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.
586 Disable BERT OS support on buggy BIOSes.
588 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
589 bttv.radio= Most important insmod options are available as
591 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
594 bulk_remove=off [PPC] This parameter disables the use of the pSeries
595 firmware feature for flushing multiple hpte entries
598 c101= [NET] Moxa C101 synchronous serial card
600 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
601 Sometimes CPU hardware bugs make them report the cache
602 size incorrectly. The kernel will attempt work arounds
603 to fix known problems, but for some CPUs it is not
604 possible to determine what the correct size should be.
605 This option provides an override for these situations.
607 ca_keys= [KEYS] This parameter identifies a specific key(s) on
608 the system trusted keyring to be used for certificate
610 format: { id:<keyid> | builtin }
612 cca= [MIPS] Override the kernel pages' cache coherency
613 algorithm. Accepted values range from 0 to 7
614 inclusive. See arch/mips/include/asm/pgtable-bits.h
615 for platform specific values (SB1, Loongson3 and
618 ccw_timeout_log [S390]
619 See Documentation/s390/CommonIO for details.
621 cgroup_disable= [KNL] Disable a particular controller
622 Format: {name of the controller(s) to disable}
623 The effects of cgroup_disable=foo are:
624 - foo isn't auto-mounted if you mount all cgroups in
626 - foo isn't visible as an individually mountable
628 {Currently only "memory" controller deal with this and
629 cut the overhead, others just disable the usage. So
630 only cgroup_disable=memory is actually worthy}
632 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
633 Format: { controller[,controller...] | "all" }
634 Like cgroup_disable, but only applies to cgroup v1;
635 the blacklisted controllers remain available in cgroup2.
637 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
639 nosocket -- Disable socket memory accounting.
640 nokmem -- Disable kernel memory accounting.
642 checkreqprot [SELINUX] Set initial checkreqprot flag value.
643 Format: { "0" | "1" }
644 See security/selinux/Kconfig help text.
645 0 -- check protection applied by kernel (includes
646 any implied execute protection).
647 1 -- check protection requested by application.
648 Default value is set via a kernel config option.
649 Value can be changed at runtime via
650 /selinux/checkreqprot.
653 See Documentation/s390/CommonIO for details.
656 Prevents the clock framework from automatically gating
657 clocks that have not been explicitly enabled by a Linux
658 device driver but are enabled in hardware at reset or
659 by the bootloader/firmware. Note that this does not
660 force such clocks to be always-on nor does it reserve
661 those clocks in any way. This parameter is useful for
662 debug and development, but should not be needed on a
663 platform with proper driver support. For more
664 information, see Documentation/clk.txt.
666 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
668 Forces specified clocksource (if available) to be used
669 when calculating gettimeofday(). If specified
670 clocksource is not available, it defaults to PIT.
671 Format: { pit | tsc | cyclone | pmtmr }
673 clocksource= Override the default clocksource
675 Override the default clocksource and use the clocksource
676 with the name specified.
677 Some clocksource names to choose from, depending on
679 [all] jiffies (this is the base, fallback clocksource)
681 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
682 pxa_timer,timer3,32k_counter,timer0_1
684 [X86-32] pit,hpet,tsc;
685 scx200_hrt on Geode; cyclone on IBM x440
693 clearcpuid=BITNUM [X86]
694 Disable CPUID feature X for the kernel. See
695 arch/x86/include/asm/cpufeatures.h for the valid bit
696 numbers. Note the Linux specific bits are not necessarily
697 stable over kernel options, but the vendor specific
699 Also note that user programs calling CPUID directly
700 or using the feature without checking anything
701 will still see it. This just prevents it from
702 being used by the kernel or shown in /proc/cpuinfo.
703 Also note the kernel might malfunction if you disable
706 cma=nn[MG]@[start[MG][-end[MG]]]
708 Sets the size of kernel global memory area for
709 contiguous memory allocations and optionally the
710 placement constraint by the physical address range of
711 memory allocations. A value of 0 disables CMA
712 altogether. For more information, see
713 include/linux/dma-contiguous.h
715 cmo_free_hint= [PPC] Format: { yes | no }
716 Specify whether pages are marked as being inactive
717 when they are freed. This is used in CMO environments
718 to determine OS memory pressure for page stealing by
722 coherent_pool=nn[KMG] [ARM,KNL]
723 Sets the size of memory pool for coherent, atomic dma
724 allocations, by default set to 256K.
726 code_bytes [X86] How many bytes of object code to print
731 com20020= [HW,NET] ARCnet - COM20020 chipset
733 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
735 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
739 ARCnet - COM90xx chipset (memory-mapped buffers)
740 Format: <io>[,<irq>[,<memstart>]]
742 condev= [HW,S390] console device
745 console= [KNL] Output console device and options.
747 tty<n> Use the virtual console device <n>.
751 Use the specified serial port. The options are of
752 the form "bbbbpnf", where "bbbb" is the baud rate,
753 "p" is parity ("n", "o", or "e"), "n" is number of
754 bits, and "f" is flow control ("r" for RTS or
755 omit it). Default is "9600n8".
757 See Documentation/serial-console.txt for more
759 Documentation/networking/netconsole.txt for an
762 uart[8250],io,<addr>[,options]
763 uart[8250],mmio,<addr>[,options]
764 uart[8250],mmio16,<addr>[,options]
765 uart[8250],mmio32,<addr>[,options]
766 uart[8250],0x<addr>[,options]
767 Start an early, polled-mode console on the 8250/16550
768 UART at the specified I/O port or MMIO address,
769 switching to the matching ttyS device later.
770 MMIO inter-register address stride is either 8-bit
771 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
772 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
773 to be equivalent to 'mmio'. 'options' are specified in
774 the same format described for ttyS above; if unspecified,
775 the h/w is not re-initialized.
777 hvc<n> Use the hypervisor console device <n>. This is for
778 both Xen and PowerPC hypervisors.
780 If the device connected to the port is not a TTY but a braille
781 device, prepend "brl," before the device type, for instance
783 For now, only VisioBraille is supported.
785 consoleblank= [KNL] The console blank (screen saver) timeout in
786 seconds. Defaults to 10*60 = 10mins. A value of 0
787 disables the blank timer.
790 [KNL] Change the default value for
791 /proc/<pid>/coredump_filter.
792 See also Documentation/filesystems/proc.txt.
794 cpuidle.off=1 [CPU_IDLE]
795 disable the cpuidle sub-system
798 [X86] Delay for N microsec between assert and de-assert
799 of APIC INIT to start processors. This delay occurs
800 on every CPU online, such as boot, and resume from suspend.
803 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
805 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
807 crashkernel=size[KMG][@offset[KMG]]
808 [KNL] Using kexec, Linux can switch to a 'crash kernel'
809 upon panic. This parameter reserves the physical
810 memory region [offset, offset + size] for that kernel
811 image. If '@offset' is omitted, then a suitable offset
812 is selected automatically. Check
813 Documentation/kdump/kdump.txt for further details.
815 crashkernel=range1:size1[,range2:size2,...][@offset]
816 [KNL] Same as above, but depends on the memory
817 in the running system. The syntax of range is
818 start-[end] where start and end are both
819 a memory unit (amount[KMG]). See also
820 Documentation/kdump/kdump.txt for an example.
822 crashkernel=size[KMG],high
823 [KNL, x86_64] range could be above 4G. Allow kernel
824 to allocate physical memory region from top, so could
825 be above 4G if system have more than 4G ram installed.
826 Otherwise memory region will be allocated below 4G, if
828 It will be ignored if crashkernel=X is specified.
829 crashkernel=size[KMG],low
830 [KNL, x86_64] range under 4G. When crashkernel=X,high
831 is passed, kernel could allocate physical memory region
832 above 4G, that cause second kernel crash on system
833 that require some amount of low memory, e.g. swiotlb
834 requires at least 64M+32K low memory, also enough extra
835 low memory is needed to make sure DMA buffers for 32-bit
836 devices won't run out. Kernel would try to allocate at
837 at least 256M below 4G automatically.
838 This one let user to specify own low range under 4G
839 for second kernel instead.
840 0: to disable low allocation.
841 It will be ignored when crashkernel=X,high is not used
842 or memory reserved is below 4G.
845 [KNL] Disable crypto self-tests
850 cs89x0_media= [HW,NET]
851 Format: { rj45 | aui | bnc }
854 See header of drivers/s390/block/dasd_devmap.c.
856 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
857 (one device per port)
858 Format: <port#>,<type>
859 See also Documentation/input/joystick-parport.txt
861 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
862 time. See Documentation/dynamic-debug-howto.txt for
863 details. Deprecated, see dyndbg.
865 debug [KNL] Enable kernel debugging (events log level).
868 [KNL] verbose self-tests
870 Print debugging info while doing the locking API
872 We default to 0 (no extra messages), setting it to
873 1 will print _a lot_ more information - normally
874 only useful to kernel developers.
876 debug_objects [KNL] Enable object debugging
879 [KNL] Disable object debugging
881 debug_guardpage_minorder=
882 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
883 parameter allows control of the order of pages that will
884 be intentionally kept free (and hence protected) by the
885 buddy allocator. Bigger value increase the probability
886 of catching random memory corruption, but reduce the
887 amount of memory for normal system use. The maximum
888 possible value is MAX_ORDER/2. Setting this parameter
889 to 1 or 2 should be enough to identify most random
890 memory corruption problems caused by bugs in kernel or
891 driver code when a CPU writes to (or reads from) a
892 random memory location. Note that there exists a class
893 of memory corruptions problems caused by buggy H/W or
894 F/W or by drivers badly programing DMA (basically when
895 memory is written at bus level and the CPU MMU is
896 bypassed) which are not detectable by
897 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
898 tracking down these problems.
901 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
902 parameter enables the feature at boot time. In
903 default, it is disabled. We can avoid allocating huge
904 chunk of memory for debug pagealloc if we don't enable
905 it at boot time and the system will work mostly same
906 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
907 on: enable the feature
909 debugpat [X86] Enable PAT debugging
911 decnet.addr= [HW,NET]
912 Format: <area>[,<node>]
913 See also Documentation/networking/decnet.txt.
916 [same as hugepagesz=] The size of the default
917 HugeTLB page size. This is the size represented by
918 the legacy /proc/ hugepages APIs, used for SHM, and
919 default size when mounting hugetlbfs filesystems.
920 Defaults to the default architecture's huge page size
924 Set number of hash buckets for dentry cache.
927 See Documentation/networking/ipv6.txt.
929 disable_cpu_apicid= [X86,APIC,SMP]
931 The number of initial APIC ID for the
932 corresponding CPU to be disabled at boot,
933 mostly used for the kdump 2nd kernel to
934 disable BSP to wake up multiple CPUs without
935 causing system reset or hang due to sending
938 disable_ddw [PPC/PSERIES]
939 Disable Dynamic DMA Window support. Use this if
940 to workaround buggy firmware.
943 See Documentation/networking/ipv6.txt.
945 disable_mtrr_cleanup [X86]
946 The kernel tries to adjust MTRR layout from continuous
947 to discrete, to make X server driver able to add WB
948 entry later. This parameter disables that.
950 disable_mtrr_trim [X86, Intel and AMD only]
951 By default the kernel will trim any uncacheable
952 memory out of your available memory pool based on
953 MTRR settings. This parameter disables that behavior,
954 possibly causing your machine to run very slowly.
956 disable_timer_pin_1 [X86]
957 Disable PIN 1 of APIC timer
958 Can be useful to work around chipset bugs.
960 dis_ucode_ldr [X86] Disable the microcode loader.
962 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
963 this option disables the debugging code at boot.
965 dma_debug_entries=<number>
966 This option allows to tune the number of preallocated
967 entries for DMA-API debugging code. One entry is
968 required per DMA-API allocation. Use this if the
969 DMA-API debugging code disables itself because the
970 architectural default is too low.
972 dma_debug_driver=<driver_name>
973 With this option the DMA-API debugging driver
974 filter feature can be enabled at boot time. Just
975 pass the driver to filter for as the parameter.
976 The filter can be disabled or changed to another
977 driver later using sysfs.
979 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
980 Broken monitors, graphic adapters, KVMs and EDIDless
981 panels may send no or incorrect EDID data sets.
982 This parameter allows to specify an EDID data sets
983 in the /lib/firmware directory that are used instead.
984 Generic built-in EDID data sets are used, if one of
985 edid/1024x768.bin, edid/1280x1024.bin,
986 edid/1680x1050.bin, or edid/1920x1080.bin is given
987 and no file with the same name exists. Details and
988 instructions how to build your own EDID data are
989 available in Documentation/EDID/HOWTO.txt. An EDID
990 data set will only be used for a particular connector,
991 if its name and a colon are prepended to the EDID
992 name. Each connector may use a unique EDID data
993 set by separating the files with a comma. An EDID
994 data set with no connector name will be used for
995 any connectors not explicitly specified.
999 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1000 module.dyndbg[="val"]
1001 Enable debug messages at boot time. See
1002 Documentation/dynamic-debug-howto.txt for details.
1004 nompx [X86] Disables Intel Memory Protection Extensions.
1005 See Documentation/x86/intel_mpx.txt for more
1006 information about the feature.
1008 nopku [X86] Disable Memory Protection Keys CPU feature found
1012 on enable eager fpu restore
1013 off disable eager fpu restore
1014 auto selects the default scheme, which automatically
1015 enables eagerfpu restore for xsaveopt.
1017 module.async_probe [KNL]
1018 Enable asynchronous probe on this module.
1020 early_ioremap_debug [KNL]
1021 Enable debug messages in early_ioremap support. This
1022 is useful for tracking down temporary early mappings
1023 which are not unmapped.
1025 earlycon= [KNL] Output early console device and options.
1027 When used with no options, the early console is
1028 determined by the stdout-path property in device
1032 Start an early, polled-mode console on a cadence serial
1033 port at the specified address. The cadence serial port
1034 must already be setup and configured. Options are not
1037 uart[8250],io,<addr>[,options]
1038 uart[8250],mmio,<addr>[,options]
1039 uart[8250],mmio32,<addr>[,options]
1040 uart[8250],mmio32be,<addr>[,options]
1041 uart[8250],0x<addr>[,options]
1042 Start an early, polled-mode console on the 8250/16550
1043 UART at the specified I/O port or MMIO address.
1044 MMIO inter-register address stride is either 8-bit
1045 (mmio) or 32-bit (mmio32 or mmio32be).
1046 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1047 to be equivalent to 'mmio'. 'options' are specified
1048 in the same format described for "console=ttyS<n>"; if
1049 unspecified, the h/w is not initialized.
1053 Start an early, polled-mode console on a pl011 serial
1054 port at the specified address. The pl011 serial port
1055 must already be setup and configured. Options are not
1056 yet supported. If 'mmio32' is specified, then only
1057 the driver will use only 32-bit accessors to read/write
1058 the device registers.
1061 Start an early, polled-mode console on a meson serial
1062 port at the specified address. The serial port must
1063 already be setup and configured. Options are not yet
1067 Start an early, polled-mode console on an msm serial
1068 port at the specified address. The serial port
1069 must already be setup and configured. Options are not
1072 msm_serial_dm,<addr>
1073 Start an early, polled-mode console on an msm serial
1074 dm port at the specified address. The serial port
1075 must already be setup and configured. Options are not
1078 smh Use ARM semihosting calls for early console.
1086 Use early console provided by serial driver available
1087 on Samsung SoCs, requires selecting proper type and
1088 a correct base address of the selected UART port. The
1089 serial port must already be setup and configured.
1090 Options are not yet supported.
1094 Use early console provided by Freescale LP UART driver
1095 found on Freescale Vybrid and QorIQ LS1021A processors.
1096 A valid base address must be provided, and the serial
1097 port must already be setup and configured.
1099 armada3700_uart,<addr>
1100 Start an early, polled-mode console on the
1101 Armada 3700 serial port at the specified
1102 address. The serial port must already be setup
1103 and configured. Options are not yet supported.
1105 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1109 earlyprintk=serial[,ttySn[,baudrate]]
1110 earlyprintk=serial[,0x...[,baudrate]]
1111 earlyprintk=ttySn[,baudrate]
1112 earlyprintk=dbgp[debugController#]
1113 earlyprintk=pciserial,bus:device.function[,baudrate]
1115 earlyprintk is useful when the kernel crashes before
1116 the normal console is initialized. It is not enabled by
1117 default because it has some cosmetic problems.
1119 Append ",keep" to not disable it when the real console
1122 Only one of vga, efi, serial, or usb debug port can
1125 Currently only ttyS0 and ttyS1 may be specified by
1126 name. Other I/O ports may be explicitly specified
1127 on some architectures (x86 and arm at least) by
1128 replacing ttySn with an I/O port address, like this:
1129 earlyprintk=serial,0x1008,115200
1130 You can find the port for a given device in
1131 /proc/tty/driver/serial:
1132 2: uart:ST16650V2 port:00001008 irq:18 ...
1134 Interaction with the standard serial driver is not
1137 The VGA and EFI output is eventually overwritten by
1140 The xen output can only be used by Xen PV guests.
1142 edac_report= [HW,EDAC] Control how to report EDAC event
1143 Format: {"on" | "off" | "force"}
1144 on: enable EDAC to report H/W event. May be overridden
1145 by other higher priority error reporting module.
1146 off: disable H/W event reporting through EDAC.
1147 force: enforce the use of EDAC to report H/W event.
1150 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1153 This is designed to be used in conjunction with
1154 the boot argument: earlyprintk=vga
1157 Format: {"off" | "on" | "skip[mbr]"}
1160 Format: { "old_map", "nochunk", "noruntime", "debug" }
1161 old_map [X86-64]: switch to the old ioremap-based EFI
1162 runtime services mapping. 32-bit still uses this one by
1164 nochunk: disable reading files in "chunks" in the EFI
1165 boot stub, as chunking can cause problems with some
1166 firmware implementations.
1167 noruntime : disable EFI runtime services support
1168 debug: enable misc debug output
1170 efi_no_storage_paranoia [EFI; X86]
1171 Using this parameter you can use more than 50% of
1172 your efi variable storage. Use this parameter only if
1173 you are really sure that your UEFI does sane gc and
1174 fulfills the spec otherwise your board may brick.
1176 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1177 Add arbitrary attribute to specific memory range by
1178 updating original EFI memory map.
1179 Region of memory which aa attribute is added to is
1181 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1182 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1183 attribute is added to range 0x100000000-0x180000000 and
1184 0x10a0000000-0x1120000000.
1186 Using this parameter you can do debugging of EFI memmap
1187 related feature. For example, you can do debugging of
1188 Address Range Mirroring feature even if your box
1191 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1192 that is to be dynamically loaded by Linux. If there are
1193 multiple variables with the same name but with different
1194 vendor GUIDs, all of them will be loaded. See
1195 Documentation/acpi/ssdt-overlays.txt for details.
1198 eisa_irq_edge= [PARISC,HW]
1199 See header of drivers/parisc/eisa.c.
1202 See comment before function elanfreq_setup() in
1203 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1206 Format: {"cfq" | "deadline" | "noop"}
1207 See Documentation/block/cfq-iosched.txt and
1208 Documentation/block/deadline-iosched.txt for details.
1210 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1211 Specifies physical address of start of kernel core
1212 image elf header and optionally the size. Generally
1213 kexec loader will pass this option to capture kernel.
1214 See Documentation/kdump/kdump.txt for details.
1216 enable_mtrr_cleanup [X86]
1217 The kernel tries to adjust MTRR layout from continuous
1218 to discrete, to make X server driver able to add WB
1219 entry later. This parameter enables that.
1221 enable_timer_pin_1 [X86]
1222 Enable PIN 1 of APIC timer
1223 Can be useful to work around chipset bugs
1224 (in particular on some ATI chipsets).
1225 The kernel tries to set a reasonable default.
1227 enforcing [SELINUX] Set initial enforcing status.
1229 See security/selinux/Kconfig help text.
1230 0 -- permissive (log only, no denials).
1231 1 -- enforcing (deny and log).
1233 Value can be changed at runtime via /selinux/enforce.
1236 Disable Error Record Serialization Table (ERST)
1239 ether= [HW,NET] Ethernet cards parameters
1240 This option is obsoleted by the "netdev=" option, which
1241 has equivalent usage. See its documentation for details.
1245 Permit 'security.evm' to be updated regardless of
1246 current integrity status.
1250 fail_make_request=[KNL]
1251 General fault injection mechanism.
1252 Format: <interval>,<probability>,<space>,<times>
1253 See also Documentation/fault-injection/.
1256 See Documentation/blockdev/floppy.txt.
1258 force_pal_cache_flush
1259 [IA-64] Avoid check_sal_cache_flush which may hang on
1260 buggy SAL_CACHE_FLUSH implementations. Using this
1261 parameter will force ia64_sal_cache_flush to call
1262 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1265 Forcefully enable Physical Address Extension (PAE).
1266 Many Pentium M systems disable PAE but may have a
1267 functionally usable PAE implementation.
1268 Warning: use of this parameter will taint the kernel
1269 and may cause unknown problems.
1272 [FTRACE] will set and start the specified tracer
1273 as early as possible in order to facilitate early
1276 ftrace_dump_on_oops[=orig_cpu]
1277 [FTRACE] will dump the trace buffers on oops.
1278 If no parameter is passed, ftrace will dump
1279 buffers of all CPUs, but if you pass orig_cpu, it will
1280 dump only the buffer of the CPU that triggered the
1283 ftrace_filter=[function-list]
1284 [FTRACE] Limit the functions traced by the function
1285 tracer at boot up. function-list is a comma separated
1286 list of functions. This list can be changed at run
1287 time by the set_ftrace_filter file in the debugfs
1290 ftrace_notrace=[function-list]
1291 [FTRACE] Do not trace the functions specified in
1292 function-list. This list can be changed at run time
1293 by the set_ftrace_notrace file in the debugfs
1296 ftrace_graph_filter=[function-list]
1297 [FTRACE] Limit the top level callers functions traced
1298 by the function graph tracer at boot up.
1299 function-list is a comma separated list of functions
1300 that can be changed at run time by the
1301 set_graph_function file in the debugfs tracing directory.
1303 ftrace_graph_notrace=[function-list]
1304 [FTRACE] Do not trace from the functions specified in
1305 function-list. This list is a comma separated list of
1306 functions that can be changed at run time by the
1307 set_graph_notrace file in the debugfs tracing directory.
1310 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1311 support via parallel port (up to 5 devices per port)
1312 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1313 See also Documentation/input/joystick-parport.txt
1317 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1321 gcov_persist= [GCOV] When non-zero (default), profiling data for
1322 kernel modules is saved and remains accessible via
1323 debugfs, even when the module is unloaded/reloaded.
1324 When zero, profiling data is discarded and associated
1325 debugfs files are removed at module unload time.
1327 gpt [EFI] Forces disk with valid GPT signature but
1328 invalid Protective MBR to be treated as GPT. If the
1329 primary GPT is corrupted, it enables the backup/alternate
1330 GPT to be used instead.
1332 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1333 the "Enable 0" bit of the configuration register.
1336 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1337 the "Enable 0" bit of the configuration register.
1340 grcan.select= [HW] Select which physical interface to use.
1343 grcan.txsize= [HW] Sets the size of the tx buffer.
1344 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1346 grcan.rxsize= [HW] Sets the size of the rx buffer.
1347 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1350 hardlockup_all_cpu_backtrace=
1351 [KNL] Should the hard-lockup detector generate
1352 backtraces on all cpus.
1355 hashdist= [KNL,NUMA] Large hashes allocated during boot
1356 are distributed across NUMA nodes. Defaults on
1357 for 64-bit NUMA, off otherwise.
1358 Format: 0 | 1 (for off | on)
1360 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1362 hd= [EIDE] (E)IDE hard drive subsystem geometry
1363 Format: <cyl>,<head>,<sect>
1366 Disable Hardware Error Source Table (HEST) support;
1367 corresponding firmware-first mode error processing
1368 logic will be disabled.
1370 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1371 size of <nn>. This works even on boxes that have no
1372 highmem otherwise. This also works to reduce highmem
1373 size on bigger boxes.
1375 highres= [KNL] Enable/disable high resolution timer mode.
1376 Valid parameters: "on", "off"
1380 See Documentation/isdn/README.HiSax.
1384 hpet= [X86-32,HPET] option to control HPET usage
1385 Format: { enable (default) | disable | force |
1387 disable: disable HPET and use PIT instead
1388 force: allow force enabled of undocumented chips (ICH4,
1390 verbose: show contents of HPET registers during setup
1392 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1393 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1395 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1396 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1397 On x86-64 and powerpc, this option can be specified
1398 multiple times interleaved with hugepages= to reserve
1399 huge pages of different sizes. Valid pages sizes on
1400 x86-64 are 2M (when the CPU supports "pse") and 1G
1401 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1403 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1404 terminal devices. Valid values: 0..8
1405 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1406 If specified, z/VM IUCV HVC accepts connections
1407 from listed z/VM user IDs only.
1409 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1410 hardware thread id mappings.
1411 Format: <cpu>:<hwthread>
1414 Do not unregister boot console at start. This is only
1415 useful for debugging when something happens in the window
1416 between unregistering the boot console and initializing
1419 i2c_bus= [HW] Override the default board specific I2C bus speed
1420 or register an additional I2C bus that is not
1421 registered from board initialization code.
1425 i8042.debug [HW] Toggle i8042 debug mode
1426 i8042.unmask_kbd_data
1427 [HW] Enable printing of interrupt data from the KBD port
1428 (disabled by default, and as a pre-condition
1429 requires that i8042.debug=1 be enabled)
1430 i8042.direct [HW] Put keyboard port into non-translated mode
1431 i8042.dumbkbd [HW] Pretend that controller can only read data from
1432 keyboard and cannot control its state
1433 (Don't attempt to blink the leds)
1434 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1435 i8042.nokbd [HW] Don't check/create keyboard port
1436 i8042.noloop [HW] Disable the AUX Loopback command while probing
1438 i8042.nomux [HW] Don't check presence of an active multiplexing
1440 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1442 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1443 i8042.reset [HW] Reset the controller during init and cleanup
1444 i8042.unlock [HW] Unlock (ignore) the keylock
1445 i8042.kbdreset [HW] Reset device connected to KBD port
1449 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1450 indicates that the driver is running on unsupported
1452 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1453 does not match list of supported models.
1455 [HW] Report power status in /proc/i8k
1456 (disabled by default)
1457 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1460 i915.invert_brightness=
1461 [DRM] Invert the sense of the variable that is used to
1462 set the brightness of the panel backlight. Normally a
1463 brightness value of 0 indicates backlight switched off,
1464 and the maximum of the brightness value sets the backlight
1465 to maximum brightness. If this parameter is set to 0
1466 (default) and the machine requires it, or this parameter
1467 is set to 1, a brightness value of 0 sets the backlight
1468 to maximum brightness, and the maximum of the brightness
1469 value switches the backlight off.
1470 -1 -- never invert brightness
1471 0 -- machine default
1472 1 -- force brightness inversion
1475 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1477 ide-core.nodma= [HW] (E)IDE subsystem
1478 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1479 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1480 .cdrom .chs .ignore_cable are additional options
1481 See Documentation/ide/ide.txt.
1483 ide-generic.probe-mask= [HW] (E)IDE subsystem
1485 Probe mask for legacy ISA IDE ports. Depending on
1486 platform up to 6 ports are supported, enabled by
1487 setting corresponding bits in the mask to 1. The
1488 default value is 0x0, which has a special meaning.
1489 On systems that have PCI, it triggers scanning the
1490 PCI bus for the first and the second port, which
1491 are then probed. On systems without PCI the value
1492 of 0x0 enables probing the two first ports as if it
1495 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1496 Claim all unknown PCI IDE storage controllers.
1499 Format: idle=poll, idle=halt, idle=nomwait
1500 Poll forces a polling idle loop that can slightly
1501 improve the performance of waking up a idle CPU, but
1502 will use a lot of power and make the system run hot.
1504 idle=halt: Halt is forced to be used for CPU idle.
1505 In such case C2/C3 won't be used again.
1506 idle=nomwait: Disable mwait for CPU C-states
1508 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1509 Format: { strict | legacy | 2008 | relaxed }
1512 Choose which programs will be accepted for execution
1513 based on the IEEE 754 NaN encoding(s) supported by
1514 the FPU and the NaN encoding requested with the value
1515 of an ELF file header flag individually set by each
1516 binary. Hardware implementations are permitted to
1517 support either or both of the legacy and the 2008 NaN
1520 Available settings are as follows:
1521 strict accept binaries that request a NaN encoding
1522 supported by the FPU
1523 legacy only accept legacy-NaN binaries, if supported
1525 2008 only accept 2008-NaN binaries, if supported
1527 relaxed accept any binaries regardless of whether
1528 supported by the FPU
1530 The FPU emulator is always able to support both NaN
1531 encodings, so if no FPU hardware is present or it has
1532 been disabled with 'nofpu', then the settings of
1533 'legacy' and '2008' strap the emulator accordingly,
1534 'relaxed' straps the emulator for both legacy-NaN and
1535 2008-NaN, whereas 'strict' enables legacy-NaN only on
1536 legacy processors and both NaN encodings on MIPS32 or
1539 The setting for ABS.fmt/NEG.fmt instruction execution
1540 mode generally follows that for the NaN encoding,
1541 except where unsupported by hardware.
1543 ignore_loglevel [KNL]
1544 Ignore loglevel setting - this will print /all/
1545 kernel messages to the console. Useful for debugging.
1546 We also add it as printk module parameter, so users
1547 could change it dynamically, usually by
1548 /sys/module/printk/parameters/ignore_loglevel.
1551 Ignore RLIMIT_DATA setting for data mappings,
1552 print warning at first misuse. Can be changed via
1553 /sys/module/kernel/parameters/ignore_rlimit_data.
1555 ihash_entries= [KNL]
1556 Set number of hash buckets for inode cache.
1558 ima_appraise= [IMA] appraise integrity measurements
1559 Format: { "off" | "enforce" | "fix" | "log" }
1562 ima_appraise_tcb [IMA]
1563 The builtin appraise policy appraises all files
1567 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1571 The list of supported hash algorithms is defined
1572 in crypto/hash_info.h.
1575 The builtin measurement policy to load during IMA
1576 setup. Specyfing "tcb" as the value, measures all
1577 programs exec'd, files mmap'd for exec, and all files
1578 opened with the read mode bit set by either the
1579 effective uid (euid=0) or uid=0.
1582 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1583 Load a policy which meets the needs of the Trusted
1584 Computing Base. This means IMA will measure all
1585 programs exec'd, files mmap'd for exec, and all files
1586 opened for read by uid=0.
1589 Select one of defined IMA measurements template formats.
1590 Formats: { "ima" | "ima-ng" | "ima-sig" }
1594 [IMA] Define a custom template format.
1595 Format: { "field1|...|fieldN" }
1597 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1598 Format: <min_file_size>
1599 Set the minimal file size for using asynchronous hash.
1600 If left unspecified, ahash usage is disabled.
1602 ahash performance varies for different data sizes on
1603 different crypto accelerators. This option can be used
1604 to achieve the best performance for a particular HW.
1606 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1608 Set hashing buffer size. Default: 4k.
1610 ahash performance varies for different chunk sizes on
1611 different crypto accelerators. This option can be used
1612 to achieve best performance for particular HW.
1616 Run specified binary instead of /sbin/init as init
1619 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1620 for working out where the kernel is dying during
1623 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1624 initcall functions. Useful for debugging built-in
1625 modules and initcalls.
1627 initrd= [BOOT] Specify the location of the initial ramdisk
1629 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1632 int_pln_enable [x86] Enable power limit notification interrupt
1634 integrity_audit=[IMA]
1635 Format: { "0" | "1" }
1636 0 -- basic integrity auditing messages. (Default)
1637 1 -- additional integrity auditing messages.
1639 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1641 Enable intel iommu driver.
1643 Disable intel iommu driver.
1644 igfx_off [Default Off]
1645 By default, gfx is mapped as normal device. If a gfx
1646 device has a dedicated DMAR unit, the DMAR unit is
1647 bypassed by not enabling DMAR with this option. In
1648 this case, gfx device will use physical address for
1651 With this option iommu will not optimize to look
1652 for io virtual address below 32-bit forcing dual
1653 address cycle on pci bus for cards supporting greater
1654 than 32-bit addressing. The default is to look
1655 for translation below 32-bit and if not available
1656 then look in the higher range.
1657 strict [Default Off]
1658 With this option on every unmap_single operation will
1659 result in a hardware IOTLB flush operation as opposed
1660 to batching them for performance.
1661 sp_off [Default Off]
1662 By default, super page will be supported if Intel IOMMU
1663 has the capability. With this option, super page will
1665 ecs_off [Default Off]
1666 By default, extended context tables will be supported if
1667 the hardware advertises that it has support both for the
1668 extended tables themselves, and also PASID support. With
1669 this option set, extended tables will not be used even
1670 on hardware which claims to support them.
1672 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1673 0 disables intel_idle and fall back on acpi_idle.
1674 1 to 6 specify maximum depth of C-state.
1678 Do not enable intel_pstate as the default
1679 scaling driver for the supported processors
1681 Enable intel_pstate on systems that prohibit it by default
1682 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1683 instead of acpi-cpufreq may disable platform features, such
1684 as thermal controls and power capping, that rely on ACPI
1685 P-States information being indicated to OSPM and therefore
1686 should be used with caution. This option does not work with
1687 processors that aren't supported by the intel_pstate driver
1688 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1690 Do not enable hardware P state control (HWP)
1693 Only load intel_pstate on systems which support
1694 hardware P state control (HWP) if available.
1696 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1697 Description Table, specifies preferred power management
1698 profile as "Enterprise Server" or "Performance Server",
1699 then this feature is turned on by default.
1701 intremap= [X86-64, Intel-IOMMU]
1702 on enable Interrupt Remapping (default)
1703 off disable Interrupt Remapping
1704 nosid disable Source ID checking
1706 BIOS x2APIC opt-out request will be ignored
1707 nopost disable Interrupt Posting
1709 iomem= Disable strict checking of access to MMIO memory
1710 strict regions from userspace.
1725 nobypass [PPC/POWERNV]
1726 Disable IOMMU bypass, using IOMMU for PCI devices.
1729 io7= [HW] IO7 for Marvel based alpha systems
1730 See comment before marvel_specify_io7 in
1731 arch/alpha/kernel/core_marvel.c.
1733 io_delay= [X86] I/O delay method
1735 Standard port 0x80 based delay
1737 Alternate port 0xed based delay (needed on some systems)
1739 Simple two microseconds delay
1744 See Documentation/filesystems/nfs/nfsroot.txt.
1746 irqaffinity= [SMP] Set the default irq affinity mask
1748 <cpu number>,...,<cpu number>
1750 <cpu number>-<cpu number>
1751 (must be a positive range in ascending order)
1753 <cpu number>,...,<cpu number>-<cpu number>
1756 When an interrupt is not handled search all handlers
1757 for it. Intended to get systems with badly broken
1761 When an interrupt is not handled search all handlers
1762 for it. Also check all handlers each timer
1763 interrupt. Intended to get systems with badly broken
1767 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1769 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1771 <cpu number>,...,<cpu number>
1773 <cpu number>-<cpu number>
1774 (must be a positive range in ascending order)
1776 <cpu number>,...,<cpu number>-<cpu number>
1778 This option can be used to specify one or more CPUs
1779 to isolate from the general SMP balancing and scheduling
1780 algorithms. You can move a process onto or off an
1781 "isolated" CPU via the CPU affinity syscalls or cpuset.
1782 <cpu number> begins at 0 and the maximum value is
1783 "number of CPUs in system - 1".
1785 This option is the preferred way to isolate CPUs. The
1786 alternative -- manually setting the CPU mask of all
1787 tasks in the system -- can cause problems and
1788 suboptimal load balancer performance.
1792 ivrs_ioapic [HW,X86_64]
1793 Provide an override to the IOAPIC-ID<->DEVICE-ID
1794 mapping provided in the IVRS ACPI table. For
1795 example, to map IOAPIC-ID decimal 10 to
1796 PCI device 00:14.0 write the parameter as:
1797 ivrs_ioapic[10]=00:14.0
1799 ivrs_hpet [HW,X86_64]
1800 Provide an override to the HPET-ID<->DEVICE-ID
1801 mapping provided in the IVRS ACPI table. For
1802 example, to map HPET-ID decimal 0 to
1803 PCI device 00:14.0 write the parameter as:
1804 ivrs_hpet[0]=00:14.0
1806 ivrs_acpihid [HW,X86_64]
1807 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1808 mapping provided in the IVRS ACPI table. For
1809 example, to map UART-HID:UID AMD0020:0 to
1810 PCI device 00:14.5 write the parameter as:
1811 ivrs_acpihid[00:14.5]=AMD0020:0
1813 js= [HW,JOY] Analog joystick
1814 See Documentation/input/joystick.txt.
1817 Enable/disable kernel and module base offset ASLR
1818 (Address Space Layout Randomization) if built into
1819 the kernel. When CONFIG_HIBERNATION is selected,
1820 kASLR is disabled by default. When kASLR is enabled,
1821 hibernation will be disabled.
1825 kernelcore= [KNL,X86,IA-64,PPC]
1826 Format: nn[KMGTPE] | "mirror"
1828 specifies the amount of memory usable by the kernel
1829 for non-movable allocations. The requested amount is
1830 spread evenly throughout all nodes in the system. The
1831 remaining memory in each node is used for Movable
1832 pages. In the event, a node is too small to have both
1833 kernelcore and Movable pages, kernelcore pages will
1834 take priority and other nodes will have a larger number
1835 of Movable pages. The Movable zone is used for the
1836 allocation of pages that may be reclaimed or moved
1837 by the page migration subsystem. This means that
1838 HugeTLB pages may not be allocated from this zone.
1839 Note that allocations like PTEs-from-HighMem still
1840 use the HighMem zone if it exists, and the Normal
1841 zone if it does not.
1843 Instead of specifying the amount of memory (nn[KMGTPE]),
1844 you can specify "mirror" option. In case "mirror"
1845 option is specified, mirrored (reliable) memory is used
1846 for non-movable allocations and remaining memory is used
1847 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1848 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1851 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1852 Format: <Controller#>[,poll interval]
1853 The controller # is the number of the ehci usb debug
1854 port as it is probed via PCI. The poll interval is
1855 optional and is the number seconds in between
1856 each poll cycle to the debug port in case you need
1857 the functionality for interrupting the kernel with
1858 gdb or control-c on the dbgp connection. When
1859 not using this parameter you use sysrq-g to break into
1860 the kernel debugger.
1862 kgdboc= [KGDB,HW] kgdb over consoles.
1863 Requires a tty driver that supports console polling,
1864 or a supported polling keyboard driver (non-usb).
1865 Serial only format: <serial_device>[,baud]
1866 keyboard only format: kbd
1867 keyboard and serial format: kbd,<serial_device>[,baud]
1868 Optional Kernel mode setting:
1869 kms, kbd format: kms,kbd
1870 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1872 kgdbwait [KGDB] Stop kernel execution and enter the
1873 kernel debugger at the earliest opportunity.
1875 kmac= [MIPS] korina ethernet MAC address.
1876 Configure the RouterBoard 532 series on-chip
1877 Ethernet adapter MAC address.
1879 kmemleak= [KNL] Boot-time kmemleak enable/disable
1880 Valid arguments: on, off
1882 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1885 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1886 Valid arguments: 0, 1, 2
1887 kmemcheck=0 (disabled)
1888 kmemcheck=1 (enabled)
1889 kmemcheck=2 (one-shot mode)
1890 Default: 2 (one-shot mode)
1892 kstack=N [X86] Print N words from the kernel stack
1895 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1896 Default is 0 (don't ignore, but inject #GP)
1898 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1902 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1903 Default is 1 (enabled)
1905 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1907 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1909 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1910 (virtualized MMU) support on capable Intel chips.
1911 Default is 1 (enabled)
1913 kvm-intel.emulate_invalid_guest_state=
1914 [KVM,Intel] Enable emulation of invalid guest states
1915 Default is 0 (disabled)
1917 kvm-intel.flexpriority=
1918 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1919 Default is 1 (enabled)
1922 [KVM,Intel] Enable VMX nesting (nVMX).
1923 Default is 0 (disabled)
1925 kvm-intel.unrestricted_guest=
1926 [KVM,Intel] Disable unrestricted guest feature
1927 (virtualized real and unpaged mode) on capable
1928 Intel chips. Default is 1 (enabled)
1930 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1931 feature (tagged TLBs) on capable Intel chips.
1932 Default is 1 (enabled)
1938 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1941 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1942 value for LAPIC timer one-shot implementation. Default
1943 back to the programmable timer unit in the LAPIC.
1945 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1948 libata.dma= [LIBATA] DMA control
1949 libata.dma=0 Disable all PATA and SATA DMA
1950 libata.dma=1 PATA and SATA Disk DMA only
1951 libata.dma=2 ATAPI (CDROM) DMA only
1952 libata.dma=4 Compact Flash DMA only
1953 Combinations also work, so libata.dma=3 enables DMA
1954 for disks and CDROMs, but not CFs.
1956 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1957 libata.ignore_hpa=0 keep BIOS limits (default)
1958 libata.ignore_hpa=1 ignore limits, using full disk
1960 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1964 libata.force= [LIBATA] Force configurations. The format is comma
1965 separated list of "[ID:]VAL" where ID is
1966 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1967 matching port, link or device. Basically, it matches
1968 the ATA ID string printed on console by libata. If
1969 the whole ID part is omitted, the last PORT and DEVICE
1970 values are used. If ID hasn't been specified yet, the
1971 configuration applies to all ports, links and devices.
1973 If only DEVICE is omitted, the parameter applies to
1974 the port and all links and devices behind it. DEVICE
1975 number of 0 either selects the first device or the
1976 first fan-out link behind PMP device. It does not
1977 select the host link. DEVICE number of 15 selects the
1978 host link and device attached to it.
1980 The VAL specifies the configuration to force. As long
1981 as there's no ambiguity shortcut notation is allowed.
1982 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1983 The following configurations can be forced.
1985 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1986 Any ID with matching PORT is used.
1988 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1990 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1991 udma[/][16,25,33,44,66,100,133] notation is also
1994 * [no]ncq: Turn on or off NCQ.
1996 * [no]ncqtrim: Turn off queued DSM TRIM.
1998 * nohrst, nosrst, norst: suppress hard, soft
2001 * rstonce: only attempt one reset during
2002 hot-unplug link recovery
2004 * dump_id: dump IDENTIFY data.
2006 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2008 * disable: Disable this device.
2010 If there are multiple matching configurations changing
2011 the same attribute, the last one is used.
2013 memblock=debug [KNL] Enable memblock debug messages.
2015 load_ramdisk= [RAM] List of ramdisks to load from floppy
2016 See Documentation/blockdev/ramdisk.txt.
2018 lockd.nlm_grace_period=P [NFS] Assign grace period.
2021 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2024 lockd.nlm_timeout=T [NFS] Assign timeout value.
2027 lockd.nlm_udpport=M [NFS] Assign UDP port.
2030 locktorture.nreaders_stress= [KNL]
2031 Set the number of locking read-acquisition kthreads.
2032 Defaults to being automatically set based on the
2033 number of online CPUs.
2035 locktorture.nwriters_stress= [KNL]
2036 Set the number of locking write-acquisition kthreads.
2038 locktorture.onoff_holdoff= [KNL]
2039 Set time (s) after boot for CPU-hotplug testing.
2041 locktorture.onoff_interval= [KNL]
2042 Set time (s) between CPU-hotplug operations, or
2043 zero to disable CPU-hotplug testing.
2045 locktorture.shuffle_interval= [KNL]
2046 Set task-shuffle interval (jiffies). Shuffling
2047 tasks allows some CPUs to go into dyntick-idle
2048 mode during the locktorture test.
2050 locktorture.shutdown_secs= [KNL]
2051 Set time (s) after boot system shutdown. This
2052 is useful for hands-off automated testing.
2054 locktorture.stat_interval= [KNL]
2055 Time (s) between statistics printk()s.
2057 locktorture.stutter= [KNL]
2058 Time (s) to stutter testing, for example,
2059 specifying five seconds causes the test to run for
2060 five seconds, wait for five seconds, and so on.
2061 This tests the locking primitive's ability to
2062 transition abruptly to and from idle.
2064 locktorture.torture_runnable= [BOOT]
2065 Start locktorture running at boot time.
2067 locktorture.torture_type= [KNL]
2068 Specify the locking implementation to test.
2070 locktorture.verbose= [KNL]
2071 Enable additional printk() statements.
2073 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2076 loglevel= All Kernel Messages with a loglevel smaller than the
2077 console loglevel will be printed to the console. It can
2078 also be changed with klogd or other programs. The
2079 loglevels are defined as follows:
2081 0 (KERN_EMERG) system is unusable
2082 1 (KERN_ALERT) action must be taken immediately
2083 2 (KERN_CRIT) critical conditions
2084 3 (KERN_ERR) error conditions
2085 4 (KERN_WARNING) warning conditions
2086 5 (KERN_NOTICE) normal but significant condition
2087 6 (KERN_INFO) informational
2088 7 (KERN_DEBUG) debug-level messages
2090 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2091 in bytes. n must be a power of two and greater
2092 than the minimal size. The minimal size is defined
2093 by LOG_BUF_SHIFT kernel config parameter. There is
2094 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2095 that allows to increase the default size depending on
2096 the number of CPUs. See init/Kconfig for more details.
2098 logo.nologo [FB] Disables display of the built-in Linux logo.
2099 This may be used to provide more screen space for
2100 kernel log messages and is useful when debugging
2101 kernel boot problems.
2103 lp=0 [LP] Specify parallel ports to use, e.g,
2104 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2105 lp=reset first parallel port). 'lp=0' disables the
2106 lp=auto printer driver. 'lp=reset' (which can be
2107 specified in addition to the ports) causes
2108 attached printers to be reset. Using
2109 lp=port1,port2,... specifies the parallel ports
2110 to associate lp devices with, starting with
2111 lp0. A port specification may be 'none' to skip
2112 that lp device, or a parport name such as
2113 'parport0'. Specifying 'lp=auto' instead of a
2114 port specification list means that device IDs
2115 from each port should be examined, to see if
2116 an IEEE 1284-compliant printer is attached; if
2117 so, the driver will manage that printer.
2118 See also header of drivers/char/lp.c.
2121 Sets loops_per_jiffy to given constant, thus avoiding
2122 time-consuming boot-time autodetection (up to 250 ms per
2123 CPU). 0 enables autodetection (default). To determine
2124 the correct value for your kernel, boot with normal
2125 autodetection and see what value is printed. Note that
2126 on SMP systems the preset will be applied to all CPUs,
2127 which is likely to cause problems if your CPUs need
2128 significantly divergent settings. An incorrect value
2129 will cause delays in the kernel to be wrong, leading to
2130 unpredictable I/O errors and other breakage. Although
2131 unlikely, in the extreme case this might damage your
2135 Format: <io>,<irq>,<dma>
2137 machvec= [IA-64] Force the use of a particular machine-vector
2138 (machvec) in a generic kernel.
2139 Example: machvec=hpzx1_swiotlb
2141 machtype= [Loongson] Share the same kernel image file between different
2143 Example: machtype=lemote-yeeloong-2f-7inch
2145 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2146 than or equal to this physical address is ignored.
2148 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2149 should make use of. maxcpus=n : n >= 0 limits the
2150 kernel to using 'n' processors. n=0 is a special case,
2151 it is equivalent to "nosmp", which also disables
2154 max_loop= [LOOP] The number of loop block devices that get
2155 (loop.max_loop) unconditionally pre-created at init time. The default
2156 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2157 of statically allocating a predefined number, loop
2158 devices can be requested on-demand with the
2159 /dev/loop-control interface.
2161 mce [X86-32] Machine Check Exception
2163 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2165 md= [HW] RAID subsystems devices and level
2166 See Documentation/md.txt.
2169 Format: <first>,<last>
2170 Specifies range of consoles to be captured by the MDA.
2172 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2173 Amount of memory to be used when the kernel is not able
2174 to see the whole system memory or for test.
2175 [X86] Work as limiting max address. Use together
2176 with memmap= to avoid physical address space collisions.
2177 Without memmap= PCI devices could be placed at addresses
2178 belonging to unused RAM.
2180 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2184 [KNL,SH] Allow user to override the default size for
2185 per-device physically contiguous DMA buffers.
2187 memhp_default_state=online/offline
2188 [KNL] Set the initial state for the memory hotplug
2189 onlining policy. If not specified, the default value is
2190 set according to the
2191 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2193 See Documentation/memory-hotplug.txt.
2195 memmap=exactmap [KNL,X86] Enable setting of an exact
2196 E820 memory map, as specified by the user.
2197 Such memmap=exactmap lines can be constructed based on
2198 BIOS output or other requirements. See the memmap=nn@ss
2201 memmap=nn[KMG]@ss[KMG]
2202 [KNL] Force usage of a specific region of memory.
2203 Region of memory to be used is from ss to ss+nn.
2205 memmap=nn[KMG]#ss[KMG]
2206 [KNL,ACPI] Mark specific memory as ACPI data.
2207 Region of memory to be marked is from ss to ss+nn.
2209 memmap=nn[KMG]$ss[KMG]
2210 [KNL,ACPI] Mark specific memory as reserved.
2211 Region of memory to be reserved is from ss to ss+nn.
2212 Example: Exclude memory from 0x18690000-0x1869ffff
2213 memmap=64K$0x18690000
2215 memmap=0x10000$0x18690000
2217 memmap=nn[KMG]!ss[KMG]
2218 [KNL,X86] Mark specific memory as protected.
2219 Region of memory to be used, from ss to ss+nn.
2220 The memory region may be marked as e820 type 12 (0xc)
2221 and is NVDIMM or ADR memory.
2223 memory_corruption_check=0/1 [X86]
2224 Some BIOSes seem to corrupt the first 64k of
2225 memory when doing things like suspend/resume.
2226 Setting this option will scan the memory
2227 looking for corruption. Enabling this will
2228 both detect corruption and prevent the kernel
2229 from using the memory being corrupted.
2230 However, its intended as a diagnostic tool; if
2231 repeatable BIOS-originated corruption always
2232 affects the same memory, you can use memmap=
2233 to prevent the kernel from using that memory.
2235 memory_corruption_check_size=size [X86]
2236 By default it checks for corruption in the low
2237 64k, making this memory unavailable for normal
2238 use. Use this parameter to scan for
2239 corruption in more or less memory.
2241 memory_corruption_check_period=seconds [X86]
2242 By default it checks for corruption every 60
2243 seconds. Use this parameter to check at some
2244 other rate. 0 disables periodic checking.
2246 memtest= [KNL,X86,ARM] Enable memtest
2248 default : 0 <disable>
2249 Specifies the number of memtest passes to be
2250 performed. Each pass selects another test
2251 pattern from a given set of patterns. Memtest
2252 fills the memory with this pattern, validates
2253 memory contents and reserves bad memory
2254 regions that are detected.
2256 meye.*= [HW] Set MotionEye Camera parameters
2257 See Documentation/video4linux/meye.txt.
2259 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2260 Multi-Function General Purpose Timers on AMD Geode
2263 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2264 the BIOS has incorrectly applied a workaround. TinyBIOS
2265 version 0.98 is known to be affected, 0.99 fixes the
2266 problem by letting the user disable the workaround.
2270 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2271 physical address is ignored.
2273 mini2440= [ARM,HW,KNL]
2274 Format:[0..2][b][c][t]
2276 MINI2440 configuration specification:
2277 0 - The attached screen is the 3.5" TFT
2278 1 - The attached screen is the 7" TFT
2279 2 - The VGA Shield is attached (1024x768)
2280 Leaving out the screen size parameter will not load
2281 the TFT driver, and the framebuffer will be left
2283 b - Enable backlight. The TFT backlight pin will be
2284 linked to the kernel VESA blanking code and a GPIO
2285 LED. This parameter is not necessary when using the
2287 c - Enable the s3c camera interface.
2288 t - Reserved for enabling touchscreen support. The
2289 touchscreen support is not enabled in the mainstream
2290 kernel as of 2.6.30, a preliminary port can be found
2291 in the "bleeding edge" mini2440 support kernel at
2292 http://repo.or.cz/w/linux-2.6/mini2440.git
2295 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2296 parameter allows control of the logging verbosity for
2297 the additional memory initialisation checks. A value
2298 of 0 disables mminit logging and a level of 4 will
2299 log everything. Information is printed at KERN_DEBUG
2300 so loglevel=8 may also need to be specified.
2303 [KNL] When CONFIG_MODULE_SIG is set, this means that
2304 modules without (valid) signatures will fail to load.
2305 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2306 is always true, so this option does nothing.
2309 [MOUSE] Maximum time between finger touching and
2310 leaving touchpad surface for touch to be considered
2311 a tap and be reported as a left button click (for
2312 touchpads working in absolute mode only).
2314 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2315 reporting absolute coordinates, such as tablets
2316 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2317 reporting absolute coordinates, such as tablets
2319 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2320 is similar to kernelcore except it specifies the
2321 amount of memory used for migratable allocations.
2322 If both kernelcore and movablecore is specified,
2323 then kernelcore will be at *least* the specified
2324 value but may be more. If movablecore on its own
2325 is specified, the administrator must be careful
2326 that the amount of memory usable for all allocations
2329 movable_node [KNL,X86] Boot-time switch to enable the effects
2330 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2332 MTD_Partition= [MTD]
2333 Format: <name>,<region-number>,<size>,<offset>
2335 MTD_Region= [MTD] Format:
2336 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2339 See drivers/mtd/cmdlinepart.c.
2341 multitce=off [PPC] This parameter disables the use of the pSeries
2342 firmware feature for updating multiple TCE entries
2345 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2347 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2349 boundary - index of last SLC block on Flex-OneNAND.
2350 The remaining blocks are configured as MLC blocks.
2351 lock - Configure if Flex-OneNAND boundary should be locked.
2352 Once locked, the boundary cannot be changed.
2353 1 indicates lock status, 0 indicates unlock status.
2356 ARM/S3C2412 JIVE boot control
2358 See arch/arm/mach-s3c2412/mach-jive.c
2360 mtouchusb.raw_coordinates=
2361 [HW] Make the MicroTouch USB driver use raw coordinates
2362 ('y', default) or cooked coordinates ('n')
2364 mtrr_chunk_size=nn[KMG] [X86]
2365 used for mtrr cleanup. It is largest continuous chunk
2366 that could hold holes aka. UC entries.
2368 mtrr_gran_size=nn[KMG] [X86]
2369 Used for mtrr cleanup. It is granularity of mtrr block.
2371 Large value could prevent small alignment from
2374 mtrr_spare_reg_nr=n [X86]
2376 Range: 0,7 : spare reg number
2378 Used for mtrr cleanup. It is spare mtrr entries number.
2379 Set to 2 or more if your graphical card needs more.
2381 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2383 netdev= [NET] Network devices parameters
2384 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2385 Note that mem_start is often overloaded to mean
2386 something different and driver-specific.
2387 This usage is only documented in each driver source
2391 [NETFILTER] Enable connection tracking flow accounting
2392 0 to disable accounting
2393 1 to enable accounting
2396 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2397 See Documentation/filesystems/nfs/nfsroot.txt.
2399 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2400 See Documentation/filesystems/nfs/nfsroot.txt.
2402 nfsrootdebug [NFS] enable nfsroot debugging messages.
2403 See Documentation/filesystems/nfs/nfsroot.txt.
2405 nfs.callback_tcpport=
2406 [NFS] set the TCP port on which the NFSv4 callback
2407 channel should listen.
2410 [NFS] sets the pathname to the program which is used
2411 to update the NFS client cache entries.
2413 nfs.cache_getent_timeout=
2414 [NFS] sets the timeout after which an attempt to
2415 update a cache entry is deemed to have failed.
2417 nfs.idmap_cache_timeout=
2418 [NFS] set the maximum lifetime for idmapper cache
2422 [NFS] enable 64-bit inode numbers.
2423 If zero, the NFS client will fake up a 32-bit inode
2424 number for the readdir() and stat() syscalls instead
2425 of returning the full 64-bit number.
2426 The default is to return 64-bit inode numbers.
2428 nfs.max_session_slots=
2429 [NFSv4.1] Sets the maximum number of session slots
2430 the client will attempt to negotiate with the server.
2431 This limits the number of simultaneous RPC requests
2432 that the client can send to the NFSv4.1 server.
2433 Note that there is little point in setting this
2434 value higher than the max_tcp_slot_table_limit.
2436 nfs.nfs4_disable_idmapping=
2437 [NFSv4] When set to the default of '1', this option
2438 ensures that both the RPC level authentication
2439 scheme and the NFS level operations agree to use
2440 numeric uids/gids if the mount is using the
2441 'sec=sys' security flavour. In effect it is
2442 disabling idmapping, which can make migration from
2443 legacy NFSv2/v3 systems to NFSv4 easier.
2444 Servers that do not support this mode of operation
2445 will be autodetected by the client, and it will fall
2446 back to using the idmapper.
2447 To turn off this behaviour, set the value to '0'.
2449 [NFS4] Specify an additional fixed unique ident-
2450 ification string that NFSv4 clients can insert into
2451 their nfs_client_id4 string. This is typically a
2452 UUID that is generated at system install time.
2454 nfs.send_implementation_id =
2455 [NFSv4.1] Send client implementation identification
2456 information in exchange_id requests.
2457 If zero, no implementation identification information
2459 The default is to send the implementation identification
2462 nfs.recover_lost_locks =
2463 [NFSv4] Attempt to recover locks that were lost due
2464 to a lease timeout on the server. Please note that
2465 doing this risks data corruption, since there are
2466 no guarantees that the file will remain unchanged
2467 after the locks are lost.
2468 If you want to enable the kernel legacy behaviour of
2469 attempting to recover these locks, then set this
2471 The default parameter value of '0' causes the kernel
2472 not to attempt recovery of lost locks.
2474 nfs4.layoutstats_timer =
2475 [NFSv4.2] Change the rate at which the kernel sends
2476 layoutstats to the pNFS metadata server.
2478 Setting this to value to 0 causes the kernel to use
2479 whatever value is the default set by the layout
2480 driver. A non-zero value sets the minimum interval
2481 in seconds between layoutstats transmissions.
2483 nfsd.nfs4_disable_idmapping=
2484 [NFSv4] When set to the default of '1', the NFSv4
2485 server will return only numeric uids and gids to
2486 clients using auth_sys, and will accept numeric uids
2487 and gids from such clients. This is intended to ease
2488 migration from NFSv2/v3.
2490 objlayoutdriver.osd_login_prog=
2491 [NFS] [OBJLAYOUT] sets the pathname to the program which
2492 is used to automatically discover and login into new
2493 osd-targets. Please see:
2494 Documentation/filesystems/pnfs.txt for more explanations
2496 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2497 when a NMI is triggered.
2498 Format: [state][,regs][,debounce][,die]
2500 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2501 Format: [panic,][nopanic,][num]
2503 0 - turn hardlockup detector in nmi_watchdog off
2504 1 - turn hardlockup detector in nmi_watchdog on
2505 When panic is specified, panic when an NMI watchdog
2506 timeout occurs (or 'nopanic' to override the opposite
2507 default). To disable both hard and soft lockup detectors,
2508 please see 'nowatchdog'.
2509 This is useful when you use a panic=... timeout and
2510 need the box quickly up again.
2512 netpoll.carrier_timeout=
2513 [NET] Specifies amount of time (in seconds) that
2514 netpoll should wait for a carrier. By default netpoll
2517 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2518 emulation library even if a 387 maths coprocessor
2522 [HW] Never suspend the console
2523 Disable suspending of consoles during suspend and
2524 hibernate operations. Once disabled, debugging
2525 messages can reach various consoles while the rest
2526 of the system is being put to sleep (ie, while
2527 debugging driver suspend/resume hooks). This may
2528 not work reliably with all consoles, but is known
2529 to work with serial and VGA consoles.
2530 To facilitate more flexible debugging, we also add
2531 console_suspend, a printk module parameter to control
2532 it. Users could use console_suspend (usually
2533 /sys/module/printk/parameters/console_suspend) to
2534 turn on/off it dynamically.
2536 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2537 caches in the slab allocator. Saves per-node memory,
2538 but will impact performance.
2542 noapic [SMP,APIC] Tells the kernel to not make use of any
2543 IOAPICs that may be present in the system.
2545 noautogroup Disable scheduler automatic task group creation.
2547 nobats [PPC] Do not use BATs for mapping kernel lowmem
2548 on "Classic" PPC cores.
2552 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2554 nodelayacct [KNL] Disable per-task delay accounting
2556 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2558 nodsp [SH] Disable hardware DSP at boot time.
2560 noefi Disable EFI runtime services support.
2565 On X86-32 available only on PAE configured kernels.
2566 noexec=on: enable non-executable mappings (default)
2567 noexec=off: disable non-executable mappings
2570 Disable SMAP (Supervisor Mode Access Prevention)
2571 even if it is supported by processor.
2574 Disable SMEP (Supervisor Mode Execution Prevention)
2575 even if it is supported by processor.
2578 This affects only 32-bit executables.
2579 noexec32=on: enable non-executable mappings (default)
2580 read doesn't imply executable mappings
2581 noexec32=off: disable non-executable mappings
2582 read implies executable mappings
2584 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2586 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2587 register save and restore. The kernel will only save
2588 legacy floating-point registers on task switch.
2590 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2592 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2593 Equivalent to smt=1.
2595 noxsave [BUGS=X86] Disables x86 extended register state save
2596 and restore using xsave. The kernel will fallback to
2597 enabling legacy floating-point and sse state.
2599 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2600 register states. The kernel will fall back to use
2601 xsave to save the states. By using this parameter,
2602 performance of saving the states is degraded because
2603 xsave doesn't support modified optimization while
2604 xsaveopt supports it on xsaveopt enabled systems.
2606 noxsaves [X86] Disables xsaves and xrstors used in saving and
2607 restoring x86 extended register state in compacted
2608 form of xsave area. The kernel will fall back to use
2609 xsaveopt and xrstor to save and restore the states
2610 in standard form of xsave area. By using this
2611 parameter, xsave area per process might occupy more
2612 memory on xsaves enabled systems.
2614 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2615 wfi(ARM) instruction doesn't work correctly and not to
2616 use it. This is also useful when using JTAG debugger.
2618 no_file_caps Tells the kernel not to honor file capabilities. The
2619 only way then for a file to be executed with privilege
2620 is to be setuid root or executed by root.
2622 nohalt [IA-64] Tells the kernel not to use the power saving
2623 function PAL_HALT_LIGHT when idle. This increases
2624 power-consumption. On the positive side, it reduces
2625 interrupt wake-up latency, which may improve performance
2626 in certain environments such as networked servers or
2629 nohibernate [HIBERNATION] Disable hibernation and resume.
2631 nohz= [KNL] Boottime enable/disable dynamic ticks
2632 Valid arguments: on, off
2635 nohz_full= [KNL,BOOT]
2636 In kernels built with CONFIG_NO_HZ_FULL=y, set
2637 the specified list of CPUs whose tick will be stopped
2638 whenever possible. The boot CPU will be forced outside
2639 the range to maintain the timekeeping.
2640 The CPUs in this range must also be included in the
2643 noiotrap [SH] Disables trapped I/O port accesses.
2645 noirqdebug [X86-32] Disables the code which attempts to detect and
2646 disable unhandled interrupt sources.
2648 no_timer_check [X86,APIC] Disables the code which tests for
2649 broken timer IRQ sources.
2651 noisapnp [ISAPNP] Disables ISA PnP code.
2653 noinitrd [RAM] Tells the kernel not to load any configured
2656 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2658 [Deprecated - use intremap=off]
2662 noinvpcid [X86] Disable the INVPCID cpu feature.
2664 nojitter [IA-64] Disables jitter checking for ITC timers.
2666 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2668 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2671 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2672 steal time is computed, but won't influence scheduler
2675 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2677 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2679 noltlbs [PPC] Do not use large page/tlb entries for kernel
2680 lowmem mapping on PPC40x and PPC8xx
2682 nomca [IA-64] Disable machine check abort handling
2684 nomce [X86-32] Disable Machine Check Exception
2686 nomfgpt [X86-32] Disable Multi-Function General Purpose
2687 Timer usage (for AMD Geode machines).
2689 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2690 shutdown the other cpus. Instead use the REBOOT_VECTOR
2693 nomodule Disable module load
2695 nopat [X86] Disable PAT (page attribute table extension of
2696 pagetables) support.
2698 norandmaps Don't use address space randomization. Equivalent to
2699 echo 0 > /proc/sys/kernel/randomize_va_space
2701 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2703 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2704 with UP alternatives
2706 nordrand [X86] Disable kernel use of the RDRAND and
2707 RDSEED instructions even if they are supported
2708 by the processor. RDRAND and RDSEED are still
2709 available to user space applications.
2711 noresume [SWSUSP] Disables resume and restores original swap
2714 no-scroll [VGA] Disables scrollback.
2715 This is required for the Braillex ib80-piezo Braille
2716 reader made by F.H. Papenmeier (Germany).
2720 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2722 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2723 and disable the IO APIC. legacy for "maxcpus=0".
2725 nosoftlockup [KNL] Disable the soft-lockup detector.
2727 nosync [HW,M68K] Disables sync negotiation for all devices.
2729 notsc [BUGS=X86-32] Disable Time Stamp Counter
2731 nowatchdog [KNL] Disable both lockup detectors, i.e.
2732 soft-lockup and NMI watchdog (hard-lockup).
2736 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2738 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2739 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2740 Some features depend on CPU0. Known dependencies are:
2741 1. Resume from suspend/hibernate depends on CPU0.
2742 Suspend/hibernate will fail if CPU0 is offline and you
2743 need to online CPU0 before suspend/hibernate.
2744 2. PIC interrupts also depend on CPU0. CPU0 can't be
2745 removed if a PIC interrupt is detected.
2746 It's said poweroff/reboot may depend on CPU0 on some
2747 machines although I haven't seen such issues so far
2748 after CPU0 is offline on a few tested machines.
2749 If the dependencies are under your control, you can
2750 turn on cpu0_hotplug.
2752 nptcg= [IA-64] Override max number of concurrent global TLB
2753 purges which is reported from either PAL_VM_SUMMARY or
2756 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2757 could support. nr_cpus=n : n >= 1 limits the kernel to
2758 supporting 'n' processors. Later in runtime you can not
2759 use hotplug cpu feature to put more cpu back to online.
2760 just like you compile the kernel NR_CPUS=n
2762 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2764 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2765 Allowed values are enable and disable
2767 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2768 one of ['zone', 'node', 'default'] can be specified
2769 This can be set from sysctl after boot.
2770 See Documentation/sysctl/vm.txt for details.
2772 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2773 See Documentation/debugging-via-ohci1394.txt for more
2776 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2777 Rather than timing out after 20 ms if an EC
2778 command is not properly ACKed, override the length
2779 of the timeout. We have interrupts disabled while
2780 waiting for the ACK, so if this is set too high
2781 interrupts *may* be lost!
2783 omap_mux= [OMAP] Override bootloader pin multiplexing.
2784 Format: <mux_mode0.mode_name=value>...
2785 For example, to override I2C bus2:
2786 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2788 oprofile.timer= [HW]
2789 Use timer interrupt instead of performance counters
2791 oprofile.cpu_type= Force an oprofile cpu type
2792 This might be useful if you have an older oprofile
2793 userland or if you want common events.
2794 Format: { arch_perfmon }
2795 arch_perfmon: [X86] Force use of architectural
2796 perfmon on Intel CPUs instead of the
2797 CPU specific event set.
2798 timer: [X86] Force use of architectural NMI
2799 timer mode (see also oprofile.timer
2800 for generic hr timer mode)
2801 [s390] Force legacy basic mode sampling
2802 (report cpu_type "timer")
2804 oops=panic Always panic on oopses. Default is to just kill the
2805 process, but there is a small probability of
2806 deadlocking the machine.
2807 This will also cause panics on machine check exceptions.
2808 Useful together with panic=30 to trigger a reboot.
2811 See Documentation/sound/oss/oss-parameters.txt
2813 page_owner= [KNL] Boot-time page_owner enabling option.
2814 Storage of the information about who allocated
2815 each page is disabled in default. With this switch,
2817 on: enable the feature
2819 page_poison= [KNL] Boot-time parameter changing the state of
2820 poisoning on the buddy allocator.
2821 off: turn off poisoning
2822 on: turn on poisoning
2824 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2825 timeout > 0: seconds before rebooting
2826 timeout = 0: wait forever
2827 timeout < 0: reboot immediately
2830 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2833 crash_kexec_post_notifiers
2834 Run kdump after running panic-notifiers and dumping
2835 kmsg. This only for the users who doubt kdump always
2836 succeeds in any situation.
2837 Note that this also increases risks of kdump failure,
2838 because some panic notifiers can make the crashed
2839 kernel more unstable.
2841 parkbd.port= [HW] Parallel port number the keyboard adapter is
2842 connected to, default is 0.
2844 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2845 0 for XT, 1 for AT (default is AT).
2848 parport= [HW,PPT] Specify parallel ports. 0 disables.
2849 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2850 Use 'auto' to force the driver to use any
2851 IRQ/DMA settings detected (the default is to
2852 ignore detected IRQ/DMA settings because of
2853 possible conflicts). You can specify the base
2854 address, IRQ, and DMA settings; IRQ and DMA
2855 should be numbers, or 'auto' (for using detected
2856 settings on that particular port), or 'nofifo'
2857 (to avoid using a FIFO even if it is detected).
2858 Parallel ports are assigned in the order they
2859 are specified on the command line, starting
2862 parport_init_mode= [HW,PPT]
2863 Configure VIA parallel port to operate in
2864 a specific mode. This is necessary on Pegasos
2865 computer where firmware has no options for setting
2866 up parallel port mode and sets it to spp.
2867 Currently this function knows 686a and 8231 chips.
2868 Format: [spp|ps2|epp|ecp|ecpepp]
2871 Halt all CPUs after the first oops has been printed for
2872 the specified number of seconds. This is to be used if
2873 your oopses keep scrolling off the screen.
2878 See header of drivers/block/paride/pcd.c.
2879 See also Documentation/blockdev/paride.txt.
2881 pci=option[,option...] [PCI] various PCI subsystem options:
2882 earlydump [X86] dump PCI config space before the kernel
2884 off [X86] don't probe for the PCI bus
2885 bios [X86-32] force use of PCI BIOS, don't access
2886 the hardware directly. Use this if your machine
2887 has a non-standard PCI host bridge.
2888 nobios [X86-32] disallow use of PCI BIOS, only direct
2889 hardware access methods are allowed. Use this
2890 if you experience crashes upon bootup and you
2891 suspect they are caused by the BIOS.
2892 conf1 [X86] Force use of PCI Configuration Access
2893 Mechanism 1 (config address in IO port 0xCF8,
2894 data in IO port 0xCFC, both 32-bit).
2895 conf2 [X86] Force use of PCI Configuration Access
2896 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2897 the function, IO port 0xCFA, also 8-bit, sets
2898 bus number. The config space is then accessed
2899 through ports 0xC000-0xCFFF).
2900 See http://wiki.osdev.org/PCI for more info
2901 on the configuration access mechanisms.
2902 noaer [PCIE] If the PCIEAER kernel config parameter is
2903 enabled, this kernel boot option can be used to
2904 disable the use of PCIE advanced error reporting.
2905 nodomains [PCI] Disable support for multiple PCI
2906 root domains (aka PCI segments, in ACPI-speak).
2907 nommconf [X86] Disable use of MMCONFIG for PCI
2909 check_enable_amd_mmconf [X86] check for and enable
2910 properly configured MMIO access to PCI
2911 config space on AMD family 10h CPU
2912 nomsi [MSI] If the PCI_MSI kernel config parameter is
2913 enabled, this kernel boot option can be used to
2914 disable the use of MSI interrupts system-wide.
2915 noioapicquirk [APIC] Disable all boot interrupt quirks.
2916 Safety option to keep boot IRQs enabled. This
2917 should never be necessary.
2918 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2919 primary IO-APIC for bridges that cannot disable
2920 boot IRQs. This fixes a source of spurious IRQs
2921 when the system masks IRQs.
2922 noioapicreroute [APIC] Disable workaround that uses the
2923 boot IRQ equivalent of an IRQ that connects to
2924 a chipset where boot IRQs cannot be disabled.
2925 The opposite of ioapicreroute.
2926 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2927 routing table. These calls are known to be buggy
2928 on several machines and they hang the machine
2929 when used, but on other computers it's the only
2930 way to get the interrupt routing table. Try
2931 this option if the kernel is unable to allocate
2932 IRQs or discover secondary PCI buses on your
2934 rom [X86] Assign address space to expansion ROMs.
2935 Use with caution as certain devices share
2936 address decoders between ROMs and other
2938 norom [X86] Do not assign address space to
2939 expansion ROMs that do not already have
2940 BIOS assigned address ranges.
2941 nobar [X86] Do not assign address space to the
2942 BARs that weren't assigned by the BIOS.
2943 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2944 assigned automatically to PCI devices. You can
2945 make the kernel exclude IRQs of your ISA cards
2947 pirqaddr=0xAAAAA [X86] Specify the physical address
2948 of the PIRQ table (normally generated
2949 by the BIOS) if it is outside the
2950 F0000h-100000h range.
2951 lastbus=N [X86] Scan all buses thru bus #N. Can be
2952 useful if the kernel is unable to find your
2953 secondary buses and you want to tell it
2954 explicitly which ones they are.
2955 assign-busses [X86] Always assign all PCI bus
2956 numbers ourselves, overriding
2957 whatever the firmware may have done.
2958 usepirqmask [X86] Honor the possible IRQ mask stored
2959 in the BIOS $PIR table. This is needed on
2960 some systems with broken BIOSes, notably
2961 some HP Pavilion N5400 and Omnibook XE3
2962 notebooks. This will have no effect if ACPI
2963 IRQ routing is enabled.
2964 noacpi [X86] Do not use ACPI for IRQ routing
2965 or for PCI scanning.
2966 use_crs [X86] Use PCI host bridge window information
2967 from ACPI. On BIOSes from 2008 or later, this
2968 is enabled by default. If you need to use this,
2969 please report a bug.
2970 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2971 If you need to use this, please report a bug.
2972 routeirq Do IRQ routing for all PCI devices.
2973 This is normally done in pci_enable_device(),
2974 so this option is a temporary workaround
2975 for broken drivers that don't call it.
2976 skip_isa_align [X86] do not align io start addr, so can
2977 handle more pci cards
2978 noearly [X86] Don't do any early type 1 scanning.
2979 This might help on some broken boards which
2980 machine check when some devices' config space
2981 is read. But various workarounds are disabled
2982 and some IOMMU drivers will not work.
2983 bfsort Sort PCI devices into breadth-first order.
2984 This sorting is done to get a device
2985 order compatible with older (<= 2.4) kernels.
2986 nobfsort Don't sort PCI devices into breadth-first order.
2987 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2988 tuning and use the BIOS-configured MPS defaults.
2989 pcie_bus_safe Set every device's MPS to the largest value
2990 supported by all devices below the root complex.
2991 pcie_bus_perf Set device MPS to the largest allowable MPS
2992 based on its parent bus. Also set MRRS (Max
2993 Read Request Size) to the largest supported
2994 value (no larger than the MPS that the device
2995 or bus can support) for best performance.
2996 pcie_bus_peer2peer Set every device's MPS to 128B, which
2997 every device is guaranteed to support. This
2998 configuration allows peer-to-peer DMA between
2999 any pair of devices, possibly at the cost of
3000 reduced performance. This also guarantees
3001 that hot-added devices will work.
3002 cbiosize=nn[KMG] The fixed amount of bus space which is
3003 reserved for the CardBus bridge's IO window.
3004 The default value is 256 bytes.
3005 cbmemsize=nn[KMG] The fixed amount of bus space which is
3006 reserved for the CardBus bridge's memory
3007 window. The default value is 64 megabytes.
3010 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3011 Specifies alignment and device to reassign
3012 aligned memory resources.
3013 If <order of align> is not specified,
3014 PAGE_SIZE is used as alignment.
3015 PCI-PCI bridge can be specified, if resource
3016 windows need to be expanded.
3017 ecrc= Enable/disable PCIe ECRC (transaction layer
3018 end-to-end CRC checking).
3019 bios: Use BIOS/firmware settings. This is the
3023 hpiosize=nn[KMG] The fixed amount of bus space which is
3024 reserved for hotplug bridge's IO window.
3025 Default size is 256 bytes.
3026 hpmemsize=nn[KMG] The fixed amount of bus space which is
3027 reserved for hotplug bridge's memory window.
3028 Default size is 2 megabytes.
3029 realloc= Enable/disable reallocating PCI bridge resources
3030 if allocations done by BIOS are too small to
3031 accommodate resources required by all child
3033 off: Turn realloc off
3035 realloc same as realloc=on
3036 noari do not use PCIe ARI.
3037 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3038 only look for one device below a PCIe downstream
3041 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3044 force Enable ASPM even on devices that claim not to support it.
3045 WARNING: Forcing ASPM on may cause system lockups.
3047 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3048 nomsi Do not use MSI for PCI Express Native Hotplug (this
3049 makes all PCIe ports use INTx for hotplug services).
3051 pcie_ports= [PCIE] PCIe ports handling:
3052 auto Ask the BIOS whether or not to use native PCIe services
3053 associated with PCIe ports (PME, hot-plug, AER). Use
3054 them only if that is allowed by the BIOS.
3055 native Use native PCIe services associated with PCIe ports
3057 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3060 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3061 nomsi Do not use MSI for native PCIe PME signaling (this makes
3062 all PCIe root ports use INTx for all services).
3064 pcmv= [HW,PCMCIA] BadgePAD 4
3068 Keep all power-domains already enabled by bootloader on,
3069 even if no driver has claimed them. This is useful
3070 for debug and development, but should not be
3071 needed on a platform with proper driver support.
3074 See Documentation/blockdev/paride.txt.
3076 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3079 See arch/parisc/kernel/pdc_chassis.c
3081 percpu_alloc= Select which percpu first chunk allocator to use.
3082 Currently supported values are "embed" and "page".
3083 Archs may support subset or none of the selections.
3084 See comments in mm/percpu.c for details on each
3085 allocator. This parameter is primarily for debugging
3086 and performance comparison.
3089 See Documentation/blockdev/paride.txt.
3092 See Documentation/blockdev/paride.txt.
3094 pirq= [SMP,APIC] Manual mp-table setup
3095 See Documentation/x86/i386/IO-APIC.txt.
3097 plip= [PPT,NET] Parallel port network link
3098 Format: { parport<nr> | timid | 0 }
3099 See also Documentation/parport.txt.
3101 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3102 Override pmtimer IOPort with a hex value.
3106 Enable PNP debug messages (depends on the
3107 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3108 via /sys/module/pnp/parameters/debug. We always show
3109 current resource usage; turning this on also shows
3110 possible settings and some assignment information.
3116 { on | off | curr | res | no-curr | no-res }
3119 [ISAPNP] Exclude IRQs for the autoconfiguration
3122 [ISAPNP] Exclude DMAs for the autoconfiguration
3124 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3125 Ranges are in pairs (I/O port base and size).
3128 [ISAPNP] Exclude memory regions for the
3130 Ranges are in pairs (memory base and size).
3132 ports= [IP_VS_FTP] IPVS ftp helper module
3134 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3136 Format: <port>,<port>....
3138 ppc_strict_facility_enable
3139 [PPC] This option catches any kernel floating point,
3140 Altivec, VSX and SPE outside of regions specifically
3141 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3142 There is some performance impact when enabling this.
3144 print-fatal-signals=
3145 [KNL] debug: print fatal signals
3147 If enabled, warn about various signal handling
3148 related application anomalies: too many signals,
3149 too many POSIX.1 timers, fatal signals causing a
3152 If you hit the warning due to signal overflow,
3153 you might want to try "ulimit -i unlimited".
3157 printk.always_kmsg_dump=
3158 Trigger kmsg_dump for cases other than kernel oops or
3160 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3163 printk.time= Show timing data prefixed to each printk message line
3164 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3166 processor.max_cstate= [HW,ACPI]
3167 Limit processor to maximum C-state
3168 max_cstate=9 overrides any DMI blacklist limit.
3170 processor.nocst [HW,ACPI]
3171 Ignore the _CST method to determine C-states,
3172 instead using the legacy FADT method
3174 profile= [KNL] Enable kernel profiling via /proc/profile
3175 Format: [schedule,]<number>
3176 Param: "schedule" - profile schedule points.
3177 Param: <number> - step/bucket size as a power of 2 for
3178 statistical time based profiling.
3179 Param: "sleep" - profile D-state sleeping (millisecs).
3180 Requires CONFIG_SCHEDSTATS
3181 Param: "kvm" - profile VM exits.
3183 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3185 See Documentation/blockdev/ramdisk.txt.
3187 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3188 probe for; one of (bare|imps|exps|lifebook|any).
3189 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3191 psmouse.resetafter= [HW,MOUSE]
3192 Try to reset the device after so many bad packets
3195 [HW,MOUSE] Set desired mouse resolution, in dpi.
3196 psmouse.smartscroll=
3197 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3198 0 = disabled, 1 = enabled (default).
3200 pstore.backend= Specify the name of the pstore backend to use
3203 See Documentation/blockdev/paride.txt.
3206 [KNL] Number of legacy pty's. Overwrites compiled-in
3209 quiet [KNL] Disable most log messages
3214 See Documentation/md.txt.
3216 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3217 See Documentation/blockdev/ramdisk.txt.
3220 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3221 the specified list of CPUs to be no-callback CPUs.
3222 Invocation of these CPUs' RCU callbacks will
3223 be offloaded to "rcuox/N" kthreads created for
3224 that purpose, where "x" is "b" for RCU-bh, "p"
3225 for RCU-preempt, and "s" for RCU-sched, and "N"
3226 is the CPU number. This reduces OS jitter on the
3227 offloaded CPUs, which can be useful for HPC and
3228 real-time workloads. It can also improve energy
3229 efficiency for asymmetric multiprocessors.
3232 Rather than requiring that offloaded CPUs
3233 (specified by rcu_nocbs= above) explicitly
3234 awaken the corresponding "rcuoN" kthreads,
3235 make these kthreads poll for callbacks.
3236 This improves the real-time response for the
3237 offloaded CPUs by relieving them of the need to
3238 wake up the corresponding kthread, but degrades
3239 energy efficiency by requiring that the kthreads
3240 periodically wake up to do the polling.
3242 rcutree.blimit= [KNL]
3243 Set maximum number of finished RCU callbacks to
3244 process in one batch.
3246 rcutree.dump_tree= [KNL]
3247 Dump the structure of the rcu_node combining tree
3248 out at early boot. This is used for diagnostic
3249 purposes, to verify correct tree setup.
3251 rcutree.gp_cleanup_delay= [KNL]
3252 Set the number of jiffies to delay each step of
3253 RCU grace-period cleanup. This only has effect
3254 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3256 rcutree.gp_init_delay= [KNL]
3257 Set the number of jiffies to delay each step of
3258 RCU grace-period initialization. This only has
3259 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3262 rcutree.gp_preinit_delay= [KNL]
3263 Set the number of jiffies to delay each step of
3264 RCU grace-period pre-initialization, that is,
3265 the propagation of recent CPU-hotplug changes up
3266 the rcu_node combining tree. This only has effect
3267 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3269 rcutree.rcu_fanout_exact= [KNL]
3270 Disable autobalancing of the rcu_node combining
3271 tree. This is used by rcutorture, and might
3272 possibly be useful for architectures having high
3273 cache-to-cache transfer latencies.
3275 rcutree.rcu_fanout_leaf= [KNL]
3276 Change the number of CPUs assigned to each
3277 leaf rcu_node structure. Useful for very
3278 large systems, which will choose the value 64,
3279 and for NUMA systems with large remote-access
3280 latencies, which will choose a value aligned
3281 with the appropriate hardware boundaries.
3283 rcutree.jiffies_till_sched_qs= [KNL]
3284 Set required age in jiffies for a
3285 given grace period before RCU starts
3286 soliciting quiescent-state help from
3287 rcu_note_context_switch().
3289 rcutree.jiffies_till_first_fqs= [KNL]
3290 Set delay from grace-period initialization to
3291 first attempt to force quiescent states.
3292 Units are jiffies, minimum value is zero,
3293 and maximum value is HZ.
3295 rcutree.jiffies_till_next_fqs= [KNL]
3296 Set delay between subsequent attempts to force
3297 quiescent states. Units are jiffies, minimum
3298 value is one, and maximum value is HZ.
3300 rcutree.kthread_prio= [KNL,BOOT]
3301 Set the SCHED_FIFO priority of the RCU per-CPU
3302 kthreads (rcuc/N). This value is also used for
3303 the priority of the RCU boost threads (rcub/N)
3304 and for the RCU grace-period kthreads (rcu_bh,
3305 rcu_preempt, and rcu_sched). If RCU_BOOST is
3306 set, valid values are 1-99 and the default is 1
3307 (the least-favored priority). Otherwise, when
3308 RCU_BOOST is not set, valid values are 0-99 and
3309 the default is zero (non-realtime operation).
3311 rcutree.rcu_nocb_leader_stride= [KNL]
3312 Set the number of NOCB kthread groups, which
3313 defaults to the square root of the number of
3314 CPUs. Larger numbers reduces the wakeup overhead
3315 on the per-CPU grace-period kthreads, but increases
3316 that same overhead on each group's leader.
3318 rcutree.qhimark= [KNL]
3319 Set threshold of queued RCU callbacks beyond which
3320 batch limiting is disabled.
3322 rcutree.qlowmark= [KNL]
3323 Set threshold of queued RCU callbacks below which
3324 batch limiting is re-enabled.
3326 rcutree.rcu_idle_gp_delay= [KNL]
3327 Set wakeup interval for idle CPUs that have
3328 RCU callbacks (RCU_FAST_NO_HZ=y).
3330 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3331 Set wakeup interval for idle CPUs that have
3332 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3333 Lazy RCU callbacks are those which RCU can
3334 prove do nothing more than free memory.
3336 rcuperf.gp_exp= [KNL]
3337 Measure performance of expedited synchronous
3338 grace-period primitives.
3340 rcuperf.holdoff= [KNL]
3341 Set test-start holdoff period. The purpose of
3342 this parameter is to delay the start of the
3343 test until boot completes in order to avoid
3346 rcuperf.nreaders= [KNL]
3347 Set number of RCU readers. The value -1 selects
3348 N, where N is the number of CPUs. A value
3349 "n" less than -1 selects N-n+1, where N is again
3350 the number of CPUs. For example, -2 selects N
3351 (the number of CPUs), -3 selects N+1, and so on.
3352 A value of "n" less than or equal to -N selects
3355 rcuperf.nwriters= [KNL]
3356 Set number of RCU writers. The values operate
3357 the same as for rcuperf.nreaders.
3358 N, where N is the number of CPUs
3360 rcuperf.perf_runnable= [BOOT]
3361 Start rcuperf running at boot time.
3363 rcuperf.shutdown= [KNL]
3364 Shut the system down after performance tests
3365 complete. This is useful for hands-off automated
3368 rcuperf.perf_type= [KNL]
3369 Specify the RCU implementation to test.
3371 rcuperf.verbose= [KNL]
3372 Enable additional printk() statements.
3374 rcutorture.cbflood_inter_holdoff= [KNL]
3375 Set holdoff time (jiffies) between successive
3376 callback-flood tests.
3378 rcutorture.cbflood_intra_holdoff= [KNL]
3379 Set holdoff time (jiffies) between successive
3380 bursts of callbacks within a given callback-flood
3383 rcutorture.cbflood_n_burst= [KNL]
3384 Set the number of bursts making up a given
3385 callback-flood test. Set this to zero to
3386 disable callback-flood testing.
3388 rcutorture.cbflood_n_per_burst= [KNL]
3389 Set the number of callbacks to be registered
3390 in a given burst of a callback-flood test.
3392 rcutorture.fqs_duration= [KNL]
3393 Set duration of force_quiescent_state bursts
3396 rcutorture.fqs_holdoff= [KNL]
3397 Set holdoff time within force_quiescent_state bursts
3400 rcutorture.fqs_stutter= [KNL]
3401 Set wait time between force_quiescent_state bursts
3404 rcutorture.gp_cond= [KNL]
3405 Use conditional/asynchronous update-side
3406 primitives, if available.
3408 rcutorture.gp_exp= [KNL]
3409 Use expedited update-side primitives, if available.
3411 rcutorture.gp_normal= [KNL]
3412 Use normal (non-expedited) asynchronous
3413 update-side primitives, if available.
3415 rcutorture.gp_sync= [KNL]
3416 Use normal (non-expedited) synchronous
3417 update-side primitives, if available. If all
3418 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3419 rcutorture.gp_normal=, and rcutorture.gp_sync=
3420 are zero, rcutorture acts as if is interpreted
3421 they are all non-zero.
3423 rcutorture.n_barrier_cbs= [KNL]
3424 Set callbacks/threads for rcu_barrier() testing.
3426 rcutorture.nfakewriters= [KNL]
3427 Set number of concurrent RCU writers. These just
3428 stress RCU, they don't participate in the actual
3429 test, hence the "fake".
3431 rcutorture.nreaders= [KNL]
3432 Set number of RCU readers. The value -1 selects
3433 N-1, where N is the number of CPUs. A value
3434 "n" less than -1 selects N-n-2, where N is again
3435 the number of CPUs. For example, -2 selects N
3436 (the number of CPUs), -3 selects N+1, and so on.
3438 rcutorture.object_debug= [KNL]
3439 Enable debug-object double-call_rcu() testing.
3441 rcutorture.onoff_holdoff= [KNL]
3442 Set time (s) after boot for CPU-hotplug testing.
3444 rcutorture.onoff_interval= [KNL]
3445 Set time (s) between CPU-hotplug operations, or
3446 zero to disable CPU-hotplug testing.
3448 rcutorture.shuffle_interval= [KNL]
3449 Set task-shuffle interval (s). Shuffling tasks
3450 allows some CPUs to go into dyntick-idle mode
3451 during the rcutorture test.
3453 rcutorture.shutdown_secs= [KNL]
3454 Set time (s) after boot system shutdown. This
3455 is useful for hands-off automated testing.
3457 rcutorture.stall_cpu= [KNL]
3458 Duration of CPU stall (s) to test RCU CPU stall
3459 warnings, zero to disable.
3461 rcutorture.stall_cpu_holdoff= [KNL]
3462 Time to wait (s) after boot before inducing stall.
3464 rcutorture.stat_interval= [KNL]
3465 Time (s) between statistics printk()s.
3467 rcutorture.stutter= [KNL]
3468 Time (s) to stutter testing, for example, specifying
3469 five seconds causes the test to run for five seconds,
3470 wait for five seconds, and so on. This tests RCU's
3471 ability to transition abruptly to and from idle.
3473 rcutorture.test_boost= [KNL]
3474 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3475 "Maybe" means test if the RCU implementation
3476 under test support RCU priority boosting.
3478 rcutorture.test_boost_duration= [KNL]
3479 Duration (s) of each individual boost test.
3481 rcutorture.test_boost_interval= [KNL]
3482 Interval (s) between each boost test.
3484 rcutorture.test_no_idle_hz= [KNL]
3485 Test RCU's dyntick-idle handling. See also the
3486 rcutorture.shuffle_interval parameter.
3488 rcutorture.torture_runnable= [BOOT]
3489 Start rcutorture running at boot time.
3491 rcutorture.torture_type= [KNL]
3492 Specify the RCU implementation to test.
3494 rcutorture.verbose= [KNL]
3495 Enable additional printk() statements.
3497 rcupdate.rcu_cpu_stall_suppress= [KNL]
3498 Suppress RCU CPU stall warning messages.
3500 rcupdate.rcu_cpu_stall_timeout= [KNL]
3501 Set timeout for RCU CPU stall warning messages.
3503 rcupdate.rcu_expedited= [KNL]
3504 Use expedited grace-period primitives, for
3505 example, synchronize_rcu_expedited() instead
3506 of synchronize_rcu(). This reduces latency,
3507 but can increase CPU utilization, degrade
3508 real-time latency, and degrade energy efficiency.
3509 No effect on CONFIG_TINY_RCU kernels.
3511 rcupdate.rcu_normal= [KNL]
3512 Use only normal grace-period primitives,
3513 for example, synchronize_rcu() instead of
3514 synchronize_rcu_expedited(). This improves
3515 real-time latency, CPU utilization, and
3516 energy efficiency, but can expose users to
3517 increased grace-period latency. This parameter
3518 overrides rcupdate.rcu_expedited. No effect on
3519 CONFIG_TINY_RCU kernels.
3521 rcupdate.rcu_normal_after_boot= [KNL]
3522 Once boot has completed (that is, after
3523 rcu_end_inkernel_boot() has been invoked), use
3524 only normal grace-period primitives. No effect
3525 on CONFIG_TINY_RCU kernels.
3527 rcupdate.rcu_task_stall_timeout= [KNL]
3528 Set timeout in jiffies for RCU task stall warning
3529 messages. Disable with a value less than or equal
3532 rcupdate.rcu_self_test= [KNL]
3533 Run the RCU early boot self tests
3535 rcupdate.rcu_self_test_bh= [KNL]
3536 Run the RCU bh early boot self tests
3538 rcupdate.rcu_self_test_sched= [KNL]
3539 Run the RCU sched early boot self tests
3543 Run specified binary instead of /init from the ramdisk,
3544 used for early userspace startup. See initrd.
3547 Format (x86 or x86_64):
3548 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3550 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3552 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3553 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3554 reboot_force is either force or not specified,
3555 reboot_cpu is s[mp]#### with #### being the processor
3556 to be used for rebooting.
3559 [KNL, SMP] Set scheduler's default relax_domain_level.
3560 See Documentation/cgroups/cpusets.txt.
3562 relative_sleep_states=
3563 [SUSPEND] Use sleep state labeling where the deepest
3564 state available other than hibernation is always "mem".
3565 Format: { "0" | "1" }
3566 0 -- Traditional sleep state labels.
3567 1 -- Relative sleep state labels.
3569 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3571 reservetop= [X86-32]
3573 Reserves a hole at the top of the kernel virtual
3578 Set the amount of memory to reserve for BIOS at
3579 the bottom of the address space.
3581 reset_devices [KNL] Force drivers to reset the underlying device
3582 during initialization.
3585 Specify the partition device for software suspend
3587 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3589 resume_offset= [SWSUSP]
3590 Specify the offset from the beginning of the partition
3591 given by "resume=" at which the swap header is located,
3592 in <PAGE_SIZE> units (needed only for swap files).
3593 See Documentation/power/swsusp-and-swap-files.txt
3595 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3596 read the resume files
3598 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3599 Useful for devices that are detected asynchronously
3600 (e.g. USB and MMC devices).
3602 hibernate= [HIBERNATION]
3603 noresume Don't check if there's a hibernation image
3604 present during boot.
3605 nocompress Don't compress/decompress hibernation images.
3606 no Disable hibernation and resume.
3608 retain_initrd [RAM] Keep initrd memory after extraction
3610 rfkill.default_state=
3611 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3612 etc. communication is blocked by default.
3615 rfkill.master_switch_mode=
3616 0 The "airplane mode" button does nothing.
3617 1 The "airplane mode" button toggles between everything
3618 blocked and the previous configuration.
3619 2 The "airplane mode" button toggles between everything
3620 blocked and everything unblocked.
3622 rhash_entries= [KNL,NET]
3623 Set number of hash buckets for route cache
3625 ro [KNL] Mount root device read-only on boot
3628 on Mark read-only kernel memory as read-only (default).
3629 off Leave read-only kernel memory writable for debugging.
3632 Enable the uart passthrough on the designated usb port
3633 on Rockchip SoCs. When active, the signals of the
3634 debug-uart get routed to the D+ and D- pins of the usb
3635 port and the regular usb controller gets disabled.
3637 root= [KNL] Root filesystem
3638 See name_to_dev_t comment in init/do_mounts.c.
3640 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3641 mount the root filesystem
3643 rootflags= [KNL] Set root filesystem mount option string
3645 rootfstype= [KNL] Set root filesystem type
3647 rootwait [KNL] Wait (indefinitely) for root device to show up.
3648 Useful for devices that are detected asynchronously
3649 (e.g. USB and MMC devices).
3651 rproc_mem=nn[KMG][@address]
3652 [KNL,ARM,CMA] Remoteproc physical memory block.
3653 Memory area to be used by remote processor image,
3656 rw [KNL] Mount root device read-write on boot
3658 S [KNL] Run init in single mode
3660 s390_iommu= [HW,S390]
3661 Set s390 IOTLB flushing mode
3663 With strict flushing every unmap operation will result in
3664 an IOTLB flush. Default is lazy flushing before reuse,
3668 See drivers/net/irda/sa1100_ir.c.
3670 sbni= [NET] Granch SBNI12 leased line adapter
3672 sched_debug [KNL] Enables verbose scheduler debug messages.
3674 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3675 Allowed values are enable and disable. This feature
3676 incurs a small amount of overhead in the scheduler
3677 but is useful for debugging and performance tuning.
3679 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3680 xtime_lock contention on larger systems, and/or RCU lock
3681 contention on all systems with CONFIG_MAXSMP set.
3682 Format: { "0" | "1" }
3683 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3685 Note: increases power consumption, thus should only be
3686 enabled if running jitter sensitive (HPC/RT) workloads.
3688 security= [SECURITY] Choose a security module to enable at boot.
3689 If this boot parameter is not specified, only the first
3690 security module asking for security registration will be
3691 loaded. An invalid security module name will be treated
3692 as if no module has been chosen.
3694 selinux= [SELINUX] Disable or enable SELinux at boot time.
3695 Format: { "0" | "1" }
3696 See security/selinux/Kconfig help text.
3699 Default value is set via kernel config option.
3700 If enabled at boot time, /selinux/disable can be used
3701 later to disable prior to initial policy load.
3703 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3704 Format: { "0" | "1" }
3705 See security/apparmor/Kconfig help text
3708 Default value is set via kernel config option.
3710 serialnumber [BUGS=X86-32]
3713 Maximal number of shapers.
3715 show_msr= [x86] show boot-time MSR settings
3716 Format: { <integer> }
3717 Show boot-time (BIOS-initialized) MSR settings.
3718 The parameter means the number of CPUs to show,
3719 for example 1 means boot CPU only.
3727 Disable merging of slabs with similar size. May be
3728 necessary if there is some reason to distinguish
3729 allocs to different slabs. Debug options disable
3730 merging on their own.
3731 For more information see Documentation/vm/slub.txt.
3733 slab_max_order= [MM, SLAB]
3734 Determines the maximum allowed order for slabs.
3735 A high setting may cause OOMs due to memory
3736 fragmentation. Defaults to 1 for systems with
3737 more than 32MB of RAM, 0 otherwise.
3739 slub_debug[=options[,slabs]] [MM, SLUB]
3740 Enabling slub_debug allows one to determine the
3741 culprit if slab objects become corrupted. Enabling
3742 slub_debug can create guard zones around objects and
3743 may poison objects when not in use. Also tracks the
3744 last alloc / free. For more information see
3745 Documentation/vm/slub.txt.
3747 slub_max_order= [MM, SLUB]
3748 Determines the maximum allowed order for slabs.
3749 A high setting may cause OOMs due to memory
3750 fragmentation. For more information see
3751 Documentation/vm/slub.txt.
3753 slub_min_objects= [MM, SLUB]
3754 The minimum number of objects per slab. SLUB will
3755 increase the slab order up to slub_max_order to
3756 generate a sufficiently large slab able to contain
3757 the number of objects indicated. The higher the number
3758 of objects the smaller the overhead of tracking slabs
3759 and the less frequently locks need to be acquired.
3760 For more information see Documentation/vm/slub.txt.
3762 slub_min_order= [MM, SLUB]
3763 Determines the minimum page order for slabs. Must be
3764 lower than slub_max_order.
3765 For more information see Documentation/vm/slub.txt.
3767 slub_nomerge [MM, SLUB]
3768 Same with slab_nomerge. This is supported for legacy.
3769 See slab_nomerge for more information.
3772 Format: <io1>[,<io2>[,...,<io8>]]
3774 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3775 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3776 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3777 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3778 smsc-ircc2.ircc_irq= [HW] IRQ line
3779 smsc-ircc2.ircc_dma= [HW] DMA channel
3780 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3781 0: Toshiba Satellite 1800 (GP data pin select)
3782 1: Fast pin select (default)
3785 smt [KNL,S390] Set the maximum number of threads (logical
3786 CPUs) to use per physical CPU on systems capable of
3787 symmetric multithreading (SMT). Will be capped to the
3788 actual hardware limit.
3790 Default: -1 (no limit)
3793 [KNL] Should the soft-lockup detector generate panics.
3796 softlockup_all_cpu_backtrace=
3797 [KNL] Should the soft-lockup detector generate
3798 backtraces on all cpus.
3801 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3802 See Documentation/laptops/sonypi.txt
3804 spia_io_base= [HW,MTD]
3810 Enabled the stack tracer on boot up.
3812 stacktrace_filter=[function-list]
3813 [FTRACE] Limit the functions that the stack tracer
3814 will trace at boot up. function-list is a comma separated
3815 list of functions. This list can be changed at run
3816 time by the stack_trace_filter file in the debugfs
3817 tracing directory. Note, this enables stack tracing
3818 and the stacktrace above is not needed.
3822 Set the STI (builtin display/keyboard on the HP-PARISC
3823 machines) console (graphic card) which should be used
3824 as the initial boot-console.
3825 See also comment in drivers/video/console/sticore.c.
3828 See comment in drivers/video/console/sticore.c.
3831 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3833 sunrpc.min_resvport=
3834 sunrpc.max_resvport=
3836 SunRPC servers often require that client requests
3837 originate from a privileged port (i.e. a port in the
3838 range 0 < portnr < 1024).
3839 An administrator who wishes to reserve some of these
3840 ports for other uses may adjust the range that the
3841 kernel's sunrpc client considers to be privileged
3842 using these two parameters to set the minimum and
3843 maximum port values.
3847 Control how the NFS server code allocates CPUs to
3848 service thread pools. Depending on how many NICs
3849 you have and where their interrupts are bound, this
3850 option will affect which CPUs will do NFS serving.
3851 Note: this parameter cannot be changed while the
3852 NFS server is running.
3854 auto the server chooses an appropriate mode
3855 automatically using heuristics
3856 global a single global pool contains all CPUs
3857 percpu one pool for each CPU
3858 pernode one pool for each NUMA node (equivalent
3859 to global on non-NUMA machines)
3861 sunrpc.tcp_slot_table_entries=
3862 sunrpc.udp_slot_table_entries=
3864 Sets the upper limit on the number of simultaneous
3865 RPC calls that can be sent from the client to a
3866 server. Increasing these values may allow you to
3867 improve throughput, but will also increase the
3868 amount of memory reserved for use by the client.
3870 suspend.pm_test_delay=
3872 Sets the number of seconds to remain in a suspend test
3873 mode before resuming the system (see
3874 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3875 is set. Default value is 5.
3878 [KNL] Enable accounting of swap in memory resource
3879 controller if no parameter or 1 is given or disable
3880 it if 0 is given (See Documentation/cgroups/memory.txt)
3882 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3883 Format: { <int> | force }
3884 <int> -- Number of I/O TLB slabs
3885 force -- force using of bounce buffers even if they
3886 wouldn't be automatically used by the kernel
3890 sysfs.deprecated=0|1 [KNL]
3891 Enable/disable old style sysfs layout for old udev
3892 on older distributions. When this option is enabled
3893 very new udev will not work anymore. When this option
3894 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3895 in older udev will not work anymore.
3896 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3897 the kernel configuration.
3899 sysrq_always_enabled
3901 Ignore sysrq setting - this boot parameter will
3902 neutralize any effect of /proc/sys/kernel/sysrq.
3903 Useful for debugging.
3905 tcpmhash_entries= [KNL,NET]
3906 Set the number of tcp_metrics_hash slots.
3907 Default value is 8192 or 16384 depending on total
3908 ram pages. This is used to specify the TCP metrics
3909 cache size. See Documentation/networking/ip-sysctl.txt
3910 "tcp_no_metrics_save" section for more details.
3914 test_suspend= [SUSPEND][,N]
3915 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3916 standby suspend) or "freeze" (for suspend type freeze)
3917 as the system sleep state during system startup with
3918 the optional capability to repeat N number of times.
3919 The system is woken from this state using a
3920 wakeup-capable RTC alarm.
3922 thash_entries= [KNL,NET]
3923 Set number of hash buckets for TCP connection
3925 thermal.act= [HW,ACPI]
3926 -1: disable all active trip points in all thermal zones
3927 <degrees C>: override all lowest active trip points
3929 thermal.crt= [HW,ACPI]
3930 -1: disable all critical trip points in all thermal zones
3931 <degrees C>: override all critical trip points
3933 thermal.nocrt= [HW,ACPI]
3934 Set to disable actions on ACPI thermal zone
3935 critical and hot trip points.
3937 thermal.off= [HW,ACPI]
3938 1: disable ACPI thermal control
3940 thermal.psv= [HW,ACPI]
3941 -1: disable all passive trip points
3942 <degrees C>: override all passive trip points to this
3945 thermal.tzp= [HW,ACPI]
3946 Specify global default ACPI thermal zone polling rate
3947 <deci-seconds>: poll all this frequency
3948 0: no polling (default)
3951 Force threading of all interrupt handlers except those
3952 marked explicitly IRQF_NO_THREAD.
3955 Enable the Transcendent memory driver if built-in.
3957 tmem.cleancache=0|1 [KNL, XEN]
3958 Default is on (1). Disable the usage of the cleancache
3959 API to send anonymous pages to the hypervisor.
3961 tmem.frontswap=0|1 [KNL, XEN]
3962 Default is on (1). Disable the usage of the frontswap
3963 API to send swap pages to the hypervisor. If disabled
3964 the selfballooning and selfshrinking are force disabled.
3966 tmem.selfballooning=0|1 [KNL, XEN]
3967 Default is on (1). Disable the driving of swap pages
3970 tmem.selfshrinking=0|1 [KNL, XEN]
3971 Default is on (1). Partial swapoff that immediately
3972 transfers pages from Xen hypervisor back to the
3973 kernel based on different criteria.
3977 Specify if the kernel should make use of the cpu
3978 topology information if the hardware supports this.
3979 The scheduler will make use of this information and
3980 e.g. base its process migration decisions on it.
3983 topology_updates= [KNL, PPC, NUMA]
3985 Specify if the kernel should ignore (off)
3986 topology updates sent by the hypervisor to this
3991 tpm_suspend_pcr=[HW,TPM]
3992 Format: integer pcr id
3993 Specify that at suspend time, the tpm driver
3994 should extend the specified pcr with zeros,
3995 as a workaround for some chips which fail to
3996 flush the last written pcr on TPM_SaveState.
3997 This will guarantee that all the other pcrs
4000 trace_buf_size=nn[KMG]
4001 [FTRACE] will set tracing buffer size on each cpu.
4003 trace_event=[event-list]
4004 [FTRACE] Set and start specified trace events in order
4005 to facilitate early boot debugging.
4006 See also Documentation/trace/events.txt
4008 trace_options=[option-list]
4009 [FTRACE] Enable or disable tracer options at boot.
4010 The option-list is a comma delimited list of options
4011 that can be enabled or disabled just as if you were
4012 to echo the option name into
4014 /sys/kernel/debug/tracing/trace_options
4016 For example, to enable stacktrace option (to dump the
4017 stack trace of each event), add to the command line:
4019 trace_options=stacktrace
4021 See also Documentation/trace/ftrace.txt "trace options"
4025 Have the tracepoints sent to printk as well as the
4026 tracing ring buffer. This is useful for early boot up
4027 where the system hangs or reboots and does not give the
4028 option for reading the tracing buffer or performing a
4029 ftrace_dump_on_oops.
4031 To turn off having tracepoints sent to printk,
4032 echo 0 > /proc/sys/kernel/tracepoint_printk
4033 Note, echoing 1 into this file without the
4034 tracepoint_printk kernel cmdline option has no effect.
4038 Having tracepoints sent to printk() and activating high
4039 frequency tracepoints such as irq or sched, can cause
4040 the system to live lock.
4043 [FTRACE] enable this option to disable tracing when a
4044 warning is hit. This turns off "tracing_on". Tracing can
4045 be enabled again by echoing '1' into the "tracing_on"
4046 file located in /sys/kernel/debug/tracing/
4048 This option is useful, as it disables the trace before
4049 the WARNING dump is called, which prevents the trace to
4050 be filled with content caused by the warning output.
4052 This option can also be set at run time via the sysctl
4053 option: kernel/traceoff_on_warning
4055 transparent_hugepage=
4057 Format: [always|madvise|never]
4058 Can be used to control the default behavior of the system
4059 with respect to transparent hugepages.
4060 See Documentation/vm/transhuge.txt for more details.
4062 tsc= Disable clocksource stability checks for TSC.
4064 [x86] reliable: mark tsc clocksource as reliable, this
4065 disables clocksource verification at runtime, as well
4066 as the stability checks done at bootup. Used to enable
4067 high-resolution timer mode on older hardware, and in
4068 virtualized environment.
4069 [x86] noirqtime: Do not use TSC to do irq accounting.
4070 Used to run time disable IRQ_TIME_ACCOUNTING on any
4071 platforms where RDTSC is slow and this accounting
4074 turbografx.map[2|3]= [HW,JOY]
4075 TurboGraFX parallel port interface
4077 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4078 See also Documentation/input/joystick-parport.txt
4080 udbg-immortal [PPC] When debugging early kernel crashes that
4081 happen after console_init() and before a proper
4082 console driver takes over, this boot options might
4083 help "seeing" what's going on.
4085 uhash_entries= [KNL,NET]
4086 Set number of hash buckets for UDP/UDP-Lite connections
4089 [USB] Ignore overcurrent events (default N).
4090 Some badly-designed motherboards generate lots of
4091 bogus events, for ports that aren't wired to
4092 anything. Set this parameter to avoid log spamming.
4093 Note that genuine overcurrent events won't be
4097 [X86] Cause panic on unknown NMI.
4099 usbcore.authorized_default=
4100 [USB] Default USB device authorization:
4101 (default -1 = authorized except for wireless USB,
4102 0 = not authorized, 1 = authorized)
4104 usbcore.autosuspend=
4105 [USB] The autosuspend time delay (in seconds) used
4106 for newly-detected USB devices (default 2). This
4107 is the time required before an idle device will be
4108 autosuspended. Devices for which the delay is set
4109 to a negative value won't be autosuspended at all.
4111 usbcore.usbfs_snoop=
4112 [USB] Set to log all usbfs traffic (default 0 = off).
4114 usbcore.usbfs_snoop_max=
4115 [USB] Maximum number of bytes to snoop in each URB
4118 usbcore.blinkenlights=
4119 [USB] Set to cycle leds on hubs (default 0 = off).
4121 usbcore.old_scheme_first=
4122 [USB] Start with the old device initialization
4123 scheme (default 0 = off).
4125 usbcore.usbfs_memory_mb=
4126 [USB] Memory limit (in MB) for buffers allocated by
4127 usbfs (default = 16, 0 = max = 2047).
4129 usbcore.use_both_schemes=
4130 [USB] Try the other device initialization scheme
4131 if the first one fails (default 1 = enabled).
4133 usbcore.initial_descriptor_timeout=
4134 [USB] Specifies timeout for the initial 64-byte
4135 USB_REQ_GET_DESCRIPTOR request in milliseconds
4136 (default 5000 = 5.0 seconds).
4138 usbcore.nousb [USB] Disable the USB subsystem
4141 [USBHID] The interval which mice are to be polled at.
4143 usb-storage.delay_use=
4144 [UMS] The delay in seconds before a new device is
4145 scanned for Logical Units (default 1).
4148 [UMS] A list of quirks entries to supplement or
4149 override the built-in unusual_devs list. List
4150 entries are separated by commas. Each entry has
4151 the form VID:PID:Flags where VID and PID are Vendor
4152 and Product ID values (4-digit hex numbers) and
4153 Flags is a set of characters, each corresponding
4154 to a common usb-storage quirk flag as follows:
4155 a = SANE_SENSE (collect more than 18 bytes
4157 b = BAD_SENSE (don't collect more than 18
4158 bytes of sense data);
4159 c = FIX_CAPACITY (decrease the reported
4160 device capacity by one sector);
4161 d = NO_READ_DISC_INFO (don't use
4162 READ_DISC_INFO command);
4163 e = NO_READ_CAPACITY_16 (don't use
4164 READ_CAPACITY_16 command);
4165 f = NO_REPORT_OPCODES (don't use report opcodes
4167 g = MAX_SECTORS_240 (don't transfer more than
4168 240 sectors at a time, uas only);
4169 h = CAPACITY_HEURISTICS (decrease the
4170 reported device capacity by one
4171 sector if the number is odd);
4172 i = IGNORE_DEVICE (don't bind to this
4174 j = NO_REPORT_LUNS (don't use report luns
4176 l = NOT_LOCKABLE (don't try to lock and
4177 unlock ejectable media);
4178 m = MAX_SECTORS_64 (don't transfer more
4179 than 64 sectors = 32 KB at a time);
4180 n = INITIAL_READ10 (force a retry of the
4181 initial READ(10) command);
4182 o = CAPACITY_OK (accept the capacity
4183 reported by the device);
4184 p = WRITE_CACHE (the device cache is ON
4186 r = IGNORE_RESIDUE (the device reports
4187 bogus residue values);
4188 s = SINGLE_LUN (the device has only one
4190 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4191 commands, uas only);
4192 u = IGNORE_UAS (don't bind to the uas driver);
4193 w = NO_WP_DETECT (don't test whether the
4194 medium is write-protected).
4195 Example: quirks=0419:aaf5:rl,0421:0433:rc
4197 user_debug= [KNL,ARM]
4199 See arch/arm/Kconfig.debug help text.
4200 1 - undefined instruction events
4202 4 - invalid data aborts
4205 Example: user_debug=31
4208 [X86] Flags controlling user PTE allocations.
4210 nohigh = do not allocate PTE pages in
4211 HIGHMEM regardless of setting
4215 On X86_32, this is an alias for vdso32=. Otherwise:
4217 vdso=1: enable VDSO (the default)
4218 vdso=0: disable VDSO mapping
4220 vdso32= [X86] Control the 32-bit vDSO
4221 vdso32=1: enable 32-bit VDSO
4222 vdso32=0 or vdso32=2: disable 32-bit VDSO
4224 See the help text for CONFIG_COMPAT_VDSO for more
4225 details. If CONFIG_COMPAT_VDSO is set, the default is
4226 vdso32=0; otherwise, the default is vdso32=1.
4228 For compatibility with older kernels, vdso32=2 is an
4231 Try vdso32=0 if you encounter an error that says:
4232 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4235 vector=percpu: enable percpu vector domain
4237 video= [FB] Frame buffer configuration
4238 See Documentation/fb/modedb.txt.
4240 video.brightness_switch_enabled= [0,1]
4241 If set to 1, on receiving an ACPI notify event
4242 generated by hotkey, video driver will adjust brightness
4243 level and then send out the event to user space through
4244 the allocated input device; If set to 0, video driver
4245 will only send out the event without touching backlight
4250 [VMMIO] Memory mapped virtio (platform) device.
4252 <size>@<baseaddr>:<irq>[:<id>]
4254 <size> := size (can use standard suffixes
4256 <baseaddr> := physical base address
4257 <irq> := interrupt number (as passed to
4259 <id> := (optional) platform device id
4261 virtio_mmio.device=1K@0x100b0000:48:7
4263 Can be used multiple times for multiple devices.
4265 vga= [BOOT,X86-32] Select a particular video mode
4266 See Documentation/x86/boot.txt and
4267 Documentation/svga.txt.
4268 Use vga=ask for menu.
4269 This is actually a boot loader parameter; the value is
4270 passed to the kernel using a special protocol.
4272 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4273 size of <nn>. This can be used to increase the
4274 minimum size (128MB on x86). It can also be used to
4275 decrease the size and leave more room for directly
4278 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4281 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4284 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4288 Controls the behavior of vsyscalls (i.e. calls to
4289 fixed addresses of 0xffffffffff600x00 from legacy
4290 code). Most statically-linked binaries and older
4291 versions of glibc use these calls. Because these
4292 functions are at fixed addresses, they make nice
4293 targets for exploits that can control RIP.
4295 emulate [default] Vsyscalls turn into traps and are
4296 emulated reasonably safely.
4298 native Vsyscalls are native syscall instructions.
4299 This is a little bit faster than trapping
4300 and makes a few dynamic recompilers work
4301 better than they would in emulation mode.
4302 It also makes exploits much easier to write.
4304 none Vsyscalls don't work at all. This makes
4305 them quite hard to use for exploits but
4306 might break your system.
4308 vt.color= [VT] Default text color.
4309 Format: 0xYX, X = foreground, Y = background.
4310 Default: 0x07 = light gray on black.
4312 vt.cur_default= [VT] Default cursor shape.
4313 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4314 the parameters of the <Esc>[?A;B;Cc escape sequence;
4315 see VGA-softcursor.txt. Default: 2 = underline.
4317 vt.default_blu= [VT]
4318 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4319 Change the default blue palette of the console.
4320 This is a 16-member array composed of values
4323 vt.default_grn= [VT]
4324 Format: <green0>,<green1>,<green2>,...,<green15>
4325 Change the default green palette of the console.
4326 This is a 16-member array composed of values
4329 vt.default_red= [VT]
4330 Format: <red0>,<red1>,<red2>,...,<red15>
4331 Change the default red palette of the console.
4332 This is a 16-member array composed of values
4338 Set system-wide default UTF-8 mode for all tty's.
4339 Default is 1, i.e. UTF-8 mode is enabled for all
4340 newly opened terminals.
4342 vt.global_cursor_default=
4345 Set system-wide default for whether a cursor
4346 is shown on new VTs. Default is -1,
4347 i.e. cursors will be created by default unless
4348 overridden by individual drivers. 0 will hide
4349 cursors, 1 will display them.
4351 vt.italic= [VT] Default color for italic text; 0-15.
4354 vt.underline= [VT] Default color for underlined text; 0-15.
4357 watchdog timers [HW,WDT] For information on watchdog timers,
4358 see Documentation/watchdog/watchdog-parameters.txt
4359 or other driver-specific files in the
4360 Documentation/watchdog/ directory.
4362 workqueue.watchdog_thresh=
4363 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4364 warn stall conditions and dump internal state to
4365 help debugging. 0 disables workqueue stall
4366 detection; otherwise, it's the stall threshold
4367 duration in seconds. The default value is 30 and
4368 it can be updated at runtime by writing to the
4369 corresponding sysfs file.
4371 workqueue.disable_numa
4372 By default, all work items queued to unbound
4373 workqueues are affine to the NUMA nodes they're
4374 issued on, which results in better behavior in
4375 general. If NUMA affinity needs to be disabled for
4376 whatever reason, this option can be used. Note
4377 that this also can be controlled per-workqueue for
4378 workqueues visible under /sys/bus/workqueue/.
4380 workqueue.power_efficient
4381 Per-cpu workqueues are generally preferred because
4382 they show better performance thanks to cache
4383 locality; unfortunately, per-cpu workqueues tend to
4384 be more power hungry than unbound workqueues.
4386 Enabling this makes the per-cpu workqueues which
4387 were observed to contribute significantly to power
4388 consumption unbound, leading to measurably lower
4389 power usage at the cost of small performance
4392 The default value of this parameter is determined by
4393 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4395 workqueue.debug_force_rr_cpu
4396 Workqueue used to implicitly guarantee that work
4397 items queued without explicit CPU specified are put
4398 on the local CPU. This guarantee is no longer true
4399 and while local CPU is still preferred work items
4400 may be put on foreign CPUs. This debug option
4401 forces round-robin CPU selection to flush out
4402 usages which depend on the now broken guarantee.
4403 When enabled, memory and cache locality will be
4406 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4407 default x2apic cluster mode on platforms
4410 x86_intel_mid_timer= [X86-32,APBT]
4411 Choose timer option for x86 Intel MID platform.
4412 Two valid options are apbt timer only and lapic timer
4413 plus one apbt timer for broadcast timer.
4414 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4416 xen_512gb_limit [KNL,X86-64,XEN]
4417 Restricts the kernel running paravirtualized under Xen
4418 to use only up to 512 GB of RAM. The reason to do so is
4419 crash analysis tools and Xen tools for doing domain
4420 save/restore/migration must be enabled to handle larger
4423 xen_emul_unplug= [HW,X86,XEN]
4424 Unplug Xen emulated devices
4425 Format: [unplug0,][unplug1]
4426 ide-disks -- unplug primary master IDE devices
4427 aux-ide-disks -- unplug non-primary-master IDE devices
4428 nics -- unplug network devices
4429 all -- unplug all emulated devices (NICs and IDE disks)
4430 unnecessary -- unplugging emulated devices is
4431 unnecessary even if the host did not respond to
4433 never -- do not unplug even if version check succeeds
4435 xen_nopvspin [X86,XEN]
4436 Disables the ticketlock slowpath using Xen PV
4440 Disables the PV optimizations forcing the HVM guest to
4441 run as generic HVM guest with no PV drivers.
4443 xirc2ps_cs= [NET,PCMCIA]
4445 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4447 ______________________________________________________________________
4451 Add more DRM drivers.
projects / cascardo / linux.git / blob