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"
39 Some kernel parameters take a list of CPUs as a value, e.g. isolcpus,
40 nohz_full, irqaffinity, rcu_nocbs. The format of this list is:
42 <cpu number>,...,<cpu number>
46 <cpu number>-<cpu number>
47 (must be a positive range in ascending order)
51 <cpu number>,...,<cpu number>-<cpu number>
53 Note that for the special case of a range one can split the range into equal
54 sized groups and for each group use some amount from the beginning of that
57 <cpu number>-cpu number>:<used size>/<group size>
59 For example one can add to the command line following parameter:
61 isolcpus=1,2,10-20,100-2000:2/25
63 where the final item represents CPUs 100,101,125,126,150,151,...
67 This document may not be entirely up to date and comprehensive. The command
68 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
69 module. Loadable modules, after being loaded into the running kernel, also
70 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
71 parameters may be changed at runtime by the command
72 "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
74 The parameters listed below are only valid if certain kernel build options were
75 enabled and if respective hardware is present. The text in square brackets at
76 the beginning of each description states the restrictions within which a
77 parameter is applicable:
79 ACPI ACPI support is enabled.
80 AGP AGP (Accelerated Graphics Port) is enabled.
81 ALSA ALSA sound support is enabled.
82 APIC APIC support is enabled.
83 APM Advanced Power Management support is enabled.
84 ARM ARM architecture is enabled.
85 AVR32 AVR32 architecture is enabled.
86 AX25 Appropriate AX.25 support is enabled.
87 BLACKFIN Blackfin architecture is enabled.
88 CLK Common clock infrastructure is enabled.
89 CMA Contiguous Memory Area support is enabled.
90 DRM Direct Rendering Management support is enabled.
91 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
92 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
93 EFI EFI Partitioning (GPT) is enabled
94 EIDE EIDE/ATAPI support is enabled.
95 EVM Extended Verification Module
96 FB The frame buffer device is enabled.
97 FTRACE Function tracing enabled.
98 GCOV GCOV profiling is enabled.
99 HW Appropriate hardware is enabled.
100 IA-64 IA-64 architecture is enabled.
101 IMA Integrity measurement architecture is enabled.
102 IOSCHED More than one I/O scheduler is enabled.
103 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
104 IPV6 IPv6 support is enabled.
105 ISAPNP ISA PnP code is enabled.
106 ISDN Appropriate ISDN support is enabled.
107 JOY Appropriate joystick support is enabled.
108 KGDB Kernel debugger support is enabled.
109 KVM Kernel Virtual Machine support is enabled.
110 LIBATA Libata driver is enabled
111 LP Printer support is enabled.
112 LOOP Loopback device support is enabled.
113 M68k M68k architecture is enabled.
114 These options have more detailed description inside of
115 Documentation/m68k/kernel-options.txt.
116 MDA MDA console support is enabled.
117 MIPS MIPS architecture is enabled.
118 MOUSE Appropriate mouse support is enabled.
119 MSI Message Signaled Interrupts (PCI).
120 MTD MTD (Memory Technology Device) support is enabled.
121 NET Appropriate network support is enabled.
122 NUMA NUMA support is enabled.
123 NFS Appropriate NFS support is enabled.
124 OSS OSS sound support is enabled.
125 PV_OPS A paravirtualized kernel is enabled.
126 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
127 PARISC The PA-RISC architecture is enabled.
128 PCI PCI bus support is enabled.
129 PCIE PCI Express support is enabled.
130 PCMCIA The PCMCIA subsystem is enabled.
131 PNP Plug & Play support is enabled.
132 PPC PowerPC architecture is enabled.
133 PPT Parallel port support is enabled.
134 PS2 Appropriate PS/2 support is enabled.
135 RAM RAM disk support is enabled.
136 S390 S390 architecture is enabled.
137 SCSI Appropriate SCSI support is enabled.
138 A lot of drivers have their options described inside
139 the Documentation/scsi/ sub-directory.
140 SECURITY Different security models are enabled.
141 SELINUX SELinux support is enabled.
142 APPARMOR AppArmor support is enabled.
143 SERIAL Serial support is enabled.
144 SH SuperH architecture is enabled.
145 SMP The kernel is an SMP kernel.
146 SPARC Sparc architecture is enabled.
147 SWSUSP Software suspend (hibernation) is enabled.
148 SUSPEND System suspend states are enabled.
149 TPM TPM drivers are enabled.
150 TS Appropriate touchscreen support is enabled.
151 UMS USB Mass Storage support is enabled.
152 USB USB support is enabled.
153 USBHID USB Human Interface Device support is enabled.
154 V4L Video For Linux support is enabled.
155 VMMIO Driver for memory mapped virtio devices is enabled.
156 VGA The VGA console has been enabled.
157 VT Virtual terminal support is enabled.
158 WDT Watchdog support is enabled.
159 XT IBM PC/XT MFM hard disk support is enabled.
160 X86-32 X86-32, aka i386 architecture is enabled.
161 X86-64 X86-64 architecture is enabled.
162 More X86-64 boot options can be found in
163 Documentation/x86/x86_64/boot-options.txt .
164 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
165 X86_UV SGI UV support is enabled.
166 XEN Xen support is enabled
168 In addition, the following text indicates that the option:
170 BUGS= Relates to possible processor bugs on the said processor.
171 KNL Is a kernel start-up parameter.
172 BOOT Is a boot loader parameter.
174 Parameters denoted with BOOT are actually interpreted by the boot
175 loader, and have no meaning to the kernel directly.
176 Do not modify the syntax of boot loader parameters without extreme
177 need or coordination with <Documentation/x86/boot.txt>.
179 There are also arch-specific kernel-parameters not documented here.
180 See for example <Documentation/x86/x86_64/boot-options.txt>.
182 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
183 a trailing = on the name of any parameter states that that parameter will
184 be entered as an environment variable, whereas its absence indicates that
185 it will appear as a kernel argument readable via /proc/cmdline by programs
186 running once the system is up.
188 The number of kernel parameters is not limited, but the length of the
189 complete command line (parameters including spaces etc.) is limited to
190 a fixed number of characters. This limit depends on the architecture
191 and is between 256 and 4096 characters. It is defined in the file
192 ./include/asm/setup.h as COMMAND_LINE_SIZE.
194 Finally, the [KMG] suffix is commonly described after a number of kernel
195 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
196 multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
197 bytes respectively. Such letter suffixes can also be entirely omitted.
200 acpi= [HW,ACPI,X86,ARM64]
201 Advanced Configuration and Power Interface
202 Format: { force | on | off | strict | noirq | rsdt |
204 force -- enable ACPI if default was off
205 on -- enable ACPI but allow fallback to DT [arm64]
206 off -- disable ACPI if default was on
207 noirq -- do not use ACPI for IRQ routing
208 strict -- Be less tolerant of platforms that are not
209 strictly ACPI specification compliant.
210 rsdt -- prefer RSDT over (default) XSDT
211 copy_dsdt -- copy DSDT to memory
212 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
215 See also Documentation/power/runtime_pm.txt, pci=noacpi
217 acpi_apic_instance= [ACPI, IOAPIC]
219 2: use 2nd APIC table, if available
220 1,0: use 1st APIC table
223 acpi_backlight= [HW,ACPI]
224 acpi_backlight=vendor
226 If set to vendor, prefer vendor specific driver
227 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
228 of the ACPI video.ko driver.
230 acpi_force_32bit_fadt_addr
231 force FADT to use 32 bit addresses rather than the
232 64 bit X_* addresses. Some firmware have broken 64
233 bit addresses for force ACPI ignore these and use
234 the older legacy 32 bit addresses.
236 acpica_no_return_repair [HW, ACPI]
237 Disable AML predefined validation mechanism
238 This mechanism can repair the evaluation result to make
239 the return objects more ACPI specification compliant.
240 This option is useful for developers to identify the
241 root cause of an AML interpreter issue when the issue
242 has something to do with the repair mechanism.
244 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
245 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
247 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
248 debug output. Bits in debug_layer correspond to a
249 _COMPONENT in an ACPI source file, e.g.,
250 #define _COMPONENT ACPI_PCI_COMPONENT
251 Bits in debug_level correspond to a level in
252 ACPI_DEBUG_PRINT statements, e.g.,
253 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
254 The debug_level mask defaults to "info". See
255 Documentation/acpi/debug.txt for more information about
256 debug layers and levels.
258 Enable processor driver info messages:
259 acpi.debug_layer=0x20000000
260 Enable PCI/PCI interrupt routing info messages:
261 acpi.debug_layer=0x400000
262 Enable AML "Debug" output, i.e., stores to the Debug
263 object while interpreting AML:
264 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
265 Enable all messages related to ACPI hardware:
266 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
268 Some values produce so much output that the system is
269 unusable. The "log_buf_len" parameter may be useful
270 if you need to capture more output.
272 acpi_enforce_resources= [ACPI]
273 { strict | lax | no }
274 Check for resource conflicts between native drivers
275 and ACPI OperationRegions (SystemIO and SystemMemory
276 only). IO ports and memory declared in ACPI might be
277 used by the ACPI subsystem in arbitrary AML code and
278 can interfere with legacy drivers.
279 strict (default): access to resources claimed by ACPI
280 is denied; legacy drivers trying to access reserved
281 resources will fail to bind to device using them.
282 lax: access to resources claimed by ACPI is allowed;
283 legacy drivers trying to access reserved resources
284 will bind successfully but a warning message is logged.
285 no: ACPI OperationRegions are not marked as reserved,
286 no further checks are performed.
288 acpi_force_table_verification [HW,ACPI]
289 Enable table checksum verification during early stage.
290 By default, this is disabled due to x86 early mapping
293 acpi_irq_balance [HW,ACPI]
294 ACPI will balance active IRQs
297 acpi_irq_nobalance [HW,ACPI]
298 ACPI will not move active IRQs (default)
301 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
302 Format: <irq>,<irq>...
304 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
306 Format: <irq>,<irq>...
308 acpi_no_auto_serialize [HW,ACPI]
309 Disable auto-serialization of AML methods
310 AML control methods that contain the opcodes to create
311 named objects will be marked as "Serialized" by the
312 auto-serialization feature.
313 This feature is enabled by default.
314 This option allows to turn off the feature.
316 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
319 acpi_no_static_ssdt [HW,ACPI]
320 Disable installation of static SSDTs at early boot time
321 By default, SSDTs contained in the RSDT/XSDT will be
322 installed automatically and they will appear under
323 /sys/firmware/acpi/tables.
324 This option turns off this feature.
325 Note that specifying this option does not affect
326 dynamic table installation which will install SSDT
327 tables to /sys/firmware/acpi/tables/dynamic.
329 acpi_rsdp= [ACPI,EFI,KEXEC]
330 Pass the RSDP address to the kernel, mostly used
331 on machines running EFI runtime service to boot the
332 second kernel for kdump.
334 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
335 Format: To spoof as Windows 98: ="Microsoft Windows"
337 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
338 of 2 which is mandated by ACPI 6) as the supported ACPI
339 specification revision (when using this switch, it may
340 be necessary to carry out a cold reboot _twice_ in a
341 row to make it take effect on the platform firmware).
343 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
344 acpi_osi="string1" # add string1
345 acpi_osi="!string2" # remove string2
346 acpi_osi=!* # remove all strings
347 acpi_osi=! # disable all built-in OS vendor
349 acpi_osi=!! # enable all built-in OS vendor
351 acpi_osi= # disable all strings
353 'acpi_osi=!' can be used in combination with single or
354 multiple 'acpi_osi="string1"' to support specific OS
355 vendor string(s). Note that such command can only
356 affect the default state of the OS vendor strings, thus
357 it cannot affect the default state of the feature group
358 strings and the current state of the OS vendor strings,
359 specifying it multiple times through kernel command line
360 is meaningless. This command is useful when one do not
361 care about the state of the feature group strings which
362 should be controlled by the OSPM.
364 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
365 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
366 can make '_OSI("Windows 2000")' TRUE.
368 'acpi_osi=' cannot be used in combination with other
369 'acpi_osi=' command lines, the _OSI method will not
370 exist in the ACPI namespace. NOTE that such command can
371 only affect the _OSI support state, thus specifying it
372 multiple times through kernel command line is also
375 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
378 'acpi_osi=!*' can be used in combination with single or
379 multiple 'acpi_osi="string1"' to support specific
380 string(s). Note that such command can affect the
381 current state of both the OS vendor strings and the
382 feature group strings, thus specifying it multiple times
383 through kernel command line is meaningful. But it may
384 still not able to affect the final state of a string if
385 there are quirks related to this string. This command
386 is useful when one want to control the state of the
387 feature group strings to debug BIOS issues related to
390 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
391 '_OSI("Module Device")' FALSE.
392 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
393 '_OSI("Module Device")' TRUE.
394 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
396 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
398 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
399 they all will make '_OSI("Windows 2000")' TRUE.
402 Override the pmtimer bug detection: force the kernel
403 to assume that this machine's pmtimer latches its value
404 and always returns good values.
406 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
407 Format: { level | edge | high | low }
409 acpi_skip_timer_override [HW,ACPI]
410 Recognize and ignore IRQ0/pin2 Interrupt Override.
411 For broken nForce2 BIOS resulting in XT-PIC timer.
413 acpi_sleep= [HW,ACPI] Sleep options
414 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
415 old_ordering, nonvs, sci_force_enable }
416 See Documentation/power/video.txt for information on
418 s3_beep is for debugging; it makes the PC's speaker beep
419 as soon as the kernel's real-mode entry point is called.
420 s4_nohwsig prevents ACPI hardware signature from being
421 used during resume from hibernation.
422 old_ordering causes the ACPI 1.0 ordering of the _PTS
423 control method, with respect to putting devices into
424 low power states, to be enforced (the ACPI 2.0 ordering
425 of _PTS is used by default).
426 nonvs prevents the kernel from saving/restoring the
427 ACPI NVS memory during suspend/hibernation and resume.
428 sci_force_enable causes the kernel to set SCI_EN directly
429 on resume from S1/S3 (which is against the ACPI spec,
430 but some broken systems don't work without it).
432 acpi_use_timer_override [HW,ACPI]
433 Use timer override. For some broken Nvidia NF5 boards
434 that require a timer override, but don't have HPET
436 add_efi_memmap [EFI; X86] Include EFI memory map in
437 kernel's map of available physical RAM.
440 { off | try_unsupported }
441 off: disable AGP support
442 try_unsupported: try to drive unsupported chipsets
443 (may crash computer or cause data corruption)
446 See Documentation/sound/alsa/alsa-parameters.txt
449 Allow the default userspace alignment fault handler
450 behaviour to be specified. Bit 0 enables warnings,
451 bit 1 enables fixups, and bit 2 sends a segfault.
453 align_va_addr= [X86-64]
454 Align virtual addresses by clearing slice [14:12] when
455 allocating a VMA at process creation time. This option
456 gives you up to 3% performance improvement on AMD F15h
457 machines (where it is enabled by default) for a
458 CPU-intensive style benchmark, and it can vary highly in
459 a microbenchmark depending on workload and compiler.
461 32: only for 32-bit processes
462 64: only for 64-bit processes
463 on: enable for both 32- and 64-bit processes
464 off: disable for both 32- and 64-bit processes
466 alloc_snapshot [FTRACE]
467 Allocate the ftrace snapshot buffer on boot up when the
468 main buffer is allocated. This is handy if debugging
469 and you need to use tracing_snapshot() on boot up, and
470 do not want to use tracing_snapshot_alloc() as it needs
471 to be done where GFP_KERNEL allocations are allowed.
473 amd_iommu= [HW,X86-64]
474 Pass parameters to the AMD IOMMU driver in the system.
476 fullflush - enable flushing of IO/TLB entries when
477 they are unmapped. Otherwise they are
478 flushed before they will be reused, which
480 off - do not initialize any AMD IOMMU found in
482 force_isolation - Force device isolation for all
483 devices. The IOMMU driver is not
484 allowed anymore to lift isolation
485 requirements as needed. This option
486 does not override iommu=pt
488 amd_iommu_dump= [HW,X86-64]
489 Enable AMD IOMMU driver option to dump the ACPI table
490 for AMD IOMMU. With this option enabled, AMD IOMMU
491 driver will print ACPI tables for AMD IOMMU during
492 IOMMU initialization.
494 amd_iommu_intr= [HW,X86-64]
495 Specifies one of the following AMD IOMMU interrupt
497 legacy - Use legacy interrupt remapping mode.
498 vapic - Use virtual APIC mode, which allows IOMMU
499 to inject interrupts directly into guest.
500 This mode requires kvm-amd.avic=1.
501 (Default when IOMMU HW support is present.)
503 amijoy.map= [HW,JOY] Amiga joystick support
504 Map of devices attached to JOY0DAT and JOY1DAT
506 See also Documentation/input/joystick.txt
508 analog.map= [HW,JOY] Analog joystick and gamepad support
509 Specifies type or capabilities of an analog joystick
510 connected to one of 16 gameports
511 Format: <type1>,<type2>,..<type16>
514 Power management functions (SPARCstation-4/5 + deriv.)
516 Disable APC CPU standby support. SPARCstation-Fox does
517 not play well with APC CPU idle - disable it if you have
518 APC and your system crashes randomly.
520 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
521 Change the output verbosity whilst booting
522 Format: { quiet (default) | verbose | debug }
523 Change the amount of debugging information output
524 when initialising the APIC and IO-APIC components.
526 apic_extnmi= [APIC,X86] External NMI delivery setting
527 Format: { bsp (default) | all | none }
528 bsp: External NMI is delivered only to CPU 0
529 all: External NMIs are broadcast to all CPUs as a
531 none: External NMI is masked for all CPUs. This is
532 useful so that a dump capture kernel won't be
536 See Documentation/networking/ipv6.txt.
538 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
539 Limit apic dumping. The parameter defines the maximal
540 number of local apics being dumped. Also it is possible
541 to set it to "all" by meaning -- no limit here.
542 Format: { 1 (default) | 2 | ... | all }.
543 The parameter valid if only apic=debug or
544 apic=verbose is specified.
545 Example: apic=debug show_lapic=all
547 apm= [APM] Advanced Power Management
548 See header of arch/x86/kernel/apm_32.c.
550 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
551 Format: <io>,<irq>,<nodeID>
555 atarimouse= [HW,MOUSE] Atari Mouse
557 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
558 EzKey and similar keyboards
560 atkbd.reset= [HW] Reset keyboard during initialization
562 atkbd.set= [HW] Select keyboard code set
563 Format: <int> (2 = AT (default), 3 = PS/2)
565 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
568 atkbd.softraw= [HW] Choose between synthetic and real raw mode
569 Format: <bool> (0 = real, 1 = synthetic (default))
571 atkbd.softrepeat= [HW]
572 Use software keyboard repeat
574 audit= [KNL] Enable the audit sub-system
575 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
576 0 - kernel audit is disabled and can not be enabled
577 until the next reboot
578 unset - kernel audit is initialized but disabled and
579 will be fully enabled by the userspace auditd.
580 1 - kernel audit is initialized and partially enabled,
581 storing at most audit_backlog_limit messages in
582 RAM until it is fully enabled by the userspace
586 audit_backlog_limit= [KNL] Set the audit queue size limit.
587 Format: <int> (must be >=0)
590 bau= [X86_UV] Enable the BAU on SGI UV. The default
591 behavior is to disable the BAU (i.e. bau=0).
592 Format: { "0" | "1" }
595 unset - Disable the BAU.
597 baycom_epp= [HW,AX25]
600 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
602 See header of drivers/net/hamradio/baycom_par.c.
604 baycom_ser_fdx= [HW,AX25]
605 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
606 Format: <io>,<irq>,<mode>[,<baud>]
607 See header of drivers/net/hamradio/baycom_ser_fdx.c.
609 baycom_ser_hdx= [HW,AX25]
610 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
611 Format: <io>,<irq>,<mode>
612 See header of drivers/net/hamradio/baycom_ser_hdx.c.
614 blkdevparts= Manual partition parsing of block device(s) for
615 embedded devices based on command line input.
616 See Documentation/block/cmdline-partition.txt
618 boot_delay= Milliseconds to delay each printk during boot.
619 Values larger than 10 seconds (10000) are changed to
623 bootmem_debug [KNL] Enable bootmem allocator debug messages.
626 Disable BERT OS support on buggy BIOSes.
628 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
629 bttv.radio= Most important insmod options are available as
631 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
634 bulk_remove=off [PPC] This parameter disables the use of the pSeries
635 firmware feature for flushing multiple hpte entries
638 c101= [NET] Moxa C101 synchronous serial card
640 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
641 Sometimes CPU hardware bugs make them report the cache
642 size incorrectly. The kernel will attempt work arounds
643 to fix known problems, but for some CPUs it is not
644 possible to determine what the correct size should be.
645 This option provides an override for these situations.
647 ca_keys= [KEYS] This parameter identifies a specific key(s) on
648 the system trusted keyring to be used for certificate
650 format: { id:<keyid> | builtin }
652 cca= [MIPS] Override the kernel pages' cache coherency
653 algorithm. Accepted values range from 0 to 7
654 inclusive. See arch/mips/include/asm/pgtable-bits.h
655 for platform specific values (SB1, Loongson3 and
658 ccw_timeout_log [S390]
659 See Documentation/s390/CommonIO for details.
661 cgroup_disable= [KNL] Disable a particular controller
662 Format: {name of the controller(s) to disable}
663 The effects of cgroup_disable=foo are:
664 - foo isn't auto-mounted if you mount all cgroups in
666 - foo isn't visible as an individually mountable
668 {Currently only "memory" controller deal with this and
669 cut the overhead, others just disable the usage. So
670 only cgroup_disable=memory is actually worthy}
672 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
673 Format: { controller[,controller...] | "all" }
674 Like cgroup_disable, but only applies to cgroup v1;
675 the blacklisted controllers remain available in cgroup2.
677 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
679 nosocket -- Disable socket memory accounting.
680 nokmem -- Disable kernel memory accounting.
682 checkreqprot [SELINUX] Set initial checkreqprot flag value.
683 Format: { "0" | "1" }
684 See security/selinux/Kconfig help text.
685 0 -- check protection applied by kernel (includes
686 any implied execute protection).
687 1 -- check protection requested by application.
688 Default value is set via a kernel config option.
689 Value can be changed at runtime via
690 /selinux/checkreqprot.
693 See Documentation/s390/CommonIO for details.
696 Prevents the clock framework from automatically gating
697 clocks that have not been explicitly enabled by a Linux
698 device driver but are enabled in hardware at reset or
699 by the bootloader/firmware. Note that this does not
700 force such clocks to be always-on nor does it reserve
701 those clocks in any way. This parameter is useful for
702 debug and development, but should not be needed on a
703 platform with proper driver support. For more
704 information, see Documentation/clk.txt.
706 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
708 Forces specified clocksource (if available) to be used
709 when calculating gettimeofday(). If specified
710 clocksource is not available, it defaults to PIT.
711 Format: { pit | tsc | cyclone | pmtmr }
713 clocksource= Override the default clocksource
715 Override the default clocksource and use the clocksource
716 with the name specified.
717 Some clocksource names to choose from, depending on
719 [all] jiffies (this is the base, fallback clocksource)
721 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
722 pxa_timer,timer3,32k_counter,timer0_1
724 [X86-32] pit,hpet,tsc;
725 scx200_hrt on Geode; cyclone on IBM x440
733 clocksource.arm_arch_timer.evtstrm=
736 Enable/disable the eventstream feature of the ARM
737 architected timer so that code using WFE-based polling
738 loops can be debugged more effectively on production
741 clocksource.arm_arch_timer.fsl-a008585=
744 Enable/disable the workaround of Freescale/NXP
745 erratum A-008585. This can be useful for KVM
746 guests, if the guest device tree doesn't show the
747 erratum. If unspecified, the workaround is
748 enabled based on the device tree.
750 clearcpuid=BITNUM [X86]
751 Disable CPUID feature X for the kernel. See
752 arch/x86/include/asm/cpufeatures.h for the valid bit
753 numbers. Note the Linux specific bits are not necessarily
754 stable over kernel options, but the vendor specific
756 Also note that user programs calling CPUID directly
757 or using the feature without checking anything
758 will still see it. This just prevents it from
759 being used by the kernel or shown in /proc/cpuinfo.
760 Also note the kernel might malfunction if you disable
763 cma=nn[MG]@[start[MG][-end[MG]]]
765 Sets the size of kernel global memory area for
766 contiguous memory allocations and optionally the
767 placement constraint by the physical address range of
768 memory allocations. A value of 0 disables CMA
769 altogether. For more information, see
770 include/linux/dma-contiguous.h
772 cmo_free_hint= [PPC] Format: { yes | no }
773 Specify whether pages are marked as being inactive
774 when they are freed. This is used in CMO environments
775 to determine OS memory pressure for page stealing by
779 coherent_pool=nn[KMG] [ARM,KNL]
780 Sets the size of memory pool for coherent, atomic dma
781 allocations, by default set to 256K.
783 code_bytes [X86] How many bytes of object code to print
788 com20020= [HW,NET] ARCnet - COM20020 chipset
790 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
792 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
796 ARCnet - COM90xx chipset (memory-mapped buffers)
797 Format: <io>[,<irq>[,<memstart>]]
799 condev= [HW,S390] console device
802 console= [KNL] Output console device and options.
804 tty<n> Use the virtual console device <n>.
808 Use the specified serial port. The options are of
809 the form "bbbbpnf", where "bbbb" is the baud rate,
810 "p" is parity ("n", "o", or "e"), "n" is number of
811 bits, and "f" is flow control ("r" for RTS or
812 omit it). Default is "9600n8".
814 See Documentation/serial-console.txt for more
816 Documentation/networking/netconsole.txt for an
819 uart[8250],io,<addr>[,options]
820 uart[8250],mmio,<addr>[,options]
821 uart[8250],mmio16,<addr>[,options]
822 uart[8250],mmio32,<addr>[,options]
823 uart[8250],0x<addr>[,options]
824 Start an early, polled-mode console on the 8250/16550
825 UART at the specified I/O port or MMIO address,
826 switching to the matching ttyS device later.
827 MMIO inter-register address stride is either 8-bit
828 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
829 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
830 to be equivalent to 'mmio'. 'options' are specified in
831 the same format described for ttyS above; if unspecified,
832 the h/w is not re-initialized.
834 hvc<n> Use the hypervisor console device <n>. This is for
835 both Xen and PowerPC hypervisors.
837 If the device connected to the port is not a TTY but a braille
838 device, prepend "brl," before the device type, for instance
840 For now, only VisioBraille is supported.
842 consoleblank= [KNL] The console blank (screen saver) timeout in
843 seconds. Defaults to 10*60 = 10mins. A value of 0
844 disables the blank timer.
847 [KNL] Change the default value for
848 /proc/<pid>/coredump_filter.
849 See also Documentation/filesystems/proc.txt.
851 cpuidle.off=1 [CPU_IDLE]
852 disable the cpuidle sub-system
855 [X86] Delay for N microsec between assert and de-assert
856 of APIC INIT to start processors. This delay occurs
857 on every CPU online, such as boot, and resume from suspend.
860 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
862 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
864 crashkernel=size[KMG][@offset[KMG]]
865 [KNL] Using kexec, Linux can switch to a 'crash kernel'
866 upon panic. This parameter reserves the physical
867 memory region [offset, offset + size] for that kernel
868 image. If '@offset' is omitted, then a suitable offset
869 is selected automatically. Check
870 Documentation/kdump/kdump.txt for further details.
872 crashkernel=range1:size1[,range2:size2,...][@offset]
873 [KNL] Same as above, but depends on the memory
874 in the running system. The syntax of range is
875 start-[end] where start and end are both
876 a memory unit (amount[KMG]). See also
877 Documentation/kdump/kdump.txt for an example.
879 crashkernel=size[KMG],high
880 [KNL, x86_64] range could be above 4G. Allow kernel
881 to allocate physical memory region from top, so could
882 be above 4G if system have more than 4G ram installed.
883 Otherwise memory region will be allocated below 4G, if
885 It will be ignored if crashkernel=X is specified.
886 crashkernel=size[KMG],low
887 [KNL, x86_64] range under 4G. When crashkernel=X,high
888 is passed, kernel could allocate physical memory region
889 above 4G, that cause second kernel crash on system
890 that require some amount of low memory, e.g. swiotlb
891 requires at least 64M+32K low memory, also enough extra
892 low memory is needed to make sure DMA buffers for 32-bit
893 devices won't run out. Kernel would try to allocate at
894 at least 256M below 4G automatically.
895 This one let user to specify own low range under 4G
896 for second kernel instead.
897 0: to disable low allocation.
898 It will be ignored when crashkernel=X,high is not used
899 or memory reserved is below 4G.
902 [KNL] Disable crypto self-tests
907 cs89x0_media= [HW,NET]
908 Format: { rj45 | aui | bnc }
911 See header of drivers/s390/block/dasd_devmap.c.
913 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
914 (one device per port)
915 Format: <port#>,<type>
916 See also Documentation/input/joystick-parport.txt
918 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
919 time. See Documentation/dynamic-debug-howto.txt for
920 details. Deprecated, see dyndbg.
922 debug [KNL] Enable kernel debugging (events log level).
925 [KNL] verbose self-tests
927 Print debugging info while doing the locking API
929 We default to 0 (no extra messages), setting it to
930 1 will print _a lot_ more information - normally
931 only useful to kernel developers.
933 debug_objects [KNL] Enable object debugging
936 [KNL] Disable object debugging
938 debug_guardpage_minorder=
939 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
940 parameter allows control of the order of pages that will
941 be intentionally kept free (and hence protected) by the
942 buddy allocator. Bigger value increase the probability
943 of catching random memory corruption, but reduce the
944 amount of memory for normal system use. The maximum
945 possible value is MAX_ORDER/2. Setting this parameter
946 to 1 or 2 should be enough to identify most random
947 memory corruption problems caused by bugs in kernel or
948 driver code when a CPU writes to (or reads from) a
949 random memory location. Note that there exists a class
950 of memory corruptions problems caused by buggy H/W or
951 F/W or by drivers badly programing DMA (basically when
952 memory is written at bus level and the CPU MMU is
953 bypassed) which are not detectable by
954 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
955 tracking down these problems.
958 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
959 parameter enables the feature at boot time. In
960 default, it is disabled. We can avoid allocating huge
961 chunk of memory for debug pagealloc if we don't enable
962 it at boot time and the system will work mostly same
963 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
964 on: enable the feature
966 debugpat [X86] Enable PAT debugging
968 decnet.addr= [HW,NET]
969 Format: <area>[,<node>]
970 See also Documentation/networking/decnet.txt.
973 [same as hugepagesz=] The size of the default
974 HugeTLB page size. This is the size represented by
975 the legacy /proc/ hugepages APIs, used for SHM, and
976 default size when mounting hugetlbfs filesystems.
977 Defaults to the default architecture's huge page size
981 Set number of hash buckets for dentry cache.
983 disable_1tb_segments [PPC]
984 Disables the use of 1TB hash page table segments. This
985 causes the kernel to fall back to 256MB segments which
986 can be useful when debugging issues that require an SLB
990 See Documentation/networking/ipv6.txt.
993 Disable RADIX MMU mode on POWER9
995 disable_cpu_apicid= [X86,APIC,SMP]
997 The number of initial APIC ID for the
998 corresponding CPU to be disabled at boot,
999 mostly used for the kdump 2nd kernel to
1000 disable BSP to wake up multiple CPUs without
1001 causing system reset or hang due to sending
1002 INIT from AP to BSP.
1004 disable_ddw [PPC/PSERIES]
1005 Disable Dynamic DMA Window support. Use this if
1006 to workaround buggy firmware.
1008 disable_ipv6= [IPV6]
1009 See Documentation/networking/ipv6.txt.
1011 disable_mtrr_cleanup [X86]
1012 The kernel tries to adjust MTRR layout from continuous
1013 to discrete, to make X server driver able to add WB
1014 entry later. This parameter disables that.
1016 disable_mtrr_trim [X86, Intel and AMD only]
1017 By default the kernel will trim any uncacheable
1018 memory out of your available memory pool based on
1019 MTRR settings. This parameter disables that behavior,
1020 possibly causing your machine to run very slowly.
1022 disable_timer_pin_1 [X86]
1023 Disable PIN 1 of APIC timer
1024 Can be useful to work around chipset bugs.
1026 dis_ucode_ldr [X86] Disable the microcode loader.
1028 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1029 this option disables the debugging code at boot.
1031 dma_debug_entries=<number>
1032 This option allows to tune the number of preallocated
1033 entries for DMA-API debugging code. One entry is
1034 required per DMA-API allocation. Use this if the
1035 DMA-API debugging code disables itself because the
1036 architectural default is too low.
1038 dma_debug_driver=<driver_name>
1039 With this option the DMA-API debugging driver
1040 filter feature can be enabled at boot time. Just
1041 pass the driver to filter for as the parameter.
1042 The filter can be disabled or changed to another
1043 driver later using sysfs.
1045 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1046 Broken monitors, graphic adapters, KVMs and EDIDless
1047 panels may send no or incorrect EDID data sets.
1048 This parameter allows to specify an EDID data sets
1049 in the /lib/firmware directory that are used instead.
1050 Generic built-in EDID data sets are used, if one of
1051 edid/1024x768.bin, edid/1280x1024.bin,
1052 edid/1680x1050.bin, or edid/1920x1080.bin is given
1053 and no file with the same name exists. Details and
1054 instructions how to build your own EDID data are
1055 available in Documentation/EDID/HOWTO.txt. An EDID
1056 data set will only be used for a particular connector,
1057 if its name and a colon are prepended to the EDID
1058 name. Each connector may use a unique EDID data
1059 set by separating the files with a comma. An EDID
1060 data set with no connector name will be used for
1061 any connectors not explicitly specified.
1065 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1066 module.dyndbg[="val"]
1067 Enable debug messages at boot time. See
1068 Documentation/dynamic-debug-howto.txt for details.
1070 nompx [X86] Disables Intel Memory Protection Extensions.
1071 See Documentation/x86/intel_mpx.txt for more
1072 information about the feature.
1074 nopku [X86] Disable Memory Protection Keys CPU feature found
1078 on enable eager fpu restore
1079 off disable eager fpu restore
1080 auto selects the default scheme, which automatically
1081 enables eagerfpu restore for xsaveopt.
1083 module.async_probe [KNL]
1084 Enable asynchronous probe on this module.
1086 early_ioremap_debug [KNL]
1087 Enable debug messages in early_ioremap support. This
1088 is useful for tracking down temporary early mappings
1089 which are not unmapped.
1091 earlycon= [KNL] Output early console device and options.
1093 When used with no options, the early console is
1094 determined by the stdout-path property in device
1097 cdns,<addr>[,options]
1098 Start an early, polled-mode console on a Cadence
1099 (xuartps) serial port at the specified address. Only
1100 supported option is baud rate. If baud rate is not
1101 specified, the serial port must already be setup and
1104 uart[8250],io,<addr>[,options]
1105 uart[8250],mmio,<addr>[,options]
1106 uart[8250],mmio32,<addr>[,options]
1107 uart[8250],mmio32be,<addr>[,options]
1108 uart[8250],0x<addr>[,options]
1109 Start an early, polled-mode console on the 8250/16550
1110 UART at the specified I/O port or MMIO address.
1111 MMIO inter-register address stride is either 8-bit
1112 (mmio) or 32-bit (mmio32 or mmio32be).
1113 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1114 to be equivalent to 'mmio'. 'options' are specified
1115 in the same format described for "console=ttyS<n>"; if
1116 unspecified, the h/w is not initialized.
1120 Start an early, polled-mode console on a pl011 serial
1121 port at the specified address. The pl011 serial port
1122 must already be setup and configured. Options are not
1123 yet supported. If 'mmio32' is specified, then only
1124 the driver will use only 32-bit accessors to read/write
1125 the device registers.
1128 Start an early, polled-mode console on a meson serial
1129 port at the specified address. The serial port must
1130 already be setup and configured. Options are not yet
1134 Start an early, polled-mode console on an msm serial
1135 port at the specified address. The serial port
1136 must already be setup and configured. Options are not
1139 msm_serial_dm,<addr>
1140 Start an early, polled-mode console on an msm serial
1141 dm port at the specified address. The serial port
1142 must already be setup and configured. Options are not
1145 smh Use ARM semihosting calls for early console.
1153 Use early console provided by serial driver available
1154 on Samsung SoCs, requires selecting proper type and
1155 a correct base address of the selected UART port. The
1156 serial port must already be setup and configured.
1157 Options are not yet supported.
1161 Use early console provided by Freescale LP UART driver
1162 found on Freescale Vybrid and QorIQ LS1021A processors.
1163 A valid base address must be provided, and the serial
1164 port must already be setup and configured.
1166 armada3700_uart,<addr>
1167 Start an early, polled-mode console on the
1168 Armada 3700 serial port at the specified
1169 address. The serial port must already be setup
1170 and configured. Options are not yet supported.
1172 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1176 earlyprintk=serial[,ttySn[,baudrate]]
1177 earlyprintk=serial[,0x...[,baudrate]]
1178 earlyprintk=ttySn[,baudrate]
1179 earlyprintk=dbgp[debugController#]
1180 earlyprintk=pciserial,bus:device.function[,baudrate]
1182 earlyprintk is useful when the kernel crashes before
1183 the normal console is initialized. It is not enabled by
1184 default because it has some cosmetic problems.
1186 Append ",keep" to not disable it when the real console
1189 Only one of vga, efi, serial, or usb debug port can
1192 Currently only ttyS0 and ttyS1 may be specified by
1193 name. Other I/O ports may be explicitly specified
1194 on some architectures (x86 and arm at least) by
1195 replacing ttySn with an I/O port address, like this:
1196 earlyprintk=serial,0x1008,115200
1197 You can find the port for a given device in
1198 /proc/tty/driver/serial:
1199 2: uart:ST16650V2 port:00001008 irq:18 ...
1201 Interaction with the standard serial driver is not
1204 The VGA and EFI output is eventually overwritten by
1207 The xen output can only be used by Xen PV guests.
1209 edac_report= [HW,EDAC] Control how to report EDAC event
1210 Format: {"on" | "off" | "force"}
1211 on: enable EDAC to report H/W event. May be overridden
1212 by other higher priority error reporting module.
1213 off: disable H/W event reporting through EDAC.
1214 force: enforce the use of EDAC to report H/W event.
1217 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1220 This is designed to be used in conjunction with
1221 the boot argument: earlyprintk=vga
1224 Format: {"off" | "on" | "skip[mbr]"}
1227 Format: { "old_map", "nochunk", "noruntime", "debug" }
1228 old_map [X86-64]: switch to the old ioremap-based EFI
1229 runtime services mapping. 32-bit still uses this one by
1231 nochunk: disable reading files in "chunks" in the EFI
1232 boot stub, as chunking can cause problems with some
1233 firmware implementations.
1234 noruntime : disable EFI runtime services support
1235 debug: enable misc debug output
1237 efi_no_storage_paranoia [EFI; X86]
1238 Using this parameter you can use more than 50% of
1239 your efi variable storage. Use this parameter only if
1240 you are really sure that your UEFI does sane gc and
1241 fulfills the spec otherwise your board may brick.
1243 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1244 Add arbitrary attribute to specific memory range by
1245 updating original EFI memory map.
1246 Region of memory which aa attribute is added to is
1248 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1249 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1250 attribute is added to range 0x100000000-0x180000000 and
1251 0x10a0000000-0x1120000000.
1253 Using this parameter you can do debugging of EFI memmap
1254 related feature. For example, you can do debugging of
1255 Address Range Mirroring feature even if your box
1258 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1259 that is to be dynamically loaded by Linux. If there are
1260 multiple variables with the same name but with different
1261 vendor GUIDs, all of them will be loaded. See
1262 Documentation/acpi/ssdt-overlays.txt for details.
1265 eisa_irq_edge= [PARISC,HW]
1266 See header of drivers/parisc/eisa.c.
1269 See comment before function elanfreq_setup() in
1270 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1273 Format: {"cfq" | "deadline" | "noop"}
1274 See Documentation/block/cfq-iosched.txt and
1275 Documentation/block/deadline-iosched.txt for details.
1277 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1278 Specifies physical address of start of kernel core
1279 image elf header and optionally the size. Generally
1280 kexec loader will pass this option to capture kernel.
1281 See Documentation/kdump/kdump.txt for details.
1283 enable_mtrr_cleanup [X86]
1284 The kernel tries to adjust MTRR layout from continuous
1285 to discrete, to make X server driver able to add WB
1286 entry later. This parameter enables that.
1288 enable_timer_pin_1 [X86]
1289 Enable PIN 1 of APIC timer
1290 Can be useful to work around chipset bugs
1291 (in particular on some ATI chipsets).
1292 The kernel tries to set a reasonable default.
1294 enforcing [SELINUX] Set initial enforcing status.
1296 See security/selinux/Kconfig help text.
1297 0 -- permissive (log only, no denials).
1298 1 -- enforcing (deny and log).
1300 Value can be changed at runtime via /selinux/enforce.
1303 Disable Error Record Serialization Table (ERST)
1306 ether= [HW,NET] Ethernet cards parameters
1307 This option is obsoleted by the "netdev=" option, which
1308 has equivalent usage. See its documentation for details.
1312 Permit 'security.evm' to be updated regardless of
1313 current integrity status.
1317 fail_make_request=[KNL]
1318 General fault injection mechanism.
1319 Format: <interval>,<probability>,<space>,<times>
1320 See also Documentation/fault-injection/.
1323 See Documentation/blockdev/floppy.txt.
1325 force_pal_cache_flush
1326 [IA-64] Avoid check_sal_cache_flush which may hang on
1327 buggy SAL_CACHE_FLUSH implementations. Using this
1328 parameter will force ia64_sal_cache_flush to call
1329 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1332 Forcefully enable Physical Address Extension (PAE).
1333 Many Pentium M systems disable PAE but may have a
1334 functionally usable PAE implementation.
1335 Warning: use of this parameter will taint the kernel
1336 and may cause unknown problems.
1339 [FTRACE] will set and start the specified tracer
1340 as early as possible in order to facilitate early
1343 ftrace_dump_on_oops[=orig_cpu]
1344 [FTRACE] will dump the trace buffers on oops.
1345 If no parameter is passed, ftrace will dump
1346 buffers of all CPUs, but if you pass orig_cpu, it will
1347 dump only the buffer of the CPU that triggered the
1350 ftrace_filter=[function-list]
1351 [FTRACE] Limit the functions traced by the function
1352 tracer at boot up. function-list is a comma separated
1353 list of functions. This list can be changed at run
1354 time by the set_ftrace_filter file in the debugfs
1357 ftrace_notrace=[function-list]
1358 [FTRACE] Do not trace the functions specified in
1359 function-list. This list can be changed at run time
1360 by the set_ftrace_notrace file in the debugfs
1363 ftrace_graph_filter=[function-list]
1364 [FTRACE] Limit the top level callers functions traced
1365 by the function graph tracer at boot up.
1366 function-list is a comma separated list of functions
1367 that can be changed at run time by the
1368 set_graph_function file in the debugfs tracing directory.
1370 ftrace_graph_notrace=[function-list]
1371 [FTRACE] Do not trace from the functions specified in
1372 function-list. This list is a comma separated list of
1373 functions that can be changed at run time by the
1374 set_graph_notrace file in the debugfs tracing directory.
1377 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1378 support via parallel port (up to 5 devices per port)
1379 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1380 See also Documentation/input/joystick-parport.txt
1384 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1388 gcov_persist= [GCOV] When non-zero (default), profiling data for
1389 kernel modules is saved and remains accessible via
1390 debugfs, even when the module is unloaded/reloaded.
1391 When zero, profiling data is discarded and associated
1392 debugfs files are removed at module unload time.
1394 goldfish [X86] Enable the goldfish android emulator platform.
1395 Don't use this when you are not running on the
1398 gpt [EFI] Forces disk with valid GPT signature but
1399 invalid Protective MBR to be treated as GPT. If the
1400 primary GPT is corrupted, it enables the backup/alternate
1401 GPT to be used instead.
1403 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1404 the "Enable 0" bit of the configuration register.
1407 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1408 the "Enable 0" bit of the configuration register.
1411 grcan.select= [HW] Select which physical interface to use.
1414 grcan.txsize= [HW] Sets the size of the tx buffer.
1415 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1417 grcan.rxsize= [HW] Sets the size of the rx buffer.
1418 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1421 gpio-mockup.gpio_mockup_ranges
1422 [HW] Sets the ranges of gpiochip of for this device.
1423 Format: <start1>,<end1>,<start2>,<end2>...
1425 hardlockup_all_cpu_backtrace=
1426 [KNL] Should the hard-lockup detector generate
1427 backtraces on all cpus.
1430 hashdist= [KNL,NUMA] Large hashes allocated during boot
1431 are distributed across NUMA nodes. Defaults on
1432 for 64-bit NUMA, off otherwise.
1433 Format: 0 | 1 (for off | on)
1435 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1437 hd= [EIDE] (E)IDE hard drive subsystem geometry
1438 Format: <cyl>,<head>,<sect>
1441 Disable Hardware Error Source Table (HEST) support;
1442 corresponding firmware-first mode error processing
1443 logic will be disabled.
1445 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1446 size of <nn>. This works even on boxes that have no
1447 highmem otherwise. This also works to reduce highmem
1448 size on bigger boxes.
1450 highres= [KNL] Enable/disable high resolution timer mode.
1451 Valid parameters: "on", "off"
1455 See Documentation/isdn/README.HiSax.
1459 hpet= [X86-32,HPET] option to control HPET usage
1460 Format: { enable (default) | disable | force |
1462 disable: disable HPET and use PIT instead
1463 force: allow force enabled of undocumented chips (ICH4,
1465 verbose: show contents of HPET registers during setup
1467 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1468 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1470 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1471 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1472 On x86-64 and powerpc, this option can be specified
1473 multiple times interleaved with hugepages= to reserve
1474 huge pages of different sizes. Valid pages sizes on
1475 x86-64 are 2M (when the CPU supports "pse") and 1G
1476 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1478 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1479 terminal devices. Valid values: 0..8
1480 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1481 If specified, z/VM IUCV HVC accepts connections
1482 from listed z/VM user IDs only.
1484 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1485 hardware thread id mappings.
1486 Format: <cpu>:<hwthread>
1489 Do not unregister boot console at start. This is only
1490 useful for debugging when something happens in the window
1491 between unregistering the boot console and initializing
1494 i2c_bus= [HW] Override the default board specific I2C bus speed
1495 or register an additional I2C bus that is not
1496 registered from board initialization code.
1500 i8042.debug [HW] Toggle i8042 debug mode
1501 i8042.unmask_kbd_data
1502 [HW] Enable printing of interrupt data from the KBD port
1503 (disabled by default, and as a pre-condition
1504 requires that i8042.debug=1 be enabled)
1505 i8042.direct [HW] Put keyboard port into non-translated mode
1506 i8042.dumbkbd [HW] Pretend that controller can only read data from
1507 keyboard and cannot control its state
1508 (Don't attempt to blink the leds)
1509 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1510 i8042.nokbd [HW] Don't check/create keyboard port
1511 i8042.noloop [HW] Disable the AUX Loopback command while probing
1513 i8042.nomux [HW] Don't check presence of an active multiplexing
1515 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1517 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1518 i8042.reset [HW] Reset the controller during init, cleanup and
1519 suspend-to-ram transitions, only during s2r
1520 transitions, or never reset
1521 Format: { 1 | Y | y | 0 | N | n }
1522 1, Y, y: always reset controller
1523 0, N, n: don't ever reset controller
1524 Default: only on s2r transitions on x86; most other
1525 architectures force reset to be always executed
1526 i8042.unlock [HW] Unlock (ignore) the keylock
1527 i8042.kbdreset [HW] Reset device connected to KBD port
1531 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1532 indicates that the driver is running on unsupported
1534 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1535 does not match list of supported models.
1537 [HW] Report power status in /proc/i8k
1538 (disabled by default)
1539 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1542 i915.invert_brightness=
1543 [DRM] Invert the sense of the variable that is used to
1544 set the brightness of the panel backlight. Normally a
1545 brightness value of 0 indicates backlight switched off,
1546 and the maximum of the brightness value sets the backlight
1547 to maximum brightness. If this parameter is set to 0
1548 (default) and the machine requires it, or this parameter
1549 is set to 1, a brightness value of 0 sets the backlight
1550 to maximum brightness, and the maximum of the brightness
1551 value switches the backlight off.
1552 -1 -- never invert brightness
1553 0 -- machine default
1554 1 -- force brightness inversion
1557 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1559 ide-core.nodma= [HW] (E)IDE subsystem
1560 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1561 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1562 .cdrom .chs .ignore_cable are additional options
1563 See Documentation/ide/ide.txt.
1565 ide-generic.probe-mask= [HW] (E)IDE subsystem
1567 Probe mask for legacy ISA IDE ports. Depending on
1568 platform up to 6 ports are supported, enabled by
1569 setting corresponding bits in the mask to 1. The
1570 default value is 0x0, which has a special meaning.
1571 On systems that have PCI, it triggers scanning the
1572 PCI bus for the first and the second port, which
1573 are then probed. On systems without PCI the value
1574 of 0x0 enables probing the two first ports as if it
1577 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1578 Claim all unknown PCI IDE storage controllers.
1581 Format: idle=poll, idle=halt, idle=nomwait
1582 Poll forces a polling idle loop that can slightly
1583 improve the performance of waking up a idle CPU, but
1584 will use a lot of power and make the system run hot.
1586 idle=halt: Halt is forced to be used for CPU idle.
1587 In such case C2/C3 won't be used again.
1588 idle=nomwait: Disable mwait for CPU C-states
1590 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1591 Format: { strict | legacy | 2008 | relaxed }
1594 Choose which programs will be accepted for execution
1595 based on the IEEE 754 NaN encoding(s) supported by
1596 the FPU and the NaN encoding requested with the value
1597 of an ELF file header flag individually set by each
1598 binary. Hardware implementations are permitted to
1599 support either or both of the legacy and the 2008 NaN
1602 Available settings are as follows:
1603 strict accept binaries that request a NaN encoding
1604 supported by the FPU
1605 legacy only accept legacy-NaN binaries, if supported
1607 2008 only accept 2008-NaN binaries, if supported
1609 relaxed accept any binaries regardless of whether
1610 supported by the FPU
1612 The FPU emulator is always able to support both NaN
1613 encodings, so if no FPU hardware is present or it has
1614 been disabled with 'nofpu', then the settings of
1615 'legacy' and '2008' strap the emulator accordingly,
1616 'relaxed' straps the emulator for both legacy-NaN and
1617 2008-NaN, whereas 'strict' enables legacy-NaN only on
1618 legacy processors and both NaN encodings on MIPS32 or
1621 The setting for ABS.fmt/NEG.fmt instruction execution
1622 mode generally follows that for the NaN encoding,
1623 except where unsupported by hardware.
1625 ignore_loglevel [KNL]
1626 Ignore loglevel setting - this will print /all/
1627 kernel messages to the console. Useful for debugging.
1628 We also add it as printk module parameter, so users
1629 could change it dynamically, usually by
1630 /sys/module/printk/parameters/ignore_loglevel.
1633 Ignore RLIMIT_DATA setting for data mappings,
1634 print warning at first misuse. Can be changed via
1635 /sys/module/kernel/parameters/ignore_rlimit_data.
1637 ihash_entries= [KNL]
1638 Set number of hash buckets for inode cache.
1640 ima_appraise= [IMA] appraise integrity measurements
1641 Format: { "off" | "enforce" | "fix" | "log" }
1644 ima_appraise_tcb [IMA]
1645 The builtin appraise policy appraises all files
1649 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1653 The list of supported hash algorithms is defined
1654 in crypto/hash_info.h.
1657 The builtin measurement policy to load during IMA
1658 setup. Specyfing "tcb" as the value, measures all
1659 programs exec'd, files mmap'd for exec, and all files
1660 opened with the read mode bit set by either the
1661 effective uid (euid=0) or uid=0.
1664 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1665 Load a policy which meets the needs of the Trusted
1666 Computing Base. This means IMA will measure all
1667 programs exec'd, files mmap'd for exec, and all files
1668 opened for read by uid=0.
1671 Select one of defined IMA measurements template formats.
1672 Formats: { "ima" | "ima-ng" | "ima-sig" }
1676 [IMA] Define a custom template format.
1677 Format: { "field1|...|fieldN" }
1679 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1680 Format: <min_file_size>
1681 Set the minimal file size for using asynchronous hash.
1682 If left unspecified, ahash usage is disabled.
1684 ahash performance varies for different data sizes on
1685 different crypto accelerators. This option can be used
1686 to achieve the best performance for a particular HW.
1688 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1690 Set hashing buffer size. Default: 4k.
1692 ahash performance varies for different chunk sizes on
1693 different crypto accelerators. This option can be used
1694 to achieve best performance for particular HW.
1698 Run specified binary instead of /sbin/init as init
1701 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1702 for working out where the kernel is dying during
1705 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1706 initcall functions. Useful for debugging built-in
1707 modules and initcalls.
1709 initrd= [BOOT] Specify the location of the initial ramdisk
1711 init_pkru= [x86] Specify the default memory protection keys rights
1712 register contents for all processes. 0x55555554 by
1713 default (disallow access to all but pkey 0). Can
1714 override in debugfs after boot.
1716 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1719 int_pln_enable [x86] Enable power limit notification interrupt
1721 integrity_audit=[IMA]
1722 Format: { "0" | "1" }
1723 0 -- basic integrity auditing messages. (Default)
1724 1 -- additional integrity auditing messages.
1726 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1728 Enable intel iommu driver.
1730 Disable intel iommu driver.
1731 igfx_off [Default Off]
1732 By default, gfx is mapped as normal device. If a gfx
1733 device has a dedicated DMAR unit, the DMAR unit is
1734 bypassed by not enabling DMAR with this option. In
1735 this case, gfx device will use physical address for
1738 With this option iommu will not optimize to look
1739 for io virtual address below 32-bit forcing dual
1740 address cycle on pci bus for cards supporting greater
1741 than 32-bit addressing. The default is to look
1742 for translation below 32-bit and if not available
1743 then look in the higher range.
1744 strict [Default Off]
1745 With this option on every unmap_single operation will
1746 result in a hardware IOTLB flush operation as opposed
1747 to batching them for performance.
1748 sp_off [Default Off]
1749 By default, super page will be supported if Intel IOMMU
1750 has the capability. With this option, super page will
1752 ecs_off [Default Off]
1753 By default, extended context tables will be supported if
1754 the hardware advertises that it has support both for the
1755 extended tables themselves, and also PASID support. With
1756 this option set, extended tables will not be used even
1757 on hardware which claims to support them.
1759 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1760 0 disables intel_idle and fall back on acpi_idle.
1761 1 to 9 specify maximum depth of C-state.
1765 Do not enable intel_pstate as the default
1766 scaling driver for the supported processors
1768 Enable intel_pstate on systems that prohibit it by default
1769 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1770 instead of acpi-cpufreq may disable platform features, such
1771 as thermal controls and power capping, that rely on ACPI
1772 P-States information being indicated to OSPM and therefore
1773 should be used with caution. This option does not work with
1774 processors that aren't supported by the intel_pstate driver
1775 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1777 Do not enable hardware P state control (HWP)
1780 Only load intel_pstate on systems which support
1781 hardware P state control (HWP) if available.
1783 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1784 Description Table, specifies preferred power management
1785 profile as "Enterprise Server" or "Performance Server",
1786 then this feature is turned on by default.
1788 intremap= [X86-64, Intel-IOMMU]
1789 on enable Interrupt Remapping (default)
1790 off disable Interrupt Remapping
1791 nosid disable Source ID checking
1793 BIOS x2APIC opt-out request will be ignored
1794 nopost disable Interrupt Posting
1796 iomem= Disable strict checking of access to MMIO memory
1797 strict regions from userspace.
1812 nobypass [PPC/POWERNV]
1813 Disable IOMMU bypass, using IOMMU for PCI devices.
1816 io7= [HW] IO7 for Marvel based alpha systems
1817 See comment before marvel_specify_io7 in
1818 arch/alpha/kernel/core_marvel.c.
1820 io_delay= [X86] I/O delay method
1822 Standard port 0x80 based delay
1824 Alternate port 0xed based delay (needed on some systems)
1826 Simple two microseconds delay
1831 See Documentation/filesystems/nfs/nfsroot.txt.
1833 irqaffinity= [SMP] Set the default irq affinity mask
1834 The argument is a cpu list, as described above.
1837 When an interrupt is not handled search all handlers
1838 for it. Intended to get systems with badly broken
1842 When an interrupt is not handled search all handlers
1843 for it. Also check all handlers each timer
1844 interrupt. Intended to get systems with badly broken
1848 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1850 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1851 The argument is a cpu list, as described above.
1853 This option can be used to specify one or more CPUs
1854 to isolate from the general SMP balancing and scheduling
1855 algorithms. You can move a process onto or off an
1856 "isolated" CPU via the CPU affinity syscalls or cpuset.
1857 <cpu number> begins at 0 and the maximum value is
1858 "number of CPUs in system - 1".
1860 This option is the preferred way to isolate CPUs. The
1861 alternative -- manually setting the CPU mask of all
1862 tasks in the system -- can cause problems and
1863 suboptimal load balancer performance.
1867 ivrs_ioapic [HW,X86_64]
1868 Provide an override to the IOAPIC-ID<->DEVICE-ID
1869 mapping provided in the IVRS ACPI table. For
1870 example, to map IOAPIC-ID decimal 10 to
1871 PCI device 00:14.0 write the parameter as:
1872 ivrs_ioapic[10]=00:14.0
1874 ivrs_hpet [HW,X86_64]
1875 Provide an override to the HPET-ID<->DEVICE-ID
1876 mapping provided in the IVRS ACPI table. For
1877 example, to map HPET-ID decimal 0 to
1878 PCI device 00:14.0 write the parameter as:
1879 ivrs_hpet[0]=00:14.0
1881 ivrs_acpihid [HW,X86_64]
1882 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1883 mapping provided in the IVRS ACPI table. For
1884 example, to map UART-HID:UID AMD0020:0 to
1885 PCI device 00:14.5 write the parameter as:
1886 ivrs_acpihid[00:14.5]=AMD0020:0
1888 js= [HW,JOY] Analog joystick
1889 See Documentation/input/joystick.txt.
1892 When CONFIG_RANDOMIZE_BASE is set, this disables
1893 kernel and module base offset ASLR (Address Space
1894 Layout Randomization).
1898 kernelcore= [KNL,X86,IA-64,PPC]
1899 Format: nn[KMGTPE] | "mirror"
1901 specifies the amount of memory usable by the kernel
1902 for non-movable allocations. The requested amount is
1903 spread evenly throughout all nodes in the system. The
1904 remaining memory in each node is used for Movable
1905 pages. In the event, a node is too small to have both
1906 kernelcore and Movable pages, kernelcore pages will
1907 take priority and other nodes will have a larger number
1908 of Movable pages. The Movable zone is used for the
1909 allocation of pages that may be reclaimed or moved
1910 by the page migration subsystem. This means that
1911 HugeTLB pages may not be allocated from this zone.
1912 Note that allocations like PTEs-from-HighMem still
1913 use the HighMem zone if it exists, and the Normal
1914 zone if it does not.
1916 Instead of specifying the amount of memory (nn[KMGTPE]),
1917 you can specify "mirror" option. In case "mirror"
1918 option is specified, mirrored (reliable) memory is used
1919 for non-movable allocations and remaining memory is used
1920 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1921 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1924 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1925 Format: <Controller#>[,poll interval]
1926 The controller # is the number of the ehci usb debug
1927 port as it is probed via PCI. The poll interval is
1928 optional and is the number seconds in between
1929 each poll cycle to the debug port in case you need
1930 the functionality for interrupting the kernel with
1931 gdb or control-c on the dbgp connection. When
1932 not using this parameter you use sysrq-g to break into
1933 the kernel debugger.
1935 kgdboc= [KGDB,HW] kgdb over consoles.
1936 Requires a tty driver that supports console polling,
1937 or a supported polling keyboard driver (non-usb).
1938 Serial only format: <serial_device>[,baud]
1939 keyboard only format: kbd
1940 keyboard and serial format: kbd,<serial_device>[,baud]
1941 Optional Kernel mode setting:
1942 kms, kbd format: kms,kbd
1943 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1945 kgdbwait [KGDB] Stop kernel execution and enter the
1946 kernel debugger at the earliest opportunity.
1948 kmac= [MIPS] korina ethernet MAC address.
1949 Configure the RouterBoard 532 series on-chip
1950 Ethernet adapter MAC address.
1952 kmemleak= [KNL] Boot-time kmemleak enable/disable
1953 Valid arguments: on, off
1955 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1958 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1959 Valid arguments: 0, 1, 2
1960 kmemcheck=0 (disabled)
1961 kmemcheck=1 (enabled)
1962 kmemcheck=2 (one-shot mode)
1963 Default: 2 (one-shot mode)
1965 kstack=N [X86] Print N words from the kernel stack
1968 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1969 Default is 0 (don't ignore, but inject #GP)
1971 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1975 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1976 Default is 1 (enabled)
1978 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1980 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1982 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1983 (virtualized MMU) support on capable Intel chips.
1984 Default is 1 (enabled)
1986 kvm-intel.emulate_invalid_guest_state=
1987 [KVM,Intel] Enable emulation of invalid guest states
1988 Default is 0 (disabled)
1990 kvm-intel.flexpriority=
1991 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1992 Default is 1 (enabled)
1995 [KVM,Intel] Enable VMX nesting (nVMX).
1996 Default is 0 (disabled)
1998 kvm-intel.unrestricted_guest=
1999 [KVM,Intel] Disable unrestricted guest feature
2000 (virtualized real and unpaged mode) on capable
2001 Intel chips. Default is 1 (enabled)
2003 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2004 feature (tagged TLBs) on capable Intel chips.
2005 Default is 1 (enabled)
2011 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2014 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2015 value for LAPIC timer one-shot implementation. Default
2016 back to the programmable timer unit in the LAPIC.
2018 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2021 libata.dma= [LIBATA] DMA control
2022 libata.dma=0 Disable all PATA and SATA DMA
2023 libata.dma=1 PATA and SATA Disk DMA only
2024 libata.dma=2 ATAPI (CDROM) DMA only
2025 libata.dma=4 Compact Flash DMA only
2026 Combinations also work, so libata.dma=3 enables DMA
2027 for disks and CDROMs, but not CFs.
2029 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2030 libata.ignore_hpa=0 keep BIOS limits (default)
2031 libata.ignore_hpa=1 ignore limits, using full disk
2033 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2037 libata.force= [LIBATA] Force configurations. The format is comma
2038 separated list of "[ID:]VAL" where ID is
2039 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2040 matching port, link or device. Basically, it matches
2041 the ATA ID string printed on console by libata. If
2042 the whole ID part is omitted, the last PORT and DEVICE
2043 values are used. If ID hasn't been specified yet, the
2044 configuration applies to all ports, links and devices.
2046 If only DEVICE is omitted, the parameter applies to
2047 the port and all links and devices behind it. DEVICE
2048 number of 0 either selects the first device or the
2049 first fan-out link behind PMP device. It does not
2050 select the host link. DEVICE number of 15 selects the
2051 host link and device attached to it.
2053 The VAL specifies the configuration to force. As long
2054 as there's no ambiguity shortcut notation is allowed.
2055 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2056 The following configurations can be forced.
2058 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2059 Any ID with matching PORT is used.
2061 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2063 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2064 udma[/][16,25,33,44,66,100,133] notation is also
2067 * [no]ncq: Turn on or off NCQ.
2069 * [no]ncqtrim: Turn off queued DSM TRIM.
2071 * nohrst, nosrst, norst: suppress hard, soft
2074 * rstonce: only attempt one reset during
2075 hot-unplug link recovery
2077 * dump_id: dump IDENTIFY data.
2079 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2081 * disable: Disable this device.
2083 If there are multiple matching configurations changing
2084 the same attribute, the last one is used.
2086 memblock=debug [KNL] Enable memblock debug messages.
2088 load_ramdisk= [RAM] List of ramdisks to load from floppy
2089 See Documentation/blockdev/ramdisk.txt.
2091 lockd.nlm_grace_period=P [NFS] Assign grace period.
2094 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2097 lockd.nlm_timeout=T [NFS] Assign timeout value.
2100 lockd.nlm_udpport=M [NFS] Assign UDP port.
2103 locktorture.nreaders_stress= [KNL]
2104 Set the number of locking read-acquisition kthreads.
2105 Defaults to being automatically set based on the
2106 number of online CPUs.
2108 locktorture.nwriters_stress= [KNL]
2109 Set the number of locking write-acquisition kthreads.
2111 locktorture.onoff_holdoff= [KNL]
2112 Set time (s) after boot for CPU-hotplug testing.
2114 locktorture.onoff_interval= [KNL]
2115 Set time (s) between CPU-hotplug operations, or
2116 zero to disable CPU-hotplug testing.
2118 locktorture.shuffle_interval= [KNL]
2119 Set task-shuffle interval (jiffies). Shuffling
2120 tasks allows some CPUs to go into dyntick-idle
2121 mode during the locktorture test.
2123 locktorture.shutdown_secs= [KNL]
2124 Set time (s) after boot system shutdown. This
2125 is useful for hands-off automated testing.
2127 locktorture.stat_interval= [KNL]
2128 Time (s) between statistics printk()s.
2130 locktorture.stutter= [KNL]
2131 Time (s) to stutter testing, for example,
2132 specifying five seconds causes the test to run for
2133 five seconds, wait for five seconds, and so on.
2134 This tests the locking primitive's ability to
2135 transition abruptly to and from idle.
2137 locktorture.torture_runnable= [BOOT]
2138 Start locktorture running at boot time.
2140 locktorture.torture_type= [KNL]
2141 Specify the locking implementation to test.
2143 locktorture.verbose= [KNL]
2144 Enable additional printk() statements.
2146 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2149 loglevel= All Kernel Messages with a loglevel smaller than the
2150 console loglevel will be printed to the console. It can
2151 also be changed with klogd or other programs. The
2152 loglevels are defined as follows:
2154 0 (KERN_EMERG) system is unusable
2155 1 (KERN_ALERT) action must be taken immediately
2156 2 (KERN_CRIT) critical conditions
2157 3 (KERN_ERR) error conditions
2158 4 (KERN_WARNING) warning conditions
2159 5 (KERN_NOTICE) normal but significant condition
2160 6 (KERN_INFO) informational
2161 7 (KERN_DEBUG) debug-level messages
2163 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2164 in bytes. n must be a power of two and greater
2165 than the minimal size. The minimal size is defined
2166 by LOG_BUF_SHIFT kernel config parameter. There is
2167 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2168 that allows to increase the default size depending on
2169 the number of CPUs. See init/Kconfig for more details.
2171 logo.nologo [FB] Disables display of the built-in Linux logo.
2172 This may be used to provide more screen space for
2173 kernel log messages and is useful when debugging
2174 kernel boot problems.
2176 lp=0 [LP] Specify parallel ports to use, e.g,
2177 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2178 lp=reset first parallel port). 'lp=0' disables the
2179 lp=auto printer driver. 'lp=reset' (which can be
2180 specified in addition to the ports) causes
2181 attached printers to be reset. Using
2182 lp=port1,port2,... specifies the parallel ports
2183 to associate lp devices with, starting with
2184 lp0. A port specification may be 'none' to skip
2185 that lp device, or a parport name such as
2186 'parport0'. Specifying 'lp=auto' instead of a
2187 port specification list means that device IDs
2188 from each port should be examined, to see if
2189 an IEEE 1284-compliant printer is attached; if
2190 so, the driver will manage that printer.
2191 See also header of drivers/char/lp.c.
2194 Sets loops_per_jiffy to given constant, thus avoiding
2195 time-consuming boot-time autodetection (up to 250 ms per
2196 CPU). 0 enables autodetection (default). To determine
2197 the correct value for your kernel, boot with normal
2198 autodetection and see what value is printed. Note that
2199 on SMP systems the preset will be applied to all CPUs,
2200 which is likely to cause problems if your CPUs need
2201 significantly divergent settings. An incorrect value
2202 will cause delays in the kernel to be wrong, leading to
2203 unpredictable I/O errors and other breakage. Although
2204 unlikely, in the extreme case this might damage your
2208 Format: <io>,<irq>,<dma>
2210 machvec= [IA-64] Force the use of a particular machine-vector
2211 (machvec) in a generic kernel.
2212 Example: machvec=hpzx1_swiotlb
2214 machtype= [Loongson] Share the same kernel image file between different
2216 Example: machtype=lemote-yeeloong-2f-7inch
2218 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2219 than or equal to this physical address is ignored.
2221 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2222 will bring up during bootup. maxcpus=n : n >= 0 limits
2223 the kernel to bring up 'n' processors. Surely after
2224 bootup you can bring up the other plugged cpu by executing
2225 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2226 only takes effect during system bootup.
2227 While n=0 is a special case, it is equivalent to "nosmp",
2228 which also disables the IO APIC.
2230 max_loop= [LOOP] The number of loop block devices that get
2231 (loop.max_loop) unconditionally pre-created at init time. The default
2232 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2233 of statically allocating a predefined number, loop
2234 devices can be requested on-demand with the
2235 /dev/loop-control interface.
2237 mce [X86-32] Machine Check Exception
2239 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2241 md= [HW] RAID subsystems devices and level
2242 See Documentation/md.txt.
2245 Format: <first>,<last>
2246 Specifies range of consoles to be captured by the MDA.
2248 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2249 Amount of memory to be used when the kernel is not able
2250 to see the whole system memory or for test.
2251 [X86] Work as limiting max address. Use together
2252 with memmap= to avoid physical address space collisions.
2253 Without memmap= PCI devices could be placed at addresses
2254 belonging to unused RAM.
2256 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2260 [KNL,SH] Allow user to override the default size for
2261 per-device physically contiguous DMA buffers.
2263 memhp_default_state=online/offline
2264 [KNL] Set the initial state for the memory hotplug
2265 onlining policy. If not specified, the default value is
2266 set according to the
2267 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2269 See Documentation/memory-hotplug.txt.
2271 memmap=exactmap [KNL,X86] Enable setting of an exact
2272 E820 memory map, as specified by the user.
2273 Such memmap=exactmap lines can be constructed based on
2274 BIOS output or other requirements. See the memmap=nn@ss
2277 memmap=nn[KMG]@ss[KMG]
2278 [KNL] Force usage of a specific region of memory.
2279 Region of memory to be used is from ss to ss+nn.
2281 memmap=nn[KMG]#ss[KMG]
2282 [KNL,ACPI] Mark specific memory as ACPI data.
2283 Region of memory to be marked is from ss to ss+nn.
2285 memmap=nn[KMG]$ss[KMG]
2286 [KNL,ACPI] Mark specific memory as reserved.
2287 Region of memory to be reserved is from ss to ss+nn.
2288 Example: Exclude memory from 0x18690000-0x1869ffff
2289 memmap=64K$0x18690000
2291 memmap=0x10000$0x18690000
2293 memmap=nn[KMG]!ss[KMG]
2294 [KNL,X86] Mark specific memory as protected.
2295 Region of memory to be used, from ss to ss+nn.
2296 The memory region may be marked as e820 type 12 (0xc)
2297 and is NVDIMM or ADR memory.
2299 memory_corruption_check=0/1 [X86]
2300 Some BIOSes seem to corrupt the first 64k of
2301 memory when doing things like suspend/resume.
2302 Setting this option will scan the memory
2303 looking for corruption. Enabling this will
2304 both detect corruption and prevent the kernel
2305 from using the memory being corrupted.
2306 However, its intended as a diagnostic tool; if
2307 repeatable BIOS-originated corruption always
2308 affects the same memory, you can use memmap=
2309 to prevent the kernel from using that memory.
2311 memory_corruption_check_size=size [X86]
2312 By default it checks for corruption in the low
2313 64k, making this memory unavailable for normal
2314 use. Use this parameter to scan for
2315 corruption in more or less memory.
2317 memory_corruption_check_period=seconds [X86]
2318 By default it checks for corruption every 60
2319 seconds. Use this parameter to check at some
2320 other rate. 0 disables periodic checking.
2322 memtest= [KNL,X86,ARM] Enable memtest
2324 default : 0 <disable>
2325 Specifies the number of memtest passes to be
2326 performed. Each pass selects another test
2327 pattern from a given set of patterns. Memtest
2328 fills the memory with this pattern, validates
2329 memory contents and reserves bad memory
2330 regions that are detected.
2332 meye.*= [HW] Set MotionEye Camera parameters
2333 See Documentation/video4linux/meye.txt.
2335 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2336 Multi-Function General Purpose Timers on AMD Geode
2339 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2340 the BIOS has incorrectly applied a workaround. TinyBIOS
2341 version 0.98 is known to be affected, 0.99 fixes the
2342 problem by letting the user disable the workaround.
2346 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2347 physical address is ignored.
2349 mini2440= [ARM,HW,KNL]
2350 Format:[0..2][b][c][t]
2352 MINI2440 configuration specification:
2353 0 - The attached screen is the 3.5" TFT
2354 1 - The attached screen is the 7" TFT
2355 2 - The VGA Shield is attached (1024x768)
2356 Leaving out the screen size parameter will not load
2357 the TFT driver, and the framebuffer will be left
2359 b - Enable backlight. The TFT backlight pin will be
2360 linked to the kernel VESA blanking code and a GPIO
2361 LED. This parameter is not necessary when using the
2363 c - Enable the s3c camera interface.
2364 t - Reserved for enabling touchscreen support. The
2365 touchscreen support is not enabled in the mainstream
2366 kernel as of 2.6.30, a preliminary port can be found
2367 in the "bleeding edge" mini2440 support kernel at
2368 http://repo.or.cz/w/linux-2.6/mini2440.git
2371 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2372 parameter allows control of the logging verbosity for
2373 the additional memory initialisation checks. A value
2374 of 0 disables mminit logging and a level of 4 will
2375 log everything. Information is printed at KERN_DEBUG
2376 so loglevel=8 may also need to be specified.
2379 [KNL] When CONFIG_MODULE_SIG is set, this means that
2380 modules without (valid) signatures will fail to load.
2381 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2382 is always true, so this option does nothing.
2384 module_blacklist= [KNL] Do not load a comma-separated list of
2385 modules. Useful for debugging problem modules.
2388 [MOUSE] Maximum time between finger touching and
2389 leaving touchpad surface for touch to be considered
2390 a tap and be reported as a left button click (for
2391 touchpads working in absolute mode only).
2393 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2394 reporting absolute coordinates, such as tablets
2395 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2396 reporting absolute coordinates, such as tablets
2398 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2399 is similar to kernelcore except it specifies the
2400 amount of memory used for migratable allocations.
2401 If both kernelcore and movablecore is specified,
2402 then kernelcore will be at *least* the specified
2403 value but may be more. If movablecore on its own
2404 is specified, the administrator must be careful
2405 that the amount of memory usable for all allocations
2408 movable_node [KNL,X86] Boot-time switch to enable the effects
2409 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2411 MTD_Partition= [MTD]
2412 Format: <name>,<region-number>,<size>,<offset>
2414 MTD_Region= [MTD] Format:
2415 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2418 See drivers/mtd/cmdlinepart.c.
2420 multitce=off [PPC] This parameter disables the use of the pSeries
2421 firmware feature for updating multiple TCE entries
2424 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2426 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2428 boundary - index of last SLC block on Flex-OneNAND.
2429 The remaining blocks are configured as MLC blocks.
2430 lock - Configure if Flex-OneNAND boundary should be locked.
2431 Once locked, the boundary cannot be changed.
2432 1 indicates lock status, 0 indicates unlock status.
2435 ARM/S3C2412 JIVE boot control
2437 See arch/arm/mach-s3c2412/mach-jive.c
2439 mtouchusb.raw_coordinates=
2440 [HW] Make the MicroTouch USB driver use raw coordinates
2441 ('y', default) or cooked coordinates ('n')
2443 mtrr_chunk_size=nn[KMG] [X86]
2444 used for mtrr cleanup. It is largest continuous chunk
2445 that could hold holes aka. UC entries.
2447 mtrr_gran_size=nn[KMG] [X86]
2448 Used for mtrr cleanup. It is granularity of mtrr block.
2450 Large value could prevent small alignment from
2453 mtrr_spare_reg_nr=n [X86]
2455 Range: 0,7 : spare reg number
2457 Used for mtrr cleanup. It is spare mtrr entries number.
2458 Set to 2 or more if your graphical card needs more.
2460 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2462 netdev= [NET] Network devices parameters
2463 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2464 Note that mem_start is often overloaded to mean
2465 something different and driver-specific.
2466 This usage is only documented in each driver source
2470 [NETFILTER] Enable connection tracking flow accounting
2471 0 to disable accounting
2472 1 to enable accounting
2475 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2476 See Documentation/filesystems/nfs/nfsroot.txt.
2478 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2479 See Documentation/filesystems/nfs/nfsroot.txt.
2481 nfsrootdebug [NFS] enable nfsroot debugging messages.
2482 See Documentation/filesystems/nfs/nfsroot.txt.
2484 nfs.callback_nr_threads=
2485 [NFSv4] set the total number of threads that the
2486 NFS client will assign to service NFSv4 callback
2489 nfs.callback_tcpport=
2490 [NFS] set the TCP port on which the NFSv4 callback
2491 channel should listen.
2494 [NFS] sets the pathname to the program which is used
2495 to update the NFS client cache entries.
2497 nfs.cache_getent_timeout=
2498 [NFS] sets the timeout after which an attempt to
2499 update a cache entry is deemed to have failed.
2501 nfs.idmap_cache_timeout=
2502 [NFS] set the maximum lifetime for idmapper cache
2506 [NFS] enable 64-bit inode numbers.
2507 If zero, the NFS client will fake up a 32-bit inode
2508 number for the readdir() and stat() syscalls instead
2509 of returning the full 64-bit number.
2510 The default is to return 64-bit inode numbers.
2512 nfs.max_session_cb_slots=
2513 [NFSv4.1] Sets the maximum number of session
2514 slots the client will assign to the callback
2515 channel. This determines the maximum number of
2516 callbacks the client will process in parallel for
2517 a particular server.
2519 nfs.max_session_slots=
2520 [NFSv4.1] Sets the maximum number of session slots
2521 the client will attempt to negotiate with the server.
2522 This limits the number of simultaneous RPC requests
2523 that the client can send to the NFSv4.1 server.
2524 Note that there is little point in setting this
2525 value higher than the max_tcp_slot_table_limit.
2527 nfs.nfs4_disable_idmapping=
2528 [NFSv4] When set to the default of '1', this option
2529 ensures that both the RPC level authentication
2530 scheme and the NFS level operations agree to use
2531 numeric uids/gids if the mount is using the
2532 'sec=sys' security flavour. In effect it is
2533 disabling idmapping, which can make migration from
2534 legacy NFSv2/v3 systems to NFSv4 easier.
2535 Servers that do not support this mode of operation
2536 will be autodetected by the client, and it will fall
2537 back to using the idmapper.
2538 To turn off this behaviour, set the value to '0'.
2540 [NFS4] Specify an additional fixed unique ident-
2541 ification string that NFSv4 clients can insert into
2542 their nfs_client_id4 string. This is typically a
2543 UUID that is generated at system install time.
2545 nfs.send_implementation_id =
2546 [NFSv4.1] Send client implementation identification
2547 information in exchange_id requests.
2548 If zero, no implementation identification information
2550 The default is to send the implementation identification
2553 nfs.recover_lost_locks =
2554 [NFSv4] Attempt to recover locks that were lost due
2555 to a lease timeout on the server. Please note that
2556 doing this risks data corruption, since there are
2557 no guarantees that the file will remain unchanged
2558 after the locks are lost.
2559 If you want to enable the kernel legacy behaviour of
2560 attempting to recover these locks, then set this
2562 The default parameter value of '0' causes the kernel
2563 not to attempt recovery of lost locks.
2565 nfs4.layoutstats_timer =
2566 [NFSv4.2] Change the rate at which the kernel sends
2567 layoutstats to the pNFS metadata server.
2569 Setting this to value to 0 causes the kernel to use
2570 whatever value is the default set by the layout
2571 driver. A non-zero value sets the minimum interval
2572 in seconds between layoutstats transmissions.
2574 nfsd.nfs4_disable_idmapping=
2575 [NFSv4] When set to the default of '1', the NFSv4
2576 server will return only numeric uids and gids to
2577 clients using auth_sys, and will accept numeric uids
2578 and gids from such clients. This is intended to ease
2579 migration from NFSv2/v3.
2581 objlayoutdriver.osd_login_prog=
2582 [NFS] [OBJLAYOUT] sets the pathname to the program which
2583 is used to automatically discover and login into new
2584 osd-targets. Please see:
2585 Documentation/filesystems/pnfs.txt for more explanations
2587 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2588 when a NMI is triggered.
2589 Format: [state][,regs][,debounce][,die]
2591 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2592 Format: [panic,][nopanic,][num]
2594 0 - turn hardlockup detector in nmi_watchdog off
2595 1 - turn hardlockup detector in nmi_watchdog on
2596 When panic is specified, panic when an NMI watchdog
2597 timeout occurs (or 'nopanic' to override the opposite
2598 default). To disable both hard and soft lockup detectors,
2599 please see 'nowatchdog'.
2600 This is useful when you use a panic=... timeout and
2601 need the box quickly up again.
2603 netpoll.carrier_timeout=
2604 [NET] Specifies amount of time (in seconds) that
2605 netpoll should wait for a carrier. By default netpoll
2608 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2609 emulation library even if a 387 maths coprocessor
2613 [HW] Never suspend the console
2614 Disable suspending of consoles during suspend and
2615 hibernate operations. Once disabled, debugging
2616 messages can reach various consoles while the rest
2617 of the system is being put to sleep (ie, while
2618 debugging driver suspend/resume hooks). This may
2619 not work reliably with all consoles, but is known
2620 to work with serial and VGA consoles.
2621 To facilitate more flexible debugging, we also add
2622 console_suspend, a printk module parameter to control
2623 it. Users could use console_suspend (usually
2624 /sys/module/printk/parameters/console_suspend) to
2625 turn on/off it dynamically.
2627 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2628 caches in the slab allocator. Saves per-node memory,
2629 but will impact performance.
2633 noapic [SMP,APIC] Tells the kernel to not make use of any
2634 IOAPICs that may be present in the system.
2636 noautogroup Disable scheduler automatic task group creation.
2638 nobats [PPC] Do not use BATs for mapping kernel lowmem
2639 on "Classic" PPC cores.
2643 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2645 nodelayacct [KNL] Disable per-task delay accounting
2647 nodsp [SH] Disable hardware DSP at boot time.
2649 noefi Disable EFI runtime services support.
2654 On X86-32 available only on PAE configured kernels.
2655 noexec=on: enable non-executable mappings (default)
2656 noexec=off: disable non-executable mappings
2659 Disable SMAP (Supervisor Mode Access Prevention)
2660 even if it is supported by processor.
2663 Disable SMEP (Supervisor Mode Execution Prevention)
2664 even if it is supported by processor.
2667 This affects only 32-bit executables.
2668 noexec32=on: enable non-executable mappings (default)
2669 read doesn't imply executable mappings
2670 noexec32=off: disable non-executable mappings
2671 read implies executable mappings
2673 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2675 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2676 register save and restore. The kernel will only save
2677 legacy floating-point registers on task switch.
2679 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2681 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2682 Equivalent to smt=1.
2684 noxsave [BUGS=X86] Disables x86 extended register state save
2685 and restore using xsave. The kernel will fallback to
2686 enabling legacy floating-point and sse state.
2688 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2689 register states. The kernel will fall back to use
2690 xsave to save the states. By using this parameter,
2691 performance of saving the states is degraded because
2692 xsave doesn't support modified optimization while
2693 xsaveopt supports it on xsaveopt enabled systems.
2695 noxsaves [X86] Disables xsaves and xrstors used in saving and
2696 restoring x86 extended register state in compacted
2697 form of xsave area. The kernel will fall back to use
2698 xsaveopt and xrstor to save and restore the states
2699 in standard form of xsave area. By using this
2700 parameter, xsave area per process might occupy more
2701 memory on xsaves enabled systems.
2703 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2704 wfi(ARM) instruction doesn't work correctly and not to
2705 use it. This is also useful when using JTAG debugger.
2707 no_file_caps Tells the kernel not to honor file capabilities. The
2708 only way then for a file to be executed with privilege
2709 is to be setuid root or executed by root.
2711 nohalt [IA-64] Tells the kernel not to use the power saving
2712 function PAL_HALT_LIGHT when idle. This increases
2713 power-consumption. On the positive side, it reduces
2714 interrupt wake-up latency, which may improve performance
2715 in certain environments such as networked servers or
2718 nohibernate [HIBERNATION] Disable hibernation and resume.
2720 nohz= [KNL] Boottime enable/disable dynamic ticks
2721 Valid arguments: on, off
2724 nohz_full= [KNL,BOOT]
2725 The argument is a cpu list, as described above.
2726 In kernels built with CONFIG_NO_HZ_FULL=y, set
2727 the specified list of CPUs whose tick will be stopped
2728 whenever possible. The boot CPU will be forced outside
2729 the range to maintain the timekeeping.
2730 The CPUs in this range must also be included in the
2733 noiotrap [SH] Disables trapped I/O port accesses.
2735 noirqdebug [X86-32] Disables the code which attempts to detect and
2736 disable unhandled interrupt sources.
2738 no_timer_check [X86,APIC] Disables the code which tests for
2739 broken timer IRQ sources.
2741 noisapnp [ISAPNP] Disables ISA PnP code.
2743 noinitrd [RAM] Tells the kernel not to load any configured
2746 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2748 [Deprecated - use intremap=off]
2752 noinvpcid [X86] Disable the INVPCID cpu feature.
2754 nojitter [IA-64] Disables jitter checking for ITC timers.
2756 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2758 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2761 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2762 steal time is computed, but won't influence scheduler
2765 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2767 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2769 noltlbs [PPC] Do not use large page/tlb entries for kernel
2770 lowmem mapping on PPC40x and PPC8xx
2772 nomca [IA-64] Disable machine check abort handling
2774 nomce [X86-32] Disable Machine Check Exception
2776 nomfgpt [X86-32] Disable Multi-Function General Purpose
2777 Timer usage (for AMD Geode machines).
2779 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2780 shutdown the other cpus. Instead use the REBOOT_VECTOR
2783 nomodule Disable module load
2785 nopat [X86] Disable PAT (page attribute table extension of
2786 pagetables) support.
2788 norandmaps Don't use address space randomization. Equivalent to
2789 echo 0 > /proc/sys/kernel/randomize_va_space
2791 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2793 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2794 with UP alternatives
2796 nordrand [X86] Disable kernel use of the RDRAND and
2797 RDSEED instructions even if they are supported
2798 by the processor. RDRAND and RDSEED are still
2799 available to user space applications.
2801 noresume [SWSUSP] Disables resume and restores original swap
2804 no-scroll [VGA] Disables scrollback.
2805 This is required for the Braillex ib80-piezo Braille
2806 reader made by F.H. Papenmeier (Germany).
2810 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2812 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2813 and disable the IO APIC. legacy for "maxcpus=0".
2815 nosoftlockup [KNL] Disable the soft-lockup detector.
2817 nosync [HW,M68K] Disables sync negotiation for all devices.
2819 notsc [BUGS=X86-32] Disable Time Stamp Counter
2821 nowatchdog [KNL] Disable both lockup detectors, i.e.
2822 soft-lockup and NMI watchdog (hard-lockup).
2826 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2828 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2829 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2830 Some features depend on CPU0. Known dependencies are:
2831 1. Resume from suspend/hibernate depends on CPU0.
2832 Suspend/hibernate will fail if CPU0 is offline and you
2833 need to online CPU0 before suspend/hibernate.
2834 2. PIC interrupts also depend on CPU0. CPU0 can't be
2835 removed if a PIC interrupt is detected.
2836 It's said poweroff/reboot may depend on CPU0 on some
2837 machines although I haven't seen such issues so far
2838 after CPU0 is offline on a few tested machines.
2839 If the dependencies are under your control, you can
2840 turn on cpu0_hotplug.
2842 nptcg= [IA-64] Override max number of concurrent global TLB
2843 purges which is reported from either PAL_VM_SUMMARY or
2846 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2847 could support. nr_cpus=n : n >= 1 limits the kernel to
2848 support 'n' processors. It could be larger than the
2849 number of already plugged CPU during bootup, later in
2850 runtime you can physically add extra cpu until it reaches
2851 n. So during boot up some boot time memory for per-cpu
2852 variables need be pre-allocated for later physical cpu
2855 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2857 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2858 Allowed values are enable and disable
2860 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2861 one of ['zone', 'node', 'default'] can be specified
2862 This can be set from sysctl after boot.
2863 See Documentation/sysctl/vm.txt for details.
2865 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2866 See Documentation/debugging-via-ohci1394.txt for more
2869 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2870 Rather than timing out after 20 ms if an EC
2871 command is not properly ACKed, override the length
2872 of the timeout. We have interrupts disabled while
2873 waiting for the ACK, so if this is set too high
2874 interrupts *may* be lost!
2876 omap_mux= [OMAP] Override bootloader pin multiplexing.
2877 Format: <mux_mode0.mode_name=value>...
2878 For example, to override I2C bus2:
2879 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2881 oprofile.timer= [HW]
2882 Use timer interrupt instead of performance counters
2884 oprofile.cpu_type= Force an oprofile cpu type
2885 This might be useful if you have an older oprofile
2886 userland or if you want common events.
2887 Format: { arch_perfmon }
2888 arch_perfmon: [X86] Force use of architectural
2889 perfmon on Intel CPUs instead of the
2890 CPU specific event set.
2891 timer: [X86] Force use of architectural NMI
2892 timer mode (see also oprofile.timer
2893 for generic hr timer mode)
2895 oops=panic Always panic on oopses. Default is to just kill the
2896 process, but there is a small probability of
2897 deadlocking the machine.
2898 This will also cause panics on machine check exceptions.
2899 Useful together with panic=30 to trigger a reboot.
2902 See Documentation/sound/oss/oss-parameters.txt
2904 page_owner= [KNL] Boot-time page_owner enabling option.
2905 Storage of the information about who allocated
2906 each page is disabled in default. With this switch,
2908 on: enable the feature
2910 page_poison= [KNL] Boot-time parameter changing the state of
2911 poisoning on the buddy allocator.
2912 off: turn off poisoning
2913 on: turn on poisoning
2915 panic= [KNL] Kernel behaviour on panic: delay <timeout>
2916 timeout > 0: seconds before rebooting
2917 timeout = 0: wait forever
2918 timeout < 0: reboot immediately
2921 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2924 crash_kexec_post_notifiers
2925 Run kdump after running panic-notifiers and dumping
2926 kmsg. This only for the users who doubt kdump always
2927 succeeds in any situation.
2928 Note that this also increases risks of kdump failure,
2929 because some panic notifiers can make the crashed
2930 kernel more unstable.
2932 parkbd.port= [HW] Parallel port number the keyboard adapter is
2933 connected to, default is 0.
2935 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2936 0 for XT, 1 for AT (default is AT).
2939 parport= [HW,PPT] Specify parallel ports. 0 disables.
2940 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2941 Use 'auto' to force the driver to use any
2942 IRQ/DMA settings detected (the default is to
2943 ignore detected IRQ/DMA settings because of
2944 possible conflicts). You can specify the base
2945 address, IRQ, and DMA settings; IRQ and DMA
2946 should be numbers, or 'auto' (for using detected
2947 settings on that particular port), or 'nofifo'
2948 (to avoid using a FIFO even if it is detected).
2949 Parallel ports are assigned in the order they
2950 are specified on the command line, starting
2953 parport_init_mode= [HW,PPT]
2954 Configure VIA parallel port to operate in
2955 a specific mode. This is necessary on Pegasos
2956 computer where firmware has no options for setting
2957 up parallel port mode and sets it to spp.
2958 Currently this function knows 686a and 8231 chips.
2959 Format: [spp|ps2|epp|ecp|ecpepp]
2962 Halt all CPUs after the first oops has been printed for
2963 the specified number of seconds. This is to be used if
2964 your oopses keep scrolling off the screen.
2969 See header of drivers/block/paride/pcd.c.
2970 See also Documentation/blockdev/paride.txt.
2972 pci=option[,option...] [PCI] various PCI subsystem options:
2973 earlydump [X86] dump PCI config space before the kernel
2975 off [X86] don't probe for the PCI bus
2976 bios [X86-32] force use of PCI BIOS, don't access
2977 the hardware directly. Use this if your machine
2978 has a non-standard PCI host bridge.
2979 nobios [X86-32] disallow use of PCI BIOS, only direct
2980 hardware access methods are allowed. Use this
2981 if you experience crashes upon bootup and you
2982 suspect they are caused by the BIOS.
2983 conf1 [X86] Force use of PCI Configuration Access
2984 Mechanism 1 (config address in IO port 0xCF8,
2985 data in IO port 0xCFC, both 32-bit).
2986 conf2 [X86] Force use of PCI Configuration Access
2987 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2988 the function, IO port 0xCFA, also 8-bit, sets
2989 bus number. The config space is then accessed
2990 through ports 0xC000-0xCFFF).
2991 See http://wiki.osdev.org/PCI for more info
2992 on the configuration access mechanisms.
2993 noaer [PCIE] If the PCIEAER kernel config parameter is
2994 enabled, this kernel boot option can be used to
2995 disable the use of PCIE advanced error reporting.
2996 nodomains [PCI] Disable support for multiple PCI
2997 root domains (aka PCI segments, in ACPI-speak).
2998 nommconf [X86] Disable use of MMCONFIG for PCI
3000 check_enable_amd_mmconf [X86] check for and enable
3001 properly configured MMIO access to PCI
3002 config space on AMD family 10h CPU
3003 nomsi [MSI] If the PCI_MSI kernel config parameter is
3004 enabled, this kernel boot option can be used to
3005 disable the use of MSI interrupts system-wide.
3006 noioapicquirk [APIC] Disable all boot interrupt quirks.
3007 Safety option to keep boot IRQs enabled. This
3008 should never be necessary.
3009 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3010 primary IO-APIC for bridges that cannot disable
3011 boot IRQs. This fixes a source of spurious IRQs
3012 when the system masks IRQs.
3013 noioapicreroute [APIC] Disable workaround that uses the
3014 boot IRQ equivalent of an IRQ that connects to
3015 a chipset where boot IRQs cannot be disabled.
3016 The opposite of ioapicreroute.
3017 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3018 routing table. These calls are known to be buggy
3019 on several machines and they hang the machine
3020 when used, but on other computers it's the only
3021 way to get the interrupt routing table. Try
3022 this option if the kernel is unable to allocate
3023 IRQs or discover secondary PCI buses on your
3025 rom [X86] Assign address space to expansion ROMs.
3026 Use with caution as certain devices share
3027 address decoders between ROMs and other
3029 norom [X86] Do not assign address space to
3030 expansion ROMs that do not already have
3031 BIOS assigned address ranges.
3032 nobar [X86] Do not assign address space to the
3033 BARs that weren't assigned by the BIOS.
3034 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3035 assigned automatically to PCI devices. You can
3036 make the kernel exclude IRQs of your ISA cards
3038 pirqaddr=0xAAAAA [X86] Specify the physical address
3039 of the PIRQ table (normally generated
3040 by the BIOS) if it is outside the
3041 F0000h-100000h range.
3042 lastbus=N [X86] Scan all buses thru bus #N. Can be
3043 useful if the kernel is unable to find your
3044 secondary buses and you want to tell it
3045 explicitly which ones they are.
3046 assign-busses [X86] Always assign all PCI bus
3047 numbers ourselves, overriding
3048 whatever the firmware may have done.
3049 usepirqmask [X86] Honor the possible IRQ mask stored
3050 in the BIOS $PIR table. This is needed on
3051 some systems with broken BIOSes, notably
3052 some HP Pavilion N5400 and Omnibook XE3
3053 notebooks. This will have no effect if ACPI
3054 IRQ routing is enabled.
3055 noacpi [X86] Do not use ACPI for IRQ routing
3056 or for PCI scanning.
3057 use_crs [X86] Use PCI host bridge window information
3058 from ACPI. On BIOSes from 2008 or later, this
3059 is enabled by default. If you need to use this,
3060 please report a bug.
3061 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3062 If you need to use this, please report a bug.
3063 routeirq Do IRQ routing for all PCI devices.
3064 This is normally done in pci_enable_device(),
3065 so this option is a temporary workaround
3066 for broken drivers that don't call it.
3067 skip_isa_align [X86] do not align io start addr, so can
3068 handle more pci cards
3069 noearly [X86] Don't do any early type 1 scanning.
3070 This might help on some broken boards which
3071 machine check when some devices' config space
3072 is read. But various workarounds are disabled
3073 and some IOMMU drivers will not work.
3074 bfsort Sort PCI devices into breadth-first order.
3075 This sorting is done to get a device
3076 order compatible with older (<= 2.4) kernels.
3077 nobfsort Don't sort PCI devices into breadth-first order.
3078 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3079 tuning and use the BIOS-configured MPS defaults.
3080 pcie_bus_safe Set every device's MPS to the largest value
3081 supported by all devices below the root complex.
3082 pcie_bus_perf Set device MPS to the largest allowable MPS
3083 based on its parent bus. Also set MRRS (Max
3084 Read Request Size) to the largest supported
3085 value (no larger than the MPS that the device
3086 or bus can support) for best performance.
3087 pcie_bus_peer2peer Set every device's MPS to 128B, which
3088 every device is guaranteed to support. This
3089 configuration allows peer-to-peer DMA between
3090 any pair of devices, possibly at the cost of
3091 reduced performance. This also guarantees
3092 that hot-added devices will work.
3093 cbiosize=nn[KMG] The fixed amount of bus space which is
3094 reserved for the CardBus bridge's IO window.
3095 The default value is 256 bytes.
3096 cbmemsize=nn[KMG] The fixed amount of bus space which is
3097 reserved for the CardBus bridge's memory
3098 window. The default value is 64 megabytes.
3101 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3102 [<order of align>@]pci:<vendor>:<device>\
3103 [:<subvendor>:<subdevice>][; ...]
3104 Specifies alignment and device to reassign
3105 aligned memory resources.
3106 If <order of align> is not specified,
3107 PAGE_SIZE is used as alignment.
3108 PCI-PCI bridge can be specified, if resource
3109 windows need to be expanded.
3110 To specify the alignment for several
3111 instances of a device, the PCI vendor,
3112 device, subvendor, and subdevice may be
3113 specified, e.g., 4096@pci:8086:9c22:103c:198f
3114 ecrc= Enable/disable PCIe ECRC (transaction layer
3115 end-to-end CRC checking).
3116 bios: Use BIOS/firmware settings. This is the
3120 hpiosize=nn[KMG] The fixed amount of bus space which is
3121 reserved for hotplug bridge's IO window.
3122 Default size is 256 bytes.
3123 hpmemsize=nn[KMG] The fixed amount of bus space which is
3124 reserved for hotplug bridge's memory window.
3125 Default size is 2 megabytes.
3126 hpbussize=nn The minimum amount of additional bus numbers
3127 reserved for buses below a hotplug bridge.
3129 realloc= Enable/disable reallocating PCI bridge resources
3130 if allocations done by BIOS are too small to
3131 accommodate resources required by all child
3133 off: Turn realloc off
3135 realloc same as realloc=on
3136 noari do not use PCIe ARI.
3137 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3138 only look for one device below a PCIe downstream
3141 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3144 force Enable ASPM even on devices that claim not to support it.
3145 WARNING: Forcing ASPM on may cause system lockups.
3147 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3148 nomsi Do not use MSI for PCI Express Native Hotplug (this
3149 makes all PCIe ports use INTx for hotplug services).
3151 pcie_ports= [PCIE] PCIe ports handling:
3152 auto Ask the BIOS whether or not to use native PCIe services
3153 associated with PCIe ports (PME, hot-plug, AER). Use
3154 them only if that is allowed by the BIOS.
3155 native Use native PCIe services associated with PCIe ports
3157 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3160 pcie_port_pm= [PCIE] PCIe port power management handling:
3161 off Disable power management of all PCIe ports
3162 force Forcibly enable power management of all PCIe ports
3164 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3165 nomsi Do not use MSI for native PCIe PME signaling (this makes
3166 all PCIe root ports use INTx for all services).
3168 pcmv= [HW,PCMCIA] BadgePAD 4
3172 Keep all power-domains already enabled by bootloader on,
3173 even if no driver has claimed them. This is useful
3174 for debug and development, but should not be
3175 needed on a platform with proper driver support.
3178 See Documentation/blockdev/paride.txt.
3180 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3183 See arch/parisc/kernel/pdc_chassis.c
3185 percpu_alloc= Select which percpu first chunk allocator to use.
3186 Currently supported values are "embed" and "page".
3187 Archs may support subset or none of the selections.
3188 See comments in mm/percpu.c for details on each
3189 allocator. This parameter is primarily for debugging
3190 and performance comparison.
3193 See Documentation/blockdev/paride.txt.
3196 See Documentation/blockdev/paride.txt.
3198 pirq= [SMP,APIC] Manual mp-table setup
3199 See Documentation/x86/i386/IO-APIC.txt.
3201 plip= [PPT,NET] Parallel port network link
3202 Format: { parport<nr> | timid | 0 }
3203 See also Documentation/parport.txt.
3205 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3206 Override pmtimer IOPort with a hex value.
3210 Enable PNP debug messages (depends on the
3211 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3212 via /sys/module/pnp/parameters/debug. We always show
3213 current resource usage; turning this on also shows
3214 possible settings and some assignment information.
3220 { on | off | curr | res | no-curr | no-res }
3223 [ISAPNP] Exclude IRQs for the autoconfiguration
3226 [ISAPNP] Exclude DMAs for the autoconfiguration
3228 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3229 Ranges are in pairs (I/O port base and size).
3232 [ISAPNP] Exclude memory regions for the
3234 Ranges are in pairs (memory base and size).
3236 ports= [IP_VS_FTP] IPVS ftp helper module
3238 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3240 Format: <port>,<port>....
3242 ppc_strict_facility_enable
3243 [PPC] This option catches any kernel floating point,
3244 Altivec, VSX and SPE outside of regions specifically
3245 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3246 There is some performance impact when enabling this.
3248 print-fatal-signals=
3249 [KNL] debug: print fatal signals
3251 If enabled, warn about various signal handling
3252 related application anomalies: too many signals,
3253 too many POSIX.1 timers, fatal signals causing a
3256 If you hit the warning due to signal overflow,
3257 you might want to try "ulimit -i unlimited".
3261 printk.always_kmsg_dump=
3262 Trigger kmsg_dump for cases other than kernel oops or
3264 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3267 printk.devkmsg={on,off,ratelimit}
3268 Control writing to /dev/kmsg.
3269 on - unlimited logging to /dev/kmsg from userspace
3270 off - logging to /dev/kmsg disabled
3271 ratelimit - ratelimit the logging
3274 printk.time= Show timing data prefixed to each printk message line
3275 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3277 processor.max_cstate= [HW,ACPI]
3278 Limit processor to maximum C-state
3279 max_cstate=9 overrides any DMI blacklist limit.
3281 processor.nocst [HW,ACPI]
3282 Ignore the _CST method to determine C-states,
3283 instead using the legacy FADT method
3285 profile= [KNL] Enable kernel profiling via /proc/profile
3286 Format: [schedule,]<number>
3287 Param: "schedule" - profile schedule points.
3288 Param: <number> - step/bucket size as a power of 2 for
3289 statistical time based profiling.
3290 Param: "sleep" - profile D-state sleeping (millisecs).
3291 Requires CONFIG_SCHEDSTATS
3292 Param: "kvm" - profile VM exits.
3294 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3296 See Documentation/blockdev/ramdisk.txt.
3298 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3299 probe for; one of (bare|imps|exps|lifebook|any).
3300 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3302 psmouse.resetafter= [HW,MOUSE]
3303 Try to reset the device after so many bad packets
3306 [HW,MOUSE] Set desired mouse resolution, in dpi.
3307 psmouse.smartscroll=
3308 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3309 0 = disabled, 1 = enabled (default).
3311 pstore.backend= Specify the name of the pstore backend to use
3314 See Documentation/blockdev/paride.txt.
3317 [KNL] Number of legacy pty's. Overwrites compiled-in
3320 quiet [KNL] Disable most log messages
3325 See Documentation/md.txt.
3327 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3328 See Documentation/blockdev/ramdisk.txt.
3331 The argument is a cpu list, as described above.
3333 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3334 the specified list of CPUs to be no-callback CPUs.
3335 Invocation of these CPUs' RCU callbacks will
3336 be offloaded to "rcuox/N" kthreads created for
3337 that purpose, where "x" is "b" for RCU-bh, "p"
3338 for RCU-preempt, and "s" for RCU-sched, and "N"
3339 is the CPU number. This reduces OS jitter on the
3340 offloaded CPUs, which can be useful for HPC and
3341 real-time workloads. It can also improve energy
3342 efficiency for asymmetric multiprocessors.
3345 Rather than requiring that offloaded CPUs
3346 (specified by rcu_nocbs= above) explicitly
3347 awaken the corresponding "rcuoN" kthreads,
3348 make these kthreads poll for callbacks.
3349 This improves the real-time response for the
3350 offloaded CPUs by relieving them of the need to
3351 wake up the corresponding kthread, but degrades
3352 energy efficiency by requiring that the kthreads
3353 periodically wake up to do the polling.
3355 rcutree.blimit= [KNL]
3356 Set maximum number of finished RCU callbacks to
3357 process in one batch.
3359 rcutree.dump_tree= [KNL]
3360 Dump the structure of the rcu_node combining tree
3361 out at early boot. This is used for diagnostic
3362 purposes, to verify correct tree setup.
3364 rcutree.gp_cleanup_delay= [KNL]
3365 Set the number of jiffies to delay each step of
3366 RCU grace-period cleanup. This only has effect
3367 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3369 rcutree.gp_init_delay= [KNL]
3370 Set the number of jiffies to delay each step of
3371 RCU grace-period initialization. This only has
3372 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3375 rcutree.gp_preinit_delay= [KNL]
3376 Set the number of jiffies to delay each step of
3377 RCU grace-period pre-initialization, that is,
3378 the propagation of recent CPU-hotplug changes up
3379 the rcu_node combining tree. This only has effect
3380 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3382 rcutree.rcu_fanout_exact= [KNL]
3383 Disable autobalancing of the rcu_node combining
3384 tree. This is used by rcutorture, and might
3385 possibly be useful for architectures having high
3386 cache-to-cache transfer latencies.
3388 rcutree.rcu_fanout_leaf= [KNL]
3389 Change the number of CPUs assigned to each
3390 leaf rcu_node structure. Useful for very
3391 large systems, which will choose the value 64,
3392 and for NUMA systems with large remote-access
3393 latencies, which will choose a value aligned
3394 with the appropriate hardware boundaries.
3396 rcutree.jiffies_till_sched_qs= [KNL]
3397 Set required age in jiffies for a
3398 given grace period before RCU starts
3399 soliciting quiescent-state help from
3400 rcu_note_context_switch().
3402 rcutree.jiffies_till_first_fqs= [KNL]
3403 Set delay from grace-period initialization to
3404 first attempt to force quiescent states.
3405 Units are jiffies, minimum value is zero,
3406 and maximum value is HZ.
3408 rcutree.jiffies_till_next_fqs= [KNL]
3409 Set delay between subsequent attempts to force
3410 quiescent states. Units are jiffies, minimum
3411 value is one, and maximum value is HZ.
3413 rcutree.kthread_prio= [KNL,BOOT]
3414 Set the SCHED_FIFO priority of the RCU per-CPU
3415 kthreads (rcuc/N). This value is also used for
3416 the priority of the RCU boost threads (rcub/N)
3417 and for the RCU grace-period kthreads (rcu_bh,
3418 rcu_preempt, and rcu_sched). If RCU_BOOST is
3419 set, valid values are 1-99 and the default is 1
3420 (the least-favored priority). Otherwise, when
3421 RCU_BOOST is not set, valid values are 0-99 and
3422 the default is zero (non-realtime operation).
3424 rcutree.rcu_nocb_leader_stride= [KNL]
3425 Set the number of NOCB kthread groups, which
3426 defaults to the square root of the number of
3427 CPUs. Larger numbers reduces the wakeup overhead
3428 on the per-CPU grace-period kthreads, but increases
3429 that same overhead on each group's leader.
3431 rcutree.qhimark= [KNL]
3432 Set threshold of queued RCU callbacks beyond which
3433 batch limiting is disabled.
3435 rcutree.qlowmark= [KNL]
3436 Set threshold of queued RCU callbacks below which
3437 batch limiting is re-enabled.
3439 rcutree.rcu_idle_gp_delay= [KNL]
3440 Set wakeup interval for idle CPUs that have
3441 RCU callbacks (RCU_FAST_NO_HZ=y).
3443 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3444 Set wakeup interval for idle CPUs that have
3445 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3446 Lazy RCU callbacks are those which RCU can
3447 prove do nothing more than free memory.
3449 rcuperf.gp_exp= [KNL]
3450 Measure performance of expedited synchronous
3451 grace-period primitives.
3453 rcuperf.holdoff= [KNL]
3454 Set test-start holdoff period. The purpose of
3455 this parameter is to delay the start of the
3456 test until boot completes in order to avoid
3459 rcuperf.nreaders= [KNL]
3460 Set number of RCU readers. The value -1 selects
3461 N, where N is the number of CPUs. A value
3462 "n" less than -1 selects N-n+1, where N is again
3463 the number of CPUs. For example, -2 selects N
3464 (the number of CPUs), -3 selects N+1, and so on.
3465 A value of "n" less than or equal to -N selects
3468 rcuperf.nwriters= [KNL]
3469 Set number of RCU writers. The values operate
3470 the same as for rcuperf.nreaders.
3471 N, where N is the number of CPUs
3473 rcuperf.perf_runnable= [BOOT]
3474 Start rcuperf running at boot time.
3476 rcuperf.shutdown= [KNL]
3477 Shut the system down after performance tests
3478 complete. This is useful for hands-off automated
3481 rcuperf.perf_type= [KNL]
3482 Specify the RCU implementation to test.
3484 rcuperf.verbose= [KNL]
3485 Enable additional printk() statements.
3487 rcutorture.cbflood_inter_holdoff= [KNL]
3488 Set holdoff time (jiffies) between successive
3489 callback-flood tests.
3491 rcutorture.cbflood_intra_holdoff= [KNL]
3492 Set holdoff time (jiffies) between successive
3493 bursts of callbacks within a given callback-flood
3496 rcutorture.cbflood_n_burst= [KNL]
3497 Set the number of bursts making up a given
3498 callback-flood test. Set this to zero to
3499 disable callback-flood testing.
3501 rcutorture.cbflood_n_per_burst= [KNL]
3502 Set the number of callbacks to be registered
3503 in a given burst of a callback-flood test.
3505 rcutorture.fqs_duration= [KNL]
3506 Set duration of force_quiescent_state bursts
3509 rcutorture.fqs_holdoff= [KNL]
3510 Set holdoff time within force_quiescent_state bursts
3513 rcutorture.fqs_stutter= [KNL]
3514 Set wait time between force_quiescent_state bursts
3517 rcutorture.gp_cond= [KNL]
3518 Use conditional/asynchronous update-side
3519 primitives, if available.
3521 rcutorture.gp_exp= [KNL]
3522 Use expedited update-side primitives, if available.
3524 rcutorture.gp_normal= [KNL]
3525 Use normal (non-expedited) asynchronous
3526 update-side primitives, if available.
3528 rcutorture.gp_sync= [KNL]
3529 Use normal (non-expedited) synchronous
3530 update-side primitives, if available. If all
3531 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3532 rcutorture.gp_normal=, and rcutorture.gp_sync=
3533 are zero, rcutorture acts as if is interpreted
3534 they are all non-zero.
3536 rcutorture.n_barrier_cbs= [KNL]
3537 Set callbacks/threads for rcu_barrier() testing.
3539 rcutorture.nfakewriters= [KNL]
3540 Set number of concurrent RCU writers. These just
3541 stress RCU, they don't participate in the actual
3542 test, hence the "fake".
3544 rcutorture.nreaders= [KNL]
3545 Set number of RCU readers. The value -1 selects
3546 N-1, where N is the number of CPUs. A value
3547 "n" less than -1 selects N-n-2, where N is again
3548 the number of CPUs. For example, -2 selects N
3549 (the number of CPUs), -3 selects N+1, and so on.
3551 rcutorture.object_debug= [KNL]
3552 Enable debug-object double-call_rcu() testing.
3554 rcutorture.onoff_holdoff= [KNL]
3555 Set time (s) after boot for CPU-hotplug testing.
3557 rcutorture.onoff_interval= [KNL]
3558 Set time (s) between CPU-hotplug operations, or
3559 zero to disable CPU-hotplug testing.
3561 rcutorture.shuffle_interval= [KNL]
3562 Set task-shuffle interval (s). Shuffling tasks
3563 allows some CPUs to go into dyntick-idle mode
3564 during the rcutorture test.
3566 rcutorture.shutdown_secs= [KNL]
3567 Set time (s) after boot system shutdown. This
3568 is useful for hands-off automated testing.
3570 rcutorture.stall_cpu= [KNL]
3571 Duration of CPU stall (s) to test RCU CPU stall
3572 warnings, zero to disable.
3574 rcutorture.stall_cpu_holdoff= [KNL]
3575 Time to wait (s) after boot before inducing stall.
3577 rcutorture.stat_interval= [KNL]
3578 Time (s) between statistics printk()s.
3580 rcutorture.stutter= [KNL]
3581 Time (s) to stutter testing, for example, specifying
3582 five seconds causes the test to run for five seconds,
3583 wait for five seconds, and so on. This tests RCU's
3584 ability to transition abruptly to and from idle.
3586 rcutorture.test_boost= [KNL]
3587 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3588 "Maybe" means test if the RCU implementation
3589 under test support RCU priority boosting.
3591 rcutorture.test_boost_duration= [KNL]
3592 Duration (s) of each individual boost test.
3594 rcutorture.test_boost_interval= [KNL]
3595 Interval (s) between each boost test.
3597 rcutorture.test_no_idle_hz= [KNL]
3598 Test RCU's dyntick-idle handling. See also the
3599 rcutorture.shuffle_interval parameter.
3601 rcutorture.torture_runnable= [BOOT]
3602 Start rcutorture running at boot time.
3604 rcutorture.torture_type= [KNL]
3605 Specify the RCU implementation to test.
3607 rcutorture.verbose= [KNL]
3608 Enable additional printk() statements.
3610 rcupdate.rcu_cpu_stall_suppress= [KNL]
3611 Suppress RCU CPU stall warning messages.
3613 rcupdate.rcu_cpu_stall_timeout= [KNL]
3614 Set timeout for RCU CPU stall warning messages.
3616 rcupdate.rcu_expedited= [KNL]
3617 Use expedited grace-period primitives, for
3618 example, synchronize_rcu_expedited() instead
3619 of synchronize_rcu(). This reduces latency,
3620 but can increase CPU utilization, degrade
3621 real-time latency, and degrade energy efficiency.
3622 No effect on CONFIG_TINY_RCU kernels.
3624 rcupdate.rcu_normal= [KNL]
3625 Use only normal grace-period primitives,
3626 for example, synchronize_rcu() instead of
3627 synchronize_rcu_expedited(). This improves
3628 real-time latency, CPU utilization, and
3629 energy efficiency, but can expose users to
3630 increased grace-period latency. This parameter
3631 overrides rcupdate.rcu_expedited. No effect on
3632 CONFIG_TINY_RCU kernels.
3634 rcupdate.rcu_normal_after_boot= [KNL]
3635 Once boot has completed (that is, after
3636 rcu_end_inkernel_boot() has been invoked), use
3637 only normal grace-period primitives. No effect
3638 on CONFIG_TINY_RCU kernels.
3640 rcupdate.rcu_task_stall_timeout= [KNL]
3641 Set timeout in jiffies for RCU task stall warning
3642 messages. Disable with a value less than or equal
3645 rcupdate.rcu_self_test= [KNL]
3646 Run the RCU early boot self tests
3648 rcupdate.rcu_self_test_bh= [KNL]
3649 Run the RCU bh early boot self tests
3651 rcupdate.rcu_self_test_sched= [KNL]
3652 Run the RCU sched early boot self tests
3656 Run specified binary instead of /init from the ramdisk,
3657 used for early userspace startup. See initrd.
3660 Format (x86 or x86_64):
3661 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3663 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3665 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3666 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3667 reboot_force is either force or not specified,
3668 reboot_cpu is s[mp]#### with #### being the processor
3669 to be used for rebooting.
3672 [KNL, SMP] Set scheduler's default relax_domain_level.
3673 See Documentation/cgroup-v1/cpusets.txt.
3675 relative_sleep_states=
3676 [SUSPEND] Use sleep state labeling where the deepest
3677 state available other than hibernation is always "mem".
3678 Format: { "0" | "1" }
3679 0 -- Traditional sleep state labels.
3680 1 -- Relative sleep state labels.
3682 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3684 reservetop= [X86-32]
3686 Reserves a hole at the top of the kernel virtual
3691 Set the amount of memory to reserve for BIOS at
3692 the bottom of the address space.
3694 reset_devices [KNL] Force drivers to reset the underlying device
3695 during initialization.
3698 Specify the partition device for software suspend
3700 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3702 resume_offset= [SWSUSP]
3703 Specify the offset from the beginning of the partition
3704 given by "resume=" at which the swap header is located,
3705 in <PAGE_SIZE> units (needed only for swap files).
3706 See Documentation/power/swsusp-and-swap-files.txt
3708 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3709 read the resume files
3711 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3712 Useful for devices that are detected asynchronously
3713 (e.g. USB and MMC devices).
3715 hibernate= [HIBERNATION]
3716 noresume Don't check if there's a hibernation image
3717 present during boot.
3718 nocompress Don't compress/decompress hibernation images.
3719 no Disable hibernation and resume.
3720 protect_image Turn on image protection during restoration
3721 (that will set all pages holding image data
3722 during restoration read-only).
3724 retain_initrd [RAM] Keep initrd memory after extraction
3726 rfkill.default_state=
3727 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3728 etc. communication is blocked by default.
3731 rfkill.master_switch_mode=
3732 0 The "airplane mode" button does nothing.
3733 1 The "airplane mode" button toggles between everything
3734 blocked and the previous configuration.
3735 2 The "airplane mode" button toggles between everything
3736 blocked and everything unblocked.
3738 rhash_entries= [KNL,NET]
3739 Set number of hash buckets for route cache
3741 ro [KNL] Mount root device read-only on boot
3744 on Mark read-only kernel memory as read-only (default).
3745 off Leave read-only kernel memory writable for debugging.
3748 Enable the uart passthrough on the designated usb port
3749 on Rockchip SoCs. When active, the signals of the
3750 debug-uart get routed to the D+ and D- pins of the usb
3751 port and the regular usb controller gets disabled.
3753 root= [KNL] Root filesystem
3754 See name_to_dev_t comment in init/do_mounts.c.
3756 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3757 mount the root filesystem
3759 rootflags= [KNL] Set root filesystem mount option string
3761 rootfstype= [KNL] Set root filesystem type
3763 rootwait [KNL] Wait (indefinitely) for root device to show up.
3764 Useful for devices that are detected asynchronously
3765 (e.g. USB and MMC devices).
3767 rproc_mem=nn[KMG][@address]
3768 [KNL,ARM,CMA] Remoteproc physical memory block.
3769 Memory area to be used by remote processor image,
3772 rw [KNL] Mount root device read-write on boot
3774 S [KNL] Run init in single mode
3776 s390_iommu= [HW,S390]
3777 Set s390 IOTLB flushing mode
3779 With strict flushing every unmap operation will result in
3780 an IOTLB flush. Default is lazy flushing before reuse,
3784 See drivers/net/irda/sa1100_ir.c.
3786 sbni= [NET] Granch SBNI12 leased line adapter
3788 sched_debug [KNL] Enables verbose scheduler debug messages.
3790 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3791 Allowed values are enable and disable. This feature
3792 incurs a small amount of overhead in the scheduler
3793 but is useful for debugging and performance tuning.
3795 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3796 xtime_lock contention on larger systems, and/or RCU lock
3797 contention on all systems with CONFIG_MAXSMP set.
3798 Format: { "0" | "1" }
3799 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3801 Note: increases power consumption, thus should only be
3802 enabled if running jitter sensitive (HPC/RT) workloads.
3804 security= [SECURITY] Choose a security module to enable at boot.
3805 If this boot parameter is not specified, only the first
3806 security module asking for security registration will be
3807 loaded. An invalid security module name will be treated
3808 as if no module has been chosen.
3810 selinux= [SELINUX] Disable or enable SELinux at boot time.
3811 Format: { "0" | "1" }
3812 See security/selinux/Kconfig help text.
3815 Default value is set via kernel config option.
3816 If enabled at boot time, /selinux/disable can be used
3817 later to disable prior to initial policy load.
3819 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3820 Format: { "0" | "1" }
3821 See security/apparmor/Kconfig help text
3824 Default value is set via kernel config option.
3826 serialnumber [BUGS=X86-32]
3829 Maximal number of shapers.
3831 show_msr= [x86] show boot-time MSR settings
3832 Format: { <integer> }
3833 Show boot-time (BIOS-initialized) MSR settings.
3834 The parameter means the number of CPUs to show,
3835 for example 1 means boot CPU only.
3843 Disable merging of slabs with similar size. May be
3844 necessary if there is some reason to distinguish
3845 allocs to different slabs. Debug options disable
3846 merging on their own.
3847 For more information see Documentation/vm/slub.txt.
3849 slab_max_order= [MM, SLAB]
3850 Determines the maximum allowed order for slabs.
3851 A high setting may cause OOMs due to memory
3852 fragmentation. Defaults to 1 for systems with
3853 more than 32MB of RAM, 0 otherwise.
3855 slub_debug[=options[,slabs]] [MM, SLUB]
3856 Enabling slub_debug allows one to determine the
3857 culprit if slab objects become corrupted. Enabling
3858 slub_debug can create guard zones around objects and
3859 may poison objects when not in use. Also tracks the
3860 last alloc / free. For more information see
3861 Documentation/vm/slub.txt.
3863 slub_max_order= [MM, SLUB]
3864 Determines the maximum allowed order for slabs.
3865 A high setting may cause OOMs due to memory
3866 fragmentation. For more information see
3867 Documentation/vm/slub.txt.
3869 slub_min_objects= [MM, SLUB]
3870 The minimum number of objects per slab. SLUB will
3871 increase the slab order up to slub_max_order to
3872 generate a sufficiently large slab able to contain
3873 the number of objects indicated. The higher the number
3874 of objects the smaller the overhead of tracking slabs
3875 and the less frequently locks need to be acquired.
3876 For more information see Documentation/vm/slub.txt.
3878 slub_min_order= [MM, SLUB]
3879 Determines the minimum page order for slabs. Must be
3880 lower than slub_max_order.
3881 For more information see Documentation/vm/slub.txt.
3883 slub_nomerge [MM, SLUB]
3884 Same with slab_nomerge. This is supported for legacy.
3885 See slab_nomerge for more information.
3888 Format: <io1>[,<io2>[,...,<io8>]]
3890 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3891 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3892 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3893 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3894 smsc-ircc2.ircc_irq= [HW] IRQ line
3895 smsc-ircc2.ircc_dma= [HW] DMA channel
3896 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3897 0: Toshiba Satellite 1800 (GP data pin select)
3898 1: Fast pin select (default)
3901 smt [KNL,S390] Set the maximum number of threads (logical
3902 CPUs) to use per physical CPU on systems capable of
3903 symmetric multithreading (SMT). Will be capped to the
3904 actual hardware limit.
3906 Default: -1 (no limit)
3909 [KNL] Should the soft-lockup detector generate panics.
3912 softlockup_all_cpu_backtrace=
3913 [KNL] Should the soft-lockup detector generate
3914 backtraces on all cpus.
3917 sonypi.*= [HW] Sony Programmable I/O Control Device driver
3918 See Documentation/laptops/sonypi.txt
3920 spia_io_base= [HW,MTD]
3926 Enabled the stack tracer on boot up.
3928 stacktrace_filter=[function-list]
3929 [FTRACE] Limit the functions that the stack tracer
3930 will trace at boot up. function-list is a comma separated
3931 list of functions. This list can be changed at run
3932 time by the stack_trace_filter file in the debugfs
3933 tracing directory. Note, this enables stack tracing
3934 and the stacktrace above is not needed.
3938 Set the STI (builtin display/keyboard on the HP-PARISC
3939 machines) console (graphic card) which should be used
3940 as the initial boot-console.
3941 See also comment in drivers/video/console/sticore.c.
3944 See comment in drivers/video/console/sticore.c.
3947 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3949 sunrpc.min_resvport=
3950 sunrpc.max_resvport=
3952 SunRPC servers often require that client requests
3953 originate from a privileged port (i.e. a port in the
3954 range 0 < portnr < 1024).
3955 An administrator who wishes to reserve some of these
3956 ports for other uses may adjust the range that the
3957 kernel's sunrpc client considers to be privileged
3958 using these two parameters to set the minimum and
3959 maximum port values.
3961 sunrpc.svc_rpc_per_connection_limit=
3963 Limit the number of requests that the server will
3964 process in parallel from a single connection.
3965 The default value is 0 (no limit).
3969 Control how the NFS server code allocates CPUs to
3970 service thread pools. Depending on how many NICs
3971 you have and where their interrupts are bound, this
3972 option will affect which CPUs will do NFS serving.
3973 Note: this parameter cannot be changed while the
3974 NFS server is running.
3976 auto the server chooses an appropriate mode
3977 automatically using heuristics
3978 global a single global pool contains all CPUs
3979 percpu one pool for each CPU
3980 pernode one pool for each NUMA node (equivalent
3981 to global on non-NUMA machines)
3983 sunrpc.tcp_slot_table_entries=
3984 sunrpc.udp_slot_table_entries=
3986 Sets the upper limit on the number of simultaneous
3987 RPC calls that can be sent from the client to a
3988 server. Increasing these values may allow you to
3989 improve throughput, but will also increase the
3990 amount of memory reserved for use by the client.
3992 suspend.pm_test_delay=
3994 Sets the number of seconds to remain in a suspend test
3995 mode before resuming the system (see
3996 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3997 is set. Default value is 5.
4000 [KNL] Enable accounting of swap in memory resource
4001 controller if no parameter or 1 is given or disable
4002 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4004 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4005 Format: { <int> | force | noforce }
4006 <int> -- Number of I/O TLB slabs
4007 force -- force using of bounce buffers even if they
4008 wouldn't be automatically used by the kernel
4009 noforce -- Never use bounce buffers (for debugging)
4013 sysfs.deprecated=0|1 [KNL]
4014 Enable/disable old style sysfs layout for old udev
4015 on older distributions. When this option is enabled
4016 very new udev will not work anymore. When this option
4017 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4018 in older udev will not work anymore.
4019 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4020 the kernel configuration.
4022 sysrq_always_enabled
4024 Ignore sysrq setting - this boot parameter will
4025 neutralize any effect of /proc/sys/kernel/sysrq.
4026 Useful for debugging.
4028 tcpmhash_entries= [KNL,NET]
4029 Set the number of tcp_metrics_hash slots.
4030 Default value is 8192 or 16384 depending on total
4031 ram pages. This is used to specify the TCP metrics
4032 cache size. See Documentation/networking/ip-sysctl.txt
4033 "tcp_no_metrics_save" section for more details.
4037 test_suspend= [SUSPEND][,N]
4038 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4039 standby suspend) or "freeze" (for suspend type freeze)
4040 as the system sleep state during system startup with
4041 the optional capability to repeat N number of times.
4042 The system is woken from this state using a
4043 wakeup-capable RTC alarm.
4045 thash_entries= [KNL,NET]
4046 Set number of hash buckets for TCP connection
4048 thermal.act= [HW,ACPI]
4049 -1: disable all active trip points in all thermal zones
4050 <degrees C>: override all lowest active trip points
4052 thermal.crt= [HW,ACPI]
4053 -1: disable all critical trip points in all thermal zones
4054 <degrees C>: override all critical trip points
4056 thermal.nocrt= [HW,ACPI]
4057 Set to disable actions on ACPI thermal zone
4058 critical and hot trip points.
4060 thermal.off= [HW,ACPI]
4061 1: disable ACPI thermal control
4063 thermal.psv= [HW,ACPI]
4064 -1: disable all passive trip points
4065 <degrees C>: override all passive trip points to this
4068 thermal.tzp= [HW,ACPI]
4069 Specify global default ACPI thermal zone polling rate
4070 <deci-seconds>: poll all this frequency
4071 0: no polling (default)
4074 Force threading of all interrupt handlers except those
4075 marked explicitly IRQF_NO_THREAD.
4078 Enable the Transcendent memory driver if built-in.
4080 tmem.cleancache=0|1 [KNL, XEN]
4081 Default is on (1). Disable the usage of the cleancache
4082 API to send anonymous pages to the hypervisor.
4084 tmem.frontswap=0|1 [KNL, XEN]
4085 Default is on (1). Disable the usage of the frontswap
4086 API to send swap pages to the hypervisor. If disabled
4087 the selfballooning and selfshrinking are force disabled.
4089 tmem.selfballooning=0|1 [KNL, XEN]
4090 Default is on (1). Disable the driving of swap pages
4093 tmem.selfshrinking=0|1 [KNL, XEN]
4094 Default is on (1). Partial swapoff that immediately
4095 transfers pages from Xen hypervisor back to the
4096 kernel based on different criteria.
4100 Specify if the kernel should make use of the cpu
4101 topology information if the hardware supports this.
4102 The scheduler will make use of this information and
4103 e.g. base its process migration decisions on it.
4106 topology_updates= [KNL, PPC, NUMA]
4108 Specify if the kernel should ignore (off)
4109 topology updates sent by the hypervisor to this
4114 tpm_suspend_pcr=[HW,TPM]
4115 Format: integer pcr id
4116 Specify that at suspend time, the tpm driver
4117 should extend the specified pcr with zeros,
4118 as a workaround for some chips which fail to
4119 flush the last written pcr on TPM_SaveState.
4120 This will guarantee that all the other pcrs
4123 trace_buf_size=nn[KMG]
4124 [FTRACE] will set tracing buffer size on each cpu.
4126 trace_event=[event-list]
4127 [FTRACE] Set and start specified trace events in order
4128 to facilitate early boot debugging. The event-list is a
4129 comma separated list of trace events to enable. See
4130 also Documentation/trace/events.txt
4132 trace_options=[option-list]
4133 [FTRACE] Enable or disable tracer options at boot.
4134 The option-list is a comma delimited list of options
4135 that can be enabled or disabled just as if you were
4136 to echo the option name into
4138 /sys/kernel/debug/tracing/trace_options
4140 For example, to enable stacktrace option (to dump the
4141 stack trace of each event), add to the command line:
4143 trace_options=stacktrace
4145 See also Documentation/trace/ftrace.txt "trace options"
4149 Have the tracepoints sent to printk as well as the
4150 tracing ring buffer. This is useful for early boot up
4151 where the system hangs or reboots and does not give the
4152 option for reading the tracing buffer or performing a
4153 ftrace_dump_on_oops.
4155 To turn off having tracepoints sent to printk,
4156 echo 0 > /proc/sys/kernel/tracepoint_printk
4157 Note, echoing 1 into this file without the
4158 tracepoint_printk kernel cmdline option has no effect.
4162 Having tracepoints sent to printk() and activating high
4163 frequency tracepoints such as irq or sched, can cause
4164 the system to live lock.
4167 [FTRACE] enable this option to disable tracing when a
4168 warning is hit. This turns off "tracing_on". Tracing can
4169 be enabled again by echoing '1' into the "tracing_on"
4170 file located in /sys/kernel/debug/tracing/
4172 This option is useful, as it disables the trace before
4173 the WARNING dump is called, which prevents the trace to
4174 be filled with content caused by the warning output.
4176 This option can also be set at run time via the sysctl
4177 option: kernel/traceoff_on_warning
4179 transparent_hugepage=
4181 Format: [always|madvise|never]
4182 Can be used to control the default behavior of the system
4183 with respect to transparent hugepages.
4184 See Documentation/vm/transhuge.txt for more details.
4186 tsc= Disable clocksource stability checks for TSC.
4188 [x86] reliable: mark tsc clocksource as reliable, this
4189 disables clocksource verification at runtime, as well
4190 as the stability checks done at bootup. Used to enable
4191 high-resolution timer mode on older hardware, and in
4192 virtualized environment.
4193 [x86] noirqtime: Do not use TSC to do irq accounting.
4194 Used to run time disable IRQ_TIME_ACCOUNTING on any
4195 platforms where RDTSC is slow and this accounting
4198 turbografx.map[2|3]= [HW,JOY]
4199 TurboGraFX parallel port interface
4201 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4202 See also Documentation/input/joystick-parport.txt
4204 udbg-immortal [PPC] When debugging early kernel crashes that
4205 happen after console_init() and before a proper
4206 console driver takes over, this boot options might
4207 help "seeing" what's going on.
4209 uhash_entries= [KNL,NET]
4210 Set number of hash buckets for UDP/UDP-Lite connections
4213 [USB] Ignore overcurrent events (default N).
4214 Some badly-designed motherboards generate lots of
4215 bogus events, for ports that aren't wired to
4216 anything. Set this parameter to avoid log spamming.
4217 Note that genuine overcurrent events won't be
4221 [X86] Cause panic on unknown NMI.
4223 usbcore.authorized_default=
4224 [USB] Default USB device authorization:
4225 (default -1 = authorized except for wireless USB,
4226 0 = not authorized, 1 = authorized)
4228 usbcore.autosuspend=
4229 [USB] The autosuspend time delay (in seconds) used
4230 for newly-detected USB devices (default 2). This
4231 is the time required before an idle device will be
4232 autosuspended. Devices for which the delay is set
4233 to a negative value won't be autosuspended at all.
4235 usbcore.usbfs_snoop=
4236 [USB] Set to log all usbfs traffic (default 0 = off).
4238 usbcore.usbfs_snoop_max=
4239 [USB] Maximum number of bytes to snoop in each URB
4242 usbcore.blinkenlights=
4243 [USB] Set to cycle leds on hubs (default 0 = off).
4245 usbcore.old_scheme_first=
4246 [USB] Start with the old device initialization
4247 scheme (default 0 = off).
4249 usbcore.usbfs_memory_mb=
4250 [USB] Memory limit (in MB) for buffers allocated by
4251 usbfs (default = 16, 0 = max = 2047).
4253 usbcore.use_both_schemes=
4254 [USB] Try the other device initialization scheme
4255 if the first one fails (default 1 = enabled).
4257 usbcore.initial_descriptor_timeout=
4258 [USB] Specifies timeout for the initial 64-byte
4259 USB_REQ_GET_DESCRIPTOR request in milliseconds
4260 (default 5000 = 5.0 seconds).
4262 usbcore.nousb [USB] Disable the USB subsystem
4265 [USBHID] The interval which mice are to be polled at.
4267 usb-storage.delay_use=
4268 [UMS] The delay in seconds before a new device is
4269 scanned for Logical Units (default 1).
4272 [UMS] A list of quirks entries to supplement or
4273 override the built-in unusual_devs list. List
4274 entries are separated by commas. Each entry has
4275 the form VID:PID:Flags where VID and PID are Vendor
4276 and Product ID values (4-digit hex numbers) and
4277 Flags is a set of characters, each corresponding
4278 to a common usb-storage quirk flag as follows:
4279 a = SANE_SENSE (collect more than 18 bytes
4281 b = BAD_SENSE (don't collect more than 18
4282 bytes of sense data);
4283 c = FIX_CAPACITY (decrease the reported
4284 device capacity by one sector);
4285 d = NO_READ_DISC_INFO (don't use
4286 READ_DISC_INFO command);
4287 e = NO_READ_CAPACITY_16 (don't use
4288 READ_CAPACITY_16 command);
4289 f = NO_REPORT_OPCODES (don't use report opcodes
4291 g = MAX_SECTORS_240 (don't transfer more than
4292 240 sectors at a time, uas only);
4293 h = CAPACITY_HEURISTICS (decrease the
4294 reported device capacity by one
4295 sector if the number is odd);
4296 i = IGNORE_DEVICE (don't bind to this
4298 j = NO_REPORT_LUNS (don't use report luns
4300 l = NOT_LOCKABLE (don't try to lock and
4301 unlock ejectable media);
4302 m = MAX_SECTORS_64 (don't transfer more
4303 than 64 sectors = 32 KB at a time);
4304 n = INITIAL_READ10 (force a retry of the
4305 initial READ(10) command);
4306 o = CAPACITY_OK (accept the capacity
4307 reported by the device);
4308 p = WRITE_CACHE (the device cache is ON
4310 r = IGNORE_RESIDUE (the device reports
4311 bogus residue values);
4312 s = SINGLE_LUN (the device has only one
4314 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4315 commands, uas only);
4316 u = IGNORE_UAS (don't bind to the uas driver);
4317 w = NO_WP_DETECT (don't test whether the
4318 medium is write-protected).
4319 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4320 even if the device claims no cache)
4321 Example: quirks=0419:aaf5:rl,0421:0433:rc
4323 user_debug= [KNL,ARM]
4325 See arch/arm/Kconfig.debug help text.
4326 1 - undefined instruction events
4328 4 - invalid data aborts
4331 Example: user_debug=31
4334 [X86] Flags controlling user PTE allocations.
4336 nohigh = do not allocate PTE pages in
4337 HIGHMEM regardless of setting
4341 On X86_32, this is an alias for vdso32=. Otherwise:
4343 vdso=1: enable VDSO (the default)
4344 vdso=0: disable VDSO mapping
4346 vdso32= [X86] Control the 32-bit vDSO
4347 vdso32=1: enable 32-bit VDSO
4348 vdso32=0 or vdso32=2: disable 32-bit VDSO
4350 See the help text for CONFIG_COMPAT_VDSO for more
4351 details. If CONFIG_COMPAT_VDSO is set, the default is
4352 vdso32=0; otherwise, the default is vdso32=1.
4354 For compatibility with older kernels, vdso32=2 is an
4357 Try vdso32=0 if you encounter an error that says:
4358 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4361 vector=percpu: enable percpu vector domain
4363 video= [FB] Frame buffer configuration
4364 See Documentation/fb/modedb.txt.
4366 video.brightness_switch_enabled= [0,1]
4367 If set to 1, on receiving an ACPI notify event
4368 generated by hotkey, video driver will adjust brightness
4369 level and then send out the event to user space through
4370 the allocated input device; If set to 0, video driver
4371 will only send out the event without touching backlight
4376 [VMMIO] Memory mapped virtio (platform) device.
4378 <size>@<baseaddr>:<irq>[:<id>]
4380 <size> := size (can use standard suffixes
4382 <baseaddr> := physical base address
4383 <irq> := interrupt number (as passed to
4385 <id> := (optional) platform device id
4387 virtio_mmio.device=1K@0x100b0000:48:7
4389 Can be used multiple times for multiple devices.
4391 vga= [BOOT,X86-32] Select a particular video mode
4392 See Documentation/x86/boot.txt and
4393 Documentation/svga.txt.
4394 Use vga=ask for menu.
4395 This is actually a boot loader parameter; the value is
4396 passed to the kernel using a special protocol.
4398 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4399 size of <nn>. This can be used to increase the
4400 minimum size (128MB on x86). It can also be used to
4401 decrease the size and leave more room for directly
4404 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4407 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4410 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4414 Controls the behavior of vsyscalls (i.e. calls to
4415 fixed addresses of 0xffffffffff600x00 from legacy
4416 code). Most statically-linked binaries and older
4417 versions of glibc use these calls. Because these
4418 functions are at fixed addresses, they make nice
4419 targets for exploits that can control RIP.
4421 emulate [default] Vsyscalls turn into traps and are
4422 emulated reasonably safely.
4424 native Vsyscalls are native syscall instructions.
4425 This is a little bit faster than trapping
4426 and makes a few dynamic recompilers work
4427 better than they would in emulation mode.
4428 It also makes exploits much easier to write.
4430 none Vsyscalls don't work at all. This makes
4431 them quite hard to use for exploits but
4432 might break your system.
4434 vt.color= [VT] Default text color.
4435 Format: 0xYX, X = foreground, Y = background.
4436 Default: 0x07 = light gray on black.
4438 vt.cur_default= [VT] Default cursor shape.
4439 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4440 the parameters of the <Esc>[?A;B;Cc escape sequence;
4441 see VGA-softcursor.txt. Default: 2 = underline.
4443 vt.default_blu= [VT]
4444 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4445 Change the default blue palette of the console.
4446 This is a 16-member array composed of values
4449 vt.default_grn= [VT]
4450 Format: <green0>,<green1>,<green2>,...,<green15>
4451 Change the default green palette of the console.
4452 This is a 16-member array composed of values
4455 vt.default_red= [VT]
4456 Format: <red0>,<red1>,<red2>,...,<red15>
4457 Change the default red palette of the console.
4458 This is a 16-member array composed of values
4464 Set system-wide default UTF-8 mode for all tty's.
4465 Default is 1, i.e. UTF-8 mode is enabled for all
4466 newly opened terminals.
4468 vt.global_cursor_default=
4471 Set system-wide default for whether a cursor
4472 is shown on new VTs. Default is -1,
4473 i.e. cursors will be created by default unless
4474 overridden by individual drivers. 0 will hide
4475 cursors, 1 will display them.
4477 vt.italic= [VT] Default color for italic text; 0-15.
4480 vt.underline= [VT] Default color for underlined text; 0-15.
4483 watchdog timers [HW,WDT] For information on watchdog timers,
4484 see Documentation/watchdog/watchdog-parameters.txt
4485 or other driver-specific files in the
4486 Documentation/watchdog/ directory.
4488 workqueue.watchdog_thresh=
4489 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4490 warn stall conditions and dump internal state to
4491 help debugging. 0 disables workqueue stall
4492 detection; otherwise, it's the stall threshold
4493 duration in seconds. The default value is 30 and
4494 it can be updated at runtime by writing to the
4495 corresponding sysfs file.
4497 workqueue.disable_numa
4498 By default, all work items queued to unbound
4499 workqueues are affine to the NUMA nodes they're
4500 issued on, which results in better behavior in
4501 general. If NUMA affinity needs to be disabled for
4502 whatever reason, this option can be used. Note
4503 that this also can be controlled per-workqueue for
4504 workqueues visible under /sys/bus/workqueue/.
4506 workqueue.power_efficient
4507 Per-cpu workqueues are generally preferred because
4508 they show better performance thanks to cache
4509 locality; unfortunately, per-cpu workqueues tend to
4510 be more power hungry than unbound workqueues.
4512 Enabling this makes the per-cpu workqueues which
4513 were observed to contribute significantly to power
4514 consumption unbound, leading to measurably lower
4515 power usage at the cost of small performance
4518 The default value of this parameter is determined by
4519 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4521 workqueue.debug_force_rr_cpu
4522 Workqueue used to implicitly guarantee that work
4523 items queued without explicit CPU specified are put
4524 on the local CPU. This guarantee is no longer true
4525 and while local CPU is still preferred work items
4526 may be put on foreign CPUs. This debug option
4527 forces round-robin CPU selection to flush out
4528 usages which depend on the now broken guarantee.
4529 When enabled, memory and cache locality will be
4532 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4533 default x2apic cluster mode on platforms
4536 x86_intel_mid_timer= [X86-32,APBT]
4537 Choose timer option for x86 Intel MID platform.
4538 Two valid options are apbt timer only and lapic timer
4539 plus one apbt timer for broadcast timer.
4540 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4542 xen_512gb_limit [KNL,X86-64,XEN]
4543 Restricts the kernel running paravirtualized under Xen
4544 to use only up to 512 GB of RAM. The reason to do so is
4545 crash analysis tools and Xen tools for doing domain
4546 save/restore/migration must be enabled to handle larger
4549 xen_emul_unplug= [HW,X86,XEN]
4550 Unplug Xen emulated devices
4551 Format: [unplug0,][unplug1]
4552 ide-disks -- unplug primary master IDE devices
4553 aux-ide-disks -- unplug non-primary-master IDE devices
4554 nics -- unplug network devices
4555 all -- unplug all emulated devices (NICs and IDE disks)
4556 unnecessary -- unplugging emulated devices is
4557 unnecessary even if the host did not respond to
4559 never -- do not unplug even if version check succeeds
4561 xen_nopvspin [X86,XEN]
4562 Disables the ticketlock slowpath using Xen PV
4566 Disables the PV optimizations forcing the HVM guest to
4567 run as generic HVM guest with no PV drivers.
4569 xirc2ps_cs= [NET,PCMCIA]
4571 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4573 ______________________________________________________________________
4577 Add more DRM drivers.
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