1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
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"
16 See also Documentation/power/runtime_pm.rst, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
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]
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_EVENTS
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 AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
116 Format: <byte> or <bitmap-list>
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
139 acpi_no_watchdog [HW,ACPI,WDT]
140 Ignore the ACPI-based watchdog interface (WDAT) and let
141 a native driver control the watchdog device instead.
143 acpi_rsdp= [ACPI,EFI,KEXEC]
144 Pass the RSDP address to the kernel, mostly used
145 on machines running EFI runtime service to boot the
146 second kernel for kdump.
148 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
149 Format: To spoof as Windows 98: ="Microsoft Windows"
151 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
152 of 2 which is mandated by ACPI 6) as the supported ACPI
153 specification revision (when using this switch, it may
154 be necessary to carry out a cold reboot _twice_ in a
155 row to make it take effect on the platform firmware).
157 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
158 acpi_osi="string1" # add string1
159 acpi_osi="!string2" # remove string2
160 acpi_osi=!* # remove all strings
161 acpi_osi=! # disable all built-in OS vendor
163 acpi_osi=!! # enable all built-in OS vendor
165 acpi_osi= # disable all strings
167 'acpi_osi=!' can be used in combination with single or
168 multiple 'acpi_osi="string1"' to support specific OS
169 vendor string(s). Note that such command can only
170 affect the default state of the OS vendor strings, thus
171 it cannot affect the default state of the feature group
172 strings and the current state of the OS vendor strings,
173 specifying it multiple times through kernel command line
174 is meaningless. This command is useful when one do not
175 care about the state of the feature group strings which
176 should be controlled by the OSPM.
178 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
179 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
180 can make '_OSI("Windows 2000")' TRUE.
182 'acpi_osi=' cannot be used in combination with other
183 'acpi_osi=' command lines, the _OSI method will not
184 exist in the ACPI namespace. NOTE that such command can
185 only affect the _OSI support state, thus specifying it
186 multiple times through kernel command line is also
189 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
192 'acpi_osi=!*' can be used in combination with single or
193 multiple 'acpi_osi="string1"' to support specific
194 string(s). Note that such command can affect the
195 current state of both the OS vendor strings and the
196 feature group strings, thus specifying it multiple times
197 through kernel command line is meaningful. But it may
198 still not able to affect the final state of a string if
199 there are quirks related to this string. This command
200 is useful when one want to control the state of the
201 feature group strings to debug BIOS issues related to
204 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
205 '_OSI("Module Device")' FALSE.
206 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
207 '_OSI("Module Device")' TRUE.
208 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
210 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
212 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
213 they all will make '_OSI("Windows 2000")' TRUE.
216 Override the pmtimer bug detection: force the kernel
217 to assume that this machine's pmtimer latches its value
218 and always returns good values.
220 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
221 Format: { level | edge | high | low }
223 acpi_skip_timer_override [HW,ACPI]
224 Recognize and ignore IRQ0/pin2 Interrupt Override.
225 For broken nForce2 BIOS resulting in XT-PIC timer.
227 acpi_sleep= [HW,ACPI] Sleep options
228 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
229 old_ordering, nonvs, sci_force_enable, nobl }
230 See Documentation/power/video.rst for information on
232 s3_beep is for debugging; it makes the PC's speaker beep
233 as soon as the kernel's real-mode entry point is called.
234 s4_nohwsig prevents ACPI hardware signature from being
235 used during resume from hibernation.
236 old_ordering causes the ACPI 1.0 ordering of the _PTS
237 control method, with respect to putting devices into
238 low power states, to be enforced (the ACPI 2.0 ordering
239 of _PTS is used by default).
240 nonvs prevents the kernel from saving/restoring the
241 ACPI NVS memory during suspend/hibernation and resume.
242 sci_force_enable causes the kernel to set SCI_EN directly
243 on resume from S1/S3 (which is against the ACPI spec,
244 but some broken systems don't work without it).
245 nobl causes the internal blacklist of systems known to
246 behave incorrectly in some ways with respect to system
247 suspend and resume to be ignored (use wisely).
249 acpi_use_timer_override [HW,ACPI]
250 Use timer override. For some broken Nvidia NF5 boards
251 that require a timer override, but don't have HPET
253 add_efi_memmap [EFI; X86] Include EFI memory map in
254 kernel's map of available physical RAM.
257 { off | try_unsupported }
258 off: disable AGP support
259 try_unsupported: try to drive unsupported chipsets
260 (may crash computer or cause data corruption)
263 See Documentation/sound/alsa-configuration.rst
266 Allow the default userspace alignment fault handler
267 behaviour to be specified. Bit 0 enables warnings,
268 bit 1 enables fixups, and bit 2 sends a segfault.
270 align_va_addr= [X86-64]
271 Align virtual addresses by clearing slice [14:12] when
272 allocating a VMA at process creation time. This option
273 gives you up to 3% performance improvement on AMD F15h
274 machines (where it is enabled by default) for a
275 CPU-intensive style benchmark, and it can vary highly in
276 a microbenchmark depending on workload and compiler.
278 32: only for 32-bit processes
279 64: only for 64-bit processes
280 on: enable for both 32- and 64-bit processes
281 off: disable for both 32- and 64-bit processes
283 alloc_snapshot [FTRACE]
284 Allocate the ftrace snapshot buffer on boot up when the
285 main buffer is allocated. This is handy if debugging
286 and you need to use tracing_snapshot() on boot up, and
287 do not want to use tracing_snapshot_alloc() as it needs
288 to be done where GFP_KERNEL allocations are allowed.
290 allow_mismatched_32bit_el0 [ARM64]
291 Allow execve() of 32-bit applications and setting of the
292 PER_LINUX32 personality on systems where only a strict
293 subset of the CPUs support 32-bit EL0. When this
294 parameter is present, the set of CPUs supporting 32-bit
295 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
296 and hot-unplug operations may be restricted.
298 See Documentation/arm64/asymmetric-32bit.rst for more
301 amd_iommu= [HW,X86-64]
302 Pass parameters to the AMD IOMMU driver in the system.
304 fullflush - Deprecated, equivalent to iommu.strict=1
305 off - do not initialize any AMD IOMMU found in
307 force_isolation - Force device isolation for all
308 devices. The IOMMU driver is not
309 allowed anymore to lift isolation
310 requirements as needed. This option
311 does not override iommu=pt
312 force_enable - Force enable the IOMMU on platforms known
313 to be buggy with IOMMU enabled. Use this
316 amd_iommu_dump= [HW,X86-64]
317 Enable AMD IOMMU driver option to dump the ACPI table
318 for AMD IOMMU. With this option enabled, AMD IOMMU
319 driver will print ACPI tables for AMD IOMMU during
320 IOMMU initialization.
322 amd_iommu_intr= [HW,X86-64]
323 Specifies one of the following AMD IOMMU interrupt
325 legacy - Use legacy interrupt remapping mode.
326 vapic - Use virtual APIC mode, which allows IOMMU
327 to inject interrupts directly into guest.
328 This mode requires kvm-amd.avic=1.
329 (Default when IOMMU HW support is present.)
331 amijoy.map= [HW,JOY] Amiga joystick support
332 Map of devices attached to JOY0DAT and JOY1DAT
334 See also Documentation/input/joydev/joystick.rst
336 analog.map= [HW,JOY] Analog joystick and gamepad support
337 Specifies type or capabilities of an analog joystick
338 connected to one of 16 gameports
339 Format: <type1>,<type2>,..<type16>
342 Power management functions (SPARCstation-4/5 + deriv.)
344 Disable APC CPU standby support. SPARCstation-Fox does
345 not play well with APC CPU idle - disable it if you have
346 APC and your system crashes randomly.
348 apic= [APIC,X86] Advanced Programmable Interrupt Controller
349 Change the output verbosity while booting
350 Format: { quiet (default) | verbose | debug }
351 Change the amount of debugging information output
352 when initialising the APIC and IO-APIC components.
353 For X86-32, this can also be used to specify an APIC
355 Format: apic=driver_name
356 Examples: apic=bigsmp
358 apic_extnmi= [APIC,X86] External NMI delivery setting
359 Format: { bsp (default) | all | none }
360 bsp: External NMI is delivered only to CPU 0
361 all: External NMIs are broadcast to all CPUs as a
363 none: External NMI is masked for all CPUs. This is
364 useful so that a dump capture kernel won't be
368 See Documentation/networking/ipv6.rst.
370 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
371 Limit apic dumping. The parameter defines the maximal
372 number of local apics being dumped. Also it is possible
373 to set it to "all" by meaning -- no limit here.
374 Format: { 1 (default) | 2 | ... | all }.
375 The parameter valid if only apic=debug or
376 apic=verbose is specified.
377 Example: apic=debug show_lapic=all
379 apm= [APM] Advanced Power Management
380 See header of arch/x86/kernel/apm_32.c.
382 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
383 Format: <io>,<irq>,<nodeID>
385 arm64.nobti [ARM64] Unconditionally disable Branch Target
386 Identification support
388 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
391 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension
396 atarimouse= [HW,MOUSE] Atari Mouse
398 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
399 EzKey and similar keyboards
401 atkbd.reset= [HW] Reset keyboard during initialization
403 atkbd.set= [HW] Select keyboard code set
404 Format: <int> (2 = AT (default), 3 = PS/2)
406 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
409 atkbd.softraw= [HW] Choose between synthetic and real raw mode
410 Format: <bool> (0 = real, 1 = synthetic (default))
412 atkbd.softrepeat= [HW]
413 Use software keyboard repeat
415 audit= [KNL] Enable the audit sub-system
416 Format: { "0" | "1" | "off" | "on" }
417 0 | off - kernel audit is disabled and can not be
418 enabled until the next reboot
419 unset - kernel audit is initialized but disabled and
420 will be fully enabled by the userspace auditd.
421 1 | on - kernel audit is initialized and partially
422 enabled, storing at most audit_backlog_limit
423 messages in RAM until it is fully enabled by the
427 audit_backlog_limit= [KNL] Set the audit queue size limit.
428 Format: <int> (must be >=0)
431 bau= [X86_UV] Enable the BAU on SGI UV. The default
432 behavior is to disable the BAU (i.e. bau=0).
433 Format: { "0" | "1" }
436 unset - Disable the BAU.
438 baycom_epp= [HW,AX25]
441 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
443 See header of drivers/net/hamradio/baycom_par.c.
445 baycom_ser_fdx= [HW,AX25]
446 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
447 Format: <io>,<irq>,<mode>[,<baud>]
448 See header of drivers/net/hamradio/baycom_ser_fdx.c.
450 baycom_ser_hdx= [HW,AX25]
451 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
452 Format: <io>,<irq>,<mode>
453 See header of drivers/net/hamradio/baycom_ser_hdx.c.
455 blkdevparts= Manual partition parsing of block device(s) for
456 embedded devices based on command line input.
457 See Documentation/block/cmdline-partition.rst
459 boot_delay= Milliseconds to delay each printk during boot.
460 Values larger than 10 seconds (10000) are changed to
465 Extended command line options can be added to an initrd
466 and this will cause the kernel to look for it.
468 See Documentation/admin-guide/bootconfig.rst
471 Disable BERT OS support on buggy BIOSes.
473 bgrt_disable [ACPI][X86]
474 Disable BGRT to avoid flickering OEM logo.
476 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
477 bttv.radio= Most important insmod options are available as
479 bttv.pll= See Documentation/admin-guide/media/bttv.rst
482 bulk_remove=off [PPC] This parameter disables the use of the pSeries
483 firmware feature for flushing multiple hpte entries
486 c101= [NET] Moxa C101 synchronous serial card
488 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
489 Sometimes CPU hardware bugs make them report the cache
490 size incorrectly. The kernel will attempt work arounds
491 to fix known problems, but for some CPUs it is not
492 possible to determine what the correct size should be.
493 This option provides an override for these situations.
496 [NET] Specifies amount of time (in seconds) that
497 the kernel should wait for a network carrier. By default
498 it waits 120 seconds.
500 ca_keys= [KEYS] This parameter identifies a specific key(s) on
501 the system trusted keyring to be used for certificate
503 format: { id:<keyid> | builtin }
505 cca= [MIPS] Override the kernel pages' cache coherency
506 algorithm. Accepted values range from 0 to 7
507 inclusive. See arch/mips/include/asm/pgtable-bits.h
508 for platform specific values (SB1, Loongson3 and
511 ccw_timeout_log [S390]
512 See Documentation/s390/common_io.rst for details.
514 cgroup_disable= [KNL] Disable a particular controller or optional feature
515 Format: {name of the controller(s) or feature(s) to disable}
516 The effects of cgroup_disable=foo are:
517 - foo isn't auto-mounted if you mount all cgroups in
519 - foo isn't visible as an individually mountable
521 - if foo is an optional feature then the feature is
522 disabled and corresponding cgroup files are not
524 {Currently only "memory" controller deal with this and
525 cut the overhead, others just disable the usage. So
526 only cgroup_disable=memory is actually worthy}
527 Specifying "pressure" disables per-cgroup pressure
528 stall information accounting feature
530 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
531 Format: { { controller | "all" | "named" }
532 [,{ controller | "all" | "named" }...] }
533 Like cgroup_disable, but only applies to cgroup v1;
534 the blacklisted controllers remain available in cgroup2.
535 "all" blacklists all controllers and "named" disables
536 named mounts. Specifying both "all" and "named" disables
539 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
541 nosocket -- Disable socket memory accounting.
542 nokmem -- Disable kernel memory accounting.
544 checkreqprot [SELINUX] Set initial checkreqprot flag value.
545 Format: { "0" | "1" }
546 See security/selinux/Kconfig help text.
547 0 -- check protection applied by kernel (includes
548 any implied execute protection).
549 1 -- check protection requested by application.
550 Default value is set via a kernel config option.
551 Value can be changed at runtime via
552 /sys/fs/selinux/checkreqprot.
553 Setting checkreqprot to 1 is deprecated.
556 See Documentation/s390/common_io.rst for details.
559 Prevents the clock framework from automatically gating
560 clocks that have not been explicitly enabled by a Linux
561 device driver but are enabled in hardware at reset or
562 by the bootloader/firmware. Note that this does not
563 force such clocks to be always-on nor does it reserve
564 those clocks in any way. This parameter is useful for
565 debug and development, but should not be needed on a
566 platform with proper driver support. For more
567 information, see Documentation/driver-api/clk.rst.
569 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
571 Forces specified clocksource (if available) to be used
572 when calculating gettimeofday(). If specified
573 clocksource is not available, it defaults to PIT.
574 Format: { pit | tsc | cyclone | pmtmr }
576 clocksource= Override the default clocksource
578 Override the default clocksource and use the clocksource
579 with the name specified.
580 Some clocksource names to choose from, depending on
582 [all] jiffies (this is the base, fallback clocksource)
584 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
585 pxa_timer,timer3,32k_counter,timer0_1
586 [X86-32] pit,hpet,tsc;
587 scx200_hrt on Geode; cyclone on IBM x440
595 clocksource.arm_arch_timer.evtstrm=
598 Enable/disable the eventstream feature of the ARM
599 architected timer so that code using WFE-based polling
600 loops can be debugged more effectively on production
603 clocksource.max_cswd_read_retries= [KNL]
604 Number of clocksource_watchdog() retries due to
605 external delays before the clock will be marked
606 unstable. Defaults to three retries, that is,
607 four attempts to read the clock under test.
609 clocksource.verify_n_cpus= [KNL]
610 Limit the number of CPUs checked for clocksources
611 marked with CLOCK_SOURCE_VERIFY_PERCPU that
612 are marked unstable due to excessive skew.
613 A negative value says to check all CPUs, while
614 zero says not to check any. Values larger than
615 nr_cpu_ids are silently truncated to nr_cpu_ids.
616 The actual CPUs are chosen randomly, with
617 no replacement if the same CPU is chosen twice.
619 clocksource-wdtest.holdoff= [KNL]
620 Set the time in seconds that the clocksource
621 watchdog test waits before commencing its tests.
622 Defaults to zero when built as a module and to
623 10 seconds when built into the kernel.
625 clearcpuid=BITNUM[,BITNUM...] [X86]
626 Disable CPUID feature X for the kernel. See
627 arch/x86/include/asm/cpufeatures.h for the valid bit
628 numbers. Note the Linux specific bits are not necessarily
629 stable over kernel options, but the vendor specific
631 Also note that user programs calling CPUID directly
632 or using the feature without checking anything
633 will still see it. This just prevents it from
634 being used by the kernel or shown in /proc/cpuinfo.
635 Also note the kernel might malfunction if you disable
638 cma=nn[MG]@[start[MG][-end[MG]]]
640 Sets the size of kernel global memory area for
641 contiguous memory allocations and optionally the
642 placement constraint by the physical address range of
643 memory allocations. A value of 0 disables CMA
644 altogether. For more information, see
645 kernel/dma/contiguous.c
649 Sets the size of kernel per-numa memory area for
650 contiguous memory allocations. A value of 0 disables
651 per-numa CMA altogether. And If this option is not
652 specificed, the default value is 0.
653 With per-numa CMA enabled, DMA users on node nid will
654 first try to allocate buffer from the pernuma area
655 which is located in node nid, if the allocation fails,
656 they will fallback to the global default memory area.
658 cmo_free_hint= [PPC] Format: { yes | no }
659 Specify whether pages are marked as being inactive
660 when they are freed. This is used in CMO environments
661 to determine OS memory pressure for page stealing by
665 coherent_pool=nn[KMG] [ARM,KNL]
666 Sets the size of memory pool for coherent, atomic dma
667 allocations, by default set to 256K.
669 com20020= [HW,NET] ARCnet - COM20020 chipset
671 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
673 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
677 ARCnet - COM90xx chipset (memory-mapped buffers)
678 Format: <io>[,<irq>[,<memstart>]]
680 condev= [HW,S390] console device
683 console= [KNL] Output console device and options.
685 tty<n> Use the virtual console device <n>.
689 Use the specified serial port. The options are of
690 the form "bbbbpnf", where "bbbb" is the baud rate,
691 "p" is parity ("n", "o", or "e"), "n" is number of
692 bits, and "f" is flow control ("r" for RTS or
693 omit it). Default is "9600n8".
695 See Documentation/admin-guide/serial-console.rst for more
697 Documentation/networking/netconsole.rst for an
700 uart[8250],io,<addr>[,options]
701 uart[8250],mmio,<addr>[,options]
702 uart[8250],mmio16,<addr>[,options]
703 uart[8250],mmio32,<addr>[,options]
704 uart[8250],0x<addr>[,options]
705 Start an early, polled-mode console on the 8250/16550
706 UART at the specified I/O port or MMIO address,
707 switching to the matching ttyS device later.
708 MMIO inter-register address stride is either 8-bit
709 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
710 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
711 to be equivalent to 'mmio'. 'options' are specified in
712 the same format described for ttyS above; if unspecified,
713 the h/w is not re-initialized.
715 hvc<n> Use the hypervisor console device <n>. This is for
716 both Xen and PowerPC hypervisors.
718 If the device connected to the port is not a TTY but a braille
719 device, prepend "brl," before the device type, for instance
721 For now, only VisioBraille is supported.
724 [KNL] Change console messages format
726 By default we print messages on consoles in
727 "[time stamp] text\n" format (time stamp may not be
728 printed, depending on CONFIG_PRINTK_TIME or
729 `printk_time' param).
731 Switch to syslog format: "<%u>[time stamp] text\n"
732 IOW, each message will have a facility and loglevel
733 prefix. The format is similar to one used by syslog()
734 syscall, or to executing "dmesg -S --raw" or to reading
737 consoleblank= [KNL] The console blank (screen saver) timeout in
738 seconds. A value of 0 disables the blank timer.
742 [KNL] Change the default value for
743 /proc/<pid>/coredump_filter.
744 See also Documentation/filesystems/proc.rst.
746 coresight_cpu_debug.enable
749 Enable/disable the CPU sampling based debugging.
750 0: default value, disable debugging
751 1: enable debugging at boot time
753 cpuidle.off=1 [CPU_IDLE]
754 disable the cpuidle sub-system
757 [CPU_IDLE] Name of the cpuidle governor to use.
759 cpufreq.off=1 [CPU_FREQ]
760 disable the cpufreq sub-system
762 cpufreq.default_governor=
763 [CPU_FREQ] Name of the default cpufreq governor or
764 policy to use. This governor must be registered in the
765 kernel before the cpufreq driver probes.
768 [X86] Delay for N microsec between assert and de-assert
769 of APIC INIT to start processors. This delay occurs
770 on every CPU online, such as boot, and resume from suspend.
773 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
775 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
777 crashkernel=size[KMG][@offset[KMG]]
778 [KNL] Using kexec, Linux can switch to a 'crash kernel'
779 upon panic. This parameter reserves the physical
780 memory region [offset, offset + size] for that kernel
781 image. If '@offset' is omitted, then a suitable offset
782 is selected automatically.
783 [KNL, X86-64] Select a region under 4G first, and
784 fall back to reserve region above 4G when '@offset'
785 hasn't been specified.
786 See Documentation/admin-guide/kdump/kdump.rst for further details.
788 crashkernel=range1:size1[,range2:size2,...][@offset]
789 [KNL] Same as above, but depends on the memory
790 in the running system. The syntax of range is
791 start-[end] where start and end are both
792 a memory unit (amount[KMG]). See also
793 Documentation/admin-guide/kdump/kdump.rst for an example.
795 crashkernel=size[KMG],high
796 [KNL, X86-64] range could be above 4G. Allow kernel
797 to allocate physical memory region from top, so could
798 be above 4G if system have more than 4G ram installed.
799 Otherwise memory region will be allocated below 4G, if
801 It will be ignored if crashkernel=X is specified.
802 crashkernel=size[KMG],low
803 [KNL, X86-64] range under 4G. When crashkernel=X,high
804 is passed, kernel could allocate physical memory region
805 above 4G, that cause second kernel crash on system
806 that require some amount of low memory, e.g. swiotlb
807 requires at least 64M+32K low memory, also enough extra
808 low memory is needed to make sure DMA buffers for 32-bit
809 devices won't run out. Kernel would try to allocate at
810 at least 256M below 4G automatically.
811 This one let user to specify own low range under 4G
812 for second kernel instead.
813 0: to disable low allocation.
814 It will be ignored when crashkernel=X,high is not used
815 or memory reserved is below 4G.
818 [KNL] Disable crypto self-tests
823 cs89x0_media= [HW,NET]
824 Format: { rj45 | aui | bnc }
826 csdlock_debug= [KNL] Enable debug add-ons of cross-CPU function call
827 handling. When switched on, additional debug data is
828 printed to the console in case a hanging CPU is
829 detected, and that CPU is pinged again in order to try
830 to resolve the hang situation.
831 0: disable csdlock debugging (default)
832 1: enable basic csdlock debugging (minor impact)
833 ext: enable extended csdlock debugging (more impact,
837 See header of drivers/s390/block/dasd_devmap.c.
839 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
840 (one device per port)
841 Format: <port#>,<type>
842 See also Documentation/input/devices/joystick-parport.rst
844 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
846 Documentation/admin-guide/dynamic-debug-howto.rst for
847 details. Deprecated, see dyndbg.
849 debug [KNL] Enable kernel debugging (events log level).
852 [KNL] Enable printing [hashed] pointers early in the
853 boot sequence. If enabled, we use a weak hash instead
854 of siphash to hash pointers. Use this option if you are
855 seeing instances of '(___ptrval___)') and need to see a
856 value (hashed pointer) instead. Cryptographically
857 insecure, please do not use on production kernels.
860 [KNL] verbose locking self-tests
862 Print debugging info while doing the locking API
864 Bitmask for the various LOCKTYPE_ tests. Defaults to 0
865 (no extra messages), setting it to -1 (all bits set)
866 will print _a_lot_ more information - normally only
867 useful to lockdep developers.
869 debug_objects [KNL] Enable object debugging
872 [KNL] Disable object debugging
874 debug_guardpage_minorder=
875 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
876 parameter allows control of the order of pages that will
877 be intentionally kept free (and hence protected) by the
878 buddy allocator. Bigger value increase the probability
879 of catching random memory corruption, but reduce the
880 amount of memory for normal system use. The maximum
881 possible value is MAX_ORDER/2. Setting this parameter
882 to 1 or 2 should be enough to identify most random
883 memory corruption problems caused by bugs in kernel or
884 driver code when a CPU writes to (or reads from) a
885 random memory location. Note that there exists a class
886 of memory corruptions problems caused by buggy H/W or
887 F/W or by drivers badly programing DMA (basically when
888 memory is written at bus level and the CPU MMU is
889 bypassed) which are not detectable by
890 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
891 tracking down these problems.
894 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
895 enables the feature at boot time. By default, it is
896 disabled and the system will work mostly the same as a
897 kernel built without CONFIG_DEBUG_PAGEALLOC.
898 Note: to get most of debug_pagealloc error reports, it's
899 useful to also enable the page_owner functionality.
900 on: enable the feature
902 debugfs= [KNL] This parameter enables what is exposed to userspace
903 and debugfs internal clients.
904 Format: { on, no-mount, off }
905 on: All functions are enabled.
907 Filesystem is not registered but kernel clients can
908 access APIs and a crashkernel can be used to read
909 its content. There is nothing to mount.
910 off: Filesystem is not registered and clients
911 get a -EPERM as result when trying to register files
912 or directories within debugfs.
913 This is equivalent of the runtime functionality if
914 debugfs was not enabled in the kernel at all.
915 Default value is set in build-time with a kernel configuration.
917 debugpat [X86] Enable PAT debugging
919 decnet.addr= [HW,NET]
920 Format: <area>[,<node>]
921 See also Documentation/networking/decnet.rst.
924 [HW] The size of the default HugeTLB page. This is
925 the size represented by the legacy /proc/ hugepages
926 APIs. In addition, this is the default hugetlb size
927 used for shmget(), mmap() and mounting hugetlbfs
928 filesystems. If not specified, defaults to the
929 architecture's default huge page size. Huge page
930 sizes are architecture dependent. See also
931 Documentation/admin-guide/mm/hugetlbpage.rst.
934 deferred_probe_timeout=
935 [KNL] Debugging option to set a timeout in seconds for
936 deferred probe to give up waiting on dependencies to
937 probe. Only specific dependencies (subsystems or
938 drivers) that have opted in will be ignored. A timeout of 0
939 will timeout at the end of initcalls. This option will also
940 dump out devices still on the deferred probe list after
944 Format: { on | off | def_only | inf_only | always }
945 on: s390 zlib hardware support for compression on
946 level 1 and decompression (default)
947 off: No s390 zlib hardware support
948 def_only: s390 zlib hardware support for deflate
949 only (compression on level 1)
950 inf_only: s390 zlib hardware support for inflate
952 always: Same as 'on' but ignores the selected compression
953 level always using hardware support (used for debugging)
956 Set number of hash buckets for dentry cache.
958 disable_1tb_segments [PPC]
959 Disables the use of 1TB hash page table segments. This
960 causes the kernel to fall back to 256MB segments which
961 can be useful when debugging issues that require an SLB
965 Limits the number of kernel SLB entries, and flushes
966 them frequently to increase the rate of SLB faults
970 See Documentation/networking/ipv6.rst.
973 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
974 hardening is enabled for this boot. Hardened
975 usercopy checking is used to protect the kernel
976 from reading or writing beyond known memory
977 allocation boundaries as a proactive defense
978 against bounds-checking flaws in the kernel's
979 copy_to_user()/copy_from_user() interface.
980 on Perform hardened usercopy checks (default).
981 off Disable hardened usercopy checks.
984 Disable RADIX MMU mode on POWER9
986 radix_hcall_invalidate=on [PPC/PSERIES]
987 Disable RADIX GTSE feature and use hcall for TLB
991 Disable TLBIE instruction. Currently does not work
992 with KVM, with HASH MMU, or with coherent accelerators.
994 disable_cpu_apicid= [X86,APIC,SMP]
996 The number of initial APIC ID for the
997 corresponding CPU to be disabled at boot,
998 mostly used for the kdump 2nd kernel to
999 disable BSP to wake up multiple CPUs without
1000 causing system reset or hang due to sending
1001 INIT from AP to BSP.
1003 disable_ddw [PPC/PSERIES]
1004 Disable Dynamic DMA Window support. Use this
1005 to workaround buggy firmware.
1007 disable_ipv6= [IPV6]
1008 See Documentation/networking/ipv6.rst.
1010 disable_mtrr_cleanup [X86]
1011 The kernel tries to adjust MTRR layout from continuous
1012 to discrete, to make X server driver able to add WB
1013 entry later. This parameter disables that.
1015 disable_mtrr_trim [X86, Intel and AMD only]
1016 By default the kernel will trim any uncacheable
1017 memory out of your available memory pool based on
1018 MTRR settings. This parameter disables that behavior,
1019 possibly causing your machine to run very slowly.
1021 disable_timer_pin_1 [X86]
1022 Disable PIN 1 of APIC timer
1023 Can be useful to work around chipset bugs.
1025 dis_ucode_ldr [X86] Disable the microcode loader.
1027 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1028 this option disables the debugging code at boot.
1030 dma_debug_entries=<number>
1031 This option allows to tune the number of preallocated
1032 entries for DMA-API debugging code. One entry is
1033 required per DMA-API allocation. Use this if the
1034 DMA-API debugging code disables itself because the
1035 architectural default is too low.
1037 dma_debug_driver=<driver_name>
1038 With this option the DMA-API debugging driver
1039 filter feature can be enabled at boot time. Just
1040 pass the driver to filter for as the parameter.
1041 The filter can be disabled or changed to another
1042 driver later using sysfs.
1044 driver_async_probe= [KNL]
1045 List of driver names to be probed asynchronously.
1046 Format: <driver_name1>,<driver_name2>...
1048 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1049 Broken monitors, graphic adapters, KVMs and EDIDless
1050 panels may send no or incorrect EDID data sets.
1051 This parameter allows to specify an EDID data sets
1052 in the /lib/firmware directory that are used instead.
1053 Generic built-in EDID data sets are used, if one of
1054 edid/1024x768.bin, edid/1280x1024.bin,
1055 edid/1680x1050.bin, or edid/1920x1080.bin is given
1056 and no file with the same name exists. Details and
1057 instructions how to build your own EDID data are
1058 available in Documentation/admin-guide/edid.rst. An EDID
1059 data set will only be used for a particular connector,
1060 if its name and a colon are prepended to the EDID
1061 name. Each connector may use a unique EDID data
1062 set by separating the files with a comma. An EDID
1063 data set with no connector name will be used for
1064 any connectors not explicitly specified.
1069 Format: {"off" | "known"}
1070 Control how the dt_cpu_ftrs device-tree binding is
1071 used for CPU feature discovery and setup (if it
1073 off: Do not use it, fall back to legacy cpu table.
1074 known: Do not pass through unknown features to guests
1075 or userspace, only those that the kernel is aware of.
1077 dump_apple_properties [X86]
1078 Dump name and content of EFI device properties on
1079 x86 Macs. Useful for driver authors to determine
1080 what data is available or for reverse-engineering.
1082 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1083 <module>.dyndbg[="val"]
1084 Enable debug messages at boot time. See
1085 Documentation/admin-guide/dynamic-debug-howto.rst
1088 nopku [X86] Disable Memory Protection Keys CPU feature found
1091 <module>.async_probe [KNL]
1092 Enable asynchronous probe on this module.
1094 early_ioremap_debug [KNL]
1095 Enable debug messages in early_ioremap support. This
1096 is useful for tracking down temporary early mappings
1097 which are not unmapped.
1099 earlycon= [KNL] Output early console device and options.
1101 When used with no options, the early console is
1102 determined by stdout-path property in device tree's
1103 chosen node or the ACPI SPCR table if supported by
1106 cdns,<addr>[,options]
1107 Start an early, polled-mode console on a Cadence
1108 (xuartps) serial port at the specified address. Only
1109 supported option is baud rate. If baud rate is not
1110 specified, the serial port must already be setup and
1113 uart[8250],io,<addr>[,options]
1114 uart[8250],mmio,<addr>[,options]
1115 uart[8250],mmio32,<addr>[,options]
1116 uart[8250],mmio32be,<addr>[,options]
1117 uart[8250],0x<addr>[,options]
1118 Start an early, polled-mode console on the 8250/16550
1119 UART at the specified I/O port or MMIO address.
1120 MMIO inter-register address stride is either 8-bit
1121 (mmio) or 32-bit (mmio32 or mmio32be).
1122 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1123 to be equivalent to 'mmio'. 'options' are specified
1124 in the same format described for "console=ttyS<n>"; if
1125 unspecified, the h/w is not initialized.
1129 Start an early, polled-mode console on a pl011 serial
1130 port at the specified address. The pl011 serial port
1131 must already be setup and configured. Options are not
1132 yet supported. If 'mmio32' is specified, then only
1133 the driver will use only 32-bit accessors to read/write
1134 the device registers.
1137 Start an early console on a litex serial port at the
1138 specified address. The serial port must already be
1139 setup and configured. Options are not yet supported.
1142 Start an early, polled-mode console on a meson serial
1143 port at the specified address. The serial port must
1144 already be setup and configured. Options are not yet
1148 Start an early, polled-mode console on an msm serial
1149 port at the specified address. The serial port
1150 must already be setup and configured. Options are not
1153 msm_serial_dm,<addr>
1154 Start an early, polled-mode console on an msm serial
1155 dm port at the specified address. The serial port
1156 must already be setup and configured. Options are not
1160 Start an early, polled-mode console on a serial port
1161 of an Actions Semi SoC, such as S500 or S900, at the
1162 specified address. The serial port must already be
1163 setup and configured. Options are not yet supported.
1166 Start an early, polled-mode console on a serial port
1167 of an RDA Micro SoC, such as RDA8810PL, at the
1168 specified address. The serial port must already be
1169 setup and configured. Options are not yet supported.
1172 Use RISC-V SBI (Supervisor Binary Interface) for early
1175 smh Use ARM semihosting calls for early console.
1183 Use early console provided by serial driver available
1184 on Samsung SoCs, requires selecting proper type and
1185 a correct base address of the selected UART port. The
1186 serial port must already be setup and configured.
1187 Options are not yet supported.
1190 Start an early, polled-mode console on a lantiq serial
1191 (lqasc) port at the specified address. The serial port
1192 must already be setup and configured. Options are not
1197 Use early console provided by Freescale LP UART driver
1198 found on Freescale Vybrid and QorIQ LS1021A processors.
1199 A valid base address must be provided, and the serial
1200 port must already be setup and configured.
1204 Start an early, polled-mode, output-only console on the
1205 Freescale i.MX UART at the specified address. The UART
1206 must already be setup and configured.
1209 Start an early, polled-mode console on the
1210 Armada 3700 serial port at the specified
1211 address. The serial port must already be setup
1212 and configured. Options are not yet supported.
1215 Start an early, polled-mode console on a Qualcomm
1216 Generic Interface (GENI) based serial port at the
1217 specified address. The serial port must already be
1218 setup and configured. Options are not yet supported.
1221 Start an early, unaccelerated console on the EFI
1222 memory mapped framebuffer (if available). On cache
1223 coherent non-x86 systems that use system memory for
1224 the framebuffer, pass the 'ram' option so that it is
1225 mapped with the correct attributes.
1228 Use early console provided by Freescale LINFlexD UART
1229 serial driver for NXP S32V234 SoCs. A valid base
1230 address must be provided, and the serial port must
1231 already be setup and configured.
1233 earlyprintk= [X86,SH,ARM,M68k,S390]
1237 earlyprintk=serial[,ttySn[,baudrate]]
1238 earlyprintk=serial[,0x...[,baudrate]]
1239 earlyprintk=ttySn[,baudrate]
1240 earlyprintk=dbgp[debugController#]
1241 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1242 earlyprintk=xdbc[xhciController#]
1244 earlyprintk is useful when the kernel crashes before
1245 the normal console is initialized. It is not enabled by
1246 default because it has some cosmetic problems.
1248 Append ",keep" to not disable it when the real console
1251 Only one of vga, efi, serial, or usb debug port can
1254 Currently only ttyS0 and ttyS1 may be specified by
1255 name. Other I/O ports may be explicitly specified
1256 on some architectures (x86 and arm at least) by
1257 replacing ttySn with an I/O port address, like this:
1258 earlyprintk=serial,0x1008,115200
1259 You can find the port for a given device in
1260 /proc/tty/driver/serial:
1261 2: uart:ST16650V2 port:00001008 irq:18 ...
1263 Interaction with the standard serial driver is not
1266 The VGA and EFI output is eventually overwritten by
1269 The xen option can only be used in Xen domains.
1271 The sclp output can only be used on s390.
1273 The optional "force" to "pciserial" enables use of a
1274 PCI device even when its classcode is not of the
1277 edac_report= [HW,EDAC] Control how to report EDAC event
1278 Format: {"on" | "off" | "force"}
1279 on: enable EDAC to report H/W event. May be overridden
1280 by other higher priority error reporting module.
1281 off: disable H/W event reporting through EDAC.
1282 force: enforce the use of EDAC to report H/W event.
1285 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1288 This is designed to be used in conjunction with
1289 the boot argument: earlyprintk=vga
1291 This parameter works in place of the kgdboc parameter
1292 but can only be used if the backing tty is available
1293 very early in the boot process. For early debugging
1294 via a serial port see kgdboc_earlycon instead.
1297 Format: {"off" | "on" | "skip[mbr]"}
1300 Format: { "debug", "disable_early_pci_dma",
1301 "nochunk", "noruntime", "nosoftreserve",
1302 "novamap", "no_disable_early_pci_dma" }
1303 debug: enable misc debug output.
1304 disable_early_pci_dma: disable the busmaster bit on all
1305 PCI bridges while in the EFI boot stub.
1306 nochunk: disable reading files in "chunks" in the EFI
1307 boot stub, as chunking can cause problems with some
1308 firmware implementations.
1309 noruntime : disable EFI runtime services support
1310 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1311 attribute may cause the kernel to reserve the
1312 memory range for a memory mapping driver to
1313 claim. Specify efi=nosoftreserve to disable this
1314 reservation and treat the memory by its base type
1315 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1316 novamap: do not call SetVirtualAddressMap().
1317 no_disable_early_pci_dma: Leave the busmaster bit set
1318 on all PCI bridges while in the EFI boot stub
1320 efi_no_storage_paranoia [EFI; X86]
1321 Using this parameter you can use more than 50% of
1322 your efi variable storage. Use this parameter only if
1323 you are really sure that your UEFI does sane gc and
1324 fulfills the spec otherwise your board may brick.
1326 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1327 Add arbitrary attribute to specific memory range by
1328 updating original EFI memory map.
1329 Region of memory which aa attribute is added to is
1332 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1333 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1334 attribute is added to range 0x100000000-0x180000000 and
1335 0x10a0000000-0x1120000000.
1337 If efi_fake_mem=8G@9G:0x40000 is specified, the
1338 EFI_MEMORY_SP(0x40000) attribute is added to
1339 range 0x240000000-0x43fffffff.
1341 Using this parameter you can do debugging of EFI memmap
1342 related features. For example, you can do debugging of
1343 Address Range Mirroring feature even if your box
1344 doesn't support it, or mark specific memory as
1347 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1348 that is to be dynamically loaded by Linux. If there are
1349 multiple variables with the same name but with different
1350 vendor GUIDs, all of them will be loaded. See
1351 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1354 eisa_irq_edge= [PARISC,HW]
1355 See header of drivers/parisc/eisa.c.
1358 See comment before function elanfreq_setup() in
1359 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1361 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1362 Specifies physical address of start of kernel core
1363 image elf header and optionally the size. Generally
1364 kexec loader will pass this option to capture kernel.
1365 See Documentation/admin-guide/kdump/kdump.rst for details.
1367 enable_mtrr_cleanup [X86]
1368 The kernel tries to adjust MTRR layout from continuous
1369 to discrete, to make X server driver able to add WB
1370 entry later. This parameter enables that.
1372 enable_timer_pin_1 [X86]
1373 Enable PIN 1 of APIC timer
1374 Can be useful to work around chipset bugs
1375 (in particular on some ATI chipsets).
1376 The kernel tries to set a reasonable default.
1378 enforcing [SELINUX] Set initial enforcing status.
1380 See security/selinux/Kconfig help text.
1381 0 -- permissive (log only, no denials).
1382 1 -- enforcing (deny and log).
1384 Value can be changed at runtime via
1385 /sys/fs/selinux/enforce.
1388 Disable Error Record Serialization Table (ERST)
1391 ether= [HW,NET] Ethernet cards parameters
1392 This option is obsoleted by the "netdev=" option, which
1393 has equivalent usage. See its documentation for details.
1397 Permit 'security.evm' to be updated regardless of
1398 current integrity status.
1403 fail_make_request=[KNL]
1404 General fault injection mechanism.
1405 Format: <interval>,<probability>,<space>,<times>
1406 See also Documentation/fault-injection/.
1409 Format: { initns | none }
1410 See Documentation/admin-guide/sysctl/net.rst for
1411 fb_tunnels_only_for_init_ns
1414 See Documentation/admin-guide/blockdev/floppy.rst.
1416 force_pal_cache_flush
1417 [IA-64] Avoid check_sal_cache_flush which may hang on
1418 buggy SAL_CACHE_FLUSH implementations. Using this
1419 parameter will force ia64_sal_cache_flush to call
1420 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1423 Forcefully enable Physical Address Extension (PAE).
1424 Many Pentium M systems disable PAE but may have a
1425 functionally usable PAE implementation.
1426 Warning: use of this parameter will taint the kernel
1427 and may cause unknown problems.
1430 [FTRACE] will set and start the specified tracer
1431 as early as possible in order to facilitate early
1434 ftrace_dump_on_oops[=orig_cpu]
1435 [FTRACE] will dump the trace buffers on oops.
1436 If no parameter is passed, ftrace will dump
1437 buffers of all CPUs, but if you pass orig_cpu, it will
1438 dump only the buffer of the CPU that triggered the
1441 ftrace_filter=[function-list]
1442 [FTRACE] Limit the functions traced by the function
1443 tracer at boot up. function-list is a comma-separated
1444 list of functions. This list can be changed at run
1445 time by the set_ftrace_filter file in the debugfs
1448 ftrace_notrace=[function-list]
1449 [FTRACE] Do not trace the functions specified in
1450 function-list. This list can be changed at run time
1451 by the set_ftrace_notrace file in the debugfs
1454 ftrace_graph_filter=[function-list]
1455 [FTRACE] Limit the top level callers functions traced
1456 by the function graph tracer at boot up.
1457 function-list is a comma-separated list of functions
1458 that can be changed at run time by the
1459 set_graph_function file in the debugfs tracing directory.
1461 ftrace_graph_notrace=[function-list]
1462 [FTRACE] Do not trace from the functions specified in
1463 function-list. This list is a comma-separated list of
1464 functions that can be changed at run time by the
1465 set_graph_notrace file in the debugfs tracing directory.
1467 ftrace_graph_max_depth=<uint>
1468 [FTRACE] Used with the function graph tracer. This is
1469 the max depth it will trace into a function. This value
1470 can be changed at run time by the max_graph_depth file
1471 in the tracefs tracing directory. default: 0 (no limit)
1473 fw_devlink= [KNL] Create device links between consumer and supplier
1474 devices by scanning the firmware to infer the
1475 consumer/supplier relationships. This feature is
1476 especially useful when drivers are loaded as modules as
1477 it ensures proper ordering of tasks like device probing
1478 (suppliers first, then consumers), supplier boot state
1479 clean up (only after all consumers have probed),
1480 suspend/resume & runtime PM (consumers first, then
1482 Format: { off | permissive | on | rpm }
1483 off -- Don't create device links from firmware info.
1484 permissive -- Create device links from firmware info
1485 but use it only for ordering boot state clean
1486 up (sync_state() calls).
1487 on -- Create device links from firmware info and use it
1488 to enforce probe and suspend/resume ordering.
1489 rpm -- Like "on", but also use to order runtime PM.
1491 fw_devlink.strict=<bool>
1492 [KNL] Treat all inferred dependencies as mandatory
1493 dependencies. This only applies for fw_devlink=on|rpm.
1497 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1498 support via parallel port (up to 5 devices per port)
1499 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1500 See also Documentation/input/devices/joystick-parport.rst
1504 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART
1508 gcov_persist= [GCOV] When non-zero (default), profiling data for
1509 kernel modules is saved and remains accessible via
1510 debugfs, even when the module is unloaded/reloaded.
1511 When zero, profiling data is discarded and associated
1512 debugfs files are removed at module unload time.
1514 goldfish [X86] Enable the goldfish android emulator platform.
1515 Don't use this when you are not running on the
1518 gpio-mockup.gpio_mockup_ranges
1519 [HW] Sets the ranges of gpiochip of for this device.
1520 Format: <start1>,<end1>,<start2>,<end2>...
1521 gpio-mockup.gpio_mockup_named_lines
1522 [HW] Let the driver know GPIO lines should be named.
1524 gpt [EFI] Forces disk with valid GPT signature but
1525 invalid Protective MBR to be treated as GPT. If the
1526 primary GPT is corrupted, it enables the backup/alternate
1527 GPT to be used instead.
1529 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1530 the "Enable 0" bit of the configuration register.
1533 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1534 the "Enable 0" bit of the configuration register.
1537 grcan.select= [HW] Select which physical interface to use.
1540 grcan.txsize= [HW] Sets the size of the tx buffer.
1541 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1543 grcan.rxsize= [HW] Sets the size of the rx buffer.
1544 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1547 hardlockup_all_cpu_backtrace=
1548 [KNL] Should the hard-lockup detector generate
1549 backtraces on all cpus.
1552 hashdist= [KNL,NUMA] Large hashes allocated during boot
1553 are distributed across NUMA nodes. Defaults on
1554 for 64-bit NUMA, off otherwise.
1555 Format: 0 | 1 (for off | on)
1557 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1559 hd= [EIDE] (E)IDE hard drive subsystem geometry
1560 Format: <cyl>,<head>,<sect>
1563 Disable Hardware Error Source Table (HEST) support;
1564 corresponding firmware-first mode error processing
1565 logic will be disabled.
1567 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1568 size of <nn>. This works even on boxes that have no
1569 highmem otherwise. This also works to reduce highmem
1570 size on bigger boxes.
1572 highres= [KNL] Enable/disable high resolution timer mode.
1573 Valid parameters: "on", "off"
1578 hpet= [X86-32,HPET] option to control HPET usage
1579 Format: { enable (default) | disable | force |
1581 disable: disable HPET and use PIT instead
1582 force: allow force enabled of undocumented chips (ICH4,
1584 verbose: show contents of HPET registers during setup
1586 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1587 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1589 hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation
1590 of gigantic hugepages.
1593 Reserve a CMA area of given size and allocate gigantic
1594 hugepages using the CMA allocator. If enabled, the
1595 boot-time allocation of gigantic hugepages is skipped.
1597 hugepages= [HW] Number of HugeTLB pages to allocate at boot.
1598 If this follows hugepagesz (below), it specifies
1599 the number of pages of hugepagesz to be allocated.
1600 If this is the first HugeTLB parameter on the command
1601 line, it specifies the number of pages to allocate for
1602 the default huge page size. See also
1603 Documentation/admin-guide/mm/hugetlbpage.rst.
1607 [HW] The size of the HugeTLB pages. This is used in
1608 conjunction with hugepages (above) to allocate huge
1609 pages of a specific size at boot. The pair
1610 hugepagesz=X hugepages=Y can be specified once for
1611 each supported huge page size. Huge page sizes are
1612 architecture dependent. See also
1613 Documentation/admin-guide/mm/hugetlbpage.rst.
1616 hugetlb_free_vmemmap=
1617 [KNL] Reguires CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
1619 Allows heavy hugetlb users to free up some more
1620 memory (6 * PAGE_SIZE for each 2MB hugetlb page).
1621 Format: { on | off (default) }
1623 on: enable the feature
1624 off: disable the feature
1626 Built with CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON=y,
1629 This is not compatible with memory_hotplug.memmap_on_memory.
1630 If both parameters are enabled, hugetlb_free_vmemmap takes
1631 precedence over memory_hotplug.memmap_on_memory.
1634 [KNL] Should the hung task detector generate panics.
1637 A value of 1 instructs the kernel to panic when a
1638 hung task is detected. The default value is controlled
1639 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1640 option. The value selected by this boot parameter can
1641 be changed later by the kernel.hung_task_panic sysctl.
1643 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1644 terminal devices. Valid values: 0..8
1645 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1646 If specified, z/VM IUCV HVC accepts connections
1647 from listed z/VM user IDs only.
1649 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1650 which allow the hypervisor to 'idle' the
1651 guest on lock contention.
1654 Do not unregister boot console at start. This is only
1655 useful for debugging when something happens in the window
1656 between unregistering the boot console and initializing
1659 i2c_bus= [HW] Override the default board specific I2C bus speed
1660 or register an additional I2C bus that is not
1661 registered from board initialization code.
1665 i8042.debug [HW] Toggle i8042 debug mode
1666 i8042.unmask_kbd_data
1667 [HW] Enable printing of interrupt data from the KBD port
1668 (disabled by default, and as a pre-condition
1669 requires that i8042.debug=1 be enabled)
1670 i8042.direct [HW] Put keyboard port into non-translated mode
1671 i8042.dumbkbd [HW] Pretend that controller can only read data from
1672 keyboard and cannot control its state
1673 (Don't attempt to blink the leds)
1674 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1675 i8042.nokbd [HW] Don't check/create keyboard port
1676 i8042.noloop [HW] Disable the AUX Loopback command while probing
1678 i8042.nomux [HW] Don't check presence of an active multiplexing
1680 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1682 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1683 i8042.reset [HW] Reset the controller during init, cleanup and
1684 suspend-to-ram transitions, only during s2r
1685 transitions, or never reset
1686 Format: { 1 | Y | y | 0 | N | n }
1687 1, Y, y: always reset controller
1688 0, N, n: don't ever reset controller
1689 Default: only on s2r transitions on x86; most other
1690 architectures force reset to be always executed
1691 i8042.unlock [HW] Unlock (ignore) the keylock
1692 i8042.kbdreset [HW] Reset device connected to KBD port
1696 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1697 indicates that the driver is running on unsupported
1699 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1700 does not match list of supported models.
1702 [HW] Report power status in /proc/i8k
1703 (disabled by default)
1704 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1707 i915.invert_brightness=
1708 [DRM] Invert the sense of the variable that is used to
1709 set the brightness of the panel backlight. Normally a
1710 brightness value of 0 indicates backlight switched off,
1711 and the maximum of the brightness value sets the backlight
1712 to maximum brightness. If this parameter is set to 0
1713 (default) and the machine requires it, or this parameter
1714 is set to 1, a brightness value of 0 sets the backlight
1715 to maximum brightness, and the maximum of the brightness
1716 value switches the backlight off.
1717 -1 -- never invert brightness
1718 0 -- machine default
1719 1 -- force brightness inversion
1722 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1724 ide-core.nodma= [HW] (E)IDE subsystem
1725 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1726 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1727 .cdrom .chs .ignore_cable are additional options
1728 See Documentation/ide/ide.rst.
1730 ide-generic.probe-mask= [HW] (E)IDE subsystem
1732 Probe mask for legacy ISA IDE ports. Depending on
1733 platform up to 6 ports are supported, enabled by
1734 setting corresponding bits in the mask to 1. The
1735 default value is 0x0, which has a special meaning.
1736 On systems that have PCI, it triggers scanning the
1737 PCI bus for the first and the second port, which
1738 are then probed. On systems without PCI the value
1739 of 0x0 enables probing the two first ports as if it
1742 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1743 Claim all unknown PCI IDE storage controllers.
1746 Format: idle=poll, idle=halt, idle=nomwait
1747 Poll forces a polling idle loop that can slightly
1748 improve the performance of waking up a idle CPU, but
1749 will use a lot of power and make the system run hot.
1751 idle=halt: Halt is forced to be used for CPU idle.
1752 In such case C2/C3 won't be used again.
1753 idle=nomwait: Disable mwait for CPU C-states
1757 Allow force disabling of Shared Virtual Memory (SVA)
1758 support for the idxd driver. By default it is set to
1761 idxd.tc_override= [HW]
1763 Allow override of default traffic class configuration
1764 for the device. By default it is set to false (0).
1766 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1767 Format: { strict | legacy | 2008 | relaxed }
1770 Choose which programs will be accepted for execution
1771 based on the IEEE 754 NaN encoding(s) supported by
1772 the FPU and the NaN encoding requested with the value
1773 of an ELF file header flag individually set by each
1774 binary. Hardware implementations are permitted to
1775 support either or both of the legacy and the 2008 NaN
1778 Available settings are as follows:
1779 strict accept binaries that request a NaN encoding
1780 supported by the FPU
1781 legacy only accept legacy-NaN binaries, if supported
1783 2008 only accept 2008-NaN binaries, if supported
1785 relaxed accept any binaries regardless of whether
1786 supported by the FPU
1788 The FPU emulator is always able to support both NaN
1789 encodings, so if no FPU hardware is present or it has
1790 been disabled with 'nofpu', then the settings of
1791 'legacy' and '2008' strap the emulator accordingly,
1792 'relaxed' straps the emulator for both legacy-NaN and
1793 2008-NaN, whereas 'strict' enables legacy-NaN only on
1794 legacy processors and both NaN encodings on MIPS32 or
1797 The setting for ABS.fmt/NEG.fmt instruction execution
1798 mode generally follows that for the NaN encoding,
1799 except where unsupported by hardware.
1801 ignore_loglevel [KNL]
1802 Ignore loglevel setting - this will print /all/
1803 kernel messages to the console. Useful for debugging.
1804 We also add it as printk module parameter, so users
1805 could change it dynamically, usually by
1806 /sys/module/printk/parameters/ignore_loglevel.
1809 Ignore RLIMIT_DATA setting for data mappings,
1810 print warning at first misuse. Can be changed via
1811 /sys/module/kernel/parameters/ignore_rlimit_data.
1813 ihash_entries= [KNL]
1814 Set number of hash buckets for inode cache.
1816 ima_appraise= [IMA] appraise integrity measurements
1817 Format: { "off" | "enforce" | "fix" | "log" }
1820 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1821 The builtin appraise policy appraises all files
1824 ima_canonical_fmt [IMA]
1825 Use the canonical format for the binary runtime
1826 measurements, instead of host native format.
1829 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1833 The list of supported hash algorithms is defined
1834 in crypto/hash_info.h.
1837 The builtin policies to load during IMA setup.
1838 Format: "tcb | appraise_tcb | secure_boot |
1839 fail_securely | critical_data"
1841 The "tcb" policy measures all programs exec'd, files
1842 mmap'd for exec, and all files opened with the read
1843 mode bit set by either the effective uid (euid=0) or
1846 The "appraise_tcb" policy appraises the integrity of
1847 all files owned by root.
1849 The "secure_boot" policy appraises the integrity
1850 of files (eg. kexec kernel image, kernel modules,
1851 firmware, policy, etc) based on file signatures.
1853 The "fail_securely" policy forces file signature
1854 verification failure also on privileged mounted
1855 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1858 The "critical_data" policy measures kernel integrity
1861 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1862 Load a policy which meets the needs of the Trusted
1863 Computing Base. This means IMA will measure all
1864 programs exec'd, files mmap'd for exec, and all files
1865 opened for read by uid=0.
1868 Select one of defined IMA measurements template formats.
1869 Formats: { "ima" | "ima-ng" | "ima-sig" }
1873 [IMA] Define a custom template format.
1874 Format: { "field1|...|fieldN" }
1876 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1877 Format: <min_file_size>
1878 Set the minimal file size for using asynchronous hash.
1879 If left unspecified, ahash usage is disabled.
1881 ahash performance varies for different data sizes on
1882 different crypto accelerators. This option can be used
1883 to achieve the best performance for a particular HW.
1885 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1887 Set hashing buffer size. Default: 4k.
1889 ahash performance varies for different chunk sizes on
1890 different crypto accelerators. This option can be used
1891 to achieve best performance for particular HW.
1895 Run specified binary instead of /sbin/init as init
1898 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1899 for working out where the kernel is dying during
1902 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1903 initcall functions. Useful for debugging built-in
1904 modules and initcalls.
1906 initramfs_async= [KNL]
1909 This parameter controls whether the initramfs
1910 image is unpacked asynchronously, concurrently
1911 with devices being probed and
1912 initialized. This should normally just work,
1913 but as a debugging aid, one can get the
1914 historical behaviour of the initramfs
1915 unpacking being completed before device_ and
1918 initrd= [BOOT] Specify the location of the initial ramdisk
1920 initrdmem= [KNL] Specify a physical address and size from which to
1921 load the initrd. If an initrd is compiled in or
1922 specified in the bootparams, it takes priority over this
1924 Format: ss[KMG],nn[KMG]
1927 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
1930 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
1932 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
1934 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
1936 init_pkru= [X86] Specify the default memory protection keys rights
1937 register contents for all processes. 0x55555554 by
1938 default (disallow access to all but pkey 0). Can
1939 override in debugfs after boot.
1941 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1944 int_pln_enable [X86] Enable power limit notification interrupt
1946 integrity_audit=[IMA]
1947 Format: { "0" | "1" }
1948 0 -- basic integrity auditing messages. (Default)
1949 1 -- additional integrity auditing messages.
1951 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1953 Enable intel iommu driver.
1955 Disable intel iommu driver.
1956 igfx_off [Default Off]
1957 By default, gfx is mapped as normal device. If a gfx
1958 device has a dedicated DMAR unit, the DMAR unit is
1959 bypassed by not enabling DMAR with this option. In
1960 this case, gfx device will use physical address for
1962 strict [Default Off]
1963 Deprecated, equivalent to iommu.strict=1.
1964 sp_off [Default Off]
1965 By default, super page will be supported if Intel IOMMU
1966 has the capability. With this option, super page will
1969 Enable the Intel IOMMU scalable mode if the hardware
1970 advertises that it has support for the scalable mode
1973 Disallow use of the Intel IOMMU scalable mode.
1974 tboot_noforce [Default Off]
1975 Do not force the Intel IOMMU enabled under tboot.
1976 By default, tboot will force Intel IOMMU on, which
1977 could harm performance of some high-throughput
1978 devices like 40GBit network cards, even if identity
1980 Note that using this option lowers the security
1981 provided by tboot because it makes the system
1982 vulnerable to DMA attacks.
1984 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1985 0 disables intel_idle and fall back on acpi_idle.
1986 1 to 9 specify maximum depth of C-state.
1990 Do not enable intel_pstate as the default
1991 scaling driver for the supported processors
1993 Use intel_pstate as a scaling driver, but configure it
1994 to work with generic cpufreq governors (instead of
1995 enabling its internal governor). This mode cannot be
1996 used along with the hardware-managed P-states (HWP)
1999 Enable intel_pstate on systems that prohibit it by default
2000 in favor of acpi-cpufreq. Forcing the intel_pstate driver
2001 instead of acpi-cpufreq may disable platform features, such
2002 as thermal controls and power capping, that rely on ACPI
2003 P-States information being indicated to OSPM and therefore
2004 should be used with caution. This option does not work with
2005 processors that aren't supported by the intel_pstate driver
2006 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2008 Do not enable hardware P state control (HWP)
2011 Only load intel_pstate on systems which support
2012 hardware P state control (HWP) if available.
2014 Enforce ACPI _PPC performance limits. If the Fixed ACPI
2015 Description Table, specifies preferred power management
2016 profile as "Enterprise Server" or "Performance Server",
2017 then this feature is turned on by default.
2019 Allow per-logical-CPU P-State performance control limits using
2020 cpufreq sysfs interface
2022 intremap= [X86-64, Intel-IOMMU]
2023 on enable Interrupt Remapping (default)
2024 off disable Interrupt Remapping
2025 nosid disable Source ID checking
2027 BIOS x2APIC opt-out request will be ignored
2028 nopost disable Interrupt Posting
2030 iomem= Disable strict checking of access to MMIO memory
2031 strict regions from userspace.
2046 nobypass [PPC/POWERNV]
2047 Disable IOMMU bypass, using IOMMU for PCI devices.
2049 iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices.
2050 Format: { "0" | "1" }
2051 0 - Try to allocate a 32-bit DMA address first, before
2052 falling back to the full range if needed.
2053 1 - Allocate directly from the full usable range,
2054 forcing Dual Address Cycle for PCI cards supporting
2055 greater than 32-bit addressing.
2057 iommu.strict= [ARM64, X86] Configure TLB invalidation behaviour
2058 Format: { "0" | "1" }
2060 Request that DMA unmap operations use deferred
2061 invalidation of hardware TLBs, for increased
2062 throughput at the cost of reduced device isolation.
2063 Will fall back to strict mode if not supported by
2064 the relevant IOMMU driver.
2066 DMA unmap operations invalidate IOMMU hardware TLBs
2068 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}.
2069 Note: on x86, strict mode specified via one of the
2070 legacy driver-specific options takes precedence.
2073 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
2074 Format: { "0" | "1" }
2075 0 - Use IOMMU translation for DMA.
2076 1 - Bypass the IOMMU for DMA.
2077 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
2079 io7= [HW] IO7 for Marvel-based Alpha systems
2080 See comment before marvel_specify_io7 in
2081 arch/alpha/kernel/core_marvel.c.
2083 io_delay= [X86] I/O delay method
2085 Standard port 0x80 based delay
2087 Alternate port 0xed based delay (needed on some systems)
2089 Simple two microseconds delay
2094 See Documentation/admin-guide/nfs/nfsroot.rst.
2096 ipcmni_extend [KNL] Extend the maximum number of unique System V
2097 IPC identifiers from 32,768 to 16,777,216.
2099 irqaffinity= [SMP] Set the default irq affinity mask
2100 The argument is a cpu list, as described above.
2102 irqchip.gicv2_force_probe=
2105 Force the kernel to look for the second 4kB page
2106 of a GICv2 controller even if the memory range
2107 exposed by the device tree is too small.
2109 irqchip.gicv3_nolpi=
2111 Force the kernel to ignore the availability of
2112 LPIs (and by consequence ITSs). Intended for system
2113 that use the kernel as a bootloader, and thus want
2114 to let secondary kernels in charge of setting up
2117 irqchip.gicv3_pseudo_nmi= [ARM64]
2118 Enables support for pseudo-NMIs in the kernel. This
2119 requires the kernel to be built with
2120 CONFIG_ARM64_PSEUDO_NMI.
2123 When an interrupt is not handled search all handlers
2124 for it. Intended to get systems with badly broken
2128 When an interrupt is not handled search all handlers
2129 for it. Also check all handlers each timer
2130 interrupt. Intended to get systems with badly broken
2134 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2136 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2137 [Deprecated - use cpusets instead]
2138 Format: [flag-list,]<cpu-list>
2140 Specify one or more CPUs to isolate from disturbances
2141 specified in the flag list (default: domain):
2144 Disable the tick when a single task runs.
2146 A residual 1Hz tick is offloaded to workqueues, which you
2147 need to affine to housekeeping through the global
2148 workqueue's affinity configured via the
2149 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2150 by using the 'domain' flag described below.
2152 NOTE: by default the global workqueue runs on all CPUs,
2153 so to protect individual CPUs the 'cpumask' file has to
2154 be configured manually after bootup.
2157 Isolate from the general SMP balancing and scheduling
2158 algorithms. Note that performing domain isolation this way
2159 is irreversible: it's not possible to bring back a CPU to
2160 the domains once isolated through isolcpus. It's strongly
2161 advised to use cpusets instead to disable scheduler load
2162 balancing through the "cpuset.sched_load_balance" file.
2163 It offers a much more flexible interface where CPUs can
2164 move in and out of an isolated set anytime.
2166 You can move a process onto or off an "isolated" CPU via
2167 the CPU affinity syscalls or cpuset.
2168 <cpu number> begins at 0 and the maximum value is
2169 "number of CPUs in system - 1".
2173 Isolate from being targeted by managed interrupts
2174 which have an interrupt mask containing isolated
2175 CPUs. The affinity of managed interrupts is
2176 handled by the kernel and cannot be changed via
2177 the /proc/irq/* interfaces.
2179 This isolation is best effort and only effective
2180 if the automatically assigned interrupt mask of a
2181 device queue contains isolated and housekeeping
2182 CPUs. If housekeeping CPUs are online then such
2183 interrupts are directed to the housekeeping CPU
2184 so that IO submitted on the housekeeping CPU
2185 cannot disturb the isolated CPU.
2187 If a queue's affinity mask contains only isolated
2188 CPUs then this parameter has no effect on the
2189 interrupt routing decision, though interrupts are
2190 only delivered when tasks running on those
2191 isolated CPUs submit IO. IO submitted on
2192 housekeeping CPUs has no influence on those
2195 The format of <cpu-list> is described above.
2199 ivrs_ioapic [HW,X86-64]
2200 Provide an override to the IOAPIC-ID<->DEVICE-ID
2201 mapping provided in the IVRS ACPI table. For
2202 example, to map IOAPIC-ID decimal 10 to
2203 PCI device 00:14.0 write the parameter as:
2204 ivrs_ioapic[10]=00:14.0
2206 ivrs_hpet [HW,X86-64]
2207 Provide an override to the HPET-ID<->DEVICE-ID
2208 mapping provided in the IVRS ACPI table. For
2209 example, to map HPET-ID decimal 0 to
2210 PCI device 00:14.0 write the parameter as:
2211 ivrs_hpet[0]=00:14.0
2213 ivrs_acpihid [HW,X86-64]
2214 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2215 mapping provided in the IVRS ACPI table. For
2216 example, to map UART-HID:UID AMD0020:0 to
2217 PCI device 00:14.5 write the parameter as:
2218 ivrs_acpihid[00:14.5]=AMD0020:0
2220 js= [HW,JOY] Analog joystick
2221 See Documentation/input/joydev/joystick.rst.
2224 When CONFIG_RANDOMIZE_BASE is set, this disables
2225 kernel and module base offset ASLR (Address Space
2226 Layout Randomization).
2229 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2230 report on every invalid memory access. Without this
2231 parameter KASAN will print report only for the first
2236 kernelcore= [KNL,X86,IA-64,PPC]
2237 Format: nn[KMGTPE] | nn% | "mirror"
2238 This parameter specifies the amount of memory usable by
2239 the kernel for non-movable allocations. The requested
2240 amount is spread evenly throughout all nodes in the
2241 system as ZONE_NORMAL. The remaining memory is used for
2242 movable memory in its own zone, ZONE_MOVABLE. In the
2243 event, a node is too small to have both ZONE_NORMAL and
2244 ZONE_MOVABLE, kernelcore memory will take priority and
2245 other nodes will have a larger ZONE_MOVABLE.
2247 ZONE_MOVABLE is used for the allocation of pages that
2248 may be reclaimed or moved by the page migration
2249 subsystem. Note that allocations like PTEs-from-HighMem
2250 still use the HighMem zone if it exists, and the Normal
2251 zone if it does not.
2253 It is possible to specify the exact amount of memory in
2254 the form of "nn[KMGTPE]", a percentage of total system
2255 memory in the form of "nn%", or "mirror". If "mirror"
2256 option is specified, mirrored (reliable) memory is used
2257 for non-movable allocations and remaining memory is used
2258 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2259 are exclusive, so you cannot specify multiple forms.
2261 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
2262 Format: <Controller#>[,poll interval]
2263 The controller # is the number of the ehci usb debug
2264 port as it is probed via PCI. The poll interval is
2265 optional and is the number seconds in between
2266 each poll cycle to the debug port in case you need
2267 the functionality for interrupting the kernel with
2268 gdb or control-c on the dbgp connection. When
2269 not using this parameter you use sysrq-g to break into
2270 the kernel debugger.
2272 kgdboc= [KGDB,HW] kgdb over consoles.
2273 Requires a tty driver that supports console polling,
2274 or a supported polling keyboard driver (non-usb).
2275 Serial only format: <serial_device>[,baud]
2276 keyboard only format: kbd
2277 keyboard and serial format: kbd,<serial_device>[,baud]
2278 Optional Kernel mode setting:
2279 kms, kbd format: kms,kbd
2280 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2282 kgdboc_earlycon= [KGDB,HW]
2283 If the boot console provides the ability to read
2284 characters and can work in polling mode, you can use
2285 this parameter to tell kgdb to use it as a backend
2286 until the normal console is registered. Intended to
2287 be used together with the kgdboc parameter which
2288 specifies the normal console to transition to.
2290 The name of the early console should be specified
2291 as the value of this parameter. Note that the name of
2292 the early console might be different than the tty
2293 name passed to kgdboc. It's OK to leave the value
2294 blank and the first boot console that implements
2295 read() will be picked.
2297 kgdbwait [KGDB] Stop kernel execution and enter the
2298 kernel debugger at the earliest opportunity.
2300 kmac= [MIPS] Korina ethernet MAC address.
2301 Configure the RouterBoard 532 series on-chip
2302 Ethernet adapter MAC address.
2304 kmemleak= [KNL] Boot-time kmemleak enable/disable
2305 Valid arguments: on, off
2307 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2310 kprobe_event=[probe-list]
2311 [FTRACE] Add kprobe events and enable at boot time.
2312 The probe-list is a semicolon delimited list of probe
2313 definitions. Each definition is same as kprobe_events
2314 interface, but the parameters are comma delimited.
2315 For example, to add a kprobe event on vfs_read with
2316 arg1 and arg2, add to the command line;
2318 kprobe_event=p,vfs_read,$arg1,$arg2
2320 See also Documentation/trace/kprobetrace.rst "Kernel
2321 Boot Parameter" section.
2323 kpti= [ARM64] Control page table isolation of user
2324 and kernel address spaces.
2325 Default: enabled on cores which need mitigation.
2329 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2330 Default is 0 (don't ignore, but inject #GP)
2332 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2333 Default is false (don't support).
2335 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
2340 [KVM] Controls the software workaround for the
2341 X86_BUG_ITLB_MULTIHIT bug.
2342 force : Always deploy workaround.
2343 off : Never deploy workaround.
2344 auto : Deploy workaround based on the presence of
2345 X86_BUG_ITLB_MULTIHIT.
2349 If the software workaround is enabled for the host,
2350 guests do need not to enable it for nested guests.
2352 kvm.nx_huge_pages_recovery_ratio=
2353 [KVM] Controls how many 4KiB pages are periodically zapped
2354 back to huge pages. 0 disables the recovery, otherwise if
2355 the value is N KVM will zap 1/Nth of the 4KiB pages every
2356 minute. The default is 60.
2358 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2359 Default is 1 (enabled)
2361 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2363 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2366 [KVM,ARM] Select one of KVM/arm64's modes of operation.
2368 nvhe: Standard nVHE-based mode, without support for
2371 protected: nVHE-based mode with support for guests whose
2372 state is kept private from the host.
2373 Not valid if the kernel is running in EL2.
2375 Defaults to VHE/nVHE based on hardware support.
2377 kvm-arm.vgic_v3_group0_trap=
2378 [KVM,ARM] Trap guest accesses to GICv3 group-0
2381 kvm-arm.vgic_v3_group1_trap=
2382 [KVM,ARM] Trap guest accesses to GICv3 group-1
2385 kvm-arm.vgic_v3_common_trap=
2386 [KVM,ARM] Trap guest accesses to GICv3 common
2389 kvm-arm.vgic_v4_enable=
2390 [KVM,ARM] Allow use of GICv4 for direct injection of
2393 kvm_cma_resv_ratio=n [PPC]
2394 Reserves given percentage from system memory area for
2395 contiguous memory allocation for KVM hash pagetable
2397 By default it reserves 5% of total system memory.
2401 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2402 (virtualized MMU) support on capable Intel chips.
2403 Default is 1 (enabled)
2405 kvm-intel.emulate_invalid_guest_state=
2406 [KVM,Intel] Enable emulation of invalid guest states
2407 Default is 0 (disabled)
2409 kvm-intel.flexpriority=
2410 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2411 Default is 1 (enabled)
2414 [KVM,Intel] Enable VMX nesting (nVMX).
2415 Default is 0 (disabled)
2417 kvm-intel.unrestricted_guest=
2418 [KVM,Intel] Disable unrestricted guest feature
2419 (virtualized real and unpaged mode) on capable
2420 Intel chips. Default is 1 (enabled)
2422 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2425 Valid arguments: never, cond, always
2427 always: L1D cache flush on every VMENTER.
2428 cond: Flush L1D on VMENTER only when the code between
2429 VMEXIT and VMENTER can leak host memory.
2430 never: Disables the mitigation
2432 Default is cond (do L1 cache flush in specific instances)
2434 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2435 feature (tagged TLBs) on capable Intel chips.
2436 Default is 1 (enabled)
2438 l1d_flush= [X86,INTEL]
2439 Control mitigation for L1D based snooping vulnerability.
2441 Certain CPUs are vulnerable to an exploit against CPU
2442 internal buffers which can forward information to a
2443 disclosure gadget under certain conditions.
2445 In vulnerable processors, the speculatively
2446 forwarded data can be used in a cache side channel
2447 attack, to access data to which the attacker does
2448 not have direct access.
2450 This parameter controls the mitigation. The
2453 on - enable the interface for the mitigation
2455 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2458 The kernel PTE inversion protection is unconditionally
2459 enabled and cannot be disabled.
2462 Provides all available mitigations for the
2463 L1TF vulnerability. Disables SMT and
2464 enables all mitigations in the
2465 hypervisors, i.e. unconditional L1D flush.
2467 SMT control and L1D flush control via the
2468 sysfs interface is still possible after
2469 boot. Hypervisors will issue a warning
2470 when the first VM is started in a
2471 potentially insecure configuration,
2472 i.e. SMT enabled or L1D flush disabled.
2475 Same as 'full', but disables SMT and L1D
2476 flush runtime control. Implies the
2477 'nosmt=force' command line option.
2478 (i.e. sysfs control of SMT is disabled.)
2481 Leaves SMT enabled and enables the default
2482 hypervisor mitigation, i.e. conditional
2485 SMT control and L1D flush control via the
2486 sysfs interface is still possible after
2487 boot. Hypervisors will issue a warning
2488 when the first VM is started in a
2489 potentially insecure configuration,
2490 i.e. SMT enabled or L1D flush disabled.
2494 Disables SMT and enables the default
2495 hypervisor mitigation.
2497 SMT control and L1D flush control via the
2498 sysfs interface is still possible after
2499 boot. Hypervisors will issue a warning
2500 when the first VM is started in a
2501 potentially insecure configuration,
2502 i.e. SMT enabled or L1D flush disabled.
2505 Same as 'flush', but hypervisors will not
2506 warn when a VM is started in a potentially
2507 insecure configuration.
2510 Disables hypervisor mitigations and doesn't
2512 It also drops the swap size and available
2513 RAM limit restriction on both hypervisor and
2518 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2524 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2527 lapic= [X86,APIC] Do not use TSC deadline
2528 value for LAPIC timer one-shot implementation. Default
2529 back to the programmable timer unit in the LAPIC.
2530 Format: notscdeadline
2532 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2535 libata.dma= [LIBATA] DMA control
2536 libata.dma=0 Disable all PATA and SATA DMA
2537 libata.dma=1 PATA and SATA Disk DMA only
2538 libata.dma=2 ATAPI (CDROM) DMA only
2539 libata.dma=4 Compact Flash DMA only
2540 Combinations also work, so libata.dma=3 enables DMA
2541 for disks and CDROMs, but not CFs.
2543 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2544 libata.ignore_hpa=0 keep BIOS limits (default)
2545 libata.ignore_hpa=1 ignore limits, using full disk
2547 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2551 libata.force= [LIBATA] Force configurations. The format is comma-
2552 separated list of "[ID:]VAL" where ID is
2553 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2554 matching port, link or device. Basically, it matches
2555 the ATA ID string printed on console by libata. If
2556 the whole ID part is omitted, the last PORT and DEVICE
2557 values are used. If ID hasn't been specified yet, the
2558 configuration applies to all ports, links and devices.
2560 If only DEVICE is omitted, the parameter applies to
2561 the port and all links and devices behind it. DEVICE
2562 number of 0 either selects the first device or the
2563 first fan-out link behind PMP device. It does not
2564 select the host link. DEVICE number of 15 selects the
2565 host link and device attached to it.
2567 The VAL specifies the configuration to force. As long
2568 as there's no ambiguity shortcut notation is allowed.
2569 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2570 The following configurations can be forced.
2572 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2573 Any ID with matching PORT is used.
2575 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2577 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2578 udma[/][16,25,33,44,66,100,133] notation is also
2581 * [no]ncq: Turn on or off NCQ.
2583 * [no]ncqtrim: Turn off queued DSM TRIM.
2585 * nohrst, nosrst, norst: suppress hard, soft
2588 * rstonce: only attempt one reset during
2589 hot-unplug link recovery
2591 * dump_id: dump IDENTIFY data.
2593 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2595 * disable: Disable this device.
2597 If there are multiple matching configurations changing
2598 the same attribute, the last one is used.
2600 memblock=debug [KNL] Enable memblock debug messages.
2602 load_ramdisk= [RAM] [Deprecated]
2604 lockd.nlm_grace_period=P [NFS] Assign grace period.
2607 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2610 lockd.nlm_timeout=T [NFS] Assign timeout value.
2613 lockd.nlm_udpport=M [NFS] Assign UDP port.
2616 lockdown= [SECURITY]
2617 { integrity | confidentiality }
2618 Enable the kernel lockdown feature. If set to
2619 integrity, kernel features that allow userland to
2620 modify the running kernel are disabled. If set to
2621 confidentiality, kernel features that allow userland
2622 to extract confidential information from the kernel
2625 locktorture.nreaders_stress= [KNL]
2626 Set the number of locking read-acquisition kthreads.
2627 Defaults to being automatically set based on the
2628 number of online CPUs.
2630 locktorture.nwriters_stress= [KNL]
2631 Set the number of locking write-acquisition kthreads.
2633 locktorture.onoff_holdoff= [KNL]
2634 Set time (s) after boot for CPU-hotplug testing.
2636 locktorture.onoff_interval= [KNL]
2637 Set time (s) between CPU-hotplug operations, or
2638 zero to disable CPU-hotplug testing.
2640 locktorture.shuffle_interval= [KNL]
2641 Set task-shuffle interval (jiffies). Shuffling
2642 tasks allows some CPUs to go into dyntick-idle
2643 mode during the locktorture test.
2645 locktorture.shutdown_secs= [KNL]
2646 Set time (s) after boot system shutdown. This
2647 is useful for hands-off automated testing.
2649 locktorture.stat_interval= [KNL]
2650 Time (s) between statistics printk()s.
2652 locktorture.stutter= [KNL]
2653 Time (s) to stutter testing, for example,
2654 specifying five seconds causes the test to run for
2655 five seconds, wait for five seconds, and so on.
2656 This tests the locking primitive's ability to
2657 transition abruptly to and from idle.
2659 locktorture.torture_type= [KNL]
2660 Specify the locking implementation to test.
2662 locktorture.verbose= [KNL]
2663 Enable additional printk() statements.
2665 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2668 loglevel= All Kernel Messages with a loglevel smaller than the
2669 console loglevel will be printed to the console. It can
2670 also be changed with klogd or other programs. The
2671 loglevels are defined as follows:
2673 0 (KERN_EMERG) system is unusable
2674 1 (KERN_ALERT) action must be taken immediately
2675 2 (KERN_CRIT) critical conditions
2676 3 (KERN_ERR) error conditions
2677 4 (KERN_WARNING) warning conditions
2678 5 (KERN_NOTICE) normal but significant condition
2679 6 (KERN_INFO) informational
2680 7 (KERN_DEBUG) debug-level messages
2682 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2683 in bytes. n must be a power of two and greater
2684 than the minimal size. The minimal size is defined
2685 by LOG_BUF_SHIFT kernel config parameter. There is
2686 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2687 that allows to increase the default size depending on
2688 the number of CPUs. See init/Kconfig for more details.
2690 logo.nologo [FB] Disables display of the built-in Linux logo.
2691 This may be used to provide more screen space for
2692 kernel log messages and is useful when debugging
2693 kernel boot problems.
2695 lp=0 [LP] Specify parallel ports to use, e.g,
2696 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2697 lp=reset first parallel port). 'lp=0' disables the
2698 lp=auto printer driver. 'lp=reset' (which can be
2699 specified in addition to the ports) causes
2700 attached printers to be reset. Using
2701 lp=port1,port2,... specifies the parallel ports
2702 to associate lp devices with, starting with
2703 lp0. A port specification may be 'none' to skip
2704 that lp device, or a parport name such as
2705 'parport0'. Specifying 'lp=auto' instead of a
2706 port specification list means that device IDs
2707 from each port should be examined, to see if
2708 an IEEE 1284-compliant printer is attached; if
2709 so, the driver will manage that printer.
2710 See also header of drivers/char/lp.c.
2713 Sets loops_per_jiffy to given constant, thus avoiding
2714 time-consuming boot-time autodetection (up to 250 ms per
2715 CPU). 0 enables autodetection (default). To determine
2716 the correct value for your kernel, boot with normal
2717 autodetection and see what value is printed. Note that
2718 on SMP systems the preset will be applied to all CPUs,
2719 which is likely to cause problems if your CPUs need
2720 significantly divergent settings. An incorrect value
2721 will cause delays in the kernel to be wrong, leading to
2722 unpredictable I/O errors and other breakage. Although
2723 unlikely, in the extreme case this might damage your
2727 Format: <io>,<irq>,<dma>
2729 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2732 [SECURITY] Choose order of LSM initialization. This
2733 overrides CONFIG_LSM, and the "security=" parameter.
2735 machvec= [IA-64] Force the use of a particular machine-vector
2736 (machvec) in a generic kernel.
2737 Example: machvec=hpzx1
2739 machtype= [Loongson] Share the same kernel image file between
2740 different yeeloong laptops.
2741 Example: machtype=lemote-yeeloong-2f-7inch
2743 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2744 than or equal to this physical address is ignored.
2746 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2747 will bring up during bootup. maxcpus=n : n >= 0 limits
2748 the kernel to bring up 'n' processors. Surely after
2749 bootup you can bring up the other plugged cpu by executing
2750 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2751 only takes effect during system bootup.
2752 While n=0 is a special case, it is equivalent to "nosmp",
2753 which also disables the IO APIC.
2755 max_loop= [LOOP] The number of loop block devices that get
2756 (loop.max_loop) unconditionally pre-created at init time. The default
2757 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2758 of statically allocating a predefined number, loop
2759 devices can be requested on-demand with the
2760 /dev/loop-control interface.
2762 mce [X86-32] Machine Check Exception
2764 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2766 md= [HW] RAID subsystems devices and level
2767 See Documentation/admin-guide/md.rst.
2770 Format: <first>,<last>
2771 Specifies range of consoles to be captured by the MDA.
2774 Control mitigation for the Micro-architectural Data
2775 Sampling (MDS) vulnerability.
2777 Certain CPUs are vulnerable to an exploit against CPU
2778 internal buffers which can forward information to a
2779 disclosure gadget under certain conditions.
2781 In vulnerable processors, the speculatively
2782 forwarded data can be used in a cache side channel
2783 attack, to access data to which the attacker does
2784 not have direct access.
2786 This parameter controls the MDS mitigation. The
2789 full - Enable MDS mitigation on vulnerable CPUs
2790 full,nosmt - Enable MDS mitigation and disable
2791 SMT on vulnerable CPUs
2792 off - Unconditionally disable MDS mitigation
2794 On TAA-affected machines, mds=off can be prevented by
2795 an active TAA mitigation as both vulnerabilities are
2796 mitigated with the same mechanism so in order to disable
2797 this mitigation, you need to specify tsx_async_abort=off
2800 Not specifying this option is equivalent to
2803 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2805 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2806 Amount of memory to be used in cases as follows:
2809 2 when the kernel is not able to see the whole system memory;
2810 3 memory that lies after 'mem=' boundary is excluded from
2811 the hypervisor, then assigned to KVM guests.
2813 [X86] Work as limiting max address. Use together
2814 with memmap= to avoid physical address space collisions.
2815 Without memmap= PCI devices could be placed at addresses
2816 belonging to unused RAM.
2818 Note that this only takes effects during boot time since
2819 in above case 3, memory may need be hot added after boot
2820 if system memory of hypervisor is not sufficient.
2822 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2826 [KNL,SH] Allow user to override the default size for
2827 per-device physically contiguous DMA buffers.
2829 memhp_default_state=online/offline
2830 [KNL] Set the initial state for the memory hotplug
2831 onlining policy. If not specified, the default value is
2832 set according to the
2833 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2835 See Documentation/admin-guide/mm/memory-hotplug.rst.
2837 memmap=exactmap [KNL,X86] Enable setting of an exact
2838 E820 memory map, as specified by the user.
2839 Such memmap=exactmap lines can be constructed based on
2840 BIOS output or other requirements. See the memmap=nn@ss
2843 memmap=nn[KMG]@ss[KMG]
2844 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory.
2845 Region of memory to be used is from ss to ss+nn.
2846 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2847 which limits max address to nn[KMG].
2848 Multiple different regions can be specified,
2851 memmap=100M@2G,100M#3G,1G!1024G
2853 memmap=nn[KMG]#ss[KMG]
2854 [KNL,ACPI] Mark specific memory as ACPI data.
2855 Region of memory to be marked is from ss to ss+nn.
2857 memmap=nn[KMG]$ss[KMG]
2858 [KNL,ACPI] Mark specific memory as reserved.
2859 Region of memory to be reserved is from ss to ss+nn.
2860 Example: Exclude memory from 0x18690000-0x1869ffff
2861 memmap=64K$0x18690000
2863 memmap=0x10000$0x18690000
2864 Some bootloaders may need an escape character before '$',
2865 like Grub2, otherwise '$' and the following number
2868 memmap=nn[KMG]!ss[KMG]
2869 [KNL,X86] Mark specific memory as protected.
2870 Region of memory to be used, from ss to ss+nn.
2871 The memory region may be marked as e820 type 12 (0xc)
2872 and is NVDIMM or ADR memory.
2874 memmap=<size>%<offset>-<oldtype>+<newtype>
2875 [KNL,ACPI] Convert memory within the specified region
2876 from <oldtype> to <newtype>. If "-<oldtype>" is left
2877 out, the whole region will be marked as <newtype>,
2878 even if previously unavailable. If "+<newtype>" is left
2879 out, matching memory will be removed. Types are
2880 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2881 3 = ACPI, 12 = PRAM.
2883 memory_corruption_check=0/1 [X86]
2884 Some BIOSes seem to corrupt the first 64k of
2885 memory when doing things like suspend/resume.
2886 Setting this option will scan the memory
2887 looking for corruption. Enabling this will
2888 both detect corruption and prevent the kernel
2889 from using the memory being corrupted.
2890 However, its intended as a diagnostic tool; if
2891 repeatable BIOS-originated corruption always
2892 affects the same memory, you can use memmap=
2893 to prevent the kernel from using that memory.
2895 memory_corruption_check_size=size [X86]
2896 By default it checks for corruption in the low
2897 64k, making this memory unavailable for normal
2898 use. Use this parameter to scan for
2899 corruption in more or less memory.
2901 memory_corruption_check_period=seconds [X86]
2902 By default it checks for corruption every 60
2903 seconds. Use this parameter to check at some
2904 other rate. 0 disables periodic checking.
2906 memory_hotplug.memmap_on_memory
2907 [KNL,X86,ARM] Boolean flag to enable this feature.
2908 Format: {on | off (default)}
2909 When enabled, runtime hotplugged memory will
2910 allocate its internal metadata (struct pages)
2911 from the hotadded memory which will allow to
2912 hotadd a lot of memory without requiring
2913 additional memory to do so.
2914 This feature is disabled by default because it
2915 has some implication on large (e.g. GB)
2916 allocations in some configurations (e.g. small
2918 The state of the flag can be read in
2919 /sys/module/memory_hotplug/parameters/memmap_on_memory.
2920 Note that even when enabled, there are a few cases where
2921 the feature is not effective.
2923 This is not compatible with hugetlb_free_vmemmap. If
2924 both parameters are enabled, hugetlb_free_vmemmap takes
2925 precedence over memory_hotplug.memmap_on_memory.
2927 memtest= [KNL,X86,ARM,PPC,RISCV] Enable memtest
2929 default : 0 <disable>
2930 Specifies the number of memtest passes to be
2931 performed. Each pass selects another test
2932 pattern from a given set of patterns. Memtest
2933 fills the memory with this pattern, validates
2934 memory contents and reserves bad memory
2935 regions that are detected.
2937 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2938 Valid arguments: on, off
2939 Default (depends on kernel configuration option):
2940 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2941 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2942 mem_encrypt=on: Activate SME
2943 mem_encrypt=off: Do not activate SME
2945 Refer to Documentation/virt/kvm/amd-memory-encryption.rst
2946 for details on when memory encryption can be activated.
2948 mem_sleep_default= [SUSPEND] Default system suspend mode:
2949 s2idle - Suspend-To-Idle
2950 shallow - Power-On Suspend or equivalent (if supported)
2951 deep - Suspend-To-RAM or equivalent (if supported)
2952 See Documentation/admin-guide/pm/sleep-states.rst.
2954 meye.*= [HW] Set MotionEye Camera parameters
2955 See Documentation/admin-guide/media/meye.rst.
2957 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2958 Multi-Function General Purpose Timers on AMD Geode
2961 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2962 the BIOS has incorrectly applied a workaround. TinyBIOS
2963 version 0.98 is known to be affected, 0.99 fixes the
2964 problem by letting the user disable the workaround.
2968 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2969 physical address is ignored.
2971 mini2440= [ARM,HW,KNL]
2972 Format:[0..2][b][c][t]
2974 MINI2440 configuration specification:
2975 0 - The attached screen is the 3.5" TFT
2976 1 - The attached screen is the 7" TFT
2977 2 - The VGA Shield is attached (1024x768)
2978 Leaving out the screen size parameter will not load
2979 the TFT driver, and the framebuffer will be left
2981 b - Enable backlight. The TFT backlight pin will be
2982 linked to the kernel VESA blanking code and a GPIO
2983 LED. This parameter is not necessary when using the
2985 c - Enable the s3c camera interface.
2986 t - Reserved for enabling touchscreen support. The
2987 touchscreen support is not enabled in the mainstream
2988 kernel as of 2.6.30, a preliminary port can be found
2989 in the "bleeding edge" mini2440 support kernel at
2990 https://repo.or.cz/w/linux-2.6/mini2440.git
2993 [X86,PPC,S390,ARM64] Control optional mitigations for
2994 CPU vulnerabilities. This is a set of curated,
2995 arch-independent options, each of which is an
2996 aggregation of existing arch-specific options.
2999 Disable all optional CPU mitigations. This
3000 improves system performance, but it may also
3001 expose users to several CPU vulnerabilities.
3002 Equivalent to: nopti [X86,PPC]
3004 nospectre_v1 [X86,PPC]
3006 nospectre_v2 [X86,PPC,S390,ARM64]
3007 spectre_v2_user=off [X86]
3008 spec_store_bypass_disable=off [X86,PPC]
3009 ssbd=force-off [ARM64]
3012 tsx_async_abort=off [X86]
3013 kvm.nx_huge_pages=off [X86]
3014 no_entry_flush [PPC]
3015 no_uaccess_flush [PPC]
3018 This does not have any effect on
3019 kvm.nx_huge_pages when
3020 kvm.nx_huge_pages=force.
3023 Mitigate all CPU vulnerabilities, but leave SMT
3024 enabled, even if it's vulnerable. This is for
3025 users who don't want to be surprised by SMT
3026 getting disabled across kernel upgrades, or who
3027 have other ways of avoiding SMT-based attacks.
3028 Equivalent to: (default behavior)
3031 Mitigate all CPU vulnerabilities, disabling SMT
3032 if needed. This is for users who always want to
3033 be fully mitigated, even if it means losing SMT.
3034 Equivalent to: l1tf=flush,nosmt [X86]
3035 mds=full,nosmt [X86]
3036 tsx_async_abort=full,nosmt [X86]
3039 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
3040 parameter allows control of the logging verbosity for
3041 the additional memory initialisation checks. A value
3042 of 0 disables mminit logging and a level of 4 will
3043 log everything. Information is printed at KERN_DEBUG
3044 so loglevel=8 may also need to be specified.
3047 [KNL] When CONFIG_MODULE_SIG is set, this means that
3048 modules without (valid) signatures will fail to load.
3049 Note that if CONFIG_MODULE_SIG_FORCE is set, that
3050 is always true, so this option does nothing.
3052 module_blacklist= [KNL] Do not load a comma-separated list of
3053 modules. Useful for debugging problem modules.
3056 [MOUSE] Maximum time between finger touching and
3057 leaving touchpad surface for touch to be considered
3058 a tap and be reported as a left button click (for
3059 touchpads working in absolute mode only).
3061 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
3062 reporting absolute coordinates, such as tablets
3063 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
3064 reporting absolute coordinates, such as tablets
3066 movablecore= [KNL,X86,IA-64,PPC]
3067 Format: nn[KMGTPE] | nn%
3068 This parameter is the complement to kernelcore=, it
3069 specifies the amount of memory used for migratable
3070 allocations. If both kernelcore and movablecore is
3071 specified, then kernelcore will be at *least* the
3072 specified value but may be more. If movablecore on its
3073 own is specified, the administrator must be careful
3074 that the amount of memory usable for all allocations
3077 movable_node [KNL] Boot-time switch to make hotplugable memory
3078 NUMA nodes to be movable. This means that the memory
3079 of such nodes will be usable only for movable
3080 allocations which rules out almost all kernel
3081 allocations. Use with caution!
3083 MTD_Partition= [MTD]
3084 Format: <name>,<region-number>,<size>,<offset>
3086 MTD_Region= [MTD] Format:
3087 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
3090 See drivers/mtd/parsers/cmdlinepart.c
3092 multitce=off [PPC] This parameter disables the use of the pSeries
3093 firmware feature for updating multiple TCE entries
3096 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
3098 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
3100 boundary - index of last SLC block on Flex-OneNAND.
3101 The remaining blocks are configured as MLC blocks.
3102 lock - Configure if Flex-OneNAND boundary should be locked.
3103 Once locked, the boundary cannot be changed.
3104 1 indicates lock status, 0 indicates unlock status.
3107 ARM/S3C2412 JIVE boot control
3109 See arch/arm/mach-s3c/mach-jive.c
3111 mtouchusb.raw_coordinates=
3112 [HW] Make the MicroTouch USB driver use raw coordinates
3113 ('y', default) or cooked coordinates ('n')
3115 mtrr_chunk_size=nn[KMG] [X86]
3116 used for mtrr cleanup. It is largest continuous chunk
3117 that could hold holes aka. UC entries.
3119 mtrr_gran_size=nn[KMG] [X86]
3120 Used for mtrr cleanup. It is granularity of mtrr block.
3122 Large value could prevent small alignment from
3125 mtrr_spare_reg_nr=n [X86]
3127 Range: 0,7 : spare reg number
3129 Used for mtrr cleanup. It is spare mtrr entries number.
3130 Set to 2 or more if your graphical card needs more.
3132 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
3134 netdev= [NET] Network devices parameters
3135 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
3136 Note that mem_start is often overloaded to mean
3137 something different and driver-specific.
3138 This usage is only documented in each driver source
3142 [NETFILTER] Enable connection tracking flow accounting
3143 0 to disable accounting
3144 1 to enable accounting
3147 nfsaddrs= [NFS] Deprecated. Use ip= instead.
3148 See Documentation/admin-guide/nfs/nfsroot.rst.
3150 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
3151 See Documentation/admin-guide/nfs/nfsroot.rst.
3153 nfsrootdebug [NFS] enable nfsroot debugging messages.
3154 See Documentation/admin-guide/nfs/nfsroot.rst.
3156 nfs.callback_nr_threads=
3157 [NFSv4] set the total number of threads that the
3158 NFS client will assign to service NFSv4 callback
3161 nfs.callback_tcpport=
3162 [NFS] set the TCP port on which the NFSv4 callback
3163 channel should listen.
3166 [NFS] sets the pathname to the program which is used
3167 to update the NFS client cache entries.
3169 nfs.cache_getent_timeout=
3170 [NFS] sets the timeout after which an attempt to
3171 update a cache entry is deemed to have failed.
3173 nfs.idmap_cache_timeout=
3174 [NFS] set the maximum lifetime for idmapper cache
3178 [NFS] enable 64-bit inode numbers.
3179 If zero, the NFS client will fake up a 32-bit inode
3180 number for the readdir() and stat() syscalls instead
3181 of returning the full 64-bit number.
3182 The default is to return 64-bit inode numbers.
3184 nfs.max_session_cb_slots=
3185 [NFSv4.1] Sets the maximum number of session
3186 slots the client will assign to the callback
3187 channel. This determines the maximum number of
3188 callbacks the client will process in parallel for
3189 a particular server.
3191 nfs.max_session_slots=
3192 [NFSv4.1] Sets the maximum number of session slots
3193 the client will attempt to negotiate with the server.
3194 This limits the number of simultaneous RPC requests
3195 that the client can send to the NFSv4.1 server.
3196 Note that there is little point in setting this
3197 value higher than the max_tcp_slot_table_limit.
3199 nfs.nfs4_disable_idmapping=
3200 [NFSv4] When set to the default of '1', this option
3201 ensures that both the RPC level authentication
3202 scheme and the NFS level operations agree to use
3203 numeric uids/gids if the mount is using the
3204 'sec=sys' security flavour. In effect it is
3205 disabling idmapping, which can make migration from
3206 legacy NFSv2/v3 systems to NFSv4 easier.
3207 Servers that do not support this mode of operation
3208 will be autodetected by the client, and it will fall
3209 back to using the idmapper.
3210 To turn off this behaviour, set the value to '0'.
3212 [NFS4] Specify an additional fixed unique ident-
3213 ification string that NFSv4 clients can insert into
3214 their nfs_client_id4 string. This is typically a
3215 UUID that is generated at system install time.
3217 nfs.send_implementation_id =
3218 [NFSv4.1] Send client implementation identification
3219 information in exchange_id requests.
3220 If zero, no implementation identification information
3222 The default is to send the implementation identification
3225 nfs.recover_lost_locks =
3226 [NFSv4] Attempt to recover locks that were lost due
3227 to a lease timeout on the server. Please note that
3228 doing this risks data corruption, since there are
3229 no guarantees that the file will remain unchanged
3230 after the locks are lost.
3231 If you want to enable the kernel legacy behaviour of
3232 attempting to recover these locks, then set this
3234 The default parameter value of '0' causes the kernel
3235 not to attempt recovery of lost locks.
3237 nfs4.layoutstats_timer =
3238 [NFSv4.2] Change the rate at which the kernel sends
3239 layoutstats to the pNFS metadata server.
3241 Setting this to value to 0 causes the kernel to use
3242 whatever value is the default set by the layout
3243 driver. A non-zero value sets the minimum interval
3244 in seconds between layoutstats transmissions.
3246 nfsd.nfs4_disable_idmapping=
3247 [NFSv4] When set to the default of '1', the NFSv4
3248 server will return only numeric uids and gids to
3249 clients using auth_sys, and will accept numeric uids
3250 and gids from such clients. This is intended to ease
3251 migration from NFSv2/v3.
3253 nmi_backtrace.backtrace_idle [KNL]
3254 Dump stacks even of idle CPUs in response to an
3255 NMI stack-backtrace request.
3257 nmi_debug= [KNL,SH] Specify one or more actions to take
3258 when a NMI is triggered.
3259 Format: [state][,regs][,debounce][,die]
3261 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3262 Format: [panic,][nopanic,][num]
3264 0 - turn hardlockup detector in nmi_watchdog off
3265 1 - turn hardlockup detector in nmi_watchdog on
3266 When panic is specified, panic when an NMI watchdog
3267 timeout occurs (or 'nopanic' to not panic on an NMI
3268 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3269 To disable both hard and soft lockup detectors,
3270 please see 'nowatchdog'.
3271 This is useful when you use a panic=... timeout and
3272 need the box quickly up again.
3274 These settings can be accessed at runtime via
3275 the nmi_watchdog and hardlockup_panic sysctls.
3277 netpoll.carrier_timeout=
3278 [NET] Specifies amount of time (in seconds) that
3279 netpoll should wait for a carrier. By default netpoll
3282 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3283 emulation library even if a 387 maths coprocessor
3286 no5lvl [X86-64] Disable 5-level paging mode. Forces
3287 kernel to use 4-level paging instead.
3289 nofsgsbase [X86] Disables FSGSBASE instructions.
3292 [HW] Never suspend the console
3293 Disable suspending of consoles during suspend and
3294 hibernate operations. Once disabled, debugging
3295 messages can reach various consoles while the rest
3296 of the system is being put to sleep (ie, while
3297 debugging driver suspend/resume hooks). This may
3298 not work reliably with all consoles, but is known
3299 to work with serial and VGA consoles.
3300 To facilitate more flexible debugging, we also add
3301 console_suspend, a printk module parameter to control
3302 it. Users could use console_suspend (usually
3303 /sys/module/printk/parameters/console_suspend) to
3304 turn on/off it dynamically.
3306 novmcoredd [KNL,KDUMP]
3307 Disable device dump. Device dump allows drivers to
3308 append dump data to vmcore so you can collect driver
3309 specified debug info. Drivers can append the data
3310 without any limit and this data is stored in memory,
3311 so this may cause significant memory stress. Disabling
3312 device dump can help save memory but the driver debug
3313 data will be no longer available. This parameter
3314 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
3317 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
3318 caches in the slab allocator. Saves per-node memory,
3319 but will impact performance.
3323 noaltinstr [S390] Disables alternative instructions patching
3324 (CPU alternatives feature).
3326 noapic [SMP,APIC] Tells the kernel to not make use of any
3327 IOAPICs that may be present in the system.
3329 noautogroup Disable scheduler automatic task group creation.
3331 nobats [PPC] Do not use BATs for mapping kernel lowmem
3332 on "Classic" PPC cores.
3336 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
3338 delayacct [KNL] Enable per-task delay accounting
3340 nodsp [SH] Disable hardware DSP at boot time.
3342 noefi Disable EFI runtime services support.
3344 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel.
3349 On X86-32 available only on PAE configured kernels.
3350 noexec=on: enable non-executable mappings (default)
3351 noexec=off: disable non-executable mappings
3354 Disable SMAP (Supervisor Mode Access Prevention)
3355 even if it is supported by processor.
3358 Disable SMEP (Supervisor Mode Execution Prevention)
3359 even if it is supported by processor.
3362 This affects only 32-bit executables.
3363 noexec32=on: enable non-executable mappings (default)
3364 read doesn't imply executable mappings
3365 noexec32=off: disable non-executable mappings
3366 read implies executable mappings
3368 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3370 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3371 register save and restore. The kernel will only save
3372 legacy floating-point registers on task switch.
3374 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings.
3376 nohugevmalloc [PPC] Disable kernel huge vmalloc mappings.
3378 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
3379 Equivalent to smt=1.
3381 [KNL,X86] Disable symmetric multithreading (SMT).
3382 nosmt=force: Force disable SMT, cannot be undone
3383 via the sysfs control file.
3385 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3386 (bounds check bypass). With this option data leaks are
3387 possible in the system.
3389 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
3390 the Spectre variant 2 (indirect branch prediction)
3391 vulnerability. System may allow data leaks with this
3394 nospec_store_bypass_disable
3395 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3398 [PPC] Don't flush the L1-D cache after accessing user data.
3400 noxsave [BUGS=X86] Disables x86 extended register state save
3401 and restore using xsave. The kernel will fallback to
3402 enabling legacy floating-point and sse state.
3404 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
3405 register states. The kernel will fall back to use
3406 xsave to save the states. By using this parameter,
3407 performance of saving the states is degraded because
3408 xsave doesn't support modified optimization while
3409 xsaveopt supports it on xsaveopt enabled systems.
3411 noxsaves [X86] Disables xsaves and xrstors used in saving and
3412 restoring x86 extended register state in compacted
3413 form of xsave area. The kernel will fall back to use
3414 xsaveopt and xrstor to save and restore the states
3415 in standard form of xsave area. By using this
3416 parameter, xsave area per process might occupy more
3417 memory on xsaves enabled systems.
3419 nohlt [ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait
3420 in do_idle() and not use the arch_cpu_idle()
3421 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
3422 to be effective. This is useful on platforms where the
3423 sleep(SH) or wfi(ARM,ARM64) instructions do not work
3424 correctly or when doing power measurements to evalute
3425 the impact of the sleep instructions. This is also
3426 useful when using JTAG debugger.
3428 no_file_caps Tells the kernel not to honor file capabilities. The
3429 only way then for a file to be executed with privilege
3430 is to be setuid root or executed by root.
3432 nohalt [IA-64] Tells the kernel not to use the power saving
3433 function PAL_HALT_LIGHT when idle. This increases
3434 power-consumption. On the positive side, it reduces
3435 interrupt wake-up latency, which may improve performance
3436 in certain environments such as networked servers or
3440 Force pointers printed to the console or buffers to be
3441 unhashed. By default, when a pointer is printed via %p
3442 format string, that pointer is "hashed", i.e. obscured
3443 by hashing the pointer value. This is a security feature
3444 that hides actual kernel addresses from unprivileged
3445 users, but it also makes debugging the kernel more
3446 difficult since unequal pointers can no longer be
3447 compared. However, if this command-line option is
3448 specified, then all normal pointers will have their true
3449 value printed. Pointers printed via %pK may still be
3450 hashed. This option should only be specified when
3451 debugging the kernel. Please do not use on production
3454 nohibernate [HIBERNATION] Disable hibernation and resume.
3456 nohz= [KNL] Boottime enable/disable dynamic ticks
3457 Valid arguments: on, off
3460 nohz_full= [KNL,BOOT,SMP,ISOL]
3461 The argument is a cpu list, as described above.
3462 In kernels built with CONFIG_NO_HZ_FULL=y, set
3463 the specified list of CPUs whose tick will be stopped
3464 whenever possible. The boot CPU will be forced outside
3465 the range to maintain the timekeeping. Any CPUs
3466 in this list will have their RCU callbacks offloaded,
3467 just as if they had also been called out in the
3468 rcu_nocbs= boot parameter.
3470 noiotrap [SH] Disables trapped I/O port accesses.
3472 noirqdebug [X86-32] Disables the code which attempts to detect and
3473 disable unhandled interrupt sources.
3475 no_timer_check [X86,APIC] Disables the code which tests for
3476 broken timer IRQ sources.
3478 noisapnp [ISAPNP] Disables ISA PnP code.
3480 noinitrd [RAM] Tells the kernel not to load any configured
3483 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3485 [Deprecated - use intremap=off]
3489 noinvpcid [X86] Disable the INVPCID cpu feature.
3491 nojitter [IA-64] Disables jitter checking for ITC timers.
3493 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3495 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3499 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3500 clock and use the default one.
3502 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time
3503 accounting. steal time is computed, but won't
3504 influence scheduler behaviour
3506 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3508 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3510 noltlbs [PPC] Do not use large page/tlb entries for kernel
3511 lowmem mapping on PPC40x and PPC8xx
3513 nomca [IA-64] Disable machine check abort handling
3515 nomce [X86-32] Disable Machine Check Exception
3517 nomfgpt [X86-32] Disable Multi-Function General Purpose
3518 Timer usage (for AMD Geode machines).
3520 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3521 shutdown the other cpus. Instead use the REBOOT_VECTOR
3524 nomodule Disable module load
3526 nopat [X86] Disable PAT (page attribute table extension of
3527 pagetables) support.
3529 nopcid [X86-64] Disable the PCID cpu feature.
3531 norandmaps Don't use address space randomization. Equivalent to
3532 echo 0 > /proc/sys/kernel/randomize_va_space
3534 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3535 with UP alternatives
3537 nordrand [X86] Disable kernel use of the RDRAND and
3538 RDSEED instructions even if they are supported
3539 by the processor. RDRAND and RDSEED are still
3540 available to user space applications.
3542 noresume [SWSUSP] Disables resume and restores original swap
3545 no-scroll [VGA] Disables scrollback.
3546 This is required for the Braillex ib80-piezo Braille
3547 reader made by F.H. Papenmeier (Germany).
3551 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3553 nosgx [X86-64,SGX] Disables Intel SGX kernel support.
3555 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3556 and disable the IO APIC. legacy for "maxcpus=0".
3558 nosoftlockup [KNL] Disable the soft-lockup detector.
3560 nosync [HW,M68K] Disables sync negotiation for all devices.
3562 nowatchdog [KNL] Disable both lockup detectors, i.e.
3563 soft-lockup and NMI watchdog (hard-lockup).
3567 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3569 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3570 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3571 Some features depend on CPU0. Known dependencies are:
3572 1. Resume from suspend/hibernate depends on CPU0.
3573 Suspend/hibernate will fail if CPU0 is offline and you
3574 need to online CPU0 before suspend/hibernate.
3575 2. PIC interrupts also depend on CPU0. CPU0 can't be
3576 removed if a PIC interrupt is detected.
3577 It's said poweroff/reboot may depend on CPU0 on some
3578 machines although I haven't seen such issues so far
3579 after CPU0 is offline on a few tested machines.
3580 If the dependencies are under your control, you can
3581 turn on cpu0_hotplug.
3583 nps_mtm_hs_ctr= [KNL,ARC]
3584 This parameter sets the maximum duration, in
3585 cycles, each HW thread of the CTOP can run
3586 without interruptions, before HW switches it.
3587 The actual maximum duration is 16 times this
3589 Format: integer between 1 and 255
3592 nptcg= [IA-64] Override max number of concurrent global TLB
3593 purges which is reported from either PAL_VM_SUMMARY or
3596 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3597 could support. nr_cpus=n : n >= 1 limits the kernel to
3598 support 'n' processors. It could be larger than the
3599 number of already plugged CPU during bootup, later in
3600 runtime you can physically add extra cpu until it reaches
3601 n. So during boot up some boot time memory for per-cpu
3602 variables need be pre-allocated for later physical cpu
3605 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3607 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only
3608 set up a single NUMA node spanning all memory.
3610 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
3612 Allowed values are enable and disable
3614 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3615 'node', 'default' can be specified
3616 This can be set from sysctl after boot.
3617 See Documentation/admin-guide/sysctl/vm.rst for details.
3619 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3620 See Documentation/core-api/debugging-via-ohci1394.rst for more
3623 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3624 Rather than timing out after 20 ms if an EC
3625 command is not properly ACKed, override the length
3626 of the timeout. We have interrupts disabled while
3627 waiting for the ACK, so if this is set too high
3628 interrupts *may* be lost!
3630 omap_mux= [OMAP] Override bootloader pin multiplexing.
3631 Format: <mux_mode0.mode_name=value>...
3632 For example, to override I2C bus2:
3633 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3635 oops=panic Always panic on oopses. Default is to just kill the
3636 process, but there is a small probability of
3637 deadlocking the machine.
3638 This will also cause panics on machine check exceptions.
3639 Useful together with panic=30 to trigger a reboot.
3642 [KNL] Boolean flag to control whether the page allocator
3643 should randomize its free lists. The randomization may
3644 be automatically enabled if the kernel detects it is
3645 running on a platform with a direct-mapped memory-side
3646 cache, and this parameter can be used to
3647 override/disable that behavior. The state of the flag
3648 can be read from sysfs at:
3649 /sys/module/page_alloc/parameters/shuffle.
3651 page_owner= [KNL] Boot-time page_owner enabling option.
3652 Storage of the information about who allocated
3653 each page is disabled in default. With this switch,
3655 on: enable the feature
3657 page_poison= [KNL] Boot-time parameter changing the state of
3658 poisoning on the buddy allocator, available with
3659 CONFIG_PAGE_POISONING=y.
3660 off: turn off poisoning (default)
3661 on: turn on poisoning
3663 page_reporting.page_reporting_order=
3664 [KNL] Minimal page reporting order
3666 Adjust the minimal page reporting order. The page
3667 reporting is disabled when it exceeds (MAX_ORDER-1).
3669 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3670 timeout > 0: seconds before rebooting
3671 timeout = 0: wait forever
3672 timeout < 0: reboot immediately
3675 panic_print= Bitmask for printing system info when panic happens.
3676 User can chose combination of the following bits:
3677 bit 0: print all tasks info
3678 bit 1: print system memory info
3679 bit 2: print timer info
3680 bit 3: print locks info if CONFIG_LOCKDEP is on
3681 bit 4: print ftrace buffer
3682 bit 5: print all printk messages in buffer
3684 panic_on_taint= Bitmask for conditionally calling panic() in add_taint()
3685 Format: <hex>[,nousertaint]
3686 Hexadecimal bitmask representing the set of TAINT flags
3687 that will cause the kernel to panic when add_taint() is
3688 called with any of the flags in this set.
3689 The optional switch "nousertaint" can be utilized to
3690 prevent userspace forced crashes by writing to sysctl
3691 /proc/sys/kernel/tainted any flagset matching with the
3692 bitmask set on panic_on_taint.
3693 See Documentation/admin-guide/tainted-kernels.rst for
3694 extra details on the taint flags that users can pick
3695 to compose the bitmask to assign to panic_on_taint.
3697 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3700 crash_kexec_post_notifiers
3701 Run kdump after running panic-notifiers and dumping
3702 kmsg. This only for the users who doubt kdump always
3703 succeeds in any situation.
3704 Note that this also increases risks of kdump failure,
3705 because some panic notifiers can make the crashed
3706 kernel more unstable.
3708 parkbd.port= [HW] Parallel port number the keyboard adapter is
3709 connected to, default is 0.
3711 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3712 0 for XT, 1 for AT (default is AT).
3715 parport= [HW,PPT] Specify parallel ports. 0 disables.
3716 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3717 Use 'auto' to force the driver to use any
3718 IRQ/DMA settings detected (the default is to
3719 ignore detected IRQ/DMA settings because of
3720 possible conflicts). You can specify the base
3721 address, IRQ, and DMA settings; IRQ and DMA
3722 should be numbers, or 'auto' (for using detected
3723 settings on that particular port), or 'nofifo'
3724 (to avoid using a FIFO even if it is detected).
3725 Parallel ports are assigned in the order they
3726 are specified on the command line, starting
3729 parport_init_mode= [HW,PPT]
3730 Configure VIA parallel port to operate in
3731 a specific mode. This is necessary on Pegasos
3732 computer where firmware has no options for setting
3733 up parallel port mode and sets it to spp.
3734 Currently this function knows 686a and 8231 chips.
3735 Format: [spp|ps2|epp|ecp|ecpepp]
3737 pata_legacy.all= [HW,LIBATA]
3739 Set to non-zero to probe primary and secondary ISA
3740 port ranges on PCI systems where no PCI PATA device
3741 has been found at either range. Disabled by default.
3743 pata_legacy.autospeed= [HW,LIBATA]
3745 Set to non-zero if a chip is present that snoops speed
3746 changes. Disabled by default.
3748 pata_legacy.ht6560a= [HW,LIBATA]
3750 Set to 1, 2, or 3 for HT 6560A on the primary channel,
3751 the secondary channel, or both channels respectively.
3752 Disabled by default.
3754 pata_legacy.ht6560b= [HW,LIBATA]
3756 Set to 1, 2, or 3 for HT 6560B on the primary channel,
3757 the secondary channel, or both channels respectively.
3758 Disabled by default.
3760 pata_legacy.iordy_mask= [HW,LIBATA]
3762 IORDY enable mask. Set individual bits to allow IORDY
3763 for the respective channel. Bit 0 is for the first
3764 legacy channel handled by this driver, bit 1 is for
3765 the second channel, and so on. The sequence will often
3766 correspond to the primary legacy channel, the secondary
3767 legacy channel, and so on, but the handling of a PCI
3768 bus and the use of other driver options may interfere
3769 with the sequence. By default IORDY is allowed across
3772 pata_legacy.opti82c46x= [HW,LIBATA]
3774 Set to 1, 2, or 3 for Opti 82c611A on the primary
3775 channel, the secondary channel, or both channels
3776 respectively. Disabled by default.
3778 pata_legacy.opti82c611a= [HW,LIBATA]
3780 Set to 1, 2, or 3 for Opti 82c465MV on the primary
3781 channel, the secondary channel, or both channels
3782 respectively. Disabled by default.
3784 pata_legacy.pio_mask= [HW,LIBATA]
3786 PIO mode mask for autospeed devices. Set individual
3787 bits to allow the use of the respective PIO modes.
3788 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
3789 All modes allowed by default.
3791 pata_legacy.probe_all= [HW,LIBATA]
3793 Set to non-zero to probe tertiary and further ISA
3794 port ranges on PCI systems. Disabled by default.
3796 pata_legacy.probe_mask= [HW,LIBATA]
3798 Probe mask for legacy ISA PATA ports. Depending on
3799 platform configuration and the use of other driver
3800 options up to 6 legacy ports are supported: 0x1f0,
3801 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
3802 of individual ports can be disabled by setting the
3803 corresponding bits in the mask to 1. Bit 0 is for
3804 the first port in the list above (0x1f0), and so on.
3805 By default all supported ports are probed.
3807 pata_legacy.qdi= [HW,LIBATA]
3809 Set to non-zero to probe QDI controllers. By default
3810 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
3812 pata_legacy.winbond= [HW,LIBATA]
3814 Set to non-zero to probe Winbond controllers. Use
3815 the standard I/O port (0x130) if 1, otherwise the
3816 value given is the I/O port to use (typically 0x1b0).
3817 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
3820 pata_platform.pio_mask= [HW,LIBATA]
3822 Supported PIO mode mask. Set individual bits to allow
3823 the use of the respective PIO modes. Bit 0 is for
3824 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
3828 Halt all CPUs after the first oops has been printed for
3829 the specified number of seconds. This is to be used if
3830 your oopses keep scrolling off the screen.
3835 See header of drivers/block/paride/pcd.c.
3836 See also Documentation/admin-guide/blockdev/paride.rst.
3838 pci=option[,option...] [PCI] various PCI subsystem options.
3840 Some options herein operate on a specific device
3841 or a set of devices (<pci_dev>). These are
3842 specified in one of the following formats:
3844 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3845 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3847 Note: the first format specifies a PCI
3848 bus/device/function address which may change
3849 if new hardware is inserted, if motherboard
3850 firmware changes, or due to changes caused
3851 by other kernel parameters. If the
3852 domain is left unspecified, it is
3853 taken to be zero. Optionally, a path
3854 to a device through multiple device/function
3855 addresses can be specified after the base
3856 address (this is more robust against
3857 renumbering issues). The second format
3858 selects devices using IDs from the
3859 configuration space which may match multiple
3860 devices in the system.
3862 earlydump dump PCI config space before the kernel
3864 off [X86] don't probe for the PCI bus
3865 bios [X86-32] force use of PCI BIOS, don't access
3866 the hardware directly. Use this if your machine
3867 has a non-standard PCI host bridge.
3868 nobios [X86-32] disallow use of PCI BIOS, only direct
3869 hardware access methods are allowed. Use this
3870 if you experience crashes upon bootup and you
3871 suspect they are caused by the BIOS.
3872 conf1 [X86] Force use of PCI Configuration Access
3873 Mechanism 1 (config address in IO port 0xCF8,
3874 data in IO port 0xCFC, both 32-bit).
3875 conf2 [X86] Force use of PCI Configuration Access
3876 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3877 the function, IO port 0xCFA, also 8-bit, sets
3878 bus number. The config space is then accessed
3879 through ports 0xC000-0xCFFF).
3880 See http://wiki.osdev.org/PCI for more info
3881 on the configuration access mechanisms.
3882 noaer [PCIE] If the PCIEAER kernel config parameter is
3883 enabled, this kernel boot option can be used to
3884 disable the use of PCIE advanced error reporting.
3885 nodomains [PCI] Disable support for multiple PCI
3886 root domains (aka PCI segments, in ACPI-speak).
3887 nommconf [X86] Disable use of MMCONFIG for PCI
3889 check_enable_amd_mmconf [X86] check for and enable
3890 properly configured MMIO access to PCI
3891 config space on AMD family 10h CPU
3892 nomsi [MSI] If the PCI_MSI kernel config parameter is
3893 enabled, this kernel boot option can be used to
3894 disable the use of MSI interrupts system-wide.
3895 noioapicquirk [APIC] Disable all boot interrupt quirks.
3896 Safety option to keep boot IRQs enabled. This
3897 should never be necessary.
3898 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3899 primary IO-APIC for bridges that cannot disable
3900 boot IRQs. This fixes a source of spurious IRQs
3901 when the system masks IRQs.
3902 noioapicreroute [APIC] Disable workaround that uses the
3903 boot IRQ equivalent of an IRQ that connects to
3904 a chipset where boot IRQs cannot be disabled.
3905 The opposite of ioapicreroute.
3906 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3907 routing table. These calls are known to be buggy
3908 on several machines and they hang the machine
3909 when used, but on other computers it's the only
3910 way to get the interrupt routing table. Try
3911 this option if the kernel is unable to allocate
3912 IRQs or discover secondary PCI buses on your
3914 rom [X86] Assign address space to expansion ROMs.
3915 Use with caution as certain devices share
3916 address decoders between ROMs and other
3918 norom [X86] Do not assign address space to
3919 expansion ROMs that do not already have
3920 BIOS assigned address ranges.
3921 nobar [X86] Do not assign address space to the
3922 BARs that weren't assigned by the BIOS.
3923 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3924 assigned automatically to PCI devices. You can
3925 make the kernel exclude IRQs of your ISA cards
3927 pirqaddr=0xAAAAA [X86] Specify the physical address
3928 of the PIRQ table (normally generated
3929 by the BIOS) if it is outside the
3930 F0000h-100000h range.
3931 lastbus=N [X86] Scan all buses thru bus #N. Can be
3932 useful if the kernel is unable to find your
3933 secondary buses and you want to tell it
3934 explicitly which ones they are.
3935 assign-busses [X86] Always assign all PCI bus
3936 numbers ourselves, overriding
3937 whatever the firmware may have done.
3938 usepirqmask [X86] Honor the possible IRQ mask stored
3939 in the BIOS $PIR table. This is needed on
3940 some systems with broken BIOSes, notably
3941 some HP Pavilion N5400 and Omnibook XE3
3942 notebooks. This will have no effect if ACPI
3943 IRQ routing is enabled.
3944 noacpi [X86] Do not use ACPI for IRQ routing
3945 or for PCI scanning.
3946 use_crs [X86] Use PCI host bridge window information
3947 from ACPI. On BIOSes from 2008 or later, this
3948 is enabled by default. If you need to use this,
3949 please report a bug.
3950 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3951 If you need to use this, please report a bug.
3952 routeirq Do IRQ routing for all PCI devices.
3953 This is normally done in pci_enable_device(),
3954 so this option is a temporary workaround
3955 for broken drivers that don't call it.
3956 skip_isa_align [X86] do not align io start addr, so can
3957 handle more pci cards
3958 noearly [X86] Don't do any early type 1 scanning.
3959 This might help on some broken boards which
3960 machine check when some devices' config space
3961 is read. But various workarounds are disabled
3962 and some IOMMU drivers will not work.
3963 bfsort Sort PCI devices into breadth-first order.
3964 This sorting is done to get a device
3965 order compatible with older (<= 2.4) kernels.
3966 nobfsort Don't sort PCI devices into breadth-first order.
3967 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3968 tuning and use the BIOS-configured MPS defaults.
3969 pcie_bus_safe Set every device's MPS to the largest value
3970 supported by all devices below the root complex.
3971 pcie_bus_perf Set device MPS to the largest allowable MPS
3972 based on its parent bus. Also set MRRS (Max
3973 Read Request Size) to the largest supported
3974 value (no larger than the MPS that the device
3975 or bus can support) for best performance.
3976 pcie_bus_peer2peer Set every device's MPS to 128B, which
3977 every device is guaranteed to support. This
3978 configuration allows peer-to-peer DMA between
3979 any pair of devices, possibly at the cost of
3980 reduced performance. This also guarantees
3981 that hot-added devices will work.
3982 cbiosize=nn[KMG] The fixed amount of bus space which is
3983 reserved for the CardBus bridge's IO window.
3984 The default value is 256 bytes.
3985 cbmemsize=nn[KMG] The fixed amount of bus space which is
3986 reserved for the CardBus bridge's memory
3987 window. The default value is 64 megabytes.
3990 [<order of align>@]<pci_dev>[; ...]
3991 Specifies alignment and device to reassign
3992 aligned memory resources. How to
3993 specify the device is described above.
3994 If <order of align> is not specified,
3995 PAGE_SIZE is used as alignment.
3996 A PCI-PCI bridge can be specified if resource
3997 windows need to be expanded.
3998 To specify the alignment for several
3999 instances of a device, the PCI vendor,
4000 device, subvendor, and subdevice may be
4001 specified, e.g., 12@pci:8086:9c22:103c:198f
4002 for 4096-byte alignment.
4003 ecrc= Enable/disable PCIe ECRC (transaction layer
4004 end-to-end CRC checking).
4005 bios: Use BIOS/firmware settings. This is the
4009 hpiosize=nn[KMG] The fixed amount of bus space which is
4010 reserved for hotplug bridge's IO window.
4011 Default size is 256 bytes.
4012 hpmmiosize=nn[KMG] The fixed amount of bus space which is
4013 reserved for hotplug bridge's MMIO window.
4014 Default size is 2 megabytes.
4015 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
4016 reserved for hotplug bridge's MMIO_PREF window.
4017 Default size is 2 megabytes.
4018 hpmemsize=nn[KMG] The fixed amount of bus space which is
4019 reserved for hotplug bridge's MMIO and
4021 Default size is 2 megabytes.
4022 hpbussize=nn The minimum amount of additional bus numbers
4023 reserved for buses below a hotplug bridge.
4025 realloc= Enable/disable reallocating PCI bridge resources
4026 if allocations done by BIOS are too small to
4027 accommodate resources required by all child
4029 off: Turn realloc off
4031 realloc same as realloc=on
4032 noari do not use PCIe ARI.
4033 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
4034 do not use PCIe ATS (and IOMMU device IOTLB).
4035 pcie_scan_all Scan all possible PCIe devices. Otherwise we
4036 only look for one device below a PCIe downstream
4038 big_root_window Try to add a big 64bit memory window to the PCIe
4039 root complex on AMD CPUs. Some GFX hardware
4040 can resize a BAR to allow access to all VRAM.
4041 Adding the window is slightly risky (it may
4042 conflict with unreported devices), so this
4044 disable_acs_redir=<pci_dev>[; ...]
4045 Specify one or more PCI devices (in the format
4046 specified above) separated by semicolons.
4047 Each device specified will have the PCI ACS
4048 redirect capabilities forced off which will
4049 allow P2P traffic between devices through
4050 bridges without forcing it upstream. Note:
4051 this removes isolation between devices and
4052 may put more devices in an IOMMU group.
4053 force_floating [S390] Force usage of floating interrupts.
4054 nomio [S390] Do not use MIO instructions.
4055 norid [S390] ignore the RID field and force use of
4056 one PCI domain per PCI function
4058 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
4061 force Enable ASPM even on devices that claim not to support it.
4062 WARNING: Forcing ASPM on may cause system lockups.
4064 pcie_ports= [PCIE] PCIe port services handling:
4065 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
4066 even if the platform doesn't give the OS permission to
4067 use them. This may cause conflicts if the platform
4068 also tries to use these services.
4069 dpc-native Use native PCIe service for DPC only. May
4070 cause conflicts if firmware uses AER or DPC.
4071 compat Disable native PCIe services (PME, AER, DPC, PCIe
4074 pcie_port_pm= [PCIE] PCIe port power management handling:
4075 off Disable power management of all PCIe ports
4076 force Forcibly enable power management of all PCIe ports
4078 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
4079 nomsi Do not use MSI for native PCIe PME signaling (this makes
4080 all PCIe root ports use INTx for all services).
4082 pcmv= [HW,PCMCIA] BadgePAD 4
4086 Keep all power-domains already enabled by bootloader on,
4087 even if no driver has claimed them. This is useful
4088 for debug and development, but should not be
4089 needed on a platform with proper driver support.
4092 See Documentation/admin-guide/blockdev/paride.rst.
4094 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
4097 See arch/parisc/kernel/pdc_chassis.c
4099 percpu_alloc= Select which percpu first chunk allocator to use.
4100 Currently supported values are "embed" and "page".
4101 Archs may support subset or none of the selections.
4102 See comments in mm/percpu.c for details on each
4103 allocator. This parameter is primarily for debugging
4104 and performance comparison.
4107 See Documentation/admin-guide/blockdev/paride.rst.
4110 See Documentation/admin-guide/blockdev/paride.rst.
4112 pirq= [SMP,APIC] Manual mp-table setup
4113 See Documentation/x86/i386/IO-APIC.rst.
4115 plip= [PPT,NET] Parallel port network link
4116 Format: { parport<nr> | timid | 0 }
4117 See also Documentation/admin-guide/parport.rst.
4119 pmtmr= [X86] Manual setup of pmtmr I/O Port.
4120 Override pmtimer IOPort with a hex value.
4123 pm_debug_messages [SUSPEND,KNL]
4124 Enable suspend/resume debug messages during boot up.
4127 Enable PNP debug messages (depends on the
4128 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
4129 via /sys/module/pnp/parameters/debug. We always show
4130 current resource usage; turning this on also shows
4131 possible settings and some assignment information.
4137 { on | off | curr | res | no-curr | no-res }
4140 [ISAPNP] Exclude IRQs for the autoconfiguration
4143 [ISAPNP] Exclude DMAs for the autoconfiguration
4145 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
4146 Ranges are in pairs (I/O port base and size).
4149 [ISAPNP] Exclude memory regions for the
4151 Ranges are in pairs (memory base and size).
4153 ports= [IP_VS_FTP] IPVS ftp helper module
4155 Up to 8 (IP_VS_APP_MAX_PORTS) ports
4157 Format: <port>,<port>....
4159 powersave=off [PPC] This option disables power saving features.
4160 It specifically disables cpuidle and sets the
4161 platform machine description specific power_save
4162 function to NULL. On Idle the CPU just reduces
4165 ppc_strict_facility_enable
4166 [PPC] This option catches any kernel floating point,
4167 Altivec, VSX and SPE outside of regions specifically
4168 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
4169 There is some performance impact when enabling this.
4173 Disable Hardware Transactional Memory
4176 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
4177 none - Limited to cond_resched() calls
4178 voluntary - Limited to cond_resched() and might_sleep() calls
4179 full - Any section that isn't explicitly preempt disabled
4180 can be preempted anytime.
4182 print-fatal-signals=
4183 [KNL] debug: print fatal signals
4185 If enabled, warn about various signal handling
4186 related application anomalies: too many signals,
4187 too many POSIX.1 timers, fatal signals causing a
4190 If you hit the warning due to signal overflow,
4191 you might want to try "ulimit -i unlimited".
4195 printk.always_kmsg_dump=
4196 Trigger kmsg_dump for cases other than kernel oops or
4198 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4201 printk.console_no_auto_verbose=
4202 Disable console loglevel raise on oops, panic
4203 or lockdep-detected issues (only if lock debug is on).
4204 With an exception to setups with low baudrate on
4205 serial console, keeping this 0 is a good choice
4206 in order to provide more debug information.
4208 default: 0 (auto_verbose is enabled)
4210 printk.devkmsg={on,off,ratelimit}
4211 Control writing to /dev/kmsg.
4212 on - unlimited logging to /dev/kmsg from userspace
4213 off - logging to /dev/kmsg disabled
4214 ratelimit - ratelimit the logging
4217 printk.time= Show timing data prefixed to each printk message line
4218 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4220 processor.max_cstate= [HW,ACPI]
4221 Limit processor to maximum C-state
4222 max_cstate=9 overrides any DMI blacklist limit.
4224 processor.nocst [HW,ACPI]
4225 Ignore the _CST method to determine C-states,
4226 instead using the legacy FADT method
4228 profile= [KNL] Enable kernel profiling via /proc/profile
4229 Format: [<profiletype>,]<number>
4230 Param: <profiletype>: "schedule", "sleep", or "kvm"
4231 [defaults to kernel profiling]
4232 Param: "schedule" - profile schedule points.
4233 Param: "sleep" - profile D-state sleeping (millisecs).
4234 Requires CONFIG_SCHEDSTATS
4235 Param: "kvm" - profile VM exits.
4236 Param: <number> - step/bucket size as a power of 2 for
4237 statistical time based profiling.
4239 prompt_ramdisk= [RAM] [Deprecated]
4241 prot_virt= [S390] enable hosting protected virtual machines
4242 isolated from the hypervisor (if hardware supports
4246 psi= [KNL] Enable or disable pressure stall information
4250 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
4251 probe for; one of (bare|imps|exps|lifebook|any).
4252 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
4254 psmouse.resetafter= [HW,MOUSE]
4255 Try to reset the device after so many bad packets
4258 [HW,MOUSE] Set desired mouse resolution, in dpi.
4259 psmouse.smartscroll=
4260 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
4261 0 = disabled, 1 = enabled (default).
4263 pstore.backend= Specify the name of the pstore backend to use
4266 See Documentation/admin-guide/blockdev/paride.rst.
4268 pti= [X86-64] Control Page Table Isolation of user and
4269 kernel address spaces. Disabling this feature
4270 removes hardening, but improves performance of
4271 system calls and interrupts.
4273 on - unconditionally enable
4274 off - unconditionally disable
4275 auto - kernel detects whether your CPU model is
4276 vulnerable to issues that PTI mitigates
4278 Not specifying this option is equivalent to pti=auto.
4281 Equivalent to pti=off
4284 [KNL] Number of legacy pty's. Overwrites compiled-in
4287 quiet [KNL] Disable most log messages
4292 See Documentation/admin-guide/md.rst.
4294 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
4295 See Documentation/admin-guide/blockdev/ramdisk.rst.
4297 ramdisk_start= [RAM] RAM disk image start address
4299 random.trust_cpu={on,off}
4300 [KNL] Enable or disable trusting the use of the
4301 CPU's random number generator (if available) to
4302 fully seed the kernel's CRNG. Default is controlled
4303 by CONFIG_RANDOM_TRUST_CPU.
4305 randomize_kstack_offset=
4306 [KNL] Enable or disable kernel stack offset
4307 randomization, which provides roughly 5 bits of
4308 entropy, frustrating memory corruption attacks
4309 that depend on stack address determinism or
4310 cross-syscall address exposures. This is only
4311 available on architectures that have defined
4312 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
4313 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4314 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
4316 ras=option[,option,...] [KNL] RAS-specific options
4319 Disable the Correctable Errors Collector,
4320 see CONFIG_RAS_CEC help text.
4323 The argument is a cpu list, as described above.
4325 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
4326 the specified list of CPUs to be no-callback CPUs.
4327 Invocation of these CPUs' RCU callbacks will be
4328 offloaded to "rcuox/N" kthreads created for that
4329 purpose, where "x" is "p" for RCU-preempt, and
4330 "s" for RCU-sched, and "N" is the CPU number.
4331 This reduces OS jitter on the offloaded CPUs,
4332 which can be useful for HPC and real-time
4333 workloads. It can also improve energy efficiency
4334 for asymmetric multiprocessors.
4337 Rather than requiring that offloaded CPUs
4338 (specified by rcu_nocbs= above) explicitly
4339 awaken the corresponding "rcuoN" kthreads,
4340 make these kthreads poll for callbacks.
4341 This improves the real-time response for the
4342 offloaded CPUs by relieving them of the need to
4343 wake up the corresponding kthread, but degrades
4344 energy efficiency by requiring that the kthreads
4345 periodically wake up to do the polling.
4347 rcutree.blimit= [KNL]
4348 Set maximum number of finished RCU callbacks to
4349 process in one batch.
4351 rcutree.dump_tree= [KNL]
4352 Dump the structure of the rcu_node combining tree
4353 out at early boot. This is used for diagnostic
4354 purposes, to verify correct tree setup.
4356 rcutree.gp_cleanup_delay= [KNL]
4357 Set the number of jiffies to delay each step of
4358 RCU grace-period cleanup.
4360 rcutree.gp_init_delay= [KNL]
4361 Set the number of jiffies to delay each step of
4362 RCU grace-period initialization.
4364 rcutree.gp_preinit_delay= [KNL]
4365 Set the number of jiffies to delay each step of
4366 RCU grace-period pre-initialization, that is,
4367 the propagation of recent CPU-hotplug changes up
4368 the rcu_node combining tree.
4370 rcutree.use_softirq= [KNL]
4371 If set to zero, move all RCU_SOFTIRQ processing to
4372 per-CPU rcuc kthreads. Defaults to a non-zero
4373 value, meaning that RCU_SOFTIRQ is used by default.
4374 Specify rcutree.use_softirq=0 to use rcuc kthreads.
4376 But note that CONFIG_PREEMPT_RT=y kernels disable
4377 this kernel boot parameter, forcibly setting it
4380 rcutree.rcu_fanout_exact= [KNL]
4381 Disable autobalancing of the rcu_node combining
4382 tree. This is used by rcutorture, and might
4383 possibly be useful for architectures having high
4384 cache-to-cache transfer latencies.
4386 rcutree.rcu_fanout_leaf= [KNL]
4387 Change the number of CPUs assigned to each
4388 leaf rcu_node structure. Useful for very
4389 large systems, which will choose the value 64,
4390 and for NUMA systems with large remote-access
4391 latencies, which will choose a value aligned
4392 with the appropriate hardware boundaries.
4394 rcutree.rcu_min_cached_objs= [KNL]
4395 Minimum number of objects which are cached and
4396 maintained per one CPU. Object size is equal
4397 to PAGE_SIZE. The cache allows to reduce the
4398 pressure to page allocator, also it makes the
4399 whole algorithm to behave better in low memory
4402 rcutree.rcu_delay_page_cache_fill_msec= [KNL]
4403 Set the page-cache refill delay (in milliseconds)
4404 in response to low-memory conditions. The range
4405 of permitted values is in the range 0:100000.
4407 rcutree.jiffies_till_first_fqs= [KNL]
4408 Set delay from grace-period initialization to
4409 first attempt to force quiescent states.
4410 Units are jiffies, minimum value is zero,
4411 and maximum value is HZ.
4413 rcutree.jiffies_till_next_fqs= [KNL]
4414 Set delay between subsequent attempts to force
4415 quiescent states. Units are jiffies, minimum
4416 value is one, and maximum value is HZ.
4418 rcutree.jiffies_till_sched_qs= [KNL]
4419 Set required age in jiffies for a
4420 given grace period before RCU starts
4421 soliciting quiescent-state help from
4422 rcu_note_context_switch() and cond_resched().
4423 If not specified, the kernel will calculate
4424 a value based on the most recent settings
4425 of rcutree.jiffies_till_first_fqs
4426 and rcutree.jiffies_till_next_fqs.
4427 This calculated value may be viewed in
4428 rcutree.jiffies_to_sched_qs. Any attempt to set
4429 rcutree.jiffies_to_sched_qs will be cheerfully
4432 rcutree.kthread_prio= [KNL,BOOT]
4433 Set the SCHED_FIFO priority of the RCU per-CPU
4434 kthreads (rcuc/N). This value is also used for
4435 the priority of the RCU boost threads (rcub/N)
4436 and for the RCU grace-period kthreads (rcu_bh,
4437 rcu_preempt, and rcu_sched). If RCU_BOOST is
4438 set, valid values are 1-99 and the default is 1
4439 (the least-favored priority). Otherwise, when
4440 RCU_BOOST is not set, valid values are 0-99 and
4441 the default is zero (non-realtime operation).
4443 rcutree.rcu_nocb_gp_stride= [KNL]
4444 Set the number of NOCB callback kthreads in
4445 each group, which defaults to the square root
4446 of the number of CPUs. Larger numbers reduce
4447 the wakeup overhead on the global grace-period
4448 kthread, but increases that same overhead on
4449 each group's NOCB grace-period kthread.
4451 rcutree.qhimark= [KNL]
4452 Set threshold of queued RCU callbacks beyond which
4453 batch limiting is disabled.
4455 rcutree.qlowmark= [KNL]
4456 Set threshold of queued RCU callbacks below which
4457 batch limiting is re-enabled.
4459 rcutree.qovld= [KNL]
4460 Set threshold of queued RCU callbacks beyond which
4461 RCU's force-quiescent-state scan will aggressively
4462 enlist help from cond_resched() and sched IPIs to
4463 help CPUs more quickly reach quiescent states.
4464 Set to less than zero to make this be set based
4465 on rcutree.qhimark at boot time and to zero to
4466 disable more aggressive help enlistment.
4468 rcutree.rcu_idle_gp_delay= [KNL]
4469 Set wakeup interval for idle CPUs that have
4470 RCU callbacks (RCU_FAST_NO_HZ=y).
4472 rcutree.rcu_kick_kthreads= [KNL]
4473 Cause the grace-period kthread to get an extra
4474 wake_up() if it sleeps three times longer than
4475 it should at force-quiescent-state time.
4476 This wake_up() will be accompanied by a
4477 WARN_ONCE() splat and an ftrace_dump().
4479 rcutree.rcu_unlock_delay= [KNL]
4480 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
4481 this specifies an rcu_read_unlock()-time delay
4482 in microseconds. This defaults to zero.
4483 Larger delays increase the probability of
4484 catching RCU pointer leaks, that is, buggy use
4485 of RCU-protected pointers after the relevant
4486 rcu_read_unlock() has completed.
4488 rcutree.sysrq_rcu= [KNL]
4489 Commandeer a sysrq key to dump out Tree RCU's
4490 rcu_node tree with an eye towards determining
4491 why a new grace period has not yet started.
4493 rcuscale.gp_async= [KNL]
4494 Measure performance of asynchronous
4495 grace-period primitives such as call_rcu().
4497 rcuscale.gp_async_max= [KNL]
4498 Specify the maximum number of outstanding
4499 callbacks per writer thread. When a writer
4500 thread exceeds this limit, it invokes the
4501 corresponding flavor of rcu_barrier() to allow
4502 previously posted callbacks to drain.
4504 rcuscale.gp_exp= [KNL]
4505 Measure performance of expedited synchronous
4506 grace-period primitives.
4508 rcuscale.holdoff= [KNL]
4509 Set test-start holdoff period. The purpose of
4510 this parameter is to delay the start of the
4511 test until boot completes in order to avoid
4514 rcuscale.kfree_rcu_test= [KNL]
4515 Set to measure performance of kfree_rcu() flooding.
4517 rcuscale.kfree_rcu_test_double= [KNL]
4518 Test the double-argument variant of kfree_rcu().
4519 If this parameter has the same value as
4520 rcuscale.kfree_rcu_test_single, both the single-
4521 and double-argument variants are tested.
4523 rcuscale.kfree_rcu_test_single= [KNL]
4524 Test the single-argument variant of kfree_rcu().
4525 If this parameter has the same value as
4526 rcuscale.kfree_rcu_test_double, both the single-
4527 and double-argument variants are tested.
4529 rcuscale.kfree_nthreads= [KNL]
4530 The number of threads running loops of kfree_rcu().
4532 rcuscale.kfree_alloc_num= [KNL]
4533 Number of allocations and frees done in an iteration.
4535 rcuscale.kfree_loops= [KNL]
4536 Number of loops doing rcuscale.kfree_alloc_num number
4537 of allocations and frees.
4539 rcuscale.nreaders= [KNL]
4540 Set number of RCU readers. The value -1 selects
4541 N, where N is the number of CPUs. A value
4542 "n" less than -1 selects N-n+1, where N is again
4543 the number of CPUs. For example, -2 selects N
4544 (the number of CPUs), -3 selects N+1, and so on.
4545 A value of "n" less than or equal to -N selects
4548 rcuscale.nwriters= [KNL]
4549 Set number of RCU writers. The values operate
4550 the same as for rcuscale.nreaders.
4551 N, where N is the number of CPUs
4553 rcuscale.perf_type= [KNL]
4554 Specify the RCU implementation to test.
4556 rcuscale.shutdown= [KNL]
4557 Shut the system down after performance tests
4558 complete. This is useful for hands-off automated
4561 rcuscale.verbose= [KNL]
4562 Enable additional printk() statements.
4564 rcuscale.writer_holdoff= [KNL]
4565 Write-side holdoff between grace periods,
4566 in microseconds. The default of zero says
4569 rcutorture.fqs_duration= [KNL]
4570 Set duration of force_quiescent_state bursts
4573 rcutorture.fqs_holdoff= [KNL]
4574 Set holdoff time within force_quiescent_state bursts
4577 rcutorture.fqs_stutter= [KNL]
4578 Set wait time between force_quiescent_state bursts
4581 rcutorture.fwd_progress= [KNL]
4582 Enable RCU grace-period forward-progress testing
4583 for the types of RCU supporting this notion.
4585 rcutorture.fwd_progress_div= [KNL]
4586 Specify the fraction of a CPU-stall-warning
4587 period to do tight-loop forward-progress testing.
4589 rcutorture.fwd_progress_holdoff= [KNL]
4590 Number of seconds to wait between successive
4591 forward-progress tests.
4593 rcutorture.fwd_progress_need_resched= [KNL]
4594 Enclose cond_resched() calls within checks for
4595 need_resched() during tight-loop forward-progress
4598 rcutorture.gp_cond= [KNL]
4599 Use conditional/asynchronous update-side
4600 primitives, if available.
4602 rcutorture.gp_exp= [KNL]
4603 Use expedited update-side primitives, if available.
4605 rcutorture.gp_normal= [KNL]
4606 Use normal (non-expedited) asynchronous
4607 update-side primitives, if available.
4609 rcutorture.gp_sync= [KNL]
4610 Use normal (non-expedited) synchronous
4611 update-side primitives, if available. If all
4612 of rcutorture.gp_cond=, rcutorture.gp_exp=,
4613 rcutorture.gp_normal=, and rcutorture.gp_sync=
4614 are zero, rcutorture acts as if is interpreted
4615 they are all non-zero.
4617 rcutorture.irqreader= [KNL]
4618 Run RCU readers from irq handlers, or, more
4619 accurately, from a timer handler. Not all RCU
4620 flavors take kindly to this sort of thing.
4622 rcutorture.leakpointer= [KNL]
4623 Leak an RCU-protected pointer out of the reader.
4624 This can of course result in splats, and is
4625 intended to test the ability of things like
4626 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
4629 rcutorture.n_barrier_cbs= [KNL]
4630 Set callbacks/threads for rcu_barrier() testing.
4632 rcutorture.nfakewriters= [KNL]
4633 Set number of concurrent RCU writers. These just
4634 stress RCU, they don't participate in the actual
4635 test, hence the "fake".
4637 rcutorture.nocbs_nthreads= [KNL]
4638 Set number of RCU callback-offload togglers.
4639 Zero (the default) disables toggling.
4641 rcutorture.nocbs_toggle= [KNL]
4642 Set the delay in milliseconds between successive
4643 callback-offload toggling attempts.
4645 rcutorture.nreaders= [KNL]
4646 Set number of RCU readers. The value -1 selects
4647 N-1, where N is the number of CPUs. A value
4648 "n" less than -1 selects N-n-2, where N is again
4649 the number of CPUs. For example, -2 selects N
4650 (the number of CPUs), -3 selects N+1, and so on.
4652 rcutorture.object_debug= [KNL]
4653 Enable debug-object double-call_rcu() testing.
4655 rcutorture.onoff_holdoff= [KNL]
4656 Set time (s) after boot for CPU-hotplug testing.
4658 rcutorture.onoff_interval= [KNL]
4659 Set time (jiffies) between CPU-hotplug operations,
4660 or zero to disable CPU-hotplug testing.
4662 rcutorture.read_exit= [KNL]
4663 Set the number of read-then-exit kthreads used
4664 to test the interaction of RCU updaters and
4665 task-exit processing.
4667 rcutorture.read_exit_burst= [KNL]
4668 The number of times in a given read-then-exit
4669 episode that a set of read-then-exit kthreads
4672 rcutorture.read_exit_delay= [KNL]
4673 The delay, in seconds, between successive
4674 read-then-exit testing episodes.
4676 rcutorture.shuffle_interval= [KNL]
4677 Set task-shuffle interval (s). Shuffling tasks
4678 allows some CPUs to go into dyntick-idle mode
4679 during the rcutorture test.
4681 rcutorture.shutdown_secs= [KNL]
4682 Set time (s) after boot system shutdown. This
4683 is useful for hands-off automated testing.
4685 rcutorture.stall_cpu= [KNL]
4686 Duration of CPU stall (s) to test RCU CPU stall
4687 warnings, zero to disable.
4689 rcutorture.stall_cpu_block= [KNL]
4690 Sleep while stalling if set. This will result
4691 in warnings from preemptible RCU in addition
4692 to any other stall-related activity.
4694 rcutorture.stall_cpu_holdoff= [KNL]
4695 Time to wait (s) after boot before inducing stall.
4697 rcutorture.stall_cpu_irqsoff= [KNL]
4698 Disable interrupts while stalling if set.
4700 rcutorture.stall_gp_kthread= [KNL]
4701 Duration (s) of forced sleep within RCU
4702 grace-period kthread to test RCU CPU stall
4703 warnings, zero to disable. If both stall_cpu
4704 and stall_gp_kthread are specified, the
4705 kthread is starved first, then the CPU.
4707 rcutorture.stat_interval= [KNL]
4708 Time (s) between statistics printk()s.
4710 rcutorture.stutter= [KNL]
4711 Time (s) to stutter testing, for example, specifying
4712 five seconds causes the test to run for five seconds,
4713 wait for five seconds, and so on. This tests RCU's
4714 ability to transition abruptly to and from idle.
4716 rcutorture.test_boost= [KNL]
4717 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4718 "Maybe" means test if the RCU implementation
4719 under test support RCU priority boosting.
4721 rcutorture.test_boost_duration= [KNL]
4722 Duration (s) of each individual boost test.
4724 rcutorture.test_boost_interval= [KNL]
4725 Interval (s) between each boost test.
4727 rcutorture.test_no_idle_hz= [KNL]
4728 Test RCU's dyntick-idle handling. See also the
4729 rcutorture.shuffle_interval parameter.
4731 rcutorture.torture_type= [KNL]
4732 Specify the RCU implementation to test.
4734 rcutorture.verbose= [KNL]
4735 Enable additional printk() statements.
4737 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
4738 Dump ftrace buffer after reporting RCU CPU
4741 rcupdate.rcu_cpu_stall_suppress= [KNL]
4742 Suppress RCU CPU stall warning messages.
4744 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
4745 Suppress RCU CPU stall warning messages and
4746 rcutorture writer stall warnings that occur
4747 during early boot, that is, during the time
4748 before the init task is spawned.
4750 rcupdate.rcu_cpu_stall_timeout= [KNL]
4751 Set timeout for RCU CPU stall warning messages.
4753 rcupdate.rcu_expedited= [KNL]
4754 Use expedited grace-period primitives, for
4755 example, synchronize_rcu_expedited() instead
4756 of synchronize_rcu(). This reduces latency,
4757 but can increase CPU utilization, degrade
4758 real-time latency, and degrade energy efficiency.
4759 No effect on CONFIG_TINY_RCU kernels.
4761 rcupdate.rcu_normal= [KNL]
4762 Use only normal grace-period primitives,
4763 for example, synchronize_rcu() instead of
4764 synchronize_rcu_expedited(). This improves
4765 real-time latency, CPU utilization, and
4766 energy efficiency, but can expose users to
4767 increased grace-period latency. This parameter
4768 overrides rcupdate.rcu_expedited. No effect on
4769 CONFIG_TINY_RCU kernels.
4771 rcupdate.rcu_normal_after_boot= [KNL]
4772 Once boot has completed (that is, after
4773 rcu_end_inkernel_boot() has been invoked), use
4774 only normal grace-period primitives. No effect
4775 on CONFIG_TINY_RCU kernels.
4777 But note that CONFIG_PREEMPT_RT=y kernels enables
4778 this kernel boot parameter, forcibly setting
4779 it to the value one, that is, converting any
4780 post-boot attempt at an expedited RCU grace
4781 period to instead use normal non-expedited
4782 grace-period processing.
4784 rcupdate.rcu_task_ipi_delay= [KNL]
4785 Set time in jiffies during which RCU tasks will
4786 avoid sending IPIs, starting with the beginning
4787 of a given grace period. Setting a large
4788 number avoids disturbing real-time workloads,
4789 but lengthens grace periods.
4791 rcupdate.rcu_task_stall_timeout= [KNL]
4792 Set timeout in jiffies for RCU task stall warning
4793 messages. Disable with a value less than or equal
4796 rcupdate.rcu_self_test= [KNL]
4797 Run the RCU early boot self tests
4801 Run specified binary instead of /init from the ramdisk,
4802 used for early userspace startup. See initrd.
4805 force - Override the decision by the kernel to hide the
4806 advertisement of RDRAND support (this affects
4807 certain AMD processors because of buggy BIOS
4808 support, specifically around the suspend/resume
4812 Turn on/off individual RDT features. List is:
4813 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
4815 E.g. to turn on cmt and turn off mba use:
4819 Format (x86 or x86_64):
4820 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \
4822 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
4824 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
4825 (prefix with 'panic_' to set mode for panic
4827 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
4828 reboot_force is either force or not specified,
4829 reboot_cpu is s[mp]#### with #### being the processor
4830 to be used for rebooting.
4832 refscale.holdoff= [KNL]
4833 Set test-start holdoff period. The purpose of
4834 this parameter is to delay the start of the
4835 test until boot completes in order to avoid
4838 refscale.loops= [KNL]
4839 Set the number of loops over the synchronization
4840 primitive under test. Increasing this number
4841 reduces noise due to loop start/end overhead,
4842 but the default has already reduced the per-pass
4843 noise to a handful of picoseconds on ca. 2020
4846 refscale.nreaders= [KNL]
4847 Set number of readers. The default value of -1
4848 selects N, where N is roughly 75% of the number
4849 of CPUs. A value of zero is an interesting choice.
4851 refscale.nruns= [KNL]
4852 Set number of runs, each of which is dumped onto
4855 refscale.readdelay= [KNL]
4856 Set the read-side critical-section duration,
4857 measured in microseconds.
4859 refscale.scale_type= [KNL]
4860 Specify the read-protection implementation to test.
4862 refscale.shutdown= [KNL]
4863 Shut down the system at the end of the performance
4864 test. This defaults to 1 (shut it down) when
4865 refscale is built into the kernel and to 0 (leave
4866 it running) when refscale is built as a module.
4868 refscale.verbose= [KNL]
4869 Enable additional printk() statements.
4871 refscale.verbose_batched= [KNL]
4872 Batch the additional printk() statements. If zero
4873 (the default) or negative, print everything. Otherwise,
4874 print every Nth verbose statement, where N is the value
4878 [KNL, SMP] Set scheduler's default relax_domain_level.
4879 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
4881 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
4882 Format: <base1>,<size1>[,<base2>,<size2>,...]
4883 Reserve I/O ports or memory so the kernel won't use
4884 them. If <base> is less than 0x10000, the region
4885 is assumed to be I/O ports; otherwise it is memory.
4887 reservetop= [X86-32]
4889 Reserves a hole at the top of the kernel virtual
4892 reset_devices [KNL] Force drivers to reset the underlying device
4893 during initialization.
4896 Specify the partition device for software suspend
4898 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
4900 resume_offset= [SWSUSP]
4901 Specify the offset from the beginning of the partition
4902 given by "resume=" at which the swap header is located,
4903 in <PAGE_SIZE> units (needed only for swap files).
4904 See Documentation/power/swsusp-and-swap-files.rst
4906 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
4907 read the resume files
4909 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
4910 Useful for devices that are detected asynchronously
4911 (e.g. USB and MMC devices).
4913 hibernate= [HIBERNATION]
4914 noresume Don't check if there's a hibernation image
4915 present during boot.
4916 nocompress Don't compress/decompress hibernation images.
4917 no Disable hibernation and resume.
4918 protect_image Turn on image protection during restoration
4919 (that will set all pages holding image data
4920 during restoration read-only).
4922 retain_initrd [RAM] Keep initrd memory after extraction
4924 rfkill.default_state=
4925 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
4926 etc. communication is blocked by default.
4929 rfkill.master_switch_mode=
4930 0 The "airplane mode" button does nothing.
4931 1 The "airplane mode" button toggles between everything
4932 blocked and the previous configuration.
4933 2 The "airplane mode" button toggles between everything
4934 blocked and everything unblocked.
4936 rhash_entries= [KNL,NET]
4937 Set number of hash buckets for route cache
4940 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4943 ro [KNL] Mount root device read-only on boot
4946 on Mark read-only kernel memory as read-only (default).
4947 off Leave read-only kernel memory writable for debugging.
4950 Enable the uart passthrough on the designated usb port
4951 on Rockchip SoCs. When active, the signals of the
4952 debug-uart get routed to the D+ and D- pins of the usb
4953 port and the regular usb controller gets disabled.
4955 root= [KNL] Root filesystem
4956 See name_to_dev_t comment in init/do_mounts.c.
4958 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4959 mount the root filesystem
4961 rootflags= [KNL] Set root filesystem mount option string
4963 rootfstype= [KNL] Set root filesystem type
4965 rootwait [KNL] Wait (indefinitely) for root device to show up.
4966 Useful for devices that are detected asynchronously
4967 (e.g. USB and MMC devices).
4969 rproc_mem=nn[KMG][@address]
4970 [KNL,ARM,CMA] Remoteproc physical memory block.
4971 Memory area to be used by remote processor image,
4974 rw [KNL] Mount root device read-write on boot
4976 S [KNL] Run init in single mode
4978 s390_iommu= [HW,S390]
4979 Set s390 IOTLB flushing mode
4981 With strict flushing every unmap operation will result in
4982 an IOTLB flush. Default is lazy flushing before reuse,
4986 See drivers/net/irda/sa1100_ir.c.
4988 sched_verbose [KNL] Enables verbose scheduler debug messages.
4990 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4991 Allowed values are enable and disable. This feature
4992 incurs a small amount of overhead in the scheduler
4993 but is useful for debugging and performance tuning.
4995 sched_thermal_decay_shift=
4996 [KNL, SMP] Set a decay shift for scheduler thermal
4997 pressure signal. Thermal pressure signal follows the
4998 default decay period of other scheduler pelt
4999 signals(usually 32 ms but configurable). Setting
5000 sched_thermal_decay_shift will left shift the decay
5001 period for the thermal pressure signal by the shift
5003 i.e. with the default pelt decay period of 32 ms
5004 sched_thermal_decay_shift thermal pressure decay pr
5008 Format: integer between 0 and 10
5011 scftorture.holdoff= [KNL]
5012 Number of seconds to hold off before starting
5013 test. Defaults to zero for module insertion and
5014 to 10 seconds for built-in smp_call_function()
5017 scftorture.longwait= [KNL]
5018 Request ridiculously long waits randomly selected
5019 up to the chosen limit in seconds. Zero (the
5020 default) disables this feature. Please note
5021 that requesting even small non-zero numbers of
5022 seconds can result in RCU CPU stall warnings,
5023 softlockup complaints, and so on.
5025 scftorture.nthreads= [KNL]
5026 Number of kthreads to spawn to invoke the
5027 smp_call_function() family of functions.
5028 The default of -1 specifies a number of kthreads
5029 equal to the number of CPUs.
5031 scftorture.onoff_holdoff= [KNL]
5032 Number seconds to wait after the start of the
5033 test before initiating CPU-hotplug operations.
5035 scftorture.onoff_interval= [KNL]
5036 Number seconds to wait between successive
5037 CPU-hotplug operations. Specifying zero (which
5038 is the default) disables CPU-hotplug operations.
5040 scftorture.shutdown_secs= [KNL]
5041 The number of seconds following the start of the
5042 test after which to shut down the system. The
5043 default of zero avoids shutting down the system.
5044 Non-zero values are useful for automated tests.
5046 scftorture.stat_interval= [KNL]
5047 The number of seconds between outputting the
5048 current test statistics to the console. A value
5049 of zero disables statistics output.
5051 scftorture.stutter_cpus= [KNL]
5052 The number of jiffies to wait between each change
5053 to the set of CPUs under test.
5055 scftorture.use_cpus_read_lock= [KNL]
5056 Use use_cpus_read_lock() instead of the default
5057 preempt_disable() to disable CPU hotplug
5058 while invoking one of the smp_call_function*()
5061 scftorture.verbose= [KNL]
5062 Enable additional printk() statements.
5064 scftorture.weight_single= [KNL]
5065 The probability weighting to use for the
5066 smp_call_function_single() function with a zero
5067 "wait" parameter. A value of -1 selects the
5068 default if all other weights are -1. However,
5069 if at least one weight has some other value, a
5070 value of -1 will instead select a weight of zero.
5072 scftorture.weight_single_wait= [KNL]
5073 The probability weighting to use for the
5074 smp_call_function_single() function with a
5075 non-zero "wait" parameter. See weight_single.
5077 scftorture.weight_many= [KNL]
5078 The probability weighting to use for the
5079 smp_call_function_many() function with a zero
5080 "wait" parameter. See weight_single.
5081 Note well that setting a high probability for
5082 this weighting can place serious IPI load
5085 scftorture.weight_many_wait= [KNL]
5086 The probability weighting to use for the
5087 smp_call_function_many() function with a
5088 non-zero "wait" parameter. See weight_single
5091 scftorture.weight_all= [KNL]
5092 The probability weighting to use for the
5093 smp_call_function_all() function with a zero
5094 "wait" parameter. See weight_single and
5097 scftorture.weight_all_wait= [KNL]
5098 The probability weighting to use for the
5099 smp_call_function_all() function with a
5100 non-zero "wait" parameter. See weight_single
5103 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
5104 xtime_lock contention on larger systems, and/or RCU lock
5105 contention on all systems with CONFIG_MAXSMP set.
5106 Format: { "0" | "1" }
5107 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
5109 Note: increases power consumption, thus should only be
5110 enabled if running jitter sensitive (HPC/RT) workloads.
5112 security= [SECURITY] Choose a legacy "major" security module to
5113 enable at boot. This has been deprecated by the
5116 selinux= [SELINUX] Disable or enable SELinux at boot time.
5117 Format: { "0" | "1" }
5118 See security/selinux/Kconfig help text.
5123 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
5124 Format: { "0" | "1" }
5125 See security/apparmor/Kconfig help text
5128 Default value is set via kernel config option.
5130 serialnumber [BUGS=X86-32]
5133 Maximal number of shapers.
5141 Enable merging of slabs with similar size when the
5142 kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
5145 Disable merging of slabs with similar size. May be
5146 necessary if there is some reason to distinguish
5147 allocs to different slabs, especially in hardened
5148 environments where the risk of heap overflows and
5149 layout control by attackers can usually be
5150 frustrated by disabling merging. This will reduce
5151 most of the exposure of a heap attack to a single
5152 cache (risks via metadata attacks are mostly
5153 unchanged). Debug options disable merging on their
5155 For more information see Documentation/vm/slub.rst.
5157 slab_max_order= [MM, SLAB]
5158 Determines the maximum allowed order for slabs.
5159 A high setting may cause OOMs due to memory
5160 fragmentation. Defaults to 1 for systems with
5161 more than 32MB of RAM, 0 otherwise.
5163 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB]
5164 Enabling slub_debug allows one to determine the
5165 culprit if slab objects become corrupted. Enabling
5166 slub_debug can create guard zones around objects and
5167 may poison objects when not in use. Also tracks the
5168 last alloc / free. For more information see
5169 Documentation/vm/slub.rst.
5171 slub_max_order= [MM, SLUB]
5172 Determines the maximum allowed order for slabs.
5173 A high setting may cause OOMs due to memory
5174 fragmentation. For more information see
5175 Documentation/vm/slub.rst.
5177 slub_min_objects= [MM, SLUB]
5178 The minimum number of objects per slab. SLUB will
5179 increase the slab order up to slub_max_order to
5180 generate a sufficiently large slab able to contain
5181 the number of objects indicated. The higher the number
5182 of objects the smaller the overhead of tracking slabs
5183 and the less frequently locks need to be acquired.
5184 For more information see Documentation/vm/slub.rst.
5186 slub_min_order= [MM, SLUB]
5187 Determines the minimum page order for slabs. Must be
5188 lower than slub_max_order.
5189 For more information see Documentation/vm/slub.rst.
5191 slub_merge [MM, SLUB]
5192 Same with slab_merge.
5194 slub_nomerge [MM, SLUB]
5195 Same with slab_nomerge. This is supported for legacy.
5196 See slab_nomerge for more information.
5199 Format: <io1>[,<io2>[,...,<io8>]]
5201 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
5202 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
5203 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
5204 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
5205 smsc-ircc2.ircc_irq= [HW] IRQ line
5206 smsc-ircc2.ircc_dma= [HW] DMA channel
5207 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
5208 0: Toshiba Satellite 1800 (GP data pin select)
5209 1: Fast pin select (default)
5212 smt [KNL,S390] Set the maximum number of threads (logical
5213 CPUs) to use per physical CPU on systems capable of
5214 symmetric multithreading (SMT). Will be capped to the
5215 actual hardware limit.
5217 Default: -1 (no limit)
5220 [KNL] Should the soft-lockup detector generate panics.
5223 A value of 1 instructs the soft-lockup detector
5224 to panic the machine when a soft-lockup occurs. It is
5225 also controlled by the kernel.softlockup_panic sysctl
5226 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
5227 respective build-time switch to that functionality.
5229 softlockup_all_cpu_backtrace=
5230 [KNL] Should the soft-lockup detector generate
5231 backtraces on all cpus.
5234 sonypi.*= [HW] Sony Programmable I/O Control Device driver
5235 See Documentation/admin-guide/laptops/sonypi.rst
5237 spectre_v2= [X86] Control mitigation of Spectre variant 2
5238 (indirect branch speculation) vulnerability.
5239 The default operation protects the kernel from
5242 on - unconditionally enable, implies
5244 off - unconditionally disable, implies
5246 auto - kernel detects whether your CPU model is
5249 Selecting 'on' will, and 'auto' may, choose a
5250 mitigation method at run time according to the
5251 CPU, the available microcode, the setting of the
5252 CONFIG_RETPOLINE configuration option, and the
5253 compiler with which the kernel was built.
5255 Selecting 'on' will also enable the mitigation
5256 against user space to user space task attacks.
5258 Selecting 'off' will disable both the kernel and
5259 the user space protections.
5261 Specific mitigations can also be selected manually:
5263 retpoline - replace indirect branches
5264 retpoline,generic - google's original retpoline
5265 retpoline,amd - AMD-specific minimal thunk
5267 Not specifying this option is equivalent to
5271 [X86] Control mitigation of Spectre variant 2
5272 (indirect branch speculation) vulnerability between
5275 on - Unconditionally enable mitigations. Is
5276 enforced by spectre_v2=on
5278 off - Unconditionally disable mitigations. Is
5279 enforced by spectre_v2=off
5281 prctl - Indirect branch speculation is enabled,
5282 but mitigation can be enabled via prctl
5283 per thread. The mitigation control state
5284 is inherited on fork.
5287 - Like "prctl" above, but only STIBP is
5288 controlled per thread. IBPB is issued
5289 always when switching between different user
5293 - Same as "prctl" above, but all seccomp
5294 threads will enable the mitigation unless
5295 they explicitly opt out.
5298 - Like "seccomp" above, but only STIBP is
5299 controlled per thread. IBPB is issued
5300 always when switching between different
5301 user space processes.
5303 auto - Kernel selects the mitigation depending on
5304 the available CPU features and vulnerability.
5307 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
5309 Not specifying this option is equivalent to
5310 spectre_v2_user=auto.
5312 spec_store_bypass_disable=
5313 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
5314 (Speculative Store Bypass vulnerability)
5316 Certain CPUs are vulnerable to an exploit against a
5317 a common industry wide performance optimization known
5318 as "Speculative Store Bypass" in which recent stores
5319 to the same memory location may not be observed by
5320 later loads during speculative execution. The idea
5321 is that such stores are unlikely and that they can
5322 be detected prior to instruction retirement at the
5323 end of a particular speculation execution window.
5325 In vulnerable processors, the speculatively forwarded
5326 store can be used in a cache side channel attack, for
5327 example to read memory to which the attacker does not
5328 directly have access (e.g. inside sandboxed code).
5330 This parameter controls whether the Speculative Store
5331 Bypass optimization is used.
5333 On x86 the options are:
5335 on - Unconditionally disable Speculative Store Bypass
5336 off - Unconditionally enable Speculative Store Bypass
5337 auto - Kernel detects whether the CPU model contains an
5338 implementation of Speculative Store Bypass and
5339 picks the most appropriate mitigation. If the
5340 CPU is not vulnerable, "off" is selected. If the
5341 CPU is vulnerable the default mitigation is
5342 architecture and Kconfig dependent. See below.
5343 prctl - Control Speculative Store Bypass per thread
5344 via prctl. Speculative Store Bypass is enabled
5345 for a process by default. The state of the control
5346 is inherited on fork.
5347 seccomp - Same as "prctl" above, but all seccomp threads
5348 will disable SSB unless they explicitly opt out.
5350 Default mitigations:
5351 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
5353 On powerpc the options are:
5355 on,auto - On Power8 and Power9 insert a store-forwarding
5356 barrier on kernel entry and exit. On Power7
5357 perform a software flush on kernel entry and
5361 Not specifying this option is equivalent to
5362 spec_store_bypass_disable=auto.
5364 spia_io_base= [HW,MTD]
5370 [X86] Enable split lock detection or bus lock detection
5372 When enabled (and if hardware support is present), atomic
5373 instructions that access data across cache line
5374 boundaries will result in an alignment check exception
5375 for split lock detection or a debug exception for
5380 warn - the kernel will emit rate-limited warnings
5381 about applications triggering the #AC
5382 exception or the #DB exception. This mode is
5383 the default on CPUs that support split lock
5384 detection or bus lock detection. Default
5385 behavior is by #AC if both features are
5386 enabled in hardware.
5388 fatal - the kernel will send SIGBUS to applications
5389 that trigger the #AC exception or the #DB
5390 exception. Default behavior is by #AC if
5391 both features are enabled in hardware.
5394 Set system wide rate limit to N bus locks
5395 per second for bus lock detection.
5398 N/A for split lock detection.
5401 If an #AC exception is hit in the kernel or in
5402 firmware (i.e. not while executing in user mode)
5403 the kernel will oops in either "warn" or "fatal"
5406 #DB exception for bus lock is triggered only when
5410 Control the Special Register Buffer Data Sampling
5413 Certain CPUs are vulnerable to an MDS-like
5414 exploit which can leak bits from the random
5417 By default, this issue is mitigated by
5418 microcode. However, the microcode fix can cause
5419 the RDRAND and RDSEED instructions to become
5420 much slower. Among other effects, this will
5421 result in reduced throughput from /dev/urandom.
5423 The microcode mitigation can be disabled with
5424 the following option:
5426 off: Disable mitigation and remove
5427 performance impact to RDRAND and RDSEED
5429 srcutree.counter_wrap_check [KNL]
5430 Specifies how frequently to check for
5431 grace-period sequence counter wrap for the
5432 srcu_data structure's ->srcu_gp_seq_needed field.
5433 The greater the number of bits set in this kernel
5434 parameter, the less frequently counter wrap will
5435 be checked for. Note that the bottom two bits
5438 srcutree.exp_holdoff [KNL]
5439 Specifies how many nanoseconds must elapse
5440 since the end of the last SRCU grace period for
5441 a given srcu_struct until the next normal SRCU
5442 grace period will be considered for automatic
5443 expediting. Set to zero to disable automatic
5447 Speculative Store Bypass Disable control
5449 On CPUs that are vulnerable to the Speculative
5450 Store Bypass vulnerability and offer a
5451 firmware based mitigation, this parameter
5452 indicates how the mitigation should be used:
5454 force-on: Unconditionally enable mitigation for
5455 for both kernel and userspace
5456 force-off: Unconditionally disable mitigation for
5457 for both kernel and userspace
5458 kernel: Always enable mitigation in the
5459 kernel, and offer a prctl interface
5460 to allow userspace to register its
5461 interest in being mitigated too.
5463 stack_guard_gap= [MM]
5464 override the default stack gap protection. The value
5465 is in page units and it defines how many pages prior
5466 to (for stacks growing down) resp. after (for stacks
5467 growing up) the main stack are reserved for no other
5468 mapping. Default value is 256 pages.
5470 stack_depot_disable= [KNL]
5471 Setting this to true through kernel command line will
5472 disable the stack depot thereby saving the static memory
5473 consumed by the stack hash table. By default this is set
5477 Enabled the stack tracer on boot up.
5479 stacktrace_filter=[function-list]
5480 [FTRACE] Limit the functions that the stack tracer
5481 will trace at boot up. function-list is a comma-separated
5482 list of functions. This list can be changed at run
5483 time by the stack_trace_filter file in the debugfs
5484 tracing directory. Note, this enables stack tracing
5485 and the stacktrace above is not needed.
5489 Set the STI (builtin display/keyboard on the HP-PARISC
5490 machines) console (graphic card) which should be used
5491 as the initial boot-console.
5492 See also comment in drivers/video/console/sticore.c.
5495 See comment in drivers/video/console/sticore.c.
5498 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
5500 sunrpc.min_resvport=
5501 sunrpc.max_resvport=
5503 SunRPC servers often require that client requests
5504 originate from a privileged port (i.e. a port in the
5505 range 0 < portnr < 1024).
5506 An administrator who wishes to reserve some of these
5507 ports for other uses may adjust the range that the
5508 kernel's sunrpc client considers to be privileged
5509 using these two parameters to set the minimum and
5510 maximum port values.
5512 sunrpc.svc_rpc_per_connection_limit=
5514 Limit the number of requests that the server will
5515 process in parallel from a single connection.
5516 The default value is 0 (no limit).
5520 Control how the NFS server code allocates CPUs to
5521 service thread pools. Depending on how many NICs
5522 you have and where their interrupts are bound, this
5523 option will affect which CPUs will do NFS serving.
5524 Note: this parameter cannot be changed while the
5525 NFS server is running.
5527 auto the server chooses an appropriate mode
5528 automatically using heuristics
5529 global a single global pool contains all CPUs
5530 percpu one pool for each CPU
5531 pernode one pool for each NUMA node (equivalent
5532 to global on non-NUMA machines)
5534 sunrpc.tcp_slot_table_entries=
5535 sunrpc.udp_slot_table_entries=
5537 Sets the upper limit on the number of simultaneous
5538 RPC calls that can be sent from the client to a
5539 server. Increasing these values may allow you to
5540 improve throughput, but will also increase the
5541 amount of memory reserved for use by the client.
5543 suspend.pm_test_delay=
5545 Sets the number of seconds to remain in a suspend test
5546 mode before resuming the system (see
5547 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
5548 is set. Default value is 5.
5551 Format: { on | off | y | n | 1 | 0 }
5552 This parameter controls use of the Protected
5553 Execution Facility on pSeries.
5556 [KNL] Enable accounting of swap in memory resource
5557 controller if no parameter or 1 is given or disable
5558 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
5560 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
5561 Format: { <int> | force | noforce }
5562 <int> -- Number of I/O TLB slabs
5563 force -- force using of bounce buffers even if they
5564 wouldn't be automatically used by the kernel
5565 noforce -- Never use bounce buffers (for debugging)
5570 Set a sysctl parameter, right before loading the init
5571 process, as if the value was written to the respective
5572 /proc/sys/... file. Both '.' and '/' are recognized as
5573 separators. Unrecognized parameters and invalid values
5574 are reported in the kernel log. Sysctls registered
5575 later by a loaded module cannot be set this way.
5576 Example: sysctl.vm.swappiness=40
5578 sysfs.deprecated=0|1 [KNL]
5579 Enable/disable old style sysfs layout for old udev
5580 on older distributions. When this option is enabled
5581 very new udev will not work anymore. When this option
5582 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
5583 in older udev will not work anymore.
5584 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
5585 the kernel configuration.
5587 sysrq_always_enabled
5589 Ignore sysrq setting - this boot parameter will
5590 neutralize any effect of /proc/sys/kernel/sysrq.
5591 Useful for debugging.
5593 tcpmhash_entries= [KNL,NET]
5594 Set the number of tcp_metrics_hash slots.
5595 Default value is 8192 or 16384 depending on total
5596 ram pages. This is used to specify the TCP metrics
5597 cache size. See Documentation/networking/ip-sysctl.rst
5598 "tcp_no_metrics_save" section for more details.
5602 test_suspend= [SUSPEND][,N]
5603 Specify "mem" (for Suspend-to-RAM) or "standby" (for
5604 standby suspend) or "freeze" (for suspend type freeze)
5605 as the system sleep state during system startup with
5606 the optional capability to repeat N number of times.
5607 The system is woken from this state using a
5608 wakeup-capable RTC alarm.
5610 thash_entries= [KNL,NET]
5611 Set number of hash buckets for TCP connection
5613 thermal.act= [HW,ACPI]
5614 -1: disable all active trip points in all thermal zones
5615 <degrees C>: override all lowest active trip points
5617 thermal.crt= [HW,ACPI]
5618 -1: disable all critical trip points in all thermal zones
5619 <degrees C>: override all critical trip points
5621 thermal.nocrt= [HW,ACPI]
5622 Set to disable actions on ACPI thermal zone
5623 critical and hot trip points.
5625 thermal.off= [HW,ACPI]
5626 1: disable ACPI thermal control
5628 thermal.psv= [HW,ACPI]
5629 -1: disable all passive trip points
5630 <degrees C>: override all passive trip points to this
5633 thermal.tzp= [HW,ACPI]
5634 Specify global default ACPI thermal zone polling rate
5635 <deci-seconds>: poll all this frequency
5636 0: no polling (default)
5639 Force threading of all interrupt handlers except those
5640 marked explicitly IRQF_NO_THREAD.
5644 Specify if the kernel should make use of the cpu
5645 topology information if the hardware supports this.
5646 The scheduler will make use of this information and
5647 e.g. base its process migration decisions on it.
5650 topology_updates= [KNL, PPC, NUMA]
5652 Specify if the kernel should ignore (off)
5653 topology updates sent by the hypervisor to this
5656 torture.disable_onoff_at_boot= [KNL]
5657 Prevent the CPU-hotplug component of torturing
5658 until after init has spawned.
5660 torture.ftrace_dump_at_shutdown= [KNL]
5661 Dump the ftrace buffer at torture-test shutdown,
5662 even if there were no errors. This can be a
5663 very costly operation when many torture tests
5664 are running concurrently, especially on systems
5665 with rotating-rust storage.
5667 torture.verbose_sleep_frequency= [KNL]
5668 Specifies how many verbose printk()s should be
5669 emitted between each sleep. The default of zero
5670 disables verbose-printk() sleeping.
5672 torture.verbose_sleep_duration= [KNL]
5673 Duration of each verbose-printk() sleep in jiffies.
5677 tpm_suspend_pcr=[HW,TPM]
5678 Format: integer pcr id
5679 Specify that at suspend time, the tpm driver
5680 should extend the specified pcr with zeros,
5681 as a workaround for some chips which fail to
5682 flush the last written pcr on TPM_SaveState.
5683 This will guarantee that all the other pcrs
5686 trace_buf_size=nn[KMG]
5687 [FTRACE] will set tracing buffer size on each cpu.
5689 trace_event=[event-list]
5690 [FTRACE] Set and start specified trace events in order
5691 to facilitate early boot debugging. The event-list is a
5692 comma-separated list of trace events to enable. See
5693 also Documentation/trace/events.rst
5695 trace_options=[option-list]
5696 [FTRACE] Enable or disable tracer options at boot.
5697 The option-list is a comma delimited list of options
5698 that can be enabled or disabled just as if you were
5699 to echo the option name into
5701 /sys/kernel/debug/tracing/trace_options
5703 For example, to enable stacktrace option (to dump the
5704 stack trace of each event), add to the command line:
5706 trace_options=stacktrace
5708 See also Documentation/trace/ftrace.rst "trace options"
5712 Have the tracepoints sent to printk as well as the
5713 tracing ring buffer. This is useful for early boot up
5714 where the system hangs or reboots and does not give the
5715 option for reading the tracing buffer or performing a
5716 ftrace_dump_on_oops.
5718 To turn off having tracepoints sent to printk,
5719 echo 0 > /proc/sys/kernel/tracepoint_printk
5720 Note, echoing 1 into this file without the
5721 tracepoint_printk kernel cmdline option has no effect.
5723 The tp_printk_stop_on_boot (see below) can also be used
5724 to stop the printing of events to console at
5729 Having tracepoints sent to printk() and activating high
5730 frequency tracepoints such as irq or sched, can cause
5731 the system to live lock.
5733 tp_printk_stop_on_boot[FTRACE]
5734 When tp_printk (above) is set, it can cause a lot of noise
5735 on the console. It may be useful to only include the
5736 printing of events during boot up, as user space may
5737 make the system inoperable.
5739 This command line option will stop the printing of events
5740 to console at the late_initcall_sync() time frame.
5743 [FTRACE] enable this option to disable tracing when a
5744 warning is hit. This turns off "tracing_on". Tracing can
5745 be enabled again by echoing '1' into the "tracing_on"
5746 file located in /sys/kernel/debug/tracing/
5748 This option is useful, as it disables the trace before
5749 the WARNING dump is called, which prevents the trace to
5750 be filled with content caused by the warning output.
5752 This option can also be set at run time via the sysctl
5753 option: kernel/traceoff_on_warning
5755 transparent_hugepage=
5757 Format: [always|madvise|never]
5758 Can be used to control the default behavior of the system
5759 with respect to transparent hugepages.
5760 See Documentation/admin-guide/mm/transhuge.rst
5763 trusted.source= [KEYS]
5765 This parameter identifies the trust source as a backend
5766 for trusted keys implementation. Supported trust
5770 If not specified then it defaults to iterating through
5771 the trust source list starting with TPM and assigns the
5772 first trust source as a backend which is initialized
5773 successfully during iteration.
5775 tsc= Disable clocksource stability checks for TSC.
5777 [x86] reliable: mark tsc clocksource as reliable, this
5778 disables clocksource verification at runtime, as well
5779 as the stability checks done at bootup. Used to enable
5780 high-resolution timer mode on older hardware, and in
5781 virtualized environment.
5782 [x86] noirqtime: Do not use TSC to do irq accounting.
5783 Used to run time disable IRQ_TIME_ACCOUNTING on any
5784 platforms where RDTSC is slow and this accounting
5786 [x86] unstable: mark the TSC clocksource as unstable, this
5787 marks the TSC unconditionally unstable at bootup and
5788 avoids any further wobbles once the TSC watchdog notices.
5789 [x86] nowatchdog: disable clocksource watchdog. Used
5790 in situations with strict latency requirements (where
5791 interruptions from clocksource watchdog are not
5794 tsc_early_khz= [X86] Skip early TSC calibration and use the given
5795 value instead. Useful when the early TSC frequency discovery
5796 procedure is not reliable, such as on overclocked systems
5797 with CPUID.16h support and partial CPUID.15h support.
5798 Format: <unsigned int>
5800 tsx= [X86] Control Transactional Synchronization
5801 Extensions (TSX) feature in Intel processors that
5802 support TSX control.
5804 This parameter controls the TSX feature. The options are:
5806 on - Enable TSX on the system. Although there are
5807 mitigations for all known security vulnerabilities,
5808 TSX has been known to be an accelerator for
5809 several previous speculation-related CVEs, and
5810 so there may be unknown security risks associated
5811 with leaving it enabled.
5813 off - Disable TSX on the system. (Note that this
5814 option takes effect only on newer CPUs which are
5815 not vulnerable to MDS, i.e., have
5816 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
5817 the new IA32_TSX_CTRL MSR through a microcode
5818 update. This new MSR allows for the reliable
5819 deactivation of the TSX functionality.)
5821 auto - Disable TSX if X86_BUG_TAA is present,
5822 otherwise enable TSX on the system.
5824 Not specifying this option is equivalent to tsx=off.
5826 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5829 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
5830 Abort (TAA) vulnerability.
5832 Similar to Micro-architectural Data Sampling (MDS)
5833 certain CPUs that support Transactional
5834 Synchronization Extensions (TSX) are vulnerable to an
5835 exploit against CPU internal buffers which can forward
5836 information to a disclosure gadget under certain
5839 In vulnerable processors, the speculatively forwarded
5840 data can be used in a cache side channel attack, to
5841 access data to which the attacker does not have direct
5844 This parameter controls the TAA mitigation. The
5847 full - Enable TAA mitigation on vulnerable CPUs
5850 full,nosmt - Enable TAA mitigation and disable SMT on
5851 vulnerable CPUs. If TSX is disabled, SMT
5852 is not disabled because CPU is not
5853 vulnerable to cross-thread TAA attacks.
5854 off - Unconditionally disable TAA mitigation
5856 On MDS-affected machines, tsx_async_abort=off can be
5857 prevented by an active MDS mitigation as both vulnerabilities
5858 are mitigated with the same mechanism so in order to disable
5859 this mitigation, you need to specify mds=off too.
5861 Not specifying this option is equivalent to
5862 tsx_async_abort=full. On CPUs which are MDS affected
5863 and deploy MDS mitigation, TAA mitigation is not
5864 required and doesn't provide any additional
5868 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
5870 turbografx.map[2|3]= [HW,JOY]
5871 TurboGraFX parallel port interface
5873 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
5874 See also Documentation/input/devices/joystick-parport.rst
5876 udbg-immortal [PPC] When debugging early kernel crashes that
5877 happen after console_init() and before a proper
5878 console driver takes over, this boot options might
5879 help "seeing" what's going on.
5881 uhash_entries= [KNL,NET]
5882 Set number of hash buckets for UDP/UDP-Lite connections
5885 [USB] Ignore overcurrent events (default N).
5886 Some badly-designed motherboards generate lots of
5887 bogus events, for ports that aren't wired to
5888 anything. Set this parameter to avoid log spamming.
5889 Note that genuine overcurrent events won't be
5893 [X86] Cause panic on unknown NMI.
5895 usbcore.authorized_default=
5896 [USB] Default USB device authorization:
5897 (default -1 = authorized except for wireless USB,
5898 0 = not authorized, 1 = authorized, 2 = authorized
5899 if device connected to internal port)
5901 usbcore.autosuspend=
5902 [USB] The autosuspend time delay (in seconds) used
5903 for newly-detected USB devices (default 2). This
5904 is the time required before an idle device will be
5905 autosuspended. Devices for which the delay is set
5906 to a negative value won't be autosuspended at all.
5908 usbcore.usbfs_snoop=
5909 [USB] Set to log all usbfs traffic (default 0 = off).
5911 usbcore.usbfs_snoop_max=
5912 [USB] Maximum number of bytes to snoop in each URB
5915 usbcore.blinkenlights=
5916 [USB] Set to cycle leds on hubs (default 0 = off).
5918 usbcore.old_scheme_first=
5919 [USB] Start with the old device initialization
5920 scheme (default 0 = off).
5922 usbcore.usbfs_memory_mb=
5923 [USB] Memory limit (in MB) for buffers allocated by
5924 usbfs (default = 16, 0 = max = 2047).
5926 usbcore.use_both_schemes=
5927 [USB] Try the other device initialization scheme
5928 if the first one fails (default 1 = enabled).
5930 usbcore.initial_descriptor_timeout=
5931 [USB] Specifies timeout for the initial 64-byte
5932 USB_REQ_GET_DESCRIPTOR request in milliseconds
5933 (default 5000 = 5.0 seconds).
5935 usbcore.nousb [USB] Disable the USB subsystem
5938 [USB] A list of quirk entries to augment the built-in
5939 usb core quirk list. List entries are separated by
5940 commas. Each entry has the form
5941 VendorID:ProductID:Flags. The IDs are 4-digit hex
5942 numbers and Flags is a set of letters. Each letter
5943 will change the built-in quirk; setting it if it is
5944 clear and clearing it if it is set. The letters have
5945 the following meanings:
5946 a = USB_QUIRK_STRING_FETCH_255 (string
5947 descriptors must not be fetched using
5949 b = USB_QUIRK_RESET_RESUME (device can't resume
5950 correctly so reset it instead);
5951 c = USB_QUIRK_NO_SET_INTF (device can't handle
5952 Set-Interface requests);
5953 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
5954 handle its Configuration or Interface
5956 e = USB_QUIRK_RESET (device can't be reset
5957 (e.g morph devices), don't use reset);
5958 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
5959 more interface descriptions than the
5960 bNumInterfaces count, and can't handle
5961 talking to these interfaces);
5962 g = USB_QUIRK_DELAY_INIT (device needs a pause
5963 during initialization, after we read
5964 the device descriptor);
5965 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
5966 high speed and super speed interrupt
5967 endpoints, the USB 2.0 and USB 3.0 spec
5968 require the interval in microframes (1
5969 microframe = 125 microseconds) to be
5970 calculated as interval = 2 ^
5972 Devices with this quirk report their
5973 bInterval as the result of this
5974 calculation instead of the exponent
5975 variable used in the calculation);
5976 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
5977 handle device_qualifier descriptor
5979 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
5980 generates spurious wakeup, ignore
5981 remote wakeup capability);
5982 k = USB_QUIRK_NO_LPM (device can't handle Link
5984 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
5985 (Device reports its bInterval as linear
5986 frames instead of the USB 2.0
5988 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
5989 to be disconnected before suspend to
5990 prevent spurious wakeup);
5991 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
5992 pause after every control message);
5993 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
5994 delay after resetting its port);
5995 Example: quirks=0781:5580:bk,0a5c:5834:gij
5998 [USBHID] The interval which mice are to be polled at.
6001 [USBHID] The interval which joysticks are to be polled at.
6004 [USBHID] The interval which keyboards are to be polled at.
6006 usb-storage.delay_use=
6007 [UMS] The delay in seconds before a new device is
6008 scanned for Logical Units (default 1).
6011 [UMS] A list of quirks entries to supplement or
6012 override the built-in unusual_devs list. List
6013 entries are separated by commas. Each entry has
6014 the form VID:PID:Flags where VID and PID are Vendor
6015 and Product ID values (4-digit hex numbers) and
6016 Flags is a set of characters, each corresponding
6017 to a common usb-storage quirk flag as follows:
6018 a = SANE_SENSE (collect more than 18 bytes
6019 of sense data, not on uas);
6020 b = BAD_SENSE (don't collect more than 18
6021 bytes of sense data, not on uas);
6022 c = FIX_CAPACITY (decrease the reported
6023 device capacity by one sector);
6024 d = NO_READ_DISC_INFO (don't use
6025 READ_DISC_INFO command, not on uas);
6026 e = NO_READ_CAPACITY_16 (don't use
6027 READ_CAPACITY_16 command);
6028 f = NO_REPORT_OPCODES (don't use report opcodes
6030 g = MAX_SECTORS_240 (don't transfer more than
6031 240 sectors at a time, uas only);
6032 h = CAPACITY_HEURISTICS (decrease the
6033 reported device capacity by one
6034 sector if the number is odd);
6035 i = IGNORE_DEVICE (don't bind to this
6037 j = NO_REPORT_LUNS (don't use report luns
6039 k = NO_SAME (do not use WRITE_SAME, uas only)
6040 l = NOT_LOCKABLE (don't try to lock and
6041 unlock ejectable media, not on uas);
6042 m = MAX_SECTORS_64 (don't transfer more
6043 than 64 sectors = 32 KB at a time,
6045 n = INITIAL_READ10 (force a retry of the
6046 initial READ(10) command, not on uas);
6047 o = CAPACITY_OK (accept the capacity
6048 reported by the device, not on uas);
6049 p = WRITE_CACHE (the device cache is ON
6050 by default, not on uas);
6051 r = IGNORE_RESIDUE (the device reports
6052 bogus residue values, not on uas);
6053 s = SINGLE_LUN (the device has only one
6055 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
6056 commands, uas only);
6057 u = IGNORE_UAS (don't bind to the uas driver);
6058 w = NO_WP_DETECT (don't test whether the
6059 medium is write-protected).
6060 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
6061 even if the device claims no cache,
6063 Example: quirks=0419:aaf5:rl,0421:0433:rc
6065 user_debug= [KNL,ARM]
6067 See arch/arm/Kconfig.debug help text.
6068 1 - undefined instruction events
6070 4 - invalid data aborts
6073 Example: user_debug=31
6076 [X86] Flags controlling user PTE allocations.
6078 nohigh = do not allocate PTE pages in
6079 HIGHMEM regardless of setting
6083 On X86_32, this is an alias for vdso32=. Otherwise:
6085 vdso=1: enable VDSO (the default)
6086 vdso=0: disable VDSO mapping
6088 vdso32= [X86] Control the 32-bit vDSO
6089 vdso32=1: enable 32-bit VDSO
6090 vdso32=0 or vdso32=2: disable 32-bit VDSO
6092 See the help text for CONFIG_COMPAT_VDSO for more
6093 details. If CONFIG_COMPAT_VDSO is set, the default is
6094 vdso32=0; otherwise, the default is vdso32=1.
6096 For compatibility with older kernels, vdso32=2 is an
6099 Try vdso32=0 if you encounter an error that says:
6100 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
6103 vector=percpu: enable percpu vector domain
6105 video= [FB] Frame buffer configuration
6106 See Documentation/fb/modedb.rst.
6108 video.brightness_switch_enabled= [0,1]
6109 If set to 1, on receiving an ACPI notify event
6110 generated by hotkey, video driver will adjust brightness
6111 level and then send out the event to user space through
6112 the allocated input device; If set to 0, video driver
6113 will only send out the event without touching backlight
6118 [VMMIO] Memory mapped virtio (platform) device.
6120 <size>@<baseaddr>:<irq>[:<id>]
6122 <size> := size (can use standard suffixes
6124 <baseaddr> := physical base address
6125 <irq> := interrupt number (as passed to
6127 <id> := (optional) platform device id
6129 virtio_mmio.device=1K@0x100b0000:48:7
6131 Can be used multiple times for multiple devices.
6133 vga= [BOOT,X86-32] Select a particular video mode
6134 See Documentation/x86/boot.rst and
6135 Documentation/admin-guide/svga.rst.
6136 Use vga=ask for menu.
6137 This is actually a boot loader parameter; the value is
6138 passed to the kernel using a special protocol.
6140 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
6141 May slow down system boot speed, especially when
6142 enabled on systems with a large amount of memory.
6143 All options are enabled by default, and this
6144 interface is meant to allow for selectively
6145 enabling or disabling specific virtual memory
6148 Available options are:
6149 P Enable page structure init time poisoning
6150 - Disable all of the above options
6152 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
6153 size of <nn>. This can be used to increase the
6154 minimum size (128MB on x86). It can also be used to
6155 decrease the size and leave more room for directly
6158 vmcp_cma=nn[MG] [KNL,S390]
6159 Sets the memory size reserved for contiguous memory
6160 allocations for the vmcp device driver.
6162 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
6165 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
6168 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
6172 Controls the behavior of vsyscalls (i.e. calls to
6173 fixed addresses of 0xffffffffff600x00 from legacy
6174 code). Most statically-linked binaries and older
6175 versions of glibc use these calls. Because these
6176 functions are at fixed addresses, they make nice
6177 targets for exploits that can control RIP.
6179 emulate [default] Vsyscalls turn into traps and are
6180 emulated reasonably safely. The vsyscall
6183 xonly Vsyscalls turn into traps and are
6184 emulated reasonably safely. The vsyscall
6185 page is not readable.
6187 none Vsyscalls don't work at all. This makes
6188 them quite hard to use for exploits but
6189 might break your system.
6191 vt.color= [VT] Default text color.
6192 Format: 0xYX, X = foreground, Y = background.
6193 Default: 0x07 = light gray on black.
6195 vt.cur_default= [VT] Default cursor shape.
6196 Format: 0xCCBBAA, where AA, BB, and CC are the same as
6197 the parameters of the <Esc>[?A;B;Cc escape sequence;
6198 see VGA-softcursor.txt. Default: 2 = underline.
6200 vt.default_blu= [VT]
6201 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
6202 Change the default blue palette of the console.
6203 This is a 16-member array composed of values
6206 vt.default_grn= [VT]
6207 Format: <green0>,<green1>,<green2>,...,<green15>
6208 Change the default green palette of the console.
6209 This is a 16-member array composed of values
6212 vt.default_red= [VT]
6213 Format: <red0>,<red1>,<red2>,...,<red15>
6214 Change the default red palette of the console.
6215 This is a 16-member array composed of values
6221 Set system-wide default UTF-8 mode for all tty's.
6222 Default is 1, i.e. UTF-8 mode is enabled for all
6223 newly opened terminals.
6225 vt.global_cursor_default=
6228 Set system-wide default for whether a cursor
6229 is shown on new VTs. Default is -1,
6230 i.e. cursors will be created by default unless
6231 overridden by individual drivers. 0 will hide
6232 cursors, 1 will display them.
6234 vt.italic= [VT] Default color for italic text; 0-15.
6237 vt.underline= [VT] Default color for underlined text; 0-15.
6240 watchdog timers [HW,WDT] For information on watchdog timers,
6241 see Documentation/watchdog/watchdog-parameters.rst
6242 or other driver-specific files in the
6243 Documentation/watchdog/ directory.
6247 Set the hard lockup detector stall duration
6248 threshold in seconds. The soft lockup detector
6249 threshold is set to twice the value. A value of 0
6250 disables both lockup detectors. Default is 10
6253 workqueue.watchdog_thresh=
6254 If CONFIG_WQ_WATCHDOG is configured, workqueue can
6255 warn stall conditions and dump internal state to
6256 help debugging. 0 disables workqueue stall
6257 detection; otherwise, it's the stall threshold
6258 duration in seconds. The default value is 30 and
6259 it can be updated at runtime by writing to the
6260 corresponding sysfs file.
6262 workqueue.disable_numa
6263 By default, all work items queued to unbound
6264 workqueues are affine to the NUMA nodes they're
6265 issued on, which results in better behavior in
6266 general. If NUMA affinity needs to be disabled for
6267 whatever reason, this option can be used. Note
6268 that this also can be controlled per-workqueue for
6269 workqueues visible under /sys/bus/workqueue/.
6271 workqueue.power_efficient
6272 Per-cpu workqueues are generally preferred because
6273 they show better performance thanks to cache
6274 locality; unfortunately, per-cpu workqueues tend to
6275 be more power hungry than unbound workqueues.
6277 Enabling this makes the per-cpu workqueues which
6278 were observed to contribute significantly to power
6279 consumption unbound, leading to measurably lower
6280 power usage at the cost of small performance
6283 The default value of this parameter is determined by
6284 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
6286 workqueue.debug_force_rr_cpu
6287 Workqueue used to implicitly guarantee that work
6288 items queued without explicit CPU specified are put
6289 on the local CPU. This guarantee is no longer true
6290 and while local CPU is still preferred work items
6291 may be put on foreign CPUs. This debug option
6292 forces round-robin CPU selection to flush out
6293 usages which depend on the now broken guarantee.
6294 When enabled, memory and cache locality will be
6297 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
6298 default x2apic cluster mode on platforms
6301 xen_512gb_limit [KNL,X86-64,XEN]
6302 Restricts the kernel running paravirtualized under Xen
6303 to use only up to 512 GB of RAM. The reason to do so is
6304 crash analysis tools and Xen tools for doing domain
6305 save/restore/migration must be enabled to handle larger
6308 xen_emul_unplug= [HW,X86,XEN]
6309 Unplug Xen emulated devices
6310 Format: [unplug0,][unplug1]
6311 ide-disks -- unplug primary master IDE devices
6312 aux-ide-disks -- unplug non-primary-master IDE devices
6313 nics -- unplug network devices
6314 all -- unplug all emulated devices (NICs and IDE disks)
6315 unnecessary -- unplugging emulated devices is
6316 unnecessary even if the host did not respond to
6318 never -- do not unplug even if version check succeeds
6320 xen_legacy_crash [X86,XEN]
6321 Crash from Xen panic notifier, without executing late
6322 panic() code such as dumping handler.
6324 xen_nopvspin [X86,XEN]
6325 Disables the qspinlock slowpath using Xen PV optimizations.
6326 This parameter is obsoleted by "nopvspin" parameter, which
6327 has equivalent effect for XEN platform.
6330 Disables the PV optimizations forcing the HVM guest to
6331 run as generic HVM guest with no PV drivers.
6332 This option is obsoleted by the "nopv" option, which
6333 has equivalent effect for XEN platform.
6335 xen_no_vector_callback
6336 [KNL,X86,XEN] Disable the vector callback for Xen
6337 event channel interrupts.
6339 xen_scrub_pages= [XEN]
6340 Boolean option to control scrubbing pages before giving them back
6341 to Xen, for use by other domains. Can be also changed at runtime
6342 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
6343 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
6345 xen_timer_slop= [X86-64,XEN]
6346 Set the timer slop (in nanoseconds) for the virtual Xen
6347 timers (default is 100000). This adjusts the minimum
6348 delta of virtualized Xen timers, where lower values
6349 improve timer resolution at the expense of processing
6350 more timer interrupts.
6352 xen.event_eoi_delay= [XEN]
6353 How long to delay EOI handling in case of event
6354 storms (jiffies). Default is 10.
6356 xen.event_loop_timeout= [XEN]
6357 After which time (jiffies) the event handling loop
6358 should start to delay EOI handling. Default is 2.
6360 xen.fifo_events= [XEN]
6361 Boolean parameter to disable using fifo event handling
6362 even if available. Normally fifo event handling is
6363 preferred over the 2-level event handling, as it is
6364 fairer and the number of possible event channels is
6365 much higher. Default is on (use fifo events).
6367 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
6368 Disables the PV optimizations forcing the guest to run
6369 as generic guest with no PV drivers. Currently support
6370 XEN HVM, KVM, HYPER_V and VMWARE guest.
6372 nopvspin [X86,XEN,KVM]
6373 Disables the qspinlock slow path using PV optimizations
6374 which allow the hypervisor to 'idle' the guest on lock
6377 xirc2ps_cs= [NET,PCMCIA]
6379 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
6382 By default on POWER9 and above, the kernel will
6383 natively use the XIVE interrupt controller. This option
6384 allows the fallback firmware mode to be used:
6386 off Fallback to firmware control of XIVE interrupt
6387 controller on both pseries and powernv
6388 platforms. Only useful on POWER9 and above.
6390 xhci-hcd.quirks [USB,KNL]
6391 A hex value specifying bitmask with supplemental xhci
6392 host controller quirks. Meaning of each bit can be
6393 consulted in header drivers/usb/host/xhci.h.
6396 Format: { early | on | rw | ro | off }
6397 Controls if xmon debugger is enabled. Default is off.
6398 Passing only "xmon" is equivalent to "xmon=early".
6399 early Call xmon as early as possible on boot; xmon
6400 debugger is called from setup_arch().
6401 on xmon debugger hooks will be installed so xmon
6402 is only called on a kernel crash. Default mode,
6403 i.e. either "ro" or "rw" mode, is controlled
6404 with CONFIG_XMON_DEFAULT_RO_MODE.
6405 rw xmon debugger hooks will be installed so xmon
6406 is called only on a kernel crash, mode is write,
6407 meaning SPR registers, memory and, other data
6408 can be written using xmon commands.
6409 ro same as "rw" option above but SPR registers,
6410 memory, and other data can't be written using
6412 off xmon is disabled.
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