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
325 amd_iommu_dump= [HW,X86-64]
326 Enable AMD IOMMU driver option to dump the ACPI table
327 for AMD IOMMU. With this option enabled, AMD IOMMU
328 driver will print ACPI tables for AMD IOMMU during
329 IOMMU initialization.
331 amd_iommu_intr= [HW,X86-64]
332 Specifies one of the following AMD IOMMU interrupt
334 legacy - Use legacy interrupt remapping mode.
335 vapic - Use virtual APIC mode, which allows IOMMU
336 to inject interrupts directly into guest.
337 This mode requires kvm-amd.avic=1.
338 (Default when IOMMU HW support is present.)
340 amijoy.map= [HW,JOY] Amiga joystick support
341 Map of devices attached to JOY0DAT and JOY1DAT
343 See also Documentation/input/joydev/joystick.rst
345 analog.map= [HW,JOY] Analog joystick and gamepad support
346 Specifies type or capabilities of an analog joystick
347 connected to one of 16 gameports
348 Format: <type1>,<type2>,..<type16>
351 Power management functions (SPARCstation-4/5 + deriv.)
353 Disable APC CPU standby support. SPARCstation-Fox does
354 not play well with APC CPU idle - disable it if you have
355 APC and your system crashes randomly.
357 apic= [APIC,X86] Advanced Programmable Interrupt Controller
358 Change the output verbosity while booting
359 Format: { quiet (default) | verbose | debug }
360 Change the amount of debugging information output
361 when initialising the APIC and IO-APIC components.
362 For X86-32, this can also be used to specify an APIC
364 Format: apic=driver_name
365 Examples: apic=bigsmp
367 apic_extnmi= [APIC,X86] External NMI delivery setting
368 Format: { bsp (default) | all | none }
369 bsp: External NMI is delivered only to CPU 0
370 all: External NMIs are broadcast to all CPUs as a
372 none: External NMI is masked for all CPUs. This is
373 useful so that a dump capture kernel won't be
377 See Documentation/networking/ipv6.rst.
379 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
380 Limit apic dumping. The parameter defines the maximal
381 number of local apics being dumped. Also it is possible
382 to set it to "all" by meaning -- no limit here.
383 Format: { 1 (default) | 2 | ... | all }.
384 The parameter valid if only apic=debug or
385 apic=verbose is specified.
386 Example: apic=debug show_lapic=all
388 apm= [APM] Advanced Power Management
389 See header of arch/x86/kernel/apm_32.c.
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
405 atarimouse= [HW,MOUSE] Atari Mouse
407 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
408 EzKey and similar keyboards
410 atkbd.reset= [HW] Reset keyboard during initialization
412 atkbd.set= [HW] Select keyboard code set
413 Format: <int> (2 = AT (default), 3 = PS/2)
415 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
418 atkbd.softraw= [HW] Choose between synthetic and real raw mode
419 Format: <bool> (0 = real, 1 = synthetic (default))
421 atkbd.softrepeat= [HW]
422 Use software keyboard repeat
424 audit= [KNL] Enable the audit sub-system
425 Format: { "0" | "1" | "off" | "on" }
426 0 | off - kernel audit is disabled and can not be
427 enabled until the next reboot
428 unset - kernel audit is initialized but disabled and
429 will be fully enabled by the userspace auditd.
430 1 | on - kernel audit is initialized and partially
431 enabled, storing at most audit_backlog_limit
432 messages in RAM until it is fully enabled by the
436 audit_backlog_limit= [KNL] Set the audit queue size limit.
437 Format: <int> (must be >=0)
440 bau= [X86_UV] Enable the BAU on SGI UV. The default
441 behavior is to disable the BAU (i.e. bau=0).
442 Format: { "0" | "1" }
445 unset - Disable the BAU.
447 baycom_epp= [HW,AX25]
450 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
452 See header of drivers/net/hamradio/baycom_par.c.
454 baycom_ser_fdx= [HW,AX25]
455 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
456 Format: <io>,<irq>,<mode>[,<baud>]
457 See header of drivers/net/hamradio/baycom_ser_fdx.c.
459 baycom_ser_hdx= [HW,AX25]
460 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
461 Format: <io>,<irq>,<mode>
462 See header of drivers/net/hamradio/baycom_ser_hdx.c.
464 blkdevparts= Manual partition parsing of block device(s) for
465 embedded devices based on command line input.
466 See Documentation/block/cmdline-partition.rst
468 boot_delay= Milliseconds to delay each printk during boot.
469 Values larger than 10 seconds (10000) are changed to
474 Extended command line options can be added to an initrd
475 and this will cause the kernel to look for it.
477 See Documentation/admin-guide/bootconfig.rst
480 Disable BERT OS support on buggy BIOSes.
482 bgrt_disable [ACPI][X86]
483 Disable BGRT to avoid flickering OEM logo.
485 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
486 bttv.radio= Most important insmod options are available as
488 bttv.pll= See Documentation/admin-guide/media/bttv.rst
491 bulk_remove=off [PPC] This parameter disables the use of the pSeries
492 firmware feature for flushing multiple hpte entries
495 c101= [NET] Moxa C101 synchronous serial card
497 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
498 Sometimes CPU hardware bugs make them report the cache
499 size incorrectly. The kernel will attempt work arounds
500 to fix known problems, but for some CPUs it is not
501 possible to determine what the correct size should be.
502 This option provides an override for these situations.
505 [NET] Specifies amount of time (in seconds) that
506 the kernel should wait for a network carrier. By default
507 it waits 120 seconds.
509 ca_keys= [KEYS] This parameter identifies a specific key(s) on
510 the system trusted keyring to be used for certificate
512 format: { id:<keyid> | builtin }
514 cca= [MIPS] Override the kernel pages' cache coherency
515 algorithm. Accepted values range from 0 to 7
516 inclusive. See arch/mips/include/asm/pgtable-bits.h
517 for platform specific values (SB1, Loongson3 and
520 ccw_timeout_log [S390]
521 See Documentation/s390/common_io.rst for details.
523 cgroup_disable= [KNL] Disable a particular controller or optional feature
524 Format: {name of the controller(s) or feature(s) to disable}
525 The effects of cgroup_disable=foo are:
526 - foo isn't auto-mounted if you mount all cgroups in
528 - foo isn't visible as an individually mountable
530 - if foo is an optional feature then the feature is
531 disabled and corresponding cgroup files are not
533 {Currently only "memory" controller deal with this and
534 cut the overhead, others just disable the usage. So
535 only cgroup_disable=memory is actually worthy}
536 Specifying "pressure" disables per-cgroup pressure
537 stall information accounting feature
539 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
540 Format: { { controller | "all" | "named" }
541 [,{ controller | "all" | "named" }...] }
542 Like cgroup_disable, but only applies to cgroup v1;
543 the blacklisted controllers remain available in cgroup2.
544 "all" blacklists all controllers and "named" disables
545 named mounts. Specifying both "all" and "named" disables
548 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
550 nosocket -- Disable socket memory accounting.
551 nokmem -- Disable kernel memory accounting.
553 checkreqprot [SELINUX] Set initial checkreqprot flag value.
554 Format: { "0" | "1" }
555 See security/selinux/Kconfig help text.
556 0 -- check protection applied by kernel (includes
557 any implied execute protection).
558 1 -- check protection requested by application.
559 Default value is set via a kernel config option.
560 Value can be changed at runtime via
561 /sys/fs/selinux/checkreqprot.
562 Setting checkreqprot to 1 is deprecated.
565 See Documentation/s390/common_io.rst for details.
568 Prevents the clock framework from automatically gating
569 clocks that have not been explicitly enabled by a Linux
570 device driver but are enabled in hardware at reset or
571 by the bootloader/firmware. Note that this does not
572 force such clocks to be always-on nor does it reserve
573 those clocks in any way. This parameter is useful for
574 debug and development, but should not be needed on a
575 platform with proper driver support. For more
576 information, see Documentation/driver-api/clk.rst.
578 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
580 Forces specified clocksource (if available) to be used
581 when calculating gettimeofday(). If specified
582 clocksource is not available, it defaults to PIT.
583 Format: { pit | tsc | cyclone | pmtmr }
585 clocksource= Override the default clocksource
587 Override the default clocksource and use the clocksource
588 with the name specified.
589 Some clocksource names to choose from, depending on
591 [all] jiffies (this is the base, fallback clocksource)
593 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
594 pxa_timer,timer3,32k_counter,timer0_1
595 [X86-32] pit,hpet,tsc;
596 scx200_hrt on Geode; cyclone on IBM x440
604 clocksource.arm_arch_timer.evtstrm=
607 Enable/disable the eventstream feature of the ARM
608 architected timer so that code using WFE-based polling
609 loops can be debugged more effectively on production
612 clocksource.max_cswd_read_retries= [KNL]
613 Number of clocksource_watchdog() retries due to
614 external delays before the clock will be marked
615 unstable. Defaults to two retries, that is,
616 three attempts to read the clock under test.
618 clocksource.verify_n_cpus= [KNL]
619 Limit the number of CPUs checked for clocksources
620 marked with CLOCK_SOURCE_VERIFY_PERCPU that
621 are marked unstable due to excessive skew.
622 A negative value says to check all CPUs, while
623 zero says not to check any. Values larger than
624 nr_cpu_ids are silently truncated to nr_cpu_ids.
625 The actual CPUs are chosen randomly, with
626 no replacement if the same CPU is chosen twice.
628 clocksource-wdtest.holdoff= [KNL]
629 Set the time in seconds that the clocksource
630 watchdog test waits before commencing its tests.
631 Defaults to zero when built as a module and to
632 10 seconds when built into the kernel.
634 clearcpuid=BITNUM[,BITNUM...] [X86]
635 Disable CPUID feature X for the kernel. See
636 arch/x86/include/asm/cpufeatures.h for the valid bit
637 numbers. Note the Linux specific bits are not necessarily
638 stable over kernel options, but the vendor specific
640 Also note that user programs calling CPUID directly
641 or using the feature without checking anything
642 will still see it. This just prevents it from
643 being used by the kernel or shown in /proc/cpuinfo.
644 Also note the kernel might malfunction if you disable
647 cma=nn[MG]@[start[MG][-end[MG]]]
649 Sets the size of kernel global memory area for
650 contiguous memory allocations and optionally the
651 placement constraint by the physical address range of
652 memory allocations. A value of 0 disables CMA
653 altogether. For more information, see
654 kernel/dma/contiguous.c
658 Sets the size of kernel per-numa memory area for
659 contiguous memory allocations. A value of 0 disables
660 per-numa CMA altogether. And If this option is not
661 specificed, the default value is 0.
662 With per-numa CMA enabled, DMA users on node nid will
663 first try to allocate buffer from the pernuma area
664 which is located in node nid, if the allocation fails,
665 they will fallback to the global default memory area.
667 cmo_free_hint= [PPC] Format: { yes | no }
668 Specify whether pages are marked as being inactive
669 when they are freed. This is used in CMO environments
670 to determine OS memory pressure for page stealing by
674 coherent_pool=nn[KMG] [ARM,KNL]
675 Sets the size of memory pool for coherent, atomic dma
676 allocations, by default set to 256K.
678 com20020= [HW,NET] ARCnet - COM20020 chipset
680 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
682 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
686 ARCnet - COM90xx chipset (memory-mapped buffers)
687 Format: <io>[,<irq>[,<memstart>]]
689 condev= [HW,S390] console device
692 console= [KNL] Output console device and options.
694 tty<n> Use the virtual console device <n>.
698 Use the specified serial port. The options are of
699 the form "bbbbpnf", where "bbbb" is the baud rate,
700 "p" is parity ("n", "o", or "e"), "n" is number of
701 bits, and "f" is flow control ("r" for RTS or
702 omit it). Default is "9600n8".
704 See Documentation/admin-guide/serial-console.rst for more
706 Documentation/networking/netconsole.rst for an
709 uart[8250],io,<addr>[,options]
710 uart[8250],mmio,<addr>[,options]
711 uart[8250],mmio16,<addr>[,options]
712 uart[8250],mmio32,<addr>[,options]
713 uart[8250],0x<addr>[,options]
714 Start an early, polled-mode console on the 8250/16550
715 UART at the specified I/O port or MMIO address,
716 switching to the matching ttyS device later.
717 MMIO inter-register address stride is either 8-bit
718 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
719 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
720 to be equivalent to 'mmio'. 'options' are specified in
721 the same format described for ttyS above; if unspecified,
722 the h/w is not re-initialized.
724 hvc<n> Use the hypervisor console device <n>. This is for
725 both Xen and PowerPC hypervisors.
728 Use to disable console output, i.e., to have kernel
729 console messages discarded.
730 This must be the only console= parameter used on the
733 If the device connected to the port is not a TTY but a braille
734 device, prepend "brl," before the device type, for instance
736 For now, only VisioBraille is supported.
739 [KNL] Change console messages format
741 By default we print messages on consoles in
742 "[time stamp] text\n" format (time stamp may not be
743 printed, depending on CONFIG_PRINTK_TIME or
744 `printk_time' param).
746 Switch to syslog format: "<%u>[time stamp] text\n"
747 IOW, each message will have a facility and loglevel
748 prefix. The format is similar to one used by syslog()
749 syscall, or to executing "dmesg -S --raw" or to reading
752 consoleblank= [KNL] The console blank (screen saver) timeout in
753 seconds. A value of 0 disables the blank timer.
757 [KNL] Change the default value for
758 /proc/<pid>/coredump_filter.
759 See also Documentation/filesystems/proc.rst.
761 coresight_cpu_debug.enable
764 Enable/disable the CPU sampling based debugging.
765 0: default value, disable debugging
766 1: enable debugging at boot time
768 cpuidle.off=1 [CPU_IDLE]
769 disable the cpuidle sub-system
772 [CPU_IDLE] Name of the cpuidle governor to use.
774 cpufreq.off=1 [CPU_FREQ]
775 disable the cpufreq sub-system
777 cpufreq.default_governor=
778 [CPU_FREQ] Name of the default cpufreq governor or
779 policy to use. This governor must be registered in the
780 kernel before the cpufreq driver probes.
783 [X86] Delay for N microsec between assert and de-assert
784 of APIC INIT to start processors. This delay occurs
785 on every CPU online, such as boot, and resume from suspend.
788 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
790 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
792 crashkernel=size[KMG][@offset[KMG]]
793 [KNL] Using kexec, Linux can switch to a 'crash kernel'
794 upon panic. This parameter reserves the physical
795 memory region [offset, offset + size] for that kernel
796 image. If '@offset' is omitted, then a suitable offset
797 is selected automatically.
798 [KNL, X86-64] Select a region under 4G first, and
799 fall back to reserve region above 4G when '@offset'
800 hasn't been specified.
801 See Documentation/admin-guide/kdump/kdump.rst for further details.
803 crashkernel=range1:size1[,range2:size2,...][@offset]
804 [KNL] Same as above, but depends on the memory
805 in the running system. The syntax of range is
806 start-[end] where start and end are both
807 a memory unit (amount[KMG]). See also
808 Documentation/admin-guide/kdump/kdump.rst for an example.
810 crashkernel=size[KMG],high
811 [KNL, X86-64] range could be above 4G. Allow kernel
812 to allocate physical memory region from top, so could
813 be above 4G if system have more than 4G ram installed.
814 Otherwise memory region will be allocated below 4G, if
816 It will be ignored if crashkernel=X is specified.
817 crashkernel=size[KMG],low
818 [KNL, X86-64] range under 4G. When crashkernel=X,high
819 is passed, kernel could allocate physical memory region
820 above 4G, that cause second kernel crash on system
821 that require some amount of low memory, e.g. swiotlb
822 requires at least 64M+32K low memory, also enough extra
823 low memory is needed to make sure DMA buffers for 32-bit
824 devices won't run out. Kernel would try to allocate at
825 at least 256M below 4G automatically.
826 This one let user to specify own low range under 4G
827 for second kernel instead.
828 0: to disable low allocation.
829 It will be ignored when crashkernel=X,high is not used
830 or memory reserved is below 4G.
833 [KNL] Disable crypto self-tests
838 cs89x0_media= [HW,NET]
839 Format: { rj45 | aui | bnc }
841 csdlock_debug= [KNL] Enable debug add-ons of cross-CPU function call
842 handling. When switched on, additional debug data is
843 printed to the console in case a hanging CPU is
844 detected, and that CPU is pinged again in order to try
845 to resolve the hang situation.
846 0: disable csdlock debugging (default)
847 1: enable basic csdlock debugging (minor impact)
848 ext: enable extended csdlock debugging (more impact,
852 See header of drivers/s390/block/dasd_devmap.c.
854 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
855 (one device per port)
856 Format: <port#>,<type>
857 See also Documentation/input/devices/joystick-parport.rst
859 debug [KNL] Enable kernel debugging (events log level).
862 [KNL] Enable printing [hashed] pointers early in the
863 boot sequence. If enabled, we use a weak hash instead
864 of siphash to hash pointers. Use this option if you are
865 seeing instances of '(___ptrval___)') and need to see a
866 value (hashed pointer) instead. Cryptographically
867 insecure, please do not use on production kernels.
870 [KNL] verbose locking self-tests
872 Print debugging info while doing the locking API
874 Bitmask for the various LOCKTYPE_ tests. Defaults to 0
875 (no extra messages), setting it to -1 (all bits set)
876 will print _a_lot_ more information - normally only
877 useful to lockdep developers.
879 debug_objects [KNL] Enable object debugging
882 [KNL] Disable object debugging
884 debug_guardpage_minorder=
885 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
886 parameter allows control of the order of pages that will
887 be intentionally kept free (and hence protected) by the
888 buddy allocator. Bigger value increase the probability
889 of catching random memory corruption, but reduce the
890 amount of memory for normal system use. The maximum
891 possible value is MAX_ORDER/2. Setting this parameter
892 to 1 or 2 should be enough to identify most random
893 memory corruption problems caused by bugs in kernel or
894 driver code when a CPU writes to (or reads from) a
895 random memory location. Note that there exists a class
896 of memory corruptions problems caused by buggy H/W or
897 F/W or by drivers badly programing DMA (basically when
898 memory is written at bus level and the CPU MMU is
899 bypassed) which are not detectable by
900 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
901 tracking down these problems.
904 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
905 enables the feature at boot time. By default, it is
906 disabled and the system will work mostly the same as a
907 kernel built without CONFIG_DEBUG_PAGEALLOC.
908 Note: to get most of debug_pagealloc error reports, it's
909 useful to also enable the page_owner functionality.
910 on: enable the feature
912 debugfs= [KNL] This parameter enables what is exposed to userspace
913 and debugfs internal clients.
914 Format: { on, no-mount, off }
915 on: All functions are enabled.
917 Filesystem is not registered but kernel clients can
918 access APIs and a crashkernel can be used to read
919 its content. There is nothing to mount.
920 off: Filesystem is not registered and clients
921 get a -EPERM as result when trying to register files
922 or directories within debugfs.
923 This is equivalent of the runtime functionality if
924 debugfs was not enabled in the kernel at all.
925 Default value is set in build-time with a kernel configuration.
927 debugpat [X86] Enable PAT debugging
929 decnet.addr= [HW,NET]
930 Format: <area>[,<node>]
931 See also Documentation/networking/decnet.rst.
934 [HW] The size of the default HugeTLB page. This is
935 the size represented by the legacy /proc/ hugepages
936 APIs. In addition, this is the default hugetlb size
937 used for shmget(), mmap() and mounting hugetlbfs
938 filesystems. If not specified, defaults to the
939 architecture's default huge page size. Huge page
940 sizes are architecture dependent. See also
941 Documentation/admin-guide/mm/hugetlbpage.rst.
944 deferred_probe_timeout=
945 [KNL] Debugging option to set a timeout in seconds for
946 deferred probe to give up waiting on dependencies to
947 probe. Only specific dependencies (subsystems or
948 drivers) that have opted in will be ignored. A timeout of 0
949 will timeout at the end of initcalls. This option will also
950 dump out devices still on the deferred probe list after
953 dell_smm_hwmon.ignore_dmi=
954 [HW] Continue probing hardware even if DMI data
955 indicates that the driver is running on unsupported
958 dell_smm_hwmon.force=
959 [HW] Activate driver even if SMM BIOS signature does
960 not match list of supported models and enable otherwise
961 blacklisted features.
963 dell_smm_hwmon.power_status=
964 [HW] Report power status in /proc/i8k
965 (disabled by default).
967 dell_smm_hwmon.restricted=
968 [HW] Allow controlling fans only if SYS_ADMIN
971 dell_smm_hwmon.fan_mult=
972 [HW] Factor to multiply fan speed with.
974 dell_smm_hwmon.fan_max=
975 [HW] Maximum configurable fan speed.
978 Format: { on | off | def_only | inf_only | always }
979 on: s390 zlib hardware support for compression on
980 level 1 and decompression (default)
981 off: No s390 zlib hardware support
982 def_only: s390 zlib hardware support for deflate
983 only (compression on level 1)
984 inf_only: s390 zlib hardware support for inflate
986 always: Same as 'on' but ignores the selected compression
987 level always using hardware support (used for debugging)
990 Set number of hash buckets for dentry cache.
992 disable_1tb_segments [PPC]
993 Disables the use of 1TB hash page table segments. This
994 causes the kernel to fall back to 256MB segments which
995 can be useful when debugging issues that require an SLB
999 Limits the number of kernel SLB entries, and flushes
1000 them frequently to increase the rate of SLB faults
1001 on kernel addresses.
1004 See Documentation/networking/ipv6.rst.
1007 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
1008 hardening is enabled for this boot. Hardened
1009 usercopy checking is used to protect the kernel
1010 from reading or writing beyond known memory
1011 allocation boundaries as a proactive defense
1012 against bounds-checking flaws in the kernel's
1013 copy_to_user()/copy_from_user() interface.
1014 on Perform hardened usercopy checks (default).
1015 off Disable hardened usercopy checks.
1018 Disable RADIX MMU mode on POWER9
1020 radix_hcall_invalidate=on [PPC/PSERIES]
1021 Disable RADIX GTSE feature and use hcall for TLB
1025 Disable TLBIE instruction. Currently does not work
1026 with KVM, with HASH MMU, or with coherent accelerators.
1028 disable_cpu_apicid= [X86,APIC,SMP]
1030 The number of initial APIC ID for the
1031 corresponding CPU to be disabled at boot,
1032 mostly used for the kdump 2nd kernel to
1033 disable BSP to wake up multiple CPUs without
1034 causing system reset or hang due to sending
1035 INIT from AP to BSP.
1037 disable_ddw [PPC/PSERIES]
1038 Disable Dynamic DMA Window support. Use this
1039 to workaround buggy firmware.
1041 disable_ipv6= [IPV6]
1042 See Documentation/networking/ipv6.rst.
1044 disable_mtrr_cleanup [X86]
1045 The kernel tries to adjust MTRR layout from continuous
1046 to discrete, to make X server driver able to add WB
1047 entry later. This parameter disables that.
1049 disable_mtrr_trim [X86, Intel and AMD only]
1050 By default the kernel will trim any uncacheable
1051 memory out of your available memory pool based on
1052 MTRR settings. This parameter disables that behavior,
1053 possibly causing your machine to run very slowly.
1055 disable_timer_pin_1 [X86]
1056 Disable PIN 1 of APIC timer
1057 Can be useful to work around chipset bugs.
1059 dis_ucode_ldr [X86] Disable the microcode loader.
1061 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
1062 this option disables the debugging code at boot.
1064 dma_debug_entries=<number>
1065 This option allows to tune the number of preallocated
1066 entries for DMA-API debugging code. One entry is
1067 required per DMA-API allocation. Use this if the
1068 DMA-API debugging code disables itself because the
1069 architectural default is too low.
1071 dma_debug_driver=<driver_name>
1072 With this option the DMA-API debugging driver
1073 filter feature can be enabled at boot time. Just
1074 pass the driver to filter for as the parameter.
1075 The filter can be disabled or changed to another
1076 driver later using sysfs.
1078 driver_async_probe= [KNL]
1079 List of driver names to be probed asynchronously.
1080 Format: <driver_name1>,<driver_name2>...
1082 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1083 Broken monitors, graphic adapters, KVMs and EDIDless
1084 panels may send no or incorrect EDID data sets.
1085 This parameter allows to specify an EDID data sets
1086 in the /lib/firmware directory that are used instead.
1087 Generic built-in EDID data sets are used, if one of
1088 edid/1024x768.bin, edid/1280x1024.bin,
1089 edid/1680x1050.bin, or edid/1920x1080.bin is given
1090 and no file with the same name exists. Details and
1091 instructions how to build your own EDID data are
1092 available in Documentation/admin-guide/edid.rst. An EDID
1093 data set will only be used for a particular connector,
1094 if its name and a colon are prepended to the EDID
1095 name. Each connector may use a unique EDID data
1096 set by separating the files with a comma. An EDID
1097 data set with no connector name will be used for
1098 any connectors not explicitly specified.
1103 Format: {"off" | "known"}
1104 Control how the dt_cpu_ftrs device-tree binding is
1105 used for CPU feature discovery and setup (if it
1107 off: Do not use it, fall back to legacy cpu table.
1108 known: Do not pass through unknown features to guests
1109 or userspace, only those that the kernel is aware of.
1111 dump_apple_properties [X86]
1112 Dump name and content of EFI device properties on
1113 x86 Macs. Useful for driver authors to determine
1114 what data is available or for reverse-engineering.
1116 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
1117 <module>.dyndbg[="val"]
1118 Enable debug messages at boot time. See
1119 Documentation/admin-guide/dynamic-debug-howto.rst
1122 nopku [X86] Disable Memory Protection Keys CPU feature found
1125 <module>.async_probe [KNL]
1126 Enable asynchronous probe on this module.
1128 early_ioremap_debug [KNL]
1129 Enable debug messages in early_ioremap support. This
1130 is useful for tracking down temporary early mappings
1131 which are not unmapped.
1133 earlycon= [KNL] Output early console device and options.
1135 When used with no options, the early console is
1136 determined by stdout-path property in device tree's
1137 chosen node or the ACPI SPCR table if supported by
1140 cdns,<addr>[,options]
1141 Start an early, polled-mode console on a Cadence
1142 (xuartps) serial port at the specified address. Only
1143 supported option is baud rate. If baud rate is not
1144 specified, the serial port must already be setup and
1147 uart[8250],io,<addr>[,options]
1148 uart[8250],mmio,<addr>[,options]
1149 uart[8250],mmio32,<addr>[,options]
1150 uart[8250],mmio32be,<addr>[,options]
1151 uart[8250],0x<addr>[,options]
1152 Start an early, polled-mode console on the 8250/16550
1153 UART at the specified I/O port or MMIO address.
1154 MMIO inter-register address stride is either 8-bit
1155 (mmio) or 32-bit (mmio32 or mmio32be).
1156 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1157 to be equivalent to 'mmio'. 'options' are specified
1158 in the same format described for "console=ttyS<n>"; if
1159 unspecified, the h/w is not initialized.
1163 Start an early, polled-mode console on a pl011 serial
1164 port at the specified address. The pl011 serial port
1165 must already be setup and configured. Options are not
1166 yet supported. If 'mmio32' is specified, then only
1167 the driver will use only 32-bit accessors to read/write
1168 the device registers.
1171 Start an early console on a litex serial port at the
1172 specified address. The serial port must already be
1173 setup and configured. Options are not yet supported.
1176 Start an early, polled-mode console on a meson serial
1177 port at the specified address. The serial port must
1178 already be setup and configured. Options are not yet
1182 Start an early, polled-mode console on an msm serial
1183 port at the specified address. The serial port
1184 must already be setup and configured. Options are not
1187 msm_serial_dm,<addr>
1188 Start an early, polled-mode console on an msm serial
1189 dm port at the specified address. The serial port
1190 must already be setup and configured. Options are not
1194 Start an early, polled-mode console on a serial port
1195 of an Actions Semi SoC, such as S500 or S900, at the
1196 specified address. The serial port must already be
1197 setup and configured. Options are not yet supported.
1200 Start an early, polled-mode console on a serial port
1201 of an RDA Micro SoC, such as RDA8810PL, at the
1202 specified address. The serial port must already be
1203 setup and configured. Options are not yet supported.
1206 Use RISC-V SBI (Supervisor Binary Interface) for early
1209 smh Use ARM semihosting calls for early console.
1217 Use early console provided by serial driver available
1218 on Samsung SoCs, requires selecting proper type and
1219 a correct base address of the selected UART port. The
1220 serial port must already be setup and configured.
1221 Options are not yet supported.
1224 Start an early, polled-mode console on a lantiq serial
1225 (lqasc) port at the specified address. The serial port
1226 must already be setup and configured. Options are not
1231 Use early console provided by Freescale LP UART driver
1232 found on Freescale Vybrid and QorIQ LS1021A processors.
1233 A valid base address must be provided, and the serial
1234 port must already be setup and configured.
1238 Start an early, polled-mode, output-only console on the
1239 Freescale i.MX UART at the specified address. The UART
1240 must already be setup and configured.
1243 Start an early, polled-mode console on the
1244 Armada 3700 serial port at the specified
1245 address. The serial port must already be setup
1246 and configured. Options are not yet supported.
1249 Start an early, polled-mode console on a Qualcomm
1250 Generic Interface (GENI) based serial port at the
1251 specified address. The serial port must already be
1252 setup and configured. Options are not yet supported.
1255 Start an early, unaccelerated console on the EFI
1256 memory mapped framebuffer (if available). On cache
1257 coherent non-x86 systems that use system memory for
1258 the framebuffer, pass the 'ram' option so that it is
1259 mapped with the correct attributes.
1262 Use early console provided by Freescale LINFlexD UART
1263 serial driver for NXP S32V234 SoCs. A valid base
1264 address must be provided, and the serial port must
1265 already be setup and configured.
1267 earlyprintk= [X86,SH,ARM,M68k,S390]
1271 earlyprintk=serial[,ttySn[,baudrate]]
1272 earlyprintk=serial[,0x...[,baudrate]]
1273 earlyprintk=ttySn[,baudrate]
1274 earlyprintk=dbgp[debugController#]
1275 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1276 earlyprintk=xdbc[xhciController#]
1278 earlyprintk is useful when the kernel crashes before
1279 the normal console is initialized. It is not enabled by
1280 default because it has some cosmetic problems.
1282 Append ",keep" to not disable it when the real console
1285 Only one of vga, efi, serial, or usb debug port can
1288 Currently only ttyS0 and ttyS1 may be specified by
1289 name. Other I/O ports may be explicitly specified
1290 on some architectures (x86 and arm at least) by
1291 replacing ttySn with an I/O port address, like this:
1292 earlyprintk=serial,0x1008,115200
1293 You can find the port for a given device in
1294 /proc/tty/driver/serial:
1295 2: uart:ST16650V2 port:00001008 irq:18 ...
1297 Interaction with the standard serial driver is not
1300 The VGA and EFI output is eventually overwritten by
1303 The xen option can only be used in Xen domains.
1305 The sclp output can only be used on s390.
1307 The optional "force" to "pciserial" enables use of a
1308 PCI device even when its classcode is not of the
1311 edac_report= [HW,EDAC] Control how to report EDAC event
1312 Format: {"on" | "off" | "force"}
1313 on: enable EDAC to report H/W event. May be overridden
1314 by other higher priority error reporting module.
1315 off: disable H/W event reporting through EDAC.
1316 force: enforce the use of EDAC to report H/W event.
1319 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1322 This is designed to be used in conjunction with
1323 the boot argument: earlyprintk=vga
1325 This parameter works in place of the kgdboc parameter
1326 but can only be used if the backing tty is available
1327 very early in the boot process. For early debugging
1328 via a serial port see kgdboc_earlycon instead.
1331 Format: {"off" | "on" | "skip[mbr]"}
1334 Format: { "debug", "disable_early_pci_dma",
1335 "nochunk", "noruntime", "nosoftreserve",
1336 "novamap", "no_disable_early_pci_dma" }
1337 debug: enable misc debug output.
1338 disable_early_pci_dma: disable the busmaster bit on all
1339 PCI bridges while in the EFI boot stub.
1340 nochunk: disable reading files in "chunks" in the EFI
1341 boot stub, as chunking can cause problems with some
1342 firmware implementations.
1343 noruntime : disable EFI runtime services support
1344 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
1345 attribute may cause the kernel to reserve the
1346 memory range for a memory mapping driver to
1347 claim. Specify efi=nosoftreserve to disable this
1348 reservation and treat the memory by its base type
1349 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1350 novamap: do not call SetVirtualAddressMap().
1351 no_disable_early_pci_dma: Leave the busmaster bit set
1352 on all PCI bridges while in the EFI boot stub
1354 efi_no_storage_paranoia [EFI; X86]
1355 Using this parameter you can use more than 50% of
1356 your efi variable storage. Use this parameter only if
1357 you are really sure that your UEFI does sane gc and
1358 fulfills the spec otherwise your board may brick.
1360 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1361 Add arbitrary attribute to specific memory range by
1362 updating original EFI memory map.
1363 Region of memory which aa attribute is added to is
1366 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1367 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1368 attribute is added to range 0x100000000-0x180000000 and
1369 0x10a0000000-0x1120000000.
1371 If efi_fake_mem=8G@9G:0x40000 is specified, the
1372 EFI_MEMORY_SP(0x40000) attribute is added to
1373 range 0x240000000-0x43fffffff.
1375 Using this parameter you can do debugging of EFI memmap
1376 related features. For example, you can do debugging of
1377 Address Range Mirroring feature even if your box
1378 doesn't support it, or mark specific memory as
1381 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1382 that is to be dynamically loaded by Linux. If there are
1383 multiple variables with the same name but with different
1384 vendor GUIDs, all of them will be loaded. See
1385 Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1388 eisa_irq_edge= [PARISC,HW]
1389 See header of drivers/parisc/eisa.c.
1392 See comment before function elanfreq_setup() in
1393 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1395 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1396 Specifies physical address of start of kernel core
1397 image elf header and optionally the size. Generally
1398 kexec loader will pass this option to capture kernel.
1399 See Documentation/admin-guide/kdump/kdump.rst for details.
1401 enable_mtrr_cleanup [X86]
1402 The kernel tries to adjust MTRR layout from continuous
1403 to discrete, to make X server driver able to add WB
1404 entry later. This parameter enables that.
1406 enable_timer_pin_1 [X86]
1407 Enable PIN 1 of APIC timer
1408 Can be useful to work around chipset bugs
1409 (in particular on some ATI chipsets).
1410 The kernel tries to set a reasonable default.
1412 enforcing [SELINUX] Set initial enforcing status.
1414 See security/selinux/Kconfig help text.
1415 0 -- permissive (log only, no denials).
1416 1 -- enforcing (deny and log).
1418 Value can be changed at runtime via
1419 /sys/fs/selinux/enforce.
1422 Disable Error Record Serialization Table (ERST)
1425 ether= [HW,NET] Ethernet cards parameters
1426 This option is obsoleted by the "netdev=" option, which
1427 has equivalent usage. See its documentation for details.
1431 Permit 'security.evm' to be updated regardless of
1432 current integrity status.
1437 fail_make_request=[KNL]
1438 General fault injection mechanism.
1439 Format: <interval>,<probability>,<space>,<times>
1440 See also Documentation/fault-injection/.
1443 Format: { initns | none }
1444 See Documentation/admin-guide/sysctl/net.rst for
1445 fb_tunnels_only_for_init_ns
1448 See Documentation/admin-guide/blockdev/floppy.rst.
1450 force_pal_cache_flush
1451 [IA-64] Avoid check_sal_cache_flush which may hang on
1452 buggy SAL_CACHE_FLUSH implementations. Using this
1453 parameter will force ia64_sal_cache_flush to call
1454 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1457 Forcefully enable Physical Address Extension (PAE).
1458 Many Pentium M systems disable PAE but may have a
1459 functionally usable PAE implementation.
1460 Warning: use of this parameter will taint the kernel
1461 and may cause unknown problems.
1464 [FTRACE] will set and start the specified tracer
1465 as early as possible in order to facilitate early
1468 ftrace_boot_snapshot
1469 [FTRACE] On boot up, a snapshot will be taken of the
1470 ftrace ring buffer that can be read at:
1471 /sys/kernel/tracing/snapshot.
1472 This is useful if you need tracing information from kernel
1473 boot up that is likely to be overridden by user space
1474 start up functionality.
1476 ftrace_dump_on_oops[=orig_cpu]
1477 [FTRACE] will dump the trace buffers on oops.
1478 If no parameter is passed, ftrace will dump
1479 buffers of all CPUs, but if you pass orig_cpu, it will
1480 dump only the buffer of the CPU that triggered the
1483 ftrace_filter=[function-list]
1484 [FTRACE] Limit the functions traced by the function
1485 tracer at boot up. function-list is a comma-separated
1486 list of functions. This list can be changed at run
1487 time by the set_ftrace_filter file in the debugfs
1490 ftrace_notrace=[function-list]
1491 [FTRACE] Do not trace the functions specified in
1492 function-list. This list can be changed at run time
1493 by the set_ftrace_notrace file in the debugfs
1496 ftrace_graph_filter=[function-list]
1497 [FTRACE] Limit the top level callers functions traced
1498 by the function graph tracer at boot up.
1499 function-list is a comma-separated list of functions
1500 that can be changed at run time by the
1501 set_graph_function file in the debugfs tracing directory.
1503 ftrace_graph_notrace=[function-list]
1504 [FTRACE] Do not trace from the functions specified in
1505 function-list. This list is a comma-separated list of
1506 functions that can be changed at run time by the
1507 set_graph_notrace file in the debugfs tracing directory.
1509 ftrace_graph_max_depth=<uint>
1510 [FTRACE] Used with the function graph tracer. This is
1511 the max depth it will trace into a function. This value
1512 can be changed at run time by the max_graph_depth file
1513 in the tracefs tracing directory. default: 0 (no limit)
1515 fw_devlink= [KNL] Create device links between consumer and supplier
1516 devices by scanning the firmware to infer the
1517 consumer/supplier relationships. This feature is
1518 especially useful when drivers are loaded as modules as
1519 it ensures proper ordering of tasks like device probing
1520 (suppliers first, then consumers), supplier boot state
1521 clean up (only after all consumers have probed),
1522 suspend/resume & runtime PM (consumers first, then
1524 Format: { off | permissive | on | rpm }
1525 off -- Don't create device links from firmware info.
1526 permissive -- Create device links from firmware info
1527 but use it only for ordering boot state clean
1528 up (sync_state() calls).
1529 on -- Create device links from firmware info and use it
1530 to enforce probe and suspend/resume ordering.
1531 rpm -- Like "on", but also use to order runtime PM.
1533 fw_devlink.strict=<bool>
1534 [KNL] Treat all inferred dependencies as mandatory
1535 dependencies. This only applies for fw_devlink=on|rpm.
1539 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1540 support via parallel port (up to 5 devices per port)
1541 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1542 See also Documentation/input/devices/joystick-parport.rst
1546 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART
1550 gcov_persist= [GCOV] When non-zero (default), profiling data for
1551 kernel modules is saved and remains accessible via
1552 debugfs, even when the module is unloaded/reloaded.
1553 When zero, profiling data is discarded and associated
1554 debugfs files are removed at module unload time.
1556 goldfish [X86] Enable the goldfish android emulator platform.
1557 Don't use this when you are not running on the
1560 gpio-mockup.gpio_mockup_ranges
1561 [HW] Sets the ranges of gpiochip of for this device.
1562 Format: <start1>,<end1>,<start2>,<end2>...
1563 gpio-mockup.gpio_mockup_named_lines
1564 [HW] Let the driver know GPIO lines should be named.
1566 gpt [EFI] Forces disk with valid GPT signature but
1567 invalid Protective MBR to be treated as GPT. If the
1568 primary GPT is corrupted, it enables the backup/alternate
1569 GPT to be used instead.
1571 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1572 the "Enable 0" bit of the configuration register.
1575 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1576 the "Enable 0" bit of the configuration register.
1579 grcan.select= [HW] Select which physical interface to use.
1582 grcan.txsize= [HW] Sets the size of the tx buffer.
1583 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1585 grcan.rxsize= [HW] Sets the size of the rx buffer.
1586 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1589 hardlockup_all_cpu_backtrace=
1590 [KNL] Should the hard-lockup detector generate
1591 backtraces on all cpus.
1594 hashdist= [KNL,NUMA] Large hashes allocated during boot
1595 are distributed across NUMA nodes. Defaults on
1596 for 64-bit NUMA, off otherwise.
1597 Format: 0 | 1 (for off | on)
1599 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1601 hd= [EIDE] (E)IDE hard drive subsystem geometry
1602 Format: <cyl>,<head>,<sect>
1605 Disable Hardware Error Source Table (HEST) support;
1606 corresponding firmware-first mode error processing
1607 logic will be disabled.
1609 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1610 size of <nn>. This works even on boxes that have no
1611 highmem otherwise. This also works to reduce highmem
1612 size on bigger boxes.
1614 highres= [KNL] Enable/disable high resolution timer mode.
1615 Valid parameters: "on", "off"
1620 hpet= [X86-32,HPET] option to control HPET usage
1621 Format: { enable (default) | disable | force |
1623 disable: disable HPET and use PIT instead
1624 force: allow force enabled of undocumented chips (ICH4,
1626 verbose: show contents of HPET registers during setup
1628 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1629 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1631 hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation
1632 of gigantic hugepages. Or using node format, the size
1633 of a CMA area per node can be specified.
1634 Format: nn[KMGTPE] or (node format)
1635 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]]
1637 Reserve a CMA area of given size and allocate gigantic
1638 hugepages using the CMA allocator. If enabled, the
1639 boot-time allocation of gigantic hugepages is skipped.
1641 hugepages= [HW] Number of HugeTLB pages to allocate at boot.
1642 If this follows hugepagesz (below), it specifies
1643 the number of pages of hugepagesz to be allocated.
1644 If this is the first HugeTLB parameter on the command
1645 line, it specifies the number of pages to allocate for
1646 the default huge page size. If using node format, the
1647 number of pages to allocate per-node can be specified.
1648 See also Documentation/admin-guide/mm/hugetlbpage.rst.
1649 Format: <integer> or (node format)
1650 <node>:<integer>[,<node>:<integer>]
1653 [HW] The size of the HugeTLB pages. This is used in
1654 conjunction with hugepages (above) to allocate huge
1655 pages of a specific size at boot. The pair
1656 hugepagesz=X hugepages=Y can be specified once for
1657 each supported huge page size. Huge page sizes are
1658 architecture dependent. See also
1659 Documentation/admin-guide/mm/hugetlbpage.rst.
1662 hugetlb_free_vmemmap=
1663 [KNL] Reguires CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
1665 Allows heavy hugetlb users to free up some more
1666 memory (7 * PAGE_SIZE for each 2MB hugetlb page).
1667 Format: { on | off (default) }
1669 on: enable the feature
1670 off: disable the feature
1672 Built with CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON=y,
1675 This is not compatible with memory_hotplug.memmap_on_memory.
1676 If both parameters are enabled, hugetlb_free_vmemmap takes
1677 precedence over memory_hotplug.memmap_on_memory.
1680 [KNL] Should the hung task detector generate panics.
1683 A value of 1 instructs the kernel to panic when a
1684 hung task is detected. The default value is controlled
1685 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1686 option. The value selected by this boot parameter can
1687 be changed later by the kernel.hung_task_panic sysctl.
1689 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1690 terminal devices. Valid values: 0..8
1691 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1692 If specified, z/VM IUCV HVC accepts connections
1693 from listed z/VM user IDs only.
1695 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1696 which allow the hypervisor to 'idle' the
1697 guest on lock contention.
1700 Do not unregister boot console at start. This is only
1701 useful for debugging when something happens in the window
1702 between unregistering the boot console and initializing
1705 i2c_bus= [HW] Override the default board specific I2C bus speed
1706 or register an additional I2C bus that is not
1707 registered from board initialization code.
1711 i8042.debug [HW] Toggle i8042 debug mode
1712 i8042.unmask_kbd_data
1713 [HW] Enable printing of interrupt data from the KBD port
1714 (disabled by default, and as a pre-condition
1715 requires that i8042.debug=1 be enabled)
1716 i8042.direct [HW] Put keyboard port into non-translated mode
1717 i8042.dumbkbd [HW] Pretend that controller can only read data from
1718 keyboard and cannot control its state
1719 (Don't attempt to blink the leds)
1720 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1721 i8042.nokbd [HW] Don't check/create keyboard port
1722 i8042.noloop [HW] Disable the AUX Loopback command while probing
1724 i8042.nomux [HW] Don't check presence of an active multiplexing
1726 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1728 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1729 i8042.reset [HW] Reset the controller during init, cleanup and
1730 suspend-to-ram transitions, only during s2r
1731 transitions, or never reset
1732 Format: { 1 | Y | y | 0 | N | n }
1733 1, Y, y: always reset controller
1734 0, N, n: don't ever reset controller
1735 Default: only on s2r transitions on x86; most other
1736 architectures force reset to be always executed
1737 i8042.unlock [HW] Unlock (ignore) the keylock
1738 i8042.kbdreset [HW] Reset device connected to KBD port
1740 [HW] Allow deferred probing upon i8042 probe errors
1744 i915.invert_brightness=
1745 [DRM] Invert the sense of the variable that is used to
1746 set the brightness of the panel backlight. Normally a
1747 brightness value of 0 indicates backlight switched off,
1748 and the maximum of the brightness value sets the backlight
1749 to maximum brightness. If this parameter is set to 0
1750 (default) and the machine requires it, or this parameter
1751 is set to 1, a brightness value of 0 sets the backlight
1752 to maximum brightness, and the maximum of the brightness
1753 value switches the backlight off.
1754 -1 -- never invert brightness
1755 0 -- machine default
1756 1 -- force brightness inversion
1759 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1761 ide-core.nodma= [HW] (E)IDE subsystem
1762 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1763 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1764 .cdrom .chs .ignore_cable are additional options
1765 See Documentation/ide/ide.rst.
1767 ide-generic.probe-mask= [HW] (E)IDE subsystem
1769 Probe mask for legacy ISA IDE ports. Depending on
1770 platform up to 6 ports are supported, enabled by
1771 setting corresponding bits in the mask to 1. The
1772 default value is 0x0, which has a special meaning.
1773 On systems that have PCI, it triggers scanning the
1774 PCI bus for the first and the second port, which
1775 are then probed. On systems without PCI the value
1776 of 0x0 enables probing the two first ports as if it
1779 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1780 Claim all unknown PCI IDE storage controllers.
1783 Format: idle=poll, idle=halt, idle=nomwait
1784 Poll forces a polling idle loop that can slightly
1785 improve the performance of waking up a idle CPU, but
1786 will use a lot of power and make the system run hot.
1788 idle=halt: Halt is forced to be used for CPU idle.
1789 In such case C2/C3 won't be used again.
1790 idle=nomwait: Disable mwait for CPU C-states
1794 Allow force disabling of Shared Virtual Memory (SVA)
1795 support for the idxd driver. By default it is set to
1798 idxd.tc_override= [HW]
1800 Allow override of default traffic class configuration
1801 for the device. By default it is set to false (0).
1803 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1804 Format: { strict | legacy | 2008 | relaxed }
1807 Choose which programs will be accepted for execution
1808 based on the IEEE 754 NaN encoding(s) supported by
1809 the FPU and the NaN encoding requested with the value
1810 of an ELF file header flag individually set by each
1811 binary. Hardware implementations are permitted to
1812 support either or both of the legacy and the 2008 NaN
1815 Available settings are as follows:
1816 strict accept binaries that request a NaN encoding
1817 supported by the FPU
1818 legacy only accept legacy-NaN binaries, if supported
1820 2008 only accept 2008-NaN binaries, if supported
1822 relaxed accept any binaries regardless of whether
1823 supported by the FPU
1825 The FPU emulator is always able to support both NaN
1826 encodings, so if no FPU hardware is present or it has
1827 been disabled with 'nofpu', then the settings of
1828 'legacy' and '2008' strap the emulator accordingly,
1829 'relaxed' straps the emulator for both legacy-NaN and
1830 2008-NaN, whereas 'strict' enables legacy-NaN only on
1831 legacy processors and both NaN encodings on MIPS32 or
1834 The setting for ABS.fmt/NEG.fmt instruction execution
1835 mode generally follows that for the NaN encoding,
1836 except where unsupported by hardware.
1838 ignore_loglevel [KNL]
1839 Ignore loglevel setting - this will print /all/
1840 kernel messages to the console. Useful for debugging.
1841 We also add it as printk module parameter, so users
1842 could change it dynamically, usually by
1843 /sys/module/printk/parameters/ignore_loglevel.
1846 Ignore RLIMIT_DATA setting for data mappings,
1847 print warning at first misuse. Can be changed via
1848 /sys/module/kernel/parameters/ignore_rlimit_data.
1850 ihash_entries= [KNL]
1851 Set number of hash buckets for inode cache.
1853 ima_appraise= [IMA] appraise integrity measurements
1854 Format: { "off" | "enforce" | "fix" | "log" }
1857 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead.
1858 The builtin appraise policy appraises all files
1861 ima_canonical_fmt [IMA]
1862 Use the canonical format for the binary runtime
1863 measurements, instead of host native format.
1866 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1870 The list of supported hash algorithms is defined
1871 in crypto/hash_info.h.
1874 The builtin policies to load during IMA setup.
1875 Format: "tcb | appraise_tcb | secure_boot |
1876 fail_securely | critical_data"
1878 The "tcb" policy measures all programs exec'd, files
1879 mmap'd for exec, and all files opened with the read
1880 mode bit set by either the effective uid (euid=0) or
1883 The "appraise_tcb" policy appraises the integrity of
1884 all files owned by root.
1886 The "secure_boot" policy appraises the integrity
1887 of files (eg. kexec kernel image, kernel modules,
1888 firmware, policy, etc) based on file signatures.
1890 The "fail_securely" policy forces file signature
1891 verification failure also on privileged mounted
1892 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1895 The "critical_data" policy measures kernel integrity
1898 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1899 Load a policy which meets the needs of the Trusted
1900 Computing Base. This means IMA will measure all
1901 programs exec'd, files mmap'd for exec, and all files
1902 opened for read by uid=0.
1905 Select one of defined IMA measurements template formats.
1906 Formats: { "ima" | "ima-ng" | "ima-sig" }
1910 [IMA] Define a custom template format.
1911 Format: { "field1|...|fieldN" }
1913 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1914 Format: <min_file_size>
1915 Set the minimal file size for using asynchronous hash.
1916 If left unspecified, ahash usage is disabled.
1918 ahash performance varies for different data sizes on
1919 different crypto accelerators. This option can be used
1920 to achieve the best performance for a particular HW.
1922 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1924 Set hashing buffer size. Default: 4k.
1926 ahash performance varies for different chunk sizes on
1927 different crypto accelerators. This option can be used
1928 to achieve best performance for particular HW.
1932 Run specified binary instead of /sbin/init as init
1935 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1936 for working out where the kernel is dying during
1939 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1940 initcall functions. Useful for debugging built-in
1941 modules and initcalls.
1943 initramfs_async= [KNL]
1946 This parameter controls whether the initramfs
1947 image is unpacked asynchronously, concurrently
1948 with devices being probed and
1949 initialized. This should normally just work,
1950 but as a debugging aid, one can get the
1951 historical behaviour of the initramfs
1952 unpacking being completed before device_ and
1955 initrd= [BOOT] Specify the location of the initial ramdisk
1957 initrdmem= [KNL] Specify a physical address and size from which to
1958 load the initrd. If an initrd is compiled in or
1959 specified in the bootparams, it takes priority over this
1961 Format: ss[KMG],nn[KMG]
1964 init_on_alloc= [MM] Fill newly allocated pages and heap objects with
1967 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
1969 init_on_free= [MM] Fill freed pages and heap objects with zeroes.
1971 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
1973 init_pkru= [X86] Specify the default memory protection keys rights
1974 register contents for all processes. 0x55555554 by
1975 default (disallow access to all but pkey 0). Can
1976 override in debugfs after boot.
1978 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1981 int_pln_enable [X86] Enable power limit notification interrupt
1983 integrity_audit=[IMA]
1984 Format: { "0" | "1" }
1985 0 -- basic integrity auditing messages. (Default)
1986 1 -- additional integrity auditing messages.
1988 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1990 Enable intel iommu driver.
1992 Disable intel iommu driver.
1993 igfx_off [Default Off]
1994 By default, gfx is mapped as normal device. If a gfx
1995 device has a dedicated DMAR unit, the DMAR unit is
1996 bypassed by not enabling DMAR with this option. In
1997 this case, gfx device will use physical address for
1999 strict [Default Off]
2000 Deprecated, equivalent to iommu.strict=1.
2001 sp_off [Default Off]
2002 By default, super page will be supported if Intel IOMMU
2003 has the capability. With this option, super page will
2006 Enable the Intel IOMMU scalable mode if the hardware
2007 advertises that it has support for the scalable mode
2010 Disallow use of the Intel IOMMU scalable mode.
2011 tboot_noforce [Default Off]
2012 Do not force the Intel IOMMU enabled under tboot.
2013 By default, tboot will force Intel IOMMU on, which
2014 could harm performance of some high-throughput
2015 devices like 40GBit network cards, even if identity
2017 Note that using this option lowers the security
2018 provided by tboot because it makes the system
2019 vulnerable to DMA attacks.
2021 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
2022 0 disables intel_idle and fall back on acpi_idle.
2023 1 to 9 specify maximum depth of C-state.
2027 Do not enable intel_pstate as the default
2028 scaling driver for the supported processors
2030 Use intel_pstate as a scaling driver, but configure it
2031 to work with generic cpufreq governors (instead of
2032 enabling its internal governor). This mode cannot be
2033 used along with the hardware-managed P-states (HWP)
2036 Enable intel_pstate on systems that prohibit it by default
2037 in favor of acpi-cpufreq. Forcing the intel_pstate driver
2038 instead of acpi-cpufreq may disable platform features, such
2039 as thermal controls and power capping, that rely on ACPI
2040 P-States information being indicated to OSPM and therefore
2041 should be used with caution. This option does not work with
2042 processors that aren't supported by the intel_pstate driver
2043 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2045 Do not enable hardware P state control (HWP)
2048 Only load intel_pstate on systems which support
2049 hardware P state control (HWP) if available.
2051 Enforce ACPI _PPC performance limits. If the Fixed ACPI
2052 Description Table, specifies preferred power management
2053 profile as "Enterprise Server" or "Performance Server",
2054 then this feature is turned on by default.
2056 Allow per-logical-CPU P-State performance control limits using
2057 cpufreq sysfs interface
2059 intremap= [X86-64, Intel-IOMMU]
2060 on enable Interrupt Remapping (default)
2061 off disable Interrupt Remapping
2062 nosid disable Source ID checking
2064 BIOS x2APIC opt-out request will be ignored
2065 nopost disable Interrupt Posting
2067 iomem= Disable strict checking of access to MMIO memory
2068 strict regions from userspace.
2083 nobypass [PPC/POWERNV]
2084 Disable IOMMU bypass, using IOMMU for PCI devices.
2086 iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices.
2087 Format: { "0" | "1" }
2088 0 - Try to allocate a 32-bit DMA address first, before
2089 falling back to the full range if needed.
2090 1 - Allocate directly from the full usable range,
2091 forcing Dual Address Cycle for PCI cards supporting
2092 greater than 32-bit addressing.
2094 iommu.strict= [ARM64, X86] Configure TLB invalidation behaviour
2095 Format: { "0" | "1" }
2097 Request that DMA unmap operations use deferred
2098 invalidation of hardware TLBs, for increased
2099 throughput at the cost of reduced device isolation.
2100 Will fall back to strict mode if not supported by
2101 the relevant IOMMU driver.
2103 DMA unmap operations invalidate IOMMU hardware TLBs
2105 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}.
2106 Note: on x86, strict mode specified via one of the
2107 legacy driver-specific options takes precedence.
2110 [ARM64, X86] Configure DMA to bypass the IOMMU by default.
2111 Format: { "0" | "1" }
2112 0 - Use IOMMU translation for DMA.
2113 1 - Bypass the IOMMU for DMA.
2114 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
2116 io7= [HW] IO7 for Marvel-based Alpha systems
2117 See comment before marvel_specify_io7 in
2118 arch/alpha/kernel/core_marvel.c.
2120 io_delay= [X86] I/O delay method
2122 Standard port 0x80 based delay
2124 Alternate port 0xed based delay (needed on some systems)
2126 Simple two microseconds delay
2131 See Documentation/admin-guide/nfs/nfsroot.rst.
2133 ipcmni_extend [KNL] Extend the maximum number of unique System V
2134 IPC identifiers from 32,768 to 16,777,216.
2136 irqaffinity= [SMP] Set the default irq affinity mask
2137 The argument is a cpu list, as described above.
2139 irqchip.gicv2_force_probe=
2142 Force the kernel to look for the second 4kB page
2143 of a GICv2 controller even if the memory range
2144 exposed by the device tree is too small.
2146 irqchip.gicv3_nolpi=
2148 Force the kernel to ignore the availability of
2149 LPIs (and by consequence ITSs). Intended for system
2150 that use the kernel as a bootloader, and thus want
2151 to let secondary kernels in charge of setting up
2154 irqchip.gicv3_pseudo_nmi= [ARM64]
2155 Enables support for pseudo-NMIs in the kernel. This
2156 requires the kernel to be built with
2157 CONFIG_ARM64_PSEUDO_NMI.
2160 When an interrupt is not handled search all handlers
2161 for it. Intended to get systems with badly broken
2165 When an interrupt is not handled search all handlers
2166 for it. Also check all handlers each timer
2167 interrupt. Intended to get systems with badly broken
2171 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
2173 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
2174 [Deprecated - use cpusets instead]
2175 Format: [flag-list,]<cpu-list>
2177 Specify one or more CPUs to isolate from disturbances
2178 specified in the flag list (default: domain):
2181 Disable the tick when a single task runs.
2183 A residual 1Hz tick is offloaded to workqueues, which you
2184 need to affine to housekeeping through the global
2185 workqueue's affinity configured via the
2186 /sys/devices/virtual/workqueue/cpumask sysfs file, or
2187 by using the 'domain' flag described below.
2189 NOTE: by default the global workqueue runs on all CPUs,
2190 so to protect individual CPUs the 'cpumask' file has to
2191 be configured manually after bootup.
2194 Isolate from the general SMP balancing and scheduling
2195 algorithms. Note that performing domain isolation this way
2196 is irreversible: it's not possible to bring back a CPU to
2197 the domains once isolated through isolcpus. It's strongly
2198 advised to use cpusets instead to disable scheduler load
2199 balancing through the "cpuset.sched_load_balance" file.
2200 It offers a much more flexible interface where CPUs can
2201 move in and out of an isolated set anytime.
2203 You can move a process onto or off an "isolated" CPU via
2204 the CPU affinity syscalls or cpuset.
2205 <cpu number> begins at 0 and the maximum value is
2206 "number of CPUs in system - 1".
2210 Isolate from being targeted by managed interrupts
2211 which have an interrupt mask containing isolated
2212 CPUs. The affinity of managed interrupts is
2213 handled by the kernel and cannot be changed via
2214 the /proc/irq/* interfaces.
2216 This isolation is best effort and only effective
2217 if the automatically assigned interrupt mask of a
2218 device queue contains isolated and housekeeping
2219 CPUs. If housekeeping CPUs are online then such
2220 interrupts are directed to the housekeeping CPU
2221 so that IO submitted on the housekeeping CPU
2222 cannot disturb the isolated CPU.
2224 If a queue's affinity mask contains only isolated
2225 CPUs then this parameter has no effect on the
2226 interrupt routing decision, though interrupts are
2227 only delivered when tasks running on those
2228 isolated CPUs submit IO. IO submitted on
2229 housekeeping CPUs has no influence on those
2232 The format of <cpu-list> is described above.
2236 ivrs_ioapic [HW,X86-64]
2237 Provide an override to the IOAPIC-ID<->DEVICE-ID
2238 mapping provided in the IVRS ACPI table. For
2239 example, to map IOAPIC-ID decimal 10 to
2240 PCI device 00:14.0 write the parameter as:
2241 ivrs_ioapic[10]=00:14.0
2243 ivrs_hpet [HW,X86-64]
2244 Provide an override to the HPET-ID<->DEVICE-ID
2245 mapping provided in the IVRS ACPI table. For
2246 example, to map HPET-ID decimal 0 to
2247 PCI device 00:14.0 write the parameter as:
2248 ivrs_hpet[0]=00:14.0
2250 ivrs_acpihid [HW,X86-64]
2251 Provide an override to the ACPI-HID:UID<->DEVICE-ID
2252 mapping provided in the IVRS ACPI table. For
2253 example, to map UART-HID:UID AMD0020:0 to
2254 PCI device 00:14.5 write the parameter as:
2255 ivrs_acpihid[00:14.5]=AMD0020:0
2257 js= [HW,JOY] Analog joystick
2258 See Documentation/input/joydev/joystick.rst.
2261 When CONFIG_RANDOMIZE_BASE is set, this disables
2262 kernel and module base offset ASLR (Address Space
2263 Layout Randomization).
2266 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
2267 report on every invalid memory access. Without this
2268 parameter KASAN will print report only for the first
2273 kernelcore= [KNL,X86,IA-64,PPC]
2274 Format: nn[KMGTPE] | nn% | "mirror"
2275 This parameter specifies the amount of memory usable by
2276 the kernel for non-movable allocations. The requested
2277 amount is spread evenly throughout all nodes in the
2278 system as ZONE_NORMAL. The remaining memory is used for
2279 movable memory in its own zone, ZONE_MOVABLE. In the
2280 event, a node is too small to have both ZONE_NORMAL and
2281 ZONE_MOVABLE, kernelcore memory will take priority and
2282 other nodes will have a larger ZONE_MOVABLE.
2284 ZONE_MOVABLE is used for the allocation of pages that
2285 may be reclaimed or moved by the page migration
2286 subsystem. Note that allocations like PTEs-from-HighMem
2287 still use the HighMem zone if it exists, and the Normal
2288 zone if it does not.
2290 It is possible to specify the exact amount of memory in
2291 the form of "nn[KMGTPE]", a percentage of total system
2292 memory in the form of "nn%", or "mirror". If "mirror"
2293 option is specified, mirrored (reliable) memory is used
2294 for non-movable allocations and remaining memory is used
2295 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
2296 are exclusive, so you cannot specify multiple forms.
2298 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
2299 Format: <Controller#>[,poll interval]
2300 The controller # is the number of the ehci usb debug
2301 port as it is probed via PCI. The poll interval is
2302 optional and is the number seconds in between
2303 each poll cycle to the debug port in case you need
2304 the functionality for interrupting the kernel with
2305 gdb or control-c on the dbgp connection. When
2306 not using this parameter you use sysrq-g to break into
2307 the kernel debugger.
2309 kgdboc= [KGDB,HW] kgdb over consoles.
2310 Requires a tty driver that supports console polling,
2311 or a supported polling keyboard driver (non-usb).
2312 Serial only format: <serial_device>[,baud]
2313 keyboard only format: kbd
2314 keyboard and serial format: kbd,<serial_device>[,baud]
2315 Optional Kernel mode setting:
2316 kms, kbd format: kms,kbd
2317 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
2319 kgdboc_earlycon= [KGDB,HW]
2320 If the boot console provides the ability to read
2321 characters and can work in polling mode, you can use
2322 this parameter to tell kgdb to use it as a backend
2323 until the normal console is registered. Intended to
2324 be used together with the kgdboc parameter which
2325 specifies the normal console to transition to.
2327 The name of the early console should be specified
2328 as the value of this parameter. Note that the name of
2329 the early console might be different than the tty
2330 name passed to kgdboc. It's OK to leave the value
2331 blank and the first boot console that implements
2332 read() will be picked.
2334 kgdbwait [KGDB] Stop kernel execution and enter the
2335 kernel debugger at the earliest opportunity.
2337 kmac= [MIPS] Korina ethernet MAC address.
2338 Configure the RouterBoard 532 series on-chip
2339 Ethernet adapter MAC address.
2341 kmemleak= [KNL] Boot-time kmemleak enable/disable
2342 Valid arguments: on, off
2344 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
2347 kprobe_event=[probe-list]
2348 [FTRACE] Add kprobe events and enable at boot time.
2349 The probe-list is a semicolon delimited list of probe
2350 definitions. Each definition is same as kprobe_events
2351 interface, but the parameters are comma delimited.
2352 For example, to add a kprobe event on vfs_read with
2353 arg1 and arg2, add to the command line;
2355 kprobe_event=p,vfs_read,$arg1,$arg2
2357 See also Documentation/trace/kprobetrace.rst "Kernel
2358 Boot Parameter" section.
2360 kpti= [ARM64] Control page table isolation of user
2361 and kernel address spaces.
2362 Default: enabled on cores which need mitigation.
2366 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
2367 Default is 0 (don't ignore, but inject #GP)
2369 kvm.eager_page_split=
2370 [KVM,X86] Controls whether or not KVM will try to
2371 proactively split all huge pages during dirty logging.
2372 Eager page splitting reduces interruptions to vCPU
2373 execution by eliminating the write-protection faults
2374 and MMU lock contention that would otherwise be
2375 required to split huge pages lazily.
2377 VM workloads that rarely perform writes or that write
2378 only to a small region of VM memory may benefit from
2379 disabling eager page splitting to allow huge pages to
2380 still be used for reads.
2382 The behavior of eager page splitting depends on whether
2383 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If
2384 disabled, all huge pages in a memslot will be eagerly
2385 split when dirty logging is enabled on that memslot. If
2386 enabled, eager page splitting will be performed during
2387 the KVM_CLEAR_DIRTY ioctl, and only for the pages being
2390 Eager page splitting currently only supports splitting
2391 huge pages mapped by the TDP MMU.
2395 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
2396 Default is false (don't support).
2399 [KVM] Controls the software workaround for the
2400 X86_BUG_ITLB_MULTIHIT bug.
2401 force : Always deploy workaround.
2402 off : Never deploy workaround.
2403 auto : Deploy workaround based on the presence of
2404 X86_BUG_ITLB_MULTIHIT.
2408 If the software workaround is enabled for the host,
2409 guests do need not to enable it for nested guests.
2411 kvm.nx_huge_pages_recovery_ratio=
2412 [KVM] Controls how many 4KiB pages are periodically zapped
2413 back to huge pages. 0 disables the recovery, otherwise if
2414 the value is N KVM will zap 1/Nth of the 4KiB pages every
2415 period (see below). The default is 60.
2417 kvm.nx_huge_pages_recovery_period_ms=
2418 [KVM] Controls the time period at which KVM zaps 4KiB pages
2419 back to huge pages. If the value is a non-zero N, KVM will
2420 zap a portion (see ratio above) of the pages every N msecs.
2421 If the value is 0 (the default), KVM will pick a period based
2422 on the ratio, such that a page is zapped after 1 hour on average.
2424 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
2425 Default is 1 (enabled)
2427 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
2429 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
2432 [KVM,ARM] Select one of KVM/arm64's modes of operation.
2434 none: Forcefully disable KVM.
2436 nvhe: Standard nVHE-based mode, without support for
2439 protected: nVHE-based mode with support for guests whose
2440 state is kept private from the host.
2441 Not valid if the kernel is running in EL2.
2443 Defaults to VHE/nVHE based on hardware support. Setting
2444 mode to "protected" will disable kexec and hibernation
2447 kvm-arm.vgic_v3_group0_trap=
2448 [KVM,ARM] Trap guest accesses to GICv3 group-0
2451 kvm-arm.vgic_v3_group1_trap=
2452 [KVM,ARM] Trap guest accesses to GICv3 group-1
2455 kvm-arm.vgic_v3_common_trap=
2456 [KVM,ARM] Trap guest accesses to GICv3 common
2459 kvm-arm.vgic_v4_enable=
2460 [KVM,ARM] Allow use of GICv4 for direct injection of
2463 kvm_cma_resv_ratio=n [PPC]
2464 Reserves given percentage from system memory area for
2465 contiguous memory allocation for KVM hash pagetable
2467 By default it reserves 5% of total system memory.
2471 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2472 (virtualized MMU) support on capable Intel chips.
2473 Default is 1 (enabled)
2475 kvm-intel.emulate_invalid_guest_state=
2476 [KVM,Intel] Disable emulation of invalid guest state.
2477 Ignored if kvm-intel.enable_unrestricted_guest=1, as
2478 guest state is never invalid for unrestricted guests.
2479 This param doesn't apply to nested guests (L2), as KVM
2480 never emulates invalid L2 guest state.
2481 Default is 1 (enabled)
2483 kvm-intel.flexpriority=
2484 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2485 Default is 1 (enabled)
2488 [KVM,Intel] Enable VMX nesting (nVMX).
2489 Default is 0 (disabled)
2491 kvm-intel.unrestricted_guest=
2492 [KVM,Intel] Disable unrestricted guest feature
2493 (virtualized real and unpaged mode) on capable
2494 Intel chips. Default is 1 (enabled)
2496 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2499 Valid arguments: never, cond, always
2501 always: L1D cache flush on every VMENTER.
2502 cond: Flush L1D on VMENTER only when the code between
2503 VMEXIT and VMENTER can leak host memory.
2504 never: Disables the mitigation
2506 Default is cond (do L1 cache flush in specific instances)
2508 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2509 feature (tagged TLBs) on capable Intel chips.
2510 Default is 1 (enabled)
2512 l1d_flush= [X86,INTEL]
2513 Control mitigation for L1D based snooping vulnerability.
2515 Certain CPUs are vulnerable to an exploit against CPU
2516 internal buffers which can forward information to a
2517 disclosure gadget under certain conditions.
2519 In vulnerable processors, the speculatively
2520 forwarded data can be used in a cache side channel
2521 attack, to access data to which the attacker does
2522 not have direct access.
2524 This parameter controls the mitigation. The
2527 on - enable the interface for the mitigation
2529 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2532 The kernel PTE inversion protection is unconditionally
2533 enabled and cannot be disabled.
2536 Provides all available mitigations for the
2537 L1TF vulnerability. Disables SMT and
2538 enables all mitigations in the
2539 hypervisors, i.e. unconditional L1D flush.
2541 SMT control and L1D flush control via the
2542 sysfs interface is still possible after
2543 boot. Hypervisors will issue a warning
2544 when the first VM is started in a
2545 potentially insecure configuration,
2546 i.e. SMT enabled or L1D flush disabled.
2549 Same as 'full', but disables SMT and L1D
2550 flush runtime control. Implies the
2551 'nosmt=force' command line option.
2552 (i.e. sysfs control of SMT is disabled.)
2555 Leaves SMT enabled and enables the default
2556 hypervisor mitigation, i.e. conditional
2559 SMT control and L1D flush control via the
2560 sysfs interface is still possible after
2561 boot. Hypervisors will issue a warning
2562 when the first VM is started in a
2563 potentially insecure configuration,
2564 i.e. SMT enabled or L1D flush disabled.
2568 Disables SMT and enables the default
2569 hypervisor mitigation.
2571 SMT control and L1D flush control via the
2572 sysfs interface is still possible after
2573 boot. Hypervisors will issue a warning
2574 when the first VM is started in a
2575 potentially insecure configuration,
2576 i.e. SMT enabled or L1D flush disabled.
2579 Same as 'flush', but hypervisors will not
2580 warn when a VM is started in a potentially
2581 insecure configuration.
2584 Disables hypervisor mitigations and doesn't
2586 It also drops the swap size and available
2587 RAM limit restriction on both hypervisor and
2592 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst
2598 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2601 lapic= [X86,APIC] Do not use TSC deadline
2602 value for LAPIC timer one-shot implementation. Default
2603 back to the programmable timer unit in the LAPIC.
2604 Format: notscdeadline
2606 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2609 libata.dma= [LIBATA] DMA control
2610 libata.dma=0 Disable all PATA and SATA DMA
2611 libata.dma=1 PATA and SATA Disk DMA only
2612 libata.dma=2 ATAPI (CDROM) DMA only
2613 libata.dma=4 Compact Flash DMA only
2614 Combinations also work, so libata.dma=3 enables DMA
2615 for disks and CDROMs, but not CFs.
2617 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2618 libata.ignore_hpa=0 keep BIOS limits (default)
2619 libata.ignore_hpa=1 ignore limits, using full disk
2621 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2625 libata.force= [LIBATA] Force configurations. The format is comma-
2626 separated list of "[ID:]VAL" where ID is
2627 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2628 matching port, link or device. Basically, it matches
2629 the ATA ID string printed on console by libata. If
2630 the whole ID part is omitted, the last PORT and DEVICE
2631 values are used. If ID hasn't been specified yet, the
2632 configuration applies to all ports, links and devices.
2634 If only DEVICE is omitted, the parameter applies to
2635 the port and all links and devices behind it. DEVICE
2636 number of 0 either selects the first device or the
2637 first fan-out link behind PMP device. It does not
2638 select the host link. DEVICE number of 15 selects the
2639 host link and device attached to it.
2641 The VAL specifies the configuration to force. As long
2642 as there's no ambiguity shortcut notation is allowed.
2643 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2644 The following configurations can be forced.
2646 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2647 Any ID with matching PORT is used.
2649 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2651 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2652 udma[/][16,25,33,44,66,100,133] notation is also
2655 * [no]ncq: Turn on or off NCQ.
2657 * [no]ncqtrim: Turn off queued DSM TRIM.
2659 * nohrst, nosrst, norst: suppress hard, soft
2662 * rstonce: only attempt one reset during
2663 hot-unplug link recovery
2665 * dump_id: dump IDENTIFY data.
2667 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2669 * disable: Disable this device.
2671 If there are multiple matching configurations changing
2672 the same attribute, the last one is used.
2674 memblock=debug [KNL] Enable memblock debug messages.
2676 load_ramdisk= [RAM] [Deprecated]
2678 lockd.nlm_grace_period=P [NFS] Assign grace period.
2681 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2684 lockd.nlm_timeout=T [NFS] Assign timeout value.
2687 lockd.nlm_udpport=M [NFS] Assign UDP port.
2690 lockdown= [SECURITY]
2691 { integrity | confidentiality }
2692 Enable the kernel lockdown feature. If set to
2693 integrity, kernel features that allow userland to
2694 modify the running kernel are disabled. If set to
2695 confidentiality, kernel features that allow userland
2696 to extract confidential information from the kernel
2699 locktorture.nreaders_stress= [KNL]
2700 Set the number of locking read-acquisition kthreads.
2701 Defaults to being automatically set based on the
2702 number of online CPUs.
2704 locktorture.nwriters_stress= [KNL]
2705 Set the number of locking write-acquisition kthreads.
2707 locktorture.onoff_holdoff= [KNL]
2708 Set time (s) after boot for CPU-hotplug testing.
2710 locktorture.onoff_interval= [KNL]
2711 Set time (s) between CPU-hotplug operations, or
2712 zero to disable CPU-hotplug testing.
2714 locktorture.shuffle_interval= [KNL]
2715 Set task-shuffle interval (jiffies). Shuffling
2716 tasks allows some CPUs to go into dyntick-idle
2717 mode during the locktorture test.
2719 locktorture.shutdown_secs= [KNL]
2720 Set time (s) after boot system shutdown. This
2721 is useful for hands-off automated testing.
2723 locktorture.stat_interval= [KNL]
2724 Time (s) between statistics printk()s.
2726 locktorture.stutter= [KNL]
2727 Time (s) to stutter testing, for example,
2728 specifying five seconds causes the test to run for
2729 five seconds, wait for five seconds, and so on.
2730 This tests the locking primitive's ability to
2731 transition abruptly to and from idle.
2733 locktorture.torture_type= [KNL]
2734 Specify the locking implementation to test.
2736 locktorture.verbose= [KNL]
2737 Enable additional printk() statements.
2739 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2742 loglevel= All Kernel Messages with a loglevel smaller than the
2743 console loglevel will be printed to the console. It can
2744 also be changed with klogd or other programs. The
2745 loglevels are defined as follows:
2747 0 (KERN_EMERG) system is unusable
2748 1 (KERN_ALERT) action must be taken immediately
2749 2 (KERN_CRIT) critical conditions
2750 3 (KERN_ERR) error conditions
2751 4 (KERN_WARNING) warning conditions
2752 5 (KERN_NOTICE) normal but significant condition
2753 6 (KERN_INFO) informational
2754 7 (KERN_DEBUG) debug-level messages
2756 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2757 in bytes. n must be a power of two and greater
2758 than the minimal size. The minimal size is defined
2759 by LOG_BUF_SHIFT kernel config parameter. There is
2760 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2761 that allows to increase the default size depending on
2762 the number of CPUs. See init/Kconfig for more details.
2764 logo.nologo [FB] Disables display of the built-in Linux logo.
2765 This may be used to provide more screen space for
2766 kernel log messages and is useful when debugging
2767 kernel boot problems.
2769 lp=0 [LP] Specify parallel ports to use, e.g,
2770 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2771 lp=reset first parallel port). 'lp=0' disables the
2772 lp=auto printer driver. 'lp=reset' (which can be
2773 specified in addition to the ports) causes
2774 attached printers to be reset. Using
2775 lp=port1,port2,... specifies the parallel ports
2776 to associate lp devices with, starting with
2777 lp0. A port specification may be 'none' to skip
2778 that lp device, or a parport name such as
2779 'parport0'. Specifying 'lp=auto' instead of a
2780 port specification list means that device IDs
2781 from each port should be examined, to see if
2782 an IEEE 1284-compliant printer is attached; if
2783 so, the driver will manage that printer.
2784 See also header of drivers/char/lp.c.
2787 Sets loops_per_jiffy to given constant, thus avoiding
2788 time-consuming boot-time autodetection (up to 250 ms per
2789 CPU). 0 enables autodetection (default). To determine
2790 the correct value for your kernel, boot with normal
2791 autodetection and see what value is printed. Note that
2792 on SMP systems the preset will be applied to all CPUs,
2793 which is likely to cause problems if your CPUs need
2794 significantly divergent settings. An incorrect value
2795 will cause delays in the kernel to be wrong, leading to
2796 unpredictable I/O errors and other breakage. Although
2797 unlikely, in the extreme case this might damage your
2801 Format: <io>,<irq>,<dma>
2803 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2806 [SECURITY] Choose order of LSM initialization. This
2807 overrides CONFIG_LSM, and the "security=" parameter.
2809 machvec= [IA-64] Force the use of a particular machine-vector
2810 (machvec) in a generic kernel.
2811 Example: machvec=hpzx1
2813 machtype= [Loongson] Share the same kernel image file between
2814 different yeeloong laptops.
2815 Example: machtype=lemote-yeeloong-2f-7inch
2817 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2818 than or equal to this physical address is ignored.
2820 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2821 will bring up during bootup. maxcpus=n : n >= 0 limits
2822 the kernel to bring up 'n' processors. Surely after
2823 bootup you can bring up the other plugged cpu by executing
2824 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2825 only takes effect during system bootup.
2826 While n=0 is a special case, it is equivalent to "nosmp",
2827 which also disables the IO APIC.
2829 max_loop= [LOOP] The number of loop block devices that get
2830 (loop.max_loop) unconditionally pre-created at init time. The default
2831 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2832 of statically allocating a predefined number, loop
2833 devices can be requested on-demand with the
2834 /dev/loop-control interface.
2836 mce [X86-32] Machine Check Exception
2838 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst
2840 md= [HW] RAID subsystems devices and level
2841 See Documentation/admin-guide/md.rst.
2844 Format: <first>,<last>
2845 Specifies range of consoles to be captured by the MDA.
2848 Control mitigation for the Micro-architectural Data
2849 Sampling (MDS) vulnerability.
2851 Certain CPUs are vulnerable to an exploit against CPU
2852 internal buffers which can forward information to a
2853 disclosure gadget under certain conditions.
2855 In vulnerable processors, the speculatively
2856 forwarded data can be used in a cache side channel
2857 attack, to access data to which the attacker does
2858 not have direct access.
2860 This parameter controls the MDS mitigation. The
2863 full - Enable MDS mitigation on vulnerable CPUs
2864 full,nosmt - Enable MDS mitigation and disable
2865 SMT on vulnerable CPUs
2866 off - Unconditionally disable MDS mitigation
2868 On TAA-affected machines, mds=off can be prevented by
2869 an active TAA mitigation as both vulnerabilities are
2870 mitigated with the same mechanism so in order to disable
2871 this mitigation, you need to specify tsx_async_abort=off
2874 Not specifying this option is equivalent to
2877 For details see: Documentation/admin-guide/hw-vuln/mds.rst
2879 mem=nn[KMG] [HEXAGON] Set the memory size.
2880 Must be specified, otherwise memory size will be 0.
2882 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2883 Amount of memory to be used in cases as follows:
2886 2 when the kernel is not able to see the whole system memory;
2887 3 memory that lies after 'mem=' boundary is excluded from
2888 the hypervisor, then assigned to KVM guests.
2889 4 to limit the memory available for kdump kernel.
2891 [ARC,MICROBLAZE] - the limit applies only to low memory,
2892 high memory is not affected.
2894 [ARM64] - only limits memory covered by the linear
2895 mapping. The NOMAP regions are not affected.
2897 [X86] Work as limiting max address. Use together
2898 with memmap= to avoid physical address space collisions.
2899 Without memmap= PCI devices could be placed at addresses
2900 belonging to unused RAM.
2902 Note that this only takes effects during boot time since
2903 in above case 3, memory may need be hot added after boot
2904 if system memory of hypervisor is not sufficient.
2907 [ARM,MIPS] - override the memory layout reported by
2909 Define a memory region of size nn[KMG] starting at
2911 Multiple different regions can be specified with
2912 multiple mem= parameters on the command line.
2914 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2918 [KNL,SH] Allow user to override the default size for
2919 per-device physically contiguous DMA buffers.
2921 memhp_default_state=online/offline
2922 [KNL] Set the initial state for the memory hotplug
2923 onlining policy. If not specified, the default value is
2924 set according to the
2925 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2927 See Documentation/admin-guide/mm/memory-hotplug.rst.
2929 memmap=exactmap [KNL,X86] Enable setting of an exact
2930 E820 memory map, as specified by the user.
2931 Such memmap=exactmap lines can be constructed based on
2932 BIOS output or other requirements. See the memmap=nn@ss
2935 memmap=nn[KMG]@ss[KMG]
2936 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory.
2937 Region of memory to be used is from ss to ss+nn.
2938 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2939 which limits max address to nn[KMG].
2940 Multiple different regions can be specified,
2943 memmap=100M@2G,100M#3G,1G!1024G
2945 memmap=nn[KMG]#ss[KMG]
2946 [KNL,ACPI] Mark specific memory as ACPI data.
2947 Region of memory to be marked is from ss to ss+nn.
2949 memmap=nn[KMG]$ss[KMG]
2950 [KNL,ACPI] Mark specific memory as reserved.
2951 Region of memory to be reserved is from ss to ss+nn.
2952 Example: Exclude memory from 0x18690000-0x1869ffff
2953 memmap=64K$0x18690000
2955 memmap=0x10000$0x18690000
2956 Some bootloaders may need an escape character before '$',
2957 like Grub2, otherwise '$' and the following number
2960 memmap=nn[KMG]!ss[KMG]
2961 [KNL,X86] Mark specific memory as protected.
2962 Region of memory to be used, from ss to ss+nn.
2963 The memory region may be marked as e820 type 12 (0xc)
2964 and is NVDIMM or ADR memory.
2966 memmap=<size>%<offset>-<oldtype>+<newtype>
2967 [KNL,ACPI] Convert memory within the specified region
2968 from <oldtype> to <newtype>. If "-<oldtype>" is left
2969 out, the whole region will be marked as <newtype>,
2970 even if previously unavailable. If "+<newtype>" is left
2971 out, matching memory will be removed. Types are
2972 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2973 3 = ACPI, 12 = PRAM.
2975 memory_corruption_check=0/1 [X86]
2976 Some BIOSes seem to corrupt the first 64k of
2977 memory when doing things like suspend/resume.
2978 Setting this option will scan the memory
2979 looking for corruption. Enabling this will
2980 both detect corruption and prevent the kernel
2981 from using the memory being corrupted.
2982 However, its intended as a diagnostic tool; if
2983 repeatable BIOS-originated corruption always
2984 affects the same memory, you can use memmap=
2985 to prevent the kernel from using that memory.
2987 memory_corruption_check_size=size [X86]
2988 By default it checks for corruption in the low
2989 64k, making this memory unavailable for normal
2990 use. Use this parameter to scan for
2991 corruption in more or less memory.
2993 memory_corruption_check_period=seconds [X86]
2994 By default it checks for corruption every 60
2995 seconds. Use this parameter to check at some
2996 other rate. 0 disables periodic checking.
2998 memory_hotplug.memmap_on_memory
2999 [KNL,X86,ARM] Boolean flag to enable this feature.
3000 Format: {on | off (default)}
3001 When enabled, runtime hotplugged memory will
3002 allocate its internal metadata (struct pages)
3003 from the hotadded memory which will allow to
3004 hotadd a lot of memory without requiring
3005 additional memory to do so.
3006 This feature is disabled by default because it
3007 has some implication on large (e.g. GB)
3008 allocations in some configurations (e.g. small
3010 The state of the flag can be read in
3011 /sys/module/memory_hotplug/parameters/memmap_on_memory.
3012 Note that even when enabled, there are a few cases where
3013 the feature is not effective.
3015 This is not compatible with hugetlb_free_vmemmap. If
3016 both parameters are enabled, hugetlb_free_vmemmap takes
3017 precedence over memory_hotplug.memmap_on_memory.
3019 memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest
3021 default : 0 <disable>
3022 Specifies the number of memtest passes to be
3023 performed. Each pass selects another test
3024 pattern from a given set of patterns. Memtest
3025 fills the memory with this pattern, validates
3026 memory contents and reserves bad memory
3027 regions that are detected.
3029 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
3030 Valid arguments: on, off
3031 Default (depends on kernel configuration option):
3032 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
3033 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
3034 mem_encrypt=on: Activate SME
3035 mem_encrypt=off: Do not activate SME
3037 Refer to Documentation/virt/kvm/amd-memory-encryption.rst
3038 for details on when memory encryption can be activated.
3040 mem_sleep_default= [SUSPEND] Default system suspend mode:
3041 s2idle - Suspend-To-Idle
3042 shallow - Power-On Suspend or equivalent (if supported)
3043 deep - Suspend-To-RAM or equivalent (if supported)
3044 See Documentation/admin-guide/pm/sleep-states.rst.
3046 meye.*= [HW] Set MotionEye Camera parameters
3047 See Documentation/admin-guide/media/meye.rst.
3049 mfgpt_irq= [IA-32] Specify the IRQ to use for the
3050 Multi-Function General Purpose Timers on AMD Geode
3053 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
3054 the BIOS has incorrectly applied a workaround. TinyBIOS
3055 version 0.98 is known to be affected, 0.99 fixes the
3056 problem by letting the user disable the workaround.
3060 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
3061 physical address is ignored.
3063 mini2440= [ARM,HW,KNL]
3064 Format:[0..2][b][c][t]
3066 MINI2440 configuration specification:
3067 0 - The attached screen is the 3.5" TFT
3068 1 - The attached screen is the 7" TFT
3069 2 - The VGA Shield is attached (1024x768)
3070 Leaving out the screen size parameter will not load
3071 the TFT driver, and the framebuffer will be left
3073 b - Enable backlight. The TFT backlight pin will be
3074 linked to the kernel VESA blanking code and a GPIO
3075 LED. This parameter is not necessary when using the
3077 c - Enable the s3c camera interface.
3078 t - Reserved for enabling touchscreen support. The
3079 touchscreen support is not enabled in the mainstream
3080 kernel as of 2.6.30, a preliminary port can be found
3081 in the "bleeding edge" mini2440 support kernel at
3082 https://repo.or.cz/w/linux-2.6/mini2440.git
3085 [X86,PPC,S390,ARM64] Control optional mitigations for
3086 CPU vulnerabilities. This is a set of curated,
3087 arch-independent options, each of which is an
3088 aggregation of existing arch-specific options.
3091 Disable all optional CPU mitigations. This
3092 improves system performance, but it may also
3093 expose users to several CPU vulnerabilities.
3094 Equivalent to: nopti [X86,PPC]
3096 nospectre_v1 [X86,PPC]
3098 nospectre_v2 [X86,PPC,S390,ARM64]
3099 spectre_v2_user=off [X86]
3100 spec_store_bypass_disable=off [X86,PPC]
3101 ssbd=force-off [ARM64]
3104 tsx_async_abort=off [X86]
3105 kvm.nx_huge_pages=off [X86]
3106 no_entry_flush [PPC]
3107 no_uaccess_flush [PPC]
3108 mmio_stale_data=off [X86]
3111 This does not have any effect on
3112 kvm.nx_huge_pages when
3113 kvm.nx_huge_pages=force.
3116 Mitigate all CPU vulnerabilities, but leave SMT
3117 enabled, even if it's vulnerable. This is for
3118 users who don't want to be surprised by SMT
3119 getting disabled across kernel upgrades, or who
3120 have other ways of avoiding SMT-based attacks.
3121 Equivalent to: (default behavior)
3124 Mitigate all CPU vulnerabilities, disabling SMT
3125 if needed. This is for users who always want to
3126 be fully mitigated, even if it means losing SMT.
3127 Equivalent to: l1tf=flush,nosmt [X86]
3128 mds=full,nosmt [X86]
3129 tsx_async_abort=full,nosmt [X86]
3130 mmio_stale_data=full,nosmt [X86]
3133 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
3134 parameter allows control of the logging verbosity for
3135 the additional memory initialisation checks. A value
3136 of 0 disables mminit logging and a level of 4 will
3137 log everything. Information is printed at KERN_DEBUG
3138 so loglevel=8 may also need to be specified.
3141 [X86,INTEL] Control mitigation for the Processor
3142 MMIO Stale Data vulnerabilities.
3144 Processor MMIO Stale Data is a class of
3145 vulnerabilities that may expose data after an MMIO
3146 operation. Exposed data could originate or end in
3147 the same CPU buffers as affected by MDS and TAA.
3148 Therefore, similar to MDS and TAA, the mitigation
3149 is to clear the affected CPU buffers.
3151 This parameter controls the mitigation. The
3154 full - Enable mitigation on vulnerable CPUs
3156 full,nosmt - Enable mitigation and disable SMT on
3159 off - Unconditionally disable mitigation
3161 On MDS or TAA affected machines,
3162 mmio_stale_data=off can be prevented by an active
3163 MDS or TAA mitigation as these vulnerabilities are
3164 mitigated with the same mechanism so in order to
3165 disable this mitigation, you need to specify
3166 mds=off and tsx_async_abort=off too.
3168 Not specifying this option is equivalent to
3169 mmio_stale_data=full.
3172 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
3175 [KNL] When CONFIG_MODULE_SIG is set, this means that
3176 modules without (valid) signatures will fail to load.
3177 Note that if CONFIG_MODULE_SIG_FORCE is set, that
3178 is always true, so this option does nothing.
3180 module_blacklist= [KNL] Do not load a comma-separated list of
3181 modules. Useful for debugging problem modules.
3184 [MOUSE] Maximum time between finger touching and
3185 leaving touchpad surface for touch to be considered
3186 a tap and be reported as a left button click (for
3187 touchpads working in absolute mode only).
3189 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
3190 reporting absolute coordinates, such as tablets
3191 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
3192 reporting absolute coordinates, such as tablets
3194 movablecore= [KNL,X86,IA-64,PPC]
3195 Format: nn[KMGTPE] | nn%
3196 This parameter is the complement to kernelcore=, it
3197 specifies the amount of memory used for migratable
3198 allocations. If both kernelcore and movablecore is
3199 specified, then kernelcore will be at *least* the
3200 specified value but may be more. If movablecore on its
3201 own is specified, the administrator must be careful
3202 that the amount of memory usable for all allocations
3205 movable_node [KNL] Boot-time switch to make hotplugable memory
3206 NUMA nodes to be movable. This means that the memory
3207 of such nodes will be usable only for movable
3208 allocations which rules out almost all kernel
3209 allocations. Use with caution!
3211 MTD_Partition= [MTD]
3212 Format: <name>,<region-number>,<size>,<offset>
3214 MTD_Region= [MTD] Format:
3215 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
3218 See drivers/mtd/parsers/cmdlinepart.c
3220 multitce=off [PPC] This parameter disables the use of the pSeries
3221 firmware feature for updating multiple TCE entries
3224 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
3226 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
3228 boundary - index of last SLC block on Flex-OneNAND.
3229 The remaining blocks are configured as MLC blocks.
3230 lock - Configure if Flex-OneNAND boundary should be locked.
3231 Once locked, the boundary cannot be changed.
3232 1 indicates lock status, 0 indicates unlock status.
3235 ARM/S3C2412 JIVE boot control
3237 See arch/arm/mach-s3c/mach-jive.c
3239 mtouchusb.raw_coordinates=
3240 [HW] Make the MicroTouch USB driver use raw coordinates
3241 ('y', default) or cooked coordinates ('n')
3243 mtrr_chunk_size=nn[KMG] [X86]
3244 used for mtrr cleanup. It is largest continuous chunk
3245 that could hold holes aka. UC entries.
3247 mtrr_gran_size=nn[KMG] [X86]
3248 Used for mtrr cleanup. It is granularity of mtrr block.
3250 Large value could prevent small alignment from
3253 mtrr_spare_reg_nr=n [X86]
3255 Range: 0,7 : spare reg number
3257 Used for mtrr cleanup. It is spare mtrr entries number.
3258 Set to 2 or more if your graphical card needs more.
3260 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
3262 netdev= [NET] Network devices parameters
3263 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
3264 Note that mem_start is often overloaded to mean
3265 something different and driver-specific.
3266 This usage is only documented in each driver source
3270 [NETFILTER] Enable connection tracking flow accounting
3271 0 to disable accounting
3272 1 to enable accounting
3275 nfsaddrs= [NFS] Deprecated. Use ip= instead.
3276 See Documentation/admin-guide/nfs/nfsroot.rst.
3278 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
3279 See Documentation/admin-guide/nfs/nfsroot.rst.
3281 nfsrootdebug [NFS] enable nfsroot debugging messages.
3282 See Documentation/admin-guide/nfs/nfsroot.rst.
3284 nfs.callback_nr_threads=
3285 [NFSv4] set the total number of threads that the
3286 NFS client will assign to service NFSv4 callback
3289 nfs.callback_tcpport=
3290 [NFS] set the TCP port on which the NFSv4 callback
3291 channel should listen.
3294 [NFS] sets the pathname to the program which is used
3295 to update the NFS client cache entries.
3297 nfs.cache_getent_timeout=
3298 [NFS] sets the timeout after which an attempt to
3299 update a cache entry is deemed to have failed.
3301 nfs.idmap_cache_timeout=
3302 [NFS] set the maximum lifetime for idmapper cache
3306 [NFS] enable 64-bit inode numbers.
3307 If zero, the NFS client will fake up a 32-bit inode
3308 number for the readdir() and stat() syscalls instead
3309 of returning the full 64-bit number.
3310 The default is to return 64-bit inode numbers.
3312 nfs.max_session_cb_slots=
3313 [NFSv4.1] Sets the maximum number of session
3314 slots the client will assign to the callback
3315 channel. This determines the maximum number of
3316 callbacks the client will process in parallel for
3317 a particular server.
3319 nfs.max_session_slots=
3320 [NFSv4.1] Sets the maximum number of session slots
3321 the client will attempt to negotiate with the server.
3322 This limits the number of simultaneous RPC requests
3323 that the client can send to the NFSv4.1 server.
3324 Note that there is little point in setting this
3325 value higher than the max_tcp_slot_table_limit.
3327 nfs.nfs4_disable_idmapping=
3328 [NFSv4] When set to the default of '1', this option
3329 ensures that both the RPC level authentication
3330 scheme and the NFS level operations agree to use
3331 numeric uids/gids if the mount is using the
3332 'sec=sys' security flavour. In effect it is
3333 disabling idmapping, which can make migration from
3334 legacy NFSv2/v3 systems to NFSv4 easier.
3335 Servers that do not support this mode of operation
3336 will be autodetected by the client, and it will fall
3337 back to using the idmapper.
3338 To turn off this behaviour, set the value to '0'.
3340 [NFS4] Specify an additional fixed unique ident-
3341 ification string that NFSv4 clients can insert into
3342 their nfs_client_id4 string. This is typically a
3343 UUID that is generated at system install time.
3345 nfs.send_implementation_id =
3346 [NFSv4.1] Send client implementation identification
3347 information in exchange_id requests.
3348 If zero, no implementation identification information
3350 The default is to send the implementation identification
3353 nfs.recover_lost_locks =
3354 [NFSv4] Attempt to recover locks that were lost due
3355 to a lease timeout on the server. Please note that
3356 doing this risks data corruption, since there are
3357 no guarantees that the file will remain unchanged
3358 after the locks are lost.
3359 If you want to enable the kernel legacy behaviour of
3360 attempting to recover these locks, then set this
3362 The default parameter value of '0' causes the kernel
3363 not to attempt recovery of lost locks.
3365 nfs4.layoutstats_timer =
3366 [NFSv4.2] Change the rate at which the kernel sends
3367 layoutstats to the pNFS metadata server.
3369 Setting this to value to 0 causes the kernel to use
3370 whatever value is the default set by the layout
3371 driver. A non-zero value sets the minimum interval
3372 in seconds between layoutstats transmissions.
3374 nfsd.inter_copy_offload_enable =
3375 [NFSv4.2] When set to 1, the server will support
3376 server-to-server copies for which this server is
3377 the destination of the copy.
3379 nfsd.nfsd4_ssc_umount_timeout =
3380 [NFSv4.2] When used as the destination of a
3381 server-to-server copy, knfsd temporarily mounts
3382 the source server. It caches the mount in case
3383 it will be needed again, and discards it if not
3384 used for the number of milliseconds specified by
3387 nfsd.nfs4_disable_idmapping=
3388 [NFSv4] When set to the default of '1', the NFSv4
3389 server will return only numeric uids and gids to
3390 clients using auth_sys, and will accept numeric uids
3391 and gids from such clients. This is intended to ease
3392 migration from NFSv2/v3.
3395 nmi_backtrace.backtrace_idle [KNL]
3396 Dump stacks even of idle CPUs in response to an
3397 NMI stack-backtrace request.
3399 nmi_debug= [KNL,SH] Specify one or more actions to take
3400 when a NMI is triggered.
3401 Format: [state][,regs][,debounce][,die]
3403 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
3404 Format: [panic,][nopanic,][num]
3406 0 - turn hardlockup detector in nmi_watchdog off
3407 1 - turn hardlockup detector in nmi_watchdog on
3408 When panic is specified, panic when an NMI watchdog
3409 timeout occurs (or 'nopanic' to not panic on an NMI
3410 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set)
3411 To disable both hard and soft lockup detectors,
3412 please see 'nowatchdog'.
3413 This is useful when you use a panic=... timeout and
3414 need the box quickly up again.
3416 These settings can be accessed at runtime via
3417 the nmi_watchdog and hardlockup_panic sysctls.
3419 netpoll.carrier_timeout=
3420 [NET] Specifies amount of time (in seconds) that
3421 netpoll should wait for a carrier. By default netpoll
3424 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
3425 emulation library even if a 387 maths coprocessor
3428 no5lvl [X86-64] Disable 5-level paging mode. Forces
3429 kernel to use 4-level paging instead.
3431 nofsgsbase [X86] Disables FSGSBASE instructions.
3434 [HW] Never suspend the console
3435 Disable suspending of consoles during suspend and
3436 hibernate operations. Once disabled, debugging
3437 messages can reach various consoles while the rest
3438 of the system is being put to sleep (ie, while
3439 debugging driver suspend/resume hooks). This may
3440 not work reliably with all consoles, but is known
3441 to work with serial and VGA consoles.
3442 To facilitate more flexible debugging, we also add
3443 console_suspend, a printk module parameter to control
3444 it. Users could use console_suspend (usually
3445 /sys/module/printk/parameters/console_suspend) to
3446 turn on/off it dynamically.
3448 novmcoredd [KNL,KDUMP]
3449 Disable device dump. Device dump allows drivers to
3450 append dump data to vmcore so you can collect driver
3451 specified debug info. Drivers can append the data
3452 without any limit and this data is stored in memory,
3453 so this may cause significant memory stress. Disabling
3454 device dump can help save memory but the driver debug
3455 data will be no longer available. This parameter
3456 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP
3459 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
3460 caches in the slab allocator. Saves per-node memory,
3461 but will impact performance.
3465 noaltinstr [S390] Disables alternative instructions patching
3466 (CPU alternatives feature).
3468 noapic [SMP,APIC] Tells the kernel to not make use of any
3469 IOAPICs that may be present in the system.
3471 noautogroup Disable scheduler automatic task group creation.
3473 nobats [PPC] Do not use BATs for mapping kernel lowmem
3474 on "Classic" PPC cores.
3478 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
3480 delayacct [KNL] Enable per-task delay accounting
3482 nodsp [SH] Disable hardware DSP at boot time.
3484 noefi Disable EFI runtime services support.
3486 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel.
3491 On X86-32 available only on PAE configured kernels.
3492 noexec=on: enable non-executable mappings (default)
3493 noexec=off: disable non-executable mappings
3496 Disable SMAP (Supervisor Mode Access Prevention)
3497 even if it is supported by processor.
3500 Disable SMEP (Supervisor Mode Execution Prevention)
3501 even if it is supported by processor.
3504 This affects only 32-bit executables.
3505 noexec32=on: enable non-executable mappings (default)
3506 read doesn't imply executable mappings
3507 noexec32=off: disable non-executable mappings
3508 read implies executable mappings
3510 nofpu [MIPS,SH] Disable hardware FPU at boot time.
3512 nofxsr [BUGS=X86-32] Disables x86 floating point extended
3513 register save and restore. The kernel will only save
3514 legacy floating-point registers on task switch.
3516 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings.
3518 nohugevmalloc [PPC] Disable kernel huge vmalloc mappings.
3520 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
3521 Equivalent to smt=1.
3523 [KNL,X86] Disable symmetric multithreading (SMT).
3524 nosmt=force: Force disable SMT, cannot be undone
3525 via the sysfs control file.
3527 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
3528 (bounds check bypass). With this option data leaks are
3529 possible in the system.
3531 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
3532 the Spectre variant 2 (indirect branch prediction)
3533 vulnerability. System may allow data leaks with this
3536 nospec_store_bypass_disable
3537 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
3540 [PPC] Don't flush the L1-D cache after accessing user data.
3542 noxsave [BUGS=X86] Disables x86 extended register state save
3543 and restore using xsave. The kernel will fallback to
3544 enabling legacy floating-point and sse state.
3546 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
3547 register states. The kernel will fall back to use
3548 xsave to save the states. By using this parameter,
3549 performance of saving the states is degraded because
3550 xsave doesn't support modified optimization while
3551 xsaveopt supports it on xsaveopt enabled systems.
3553 noxsaves [X86] Disables xsaves and xrstors used in saving and
3554 restoring x86 extended register state in compacted
3555 form of xsave area. The kernel will fall back to use
3556 xsaveopt and xrstor to save and restore the states
3557 in standard form of xsave area. By using this
3558 parameter, xsave area per process might occupy more
3559 memory on xsaves enabled systems.
3561 nohlt [ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait
3562 in do_idle() and not use the arch_cpu_idle()
3563 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
3564 to be effective. This is useful on platforms where the
3565 sleep(SH) or wfi(ARM,ARM64) instructions do not work
3566 correctly or when doing power measurements to evalute
3567 the impact of the sleep instructions. This is also
3568 useful when using JTAG debugger.
3570 no_file_caps Tells the kernel not to honor file capabilities. The
3571 only way then for a file to be executed with privilege
3572 is to be setuid root or executed by root.
3574 nohalt [IA-64] Tells the kernel not to use the power saving
3575 function PAL_HALT_LIGHT when idle. This increases
3576 power-consumption. On the positive side, it reduces
3577 interrupt wake-up latency, which may improve performance
3578 in certain environments such as networked servers or
3582 Force pointers printed to the console or buffers to be
3583 unhashed. By default, when a pointer is printed via %p
3584 format string, that pointer is "hashed", i.e. obscured
3585 by hashing the pointer value. This is a security feature
3586 that hides actual kernel addresses from unprivileged
3587 users, but it also makes debugging the kernel more
3588 difficult since unequal pointers can no longer be
3589 compared. However, if this command-line option is
3590 specified, then all normal pointers will have their true
3591 value printed. This option should only be specified when
3592 debugging the kernel. Please do not use on production
3595 nohibernate [HIBERNATION] Disable hibernation and resume.
3597 nohz= [KNL] Boottime enable/disable dynamic ticks
3598 Valid arguments: on, off
3601 nohz_full= [KNL,BOOT,SMP,ISOL]
3602 The argument is a cpu list, as described above.
3603 In kernels built with CONFIG_NO_HZ_FULL=y, set
3604 the specified list of CPUs whose tick will be stopped
3605 whenever possible. The boot CPU will be forced outside
3606 the range to maintain the timekeeping. Any CPUs
3607 in this list will have their RCU callbacks offloaded,
3608 just as if they had also been called out in the
3609 rcu_nocbs= boot parameter.
3611 noiotrap [SH] Disables trapped I/O port accesses.
3613 noirqdebug [X86-32] Disables the code which attempts to detect and
3614 disable unhandled interrupt sources.
3616 no_timer_check [X86,APIC] Disables the code which tests for
3617 broken timer IRQ sources.
3619 noisapnp [ISAPNP] Disables ISA PnP code.
3621 noinitrd [RAM] Tells the kernel not to load any configured
3624 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
3626 [Deprecated - use intremap=off]
3630 noinvpcid [X86] Disable the INVPCID cpu feature.
3632 nojitter [IA-64] Disables jitter checking for ITC timers.
3634 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
3636 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
3640 [X86,PV_OPS] Disable paravirtualized VMware scheduler
3641 clock and use the default one.
3643 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time
3644 accounting. steal time is computed, but won't
3645 influence scheduler behaviour
3647 nolapic [X86-32,APIC] Do not enable or use the local APIC.
3649 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
3651 noltlbs [PPC] Do not use large page/tlb entries for kernel
3652 lowmem mapping on PPC40x and PPC8xx
3654 nomca [IA-64] Disable machine check abort handling
3656 nomce [X86-32] Disable Machine Check Exception
3658 nomfgpt [X86-32] Disable Multi-Function General Purpose
3659 Timer usage (for AMD Geode machines).
3661 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
3662 shutdown the other cpus. Instead use the REBOOT_VECTOR
3665 nomodeset Disable kernel modesetting. DRM drivers will not perform
3666 display-mode changes or accelerated rendering. Only the
3667 system framebuffer will be available for use if this was
3668 set-up by the firmware or boot loader.
3670 Useful as fallback, or for testing and debugging.
3672 nomodule Disable module load
3674 nopat [X86] Disable PAT (page attribute table extension of
3675 pagetables) support.
3677 nopcid [X86-64] Disable the PCID cpu feature.
3679 norandmaps Don't use address space randomization. Equivalent to
3680 echo 0 > /proc/sys/kernel/randomize_va_space
3682 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
3683 with UP alternatives
3685 nordrand [X86] Disable kernel use of the RDRAND and
3686 RDSEED instructions even if they are supported
3687 by the processor. RDRAND and RDSEED are still
3688 available to user space applications.
3690 noresume [SWSUSP] Disables resume and restores original swap
3693 no-scroll [VGA] Disables scrollback.
3694 This is required for the Braillex ib80-piezo Braille
3695 reader made by F.H. Papenmeier (Germany).
3699 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
3701 nosgx [X86-64,SGX] Disables Intel SGX kernel support.
3703 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
3704 and disable the IO APIC. legacy for "maxcpus=0".
3706 nosoftlockup [KNL] Disable the soft-lockup detector.
3708 nosync [HW,M68K] Disables sync negotiation for all devices.
3710 nowatchdog [KNL] Disable both lockup detectors, i.e.
3711 soft-lockup and NMI watchdog (hard-lockup).
3715 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
3717 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
3718 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
3719 Some features depend on CPU0. Known dependencies are:
3720 1. Resume from suspend/hibernate depends on CPU0.
3721 Suspend/hibernate will fail if CPU0 is offline and you
3722 need to online CPU0 before suspend/hibernate.
3723 2. PIC interrupts also depend on CPU0. CPU0 can't be
3724 removed if a PIC interrupt is detected.
3725 It's said poweroff/reboot may depend on CPU0 on some
3726 machines although I haven't seen such issues so far
3727 after CPU0 is offline on a few tested machines.
3728 If the dependencies are under your control, you can
3729 turn on cpu0_hotplug.
3731 nps_mtm_hs_ctr= [KNL,ARC]
3732 This parameter sets the maximum duration, in
3733 cycles, each HW thread of the CTOP can run
3734 without interruptions, before HW switches it.
3735 The actual maximum duration is 16 times this
3737 Format: integer between 1 and 255
3740 nptcg= [IA-64] Override max number of concurrent global TLB
3741 purges which is reported from either PAL_VM_SUMMARY or
3744 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3745 could support. nr_cpus=n : n >= 1 limits the kernel to
3746 support 'n' processors. It could be larger than the
3747 number of already plugged CPU during bootup, later in
3748 runtime you can physically add extra cpu until it reaches
3749 n. So during boot up some boot time memory for per-cpu
3750 variables need be pre-allocated for later physical cpu
3753 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3755 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only
3756 set up a single NUMA node spanning all memory.
3758 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
3760 Allowed values are enable and disable
3762 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3763 'node', 'default' can be specified
3764 This can be set from sysctl after boot.
3765 See Documentation/admin-guide/sysctl/vm.rst for details.
3767 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3768 See Documentation/core-api/debugging-via-ohci1394.rst for more
3771 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3772 Rather than timing out after 20 ms if an EC
3773 command is not properly ACKed, override the length
3774 of the timeout. We have interrupts disabled while
3775 waiting for the ACK, so if this is set too high
3776 interrupts *may* be lost!
3778 omap_mux= [OMAP] Override bootloader pin multiplexing.
3779 Format: <mux_mode0.mode_name=value>...
3780 For example, to override I2C bus2:
3781 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3783 oops=panic Always panic on oopses. Default is to just kill the
3784 process, but there is a small probability of
3785 deadlocking the machine.
3786 This will also cause panics on machine check exceptions.
3787 Useful together with panic=30 to trigger a reboot.
3790 [KNL] Boolean flag to control whether the page allocator
3791 should randomize its free lists. The randomization may
3792 be automatically enabled if the kernel detects it is
3793 running on a platform with a direct-mapped memory-side
3794 cache, and this parameter can be used to
3795 override/disable that behavior. The state of the flag
3796 can be read from sysfs at:
3797 /sys/module/page_alloc/parameters/shuffle.
3799 page_owner= [KNL] Boot-time page_owner enabling option.
3800 Storage of the information about who allocated
3801 each page is disabled in default. With this switch,
3803 on: enable the feature
3805 page_poison= [KNL] Boot-time parameter changing the state of
3806 poisoning on the buddy allocator, available with
3807 CONFIG_PAGE_POISONING=y.
3808 off: turn off poisoning (default)
3809 on: turn on poisoning
3811 page_reporting.page_reporting_order=
3812 [KNL] Minimal page reporting order
3814 Adjust the minimal page reporting order. The page
3815 reporting is disabled when it exceeds (MAX_ORDER-1).
3817 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3818 timeout > 0: seconds before rebooting
3819 timeout = 0: wait forever
3820 timeout < 0: reboot immediately
3823 panic_print= Bitmask for printing system info when panic happens.
3824 User can chose combination of the following bits:
3825 bit 0: print all tasks info
3826 bit 1: print system memory info
3827 bit 2: print timer info
3828 bit 3: print locks info if CONFIG_LOCKDEP is on
3829 bit 4: print ftrace buffer
3830 bit 5: print all printk messages in buffer
3831 bit 6: print all CPUs backtrace (if available in the arch)
3832 *Be aware* that this option may print a _lot_ of lines,
3833 so there are risks of losing older messages in the log.
3834 Use this option carefully, maybe worth to setup a
3835 bigger log buffer with "log_buf_len" along with this.
3837 panic_on_taint= Bitmask for conditionally calling panic() in add_taint()
3838 Format: <hex>[,nousertaint]
3839 Hexadecimal bitmask representing the set of TAINT flags
3840 that will cause the kernel to panic when add_taint() is
3841 called with any of the flags in this set.
3842 The optional switch "nousertaint" can be utilized to
3843 prevent userspace forced crashes by writing to sysctl
3844 /proc/sys/kernel/tainted any flagset matching with the
3845 bitmask set on panic_on_taint.
3846 See Documentation/admin-guide/tainted-kernels.rst for
3847 extra details on the taint flags that users can pick
3848 to compose the bitmask to assign to panic_on_taint.
3850 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3853 crash_kexec_post_notifiers
3854 Run kdump after running panic-notifiers and dumping
3855 kmsg. This only for the users who doubt kdump always
3856 succeeds in any situation.
3857 Note that this also increases risks of kdump failure,
3858 because some panic notifiers can make the crashed
3859 kernel more unstable.
3861 parkbd.port= [HW] Parallel port number the keyboard adapter is
3862 connected to, default is 0.
3864 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3865 0 for XT, 1 for AT (default is AT).
3868 parport= [HW,PPT] Specify parallel ports. 0 disables.
3869 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3870 Use 'auto' to force the driver to use any
3871 IRQ/DMA settings detected (the default is to
3872 ignore detected IRQ/DMA settings because of
3873 possible conflicts). You can specify the base
3874 address, IRQ, and DMA settings; IRQ and DMA
3875 should be numbers, or 'auto' (for using detected
3876 settings on that particular port), or 'nofifo'
3877 (to avoid using a FIFO even if it is detected).
3878 Parallel ports are assigned in the order they
3879 are specified on the command line, starting
3882 parport_init_mode= [HW,PPT]
3883 Configure VIA parallel port to operate in
3884 a specific mode. This is necessary on Pegasos
3885 computer where firmware has no options for setting
3886 up parallel port mode and sets it to spp.
3887 Currently this function knows 686a and 8231 chips.
3888 Format: [spp|ps2|epp|ecp|ecpepp]
3890 pata_legacy.all= [HW,LIBATA]
3892 Set to non-zero to probe primary and secondary ISA
3893 port ranges on PCI systems where no PCI PATA device
3894 has been found at either range. Disabled by default.
3896 pata_legacy.autospeed= [HW,LIBATA]
3898 Set to non-zero if a chip is present that snoops speed
3899 changes. Disabled by default.
3901 pata_legacy.ht6560a= [HW,LIBATA]
3903 Set to 1, 2, or 3 for HT 6560A on the primary channel,
3904 the secondary channel, or both channels respectively.
3905 Disabled by default.
3907 pata_legacy.ht6560b= [HW,LIBATA]
3909 Set to 1, 2, or 3 for HT 6560B on the primary channel,
3910 the secondary channel, or both channels respectively.
3911 Disabled by default.
3913 pata_legacy.iordy_mask= [HW,LIBATA]
3915 IORDY enable mask. Set individual bits to allow IORDY
3916 for the respective channel. Bit 0 is for the first
3917 legacy channel handled by this driver, bit 1 is for
3918 the second channel, and so on. The sequence will often
3919 correspond to the primary legacy channel, the secondary
3920 legacy channel, and so on, but the handling of a PCI
3921 bus and the use of other driver options may interfere
3922 with the sequence. By default IORDY is allowed across
3925 pata_legacy.opti82c46x= [HW,LIBATA]
3927 Set to 1, 2, or 3 for Opti 82c611A on the primary
3928 channel, the secondary channel, or both channels
3929 respectively. Disabled by default.
3931 pata_legacy.opti82c611a= [HW,LIBATA]
3933 Set to 1, 2, or 3 for Opti 82c465MV on the primary
3934 channel, the secondary channel, or both channels
3935 respectively. Disabled by default.
3937 pata_legacy.pio_mask= [HW,LIBATA]
3939 PIO mode mask for autospeed devices. Set individual
3940 bits to allow the use of the respective PIO modes.
3941 Bit 0 is for mode 0, bit 1 is for mode 1, and so on.
3942 All modes allowed by default.
3944 pata_legacy.probe_all= [HW,LIBATA]
3946 Set to non-zero to probe tertiary and further ISA
3947 port ranges on PCI systems. Disabled by default.
3949 pata_legacy.probe_mask= [HW,LIBATA]
3951 Probe mask for legacy ISA PATA ports. Depending on
3952 platform configuration and the use of other driver
3953 options up to 6 legacy ports are supported: 0x1f0,
3954 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing
3955 of individual ports can be disabled by setting the
3956 corresponding bits in the mask to 1. Bit 0 is for
3957 the first port in the list above (0x1f0), and so on.
3958 By default all supported ports are probed.
3960 pata_legacy.qdi= [HW,LIBATA]
3962 Set to non-zero to probe QDI controllers. By default
3963 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise.
3965 pata_legacy.winbond= [HW,LIBATA]
3967 Set to non-zero to probe Winbond controllers. Use
3968 the standard I/O port (0x130) if 1, otherwise the
3969 value given is the I/O port to use (typically 0x1b0).
3970 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE,
3973 pata_platform.pio_mask= [HW,LIBATA]
3975 Supported PIO mode mask. Set individual bits to allow
3976 the use of the respective PIO modes. Bit 0 is for
3977 mode 0, bit 1 is for mode 1, and so on. Mode 0 only
3981 Halt all CPUs after the first oops has been printed for
3982 the specified number of seconds. This is to be used if
3983 your oopses keep scrolling off the screen.
3988 See header of drivers/block/paride/pcd.c.
3989 See also Documentation/admin-guide/blockdev/paride.rst.
3991 pci=option[,option...] [PCI] various PCI subsystem options.
3993 Some options herein operate on a specific device
3994 or a set of devices (<pci_dev>). These are
3995 specified in one of the following formats:
3997 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3998 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
4000 Note: the first format specifies a PCI
4001 bus/device/function address which may change
4002 if new hardware is inserted, if motherboard
4003 firmware changes, or due to changes caused
4004 by other kernel parameters. If the
4005 domain is left unspecified, it is
4006 taken to be zero. Optionally, a path
4007 to a device through multiple device/function
4008 addresses can be specified after the base
4009 address (this is more robust against
4010 renumbering issues). The second format
4011 selects devices using IDs from the
4012 configuration space which may match multiple
4013 devices in the system.
4015 earlydump dump PCI config space before the kernel
4017 off [X86] don't probe for the PCI bus
4018 bios [X86-32] force use of PCI BIOS, don't access
4019 the hardware directly. Use this if your machine
4020 has a non-standard PCI host bridge.
4021 nobios [X86-32] disallow use of PCI BIOS, only direct
4022 hardware access methods are allowed. Use this
4023 if you experience crashes upon bootup and you
4024 suspect they are caused by the BIOS.
4025 conf1 [X86] Force use of PCI Configuration Access
4026 Mechanism 1 (config address in IO port 0xCF8,
4027 data in IO port 0xCFC, both 32-bit).
4028 conf2 [X86] Force use of PCI Configuration Access
4029 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
4030 the function, IO port 0xCFA, also 8-bit, sets
4031 bus number. The config space is then accessed
4032 through ports 0xC000-0xCFFF).
4033 See http://wiki.osdev.org/PCI for more info
4034 on the configuration access mechanisms.
4035 noaer [PCIE] If the PCIEAER kernel config parameter is
4036 enabled, this kernel boot option can be used to
4037 disable the use of PCIE advanced error reporting.
4038 nodomains [PCI] Disable support for multiple PCI
4039 root domains (aka PCI segments, in ACPI-speak).
4040 nommconf [X86] Disable use of MMCONFIG for PCI
4042 check_enable_amd_mmconf [X86] check for and enable
4043 properly configured MMIO access to PCI
4044 config space on AMD family 10h CPU
4045 nomsi [MSI] If the PCI_MSI kernel config parameter is
4046 enabled, this kernel boot option can be used to
4047 disable the use of MSI interrupts system-wide.
4048 noioapicquirk [APIC] Disable all boot interrupt quirks.
4049 Safety option to keep boot IRQs enabled. This
4050 should never be necessary.
4051 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
4052 primary IO-APIC for bridges that cannot disable
4053 boot IRQs. This fixes a source of spurious IRQs
4054 when the system masks IRQs.
4055 noioapicreroute [APIC] Disable workaround that uses the
4056 boot IRQ equivalent of an IRQ that connects to
4057 a chipset where boot IRQs cannot be disabled.
4058 The opposite of ioapicreroute.
4059 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
4060 routing table. These calls are known to be buggy
4061 on several machines and they hang the machine
4062 when used, but on other computers it's the only
4063 way to get the interrupt routing table. Try
4064 this option if the kernel is unable to allocate
4065 IRQs or discover secondary PCI buses on your
4067 rom [X86] Assign address space to expansion ROMs.
4068 Use with caution as certain devices share
4069 address decoders between ROMs and other
4071 norom [X86] Do not assign address space to
4072 expansion ROMs that do not already have
4073 BIOS assigned address ranges.
4074 nobar [X86] Do not assign address space to the
4075 BARs that weren't assigned by the BIOS.
4076 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
4077 assigned automatically to PCI devices. You can
4078 make the kernel exclude IRQs of your ISA cards
4080 pirqaddr=0xAAAAA [X86] Specify the physical address
4081 of the PIRQ table (normally generated
4082 by the BIOS) if it is outside the
4083 F0000h-100000h range.
4084 lastbus=N [X86] Scan all buses thru bus #N. Can be
4085 useful if the kernel is unable to find your
4086 secondary buses and you want to tell it
4087 explicitly which ones they are.
4088 assign-busses [X86] Always assign all PCI bus
4089 numbers ourselves, overriding
4090 whatever the firmware may have done.
4091 usepirqmask [X86] Honor the possible IRQ mask stored
4092 in the BIOS $PIR table. This is needed on
4093 some systems with broken BIOSes, notably
4094 some HP Pavilion N5400 and Omnibook XE3
4095 notebooks. This will have no effect if ACPI
4096 IRQ routing is enabled.
4097 noacpi [X86] Do not use ACPI for IRQ routing
4098 or for PCI scanning.
4099 use_crs [X86] Use PCI host bridge window information
4100 from ACPI. On BIOSes from 2008 or later, this
4101 is enabled by default. If you need to use this,
4102 please report a bug.
4103 nocrs [X86] Ignore PCI host bridge windows from ACPI.
4104 If you need to use this, please report a bug.
4105 routeirq Do IRQ routing for all PCI devices.
4106 This is normally done in pci_enable_device(),
4107 so this option is a temporary workaround
4108 for broken drivers that don't call it.
4109 skip_isa_align [X86] do not align io start addr, so can
4110 handle more pci cards
4111 noearly [X86] Don't do any early type 1 scanning.
4112 This might help on some broken boards which
4113 machine check when some devices' config space
4114 is read. But various workarounds are disabled
4115 and some IOMMU drivers will not work.
4116 bfsort Sort PCI devices into breadth-first order.
4117 This sorting is done to get a device
4118 order compatible with older (<= 2.4) kernels.
4119 nobfsort Don't sort PCI devices into breadth-first order.
4120 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
4121 tuning and use the BIOS-configured MPS defaults.
4122 pcie_bus_safe Set every device's MPS to the largest value
4123 supported by all devices below the root complex.
4124 pcie_bus_perf Set device MPS to the largest allowable MPS
4125 based on its parent bus. Also set MRRS (Max
4126 Read Request Size) to the largest supported
4127 value (no larger than the MPS that the device
4128 or bus can support) for best performance.
4129 pcie_bus_peer2peer Set every device's MPS to 128B, which
4130 every device is guaranteed to support. This
4131 configuration allows peer-to-peer DMA between
4132 any pair of devices, possibly at the cost of
4133 reduced performance. This also guarantees
4134 that hot-added devices will work.
4135 cbiosize=nn[KMG] The fixed amount of bus space which is
4136 reserved for the CardBus bridge's IO window.
4137 The default value is 256 bytes.
4138 cbmemsize=nn[KMG] The fixed amount of bus space which is
4139 reserved for the CardBus bridge's memory
4140 window. The default value is 64 megabytes.
4143 [<order of align>@]<pci_dev>[; ...]
4144 Specifies alignment and device to reassign
4145 aligned memory resources. How to
4146 specify the device is described above.
4147 If <order of align> is not specified,
4148 PAGE_SIZE is used as alignment.
4149 A PCI-PCI bridge can be specified if resource
4150 windows need to be expanded.
4151 To specify the alignment for several
4152 instances of a device, the PCI vendor,
4153 device, subvendor, and subdevice may be
4154 specified, e.g., 12@pci:8086:9c22:103c:198f
4155 for 4096-byte alignment.
4156 ecrc= Enable/disable PCIe ECRC (transaction layer
4157 end-to-end CRC checking).
4158 bios: Use BIOS/firmware settings. This is the
4162 hpiosize=nn[KMG] The fixed amount of bus space which is
4163 reserved for hotplug bridge's IO window.
4164 Default size is 256 bytes.
4165 hpmmiosize=nn[KMG] The fixed amount of bus space which is
4166 reserved for hotplug bridge's MMIO window.
4167 Default size is 2 megabytes.
4168 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is
4169 reserved for hotplug bridge's MMIO_PREF window.
4170 Default size is 2 megabytes.
4171 hpmemsize=nn[KMG] The fixed amount of bus space which is
4172 reserved for hotplug bridge's MMIO and
4174 Default size is 2 megabytes.
4175 hpbussize=nn The minimum amount of additional bus numbers
4176 reserved for buses below a hotplug bridge.
4178 realloc= Enable/disable reallocating PCI bridge resources
4179 if allocations done by BIOS are too small to
4180 accommodate resources required by all child
4182 off: Turn realloc off
4184 realloc same as realloc=on
4185 noari do not use PCIe ARI.
4186 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
4187 do not use PCIe ATS (and IOMMU device IOTLB).
4188 pcie_scan_all Scan all possible PCIe devices. Otherwise we
4189 only look for one device below a PCIe downstream
4191 big_root_window Try to add a big 64bit memory window to the PCIe
4192 root complex on AMD CPUs. Some GFX hardware
4193 can resize a BAR to allow access to all VRAM.
4194 Adding the window is slightly risky (it may
4195 conflict with unreported devices), so this
4197 disable_acs_redir=<pci_dev>[; ...]
4198 Specify one or more PCI devices (in the format
4199 specified above) separated by semicolons.
4200 Each device specified will have the PCI ACS
4201 redirect capabilities forced off which will
4202 allow P2P traffic between devices through
4203 bridges without forcing it upstream. Note:
4204 this removes isolation between devices and
4205 may put more devices in an IOMMU group.
4206 force_floating [S390] Force usage of floating interrupts.
4207 nomio [S390] Do not use MIO instructions.
4208 norid [S390] ignore the RID field and force use of
4209 one PCI domain per PCI function
4211 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
4214 force Enable ASPM even on devices that claim not to support it.
4215 WARNING: Forcing ASPM on may cause system lockups.
4217 pcie_ports= [PCIE] PCIe port services handling:
4218 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
4219 even if the platform doesn't give the OS permission to
4220 use them. This may cause conflicts if the platform
4221 also tries to use these services.
4222 dpc-native Use native PCIe service for DPC only. May
4223 cause conflicts if firmware uses AER or DPC.
4224 compat Disable native PCIe services (PME, AER, DPC, PCIe
4227 pcie_port_pm= [PCIE] PCIe port power management handling:
4228 off Disable power management of all PCIe ports
4229 force Forcibly enable power management of all PCIe ports
4231 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
4232 nomsi Do not use MSI for native PCIe PME signaling (this makes
4233 all PCIe root ports use INTx for all services).
4235 pcmv= [HW,PCMCIA] BadgePAD 4
4239 Keep all power-domains already enabled by bootloader on,
4240 even if no driver has claimed them. This is useful
4241 for debug and development, but should not be
4242 needed on a platform with proper driver support.
4245 See Documentation/admin-guide/blockdev/paride.rst.
4247 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
4250 See arch/parisc/kernel/pdc_chassis.c
4252 percpu_alloc= Select which percpu first chunk allocator to use.
4253 Currently supported values are "embed" and "page".
4254 Archs may support subset or none of the selections.
4255 See comments in mm/percpu.c for details on each
4256 allocator. This parameter is primarily for debugging
4257 and performance comparison.
4260 See Documentation/admin-guide/blockdev/paride.rst.
4263 See Documentation/admin-guide/blockdev/paride.rst.
4265 pirq= [SMP,APIC] Manual mp-table setup
4266 See Documentation/x86/i386/IO-APIC.rst.
4268 plip= [PPT,NET] Parallel port network link
4269 Format: { parport<nr> | timid | 0 }
4270 See also Documentation/admin-guide/parport.rst.
4272 pmtmr= [X86] Manual setup of pmtmr I/O Port.
4273 Override pmtimer IOPort with a hex value.
4276 pmu_override= [PPC] Override the PMU.
4277 This option takes over the PMU facility, so it is no
4278 longer usable by perf. Setting this option starts the
4279 PMU counters by setting MMCR0 to 0 (the FC bit is
4280 cleared). If a number is given, then MMCR1 is set to
4281 that number, otherwise (e.g., 'pmu_override=on'), MMCR1
4284 pm_debug_messages [SUSPEND,KNL]
4285 Enable suspend/resume debug messages during boot up.
4288 Enable PNP debug messages (depends on the
4289 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
4290 via /sys/module/pnp/parameters/debug. We always show
4291 current resource usage; turning this on also shows
4292 possible settings and some assignment information.
4298 { on | off | curr | res | no-curr | no-res }
4301 [ISAPNP] Exclude IRQs for the autoconfiguration
4304 [ISAPNP] Exclude DMAs for the autoconfiguration
4306 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
4307 Ranges are in pairs (I/O port base and size).
4310 [ISAPNP] Exclude memory regions for the
4312 Ranges are in pairs (memory base and size).
4314 ports= [IP_VS_FTP] IPVS ftp helper module
4316 Up to 8 (IP_VS_APP_MAX_PORTS) ports
4318 Format: <port>,<port>....
4320 powersave=off [PPC] This option disables power saving features.
4321 It specifically disables cpuidle and sets the
4322 platform machine description specific power_save
4323 function to NULL. On Idle the CPU just reduces
4326 ppc_strict_facility_enable
4327 [PPC] This option catches any kernel floating point,
4328 Altivec, VSX and SPE outside of regions specifically
4329 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
4330 There is some performance impact when enabling this.
4334 Disable Hardware Transactional Memory
4337 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
4338 none - Limited to cond_resched() calls
4339 voluntary - Limited to cond_resched() and might_sleep() calls
4340 full - Any section that isn't explicitly preempt disabled
4341 can be preempted anytime.
4343 print-fatal-signals=
4344 [KNL] debug: print fatal signals
4346 If enabled, warn about various signal handling
4347 related application anomalies: too many signals,
4348 too many POSIX.1 timers, fatal signals causing a
4351 If you hit the warning due to signal overflow,
4352 you might want to try "ulimit -i unlimited".
4356 printk.always_kmsg_dump=
4357 Trigger kmsg_dump for cases other than kernel oops or
4359 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4362 printk.console_no_auto_verbose=
4363 Disable console loglevel raise on oops, panic
4364 or lockdep-detected issues (only if lock debug is on).
4365 With an exception to setups with low baudrate on
4366 serial console, keeping this 0 is a good choice
4367 in order to provide more debug information.
4369 default: 0 (auto_verbose is enabled)
4371 printk.devkmsg={on,off,ratelimit}
4372 Control writing to /dev/kmsg.
4373 on - unlimited logging to /dev/kmsg from userspace
4374 off - logging to /dev/kmsg disabled
4375 ratelimit - ratelimit the logging
4378 printk.time= Show timing data prefixed to each printk message line
4379 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4381 processor.max_cstate= [HW,ACPI]
4382 Limit processor to maximum C-state
4383 max_cstate=9 overrides any DMI blacklist limit.
4385 processor.nocst [HW,ACPI]
4386 Ignore the _CST method to determine C-states,
4387 instead using the legacy FADT method
4389 profile= [KNL] Enable kernel profiling via /proc/profile
4390 Format: [<profiletype>,]<number>
4391 Param: <profiletype>: "schedule", "sleep", or "kvm"
4392 [defaults to kernel profiling]
4393 Param: "schedule" - profile schedule points.
4394 Param: "sleep" - profile D-state sleeping (millisecs).
4395 Requires CONFIG_SCHEDSTATS
4396 Param: "kvm" - profile VM exits.
4397 Param: <number> - step/bucket size as a power of 2 for
4398 statistical time based profiling.
4400 prompt_ramdisk= [RAM] [Deprecated]
4402 prot_virt= [S390] enable hosting protected virtual machines
4403 isolated from the hypervisor (if hardware supports
4407 psi= [KNL] Enable or disable pressure stall information
4411 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
4412 probe for; one of (bare|imps|exps|lifebook|any).
4413 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
4415 psmouse.resetafter= [HW,MOUSE]
4416 Try to reset the device after so many bad packets
4419 [HW,MOUSE] Set desired mouse resolution, in dpi.
4420 psmouse.smartscroll=
4421 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
4422 0 = disabled, 1 = enabled (default).
4424 pstore.backend= Specify the name of the pstore backend to use
4427 See Documentation/admin-guide/blockdev/paride.rst.
4429 pti= [X86-64] Control Page Table Isolation of user and
4430 kernel address spaces. Disabling this feature
4431 removes hardening, but improves performance of
4432 system calls and interrupts.
4434 on - unconditionally enable
4435 off - unconditionally disable
4436 auto - kernel detects whether your CPU model is
4437 vulnerable to issues that PTI mitigates
4439 Not specifying this option is equivalent to pti=auto.
4442 Equivalent to pti=off
4445 [KNL] Number of legacy pty's. Overwrites compiled-in
4448 quiet [KNL] Disable most log messages
4453 See Documentation/admin-guide/md.rst.
4455 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
4456 See Documentation/admin-guide/blockdev/ramdisk.rst.
4458 ramdisk_start= [RAM] RAM disk image start address
4460 random.trust_cpu={on,off}
4461 [KNL] Enable or disable trusting the use of the
4462 CPU's random number generator (if available) to
4463 fully seed the kernel's CRNG. Default is controlled
4464 by CONFIG_RANDOM_TRUST_CPU.
4466 random.trust_bootloader={on,off}
4467 [KNL] Enable or disable trusting the use of a
4468 seed passed by the bootloader (if available) to
4469 fully seed the kernel's CRNG. Default is controlled
4470 by CONFIG_RANDOM_TRUST_BOOTLOADER.
4472 randomize_kstack_offset=
4473 [KNL] Enable or disable kernel stack offset
4474 randomization, which provides roughly 5 bits of
4475 entropy, frustrating memory corruption attacks
4476 that depend on stack address determinism or
4477 cross-syscall address exposures. This is only
4478 available on architectures that have defined
4479 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET.
4480 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
4481 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT.
4483 ras=option[,option,...] [KNL] RAS-specific options
4486 Disable the Correctable Errors Collector,
4487 see CONFIG_RAS_CEC help text.
4489 rcu_nocbs[=cpu-list]
4490 [KNL] The optional argument is a cpu list,
4493 In kernels built with CONFIG_RCU_NOCB_CPU=y,
4494 enable the no-callback CPU mode, which prevents
4495 such CPUs' callbacks from being invoked in
4496 softirq context. Invocation of such CPUs' RCU
4497 callbacks will instead be offloaded to "rcuox/N"
4498 kthreads created for that purpose, where "x" is
4499 "p" for RCU-preempt, "s" for RCU-sched, and "g"
4500 for the kthreads that mediate grace periods; and
4501 "N" is the CPU number. This reduces OS jitter on
4502 the offloaded CPUs, which can be useful for HPC
4503 and real-time workloads. It can also improve
4504 energy efficiency for asymmetric multiprocessors.
4506 If a cpulist is passed as an argument, the specified
4507 list of CPUs is set to no-callback mode from boot.
4509 Otherwise, if the '=' sign and the cpulist
4510 arguments are omitted, no CPU will be set to
4511 no-callback mode from boot but the mode may be
4512 toggled at runtime via cpusets.
4515 Rather than requiring that offloaded CPUs
4516 (specified by rcu_nocbs= above) explicitly
4517 awaken the corresponding "rcuoN" kthreads,
4518 make these kthreads poll for callbacks.
4519 This improves the real-time response for the
4520 offloaded CPUs by relieving them of the need to
4521 wake up the corresponding kthread, but degrades
4522 energy efficiency by requiring that the kthreads
4523 periodically wake up to do the polling.
4525 rcutree.blimit= [KNL]
4526 Set maximum number of finished RCU callbacks to
4527 process in one batch.
4529 rcutree.dump_tree= [KNL]
4530 Dump the structure of the rcu_node combining tree
4531 out at early boot. This is used for diagnostic
4532 purposes, to verify correct tree setup.
4534 rcutree.gp_cleanup_delay= [KNL]
4535 Set the number of jiffies to delay each step of
4536 RCU grace-period cleanup.
4538 rcutree.gp_init_delay= [KNL]
4539 Set the number of jiffies to delay each step of
4540 RCU grace-period initialization.
4542 rcutree.gp_preinit_delay= [KNL]
4543 Set the number of jiffies to delay each step of
4544 RCU grace-period pre-initialization, that is,
4545 the propagation of recent CPU-hotplug changes up
4546 the rcu_node combining tree.
4548 rcutree.use_softirq= [KNL]
4549 If set to zero, move all RCU_SOFTIRQ processing to
4550 per-CPU rcuc kthreads. Defaults to a non-zero
4551 value, meaning that RCU_SOFTIRQ is used by default.
4552 Specify rcutree.use_softirq=0 to use rcuc kthreads.
4554 But note that CONFIG_PREEMPT_RT=y kernels disable
4555 this kernel boot parameter, forcibly setting it
4558 rcutree.rcu_fanout_exact= [KNL]
4559 Disable autobalancing of the rcu_node combining
4560 tree. This is used by rcutorture, and might
4561 possibly be useful for architectures having high
4562 cache-to-cache transfer latencies.
4564 rcutree.rcu_fanout_leaf= [KNL]
4565 Change the number of CPUs assigned to each
4566 leaf rcu_node structure. Useful for very
4567 large systems, which will choose the value 64,
4568 and for NUMA systems with large remote-access
4569 latencies, which will choose a value aligned
4570 with the appropriate hardware boundaries.
4572 rcutree.rcu_min_cached_objs= [KNL]
4573 Minimum number of objects which are cached and
4574 maintained per one CPU. Object size is equal
4575 to PAGE_SIZE. The cache allows to reduce the
4576 pressure to page allocator, also it makes the
4577 whole algorithm to behave better in low memory
4580 rcutree.rcu_delay_page_cache_fill_msec= [KNL]
4581 Set the page-cache refill delay (in milliseconds)
4582 in response to low-memory conditions. The range
4583 of permitted values is in the range 0:100000.
4585 rcutree.jiffies_till_first_fqs= [KNL]
4586 Set delay from grace-period initialization to
4587 first attempt to force quiescent states.
4588 Units are jiffies, minimum value is zero,
4589 and maximum value is HZ.
4591 rcutree.jiffies_till_next_fqs= [KNL]
4592 Set delay between subsequent attempts to force
4593 quiescent states. Units are jiffies, minimum
4594 value is one, and maximum value is HZ.
4596 rcutree.jiffies_till_sched_qs= [KNL]
4597 Set required age in jiffies for a
4598 given grace period before RCU starts
4599 soliciting quiescent-state help from
4600 rcu_note_context_switch() and cond_resched().
4601 If not specified, the kernel will calculate
4602 a value based on the most recent settings
4603 of rcutree.jiffies_till_first_fqs
4604 and rcutree.jiffies_till_next_fqs.
4605 This calculated value may be viewed in
4606 rcutree.jiffies_to_sched_qs. Any attempt to set
4607 rcutree.jiffies_to_sched_qs will be cheerfully
4610 rcutree.kthread_prio= [KNL,BOOT]
4611 Set the SCHED_FIFO priority of the RCU per-CPU
4612 kthreads (rcuc/N). This value is also used for
4613 the priority of the RCU boost threads (rcub/N)
4614 and for the RCU grace-period kthreads (rcu_bh,
4615 rcu_preempt, and rcu_sched). If RCU_BOOST is
4616 set, valid values are 1-99 and the default is 1
4617 (the least-favored priority). Otherwise, when
4618 RCU_BOOST is not set, valid values are 0-99 and
4619 the default is zero (non-realtime operation).
4620 When RCU_NOCB_CPU is set, also adjust the
4621 priority of NOCB callback kthreads.
4623 rcutree.rcu_nocb_gp_stride= [KNL]
4624 Set the number of NOCB callback kthreads in
4625 each group, which defaults to the square root
4626 of the number of CPUs. Larger numbers reduce
4627 the wakeup overhead on the global grace-period
4628 kthread, but increases that same overhead on
4629 each group's NOCB grace-period kthread.
4631 rcutree.qhimark= [KNL]
4632 Set threshold of queued RCU callbacks beyond which
4633 batch limiting is disabled.
4635 rcutree.qlowmark= [KNL]
4636 Set threshold of queued RCU callbacks below which
4637 batch limiting is re-enabled.
4639 rcutree.qovld= [KNL]
4640 Set threshold of queued RCU callbacks beyond which
4641 RCU's force-quiescent-state scan will aggressively
4642 enlist help from cond_resched() and sched IPIs to
4643 help CPUs more quickly reach quiescent states.
4644 Set to less than zero to make this be set based
4645 on rcutree.qhimark at boot time and to zero to
4646 disable more aggressive help enlistment.
4648 rcutree.rcu_kick_kthreads= [KNL]
4649 Cause the grace-period kthread to get an extra
4650 wake_up() if it sleeps three times longer than
4651 it should at force-quiescent-state time.
4652 This wake_up() will be accompanied by a
4653 WARN_ONCE() splat and an ftrace_dump().
4655 rcutree.rcu_unlock_delay= [KNL]
4656 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels,
4657 this specifies an rcu_read_unlock()-time delay
4658 in microseconds. This defaults to zero.
4659 Larger delays increase the probability of
4660 catching RCU pointer leaks, that is, buggy use
4661 of RCU-protected pointers after the relevant
4662 rcu_read_unlock() has completed.
4664 rcutree.sysrq_rcu= [KNL]
4665 Commandeer a sysrq key to dump out Tree RCU's
4666 rcu_node tree with an eye towards determining
4667 why a new grace period has not yet started.
4669 rcuscale.gp_async= [KNL]
4670 Measure performance of asynchronous
4671 grace-period primitives such as call_rcu().
4673 rcuscale.gp_async_max= [KNL]
4674 Specify the maximum number of outstanding
4675 callbacks per writer thread. When a writer
4676 thread exceeds this limit, it invokes the
4677 corresponding flavor of rcu_barrier() to allow
4678 previously posted callbacks to drain.
4680 rcuscale.gp_exp= [KNL]
4681 Measure performance of expedited synchronous
4682 grace-period primitives.
4684 rcuscale.holdoff= [KNL]
4685 Set test-start holdoff period. The purpose of
4686 this parameter is to delay the start of the
4687 test until boot completes in order to avoid
4690 rcuscale.kfree_rcu_test= [KNL]
4691 Set to measure performance of kfree_rcu() flooding.
4693 rcuscale.kfree_rcu_test_double= [KNL]
4694 Test the double-argument variant of kfree_rcu().
4695 If this parameter has the same value as
4696 rcuscale.kfree_rcu_test_single, both the single-
4697 and double-argument variants are tested.
4699 rcuscale.kfree_rcu_test_single= [KNL]
4700 Test the single-argument variant of kfree_rcu().
4701 If this parameter has the same value as
4702 rcuscale.kfree_rcu_test_double, both the single-
4703 and double-argument variants are tested.
4705 rcuscale.kfree_nthreads= [KNL]
4706 The number of threads running loops of kfree_rcu().
4708 rcuscale.kfree_alloc_num= [KNL]
4709 Number of allocations and frees done in an iteration.
4711 rcuscale.kfree_loops= [KNL]
4712 Number of loops doing rcuscale.kfree_alloc_num number
4713 of allocations and frees.
4715 rcuscale.nreaders= [KNL]
4716 Set number of RCU readers. The value -1 selects
4717 N, where N is the number of CPUs. A value
4718 "n" less than -1 selects N-n+1, where N is again
4719 the number of CPUs. For example, -2 selects N
4720 (the number of CPUs), -3 selects N+1, and so on.
4721 A value of "n" less than or equal to -N selects
4724 rcuscale.nwriters= [KNL]
4725 Set number of RCU writers. The values operate
4726 the same as for rcuscale.nreaders.
4727 N, where N is the number of CPUs
4729 rcuscale.perf_type= [KNL]
4730 Specify the RCU implementation to test.
4732 rcuscale.shutdown= [KNL]
4733 Shut the system down after performance tests
4734 complete. This is useful for hands-off automated
4737 rcuscale.verbose= [KNL]
4738 Enable additional printk() statements.
4740 rcuscale.writer_holdoff= [KNL]
4741 Write-side holdoff between grace periods,
4742 in microseconds. The default of zero says
4745 rcutorture.fqs_duration= [KNL]
4746 Set duration of force_quiescent_state bursts
4749 rcutorture.fqs_holdoff= [KNL]
4750 Set holdoff time within force_quiescent_state bursts
4753 rcutorture.fqs_stutter= [KNL]
4754 Set wait time between force_quiescent_state bursts
4757 rcutorture.fwd_progress= [KNL]
4758 Specifies the number of kthreads to be used
4759 for RCU grace-period forward-progress testing
4760 for the types of RCU supporting this notion.
4761 Defaults to 1 kthread, values less than zero or
4762 greater than the number of CPUs cause the number
4765 rcutorture.fwd_progress_div= [KNL]
4766 Specify the fraction of a CPU-stall-warning
4767 period to do tight-loop forward-progress testing.
4769 rcutorture.fwd_progress_holdoff= [KNL]
4770 Number of seconds to wait between successive
4771 forward-progress tests.
4773 rcutorture.fwd_progress_need_resched= [KNL]
4774 Enclose cond_resched() calls within checks for
4775 need_resched() during tight-loop forward-progress
4778 rcutorture.gp_cond= [KNL]
4779 Use conditional/asynchronous update-side
4780 primitives, if available.
4782 rcutorture.gp_exp= [KNL]
4783 Use expedited update-side primitives, if available.
4785 rcutorture.gp_normal= [KNL]
4786 Use normal (non-expedited) asynchronous
4787 update-side primitives, if available.
4789 rcutorture.gp_sync= [KNL]
4790 Use normal (non-expedited) synchronous
4791 update-side primitives, if available. If all
4792 of rcutorture.gp_cond=, rcutorture.gp_exp=,
4793 rcutorture.gp_normal=, and rcutorture.gp_sync=
4794 are zero, rcutorture acts as if is interpreted
4795 they are all non-zero.
4797 rcutorture.irqreader= [KNL]
4798 Run RCU readers from irq handlers, or, more
4799 accurately, from a timer handler. Not all RCU
4800 flavors take kindly to this sort of thing.
4802 rcutorture.leakpointer= [KNL]
4803 Leak an RCU-protected pointer out of the reader.
4804 This can of course result in splats, and is
4805 intended to test the ability of things like
4806 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect
4809 rcutorture.n_barrier_cbs= [KNL]
4810 Set callbacks/threads for rcu_barrier() testing.
4812 rcutorture.nfakewriters= [KNL]
4813 Set number of concurrent RCU writers. These just
4814 stress RCU, they don't participate in the actual
4815 test, hence the "fake".
4817 rcutorture.nocbs_nthreads= [KNL]
4818 Set number of RCU callback-offload togglers.
4819 Zero (the default) disables toggling.
4821 rcutorture.nocbs_toggle= [KNL]
4822 Set the delay in milliseconds between successive
4823 callback-offload toggling attempts.
4825 rcutorture.nreaders= [KNL]
4826 Set number of RCU readers. The value -1 selects
4827 N-1, where N is the number of CPUs. A value
4828 "n" less than -1 selects N-n-2, where N is again
4829 the number of CPUs. For example, -2 selects N
4830 (the number of CPUs), -3 selects N+1, and so on.
4832 rcutorture.object_debug= [KNL]
4833 Enable debug-object double-call_rcu() testing.
4835 rcutorture.onoff_holdoff= [KNL]
4836 Set time (s) after boot for CPU-hotplug testing.
4838 rcutorture.onoff_interval= [KNL]
4839 Set time (jiffies) between CPU-hotplug operations,
4840 or zero to disable CPU-hotplug testing.
4842 rcutorture.read_exit= [KNL]
4843 Set the number of read-then-exit kthreads used
4844 to test the interaction of RCU updaters and
4845 task-exit processing.
4847 rcutorture.read_exit_burst= [KNL]
4848 The number of times in a given read-then-exit
4849 episode that a set of read-then-exit kthreads
4852 rcutorture.read_exit_delay= [KNL]
4853 The delay, in seconds, between successive
4854 read-then-exit testing episodes.
4856 rcutorture.shuffle_interval= [KNL]
4857 Set task-shuffle interval (s). Shuffling tasks
4858 allows some CPUs to go into dyntick-idle mode
4859 during the rcutorture test.
4861 rcutorture.shutdown_secs= [KNL]
4862 Set time (s) after boot system shutdown. This
4863 is useful for hands-off automated testing.
4865 rcutorture.stall_cpu= [KNL]
4866 Duration of CPU stall (s) to test RCU CPU stall
4867 warnings, zero to disable.
4869 rcutorture.stall_cpu_block= [KNL]
4870 Sleep while stalling if set. This will result
4871 in warnings from preemptible RCU in addition
4872 to any other stall-related activity.
4874 rcutorture.stall_cpu_holdoff= [KNL]
4875 Time to wait (s) after boot before inducing stall.
4877 rcutorture.stall_cpu_irqsoff= [KNL]
4878 Disable interrupts while stalling if set.
4880 rcutorture.stall_gp_kthread= [KNL]
4881 Duration (s) of forced sleep within RCU
4882 grace-period kthread to test RCU CPU stall
4883 warnings, zero to disable. If both stall_cpu
4884 and stall_gp_kthread are specified, the
4885 kthread is starved first, then the CPU.
4887 rcutorture.stat_interval= [KNL]
4888 Time (s) between statistics printk()s.
4890 rcutorture.stutter= [KNL]
4891 Time (s) to stutter testing, for example, specifying
4892 five seconds causes the test to run for five seconds,
4893 wait for five seconds, and so on. This tests RCU's
4894 ability to transition abruptly to and from idle.
4896 rcutorture.test_boost= [KNL]
4897 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
4898 "Maybe" means test if the RCU implementation
4899 under test support RCU priority boosting.
4901 rcutorture.test_boost_duration= [KNL]
4902 Duration (s) of each individual boost test.
4904 rcutorture.test_boost_interval= [KNL]
4905 Interval (s) between each boost test.
4907 rcutorture.test_no_idle_hz= [KNL]
4908 Test RCU's dyntick-idle handling. See also the
4909 rcutorture.shuffle_interval parameter.
4911 rcutorture.torture_type= [KNL]
4912 Specify the RCU implementation to test.
4914 rcutorture.verbose= [KNL]
4915 Enable additional printk() statements.
4917 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL]
4918 Dump ftrace buffer after reporting RCU CPU
4921 rcupdate.rcu_cpu_stall_suppress= [KNL]
4922 Suppress RCU CPU stall warning messages.
4924 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL]
4925 Suppress RCU CPU stall warning messages and
4926 rcutorture writer stall warnings that occur
4927 during early boot, that is, during the time
4928 before the init task is spawned.
4930 rcupdate.rcu_cpu_stall_timeout= [KNL]
4931 Set timeout for RCU CPU stall warning messages.
4933 rcupdate.rcu_expedited= [KNL]
4934 Use expedited grace-period primitives, for
4935 example, synchronize_rcu_expedited() instead
4936 of synchronize_rcu(). This reduces latency,
4937 but can increase CPU utilization, degrade
4938 real-time latency, and degrade energy efficiency.
4939 No effect on CONFIG_TINY_RCU kernels.
4941 rcupdate.rcu_normal= [KNL]
4942 Use only normal grace-period primitives,
4943 for example, synchronize_rcu() instead of
4944 synchronize_rcu_expedited(). This improves
4945 real-time latency, CPU utilization, and
4946 energy efficiency, but can expose users to
4947 increased grace-period latency. This parameter
4948 overrides rcupdate.rcu_expedited. No effect on
4949 CONFIG_TINY_RCU kernels.
4951 rcupdate.rcu_normal_after_boot= [KNL]
4952 Once boot has completed (that is, after
4953 rcu_end_inkernel_boot() has been invoked), use
4954 only normal grace-period primitives. No effect
4955 on CONFIG_TINY_RCU kernels.
4957 But note that CONFIG_PREEMPT_RT=y kernels enables
4958 this kernel boot parameter, forcibly setting
4959 it to the value one, that is, converting any
4960 post-boot attempt at an expedited RCU grace
4961 period to instead use normal non-expedited
4962 grace-period processing.
4964 rcupdate.rcu_task_collapse_lim= [KNL]
4965 Set the maximum number of callbacks present
4966 at the beginning of a grace period that allows
4967 the RCU Tasks flavors to collapse back to using
4968 a single callback queue. This switching only
4969 occurs when rcupdate.rcu_task_enqueue_lim is
4970 set to the default value of -1.
4972 rcupdate.rcu_task_contend_lim= [KNL]
4973 Set the minimum number of callback-queuing-time
4974 lock-contention events per jiffy required to
4975 cause the RCU Tasks flavors to switch to per-CPU
4976 callback queuing. This switching only occurs
4977 when rcupdate.rcu_task_enqueue_lim is set to
4978 the default value of -1.
4980 rcupdate.rcu_task_enqueue_lim= [KNL]
4981 Set the number of callback queues to use for the
4982 RCU Tasks family of RCU flavors. The default
4983 of -1 allows this to be automatically (and
4984 dynamically) adjusted. This parameter is intended
4987 rcupdate.rcu_task_ipi_delay= [KNL]
4988 Set time in jiffies during which RCU tasks will
4989 avoid sending IPIs, starting with the beginning
4990 of a given grace period. Setting a large
4991 number avoids disturbing real-time workloads,
4992 but lengthens grace periods.
4994 rcupdate.rcu_task_stall_timeout= [KNL]
4995 Set timeout in jiffies for RCU task stall warning
4996 messages. Disable with a value less than or equal
4999 rcupdate.rcu_self_test= [KNL]
5000 Run the RCU early boot self tests
5004 Run specified binary instead of /init from the ramdisk,
5005 used for early userspace startup. See initrd.
5008 force - Override the decision by the kernel to hide the
5009 advertisement of RDRAND support (this affects
5010 certain AMD processors because of buggy BIOS
5011 support, specifically around the suspend/resume
5015 Turn on/off individual RDT features. List is:
5016 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
5018 E.g. to turn on cmt and turn off mba use:
5022 Format (x86 or x86_64):
5023 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \
5025 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
5027 Where reboot_mode is one of warm (soft) or cold (hard) or gpio
5028 (prefix with 'panic_' to set mode for panic
5030 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
5031 reboot_force is either force or not specified,
5032 reboot_cpu is s[mp]#### with #### being the processor
5033 to be used for rebooting.
5035 refscale.holdoff= [KNL]
5036 Set test-start holdoff period. The purpose of
5037 this parameter is to delay the start of the
5038 test until boot completes in order to avoid
5041 refscale.loops= [KNL]
5042 Set the number of loops over the synchronization
5043 primitive under test. Increasing this number
5044 reduces noise due to loop start/end overhead,
5045 but the default has already reduced the per-pass
5046 noise to a handful of picoseconds on ca. 2020
5049 refscale.nreaders= [KNL]
5050 Set number of readers. The default value of -1
5051 selects N, where N is roughly 75% of the number
5052 of CPUs. A value of zero is an interesting choice.
5054 refscale.nruns= [KNL]
5055 Set number of runs, each of which is dumped onto
5058 refscale.readdelay= [KNL]
5059 Set the read-side critical-section duration,
5060 measured in microseconds.
5062 refscale.scale_type= [KNL]
5063 Specify the read-protection implementation to test.
5065 refscale.shutdown= [KNL]
5066 Shut down the system at the end of the performance
5067 test. This defaults to 1 (shut it down) when
5068 refscale is built into the kernel and to 0 (leave
5069 it running) when refscale is built as a module.
5071 refscale.verbose= [KNL]
5072 Enable additional printk() statements.
5074 refscale.verbose_batched= [KNL]
5075 Batch the additional printk() statements. If zero
5076 (the default) or negative, print everything. Otherwise,
5077 print every Nth verbose statement, where N is the value
5081 [KNL, SMP] Set scheduler's default relax_domain_level.
5082 See Documentation/admin-guide/cgroup-v1/cpusets.rst.
5084 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
5085 Format: <base1>,<size1>[,<base2>,<size2>,...]
5086 Reserve I/O ports or memory so the kernel won't use
5087 them. If <base> is less than 0x10000, the region
5088 is assumed to be I/O ports; otherwise it is memory.
5090 reservetop= [X86-32]
5092 Reserves a hole at the top of the kernel virtual
5095 reset_devices [KNL] Force drivers to reset the underlying device
5096 during initialization.
5099 Specify the partition device for software suspend
5101 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
5103 resume_offset= [SWSUSP]
5104 Specify the offset from the beginning of the partition
5105 given by "resume=" at which the swap header is located,
5106 in <PAGE_SIZE> units (needed only for swap files).
5107 See Documentation/power/swsusp-and-swap-files.rst
5109 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
5110 read the resume files
5112 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
5113 Useful for devices that are detected asynchronously
5114 (e.g. USB and MMC devices).
5116 hibernate= [HIBERNATION]
5117 noresume Don't check if there's a hibernation image
5118 present during boot.
5119 nocompress Don't compress/decompress hibernation images.
5120 no Disable hibernation and resume.
5121 protect_image Turn on image protection during restoration
5122 (that will set all pages holding image data
5123 during restoration read-only).
5125 retain_initrd [RAM] Keep initrd memory after extraction
5127 rfkill.default_state=
5128 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
5129 etc. communication is blocked by default.
5132 rfkill.master_switch_mode=
5133 0 The "airplane mode" button does nothing.
5134 1 The "airplane mode" button toggles between everything
5135 blocked and the previous configuration.
5136 2 The "airplane mode" button toggles between everything
5137 blocked and everything unblocked.
5139 rhash_entries= [KNL,NET]
5140 Set number of hash buckets for route cache
5143 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
5146 ro [KNL] Mount root device read-only on boot
5149 on Mark read-only kernel memory as read-only (default).
5150 off Leave read-only kernel memory writable for debugging.
5153 Enable the uart passthrough on the designated usb port
5154 on Rockchip SoCs. When active, the signals of the
5155 debug-uart get routed to the D+ and D- pins of the usb
5156 port and the regular usb controller gets disabled.
5158 root= [KNL] Root filesystem
5159 See name_to_dev_t comment in init/do_mounts.c.
5161 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
5162 mount the root filesystem
5164 rootflags= [KNL] Set root filesystem mount option string
5166 rootfstype= [KNL] Set root filesystem type
5168 rootwait [KNL] Wait (indefinitely) for root device to show up.
5169 Useful for devices that are detected asynchronously
5170 (e.g. USB and MMC devices).
5172 rproc_mem=nn[KMG][@address]
5173 [KNL,ARM,CMA] Remoteproc physical memory block.
5174 Memory area to be used by remote processor image,
5177 rw [KNL] Mount root device read-write on boot
5179 S [KNL] Run init in single mode
5181 s390_iommu= [HW,S390]
5182 Set s390 IOTLB flushing mode
5184 With strict flushing every unmap operation will result in
5185 an IOTLB flush. Default is lazy flushing before reuse,
5188 s390_iommu_aperture= [KNL,S390]
5189 Specifies the size of the per device DMA address space
5190 accessible through the DMA and IOMMU APIs as a decimal
5191 factor of the size of main memory.
5192 The default is 1 meaning that one can concurrently use
5193 as many DMA addresses as physical memory is installed,
5194 if supported by hardware, and thus map all of memory
5195 once. With a value of 2 one can map all of memory twice
5196 and so on. As a special case a factor of 0 imposes no
5197 restrictions other than those given by hardware at the
5198 cost of significant additional memory use for tables.
5201 See drivers/net/irda/sa1100_ir.c.
5203 sched_verbose [KNL] Enables verbose scheduler debug messages.
5205 schedstats= [KNL,X86] Enable or disable scheduled statistics.
5206 Allowed values are enable and disable. This feature
5207 incurs a small amount of overhead in the scheduler
5208 but is useful for debugging and performance tuning.
5210 sched_thermal_decay_shift=
5211 [KNL, SMP] Set a decay shift for scheduler thermal
5212 pressure signal. Thermal pressure signal follows the
5213 default decay period of other scheduler pelt
5214 signals(usually 32 ms but configurable). Setting
5215 sched_thermal_decay_shift will left shift the decay
5216 period for the thermal pressure signal by the shift
5218 i.e. with the default pelt decay period of 32 ms
5219 sched_thermal_decay_shift thermal pressure decay pr
5223 Format: integer between 0 and 10
5226 scftorture.holdoff= [KNL]
5227 Number of seconds to hold off before starting
5228 test. Defaults to zero for module insertion and
5229 to 10 seconds for built-in smp_call_function()
5232 scftorture.longwait= [KNL]
5233 Request ridiculously long waits randomly selected
5234 up to the chosen limit in seconds. Zero (the
5235 default) disables this feature. Please note
5236 that requesting even small non-zero numbers of
5237 seconds can result in RCU CPU stall warnings,
5238 softlockup complaints, and so on.
5240 scftorture.nthreads= [KNL]
5241 Number of kthreads to spawn to invoke the
5242 smp_call_function() family of functions.
5243 The default of -1 specifies a number of kthreads
5244 equal to the number of CPUs.
5246 scftorture.onoff_holdoff= [KNL]
5247 Number seconds to wait after the start of the
5248 test before initiating CPU-hotplug operations.
5250 scftorture.onoff_interval= [KNL]
5251 Number seconds to wait between successive
5252 CPU-hotplug operations. Specifying zero (which
5253 is the default) disables CPU-hotplug operations.
5255 scftorture.shutdown_secs= [KNL]
5256 The number of seconds following the start of the
5257 test after which to shut down the system. The
5258 default of zero avoids shutting down the system.
5259 Non-zero values are useful for automated tests.
5261 scftorture.stat_interval= [KNL]
5262 The number of seconds between outputting the
5263 current test statistics to the console. A value
5264 of zero disables statistics output.
5266 scftorture.stutter_cpus= [KNL]
5267 The number of jiffies to wait between each change
5268 to the set of CPUs under test.
5270 scftorture.use_cpus_read_lock= [KNL]
5271 Use use_cpus_read_lock() instead of the default
5272 preempt_disable() to disable CPU hotplug
5273 while invoking one of the smp_call_function*()
5276 scftorture.verbose= [KNL]
5277 Enable additional printk() statements.
5279 scftorture.weight_single= [KNL]
5280 The probability weighting to use for the
5281 smp_call_function_single() function with a zero
5282 "wait" parameter. A value of -1 selects the
5283 default if all other weights are -1. However,
5284 if at least one weight has some other value, a
5285 value of -1 will instead select a weight of zero.
5287 scftorture.weight_single_wait= [KNL]
5288 The probability weighting to use for the
5289 smp_call_function_single() function with a
5290 non-zero "wait" parameter. See weight_single.
5292 scftorture.weight_many= [KNL]
5293 The probability weighting to use for the
5294 smp_call_function_many() function with a zero
5295 "wait" parameter. See weight_single.
5296 Note well that setting a high probability for
5297 this weighting can place serious IPI load
5300 scftorture.weight_many_wait= [KNL]
5301 The probability weighting to use for the
5302 smp_call_function_many() function with a
5303 non-zero "wait" parameter. See weight_single
5306 scftorture.weight_all= [KNL]
5307 The probability weighting to use for the
5308 smp_call_function_all() function with a zero
5309 "wait" parameter. See weight_single and
5312 scftorture.weight_all_wait= [KNL]
5313 The probability weighting to use for the
5314 smp_call_function_all() function with a
5315 non-zero "wait" parameter. See weight_single
5318 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
5319 xtime_lock contention on larger systems, and/or RCU lock
5320 contention on all systems with CONFIG_MAXSMP set.
5321 Format: { "0" | "1" }
5322 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
5324 Note: increases power consumption, thus should only be
5325 enabled if running jitter sensitive (HPC/RT) workloads.
5327 security= [SECURITY] Choose a legacy "major" security module to
5328 enable at boot. This has been deprecated by the
5331 selinux= [SELINUX] Disable or enable SELinux at boot time.
5332 Format: { "0" | "1" }
5333 See security/selinux/Kconfig help text.
5338 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
5339 Format: { "0" | "1" }
5340 See security/apparmor/Kconfig help text
5343 Default value is set via kernel config option.
5345 serialnumber [BUGS=X86-32]
5348 Maximal number of shapers.
5356 Enable merging of slabs with similar size when the
5357 kernel is built without CONFIG_SLAB_MERGE_DEFAULT.
5360 Disable merging of slabs with similar size. May be
5361 necessary if there is some reason to distinguish
5362 allocs to different slabs, especially in hardened
5363 environments where the risk of heap overflows and
5364 layout control by attackers can usually be
5365 frustrated by disabling merging. This will reduce
5366 most of the exposure of a heap attack to a single
5367 cache (risks via metadata attacks are mostly
5368 unchanged). Debug options disable merging on their
5370 For more information see Documentation/vm/slub.rst.
5372 slab_max_order= [MM, SLAB]
5373 Determines the maximum allowed order for slabs.
5374 A high setting may cause OOMs due to memory
5375 fragmentation. Defaults to 1 for systems with
5376 more than 32MB of RAM, 0 otherwise.
5378 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB]
5379 Enabling slub_debug allows one to determine the
5380 culprit if slab objects become corrupted. Enabling
5381 slub_debug can create guard zones around objects and
5382 may poison objects when not in use. Also tracks the
5383 last alloc / free. For more information see
5384 Documentation/vm/slub.rst.
5386 slub_max_order= [MM, SLUB]
5387 Determines the maximum allowed order for slabs.
5388 A high setting may cause OOMs due to memory
5389 fragmentation. For more information see
5390 Documentation/vm/slub.rst.
5392 slub_min_objects= [MM, SLUB]
5393 The minimum number of objects per slab. SLUB will
5394 increase the slab order up to slub_max_order to
5395 generate a sufficiently large slab able to contain
5396 the number of objects indicated. The higher the number
5397 of objects the smaller the overhead of tracking slabs
5398 and the less frequently locks need to be acquired.
5399 For more information see Documentation/vm/slub.rst.
5401 slub_min_order= [MM, SLUB]
5402 Determines the minimum page order for slabs. Must be
5403 lower than slub_max_order.
5404 For more information see Documentation/vm/slub.rst.
5406 slub_merge [MM, SLUB]
5407 Same with slab_merge.
5409 slub_nomerge [MM, SLUB]
5410 Same with slab_nomerge. This is supported for legacy.
5411 See slab_nomerge for more information.
5414 Format: <io1>[,<io2>[,...,<io8>]]
5416 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
5417 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
5418 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
5419 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
5420 smsc-ircc2.ircc_irq= [HW] IRQ line
5421 smsc-ircc2.ircc_dma= [HW] DMA channel
5422 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
5423 0: Toshiba Satellite 1800 (GP data pin select)
5424 1: Fast pin select (default)
5427 smt [KNL,S390] Set the maximum number of threads (logical
5428 CPUs) to use per physical CPU on systems capable of
5429 symmetric multithreading (SMT). Will be capped to the
5430 actual hardware limit.
5432 Default: -1 (no limit)
5435 [KNL] Should the soft-lockup detector generate panics.
5438 A value of 1 instructs the soft-lockup detector
5439 to panic the machine when a soft-lockup occurs. It is
5440 also controlled by the kernel.softlockup_panic sysctl
5441 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
5442 respective build-time switch to that functionality.
5444 softlockup_all_cpu_backtrace=
5445 [KNL] Should the soft-lockup detector generate
5446 backtraces on all cpus.
5449 sonypi.*= [HW] Sony Programmable I/O Control Device driver
5450 See Documentation/admin-guide/laptops/sonypi.rst
5452 spectre_v2= [X86] Control mitigation of Spectre variant 2
5453 (indirect branch speculation) vulnerability.
5454 The default operation protects the kernel from
5457 on - unconditionally enable, implies
5459 off - unconditionally disable, implies
5461 auto - kernel detects whether your CPU model is
5464 Selecting 'on' will, and 'auto' may, choose a
5465 mitigation method at run time according to the
5466 CPU, the available microcode, the setting of the
5467 CONFIG_RETPOLINE configuration option, and the
5468 compiler with which the kernel was built.
5470 Selecting 'on' will also enable the mitigation
5471 against user space to user space task attacks.
5473 Selecting 'off' will disable both the kernel and
5474 the user space protections.
5476 Specific mitigations can also be selected manually:
5478 retpoline - replace indirect branches
5479 retpoline,generic - Retpolines
5480 retpoline,lfence - LFENCE; indirect branch
5481 retpoline,amd - alias for retpoline,lfence
5482 eibrs - enhanced IBRS
5483 eibrs,retpoline - enhanced IBRS + Retpolines
5484 eibrs,lfence - enhanced IBRS + LFENCE
5486 Not specifying this option is equivalent to
5490 [X86] Control mitigation of Spectre variant 2
5491 (indirect branch speculation) vulnerability between
5494 on - Unconditionally enable mitigations. Is
5495 enforced by spectre_v2=on
5497 off - Unconditionally disable mitigations. Is
5498 enforced by spectre_v2=off
5500 prctl - Indirect branch speculation is enabled,
5501 but mitigation can be enabled via prctl
5502 per thread. The mitigation control state
5503 is inherited on fork.
5506 - Like "prctl" above, but only STIBP is
5507 controlled per thread. IBPB is issued
5508 always when switching between different user
5512 - Same as "prctl" above, but all seccomp
5513 threads will enable the mitigation unless
5514 they explicitly opt out.
5517 - Like "seccomp" above, but only STIBP is
5518 controlled per thread. IBPB is issued
5519 always when switching between different
5520 user space processes.
5522 auto - Kernel selects the mitigation depending on
5523 the available CPU features and vulnerability.
5525 Default mitigation: "prctl"
5527 Not specifying this option is equivalent to
5528 spectre_v2_user=auto.
5530 spec_store_bypass_disable=
5531 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
5532 (Speculative Store Bypass vulnerability)
5534 Certain CPUs are vulnerable to an exploit against a
5535 a common industry wide performance optimization known
5536 as "Speculative Store Bypass" in which recent stores
5537 to the same memory location may not be observed by
5538 later loads during speculative execution. The idea
5539 is that such stores are unlikely and that they can
5540 be detected prior to instruction retirement at the
5541 end of a particular speculation execution window.
5543 In vulnerable processors, the speculatively forwarded
5544 store can be used in a cache side channel attack, for
5545 example to read memory to which the attacker does not
5546 directly have access (e.g. inside sandboxed code).
5548 This parameter controls whether the Speculative Store
5549 Bypass optimization is used.
5551 On x86 the options are:
5553 on - Unconditionally disable Speculative Store Bypass
5554 off - Unconditionally enable Speculative Store Bypass
5555 auto - Kernel detects whether the CPU model contains an
5556 implementation of Speculative Store Bypass and
5557 picks the most appropriate mitigation. If the
5558 CPU is not vulnerable, "off" is selected. If the
5559 CPU is vulnerable the default mitigation is
5560 architecture and Kconfig dependent. See below.
5561 prctl - Control Speculative Store Bypass per thread
5562 via prctl. Speculative Store Bypass is enabled
5563 for a process by default. The state of the control
5564 is inherited on fork.
5565 seccomp - Same as "prctl" above, but all seccomp threads
5566 will disable SSB unless they explicitly opt out.
5568 Default mitigations:
5571 On powerpc the options are:
5573 on,auto - On Power8 and Power9 insert a store-forwarding
5574 barrier on kernel entry and exit. On Power7
5575 perform a software flush on kernel entry and
5579 Not specifying this option is equivalent to
5580 spec_store_bypass_disable=auto.
5582 spia_io_base= [HW,MTD]
5588 [X86] Enable split lock detection or bus lock detection
5590 When enabled (and if hardware support is present), atomic
5591 instructions that access data across cache line
5592 boundaries will result in an alignment check exception
5593 for split lock detection or a debug exception for
5598 warn - the kernel will emit rate-limited warnings
5599 about applications triggering the #AC
5600 exception or the #DB exception. This mode is
5601 the default on CPUs that support split lock
5602 detection or bus lock detection. Default
5603 behavior is by #AC if both features are
5604 enabled in hardware.
5606 fatal - the kernel will send SIGBUS to applications
5607 that trigger the #AC exception or the #DB
5608 exception. Default behavior is by #AC if
5609 both features are enabled in hardware.
5612 Set system wide rate limit to N bus locks
5613 per second for bus lock detection.
5616 N/A for split lock detection.
5619 If an #AC exception is hit in the kernel or in
5620 firmware (i.e. not while executing in user mode)
5621 the kernel will oops in either "warn" or "fatal"
5624 #DB exception for bus lock is triggered only when
5628 Control the Special Register Buffer Data Sampling
5631 Certain CPUs are vulnerable to an MDS-like
5632 exploit which can leak bits from the random
5635 By default, this issue is mitigated by
5636 microcode. However, the microcode fix can cause
5637 the RDRAND and RDSEED instructions to become
5638 much slower. Among other effects, this will
5639 result in reduced throughput from /dev/urandom.
5641 The microcode mitigation can be disabled with
5642 the following option:
5644 off: Disable mitigation and remove
5645 performance impact to RDRAND and RDSEED
5647 srcutree.counter_wrap_check [KNL]
5648 Specifies how frequently to check for
5649 grace-period sequence counter wrap for the
5650 srcu_data structure's ->srcu_gp_seq_needed field.
5651 The greater the number of bits set in this kernel
5652 parameter, the less frequently counter wrap will
5653 be checked for. Note that the bottom two bits
5656 srcutree.exp_holdoff [KNL]
5657 Specifies how many nanoseconds must elapse
5658 since the end of the last SRCU grace period for
5659 a given srcu_struct until the next normal SRCU
5660 grace period will be considered for automatic
5661 expediting. Set to zero to disable automatic
5665 Speculative Store Bypass Disable control
5667 On CPUs that are vulnerable to the Speculative
5668 Store Bypass vulnerability and offer a
5669 firmware based mitigation, this parameter
5670 indicates how the mitigation should be used:
5672 force-on: Unconditionally enable mitigation for
5673 for both kernel and userspace
5674 force-off: Unconditionally disable mitigation for
5675 for both kernel and userspace
5676 kernel: Always enable mitigation in the
5677 kernel, and offer a prctl interface
5678 to allow userspace to register its
5679 interest in being mitigated too.
5681 stack_guard_gap= [MM]
5682 override the default stack gap protection. The value
5683 is in page units and it defines how many pages prior
5684 to (for stacks growing down) resp. after (for stacks
5685 growing up) the main stack are reserved for no other
5686 mapping. Default value is 256 pages.
5688 stack_depot_disable= [KNL]
5689 Setting this to true through kernel command line will
5690 disable the stack depot thereby saving the static memory
5691 consumed by the stack hash table. By default this is set
5695 Enabled the stack tracer on boot up.
5697 stacktrace_filter=[function-list]
5698 [FTRACE] Limit the functions that the stack tracer
5699 will trace at boot up. function-list is a comma-separated
5700 list of functions. This list can be changed at run
5701 time by the stack_trace_filter file in the debugfs
5702 tracing directory. Note, this enables stack tracing
5703 and the stacktrace above is not needed.
5707 Set the STI (builtin display/keyboard on the HP-PARISC
5708 machines) console (graphic card) which should be used
5709 as the initial boot-console.
5710 See also comment in drivers/video/console/sticore.c.
5713 See comment in drivers/video/console/sticore.c.
5716 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
5721 Enable or disable strict sigaltstack size checks
5722 against the required signal frame size which
5723 depends on the supported FPU features. This can
5724 be used to filter out binaries which have
5725 not yet been made aware of AT_MINSIGSTKSZ.
5727 sunrpc.min_resvport=
5728 sunrpc.max_resvport=
5730 SunRPC servers often require that client requests
5731 originate from a privileged port (i.e. a port in the
5732 range 0 < portnr < 1024).
5733 An administrator who wishes to reserve some of these
5734 ports for other uses may adjust the range that the
5735 kernel's sunrpc client considers to be privileged
5736 using these two parameters to set the minimum and
5737 maximum port values.
5739 sunrpc.svc_rpc_per_connection_limit=
5741 Limit the number of requests that the server will
5742 process in parallel from a single connection.
5743 The default value is 0 (no limit).
5747 Control how the NFS server code allocates CPUs to
5748 service thread pools. Depending on how many NICs
5749 you have and where their interrupts are bound, this
5750 option will affect which CPUs will do NFS serving.
5751 Note: this parameter cannot be changed while the
5752 NFS server is running.
5754 auto the server chooses an appropriate mode
5755 automatically using heuristics
5756 global a single global pool contains all CPUs
5757 percpu one pool for each CPU
5758 pernode one pool for each NUMA node (equivalent
5759 to global on non-NUMA machines)
5761 sunrpc.tcp_slot_table_entries=
5762 sunrpc.udp_slot_table_entries=
5764 Sets the upper limit on the number of simultaneous
5765 RPC calls that can be sent from the client to a
5766 server. Increasing these values may allow you to
5767 improve throughput, but will also increase the
5768 amount of memory reserved for use by the client.
5770 suspend.pm_test_delay=
5772 Sets the number of seconds to remain in a suspend test
5773 mode before resuming the system (see
5774 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
5775 is set. Default value is 5.
5778 Format: { on | off | y | n | 1 | 0 }
5779 This parameter controls use of the Protected
5780 Execution Facility on pSeries.
5783 [KNL] Enable accounting of swap in memory resource
5784 controller if no parameter or 1 is given or disable
5785 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst)
5787 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
5788 Format: { <int> | force | noforce }
5789 <int> -- Number of I/O TLB slabs
5790 force -- force using of bounce buffers even if they
5791 wouldn't be automatically used by the kernel
5792 noforce -- Never use bounce buffers (for debugging)
5797 Set a sysctl parameter, right before loading the init
5798 process, as if the value was written to the respective
5799 /proc/sys/... file. Both '.' and '/' are recognized as
5800 separators. Unrecognized parameters and invalid values
5801 are reported in the kernel log. Sysctls registered
5802 later by a loaded module cannot be set this way.
5803 Example: sysctl.vm.swappiness=40
5805 sysfs.deprecated=0|1 [KNL]
5806 Enable/disable old style sysfs layout for old udev
5807 on older distributions. When this option is enabled
5808 very new udev will not work anymore. When this option
5809 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
5810 in older udev will not work anymore.
5811 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
5812 the kernel configuration.
5814 sysrq_always_enabled
5816 Ignore sysrq setting - this boot parameter will
5817 neutralize any effect of /proc/sys/kernel/sysrq.
5818 Useful for debugging.
5820 tcpmhash_entries= [KNL,NET]
5821 Set the number of tcp_metrics_hash slots.
5822 Default value is 8192 or 16384 depending on total
5823 ram pages. This is used to specify the TCP metrics
5824 cache size. See Documentation/networking/ip-sysctl.rst
5825 "tcp_no_metrics_save" section for more details.
5829 test_suspend= [SUSPEND][,N]
5830 Specify "mem" (for Suspend-to-RAM) or "standby" (for
5831 standby suspend) or "freeze" (for suspend type freeze)
5832 as the system sleep state during system startup with
5833 the optional capability to repeat N number of times.
5834 The system is woken from this state using a
5835 wakeup-capable RTC alarm.
5837 thash_entries= [KNL,NET]
5838 Set number of hash buckets for TCP connection
5840 thermal.act= [HW,ACPI]
5841 -1: disable all active trip points in all thermal zones
5842 <degrees C>: override all lowest active trip points
5844 thermal.crt= [HW,ACPI]
5845 -1: disable all critical trip points in all thermal zones
5846 <degrees C>: override all critical trip points
5848 thermal.nocrt= [HW,ACPI]
5849 Set to disable actions on ACPI thermal zone
5850 critical and hot trip points.
5852 thermal.off= [HW,ACPI]
5853 1: disable ACPI thermal control
5855 thermal.psv= [HW,ACPI]
5856 -1: disable all passive trip points
5857 <degrees C>: override all passive trip points to this
5860 thermal.tzp= [HW,ACPI]
5861 Specify global default ACPI thermal zone polling rate
5862 <deci-seconds>: poll all this frequency
5863 0: no polling (default)
5866 Force threading of all interrupt handlers except those
5867 marked explicitly IRQF_NO_THREAD.
5871 Specify if the kernel should make use of the cpu
5872 topology information if the hardware supports this.
5873 The scheduler will make use of this information and
5874 e.g. base its process migration decisions on it.
5877 topology_updates= [KNL, PPC, NUMA]
5879 Specify if the kernel should ignore (off)
5880 topology updates sent by the hypervisor to this
5883 torture.disable_onoff_at_boot= [KNL]
5884 Prevent the CPU-hotplug component of torturing
5885 until after init has spawned.
5887 torture.ftrace_dump_at_shutdown= [KNL]
5888 Dump the ftrace buffer at torture-test shutdown,
5889 even if there were no errors. This can be a
5890 very costly operation when many torture tests
5891 are running concurrently, especially on systems
5892 with rotating-rust storage.
5894 torture.verbose_sleep_frequency= [KNL]
5895 Specifies how many verbose printk()s should be
5896 emitted between each sleep. The default of zero
5897 disables verbose-printk() sleeping.
5899 torture.verbose_sleep_duration= [KNL]
5900 Duration of each verbose-printk() sleep in jiffies.
5904 tpm_suspend_pcr=[HW,TPM]
5905 Format: integer pcr id
5906 Specify that at suspend time, the tpm driver
5907 should extend the specified pcr with zeros,
5908 as a workaround for some chips which fail to
5909 flush the last written pcr on TPM_SaveState.
5910 This will guarantee that all the other pcrs
5913 trace_buf_size=nn[KMG]
5914 [FTRACE] will set tracing buffer size on each cpu.
5916 trace_event=[event-list]
5917 [FTRACE] Set and start specified trace events in order
5918 to facilitate early boot debugging. The event-list is a
5919 comma-separated list of trace events to enable. See
5920 also Documentation/trace/events.rst
5922 trace_options=[option-list]
5923 [FTRACE] Enable or disable tracer options at boot.
5924 The option-list is a comma delimited list of options
5925 that can be enabled or disabled just as if you were
5926 to echo the option name into
5928 /sys/kernel/debug/tracing/trace_options
5930 For example, to enable stacktrace option (to dump the
5931 stack trace of each event), add to the command line:
5933 trace_options=stacktrace
5935 See also Documentation/trace/ftrace.rst "trace options"
5939 Have the tracepoints sent to printk as well as the
5940 tracing ring buffer. This is useful for early boot up
5941 where the system hangs or reboots and does not give the
5942 option for reading the tracing buffer or performing a
5943 ftrace_dump_on_oops.
5945 To turn off having tracepoints sent to printk,
5946 echo 0 > /proc/sys/kernel/tracepoint_printk
5947 Note, echoing 1 into this file without the
5948 tracepoint_printk kernel cmdline option has no effect.
5950 The tp_printk_stop_on_boot (see below) can also be used
5951 to stop the printing of events to console at
5956 Having tracepoints sent to printk() and activating high
5957 frequency tracepoints such as irq or sched, can cause
5958 the system to live lock.
5960 tp_printk_stop_on_boot[FTRACE]
5961 When tp_printk (above) is set, it can cause a lot of noise
5962 on the console. It may be useful to only include the
5963 printing of events during boot up, as user space may
5964 make the system inoperable.
5966 This command line option will stop the printing of events
5967 to console at the late_initcall_sync() time frame.
5970 [FTRACE] enable this option to disable tracing when a
5971 warning is hit. This turns off "tracing_on". Tracing can
5972 be enabled again by echoing '1' into the "tracing_on"
5973 file located in /sys/kernel/debug/tracing/
5975 This option is useful, as it disables the trace before
5976 the WARNING dump is called, which prevents the trace to
5977 be filled with content caused by the warning output.
5979 This option can also be set at run time via the sysctl
5980 option: kernel/traceoff_on_warning
5982 transparent_hugepage=
5984 Format: [always|madvise|never]
5985 Can be used to control the default behavior of the system
5986 with respect to transparent hugepages.
5987 See Documentation/admin-guide/mm/transhuge.rst
5990 trusted.source= [KEYS]
5992 This parameter identifies the trust source as a backend
5993 for trusted keys implementation. Supported trust
5997 If not specified then it defaults to iterating through
5998 the trust source list starting with TPM and assigns the
5999 first trust source as a backend which is initialized
6000 successfully during iteration.
6002 tsc= Disable clocksource stability checks for TSC.
6004 [x86] reliable: mark tsc clocksource as reliable, this
6005 disables clocksource verification at runtime, as well
6006 as the stability checks done at bootup. Used to enable
6007 high-resolution timer mode on older hardware, and in
6008 virtualized environment.
6009 [x86] noirqtime: Do not use TSC to do irq accounting.
6010 Used to run time disable IRQ_TIME_ACCOUNTING on any
6011 platforms where RDTSC is slow and this accounting
6013 [x86] unstable: mark the TSC clocksource as unstable, this
6014 marks the TSC unconditionally unstable at bootup and
6015 avoids any further wobbles once the TSC watchdog notices.
6016 [x86] nowatchdog: disable clocksource watchdog. Used
6017 in situations with strict latency requirements (where
6018 interruptions from clocksource watchdog are not
6021 tsc_early_khz= [X86] Skip early TSC calibration and use the given
6022 value instead. Useful when the early TSC frequency discovery
6023 procedure is not reliable, such as on overclocked systems
6024 with CPUID.16h support and partial CPUID.15h support.
6025 Format: <unsigned int>
6027 tsx= [X86] Control Transactional Synchronization
6028 Extensions (TSX) feature in Intel processors that
6029 support TSX control.
6031 This parameter controls the TSX feature. The options are:
6033 on - Enable TSX on the system. Although there are
6034 mitigations for all known security vulnerabilities,
6035 TSX has been known to be an accelerator for
6036 several previous speculation-related CVEs, and
6037 so there may be unknown security risks associated
6038 with leaving it enabled.
6040 off - Disable TSX on the system. (Note that this
6041 option takes effect only on newer CPUs which are
6042 not vulnerable to MDS, i.e., have
6043 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get
6044 the new IA32_TSX_CTRL MSR through a microcode
6045 update. This new MSR allows for the reliable
6046 deactivation of the TSX functionality.)
6048 auto - Disable TSX if X86_BUG_TAA is present,
6049 otherwise enable TSX on the system.
6051 Not specifying this option is equivalent to tsx=off.
6053 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6056 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
6057 Abort (TAA) vulnerability.
6059 Similar to Micro-architectural Data Sampling (MDS)
6060 certain CPUs that support Transactional
6061 Synchronization Extensions (TSX) are vulnerable to an
6062 exploit against CPU internal buffers which can forward
6063 information to a disclosure gadget under certain
6066 In vulnerable processors, the speculatively forwarded
6067 data can be used in a cache side channel attack, to
6068 access data to which the attacker does not have direct
6071 This parameter controls the TAA mitigation. The
6074 full - Enable TAA mitigation on vulnerable CPUs
6077 full,nosmt - Enable TAA mitigation and disable SMT on
6078 vulnerable CPUs. If TSX is disabled, SMT
6079 is not disabled because CPU is not
6080 vulnerable to cross-thread TAA attacks.
6081 off - Unconditionally disable TAA mitigation
6083 On MDS-affected machines, tsx_async_abort=off can be
6084 prevented by an active MDS mitigation as both vulnerabilities
6085 are mitigated with the same mechanism so in order to disable
6086 this mitigation, you need to specify mds=off too.
6088 Not specifying this option is equivalent to
6089 tsx_async_abort=full. On CPUs which are MDS affected
6090 and deploy MDS mitigation, TAA mitigation is not
6091 required and doesn't provide any additional
6095 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
6097 turbografx.map[2|3]= [HW,JOY]
6098 TurboGraFX parallel port interface
6100 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
6101 See also Documentation/input/devices/joystick-parport.rst
6103 udbg-immortal [PPC] When debugging early kernel crashes that
6104 happen after console_init() and before a proper
6105 console driver takes over, this boot options might
6106 help "seeing" what's going on.
6108 uhash_entries= [KNL,NET]
6109 Set number of hash buckets for UDP/UDP-Lite connections
6112 [USB] Ignore overcurrent events (default N).
6113 Some badly-designed motherboards generate lots of
6114 bogus events, for ports that aren't wired to
6115 anything. Set this parameter to avoid log spamming.
6116 Note that genuine overcurrent events won't be
6120 [X86] Cause panic on unknown NMI.
6122 usbcore.authorized_default=
6123 [USB] Default USB device authorization:
6124 (default -1 = authorized except for wireless USB,
6125 0 = not authorized, 1 = authorized, 2 = authorized
6126 if device connected to internal port)
6128 usbcore.autosuspend=
6129 [USB] The autosuspend time delay (in seconds) used
6130 for newly-detected USB devices (default 2). This
6131 is the time required before an idle device will be
6132 autosuspended. Devices for which the delay is set
6133 to a negative value won't be autosuspended at all.
6135 usbcore.usbfs_snoop=
6136 [USB] Set to log all usbfs traffic (default 0 = off).
6138 usbcore.usbfs_snoop_max=
6139 [USB] Maximum number of bytes to snoop in each URB
6142 usbcore.blinkenlights=
6143 [USB] Set to cycle leds on hubs (default 0 = off).
6145 usbcore.old_scheme_first=
6146 [USB] Start with the old device initialization
6147 scheme (default 0 = off).
6149 usbcore.usbfs_memory_mb=
6150 [USB] Memory limit (in MB) for buffers allocated by
6151 usbfs (default = 16, 0 = max = 2047).
6153 usbcore.use_both_schemes=
6154 [USB] Try the other device initialization scheme
6155 if the first one fails (default 1 = enabled).
6157 usbcore.initial_descriptor_timeout=
6158 [USB] Specifies timeout for the initial 64-byte
6159 USB_REQ_GET_DESCRIPTOR request in milliseconds
6160 (default 5000 = 5.0 seconds).
6162 usbcore.nousb [USB] Disable the USB subsystem
6165 [USB] A list of quirk entries to augment the built-in
6166 usb core quirk list. List entries are separated by
6167 commas. Each entry has the form
6168 VendorID:ProductID:Flags. The IDs are 4-digit hex
6169 numbers and Flags is a set of letters. Each letter
6170 will change the built-in quirk; setting it if it is
6171 clear and clearing it if it is set. The letters have
6172 the following meanings:
6173 a = USB_QUIRK_STRING_FETCH_255 (string
6174 descriptors must not be fetched using
6176 b = USB_QUIRK_RESET_RESUME (device can't resume
6177 correctly so reset it instead);
6178 c = USB_QUIRK_NO_SET_INTF (device can't handle
6179 Set-Interface requests);
6180 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
6181 handle its Configuration or Interface
6183 e = USB_QUIRK_RESET (device can't be reset
6184 (e.g morph devices), don't use reset);
6185 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
6186 more interface descriptions than the
6187 bNumInterfaces count, and can't handle
6188 talking to these interfaces);
6189 g = USB_QUIRK_DELAY_INIT (device needs a pause
6190 during initialization, after we read
6191 the device descriptor);
6192 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
6193 high speed and super speed interrupt
6194 endpoints, the USB 2.0 and USB 3.0 spec
6195 require the interval in microframes (1
6196 microframe = 125 microseconds) to be
6197 calculated as interval = 2 ^
6199 Devices with this quirk report their
6200 bInterval as the result of this
6201 calculation instead of the exponent
6202 variable used in the calculation);
6203 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
6204 handle device_qualifier descriptor
6206 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
6207 generates spurious wakeup, ignore
6208 remote wakeup capability);
6209 k = USB_QUIRK_NO_LPM (device can't handle Link
6211 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
6212 (Device reports its bInterval as linear
6213 frames instead of the USB 2.0
6215 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
6216 to be disconnected before suspend to
6217 prevent spurious wakeup);
6218 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
6219 pause after every control message);
6220 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
6221 delay after resetting its port);
6222 Example: quirks=0781:5580:bk,0a5c:5834:gij
6225 [USBHID] The interval which mice are to be polled at.
6228 [USBHID] The interval which joysticks are to be polled at.
6231 [USBHID] The interval which keyboards are to be polled at.
6233 usb-storage.delay_use=
6234 [UMS] The delay in seconds before a new device is
6235 scanned for Logical Units (default 1).
6238 [UMS] A list of quirks entries to supplement or
6239 override the built-in unusual_devs list. List
6240 entries are separated by commas. Each entry has
6241 the form VID:PID:Flags where VID and PID are Vendor
6242 and Product ID values (4-digit hex numbers) and
6243 Flags is a set of characters, each corresponding
6244 to a common usb-storage quirk flag as follows:
6245 a = SANE_SENSE (collect more than 18 bytes
6246 of sense data, not on uas);
6247 b = BAD_SENSE (don't collect more than 18
6248 bytes of sense data, not on uas);
6249 c = FIX_CAPACITY (decrease the reported
6250 device capacity by one sector);
6251 d = NO_READ_DISC_INFO (don't use
6252 READ_DISC_INFO command, not on uas);
6253 e = NO_READ_CAPACITY_16 (don't use
6254 READ_CAPACITY_16 command);
6255 f = NO_REPORT_OPCODES (don't use report opcodes
6257 g = MAX_SECTORS_240 (don't transfer more than
6258 240 sectors at a time, uas only);
6259 h = CAPACITY_HEURISTICS (decrease the
6260 reported device capacity by one
6261 sector if the number is odd);
6262 i = IGNORE_DEVICE (don't bind to this
6264 j = NO_REPORT_LUNS (don't use report luns
6266 k = NO_SAME (do not use WRITE_SAME, uas only)
6267 l = NOT_LOCKABLE (don't try to lock and
6268 unlock ejectable media, not on uas);
6269 m = MAX_SECTORS_64 (don't transfer more
6270 than 64 sectors = 32 KB at a time,
6272 n = INITIAL_READ10 (force a retry of the
6273 initial READ(10) command, not on uas);
6274 o = CAPACITY_OK (accept the capacity
6275 reported by the device, not on uas);
6276 p = WRITE_CACHE (the device cache is ON
6277 by default, not on uas);
6278 r = IGNORE_RESIDUE (the device reports
6279 bogus residue values, not on uas);
6280 s = SINGLE_LUN (the device has only one
6282 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
6283 commands, uas only);
6284 u = IGNORE_UAS (don't bind to the uas driver);
6285 w = NO_WP_DETECT (don't test whether the
6286 medium is write-protected).
6287 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
6288 even if the device claims no cache,
6290 Example: quirks=0419:aaf5:rl,0421:0433:rc
6292 user_debug= [KNL,ARM]
6294 See arch/arm/Kconfig.debug help text.
6295 1 - undefined instruction events
6297 4 - invalid data aborts
6300 Example: user_debug=31
6303 [X86] Flags controlling user PTE allocations.
6305 nohigh = do not allocate PTE pages in
6306 HIGHMEM regardless of setting
6310 On X86_32, this is an alias for vdso32=. Otherwise:
6312 vdso=1: enable VDSO (the default)
6313 vdso=0: disable VDSO mapping
6315 vdso32= [X86] Control the 32-bit vDSO
6316 vdso32=1: enable 32-bit VDSO
6317 vdso32=0 or vdso32=2: disable 32-bit VDSO
6319 See the help text for CONFIG_COMPAT_VDSO for more
6320 details. If CONFIG_COMPAT_VDSO is set, the default is
6321 vdso32=0; otherwise, the default is vdso32=1.
6323 For compatibility with older kernels, vdso32=2 is an
6326 Try vdso32=0 if you encounter an error that says:
6327 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
6330 vector=percpu: enable percpu vector domain
6332 video= [FB] Frame buffer configuration
6333 See Documentation/fb/modedb.rst.
6335 video.brightness_switch_enabled= [0,1]
6336 If set to 1, on receiving an ACPI notify event
6337 generated by hotkey, video driver will adjust brightness
6338 level and then send out the event to user space through
6339 the allocated input device; If set to 0, video driver
6340 will only send out the event without touching backlight
6345 [VMMIO] Memory mapped virtio (platform) device.
6347 <size>@<baseaddr>:<irq>[:<id>]
6349 <size> := size (can use standard suffixes
6351 <baseaddr> := physical base address
6352 <irq> := interrupt number (as passed to
6354 <id> := (optional) platform device id
6356 virtio_mmio.device=1K@0x100b0000:48:7
6358 Can be used multiple times for multiple devices.
6360 vga= [BOOT,X86-32] Select a particular video mode
6361 See Documentation/x86/boot.rst and
6362 Documentation/admin-guide/svga.rst.
6363 Use vga=ask for menu.
6364 This is actually a boot loader parameter; the value is
6365 passed to the kernel using a special protocol.
6367 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
6368 May slow down system boot speed, especially when
6369 enabled on systems with a large amount of memory.
6370 All options are enabled by default, and this
6371 interface is meant to allow for selectively
6372 enabling or disabling specific virtual memory
6375 Available options are:
6376 P Enable page structure init time poisoning
6377 - Disable all of the above options
6379 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
6380 size of <nn>. This can be used to increase the
6381 minimum size (128MB on x86). It can also be used to
6382 decrease the size and leave more room for directly
6385 vmcp_cma=nn[MG] [KNL,S390]
6386 Sets the memory size reserved for contiguous memory
6387 allocations for the vmcp device driver.
6389 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
6392 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
6395 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
6399 Controls the behavior of vsyscalls (i.e. calls to
6400 fixed addresses of 0xffffffffff600x00 from legacy
6401 code). Most statically-linked binaries and older
6402 versions of glibc use these calls. Because these
6403 functions are at fixed addresses, they make nice
6404 targets for exploits that can control RIP.
6406 emulate [default] Vsyscalls turn into traps and are
6407 emulated reasonably safely. The vsyscall
6410 xonly Vsyscalls turn into traps and are
6411 emulated reasonably safely. The vsyscall
6412 page is not readable.
6414 none Vsyscalls don't work at all. This makes
6415 them quite hard to use for exploits but
6416 might break your system.
6418 vt.color= [VT] Default text color.
6419 Format: 0xYX, X = foreground, Y = background.
6420 Default: 0x07 = light gray on black.
6422 vt.cur_default= [VT] Default cursor shape.
6423 Format: 0xCCBBAA, where AA, BB, and CC are the same as
6424 the parameters of the <Esc>[?A;B;Cc escape sequence;
6425 see VGA-softcursor.txt. Default: 2 = underline.
6427 vt.default_blu= [VT]
6428 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
6429 Change the default blue palette of the console.
6430 This is a 16-member array composed of values
6433 vt.default_grn= [VT]
6434 Format: <green0>,<green1>,<green2>,...,<green15>
6435 Change the default green palette of the console.
6436 This is a 16-member array composed of values
6439 vt.default_red= [VT]
6440 Format: <red0>,<red1>,<red2>,...,<red15>
6441 Change the default red palette of the console.
6442 This is a 16-member array composed of values
6448 Set system-wide default UTF-8 mode for all tty's.
6449 Default is 1, i.e. UTF-8 mode is enabled for all
6450 newly opened terminals.
6452 vt.global_cursor_default=
6455 Set system-wide default for whether a cursor
6456 is shown on new VTs. Default is -1,
6457 i.e. cursors will be created by default unless
6458 overridden by individual drivers. 0 will hide
6459 cursors, 1 will display them.
6461 vt.italic= [VT] Default color for italic text; 0-15.
6464 vt.underline= [VT] Default color for underlined text; 0-15.
6467 watchdog timers [HW,WDT] For information on watchdog timers,
6468 see Documentation/watchdog/watchdog-parameters.rst
6469 or other driver-specific files in the
6470 Documentation/watchdog/ directory.
6474 Set the hard lockup detector stall duration
6475 threshold in seconds. The soft lockup detector
6476 threshold is set to twice the value. A value of 0
6477 disables both lockup detectors. Default is 10
6480 workqueue.watchdog_thresh=
6481 If CONFIG_WQ_WATCHDOG is configured, workqueue can
6482 warn stall conditions and dump internal state to
6483 help debugging. 0 disables workqueue stall
6484 detection; otherwise, it's the stall threshold
6485 duration in seconds. The default value is 30 and
6486 it can be updated at runtime by writing to the
6487 corresponding sysfs file.
6489 workqueue.disable_numa
6490 By default, all work items queued to unbound
6491 workqueues are affine to the NUMA nodes they're
6492 issued on, which results in better behavior in
6493 general. If NUMA affinity needs to be disabled for
6494 whatever reason, this option can be used. Note
6495 that this also can be controlled per-workqueue for
6496 workqueues visible under /sys/bus/workqueue/.
6498 workqueue.power_efficient
6499 Per-cpu workqueues are generally preferred because
6500 they show better performance thanks to cache
6501 locality; unfortunately, per-cpu workqueues tend to
6502 be more power hungry than unbound workqueues.
6504 Enabling this makes the per-cpu workqueues which
6505 were observed to contribute significantly to power
6506 consumption unbound, leading to measurably lower
6507 power usage at the cost of small performance
6510 The default value of this parameter is determined by
6511 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
6513 workqueue.debug_force_rr_cpu
6514 Workqueue used to implicitly guarantee that work
6515 items queued without explicit CPU specified are put
6516 on the local CPU. This guarantee is no longer true
6517 and while local CPU is still preferred work items
6518 may be put on foreign CPUs. This debug option
6519 forces round-robin CPU selection to flush out
6520 usages which depend on the now broken guarantee.
6521 When enabled, memory and cache locality will be
6524 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
6525 default x2apic cluster mode on platforms
6528 xen_512gb_limit [KNL,X86-64,XEN]
6529 Restricts the kernel running paravirtualized under Xen
6530 to use only up to 512 GB of RAM. The reason to do so is
6531 crash analysis tools and Xen tools for doing domain
6532 save/restore/migration must be enabled to handle larger
6535 xen_emul_unplug= [HW,X86,XEN]
6536 Unplug Xen emulated devices
6537 Format: [unplug0,][unplug1]
6538 ide-disks -- unplug primary master IDE devices
6539 aux-ide-disks -- unplug non-primary-master IDE devices
6540 nics -- unplug network devices
6541 all -- unplug all emulated devices (NICs and IDE disks)
6542 unnecessary -- unplugging emulated devices is
6543 unnecessary even if the host did not respond to
6545 never -- do not unplug even if version check succeeds
6547 xen_legacy_crash [X86,XEN]
6548 Crash from Xen panic notifier, without executing late
6549 panic() code such as dumping handler.
6551 xen_nopvspin [X86,XEN]
6552 Disables the qspinlock slowpath using Xen PV optimizations.
6553 This parameter is obsoleted by "nopvspin" parameter, which
6554 has equivalent effect for XEN platform.
6557 Disables the PV optimizations forcing the HVM guest to
6558 run as generic HVM guest with no PV drivers.
6559 This option is obsoleted by the "nopv" option, which
6560 has equivalent effect for XEN platform.
6562 xen_no_vector_callback
6563 [KNL,X86,XEN] Disable the vector callback for Xen
6564 event channel interrupts.
6566 xen_scrub_pages= [XEN]
6567 Boolean option to control scrubbing pages before giving them back
6568 to Xen, for use by other domains. Can be also changed at runtime
6569 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
6570 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
6572 xen_timer_slop= [X86-64,XEN]
6573 Set the timer slop (in nanoseconds) for the virtual Xen
6574 timers (default is 100000). This adjusts the minimum
6575 delta of virtualized Xen timers, where lower values
6576 improve timer resolution at the expense of processing
6577 more timer interrupts.
6579 xen.balloon_boot_timeout= [XEN]
6580 The time (in seconds) to wait before giving up to boot
6581 in case initial ballooning fails to free enough memory.
6582 Applies only when running as HVM or PVH guest and
6583 started with less memory configured than allowed at
6584 max. Default is 180.
6586 xen.event_eoi_delay= [XEN]
6587 How long to delay EOI handling in case of event
6588 storms (jiffies). Default is 10.
6590 xen.event_loop_timeout= [XEN]
6591 After which time (jiffies) the event handling loop
6592 should start to delay EOI handling. Default is 2.
6594 xen.fifo_events= [XEN]
6595 Boolean parameter to disable using fifo event handling
6596 even if available. Normally fifo event handling is
6597 preferred over the 2-level event handling, as it is
6598 fairer and the number of possible event channels is
6599 much higher. Default is on (use fifo events).
6601 nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
6602 Disables the PV optimizations forcing the guest to run
6603 as generic guest with no PV drivers. Currently support
6604 XEN HVM, KVM, HYPER_V and VMWARE guest.
6606 nopvspin [X86,XEN,KVM]
6607 Disables the qspinlock slow path using PV optimizations
6608 which allow the hypervisor to 'idle' the guest on lock
6611 xirc2ps_cs= [NET,PCMCIA]
6613 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
6616 By default on POWER9 and above, the kernel will
6617 natively use the XIVE interrupt controller. This option
6618 allows the fallback firmware mode to be used:
6620 off Fallback to firmware control of XIVE interrupt
6621 controller on both pseries and powernv
6622 platforms. Only useful on POWER9 and above.
6624 xive.store-eoi=off [PPC]
6625 By default on POWER10 and above, the kernel will use
6626 stores for EOI handling when the XIVE interrupt mode
6627 is active. This option allows the XIVE driver to use
6628 loads instead, as on POWER9.
6630 xhci-hcd.quirks [USB,KNL]
6631 A hex value specifying bitmask with supplemental xhci
6632 host controller quirks. Meaning of each bit can be
6633 consulted in header drivers/usb/host/xhci.h.
6636 Format: { early | on | rw | ro | off }
6637 Controls if xmon debugger is enabled. Default is off.
6638 Passing only "xmon" is equivalent to "xmon=early".
6639 early Call xmon as early as possible on boot; xmon
6640 debugger is called from setup_arch().
6641 on xmon debugger hooks will be installed so xmon
6642 is only called on a kernel crash. Default mode,
6643 i.e. either "ro" or "rw" mode, is controlled
6644 with CONFIG_XMON_DEFAULT_RO_MODE.
6645 rw xmon debugger hooks will be installed so xmon
6646 is called only on a kernel crash, mode is write,
6647 meaning SPR registers, memory and, other data
6648 can be written using xmon commands.
6649 ro same as "rw" option above but SPR registers,
6650 memory, and other data can't be written using
6652 off xmon is disabled.
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