_cache_flush which may hang on
1257 buggy SAL_CACHE_FLUSH implementations. Using this
1258 parameter will force ia64_sal_cache_flush to call
1259 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1262 Forcefully enable Physical Address Extension (PAE).
1263 Many Pentium M systems disable PAE but may have a
1264 functionally usable PAE implementation.
1265 Warning: use of this parameter will taint the kernel
1266 and may cause unknown problems.
1269 [FTRACE] will set and start the specified tracer
1270 as early as possible in order to facilitate early
1273 ftrace_dump_on_oops[=orig_cpu]
1274 [FTRACE] will dump the trace buffers on oops.
1275 If no parameter is passed, ftrace will dump
1276 buffers of all CPUs, but if you pass orig_cpu, it will
1277 dump only the buffer of the CPU that triggered the
1280 ftrace_filter=[function-list]
1281 [FTRACE] Limit the functions traced by the function
1282 tracer at boot up. function-list is a comma separated
1283 list of functions. This list can be changed at run
1284 time by the set_ftrace_filter file in the debugfs
1287 ftrace_notrace=[function-list]
1288 [FTRACE] Do not trace the functions specified in
1289 function-list. This list can be changed at run time
1290 by the set_ftrace_notrace file in the debugfs
1293 ftrace_graph_filter=[function-list]
1294 [FTRACE] Limit the top level callers functions traced
1295 by the function graph tracer at boot up.
1296 function-list is a comma separated list of functions
1297 that can be changed at run time by the
1298 set_graph_function file in the debugfs tracing directory.
1300 ftrace_graph_notrace=[function-list]
1301 [FTRACE] Do not trace from the functions specified in
1302 function-list. This list is a comma separated list of
1303 functions that can be changed at run time by the
1304 set_graph_notrace file in the debugfs tracing directory.
1307 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1308 support via parallel port (up to 5 devices per port)
1309 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1310 See also Documentation/input/joystick-parport.txt
1314 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1318 gcov_persist= [GCOV] When non-zero (default), profiling data for
1319 kernel modules is saved and remains accessible via
1320 debugfs, even when the module is unloaded/reloaded.
1321 When zero, profiling data is discarded and associated
1322 debugfs files are removed at module unload time.
1324 gpt [EFI] Forces disk with valid GPT signature but
1325 invalid Protective MBR to be treated as GPT. If the
1326 primary GPT is corrupted, it enables the backup/alternate
1327 GPT to be used instead.
1329 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1330 the "Enable 0" bit of the configuration register.
1333 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1334 the "Enable 0" bit of the configuration register.
1337 grcan.select= [HW] Select which physical interface to use.
1340 grcan.txsize= [HW] Sets the size of the tx buffer.
1341 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1343 grcan.rxsize= [HW] Sets the size of the rx buffer.
1344 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1347 hardlockup_all_cpu_backtrace=
1348 [KNL] Should the hard-lockup detector generate
1349 backtraces on all cpus.
1352 hashdist= [KNL,NUMA] Large hashes allocated during boot
1353 are distributed across NUMA nodes. Defaults on
1354 for 64-bit NUMA, off otherwise.
1355 Format: 0 | 1 (for off | on)
1357 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1359 hd= [EIDE] (E)IDE hard drive subsystem geometry
1360 Format: <cyl>,<head>,<sect>
1363 Disable Hardware Error Source Table (HEST) support;
1364 corresponding firmware-first mode error processing
1365 logic will be disabled.
1367 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1368 size of <nn>. This works even on boxes that have no
1369 highmem otherwise. This also works to reduce highmem
1370 size on bigger boxes.
1372 highres= [KNL] Enable/disable high resolution timer mode.
1373 Valid parameters: "on", "off"
1377 See Documentation/isdn/README.HiSax.
1381 hpet= [X86-32,HPET] option to control HPET usage
1382 Format: { enable (default) | disable | force |
1384 disable: disable HPET and use PIT instead
1385 force: allow force enabled of undocumented chips (ICH4,
1387 verbose: show contents of HPET registers during setup
1389 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1390 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1392 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1393 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1394 On x86-64 and powerpc, this option can be specified
1395 multiple times interleaved with hugepages= to reserve
1396 huge pages of different sizes. Valid pages sizes on
1397 x86-64 are 2M (when the CPU supports "pse") and 1G
1398 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1400 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1401 terminal devices. Valid values: 0..8
1402 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1403 If specified, z/VM IUCV HVC accepts connections
1404 from listed z/VM user IDs only.
1406 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1407 hardware thread id mappings.
1408 Format: <cpu>:<hwthread>
1411 Do not unregister boot console at start. This is only
1412 useful for debugging when something happens in the window
1413 between unregistering the boot console and initializing
1416 i2c_bus= [HW] Override the default board specific I2C bus speed
1417 or register an additional I2C bus that is not
1418 registered from board initialization code.
1422 i8042.debug [HW] Toggle i8042 debug mode
1423 i8042.unmask_kbd_data
1424 [HW] Enable printing of interrupt data from the KBD port
1425 (disabled by default, and as a pre-condition
1426 requires that i8042.debug=1 be enabled)
1427 i8042.direct [HW] Put keyboard port into non-translated mode
1428 i8042.dumbkbd [HW] Pretend that controller can only read data from
1429 keyboard and cannot control its state
1430 (Don't attempt to blink the leds)
1431 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1432 i8042.nokbd [HW] Don't check/create keyboard port
1433 i8042.noloop [HW] Disable the AUX Loopback command while probing
1435 i8042.nomux [HW] Don't check presence of an active multiplexing
1437 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1439 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1440 i8042.reset [HW] Reset the controller during init and cleanup
1441 i8042.unlock [HW] Unlock (ignore) the keylock
1442 i8042.kbdreset [HW] Reset device connected to KBD port
1446 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1447 indicates that the driver is running on unsupported
1449 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1450 does not match list of supported models.
1452 [HW] Report power status in /proc/i8k
1453 (disabled by default)
1454 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1457 i915.invert_brightness=
1458 [DRM] Invert the sense of the variable that is used to
1459 set the brightness of the panel backlight. Normally a
1460 brightness value of 0 indicates backlight switched off,
1461 and the maximum of the brightness value sets the backlight
1462 to maximum brightness. If this parameter is set to 0
1463 (default) and the machine requires it, or this parameter
1464 is set to 1, a brightness value of 0 sets the backlight
1465 to maximum brightness, and the maximum of the brightness
1466 value switches the backlight off.
1467 -1 -- never invert brightness
1468 0 -- machine default
1469 1 -- force brightness inversion
1472 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1474 ide-core.nodma= [HW] (E)IDE subsystem
1475 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1476 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1477 .cdrom .chs .ignore_cable are additional options
1478 See Documentation/ide/ide.txt.
1480 ide-generic.probe-mask= [HW] (E)IDE subsystem
1482 Probe mask for legacy ISA IDE ports. Depending on
1483 platform up to 6 ports are supported, enabled by
1484 setting corresponding bits in the mask to 1. The
1485 default value is 0x0, which has a special meaning.
1486 On systems that have PCI, it triggers scanning the
1487 PCI bus for the first and the second port, which
1488 are then probed. On systems without PCI the value
1489 of 0x0 enables probing the two first ports as if it
1492 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1493 Claim all unknown PCI IDE storage controllers.
1496 Format: idle=poll, idle=halt, idle=nomwait
1497 Poll forces a polling idle loop that can slightly
1498 improve the performance of waking up a idle CPU, but
1499 will use a lot of power and make the system run hot.
1501 idle=halt: Halt is forced to be used for CPU idle.
1502 In such case C2/C3 won't be used again.
1503 idle=nomwait: Disable mwait for CPU C-states
1505 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1506 Format: { strict | legacy | 2008 | relaxed }
1509 Choose which programs will be accepted for execution
1510 based on the IEEE 754 NaN encoding(s) supported by
1511 the FPU and the NaN encoding requested with the value
1512 of an ELF file header flag individually set by each
1513 binary. Hardware implementations are permitted to
1514 support either or both of the legacy and the 2008 NaN
1517 Available settings are as follows:
1518 strict accept binaries that request a NaN encoding
1519 supported by the FPU
1520 legacy only accept legacy-NaN binaries, if supported
1522 2008 only accept 2008-NaN binaries, if supported
1524 relaxed accept any binaries regardless of whether
1525 supported by the FPU
1527 The FPU emulator is always able to support both NaN
1528 encodings, so if no FPU hardware is present or it has
1529 been disabled with 'nofpu', then the settings of
1530 'legacy' and '2008' strap the emulator accordingly,
1531 'relaxed' straps the emulator for both legacy-NaN and
1532 2008-NaN, whereas 'strict' enables legacy-NaN only on
1533 legacy processors and both NaN encodings on MIPS32 or
1536 The setting for ABS.fmt/NEG.fmt instruction execution
1537 mode generally follows that for the NaN encoding,
1538 except where unsupported by hardware.
1540 ignore_loglevel [KNL]
1541 Ignore loglevel setting - this will print /all/
1542 kernel messages to the console. Useful for debugging.
1543 We also add it as printk module parameter, so users
1544 could change it dynamically, usually by
1545 /sys/module/printk/parameters/ignore_loglevel.
1548 Ignore RLIMIT_DATA setting for data mappings,
1549 print warning at first misuse. Can be changed via
1550 /sys/module/kernel/parameters/ignore_rlimit_data.
1552 ihash_entries= [KNL]
1553 Set number of hash buckets for inode cache.
1555 ima_appraise= [IMA] appraise integrity measurements
1556 Format: { "off" | "enforce" | "fix" | "log" }
1559 ima_appraise_tcb [IMA]
1560 The builtin appraise policy appraises all files
1564 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1568 The list of supported hash algorithms is defined
1569 in crypto/hash_info.h.
1572 The builtin measurement policy to load during IMA
1573 setup. Specyfing "tcb" as the value, measures all
1574 programs exec'd, files mmap'd for exec, and all files
1575 opened with the read mode bit set by either the
1576 effective uid (euid=0) or uid=0.
1579 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1580 Load a policy which meets the needs of the Trusted
1581 Computing Base. This means IMA will measure all
1582 programs exec'd, files mmap'd for exec, and all files
1583 opened for read by uid=0.
1586 Select one of defined IMA measurements template formats.
1587 Formats: { "ima" | "ima-ng" | "ima-sig" }
1591 [IMA] Define a custom template format.
1592 Format: { "field1|...|fieldN" }
1594 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1595 Format: <min_file_size>
1596 Set the minimal file size for using asynchronous hash.
1597 If left unspecified, ahash usage is disabled.
1599 ahash performance varies for different data sizes on
1600 different crypto accelerators. This option can be used
1601 to achieve the best performance for a particular HW.
1603 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1605 Set hashing buffer size. Default: 4k.
1607 ahash performance varies for different chunk sizes on
1608 different crypto accelerators. This option can be used
1609 to achieve best performance for particular HW.
1613 Run specified binary instead of /sbin/init as init
1616 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1617 for working out where the kernel is dying during
1620 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1621 initcall functions. Useful for debugging built-in
1622 modules and initcalls.
1624 initrd= [BOOT] Specify the location of the initial ramdisk
1626 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1629 int_pln_enable [x86] Enable power limit notification interrupt
1631 integrity_audit=[IMA]
1632 Format: { "0" | "1" }
1633 0 -- basic integrity auditing messages. (Default)
1634 1 -- additional integrity auditing messages.
1636 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1638 Enable intel iommu driver.
1640 Disable intel iommu driver.
1641 igfx_off [Default Off]
1642 By default, gfx is mapped as normal device. If a gfx
1643 device has a dedicated DMAR unit, the DMAR unit is
1644 bypassed by not enabling DMAR with this option. In
1645 this case, gfx device will use physical address for
1648 With this option iommu will not optimize to look
1649 for io virtual address below 32-bit forcing dual
1650 address cycle on pci bus for cards supporting greater
1651 than 32-bit addressing. The default is to look
1652 for translation below 32-bit and if not available
1653 then look in the higher range.
1654 strict [Default Off]
1655 With this option on every unmap_single operation will
1656 result in a hardware IOTLB flush operation as opposed
1657 to batching them for performance.
1658 sp_off [Default Off]
1659 By default, super page will be supported if Intel IOMMU
1660 has the capability. With this option, super page will
1662 ecs_off [Default Off]
1663 By default, extended context tables will be supported if
1664 the hardware advertises that it has support both for the
1665 extended tables themselves, and also PASID support. With
1666 this option set, extended tables will not be used even
1667 on hardware which claims to support them.
1669 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1670 0 disables intel_idle and fall back on acpi_idle.
1671 1 to 6 specify maximum depth of C-state.
1675 Do not enable intel_pstate as the default
1676 scaling driver for the supported processors
1678 Enable intel_pstate on systems that prohibit it by default
1679 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1680 instead of acpi-cpufreq may disable platform features, such
1681 as thermal controls and power capping, that rely on ACPI
1682 P-States information being indicated to OSPM and therefore
1683 should be used with caution. This option does not work with
1684 processors that aren't supported by the intel_pstate driver
1685 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1687 Do not enable hardware P state control (HWP)
1690 Only load intel_pstate on systems which support
1691 hardware P state control (HWP) if available.
1693 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1694 Description Table, specifies preferred power management
1695 profile as "Enterprise Server" or "Performance Server",
1696 then this feature is turned on by default.
1698 intremap= [X86-64, Intel-IOMMU]
1699 on enable Interrupt Remapping (default)
1700 off disable Interrupt Remapping
1701 nosid disable Source ID checking
1703 BIOS x2APIC opt-out request will be ignored
1704 nopost disable Interrupt Posting
1706 iomem= Disable strict checking of access to MMIO memory
1707 strict regions from userspace.
1722 nobypass [PPC/POWERNV]
1723 Disable IOMMU bypass, using IOMMU for PCI devices.
1726 io7= [HW] IO7 for Marvel based alpha systems
1727 See comment before marvel_specify_io7 in
1728 arch/alpha/kernel/core_marvel.c.
1730 io_delay= [X86] I/O delay method
1732 Standard port 0x80 based delay
1734 Alternate port 0xed based delay (needed on some systems)
1736 Simple two microseconds delay
1741 See Documentation/filesystems/nfs/nfsroot.txt.
1743 irqaffinity= [SMP] Set the default irq affinity mask
1745 <cpu number>,...,<cpu number>
1747 <cpu number>-<cpu number>
1748 (must be a positive range in ascending order)
1750 <cpu number>,...,<cpu number>-<cpu number>
1753 When an interrupt is not handled search all handlers
1754 for it. Intended to get systems with badly broken
1758 When an interrupt is not handled search all handlers
1759 for it. Also check all handlers each timer
1760 interrupt. Intended to get systems with badly broken
1764 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1766 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1768 <cpu number>,...,<cpu number>
1770 <cpu number>-<cpu number>
1771 (must be a positive range in ascending order)
1773 <cpu number>,...,<cpu number>-<cpu number>
1775 This option can be used to specify one or more CPUs
1776 to isolate from the general SMP balancing and scheduling
1777 algorithms. You can move a process onto or off an
1778 "isolated" CPU via the CPU affinity syscalls or cpuset.
1779 <cpu number> begins at 0 and the maximum value is
1780 "number of CPUs in system - 1".
1782 This option is the preferred way to isolate CPUs. The
1783 alternative -- manually setting the CPU mask of all
1784 tasks in the system -- can cause problems and
1785 suboptimal load balancer performance.
1789 ivrs_ioapic [HW,X86_64]
1790 Provide an override to the IOAPIC-ID<->DEVICE-ID
1791 mapping provided in the IVRS ACPI table. For
1792 example, to map IOAPIC-ID decimal 10 to
1793 PCI device 00:14.0 write the parameter as:
1794 ivrs_ioapic[10]=00:14.0
1796 ivrs_hpet [HW,X86_64]
1797 Provide an override to the HPET-ID<->DEVICE-ID
1798 mapping provided in the IVRS ACPI table. For
1799 example, to map HPET-ID decimal 0 to
1800 PCI device 00:14.0 write the parameter as:
1801 ivrs_hpet[0]=00:14.0
1803 ivrs_acpihid [HW,X86_64]
1804 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1805 mapping provided in the IVRS ACPI table. For
1806 example, to map UART-HID:UID AMD0020:0 to
1807 PCI device 00:14.5 write the parameter as:
1808 ivrs_acpihid[00:14.5]=AMD0020:0
1810 js= [HW,JOY] Analog joystick
1811 See Documentation/input/joystick.txt.
1814 Enable/disable kernel and module base offset ASLR
1815 (Address Space Layout Randomization) if built into
1816 the kernel. When CONFIG_HIBERNATION is selected,
1817 kASLR is disabled by default. When kASLR is enabled,
1818 hibernation will be disabled.
1822 kernelcore= [KNL,X86,IA-64,PPC]
1823 Format: nn[KMGTPE] | "mirror"
1825 specifies the amount of memory usable by the kernel
1826 for non-movable allocations. The requested amount is
1827 spread evenly throughout all nodes in the system. The
1828 remaining memory in each node is used for Movable
1829 pages. In the event, a node is too small to have both
1830 kernelcore and Movable pages, kernelcore pages will
1831 take priority and other nodes will have a larger number
1832 of Movable pages. The Movable zone is used for the
1833 allocation of pages that may be reclaimed or moved
1834 by the page migration subsystem. This means that
1835 HugeTLB pages may not be allocated from this zone.
1836 Note that allocations like PTEs-from-HighMem still
1837 use the HighMem zone if it exists, and the Normal
1838 zone if it does not.
1840 Instead of specifying the amount of memory (nn[KMGTPE]),
1841 you can specify "mirror" option. In case "mirror"
1842 option is specified, mirrored (reliable) memory is used
1843 for non-movable allocations and remaining memory is used
1844 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1845 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1848 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1849 Format: <Controller#>[,poll interval]
1850 The controller # is the number of the ehci usb debug
1851 port as it is probed via PCI. The poll interval is
1852 optional and is the number seconds in between
1853 each poll cycle to the debug port in case you need
1854 the functionality for interrupting the kernel with
1855 gdb or control-c on the dbgp connection. When
1856 not using this parameter you use sysrq-g to break into
1857 the kernel debugger.
1859 kgdboc= [KGDB,HW] kgdb over consoles.
1860 Requires a tty driver that supports console polling,
1861 or a supported polling keyboard driver (non-usb).
1862 Serial only format: <serial_device>[,baud]
1863 keyboard only format: kbd
1864 keyboard and serial format: kbd,<serial_device>[,baud]
1865 Optional Kernel mode setting:
1866 kms, kbd format: kms,kbd
1867 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1869 kgdbwait [KGDB] Stop kernel execution and enter the
1870 kernel debugger at the earliest opportunity.
1872 kmac= [MIPS] korina ethernet MAC address.
1873 Configure the RouterBoard 532 series on-chip
1874 Ethernet adapter MAC address.
1876 kmemleak= [KNL] Boot-time kmemleak enable/disable
1877 Valid arguments: on, off
1879 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1882 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1883 Valid arguments: 0, 1, 2
1884 kmemcheck=0 (disabled)
1885 kmemcheck=1 (enabled)
1886 kmemcheck=2 (one-shot mode)
1887 Default: 2 (one-shot mode)
1889 kstack=N [X86] Print N words from the kernel stack
1892 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1893 Default is 0 (don't ignore, but inject #GP)
1895 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1899 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1900 Default is 1 (enabled)
1902 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1904 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1906 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1907 (virtualized MMU) support on capable Intel chips.
1908 Default is 1 (enabled)
1910 kvm-intel.emulate_invalid_guest_state=
1911 [KVM,Intel] Enable emulation of invalid guest states
1912 Default is 0 (disabled)
1914 kvm-intel.flexpriority=
1915 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1916 Default is 1 (enabled)
1919 [KVM,Intel] Enable VMX nesting (nVMX).
1920 Default is 0 (disabled)
1922 kvm-intel.unrestricted_guest=
1923 [KVM,Intel] Disable unrestricted guest feature
1924 (virtualized real and unpaged mode) on capable
1925 Intel chips. Default is 1 (enabled)
1927 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1928 feature (tagged TLBs) on capable Intel chips.
1929 Default is 1 (enabled)
1935 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1938 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1939 value for LAPIC timer one-shot implementation. Default
1940 back to the programmable timer unit in the LAPIC.
1942 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1945 libata.dma= [LIBATA] DMA control
1946 libata.dma=0 Disable all PATA and SATA DMA
1947 libata.dma=1 PATA and SATA Disk DMA only
1948 libata.dma=2 ATAPI (CDROM) DMA only
1949 libata.dma=4 Compact Flash DMA only
1950 Combinations also work, so libata.dma=3 enables DMA
1951 for disks and CDROMs, but not CFs.
1953 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1954 libata.ignore_hpa=0 keep BIOS limits (default)
1955 libata.ignore_hpa=1 ignore limits, using full disk
1957 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1961 libata.force= [LIBATA] Force configurations. The format is comma
1962 separated list of "[ID:]VAL" where ID is
1963 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1964 matching port, link or device. Basically, it matches
1965 the ATA ID string printed on console by libata. If
1966 the whole ID part is omitted, the last PORT and DEVICE
1967 values are used. If ID hasn't been specified yet, the
1968 configuration applies to all ports, links and devices.
1970 If only DEVICE is omitted, the parameter applies to
1971 the port and all links and devices behind it. DEVICE
1972 number of 0 either selects the first device or the
1973 first fan-out link behind PMP device. It does not
1974 select the host link. DEVICE number of 15 selects the
1975 host link and device attached to it.
1977 The VAL specifies the configuration to force. As long
1978 as there's no ambiguity shortcut notation is allowed.
1979 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1980 The following configurations can be forced.
1982 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1983 Any ID with matching PORT is used.
1985 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1987 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1988 udma[/][16,25,33,44,66,100,133] notation is also
1991 * [no]ncq: Turn on or off NCQ.
1993 * [no]ncqtrim: Turn off queued DSM TRIM.
1995 * nohrst, nosrst, norst: suppress hard, soft
1998 * rstonce: only attempt one reset during
1999 hot-unplug link recovery
2001 * dump_id: dump IDENTIFY data.
2003 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2005 * disable: Disable this device.
2007 If there are multiple matching configurations changing
2008 the same attribute, the last one is used.
2010 memblock=debug [KNL] Enable memblock debug messages.
2012 load_ramdisk= [RAM] List of ramdisks to load from floppy
2013 See Documentation/blockdev/ramdisk.txt.
2015 lockd.nlm_grace_period=P [NFS] Assign grace period.
2018 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2021 lockd.nlm_timeout=T [NFS] Assign timeout value.
2024 lockd.nlm_udpport=M [NFS] Assign UDP port.
2027 locktorture.nreaders_stress= [KNL]
2028 Set the number of locking read-acquisition kthreads.
2029 Defaults to being automatically set based on the
2030 number of online CPUs.
2032 locktorture.nwriters_stress= [KNL]
2033 Set the number of locking write-acquisition kthreads.
2035 locktorture.onoff_holdoff= [KNL]
2036 Set time (s) after boot for CPU-hotplug testing.
2038 locktorture.onoff_interval= [KNL]
2039 Set time (s) between CPU-hotplug operations, or
2040 zero to disable CPU-hotplug testing.
2042 locktorture.shuffle_interval= [KNL]
2043 Set task-shuffle interval (jiffies). Shuffling
2044 tasks allows some CPUs to go into dyntick-idle
2045 mode during the locktorture test.
2047 locktorture.shutdown_secs= [KNL]
2048 Set time (s) after boot system shutdown. This
2049 is useful for hands-off automated testing.
2051 locktorture.stat_interval= [KNL]
2052 Time (s) between statistics printk()s.
2054 locktorture.stutter= [KNL]
2055 Time (s) to stutter testing, for example,
2056 specifying five seconds causes the test to run for
2057 five seconds, wait for five seconds, and so on.
2058 This tests the locking primitive's ability to
2059 transition abruptly to and from idle.
2061 locktorture.torture_runnable= [BOOT]
2062 Start locktorture running at boot time.
2064 locktorture.torture_type= [KNL]
2065 Specify the locking implementation to test.
2067 locktorture.verbose= [KNL]
2068 Enable additional printk() statements.
2070 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2073 loglevel= All Kernel Messages with a loglevel smaller than the
2074 console loglevel will be printed to the console. It can
2075 also be changed with klogd or other programs. The
2076 loglevels are defined as follows:
2078 0 (KERN_EMERG) system is unusable
2079 1 (KERN_ALERT) action must be taken immediately
2080 2 (KERN_CRIT) critical conditions
2081 3 (KERN_ERR) error conditions
2082 4 (KERN_WARNING) warning conditions
2083 5 (KERN_NOTICE) normal but significant condition
2084 6 (KERN_INFO) informational
2085 7 (KERN_DEBUG) debug-level messages
2087 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2088 in bytes. n must be a power of two and greater
2089 than the minimal size. The minimal size is defined
2090 by LOG_BUF_SHIFT kernel config parameter. There is
2091 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2092 that allows to increase the default size depending on
2093 the number of CPUs. See init/Kconfig for more details.
2095 logo.nologo [FB] Disables display of the built-in Linux logo.
2096 This may be used to provide more screen space for
2097 kernel log messages and is useful when debugging
2098 kernel boot problems.
2100 lp=0 [LP] Specify parallel ports to use, e.g,
2101 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2102 lp=reset first parallel port). 'lp=0' disables the
2103 lp=auto printer driver. 'lp=reset' (which can be
2104 specified in addition to the ports) causes
2105 attached printers to be reset. Using
2106 lp=port1,port2,... specifies the parallel ports
2107 to associate lp devices with, starting with
2108 lp0. A port specification may be 'none' to skip
2109 that lp device, or a parport name such as
2110 'parport0'. Specifying 'lp=auto' instead of a
2111 port specification list means that device IDs
2112 from each port should be examined, to see if
2113 an IEEE 1284-compliant printer is attached; if
2114 so, the driver will manage that printer.
2115 See also header of drivers/char/lp.c.
2118 Sets loops_per_jiffy to given constant, thus avoiding
2119 time-consuming boot-time autodetection (up to 250 ms per
2120 CPU). 0 enables autodetection (default). To determine
2121 the correct value for your kernel, boot with normal
2122 autodetection and see what value is printed. Note that
2123 on SMP systems the preset will be applied to all CPUs,
2124 which is likely to cause problems if your CPUs need
2125 significantly divergent settings. An incorrect value
2126 will cause delays in the kernel to be wrong, leading to
2127 unpredictable I/O errors and other breakage. Although
2128 unlikely, in the extreme case this might damage your
2132 Format: <io>,<irq>,<dma>
2134 machvec= [IA-64] Force the use of a particular machine-vector
2135 (machvec) in a generic kernel.
2136 Example: machvec=hpzx1_swiotlb
2138 machtype= [Loongson] Share the same kernel image file between different
2140 Example: machtype=lemote-yeeloong-2f-7inch
2142 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2143 than or equal to this physical address is ignored.
2145 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2146 should make use of. maxcpus=n : n >= 0 limits the
2147 kernel to using 'n' processors. n=0 is a special case,
2148 it is equivalent to "nosmp", which also disables
2151 max_loop= [LOOP] The number of loop block devices that get
2152 (loop.max_loop) unconditionally pre-created at init time. The default
2153 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2154 of statically allocating a predefined number, loop
2155 devices can be requested on-demand with the
2156 /dev/loop-control interface.
2158 mce [X86-32] Machine Check Exception
2160 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2162 md= [HW] RAID subsystems devices and level
2163 See Documentation/md.txt.
2166 Format: <first>,<last>
2167 Specifies range of consoles to be captured by the MDA.
2169 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2170 Amount of memory to be used when the kernel is not able
2171 to see the whole system memory or for test.
2172 [X86] Work as limiting max address. Use together
2173 with memmap= to avoid physical address space collisions.
2174 Without memmap= PCI devices could be placed at addresses
2175 belonging to unused RAM.
2177 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2181 [KNL,SH] Allow user to override the default size for
2182 per-device physically contiguous DMA buffers.
2184 memhp_default_state=online/offline
2185 [KNL] Set the initial state for the memory hotplug
2186 onlining policy. If not specified, the default value is
2187 set according to the
2188 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2190 See Documentation/memory-hotplug.txt.
2192 memmap=exactmap [KNL,X86] Enable setting of an exact
2193 E820 memory map, as specified by the user.
2194 Such memmap=exactmap lines can be constructed based on
2195 BIOS output or other requirements. See the memmap=nn@ss
2198 memmap=nn[KMG]@ss[KMG]
2199 [KNL] Force usage of a specific region of memory.
2200 Region of memory to be used is from ss to ss+nn.
2202 memmap=nn[KMG]#ss[KMG]
2203 [KNL,ACPI] Mark specific memory as ACPI data.
2204 Region of memory to be marked is from ss to ss+nn.
2206 memmap=nn[KMG]$ss[KMG]
2207 [KNL,ACPI] Mark specific memory as reserved.
2208 Region of memory to be reserved is from ss to ss+nn.
2209 Example: Exclude memory from 0x18690000-0x1869ffff
2210 memmap=64K$0x18690000
2212 memmap=0x10000$0x18690000
2214 memmap=nn[KMG]!ss[KMG]
2215 [KNL,X86] Mark specific memory as protected.
2216 Region of memory to be used, from ss to ss+nn.
2217 The memory region may be marked as e820 type 12 (0xc)
2218 and is NVDIMM or ADR memory.
2220 memory_corruption_check=0/1 [X86]
2221 Some BIOSes seem to corrupt the first 64k of
2222 memory when doing things like suspend/resume.
2223 Setting this option will scan the memory
2224 looking for corruption. Enabling this will
2225 both detect corruption and prevent the kernel
2226 from using the memory being corrupted.
2227 However, its intended as a diagnostic tool; if
2228 repeatable BIOS-originated corruption always
2229 affects the same memory, you can use memmap=
2230 to prevent the kernel from using that memory.
2232 memory_corruption_check_size=size [X86]
2233 By default it checks for corruption in the low
2234 64k, making this memory unavailable for normal
2235 use. Use this parameter to scan for
2236 corruption in more or less memory.
2238 memory_corruption_check_period=seconds [X86]
2239 By default it checks for corruption every 60
2240 seconds. Use this parameter to check at some
2241 other rate. 0 disables periodic checking.
2243 memtest= [KNL,X86,ARM] Enable memtest
2245 default : 0 <disable>
2246 Specifies the number of memtest passes to be
2247 performed. Each pass selects another test
2248 pattern from a given set of patterns. Memtest
2249 fills the memory with this pattern, validates
2250 memory contents and reserves bad memory
2251 regions that are detected.
2253 meye.*= [HW] Set MotionEye Camera parameters
2254 See Documentation/video4linux/meye.txt.
2256 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2257 Multi-Function General Purpose Timers on AMD Geode
2260 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2261 the BIOS has incorrectly applied a workaround. TinyBIOS
2262 version 0.98 is known to be affected, 0.99 fixes the
2263 problem by letting the user disable the workaround.
2267 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2268 physical address is ignored.
2270 mini2440= [ARM,HW,KNL]
2271 Format:[0..2][b][c][t]
2273 MINI2440 configuration specification:
2274 0 - The attached screen is the 3.5" TFT
2275 1 - The attached screen is the 7" TFT
2276 2 - The VGA Shield is attached (1024x768)
2277 Leaving out the screen size parameter will not load
2278 the TFT driver, and the framebuffer will be left
2280 b - Enable backlight. The TFT backlight pin will be
2281 linked to the kernel VESA blanking code and a GPIO
2282 LED. This parameter is not necessary when using the
2284 c - Enable the s3c camera interface.
2285 t - Reserved for enabling touchscreen support. The
2286 touchscreen support is not enabled in the mainstream
2287 kernel as of 2.6.30, a preliminary port can be found
2288 in the "bleeding edge" mini2440 support kernel at
2289 http://repo.or.cz/w/linux-2.6/mini2440.git
2292 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2293 parameter allows control of the logging verbosity for
2294 the additional memory initialisation checks. A value
2295 of 0 disables mminit logging and a level of 4 will
2296 log everything. Information is printed at KERN_DEBUG
2297 so loglevel=8 may also need to be specified.
2300 [KNL] When CONFIG_MODULE_SIG is set, this means that
2301 modules without (valid) signatures will fail to load.
2302 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2303 is always true, so this option does nothing.
2306 [MOUSE] Maximum time between finger touching and
2307 leaving touchpad surface for touch to be considered
2308 a tap and be reported as a left button click (for
2309 touchpads working in absolute mode only).
2311 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2312 reporting absolute coordinates, such as tablets
2313 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2314 reporting absolute coordinates, such as tablets
2316 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2317 is similar to kernelcore except it specifies the
2318 amount of memory used for migratable allocations.
2319 If both kernelcore and movablecore is specified,
2320 then kernelcore will be at *least* the specified
2321 value but may be more. If movablecore on its own
2322 is specified, the administrator must be careful
2323 that the amount of memory usable for all allocations
2326 movable_node [KNL,X86] Boot-time switch to enable the effects
2327 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2329 MTD_Partition= [MTD]
2330 Format: <name>,<region-number>,<size>,<offset>
2332 MTD_Region= [MTD] Format:
2333 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2336 See drivers/mtd/cmdlinepart.c.
2338 multitce=off [PPC] This parameter disables the use of the pSeries
2339 firmware feature for updating multiple TCE entries
2342 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2344 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2346 boundary - index of last SLC block on Flex-OneNAND.
2347 The remaining blocks are configured as MLC blocks.
2348 lock - Configure if Flex-OneNAND boundary should be locked.
2349 Once locked, the boundary cannot be changed.
2350 1 indicates lock status, 0 indicates unlock status.
2353 ARM/S3C2412 JIVE boot control
2355 See arch/arm/mach-s3c2412/mach-jive.c
2357 mtouchusb.raw_coordinates=
2358 [HW] Make the MicroTouch USB driver use raw coordinates
2359 ('y', default) or cooked coordinates ('n')
2361 mtrr_chunk_size=nn[KMG] [X86]
2362 used for mtrr cleanup. It is largest continuous chunk
2363 that could hold holes aka. UC entries.
2365 mtrr_gran_size=nn[KMG] [X86]
2366 Used for mtrr cleanup. It is granularity of mtrr block.
2368 Large value could prevent small alignment from
2371 mtrr_spare_reg_nr=n [X86]
2373 Range: 0,7 : spare reg number
2375 Used for mtrr cleanup. It is spare mtrr entries number.
2376 Set to 2 or more if your graphical card needs more.
2378 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2380 netdev= [NET] Network devices parameters
2381 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2382 Note that mem_start is often overloaded to mean
2383 something different and driver-specific.
2384 This usage is only documented in each driver source
2388 [NETFILTER] Enable connection tracking flow accounting
2389 0 to disable accounting
2390 1 to enable accounting
2393 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2394 See Documentation/filesystems/nfs/nfsroot.txt.
2396 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2397 See Documentation/filesystems/nfs/nfsroot.txt.
2399 nfsrootdebug [NFS] enable nfsroot debugging messages.
2400 See Documentation/filesystems/nfs/nfsroot.txt.
2402 nfs.callback_tcpport=
2403 [NFS] set the TCP port on which the NFSv4 callback
2404 channel should listen.
2407 [NFS] sets the pathname to the program which is used
2408 to update the NFS client cache entries.
2410 nfs.cache_getent_timeout=
2411 [NFS] sets the timeout after which an attempt to
2412 update a cache entry is deemed to have failed.
2414 nfs.idmap_cache_timeout=
2415 [NFS] set the maximum lifetime for idmapper cache
2419 [NFS] enable 64-bit inode numbers.
2420 If zero, the NFS client will fake up a 32-bit inode
2421 number for the readdir() and stat() syscalls instead
2422 of returning the full 64-bit number.
2423 The default is to return 64-bit inode numbers.
2425 nfs.max_session_slots=
2426 [NFSv4.1] Sets the maximum number of session slots
2427 the client will attempt to negotiate with the server.
2428 This limits the number of simultaneous RPC requests
2429 that the client can send to the NFSv4.1 server.
2430 Note that there is little point in setting this
2431 value higher than the max_tcp_slot_table_limit.
2433 nfs.nfs4_disable_idmapping=
2434 [NFSv4] When set to the default of '1', this option
2435 ensures that both the RPC level authentication
2436 scheme and the NFS level operations agree to use
2437 numeric uids/gids if the mount is using the
2438 'sec=sys' security flavour. In effect it is
2439 disabling idmapping, which can make migration from
2440 legacy NFSv2/v3 systems to NFSv4 easier.
2441 Servers that do not support this mode of operation
2442 will be autodetected by the client, and it will fall
2443 back to using the idmapper.
2444 To turn off this behaviour, set the value to '0'.
2446 [NFS4] Specify an additional fixed unique ident-
2447 ification string that NFSv4 clients can insert into
2448 their nfs_client_id4 string. This is typically a
2449 UUID that is generated at system install time.
2451 nfs.send_implementation_id =
2452 [NFSv4.1] Send client implementation identification
2453 information in exchange_id requests.
2454 If zero, no implementation identification information
2456 The default is to send the implementation identification
2459 nfs.recover_lost_locks =
2460 [NFSv4] Attempt to recover locks that were lost due
2461 to a lease timeout on the server. Please note that
2462 doing this risks data corruption, since there are
2463 no guarantees that the file will remain unchanged
2464 after the locks are lost.
2465 If you want to enable the kernel legacy behaviour of
2466 attempting to recover these locks, then set this
2468 The default parameter value of '0' causes the kernel
2469 not to attempt recovery of lost locks.
2471 nfs4.layoutstats_timer =
2472 [NFSv4.2] Change the rate at which the kernel sends
2473 layoutstats to the pNFS metadata server.
2475 Setting this to value to 0 causes the kernel to use
2476 whatever value is the default set by the layout
2477 driver. A non-zero value sets the minimum interval
2478 in seconds between layoutstats transmissions.
2480 nfsd.nfs4_disable_idmapping=
2481 [NFSv4] When set to the default of '1', the NFSv4
2482 server will return only numeric uids and gids to
2483 clients using auth_sys, and will accept numeric uids
2484 and gids from such clients. This is intended to ease
2485 migration from NFSv2/v3.
2487 objlayoutdriver.osd_login_prog=
2488 [NFS] [OBJLAYOUT] sets the pathname to the program which
2489 is used to automatically discover and login into new
2490 osd-targets. Please see:
2491 Documentation/filesystems/pnfs.txt for more explanations
2493 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2494 when a NMI is triggered.
2495 Format: [state][,regs][,debounce][,die]
2497 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2498 Format: [panic,][nopanic,][num]
2500 0 - turn hardlockup detector in nmi_watchdog off
2501 1 - turn hardlockup detector in nmi_watchdog on
2502 When panic is specified, panic when an NMI watchdog
2503 timeout occurs (or 'nopanic' to override the opposite
2504 default). To disable both hard and soft lockup detectors,
2505 please see 'nowatchdog'.
2506 This is useful when you use a panic=... timeout and
2507 need the box quickly up again.
2509 netpoll.carrier_timeout=
2510 [NET] Specifies amount of time (in seconds) that
2511 netpoll should wait for a carrier. By default netpoll
2514 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2515 emulation library even if a 387 maths coprocessor
2519 [HW] Never suspend the console
2520 Disable suspending of consoles during suspend and
2521 hibernate operations. Once disabled, debugging
2522 messages can reach various consoles while the rest
2523 of the system is being put to sleep (ie, while
2524 debugging driver suspend/resume hooks). This may
2525 not work reliably with all consoles, but is known
2526 to work with serial and VGA consoles.
2527 To facilitate more flexible debugging, we also add
2528 console_suspend, a printk module parameter to control
2529 it. Users could use console_suspend (usually
2530 /sys/module/printk/parameters/console_suspend) to
2531 turn on/off it dynamically.
2533 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2534 caches in the slab allocator. Saves per-node memory,
2535 but will impact performance.
2539 noapic [SMP,APIC] Tells the kernel to not make use of any
2540 IOAPICs that may be present in the system.
2542 noautogroup Disable scheduler automatic task group creation.
2544 nobats [PPC] Do not use BATs for mapping kernel lowmem
2545 on "Classic" PPC cores.
2549 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2551 nodelayacct [KNL] Disable per-task delay accounting
2553 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2555 nodsp [SH] Disable hardware DSP at boot time.
2557 noefi Disable EFI runtime services support.
2562 On X86-32 available only on PAE configured kernels.
2563 noexec=on: enable non-executable mappings (default)
2564 noexec=off: disable non-executable mappings
2567 Disable SMAP (Supervisor Mode Access Prevention)
2568 even if it is supported by processor.
2571 Disable SMEP (Supervisor Mode Execution Prevention)
2572 even if it is supported by processor.
2575 This affects only 32-bit executables.
2576 noexec32=on: enable non-executable mappings (default)
2577 read doesn't imply executable mappings
2578 noexec32=off: disable non-executable mappings
2579 read implies executable mappings
2581 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2583 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2584 register save and restore. The kernel will only save
2585 legacy floating-point registers on task switch.
2587 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2589 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2590 Equivalent to smt=1.
2592 noxsave [BUGS=X86] Disables x86 extended register state save
2593 and restore using xsave. The kernel will fallback to
2594 enabling legacy floating-point and sse state.
2596 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2597 register states. The kernel will fall back to use
2598 xsave to save the states. By using this parameter,
2599 performance of saving the states is degraded because
2600 xsave doesn't support modified optimization while
2601 xsaveopt supports it on xsaveopt enabled systems.
2603 noxsaves [X86] Disables xsaves and xrstors used in saving and
2604 restoring x86 extended register state in compacted
2605 form of xsave area. The kernel will fall back to use
2606 xsaveopt and xrstor to save and restore the states
2607 in standard form of xsave area. By using this
2608 parameter, xsave area per process might occupy more
2609 memory on xsaves enabled systems.
2611 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2612 wfi(ARM) instruction doesn't work correctly and not to
2613 use it. This is also useful when using JTAG debugger.
2615 no_file_caps Tells the kernel not to honor file capabilities. The
2616 only way then for a file to be executed with privilege
2617 is to be setuid root or executed by root.
2619 nohalt [IA-64] Tells the kernel not to use the power saving
2620 function PAL_HALT_LIGHT when idle. This increases
2621 power-consumption. On the positive side, it reduces
2622 interrupt wake-up latency, which may improve performance
2623 in certain environments such as networked servers or
2626 nohibernate [HIBERNATION] Disable hibernation and resume.
2628 nohz= [KNL] Boottime enable/disable dynamic ticks
2629 Valid arguments: on, off
2632 nohz_full= [KNL,BOOT]
2633 In kernels built with CONFIG_NO_HZ_FULL=y, set
2634 the specified list of CPUs whose tick will be stopped
2635 whenever possible. The boot CPU will be forced outside
2636 the range to maintain the timekeeping.
2637 The CPUs in this range must also be included in the
2640 noiotrap [SH] Disables trapped I/O port accesses.
2642 noirqdebug [X86-32] Disables the code which attempts to detect and
2643 disable unhandled interrupt sources.
2645 no_timer_check [X86,APIC] Disables the code which tests for
2646 broken timer IRQ sources.
2648 noisapnp [ISAPNP] Disables ISA PnP code.
2650 noinitrd [RAM] Tells the kernel not to load any configured
2653 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2655 [Deprecated - use intremap=off]
2659 noinvpcid [X86] Disable the INVPCID cpu feature.
2661 nojitter [IA-64] Disables jitter checking for ITC timers.
2663 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2665 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2668 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2669 steal time is computed, but won't influence scheduler
2672 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2674 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2676 noltlbs [PPC] Do not use large page/tlb entries for kernel
2677 lowmem mapping on PPC40x and PPC8xx
2679 nomca [IA-64] Disable machine check abort handling
2681 nomce [X86-32] Disable Machine Check Exception
2683 nomfgpt [X86-32] Disable Multi-Function General Purpose
2684 Timer usage (for AMD Geode machines).
2686 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2687 shutdown the other cpus. Instead use the REBOOT_VECTOR
2690 nomodule Disable module load
2692 nopat [X86] Disable PAT (page attribute table extension of
2693 pagetables) support.
2695 norandmaps Don't use address space randomization. Equivalent to
2696 echo 0 > /proc/sys/kernel/randomize_va_space
2698 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2700 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2701 with UP alternatives
2703 nordrand [X86] Disable kernel use of the RDRAND and
2704 RDSEED instructions even if they are supported
2705 by the processor. RDRAND and RDSEED are still
2706 available to user space applications.
2708 noresume [SWSUSP] Disables resume and restores original swap
2711 no-scroll [VGA] Disables scrollback.
2712 This is required for the Braillex ib80-piezo Braille
2713 reader made by F.H. Papenmeier (Germany).
2717 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2719 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2720 and disable the IO APIC. legacy for "maxcpus=0".
2722 nosoftlockup [KNL] Disable the soft-lockup detector.
2724 nosync [HW,M68K] Disables sync negotiation for all devices.
2726 notsc [BUGS=X86-32] Disable Time Stamp Counter
2728 nowatchdog [KNL] Disable both lockup detectors, i.e.
2729 soft-lockup and NMI watchdog (hard-lockup).
2733 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2735 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2736 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2737 Some features depend on CPU0. Known dependencies are:
2738 1. Resume from suspend/hibernate depends on CPU0.
2739 Suspend/hibernate will fail if CPU0 is offline and you
2740 need to online CPU0 before suspend/hibernate.
2741 2. PIC interrupts also depend on CPU0. CPU0 can't be
2742 removed if a PIC interrupt is detected.
2743 It's said poweroff/reboot may depend on CPU0 on some
2744 machines although I haven't seen such issues so far
2745 after CPU0 is offline on a few tested machines.
2746 If the dependencies are under your control, you can
2747 turn on cpu0_hotplug.
2749 nptcg= [IA-64] Override max number of concurrent global TLB
2750 purges which is reported from either PAL_VM_SUMMARY or
2753 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2754 could support. nr_cpus=n : n >= 1 limits the kernel to
2755 supporting 'n' processors. Later in runtime you can not
2756 use hotplug cpu feature to put more cpu back to online.
2757 just like you compile the kernel NR_CPUS=n
2759 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2761 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2762 Allowed values are enable and disable
2764 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2765 one of ['zone', 'node', 'default'] can be specified
2766 This can be set from sysctl after boot.
2767 See Documentation/sysctl/vm.txt for details.
2769 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2770 See Documentation/debugging-via-ohci1394.txt for more
2773 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2774 Rather than timing out after 20 ms if an EC
2775 command is not properly ACKed, override the length
2776 of the timeout. We have interrupts disabled while
2777 waiting for the ACK, so if this is set too high
2778 interrupts *may* be lost!
2780 omap_mux= [OMAP] Override bootloader pin multiplexing.
2781 Format: <mux_mode0.mode_name=value>...
2782 For example, to override I2C bus2:
2783 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2785 oprofile.timer= [HW]
2786 Use timer interrupt instead of performance counters
2788 oprofile.cpu_type= Force an oprofile cpu type
2789 This might be useful if you have an older oprofile
2790 userland or if you want common events.
2791 Format: { arch_perfmon }
2792 arch_perfmon: [X86] Force use of architectural
2793 perfmon on Intel CPUs instead of the
2794 CPU specific event set.
2795 timer: [X86] Force use of architectural NMI
2796 timer mode (see also oprofile.timer
2797 for generic hr timer mode)
2798 [s390] Force legacy basic mode sampling
2799 (report cpu_type "timer")
2801 oops=panic Always panic on oopses. Default is to just kill the
2802 process, but there is a small probability of
2803 deadlocking the machine.
2804 This will also cause panics on machine check exceptions.
2805 Useful together with panic=30 to trigger a reboot.
2808 See Documentation/sound/oss/oss-parameters.txt
2810 page_owner= [KNL] Boot-time page_owner enabling option.
2811 Storage of the information about who allocated
2812 each page is disabled in default. With this switch,
2814 on: enable the feature
2816 page_poison= [KNL] Boot-time parameter changing the state of
2817 poisoning on the buddy allocator.
2818 off: turn off poisoning
2819 on: turn on poisoning
2821 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2822 timeout > 0: seconds before rebooting
2823 timeout = 0: wait forever
2824 timeout < 0: reboot immediately
2827 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2830 crash_kexec_post_notifiers
2831 Run kdump after running panic-notifiers and dumping
2832 kmsg. This only for the users who doubt kdump always
2833 succeeds in any situation.
2834 Note that this also increases risks of kdump failure,
2835 because some panic notifiers can make the crashed
2836 kernel more unstable.
2838 parkbd.port= [HW] Parallel port number the keyboard adapter is
2839 connected to, default is 0.
2841 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2842 0 for XT, 1 for AT (default is AT).
2845 parport= [HW,PPT] Specify parallel ports. 0 disables.
2846 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2847 Use 'auto' to force the driver to use any
2848 IRQ/DMA settings detected (the default is to
2849 ignore detected IRQ/DMA settings because of
2850 possible conflicts). You can specify the base
2851 address, IRQ, and DMA settings; IRQ and DMA
2852 should be numbers, or 'auto' (for using detected
2853 settings on that particular port), or 'nofifo'
2854 (to avoid using a FIFO even if it is detected).
2855 Parallel ports are assigned in the order they
2856 are specified on the command line, starting
2859 parport_init_mode= [HW,PPT]
2860 Configure VIA parallel port to operate in
2861 a specific mode. This is necessary on Pegasos
2862 computer where firmware has no options for setting
2863 up parallel port mode and sets it to spp.
2864 Currently this function knows 686a and 8231 chips.
2865 Format: [spp|ps2|epp|ecp|ecpepp]
2868 Halt all CPUs after the first oops has been printed for
2869 the specified number of seconds. This is to be used if
2870 your oopses keep scrolling off the screen.
2875 See header of drivers/block/paride/pcd.c.
2876 See also Documentation/blockdev/paride.txt.
2878 pci=option[,option...] [PCI] various PCI subsystem options:
2879 earlydump [X86] dump PCI config space before the kernel
2881 off [X86] don't probe for the PCI bus
2882 bios [X86-32] force use of PCI BIOS, don't access
2883 the hardware directly. Use this if your machine
2884 has a non-standard PCI host bridge.
2885 nobios [X86-32] disallow use of PCI BIOS, only direct
2886 hardware access methods are allowed. Use this
2887 if you experience crashes upon bootup and you
2888 suspect they are caused by the BIOS.
2889 conf1 [X86] Force use of PCI Configuration Access
2890 Mechanism 1 (config address in IO port 0xCF8,
2891 data in IO port 0xCFC, both 32-bit).
2892 conf2 [X86] Force use of PCI Configuration Access
2893 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2894 the function, IO port 0xCFA, also 8-bit, sets
2895 bus number. The config space is then accessed
2896 through ports 0xC000-0xCFFF).
2897 See http://wiki.osdev.org/PCI for more info
2898 on the configuration access mechanisms.
2899 noaer [PCIE] If the PCIEAER kernel config parameter is
2900 enabled, this kernel boot option can be used to
2901 disable the use of PCIE advanced error reporting.
2902 nodomains [PCI] Disable support for multiple PCI
2903 root domains (aka PCI segments, in ACPI-speak).
2904 nommconf [X86] Disable use of MMCONFIG for PCI
2906 check_enable_amd_mmconf [X86] check for and enable
2907 properly configured MMIO access to PCI
2908 config space on AMD family 10h CPU
2909 nomsi [MSI] If the PCI_MSI kernel config parameter is
2910 enabled, this kernel boot option can be used to
2911 disable the use of MSI interrupts system-wide.
2912 noioapicquirk [APIC] Disable all boot interrupt quirks.
2913 Safety option to keep boot IRQs enabled. This
2914 should never be necessary.
2915 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2916 primary IO-APIC for bridges that cannot disable
2917 boot IRQs. This fixes a source of spurious IRQs
2918 when the system masks IRQs.
2919 noioapicreroute [APIC] Disable workaround that uses the
2920 boot IRQ equivalent of an IRQ that connects to
2921 a chipset where boot IRQs cannot be disabled.
2922 The opposite of ioapicreroute.
2923 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2924 routing table. These calls are known to be buggy
2925 on several machines and they hang the machine
2926 when used, but on other computers it's the only
2927 way to get the interrupt routing table. Try
2928 this option if the kernel is unable to allocate
2929 IRQs or discover secondary PCI buses on your
2931 rom [X86] Assign address space to expansion ROMs.
2932 Use with caution as certain devices share
2933 address decoders between ROMs and other
2935 norom [X86] Do not assign address space to
2936 expansion ROMs that do not already have
2937 BIOS assigned address ranges.
2938 nobar [X86] Do not assign address space to the
2939 BARs that weren't assigned by the BIOS.
2940 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2941 assigned automatically to PCI devices. You can
2942 make the kernel exclude IRQs of your ISA cards
2944 pirqaddr=0xAAAAA [X86] Specify the physical address
2945 of the PIRQ table (normally generated
2946 by the BIOS) if it is outside the
2947 F0000h-100000h range.
2948 lastbus=N [X86] Scan all buses thru bus #N. Can be
2949 useful if the kernel is unable to find your
2950 secondary buses and you want to tell it
2951 explicitly which ones they are.
2952 assign-busses [X86] Always assign all PCI bus
2953 numbers ourselves, overriding
2954 whatever the firmware may have done.
2955 usepirqmask [X86] Honor the possible IRQ mask stored
2956 in the BIOS $PIR table. This is needed on
2957 some systems with broken BIOSes, notably
2958 some HP Pavilion N5400 and Omnibook XE3
2959 notebooks. This will have no effect if ACPI
2960 IRQ routing is enabled.
2961 noacpi [X86] Do not use ACPI for IRQ routing
2962 or for PCI scanning.
2963 use_crs [X86] Use PCI host bridge window information
2964 from ACPI. On BIOSes from 2008 or later, this
2965 is enabled by default. If you need to use this,
2966 please report a bug.
2967 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2968 If you need to use this, please report a bug.
2969 routeirq Do IRQ routing for all PCI devices.
2970 This is normally done in pci_enable_device(),
2971 so this option is a temporary workaround
2972 for broken drivers that don't call it.
2973 skip_isa_align [X86] do not align io start addr, so can
2974 handle more pci cards
2975 noearly [X86] Don't do any early type 1 scanning.
2976 This might help on some broken boards which
2977 machine check when some devices' config space
2978 is read. But various workarounds are disabled
2979 and some IOMMU drivers will not work.
2980 bfsort Sort PCI devices into breadth-first order.
2981 This sorting is done to get a device
2982 order compatible with older (<= 2.4) kernels.
2983 nobfsort Don't sort PCI devices into breadth-first order.
2984 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2985 tuning and use the BIOS-configured MPS defaults.
2986 pcie_bus_safe Set every device's MPS to the largest value
2987 supported by all devices below the root complex.
2988 pcie_bus_perf Set device MPS to the largest allowable MPS
2989 based on its parent bus. Also set MRRS (Max
2990 Read Request Size) to the largest supported
2991 value (no larger than the MPS that the device
2992 or bus can support) for best performance.
2993 pcie_bus_peer2peer Set every device's MPS to 128B, which
2994 every device is guaranteed to support. This
2995 configuration allows peer-to-peer DMA between
2996 any pair of devices, possibly at the cost of
2997 reduced performance. This also guarantees
2998 that hot-added devices will work.
2999 cbiosize=nn[KMG] The fixed amount of bus space which is
3000 reserved for the CardBus bridge's IO window.
3001 The default value is 256 bytes.
3002 cbmemsize=nn[KMG] The fixed amount of bus space which is
3003 reserved for the CardBus bridge's memory
3004 window. The default value is 64 megabytes.
3007 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3008 Specifies alignment and device to reassign
3009 aligned memory resources.
3010 If <order of align> is not specified,
3011 PAGE_SIZE is used as alignment.
3012 PCI-PCI bridge can be specified, if resource
3013 windows need to be expanded.
3014 ecrc= Enable/disable PCIe ECRC (transaction layer
3015 end-to-end CRC checking).
3016 bios: Use BIOS/firmware settings. This is the
3020 hpiosize=nn[KMG] The fixed amount of bus space which is
3021 reserved for hotplug bridge's IO window.
3022 Default size is 256 bytes.
3023 hpmemsize=nn[KMG] The fixed amount of bus space which is
3024 reserved for hotplug bridge's memory window.
3025 Default size is 2 megabytes.
3026 realloc= Enable/disable reallocating PCI bridge resources
3027 if allocations done by BIOS are too small to
3028 accommodate resources required by all child
3030 off: Turn realloc off
3032 realloc same as realloc=on
3033 noari do not use PCIe ARI.
3034 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3035 only look for one device below a PCIe downstream
3038 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3041 force Enable ASPM even on devices that claim not to support it.
3042 WARNING: Forcing ASPM on may cause system lockups.
3044 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3045 nomsi Do not use MSI for PCI Express Native Hotplug (this
3046 makes all PCIe ports use INTx for hotplug services).
3048 pcie_ports= [PCIE] PCIe ports handling:
3049 auto Ask the BIOS whether or not to use native PCIe services
3050 associated with PCIe ports (PME, hot-plug, AER). Use
3051 them only if that is allowed by the BIOS.
3052 native Use native PCIe services associated with PCIe ports
3054 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3057 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3058 nomsi Do not use MSI for native PCIe PME signaling (this makes
3059 all PCIe root ports use INTx for all services).
3061 pcmv= [HW,PCMCIA] BadgePAD 4
3065 Keep all power-domains already enabled by bootloader on,
3066 even if no driver has claimed them. This is useful
3067 for debug and development, but should not be
3068 needed on a platform with proper driver support.
3071 See Documentation/blockdev/paride.txt.
3073 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3076 See arch/parisc/kernel/pdc_chassis.c
3078 percpu_alloc= Select which percpu first chunk allocator to use.
3079 Currently supported values are "embed" and "page".
3080 Archs may support subset or none of the selections.
3081 See comments in mm/percpu.c for details on each
3082 allocator. This parameter is primarily for debugging
3083 and performance comparison.
3086 See Documentation/blockdev/paride.txt.
3089 See Documentation/blockdev/paride.txt.
3091 pirq= [SMP,APIC] Manual mp-table setup
3092 See Documentation/x86/i386/IO-APIC.txt.
3094 plip= [PPT,NET] Parallel port network link
3095 Format: { parport<nr> | timid | 0 }
3096 See also Documentation/parport.txt.
3098 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3099 Override pmtimer IOPort with a hex value.
3103 Enable PNP debug messages (depends on the
3104 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3105 via /sys/module/pnp/parameters/debug. We always show
3106 current resource usage; turning this on also shows
3107 possible settings and some assignment information.
3113 { on | off | curr | res | no-curr | no-res }
3116 [ISAPNP] Exclude IRQs for the autoconfiguration
3119 [ISAPNP] Exclude DMAs for the autoconfiguration
3121 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3122 Ranges are in pairs (I/O port base and size).
3125 [ISAPNP] Exclude memory regions for the
3127 Ranges are in pairs (memory base and size).
3129 ports= [IP_VS_FTP] IPVS ftp helper module
3131 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3133 Format: <port>,<port>....
3135 ppc_strict_facility_enable
3136 [PPC] This option catches any kernel floating point,
3137 Altivec, VSX and SPE outside of regions specifically
3138 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3139 There is some performance impact when enabling this.
3141 print-fatal-signals=
3142 [KNL] debug: print fatal signals
3144 If enabled, warn about various signal handling
3145 related application anomalies: too many signals,
3146 too many POSIX.1 timers, fatal signals causing a
3149 If you hit the warning due to signal overflow,
3150 you might want to try "ulimit -i unlimited".
3154 printk.always_kmsg_dump=
3155 Trigger kmsg_dump for cases other than kernel oops or
3157 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3160 printk.time= Show timing data prefixed to each printk message line
3161 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3163 processor.max_cstate= [HW,ACPI]
3164 Limit processor to maximum C-state
3165 max_cstate=9 overrides any DMI blacklist limit.
3167 processor.nocst [HW,ACPI]
3168 Ignore the _CST method to determine C-states,
3169 instead using the legacy FADT method
3171 profile= [KNL] Enable kernel profiling via /proc/profile
3172 Format: [schedule,]<number>
3173 Param: "schedule" - profile schedule points.
3174 Param: <number> - step/bucket size as a power of 2 for
3175 statistical time based profiling.
3176 Param: "sleep" - profile D-state sleeping (millisecs).
3177 Requires CONFIG_SCHEDSTATS
3178 Param: "kvm" - profile VM exits.
3180 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3182 See Documentation/blockdev/ramdisk.txt.
3184 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3185 probe for; one of (bare|imps|exps|lifebook|any).
3186 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3188 psmouse.resetafter= [HW,MOUSE]
3189 Try to reset the device after so many bad packets
3192 [HW,MOUSE] Set desired mouse resolution, in dpi.
3193 psmouse.smartscroll=
3194 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3195 0 = disabled, 1 = enabled (default).
3197 pstore.backend= Specify the name of the pstore backend to use
3200 See Documentation/blockdev/paride.txt.
3203 [KNL] Number of legacy pty's. Overwrites compiled-in
3206 quiet [KNL] Disable most log messages
3211 See Documentation/md.txt.
3213 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3214 See Documentation/blockdev/ramdisk.txt.
3217 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3218 the specified list of CPUs to be no-callback CPUs.
3219 Invocation of these CPUs' RCU callbacks will
3220 be offloaded to "rcuox/N" kthreads created for
3221 that purpose, where "x" is "b" for RCU-bh, "p"
3222 for RCU-preempt, and "s" for RCU-sched, and "N"
3223 is the CPU number. This reduces OS jitter on the
3224 offloaded CPUs, which can be useful for HPC and
3225 real-time workloads. It can also improve energy
3226 efficiency for asymmetric multiprocessors.
3229 Rather than requiring that offloaded CPUs
3230 (specified by rcu_nocbs= above) explicitly
3231 awaken the corresponding "rcuoN" kthreads,
3232 make these kthreads poll for callbacks.
3233 This improves the real-time response for the
3234 offloaded CPUs by relieving them of the need to
3235 wake up the corresponding kthread, but degrades
3236 energy efficiency by requiring that the kthreads
3237 periodically wake up to do the polling.
3239 rcutree.blimit= [KNL]
3240 Set maximum number of finished RCU callbacks to
3241 process in one batch.
3243 rcutree.dump_tree= [KNL]
3244 Dump the structure of the rcu_node combining tree
3245 out at early boot. This is used for diagnostic
3246 purposes, to verify correct tree setup.
3248 rcutree.gp_cleanup_delay= [KNL]
3249 Set the number of jiffies to delay each step of
3250 RCU grace-period cleanup. This only has effect
3251 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3253 rcutree.gp_init_delay= [KNL]
3254 Set the number of jiffies to delay each step of
3255 RCU grace-period initialization. This only has
3256 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3259 rcutree.gp_preinit_delay= [KNL]
3260 Set the number of jiffies to delay each step of
3261 RCU grace-period pre-initialization, that is,
3262 the propagation of recent CPU-hotplug changes up
3263 the rcu_node combining tree. This only has effect
3264 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3266 rcutree.rcu_fanout_exact= [KNL]
3267 Disable autobalancing of the rcu_node combining
3268 tree. This is used by rcutorture, and might
3269 possibly be useful for architectures having high
3270 cache-to-cache transfer latencies.
3272 rcutree.rcu_fanout_leaf= [KNL]
3273 Change the number of CPUs assigned to each
3274 leaf rcu_node structure. Useful for very
3275 large systems, which will choose the value 64,
3276 and for NUMA systems with large remote-access
3277 latencies, which will choose a value aligned
3278 with the appropriate hardware boundaries.
3280 rcutree.jiffies_till_sched_qs= [KNL]
3281 Set required age in jiffies for a
3282 given grace period before RCU starts
3283 soliciting quiescent-state help from
3284 rcu_note_context_switch().
3286 rcutree.jiffies_till_first_fqs= [KNL]
3287 Set delay from grace-period initialization to
3288 first attempt to force quiescent states.
3289 Units are jiffies, minimum value is zero,
3290 and maximum value is HZ.
3292 rcutree.jiffies_till_next_fqs= [KNL]
3293 Set delay between subsequent attempts to force
3294 quiescent states. Units are jiffies, minimum
3295 value is one, and maximum value is HZ.
3297 rcutree.kthread_prio= [KNL,BOOT]
3298 Set the SCHED_FIFO priority of the RCU per-CPU
3299 kthreads (rcuc/N). This value is also used for
3300 the priority of the RCU boost threads (rcub/N)
3301 and for the RCU grace-period kthreads (rcu_bh,
3302 rcu_preempt, and rcu_sched). If RCU_BOOST is
3303 set, valid values are 1-99 and the default is 1
3304 (the least-favored priority). Otherwise, when
3305 RCU_BOOST is not set, valid values are 0-99 and
3306 the default is zero (non-realtime operation).
3308 rcutree.rcu_nocb_leader_stride= [KNL]
3309 Set the number of NOCB kthread groups, which
3310 defaults to the square root of the number of
3311 CPUs. Larger numbers reduces the wakeup overhead
3312 on the per-CPU grace-period kthreads, but increases
3313 that same overhead on each group's leader.
3315 rcutree.qhimark= [KNL]
3316 Set threshold of queued RCU callbacks beyond which
3317 batch limiting is disabled.
3319 rcutree.qlowmark= [KNL]
3320 Set threshold of queued RCU callbacks below which
3321 batch limiting is re-enabled.
3323 rcutree.rcu_idle_gp_delay= [KNL]
3324 Set wakeup interval for idle CPUs that have
3325 RCU callbacks (RCU_FAST_NO_HZ=y).
3327 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3328 Set wakeup interval for idle CPUs that have
3329 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3330 Lazy RCU callbacks are those which RCU can
3331 prove do nothing more than free memory.
3333 rcuperf.gp_exp= [KNL]
3334 Measure performance of expedited synchronous
3335 grace-period primitives.
3337 rcuperf.holdoff= [KNL]
3338 Set test-start holdoff period. The purpose of
3339 this parameter is to delay the start of the
3340 test until boot completes in order to avoid
3343 rcuperf.nreaders= [KNL]
3344 Set number of RCU readers. The value -1 selects
3345 N, where N is the number of CPUs. A value
3346 "n" less than -1 selects N-n+1, where N is again
3347 the number of CPUs. For example, -2 selects N
3348 (the number of CPUs), -3 selects N+1, and so on.
3349 A value of "n" less than or equal to -N selects
3352 rcuperf.nwriters= [KNL]
3353 Set number of RCU writers. The values operate
3354 the same as for rcuperf.nreaders.
3355 N, where N is the number of CPUs
3357 rcuperf.perf_runnable= [BOOT]
3358 Start rcuperf running at boot time.
3360 rcuperf.shutdown= [KNL]
3361 Shut the system down after performance tests
3362 complete. This is useful for hands-off automated
3365 rcuperf.perf_type= [KNL]
3366 Specify the RCU implementation to test.
3368 rcuperf.verbose= [KNL]
3369 Enable additional printk() statements.
3371 rcutorture.cbflood_inter_holdoff= [KNL]
3372 Set holdoff time (jiffies) between successive
3373 callback-flood tests.
3375 rcutorture.cbflood_intra_holdoff= [KNL]
3376 Set holdoff time (jiffies) between successive
3377 bursts of callbacks within a given callback-flood
3380 rcutorture.cbflood_n_burst= [KNL]
3381 Set the number of bursts making up a given
3382 callback-flood test. Set this to zero to
3383 disable callback-flood testing.
3385 rcutorture.cbflood_n_per_burst= [KNL]
3386 Set the number of callbacks to be registered
3387 in a given burst of a callback-flood test.
3389 rcutorture.fqs_duration= [KNL]
3390 Set duration of force_quiescent_state bursts
3393 rcutorture.fqs_holdoff= [KNL]
3394 Set holdoff time within force_quiescent_state bursts
3397 rcutorture.fqs_stutter= [KNL]
3398 Set wait time between force_quiescent_state bursts
3401 rcutorture.gp_cond= [KNL]
3402 Use conditional/asynchronous update-side
3403 primitives, if available.
3405 rcutorture.gp_exp= [KNL]
3406 Use expedited update-side primitives, if available.
3408 rcutorture.gp_normal= [KNL]
3409 Use normal (non-expedited) asynchronous
3410 update-side primitives, if available.
3412 rcutorture.gp_sync= [KNL]
3413 Use normal (non-expedited) synchronous
3414 update-side primitives, if available. If all
3415 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3416 rcutorture.gp_normal=, and rcutorture.gp_sync=
3417 are zero, rcutorture acts as if is interpreted
3418 they are all non-zero.
3420 rcutorture.n_barrier_cbs= [KNL]
3421 Set callbacks/threads for rcu_barrier() testing.
3423 rcutorture.nfakewriters= [KNL]
3424 Set number of concurrent RCU writers. These just
3425 stress RCU, they don't participate in the actual
3426 test, hence the "fake".
3428 rcutorture.nreaders= [KNL]
3429 Set number of RCU readers. The value -1 selects
3430 N-1, where N is the number of CPUs. A value
3431 "n" less than -1 selects N-n-2, where N is again
3432 the number of CPUs. For example, -2 selects N
3433 (the number of CPUs), -3 selects N+1, and so on.
3435 rcutorture.object_debug= [KNL]
3436 Enable debug-object double-call_rcu() testing.
3438 rcutorture.onoff_holdoff= [KNL]
3439 Set time (s) after boot for CPU-hotplug testing.
3441 rcutorture.onoff_interval= [KNL]
3442 Set time (s) between CPU-hotplug operations, or
3443 zero to disable CPU-hotplug testing.
3445 rcutorture.shuffle_interval= [KNL]
3446 Set task-shuffle interval (s). Shuffling tasks
3447 allows some CPUs to go into dyntick-idle mode
3448 during the rcutorture test.
3450 rcutorture.shutdown_secs= [KNL]
3451 Set time (s) after boot system shutdown. This
3452 is useful for hands-off automated testing.
3454 rcutorture.stall_cpu= [KNL]
3455 Duration of CPU stall (s) to test RCU CPU stall
3456 warnings, zero to disable.
3458 rcutorture.stall_cpu_holdoff= [KNL]
3459 Time to wait (s) after boot before inducing stall.
3461 rcutorture.stat_interval= [KNL]
3462 Time (s) between statistics printk()s.
3464 rcutorture.stutter= [KNL]
3465 Time (s) to stutter testing, for example, specifying
3466 five seconds causes the test to run for five seconds,
3467 wait for five seconds, and so on. This tests RCU's
3468 ability to transition abruptly to and from idle.
3470 rcutorture.test_boost= [KNL]
3471 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3472 "Maybe" means test if the RCU implementation
3473 under test support RCU priority boosting.
3475 rcutorture.test_boost_duration= [KNL]
3476 Duration (s) of each individual boost test.
3478 rcutorture.test_boost_interval= [KNL]
3479 Interval (s) between each boost test.
3481 rcutorture.test_no_idle_hz= [KNL]
3482 Test RCU's dyntick-idle handling. See also the
3483 rcutorture.shuffle_interval parameter.
3485 rcutorture.torture_runnable= [BOOT]
3486 Start rcutorture running at boot time.
3488 rcutorture.torture_type= [KNL]
3489 Specify the RCU implementation to test.
3491 rcutorture.verbose= [KNL]
3492 Enable additional printk() statements.
3494 rcupdate.rcu_cpu_stall_suppress= [KNL]
3495 Suppress RCU CPU stall warning messages.
3497 rcupdate.rcu_cpu_stall_timeout= [KNL]
3498 Set timeout for RCU CPU stall warning messages.
3500 rcupdate.rcu_expedited= [KNL]
3501 Use expedited grace-period primitives, for
3502 example, synchronize_rcu_expedited() instead
3503 of synchronize_rcu(). This reduces latency,
3504 but can increase CPU utilization, degrade
3505 real-time latency, and degrade energy efficiency.
3506 No effect on CONFIG_TINY_RCU kernels.
3508 rcupdate.rcu_normal= [KNL]
3509 Use only normal grace-period primitives,
3510 for example, synchronize_rcu() instead of
3511 synchronize_rcu_expedited(). This improves
3512 real-time latency, CPU utilization, and
3513 energy efficiency, but can expose users to
3514 increased grace-period latency. This parameter
3515 overrides rcupdate.rcu_expedited. No effect on
3516 CONFIG_TINY_RCU kernels.
3518 rcupdate.rcu_normal_after_boot= [KNL]
3519 Once boot has completed (that is, after
3520 rcu_end_inkernel_boot() has been invoked), use
3521 only normal grace-period primitives. No effect
3522 on CONFIG_TINY_RCU kernels.
3524 rcupdate.rcu_task_stall_timeout= [KNL]
3525 Set timeout in jiffies for RCU task stall warning
3526 messages. Disable with a value less than or equal
3529 rcupdate.rcu_self_test= [KNL]
3530 Run the RCU early boot self tests
3532 rcupdate.rcu_self_test_bh= [KNL]
3533 Run the RCU bh early boot self tests
3535 rcupdate.rcu_self_test_sched= [KNL]
3536 Run the RCU sched early boot self tests
3540 Run specified binary instead of /init from the ramdisk,
3541 used for early userspace startup. See initrd.
3544 Format (x86 or x86_64):
3545 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3547 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3549 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3550 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3551 reboot_force is either force or not specified,
3552 reboot_cpu is s[mp]#### with #### being the processor
3553 to be used for rebooting.
3556 [KNL, SMP] Set scheduler's default relax_domain_level.
3557 See Documentation/cgroups/cpusets.txt.
3559 relative_sleep_states=
3560 [SUSPEND] Use sleep state labeling where the deepest
3561 state available other than hibernation is always "mem".
3562 Format: { "0" | "1" }
3563 0 -- Traditional sleep state labels.
3564 1 -- Relative sleep state labels.
3566 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3568 reservetop= [X86-32]
3570 Reserves a hole at the top of the kernel virtual
3575 Set the amount of memory to reserve for BIOS at
3576 the bottom of the address space.
3578 reset_devices [KNL] Force drivers to reset the underlying device
3579 during initialization.
3582 Specify the partition device for software suspend
3584 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3586 resume_offset= [SWSUSP]
3587 Specify the offset from the beginning of the partition
3588 given by "resume=" at which the swap header is located,
3589 in <PAGE_SIZE> units (needed only for swap files).
3590 See Documentation/power/swsusp-and-swap-files.txt
3592 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3593 read the resume files
3595 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3596 Useful for devices that are detected asynchronously
3597 (e.g. USB and MMC devices).
3599 hibernate= [HIBERNATION]
3600 noresume Don't check if there's a hibernation image
3601 present during boot.
3602 nocompress Don't compress/decompress hibernation images.
3603 no Disable hibernation and resume.
3605 retain_initrd [RAM] Keep initrd memory after extraction
3607 rfkill.default_state=
3608 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3609 etc. communication is blocked by default.
3612 rfkill.master_switch_mode=
3613 0 The "airplane mode" button does nothing.
3614 1 The "airplane mode" button toggles between everything
3615 blocked and the previous configuration.
3616 2 The "airplane mode" button toggles between everything
3617 blocked and everything unblocked.
3619 rhash_entries= [KNL,NET]
3620 Set number of hash buckets for route cache
3622 ro [KNL] Mount root device read-only on boot
3625 on Mark read-only kernel memory as read-only (default).
3626 off Leave read-only kernel memory writable for debugging.
3629 Enable the uart passthrough on the designated usb port
3630 on Rockchip SoCs. When active, the signals of the
3631 debug-uart get routed to the D+ and D- pins of the usb
3632 port and the regular usb controller gets disabled.
3634 root= [KNL] Root filesystem
3635 See name_to_dev_t comment in init/do_mounts.c.
3637 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3638 mount the root filesystem
3640 rootflags= [KNL] Set root filesystem mount option string
3642 rootfstype= [KNL] Set root filesystem type
3644 rootwait [KNL] Wait (indefinitely) for root device to show up.
3645 Useful for devices that are detected asynchronously
3646 (e.g. USB and MMC devices).
3648 rproc_mem=nn[KMG][@address]
3649 [KNL,ARM,CMA] Remoteproc physical memory block.
3650 Memory area to be used by remote processor image,
3653 rw [KNL] Mount root device read-write on boot
3655 S [KNL] Run init in single mode
3657 s390_iommu= [HW,S390]
3658 Set s390 IOTLB flushing mode
3660 With strict flushing every unmap operation will result in
3661 an IOTLB flush. Default is lazy flushing before reuse,
3665 See drivers/net/irda/sa1100_ir.c.
3667 sbni= [NET] Granch SBNI12 leased line adapter
3669 sched_debug [KNL] Enables verbose scheduler debug messages.
3671 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3672 Allowed values are enable and disable. This feature
3673 incurs a small amount of overhead in the scheduler
3674 but is useful for debugging and performance tuning.
3676 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3677 xtime_lock contention on larger systems, and/or RCU lock
3678 contention on all systems with CONFIG_MAXSMP set.
3679 Format: { "0" | "1" }
3680 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3682 Note: increases power consumption, thus should only be
3683 enabled if running jitter sensitive (HPC/RT) workloads.
3685 security= [SECURITY] Choose a security module to enable at boot.
3686 If this boot parameter is not specified, only the first
3687 security module asking for security registration will be
3688 loaded. An invalid security module name will be treated
3689 as if no module has been chosen.
3691 selinux= [SELINUX] Disable or enable SELinux at boot time.
3692 Format: { "0" | "1" }
3693 See security/selinux/Kconfig help text.
3696 Default value is set via kernel config option.
3697 If enabled at boot time, /selinux/disable can be used
3698 later to disable prior to initial policy load.
3700 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3701 Format: { "0" | "1" }
3702 See security/apparmor/Kconfig help text
3705 Default value is set via kernel config option.
3707 serialnumber [BUGS=X86-32]
3710 Maximal number of shapers.
3712 show_msr= [x86] show boot-time MSR settings
3713 Format: { <integer> }
3714 Show boot-time (BIOS-initialized) MSR settings.
3715 The parameter means the number of CPUs to show,
3716 for example 1 means boot CPU only.
3724 Disable merging of slabs with similar size. May be
3725 necessary if there is some reason to distinguish
3726 allocs to different slabs. Debug options disable
3727 merging on their own.
3728 For more information see Documentation/vm/slub.txt.
3730 slab_max_order= [MM, SLAB]
3731 Determines the maximum allowed order for slabs.
3732 A high setting may cause OOMs due to memory
3733 fragmentation. Defaults to 1 for systems with
3734 more than 32MB of RAM, 0 otherwise.
3736 slub_debug[=options[,slabs]] [MM, SLUB]
3737 Enabling slub_debug allows one to determine the
3738 culprit if slab objects become corrupted. Enabling
3739 slub_debug can create guard zones around objects and
3740 may poison objects when not in use. Also tracks the
3741 last alloc / free. For more information see
3742 Documentation/vm/slub.txt.
3744 slub_max_order= [MM, SLUB]
3745 Determines the maximum allowed order for slabs.
3746 A high setting may cause OOMs due to memory
3747 fragmentation. For more information see
3748 Documentation/vm/slub.txt.
3750 slub_min_objects= [MM, SLUB]
3751 The minimum number of objects per slab. SLUB will
3752 increase the slab order up to slub_max_order to
3753 generate a sufficiently large slab able to contain
3754 the number of objects indicated. The higher the number
3755 of objects the smaller the overhead of tracking slabs
3756 and the less frequently locks need to be acquired.
3757 For more information see Documentation/vm/slub.txt.
3759 slub_min_order= [MM, SLUB]
3760 Determines the minimum page order for slabs. Must be
3761 lower than slub_max_order.
3762 For more information see Documentation/vm/slub.txt.
3764 slub_nomerge [MM, SLUB]
3765 Same with slab_nomerge. This is supported for legacy.
3766 See slab_nomerge for more information.
3769 Format: <io1>[,<io2>[,...,<io8>]]
3771 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3772 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3773 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3774 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3775 smsc-ircc2.ircc_irq= [HW] IRQ line
3776 smsc-ircc2.ircc_dma= [HW] DMA channel
3777 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3778 0: Toshiba Satellite 1800 (GP data pin select)
3779 1: Fast pin select (default)
3782 smt [KNL,S390] Set the maximum number of threads (logical
3783 CPUs) to use per physical CPU on systems capable of
3784 symmetric multithreading (SMT). Will be capped to the
3785 actual hardware limit.
3787 Default: -1 (no limit)
3790 [KNL] Should the soft-lockup detector generate panics.
3793 softlockup_all_cpu_backtrace=
3794 [KNL] Should the soft-lockup detector generate
3795 backtraces on all cpus.
3798 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3799 See Documentation/laptops/sonypi.txt
3801 spia_io_base= [HW,MTD]
3807 Enabled the stack tracer on boot up.
3809 stacktrace_filter=[function-list]
3810 [FTRACE] Limit the functions that the stack tracer
3811 will trace at boot up. function-list is a comma separated
3812 list of functions. This list can be changed at run
3813 time by the stack_trace_filter file in the debugfs
3814 tracing directory. Note, this enables stack tracing
3815 and the stacktrace above is not needed.
3819 Set the STI (builtin display/keyboard on the HP-PARISC
3820 machines) console (graphic card) which should be used
3821 as the initial boot-console.
3822 See also comment in drivers/video/console/sticore.c.
3825 See comment in drivers/video/console/sticore.c.
3828 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3830 sunrpc.min_resvport=
3831 sunrpc.max_resvport=
3833 SunRPC servers often require that client requests
3834 originate from a privileged port (i.e. a port in the
3835 range 0 < portnr < 1024).
3836 An administrator who wishes to reserve some of these
3837 ports for other uses may adjust the range that the
3838 kernel's sunrpc client considers to be privileged
3839 using these two parameters to set the minimum and
3840 maximum port values.
3844 Control how the NFS server code allocates CPUs to
3845 service thread pools. Depending on how many NICs
3846 you have and where their interrupts are bound, this
3847 option will affect which CPUs will do NFS serving.
3848 Note: this parameter cannot be changed while the
3849 NFS server is running.
3851 auto the server chooses an appropriate mode
3852 automatically using heuristics
3853 global a single global pool contains all CPUs
3854 percpu one pool for each CPU
3855 pernode one pool for each NUMA node (equivalent
3856 to global on non-NUMA machines)
3858 sunrpc.tcp_slot_table_entries=
3859 sunrpc.udp_slot_table_entries=
3861 Sets the upper limit on the number of simultaneous
3862 RPC calls that can be sent from the client to a
3863 server. Increasing these values may allow you to
3864 improve throughput, but will also increase the
3865 amount of memory reserved for use by the client.
3867 suspend.pm_test_delay=
3869 Sets the number of seconds to remain in a suspend test
3870 mode before resuming the system (see
3871 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3872 is set. Default value is 5.
3875 [KNL] Enable accounting of swap in memory resource
3876 controller if no parameter or 1 is given or disable
3877 it if 0 is given (See Documentation/cgroups/memory.txt)
3879 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3880 Format: { <int> | force }
3881 <int> -- Number of I/O TLB slabs
3882 force -- force using of bounce buffers even if they
3883 wouldn't be automatically used by the kernel
3887 sysfs.deprecated=0|1 [KNL]
3888 Enable/disable old style sysfs layout for old udev
3889 on older distributions. When this option is enabled
3890 very new udev will not work anymore. When this option
3891 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3892 in older udev will not work anymore.
3893 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3894 the kernel configuration.
3896 sysrq_always_enabled
3898 Ignore sysrq setting - this boot parameter will
3899 neutralize any effect of /proc/sys/kernel/sysrq.
3900 Useful for debugging.
3902 tcpmhash_entries= [KNL,NET]
3903 Set the number of tcp_metrics_hash slots.
3904 Default value is 8192 or 16384 depending on total
3905 ram pages. This is used to specify the TCP metrics
3906 cache size. See Documentation/networking/ip-sysctl.txt
3907 "tcp_no_metrics_save" section for more details.
3911 test_suspend= [SUSPEND][,N]
3912 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3913 standby suspend) or "freeze" (for suspend type freeze)
3914 as the system sleep state during system startup with
3915 the optional capability to repeat N number of times.
3916 The system is woken from this state using a
3917 wakeup-capable RTC alarm.
3919 thash_entries= [KNL,NET]
3920 Set number of hash buckets for TCP connection
3922 thermal.act= [HW,ACPI]
3923 -1: disable all active trip points in all thermal zones
3924 <degrees C>: override all lowest active trip points
3926 thermal.crt= [HW,ACPI]
3927 -1: disable all critical trip points in all thermal zones
3928 <degrees C>: override all critical trip points
3930 thermal.nocrt= [HW,ACPI]
3931 Set to disable actions on ACPI thermal zone
3932 critical and hot trip points.
3934 thermal.off= [HW,ACPI]
3935 1: disable ACPI thermal control
3937 thermal.psv= [HW,ACPI]
3938 -1: disable all passive trip points
3939 <degrees C>: override all passive trip points to this
3942 thermal.tzp= [HW,ACPI]
3943 Specify global default ACPI thermal zone polling rate
3944 <deci-seconds>: poll all this frequency
3945 0: no polling (default)
3948 Force threading of all interrupt handlers except those
3949 marked explicitly IRQF_NO_THREAD.
3952 Enable the Transcendent memory driver if built-in.
3954 tmem.cleancache=0|1 [KNL, XEN]
3955 Default is on (1). Disable the usage of the cleancache
3956 API to send anonymous pages to the hypervisor.
3958 tmem.frontswap=0|1 [KNL, XEN]
3959 Default is on (1). Disable the usage of the frontswap
3960 API to send swap pages to the hypervisor. If disabled
3961 the selfballooning and selfshrinking are force disabled.
3963 tmem.selfballooning=0|1 [KNL, XEN]
3964 Default is on (1). Disable the driving of swap pages
3967 tmem.selfshrinking=0|1 [KNL, XEN]
3968 Default is on (1). Partial swapoff that immediately
3969 transfers pages from Xen hypervisor back to the
3970 kernel based on different criteria.
3974 Specify if the kernel should make use of the cpu
3975 topology information if the hardware supports this.
3976 The scheduler will make use of this information and
3977 e.g. base its process migration decisions on it.
3980 topology_updates= [KNL, PPC, NUMA]
3982 Specify if the kernel should ignore (off)
3983 topology updates sent by the hypervisor to this
3988 tpm_suspend_pcr=[HW,TPM]
3989 Format: integer pcr id
3990 Specify that at suspend time, the tpm driver
3991 should extend the specified pcr with zeros,
3992 as a workaround for some chips which fail to
3993 flush the last written pcr on TPM_SaveState.
3994 This will guarantee that all the other pcrs
3997 trace_buf_size=nn[KMG]
3998 [FTRACE] will set tracing buffer size on each cpu.
4000 trace_event=[event-list]
4001 [FTRACE] Set and start specified trace events in order
4002 to facilitate early boot debugging.
4003 See also Documentation/trace/events.txt
4005 trace_options=[option-list]
4006 [FTRACE] Enable or disable tracer options at boot.
4007 The option-list is a comma delimited list of options
4008 that can be enabled or disabled just as if you were
4009 to echo the option name into
4011 /sys/kernel/debug/tracing/trace_options
4013 For example, to enable stacktrace option (to dump the
4014 stack trace of each event), add to the command line:
4016 trace_options=stacktrace
4018 See also Documentation/trace/ftrace.txt "trace options"
4022 Have the tracepoints sent to printk as well as the
4023 tracing ring buffer. This is useful for early boot up
4024 where the system hangs or reboots and does not give the
4025 option for reading the tracing buffer or performing a
4026 ftrace_dump_on_oops.
4028 To turn off having tracepoints sent to printk,
4029 echo 0 > /proc/sys/kernel/tracepoint_printk
4030 Note, echoing 1 into this file without the
4031 tracepoint_printk kernel cmdline option has no effect.
4035 Having tracepoints sent to printk() and activating high
4036 frequency tracepoints such as irq or sched, can cause
4037 the system to live lock.
4040 [FTRACE] enable this option to disable tracing when a
4041 warning is hit. This turns off "tracing_on". Tracing can
4042 be enabled again by echoing '1' into the "tracing_on"
4043 file located in /sys/kernel/debug/tracing/
4045 This option is useful, as it disables the trace before
4046 the WARNING dump is called, which prevents the trace to
4047 be filled with content caused by the warning output.
4049 This option can also be set at run time via the sysctl
4050 option: kernel/traceoff_on_warning
4052 transparent_hugepage=
4054 Format: [always|madvise|never]
4055 Can be used to control the default behavior of the system
4056 with respect to transparent hugepages.
4057 See Documentation/vm/transhuge.txt for more details.
4059 tsc= Disable clocksource stability checks for TSC.
4061 [x86] reliable: mark tsc clocksource as reliable, this
4062 disables clocksource verification at runtime, as well
4063 as the stability checks done at bootup. Used to enable
4064 high-resolution timer mode on older hardware, and in
4065 virtualized environment.
4066 [x86] noirqtime: Do not use TSC to do irq accounting.
4067 Used to run time disable IRQ_TIME_ACCOUNTING on any
4068 platforms where RDTSC is slow and this accounting
4071 turbografx.map[2|3]= [HW,JOY]
4072 TurboGraFX parallel port interface
4074 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4075 See also Documentation/input/joystick-parport.txt
4077 udbg-immortal [PPC] When debugging early kernel crashes that
4078 happen after console_init() and before a proper
4079 console driver takes over, this boot options might
4080 help "seeing" what's going on.
4082 uhash_entries= [KNL,NET]
4083 Set number of hash buckets for UDP/UDP-Lite connections
4086 [USB] Ignore overcurrent events (default N).
4087 Some badly-designed motherboards generate lots of
4088 bogus events, for ports that aren't wired to
4089 anything. Set this parameter to avoid log spamming.
4090 Note that genuine overcurrent events won't be
4094 [X86] Cause panic on unknown NMI.
4096 usbcore.authorized_default=
4097 [USB] Default USB device authorization:
4098 (default -1 = authorized except for wireless USB,
4099 0 = not authorized, 1 = authorized)
4101 usbcore.autosuspend=
4102 [USB] The autosuspend time delay (in seconds) used
4103 for newly-detected USB devices (default 2). This
4104 is the time required before an idle device will be
4105 autosuspended. Devices for which the delay is set
4106 to a negative value won't be autosuspended at all.
4108 usbcore.usbfs_snoop=
4109 [USB] Set to log all usbfs traffic (default 0 = off).
4111 usbcore.usbfs_snoop_max=
4112 [USB] Maximum number of bytes to snoop in each URB
4115 usbcore.blinkenlights=
4116 [USB] Set to cycle leds on hubs (default 0 = off).
4118 usbcore.old_scheme_first=
4119 [USB] Start with the old device initialization
4120 scheme (default 0 = off).
4122 usbcore.usbfs_memory_mb=
4123 [USB] Memory limit (in MB) for buffers allocated by
4124 usbfs (default = 16, 0 = max = 2047).
4126 usbcore.use_both_schemes=
4127 [USB] Try the other device initialization scheme
4128 if the first one fails (default 1 = enabled).
4130 usbcore.initial_descriptor_timeout=
4131 [USB] Specifies timeout for the initial 64-byte
4132 USB_REQ_GET_DESCRIPTOR request in milliseconds
4133 (default 5000 = 5.0 seconds).
4135 usbcore.nousb [USB] Disable the USB subsystem
4138 [USBHID] The interval which mice are to be polled at.
4140 usb-storage.delay_use=
4141 [UMS] The delay in seconds before a new device is
4142 scanned for Logical Units (default 1).
4145 [UMS] A list of quirks entries to supplement or
4146 override the built-in unusual_devs list. List
4147 entries are separated by commas. Each entry has
4148 the form VID:PID:Flags where VID and PID are Vendor
4149 and Product ID values (4-digit hex numbers) and
4150 Flags is a set of characters, each corresponding
4151 to a common usb-storage quirk flag as follows:
4152 a = SANE_SENSE (collect more than 18 bytes
4154 b = BAD_SENSE (don't collect more than 18
4155 bytes of sense data);
4156 c = FIX_CAPACITY (decrease the reported
4157 device capacity by one sector);
4158 d = NO_READ_DISC_INFO (don't use
4159 READ_DISC_INFO command);
4160 e = NO_READ_CAPACITY_16 (don't use
4161 READ_CAPACITY_16 command);
4162 f = NO_REPORT_OPCODES (don't use report opcodes
4164 g = MAX_SECTORS_240 (don't transfer more than
4165 240 sectors at a time, uas only);
4166 h = CAPACITY_HEURISTICS (decrease the
4167 reported device capacity by one
4168 sector if the number is odd);
4169 i = IGNORE_DEVICE (don't bind to this
4171 j = NO_REPORT_LUNS (don't use report luns
4173 l = NOT_LOCKABLE (don't try to lock and
4174 unlock ejectable media);
4175 m = MAX_SECTORS_64 (don't transfer more
4176 than 64 sectors = 32 KB at a time);
4177 n = INITIAL_READ10 (force a retry of the
4178 initial READ(10) command);
4179 o = CAPACITY_OK (accept the capacity
4180 reported by the device);
4181 p = WRITE_CACHE (the device cache is ON
4183 r = IGNORE_RESIDUE (the device reports
4184 bogus residue values);
4185 s = SINGLE_LUN (the device has only one
4187 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4188 commands, uas only);
4189 u = IGNORE_UAS (don't bind to the uas driver);
4190 w = NO_WP_DETECT (don't test whether the
4191 medium is write-protected).
4192 Example: quirks=0419:aaf5:rl,0421:0433:rc
4194 user_debug= [KNL,ARM]
4196 See arch/arm/Kconfig.debug help text.
4197 1 - undefined instruction events
4199 4 - invalid data aborts
4202 Example: user_debug=31
4205 [X86] Flags controlling user PTE allocations.
4207 nohigh = do not allocate PTE pages in
4208 HIGHMEM regardless of setting
4212 On X86_32, this is an alias for vdso32=. Otherwise:
4214 vdso=1: enable VDSO (the default)
4215 vdso=0: disable VDSO mapping
4217 vdso32= [X86] Control the 32-bit vDSO
4218 vdso32=1: enable 32-bit VDSO
4219 vdso32=0 or vdso32=2: disable 32-bit VDSO
4221 See the help text for CONFIG_COMPAT_VDSO for more
4222 details. If CONFIG_COMPAT_VDSO is set, the default is
4223 vdso32=0; otherwise, the default is vdso32=1.
4225 For compatibility with older kernels, vdso32=2 is an
4228 Try vdso32=0 if you encounter an error that says:
4229 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4232 vector=percpu: enable percpu vector domain
4234 video= [FB] Frame buffer configuration
4235 See Documentation/fb/modedb.txt.
4237 video.brightness_switch_enabled= [0,1]
4238 If set to 1, on receiving an ACPI notify event
4239 generated by hotkey, video driver will adjust brightness
4240 level and then send out the event to user space through
4241 the allocated input device; If set to 0, video driver
4242 will only send out the event without touching backlight
4247 [VMMIO] Memory mapped virtio (platform) device.
4249 <size>@<baseaddr>:<irq>[:<id>]
4251 <size> := size (can use standard suffixes
4253 <baseaddr> := physical base address
4254 <irq> := interrupt number (as passed to
4256 <id> := (optional) platform device id
4258 virtio_mmio.device=1K@0x100b0000:48:7
4260 Can be used multiple times for multiple devices.
4262 vga= [BOOT,X86-32] Select a particular video mode
4263 See Documentation/x86/boot.txt and
4264 Documentation/svga.txt.
4265 Use vga=ask for menu.
4266 This is actually a boot loader parameter; the value is
4267 passed to the kernel using a special protocol.
4269 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4270 size of <nn>. This can be used to increase the
4271 minimum size (128MB on x86). It can also be used to
4272 decrease the size and leave more room for directly
4275 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4278 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4281 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4285 Controls the behavior of vsyscalls (i.e. calls to
4286 fixed addresses of 0xffffffffff600x00 from legacy
4287 code). Most statically-linked binaries and older
4288 versions of glibc use these calls. Because these
4289 functions are at fixed addresses, they make nice
4290 targets for exploits that can control RIP.
4292 emulate [default] Vsyscalls turn into traps and are
4293 emulated reasonably safely.
4295 native Vsyscalls are native syscall instructions.
4296 This is a little bit faster than trapping
4297 and makes a few dynamic recompilers work
4298 better than they would in emulation mode.
4299 It also makes exploits much easier to write.
4301 none Vsyscalls don't work at all. This makes
4302 them quite hard to use for exploits but
4303 might break your system.
4305 vt.color= [VT] Default text color.
4306 Format: 0xYX, X = foreground, Y = background.
4307 Default: 0x07 = light gray on black.
4309 vt.cur_default= [VT] Default cursor shape.
4310 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4311 the parameters of the <Esc>[?A;B;Cc escape sequence;
4312 see VGA-softcursor.txt. Default: 2 = underline.
4314 vt.default_blu= [VT]
4315 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4316 Change the default blue palette of the console.
4317 This is a 16-member array composed of values
4320 vt.default_grn= [VT]
4321 Format: <green0>,<green1>,<green2>,...,<green15>
4322 Change the default green palette of the console.
4323 This is a 16-member array composed of values
4326 vt.default_red= [VT]
4327 Format: <red0>,<red1>,<red2>,...,<red15>
4328 Change the default red palette of the console.
4329 This is a 16-member array composed of values
4335 Set system-wide default UTF-8 mode for all tty's.
4336 Default is 1, i.e. UTF-8 mode is enabled for all
4337 newly opened terminals.
4339 vt.global_cursor_default=
4342 Set system-wide default for whether a cursor
4343 is shown on new VTs. Default is -1,
4344 i.e. cursors will be created by default unless
4345 overridden by individual drivers. 0 will hide
4346 cursors, 1 will display them.
4348 vt.italic= [VT] Default color for italic text; 0-15.
4351 vt.underline= [VT] Default color for underlined text; 0-15.
4354 watchdog timers [HW,WDT] For information on watchdog timers,
4355 see Documentation/watchdog/watchdog-parameters.txt
4356 or other driver-specific files in the
4357 Documentation/watchdog/ directory.
4359 workqueue.watchdog_thresh=
4360 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4361 warn stall conditions and dump internal state to
4362 help debugging. 0 disables workqueue stall
4363 detection; otherwise, it's the stall threshold
4364 duration in seconds. The default value is 30 and
4365 it can be updated at runtime by writing to the
4366 corresponding sysfs file.
4368 workqueue.disable_numa
4369 By default, all work items queued to unbound
4370 workqueues are affine to the NUMA nodes they're
4371 issued on, which results in better behavior in
4372 general. If NUMA affinity needs to be disabled for
4373 whatever reason, this option can be used. Note
4374 that this also can be controlled per-workqueue for
4375 workqueues visible under /sys/bus/workqueue/.
4377 workqueue.power_efficient
4378 Per-cpu workqueues are generally preferred because
4379 they show better performance thanks to cache
4380 locality; unfortunately, per-cpu workqueues tend to
4381 be more power hungry than unbound workqueues.
4383 Enabling this makes the per-cpu workqueues which
4384 were observed to contribute significantly to power
4385 consumption unbound, leading to measurably lower
4386 power usage at the cost of small performance
4389 The default value of this parameter is determined by
4390 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4392 workqueue.debug_force_rr_cpu
4393 Workqueue used to implicitly guarantee that work
4394 items queued without explicit CPU specified are put
4395 on the local CPU. This guarantee is no longer true
4396 and while local CPU is still preferred work items
4397 may be put on foreign CPUs. This debug option
4398 forces round-robin CPU selection to flush out
4399 usages which depend on the now broken guarantee.
4400 When enabled, memory and cache locality will be
4403 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4404 default x2apic cluster mode on platforms
4407 x86_intel_mid_timer= [X86-32,APBT]
4408 Choose timer option for x86 Intel MID platform.
4409 Two valid options are apbt timer only and lapic timer
4410 plus one apbt timer for broadcast timer.
4411 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4413 xen_512gb_limit [KNL,X86-64,XEN]
4414 Restricts the kernel running paravirtualized under Xen
4415 to use only up to 512 GB of RAM. The reason to do so is
4416 crash analysis tools and Xen tools for doing domain
4417 save/restore/migration must be enabled to handle larger
4420 xen_emul_unplug= [HW,X86,XEN]
4421 Unplug Xen emulated devices
4422 Format: [unplug0,][unplug1]
4423 ide-disks -- unplug primary master IDE devices
4424 aux-ide-disks -- unplug non-primary-master IDE devices
4425 nics -- unplug network devices
4426 all -- unplug all emulated devices (NICs and IDE disks)
4427 unnecessary -- unplugging emulated devices is
4428 unnecessary even if the host did not respond to
4430 never -- do not unplug even if version check succeeds
4432 xen_nopvspin [X86,XEN]
4433 Disables the ticketlock slowpath using Xen PV
4437 Disables the PV optimizations forcing the HVM guest to
4438 run as generic HVM guest with no PV drivers.
4440 xirc2ps_cs= [NET,PCMCIA]
4442 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4444 ______________________________________________________________________
4448 Add more DRM drivers.
projects / cascardo / linux.git / blob