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_hwsig,
229 s4_nohwsig, old_ordering, nonvs,
230 sci_force_enable, nobl }
231 See Documentation/power/video.rst for information on
233 s3_beep is for debugging; it makes the PC's speaker beep
234 as soon as the kernel's real-mode entry point is called.
235 s4_hwsig causes the kernel to check the ACPI hardware
236 signature during resume from hibernation, and gracefully
237 refuse to resume if it has changed. This complies with
238 the ACPI specification but not with reality, since
239 Windows does not do this and many laptops do change it
240 on docking. So the default behaviour is to allow resume
241 and simply warn when the signature changes, unless the
242 s4_hwsig option is enabled.
243 s4_nohwsig prevents ACPI hardware signature from being
244 used (or even warned about) during resume.
245 old_ordering causes the ACPI 1.0 ordering of the _PTS
246 control method, with respect to putting devices into
247 low power states, to be enforced (the ACPI 2.0 ordering
248 of _PTS is used by default).
249 nonvs prevents the kernel from saving/restoring the
250 ACPI NVS memory during suspend/hibernation and resume.
251 sci_force_enable causes the kernel to set SCI_EN directly
252 on resume from S1/S3 (which is against the ACPI spec,
253 but some broken systems don't work without it).
254 nobl causes the internal blacklist of systems known to
255 behave incorrectly in some ways with respect to system
256 suspend and resume to be ignored (use wisely).
258 acpi_use_timer_override [HW,ACPI]
259 Use timer override. For some broken Nvidia NF5 boards
260 that require a timer override, but don't have HPET
262 add_efi_memmap [EFI; X86] Include EFI memory map in
263 kernel's map of available physical RAM.
266 { off | try_unsupported }
267 off: disable AGP support
268 try_unsupported: try to drive unsupported chipsets
269 (may crash computer or cause data corruption)
272 See Documentation/sound/alsa-configuration.rst
275 Allow the default userspace alignment fault handler
276 behaviour to be specified. Bit 0 enables warnings,
277 bit 1 enables fixups, and bit 2 sends a segfault.
279 align_va_addr= [X86-64]
280 Align virtual addresses by clearing slice [14:12] when
281 allocating a VMA at process creation time. This option
282 gives you up to 3% performance improvement on AMD F15h
283 machines (where it is enabled by default) for a
284 CPU-intensive style benchmark, and it can vary highly in
285 a microbenchmark depending on workload and compiler.
287 32: only for 32-bit processes
288 64: only for 64-bit processes
289 on: enable for both 32- and 64-bit processes
290 off: disable for both 32- and 64-bit processes
292 alloc_snapshot [FTRACE]
293 Allocate the ftrace snapshot buffer on boot up when the
294 main buffer is allocated. This is handy if debugging
295 and you need to use tracing_snapshot() on boot up, and
296 do not want to use tracing_snapshot_alloc() as it needs
297 to be done where GFP_KERNEL allocations are allowed.
299 allow_mismatched_32bit_el0 [ARM64]
300 Allow execve() of 32-bit applications and setting of the
301 PER_LINUX32 personality on systems where only a strict
302 subset of the CPUs support 32-bit EL0. When this
303 parameter is present, the set of CPUs supporting 32-bit
304 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0
305 and hot-unplug operations may be restricted.
307 See Documentation/arm64/asymmetric-32bit.rst for more
310 amd_iommu= [HW,X86-64]
311 Pass parameters to the AMD IOMMU driver in the system.
313 fullflush - Deprecated, equivalent to iommu.strict=1
314 off - do not initialize any AMD IOMMU found in
316 force_isolation - Force device isolation for all
317 devices. The IOMMU driver is not
318 allowed anymore to lift isolation
319 requirements as needed. This option
320 does not override iommu=pt
321 force_enable - Force enable the IOMMU on platforms known
322 to be buggy with IOMMU enabled. Use this
324 pgtbl_v1 - Use v1 page table for DMA-API (Default).
325 pgtbl_v2 - Use v2 page table for DMA-API.
327 amd_iommu_dump= [HW,X86-64]
328 Enable AMD IOMMU driver option to dump the ACPI table
329 for AMD IOMMU. With this option enabled, AMD IOMMU
330 driver will print ACPI tables for AMD IOMMU during
331 IOMMU initialization.
333 amd_iommu_intr= [HW,X86-64]
334 Specifies one of the following AMD IOMMU interrupt
336 legacy - Use legacy interrupt remapping mode.
337 vapic - Use virtual APIC mode, which allows IOMMU
338 to inject interrupts directly into guest.
339 This mode requires kvm-amd.avic=1.
340 (Default when IOMMU HW support is present.)
342 amijoy.map= [HW,JOY] Amiga joystick support
343 Map of devices attached to JOY0DAT and JOY1DAT
345 See also Documentation/input/joydev/joystick.rst
347 analog.map= [HW,JOY] Analog joystick and gamepad support
348 Specifies type or capabilities of an analog joystick
349 connected to one of 16 gameports
350 Format: <type1>,<type2>,..<type16>
353 Power management functions (SPARCstation-4/5 + deriv.)
355 Disable APC CPU standby support. SPARCstation-Fox does
356 not play well with APC CPU idle - disable it if you have
357 APC and your system crashes randomly.
359 apic= [APIC,X86] Advanced Programmable Interrupt Controller
360 Change the output verbosity while booting
361 Format: { quiet (default) | verbose | debug }
362 Change the amount of debugging information output
363 when initialising the APIC and IO-APIC components.
364 For X86-32, this can also be used to specify an APIC
366 Format: apic=driver_name
367 Examples: apic=bigsmp
369 apic_extnmi= [APIC,X86] External NMI delivery setting
370 Format: { bsp (default) | all | none }
371 bsp: External NMI is delivered only to CPU 0
372 all: External NMIs are broadcast to all CPUs as a
374 none: External NMI is masked for all CPUs. This is
375 useful so that a dump capture kernel won't be
379 See Documentation/networking/ipv6.rst.
381 apm= [APM] Advanced Power Management
382 See header of arch/x86/kernel/apm_32.c.
384 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
385 Format: { "0" | "1" }
386 See security/apparmor/Kconfig help text
389 Default value is set via kernel config option.
391 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
392 Format: <io>,<irq>,<nodeID>
394 arm64.nobti [ARM64] Unconditionally disable Branch Target
395 Identification support
397 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication
400 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension
403 arm64.nosve [ARM64] Unconditionally disable Scalable Vector
406 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix
411 atarimouse= [HW,MOUSE] Atari Mouse
413 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
414 EzKey and similar keyboards
416 atkbd.reset= [HW] Reset keyboard during initialization
418 atkbd.set= [HW] Select keyboard code set
419 Format: <int> (2 = AT (default), 3 = PS/2)
421 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
424 atkbd.softraw= [HW] Choose between synthetic and real raw mode
425 Format: <bool> (0 = real, 1 = synthetic (default))
427 atkbd.softrepeat= [HW]
428 Use software keyboard repeat
430 audit= [KNL] Enable the audit sub-system
431 Format: { "0" | "1" | "off" | "on" }
432 0 | off - kernel audit is disabled and can not be
433 enabled until the next reboot
434 unset - kernel audit is initialized but disabled and
435 will be fully enabled by the userspace auditd.
436 1 | on - kernel audit is initialized and partially
437 enabled, storing at most audit_backlog_limit
438 messages in RAM until it is fully enabled by the
442 audit_backlog_limit= [KNL] Set the audit queue size limit.
443 Format: <int> (must be >=0)
446 bau= [X86_UV] Enable the BAU on SGI UV. The default
447 behavior is to disable the BAU (i.e. bau=0).
448 Format: { "0" | "1" }
451 unset - Disable the BAU.
453 baycom_epp= [HW,AX25]
456 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
458 See header of drivers/net/hamradio/baycom_par.c.
460 baycom_ser_fdx= [HW,AX25]
461 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
462 Format: <io>,<irq>,<mode>[,<baud>]
463 See header of drivers/net/hamradio/baycom_ser_fdx.c.
465 baycom_ser_hdx= [HW,AX25]
466 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
467 Format: <io>,<irq>,<mode>
468 See header of drivers/net/hamradio/baycom_ser_hdx.c.
471 Disable BERT OS support on buggy BIOSes.
473 bgrt_disable [ACPI][X86]
474 Disable BGRT to avoid flickering OEM logo.
476 blkdevparts= Manual partition parsing of block device(s) for
477 embedded devices based on command line input.
478 See Documentation/block/cmdline-partition.rst
480 boot_delay= Milliseconds to delay each printk during boot.
481 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled,
482 and you may also have to specify "lpj=". Boot_delay
483 values larger than 10 seconds (10000) are assumed
484 erroneous and ignored.
488 Extended command line options can be added to an initrd
489 and this will cause the kernel to look for it.
491 See Documentation/admin-guide/bootconfig.rst
493 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
494 bttv.radio= Most important insmod options are available as
496 bttv.pll= See Documentation/admin-guide/media/bttv.rst
499 bulk_remove=off [PPC] This parameter disables the use of the pSeries
500 firmware feature for flushing multiple hpte entries
503 c101= [NET] Moxa C101 synchronous serial card
505 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
506 Sometimes CPU hardware bugs make them report the cache
507 size incorrectly. The kernel will attempt work arounds
508 to fix known problems, but for some CPUs it is not
509 possible to determine what the correct size should be.
510 This option provides an override for these situations.
513 [NET] Specifies amount of time (in seconds) that
514 the kernel should wait for a network carrier. By default
515 it waits 120 seconds.
517 ca_keys= [KEYS] This parameter identifies a specific key(s) on
518 the system trusted keyring to be used for certificate
520 format: { id:<keyid> | builtin }
522 cca= [MIPS] Override the kernel pages' cache coherency
523 algorithm. Accepted values range from 0 to 7
524 inclusive. See arch/mips/include/asm/pgtable-bits.h
525 for platform specific values (SB1, Loongson3 and
528 ccw_timeout_log [S390]
529 See Documentation/s390/common_io.rst for details.
531 cgroup_disable= [KNL] Disable a particular controller or optional feature
532 Format: {name of the controller(s) or feature(s) to disable}
533 The effects of cgroup_disable=foo are:
534 - foo isn't auto-mounted if you mount all cgroups in
536 - foo isn't visible as an individually mountable
538 - if foo is an optional feature then the feature is
539 disabled and corresponding cgroup files are not
541 {Currently only "memory" controller deal with this and
542 cut the overhead, others just disable the usage. So
543 only cgroup_disable=memory is actually worthy}
544 Specifying "pressure" disables per-cgroup pressure
545 stall information accounting feature
547 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
548 Format: { { controller | "all" | "named" }
549 [,{ controller | "all" | "named" }...] }
550 Like cgroup_disable, but only applies to cgroup v1;
551 the blacklisted controllers remain available in cgroup2.
552 "all" blacklists all controllers and "named" disables
553 named mounts. Specifying both "all" and "named" disables
556 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
558 nosocket -- Disable socket memory accounting.
559 nokmem -- Disable kernel memory accounting.
560 nobpf -- Disable BPF memory accounting.
562 checkreqprot= [SELINUX] Set initial checkreqprot flag value.
563 Format: { "0" | "1" }
564 See security/selinux/Kconfig help text.
565 0 -- check protection applied by kernel (includes
566 any implied execute protection).
567 1 -- check protection requested by application.
568 Default value is set via a kernel config option.
569 Value can be changed at runtime via
570 /sys/fs/selinux/checkreqprot.
571 Setting checkreqprot to 1 is deprecated.
574 See Documentation/s390/common_io.rst for details.
576 clearcpuid=X[,X...] [X86]
577 Disable CPUID feature X for the kernel. See
578 arch/x86/include/asm/cpufeatures.h for the valid bit
579 numbers X. Note the Linux-specific bits are not necessarily
580 stable over kernel options, but the vendor-specific
582 X can also be a string as appearing in the flags: line
583 in /proc/cpuinfo which does not have the above
584 instability issue. However, not all features have names
586 Note that using this option will taint your kernel.
587 Also note that user programs calling CPUID directly
588 or using the feature without checking anything
589 will still see it. This just prevents it from
590 being used by the kernel or shown in /proc/cpuinfo.
591 Also note the kernel might malfunction if you disable
596 Prevents the clock framework from automatically gating
597 clocks that have not been explicitly enabled by a Linux
598 device driver but are enabled in hardware at reset or
599 by the bootloader/firmware. Note that this does not
600 force such clocks to be always-on nor does it reserve
601 those clocks in any way. This parameter is useful for
602 debug and development, but should not be needed on a
603 platform with proper driver support. For more
604 information, see Documentation/driver-api/clk.rst.
606 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
608 Forces specified clocksource (if available) to be used
609 when calculating gettimeofday(). If specified
610 clocksource is not available, it defaults to PIT.
611 Format: { pit | tsc | cyclone | pmtmr }
613 clocksource= Override the default clocksource
615 Override the default clocksource and use the clocksource
616 with the name specified.
617 Some clocksource names to choose from, depending on
619 [all] jiffies (this is the base, fallback clocksource)
621 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
622 pxa_timer,timer3,32k_counter,timer0_1
623 [X86-32] pit,hpet,tsc;
624 scx200_hrt on Geode; cyclone on IBM x440
632 clocksource.arm_arch_timer.evtstrm=
635 Enable/disable the eventstream feature of the ARM
636 architected timer so that code using WFE-based polling
637 loops can be debugged more effectively on production
640 clocksource.max_cswd_read_retries= [KNL]
641 Number of clocksource_watchdog() retries due to
642 external delays before the clock will be marked
643 unstable. Defaults to two retries, that is,
644 three attempts to read the clock under test.
646 clocksource.verify_n_cpus= [KNL]
647 Limit the number of CPUs checked for clocksources
648 marked with CLOCK_SOURCE_VERIFY_PERCPU that
649 are marked unstable due to excessive skew.
650 A negative value says to check all CPUs, while
651 zero says not to check any. Values larger than
652 nr_cpu_ids are silently truncated to nr_cpu_ids.
653 The actual CPUs are chosen randomly, with
654 no replacement if the same CPU is chosen twice.
656 clocksource-wdtest.holdoff= [KNL]
657 Set the time in seconds that the clocksource
658 watchdog test waits before commencing its tests.
659 Defaults to zero when built as a module and to
660 10 seconds when built into the kernel.
662 cma=nn[MG]@[start[MG][-end[MG]]]
664 Sets the size of kernel global memory area for
665 contiguous memory allocations and optionally the
666 placement constraint by the physical address range of
667 memory allocations. A value of 0 disables CMA
668 altogether. For more information, see
669 kernel/dma/contiguous.c
673 Sets the size of kernel per-numa memory area for
674 contiguous memory allocations. A value of 0 disables
675 per-numa CMA altogether. And If this option is not
676 specified, the default value is 0.
677 With per-numa CMA enabled, DMA users on node nid will
678 first try to allocate buffer from the pernuma area
679 which is located in node nid, if the allocation fails,
680 they will fallback to the global default memory area.
682 cmo_free_hint= [PPC] Format: { yes | no }
683 Specify whether pages are marked as being inactive
684 when they are freed. This is used in CMO environments
685 to determine OS memory pressure for page stealing by
689 coherent_pool=nn[KMG] [ARM,KNL]
690 Sets the size of memory pool for coherent, atomic dma
691 allocations, by default set to 256K.
693 com20020= [HW,NET] ARCnet - COM20020 chipset
695 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
697 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
701 ARCnet - COM90xx chipset (memory-mapped buffers)
702 Format: <io>[,<irq>[,<memstart>]]
704 condev= [HW,S390] console device
707 con3215_drop= [S390] 3215 console drop mode.
709 When set to true, drop data on the 3215 console when
710 the console buffer is full. In this case the
711 operator using a 3270 terminal emulator (for example
712 x3270) does not have to enter the clear key for the
713 console output to advance and the kernel to continue.
714 This leads to a much faster boot time when a 3270
715 terminal emulator is active. If no 3270 terminal
716 emulator is used, this parameter has no effect.
718 console= [KNL] Output console device and options.
720 tty<n> Use the virtual console device <n>.
724 Use the specified serial port. The options are of
725 the form "bbbbpnf", where "bbbb" is the baud rate,
726 "p" is parity ("n", "o", or "e"), "n" is number of
727 bits, and "f" is flow control ("r" for RTS or
728 omit it). Default is "9600n8".
730 See Documentation/admin-guide/serial-console.rst for more
732 Documentation/networking/netconsole.rst for an
735 uart[8250],io,<addr>[,options]
736 uart[8250],mmio,<addr>[,options]
737 uart[8250],mmio16,<addr>[,options]
738 uart[8250],mmio32,<addr>[,options]
739 uart[8250],0x<addr>[,options]
740 Start an early, polled-mode console on the 8250/16550
741 UART at the specified I/O port or MMIO address,
742 switching to the matching ttyS device later.
743 MMIO inter-register address stride is either 8-bit
744 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
745 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
746 to be equivalent to 'mmio'. 'options' are specified in
747 the same format described for ttyS above; if unspecified,
748 the h/w is not re-initialized.
750 hvc<n> Use the hypervisor console device <n>. This is for
751 both Xen and PowerPC hypervisors.
754 Use to disable console output, i.e., to have kernel
755 console messages discarded.
756 This must be the only console= parameter used on the
759 If the device connected to the port is not a TTY but a braille
760 device, prepend "brl," before the device type, for instance
762 For now, only VisioBraille is supported.
765 [KNL] Change console messages format
767 By default we print messages on consoles in
768 "[time stamp] text\n" format (time stamp may not be
769 printed, depending on CONFIG_PRINTK_TIME or
770 `printk_time' param).
772 Switch to syslog format: "<%u>[time stamp] text\n"
773 IOW, each message will have a facility and loglevel
774 prefix. The format is similar to one used by syslog()
775 syscall, or to executing "dmesg -S --raw" or to reading
778 consoleblank= [KNL] The console blank (screen saver) timeout in
779 seconds. A value of 0 disables the blank timer.
783 [KNL] Change the default value for
784 /proc/<pid>/coredump_filter.
785 See also Documentation/filesystems/proc.rst.
787 coresight_cpu_debug.enable
790 Enable/disable the CPU sampling based debugging.
791 0: default value, disable debugging
792 1: enable debugging at boot time
794 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
796 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
798 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
799 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
800 Some features depend on CPU0. Known dependencies are:
801 1. Resume from suspend/hibernate depends on CPU0.
802 Suspend/hibernate will fail if CPU0 is offline and you
803 need to online CPU0 before suspend/hibernate.
804 2. PIC interrupts also depend on CPU0. CPU0 can't be
805 removed if a PIC interrupt is detected.
806 It's said poweroff/reboot may depend on CPU0 on some
807 machines although I haven't seen such issues so far
808 after CPU0 is offline on a few tested machines.
809 If the dependencies are under your control, you can
810 turn on cpu0_hotplug.
812 cpuidle.off=1 [CPU_IDLE]
813 disable the cpuidle sub-system
816 [CPU_IDLE] Name of the cpuidle governor to use.
818 cpufreq.off=1 [CPU_FREQ]
819 disable the cpufreq sub-system
821 cpufreq.default_governor=
822 [CPU_FREQ] Name of the default cpufreq governor or
823 policy to use. This governor must be registered in the
824 kernel before the cpufreq driver probes.
827 [X86] Delay for N microsec between assert and de-assert
828 of APIC INIT to start processors. This delay occurs
829 on every CPU online, such as boot, and resume from suspend.
832 crash_kexec_post_notifiers
833 Run kdump after running panic-notifiers and dumping
834 kmsg. This only for the users who doubt kdump always
835 succeeds in any situation.
836 Note that this also increases risks of kdump failure,
837 because some panic notifiers can make the crashed
838 kernel more unstable.
840 crashkernel=size[KMG][@offset[KMG]]
841 [KNL] Using kexec, Linux can switch to a 'crash kernel'
842 upon panic. This parameter reserves the physical
843 memory region [offset, offset + size] for that kernel
844 image. If '@offset' is omitted, then a suitable offset
845 is selected automatically.
846 [KNL, X86-64, ARM64] Select a region under 4G first, and
847 fall back to reserve region above 4G when '@offset'
848 hasn't been specified.
849 See Documentation/admin-guide/kdump/kdump.rst for further details.
851 crashkernel=range1:size1[,range2:size2,...][@offset]
852 [KNL] Same as above, but depends on the memory
853 in the running system. The syntax of range is
854 start-[end] where start and end are both
855 a memory unit (amount[KMG]). See also
856 Documentation/admin-guide/kdump/kdump.rst for an example.
858 crashkernel=size[KMG],high
859 [KNL, X86-64, ARM64] range could be above 4G. Allow kernel
860 to allocate physical memory region from top, so could
861 be above 4G if system have more than 4G ram installed.
862 Otherwise memory region will be allocated below 4G, if
864 It will be ignored if crashkernel=X is specified.
865 crashkernel=size[KMG],low
866 [KNL, X86-64, ARM64] range under 4G. When crashkernel=X,high
867 is passed, kernel could allocate physical memory region
868 above 4G, that cause second kernel crash on system
869 that require some amount of low memory, e.g. swiotlb
870 requires at least 64M+32K low memory, also enough extra
871 low memory is needed to make sure DMA buffers for 32-bit
872 devices won't run out. Kernel would try to allocate
873 default size of memory below 4G automatically. The default
874 size is platform dependent.
875 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB)
877 This one lets the user specify own low range under 4G
878 for second kernel instead.
879 0: to disable low allocation.
880 It will be ignored when crashkernel=X,high is not used
881 or memory reserved is below 4G.
884 [KNL] Disable crypto self-tests
889 cs89x0_media= [HW,NET]
890 Format: { rj45 | aui | bnc }
892 csdlock_debug= [KNL] Enable debug add-ons of cross-CPU function call
893 handling. When switched on, additional debug data is
894 printed to the console in case a hanging CPU is
895 detected, and that CPU is pinged again in order to try
896 to resolve the hang situation.
897 0: disable csdlock debugging (default)
898 1: enable basic csdlock debugging (minor impact)
899 ext: enable extended csdlock debugging (more impact,
903 See header of drivers/s390/block/dasd_devmap.c.
905 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
906 (one device per port)
907 Format: <port#>,<type>
908 See also Documentation/input/devices/joystick-parport.rst
910 debug [KNL] Enable kernel debugging (events log level).
913 [KNL] Enable printing [hashed] pointers early in the
914 boot sequence. If enabled, we use a weak hash instead
915 of siphash to hash pointers. Use this option if you are
916 seeing instances of '(___ptrval___)') and need to see a
917 value (hashed pointer) instead. Cryptographically
918 insecure, please do not use on production kernels.
921 [KNL] verbose locking self-tests
923 Print debugging info while doing the locking API
925 Bitmask for the various LOCKTYPE_ tests. Defaults to 0
926 (no extra messages), setting it to -1 (all bits set)
927 will print _a_lot_ more information - normally only
928 useful to lockdep developers.
930 debug_objects [KNL] Enable object debugging
933 [KNL] Disable object debugging
935 debug_guardpage_minorder=
936 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
937 parameter allows control of the order of pages that will
938 be intentionally kept free (and hence protected) by the
939 buddy allocator. Bigger value increase the probability
940 of catching random memory corruption, but reduce the
941 amount of memory for normal system use. The maximum
942 possible value is MAX_ORDER/2. Setting this parameter
943 to 1 or 2 should be enough to identify most random
944 memory corruption problems caused by bugs in kernel or
945 driver code when a CPU writes to (or reads from) a
946 random memory location. Note that there exists a class
947 of memory corruptions problems caused by buggy H/W or
948 F/W or by drivers badly programming DMA (basically when
949 memory is written at bus level and the CPU MMU is
950 bypassed) which are not detectable by
951 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
952 tracking down these problems.
955 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
956 enables the feature at boot time. By default, it is
957 disabled and the system will work mostly the same as a
958 kernel built without CONFIG_DEBUG_PAGEALLOC.
959 Note: to get most of debug_pagealloc error reports, it's
960 useful to also enable the page_owner functionality.
961 on: enable the feature
963 debugfs= [KNL] This parameter enables what is exposed to userspace
964 and debugfs internal clients.
965 Format: { on, no-mount, off }
966 on: All functions are enabled.
968 Filesystem is not registered but kernel clients can
969 access APIs and a crashkernel can be used to read
970 its content. There is nothing to mount.
971 off: Filesystem is not registered and clients
972 get a -EPERM as result when trying to register files
973 or directories within debugfs.
974 This is equivalent of the runtime functionality if
975 debugfs was not enabled in the kernel at all.
976 Default value is set in build-time with a kernel configuration.
978 debugpat [X86] Enable PAT debugging
981 [HW] The size of the default HugeTLB page. This is
982 the size represented by the legacy /proc/ hugepages
983 APIs. In addition, this is the default hugetlb size
984 used for shmget(), mmap() and mounting hugetlbfs
985 filesystems. If not specified, defaults to the
986 architecture's default huge page size. Huge page
987 sizes are architecture dependent. See also
988 Documentation/admin-guide/mm/hugetlbpage.rst.
991 deferred_probe_timeout=
992 [KNL] Debugging option to set a timeout in seconds for
993 deferred probe to give up waiting on dependencies to
994 probe. Only specific dependencies (subsystems or
995 drivers) that have opted in will be ignored. A timeout
996 of 0 will timeout at the end of initcalls. If the time
997 out hasn't expired, it'll be restarted by each
998 successful driver registration. This option will also
999 dump out devices still on the deferred probe list after
1002 delayacct [KNL] Enable per-task delay accounting
1004 dell_smm_hwmon.ignore_dmi=
1005 [HW] Continue probing hardware even if DMI data
1006 indicates that the driver is running on unsupported
1009 dell_smm_hwmon.force=
1010 [HW] Activate driver even if SMM BIOS signature does
1011 not match list of supported models and enable otherwise
1012 blacklisted features.
1014 dell_smm_hwmon.power_status=
1015 [HW] Report power status in /proc/i8k
1016 (disabled by default).
1018 dell_smm_hwmon.restricted=
1019 [HW] Allow controlling fans only if SYS_ADMIN
1022 dell_smm_hwmon.fan_mult=
1023 [HW] Factor to multiply fan speed with.
1025 dell_smm_hwmon.fan_max=
1026 [HW] Maximum configurable fan speed.
1029 Format: { on | off | def_only | inf_only | always }
1030 on: s390 zlib hardware support for compression on
1031 level 1 and decompression (default)
1032 off: No s390 zlib hardware support
1033 def_only: s390 zlib hardware support for deflate
1034 only (compression on level 1)
1035 inf_only: s390 zlib hardware support for inflate
1036 only (decompression)
1037 always: Same as 'on' but ignores the selected compression
1038 level always using hardware support (used for debugging)
1040 dhash_entries= [KNL]
1041 Set number of hash buckets for dentry cache.
1043 disable_1tb_segments [PPC]
1044 Disables the use of 1TB hash page table segments. This
1045 causes the kernel to fall back to 256MB segments which
1046 can be useful when debugging issues that require an SLB
1050 See Documentation/networking/ipv6.rst.
1053 Disable RADIX MMU mode on POWER9
1056 Disable TLBIE instruction. Currently does not work
1057 with KVM, with HASH MMU, or with coherent accelerators.
1059 disable_cpu_apicid= [X86,APIC,SMP]
1061 The number of initial APIC ID for the
1062 corresponding CPU to be disabled at boot,
1063 mostly used for the kdump 2nd kernel to
1064 disable BSP to wake up multiple CPUs without
1065 causing system reset or hang due to sending
1066 INIT from AP to BSP.
1068 disable_ddw [PPC/PSERIES]
1069 Disable Dynamic DMA Window support. Use this
1070 to workaround buggy firmware.
1072 disable_ipv6= [IPV6]
1073 See Documentation/networking/ipv6.rst.
1075 disable_mtrr_cleanup [X86]
1076 The kernel tries to adjust MTRR layout from continuous
1077 to discrete, to make X server driver able to add WB
1078 entry later. This parameter disables that.
1080 disable_mtrr_trim [X86, Intel and AMD only]
1081 By default the kernel will trim any uncacheable
1082 memory out of your available memory pool based on
1083 MTRR settings. This parameter disables that behavior,
1084 possibly causing your machine to run very slowly.
1086 disable_timer_pin_1 [X86]
1087 Disable PIN 1 of APIC timer
1088 Can be useful to work around chipset bugs.
1090 dis_ucode_ldr [X86] Disable the microcode loader.
1092 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1093 this option disables the debugging code at boot.
1095 dma_debug_entries=<number>
1096 This option allows to tune the number of preallocated
1097 entries for DMA-API debugging code. One entry is
1098 required per DMA-API allocation. Use this if the
1099 DMA-API debugging code disables itself because the
1100 architectural default is too low.
1102 dma_debug_driver=<driver_name>
1103 With this option the DMA-API debugging driver
1104 filter feature can be enabled at boot time. Just
1105 pass the driver to filter for as the parameter.
1106 The filter can be disabled or changed to another
1107 driver later using sysfs.
1109 driver_async_probe= [KNL]
1110 List of driver names to be probed asynchronously. *
1111 matches with all driver names. If * is specified, the
1112 rest of the listed driver names are those that will NOT
1114 Format: <driver_name1>,<driver_name2>...
1116 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1117 Broken monitors, graphic adapters, KVMs and EDIDless
1118 panels may send no or incorrect EDID data sets.
1119 This parameter allows to specify an EDID data sets
1120 in the /lib/firmware directory that are used instead.
1121 Generic built-in EDID data sets are used, if one of
1122 edid/1024x768.bin, edid/1280x1024.bin,
1123 edid/1680x1050.bin, or edid/1920x1080.bin is given
1124 and no file with the same name exists. Details and
1125 instructions how to build your own EDID data are
1126 available in Documentation/admin-guide/edid.rst. An EDID
1127 data set will only be used for a particular connector,
1128 if its name and a colon are prepended to the EDID
1129 name. Each connector may use a unique EDID data
1130 set by separating the files with a comma. An EDID
1131 data set with no connector name will be used for
1132 any connectors not explicitly specified.
1137 Format: {"off" | "known"}
1138 Control how the dt_cpu_ftrs device-tree binding is
1139 used for CPU feature discovery and setup (if it
1141 off: Do not use it, fall back to legacy cpu table.
1142 known: Do not pass through unknown features to guests
1143 or userspace, only those that the kernel is aware of.
1145 dump_apple_properties [X86]
1146 Dump name and content of EFI device properties on
1147 x86 Macs. Useful for driver authors to determine
1148 what data is available or for reverse-engineering.
1150 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1151 <module>.dyndbg[="val"]
1152 Enable debug messages at boot time. See
1153 Documentation/admin-guide/dynamic-debug-howto.rst
1156 early_ioremap_debug [KNL]
1157 Enable debug messages in early_ioremap support. This
1158 is useful for tracking down temporary early mappings
1159 which are not unmapped.
1161 earlycon= [KNL] Output early console device and options.
1163 When used with no options, the early console is
1164 determined by stdout-path property in device tree's
1165 chosen node or the ACPI SPCR table if supported by
1168 cdns,<addr>[,options]
1169 Start an early, polled-mode console on a Cadence
1170 (xuartps) serial port at the specified address. Only
1171 supported option is baud rate. If baud rate is not
1172 specified, the serial port must already be setup and
1175 uart[8250],io,<addr>[,options[,uartclk]]
1176 uart[8250],mmio,<addr>[,options[,uartclk]]
1177 uart[8250],mmio32,<addr>[,options[,uartclk]]
1178 uart[8250],mmio32be,<addr>[,options[,uartclk]]
1179 uart[8250],0x<addr>[,options]
1180 Start an early, polled-mode console on the 8250/16550
1181 UART at the specified I/O port or MMIO address.
1182 MMIO inter-register address stride is either 8-bit
1183 (mmio) or 32-bit (mmio32 or mmio32be).
1184 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1185 to be equivalent to 'mmio'. 'options' are specified
1186 in the same format described for "console=ttyS<n>"; if
1187 unspecified, the h/w is not initialized. 'uartclk' is
1188 the uart clock frequency; if unspecified, it is set
1189 to 'BASE_BAUD' * 16.
1193 Start an early, polled-mode console on a pl011 serial
1194 port at the specified address. The pl011 serial port
1195 must already be setup and configured. Options are not
1196 yet supported. If 'mmio32' is specified, then only
1197 the driver will use only 32-bit accessors to read/write
1198 the device registers.
1201 Start an early console on a litex serial port at the
1202 specified address. The serial port must already be
1203 setup and configured. Options are not yet supported.
1206 Start an early, polled-mode console on a meson serial
1207 port at the specified address. The serial port must
1208 already be setup and configured. Options are not yet
1212 Start an early, polled-mode console on an msm serial
1213 port at the specified address. The serial port
1214 must already be setup and configured. Options are not
1217 msm_serial_dm,<addr>
1218 Start an early, polled-mode console on an msm serial
1219 dm port at the specified address. The serial port
1220 must already be setup and configured. Options are not
1224 Start an early, polled-mode console on a serial port
1225 of an Actions Semi SoC, such as S500 or S900, at the
1226 specified address. The serial port must already be
1227 setup and configured. Options are not yet supported.
1230 Start an early, polled-mode console on a serial port
1231 of an RDA Micro SoC, such as RDA8810PL, at the
1232 specified address. The serial port must already be
1233 setup and configured. Options are not yet supported.
1236 Use RISC-V SBI (Supervisor Binary Interface) for early
1239 smh Use ARM semihosting calls for early console.
1247 Use early console provided by serial driver available
1248 on Samsung SoCs, requires selecting proper type and
1249 a correct base address of the selected UART port. The
1250 serial port must already be setup and configured.
1251 Options are not yet supported.
1254 Start an early, polled-mode console on a lantiq serial
1255 (lqasc) port at the specified address. The serial port
1256 must already be setup and configured. Options are not
1261 Use early console provided by Freescale LP UART driver
1262 found on Freescale Vybrid and QorIQ LS1021A processors.
1263 A valid base address must be provided, and the serial
1264 port must already be setup and configured.
1268 Start an early, polled-mode, output-only console on the
1269 Freescale i.MX UART at the specified address. The UART
1270 must already be setup and configured.
1273 Start an early, polled-mode console on the
1274 Armada 3700 serial port at the specified
1275 address. The serial port must already be setup
1276 and configured. Options are not yet supported.
1279 Start an early, polled-mode console on a Qualcomm
1280 Generic Interface (GENI) based serial port at the
1281 specified address. The serial port must already be
1282 setup and configured. Options are not yet supported.
1285 Start an early, unaccelerated console on the EFI
1286 memory mapped framebuffer (if available). On cache
1287 coherent non-x86 systems that use system memory for
1288 the framebuffer, pass the 'ram' option so that it is
1289 mapped with the correct attributes.
1292 Use early console provided by Freescale LINFlexD UART
1293 serial driver for NXP S32V234 SoCs. A valid base
1294 address must be provided, and the serial port must
1295 already be setup and configured.
1297 earlyprintk= [X86,SH,ARM,M68k,S390]
1301 earlyprintk=serial[,ttySn[,baudrate]]
1302 earlyprintk=serial[,0x...[,baudrate]]
1303 earlyprintk=ttySn[,baudrate]
1304 earlyprintk=dbgp[debugController#]
1305 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1306 earlyprintk=xdbc[xhciController#]
1308 earlyprintk is useful when the kernel crashes before
1309 the normal console is initialized. It is not enabled by
1310 default because it has some cosmetic problems.
1312 Append ",keep" to not disable it when the real console
1315 Only one of vga, serial, or usb debug port can
1318 Currently only ttyS0 and ttyS1 may be specified by
1319 name. Other I/O ports may be explicitly specified
1320 on some architectures (x86 and arm at least) by
1321 replacing ttySn with an I/O port address, like this:
1322 earlyprintk=serial,0x1008,115200
1323 You can find the port for a given device in
1324 /proc/tty/driver/serial:
1325 2: uart:ST16650V2 port:00001008 irq:18 ...
1327 Interaction with the standard serial driver is not
1330 The VGA output is eventually overwritten by
1333 The xen option can only be used in Xen domains.
1335 The sclp output can only be used on s390.
1337 The optional "force" to "pciserial" enables use of a
1338 PCI device even when its classcode is not of the
1341 edac_report= [HW,EDAC] Control how to report EDAC event
1342 Format: {"on" | "off" | "force"}
1343 on: enable EDAC to report H/W event. May be overridden
1344 by other higher priority error reporting module.
1345 off: disable H/W event reporting through EDAC.
1346 force: enforce the use of EDAC to report H/W event.
1350 Format: {"off" | "on" | "skip[mbr]"}
1353 Format: { "debug", "disable_early_pci_dma",
1354 "nochunk", "noruntime", "nosoftreserve",
1355 "novamap", "no_disable_early_pci_dma" }
1356 debug: enable misc debug output.
1357 disable_early_pci_dma: disable the busmaster bit on all
1358 PCI bridges while in the EFI boot stub.
1359 nochunk: disable reading files in "chunks" in the EFI
1360 boot stub, as chunking can cause problems with some
1361 firmware implementations.
1362 noruntime : disable EFI runtime services support
1363 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1364 attribute may cause the kernel to reserve the
1365 memory range for a memory mapping driver to
1366 claim. Specify efi=nosoftreserve to disable this
1367 reservation and treat the memory by its base type
1368 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1369 novamap: do not call SetVirtualAddressMap().
1370 no_disable_early_pci_dma: Leave the busmaster bit set
1371 on all PCI bridges while in the EFI boot stub
1373 efi_no_storage_paranoia [EFI; X86]
1374 Using this parameter you can use more than 50% of
1375 your efi variable storage. Use this parameter only if
1376 you are really sure that your UEFI does sane gc and
1377 fulfills the spec otherwise your board may brick.
1379 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1380 Add arbitrary attribute to specific memory range by
1381 updating original EFI memory map.
1382 Region of memory which aa attribute is added to is
1385 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1386 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1387 attribute is added to range 0x100000000-0x180000000 and
1388 0x10a0000000-0x1120000000.
1390 If efi_fake_mem=8G@9G:0x40000 is specified, the
1391 EFI_MEMORY_SP(0x40000) attribute is added to
1392 range 0x240000000-0x43fffffff.
1394 Using this parameter you can do debugging of EFI memmap
1395 related features. For example, you can do debugging of
1396 Address Range Mirroring feature even if your box
1397 doesn't support it, or mark specific memory as
1400 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1401 that is to be dynamically loaded by Linux. If there are
1402 multiple variables with the same name but with different
1403 vendor GUIDs, all of them will be loaded. See
1404 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1407 eisa_irq_edge= [PARISC,HW]
1408 See header of drivers/parisc/eisa.c.
1410 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1413 This is designed to be used in conjunction with
1414 the boot argument: earlyprintk=vga
1416 This parameter works in place of the kgdboc parameter
1417 but can only be used if the backing tty is available
1418 very early in the boot process. For early debugging
1419 via a serial port see kgdboc_earlycon instead.
1422 See comment before function elanfreq_setup() in
1423 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1425 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1426 Specifies physical address of start of kernel core
1427 image elf header and optionally the size. Generally
1428 kexec loader will pass this option to capture kernel.
1429 See Documentation/admin-guide/kdump/kdump.rst for details.
1431 enable_mtrr_cleanup [X86]
1432 The kernel tries to adjust MTRR layout from continuous
1433 to discrete, to make X server driver able to add WB
1434 entry later. This parameter enables that.
1436 enable_timer_pin_1 [X86]
1437 Enable PIN 1 of APIC timer
1438 Can be useful to work around chipset bugs
1439 (in particular on some ATI chipsets).
1440 The kernel tries to set a reasonable default.
1442 enforcing= [SELINUX] Set initial enforcing status.
1444 See security/selinux/Kconfig help text.
1445 0 -- permissive (log only, no denials).
1446 1 -- enforcing (deny and log).
1448 Value can be changed at runtime via
1449 /sys/fs/selinux/enforce.
1452 Disable Error Record Serialization Table (ERST)
1455 ether= [HW,NET] Ethernet cards parameters
1456 This option is obsoleted by the "netdev=" option, which
1457 has equivalent usage. See its documentation for details.
1461 Permit 'security.evm' to be updated regardless of
1462 current integrity status.
1464 early_page_ext [KNL] Enforces page_ext initialization to earlier
1465 stages so cover more early boot allocations.
1466 Please note that as side effect some optimizations
1467 might be disabled to achieve that (e.g. parallelized
1468 memory initialization is disabled) so the boot process
1469 might take longer, especially on systems with a lot of
1470 memory. Available with CONFIG_PAGE_EXTENSION=y.
1475 fail_make_request=[KNL]
1476 General fault injection mechanism.
1477 Format: <interval>,<probability>,<space>,<times>
1478 See also Documentation/fault-injection/.
1481 Format: { initns | none }
1482 See Documentation/admin-guide/sysctl/net.rst for
1483 fb_tunnels_only_for_init_ns
1486 See Documentation/admin-guide/blockdev/floppy.rst.
1488 force_pal_cache_flush
1489 [IA-64] Avoid check_sal_cache_flush which may hang on
1490 buggy SAL_CACHE_FLUSH implementations. Using this
1491 parameter will force ia64_sal_cache_flush to call
1492 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1495 Forcefully enable Physical Address Extension (PAE).
1496 Many Pentium M systems disable PAE but may have a
1497 functionally usable PAE implementation.
1498 Warning: use of this parameter will taint the kernel
1499 and may cause unknown problems.
1502 [FTRACE] will set and start the specified tracer
1503 as early as possible in order to facilitate early
1506 ftrace_boot_snapshot
1507 [FTRACE] On boot up, a snapshot will be taken of the
1508 ftrace ring buffer that can be read at:
1509 /sys/kernel/tracing/snapshot.
1510 This is useful if you need tracing information from kernel
1511 boot up that is likely to be overridden by user space
1512 start up functionality.
1514 Optionally, the snapshot can also be defined for a tracing
1515 instance that was created by the trace_instance= command
1518 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo
1520 The above will cause the "foo" tracing instance to trigger
1521 a snapshot at the end of boot up.
1523 ftrace_dump_on_oops[=orig_cpu]
1524 [FTRACE] will dump the trace buffers on oops.
1525 If no parameter is passed, ftrace will dump
1526 buffers of all CPUs, but if you pass orig_cpu, it will
1527 dump only the buffer of the CPU that triggered the
1530 ftrace_filter=[function-list]
1531 [FTRACE] Limit the functions traced by the function
1532 tracer at boot up. function-list is a comma-separated
1533 list of functions. This list can be changed at run
1534 time by the set_ftrace_filter file in the debugfs
1537 ftrace_notrace=[function-list]
1538 [FTRACE] Do not trace the functions specified in
1539 function-list. This list can be changed at run time
1540 by the set_ftrace_notrace file in the debugfs
1543 ftrace_graph_filter=[function-list]
1544 [FTRACE] Limit the top level callers functions traced
1545 by the function graph tracer at boot up.
1546 function-list is a comma-separated list of functions
1547 that can be changed at run time by the
1548 set_graph_function file in the debugfs tracing directory.
1550 ftrace_graph_notrace=[function-list]
1551 [FTRACE] Do not trace from the functions specified in
1552 function-list. This list is a comma-separated list of
1553 functions that can be changed at run time by the
1554 set_graph_notrace file in the debugfs tracing directory.
1556 ftrace_graph_max_depth=<uint>
1557 [FTRACE] Used with the function graph tracer. This is
1558 the max depth it will trace into a function. This value
1559 can be changed at run time by the max_graph_depth file
1560 in the tracefs tracing directory. default: 0 (no limit)
1562 fw_devlink= [KNL] Create device links between consumer and supplier
1563 devices by scanning the firmware to infer the
1564 consumer/supplier relationships. This feature is
1565 especially useful when drivers are loaded as modules as
1566 it ensures proper ordering of tasks like device probing
1567 (suppliers first, then consumers), supplier boot state
1568 clean up (only after all consumers have probed),
1569 suspend/resume & runtime PM (consumers first, then
1571 Format: { off | permissive | on | rpm }
1572 off -- Don't create device links from firmware info.
1573 permissive -- Create device links from firmware info
1574 but use it only for ordering boot state clean
1575 up (sync_state() calls).
1576 on -- Create device links from firmware info and use it
1577 to enforce probe and suspend/resume ordering.
1578 rpm -- Like "on", but also use to order runtime PM.
1580 fw_devlink.strict=<bool>
1581 [KNL] Treat all inferred dependencies as mandatory
1582 dependencies. This only applies for fw_devlink=on|rpm.
1586 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1587 support via parallel port (up to 5 devices per port)
1588 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1589 See also Documentation/input/devices/joystick-parport.rst
1593 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART
1597 gcov_persist= [GCOV] When non-zero (default), profiling data for
1598 kernel modules is saved and remains accessible via
1599 debugfs, even when the module is unloaded/reloaded.
1600 When zero, profiling data is discarded and associated
1601 debugfs files are removed at module unload time.
1603 goldfish [X86] Enable the goldfish android emulator platform.
1604 Don't use this when you are not running on the
1607 gpio-mockup.gpio_mockup_ranges
1608 [HW] Sets the ranges of gpiochip of for this device.
1609 Format: <start1>,<end1>,<start2>,<end2>...
1610 gpio-mockup.gpio_mockup_named_lines
1611 [HW] Let the driver know GPIO lines should be named.
1613 gpt [EFI] Forces disk with valid GPT signature but
1614 invalid Protective MBR to be treated as GPT. If the
1615 primary GPT is corrupted, it enables the backup/alternate
1616 GPT to be used instead.
1618 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1619 the "Enable 0" bit of the configuration register.
1622 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1623 the "Enable 0" bit of the configuration register.
1626 grcan.select= [HW] Select which physical interface to use.
1629 grcan.txsize= [HW] Sets the size of the tx buffer.
1630 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1632 grcan.rxsize= [HW] Sets the size of the rx buffer.
1633 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1637 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
1638 hardening is enabled for this boot. Hardened
1639 usercopy checking is used to protect the kernel
1640 from reading or writing beyond known memory
1641 allocation boundaries as a proactive defense
1642 against bounds-checking flaws in the kernel's
1643 copy_to_user()/copy_from_user() interface.
1644 on Perform hardened usercopy checks (default).
1645 off Disable hardened usercopy checks.
1647 hardlockup_all_cpu_backtrace=
1648 [KNL] Should the hard-lockup detector generate
1649 backtraces on all cpus.
1652 hashdist= [KNL,NUMA] Large hashes allocated during boot
1653 are distributed across NUMA nodes. Defaults on
1654 for 64-bit NUMA, off otherwise.
1655 Format: 0 | 1 (for off | on)
1657 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1659 hd= [EIDE] (E)IDE hard drive subsystem geometry
1660 Format: <cyl>,<head>,<sect>
1663 Disable Hardware Error Source Table (HEST) support;
1664 corresponding firmware-first mode error processing
1665 logic will be disabled.
1667 hibernate= [HIBERNATION]
1668 noresume Don't check if there's a hibernation image
1669 present during boot.
1670 nocompress Don't compress/decompress hibernation images.
1671 no Disable hibernation and resume.
1672 protect_image Turn on image protection during restoration
1673 (that will set all pages holding image data
1674 during restoration read-only).
1676 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1677 size of <nn>. This works even on boxes that have no
1678 highmem otherwise. This also works to reduce highmem
1679 size on bigger boxes.
1681 highres= [KNL] Enable/disable high resolution timer mode.
1682 Valid parameters: "on", "off"
1687 hostname= [KNL] Set the hostname (aka UTS nodename).
1689 This allows setting the system's hostname during early
1690 startup. This sets the name returned by gethostname.
1691 Using this parameter to set the hostname makes it
1692 possible to ensure the hostname is correctly set before
1693 any userspace processes run, avoiding the possibility
1694 that a process may call gethostname before the hostname
1695 has been explicitly set, resulting in the calling
1696 process getting an incorrect result. The string must
1697 not exceed the maximum allowed hostname length (usually
1698 64 characters) and will be truncated otherwise.
1700 hpet= [X86-32,HPET] option to control HPET usage
1701 Format: { enable (default) | disable | force |
1703 disable: disable HPET and use PIT instead
1704 force: allow force enabled of undocumented chips (ICH4,
1706 verbose: show contents of HPET registers during setup
1708 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1709 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1711 hugepages= [HW] Number of HugeTLB pages to allocate at boot.
1712 If this follows hugepagesz (below), it specifies
1713 the number of pages of hugepagesz to be allocated.
1714 If this is the first HugeTLB parameter on the command
1715 line, it specifies the number of pages to allocate for
1716 the default huge page size. If using node format, the
1717 number of pages to allocate per-node can be specified.
1718 See also Documentation/admin-guide/mm/hugetlbpage.rst.
1719 Format: <integer> or (node format)
1720 <node>:<integer>[,<node>:<integer>]
1723 [HW] The size of the HugeTLB pages. This is used in
1724 conjunction with hugepages (above) to allocate huge
1725 pages of a specific size at boot. The pair
1726 hugepagesz=X hugepages=Y can be specified once for
1727 each supported huge page size. Huge page sizes are
1728 architecture dependent. See also
1729 Documentation/admin-guide/mm/hugetlbpage.rst.
1732 hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation
1733 of gigantic hugepages. Or using node format, the size
1734 of a CMA area per node can be specified.
1735 Format: nn[KMGTPE] or (node format)
1736 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]]
1738 Reserve a CMA area of given size and allocate gigantic
1739 hugepages using the CMA allocator. If enabled, the
1740 boot-time allocation of gigantic hugepages is skipped.
1742 hugetlb_free_vmemmap=
1743 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
1745 Control if HugeTLB Vmemmap Optimization (HVO) is enabled.
1746 Allows heavy hugetlb users to free up some more
1747 memory (7 * PAGE_SIZE for each 2MB hugetlb page).
1748 Format: { on | off (default) }
1753 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y,
1756 Note that the vmemmap pages may be allocated from the added
1757 memory block itself when memory_hotplug.memmap_on_memory is
1758 enabled, those vmemmap pages cannot be optimized even if this
1759 feature is enabled. Other vmemmap pages not allocated from
1760 the added memory block itself do not be affected.
1763 [KNL] Should the hung task detector generate panics.
1766 A value of 1 instructs the kernel to panic when a
1767 hung task is detected. The default value is controlled
1768 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1769 option. The value selected by this boot parameter can
1770 be changed later by the kernel.hung_task_panic sysctl.
1772 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1773 terminal devices. Valid values: 0..8
1774 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1775 If specified, z/VM IUCV HVC accepts connections
1776 from listed z/VM user IDs only.
1778 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1779 which allow the hypervisor to 'idle' the
1780 guest on lock contention.
1782 i2c_bus= [HW] Override the default board specific I2C bus speed
1783 or register an additional I2C bus that is not
1784 registered from board initialization code.
1788 i8042.debug [HW] Toggle i8042 debug mode
1789 i8042.unmask_kbd_data
1790 [HW] Enable printing of interrupt data from the KBD port
1791 (disabled by default, and as a pre-condition
1792 requires that i8042.debug=1 be enabled)
1793 i8042.direct [HW] Put keyboard port into non-translated mode
1794 i8042.dumbkbd [HW] Pretend that controller can only read data from
1795 keyboard and cannot control its state
1796 (Don't attempt to blink the leds)
1797 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1798 i8042.nokbd [HW] Don't check/create keyboard port
1799 i8042.noloop [HW] Disable the AUX Loopback command while probing
1801 i8042.nomux [HW] Don't check presence of an active multiplexing
1803 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1805 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1806 i8042.reset [HW] Reset the controller during init, cleanup and
1807 suspend-to-ram transitions, only during s2r
1808 transitions, or never reset
1809 Format: { 1 | Y | y | 0 | N | n }
1810 1, Y, y: always reset controller
1811 0, N, n: don't ever reset controller
1812 Default: only on s2r transitions on x86; most other
1813 architectures force reset to be always executed
1814 i8042.unlock [HW] Unlock (ignore) the keylock
1815 i8042.kbdreset [HW] Reset device connected to KBD port
1817 [HW] Allow deferred probing upon i8042 probe errors
1821 i915.invert_brightness=
1822 [DRM] Invert the sense of the variable that is used to
1823 set the brightness of the panel backlight. Normally a
1824 brightness value of 0 indicates backlight switched off,
1825 and the maximum of the brightness value sets the backlight
1826 to maximum brightness. If this parameter is set to 0
1827 (default) and the machine requires it, or this parameter
1828 is set to 1, a brightness value of 0 sets the backlight
1829 to maximum brightness, and the maximum of the brightness
1830 value switches the backlight off.
1831 -1 -- never invert brightness
1832 0 -- machine default
1833 1 -- force brightness inversion
1836 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1840 Format: idle=poll, idle=halt, idle=nomwait
1841 Poll forces a polling idle loop that can slightly
1842 improve the performance of waking up a idle CPU, but
1843 will use a lot of power and make the system run hot.
1845 idle=halt: Halt is forced to be used for CPU idle.
1846 In such case C2/C3 won't be used again.
1847 idle=nomwait: Disable mwait for CPU C-states
1851 Allow force disabling of Shared Virtual Memory (SVA)
1852 support for the idxd driver. By default it is set to
1855 idxd.tc_override= [HW]
1857 Allow override of default traffic class configuration
1858 for the device. By default it is set to false (0).
1860 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1861 Format: { strict | legacy | 2008 | relaxed }
1864 Choose which programs will be accepted for execution
1865 based on the IEEE 754 NaN encoding(s) supported by
1866 the FPU and the NaN encoding requested with the value
1867 of an ELF file header flag individually set by each
1868 binary. Hardware implementations are permitted to
1869 support either or both of the legacy and the 2008 NaN
1872 Available settings are as follows:
1873 strict accept binaries that request a NaN encoding
1874 supported by the FPU
1875 legacy only accept legacy-NaN binaries, if supported
1877 2008 only accept 2008-NaN binaries, if supported
1879 relaxed accept any binaries regardless of whether
1880 supported by the FPU
1882 The FPU emulator is always able to support both NaN
1883 encodings, so if no FPU hardware is present or it has
1884 been disabled with 'nofpu', then the settings of
1885 'legacy' and '2008' strap the emulator accordingly,
1886 'relaxed' straps the emulator for both legacy-NaN and
1887 2008-NaN, whereas 'strict' enables legacy-NaN only on
1888 legacy processors and both NaN encodings on MIPS32 or
1891 The setting for ABS.fmt/NEG.fmt instruction execution
1892 mode generally follows that for the NaN encoding,
1893 except where unsupported by hardware.
1895 ignore_loglevel [KNL]
1896 Ignore loglevel setting - this will print /all/
1897 kernel messages to the console. Useful for debugging.
1898 We also add it as printk module parameter, so users
1899 could change it dynamically, usually by
1900 /sys/module/printk/parameters/ignore_loglevel.
1903 Ignore RLIMIT_DATA setting for data mappings,
1904 print warning at first misuse. Can be changed via
1905 /sys/module/kernel/parameters/ignore_rlimit_data.
1907 ihash_entries= [KNL]
1908 Set number of hash buckets for inode cache.
1910 ima_appraise= [IMA] appraise integrity measurements
1911 Format: { "off" | "enforce" | "fix" | "log" }
1914 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1915 The builtin appraise policy appraises all files
1918 ima_canonical_fmt [IMA]
1919 Use the canonical format for the binary runtime
1920 measurements, instead of host native format.
1923 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1927 The list of supported hash algorithms is defined
1928 in crypto/hash_info.h.
1931 The builtin policies to load during IMA setup.
1932 Format: "tcb | appraise_tcb | secure_boot |
1933 fail_securely | critical_data"
1935 The "tcb" policy measures all programs exec'd, files
1936 mmap'd for exec, and all files opened with the read
1937 mode bit set by either the effective uid (euid=0) or
1940 The "appraise_tcb" policy appraises the integrity of
1941 all files owned by root.
1943 The "secure_boot" policy appraises the integrity
1944 of files (eg. kexec kernel image, kernel modules,
1945 firmware, policy, etc) based on file signatures.
1947 The "fail_securely" policy forces file signature
1948 verification failure also on privileged mounted
1949 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1952 The "critical_data" policy measures kernel integrity
1955 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1956 Load a policy which meets the needs of the Trusted
1957 Computing Base. This means IMA will measure all
1958 programs exec'd, files mmap'd for exec, and all files
1959 opened for read by uid=0.
1962 Select one of defined IMA measurements template formats.
1963 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" |
1968 [IMA] Define a custom template format.
1969 Format: { "field1|...|fieldN" }
1971 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1972 Format: <min_file_size>
1973 Set the minimal file size for using asynchronous hash.
1974 If left unspecified, ahash usage is disabled.
1976 ahash performance varies for different data sizes on
1977 different crypto accelerators. This option can be used
1978 to achieve the best performance for a particular HW.
1980 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1982 Set hashing buffer size. Default: 4k.
1984 ahash performance varies for different chunk sizes on
1985 different crypto accelerators. This option can be used
1986 to achieve best performance for particular HW.
1990 Run specified binary instead of /sbin/init as init
1993 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1994 for working out where the kernel is dying during
1997 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1998 initcall functions. Useful for debugging built-in
1999 modules and initcalls.
2001 initramfs_async= [KNL]
2004 This parameter controls whether the initramfs
2005 image is unpacked asynchronously, concurrently
2006 with devices being probed and
2007 initialized. This should normally just work,
2008 but as a debugging aid, one can get the
2009 historical behaviour of the initramfs
2010 unpacking being completed before device_ and
2013 initrd= [BOOT] Specify the location of the initial ramdisk
2015 initrdmem= [KNL] Specify a physical address and size from which to
2016 load the initrd. If an initrd is compiled in or
2017 specified in the bootparams, it takes priority over this
2019 Format: ss[KMG],nn[KMG]
2022 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
2025 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
2027 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
2029 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
2031 init_pkru= [X86] Specify the default memory protection keys rights
2032 register contents for all processes. 0x55555554 by
2033 default (disallow access to all but pkey 0). Can
2034 override in debugfs after boot.
2036 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
2039 int_pln_enable [X86] Enable power limit notification interrupt
2041 integrity_audit=[IMA]
2042 Format: { "0" | "1" }
2043 0 -- basic integrity auditing messages. (Default)
2044 1 -- additional integrity auditing messages.
2046 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
2048 Enable intel iommu driver.
2050 Disable intel iommu driver.
2051 igfx_off [Default Off]
2052 By default, gfx is mapped as normal device. If a gfx
2053 device has a dedicated DMAR unit, the DMAR unit is
2054 bypassed by not enabling DMAR with this option. In
2055 this case, gfx device will use physical address for
2057 strict [Default Off]
2058 Deprecated, equivalent to iommu.strict=1.
2059 sp_off [Default Off]
2060 By default, super page will be supported if Intel IOMMU
2061 has the capability. With this option, super page will
2064 Enable the Intel IOMMU scalable mode if the hardware
2065 advertises that it has support for the scalable mode
2068 Disallow use of the Intel IOMMU scalable mode.
2069 tboot_noforce [Default Off]
2070 Do not force the Intel IOMMU enabled under tboot.
2071 By default, tboot will force Intel IOMMU on, which
2072 could harm performance of some high-throughput
2073 devices like 40GBit network cards, even if identity
2075 Note that using this option lowers the security
2076 provided by tboot because it makes the system
2077 vulnerable to DMA attacks.
2079 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
2080 0 disables intel_idle and fall back on acpi_idle.
2081 1 to 9 specify maximum depth of C-state.
2085 Do not enable intel_pstate as the default
2086 scaling driver for the supported processors
2088 Use intel_pstate as a scaling driver, but configure it
2089 to work with generic cpufreq governors (instead of
2090 enabling its internal governor). This mode cannot be
2091 used along with the hardware-managed P-states (HWP)
2094 Enable intel_pstate on systems that prohibit it by default
2095 in favor of acpi-cpufreq. Forcing the intel_pstate driver
2096 instead of acpi-cpufreq may disable platform features, such
2097 as thermal controls and power capping, that rely on ACPI
2098 P-States information being indicated to OSPM and therefore
2099 should be used with caution. This option does not work with
2100 processors that aren't supported by the intel_pstate driver
2101 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2103 Do not enable hardware P state control (HWP)
2106 Only load intel_pstate on systems which support
2107 hardware P state control (HWP) if available.
2109 Enforce ACPI _PPC performance limits. If the Fixed ACPI
2110 Description Table, specifies preferred power management
2111 profile as "Enterprise Server" or "Performance Server",
2112 then this feature is turned on by default.
2114 Allow per-logical-CPU P-State performance control limits using
2115 cpufreq sysfs interface
2117 intremap= [X86-64, Intel-IOMMU]
2118 on enable Interrupt Remapping (default)
2119 off disable Interrupt Remapping
2120 nosid disable Source ID checking
2122 BIOS x2APIC opt-out request will be ignored
2123 nopost disable Interrupt Posting
2125 iomem= Disable strict checking of access to MMIO memory
2126 strict regions from userspace.
2141 nobypass [PPC/POWERNV]
2142 Disable IOMMU bypass, using IOMMU for PCI devices.
2144 iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices.
2145 Format: { "0" | "1" }
2146 0 - Try to allocate a 32-bit DMA address first, before
2147 falling back to the full range if needed.
2148 1 - Allocate directly from the full usable range,
2149 forcing Dual Address Cycle for PCI cards supporting
2150 greater than 32-bit addressing.
2152 iommu.strict= [ARM64, X86] Configure TLB invalidation behaviour
2153 Format: { "0" | "1" }
2155 Request that DMA unmap operations use deferred
2156 invalidation of hardware TLBs, for increased
2157 throughput at the cost of reduced device isolation.
2158 Will fall back to strict mode if not supported by
2159 the relevant IOMMU driver.
2161 DMA unmap operations invalidate IOMMU hardware TLBs
2163 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}.
2164 Note: on x86, strict mode specified via one of the
2165 legacy driver-specific options takes precedence.
2168 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
2169 Format: { "0" | "1" }
2170 0 - Use IOMMU translation for DMA.
2171 1 - Bypass the IOMMU for DMA.
2172 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
2174 io7= [HW] IO7 for Marvel-based Alpha systems
2175 See comment before marvel_specify_io7 in
2176 arch/alpha/kernel/core_marvel.c.
2178 io_delay= [X86] I/O delay method
2180 Standard port 0x80 based delay
2182 Alternate port 0xed based delay (needed on some systems)
2184 Simple two microseconds delay
2189 See Documentation/admin-guide/nfs/nfsroot.rst.
2191 ipcmni_extend [KNL] Extend the maximum number of unique System V
2192 IPC identifiers from 32,768 to 16,777,216.
2194 irqaffinity= [SMP] Set the default irq affinity mask
2195 The argument is a cpu list, as described above.
2197 irqchip.gicv2_force_probe=
2200 Force the kernel to look for the second 4kB page
2201 of a GICv2 controller even if the memory range
2202 exposed by the device tree is too small.
2204 irqchip.gicv3_nolpi=
2206 Force the kernel to ignore the availability of
2207 LPIs (and by consequence ITSs). Intended for system
2208 that use the kernel as a bootloader, and thus want
2209 to let secondary kernels in charge of setting up
2212 irqchip.gicv3_pseudo_nmi= [ARM64]
2213 Enables support for pseudo-NMIs in the kernel. This
2214 requires the kernel to be built with
2215 CONFIG_ARM64_PSEUDO_NMI.
2218 When an interrupt is not handled search all handlers
2219 for it. Intended to get systems with badly broken
2223 When an interrupt is not handled search all handlers
2224 for it. Also check all handlers each timer
2225 interrupt. Intended to get systems with badly broken
2229 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2231 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2232 [Deprecated - use cpusets instead]
2233 Format: [flag-list,]<cpu-list>
2235 Specify one or more CPUs to isolate from disturbances
2236 specified in the flag list (default: domain):
2239 Disable the tick when a single task runs.
2241 A residual 1Hz tick is offloaded to workqueues, which you
2242 need to affine to housekeeping through the global
2243 workqueue's affinity configured via the
2244 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2245 by using the 'domain' flag described below.
2247 NOTE: by default the global workqueue runs on all CPUs,
2248 so to protect individual CPUs the 'cpumask' file has to
2249 be configured manually after bootup.
2252 Isolate from the general SMP balancing and scheduling
2253 algorithms. Note that performing domain isolation this way
2254 is irreversible: it's not possible to bring back a CPU to
2255 the domains once isolated through isolcpus. It's strongly
2256 advised to use cpusets instead to disable scheduler load
2257 balancing through the "cpuset.sched_load_balance" file.
2258 It offers a much more flexible interface where CPUs can
2259 move in and out of an isolated set anytime.
2261 You can move a process onto or off an "isolated" CPU via
2262 the CPU affinity syscalls or cpuset.
2263 <cpu number> begins at 0 and the maximum value is
2264 "number of CPUs in system - 1".
2268 Isolate from being targeted by managed interrupts
2269 which have an interrupt mask containing isolated
2270 CPUs. The affinity of managed interrupts is
2271 handled by the kernel and cannot be changed via
2272 the /proc/irq/* interfaces.
2274 This isolation is best effort and only effective
2275 if the automatically assigned interrupt mask of a
2276 device queue contains isolated and housekeeping
2277 CPUs. If housekeeping CPUs are online then such
2278 interrupts are directed to the housekeeping CPU
2279 so that IO submitted on the housekeeping CPU
2280 cannot disturb the isolated CPU.
2282 If a queue's affinity mask contains only isolated
2283 CPUs then this parameter has no effect on the
2284 interrupt routing decision, though interrupts are
2285 only delivered when tasks running on those
2286 isolated CPUs submit IO. IO submitted on
2287 housekeeping CPUs has no influence on those
2290 The format of <cpu-list> is described above.
2294 ivrs_ioapic [HW,X86-64]
2295 Provide an override to the IOAPIC-ID<->DEVICE-ID
2296 mapping provided in the IVRS ACPI table.
2297 By default, PCI segment is 0, and can be omitted.
2299 For example, to map IOAPIC-ID decimal 10 to
2300 PCI segment 0x1 and PCI device 00:14.0,
2301 write the parameter as:
2302 ivrs_ioapic=10@0001:00:14.0
2305 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0
2306 write the parameter as:
2307 ivrs_ioapic[10]=00:14.0
2308 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and
2309 PCI device 00:14.0 write the parameter as:
2310 ivrs_ioapic[10]=0001:00:14.0
2312 ivrs_hpet [HW,X86-64]
2313 Provide an override to the HPET-ID<->DEVICE-ID
2314 mapping provided in the IVRS ACPI table.
2315 By default, PCI segment is 0, and can be omitted.
2317 For example, to map HPET-ID decimal 10 to
2318 PCI segment 0x1 and PCI device 00:14.0,
2319 write the parameter as:
2320 ivrs_hpet=10@0001:00:14.0
2323 * To map HPET-ID decimal 0 to PCI device 00:14.0
2324 write the parameter as:
2325 ivrs_hpet[0]=00:14.0
2326 * To map HPET-ID decimal 10 to PCI segment 0x1 and
2327 PCI device 00:14.0 write the parameter as:
2328 ivrs_ioapic[10]=0001:00:14.0
2330 ivrs_acpihid [HW,X86-64]
2331 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2332 mapping provided in the IVRS ACPI table.
2333 By default, PCI segment is 0, and can be omitted.
2335 For example, to map UART-HID:UID AMD0020:0 to
2336 PCI segment 0x1 and PCI device ID 00:14.5,
2337 write the parameter as:
2338 ivrs_acpihid=AMD0020:0@0001:00:14.5
2341 * To map UART-HID:UID AMD0020:0 to PCI segment is 0,
2342 PCI device ID 00:14.5, write the parameter as:
2343 ivrs_acpihid[00:14.5]=AMD0020:0
2344 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and
2345 PCI device ID 00:14.5, write the parameter as:
2346 ivrs_acpihid[0001:00:14.5]=AMD0020:0
2348 js= [HW,JOY] Analog joystick
2349 See Documentation/input/joydev/joystick.rst.
2352 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2353 report on every invalid memory access. Without this
2354 parameter KASAN will print report only for the first
2358 Do not unregister boot console at start. This is only
2359 useful for debugging when something happens in the window
2360 between unregistering the boot console and initializing
2365 kernelcore= [KNL,X86,IA-64,PPC]
2366 Format: nn[KMGTPE] | nn% | "mirror"
2367 This parameter specifies the amount of memory usable by
2368 the kernel for non-movable allocations. The requested
2369 amount is spread evenly throughout all nodes in the
2370 system as ZONE_NORMAL. The remaining memory is used for
2371 movable memory in its own zone, ZONE_MOVABLE. In the
2372 event, a node is too small to have both ZONE_NORMAL and
2373 ZONE_MOVABLE, kernelcore memory will take priority and
2374 other nodes will have a larger ZONE_MOVABLE.
2376 ZONE_MOVABLE is used for the allocation of pages that
2377 may be reclaimed or moved by the page migration
2378 subsystem. Note that allocations like PTEs-from-HighMem
2379 still use the HighMem zone if it exists, and the Normal
2380 zone if it does not.
2382 It is possible to specify the exact amount of memory in
2383 the form of "nn[KMGTPE]", a percentage of total system
2384 memory in the form of "nn%", or "mirror". If "mirror"
2385 option is specified, mirrored (reliable) memory is used
2386 for non-movable allocations and remaining memory is used
2387 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2388 are exclusive, so you cannot specify multiple forms.
2390 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
2391 Format: <Controller#>[,poll interval]
2392 The controller # is the number of the ehci usb debug
2393 port as it is probed via PCI. The poll interval is
2394 optional and is the number seconds in between
2395 each poll cycle to the debug port in case you need
2396 the functionality for interrupting the kernel with
2397 gdb or control-c on the dbgp connection. When
2398 not using this parameter you use sysrq-g to break into
2399 the kernel debugger.
2401 kgdboc= [KGDB,HW] kgdb over consoles.
2402 Requires a tty driver that supports console polling,
2403 or a supported polling keyboard driver (non-usb).
2404 Serial only format: <serial_device>[,baud]
2405 keyboard only format: kbd
2406 keyboard and serial format: kbd,<serial_device>[,baud]
2407 Optional Kernel mode setting:
2408 kms, kbd format: kms,kbd
2409 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2411 kgdboc_earlycon= [KGDB,HW]
2412 If the boot console provides the ability to read
2413 characters and can work in polling mode, you can use
2414 this parameter to tell kgdb to use it as a backend
2415 until the normal console is registered. Intended to
2416 be used together with the kgdboc parameter which
2417 specifies the normal console to transition to.
2419 The name of the early console should be specified
2420 as the value of this parameter. Note that the name of
2421 the early console might be different than the tty
2422 name passed to kgdboc. It's OK to leave the value
2423 blank and the first boot console that implements
2424 read() will be picked.
2426 kgdbwait [KGDB] Stop kernel execution and enter the
2427 kernel debugger at the earliest opportunity.
2429 kmac= [MIPS] Korina ethernet MAC address.
2430 Configure the RouterBoard 532 series on-chip
2431 Ethernet adapter MAC address.
2433 kmemleak= [KNL] Boot-time kmemleak enable/disable
2434 Valid arguments: on, off
2436 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2439 kprobe_event=[probe-list]
2440 [FTRACE] Add kprobe events and enable at boot time.
2441 The probe-list is a semicolon delimited list of probe
2442 definitions. Each definition is same as kprobe_events
2443 interface, but the parameters are comma delimited.
2444 For example, to add a kprobe event on vfs_read with
2445 arg1 and arg2, add to the command line;
2447 kprobe_event=p,vfs_read,$arg1,$arg2
2449 See also Documentation/trace/kprobetrace.rst "Kernel
2450 Boot Parameter" section.
2452 kpti= [ARM64] Control page table isolation of user
2453 and kernel address spaces.
2454 Default: enabled on cores which need mitigation.
2458 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires
2459 CONFIG_KUNIT to be set to be fully enabled. The
2460 default value can be overridden via
2461 KUNIT_DEFAULT_ENABLED.
2462 Default is 1 (enabled)
2464 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2465 Default is 0 (don't ignore, but inject #GP)
2467 kvm.eager_page_split=
2468 [KVM,X86] Controls whether or not KVM will try to
2469 proactively split all huge pages during dirty logging.
2470 Eager page splitting reduces interruptions to vCPU
2471 execution by eliminating the write-protection faults
2472 and MMU lock contention that would otherwise be
2473 required to split huge pages lazily.
2475 VM workloads that rarely perform writes or that write
2476 only to a small region of VM memory may benefit from
2477 disabling eager page splitting to allow huge pages to
2478 still be used for reads.
2480 The behavior of eager page splitting depends on whether
2481 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If
2482 disabled, all huge pages in a memslot will be eagerly
2483 split when dirty logging is enabled on that memslot. If
2484 enabled, eager page splitting will be performed during
2485 the KVM_CLEAR_DIRTY ioctl, and only for the pages being
2488 Eager page splitting is only supported when kvm.tdp_mmu=Y.
2492 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2493 Default is false (don't support).
2496 [KVM] Controls the software workaround for the
2497 X86_BUG_ITLB_MULTIHIT bug.
2498 force : Always deploy workaround.
2499 off : Never deploy workaround.
2500 auto : Deploy workaround based on the presence of
2501 X86_BUG_ITLB_MULTIHIT.
2505 If the software workaround is enabled for the host,
2506 guests do need not to enable it for nested guests.
2508 kvm.nx_huge_pages_recovery_ratio=
2509 [KVM] Controls how many 4KiB pages are periodically zapped
2510 back to huge pages. 0 disables the recovery, otherwise if
2511 the value is N KVM will zap 1/Nth of the 4KiB pages every
2512 period (see below). The default is 60.
2514 kvm.nx_huge_pages_recovery_period_ms=
2515 [KVM] Controls the time period at which KVM zaps 4KiB pages
2516 back to huge pages. If the value is a non-zero N, KVM will
2517 zap a portion (see ratio above) of the pages every N msecs.
2518 If the value is 0 (the default), KVM will pick a period based
2519 on the ratio, such that a page is zapped after 1 hour on average.
2521 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2522 Default is 1 (enabled)
2524 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2526 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2529 [KVM,ARM] Select one of KVM/arm64's modes of operation.
2531 none: Forcefully disable KVM.
2533 nvhe: Standard nVHE-based mode, without support for
2536 protected: nVHE-based mode with support for guests whose
2537 state is kept private from the host.
2539 nested: VHE-based mode with support for nested
2540 virtualization. Requires at least ARMv8.3
2543 Defaults to VHE/nVHE based on hardware support. Setting
2544 mode to "protected" will disable kexec and hibernation
2545 for the host. "nested" is experimental and should be
2546 used with extreme caution.
2548 kvm-arm.vgic_v3_group0_trap=
2549 [KVM,ARM] Trap guest accesses to GICv3 group-0
2552 kvm-arm.vgic_v3_group1_trap=
2553 [KVM,ARM] Trap guest accesses to GICv3 group-1
2556 kvm-arm.vgic_v3_common_trap=
2557 [KVM,ARM] Trap guest accesses to GICv3 common
2560 kvm-arm.vgic_v4_enable=
2561 [KVM,ARM] Allow use of GICv4 for direct injection of
2564 kvm_cma_resv_ratio=n [PPC]
2565 Reserves given percentage from system memory area for
2566 contiguous memory allocation for KVM hash pagetable
2568 By default it reserves 5% of total system memory.
2572 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2573 (virtualized MMU) support on capable Intel chips.
2574 Default is 1 (enabled)
2576 kvm-intel.emulate_invalid_guest_state=
2577 [KVM,Intel] Disable emulation of invalid guest state.
2578 Ignored if kvm-intel.enable_unrestricted_guest=1, as
2579 guest state is never invalid for unrestricted guests.
2580 This param doesn't apply to nested guests (L2), as KVM
2581 never emulates invalid L2 guest state.
2582 Default is 1 (enabled)
2584 kvm-intel.flexpriority=
2585 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2586 Default is 1 (enabled)
2589 [KVM,Intel] Enable VMX nesting (nVMX).
2590 Default is 0 (disabled)
2592 kvm-intel.unrestricted_guest=
2593 [KVM,Intel] Disable unrestricted guest feature
2594 (virtualized real and unpaged mode) on capable
2595 Intel chips. Default is 1 (enabled)
2597 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2600 Valid arguments: never, cond, always
2602 always: L1D cache flush on every VMENTER.
2603 cond: Flush L1D on VMENTER only when the code between
2604 VMEXIT and VMENTER can leak host memory.
2605 never: Disables the mitigation
2607 Default is cond (do L1 cache flush in specific instances)
2609 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2610 feature (tagged TLBs) on capable Intel chips.
2611 Default is 1 (enabled)
2613 l1d_flush= [X86,INTEL]
2614 Control mitigation for L1D based snooping vulnerability.
2616 Certain CPUs are vulnerable to an exploit against CPU
2617 internal buffers which can forward information to a
2618 disclosure gadget under certain conditions.
2620 In vulnerable processors, the speculatively
2621 forwarded data can be used in a cache side channel
2622 attack, to access data to which the attacker does
2623 not have direct access.
2625 This parameter controls the mitigation. The
2628 on - enable the interface for the mitigation
2630 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2633 The kernel PTE inversion protection is unconditionally
2634 enabled and cannot be disabled.
2637 Provides all available mitigations for the
2638 L1TF vulnerability. Disables SMT and
2639 enables all mitigations in the
2640 hypervisors, i.e. unconditional L1D flush.
2642 SMT control and L1D flush control via the
2643 sysfs interface is still possible after
2644 boot. Hypervisors will issue a warning
2645 when the first VM is started in a
2646 potentially insecure configuration,
2647 i.e. SMT enabled or L1D flush disabled.
2650 Same as 'full', but disables SMT and L1D
2651 flush runtime control. Implies the
2652 'nosmt=force' command line option.
2653 (i.e. sysfs control of SMT is disabled.)
2656 Leaves SMT enabled and enables the default
2657 hypervisor mitigation, i.e. conditional
2660 SMT control and L1D flush control via the
2661 sysfs interface is still possible after
2662 boot. Hypervisors will issue a warning
2663 when the first VM is started in a
2664 potentially insecure configuration,
2665 i.e. SMT enabled or L1D flush disabled.
2669 Disables SMT and enables the default
2670 hypervisor mitigation.
2672 SMT control and L1D flush control via the
2673 sysfs interface is still possible after
2674 boot. Hypervisors will issue a warning
2675 when the first VM is started in a
2676 potentially insecure configuration,
2677 i.e. SMT enabled or L1D flush disabled.
2680 Same as 'flush', but hypervisors will not
2681 warn when a VM is started in a potentially
2682 insecure configuration.
2685 Disables hypervisor mitigations and doesn't
2687 It also drops the swap size and available
2688 RAM limit restriction on both hypervisor and
2693 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2699 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2702 lapic= [X86,APIC] Do not use TSC deadline
2703 value for LAPIC timer one-shot implementation. Default
2704 back to the programmable timer unit in the LAPIC.
2705 Format: notscdeadline
2707 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2710 libata.dma= [LIBATA] DMA control
2711 libata.dma=0 Disable all PATA and SATA DMA
2712 libata.dma=1 PATA and SATA Disk DMA only
2713 libata.dma=2 ATAPI (CDROM) DMA only
2714 libata.dma=4 Compact Flash DMA only
2715 Combinations also work, so libata.dma=3 enables DMA
2716 for disks and CDROMs, but not CFs.
2718 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2719 libata.ignore_hpa=0 keep BIOS limits (default)
2720 libata.ignore_hpa=1 ignore limits, using full disk
2722 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2726 libata.force= [LIBATA] Force configurations. The format is a comma-
2727 separated list of "[ID:]VAL" where ID is PORT[.DEVICE].
2728 PORT and DEVICE are decimal numbers matching port, link
2729 or device. Basically, it matches the ATA ID string
2730 printed on console by libata. If the whole ID part is
2731 omitted, the last PORT and DEVICE values are used. If
2732 ID hasn't been specified yet, the configuration applies
2733 to all ports, links and devices.
2735 If only DEVICE is omitted, the parameter applies to
2736 the port and all links and devices behind it. DEVICE
2737 number of 0 either selects the first device or the
2738 first fan-out link behind PMP device. It does not
2739 select the host link. DEVICE number of 15 selects the
2740 host link and device attached to it.
2742 The VAL specifies the configuration to force. As long
2743 as there is no ambiguity, shortcut notation is allowed.
2744 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2745 The following configurations can be forced.
2747 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2748 Any ID with matching PORT is used.
2750 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2752 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2753 udma[/][16,25,33,44,66,100,133] notation is also
2756 * nohrst, nosrst, norst: suppress hard, soft and both
2759 * rstonce: only attempt one reset during hot-unplug
2762 * [no]dbdelay: Enable or disable the extra 200ms delay
2763 before debouncing a link PHY and device presence
2766 * [no]ncq: Turn on or off NCQ.
2768 * [no]ncqtrim: Enable or disable queued DSM TRIM.
2770 * [no]ncqati: Enable or disable NCQ trim on ATI chipset.
2772 * [no]trim: Enable or disable (unqueued) TRIM.
2774 * trim_zero: Indicate that TRIM command zeroes data.
2776 * max_trim_128m: Set 128M maximum trim size limit.
2778 * [no]dma: Turn on or off DMA transfers.
2780 * atapi_dmadir: Enable ATAPI DMADIR bridge support.
2782 * atapi_mod16_dma: Enable the use of ATAPI DMA for
2783 commands that are not a multiple of 16 bytes.
2785 * [no]dmalog: Enable or disable the use of the
2786 READ LOG DMA EXT command to access logs.
2788 * [no]iddevlog: Enable or disable access to the
2789 identify device data log.
2791 * [no]logdir: Enable or disable access to the general
2792 purpose log directory.
2794 * max_sec_128: Set transfer size limit to 128 sectors.
2796 * max_sec_1024: Set or clear transfer size limit to
2799 * max_sec_lba48: Set or clear transfer size limit to
2802 * [no]lpm: Enable or disable link power management.
2804 * [no]setxfer: Indicate if transfer speed mode setting
2807 * [no]fua: Disable or enable FUA (Force Unit Access)
2808 support for devices supporting this feature.
2810 * dump_id: Dump IDENTIFY data.
2812 * disable: Disable this device.
2814 If there are multiple matching configurations changing
2815 the same attribute, the last one is used.
2817 load_ramdisk= [RAM] [Deprecated]
2819 lockd.nlm_grace_period=P [NFS] Assign grace period.
2822 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2825 lockd.nlm_timeout=T [NFS] Assign timeout value.
2828 lockd.nlm_udpport=M [NFS] Assign UDP port.
2831 lockdown= [SECURITY]
2832 { integrity | confidentiality }
2833 Enable the kernel lockdown feature. If set to
2834 integrity, kernel features that allow userland to
2835 modify the running kernel are disabled. If set to
2836 confidentiality, kernel features that allow userland
2837 to extract confidential information from the kernel
2840 locktorture.nreaders_stress= [KNL]
2841 Set the number of locking read-acquisition kthreads.
2842 Defaults to being automatically set based on the
2843 number of online CPUs.
2845 locktorture.nwriters_stress= [KNL]
2846 Set the number of locking write-acquisition kthreads.
2848 locktorture.onoff_holdoff= [KNL]
2849 Set time (s) after boot for CPU-hotplug testing.
2851 locktorture.onoff_interval= [KNL]
2852 Set time (s) between CPU-hotplug operations, or
2853 zero to disable CPU-hotplug testing.
2855 locktorture.shuffle_interval= [KNL]
2856 Set task-shuffle interval (jiffies). Shuffling
2857 tasks allows some CPUs to go into dyntick-idle
2858 mode during the locktorture test.
2860 locktorture.shutdown_secs= [KNL]
2861 Set time (s) after boot system shutdown. This
2862 is useful for hands-off automated testing.
2864 locktorture.stat_interval= [KNL]
2865 Time (s) between statistics printk()s.
2867 locktorture.stutter= [KNL]
2868 Time (s) to stutter testing, for example,
2869 specifying five seconds causes the test to run for
2870 five seconds, wait for five seconds, and so on.
2871 This tests the locking primitive's ability to
2872 transition abruptly to and from idle.
2874 locktorture.torture_type= [KNL]
2875 Specify the locking implementation to test.
2877 locktorture.verbose= [KNL]
2878 Enable additional printk() statements.
2880 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2883 loglevel= All Kernel Messages with a loglevel smaller than the
2884 console loglevel will be printed to the console. It can
2885 also be changed with klogd or other programs. The
2886 loglevels are defined as follows:
2888 0 (KERN_EMERG) system is unusable
2889 1 (KERN_ALERT) action must be taken immediately
2890 2 (KERN_CRIT) critical conditions
2891 3 (KERN_ERR) error conditions
2892 4 (KERN_WARNING) warning conditions
2893 5 (KERN_NOTICE) normal but significant condition
2894 6 (KERN_INFO) informational
2895 7 (KERN_DEBUG) debug-level messages
2897 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2898 in bytes. n must be a power of two and greater
2899 than the minimal size. The minimal size is defined
2900 by LOG_BUF_SHIFT kernel config parameter. There is
2901 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2902 that allows to increase the default size depending on
2903 the number of CPUs. See init/Kconfig for more details.
2905 logo.nologo [FB] Disables display of the built-in Linux logo.
2906 This may be used to provide more screen space for
2907 kernel log messages and is useful when debugging
2908 kernel boot problems.
2910 lp=0 [LP] Specify parallel ports to use, e.g,
2911 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2912 lp=reset first parallel port). 'lp=0' disables the
2913 lp=auto printer driver. 'lp=reset' (which can be
2914 specified in addition to the ports) causes
2915 attached printers to be reset. Using
2916 lp=port1,port2,... specifies the parallel ports
2917 to associate lp devices with, starting with
2918 lp0. A port specification may be 'none' to skip
2919 that lp device, or a parport name such as
2920 'parport0'. Specifying 'lp=auto' instead of a
2921 port specification list means that device IDs
2922 from each port should be examined, to see if
2923 an IEEE 1284-compliant printer is attached; if
2924 so, the driver will manage that printer.
2925 See also header of drivers/char/lp.c.
2928 Sets loops_per_jiffy to given constant, thus avoiding
2929 time-consuming boot-time autodetection (up to 250 ms per
2930 CPU). 0 enables autodetection (default). To determine
2931 the correct value for your kernel, boot with normal
2932 autodetection and see what value is printed. Note that
2933 on SMP systems the preset will be applied to all CPUs,
2934 which is likely to cause problems if your CPUs need
2935 significantly divergent settings. An incorrect value
2936 will cause delays in the kernel to be wrong, leading to
2937 unpredictable I/O errors and other breakage. Although
2938 unlikely, in the extreme case this might damage your
2942 Format: <io>,<irq>,<dma>
2944 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2947 [SECURITY] Choose order of LSM initialization. This
2948 overrides CONFIG_LSM, and the "security=" parameter.
2950 machvec= [IA-64] Force the use of a particular machine-vector
2951 (machvec) in a generic kernel.
2952 Example: machvec=hpzx1
2954 machtype= [Loongson] Share the same kernel image file between
2955 different yeeloong laptops.
2956 Example: machtype=lemote-yeeloong-2f-7inch
2958 max_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory greater
2959 than or equal to this physical address is ignored.
2961 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2962 will bring up during bootup. maxcpus=n : n >= 0 limits
2963 the kernel to bring up 'n' processors. Surely after
2964 bootup you can bring up the other plugged cpu by executing
2965 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2966 only takes effect during system bootup.
2967 While n=0 is a special case, it is equivalent to "nosmp",
2968 which also disables the IO APIC.
2970 max_loop= [LOOP] The number of loop block devices that get
2971 (loop.max_loop) unconditionally pre-created at init time. The default
2972 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2973 of statically allocating a predefined number, loop
2974 devices can be requested on-demand with the
2975 /dev/loop-control interface.
2977 mce [X86-32] Machine Check Exception
2979 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2981 md= [HW] RAID subsystems devices and level
2982 See Documentation/admin-guide/md.rst.
2985 Format: <first>,<last>
2986 Specifies range of consoles to be captured by the MDA.
2989 Control mitigation for the Micro-architectural Data
2990 Sampling (MDS) vulnerability.
2992 Certain CPUs are vulnerable to an exploit against CPU
2993 internal buffers which can forward information to a
2994 disclosure gadget under certain conditions.
2996 In vulnerable processors, the speculatively
2997 forwarded data can be used in a cache side channel
2998 attack, to access data to which the attacker does
2999 not have direct access.
3001 This parameter controls the MDS mitigation. The
3004 full - Enable MDS mitigation on vulnerable CPUs
3005 full,nosmt - Enable MDS mitigation and disable
3006 SMT on vulnerable CPUs
3007 off - Unconditionally disable MDS mitigation
3009 On TAA-affected machines, mds=off can be prevented by
3010 an active TAA mitigation as both vulnerabilities are
3011 mitigated with the same mechanism so in order to disable
3012 this mitigation, you need to specify tsx_async_abort=off
3015 Not specifying this option is equivalent to
3018 For details see: Documentation/admin-guide/hw-vuln/mds.rst
3020 mem=nn[KMG] [HEXAGON] Set the memory size.
3021 Must be specified, otherwise memory size will be 0.
3023 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
3024 Amount of memory to be used in cases as follows:
3027 2 when the kernel is not able to see the whole system memory;
3028 3 memory that lies after 'mem=' boundary is excluded from
3029 the hypervisor, then assigned to KVM guests.
3030 4 to limit the memory available for kdump kernel.
3032 [ARC,MICROBLAZE] - the limit applies only to low memory,
3033 high memory is not affected.
3035 [ARM64] - only limits memory covered by the linear
3036 mapping. The NOMAP regions are not affected.
3038 [X86] Work as limiting max address. Use together
3039 with memmap= to avoid physical address space collisions.
3040 Without memmap= PCI devices could be placed at addresses
3041 belonging to unused RAM.
3043 Note that this only takes effects during boot time since
3044 in above case 3, memory may need be hot added after boot
3045 if system memory of hypervisor is not sufficient.
3048 [ARM,MIPS] - override the memory layout reported by
3050 Define a memory region of size nn[KMG] starting at
3052 Multiple different regions can be specified with
3053 multiple mem= parameters on the command line.
3055 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
3058 memblock=debug [KNL] Enable memblock debug messages.
3061 [KNL,SH] Allow user to override the default size for
3062 per-device physically contiguous DMA buffers.
3064 memhp_default_state=online/offline
3065 [KNL] Set the initial state for the memory hotplug
3066 onlining policy. If not specified, the default value is
3067 set according to the
3068 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
3070 See Documentation/admin-guide/mm/memory-hotplug.rst.
3072 memmap=exactmap [KNL,X86] Enable setting of an exact
3073 E820 memory map, as specified by the user.
3074 Such memmap=exactmap lines can be constructed based on
3075 BIOS output or other requirements. See the memmap=nn@ss
3078 memmap=nn[KMG]@ss[KMG]
3079 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory.
3080 Region of memory to be used is from ss to ss+nn.
3081 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
3082 which limits max address to nn[KMG].
3083 Multiple different regions can be specified,
3086 memmap=100M@2G,100M#3G,1G!1024G
3088 memmap=nn[KMG]#ss[KMG]
3089 [KNL,ACPI] Mark specific memory as ACPI data.
3090 Region of memory to be marked is from ss to ss+nn.
3092 memmap=nn[KMG]$ss[KMG]
3093 [KNL,ACPI] Mark specific memory as reserved.
3094 Region of memory to be reserved is from ss to ss+nn.
3095 Example: Exclude memory from 0x18690000-0x1869ffff
3096 memmap=64K$0x18690000
3098 memmap=0x10000$0x18690000
3099 Some bootloaders may need an escape character before '$',
3100 like Grub2, otherwise '$' and the following number
3103 memmap=nn[KMG]!ss[KMG]
3104 [KNL,X86] Mark specific memory as protected.
3105 Region of memory to be used, from ss to ss+nn.
3106 The memory region may be marked as e820 type 12 (0xc)
3107 and is NVDIMM or ADR memory.
3109 memmap=<size>%<offset>-<oldtype>+<newtype>
3110 [KNL,ACPI] Convert memory within the specified region
3111 from <oldtype> to <newtype>. If "-<oldtype>" is left
3112 out, the whole region will be marked as <newtype>,
3113 even if previously unavailable. If "+<newtype>" is left
3114 out, matching memory will be removed. Types are
3115 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
3116 3 = ACPI, 12 = PRAM.
3118 memory_corruption_check=0/1 [X86]
3119 Some BIOSes seem to corrupt the first 64k of
3120 memory when doing things like suspend/resume.
3121 Setting this option will scan the memory
3122 looking for corruption. Enabling this will
3123 both detect corruption and prevent the kernel
3124 from using the memory being corrupted.
3125 However, its intended as a diagnostic tool; if
3126 repeatable BIOS-originated corruption always
3127 affects the same memory, you can use memmap=
3128 to prevent the kernel from using that memory.
3130 memory_corruption_check_size=size [X86]
3131 By default it checks for corruption in the low
3132 64k, making this memory unavailable for normal
3133 use. Use this parameter to scan for
3134 corruption in more or less memory.
3136 memory_corruption_check_period=seconds [X86]
3137 By default it checks for corruption every 60
3138 seconds. Use this parameter to check at some
3139 other rate. 0 disables periodic checking.
3141 memory_hotplug.memmap_on_memory
3142 [KNL,X86,ARM] Boolean flag to enable this feature.
3143 Format: {on | off (default)}
3144 When enabled, runtime hotplugged memory will
3145 allocate its internal metadata (struct pages,
3146 those vmemmap pages cannot be optimized even
3147 if hugetlb_free_vmemmap is enabled) from the
3148 hotadded memory which will allow to hotadd a
3149 lot of memory without requiring additional
3151 This feature is disabled by default because it
3152 has some implication on large (e.g. GB)
3153 allocations in some configurations (e.g. small
3155 The state of the flag can be read in
3156 /sys/module/memory_hotplug/parameters/memmap_on_memory.
3157 Note that even when enabled, there are a few cases where
3158 the feature is not effective.
3160 memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest
3162 default : 0 <disable>
3163 Specifies the number of memtest passes to be
3164 performed. Each pass selects another test
3165 pattern from a given set of patterns. Memtest
3166 fills the memory with this pattern, validates
3167 memory contents and reserves bad memory
3168 regions that are detected.
3170 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
3171 Valid arguments: on, off
3172 Default (depends on kernel configuration option):
3173 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
3174 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
3175 mem_encrypt=on: Activate SME
3176 mem_encrypt=off: Do not activate SME
3178 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst
3179 for details on when memory encryption can be activated.
3181 mem_sleep_default= [SUSPEND] Default system suspend mode:
3182 s2idle - Suspend-To-Idle
3183 shallow - Power-On Suspend or equivalent (if supported)
3184 deep - Suspend-To-RAM or equivalent (if supported)
3185 See Documentation/admin-guide/pm/sleep-states.rst.
3187 meye.*= [HW] Set MotionEye Camera parameters
3188 See Documentation/admin-guide/media/meye.rst.
3190 mfgpt_irq= [IA-32] Specify the IRQ to use for the
3191 Multi-Function General Purpose Timers on AMD Geode
3194 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
3195 the BIOS has incorrectly applied a workaround. TinyBIOS
3196 version 0.98 is known to be affected, 0.99 fixes the
3197 problem by letting the user disable the workaround.
3201 min_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory below this
3202 physical address is ignored.
3204 mini2440= [ARM,HW,KNL]
3205 Format:[0..2][b][c][t]
3207 MINI2440 configuration specification:
3208 0 - The attached screen is the 3.5" TFT
3209 1 - The attached screen is the 7" TFT
3210 2 - The VGA Shield is attached (1024x768)
3211 Leaving out the screen size parameter will not load
3212 the TFT driver, and the framebuffer will be left
3214 b - Enable backlight. The TFT backlight pin will be
3215 linked to the kernel VESA blanking code and a GPIO
3216 LED. This parameter is not necessary when using the
3218 c - Enable the s3c camera interface.
3219 t - Reserved for enabling touchscreen support. The
3220 touchscreen support is not enabled in the mainstream
3221 kernel as of 2.6.30, a preliminary port can be found
3222 in the "bleeding edge" mini2440 support kernel at
3223 https://repo.or.cz/w/linux-2.6/mini2440.git
3226 [X86,PPC,S390,ARM64] Control optional mitigations for
3227 CPU vulnerabilities. This is a set of curated,
3228 arch-independent options, each of which is an
3229 aggregation of existing arch-specific options.
3232 Disable all optional CPU mitigations. This
3233 improves system performance, but it may also
3234 expose users to several CPU vulnerabilities.
3235 Equivalent to: nopti [X86,PPC]
3236 if nokaslr then kpti=0 [ARM64]
3237 nospectre_v1 [X86,PPC]
3239 nospectre_v2 [X86,PPC,S390,ARM64]
3240 spectre_v2_user=off [X86]
3241 spec_store_bypass_disable=off [X86,PPC]
3242 ssbd=force-off [ARM64]
3243 nospectre_bhb [ARM64]
3246 tsx_async_abort=off [X86]
3247 kvm.nx_huge_pages=off [X86]
3248 srbds=off [X86,INTEL]
3249 no_entry_flush [PPC]
3250 no_uaccess_flush [PPC]
3251 mmio_stale_data=off [X86]
3255 This does not have any effect on
3256 kvm.nx_huge_pages when
3257 kvm.nx_huge_pages=force.
3260 Mitigate all CPU vulnerabilities, but leave SMT
3261 enabled, even if it's vulnerable. This is for
3262 users who don't want to be surprised by SMT
3263 getting disabled across kernel upgrades, or who
3264 have other ways of avoiding SMT-based attacks.
3265 Equivalent to: (default behavior)
3268 Mitigate all CPU vulnerabilities, disabling SMT
3269 if needed. This is for users who always want to
3270 be fully mitigated, even if it means losing SMT.
3271 Equivalent to: l1tf=flush,nosmt [X86]
3272 mds=full,nosmt [X86]
3273 tsx_async_abort=full,nosmt [X86]
3274 mmio_stale_data=full,nosmt [X86]
3275 retbleed=auto,nosmt [X86]
3278 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
3279 parameter allows control of the logging verbosity for
3280 the additional memory initialisation checks. A value
3281 of 0 disables mminit logging and a level of 4 will
3282 log everything. Information is printed at KERN_DEBUG
3283 so loglevel=8 may also need to be specified.
3286 [X86,INTEL] Control mitigation for the Processor
3287 MMIO Stale Data vulnerabilities.
3289 Processor MMIO Stale Data is a class of
3290 vulnerabilities that may expose data after an MMIO
3291 operation. Exposed data could originate or end in
3292 the same CPU buffers as affected by MDS and TAA.
3293 Therefore, similar to MDS and TAA, the mitigation
3294 is to clear the affected CPU buffers.
3296 This parameter controls the mitigation. The
3299 full - Enable mitigation on vulnerable CPUs
3301 full,nosmt - Enable mitigation and disable SMT on
3304 off - Unconditionally disable mitigation
3306 On MDS or TAA affected machines,
3307 mmio_stale_data=off can be prevented by an active
3308 MDS or TAA mitigation as these vulnerabilities are
3309 mitigated with the same mechanism so in order to
3310 disable this mitigation, you need to specify
3311 mds=off and tsx_async_abort=off too.
3313 Not specifying this option is equivalent to
3314 mmio_stale_data=full.
3317 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
3319 <module>.async_probe[=<bool>] [KNL]
3320 If no <bool> value is specified or if the value
3321 specified is not a valid <bool>, enable asynchronous
3322 probe on this module. Otherwise, enable/disable
3323 asynchronous probe on this module as indicated by the
3324 <bool> value. See also: module.async_probe
3326 module.async_probe=<bool>
3327 [KNL] When set to true, modules will use async probing
3328 by default. To enable/disable async probing for a
3329 specific module, use the module specific control that
3330 is documented under <module>.async_probe. When both
3331 module.async_probe and <module>.async_probe are
3332 specified, <module>.async_probe takes precedence for
3333 the specific module.
3336 [KNL] When CONFIG_MODULE_SIG is set, this means that
3337 modules without (valid) signatures will fail to load.
3338 Note that if CONFIG_MODULE_SIG_FORCE is set, that
3339 is always true, so this option does nothing.
3341 module_blacklist= [KNL] Do not load a comma-separated list of
3342 modules. Useful for debugging problem modules.
3345 [MOUSE] Maximum time between finger touching and
3346 leaving touchpad surface for touch to be considered
3347 a tap and be reported as a left button click (for
3348 touchpads working in absolute mode only).
3350 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
3351 reporting absolute coordinates, such as tablets
3352 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
3353 reporting absolute coordinates, such as tablets
3355 movablecore= [KNL,X86,IA-64,PPC]
3356 Format: nn[KMGTPE] | nn%
3357 This parameter is the complement to kernelcore=, it
3358 specifies the amount of memory used for migratable
3359 allocations. If both kernelcore and movablecore is
3360 specified, then kernelcore will be at *least* the
3361 specified value but may be more. If movablecore on its
3362 own is specified, the administrator must be careful
3363 that the amount of memory usable for all allocations
3366 movable_node [KNL] Boot-time switch to make hotplugable memory
3367 NUMA nodes to be movable. This means that the memory
3368 of such nodes will be usable only for movable
3369 allocations which rules out almost all kernel
3370 allocations. Use with caution!
3372 MTD_Partition= [MTD]
3373 Format: <name>,<region-number>,<size>,<offset>
3375 MTD_Region= [MTD] Format:
3376 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
3379 See drivers/mtd/parsers/cmdlinepart.c
3382 ARM/S3C2412 JIVE boot control
3384 See arch/arm/mach-s3c/mach-jive.c
3386 mtouchusb.raw_coordinates=
3387 [HW] Make the MicroTouch USB driver use raw coordinates
3388 ('y', default) or cooked coordinates ('n')
3390 mtrr_chunk_size=nn[KMG] [X86]
3391 used for mtrr cleanup. It is largest continuous chunk
3392 that could hold holes aka. UC entries.
3394 mtrr_gran_size=nn[KMG] [X86]
3395 Used for mtrr cleanup. It is granularity of mtrr block.
3397 Large value could prevent small alignment from
3400 mtrr_spare_reg_nr=n [X86]
3402 Range: 0,7 : spare reg number
3404 Used for mtrr cleanup. It is spare mtrr entries number.
3405 Set to 2 or more if your graphical card needs more.
3407 multitce=off [PPC] This parameter disables the use of the pSeries
3408 firmware feature for updating multiple TCE entries
3411 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
3413 netdev= [NET] Network devices parameters
3414 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
3415 Note that mem_start is often overloaded to mean
3416 something different and driver-specific.
3417 This usage is only documented in each driver source
3420 netpoll.carrier_timeout=
3421 [NET] Specifies amount of time (in seconds) that
3422 netpoll should wait for a carrier. By default netpoll
3426 [NETFILTER] Enable connection tracking flow accounting
3427 0 to disable accounting
3428 1 to enable accounting
3431 nfsaddrs= [NFS] Deprecated. Use ip= instead.
3432 See Documentation/admin-guide/nfs/nfsroot.rst.
3434 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
3435 See Documentation/admin-guide/nfs/nfsroot.rst.
3437 nfsrootdebug [NFS] enable nfsroot debugging messages.
3438 See Documentation/admin-guide/nfs/nfsroot.rst.
3440 nfs.callback_nr_threads=
3441 [NFSv4] set the total number of threads that the
3442 NFS client will assign to service NFSv4 callback
3445 nfs.callback_tcpport=
3446 [NFS] set the TCP port on which the NFSv4 callback
3447 channel should listen.
3450 [NFS] sets the pathname to the program which is used
3451 to update the NFS client cache entries.
3453 nfs.cache_getent_timeout=
3454 [NFS] sets the timeout after which an attempt to
3455 update a cache entry is deemed to have failed.
3457 nfs.idmap_cache_timeout=
3458 [NFS] set the maximum lifetime for idmapper cache
3462 [NFS] enable 64-bit inode numbers.
3463 If zero, the NFS client will fake up a 32-bit inode
3464 number for the readdir() and stat() syscalls instead
3465 of returning the full 64-bit number.
3466 The default is to return 64-bit inode numbers.
3468 nfs.max_session_cb_slots=
3469 [NFSv4.1] Sets the maximum number of session
3470 slots the client will assign to the callback
3471 channel. This determines the maximum number of
3472 callbacks the client will process in parallel for
3473 a particular server.
3475 nfs.max_session_slots=
3476 [NFSv4.1] Sets the maximum number of session slots
3477 the client will attempt to negotiate with the server.
3478 This limits the number of simultaneous RPC requests
3479 that the client can send to the NFSv4.1 server.
3480 Note that there is little point in setting this
3481 value higher than the max_tcp_slot_table_limit.
3483 nfs.nfs4_disable_idmapping=
3484 [NFSv4] When set to the default of '1', this option
3485 ensures that both the RPC level authentication
3486 scheme and the NFS level operations agree to use
3487 numeric uids/gids if the mount is using the
3488 'sec=sys' security flavour. In effect it is
3489 disabling idmapping, which can make migration from
3490 legacy NFSv2/v3 systems to NFSv4 easier.
3491 Servers that do not support this mode of operation
3492 will be autodetected by the client, and it will fall
3493 back to using the idmapper.
3494 To turn off this behaviour, set the value to '0'.
3496 [NFS4] Specify an additional fixed unique ident-
3497 ification string that NFSv4 clients can insert into
3498 their nfs_client_id4 string. This is typically a
3499 UUID that is generated at system install time.
3501 nfs.send_implementation_id =
3502 [NFSv4.1] Send client implementation identification
3503 information in exchange_id requests.
3504 If zero, no implementation identification information
3506 The default is to send the implementation identification
3509 nfs.recover_lost_locks =
3510 [NFSv4] Attempt to recover locks that were lost due
3511 to a lease timeout on the server. Please note that
3512 doing this risks data corruption, since there are
3513 no guarantees that the file will remain unchanged
3514 after the locks are lost.
3515 If you want to enable the kernel legacy behaviour of
3516 attempting to recover these locks, then set this
3518 The default parameter value of '0' causes the kernel
3519 not to attempt recovery of lost locks.
3521 nfs4.layoutstats_timer =
3522 [NFSv4.2] Change the rate at which the kernel sends
3523 layoutstats to the pNFS metadata server.
3525 Setting this to value to 0 causes the kernel to use
3526 whatever value is the default set by the layout
3527 driver. A non-zero value sets the minimum interval
3528 in seconds between layoutstats transmissions.
3530 nfsd.inter_copy_offload_enable =
3531 [NFSv4.2] When set to 1, the server will support
3532 server-to-server copies for which this server is
3533 the destination of the copy.
3535 nfsd.nfsd4_ssc_umount_timeout =
3536 [NFSv4.2] When used as the destination of a
3537 server-to-server copy, knfsd temporarily mounts
3538 the source server. It caches the mount in case
3539 it will be needed again, and discards it if not
3540 used for the number of milliseconds specified by
3543 nfsd.nfs4_disable_idmapping=
3544 [NFSv4] When set to the default of '1', the NFSv4
3545 server will return only numeric uids and gids to
3546 clients using auth_sys, and will accept numeric uids
3547 and gids from such clients. This is intended to ease
3548 migration from NFSv2/v3.
3551 nmi_backtrace.backtrace_idle [KNL]
3552 Dump stacks even of idle CPUs in response to an
3553 NMI stack-backtrace request.
3555 nmi_debug= [KNL,SH] Specify one or more actions to take
3556 when a NMI is triggered.
3557 Format: [state][,regs][,debounce][,die]
3559 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3560 Format: [panic,][nopanic,][num]
3562 0 - turn hardlockup detector in nmi_watchdog off
3563 1 - turn hardlockup detector in nmi_watchdog on
3564 When panic is specified, panic when an NMI watchdog
3565 timeout occurs (or 'nopanic' to not panic on an NMI
3566 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3567 To disable both hard and soft lockup detectors,
3568 please see 'nowatchdog'.
3569 This is useful when you use a panic=... timeout and
3570 need the box quickly up again.
3572 These settings can be accessed at runtime via
3573 the nmi_watchdog and hardlockup_panic sysctls.
3575 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3576 emulation library even if a 387 maths coprocessor
3579 no4lvl [RISCV] Disable 4-level and 5-level paging modes. Forces
3580 kernel to use 3-level paging instead.
3582 no5lvl [X86-64,RISCV] Disable 5-level paging mode. Forces
3583 kernel to use 4-level paging instead.
3585 nofsgsbase [X86] Disables FSGSBASE instructions.
3588 [HW] Never suspend the console
3589 Disable suspending of consoles during suspend and
3590 hibernate operations. Once disabled, debugging
3591 messages can reach various consoles while the rest
3592 of the system is being put to sleep (ie, while
3593 debugging driver suspend/resume hooks). This may
3594 not work reliably with all consoles, but is known
3595 to work with serial and VGA consoles.
3596 To facilitate more flexible debugging, we also add
3597 console_suspend, a printk module parameter to control
3598 it. Users could use console_suspend (usually
3599 /sys/module/printk/parameters/console_suspend) to
3600 turn on/off it dynamically.
3602 novmcoredd [KNL,KDUMP]
3603 Disable device dump. Device dump allows drivers to
3604 append dump data to vmcore so you can collect driver
3605 specified debug info. Drivers can append the data
3606 without any limit and this data is stored in memory,
3607 so this may cause significant memory stress. Disabling
3608 device dump can help save memory but the driver debug
3609 data will be no longer available. This parameter
3610 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
3613 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
3614 caches in the slab allocator. Saves per-node memory,
3615 but will impact performance.
3619 noaltinstr [S390] Disables alternative instructions patching
3620 (CPU alternatives feature).
3622 noapic [SMP,APIC] Tells the kernel to not make use of any
3623 IOAPICs that may be present in the system.
3625 noautogroup Disable scheduler automatic task group creation.
3629 nodsp [SH] Disable hardware DSP at boot time.
3631 noefi Disable EFI runtime services support.
3633 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel.
3638 Disable SMAP (Supervisor Mode Access Prevention)
3639 even if it is supported by processor.
3642 Disable SMEP (Supervisor Mode Execution Prevention)
3643 even if it is supported by processor.
3646 This affects only 32-bit executables.
3647 noexec32=on: enable non-executable mappings (default)
3648 read doesn't imply executable mappings
3649 noexec32=off: disable non-executable mappings
3650 read implies executable mappings
3652 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3654 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3655 register save and restore. The kernel will only save
3656 legacy floating-point registers on task switch.
3658 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings.
3660 nohugevmalloc [KNL,X86,PPC,ARM64] Disable kernel huge vmalloc mappings.
3662 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
3663 Equivalent to smt=1.
3665 [KNL,X86] Disable symmetric multithreading (SMT).
3666 nosmt=force: Force disable SMT, cannot be undone
3667 via the sysfs control file.
3669 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3670 (bounds check bypass). With this option data leaks are
3671 possible in the system.
3673 nospectre_v2 [X86,PPC_E500,ARM64] Disable all mitigations for
3674 the Spectre variant 2 (indirect branch prediction)
3675 vulnerability. System may allow data leaks with this
3678 nospectre_bhb [ARM64] Disable all mitigations for Spectre-BHB (branch
3679 history injection) vulnerability. System may allow data leaks
3682 nospec_store_bypass_disable
3683 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3686 [PPC] Don't flush the L1-D cache after accessing user data.
3688 noxsave [BUGS=X86] Disables x86 extended register state save
3689 and restore using xsave. The kernel will fallback to
3690 enabling legacy floating-point and sse state.
3692 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
3693 register states. The kernel will fall back to use
3694 xsave to save the states. By using this parameter,
3695 performance of saving the states is degraded because
3696 xsave doesn't support modified optimization while
3697 xsaveopt supports it on xsaveopt enabled systems.
3699 noxsaves [X86] Disables xsaves and xrstors used in saving and
3700 restoring x86 extended register state in compacted
3701 form of xsave area. The kernel will fall back to use
3702 xsaveopt and xrstor to save and restore the states
3703 in standard form of xsave area. By using this
3704 parameter, xsave area per process might occupy more
3705 memory on xsaves enabled systems.
3707 nohlt [ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait
3708 in do_idle() and not use the arch_cpu_idle()
3709 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
3710 to be effective. This is useful on platforms where the
3711 sleep(SH) or wfi(ARM,ARM64) instructions do not work
3712 correctly or when doing power measurements to evaluate
3713 the impact of the sleep instructions. This is also
3714 useful when using JTAG debugger.
3716 no_file_caps Tells the kernel not to honor file capabilities. The
3717 only way then for a file to be executed with privilege
3718 is to be setuid root or executed by root.
3720 nohalt [IA-64] Tells the kernel not to use the power saving
3721 function PAL_HALT_LIGHT when idle. This increases
3722 power-consumption. On the positive side, it reduces
3723 interrupt wake-up latency, which may improve performance
3724 in certain environments such as networked servers or
3728 Force pointers printed to the console or buffers to be
3729 unhashed. By default, when a pointer is printed via %p
3730 format string, that pointer is "hashed", i.e. obscured
3731 by hashing the pointer value. This is a security feature
3732 that hides actual kernel addresses from unprivileged
3733 users, but it also makes debugging the kernel more
3734 difficult since unequal pointers can no longer be
3735 compared. However, if this command-line option is
3736 specified, then all normal pointers will have their true
3737 value printed. This option should only be specified when
3738 debugging the kernel. Please do not use on production
3741 nohibernate [HIBERNATION] Disable hibernation and resume.
3743 nohz= [KNL] Boottime enable/disable dynamic ticks
3744 Valid arguments: on, off
3747 nohz_full= [KNL,BOOT,SMP,ISOL]
3748 The argument is a cpu list, as described above.
3749 In kernels built with CONFIG_NO_HZ_FULL=y, set
3750 the specified list of CPUs whose tick will be stopped
3751 whenever possible. The boot CPU will be forced outside
3752 the range to maintain the timekeeping. Any CPUs
3753 in this list will have their RCU callbacks offloaded,
3754 just as if they had also been called out in the
3755 rcu_nocbs= boot parameter.
3757 Note that this argument takes precedence over
3758 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
3760 noiotrap [SH] Disables trapped I/O port accesses.
3762 noirqdebug [X86-32] Disables the code which attempts to detect and
3763 disable unhandled interrupt sources.
3765 no_timer_check [X86,APIC] Disables the code which tests for
3766 broken timer IRQ sources.
3768 noisapnp [ISAPNP] Disables ISA PnP code.
3770 noinitrd [RAM] Tells the kernel not to load any configured
3773 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3775 [Deprecated - use intremap=off]
3779 noinvpcid [X86] Disable the INVPCID cpu feature.
3781 nojitter [IA-64] Disables jitter checking for ITC timers.
3784 When CONFIG_RANDOMIZE_BASE is set, this disables
3785 kernel and module base offset ASLR (Address Space
3786 Layout Randomization).
3788 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3790 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3794 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3795 clock and use the default one.
3797 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES] Disable paravirtualized
3798 steal time accounting. steal time is computed, but
3799 won't influence scheduler behaviour
3801 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3803 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3805 nomca [IA-64] Disable machine check abort handling
3807 nomce [X86-32] Disable Machine Check Exception
3809 nomfgpt [X86-32] Disable Multi-Function General Purpose
3810 Timer usage (for AMD Geode machines).
3812 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3813 shutdown the other cpus. Instead use the REBOOT_VECTOR
3816 nomodeset Disable kernel modesetting. Most systems' firmware
3817 sets up a display mode and provides framebuffer memory
3818 for output. With nomodeset, DRM and fbdev drivers will
3819 not load if they could possibly displace the pre-
3820 initialized output. Only the system framebuffer will
3821 be available for use. The respective drivers will not
3822 perform display-mode changes or accelerated rendering.
3824 Useful as error fallback, or for testing and debugging.
3826 nomodule Disable module load
3828 nopat [X86] Disable PAT (page attribute table extension of
3829 pagetables) support.
3831 nopcid [X86-64] Disable the PCID cpu feature.
3833 nopku [X86] Disable Memory Protection Keys CPU feature found
3836 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
3837 Disables the PV optimizations forcing the guest to run
3838 as generic guest with no PV drivers. Currently support
3839 XEN HVM, KVM, HYPER_V and VMWARE guest.
3841 nopvspin [X86,XEN,KVM]
3842 Disables the qspinlock slow path using PV optimizations
3843 which allow the hypervisor to 'idle' the guest on lock
3846 norandmaps Don't use address space randomization. Equivalent to
3847 echo 0 > /proc/sys/kernel/randomize_va_space
3849 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3850 with UP alternatives
3852 noresume [SWSUSP] Disables resume and restores original swap
3855 no-scroll [VGA] Disables scrollback.
3856 This is required for the Braillex ib80-piezo Braille
3857 reader made by F.H. Papenmeier (Germany).
3861 nosgx [X86-64,SGX] Disables Intel SGX kernel support.
3863 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3864 and disable the IO APIC. legacy for "maxcpus=0".
3866 nosoftlockup [KNL] Disable the soft-lockup detector.
3868 nosync [HW,M68K] Disables sync negotiation for all devices.
3870 nowatchdog [KNL] Disable both lockup detectors, i.e.
3871 soft-lockup and NMI watchdog (hard-lockup).
3875 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3877 NOTE: this parameter will be ignored on systems with the
3878 LEGACY_XAPIC_DISABLED bit set in the
3879 IA32_XAPIC_DISABLE_STATUS MSR.
3881 nps_mtm_hs_ctr= [KNL,ARC]
3882 This parameter sets the maximum duration, in
3883 cycles, each HW thread of the CTOP can run
3884 without interruptions, before HW switches it.
3885 The actual maximum duration is 16 times this
3887 Format: integer between 1 and 255
3890 nptcg= [IA-64] Override max number of concurrent global TLB
3891 purges which is reported from either PAL_VM_SUMMARY or
3894 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3895 could support. nr_cpus=n : n >= 1 limits the kernel to
3896 support 'n' processors. It could be larger than the
3897 number of already plugged CPU during bootup, later in
3898 runtime you can physically add extra cpu until it reaches
3899 n. So during boot up some boot time memory for per-cpu
3900 variables need be pre-allocated for later physical cpu
3903 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3905 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only
3906 set up a single NUMA node spanning all memory.
3908 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
3910 Allowed values are enable and disable
3912 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3913 'node', 'default' can be specified
3914 This can be set from sysctl after boot.
3915 See Documentation/admin-guide/sysctl/vm.rst for details.
3917 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3918 See Documentation/core-api/debugging-via-ohci1394.rst for more
3921 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3922 Rather than timing out after 20 ms if an EC
3923 command is not properly ACKed, override the length
3924 of the timeout. We have interrupts disabled while
3925 waiting for the ACK, so if this is set too high
3926 interrupts *may* be lost!
3928 omap_mux= [OMAP] Override bootloader pin multiplexing.
3929 Format: <mux_mode0.mode_name=value>...
3930 For example, to override I2C bus2:
3931 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3933 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
3935 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
3937 boundary - index of last SLC block on Flex-OneNAND.
3938 The remaining blocks are configured as MLC blocks.
3939 lock - Configure if Flex-OneNAND boundary should be locked.
3940 Once locked, the boundary cannot be changed.
3941 1 indicates lock status, 0 indicates unlock status.
3943 oops=panic Always panic on oopses. Default is to just kill the
3944 process, but there is a small probability of
3945 deadlocking the machine.
3946 This will also cause panics on machine check exceptions.
3947 Useful together with panic=30 to trigger a reboot.
3950 [KNL] Boolean flag to control whether the page allocator
3951 should randomize its free lists. The randomization may
3952 be automatically enabled if the kernel detects it is
3953 running on a platform with a direct-mapped memory-side
3954 cache, and this parameter can be used to
3955 override/disable that behavior. The state of the flag
3956 can be read from sysfs at:
3957 /sys/module/page_alloc/parameters/shuffle.
3959 page_owner= [KNL] Boot-time page_owner enabling option.
3960 Storage of the information about who allocated
3961 each page is disabled in default. With this switch,
3963 on: enable the feature
3965 page_poison= [KNL] Boot-time parameter changing the state of
3966 poisoning on the buddy allocator, available with
3967 CONFIG_PAGE_POISONING=y.
3968 off: turn off poisoning (default)
3969 on: turn on poisoning
3971 page_reporting.page_reporting_order=
3972 [KNL] Minimal page reporting order
3974 Adjust the minimal page reporting order. The page
3975 reporting is disabled when it exceeds (MAX_ORDER-1).
3977 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3978 timeout > 0: seconds before rebooting
3979 timeout = 0: wait forever
3980 timeout < 0: reboot immediately
3983 panic_print= Bitmask for printing system info when panic happens.
3984 User can chose combination of the following bits:
3985 bit 0: print all tasks info
3986 bit 1: print system memory info
3987 bit 2: print timer info
3988 bit 3: print locks info if CONFIG_LOCKDEP is on
3989 bit 4: print ftrace buffer
3990 bit 5: print all printk messages in buffer
3991 bit 6: print all CPUs backtrace (if available in the arch)
3992 *Be aware* that this option may print a _lot_ of lines,
3993 so there are risks of losing older messages in the log.
3994 Use this option carefully, maybe worth to setup a
3995 bigger log buffer with "log_buf_len" along with this.
3997 panic_on_taint= Bitmask for conditionally calling panic() in add_taint()
3998 Format: <hex>[,nousertaint]
3999 Hexadecimal bitmask representing the set of TAINT flags
4000 that will cause the kernel to panic when add_taint() is
4001 called with any of the flags in this set.
4002 The optional switch "nousertaint" can be utilized to
4003 prevent userspace forced crashes by writing to sysctl
4004 /proc/sys/kernel/tainted any flagset matching with the
4005 bitmask set on panic_on_taint.
4006 See Documentation/admin-guide/tainted-kernels.rst for
4007 extra details on the taint flags that users can pick
4008 to compose the bitmask to assign to panic_on_taint.
4010 panic_on_warn panic() instead of WARN(). Useful to cause kdump
4013 parkbd.port= [HW] Parallel port number the keyboard adapter is
4014 connected to, default is 0.
4016 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
4017 0 for XT, 1 for AT (default is AT).
4020 parport= [HW,PPT] Specify parallel ports. 0 disables.
4021 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
4022 Use 'auto' to force the driver to use any
4023 IRQ/DMA settings detected (the default is to
4024 ignore detected IRQ/DMA settings because of
4025 possible conflicts). You can specify the base
4026 address, IRQ, and DMA settings; IRQ and DMA
4027 should be numbers, or 'auto' (for using detected
4028 settings on that particular port), or 'nofifo'
4029 (to avoid using a FIFO even if it is detected).
4030 Parallel ports are assigned in the order they
4031 are specified on the command line, starting
4034 parport_init_mode= [HW,PPT]
4035 Configure VIA parallel port to operate in
4036 a specific mode. This is necessary on Pegasos
4037 computer where firmware has no options for setting
4038 up parallel port mode and sets it to spp.
4039 Currently this function knows 686a and 8231 chips.
4040 Format: [spp|ps2|epp|ecp|ecpepp]
4042 pata_legacy.all= [HW,LIBATA]
4044 Set to non-zero to probe primary and secondary ISA
4045 port ranges on PCI systems where no PCI PATA device
4046 has been found at either range. Disabled by default.
4048 pata_legacy.autospeed= [HW,LIBATA]
4050 Set to non-zero if a chip is present that snoops speed
4051 changes. Disabled by default.
4053 pata_legacy.ht6560a= [HW,LIBATA]
4055 Set to 1, 2, or 3 for HT 6560A on the primary channel,
4056 the secondary channel, or both channels respectively.
4057 Disabled by default.
4059 pata_legacy.ht6560b= [HW,LIBATA]
4061 Set to 1, 2, or 3 for HT 6560B on the primary channel,
4062 the secondary channel, or both channels respectively.
4063 Disabled by default.
4065 pata_legacy.iordy_mask= [HW,LIBATA]
4067 IORDY enable mask. Set individual bits to allow IORDY
4068 for the respective channel. Bit 0 is for the first
4069 legacy channel handled by this driver, bit 1 is for
4070 the second channel, and so on. The sequence will often
4071 correspond to the primary legacy channel, the secondary
4072 legacy channel, and so on, but the handling of a PCI
4073 bus and the use of other driver options may interfere
4074 with the sequence. By default IORDY is allowed across
4077 pata_legacy.opti82c46x= [HW,LIBATA]
4079 Set to 1, 2, or 3 for Opti 82c611A on the primary
4080 channel, the secondary channel, or both channels
4081 respectively. Disabled by default.
4083 pata_legacy.opti82c611a= [HW,LIBATA]
4085 Set to 1, 2, or 3 for Opti 82c465MV on the primary
4086 channel, the secondary channel, or both channels
4087 respectively. Disabled by default.
4089 pata_legacy.pio_mask= [HW,LIBATA]
4091 PIO mode mask for autospeed devices. Set individual
4092 bits to allow the use of the respective PIO modes.
4093 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
4094 All modes allowed by default.
4096 pata_legacy.probe_all= [HW,LIBATA]
4098 Set to non-zero to probe tertiary and further ISA
4099 port ranges on PCI systems. Disabled by default.
4101 pata_legacy.probe_mask= [HW,LIBATA]
4103 Probe mask for legacy ISA PATA ports. Depending on
4104 platform configuration and the use of other driver
4105 options up to 6 legacy ports are supported: 0x1f0,
4106 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
4107 of individual ports can be disabled by setting the
4108 corresponding bits in the mask to 1. Bit 0 is for
4109 the first port in the list above (0x1f0), and so on.
4110 By default all supported ports are probed.
4112 pata_legacy.qdi= [HW,LIBATA]
4114 Set to non-zero to probe QDI controllers. By default
4115 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
4117 pata_legacy.winbond= [HW,LIBATA]
4119 Set to non-zero to probe Winbond controllers. Use
4120 the standard I/O port (0x130) if 1, otherwise the
4121 value given is the I/O port to use (typically 0x1b0).
4122 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
4125 pata_platform.pio_mask= [HW,LIBATA]
4127 Supported PIO mode mask. Set individual bits to allow
4128 the use of the respective PIO modes. Bit 0 is for
4129 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
4133 Halt all CPUs after the first oops has been printed for
4134 the specified number of seconds. This is to be used if
4135 your oopses keep scrolling off the screen.
4139 pci=option[,option...] [PCI] various PCI subsystem options.
4141 Some options herein operate on a specific device
4142 or a set of devices (<pci_dev>). These are
4143 specified in one of the following formats:
4145 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
4146 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
4148 Note: the first format specifies a PCI
4149 bus/device/function address which may change
4150 if new hardware is inserted, if motherboard
4151 firmware changes, or due to changes caused
4152 by other kernel parameters. If the
4153 domain is left unspecified, it is
4154 taken to be zero. Optionally, a path
4155 to a device through multiple device/function
4156 addresses can be specified after the base
4157 address (this is more robust against
4158 renumbering issues). The second format
4159 selects devices using IDs from the
4160 configuration space which may match multiple
4161 devices in the system.
4163 earlydump dump PCI config space before the kernel
4165 off [X86] don't probe for the PCI bus
4166 bios [X86-32] force use of PCI BIOS, don't access
4167 the hardware directly. Use this if your machine
4168 has a non-standard PCI host bridge.
4169 nobios [X86-32] disallow use of PCI BIOS, only direct
4170 hardware access methods are allowed. Use this
4171 if you experience crashes upon bootup and you
4172 suspect they are caused by the BIOS.
4173 conf1 [X86] Force use of PCI Configuration Access
4174 Mechanism 1 (config address in IO port 0xCF8,
4175 data in IO port 0xCFC, both 32-bit).
4176 conf2 [X86] Force use of PCI Configuration Access
4177 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
4178 the function, IO port 0xCFA, also 8-bit, sets
4179 bus number. The config space is then accessed
4180 through ports 0xC000-0xCFFF).
4181 See http://wiki.osdev.org/PCI for more info
4182 on the configuration access mechanisms.
4183 noaer [PCIE] If the PCIEAER kernel config parameter is
4184 enabled, this kernel boot option can be used to
4185 disable the use of PCIE advanced error reporting.
4186 nodomains [PCI] Disable support for multiple PCI
4187 root domains (aka PCI segments, in ACPI-speak).
4188 nommconf [X86] Disable use of MMCONFIG for PCI
4190 check_enable_amd_mmconf [X86] check for and enable
4191 properly configured MMIO access to PCI
4192 config space on AMD family 10h CPU
4193 nomsi [MSI] If the PCI_MSI kernel config parameter is
4194 enabled, this kernel boot option can be used to
4195 disable the use of MSI interrupts system-wide.
4196 noioapicquirk [APIC] Disable all boot interrupt quirks.
4197 Safety option to keep boot IRQs enabled. This
4198 should never be necessary.
4199 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
4200 primary IO-APIC for bridges that cannot disable
4201 boot IRQs. This fixes a source of spurious IRQs
4202 when the system masks IRQs.
4203 noioapicreroute [APIC] Disable workaround that uses the
4204 boot IRQ equivalent of an IRQ that connects to
4205 a chipset where boot IRQs cannot be disabled.
4206 The opposite of ioapicreroute.
4207 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
4208 routing table. These calls are known to be buggy
4209 on several machines and they hang the machine
4210 when used, but on other computers it's the only
4211 way to get the interrupt routing table. Try
4212 this option if the kernel is unable to allocate
4213 IRQs or discover secondary PCI buses on your
4215 rom [X86] Assign address space to expansion ROMs.
4216 Use with caution as certain devices share
4217 address decoders between ROMs and other
4219 norom [X86] Do not assign address space to
4220 expansion ROMs that do not already have
4221 BIOS assigned address ranges.
4222 nobar [X86] Do not assign address space to the
4223 BARs that weren't assigned by the BIOS.
4224 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
4225 assigned automatically to PCI devices. You can
4226 make the kernel exclude IRQs of your ISA cards
4228 pirqaddr=0xAAAAA [X86] Specify the physical address
4229 of the PIRQ table (normally generated
4230 by the BIOS) if it is outside the
4231 F0000h-100000h range.
4232 lastbus=N [X86] Scan all buses thru bus #N. Can be
4233 useful if the kernel is unable to find your
4234 secondary buses and you want to tell it
4235 explicitly which ones they are.
4236 assign-busses [X86] Always assign all PCI bus
4237 numbers ourselves, overriding
4238 whatever the firmware may have done.
4239 usepirqmask [X86] Honor the possible IRQ mask stored
4240 in the BIOS $PIR table. This is needed on
4241 some systems with broken BIOSes, notably
4242 some HP Pavilion N5400 and Omnibook XE3
4243 notebooks. This will have no effect if ACPI
4244 IRQ routing is enabled.
4245 noacpi [X86] Do not use ACPI for IRQ routing
4246 or for PCI scanning.
4247 use_crs [X86] Use PCI host bridge window information
4248 from ACPI. On BIOSes from 2008 or later, this
4249 is enabled by default. If you need to use this,
4250 please report a bug.
4251 nocrs [X86] Ignore PCI host bridge windows from ACPI.
4252 If you need to use this, please report a bug.
4253 use_e820 [X86] Use E820 reservations to exclude parts of
4254 PCI host bridge windows. This is a workaround
4255 for BIOS defects in host bridge _CRS methods.
4256 If you need to use this, please report a bug to
4257 <linux-pci@vger.kernel.org>.
4258 no_e820 [X86] Ignore E820 reservations for PCI host
4259 bridge windows. This is the default on modern
4260 hardware. If you need to use this, please report
4261 a bug to <linux-pci@vger.kernel.org>.
4262 routeirq Do IRQ routing for all PCI devices.
4263 This is normally done in pci_enable_device(),
4264 so this option is a temporary workaround
4265 for broken drivers that don't call it.
4266 skip_isa_align [X86] do not align io start addr, so can
4267 handle more pci cards
4268 noearly [X86] Don't do any early type 1 scanning.
4269 This might help on some broken boards which
4270 machine check when some devices' config space
4271 is read. But various workarounds are disabled
4272 and some IOMMU drivers will not work.
4273 bfsort Sort PCI devices into breadth-first order.
4274 This sorting is done to get a device
4275 order compatible with older (<= 2.4) kernels.
4276 nobfsort Don't sort PCI devices into breadth-first order.
4277 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
4278 tuning and use the BIOS-configured MPS defaults.
4279 pcie_bus_safe Set every device's MPS to the largest value
4280 supported by all devices below the root complex.
4281 pcie_bus_perf Set device MPS to the largest allowable MPS
4282 based on its parent bus. Also set MRRS (Max
4283 Read Request Size) to the largest supported
4284 value (no larger than the MPS that the device
4285 or bus can support) for best performance.
4286 pcie_bus_peer2peer Set every device's MPS to 128B, which
4287 every device is guaranteed to support. This
4288 configuration allows peer-to-peer DMA between
4289 any pair of devices, possibly at the cost of
4290 reduced performance. This also guarantees
4291 that hot-added devices will work.
4292 cbiosize=nn[KMG] The fixed amount of bus space which is
4293 reserved for the CardBus bridge's IO window.
4294 The default value is 256 bytes.
4295 cbmemsize=nn[KMG] The fixed amount of bus space which is
4296 reserved for the CardBus bridge's memory
4297 window. The default value is 64 megabytes.
4300 [<order of align>@]<pci_dev>[; ...]
4301 Specifies alignment and device to reassign
4302 aligned memory resources. How to
4303 specify the device is described above.
4304 If <order of align> is not specified,
4305 PAGE_SIZE is used as alignment.
4306 A PCI-PCI bridge can be specified if resource
4307 windows need to be expanded.
4308 To specify the alignment for several
4309 instances of a device, the PCI vendor,
4310 device, subvendor, and subdevice may be
4311 specified, e.g., 12@pci:8086:9c22:103c:198f
4312 for 4096-byte alignment.
4313 ecrc= Enable/disable PCIe ECRC (transaction layer
4314 end-to-end CRC checking). Only effective if
4315 OS has native AER control (either granted by
4316 ACPI _OSC or forced via "pcie_ports=native")
4317 bios: Use BIOS/firmware settings. This is the
4321 hpiosize=nn[KMG] The fixed amount of bus space which is
4322 reserved for hotplug bridge's IO window.
4323 Default size is 256 bytes.
4324 hpmmiosize=nn[KMG] The fixed amount of bus space which is
4325 reserved for hotplug bridge's MMIO window.
4326 Default size is 2 megabytes.
4327 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
4328 reserved for hotplug bridge's MMIO_PREF window.
4329 Default size is 2 megabytes.
4330 hpmemsize=nn[KMG] The fixed amount of bus space which is
4331 reserved for hotplug bridge's MMIO and
4333 Default size is 2 megabytes.
4334 hpbussize=nn The minimum amount of additional bus numbers
4335 reserved for buses below a hotplug bridge.
4337 realloc= Enable/disable reallocating PCI bridge resources
4338 if allocations done by BIOS are too small to
4339 accommodate resources required by all child
4341 off: Turn realloc off
4343 realloc same as realloc=on
4344 noari do not use PCIe ARI.
4345 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
4346 do not use PCIe ATS (and IOMMU device IOTLB).
4347 pcie_scan_all Scan all possible PCIe devices. Otherwise we
4348 only look for one device below a PCIe downstream
4350 big_root_window Try to add a big 64bit memory window to the PCIe
4351 root complex on AMD CPUs. Some GFX hardware
4352 can resize a BAR to allow access to all VRAM.
4353 Adding the window is slightly risky (it may
4354 conflict with unreported devices), so this
4356 disable_acs_redir=<pci_dev>[; ...]
4357 Specify one or more PCI devices (in the format
4358 specified above) separated by semicolons.
4359 Each device specified will have the PCI ACS
4360 redirect capabilities forced off which will
4361 allow P2P traffic between devices through
4362 bridges without forcing it upstream. Note:
4363 this removes isolation between devices and
4364 may put more devices in an IOMMU group.
4365 force_floating [S390] Force usage of floating interrupts.
4366 nomio [S390] Do not use MIO instructions.
4367 norid [S390] ignore the RID field and force use of
4368 one PCI domain per PCI function
4370 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
4373 force Enable ASPM even on devices that claim not to support it.
4374 WARNING: Forcing ASPM on may cause system lockups.
4376 pcie_ports= [PCIE] PCIe port services handling:
4377 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
4378 even if the platform doesn't give the OS permission to
4379 use them. This may cause conflicts if the platform
4380 also tries to use these services.
4381 dpc-native Use native PCIe service for DPC only. May
4382 cause conflicts if firmware uses AER or DPC.
4383 compat Disable native PCIe services (PME, AER, DPC, PCIe
4386 pcie_port_pm= [PCIE] PCIe port power management handling:
4387 off Disable power management of all PCIe ports
4388 force Forcibly enable power management of all PCIe ports
4390 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
4391 nomsi Do not use MSI for native PCIe PME signaling (this makes
4392 all PCIe root ports use INTx for all services).
4394 pcmv= [HW,PCMCIA] BadgePAD 4
4398 Keep all power-domains already enabled by bootloader on,
4399 even if no driver has claimed them. This is useful
4400 for debug and development, but should not be
4401 needed on a platform with proper driver support.
4403 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
4406 See arch/parisc/kernel/pdc_chassis.c
4408 percpu_alloc= Select which percpu first chunk allocator to use.
4409 Currently supported values are "embed" and "page".
4410 Archs may support subset or none of the selections.
4411 See comments in mm/percpu.c for details on each
4412 allocator. This parameter is primarily for debugging
4413 and performance comparison.
4415 pirq= [SMP,APIC] Manual mp-table setup
4416 See Documentation/x86/i386/IO-APIC.rst.
4418 plip= [PPT,NET] Parallel port network link
4419 Format: { parport<nr> | timid | 0 }
4420 See also Documentation/admin-guide/parport.rst.
4422 pmtmr= [X86] Manual setup of pmtmr I/O Port.
4423 Override pmtimer IOPort with a hex value.
4426 pmu_override= [PPC] Override the PMU.
4427 This option takes over the PMU facility, so it is no
4428 longer usable by perf. Setting this option starts the
4429 PMU counters by setting MMCR0 to 0 (the FC bit is
4430 cleared). If a number is given, then MMCR1 is set to
4431 that number, otherwise (e.g., 'pmu_override=on'), MMCR1
4434 pm_debug_messages [SUSPEND,KNL]
4435 Enable suspend/resume debug messages during boot up.
4438 Enable PNP debug messages (depends on the
4439 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
4440 via /sys/module/pnp/parameters/debug. We always show
4441 current resource usage; turning this on also shows
4442 possible settings and some assignment information.
4448 { on | off | curr | res | no-curr | no-res }
4451 [ISAPNP] Exclude IRQs for the autoconfiguration
4454 [ISAPNP] Exclude DMAs for the autoconfiguration
4456 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
4457 Ranges are in pairs (I/O port base and size).
4460 [ISAPNP] Exclude memory regions for the
4462 Ranges are in pairs (memory base and size).
4464 ports= [IP_VS_FTP] IPVS ftp helper module
4466 Up to 8 (IP_VS_APP_MAX_PORTS) ports
4468 Format: <port>,<port>....
4470 powersave=off [PPC] This option disables power saving features.
4471 It specifically disables cpuidle and sets the
4472 platform machine description specific power_save
4473 function to NULL. On Idle the CPU just reduces
4476 ppc_strict_facility_enable
4477 [PPC] This option catches any kernel floating point,
4478 Altivec, VSX and SPE outside of regions specifically
4479 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
4480 There is some performance impact when enabling this.
4484 Disable Hardware Transactional Memory
4487 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
4488 none - Limited to cond_resched() calls
4489 voluntary - Limited to cond_resched() and might_sleep() calls
4490 full - Any section that isn't explicitly preempt disabled
4491 can be preempted anytime.
4493 print-fatal-signals=
4494 [KNL] debug: print fatal signals
4496 If enabled, warn about various signal handling
4497 related application anomalies: too many signals,
4498 too many POSIX.1 timers, fatal signals causing a
4501 If you hit the warning due to signal overflow,
4502 you might want to try "ulimit -i unlimited".
4506 printk.always_kmsg_dump=
4507 Trigger kmsg_dump for cases other than kernel oops or
4509 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4512 printk.console_no_auto_verbose=
4513 Disable console loglevel raise on oops, panic
4514 or lockdep-detected issues (only if lock debug is on).
4515 With an exception to setups with low baudrate on
4516 serial console, keeping this 0 is a good choice
4517 in order to provide more debug information.
4519 default: 0 (auto_verbose is enabled)
4521 printk.devkmsg={on,off,ratelimit}
4522 Control writing to /dev/kmsg.
4523 on - unlimited logging to /dev/kmsg from userspace
4524 off - logging to /dev/kmsg disabled
4525 ratelimit - ratelimit the logging
4528 printk.time= Show timing data prefixed to each printk message line
4529 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4531 processor.max_cstate= [HW,ACPI]
4532 Limit processor to maximum C-state
4533 max_cstate=9 overrides any DMI blacklist limit.
4535 processor.nocst [HW,ACPI]
4536 Ignore the _CST method to determine C-states,
4537 instead using the legacy FADT method
4539 profile= [KNL] Enable kernel profiling via /proc/profile
4540 Format: [<profiletype>,]<number>
4541 Param: <profiletype>: "schedule", "sleep", or "kvm"
4542 [defaults to kernel profiling]
4543 Param: "schedule" - profile schedule points.
4544 Param: "sleep" - profile D-state sleeping (millisecs).
4545 Requires CONFIG_SCHEDSTATS
4546 Param: "kvm" - profile VM exits.
4547 Param: <number> - step/bucket size as a power of 2 for
4548 statistical time based profiling.
4550 prompt_ramdisk= [RAM] [Deprecated]
4552 prot_virt= [S390] enable hosting protected virtual machines
4553 isolated from the hypervisor (if hardware supports
4557 psi= [KNL] Enable or disable pressure stall information
4561 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
4562 probe for; one of (bare|imps|exps|lifebook|any).
4563 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
4565 psmouse.resetafter= [HW,MOUSE]
4566 Try to reset the device after so many bad packets
4569 [HW,MOUSE] Set desired mouse resolution, in dpi.
4570 psmouse.smartscroll=
4571 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
4572 0 = disabled, 1 = enabled (default).
4574 pstore.backend= Specify the name of the pstore backend to use
4576 pti= [X86-64] Control Page Table Isolation of user and
4577 kernel address spaces. Disabling this feature
4578 removes hardening, but improves performance of
4579 system calls and interrupts.
4581 on - unconditionally enable
4582 off - unconditionally disable
4583 auto - kernel detects whether your CPU model is
4584 vulnerable to issues that PTI mitigates
4586 Not specifying this option is equivalent to pti=auto.
4589 Equivalent to pti=off
4592 [KNL] Number of legacy pty's. Overwrites compiled-in
4595 quiet [KNL] Disable most log messages
4599 radix_hcall_invalidate=on [PPC/PSERIES]
4600 Disable RADIX GTSE feature and use hcall for TLB
4604 See Documentation/admin-guide/md.rst.
4606 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
4607 See Documentation/admin-guide/blockdev/ramdisk.rst.
4609 ramdisk_start= [RAM] RAM disk image start address
4611 random.trust_cpu=off
4612 [KNL] Disable trusting the use of the CPU's
4613 random number generator (if available) to
4614 initialize the kernel's RNG.
4616 random.trust_bootloader=off
4617 [KNL] Disable trusting the use of the a seed
4618 passed by the bootloader (if available) to
4619 initialize the kernel's RNG.
4621 randomize_kstack_offset=
4622 [KNL] Enable or disable kernel stack offset
4623 randomization, which provides roughly 5 bits of
4624 entropy, frustrating memory corruption attacks
4625 that depend on stack address determinism or
4626 cross-syscall address exposures. This is only
4627 available on architectures that have defined
4628 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
4629 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4630 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
4632 ras=option[,option,...] [KNL] RAS-specific options
4635 Disable the Correctable Errors Collector,
4636 see CONFIG_RAS_CEC help text.
4638 rcu_nocbs[=cpu-list]
4639 [KNL] The optional argument is a cpu list,
4642 In kernels built with CONFIG_RCU_NOCB_CPU=y,
4643 enable the no-callback CPU mode, which prevents
4644 such CPUs' callbacks from being invoked in
4645 softirq context. Invocation of such CPUs' RCU
4646 callbacks will instead be offloaded to "rcuox/N"
4647 kthreads created for that purpose, where "x" is
4648 "p" for RCU-preempt, "s" for RCU-sched, and "g"
4649 for the kthreads that mediate grace periods; and
4650 "N" is the CPU number. This reduces OS jitter on
4651 the offloaded CPUs, which can be useful for HPC
4652 and real-time workloads. It can also improve
4653 energy efficiency for asymmetric multiprocessors.
4655 If a cpulist is passed as an argument, the specified
4656 list of CPUs is set to no-callback mode from boot.
4658 Otherwise, if the '=' sign and the cpulist
4659 arguments are omitted, no CPU will be set to
4660 no-callback mode from boot but the mode may be
4661 toggled at runtime via cpusets.
4663 Note that this argument takes precedence over
4664 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
4667 Rather than requiring that offloaded CPUs
4668 (specified by rcu_nocbs= above) explicitly
4669 awaken the corresponding "rcuoN" kthreads,
4670 make these kthreads poll for callbacks.
4671 This improves the real-time response for the
4672 offloaded CPUs by relieving them of the need to
4673 wake up the corresponding kthread, but degrades
4674 energy efficiency by requiring that the kthreads
4675 periodically wake up to do the polling.
4677 rcutree.blimit= [KNL]
4678 Set maximum number of finished RCU callbacks to
4679 process in one batch.
4681 rcutree.dump_tree= [KNL]
4682 Dump the structure of the rcu_node combining tree
4683 out at early boot. This is used for diagnostic
4684 purposes, to verify correct tree setup.
4686 rcutree.gp_cleanup_delay= [KNL]
4687 Set the number of jiffies to delay each step of
4688 RCU grace-period cleanup.
4690 rcutree.gp_init_delay= [KNL]
4691 Set the number of jiffies to delay each step of
4692 RCU grace-period initialization.
4694 rcutree.gp_preinit_delay= [KNL]
4695 Set the number of jiffies to delay each step of
4696 RCU grace-period pre-initialization, that is,
4697 the propagation of recent CPU-hotplug changes up
4698 the rcu_node combining tree.
4700 rcutree.use_softirq= [KNL]
4701 If set to zero, move all RCU_SOFTIRQ processing to
4702 per-CPU rcuc kthreads. Defaults to a non-zero
4703 value, meaning that RCU_SOFTIRQ is used by default.
4704 Specify rcutree.use_softirq=0 to use rcuc kthreads.
4706 But note that CONFIG_PREEMPT_RT=y kernels disable
4707 this kernel boot parameter, forcibly setting it
4710 rcutree.rcu_fanout_exact= [KNL]
4711 Disable autobalancing of the rcu_node combining
4712 tree. This is used by rcutorture, and might
4713 possibly be useful for architectures having high
4714 cache-to-cache transfer latencies.
4716 rcutree.rcu_fanout_leaf= [KNL]
4717 Change the number of CPUs assigned to each
4718 leaf rcu_node structure. Useful for very
4719 large systems, which will choose the value 64,
4720 and for NUMA systems with large remote-access
4721 latencies, which will choose a value aligned
4722 with the appropriate hardware boundaries.
4724 rcutree.rcu_min_cached_objs= [KNL]
4725 Minimum number of objects which are cached and
4726 maintained per one CPU. Object size is equal
4727 to PAGE_SIZE. The cache allows to reduce the
4728 pressure to page allocator, also it makes the
4729 whole algorithm to behave better in low memory
4732 rcutree.rcu_delay_page_cache_fill_msec= [KNL]
4733 Set the page-cache refill delay (in milliseconds)
4734 in response to low-memory conditions. The range
4735 of permitted values is in the range 0:100000.
4737 rcutree.jiffies_till_first_fqs= [KNL]
4738 Set delay from grace-period initialization to
4739 first attempt to force quiescent states.
4740 Units are jiffies, minimum value is zero,
4741 and maximum value is HZ.
4743 rcutree.jiffies_till_next_fqs= [KNL]
4744 Set delay between subsequent attempts to force
4745 quiescent states. Units are jiffies, minimum
4746 value is one, and maximum value is HZ.
4748 rcutree.jiffies_till_sched_qs= [KNL]
4749 Set required age in jiffies for a
4750 given grace period before RCU starts
4751 soliciting quiescent-state help from
4752 rcu_note_context_switch() and cond_resched().
4753 If not specified, the kernel will calculate
4754 a value based on the most recent settings
4755 of rcutree.jiffies_till_first_fqs
4756 and rcutree.jiffies_till_next_fqs.
4757 This calculated value may be viewed in
4758 rcutree.jiffies_to_sched_qs. Any attempt to set
4759 rcutree.jiffies_to_sched_qs will be cheerfully
4762 rcutree.kthread_prio= [KNL,BOOT]
4763 Set the SCHED_FIFO priority of the RCU per-CPU
4764 kthreads (rcuc/N). This value is also used for
4765 the priority of the RCU boost threads (rcub/N)
4766 and for the RCU grace-period kthreads (rcu_bh,
4767 rcu_preempt, and rcu_sched). If RCU_BOOST is
4768 set, valid values are 1-99 and the default is 1
4769 (the least-favored priority). Otherwise, when
4770 RCU_BOOST is not set, valid values are 0-99 and
4771 the default is zero (non-realtime operation).
4772 When RCU_NOCB_CPU is set, also adjust the
4773 priority of NOCB callback kthreads.
4775 rcutree.rcu_divisor= [KNL]
4776 Set the shift-right count to use to compute
4777 the callback-invocation batch limit bl from
4778 the number of callbacks queued on this CPU.
4779 The result will be bounded below by the value of
4780 the rcutree.blimit kernel parameter. Every bl
4781 callbacks, the softirq handler will exit in
4782 order to allow the CPU to do other work.
4784 Please note that this callback-invocation batch
4785 limit applies only to non-offloaded callback
4786 invocation. Offloaded callbacks are instead
4787 invoked in the context of an rcuoc kthread, which
4788 scheduler will preempt as it does any other task.
4790 rcutree.nocb_nobypass_lim_per_jiffy= [KNL]
4791 On callback-offloaded (rcu_nocbs) CPUs,
4792 RCU reduces the lock contention that would
4793 otherwise be caused by callback floods through
4794 use of the ->nocb_bypass list. However, in the
4795 common non-flooded case, RCU queues directly to
4796 the main ->cblist in order to avoid the extra
4797 overhead of the ->nocb_bypass list and its lock.
4798 But if there are too many callbacks queued during
4799 a single jiffy, RCU pre-queues the callbacks into
4800 the ->nocb_bypass queue. The definition of "too
4801 many" is supplied by this kernel boot parameter.
4803 rcutree.rcu_nocb_gp_stride= [KNL]
4804 Set the number of NOCB callback kthreads in
4805 each group, which defaults to the square root
4806 of the number of CPUs. Larger numbers reduce
4807 the wakeup overhead on the global grace-period
4808 kthread, but increases that same overhead on
4809 each group's NOCB grace-period kthread.
4811 rcutree.qhimark= [KNL]
4812 Set threshold of queued RCU callbacks beyond which
4813 batch limiting is disabled.
4815 rcutree.qlowmark= [KNL]
4816 Set threshold of queued RCU callbacks below which
4817 batch limiting is re-enabled.
4819 rcutree.qovld= [KNL]
4820 Set threshold of queued RCU callbacks beyond which
4821 RCU's force-quiescent-state scan will aggressively
4822 enlist help from cond_resched() and sched IPIs to
4823 help CPUs more quickly reach quiescent states.
4824 Set to less than zero to make this be set based
4825 on rcutree.qhimark at boot time and to zero to
4826 disable more aggressive help enlistment.
4828 rcutree.rcu_kick_kthreads= [KNL]
4829 Cause the grace-period kthread to get an extra
4830 wake_up() if it sleeps three times longer than
4831 it should at force-quiescent-state time.
4832 This wake_up() will be accompanied by a
4833 WARN_ONCE() splat and an ftrace_dump().
4835 rcutree.rcu_unlock_delay= [KNL]
4836 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
4837 this specifies an rcu_read_unlock()-time delay
4838 in microseconds. This defaults to zero.
4839 Larger delays increase the probability of
4840 catching RCU pointer leaks, that is, buggy use
4841 of RCU-protected pointers after the relevant
4842 rcu_read_unlock() has completed.
4844 rcutree.sysrq_rcu= [KNL]
4845 Commandeer a sysrq key to dump out Tree RCU's
4846 rcu_node tree with an eye towards determining
4847 why a new grace period has not yet started.
4849 rcuscale.gp_async= [KNL]
4850 Measure performance of asynchronous
4851 grace-period primitives such as call_rcu().
4853 rcuscale.gp_async_max= [KNL]
4854 Specify the maximum number of outstanding
4855 callbacks per writer thread. When a writer
4856 thread exceeds this limit, it invokes the
4857 corresponding flavor of rcu_barrier() to allow
4858 previously posted callbacks to drain.
4860 rcuscale.gp_exp= [KNL]
4861 Measure performance of expedited synchronous
4862 grace-period primitives.
4864 rcuscale.holdoff= [KNL]
4865 Set test-start holdoff period. The purpose of
4866 this parameter is to delay the start of the
4867 test until boot completes in order to avoid
4870 rcuscale.kfree_rcu_test= [KNL]
4871 Set to measure performance of kfree_rcu() flooding.
4873 rcuscale.kfree_rcu_test_double= [KNL]
4874 Test the double-argument variant of kfree_rcu().
4875 If this parameter has the same value as
4876 rcuscale.kfree_rcu_test_single, both the single-
4877 and double-argument variants are tested.
4879 rcuscale.kfree_rcu_test_single= [KNL]
4880 Test the single-argument variant of kfree_rcu().
4881 If this parameter has the same value as
4882 rcuscale.kfree_rcu_test_double, both the single-
4883 and double-argument variants are tested.
4885 rcuscale.kfree_nthreads= [KNL]
4886 The number of threads running loops of kfree_rcu().
4888 rcuscale.kfree_alloc_num= [KNL]
4889 Number of allocations and frees done in an iteration.
4891 rcuscale.kfree_loops= [KNL]
4892 Number of loops doing rcuscale.kfree_alloc_num number
4893 of allocations and frees.
4895 rcuscale.nreaders= [KNL]
4896 Set number of RCU readers. The value -1 selects
4897 N, where N is the number of CPUs. A value
4898 "n" less than -1 selects N-n+1, where N is again
4899 the number of CPUs. For example, -2 selects N
4900 (the number of CPUs), -3 selects N+1, and so on.
4901 A value of "n" less than or equal to -N selects
4904 rcuscale.nwriters= [KNL]
4905 Set number of RCU writers. The values operate
4906 the same as for rcuscale.nreaders.
4907 N, where N is the number of CPUs
4909 rcuscale.perf_type= [KNL]
4910 Specify the RCU implementation to test.
4912 rcuscale.shutdown= [KNL]
4913 Shut the system down after performance tests
4914 complete. This is useful for hands-off automated
4917 rcuscale.verbose= [KNL]
4918 Enable additional printk() statements.
4920 rcuscale.writer_holdoff= [KNL]
4921 Write-side holdoff between grace periods,
4922 in microseconds. The default of zero says
4925 rcutorture.fqs_duration= [KNL]
4926 Set duration of force_quiescent_state bursts
4929 rcutorture.fqs_holdoff= [KNL]
4930 Set holdoff time within force_quiescent_state bursts
4933 rcutorture.fqs_stutter= [KNL]
4934 Set wait time between force_quiescent_state bursts
4937 rcutorture.fwd_progress= [KNL]
4938 Specifies the number of kthreads to be used
4939 for RCU grace-period forward-progress testing
4940 for the types of RCU supporting this notion.
4941 Defaults to 1 kthread, values less than zero or
4942 greater than the number of CPUs cause the number
4945 rcutorture.fwd_progress_div= [KNL]
4946 Specify the fraction of a CPU-stall-warning
4947 period to do tight-loop forward-progress testing.
4949 rcutorture.fwd_progress_holdoff= [KNL]
4950 Number of seconds to wait between successive
4951 forward-progress tests.
4953 rcutorture.fwd_progress_need_resched= [KNL]
4954 Enclose cond_resched() calls within checks for
4955 need_resched() during tight-loop forward-progress
4958 rcutorture.gp_cond= [KNL]
4959 Use conditional/asynchronous update-side
4960 primitives, if available.
4962 rcutorture.gp_exp= [KNL]
4963 Use expedited update-side primitives, if available.
4965 rcutorture.gp_normal= [KNL]
4966 Use normal (non-expedited) asynchronous
4967 update-side primitives, if available.
4969 rcutorture.gp_sync= [KNL]
4970 Use normal (non-expedited) synchronous
4971 update-side primitives, if available. If all
4972 of rcutorture.gp_cond=, rcutorture.gp_exp=,
4973 rcutorture.gp_normal=, and rcutorture.gp_sync=
4974 are zero, rcutorture acts as if is interpreted
4975 they are all non-zero.
4977 rcutorture.irqreader= [KNL]
4978 Run RCU readers from irq handlers, or, more
4979 accurately, from a timer handler. Not all RCU
4980 flavors take kindly to this sort of thing.
4982 rcutorture.leakpointer= [KNL]
4983 Leak an RCU-protected pointer out of the reader.
4984 This can of course result in splats, and is
4985 intended to test the ability of things like
4986 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
4989 rcutorture.n_barrier_cbs= [KNL]
4990 Set callbacks/threads for rcu_barrier() testing.
4992 rcutorture.nfakewriters= [KNL]
4993 Set number of concurrent RCU writers. These just
4994 stress RCU, they don't participate in the actual
4995 test, hence the "fake".
4997 rcutorture.nocbs_nthreads= [KNL]
4998 Set number of RCU callback-offload togglers.
4999 Zero (the default) disables toggling.
5001 rcutorture.nocbs_toggle= [KNL]
5002 Set the delay in milliseconds between successive
5003 callback-offload toggling attempts.
5005 rcutorture.nreaders= [KNL]
5006 Set number of RCU readers. The value -1 selects
5007 N-1, where N is the number of CPUs. A value
5008 "n" less than -1 selects N-n-2, where N is again
5009 the number of CPUs. For example, -2 selects N
5010 (the number of CPUs), -3 selects N+1, and so on.
5012 rcutorture.object_debug= [KNL]
5013 Enable debug-object double-call_rcu() testing.
5015 rcutorture.onoff_holdoff= [KNL]
5016 Set time (s) after boot for CPU-hotplug testing.
5018 rcutorture.onoff_interval= [KNL]
5019 Set time (jiffies) between CPU-hotplug operations,
5020 or zero to disable CPU-hotplug testing.
5022 rcutorture.read_exit= [KNL]
5023 Set the number of read-then-exit kthreads used
5024 to test the interaction of RCU updaters and
5025 task-exit processing.
5027 rcutorture.read_exit_burst= [KNL]
5028 The number of times in a given read-then-exit
5029 episode that a set of read-then-exit kthreads
5032 rcutorture.read_exit_delay= [KNL]
5033 The delay, in seconds, between successive
5034 read-then-exit testing episodes.
5036 rcutorture.shuffle_interval= [KNL]
5037 Set task-shuffle interval (s). Shuffling tasks
5038 allows some CPUs to go into dyntick-idle mode
5039 during the rcutorture test.
5041 rcutorture.shutdown_secs= [KNL]
5042 Set time (s) after boot system shutdown. This
5043 is useful for hands-off automated testing.
5045 rcutorture.stall_cpu= [KNL]
5046 Duration of CPU stall (s) to test RCU CPU stall
5047 warnings, zero to disable.
5049 rcutorture.stall_cpu_block= [KNL]
5050 Sleep while stalling if set. This will result
5051 in warnings from preemptible RCU in addition
5052 to any other stall-related activity.
5054 rcutorture.stall_cpu_holdoff= [KNL]
5055 Time to wait (s) after boot before inducing stall.
5057 rcutorture.stall_cpu_irqsoff= [KNL]
5058 Disable interrupts while stalling if set.
5060 rcutorture.stall_gp_kthread= [KNL]
5061 Duration (s) of forced sleep within RCU
5062 grace-period kthread to test RCU CPU stall
5063 warnings, zero to disable. If both stall_cpu
5064 and stall_gp_kthread are specified, the
5065 kthread is starved first, then the CPU.
5067 rcutorture.stat_interval= [KNL]
5068 Time (s) between statistics printk()s.
5070 rcutorture.stutter= [KNL]
5071 Time (s) to stutter testing, for example, specifying
5072 five seconds causes the test to run for five seconds,
5073 wait for five seconds, and so on. This tests RCU's
5074 ability to transition abruptly to and from idle.
5076 rcutorture.test_boost= [KNL]
5077 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
5078 "Maybe" means test if the RCU implementation
5079 under test support RCU priority boosting.
5081 rcutorture.test_boost_duration= [KNL]
5082 Duration (s) of each individual boost test.
5084 rcutorture.test_boost_interval= [KNL]
5085 Interval (s) between each boost test.
5087 rcutorture.test_no_idle_hz= [KNL]
5088 Test RCU's dyntick-idle handling. See also the
5089 rcutorture.shuffle_interval parameter.
5091 rcutorture.torture_type= [KNL]
5092 Specify the RCU implementation to test.
5094 rcutorture.verbose= [KNL]
5095 Enable additional printk() statements.
5097 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
5098 Dump ftrace buffer after reporting RCU CPU
5101 rcupdate.rcu_cpu_stall_suppress= [KNL]
5102 Suppress RCU CPU stall warning messages.
5104 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
5105 Suppress RCU CPU stall warning messages and
5106 rcutorture writer stall warnings that occur
5107 during early boot, that is, during the time
5108 before the init task is spawned.
5110 rcupdate.rcu_cpu_stall_timeout= [KNL]
5111 Set timeout for RCU CPU stall warning messages.
5112 The value is in seconds and the maximum allowed
5113 value is 300 seconds.
5115 rcupdate.rcu_exp_cpu_stall_timeout= [KNL]
5116 Set timeout for expedited RCU CPU stall warning
5117 messages. The value is in milliseconds
5118 and the maximum allowed value is 21000
5119 milliseconds. Please note that this value is
5120 adjusted to an arch timer tick resolution.
5121 Setting this to zero causes the value from
5122 rcupdate.rcu_cpu_stall_timeout to be used (after
5123 conversion from seconds to milliseconds).
5125 rcupdate.rcu_cpu_stall_cputime= [KNL]
5126 Provide statistics on the cputime and count of
5127 interrupts and tasks during the sampling period. For
5128 multiple continuous RCU stalls, all sampling periods
5129 begin at half of the first RCU stall timeout.
5131 rcupdate.rcu_exp_stall_task_details= [KNL]
5132 Print stack dumps of any tasks blocking the
5133 current expedited RCU grace period during an
5134 expedited RCU CPU stall warning.
5136 rcupdate.rcu_expedited= [KNL]
5137 Use expedited grace-period primitives, for
5138 example, synchronize_rcu_expedited() instead
5139 of synchronize_rcu(). This reduces latency,
5140 but can increase CPU utilization, degrade
5141 real-time latency, and degrade energy efficiency.
5142 No effect on CONFIG_TINY_RCU kernels.
5144 rcupdate.rcu_normal= [KNL]
5145 Use only normal grace-period primitives,
5146 for example, synchronize_rcu() instead of
5147 synchronize_rcu_expedited(). This improves
5148 real-time latency, CPU utilization, and
5149 energy efficiency, but can expose users to
5150 increased grace-period latency. This parameter
5151 overrides rcupdate.rcu_expedited. No effect on
5152 CONFIG_TINY_RCU kernels.
5154 rcupdate.rcu_normal_after_boot= [KNL]
5155 Once boot has completed (that is, after
5156 rcu_end_inkernel_boot() has been invoked), use
5157 only normal grace-period primitives. No effect
5158 on CONFIG_TINY_RCU kernels.
5160 But note that CONFIG_PREEMPT_RT=y kernels enables
5161 this kernel boot parameter, forcibly setting
5162 it to the value one, that is, converting any
5163 post-boot attempt at an expedited RCU grace
5164 period to instead use normal non-expedited
5165 grace-period processing.
5167 rcupdate.rcu_task_collapse_lim= [KNL]
5168 Set the maximum number of callbacks present
5169 at the beginning of a grace period that allows
5170 the RCU Tasks flavors to collapse back to using
5171 a single callback queue. This switching only
5172 occurs when rcupdate.rcu_task_enqueue_lim is
5173 set to the default value of -1.
5175 rcupdate.rcu_task_contend_lim= [KNL]
5176 Set the minimum number of callback-queuing-time
5177 lock-contention events per jiffy required to
5178 cause the RCU Tasks flavors to switch to per-CPU
5179 callback queuing. This switching only occurs
5180 when rcupdate.rcu_task_enqueue_lim is set to
5181 the default value of -1.
5183 rcupdate.rcu_task_enqueue_lim= [KNL]
5184 Set the number of callback queues to use for the
5185 RCU Tasks family of RCU flavors. The default
5186 of -1 allows this to be automatically (and
5187 dynamically) adjusted. This parameter is intended
5190 rcupdate.rcu_task_ipi_delay= [KNL]
5191 Set time in jiffies during which RCU tasks will
5192 avoid sending IPIs, starting with the beginning
5193 of a given grace period. Setting a large
5194 number avoids disturbing real-time workloads,
5195 but lengthens grace periods.
5197 rcupdate.rcu_task_stall_info= [KNL]
5198 Set initial timeout in jiffies for RCU task stall
5199 informational messages, which give some indication
5200 of the problem for those not patient enough to
5201 wait for ten minutes. Informational messages are
5202 only printed prior to the stall-warning message
5203 for a given grace period. Disable with a value
5204 less than or equal to zero. Defaults to ten
5205 seconds. A change in value does not take effect
5206 until the beginning of the next grace period.
5208 rcupdate.rcu_task_stall_info_mult= [KNL]
5209 Multiplier for time interval between successive
5210 RCU task stall informational messages for a given
5211 RCU tasks grace period. This value is clamped
5212 to one through ten, inclusive. It defaults to
5213 the value three, so that the first informational
5214 message is printed 10 seconds into the grace
5215 period, the second at 40 seconds, the third at
5216 160 seconds, and then the stall warning at 600
5217 seconds would prevent a fourth at 640 seconds.
5219 rcupdate.rcu_task_stall_timeout= [KNL]
5220 Set timeout in jiffies for RCU task stall
5221 warning messages. Disable with a value less
5222 than or equal to zero. Defaults to ten minutes.
5223 A change in value does not take effect until
5224 the beginning of the next grace period.
5226 rcupdate.rcu_self_test= [KNL]
5227 Run the RCU early boot self tests
5231 Run specified binary instead of /init from the ramdisk,
5232 used for early userspace startup. See initrd.
5235 force - Override the decision by the kernel to hide the
5236 advertisement of RDRAND support (this affects
5237 certain AMD processors because of buggy BIOS
5238 support, specifically around the suspend/resume
5242 Turn on/off individual RDT features. List is:
5243 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
5245 E.g. to turn on cmt and turn off mba use:
5249 Format (x86 or x86_64):
5250 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \
5252 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
5254 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
5255 (prefix with 'panic_' to set mode for panic
5257 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
5258 reboot_force is either force or not specified,
5259 reboot_cpu is s[mp]#### with #### being the processor
5260 to be used for rebooting.
5262 refscale.holdoff= [KNL]
5263 Set test-start holdoff period. The purpose of
5264 this parameter is to delay the start of the
5265 test until boot completes in order to avoid
5268 refscale.loops= [KNL]
5269 Set the number of loops over the synchronization
5270 primitive under test. Increasing this number
5271 reduces noise due to loop start/end overhead,
5272 but the default has already reduced the per-pass
5273 noise to a handful of picoseconds on ca. 2020
5276 refscale.nreaders= [KNL]
5277 Set number of readers. The default value of -1
5278 selects N, where N is roughly 75% of the number
5279 of CPUs. A value of zero is an interesting choice.
5281 refscale.nruns= [KNL]
5282 Set number of runs, each of which is dumped onto
5285 refscale.readdelay= [KNL]
5286 Set the read-side critical-section duration,
5287 measured in microseconds.
5289 refscale.scale_type= [KNL]
5290 Specify the read-protection implementation to test.
5292 refscale.shutdown= [KNL]
5293 Shut down the system at the end of the performance
5294 test. This defaults to 1 (shut it down) when
5295 refscale is built into the kernel and to 0 (leave
5296 it running) when refscale is built as a module.
5298 refscale.verbose= [KNL]
5299 Enable additional printk() statements.
5301 refscale.verbose_batched= [KNL]
5302 Batch the additional printk() statements. If zero
5303 (the default) or negative, print everything. Otherwise,
5304 print every Nth verbose statement, where N is the value
5308 [KNL, SMP] Set scheduler's default relax_domain_level.
5309 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
5311 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
5312 Format: <base1>,<size1>[,<base2>,<size2>,...]
5313 Reserve I/O ports or memory so the kernel won't use
5314 them. If <base> is less than 0x10000, the region
5315 is assumed to be I/O ports; otherwise it is memory.
5317 reservetop= [X86-32]
5319 Reserves a hole at the top of the kernel virtual
5322 reset_devices [KNL] Force drivers to reset the underlying device
5323 during initialization.
5326 Specify the partition device for software suspend
5328 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
5330 resume_offset= [SWSUSP]
5331 Specify the offset from the beginning of the partition
5332 given by "resume=" at which the swap header is located,
5333 in <PAGE_SIZE> units (needed only for swap files).
5334 See Documentation/power/swsusp-and-swap-files.rst
5336 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
5337 read the resume files
5339 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
5340 Useful for devices that are detected asynchronously
5341 (e.g. USB and MMC devices).
5343 retain_initrd [RAM] Keep initrd memory after extraction
5345 retbleed= [X86] Control mitigation of RETBleed (Arbitrary
5346 Speculative Code Execution with Return Instructions)
5349 AMD-based UNRET and IBPB mitigations alone do not stop
5350 sibling threads from influencing the predictions of other
5351 sibling threads. For that reason, STIBP is used on pro-
5352 cessors that support it, and mitigate SMT on processors
5356 auto - automatically select a migitation
5357 auto,nosmt - automatically select a mitigation,
5358 disabling SMT if necessary for
5359 the full mitigation (only on Zen1
5360 and older without STIBP).
5361 ibpb - On AMD, mitigate short speculation
5362 windows on basic block boundaries too.
5363 Safe, highest perf impact. It also
5364 enables STIBP if present. Not suitable
5366 ibpb,nosmt - Like "ibpb" above but will disable SMT
5367 when STIBP is not available. This is
5368 the alternative for systems which do not
5370 unret - Force enable untrained return thunks,
5371 only effective on AMD f15h-f17h based
5373 unret,nosmt - Like unret, but will disable SMT when STIBP
5374 is not available. This is the alternative for
5375 systems which do not have STIBP.
5377 Selecting 'auto' will choose a mitigation method at run
5378 time according to the CPU.
5380 Not specifying this option is equivalent to retbleed=auto.
5382 rfkill.default_state=
5383 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
5384 etc. communication is blocked by default.
5387 rfkill.master_switch_mode=
5388 0 The "airplane mode" button does nothing.
5389 1 The "airplane mode" button toggles between everything
5390 blocked and the previous configuration.
5391 2 The "airplane mode" button toggles between everything
5392 blocked and everything unblocked.
5394 rhash_entries= [KNL,NET]
5395 Set number of hash buckets for route cache
5398 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
5401 ro [KNL] Mount root device read-only on boot
5404 on Mark read-only kernel memory as read-only (default).
5405 off Leave read-only kernel memory writable for debugging.
5406 full Mark read-only kernel memory and aliases as read-only
5410 Enable the uart passthrough on the designated usb port
5411 on Rockchip SoCs. When active, the signals of the
5412 debug-uart get routed to the D+ and D- pins of the usb
5413 port and the regular usb controller gets disabled.
5415 root= [KNL] Root filesystem
5416 See name_to_dev_t comment in init/do_mounts.c.
5418 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
5419 mount the root filesystem
5421 rootflags= [KNL] Set root filesystem mount option string
5423 rootfstype= [KNL] Set root filesystem type
5425 rootwait [KNL] Wait (indefinitely) for root device to show up.
5426 Useful for devices that are detected asynchronously
5427 (e.g. USB and MMC devices).
5429 rproc_mem=nn[KMG][@address]
5430 [KNL,ARM,CMA] Remoteproc physical memory block.
5431 Memory area to be used by remote processor image,
5434 rw [KNL] Mount root device read-write on boot
5436 S [KNL] Run init in single mode
5438 s390_iommu= [HW,S390]
5439 Set s390 IOTLB flushing mode
5441 With strict flushing every unmap operation will result in
5442 an IOTLB flush. Default is lazy flushing before reuse,
5445 s390_iommu_aperture= [KNL,S390]
5446 Specifies the size of the per device DMA address space
5447 accessible through the DMA and IOMMU APIs as a decimal
5448 factor of the size of main memory.
5449 The default is 1 meaning that one can concurrently use
5450 as many DMA addresses as physical memory is installed,
5451 if supported by hardware, and thus map all of memory
5452 once. With a value of 2 one can map all of memory twice
5453 and so on. As a special case a factor of 0 imposes no
5454 restrictions other than those given by hardware at the
5455 cost of significant additional memory use for tables.
5458 See drivers/net/irda/sa1100_ir.c.
5460 sched_verbose [KNL] Enables verbose scheduler debug messages.
5462 schedstats= [KNL,X86] Enable or disable scheduled statistics.
5463 Allowed values are enable and disable. This feature
5464 incurs a small amount of overhead in the scheduler
5465 but is useful for debugging and performance tuning.
5467 sched_thermal_decay_shift=
5468 [KNL, SMP] Set a decay shift for scheduler thermal
5469 pressure signal. Thermal pressure signal follows the
5470 default decay period of other scheduler pelt
5471 signals(usually 32 ms but configurable). Setting
5472 sched_thermal_decay_shift will left shift the decay
5473 period for the thermal pressure signal by the shift
5475 i.e. with the default pelt decay period of 32 ms
5476 sched_thermal_decay_shift thermal pressure decay pr
5480 Format: integer between 0 and 10
5483 scftorture.holdoff= [KNL]
5484 Number of seconds to hold off before starting
5485 test. Defaults to zero for module insertion and
5486 to 10 seconds for built-in smp_call_function()
5489 scftorture.longwait= [KNL]
5490 Request ridiculously long waits randomly selected
5491 up to the chosen limit in seconds. Zero (the
5492 default) disables this feature. Please note
5493 that requesting even small non-zero numbers of
5494 seconds can result in RCU CPU stall warnings,
5495 softlockup complaints, and so on.
5497 scftorture.nthreads= [KNL]
5498 Number of kthreads to spawn to invoke the
5499 smp_call_function() family of functions.
5500 The default of -1 specifies a number of kthreads
5501 equal to the number of CPUs.
5503 scftorture.onoff_holdoff= [KNL]
5504 Number seconds to wait after the start of the
5505 test before initiating CPU-hotplug operations.
5507 scftorture.onoff_interval= [KNL]
5508 Number seconds to wait between successive
5509 CPU-hotplug operations. Specifying zero (which
5510 is the default) disables CPU-hotplug operations.
5512 scftorture.shutdown_secs= [KNL]
5513 The number of seconds following the start of the
5514 test after which to shut down the system. The
5515 default of zero avoids shutting down the system.
5516 Non-zero values are useful for automated tests.
5518 scftorture.stat_interval= [KNL]
5519 The number of seconds between outputting the
5520 current test statistics to the console. A value
5521 of zero disables statistics output.
5523 scftorture.stutter_cpus= [KNL]
5524 The number of jiffies to wait between each change
5525 to the set of CPUs under test.
5527 scftorture.use_cpus_read_lock= [KNL]
5528 Use use_cpus_read_lock() instead of the default
5529 preempt_disable() to disable CPU hotplug
5530 while invoking one of the smp_call_function*()
5533 scftorture.verbose= [KNL]
5534 Enable additional printk() statements.
5536 scftorture.weight_single= [KNL]
5537 The probability weighting to use for the
5538 smp_call_function_single() function with a zero
5539 "wait" parameter. A value of -1 selects the
5540 default if all other weights are -1. However,
5541 if at least one weight has some other value, a
5542 value of -1 will instead select a weight of zero.
5544 scftorture.weight_single_wait= [KNL]
5545 The probability weighting to use for the
5546 smp_call_function_single() function with a
5547 non-zero "wait" parameter. See weight_single.
5549 scftorture.weight_many= [KNL]
5550 The probability weighting to use for the
5551 smp_call_function_many() function with a zero
5552 "wait" parameter. See weight_single.
5553 Note well that setting a high probability for
5554 this weighting can place serious IPI load
5557 scftorture.weight_many_wait= [KNL]
5558 The probability weighting to use for the
5559 smp_call_function_many() function with a
5560 non-zero "wait" parameter. See weight_single
5563 scftorture.weight_all= [KNL]
5564 The probability weighting to use for the
5565 smp_call_function_all() function with a zero
5566 "wait" parameter. See weight_single and
5569 scftorture.weight_all_wait= [KNL]
5570 The probability weighting to use for the
5571 smp_call_function_all() function with a
5572 non-zero "wait" parameter. See weight_single
5575 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
5576 xtime_lock contention on larger systems, and/or RCU lock
5577 contention on all systems with CONFIG_MAXSMP set.
5578 Format: { "0" | "1" }
5579 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
5581 Note: increases power consumption, thus should only be
5582 enabled if running jitter sensitive (HPC/RT) workloads.
5584 security= [SECURITY] Choose a legacy "major" security module to
5585 enable at boot. This has been deprecated by the
5588 selinux= [SELINUX] Disable or enable SELinux at boot time.
5589 Format: { "0" | "1" }
5590 See security/selinux/Kconfig help text.
5595 serialnumber [BUGS=X86-32]
5597 sev=option[,option...] [X86-64] See Documentation/x86/x86_64/boot-options.rst
5600 Maximal number of shapers.
5602 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
5603 Limit apic dumping. The parameter defines the maximal
5604 number of local apics being dumped. Also it is possible
5605 to set it to "all" by meaning -- no limit here.
5606 Format: { 1 (default) | 2 | ... | all }.
5607 The parameter valid if only apic=debug or
5608 apic=verbose is specified.
5609 Example: apic=debug show_lapic=all
5617 Enable merging of slabs with similar size when the
5618 kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
5621 Disable merging of slabs with similar size. May be
5622 necessary if there is some reason to distinguish
5623 allocs to different slabs, especially in hardened
5624 environments where the risk of heap overflows and
5625 layout control by attackers can usually be
5626 frustrated by disabling merging. This will reduce
5627 most of the exposure of a heap attack to a single
5628 cache (risks via metadata attacks are mostly
5629 unchanged). Debug options disable merging on their
5631 For more information see Documentation/mm/slub.rst.
5633 slab_max_order= [MM, SLAB]
5634 Determines the maximum allowed order for slabs.
5635 A high setting may cause OOMs due to memory
5636 fragmentation. Defaults to 1 for systems with
5637 more than 32MB of RAM, 0 otherwise.
5639 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB]
5640 Enabling slub_debug allows one to determine the
5641 culprit if slab objects become corrupted. Enabling
5642 slub_debug can create guard zones around objects and
5643 may poison objects when not in use. Also tracks the
5644 last alloc / free. For more information see
5645 Documentation/mm/slub.rst.
5647 slub_max_order= [MM, SLUB]
5648 Determines the maximum allowed order for slabs.
5649 A high setting may cause OOMs due to memory
5650 fragmentation. For more information see
5651 Documentation/mm/slub.rst.
5653 slub_min_objects= [MM, SLUB]
5654 The minimum number of objects per slab. SLUB will
5655 increase the slab order up to slub_max_order to
5656 generate a sufficiently large slab able to contain
5657 the number of objects indicated. The higher the number
5658 of objects the smaller the overhead of tracking slabs
5659 and the less frequently locks need to be acquired.
5660 For more information see Documentation/mm/slub.rst.
5662 slub_min_order= [MM, SLUB]
5663 Determines the minimum page order for slabs. Must be
5664 lower than slub_max_order.
5665 For more information see Documentation/mm/slub.rst.
5667 slub_merge [MM, SLUB]
5668 Same with slab_merge.
5670 slub_nomerge [MM, SLUB]
5671 Same with slab_nomerge. This is supported for legacy.
5672 See slab_nomerge for more information.
5675 Format: <io1>[,<io2>[,...,<io8>]]
5677 smp.csd_lock_timeout= [KNL]
5678 Specify the period of time in milliseconds
5679 that smp_call_function() and friends will wait
5680 for a CPU to release the CSD lock. This is
5681 useful when diagnosing bugs involving CPUs
5682 disabling interrupts for extended periods
5683 of time. Defaults to 5,000 milliseconds, and
5684 setting a value of zero disables this feature.
5685 This feature may be more efficiently disabled
5686 using the csdlock_debug- kernel parameter.
5688 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
5689 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
5690 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
5691 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
5692 smsc-ircc2.ircc_irq= [HW] IRQ line
5693 smsc-ircc2.ircc_dma= [HW] DMA channel
5694 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
5695 0: Toshiba Satellite 1800 (GP data pin select)
5696 1: Fast pin select (default)
5699 smt= [KNL,S390] Set the maximum number of threads (logical
5700 CPUs) to use per physical CPU on systems capable of
5701 symmetric multithreading (SMT). Will be capped to the
5702 actual hardware limit.
5704 Default: -1 (no limit)
5707 [KNL] Should the soft-lockup detector generate panics.
5710 A value of 1 instructs the soft-lockup detector
5711 to panic the machine when a soft-lockup occurs. It is
5712 also controlled by the kernel.softlockup_panic sysctl
5713 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
5714 respective build-time switch to that functionality.
5716 softlockup_all_cpu_backtrace=
5717 [KNL] Should the soft-lockup detector generate
5718 backtraces on all cpus.
5721 sonypi.*= [HW] Sony Programmable I/O Control Device driver
5722 See Documentation/admin-guide/laptops/sonypi.rst
5724 spectre_v2= [X86] Control mitigation of Spectre variant 2
5725 (indirect branch speculation) vulnerability.
5726 The default operation protects the kernel from
5729 on - unconditionally enable, implies
5731 off - unconditionally disable, implies
5733 auto - kernel detects whether your CPU model is
5736 Selecting 'on' will, and 'auto' may, choose a
5737 mitigation method at run time according to the
5738 CPU, the available microcode, the setting of the
5739 CONFIG_RETPOLINE configuration option, and the
5740 compiler with which the kernel was built.
5742 Selecting 'on' will also enable the mitigation
5743 against user space to user space task attacks.
5745 Selecting 'off' will disable both the kernel and
5746 the user space protections.
5748 Specific mitigations can also be selected manually:
5750 retpoline - replace indirect branches
5751 retpoline,generic - Retpolines
5752 retpoline,lfence - LFENCE; indirect branch
5753 retpoline,amd - alias for retpoline,lfence
5754 eibrs - Enhanced/Auto IBRS
5755 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines
5756 eibrs,lfence - Enhanced/Auto IBRS + LFENCE
5757 ibrs - use IBRS to protect kernel
5759 Not specifying this option is equivalent to
5763 [X86] Control mitigation of Spectre variant 2
5764 (indirect branch speculation) vulnerability between
5767 on - Unconditionally enable mitigations. Is
5768 enforced by spectre_v2=on
5770 off - Unconditionally disable mitigations. Is
5771 enforced by spectre_v2=off
5773 prctl - Indirect branch speculation is enabled,
5774 but mitigation can be enabled via prctl
5775 per thread. The mitigation control state
5776 is inherited on fork.
5779 - Like "prctl" above, but only STIBP is
5780 controlled per thread. IBPB is issued
5781 always when switching between different user
5785 - Same as "prctl" above, but all seccomp
5786 threads will enable the mitigation unless
5787 they explicitly opt out.
5790 - Like "seccomp" above, but only STIBP is
5791 controlled per thread. IBPB is issued
5792 always when switching between different
5793 user space processes.
5795 auto - Kernel selects the mitigation depending on
5796 the available CPU features and vulnerability.
5798 Default mitigation: "prctl"
5800 Not specifying this option is equivalent to
5801 spectre_v2_user=auto.
5803 spec_store_bypass_disable=
5804 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
5805 (Speculative Store Bypass vulnerability)
5807 Certain CPUs are vulnerable to an exploit against a
5808 a common industry wide performance optimization known
5809 as "Speculative Store Bypass" in which recent stores
5810 to the same memory location may not be observed by
5811 later loads during speculative execution. The idea
5812 is that such stores are unlikely and that they can
5813 be detected prior to instruction retirement at the
5814 end of a particular speculation execution window.
5816 In vulnerable processors, the speculatively forwarded
5817 store can be used in a cache side channel attack, for
5818 example to read memory to which the attacker does not
5819 directly have access (e.g. inside sandboxed code).
5821 This parameter controls whether the Speculative Store
5822 Bypass optimization is used.
5824 On x86 the options are:
5826 on - Unconditionally disable Speculative Store Bypass
5827 off - Unconditionally enable Speculative Store Bypass
5828 auto - Kernel detects whether the CPU model contains an
5829 implementation of Speculative Store Bypass and
5830 picks the most appropriate mitigation. If the
5831 CPU is not vulnerable, "off" is selected. If the
5832 CPU is vulnerable the default mitigation is
5833 architecture and Kconfig dependent. See below.
5834 prctl - Control Speculative Store Bypass per thread
5835 via prctl. Speculative Store Bypass is enabled
5836 for a process by default. The state of the control
5837 is inherited on fork.
5838 seccomp - Same as "prctl" above, but all seccomp threads
5839 will disable SSB unless they explicitly opt out.
5841 Default mitigations:
5844 On powerpc the options are:
5846 on,auto - On Power8 and Power9 insert a store-forwarding
5847 barrier on kernel entry and exit. On Power7
5848 perform a software flush on kernel entry and
5852 Not specifying this option is equivalent to
5853 spec_store_bypass_disable=auto.
5855 spia_io_base= [HW,MTD]
5861 [X86] Enable split lock detection or bus lock detection
5863 When enabled (and if hardware support is present), atomic
5864 instructions that access data across cache line
5865 boundaries will result in an alignment check exception
5866 for split lock detection or a debug exception for
5871 warn - the kernel will emit rate-limited warnings
5872 about applications triggering the #AC
5873 exception or the #DB exception. This mode is
5874 the default on CPUs that support split lock
5875 detection or bus lock detection. Default
5876 behavior is by #AC if both features are
5877 enabled in hardware.
5879 fatal - the kernel will send SIGBUS to applications
5880 that trigger the #AC exception or the #DB
5881 exception. Default behavior is by #AC if
5882 both features are enabled in hardware.
5885 Set system wide rate limit to N bus locks
5886 per second for bus lock detection.
5889 N/A for split lock detection.
5892 If an #AC exception is hit in the kernel or in
5893 firmware (i.e. not while executing in user mode)
5894 the kernel will oops in either "warn" or "fatal"
5897 #DB exception for bus lock is triggered only when
5901 Control the Special Register Buffer Data Sampling
5904 Certain CPUs are vulnerable to an MDS-like
5905 exploit which can leak bits from the random
5908 By default, this issue is mitigated by
5909 microcode. However, the microcode fix can cause
5910 the RDRAND and RDSEED instructions to become
5911 much slower. Among other effects, this will
5912 result in reduced throughput from /dev/urandom.
5914 The microcode mitigation can be disabled with
5915 the following option:
5917 off: Disable mitigation and remove
5918 performance impact to RDRAND and RDSEED
5920 srcutree.big_cpu_lim [KNL]
5921 Specifies the number of CPUs constituting a
5922 large system, such that srcu_struct structures
5923 should immediately allocate an srcu_node array.
5924 This kernel-boot parameter defaults to 128,
5925 but takes effect only when the low-order four
5926 bits of srcutree.convert_to_big is equal to 3
5929 srcutree.convert_to_big [KNL]
5930 Specifies under what conditions an SRCU tree
5931 srcu_struct structure will be converted to big
5932 form, that is, with an rcu_node tree:
5935 1: At init_srcu_struct() time.
5936 2: When rcutorture decides to.
5937 3: Decide at boot time (default).
5938 0x1X: Above plus if high contention.
5940 Either way, the srcu_node tree will be sized based
5941 on the actual runtime number of CPUs (nr_cpu_ids)
5942 instead of the compile-time CONFIG_NR_CPUS.
5944 srcutree.counter_wrap_check [KNL]
5945 Specifies how frequently to check for
5946 grace-period sequence counter wrap for the
5947 srcu_data structure's ->srcu_gp_seq_needed field.
5948 The greater the number of bits set in this kernel
5949 parameter, the less frequently counter wrap will
5950 be checked for. Note that the bottom two bits
5953 srcutree.exp_holdoff [KNL]
5954 Specifies how many nanoseconds must elapse
5955 since the end of the last SRCU grace period for
5956 a given srcu_struct until the next normal SRCU
5957 grace period will be considered for automatic
5958 expediting. Set to zero to disable automatic
5961 srcutree.srcu_max_nodelay [KNL]
5962 Specifies the number of no-delay instances
5963 per jiffy for which the SRCU grace period
5964 worker thread will be rescheduled with zero
5965 delay. Beyond this limit, worker thread will
5966 be rescheduled with a sleep delay of one jiffy.
5968 srcutree.srcu_max_nodelay_phase [KNL]
5969 Specifies the per-grace-period phase, number of
5970 non-sleeping polls of readers. Beyond this limit,
5971 grace period worker thread will be rescheduled
5972 with a sleep delay of one jiffy, between each
5973 rescan of the readers, for a grace period phase.
5975 srcutree.srcu_retry_check_delay [KNL]
5976 Specifies number of microseconds of non-sleeping
5977 delay between each non-sleeping poll of readers.
5979 srcutree.small_contention_lim [KNL]
5980 Specifies the number of update-side contention
5981 events per jiffy will be tolerated before
5982 initiating a conversion of an srcu_struct
5983 structure to big form. Note that the value of
5984 srcutree.convert_to_big must have the 0x10 bit
5985 set for contention-based conversions to occur.
5988 Speculative Store Bypass Disable control
5990 On CPUs that are vulnerable to the Speculative
5991 Store Bypass vulnerability and offer a
5992 firmware based mitigation, this parameter
5993 indicates how the mitigation should be used:
5995 force-on: Unconditionally enable mitigation for
5996 for both kernel and userspace
5997 force-off: Unconditionally disable mitigation for
5998 for both kernel and userspace
5999 kernel: Always enable mitigation in the
6000 kernel, and offer a prctl interface
6001 to allow userspace to register its
6002 interest in being mitigated too.
6004 stack_guard_gap= [MM]
6005 override the default stack gap protection. The value
6006 is in page units and it defines how many pages prior
6007 to (for stacks growing down) resp. after (for stacks
6008 growing up) the main stack are reserved for no other
6009 mapping. Default value is 256 pages.
6011 stack_depot_disable= [KNL]
6012 Setting this to true through kernel command line will
6013 disable the stack depot thereby saving the static memory
6014 consumed by the stack hash table. By default this is set
6018 Enabled the stack tracer on boot up.
6020 stacktrace_filter=[function-list]
6021 [FTRACE] Limit the functions that the stack tracer
6022 will trace at boot up. function-list is a comma-separated
6023 list of functions. This list can be changed at run
6024 time by the stack_trace_filter file in the debugfs
6025 tracing directory. Note, this enables stack tracing
6026 and the stacktrace above is not needed.
6030 Set the STI (builtin display/keyboard on the HP-PARISC
6031 machines) console (graphic card) which should be used
6032 as the initial boot-console.
6033 See also comment in drivers/video/console/sticore.c.
6036 See comment in drivers/video/console/sticore.c.
6039 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
6044 Enable or disable strict sigaltstack size checks
6045 against the required signal frame size which
6046 depends on the supported FPU features. This can
6047 be used to filter out binaries which have
6048 not yet been made aware of AT_MINSIGSTKSZ.
6051 Limits the number of kernel HPT entries in the hash
6052 page table to increase the rate of hash page table
6053 faults on kernel addresses.
6056 Limits the number of kernel SLB entries, and flushes
6057 them frequently to increase the rate of SLB faults
6058 on kernel addresses.
6060 sunrpc.min_resvport=
6061 sunrpc.max_resvport=
6063 SunRPC servers often require that client requests
6064 originate from a privileged port (i.e. a port in the
6065 range 0 < portnr < 1024).
6066 An administrator who wishes to reserve some of these
6067 ports for other uses may adjust the range that the
6068 kernel's sunrpc client considers to be privileged
6069 using these two parameters to set the minimum and
6070 maximum port values.
6072 sunrpc.svc_rpc_per_connection_limit=
6074 Limit the number of requests that the server will
6075 process in parallel from a single connection.
6076 The default value is 0 (no limit).
6080 Control how the NFS server code allocates CPUs to
6081 service thread pools. Depending on how many NICs
6082 you have and where their interrupts are bound, this
6083 option will affect which CPUs will do NFS serving.
6084 Note: this parameter cannot be changed while the
6085 NFS server is running.
6087 auto the server chooses an appropriate mode
6088 automatically using heuristics
6089 global a single global pool contains all CPUs
6090 percpu one pool for each CPU
6091 pernode one pool for each NUMA node (equivalent
6092 to global on non-NUMA machines)
6094 sunrpc.tcp_slot_table_entries=
6095 sunrpc.udp_slot_table_entries=
6097 Sets the upper limit on the number of simultaneous
6098 RPC calls that can be sent from the client to a
6099 server. Increasing these values may allow you to
6100 improve throughput, but will also increase the
6101 amount of memory reserved for use by the client.
6103 suspend.pm_test_delay=
6105 Sets the number of seconds to remain in a suspend test
6106 mode before resuming the system (see
6107 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
6108 is set. Default value is 5.
6111 Format: { on | off | y | n | 1 | 0 }
6112 This parameter controls use of the Protected
6113 Execution Facility on pSeries.
6115 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
6116 Format: { <int> [,<int>] | force | noforce }
6117 <int> -- Number of I/O TLB slabs
6118 <int> -- Second integer after comma. Number of swiotlb
6119 areas with their own lock. Will be rounded up
6121 force -- force using of bounce buffers even if they
6122 wouldn't be automatically used by the kernel
6123 noforce -- Never use bounce buffers (for debugging)
6128 Set a sysctl parameter, right before loading the init
6129 process, as if the value was written to the respective
6130 /proc/sys/... file. Both '.' and '/' are recognized as
6131 separators. Unrecognized parameters and invalid values
6132 are reported in the kernel log. Sysctls registered
6133 later by a loaded module cannot be set this way.
6134 Example: sysctl.vm.swappiness=40
6136 sysfs.deprecated=0|1 [KNL]
6137 Enable/disable old style sysfs layout for old udev
6138 on older distributions. When this option is enabled
6139 very new udev will not work anymore. When this option
6140 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
6141 in older udev will not work anymore.
6142 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
6143 the kernel configuration.
6145 sysrq_always_enabled
6147 Ignore sysrq setting - this boot parameter will
6148 neutralize any effect of /proc/sys/kernel/sysrq.
6149 Useful for debugging.
6151 tcpmhash_entries= [KNL,NET]
6152 Set the number of tcp_metrics_hash slots.
6153 Default value is 8192 or 16384 depending on total
6154 ram pages. This is used to specify the TCP metrics
6155 cache size. See Documentation/networking/ip-sysctl.rst
6156 "tcp_no_metrics_save" section for more details.
6160 test_suspend= [SUSPEND]
6161 Format: { "mem" | "standby" | "freeze" }[,N]
6162 Specify "mem" (for Suspend-to-RAM) or "standby" (for
6163 standby suspend) or "freeze" (for suspend type freeze)
6164 as the system sleep state during system startup with
6165 the optional capability to repeat N number of times.
6166 The system is woken from this state using a
6167 wakeup-capable RTC alarm.
6169 thash_entries= [KNL,NET]
6170 Set number of hash buckets for TCP connection
6172 thermal.act= [HW,ACPI]
6173 -1: disable all active trip points in all thermal zones
6174 <degrees C>: override all lowest active trip points
6176 thermal.crt= [HW,ACPI]
6177 -1: disable all critical trip points in all thermal zones
6178 <degrees C>: override all critical trip points
6180 thermal.nocrt= [HW,ACPI]
6181 Set to disable actions on ACPI thermal zone
6182 critical and hot trip points.
6184 thermal.off= [HW,ACPI]
6185 1: disable ACPI thermal control
6187 thermal.psv= [HW,ACPI]
6188 -1: disable all passive trip points
6189 <degrees C>: override all passive trip points to this
6192 thermal.tzp= [HW,ACPI]
6193 Specify global default ACPI thermal zone polling rate
6194 <deci-seconds>: poll all this frequency
6195 0: no polling (default)
6198 Force threading of all interrupt handlers except those
6199 marked explicitly IRQF_NO_THREAD.
6203 Specify if the kernel should make use of the cpu
6204 topology information if the hardware supports this.
6205 The scheduler will make use of this information and
6206 e.g. base its process migration decisions on it.
6209 topology_updates= [KNL, PPC, NUMA]
6211 Specify if the kernel should ignore (off)
6212 topology updates sent by the hypervisor to this
6215 torture.disable_onoff_at_boot= [KNL]
6216 Prevent the CPU-hotplug component of torturing
6217 until after init has spawned.
6219 torture.ftrace_dump_at_shutdown= [KNL]
6220 Dump the ftrace buffer at torture-test shutdown,
6221 even if there were no errors. This can be a
6222 very costly operation when many torture tests
6223 are running concurrently, especially on systems
6224 with rotating-rust storage.
6226 torture.verbose_sleep_frequency= [KNL]
6227 Specifies how many verbose printk()s should be
6228 emitted between each sleep. The default of zero
6229 disables verbose-printk() sleeping.
6231 torture.verbose_sleep_duration= [KNL]
6232 Duration of each verbose-printk() sleep in jiffies.
6236 tpm_suspend_pcr=[HW,TPM]
6237 Format: integer pcr id
6238 Specify that at suspend time, the tpm driver
6239 should extend the specified pcr with zeros,
6240 as a workaround for some chips which fail to
6241 flush the last written pcr on TPM_SaveState.
6242 This will guarantee that all the other pcrs
6246 Have the tracepoints sent to printk as well as the
6247 tracing ring buffer. This is useful for early boot up
6248 where the system hangs or reboots and does not give the
6249 option for reading the tracing buffer or performing a
6250 ftrace_dump_on_oops.
6252 To turn off having tracepoints sent to printk,
6253 echo 0 > /proc/sys/kernel/tracepoint_printk
6254 Note, echoing 1 into this file without the
6255 tracepoint_printk kernel cmdline option has no effect.
6257 The tp_printk_stop_on_boot (see below) can also be used
6258 to stop the printing of events to console at
6263 Having tracepoints sent to printk() and activating high
6264 frequency tracepoints such as irq or sched, can cause
6265 the system to live lock.
6267 tp_printk_stop_on_boot [FTRACE]
6268 When tp_printk (above) is set, it can cause a lot of noise
6269 on the console. It may be useful to only include the
6270 printing of events during boot up, as user space may
6271 make the system inoperable.
6273 This command line option will stop the printing of events
6274 to console at the late_initcall_sync() time frame.
6276 trace_buf_size=nn[KMG]
6277 [FTRACE] will set tracing buffer size on each cpu.
6279 trace_clock= [FTRACE] Set the clock used for tracing events
6281 local - Use the per CPU time stamp counter
6282 (converted into nanoseconds). Fast, but
6283 depending on the architecture, may not be
6284 in sync between CPUs.
6285 global - Event time stamps are synchronize across
6286 CPUs. May be slower than the local clock,
6287 but better for some race conditions.
6288 counter - Simple counting of events (1, 2, ..)
6289 note, some counts may be skipped due to the
6290 infrastructure grabbing the clock more than
6292 uptime - Use jiffies as the time stamp.
6293 perf - Use the same clock that perf uses.
6294 mono - Use ktime_get_mono_fast_ns() for time stamps.
6295 mono_raw - Use ktime_get_raw_fast_ns() for time
6297 boot - Use ktime_get_boot_fast_ns() for time stamps.
6298 Architectures may add more clocks. See
6299 Documentation/trace/ftrace.rst for more details.
6301 trace_event=[event-list]
6302 [FTRACE] Set and start specified trace events in order
6303 to facilitate early boot debugging. The event-list is a
6304 comma-separated list of trace events to enable. See
6305 also Documentation/trace/events.rst
6307 trace_instance=[instance-info]
6308 [FTRACE] Create a ring buffer instance early in boot up.
6309 This will be listed in:
6311 /sys/kernel/tracing/instances
6313 Events can be enabled at the time the instance is created
6316 trace_instance=<name>,<system1>:<event1>,<system2>:<event2>
6318 Note, the "<system*>:" portion is optional if the event is
6321 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall
6323 will enable the "sched_switch" event (note, the "sched:" is optional, and
6324 the same thing would happen if it was left off). The irq_handler_entry
6325 event, and all events under the "initcall" system.
6327 trace_options=[option-list]
6328 [FTRACE] Enable or disable tracer options at boot.
6329 The option-list is a comma delimited list of options
6330 that can be enabled or disabled just as if you were
6331 to echo the option name into
6333 /sys/kernel/tracing/trace_options
6335 For example, to enable stacktrace option (to dump the
6336 stack trace of each event), add to the command line:
6338 trace_options=stacktrace
6340 See also Documentation/trace/ftrace.rst "trace options"
6343 trace_trigger=[trigger-list]
6344 [FTRACE] Add a event trigger on specific events.
6345 Set a trigger on top of a specific event, with an optional
6348 The format is is "trace_trigger=<event>.<trigger>[ if <filter>],..."
6349 Where more than one trigger may be specified that are comma deliminated.
6353 trace_trigger="sched_switch.stacktrace if prev_state == 2"
6355 The above will enable the "stacktrace" trigger on the "sched_switch"
6356 event but only trigger it if the "prev_state" of the "sched_switch"
6357 event is "2" (TASK_UNINTERUPTIBLE).
6359 See also "Event triggers" in Documentation/trace/events.rst
6363 [FTRACE] enable this option to disable tracing when a
6364 warning is hit. This turns off "tracing_on". Tracing can
6365 be enabled again by echoing '1' into the "tracing_on"
6366 file located in /sys/kernel/tracing/
6368 This option is useful, as it disables the trace before
6369 the WARNING dump is called, which prevents the trace to
6370 be filled with content caused by the warning output.
6372 This option can also be set at run time via the sysctl
6373 option: kernel/traceoff_on_warning
6375 transparent_hugepage=
6377 Format: [always|madvise|never]
6378 Can be used to control the default behavior of the system
6379 with respect to transparent hugepages.
6380 See Documentation/admin-guide/mm/transhuge.rst
6383 trusted.source= [KEYS]
6385 This parameter identifies the trust source as a backend
6386 for trusted keys implementation. Supported trust
6391 If not specified then it defaults to iterating through
6392 the trust source list starting with TPM and assigns the
6393 first trust source as a backend which is initialized
6394 successfully during iteration.
6398 The RNG used to generate key material for trusted keys.
6401 - the same value as trusted.source: "tpm" or "tee"
6403 If not specified, "default" is used. In this case,
6404 the RNG's choice is left to each individual trust source.
6406 tsc= Disable clocksource stability checks for TSC.
6408 [x86] reliable: mark tsc clocksource as reliable, this
6409 disables clocksource verification at runtime, as well
6410 as the stability checks done at bootup. Used to enable
6411 high-resolution timer mode on older hardware, and in
6412 virtualized environment.
6413 [x86] noirqtime: Do not use TSC to do irq accounting.
6414 Used to run time disable IRQ_TIME_ACCOUNTING on any
6415 platforms where RDTSC is slow and this accounting
6417 [x86] unstable: mark the TSC clocksource as unstable, this
6418 marks the TSC unconditionally unstable at bootup and
6419 avoids any further wobbles once the TSC watchdog notices.
6420 [x86] nowatchdog: disable clocksource watchdog. Used
6421 in situations with strict latency requirements (where
6422 interruptions from clocksource watchdog are not
6424 [x86] recalibrate: force recalibration against a HW timer
6425 (HPET or PM timer) on systems whose TSC frequency was
6426 obtained from HW or FW using either an MSR or CPUID(0x15).
6427 Warn if the difference is more than 500 ppm.
6428 [x86] watchdog: Use TSC as the watchdog clocksource with
6429 which to check other HW timers (HPET or PM timer), but
6430 only on systems where TSC has been deemed trustworthy.
6431 This will be suppressed by an earlier tsc=nowatchdog and
6432 can be overridden by a later tsc=nowatchdog. A console
6433 message will flag any such suppression or overriding.
6435 tsc_early_khz= [X86] Skip early TSC calibration and use the given
6436 value instead. Useful when the early TSC frequency discovery
6437 procedure is not reliable, such as on overclocked systems
6438 with CPUID.16h support and partial CPUID.15h support.
6439 Format: <unsigned int>
6441 tsx= [X86] Control Transactional Synchronization
6442 Extensions (TSX) feature in Intel processors that
6443 support TSX control.
6445 This parameter controls the TSX feature. The options are:
6447 on - Enable TSX on the system. Although there are
6448 mitigations for all known security vulnerabilities,
6449 TSX has been known to be an accelerator for
6450 several previous speculation-related CVEs, and
6451 so there may be unknown security risks associated
6452 with leaving it enabled.
6454 off - Disable TSX on the system. (Note that this
6455 option takes effect only on newer CPUs which are
6456 not vulnerable to MDS, i.e., have
6457 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
6458 the new IA32_TSX_CTRL MSR through a microcode
6459 update. This new MSR allows for the reliable
6460 deactivation of the TSX functionality.)
6462 auto - Disable TSX if X86_BUG_TAA is present,
6463 otherwise enable TSX on the system.
6465 Not specifying this option is equivalent to tsx=off.
6467 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6470 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
6471 Abort (TAA) vulnerability.
6473 Similar to Micro-architectural Data Sampling (MDS)
6474 certain CPUs that support Transactional
6475 Synchronization Extensions (TSX) are vulnerable to an
6476 exploit against CPU internal buffers which can forward
6477 information to a disclosure gadget under certain
6480 In vulnerable processors, the speculatively forwarded
6481 data can be used in a cache side channel attack, to
6482 access data to which the attacker does not have direct
6485 This parameter controls the TAA mitigation. The
6488 full - Enable TAA mitigation on vulnerable CPUs
6491 full,nosmt - Enable TAA mitigation and disable SMT on
6492 vulnerable CPUs. If TSX is disabled, SMT
6493 is not disabled because CPU is not
6494 vulnerable to cross-thread TAA attacks.
6495 off - Unconditionally disable TAA mitigation
6497 On MDS-affected machines, tsx_async_abort=off can be
6498 prevented by an active MDS mitigation as both vulnerabilities
6499 are mitigated with the same mechanism so in order to disable
6500 this mitigation, you need to specify mds=off too.
6502 Not specifying this option is equivalent to
6503 tsx_async_abort=full. On CPUs which are MDS affected
6504 and deploy MDS mitigation, TAA mitigation is not
6505 required and doesn't provide any additional
6509 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6511 turbografx.map[2|3]= [HW,JOY]
6512 TurboGraFX parallel port interface
6514 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
6515 See also Documentation/input/devices/joystick-parport.rst
6517 udbg-immortal [PPC] When debugging early kernel crashes that
6518 happen after console_init() and before a proper
6519 console driver takes over, this boot options might
6520 help "seeing" what's going on.
6522 uhash_entries= [KNL,NET]
6523 Set number of hash buckets for UDP/UDP-Lite connections
6526 [USB] Ignore overcurrent events (default N).
6527 Some badly-designed motherboards generate lots of
6528 bogus events, for ports that aren't wired to
6529 anything. Set this parameter to avoid log spamming.
6530 Note that genuine overcurrent events won't be
6534 [X86] Cause panic on unknown NMI.
6536 usbcore.authorized_default=
6537 [USB] Default USB device authorization:
6538 (default -1 = authorized except for wireless USB,
6539 0 = not authorized, 1 = authorized, 2 = authorized
6540 if device connected to internal port)
6542 usbcore.autosuspend=
6543 [USB] The autosuspend time delay (in seconds) used
6544 for newly-detected USB devices (default 2). This
6545 is the time required before an idle device will be
6546 autosuspended. Devices for which the delay is set
6547 to a negative value won't be autosuspended at all.
6549 usbcore.usbfs_snoop=
6550 [USB] Set to log all usbfs traffic (default 0 = off).
6552 usbcore.usbfs_snoop_max=
6553 [USB] Maximum number of bytes to snoop in each URB
6556 usbcore.blinkenlights=
6557 [USB] Set to cycle leds on hubs (default 0 = off).
6559 usbcore.old_scheme_first=
6560 [USB] Start with the old device initialization
6561 scheme (default 0 = off).
6563 usbcore.usbfs_memory_mb=
6564 [USB] Memory limit (in MB) for buffers allocated by
6565 usbfs (default = 16, 0 = max = 2047).
6567 usbcore.use_both_schemes=
6568 [USB] Try the other device initialization scheme
6569 if the first one fails (default 1 = enabled).
6571 usbcore.initial_descriptor_timeout=
6572 [USB] Specifies timeout for the initial 64-byte
6573 USB_REQ_GET_DESCRIPTOR request in milliseconds
6574 (default 5000 = 5.0 seconds).
6576 usbcore.nousb [USB] Disable the USB subsystem
6579 [USB] A list of quirk entries to augment the built-in
6580 usb core quirk list. List entries are separated by
6581 commas. Each entry has the form
6582 VendorID:ProductID:Flags. The IDs are 4-digit hex
6583 numbers and Flags is a set of letters. Each letter
6584 will change the built-in quirk; setting it if it is
6585 clear and clearing it if it is set. The letters have
6586 the following meanings:
6587 a = USB_QUIRK_STRING_FETCH_255 (string
6588 descriptors must not be fetched using
6590 b = USB_QUIRK_RESET_RESUME (device can't resume
6591 correctly so reset it instead);
6592 c = USB_QUIRK_NO_SET_INTF (device can't handle
6593 Set-Interface requests);
6594 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
6595 handle its Configuration or Interface
6597 e = USB_QUIRK_RESET (device can't be reset
6598 (e.g morph devices), don't use reset);
6599 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
6600 more interface descriptions than the
6601 bNumInterfaces count, and can't handle
6602 talking to these interfaces);
6603 g = USB_QUIRK_DELAY_INIT (device needs a pause
6604 during initialization, after we read
6605 the device descriptor);
6606 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
6607 high speed and super speed interrupt
6608 endpoints, the USB 2.0 and USB 3.0 spec
6609 require the interval in microframes (1
6610 microframe = 125 microseconds) to be
6611 calculated as interval = 2 ^
6613 Devices with this quirk report their
6614 bInterval as the result of this
6615 calculation instead of the exponent
6616 variable used in the calculation);
6617 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
6618 handle device_qualifier descriptor
6620 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
6621 generates spurious wakeup, ignore
6622 remote wakeup capability);
6623 k = USB_QUIRK_NO_LPM (device can't handle Link
6625 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
6626 (Device reports its bInterval as linear
6627 frames instead of the USB 2.0
6629 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
6630 to be disconnected before suspend to
6631 prevent spurious wakeup);
6632 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
6633 pause after every control message);
6634 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
6635 delay after resetting its port);
6636 Example: quirks=0781:5580:bk,0a5c:5834:gij
6639 [USBHID] The interval which mice are to be polled at.
6642 [USBHID] The interval which joysticks are to be polled at.
6645 [USBHID] The interval which keyboards are to be polled at.
6647 usb-storage.delay_use=
6648 [UMS] The delay in seconds before a new device is
6649 scanned for Logical Units (default 1).
6652 [UMS] A list of quirks entries to supplement or
6653 override the built-in unusual_devs list. List
6654 entries are separated by commas. Each entry has
6655 the form VID:PID:Flags where VID and PID are Vendor
6656 and Product ID values (4-digit hex numbers) and
6657 Flags is a set of characters, each corresponding
6658 to a common usb-storage quirk flag as follows:
6659 a = SANE_SENSE (collect more than 18 bytes
6660 of sense data, not on uas);
6661 b = BAD_SENSE (don't collect more than 18
6662 bytes of sense data, not on uas);
6663 c = FIX_CAPACITY (decrease the reported
6664 device capacity by one sector);
6665 d = NO_READ_DISC_INFO (don't use
6666 READ_DISC_INFO command, not on uas);
6667 e = NO_READ_CAPACITY_16 (don't use
6668 READ_CAPACITY_16 command);
6669 f = NO_REPORT_OPCODES (don't use report opcodes
6671 g = MAX_SECTORS_240 (don't transfer more than
6672 240 sectors at a time, uas only);
6673 h = CAPACITY_HEURISTICS (decrease the
6674 reported device capacity by one
6675 sector if the number is odd);
6676 i = IGNORE_DEVICE (don't bind to this
6678 j = NO_REPORT_LUNS (don't use report luns
6680 k = NO_SAME (do not use WRITE_SAME, uas only)
6681 l = NOT_LOCKABLE (don't try to lock and
6682 unlock ejectable media, not on uas);
6683 m = MAX_SECTORS_64 (don't transfer more
6684 than 64 sectors = 32 KB at a time,
6686 n = INITIAL_READ10 (force a retry of the
6687 initial READ(10) command, not on uas);
6688 o = CAPACITY_OK (accept the capacity
6689 reported by the device, not on uas);
6690 p = WRITE_CACHE (the device cache is ON
6691 by default, not on uas);
6692 r = IGNORE_RESIDUE (the device reports
6693 bogus residue values, not on uas);
6694 s = SINGLE_LUN (the device has only one
6696 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
6697 commands, uas only);
6698 u = IGNORE_UAS (don't bind to the uas driver);
6699 w = NO_WP_DETECT (don't test whether the
6700 medium is write-protected).
6701 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
6702 even if the device claims no cache,
6704 Example: quirks=0419:aaf5:rl,0421:0433:rc
6706 user_debug= [KNL,ARM]
6708 See arch/arm/Kconfig.debug help text.
6709 1 - undefined instruction events
6711 4 - invalid data aborts
6714 Example: user_debug=31
6717 [X86] Flags controlling user PTE allocations.
6719 nohigh = do not allocate PTE pages in
6720 HIGHMEM regardless of setting
6723 vdso= [X86,SH,SPARC]
6724 On X86_32, this is an alias for vdso32=. Otherwise:
6726 vdso=1: enable VDSO (the default)
6727 vdso=0: disable VDSO mapping
6729 vdso32= [X86] Control the 32-bit vDSO
6730 vdso32=1: enable 32-bit VDSO
6731 vdso32=0 or vdso32=2: disable 32-bit VDSO
6733 See the help text for CONFIG_COMPAT_VDSO for more
6734 details. If CONFIG_COMPAT_VDSO is set, the default is
6735 vdso32=0; otherwise, the default is vdso32=1.
6737 For compatibility with older kernels, vdso32=2 is an
6740 Try vdso32=0 if you encounter an error that says:
6741 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
6744 vector=percpu: enable percpu vector domain
6746 video= [FB] Frame buffer configuration
6747 See Documentation/fb/modedb.rst.
6749 video.brightness_switch_enabled= [ACPI]
6751 If set to 1, on receiving an ACPI notify event
6752 generated by hotkey, video driver will adjust brightness
6753 level and then send out the event to user space through
6754 the allocated input device. If set to 0, video driver
6755 will only send out the event without touching backlight
6760 [VMMIO] Memory mapped virtio (platform) device.
6762 <size>@<baseaddr>:<irq>[:<id>]
6764 <size> := size (can use standard suffixes
6766 <baseaddr> := physical base address
6767 <irq> := interrupt number (as passed to
6769 <id> := (optional) platform device id
6771 virtio_mmio.device=1K@0x100b0000:48:7
6773 Can be used multiple times for multiple devices.
6775 vga= [BOOT,X86-32] Select a particular video mode
6776 See Documentation/x86/boot.rst and
6777 Documentation/admin-guide/svga.rst.
6778 Use vga=ask for menu.
6779 This is actually a boot loader parameter; the value is
6780 passed to the kernel using a special protocol.
6782 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
6783 May slow down system boot speed, especially when
6784 enabled on systems with a large amount of memory.
6785 All options are enabled by default, and this
6786 interface is meant to allow for selectively
6787 enabling or disabling specific virtual memory
6790 Available options are:
6791 P Enable page structure init time poisoning
6792 - Disable all of the above options
6794 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
6795 size of <nn>. This can be used to increase the
6796 minimum size (128MB on x86). It can also be used to
6797 decrease the size and leave more room for directly
6800 vmcp_cma=nn[MG] [KNL,S390]
6801 Sets the memory size reserved for contiguous memory
6802 allocations for the vmcp device driver.
6804 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
6807 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
6810 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
6814 Controls the behavior of vsyscalls (i.e. calls to
6815 fixed addresses of 0xffffffffff600x00 from legacy
6816 code). Most statically-linked binaries and older
6817 versions of glibc use these calls. Because these
6818 functions are at fixed addresses, they make nice
6819 targets for exploits that can control RIP.
6821 emulate Vsyscalls turn into traps and are emulated
6822 reasonably safely. The vsyscall page is
6825 xonly [default] Vsyscalls turn into traps and are
6826 emulated reasonably safely. The vsyscall
6827 page is not readable.
6829 none Vsyscalls don't work at all. This makes
6830 them quite hard to use for exploits but
6831 might break your system.
6833 vt.color= [VT] Default text color.
6834 Format: 0xYX, X = foreground, Y = background.
6835 Default: 0x07 = light gray on black.
6837 vt.cur_default= [VT] Default cursor shape.
6838 Format: 0xCCBBAA, where AA, BB, and CC are the same as
6839 the parameters of the <Esc>[?A;B;Cc escape sequence;
6840 see VGA-softcursor.txt. Default: 2 = underline.
6842 vt.default_blu= [VT]
6843 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
6844 Change the default blue palette of the console.
6845 This is a 16-member array composed of values
6848 vt.default_grn= [VT]
6849 Format: <green0>,<green1>,<green2>,...,<green15>
6850 Change the default green palette of the console.
6851 This is a 16-member array composed of values
6854 vt.default_red= [VT]
6855 Format: <red0>,<red1>,<red2>,...,<red15>
6856 Change the default red palette of the console.
6857 This is a 16-member array composed of values
6863 Set system-wide default UTF-8 mode for all tty's.
6864 Default is 1, i.e. UTF-8 mode is enabled for all
6865 newly opened terminals.
6867 vt.global_cursor_default=
6870 Set system-wide default for whether a cursor
6871 is shown on new VTs. Default is -1,
6872 i.e. cursors will be created by default unless
6873 overridden by individual drivers. 0 will hide
6874 cursors, 1 will display them.
6876 vt.italic= [VT] Default color for italic text; 0-15.
6879 vt.underline= [VT] Default color for underlined text; 0-15.
6882 watchdog timers [HW,WDT] For information on watchdog timers,
6883 see Documentation/watchdog/watchdog-parameters.rst
6884 or other driver-specific files in the
6885 Documentation/watchdog/ directory.
6889 Set the hard lockup detector stall duration
6890 threshold in seconds. The soft lockup detector
6891 threshold is set to twice the value. A value of 0
6892 disables both lockup detectors. Default is 10
6895 workqueue.watchdog_thresh=
6896 If CONFIG_WQ_WATCHDOG is configured, workqueue can
6897 warn stall conditions and dump internal state to
6898 help debugging. 0 disables workqueue stall
6899 detection; otherwise, it's the stall threshold
6900 duration in seconds. The default value is 30 and
6901 it can be updated at runtime by writing to the
6902 corresponding sysfs file.
6904 workqueue.disable_numa
6905 By default, all work items queued to unbound
6906 workqueues are affine to the NUMA nodes they're
6907 issued on, which results in better behavior in
6908 general. If NUMA affinity needs to be disabled for
6909 whatever reason, this option can be used. Note
6910 that this also can be controlled per-workqueue for
6911 workqueues visible under /sys/bus/workqueue/.
6913 workqueue.power_efficient
6914 Per-cpu workqueues are generally preferred because
6915 they show better performance thanks to cache
6916 locality; unfortunately, per-cpu workqueues tend to
6917 be more power hungry than unbound workqueues.
6919 Enabling this makes the per-cpu workqueues which
6920 were observed to contribute significantly to power
6921 consumption unbound, leading to measurably lower
6922 power usage at the cost of small performance
6925 The default value of this parameter is determined by
6926 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
6928 workqueue.debug_force_rr_cpu
6929 Workqueue used to implicitly guarantee that work
6930 items queued without explicit CPU specified are put
6931 on the local CPU. This guarantee is no longer true
6932 and while local CPU is still preferred work items
6933 may be put on foreign CPUs. This debug option
6934 forces round-robin CPU selection to flush out
6935 usages which depend on the now broken guarantee.
6936 When enabled, memory and cache locality will be
6939 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
6940 default x2apic cluster mode on platforms
6943 xen_512gb_limit [KNL,X86-64,XEN]
6944 Restricts the kernel running paravirtualized under Xen
6945 to use only up to 512 GB of RAM. The reason to do so is
6946 crash analysis tools and Xen tools for doing domain
6947 save/restore/migration must be enabled to handle larger
6950 xen_emul_unplug= [HW,X86,XEN]
6951 Unplug Xen emulated devices
6952 Format: [unplug0,][unplug1]
6953 ide-disks -- unplug primary master IDE devices
6954 aux-ide-disks -- unplug non-primary-master IDE devices
6955 nics -- unplug network devices
6956 all -- unplug all emulated devices (NICs and IDE disks)
6957 unnecessary -- unplugging emulated devices is
6958 unnecessary even if the host did not respond to
6960 never -- do not unplug even if version check succeeds
6962 xen_legacy_crash [X86,XEN]
6963 Crash from Xen panic notifier, without executing late
6964 panic() code such as dumping handler.
6966 xen_msr_safe= [X86,XEN]
6968 Select whether to always use non-faulting (safe) MSR
6969 access functions when running as Xen PV guest. The
6970 default value is controlled by CONFIG_XEN_PV_MSR_SAFE.
6972 xen_nopvspin [X86,XEN]
6973 Disables the qspinlock slowpath using Xen PV optimizations.
6974 This parameter is obsoleted by "nopvspin" parameter, which
6975 has equivalent effect for XEN platform.
6978 Disables the PV optimizations forcing the HVM guest to
6979 run as generic HVM guest with no PV drivers.
6980 This option is obsoleted by the "nopv" option, which
6981 has equivalent effect for XEN platform.
6983 xen_no_vector_callback
6984 [KNL,X86,XEN] Disable the vector callback for Xen
6985 event channel interrupts.
6987 xen_scrub_pages= [XEN]
6988 Boolean option to control scrubbing pages before giving them back
6989 to Xen, for use by other domains. Can be also changed at runtime
6990 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
6991 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
6993 xen_timer_slop= [X86-64,XEN]
6994 Set the timer slop (in nanoseconds) for the virtual Xen
6995 timers (default is 100000). This adjusts the minimum
6996 delta of virtualized Xen timers, where lower values
6997 improve timer resolution at the expense of processing
6998 more timer interrupts.
7000 xen.balloon_boot_timeout= [XEN]
7001 The time (in seconds) to wait before giving up to boot
7002 in case initial ballooning fails to free enough memory.
7003 Applies only when running as HVM or PVH guest and
7004 started with less memory configured than allowed at
7005 max. Default is 180.
7007 xen.event_eoi_delay= [XEN]
7008 How long to delay EOI handling in case of event
7009 storms (jiffies). Default is 10.
7011 xen.event_loop_timeout= [XEN]
7012 After which time (jiffies) the event handling loop
7013 should start to delay EOI handling. Default is 2.
7015 xen.fifo_events= [XEN]
7016 Boolean parameter to disable using fifo event handling
7017 even if available. Normally fifo event handling is
7018 preferred over the 2-level event handling, as it is
7019 fairer and the number of possible event channels is
7020 much higher. Default is on (use fifo events).
7022 xirc2ps_cs= [NET,PCMCIA]
7024 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
7027 By default on POWER9 and above, the kernel will
7028 natively use the XIVE interrupt controller. This option
7029 allows the fallback firmware mode to be used:
7031 off Fallback to firmware control of XIVE interrupt
7032 controller on both pseries and powernv
7033 platforms. Only useful on POWER9 and above.
7035 xive.store-eoi=off [PPC]
7036 By default on POWER10 and above, the kernel will use
7037 stores for EOI handling when the XIVE interrupt mode
7038 is active. This option allows the XIVE driver to use
7039 loads instead, as on POWER9.
7041 xhci-hcd.quirks [USB,KNL]
7042 A hex value specifying bitmask with supplemental xhci
7043 host controller quirks. Meaning of each bit can be
7044 consulted in header drivers/usb/host/xhci.h.
7047 Format: { early | on | rw | ro | off }
7048 Controls if xmon debugger is enabled. Default is off.
7049 Passing only "xmon" is equivalent to "xmon=early".
7050 early Call xmon as early as possible on boot; xmon
7051 debugger is called from setup_arch().
7052 on xmon debugger hooks will be installed so xmon
7053 is only called on a kernel crash. Default mode,
7054 i.e. either "ro" or "rw" mode, is controlled
7055 with CONFIG_XMON_DEFAULT_RO_MODE.
7056 rw xmon debugger hooks will be installed so xmon
7057 is called only on a kernel crash, mode is write,
7058 meaning SPR registers, memory and, other data
7059 can be written using xmon commands.
7060 ro same as "rw" option above but SPR registers,
7061 memory, and other data can't be written using
7063 off xmon is disabled.
7067 Do not enable amd_pstate as the default
7068 scaling driver for the supported processors
7070 Use amd_pstate as a scaling driver, driver requests a
7071 desired performance on this abstract scale and the power
7072 management firmware translates the requests into actual
7073 hardware states (core frequency, data fabric and memory
7076 Use amd_pstate_epp driver instance as the scaling driver,
7077 driver provides a hint to the hardware if software wants
7078 to bias toward performance (0x0) or energy efficiency (0xff)
7079 to the CPPC firmware. then CPPC power algorithm will
7080 calculate the runtime workload and adjust the realtime cores
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