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 amd_iommu_intr= [HW,X86-64]
464 Specifies one of the following AMD IOMMU interrupt
466 legacy - Use legacy interrupt remapping mode.
467 vapic - Use virtual APIC mode, which allows IOMMU
468 to inject interrupts directly into guest.
469 This mode requires kvm-amd.avic=1.
470 (Default when IOMMU HW support is present.)
472 amijoy.map= [HW,JOY] Amiga joystick support
473 Map of devices attached to JOY0DAT and JOY1DAT
475 See also Documentation/input/joystick.txt
477 analog.map= [HW,JOY] Analog joystick and gamepad support
478 Specifies type or capabilities of an analog joystick
479 connected to one of 16 gameports
480 Format: <type1>,<type2>,..<type16>
483 Power management functions (SPARCstation-4/5 + deriv.)
485 Disable APC CPU standby support. SPARCstation-Fox does
486 not play well with APC CPU idle - disable it if you have
487 APC and your system crashes randomly.
489 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
490 Change the output verbosity whilst booting
491 Format: { quiet (default) | verbose | debug }
492 Change the amount of debugging information output
493 when initialising the APIC and IO-APIC components.
495 apic_extnmi= [APIC,X86] External NMI delivery setting
496 Format: { bsp (default) | all | none }
497 bsp: External NMI is delivered only to CPU 0
498 all: External NMIs are broadcast to all CPUs as a
500 none: External NMI is masked for all CPUs. This is
501 useful so that a dump capture kernel won't be
505 See Documentation/networking/ipv6.txt.
507 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
508 Limit apic dumping. The parameter defines the maximal
509 number of local apics being dumped. Also it is possible
510 to set it to "all" by meaning -- no limit here.
511 Format: { 1 (default) | 2 | ... | all }.
512 The parameter valid if only apic=debug or
513 apic=verbose is specified.
514 Example: apic=debug show_lapic=all
516 apm= [APM] Advanced Power Management
517 See header of arch/x86/kernel/apm_32.c.
519 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
520 Format: <io>,<irq>,<nodeID>
524 atarimouse= [HW,MOUSE] Atari Mouse
526 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
527 EzKey and similar keyboards
529 atkbd.reset= [HW] Reset keyboard during initialization
531 atkbd.set= [HW] Select keyboard code set
532 Format: <int> (2 = AT (default), 3 = PS/2)
534 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
537 atkbd.softraw= [HW] Choose between synthetic and real raw mode
538 Format: <bool> (0 = real, 1 = synthetic (default))
540 atkbd.softrepeat= [HW]
541 Use software keyboard repeat
543 audit= [KNL] Enable the audit sub-system
544 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
545 0 - kernel audit is disabled and can not be enabled
546 until the next reboot
547 unset - kernel audit is initialized but disabled and
548 will be fully enabled by the userspace auditd.
549 1 - kernel audit is initialized and partially enabled,
550 storing at most audit_backlog_limit messages in
551 RAM until it is fully enabled by the userspace
555 audit_backlog_limit= [KNL] Set the audit queue size limit.
556 Format: <int> (must be >=0)
559 bau= [X86_UV] Enable the BAU on SGI UV. The default
560 behavior is to disable the BAU (i.e. bau=0).
561 Format: { "0" | "1" }
564 unset - Disable the BAU.
566 baycom_epp= [HW,AX25]
569 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
571 See header of drivers/net/hamradio/baycom_par.c.
573 baycom_ser_fdx= [HW,AX25]
574 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
575 Format: <io>,<irq>,<mode>[,<baud>]
576 See header of drivers/net/hamradio/baycom_ser_fdx.c.
578 baycom_ser_hdx= [HW,AX25]
579 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
580 Format: <io>,<irq>,<mode>
581 See header of drivers/net/hamradio/baycom_ser_hdx.c.
583 blkdevparts= Manual partition parsing of block device(s) for
584 embedded devices based on command line input.
585 See Documentation/block/cmdline-partition.txt
587 boot_delay= Milliseconds to delay each printk during boot.
588 Values larger than 10 seconds (10000) are changed to
592 bootmem_debug [KNL] Enable bootmem allocator debug messages.
595 Disable BERT OS support on buggy BIOSes.
597 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
598 bttv.radio= Most important insmod options are available as
600 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
603 bulk_remove=off [PPC] This parameter disables the use of the pSeries
604 firmware feature for flushing multiple hpte entries
607 c101= [NET] Moxa C101 synchronous serial card
609 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
610 Sometimes CPU hardware bugs make them report the cache
611 size incorrectly. The kernel will attempt work arounds
612 to fix known problems, but for some CPUs it is not
613 possible to determine what the correct size should be.
614 This option provides an override for these situations.
616 ca_keys= [KEYS] This parameter identifies a specific key(s) on
617 the system trusted keyring to be used for certificate
619 format: { id:<keyid> | builtin }
621 cca= [MIPS] Override the kernel pages' cache coherency
622 algorithm. Accepted values range from 0 to 7
623 inclusive. See arch/mips/include/asm/pgtable-bits.h
624 for platform specific values (SB1, Loongson3 and
627 ccw_timeout_log [S390]
628 See Documentation/s390/CommonIO for details.
630 cgroup_disable= [KNL] Disable a particular controller
631 Format: {name of the controller(s) to disable}
632 The effects of cgroup_disable=foo are:
633 - foo isn't auto-mounted if you mount all cgroups in
635 - foo isn't visible as an individually mountable
637 {Currently only "memory" controller deal with this and
638 cut the overhead, others just disable the usage. So
639 only cgroup_disable=memory is actually worthy}
641 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
642 Format: { controller[,controller...] | "all" }
643 Like cgroup_disable, but only applies to cgroup v1;
644 the blacklisted controllers remain available in cgroup2.
646 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
648 nosocket -- Disable socket memory accounting.
649 nokmem -- Disable kernel memory accounting.
651 checkreqprot [SELINUX] Set initial checkreqprot flag value.
652 Format: { "0" | "1" }
653 See security/selinux/Kconfig help text.
654 0 -- check protection applied by kernel (includes
655 any implied execute protection).
656 1 -- check protection requested by application.
657 Default value is set via a kernel config option.
658 Value can be changed at runtime via
659 /selinux/checkreqprot.
662 See Documentation/s390/CommonIO for details.
665 Prevents the clock framework from automatically gating
666 clocks that have not been explicitly enabled by a Linux
667 device driver but are enabled in hardware at reset or
668 by the bootloader/firmware. Note that this does not
669 force such clocks to be always-on nor does it reserve
670 those clocks in any way. This parameter is useful for
671 debug and development, but should not be needed on a
672 platform with proper driver support. For more
673 information, see Documentation/clk.txt.
675 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
677 Forces specified clocksource (if available) to be used
678 when calculating gettimeofday(). If specified
679 clocksource is not available, it defaults to PIT.
680 Format: { pit | tsc | cyclone | pmtmr }
682 clocksource= Override the default clocksource
684 Override the default clocksource and use the clocksource
685 with the name specified.
686 Some clocksource names to choose from, depending on
688 [all] jiffies (this is the base, fallback clocksource)
690 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
691 pxa_timer,timer3,32k_counter,timer0_1
693 [X86-32] pit,hpet,tsc;
694 scx200_hrt on Geode; cyclone on IBM x440
702 clocksource.arm_arch_timer.evtstrm=
705 Enable/disable the eventstream feature of the ARM
706 architected timer so that code using WFE-based polling
707 loops can be debugged more effectively on production
710 clearcpuid=BITNUM [X86]
711 Disable CPUID feature X for the kernel. See
712 arch/x86/include/asm/cpufeatures.h for the valid bit
713 numbers. Note the Linux specific bits are not necessarily
714 stable over kernel options, but the vendor specific
716 Also note that user programs calling CPUID directly
717 or using the feature without checking anything
718 will still see it. This just prevents it from
719 being used by the kernel or shown in /proc/cpuinfo.
720 Also note the kernel might malfunction if you disable
723 cma=nn[MG]@[start[MG][-end[MG]]]
725 Sets the size of kernel global memory area for
726 contiguous memory allocations and optionally the
727 placement constraint by the physical address range of
728 memory allocations. A value of 0 disables CMA
729 altogether. For more information, see
730 include/linux/dma-contiguous.h
732 cmo_free_hint= [PPC] Format: { yes | no }
733 Specify whether pages are marked as being inactive
734 when they are freed. This is used in CMO environments
735 to determine OS memory pressure for page stealing by
739 coherent_pool=nn[KMG] [ARM,KNL]
740 Sets the size of memory pool for coherent, atomic dma
741 allocations, by default set to 256K.
743 code_bytes [X86] How many bytes of object code to print
748 com20020= [HW,NET] ARCnet - COM20020 chipset
750 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
752 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
756 ARCnet - COM90xx chipset (memory-mapped buffers)
757 Format: <io>[,<irq>[,<memstart>]]
759 condev= [HW,S390] console device
762 console= [KNL] Output console device and options.
764 tty<n> Use the virtual console device <n>.
768 Use the specified serial port. The options are of
769 the form "bbbbpnf", where "bbbb" is the baud rate,
770 "p" is parity ("n", "o", or "e"), "n" is number of
771 bits, and "f" is flow control ("r" for RTS or
772 omit it). Default is "9600n8".
774 See Documentation/serial-console.txt for more
776 Documentation/networking/netconsole.txt for an
779 uart[8250],io,<addr>[,options]
780 uart[8250],mmio,<addr>[,options]
781 uart[8250],mmio16,<addr>[,options]
782 uart[8250],mmio32,<addr>[,options]
783 uart[8250],0x<addr>[,options]
784 Start an early, polled-mode console on the 8250/16550
785 UART at the specified I/O port or MMIO address,
786 switching to the matching ttyS device later.
787 MMIO inter-register address stride is either 8-bit
788 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
789 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
790 to be equivalent to 'mmio'. 'options' are specified in
791 the same format described for ttyS above; if unspecified,
792 the h/w is not re-initialized.
794 hvc<n> Use the hypervisor console device <n>. This is for
795 both Xen and PowerPC hypervisors.
797 If the device connected to the port is not a TTY but a braille
798 device, prepend "brl," before the device type, for instance
800 For now, only VisioBraille is supported.
802 consoleblank= [KNL] The console blank (screen saver) timeout in
803 seconds. Defaults to 10*60 = 10mins. A value of 0
804 disables the blank timer.
807 [KNL] Change the default value for
808 /proc/<pid>/coredump_filter.
809 See also Documentation/filesystems/proc.txt.
811 cpuidle.off=1 [CPU_IDLE]
812 disable the cpuidle sub-system
815 [X86] Delay for N microsec between assert and de-assert
816 of APIC INIT to start processors. This delay occurs
817 on every CPU online, such as boot, and resume from suspend.
820 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
822 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
824 crashkernel=size[KMG][@offset[KMG]]
825 [KNL] Using kexec, Linux can switch to a 'crash kernel'
826 upon panic. This parameter reserves the physical
827 memory region [offset, offset + size] for that kernel
828 image. If '@offset' is omitted, then a suitable offset
829 is selected automatically. Check
830 Documentation/kdump/kdump.txt for further details.
832 crashkernel=range1:size1[,range2:size2,...][@offset]
833 [KNL] Same as above, but depends on the memory
834 in the running system. The syntax of range is
835 start-[end] where start and end are both
836 a memory unit (amount[KMG]). See also
837 Documentation/kdump/kdump.txt for an example.
839 crashkernel=size[KMG],high
840 [KNL, x86_64] range could be above 4G. Allow kernel
841 to allocate physical memory region from top, so could
842 be above 4G if system have more than 4G ram installed.
843 Otherwise memory region will be allocated below 4G, if
845 It will be ignored if crashkernel=X is specified.
846 crashkernel=size[KMG],low
847 [KNL, x86_64] range under 4G. When crashkernel=X,high
848 is passed, kernel could allocate physical memory region
849 above 4G, that cause second kernel crash on system
850 that require some amount of low memory, e.g. swiotlb
851 requires at least 64M+32K low memory, also enough extra
852 low memory is needed to make sure DMA buffers for 32-bit
853 devices won't run out. Kernel would try to allocate at
854 at least 256M below 4G automatically.
855 This one let user to specify own low range under 4G
856 for second kernel instead.
857 0: to disable low allocation.
858 It will be ignored when crashkernel=X,high is not used
859 or memory reserved is below 4G.
862 [KNL] Disable crypto self-tests
867 cs89x0_media= [HW,NET]
868 Format: { rj45 | aui | bnc }
871 See header of drivers/s390/block/dasd_devmap.c.
873 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
874 (one device per port)
875 Format: <port#>,<type>
876 See also Documentation/input/joystick-parport.txt
878 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
879 time. See Documentation/dynamic-debug-howto.txt for
880 details. Deprecated, see dyndbg.
882 debug [KNL] Enable kernel debugging (events log level).
885 [KNL] verbose self-tests
887 Print debugging info while doing the locking API
889 We default to 0 (no extra messages), setting it to
890 1 will print _a lot_ more information - normally
891 only useful to kernel developers.
893 debug_objects [KNL] Enable object debugging
896 [KNL] Disable object debugging
898 debug_guardpage_minorder=
899 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
900 parameter allows control of the order of pages that will
901 be intentionally kept free (and hence protected) by the
902 buddy allocator. Bigger value increase the probability
903 of catching random memory corruption, but reduce the
904 amount of memory for normal system use. The maximum
905 possible value is MAX_ORDER/2. Setting this parameter
906 to 1 or 2 should be enough to identify most random
907 memory corruption problems caused by bugs in kernel or
908 driver code when a CPU writes to (or reads from) a
909 random memory location. Note that there exists a class
910 of memory corruptions problems caused by buggy H/W or
911 F/W or by drivers badly programing DMA (basically when
912 memory is written at bus level and the CPU MMU is
913 bypassed) which are not detectable by
914 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
915 tracking down these problems.
918 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
919 parameter enables the feature at boot time. In
920 default, it is disabled. We can avoid allocating huge
921 chunk of memory for debug pagealloc if we don't enable
922 it at boot time and the system will work mostly same
923 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
924 on: enable the feature
926 debugpat [X86] Enable PAT debugging
928 decnet.addr= [HW,NET]
929 Format: <area>[,<node>]
930 See also Documentation/networking/decnet.txt.
933 [same as hugepagesz=] The size of the default
934 HugeTLB page size. This is the size represented by
935 the legacy /proc/ hugepages APIs, used for SHM, and
936 default size when mounting hugetlbfs filesystems.
937 Defaults to the default architecture's huge page size
941 Set number of hash buckets for dentry cache.
943 disable_1tb_segments [PPC]
944 Disables the use of 1TB hash page table segments. This
945 causes the kernel to fall back to 256MB segments which
946 can be useful when debugging issues that require an SLB
950 See Documentation/networking/ipv6.txt.
953 Disable RADIX MMU mode on POWER9
955 disable_cpu_apicid= [X86,APIC,SMP]
957 The number of initial APIC ID for the
958 corresponding CPU to be disabled at boot,
959 mostly used for the kdump 2nd kernel to
960 disable BSP to wake up multiple CPUs without
961 causing system reset or hang due to sending
964 disable_ddw [PPC/PSERIES]
965 Disable Dynamic DMA Window support. Use this if
966 to workaround buggy firmware.
969 See Documentation/networking/ipv6.txt.
971 disable_mtrr_cleanup [X86]
972 The kernel tries to adjust MTRR layout from continuous
973 to discrete, to make X server driver able to add WB
974 entry later. This parameter disables that.
976 disable_mtrr_trim [X86, Intel and AMD only]
977 By default the kernel will trim any uncacheable
978 memory out of your available memory pool based on
979 MTRR settings. This parameter disables that behavior,
980 possibly causing your machine to run very slowly.
982 disable_timer_pin_1 [X86]
983 Disable PIN 1 of APIC timer
984 Can be useful to work around chipset bugs.
986 dis_ucode_ldr [X86] Disable the microcode loader.
988 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
989 this option disables the debugging code at boot.
991 dma_debug_entries=<number>
992 This option allows to tune the number of preallocated
993 entries for DMA-API debugging code. One entry is
994 required per DMA-API allocation. Use this if the
995 DMA-API debugging code disables itself because the
996 architectural default is too low.
998 dma_debug_driver=<driver_name>
999 With this option the DMA-API debugging driver
1000 filter feature can be enabled at boot time. Just
1001 pass the driver to filter for as the parameter.
1002 The filter can be disabled or changed to another
1003 driver later using sysfs.
1005 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1006 Broken monitors, graphic adapters, KVMs and EDIDless
1007 panels may send no or incorrect EDID data sets.
1008 This parameter allows to specify an EDID data sets
1009 in the /lib/firmware directory that are used instead.
1010 Generic built-in EDID data sets are used, if one of
1011 edid/1024x768.bin, edid/1280x1024.bin,
1012 edid/1680x1050.bin, or edid/1920x1080.bin is given
1013 and no file with the same name exists. Details and
1014 instructions how to build your own EDID data are
1015 available in Documentation/EDID/HOWTO.txt. An EDID
1016 data set will only be used for a particular connector,
1017 if its name and a colon are prepended to the EDID
1018 name. Each connector may use a unique EDID data
1019 set by separating the files with a comma. An EDID
1020 data set with no connector name will be used for
1021 any connectors not explicitly specified.
1025 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1026 module.dyndbg[="val"]
1027 Enable debug messages at boot time. See
1028 Documentation/dynamic-debug-howto.txt for details.
1030 nompx [X86] Disables Intel Memory Protection Extensions.
1031 See Documentation/x86/intel_mpx.txt for more
1032 information about the feature.
1034 nopku [X86] Disable Memory Protection Keys CPU feature found
1038 on enable eager fpu restore
1039 off disable eager fpu restore
1040 auto selects the default scheme, which automatically
1041 enables eagerfpu restore for xsaveopt.
1043 module.async_probe [KNL]
1044 Enable asynchronous probe on this module.
1046 early_ioremap_debug [KNL]
1047 Enable debug messages in early_ioremap support. This
1048 is useful for tracking down temporary early mappings
1049 which are not unmapped.
1051 earlycon= [KNL] Output early console device and options.
1053 When used with no options, the early console is
1054 determined by the stdout-path property in device
1058 Start an early, polled-mode console on a cadence serial
1059 port at the specified address. The cadence serial port
1060 must already be setup and configured. Options are not
1063 uart[8250],io,<addr>[,options]
1064 uart[8250],mmio,<addr>[,options]
1065 uart[8250],mmio32,<addr>[,options]
1066 uart[8250],mmio32be,<addr>[,options]
1067 uart[8250],0x<addr>[,options]
1068 Start an early, polled-mode console on the 8250/16550
1069 UART at the specified I/O port or MMIO address.
1070 MMIO inter-register address stride is either 8-bit
1071 (mmio) or 32-bit (mmio32 or mmio32be).
1072 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1073 to be equivalent to 'mmio'. 'options' are specified
1074 in the same format described for "console=ttyS<n>"; if
1075 unspecified, the h/w is not initialized.
1079 Start an early, polled-mode console on a pl011 serial
1080 port at the specified address. The pl011 serial port
1081 must already be setup and configured. Options are not
1082 yet supported. If 'mmio32' is specified, then only
1083 the driver will use only 32-bit accessors to read/write
1084 the device registers.
1087 Start an early, polled-mode console on a meson serial
1088 port at the specified address. The serial port must
1089 already be setup and configured. Options are not yet
1093 Start an early, polled-mode console on an msm serial
1094 port at the specified address. The serial port
1095 must already be setup and configured. Options are not
1098 msm_serial_dm,<addr>
1099 Start an early, polled-mode console on an msm serial
1100 dm port at the specified address. The serial port
1101 must already be setup and configured. Options are not
1104 smh Use ARM semihosting calls for early console.
1112 Use early console provided by serial driver available
1113 on Samsung SoCs, requires selecting proper type and
1114 a correct base address of the selected UART port. The
1115 serial port must already be setup and configured.
1116 Options are not yet supported.
1120 Use early console provided by Freescale LP UART driver
1121 found on Freescale Vybrid and QorIQ LS1021A processors.
1122 A valid base address must be provided, and the serial
1123 port must already be setup and configured.
1125 armada3700_uart,<addr>
1126 Start an early, polled-mode console on the
1127 Armada 3700 serial port at the specified
1128 address. The serial port must already be setup
1129 and configured. Options are not yet supported.
1131 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1135 earlyprintk=serial[,ttySn[,baudrate]]
1136 earlyprintk=serial[,0x...[,baudrate]]
1137 earlyprintk=ttySn[,baudrate]
1138 earlyprintk=dbgp[debugController#]
1139 earlyprintk=pciserial,bus:device.function[,baudrate]
1141 earlyprintk is useful when the kernel crashes before
1142 the normal console is initialized. It is not enabled by
1143 default because it has some cosmetic problems.
1145 Append ",keep" to not disable it when the real console
1148 Only one of vga, efi, serial, or usb debug port can
1151 Currently only ttyS0 and ttyS1 may be specified by
1152 name. Other I/O ports may be explicitly specified
1153 on some architectures (x86 and arm at least) by
1154 replacing ttySn with an I/O port address, like this:
1155 earlyprintk=serial,0x1008,115200
1156 You can find the port for a given device in
1157 /proc/tty/driver/serial:
1158 2: uart:ST16650V2 port:00001008 irq:18 ...
1160 Interaction with the standard serial driver is not
1163 The VGA and EFI output is eventually overwritten by
1166 The xen output can only be used by Xen PV guests.
1168 edac_report= [HW,EDAC] Control how to report EDAC event
1169 Format: {"on" | "off" | "force"}
1170 on: enable EDAC to report H/W event. May be overridden
1171 by other higher priority error reporting module.
1172 off: disable H/W event reporting through EDAC.
1173 force: enforce the use of EDAC to report H/W event.
1176 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1179 This is designed to be used in conjunction with
1180 the boot argument: earlyprintk=vga
1183 Format: {"off" | "on" | "skip[mbr]"}
1186 Format: { "old_map", "nochunk", "noruntime", "debug" }
1187 old_map [X86-64]: switch to the old ioremap-based EFI
1188 runtime services mapping. 32-bit still uses this one by
1190 nochunk: disable reading files in "chunks" in the EFI
1191 boot stub, as chunking can cause problems with some
1192 firmware implementations.
1193 noruntime : disable EFI runtime services support
1194 debug: enable misc debug output
1196 efi_no_storage_paranoia [EFI; X86]
1197 Using this parameter you can use more than 50% of
1198 your efi variable storage. Use this parameter only if
1199 you are really sure that your UEFI does sane gc and
1200 fulfills the spec otherwise your board may brick.
1202 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1203 Add arbitrary attribute to specific memory range by
1204 updating original EFI memory map.
1205 Region of memory which aa attribute is added to is
1207 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1208 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1209 attribute is added to range 0x100000000-0x180000000 and
1210 0x10a0000000-0x1120000000.
1212 Using this parameter you can do debugging of EFI memmap
1213 related feature. For example, you can do debugging of
1214 Address Range Mirroring feature even if your box
1217 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1218 that is to be dynamically loaded by Linux. If there are
1219 multiple variables with the same name but with different
1220 vendor GUIDs, all of them will be loaded. See
1221 Documentation/acpi/ssdt-overlays.txt for details.
1224 eisa_irq_edge= [PARISC,HW]
1225 See header of drivers/parisc/eisa.c.
1228 See comment before function elanfreq_setup() in
1229 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1232 Format: {"cfq" | "deadline" | "noop"}
1233 See Documentation/block/cfq-iosched.txt and
1234 Documentation/block/deadline-iosched.txt for details.
1236 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1237 Specifies physical address of start of kernel core
1238 image elf header and optionally the size. Generally
1239 kexec loader will pass this option to capture kernel.
1240 See Documentation/kdump/kdump.txt for details.
1242 enable_mtrr_cleanup [X86]
1243 The kernel tries to adjust MTRR layout from continuous
1244 to discrete, to make X server driver able to add WB
1245 entry later. This parameter enables that.
1247 enable_timer_pin_1 [X86]
1248 Enable PIN 1 of APIC timer
1249 Can be useful to work around chipset bugs
1250 (in particular on some ATI chipsets).
1251 The kernel tries to set a reasonable default.
1253 enforcing [SELINUX] Set initial enforcing status.
1255 See security/selinux/Kconfig help text.
1256 0 -- permissive (log only, no denials).
1257 1 -- enforcing (deny and log).
1259 Value can be changed at runtime via /selinux/enforce.
1262 Disable Error Record Serialization Table (ERST)
1265 ether= [HW,NET] Ethernet cards parameters
1266 This option is obsoleted by the "netdev=" option, which
1267 has equivalent usage. See its documentation for details.
1271 Permit 'security.evm' to be updated regardless of
1272 current integrity status.
1276 fail_make_request=[KNL]
1277 General fault injection mechanism.
1278 Format: <interval>,<probability>,<space>,<times>
1279 See also Documentation/fault-injection/.
1282 See Documentation/blockdev/floppy.txt.
1284 force_pal_cache_flush
1285 [IA-64] Avoid check_sal_cache_flush which may hang on
1286 buggy SAL_CACHE_FLUSH implementations. Using this
1287 parameter will force ia64_sal_cache_flush to call
1288 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1291 Forcefully enable Physical Address Extension (PAE).
1292 Many Pentium M systems disable PAE but may have a
1293 functionally usable PAE implementation.
1294 Warning: use of this parameter will taint the kernel
1295 and may cause unknown problems.
1298 [FTRACE] will set and start the specified tracer
1299 as early as possible in order to facilitate early
1302 ftrace_dump_on_oops[=orig_cpu]
1303 [FTRACE] will dump the trace buffers on oops.
1304 If no parameter is passed, ftrace will dump
1305 buffers of all CPUs, but if you pass orig_cpu, it will
1306 dump only the buffer of the CPU that triggered the
1309 ftrace_filter=[function-list]
1310 [FTRACE] Limit the functions traced by the function
1311 tracer at boot up. function-list is a comma separated
1312 list of functions. This list can be changed at run
1313 time by the set_ftrace_filter file in the debugfs
1316 ftrace_notrace=[function-list]
1317 [FTRACE] Do not trace the functions specified in
1318 function-list. This list can be changed at run time
1319 by the set_ftrace_notrace file in the debugfs
1322 ftrace_graph_filter=[function-list]
1323 [FTRACE] Limit the top level callers functions traced
1324 by the function graph tracer at boot up.
1325 function-list is a comma separated list of functions
1326 that can be changed at run time by the
1327 set_graph_function file in the debugfs tracing directory.
1329 ftrace_graph_notrace=[function-list]
1330 [FTRACE] Do not trace from the functions specified in
1331 function-list. This list is a comma separated list of
1332 functions that can be changed at run time by the
1333 set_graph_notrace file in the debugfs tracing directory.
1336 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1337 support via parallel port (up to 5 devices per port)
1338 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1339 See also Documentation/input/joystick-parport.txt
1343 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1347 gcov_persist= [GCOV] When non-zero (default), profiling data for
1348 kernel modules is saved and remains accessible via
1349 debugfs, even when the module is unloaded/reloaded.
1350 When zero, profiling data is discarded and associated
1351 debugfs files are removed at module unload time.
1353 gpt [EFI] Forces disk with valid GPT signature but
1354 invalid Protective MBR to be treated as GPT. If the
1355 primary GPT is corrupted, it enables the backup/alternate
1356 GPT to be used instead.
1358 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1359 the "Enable 0" bit of the configuration register.
1362 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1363 the "Enable 0" bit of the configuration register.
1366 grcan.select= [HW] Select which physical interface to use.
1369 grcan.txsize= [HW] Sets the size of the tx buffer.
1370 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1372 grcan.rxsize= [HW] Sets the size of the rx buffer.
1373 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1376 hardlockup_all_cpu_backtrace=
1377 [KNL] Should the hard-lockup detector generate
1378 backtraces on all cpus.
1381 hashdist= [KNL,NUMA] Large hashes allocated during boot
1382 are distributed across NUMA nodes. Defaults on
1383 for 64-bit NUMA, off otherwise.
1384 Format: 0 | 1 (for off | on)
1386 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1388 hd= [EIDE] (E)IDE hard drive subsystem geometry
1389 Format: <cyl>,<head>,<sect>
1392 Disable Hardware Error Source Table (HEST) support;
1393 corresponding firmware-first mode error processing
1394 logic will be disabled.
1396 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1397 size of <nn>. This works even on boxes that have no
1398 highmem otherwise. This also works to reduce highmem
1399 size on bigger boxes.
1401 highres= [KNL] Enable/disable high resolution timer mode.
1402 Valid parameters: "on", "off"
1406 See Documentation/isdn/README.HiSax.
1410 hpet= [X86-32,HPET] option to control HPET usage
1411 Format: { enable (default) | disable | force |
1413 disable: disable HPET and use PIT instead
1414 force: allow force enabled of undocumented chips (ICH4,
1416 verbose: show contents of HPET registers during setup
1418 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1419 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1421 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1422 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1423 On x86-64 and powerpc, this option can be specified
1424 multiple times interleaved with hugepages= to reserve
1425 huge pages of different sizes. Valid pages sizes on
1426 x86-64 are 2M (when the CPU supports "pse") and 1G
1427 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1429 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1430 terminal devices. Valid values: 0..8
1431 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1432 If specified, z/VM IUCV HVC accepts connections
1433 from listed z/VM user IDs only.
1435 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1436 hardware thread id mappings.
1437 Format: <cpu>:<hwthread>
1440 Do not unregister boot console at start. This is only
1441 useful for debugging when something happens in the window
1442 between unregistering the boot console and initializing
1445 i2c_bus= [HW] Override the default board specific I2C bus speed
1446 or register an additional I2C bus that is not
1447 registered from board initialization code.
1451 i8042.debug [HW] Toggle i8042 debug mode
1452 i8042.unmask_kbd_data
1453 [HW] Enable printing of interrupt data from the KBD port
1454 (disabled by default, and as a pre-condition
1455 requires that i8042.debug=1 be enabled)
1456 i8042.direct [HW] Put keyboard port into non-translated mode
1457 i8042.dumbkbd [HW] Pretend that controller can only read data from
1458 keyboard and cannot control its state
1459 (Don't attempt to blink the leds)
1460 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1461 i8042.nokbd [HW] Don't check/create keyboard port
1462 i8042.noloop [HW] Disable the AUX Loopback command while probing
1464 i8042.nomux [HW] Don't check presence of an active multiplexing
1466 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1468 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1469 i8042.reset [HW] Reset the controller during init and cleanup
1470 i8042.unlock [HW] Unlock (ignore) the keylock
1471 i8042.kbdreset [HW] Reset device connected to KBD port
1475 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1476 indicates that the driver is running on unsupported
1478 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1479 does not match list of supported models.
1481 [HW] Report power status in /proc/i8k
1482 (disabled by default)
1483 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1486 i915.invert_brightness=
1487 [DRM] Invert the sense of the variable that is used to
1488 set the brightness of the panel backlight. Normally a
1489 brightness value of 0 indicates backlight switched off,
1490 and the maximum of the brightness value sets the backlight
1491 to maximum brightness. If this parameter is set to 0
1492 (default) and the machine requires it, or this parameter
1493 is set to 1, a brightness value of 0 sets the backlight
1494 to maximum brightness, and the maximum of the brightness
1495 value switches the backlight off.
1496 -1 -- never invert brightness
1497 0 -- machine default
1498 1 -- force brightness inversion
1501 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1503 ide-core.nodma= [HW] (E)IDE subsystem
1504 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1505 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1506 .cdrom .chs .ignore_cable are additional options
1507 See Documentation/ide/ide.txt.
1509 ide-generic.probe-mask= [HW] (E)IDE subsystem
1511 Probe mask for legacy ISA IDE ports. Depending on
1512 platform up to 6 ports are supported, enabled by
1513 setting corresponding bits in the mask to 1. The
1514 default value is 0x0, which has a special meaning.
1515 On systems that have PCI, it triggers scanning the
1516 PCI bus for the first and the second port, which
1517 are then probed. On systems without PCI the value
1518 of 0x0 enables probing the two first ports as if it
1521 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1522 Claim all unknown PCI IDE storage controllers.
1525 Format: idle=poll, idle=halt, idle=nomwait
1526 Poll forces a polling idle loop that can slightly
1527 improve the performance of waking up a idle CPU, but
1528 will use a lot of power and make the system run hot.
1530 idle=halt: Halt is forced to be used for CPU idle.
1531 In such case C2/C3 won't be used again.
1532 idle=nomwait: Disable mwait for CPU C-states
1534 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1535 Format: { strict | legacy | 2008 | relaxed }
1538 Choose which programs will be accepted for execution
1539 based on the IEEE 754 NaN encoding(s) supported by
1540 the FPU and the NaN encoding requested with the value
1541 of an ELF file header flag individually set by each
1542 binary. Hardware implementations are permitted to
1543 support either or both of the legacy and the 2008 NaN
1546 Available settings are as follows:
1547 strict accept binaries that request a NaN encoding
1548 supported by the FPU
1549 legacy only accept legacy-NaN binaries, if supported
1551 2008 only accept 2008-NaN binaries, if supported
1553 relaxed accept any binaries regardless of whether
1554 supported by the FPU
1556 The FPU emulator is always able to support both NaN
1557 encodings, so if no FPU hardware is present or it has
1558 been disabled with 'nofpu', then the settings of
1559 'legacy' and '2008' strap the emulator accordingly,
1560 'relaxed' straps the emulator for both legacy-NaN and
1561 2008-NaN, whereas 'strict' enables legacy-NaN only on
1562 legacy processors and both NaN encodings on MIPS32 or
1565 The setting for ABS.fmt/NEG.fmt instruction execution
1566 mode generally follows that for the NaN encoding,
1567 except where unsupported by hardware.
1569 ignore_loglevel [KNL]
1570 Ignore loglevel setting - this will print /all/
1571 kernel messages to the console. Useful for debugging.
1572 We also add it as printk module parameter, so users
1573 could change it dynamically, usually by
1574 /sys/module/printk/parameters/ignore_loglevel.
1577 Ignore RLIMIT_DATA setting for data mappings,
1578 print warning at first misuse. Can be changed via
1579 /sys/module/kernel/parameters/ignore_rlimit_data.
1581 ihash_entries= [KNL]
1582 Set number of hash buckets for inode cache.
1584 ima_appraise= [IMA] appraise integrity measurements
1585 Format: { "off" | "enforce" | "fix" | "log" }
1588 ima_appraise_tcb [IMA]
1589 The builtin appraise policy appraises all files
1593 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1597 The list of supported hash algorithms is defined
1598 in crypto/hash_info.h.
1601 The builtin measurement policy to load during IMA
1602 setup. Specyfing "tcb" as the value, measures all
1603 programs exec'd, files mmap'd for exec, and all files
1604 opened with the read mode bit set by either the
1605 effective uid (euid=0) or uid=0.
1608 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1609 Load a policy which meets the needs of the Trusted
1610 Computing Base. This means IMA will measure all
1611 programs exec'd, files mmap'd for exec, and all files
1612 opened for read by uid=0.
1615 Select one of defined IMA measurements template formats.
1616 Formats: { "ima" | "ima-ng" | "ima-sig" }
1620 [IMA] Define a custom template format.
1621 Format: { "field1|...|fieldN" }
1623 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1624 Format: <min_file_size>
1625 Set the minimal file size for using asynchronous hash.
1626 If left unspecified, ahash usage is disabled.
1628 ahash performance varies for different data sizes on
1629 different crypto accelerators. This option can be used
1630 to achieve the best performance for a particular HW.
1632 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1634 Set hashing buffer size. Default: 4k.
1636 ahash performance varies for different chunk sizes on
1637 different crypto accelerators. This option can be used
1638 to achieve best performance for particular HW.
1642 Run specified binary instead of /sbin/init as init
1645 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1646 for working out where the kernel is dying during
1649 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1650 initcall functions. Useful for debugging built-in
1651 modules and initcalls.
1653 initrd= [BOOT] Specify the location of the initial ramdisk
1655 init_pkru= [x86] Specify the default memory protection keys rights
1656 register contents for all processes. 0x55555554 by
1657 default (disallow access to all but pkey 0). Can
1658 override in debugfs after boot.
1660 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1663 int_pln_enable [x86] Enable power limit notification interrupt
1665 integrity_audit=[IMA]
1666 Format: { "0" | "1" }
1667 0 -- basic integrity auditing messages. (Default)
1668 1 -- additional integrity auditing messages.
1670 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1672 Enable intel iommu driver.
1674 Disable intel iommu driver.
1675 igfx_off [Default Off]
1676 By default, gfx is mapped as normal device. If a gfx
1677 device has a dedicated DMAR unit, the DMAR unit is
1678 bypassed by not enabling DMAR with this option. In
1679 this case, gfx device will use physical address for
1682 With this option iommu will not optimize to look
1683 for io virtual address below 32-bit forcing dual
1684 address cycle on pci bus for cards supporting greater
1685 than 32-bit addressing. The default is to look
1686 for translation below 32-bit and if not available
1687 then look in the higher range.
1688 strict [Default Off]
1689 With this option on every unmap_single operation will
1690 result in a hardware IOTLB flush operation as opposed
1691 to batching them for performance.
1692 sp_off [Default Off]
1693 By default, super page will be supported if Intel IOMMU
1694 has the capability. With this option, super page will
1696 ecs_off [Default Off]
1697 By default, extended context tables will be supported if
1698 the hardware advertises that it has support both for the
1699 extended tables themselves, and also PASID support. With
1700 this option set, extended tables will not be used even
1701 on hardware which claims to support them.
1703 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1704 0 disables intel_idle and fall back on acpi_idle.
1705 1 to 9 specify maximum depth of C-state.
1709 Do not enable intel_pstate as the default
1710 scaling driver for the supported processors
1712 Enable intel_pstate on systems that prohibit it by default
1713 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1714 instead of acpi-cpufreq may disable platform features, such
1715 as thermal controls and power capping, that rely on ACPI
1716 P-States information being indicated to OSPM and therefore
1717 should be used with caution. This option does not work with
1718 processors that aren't supported by the intel_pstate driver
1719 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1721 Do not enable hardware P state control (HWP)
1724 Only load intel_pstate on systems which support
1725 hardware P state control (HWP) if available.
1727 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1728 Description Table, specifies preferred power management
1729 profile as "Enterprise Server" or "Performance Server",
1730 then this feature is turned on by default.
1732 intremap= [X86-64, Intel-IOMMU]
1733 on enable Interrupt Remapping (default)
1734 off disable Interrupt Remapping
1735 nosid disable Source ID checking
1737 BIOS x2APIC opt-out request will be ignored
1738 nopost disable Interrupt Posting
1740 iomem= Disable strict checking of access to MMIO memory
1741 strict regions from userspace.
1756 nobypass [PPC/POWERNV]
1757 Disable IOMMU bypass, using IOMMU for PCI devices.
1760 io7= [HW] IO7 for Marvel based alpha systems
1761 See comment before marvel_specify_io7 in
1762 arch/alpha/kernel/core_marvel.c.
1764 io_delay= [X86] I/O delay method
1766 Standard port 0x80 based delay
1768 Alternate port 0xed based delay (needed on some systems)
1770 Simple two microseconds delay
1775 See Documentation/filesystems/nfs/nfsroot.txt.
1777 irqaffinity= [SMP] Set the default irq affinity mask
1779 <cpu number>,...,<cpu number>
1781 <cpu number>-<cpu number>
1782 (must be a positive range in ascending order)
1784 <cpu number>,...,<cpu number>-<cpu number>
1787 When an interrupt is not handled search all handlers
1788 for it. Intended to get systems with badly broken
1792 When an interrupt is not handled search all handlers
1793 for it. Also check all handlers each timer
1794 interrupt. Intended to get systems with badly broken
1798 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1800 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1802 <cpu number>,...,<cpu number>
1804 <cpu number>-<cpu number>
1805 (must be a positive range in ascending order)
1807 <cpu number>,...,<cpu number>-<cpu number>
1809 This option can be used to specify one or more CPUs
1810 to isolate from the general SMP balancing and scheduling
1811 algorithms. You can move a process onto or off an
1812 "isolated" CPU via the CPU affinity syscalls or cpuset.
1813 <cpu number> begins at 0 and the maximum value is
1814 "number of CPUs in system - 1".
1816 This option is the preferred way to isolate CPUs. The
1817 alternative -- manually setting the CPU mask of all
1818 tasks in the system -- can cause problems and
1819 suboptimal load balancer performance.
1823 ivrs_ioapic [HW,X86_64]
1824 Provide an override to the IOAPIC-ID<->DEVICE-ID
1825 mapping provided in the IVRS ACPI table. For
1826 example, to map IOAPIC-ID decimal 10 to
1827 PCI device 00:14.0 write the parameter as:
1828 ivrs_ioapic[10]=00:14.0
1830 ivrs_hpet [HW,X86_64]
1831 Provide an override to the HPET-ID<->DEVICE-ID
1832 mapping provided in the IVRS ACPI table. For
1833 example, to map HPET-ID decimal 0 to
1834 PCI device 00:14.0 write the parameter as:
1835 ivrs_hpet[0]=00:14.0
1837 ivrs_acpihid [HW,X86_64]
1838 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1839 mapping provided in the IVRS ACPI table. For
1840 example, to map UART-HID:UID AMD0020:0 to
1841 PCI device 00:14.5 write the parameter as:
1842 ivrs_acpihid[00:14.5]=AMD0020:0
1844 js= [HW,JOY] Analog joystick
1845 See Documentation/input/joystick.txt.
1848 When CONFIG_RANDOMIZE_BASE is set, this disables
1849 kernel and module base offset ASLR (Address Space
1850 Layout Randomization).
1854 kernelcore= [KNL,X86,IA-64,PPC]
1855 Format: nn[KMGTPE] | "mirror"
1857 specifies the amount of memory usable by the kernel
1858 for non-movable allocations. The requested amount is
1859 spread evenly throughout all nodes in the system. The
1860 remaining memory in each node is used for Movable
1861 pages. In the event, a node is too small to have both
1862 kernelcore and Movable pages, kernelcore pages will
1863 take priority and other nodes will have a larger number
1864 of Movable pages. The Movable zone is used for the
1865 allocation of pages that may be reclaimed or moved
1866 by the page migration subsystem. This means that
1867 HugeTLB pages may not be allocated from this zone.
1868 Note that allocations like PTEs-from-HighMem still
1869 use the HighMem zone if it exists, and the Normal
1870 zone if it does not.
1872 Instead of specifying the amount of memory (nn[KMGTPE]),
1873 you can specify "mirror" option. In case "mirror"
1874 option is specified, mirrored (reliable) memory is used
1875 for non-movable allocations and remaining memory is used
1876 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1877 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1880 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1881 Format: <Controller#>[,poll interval]
1882 The controller # is the number of the ehci usb debug
1883 port as it is probed via PCI. The poll interval is
1884 optional and is the number seconds in between
1885 each poll cycle to the debug port in case you need
1886 the functionality for interrupting the kernel with
1887 gdb or control-c on the dbgp connection. When
1888 not using this parameter you use sysrq-g to break into
1889 the kernel debugger.
1891 kgdboc= [KGDB,HW] kgdb over consoles.
1892 Requires a tty driver that supports console polling,
1893 or a supported polling keyboard driver (non-usb).
1894 Serial only format: <serial_device>[,baud]
1895 keyboard only format: kbd
1896 keyboard and serial format: kbd,<serial_device>[,baud]
1897 Optional Kernel mode setting:
1898 kms, kbd format: kms,kbd
1899 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1901 kgdbwait [KGDB] Stop kernel execution and enter the
1902 kernel debugger at the earliest opportunity.
1904 kmac= [MIPS] korina ethernet MAC address.
1905 Configure the RouterBoard 532 series on-chip
1906 Ethernet adapter MAC address.
1908 kmemleak= [KNL] Boot-time kmemleak enable/disable
1909 Valid arguments: on, off
1911 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1914 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1915 Valid arguments: 0, 1, 2
1916 kmemcheck=0 (disabled)
1917 kmemcheck=1 (enabled)
1918 kmemcheck=2 (one-shot mode)
1919 Default: 2 (one-shot mode)
1921 kstack=N [X86] Print N words from the kernel stack
1924 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1925 Default is 0 (don't ignore, but inject #GP)
1927 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1931 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1932 Default is 1 (enabled)
1934 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1936 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1938 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1939 (virtualized MMU) support on capable Intel chips.
1940 Default is 1 (enabled)
1942 kvm-intel.emulate_invalid_guest_state=
1943 [KVM,Intel] Enable emulation of invalid guest states
1944 Default is 0 (disabled)
1946 kvm-intel.flexpriority=
1947 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1948 Default is 1 (enabled)
1951 [KVM,Intel] Enable VMX nesting (nVMX).
1952 Default is 0 (disabled)
1954 kvm-intel.unrestricted_guest=
1955 [KVM,Intel] Disable unrestricted guest feature
1956 (virtualized real and unpaged mode) on capable
1957 Intel chips. Default is 1 (enabled)
1959 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1960 feature (tagged TLBs) on capable Intel chips.
1961 Default is 1 (enabled)
1967 lapic [X86-32,APIC] Enable the local APIC even if BIOS
1970 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1971 value for LAPIC timer one-shot implementation. Default
1972 back to the programmable timer unit in the LAPIC.
1974 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1977 libata.dma= [LIBATA] DMA control
1978 libata.dma=0 Disable all PATA and SATA DMA
1979 libata.dma=1 PATA and SATA Disk DMA only
1980 libata.dma=2 ATAPI (CDROM) DMA only
1981 libata.dma=4 Compact Flash DMA only
1982 Combinations also work, so libata.dma=3 enables DMA
1983 for disks and CDROMs, but not CFs.
1985 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1986 libata.ignore_hpa=0 keep BIOS limits (default)
1987 libata.ignore_hpa=1 ignore limits, using full disk
1989 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1993 libata.force= [LIBATA] Force configurations. The format is comma
1994 separated list of "[ID:]VAL" where ID is
1995 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1996 matching port, link or device. Basically, it matches
1997 the ATA ID string printed on console by libata. If
1998 the whole ID part is omitted, the last PORT and DEVICE
1999 values are used. If ID hasn't been specified yet, the
2000 configuration applies to all ports, links and devices.
2002 If only DEVICE is omitted, the parameter applies to
2003 the port and all links and devices behind it. DEVICE
2004 number of 0 either selects the first device or the
2005 first fan-out link behind PMP device. It does not
2006 select the host link. DEVICE number of 15 selects the
2007 host link and device attached to it.
2009 The VAL specifies the configuration to force. As long
2010 as there's no ambiguity shortcut notation is allowed.
2011 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2012 The following configurations can be forced.
2014 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2015 Any ID with matching PORT is used.
2017 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2019 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2020 udma[/][16,25,33,44,66,100,133] notation is also
2023 * [no]ncq: Turn on or off NCQ.
2025 * [no]ncqtrim: Turn off queued DSM TRIM.
2027 * nohrst, nosrst, norst: suppress hard, soft
2030 * rstonce: only attempt one reset during
2031 hot-unplug link recovery
2033 * dump_id: dump IDENTIFY data.
2035 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2037 * disable: Disable this device.
2039 If there are multiple matching configurations changing
2040 the same attribute, the last one is used.
2042 memblock=debug [KNL] Enable memblock debug messages.
2044 load_ramdisk= [RAM] List of ramdisks to load from floppy
2045 See Documentation/blockdev/ramdisk.txt.
2047 lockd.nlm_grace_period=P [NFS] Assign grace period.
2050 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2053 lockd.nlm_timeout=T [NFS] Assign timeout value.
2056 lockd.nlm_udpport=M [NFS] Assign UDP port.
2059 locktorture.nreaders_stress= [KNL]
2060 Set the number of locking read-acquisition kthreads.
2061 Defaults to being automatically set based on the
2062 number of online CPUs.
2064 locktorture.nwriters_stress= [KNL]
2065 Set the number of locking write-acquisition kthreads.
2067 locktorture.onoff_holdoff= [KNL]
2068 Set time (s) after boot for CPU-hotplug testing.
2070 locktorture.onoff_interval= [KNL]
2071 Set time (s) between CPU-hotplug operations, or
2072 zero to disable CPU-hotplug testing.
2074 locktorture.shuffle_interval= [KNL]
2075 Set task-shuffle interval (jiffies). Shuffling
2076 tasks allows some CPUs to go into dyntick-idle
2077 mode during the locktorture test.
2079 locktorture.shutdown_secs= [KNL]
2080 Set time (s) after boot system shutdown. This
2081 is useful for hands-off automated testing.
2083 locktorture.stat_interval= [KNL]
2084 Time (s) between statistics printk()s.
2086 locktorture.stutter= [KNL]
2087 Time (s) to stutter testing, for example,
2088 specifying five seconds causes the test to run for
2089 five seconds, wait for five seconds, and so on.
2090 This tests the locking primitive's ability to
2091 transition abruptly to and from idle.
2093 locktorture.torture_runnable= [BOOT]
2094 Start locktorture running at boot time.
2096 locktorture.torture_type= [KNL]
2097 Specify the locking implementation to test.
2099 locktorture.verbose= [KNL]
2100 Enable additional printk() statements.
2102 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2105 loglevel= All Kernel Messages with a loglevel smaller than the
2106 console loglevel will be printed to the console. It can
2107 also be changed with klogd or other programs. The
2108 loglevels are defined as follows:
2110 0 (KERN_EMERG) system is unusable
2111 1 (KERN_ALERT) action must be taken immediately
2112 2 (KERN_CRIT) critical conditions
2113 3 (KERN_ERR) error conditions
2114 4 (KERN_WARNING) warning conditions
2115 5 (KERN_NOTICE) normal but significant condition
2116 6 (KERN_INFO) informational
2117 7 (KERN_DEBUG) debug-level messages
2119 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2120 in bytes. n must be a power of two and greater
2121 than the minimal size. The minimal size is defined
2122 by LOG_BUF_SHIFT kernel config parameter. There is
2123 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2124 that allows to increase the default size depending on
2125 the number of CPUs. See init/Kconfig for more details.
2127 logo.nologo [FB] Disables display of the built-in Linux logo.
2128 This may be used to provide more screen space for
2129 kernel log messages and is useful when debugging
2130 kernel boot problems.
2132 lp=0 [LP] Specify parallel ports to use, e.g,
2133 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2134 lp=reset first parallel port). 'lp=0' disables the
2135 lp=auto printer driver. 'lp=reset' (which can be
2136 specified in addition to the ports) causes
2137 attached printers to be reset. Using
2138 lp=port1,port2,... specifies the parallel ports
2139 to associate lp devices with, starting with
2140 lp0. A port specification may be 'none' to skip
2141 that lp device, or a parport name such as
2142 'parport0'. Specifying 'lp=auto' instead of a
2143 port specification list means that device IDs
2144 from each port should be examined, to see if
2145 an IEEE 1284-compliant printer is attached; if
2146 so, the driver will manage that printer.
2147 See also header of drivers/char/lp.c.
2150 Sets loops_per_jiffy to given constant, thus avoiding
2151 time-consuming boot-time autodetection (up to 250 ms per
2152 CPU). 0 enables autodetection (default). To determine
2153 the correct value for your kernel, boot with normal
2154 autodetection and see what value is printed. Note that
2155 on SMP systems the preset will be applied to all CPUs,
2156 which is likely to cause problems if your CPUs need
2157 significantly divergent settings. An incorrect value
2158 will cause delays in the kernel to be wrong, leading to
2159 unpredictable I/O errors and other breakage. Although
2160 unlikely, in the extreme case this might damage your
2164 Format: <io>,<irq>,<dma>
2166 machvec= [IA-64] Force the use of a particular machine-vector
2167 (machvec) in a generic kernel.
2168 Example: machvec=hpzx1_swiotlb
2170 machtype= [Loongson] Share the same kernel image file between different
2172 Example: machtype=lemote-yeeloong-2f-7inch
2174 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2175 than or equal to this physical address is ignored.
2177 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2178 will bring up during bootup. maxcpus=n : n >= 0 limits
2179 the kernel to bring up 'n' processors. Surely after
2180 bootup you can bring up the other plugged cpu by executing
2181 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2182 only takes effect during system bootup.
2183 While n=0 is a special case, it is equivalent to "nosmp",
2184 which also disables the IO APIC.
2186 max_loop= [LOOP] The number of loop block devices that get
2187 (loop.max_loop) unconditionally pre-created at init time. The default
2188 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2189 of statically allocating a predefined number, loop
2190 devices can be requested on-demand with the
2191 /dev/loop-control interface.
2193 mce [X86-32] Machine Check Exception
2195 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2197 md= [HW] RAID subsystems devices and level
2198 See Documentation/md.txt.
2201 Format: <first>,<last>
2202 Specifies range of consoles to be captured by the MDA.
2204 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2205 Amount of memory to be used when the kernel is not able
2206 to see the whole system memory or for test.
2207 [X86] Work as limiting max address. Use together
2208 with memmap= to avoid physical address space collisions.
2209 Without memmap= PCI devices could be placed at addresses
2210 belonging to unused RAM.
2212 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2216 [KNL,SH] Allow user to override the default size for
2217 per-device physically contiguous DMA buffers.
2219 memhp_default_state=online/offline
2220 [KNL] Set the initial state for the memory hotplug
2221 onlining policy. If not specified, the default value is
2222 set according to the
2223 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2225 See Documentation/memory-hotplug.txt.
2227 memmap=exactmap [KNL,X86] Enable setting of an exact
2228 E820 memory map, as specified by the user.
2229 Such memmap=exactmap lines can be constructed based on
2230 BIOS output or other requirements. See the memmap=nn@ss
2233 memmap=nn[KMG]@ss[KMG]
2234 [KNL] Force usage of a specific region of memory.
2235 Region of memory to be used is from ss to ss+nn.
2237 memmap=nn[KMG]#ss[KMG]
2238 [KNL,ACPI] Mark specific memory as ACPI data.
2239 Region of memory to be marked is from ss to ss+nn.
2241 memmap=nn[KMG]$ss[KMG]
2242 [KNL,ACPI] Mark specific memory as reserved.
2243 Region of memory to be reserved is from ss to ss+nn.
2244 Example: Exclude memory from 0x18690000-0x1869ffff
2245 memmap=64K$0x18690000
2247 memmap=0x10000$0x18690000
2249 memmap=nn[KMG]!ss[KMG]
2250 [KNL,X86] Mark specific memory as protected.
2251 Region of memory to be used, from ss to ss+nn.
2252 The memory region may be marked as e820 type 12 (0xc)
2253 and is NVDIMM or ADR memory.
2255 memory_corruption_check=0/1 [X86]
2256 Some BIOSes seem to corrupt the first 64k of
2257 memory when doing things like suspend/resume.
2258 Setting this option will scan the memory
2259 looking for corruption. Enabling this will
2260 both detect corruption and prevent the kernel
2261 from using the memory being corrupted.
2262 However, its intended as a diagnostic tool; if
2263 repeatable BIOS-originated corruption always
2264 affects the same memory, you can use memmap=
2265 to prevent the kernel from using that memory.
2267 memory_corruption_check_size=size [X86]
2268 By default it checks for corruption in the low
2269 64k, making this memory unavailable for normal
2270 use. Use this parameter to scan for
2271 corruption in more or less memory.
2273 memory_corruption_check_period=seconds [X86]
2274 By default it checks for corruption every 60
2275 seconds. Use this parameter to check at some
2276 other rate. 0 disables periodic checking.
2278 memtest= [KNL,X86,ARM] Enable memtest
2280 default : 0 <disable>
2281 Specifies the number of memtest passes to be
2282 performed. Each pass selects another test
2283 pattern from a given set of patterns. Memtest
2284 fills the memory with this pattern, validates
2285 memory contents and reserves bad memory
2286 regions that are detected.
2288 meye.*= [HW] Set MotionEye Camera parameters
2289 See Documentation/video4linux/meye.txt.
2291 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2292 Multi-Function General Purpose Timers on AMD Geode
2295 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2296 the BIOS has incorrectly applied a workaround. TinyBIOS
2297 version 0.98 is known to be affected, 0.99 fixes the
2298 problem by letting the user disable the workaround.
2302 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2303 physical address is ignored.
2305 mini2440= [ARM,HW,KNL]
2306 Format:[0..2][b][c][t]
2308 MINI2440 configuration specification:
2309 0 - The attached screen is the 3.5" TFT
2310 1 - The attached screen is the 7" TFT
2311 2 - The VGA Shield is attached (1024x768)
2312 Leaving out the screen size parameter will not load
2313 the TFT driver, and the framebuffer will be left
2315 b - Enable backlight. The TFT backlight pin will be
2316 linked to the kernel VESA blanking code and a GPIO
2317 LED. This parameter is not necessary when using the
2319 c - Enable the s3c camera interface.
2320 t - Reserved for enabling touchscreen support. The
2321 touchscreen support is not enabled in the mainstream
2322 kernel as of 2.6.30, a preliminary port can be found
2323 in the "bleeding edge" mini2440 support kernel at
2324 http://repo.or.cz/w/linux-2.6/mini2440.git
2327 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2328 parameter allows control of the logging verbosity for
2329 the additional memory initialisation checks. A value
2330 of 0 disables mminit logging and a level of 4 will
2331 log everything. Information is printed at KERN_DEBUG
2332 so loglevel=8 may also need to be specified.
2335 [KNL] When CONFIG_MODULE_SIG is set, this means that
2336 modules without (valid) signatures will fail to load.
2337 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2338 is always true, so this option does nothing.
2340 module_blacklist= [KNL] Do not load a comma-separated list of
2341 modules. Useful for debugging problem modules.
2344 [MOUSE] Maximum time between finger touching and
2345 leaving touchpad surface for touch to be considered
2346 a tap and be reported as a left button click (for
2347 touchpads working in absolute mode only).
2349 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2350 reporting absolute coordinates, such as tablets
2351 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2352 reporting absolute coordinates, such as tablets
2354 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2355 is similar to kernelcore except it specifies the
2356 amount of memory used for migratable allocations.
2357 If both kernelcore and movablecore is specified,
2358 then kernelcore will be at *least* the specified
2359 value but may be more. If movablecore on its own
2360 is specified, the administrator must be careful
2361 that the amount of memory usable for all allocations
2364 movable_node [KNL,X86] Boot-time switch to enable the effects
2365 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2367 MTD_Partition= [MTD]
2368 Format: <name>,<region-number>,<size>,<offset>
2370 MTD_Region= [MTD] Format:
2371 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2374 See drivers/mtd/cmdlinepart.c.
2376 multitce=off [PPC] This parameter disables the use of the pSeries
2377 firmware feature for updating multiple TCE entries
2380 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2382 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2384 boundary - index of last SLC block on Flex-OneNAND.
2385 The remaining blocks are configured as MLC blocks.
2386 lock - Configure if Flex-OneNAND boundary should be locked.
2387 Once locked, the boundary cannot be changed.
2388 1 indicates lock status, 0 indicates unlock status.
2391 ARM/S3C2412 JIVE boot control
2393 See arch/arm/mach-s3c2412/mach-jive.c
2395 mtouchusb.raw_coordinates=
2396 [HW] Make the MicroTouch USB driver use raw coordinates
2397 ('y', default) or cooked coordinates ('n')
2399 mtrr_chunk_size=nn[KMG] [X86]
2400 used for mtrr cleanup. It is largest continuous chunk
2401 that could hold holes aka. UC entries.
2403 mtrr_gran_size=nn[KMG] [X86]
2404 Used for mtrr cleanup. It is granularity of mtrr block.
2406 Large value could prevent small alignment from
2409 mtrr_spare_reg_nr=n [X86]
2411 Range: 0,7 : spare reg number
2413 Used for mtrr cleanup. It is spare mtrr entries number.
2414 Set to 2 or more if your graphical card needs more.
2416 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2418 netdev= [NET] Network devices parameters
2419 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2420 Note that mem_start is often overloaded to mean
2421 something different and driver-specific.
2422 This usage is only documented in each driver source
2426 [NETFILTER] Enable connection tracking flow accounting
2427 0 to disable accounting
2428 1 to enable accounting
2431 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2432 See Documentation/filesystems/nfs/nfsroot.txt.
2434 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2435 See Documentation/filesystems/nfs/nfsroot.txt.
2437 nfsrootdebug [NFS] enable nfsroot debugging messages.
2438 See Documentation/filesystems/nfs/nfsroot.txt.
2440 nfs.callback_tcpport=
2441 [NFS] set the TCP port on which the NFSv4 callback
2442 channel should listen.
2445 [NFS] sets the pathname to the program which is used
2446 to update the NFS client cache entries.
2448 nfs.cache_getent_timeout=
2449 [NFS] sets the timeout after which an attempt to
2450 update a cache entry is deemed to have failed.
2452 nfs.idmap_cache_timeout=
2453 [NFS] set the maximum lifetime for idmapper cache
2457 [NFS] enable 64-bit inode numbers.
2458 If zero, the NFS client will fake up a 32-bit inode
2459 number for the readdir() and stat() syscalls instead
2460 of returning the full 64-bit number.
2461 The default is to return 64-bit inode numbers.
2463 nfs.max_session_slots=
2464 [NFSv4.1] Sets the maximum number of session slots
2465 the client will attempt to negotiate with the server.
2466 This limits the number of simultaneous RPC requests
2467 that the client can send to the NFSv4.1 server.
2468 Note that there is little point in setting this
2469 value higher than the max_tcp_slot_table_limit.
2471 nfs.nfs4_disable_idmapping=
2472 [NFSv4] When set to the default of '1', this option
2473 ensures that both the RPC level authentication
2474 scheme and the NFS level operations agree to use
2475 numeric uids/gids if the mount is using the
2476 'sec=sys' security flavour. In effect it is
2477 disabling idmapping, which can make migration from
2478 legacy NFSv2/v3 systems to NFSv4 easier.
2479 Servers that do not support this mode of operation
2480 will be autodetected by the client, and it will fall
2481 back to using the idmapper.
2482 To turn off this behaviour, set the value to '0'.
2484 [NFS4] Specify an additional fixed unique ident-
2485 ification string that NFSv4 clients can insert into
2486 their nfs_client_id4 string. This is typically a
2487 UUID that is generated at system install time.
2489 nfs.send_implementation_id =
2490 [NFSv4.1] Send client implementation identification
2491 information in exchange_id requests.
2492 If zero, no implementation identification information
2494 The default is to send the implementation identification
2497 nfs.recover_lost_locks =
2498 [NFSv4] Attempt to recover locks that were lost due
2499 to a lease timeout on the server. Please note that
2500 doing this risks data corruption, since there are
2501 no guarantees that the file will remain unchanged
2502 after the locks are lost.
2503 If you want to enable the kernel legacy behaviour of
2504 attempting to recover these locks, then set this
2506 The default parameter value of '0' causes the kernel
2507 not to attempt recovery of lost locks.
2509 nfs4.layoutstats_timer =
2510 [NFSv4.2] Change the rate at which the kernel sends
2511 layoutstats to the pNFS metadata server.
2513 Setting this to value to 0 causes the kernel to use
2514 whatever value is the default set by the layout
2515 driver. A non-zero value sets the minimum interval
2516 in seconds between layoutstats transmissions.
2518 nfsd.nfs4_disable_idmapping=
2519 [NFSv4] When set to the default of '1', the NFSv4
2520 server will return only numeric uids and gids to
2521 clients using auth_sys, and will accept numeric uids
2522 and gids from such clients. This is intended to ease
2523 migration from NFSv2/v3.
2525 objlayoutdriver.osd_login_prog=
2526 [NFS] [OBJLAYOUT] sets the pathname to the program which
2527 is used to automatically discover and login into new
2528 osd-targets. Please see:
2529 Documentation/filesystems/pnfs.txt for more explanations
2531 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2532 when a NMI is triggered.
2533 Format: [state][,regs][,debounce][,die]
2535 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2536 Format: [panic,][nopanic,][num]
2538 0 - turn hardlockup detector in nmi_watchdog off
2539 1 - turn hardlockup detector in nmi_watchdog on
2540 When panic is specified, panic when an NMI watchdog
2541 timeout occurs (or 'nopanic' to override the opposite
2542 default). To disable both hard and soft lockup detectors,
2543 please see 'nowatchdog'.
2544 This is useful when you use a panic=... timeout and
2545 need the box quickly up again.
2547 netpoll.carrier_timeout=
2548 [NET] Specifies amount of time (in seconds) that
2549 netpoll should wait for a carrier. By default netpoll
2552 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2553 emulation library even if a 387 maths coprocessor
2557 [HW] Never suspend the console
2558 Disable suspending of consoles during suspend and
2559 hibernate operations. Once disabled, debugging
2560 messages can reach various consoles while the rest
2561 of the system is being put to sleep (ie, while
2562 debugging driver suspend/resume hooks). This may
2563 not work reliably with all consoles, but is known
2564 to work with serial and VGA consoles.
2565 To facilitate more flexible debugging, we also add
2566 console_suspend, a printk module parameter to control
2567 it. Users could use console_suspend (usually
2568 /sys/module/printk/parameters/console_suspend) to
2569 turn on/off it dynamically.
2571 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2572 caches in the slab allocator. Saves per-node memory,
2573 but will impact performance.
2577 noapic [SMP,APIC] Tells the kernel to not make use of any
2578 IOAPICs that may be present in the system.
2580 noautogroup Disable scheduler automatic task group creation.
2582 nobats [PPC] Do not use BATs for mapping kernel lowmem
2583 on "Classic" PPC cores.
2587 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2589 nodelayacct [KNL] Disable per-task delay accounting
2591 nodsp [SH] Disable hardware DSP at boot time.
2593 noefi Disable EFI runtime services support.
2598 On X86-32 available only on PAE configured kernels.
2599 noexec=on: enable non-executable mappings (default)
2600 noexec=off: disable non-executable mappings
2603 Disable SMAP (Supervisor Mode Access Prevention)
2604 even if it is supported by processor.
2607 Disable SMEP (Supervisor Mode Execution Prevention)
2608 even if it is supported by processor.
2611 This affects only 32-bit executables.
2612 noexec32=on: enable non-executable mappings (default)
2613 read doesn't imply executable mappings
2614 noexec32=off: disable non-executable mappings
2615 read implies executable mappings
2617 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2619 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2620 register save and restore. The kernel will only save
2621 legacy floating-point registers on task switch.
2623 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2625 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2626 Equivalent to smt=1.
2628 noxsave [BUGS=X86] Disables x86 extended register state save
2629 and restore using xsave. The kernel will fallback to
2630 enabling legacy floating-point and sse state.
2632 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2633 register states. The kernel will fall back to use
2634 xsave to save the states. By using this parameter,
2635 performance of saving the states is degraded because
2636 xsave doesn't support modified optimization while
2637 xsaveopt supports it on xsaveopt enabled systems.
2639 noxsaves [X86] Disables xsaves and xrstors used in saving and
2640 restoring x86 extended register state in compacted
2641 form of xsave area. The kernel will fall back to use
2642 xsaveopt and xrstor to save and restore the states
2643 in standard form of xsave area. By using this
2644 parameter, xsave area per process might occupy more
2645 memory on xsaves enabled systems.
2647 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2648 wfi(ARM) instruction doesn't work correctly and not to
2649 use it. This is also useful when using JTAG debugger.
2651 no_file_caps Tells the kernel not to honor file capabilities. The
2652 only way then for a file to be executed with privilege
2653 is to be setuid root or executed by root.
2655 nohalt [IA-64] Tells the kernel not to use the power saving
2656 function PAL_HALT_LIGHT when idle. This increases
2657 power-consumption. On the positive side, it reduces
2658 interrupt wake-up latency, which may improve performance
2659 in certain environments such as networked servers or
2662 nohibernate [HIBERNATION] Disable hibernation and resume.
2664 nohz= [KNL] Boottime enable/disable dynamic ticks
2665 Valid arguments: on, off
2668 nohz_full= [KNL,BOOT]
2669 In kernels built with CONFIG_NO_HZ_FULL=y, set
2670 the specified list of CPUs whose tick will be stopped
2671 whenever possible. The boot CPU will be forced outside
2672 the range to maintain the timekeeping.
2673 The CPUs in this range must also be included in the
2676 noiotrap [SH] Disables trapped I/O port accesses.
2678 noirqdebug [X86-32] Disables the code which attempts to detect and
2679 disable unhandled interrupt sources.
2681 no_timer_check [X86,APIC] Disables the code which tests for
2682 broken timer IRQ sources.
2684 noisapnp [ISAPNP] Disables ISA PnP code.
2686 noinitrd [RAM] Tells the kernel not to load any configured
2689 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2691 [Deprecated - use intremap=off]
2695 noinvpcid [X86] Disable the INVPCID cpu feature.
2697 nojitter [IA-64] Disables jitter checking for ITC timers.
2699 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2701 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2704 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2705 steal time is computed, but won't influence scheduler
2708 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2710 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2712 noltlbs [PPC] Do not use large page/tlb entries for kernel
2713 lowmem mapping on PPC40x and PPC8xx
2715 nomca [IA-64] Disable machine check abort handling
2717 nomce [X86-32] Disable Machine Check Exception
2719 nomfgpt [X86-32] Disable Multi-Function General Purpose
2720 Timer usage (for AMD Geode machines).
2722 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2723 shutdown the other cpus. Instead use the REBOOT_VECTOR
2726 nomodule Disable module load
2728 nopat [X86] Disable PAT (page attribute table extension of
2729 pagetables) support.
2731 norandmaps Don't use address space randomization. Equivalent to
2732 echo 0 > /proc/sys/kernel/randomize_va_space
2734 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2736 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2737 with UP alternatives
2739 nordrand [X86] Disable kernel use of the RDRAND and
2740 RDSEED instructions even if they are supported
2741 by the processor. RDRAND and RDSEED are still
2742 available to user space applications.
2744 noresume [SWSUSP] Disables resume and restores original swap
2747 no-scroll [VGA] Disables scrollback.
2748 This is required for the Braillex ib80-piezo Braille
2749 reader made by F.H. Papenmeier (Germany).
2753 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2755 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2756 and disable the IO APIC. legacy for "maxcpus=0".
2758 nosoftlockup [KNL] Disable the soft-lockup detector.
2760 nosync [HW,M68K] Disables sync negotiation for all devices.
2762 notsc [BUGS=X86-32] Disable Time Stamp Counter
2764 nowatchdog [KNL] Disable both lockup detectors, i.e.
2765 soft-lockup and NMI watchdog (hard-lockup).
2769 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2771 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2772 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2773 Some features depend on CPU0. Known dependencies are:
2774 1. Resume from suspend/hibernate depends on CPU0.
2775 Suspend/hibernate will fail if CPU0 is offline and you
2776 need to online CPU0 before suspend/hibernate.
2777 2. PIC interrupts also depend on CPU0. CPU0 can't be
2778 removed if a PIC interrupt is detected.
2779 It's said poweroff/reboot may depend on CPU0 on some
2780 machines although I haven't seen such issues so far
2781 after CPU0 is offline on a few tested machines.
2782 If the dependencies are under your control, you can
2783 turn on cpu0_hotplug.
2785 nptcg= [IA-64] Override max number of concurrent global TLB
2786 purges which is reported from either PAL_VM_SUMMARY or
2789 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2790 could support. nr_cpus=n : n >= 1 limits the kernel to
2791 support 'n' processors. It could be larger than the
2792 number of already plugged CPU during bootup, later in
2793 runtime you can physically add extra cpu until it reaches
2794 n. So during boot up some boot time memory for per-cpu
2795 variables need be pre-allocated for later physical cpu
2798 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2800 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2801 Allowed values are enable and disable
2803 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2804 one of ['zone', 'node', 'default'] can be specified
2805 This can be set from sysctl after boot.
2806 See Documentation/sysctl/vm.txt for details.
2808 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2809 See Documentation/debugging-via-ohci1394.txt for more
2812 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2813 Rather than timing out after 20 ms if an EC
2814 command is not properly ACKed, override the length
2815 of the timeout. We have interrupts disabled while
2816 waiting for the ACK, so if this is set too high
2817 interrupts *may* be lost!
2819 omap_mux= [OMAP] Override bootloader pin multiplexing.
2820 Format: <mux_mode0.mode_name=value>...
2821 For example, to override I2C bus2:
2822 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2824 oprofile.timer= [HW]
2825 Use timer interrupt instead of performance counters
2827 oprofile.cpu_type= Force an oprofile cpu type
2828 This might be useful if you have an older oprofile
2829 userland or if you want common events.
2830 Format: { arch_perfmon }
2831 arch_perfmon: [X86] Force use of architectural
2832 perfmon on Intel CPUs instead of the
2833 CPU specific event set.
2834 timer: [X86] Force use of architectural NMI
2835 timer mode (see also oprofile.timer
2836 for generic hr timer mode)
2838 oops=panic Always panic on oopses. Default is to just kill the
2839 process, but there is a small probability of
2840 deadlocking the machine.
2841 This will also cause panics on machine check exceptions.
2842 Useful together with panic=30 to trigger a reboot.
2845 See Documentation/sound/oss/oss-parameters.txt
2847 page_owner= [KNL] Boot-time page_owner enabling option.
2848 Storage of the information about who allocated
2849 each page is disabled in default. With this switch,
2851 on: enable the feature
2853 page_poison= [KNL] Boot-time parameter changing the state of
2854 poisoning on the buddy allocator.
2855 off: turn off poisoning
2856 on: turn on poisoning
2858 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2859 timeout > 0: seconds before rebooting
2860 timeout = 0: wait forever
2861 timeout < 0: reboot immediately
2864 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2867 crash_kexec_post_notifiers
2868 Run kdump after running panic-notifiers and dumping
2869 kmsg. This only for the users who doubt kdump always
2870 succeeds in any situation.
2871 Note that this also increases risks of kdump failure,
2872 because some panic notifiers can make the crashed
2873 kernel more unstable.
2875 parkbd.port= [HW] Parallel port number the keyboard adapter is
2876 connected to, default is 0.
2878 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2879 0 for XT, 1 for AT (default is AT).
2882 parport= [HW,PPT] Specify parallel ports. 0 disables.
2883 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2884 Use 'auto' to force the driver to use any
2885 IRQ/DMA settings detected (the default is to
2886 ignore detected IRQ/DMA settings because of
2887 possible conflicts). You can specify the base
2888 address, IRQ, and DMA settings; IRQ and DMA
2889 should be numbers, or 'auto' (for using detected
2890 settings on that particular port), or 'nofifo'
2891 (to avoid using a FIFO even if it is detected).
2892 Parallel ports are assigned in the order they
2893 are specified on the command line, starting
2896 parport_init_mode= [HW,PPT]
2897 Configure VIA parallel port to operate in
2898 a specific mode. This is necessary on Pegasos
2899 computer where firmware has no options for setting
2900 up parallel port mode and sets it to spp.
2901 Currently this function knows 686a and 8231 chips.
2902 Format: [spp|ps2|epp|ecp|ecpepp]
2905 Halt all CPUs after the first oops has been printed for
2906 the specified number of seconds. This is to be used if
2907 your oopses keep scrolling off the screen.
2912 See header of drivers/block/paride/pcd.c.
2913 See also Documentation/blockdev/paride.txt.
2915 pci=option[,option...] [PCI] various PCI subsystem options:
2916 earlydump [X86] dump PCI config space before the kernel
2918 off [X86] don't probe for the PCI bus
2919 bios [X86-32] force use of PCI BIOS, don't access
2920 the hardware directly. Use this if your machine
2921 has a non-standard PCI host bridge.
2922 nobios [X86-32] disallow use of PCI BIOS, only direct
2923 hardware access methods are allowed. Use this
2924 if you experience crashes upon bootup and you
2925 suspect they are caused by the BIOS.
2926 conf1 [X86] Force use of PCI Configuration Access
2927 Mechanism 1 (config address in IO port 0xCF8,
2928 data in IO port 0xCFC, both 32-bit).
2929 conf2 [X86] Force use of PCI Configuration Access
2930 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2931 the function, IO port 0xCFA, also 8-bit, sets
2932 bus number. The config space is then accessed
2933 through ports 0xC000-0xCFFF).
2934 See http://wiki.osdev.org/PCI for more info
2935 on the configuration access mechanisms.
2936 noaer [PCIE] If the PCIEAER kernel config parameter is
2937 enabled, this kernel boot option can be used to
2938 disable the use of PCIE advanced error reporting.
2939 nodomains [PCI] Disable support for multiple PCI
2940 root domains (aka PCI segments, in ACPI-speak).
2941 nommconf [X86] Disable use of MMCONFIG for PCI
2943 check_enable_amd_mmconf [X86] check for and enable
2944 properly configured MMIO access to PCI
2945 config space on AMD family 10h CPU
2946 nomsi [MSI] If the PCI_MSI kernel config parameter is
2947 enabled, this kernel boot option can be used to
2948 disable the use of MSI interrupts system-wide.
2949 noioapicquirk [APIC] Disable all boot interrupt quirks.
2950 Safety option to keep boot IRQs enabled. This
2951 should never be necessary.
2952 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2953 primary IO-APIC for bridges that cannot disable
2954 boot IRQs. This fixes a source of spurious IRQs
2955 when the system masks IRQs.
2956 noioapicreroute [APIC] Disable workaround that uses the
2957 boot IRQ equivalent of an IRQ that connects to
2958 a chipset where boot IRQs cannot be disabled.
2959 The opposite of ioapicreroute.
2960 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2961 routing table. These calls are known to be buggy
2962 on several machines and they hang the machine
2963 when used, but on other computers it's the only
2964 way to get the interrupt routing table. Try
2965 this option if the kernel is unable to allocate
2966 IRQs or discover secondary PCI buses on your
2968 rom [X86] Assign address space to expansion ROMs.
2969 Use with caution as certain devices share
2970 address decoders between ROMs and other
2972 norom [X86] Do not assign address space to
2973 expansion ROMs that do not already have
2974 BIOS assigned address ranges.
2975 nobar [X86] Do not assign address space to the
2976 BARs that weren't assigned by the BIOS.
2977 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2978 assigned automatically to PCI devices. You can
2979 make the kernel exclude IRQs of your ISA cards
2981 pirqaddr=0xAAAAA [X86] Specify the physical address
2982 of the PIRQ table (normally generated
2983 by the BIOS) if it is outside the
2984 F0000h-100000h range.
2985 lastbus=N [X86] Scan all buses thru bus #N. Can be
2986 useful if the kernel is unable to find your
2987 secondary buses and you want to tell it
2988 explicitly which ones they are.
2989 assign-busses [X86] Always assign all PCI bus
2990 numbers ourselves, overriding
2991 whatever the firmware may have done.
2992 usepirqmask [X86] Honor the possible IRQ mask stored
2993 in the BIOS $PIR table. This is needed on
2994 some systems with broken BIOSes, notably
2995 some HP Pavilion N5400 and Omnibook XE3
2996 notebooks. This will have no effect if ACPI
2997 IRQ routing is enabled.
2998 noacpi [X86] Do not use ACPI for IRQ routing
2999 or for PCI scanning.
3000 use_crs [X86] Use PCI host bridge window information
3001 from ACPI. On BIOSes from 2008 or later, this
3002 is enabled by default. If you need to use this,
3003 please report a bug.
3004 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3005 If you need to use this, please report a bug.
3006 routeirq Do IRQ routing for all PCI devices.
3007 This is normally done in pci_enable_device(),
3008 so this option is a temporary workaround
3009 for broken drivers that don't call it.
3010 skip_isa_align [X86] do not align io start addr, so can
3011 handle more pci cards
3012 noearly [X86] Don't do any early type 1 scanning.
3013 This might help on some broken boards which
3014 machine check when some devices' config space
3015 is read. But various workarounds are disabled
3016 and some IOMMU drivers will not work.
3017 bfsort Sort PCI devices into breadth-first order.
3018 This sorting is done to get a device
3019 order compatible with older (<= 2.4) kernels.
3020 nobfsort Don't sort PCI devices into breadth-first order.
3021 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3022 tuning and use the BIOS-configured MPS defaults.
3023 pcie_bus_safe Set every device's MPS to the largest value
3024 supported by all devices below the root complex.
3025 pcie_bus_perf Set device MPS to the largest allowable MPS
3026 based on its parent bus. Also set MRRS (Max
3027 Read Request Size) to the largest supported
3028 value (no larger than the MPS that the device
3029 or bus can support) for best performance.
3030 pcie_bus_peer2peer Set every device's MPS to 128B, which
3031 every device is guaranteed to support. This
3032 configuration allows peer-to-peer DMA between
3033 any pair of devices, possibly at the cost of
3034 reduced performance. This also guarantees
3035 that hot-added devices will work.
3036 cbiosize=nn[KMG] The fixed amount of bus space which is
3037 reserved for the CardBus bridge's IO window.
3038 The default value is 256 bytes.
3039 cbmemsize=nn[KMG] The fixed amount of bus space which is
3040 reserved for the CardBus bridge's memory
3041 window. The default value is 64 megabytes.
3044 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3045 [<order of align>@]pci:<vendor>:<device>\
3046 [:<subvendor>:<subdevice>][; ...]
3047 Specifies alignment and device to reassign
3048 aligned memory resources.
3049 If <order of align> is not specified,
3050 PAGE_SIZE is used as alignment.
3051 PCI-PCI bridge can be specified, if resource
3052 windows need to be expanded.
3053 To specify the alignment for several
3054 instances of a device, the PCI vendor,
3055 device, subvendor, and subdevice may be
3056 specified, e.g., 4096@pci:8086:9c22:103c:198f
3057 ecrc= Enable/disable PCIe ECRC (transaction layer
3058 end-to-end CRC checking).
3059 bios: Use BIOS/firmware settings. This is the
3063 hpiosize=nn[KMG] The fixed amount of bus space which is
3064 reserved for hotplug bridge's IO window.
3065 Default size is 256 bytes.
3066 hpmemsize=nn[KMG] The fixed amount of bus space which is
3067 reserved for hotplug bridge's memory window.
3068 Default size is 2 megabytes.
3069 hpbussize=nn The minimum amount of additional bus numbers
3070 reserved for buses below a hotplug bridge.
3072 realloc= Enable/disable reallocating PCI bridge resources
3073 if allocations done by BIOS are too small to
3074 accommodate resources required by all child
3076 off: Turn realloc off
3078 realloc same as realloc=on
3079 noari do not use PCIe ARI.
3080 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3081 only look for one device below a PCIe downstream
3084 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3087 force Enable ASPM even on devices that claim not to support it.
3088 WARNING: Forcing ASPM on may cause system lockups.
3090 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3091 nomsi Do not use MSI for PCI Express Native Hotplug (this
3092 makes all PCIe ports use INTx for hotplug services).
3094 pcie_ports= [PCIE] PCIe ports handling:
3095 auto Ask the BIOS whether or not to use native PCIe services
3096 associated with PCIe ports (PME, hot-plug, AER). Use
3097 them only if that is allowed by the BIOS.
3098 native Use native PCIe services associated with PCIe ports
3100 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3103 pcie_port_pm= [PCIE] PCIe port power management handling:
3104 off Disable power management of all PCIe ports
3105 force Forcibly enable power management of all PCIe ports
3107 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3108 nomsi Do not use MSI for native PCIe PME signaling (this makes
3109 all PCIe root ports use INTx for all services).
3111 pcmv= [HW,PCMCIA] BadgePAD 4
3115 Keep all power-domains already enabled by bootloader on,
3116 even if no driver has claimed them. This is useful
3117 for debug and development, but should not be
3118 needed on a platform with proper driver support.
3121 See Documentation/blockdev/paride.txt.
3123 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3126 See arch/parisc/kernel/pdc_chassis.c
3128 percpu_alloc= Select which percpu first chunk allocator to use.
3129 Currently supported values are "embed" and "page".
3130 Archs may support subset or none of the selections.
3131 See comments in mm/percpu.c for details on each
3132 allocator. This parameter is primarily for debugging
3133 and performance comparison.
3136 See Documentation/blockdev/paride.txt.
3139 See Documentation/blockdev/paride.txt.
3141 pirq= [SMP,APIC] Manual mp-table setup
3142 See Documentation/x86/i386/IO-APIC.txt.
3144 plip= [PPT,NET] Parallel port network link
3145 Format: { parport<nr> | timid | 0 }
3146 See also Documentation/parport.txt.
3148 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3149 Override pmtimer IOPort with a hex value.
3153 Enable PNP debug messages (depends on the
3154 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3155 via /sys/module/pnp/parameters/debug. We always show
3156 current resource usage; turning this on also shows
3157 possible settings and some assignment information.
3163 { on | off | curr | res | no-curr | no-res }
3166 [ISAPNP] Exclude IRQs for the autoconfiguration
3169 [ISAPNP] Exclude DMAs for the autoconfiguration
3171 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3172 Ranges are in pairs (I/O port base and size).
3175 [ISAPNP] Exclude memory regions for the
3177 Ranges are in pairs (memory base and size).
3179 ports= [IP_VS_FTP] IPVS ftp helper module
3181 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3183 Format: <port>,<port>....
3185 ppc_strict_facility_enable
3186 [PPC] This option catches any kernel floating point,
3187 Altivec, VSX and SPE outside of regions specifically
3188 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3189 There is some performance impact when enabling this.
3191 print-fatal-signals=
3192 [KNL] debug: print fatal signals
3194 If enabled, warn about various signal handling
3195 related application anomalies: too many signals,
3196 too many POSIX.1 timers, fatal signals causing a
3199 If you hit the warning due to signal overflow,
3200 you might want to try "ulimit -i unlimited".
3204 printk.always_kmsg_dump=
3205 Trigger kmsg_dump for cases other than kernel oops or
3207 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3210 printk.devkmsg={on,off,ratelimit}
3211 Control writing to /dev/kmsg.
3212 on - unlimited logging to /dev/kmsg from userspace
3213 off - logging to /dev/kmsg disabled
3214 ratelimit - ratelimit the logging
3217 printk.time= Show timing data prefixed to each printk message line
3218 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3220 processor.max_cstate= [HW,ACPI]
3221 Limit processor to maximum C-state
3222 max_cstate=9 overrides any DMI blacklist limit.
3224 processor.nocst [HW,ACPI]
3225 Ignore the _CST method to determine C-states,
3226 instead using the legacy FADT method
3228 profile= [KNL] Enable kernel profiling via /proc/profile
3229 Format: [schedule,]<number>
3230 Param: "schedule" - profile schedule points.
3231 Param: <number> - step/bucket size as a power of 2 for
3232 statistical time based profiling.
3233 Param: "sleep" - profile D-state sleeping (millisecs).
3234 Requires CONFIG_SCHEDSTATS
3235 Param: "kvm" - profile VM exits.
3237 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3239 See Documentation/blockdev/ramdisk.txt.
3241 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3242 probe for; one of (bare|imps|exps|lifebook|any).
3243 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3245 psmouse.resetafter= [HW,MOUSE]
3246 Try to reset the device after so many bad packets
3249 [HW,MOUSE] Set desired mouse resolution, in dpi.
3250 psmouse.smartscroll=
3251 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3252 0 = disabled, 1 = enabled (default).
3254 pstore.backend= Specify the name of the pstore backend to use
3257 See Documentation/blockdev/paride.txt.
3260 [KNL] Number of legacy pty's. Overwrites compiled-in
3263 quiet [KNL] Disable most log messages
3268 See Documentation/md.txt.
3271 Enable a very simple form of latent entropy extraction
3272 from the first 4GB of memory as the bootmem allocator
3273 passes the memory pages to the buddy allocator.
3275 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3276 See Documentation/blockdev/ramdisk.txt.
3279 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3280 the specified list of CPUs to be no-callback CPUs.
3281 Invocation of these CPUs' RCU callbacks will
3282 be offloaded to "rcuox/N" kthreads created for
3283 that purpose, where "x" is "b" for RCU-bh, "p"
3284 for RCU-preempt, and "s" for RCU-sched, and "N"
3285 is the CPU number. This reduces OS jitter on the
3286 offloaded CPUs, which can be useful for HPC and
3287 real-time workloads. It can also improve energy
3288 efficiency for asymmetric multiprocessors.
3291 Rather than requiring that offloaded CPUs
3292 (specified by rcu_nocbs= above) explicitly
3293 awaken the corresponding "rcuoN" kthreads,
3294 make these kthreads poll for callbacks.
3295 This improves the real-time response for the
3296 offloaded CPUs by relieving them of the need to
3297 wake up the corresponding kthread, but degrades
3298 energy efficiency by requiring that the kthreads
3299 periodically wake up to do the polling.
3301 rcutree.blimit= [KNL]
3302 Set maximum number of finished RCU callbacks to
3303 process in one batch.
3305 rcutree.dump_tree= [KNL]
3306 Dump the structure of the rcu_node combining tree
3307 out at early boot. This is used for diagnostic
3308 purposes, to verify correct tree setup.
3310 rcutree.gp_cleanup_delay= [KNL]
3311 Set the number of jiffies to delay each step of
3312 RCU grace-period cleanup. This only has effect
3313 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3315 rcutree.gp_init_delay= [KNL]
3316 Set the number of jiffies to delay each step of
3317 RCU grace-period initialization. This only has
3318 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3321 rcutree.gp_preinit_delay= [KNL]
3322 Set the number of jiffies to delay each step of
3323 RCU grace-period pre-initialization, that is,
3324 the propagation of recent CPU-hotplug changes up
3325 the rcu_node combining tree. This only has effect
3326 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3328 rcutree.rcu_fanout_exact= [KNL]
3329 Disable autobalancing of the rcu_node combining
3330 tree. This is used by rcutorture, and might
3331 possibly be useful for architectures having high
3332 cache-to-cache transfer latencies.
3334 rcutree.rcu_fanout_leaf= [KNL]
3335 Change the number of CPUs assigned to each
3336 leaf rcu_node structure. Useful for very
3337 large systems, which will choose the value 64,
3338 and for NUMA systems with large remote-access
3339 latencies, which will choose a value aligned
3340 with the appropriate hardware boundaries.
3342 rcutree.jiffies_till_sched_qs= [KNL]
3343 Set required age in jiffies for a
3344 given grace period before RCU starts
3345 soliciting quiescent-state help from
3346 rcu_note_context_switch().
3348 rcutree.jiffies_till_first_fqs= [KNL]
3349 Set delay from grace-period initialization to
3350 first attempt to force quiescent states.
3351 Units are jiffies, minimum value is zero,
3352 and maximum value is HZ.
3354 rcutree.jiffies_till_next_fqs= [KNL]
3355 Set delay between subsequent attempts to force
3356 quiescent states. Units are jiffies, minimum
3357 value is one, and maximum value is HZ.
3359 rcutree.kthread_prio= [KNL,BOOT]
3360 Set the SCHED_FIFO priority of the RCU per-CPU
3361 kthreads (rcuc/N). This value is also used for
3362 the priority of the RCU boost threads (rcub/N)
3363 and for the RCU grace-period kthreads (rcu_bh,
3364 rcu_preempt, and rcu_sched). If RCU_BOOST is
3365 set, valid values are 1-99 and the default is 1
3366 (the least-favored priority). Otherwise, when
3367 RCU_BOOST is not set, valid values are 0-99 and
3368 the default is zero (non-realtime operation).
3370 rcutree.rcu_nocb_leader_stride= [KNL]
3371 Set the number of NOCB kthread groups, which
3372 defaults to the square root of the number of
3373 CPUs. Larger numbers reduces the wakeup overhead
3374 on the per-CPU grace-period kthreads, but increases
3375 that same overhead on each group's leader.
3377 rcutree.qhimark= [KNL]
3378 Set threshold of queued RCU callbacks beyond which
3379 batch limiting is disabled.
3381 rcutree.qlowmark= [KNL]
3382 Set threshold of queued RCU callbacks below which
3383 batch limiting is re-enabled.
3385 rcutree.rcu_idle_gp_delay= [KNL]
3386 Set wakeup interval for idle CPUs that have
3387 RCU callbacks (RCU_FAST_NO_HZ=y).
3389 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3390 Set wakeup interval for idle CPUs that have
3391 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3392 Lazy RCU callbacks are those which RCU can
3393 prove do nothing more than free memory.
3395 rcuperf.gp_exp= [KNL]
3396 Measure performance of expedited synchronous
3397 grace-period primitives.
3399 rcuperf.holdoff= [KNL]
3400 Set test-start holdoff period. The purpose of
3401 this parameter is to delay the start of the
3402 test until boot completes in order to avoid
3405 rcuperf.nreaders= [KNL]
3406 Set number of RCU readers. The value -1 selects
3407 N, where N is the number of CPUs. A value
3408 "n" less than -1 selects N-n+1, where N is again
3409 the number of CPUs. For example, -2 selects N
3410 (the number of CPUs), -3 selects N+1, and so on.
3411 A value of "n" less than or equal to -N selects
3414 rcuperf.nwriters= [KNL]
3415 Set number of RCU writers. The values operate
3416 the same as for rcuperf.nreaders.
3417 N, where N is the number of CPUs
3419 rcuperf.perf_runnable= [BOOT]
3420 Start rcuperf running at boot time.
3422 rcuperf.shutdown= [KNL]
3423 Shut the system down after performance tests
3424 complete. This is useful for hands-off automated
3427 rcuperf.perf_type= [KNL]
3428 Specify the RCU implementation to test.
3430 rcuperf.verbose= [KNL]
3431 Enable additional printk() statements.
3433 rcutorture.cbflood_inter_holdoff= [KNL]
3434 Set holdoff time (jiffies) between successive
3435 callback-flood tests.
3437 rcutorture.cbflood_intra_holdoff= [KNL]
3438 Set holdoff time (jiffies) between successive
3439 bursts of callbacks within a given callback-flood
3442 rcutorture.cbflood_n_burst= [KNL]
3443 Set the number of bursts making up a given
3444 callback-flood test. Set this to zero to
3445 disable callback-flood testing.
3447 rcutorture.cbflood_n_per_burst= [KNL]
3448 Set the number of callbacks to be registered
3449 in a given burst of a callback-flood test.
3451 rcutorture.fqs_duration= [KNL]
3452 Set duration of force_quiescent_state bursts
3455 rcutorture.fqs_holdoff= [KNL]
3456 Set holdoff time within force_quiescent_state bursts
3459 rcutorture.fqs_stutter= [KNL]
3460 Set wait time between force_quiescent_state bursts
3463 rcutorture.gp_cond= [KNL]
3464 Use conditional/asynchronous update-side
3465 primitives, if available.
3467 rcutorture.gp_exp= [KNL]
3468 Use expedited update-side primitives, if available.
3470 rcutorture.gp_normal= [KNL]
3471 Use normal (non-expedited) asynchronous
3472 update-side primitives, if available.
3474 rcutorture.gp_sync= [KNL]
3475 Use normal (non-expedited) synchronous
3476 update-side primitives, if available. If all
3477 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3478 rcutorture.gp_normal=, and rcutorture.gp_sync=
3479 are zero, rcutorture acts as if is interpreted
3480 they are all non-zero.
3482 rcutorture.n_barrier_cbs= [KNL]
3483 Set callbacks/threads for rcu_barrier() testing.
3485 rcutorture.nfakewriters= [KNL]
3486 Set number of concurrent RCU writers. These just
3487 stress RCU, they don't participate in the actual
3488 test, hence the "fake".
3490 rcutorture.nreaders= [KNL]
3491 Set number of RCU readers. The value -1 selects
3492 N-1, where N is the number of CPUs. A value
3493 "n" less than -1 selects N-n-2, where N is again
3494 the number of CPUs. For example, -2 selects N
3495 (the number of CPUs), -3 selects N+1, and so on.
3497 rcutorture.object_debug= [KNL]
3498 Enable debug-object double-call_rcu() testing.
3500 rcutorture.onoff_holdoff= [KNL]
3501 Set time (s) after boot for CPU-hotplug testing.
3503 rcutorture.onoff_interval= [KNL]
3504 Set time (s) between CPU-hotplug operations, or
3505 zero to disable CPU-hotplug testing.
3507 rcutorture.shuffle_interval= [KNL]
3508 Set task-shuffle interval (s). Shuffling tasks
3509 allows some CPUs to go into dyntick-idle mode
3510 during the rcutorture test.
3512 rcutorture.shutdown_secs= [KNL]
3513 Set time (s) after boot system shutdown. This
3514 is useful for hands-off automated testing.
3516 rcutorture.stall_cpu= [KNL]
3517 Duration of CPU stall (s) to test RCU CPU stall
3518 warnings, zero to disable.
3520 rcutorture.stall_cpu_holdoff= [KNL]
3521 Time to wait (s) after boot before inducing stall.
3523 rcutorture.stat_interval= [KNL]
3524 Time (s) between statistics printk()s.
3526 rcutorture.stutter= [KNL]
3527 Time (s) to stutter testing, for example, specifying
3528 five seconds causes the test to run for five seconds,
3529 wait for five seconds, and so on. This tests RCU's
3530 ability to transition abruptly to and from idle.
3532 rcutorture.test_boost= [KNL]
3533 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3534 "Maybe" means test if the RCU implementation
3535 under test support RCU priority boosting.
3537 rcutorture.test_boost_duration= [KNL]
3538 Duration (s) of each individual boost test.
3540 rcutorture.test_boost_interval= [KNL]
3541 Interval (s) between each boost test.
3543 rcutorture.test_no_idle_hz= [KNL]
3544 Test RCU's dyntick-idle handling. See also the
3545 rcutorture.shuffle_interval parameter.
3547 rcutorture.torture_runnable= [BOOT]
3548 Start rcutorture running at boot time.
3550 rcutorture.torture_type= [KNL]
3551 Specify the RCU implementation to test.
3553 rcutorture.verbose= [KNL]
3554 Enable additional printk() statements.
3556 rcupdate.rcu_cpu_stall_suppress= [KNL]
3557 Suppress RCU CPU stall warning messages.
3559 rcupdate.rcu_cpu_stall_timeout= [KNL]
3560 Set timeout for RCU CPU stall warning messages.
3562 rcupdate.rcu_expedited= [KNL]
3563 Use expedited grace-period primitives, for
3564 example, synchronize_rcu_expedited() instead
3565 of synchronize_rcu(). This reduces latency,
3566 but can increase CPU utilization, degrade
3567 real-time latency, and degrade energy efficiency.
3568 No effect on CONFIG_TINY_RCU kernels.
3570 rcupdate.rcu_normal= [KNL]
3571 Use only normal grace-period primitives,
3572 for example, synchronize_rcu() instead of
3573 synchronize_rcu_expedited(). This improves
3574 real-time latency, CPU utilization, and
3575 energy efficiency, but can expose users to
3576 increased grace-period latency. This parameter
3577 overrides rcupdate.rcu_expedited. No effect on
3578 CONFIG_TINY_RCU kernels.
3580 rcupdate.rcu_normal_after_boot= [KNL]
3581 Once boot has completed (that is, after
3582 rcu_end_inkernel_boot() has been invoked), use
3583 only normal grace-period primitives. No effect
3584 on CONFIG_TINY_RCU kernels.
3586 rcupdate.rcu_task_stall_timeout= [KNL]
3587 Set timeout in jiffies for RCU task stall warning
3588 messages. Disable with a value less than or equal
3591 rcupdate.rcu_self_test= [KNL]
3592 Run the RCU early boot self tests
3594 rcupdate.rcu_self_test_bh= [KNL]
3595 Run the RCU bh early boot self tests
3597 rcupdate.rcu_self_test_sched= [KNL]
3598 Run the RCU sched early boot self tests
3602 Run specified binary instead of /init from the ramdisk,
3603 used for early userspace startup. See initrd.
3606 Format (x86 or x86_64):
3607 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3609 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3611 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3612 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3613 reboot_force is either force or not specified,
3614 reboot_cpu is s[mp]#### with #### being the processor
3615 to be used for rebooting.
3618 [KNL, SMP] Set scheduler's default relax_domain_level.
3619 See Documentation/cgroup-v1/cpusets.txt.
3621 relative_sleep_states=
3622 [SUSPEND] Use sleep state labeling where the deepest
3623 state available other than hibernation is always "mem".
3624 Format: { "0" | "1" }
3625 0 -- Traditional sleep state labels.
3626 1 -- Relative sleep state labels.
3628 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3630 reservetop= [X86-32]
3632 Reserves a hole at the top of the kernel virtual
3637 Set the amount of memory to reserve for BIOS at
3638 the bottom of the address space.
3640 reset_devices [KNL] Force drivers to reset the underlying device
3641 during initialization.
3644 Specify the partition device for software suspend
3646 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3648 resume_offset= [SWSUSP]
3649 Specify the offset from the beginning of the partition
3650 given by "resume=" at which the swap header is located,
3651 in <PAGE_SIZE> units (needed only for swap files).
3652 See Documentation/power/swsusp-and-swap-files.txt
3654 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3655 read the resume files
3657 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3658 Useful for devices that are detected asynchronously
3659 (e.g. USB and MMC devices).
3661 hibernate= [HIBERNATION]
3662 noresume Don't check if there's a hibernation image
3663 present during boot.
3664 nocompress Don't compress/decompress hibernation images.
3665 no Disable hibernation and resume.
3666 protect_image Turn on image protection during restoration
3667 (that will set all pages holding image data
3668 during restoration read-only).
3670 retain_initrd [RAM] Keep initrd memory after extraction
3672 rfkill.default_state=
3673 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3674 etc. communication is blocked by default.
3677 rfkill.master_switch_mode=
3678 0 The "airplane mode" button does nothing.
3679 1 The "airplane mode" button toggles between everything
3680 blocked and the previous configuration.
3681 2 The "airplane mode" button toggles between everything
3682 blocked and everything unblocked.
3684 rhash_entries= [KNL,NET]
3685 Set number of hash buckets for route cache
3687 ro [KNL] Mount root device read-only on boot
3690 on Mark read-only kernel memory as read-only (default).
3691 off Leave read-only kernel memory writable for debugging.
3694 Enable the uart passthrough on the designated usb port
3695 on Rockchip SoCs. When active, the signals of the
3696 debug-uart get routed to the D+ and D- pins of the usb
3697 port and the regular usb controller gets disabled.
3699 root= [KNL] Root filesystem
3700 See name_to_dev_t comment in init/do_mounts.c.
3702 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3703 mount the root filesystem
3705 rootflags= [KNL] Set root filesystem mount option string
3707 rootfstype= [KNL] Set root filesystem type
3709 rootwait [KNL] Wait (indefinitely) for root device to show up.
3710 Useful for devices that are detected asynchronously
3711 (e.g. USB and MMC devices).
3713 rproc_mem=nn[KMG][@address]
3714 [KNL,ARM,CMA] Remoteproc physical memory block.
3715 Memory area to be used by remote processor image,
3718 rw [KNL] Mount root device read-write on boot
3720 S [KNL] Run init in single mode
3722 s390_iommu= [HW,S390]
3723 Set s390 IOTLB flushing mode
3725 With strict flushing every unmap operation will result in
3726 an IOTLB flush. Default is lazy flushing before reuse,
3730 See drivers/net/irda/sa1100_ir.c.
3732 sbni= [NET] Granch SBNI12 leased line adapter
3734 sched_debug [KNL] Enables verbose scheduler debug messages.
3736 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3737 Allowed values are enable and disable. This feature
3738 incurs a small amount of overhead in the scheduler
3739 but is useful for debugging and performance tuning.
3741 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3742 xtime_lock contention on larger systems, and/or RCU lock
3743 contention on all systems with CONFIG_MAXSMP set.
3744 Format: { "0" | "1" }
3745 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3747 Note: increases power consumption, thus should only be
3748 enabled if running jitter sensitive (HPC/RT) workloads.
3750 security= [SECURITY] Choose a security module to enable at boot.
3751 If this boot parameter is not specified, only the first
3752 security module asking for security registration will be
3753 loaded. An invalid security module name will be treated
3754 as if no module has been chosen.
3756 selinux= [SELINUX] Disable or enable SELinux at boot time.
3757 Format: { "0" | "1" }
3758 See security/selinux/Kconfig help text.
3761 Default value is set via kernel config option.
3762 If enabled at boot time, /selinux/disable can be used
3763 later to disable prior to initial policy load.
3765 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3766 Format: { "0" | "1" }
3767 See security/apparmor/Kconfig help text
3770 Default value is set via kernel config option.
3772 serialnumber [BUGS=X86-32]
3775 Maximal number of shapers.
3777 show_msr= [x86] show boot-time MSR settings
3778 Format: { <integer> }
3779 Show boot-time (BIOS-initialized) MSR settings.
3780 The parameter means the number of CPUs to show,
3781 for example 1 means boot CPU only.
3789 Disable merging of slabs with similar size. May be
3790 necessary if there is some reason to distinguish
3791 allocs to different slabs. Debug options disable
3792 merging on their own.
3793 For more information see Documentation/vm/slub.txt.
3795 slab_max_order= [MM, SLAB]
3796 Determines the maximum allowed order for slabs.
3797 A high setting may cause OOMs due to memory
3798 fragmentation. Defaults to 1 for systems with
3799 more than 32MB of RAM, 0 otherwise.
3801 slub_debug[=options[,slabs]] [MM, SLUB]
3802 Enabling slub_debug allows one to determine the
3803 culprit if slab objects become corrupted. Enabling
3804 slub_debug can create guard zones around objects and
3805 may poison objects when not in use. Also tracks the
3806 last alloc / free. For more information see
3807 Documentation/vm/slub.txt.
3809 slub_max_order= [MM, SLUB]
3810 Determines the maximum allowed order for slabs.
3811 A high setting may cause OOMs due to memory
3812 fragmentation. For more information see
3813 Documentation/vm/slub.txt.
3815 slub_min_objects= [MM, SLUB]
3816 The minimum number of objects per slab. SLUB will
3817 increase the slab order up to slub_max_order to
3818 generate a sufficiently large slab able to contain
3819 the number of objects indicated. The higher the number
3820 of objects the smaller the overhead of tracking slabs
3821 and the less frequently locks need to be acquired.
3822 For more information see Documentation/vm/slub.txt.
3824 slub_min_order= [MM, SLUB]
3825 Determines the minimum page order for slabs. Must be
3826 lower than slub_max_order.
3827 For more information see Documentation/vm/slub.txt.
3829 slub_nomerge [MM, SLUB]
3830 Same with slab_nomerge. This is supported for legacy.
3831 See slab_nomerge for more information.
3834 Format: <io1>[,<io2>[,...,<io8>]]
3836 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3837 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3838 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3839 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3840 smsc-ircc2.ircc_irq= [HW] IRQ line
3841 smsc-ircc2.ircc_dma= [HW] DMA channel
3842 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3843 0: Toshiba Satellite 1800 (GP data pin select)
3844 1: Fast pin select (default)
3847 smt [KNL,S390] Set the maximum number of threads (logical
3848 CPUs) to use per physical CPU on systems capable of
3849 symmetric multithreading (SMT). Will be capped to the
3850 actual hardware limit.
3852 Default: -1 (no limit)
3855 [KNL] Should the soft-lockup detector generate panics.
3858 softlockup_all_cpu_backtrace=
3859 [KNL] Should the soft-lockup detector generate
3860 backtraces on all cpus.
3863 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3864 See Documentation/laptops/sonypi.txt
3866 spia_io_base= [HW,MTD]
3872 Enabled the stack tracer on boot up.
3874 stacktrace_filter=[function-list]
3875 [FTRACE] Limit the functions that the stack tracer
3876 will trace at boot up. function-list is a comma separated
3877 list of functions. This list can be changed at run
3878 time by the stack_trace_filter file in the debugfs
3879 tracing directory. Note, this enables stack tracing
3880 and the stacktrace above is not needed.
3884 Set the STI (builtin display/keyboard on the HP-PARISC
3885 machines) console (graphic card) which should be used
3886 as the initial boot-console.
3887 See also comment in drivers/video/console/sticore.c.
3890 See comment in drivers/video/console/sticore.c.
3893 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3895 sunrpc.min_resvport=
3896 sunrpc.max_resvport=
3898 SunRPC servers often require that client requests
3899 originate from a privileged port (i.e. a port in the
3900 range 0 < portnr < 1024).
3901 An administrator who wishes to reserve some of these
3902 ports for other uses may adjust the range that the
3903 kernel's sunrpc client considers to be privileged
3904 using these two parameters to set the minimum and
3905 maximum port values.
3907 sunrpc.svc_rpc_per_connection_limit=
3909 Limit the number of requests that the server will
3910 process in parallel from a single connection.
3911 The default value is 0 (no limit).
3915 Control how the NFS server code allocates CPUs to
3916 service thread pools. Depending on how many NICs
3917 you have and where their interrupts are bound, this
3918 option will affect which CPUs will do NFS serving.
3919 Note: this parameter cannot be changed while the
3920 NFS server is running.
3922 auto the server chooses an appropriate mode
3923 automatically using heuristics
3924 global a single global pool contains all CPUs
3925 percpu one pool for each CPU
3926 pernode one pool for each NUMA node (equivalent
3927 to global on non-NUMA machines)
3929 sunrpc.tcp_slot_table_entries=
3930 sunrpc.udp_slot_table_entries=
3932 Sets the upper limit on the number of simultaneous
3933 RPC calls that can be sent from the client to a
3934 server. Increasing these values may allow you to
3935 improve throughput, but will also increase the
3936 amount of memory reserved for use by the client.
3938 suspend.pm_test_delay=
3940 Sets the number of seconds to remain in a suspend test
3941 mode before resuming the system (see
3942 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3943 is set. Default value is 5.
3946 [KNL] Enable accounting of swap in memory resource
3947 controller if no parameter or 1 is given or disable
3948 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
3950 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3951 Format: { <int> | force }
3952 <int> -- Number of I/O TLB slabs
3953 force -- force using of bounce buffers even if they
3954 wouldn't be automatically used by the kernel
3958 sysfs.deprecated=0|1 [KNL]
3959 Enable/disable old style sysfs layout for old udev
3960 on older distributions. When this option is enabled
3961 very new udev will not work anymore. When this option
3962 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3963 in older udev will not work anymore.
3964 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3965 the kernel configuration.
3967 sysrq_always_enabled
3969 Ignore sysrq setting - this boot parameter will
3970 neutralize any effect of /proc/sys/kernel/sysrq.
3971 Useful for debugging.
3973 tcpmhash_entries= [KNL,NET]
3974 Set the number of tcp_metrics_hash slots.
3975 Default value is 8192 or 16384 depending on total
3976 ram pages. This is used to specify the TCP metrics
3977 cache size. See Documentation/networking/ip-sysctl.txt
3978 "tcp_no_metrics_save" section for more details.
3982 test_suspend= [SUSPEND][,N]
3983 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3984 standby suspend) or "freeze" (for suspend type freeze)
3985 as the system sleep state during system startup with
3986 the optional capability to repeat N number of times.
3987 The system is woken from this state using a
3988 wakeup-capable RTC alarm.
3990 thash_entries= [KNL,NET]
3991 Set number of hash buckets for TCP connection
3993 thermal.act= [HW,ACPI]
3994 -1: disable all active trip points in all thermal zones
3995 <degrees C>: override all lowest active trip points
3997 thermal.crt= [HW,ACPI]
3998 -1: disable all critical trip points in all thermal zones
3999 <degrees C>: override all critical trip points
4001 thermal.nocrt= [HW,ACPI]
4002 Set to disable actions on ACPI thermal zone
4003 critical and hot trip points.
4005 thermal.off= [HW,ACPI]
4006 1: disable ACPI thermal control
4008 thermal.psv= [HW,ACPI]
4009 -1: disable all passive trip points
4010 <degrees C>: override all passive trip points to this
4013 thermal.tzp= [HW,ACPI]
4014 Specify global default ACPI thermal zone polling rate
4015 <deci-seconds>: poll all this frequency
4016 0: no polling (default)
4019 Force threading of all interrupt handlers except those
4020 marked explicitly IRQF_NO_THREAD.
4023 Enable the Transcendent memory driver if built-in.
4025 tmem.cleancache=0|1 [KNL, XEN]
4026 Default is on (1). Disable the usage of the cleancache
4027 API to send anonymous pages to the hypervisor.
4029 tmem.frontswap=0|1 [KNL, XEN]
4030 Default is on (1). Disable the usage of the frontswap
4031 API to send swap pages to the hypervisor. If disabled
4032 the selfballooning and selfshrinking are force disabled.
4034 tmem.selfballooning=0|1 [KNL, XEN]
4035 Default is on (1). Disable the driving of swap pages
4038 tmem.selfshrinking=0|1 [KNL, XEN]
4039 Default is on (1). Partial swapoff that immediately
4040 transfers pages from Xen hypervisor back to the
4041 kernel based on different criteria.
4045 Specify if the kernel should make use of the cpu
4046 topology information if the hardware supports this.
4047 The scheduler will make use of this information and
4048 e.g. base its process migration decisions on it.
4051 topology_updates= [KNL, PPC, NUMA]
4053 Specify if the kernel should ignore (off)
4054 topology updates sent by the hypervisor to this
4059 tpm_suspend_pcr=[HW,TPM]
4060 Format: integer pcr id
4061 Specify that at suspend time, the tpm driver
4062 should extend the specified pcr with zeros,
4063 as a workaround for some chips which fail to
4064 flush the last written pcr on TPM_SaveState.
4065 This will guarantee that all the other pcrs
4068 trace_buf_size=nn[KMG]
4069 [FTRACE] will set tracing buffer size on each cpu.
4071 trace_event=[event-list]
4072 [FTRACE] Set and start specified trace events in order
4073 to facilitate early boot debugging. The event-list is a
4074 comma separated list of trace events to enable. See
4075 also Documentation/trace/events.txt
4077 trace_options=[option-list]
4078 [FTRACE] Enable or disable tracer options at boot.
4079 The option-list is a comma delimited list of options
4080 that can be enabled or disabled just as if you were
4081 to echo the option name into
4083 /sys/kernel/debug/tracing/trace_options
4085 For example, to enable stacktrace option (to dump the
4086 stack trace of each event), add to the command line:
4088 trace_options=stacktrace
4090 See also Documentation/trace/ftrace.txt "trace options"
4094 Have the tracepoints sent to printk as well as the
4095 tracing ring buffer. This is useful for early boot up
4096 where the system hangs or reboots and does not give the
4097 option for reading the tracing buffer or performing a
4098 ftrace_dump_on_oops.
4100 To turn off having tracepoints sent to printk,
4101 echo 0 > /proc/sys/kernel/tracepoint_printk
4102 Note, echoing 1 into this file without the
4103 tracepoint_printk kernel cmdline option has no effect.
4107 Having tracepoints sent to printk() and activating high
4108 frequency tracepoints such as irq or sched, can cause
4109 the system to live lock.
4112 [FTRACE] enable this option to disable tracing when a
4113 warning is hit. This turns off "tracing_on". Tracing can
4114 be enabled again by echoing '1' into the "tracing_on"
4115 file located in /sys/kernel/debug/tracing/
4117 This option is useful, as it disables the trace before
4118 the WARNING dump is called, which prevents the trace to
4119 be filled with content caused by the warning output.
4121 This option can also be set at run time via the sysctl
4122 option: kernel/traceoff_on_warning
4124 transparent_hugepage=
4126 Format: [always|madvise|never]
4127 Can be used to control the default behavior of the system
4128 with respect to transparent hugepages.
4129 See Documentation/vm/transhuge.txt for more details.
4131 tsc= Disable clocksource stability checks for TSC.
4133 [x86] reliable: mark tsc clocksource as reliable, this
4134 disables clocksource verification at runtime, as well
4135 as the stability checks done at bootup. Used to enable
4136 high-resolution timer mode on older hardware, and in
4137 virtualized environment.
4138 [x86] noirqtime: Do not use TSC to do irq accounting.
4139 Used to run time disable IRQ_TIME_ACCOUNTING on any
4140 platforms where RDTSC is slow and this accounting
4143 turbografx.map[2|3]= [HW,JOY]
4144 TurboGraFX parallel port interface
4146 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4147 See also Documentation/input/joystick-parport.txt
4149 udbg-immortal [PPC] When debugging early kernel crashes that
4150 happen after console_init() and before a proper
4151 console driver takes over, this boot options might
4152 help "seeing" what's going on.
4154 uhash_entries= [KNL,NET]
4155 Set number of hash buckets for UDP/UDP-Lite connections
4158 [USB] Ignore overcurrent events (default N).
4159 Some badly-designed motherboards generate lots of
4160 bogus events, for ports that aren't wired to
4161 anything. Set this parameter to avoid log spamming.
4162 Note that genuine overcurrent events won't be
4166 [X86] Cause panic on unknown NMI.
4168 usbcore.authorized_default=
4169 [USB] Default USB device authorization:
4170 (default -1 = authorized except for wireless USB,
4171 0 = not authorized, 1 = authorized)
4173 usbcore.autosuspend=
4174 [USB] The autosuspend time delay (in seconds) used
4175 for newly-detected USB devices (default 2). This
4176 is the time required before an idle device will be
4177 autosuspended. Devices for which the delay is set
4178 to a negative value won't be autosuspended at all.
4180 usbcore.usbfs_snoop=
4181 [USB] Set to log all usbfs traffic (default 0 = off).
4183 usbcore.usbfs_snoop_max=
4184 [USB] Maximum number of bytes to snoop in each URB
4187 usbcore.blinkenlights=
4188 [USB] Set to cycle leds on hubs (default 0 = off).
4190 usbcore.old_scheme_first=
4191 [USB] Start with the old device initialization
4192 scheme (default 0 = off).
4194 usbcore.usbfs_memory_mb=
4195 [USB] Memory limit (in MB) for buffers allocated by
4196 usbfs (default = 16, 0 = max = 2047).
4198 usbcore.use_both_schemes=
4199 [USB] Try the other device initialization scheme
4200 if the first one fails (default 1 = enabled).
4202 usbcore.initial_descriptor_timeout=
4203 [USB] Specifies timeout for the initial 64-byte
4204 USB_REQ_GET_DESCRIPTOR request in milliseconds
4205 (default 5000 = 5.0 seconds).
4207 usbcore.nousb [USB] Disable the USB subsystem
4210 [USBHID] The interval which mice are to be polled at.
4212 usb-storage.delay_use=
4213 [UMS] The delay in seconds before a new device is
4214 scanned for Logical Units (default 1).
4217 [UMS] A list of quirks entries to supplement or
4218 override the built-in unusual_devs list. List
4219 entries are separated by commas. Each entry has
4220 the form VID:PID:Flags where VID and PID are Vendor
4221 and Product ID values (4-digit hex numbers) and
4222 Flags is a set of characters, each corresponding
4223 to a common usb-storage quirk flag as follows:
4224 a = SANE_SENSE (collect more than 18 bytes
4226 b = BAD_SENSE (don't collect more than 18
4227 bytes of sense data);
4228 c = FIX_CAPACITY (decrease the reported
4229 device capacity by one sector);
4230 d = NO_READ_DISC_INFO (don't use
4231 READ_DISC_INFO command);
4232 e = NO_READ_CAPACITY_16 (don't use
4233 READ_CAPACITY_16 command);
4234 f = NO_REPORT_OPCODES (don't use report opcodes
4236 g = MAX_SECTORS_240 (don't transfer more than
4237 240 sectors at a time, uas only);
4238 h = CAPACITY_HEURISTICS (decrease the
4239 reported device capacity by one
4240 sector if the number is odd);
4241 i = IGNORE_DEVICE (don't bind to this
4243 j = NO_REPORT_LUNS (don't use report luns
4245 l = NOT_LOCKABLE (don't try to lock and
4246 unlock ejectable media);
4247 m = MAX_SECTORS_64 (don't transfer more
4248 than 64 sectors = 32 KB at a time);
4249 n = INITIAL_READ10 (force a retry of the
4250 initial READ(10) command);
4251 o = CAPACITY_OK (accept the capacity
4252 reported by the device);
4253 p = WRITE_CACHE (the device cache is ON
4255 r = IGNORE_RESIDUE (the device reports
4256 bogus residue values);
4257 s = SINGLE_LUN (the device has only one
4259 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4260 commands, uas only);
4261 u = IGNORE_UAS (don't bind to the uas driver);
4262 w = NO_WP_DETECT (don't test whether the
4263 medium is write-protected).
4264 Example: quirks=0419:aaf5:rl,0421:0433:rc
4266 user_debug= [KNL,ARM]
4268 See arch/arm/Kconfig.debug help text.
4269 1 - undefined instruction events
4271 4 - invalid data aborts
4274 Example: user_debug=31
4277 [X86] Flags controlling user PTE allocations.
4279 nohigh = do not allocate PTE pages in
4280 HIGHMEM regardless of setting
4284 On X86_32, this is an alias for vdso32=. Otherwise:
4286 vdso=1: enable VDSO (the default)
4287 vdso=0: disable VDSO mapping
4289 vdso32= [X86] Control the 32-bit vDSO
4290 vdso32=1: enable 32-bit VDSO
4291 vdso32=0 or vdso32=2: disable 32-bit VDSO
4293 See the help text for CONFIG_COMPAT_VDSO for more
4294 details. If CONFIG_COMPAT_VDSO is set, the default is
4295 vdso32=0; otherwise, the default is vdso32=1.
4297 For compatibility with older kernels, vdso32=2 is an
4300 Try vdso32=0 if you encounter an error that says:
4301 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4304 vector=percpu: enable percpu vector domain
4306 video= [FB] Frame buffer configuration
4307 See Documentation/fb/modedb.txt.
4309 video.brightness_switch_enabled= [0,1]
4310 If set to 1, on receiving an ACPI notify event
4311 generated by hotkey, video driver will adjust brightness
4312 level and then send out the event to user space through
4313 the allocated input device; If set to 0, video driver
4314 will only send out the event without touching backlight
4319 [VMMIO] Memory mapped virtio (platform) device.
4321 <size>@<baseaddr>:<irq>[:<id>]
4323 <size> := size (can use standard suffixes
4325 <baseaddr> := physical base address
4326 <irq> := interrupt number (as passed to
4328 <id> := (optional) platform device id
4330 virtio_mmio.device=1K@0x100b0000:48:7
4332 Can be used multiple times for multiple devices.
4334 vga= [BOOT,X86-32] Select a particular video mode
4335 See Documentation/x86/boot.txt and
4336 Documentation/svga.txt.
4337 Use vga=ask for menu.
4338 This is actually a boot loader parameter; the value is
4339 passed to the kernel using a special protocol.
4341 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4342 size of <nn>. This can be used to increase the
4343 minimum size (128MB on x86). It can also be used to
4344 decrease the size and leave more room for directly
4347 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4350 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4353 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4357 Controls the behavior of vsyscalls (i.e. calls to
4358 fixed addresses of 0xffffffffff600x00 from legacy
4359 code). Most statically-linked binaries and older
4360 versions of glibc use these calls. Because these
4361 functions are at fixed addresses, they make nice
4362 targets for exploits that can control RIP.
4364 emulate [default] Vsyscalls turn into traps and are
4365 emulated reasonably safely.
4367 native Vsyscalls are native syscall instructions.
4368 This is a little bit faster than trapping
4369 and makes a few dynamic recompilers work
4370 better than they would in emulation mode.
4371 It also makes exploits much easier to write.
4373 none Vsyscalls don't work at all. This makes
4374 them quite hard to use for exploits but
4375 might break your system.
4377 vt.color= [VT] Default text color.
4378 Format: 0xYX, X = foreground, Y = background.
4379 Default: 0x07 = light gray on black.
4381 vt.cur_default= [VT] Default cursor shape.
4382 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4383 the parameters of the <Esc>[?A;B;Cc escape sequence;
4384 see VGA-softcursor.txt. Default: 2 = underline.
4386 vt.default_blu= [VT]
4387 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4388 Change the default blue palette of the console.
4389 This is a 16-member array composed of values
4392 vt.default_grn= [VT]
4393 Format: <green0>,<green1>,<green2>,...,<green15>
4394 Change the default green palette of the console.
4395 This is a 16-member array composed of values
4398 vt.default_red= [VT]
4399 Format: <red0>,<red1>,<red2>,...,<red15>
4400 Change the default red palette of the console.
4401 This is a 16-member array composed of values
4407 Set system-wide default UTF-8 mode for all tty's.
4408 Default is 1, i.e. UTF-8 mode is enabled for all
4409 newly opened terminals.
4411 vt.global_cursor_default=
4414 Set system-wide default for whether a cursor
4415 is shown on new VTs. Default is -1,
4416 i.e. cursors will be created by default unless
4417 overridden by individual drivers. 0 will hide
4418 cursors, 1 will display them.
4420 vt.italic= [VT] Default color for italic text; 0-15.
4423 vt.underline= [VT] Default color for underlined text; 0-15.
4426 watchdog timers [HW,WDT] For information on watchdog timers,
4427 see Documentation/watchdog/watchdog-parameters.txt
4428 or other driver-specific files in the
4429 Documentation/watchdog/ directory.
4431 workqueue.watchdog_thresh=
4432 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4433 warn stall conditions and dump internal state to
4434 help debugging. 0 disables workqueue stall
4435 detection; otherwise, it's the stall threshold
4436 duration in seconds. The default value is 30 and
4437 it can be updated at runtime by writing to the
4438 corresponding sysfs file.
4440 workqueue.disable_numa
4441 By default, all work items queued to unbound
4442 workqueues are affine to the NUMA nodes they're
4443 issued on, which results in better behavior in
4444 general. If NUMA affinity needs to be disabled for
4445 whatever reason, this option can be used. Note
4446 that this also can be controlled per-workqueue for
4447 workqueues visible under /sys/bus/workqueue/.
4449 workqueue.power_efficient
4450 Per-cpu workqueues are generally preferred because
4451 they show better performance thanks to cache
4452 locality; unfortunately, per-cpu workqueues tend to
4453 be more power hungry than unbound workqueues.
4455 Enabling this makes the per-cpu workqueues which
4456 were observed to contribute significantly to power
4457 consumption unbound, leading to measurably lower
4458 power usage at the cost of small performance
4461 The default value of this parameter is determined by
4462 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4464 workqueue.debug_force_rr_cpu
4465 Workqueue used to implicitly guarantee that work
4466 items queued without explicit CPU specified are put
4467 on the local CPU. This guarantee is no longer true
4468 and while local CPU is still preferred work items
4469 may be put on foreign CPUs. This debug option
4470 forces round-robin CPU selection to flush out
4471 usages which depend on the now broken guarantee.
4472 When enabled, memory and cache locality will be
4475 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4476 default x2apic cluster mode on platforms
4479 x86_intel_mid_timer= [X86-32,APBT]
4480 Choose timer option for x86 Intel MID platform.
4481 Two valid options are apbt timer only and lapic timer
4482 plus one apbt timer for broadcast timer.
4483 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4485 xen_512gb_limit [KNL,X86-64,XEN]
4486 Restricts the kernel running paravirtualized under Xen
4487 to use only up to 512 GB of RAM. The reason to do so is
4488 crash analysis tools and Xen tools for doing domain
4489 save/restore/migration must be enabled to handle larger
4492 xen_emul_unplug= [HW,X86,XEN]
4493 Unplug Xen emulated devices
4494 Format: [unplug0,][unplug1]
4495 ide-disks -- unplug primary master IDE devices
4496 aux-ide-disks -- unplug non-primary-master IDE devices
4497 nics -- unplug network devices
4498 all -- unplug all emulated devices (NICs and IDE disks)
4499 unnecessary -- unplugging emulated devices is
4500 unnecessary even if the host did not respond to
4502 never -- do not unplug even if version check succeeds
4504 xen_nopvspin [X86,XEN]
4505 Disables the ticketlock slowpath using Xen PV
4509 Disables the PV optimizations forcing the HVM guest to
4510 run as generic HVM guest with no PV drivers.
4512 xirc2ps_cs= [NET,PCMCIA]
4514 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4516 ______________________________________________________________________
4520 Add more DRM drivers.
projects / deliverable / linux.git / blob