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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
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
26 loadable modules too.
28 Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30 can also be entered as
31 log-buf-len=1M print_fatal_signals=1
33 Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
36 cpu lists:
37 ----------
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>
44 or
46 <cpu number>-<cpu number>
47 (must be a positive range in ascending order)
49 or a mixture
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
55 group:
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 |
203 copy_dsdt }
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"
213 are available
215 See also Documentation/power/runtime_pm.txt, pci=noacpi
217 acpi_apic_instance= [ACPI, IOAPIC]
218 Format: <int>
219 2: use 2nd APIC table, if available
220 1,0: use 1st APIC table
221 default: 0
223 acpi_backlight= [HW,ACPI]
224 acpi_backlight=vendor
225 acpi_backlight=video
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]
246 Format: <int>
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
291 size limitation.
293 acpi_irq_balance [HW,ACPI]
294 ACPI will balance active IRQs
295 default in APIC mode
297 acpi_irq_nobalance [HW,ACPI]
298 ACPI will not move active IRQs (default)
299 default in PIC mode
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
305 use by PCI
306 Format: <irq>,<irq>...
308 acpi_mask_gpe= [HW,ACPI]
309 Due to the existence of _Lxx/_Exx, some GPEs triggered
310 by unsupported hardware/firmware features can result in
311 GPE floodings that cannot be automatically disabled by
312 the GPE dispatcher.
313 This facility can be used to prevent such uncontrolled
314 GPE floodings.
315 Format: <int>
317 acpi_no_auto_serialize [HW,ACPI]
318 Disable auto-serialization of AML methods
319 AML control methods that contain the opcodes to create
320 named objects will be marked as "Serialized" by the
321 auto-serialization feature.
322 This feature is enabled by default.
323 This option allows to turn off the feature.
325 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
326 kernels.
328 acpi_no_static_ssdt [HW,ACPI]
329 Disable installation of static SSDTs at early boot time
330 By default, SSDTs contained in the RSDT/XSDT will be
331 installed automatically and they will appear under
332 /sys/firmware/acpi/tables.
333 This option turns off this feature.
334 Note that specifying this option does not affect
335 dynamic table installation which will install SSDT
336 tables to /sys/firmware/acpi/tables/dynamic.
338 acpi_no_watchdog [HW,ACPI,WDT]
339 Ignore the ACPI-based watchdog interface (WDAT) and let
340 a native driver control the watchdog device instead.
342 acpi_rsdp= [ACPI,EFI,KEXEC]
343 Pass the RSDP address to the kernel, mostly used
344 on machines running EFI runtime service to boot the
345 second kernel for kdump.
347 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
348 Format: To spoof as Windows 98: ="Microsoft Windows"
350 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
351 of 2 which is mandated by ACPI 6) as the supported ACPI
352 specification revision (when using this switch, it may
353 be necessary to carry out a cold reboot _twice_ in a
354 row to make it take effect on the platform firmware).
356 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
357 acpi_osi="string1" # add string1
358 acpi_osi="!string2" # remove string2
359 acpi_osi=!* # remove all strings
360 acpi_osi=! # disable all built-in OS vendor
361 strings
362 acpi_osi=!! # enable all built-in OS vendor
363 strings
364 acpi_osi= # disable all strings
366 'acpi_osi=!' can be used in combination with single or
367 multiple 'acpi_osi="string1"' to support specific OS
368 vendor string(s). Note that such command can only
369 affect the default state of the OS vendor strings, thus
370 it cannot affect the default state of the feature group
371 strings and the current state of the OS vendor strings,
372 specifying it multiple times through kernel command line
373 is meaningless. This command is useful when one do not
374 care about the state of the feature group strings which
375 should be controlled by the OSPM.
376 Examples:
377 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
378 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
379 can make '_OSI("Windows 2000")' TRUE.
381 'acpi_osi=' cannot be used in combination with other
382 'acpi_osi=' command lines, the _OSI method will not
383 exist in the ACPI namespace. NOTE that such command can
384 only affect the _OSI support state, thus specifying it
385 multiple times through kernel command line is also
386 meaningless.
387 Examples:
388 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
389 FALSE.
391 'acpi_osi=!*' can be used in combination with single or
392 multiple 'acpi_osi="string1"' to support specific
393 string(s). Note that such command can affect the
394 current state of both the OS vendor strings and the
395 feature group strings, thus specifying it multiple times
396 through kernel command line is meaningful. But it may
397 still not able to affect the final state of a string if
398 there are quirks related to this string. This command
399 is useful when one want to control the state of the
400 feature group strings to debug BIOS issues related to
401 the OSPM features.
402 Examples:
403 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
404 '_OSI("Module Device")' FALSE.
405 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
406 '_OSI("Module Device")' TRUE.
407 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
408 equivalent to
409 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
410 and
411 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
412 they all will make '_OSI("Windows 2000")' TRUE.
414 acpi_pm_good [X86]
415 Override the pmtimer bug detection: force the kernel
416 to assume that this machine's pmtimer latches its value
417 and always returns good values.
419 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
420 Format: { level | edge | high | low }
422 acpi_skip_timer_override [HW,ACPI]
423 Recognize and ignore IRQ0/pin2 Interrupt Override.
424 For broken nForce2 BIOS resulting in XT-PIC timer.
426 acpi_sleep= [HW,ACPI] Sleep options
427 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
428 old_ordering, nonvs, sci_force_enable }
429 See Documentation/power/video.txt for information on
430 s3_bios and s3_mode.
431 s3_beep is for debugging; it makes the PC's speaker beep
432 as soon as the kernel's real-mode entry point is called.
433 s4_nohwsig prevents ACPI hardware signature from being
434 used during resume from hibernation.
435 old_ordering causes the ACPI 1.0 ordering of the _PTS
436 control method, with respect to putting devices into
437 low power states, to be enforced (the ACPI 2.0 ordering
438 of _PTS is used by default).
439 nonvs prevents the kernel from saving/restoring the
440 ACPI NVS memory during suspend/hibernation and resume.
441 sci_force_enable causes the kernel to set SCI_EN directly
442 on resume from S1/S3 (which is against the ACPI spec,
443 but some broken systems don't work without it).
445 acpi_use_timer_override [HW,ACPI]
446 Use timer override. For some broken Nvidia NF5 boards
447 that require a timer override, but don't have HPET
449 add_efi_memmap [EFI; X86] Include EFI memory map in
450 kernel's map of available physical RAM.
452 agp= [AGP]
453 { off | try_unsupported }
454 off: disable AGP support
455 try_unsupported: try to drive unsupported chipsets
456 (may crash computer or cause data corruption)
458 ALSA [HW,ALSA]
459 See Documentation/sound/alsa/alsa-parameters.txt
461 alignment= [KNL,ARM]
462 Allow the default userspace alignment fault handler
463 behaviour to be specified. Bit 0 enables warnings,
464 bit 1 enables fixups, and bit 2 sends a segfault.
466 align_va_addr= [X86-64]
467 Align virtual addresses by clearing slice [14:12] when
468 allocating a VMA at process creation time. This option
469 gives you up to 3% performance improvement on AMD F15h
470 machines (where it is enabled by default) for a
471 CPU-intensive style benchmark, and it can vary highly in
472 a microbenchmark depending on workload and compiler.
474 32: only for 32-bit processes
475 64: only for 64-bit processes
476 on: enable for both 32- and 64-bit processes
477 off: disable for both 32- and 64-bit processes
479 alloc_snapshot [FTRACE]
480 Allocate the ftrace snapshot buffer on boot up when the
481 main buffer is allocated. This is handy if debugging
482 and you need to use tracing_snapshot() on boot up, and
483 do not want to use tracing_snapshot_alloc() as it needs
484 to be done where GFP_KERNEL allocations are allowed.
486 amd_iommu= [HW,X86-64]
487 Pass parameters to the AMD IOMMU driver in the system.
488 Possible values are:
489 fullflush - enable flushing of IO/TLB entries when
490 they are unmapped. Otherwise they are
491 flushed before they will be reused, which
492 is a lot of faster
493 off - do not initialize any AMD IOMMU found in
494 the system
495 force_isolation - Force device isolation for all
496 devices. The IOMMU driver is not
497 allowed anymore to lift isolation
498 requirements as needed. This option
499 does not override iommu=pt
501 amd_iommu_dump= [HW,X86-64]
502 Enable AMD IOMMU driver option to dump the ACPI table
503 for AMD IOMMU. With this option enabled, AMD IOMMU
504 driver will print ACPI tables for AMD IOMMU during
505 IOMMU initialization.
507 amd_iommu_intr= [HW,X86-64]
508 Specifies one of the following AMD IOMMU interrupt
509 remapping modes:
510 legacy - Use legacy interrupt remapping mode.
511 vapic - Use virtual APIC mode, which allows IOMMU
512 to inject interrupts directly into guest.
513 This mode requires kvm-amd.avic=1.
514 (Default when IOMMU HW support is present.)
516 amijoy.map= [HW,JOY] Amiga joystick support
517 Map of devices attached to JOY0DAT and JOY1DAT
518 Format: <a>,<b>
519 See also Documentation/input/joystick.txt
521 analog.map= [HW,JOY] Analog joystick and gamepad support
522 Specifies type or capabilities of an analog joystick
523 connected to one of 16 gameports
524 Format: <type1>,<type2>,..<type16>
526 apc= [HW,SPARC]
527 Power management functions (SPARCstation-4/5 + deriv.)
528 Format: noidle
529 Disable APC CPU standby support. SPARCstation-Fox does
530 not play well with APC CPU idle - disable it if you have
531 APC and your system crashes randomly.
533 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
534 Change the output verbosity whilst booting
535 Format: { quiet (default) | verbose | debug }
536 Change the amount of debugging information output
537 when initialising the APIC and IO-APIC components.
539 apic_extnmi= [APIC,X86] External NMI delivery setting
540 Format: { bsp (default) | all | none }
541 bsp: External NMI is delivered only to CPU 0
542 all: External NMIs are broadcast to all CPUs as a
543 backup of CPU 0
544 none: External NMI is masked for all CPUs. This is
545 useful so that a dump capture kernel won't be
546 shot down by NMI
548 autoconf= [IPV6]
549 See Documentation/networking/ipv6.txt.
551 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
552 Limit apic dumping. The parameter defines the maximal
553 number of local apics being dumped. Also it is possible
554 to set it to "all" by meaning -- no limit here.
555 Format: { 1 (default) | 2 | ... | all }.
556 The parameter valid if only apic=debug or
557 apic=verbose is specified.
558 Example: apic=debug show_lapic=all
560 apm= [APM] Advanced Power Management
561 See header of arch/x86/kernel/apm_32.c.
563 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
564 Format: <io>,<irq>,<nodeID>
566 ataflop= [HW,M68k]
568 atarimouse= [HW,MOUSE] Atari Mouse
570 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
571 EzKey and similar keyboards
573 atkbd.reset= [HW] Reset keyboard during initialization
575 atkbd.set= [HW] Select keyboard code set
576 Format: <int> (2 = AT (default), 3 = PS/2)
578 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
579 keyboards
581 atkbd.softraw= [HW] Choose between synthetic and real raw mode
582 Format: <bool> (0 = real, 1 = synthetic (default))
584 atkbd.softrepeat= [HW]
585 Use software keyboard repeat
587 audit= [KNL] Enable the audit sub-system
588 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
589 0 - kernel audit is disabled and can not be enabled
590 until the next reboot
591 unset - kernel audit is initialized but disabled and
592 will be fully enabled by the userspace auditd.
593 1 - kernel audit is initialized and partially enabled,
594 storing at most audit_backlog_limit messages in
595 RAM until it is fully enabled by the userspace
596 auditd.
597 Default: unset
599 audit_backlog_limit= [KNL] Set the audit queue size limit.
600 Format: <int> (must be >=0)
601 Default: 64
603 bau= [X86_UV] Enable the BAU on SGI UV. The default
604 behavior is to disable the BAU (i.e. bau=0).
605 Format: { "0" | "1" }
606 0 - Disable the BAU.
607 1 - Enable the BAU.
608 unset - Disable the BAU.
610 baycom_epp= [HW,AX25]
611 Format: <io>,<mode>
613 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
614 Format: <io>,<mode>
615 See header of drivers/net/hamradio/baycom_par.c.
617 baycom_ser_fdx= [HW,AX25]
618 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
619 Format: <io>,<irq>,<mode>[,<baud>]
620 See header of drivers/net/hamradio/baycom_ser_fdx.c.
622 baycom_ser_hdx= [HW,AX25]
623 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
624 Format: <io>,<irq>,<mode>
625 See header of drivers/net/hamradio/baycom_ser_hdx.c.
627 blkdevparts= Manual partition parsing of block device(s) for
628 embedded devices based on command line input.
629 See Documentation/block/cmdline-partition.txt
631 boot_delay= Milliseconds to delay each printk during boot.
632 Values larger than 10 seconds (10000) are changed to
633 no delay (0).
634 Format: integer
636 bootmem_debug [KNL] Enable bootmem allocator debug messages.
638 bert_disable [ACPI]
639 Disable BERT OS support on buggy BIOSes.
641 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
642 bttv.radio= Most important insmod options are available as
643 kernel args too.
644 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
645 bttv.tuner=
647 bulk_remove=off [PPC] This parameter disables the use of the pSeries
648 firmware feature for flushing multiple hpte entries
649 at a time.
651 c101= [NET] Moxa C101 synchronous serial card
653 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
654 Sometimes CPU hardware bugs make them report the cache
655 size incorrectly. The kernel will attempt work arounds
656 to fix known problems, but for some CPUs it is not
657 possible to determine what the correct size should be.
658 This option provides an override for these situations.
660 ca_keys= [KEYS] This parameter identifies a specific key(s) on
661 the system trusted keyring to be used for certificate
662 trust validation.
663 format: { id:<keyid> | builtin }
665 cca= [MIPS] Override the kernel pages' cache coherency
666 algorithm. Accepted values range from 0 to 7
667 inclusive. See arch/mips/include/asm/pgtable-bits.h
668 for platform specific values (SB1, Loongson3 and
669 others).
671 ccw_timeout_log [S390]
672 See Documentation/s390/CommonIO for details.
674 cgroup_disable= [KNL] Disable a particular controller
675 Format: {name of the controller(s) to disable}
676 The effects of cgroup_disable=foo are:
677 - foo isn't auto-mounted if you mount all cgroups in
678 a single hierarchy
679 - foo isn't visible as an individually mountable
680 subsystem
681 {Currently only "memory" controller deal with this and
682 cut the overhead, others just disable the usage. So
683 only cgroup_disable=memory is actually worthy}
685 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
686 Format: { controller[,controller...] | "all" }
687 Like cgroup_disable, but only applies to cgroup v1;
688 the blacklisted controllers remain available in cgroup2.
690 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
691 Format: <string>
692 nosocket -- Disable socket memory accounting.
693 nokmem -- Disable kernel memory accounting.
695 checkreqprot [SELINUX] Set initial checkreqprot flag value.
696 Format: { "0" | "1" }
697 See security/selinux/Kconfig help text.
698 0 -- check protection applied by kernel (includes
699 any implied execute protection).
700 1 -- check protection requested by application.
701 Default value is set via a kernel config option.
702 Value can be changed at runtime via
703 /selinux/checkreqprot.
705 cio_ignore= [S390]
706 See Documentation/s390/CommonIO for details.
707 clk_ignore_unused
708 [CLK]
709 Prevents the clock framework from automatically gating
710 clocks that have not been explicitly enabled by a Linux
711 device driver but are enabled in hardware at reset or
712 by the bootloader/firmware. Note that this does not
713 force such clocks to be always-on nor does it reserve
714 those clocks in any way. This parameter is useful for
715 debug and development, but should not be needed on a
716 platform with proper driver support. For more
717 information, see Documentation/clk.txt.
719 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
720 [Deprecated]
721 Forces specified clocksource (if available) to be used
722 when calculating gettimeofday(). If specified
723 clocksource is not available, it defaults to PIT.
724 Format: { pit | tsc | cyclone | pmtmr }
726 clocksource= Override the default clocksource
727 Format: <string>
728 Override the default clocksource and use the clocksource
729 with the name specified.
730 Some clocksource names to choose from, depending on
731 the platform:
732 [all] jiffies (this is the base, fallback clocksource)
733 [ACPI] acpi_pm
734 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
735 pxa_timer,timer3,32k_counter,timer0_1
736 [AVR32] avr32
737 [X86-32] pit,hpet,tsc;
738 scx200_hrt on Geode; cyclone on IBM x440
739 [MIPS] MIPS
740 [PARISC] cr16
741 [S390] tod
742 [SH] SuperH
743 [SPARC64] tick
744 [X86-64] hpet,tsc
746 clocksource.arm_arch_timer.evtstrm=
747 [ARM,ARM64]
748 Format: <bool>
749 Enable/disable the eventstream feature of the ARM
750 architected timer so that code using WFE-based polling
751 loops can be debugged more effectively on production
752 systems.
754 clocksource.arm_arch_timer.fsl-a008585=
755 [ARM64]
756 Format: <bool>
757 Enable/disable the workaround of Freescale/NXP
758 erratum A-008585. This can be useful for KVM
759 guests, if the guest device tree doesn't show the
760 erratum. If unspecified, the workaround is
761 enabled based on the device tree.
763 clearcpuid=BITNUM [X86]
764 Disable CPUID feature X for the kernel. See
765 arch/x86/include/asm/cpufeatures.h for the valid bit
766 numbers. Note the Linux specific bits are not necessarily
767 stable over kernel options, but the vendor specific
768 ones should be.
769 Also note that user programs calling CPUID directly
770 or using the feature without checking anything
771 will still see it. This just prevents it from
772 being used by the kernel or shown in /proc/cpuinfo.
773 Also note the kernel might malfunction if you disable
774 some critical bits.
776 cma=nn[MG]@[start[MG][-end[MG]]]
777 [ARM,X86,KNL]
778 Sets the size of kernel global memory area for
779 contiguous memory allocations and optionally the
780 placement constraint by the physical address range of
781 memory allocations. A value of 0 disables CMA
782 altogether. For more information, see
783 include/linux/dma-contiguous.h
785 cmo_free_hint= [PPC] Format: { yes | no }
786 Specify whether pages are marked as being inactive
787 when they are freed. This is used in CMO environments
788 to determine OS memory pressure for page stealing by
789 a hypervisor.
790 Default: yes
792 coherent_pool=nn[KMG] [ARM,KNL]
793 Sets the size of memory pool for coherent, atomic dma
794 allocations, by default set to 256K.
796 code_bytes [X86] How many bytes of object code to print
797 in an oops report.
798 Range: 0 - 8192
799 Default: 64
801 com20020= [HW,NET] ARCnet - COM20020 chipset
802 Format:
803 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
805 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
806 Format: <io>[,<irq>]
808 com90xx= [HW,NET]
809 ARCnet - COM90xx chipset (memory-mapped buffers)
810 Format: <io>[,<irq>[,<memstart>]]
812 condev= [HW,S390] console device
813 conmode=
815 console= [KNL] Output console device and options.
817 tty<n> Use the virtual console device <n>.
819 ttyS<n>[,options]
820 ttyUSB0[,options]
821 Use the specified serial port. The options are of
822 the form "bbbbpnf", where "bbbb" is the baud rate,
823 "p" is parity ("n", "o", or "e"), "n" is number of
824 bits, and "f" is flow control ("r" for RTS or
825 omit it). Default is "9600n8".
827 See Documentation/serial-console.txt for more
828 information. See
829 Documentation/networking/netconsole.txt for an
830 alternative.
832 uart[8250],io,<addr>[,options]
833 uart[8250],mmio,<addr>[,options]
834 uart[8250],mmio16,<addr>[,options]
835 uart[8250],mmio32,<addr>[,options]
836 uart[8250],0x<addr>[,options]
837 Start an early, polled-mode console on the 8250/16550
838 UART at the specified I/O port or MMIO address,
839 switching to the matching ttyS device later.
840 MMIO inter-register address stride is either 8-bit
841 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
842 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
843 to be equivalent to 'mmio'. 'options' are specified in
844 the same format described for ttyS above; if unspecified,
845 the h/w is not re-initialized.
847 hvc<n> Use the hypervisor console device <n>. This is for
848 both Xen and PowerPC hypervisors.
850 If the device connected to the port is not a TTY but a braille
851 device, prepend "brl," before the device type, for instance
852 console=brl,ttyS0
853 For now, only VisioBraille is supported.
855 consoleblank= [KNL] The console blank (screen saver) timeout in
856 seconds. Defaults to 10*60 = 10mins. A value of 0
857 disables the blank timer.
859 coredump_filter=
860 [KNL] Change the default value for
861 /proc/<pid>/coredump_filter.
862 See also Documentation/filesystems/proc.txt.
864 cpuidle.off=1 [CPU_IDLE]
865 disable the cpuidle sub-system
867 cpu_init_udelay=N
868 [X86] Delay for N microsec between assert and de-assert
869 of APIC INIT to start processors. This delay occurs
870 on every CPU online, such as boot, and resume from suspend.
871 Default: 10000
873 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
874 Format:
875 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
877 crashkernel=size[KMG][@offset[KMG]]
878 [KNL] Using kexec, Linux can switch to a 'crash kernel'
879 upon panic. This parameter reserves the physical
880 memory region [offset, offset + size] for that kernel
881 image. If '@offset' is omitted, then a suitable offset
882 is selected automatically. Check
883 Documentation/kdump/kdump.txt for further details.
885 crashkernel=range1:size1[,range2:size2,...][@offset]
886 [KNL] Same as above, but depends on the memory
887 in the running system. The syntax of range is
888 start-[end] where start and end are both
889 a memory unit (amount[KMG]). See also
890 Documentation/kdump/kdump.txt for an example.
892 crashkernel=size[KMG],high
893 [KNL, x86_64] range could be above 4G. Allow kernel
894 to allocate physical memory region from top, so could
895 be above 4G if system have more than 4G ram installed.
896 Otherwise memory region will be allocated below 4G, if
897 available.
898 It will be ignored if crashkernel=X is specified.
899 crashkernel=size[KMG],low
900 [KNL, x86_64] range under 4G. When crashkernel=X,high
901 is passed, kernel could allocate physical memory region
902 above 4G, that cause second kernel crash on system
903 that require some amount of low memory, e.g. swiotlb
904 requires at least 64M+32K low memory, also enough extra
905 low memory is needed to make sure DMA buffers for 32-bit
906 devices won't run out. Kernel would try to allocate at
907 at least 256M below 4G automatically.
908 This one let user to specify own low range under 4G
909 for second kernel instead.
910 0: to disable low allocation.
911 It will be ignored when crashkernel=X,high is not used
912 or memory reserved is below 4G.
914 cryptomgr.notests
915 [KNL] Disable crypto self-tests
917 cs89x0_dma= [HW,NET]
918 Format: <dma>
920 cs89x0_media= [HW,NET]
921 Format: { rj45 | aui | bnc }
923 dasd= [HW,NET]
924 See header of drivers/s390/block/dasd_devmap.c.
926 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
927 (one device per port)
928 Format: <port#>,<type>
929 See also Documentation/input/joystick-parport.txt
931 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
932 time. See Documentation/dynamic-debug-howto.txt for
933 details. Deprecated, see dyndbg.
935 debug [KNL] Enable kernel debugging (events log level).
937 debug_locks_verbose=
938 [KNL] verbose self-tests
939 Format=<0|1>
940 Print debugging info while doing the locking API
941 self-tests.
942 We default to 0 (no extra messages), setting it to
943 1 will print _a lot_ more information - normally
944 only useful to kernel developers.
946 debug_objects [KNL] Enable object debugging
948 no_debug_objects
949 [KNL] Disable object debugging
951 debug_guardpage_minorder=
952 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
953 parameter allows control of the order of pages that will
954 be intentionally kept free (and hence protected) by the
955 buddy allocator. Bigger value increase the probability
956 of catching random memory corruption, but reduce the
957 amount of memory for normal system use. The maximum
958 possible value is MAX_ORDER/2. Setting this parameter
959 to 1 or 2 should be enough to identify most random
960 memory corruption problems caused by bugs in kernel or
961 driver code when a CPU writes to (or reads from) a
962 random memory location. Note that there exists a class
963 of memory corruptions problems caused by buggy H/W or
964 F/W or by drivers badly programing DMA (basically when
965 memory is written at bus level and the CPU MMU is
966 bypassed) which are not detectable by
967 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
968 tracking down these problems.
970 debug_pagealloc=
971 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
972 parameter enables the feature at boot time. In
973 default, it is disabled. We can avoid allocating huge
974 chunk of memory for debug pagealloc if we don't enable
975 it at boot time and the system will work mostly same
976 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
977 on: enable the feature
979 debugpat [X86] Enable PAT debugging
981 decnet.addr= [HW,NET]
982 Format: <area>[,<node>]
983 See also Documentation/networking/decnet.txt.
985 default_hugepagesz=
986 [same as hugepagesz=] The size of the default
987 HugeTLB page size. This is the size represented by
988 the legacy /proc/ hugepages APIs, used for SHM, and
989 default size when mounting hugetlbfs filesystems.
990 Defaults to the default architecture's huge page size
991 if not specified.
993 dhash_entries= [KNL]
994 Set number of hash buckets for dentry cache.
996 disable_1tb_segments [PPC]
997 Disables the use of 1TB hash page table segments. This
998 causes the kernel to fall back to 256MB segments which
999 can be useful when debugging issues that require an SLB
1000 miss to occur.
1002 disable= [IPV6]
1003 See Documentation/networking/ipv6.txt.
1005 disable_radix [PPC]
1006 Disable RADIX MMU mode on POWER9
1008 disable_cpu_apicid= [X86,APIC,SMP]
1009 Format: <int>
1010 The number of initial APIC ID for the
1011 corresponding CPU to be disabled at boot,
1012 mostly used for the kdump 2nd kernel to
1013 disable BSP to wake up multiple CPUs without
1014 causing system reset or hang due to sending
1015 INIT from AP to BSP.
1017 disable_ddw [PPC/PSERIES]
1018 Disable Dynamic DMA Window support. Use this if
1019 to workaround buggy firmware.
1021 disable_ipv6= [IPV6]
1022 See Documentation/networking/ipv6.txt.
1024 disable_mtrr_cleanup [X86]
1025 The kernel tries to adjust MTRR layout from continuous
1026 to discrete, to make X server driver able to add WB
1027 entry later. This parameter disables that.
1029 disable_mtrr_trim [X86, Intel and AMD only]
1030 By default the kernel will trim any uncacheable
1031 memory out of your available memory pool based on
1032 MTRR settings. This parameter disables that behavior,
1033 possibly causing your machine to run very slowly.
1035 disable_timer_pin_1 [X86]
1036 Disable PIN 1 of APIC timer
1037 Can be useful to work around chipset bugs.
1039 dis_ucode_ldr [X86] Disable the microcode loader.
1041 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1042 this option disables the debugging code at boot.
1044 dma_debug_entries=<number>
1045 This option allows to tune the number of preallocated
1046 entries for DMA-API debugging code. One entry is
1047 required per DMA-API allocation. Use this if the
1048 DMA-API debugging code disables itself because the
1049 architectural default is too low.
1051 dma_debug_driver=<driver_name>
1052 With this option the DMA-API debugging driver
1053 filter feature can be enabled at boot time. Just
1054 pass the driver to filter for as the parameter.
1055 The filter can be disabled or changed to another
1056 driver later using sysfs.
1058 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1059 Broken monitors, graphic adapters, KVMs and EDIDless
1060 panels may send no or incorrect EDID data sets.
1061 This parameter allows to specify an EDID data sets
1062 in the /lib/firmware directory that are used instead.
1063 Generic built-in EDID data sets are used, if one of
1064 edid/1024x768.bin, edid/1280x1024.bin,
1065 edid/1680x1050.bin, or edid/1920x1080.bin is given
1066 and no file with the same name exists. Details and
1067 instructions how to build your own EDID data are
1068 available in Documentation/EDID/HOWTO.txt. An EDID
1069 data set will only be used for a particular connector,
1070 if its name and a colon are prepended to the EDID
1071 name. Each connector may use a unique EDID data
1072 set by separating the files with a comma. An EDID
1073 data set with no connector name will be used for
1074 any connectors not explicitly specified.
1076 dscc4.setup= [NET]
1078 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1079 module.dyndbg[="val"]
1080 Enable debug messages at boot time. See
1081 Documentation/dynamic-debug-howto.txt for details.
1083 nompx [X86] Disables Intel Memory Protection Extensions.
1084 See Documentation/x86/intel_mpx.txt for more
1085 information about the feature.
1087 nopku [X86] Disable Memory Protection Keys CPU feature found
1088 in some Intel CPUs.
1090 module.async_probe [KNL]
1091 Enable asynchronous probe on this module.
1093 early_ioremap_debug [KNL]
1094 Enable debug messages in early_ioremap support. This
1095 is useful for tracking down temporary early mappings
1096 which are not unmapped.
1098 earlycon= [KNL] Output early console device and options.
1100 When used with no options, the early console is
1101 determined by the stdout-path property in device
1102 tree's chosen node.
1104 cdns,<addr>[,options]
1105 Start an early, polled-mode console on a Cadence
1106 (xuartps) serial port at the specified address. Only
1107 supported option is baud rate. If baud rate is not
1108 specified, the serial port must already be setup and
1109 configured.
1111 uart[8250],io,<addr>[,options]
1112 uart[8250],mmio,<addr>[,options]
1113 uart[8250],mmio32,<addr>[,options]
1114 uart[8250],mmio32be,<addr>[,options]
1115 uart[8250],0x<addr>[,options]
1116 Start an early, polled-mode console on the 8250/16550
1117 UART at the specified I/O port or MMIO address.
1118 MMIO inter-register address stride is either 8-bit
1119 (mmio) or 32-bit (mmio32 or mmio32be).
1120 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1121 to be equivalent to 'mmio'. 'options' are specified
1122 in the same format described for "console=ttyS<n>"; if
1123 unspecified, the h/w is not initialized.
1125 pl011,<addr>
1126 pl011,mmio32,<addr>
1127 Start an early, polled-mode console on a pl011 serial
1128 port at the specified address. The pl011 serial port
1129 must already be setup and configured. Options are not
1130 yet supported. If 'mmio32' is specified, then only
1131 the driver will use only 32-bit accessors to read/write
1132 the device registers.
1134 meson,<addr>
1135 Start an early, polled-mode console on a meson serial
1136 port at the specified address. The serial port must
1137 already be setup and configured. Options are not yet
1138 supported.
1140 msm_serial,<addr>
1141 Start an early, polled-mode console on an msm serial
1142 port at the specified address. The serial port
1143 must already be setup and configured. Options are not
1144 yet supported.
1146 msm_serial_dm,<addr>
1147 Start an early, polled-mode console on an msm serial
1148 dm port at the specified address. The serial port
1149 must already be setup and configured. Options are not
1150 yet supported.
1152 smh Use ARM semihosting calls for early console.
1154 s3c2410,<addr>
1155 s3c2412,<addr>
1156 s3c2440,<addr>
1157 s3c6400,<addr>
1158 s5pv210,<addr>
1159 exynos4210,<addr>
1160 Use early console provided by serial driver available
1161 on Samsung SoCs, requires selecting proper type and
1162 a correct base address of the selected UART port. The
1163 serial port must already be setup and configured.
1164 Options are not yet supported.
1166 lpuart,<addr>
1167 lpuart32,<addr>
1168 Use early console provided by Freescale LP UART driver
1169 found on Freescale Vybrid and QorIQ LS1021A processors.
1170 A valid base address must be provided, and the serial
1171 port must already be setup and configured.
1173 armada3700_uart,<addr>
1174 Start an early, polled-mode console on the
1175 Armada 3700 serial port at the specified
1176 address. The serial port must already be setup
1177 and configured. Options are not yet supported.
1179 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1180 earlyprintk=vga
1181 earlyprintk=efi
1182 earlyprintk=xen
1183 earlyprintk=serial[,ttySn[,baudrate]]
1184 earlyprintk=serial[,0x...[,baudrate]]
1185 earlyprintk=ttySn[,baudrate]
1186 earlyprintk=dbgp[debugController#]
1187 earlyprintk=pciserial,bus:device.function[,baudrate]
1189 earlyprintk is useful when the kernel crashes before
1190 the normal console is initialized. It is not enabled by
1191 default because it has some cosmetic problems.
1193 Append ",keep" to not disable it when the real console
1194 takes over.
1196 Only one of vga, efi, serial, or usb debug port can
1197 be used at a time.
1199 Currently only ttyS0 and ttyS1 may be specified by
1200 name. Other I/O ports may be explicitly specified
1201 on some architectures (x86 and arm at least) by
1202 replacing ttySn with an I/O port address, like this:
1203 earlyprintk=serial,0x1008,115200
1204 You can find the port for a given device in
1205 /proc/tty/driver/serial:
1206 2: uart:ST16650V2 port:00001008 irq:18 ...
1208 Interaction with the standard serial driver is not
1209 very good.
1211 The VGA and EFI output is eventually overwritten by
1212 the real console.
1214 The xen output can only be used by Xen PV guests.
1216 edac_report= [HW,EDAC] Control how to report EDAC event
1217 Format: {"on" | "off" | "force"}
1218 on: enable EDAC to report H/W event. May be overridden
1219 by other higher priority error reporting module.
1220 off: disable H/W event reporting through EDAC.
1221 force: enforce the use of EDAC to report H/W event.
1222 default: on.
1224 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1225 ekgdboc=kbd
1227 This is designed to be used in conjunction with
1228 the boot argument: earlyprintk=vga
1230 edd= [EDD]
1231 Format: {"off" | "on" | "skip[mbr]"}
1233 efi= [EFI]
1234 Format: { "old_map", "nochunk", "noruntime", "debug" }
1235 old_map [X86-64]: switch to the old ioremap-based EFI
1236 runtime services mapping. 32-bit still uses this one by
1237 default.
1238 nochunk: disable reading files in "chunks" in the EFI
1239 boot stub, as chunking can cause problems with some
1240 firmware implementations.
1241 noruntime : disable EFI runtime services support
1242 debug: enable misc debug output
1244 efi_no_storage_paranoia [EFI; X86]
1245 Using this parameter you can use more than 50% of
1246 your efi variable storage. Use this parameter only if
1247 you are really sure that your UEFI does sane gc and
1248 fulfills the spec otherwise your board may brick.
1250 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1251 Add arbitrary attribute to specific memory range by
1252 updating original EFI memory map.
1253 Region of memory which aa attribute is added to is
1254 from ss to ss+nn.
1255 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1256 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1257 attribute is added to range 0x100000000-0x180000000 and
1258 0x10a0000000-0x1120000000.
1260 Using this parameter you can do debugging of EFI memmap
1261 related feature. For example, you can do debugging of
1262 Address Range Mirroring feature even if your box
1263 doesn't support it.
1265 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1266 that is to be dynamically loaded by Linux. If there are
1267 multiple variables with the same name but with different
1268 vendor GUIDs, all of them will be loaded. See
1269 Documentation/acpi/ssdt-overlays.txt for details.
1272 eisa_irq_edge= [PARISC,HW]
1273 See header of drivers/parisc/eisa.c.
1275 elanfreq= [X86-32]
1276 See comment before function elanfreq_setup() in
1277 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1279 elevator= [IOSCHED]
1280 Format: {"cfq" | "deadline" | "noop"}
1281 See Documentation/block/cfq-iosched.txt and
1282 Documentation/block/deadline-iosched.txt for details.
1284 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1285 Specifies physical address of start of kernel core
1286 image elf header and optionally the size. Generally
1287 kexec loader will pass this option to capture kernel.
1288 See Documentation/kdump/kdump.txt for details.
1290 enable_mtrr_cleanup [X86]
1291 The kernel tries to adjust MTRR layout from continuous
1292 to discrete, to make X server driver able to add WB
1293 entry later. This parameter enables that.
1295 enable_timer_pin_1 [X86]
1296 Enable PIN 1 of APIC timer
1297 Can be useful to work around chipset bugs
1298 (in particular on some ATI chipsets).
1299 The kernel tries to set a reasonable default.
1301 enforcing [SELINUX] Set initial enforcing status.
1302 Format: {"0" | "1"}
1303 See security/selinux/Kconfig help text.
1304 0 -- permissive (log only, no denials).
1305 1 -- enforcing (deny and log).
1306 Default value is 0.
1307 Value can be changed at runtime via /selinux/enforce.
1309 erst_disable [ACPI]
1310 Disable Error Record Serialization Table (ERST)
1311 support.
1313 ether= [HW,NET] Ethernet cards parameters
1314 This option is obsoleted by the "netdev=" option, which
1315 has equivalent usage. See its documentation for details.
1317 evm= [EVM]
1318 Format: { "fix" }
1319 Permit 'security.evm' to be updated regardless of
1320 current integrity status.
1322 failslab=
1323 fail_page_alloc=
1324 fail_make_request=[KNL]
1325 General fault injection mechanism.
1326 Format: <interval>,<probability>,<space>,<times>
1327 See also Documentation/fault-injection/.
1329 floppy= [HW]
1330 See Documentation/blockdev/floppy.txt.
1332 force_pal_cache_flush
1333 [IA-64] Avoid check_sal_cache_flush which may hang on
1334 buggy SAL_CACHE_FLUSH implementations. Using this
1335 parameter will force ia64_sal_cache_flush to call
1336 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1338 forcepae [X86-32]
1339 Forcefully enable Physical Address Extension (PAE).
1340 Many Pentium M systems disable PAE but may have a
1341 functionally usable PAE implementation.
1342 Warning: use of this parameter will taint the kernel
1343 and may cause unknown problems.
1345 ftrace=[tracer]
1346 [FTRACE] will set and start the specified tracer
1347 as early as possible in order to facilitate early
1348 boot debugging.
1350 ftrace_dump_on_oops[=orig_cpu]
1351 [FTRACE] will dump the trace buffers on oops.
1352 If no parameter is passed, ftrace will dump
1353 buffers of all CPUs, but if you pass orig_cpu, it will
1354 dump only the buffer of the CPU that triggered the
1355 oops.
1357 ftrace_filter=[function-list]
1358 [FTRACE] Limit the functions traced by the function
1359 tracer at boot up. function-list is a comma separated
1360 list of functions. This list can be changed at run
1361 time by the set_ftrace_filter file in the debugfs
1362 tracing directory.
1364 ftrace_notrace=[function-list]
1365 [FTRACE] Do not trace the functions specified in
1366 function-list. This list can be changed at run time
1367 by the set_ftrace_notrace file in the debugfs
1368 tracing directory.
1370 ftrace_graph_filter=[function-list]
1371 [FTRACE] Limit the top level callers functions traced
1372 by the function graph tracer at boot up.
1373 function-list is a comma separated list of functions
1374 that can be changed at run time by the
1375 set_graph_function file in the debugfs tracing directory.
1377 ftrace_graph_notrace=[function-list]
1378 [FTRACE] Do not trace from the functions specified in
1379 function-list. This list is a comma separated list of
1380 functions that can be changed at run time by the
1381 set_graph_notrace file in the debugfs tracing directory.
1383 gamecon.map[2|3]=
1384 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1385 support via parallel port (up to 5 devices per port)
1386 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1387 See also Documentation/input/joystick-parport.txt
1389 gamma= [HW,DRM]
1391 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1392 Format: off | on
1393 default: on
1395 gcov_persist= [GCOV] When non-zero (default), profiling data for
1396 kernel modules is saved and remains accessible via
1397 debugfs, even when the module is unloaded/reloaded.
1398 When zero, profiling data is discarded and associated
1399 debugfs files are removed at module unload time.
1401 goldfish [X86] Enable the goldfish android emulator platform.
1402 Don't use this when you are not running on the
1403 android emulator
1405 gpt [EFI] Forces disk with valid GPT signature but
1406 invalid Protective MBR to be treated as GPT. If the
1407 primary GPT is corrupted, it enables the backup/alternate
1408 GPT to be used instead.
1410 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1411 the "Enable 0" bit of the configuration register.
1412 Format: 0 | 1
1413 Default: 0
1414 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1415 the "Enable 0" bit of the configuration register.
1416 Format: 0 | 1
1417 Default: 0
1418 grcan.select= [HW] Select which physical interface to use.
1419 Format: 0 | 1
1420 Default: 0
1421 grcan.txsize= [HW] Sets the size of the tx buffer.
1422 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1423 Default: 1024
1424 grcan.rxsize= [HW] Sets the size of the rx buffer.
1425 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1426 Default: 1024
1428 gpio-mockup.gpio_mockup_ranges
1429 [HW] Sets the ranges of gpiochip of for this device.
1430 Format: <start1>,<end1>,<start2>,<end2>...
1432 hardlockup_all_cpu_backtrace=
1433 [KNL] Should the hard-lockup detector generate
1434 backtraces on all cpus.
1435 Format: <integer>
1437 hashdist= [KNL,NUMA] Large hashes allocated during boot
1438 are distributed across NUMA nodes. Defaults on
1439 for 64-bit NUMA, off otherwise.
1440 Format: 0 | 1 (for off | on)
1442 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1444 hd= [EIDE] (E)IDE hard drive subsystem geometry
1445 Format: <cyl>,<head>,<sect>
1447 hest_disable [ACPI]
1448 Disable Hardware Error Source Table (HEST) support;
1449 corresponding firmware-first mode error processing
1450 logic will be disabled.
1452 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1453 size of <nn>. This works even on boxes that have no
1454 highmem otherwise. This also works to reduce highmem
1455 size on bigger boxes.
1457 highres= [KNL] Enable/disable high resolution timer mode.
1458 Valid parameters: "on", "off"
1459 Default: "on"
1461 hisax= [HW,ISDN]
1462 See Documentation/isdn/README.HiSax.
1464 hlt [BUGS=ARM,SH]
1466 hpet= [X86-32,HPET] option to control HPET usage
1467 Format: { enable (default) | disable | force |
1468 verbose }
1469 disable: disable HPET and use PIT instead
1470 force: allow force enabled of undocumented chips (ICH4,
1471 VIA, nVidia)
1472 verbose: show contents of HPET registers during setup
1474 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1475 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1477 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1478 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1479 On x86-64 and powerpc, this option can be specified
1480 multiple times interleaved with hugepages= to reserve
1481 huge pages of different sizes. Valid pages sizes on
1482 x86-64 are 2M (when the CPU supports "pse") and 1G
1483 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1485 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1486 terminal devices. Valid values: 0..8
1487 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1488 If specified, z/VM IUCV HVC accepts connections
1489 from listed z/VM user IDs only.
1491 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1492 hardware thread id mappings.
1493 Format: <cpu>:<hwthread>
1495 keep_bootcon [KNL]
1496 Do not unregister boot console at start. This is only
1497 useful for debugging when something happens in the window
1498 between unregistering the boot console and initializing
1499 the real console.
1501 i2c_bus= [HW] Override the default board specific I2C bus speed
1502 or register an additional I2C bus that is not
1503 registered from board initialization code.
1504 Format:
1505 <bus_id>,<clkrate>
1507 i8042.debug [HW] Toggle i8042 debug mode
1508 i8042.unmask_kbd_data
1509 [HW] Enable printing of interrupt data from the KBD port
1510 (disabled by default, and as a pre-condition
1511 requires that i8042.debug=1 be enabled)
1512 i8042.direct [HW] Put keyboard port into non-translated mode
1513 i8042.dumbkbd [HW] Pretend that controller can only read data from
1514 keyboard and cannot control its state
1515 (Don't attempt to blink the leds)
1516 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1517 i8042.nokbd [HW] Don't check/create keyboard port
1518 i8042.noloop [HW] Disable the AUX Loopback command while probing
1519 for the AUX port
1520 i8042.nomux [HW] Don't check presence of an active multiplexing
1521 controller
1522 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1523 controllers
1524 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1525 i8042.reset [HW] Reset the controller during init, cleanup and
1526 suspend-to-ram transitions, only during s2r
1527 transitions, or never reset
1528 Format: { 1 | Y | y | 0 | N | n }
1529 1, Y, y: always reset controller
1530 0, N, n: don't ever reset controller
1531 Default: only on s2r transitions on x86; most other
1532 architectures force reset to be always executed
1533 i8042.unlock [HW] Unlock (ignore) the keylock
1534 i8042.kbdreset [HW] Reset device connected to KBD port
1536 i810= [HW,DRM]
1538 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1539 indicates that the driver is running on unsupported
1540 hardware.
1541 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1542 does not match list of supported models.
1543 i8k.power_status
1544 [HW] Report power status in /proc/i8k
1545 (disabled by default)
1546 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1547 capability is set.
1549 i915.invert_brightness=
1550 [DRM] Invert the sense of the variable that is used to
1551 set the brightness of the panel backlight. Normally a
1552 brightness value of 0 indicates backlight switched off,
1553 and the maximum of the brightness value sets the backlight
1554 to maximum brightness. If this parameter is set to 0
1555 (default) and the machine requires it, or this parameter
1556 is set to 1, a brightness value of 0 sets the backlight
1557 to maximum brightness, and the maximum of the brightness
1558 value switches the backlight off.
1559 -1 -- never invert brightness
1560 0 -- machine default
1561 1 -- force brightness inversion
1563 icn= [HW,ISDN]
1564 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1566 ide-core.nodma= [HW] (E)IDE subsystem
1567 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1568 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1569 .cdrom .chs .ignore_cable are additional options
1570 See Documentation/ide/ide.txt.
1572 ide-generic.probe-mask= [HW] (E)IDE subsystem
1573 Format: <int>
1574 Probe mask for legacy ISA IDE ports. Depending on
1575 platform up to 6 ports are supported, enabled by
1576 setting corresponding bits in the mask to 1. The
1577 default value is 0x0, which has a special meaning.
1578 On systems that have PCI, it triggers scanning the
1579 PCI bus for the first and the second port, which
1580 are then probed. On systems without PCI the value
1581 of 0x0 enables probing the two first ports as if it
1582 was 0x3.
1584 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1585 Claim all unknown PCI IDE storage controllers.
1587 idle= [X86]
1588 Format: idle=poll, idle=halt, idle=nomwait
1589 Poll forces a polling idle loop that can slightly
1590 improve the performance of waking up a idle CPU, but
1591 will use a lot of power and make the system run hot.
1592 Not recommended.
1593 idle=halt: Halt is forced to be used for CPU idle.
1594 In such case C2/C3 won't be used again.
1595 idle=nomwait: Disable mwait for CPU C-states
1597 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1598 Format: { strict | legacy | 2008 | relaxed }
1599 Default: strict
1601 Choose which programs will be accepted for execution
1602 based on the IEEE 754 NaN encoding(s) supported by
1603 the FPU and the NaN encoding requested with the value
1604 of an ELF file header flag individually set by each
1605 binary. Hardware implementations are permitted to
1606 support either or both of the legacy and the 2008 NaN
1607 encoding mode.
1609 Available settings are as follows:
1610 strict accept binaries that request a NaN encoding
1611 supported by the FPU
1612 legacy only accept legacy-NaN binaries, if supported
1613 by the FPU
1614 2008 only accept 2008-NaN binaries, if supported
1615 by the FPU
1616 relaxed accept any binaries regardless of whether
1617 supported by the FPU
1619 The FPU emulator is always able to support both NaN
1620 encodings, so if no FPU hardware is present or it has
1621 been disabled with 'nofpu', then the settings of
1622 'legacy' and '2008' strap the emulator accordingly,
1623 'relaxed' straps the emulator for both legacy-NaN and
1624 2008-NaN, whereas 'strict' enables legacy-NaN only on
1625 legacy processors and both NaN encodings on MIPS32 or
1626 MIPS64 CPUs.
1628 The setting for ABS.fmt/NEG.fmt instruction execution
1629 mode generally follows that for the NaN encoding,
1630 except where unsupported by hardware.
1632 ignore_loglevel [KNL]
1633 Ignore loglevel setting - this will print /all/
1634 kernel messages to the console. Useful for debugging.
1635 We also add it as printk module parameter, so users
1636 could change it dynamically, usually by
1637 /sys/module/printk/parameters/ignore_loglevel.
1639 ignore_rlimit_data
1640 Ignore RLIMIT_DATA setting for data mappings,
1641 print warning at first misuse. Can be changed via
1642 /sys/module/kernel/parameters/ignore_rlimit_data.
1644 ihash_entries= [KNL]
1645 Set number of hash buckets for inode cache.
1647 ima_appraise= [IMA] appraise integrity measurements
1648 Format: { "off" | "enforce" | "fix" | "log" }
1649 default: "enforce"
1651 ima_appraise_tcb [IMA]
1652 The builtin appraise policy appraises all files
1653 owned by uid=0.
1655 ima_hash= [IMA]
1656 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1657 | sha512 | ... }
1658 default: "sha1"
1660 The list of supported hash algorithms is defined
1661 in crypto/hash_info.h.
1663 ima_policy= [IMA]
1664 The builtin measurement policy to load during IMA
1665 setup. Specyfing "tcb" as the value, measures all
1666 programs exec'd, files mmap'd for exec, and all files
1667 opened with the read mode bit set by either the
1668 effective uid (euid=0) or uid=0.
1669 Format: "tcb"
1671 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1672 Load a policy which meets the needs of the Trusted
1673 Computing Base. This means IMA will measure all
1674 programs exec'd, files mmap'd for exec, and all files
1675 opened for read by uid=0.
1677 ima_template= [IMA]
1678 Select one of defined IMA measurements template formats.
1679 Formats: { "ima" | "ima-ng" | "ima-sig" }
1680 Default: "ima-ng"
1682 ima_template_fmt=
1683 [IMA] Define a custom template format.
1684 Format: { "field1|...|fieldN" }
1686 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1687 Format: <min_file_size>
1688 Set the minimal file size for using asynchronous hash.
1689 If left unspecified, ahash usage is disabled.
1691 ahash performance varies for different data sizes on
1692 different crypto accelerators. This option can be used
1693 to achieve the best performance for a particular HW.
1695 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1696 Format: <bufsize>
1697 Set hashing buffer size. Default: 4k.
1699 ahash performance varies for different chunk sizes on
1700 different crypto accelerators. This option can be used
1701 to achieve best performance for particular HW.
1703 init= [KNL]
1704 Format: <full_path>
1705 Run specified binary instead of /sbin/init as init
1706 process.
1708 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1709 for working out where the kernel is dying during
1710 startup.
1712 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1713 initcall functions. Useful for debugging built-in
1714 modules and initcalls.
1716 initrd= [BOOT] Specify the location of the initial ramdisk
1718 init_pkru= [x86] Specify the default memory protection keys rights
1719 register contents for all processes. 0x55555554 by
1720 default (disallow access to all but pkey 0). Can
1721 override in debugfs after boot.
1723 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1724 Format: <irq>
1726 int_pln_enable [x86] Enable power limit notification interrupt
1728 integrity_audit=[IMA]
1729 Format: { "0" | "1" }
1730 0 -- basic integrity auditing messages. (Default)
1731 1 -- additional integrity auditing messages.
1733 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1734 on
1735 Enable intel iommu driver.
1736 off
1737 Disable intel iommu driver.
1738 igfx_off [Default Off]
1739 By default, gfx is mapped as normal device. If a gfx
1740 device has a dedicated DMAR unit, the DMAR unit is
1741 bypassed by not enabling DMAR with this option. In
1742 this case, gfx device will use physical address for
1743 DMA.
1744 forcedac [x86_64]
1745 With this option iommu will not optimize to look
1746 for io virtual address below 32-bit forcing dual
1747 address cycle on pci bus for cards supporting greater
1748 than 32-bit addressing. The default is to look
1749 for translation below 32-bit and if not available
1750 then look in the higher range.
1751 strict [Default Off]
1752 With this option on every unmap_single operation will
1753 result in a hardware IOTLB flush operation as opposed
1754 to batching them for performance.
1755 sp_off [Default Off]
1756 By default, super page will be supported if Intel IOMMU
1757 has the capability. With this option, super page will
1758 not be supported.
1759 ecs_off [Default Off]
1760 By default, extended context tables will be supported if
1761 the hardware advertises that it has support both for the
1762 extended tables themselves, and also PASID support. With
1763 this option set, extended tables will not be used even
1764 on hardware which claims to support them.
1766 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1767 0 disables intel_idle and fall back on acpi_idle.
1768 1 to 9 specify maximum depth of C-state.
1770 intel_pstate= [X86]
1771 disable
1772 Do not enable intel_pstate as the default
1773 scaling driver for the supported processors
1774 force
1775 Enable intel_pstate on systems that prohibit it by default
1776 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1777 instead of acpi-cpufreq may disable platform features, such
1778 as thermal controls and power capping, that rely on ACPI
1779 P-States information being indicated to OSPM and therefore
1780 should be used with caution. This option does not work with
1781 processors that aren't supported by the intel_pstate driver
1782 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1783 no_hwp
1784 Do not enable hardware P state control (HWP)
1785 if available.
1786 hwp_only
1787 Only load intel_pstate on systems which support
1788 hardware P state control (HWP) if available.
1789 support_acpi_ppc
1790 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1791 Description Table, specifies preferred power management
1792 profile as "Enterprise Server" or "Performance Server",
1793 then this feature is turned on by default.
1795 intremap= [X86-64, Intel-IOMMU]
1796 on enable Interrupt Remapping (default)
1797 off disable Interrupt Remapping
1798 nosid disable Source ID checking
1799 no_x2apic_optout
1800 BIOS x2APIC opt-out request will be ignored
1801 nopost disable Interrupt Posting
1803 iomem= Disable strict checking of access to MMIO memory
1804 strict regions from userspace.
1805 relaxed
1807 iommu= [x86]
1808 off
1809 force
1810 noforce
1811 biomerge
1812 panic
1813 nopanic
1814 merge
1815 nomerge
1816 forcesac
1817 soft
1818 pt [x86, IA-64]
1819 nobypass [PPC/POWERNV]
1820 Disable IOMMU bypass, using IOMMU for PCI devices.
1823 io7= [HW] IO7 for Marvel based alpha systems
1824 See comment before marvel_specify_io7 in
1825 arch/alpha/kernel/core_marvel.c.
1827 io_delay= [X86] I/O delay method
1828 0x80
1829 Standard port 0x80 based delay
1830 0xed
1831 Alternate port 0xed based delay (needed on some systems)
1832 udelay
1833 Simple two microseconds delay
1834 none
1835 No delay
1837 ip= [IP_PNP]
1838 See Documentation/filesystems/nfs/nfsroot.txt.
1840 irqaffinity= [SMP] Set the default irq affinity mask
1841 The argument is a cpu list, as described above.
1843 irqfixup [HW]
1844 When an interrupt is not handled search all handlers
1845 for it. Intended to get systems with badly broken
1846 firmware running.
1848 irqpoll [HW]
1849 When an interrupt is not handled search all handlers
1850 for it. Also check all handlers each timer
1851 interrupt. Intended to get systems with badly broken
1852 firmware running.
1854 isapnp= [ISAPNP]
1855 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1857 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1858 The argument is a cpu list, as described above.
1860 This option can be used to specify one or more CPUs
1861 to isolate from the general SMP balancing and scheduling
1862 algorithms. You can move a process onto or off an
1863 "isolated" CPU via the CPU affinity syscalls or cpuset.
1864 <cpu number> begins at 0 and the maximum value is
1865 "number of CPUs in system - 1".
1867 This option is the preferred way to isolate CPUs. The
1868 alternative -- manually setting the CPU mask of all
1869 tasks in the system -- can cause problems and
1870 suboptimal load balancer performance.
1872 iucv= [HW,NET]
1874 ivrs_ioapic [HW,X86_64]
1875 Provide an override to the IOAPIC-ID<->DEVICE-ID
1876 mapping provided in the IVRS ACPI table. For
1877 example, to map IOAPIC-ID decimal 10 to
1878 PCI device 00:14.0 write the parameter as:
1879 ivrs_ioapic[10]=00:14.0
1881 ivrs_hpet [HW,X86_64]
1882 Provide an override to the HPET-ID<->DEVICE-ID
1883 mapping provided in the IVRS ACPI table. For
1884 example, to map HPET-ID decimal 0 to
1885 PCI device 00:14.0 write the parameter as:
1886 ivrs_hpet[0]=00:14.0
1888 ivrs_acpihid [HW,X86_64]
1889 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1890 mapping provided in the IVRS ACPI table. For
1891 example, to map UART-HID:UID AMD0020:0 to
1892 PCI device 00:14.5 write the parameter as:
1893 ivrs_acpihid[00:14.5]=AMD0020:0
1895 js= [HW,JOY] Analog joystick
1896 See Documentation/input/joystick.txt.
1898 nokaslr [KNL]
1899 When CONFIG_RANDOMIZE_BASE is set, this disables
1900 kernel and module base offset ASLR (Address Space
1901 Layout Randomization).
1903 keepinitrd [HW,ARM]
1905 kernelcore= [KNL,X86,IA-64,PPC]
1906 Format: nn[KMGTPE] | "mirror"
1907 This parameter
1908 specifies the amount of memory usable by the kernel
1909 for non-movable allocations. The requested amount is
1910 spread evenly throughout all nodes in the system. The
1911 remaining memory in each node is used for Movable
1912 pages. In the event, a node is too small to have both
1913 kernelcore and Movable pages, kernelcore pages will
1914 take priority and other nodes will have a larger number
1915 of Movable pages. The Movable zone is used for the
1916 allocation of pages that may be reclaimed or moved
1917 by the page migration subsystem. This means that
1918 HugeTLB pages may not be allocated from this zone.
1919 Note that allocations like PTEs-from-HighMem still
1920 use the HighMem zone if it exists, and the Normal
1921 zone if it does not.
1923 Instead of specifying the amount of memory (nn[KMGTPE]),
1924 you can specify "mirror" option. In case "mirror"
1925 option is specified, mirrored (reliable) memory is used
1926 for non-movable allocations and remaining memory is used
1927 for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1928 so you can NOT specify nn[KMGTPE] and "mirror" at the same
1929 time.
1931 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1932 Format: <Controller#>[,poll interval]
1933 The controller # is the number of the ehci usb debug
1934 port as it is probed via PCI. The poll interval is
1935 optional and is the number seconds in between
1936 each poll cycle to the debug port in case you need
1937 the functionality for interrupting the kernel with
1938 gdb or control-c on the dbgp connection. When
1939 not using this parameter you use sysrq-g to break into
1940 the kernel debugger.
1942 kgdboc= [KGDB,HW] kgdb over consoles.
1943 Requires a tty driver that supports console polling,
1944 or a supported polling keyboard driver (non-usb).
1945 Serial only format: <serial_device>[,baud]
1946 keyboard only format: kbd
1947 keyboard and serial format: kbd,<serial_device>[,baud]
1948 Optional Kernel mode setting:
1949 kms, kbd format: kms,kbd
1950 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1952 kgdbwait [KGDB] Stop kernel execution and enter the
1953 kernel debugger at the earliest opportunity.
1955 kmac= [MIPS] korina ethernet MAC address.
1956 Configure the RouterBoard 532 series on-chip
1957 Ethernet adapter MAC address.
1959 kmemleak= [KNL] Boot-time kmemleak enable/disable
1960 Valid arguments: on, off
1961 Default: on
1962 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1963 the default is off.
1965 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1966 Valid arguments: 0, 1, 2
1967 kmemcheck=0 (disabled)
1968 kmemcheck=1 (enabled)
1969 kmemcheck=2 (one-shot mode)
1970 Default: 2 (one-shot mode)
1972 kpti= [ARM64] Control page table isolation of user
1973 and kernel address spaces.
1974 Default: enabled on cores which need mitigation.
1975 0: force disabled
1976 1: force enabled
1978 kstack=N [X86] Print N words from the kernel stack
1979 in oops dumps.
1981 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1982 Default is 0 (don't ignore, but inject #GP)
1984 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1985 KVM MMU at runtime.
1986 Default is 0 (off)
1988 kvm.nx_huge_pages=
1989 [KVM] Controls the software workaround for the
1990 X86_BUG_ITLB_MULTIHIT bug.
1991 force : Always deploy workaround.
1992 off : Never deploy workaround.
1993 auto : Deploy workaround based on the presence of
1994 X86_BUG_ITLB_MULTIHIT.
1996 Default is 'auto'.
1998 If the software workaround is enabled for the host,
1999 guests do need not to enable it for nested guests.
2001 kvm.nx_huge_pages_recovery_ratio=
2002 [KVM] Controls how many 4KiB pages are periodically zapped
2003 back to huge pages. 0 disables the recovery, otherwise if
2004 the value is N KVM will zap 1/Nth of the 4KiB pages every
2005 minute. The default is 60.
2007 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2008 Default is 1 (enabled)
2010 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2011 for all guests.
2012 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2014 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2015 (virtualized MMU) support on capable Intel chips.
2016 Default is 1 (enabled)
2018 kvm-intel.emulate_invalid_guest_state=
2019 [KVM,Intel] Enable emulation of invalid guest states
2020 Default is 0 (disabled)
2022 kvm-intel.flexpriority=
2023 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2024 Default is 1 (enabled)
2026 kvm-intel.nested=
2027 [KVM,Intel] Enable VMX nesting (nVMX).
2028 Default is 0 (disabled)
2030 kvm-intel.unrestricted_guest=
2031 [KVM,Intel] Disable unrestricted guest feature
2032 (virtualized real and unpaged mode) on capable
2033 Intel chips. Default is 1 (enabled)
2035 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2036 CVE-2018-3620.
2038 Valid arguments: never, cond, always
2040 always: L1D cache flush on every VMENTER.
2041 cond: Flush L1D on VMENTER only when the code between
2042 VMEXIT and VMENTER can leak host memory.
2043 never: Disables the mitigation
2045 Default is cond (do L1 cache flush in specific instances)
2047 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2048 feature (tagged TLBs) on capable Intel chips.
2049 Default is 1 (enabled)
2051 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2052 affected CPUs
2054 The kernel PTE inversion protection is unconditionally
2055 enabled and cannot be disabled.
2057 full
2058 Provides all available mitigations for the
2059 L1TF vulnerability. Disables SMT and
2060 enables all mitigations in the
2061 hypervisors, i.e. unconditional L1D flush.
2063 SMT control and L1D flush control via the
2064 sysfs interface is still possible after
2065 boot. Hypervisors will issue a warning
2066 when the first VM is started in a
2067 potentially insecure configuration,
2068 i.e. SMT enabled or L1D flush disabled.
2070 full,force
2071 Same as 'full', but disables SMT and L1D
2072 flush runtime control. Implies the
2073 'nosmt=force' command line option.
2074 (i.e. sysfs control of SMT is disabled.)
2076 flush
2077 Leaves SMT enabled and enables the default
2078 hypervisor mitigation, i.e. conditional
2079 L1D flush.
2081 SMT control and L1D flush control via the
2082 sysfs interface is still possible after
2083 boot. Hypervisors will issue a warning
2084 when the first VM is started in a
2085 potentially insecure configuration,
2086 i.e. SMT enabled or L1D flush disabled.
2088 flush,nosmt
2090 Disables SMT and enables the default
2091 hypervisor mitigation.
2093 SMT control and L1D flush control via the
2094 sysfs interface is still possible after
2095 boot. Hypervisors will issue a warning
2096 when the first VM is started in a
2097 potentially insecure configuration,
2098 i.e. SMT enabled or L1D flush disabled.
2100 flush,nowarn
2101 Same as 'flush', but hypervisors will not
2102 warn when a VM is started in a potentially
2103 insecure configuration.
2105 off
2106 Disables hypervisor mitigations and doesn't
2107 emit any warnings.
2108 It also drops the swap size and available
2109 RAM limit restriction on both hypervisor and
2110 bare metal.
2112 Default is 'flush'.
2114 For details see: Documentation/hw-vuln/l1tf.rst
2116 l2cr= [PPC]
2118 l3cr= [PPC]
2120 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2121 disabled it.
2123 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2124 value for LAPIC timer one-shot implementation. Default
2125 back to the programmable timer unit in the LAPIC.
2127 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2128 in C2 power state.
2130 libata.dma= [LIBATA] DMA control
2131 libata.dma=0 Disable all PATA and SATA DMA
2132 libata.dma=1 PATA and SATA Disk DMA only
2133 libata.dma=2 ATAPI (CDROM) DMA only
2134 libata.dma=4 Compact Flash DMA only
2135 Combinations also work, so libata.dma=3 enables DMA
2136 for disks and CDROMs, but not CFs.
2138 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2139 libata.ignore_hpa=0 keep BIOS limits (default)
2140 libata.ignore_hpa=1 ignore limits, using full disk
2142 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2143 when set.
2144 Format: <int>
2146 libata.force= [LIBATA] Force configurations. The format is comma
2147 separated list of "[ID:]VAL" where ID is
2148 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2149 matching port, link or device. Basically, it matches
2150 the ATA ID string printed on console by libata. If
2151 the whole ID part is omitted, the last PORT and DEVICE
2152 values are used. If ID hasn't been specified yet, the
2153 configuration applies to all ports, links and devices.
2155 If only DEVICE is omitted, the parameter applies to
2156 the port and all links and devices behind it. DEVICE
2157 number of 0 either selects the first device or the
2158 first fan-out link behind PMP device. It does not
2159 select the host link. DEVICE number of 15 selects the
2160 host link and device attached to it.
2162 The VAL specifies the configuration to force. As long
2163 as there's no ambiguity shortcut notation is allowed.
2164 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2165 The following configurations can be forced.
2167 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2168 Any ID with matching PORT is used.
2170 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2172 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2173 udma[/][16,25,33,44,66,100,133] notation is also
2174 allowed.
2176 * [no]ncq: Turn on or off NCQ.
2178 * [no]ncqtrim: Turn off queued DSM TRIM.
2180 * nohrst, nosrst, norst: suppress hard, soft
2181 and both resets.
2183 * rstonce: only attempt one reset during
2184 hot-unplug link recovery
2186 * dump_id: dump IDENTIFY data.
2188 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2190 * disable: Disable this device.
2192 If there are multiple matching configurations changing
2193 the same attribute, the last one is used.
2195 memblock=debug [KNL] Enable memblock debug messages.
2197 load_ramdisk= [RAM] List of ramdisks to load from floppy
2198 See Documentation/blockdev/ramdisk.txt.
2200 lockd.nlm_grace_period=P [NFS] Assign grace period.
2201 Format: <integer>
2203 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2204 Format: <integer>
2206 lockd.nlm_timeout=T [NFS] Assign timeout value.
2207 Format: <integer>
2209 lockd.nlm_udpport=M [NFS] Assign UDP port.
2210 Format: <integer>
2212 locktorture.nreaders_stress= [KNL]
2213 Set the number of locking read-acquisition kthreads.
2214 Defaults to being automatically set based on the
2215 number of online CPUs.
2217 locktorture.nwriters_stress= [KNL]
2218 Set the number of locking write-acquisition kthreads.
2220 locktorture.onoff_holdoff= [KNL]
2221 Set time (s) after boot for CPU-hotplug testing.
2223 locktorture.onoff_interval= [KNL]
2224 Set time (s) between CPU-hotplug operations, or
2225 zero to disable CPU-hotplug testing.
2227 locktorture.shuffle_interval= [KNL]
2228 Set task-shuffle interval (jiffies). Shuffling
2229 tasks allows some CPUs to go into dyntick-idle
2230 mode during the locktorture test.
2232 locktorture.shutdown_secs= [KNL]
2233 Set time (s) after boot system shutdown. This
2234 is useful for hands-off automated testing.
2236 locktorture.stat_interval= [KNL]
2237 Time (s) between statistics printk()s.
2239 locktorture.stutter= [KNL]
2240 Time (s) to stutter testing, for example,
2241 specifying five seconds causes the test to run for
2242 five seconds, wait for five seconds, and so on.
2243 This tests the locking primitive's ability to
2244 transition abruptly to and from idle.
2246 locktorture.torture_runnable= [BOOT]
2247 Start locktorture running at boot time.
2249 locktorture.torture_type= [KNL]
2250 Specify the locking implementation to test.
2252 locktorture.verbose= [KNL]
2253 Enable additional printk() statements.
2255 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2256 Format: <irq>
2258 loglevel= All Kernel Messages with a loglevel smaller than the
2259 console loglevel will be printed to the console. It can
2260 also be changed with klogd or other programs. The
2261 loglevels are defined as follows:
2263 0 (KERN_EMERG) system is unusable
2264 1 (KERN_ALERT) action must be taken immediately
2265 2 (KERN_CRIT) critical conditions
2266 3 (KERN_ERR) error conditions
2267 4 (KERN_WARNING) warning conditions
2268 5 (KERN_NOTICE) normal but significant condition
2269 6 (KERN_INFO) informational
2270 7 (KERN_DEBUG) debug-level messages
2272 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2273 in bytes. n must be a power of two and greater
2274 than the minimal size. The minimal size is defined
2275 by LOG_BUF_SHIFT kernel config parameter. There is
2276 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2277 that allows to increase the default size depending on
2278 the number of CPUs. See init/Kconfig for more details.
2280 logo.nologo [FB] Disables display of the built-in Linux logo.
2281 This may be used to provide more screen space for
2282 kernel log messages and is useful when debugging
2283 kernel boot problems.
2285 lp=0 [LP] Specify parallel ports to use, e.g,
2286 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2287 lp=reset first parallel port). 'lp=0' disables the
2288 lp=auto printer driver. 'lp=reset' (which can be
2289 specified in addition to the ports) causes
2290 attached printers to be reset. Using
2291 lp=port1,port2,... specifies the parallel ports
2292 to associate lp devices with, starting with
2293 lp0. A port specification may be 'none' to skip
2294 that lp device, or a parport name such as
2295 'parport0'. Specifying 'lp=auto' instead of a
2296 port specification list means that device IDs
2297 from each port should be examined, to see if
2298 an IEEE 1284-compliant printer is attached; if
2299 so, the driver will manage that printer.
2300 See also header of drivers/char/lp.c.
2302 lpj=n [KNL]
2303 Sets loops_per_jiffy to given constant, thus avoiding
2304 time-consuming boot-time autodetection (up to 250 ms per
2305 CPU). 0 enables autodetection (default). To determine
2306 the correct value for your kernel, boot with normal
2307 autodetection and see what value is printed. Note that
2308 on SMP systems the preset will be applied to all CPUs,
2309 which is likely to cause problems if your CPUs need
2310 significantly divergent settings. An incorrect value
2311 will cause delays in the kernel to be wrong, leading to
2312 unpredictable I/O errors and other breakage. Although
2313 unlikely, in the extreme case this might damage your
2314 hardware.
2316 ltpc= [NET]
2317 Format: <io>,<irq>,<dma>
2319 machvec= [IA-64] Force the use of a particular machine-vector
2320 (machvec) in a generic kernel.
2321 Example: machvec=hpzx1_swiotlb
2323 machtype= [Loongson] Share the same kernel image file between different
2324 yeeloong laptop.
2325 Example: machtype=lemote-yeeloong-2f-7inch
2327 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2328 than or equal to this physical address is ignored.
2330 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2331 will bring up during bootup. maxcpus=n : n >= 0 limits
2332 the kernel to bring up 'n' processors. Surely after
2333 bootup you can bring up the other plugged cpu by executing
2334 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2335 only takes effect during system bootup.
2336 While n=0 is a special case, it is equivalent to "nosmp",
2337 which also disables the IO APIC.
2339 max_loop= [LOOP] The number of loop block devices that get
2340 (loop.max_loop) unconditionally pre-created at init time. The default
2341 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2342 of statically allocating a predefined number, loop
2343 devices can be requested on-demand with the
2344 /dev/loop-control interface.
2346 mce [X86-32] Machine Check Exception
2348 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2350 md= [HW] RAID subsystems devices and level
2351 See Documentation/md.txt.
2353 mdacon= [MDA]
2354 Format: <first>,<last>
2355 Specifies range of consoles to be captured by the MDA.
2357 mds= [X86,INTEL]
2358 Control mitigation for the Micro-architectural Data
2359 Sampling (MDS) vulnerability.
2361 Certain CPUs are vulnerable to an exploit against CPU
2362 internal buffers which can forward information to a
2363 disclosure gadget under certain conditions.
2365 In vulnerable processors, the speculatively
2366 forwarded data can be used in a cache side channel
2367 attack, to access data to which the attacker does
2368 not have direct access.
2370 This parameter controls the MDS mitigation. The
2371 options are:
2373 full - Enable MDS mitigation on vulnerable CPUs
2374 full,nosmt - Enable MDS mitigation and disable
2375 SMT on vulnerable CPUs
2376 off - Unconditionally disable MDS mitigation
2378 On TAA-affected machines, mds=off can be prevented by
2379 an active TAA mitigation as both vulnerabilities are
2380 mitigated with the same mechanism so in order to disable
2381 this mitigation, you need to specify tsx_async_abort=off
2382 too.
2384 Not specifying this option is equivalent to
2385 mds=full.
2387 For details see: Documentation/hw-vuln/mds.rst
2389 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2390 Amount of memory to be used when the kernel is not able
2391 to see the whole system memory or for test.
2392 [X86] Work as limiting max address. Use together
2393 with memmap= to avoid physical address space collisions.
2394 Without memmap= PCI devices could be placed at addresses
2395 belonging to unused RAM.
2397 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2398 memory.
2400 memchunk=nn[KMG]
2401 [KNL,SH] Allow user to override the default size for
2402 per-device physically contiguous DMA buffers.
2404 memhp_default_state=online/offline
2405 [KNL] Set the initial state for the memory hotplug
2406 onlining policy. If not specified, the default value is
2407 set according to the
2408 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2409 option.
2410 See Documentation/memory-hotplug.txt.
2412 memmap=exactmap [KNL,X86] Enable setting of an exact
2413 E820 memory map, as specified by the user.
2414 Such memmap=exactmap lines can be constructed based on
2415 BIOS output or other requirements. See the memmap=nn@ss
2416 option description.
2418 memmap=nn[KMG]@ss[KMG]
2419 [KNL] Force usage of a specific region of memory.
2420 Region of memory to be used is from ss to ss+nn.
2422 memmap=nn[KMG]#ss[KMG]
2423 [KNL,ACPI] Mark specific memory as ACPI data.
2424 Region of memory to be marked is from ss to ss+nn.
2426 memmap=nn[KMG]$ss[KMG]
2427 [KNL,ACPI] Mark specific memory as reserved.
2428 Region of memory to be reserved is from ss to ss+nn.
2429 Example: Exclude memory from 0x18690000-0x1869ffff
2430 memmap=64K$0x18690000
2431 or
2432 memmap=0x10000$0x18690000
2434 memmap=nn[KMG]!ss[KMG]
2435 [KNL,X86] Mark specific memory as protected.
2436 Region of memory to be used, from ss to ss+nn.
2437 The memory region may be marked as e820 type 12 (0xc)
2438 and is NVDIMM or ADR memory.
2440 memory_corruption_check=0/1 [X86]
2441 Some BIOSes seem to corrupt the first 64k of
2442 memory when doing things like suspend/resume.
2443 Setting this option will scan the memory
2444 looking for corruption. Enabling this will
2445 both detect corruption and prevent the kernel
2446 from using the memory being corrupted.
2447 However, its intended as a diagnostic tool; if
2448 repeatable BIOS-originated corruption always
2449 affects the same memory, you can use memmap=
2450 to prevent the kernel from using that memory.
2452 memory_corruption_check_size=size [X86]
2453 By default it checks for corruption in the low
2454 64k, making this memory unavailable for normal
2455 use. Use this parameter to scan for
2456 corruption in more or less memory.
2458 memory_corruption_check_period=seconds [X86]
2459 By default it checks for corruption every 60
2460 seconds. Use this parameter to check at some
2461 other rate. 0 disables periodic checking.
2463 memtest= [KNL,X86,ARM] Enable memtest
2464 Format: <integer>
2465 default : 0 <disable>
2466 Specifies the number of memtest passes to be
2467 performed. Each pass selects another test
2468 pattern from a given set of patterns. Memtest
2469 fills the memory with this pattern, validates
2470 memory contents and reserves bad memory
2471 regions that are detected.
2473 meye.*= [HW] Set MotionEye Camera parameters
2474 See Documentation/video4linux/meye.txt.
2476 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2477 Multi-Function General Purpose Timers on AMD Geode
2478 platforms.
2480 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2481 the BIOS has incorrectly applied a workaround. TinyBIOS
2482 version 0.98 is known to be affected, 0.99 fixes the
2483 problem by letting the user disable the workaround.
2485 mga= [HW,DRM]
2487 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2488 physical address is ignored.
2490 mini2440= [ARM,HW,KNL]
2491 Format:[0..2][b][c][t]
2492 Default: "0tb"
2493 MINI2440 configuration specification:
2494 0 - The attached screen is the 3.5" TFT
2495 1 - The attached screen is the 7" TFT
2496 2 - The VGA Shield is attached (1024x768)
2497 Leaving out the screen size parameter will not load
2498 the TFT driver, and the framebuffer will be left
2499 unconfigured.
2500 b - Enable backlight. The TFT backlight pin will be
2501 linked to the kernel VESA blanking code and a GPIO
2502 LED. This parameter is not necessary when using the
2503 VGA shield.
2504 c - Enable the s3c camera interface.
2505 t - Reserved for enabling touchscreen support. The
2506 touchscreen support is not enabled in the mainstream
2507 kernel as of 2.6.30, a preliminary port can be found
2508 in the "bleeding edge" mini2440 support kernel at
2509 http://repo.or.cz/w/linux-2.6/mini2440.git
2511 mitigations=
2512 [X86] Control optional mitigations for CPU
2513 vulnerabilities. This is a set of curated,
2514 arch-independent options, each of which is an
2515 aggregation of existing arch-specific options.
2517 off
2518 Disable all optional CPU mitigations. This
2519 improves system performance, but it may also
2520 expose users to several CPU vulnerabilities.
2521 Equivalent to: nopti [X86]
2522 nospectre_v1 [X86]
2523 nospectre_v2 [X86]
2524 spectre_v2_user=off [X86]
2525 spec_store_bypass_disable=off [X86]
2526 l1tf=off [X86]
2527 mds=off [X86]
2528 tsx_async_abort=off [X86]
2529 kvm.nx_huge_pages=off [X86]
2531 Exceptions:
2532 This does not have any effect on
2533 kvm.nx_huge_pages when
2534 kvm.nx_huge_pages=force.
2536 auto (default)
2537 Mitigate all CPU vulnerabilities, but leave SMT
2538 enabled, even if it's vulnerable. This is for
2539 users who don't want to be surprised by SMT
2540 getting disabled across kernel upgrades, or who
2541 have other ways of avoiding SMT-based attacks.
2542 Equivalent to: (default behavior)
2544 auto,nosmt
2545 Mitigate all CPU vulnerabilities, disabling SMT
2546 if needed. This is for users who always want to
2547 be fully mitigated, even if it means losing SMT.
2548 Equivalent to: l1tf=flush,nosmt [X86]
2549 mds=full,nosmt [X86]
2550 tsx_async_abort=full,nosmt [X86]
2552 mminit_loglevel=
2553 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2554 parameter allows control of the logging verbosity for
2555 the additional memory initialisation checks. A value
2556 of 0 disables mminit logging and a level of 4 will
2557 log everything. Information is printed at KERN_DEBUG
2558 so loglevel=8 may also need to be specified.
2560 module.sig_enforce
2561 [KNL] When CONFIG_MODULE_SIG is set, this means that
2562 modules without (valid) signatures will fail to load.
2563 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2564 is always true, so this option does nothing.
2566 module_blacklist= [KNL] Do not load a comma-separated list of
2567 modules. Useful for debugging problem modules.
2569 mousedev.tap_time=
2570 [MOUSE] Maximum time between finger touching and
2571 leaving touchpad surface for touch to be considered
2572 a tap and be reported as a left button click (for
2573 touchpads working in absolute mode only).
2574 Format: <msecs>
2575 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2576 reporting absolute coordinates, such as tablets
2577 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2578 reporting absolute coordinates, such as tablets
2580 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
2581 is similar to kernelcore except it specifies the
2582 amount of memory used for migratable allocations.
2583 If both kernelcore and movablecore is specified,
2584 then kernelcore will be at *least* the specified
2585 value but may be more. If movablecore on its own
2586 is specified, the administrator must be careful
2587 that the amount of memory usable for all allocations
2588 is not too small.
2590 movable_node [KNL,X86] Boot-time switch to enable the effects
2591 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2593 MTD_Partition= [MTD]
2594 Format: <name>,<region-number>,<size>,<offset>
2596 MTD_Region= [MTD] Format:
2597 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2599 mtdparts= [MTD]
2600 See drivers/mtd/cmdlinepart.c.
2602 multitce=off [PPC] This parameter disables the use of the pSeries
2603 firmware feature for updating multiple TCE entries
2604 at a time.
2606 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2608 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2610 boundary - index of last SLC block on Flex-OneNAND.
2611 The remaining blocks are configured as MLC blocks.
2612 lock - Configure if Flex-OneNAND boundary should be locked.
2613 Once locked, the boundary cannot be changed.
2614 1 indicates lock status, 0 indicates unlock status.
2616 mtdset= [ARM]
2617 ARM/S3C2412 JIVE boot control
2619 See arch/arm/mach-s3c2412/mach-jive.c
2621 mtouchusb.raw_coordinates=
2622 [HW] Make the MicroTouch USB driver use raw coordinates
2623 ('y', default) or cooked coordinates ('n')
2625 mtrr_chunk_size=nn[KMG] [X86]
2626 used for mtrr cleanup. It is largest continuous chunk
2627 that could hold holes aka. UC entries.
2629 mtrr_gran_size=nn[KMG] [X86]
2630 Used for mtrr cleanup. It is granularity of mtrr block.
2631 Default is 1.
2632 Large value could prevent small alignment from
2633 using up MTRRs.
2635 mtrr_spare_reg_nr=n [X86]
2636 Format: <integer>
2637 Range: 0,7 : spare reg number
2638 Default : 1
2639 Used for mtrr cleanup. It is spare mtrr entries number.
2640 Set to 2 or more if your graphical card needs more.
2642 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2644 netdev= [NET] Network devices parameters
2645 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2646 Note that mem_start is often overloaded to mean
2647 something different and driver-specific.
2648 This usage is only documented in each driver source
2649 file if at all.
2651 nf_conntrack.acct=
2652 [NETFILTER] Enable connection tracking flow accounting
2653 0 to disable accounting
2654 1 to enable accounting
2655 Default value is 0.
2657 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2658 See Documentation/filesystems/nfs/nfsroot.txt.
2660 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2661 See Documentation/filesystems/nfs/nfsroot.txt.
2663 nfsrootdebug [NFS] enable nfsroot debugging messages.
2664 See Documentation/filesystems/nfs/nfsroot.txt.
2666 nfs.callback_nr_threads=
2667 [NFSv4] set the total number of threads that the
2668 NFS client will assign to service NFSv4 callback
2669 requests.
2671 nfs.callback_tcpport=
2672 [NFS] set the TCP port on which the NFSv4 callback
2673 channel should listen.
2675 nfs.cache_getent=
2676 [NFS] sets the pathname to the program which is used
2677 to update the NFS client cache entries.
2679 nfs.cache_getent_timeout=
2680 [NFS] sets the timeout after which an attempt to
2681 update a cache entry is deemed to have failed.
2683 nfs.idmap_cache_timeout=
2684 [NFS] set the maximum lifetime for idmapper cache
2685 entries.
2687 nfs.enable_ino64=
2688 [NFS] enable 64-bit inode numbers.
2689 If zero, the NFS client will fake up a 32-bit inode
2690 number for the readdir() and stat() syscalls instead
2691 of returning the full 64-bit number.
2692 The default is to return 64-bit inode numbers.
2694 nfs.max_session_cb_slots=
2695 [NFSv4.1] Sets the maximum number of session
2696 slots the client will assign to the callback
2697 channel. This determines the maximum number of
2698 callbacks the client will process in parallel for
2699 a particular server.
2701 nfs.max_session_slots=
2702 [NFSv4.1] Sets the maximum number of session slots
2703 the client will attempt to negotiate with the server.
2704 This limits the number of simultaneous RPC requests
2705 that the client can send to the NFSv4.1 server.
2706 Note that there is little point in setting this
2707 value higher than the max_tcp_slot_table_limit.
2709 nfs.nfs4_disable_idmapping=
2710 [NFSv4] When set to the default of '1', this option
2711 ensures that both the RPC level authentication
2712 scheme and the NFS level operations agree to use
2713 numeric uids/gids if the mount is using the
2714 'sec=sys' security flavour. In effect it is
2715 disabling idmapping, which can make migration from
2716 legacy NFSv2/v3 systems to NFSv4 easier.
2717 Servers that do not support this mode of operation
2718 will be autodetected by the client, and it will fall
2719 back to using the idmapper.
2720 To turn off this behaviour, set the value to '0'.
2721 nfs.nfs4_unique_id=
2722 [NFS4] Specify an additional fixed unique ident-
2723 ification string that NFSv4 clients can insert into
2724 their nfs_client_id4 string. This is typically a
2725 UUID that is generated at system install time.
2727 nfs.send_implementation_id =
2728 [NFSv4.1] Send client implementation identification
2729 information in exchange_id requests.
2730 If zero, no implementation identification information
2731 will be sent.
2732 The default is to send the implementation identification
2733 information.
2735 nfs.recover_lost_locks =
2736 [NFSv4] Attempt to recover locks that were lost due
2737 to a lease timeout on the server. Please note that
2738 doing this risks data corruption, since there are
2739 no guarantees that the file will remain unchanged
2740 after the locks are lost.
2741 If you want to enable the kernel legacy behaviour of
2742 attempting to recover these locks, then set this
2743 parameter to '1'.
2744 The default parameter value of '0' causes the kernel
2745 not to attempt recovery of lost locks.
2747 nfs4.layoutstats_timer =
2748 [NFSv4.2] Change the rate at which the kernel sends
2749 layoutstats to the pNFS metadata server.
2751 Setting this to value to 0 causes the kernel to use
2752 whatever value is the default set by the layout
2753 driver. A non-zero value sets the minimum interval
2754 in seconds between layoutstats transmissions.
2756 nfsd.nfs4_disable_idmapping=
2757 [NFSv4] When set to the default of '1', the NFSv4
2758 server will return only numeric uids and gids to
2759 clients using auth_sys, and will accept numeric uids
2760 and gids from such clients. This is intended to ease
2761 migration from NFSv2/v3.
2763 objlayoutdriver.osd_login_prog=
2764 [NFS] [OBJLAYOUT] sets the pathname to the program which
2765 is used to automatically discover and login into new
2766 osd-targets. Please see:
2767 Documentation/filesystems/pnfs.txt for more explanations
2769 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
2770 when a NMI is triggered.
2771 Format: [state][,regs][,debounce][,die]
2773 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2774 Format: [panic,][nopanic,][num]
2775 Valid num: 0 or 1
2776 0 - turn hardlockup detector in nmi_watchdog off
2777 1 - turn hardlockup detector in nmi_watchdog on
2778 When panic is specified, panic when an NMI watchdog
2779 timeout occurs (or 'nopanic' to override the opposite
2780 default). To disable both hard and soft lockup detectors,
2781 please see 'nowatchdog'.
2782 This is useful when you use a panic=... timeout and
2783 need the box quickly up again.
2785 netpoll.carrier_timeout=
2786 [NET] Specifies amount of time (in seconds) that
2787 netpoll should wait for a carrier. By default netpoll
2788 waits 4 seconds.
2790 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2791 emulation library even if a 387 maths coprocessor
2792 is present.
2794 no_console_suspend
2795 [HW] Never suspend the console
2796 Disable suspending of consoles during suspend and
2797 hibernate operations. Once disabled, debugging
2798 messages can reach various consoles while the rest
2799 of the system is being put to sleep (ie, while
2800 debugging driver suspend/resume hooks). This may
2801 not work reliably with all consoles, but is known
2802 to work with serial and VGA consoles.
2803 To facilitate more flexible debugging, we also add
2804 console_suspend, a printk module parameter to control
2805 it. Users could use console_suspend (usually
2806 /sys/module/printk/parameters/console_suspend) to
2807 turn on/off it dynamically.
2809 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2810 caches in the slab allocator. Saves per-node memory,
2811 but will impact performance.
2813 noalign [KNL,ARM]
2815 noaltinstr [S390] Disables alternative instructions patching
2816 (CPU alternatives feature).
2818 noapic [SMP,APIC] Tells the kernel to not make use of any
2819 IOAPICs that may be present in the system.
2821 noautogroup Disable scheduler automatic task group creation.
2823 nobats [PPC] Do not use BATs for mapping kernel lowmem
2824 on "Classic" PPC cores.
2826 nocache [ARM]
2828 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2830 nodelayacct [KNL] Disable per-task delay accounting
2832 nodsp [SH] Disable hardware DSP at boot time.
2834 noefi Disable EFI runtime services support.
2836 noexec [IA-64]
2838 noexec [X86]
2839 On X86-32 available only on PAE configured kernels.
2840 noexec=on: enable non-executable mappings (default)
2841 noexec=off: disable non-executable mappings
2843 nosmap [X86]
2844 Disable SMAP (Supervisor Mode Access Prevention)
2845 even if it is supported by processor.
2847 nosmep [X86]
2848 Disable SMEP (Supervisor Mode Execution Prevention)
2849 even if it is supported by processor.
2851 noexec32 [X86-64]
2852 This affects only 32-bit executables.
2853 noexec32=on: enable non-executable mappings (default)
2854 read doesn't imply executable mappings
2855 noexec32=off: disable non-executable mappings
2856 read implies executable mappings
2858 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2860 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2861 register save and restore. The kernel will only save
2862 legacy floating-point registers on task switch.
2864 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2866 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2867 Equivalent to smt=1.
2869 [KNL,x86] Disable symmetric multithreading (SMT).
2870 nosmt=force: Force disable SMT, cannot be undone
2871 via the sysfs control file.
2873 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
2874 (bounds check bypass). With this option data leaks are
2875 possible in the system.
2877 nospectre_v2 [X86,PPC_FSL_BOOK3E] Disable all mitigations for the Spectre variant 2
2878 (indirect branch prediction) vulnerability. System may
2879 allow data leaks with this option, which is equivalent
2880 to spectre_v2=off.
2882 nospec_store_bypass_disable
2883 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2885 noxsave [BUGS=X86] Disables x86 extended register state save
2886 and restore using xsave. The kernel will fallback to
2887 enabling legacy floating-point and sse state.
2889 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2890 register states. The kernel will fall back to use
2891 xsave to save the states. By using this parameter,
2892 performance of saving the states is degraded because
2893 xsave doesn't support modified optimization while
2894 xsaveopt supports it on xsaveopt enabled systems.
2896 noxsaves [X86] Disables xsaves and xrstors used in saving and
2897 restoring x86 extended register state in compacted
2898 form of xsave area. The kernel will fall back to use
2899 xsaveopt and xrstor to save and restore the states
2900 in standard form of xsave area. By using this
2901 parameter, xsave area per process might occupy more
2902 memory on xsaves enabled systems.
2904 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2905 wfi(ARM) instruction doesn't work correctly and not to
2906 use it. This is also useful when using JTAG debugger.
2908 no_file_caps Tells the kernel not to honor file capabilities. The
2909 only way then for a file to be executed with privilege
2910 is to be setuid root or executed by root.
2912 nohalt [IA-64] Tells the kernel not to use the power saving
2913 function PAL_HALT_LIGHT when idle. This increases
2914 power-consumption. On the positive side, it reduces
2915 interrupt wake-up latency, which may improve performance
2916 in certain environments such as networked servers or
2917 real-time systems.
2919 nohibernate [HIBERNATION] Disable hibernation and resume.
2921 nohz= [KNL] Boottime enable/disable dynamic ticks
2922 Valid arguments: on, off
2923 Default: on
2925 nohz_full= [KNL,BOOT]
2926 The argument is a cpu list, as described above.
2927 In kernels built with CONFIG_NO_HZ_FULL=y, set
2928 the specified list of CPUs whose tick will be stopped
2929 whenever possible. The boot CPU will be forced outside
2930 the range to maintain the timekeeping.
2931 The CPUs in this range must also be included in the
2932 rcu_nocbs= set.
2934 noiotrap [SH] Disables trapped I/O port accesses.
2936 noirqdebug [X86-32] Disables the code which attempts to detect and
2937 disable unhandled interrupt sources.
2939 no_timer_check [X86,APIC] Disables the code which tests for
2940 broken timer IRQ sources.
2942 noisapnp [ISAPNP] Disables ISA PnP code.
2944 noinitrd [RAM] Tells the kernel not to load any configured
2945 initial RAM disk.
2947 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2948 remapping.
2949 [Deprecated - use intremap=off]
2951 nointroute [IA-64]
2953 noinvpcid [X86] Disable the INVPCID cpu feature.
2955 nojitter [IA-64] Disables jitter checking for ITC timers.
2957 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2959 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2960 fault handling.
2962 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2963 steal time is computed, but won't influence scheduler
2964 behaviour
2966 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2968 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2970 noltlbs [PPC] Do not use large page/tlb entries for kernel
2971 lowmem mapping on PPC40x and PPC8xx
2973 nomca [IA-64] Disable machine check abort handling
2975 nomce [X86-32] Disable Machine Check Exception
2977 nomfgpt [X86-32] Disable Multi-Function General Purpose
2978 Timer usage (for AMD Geode machines).
2980 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2981 shutdown the other cpus. Instead use the REBOOT_VECTOR
2982 irq.
2984 nomodule Disable module load
2986 nopat [X86] Disable PAT (page attribute table extension of
2987 pagetables) support.
2989 nopcid [X86-64] Disable the PCID cpu feature.
2991 norandmaps Don't use address space randomization. Equivalent to
2992 echo 0 > /proc/sys/kernel/randomize_va_space
2994 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2995 with UP alternatives
2997 nordrand [X86] Disable kernel use of the RDRAND and
2998 RDSEED instructions even if they are supported
2999 by the processor. RDRAND and RDSEED are still
3000 available to user space applications.
3002 noresume [SWSUSP] Disables resume and restores original swap
3003 space.
3005 no-scroll [VGA] Disables scrollback.
3006 This is required for the Braillex ib80-piezo Braille
3007 reader made by F.H. Papenmeier (Germany).
3009 nosbagart [IA-64]
3011 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3013 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3014 and disable the IO APIC. legacy for "maxcpus=0".
3016 nosoftlockup [KNL] Disable the soft-lockup detector.
3018 nosync [HW,M68K] Disables sync negotiation for all devices.
3020 notsc [BUGS=X86-32] Disable Time Stamp Counter
3022 nowatchdog [KNL] Disable both lockup detectors, i.e.
3023 soft-lockup and NMI watchdog (hard-lockup).
3025 nowb [ARM]
3027 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3029 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3030 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3031 Some features depend on CPU0. Known dependencies are:
3032 1. Resume from suspend/hibernate depends on CPU0.
3033 Suspend/hibernate will fail if CPU0 is offline and you
3034 need to online CPU0 before suspend/hibernate.
3035 2. PIC interrupts also depend on CPU0. CPU0 can't be
3036 removed if a PIC interrupt is detected.
3037 It's said poweroff/reboot may depend on CPU0 on some
3038 machines although I haven't seen such issues so far
3039 after CPU0 is offline on a few tested machines.
3040 If the dependencies are under your control, you can
3041 turn on cpu0_hotplug.
3043 nptcg= [IA-64] Override max number of concurrent global TLB
3044 purges which is reported from either PAL_VM_SUMMARY or
3045 SAL PALO.
3047 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3048 could support. nr_cpus=n : n >= 1 limits the kernel to
3049 support 'n' processors. It could be larger than the
3050 number of already plugged CPU during bootup, later in
3051 runtime you can physically add extra cpu until it reaches
3052 n. So during boot up some boot time memory for per-cpu
3053 variables need be pre-allocated for later physical cpu
3054 hot plugging.
3056 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3058 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3059 Allowed values are enable and disable
3061 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3062 one of ['zone', 'node', 'default'] can be specified
3063 This can be set from sysctl after boot.
3064 See Documentation/sysctl/vm.txt for details.
3066 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3067 See Documentation/debugging-via-ohci1394.txt for more
3068 info.
3070 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3071 Rather than timing out after 20 ms if an EC
3072 command is not properly ACKed, override the length
3073 of the timeout. We have interrupts disabled while
3074 waiting for the ACK, so if this is set too high
3075 interrupts *may* be lost!
3077 omap_mux= [OMAP] Override bootloader pin multiplexing.
3078 Format: <mux_mode0.mode_name=value>...
3079 For example, to override I2C bus2:
3080 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3082 oprofile.timer= [HW]
3083 Use timer interrupt instead of performance counters
3085 oprofile.cpu_type= Force an oprofile cpu type
3086 This might be useful if you have an older oprofile
3087 userland or if you want common events.
3088 Format: { arch_perfmon }
3089 arch_perfmon: [X86] Force use of architectural
3090 perfmon on Intel CPUs instead of the
3091 CPU specific event set.
3092 timer: [X86] Force use of architectural NMI
3093 timer mode (see also oprofile.timer
3094 for generic hr timer mode)
3096 oops=panic Always panic on oopses. Default is to just kill the
3097 process, but there is a small probability of
3098 deadlocking the machine.
3099 This will also cause panics on machine check exceptions.
3100 Useful together with panic=30 to trigger a reboot.
3102 OSS [HW,OSS]
3103 See Documentation/sound/oss/oss-parameters.txt
3105 page_owner= [KNL] Boot-time page_owner enabling option.
3106 Storage of the information about who allocated
3107 each page is disabled in default. With this switch,
3108 we can turn it on.
3109 on: enable the feature
3111 page_poison= [KNL] Boot-time parameter changing the state of
3112 poisoning on the buddy allocator.
3113 off: turn off poisoning
3114 on: turn on poisoning
3116 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3117 timeout > 0: seconds before rebooting
3118 timeout = 0: wait forever
3119 timeout < 0: reboot immediately
3120 Format: <timeout>
3122 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3123 on a WARN().
3125 crash_kexec_post_notifiers
3126 Run kdump after running panic-notifiers and dumping
3127 kmsg. This only for the users who doubt kdump always
3128 succeeds in any situation.
3129 Note that this also increases risks of kdump failure,
3130 because some panic notifiers can make the crashed
3131 kernel more unstable.
3133 parkbd.port= [HW] Parallel port number the keyboard adapter is
3134 connected to, default is 0.
3135 Format: <parport#>
3136 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3137 0 for XT, 1 for AT (default is AT).
3138 Format: <mode>
3140 parport= [HW,PPT] Specify parallel ports. 0 disables.
3141 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3142 Use 'auto' to force the driver to use any
3143 IRQ/DMA settings detected (the default is to
3144 ignore detected IRQ/DMA settings because of
3145 possible conflicts). You can specify the base
3146 address, IRQ, and DMA settings; IRQ and DMA
3147 should be numbers, or 'auto' (for using detected
3148 settings on that particular port), or 'nofifo'
3149 (to avoid using a FIFO even if it is detected).
3150 Parallel ports are assigned in the order they
3151 are specified on the command line, starting
3152 with parport0.
3154 parport_init_mode= [HW,PPT]
3155 Configure VIA parallel port to operate in
3156 a specific mode. This is necessary on Pegasos
3157 computer where firmware has no options for setting
3158 up parallel port mode and sets it to spp.
3159 Currently this function knows 686a and 8231 chips.
3160 Format: [spp|ps2|epp|ecp|ecpepp]
3162 pause_on_oops=
3163 Halt all CPUs after the first oops has been printed for
3164 the specified number of seconds. This is to be used if
3165 your oopses keep scrolling off the screen.
3167 pcbit= [HW,ISDN]
3169 pcd. [PARIDE]
3170 See header of drivers/block/paride/pcd.c.
3171 See also Documentation/blockdev/paride.txt.
3173 pci=option[,option...] [PCI] various PCI subsystem options:
3174 earlydump [X86] dump PCI config space before the kernel
3175 changes anything
3176 off [X86] don't probe for the PCI bus
3177 bios [X86-32] force use of PCI BIOS, don't access
3178 the hardware directly. Use this if your machine
3179 has a non-standard PCI host bridge.
3180 nobios [X86-32] disallow use of PCI BIOS, only direct
3181 hardware access methods are allowed. Use this
3182 if you experience crashes upon bootup and you
3183 suspect they are caused by the BIOS.
3184 conf1 [X86] Force use of PCI Configuration Access
3185 Mechanism 1 (config address in IO port 0xCF8,
3186 data in IO port 0xCFC, both 32-bit).
3187 conf2 [X86] Force use of PCI Configuration Access
3188 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3189 the function, IO port 0xCFA, also 8-bit, sets
3190 bus number. The config space is then accessed
3191 through ports 0xC000-0xCFFF).
3192 See http://wiki.osdev.org/PCI for more info
3193 on the configuration access mechanisms.
3194 noaer [PCIE] If the PCIEAER kernel config parameter is
3195 enabled, this kernel boot option can be used to
3196 disable the use of PCIE advanced error reporting.
3197 nodomains [PCI] Disable support for multiple PCI
3198 root domains (aka PCI segments, in ACPI-speak).
3199 nommconf [X86] Disable use of MMCONFIG for PCI
3200 Configuration
3201 check_enable_amd_mmconf [X86] check for and enable
3202 properly configured MMIO access to PCI
3203 config space on AMD family 10h CPU
3204 nomsi [MSI] If the PCI_MSI kernel config parameter is
3205 enabled, this kernel boot option can be used to
3206 disable the use of MSI interrupts system-wide.
3207 noioapicquirk [APIC] Disable all boot interrupt quirks.
3208 Safety option to keep boot IRQs enabled. This
3209 should never be necessary.
3210 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3211 primary IO-APIC for bridges that cannot disable
3212 boot IRQs. This fixes a source of spurious IRQs
3213 when the system masks IRQs.
3214 noioapicreroute [APIC] Disable workaround that uses the
3215 boot IRQ equivalent of an IRQ that connects to
3216 a chipset where boot IRQs cannot be disabled.
3217 The opposite of ioapicreroute.
3218 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3219 routing table. These calls are known to be buggy
3220 on several machines and they hang the machine
3221 when used, but on other computers it's the only
3222 way to get the interrupt routing table. Try
3223 this option if the kernel is unable to allocate
3224 IRQs or discover secondary PCI buses on your
3225 motherboard.
3226 rom [X86] Assign address space to expansion ROMs.
3227 Use with caution as certain devices share
3228 address decoders between ROMs and other
3229 resources.
3230 norom [X86] Do not assign address space to
3231 expansion ROMs that do not already have
3232 BIOS assigned address ranges.
3233 nobar [X86] Do not assign address space to the
3234 BARs that weren't assigned by the BIOS.
3235 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3236 assigned automatically to PCI devices. You can
3237 make the kernel exclude IRQs of your ISA cards
3238 this way.
3239 pirqaddr=0xAAAAA [X86] Specify the physical address
3240 of the PIRQ table (normally generated
3241 by the BIOS) if it is outside the
3242 F0000h-100000h range.
3243 lastbus=N [X86] Scan all buses thru bus #N. Can be
3244 useful if the kernel is unable to find your
3245 secondary buses and you want to tell it
3246 explicitly which ones they are.
3247 assign-busses [X86] Always assign all PCI bus
3248 numbers ourselves, overriding
3249 whatever the firmware may have done.
3250 usepirqmask [X86] Honor the possible IRQ mask stored
3251 in the BIOS $PIR table. This is needed on
3252 some systems with broken BIOSes, notably
3253 some HP Pavilion N5400 and Omnibook XE3
3254 notebooks. This will have no effect if ACPI
3255 IRQ routing is enabled.
3256 noacpi [X86] Do not use ACPI for IRQ routing
3257 or for PCI scanning.
3258 use_crs [X86] Use PCI host bridge window information
3259 from ACPI. On BIOSes from 2008 or later, this
3260 is enabled by default. If you need to use this,
3261 please report a bug.
3262 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3263 If you need to use this, please report a bug.
3264 routeirq Do IRQ routing for all PCI devices.
3265 This is normally done in pci_enable_device(),
3266 so this option is a temporary workaround
3267 for broken drivers that don't call it.
3268 skip_isa_align [X86] do not align io start addr, so can
3269 handle more pci cards
3270 noearly [X86] Don't do any early type 1 scanning.
3271 This might help on some broken boards which
3272 machine check when some devices' config space
3273 is read. But various workarounds are disabled
3274 and some IOMMU drivers will not work.
3275 bfsort Sort PCI devices into breadth-first order.
3276 This sorting is done to get a device
3277 order compatible with older (<= 2.4) kernels.
3278 nobfsort Don't sort PCI devices into breadth-first order.
3279 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3280 tuning and use the BIOS-configured MPS defaults.
3281 pcie_bus_safe Set every device's MPS to the largest value
3282 supported by all devices below the root complex.
3283 pcie_bus_perf Set device MPS to the largest allowable MPS
3284 based on its parent bus. Also set MRRS (Max
3285 Read Request Size) to the largest supported
3286 value (no larger than the MPS that the device
3287 or bus can support) for best performance.
3288 pcie_bus_peer2peer Set every device's MPS to 128B, which
3289 every device is guaranteed to support. This
3290 configuration allows peer-to-peer DMA between
3291 any pair of devices, possibly at the cost of
3292 reduced performance. This also guarantees
3293 that hot-added devices will work.
3294 cbiosize=nn[KMG] The fixed amount of bus space which is
3295 reserved for the CardBus bridge's IO window.
3296 The default value is 256 bytes.
3297 cbmemsize=nn[KMG] The fixed amount of bus space which is
3298 reserved for the CardBus bridge's memory
3299 window. The default value is 64 megabytes.
3300 resource_alignment=
3301 Format:
3302 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3303 [<order of align>@]pci:<vendor>:<device>\
3304 [:<subvendor>:<subdevice>][; ...]
3305 Specifies alignment and device to reassign
3306 aligned memory resources.
3307 If <order of align> is not specified,
3308 PAGE_SIZE is used as alignment.
3309 PCI-PCI bridge can be specified, if resource
3310 windows need to be expanded.
3311 To specify the alignment for several
3312 instances of a device, the PCI vendor,
3313 device, subvendor, and subdevice may be
3314 specified, e.g., 4096@pci:8086:9c22:103c:198f
3315 ecrc= Enable/disable PCIe ECRC (transaction layer
3316 end-to-end CRC checking).
3317 bios: Use BIOS/firmware settings. This is the
3318 the default.
3319 off: Turn ECRC off
3320 on: Turn ECRC on.
3321 hpiosize=nn[KMG] The fixed amount of bus space which is
3322 reserved for hotplug bridge's IO window.
3323 Default size is 256 bytes.
3324 hpmemsize=nn[KMG] The fixed amount of bus space which is
3325 reserved for hotplug bridge's memory window.
3326 Default size is 2 megabytes.
3327 hpbussize=nn The minimum amount of additional bus numbers
3328 reserved for buses below a hotplug bridge.
3329 Default is 1.
3330 realloc= Enable/disable reallocating PCI bridge resources
3331 if allocations done by BIOS are too small to
3332 accommodate resources required by all child
3333 devices.
3334 off: Turn realloc off
3335 on: Turn realloc on
3336 realloc same as realloc=on
3337 noari do not use PCIe ARI.
3338 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3339 only look for one device below a PCIe downstream
3340 port.
3342 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3343 Management.
3344 off Disable ASPM.
3345 force Enable ASPM even on devices that claim not to support it.
3346 WARNING: Forcing ASPM on may cause system lockups.
3348 pcie_hp= [PCIE] PCI Express Hotplug driver options:
3349 nomsi Do not use MSI for PCI Express Native Hotplug (this
3350 makes all PCIe ports use INTx for hotplug services).
3352 pcie_ports= [PCIE] PCIe ports handling:
3353 auto Ask the BIOS whether or not to use native PCIe services
3354 associated with PCIe ports (PME, hot-plug, AER). Use
3355 them only if that is allowed by the BIOS.
3356 native Use native PCIe services associated with PCIe ports
3357 unconditionally.
3358 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3359 ports driver.
3361 pcie_port_pm= [PCIE] PCIe port power management handling:
3362 off Disable power management of all PCIe ports
3363 force Forcibly enable power management of all PCIe ports
3365 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3366 nomsi Do not use MSI for native PCIe PME signaling (this makes
3367 all PCIe root ports use INTx for all services).
3369 pcmv= [HW,PCMCIA] BadgePAD 4
3371 pd_ignore_unused
3372 [PM]
3373 Keep all power-domains already enabled by bootloader on,
3374 even if no driver has claimed them. This is useful
3375 for debug and development, but should not be
3376 needed on a platform with proper driver support.
3378 pd. [PARIDE]
3379 See Documentation/blockdev/paride.txt.
3381 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3382 boot time.
3383 Format: { 0 | 1 }
3384 See arch/parisc/kernel/pdc_chassis.c
3386 percpu_alloc= Select which percpu first chunk allocator to use.
3387 Currently supported values are "embed" and "page".
3388 Archs may support subset or none of the selections.
3389 See comments in mm/percpu.c for details on each
3390 allocator. This parameter is primarily for debugging
3391 and performance comparison.
3393 pf. [PARIDE]
3394 See Documentation/blockdev/paride.txt.
3396 pg. [PARIDE]
3397 See Documentation/blockdev/paride.txt.
3399 pirq= [SMP,APIC] Manual mp-table setup
3400 See Documentation/x86/i386/IO-APIC.txt.
3402 plip= [PPT,NET] Parallel port network link
3403 Format: { parport<nr> | timid | 0 }
3404 See also Documentation/parport.txt.
3406 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3407 Override pmtimer IOPort with a hex value.
3408 e.g. pmtmr=0x508
3410 pnp.debug=1 [PNP]
3411 Enable PNP debug messages (depends on the
3412 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3413 via /sys/module/pnp/parameters/debug. We always show
3414 current resource usage; turning this on also shows
3415 possible settings and some assignment information.
3417 pnpacpi= [ACPI]
3418 { off }
3420 pnpbios= [ISAPNP]
3421 { on | off | curr | res | no-curr | no-res }
3423 pnp_reserve_irq=
3424 [ISAPNP] Exclude IRQs for the autoconfiguration
3426 pnp_reserve_dma=
3427 [ISAPNP] Exclude DMAs for the autoconfiguration
3429 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3430 Ranges are in pairs (I/O port base and size).
3432 pnp_reserve_mem=
3433 [ISAPNP] Exclude memory regions for the
3434 autoconfiguration.
3435 Ranges are in pairs (memory base and size).
3437 ports= [IP_VS_FTP] IPVS ftp helper module
3438 Default is 21.
3439 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3440 may be specified.
3441 Format: <port>,<port>....
3443 ppc_strict_facility_enable
3444 [PPC] This option catches any kernel floating point,
3445 Altivec, VSX and SPE outside of regions specifically
3446 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3447 There is some performance impact when enabling this.
3449 print-fatal-signals=
3450 [KNL] debug: print fatal signals
3452 If enabled, warn about various signal handling
3453 related application anomalies: too many signals,
3454 too many POSIX.1 timers, fatal signals causing a
3455 coredump - etc.
3457 If you hit the warning due to signal overflow,
3458 you might want to try "ulimit -i unlimited".
3460 default: off.
3462 printk.always_kmsg_dump=
3463 Trigger kmsg_dump for cases other than kernel oops or
3464 panics
3465 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3466 default: disabled
3468 printk.devkmsg={on,off,ratelimit}
3469 Control writing to /dev/kmsg.
3470 on - unlimited logging to /dev/kmsg from userspace
3471 off - logging to /dev/kmsg disabled
3472 ratelimit - ratelimit the logging
3473 Default: ratelimit
3475 printk.time= Show timing data prefixed to each printk message line
3476 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3478 processor.max_cstate= [HW,ACPI]
3479 Limit processor to maximum C-state
3480 max_cstate=9 overrides any DMI blacklist limit.
3482 processor.nocst [HW,ACPI]
3483 Ignore the _CST method to determine C-states,
3484 instead using the legacy FADT method
3486 profile= [KNL] Enable kernel profiling via /proc/profile
3487 Format: [schedule,]<number>
3488 Param: "schedule" - profile schedule points.
3489 Param: <number> - step/bucket size as a power of 2 for
3490 statistical time based profiling.
3491 Param: "sleep" - profile D-state sleeping (millisecs).
3492 Requires CONFIG_SCHEDSTATS
3493 Param: "kvm" - profile VM exits.
3495 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3496 before loading.
3497 See Documentation/blockdev/ramdisk.txt.
3499 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3500 probe for; one of (bare|imps|exps|lifebook|any).
3501 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3502 per second.
3503 psmouse.resetafter= [HW,MOUSE]
3504 Try to reset the device after so many bad packets
3505 (0 = never).
3506 psmouse.resolution=
3507 [HW,MOUSE] Set desired mouse resolution, in dpi.
3508 psmouse.smartscroll=
3509 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3510 0 = disabled, 1 = enabled (default).
3512 pstore.backend= Specify the name of the pstore backend to use
3514 pt. [PARIDE]
3515 See Documentation/blockdev/paride.txt.
3517 pti= [X86_64] Control Page Table Isolation of user and
3518 kernel address spaces. Disabling this feature
3519 removes hardening, but improves performance of
3520 system calls and interrupts.
3522 on - unconditionally enable
3523 off - unconditionally disable
3524 auto - kernel detects whether your CPU model is
3525 vulnerable to issues that PTI mitigates
3527 Not specifying this option is equivalent to pti=auto.
3529 nopti [X86_64]
3530 Equivalent to pti=off
3532 pty.legacy_count=
3533 [KNL] Number of legacy pty's. Overwrites compiled-in
3534 default number.
3536 quiet [KNL] Disable most log messages
3538 r128= [HW,DRM]
3540 raid= [HW,RAID]
3541 See Documentation/md.txt.
3543 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3544 See Documentation/blockdev/ramdisk.txt.
3546 rcu_nocbs= [KNL]
3547 The argument is a cpu list, as described above.
3549 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3550 the specified list of CPUs to be no-callback CPUs.
3551 Invocation of these CPUs' RCU callbacks will
3552 be offloaded to "rcuox/N" kthreads created for
3553 that purpose, where "x" is "b" for RCU-bh, "p"
3554 for RCU-preempt, and "s" for RCU-sched, and "N"
3555 is the CPU number. This reduces OS jitter on the
3556 offloaded CPUs, which can be useful for HPC and
3557 real-time workloads. It can also improve energy
3558 efficiency for asymmetric multiprocessors.
3560 rcu_nocb_poll [KNL]
3561 Rather than requiring that offloaded CPUs
3562 (specified by rcu_nocbs= above) explicitly
3563 awaken the corresponding "rcuoN" kthreads,
3564 make these kthreads poll for callbacks.
3565 This improves the real-time response for the
3566 offloaded CPUs by relieving them of the need to
3567 wake up the corresponding kthread, but degrades
3568 energy efficiency by requiring that the kthreads
3569 periodically wake up to do the polling.
3571 rcutree.blimit= [KNL]
3572 Set maximum number of finished RCU callbacks to
3573 process in one batch.
3575 rcutree.dump_tree= [KNL]
3576 Dump the structure of the rcu_node combining tree
3577 out at early boot. This is used for diagnostic
3578 purposes, to verify correct tree setup.
3580 rcutree.gp_cleanup_delay= [KNL]
3581 Set the number of jiffies to delay each step of
3582 RCU grace-period cleanup. This only has effect
3583 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3585 rcutree.gp_init_delay= [KNL]
3586 Set the number of jiffies to delay each step of
3587 RCU grace-period initialization. This only has
3588 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3589 is set.
3591 rcutree.gp_preinit_delay= [KNL]
3592 Set the number of jiffies to delay each step of
3593 RCU grace-period pre-initialization, that is,
3594 the propagation of recent CPU-hotplug changes up
3595 the rcu_node combining tree. This only has effect
3596 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3598 rcutree.rcu_fanout_exact= [KNL]
3599 Disable autobalancing of the rcu_node combining
3600 tree. This is used by rcutorture, and might
3601 possibly be useful for architectures having high
3602 cache-to-cache transfer latencies.
3604 rcutree.rcu_fanout_leaf= [KNL]
3605 Change the number of CPUs assigned to each
3606 leaf rcu_node structure. Useful for very
3607 large systems, which will choose the value 64,
3608 and for NUMA systems with large remote-access
3609 latencies, which will choose a value aligned
3610 with the appropriate hardware boundaries.
3612 rcutree.jiffies_till_sched_qs= [KNL]
3613 Set required age in jiffies for a
3614 given grace period before RCU starts
3615 soliciting quiescent-state help from
3616 rcu_note_context_switch().
3618 rcutree.jiffies_till_first_fqs= [KNL]
3619 Set delay from grace-period initialization to
3620 first attempt to force quiescent states.
3621 Units are jiffies, minimum value is zero,
3622 and maximum value is HZ.
3624 rcutree.jiffies_till_next_fqs= [KNL]
3625 Set delay between subsequent attempts to force
3626 quiescent states. Units are jiffies, minimum
3627 value is one, and maximum value is HZ.
3629 rcutree.kthread_prio= [KNL,BOOT]
3630 Set the SCHED_FIFO priority of the RCU per-CPU
3631 kthreads (rcuc/N). This value is also used for
3632 the priority of the RCU boost threads (rcub/N)
3633 and for the RCU grace-period kthreads (rcu_bh,
3634 rcu_preempt, and rcu_sched). If RCU_BOOST is
3635 set, valid values are 1-99 and the default is 1
3636 (the least-favored priority). Otherwise, when
3637 RCU_BOOST is not set, valid values are 0-99 and
3638 the default is zero (non-realtime operation).
3640 rcutree.rcu_nocb_leader_stride= [KNL]
3641 Set the number of NOCB kthread groups, which
3642 defaults to the square root of the number of
3643 CPUs. Larger numbers reduces the wakeup overhead
3644 on the per-CPU grace-period kthreads, but increases
3645 that same overhead on each group's leader.
3647 rcutree.qhimark= [KNL]
3648 Set threshold of queued RCU callbacks beyond which
3649 batch limiting is disabled.
3651 rcutree.qlowmark= [KNL]
3652 Set threshold of queued RCU callbacks below which
3653 batch limiting is re-enabled.
3655 rcutree.rcu_idle_gp_delay= [KNL]
3656 Set wakeup interval for idle CPUs that have
3657 RCU callbacks (RCU_FAST_NO_HZ=y).
3659 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3660 Set wakeup interval for idle CPUs that have
3661 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3662 Lazy RCU callbacks are those which RCU can
3663 prove do nothing more than free memory.
3665 rcuperf.gp_exp= [KNL]
3666 Measure performance of expedited synchronous
3667 grace-period primitives.
3669 rcuperf.holdoff= [KNL]
3670 Set test-start holdoff period. The purpose of
3671 this parameter is to delay the start of the
3672 test until boot completes in order to avoid
3673 interference.
3675 rcuperf.nreaders= [KNL]
3676 Set number of RCU readers. The value -1 selects
3677 N, where N is the number of CPUs. A value
3678 "n" less than -1 selects N-n+1, where N is again
3679 the number of CPUs. For example, -2 selects N
3680 (the number of CPUs), -3 selects N+1, and so on.
3681 A value of "n" less than or equal to -N selects
3682 a single reader.
3684 rcuperf.nwriters= [KNL]
3685 Set number of RCU writers. The values operate
3686 the same as for rcuperf.nreaders.
3687 N, where N is the number of CPUs
3689 rcuperf.perf_runnable= [BOOT]
3690 Start rcuperf running at boot time.
3692 rcuperf.shutdown= [KNL]
3693 Shut the system down after performance tests
3694 complete. This is useful for hands-off automated
3695 testing.
3697 rcuperf.perf_type= [KNL]
3698 Specify the RCU implementation to test.
3700 rcuperf.verbose= [KNL]
3701 Enable additional printk() statements.
3703 rcutorture.cbflood_inter_holdoff= [KNL]
3704 Set holdoff time (jiffies) between successive
3705 callback-flood tests.
3707 rcutorture.cbflood_intra_holdoff= [KNL]
3708 Set holdoff time (jiffies) between successive
3709 bursts of callbacks within a given callback-flood
3710 test.
3712 rcutorture.cbflood_n_burst= [KNL]
3713 Set the number of bursts making up a given
3714 callback-flood test. Set this to zero to
3715 disable callback-flood testing.
3717 rcutorture.cbflood_n_per_burst= [KNL]
3718 Set the number of callbacks to be registered
3719 in a given burst of a callback-flood test.
3721 rcutorture.fqs_duration= [KNL]
3722 Set duration of force_quiescent_state bursts
3723 in microseconds.
3725 rcutorture.fqs_holdoff= [KNL]
3726 Set holdoff time within force_quiescent_state bursts
3727 in microseconds.
3729 rcutorture.fqs_stutter= [KNL]
3730 Set wait time between force_quiescent_state bursts
3731 in seconds.
3733 rcutorture.gp_cond= [KNL]
3734 Use conditional/asynchronous update-side
3735 primitives, if available.
3737 rcutorture.gp_exp= [KNL]
3738 Use expedited update-side primitives, if available.
3740 rcutorture.gp_normal= [KNL]
3741 Use normal (non-expedited) asynchronous
3742 update-side primitives, if available.
3744 rcutorture.gp_sync= [KNL]
3745 Use normal (non-expedited) synchronous
3746 update-side primitives, if available. If all
3747 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3748 rcutorture.gp_normal=, and rcutorture.gp_sync=
3749 are zero, rcutorture acts as if is interpreted
3750 they are all non-zero.
3752 rcutorture.n_barrier_cbs= [KNL]
3753 Set callbacks/threads for rcu_barrier() testing.
3755 rcutorture.nfakewriters= [KNL]
3756 Set number of concurrent RCU writers. These just
3757 stress RCU, they don't participate in the actual
3758 test, hence the "fake".
3760 rcutorture.nreaders= [KNL]
3761 Set number of RCU readers. The value -1 selects
3762 N-1, where N is the number of CPUs. A value
3763 "n" less than -1 selects N-n-2, where N is again
3764 the number of CPUs. For example, -2 selects N
3765 (the number of CPUs), -3 selects N+1, and so on.
3767 rcutorture.object_debug= [KNL]
3768 Enable debug-object double-call_rcu() testing.
3770 rcutorture.onoff_holdoff= [KNL]
3771 Set time (s) after boot for CPU-hotplug testing.
3773 rcutorture.onoff_interval= [KNL]
3774 Set time (s) between CPU-hotplug operations, or
3775 zero to disable CPU-hotplug testing.
3777 rcutorture.shuffle_interval= [KNL]
3778 Set task-shuffle interval (s). Shuffling tasks
3779 allows some CPUs to go into dyntick-idle mode
3780 during the rcutorture test.
3782 rcutorture.shutdown_secs= [KNL]
3783 Set time (s) after boot system shutdown. This
3784 is useful for hands-off automated testing.
3786 rcutorture.stall_cpu= [KNL]
3787 Duration of CPU stall (s) to test RCU CPU stall
3788 warnings, zero to disable.
3790 rcutorture.stall_cpu_holdoff= [KNL]
3791 Time to wait (s) after boot before inducing stall.
3793 rcutorture.stat_interval= [KNL]
3794 Time (s) between statistics printk()s.
3796 rcutorture.stutter= [KNL]
3797 Time (s) to stutter testing, for example, specifying
3798 five seconds causes the test to run for five seconds,
3799 wait for five seconds, and so on. This tests RCU's
3800 ability to transition abruptly to and from idle.
3802 rcutorture.test_boost= [KNL]
3803 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3804 "Maybe" means test if the RCU implementation
3805 under test support RCU priority boosting.
3807 rcutorture.test_boost_duration= [KNL]
3808 Duration (s) of each individual boost test.
3810 rcutorture.test_boost_interval= [KNL]
3811 Interval (s) between each boost test.
3813 rcutorture.test_no_idle_hz= [KNL]
3814 Test RCU's dyntick-idle handling. See also the
3815 rcutorture.shuffle_interval parameter.
3817 rcutorture.torture_runnable= [BOOT]
3818 Start rcutorture running at boot time.
3820 rcutorture.torture_type= [KNL]
3821 Specify the RCU implementation to test.
3823 rcutorture.verbose= [KNL]
3824 Enable additional printk() statements.
3826 rcupdate.rcu_cpu_stall_suppress= [KNL]
3827 Suppress RCU CPU stall warning messages.
3829 rcupdate.rcu_cpu_stall_timeout= [KNL]
3830 Set timeout for RCU CPU stall warning messages.
3832 rcupdate.rcu_expedited= [KNL]
3833 Use expedited grace-period primitives, for
3834 example, synchronize_rcu_expedited() instead
3835 of synchronize_rcu(). This reduces latency,
3836 but can increase CPU utilization, degrade
3837 real-time latency, and degrade energy efficiency.
3838 No effect on CONFIG_TINY_RCU kernels.
3840 rcupdate.rcu_normal= [KNL]
3841 Use only normal grace-period primitives,
3842 for example, synchronize_rcu() instead of
3843 synchronize_rcu_expedited(). This improves
3844 real-time latency, CPU utilization, and
3845 energy efficiency, but can expose users to
3846 increased grace-period latency. This parameter
3847 overrides rcupdate.rcu_expedited. No effect on
3848 CONFIG_TINY_RCU kernels.
3850 rcupdate.rcu_normal_after_boot= [KNL]
3851 Once boot has completed (that is, after
3852 rcu_end_inkernel_boot() has been invoked), use
3853 only normal grace-period primitives. No effect
3854 on CONFIG_TINY_RCU kernels.
3856 rcupdate.rcu_task_stall_timeout= [KNL]
3857 Set timeout in jiffies for RCU task stall warning
3858 messages. Disable with a value less than or equal
3859 to zero.
3861 rcupdate.rcu_self_test= [KNL]
3862 Run the RCU early boot self tests
3864 rcupdate.rcu_self_test_bh= [KNL]
3865 Run the RCU bh early boot self tests
3867 rcupdate.rcu_self_test_sched= [KNL]
3868 Run the RCU sched early boot self tests
3870 rdinit= [KNL]
3871 Format: <full_path>
3872 Run specified binary instead of /init from the ramdisk,
3873 used for early userspace startup. See initrd.
3875 rdrand= [X86]
3876 force - Override the decision by the kernel to hide the
3877 advertisement of RDRAND support (this affects
3878 certain AMD processors because of buggy BIOS
3879 support, specifically around the suspend/resume
3880 path).
3882 reboot= [KNL]
3883 Format (x86 or x86_64):
3884 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3885 [[,]s[mp]#### \
3886 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3887 [[,]f[orce]
3888 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3889 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3890 reboot_force is either force or not specified,
3891 reboot_cpu is s[mp]#### with #### being the processor
3892 to be used for rebooting.
3894 relax_domain_level=
3895 [KNL, SMP] Set scheduler's default relax_domain_level.
3896 See Documentation/cgroup-v1/cpusets.txt.
3898 relative_sleep_states=
3899 [SUSPEND] Use sleep state labeling where the deepest
3900 state available other than hibernation is always "mem".
3901 Format: { "0" | "1" }
3902 0 -- Traditional sleep state labels.
3903 1 -- Relative sleep state labels.
3905 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3907 reservetop= [X86-32]
3908 Format: nn[KMG]
3909 Reserves a hole at the top of the kernel virtual
3910 address space.
3912 reservelow= [X86]
3913 Format: nn[K]
3914 Set the amount of memory to reserve for BIOS at
3915 the bottom of the address space.
3917 reset_devices [KNL] Force drivers to reset the underlying device
3918 during initialization.
3920 resume= [SWSUSP]
3921 Specify the partition device for software suspend
3922 Format:
3923 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3925 resume_offset= [SWSUSP]
3926 Specify the offset from the beginning of the partition
3927 given by "resume=" at which the swap header is located,
3928 in <PAGE_SIZE> units (needed only for swap files).
3929 See Documentation/power/swsusp-and-swap-files.txt
3931 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3932 read the resume files
3934 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3935 Useful for devices that are detected asynchronously
3936 (e.g. USB and MMC devices).
3938 hibernate= [HIBERNATION]
3939 noresume Don't check if there's a hibernation image
3940 present during boot.
3941 nocompress Don't compress/decompress hibernation images.
3942 no Disable hibernation and resume.
3943 protect_image Turn on image protection during restoration
3944 (that will set all pages holding image data
3945 during restoration read-only).
3947 retain_initrd [RAM] Keep initrd memory after extraction
3949 rfkill.default_state=
3950 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3951 etc. communication is blocked by default.
3952 1 Unblocked.
3954 rfkill.master_switch_mode=
3955 0 The "airplane mode" button does nothing.
3956 1 The "airplane mode" button toggles between everything
3957 blocked and the previous configuration.
3958 2 The "airplane mode" button toggles between everything
3959 blocked and everything unblocked.
3961 rhash_entries= [KNL,NET]
3962 Set number of hash buckets for route cache
3964 ro [KNL] Mount root device read-only on boot
3966 rodata= [KNL]
3967 on Mark read-only kernel memory as read-only (default).
3968 off Leave read-only kernel memory writable for debugging.
3970 rockchip.usb_uart
3971 Enable the uart passthrough on the designated usb port
3972 on Rockchip SoCs. When active, the signals of the
3973 debug-uart get routed to the D+ and D- pins of the usb
3974 port and the regular usb controller gets disabled.
3976 root= [KNL] Root filesystem
3977 See name_to_dev_t comment in init/do_mounts.c.
3979 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3980 mount the root filesystem
3982 rootflags= [KNL] Set root filesystem mount option string
3984 rootfstype= [KNL] Set root filesystem type
3986 rootwait [KNL] Wait (indefinitely) for root device to show up.
3987 Useful for devices that are detected asynchronously
3988 (e.g. USB and MMC devices).
3990 rproc_mem=nn[KMG][@address]
3991 [KNL,ARM,CMA] Remoteproc physical memory block.
3992 Memory area to be used by remote processor image,
3993 managed by CMA.
3995 rw [KNL] Mount root device read-write on boot
3997 S [KNL] Run init in single mode
3999 s390_iommu= [HW,S390]
4000 Set s390 IOTLB flushing mode
4001 strict
4002 With strict flushing every unmap operation will result in
4003 an IOTLB flush. Default is lazy flushing before reuse,
4004 which is faster.
4006 sa1100ir [NET]
4007 See drivers/net/irda/sa1100_ir.c.
4009 sbni= [NET] Granch SBNI12 leased line adapter
4011 sched_debug [KNL] Enables verbose scheduler debug messages.
4013 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4014 Allowed values are enable and disable. This feature
4015 incurs a small amount of overhead in the scheduler
4016 but is useful for debugging and performance tuning.
4018 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4019 xtime_lock contention on larger systems, and/or RCU lock
4020 contention on all systems with CONFIG_MAXSMP set.
4021 Format: { "0" | "1" }
4022 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4023 1 -- enable.
4024 Note: increases power consumption, thus should only be
4025 enabled if running jitter sensitive (HPC/RT) workloads.
4027 security= [SECURITY] Choose a security module to enable at boot.
4028 If this boot parameter is not specified, only the first
4029 security module asking for security registration will be
4030 loaded. An invalid security module name will be treated
4031 as if no module has been chosen.
4033 selinux= [SELINUX] Disable or enable SELinux at boot time.
4034 Format: { "0" | "1" }
4035 See security/selinux/Kconfig help text.
4036 0 -- disable.
4037 1 -- enable.
4038 Default value is set via kernel config option.
4039 If enabled at boot time, /selinux/disable can be used
4040 later to disable prior to initial policy load.
4042 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4043 Format: { "0" | "1" }
4044 See security/apparmor/Kconfig help text
4045 0 -- disable.
4046 1 -- enable.
4047 Default value is set via kernel config option.
4049 serialnumber [BUGS=X86-32]
4051 shapers= [NET]
4052 Maximal number of shapers.
4054 show_msr= [x86] show boot-time MSR settings
4055 Format: { <integer> }
4056 Show boot-time (BIOS-initialized) MSR settings.
4057 The parameter means the number of CPUs to show,
4058 for example 1 means boot CPU only.
4060 simeth= [IA-64]
4061 simscsi=
4063 slram= [HW,MTD]
4065 slab_nomerge [MM]
4066 Disable merging of slabs with similar size. May be
4067 necessary if there is some reason to distinguish
4068 allocs to different slabs. Debug options disable
4069 merging on their own.
4070 For more information see Documentation/vm/slub.txt.
4072 slab_max_order= [MM, SLAB]
4073 Determines the maximum allowed order for slabs.
4074 A high setting may cause OOMs due to memory
4075 fragmentation. Defaults to 1 for systems with
4076 more than 32MB of RAM, 0 otherwise.
4078 slub_debug[=options[,slabs]] [MM, SLUB]
4079 Enabling slub_debug allows one to determine the
4080 culprit if slab objects become corrupted. Enabling
4081 slub_debug can create guard zones around objects and
4082 may poison objects when not in use. Also tracks the
4083 last alloc / free. For more information see
4084 Documentation/vm/slub.txt.
4086 slub_max_order= [MM, SLUB]
4087 Determines the maximum allowed order for slabs.
4088 A high setting may cause OOMs due to memory
4089 fragmentation. For more information see
4090 Documentation/vm/slub.txt.
4092 slub_min_objects= [MM, SLUB]
4093 The minimum number of objects per slab. SLUB will
4094 increase the slab order up to slub_max_order to
4095 generate a sufficiently large slab able to contain
4096 the number of objects indicated. The higher the number
4097 of objects the smaller the overhead of tracking slabs
4098 and the less frequently locks need to be acquired.
4099 For more information see Documentation/vm/slub.txt.
4101 slub_min_order= [MM, SLUB]
4102 Determines the minimum page order for slabs. Must be
4103 lower than slub_max_order.
4104 For more information see Documentation/vm/slub.txt.
4106 slub_nomerge [MM, SLUB]
4107 Same with slab_nomerge. This is supported for legacy.
4108 See slab_nomerge for more information.
4110 smart2= [HW]
4111 Format: <io1>[,<io2>[,...,<io8>]]
4113 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4114 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4115 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4116 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4117 smsc-ircc2.ircc_irq= [HW] IRQ line
4118 smsc-ircc2.ircc_dma= [HW] DMA channel
4119 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4120 0: Toshiba Satellite 1800 (GP data pin select)
4121 1: Fast pin select (default)
4122 2: ATC IRMode
4124 smt [KNL,S390] Set the maximum number of threads (logical
4125 CPUs) to use per physical CPU on systems capable of
4126 symmetric multithreading (SMT). Will be capped to the
4127 actual hardware limit.
4128 Format: <integer>
4129 Default: -1 (no limit)
4131 softlockup_panic=
4132 [KNL] Should the soft-lockup detector generate panics.
4133 Format: <integer>
4135 softlockup_all_cpu_backtrace=
4136 [KNL] Should the soft-lockup detector generate
4137 backtraces on all cpus.
4138 Format: <integer>
4140 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4141 See Documentation/laptops/sonypi.txt
4143 spectre_v2= [X86] Control mitigation of Spectre variant 2
4144 (indirect branch speculation) vulnerability.
4145 The default operation protects the kernel from
4146 user space attacks.
4148 on - unconditionally enable, implies
4149 spectre_v2_user=on
4150 off - unconditionally disable, implies
4151 spectre_v2_user=off
4152 auto - kernel detects whether your CPU model is
4153 vulnerable
4155 Selecting 'on' will, and 'auto' may, choose a
4156 mitigation method at run time according to the
4157 CPU, the available microcode, the setting of the
4158 CONFIG_RETPOLINE configuration option, and the
4159 compiler with which the kernel was built.
4161 Selecting 'on' will also enable the mitigation
4162 against user space to user space task attacks.
4164 Selecting 'off' will disable both the kernel and
4165 the user space protections.
4167 Specific mitigations can also be selected manually:
4169 retpoline - replace indirect branches
4170 retpoline,generic - google's original retpoline
4171 retpoline,amd - AMD-specific minimal thunk
4173 Not specifying this option is equivalent to
4174 spectre_v2=auto.
4176 spectre_v2_user=
4177 [X86] Control mitigation of Spectre variant 2
4178 (indirect branch speculation) vulnerability between
4179 user space tasks
4181 on - Unconditionally enable mitigations. Is
4182 enforced by spectre_v2=on
4184 off - Unconditionally disable mitigations. Is
4185 enforced by spectre_v2=off
4187 prctl - Indirect branch speculation is enabled,
4188 but mitigation can be enabled via prctl
4189 per thread. The mitigation control state
4190 is inherited on fork.
4192 prctl,ibpb
4193 - Like "prctl" above, but only STIBP is
4194 controlled per thread. IBPB is issued
4195 always when switching between different user
4196 space processes.
4198 seccomp
4199 - Same as "prctl" above, but all seccomp
4200 threads will enable the mitigation unless
4201 they explicitly opt out.
4203 seccomp,ibpb
4204 - Like "seccomp" above, but only STIBP is
4205 controlled per thread. IBPB is issued
4206 always when switching between different
4207 user space processes.
4209 auto - Kernel selects the mitigation depending on
4210 the available CPU features and vulnerability.
4212 Default mitigation:
4213 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4215 Not specifying this option is equivalent to
4216 spectre_v2_user=auto.
4218 spec_store_bypass_disable=
4219 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4220 (Speculative Store Bypass vulnerability)
4222 Certain CPUs are vulnerable to an exploit against a
4223 a common industry wide performance optimization known
4224 as "Speculative Store Bypass" in which recent stores
4225 to the same memory location may not be observed by
4226 later loads during speculative execution. The idea
4227 is that such stores are unlikely and that they can
4228 be detected prior to instruction retirement at the
4229 end of a particular speculation execution window.
4231 In vulnerable processors, the speculatively forwarded
4232 store can be used in a cache side channel attack, for
4233 example to read memory to which the attacker does not
4234 directly have access (e.g. inside sandboxed code).
4236 This parameter controls whether the Speculative Store
4237 Bypass optimization is used.
4239 on - Unconditionally disable Speculative Store Bypass
4240 off - Unconditionally enable Speculative Store Bypass
4241 auto - Kernel detects whether the CPU model contains an
4242 implementation of Speculative Store Bypass and
4243 picks the most appropriate mitigation. If the
4244 CPU is not vulnerable, "off" is selected. If the
4245 CPU is vulnerable the default mitigation is
4246 architecture and Kconfig dependent. See below.
4247 prctl - Control Speculative Store Bypass per thread
4248 via prctl. Speculative Store Bypass is enabled
4249 for a process by default. The state of the control
4250 is inherited on fork.
4251 seccomp - Same as "prctl" above, but all seccomp threads
4252 will disable SSB unless they explicitly opt out.
4254 Not specifying this option is equivalent to
4255 spec_store_bypass_disable=auto.
4257 Default mitigations:
4258 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4260 spia_io_base= [HW,MTD]
4261 spia_fio_base=
4262 spia_pedr=
4263 spia_peddr=
4265 srbds= [X86,INTEL]
4266 Control the Special Register Buffer Data Sampling
4267 (SRBDS) mitigation.
4269 Certain CPUs are vulnerable to an MDS-like
4270 exploit which can leak bits from the random
4271 number generator.
4273 By default, this issue is mitigated by
4274 microcode. However, the microcode fix can cause
4275 the RDRAND and RDSEED instructions to become
4276 much slower. Among other effects, this will
4277 result in reduced throughput from /dev/urandom.
4279 The microcode mitigation can be disabled with
4280 the following option:
4282 off: Disable mitigation and remove
4283 performance impact to RDRAND and RDSEED
4285 ssbd= [ARM64,HW]
4286 Speculative Store Bypass Disable control
4288 On CPUs that are vulnerable to the Speculative
4289 Store Bypass vulnerability and offer a
4290 firmware based mitigation, this parameter
4291 indicates how the mitigation should be used:
4293 force-on: Unconditionally enable mitigation for
4294 for both kernel and userspace
4295 force-off: Unconditionally disable mitigation for
4296 for both kernel and userspace
4297 kernel: Always enable mitigation in the
4298 kernel, and offer a prctl interface
4299 to allow userspace to register its
4300 interest in being mitigated too.
4302 stack_guard_gap= [MM]
4303 override the default stack gap protection. The value
4304 is in page units and it defines how many pages prior
4305 to (for stacks growing down) resp. after (for stacks
4306 growing up) the main stack are reserved for no other
4307 mapping. Default value is 256 pages.
4309 stacktrace [FTRACE]
4310 Enabled the stack tracer on boot up.
4312 stacktrace_filter=[function-list]
4313 [FTRACE] Limit the functions that the stack tracer
4314 will trace at boot up. function-list is a comma separated
4315 list of functions. This list can be changed at run
4316 time by the stack_trace_filter file in the debugfs
4317 tracing directory. Note, this enables stack tracing
4318 and the stacktrace above is not needed.
4320 sti= [PARISC,HW]
4321 Format: <num>
4322 Set the STI (builtin display/keyboard on the HP-PARISC
4323 machines) console (graphic card) which should be used
4324 as the initial boot-console.
4325 See also comment in drivers/video/console/sticore.c.
4327 sti_font= [HW]
4328 See comment in drivers/video/console/sticore.c.
4330 stifb= [HW]
4331 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4333 sunrpc.min_resvport=
4334 sunrpc.max_resvport=
4335 [NFS,SUNRPC]
4336 SunRPC servers often require that client requests
4337 originate from a privileged port (i.e. a port in the
4338 range 0 < portnr < 1024).
4339 An administrator who wishes to reserve some of these
4340 ports for other uses may adjust the range that the
4341 kernel's sunrpc client considers to be privileged
4342 using these two parameters to set the minimum and
4343 maximum port values.
4345 sunrpc.svc_rpc_per_connection_limit=
4346 [NFS,SUNRPC]
4347 Limit the number of requests that the server will
4348 process in parallel from a single connection.
4349 The default value is 0 (no limit).
4351 sunrpc.pool_mode=
4352 [NFS]
4353 Control how the NFS server code allocates CPUs to
4354 service thread pools. Depending on how many NICs
4355 you have and where their interrupts are bound, this
4356 option will affect which CPUs will do NFS serving.
4357 Note: this parameter cannot be changed while the
4358 NFS server is running.
4360 auto the server chooses an appropriate mode
4361 automatically using heuristics
4362 global a single global pool contains all CPUs
4363 percpu one pool for each CPU
4364 pernode one pool for each NUMA node (equivalent
4365 to global on non-NUMA machines)
4367 sunrpc.tcp_slot_table_entries=
4368 sunrpc.udp_slot_table_entries=
4369 [NFS,SUNRPC]
4370 Sets the upper limit on the number of simultaneous
4371 RPC calls that can be sent from the client to a
4372 server. Increasing these values may allow you to
4373 improve throughput, but will also increase the
4374 amount of memory reserved for use by the client.
4376 suspend.pm_test_delay=
4377 [SUSPEND]
4378 Sets the number of seconds to remain in a suspend test
4379 mode before resuming the system (see
4380 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4381 is set. Default value is 5.
4383 swapaccount=[0|1]
4384 [KNL] Enable accounting of swap in memory resource
4385 controller if no parameter or 1 is given or disable
4386 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4388 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4389 Format: { <int> | force | noforce }
4390 <int> -- Number of I/O TLB slabs
4391 force -- force using of bounce buffers even if they
4392 wouldn't be automatically used by the kernel
4393 noforce -- Never use bounce buffers (for debugging)
4395 switches= [HW,M68k]
4397 sysfs.deprecated=0|1 [KNL]
4398 Enable/disable old style sysfs layout for old udev
4399 on older distributions. When this option is enabled
4400 very new udev will not work anymore. When this option
4401 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4402 in older udev will not work anymore.
4403 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4404 the kernel configuration.
4406 sysrq_always_enabled
4407 [KNL]
4408 Ignore sysrq setting - this boot parameter will
4409 neutralize any effect of /proc/sys/kernel/sysrq.
4410 Useful for debugging.
4412 tcpmhash_entries= [KNL,NET]
4413 Set the number of tcp_metrics_hash slots.
4414 Default value is 8192 or 16384 depending on total
4415 ram pages. This is used to specify the TCP metrics
4416 cache size. See Documentation/networking/ip-sysctl.txt
4417 "tcp_no_metrics_save" section for more details.
4419 tdfx= [HW,DRM]
4421 test_suspend= [SUSPEND][,N]
4422 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4423 standby suspend) or "freeze" (for suspend type freeze)
4424 as the system sleep state during system startup with
4425 the optional capability to repeat N number of times.
4426 The system is woken from this state using a
4427 wakeup-capable RTC alarm.
4429 thash_entries= [KNL,NET]
4430 Set number of hash buckets for TCP connection
4432 thermal.act= [HW,ACPI]
4433 -1: disable all active trip points in all thermal zones
4434 <degrees C>: override all lowest active trip points
4436 thermal.crt= [HW,ACPI]
4437 -1: disable all critical trip points in all thermal zones
4438 <degrees C>: override all critical trip points
4440 thermal.nocrt= [HW,ACPI]
4441 Set to disable actions on ACPI thermal zone
4442 critical and hot trip points.
4444 thermal.off= [HW,ACPI]
4445 1: disable ACPI thermal control
4447 thermal.psv= [HW,ACPI]
4448 -1: disable all passive trip points
4449 <degrees C>: override all passive trip points to this
4450 value
4452 thermal.tzp= [HW,ACPI]
4453 Specify global default ACPI thermal zone polling rate
4454 <deci-seconds>: poll all this frequency
4455 0: no polling (default)
4457 threadirqs [KNL]
4458 Force threading of all interrupt handlers except those
4459 marked explicitly IRQF_NO_THREAD.
4461 tmem [KNL,XEN]
4462 Enable the Transcendent memory driver if built-in.
4464 tmem.cleancache=0|1 [KNL, XEN]
4465 Default is on (1). Disable the usage of the cleancache
4466 API to send anonymous pages to the hypervisor.
4468 tmem.frontswap=0|1 [KNL, XEN]
4469 Default is on (1). Disable the usage of the frontswap
4470 API to send swap pages to the hypervisor. If disabled
4471 the selfballooning and selfshrinking are force disabled.
4473 tmem.selfballooning=0|1 [KNL, XEN]
4474 Default is on (1). Disable the driving of swap pages
4475 to the hypervisor.
4477 tmem.selfshrinking=0|1 [KNL, XEN]
4478 Default is on (1). Partial swapoff that immediately
4479 transfers pages from Xen hypervisor back to the
4480 kernel based on different criteria.
4482 topology= [S390]
4483 Format: {off | on}
4484 Specify if the kernel should make use of the cpu
4485 topology information if the hardware supports this.
4486 The scheduler will make use of this information and
4487 e.g. base its process migration decisions on it.
4488 Default is on.
4490 topology_updates= [KNL, PPC, NUMA]
4491 Format: {off}
4492 Specify if the kernel should ignore (off)
4493 topology updates sent by the hypervisor to this
4494 LPAR.
4496 tp720= [HW,PS2]
4498 tpm_suspend_pcr=[HW,TPM]
4499 Format: integer pcr id
4500 Specify that at suspend time, the tpm driver
4501 should extend the specified pcr with zeros,
4502 as a workaround for some chips which fail to
4503 flush the last written pcr on TPM_SaveState.
4504 This will guarantee that all the other pcrs
4505 are saved.
4507 trace_buf_size=nn[KMG]
4508 [FTRACE] will set tracing buffer size on each cpu.
4510 trace_event=[event-list]
4511 [FTRACE] Set and start specified trace events in order
4512 to facilitate early boot debugging. The event-list is a
4513 comma separated list of trace events to enable. See
4514 also Documentation/trace/events.txt
4516 trace_options=[option-list]
4517 [FTRACE] Enable or disable tracer options at boot.
4518 The option-list is a comma delimited list of options
4519 that can be enabled or disabled just as if you were
4520 to echo the option name into
4522 /sys/kernel/debug/tracing/trace_options
4524 For example, to enable stacktrace option (to dump the
4525 stack trace of each event), add to the command line:
4527 trace_options=stacktrace
4529 See also Documentation/trace/ftrace.txt "trace options"
4530 section.
4532 tp_printk[FTRACE]
4533 Have the tracepoints sent to printk as well as the
4534 tracing ring buffer. This is useful for early boot up
4535 where the system hangs or reboots and does not give the
4536 option for reading the tracing buffer or performing a
4537 ftrace_dump_on_oops.
4539 To turn off having tracepoints sent to printk,
4540 echo 0 > /proc/sys/kernel/tracepoint_printk
4541 Note, echoing 1 into this file without the
4542 tracepoint_printk kernel cmdline option has no effect.
4544 ** CAUTION **
4546 Having tracepoints sent to printk() and activating high
4547 frequency tracepoints such as irq or sched, can cause
4548 the system to live lock.
4550 traceoff_on_warning
4551 [FTRACE] enable this option to disable tracing when a
4552 warning is hit. This turns off "tracing_on". Tracing can
4553 be enabled again by echoing '1' into the "tracing_on"
4554 file located in /sys/kernel/debug/tracing/
4556 This option is useful, as it disables the trace before
4557 the WARNING dump is called, which prevents the trace to
4558 be filled with content caused by the warning output.
4560 This option can also be set at run time via the sysctl
4561 option: kernel/traceoff_on_warning
4563 transparent_hugepage=
4564 [KNL]
4565 Format: [always|madvise|never]
4566 Can be used to control the default behavior of the system
4567 with respect to transparent hugepages.
4568 See Documentation/vm/transhuge.txt for more details.
4570 tsc= Disable clocksource stability checks for TSC.
4571 Format: <string>
4572 [x86] reliable: mark tsc clocksource as reliable, this
4573 disables clocksource verification at runtime, as well
4574 as the stability checks done at bootup. Used to enable
4575 high-resolution timer mode on older hardware, and in
4576 virtualized environment.
4577 [x86] noirqtime: Do not use TSC to do irq accounting.
4578 Used to run time disable IRQ_TIME_ACCOUNTING on any
4579 platforms where RDTSC is slow and this accounting
4580 can add overhead.
4582 tsx= [X86] Control Transactional Synchronization
4583 Extensions (TSX) feature in Intel processors that
4584 support TSX control.
4586 This parameter controls the TSX feature. The options are:
4588 on - Enable TSX on the system. Although there are
4589 mitigations for all known security vulnerabilities,
4590 TSX has been known to be an accelerator for
4591 several previous speculation-related CVEs, and
4592 so there may be unknown security risks associated
4593 with leaving it enabled.
4595 off - Disable TSX on the system. (Note that this
4596 option takes effect only on newer CPUs which are
4597 not vulnerable to MDS, i.e., have
4598 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
4599 the new IA32_TSX_CTRL MSR through a microcode
4600 update. This new MSR allows for the reliable
4601 deactivation of the TSX functionality.)
4603 auto - Disable TSX if X86_BUG_TAA is present,
4604 otherwise enable TSX on the system.
4606 Not specifying this option is equivalent to tsx=off.
4608 See Documentation/hw-vuln/tsx_async_abort.rst
4609 for more details.
4611 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
4612 Abort (TAA) vulnerability.
4614 Similar to Micro-architectural Data Sampling (MDS)
4615 certain CPUs that support Transactional
4616 Synchronization Extensions (TSX) are vulnerable to an
4617 exploit against CPU internal buffers which can forward
4618 information to a disclosure gadget under certain
4619 conditions.
4621 In vulnerable processors, the speculatively forwarded
4622 data can be used in a cache side channel attack, to
4623 access data to which the attacker does not have direct
4624 access.
4626 This parameter controls the TAA mitigation. The
4627 options are:
4629 full - Enable TAA mitigation on vulnerable CPUs
4630 if TSX is enabled.
4632 full,nosmt - Enable TAA mitigation and disable SMT on
4633 vulnerable CPUs. If TSX is disabled, SMT
4634 is not disabled because CPU is not
4635 vulnerable to cross-thread TAA attacks.
4636 off - Unconditionally disable TAA mitigation
4638 On MDS-affected machines, tsx_async_abort=off can be
4639 prevented by an active MDS mitigation as both vulnerabilities
4640 are mitigated with the same mechanism so in order to disable
4641 this mitigation, you need to specify mds=off too.
4643 Not specifying this option is equivalent to
4644 tsx_async_abort=full. On CPUs which are MDS affected
4645 and deploy MDS mitigation, TAA mitigation is not
4646 required and doesn't provide any additional
4647 mitigation.
4649 For details see:
4650 Documentation/hw-vuln/tsx_async_abort.rst
4652 turbografx.map[2|3]= [HW,JOY]
4653 TurboGraFX parallel port interface
4654 Format:
4655 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4656 See also Documentation/input/joystick-parport.txt
4658 udbg-immortal [PPC] When debugging early kernel crashes that
4659 happen after console_init() and before a proper
4660 console driver takes over, this boot options might
4661 help "seeing" what's going on.
4663 uhash_entries= [KNL,NET]
4664 Set number of hash buckets for UDP/UDP-Lite connections
4666 uhci-hcd.ignore_oc=
4667 [USB] Ignore overcurrent events (default N).
4668 Some badly-designed motherboards generate lots of
4669 bogus events, for ports that aren't wired to
4670 anything. Set this parameter to avoid log spamming.
4671 Note that genuine overcurrent events won't be
4672 reported either.
4674 unknown_nmi_panic
4675 [X86] Cause panic on unknown NMI.
4677 usbcore.authorized_default=
4678 [USB] Default USB device authorization:
4679 (default -1 = authorized except for wireless USB,
4680 0 = not authorized, 1 = authorized)
4682 usbcore.autosuspend=
4683 [USB] The autosuspend time delay (in seconds) used
4684 for newly-detected USB devices (default 2). This
4685 is the time required before an idle device will be
4686 autosuspended. Devices for which the delay is set
4687 to a negative value won't be autosuspended at all.
4689 usbcore.usbfs_snoop=
4690 [USB] Set to log all usbfs traffic (default 0 = off).
4692 usbcore.usbfs_snoop_max=
4693 [USB] Maximum number of bytes to snoop in each URB
4694 (default = 65536).
4696 usbcore.blinkenlights=
4697 [USB] Set to cycle leds on hubs (default 0 = off).
4699 usbcore.old_scheme_first=
4700 [USB] Start with the old device initialization
4701 scheme (default 0 = off).
4703 usbcore.usbfs_memory_mb=
4704 [USB] Memory limit (in MB) for buffers allocated by
4705 usbfs (default = 16, 0 = max = 2047).
4707 usbcore.use_both_schemes=
4708 [USB] Try the other device initialization scheme
4709 if the first one fails (default 1 = enabled).
4711 usbcore.initial_descriptor_timeout=
4712 [USB] Specifies timeout for the initial 64-byte
4713 USB_REQ_GET_DESCRIPTOR request in milliseconds
4714 (default 5000 = 5.0 seconds).
4716 usbcore.nousb [USB] Disable the USB subsystem
4718 usbhid.mousepoll=
4719 [USBHID] The interval which mice are to be polled at.
4721 usb-storage.delay_use=
4722 [UMS] The delay in seconds before a new device is
4723 scanned for Logical Units (default 1).
4725 usb-storage.quirks=
4726 [UMS] A list of quirks entries to supplement or
4727 override the built-in unusual_devs list. List
4728 entries are separated by commas. Each entry has
4729 the form VID:PID:Flags where VID and PID are Vendor
4730 and Product ID values (4-digit hex numbers) and
4731 Flags is a set of characters, each corresponding
4732 to a common usb-storage quirk flag as follows:
4733 a = SANE_SENSE (collect more than 18 bytes
4734 of sense data);
4735 b = BAD_SENSE (don't collect more than 18
4736 bytes of sense data);
4737 c = FIX_CAPACITY (decrease the reported
4738 device capacity by one sector);
4739 d = NO_READ_DISC_INFO (don't use
4740 READ_DISC_INFO command);
4741 e = NO_READ_CAPACITY_16 (don't use
4742 READ_CAPACITY_16 command);
4743 f = NO_REPORT_OPCODES (don't use report opcodes
4744 command, uas only);
4745 g = MAX_SECTORS_240 (don't transfer more than
4746 240 sectors at a time, uas only);
4747 h = CAPACITY_HEURISTICS (decrease the
4748 reported device capacity by one
4749 sector if the number is odd);
4750 i = IGNORE_DEVICE (don't bind to this
4751 device);
4752 j = NO_REPORT_LUNS (don't use report luns
4753 command, uas only);
4754 l = NOT_LOCKABLE (don't try to lock and
4755 unlock ejectable media);
4756 m = MAX_SECTORS_64 (don't transfer more
4757 than 64 sectors = 32 KB at a time);
4758 n = INITIAL_READ10 (force a retry of the
4759 initial READ(10) command);
4760 o = CAPACITY_OK (accept the capacity
4761 reported by the device);
4762 p = WRITE_CACHE (the device cache is ON
4763 by default);
4764 r = IGNORE_RESIDUE (the device reports
4765 bogus residue values);
4766 s = SINGLE_LUN (the device has only one
4767 Logical Unit);
4768 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4769 commands, uas only);
4770 u = IGNORE_UAS (don't bind to the uas driver);
4771 w = NO_WP_DETECT (don't test whether the
4772 medium is write-protected).
4773 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4774 even if the device claims no cache)
4775 Example: quirks=0419:aaf5:rl,0421:0433:rc
4777 user_debug= [KNL,ARM]
4778 Format: <int>
4779 See arch/arm/Kconfig.debug help text.
4780 1 - undefined instruction events
4781 2 - system calls
4782 4 - invalid data aborts
4783 8 - SIGSEGV faults
4784 16 - SIGBUS faults
4785 Example: user_debug=31
4787 userpte=
4788 [X86] Flags controlling user PTE allocations.
4790 nohigh = do not allocate PTE pages in
4791 HIGHMEM regardless of setting
4792 of CONFIG_HIGHPTE.
4794 vdso= [X86,SH]
4795 On X86_32, this is an alias for vdso32=. Otherwise:
4797 vdso=1: enable VDSO (the default)
4798 vdso=0: disable VDSO mapping
4800 vdso32= [X86] Control the 32-bit vDSO
4801 vdso32=1: enable 32-bit VDSO
4802 vdso32=0 or vdso32=2: disable 32-bit VDSO
4804 See the help text for CONFIG_COMPAT_VDSO for more
4805 details. If CONFIG_COMPAT_VDSO is set, the default is
4806 vdso32=0; otherwise, the default is vdso32=1.
4808 For compatibility with older kernels, vdso32=2 is an
4809 alias for vdso32=0.
4811 Try vdso32=0 if you encounter an error that says:
4812 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4814 vector= [IA-64,SMP]
4815 vector=percpu: enable percpu vector domain
4817 video= [FB] Frame buffer configuration
4818 See Documentation/fb/modedb.txt.
4820 video.brightness_switch_enabled= [0,1]
4821 If set to 1, on receiving an ACPI notify event
4822 generated by hotkey, video driver will adjust brightness
4823 level and then send out the event to user space through
4824 the allocated input device; If set to 0, video driver
4825 will only send out the event without touching backlight
4826 brightness level.
4827 default: 1
4829 virtio_mmio.device=
4830 [VMMIO] Memory mapped virtio (platform) device.
4832 <size>@<baseaddr>:<irq>[:<id>]
4833 where:
4834 <size> := size (can use standard suffixes
4835 like K, M and G)
4836 <baseaddr> := physical base address
4837 <irq> := interrupt number (as passed to
4838 request_irq())
4839 <id> := (optional) platform device id
4840 example:
4841 virtio_mmio.device=1K@0x100b0000:48:7
4843 Can be used multiple times for multiple devices.
4845 vga= [BOOT,X86-32] Select a particular video mode
4846 See Documentation/x86/boot.txt and
4847 Documentation/svga.txt.
4848 Use vga=ask for menu.
4849 This is actually a boot loader parameter; the value is
4850 passed to the kernel using a special protocol.
4852 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4853 size of <nn>. This can be used to increase the
4854 minimum size (128MB on x86). It can also be used to
4855 decrease the size and leave more room for directly
4856 mapped kernel RAM.
4858 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4859 Format: <command>
4861 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4862 Format: <command>
4864 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4865 Format: <command>
4867 vsyscall= [X86-64]
4868 Controls the behavior of vsyscalls (i.e. calls to
4869 fixed addresses of 0xffffffffff600x00 from legacy
4870 code). Most statically-linked binaries and older
4871 versions of glibc use these calls. Because these
4872 functions are at fixed addresses, they make nice
4873 targets for exploits that can control RIP.
4875 emulate [default] Vsyscalls turn into traps and are
4876 emulated reasonably safely.
4878 native Vsyscalls are native syscall instructions.
4879 This is a little bit faster than trapping
4880 and makes a few dynamic recompilers work
4881 better than they would in emulation mode.
4882 It also makes exploits much easier to write.
4884 none Vsyscalls don't work at all. This makes
4885 them quite hard to use for exploits but
4886 might break your system.
4888 vt.color= [VT] Default text color.
4889 Format: 0xYX, X = foreground, Y = background.
4890 Default: 0x07 = light gray on black.
4892 vt.cur_default= [VT] Default cursor shape.
4893 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4894 the parameters of the <Esc>[?A;B;Cc escape sequence;
4895 see VGA-softcursor.txt. Default: 2 = underline.
4897 vt.default_blu= [VT]
4898 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4899 Change the default blue palette of the console.
4900 This is a 16-member array composed of values
4901 ranging from 0-255.
4903 vt.default_grn= [VT]
4904 Format: <green0>,<green1>,<green2>,...,<green15>
4905 Change the default green palette of the console.
4906 This is a 16-member array composed of values
4907 ranging from 0-255.
4909 vt.default_red= [VT]
4910 Format: <red0>,<red1>,<red2>,...,<red15>
4911 Change the default red palette of the console.
4912 This is a 16-member array composed of values
4913 ranging from 0-255.
4915 vt.default_utf8=
4916 [VT]
4917 Format=<0|1>
4918 Set system-wide default UTF-8 mode for all tty's.
4919 Default is 1, i.e. UTF-8 mode is enabled for all
4920 newly opened terminals.
4922 vt.global_cursor_default=
4923 [VT]
4924 Format=<-1|0|1>
4925 Set system-wide default for whether a cursor
4926 is shown on new VTs. Default is -1,
4927 i.e. cursors will be created by default unless
4928 overridden by individual drivers. 0 will hide
4929 cursors, 1 will display them.
4931 vt.italic= [VT] Default color for italic text; 0-15.
4932 Default: 2 = green.
4934 vt.underline= [VT] Default color for underlined text; 0-15.
4935 Default: 3 = cyan.
4937 watchdog timers [HW,WDT] For information on watchdog timers,
4938 see Documentation/watchdog/watchdog-parameters.txt
4939 or other driver-specific files in the
4940 Documentation/watchdog/ directory.
4942 workqueue.watchdog_thresh=
4943 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4944 warn stall conditions and dump internal state to
4945 help debugging. 0 disables workqueue stall
4946 detection; otherwise, it's the stall threshold
4947 duration in seconds. The default value is 30 and
4948 it can be updated at runtime by writing to the
4949 corresponding sysfs file.
4951 workqueue.disable_numa
4952 By default, all work items queued to unbound
4953 workqueues are affine to the NUMA nodes they're
4954 issued on, which results in better behavior in
4955 general. If NUMA affinity needs to be disabled for
4956 whatever reason, this option can be used. Note
4957 that this also can be controlled per-workqueue for
4958 workqueues visible under /sys/bus/workqueue/.
4960 workqueue.power_efficient
4961 Per-cpu workqueues are generally preferred because
4962 they show better performance thanks to cache
4963 locality; unfortunately, per-cpu workqueues tend to
4964 be more power hungry than unbound workqueues.
4966 Enabling this makes the per-cpu workqueues which
4967 were observed to contribute significantly to power
4968 consumption unbound, leading to measurably lower
4969 power usage at the cost of small performance
4970 overhead.
4972 The default value of this parameter is determined by
4973 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4975 workqueue.debug_force_rr_cpu
4976 Workqueue used to implicitly guarantee that work
4977 items queued without explicit CPU specified are put
4978 on the local CPU. This guarantee is no longer true
4979 and while local CPU is still preferred work items
4980 may be put on foreign CPUs. This debug option
4981 forces round-robin CPU selection to flush out
4982 usages which depend on the now broken guarantee.
4983 When enabled, memory and cache locality will be
4984 impacted.
4986 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4987 default x2apic cluster mode on platforms
4988 supporting x2apic.
4990 x86_intel_mid_timer= [X86-32,APBT]
4991 Choose timer option for x86 Intel MID platform.
4992 Two valid options are apbt timer only and lapic timer
4993 plus one apbt timer for broadcast timer.
4994 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4996 xen_512gb_limit [KNL,X86-64,XEN]
4997 Restricts the kernel running paravirtualized under Xen
4998 to use only up to 512 GB of RAM. The reason to do so is
4999 crash analysis tools and Xen tools for doing domain
5000 save/restore/migration must be enabled to handle larger
5001 domains.
5003 xen_emul_unplug= [HW,X86,XEN]
5004 Unplug Xen emulated devices
5005 Format: [unplug0,][unplug1]
5006 ide-disks -- unplug primary master IDE devices
5007 aux-ide-disks -- unplug non-primary-master IDE devices
5008 nics -- unplug network devices
5009 all -- unplug all emulated devices (NICs and IDE disks)
5010 unnecessary -- unplugging emulated devices is
5011 unnecessary even if the host did not respond to
5012 the unplug protocol
5013 never -- do not unplug even if version check succeeds
5015 xen_nopvspin [X86,XEN]
5016 Disables the ticketlock slowpath using Xen PV
5017 optimizations.
5019 xen_nopv [X86]
5020 Disables the PV optimizations forcing the HVM guest to
5021 run as generic HVM guest with no PV drivers.
5023 xirc2ps_cs= [NET,PCMCIA]
5024 Format:
5025 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5027 ______________________________________________________________________
5029 TODO:
5031 Add more DRM drivers.