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.
844 cs89x0_media= [HW,NET]
845 Format: { rj45 | aui | bnc }
848 See header of drivers/s390/block/dasd_devmap.c.
850 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
851 (one device per port)
852 Format: <port#>,<type>
853 See also Documentation/input/joystick-parport.txt
855 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
856 time. See Documentation/dynamic-debug-howto.txt for
857 details. Deprecated, see dyndbg.
859 debug [KNL] Enable kernel debugging (events log level).
862 [KNL] verbose self-tests
864 Print debugging info while doing the locking API
866 We default to 0 (no extra messages), setting it to
867 1 will print _a lot_ more information - normally
868 only useful to kernel developers.
870 debug_objects [KNL] Enable object debugging
873 [KNL] Disable object debugging
875 debug_guardpage_minorder=
876 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
877 parameter allows control of the order of pages that will
878 be intentionally kept free (and hence protected) by the
879 buddy allocator. Bigger value increase the probability
880 of catching random memory corruption, but reduce the
881 amount of memory for normal system use. The maximum
882 possible value is MAX_ORDER/2. Setting this parameter
883 to 1 or 2 should be enough to identify most random
884 memory corruption problems caused by bugs in kernel or
885 driver code when a CPU writes to (or reads from) a
886 random memory location. Note that there exists a class
887 of memory corruptions problems caused by buggy H/W or
888 F/W or by drivers badly programing DMA (basically when
889 memory is written at bus level and the CPU MMU is
890 bypassed) which are not detectable by
891 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
892 tracking down these problems.
895 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
896 parameter enables the feature at boot time. In
897 default, it is disabled. We can avoid allocating huge
898 chunk of memory for debug pagealloc if we don't enable
899 it at boot time and the system will work mostly same
900 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
901 on: enable the feature
903 debugpat [X86] Enable PAT debugging
905 decnet.addr= [HW,NET]
906 Format: <area>[,<node>]
907 See also Documentation/networking/decnet.txt.
910 [same as hugepagesz=] The size of the default
911 HugeTLB page size. This is the size represented by
912 the legacy /proc/ hugepages APIs, used for SHM, and
913 default size when mounting hugetlbfs filesystems.
914 Defaults to the default architecture's huge page size
918 Set number of hash buckets for dentry cache.
921 See Documentation/networking/ipv6.txt.
923 disable_cpu_apicid= [X86,APIC,SMP]
925 The number of initial APIC ID for the
926 corresponding CPU to be disabled at boot,
927 mostly used for the kdump 2nd kernel to
928 disable BSP to wake up multiple CPUs without
929 causing system reset or hang due to sending
932 disable_ddw [PPC/PSERIES]
933 Disable Dynamic DMA Window support. Use this if
934 to workaround buggy firmware.
937 See Documentation/networking/ipv6.txt.
939 disable_mtrr_cleanup [X86]
940 The kernel tries to adjust MTRR layout from continuous
941 to discrete, to make X server driver able to add WB
942 entry later. This parameter disables that.
944 disable_mtrr_trim [X86, Intel and AMD only]
945 By default the kernel will trim any uncacheable
946 memory out of your available memory pool based on
947 MTRR settings. This parameter disables that behavior,
948 possibly causing your machine to run very slowly.
950 disable_timer_pin_1 [X86]
951 Disable PIN 1 of APIC timer
952 Can be useful to work around chipset bugs.
954 dis_ucode_ldr [X86] Disable the microcode loader.
956 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
957 this option disables the debugging code at boot.
959 dma_debug_entries=<number>
960 This option allows to tune the number of preallocated
961 entries for DMA-API debugging code. One entry is
962 required per DMA-API allocation. Use this if the
963 DMA-API debugging code disables itself because the
964 architectural default is too low.
966 dma_debug_driver=<driver_name>
967 With this option the DMA-API debugging driver
968 filter feature can be enabled at boot time. Just
969 pass the driver to filter for as the parameter.
970 The filter can be disabled or changed to another
971 driver later using sysfs.
973 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
974 Broken monitors, graphic adapters, KVMs and EDIDless
975 panels may send no or incorrect EDID data sets.
976 This parameter allows to specify an EDID data sets
977 in the /lib/firmware directory that are used instead.
978 Generic built-in EDID data sets are used, if one of
979 edid/1024x768.bin, edid/1280x1024.bin,
980 edid/1680x1050.bin, or edid/1920x1080.bin is given
981 and no file with the same name exists. Details and
982 instructions how to build your own EDID data are
983 available in Documentation/EDID/HOWTO.txt. An EDID
984 data set will only be used for a particular connector,
985 if its name and a colon are prepended to the EDID
986 name. Each connector may use a unique EDID data
987 set by separating the files with a comma. An EDID
988 data set with no connector name will be used for
989 any connectors not explicitly specified.
993 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
994 module.dyndbg[="val"]
995 Enable debug messages at boot time. See
996 Documentation/dynamic-debug-howto.txt for details.
998 nompx [X86] Disables Intel Memory Protection Extensions.
999 See Documentation/x86/intel_mpx.txt for more
1000 information about the feature.
1002 nopku [X86] Disable Memory Protection Keys CPU feature found
1006 on enable eager fpu restore
1007 off disable eager fpu restore
1008 auto selects the default scheme, which automatically
1009 enables eagerfpu restore for xsaveopt.
1011 module.async_probe [KNL]
1012 Enable asynchronous probe on this module.
1014 early_ioremap_debug [KNL]
1015 Enable debug messages in early_ioremap support. This
1016 is useful for tracking down temporary early mappings
1017 which are not unmapped.
1019 earlycon= [KNL] Output early console device and options.
1021 When used with no options, the early console is
1022 determined by the stdout-path property in device
1026 Start an early, polled-mode console on a cadence serial
1027 port at the specified address. The cadence serial port
1028 must already be setup and configured. Options are not
1031 uart[8250],io,<addr>[,options]
1032 uart[8250],mmio,<addr>[,options]
1033 uart[8250],mmio32,<addr>[,options]
1034 uart[8250],mmio32be,<addr>[,options]
1035 uart[8250],0x<addr>[,options]
1036 Start an early, polled-mode console on the 8250/16550
1037 UART at the specified I/O port or MMIO address.
1038 MMIO inter-register address stride is either 8-bit
1039 (mmio) or 32-bit (mmio32 or mmio32be).
1040 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1041 to be equivalent to 'mmio'. 'options' are specified
1042 in the same format described for "console=ttyS<n>"; if
1043 unspecified, the h/w is not initialized.
1047 Start an early, polled-mode console on a pl011 serial
1048 port at the specified address. The pl011 serial port
1049 must already be setup and configured. Options are not
1050 yet supported. If 'mmio32' is specified, then only
1051 the driver will use only 32-bit accessors to read/write
1052 the device registers.
1055 Start an early, polled-mode console on an msm serial
1056 port at the specified address. The serial port
1057 must already be setup and configured. Options are not
1060 msm_serial_dm,<addr>
1061 Start an early, polled-mode console on an msm serial
1062 dm port at the specified address. The serial port
1063 must already be setup and configured. Options are not
1066 smh Use ARM semihosting calls for early console.
1074 Use early console provided by serial driver available
1075 on Samsung SoCs, requires selecting proper type and
1076 a correct base address of the selected UART port. The
1077 serial port must already be setup and configured.
1078 Options are not yet supported.
1082 Use early console provided by Freescale LP UART driver
1083 found on Freescale Vybrid and QorIQ LS1021A processors.
1084 A valid base address must be provided, and the serial
1085 port must already be setup and configured.
1087 armada3700_uart,<addr>
1088 Start an early, polled-mode console on the
1089 Armada 3700 serial port at the specified
1090 address. The serial port must already be setup
1091 and configured. Options are not yet supported.
1093 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1097 earlyprintk=serial[,ttySn[,baudrate]]
1098 earlyprintk=serial[,0x...[,baudrate]]
1099 earlyprintk=ttySn[,baudrate]
1100 earlyprintk=dbgp[debugController#]
1101 earlyprintk=pciserial,bus:device.function[,baudrate]
1103 earlyprintk is useful when the kernel crashes before
1104 the normal console is initialized. It is not enabled by
1105 default because it has some cosmetic problems.
1107 Append ",keep" to not disable it when the real console
1110 Only one of vga, efi, serial, or usb debug port can
1113 Currently only ttyS0 and ttyS1 may be specified by
1114 name. Other I/O ports may be explicitly specified
1115 on some architectures (x86 and arm at least) by
1116 replacing ttySn with an I/O port address, like this:
1117 earlyprintk=serial,0x1008,115200
1118 You can find the port for a given device in
1119 /proc/tty/driver/serial:
1120 2: uart:ST16650V2 port:00001008 irq:18 ...
1122 Interaction with the standard serial driver is not
1125 The VGA and EFI output is eventually overwritten by
1128 The xen output can only be used by Xen PV guests.
1130 edac_report= [HW,EDAC] Control how to report EDAC event
1131 Format: {"on" | "off" | "force"}
1132 on: enable EDAC to report H/W event. May be overridden
1133 by other higher priority error reporting module.
1134 off: disable H/W event reporting through EDAC.
1135 force: enforce the use of EDAC to report H/W event.
1138 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1141 This is designed to be used in conjunction with
1142 the boot argument: earlyprintk=vga
1145 Format: {"off" | "on" | "skip[mbr]"}
1148 Format: { "old_map", "nochunk", "noruntime", "debug" }
1149 old_map [X86-64]: switch to the old ioremap-based EFI
1150 runtime services mapping. 32-bit still uses this one by
1152 nochunk: disable reading files in "chunks" in the EFI
1153 boot stub, as chunking can cause problems with some
1154 firmware implementations.
1155 noruntime : disable EFI runtime services support
1156 debug: enable misc debug output
1158 efi_no_storage_paranoia [EFI; X86]
1159 Using this parameter you can use more than 50% of
1160 your efi variable storage. Use this parameter only if
1161 you are really sure that your UEFI does sane gc and
1162 fulfills the spec otherwise your board may brick.
1164 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1165 Add arbitrary attribute to specific memory range by
1166 updating original EFI memory map.
1167 Region of memory which aa attribute is added to is
1169 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1170 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1171 attribute is added to range 0x100000000-0x180000000 and
1172 0x10a0000000-0x1120000000.
1174 Using this parameter you can do debugging of EFI memmap
1175 related feature. For example, you can do debugging of
1176 Address Range Mirroring feature even if your box
1179 eisa_irq_edge= [PARISC,HW]
1180 See header of drivers/parisc/eisa.c.
1183 See comment before function elanfreq_setup() in
1184 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1187 Format: {"cfq" | "deadline" | "noop"}
1188 See Documentation/block/cfq-iosched.txt and
1189 Documentation/block/deadline-iosched.txt for details.
1191 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1192 Specifies physical address of start of kernel core
1193 image elf header and optionally the size. Generally
1194 kexec loader will pass this option to capture kernel.
1195 See Documentation/kdump/kdump.txt for details.
1197 enable_mtrr_cleanup [X86]
1198 The kernel tries to adjust MTRR layout from continuous
1199 to discrete, to make X server driver able to add WB
1200 entry later. This parameter enables that.
1202 enable_timer_pin_1 [X86]
1203 Enable PIN 1 of APIC timer
1204 Can be useful to work around chipset bugs
1205 (in particular on some ATI chipsets).
1206 The kernel tries to set a reasonable default.
1208 enforcing [SELINUX] Set initial enforcing status.
1210 See security/selinux/Kconfig help text.
1211 0 -- permissive (log only, no denials).
1212 1 -- enforcing (deny and log).
1214 Value can be changed at runtime via /selinux/enforce.
1217 Disable Error Record Serialization Table (ERST)
1220 ether= [HW,NET] Ethernet cards parameters
1221 This option is obsoleted by the "netdev=" option, which
1222 has equivalent usage. See its documentation for details.
1226 Permit 'security.evm' to be updated regardless of
1227 current integrity status.
1231 fail_make_request=[KNL]
1232 General fault injection mechanism.
1233 Format: <interval>,<probability>,<space>,<times>
1234 See also Documentation/fault-injection/.
1237 See Documentation/blockdev/floppy.txt.
1239 force_pal_cache_flush
1240 [IA-64] Avoid check_sal_cache_flush which may hang on
1241 buggy SAL_CACHE_FLUSH implementations. Using this
1242 parameter will force ia64_sal_cache_flush to call
1243 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1246 Forcefully enable Physical Address Extension (PAE).
1247 Many Pentium M systems disable PAE but may have a
1248 functionally usable PAE implementation.
1249 Warning: use of this parameter will taint the kernel
1250 and may cause unknown problems.
1253 [FTRACE] will set and start the specified tracer
1254 as early as possible in order to facilitate early
1257 ftrace_dump_on_oops[=orig_cpu]
1258 [FTRACE] will dump the trace buffers on oops.
1259 If no parameter is passed, ftrace will dump
1260 buffers of all CPUs, but if you pass orig_cpu, it will
1261 dump only the buffer of the CPU that triggered the
1264 ftrace_filter=[function-list]
1265 [FTRACE] Limit the functions traced by the function
1266 tracer at boot up. function-list is a comma separated
1267 list of functions. This list can be changed at run
1268 time by the set_ftrace_filter file in the debugfs
1271 ftrace_notrace=[function-list]
1272 [FTRACE] Do not trace the functions specified in
1273 function-list. This list can be changed at run time
1274 by the set_ftrace_notrace file in the debugfs
1277 ftrace_graph_filter=[function-list]
1278 [FTRACE] Limit the top level callers functions traced
1279 by the function graph tracer at boot up.
1280 function-list is a comma separated list of functions
1281 that can be changed at run time by the
1282 set_graph_function file in the debugfs tracing directory.
1284 ftrace_graph_notrace=[function-list]
1285 [FTRACE] Do not trace from the functions specified in
1286 function-list. This list is a comma separated list of
1287 functions that can be changed at run time by the
1288 set_graph_notrace file in the debugfs tracing directory.
1291 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1292 support via parallel port (up to 5 devices per port)
1293 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1294 See also Documentation/input/joystick-parport.txt
1298 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1302 gcov_persist= [GCOV] When non-zero (default), profiling data for
1303 kernel modules is saved and remains accessible via
1304 debugfs, even when the module is unloaded/reloaded.
1305 When zero, profiling data is discarded and associated
1306 debugfs files are removed at module unload time.
1308 gpt [EFI] Forces disk with valid GPT signature but
1309 invalid Protective MBR to be treated as GPT. If the
1310 primary GPT is corrupted, it enables the backup/alternate
1311 GPT to be used instead.
1313 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1314 the "Enable 0" bit of the configuration register.
1317 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1318 the "Enable 0" bit of the configuration register.
1321 grcan.select= [HW] Select which physical interface to use.
1324 grcan.txsize= [HW] Sets the size of the tx buffer.
1325 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1327 grcan.rxsize= [HW] Sets the size of the rx buffer.
1328 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1331 hardlockup_all_cpu_backtrace=
1332 [KNL] Should the hard-lockup detector generate
1333 backtraces on all cpus.
1336 hashdist= [KNL,NUMA] Large hashes allocated during boot
1337 are distributed across NUMA nodes. Defaults on
1338 for 64-bit NUMA, off otherwise.
1339 Format: 0 | 1 (for off | on)
1341 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1343 hd= [EIDE] (E)IDE hard drive subsystem geometry
1344 Format: <cyl>,<head>,<sect>
1347 Disable Hardware Error Source Table (HEST) support;
1348 corresponding firmware-first mode error processing
1349 logic will be disabled.
1351 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1352 size of <nn>. This works even on boxes that have no
1353 highmem otherwise. This also works to reduce highmem
1354 size on bigger boxes.
1356 highres= [KNL] Enable/disable high resolution timer mode.
1357 Valid parameters: "on", "off"
1361 See Documentation/isdn/README.HiSax.
1365 hpet= [X86-32,HPET] option to control HPET usage
1366 Format: { enable (default) | disable | force |
1368 disable: disable HPET and use PIT instead
1369 force: allow force enabled of undocumented chips (ICH4,
1371 verbose: show contents of HPET registers during setup
1373 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1374 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1376 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1377 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1378 On x86-64 and powerpc, this option can be specified
1379 multiple times interleaved with hugepages= to reserve
1380 huge pages of different sizes. Valid pages sizes on
1381 x86-64 are 2M (when the CPU supports "pse") and 1G
1382 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1384 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1385 terminal devices. Valid values: 0..8
1386 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1387 If specified, z/VM IUCV HVC accepts connections
1388 from listed z/VM user IDs only.
1390 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1391 hardware thread id mappings.
1392 Format: <cpu>:<hwthread>
1395 Do not unregister boot console at start. This is only
1396 useful for debugging when something happens in the window
1397 between unregistering the boot console and initializing
1400 i2c_bus= [HW] Override the default board specific I2C bus speed
1401 or register an additional I2C bus that is not
1402 registered from board initialization code.
1406 i8042.debug [HW] Toggle i8042 debug mode
1407 i8042.unmask_kbd_data
1408 [HW] Enable printing of interrupt data from the KBD port
1409 (disabled by default, and as a pre-condition
1410 requires that i8042.debug=1 be enabled)
1411 i8042.direct [HW] Put keyboard port into non-translated mode
1412 i8042.dumbkbd [HW] Pretend that controller can only read data from
1413 keyboard and cannot control its state
1414 (Don't attempt to blink the leds)
1415 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1416 i8042.nokbd [HW] Don't check/create keyboard port
1417 i8042.noloop [HW] Disable the AUX Loopback command while probing
1419 i8042.nomux [HW] Don't check presence of an active multiplexing
1421 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1423 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1424 i8042.reset [HW] Reset the controller during init and cleanup
1425 i8042.unlock [HW] Unlock (ignore) the keylock
1426 i8042.kbdreset [HW] Reset device connected to KBD port
1430 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1431 indicates that the driver is running on unsupported
1433 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1434 does not match list of supported models.
1436 [HW] Report power status in /proc/i8k
1437 (disabled by default)
1438 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1441 i915.invert_brightness=
1442 [DRM] Invert the sense of the variable that is used to
1443 set the brightness of the panel backlight. Normally a
1444 brightness value of 0 indicates backlight switched off,
1445 and the maximum of the brightness value sets the backlight
1446 to maximum brightness. If this parameter is set to 0
1447 (default) and the machine requires it, or this parameter
1448 is set to 1, a brightness value of 0 sets the backlight
1449 to maximum brightness, and the maximum of the brightness
1450 value switches the backlight off.
1451 -1 -- never invert brightness
1452 0 -- machine default
1453 1 -- force brightness inversion
1456 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1458 ide-core.nodma= [HW] (E)IDE subsystem
1459 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1460 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1461 .cdrom .chs .ignore_cable are additional options
1462 See Documentation/ide/ide.txt.
1464 ide-generic.probe-mask= [HW] (E)IDE subsystem
1466 Probe mask for legacy ISA IDE ports. Depending on
1467 platform up to 6 ports are supported, enabled by
1468 setting corresponding bits in the mask to 1. The
1469 default value is 0x0, which has a special meaning.
1470 On systems that have PCI, it triggers scanning the
1471 PCI bus for the first and the second port, which
1472 are then probed. On systems without PCI the value
1473 of 0x0 enables probing the two first ports as if it
1476 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1477 Claim all unknown PCI IDE storage controllers.
1480 Format: idle=poll, idle=halt, idle=nomwait
1481 Poll forces a polling idle loop that can slightly
1482 improve the performance of waking up a idle CPU, but
1483 will use a lot of power and make the system run hot.
1485 idle=halt: Halt is forced to be used for CPU idle.
1486 In such case C2/C3 won't be used again.
1487 idle=nomwait: Disable mwait for CPU C-states
1489 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1490 Format: { strict | legacy | 2008 | relaxed }
1493 Choose which programs will be accepted for execution
1494 based on the IEEE 754 NaN encoding(s) supported by
1495 the FPU and the NaN encoding requested with the value
1496 of an ELF file header flag individually set by each
1497 binary. Hardware implementations are permitted to
1498 support either or both of the legacy and the 2008 NaN
1501 Available settings are as follows:
1502 strict accept binaries that request a NaN encoding
1503 supported by the FPU
1504 legacy only accept legacy-NaN binaries, if supported
1506 2008 only accept 2008-NaN binaries, if supported
1508 relaxed accept any binaries regardless of whether
1509 supported by the FPU
1511 The FPU emulator is always able to support both NaN
1512 encodings, so if no FPU hardware is present or it has
1513 been disabled with 'nofpu', then the settings of
1514 'legacy' and '2008' strap the emulator accordingly,
1515 'relaxed' straps the emulator for both legacy-NaN and
1516 2008-NaN, whereas 'strict' enables legacy-NaN only on
1517 legacy processors and both NaN encodings on MIPS32 or
1520 The setting for ABS.fmt/NEG.fmt instruction execution
1521 mode generally follows that for the NaN encoding,
1522 except where unsupported by hardware.
1524 ignore_loglevel [KNL]
1525 Ignore loglevel setting - this will print /all/
1526 kernel messages to the console. Useful for debugging.
1527 We also add it as printk module parameter, so users
1528 could change it dynamically, usually by
1529 /sys/module/printk/parameters/ignore_loglevel.
1532 Ignore RLIMIT_DATA setting for data mappings,
1533 print warning at first misuse. Can be changed via
1534 /sys/module/kernel/parameters/ignore_rlimit_data.
1536 ihash_entries= [KNL]
1537 Set number of hash buckets for inode cache.
1539 ima_appraise= [IMA] appraise integrity measurements
1540 Format: { "off" | "enforce" | "fix" | "log" }
1543 ima_appraise_tcb [IMA]
1544 The builtin appraise policy appraises all files
1548 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1552 The list of supported hash algorithms is defined
1553 in crypto/hash_info.h.
1556 The builtin measurement policy to load during IMA
1557 setup. Specyfing "tcb" as the value, measures all
1558 programs exec'd, files mmap'd for exec, and all files
1559 opened with the read mode bit set by either the
1560 effective uid (euid=0) or uid=0.
1563 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1564 Load a policy which meets the needs of the Trusted
1565 Computing Base. This means IMA will measure all
1566 programs exec'd, files mmap'd for exec, and all files
1567 opened for read by uid=0.
1570 Select one of defined IMA measurements template formats.
1571 Formats: { "ima" | "ima-ng" | "ima-sig" }
1575 [IMA] Define a custom template format.
1576 Format: { "field1|...|fieldN" }
1578 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1579 Format: <min_file_size>
1580 Set the minimal file size for using asynchronous hash.
1581 If left unspecified, ahash usage is disabled.
1583 ahash performance varies for different data sizes on
1584 different crypto accelerators. This option can be used
1585 to achieve the best performance for a particular HW.
1587 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1589 Set hashing buffer size. Default: 4k.
1591 ahash performance varies for different chunk sizes on
1592 different crypto accelerators. This option can be used
1593 to achieve best performance for particular HW.
1597 Run specified binary instead of /sbin/init as init
1600 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1601 for working out where the kernel is dying during
1604 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1605 initcall functions. Useful for debugging built-in
1606 modules and initcalls.
1608 initrd= [BOOT] Specify the location of the initial ramdisk
1610 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1613 int_pln_enable [x86] Enable power limit notification interrupt
1615 integrity_audit=[IMA]
1616 Format: { "0" | "1" }
1617 0 -- basic integrity auditing messages. (Default)
1618 1 -- additional integrity auditing messages.
1620 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1622 Enable intel iommu driver.
1624 Disable intel iommu driver.
1625 igfx_off [Default Off]
1626 By default, gfx is mapped as normal device. If a gfx
1627 device has a dedicated DMAR unit, the DMAR unit is
1628 bypassed by not enabling DMAR with this option. In
1629 this case, gfx device will use physical address for
1632 With this option iommu will not optimize to look
1633 for io virtual address below 32-bit forcing dual
1634 address cycle on pci bus for cards supporting greater
1635 than 32-bit addressing. The default is to look
1636 for translation below 32-bit and if not available
1637 then look in the higher range.
1638 strict [Default Off]
1639 With this option on every unmap_single operation will
1640 result in a hardware IOTLB flush operation as opposed
1641 to batching them for performance.
1642 sp_off [Default Off]
1643 By default, super page will be supported if Intel IOMMU
1644 has the capability. With this option, super page will
1646 ecs_off [Default Off]
1647 By default, extended context tables will be supported if
1648 the hardware advertises that it has support both for the
1649 extended tables themselves, and also PASID support. With
1650 this option set, extended tables will not be used even
1651 on hardware which claims to support them.
1653 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1654 0 disables intel_idle and fall back on acpi_idle.
1655 1 to 6 specify maximum depth of C-state.
1659 Do not enable intel_pstate as the default
1660 scaling driver for the supported processors
1662 Enable intel_pstate on systems that prohibit it by default
1663 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1664 instead of acpi-cpufreq may disable platform features, such
1665 as thermal controls and power capping, that rely on ACPI
1666 P-States information being indicated to OSPM and therefore
1667 should be used with caution. This option does not work with
1668 processors that aren't supported by the intel_pstate driver
1669 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1671 Do not enable hardware P state control (HWP)
1674 Only load intel_pstate on systems which support
1675 hardware P state control (HWP) if available.
1677 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1678 Description Table, specifies preferred power management
1679 profile as "Enterprise Server" or "Performance Server",
1680 then this feature is turned on by default.
1682 intremap= [X86-64, Intel-IOMMU]
1683 on enable Interrupt Remapping (default)
1684 off disable Interrupt Remapping
1685 nosid disable Source ID checking
1687 BIOS x2APIC opt-out request will be ignored
1688 nopost disable Interrupt Posting
1690 iomem= Disable strict checking of access to MMIO memory
1691 strict regions from userspace.
1706 nobypass [PPC/POWERNV]
1707 Disable IOMMU bypass, using IOMMU for PCI devices.
1710 io7= [HW] IO7 for Marvel based alpha systems
1711 See comment before marvel_specify_io7 in
1712 arch/alpha/kernel/core_marvel.c.
1714 io_delay= [X86] I/O delay method
1716 Standard port 0x80 based delay
1718 Alternate port 0xed based delay (needed on some systems)
1720 Simple two microseconds delay
1725 See Documentation/filesystems/nfs/nfsroot.txt.
1727 irqaffinity= [SMP] Set the default irq affinity mask
1729 <cpu number>,...,<cpu number>
1731 <cpu number>-<cpu number>
1732 (must be a positive range in ascending order)
1734 <cpu number>,...,<cpu number>-<cpu number>
1737 When an interrupt is not handled search all handlers
1738 for it. Intended to get systems with badly broken
1742 When an interrupt is not handled search all handlers
1743 for it. Also check all handlers each timer
1744 interrupt. Intended to get systems with badly broken
1748 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1750 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1752 <cpu number>,...,<cpu number>
1754 <cpu number>-<cpu number>
1755 (must be a positive range in ascending order)
1757 <cpu number>,...,<cpu number>-<cpu number>
1759 This option can be used to specify one or more CPUs
1760 to isolate from the general SMP balancing and scheduling
1761 algorithms. You can move a process onto or off an
1762 "isolated" CPU via the CPU affinity syscalls or cpuset.
1763 <cpu number> begins at 0 and the maximum value is
1764 "number of CPUs in system - 1".
1766 This option is the preferred way to isolate CPUs. The
1767 alternative -- manually setting the CPU mask of all
1768 tasks in the system -- can cause problems and
1769 suboptimal load balancer performance.
1773 ivrs_ioapic [HW,X86_64]
1774 Provide an override to the IOAPIC-ID<->DEVICE-ID
1775 mapping provided in the IVRS ACPI table. For
1776 example, to map IOAPIC-ID decimal 10 to
1777 PCI device 00:14.0 write the parameter as:
1778 ivrs_ioapic[10]=00:14.0
1780 ivrs_hpet [HW,X86_64]
1781 Provide an override to the HPET-ID<->DEVICE-ID
1782 mapping provided in the IVRS ACPI table. For
1783 example, to map HPET-ID decimal 0 to
1784 PCI device 00:14.0 write the parameter as:
1785 ivrs_hpet[0]=00:14.0
1787 js= [HW,JOY] Analog joystick
1788 See Documentation/input/joystick.txt.
1791 Enable/disable kernel and module base offset ASLR
1792 (Address Space Layout Randomization) if built into
1793 the kernel. When CONFIG_HIBERNATION is selected,
1794 kASLR is disabled by default. When kASLR is enabled,
1795 hibernation will be disabled.
1799 kernelcore= [KNL,X86,IA-64,PPC]
1800 Format: nn[KMGTPE] | "mirror"
1802 specifies the amount of memory usable by the kernel
1803 for non-movable allocations. The requested amount is
1804 spread evenly throughout all nodes in the system. The
1805 remaining memory in each node is used for Movable
1806 pages. In the event, a node is too small to have both
1807 kernelcore and Movable pages, kernelcore pages will
1808 take priority and other nodes will have a larger number
1809 of Movable pages. The Movable zone is used for the
1810 allocation of pages that may be reclaimed or moved
1811 by the page migration subsystem. This means that
1812 HugeTLB pages may not be allocated from this zone.
1813 Note that allocations like PTEs-from-HighMem still
1814 use the HighMem zone if it exists, and the Normal
1815 zone if it does not.
1817 Instead of specifying the amount of memory (nn[KMGTPE]),
1818 you can specify "mirror" option. In case "mirror"
1819 option is specified, mirrored (reliable) memory is used
1820 for non-movable allocations and remaining memory is used
1821 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1822 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1825 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1826 Format: <Controller#>[,poll interval]
1827 The controller # is the number of the ehci usb debug
1828 port as it is probed via PCI. The poll interval is
1829 optional and is the number seconds in between
1830 each poll cycle to the debug port in case you need
1831 the functionality for interrupting the kernel with
1832 gdb or control-c on the dbgp connection. When
1833 not using this parameter you use sysrq-g to break into
1834 the kernel debugger.
1836 kgdboc= [KGDB,HW] kgdb over consoles.
1837 Requires a tty driver that supports console polling,
1838 or a supported polling keyboard driver (non-usb).
1839 Serial only format: <serial_device>[,baud]
1840 keyboard only format: kbd
1841 keyboard and serial format: kbd,<serial_device>[,baud]
1842 Optional Kernel mode setting:
1843 kms, kbd format: kms,kbd
1844 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1846 kgdbwait [KGDB] Stop kernel execution and enter the
1847 kernel debugger at the earliest opportunity.
1849 kmac= [MIPS] korina ethernet MAC address.
1850 Configure the RouterBoard 532 series on-chip
1851 Ethernet adapter MAC address.
1853 kmemleak= [KNL] Boot-time kmemleak enable/disable
1854 Valid arguments: on, off
1856 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1859 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1860 Valid arguments: 0, 1, 2
1861 kmemcheck=0 (disabled)
1862 kmemcheck=1 (enabled)
1863 kmemcheck=2 (one-shot mode)
1864 Default: 2 (one-shot mode)
1866 kstack=N [X86] Print N words from the kernel stack
1869 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1870 Default is 0 (don't ignore, but inject #GP)
1872 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1876 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1877 Default is 1 (enabled)
1879 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1881 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1883 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1884 (virtualized MMU) support on capable Intel chips.
1885 Default is 1 (enabled)
1887 kvm-intel.emulate_invalid_guest_state=
1888 [KVM,Intel] Enable emulation of invalid guest states
1889 Default is 0 (disabled)
1891 kvm-intel.flexpriority=
1892 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1893 Default is 1 (enabled)
1896 [KVM,Intel] Enable VMX nesting (nVMX).
1897 Default is 0 (disabled)
1899 kvm-intel.unrestricted_guest=
1900 [KVM,Intel] Disable unrestricted guest feature
1901 (virtualized real and unpaged mode) on capable
1902 Intel chips. Default is 1 (enabled)
1904 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1905 feature (tagged TLBs) on capable Intel chips.
1906 Default is 1 (enabled)
1912 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1915 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1916 value for LAPIC timer one-shot implementation. Default
1917 back to the programmable timer unit in the LAPIC.
1919 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1922 libata.dma= [LIBATA] DMA control
1923 libata.dma=0 Disable all PATA and SATA DMA
1924 libata.dma=1 PATA and SATA Disk DMA only
1925 libata.dma=2 ATAPI (CDROM) DMA only
1926 libata.dma=4 Compact Flash DMA only
1927 Combinations also work, so libata.dma=3 enables DMA
1928 for disks and CDROMs, but not CFs.
1930 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1931 libata.ignore_hpa=0 keep BIOS limits (default)
1932 libata.ignore_hpa=1 ignore limits, using full disk
1934 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1938 libata.force= [LIBATA] Force configurations. The format is comma
1939 separated list of "[ID:]VAL" where ID is
1940 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1941 matching port, link or device. Basically, it matches
1942 the ATA ID string printed on console by libata. If
1943 the whole ID part is omitted, the last PORT and DEVICE
1944 values are used. If ID hasn't been specified yet, the
1945 configuration applies to all ports, links and devices.
1947 If only DEVICE is omitted, the parameter applies to
1948 the port and all links and devices behind it. DEVICE
1949 number of 0 either selects the first device or the
1950 first fan-out link behind PMP device. It does not
1951 select the host link. DEVICE number of 15 selects the
1952 host link and device attached to it.
1954 The VAL specifies the configuration to force. As long
1955 as there's no ambiguity shortcut notation is allowed.
1956 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1957 The following configurations can be forced.
1959 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1960 Any ID with matching PORT is used.
1962 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1964 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1965 udma[/][16,25,33,44,66,100,133] notation is also
1968 * [no]ncq: Turn on or off NCQ.
1970 * [no]ncqtrim: Turn off queued DSM TRIM.
1972 * nohrst, nosrst, norst: suppress hard, soft
1975 * rstonce: only attempt one reset during
1976 hot-unplug link recovery
1978 * dump_id: dump IDENTIFY data.
1980 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1982 * disable: Disable this device.
1984 If there are multiple matching configurations changing
1985 the same attribute, the last one is used.
1987 memblock=debug [KNL] Enable memblock debug messages.
1989 load_ramdisk= [RAM] List of ramdisks to load from floppy
1990 See Documentation/blockdev/ramdisk.txt.
1992 lockd.nlm_grace_period=P [NFS] Assign grace period.
1995 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1998 lockd.nlm_timeout=T [NFS] Assign timeout value.
2001 lockd.nlm_udpport=M [NFS] Assign UDP port.
2004 locktorture.nreaders_stress= [KNL]
2005 Set the number of locking read-acquisition kthreads.
2006 Defaults to being automatically set based on the
2007 number of online CPUs.
2009 locktorture.nwriters_stress= [KNL]
2010 Set the number of locking write-acquisition kthreads.
2012 locktorture.onoff_holdoff= [KNL]
2013 Set time (s) after boot for CPU-hotplug testing.
2015 locktorture.onoff_interval= [KNL]
2016 Set time (s) between CPU-hotplug operations, or
2017 zero to disable CPU-hotplug testing.
2019 locktorture.shuffle_interval= [KNL]
2020 Set task-shuffle interval (jiffies). Shuffling
2021 tasks allows some CPUs to go into dyntick-idle
2022 mode during the locktorture test.
2024 locktorture.shutdown_secs= [KNL]
2025 Set time (s) after boot system shutdown. This
2026 is useful for hands-off automated testing.
2028 locktorture.stat_interval= [KNL]
2029 Time (s) between statistics printk()s.
2031 locktorture.stutter= [KNL]
2032 Time (s) to stutter testing, for example,
2033 specifying five seconds causes the test to run for
2034 five seconds, wait for five seconds, and so on.
2035 This tests the locking primitive's ability to
2036 transition abruptly to and from idle.
2038 locktorture.torture_runnable= [BOOT]
2039 Start locktorture running at boot time.
2041 locktorture.torture_type= [KNL]
2042 Specify the locking implementation to test.
2044 locktorture.verbose= [KNL]
2045 Enable additional printk() statements.
2047 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2050 loglevel= All Kernel Messages with a loglevel smaller than the
2051 console loglevel will be printed to the console. It can
2052 also be changed with klogd or other programs. The
2053 loglevels are defined as follows:
2055 0 (KERN_EMERG) system is unusable
2056 1 (KERN_ALERT) action must be taken immediately
2057 2 (KERN_CRIT) critical conditions
2058 3 (KERN_ERR) error conditions
2059 4 (KERN_WARNING) warning conditions
2060 5 (KERN_NOTICE) normal but significant condition
2061 6 (KERN_INFO) informational
2062 7 (KERN_DEBUG) debug-level messages
2064 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2065 in bytes. n must be a power of two and greater
2066 than the minimal size. The minimal size is defined
2067 by LOG_BUF_SHIFT kernel config parameter. There is
2068 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2069 that allows to increase the default size depending on
2070 the number of CPUs. See init/Kconfig for more details.
2072 logo.nologo [FB] Disables display of the built-in Linux logo.
2073 This may be used to provide more screen space for
2074 kernel log messages and is useful when debugging
2075 kernel boot problems.
2077 lp=0 [LP] Specify parallel ports to use, e.g,
2078 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2079 lp=reset first parallel port). 'lp=0' disables the
2080 lp=auto printer driver. 'lp=reset' (which can be
2081 specified in addition to the ports) causes
2082 attached printers to be reset. Using
2083 lp=port1,port2,... specifies the parallel ports
2084 to associate lp devices with, starting with
2085 lp0. A port specification may be 'none' to skip
2086 that lp device, or a parport name such as
2087 'parport0'. Specifying 'lp=auto' instead of a
2088 port specification list means that device IDs
2089 from each port should be examined, to see if
2090 an IEEE 1284-compliant printer is attached; if
2091 so, the driver will manage that printer.
2092 See also header of drivers/char/lp.c.
2095 Sets loops_per_jiffy to given constant, thus avoiding
2096 time-consuming boot-time autodetection (up to 250 ms per
2097 CPU). 0 enables autodetection (default). To determine
2098 the correct value for your kernel, boot with normal
2099 autodetection and see what value is printed. Note that
2100 on SMP systems the preset will be applied to all CPUs,
2101 which is likely to cause problems if your CPUs need
2102 significantly divergent settings. An incorrect value
2103 will cause delays in the kernel to be wrong, leading to
2104 unpredictable I/O errors and other breakage. Although
2105 unlikely, in the extreme case this might damage your
2109 Format: <io>,<irq>,<dma>
2111 machvec= [IA-64] Force the use of a particular machine-vector
2112 (machvec) in a generic kernel.
2113 Example: machvec=hpzx1_swiotlb
2115 machtype= [Loongson] Share the same kernel image file between different
2117 Example: machtype=lemote-yeeloong-2f-7inch
2119 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2120 than or equal to this physical address is ignored.
2122 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2123 should make use of. maxcpus=n : n >= 0 limits the
2124 kernel to using 'n' processors. n=0 is a special case,
2125 it is equivalent to "nosmp", which also disables
2128 max_loop= [LOOP] The number of loop block devices that get
2129 (loop.max_loop) unconditionally pre-created at init time. The default
2130 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2131 of statically allocating a predefined number, loop
2132 devices can be requested on-demand with the
2133 /dev/loop-control interface.
2135 mce [X86-32] Machine Check Exception
2137 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2139 md= [HW] RAID subsystems devices and level
2140 See Documentation/md.txt.
2143 Format: <first>,<last>
2144 Specifies range of consoles to be captured by the MDA.
2146 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2147 Amount of memory to be used when the kernel is not able
2148 to see the whole system memory or for test.
2149 [X86] Work as limiting max address. Use together
2150 with memmap= to avoid physical address space collisions.
2151 Without memmap= PCI devices could be placed at addresses
2152 belonging to unused RAM.
2154 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2158 [KNL,SH] Allow user to override the default size for
2159 per-device physically contiguous DMA buffers.
2161 memmap=exactmap [KNL,X86] Enable setting of an exact
2162 E820 memory map, as specified by the user.
2163 Such memmap=exactmap lines can be constructed based on
2164 BIOS output or other requirements. See the memmap=nn@ss
2167 memmap=nn[KMG]@ss[KMG]
2168 [KNL] Force usage of a specific region of memory.
2169 Region of memory to be used is from ss to ss+nn.
2171 memmap=nn[KMG]#ss[KMG]
2172 [KNL,ACPI] Mark specific memory as ACPI data.
2173 Region of memory to be marked is from ss to ss+nn.
2175 memmap=nn[KMG]$ss[KMG]
2176 [KNL,ACPI] Mark specific memory as reserved.
2177 Region of memory to be reserved is from ss to ss+nn.
2178 Example: Exclude memory from 0x18690000-0x1869ffff
2179 memmap=64K$0x18690000
2181 memmap=0x10000$0x18690000
2183 memmap=nn[KMG]!ss[KMG]
2184 [KNL,X86] Mark specific memory as protected.
2185 Region of memory to be used, from ss to ss+nn.
2186 The memory region may be marked as e820 type 12 (0xc)
2187 and is NVDIMM or ADR memory.
2189 memory_corruption_check=0/1 [X86]
2190 Some BIOSes seem to corrupt the first 64k of
2191 memory when doing things like suspend/resume.
2192 Setting this option will scan the memory
2193 looking for corruption. Enabling this will
2194 both detect corruption and prevent the kernel
2195 from using the memory being corrupted.
2196 However, its intended as a diagnostic tool; if
2197 repeatable BIOS-originated corruption always
2198 affects the same memory, you can use memmap=
2199 to prevent the kernel from using that memory.
2201 memory_corruption_check_size=size [X86]
2202 By default it checks for corruption in the low
2203 64k, making this memory unavailable for normal
2204 use. Use this parameter to scan for
2205 corruption in more or less memory.
2207 memory_corruption_check_period=seconds [X86]
2208 By default it checks for corruption every 60
2209 seconds. Use this parameter to check at some
2210 other rate. 0 disables periodic checking.
2212 memtest= [KNL,X86,ARM] Enable memtest
2214 default : 0 <disable>
2215 Specifies the number of memtest passes to be
2216 performed. Each pass selects another test
2217 pattern from a given set of patterns. Memtest
2218 fills the memory with this pattern, validates
2219 memory contents and reserves bad memory
2220 regions that are detected.
2222 meye.*= [HW] Set MotionEye Camera parameters
2223 See Documentation/video4linux/meye.txt.
2225 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2226 Multi-Function General Purpose Timers on AMD Geode
2229 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2230 the BIOS has incorrectly applied a workaround. TinyBIOS
2231 version 0.98 is known to be affected, 0.99 fixes the
2232 problem by letting the user disable the workaround.
2236 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2237 physical address is ignored.
2239 mini2440= [ARM,HW,KNL]
2240 Format:[0..2][b][c][t]
2242 MINI2440 configuration specification:
2243 0 - The attached screen is the 3.5" TFT
2244 1 - The attached screen is the 7" TFT
2245 2 - The VGA Shield is attached (1024x768)
2246 Leaving out the screen size parameter will not load
2247 the TFT driver, and the framebuffer will be left
2249 b - Enable backlight. The TFT backlight pin will be
2250 linked to the kernel VESA blanking code and a GPIO
2251 LED. This parameter is not necessary when using the
2253 c - Enable the s3c camera interface.
2254 t - Reserved for enabling touchscreen support. The
2255 touchscreen support is not enabled in the mainstream
2256 kernel as of 2.6.30, a preliminary port can be found
2257 in the "bleeding edge" mini2440 support kernel at
2258 http://repo.or.cz/w/linux-2.6/mini2440.git
2261 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2262 parameter allows control of the logging verbosity for
2263 the additional memory initialisation checks. A value
2264 of 0 disables mminit logging and a level of 4 will
2265 log everything. Information is printed at KERN_DEBUG
2266 so loglevel=8 may also need to be specified.
2269 [KNL] When CONFIG_MODULE_SIG is set, this means that
2270 modules without (valid) signatures will fail to load.
2271 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2272 is always true, so this option does nothing.
2275 [MOUSE] Maximum time between finger touching and
2276 leaving touchpad surface for touch to be considered
2277 a tap and be reported as a left button click (for
2278 touchpads working in absolute mode only).
2280 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2281 reporting absolute coordinates, such as tablets
2282 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2283 reporting absolute coordinates, such as tablets
2285 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2286 is similar to kernelcore except it specifies the
2287 amount of memory used for migratable allocations.
2288 If both kernelcore and movablecore is specified,
2289 then kernelcore will be at *least* the specified
2290 value but may be more. If movablecore on its own
2291 is specified, the administrator must be careful
2292 that the amount of memory usable for all allocations
2295 movable_node [KNL,X86] Boot-time switch to enable the effects
2296 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2298 MTD_Partition= [MTD]
2299 Format: <name>,<region-number>,<size>,<offset>
2301 MTD_Region= [MTD] Format:
2302 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2305 See drivers/mtd/cmdlinepart.c.
2307 multitce=off [PPC] This parameter disables the use of the pSeries
2308 firmware feature for updating multiple TCE entries
2311 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2313 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2315 boundary - index of last SLC block on Flex-OneNAND.
2316 The remaining blocks are configured as MLC blocks.
2317 lock - Configure if Flex-OneNAND boundary should be locked.
2318 Once locked, the boundary cannot be changed.
2319 1 indicates lock status, 0 indicates unlock status.
2322 ARM/S3C2412 JIVE boot control
2324 See arch/arm/mach-s3c2412/mach-jive.c
2326 mtouchusb.raw_coordinates=
2327 [HW] Make the MicroTouch USB driver use raw coordinates
2328 ('y', default) or cooked coordinates ('n')
2330 mtrr_chunk_size=nn[KMG] [X86]
2331 used for mtrr cleanup. It is largest continuous chunk
2332 that could hold holes aka. UC entries.
2334 mtrr_gran_size=nn[KMG] [X86]
2335 Used for mtrr cleanup. It is granularity of mtrr block.
2337 Large value could prevent small alignment from
2340 mtrr_spare_reg_nr=n [X86]
2342 Range: 0,7 : spare reg number
2344 Used for mtrr cleanup. It is spare mtrr entries number.
2345 Set to 2 or more if your graphical card needs more.
2347 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2349 netdev= [NET] Network devices parameters
2350 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2351 Note that mem_start is often overloaded to mean
2352 something different and driver-specific.
2353 This usage is only documented in each driver source
2357 [NETFILTER] Enable connection tracking flow accounting
2358 0 to disable accounting
2359 1 to enable accounting
2362 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2363 See Documentation/filesystems/nfs/nfsroot.txt.
2365 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2366 See Documentation/filesystems/nfs/nfsroot.txt.
2368 nfsrootdebug [NFS] enable nfsroot debugging messages.
2369 See Documentation/filesystems/nfs/nfsroot.txt.
2371 nfs.callback_tcpport=
2372 [NFS] set the TCP port on which the NFSv4 callback
2373 channel should listen.
2376 [NFS] sets the pathname to the program which is used
2377 to update the NFS client cache entries.
2379 nfs.cache_getent_timeout=
2380 [NFS] sets the timeout after which an attempt to
2381 update a cache entry is deemed to have failed.
2383 nfs.idmap_cache_timeout=
2384 [NFS] set the maximum lifetime for idmapper cache
2388 [NFS] enable 64-bit inode numbers.
2389 If zero, the NFS client will fake up a 32-bit inode
2390 number for the readdir() and stat() syscalls instead
2391 of returning the full 64-bit number.
2392 The default is to return 64-bit inode numbers.
2394 nfs.max_session_slots=
2395 [NFSv4.1] Sets the maximum number of session slots
2396 the client will attempt to negotiate with the server.
2397 This limits the number of simultaneous RPC requests
2398 that the client can send to the NFSv4.1 server.
2399 Note that there is little point in setting this
2400 value higher than the max_tcp_slot_table_limit.
2402 nfs.nfs4_disable_idmapping=
2403 [NFSv4] When set to the default of '1', this option
2404 ensures that both the RPC level authentication
2405 scheme and the NFS level operations agree to use
2406 numeric uids/gids if the mount is using the
2407 'sec=sys' security flavour. In effect it is
2408 disabling idmapping, which can make migration from
2409 legacy NFSv2/v3 systems to NFSv4 easier.
2410 Servers that do not support this mode of operation
2411 will be autodetected by the client, and it will fall
2412 back to using the idmapper.
2413 To turn off this behaviour, set the value to '0'.
2415 [NFS4] Specify an additional fixed unique ident-
2416 ification string that NFSv4 clients can insert into
2417 their nfs_client_id4 string. This is typically a
2418 UUID that is generated at system install time.
2420 nfs.send_implementation_id =
2421 [NFSv4.1] Send client implementation identification
2422 information in exchange_id requests.
2423 If zero, no implementation identification information
2425 The default is to send the implementation identification
2428 nfs.recover_lost_locks =
2429 [NFSv4] Attempt to recover locks that were lost due
2430 to a lease timeout on the server. Please note that
2431 doing this risks data corruption, since there are
2432 no guarantees that the file will remain unchanged
2433 after the locks are lost.
2434 If you want to enable the kernel legacy behaviour of
2435 attempting to recover these locks, then set this
2437 The default parameter value of '0' causes the kernel
2438 not to attempt recovery of lost locks.
2440 nfs4.layoutstats_timer =
2441 [NFSv4.2] Change the rate at which the kernel sends
2442 layoutstats to the pNFS metadata server.
2444 Setting this to value to 0 causes the kernel to use
2445 whatever value is the default set by the layout
2446 driver. A non-zero value sets the minimum interval
2447 in seconds between layoutstats transmissions.
2449 nfsd.nfs4_disable_idmapping=
2450 [NFSv4] When set to the default of '1', the NFSv4
2451 server will return only numeric uids and gids to
2452 clients using auth_sys, and will accept numeric uids
2453 and gids from such clients. This is intended to ease
2454 migration from NFSv2/v3.
2456 objlayoutdriver.osd_login_prog=
2457 [NFS] [OBJLAYOUT] sets the pathname to the program which
2458 is used to automatically discover and login into new
2459 osd-targets. Please see:
2460 Documentation/filesystems/pnfs.txt for more explanations
2462 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2463 when a NMI is triggered.
2464 Format: [state][,regs][,debounce][,die]
2466 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2467 Format: [panic,][nopanic,][num]
2469 0 - turn hardlockup detector in nmi_watchdog off
2470 1 - turn hardlockup detector in nmi_watchdog on
2471 When panic is specified, panic when an NMI watchdog
2472 timeout occurs (or 'nopanic' to override the opposite
2473 default). To disable both hard and soft lockup detectors,
2474 please see 'nowatchdog'.
2475 This is useful when you use a panic=... timeout and
2476 need the box quickly up again.
2478 netpoll.carrier_timeout=
2479 [NET] Specifies amount of time (in seconds) that
2480 netpoll should wait for a carrier. By default netpoll
2483 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2484 emulation library even if a 387 maths coprocessor
2488 [HW] Never suspend the console
2489 Disable suspending of consoles during suspend and
2490 hibernate operations. Once disabled, debugging
2491 messages can reach various consoles while the rest
2492 of the system is being put to sleep (ie, while
2493 debugging driver suspend/resume hooks). This may
2494 not work reliably with all consoles, but is known
2495 to work with serial and VGA consoles.
2496 To facilitate more flexible debugging, we also add
2497 console_suspend, a printk module parameter to control
2498 it. Users could use console_suspend (usually
2499 /sys/module/printk/parameters/console_suspend) to
2500 turn on/off it dynamically.
2502 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2503 caches in the slab allocator. Saves per-node memory,
2504 but will impact performance.
2508 noapic [SMP,APIC] Tells the kernel to not make use of any
2509 IOAPICs that may be present in the system.
2511 noautogroup Disable scheduler automatic task group creation.
2513 nobats [PPC] Do not use BATs for mapping kernel lowmem
2514 on "Classic" PPC cores.
2518 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2520 nodelayacct [KNL] Disable per-task delay accounting
2522 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2524 nodsp [SH] Disable hardware DSP at boot time.
2526 noefi Disable EFI runtime services support.
2531 On X86-32 available only on PAE configured kernels.
2532 noexec=on: enable non-executable mappings (default)
2533 noexec=off: disable non-executable mappings
2536 Disable SMAP (Supervisor Mode Access Prevention)
2537 even if it is supported by processor.
2540 Disable SMEP (Supervisor Mode Execution Prevention)
2541 even if it is supported by processor.
2544 This affects only 32-bit executables.
2545 noexec32=on: enable non-executable mappings (default)
2546 read doesn't imply executable mappings
2547 noexec32=off: disable non-executable mappings
2548 read implies executable mappings
2550 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2552 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2553 register save and restore. The kernel will only save
2554 legacy floating-point registers on task switch.
2556 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2558 noxsave [BUGS=X86] Disables x86 extended register state save
2559 and restore using xsave. The kernel will fallback to
2560 enabling legacy floating-point and sse state.
2562 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2563 register states. The kernel will fall back to use
2564 xsave to save the states. By using this parameter,
2565 performance of saving the states is degraded because
2566 xsave doesn't support modified optimization while
2567 xsaveopt supports it on xsaveopt enabled systems.
2569 noxsaves [X86] Disables xsaves and xrstors used in saving and
2570 restoring x86 extended register state in compacted
2571 form of xsave area. The kernel will fall back to use
2572 xsaveopt and xrstor to save and restore the states
2573 in standard form of xsave area. By using this
2574 parameter, xsave area per process might occupy more
2575 memory on xsaves enabled systems.
2577 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2578 wfi(ARM) instruction doesn't work correctly and not to
2579 use it. This is also useful when using JTAG debugger.
2581 no_file_caps Tells the kernel not to honor file capabilities. The
2582 only way then for a file to be executed with privilege
2583 is to be setuid root or executed by root.
2585 nohalt [IA-64] Tells the kernel not to use the power saving
2586 function PAL_HALT_LIGHT when idle. This increases
2587 power-consumption. On the positive side, it reduces
2588 interrupt wake-up latency, which may improve performance
2589 in certain environments such as networked servers or
2592 nohibernate [HIBERNATION] Disable hibernation and resume.
2594 nohz= [KNL] Boottime enable/disable dynamic ticks
2595 Valid arguments: on, off
2598 nohz_full= [KNL,BOOT]
2599 In kernels built with CONFIG_NO_HZ_FULL=y, set
2600 the specified list of CPUs whose tick will be stopped
2601 whenever possible. The boot CPU will be forced outside
2602 the range to maintain the timekeeping.
2603 The CPUs in this range must also be included in the
2606 noiotrap [SH] Disables trapped I/O port accesses.
2608 noirqdebug [X86-32] Disables the code which attempts to detect and
2609 disable unhandled interrupt sources.
2611 no_timer_check [X86,APIC] Disables the code which tests for
2612 broken timer IRQ sources.
2614 noisapnp [ISAPNP] Disables ISA PnP code.
2616 noinitrd [RAM] Tells the kernel not to load any configured
2619 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2621 [Deprecated - use intremap=off]
2625 noinvpcid [X86] Disable the INVPCID cpu feature.
2627 nojitter [IA-64] Disables jitter checking for ITC timers.
2629 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2631 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2634 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2635 steal time is computed, but won't influence scheduler
2638 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2640 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2642 noltlbs [PPC] Do not use large page/tlb entries for kernel
2643 lowmem mapping on PPC40x and PPC8xx
2645 nomca [IA-64] Disable machine check abort handling
2647 nomce [X86-32] Disable Machine Check Exception
2649 nomfgpt [X86-32] Disable Multi-Function General Purpose
2650 Timer usage (for AMD Geode machines).
2652 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2653 shutdown the other cpus. Instead use the REBOOT_VECTOR
2656 nomodule Disable module load
2658 nopat [X86] Disable PAT (page attribute table extension of
2659 pagetables) support.
2661 norandmaps Don't use address space randomization. Equivalent to
2662 echo 0 > /proc/sys/kernel/randomize_va_space
2664 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2666 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2667 with UP alternatives
2669 nordrand [X86] Disable kernel use of the RDRAND and
2670 RDSEED instructions even if they are supported
2671 by the processor. RDRAND and RDSEED are still
2672 available to user space applications.
2674 noresume [SWSUSP] Disables resume and restores original swap
2677 no-scroll [VGA] Disables scrollback.
2678 This is required for the Braillex ib80-piezo Braille
2679 reader made by F.H. Papenmeier (Germany).
2683 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2685 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2686 and disable the IO APIC. legacy for "maxcpus=0".
2688 nosoftlockup [KNL] Disable the soft-lockup detector.
2690 nosync [HW,M68K] Disables sync negotiation for all devices.
2692 notsc [BUGS=X86-32] Disable Time Stamp Counter
2694 nowatchdog [KNL] Disable both lockup detectors, i.e.
2695 soft-lockup and NMI watchdog (hard-lockup).
2699 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2701 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2702 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2703 Some features depend on CPU0. Known dependencies are:
2704 1. Resume from suspend/hibernate depends on CPU0.
2705 Suspend/hibernate will fail if CPU0 is offline and you
2706 need to online CPU0 before suspend/hibernate.
2707 2. PIC interrupts also depend on CPU0. CPU0 can't be
2708 removed if a PIC interrupt is detected.
2709 It's said poweroff/reboot may depend on CPU0 on some
2710 machines although I haven't seen such issues so far
2711 after CPU0 is offline on a few tested machines.
2712 If the dependencies are under your control, you can
2713 turn on cpu0_hotplug.
2715 nptcg= [IA-64] Override max number of concurrent global TLB
2716 purges which is reported from either PAL_VM_SUMMARY or
2719 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2720 could support. nr_cpus=n : n >= 1 limits the kernel to
2721 supporting 'n' processors. Later in runtime you can not
2722 use hotplug cpu feature to put more cpu back to online.
2723 just like you compile the kernel NR_CPUS=n
2725 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2727 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2728 Allowed values are enable and disable
2730 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2731 one of ['zone', 'node', 'default'] can be specified
2732 This can be set from sysctl after boot.
2733 See Documentation/sysctl/vm.txt for details.
2735 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2736 See Documentation/debugging-via-ohci1394.txt for more
2739 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2740 Rather than timing out after 20 ms if an EC
2741 command is not properly ACKed, override the length
2742 of the timeout. We have interrupts disabled while
2743 waiting for the ACK, so if this is set too high
2744 interrupts *may* be lost!
2746 omap_mux= [OMAP] Override bootloader pin multiplexing.
2747 Format: <mux_mode0.mode_name=value>...
2748 For example, to override I2C bus2:
2749 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2751 oprofile.timer= [HW]
2752 Use timer interrupt instead of performance counters
2754 oprofile.cpu_type= Force an oprofile cpu type
2755 This might be useful if you have an older oprofile
2756 userland or if you want common events.
2757 Format: { arch_perfmon }
2758 arch_perfmon: [X86] Force use of architectural
2759 perfmon on Intel CPUs instead of the
2760 CPU specific event set.
2761 timer: [X86] Force use of architectural NMI
2762 timer mode (see also oprofile.timer
2763 for generic hr timer mode)
2764 [s390] Force legacy basic mode sampling
2765 (report cpu_type "timer")
2767 oops=panic Always panic on oopses. Default is to just kill the
2768 process, but there is a small probability of
2769 deadlocking the machine.
2770 This will also cause panics on machine check exceptions.
2771 Useful together with panic=30 to trigger a reboot.
2774 See Documentation/sound/oss/oss-parameters.txt
2776 page_owner= [KNL] Boot-time page_owner enabling option.
2777 Storage of the information about who allocated
2778 each page is disabled in default. With this switch,
2780 on: enable the feature
2782 page_poison= [KNL] Boot-time parameter changing the state of
2783 poisoning on the buddy allocator.
2784 off: turn off poisoning
2785 on: turn on poisoning
2787 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2788 timeout > 0: seconds before rebooting
2789 timeout = 0: wait forever
2790 timeout < 0: reboot immediately
2793 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2796 crash_kexec_post_notifiers
2797 Run kdump after running panic-notifiers and dumping
2798 kmsg. This only for the users who doubt kdump always
2799 succeeds in any situation.
2800 Note that this also increases risks of kdump failure,
2801 because some panic notifiers can make the crashed
2802 kernel more unstable.
2804 parkbd.port= [HW] Parallel port number the keyboard adapter is
2805 connected to, default is 0.
2807 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2808 0 for XT, 1 for AT (default is AT).
2811 parport= [HW,PPT] Specify parallel ports. 0 disables.
2812 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2813 Use 'auto' to force the driver to use any
2814 IRQ/DMA settings detected (the default is to
2815 ignore detected IRQ/DMA settings because of
2816 possible conflicts). You can specify the base
2817 address, IRQ, and DMA settings; IRQ and DMA
2818 should be numbers, or 'auto' (for using detected
2819 settings on that particular port), or 'nofifo'
2820 (to avoid using a FIFO even if it is detected).
2821 Parallel ports are assigned in the order they
2822 are specified on the command line, starting
2825 parport_init_mode= [HW,PPT]
2826 Configure VIA parallel port to operate in
2827 a specific mode. This is necessary on Pegasos
2828 computer where firmware has no options for setting
2829 up parallel port mode and sets it to spp.
2830 Currently this function knows 686a and 8231 chips.
2831 Format: [spp|ps2|epp|ecp|ecpepp]
2834 Halt all CPUs after the first oops has been printed for
2835 the specified number of seconds. This is to be used if
2836 your oopses keep scrolling off the screen.
2841 See header of drivers/block/paride/pcd.c.
2842 See also Documentation/blockdev/paride.txt.
2844 pci=option[,option...] [PCI] various PCI subsystem options:
2845 earlydump [X86] dump PCI config space before the kernel
2847 off [X86] don't probe for the PCI bus
2848 bios [X86-32] force use of PCI BIOS, don't access
2849 the hardware directly. Use this if your machine
2850 has a non-standard PCI host bridge.
2851 nobios [X86-32] disallow use of PCI BIOS, only direct
2852 hardware access methods are allowed. Use this
2853 if you experience crashes upon bootup and you
2854 suspect they are caused by the BIOS.
2855 conf1 [X86] Force use of PCI Configuration Access
2856 Mechanism 1 (config address in IO port 0xCF8,
2857 data in IO port 0xCFC, both 32-bit).
2858 conf2 [X86] Force use of PCI Configuration Access
2859 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2860 the function, IO port 0xCFA, also 8-bit, sets
2861 bus number. The config space is then accessed
2862 through ports 0xC000-0xCFFF).
2863 See http://wiki.osdev.org/PCI for more info
2864 on the configuration access mechanisms.
2865 noaer [PCIE] If the PCIEAER kernel config parameter is
2866 enabled, this kernel boot option can be used to
2867 disable the use of PCIE advanced error reporting.
2868 nodomains [PCI] Disable support for multiple PCI
2869 root domains (aka PCI segments, in ACPI-speak).
2870 nommconf [X86] Disable use of MMCONFIG for PCI
2872 check_enable_amd_mmconf [X86] check for and enable
2873 properly configured MMIO access to PCI
2874 config space on AMD family 10h CPU
2875 nomsi [MSI] If the PCI_MSI kernel config parameter is
2876 enabled, this kernel boot option can be used to
2877 disable the use of MSI interrupts system-wide.
2878 noioapicquirk [APIC] Disable all boot interrupt quirks.
2879 Safety option to keep boot IRQs enabled. This
2880 should never be necessary.
2881 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2882 primary IO-APIC for bridges that cannot disable
2883 boot IRQs. This fixes a source of spurious IRQs
2884 when the system masks IRQs.
2885 noioapicreroute [APIC] Disable workaround that uses the
2886 boot IRQ equivalent of an IRQ that connects to
2887 a chipset where boot IRQs cannot be disabled.
2888 The opposite of ioapicreroute.
2889 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2890 routing table. These calls are known to be buggy
2891 on several machines and they hang the machine
2892 when used, but on other computers it's the only
2893 way to get the interrupt routing table. Try
2894 this option if the kernel is unable to allocate
2895 IRQs or discover secondary PCI buses on your
2897 rom [X86] Assign address space to expansion ROMs.
2898 Use with caution as certain devices share
2899 address decoders between ROMs and other
2901 norom [X86] Do not assign address space to
2902 expansion ROMs that do not already have
2903 BIOS assigned address ranges.
2904 nobar [X86] Do not assign address space to the
2905 BARs that weren't assigned by the BIOS.
2906 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2907 assigned automatically to PCI devices. You can
2908 make the kernel exclude IRQs of your ISA cards
2910 pirqaddr=0xAAAAA [X86] Specify the physical address
2911 of the PIRQ table (normally generated
2912 by the BIOS) if it is outside the
2913 F0000h-100000h range.
2914 lastbus=N [X86] Scan all buses thru bus #N. Can be
2915 useful if the kernel is unable to find your
2916 secondary buses and you want to tell it
2917 explicitly which ones they are.
2918 assign-busses [X86] Always assign all PCI bus
2919 numbers ourselves, overriding
2920 whatever the firmware may have done.
2921 usepirqmask [X86] Honor the possible IRQ mask stored
2922 in the BIOS $PIR table. This is needed on
2923 some systems with broken BIOSes, notably
2924 some HP Pavilion N5400 and Omnibook XE3
2925 notebooks. This will have no effect if ACPI
2926 IRQ routing is enabled.
2927 noacpi [X86] Do not use ACPI for IRQ routing
2928 or for PCI scanning.
2929 use_crs [X86] Use PCI host bridge window information
2930 from ACPI. On BIOSes from 2008 or later, this
2931 is enabled by default. If you need to use this,
2932 please report a bug.
2933 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2934 If you need to use this, please report a bug.
2935 routeirq Do IRQ routing for all PCI devices.
2936 This is normally done in pci_enable_device(),
2937 so this option is a temporary workaround
2938 for broken drivers that don't call it.
2939 skip_isa_align [X86] do not align io start addr, so can
2940 handle more pci cards
2941 firmware [ARM] Do not re-enumerate the bus but instead
2942 just use the configuration from the
2943 bootloader. This is currently used on
2944 IXP2000 systems where the bus has to be
2945 configured a certain way for adjunct CPUs.
2946 noearly [X86] Don't do any early type 1 scanning.
2947 This might help on some broken boards which
2948 machine check when some devices' config space
2949 is read. But various workarounds are disabled
2950 and some IOMMU drivers will not work.
2951 bfsort Sort PCI devices into breadth-first order.
2952 This sorting is done to get a device
2953 order compatible with older (<= 2.4) kernels.
2954 nobfsort Don't sort PCI devices into breadth-first order.
2955 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2956 tuning and use the BIOS-configured MPS defaults.
2957 pcie_bus_safe Set every device's MPS to the largest value
2958 supported by all devices below the root complex.
2959 pcie_bus_perf Set device MPS to the largest allowable MPS
2960 based on its parent bus. Also set MRRS (Max
2961 Read Request Size) to the largest supported
2962 value (no larger than the MPS that the device
2963 or bus can support) for best performance.
2964 pcie_bus_peer2peer Set every device's MPS to 128B, which
2965 every device is guaranteed to support. This
2966 configuration allows peer-to-peer DMA between
2967 any pair of devices, possibly at the cost of
2968 reduced performance. This also guarantees
2969 that hot-added devices will work.
2970 cbiosize=nn[KMG] The fixed amount of bus space which is
2971 reserved for the CardBus bridge's IO window.
2972 The default value is 256 bytes.
2973 cbmemsize=nn[KMG] The fixed amount of bus space which is
2974 reserved for the CardBus bridge's memory
2975 window. The default value is 64 megabytes.
2978 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2979 Specifies alignment and device to reassign
2980 aligned memory resources.
2981 If <order of align> is not specified,
2982 PAGE_SIZE is used as alignment.
2983 PCI-PCI bridge can be specified, if resource
2984 windows need to be expanded.
2985 ecrc= Enable/disable PCIe ECRC (transaction layer
2986 end-to-end CRC checking).
2987 bios: Use BIOS/firmware settings. This is the
2991 hpiosize=nn[KMG] The fixed amount of bus space which is
2992 reserved for hotplug bridge's IO window.
2993 Default size is 256 bytes.
2994 hpmemsize=nn[KMG] The fixed amount of bus space which is
2995 reserved for hotplug bridge's memory window.
2996 Default size is 2 megabytes.
2997 realloc= Enable/disable reallocating PCI bridge resources
2998 if allocations done by BIOS are too small to
2999 accommodate resources required by all child
3001 off: Turn realloc off
3003 realloc same as realloc=on
3004 noari do not use PCIe ARI.
3005 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3006 only look for one device below a PCIe downstream
3009 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3012 force Enable ASPM even on devices that claim not to support it.
3013 WARNING: Forcing ASPM on may cause system lockups.
3015 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3016 nomsi Do not use MSI for PCI Express Native Hotplug (this
3017 makes all PCIe ports use INTx for hotplug services).
3019 pcie_ports= [PCIE] PCIe ports handling:
3020 auto Ask the BIOS whether or not to use native PCIe services
3021 associated with PCIe ports (PME, hot-plug, AER). Use
3022 them only if that is allowed by the BIOS.
3023 native Use native PCIe services associated with PCIe ports
3025 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3028 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3029 nomsi Do not use MSI for native PCIe PME signaling (this makes
3030 all PCIe root ports use INTx for all services).
3032 pcmv= [HW,PCMCIA] BadgePAD 4
3036 Keep all power-domains already enabled by bootloader on,
3037 even if no driver has claimed them. This is useful
3038 for debug and development, but should not be
3039 needed on a platform with proper driver support.
3042 See Documentation/blockdev/paride.txt.
3044 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3047 See arch/parisc/kernel/pdc_chassis.c
3049 percpu_alloc= Select which percpu first chunk allocator to use.
3050 Currently supported values are "embed" and "page".
3051 Archs may support subset or none of the selections.
3052 See comments in mm/percpu.c for details on each
3053 allocator. This parameter is primarily for debugging
3054 and performance comparison.
3057 See Documentation/blockdev/paride.txt.
3060 See Documentation/blockdev/paride.txt.
3062 pirq= [SMP,APIC] Manual mp-table setup
3063 See Documentation/x86/i386/IO-APIC.txt.
3065 plip= [PPT,NET] Parallel port network link
3066 Format: { parport<nr> | timid | 0 }
3067 See also Documentation/parport.txt.
3069 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3070 Override pmtimer IOPort with a hex value.
3074 Enable PNP debug messages (depends on the
3075 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3076 via /sys/module/pnp/parameters/debug. We always show
3077 current resource usage; turning this on also shows
3078 possible settings and some assignment information.
3084 { on | off | curr | res | no-curr | no-res }
3087 [ISAPNP] Exclude IRQs for the autoconfiguration
3090 [ISAPNP] Exclude DMAs for the autoconfiguration
3092 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3093 Ranges are in pairs (I/O port base and size).
3096 [ISAPNP] Exclude memory regions for the
3098 Ranges are in pairs (memory base and size).
3100 ports= [IP_VS_FTP] IPVS ftp helper module
3102 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3104 Format: <port>,<port>....
3106 ppc_strict_facility_enable
3107 [PPC] This option catches any kernel floating point,
3108 Altivec, VSX and SPE outside of regions specifically
3109 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3110 There is some performance impact when enabling this.
3112 print-fatal-signals=
3113 [KNL] debug: print fatal signals
3115 If enabled, warn about various signal handling
3116 related application anomalies: too many signals,
3117 too many POSIX.1 timers, fatal signals causing a
3120 If you hit the warning due to signal overflow,
3121 you might want to try "ulimit -i unlimited".
3125 printk.always_kmsg_dump=
3126 Trigger kmsg_dump for cases other than kernel oops or
3128 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3131 printk.time= Show timing data prefixed to each printk message line
3132 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3134 processor.max_cstate= [HW,ACPI]
3135 Limit processor to maximum C-state
3136 max_cstate=9 overrides any DMI blacklist limit.
3138 processor.nocst [HW,ACPI]
3139 Ignore the _CST method to determine C-states,
3140 instead using the legacy FADT method
3142 profile= [KNL] Enable kernel profiling via /proc/profile
3143 Format: [schedule,]<number>
3144 Param: "schedule" - profile schedule points.
3145 Param: <number> - step/bucket size as a power of 2 for
3146 statistical time based profiling.
3147 Param: "sleep" - profile D-state sleeping (millisecs).
3148 Requires CONFIG_SCHEDSTATS
3149 Param: "kvm" - profile VM exits.
3151 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3153 See Documentation/blockdev/ramdisk.txt.
3155 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3156 probe for; one of (bare|imps|exps|lifebook|any).
3157 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3159 psmouse.resetafter= [HW,MOUSE]
3160 Try to reset the device after so many bad packets
3163 [HW,MOUSE] Set desired mouse resolution, in dpi.
3164 psmouse.smartscroll=
3165 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3166 0 = disabled, 1 = enabled (default).
3168 pstore.backend= Specify the name of the pstore backend to use
3171 See Documentation/blockdev/paride.txt.
3174 [KNL] Number of legacy pty's. Overwrites compiled-in
3177 quiet [KNL] Disable most log messages
3182 See Documentation/md.txt.
3184 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3185 See Documentation/blockdev/ramdisk.txt.
3188 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3189 the specified list of CPUs to be no-callback CPUs.
3190 Invocation of these CPUs' RCU callbacks will
3191 be offloaded to "rcuox/N" kthreads created for
3192 that purpose, where "x" is "b" for RCU-bh, "p"
3193 for RCU-preempt, and "s" for RCU-sched, and "N"
3194 is the CPU number. This reduces OS jitter on the
3195 offloaded CPUs, which can be useful for HPC and
3196 real-time workloads. It can also improve energy
3197 efficiency for asymmetric multiprocessors.
3200 Rather than requiring that offloaded CPUs
3201 (specified by rcu_nocbs= above) explicitly
3202 awaken the corresponding "rcuoN" kthreads,
3203 make these kthreads poll for callbacks.
3204 This improves the real-time response for the
3205 offloaded CPUs by relieving them of the need to
3206 wake up the corresponding kthread, but degrades
3207 energy efficiency by requiring that the kthreads
3208 periodically wake up to do the polling.
3210 rcutree.blimit= [KNL]
3211 Set maximum number of finished RCU callbacks to
3212 process in one batch.
3214 rcutree.dump_tree= [KNL]
3215 Dump the structure of the rcu_node combining tree
3216 out at early boot. This is used for diagnostic
3217 purposes, to verify correct tree setup.
3219 rcutree.gp_cleanup_delay= [KNL]
3220 Set the number of jiffies to delay each step of
3221 RCU grace-period cleanup. This only has effect
3222 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3224 rcutree.gp_init_delay= [KNL]
3225 Set the number of jiffies to delay each step of
3226 RCU grace-period initialization. This only has
3227 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3230 rcutree.gp_preinit_delay= [KNL]
3231 Set the number of jiffies to delay each step of
3232 RCU grace-period pre-initialization, that is,
3233 the propagation of recent CPU-hotplug changes up
3234 the rcu_node combining tree. This only has effect
3235 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3237 rcutree.rcu_fanout_exact= [KNL]
3238 Disable autobalancing of the rcu_node combining
3239 tree. This is used by rcutorture, and might
3240 possibly be useful for architectures having high
3241 cache-to-cache transfer latencies.
3243 rcutree.rcu_fanout_leaf= [KNL]
3244 Change the number of CPUs assigned to each
3245 leaf rcu_node structure. Useful for very
3246 large systems, which will choose the value 64,
3247 and for NUMA systems with large remote-access
3248 latencies, which will choose a value aligned
3249 with the appropriate hardware boundaries.
3251 rcutree.jiffies_till_sched_qs= [KNL]
3252 Set required age in jiffies for a
3253 given grace period before RCU starts
3254 soliciting quiescent-state help from
3255 rcu_note_context_switch().
3257 rcutree.jiffies_till_first_fqs= [KNL]
3258 Set delay from grace-period initialization to
3259 first attempt to force quiescent states.
3260 Units are jiffies, minimum value is zero,
3261 and maximum value is HZ.
3263 rcutree.jiffies_till_next_fqs= [KNL]
3264 Set delay between subsequent attempts to force
3265 quiescent states. Units are jiffies, minimum
3266 value is one, and maximum value is HZ.
3268 rcutree.kthread_prio= [KNL,BOOT]
3269 Set the SCHED_FIFO priority of the RCU per-CPU
3270 kthreads (rcuc/N). This value is also used for
3271 the priority of the RCU boost threads (rcub/N)
3272 and for the RCU grace-period kthreads (rcu_bh,
3273 rcu_preempt, and rcu_sched). If RCU_BOOST is
3274 set, valid values are 1-99 and the default is 1
3275 (the least-favored priority). Otherwise, when
3276 RCU_BOOST is not set, valid values are 0-99 and
3277 the default is zero (non-realtime operation).
3279 rcutree.rcu_nocb_leader_stride= [KNL]
3280 Set the number of NOCB kthread groups, which
3281 defaults to the square root of the number of
3282 CPUs. Larger numbers reduces the wakeup overhead
3283 on the per-CPU grace-period kthreads, but increases
3284 that same overhead on each group's leader.
3286 rcutree.qhimark= [KNL]
3287 Set threshold of queued RCU callbacks beyond which
3288 batch limiting is disabled.
3290 rcutree.qlowmark= [KNL]
3291 Set threshold of queued RCU callbacks below which
3292 batch limiting is re-enabled.
3294 rcutree.rcu_idle_gp_delay= [KNL]
3295 Set wakeup interval for idle CPUs that have
3296 RCU callbacks (RCU_FAST_NO_HZ=y).
3298 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3299 Set wakeup interval for idle CPUs that have
3300 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3301 Lazy RCU callbacks are those which RCU can
3302 prove do nothing more than free memory.
3304 rcuperf.gp_exp= [KNL]
3305 Measure performance of expedited synchronous
3306 grace-period primitives.
3308 rcuperf.holdoff= [KNL]
3309 Set test-start holdoff period. The purpose of
3310 this parameter is to delay the start of the
3311 test until boot completes in order to avoid
3314 rcuperf.nreaders= [KNL]
3315 Set number of RCU readers. The value -1 selects
3316 N, where N is the number of CPUs. A value
3317 "n" less than -1 selects N-n+1, where N is again
3318 the number of CPUs. For example, -2 selects N
3319 (the number of CPUs), -3 selects N+1, and so on.
3320 A value of "n" less than or equal to -N selects
3323 rcuperf.nwriters= [KNL]
3324 Set number of RCU writers. The values operate
3325 the same as for rcuperf.nreaders.
3326 N, where N is the number of CPUs
3328 rcuperf.perf_runnable= [BOOT]
3329 Start rcuperf running at boot time.
3331 rcuperf.shutdown= [KNL]
3332 Shut the system down after performance tests
3333 complete. This is useful for hands-off automated
3336 rcuperf.perf_type= [KNL]
3337 Specify the RCU implementation to test.
3339 rcuperf.verbose= [KNL]
3340 Enable additional printk() statements.
3342 rcutorture.cbflood_inter_holdoff= [KNL]
3343 Set holdoff time (jiffies) between successive
3344 callback-flood tests.
3346 rcutorture.cbflood_intra_holdoff= [KNL]
3347 Set holdoff time (jiffies) between successive
3348 bursts of callbacks within a given callback-flood
3351 rcutorture.cbflood_n_burst= [KNL]
3352 Set the number of bursts making up a given
3353 callback-flood test. Set this to zero to
3354 disable callback-flood testing.
3356 rcutorture.cbflood_n_per_burst= [KNL]
3357 Set the number of callbacks to be registered
3358 in a given burst of a callback-flood test.
3360 rcutorture.fqs_duration= [KNL]
3361 Set duration of force_quiescent_state bursts
3364 rcutorture.fqs_holdoff= [KNL]
3365 Set holdoff time within force_quiescent_state bursts
3368 rcutorture.fqs_stutter= [KNL]
3369 Set wait time between force_quiescent_state bursts
3372 rcutorture.gp_cond= [KNL]
3373 Use conditional/asynchronous update-side
3374 primitives, if available.
3376 rcutorture.gp_exp= [KNL]
3377 Use expedited update-side primitives, if available.
3379 rcutorture.gp_normal= [KNL]
3380 Use normal (non-expedited) asynchronous
3381 update-side primitives, if available.
3383 rcutorture.gp_sync= [KNL]
3384 Use normal (non-expedited) synchronous
3385 update-side primitives, if available. If all
3386 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3387 rcutorture.gp_normal=, and rcutorture.gp_sync=
3388 are zero, rcutorture acts as if is interpreted
3389 they are all non-zero.
3391 rcutorture.n_barrier_cbs= [KNL]
3392 Set callbacks/threads for rcu_barrier() testing.
3394 rcutorture.nfakewriters= [KNL]
3395 Set number of concurrent RCU writers. These just
3396 stress RCU, they don't participate in the actual
3397 test, hence the "fake".
3399 rcutorture.nreaders= [KNL]
3400 Set number of RCU readers. The value -1 selects
3401 N-1, where N is the number of CPUs. A value
3402 "n" less than -1 selects N-n-2, where N is again
3403 the number of CPUs. For example, -2 selects N
3404 (the number of CPUs), -3 selects N+1, and so on.
3406 rcutorture.object_debug= [KNL]
3407 Enable debug-object double-call_rcu() testing.
3409 rcutorture.onoff_holdoff= [KNL]
3410 Set time (s) after boot for CPU-hotplug testing.
3412 rcutorture.onoff_interval= [KNL]
3413 Set time (s) between CPU-hotplug operations, or
3414 zero to disable CPU-hotplug testing.
3416 rcutorture.shuffle_interval= [KNL]
3417 Set task-shuffle interval (s). Shuffling tasks
3418 allows some CPUs to go into dyntick-idle mode
3419 during the rcutorture test.
3421 rcutorture.shutdown_secs= [KNL]
3422 Set time (s) after boot system shutdown. This
3423 is useful for hands-off automated testing.
3425 rcutorture.stall_cpu= [KNL]
3426 Duration of CPU stall (s) to test RCU CPU stall
3427 warnings, zero to disable.
3429 rcutorture.stall_cpu_holdoff= [KNL]
3430 Time to wait (s) after boot before inducing stall.
3432 rcutorture.stat_interval= [KNL]
3433 Time (s) between statistics printk()s.
3435 rcutorture.stutter= [KNL]
3436 Time (s) to stutter testing, for example, specifying
3437 five seconds causes the test to run for five seconds,
3438 wait for five seconds, and so on. This tests RCU's
3439 ability to transition abruptly to and from idle.
3441 rcutorture.test_boost= [KNL]
3442 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3443 "Maybe" means test if the RCU implementation
3444 under test support RCU priority boosting.
3446 rcutorture.test_boost_duration= [KNL]
3447 Duration (s) of each individual boost test.
3449 rcutorture.test_boost_interval= [KNL]
3450 Interval (s) between each boost test.
3452 rcutorture.test_no_idle_hz= [KNL]
3453 Test RCU's dyntick-idle handling. See also the
3454 rcutorture.shuffle_interval parameter.
3456 rcutorture.torture_runnable= [BOOT]
3457 Start rcutorture running at boot time.
3459 rcutorture.torture_type= [KNL]
3460 Specify the RCU implementation to test.
3462 rcutorture.verbose= [KNL]
3463 Enable additional printk() statements.
3465 rcupdate.rcu_cpu_stall_suppress= [KNL]
3466 Suppress RCU CPU stall warning messages.
3468 rcupdate.rcu_cpu_stall_timeout= [KNL]
3469 Set timeout for RCU CPU stall warning messages.
3471 rcupdate.rcu_expedited= [KNL]
3472 Use expedited grace-period primitives, for
3473 example, synchronize_rcu_expedited() instead
3474 of synchronize_rcu(). This reduces latency,
3475 but can increase CPU utilization, degrade
3476 real-time latency, and degrade energy efficiency.
3477 No effect on CONFIG_TINY_RCU kernels.
3479 rcupdate.rcu_normal= [KNL]
3480 Use only normal grace-period primitives,
3481 for example, synchronize_rcu() instead of
3482 synchronize_rcu_expedited(). This improves
3483 real-time latency, CPU utilization, and
3484 energy efficiency, but can expose users to
3485 increased grace-period latency. This parameter
3486 overrides rcupdate.rcu_expedited. No effect on
3487 CONFIG_TINY_RCU kernels.
3489 rcupdate.rcu_normal_after_boot= [KNL]
3490 Once boot has completed (that is, after
3491 rcu_end_inkernel_boot() has been invoked), use
3492 only normal grace-period primitives. No effect
3493 on CONFIG_TINY_RCU kernels.
3495 rcupdate.rcu_task_stall_timeout= [KNL]
3496 Set timeout in jiffies for RCU task stall warning
3497 messages. Disable with a value less than or equal
3500 rcupdate.rcu_self_test= [KNL]
3501 Run the RCU early boot self tests
3503 rcupdate.rcu_self_test_bh= [KNL]
3504 Run the RCU bh early boot self tests
3506 rcupdate.rcu_self_test_sched= [KNL]
3507 Run the RCU sched early boot self tests
3511 Run specified binary instead of /init from the ramdisk,
3512 used for early userspace startup. See initrd.
3515 Format (x86 or x86_64):
3516 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3518 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3520 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3521 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3522 reboot_force is either force or not specified,
3523 reboot_cpu is s[mp]#### with #### being the processor
3524 to be used for rebooting.
3527 [KNL, SMP] Set scheduler's default relax_domain_level.
3528 See Documentation/cgroups/cpusets.txt.
3530 relative_sleep_states=
3531 [SUSPEND] Use sleep state labeling where the deepest
3532 state available other than hibernation is always "mem".
3533 Format: { "0" | "1" }
3534 0 -- Traditional sleep state labels.
3535 1 -- Relative sleep state labels.
3537 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3539 reservetop= [X86-32]
3541 Reserves a hole at the top of the kernel virtual
3546 Set the amount of memory to reserve for BIOS at
3547 the bottom of the address space.
3549 reset_devices [KNL] Force drivers to reset the underlying device
3550 during initialization.
3553 Specify the partition device for software suspend
3555 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3557 resume_offset= [SWSUSP]
3558 Specify the offset from the beginning of the partition
3559 given by "resume=" at which the swap header is located,
3560 in <PAGE_SIZE> units (needed only for swap files).
3561 See Documentation/power/swsusp-and-swap-files.txt
3563 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3564 read the resume files
3566 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3567 Useful for devices that are detected asynchronously
3568 (e.g. USB and MMC devices).
3570 hibernate= [HIBERNATION]
3571 noresume Don't check if there's a hibernation image
3572 present during boot.
3573 nocompress Don't compress/decompress hibernation images.
3574 no Disable hibernation and resume.
3576 retain_initrd [RAM] Keep initrd memory after extraction
3578 rfkill.default_state=
3579 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3580 etc. communication is blocked by default.
3583 rfkill.master_switch_mode=
3584 0 The "airplane mode" button does nothing.
3585 1 The "airplane mode" button toggles between everything
3586 blocked and the previous configuration.
3587 2 The "airplane mode" button toggles between everything
3588 blocked and everything unblocked.
3590 rhash_entries= [KNL,NET]
3591 Set number of hash buckets for route cache
3593 ro [KNL] Mount root device read-only on boot
3596 on Mark read-only kernel memory as read-only (default).
3597 off Leave read-only kernel memory writable for debugging.
3600 Enable the uart passthrough on the designated usb port
3601 on Rockchip SoCs. When active, the signals of the
3602 debug-uart get routed to the D+ and D- pins of the usb
3603 port and the regular usb controller gets disabled.
3605 root= [KNL] Root filesystem
3606 See name_to_dev_t comment in init/do_mounts.c.
3608 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3609 mount the root filesystem
3611 rootflags= [KNL] Set root filesystem mount option string
3613 rootfstype= [KNL] Set root filesystem type
3615 rootwait [KNL] Wait (indefinitely) for root device to show up.
3616 Useful for devices that are detected asynchronously
3617 (e.g. USB and MMC devices).
3619 rproc_mem=nn[KMG][@address]
3620 [KNL,ARM,CMA] Remoteproc physical memory block.
3621 Memory area to be used by remote processor image,
3624 rw [KNL] Mount root device read-write on boot
3626 S [KNL] Run init in single mode
3628 s390_iommu= [HW,S390]
3629 Set s390 IOTLB flushing mode
3631 With strict flushing every unmap operation will result in
3632 an IOTLB flush. Default is lazy flushing before reuse,
3636 See drivers/net/irda/sa1100_ir.c.
3638 sbni= [NET] Granch SBNI12 leased line adapter
3640 sched_debug [KNL] Enables verbose scheduler debug messages.
3642 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3643 Allowed values are enable and disable. This feature
3644 incurs a small amount of overhead in the scheduler
3645 but is useful for debugging and performance tuning.
3647 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3648 xtime_lock contention on larger systems, and/or RCU lock
3649 contention on all systems with CONFIG_MAXSMP set.
3650 Format: { "0" | "1" }
3651 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3653 Note: increases power consumption, thus should only be
3654 enabled if running jitter sensitive (HPC/RT) workloads.
3656 security= [SECURITY] Choose a security module to enable at boot.
3657 If this boot parameter is not specified, only the first
3658 security module asking for security registration will be
3659 loaded. An invalid security module name will be treated
3660 as if no module has been chosen.
3662 selinux= [SELINUX] Disable or enable SELinux at boot time.
3663 Format: { "0" | "1" }
3664 See security/selinux/Kconfig help text.
3667 Default value is set via kernel config option.
3668 If enabled at boot time, /selinux/disable can be used
3669 later to disable prior to initial policy load.
3671 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3672 Format: { "0" | "1" }
3673 See security/apparmor/Kconfig help text
3676 Default value is set via kernel config option.
3678 serialnumber [BUGS=X86-32]
3681 Maximal number of shapers.
3683 show_msr= [x86] show boot-time MSR settings
3684 Format: { <integer> }
3685 Show boot-time (BIOS-initialized) MSR settings.
3686 The parameter means the number of CPUs to show,
3687 for example 1 means boot CPU only.
3695 Disable merging of slabs with similar size. May be
3696 necessary if there is some reason to distinguish
3697 allocs to different slabs. Debug options disable
3698 merging on their own.
3699 For more information see Documentation/vm/slub.txt.
3701 slab_max_order= [MM, SLAB]
3702 Determines the maximum allowed order for slabs.
3703 A high setting may cause OOMs due to memory
3704 fragmentation. Defaults to 1 for systems with
3705 more than 32MB of RAM, 0 otherwise.
3707 slub_debug[=options[,slabs]] [MM, SLUB]
3708 Enabling slub_debug allows one to determine the
3709 culprit if slab objects become corrupted. Enabling
3710 slub_debug can create guard zones around objects and
3711 may poison objects when not in use. Also tracks the
3712 last alloc / free. For more information see
3713 Documentation/vm/slub.txt.
3715 slub_max_order= [MM, SLUB]
3716 Determines the maximum allowed order for slabs.
3717 A high setting may cause OOMs due to memory
3718 fragmentation. For more information see
3719 Documentation/vm/slub.txt.
3721 slub_min_objects= [MM, SLUB]
3722 The minimum number of objects per slab. SLUB will
3723 increase the slab order up to slub_max_order to
3724 generate a sufficiently large slab able to contain
3725 the number of objects indicated. The higher the number
3726 of objects the smaller the overhead of tracking slabs
3727 and the less frequently locks need to be acquired.
3728 For more information see Documentation/vm/slub.txt.
3730 slub_min_order= [MM, SLUB]
3731 Determines the minimum page order for slabs. Must be
3732 lower than slub_max_order.
3733 For more information see Documentation/vm/slub.txt.
3735 slub_nomerge [MM, SLUB]
3736 Same with slab_nomerge. This is supported for legacy.
3737 See slab_nomerge for more information.
3740 Format: <io1>[,<io2>[,...,<io8>]]
3742 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3743 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3744 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3745 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3746 smsc-ircc2.ircc_irq= [HW] IRQ line
3747 smsc-ircc2.ircc_dma= [HW] DMA channel
3748 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3749 0: Toshiba Satellite 1800 (GP data pin select)
3750 1: Fast pin select (default)
3754 [KNL] Should the soft-lockup detector generate panics.
3757 softlockup_all_cpu_backtrace=
3758 [KNL] Should the soft-lockup detector generate
3759 backtraces on all cpus.
3762 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3763 See Documentation/laptops/sonypi.txt
3765 spia_io_base= [HW,MTD]
3771 Enabled the stack tracer on boot up.
3773 stacktrace_filter=[function-list]
3774 [FTRACE] Limit the functions that the stack tracer
3775 will trace at boot up. function-list is a comma separated
3776 list of functions. This list can be changed at run
3777 time by the stack_trace_filter file in the debugfs
3778 tracing directory. Note, this enables stack tracing
3779 and the stacktrace above is not needed.
3783 Set the STI (builtin display/keyboard on the HP-PARISC
3784 machines) console (graphic card) which should be used
3785 as the initial boot-console.
3786 See also comment in drivers/video/console/sticore.c.
3789 See comment in drivers/video/console/sticore.c.
3792 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3794 sunrpc.min_resvport=
3795 sunrpc.max_resvport=
3797 SunRPC servers often require that client requests
3798 originate from a privileged port (i.e. a port in the
3799 range 0 < portnr < 1024).
3800 An administrator who wishes to reserve some of these
3801 ports for other uses may adjust the range that the
3802 kernel's sunrpc client considers to be privileged
3803 using these two parameters to set the minimum and
3804 maximum port values.
3808 Control how the NFS server code allocates CPUs to
3809 service thread pools. Depending on how many NICs
3810 you have and where their interrupts are bound, this
3811 option will affect which CPUs will do NFS serving.
3812 Note: this parameter cannot be changed while the
3813 NFS server is running.
3815 auto the server chooses an appropriate mode
3816 automatically using heuristics
3817 global a single global pool contains all CPUs
3818 percpu one pool for each CPU
3819 pernode one pool for each NUMA node (equivalent
3820 to global on non-NUMA machines)
3822 sunrpc.tcp_slot_table_entries=
3823 sunrpc.udp_slot_table_entries=
3825 Sets the upper limit on the number of simultaneous
3826 RPC calls that can be sent from the client to a
3827 server. Increasing these values may allow you to
3828 improve throughput, but will also increase the
3829 amount of memory reserved for use by the client.
3831 suspend.pm_test_delay=
3833 Sets the number of seconds to remain in a suspend test
3834 mode before resuming the system (see
3835 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3836 is set. Default value is 5.
3839 [KNL] Enable accounting of swap in memory resource
3840 controller if no parameter or 1 is given or disable
3841 it if 0 is given (See Documentation/cgroups/memory.txt)
3843 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3844 Format: { <int> | force }
3845 <int> -- Number of I/O TLB slabs
3846 force -- force using of bounce buffers even if they
3847 wouldn't be automatically used by the kernel
3851 sysfs.deprecated=0|1 [KNL]
3852 Enable/disable old style sysfs layout for old udev
3853 on older distributions. When this option is enabled
3854 very new udev will not work anymore. When this option
3855 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3856 in older udev will not work anymore.
3857 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3858 the kernel configuration.
3860 sysrq_always_enabled
3862 Ignore sysrq setting - this boot parameter will
3863 neutralize any effect of /proc/sys/kernel/sysrq.
3864 Useful for debugging.
3866 tcpmhash_entries= [KNL,NET]
3867 Set the number of tcp_metrics_hash slots.
3868 Default value is 8192 or 16384 depending on total
3869 ram pages. This is used to specify the TCP metrics
3870 cache size. See Documentation/networking/ip-sysctl.txt
3871 "tcp_no_metrics_save" section for more details.
3875 test_suspend= [SUSPEND][,N]
3876 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3877 standby suspend) or "freeze" (for suspend type freeze)
3878 as the system sleep state during system startup with
3879 the optional capability to repeat N number of times.
3880 The system is woken from this state using a
3881 wakeup-capable RTC alarm.
3883 thash_entries= [KNL,NET]
3884 Set number of hash buckets for TCP connection
3886 thermal.act= [HW,ACPI]
3887 -1: disable all active trip points in all thermal zones
3888 <degrees C>: override all lowest active trip points
3890 thermal.crt= [HW,ACPI]
3891 -1: disable all critical trip points in all thermal zones
3892 <degrees C>: override all critical trip points
3894 thermal.nocrt= [HW,ACPI]
3895 Set to disable actions on ACPI thermal zone
3896 critical and hot trip points.
3898 thermal.off= [HW,ACPI]
3899 1: disable ACPI thermal control
3901 thermal.psv= [HW,ACPI]
3902 -1: disable all passive trip points
3903 <degrees C>: override all passive trip points to this
3906 thermal.tzp= [HW,ACPI]
3907 Specify global default ACPI thermal zone polling rate
3908 <deci-seconds>: poll all this frequency
3909 0: no polling (default)
3912 Force threading of all interrupt handlers except those
3913 marked explicitly IRQF_NO_THREAD.
3916 Enable the Transcendent memory driver if built-in.
3918 tmem.cleancache=0|1 [KNL, XEN]
3919 Default is on (1). Disable the usage of the cleancache
3920 API to send anonymous pages to the hypervisor.
3922 tmem.frontswap=0|1 [KNL, XEN]
3923 Default is on (1). Disable the usage of the frontswap
3924 API to send swap pages to the hypervisor. If disabled
3925 the selfballooning and selfshrinking are force disabled.
3927 tmem.selfballooning=0|1 [KNL, XEN]
3928 Default is on (1). Disable the driving of swap pages
3931 tmem.selfshrinking=0|1 [KNL, XEN]
3932 Default is on (1). Partial swapoff that immediately
3933 transfers pages from Xen hypervisor back to the
3934 kernel based on different criteria.
3938 Specify if the kernel should make use of the cpu
3939 topology information if the hardware supports this.
3940 The scheduler will make use of this information and
3941 e.g. base its process migration decisions on it.
3944 topology_updates= [KNL, PPC, NUMA]
3946 Specify if the kernel should ignore (off)
3947 topology updates sent by the hypervisor to this
3952 tpm_suspend_pcr=[HW,TPM]
3953 Format: integer pcr id
3954 Specify that at suspend time, the tpm driver
3955 should extend the specified pcr with zeros,
3956 as a workaround for some chips which fail to
3957 flush the last written pcr on TPM_SaveState.
3958 This will guarantee that all the other pcrs
3961 trace_buf_size=nn[KMG]
3962 [FTRACE] will set tracing buffer size on each cpu.
3964 trace_event=[event-list]
3965 [FTRACE] Set and start specified trace events in order
3966 to facilitate early boot debugging.
3967 See also Documentation/trace/events.txt
3969 trace_options=[option-list]
3970 [FTRACE] Enable or disable tracer options at boot.
3971 The option-list is a comma delimited list of options
3972 that can be enabled or disabled just as if you were
3973 to echo the option name into
3975 /sys/kernel/debug/tracing/trace_options
3977 For example, to enable stacktrace option (to dump the
3978 stack trace of each event), add to the command line:
3980 trace_options=stacktrace
3982 See also Documentation/trace/ftrace.txt "trace options"
3986 Have the tracepoints sent to printk as well as the
3987 tracing ring buffer. This is useful for early boot up
3988 where the system hangs or reboots and does not give the
3989 option for reading the tracing buffer or performing a
3990 ftrace_dump_on_oops.
3992 To turn off having tracepoints sent to printk,
3993 echo 0 > /proc/sys/kernel/tracepoint_printk
3994 Note, echoing 1 into this file without the
3995 tracepoint_printk kernel cmdline option has no effect.
3999 Having tracepoints sent to printk() and activating high
4000 frequency tracepoints such as irq or sched, can cause
4001 the system to live lock.
4004 [FTRACE] enable this option to disable tracing when a
4005 warning is hit. This turns off "tracing_on". Tracing can
4006 be enabled again by echoing '1' into the "tracing_on"
4007 file located in /sys/kernel/debug/tracing/
4009 This option is useful, as it disables the trace before
4010 the WARNING dump is called, which prevents the trace to
4011 be filled with content caused by the warning output.
4013 This option can also be set at run time via the sysctl
4014 option: kernel/traceoff_on_warning
4016 transparent_hugepage=
4018 Format: [always|madvise|never]
4019 Can be used to control the default behavior of the system
4020 with respect to transparent hugepages.
4021 See Documentation/vm/transhuge.txt for more details.
4023 tsc= Disable clocksource stability checks for TSC.
4025 [x86] reliable: mark tsc clocksource as reliable, this
4026 disables clocksource verification at runtime, as well
4027 as the stability checks done at bootup. Used to enable
4028 high-resolution timer mode on older hardware, and in
4029 virtualized environment.
4030 [x86] noirqtime: Do not use TSC to do irq accounting.
4031 Used to run time disable IRQ_TIME_ACCOUNTING on any
4032 platforms where RDTSC is slow and this accounting
4035 turbografx.map[2|3]= [HW,JOY]
4036 TurboGraFX parallel port interface
4038 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4039 See also Documentation/input/joystick-parport.txt
4041 udbg-immortal [PPC] When debugging early kernel crashes that
4042 happen after console_init() and before a proper
4043 console driver takes over, this boot options might
4044 help "seeing" what's going on.
4046 uhash_entries= [KNL,NET]
4047 Set number of hash buckets for UDP/UDP-Lite connections
4050 [USB] Ignore overcurrent events (default N).
4051 Some badly-designed motherboards generate lots of
4052 bogus events, for ports that aren't wired to
4053 anything. Set this parameter to avoid log spamming.
4054 Note that genuine overcurrent events won't be
4058 [X86] Cause panic on unknown NMI.
4060 usbcore.authorized_default=
4061 [USB] Default USB device authorization:
4062 (default -1 = authorized except for wireless USB,
4063 0 = not authorized, 1 = authorized)
4065 usbcore.autosuspend=
4066 [USB] The autosuspend time delay (in seconds) used
4067 for newly-detected USB devices (default 2). This
4068 is the time required before an idle device will be
4069 autosuspended. Devices for which the delay is set
4070 to a negative value won't be autosuspended at all.
4072 usbcore.usbfs_snoop=
4073 [USB] Set to log all usbfs traffic (default 0 = off).
4075 usbcore.usbfs_snoop_max=
4076 [USB] Maximum number of bytes to snoop in each URB
4079 usbcore.blinkenlights=
4080 [USB] Set to cycle leds on hubs (default 0 = off).
4082 usbcore.old_scheme_first=
4083 [USB] Start with the old device initialization
4084 scheme (default 0 = off).
4086 usbcore.usbfs_memory_mb=
4087 [USB] Memory limit (in MB) for buffers allocated by
4088 usbfs (default = 16, 0 = max = 2047).
4090 usbcore.use_both_schemes=
4091 [USB] Try the other device initialization scheme
4092 if the first one fails (default 1 = enabled).
4094 usbcore.initial_descriptor_timeout=
4095 [USB] Specifies timeout for the initial 64-byte
4096 USB_REQ_GET_DESCRIPTOR request in milliseconds
4097 (default 5000 = 5.0 seconds).
4099 usbcore.nousb [USB] Disable the USB subsystem
4102 [USBHID] The interval which mice are to be polled at.
4104 usb-storage.delay_use=
4105 [UMS] The delay in seconds before a new device is
4106 scanned for Logical Units (default 1).
4109 [UMS] A list of quirks entries to supplement or
4110 override the built-in unusual_devs list. List
4111 entries are separated by commas. Each entry has
4112 the form VID:PID:Flags where VID and PID are Vendor
4113 and Product ID values (4-digit hex numbers) and
4114 Flags is a set of characters, each corresponding
4115 to a common usb-storage quirk flag as follows:
4116 a = SANE_SENSE (collect more than 18 bytes
4118 b = BAD_SENSE (don't collect more than 18
4119 bytes of sense data);
4120 c = FIX_CAPACITY (decrease the reported
4121 device capacity by one sector);
4122 d = NO_READ_DISC_INFO (don't use
4123 READ_DISC_INFO command);
4124 e = NO_READ_CAPACITY_16 (don't use
4125 READ_CAPACITY_16 command);
4126 f = NO_REPORT_OPCODES (don't use report opcodes
4128 g = MAX_SECTORS_240 (don't transfer more than
4129 240 sectors at a time, uas only);
4130 h = CAPACITY_HEURISTICS (decrease the
4131 reported device capacity by one
4132 sector if the number is odd);
4133 i = IGNORE_DEVICE (don't bind to this
4135 j = NO_REPORT_LUNS (don't use report luns
4137 l = NOT_LOCKABLE (don't try to lock and
4138 unlock ejectable media);
4139 m = MAX_SECTORS_64 (don't transfer more
4140 than 64 sectors = 32 KB at a time);
4141 n = INITIAL_READ10 (force a retry of the
4142 initial READ(10) command);
4143 o = CAPACITY_OK (accept the capacity
4144 reported by the device);
4145 p = WRITE_CACHE (the device cache is ON
4147 r = IGNORE_RESIDUE (the device reports
4148 bogus residue values);
4149 s = SINGLE_LUN (the device has only one
4151 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4152 commands, uas only);
4153 u = IGNORE_UAS (don't bind to the uas driver);
4154 w = NO_WP_DETECT (don't test whether the
4155 medium is write-protected).
4156 Example: quirks=0419:aaf5:rl,0421:0433:rc
4158 user_debug= [KNL,ARM]
4160 See arch/arm/Kconfig.debug help text.
4161 1 - undefined instruction events
4163 4 - invalid data aborts
4166 Example: user_debug=31
4169 [X86] Flags controlling user PTE allocations.
4171 nohigh = do not allocate PTE pages in
4172 HIGHMEM regardless of setting
4176 On X86_32, this is an alias for vdso32=. Otherwise:
4178 vdso=1: enable VDSO (the default)
4179 vdso=0: disable VDSO mapping
4181 vdso32= [X86] Control the 32-bit vDSO
4182 vdso32=1: enable 32-bit VDSO
4183 vdso32=0 or vdso32=2: disable 32-bit VDSO
4185 See the help text for CONFIG_COMPAT_VDSO for more
4186 details. If CONFIG_COMPAT_VDSO is set, the default is
4187 vdso32=0; otherwise, the default is vdso32=1.
4189 For compatibility with older kernels, vdso32=2 is an
4192 Try vdso32=0 if you encounter an error that says:
4193 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4196 vector=percpu: enable percpu vector domain
4198 video= [FB] Frame buffer configuration
4199 See Documentation/fb/modedb.txt.
4201 video.brightness_switch_enabled= [0,1]
4202 If set to 1, on receiving an ACPI notify event
4203 generated by hotkey, video driver will adjust brightness
4204 level and then send out the event to user space through
4205 the allocated input device; If set to 0, video driver
4206 will only send out the event without touching backlight
4211 [VMMIO] Memory mapped virtio (platform) device.
4213 <size>@<baseaddr>:<irq>[:<id>]
4215 <size> := size (can use standard suffixes
4217 <baseaddr> := physical base address
4218 <irq> := interrupt number (as passed to
4220 <id> := (optional) platform device id
4222 virtio_mmio.device=1K@0x100b0000:48:7
4224 Can be used multiple times for multiple devices.
4226 vga= [BOOT,X86-32] Select a particular video mode
4227 See Documentation/x86/boot.txt and
4228 Documentation/svga.txt.
4229 Use vga=ask for menu.
4230 This is actually a boot loader parameter; the value is
4231 passed to the kernel using a special protocol.
4233 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4234 size of <nn>. This can be used to increase the
4235 minimum size (128MB on x86). It can also be used to
4236 decrease the size and leave more room for directly
4239 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4242 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4245 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4249 Controls the behavior of vsyscalls (i.e. calls to
4250 fixed addresses of 0xffffffffff600x00 from legacy
4251 code). Most statically-linked binaries and older
4252 versions of glibc use these calls. Because these
4253 functions are at fixed addresses, they make nice
4254 targets for exploits that can control RIP.
4256 emulate [default] Vsyscalls turn into traps and are
4257 emulated reasonably safely.
4259 native Vsyscalls are native syscall instructions.
4260 This is a little bit faster than trapping
4261 and makes a few dynamic recompilers work
4262 better than they would in emulation mode.
4263 It also makes exploits much easier to write.
4265 none Vsyscalls don't work at all. This makes
4266 them quite hard to use for exploits but
4267 might break your system.
4269 vt.color= [VT] Default text color.
4270 Format: 0xYX, X = foreground, Y = background.
4271 Default: 0x07 = light gray on black.
4273 vt.cur_default= [VT] Default cursor shape.
4274 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4275 the parameters of the <Esc>[?A;B;Cc escape sequence;
4276 see VGA-softcursor.txt. Default: 2 = underline.
4278 vt.default_blu= [VT]
4279 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4280 Change the default blue palette of the console.
4281 This is a 16-member array composed of values
4284 vt.default_grn= [VT]
4285 Format: <green0>,<green1>,<green2>,...,<green15>
4286 Change the default green palette of the console.
4287 This is a 16-member array composed of values
4290 vt.default_red= [VT]
4291 Format: <red0>,<red1>,<red2>,...,<red15>
4292 Change the default red palette of the console.
4293 This is a 16-member array composed of values
4299 Set system-wide default UTF-8 mode for all tty's.
4300 Default is 1, i.e. UTF-8 mode is enabled for all
4301 newly opened terminals.
4303 vt.global_cursor_default=
4306 Set system-wide default for whether a cursor
4307 is shown on new VTs. Default is -1,
4308 i.e. cursors will be created by default unless
4309 overridden by individual drivers. 0 will hide
4310 cursors, 1 will display them.
4312 vt.italic= [VT] Default color for italic text; 0-15.
4315 vt.underline= [VT] Default color for underlined text; 0-15.
4318 watchdog timers [HW,WDT] For information on watchdog timers,
4319 see Documentation/watchdog/watchdog-parameters.txt
4320 or other driver-specific files in the
4321 Documentation/watchdog/ directory.
4323 workqueue.watchdog_thresh=
4324 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4325 warn stall conditions and dump internal state to
4326 help debugging. 0 disables workqueue stall
4327 detection; otherwise, it's the stall threshold
4328 duration in seconds. The default value is 30 and
4329 it can be updated at runtime by writing to the
4330 corresponding sysfs file.
4332 workqueue.disable_numa
4333 By default, all work items queued to unbound
4334 workqueues are affine to the NUMA nodes they're
4335 issued on, which results in better behavior in
4336 general. If NUMA affinity needs to be disabled for
4337 whatever reason, this option can be used. Note
4338 that this also can be controlled per-workqueue for
4339 workqueues visible under /sys/bus/workqueue/.
4341 workqueue.power_efficient
4342 Per-cpu workqueues are generally preferred because
4343 they show better performance thanks to cache
4344 locality; unfortunately, per-cpu workqueues tend to
4345 be more power hungry than unbound workqueues.
4347 Enabling this makes the per-cpu workqueues which
4348 were observed to contribute significantly to power
4349 consumption unbound, leading to measurably lower
4350 power usage at the cost of small performance
4353 The default value of this parameter is determined by
4354 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4356 workqueue.debug_force_rr_cpu
4357 Workqueue used to implicitly guarantee that work
4358 items queued without explicit CPU specified are put
4359 on the local CPU. This guarantee is no longer true
4360 and while local CPU is still preferred work items
4361 may be put on foreign CPUs. This debug option
4362 forces round-robin CPU selection to flush out
4363 usages which depend on the now broken guarantee.
4364 When enabled, memory and cache locality will be
4367 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4368 default x2apic cluster mode on platforms
4371 x86_intel_mid_timer= [X86-32,APBT]
4372 Choose timer option for x86 Intel MID platform.
4373 Two valid options are apbt timer only and lapic timer
4374 plus one apbt timer for broadcast timer.
4375 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4377 xen_512gb_limit [KNL,X86-64,XEN]
4378 Restricts the kernel running paravirtualized under Xen
4379 to use only up to 512 GB of RAM. The reason to do so is
4380 crash analysis tools and Xen tools for doing domain
4381 save/restore/migration must be enabled to handle larger
4384 xen_emul_unplug= [HW,X86,XEN]
4385 Unplug Xen emulated devices
4386 Format: [unplug0,][unplug1]
4387 ide-disks -- unplug primary master IDE devices
4388 aux-ide-disks -- unplug non-primary-master IDE devices
4389 nics -- unplug network devices
4390 all -- unplug all emulated devices (NICs and IDE disks)
4391 unnecessary -- unplugging emulated devices is
4392 unnecessary even if the host did not respond to
4394 never -- do not unplug even if version check succeeds
4396 xen_nopvspin [X86,XEN]
4397 Disables the ticketlock slowpath using Xen PV
4401 Disables the PV optimizations forcing the HVM guest to
4402 run as generic HVM guest with no PV drivers.
4404 xirc2ps_cs= [NET,PCMCIA]
4406 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4408 ______________________________________________________________________
4412 Add more DRM drivers.
projects / linux-2.6-block.git / blob