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1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
4 copy_dsdt }
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
14 are available
16 See also Documentation/power/runtime_pm.rst, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
19 Format: <int>
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
22 default: 0
24 acpi_backlight= [HW,ACPI]
25 { vendor | video | native | none }
26 If set to vendor, prefer vendor-specific driver
27 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
28 of the ACPI video.ko driver.
29 If set to video, use the ACPI video.ko driver.
30 If set to native, use the device's native backlight mode.
31 If set to none, disable the ACPI backlight interface.
33 acpi_force_32bit_fadt_addr
34 force FADT to use 32 bit addresses rather than the
35 64 bit X_* addresses. Some firmware have broken 64
36 bit addresses for force ACPI ignore these and use
37 the older legacy 32 bit addresses.
39 acpica_no_return_repair [HW, ACPI]
40 Disable AML predefined validation mechanism
41 This mechanism can repair the evaluation result to make
42 the return objects more ACPI specification compliant.
43 This option is useful for developers to identify the
44 root cause of an AML interpreter issue when the issue
45 has something to do with the repair mechanism.
47 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
48 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
49 Format: <int>
50 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
51 debug output. Bits in debug_layer correspond to a
52 _COMPONENT in an ACPI source file, e.g.,
53 #define _COMPONENT ACPI_PCI_COMPONENT
54 Bits in debug_level correspond to a level in
55 ACPI_DEBUG_PRINT statements, e.g.,
56 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
57 The debug_level mask defaults to "info". See
58 Documentation/firmware-guide/acpi/debug.rst for more information about
59 debug layers and levels.
61 Enable processor driver info messages:
62 acpi.debug_layer=0x20000000
63 Enable PCI/PCI interrupt routing info messages:
64 acpi.debug_layer=0x400000
65 Enable AML "Debug" output, i.e., stores to the Debug
66 object while interpreting AML:
67 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
68 Enable all messages related to ACPI hardware:
69 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
71 Some values produce so much output that the system is
72 unusable. The "log_buf_len" parameter may be useful
73 if you need to capture more output.
75 acpi_enforce_resources= [ACPI]
76 { strict | lax | no }
77 Check for resource conflicts between native drivers
78 and ACPI OperationRegions (SystemIO and SystemMemory
79 only). IO ports and memory declared in ACPI might be
80 used by the ACPI subsystem in arbitrary AML code and
81 can interfere with legacy drivers.
82 strict (default): access to resources claimed by ACPI
83 is denied; legacy drivers trying to access reserved
84 resources will fail to bind to device using them.
85 lax: access to resources claimed by ACPI is allowed;
86 legacy drivers trying to access reserved resources
87 will bind successfully but a warning message is logged.
88 no: ACPI OperationRegions are not marked as reserved,
89 no further checks are performed.
91 acpi_force_table_verification [HW,ACPI]
92 Enable table checksum verification during early stage.
93 By default, this is disabled due to x86 early mapping
94 size limitation.
96 acpi_irq_balance [HW,ACPI]
97 ACPI will balance active IRQs
98 default in APIC mode
100 acpi_irq_nobalance [HW,ACPI]
101 ACPI will not move active IRQs (default)
102 default in PIC mode
104 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
105 Format: <irq>,<irq>...
107 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
108 use by PCI
109 Format: <irq>,<irq>...
111 acpi_mask_gpe= [HW,ACPI]
112 Due to the existence of _Lxx/_Exx, some GPEs triggered
113 by unsupported hardware/firmware features can result in
114 GPE floodings that cannot be automatically disabled by
115 the GPE dispatcher.
116 This facility can be used to prevent such uncontrolled
117 GPE floodings.
118 Format: <byte>
120 acpi_no_auto_serialize [HW,ACPI]
121 Disable auto-serialization of AML methods
122 AML control methods that contain the opcodes to create
123 named objects will be marked as "Serialized" by the
124 auto-serialization feature.
125 This feature is enabled by default.
126 This option allows to turn off the feature.
128 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
129 kernels.
131 acpi_no_static_ssdt [HW,ACPI]
132 Disable installation of static SSDTs at early boot time
133 By default, SSDTs contained in the RSDT/XSDT will be
134 installed automatically and they will appear under
135 /sys/firmware/acpi/tables.
136 This option turns off this feature.
137 Note that specifying this option does not affect
138 dynamic table installation which will install SSDT
139 tables to /sys/firmware/acpi/tables/dynamic.
141 acpi_no_watchdog [HW,ACPI,WDT]
142 Ignore the ACPI-based watchdog interface (WDAT) and let
143 a native driver control the watchdog device instead.
145 acpi_rsdp= [ACPI,EFI,KEXEC]
146 Pass the RSDP address to the kernel, mostly used
147 on machines running EFI runtime service to boot the
148 second kernel for kdump.
150 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
151 Format: To spoof as Windows 98: ="Microsoft Windows"
153 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
154 of 2 which is mandated by ACPI 6) as the supported ACPI
155 specification revision (when using this switch, it may
156 be necessary to carry out a cold reboot _twice_ in a
157 row to make it take effect on the platform firmware).
159 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
160 acpi_osi="string1" # add string1
161 acpi_osi="!string2" # remove string2
162 acpi_osi=!* # remove all strings
163 acpi_osi=! # disable all built-in OS vendor
164 strings
165 acpi_osi=!! # enable all built-in OS vendor
166 strings
167 acpi_osi= # disable all strings
169 'acpi_osi=!' can be used in combination with single or
170 multiple 'acpi_osi="string1"' to support specific OS
171 vendor string(s). Note that such command can only
172 affect the default state of the OS vendor strings, thus
173 it cannot affect the default state of the feature group
174 strings and the current state of the OS vendor strings,
175 specifying it multiple times through kernel command line
176 is meaningless. This command is useful when one do not
177 care about the state of the feature group strings which
178 should be controlled by the OSPM.
179 Examples:
180 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
181 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
182 can make '_OSI("Windows 2000")' TRUE.
184 'acpi_osi=' cannot be used in combination with other
185 'acpi_osi=' command lines, the _OSI method will not
186 exist in the ACPI namespace. NOTE that such command can
187 only affect the _OSI support state, thus specifying it
188 multiple times through kernel command line is also
189 meaningless.
190 Examples:
191 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
192 FALSE.
194 'acpi_osi=!*' can be used in combination with single or
195 multiple 'acpi_osi="string1"' to support specific
196 string(s). Note that such command can affect the
197 current state of both the OS vendor strings and the
198 feature group strings, thus specifying it multiple times
199 through kernel command line is meaningful. But it may
200 still not able to affect the final state of a string if
201 there are quirks related to this string. This command
202 is useful when one want to control the state of the
203 feature group strings to debug BIOS issues related to
204 the OSPM features.
205 Examples:
206 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
207 '_OSI("Module Device")' FALSE.
208 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
209 '_OSI("Module Device")' TRUE.
210 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
211 equivalent to
212 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
213 and
214 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
215 they all will make '_OSI("Windows 2000")' TRUE.
217 acpi_pm_good [X86]
218 Override the pmtimer bug detection: force the kernel
219 to assume that this machine's pmtimer latches its value
220 and always returns good values.
222 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
223 Format: { level | edge | high | low }
225 acpi_skip_timer_override [HW,ACPI]
226 Recognize and ignore IRQ0/pin2 Interrupt Override.
227 For broken nForce2 BIOS resulting in XT-PIC timer.
229 acpi_sleep= [HW,ACPI] Sleep options
230 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
231 old_ordering, nonvs, sci_force_enable, nobl }
232 See Documentation/power/video.rst for information on
233 s3_bios and s3_mode.
234 s3_beep is for debugging; it makes the PC's speaker beep
235 as soon as the kernel's real-mode entry point is called.
236 s4_nohwsig prevents ACPI hardware signature from being
237 used during resume from hibernation.
238 old_ordering causes the ACPI 1.0 ordering of the _PTS
239 control method, with respect to putting devices into
240 low power states, to be enforced (the ACPI 2.0 ordering
241 of _PTS is used by default).
242 nonvs prevents the kernel from saving/restoring the
243 ACPI NVS memory during suspend/hibernation and resume.
244 sci_force_enable causes the kernel to set SCI_EN directly
245 on resume from S1/S3 (which is against the ACPI spec,
246 but some broken systems don't work without it).
247 nobl causes the internal blacklist of systems known to
248 behave incorrectly in some ways with respect to system
249 suspend and resume to be ignored (use wisely).
251 acpi_use_timer_override [HW,ACPI]
252 Use timer override. For some broken Nvidia NF5 boards
253 that require a timer override, but don't have HPET
255 add_efi_memmap [EFI; X86] Include EFI memory map in
256 kernel's map of available physical RAM.
258 agp= [AGP]
259 { off | try_unsupported }
260 off: disable AGP support
261 try_unsupported: try to drive unsupported chipsets
262 (may crash computer or cause data corruption)
264 ALSA [HW,ALSA]
265 See Documentation/sound/alsa-configuration.rst
267 alignment= [KNL,ARM]
268 Allow the default userspace alignment fault handler
269 behaviour to be specified. Bit 0 enables warnings,
270 bit 1 enables fixups, and bit 2 sends a segfault.
272 align_va_addr= [X86-64]
273 Align virtual addresses by clearing slice [14:12] when
274 allocating a VMA at process creation time. This option
275 gives you up to 3% performance improvement on AMD F15h
276 machines (where it is enabled by default) for a
277 CPU-intensive style benchmark, and it can vary highly in
278 a microbenchmark depending on workload and compiler.
280 32: only for 32-bit processes
281 64: only for 64-bit processes
282 on: enable for both 32- and 64-bit processes
283 off: disable for both 32- and 64-bit processes
285 alloc_snapshot [FTRACE]
286 Allocate the ftrace snapshot buffer on boot up when the
287 main buffer is allocated. This is handy if debugging
288 and you need to use tracing_snapshot() on boot up, and
289 do not want to use tracing_snapshot_alloc() as it needs
290 to be done where GFP_KERNEL allocations are allowed.
292 amd_iommu= [HW,X86-64]
293 Pass parameters to the AMD IOMMU driver in the system.
294 Possible values are:
295 fullflush - enable flushing of IO/TLB entries when
296 they are unmapped. Otherwise they are
297 flushed before they will be reused, which
298 is a lot of faster
299 off - do not initialize any AMD IOMMU found in
300 the system
301 force_isolation - Force device isolation for all
302 devices. The IOMMU driver is not
303 allowed anymore to lift isolation
304 requirements as needed. This option
305 does not override iommu=pt
307 amd_iommu_dump= [HW,X86-64]
308 Enable AMD IOMMU driver option to dump the ACPI table
309 for AMD IOMMU. With this option enabled, AMD IOMMU
310 driver will print ACPI tables for AMD IOMMU during
311 IOMMU initialization.
313 amd_iommu_intr= [HW,X86-64]
314 Specifies one of the following AMD IOMMU interrupt
315 remapping modes:
316 legacy - Use legacy interrupt remapping mode.
317 vapic - Use virtual APIC mode, which allows IOMMU
318 to inject interrupts directly into guest.
319 This mode requires kvm-amd.avic=1.
320 (Default when IOMMU HW support is present.)
322 amijoy.map= [HW,JOY] Amiga joystick support
323 Map of devices attached to JOY0DAT and JOY1DAT
324 Format: <a>,<b>
325 See also Documentation/input/joydev/joystick.rst
327 analog.map= [HW,JOY] Analog joystick and gamepad support
328 Specifies type or capabilities of an analog joystick
329 connected to one of 16 gameports
330 Format: <type1>,<type2>,..<type16>
332 apc= [HW,SPARC]
333 Power management functions (SPARCstation-4/5 + deriv.)
334 Format: noidle
335 Disable APC CPU standby support. SPARCstation-Fox does
336 not play well with APC CPU idle - disable it if you have
337 APC and your system crashes randomly.
339 apic= [APIC,X86] Advanced Programmable Interrupt Controller
340 Change the output verbosity while booting
341 Format: { quiet (default) | verbose | debug }
342 Change the amount of debugging information output
343 when initialising the APIC and IO-APIC components.
344 For X86-32, this can also be used to specify an APIC
345 driver name.
346 Format: apic=driver_name
347 Examples: apic=bigsmp
349 apic_extnmi= [APIC,X86] External NMI delivery setting
350 Format: { bsp (default) | all | none }
351 bsp: External NMI is delivered only to CPU 0
352 all: External NMIs are broadcast to all CPUs as a
353 backup of CPU 0
354 none: External NMI is masked for all CPUs. This is
355 useful so that a dump capture kernel won't be
356 shot down by NMI
358 autoconf= [IPV6]
359 See Documentation/networking/ipv6.txt.
361 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
362 Limit apic dumping. The parameter defines the maximal
363 number of local apics being dumped. Also it is possible
364 to set it to "all" by meaning -- no limit here.
365 Format: { 1 (default) | 2 | ... | all }.
366 The parameter valid if only apic=debug or
367 apic=verbose is specified.
368 Example: apic=debug show_lapic=all
370 apm= [APM] Advanced Power Management
371 See header of arch/x86/kernel/apm_32.c.
373 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
374 Format: <io>,<irq>,<nodeID>
376 ataflop= [HW,M68k]
378 atarimouse= [HW,MOUSE] Atari Mouse
380 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
381 EzKey and similar keyboards
383 atkbd.reset= [HW] Reset keyboard during initialization
385 atkbd.set= [HW] Select keyboard code set
386 Format: <int> (2 = AT (default), 3 = PS/2)
388 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
389 keyboards
391 atkbd.softraw= [HW] Choose between synthetic and real raw mode
392 Format: <bool> (0 = real, 1 = synthetic (default))
394 atkbd.softrepeat= [HW]
395 Use software keyboard repeat
397 audit= [KNL] Enable the audit sub-system
398 Format: { "0" | "1" | "off" | "on" }
399 0 | off - kernel audit is disabled and can not be
400 enabled until the next reboot
401 unset - kernel audit is initialized but disabled and
402 will be fully enabled by the userspace auditd.
403 1 | on - kernel audit is initialized and partially
404 enabled, storing at most audit_backlog_limit
405 messages in RAM until it is fully enabled by the
406 userspace auditd.
407 Default: unset
409 audit_backlog_limit= [KNL] Set the audit queue size limit.
410 Format: <int> (must be >=0)
411 Default: 64
413 bau= [X86_UV] Enable the BAU on SGI UV. The default
414 behavior is to disable the BAU (i.e. bau=0).
415 Format: { "0" | "1" }
416 0 - Disable the BAU.
417 1 - Enable the BAU.
418 unset - Disable the BAU.
420 baycom_epp= [HW,AX25]
421 Format: <io>,<mode>
423 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
424 Format: <io>,<mode>
425 See header of drivers/net/hamradio/baycom_par.c.
427 baycom_ser_fdx= [HW,AX25]
428 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
429 Format: <io>,<irq>,<mode>[,<baud>]
430 See header of drivers/net/hamradio/baycom_ser_fdx.c.
432 baycom_ser_hdx= [HW,AX25]
433 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
434 Format: <io>,<irq>,<mode>
435 See header of drivers/net/hamradio/baycom_ser_hdx.c.
437 blkdevparts= Manual partition parsing of block device(s) for
438 embedded devices based on command line input.
439 See Documentation/block/cmdline-partition.rst
441 boot_delay= Milliseconds to delay each printk during boot.
442 Values larger than 10 seconds (10000) are changed to
443 no delay (0).
444 Format: integer
446 bootconfig [KNL]
447 Extended command line options can be added to an initrd
448 and this will cause the kernel to look for it.
450 See Documentation/admin-guide/bootconfig.rst
452 bert_disable [ACPI]
453 Disable BERT OS support on buggy BIOSes.
455 bgrt_disable [ACPI][X86]
456 Disable BGRT to avoid flickering OEM logo.
458 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
459 bttv.radio= Most important insmod options are available as
460 kernel args too.
461 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
462 bttv.tuner=
464 bulk_remove=off [PPC] This parameter disables the use of the pSeries
465 firmware feature for flushing multiple hpte entries
466 at a time.
468 c101= [NET] Moxa C101 synchronous serial card
470 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
471 Sometimes CPU hardware bugs make them report the cache
472 size incorrectly. The kernel will attempt work arounds
473 to fix known problems, but for some CPUs it is not
474 possible to determine what the correct size should be.
475 This option provides an override for these situations.
477 carrier_timeout=
478 [NET] Specifies amount of time (in seconds) that
479 the kernel should wait for a network carrier. By default
480 it waits 120 seconds.
482 ca_keys= [KEYS] This parameter identifies a specific key(s) on
483 the system trusted keyring to be used for certificate
484 trust validation.
485 format: { id:<keyid> | builtin }
487 cca= [MIPS] Override the kernel pages' cache coherency
488 algorithm. Accepted values range from 0 to 7
489 inclusive. See arch/mips/include/asm/pgtable-bits.h
490 for platform specific values (SB1, Loongson3 and
491 others).
493 ccw_timeout_log [S390]
494 See Documentation/s390/common_io.rst for details.
496 cgroup_disable= [KNL] Disable a particular controller
497 Format: {name of the controller(s) to disable}
498 The effects of cgroup_disable=foo are:
499 - foo isn't auto-mounted if you mount all cgroups in
500 a single hierarchy
501 - foo isn't visible as an individually mountable
502 subsystem
503 {Currently only "memory" controller deal with this and
504 cut the overhead, others just disable the usage. So
505 only cgroup_disable=memory is actually worthy}
507 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
508 Format: { { controller | "all" | "named" }
509 [,{ controller | "all" | "named" }...] }
510 Like cgroup_disable, but only applies to cgroup v1;
511 the blacklisted controllers remain available in cgroup2.
512 "all" blacklists all controllers and "named" disables
513 named mounts. Specifying both "all" and "named" disables
514 all v1 hierarchies.
516 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
517 Format: <string>
518 nosocket -- Disable socket memory accounting.
519 nokmem -- Disable kernel memory accounting.
521 checkreqprot [SELINUX] Set initial checkreqprot flag value.
522 Format: { "0" | "1" }
523 See security/selinux/Kconfig help text.
524 0 -- check protection applied by kernel (includes
525 any implied execute protection).
526 1 -- check protection requested by application.
527 Default value is set via a kernel config option.
528 Value can be changed at runtime via
529 /sys/fs/selinux/checkreqprot.
530 Setting checkreqprot to 1 is deprecated.
532 cio_ignore= [S390]
533 See Documentation/s390/common_io.rst for details.
534 clk_ignore_unused
535 [CLK]
536 Prevents the clock framework from automatically gating
537 clocks that have not been explicitly enabled by a Linux
538 device driver but are enabled in hardware at reset or
539 by the bootloader/firmware. Note that this does not
540 force such clocks to be always-on nor does it reserve
541 those clocks in any way. This parameter is useful for
542 debug and development, but should not be needed on a
543 platform with proper driver support. For more
544 information, see Documentation/driver-api/clk.rst.
546 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
547 [Deprecated]
548 Forces specified clocksource (if available) to be used
549 when calculating gettimeofday(). If specified
550 clocksource is not available, it defaults to PIT.
551 Format: { pit | tsc | cyclone | pmtmr }
553 clocksource= Override the default clocksource
554 Format: <string>
555 Override the default clocksource and use the clocksource
556 with the name specified.
557 Some clocksource names to choose from, depending on
558 the platform:
559 [all] jiffies (this is the base, fallback clocksource)
560 [ACPI] acpi_pm
561 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
562 pxa_timer,timer3,32k_counter,timer0_1
563 [X86-32] pit,hpet,tsc;
564 scx200_hrt on Geode; cyclone on IBM x440
565 [MIPS] MIPS
566 [PARISC] cr16
567 [S390] tod
568 [SH] SuperH
569 [SPARC64] tick
570 [X86-64] hpet,tsc
572 clocksource.arm_arch_timer.evtstrm=
573 [ARM,ARM64]
574 Format: <bool>
575 Enable/disable the eventstream feature of the ARM
576 architected timer so that code using WFE-based polling
577 loops can be debugged more effectively on production
578 systems.
580 clearcpuid=BITNUM [X86]
581 Disable CPUID feature X for the kernel. See
582 arch/x86/include/asm/cpufeatures.h for the valid bit
583 numbers. Note the Linux specific bits are not necessarily
584 stable over kernel options, but the vendor specific
585 ones should be.
586 Also note that user programs calling CPUID directly
587 or using the feature without checking anything
588 will still see it. This just prevents it from
589 being used by the kernel or shown in /proc/cpuinfo.
590 Also note the kernel might malfunction if you disable
591 some critical bits.
593 cma=nn[MG]@[start[MG][-end[MG]]]
594 [ARM,X86,KNL]
595 Sets the size of kernel global memory area for
596 contiguous memory allocations and optionally the
597 placement constraint by the physical address range of
598 memory allocations. A value of 0 disables CMA
599 altogether. For more information, see
600 include/linux/dma-contiguous.h
602 cmo_free_hint= [PPC] Format: { yes | no }
603 Specify whether pages are marked as being inactive
604 when they are freed. This is used in CMO environments
605 to determine OS memory pressure for page stealing by
606 a hypervisor.
607 Default: yes
609 coherent_pool=nn[KMG] [ARM,KNL]
610 Sets the size of memory pool for coherent, atomic dma
611 allocations, by default set to 256K.
613 com20020= [HW,NET] ARCnet - COM20020 chipset
614 Format:
615 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
617 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
618 Format: <io>[,<irq>]
620 com90xx= [HW,NET]
621 ARCnet - COM90xx chipset (memory-mapped buffers)
622 Format: <io>[,<irq>[,<memstart>]]
624 condev= [HW,S390] console device
625 conmode=
627 console= [KNL] Output console device and options.
629 tty<n> Use the virtual console device <n>.
631 ttyS<n>[,options]
632 ttyUSB0[,options]
633 Use the specified serial port. The options are of
634 the form "bbbbpnf", where "bbbb" is the baud rate,
635 "p" is parity ("n", "o", or "e"), "n" is number of
636 bits, and "f" is flow control ("r" for RTS or
637 omit it). Default is "9600n8".
639 See Documentation/admin-guide/serial-console.rst for more
640 information. See
641 Documentation/networking/netconsole.txt for an
642 alternative.
644 uart[8250],io,<addr>[,options]
645 uart[8250],mmio,<addr>[,options]
646 uart[8250],mmio16,<addr>[,options]
647 uart[8250],mmio32,<addr>[,options]
648 uart[8250],0x<addr>[,options]
649 Start an early, polled-mode console on the 8250/16550
650 UART at the specified I/O port or MMIO address,
651 switching to the matching ttyS device later.
652 MMIO inter-register address stride is either 8-bit
653 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
654 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
655 to be equivalent to 'mmio'. 'options' are specified in
656 the same format described for ttyS above; if unspecified,
657 the h/w is not re-initialized.
659 hvc<n> Use the hypervisor console device <n>. This is for
660 both Xen and PowerPC hypervisors.
662 If the device connected to the port is not a TTY but a braille
663 device, prepend "brl," before the device type, for instance
664 console=brl,ttyS0
665 For now, only VisioBraille is supported.
667 console_msg_format=
668 [KNL] Change console messages format
669 default
670 By default we print messages on consoles in
671 "[time stamp] text\n" format (time stamp may not be
672 printed, depending on CONFIG_PRINTK_TIME or
673 `printk_time' param).
674 syslog
675 Switch to syslog format: "<%u>[time stamp] text\n"
676 IOW, each message will have a facility and loglevel
677 prefix. The format is similar to one used by syslog()
678 syscall, or to executing "dmesg -S --raw" or to reading
679 from /proc/kmsg.
681 consoleblank= [KNL] The console blank (screen saver) timeout in
682 seconds. A value of 0 disables the blank timer.
683 Defaults to 0.
685 coredump_filter=
686 [KNL] Change the default value for
687 /proc/<pid>/coredump_filter.
688 See also Documentation/filesystems/proc.rst.
690 coresight_cpu_debug.enable
691 [ARM,ARM64]
692 Format: <bool>
693 Enable/disable the CPU sampling based debugging.
694 0: default value, disable debugging
695 1: enable debugging at boot time
697 cpuidle.off=1 [CPU_IDLE]
698 disable the cpuidle sub-system
700 cpuidle.governor=
701 [CPU_IDLE] Name of the cpuidle governor to use.
703 cpufreq.off=1 [CPU_FREQ]
704 disable the cpufreq sub-system
706 cpu_init_udelay=N
707 [X86] Delay for N microsec between assert and de-assert
708 of APIC INIT to start processors. This delay occurs
709 on every CPU online, such as boot, and resume from suspend.
710 Default: 10000
712 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
713 Format:
714 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
716 crashkernel=size[KMG][@offset[KMG]]
717 [KNL] Using kexec, Linux can switch to a 'crash kernel'
718 upon panic. This parameter reserves the physical
719 memory region [offset, offset + size] for that kernel
720 image. If '@offset' is omitted, then a suitable offset
721 is selected automatically.
722 [KNL, x86_64] select a region under 4G first, and
723 fall back to reserve region above 4G when '@offset'
724 hasn't been specified.
725 See Documentation/admin-guide/kdump/kdump.rst for further details.
727 crashkernel=range1:size1[,range2:size2,...][@offset]
728 [KNL] Same as above, but depends on the memory
729 in the running system. The syntax of range is
730 start-[end] where start and end are both
731 a memory unit (amount[KMG]). See also
732 Documentation/admin-guide/kdump/kdump.rst for an example.
734 crashkernel=size[KMG],high
735 [KNL, x86_64] range could be above 4G. Allow kernel
736 to allocate physical memory region from top, so could
737 be above 4G if system have more than 4G ram installed.
738 Otherwise memory region will be allocated below 4G, if
739 available.
740 It will be ignored if crashkernel=X is specified.
741 crashkernel=size[KMG],low
742 [KNL, x86_64] range under 4G. When crashkernel=X,high
743 is passed, kernel could allocate physical memory region
744 above 4G, that cause second kernel crash on system
745 that require some amount of low memory, e.g. swiotlb
746 requires at least 64M+32K low memory, also enough extra
747 low memory is needed to make sure DMA buffers for 32-bit
748 devices won't run out. Kernel would try to allocate at
749 at least 256M below 4G automatically.
750 This one let user to specify own low range under 4G
751 for second kernel instead.
752 0: to disable low allocation.
753 It will be ignored when crashkernel=X,high is not used
754 or memory reserved is below 4G.
756 cryptomgr.notests
757 [KNL] Disable crypto self-tests
759 cs89x0_dma= [HW,NET]
760 Format: <dma>
762 cs89x0_media= [HW,NET]
763 Format: { rj45 | aui | bnc }
765 dasd= [HW,NET]
766 See header of drivers/s390/block/dasd_devmap.c.
768 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
769 (one device per port)
770 Format: <port#>,<type>
771 See also Documentation/input/devices/joystick-parport.rst
773 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
774 time. See
775 Documentation/admin-guide/dynamic-debug-howto.rst for
776 details. Deprecated, see dyndbg.
778 debug [KNL] Enable kernel debugging (events log level).
780 debug_boot_weak_hash
781 [KNL] Enable printing [hashed] pointers early in the
782 boot sequence. If enabled, we use a weak hash instead
783 of siphash to hash pointers. Use this option if you are
784 seeing instances of '(___ptrval___)') and need to see a
785 value (hashed pointer) instead. Cryptographically
786 insecure, please do not use on production kernels.
788 debug_locks_verbose=
789 [KNL] verbose self-tests
790 Format=<0|1>
791 Print debugging info while doing the locking API
792 self-tests.
793 We default to 0 (no extra messages), setting it to
794 1 will print _a lot_ more information - normally
795 only useful to kernel developers.
797 debug_objects [KNL] Enable object debugging
799 no_debug_objects
800 [KNL] Disable object debugging
802 debug_guardpage_minorder=
803 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
804 parameter allows control of the order of pages that will
805 be intentionally kept free (and hence protected) by the
806 buddy allocator. Bigger value increase the probability
807 of catching random memory corruption, but reduce the
808 amount of memory for normal system use. The maximum
809 possible value is MAX_ORDER/2. Setting this parameter
810 to 1 or 2 should be enough to identify most random
811 memory corruption problems caused by bugs in kernel or
812 driver code when a CPU writes to (or reads from) a
813 random memory location. Note that there exists a class
814 of memory corruptions problems caused by buggy H/W or
815 F/W or by drivers badly programing DMA (basically when
816 memory is written at bus level and the CPU MMU is
817 bypassed) which are not detectable by
818 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
819 tracking down these problems.
821 debug_pagealloc=
822 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
823 enables the feature at boot time. By default, it is
824 disabled and the system will work mostly the same as a
825 kernel built without CONFIG_DEBUG_PAGEALLOC.
826 Note: to get most of debug_pagealloc error reports, it's
827 useful to also enable the page_owner functionality.
828 on: enable the feature
830 debugpat [X86] Enable PAT debugging
832 decnet.addr= [HW,NET]
833 Format: <area>[,<node>]
834 See also Documentation/networking/decnet.txt.
836 default_hugepagesz=
837 [same as hugepagesz=] The size of the default
838 HugeTLB page size. This is the size represented by
839 the legacy /proc/ hugepages APIs, used for SHM, and
840 default size when mounting hugetlbfs filesystems.
841 Defaults to the default architecture's huge page size
842 if not specified.
844 deferred_probe_timeout=
845 [KNL] Debugging option to set a timeout in seconds for
846 deferred probe to give up waiting on dependencies to
847 probe. Only specific dependencies (subsystems or
848 drivers) that have opted in will be ignored. A timeout of 0
849 will timeout at the end of initcalls. This option will also
850 dump out devices still on the deferred probe list after
851 retrying.
853 dfltcc= [HW,S390]
854 Format: { on | off | def_only | inf_only | always }
855 on: s390 zlib hardware support for compression on
856 level 1 and decompression (default)
857 off: No s390 zlib hardware support
858 def_only: s390 zlib hardware support for deflate
859 only (compression on level 1)
860 inf_only: s390 zlib hardware support for inflate
861 only (decompression)
862 always: Same as 'on' but ignores the selected compression
863 level always using hardware support (used for debugging)
865 dhash_entries= [KNL]
866 Set number of hash buckets for dentry cache.
868 disable_1tb_segments [PPC]
869 Disables the use of 1TB hash page table segments. This
870 causes the kernel to fall back to 256MB segments which
871 can be useful when debugging issues that require an SLB
872 miss to occur.
874 disable= [IPV6]
875 See Documentation/networking/ipv6.txt.
877 hardened_usercopy=
878 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
879 hardening is enabled for this boot. Hardened
880 usercopy checking is used to protect the kernel
881 from reading or writing beyond known memory
882 allocation boundaries as a proactive defense
883 against bounds-checking flaws in the kernel's
884 copy_to_user()/copy_from_user() interface.
885 on Perform hardened usercopy checks (default).
886 off Disable hardened usercopy checks.
888 disable_radix [PPC]
889 Disable RADIX MMU mode on POWER9
891 disable_tlbie [PPC]
892 Disable TLBIE instruction. Currently does not work
893 with KVM, with HASH MMU, or with coherent accelerators.
895 disable_cpu_apicid= [X86,APIC,SMP]
896 Format: <int>
897 The number of initial APIC ID for the
898 corresponding CPU to be disabled at boot,
899 mostly used for the kdump 2nd kernel to
900 disable BSP to wake up multiple CPUs without
901 causing system reset or hang due to sending
902 INIT from AP to BSP.
904 perf_v4_pmi= [X86,INTEL]
905 Format: <bool>
906 Disable Intel PMU counter freezing feature.
907 The feature only exists starting from
908 Arch Perfmon v4 (Skylake and newer).
910 disable_ddw [PPC/PSERIES]
911 Disable Dynamic DMA Window support. Use this if
912 to workaround buggy firmware.
914 disable_ipv6= [IPV6]
915 See Documentation/networking/ipv6.txt.
917 disable_mtrr_cleanup [X86]
918 The kernel tries to adjust MTRR layout from continuous
919 to discrete, to make X server driver able to add WB
920 entry later. This parameter disables that.
922 disable_mtrr_trim [X86, Intel and AMD only]
923 By default the kernel will trim any uncacheable
924 memory out of your available memory pool based on
925 MTRR settings. This parameter disables that behavior,
926 possibly causing your machine to run very slowly.
928 disable_timer_pin_1 [X86]
929 Disable PIN 1 of APIC timer
930 Can be useful to work around chipset bugs.
932 dis_ucode_ldr [X86] Disable the microcode loader.
934 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
935 this option disables the debugging code at boot.
937 dma_debug_entries=<number>
938 This option allows to tune the number of preallocated
939 entries for DMA-API debugging code. One entry is
940 required per DMA-API allocation. Use this if the
941 DMA-API debugging code disables itself because the
942 architectural default is too low.
944 dma_debug_driver=<driver_name>
945 With this option the DMA-API debugging driver
946 filter feature can be enabled at boot time. Just
947 pass the driver to filter for as the parameter.
948 The filter can be disabled or changed to another
949 driver later using sysfs.
951 driver_async_probe= [KNL]
952 List of driver names to be probed asynchronously.
953 Format: <driver_name1>,<driver_name2>...
955 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
956 Broken monitors, graphic adapters, KVMs and EDIDless
957 panels may send no or incorrect EDID data sets.
958 This parameter allows to specify an EDID data sets
959 in the /lib/firmware directory that are used instead.
960 Generic built-in EDID data sets are used, if one of
961 edid/1024x768.bin, edid/1280x1024.bin,
962 edid/1680x1050.bin, or edid/1920x1080.bin is given
963 and no file with the same name exists. Details and
964 instructions how to build your own EDID data are
965 available in Documentation/admin-guide/edid.rst. An EDID
966 data set will only be used for a particular connector,
967 if its name and a colon are prepended to the EDID
968 name. Each connector may use a unique EDID data
969 set by separating the files with a comma. An EDID
970 data set with no connector name will be used for
971 any connectors not explicitly specified.
973 dscc4.setup= [NET]
975 dt_cpu_ftrs= [PPC]
976 Format: {"off" | "known"}
977 Control how the dt_cpu_ftrs device-tree binding is
978 used for CPU feature discovery and setup (if it
979 exists).
980 off: Do not use it, fall back to legacy cpu table.
981 known: Do not pass through unknown features to guests
982 or userspace, only those that the kernel is aware of.
984 dump_apple_properties [X86]
985 Dump name and content of EFI device properties on
986 x86 Macs. Useful for driver authors to determine
987 what data is available or for reverse-engineering.
989 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
990 module.dyndbg[="val"]
991 Enable debug messages at boot time. See
992 Documentation/admin-guide/dynamic-debug-howto.rst
993 for details.
995 nopku [X86] Disable Memory Protection Keys CPU feature found
996 in some Intel CPUs.
998 module.async_probe [KNL]
999 Enable asynchronous probe on this module.
1001 early_ioremap_debug [KNL]
1002 Enable debug messages in early_ioremap support. This
1003 is useful for tracking down temporary early mappings
1004 which are not unmapped.
1006 earlycon= [KNL] Output early console device and options.
1008 When used with no options, the early console is
1009 determined by stdout-path property in device tree's
1010 chosen node or the ACPI SPCR table if supported by
1011 the platform.
1013 cdns,<addr>[,options]
1014 Start an early, polled-mode console on a Cadence
1015 (xuartps) serial port at the specified address. Only
1016 supported option is baud rate. If baud rate is not
1017 specified, the serial port must already be setup and
1018 configured.
1020 uart[8250],io,<addr>[,options]
1021 uart[8250],mmio,<addr>[,options]
1022 uart[8250],mmio32,<addr>[,options]
1023 uart[8250],mmio32be,<addr>[,options]
1024 uart[8250],0x<addr>[,options]
1025 Start an early, polled-mode console on the 8250/16550
1026 UART at the specified I/O port or MMIO address.
1027 MMIO inter-register address stride is either 8-bit
1028 (mmio) or 32-bit (mmio32 or mmio32be).
1029 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1030 to be equivalent to 'mmio'. 'options' are specified
1031 in the same format described for "console=ttyS<n>"; if
1032 unspecified, the h/w is not initialized.
1034 pl011,<addr>
1035 pl011,mmio32,<addr>
1036 Start an early, polled-mode console on a pl011 serial
1037 port at the specified address. The pl011 serial port
1038 must already be setup and configured. Options are not
1039 yet supported. If 'mmio32' is specified, then only
1040 the driver will use only 32-bit accessors to read/write
1041 the device registers.
1043 meson,<addr>
1044 Start an early, polled-mode console on a meson serial
1045 port at the specified address. The serial port must
1046 already be setup and configured. Options are not yet
1047 supported.
1049 msm_serial,<addr>
1050 Start an early, polled-mode console on an msm serial
1051 port at the specified address. The serial port
1052 must already be setup and configured. Options are not
1053 yet supported.
1055 msm_serial_dm,<addr>
1056 Start an early, polled-mode console on an msm serial
1057 dm port at the specified address. The serial port
1058 must already be setup and configured. Options are not
1059 yet supported.
1061 owl,<addr>
1062 Start an early, polled-mode console on a serial port
1063 of an Actions Semi SoC, such as S500 or S900, at the
1064 specified address. The serial port must already be
1065 setup and configured. Options are not yet supported.
1067 rda,<addr>
1068 Start an early, polled-mode console on a serial port
1069 of an RDA Micro SoC, such as RDA8810PL, at the
1070 specified address. The serial port must already be
1071 setup and configured. Options are not yet supported.
1073 sbi
1074 Use RISC-V SBI (Supervisor Binary Interface) for early
1075 console.
1077 smh Use ARM semihosting calls for early console.
1079 s3c2410,<addr>
1080 s3c2412,<addr>
1081 s3c2440,<addr>
1082 s3c6400,<addr>
1083 s5pv210,<addr>
1084 exynos4210,<addr>
1085 Use early console provided by serial driver available
1086 on Samsung SoCs, requires selecting proper type and
1087 a correct base address of the selected UART port. The
1088 serial port must already be setup and configured.
1089 Options are not yet supported.
1091 lantiq,<addr>
1092 Start an early, polled-mode console on a lantiq serial
1093 (lqasc) port at the specified address. The serial port
1094 must already be setup and configured. Options are not
1095 yet supported.
1097 lpuart,<addr>
1098 lpuart32,<addr>
1099 Use early console provided by Freescale LP UART driver
1100 found on Freescale Vybrid and QorIQ LS1021A processors.
1101 A valid base address must be provided, and the serial
1102 port must already be setup and configured.
1104 ec_imx21,<addr>
1105 ec_imx6q,<addr>
1106 Start an early, polled-mode, output-only console on the
1107 Freescale i.MX UART at the specified address. The UART
1108 must already be setup and configured.
1110 ar3700_uart,<addr>
1111 Start an early, polled-mode console on the
1112 Armada 3700 serial port at the specified
1113 address. The serial port must already be setup
1114 and configured. Options are not yet supported.
1116 qcom_geni,<addr>
1117 Start an early, polled-mode console on a Qualcomm
1118 Generic Interface (GENI) based serial port at the
1119 specified address. The serial port must already be
1120 setup and configured. Options are not yet supported.
1122 efifb,[options]
1123 Start an early, unaccelerated console on the EFI
1124 memory mapped framebuffer (if available). On cache
1125 coherent non-x86 systems that use system memory for
1126 the framebuffer, pass the 'ram' option so that it is
1127 mapped with the correct attributes.
1129 linflex,<addr>
1130 Use early console provided by Freescale LINFlexD UART
1131 serial driver for NXP S32V234 SoCs. A valid base
1132 address must be provided, and the serial port must
1133 already be setup and configured.
1135 earlyprintk= [X86,SH,ARM,M68k,S390]
1136 earlyprintk=vga
1137 earlyprintk=sclp
1138 earlyprintk=xen
1139 earlyprintk=serial[,ttySn[,baudrate]]
1140 earlyprintk=serial[,0x...[,baudrate]]
1141 earlyprintk=ttySn[,baudrate]
1142 earlyprintk=dbgp[debugController#]
1143 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1144 earlyprintk=xdbc[xhciController#]
1146 earlyprintk is useful when the kernel crashes before
1147 the normal console is initialized. It is not enabled by
1148 default because it has some cosmetic problems.
1150 Append ",keep" to not disable it when the real console
1151 takes over.
1153 Only one of vga, efi, serial, or usb debug port can
1154 be used at a time.
1156 Currently only ttyS0 and ttyS1 may be specified by
1157 name. Other I/O ports may be explicitly specified
1158 on some architectures (x86 and arm at least) by
1159 replacing ttySn with an I/O port address, like this:
1160 earlyprintk=serial,0x1008,115200
1161 You can find the port for a given device in
1162 /proc/tty/driver/serial:
1163 2: uart:ST16650V2 port:00001008 irq:18 ...
1165 Interaction with the standard serial driver is not
1166 very good.
1168 The VGA and EFI output is eventually overwritten by
1169 the real console.
1171 The xen output can only be used by Xen PV guests.
1173 The sclp output can only be used on s390.
1175 The optional "force" to "pciserial" enables use of a
1176 PCI device even when its classcode is not of the
1177 UART class.
1179 edac_report= [HW,EDAC] Control how to report EDAC event
1180 Format: {"on" | "off" | "force"}
1181 on: enable EDAC to report H/W event. May be overridden
1182 by other higher priority error reporting module.
1183 off: disable H/W event reporting through EDAC.
1184 force: enforce the use of EDAC to report H/W event.
1185 default: on.
1187 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1188 ekgdboc=kbd
1190 This is designed to be used in conjunction with
1191 the boot argument: earlyprintk=vga
1193 edd= [EDD]
1194 Format: {"off" | "on" | "skip[mbr]"}
1196 efi= [EFI]
1197 Format: { "old_map", "nochunk", "noruntime", "debug",
1198 "nosoftreserve", "disable_early_pci_dma",
1199 "no_disable_early_pci_dma" }
1200 old_map [X86-64]: switch to the old ioremap-based EFI
1201 runtime services mapping. [Needs CONFIG_X86_UV=y]
1202 nochunk: disable reading files in "chunks" in the EFI
1203 boot stub, as chunking can cause problems with some
1204 firmware implementations.
1205 noruntime : disable EFI runtime services support
1206 debug: enable misc debug output
1207 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1208 attribute may cause the kernel to reserve the
1209 memory range for a memory mapping driver to
1210 claim. Specify efi=nosoftreserve to disable this
1211 reservation and treat the memory by its base type
1212 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1213 disable_early_pci_dma: Disable the busmaster bit on all
1214 PCI bridges while in the EFI boot stub
1215 no_disable_early_pci_dma: Leave the busmaster bit set
1216 on all PCI bridges while in the EFI boot stub
1218 efi_no_storage_paranoia [EFI; X86]
1219 Using this parameter you can use more than 50% of
1220 your efi variable storage. Use this parameter only if
1221 you are really sure that your UEFI does sane gc and
1222 fulfills the spec otherwise your board may brick.
1224 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1225 Add arbitrary attribute to specific memory range by
1226 updating original EFI memory map.
1227 Region of memory which aa attribute is added to is
1228 from ss to ss+nn.
1230 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1231 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1232 attribute is added to range 0x100000000-0x180000000 and
1233 0x10a0000000-0x1120000000.
1235 If efi_fake_mem=8G@9G:0x40000 is specified, the
1236 EFI_MEMORY_SP(0x40000) attribute is added to
1237 range 0x240000000-0x43fffffff.
1239 Using this parameter you can do debugging of EFI memmap
1240 related features. For example, you can do debugging of
1241 Address Range Mirroring feature even if your box
1242 doesn't support it, or mark specific memory as
1243 "soft reserved".
1245 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1246 that is to be dynamically loaded by Linux. If there are
1247 multiple variables with the same name but with different
1248 vendor GUIDs, all of them will be loaded. See
1249 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1252 eisa_irq_edge= [PARISC,HW]
1253 See header of drivers/parisc/eisa.c.
1255 elanfreq= [X86-32]
1256 See comment before function elanfreq_setup() in
1257 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1259 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1260 Specifies physical address of start of kernel core
1261 image elf header and optionally the size. Generally
1262 kexec loader will pass this option to capture kernel.
1263 See Documentation/admin-guide/kdump/kdump.rst for details.
1265 enable_mtrr_cleanup [X86]
1266 The kernel tries to adjust MTRR layout from continuous
1267 to discrete, to make X server driver able to add WB
1268 entry later. This parameter enables that.
1270 enable_timer_pin_1 [X86]
1271 Enable PIN 1 of APIC timer
1272 Can be useful to work around chipset bugs
1273 (in particular on some ATI chipsets).
1274 The kernel tries to set a reasonable default.
1276 enforcing [SELINUX] Set initial enforcing status.
1277 Format: {"0" | "1"}
1278 See security/selinux/Kconfig help text.
1279 0 -- permissive (log only, no denials).
1280 1 -- enforcing (deny and log).
1281 Default value is 0.
1282 Value can be changed at runtime via
1283 /sys/fs/selinux/enforce.
1285 erst_disable [ACPI]
1286 Disable Error Record Serialization Table (ERST)
1287 support.
1289 ether= [HW,NET] Ethernet cards parameters
1290 This option is obsoleted by the "netdev=" option, which
1291 has equivalent usage. See its documentation for details.
1293 evm= [EVM]
1294 Format: { "fix" }
1295 Permit 'security.evm' to be updated regardless of
1296 current integrity status.
1298 failslab=
1299 fail_page_alloc=
1300 fail_make_request=[KNL]
1301 General fault injection mechanism.
1302 Format: <interval>,<probability>,<space>,<times>
1303 See also Documentation/fault-injection/.
1305 floppy= [HW]
1306 See Documentation/admin-guide/blockdev/floppy.rst.
1308 force_pal_cache_flush
1309 [IA-64] Avoid check_sal_cache_flush which may hang on
1310 buggy SAL_CACHE_FLUSH implementations. Using this
1311 parameter will force ia64_sal_cache_flush to call
1312 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1314 forcepae [X86-32]
1315 Forcefully enable Physical Address Extension (PAE).
1316 Many Pentium M systems disable PAE but may have a
1317 functionally usable PAE implementation.
1318 Warning: use of this parameter will taint the kernel
1319 and may cause unknown problems.
1321 ftrace=[tracer]
1322 [FTRACE] will set and start the specified tracer
1323 as early as possible in order to facilitate early
1324 boot debugging.
1326 ftrace_dump_on_oops[=orig_cpu]
1327 [FTRACE] will dump the trace buffers on oops.
1328 If no parameter is passed, ftrace will dump
1329 buffers of all CPUs, but if you pass orig_cpu, it will
1330 dump only the buffer of the CPU that triggered the
1331 oops.
1333 ftrace_filter=[function-list]
1334 [FTRACE] Limit the functions traced by the function
1335 tracer at boot up. function-list is a comma separated
1336 list of functions. This list can be changed at run
1337 time by the set_ftrace_filter file in the debugfs
1338 tracing directory.
1340 ftrace_notrace=[function-list]
1341 [FTRACE] Do not trace the functions specified in
1342 function-list. This list can be changed at run time
1343 by the set_ftrace_notrace file in the debugfs
1344 tracing directory.
1346 ftrace_graph_filter=[function-list]
1347 [FTRACE] Limit the top level callers functions traced
1348 by the function graph tracer at boot up.
1349 function-list is a comma separated list of functions
1350 that can be changed at run time by the
1351 set_graph_function file in the debugfs tracing directory.
1353 ftrace_graph_notrace=[function-list]
1354 [FTRACE] Do not trace from the functions specified in
1355 function-list. This list is a comma separated list of
1356 functions that can be changed at run time by the
1357 set_graph_notrace file in the debugfs tracing directory.
1359 ftrace_graph_max_depth=<uint>
1360 [FTRACE] Used with the function graph tracer. This is
1361 the max depth it will trace into a function. This value
1362 can be changed at run time by the max_graph_depth file
1363 in the tracefs tracing directory. default: 0 (no limit)
1365 fw_devlink= [KNL] Create device links between consumer and supplier
1366 devices by scanning the firmware to infer the
1367 consumer/supplier relationships. This feature is
1368 especially useful when drivers are loaded as modules as
1369 it ensures proper ordering of tasks like device probing
1370 (suppliers first, then consumers), supplier boot state
1371 clean up (only after all consumers have probed),
1372 suspend/resume & runtime PM (consumers first, then
1373 suppliers).
1374 Format: { off | permissive | on | rpm }
1375 off -- Don't create device links from firmware info.
1376 permissive -- Create device links from firmware info
1377 but use it only for ordering boot state clean
1378 up (sync_state() calls).
1379 on -- Create device links from firmware info and use it
1380 to enforce probe and suspend/resume ordering.
1381 rpm -- Like "on", but also use to order runtime PM.
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/devices/joystick-parport.rst
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 hlt [BUGS=ARM,SH]
1463 hpet= [X86-32,HPET] option to control HPET usage
1464 Format: { enable (default) | disable | force |
1465 verbose }
1466 disable: disable HPET and use PIT instead
1467 force: allow force enabled of undocumented chips (ICH4,
1468 VIA, nVidia)
1469 verbose: show contents of HPET registers during setup
1471 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1472 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1474 hugetlb_cma= [HW] The size of a cma area used for allocation
1475 of gigantic hugepages.
1476 Format: nn[KMGTPE]
1478 Reserve a cma area of given size and allocate gigantic
1479 hugepages using the cma allocator. If enabled, the
1480 boot-time allocation of gigantic hugepages is skipped.
1482 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1483 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1484 On x86-64 and powerpc, this option can be specified
1485 multiple times interleaved with hugepages= to reserve
1486 huge pages of different sizes. Valid pages sizes on
1487 x86-64 are 2M (when the CPU supports "pse") and 1G
1488 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1490 hung_task_panic=
1491 [KNL] Should the hung task detector generate panics.
1492 Format: <integer>
1494 A nonzero value instructs the kernel to panic when a
1495 hung task is detected. The default value is controlled
1496 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1497 option. The value selected by this boot parameter can
1498 be changed later by the kernel.hung_task_panic sysctl.
1500 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1501 terminal devices. Valid values: 0..8
1502 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1503 If specified, z/VM IUCV HVC accepts connections
1504 from listed z/VM user IDs only.
1506 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1507 which allow the hypervisor to 'idle' the
1508 guest on lock contention.
1510 keep_bootcon [KNL]
1511 Do not unregister boot console at start. This is only
1512 useful for debugging when something happens in the window
1513 between unregistering the boot console and initializing
1514 the real console.
1516 i2c_bus= [HW] Override the default board specific I2C bus speed
1517 or register an additional I2C bus that is not
1518 registered from board initialization code.
1519 Format:
1520 <bus_id>,<clkrate>
1522 i8042.debug [HW] Toggle i8042 debug mode
1523 i8042.unmask_kbd_data
1524 [HW] Enable printing of interrupt data from the KBD port
1525 (disabled by default, and as a pre-condition
1526 requires that i8042.debug=1 be enabled)
1527 i8042.direct [HW] Put keyboard port into non-translated mode
1528 i8042.dumbkbd [HW] Pretend that controller can only read data from
1529 keyboard and cannot control its state
1530 (Don't attempt to blink the leds)
1531 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1532 i8042.nokbd [HW] Don't check/create keyboard port
1533 i8042.noloop [HW] Disable the AUX Loopback command while probing
1534 for the AUX port
1535 i8042.nomux [HW] Don't check presence of an active multiplexing
1536 controller
1537 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1538 controllers
1539 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1540 i8042.reset [HW] Reset the controller during init, cleanup and
1541 suspend-to-ram transitions, only during s2r
1542 transitions, or never reset
1543 Format: { 1 | Y | y | 0 | N | n }
1544 1, Y, y: always reset controller
1545 0, N, n: don't ever reset controller
1546 Default: only on s2r transitions on x86; most other
1547 architectures force reset to be always executed
1548 i8042.unlock [HW] Unlock (ignore) the keylock
1549 i8042.kbdreset [HW] Reset device connected to KBD port
1551 i810= [HW,DRM]
1553 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1554 indicates that the driver is running on unsupported
1555 hardware.
1556 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1557 does not match list of supported models.
1558 i8k.power_status
1559 [HW] Report power status in /proc/i8k
1560 (disabled by default)
1561 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1562 capability is set.
1564 i915.invert_brightness=
1565 [DRM] Invert the sense of the variable that is used to
1566 set the brightness of the panel backlight. Normally a
1567 brightness value of 0 indicates backlight switched off,
1568 and the maximum of the brightness value sets the backlight
1569 to maximum brightness. If this parameter is set to 0
1570 (default) and the machine requires it, or this parameter
1571 is set to 1, a brightness value of 0 sets the backlight
1572 to maximum brightness, and the maximum of the brightness
1573 value switches the backlight off.
1574 -1 -- never invert brightness
1575 0 -- machine default
1576 1 -- force brightness inversion
1578 icn= [HW,ISDN]
1579 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1581 ide-core.nodma= [HW] (E)IDE subsystem
1582 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1583 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1584 .cdrom .chs .ignore_cable are additional options
1585 See Documentation/ide/ide.rst.
1587 ide-generic.probe-mask= [HW] (E)IDE subsystem
1588 Format: <int>
1589 Probe mask for legacy ISA IDE ports. Depending on
1590 platform up to 6 ports are supported, enabled by
1591 setting corresponding bits in the mask to 1. The
1592 default value is 0x0, which has a special meaning.
1593 On systems that have PCI, it triggers scanning the
1594 PCI bus for the first and the second port, which
1595 are then probed. On systems without PCI the value
1596 of 0x0 enables probing the two first ports as if it
1597 was 0x3.
1599 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1600 Claim all unknown PCI IDE storage controllers.
1602 idle= [X86]
1603 Format: idle=poll, idle=halt, idle=nomwait
1604 Poll forces a polling idle loop that can slightly
1605 improve the performance of waking up a idle CPU, but
1606 will use a lot of power and make the system run hot.
1607 Not recommended.
1608 idle=halt: Halt is forced to be used for CPU idle.
1609 In such case C2/C3 won't be used again.
1610 idle=nomwait: Disable mwait for CPU C-states
1612 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1613 Format: { strict | legacy | 2008 | relaxed }
1614 Default: strict
1616 Choose which programs will be accepted for execution
1617 based on the IEEE 754 NaN encoding(s) supported by
1618 the FPU and the NaN encoding requested with the value
1619 of an ELF file header flag individually set by each
1620 binary. Hardware implementations are permitted to
1621 support either or both of the legacy and the 2008 NaN
1622 encoding mode.
1624 Available settings are as follows:
1625 strict accept binaries that request a NaN encoding
1626 supported by the FPU
1627 legacy only accept legacy-NaN binaries, if supported
1628 by the FPU
1629 2008 only accept 2008-NaN binaries, if supported
1630 by the FPU
1631 relaxed accept any binaries regardless of whether
1632 supported by the FPU
1634 The FPU emulator is always able to support both NaN
1635 encodings, so if no FPU hardware is present or it has
1636 been disabled with 'nofpu', then the settings of
1637 'legacy' and '2008' strap the emulator accordingly,
1638 'relaxed' straps the emulator for both legacy-NaN and
1639 2008-NaN, whereas 'strict' enables legacy-NaN only on
1640 legacy processors and both NaN encodings on MIPS32 or
1641 MIPS64 CPUs.
1643 The setting for ABS.fmt/NEG.fmt instruction execution
1644 mode generally follows that for the NaN encoding,
1645 except where unsupported by hardware.
1647 ignore_loglevel [KNL]
1648 Ignore loglevel setting - this will print /all/
1649 kernel messages to the console. Useful for debugging.
1650 We also add it as printk module parameter, so users
1651 could change it dynamically, usually by
1652 /sys/module/printk/parameters/ignore_loglevel.
1654 ignore_rlimit_data
1655 Ignore RLIMIT_DATA setting for data mappings,
1656 print warning at first misuse. Can be changed via
1657 /sys/module/kernel/parameters/ignore_rlimit_data.
1659 ihash_entries= [KNL]
1660 Set number of hash buckets for inode cache.
1662 ima_appraise= [IMA] appraise integrity measurements
1663 Format: { "off" | "enforce" | "fix" | "log" }
1664 default: "enforce"
1666 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1667 The builtin appraise policy appraises all files
1668 owned by uid=0.
1670 ima_canonical_fmt [IMA]
1671 Use the canonical format for the binary runtime
1672 measurements, instead of host native format.
1674 ima_hash= [IMA]
1675 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1676 | sha512 | ... }
1677 default: "sha1"
1679 The list of supported hash algorithms is defined
1680 in crypto/hash_info.h.
1682 ima_policy= [IMA]
1683 The builtin policies to load during IMA setup.
1684 Format: "tcb | appraise_tcb | secure_boot |
1685 fail_securely"
1687 The "tcb" policy measures all programs exec'd, files
1688 mmap'd for exec, and all files opened with the read
1689 mode bit set by either the effective uid (euid=0) or
1690 uid=0.
1692 The "appraise_tcb" policy appraises the integrity of
1693 all files owned by root.
1695 The "secure_boot" policy appraises the integrity
1696 of files (eg. kexec kernel image, kernel modules,
1697 firmware, policy, etc) based on file signatures.
1699 The "fail_securely" policy forces file signature
1700 verification failure also on privileged mounted
1701 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1702 flag.
1704 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1705 Load a policy which meets the needs of the Trusted
1706 Computing Base. This means IMA will measure all
1707 programs exec'd, files mmap'd for exec, and all files
1708 opened for read by uid=0.
1710 ima_template= [IMA]
1711 Select one of defined IMA measurements template formats.
1712 Formats: { "ima" | "ima-ng" | "ima-sig" }
1713 Default: "ima-ng"
1715 ima_template_fmt=
1716 [IMA] Define a custom template format.
1717 Format: { "field1|...|fieldN" }
1719 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1720 Format: <min_file_size>
1721 Set the minimal file size for using asynchronous hash.
1722 If left unspecified, ahash usage is disabled.
1724 ahash performance varies for different data sizes on
1725 different crypto accelerators. This option can be used
1726 to achieve the best performance for a particular HW.
1728 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1729 Format: <bufsize>
1730 Set hashing buffer size. Default: 4k.
1732 ahash performance varies for different chunk sizes on
1733 different crypto accelerators. This option can be used
1734 to achieve best performance for particular HW.
1736 init= [KNL]
1737 Format: <full_path>
1738 Run specified binary instead of /sbin/init as init
1739 process.
1741 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1742 for working out where the kernel is dying during
1743 startup.
1745 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1746 initcall functions. Useful for debugging built-in
1747 modules and initcalls.
1749 initrd= [BOOT] Specify the location of the initial ramdisk
1751 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
1752 zeroes.
1753 Format: 0 | 1
1754 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
1756 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
1757 Format: 0 | 1
1758 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
1760 init_pkru= [x86] Specify the default memory protection keys rights
1761 register contents for all processes. 0x55555554 by
1762 default (disallow access to all but pkey 0). Can
1763 override in debugfs after boot.
1765 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1766 Format: <irq>
1768 int_pln_enable [x86] Enable power limit notification interrupt
1770 integrity_audit=[IMA]
1771 Format: { "0" | "1" }
1772 0 -- basic integrity auditing messages. (Default)
1773 1 -- additional integrity auditing messages.
1775 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1776 on
1777 Enable intel iommu driver.
1778 off
1779 Disable intel iommu driver.
1780 igfx_off [Default Off]
1781 By default, gfx is mapped as normal device. If a gfx
1782 device has a dedicated DMAR unit, the DMAR unit is
1783 bypassed by not enabling DMAR with this option. In
1784 this case, gfx device will use physical address for
1785 DMA.
1786 forcedac [x86_64]
1787 With this option iommu will not optimize to look
1788 for io virtual address below 32-bit forcing dual
1789 address cycle on pci bus for cards supporting greater
1790 than 32-bit addressing. The default is to look
1791 for translation below 32-bit and if not available
1792 then look in the higher range.
1793 strict [Default Off]
1794 With this option on every unmap_single operation will
1795 result in a hardware IOTLB flush operation as opposed
1796 to batching them for performance.
1797 sp_off [Default Off]
1798 By default, super page will be supported if Intel IOMMU
1799 has the capability. With this option, super page will
1800 not be supported.
1801 sm_on [Default Off]
1802 By default, scalable mode will be disabled even if the
1803 hardware advertises that it has support for the scalable
1804 mode translation. With this option set, scalable mode
1805 will be used on hardware which claims to support it.
1806 tboot_noforce [Default Off]
1807 Do not force the Intel IOMMU enabled under tboot.
1808 By default, tboot will force Intel IOMMU on, which
1809 could harm performance of some high-throughput
1810 devices like 40GBit network cards, even if identity
1811 mapping is enabled.
1812 Note that using this option lowers the security
1813 provided by tboot because it makes the system
1814 vulnerable to DMA attacks.
1815 nobounce [Default off]
1816 Disable bounce buffer for untrusted devices such as
1817 the Thunderbolt devices. This will treat the untrusted
1818 devices as the trusted ones, hence might expose security
1819 risks of DMA attacks.
1821 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1822 0 disables intel_idle and fall back on acpi_idle.
1823 1 to 9 specify maximum depth of C-state.
1825 intel_pstate= [X86]
1826 disable
1827 Do not enable intel_pstate as the default
1828 scaling driver for the supported processors
1829 passive
1830 Use intel_pstate as a scaling driver, but configure it
1831 to work with generic cpufreq governors (instead of
1832 enabling its internal governor). This mode cannot be
1833 used along with the hardware-managed P-states (HWP)
1834 feature.
1835 force
1836 Enable intel_pstate on systems that prohibit it by default
1837 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1838 instead of acpi-cpufreq may disable platform features, such
1839 as thermal controls and power capping, that rely on ACPI
1840 P-States information being indicated to OSPM and therefore
1841 should be used with caution. This option does not work with
1842 processors that aren't supported by the intel_pstate driver
1843 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1844 no_hwp
1845 Do not enable hardware P state control (HWP)
1846 if available.
1847 hwp_only
1848 Only load intel_pstate on systems which support
1849 hardware P state control (HWP) if available.
1850 support_acpi_ppc
1851 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1852 Description Table, specifies preferred power management
1853 profile as "Enterprise Server" or "Performance Server",
1854 then this feature is turned on by default.
1855 per_cpu_perf_limits
1856 Allow per-logical-CPU P-State performance control limits using
1857 cpufreq sysfs interface
1859 intremap= [X86-64, Intel-IOMMU]
1860 on enable Interrupt Remapping (default)
1861 off disable Interrupt Remapping
1862 nosid disable Source ID checking
1863 no_x2apic_optout
1864 BIOS x2APIC opt-out request will be ignored
1865 nopost disable Interrupt Posting
1867 iomem= Disable strict checking of access to MMIO memory
1868 strict regions from userspace.
1869 relaxed
1871 iommu= [x86]
1872 off
1873 force
1874 noforce
1875 biomerge
1876 panic
1877 nopanic
1878 merge
1879 nomerge
1880 soft
1881 pt [x86]
1882 nopt [x86]
1883 nobypass [PPC/POWERNV]
1884 Disable IOMMU bypass, using IOMMU for PCI devices.
1886 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1887 Format: { "0" | "1" }
1888 0 - Lazy mode.
1889 Request that DMA unmap operations use deferred
1890 invalidation of hardware TLBs, for increased
1891 throughput at the cost of reduced device isolation.
1892 Will fall back to strict mode if not supported by
1893 the relevant IOMMU driver.
1894 1 - Strict mode (default).
1895 DMA unmap operations invalidate IOMMU hardware TLBs
1896 synchronously.
1898 iommu.passthrough=
1899 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
1900 Format: { "0" | "1" }
1901 0 - Use IOMMU translation for DMA.
1902 1 - Bypass the IOMMU for DMA.
1903 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1905 io7= [HW] IO7 for Marvel based alpha systems
1906 See comment before marvel_specify_io7 in
1907 arch/alpha/kernel/core_marvel.c.
1909 io_delay= [X86] I/O delay method
1910 0x80
1911 Standard port 0x80 based delay
1912 0xed
1913 Alternate port 0xed based delay (needed on some systems)
1914 udelay
1915 Simple two microseconds delay
1916 none
1917 No delay
1919 ip= [IP_PNP]
1920 See Documentation/admin-guide/nfs/nfsroot.rst.
1922 ipcmni_extend [KNL] Extend the maximum number of unique System V
1923 IPC identifiers from 32,768 to 16,777,216.
1925 irqaffinity= [SMP] Set the default irq affinity mask
1926 The argument is a cpu list, as described above.
1928 irqchip.gicv2_force_probe=
1929 [ARM, ARM64]
1930 Format: <bool>
1931 Force the kernel to look for the second 4kB page
1932 of a GICv2 controller even if the memory range
1933 exposed by the device tree is too small.
1935 irqchip.gicv3_nolpi=
1936 [ARM, ARM64]
1937 Force the kernel to ignore the availability of
1938 LPIs (and by consequence ITSs). Intended for system
1939 that use the kernel as a bootloader, and thus want
1940 to let secondary kernels in charge of setting up
1941 LPIs.
1943 irqchip.gicv3_pseudo_nmi= [ARM64]
1944 Enables support for pseudo-NMIs in the kernel. This
1945 requires the kernel to be built with
1946 CONFIG_ARM64_PSEUDO_NMI.
1948 irqfixup [HW]
1949 When an interrupt is not handled search all handlers
1950 for it. Intended to get systems with badly broken
1951 firmware running.
1953 irqpoll [HW]
1954 When an interrupt is not handled search all handlers
1955 for it. Also check all handlers each timer
1956 interrupt. Intended to get systems with badly broken
1957 firmware running.
1959 isapnp= [ISAPNP]
1960 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1962 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1963 [Deprecated - use cpusets instead]
1964 Format: [flag-list,]<cpu-list>
1966 Specify one or more CPUs to isolate from disturbances
1967 specified in the flag list (default: domain):
1969 nohz
1970 Disable the tick when a single task runs.
1972 A residual 1Hz tick is offloaded to workqueues, which you
1973 need to affine to housekeeping through the global
1974 workqueue's affinity configured via the
1975 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1976 by using the 'domain' flag described below.
1978 NOTE: by default the global workqueue runs on all CPUs,
1979 so to protect individual CPUs the 'cpumask' file has to
1980 be configured manually after bootup.
1982 domain
1983 Isolate from the general SMP balancing and scheduling
1984 algorithms. Note that performing domain isolation this way
1985 is irreversible: it's not possible to bring back a CPU to
1986 the domains once isolated through isolcpus. It's strongly
1987 advised to use cpusets instead to disable scheduler load
1988 balancing through the "cpuset.sched_load_balance" file.
1989 It offers a much more flexible interface where CPUs can
1990 move in and out of an isolated set anytime.
1992 You can move a process onto or off an "isolated" CPU via
1993 the CPU affinity syscalls or cpuset.
1994 <cpu number> begins at 0 and the maximum value is
1995 "number of CPUs in system - 1".
1997 managed_irq
1999 Isolate from being targeted by managed interrupts
2000 which have an interrupt mask containing isolated
2001 CPUs. The affinity of managed interrupts is
2002 handled by the kernel and cannot be changed via
2003 the /proc/irq/* interfaces.
2005 This isolation is best effort and only effective
2006 if the automatically assigned interrupt mask of a
2007 device queue contains isolated and housekeeping
2008 CPUs. If housekeeping CPUs are online then such
2009 interrupts are directed to the housekeeping CPU
2010 so that IO submitted on the housekeeping CPU
2011 cannot disturb the isolated CPU.
2013 If a queue's affinity mask contains only isolated
2014 CPUs then this parameter has no effect on the
2015 interrupt routing decision, though interrupts are
2016 only delivered when tasks running on those
2017 isolated CPUs submit IO. IO submitted on
2018 housekeeping CPUs has no influence on those
2019 queues.
2021 The format of <cpu-list> is described above.
2023 iucv= [HW,NET]
2025 ivrs_ioapic [HW,X86_64]
2026 Provide an override to the IOAPIC-ID<->DEVICE-ID
2027 mapping provided in the IVRS ACPI table. For
2028 example, to map IOAPIC-ID decimal 10 to
2029 PCI device 00:14.0 write the parameter as:
2030 ivrs_ioapic[10]=00:14.0
2032 ivrs_hpet [HW,X86_64]
2033 Provide an override to the HPET-ID<->DEVICE-ID
2034 mapping provided in the IVRS ACPI table. For
2035 example, to map HPET-ID decimal 0 to
2036 PCI device 00:14.0 write the parameter as:
2037 ivrs_hpet[0]=00:14.0
2039 ivrs_acpihid [HW,X86_64]
2040 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2041 mapping provided in the IVRS ACPI table. For
2042 example, to map UART-HID:UID AMD0020:0 to
2043 PCI device 00:14.5 write the parameter as:
2044 ivrs_acpihid[00:14.5]=AMD0020:0
2046 js= [HW,JOY] Analog joystick
2047 See Documentation/input/joydev/joystick.rst.
2049 nokaslr [KNL]
2050 When CONFIG_RANDOMIZE_BASE is set, this disables
2051 kernel and module base offset ASLR (Address Space
2052 Layout Randomization).
2054 kasan_multi_shot
2055 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2056 report on every invalid memory access. Without this
2057 parameter KASAN will print report only for the first
2058 invalid access.
2060 keepinitrd [HW,ARM]
2062 kernelcore= [KNL,X86,IA-64,PPC]
2063 Format: nn[KMGTPE] | nn% | "mirror"
2064 This parameter specifies the amount of memory usable by
2065 the kernel for non-movable allocations. The requested
2066 amount is spread evenly throughout all nodes in the
2067 system as ZONE_NORMAL. The remaining memory is used for
2068 movable memory in its own zone, ZONE_MOVABLE. In the
2069 event, a node is too small to have both ZONE_NORMAL and
2070 ZONE_MOVABLE, kernelcore memory will take priority and
2071 other nodes will have a larger ZONE_MOVABLE.
2073 ZONE_MOVABLE is used for the allocation of pages that
2074 may be reclaimed or moved by the page migration
2075 subsystem. Note that allocations like PTEs-from-HighMem
2076 still use the HighMem zone if it exists, and the Normal
2077 zone if it does not.
2079 It is possible to specify the exact amount of memory in
2080 the form of "nn[KMGTPE]", a percentage of total system
2081 memory in the form of "nn%", or "mirror". If "mirror"
2082 option is specified, mirrored (reliable) memory is used
2083 for non-movable allocations and remaining memory is used
2084 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2085 are exclusive, so you cannot specify multiple forms.
2087 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
2088 Format: <Controller#>[,poll interval]
2089 The controller # is the number of the ehci usb debug
2090 port as it is probed via PCI. The poll interval is
2091 optional and is the number seconds in between
2092 each poll cycle to the debug port in case you need
2093 the functionality for interrupting the kernel with
2094 gdb or control-c on the dbgp connection. When
2095 not using this parameter you use sysrq-g to break into
2096 the kernel debugger.
2098 kgdboc= [KGDB,HW] kgdb over consoles.
2099 Requires a tty driver that supports console polling,
2100 or a supported polling keyboard driver (non-usb).
2101 Serial only format: <serial_device>[,baud]
2102 keyboard only format: kbd
2103 keyboard and serial format: kbd,<serial_device>[,baud]
2104 Optional Kernel mode setting:
2105 kms, kbd format: kms,kbd
2106 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2108 kgdbwait [KGDB] Stop kernel execution and enter the
2109 kernel debugger at the earliest opportunity.
2111 kmac= [MIPS] korina ethernet MAC address.
2112 Configure the RouterBoard 532 series on-chip
2113 Ethernet adapter MAC address.
2115 kmemleak= [KNL] Boot-time kmemleak enable/disable
2116 Valid arguments: on, off
2117 Default: on
2118 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2119 the default is off.
2121 kprobe_event=[probe-list]
2122 [FTRACE] Add kprobe events and enable at boot time.
2123 The probe-list is a semicolon delimited list of probe
2124 definitions. Each definition is same as kprobe_events
2125 interface, but the parameters are comma delimited.
2126 For example, to add a kprobe event on vfs_read with
2127 arg1 and arg2, add to the command line;
2129 kprobe_event=p,vfs_read,$arg1,$arg2
2131 See also Documentation/trace/kprobetrace.rst "Kernel
2132 Boot Parameter" section.
2134 kpti= [ARM64] Control page table isolation of user
2135 and kernel address spaces.
2136 Default: enabled on cores which need mitigation.
2137 0: force disabled
2138 1: force enabled
2140 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2141 Default is 0 (don't ignore, but inject #GP)
2143 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2144 Default is false (don't support).
2146 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2147 KVM MMU at runtime.
2148 Default is 0 (off)
2150 kvm.nx_huge_pages=
2151 [KVM] Controls the software workaround for the
2152 X86_BUG_ITLB_MULTIHIT bug.
2153 force : Always deploy workaround.
2154 off : Never deploy workaround.
2155 auto : Deploy workaround based on the presence of
2156 X86_BUG_ITLB_MULTIHIT.
2158 Default is 'auto'.
2160 If the software workaround is enabled for the host,
2161 guests do need not to enable it for nested guests.
2163 kvm.nx_huge_pages_recovery_ratio=
2164 [KVM] Controls how many 4KiB pages are periodically zapped
2165 back to huge pages. 0 disables the recovery, otherwise if
2166 the value is N KVM will zap 1/Nth of the 4KiB pages every
2167 minute. The default is 60.
2169 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2170 Default is 1 (enabled)
2172 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2173 for all guests.
2174 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2176 kvm-arm.vgic_v3_group0_trap=
2177 [KVM,ARM] Trap guest accesses to GICv3 group-0
2178 system registers
2180 kvm-arm.vgic_v3_group1_trap=
2181 [KVM,ARM] Trap guest accesses to GICv3 group-1
2182 system registers
2184 kvm-arm.vgic_v3_common_trap=
2185 [KVM,ARM] Trap guest accesses to GICv3 common
2186 system registers
2188 kvm-arm.vgic_v4_enable=
2189 [KVM,ARM] Allow use of GICv4 for direct injection of
2190 LPIs.
2192 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2193 (virtualized MMU) support on capable Intel chips.
2194 Default is 1 (enabled)
2196 kvm-intel.emulate_invalid_guest_state=
2197 [KVM,Intel] Enable emulation of invalid guest states
2198 Default is 0 (disabled)
2200 kvm-intel.flexpriority=
2201 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2202 Default is 1 (enabled)
2204 kvm-intel.nested=
2205 [KVM,Intel] Enable VMX nesting (nVMX).
2206 Default is 0 (disabled)
2208 kvm-intel.unrestricted_guest=
2209 [KVM,Intel] Disable unrestricted guest feature
2210 (virtualized real and unpaged mode) on capable
2211 Intel chips. Default is 1 (enabled)
2213 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2214 CVE-2018-3620.
2216 Valid arguments: never, cond, always
2218 always: L1D cache flush on every VMENTER.
2219 cond: Flush L1D on VMENTER only when the code between
2220 VMEXIT and VMENTER can leak host memory.
2221 never: Disables the mitigation
2223 Default is cond (do L1 cache flush in specific instances)
2225 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2226 feature (tagged TLBs) on capable Intel chips.
2227 Default is 1 (enabled)
2229 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2230 affected CPUs
2232 The kernel PTE inversion protection is unconditionally
2233 enabled and cannot be disabled.
2235 full
2236 Provides all available mitigations for the
2237 L1TF vulnerability. Disables SMT and
2238 enables all mitigations in the
2239 hypervisors, i.e. unconditional L1D flush.
2241 SMT control and L1D flush control via the
2242 sysfs interface is still possible after
2243 boot. Hypervisors will issue a warning
2244 when the first VM is started in a
2245 potentially insecure configuration,
2246 i.e. SMT enabled or L1D flush disabled.
2248 full,force
2249 Same as 'full', but disables SMT and L1D
2250 flush runtime control. Implies the
2251 'nosmt=force' command line option.
2252 (i.e. sysfs control of SMT is disabled.)
2254 flush
2255 Leaves SMT enabled and enables the default
2256 hypervisor mitigation, i.e. conditional
2257 L1D flush.
2259 SMT control and L1D flush control via the
2260 sysfs interface is still possible after
2261 boot. Hypervisors will issue a warning
2262 when the first VM is started in a
2263 potentially insecure configuration,
2264 i.e. SMT enabled or L1D flush disabled.
2266 flush,nosmt
2268 Disables SMT and enables the default
2269 hypervisor mitigation.
2271 SMT control and L1D flush control via the
2272 sysfs interface is still possible after
2273 boot. Hypervisors will issue a warning
2274 when the first VM is started in a
2275 potentially insecure configuration,
2276 i.e. SMT enabled or L1D flush disabled.
2278 flush,nowarn
2279 Same as 'flush', but hypervisors will not
2280 warn when a VM is started in a potentially
2281 insecure configuration.
2283 off
2284 Disables hypervisor mitigations and doesn't
2285 emit any warnings.
2286 It also drops the swap size and available
2287 RAM limit restriction on both hypervisor and
2288 bare metal.
2290 Default is 'flush'.
2292 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2294 l2cr= [PPC]
2296 l3cr= [PPC]
2298 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2299 disabled it.
2301 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2302 value for LAPIC timer one-shot implementation. Default
2303 back to the programmable timer unit in the LAPIC.
2305 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2306 in C2 power state.
2308 libata.dma= [LIBATA] DMA control
2309 libata.dma=0 Disable all PATA and SATA DMA
2310 libata.dma=1 PATA and SATA Disk DMA only
2311 libata.dma=2 ATAPI (CDROM) DMA only
2312 libata.dma=4 Compact Flash DMA only
2313 Combinations also work, so libata.dma=3 enables DMA
2314 for disks and CDROMs, but not CFs.
2316 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2317 libata.ignore_hpa=0 keep BIOS limits (default)
2318 libata.ignore_hpa=1 ignore limits, using full disk
2320 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2321 when set.
2322 Format: <int>
2324 libata.force= [LIBATA] Force configurations. The format is comma
2325 separated list of "[ID:]VAL" where ID is
2326 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2327 matching port, link or device. Basically, it matches
2328 the ATA ID string printed on console by libata. If
2329 the whole ID part is omitted, the last PORT and DEVICE
2330 values are used. If ID hasn't been specified yet, the
2331 configuration applies to all ports, links and devices.
2333 If only DEVICE is omitted, the parameter applies to
2334 the port and all links and devices behind it. DEVICE
2335 number of 0 either selects the first device or the
2336 first fan-out link behind PMP device. It does not
2337 select the host link. DEVICE number of 15 selects the
2338 host link and device attached to it.
2340 The VAL specifies the configuration to force. As long
2341 as there's no ambiguity shortcut notation is allowed.
2342 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2343 The following configurations can be forced.
2345 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2346 Any ID with matching PORT is used.
2348 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2350 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2351 udma[/][16,25,33,44,66,100,133] notation is also
2352 allowed.
2354 * [no]ncq: Turn on or off NCQ.
2356 * [no]ncqtrim: Turn off queued DSM TRIM.
2358 * nohrst, nosrst, norst: suppress hard, soft
2359 and both resets.
2361 * rstonce: only attempt one reset during
2362 hot-unplug link recovery
2364 * dump_id: dump IDENTIFY data.
2366 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2368 * disable: Disable this device.
2370 If there are multiple matching configurations changing
2371 the same attribute, the last one is used.
2373 memblock=debug [KNL] Enable memblock debug messages.
2375 load_ramdisk= [RAM] List of ramdisks to load from floppy
2376 See Documentation/admin-guide/blockdev/ramdisk.rst.
2378 lockd.nlm_grace_period=P [NFS] Assign grace period.
2379 Format: <integer>
2381 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2382 Format: <integer>
2384 lockd.nlm_timeout=T [NFS] Assign timeout value.
2385 Format: <integer>
2387 lockd.nlm_udpport=M [NFS] Assign UDP port.
2388 Format: <integer>
2390 lockdown= [SECURITY]
2391 { integrity | confidentiality }
2392 Enable the kernel lockdown feature. If set to
2393 integrity, kernel features that allow userland to
2394 modify the running kernel are disabled. If set to
2395 confidentiality, kernel features that allow userland
2396 to extract confidential information from the kernel
2397 are also disabled.
2399 locktorture.nreaders_stress= [KNL]
2400 Set the number of locking read-acquisition kthreads.
2401 Defaults to being automatically set based on the
2402 number of online CPUs.
2404 locktorture.nwriters_stress= [KNL]
2405 Set the number of locking write-acquisition kthreads.
2407 locktorture.onoff_holdoff= [KNL]
2408 Set time (s) after boot for CPU-hotplug testing.
2410 locktorture.onoff_interval= [KNL]
2411 Set time (s) between CPU-hotplug operations, or
2412 zero to disable CPU-hotplug testing.
2414 locktorture.shuffle_interval= [KNL]
2415 Set task-shuffle interval (jiffies). Shuffling
2416 tasks allows some CPUs to go into dyntick-idle
2417 mode during the locktorture test.
2419 locktorture.shutdown_secs= [KNL]
2420 Set time (s) after boot system shutdown. This
2421 is useful for hands-off automated testing.
2423 locktorture.stat_interval= [KNL]
2424 Time (s) between statistics printk()s.
2426 locktorture.stutter= [KNL]
2427 Time (s) to stutter testing, for example,
2428 specifying five seconds causes the test to run for
2429 five seconds, wait for five seconds, and so on.
2430 This tests the locking primitive's ability to
2431 transition abruptly to and from idle.
2433 locktorture.torture_type= [KNL]
2434 Specify the locking implementation to test.
2436 locktorture.verbose= [KNL]
2437 Enable additional printk() statements.
2439 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2440 Format: <irq>
2442 loglevel= All Kernel Messages with a loglevel smaller than the
2443 console loglevel will be printed to the console. It can
2444 also be changed with klogd or other programs. The
2445 loglevels are defined as follows:
2447 0 (KERN_EMERG) system is unusable
2448 1 (KERN_ALERT) action must be taken immediately
2449 2 (KERN_CRIT) critical conditions
2450 3 (KERN_ERR) error conditions
2451 4 (KERN_WARNING) warning conditions
2452 5 (KERN_NOTICE) normal but significant condition
2453 6 (KERN_INFO) informational
2454 7 (KERN_DEBUG) debug-level messages
2456 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2457 in bytes. n must be a power of two and greater
2458 than the minimal size. The minimal size is defined
2459 by LOG_BUF_SHIFT kernel config parameter. There is
2460 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2461 that allows to increase the default size depending on
2462 the number of CPUs. See init/Kconfig for more details.
2464 logo.nologo [FB] Disables display of the built-in Linux logo.
2465 This may be used to provide more screen space for
2466 kernel log messages and is useful when debugging
2467 kernel boot problems.
2469 lp=0 [LP] Specify parallel ports to use, e.g,
2470 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2471 lp=reset first parallel port). 'lp=0' disables the
2472 lp=auto printer driver. 'lp=reset' (which can be
2473 specified in addition to the ports) causes
2474 attached printers to be reset. Using
2475 lp=port1,port2,... specifies the parallel ports
2476 to associate lp devices with, starting with
2477 lp0. A port specification may be 'none' to skip
2478 that lp device, or a parport name such as
2479 'parport0'. Specifying 'lp=auto' instead of a
2480 port specification list means that device IDs
2481 from each port should be examined, to see if
2482 an IEEE 1284-compliant printer is attached; if
2483 so, the driver will manage that printer.
2484 See also header of drivers/char/lp.c.
2486 lpj=n [KNL]
2487 Sets loops_per_jiffy to given constant, thus avoiding
2488 time-consuming boot-time autodetection (up to 250 ms per
2489 CPU). 0 enables autodetection (default). To determine
2490 the correct value for your kernel, boot with normal
2491 autodetection and see what value is printed. Note that
2492 on SMP systems the preset will be applied to all CPUs,
2493 which is likely to cause problems if your CPUs need
2494 significantly divergent settings. An incorrect value
2495 will cause delays in the kernel to be wrong, leading to
2496 unpredictable I/O errors and other breakage. Although
2497 unlikely, in the extreme case this might damage your
2498 hardware.
2500 ltpc= [NET]
2501 Format: <io>,<irq>,<dma>
2503 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2505 lsm=lsm1,...,lsmN
2506 [SECURITY] Choose order of LSM initialization. This
2507 overrides CONFIG_LSM, and the "security=" parameter.
2509 machvec= [IA-64] Force the use of a particular machine-vector
2510 (machvec) in a generic kernel.
2511 Example: machvec=hpzx1
2513 machtype= [Loongson] Share the same kernel image file between different
2514 yeeloong laptop.
2515 Example: machtype=lemote-yeeloong-2f-7inch
2517 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2518 than or equal to this physical address is ignored.
2520 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2521 will bring up during bootup. maxcpus=n : n >= 0 limits
2522 the kernel to bring up 'n' processors. Surely after
2523 bootup you can bring up the other plugged cpu by executing
2524 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2525 only takes effect during system bootup.
2526 While n=0 is a special case, it is equivalent to "nosmp",
2527 which also disables the IO APIC.
2529 max_loop= [LOOP] The number of loop block devices that get
2530 (loop.max_loop) unconditionally pre-created at init time. The default
2531 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2532 of statically allocating a predefined number, loop
2533 devices can be requested on-demand with the
2534 /dev/loop-control interface.
2536 mce [X86-32] Machine Check Exception
2538 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2540 md= [HW] RAID subsystems devices and level
2541 See Documentation/admin-guide/md.rst.
2543 mdacon= [MDA]
2544 Format: <first>,<last>
2545 Specifies range of consoles to be captured by the MDA.
2547 mds= [X86,INTEL]
2548 Control mitigation for the Micro-architectural Data
2549 Sampling (MDS) vulnerability.
2551 Certain CPUs are vulnerable to an exploit against CPU
2552 internal buffers which can forward information to a
2553 disclosure gadget under certain conditions.
2555 In vulnerable processors, the speculatively
2556 forwarded data can be used in a cache side channel
2557 attack, to access data to which the attacker does
2558 not have direct access.
2560 This parameter controls the MDS mitigation. The
2561 options are:
2563 full - Enable MDS mitigation on vulnerable CPUs
2564 full,nosmt - Enable MDS mitigation and disable
2565 SMT on vulnerable CPUs
2566 off - Unconditionally disable MDS mitigation
2568 On TAA-affected machines, mds=off can be prevented by
2569 an active TAA mitigation as both vulnerabilities are
2570 mitigated with the same mechanism so in order to disable
2571 this mitigation, you need to specify tsx_async_abort=off
2572 too.
2574 Not specifying this option is equivalent to
2575 mds=full.
2577 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2579 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2580 Amount of memory to be used in cases as follows:
2582 1 for test;
2583 2 when the kernel is not able to see the whole system memory;
2584 3 memory that lies after 'mem=' boundary is excluded from
2585 the hypervisor, then assigned to KVM guests.
2587 [X86] Work as limiting max address. Use together
2588 with memmap= to avoid physical address space collisions.
2589 Without memmap= PCI devices could be placed at addresses
2590 belonging to unused RAM.
2592 Note that this only takes effects during boot time since
2593 in above case 3, memory may need be hot added after boot
2594 if system memory of hypervisor is not sufficient.
2596 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2597 memory.
2599 memchunk=nn[KMG]
2600 [KNL,SH] Allow user to override the default size for
2601 per-device physically contiguous DMA buffers.
2603 memhp_default_state=online/offline
2604 [KNL] Set the initial state for the memory hotplug
2605 onlining policy. If not specified, the default value is
2606 set according to the
2607 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2608 option.
2609 See Documentation/admin-guide/mm/memory-hotplug.rst.
2611 memmap=exactmap [KNL,X86] Enable setting of an exact
2612 E820 memory map, as specified by the user.
2613 Such memmap=exactmap lines can be constructed based on
2614 BIOS output or other requirements. See the memmap=nn@ss
2615 option description.
2617 memmap=nn[KMG]@ss[KMG]
2618 [KNL] Force usage of a specific region of memory.
2619 Region of memory to be used is from ss to ss+nn.
2620 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2621 which limits max address to nn[KMG].
2622 Multiple different regions can be specified,
2623 comma delimited.
2624 Example:
2625 memmap=100M@2G,100M#3G,1G!1024G
2627 memmap=nn[KMG]#ss[KMG]
2628 [KNL,ACPI] Mark specific memory as ACPI data.
2629 Region of memory to be marked is from ss to ss+nn.
2631 memmap=nn[KMG]$ss[KMG]
2632 [KNL,ACPI] Mark specific memory as reserved.
2633 Region of memory to be reserved is from ss to ss+nn.
2634 Example: Exclude memory from 0x18690000-0x1869ffff
2635 memmap=64K$0x18690000
2636 or
2637 memmap=0x10000$0x18690000
2638 Some bootloaders may need an escape character before '$',
2639 like Grub2, otherwise '$' and the following number
2640 will be eaten.
2642 memmap=nn[KMG]!ss[KMG]
2643 [KNL,X86] Mark specific memory as protected.
2644 Region of memory to be used, from ss to ss+nn.
2645 The memory region may be marked as e820 type 12 (0xc)
2646 and is NVDIMM or ADR memory.
2648 memmap=<size>%<offset>-<oldtype>+<newtype>
2649 [KNL,ACPI] Convert memory within the specified region
2650 from <oldtype> to <newtype>. If "-<oldtype>" is left
2651 out, the whole region will be marked as <newtype>,
2652 even if previously unavailable. If "+<newtype>" is left
2653 out, matching memory will be removed. Types are
2654 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2655 3 = ACPI, 12 = PRAM.
2657 memory_corruption_check=0/1 [X86]
2658 Some BIOSes seem to corrupt the first 64k of
2659 memory when doing things like suspend/resume.
2660 Setting this option will scan the memory
2661 looking for corruption. Enabling this will
2662 both detect corruption and prevent the kernel
2663 from using the memory being corrupted.
2664 However, its intended as a diagnostic tool; if
2665 repeatable BIOS-originated corruption always
2666 affects the same memory, you can use memmap=
2667 to prevent the kernel from using that memory.
2669 memory_corruption_check_size=size [X86]
2670 By default it checks for corruption in the low
2671 64k, making this memory unavailable for normal
2672 use. Use this parameter to scan for
2673 corruption in more or less memory.
2675 memory_corruption_check_period=seconds [X86]
2676 By default it checks for corruption every 60
2677 seconds. Use this parameter to check at some
2678 other rate. 0 disables periodic checking.
2680 memtest= [KNL,X86,ARM,PPC] Enable memtest
2681 Format: <integer>
2682 default : 0 <disable>
2683 Specifies the number of memtest passes to be
2684 performed. Each pass selects another test
2685 pattern from a given set of patterns. Memtest
2686 fills the memory with this pattern, validates
2687 memory contents and reserves bad memory
2688 regions that are detected.
2690 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2691 Valid arguments: on, off
2692 Default (depends on kernel configuration option):
2693 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2694 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2695 mem_encrypt=on: Activate SME
2696 mem_encrypt=off: Do not activate SME
2698 Refer to Documentation/virt/kvm/amd-memory-encryption.rst
2699 for details on when memory encryption can be activated.
2701 mem_sleep_default= [SUSPEND] Default system suspend mode:
2702 s2idle - Suspend-To-Idle
2703 shallow - Power-On Suspend or equivalent (if supported)
2704 deep - Suspend-To-RAM or equivalent (if supported)
2705 See Documentation/admin-guide/pm/sleep-states.rst.
2707 meye.*= [HW] Set MotionEye Camera parameters
2708 See Documentation/media/v4l-drivers/meye.rst.
2710 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2711 Multi-Function General Purpose Timers on AMD Geode
2712 platforms.
2714 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2715 the BIOS has incorrectly applied a workaround. TinyBIOS
2716 version 0.98 is known to be affected, 0.99 fixes the
2717 problem by letting the user disable the workaround.
2719 mga= [HW,DRM]
2721 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2722 physical address is ignored.
2724 mini2440= [ARM,HW,KNL]
2725 Format:[0..2][b][c][t]
2726 Default: "0tb"
2727 MINI2440 configuration specification:
2728 0 - The attached screen is the 3.5" TFT
2729 1 - The attached screen is the 7" TFT
2730 2 - The VGA Shield is attached (1024x768)
2731 Leaving out the screen size parameter will not load
2732 the TFT driver, and the framebuffer will be left
2733 unconfigured.
2734 b - Enable backlight. The TFT backlight pin will be
2735 linked to the kernel VESA blanking code and a GPIO
2736 LED. This parameter is not necessary when using the
2737 VGA shield.
2738 c - Enable the s3c camera interface.
2739 t - Reserved for enabling touchscreen support. The
2740 touchscreen support is not enabled in the mainstream
2741 kernel as of 2.6.30, a preliminary port can be found
2742 in the "bleeding edge" mini2440 support kernel at
2743 http://repo.or.cz/w/linux-2.6/mini2440.git
2745 mitigations=
2746 [X86,PPC,S390,ARM64] Control optional mitigations for
2747 CPU vulnerabilities. This is a set of curated,
2748 arch-independent options, each of which is an
2749 aggregation of existing arch-specific options.
2751 off
2752 Disable all optional CPU mitigations. This
2753 improves system performance, but it may also
2754 expose users to several CPU vulnerabilities.
2755 Equivalent to: nopti [X86,PPC]
2756 kpti=0 [ARM64]
2757 nospectre_v1 [X86,PPC]
2758 nobp=0 [S390]
2759 nospectre_v2 [X86,PPC,S390,ARM64]
2760 spectre_v2_user=off [X86]
2761 spec_store_bypass_disable=off [X86,PPC]
2762 ssbd=force-off [ARM64]
2763 l1tf=off [X86]
2764 mds=off [X86]
2765 tsx_async_abort=off [X86]
2766 kvm.nx_huge_pages=off [X86]
2768 Exceptions:
2769 This does not have any effect on
2770 kvm.nx_huge_pages when
2771 kvm.nx_huge_pages=force.
2773 auto (default)
2774 Mitigate all CPU vulnerabilities, but leave SMT
2775 enabled, even if it's vulnerable. This is for
2776 users who don't want to be surprised by SMT
2777 getting disabled across kernel upgrades, or who
2778 have other ways of avoiding SMT-based attacks.
2779 Equivalent to: (default behavior)
2781 auto,nosmt
2782 Mitigate all CPU vulnerabilities, disabling SMT
2783 if needed. This is for users who always want to
2784 be fully mitigated, even if it means losing SMT.
2785 Equivalent to: l1tf=flush,nosmt [X86]
2786 mds=full,nosmt [X86]
2787 tsx_async_abort=full,nosmt [X86]
2789 mminit_loglevel=
2790 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2791 parameter allows control of the logging verbosity for
2792 the additional memory initialisation checks. A value
2793 of 0 disables mminit logging and a level of 4 will
2794 log everything. Information is printed at KERN_DEBUG
2795 so loglevel=8 may also need to be specified.
2797 module.sig_enforce
2798 [KNL] When CONFIG_MODULE_SIG is set, this means that
2799 modules without (valid) signatures will fail to load.
2800 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2801 is always true, so this option does nothing.
2803 module_blacklist= [KNL] Do not load a comma-separated list of
2804 modules. Useful for debugging problem modules.
2806 mousedev.tap_time=
2807 [MOUSE] Maximum time between finger touching and
2808 leaving touchpad surface for touch to be considered
2809 a tap and be reported as a left button click (for
2810 touchpads working in absolute mode only).
2811 Format: <msecs>
2812 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2813 reporting absolute coordinates, such as tablets
2814 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2815 reporting absolute coordinates, such as tablets
2817 movablecore= [KNL,X86,IA-64,PPC]
2818 Format: nn[KMGTPE] | nn%
2819 This parameter is the complement to kernelcore=, it
2820 specifies the amount of memory used for migratable
2821 allocations. If both kernelcore and movablecore is
2822 specified, then kernelcore will be at *least* the
2823 specified value but may be more. If movablecore on its
2824 own is specified, the administrator must be careful
2825 that the amount of memory usable for all allocations
2826 is not too small.
2828 movable_node [KNL] Boot-time switch to make hotplugable memory
2829 NUMA nodes to be movable. This means that the memory
2830 of such nodes will be usable only for movable
2831 allocations which rules out almost all kernel
2832 allocations. Use with caution!
2834 MTD_Partition= [MTD]
2835 Format: <name>,<region-number>,<size>,<offset>
2837 MTD_Region= [MTD] Format:
2838 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2840 mtdparts= [MTD]
2841 See drivers/mtd/parsers/cmdlinepart.c
2843 multitce=off [PPC] This parameter disables the use of the pSeries
2844 firmware feature for updating multiple TCE entries
2845 at a time.
2847 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2849 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2851 boundary - index of last SLC block on Flex-OneNAND.
2852 The remaining blocks are configured as MLC blocks.
2853 lock - Configure if Flex-OneNAND boundary should be locked.
2854 Once locked, the boundary cannot be changed.
2855 1 indicates lock status, 0 indicates unlock status.
2857 mtdset= [ARM]
2858 ARM/S3C2412 JIVE boot control
2860 See arch/arm/mach-s3c2412/mach-jive.c
2862 mtouchusb.raw_coordinates=
2863 [HW] Make the MicroTouch USB driver use raw coordinates
2864 ('y', default) or cooked coordinates ('n')
2866 mtrr_chunk_size=nn[KMG] [X86]
2867 used for mtrr cleanup. It is largest continuous chunk
2868 that could hold holes aka. UC entries.
2870 mtrr_gran_size=nn[KMG] [X86]
2871 Used for mtrr cleanup. It is granularity of mtrr block.
2872 Default is 1.
2873 Large value could prevent small alignment from
2874 using up MTRRs.
2876 mtrr_spare_reg_nr=n [X86]
2877 Format: <integer>
2878 Range: 0,7 : spare reg number
2879 Default : 1
2880 Used for mtrr cleanup. It is spare mtrr entries number.
2881 Set to 2 or more if your graphical card needs more.
2883 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2885 netdev= [NET] Network devices parameters
2886 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2887 Note that mem_start is often overloaded to mean
2888 something different and driver-specific.
2889 This usage is only documented in each driver source
2890 file if at all.
2892 nf_conntrack.acct=
2893 [NETFILTER] Enable connection tracking flow accounting
2894 0 to disable accounting
2895 1 to enable accounting
2896 Default value is 0.
2898 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2899 See Documentation/admin-guide/nfs/nfsroot.rst.
2901 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2902 See Documentation/admin-guide/nfs/nfsroot.rst.
2904 nfsrootdebug [NFS] enable nfsroot debugging messages.
2905 See Documentation/admin-guide/nfs/nfsroot.rst.
2907 nfs.callback_nr_threads=
2908 [NFSv4] set the total number of threads that the
2909 NFS client will assign to service NFSv4 callback
2910 requests.
2912 nfs.callback_tcpport=
2913 [NFS] set the TCP port on which the NFSv4 callback
2914 channel should listen.
2916 nfs.cache_getent=
2917 [NFS] sets the pathname to the program which is used
2918 to update the NFS client cache entries.
2920 nfs.cache_getent_timeout=
2921 [NFS] sets the timeout after which an attempt to
2922 update a cache entry is deemed to have failed.
2924 nfs.idmap_cache_timeout=
2925 [NFS] set the maximum lifetime for idmapper cache
2926 entries.
2928 nfs.enable_ino64=
2929 [NFS] enable 64-bit inode numbers.
2930 If zero, the NFS client will fake up a 32-bit inode
2931 number for the readdir() and stat() syscalls instead
2932 of returning the full 64-bit number.
2933 The default is to return 64-bit inode numbers.
2935 nfs.max_session_cb_slots=
2936 [NFSv4.1] Sets the maximum number of session
2937 slots the client will assign to the callback
2938 channel. This determines the maximum number of
2939 callbacks the client will process in parallel for
2940 a particular server.
2942 nfs.max_session_slots=
2943 [NFSv4.1] Sets the maximum number of session slots
2944 the client will attempt to negotiate with the server.
2945 This limits the number of simultaneous RPC requests
2946 that the client can send to the NFSv4.1 server.
2947 Note that there is little point in setting this
2948 value higher than the max_tcp_slot_table_limit.
2950 nfs.nfs4_disable_idmapping=
2951 [NFSv4] When set to the default of '1', this option
2952 ensures that both the RPC level authentication
2953 scheme and the NFS level operations agree to use
2954 numeric uids/gids if the mount is using the
2955 'sec=sys' security flavour. In effect it is
2956 disabling idmapping, which can make migration from
2957 legacy NFSv2/v3 systems to NFSv4 easier.
2958 Servers that do not support this mode of operation
2959 will be autodetected by the client, and it will fall
2960 back to using the idmapper.
2961 To turn off this behaviour, set the value to '0'.
2962 nfs.nfs4_unique_id=
2963 [NFS4] Specify an additional fixed unique ident-
2964 ification string that NFSv4 clients can insert into
2965 their nfs_client_id4 string. This is typically a
2966 UUID that is generated at system install time.
2968 nfs.send_implementation_id =
2969 [NFSv4.1] Send client implementation identification
2970 information in exchange_id requests.
2971 If zero, no implementation identification information
2972 will be sent.
2973 The default is to send the implementation identification
2974 information.
2976 nfs.recover_lost_locks =
2977 [NFSv4] Attempt to recover locks that were lost due
2978 to a lease timeout on the server. Please note that
2979 doing this risks data corruption, since there are
2980 no guarantees that the file will remain unchanged
2981 after the locks are lost.
2982 If you want to enable the kernel legacy behaviour of
2983 attempting to recover these locks, then set this
2984 parameter to '1'.
2985 The default parameter value of '0' causes the kernel
2986 not to attempt recovery of lost locks.
2988 nfs4.layoutstats_timer =
2989 [NFSv4.2] Change the rate at which the kernel sends
2990 layoutstats to the pNFS metadata server.
2992 Setting this to value to 0 causes the kernel to use
2993 whatever value is the default set by the layout
2994 driver. A non-zero value sets the minimum interval
2995 in seconds between layoutstats transmissions.
2997 nfsd.nfs4_disable_idmapping=
2998 [NFSv4] When set to the default of '1', the NFSv4
2999 server will return only numeric uids and gids to
3000 clients using auth_sys, and will accept numeric uids
3001 and gids from such clients. This is intended to ease
3002 migration from NFSv2/v3.
3004 nmi_debug= [KNL,SH] Specify one or more actions to take
3005 when a NMI is triggered.
3006 Format: [state][,regs][,debounce][,die]
3008 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3009 Format: [panic,][nopanic,][num]
3010 Valid num: 0 or 1
3011 0 - turn hardlockup detector in nmi_watchdog off
3012 1 - turn hardlockup detector in nmi_watchdog on
3013 When panic is specified, panic when an NMI watchdog
3014 timeout occurs (or 'nopanic' to not panic on an NMI
3015 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3016 To disable both hard and soft lockup detectors,
3017 please see 'nowatchdog'.
3018 This is useful when you use a panic=... timeout and
3019 need the box quickly up again.
3021 These settings can be accessed at runtime via
3022 the nmi_watchdog and hardlockup_panic sysctls.
3024 netpoll.carrier_timeout=
3025 [NET] Specifies amount of time (in seconds) that
3026 netpoll should wait for a carrier. By default netpoll
3027 waits 4 seconds.
3029 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3030 emulation library even if a 387 maths coprocessor
3031 is present.
3033 no5lvl [X86-64] Disable 5-level paging mode. Forces
3034 kernel to use 4-level paging instead.
3036 no_console_suspend
3037 [HW] Never suspend the console
3038 Disable suspending of consoles during suspend and
3039 hibernate operations. Once disabled, debugging
3040 messages can reach various consoles while the rest
3041 of the system is being put to sleep (ie, while
3042 debugging driver suspend/resume hooks). This may
3043 not work reliably with all consoles, but is known
3044 to work with serial and VGA consoles.
3045 To facilitate more flexible debugging, we also add
3046 console_suspend, a printk module parameter to control
3047 it. Users could use console_suspend (usually
3048 /sys/module/printk/parameters/console_suspend) to
3049 turn on/off it dynamically.
3051 novmcoredd [KNL,KDUMP]
3052 Disable device dump. Device dump allows drivers to
3053 append dump data to vmcore so you can collect driver
3054 specified debug info. Drivers can append the data
3055 without any limit and this data is stored in memory,
3056 so this may cause significant memory stress. Disabling
3057 device dump can help save memory but the driver debug
3058 data will be no longer available. This parameter
3059 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
3060 is set.
3062 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
3063 caches in the slab allocator. Saves per-node memory,
3064 but will impact performance.
3066 noalign [KNL,ARM]
3068 noaltinstr [S390] Disables alternative instructions patching
3069 (CPU alternatives feature).
3071 noapic [SMP,APIC] Tells the kernel to not make use of any
3072 IOAPICs that may be present in the system.
3074 noautogroup Disable scheduler automatic task group creation.
3076 nobats [PPC] Do not use BATs for mapping kernel lowmem
3077 on "Classic" PPC cores.
3079 nocache [ARM]
3081 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
3083 nodelayacct [KNL] Disable per-task delay accounting
3085 nodsp [SH] Disable hardware DSP at boot time.
3087 noefi Disable EFI runtime services support.
3089 noexec [IA-64]
3091 noexec [X86]
3092 On X86-32 available only on PAE configured kernels.
3093 noexec=on: enable non-executable mappings (default)
3094 noexec=off: disable non-executable mappings
3096 nosmap [X86,PPC]
3097 Disable SMAP (Supervisor Mode Access Prevention)
3098 even if it is supported by processor.
3100 nosmep [X86,PPC]
3101 Disable SMEP (Supervisor Mode Execution Prevention)
3102 even if it is supported by processor.
3104 noexec32 [X86-64]
3105 This affects only 32-bit executables.
3106 noexec32=on: enable non-executable mappings (default)
3107 read doesn't imply executable mappings
3108 noexec32=off: disable non-executable mappings
3109 read implies executable mappings
3111 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3113 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3114 register save and restore. The kernel will only save
3115 legacy floating-point registers on task switch.
3117 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings.
3119 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
3120 Equivalent to smt=1.
3122 [KNL,x86] Disable symmetric multithreading (SMT).
3123 nosmt=force: Force disable SMT, cannot be undone
3124 via the sysfs control file.
3126 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3127 (bounds check bypass). With this option data leaks are
3128 possible in the system.
3130 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
3131 the Spectre variant 2 (indirect branch prediction)
3132 vulnerability. System may allow data leaks with this
3133 option.
3135 nospec_store_bypass_disable
3136 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3138 noxsave [BUGS=X86] Disables x86 extended register state save
3139 and restore using xsave. The kernel will fallback to
3140 enabling legacy floating-point and sse state.
3142 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
3143 register states. The kernel will fall back to use
3144 xsave to save the states. By using this parameter,
3145 performance of saving the states is degraded because
3146 xsave doesn't support modified optimization while
3147 xsaveopt supports it on xsaveopt enabled systems.
3149 noxsaves [X86] Disables xsaves and xrstors used in saving and
3150 restoring x86 extended register state in compacted
3151 form of xsave area. The kernel will fall back to use
3152 xsaveopt and xrstor to save and restore the states
3153 in standard form of xsave area. By using this
3154 parameter, xsave area per process might occupy more
3155 memory on xsaves enabled systems.
3157 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
3158 wfi(ARM) instruction doesn't work correctly and not to
3159 use it. This is also useful when using JTAG debugger.
3161 no_file_caps Tells the kernel not to honor file capabilities. The
3162 only way then for a file to be executed with privilege
3163 is to be setuid root or executed by root.
3165 nohalt [IA-64] Tells the kernel not to use the power saving
3166 function PAL_HALT_LIGHT when idle. This increases
3167 power-consumption. On the positive side, it reduces
3168 interrupt wake-up latency, which may improve performance
3169 in certain environments such as networked servers or
3170 real-time systems.
3172 nohibernate [HIBERNATION] Disable hibernation and resume.
3174 nohz= [KNL] Boottime enable/disable dynamic ticks
3175 Valid arguments: on, off
3176 Default: on
3178 nohz_full= [KNL,BOOT,SMP,ISOL]
3179 The argument is a cpu list, as described above.
3180 In kernels built with CONFIG_NO_HZ_FULL=y, set
3181 the specified list of CPUs whose tick will be stopped
3182 whenever possible. The boot CPU will be forced outside
3183 the range to maintain the timekeeping. Any CPUs
3184 in this list will have their RCU callbacks offloaded,
3185 just as if they had also been called out in the
3186 rcu_nocbs= boot parameter.
3188 noiotrap [SH] Disables trapped I/O port accesses.
3190 noirqdebug [X86-32] Disables the code which attempts to detect and
3191 disable unhandled interrupt sources.
3193 no_timer_check [X86,APIC] Disables the code which tests for
3194 broken timer IRQ sources.
3196 noisapnp [ISAPNP] Disables ISA PnP code.
3198 noinitrd [RAM] Tells the kernel not to load any configured
3199 initial RAM disk.
3201 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3202 remapping.
3203 [Deprecated - use intremap=off]
3205 nointroute [IA-64]
3207 noinvpcid [X86] Disable the INVPCID cpu feature.
3209 nojitter [IA-64] Disables jitter checking for ITC timers.
3211 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3213 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3214 fault handling.
3216 no-vmw-sched-clock
3217 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3218 clock and use the default one.
3220 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time
3221 accounting. steal time is computed, but won't
3222 influence scheduler behaviour
3224 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3226 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3228 noltlbs [PPC] Do not use large page/tlb entries for kernel
3229 lowmem mapping on PPC40x and PPC8xx
3231 nomca [IA-64] Disable machine check abort handling
3233 nomce [X86-32] Disable Machine Check Exception
3235 nomfgpt [X86-32] Disable Multi-Function General Purpose
3236 Timer usage (for AMD Geode machines).
3238 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3239 shutdown the other cpus. Instead use the REBOOT_VECTOR
3240 irq.
3242 nomodule Disable module load
3244 nopat [X86] Disable PAT (page attribute table extension of
3245 pagetables) support.
3247 nopcid [X86-64] Disable the PCID cpu feature.
3249 norandmaps Don't use address space randomization. Equivalent to
3250 echo 0 > /proc/sys/kernel/randomize_va_space
3252 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3253 with UP alternatives
3255 nordrand [X86] Disable kernel use of the RDRAND and
3256 RDSEED instructions even if they are supported
3257 by the processor. RDRAND and RDSEED are still
3258 available to user space applications.
3260 noresume [SWSUSP] Disables resume and restores original swap
3261 space.
3263 no-scroll [VGA] Disables scrollback.
3264 This is required for the Braillex ib80-piezo Braille
3265 reader made by F.H. Papenmeier (Germany).
3267 nosbagart [IA-64]
3269 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3271 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3272 and disable the IO APIC. legacy for "maxcpus=0".
3274 nosoftlockup [KNL] Disable the soft-lockup detector.
3276 nosync [HW,M68K] Disables sync negotiation for all devices.
3278 nowatchdog [KNL] Disable both lockup detectors, i.e.
3279 soft-lockup and NMI watchdog (hard-lockup).
3281 nowb [ARM]
3283 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3285 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3286 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3287 Some features depend on CPU0. Known dependencies are:
3288 1. Resume from suspend/hibernate depends on CPU0.
3289 Suspend/hibernate will fail if CPU0 is offline and you
3290 need to online CPU0 before suspend/hibernate.
3291 2. PIC interrupts also depend on CPU0. CPU0 can't be
3292 removed if a PIC interrupt is detected.
3293 It's said poweroff/reboot may depend on CPU0 on some
3294 machines although I haven't seen such issues so far
3295 after CPU0 is offline on a few tested machines.
3296 If the dependencies are under your control, you can
3297 turn on cpu0_hotplug.
3299 nps_mtm_hs_ctr= [KNL,ARC]
3300 This parameter sets the maximum duration, in
3301 cycles, each HW thread of the CTOP can run
3302 without interruptions, before HW switches it.
3303 The actual maximum duration is 16 times this
3304 parameter's value.
3305 Format: integer between 1 and 255
3306 Default: 255
3308 nptcg= [IA-64] Override max number of concurrent global TLB
3309 purges which is reported from either PAL_VM_SUMMARY or
3310 SAL PALO.
3312 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3313 could support. nr_cpus=n : n >= 1 limits the kernel to
3314 support 'n' processors. It could be larger than the
3315 number of already plugged CPU during bootup, later in
3316 runtime you can physically add extra cpu until it reaches
3317 n. So during boot up some boot time memory for per-cpu
3318 variables need be pre-allocated for later physical cpu
3319 hot plugging.
3321 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3323 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3324 Allowed values are enable and disable
3326 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3327 'node', 'default' can be specified
3328 This can be set from sysctl after boot.
3329 See Documentation/admin-guide/sysctl/vm.rst for details.
3331 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3332 See Documentation/debugging-via-ohci1394.txt for more
3333 info.
3335 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3336 Rather than timing out after 20 ms if an EC
3337 command is not properly ACKed, override the length
3338 of the timeout. We have interrupts disabled while
3339 waiting for the ACK, so if this is set too high
3340 interrupts *may* be lost!
3342 omap_mux= [OMAP] Override bootloader pin multiplexing.
3343 Format: <mux_mode0.mode_name=value>...
3344 For example, to override I2C bus2:
3345 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3347 oprofile.timer= [HW]
3348 Use timer interrupt instead of performance counters
3350 oprofile.cpu_type= Force an oprofile cpu type
3351 This might be useful if you have an older oprofile
3352 userland or if you want common events.
3353 Format: { arch_perfmon }
3354 arch_perfmon: [X86] Force use of architectural
3355 perfmon on Intel CPUs instead of the
3356 CPU specific event set.
3357 timer: [X86] Force use of architectural NMI
3358 timer mode (see also oprofile.timer
3359 for generic hr timer mode)
3361 oops=panic Always panic on oopses. Default is to just kill the
3362 process, but there is a small probability of
3363 deadlocking the machine.
3364 This will also cause panics on machine check exceptions.
3365 Useful together with panic=30 to trigger a reboot.
3367 page_alloc.shuffle=
3368 [KNL] Boolean flag to control whether the page allocator
3369 should randomize its free lists. The randomization may
3370 be automatically enabled if the kernel detects it is
3371 running on a platform with a direct-mapped memory-side
3372 cache, and this parameter can be used to
3373 override/disable that behavior. The state of the flag
3374 can be read from sysfs at:
3375 /sys/module/page_alloc/parameters/shuffle.
3377 page_owner= [KNL] Boot-time page_owner enabling option.
3378 Storage of the information about who allocated
3379 each page is disabled in default. With this switch,
3380 we can turn it on.
3381 on: enable the feature
3383 page_poison= [KNL] Boot-time parameter changing the state of
3384 poisoning on the buddy allocator, available with
3385 CONFIG_PAGE_POISONING=y.
3386 off: turn off poisoning (default)
3387 on: turn on poisoning
3389 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3390 timeout > 0: seconds before rebooting
3391 timeout = 0: wait forever
3392 timeout < 0: reboot immediately
3393 Format: <timeout>
3395 panic_print= Bitmask for printing system info when panic happens.
3396 User can chose combination of the following bits:
3397 bit 0: print all tasks info
3398 bit 1: print system memory info
3399 bit 2: print timer info
3400 bit 3: print locks info if CONFIG_LOCKDEP is on
3401 bit 4: print ftrace buffer
3402 bit 5: print all printk messages in buffer
3404 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3405 on a WARN().
3407 crash_kexec_post_notifiers
3408 Run kdump after running panic-notifiers and dumping
3409 kmsg. This only for the users who doubt kdump always
3410 succeeds in any situation.
3411 Note that this also increases risks of kdump failure,
3412 because some panic notifiers can make the crashed
3413 kernel more unstable.
3415 parkbd.port= [HW] Parallel port number the keyboard adapter is
3416 connected to, default is 0.
3417 Format: <parport#>
3418 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3419 0 for XT, 1 for AT (default is AT).
3420 Format: <mode>
3422 parport= [HW,PPT] Specify parallel ports. 0 disables.
3423 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3424 Use 'auto' to force the driver to use any
3425 IRQ/DMA settings detected (the default is to
3426 ignore detected IRQ/DMA settings because of
3427 possible conflicts). You can specify the base
3428 address, IRQ, and DMA settings; IRQ and DMA
3429 should be numbers, or 'auto' (for using detected
3430 settings on that particular port), or 'nofifo'
3431 (to avoid using a FIFO even if it is detected).
3432 Parallel ports are assigned in the order they
3433 are specified on the command line, starting
3434 with parport0.
3436 parport_init_mode= [HW,PPT]
3437 Configure VIA parallel port to operate in
3438 a specific mode. This is necessary on Pegasos
3439 computer where firmware has no options for setting
3440 up parallel port mode and sets it to spp.
3441 Currently this function knows 686a and 8231 chips.
3442 Format: [spp|ps2|epp|ecp|ecpepp]
3444 pause_on_oops=
3445 Halt all CPUs after the first oops has been printed for
3446 the specified number of seconds. This is to be used if
3447 your oopses keep scrolling off the screen.
3449 pcbit= [HW,ISDN]
3451 pcd. [PARIDE]
3452 See header of drivers/block/paride/pcd.c.
3453 See also Documentation/admin-guide/blockdev/paride.rst.
3455 pci=option[,option...] [PCI] various PCI subsystem options.
3457 Some options herein operate on a specific device
3458 or a set of devices (<pci_dev>). These are
3459 specified in one of the following formats:
3461 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3462 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3464 Note: the first format specifies a PCI
3465 bus/device/function address which may change
3466 if new hardware is inserted, if motherboard
3467 firmware changes, or due to changes caused
3468 by other kernel parameters. If the
3469 domain is left unspecified, it is
3470 taken to be zero. Optionally, a path
3471 to a device through multiple device/function
3472 addresses can be specified after the base
3473 address (this is more robust against
3474 renumbering issues). The second format
3475 selects devices using IDs from the
3476 configuration space which may match multiple
3477 devices in the system.
3479 earlydump dump PCI config space before the kernel
3480 changes anything
3481 off [X86] don't probe for the PCI bus
3482 bios [X86-32] force use of PCI BIOS, don't access
3483 the hardware directly. Use this if your machine
3484 has a non-standard PCI host bridge.
3485 nobios [X86-32] disallow use of PCI BIOS, only direct
3486 hardware access methods are allowed. Use this
3487 if you experience crashes upon bootup and you
3488 suspect they are caused by the BIOS.
3489 conf1 [X86] Force use of PCI Configuration Access
3490 Mechanism 1 (config address in IO port 0xCF8,
3491 data in IO port 0xCFC, both 32-bit).
3492 conf2 [X86] Force use of PCI Configuration Access
3493 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3494 the function, IO port 0xCFA, also 8-bit, sets
3495 bus number. The config space is then accessed
3496 through ports 0xC000-0xCFFF).
3497 See http://wiki.osdev.org/PCI for more info
3498 on the configuration access mechanisms.
3499 noaer [PCIE] If the PCIEAER kernel config parameter is
3500 enabled, this kernel boot option can be used to
3501 disable the use of PCIE advanced error reporting.
3502 nodomains [PCI] Disable support for multiple PCI
3503 root domains (aka PCI segments, in ACPI-speak).
3504 nommconf [X86] Disable use of MMCONFIG for PCI
3505 Configuration
3506 check_enable_amd_mmconf [X86] check for and enable
3507 properly configured MMIO access to PCI
3508 config space on AMD family 10h CPU
3509 nomsi [MSI] If the PCI_MSI kernel config parameter is
3510 enabled, this kernel boot option can be used to
3511 disable the use of MSI interrupts system-wide.
3512 noioapicquirk [APIC] Disable all boot interrupt quirks.
3513 Safety option to keep boot IRQs enabled. This
3514 should never be necessary.
3515 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3516 primary IO-APIC for bridges that cannot disable
3517 boot IRQs. This fixes a source of spurious IRQs
3518 when the system masks IRQs.
3519 noioapicreroute [APIC] Disable workaround that uses the
3520 boot IRQ equivalent of an IRQ that connects to
3521 a chipset where boot IRQs cannot be disabled.
3522 The opposite of ioapicreroute.
3523 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3524 routing table. These calls are known to be buggy
3525 on several machines and they hang the machine
3526 when used, but on other computers it's the only
3527 way to get the interrupt routing table. Try
3528 this option if the kernel is unable to allocate
3529 IRQs or discover secondary PCI buses on your
3530 motherboard.
3531 rom [X86] Assign address space to expansion ROMs.
3532 Use with caution as certain devices share
3533 address decoders between ROMs and other
3534 resources.
3535 norom [X86] Do not assign address space to
3536 expansion ROMs that do not already have
3537 BIOS assigned address ranges.
3538 nobar [X86] Do not assign address space to the
3539 BARs that weren't assigned by the BIOS.
3540 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3541 assigned automatically to PCI devices. You can
3542 make the kernel exclude IRQs of your ISA cards
3543 this way.
3544 pirqaddr=0xAAAAA [X86] Specify the physical address
3545 of the PIRQ table (normally generated
3546 by the BIOS) if it is outside the
3547 F0000h-100000h range.
3548 lastbus=N [X86] Scan all buses thru bus #N. Can be
3549 useful if the kernel is unable to find your
3550 secondary buses and you want to tell it
3551 explicitly which ones they are.
3552 assign-busses [X86] Always assign all PCI bus
3553 numbers ourselves, overriding
3554 whatever the firmware may have done.
3555 usepirqmask [X86] Honor the possible IRQ mask stored
3556 in the BIOS $PIR table. This is needed on
3557 some systems with broken BIOSes, notably
3558 some HP Pavilion N5400 and Omnibook XE3
3559 notebooks. This will have no effect if ACPI
3560 IRQ routing is enabled.
3561 noacpi [X86] Do not use ACPI for IRQ routing
3562 or for PCI scanning.
3563 use_crs [X86] Use PCI host bridge window information
3564 from ACPI. On BIOSes from 2008 or later, this
3565 is enabled by default. If you need to use this,
3566 please report a bug.
3567 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3568 If you need to use this, please report a bug.
3569 routeirq Do IRQ routing for all PCI devices.
3570 This is normally done in pci_enable_device(),
3571 so this option is a temporary workaround
3572 for broken drivers that don't call it.
3573 skip_isa_align [X86] do not align io start addr, so can
3574 handle more pci cards
3575 noearly [X86] Don't do any early type 1 scanning.
3576 This might help on some broken boards which
3577 machine check when some devices' config space
3578 is read. But various workarounds are disabled
3579 and some IOMMU drivers will not work.
3580 bfsort Sort PCI devices into breadth-first order.
3581 This sorting is done to get a device
3582 order compatible with older (<= 2.4) kernels.
3583 nobfsort Don't sort PCI devices into breadth-first order.
3584 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3585 tuning and use the BIOS-configured MPS defaults.
3586 pcie_bus_safe Set every device's MPS to the largest value
3587 supported by all devices below the root complex.
3588 pcie_bus_perf Set device MPS to the largest allowable MPS
3589 based on its parent bus. Also set MRRS (Max
3590 Read Request Size) to the largest supported
3591 value (no larger than the MPS that the device
3592 or bus can support) for best performance.
3593 pcie_bus_peer2peer Set every device's MPS to 128B, which
3594 every device is guaranteed to support. This
3595 configuration allows peer-to-peer DMA between
3596 any pair of devices, possibly at the cost of
3597 reduced performance. This also guarantees
3598 that hot-added devices will work.
3599 cbiosize=nn[KMG] The fixed amount of bus space which is
3600 reserved for the CardBus bridge's IO window.
3601 The default value is 256 bytes.
3602 cbmemsize=nn[KMG] The fixed amount of bus space which is
3603 reserved for the CardBus bridge's memory
3604 window. The default value is 64 megabytes.
3605 resource_alignment=
3606 Format:
3607 [<order of align>@]<pci_dev>[; ...]
3608 Specifies alignment and device to reassign
3609 aligned memory resources. How to
3610 specify the device is described above.
3611 If <order of align> is not specified,
3612 PAGE_SIZE is used as alignment.
3613 A PCI-PCI bridge can be specified if resource
3614 windows need to be expanded.
3615 To specify the alignment for several
3616 instances of a device, the PCI vendor,
3617 device, subvendor, and subdevice may be
3618 specified, e.g., 12@pci:8086:9c22:103c:198f
3619 for 4096-byte alignment.
3620 ecrc= Enable/disable PCIe ECRC (transaction layer
3621 end-to-end CRC checking).
3622 bios: Use BIOS/firmware settings. This is the
3623 the default.
3624 off: Turn ECRC off
3625 on: Turn ECRC on.
3626 hpiosize=nn[KMG] The fixed amount of bus space which is
3627 reserved for hotplug bridge's IO window.
3628 Default size is 256 bytes.
3629 hpmmiosize=nn[KMG] The fixed amount of bus space which is
3630 reserved for hotplug bridge's MMIO window.
3631 Default size is 2 megabytes.
3632 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
3633 reserved for hotplug bridge's MMIO_PREF window.
3634 Default size is 2 megabytes.
3635 hpmemsize=nn[KMG] The fixed amount of bus space which is
3636 reserved for hotplug bridge's MMIO and
3637 MMIO_PREF window.
3638 Default size is 2 megabytes.
3639 hpbussize=nn The minimum amount of additional bus numbers
3640 reserved for buses below a hotplug bridge.
3641 Default is 1.
3642 realloc= Enable/disable reallocating PCI bridge resources
3643 if allocations done by BIOS are too small to
3644 accommodate resources required by all child
3645 devices.
3646 off: Turn realloc off
3647 on: Turn realloc on
3648 realloc same as realloc=on
3649 noari do not use PCIe ARI.
3650 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3651 do not use PCIe ATS (and IOMMU device IOTLB).
3652 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3653 only look for one device below a PCIe downstream
3654 port.
3655 big_root_window Try to add a big 64bit memory window to the PCIe
3656 root complex on AMD CPUs. Some GFX hardware
3657 can resize a BAR to allow access to all VRAM.
3658 Adding the window is slightly risky (it may
3659 conflict with unreported devices), so this
3660 taints the kernel.
3661 disable_acs_redir=<pci_dev>[; ...]
3662 Specify one or more PCI devices (in the format
3663 specified above) separated by semicolons.
3664 Each device specified will have the PCI ACS
3665 redirect capabilities forced off which will
3666 allow P2P traffic between devices through
3667 bridges without forcing it upstream. Note:
3668 this removes isolation between devices and
3669 may put more devices in an IOMMU group.
3670 force_floating [S390] Force usage of floating interrupts.
3671 nomio [S390] Do not use MIO instructions.
3673 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3674 Management.
3675 off Disable ASPM.
3676 force Enable ASPM even on devices that claim not to support it.
3677 WARNING: Forcing ASPM on may cause system lockups.
3679 pcie_ports= [PCIE] PCIe port services handling:
3680 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3681 even if the platform doesn't give the OS permission to
3682 use them. This may cause conflicts if the platform
3683 also tries to use these services.
3684 dpc-native Use native PCIe service for DPC only. May
3685 cause conflicts if firmware uses AER or DPC.
3686 compat Disable native PCIe services (PME, AER, DPC, PCIe
3687 hotplug).
3689 pcie_port_pm= [PCIE] PCIe port power management handling:
3690 off Disable power management of all PCIe ports
3691 force Forcibly enable power management of all PCIe ports
3693 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3694 nomsi Do not use MSI for native PCIe PME signaling (this makes
3695 all PCIe root ports use INTx for all services).
3697 pcmv= [HW,PCMCIA] BadgePAD 4
3699 pd_ignore_unused
3700 [PM]
3701 Keep all power-domains already enabled by bootloader on,
3702 even if no driver has claimed them. This is useful
3703 for debug and development, but should not be
3704 needed on a platform with proper driver support.
3706 pd. [PARIDE]
3707 See Documentation/admin-guide/blockdev/paride.rst.
3709 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3710 boot time.
3711 Format: { 0 | 1 }
3712 See arch/parisc/kernel/pdc_chassis.c
3714 percpu_alloc= Select which percpu first chunk allocator to use.
3715 Currently supported values are "embed" and "page".
3716 Archs may support subset or none of the selections.
3717 See comments in mm/percpu.c for details on each
3718 allocator. This parameter is primarily for debugging
3719 and performance comparison.
3721 pf. [PARIDE]
3722 See Documentation/admin-guide/blockdev/paride.rst.
3724 pg. [PARIDE]
3725 See Documentation/admin-guide/blockdev/paride.rst.
3727 pirq= [SMP,APIC] Manual mp-table setup
3728 See Documentation/x86/i386/IO-APIC.rst.
3730 plip= [PPT,NET] Parallel port network link
3731 Format: { parport<nr> | timid | 0 }
3732 See also Documentation/admin-guide/parport.rst.
3734 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3735 Override pmtimer IOPort with a hex value.
3736 e.g. pmtmr=0x508
3738 pm_debug_messages [SUSPEND,KNL]
3739 Enable suspend/resume debug messages during boot up.
3741 pnp.debug=1 [PNP]
3742 Enable PNP debug messages (depends on the
3743 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3744 via /sys/module/pnp/parameters/debug. We always show
3745 current resource usage; turning this on also shows
3746 possible settings and some assignment information.
3748 pnpacpi= [ACPI]
3749 { off }
3751 pnpbios= [ISAPNP]
3752 { on | off | curr | res | no-curr | no-res }
3754 pnp_reserve_irq=
3755 [ISAPNP] Exclude IRQs for the autoconfiguration
3757 pnp_reserve_dma=
3758 [ISAPNP] Exclude DMAs for the autoconfiguration
3760 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3761 Ranges are in pairs (I/O port base and size).
3763 pnp_reserve_mem=
3764 [ISAPNP] Exclude memory regions for the
3765 autoconfiguration.
3766 Ranges are in pairs (memory base and size).
3768 ports= [IP_VS_FTP] IPVS ftp helper module
3769 Default is 21.
3770 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3771 may be specified.
3772 Format: <port>,<port>....
3774 powersave=off [PPC] This option disables power saving features.
3775 It specifically disables cpuidle and sets the
3776 platform machine description specific power_save
3777 function to NULL. On Idle the CPU just reduces
3778 execution priority.
3780 ppc_strict_facility_enable
3781 [PPC] This option catches any kernel floating point,
3782 Altivec, VSX and SPE outside of regions specifically
3783 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3784 There is some performance impact when enabling this.
3786 ppc_tm= [PPC]
3787 Format: {"off"}
3788 Disable Hardware Transactional Memory
3790 print-fatal-signals=
3791 [KNL] debug: print fatal signals
3793 If enabled, warn about various signal handling
3794 related application anomalies: too many signals,
3795 too many POSIX.1 timers, fatal signals causing a
3796 coredump - etc.
3798 If you hit the warning due to signal overflow,
3799 you might want to try "ulimit -i unlimited".
3801 default: off.
3803 printk.always_kmsg_dump=
3804 Trigger kmsg_dump for cases other than kernel oops or
3805 panics
3806 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3807 default: disabled
3809 printk.devkmsg={on,off,ratelimit}
3810 Control writing to /dev/kmsg.
3811 on - unlimited logging to /dev/kmsg from userspace
3812 off - logging to /dev/kmsg disabled
3813 ratelimit - ratelimit the logging
3814 Default: ratelimit
3816 printk.time= Show timing data prefixed to each printk message line
3817 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3819 processor.max_cstate= [HW,ACPI]
3820 Limit processor to maximum C-state
3821 max_cstate=9 overrides any DMI blacklist limit.
3823 processor.nocst [HW,ACPI]
3824 Ignore the _CST method to determine C-states,
3825 instead using the legacy FADT method
3827 profile= [KNL] Enable kernel profiling via /proc/profile
3828 Format: [<profiletype>,]<number>
3829 Param: <profiletype>: "schedule", "sleep", or "kvm"
3830 [defaults to kernel profiling]
3831 Param: "schedule" - profile schedule points.
3832 Param: "sleep" - profile D-state sleeping (millisecs).
3833 Requires CONFIG_SCHEDSTATS
3834 Param: "kvm" - profile VM exits.
3835 Param: <number> - step/bucket size as a power of 2 for
3836 statistical time based profiling.
3838 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3839 before loading.
3840 See Documentation/admin-guide/blockdev/ramdisk.rst.
3842 prot_virt= [S390] enable hosting protected virtual machines
3843 isolated from the hypervisor (if hardware supports
3844 that).
3845 Format: <bool>
3847 psi= [KNL] Enable or disable pressure stall information
3848 tracking.
3849 Format: <bool>
3851 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3852 probe for; one of (bare|imps|exps|lifebook|any).
3853 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3854 per second.
3855 psmouse.resetafter= [HW,MOUSE]
3856 Try to reset the device after so many bad packets
3857 (0 = never).
3858 psmouse.resolution=
3859 [HW,MOUSE] Set desired mouse resolution, in dpi.
3860 psmouse.smartscroll=
3861 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3862 0 = disabled, 1 = enabled (default).
3864 pstore.backend= Specify the name of the pstore backend to use
3866 pt. [PARIDE]
3867 See Documentation/admin-guide/blockdev/paride.rst.
3869 pti= [X86_64] Control Page Table Isolation of user and
3870 kernel address spaces. Disabling this feature
3871 removes hardening, but improves performance of
3872 system calls and interrupts.
3874 on - unconditionally enable
3875 off - unconditionally disable
3876 auto - kernel detects whether your CPU model is
3877 vulnerable to issues that PTI mitigates
3879 Not specifying this option is equivalent to pti=auto.
3881 nopti [X86_64]
3882 Equivalent to pti=off
3884 pty.legacy_count=
3885 [KNL] Number of legacy pty's. Overwrites compiled-in
3886 default number.
3888 quiet [KNL] Disable most log messages
3890 r128= [HW,DRM]
3892 raid= [HW,RAID]
3893 See Documentation/admin-guide/md.rst.
3895 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3896 See Documentation/admin-guide/blockdev/ramdisk.rst.
3898 random.trust_cpu={on,off}
3899 [KNL] Enable or disable trusting the use of the
3900 CPU's random number generator (if available) to
3901 fully seed the kernel's CRNG. Default is controlled
3902 by CONFIG_RANDOM_TRUST_CPU.
3904 ras=option[,option,...] [KNL] RAS-specific options
3906 cec_disable [X86]
3907 Disable the Correctable Errors Collector,
3908 see CONFIG_RAS_CEC help text.
3910 rcu_nocbs= [KNL]
3911 The argument is a cpu list, as described above,
3912 except that the string "all" can be used to
3913 specify every CPU on the system.
3915 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3916 the specified list of CPUs to be no-callback CPUs.
3917 Invocation of these CPUs' RCU callbacks will be
3918 offloaded to "rcuox/N" kthreads created for that
3919 purpose, where "x" is "p" for RCU-preempt, and
3920 "s" for RCU-sched, and "N" is the CPU number.
3921 This reduces OS jitter on the offloaded CPUs,
3922 which can be useful for HPC and real-time
3923 workloads. It can also improve energy efficiency
3924 for asymmetric multiprocessors.
3926 rcu_nocb_poll [KNL]
3927 Rather than requiring that offloaded CPUs
3928 (specified by rcu_nocbs= above) explicitly
3929 awaken the corresponding "rcuoN" kthreads,
3930 make these kthreads poll for callbacks.
3931 This improves the real-time response for the
3932 offloaded CPUs by relieving them of the need to
3933 wake up the corresponding kthread, but degrades
3934 energy efficiency by requiring that the kthreads
3935 periodically wake up to do the polling.
3937 rcutree.blimit= [KNL]
3938 Set maximum number of finished RCU callbacks to
3939 process in one batch.
3941 rcutree.dump_tree= [KNL]
3942 Dump the structure of the rcu_node combining tree
3943 out at early boot. This is used for diagnostic
3944 purposes, to verify correct tree setup.
3946 rcutree.gp_cleanup_delay= [KNL]
3947 Set the number of jiffies to delay each step of
3948 RCU grace-period cleanup.
3950 rcutree.gp_init_delay= [KNL]
3951 Set the number of jiffies to delay each step of
3952 RCU grace-period initialization.
3954 rcutree.gp_preinit_delay= [KNL]
3955 Set the number of jiffies to delay each step of
3956 RCU grace-period pre-initialization, that is,
3957 the propagation of recent CPU-hotplug changes up
3958 the rcu_node combining tree.
3960 rcutree.use_softirq= [KNL]
3961 If set to zero, move all RCU_SOFTIRQ processing to
3962 per-CPU rcuc kthreads. Defaults to a non-zero
3963 value, meaning that RCU_SOFTIRQ is used by default.
3964 Specify rcutree.use_softirq=0 to use rcuc kthreads.
3966 rcutree.rcu_fanout_exact= [KNL]
3967 Disable autobalancing of the rcu_node combining
3968 tree. This is used by rcutorture, and might
3969 possibly be useful for architectures having high
3970 cache-to-cache transfer latencies.
3972 rcutree.rcu_fanout_leaf= [KNL]
3973 Change the number of CPUs assigned to each
3974 leaf rcu_node structure. Useful for very
3975 large systems, which will choose the value 64,
3976 and for NUMA systems with large remote-access
3977 latencies, which will choose a value aligned
3978 with the appropriate hardware boundaries.
3980 rcutree.jiffies_till_first_fqs= [KNL]
3981 Set delay from grace-period initialization to
3982 first attempt to force quiescent states.
3983 Units are jiffies, minimum value is zero,
3984 and maximum value is HZ.
3986 rcutree.jiffies_till_next_fqs= [KNL]
3987 Set delay between subsequent attempts to force
3988 quiescent states. Units are jiffies, minimum
3989 value is one, and maximum value is HZ.
3991 rcutree.jiffies_till_sched_qs= [KNL]
3992 Set required age in jiffies for a
3993 given grace period before RCU starts
3994 soliciting quiescent-state help from
3995 rcu_note_context_switch() and cond_resched().
3996 If not specified, the kernel will calculate
3997 a value based on the most recent settings
3998 of rcutree.jiffies_till_first_fqs
3999 and rcutree.jiffies_till_next_fqs.
4000 This calculated value may be viewed in
4001 rcutree.jiffies_to_sched_qs. Any attempt to set
4002 rcutree.jiffies_to_sched_qs will be cheerfully
4003 overwritten.
4005 rcutree.kthread_prio= [KNL,BOOT]
4006 Set the SCHED_FIFO priority of the RCU per-CPU
4007 kthreads (rcuc/N). This value is also used for
4008 the priority of the RCU boost threads (rcub/N)
4009 and for the RCU grace-period kthreads (rcu_bh,
4010 rcu_preempt, and rcu_sched). If RCU_BOOST is
4011 set, valid values are 1-99 and the default is 1
4012 (the least-favored priority). Otherwise, when
4013 RCU_BOOST is not set, valid values are 0-99 and
4014 the default is zero (non-realtime operation).
4016 rcutree.rcu_nocb_gp_stride= [KNL]
4017 Set the number of NOCB callback kthreads in
4018 each group, which defaults to the square root
4019 of the number of CPUs. Larger numbers reduce
4020 the wakeup overhead on the global grace-period
4021 kthread, but increases that same overhead on
4022 each group's NOCB grace-period kthread.
4024 rcutree.qhimark= [KNL]
4025 Set threshold of queued RCU callbacks beyond which
4026 batch limiting is disabled.
4028 rcutree.qlowmark= [KNL]
4029 Set threshold of queued RCU callbacks below which
4030 batch limiting is re-enabled.
4032 rcutree.qovld= [KNL]
4033 Set threshold of queued RCU callbacks beyond which
4034 RCU's force-quiescent-state scan will aggressively
4035 enlist help from cond_resched() and sched IPIs to
4036 help CPUs more quickly reach quiescent states.
4037 Set to less than zero to make this be set based
4038 on rcutree.qhimark at boot time and to zero to
4039 disable more aggressive help enlistment.
4041 rcutree.rcu_idle_gp_delay= [KNL]
4042 Set wakeup interval for idle CPUs that have
4043 RCU callbacks (RCU_FAST_NO_HZ=y).
4045 rcutree.rcu_idle_lazy_gp_delay= [KNL]
4046 Set wakeup interval for idle CPUs that have
4047 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
4048 Lazy RCU callbacks are those which RCU can
4049 prove do nothing more than free memory.
4051 rcutree.rcu_kick_kthreads= [KNL]
4052 Cause the grace-period kthread to get an extra
4053 wake_up() if it sleeps three times longer than
4054 it should at force-quiescent-state time.
4055 This wake_up() will be accompanied by a
4056 WARN_ONCE() splat and an ftrace_dump().
4058 rcutree.sysrq_rcu= [KNL]
4059 Commandeer a sysrq key to dump out Tree RCU's
4060 rcu_node tree with an eye towards determining
4061 why a new grace period has not yet started.
4063 rcuperf.gp_async= [KNL]
4064 Measure performance of asynchronous
4065 grace-period primitives such as call_rcu().
4067 rcuperf.gp_async_max= [KNL]
4068 Specify the maximum number of outstanding
4069 callbacks per writer thread. When a writer
4070 thread exceeds this limit, it invokes the
4071 corresponding flavor of rcu_barrier() to allow
4072 previously posted callbacks to drain.
4074 rcuperf.gp_exp= [KNL]
4075 Measure performance of expedited synchronous
4076 grace-period primitives.
4078 rcuperf.holdoff= [KNL]
4079 Set test-start holdoff period. The purpose of
4080 this parameter is to delay the start of the
4081 test until boot completes in order to avoid
4082 interference.
4084 rcuperf.kfree_rcu_test= [KNL]
4085 Set to measure performance of kfree_rcu() flooding.
4087 rcuperf.kfree_nthreads= [KNL]
4088 The number of threads running loops of kfree_rcu().
4090 rcuperf.kfree_alloc_num= [KNL]
4091 Number of allocations and frees done in an iteration.
4093 rcuperf.kfree_loops= [KNL]
4094 Number of loops doing rcuperf.kfree_alloc_num number
4095 of allocations and frees.
4097 rcuperf.nreaders= [KNL]
4098 Set number of RCU readers. The value -1 selects
4099 N, where N is the number of CPUs. A value
4100 "n" less than -1 selects N-n+1, where N is again
4101 the number of CPUs. For example, -2 selects N
4102 (the number of CPUs), -3 selects N+1, and so on.
4103 A value of "n" less than or equal to -N selects
4104 a single reader.
4106 rcuperf.nwriters= [KNL]
4107 Set number of RCU writers. The values operate
4108 the same as for rcuperf.nreaders.
4109 N, where N is the number of CPUs
4111 rcuperf.perf_type= [KNL]
4112 Specify the RCU implementation to test.
4114 rcuperf.shutdown= [KNL]
4115 Shut the system down after performance tests
4116 complete. This is useful for hands-off automated
4117 testing.
4119 rcuperf.verbose= [KNL]
4120 Enable additional printk() statements.
4122 rcuperf.writer_holdoff= [KNL]
4123 Write-side holdoff between grace periods,
4124 in microseconds. The default of zero says
4125 no holdoff.
4127 rcutorture.fqs_duration= [KNL]
4128 Set duration of force_quiescent_state bursts
4129 in microseconds.
4131 rcutorture.fqs_holdoff= [KNL]
4132 Set holdoff time within force_quiescent_state bursts
4133 in microseconds.
4135 rcutorture.fqs_stutter= [KNL]
4136 Set wait time between force_quiescent_state bursts
4137 in seconds.
4139 rcutorture.fwd_progress= [KNL]
4140 Enable RCU grace-period forward-progress testing
4141 for the types of RCU supporting this notion.
4143 rcutorture.fwd_progress_div= [KNL]
4144 Specify the fraction of a CPU-stall-warning
4145 period to do tight-loop forward-progress testing.
4147 rcutorture.fwd_progress_holdoff= [KNL]
4148 Number of seconds to wait between successive
4149 forward-progress tests.
4151 rcutorture.fwd_progress_need_resched= [KNL]
4152 Enclose cond_resched() calls within checks for
4153 need_resched() during tight-loop forward-progress
4154 testing.
4156 rcutorture.gp_cond= [KNL]
4157 Use conditional/asynchronous update-side
4158 primitives, if available.
4160 rcutorture.gp_exp= [KNL]
4161 Use expedited update-side primitives, if available.
4163 rcutorture.gp_normal= [KNL]
4164 Use normal (non-expedited) asynchronous
4165 update-side primitives, if available.
4167 rcutorture.gp_sync= [KNL]
4168 Use normal (non-expedited) synchronous
4169 update-side primitives, if available. If all
4170 of rcutorture.gp_cond=, rcutorture.gp_exp=,
4171 rcutorture.gp_normal=, and rcutorture.gp_sync=
4172 are zero, rcutorture acts as if is interpreted
4173 they are all non-zero.
4175 rcutorture.n_barrier_cbs= [KNL]
4176 Set callbacks/threads for rcu_barrier() testing.
4178 rcutorture.nfakewriters= [KNL]
4179 Set number of concurrent RCU writers. These just
4180 stress RCU, they don't participate in the actual
4181 test, hence the "fake".
4183 rcutorture.nreaders= [KNL]
4184 Set number of RCU readers. The value -1 selects
4185 N-1, where N is the number of CPUs. A value
4186 "n" less than -1 selects N-n-2, where N is again
4187 the number of CPUs. For example, -2 selects N
4188 (the number of CPUs), -3 selects N+1, and so on.
4190 rcutorture.object_debug= [KNL]
4191 Enable debug-object double-call_rcu() testing.
4193 rcutorture.onoff_holdoff= [KNL]
4194 Set time (s) after boot for CPU-hotplug testing.
4196 rcutorture.onoff_interval= [KNL]
4197 Set time (jiffies) between CPU-hotplug operations,
4198 or zero to disable CPU-hotplug testing.
4200 rcutorture.shuffle_interval= [KNL]
4201 Set task-shuffle interval (s). Shuffling tasks
4202 allows some CPUs to go into dyntick-idle mode
4203 during the rcutorture test.
4205 rcutorture.shutdown_secs= [KNL]
4206 Set time (s) after boot system shutdown. This
4207 is useful for hands-off automated testing.
4209 rcutorture.stall_cpu= [KNL]
4210 Duration of CPU stall (s) to test RCU CPU stall
4211 warnings, zero to disable.
4213 rcutorture.stall_cpu_holdoff= [KNL]
4214 Time to wait (s) after boot before inducing stall.
4216 rcutorture.stall_cpu_irqsoff= [KNL]
4217 Disable interrupts while stalling if set.
4219 rcutorture.stat_interval= [KNL]
4220 Time (s) between statistics printk()s.
4222 rcutorture.stutter= [KNL]
4223 Time (s) to stutter testing, for example, specifying
4224 five seconds causes the test to run for five seconds,
4225 wait for five seconds, and so on. This tests RCU's
4226 ability to transition abruptly to and from idle.
4228 rcutorture.test_boost= [KNL]
4229 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4230 "Maybe" means test if the RCU implementation
4231 under test support RCU priority boosting.
4233 rcutorture.test_boost_duration= [KNL]
4234 Duration (s) of each individual boost test.
4236 rcutorture.test_boost_interval= [KNL]
4237 Interval (s) between each boost test.
4239 rcutorture.test_no_idle_hz= [KNL]
4240 Test RCU's dyntick-idle handling. See also the
4241 rcutorture.shuffle_interval parameter.
4243 rcutorture.torture_type= [KNL]
4244 Specify the RCU implementation to test.
4246 rcutorture.verbose= [KNL]
4247 Enable additional printk() statements.
4249 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
4250 Dump ftrace buffer after reporting RCU CPU
4251 stall warning.
4253 rcupdate.rcu_cpu_stall_suppress= [KNL]
4254 Suppress RCU CPU stall warning messages.
4256 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
4257 Suppress RCU CPU stall warning messages and
4258 rcutorture writer stall warnings that occur
4259 during early boot, that is, during the time
4260 before the init task is spawned.
4262 rcupdate.rcu_cpu_stall_timeout= [KNL]
4263 Set timeout for RCU CPU stall warning messages.
4265 rcupdate.rcu_expedited= [KNL]
4266 Use expedited grace-period primitives, for
4267 example, synchronize_rcu_expedited() instead
4268 of synchronize_rcu(). This reduces latency,
4269 but can increase CPU utilization, degrade
4270 real-time latency, and degrade energy efficiency.
4271 No effect on CONFIG_TINY_RCU kernels.
4273 rcupdate.rcu_normal= [KNL]
4274 Use only normal grace-period primitives,
4275 for example, synchronize_rcu() instead of
4276 synchronize_rcu_expedited(). This improves
4277 real-time latency, CPU utilization, and
4278 energy efficiency, but can expose users to
4279 increased grace-period latency. This parameter
4280 overrides rcupdate.rcu_expedited. No effect on
4281 CONFIG_TINY_RCU kernels.
4283 rcupdate.rcu_normal_after_boot= [KNL]
4284 Once boot has completed (that is, after
4285 rcu_end_inkernel_boot() has been invoked), use
4286 only normal grace-period primitives. No effect
4287 on CONFIG_TINY_RCU kernels.
4289 rcupdate.rcu_task_stall_timeout= [KNL]
4290 Set timeout in jiffies for RCU task stall warning
4291 messages. Disable with a value less than or equal
4292 to zero.
4294 rcupdate.rcu_self_test= [KNL]
4295 Run the RCU early boot self tests
4297 rdinit= [KNL]
4298 Format: <full_path>
4299 Run specified binary instead of /init from the ramdisk,
4300 used for early userspace startup. See initrd.
4302 rdrand= [X86]
4303 force - Override the decision by the kernel to hide the
4304 advertisement of RDRAND support (this affects
4305 certain AMD processors because of buggy BIOS
4306 support, specifically around the suspend/resume
4307 path).
4309 rdt= [HW,X86,RDT]
4310 Turn on/off individual RDT features. List is:
4311 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4312 mba.
4313 E.g. to turn on cmt and turn off mba use:
4314 rdt=cmt,!mba
4316 reboot= [KNL]
4317 Format (x86 or x86_64):
4318 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
4319 [[,]s[mp]#### \
4320 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4321 [[,]f[orce]
4322 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
4323 (prefix with 'panic_' to set mode for panic
4324 reboot only),
4325 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4326 reboot_force is either force or not specified,
4327 reboot_cpu is s[mp]#### with #### being the processor
4328 to be used for rebooting.
4330 relax_domain_level=
4331 [KNL, SMP] Set scheduler's default relax_domain_level.
4332 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
4334 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4335 Format: <base1>,<size1>[,<base2>,<size2>,...]
4336 Reserve I/O ports or memory so the kernel won't use
4337 them. If <base> is less than 0x10000, the region
4338 is assumed to be I/O ports; otherwise it is memory.
4340 reservetop= [X86-32]
4341 Format: nn[KMG]
4342 Reserves a hole at the top of the kernel virtual
4343 address space.
4345 reservelow= [X86]
4346 Format: nn[K]
4347 Set the amount of memory to reserve for BIOS at
4348 the bottom of the address space.
4350 reset_devices [KNL] Force drivers to reset the underlying device
4351 during initialization.
4353 resume= [SWSUSP]
4354 Specify the partition device for software suspend
4355 Format:
4356 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4358 resume_offset= [SWSUSP]
4359 Specify the offset from the beginning of the partition
4360 given by "resume=" at which the swap header is located,
4361 in <PAGE_SIZE> units (needed only for swap files).
4362 See Documentation/power/swsusp-and-swap-files.rst
4364 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4365 read the resume files
4367 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4368 Useful for devices that are detected asynchronously
4369 (e.g. USB and MMC devices).
4371 hibernate= [HIBERNATION]
4372 noresume Don't check if there's a hibernation image
4373 present during boot.
4374 nocompress Don't compress/decompress hibernation images.
4375 no Disable hibernation and resume.
4376 protect_image Turn on image protection during restoration
4377 (that will set all pages holding image data
4378 during restoration read-only).
4380 retain_initrd [RAM] Keep initrd memory after extraction
4382 rfkill.default_state=
4383 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4384 etc. communication is blocked by default.
4385 1 Unblocked.
4387 rfkill.master_switch_mode=
4388 0 The "airplane mode" button does nothing.
4389 1 The "airplane mode" button toggles between everything
4390 blocked and the previous configuration.
4391 2 The "airplane mode" button toggles between everything
4392 blocked and everything unblocked.
4394 rhash_entries= [KNL,NET]
4395 Set number of hash buckets for route cache
4397 ring3mwait=disable
4398 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4399 CPUs.
4401 ro [KNL] Mount root device read-only on boot
4403 rodata= [KNL]
4404 on Mark read-only kernel memory as read-only (default).
4405 off Leave read-only kernel memory writable for debugging.
4407 rockchip.usb_uart
4408 Enable the uart passthrough on the designated usb port
4409 on Rockchip SoCs. When active, the signals of the
4410 debug-uart get routed to the D+ and D- pins of the usb
4411 port and the regular usb controller gets disabled.
4413 root= [KNL] Root filesystem
4414 See name_to_dev_t comment in init/do_mounts.c.
4416 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4417 mount the root filesystem
4419 rootflags= [KNL] Set root filesystem mount option string
4421 rootfstype= [KNL] Set root filesystem type
4423 rootwait [KNL] Wait (indefinitely) for root device to show up.
4424 Useful for devices that are detected asynchronously
4425 (e.g. USB and MMC devices).
4427 rproc_mem=nn[KMG][@address]
4428 [KNL,ARM,CMA] Remoteproc physical memory block.
4429 Memory area to be used by remote processor image,
4430 managed by CMA.
4432 rw [KNL] Mount root device read-write on boot
4434 S [KNL] Run init in single mode
4436 s390_iommu= [HW,S390]
4437 Set s390 IOTLB flushing mode
4438 strict
4439 With strict flushing every unmap operation will result in
4440 an IOTLB flush. Default is lazy flushing before reuse,
4441 which is faster.
4443 sa1100ir [NET]
4444 See drivers/net/irda/sa1100_ir.c.
4446 sbni= [NET] Granch SBNI12 leased line adapter
4448 sched_debug [KNL] Enables verbose scheduler debug messages.
4450 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4451 Allowed values are enable and disable. This feature
4452 incurs a small amount of overhead in the scheduler
4453 but is useful for debugging and performance tuning.
4455 sched_thermal_decay_shift=
4456 [KNL, SMP] Set a decay shift for scheduler thermal
4457 pressure signal. Thermal pressure signal follows the
4458 default decay period of other scheduler pelt
4459 signals(usually 32 ms but configurable). Setting
4460 sched_thermal_decay_shift will left shift the decay
4461 period for the thermal pressure signal by the shift
4462 value.
4463 i.e. with the default pelt decay period of 32 ms
4464 sched_thermal_decay_shift thermal pressure decay pr
4465 1 64 ms
4466 2 128 ms
4467 and so on.
4468 Format: integer between 0 and 10
4469 Default is 0.
4471 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4472 xtime_lock contention on larger systems, and/or RCU lock
4473 contention on all systems with CONFIG_MAXSMP set.
4474 Format: { "0" | "1" }
4475 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4476 1 -- enable.
4477 Note: increases power consumption, thus should only be
4478 enabled if running jitter sensitive (HPC/RT) workloads.
4480 security= [SECURITY] Choose a legacy "major" security module to
4481 enable at boot. This has been deprecated by the
4482 "lsm=" parameter.
4484 selinux= [SELINUX] Disable or enable SELinux at boot time.
4485 Format: { "0" | "1" }
4486 See security/selinux/Kconfig help text.
4487 0 -- disable.
4488 1 -- enable.
4489 Default value is 1.
4491 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4492 Format: { "0" | "1" }
4493 See security/apparmor/Kconfig help text
4494 0 -- disable.
4495 1 -- enable.
4496 Default value is set via kernel config option.
4498 serialnumber [BUGS=X86-32]
4500 shapers= [NET]
4501 Maximal number of shapers.
4503 simeth= [IA-64]
4504 simscsi=
4506 slram= [HW,MTD]
4508 slab_nomerge [MM]
4509 Disable merging of slabs with similar size. May be
4510 necessary if there is some reason to distinguish
4511 allocs to different slabs, especially in hardened
4512 environments where the risk of heap overflows and
4513 layout control by attackers can usually be
4514 frustrated by disabling merging. This will reduce
4515 most of the exposure of a heap attack to a single
4516 cache (risks via metadata attacks are mostly
4517 unchanged). Debug options disable merging on their
4518 own.
4519 For more information see Documentation/vm/slub.rst.
4521 slab_max_order= [MM, SLAB]
4522 Determines the maximum allowed order for slabs.
4523 A high setting may cause OOMs due to memory
4524 fragmentation. Defaults to 1 for systems with
4525 more than 32MB of RAM, 0 otherwise.
4527 slub_debug[=options[,slabs]] [MM, SLUB]
4528 Enabling slub_debug allows one to determine the
4529 culprit if slab objects become corrupted. Enabling
4530 slub_debug can create guard zones around objects and
4531 may poison objects when not in use. Also tracks the
4532 last alloc / free. For more information see
4533 Documentation/vm/slub.rst.
4535 slub_memcg_sysfs= [MM, SLUB]
4536 Determines whether to enable sysfs directories for
4537 memory cgroup sub-caches. 1 to enable, 0 to disable.
4538 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4539 Enabling this can lead to a very high number of debug
4540 directories and files being created under
4541 /sys/kernel/slub.
4543 slub_max_order= [MM, SLUB]
4544 Determines the maximum allowed order for slabs.
4545 A high setting may cause OOMs due to memory
4546 fragmentation. For more information see
4547 Documentation/vm/slub.rst.
4549 slub_min_objects= [MM, SLUB]
4550 The minimum number of objects per slab. SLUB will
4551 increase the slab order up to slub_max_order to
4552 generate a sufficiently large slab able to contain
4553 the number of objects indicated. The higher the number
4554 of objects the smaller the overhead of tracking slabs
4555 and the less frequently locks need to be acquired.
4556 For more information see Documentation/vm/slub.rst.
4558 slub_min_order= [MM, SLUB]
4559 Determines the minimum page order for slabs. Must be
4560 lower than slub_max_order.
4561 For more information see Documentation/vm/slub.rst.
4563 slub_nomerge [MM, SLUB]
4564 Same with slab_nomerge. This is supported for legacy.
4565 See slab_nomerge for more information.
4567 smart2= [HW]
4568 Format: <io1>[,<io2>[,...,<io8>]]
4570 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4571 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4572 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4573 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4574 smsc-ircc2.ircc_irq= [HW] IRQ line
4575 smsc-ircc2.ircc_dma= [HW] DMA channel
4576 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4577 0: Toshiba Satellite 1800 (GP data pin select)
4578 1: Fast pin select (default)
4579 2: ATC IRMode
4581 smt [KNL,S390] Set the maximum number of threads (logical
4582 CPUs) to use per physical CPU on systems capable of
4583 symmetric multithreading (SMT). Will be capped to the
4584 actual hardware limit.
4585 Format: <integer>
4586 Default: -1 (no limit)
4588 softlockup_panic=
4589 [KNL] Should the soft-lockup detector generate panics.
4590 Format: <integer>
4592 A nonzero value instructs the soft-lockup detector
4593 to panic the machine when a soft-lockup occurs. It is
4594 also controlled by the kernel.softlockup_panic sysctl
4595 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
4596 respective build-time switch to that functionality.
4598 softlockup_all_cpu_backtrace=
4599 [KNL] Should the soft-lockup detector generate
4600 backtraces on all cpus.
4601 Format: <integer>
4603 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4604 See Documentation/admin-guide/laptops/sonypi.rst
4606 spectre_v2= [X86] Control mitigation of Spectre variant 2
4607 (indirect branch speculation) vulnerability.
4608 The default operation protects the kernel from
4609 user space attacks.
4611 on - unconditionally enable, implies
4612 spectre_v2_user=on
4613 off - unconditionally disable, implies
4614 spectre_v2_user=off
4615 auto - kernel detects whether your CPU model is
4616 vulnerable
4618 Selecting 'on' will, and 'auto' may, choose a
4619 mitigation method at run time according to the
4620 CPU, the available microcode, the setting of the
4621 CONFIG_RETPOLINE configuration option, and the
4622 compiler with which the kernel was built.
4624 Selecting 'on' will also enable the mitigation
4625 against user space to user space task attacks.
4627 Selecting 'off' will disable both the kernel and
4628 the user space protections.
4630 Specific mitigations can also be selected manually:
4632 retpoline - replace indirect branches
4633 retpoline,generic - google's original retpoline
4634 retpoline,amd - AMD-specific minimal thunk
4636 Not specifying this option is equivalent to
4637 spectre_v2=auto.
4639 spectre_v2_user=
4640 [X86] Control mitigation of Spectre variant 2
4641 (indirect branch speculation) vulnerability between
4642 user space tasks
4644 on - Unconditionally enable mitigations. Is
4645 enforced by spectre_v2=on
4647 off - Unconditionally disable mitigations. Is
4648 enforced by spectre_v2=off
4650 prctl - Indirect branch speculation is enabled,
4651 but mitigation can be enabled via prctl
4652 per thread. The mitigation control state
4653 is inherited on fork.
4655 prctl,ibpb
4656 - Like "prctl" above, but only STIBP is
4657 controlled per thread. IBPB is issued
4658 always when switching between different user
4659 space processes.
4661 seccomp
4662 - Same as "prctl" above, but all seccomp
4663 threads will enable the mitigation unless
4664 they explicitly opt out.
4666 seccomp,ibpb
4667 - Like "seccomp" above, but only STIBP is
4668 controlled per thread. IBPB is issued
4669 always when switching between different
4670 user space processes.
4672 auto - Kernel selects the mitigation depending on
4673 the available CPU features and vulnerability.
4675 Default mitigation:
4676 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
4678 Not specifying this option is equivalent to
4679 spectre_v2_user=auto.
4681 spec_store_bypass_disable=
4682 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4683 (Speculative Store Bypass vulnerability)
4685 Certain CPUs are vulnerable to an exploit against a
4686 a common industry wide performance optimization known
4687 as "Speculative Store Bypass" in which recent stores
4688 to the same memory location may not be observed by
4689 later loads during speculative execution. The idea
4690 is that such stores are unlikely and that they can
4691 be detected prior to instruction retirement at the
4692 end of a particular speculation execution window.
4694 In vulnerable processors, the speculatively forwarded
4695 store can be used in a cache side channel attack, for
4696 example to read memory to which the attacker does not
4697 directly have access (e.g. inside sandboxed code).
4699 This parameter controls whether the Speculative Store
4700 Bypass optimization is used.
4702 On x86 the options are:
4704 on - Unconditionally disable Speculative Store Bypass
4705 off - Unconditionally enable Speculative Store Bypass
4706 auto - Kernel detects whether the CPU model contains an
4707 implementation of Speculative Store Bypass and
4708 picks the most appropriate mitigation. If the
4709 CPU is not vulnerable, "off" is selected. If the
4710 CPU is vulnerable the default mitigation is
4711 architecture and Kconfig dependent. See below.
4712 prctl - Control Speculative Store Bypass per thread
4713 via prctl. Speculative Store Bypass is enabled
4714 for a process by default. The state of the control
4715 is inherited on fork.
4716 seccomp - Same as "prctl" above, but all seccomp threads
4717 will disable SSB unless they explicitly opt out.
4719 Default mitigations:
4720 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4722 On powerpc the options are:
4724 on,auto - On Power8 and Power9 insert a store-forwarding
4725 barrier on kernel entry and exit. On Power7
4726 perform a software flush on kernel entry and
4727 exit.
4728 off - No action.
4730 Not specifying this option is equivalent to
4731 spec_store_bypass_disable=auto.
4733 spia_io_base= [HW,MTD]
4734 spia_fio_base=
4735 spia_pedr=
4736 spia_peddr=
4738 split_lock_detect=
4739 [X86] Enable split lock detection
4741 When enabled (and if hardware support is present), atomic
4742 instructions that access data across cache line
4743 boundaries will result in an alignment check exception.
4745 off - not enabled
4747 warn - the kernel will emit rate limited warnings
4748 about applications triggering the #AC
4749 exception. This mode is the default on CPUs
4750 that supports split lock detection.
4752 fatal - the kernel will send SIGBUS to applications
4753 that trigger the #AC exception.
4755 If an #AC exception is hit in the kernel or in
4756 firmware (i.e. not while executing in user mode)
4757 the kernel will oops in either "warn" or "fatal"
4758 mode.
4760 srcutree.counter_wrap_check [KNL]
4761 Specifies how frequently to check for
4762 grace-period sequence counter wrap for the
4763 srcu_data structure's ->srcu_gp_seq_needed field.
4764 The greater the number of bits set in this kernel
4765 parameter, the less frequently counter wrap will
4766 be checked for. Note that the bottom two bits
4767 are ignored.
4769 srcutree.exp_holdoff [KNL]
4770 Specifies how many nanoseconds must elapse
4771 since the end of the last SRCU grace period for
4772 a given srcu_struct until the next normal SRCU
4773 grace period will be considered for automatic
4774 expediting. Set to zero to disable automatic
4775 expediting.
4777 ssbd= [ARM64,HW]
4778 Speculative Store Bypass Disable control
4780 On CPUs that are vulnerable to the Speculative
4781 Store Bypass vulnerability and offer a
4782 firmware based mitigation, this parameter
4783 indicates how the mitigation should be used:
4785 force-on: Unconditionally enable mitigation for
4786 for both kernel and userspace
4787 force-off: Unconditionally disable mitigation for
4788 for both kernel and userspace
4789 kernel: Always enable mitigation in the
4790 kernel, and offer a prctl interface
4791 to allow userspace to register its
4792 interest in being mitigated too.
4794 stack_guard_gap= [MM]
4795 override the default stack gap protection. The value
4796 is in page units and it defines how many pages prior
4797 to (for stacks growing down) resp. after (for stacks
4798 growing up) the main stack are reserved for no other
4799 mapping. Default value is 256 pages.
4801 stacktrace [FTRACE]
4802 Enabled the stack tracer on boot up.
4804 stacktrace_filter=[function-list]
4805 [FTRACE] Limit the functions that the stack tracer
4806 will trace at boot up. function-list is a comma separated
4807 list of functions. This list can be changed at run
4808 time by the stack_trace_filter file in the debugfs
4809 tracing directory. Note, this enables stack tracing
4810 and the stacktrace above is not needed.
4812 sti= [PARISC,HW]
4813 Format: <num>
4814 Set the STI (builtin display/keyboard on the HP-PARISC
4815 machines) console (graphic card) which should be used
4816 as the initial boot-console.
4817 See also comment in drivers/video/console/sticore.c.
4819 sti_font= [HW]
4820 See comment in drivers/video/console/sticore.c.
4822 stifb= [HW]
4823 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4825 sunrpc.min_resvport=
4826 sunrpc.max_resvport=
4827 [NFS,SUNRPC]
4828 SunRPC servers often require that client requests
4829 originate from a privileged port (i.e. a port in the
4830 range 0 < portnr < 1024).
4831 An administrator who wishes to reserve some of these
4832 ports for other uses may adjust the range that the
4833 kernel's sunrpc client considers to be privileged
4834 using these two parameters to set the minimum and
4835 maximum port values.
4837 sunrpc.svc_rpc_per_connection_limit=
4838 [NFS,SUNRPC]
4839 Limit the number of requests that the server will
4840 process in parallel from a single connection.
4841 The default value is 0 (no limit).
4843 sunrpc.pool_mode=
4844 [NFS]
4845 Control how the NFS server code allocates CPUs to
4846 service thread pools. Depending on how many NICs
4847 you have and where their interrupts are bound, this
4848 option will affect which CPUs will do NFS serving.
4849 Note: this parameter cannot be changed while the
4850 NFS server is running.
4852 auto the server chooses an appropriate mode
4853 automatically using heuristics
4854 global a single global pool contains all CPUs
4855 percpu one pool for each CPU
4856 pernode one pool for each NUMA node (equivalent
4857 to global on non-NUMA machines)
4859 sunrpc.tcp_slot_table_entries=
4860 sunrpc.udp_slot_table_entries=
4861 [NFS,SUNRPC]
4862 Sets the upper limit on the number of simultaneous
4863 RPC calls that can be sent from the client to a
4864 server. Increasing these values may allow you to
4865 improve throughput, but will also increase the
4866 amount of memory reserved for use by the client.
4868 suspend.pm_test_delay=
4869 [SUSPEND]
4870 Sets the number of seconds to remain in a suspend test
4871 mode before resuming the system (see
4872 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4873 is set. Default value is 5.
4875 svm= [PPC]
4876 Format: { on | off | y | n | 1 | 0 }
4877 This parameter controls use of the Protected
4878 Execution Facility on pSeries.
4880 swapaccount=[0|1]
4881 [KNL] Enable accounting of swap in memory resource
4882 controller if no parameter or 1 is given or disable
4883 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
4885 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4886 Format: { <int> | force | noforce }
4887 <int> -- Number of I/O TLB slabs
4888 force -- force using of bounce buffers even if they
4889 wouldn't be automatically used by the kernel
4890 noforce -- Never use bounce buffers (for debugging)
4892 switches= [HW,M68k]
4894 sysfs.deprecated=0|1 [KNL]
4895 Enable/disable old style sysfs layout for old udev
4896 on older distributions. When this option is enabled
4897 very new udev will not work anymore. When this option
4898 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4899 in older udev will not work anymore.
4900 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4901 the kernel configuration.
4903 sysrq_always_enabled
4904 [KNL]
4905 Ignore sysrq setting - this boot parameter will
4906 neutralize any effect of /proc/sys/kernel/sysrq.
4907 Useful for debugging.
4909 tcpmhash_entries= [KNL,NET]
4910 Set the number of tcp_metrics_hash slots.
4911 Default value is 8192 or 16384 depending on total
4912 ram pages. This is used to specify the TCP metrics
4913 cache size. See Documentation/networking/ip-sysctl.txt
4914 "tcp_no_metrics_save" section for more details.
4916 tdfx= [HW,DRM]
4918 test_suspend= [SUSPEND][,N]
4919 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4920 standby suspend) or "freeze" (for suspend type freeze)
4921 as the system sleep state during system startup with
4922 the optional capability to repeat N number of times.
4923 The system is woken from this state using a
4924 wakeup-capable RTC alarm.
4926 thash_entries= [KNL,NET]
4927 Set number of hash buckets for TCP connection
4929 thermal.act= [HW,ACPI]
4930 -1: disable all active trip points in all thermal zones
4931 <degrees C>: override all lowest active trip points
4933 thermal.crt= [HW,ACPI]
4934 -1: disable all critical trip points in all thermal zones
4935 <degrees C>: override all critical trip points
4937 thermal.nocrt= [HW,ACPI]
4938 Set to disable actions on ACPI thermal zone
4939 critical and hot trip points.
4941 thermal.off= [HW,ACPI]
4942 1: disable ACPI thermal control
4944 thermal.psv= [HW,ACPI]
4945 -1: disable all passive trip points
4946 <degrees C>: override all passive trip points to this
4947 value
4949 thermal.tzp= [HW,ACPI]
4950 Specify global default ACPI thermal zone polling rate
4951 <deci-seconds>: poll all this frequency
4952 0: no polling (default)
4954 threadirqs [KNL]
4955 Force threading of all interrupt handlers except those
4956 marked explicitly IRQF_NO_THREAD.
4958 topology= [S390]
4959 Format: {off | on}
4960 Specify if the kernel should make use of the cpu
4961 topology information if the hardware supports this.
4962 The scheduler will make use of this information and
4963 e.g. base its process migration decisions on it.
4964 Default is on.
4966 topology_updates= [KNL, PPC, NUMA]
4967 Format: {off}
4968 Specify if the kernel should ignore (off)
4969 topology updates sent by the hypervisor to this
4970 LPAR.
4972 torture.disable_onoff_at_boot= [KNL]
4973 Prevent the CPU-hotplug component of torturing
4974 until after init has spawned.
4976 tp720= [HW,PS2]
4978 tpm_suspend_pcr=[HW,TPM]
4979 Format: integer pcr id
4980 Specify that at suspend time, the tpm driver
4981 should extend the specified pcr with zeros,
4982 as a workaround for some chips which fail to
4983 flush the last written pcr on TPM_SaveState.
4984 This will guarantee that all the other pcrs
4985 are saved.
4987 trace_buf_size=nn[KMG]
4988 [FTRACE] will set tracing buffer size on each cpu.
4990 trace_event=[event-list]
4991 [FTRACE] Set and start specified trace events in order
4992 to facilitate early boot debugging. The event-list is a
4993 comma separated list of trace events to enable. See
4994 also Documentation/trace/events.rst
4996 trace_options=[option-list]
4997 [FTRACE] Enable or disable tracer options at boot.
4998 The option-list is a comma delimited list of options
4999 that can be enabled or disabled just as if you were
5000 to echo the option name into
5002 /sys/kernel/debug/tracing/trace_options
5004 For example, to enable stacktrace option (to dump the
5005 stack trace of each event), add to the command line:
5007 trace_options=stacktrace
5009 See also Documentation/trace/ftrace.rst "trace options"
5010 section.
5012 tp_printk[FTRACE]
5013 Have the tracepoints sent to printk as well as the
5014 tracing ring buffer. This is useful for early boot up
5015 where the system hangs or reboots and does not give the
5016 option for reading the tracing buffer or performing a
5017 ftrace_dump_on_oops.
5019 To turn off having tracepoints sent to printk,
5020 echo 0 > /proc/sys/kernel/tracepoint_printk
5021 Note, echoing 1 into this file without the
5022 tracepoint_printk kernel cmdline option has no effect.
5024 ** CAUTION **
5026 Having tracepoints sent to printk() and activating high
5027 frequency tracepoints such as irq or sched, can cause
5028 the system to live lock.
5030 traceoff_on_warning
5031 [FTRACE] enable this option to disable tracing when a
5032 warning is hit. This turns off "tracing_on". Tracing can
5033 be enabled again by echoing '1' into the "tracing_on"
5034 file located in /sys/kernel/debug/tracing/
5036 This option is useful, as it disables the trace before
5037 the WARNING dump is called, which prevents the trace to
5038 be filled with content caused by the warning output.
5040 This option can also be set at run time via the sysctl
5041 option: kernel/traceoff_on_warning
5043 transparent_hugepage=
5044 [KNL]
5045 Format: [always|madvise|never]
5046 Can be used to control the default behavior of the system
5047 with respect to transparent hugepages.
5048 See Documentation/admin-guide/mm/transhuge.rst
5049 for more details.
5051 tsc= Disable clocksource stability checks for TSC.
5052 Format: <string>
5053 [x86] reliable: mark tsc clocksource as reliable, this
5054 disables clocksource verification at runtime, as well
5055 as the stability checks done at bootup. Used to enable
5056 high-resolution timer mode on older hardware, and in
5057 virtualized environment.
5058 [x86] noirqtime: Do not use TSC to do irq accounting.
5059 Used to run time disable IRQ_TIME_ACCOUNTING on any
5060 platforms where RDTSC is slow and this accounting
5061 can add overhead.
5062 [x86] unstable: mark the TSC clocksource as unstable, this
5063 marks the TSC unconditionally unstable at bootup and
5064 avoids any further wobbles once the TSC watchdog notices.
5065 [x86] nowatchdog: disable clocksource watchdog. Used
5066 in situations with strict latency requirements (where
5067 interruptions from clocksource watchdog are not
5068 acceptable).
5070 tsx= [X86] Control Transactional Synchronization
5071 Extensions (TSX) feature in Intel processors that
5072 support TSX control.
5074 This parameter controls the TSX feature. The options are:
5076 on - Enable TSX on the system. Although there are
5077 mitigations for all known security vulnerabilities,
5078 TSX has been known to be an accelerator for
5079 several previous speculation-related CVEs, and
5080 so there may be unknown security risks associated
5081 with leaving it enabled.
5083 off - Disable TSX on the system. (Note that this
5084 option takes effect only on newer CPUs which are
5085 not vulnerable to MDS, i.e., have
5086 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
5087 the new IA32_TSX_CTRL MSR through a microcode
5088 update. This new MSR allows for the reliable
5089 deactivation of the TSX functionality.)
5091 auto - Disable TSX if X86_BUG_TAA is present,
5092 otherwise enable TSX on the system.
5094 Not specifying this option is equivalent to tsx=off.
5096 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5097 for more details.
5099 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
5100 Abort (TAA) vulnerability.
5102 Similar to Micro-architectural Data Sampling (MDS)
5103 certain CPUs that support Transactional
5104 Synchronization Extensions (TSX) are vulnerable to an
5105 exploit against CPU internal buffers which can forward
5106 information to a disclosure gadget under certain
5107 conditions.
5109 In vulnerable processors, the speculatively forwarded
5110 data can be used in a cache side channel attack, to
5111 access data to which the attacker does not have direct
5112 access.
5114 This parameter controls the TAA mitigation. The
5115 options are:
5117 full - Enable TAA mitigation on vulnerable CPUs
5118 if TSX is enabled.
5120 full,nosmt - Enable TAA mitigation and disable SMT on
5121 vulnerable CPUs. If TSX is disabled, SMT
5122 is not disabled because CPU is not
5123 vulnerable to cross-thread TAA attacks.
5124 off - Unconditionally disable TAA mitigation
5126 On MDS-affected machines, tsx_async_abort=off can be
5127 prevented by an active MDS mitigation as both vulnerabilities
5128 are mitigated with the same mechanism so in order to disable
5129 this mitigation, you need to specify mds=off too.
5131 Not specifying this option is equivalent to
5132 tsx_async_abort=full. On CPUs which are MDS affected
5133 and deploy MDS mitigation, TAA mitigation is not
5134 required and doesn't provide any additional
5135 mitigation.
5137 For details see:
5138 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5140 turbografx.map[2|3]= [HW,JOY]
5141 TurboGraFX parallel port interface
5142 Format:
5143 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
5144 See also Documentation/input/devices/joystick-parport.rst
5146 udbg-immortal [PPC] When debugging early kernel crashes that
5147 happen after console_init() and before a proper
5148 console driver takes over, this boot options might
5149 help "seeing" what's going on.
5151 uhash_entries= [KNL,NET]
5152 Set number of hash buckets for UDP/UDP-Lite connections
5154 uhci-hcd.ignore_oc=
5155 [USB] Ignore overcurrent events (default N).
5156 Some badly-designed motherboards generate lots of
5157 bogus events, for ports that aren't wired to
5158 anything. Set this parameter to avoid log spamming.
5159 Note that genuine overcurrent events won't be
5160 reported either.
5162 unknown_nmi_panic
5163 [X86] Cause panic on unknown NMI.
5165 usbcore.authorized_default=
5166 [USB] Default USB device authorization:
5167 (default -1 = authorized except for wireless USB,
5168 0 = not authorized, 1 = authorized, 2 = authorized
5169 if device connected to internal port)
5171 usbcore.autosuspend=
5172 [USB] The autosuspend time delay (in seconds) used
5173 for newly-detected USB devices (default 2). This
5174 is the time required before an idle device will be
5175 autosuspended. Devices for which the delay is set
5176 to a negative value won't be autosuspended at all.
5178 usbcore.usbfs_snoop=
5179 [USB] Set to log all usbfs traffic (default 0 = off).
5181 usbcore.usbfs_snoop_max=
5182 [USB] Maximum number of bytes to snoop in each URB
5183 (default = 65536).
5185 usbcore.blinkenlights=
5186 [USB] Set to cycle leds on hubs (default 0 = off).
5188 usbcore.old_scheme_first=
5189 [USB] Start with the old device initialization
5190 scheme, applies only to low and full-speed devices
5191 (default 0 = off).
5193 usbcore.usbfs_memory_mb=
5194 [USB] Memory limit (in MB) for buffers allocated by
5195 usbfs (default = 16, 0 = max = 2047).
5197 usbcore.use_both_schemes=
5198 [USB] Try the other device initialization scheme
5199 if the first one fails (default 1 = enabled).
5201 usbcore.initial_descriptor_timeout=
5202 [USB] Specifies timeout for the initial 64-byte
5203 USB_REQ_GET_DESCRIPTOR request in milliseconds
5204 (default 5000 = 5.0 seconds).
5206 usbcore.nousb [USB] Disable the USB subsystem
5208 usbcore.quirks=
5209 [USB] A list of quirk entries to augment the built-in
5210 usb core quirk list. List entries are separated by
5211 commas. Each entry has the form
5212 VendorID:ProductID:Flags. The IDs are 4-digit hex
5213 numbers and Flags is a set of letters. Each letter
5214 will change the built-in quirk; setting it if it is
5215 clear and clearing it if it is set. The letters have
5216 the following meanings:
5217 a = USB_QUIRK_STRING_FETCH_255 (string
5218 descriptors must not be fetched using
5219 a 255-byte read);
5220 b = USB_QUIRK_RESET_RESUME (device can't resume
5221 correctly so reset it instead);
5222 c = USB_QUIRK_NO_SET_INTF (device can't handle
5223 Set-Interface requests);
5224 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
5225 handle its Configuration or Interface
5226 strings);
5227 e = USB_QUIRK_RESET (device can't be reset
5228 (e.g morph devices), don't use reset);
5229 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
5230 more interface descriptions than the
5231 bNumInterfaces count, and can't handle
5232 talking to these interfaces);
5233 g = USB_QUIRK_DELAY_INIT (device needs a pause
5234 during initialization, after we read
5235 the device descriptor);
5236 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
5237 high speed and super speed interrupt
5238 endpoints, the USB 2.0 and USB 3.0 spec
5239 require the interval in microframes (1
5240 microframe = 125 microseconds) to be
5241 calculated as interval = 2 ^
5242 (bInterval-1).
5243 Devices with this quirk report their
5244 bInterval as the result of this
5245 calculation instead of the exponent
5246 variable used in the calculation);
5247 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
5248 handle device_qualifier descriptor
5249 requests);
5250 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
5251 generates spurious wakeup, ignore
5252 remote wakeup capability);
5253 k = USB_QUIRK_NO_LPM (device can't handle Link
5254 Power Management);
5255 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
5256 (Device reports its bInterval as linear
5257 frames instead of the USB 2.0
5258 calculation);
5259 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
5260 to be disconnected before suspend to
5261 prevent spurious wakeup);
5262 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
5263 pause after every control message);
5264 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
5265 delay after resetting its port);
5266 Example: quirks=0781:5580:bk,0a5c:5834:gij
5268 usbhid.mousepoll=
5269 [USBHID] The interval which mice are to be polled at.
5271 usbhid.jspoll=
5272 [USBHID] The interval which joysticks are to be polled at.
5274 usbhid.kbpoll=
5275 [USBHID] The interval which keyboards are to be polled at.
5277 usb-storage.delay_use=
5278 [UMS] The delay in seconds before a new device is
5279 scanned for Logical Units (default 1).
5281 usb-storage.quirks=
5282 [UMS] A list of quirks entries to supplement or
5283 override the built-in unusual_devs list. List
5284 entries are separated by commas. Each entry has
5285 the form VID:PID:Flags where VID and PID are Vendor
5286 and Product ID values (4-digit hex numbers) and
5287 Flags is a set of characters, each corresponding
5288 to a common usb-storage quirk flag as follows:
5289 a = SANE_SENSE (collect more than 18 bytes
5290 of sense data, not on uas);
5291 b = BAD_SENSE (don't collect more than 18
5292 bytes of sense data, not on uas);
5293 c = FIX_CAPACITY (decrease the reported
5294 device capacity by one sector);
5295 d = NO_READ_DISC_INFO (don't use
5296 READ_DISC_INFO command, not on uas);
5297 e = NO_READ_CAPACITY_16 (don't use
5298 READ_CAPACITY_16 command);
5299 f = NO_REPORT_OPCODES (don't use report opcodes
5300 command, uas only);
5301 g = MAX_SECTORS_240 (don't transfer more than
5302 240 sectors at a time, uas only);
5303 h = CAPACITY_HEURISTICS (decrease the
5304 reported device capacity by one
5305 sector if the number is odd);
5306 i = IGNORE_DEVICE (don't bind to this
5307 device);
5308 j = NO_REPORT_LUNS (don't use report luns
5309 command, uas only);
5310 l = NOT_LOCKABLE (don't try to lock and
5311 unlock ejectable media, not on uas);
5312 m = MAX_SECTORS_64 (don't transfer more
5313 than 64 sectors = 32 KB at a time,
5314 not on uas);
5315 n = INITIAL_READ10 (force a retry of the
5316 initial READ(10) command, not on uas);
5317 o = CAPACITY_OK (accept the capacity
5318 reported by the device, not on uas);
5319 p = WRITE_CACHE (the device cache is ON
5320 by default, not on uas);
5321 r = IGNORE_RESIDUE (the device reports
5322 bogus residue values, not on uas);
5323 s = SINGLE_LUN (the device has only one
5324 Logical Unit);
5325 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
5326 commands, uas only);
5327 u = IGNORE_UAS (don't bind to the uas driver);
5328 w = NO_WP_DETECT (don't test whether the
5329 medium is write-protected).
5330 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
5331 even if the device claims no cache,
5332 not on uas)
5333 Example: quirks=0419:aaf5:rl,0421:0433:rc
5335 user_debug= [KNL,ARM]
5336 Format: <int>
5337 See arch/arm/Kconfig.debug help text.
5338 1 - undefined instruction events
5339 2 - system calls
5340 4 - invalid data aborts
5341 8 - SIGSEGV faults
5342 16 - SIGBUS faults
5343 Example: user_debug=31
5345 userpte=
5346 [X86] Flags controlling user PTE allocations.
5348 nohigh = do not allocate PTE pages in
5349 HIGHMEM regardless of setting
5350 of CONFIG_HIGHPTE.
5352 vdso= [X86,SH]
5353 On X86_32, this is an alias for vdso32=. Otherwise:
5355 vdso=1: enable VDSO (the default)
5356 vdso=0: disable VDSO mapping
5358 vdso32= [X86] Control the 32-bit vDSO
5359 vdso32=1: enable 32-bit VDSO
5360 vdso32=0 or vdso32=2: disable 32-bit VDSO
5362 See the help text for CONFIG_COMPAT_VDSO for more
5363 details. If CONFIG_COMPAT_VDSO is set, the default is
5364 vdso32=0; otherwise, the default is vdso32=1.
5366 For compatibility with older kernels, vdso32=2 is an
5367 alias for vdso32=0.
5369 Try vdso32=0 if you encounter an error that says:
5370 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
5372 vector= [IA-64,SMP]
5373 vector=percpu: enable percpu vector domain
5375 video= [FB] Frame buffer configuration
5376 See Documentation/fb/modedb.rst.
5378 video.brightness_switch_enabled= [0,1]
5379 If set to 1, on receiving an ACPI notify event
5380 generated by hotkey, video driver will adjust brightness
5381 level and then send out the event to user space through
5382 the allocated input device; If set to 0, video driver
5383 will only send out the event without touching backlight
5384 brightness level.
5385 default: 1
5387 virtio_mmio.device=
5388 [VMMIO] Memory mapped virtio (platform) device.
5390 <size>@<baseaddr>:<irq>[:<id>]
5391 where:
5392 <size> := size (can use standard suffixes
5393 like K, M and G)
5394 <baseaddr> := physical base address
5395 <irq> := interrupt number (as passed to
5396 request_irq())
5397 <id> := (optional) platform device id
5398 example:
5399 virtio_mmio.device=1K@0x100b0000:48:7
5401 Can be used multiple times for multiple devices.
5403 vga= [BOOT,X86-32] Select a particular video mode
5404 See Documentation/x86/boot.rst and
5405 Documentation/admin-guide/svga.rst.
5406 Use vga=ask for menu.
5407 This is actually a boot loader parameter; the value is
5408 passed to the kernel using a special protocol.
5410 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
5411 May slow down system boot speed, especially when
5412 enabled on systems with a large amount of memory.
5413 All options are enabled by default, and this
5414 interface is meant to allow for selectively
5415 enabling or disabling specific virtual memory
5416 debugging features.
5418 Available options are:
5419 P Enable page structure init time poisoning
5420 - Disable all of the above options
5422 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
5423 size of <nn>. This can be used to increase the
5424 minimum size (128MB on x86). It can also be used to
5425 decrease the size and leave more room for directly
5426 mapped kernel RAM.
5428 vmcp_cma=nn[MG] [KNL,S390]
5429 Sets the memory size reserved for contiguous memory
5430 allocations for the vmcp device driver.
5432 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
5433 Format: <command>
5435 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
5436 Format: <command>
5438 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
5439 Format: <command>
5441 vsyscall= [X86-64]
5442 Controls the behavior of vsyscalls (i.e. calls to
5443 fixed addresses of 0xffffffffff600x00 from legacy
5444 code). Most statically-linked binaries and older
5445 versions of glibc use these calls. Because these
5446 functions are at fixed addresses, they make nice
5447 targets for exploits that can control RIP.
5449 emulate [default] Vsyscalls turn into traps and are
5450 emulated reasonably safely. The vsyscall
5451 page is readable.
5453 xonly Vsyscalls turn into traps and are
5454 emulated reasonably safely. The vsyscall
5455 page is not readable.
5457 none Vsyscalls don't work at all. This makes
5458 them quite hard to use for exploits but
5459 might break your system.
5461 vt.color= [VT] Default text color.
5462 Format: 0xYX, X = foreground, Y = background.
5463 Default: 0x07 = light gray on black.
5465 vt.cur_default= [VT] Default cursor shape.
5466 Format: 0xCCBBAA, where AA, BB, and CC are the same as
5467 the parameters of the <Esc>[?A;B;Cc escape sequence;
5468 see VGA-softcursor.txt. Default: 2 = underline.
5470 vt.default_blu= [VT]
5471 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
5472 Change the default blue palette of the console.
5473 This is a 16-member array composed of values
5474 ranging from 0-255.
5476 vt.default_grn= [VT]
5477 Format: <green0>,<green1>,<green2>,...,<green15>
5478 Change the default green palette of the console.
5479 This is a 16-member array composed of values
5480 ranging from 0-255.
5482 vt.default_red= [VT]
5483 Format: <red0>,<red1>,<red2>,...,<red15>
5484 Change the default red palette of the console.
5485 This is a 16-member array composed of values
5486 ranging from 0-255.
5488 vt.default_utf8=
5489 [VT]
5490 Format=<0|1>
5491 Set system-wide default UTF-8 mode for all tty's.
5492 Default is 1, i.e. UTF-8 mode is enabled for all
5493 newly opened terminals.
5495 vt.global_cursor_default=
5496 [VT]
5497 Format=<-1|0|1>
5498 Set system-wide default for whether a cursor
5499 is shown on new VTs. Default is -1,
5500 i.e. cursors will be created by default unless
5501 overridden by individual drivers. 0 will hide
5502 cursors, 1 will display them.
5504 vt.italic= [VT] Default color for italic text; 0-15.
5505 Default: 2 = green.
5507 vt.underline= [VT] Default color for underlined text; 0-15.
5508 Default: 3 = cyan.
5510 watchdog timers [HW,WDT] For information on watchdog timers,
5511 see Documentation/watchdog/watchdog-parameters.rst
5512 or other driver-specific files in the
5513 Documentation/watchdog/ directory.
5515 watchdog_thresh=
5516 [KNL]
5517 Set the hard lockup detector stall duration
5518 threshold in seconds. The soft lockup detector
5519 threshold is set to twice the value. A value of 0
5520 disables both lockup detectors. Default is 10
5521 seconds.
5523 workqueue.watchdog_thresh=
5524 If CONFIG_WQ_WATCHDOG is configured, workqueue can
5525 warn stall conditions and dump internal state to
5526 help debugging. 0 disables workqueue stall
5527 detection; otherwise, it's the stall threshold
5528 duration in seconds. The default value is 30 and
5529 it can be updated at runtime by writing to the
5530 corresponding sysfs file.
5532 workqueue.disable_numa
5533 By default, all work items queued to unbound
5534 workqueues are affine to the NUMA nodes they're
5535 issued on, which results in better behavior in
5536 general. If NUMA affinity needs to be disabled for
5537 whatever reason, this option can be used. Note
5538 that this also can be controlled per-workqueue for
5539 workqueues visible under /sys/bus/workqueue/.
5541 workqueue.power_efficient
5542 Per-cpu workqueues are generally preferred because
5543 they show better performance thanks to cache
5544 locality; unfortunately, per-cpu workqueues tend to
5545 be more power hungry than unbound workqueues.
5547 Enabling this makes the per-cpu workqueues which
5548 were observed to contribute significantly to power
5549 consumption unbound, leading to measurably lower
5550 power usage at the cost of small performance
5551 overhead.
5553 The default value of this parameter is determined by
5554 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
5556 workqueue.debug_force_rr_cpu
5557 Workqueue used to implicitly guarantee that work
5558 items queued without explicit CPU specified are put
5559 on the local CPU. This guarantee is no longer true
5560 and while local CPU is still preferred work items
5561 may be put on foreign CPUs. This debug option
5562 forces round-robin CPU selection to flush out
5563 usages which depend on the now broken guarantee.
5564 When enabled, memory and cache locality will be
5565 impacted.
5567 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5568 default x2apic cluster mode on platforms
5569 supporting x2apic.
5571 x86_intel_mid_timer= [X86-32,APBT]
5572 Choose timer option for x86 Intel MID platform.
5573 Two valid options are apbt timer only and lapic timer
5574 plus one apbt timer for broadcast timer.
5575 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5577 xen_512gb_limit [KNL,X86-64,XEN]
5578 Restricts the kernel running paravirtualized under Xen
5579 to use only up to 512 GB of RAM. The reason to do so is
5580 crash analysis tools and Xen tools for doing domain
5581 save/restore/migration must be enabled to handle larger
5582 domains.
5584 xen_emul_unplug= [HW,X86,XEN]
5585 Unplug Xen emulated devices
5586 Format: [unplug0,][unplug1]
5587 ide-disks -- unplug primary master IDE devices
5588 aux-ide-disks -- unplug non-primary-master IDE devices
5589 nics -- unplug network devices
5590 all -- unplug all emulated devices (NICs and IDE disks)
5591 unnecessary -- unplugging emulated devices is
5592 unnecessary even if the host did not respond to
5593 the unplug protocol
5594 never -- do not unplug even if version check succeeds
5596 xen_legacy_crash [X86,XEN]
5597 Crash from Xen panic notifier, without executing late
5598 panic() code such as dumping handler.
5600 xen_nopvspin [X86,XEN]
5601 Disables the ticketlock slowpath using Xen PV
5602 optimizations.
5604 xen_nopv [X86]
5605 Disables the PV optimizations forcing the HVM guest to
5606 run as generic HVM guest with no PV drivers.
5607 This option is obsoleted by the "nopv" option, which
5608 has equivalent effect for XEN platform.
5610 xen_scrub_pages= [XEN]
5611 Boolean option to control scrubbing pages before giving them back
5612 to Xen, for use by other domains. Can be also changed at runtime
5613 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5614 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5616 xen_timer_slop= [X86-64,XEN]
5617 Set the timer slop (in nanoseconds) for the virtual Xen
5618 timers (default is 100000). This adjusts the minimum
5619 delta of virtualized Xen timers, where lower values
5620 improve timer resolution at the expense of processing
5621 more timer interrupts.
5623 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
5624 Disables the PV optimizations forcing the guest to run
5625 as generic guest with no PV drivers. Currently support
5626 XEN HVM, KVM, HYPER_V and VMWARE guest.
5628 xirc2ps_cs= [NET,PCMCIA]
5629 Format:
5630 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5632 xive= [PPC]
5633 By default on POWER9 and above, the kernel will
5634 natively use the XIVE interrupt controller. This option
5635 allows the fallback firmware mode to be used:
5637 off Fallback to firmware control of XIVE interrupt
5638 controller on both pseries and powernv
5639 platforms. Only useful on POWER9 and above.
5641 xhci-hcd.quirks [USB,KNL]
5642 A hex value specifying bitmask with supplemental xhci
5643 host controller quirks. Meaning of each bit can be
5644 consulted in header drivers/usb/host/xhci.h.
5646 xmon [PPC]
5647 Format: { early | on | rw | ro | off }
5648 Controls if xmon debugger is enabled. Default is off.
5649 Passing only "xmon" is equivalent to "xmon=early".
5650 early Call xmon as early as possible on boot; xmon
5651 debugger is called from setup_arch().
5652 on xmon debugger hooks will be installed so xmon
5653 is only called on a kernel crash. Default mode,
5654 i.e. either "ro" or "rw" mode, is controlled
5655 with CONFIG_XMON_DEFAULT_RO_MODE.
5656 rw xmon debugger hooks will be installed so xmon
5657 is called only on a kernel crash, mode is write,
5658 meaning SPR registers, memory and, other data
5659 can be written using xmon commands.
5660 ro same as "rw" option above but SPR registers,
5661 memory, and other data can't be written using
5662 xmon commands.
5663 off xmon is disabled.