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 eisa_irq_edge= [PARISC,HW]
1189 See header of drivers/parisc/eisa.c.
1192 See comment before function elanfreq_setup() in
1193 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1196 Format: {"cfq" | "deadline" | "noop"}
1197 See Documentation/block/cfq-iosched.txt and
1198 Documentation/block/deadline-iosched.txt for details.
1200 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1201 Specifies physical address of start of kernel core
1202 image elf header and optionally the size. Generally
1203 kexec loader will pass this option to capture kernel.
1204 See Documentation/kdump/kdump.txt for details.
1206 enable_mtrr_cleanup [X86]
1207 The kernel tries to adjust MTRR layout from continuous
1208 to discrete, to make X server driver able to add WB
1209 entry later. This parameter enables that.
1211 enable_timer_pin_1 [X86]
1212 Enable PIN 1 of APIC timer
1213 Can be useful to work around chipset bugs
1214 (in particular on some ATI chipsets).
1215 The kernel tries to set a reasonable default.
1217 enforcing [SELINUX] Set initial enforcing status.
1219 See security/selinux/Kconfig help text.
1220 0 -- permissive (log only, no denials).
1221 1 -- enforcing (deny and log).
1223 Value can be changed at runtime via /selinux/enforce.
1226 Disable Error Record Serialization Table (ERST)
1229 ether= [HW,NET] Ethernet cards parameters
1230 This option is obsoleted by the "netdev=" option, which
1231 has equivalent usage. See its documentation for details.
1235 Permit 'security.evm' to be updated regardless of
1236 current integrity status.
1240 fail_make_request=[KNL]
1241 General fault injection mechanism.
1242 Format: <interval>,<probability>,<space>,<times>
1243 See also Documentation/fault-injection/.
1246 See Documentation/blockdev/floppy.txt.
1248 force_pal_cache_flush
1249 [IA-64] Avoid check_sal_cache_flush which may hang on
1250 buggy SAL_CACHE_FLUSH implementations. Using this
1251 parameter will force ia64_sal_cache_flush to call
1252 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1255 Forcefully enable Physical Address Extension (PAE).
1256 Many Pentium M systems disable PAE but may have a
1257 functionally usable PAE implementation.
1258 Warning: use of this parameter will taint the kernel
1259 and may cause unknown problems.
1262 [FTRACE] will set and start the specified tracer
1263 as early as possible in order to facilitate early
1266 ftrace_dump_on_oops[=orig_cpu]
1267 [FTRACE] will dump the trace buffers on oops.
1268 If no parameter is passed, ftrace will dump
1269 buffers of all CPUs, but if you pass orig_cpu, it will
1270 dump only the buffer of the CPU that triggered the
1273 ftrace_filter=[function-list]
1274 [FTRACE] Limit the functions traced by the function
1275 tracer at boot up. function-list is a comma separated
1276 list of functions. This list can be changed at run
1277 time by the set_ftrace_filter file in the debugfs
1280 ftrace_notrace=[function-list]
1281 [FTRACE] Do not trace the functions specified in
1282 function-list. This list can be changed at run time
1283 by the set_ftrace_notrace file in the debugfs
1286 ftrace_graph_filter=[function-list]
1287 [FTRACE] Limit the top level callers functions traced
1288 by the function graph tracer at boot up.
1289 function-list is a comma separated list of functions
1290 that can be changed at run time by the
1291 set_graph_function file in the debugfs tracing directory.
1293 ftrace_graph_notrace=[function-list]
1294 [FTRACE] Do not trace from the functions specified in
1295 function-list. This list is a comma separated list of
1296 functions that can be changed at run time by the
1297 set_graph_notrace file in the debugfs tracing directory.
1300 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1301 support via parallel port (up to 5 devices per port)
1302 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1303 See also Documentation/input/joystick-parport.txt
1307 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1311 gcov_persist= [GCOV] When non-zero (default), profiling data for
1312 kernel modules is saved and remains accessible via
1313 debugfs, even when the module is unloaded/reloaded.
1314 When zero, profiling data is discarded and associated
1315 debugfs files are removed at module unload time.
1317 gpt [EFI] Forces disk with valid GPT signature but
1318 invalid Protective MBR to be treated as GPT. If the
1319 primary GPT is corrupted, it enables the backup/alternate
1320 GPT to be used instead.
1322 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1323 the "Enable 0" bit of the configuration register.
1326 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1327 the "Enable 0" bit of the configuration register.
1330 grcan.select= [HW] Select which physical interface to use.
1333 grcan.txsize= [HW] Sets the size of the tx buffer.
1334 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1336 grcan.rxsize= [HW] Sets the size of the rx buffer.
1337 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1340 hardlockup_all_cpu_backtrace=
1341 [KNL] Should the hard-lockup detector generate
1342 backtraces on all cpus.
1345 hashdist= [KNL,NUMA] Large hashes allocated during boot
1346 are distributed across NUMA nodes. Defaults on
1347 for 64-bit NUMA, off otherwise.
1348 Format: 0 | 1 (for off | on)
1350 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1352 hd= [EIDE] (E)IDE hard drive subsystem geometry
1353 Format: <cyl>,<head>,<sect>
1356 Disable Hardware Error Source Table (HEST) support;
1357 corresponding firmware-first mode error processing
1358 logic will be disabled.
1360 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1361 size of <nn>. This works even on boxes that have no
1362 highmem otherwise. This also works to reduce highmem
1363 size on bigger boxes.
1365 highres= [KNL] Enable/disable high resolution timer mode.
1366 Valid parameters: "on", "off"
1370 See Documentation/isdn/README.HiSax.
1374 hpet= [X86-32,HPET] option to control HPET usage
1375 Format: { enable (default) | disable | force |
1377 disable: disable HPET and use PIT instead
1378 force: allow force enabled of undocumented chips (ICH4,
1380 verbose: show contents of HPET registers during setup
1382 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1383 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1385 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1386 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1387 On x86-64 and powerpc, this option can be specified
1388 multiple times interleaved with hugepages= to reserve
1389 huge pages of different sizes. Valid pages sizes on
1390 x86-64 are 2M (when the CPU supports "pse") and 1G
1391 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1393 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1394 terminal devices. Valid values: 0..8
1395 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1396 If specified, z/VM IUCV HVC accepts connections
1397 from listed z/VM user IDs only.
1399 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1400 hardware thread id mappings.
1401 Format: <cpu>:<hwthread>
1404 Do not unregister boot console at start. This is only
1405 useful for debugging when something happens in the window
1406 between unregistering the boot console and initializing
1409 i2c_bus= [HW] Override the default board specific I2C bus speed
1410 or register an additional I2C bus that is not
1411 registered from board initialization code.
1415 i8042.debug [HW] Toggle i8042 debug mode
1416 i8042.unmask_kbd_data
1417 [HW] Enable printing of interrupt data from the KBD port
1418 (disabled by default, and as a pre-condition
1419 requires that i8042.debug=1 be enabled)
1420 i8042.direct [HW] Put keyboard port into non-translated mode
1421 i8042.dumbkbd [HW] Pretend that controller can only read data from
1422 keyboard and cannot control its state
1423 (Don't attempt to blink the leds)
1424 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1425 i8042.nokbd [HW] Don't check/create keyboard port
1426 i8042.noloop [HW] Disable the AUX Loopback command while probing
1428 i8042.nomux [HW] Don't check presence of an active multiplexing
1430 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1432 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1433 i8042.reset [HW] Reset the controller during init and cleanup
1434 i8042.unlock [HW] Unlock (ignore) the keylock
1435 i8042.kbdreset [HW] Reset device connected to KBD port
1439 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1440 indicates that the driver is running on unsupported
1442 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1443 does not match list of supported models.
1445 [HW] Report power status in /proc/i8k
1446 (disabled by default)
1447 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1450 i915.invert_brightness=
1451 [DRM] Invert the sense of the variable that is used to
1452 set the brightness of the panel backlight. Normally a
1453 brightness value of 0 indicates backlight switched off,
1454 and the maximum of the brightness value sets the backlight
1455 to maximum brightness. If this parameter is set to 0
1456 (default) and the machine requires it, or this parameter
1457 is set to 1, a brightness value of 0 sets the backlight
1458 to maximum brightness, and the maximum of the brightness
1459 value switches the backlight off.
1460 -1 -- never invert brightness
1461 0 -- machine default
1462 1 -- force brightness inversion
1465 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1467 ide-core.nodma= [HW] (E)IDE subsystem
1468 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1469 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1470 .cdrom .chs .ignore_cable are additional options
1471 See Documentation/ide/ide.txt.
1473 ide-generic.probe-mask= [HW] (E)IDE subsystem
1475 Probe mask for legacy ISA IDE ports. Depending on
1476 platform up to 6 ports are supported, enabled by
1477 setting corresponding bits in the mask to 1. The
1478 default value is 0x0, which has a special meaning.
1479 On systems that have PCI, it triggers scanning the
1480 PCI bus for the first and the second port, which
1481 are then probed. On systems without PCI the value
1482 of 0x0 enables probing the two first ports as if it
1485 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1486 Claim all unknown PCI IDE storage controllers.
1489 Format: idle=poll, idle=halt, idle=nomwait
1490 Poll forces a polling idle loop that can slightly
1491 improve the performance of waking up a idle CPU, but
1492 will use a lot of power and make the system run hot.
1494 idle=halt: Halt is forced to be used for CPU idle.
1495 In such case C2/C3 won't be used again.
1496 idle=nomwait: Disable mwait for CPU C-states
1498 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1499 Format: { strict | legacy | 2008 | relaxed }
1502 Choose which programs will be accepted for execution
1503 based on the IEEE 754 NaN encoding(s) supported by
1504 the FPU and the NaN encoding requested with the value
1505 of an ELF file header flag individually set by each
1506 binary. Hardware implementations are permitted to
1507 support either or both of the legacy and the 2008 NaN
1510 Available settings are as follows:
1511 strict accept binaries that request a NaN encoding
1512 supported by the FPU
1513 legacy only accept legacy-NaN binaries, if supported
1515 2008 only accept 2008-NaN binaries, if supported
1517 relaxed accept any binaries regardless of whether
1518 supported by the FPU
1520 The FPU emulator is always able to support both NaN
1521 encodings, so if no FPU hardware is present or it has
1522 been disabled with 'nofpu', then the settings of
1523 'legacy' and '2008' strap the emulator accordingly,
1524 'relaxed' straps the emulator for both legacy-NaN and
1525 2008-NaN, whereas 'strict' enables legacy-NaN only on
1526 legacy processors and both NaN encodings on MIPS32 or
1529 The setting for ABS.fmt/NEG.fmt instruction execution
1530 mode generally follows that for the NaN encoding,
1531 except where unsupported by hardware.
1533 ignore_loglevel [KNL]
1534 Ignore loglevel setting - this will print /all/
1535 kernel messages to the console. Useful for debugging.
1536 We also add it as printk module parameter, so users
1537 could change it dynamically, usually by
1538 /sys/module/printk/parameters/ignore_loglevel.
1541 Ignore RLIMIT_DATA setting for data mappings,
1542 print warning at first misuse. Can be changed via
1543 /sys/module/kernel/parameters/ignore_rlimit_data.
1545 ihash_entries= [KNL]
1546 Set number of hash buckets for inode cache.
1548 ima_appraise= [IMA] appraise integrity measurements
1549 Format: { "off" | "enforce" | "fix" | "log" }
1552 ima_appraise_tcb [IMA]
1553 The builtin appraise policy appraises all files
1557 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1561 The list of supported hash algorithms is defined
1562 in crypto/hash_info.h.
1565 The builtin measurement policy to load during IMA
1566 setup. Specyfing "tcb" as the value, measures all
1567 programs exec'd, files mmap'd for exec, and all files
1568 opened with the read mode bit set by either the
1569 effective uid (euid=0) or uid=0.
1572 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1573 Load a policy which meets the needs of the Trusted
1574 Computing Base. This means IMA will measure all
1575 programs exec'd, files mmap'd for exec, and all files
1576 opened for read by uid=0.
1579 Select one of defined IMA measurements template formats.
1580 Formats: { "ima" | "ima-ng" | "ima-sig" }
1584 [IMA] Define a custom template format.
1585 Format: { "field1|...|fieldN" }
1587 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1588 Format: <min_file_size>
1589 Set the minimal file size for using asynchronous hash.
1590 If left unspecified, ahash usage is disabled.
1592 ahash performance varies for different data sizes on
1593 different crypto accelerators. This option can be used
1594 to achieve the best performance for a particular HW.
1596 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1598 Set hashing buffer size. Default: 4k.
1600 ahash performance varies for different chunk sizes on
1601 different crypto accelerators. This option can be used
1602 to achieve best performance for particular HW.
1606 Run specified binary instead of /sbin/init as init
1609 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1610 for working out where the kernel is dying during
1613 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1614 initcall functions. Useful for debugging built-in
1615 modules and initcalls.
1617 initrd= [BOOT] Specify the location of the initial ramdisk
1619 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1622 int_pln_enable [x86] Enable power limit notification interrupt
1624 integrity_audit=[IMA]
1625 Format: { "0" | "1" }
1626 0 -- basic integrity auditing messages. (Default)
1627 1 -- additional integrity auditing messages.
1629 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1631 Enable intel iommu driver.
1633 Disable intel iommu driver.
1634 igfx_off [Default Off]
1635 By default, gfx is mapped as normal device. If a gfx
1636 device has a dedicated DMAR unit, the DMAR unit is
1637 bypassed by not enabling DMAR with this option. In
1638 this case, gfx device will use physical address for
1641 With this option iommu will not optimize to look
1642 for io virtual address below 32-bit forcing dual
1643 address cycle on pci bus for cards supporting greater
1644 than 32-bit addressing. The default is to look
1645 for translation below 32-bit and if not available
1646 then look in the higher range.
1647 strict [Default Off]
1648 With this option on every unmap_single operation will
1649 result in a hardware IOTLB flush operation as opposed
1650 to batching them for performance.
1651 sp_off [Default Off]
1652 By default, super page will be supported if Intel IOMMU
1653 has the capability. With this option, super page will
1655 ecs_off [Default Off]
1656 By default, extended context tables will be supported if
1657 the hardware advertises that it has support both for the
1658 extended tables themselves, and also PASID support. With
1659 this option set, extended tables will not be used even
1660 on hardware which claims to support them.
1662 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1663 0 disables intel_idle and fall back on acpi_idle.
1664 1 to 6 specify maximum depth of C-state.
1668 Do not enable intel_pstate as the default
1669 scaling driver for the supported processors
1671 Enable intel_pstate on systems that prohibit it by default
1672 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1673 instead of acpi-cpufreq may disable platform features, such
1674 as thermal controls and power capping, that rely on ACPI
1675 P-States information being indicated to OSPM and therefore
1676 should be used with caution. This option does not work with
1677 processors that aren't supported by the intel_pstate driver
1678 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1680 Do not enable hardware P state control (HWP)
1683 Only load intel_pstate on systems which support
1684 hardware P state control (HWP) if available.
1686 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1687 Description Table, specifies preferred power management
1688 profile as "Enterprise Server" or "Performance Server",
1689 then this feature is turned on by default.
1691 intremap= [X86-64, Intel-IOMMU]
1692 on enable Interrupt Remapping (default)
1693 off disable Interrupt Remapping
1694 nosid disable Source ID checking
1696 BIOS x2APIC opt-out request will be ignored
1697 nopost disable Interrupt Posting
1699 iomem= Disable strict checking of access to MMIO memory
1700 strict regions from userspace.
1715 nobypass [PPC/POWERNV]
1716 Disable IOMMU bypass, using IOMMU for PCI devices.
1719 io7= [HW] IO7 for Marvel based alpha systems
1720 See comment before marvel_specify_io7 in
1721 arch/alpha/kernel/core_marvel.c.
1723 io_delay= [X86] I/O delay method
1725 Standard port 0x80 based delay
1727 Alternate port 0xed based delay (needed on some systems)
1729 Simple two microseconds delay
1734 See Documentation/filesystems/nfs/nfsroot.txt.
1736 irqaffinity= [SMP] Set the default irq affinity mask
1738 <cpu number>,...,<cpu number>
1740 <cpu number>-<cpu number>
1741 (must be a positive range in ascending order)
1743 <cpu number>,...,<cpu number>-<cpu number>
1746 When an interrupt is not handled search all handlers
1747 for it. Intended to get systems with badly broken
1751 When an interrupt is not handled search all handlers
1752 for it. Also check all handlers each timer
1753 interrupt. Intended to get systems with badly broken
1757 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1759 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1761 <cpu number>,...,<cpu number>
1763 <cpu number>-<cpu number>
1764 (must be a positive range in ascending order)
1766 <cpu number>,...,<cpu number>-<cpu number>
1768 This option can be used to specify one or more CPUs
1769 to isolate from the general SMP balancing and scheduling
1770 algorithms. You can move a process onto or off an
1771 "isolated" CPU via the CPU affinity syscalls or cpuset.
1772 <cpu number> begins at 0 and the maximum value is
1773 "number of CPUs in system - 1".
1775 This option is the preferred way to isolate CPUs. The
1776 alternative -- manually setting the CPU mask of all
1777 tasks in the system -- can cause problems and
1778 suboptimal load balancer performance.
1782 ivrs_ioapic [HW,X86_64]
1783 Provide an override to the IOAPIC-ID<->DEVICE-ID
1784 mapping provided in the IVRS ACPI table. For
1785 example, to map IOAPIC-ID decimal 10 to
1786 PCI device 00:14.0 write the parameter as:
1787 ivrs_ioapic[10]=00:14.0
1789 ivrs_hpet [HW,X86_64]
1790 Provide an override to the HPET-ID<->DEVICE-ID
1791 mapping provided in the IVRS ACPI table. For
1792 example, to map HPET-ID decimal 0 to
1793 PCI device 00:14.0 write the parameter as:
1794 ivrs_hpet[0]=00:14.0
1796 ivrs_acpihid [HW,X86_64]
1797 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1798 mapping provided in the IVRS ACPI table. For
1799 example, to map UART-HID:UID AMD0020:0 to
1800 PCI device 00:14.5 write the parameter as:
1801 ivrs_acpihid[00:14.5]=AMD0020:0
1803 js= [HW,JOY] Analog joystick
1804 See Documentation/input/joystick.txt.
1807 Enable/disable kernel and module base offset ASLR
1808 (Address Space Layout Randomization) if built into
1809 the kernel. When CONFIG_HIBERNATION is selected,
1810 kASLR is disabled by default. When kASLR is enabled,
1811 hibernation will be disabled.
1815 kernelcore= [KNL,X86,IA-64,PPC]
1816 Format: nn[KMGTPE] | "mirror"
1818 specifies the amount of memory usable by the kernel
1819 for non-movable allocations. The requested amount is
1820 spread evenly throughout all nodes in the system. The
1821 remaining memory in each node is used for Movable
1822 pages. In the event, a node is too small to have both
1823 kernelcore and Movable pages, kernelcore pages will
1824 take priority and other nodes will have a larger number
1825 of Movable pages. The Movable zone is used for the
1826 allocation of pages that may be reclaimed or moved
1827 by the page migration subsystem. This means that
1828 HugeTLB pages may not be allocated from this zone.
1829 Note that allocations like PTEs-from-HighMem still
1830 use the HighMem zone if it exists, and the Normal
1831 zone if it does not.
1833 Instead of specifying the amount of memory (nn[KMGTPE]),
1834 you can specify "mirror" option. In case "mirror"
1835 option is specified, mirrored (reliable) memory is used
1836 for non-movable allocations and remaining memory is used
1837 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1838 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1841 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1842 Format: <Controller#>[,poll interval]
1843 The controller # is the number of the ehci usb debug
1844 port as it is probed via PCI. The poll interval is
1845 optional and is the number seconds in between
1846 each poll cycle to the debug port in case you need
1847 the functionality for interrupting the kernel with
1848 gdb or control-c on the dbgp connection. When
1849 not using this parameter you use sysrq-g to break into
1850 the kernel debugger.
1852 kgdboc= [KGDB,HW] kgdb over consoles.
1853 Requires a tty driver that supports console polling,
1854 or a supported polling keyboard driver (non-usb).
1855 Serial only format: <serial_device>[,baud]
1856 keyboard only format: kbd
1857 keyboard and serial format: kbd,<serial_device>[,baud]
1858 Optional Kernel mode setting:
1859 kms, kbd format: kms,kbd
1860 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1862 kgdbwait [KGDB] Stop kernel execution and enter the
1863 kernel debugger at the earliest opportunity.
1865 kmac= [MIPS] korina ethernet MAC address.
1866 Configure the RouterBoard 532 series on-chip
1867 Ethernet adapter MAC address.
1869 kmemleak= [KNL] Boot-time kmemleak enable/disable
1870 Valid arguments: on, off
1872 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1875 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1876 Valid arguments: 0, 1, 2
1877 kmemcheck=0 (disabled)
1878 kmemcheck=1 (enabled)
1879 kmemcheck=2 (one-shot mode)
1880 Default: 2 (one-shot mode)
1882 kstack=N [X86] Print N words from the kernel stack
1885 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1886 Default is 0 (don't ignore, but inject #GP)
1888 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1892 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1893 Default is 1 (enabled)
1895 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1897 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1899 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1900 (virtualized MMU) support on capable Intel chips.
1901 Default is 1 (enabled)
1903 kvm-intel.emulate_invalid_guest_state=
1904 [KVM,Intel] Enable emulation of invalid guest states
1905 Default is 0 (disabled)
1907 kvm-intel.flexpriority=
1908 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1909 Default is 1 (enabled)
1912 [KVM,Intel] Enable VMX nesting (nVMX).
1913 Default is 0 (disabled)
1915 kvm-intel.unrestricted_guest=
1916 [KVM,Intel] Disable unrestricted guest feature
1917 (virtualized real and unpaged mode) on capable
1918 Intel chips. Default is 1 (enabled)
1920 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1921 feature (tagged TLBs) on capable Intel chips.
1922 Default is 1 (enabled)
1928 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1931 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1932 value for LAPIC timer one-shot implementation. Default
1933 back to the programmable timer unit in the LAPIC.
1935 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1938 libata.dma= [LIBATA] DMA control
1939 libata.dma=0 Disable all PATA and SATA DMA
1940 libata.dma=1 PATA and SATA Disk DMA only
1941 libata.dma=2 ATAPI (CDROM) DMA only
1942 libata.dma=4 Compact Flash DMA only
1943 Combinations also work, so libata.dma=3 enables DMA
1944 for disks and CDROMs, but not CFs.
1946 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1947 libata.ignore_hpa=0 keep BIOS limits (default)
1948 libata.ignore_hpa=1 ignore limits, using full disk
1950 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1954 libata.force= [LIBATA] Force configurations. The format is comma
1955 separated list of "[ID:]VAL" where ID is
1956 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1957 matching port, link or device. Basically, it matches
1958 the ATA ID string printed on console by libata. If
1959 the whole ID part is omitted, the last PORT and DEVICE
1960 values are used. If ID hasn't been specified yet, the
1961 configuration applies to all ports, links and devices.
1963 If only DEVICE is omitted, the parameter applies to
1964 the port and all links and devices behind it. DEVICE
1965 number of 0 either selects the first device or the
1966 first fan-out link behind PMP device. It does not
1967 select the host link. DEVICE number of 15 selects the
1968 host link and device attached to it.
1970 The VAL specifies the configuration to force. As long
1971 as there's no ambiguity shortcut notation is allowed.
1972 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1973 The following configurations can be forced.
1975 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1976 Any ID with matching PORT is used.
1978 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1980 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1981 udma[/][16,25,33,44,66,100,133] notation is also
1984 * [no]ncq: Turn on or off NCQ.
1986 * [no]ncqtrim: Turn off queued DSM TRIM.
1988 * nohrst, nosrst, norst: suppress hard, soft
1991 * rstonce: only attempt one reset during
1992 hot-unplug link recovery
1994 * dump_id: dump IDENTIFY data.
1996 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1998 * disable: Disable this device.
2000 If there are multiple matching configurations changing
2001 the same attribute, the last one is used.
2003 memblock=debug [KNL] Enable memblock debug messages.
2005 load_ramdisk= [RAM] List of ramdisks to load from floppy
2006 See Documentation/blockdev/ramdisk.txt.
2008 lockd.nlm_grace_period=P [NFS] Assign grace period.
2011 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2014 lockd.nlm_timeout=T [NFS] Assign timeout value.
2017 lockd.nlm_udpport=M [NFS] Assign UDP port.
2020 locktorture.nreaders_stress= [KNL]
2021 Set the number of locking read-acquisition kthreads.
2022 Defaults to being automatically set based on the
2023 number of online CPUs.
2025 locktorture.nwriters_stress= [KNL]
2026 Set the number of locking write-acquisition kthreads.
2028 locktorture.onoff_holdoff= [KNL]
2029 Set time (s) after boot for CPU-hotplug testing.
2031 locktorture.onoff_interval= [KNL]
2032 Set time (s) between CPU-hotplug operations, or
2033 zero to disable CPU-hotplug testing.
2035 locktorture.shuffle_interval= [KNL]
2036 Set task-shuffle interval (jiffies). Shuffling
2037 tasks allows some CPUs to go into dyntick-idle
2038 mode during the locktorture test.
2040 locktorture.shutdown_secs= [KNL]
2041 Set time (s) after boot system shutdown. This
2042 is useful for hands-off automated testing.
2044 locktorture.stat_interval= [KNL]
2045 Time (s) between statistics printk()s.
2047 locktorture.stutter= [KNL]
2048 Time (s) to stutter testing, for example,
2049 specifying five seconds causes the test to run for
2050 five seconds, wait for five seconds, and so on.
2051 This tests the locking primitive's ability to
2052 transition abruptly to and from idle.
2054 locktorture.torture_runnable= [BOOT]
2055 Start locktorture running at boot time.
2057 locktorture.torture_type= [KNL]
2058 Specify the locking implementation to test.
2060 locktorture.verbose= [KNL]
2061 Enable additional printk() statements.
2063 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2066 loglevel= All Kernel Messages with a loglevel smaller than the
2067 console loglevel will be printed to the console. It can
2068 also be changed with klogd or other programs. The
2069 loglevels are defined as follows:
2071 0 (KERN_EMERG) system is unusable
2072 1 (KERN_ALERT) action must be taken immediately
2073 2 (KERN_CRIT) critical conditions
2074 3 (KERN_ERR) error conditions
2075 4 (KERN_WARNING) warning conditions
2076 5 (KERN_NOTICE) normal but significant condition
2077 6 (KERN_INFO) informational
2078 7 (KERN_DEBUG) debug-level messages
2080 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2081 in bytes. n must be a power of two and greater
2082 than the minimal size. The minimal size is defined
2083 by LOG_BUF_SHIFT kernel config parameter. There is
2084 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2085 that allows to increase the default size depending on
2086 the number of CPUs. See init/Kconfig for more details.
2088 logo.nologo [FB] Disables display of the built-in Linux logo.
2089 This may be used to provide more screen space for
2090 kernel log messages and is useful when debugging
2091 kernel boot problems.
2093 lp=0 [LP] Specify parallel ports to use, e.g,
2094 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2095 lp=reset first parallel port). 'lp=0' disables the
2096 lp=auto printer driver. 'lp=reset' (which can be
2097 specified in addition to the ports) causes
2098 attached printers to be reset. Using
2099 lp=port1,port2,... specifies the parallel ports
2100 to associate lp devices with, starting with
2101 lp0. A port specification may be 'none' to skip
2102 that lp device, or a parport name such as
2103 'parport0'. Specifying 'lp=auto' instead of a
2104 port specification list means that device IDs
2105 from each port should be examined, to see if
2106 an IEEE 1284-compliant printer is attached; if
2107 so, the driver will manage that printer.
2108 See also header of drivers/char/lp.c.
2111 Sets loops_per_jiffy to given constant, thus avoiding
2112 time-consuming boot-time autodetection (up to 250 ms per
2113 CPU). 0 enables autodetection (default). To determine
2114 the correct value for your kernel, boot with normal
2115 autodetection and see what value is printed. Note that
2116 on SMP systems the preset will be applied to all CPUs,
2117 which is likely to cause problems if your CPUs need
2118 significantly divergent settings. An incorrect value
2119 will cause delays in the kernel to be wrong, leading to
2120 unpredictable I/O errors and other breakage. Although
2121 unlikely, in the extreme case this might damage your
2125 Format: <io>,<irq>,<dma>
2127 machvec= [IA-64] Force the use of a particular machine-vector
2128 (machvec) in a generic kernel.
2129 Example: machvec=hpzx1_swiotlb
2131 machtype= [Loongson] Share the same kernel image file between different
2133 Example: machtype=lemote-yeeloong-2f-7inch
2135 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2136 than or equal to this physical address is ignored.
2138 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2139 should make use of. maxcpus=n : n >= 0 limits the
2140 kernel to using 'n' processors. n=0 is a special case,
2141 it is equivalent to "nosmp", which also disables
2144 max_loop= [LOOP] The number of loop block devices that get
2145 (loop.max_loop) unconditionally pre-created at init time. The default
2146 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2147 of statically allocating a predefined number, loop
2148 devices can be requested on-demand with the
2149 /dev/loop-control interface.
2151 mce [X86-32] Machine Check Exception
2153 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2155 md= [HW] RAID subsystems devices and level
2156 See Documentation/md.txt.
2159 Format: <first>,<last>
2160 Specifies range of consoles to be captured by the MDA.
2162 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2163 Amount of memory to be used when the kernel is not able
2164 to see the whole system memory or for test.
2165 [X86] Work as limiting max address. Use together
2166 with memmap= to avoid physical address space collisions.
2167 Without memmap= PCI devices could be placed at addresses
2168 belonging to unused RAM.
2170 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2174 [KNL,SH] Allow user to override the default size for
2175 per-device physically contiguous DMA buffers.
2177 memhp_default_state=online/offline
2178 [KNL] Set the initial state for the memory hotplug
2179 onlining policy. If not specified, the default value is
2180 set according to the
2181 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2183 See Documentation/memory-hotplug.txt.
2185 memmap=exactmap [KNL,X86] Enable setting of an exact
2186 E820 memory map, as specified by the user.
2187 Such memmap=exactmap lines can be constructed based on
2188 BIOS output or other requirements. See the memmap=nn@ss
2191 memmap=nn[KMG]@ss[KMG]
2192 [KNL] Force usage of a specific region of memory.
2193 Region of memory to be used is from ss to ss+nn.
2195 memmap=nn[KMG]#ss[KMG]
2196 [KNL,ACPI] Mark specific memory as ACPI data.
2197 Region of memory to be marked is from ss to ss+nn.
2199 memmap=nn[KMG]$ss[KMG]
2200 [KNL,ACPI] Mark specific memory as reserved.
2201 Region of memory to be reserved is from ss to ss+nn.
2202 Example: Exclude memory from 0x18690000-0x1869ffff
2203 memmap=64K$0x18690000
2205 memmap=0x10000$0x18690000
2207 memmap=nn[KMG]!ss[KMG]
2208 [KNL,X86] Mark specific memory as protected.
2209 Region of memory to be used, from ss to ss+nn.
2210 The memory region may be marked as e820 type 12 (0xc)
2211 and is NVDIMM or ADR memory.
2213 memory_corruption_check=0/1 [X86]
2214 Some BIOSes seem to corrupt the first 64k of
2215 memory when doing things like suspend/resume.
2216 Setting this option will scan the memory
2217 looking for corruption. Enabling this will
2218 both detect corruption and prevent the kernel
2219 from using the memory being corrupted.
2220 However, its intended as a diagnostic tool; if
2221 repeatable BIOS-originated corruption always
2222 affects the same memory, you can use memmap=
2223 to prevent the kernel from using that memory.
2225 memory_corruption_check_size=size [X86]
2226 By default it checks for corruption in the low
2227 64k, making this memory unavailable for normal
2228 use. Use this parameter to scan for
2229 corruption in more or less memory.
2231 memory_corruption_check_period=seconds [X86]
2232 By default it checks for corruption every 60
2233 seconds. Use this parameter to check at some
2234 other rate. 0 disables periodic checking.
2236 memtest= [KNL,X86,ARM] Enable memtest
2238 default : 0 <disable>
2239 Specifies the number of memtest passes to be
2240 performed. Each pass selects another test
2241 pattern from a given set of patterns. Memtest
2242 fills the memory with this pattern, validates
2243 memory contents and reserves bad memory
2244 regions that are detected.
2246 meye.*= [HW] Set MotionEye Camera parameters
2247 See Documentation/video4linux/meye.txt.
2249 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2250 Multi-Function General Purpose Timers on AMD Geode
2253 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2254 the BIOS has incorrectly applied a workaround. TinyBIOS
2255 version 0.98 is known to be affected, 0.99 fixes the
2256 problem by letting the user disable the workaround.
2260 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2261 physical address is ignored.
2263 mini2440= [ARM,HW,KNL]
2264 Format:[0..2][b][c][t]
2266 MINI2440 configuration specification:
2267 0 - The attached screen is the 3.5" TFT
2268 1 - The attached screen is the 7" TFT
2269 2 - The VGA Shield is attached (1024x768)
2270 Leaving out the screen size parameter will not load
2271 the TFT driver, and the framebuffer will be left
2273 b - Enable backlight. The TFT backlight pin will be
2274 linked to the kernel VESA blanking code and a GPIO
2275 LED. This parameter is not necessary when using the
2277 c - Enable the s3c camera interface.
2278 t - Reserved for enabling touchscreen support. The
2279 touchscreen support is not enabled in the mainstream
2280 kernel as of 2.6.30, a preliminary port can be found
2281 in the "bleeding edge" mini2440 support kernel at
2282 http://repo.or.cz/w/linux-2.6/mini2440.git
2285 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2286 parameter allows control of the logging verbosity for
2287 the additional memory initialisation checks. A value
2288 of 0 disables mminit logging and a level of 4 will
2289 log everything. Information is printed at KERN_DEBUG
2290 so loglevel=8 may also need to be specified.
2293 [KNL] When CONFIG_MODULE_SIG is set, this means that
2294 modules without (valid) signatures will fail to load.
2295 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2296 is always true, so this option does nothing.
2299 [MOUSE] Maximum time between finger touching and
2300 leaving touchpad surface for touch to be considered
2301 a tap and be reported as a left button click (for
2302 touchpads working in absolute mode only).
2304 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2305 reporting absolute coordinates, such as tablets
2306 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2307 reporting absolute coordinates, such as tablets
2309 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2310 is similar to kernelcore except it specifies the
2311 amount of memory used for migratable allocations.
2312 If both kernelcore and movablecore is specified,
2313 then kernelcore will be at *least* the specified
2314 value but may be more. If movablecore on its own
2315 is specified, the administrator must be careful
2316 that the amount of memory usable for all allocations
2319 movable_node [KNL,X86] Boot-time switch to enable the effects
2320 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2322 MTD_Partition= [MTD]
2323 Format: <name>,<region-number>,<size>,<offset>
2325 MTD_Region= [MTD] Format:
2326 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2329 See drivers/mtd/cmdlinepart.c.
2331 multitce=off [PPC] This parameter disables the use of the pSeries
2332 firmware feature for updating multiple TCE entries
2335 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2337 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2339 boundary - index of last SLC block on Flex-OneNAND.
2340 The remaining blocks are configured as MLC blocks.
2341 lock - Configure if Flex-OneNAND boundary should be locked.
2342 Once locked, the boundary cannot be changed.
2343 1 indicates lock status, 0 indicates unlock status.
2346 ARM/S3C2412 JIVE boot control
2348 See arch/arm/mach-s3c2412/mach-jive.c
2350 mtouchusb.raw_coordinates=
2351 [HW] Make the MicroTouch USB driver use raw coordinates
2352 ('y', default) or cooked coordinates ('n')
2354 mtrr_chunk_size=nn[KMG] [X86]
2355 used for mtrr cleanup. It is largest continuous chunk
2356 that could hold holes aka. UC entries.
2358 mtrr_gran_size=nn[KMG] [X86]
2359 Used for mtrr cleanup. It is granularity of mtrr block.
2361 Large value could prevent small alignment from
2364 mtrr_spare_reg_nr=n [X86]
2366 Range: 0,7 : spare reg number
2368 Used for mtrr cleanup. It is spare mtrr entries number.
2369 Set to 2 or more if your graphical card needs more.
2371 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2373 netdev= [NET] Network devices parameters
2374 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2375 Note that mem_start is often overloaded to mean
2376 something different and driver-specific.
2377 This usage is only documented in each driver source
2381 [NETFILTER] Enable connection tracking flow accounting
2382 0 to disable accounting
2383 1 to enable accounting
2386 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2387 See Documentation/filesystems/nfs/nfsroot.txt.
2389 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2390 See Documentation/filesystems/nfs/nfsroot.txt.
2392 nfsrootdebug [NFS] enable nfsroot debugging messages.
2393 See Documentation/filesystems/nfs/nfsroot.txt.
2395 nfs.callback_tcpport=
2396 [NFS] set the TCP port on which the NFSv4 callback
2397 channel should listen.
2400 [NFS] sets the pathname to the program which is used
2401 to update the NFS client cache entries.
2403 nfs.cache_getent_timeout=
2404 [NFS] sets the timeout after which an attempt to
2405 update a cache entry is deemed to have failed.
2407 nfs.idmap_cache_timeout=
2408 [NFS] set the maximum lifetime for idmapper cache
2412 [NFS] enable 64-bit inode numbers.
2413 If zero, the NFS client will fake up a 32-bit inode
2414 number for the readdir() and stat() syscalls instead
2415 of returning the full 64-bit number.
2416 The default is to return 64-bit inode numbers.
2418 nfs.max_session_slots=
2419 [NFSv4.1] Sets the maximum number of session slots
2420 the client will attempt to negotiate with the server.
2421 This limits the number of simultaneous RPC requests
2422 that the client can send to the NFSv4.1 server.
2423 Note that there is little point in setting this
2424 value higher than the max_tcp_slot_table_limit.
2426 nfs.nfs4_disable_idmapping=
2427 [NFSv4] When set to the default of '1', this option
2428 ensures that both the RPC level authentication
2429 scheme and the NFS level operations agree to use
2430 numeric uids/gids if the mount is using the
2431 'sec=sys' security flavour. In effect it is
2432 disabling idmapping, which can make migration from
2433 legacy NFSv2/v3 systems to NFSv4 easier.
2434 Servers that do not support this mode of operation
2435 will be autodetected by the client, and it will fall
2436 back to using the idmapper.
2437 To turn off this behaviour, set the value to '0'.
2439 [NFS4] Specify an additional fixed unique ident-
2440 ification string that NFSv4 clients can insert into
2441 their nfs_client_id4 string. This is typically a
2442 UUID that is generated at system install time.
2444 nfs.send_implementation_id =
2445 [NFSv4.1] Send client implementation identification
2446 information in exchange_id requests.
2447 If zero, no implementation identification information
2449 The default is to send the implementation identification
2452 nfs.recover_lost_locks =
2453 [NFSv4] Attempt to recover locks that were lost due
2454 to a lease timeout on the server. Please note that
2455 doing this risks data corruption, since there are
2456 no guarantees that the file will remain unchanged
2457 after the locks are lost.
2458 If you want to enable the kernel legacy behaviour of
2459 attempting to recover these locks, then set this
2461 The default parameter value of '0' causes the kernel
2462 not to attempt recovery of lost locks.
2464 nfs4.layoutstats_timer =
2465 [NFSv4.2] Change the rate at which the kernel sends
2466 layoutstats to the pNFS metadata server.
2468 Setting this to value to 0 causes the kernel to use
2469 whatever value is the default set by the layout
2470 driver. A non-zero value sets the minimum interval
2471 in seconds between layoutstats transmissions.
2473 nfsd.nfs4_disable_idmapping=
2474 [NFSv4] When set to the default of '1', the NFSv4
2475 server will return only numeric uids and gids to
2476 clients using auth_sys, and will accept numeric uids
2477 and gids from such clients. This is intended to ease
2478 migration from NFSv2/v3.
2480 objlayoutdriver.osd_login_prog=
2481 [NFS] [OBJLAYOUT] sets the pathname to the program which
2482 is used to automatically discover and login into new
2483 osd-targets. Please see:
2484 Documentation/filesystems/pnfs.txt for more explanations
2486 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2487 when a NMI is triggered.
2488 Format: [state][,regs][,debounce][,die]
2490 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2491 Format: [panic,][nopanic,][num]
2493 0 - turn hardlockup detector in nmi_watchdog off
2494 1 - turn hardlockup detector in nmi_watchdog on
2495 When panic is specified, panic when an NMI watchdog
2496 timeout occurs (or 'nopanic' to override the opposite
2497 default). To disable both hard and soft lockup detectors,
2498 please see 'nowatchdog'.
2499 This is useful when you use a panic=... timeout and
2500 need the box quickly up again.
2502 netpoll.carrier_timeout=
2503 [NET] Specifies amount of time (in seconds) that
2504 netpoll should wait for a carrier. By default netpoll
2507 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2508 emulation library even if a 387 maths coprocessor
2512 [HW] Never suspend the console
2513 Disable suspending of consoles during suspend and
2514 hibernate operations. Once disabled, debugging
2515 messages can reach various consoles while the rest
2516 of the system is being put to sleep (ie, while
2517 debugging driver suspend/resume hooks). This may
2518 not work reliably with all consoles, but is known
2519 to work with serial and VGA consoles.
2520 To facilitate more flexible debugging, we also add
2521 console_suspend, a printk module parameter to control
2522 it. Users could use console_suspend (usually
2523 /sys/module/printk/parameters/console_suspend) to
2524 turn on/off it dynamically.
2526 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2527 caches in the slab allocator. Saves per-node memory,
2528 but will impact performance.
2532 noapic [SMP,APIC] Tells the kernel to not make use of any
2533 IOAPICs that may be present in the system.
2535 noautogroup Disable scheduler automatic task group creation.
2537 nobats [PPC] Do not use BATs for mapping kernel lowmem
2538 on "Classic" PPC cores.
2542 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2544 nodelayacct [KNL] Disable per-task delay accounting
2546 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2548 nodsp [SH] Disable hardware DSP at boot time.
2550 noefi Disable EFI runtime services support.
2555 On X86-32 available only on PAE configured kernels.
2556 noexec=on: enable non-executable mappings (default)
2557 noexec=off: disable non-executable mappings
2560 Disable SMAP (Supervisor Mode Access Prevention)
2561 even if it is supported by processor.
2564 Disable SMEP (Supervisor Mode Execution Prevention)
2565 even if it is supported by processor.
2568 This affects only 32-bit executables.
2569 noexec32=on: enable non-executable mappings (default)
2570 read doesn't imply executable mappings
2571 noexec32=off: disable non-executable mappings
2572 read implies executable mappings
2574 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2576 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2577 register save and restore. The kernel will only save
2578 legacy floating-point registers on task switch.
2580 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2582 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2583 Equivalent to smt=1.
2585 noxsave [BUGS=X86] Disables x86 extended register state save
2586 and restore using xsave. The kernel will fallback to
2587 enabling legacy floating-point and sse state.
2589 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2590 register states. The kernel will fall back to use
2591 xsave to save the states. By using this parameter,
2592 performance of saving the states is degraded because
2593 xsave doesn't support modified optimization while
2594 xsaveopt supports it on xsaveopt enabled systems.
2596 noxsaves [X86] Disables xsaves and xrstors used in saving and
2597 restoring x86 extended register state in compacted
2598 form of xsave area. The kernel will fall back to use
2599 xsaveopt and xrstor to save and restore the states
2600 in standard form of xsave area. By using this
2601 parameter, xsave area per process might occupy more
2602 memory on xsaves enabled systems.
2604 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2605 wfi(ARM) instruction doesn't work correctly and not to
2606 use it. This is also useful when using JTAG debugger.
2608 no_file_caps Tells the kernel not to honor file capabilities. The
2609 only way then for a file to be executed with privilege
2610 is to be setuid root or executed by root.
2612 nohalt [IA-64] Tells the kernel not to use the power saving
2613 function PAL_HALT_LIGHT when idle. This increases
2614 power-consumption. On the positive side, it reduces
2615 interrupt wake-up latency, which may improve performance
2616 in certain environments such as networked servers or
2619 nohibernate [HIBERNATION] Disable hibernation and resume.
2621 nohz= [KNL] Boottime enable/disable dynamic ticks
2622 Valid arguments: on, off
2625 nohz_full= [KNL,BOOT]
2626 In kernels built with CONFIG_NO_HZ_FULL=y, set
2627 the specified list of CPUs whose tick will be stopped
2628 whenever possible. The boot CPU will be forced outside
2629 the range to maintain the timekeeping.
2630 The CPUs in this range must also be included in the
2633 noiotrap [SH] Disables trapped I/O port accesses.
2635 noirqdebug [X86-32] Disables the code which attempts to detect and
2636 disable unhandled interrupt sources.
2638 no_timer_check [X86,APIC] Disables the code which tests for
2639 broken timer IRQ sources.
2641 noisapnp [ISAPNP] Disables ISA PnP code.
2643 noinitrd [RAM] Tells the kernel not to load any configured
2646 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2648 [Deprecated - use intremap=off]
2652 noinvpcid [X86] Disable the INVPCID cpu feature.
2654 nojitter [IA-64] Disables jitter checking for ITC timers.
2656 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2658 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2661 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2662 steal time is computed, but won't influence scheduler
2665 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2667 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2669 noltlbs [PPC] Do not use large page/tlb entries for kernel
2670 lowmem mapping on PPC40x and PPC8xx
2672 nomca [IA-64] Disable machine check abort handling
2674 nomce [X86-32] Disable Machine Check Exception
2676 nomfgpt [X86-32] Disable Multi-Function General Purpose
2677 Timer usage (for AMD Geode machines).
2679 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2680 shutdown the other cpus. Instead use the REBOOT_VECTOR
2683 nomodule Disable module load
2685 nopat [X86] Disable PAT (page attribute table extension of
2686 pagetables) support.
2688 norandmaps Don't use address space randomization. Equivalent to
2689 echo 0 > /proc/sys/kernel/randomize_va_space
2691 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2693 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2694 with UP alternatives
2696 nordrand [X86] Disable kernel use of the RDRAND and
2697 RDSEED instructions even if they are supported
2698 by the processor. RDRAND and RDSEED are still
2699 available to user space applications.
2701 noresume [SWSUSP] Disables resume and restores original swap
2704 no-scroll [VGA] Disables scrollback.
2705 This is required for the Braillex ib80-piezo Braille
2706 reader made by F.H. Papenmeier (Germany).
2710 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2712 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2713 and disable the IO APIC. legacy for "maxcpus=0".
2715 nosoftlockup [KNL] Disable the soft-lockup detector.
2717 nosync [HW,M68K] Disables sync negotiation for all devices.
2719 notsc [BUGS=X86-32] Disable Time Stamp Counter
2721 nowatchdog [KNL] Disable both lockup detectors, i.e.
2722 soft-lockup and NMI watchdog (hard-lockup).
2726 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2728 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2729 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2730 Some features depend on CPU0. Known dependencies are:
2731 1. Resume from suspend/hibernate depends on CPU0.
2732 Suspend/hibernate will fail if CPU0 is offline and you
2733 need to online CPU0 before suspend/hibernate.
2734 2. PIC interrupts also depend on CPU0. CPU0 can't be
2735 removed if a PIC interrupt is detected.
2736 It's said poweroff/reboot may depend on CPU0 on some
2737 machines although I haven't seen such issues so far
2738 after CPU0 is offline on a few tested machines.
2739 If the dependencies are under your control, you can
2740 turn on cpu0_hotplug.
2742 nptcg= [IA-64] Override max number of concurrent global TLB
2743 purges which is reported from either PAL_VM_SUMMARY or
2746 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2747 could support. nr_cpus=n : n >= 1 limits the kernel to
2748 supporting 'n' processors. Later in runtime you can not
2749 use hotplug cpu feature to put more cpu back to online.
2750 just like you compile the kernel NR_CPUS=n
2752 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2754 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2755 Allowed values are enable and disable
2757 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2758 one of ['zone', 'node', 'default'] can be specified
2759 This can be set from sysctl after boot.
2760 See Documentation/sysctl/vm.txt for details.
2762 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2763 See Documentation/debugging-via-ohci1394.txt for more
2766 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2767 Rather than timing out after 20 ms if an EC
2768 command is not properly ACKed, override the length
2769 of the timeout. We have interrupts disabled while
2770 waiting for the ACK, so if this is set too high
2771 interrupts *may* be lost!
2773 omap_mux= [OMAP] Override bootloader pin multiplexing.
2774 Format: <mux_mode0.mode_name=value>...
2775 For example, to override I2C bus2:
2776 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2778 oprofile.timer= [HW]
2779 Use timer interrupt instead of performance counters
2781 oprofile.cpu_type= Force an oprofile cpu type
2782 This might be useful if you have an older oprofile
2783 userland or if you want common events.
2784 Format: { arch_perfmon }
2785 arch_perfmon: [X86] Force use of architectural
2786 perfmon on Intel CPUs instead of the
2787 CPU specific event set.
2788 timer: [X86] Force use of architectural NMI
2789 timer mode (see also oprofile.timer
2790 for generic hr timer mode)
2791 [s390] Force legacy basic mode sampling
2792 (report cpu_type "timer")
2794 oops=panic Always panic on oopses. Default is to just kill the
2795 process, but there is a small probability of
2796 deadlocking the machine.
2797 This will also cause panics on machine check exceptions.
2798 Useful together with panic=30 to trigger a reboot.
2801 See Documentation/sound/oss/oss-parameters.txt
2803 page_owner= [KNL] Boot-time page_owner enabling option.
2804 Storage of the information about who allocated
2805 each page is disabled in default. With this switch,
2807 on: enable the feature
2809 page_poison= [KNL] Boot-time parameter changing the state of
2810 poisoning on the buddy allocator.
2811 off: turn off poisoning
2812 on: turn on poisoning
2814 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2815 timeout > 0: seconds before rebooting
2816 timeout = 0: wait forever
2817 timeout < 0: reboot immediately
2820 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2823 crash_kexec_post_notifiers
2824 Run kdump after running panic-notifiers and dumping
2825 kmsg. This only for the users who doubt kdump always
2826 succeeds in any situation.
2827 Note that this also increases risks of kdump failure,
2828 because some panic notifiers can make the crashed
2829 kernel more unstable.
2831 parkbd.port= [HW] Parallel port number the keyboard adapter is
2832 connected to, default is 0.
2834 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2835 0 for XT, 1 for AT (default is AT).
2838 parport= [HW,PPT] Specify parallel ports. 0 disables.
2839 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2840 Use 'auto' to force the driver to use any
2841 IRQ/DMA settings detected (the default is to
2842 ignore detected IRQ/DMA settings because of
2843 possible conflicts). You can specify the base
2844 address, IRQ, and DMA settings; IRQ and DMA
2845 should be numbers, or 'auto' (for using detected
2846 settings on that particular port), or 'nofifo'
2847 (to avoid using a FIFO even if it is detected).
2848 Parallel ports are assigned in the order they
2849 are specified on the command line, starting
2852 parport_init_mode= [HW,PPT]
2853 Configure VIA parallel port to operate in
2854 a specific mode. This is necessary on Pegasos
2855 computer where firmware has no options for setting
2856 up parallel port mode and sets it to spp.
2857 Currently this function knows 686a and 8231 chips.
2858 Format: [spp|ps2|epp|ecp|ecpepp]
2861 Halt all CPUs after the first oops has been printed for
2862 the specified number of seconds. This is to be used if
2863 your oopses keep scrolling off the screen.
2868 See header of drivers/block/paride/pcd.c.
2869 See also Documentation/blockdev/paride.txt.
2871 pci=option[,option...] [PCI] various PCI subsystem options:
2872 earlydump [X86] dump PCI config space before the kernel
2874 off [X86] don't probe for the PCI bus
2875 bios [X86-32] force use of PCI BIOS, don't access
2876 the hardware directly. Use this if your machine
2877 has a non-standard PCI host bridge.
2878 nobios [X86-32] disallow use of PCI BIOS, only direct
2879 hardware access methods are allowed. Use this
2880 if you experience crashes upon bootup and you
2881 suspect they are caused by the BIOS.
2882 conf1 [X86] Force use of PCI Configuration Access
2883 Mechanism 1 (config address in IO port 0xCF8,
2884 data in IO port 0xCFC, both 32-bit).
2885 conf2 [X86] Force use of PCI Configuration Access
2886 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2887 the function, IO port 0xCFA, also 8-bit, sets
2888 bus number. The config space is then accessed
2889 through ports 0xC000-0xCFFF).
2890 See http://wiki.osdev.org/PCI for more info
2891 on the configuration access mechanisms.
2892 noaer [PCIE] If the PCIEAER kernel config parameter is
2893 enabled, this kernel boot option can be used to
2894 disable the use of PCIE advanced error reporting.
2895 nodomains [PCI] Disable support for multiple PCI
2896 root domains (aka PCI segments, in ACPI-speak).
2897 nommconf [X86] Disable use of MMCONFIG for PCI
2899 check_enable_amd_mmconf [X86] check for and enable
2900 properly configured MMIO access to PCI
2901 config space on AMD family 10h CPU
2902 nomsi [MSI] If the PCI_MSI kernel config parameter is
2903 enabled, this kernel boot option can be used to
2904 disable the use of MSI interrupts system-wide.
2905 noioapicquirk [APIC] Disable all boot interrupt quirks.
2906 Safety option to keep boot IRQs enabled. This
2907 should never be necessary.
2908 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2909 primary IO-APIC for bridges that cannot disable
2910 boot IRQs. This fixes a source of spurious IRQs
2911 when the system masks IRQs.
2912 noioapicreroute [APIC] Disable workaround that uses the
2913 boot IRQ equivalent of an IRQ that connects to
2914 a chipset where boot IRQs cannot be disabled.
2915 The opposite of ioapicreroute.
2916 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2917 routing table. These calls are known to be buggy
2918 on several machines and they hang the machine
2919 when used, but on other computers it's the only
2920 way to get the interrupt routing table. Try
2921 this option if the kernel is unable to allocate
2922 IRQs or discover secondary PCI buses on your
2924 rom [X86] Assign address space to expansion ROMs.
2925 Use with caution as certain devices share
2926 address decoders between ROMs and other
2928 norom [X86] Do not assign address space to
2929 expansion ROMs that do not already have
2930 BIOS assigned address ranges.
2931 nobar [X86] Do not assign address space to the
2932 BARs that weren't assigned by the BIOS.
2933 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2934 assigned automatically to PCI devices. You can
2935 make the kernel exclude IRQs of your ISA cards
2937 pirqaddr=0xAAAAA [X86] Specify the physical address
2938 of the PIRQ table (normally generated
2939 by the BIOS) if it is outside the
2940 F0000h-100000h range.
2941 lastbus=N [X86] Scan all buses thru bus #N. Can be
2942 useful if the kernel is unable to find your
2943 secondary buses and you want to tell it
2944 explicitly which ones they are.
2945 assign-busses [X86] Always assign all PCI bus
2946 numbers ourselves, overriding
2947 whatever the firmware may have done.
2948 usepirqmask [X86] Honor the possible IRQ mask stored
2949 in the BIOS $PIR table. This is needed on
2950 some systems with broken BIOSes, notably
2951 some HP Pavilion N5400 and Omnibook XE3
2952 notebooks. This will have no effect if ACPI
2953 IRQ routing is enabled.
2954 noacpi [X86] Do not use ACPI for IRQ routing
2955 or for PCI scanning.
2956 use_crs [X86] Use PCI host bridge window information
2957 from ACPI. On BIOSes from 2008 or later, this
2958 is enabled by default. If you need to use this,
2959 please report a bug.
2960 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2961 If you need to use this, please report a bug.
2962 routeirq Do IRQ routing for all PCI devices.
2963 This is normally done in pci_enable_device(),
2964 so this option is a temporary workaround
2965 for broken drivers that don't call it.
2966 skip_isa_align [X86] do not align io start addr, so can
2967 handle more pci cards
2968 noearly [X86] Don't do any early type 1 scanning.
2969 This might help on some broken boards which
2970 machine check when some devices' config space
2971 is read. But various workarounds are disabled
2972 and some IOMMU drivers will not work.
2973 bfsort Sort PCI devices into breadth-first order.
2974 This sorting is done to get a device
2975 order compatible with older (<= 2.4) kernels.
2976 nobfsort Don't sort PCI devices into breadth-first order.
2977 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2978 tuning and use the BIOS-configured MPS defaults.
2979 pcie_bus_safe Set every device's MPS to the largest value
2980 supported by all devices below the root complex.
2981 pcie_bus_perf Set device MPS to the largest allowable MPS
2982 based on its parent bus. Also set MRRS (Max
2983 Read Request Size) to the largest supported
2984 value (no larger than the MPS that the device
2985 or bus can support) for best performance.
2986 pcie_bus_peer2peer Set every device's MPS to 128B, which
2987 every device is guaranteed to support. This
2988 configuration allows peer-to-peer DMA between
2989 any pair of devices, possibly at the cost of
2990 reduced performance. This also guarantees
2991 that hot-added devices will work.
2992 cbiosize=nn[KMG] The fixed amount of bus space which is
2993 reserved for the CardBus bridge's IO window.
2994 The default value is 256 bytes.
2995 cbmemsize=nn[KMG] The fixed amount of bus space which is
2996 reserved for the CardBus bridge's memory
2997 window. The default value is 64 megabytes.
3000 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3001 Specifies alignment and device to reassign
3002 aligned memory resources.
3003 If <order of align> is not specified,
3004 PAGE_SIZE is used as alignment.
3005 PCI-PCI bridge can be specified, if resource
3006 windows need to be expanded.
3007 ecrc= Enable/disable PCIe ECRC (transaction layer
3008 end-to-end CRC checking).
3009 bios: Use BIOS/firmware settings. This is the
3013 hpiosize=nn[KMG] The fixed amount of bus space which is
3014 reserved for hotplug bridge's IO window.
3015 Default size is 256 bytes.
3016 hpmemsize=nn[KMG] The fixed amount of bus space which is
3017 reserved for hotplug bridge's memory window.
3018 Default size is 2 megabytes.
3019 realloc= Enable/disable reallocating PCI bridge resources
3020 if allocations done by BIOS are too small to
3021 accommodate resources required by all child
3023 off: Turn realloc off
3025 realloc same as realloc=on
3026 noari do not use PCIe ARI.
3027 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3028 only look for one device below a PCIe downstream
3031 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3034 force Enable ASPM even on devices that claim not to support it.
3035 WARNING: Forcing ASPM on may cause system lockups.
3037 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3038 nomsi Do not use MSI for PCI Express Native Hotplug (this
3039 makes all PCIe ports use INTx for hotplug services).
3041 pcie_ports= [PCIE] PCIe ports handling:
3042 auto Ask the BIOS whether or not to use native PCIe services
3043 associated with PCIe ports (PME, hot-plug, AER). Use
3044 them only if that is allowed by the BIOS.
3045 native Use native PCIe services associated with PCIe ports
3047 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3050 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3051 nomsi Do not use MSI for native PCIe PME signaling (this makes
3052 all PCIe root ports use INTx for all services).
3054 pcmv= [HW,PCMCIA] BadgePAD 4
3058 Keep all power-domains already enabled by bootloader on,
3059 even if no driver has claimed them. This is useful
3060 for debug and development, but should not be
3061 needed on a platform with proper driver support.
3064 See Documentation/blockdev/paride.txt.
3066 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3069 See arch/parisc/kernel/pdc_chassis.c
3071 percpu_alloc= Select which percpu first chunk allocator to use.
3072 Currently supported values are "embed" and "page".
3073 Archs may support subset or none of the selections.
3074 See comments in mm/percpu.c for details on each
3075 allocator. This parameter is primarily for debugging
3076 and performance comparison.
3079 See Documentation/blockdev/paride.txt.
3082 See Documentation/blockdev/paride.txt.
3084 pirq= [SMP,APIC] Manual mp-table setup
3085 See Documentation/x86/i386/IO-APIC.txt.
3087 plip= [PPT,NET] Parallel port network link
3088 Format: { parport<nr> | timid | 0 }
3089 See also Documentation/parport.txt.
3091 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3092 Override pmtimer IOPort with a hex value.
3096 Enable PNP debug messages (depends on the
3097 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3098 via /sys/module/pnp/parameters/debug. We always show
3099 current resource usage; turning this on also shows
3100 possible settings and some assignment information.
3106 { on | off | curr | res | no-curr | no-res }
3109 [ISAPNP] Exclude IRQs for the autoconfiguration
3112 [ISAPNP] Exclude DMAs for the autoconfiguration
3114 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3115 Ranges are in pairs (I/O port base and size).
3118 [ISAPNP] Exclude memory regions for the
3120 Ranges are in pairs (memory base and size).
3122 ports= [IP_VS_FTP] IPVS ftp helper module
3124 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3126 Format: <port>,<port>....
3128 ppc_strict_facility_enable
3129 [PPC] This option catches any kernel floating point,
3130 Altivec, VSX and SPE outside of regions specifically
3131 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3132 There is some performance impact when enabling this.
3134 print-fatal-signals=
3135 [KNL] debug: print fatal signals
3137 If enabled, warn about various signal handling
3138 related application anomalies: too many signals,
3139 too many POSIX.1 timers, fatal signals causing a
3142 If you hit the warning due to signal overflow,
3143 you might want to try "ulimit -i unlimited".
3147 printk.always_kmsg_dump=
3148 Trigger kmsg_dump for cases other than kernel oops or
3150 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3153 printk.time= Show timing data prefixed to each printk message line
3154 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3156 processor.max_cstate= [HW,ACPI]
3157 Limit processor to maximum C-state
3158 max_cstate=9 overrides any DMI blacklist limit.
3160 processor.nocst [HW,ACPI]
3161 Ignore the _CST method to determine C-states,
3162 instead using the legacy FADT method
3164 profile= [KNL] Enable kernel profiling via /proc/profile
3165 Format: [schedule,]<number>
3166 Param: "schedule" - profile schedule points.
3167 Param: <number> - step/bucket size as a power of 2 for
3168 statistical time based profiling.
3169 Param: "sleep" - profile D-state sleeping (millisecs).
3170 Requires CONFIG_SCHEDSTATS
3171 Param: "kvm" - profile VM exits.
3173 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3175 See Documentation/blockdev/ramdisk.txt.
3177 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3178 probe for; one of (bare|imps|exps|lifebook|any).
3179 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3181 psmouse.resetafter= [HW,MOUSE]
3182 Try to reset the device after so many bad packets
3185 [HW,MOUSE] Set desired mouse resolution, in dpi.
3186 psmouse.smartscroll=
3187 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3188 0 = disabled, 1 = enabled (default).
3190 pstore.backend= Specify the name of the pstore backend to use
3193 See Documentation/blockdev/paride.txt.
3196 [KNL] Number of legacy pty's. Overwrites compiled-in
3199 quiet [KNL] Disable most log messages
3204 See Documentation/md.txt.
3206 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3207 See Documentation/blockdev/ramdisk.txt.
3210 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3211 the specified list of CPUs to be no-callback CPUs.
3212 Invocation of these CPUs' RCU callbacks will
3213 be offloaded to "rcuox/N" kthreads created for
3214 that purpose, where "x" is "b" for RCU-bh, "p"
3215 for RCU-preempt, and "s" for RCU-sched, and "N"
3216 is the CPU number. This reduces OS jitter on the
3217 offloaded CPUs, which can be useful for HPC and
3218 real-time workloads. It can also improve energy
3219 efficiency for asymmetric multiprocessors.
3222 Rather than requiring that offloaded CPUs
3223 (specified by rcu_nocbs= above) explicitly
3224 awaken the corresponding "rcuoN" kthreads,
3225 make these kthreads poll for callbacks.
3226 This improves the real-time response for the
3227 offloaded CPUs by relieving them of the need to
3228 wake up the corresponding kthread, but degrades
3229 energy efficiency by requiring that the kthreads
3230 periodically wake up to do the polling.
3232 rcutree.blimit= [KNL]
3233 Set maximum number of finished RCU callbacks to
3234 process in one batch.
3236 rcutree.dump_tree= [KNL]
3237 Dump the structure of the rcu_node combining tree
3238 out at early boot. This is used for diagnostic
3239 purposes, to verify correct tree setup.
3241 rcutree.gp_cleanup_delay= [KNL]
3242 Set the number of jiffies to delay each step of
3243 RCU grace-period cleanup. This only has effect
3244 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3246 rcutree.gp_init_delay= [KNL]
3247 Set the number of jiffies to delay each step of
3248 RCU grace-period initialization. This only has
3249 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3252 rcutree.gp_preinit_delay= [KNL]
3253 Set the number of jiffies to delay each step of
3254 RCU grace-period pre-initialization, that is,
3255 the propagation of recent CPU-hotplug changes up
3256 the rcu_node combining tree. This only has effect
3257 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3259 rcutree.rcu_fanout_exact= [KNL]
3260 Disable autobalancing of the rcu_node combining
3261 tree. This is used by rcutorture, and might
3262 possibly be useful for architectures having high
3263 cache-to-cache transfer latencies.
3265 rcutree.rcu_fanout_leaf= [KNL]
3266 Change the number of CPUs assigned to each
3267 leaf rcu_node structure. Useful for very
3268 large systems, which will choose the value 64,
3269 and for NUMA systems with large remote-access
3270 latencies, which will choose a value aligned
3271 with the appropriate hardware boundaries.
3273 rcutree.jiffies_till_sched_qs= [KNL]
3274 Set required age in jiffies for a
3275 given grace period before RCU starts
3276 soliciting quiescent-state help from
3277 rcu_note_context_switch().
3279 rcutree.jiffies_till_first_fqs= [KNL]
3280 Set delay from grace-period initialization to
3281 first attempt to force quiescent states.
3282 Units are jiffies, minimum value is zero,
3283 and maximum value is HZ.
3285 rcutree.jiffies_till_next_fqs= [KNL]
3286 Set delay between subsequent attempts to force
3287 quiescent states. Units are jiffies, minimum
3288 value is one, and maximum value is HZ.
3290 rcutree.kthread_prio= [KNL,BOOT]
3291 Set the SCHED_FIFO priority of the RCU per-CPU
3292 kthreads (rcuc/N). This value is also used for
3293 the priority of the RCU boost threads (rcub/N)
3294 and for the RCU grace-period kthreads (rcu_bh,
3295 rcu_preempt, and rcu_sched). If RCU_BOOST is
3296 set, valid values are 1-99 and the default is 1
3297 (the least-favored priority). Otherwise, when
3298 RCU_BOOST is not set, valid values are 0-99 and
3299 the default is zero (non-realtime operation).
3301 rcutree.rcu_nocb_leader_stride= [KNL]
3302 Set the number of NOCB kthread groups, which
3303 defaults to the square root of the number of
3304 CPUs. Larger numbers reduces the wakeup overhead
3305 on the per-CPU grace-period kthreads, but increases
3306 that same overhead on each group's leader.
3308 rcutree.qhimark= [KNL]
3309 Set threshold of queued RCU callbacks beyond which
3310 batch limiting is disabled.
3312 rcutree.qlowmark= [KNL]
3313 Set threshold of queued RCU callbacks below which
3314 batch limiting is re-enabled.
3316 rcutree.rcu_idle_gp_delay= [KNL]
3317 Set wakeup interval for idle CPUs that have
3318 RCU callbacks (RCU_FAST_NO_HZ=y).
3320 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3321 Set wakeup interval for idle CPUs that have
3322 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3323 Lazy RCU callbacks are those which RCU can
3324 prove do nothing more than free memory.
3326 rcuperf.gp_exp= [KNL]
3327 Measure performance of expedited synchronous
3328 grace-period primitives.
3330 rcuperf.holdoff= [KNL]
3331 Set test-start holdoff period. The purpose of
3332 this parameter is to delay the start of the
3333 test until boot completes in order to avoid
3336 rcuperf.nreaders= [KNL]
3337 Set number of RCU readers. The value -1 selects
3338 N, where N is the number of CPUs. A value
3339 "n" less than -1 selects N-n+1, where N is again
3340 the number of CPUs. For example, -2 selects N
3341 (the number of CPUs), -3 selects N+1, and so on.
3342 A value of "n" less than or equal to -N selects
3345 rcuperf.nwriters= [KNL]
3346 Set number of RCU writers. The values operate
3347 the same as for rcuperf.nreaders.
3348 N, where N is the number of CPUs
3350 rcuperf.perf_runnable= [BOOT]
3351 Start rcuperf running at boot time.
3353 rcuperf.shutdown= [KNL]
3354 Shut the system down after performance tests
3355 complete. This is useful for hands-off automated
3358 rcuperf.perf_type= [KNL]
3359 Specify the RCU implementation to test.
3361 rcuperf.verbose= [KNL]
3362 Enable additional printk() statements.
3364 rcutorture.cbflood_inter_holdoff= [KNL]
3365 Set holdoff time (jiffies) between successive
3366 callback-flood tests.
3368 rcutorture.cbflood_intra_holdoff= [KNL]
3369 Set holdoff time (jiffies) between successive
3370 bursts of callbacks within a given callback-flood
3373 rcutorture.cbflood_n_burst= [KNL]
3374 Set the number of bursts making up a given
3375 callback-flood test. Set this to zero to
3376 disable callback-flood testing.
3378 rcutorture.cbflood_n_per_burst= [KNL]
3379 Set the number of callbacks to be registered
3380 in a given burst of a callback-flood test.
3382 rcutorture.fqs_duration= [KNL]
3383 Set duration of force_quiescent_state bursts
3386 rcutorture.fqs_holdoff= [KNL]
3387 Set holdoff time within force_quiescent_state bursts
3390 rcutorture.fqs_stutter= [KNL]
3391 Set wait time between force_quiescent_state bursts
3394 rcutorture.gp_cond= [KNL]
3395 Use conditional/asynchronous update-side
3396 primitives, if available.
3398 rcutorture.gp_exp= [KNL]
3399 Use expedited update-side primitives, if available.
3401 rcutorture.gp_normal= [KNL]
3402 Use normal (non-expedited) asynchronous
3403 update-side primitives, if available.
3405 rcutorture.gp_sync= [KNL]
3406 Use normal (non-expedited) synchronous
3407 update-side primitives, if available. If all
3408 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3409 rcutorture.gp_normal=, and rcutorture.gp_sync=
3410 are zero, rcutorture acts as if is interpreted
3411 they are all non-zero.
3413 rcutorture.n_barrier_cbs= [KNL]
3414 Set callbacks/threads for rcu_barrier() testing.
3416 rcutorture.nfakewriters= [KNL]
3417 Set number of concurrent RCU writers. These just
3418 stress RCU, they don't participate in the actual
3419 test, hence the "fake".
3421 rcutorture.nreaders= [KNL]
3422 Set number of RCU readers. The value -1 selects
3423 N-1, where N is the number of CPUs. A value
3424 "n" less than -1 selects N-n-2, where N is again
3425 the number of CPUs. For example, -2 selects N
3426 (the number of CPUs), -3 selects N+1, and so on.
3428 rcutorture.object_debug= [KNL]
3429 Enable debug-object double-call_rcu() testing.
3431 rcutorture.onoff_holdoff= [KNL]
3432 Set time (s) after boot for CPU-hotplug testing.
3434 rcutorture.onoff_interval= [KNL]
3435 Set time (s) between CPU-hotplug operations, or
3436 zero to disable CPU-hotplug testing.
3438 rcutorture.shuffle_interval= [KNL]
3439 Set task-shuffle interval (s). Shuffling tasks
3440 allows some CPUs to go into dyntick-idle mode
3441 during the rcutorture test.
3443 rcutorture.shutdown_secs= [KNL]
3444 Set time (s) after boot system shutdown. This
3445 is useful for hands-off automated testing.
3447 rcutorture.stall_cpu= [KNL]
3448 Duration of CPU stall (s) to test RCU CPU stall
3449 warnings, zero to disable.
3451 rcutorture.stall_cpu_holdoff= [KNL]
3452 Time to wait (s) after boot before inducing stall.
3454 rcutorture.stat_interval= [KNL]
3455 Time (s) between statistics printk()s.
3457 rcutorture.stutter= [KNL]
3458 Time (s) to stutter testing, for example, specifying
3459 five seconds causes the test to run for five seconds,
3460 wait for five seconds, and so on. This tests RCU's
3461 ability to transition abruptly to and from idle.
3463 rcutorture.test_boost= [KNL]
3464 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3465 "Maybe" means test if the RCU implementation
3466 under test support RCU priority boosting.
3468 rcutorture.test_boost_duration= [KNL]
3469 Duration (s) of each individual boost test.
3471 rcutorture.test_boost_interval= [KNL]
3472 Interval (s) between each boost test.
3474 rcutorture.test_no_idle_hz= [KNL]
3475 Test RCU's dyntick-idle handling. See also the
3476 rcutorture.shuffle_interval parameter.
3478 rcutorture.torture_runnable= [BOOT]
3479 Start rcutorture running at boot time.
3481 rcutorture.torture_type= [KNL]
3482 Specify the RCU implementation to test.
3484 rcutorture.verbose= [KNL]
3485 Enable additional printk() statements.
3487 rcupdate.rcu_cpu_stall_suppress= [KNL]
3488 Suppress RCU CPU stall warning messages.
3490 rcupdate.rcu_cpu_stall_timeout= [KNL]
3491 Set timeout for RCU CPU stall warning messages.
3493 rcupdate.rcu_expedited= [KNL]
3494 Use expedited grace-period primitives, for
3495 example, synchronize_rcu_expedited() instead
3496 of synchronize_rcu(). This reduces latency,
3497 but can increase CPU utilization, degrade
3498 real-time latency, and degrade energy efficiency.
3499 No effect on CONFIG_TINY_RCU kernels.
3501 rcupdate.rcu_normal= [KNL]
3502 Use only normal grace-period primitives,
3503 for example, synchronize_rcu() instead of
3504 synchronize_rcu_expedited(). This improves
3505 real-time latency, CPU utilization, and
3506 energy efficiency, but can expose users to
3507 increased grace-period latency. This parameter
3508 overrides rcupdate.rcu_expedited. No effect on
3509 CONFIG_TINY_RCU kernels.
3511 rcupdate.rcu_normal_after_boot= [KNL]
3512 Once boot has completed (that is, after
3513 rcu_end_inkernel_boot() has been invoked), use
3514 only normal grace-period primitives. No effect
3515 on CONFIG_TINY_RCU kernels.
3517 rcupdate.rcu_task_stall_timeout= [KNL]
3518 Set timeout in jiffies for RCU task stall warning
3519 messages. Disable with a value less than or equal
3522 rcupdate.rcu_self_test= [KNL]
3523 Run the RCU early boot self tests
3525 rcupdate.rcu_self_test_bh= [KNL]
3526 Run the RCU bh early boot self tests
3528 rcupdate.rcu_self_test_sched= [KNL]
3529 Run the RCU sched early boot self tests
3533 Run specified binary instead of /init from the ramdisk,
3534 used for early userspace startup. See initrd.
3537 Format (x86 or x86_64):
3538 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3540 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3542 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3543 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3544 reboot_force is either force or not specified,
3545 reboot_cpu is s[mp]#### with #### being the processor
3546 to be used for rebooting.
3549 [KNL, SMP] Set scheduler's default relax_domain_level.
3550 See Documentation/cgroups/cpusets.txt.
3552 relative_sleep_states=
3553 [SUSPEND] Use sleep state labeling where the deepest
3554 state available other than hibernation is always "mem".
3555 Format: { "0" | "1" }
3556 0 -- Traditional sleep state labels.
3557 1 -- Relative sleep state labels.
3559 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3561 reservetop= [X86-32]
3563 Reserves a hole at the top of the kernel virtual
3568 Set the amount of memory to reserve for BIOS at
3569 the bottom of the address space.
3571 reset_devices [KNL] Force drivers to reset the underlying device
3572 during initialization.
3575 Specify the partition device for software suspend
3577 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3579 resume_offset= [SWSUSP]
3580 Specify the offset from the beginning of the partition
3581 given by "resume=" at which the swap header is located,
3582 in <PAGE_SIZE> units (needed only for swap files).
3583 See Documentation/power/swsusp-and-swap-files.txt
3585 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3586 read the resume files
3588 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3589 Useful for devices that are detected asynchronously
3590 (e.g. USB and MMC devices).
3592 hibernate= [HIBERNATION]
3593 noresume Don't check if there's a hibernation image
3594 present during boot.
3595 nocompress Don't compress/decompress hibernation images.
3596 no Disable hibernation and resume.
3598 retain_initrd [RAM] Keep initrd memory after extraction
3600 rfkill.default_state=
3601 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3602 etc. communication is blocked by default.
3605 rfkill.master_switch_mode=
3606 0 The "airplane mode" button does nothing.
3607 1 The "airplane mode" button toggles between everything
3608 blocked and the previous configuration.
3609 2 The "airplane mode" button toggles between everything
3610 blocked and everything unblocked.
3612 rhash_entries= [KNL,NET]
3613 Set number of hash buckets for route cache
3615 ro [KNL] Mount root device read-only on boot
3618 on Mark read-only kernel memory as read-only (default).
3619 off Leave read-only kernel memory writable for debugging.
3622 Enable the uart passthrough on the designated usb port
3623 on Rockchip SoCs. When active, the signals of the
3624 debug-uart get routed to the D+ and D- pins of the usb
3625 port and the regular usb controller gets disabled.
3627 root= [KNL] Root filesystem
3628 See name_to_dev_t comment in init/do_mounts.c.
3630 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3631 mount the root filesystem
3633 rootflags= [KNL] Set root filesystem mount option string
3635 rootfstype= [KNL] Set root filesystem type
3637 rootwait [KNL] Wait (indefinitely) for root device to show up.
3638 Useful for devices that are detected asynchronously
3639 (e.g. USB and MMC devices).
3641 rproc_mem=nn[KMG][@address]
3642 [KNL,ARM,CMA] Remoteproc physical memory block.
3643 Memory area to be used by remote processor image,
3646 rw [KNL] Mount root device read-write on boot
3648 S [KNL] Run init in single mode
3650 s390_iommu= [HW,S390]
3651 Set s390 IOTLB flushing mode
3653 With strict flushing every unmap operation will result in
3654 an IOTLB flush. Default is lazy flushing before reuse,
3658 See drivers/net/irda/sa1100_ir.c.
3660 sbni= [NET] Granch SBNI12 leased line adapter
3662 sched_debug [KNL] Enables verbose scheduler debug messages.
3664 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3665 Allowed values are enable and disable. This feature
3666 incurs a small amount of overhead in the scheduler
3667 but is useful for debugging and performance tuning.
3669 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3670 xtime_lock contention on larger systems, and/or RCU lock
3671 contention on all systems with CONFIG_MAXSMP set.
3672 Format: { "0" | "1" }
3673 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3675 Note: increases power consumption, thus should only be
3676 enabled if running jitter sensitive (HPC/RT) workloads.
3678 security= [SECURITY] Choose a security module to enable at boot.
3679 If this boot parameter is not specified, only the first
3680 security module asking for security registration will be
3681 loaded. An invalid security module name will be treated
3682 as if no module has been chosen.
3684 selinux= [SELINUX] Disable or enable SELinux at boot time.
3685 Format: { "0" | "1" }
3686 See security/selinux/Kconfig help text.
3689 Default value is set via kernel config option.
3690 If enabled at boot time, /selinux/disable can be used
3691 later to disable prior to initial policy load.
3693 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3694 Format: { "0" | "1" }
3695 See security/apparmor/Kconfig help text
3698 Default value is set via kernel config option.
3700 serialnumber [BUGS=X86-32]
3703 Maximal number of shapers.
3705 show_msr= [x86] show boot-time MSR settings
3706 Format: { <integer> }
3707 Show boot-time (BIOS-initialized) MSR settings.
3708 The parameter means the number of CPUs to show,
3709 for example 1 means boot CPU only.
3717 Disable merging of slabs with similar size. May be
3718 necessary if there is some reason to distinguish
3719 allocs to different slabs. Debug options disable
3720 merging on their own.
3721 For more information see Documentation/vm/slub.txt.
3723 slab_max_order= [MM, SLAB]
3724 Determines the maximum allowed order for slabs.
3725 A high setting may cause OOMs due to memory
3726 fragmentation. Defaults to 1 for systems with
3727 more than 32MB of RAM, 0 otherwise.
3729 slub_debug[=options[,slabs]] [MM, SLUB]
3730 Enabling slub_debug allows one to determine the
3731 culprit if slab objects become corrupted. Enabling
3732 slub_debug can create guard zones around objects and
3733 may poison objects when not in use. Also tracks the
3734 last alloc / free. For more information see
3735 Documentation/vm/slub.txt.
3737 slub_max_order= [MM, SLUB]
3738 Determines the maximum allowed order for slabs.
3739 A high setting may cause OOMs due to memory
3740 fragmentation. For more information see
3741 Documentation/vm/slub.txt.
3743 slub_min_objects= [MM, SLUB]
3744 The minimum number of objects per slab. SLUB will
3745 increase the slab order up to slub_max_order to
3746 generate a sufficiently large slab able to contain
3747 the number of objects indicated. The higher the number
3748 of objects the smaller the overhead of tracking slabs
3749 and the less frequently locks need to be acquired.
3750 For more information see Documentation/vm/slub.txt.
3752 slub_min_order= [MM, SLUB]
3753 Determines the minimum page order for slabs. Must be
3754 lower than slub_max_order.
3755 For more information see Documentation/vm/slub.txt.
3757 slub_nomerge [MM, SLUB]
3758 Same with slab_nomerge. This is supported for legacy.
3759 See slab_nomerge for more information.
3762 Format: <io1>[,<io2>[,...,<io8>]]
3764 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3765 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3766 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3767 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3768 smsc-ircc2.ircc_irq= [HW] IRQ line
3769 smsc-ircc2.ircc_dma= [HW] DMA channel
3770 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3771 0: Toshiba Satellite 1800 (GP data pin select)
3772 1: Fast pin select (default)
3775 smt [KNL,S390] Set the maximum number of threads (logical
3776 CPUs) to use per physical CPU on systems capable of
3777 symmetric multithreading (SMT). Will be capped to the
3778 actual hardware limit.
3780 Default: -1 (no limit)
3783 [KNL] Should the soft-lockup detector generate panics.
3786 softlockup_all_cpu_backtrace=
3787 [KNL] Should the soft-lockup detector generate
3788 backtraces on all cpus.
3791 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3792 See Documentation/laptops/sonypi.txt
3794 spia_io_base= [HW,MTD]
3800 Enabled the stack tracer on boot up.
3802 stacktrace_filter=[function-list]
3803 [FTRACE] Limit the functions that the stack tracer
3804 will trace at boot up. function-list is a comma separated
3805 list of functions. This list can be changed at run
3806 time by the stack_trace_filter file in the debugfs
3807 tracing directory. Note, this enables stack tracing
3808 and the stacktrace above is not needed.
3812 Set the STI (builtin display/keyboard on the HP-PARISC
3813 machines) console (graphic card) which should be used
3814 as the initial boot-console.
3815 See also comment in drivers/video/console/sticore.c.
3818 See comment in drivers/video/console/sticore.c.
3821 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3823 sunrpc.min_resvport=
3824 sunrpc.max_resvport=
3826 SunRPC servers often require that client requests
3827 originate from a privileged port (i.e. a port in the
3828 range 0 < portnr < 1024).
3829 An administrator who wishes to reserve some of these
3830 ports for other uses may adjust the range that the
3831 kernel's sunrpc client considers to be privileged
3832 using these two parameters to set the minimum and
3833 maximum port values.
3837 Control how the NFS server code allocates CPUs to
3838 service thread pools. Depending on how many NICs
3839 you have and where their interrupts are bound, this
3840 option will affect which CPUs will do NFS serving.
3841 Note: this parameter cannot be changed while the
3842 NFS server is running.
3844 auto the server chooses an appropriate mode
3845 automatically using heuristics
3846 global a single global pool contains all CPUs
3847 percpu one pool for each CPU
3848 pernode one pool for each NUMA node (equivalent
3849 to global on non-NUMA machines)
3851 sunrpc.tcp_slot_table_entries=
3852 sunrpc.udp_slot_table_entries=
3854 Sets the upper limit on the number of simultaneous
3855 RPC calls that can be sent from the client to a
3856 server. Increasing these values may allow you to
3857 improve throughput, but will also increase the
3858 amount of memory reserved for use by the client.
3860 suspend.pm_test_delay=
3862 Sets the number of seconds to remain in a suspend test
3863 mode before resuming the system (see
3864 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3865 is set. Default value is 5.
3868 [KNL] Enable accounting of swap in memory resource
3869 controller if no parameter or 1 is given or disable
3870 it if 0 is given (See Documentation/cgroups/memory.txt)
3872 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3873 Format: { <int> | force }
3874 <int> -- Number of I/O TLB slabs
3875 force -- force using of bounce buffers even if they
3876 wouldn't be automatically used by the kernel
3880 sysfs.deprecated=0|1 [KNL]
3881 Enable/disable old style sysfs layout for old udev
3882 on older distributions. When this option is enabled
3883 very new udev will not work anymore. When this option
3884 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3885 in older udev will not work anymore.
3886 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3887 the kernel configuration.
3889 sysrq_always_enabled
3891 Ignore sysrq setting - this boot parameter will
3892 neutralize any effect of /proc/sys/kernel/sysrq.
3893 Useful for debugging.
3895 tcpmhash_entries= [KNL,NET]
3896 Set the number of tcp_metrics_hash slots.
3897 Default value is 8192 or 16384 depending on total
3898 ram pages. This is used to specify the TCP metrics
3899 cache size. See Documentation/networking/ip-sysctl.txt
3900 "tcp_no_metrics_save" section for more details.
3904 test_suspend= [SUSPEND][,N]
3905 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3906 standby suspend) or "freeze" (for suspend type freeze)
3907 as the system sleep state during system startup with
3908 the optional capability to repeat N number of times.
3909 The system is woken from this state using a
3910 wakeup-capable RTC alarm.
3912 thash_entries= [KNL,NET]
3913 Set number of hash buckets for TCP connection
3915 thermal.act= [HW,ACPI]
3916 -1: disable all active trip points in all thermal zones
3917 <degrees C>: override all lowest active trip points
3919 thermal.crt= [HW,ACPI]
3920 -1: disable all critical trip points in all thermal zones
3921 <degrees C>: override all critical trip points
3923 thermal.nocrt= [HW,ACPI]
3924 Set to disable actions on ACPI thermal zone
3925 critical and hot trip points.
3927 thermal.off= [HW,ACPI]
3928 1: disable ACPI thermal control
3930 thermal.psv= [HW,ACPI]
3931 -1: disable all passive trip points
3932 <degrees C>: override all passive trip points to this
3935 thermal.tzp= [HW,ACPI]
3936 Specify global default ACPI thermal zone polling rate
3937 <deci-seconds>: poll all this frequency
3938 0: no polling (default)
3941 Force threading of all interrupt handlers except those
3942 marked explicitly IRQF_NO_THREAD.
3945 Enable the Transcendent memory driver if built-in.
3947 tmem.cleancache=0|1 [KNL, XEN]
3948 Default is on (1). Disable the usage of the cleancache
3949 API to send anonymous pages to the hypervisor.
3951 tmem.frontswap=0|1 [KNL, XEN]
3952 Default is on (1). Disable the usage of the frontswap
3953 API to send swap pages to the hypervisor. If disabled
3954 the selfballooning and selfshrinking are force disabled.
3956 tmem.selfballooning=0|1 [KNL, XEN]
3957 Default is on (1). Disable the driving of swap pages
3960 tmem.selfshrinking=0|1 [KNL, XEN]
3961 Default is on (1). Partial swapoff that immediately
3962 transfers pages from Xen hypervisor back to the
3963 kernel based on different criteria.
3967 Specify if the kernel should make use of the cpu
3968 topology information if the hardware supports this.
3969 The scheduler will make use of this information and
3970 e.g. base its process migration decisions on it.
3973 topology_updates= [KNL, PPC, NUMA]
3975 Specify if the kernel should ignore (off)
3976 topology updates sent by the hypervisor to this
3981 tpm_suspend_pcr=[HW,TPM]
3982 Format: integer pcr id
3983 Specify that at suspend time, the tpm driver
3984 should extend the specified pcr with zeros,
3985 as a workaround for some chips which fail to
3986 flush the last written pcr on TPM_SaveState.
3987 This will guarantee that all the other pcrs
3990 trace_buf_size=nn[KMG]
3991 [FTRACE] will set tracing buffer size on each cpu.
3993 trace_event=[event-list]
3994 [FTRACE] Set and start specified trace events in order
3995 to facilitate early boot debugging.
3996 See also Documentation/trace/events.txt
3998 trace_options=[option-list]
3999 [FTRACE] Enable or disable tracer options at boot.
4000 The option-list is a comma delimited list of options
4001 that can be enabled or disabled just as if you were
4002 to echo the option name into
4004 /sys/kernel/debug/tracing/trace_options
4006 For example, to enable stacktrace option (to dump the
4007 stack trace of each event), add to the command line:
4009 trace_options=stacktrace
4011 See also Documentation/trace/ftrace.txt "trace options"
4015 Have the tracepoints sent to printk as well as the
4016 tracing ring buffer. This is useful for early boot up
4017 where the system hangs or reboots and does not give the
4018 option for reading the tracing buffer or performing a
4019 ftrace_dump_on_oops.
4021 To turn off having tracepoints sent to printk,
4022 echo 0 > /proc/sys/kernel/tracepoint_printk
4023 Note, echoing 1 into this file without the
4024 tracepoint_printk kernel cmdline option has no effect.
4028 Having tracepoints sent to printk() and activating high
4029 frequency tracepoints such as irq or sched, can cause
4030 the system to live lock.
4033 [FTRACE] enable this option to disable tracing when a
4034 warning is hit. This turns off "tracing_on". Tracing can
4035 be enabled again by echoing '1' into the "tracing_on"
4036 file located in /sys/kernel/debug/tracing/
4038 This option is useful, as it disables the trace before
4039 the WARNING dump is called, which prevents the trace to
4040 be filled with content caused by the warning output.
4042 This option can also be set at run time via the sysctl
4043 option: kernel/traceoff_on_warning
4045 transparent_hugepage=
4047 Format: [always|madvise|never]
4048 Can be used to control the default behavior of the system
4049 with respect to transparent hugepages.
4050 See Documentation/vm/transhuge.txt for more details.
4052 tsc= Disable clocksource stability checks for TSC.
4054 [x86] reliable: mark tsc clocksource as reliable, this
4055 disables clocksource verification at runtime, as well
4056 as the stability checks done at bootup. Used to enable
4057 high-resolution timer mode on older hardware, and in
4058 virtualized environment.
4059 [x86] noirqtime: Do not use TSC to do irq accounting.
4060 Used to run time disable IRQ_TIME_ACCOUNTING on any
4061 platforms where RDTSC is slow and this accounting
4064 turbografx.map[2|3]= [HW,JOY]
4065 TurboGraFX parallel port interface
4067 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4068 See also Documentation/input/joystick-parport.txt
4070 udbg-immortal [PPC] When debugging early kernel crashes that
4071 happen after console_init() and before a proper
4072 console driver takes over, this boot options might
4073 help "seeing" what's going on.
4075 uhash_entries= [KNL,NET]
4076 Set number of hash buckets for UDP/UDP-Lite connections
4079 [USB] Ignore overcurrent events (default N).
4080 Some badly-designed motherboards generate lots of
4081 bogus events, for ports that aren't wired to
4082 anything. Set this parameter to avoid log spamming.
4083 Note that genuine overcurrent events won't be
4087 [X86] Cause panic on unknown NMI.
4089 usbcore.authorized_default=
4090 [USB] Default USB device authorization:
4091 (default -1 = authorized except for wireless USB,
4092 0 = not authorized, 1 = authorized)
4094 usbcore.autosuspend=
4095 [USB] The autosuspend time delay (in seconds) used
4096 for newly-detected USB devices (default 2). This
4097 is the time required before an idle device will be
4098 autosuspended. Devices for which the delay is set
4099 to a negative value won't be autosuspended at all.
4101 usbcore.usbfs_snoop=
4102 [USB] Set to log all usbfs traffic (default 0 = off).
4104 usbcore.usbfs_snoop_max=
4105 [USB] Maximum number of bytes to snoop in each URB
4108 usbcore.blinkenlights=
4109 [USB] Set to cycle leds on hubs (default 0 = off).
4111 usbcore.old_scheme_first=
4112 [USB] Start with the old device initialization
4113 scheme (default 0 = off).
4115 usbcore.usbfs_memory_mb=
4116 [USB] Memory limit (in MB) for buffers allocated by
4117 usbfs (default = 16, 0 = max = 2047).
4119 usbcore.use_both_schemes=
4120 [USB] Try the other device initialization scheme
4121 if the first one fails (default 1 = enabled).
4123 usbcore.initial_descriptor_timeout=
4124 [USB] Specifies timeout for the initial 64-byte
4125 USB_REQ_GET_DESCRIPTOR request in milliseconds
4126 (default 5000 = 5.0 seconds).
4128 usbcore.nousb [USB] Disable the USB subsystem
4131 [USBHID] The interval which mice are to be polled at.
4133 usb-storage.delay_use=
4134 [UMS] The delay in seconds before a new device is
4135 scanned for Logical Units (default 1).
4138 [UMS] A list of quirks entries to supplement or
4139 override the built-in unusual_devs list. List
4140 entries are separated by commas. Each entry has
4141 the form VID:PID:Flags where VID and PID are Vendor
4142 and Product ID values (4-digit hex numbers) and
4143 Flags is a set of characters, each corresponding
4144 to a common usb-storage quirk flag as follows:
4145 a = SANE_SENSE (collect more than 18 bytes
4147 b = BAD_SENSE (don't collect more than 18
4148 bytes of sense data);
4149 c = FIX_CAPACITY (decrease the reported
4150 device capacity by one sector);
4151 d = NO_READ_DISC_INFO (don't use
4152 READ_DISC_INFO command);
4153 e = NO_READ_CAPACITY_16 (don't use
4154 READ_CAPACITY_16 command);
4155 f = NO_REPORT_OPCODES (don't use report opcodes
4157 g = MAX_SECTORS_240 (don't transfer more than
4158 240 sectors at a time, uas only);
4159 h = CAPACITY_HEURISTICS (decrease the
4160 reported device capacity by one
4161 sector if the number is odd);
4162 i = IGNORE_DEVICE (don't bind to this
4164 j = NO_REPORT_LUNS (don't use report luns
4166 l = NOT_LOCKABLE (don't try to lock and
4167 unlock ejectable media);
4168 m = MAX_SECTORS_64 (don't transfer more
4169 than 64 sectors = 32 KB at a time);
4170 n = INITIAL_READ10 (force a retry of the
4171 initial READ(10) command);
4172 o = CAPACITY_OK (accept the capacity
4173 reported by the device);
4174 p = WRITE_CACHE (the device cache is ON
4176 r = IGNORE_RESIDUE (the device reports
4177 bogus residue values);
4178 s = SINGLE_LUN (the device has only one
4180 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4181 commands, uas only);
4182 u = IGNORE_UAS (don't bind to the uas driver);
4183 w = NO_WP_DETECT (don't test whether the
4184 medium is write-protected).
4185 Example: quirks=0419:aaf5:rl,0421:0433:rc
4187 user_debug= [KNL,ARM]
4189 See arch/arm/Kconfig.debug help text.
4190 1 - undefined instruction events
4192 4 - invalid data aborts
4195 Example: user_debug=31
4198 [X86] Flags controlling user PTE allocations.
4200 nohigh = do not allocate PTE pages in
4201 HIGHMEM regardless of setting
4205 On X86_32, this is an alias for vdso32=. Otherwise:
4207 vdso=1: enable VDSO (the default)
4208 vdso=0: disable VDSO mapping
4210 vdso32= [X86] Control the 32-bit vDSO
4211 vdso32=1: enable 32-bit VDSO
4212 vdso32=0 or vdso32=2: disable 32-bit VDSO
4214 See the help text for CONFIG_COMPAT_VDSO for more
4215 details. If CONFIG_COMPAT_VDSO is set, the default is
4216 vdso32=0; otherwise, the default is vdso32=1.
4218 For compatibility with older kernels, vdso32=2 is an
4221 Try vdso32=0 if you encounter an error that says:
4222 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4225 vector=percpu: enable percpu vector domain
4227 video= [FB] Frame buffer configuration
4228 See Documentation/fb/modedb.txt.
4230 video.brightness_switch_enabled= [0,1]
4231 If set to 1, on receiving an ACPI notify event
4232 generated by hotkey, video driver will adjust brightness
4233 level and then send out the event to user space through
4234 the allocated input device; If set to 0, video driver
4235 will only send out the event without touching backlight
4240 [VMMIO] Memory mapped virtio (platform) device.
4242 <size>@<baseaddr>:<irq>[:<id>]
4244 <size> := size (can use standard suffixes
4246 <baseaddr> := physical base address
4247 <irq> := interrupt number (as passed to
4249 <id> := (optional) platform device id
4251 virtio_mmio.device=1K@0x100b0000:48:7
4253 Can be used multiple times for multiple devices.
4255 vga= [BOOT,X86-32] Select a particular video mode
4256 See Documentation/x86/boot.txt and
4257 Documentation/svga.txt.
4258 Use vga=ask for menu.
4259 This is actually a boot loader parameter; the value is
4260 passed to the kernel using a special protocol.
4262 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4263 size of <nn>. This can be used to increase the
4264 minimum size (128MB on x86). It can also be used to
4265 decrease the size and leave more room for directly
4268 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4271 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4274 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4278 Controls the behavior of vsyscalls (i.e. calls to
4279 fixed addresses of 0xffffffffff600x00 from legacy
4280 code). Most statically-linked binaries and older
4281 versions of glibc use these calls. Because these
4282 functions are at fixed addresses, they make nice
4283 targets for exploits that can control RIP.
4285 emulate [default] Vsyscalls turn into traps and are
4286 emulated reasonably safely.
4288 native Vsyscalls are native syscall instructions.
4289 This is a little bit faster than trapping
4290 and makes a few dynamic recompilers work
4291 better than they would in emulation mode.
4292 It also makes exploits much easier to write.
4294 none Vsyscalls don't work at all. This makes
4295 them quite hard to use for exploits but
4296 might break your system.
4298 vt.color= [VT] Default text color.
4299 Format: 0xYX, X = foreground, Y = background.
4300 Default: 0x07 = light gray on black.
4302 vt.cur_default= [VT] Default cursor shape.
4303 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4304 the parameters of the <Esc>[?A;B;Cc escape sequence;
4305 see VGA-softcursor.txt. Default: 2 = underline.
4307 vt.default_blu= [VT]
4308 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4309 Change the default blue palette of the console.
4310 This is a 16-member array composed of values
4313 vt.default_grn= [VT]
4314 Format: <green0>,<green1>,<green2>,...,<green15>
4315 Change the default green palette of the console.
4316 This is a 16-member array composed of values
4319 vt.default_red= [VT]
4320 Format: <red0>,<red1>,<red2>,...,<red15>
4321 Change the default red palette of the console.
4322 This is a 16-member array composed of values
4328 Set system-wide default UTF-8 mode for all tty's.
4329 Default is 1, i.e. UTF-8 mode is enabled for all
4330 newly opened terminals.
4332 vt.global_cursor_default=
4335 Set system-wide default for whether a cursor
4336 is shown on new VTs. Default is -1,
4337 i.e. cursors will be created by default unless
4338 overridden by individual drivers. 0 will hide
4339 cursors, 1 will display them.
4341 vt.italic= [VT] Default color for italic text; 0-15.
4344 vt.underline= [VT] Default color for underlined text; 0-15.
4347 watchdog timers [HW,WDT] For information on watchdog timers,
4348 see Documentation/watchdog/watchdog-parameters.txt
4349 or other driver-specific files in the
4350 Documentation/watchdog/ directory.
4352 workqueue.watchdog_thresh=
4353 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4354 warn stall conditions and dump internal state to
4355 help debugging. 0 disables workqueue stall
4356 detection; otherwise, it's the stall threshold
4357 duration in seconds. The default value is 30 and
4358 it can be updated at runtime by writing to the
4359 corresponding sysfs file.
4361 workqueue.disable_numa
4362 By default, all work items queued to unbound
4363 workqueues are affine to the NUMA nodes they're
4364 issued on, which results in better behavior in
4365 general. If NUMA affinity needs to be disabled for
4366 whatever reason, this option can be used. Note
4367 that this also can be controlled per-workqueue for
4368 workqueues visible under /sys/bus/workqueue/.
4370 workqueue.power_efficient
4371 Per-cpu workqueues are generally preferred because
4372 they show better performance thanks to cache
4373 locality; unfortunately, per-cpu workqueues tend to
4374 be more power hungry than unbound workqueues.
4376 Enabling this makes the per-cpu workqueues which
4377 were observed to contribute significantly to power
4378 consumption unbound, leading to measurably lower
4379 power usage at the cost of small performance
4382 The default value of this parameter is determined by
4383 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4385 workqueue.debug_force_rr_cpu
4386 Workqueue used to implicitly guarantee that work
4387 items queued without explicit CPU specified are put
4388 on the local CPU. This guarantee is no longer true
4389 and while local CPU is still preferred work items
4390 may be put on foreign CPUs. This debug option
4391 forces round-robin CPU selection to flush out
4392 usages which depend on the now broken guarantee.
4393 When enabled, memory and cache locality will be
4396 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4397 default x2apic cluster mode on platforms
4400 x86_intel_mid_timer= [X86-32,APBT]
4401 Choose timer option for x86 Intel MID platform.
4402 Two valid options are apbt timer only and lapic timer
4403 plus one apbt timer for broadcast timer.
4404 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4406 xen_512gb_limit [KNL,X86-64,XEN]
4407 Restricts the kernel running paravirtualized under Xen
4408 to use only up to 512 GB of RAM. The reason to do so is
4409 crash analysis tools and Xen tools for doing domain
4410 save/restore/migration must be enabled to handle larger
4413 xen_emul_unplug= [HW,X86,XEN]
4414 Unplug Xen emulated devices
4415 Format: [unplug0,][unplug1]
4416 ide-disks -- unplug primary master IDE devices
4417 aux-ide-disks -- unplug non-primary-master IDE devices
4418 nics -- unplug network devices
4419 all -- unplug all emulated devices (NICs and IDE disks)
4420 unnecessary -- unplugging emulated devices is
4421 unnecessary even if the host did not respond to
4423 never -- do not unplug even if version check succeeds
4425 xen_nopvspin [X86,XEN]
4426 Disables the ticketlock slowpath using Xen PV
4430 Disables the PV optimizations forcing the HVM guest to
4431 run as generic HVM guest with no PV drivers.
4433 xirc2ps_cs= [NET,PCMCIA]
4435 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4437 ______________________________________________________________________
4441 Add more DRM drivers.
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